TABLE OF CONTENTS
LIST OF TABLES..................................................................................... iv
LIST OF FIGURES ................................................................................... vi
Chapter 1 Introduction to permanent monitoring systems and hardware ...1
1.1 Permanent Monitoring Systems ........................................................................ 1
1.2 HPQG Electronics Assembly............................................................................ 4
1.2.1 Printed wiring boards PQG101 and PQG202............................................. 5
1.2.2 Quartzdyne sensor ...................................................................................... 7
Chapter 2 Life cycle considerations and methodology ..............................8
2.1 Introduction ....................................................................................................... 8
2.2 Development of Life Cycle Environment Profile ............................................. 9
2.2.1 Steps in development of LCEP................................................................. 11
2.3 Effects of Environmental Factors.................................................................... 13
2.4 Summary ......................................................................................................... 21
Chapter 3 Physics of Failure based Reliability Assessment of HPQG .....24
3.1 Reliability Assessment Methodology ............................................................. 24
3.2 Virtual reliability assessment of HPQG PCBs................................................ 26
3.2.1 Design Capture ......................................................................................... 26
3.2.1.1
PQG101 ............................................................................................ 27
3.2.1.2
PQG202 ............................................................................................ 27
3.2.2 Life-Cycle Environmental Profiles........................................................... 29
3.2.2.1
Qualification and screening.............................................................. 31
3.2.2.2
Storage at test facility: ...................................................................... 31
3.2.2.3
Transportation................................................................................... 31
3.2.2.4
Storage (at destination):.................................................................... 33
3.2.2.5
Transportation (to installation site) .................................................. 33
3.2.2.6
Installation ........................................................................................ 33
3.2.2.7
Operation (including a brief period of dormancy) ........................... 34
3.2.3 Failure modes, effects and criticality analysis.......................................... 35
3.2.4 Component level design capture .............................................................. 37
3.2.5 Virtual Reliability Assessment ................................................................. 39
ii
3.2.5.1
Stress Assessment............................................................................. 40
3.2.5.1.1 Board level stress assessment ....................................................... 40
3.2.5.1.2 Component level stress analysis................................................... 45
3.2.5.2
Damage and Life Assessment .......................................................... 46
3.2.5.2.1 Component level damage and life assessment ............................. 46
3.2.5.2.2 Board level damage and life assessment ...................................... 48
3.3 Accelerated thermal testing............................................................................. 50
3.3.1 Accelerated test loads and acceleration factor.......................................... 51
3.3.2 Accelerated test setup ............................................................................... 51
3.3.3 Calibration ................................................................................................ 52
3.3.4 Failure criteria .......................................................................................... 53
3.3.5 Accelerated testing ................................................................................... 54
3.4 Visual Inspection............................................................................................. 56
Chapter 4 Results and Conclusions ...........................................................70
4.1
4.2
4.3
Upratability of the printed circuit boards ........................................................ 73
IEEE 1413 analysis ......................................................................................... 73
Contributions................................................................................................... 76
REFERENCES ..........................................................................................77
iii
LIST OF TABLES
Table 1: Environmental factors and their effects on electronic equipment for downhole
applications.................................................................................................... 14
Table 2: Examples of generic effects of combined environments on electronic products
....................................................................................................................... 18
Table 3: Details required for board modeling using calcePWA software.................... 26
Table 4: Dimensions and power dissipation of PQG101 and PQG202........................ 28
Table 5: Distribution of failure modes in occurrence-criticality matrix....................... 36
Table 6: Selected ICs for component level analysis..................................................... 37
Table 7: Component level modeling details................................................................. 39
Table 8: OP221............................................................................................................. 47
Table 9: M27C256........................................................................................................ 47
Table 10: 80C154 ......................................................................................................... 47
Table 11: DCM92......................................................................................................... 47
Table 12: VQ3001 ........................................................................................................ 47
Table 13: % Remaining life - DCM92 ......................................................................... 48
Table 14: Ranking of failures in PQG101.................................................................... 49
Table 15: Ranking of failures in PQG202.................................................................... 49
Table 16: Components showing potential failures due to shock in PQG101............... 50
Table 17: Components showing potential failures due to shock in PQG202............... 50
Table 18: Material Tg/melting points for stable operations upto 175°C...................... 51
Table 19: Acceleration factors for DCM-92 ................................................................ 51
Table 20: General description of a FMECA header ..................................................... 58
Table 21: General description of a FMECA chart........................................................ 58
iv
Table 22: FMECA header for PQG101........................................................................ 59
Table 23: FMECA chart for PQG101 .......................................................................... 59
Table 24: PQG202 General description ....................................................................... 65
Table 25: FMEA table for PQG202 ............................................................................. 65
Table 26: IEEE Std 1413 – Reliability prediction methodology questionnaire ........... 74
v
LIST OF FIGURES
Figure 1: Permanent downhole monitoring architecture ................................................ 1
Figure 2: HPQG mechanical and operational assembly................................................. 5
Figure 3: PQG101 circuit card assembly........................................................................ 6
Figure 4: PQG202 circuit card assembly........................................................................ 7
Figure 5: Effects of combined environments on electronic equipment........................ 23
Figure 6: PQG101 circuit card assembly...................................................................... 27
Figure 7: PQG101 CCA - calcePWA model................................................................ 27
Figure 8: PQG202 circuit card assembly...................................................................... 28
Figure 9: PQG202 CCA - calcePWA model................................................................ 28
Figure 10: Details of design capture - an example ....................................................... 29
Figure 11: Qualification thermal profile....................................................................... 31
Figure 12: Qualification vibration profile .................................................................... 31
Figure 13: Transportation profile for high temperature destination............................. 32
Figure 14: Transportation profile for low temperature destination .............................. 32
Figure 15: Vibration PSD profile for transportation .................................................... 33
Figure 16: Shock profile for transportation .................................................................. 33
Figure 17: Thermal profile for installation at low temperature destination ................. 34
Figure 18: Operational thermal profile......................................................................... 35
Figure 19: Operational vibration profile....................................................................... 35
Figure 20: M27C256 UV PROM Device..................................................................... 38
Figure 21: Thermal boundary conditions ..................................................................... 41
Figure 22: Thermal analysis of PQG101 at 150°C....................................................... 41
Figure 23: Thermal analysis of PQG202 at 150°C....................................................... 41
vi
Figure 24: Ideal mechanical model .............................................................................. 43
Figure 25: Worst case model........................................................................................ 43
Figure 26: Vibration boundary conditions for PQG101............................................... 43
Figure 27: Vibration boundary conditions for PQG202............................................... 43
Figure 28: PQG101 Mode 1- 313.6Hz ......................................................................... 44
Figure 29: PQG101 Vibration displacement profile .................................................... 44
Figure 30: PQG202 Mode 1 - 575.5 Hz ....................................................................... 44
Figure 31: PQG202 Vibration displacement profile .................................................... 44
Figure 32: Shock displacement of components on PQG101........................................ 45
Figure 33: Shock displacement of components on PQG202........................................ 45
Figure 34: Thermal profile - M27C256........................................................................ 46
Figure 35: DCM92 - electromigration sensitivity analysis .......................................... 48
Figure 36: DCM92 - metallization corrosion sensitivity analysis................................ 48
Figure 37: Vibration displacement profile for PQG101 with C5 and C4..................... 49
Figure 38: HPQG-1 Pressure line response.................................................................. 53
Figure 39: HPQG-1 Temperature line response........................................................... 53
Figure 40: HPQG-2 Pressure line response.................................................................. 53
Figure 41: HPQG-2 Temperature line response........................................................... 53
Figure 42: HPQG-1 Pressure line output...................................................................... 55
Figure 43: HPQG-1 Temperature line output............................................................... 55
Figure 44: HPQG-2 Pressure line output...................................................................... 55
Figure 45: HPQG-2 Temperature line output............................................................... 55
Figure 46: HPQG-1 Drift in temperature line response ............................................... 55
Figure 47: HPQG-2 Drift in temperature line response ............................................... 55
Figure 48: Cracks on capture pads ............................................................................... 56
vii
Figure 49: Solder joint on an axial leaded component ................................................. 56
Figure 50: Solder joints and via connections on the back side of the PCB.................. 56
Figure 51: Cracks on traces .......................................................................................... 56
Figure 52: Functional block diagram of the HPQG electronics ................................... 57
viii
Chapter 1
Introduction to permanent monitoring systems and
hardware
In oil extraction and production, long-term real-time monitoring of the reservoir
conditions has shown to improve and optimize the oil recovery process. For this
reason, many recently completed wells have been equipped with permanent
monitoring systems. Continuous measurement of pressure and temperature enables
engineers to observe ongoing changes in the well and make operating adjustments to
optimize recovery. In permanent monitoring systems, sensors or gauges tare placed
downhole. Modern communication provides direct access to sensor measurements.
This enables monitoring of the well behavior throughout the lifetime of the reservoir
[1] - [8].
1.1 Permanent Monitoring Systems
Downhole
gauges
Autonomous
surface
unit
Data link
Monitoring
computer
Figure 1: Permanent downhole monitoring architecture
1
A permanent monitoring system consists of downhole gauges to measure
temperature and pressure, a surface acquisition system to collect the data measured
downhole, a data link to the control facility and computers to control and monitor the
data. Figure 1 shows a schematic of the downhole monitoring system.
Reliability is key to a permanent monitoring system. Typical lifetime of a
reservoir ranges from 5 – 10 years. Permanent monitoring systems are required to
have a life equal to the useful life of the reservoir. Many studies have been performed
on the reliability of the downhole monitoring systems. Gisbergen et al [1] performed a
study where 952 pressure and temperature monitoring systems installed since 1987
were evaluated. It was found that about 40% of the failures in the permanent
monitoring systems were due to the gauge electronics. Use of dedicated electronics,
burn-in and vibration/shock testing and destructive testing at actual conditions were
suggested as remedies to overcome these defects. Another study by Drakeley et al [8]
suggests that 49.3% of the unreliability of the permanent monitoring system is
contributed by the downhole electronics module. The issue of high temperature
electronics reliability for downhole applications has also been discussed by Boer [9]
and Gigerich et al [10]. Oil-electronics equipment often uses up-screened commercial
electronics to manufacture its hardware. Even when the components are manufacturer
qualified for high temperatures the availability of these parts is becoming more and
more difficult. A number known wear out mechanisms like intermetallic growth, wire
resonance in high vibration applications, electromigration, time dependent dielectric
breakdown have been the causes attributed to majority of the on-chip electronics
failures seen in downhole environment. Pecht et al [11] [12] have discussed the on-
2
chip high temperature failure mechanisms. These failure mechanisms are critical in
downhole permanent monitoring applications due to the high temperature and long
duration of operation. McCluskey et al [13] have also discussed reliability issues
occuing with high temperature operating and/or storage conditions. Assembly related
failure mechanisms like intermetallics in solder and metal migration in traces are
accelerated at high temperatures. Vibration and shock cause cracking type failures in
printed circuit boards and components. Solder joint fatigue [14] [15] is another
mechanism accelerated by vibration, shock and temperature which is critical to
assembly level reliability in permanent downhole electronics. Humidity is another key
factor for electronics reliability. However, due to the hermetic nature of the gauge
assembly environmental factors like dust and humidity do not significantly affect the
reliability of gauge electronics.
Above studies suggest that the gauge electronics is critical to the reliability of the
permanent monitoring system. The permanent gauges form a key part of the
downhole monitoring systems. Modern gauges are typically quartz sensors along with
electronics to provide high accuracy over large range of temperature and pressure
measurements.
In this study we have identified and described the environmental factors that affect
the reliability of electronics equipment used for oil and gas production applications.
We have developed a methodology to address these concerns. Specifically, we have
assessed the reliability of one such electronics gauge used for permanent monitoring
applications for operation at temperatures higher than which it is used. This particular
gauge is called the Hyper Permanent Quartz Gauge (HPQG) developed by
3
Schlumberger for permanent monitoring applications. Majority of the HPQG
installations have operated below 100°C and have achieved required reliability targets.
However, there have been very few installations above 125°C. Our study focuses on
assessing the reliability of these gauges at operating temperatures upto 150°C. In our
study, we have identified the potential failures and failure mechanisms in the
interconnects and components of the HPQG and performed high temperature testing in
order to assess the reliability of the HPQG for high temperature loads. The following
section describes the HPQG hardware.
1.2 HPQG Electronics Assembly
The Hyper Permanent Quartz Gauge forms an integral part of Schlumberger’s
permanent monitoring system. It consists of QuartzdyneTM sensors, a mixer (PQG202
circuit board) and a digital, power and telemetry system (PQG101 circuit board). The
QuartzdyneTM sensor consists of three crystals: a temperature crystal, a pressure
crystal and a reference crystal. The oscillatory frequencies of the temperature and
pressure crystals are proportional to the temperature and the pressure they are
subjected to. The reference crystal produces a signal, which is mixed with the signals
from the pressure and temperature crystals and sent to the digitizer. The digitizer
converts the frequency data into digital bits and sends it to the telemetry system, which
then sends it uphole. Figure 2 shows a schematic setup of the HPQG in the mandrel.
The entire assembly of the HPQG, formed by the Quartzdyne sensor and the two
boards (PQG101 and PQG202), is hermetically sealed. The HPQG is designed to
4
operate upto 175°C and upto 21000 psi. A reliable operation for 5 years is expected
from it.
1.2.1 Printed wiring boards PQG101 and PQG202
The electronics for operation of the Quartz Gauges is controlled by two printed
circuit boards – PQG101 and PQG202. PQG101, which contains the digital, power
and telemetry circuits, has 61 parts totally on the board spread among 40 unique parts.
All the parts are insertion mount. It is an eight-layer Polyimide board with copper
metallization. Figure 3 shows PQG101. The functionality of the PQG101 can be
divided into two parts-
Mechanical
assembly
Operational
assembly
Steel tubing
PCB
Digitize the frequency
signals and send it to
the data acquisition unit
Mix the frequency
signals from the
crystals with the
reference frequency
Generate frequency
signals corresponding
to the pressure and
temperature conditions
Insulating sheet
(damping element)
Steel chassis
Hermetically
sealed assembly
Digitizer, Power and
telemetry board
(PQG101)
Oscillator and
mixer board
(PQG202)
Quartz sensors
(temperature,
pressure and
reference crystals)
To oil
reservoirs
Figure 2: HPQG mechanical and operational assembly
5
1. An analog part which regulates supply voltage, protects against voltage or
current overload, detects the signal on the cable, transmits the gauge’s
measurements (pressure, temperature, address) and generates for the digital
part the following information bits : POWER_OK, RESETIN*, signal on
the cable (REC_DIR and REC_INT).
2. A digital part which digitized the pressure and temperature measurement
frequencies and controls the transmission. It is built around a
microcontroller, an ASIC and a program memory.
Figure 3: PQG101 circuit card assembly
PQG202, which contains the oscillator and frequency mixing circuits to scale
down the frequency sent to PQG101 and finally to the monitoring hardware, has 79
parts on board spread among 27 unique parts. All the parts are insertion mount. It is a
six-layer Polyimide board with copper metallization. Figure 4 shows PQG202. A
detailed description of the analysis and functionality of boards is provided in the later
sections. PQG202 board consists of three oscillators each running with one quartz
resonator (located outside of the board, they are parts of a sensor). One oscillator
(Pierce type) is used for the pressure measurement and one (Colpitts type) for the
temperature measurement. The third one (Colpitts type) generates a reference
frequency. The pressure and temperature frequencies are combined with the reference
frequency resulting in two low frequency signals. After passing through low pass
filters, these two signals are outputs of the board:
6
F1 = FPressure - FReference and F2 = FReference - FTemperature
In order to excite the pressure quartz if it comes to not start, the reference
frequency is injected to the pressure quartz at a random frequency.
Figure 4: PQG202 circuit card assembly
1.2.2 Quartzdyne sensor
The sensor unit of the HPQG called the QuartzdyneTM sensor consists of quartz
crystals- a pressure crystal, a temperature crystal, and a reference crystal [16]. Quartz
resonators use the inverse piezoelectric effect to induce the resonator to vibrate at its
mechanical resonant frequency when electric fields are applied to its electrodes. An
oscillator circuit supplies the power and allows the frequency to be measured. Because
frequency (and its inverse, time) can be measured with greater precision than any
other parameter, the sensor's frequency output provides high-resolution pressure and
temperature measurement [16]. The temperature crystal changes frequency in response
to the temperature while the pressure crystal changes frequency in response to
pressure. The reference crystal gives out a signal which is mixed with the signals from
the pressure and temperature transducers and suitably scaled down for digital
measurement. The quartz crystals have proven long-term reliability under harsh
environmental conditions [17].
7
Chapter 2
Life cycle considerations and assessment methodology
Understanding and defining the environmental life cycle of electronics play a
critical role in designing for reliability. An environmental profile contains necessary
“load” information for the development and effectiveness assessment of design
guidelines, screens, and tests. It can also help reduce life cycle cost for the equipment
by making the design process robust. Electronics used for oil and gas exploration and
production applications experience a wide range of stresses owing to the varied load
conditions experienced by the system during its life. A formal method is necessary to
capture all environmental information and to develop an environmental profile.
2.1 Introduction
A life cycle environment profile (LCEP) is a forecast of events and associated
environmental conditions that equipment will experience from manufacture to end of
life [18] [19]1. Environmental loads corresponding to manufacture and assembly,
testing, handling, shipping, storage before and/or between usage, dormancy,
geographical location of installation, and operating platforms are accounted for in the
LCEP.
1
In some cases, the environmental factors experienced by constituents of the system begins before
manufacturing (e.g., storage of components from a lifetime buy of a large quantity purchased far in
advance of their use in manufacturing) [20].
8
Electronic equipment design and reliability assessment must accommodate all
environmental stresses that act on it over its life. The performance of a product
depends on the magnitude of the stresses, rate of change of stresses, and even time and
spatial variation of the stresses that are generated by the loads acting during its life
cycle. An LCEP helps to identify all possible load combinations so that the stresses
acting on the product can be identified and their effects can be accounted for in the
product’s design, test and qualification process to ensure the reliability of the
electronic equipment for its entire life [11]. Past research describes the need for life
cycle analysis of electronic products for better design to ensure product reliability [21]
[22] [23].
2.2 Development of Life Cycle Environment Profile
Before beginning the design of electronic equipment or assessing the reliability of
an existing design, used for oil and gas exploration and production applications, the
environmental conditions to be experienced by the equipment must be identified. In
the case of oil and gas application electronics, the environment can be distinctly
divided into two parts, the surface environment and the downhole environment.
Typically, the surface environment is related to handling, transport and storage while
the downhole environment is related to the actual operation of the equipment. The
equipment stresses during non-operation are as important to reliability as those
occurring during operation [18]. For example, the surface environment can be much
less severe than the downhole environment for drilling equipment, while the surface
9
environment can be more severe than the downhole environment for wireline2
equipment, for example, with shock and vibration during transportation and handling.
A life cycle profile for electronics associated with oil and gas exploration and
production should identify all events and phases that the product will experience. Data
corresponding to environmental factors, single or combined, should be incorporated in
the LCEP. For example, temperature, pressure and mechanical vibrations are principal
loads acting during operation of a permanently installed downhole gauge to monitor
pressure and temperature.
The LCEP includes the chance (probability) that a particular environmental
condition will occur during the life cycle of the equipment. For example, permanent
gauges can be installed at different depths, which will lead to different temperatures.
Accidental dropping of the equipment is another example; the number, severity and
probability of such drops must be estimated.
The places the equipment could be installed should be identified. The aim should
be to describe the range of conditions (including extreme conditions) that the tool can
endure. For example, an oil well permanent gauge surface system can be deployed in a
wide range of temperatures [26].3
2
Wireline logging involves tools lowered downhole on an electrical cable. It determines which
formations intersected by the well bore may contain hydrocarbons and takes measurements to provide
descriptive and quantitative evaluations of the rock penetrated as well as the type and amount of fluid
contained therein [24] [25].
3
The highest temperature recorded on earth is 57.77°C in Al Aziziyah, Libya in September 1922. Death
Valley, CA recorded 56.77°C in July 1913. The place that has the world’s highest average temperature
10
The operation of the electronic product can introduce new loads or modify existing
load conditions. A failure modes and effects analysis is usually performed to identify
key loads acting on the system that could pose a reliability problem. The hardware
configuration is also considered in combination with environmental loads. Hardware
configuration factors include board design, type of electronic parts and their
mechanical specifications, electrical characteristics, response of the parts and the
system as a whole, and different mechanical and electrical interfaces in the system.
2.2.1 Steps in development of LCEP
The steps in developing an LCEP are as follows:
1. Describe expected events for an item or equipment, from manufacture through
end of life. For example, in the case of a permanent downhole quartz gauge,
these events or phases include production testing and qualification, storage at
the test facility, transportation to the place of installation, storage at the place
of installation, transportation to the specific site of installation, installation,
operation, and periods of dormancy during scheduled maintenance.
is Dakol, Ethiopia, in the Danakil Depression with a mean temperature of 34.44°C. Places in Pakistan
(e.g., Pad Idan) have recorded temperatures upto 50.55°C [27]. The lowest recorded temperature on
earth till date is –89.44°C in Vostok, Antartica. Temperatures in Greenland have gone as low as -70°C
[28].
11
2. Identify significant natural4 and induced5 environmental factors or
combinations of environmental factors for each expected phase (such as
manufacturing, transportation, storage, standby, handling, installation and
operation modes). For example, for a permanent downhole gauge, the
operation phase includes high steady-state temperature, high pressure and
random vibrations.
3. Describe environmental load conditions (in both narrative and statistical form)
to which equipment will be subjected during the life cycle. Data should be
determined from real-time measurements, but may be estimated by simulation
and laboratory tests. For example, the vibrations experienced by the electronic
equipment during shipping could be obtained by a mock shipping experiment
wherein sensors can be kept with the equipment to record vibration data.
Estimated data should be replaced with actual values as determined. The
profile should show the number of measurements used to obtain the average
value and the variability of the loads.
This analysis can be used to develop environmental design criteria in accordance
with expected operating conditions, evaluate effects of change in environmental
conditions on the electronic equipment, and provide traceability for the rationale
4
Natural environment is the product’s natural ambient conditions, e.g., temperature, pressure, and
humidity.
5
Induced environment is the product’s environmental conditions related to the specific functionality of
the product, e.g., electronics on the drilling tool experience mechanical vibration during the drilling
process.
12
applied in future criteria selection [19]. A listing of typical environmental factors that
must be considered for development of electronic equipment for use in oil and gas
downhole applications [6] is included in Table 1.
2.3 Effects of Environmental Factors
Failure mechanisms in electronic equipment can be caused by steady state loads or
changes in the magnitude of the load (absolute change or rate of change). Therefore,
the nature of the application of the loads (steady state or dynamic) should be
determined. For example, failure by intermetallic growth at the wirebonds in
Integrated Circuit (IC) packages is dominated by steady-state temperature conditions,
while failures by die fracture in IC packages depend more on the rate of temperature
change. Table 1 gives environmental factors that are important considerations for
designing electronics used for oil and gas exploration and production applications
[19]. The generic effects of these factors on electronic equipment are also discussed.
Combined environments (incorporating two or more of the environmental factors)
may affect equipment reliability differently than the effects of a single environmental
factor. Effects of typical combined environments are illustrated in the matrix
relationship in Figure 5. If the combined effect of the environmental factors proves to
be more harmful than that of single environmental conditions, then the equipment
must be designed for failures arising from the combined effects.
13
Table 1: Environmental factors and their effects on electronic equipment for downhole
applications
Environmental Factors
Temperature
Principal Effects
High
(natural/induced)
Possible Failures
Thermal aging
Insulation failure because of melting
Oxidation
Alteration of electrical properties owing to changes in
Structural change
resistance
Chemical change
On-chip failures (metallization migration, Kirkendall
Softening and melting
voiding in wirebonds, slow trapping, time-dependent
Viscosity
dielectric breakdown) [11] [13] [12] [29]
reduction/evaporation
Melting of solder joints [13] [30]
Physical expansion
Unequal expansion leading to fracture [13]
Physical contraction
Alteration of electrical properties owing to changes in
Brittleness
resistance
Ionic contamination [13]
Low
Unequal expansion between components and board
leading to fracture because of coefficient of thermal
expansion (CTE) mismatch
Increased brittleness of metals
Relative humidity/moisture
High
(natural/induced)
Moisture absorption
Metallization corrosion (on-chip) [11] [32] [33]
[31]
Delamination [11] [33] [34] [35]
Chemical reaction
Loss of electrical properties owing to corrosion and
Corrosion
chemical reactions
Electrolysis
Cracking in electronic parts owing to moisture
absorption [18] [11] [33]
Reduction in electrical resistance because of
conduction through moisture
Low
Pressure
High
Desiccation
Loss of mechanical strength
Embrittlement
Structural collapse of components
Granulation
Alteration of electrical properties
Compression
Structural collapse of assemblies including electronic
(natural/induced)
components
Penetration of seals
Interference with function
Low
Expansion
Explosive expansion of assemblies
Outgassing
Alteration of electrical properties
Loss of mechanical strength
Insulation breakdown and arc over
Wind
Force application
Structural collapse
(natural)
Deposition of materials
Interference with function
Heat loss (low velocity)
Loss of mechanical strength
Heat gain (high velocity)
Mechanical interference and clogging [18]
Accelerated abrasion [18]
Accelerated low-temperature effects (low velocity)
Accelerated high-temperature effects (high velocity)
14
Environmental Factors
Principal Effects
Possible Failures
Salt spray
Chemical reactions
Increased wear of electronic parts and assemblies
(natural)
Corrosion
Alteration of electrical properties
Electrolysis
Interference with function
Surface deterioration
Increased conductivity
Metallization corrosion [18] [11] [32] [33]
Sand and dust
Abrasion
Increased wear of electronic parts owing to material
(natural)
Clogging
degradation
Interference with function
Alteration of electrical properties
Air pollution
Chemical reactions
Interference in functionality because of clogging
(natural)
Clogging
Deterioration in material properties owing to chemical
reactions
Corrosion
Rain
Physical stress
Structural collapse
(natural)
Water absorption and immersion
Increase in weight
Erosion
Electrical failure
Corrosion
Structural weakening
Removes protective coatings
Delamination and cracking [11] [33] [36]
Surface deterioration
Enhances chemical reactions like corrosion
Ionized gases
Chemical reactions
Change in electrical properties
(natural)
Corrosion
Deterioration in material properties
Change in conductivity
Freezing rain/frost/snow
Low temperature
Mechanical stress caused by CTE mismatch between
(natural)
Moisture ingress [34] [35]
structural components
Corrosion/chemical reactions
Increase in weight
Clogging
Change in electrical properties owing to change in
resistance/conductivity
Delamination [11] [33] [34] [35]
Material deterioration
On-chip failures (metallization corrosion,
delamination) [11] [32] [33]
Fungus
Clogging
Change in electrical characteristics owing to shorts and
(natural)
alteration in electrical resistance
Oxidation of structural elements of the circuit
Static electricity/electrostatic
Change in electrical response
Interference in function owing to changes in electrical
discharge
Electrical overstress
properties (resistance, voltage)
(natural/induced)
Shorts and opens in circuit caused by electrical
overstress and electrostatic discharge [21]
Chemicals
Chemical reactions
Alteration of physical and electrical properties
(induced)
Reduced dielectric strength
Insulation breakdown and arc over [11]
Metallization corrosion [12] [32] [33]
15
Environmental Factors
Explosion
Principal Effects
Severe mechanical stress
(induced)
Shock
Possible Failures
Rupture and cracking
Structural collapse of assemblies and parts
Thermal
Mechanical stress
On-chip failures (die fracture, cracking,
(induced)
electromigration, wire flexure fatigue, shear fatigue)
[11] [12] [29] [33]
Solder joint fatigue [14] [15] [37]
Unequal expansion between components and board,
leading to fracture because of CTE mismatch
Mechanical
Mechanical stress
Loss of mechanical strength
Fatigue
Interference with function
Increased wear of electronic assemblies
Solder joint fatigue [14] [15] [37]
Structural collapse of assemblies
Vibration
Vibration/
Mechanical
Loss of mechanical strength
(induced)
acceleration
stress
Interference with function
Fatigue
Increased wear of electronic assemblies
Solder joint fatigue [14] [15] [37]
Structural collapse of assemblies
Rotation
Mechanical
Twisting of electronic assemblies
stress
Intermittent interconnections
Torsional
Loss of mechanical strength
acceleration
Bending
Mechanical
Bending failure of electronic components and
stress
assemblies
Fatigue
Cracking
Thus, it is necessary to classify and determine the combined effects of
environmental factors wherever they occur. Some examples of the possible effects of
pairs of environmental factors are given in Table 2 (adopted from [19]). The effects of
each pair of environmental factors can be classified as follows:
•
Intensified deterioration
The combined effect of the environmental factors on the electronic equipment is
more than that caused by each environmental factor. For example, in the drilling
process, the electronics at the tip of the tool experience high temperature, shock and
vibrations. These factors could intensify the effect of each other. High temperatures
16
may make the material weaker, and associated shock and vibrations can then cause
cracking-type failures in the assemblies.
An increase in one environmental factor can also lead to the increase in another,
thereby intensifying the net effect. This is different from the above case where both
environmental factors affect the failure mechanism directly. For example, high
temperatures accelerate growth of some fungus and microorganisms. This can be a
problem with permanently installed downhole fixtures, which are at high
temperatures. With a small amount of humidity present, growth of microorganisms
can occur on electronic assemblies and the organic processes can cause chemical
changes and contamination, causing loss of performance.
•
Coexistence without any synergistic effects on deterioration of the
equipment
The two environmental factors act independently on the electronic equipment and
do not influence each other’s effect. For example, acoustic vibrations of the noise
produced during the drilling operations do not have any significantly additive effect on
the potential hazards caused by fungal and organic activity in the vicinity of electronic
parts.
•
Weakened net effect
The two environmental factors diminish the effect of each other. For example,
high temperature can increase outgassing of constituents of the structural material of
electronic parts, while high pressure generally decreases it. Permanently installed
downhole gauges typically experience high-temperature and high-pressure conditions.
17
The increase in one environmental factor can also lead to the reduction of another
and consequently the net effect is reduced. For example, low temperature generally
retards growth of fungus; therefore, the effects of the presence of fungus are reduced
with low temperature.
•
Incompatible
The coexistence of the environmental factors is not possible. Certain combinations
of environmental factors, e.g., snow and high temperature, cannot exist.
Table 2: Examples of generic effects of combined environments on electronic products
Combined
Environments
Classification of
Effects
High temperature and
Intensified deterioration
salt spray
High temperature and
Possible Effects
High temperature tends to increase the rate of corrosion caused by salt
spray and thereby aggravate the net effect [32].
Intensified deterioration
high relative humidity
High temperature increases the rate of moisture penetration and also the
rate of corrosion. Thus the combination can aggravate failures caused by
humidity (e.g., corrosion, delamination) [32] [36].
High temperature and
Intensified deterioration
high pressure
High temperature and
Each of these environmental factors lead to deterioration in strength of
the material and can cause structural failure in electronic assemblies.
Intensified deterioration
fungus
High temperatures provide a congenial environment for growth of
fungus and microorganisms. Thus high temperatures aggravate failures
caused by fungal growth of electronic assemblies (typically from 25°C
to 71°C) [38].
High temperature and
Intensified
Both acceleration and high temperature affect material properties. The
acceleration
deterioration/weakened net
combination, however, can reduce failure caused by fatigue/fracture
effect
because the material stress relaxes at high temperatures and becomes
more pliable. Failures caused by solder joint fatigue and cracking are
diminished by the combination. In the case of brittle materials, however,
this combination can lead to early failures because the material becomes
weak at high temperatures and can easily fracture.
High temperature and
Intensified
The erosion caused by sand may be accelerated by temperature, which
sand and dust
deterioration/weakened net
can cause wear of structural parts caused by abrasion. At the same time,
effect
high temperature also reduces the penetration of sand and dust, thereby
decreasing failures that occur from dust penetration [19].
Low temperature and
humidity
Intensified deterioration
Relative humidity increases as temperature decreases (especially in
moist conditions), and lower temperature may induce moisture
condensation. If the temperature is low enough, frost or ice may result.
Hence low temperatures can aggravate failures caused by humidity, frost
or ice (e.g., corrosion).
18
Combined
Environments
Classification of
Effects
Possible Effects
High temperature,
Intensified
Vibration, shock and high temperature affect material properties and
shock and vibration
deterioration/weakened net
cause deterioration of mechanical properties. The combination, however,
effect
reduces failure caused by fatigue/fracture, because the material stress
relaxes at high temperatures and becomes more pliable. Failures caused
by solder joint fatigue and cracking are diminished by the combination.
In case of brittle materials, however, this combination can lead to early
failures because the material becomes weak at high temperatures and
can easily fracture.
Low temperature and
Intensified deterioration
high pressure
Low temperature and
Weakened net effect
salt spray
Low temperature and
Intensified deterioration
Low temperature increases dust penetration and can aggravate failures
caused by wear of assemblies and alteration of electrical properties.
Weakened effect
fungus
Low temperature,
Low temperature reduces the corrosion caused by salt spray; The
combination produces a weakened effect [32].
sand and dust
Low temperature and
The combination can cause structural failure like leakage through seals
and airtight enclosures.
Low temperature reduces fungus growth. At subzero temperatures, fungi
remain in suspended action, thereby weakening the net effect [38].
Intensified deterioration
shock and vibration
Low temperature tends to intensify the effects of shock and vibration,
because certain materials (like aluminum) tend to go brittle at lower
temperatures. However, this is a consideration only at very low
temperatures.
Low temperature and
Intensified deterioration
acceleration
Acceleration produces either shock or vibration or both. Hence, low
temperature and acceleration intensify the effects of acceleration,
because of brittleness at low temperatures.
Humidity and high
Intensified deterioration
pressure
The effect of this combination varies with the temperature. High
temperature can aggravate the deleterious effects caused by humidity
and high pressure, indirectly aggravating the net effect on an electronic
assembly.
Humidity and salt
Intensified deterioration
spray
High humidity may dilute salt concentration and could affect the
corrosive action of the salt by increasing its mobility and spread, thereby
increasing the conductivity. Corrosion failures, like shorts and opens in
the metallization and interconnects, are typically aggravated [32].
Humidity and fungus
Intensified deterioration
Humidity, sand and
Intensified deterioration
Humidity helps the growth of fungus and microorganisms but adds
nothing to their effects [38].
dust
Humidity and
increases deterioration by corrosion.
Intensified deterioration
vibration
Humidity, shock and
Sand and dust have a natural affinity to water, and this combination
This combination tends to increase the rate of breakdown of electrical
material and connections.
Intensified deterioration
acceleration
The periods of shock and acceleration, if prolonged, aggravate the
effects of humidity, because humidity tends to deteriorate material
properties. The combination can lead to early structural failure.
Salt spray and fungus
Incompatible
This is considered an incompatible combination.
High pressure and
Intensified deterioration
This combination intensifies structural failures in electronic and
vibration
electrical equipment.
19
Combined
Environments
Classification of
Effects
High pressure, shock
Intensified deterioration
and acceleration
Possible Effects
This combination intensifies structural failures in electronic and
electrical equipment.
Salt spray and dust
Intensified deterioration
Sand and dust have natural affinity to water, and this combination
Salt spray, shock or
Coexistence without any
These combinations produce no added effect.
acceleration
synergistic effects on
increases deterioration by corrosion.
deterioration of the
equipment
Salt spray and
Intensified deterioration
This combination tends to increase the rate of breakdown of electrical
Incompatible
This is considered an incompatible combination.
Intensified deterioration
Vibration increases the wearing effects of sand and dust.
Coexistence without any
Since shock is a form of vibration, this combination doesn’t produce any
synergistic effects on
added effects.
vibration
Salt spray and
material and connections.
explosive atmosphere
Sand, dust and
vibration
Shock and vibration
deterioration of the
equipment
Vibration and
Intensified deterioration
acceleration
This combination produces increased effects when encountered with
high temperatures and low pressures (typically in the oil suction
regions).
High temperature and
Intensified deterioration
low pressure
As pressure decreases, outgassing of constituents of materials increases;
as temperature increases, outgassing increases. Hence, each tends to
intensify the effects of the other.
High temperature and
Coexistence without any
Temperature has minimal effect on the ignition of an explosive
explosive atmosphere
synergistic effects on
atmosphere but does affect the air-vapor ratio, which is an important
deterioration of the
consideration.
equipment
High pressure and
Intensified deterioration
explosive atmosphere
Low temperature and
High pressure aggravates effects of explosion and thereby enhances the
hazards of an explosive atmosphere.
Intensified deterioration
low pressure
This combination can accelerate leakage through seals and airtight
regions. It can cause material deterioration and loss of functionality in
hermetic parts (which are typically used in oil electronics equipment)
[39] [40].
Low temperature and
Coexistence without any
Temperature has minimal effect on the ignition of an explosive
explosive atmosphere
synergistic effects on
atmosphere but does affect the air-vapor ratio, which is an important
deterioration of the
consideration.
equipment
Humidity and
Weakened net effect
explosive atmosphere
Low pressure and salt
spray
Humidity has no effect on the ignition of an explosive atmosphere, but a
high humidity will reduce the pressure of an explosion.
Intensified deterioration
This combination can lead to increased penetration of moisture into the
equipment and thus enhance the rate of material deterioration and
corrosion related failure mechanisms.
20
Combined
Environments
Classification of
Effects
Low pressure and
Coexistence without any
fungus
synergistic effects on
Possible Effects
This combination does not add to overall effects.
deterioration of the
equipment
Low pressure and
Intensified deterioration
explosive atmosphere
At low pressures, an electrical discharge is easier to develop, but the
explosive atmosphere is harder to ignite.
2.4 Summary
In oil and gas exploration and production, an unreliable product can put large
amounts of investment at risk. A major portion of a product’s cost is committed during
the design phase. Making changes to a design after production is expensive. An LCEP
for electronics used for oil and gas exploration and production will help to incorporate
environmental load conditions in the product’s design process. It will help identify
phases of most damage and the loads that cause most damage during those phases. The
determination of LCEP, thus, will improve the life cycle cost of the electronic product
by reducing failure, reducing overdesign and improving protection during phases that
are found to be most damaging.
In this chapter we have presented a standard methodology for developing an LCEP
for electronics used in oil and gas exploration and production applications. Key steps
of identifying significant phases in the life of the electronic equipment, identifying the
environmental loads acting on the equipment during each of these phases, and
quantifying these loads based on analysis, experience and experimentation have been
demonstrated. Environmental factors that are critical to the reliability of electronic
equipment used for oil and gas exploration and production applications have been
identified and their effects have been discussed. The procedure mentioned above is
21
used in order to develop the life cycle profile for the HPQG in order to assess its
reliability.
22
1
1,3
1
1
3
1–
1
1–
3
2
3
1
3
1
2
1
1
2
1
2
3
1–
1
1
1
1
1
1
1
1–
1–
1
1
4
2
1–
2
1–
1
1
2
1
2
3
2
1
1–
1–
3
1–
2
1–
1
2
2
2
2
3
1–
1–
1–
1–
1
1
1
1
2
3
3
2
3
2
2
2
2
1–
2
3
1–
1–
1–
3
1
1–
2
1
1
1–
1–
2
1–
1–
1–
1–
1
2
2
1
1–
1–
2
1–
2
3
2
2
2
2
1–
1
2
4
1
2
2
2
1–
2
1–
2
3
2
2
2
2
1
2
2
2
2
2
2
2
3
2
2
2
2
2
2
2
2
2
3
3
3
3
2
1
1
2
2
2
Humidity
High pressure
Low pressure
Wind
Salt Spray
Sand and dust
Snow
Rain
Chemicals/gases
Fog
Air pollution
Freezing rain
Fungus
Acceleration
Explosion
Shock
Figure 5: Effects of combined environments on electronic equipment (adopted from [2])
Vibration
1
1
1
1–
1
3
4
1
1
3
1
4
1
1,3
2
1
1,3
Low temperature
4
High temperature
23
High
temperature
Low
temperature
Humidity
High pressure
Low pressure
Wind
Salt spray
Sand and dust
Snow
Rain
Chemicals/gases
Fog
Air pollution
Freezing rain
Fungus
Acceleration
Explosion
Shock
Vibration
1 Intensified deterioration
2 Coexistence without any synergistic deterioration
3 Weakened net effect
4 Incompatible
(–) Minus sign indicates that intensification through
combination is weak or doubtful
Chapter 3
Physics of Failure based Reliability Assessment of HPQG
High temperature, vibration and shock environments primarily characterize the life
cycle of the HPQG. Majority of the HPQG applications have been below 100°C. In
this chapter we present a systematic effort to study the reliability of the printed wiring
boards used in the HPQG considering its entire life cycle for operation at higher
temperatures close to 150°C. A physics of failure approach for reliability assessment
of the HPQG printed circuit boards (PQG101 and PQG202) using thermo-mechanical
simulations and accelerated testing has been used. We have identified leading
degradation mechanisms at the interconnect (board) level as well as at the
package/chip level. Accelerated thermal test has been performed to assess reliability of
the boards under high temperature operation.
3.1 Reliability Assessment Methodology
Past efforts on reliability qualification of the permanent monitoring gauges have
primarily been statistical in nature and were based on field data [1]-[8]. Majority of the
HPQG installations have been for application below 100°C and they have achieved a
reliability target for 5 years. Installations above 125°C have been few and inadequate
for any statistical conclusions. In order to assess the reliability of the HPQG for
operation at 150°C, physics of failure based reliability assessment methodology was
24
adopted. Pecht et al [26] have suggested an engineering approach for assessment of
reliability of oil electronics based on a “Physics-of-failure” approach.
The physics of failure approach is a methodology developed to assess product
reliability based on failure mechanisms, failure modes, defect magnitudes and
environmental stresses for the application under consideration. POF is an approach to
aid in the design, manufacture and application of a product to expected life-cycle
stresses. It provides a more scientific way to assessing reliability than the traditional
statistical methods. Reliability assessment involves the evaluation of the products
potential to survive for the mission life in the application environment. The physicsof-failure based assessment of electronic product has the following steps –
1. Virtual reliability assessment
a. Design capture
b. Defining life cycle environmental loads
c. Failure modes and effects and analysis
d. Stress assessment
e. Damage and life assessment
2. Accelerated reliability testing
3. Reliability assessment
There is documented evidence on how physics of failure provides a better means
for reliability prediction [41] - [46]. Physics of failure methodology has been
successfully used for reliability assessment of electronic modules for various
applications e.g., space, automotive etc. [55]. Reliability assessment of printed circuit
25
boards PQG101 and PQG202 using physics of failure methodology is described in the
following sections.
3.2 Virtual reliability assessment of HPQG PCBs
Virtual reliability assessment is a methodology for assessing electronics through
the use of validated failure models and simulation tools. The methodology involves
the application of simulation software to model the physical hardware and to
determine the probability of the system meeting the desired life goals. The virtual
qualification was performed using calcePWA software [56] and CADMP software
[46]. CalcePWA software was used for determining assembly level (PCB level)
interconnect failures while CADMP was used to model the ICs on the printed circuit
board for further on-chip failure mechanisms.
3.2.1 Design Capture
As described earlier, the HPQG consists of two PCBs – PQG101 and PQG202.
The boards PQG101 and PQG202 were modeled using calcePWA software. Table 3
shows the information required for the modeling of the boards.
Table 3: Details required for board modeling using calcePWA software
Part information
Interconnect information
Dimensions (x, y, z)
Solder area and height
Location on PCB (x,y)
Lead geometry and dimensions
Package standoff
Solder material
ThetaJC
Lead material
Operational power dissipation
Package material
Board information
Board layers and composition
Board dimension (x,y,z)
Number of drill holes (vias)
Via and capture pad geometry
Materials – Board, solder, trace, via,
pad
All the parts in PQG101 and PQG202 were insertion mount. All ICs were dual
inline packages, all connectors were modeled as single inline packages, axial diodes,
26
inductors and resistors were modeled as axial packages, canned transistors and boxtype resistors and capacitors were modeled as pin grid array packages. All
interconnects were soldered with High Melting Point solder (HMP). Parts were either
ceramic or metal. Lead material was either Alloy42 or copper.
3.2.1.1 PQG101
PQG101 is an 8-layer single sided polyimide board (8 layers of copper and 7
layers of polyamide). The board is clamped at 6 points to support it on a steel chassis.
There are 61 parts (40 unique) on board – 12 active (diodes, transistors and ICs) and
49 passive (resistors, capacitors, and connectors). There are 490 drill holes in all – 116
vias, 374 component lead holes (4 types) and clamping holes. Figure 7 shows the
PQG101 CCA modeled in calcePWA.
Figure 6: PQG101 circuit card assembly
Figure 7: PQG101 CCA - calcePWA model
3.2.1.2 PQG202
PQG202 is a 6-layer single sided polyimide board (6 layers of copper and 5 layers
of polyamide). The board is clamped at 5 points to support it on a steel chassis. There
are 79 parts (27 unique) – 61 passive (inductors, capacitors, resistors and connectors)
and 12 passive (diodes, transistors and IC devices). There are 392 drill holes – 137
vias, 250 component lead holes (5 types) and 5 clamping holes. Figure 8 shows the
27
circuit card assembly PQG202. Figure 9 shows the PQG202 modeled in calcePWA.
Table 4 gives the dimensions of the boards, the layer thickness and the power
dissipation of the boards. Figure 10 shows an example of the design capture details for
one capacitor and one via.
Figure 8: PQG202 circuit card assembly
Figure 9: PQG202 CCA - calcePWA model
Table 4: Dimensions and power dissipation of PQG101 and PQG202
PQG101
PQG202
Length X Width
(in)
14.64 X 0.90
7.93 X 0.92
Thickness
(in)
0.063
0.063
28
Power Dissipation
(W)
3.116
0.661
3.2.2 Life-Cycle Environmental Profiles
A life-cycle environment profile is a forecast of events and associated
environmental conditions that equipment will experience from manufacturing to end
of life [19]. Life-cycle environment profile information is necessary for both the
simulation of the HPQG for its life cycle, and for understanding and interpreting the
physical analysis observations. The product’s life-cycle environment describes the
storage, handling and application scenario of the product, as well as the expected
severity and duration of the load conditions for each scenario. Load conditions include
temperature, humidity, pressure levels, vibration or shock loads, chemically aggressive
or inert environments, sand, dust, electromagnetic radiation levels, and loads caused
via
C8 – E082311 Capacitor (PQG202)
Via-D0.7 - D1.4 (PQG101)
100pF, 50V Ceramic Capacitor
Drill size – 701um
Power dissipation – 0.36 mW
Pad size – 1450um
Package dimensions – 7.6x2.4x6.11 mm
Plating material – Cu
Package standoff – 0.42mm
Finish material – Au
IO span – 6mm
Pad thickness – 35um
Lead thickness – 0.58mm
Plating thickness – 10-12um
Modeled as a Pin Grid Array package with two leads
Finish thickness – 2um
Figure 10: Details of design capture - an example
29
by operational parameters such as current, voltage and power [18]. The reliability of
the HPQG electronics is primarily affected by three environmental conditions –
1. Temperature
2. Vibration
3. Shock
Other factors like humidity, sand, dust, rain can be neglected due to the hermetic
assembly of the gauges. Another critical environmental factor in downhole gauges is
pressure. However, pressure is critical to ensure the reliability of the mandrel in which
the gauges are housed rather than the electronics themselves.
The different stages in the life cycle of the HPQG can the corresponding
environmental loads are described as follows –
1. Qualification and screening
2. Storage at test facility
3. Transportation
4. Storage at destination
5. Transportation to usage site
6. Installation
7. Operation
The different stages in the life cycle of the HPQG with the corresponding
environmental loads are described as follows -
30
3.2.2.1 Qualification and screening
During qualification the boards are taken through a temperature step test from
25°C to 150°C (operating temperature) and back in steps of 25°C. The dwell at each
temperature is 30 mins. The ramp rate is 3°C/min. The step test is performed for one
week. The boards are also subjected to a mild vibration in order to fine defects in the
assembly process. Figure 11 shows the thermal profile for qualification and Figure 12
shows the vibration profile.
3.2.2.2 Storage at test facility:
After the boards have been tested they remain in the testing facility for about a
week before they are shipped to the site of use. During this time they are kept in a
controlled steady temperature of about 25°C.
0.035
1 40
0.03
1 20
0.025
PSD (g^2/Hz)
T e m pe ratu re (
1 60
1 00
80
60
40
0.01
0.005
20
0
0 .0 0
0.02
0.015
0
0 .50
1 .00
1 .5 0
2 .0 0
2 .5 0
0
3 .0 0
50
100
150
200
250
300
350
Frequency (Hz)
T im e (d a y s )
Figure 11: Qualification thermal profile
Figure 12: Qualification vibration profile
3.2.2.3 Transportation
Transportation profile (especially thermal profile) depends on the origin and
destination environmental conditions. Two different profiles were developed in order
31
to have a more comprehensive approach. The profiles were for transportation under
two scenarios –
1. From 43°C to -70°C (from hot source to cold destination)
2. From -24°C to 58°C (from cold source to hot destination)
However, simulation results show that transportation in both cases have arguably
the same effect on the reliability of the electronic boards. Moreover, the thermal loads
during this transportation do not contribute significantly to the aging of the two
boards. Hence only the first case is presented in this paper as the results in both cases
are almost the same. The transportation phase was developed for a 40 day period
80
60
60
40
40
20
Tem perature (C
Temperature (C)
consisting of transportation by air (one day) and land.
20
0
-20
0
-20
-40
-40
-60
-60
0
5
10
15
20
25
30
35
40
-80
0
Time (days)
5
10
15
20
25
30
35
40
Tim e (days)
Figure 13: Transportation profile for high
temperature destination
Figure 14: Transportation profile for low
temperature destination
The permanent monitoring gauge experiences random vibrations during its
transportation. The vibration profile was determined by placing sensors along with the
gauge during an actual shipping process. Figure 15 shows the vibration profile during
transportation. The gauge may face severe shocks during transportation due to
accidental drops and mishandling. The worst case shock level which the tool can
32
experience was estimated to be 500g in 2ms duration. Figure 16 shows the shock
profile.
Acceleration (g)
0.7
PSD (g2/Hz)
0.6
0.5
0.4
0.3
0.2
0.1
600
400
200
0
0
0
0
500
1000
1500
2000
2500
0.5
1
1.5
2
Time (ms)
Frequency (Hz)
Figure 15: Vibration PSD profile for
transportation
Figure 16: Shock profile for transportation
3.2.2.4 Storage (at destination):
The electronics once transported to the destination may be stored for about a
month before actual installation. As the equipment is stored inside a storage facility, it
undergoes moderate fluctuations in temperature due to daily variations. The storage
period is typically 6 weeks. For this simulation the variations are taken between 20°C
to 30°C.
3.2.2.5 Transportation (to installation site)
The downhole monitoring electronics is taken to the installation site from the
storage facility. The transportation vibration and shock conditions were taken from the
previous profile. The temperature profile depends on the destination and for the low
temperature case it was taken as a variation between -65°C to -70°C.
3.2.2.6 Installation
The installation of the downhole monitoring electronics typically takes 30 hours.
During this the equipment is subjected to temperature loads (both temperature shock
33
and gradient) and shock loads. The thermal profile consists of a sudden temperature
rise when the tool is brought in contact with the hot liquid and then a gradual change
in temperature as the tool is lowered down. The thermal profile for the installation
phase is shown in Figure 17. Shock profile during installation is the same as discussed
Temperature (C)
for the transportation profile and is shown in Figure 16.
200
150
100
50
0
-50
-100
0
10
20
30
Time (hours)
Figure 17: Thermal profile for installation at low temperature destination
3.2.2.7 Operation (including a brief period of dormancy)
Normal operation of the gauge electronics is at a constant temperature of 150°C
(operating temperature) for 5 years. Every six months the boards are brought down to
a temperature of 25°C for a day for maintenance purposes. Figure 18 shows the
thermal profile during operation. The vibration experienced by the boards during
operation is shown in Figure 19.
34
0.2
2
PSD (g /Hz)
Temperature (C)
160
140
120
100
80
60
40
20
0
0.15
0.1
0.05
0
0
50
100
150
0
200
100
200
300
400
500
Frequency (Hz)
Time (days)
Figure 18: Operational thermal profile
Figure 19: Operational vibration profile
The above described was modeled using calcePWA. The profiles were used for
damage and life analysis of the printed circuit boards.
3.2.3 Failure modes, effects and criticality analysis
A FMECA involves a systematic review to identify single point failures, and the
causes and effects of such failures. For each subsystem the failure modes and their
effects on the rest of the system are evaluated and recorded on a FMEA worksheet as
described in Table 20 and Table 21. To complete the FMECA criticalities are assigned
to the failures6.
The failure modes, effects and criticality analysis for the printed circuit boards was
done according to the following methodology:
1. Definition of the system (which components are within the boundaries of
the study).
2. Definition of the main functions of the system.
6
The FMECA was performed by Schlumberger. Based on the results from the reliability analysis,
certain recommendations were made in order to modify the FMECA to include more failures.
35
3. Description of the operational modes of the system and the operational and
environmental stresses that may affect the system.
4. System breakdown into subsystems that can be handled effectively.
5. Preparation of a complete component list for each subsystem.
6. Identification of failures and their effects recorded on FMECA worksheets.
7. Determination of criticality for each failure.
Failure modes and effects were classified based on their criticality and probability
of occurrence based on the following matrices
High
Likely during five years of
operation
Moderate Possible during five years of
operation
Low
Unlikely during five years of
operation
Critical
Mission critical failure causing permanent loss
of electrical connection to downhole equipment.
Major
Failure that results in some lost data and requires
a change in operating conditions or procedures
to continue.
Nuisance
Failures that allows operation to continue and
data to flow.
Based on criticality
Based on occurrence
Figure 52 shows the functional blocks in the HPQG. The complete FMECA charts
are shown in Table 22 to Table 25.
Table 5: Distribution of failure modes in occurrence-criticality matrix
Probability\Criticality
Nuisance
Major
Critical
4
10
8
15
High
Moderate
Low
1
The 10 critical failures with moderate probability of occurrence are listed as
follows:
36
•
Bad soldering or open circuits in the cable line driver VQ3001 (Dual N&P
MOSFET)
•
Bad PCB board open circuits VQ3001(Dual N&P MOSFET)
•
R1 varies out of specification
•
Bad solder, bond-wire, circuitry or PCB failure at 80C154 µController, which
manages address & data
•
Bad solder, bond-wire, circuitry or PCB failure at 80C154 µController, which
managers I/O pins
•
Premature loss of stored M27C256 PROM program
•
Bad solder, bond-wire, circuitry or PCB failure at M27C256 PROM
•
Bad solder, bond-wire, or PCB failure of Digitizer DCM92 (Gate Array)
•
Degradation of Clock Crystal (Y1) or failure of C14, C15 (out of specification
C or R, short or open)
•
Bad DCM92 or bad solder, bond-wire, or PCB failure at the DCM92 digitizer
3.2.4 Component level design capture
Based on the results from the FMECA, 5 ICs were identified for further
component level analysis based on package and IC level failure mechanisms. The ICs
selected for further analysis are shown in Table 6.
Table 6: Selected ICs for component level analysis
IC Device
Description
Power
FMECA class
OP221
Dual low power Op-Amp
0.00561 W
Critical - low
VQ3001
Dual N & P MOSFET
0.072 W
Critical - moderate
80C154
Microcontroller
0.15 W
Critical - moderate
37
M27C256
UV PROM
0.06 W
Critical - moderate
DCM92
Gate Array
0.25W
Critical - moderate
The ICs were modeled using CADMP-II software. Package and IC level
information was required in modeling the ICs. Figure 20 shows the CADMP model
Figure 20: M27C256 UV PROM Device
for M27C256 PROM device and Table 7 shows some of associated design details.
Apart from the details listed, geometry and dimensions for each of the layers like case,
lid, seal, die attach and lead frame was entered in order to model the component.
38
Table 7: Component level modeling details
Manufacturer Data
Package level details
Die level details
Dual Inline Ceramic Package – 3.73 × 1.34 × 0.45
cm
Case material – 90% Alumina
Lid material – 90% Alumina
Die Attach Metallization – Bare base
Die Attach material – Silver Glass
Die Attach Temperature – 435oC (8-12 min)
Bond Finger metallization – Aluminum
Bonding Wire – 31.75 µm dia
Bonding method – Ultrasonic Wedge
Seal material – Vitreous glass
Seal temperature – 440oC (10-13min) – Dry Air
Lead frame material – Alloy 42 Aluminated
Lead finish – Tin plating
Cavity moisture - <5000 ppm
Dimensions and geometry of the lead, attach and
seal layers were also given
Die size – 2.06 x 1.39 mm (0.28 mm thickness)
Semiconductor material - silicon
Gate oxide thickness – 150 Å (Area – 1e-6 m2)
Metal thickness – 5000 Å
Metal width – 2 µm
Metallization – Al – 1%Si – 0.5%Cu
Passivation – 5000 Å USG/8000 Å PSG/7000 Å
SiON
Dimensions of the metallization was also given
Calculated values
Assumed values
Power dissipation – 0.018 W
Worst case current density – 2e+7 A/m2
Current – 30 mA
Barrier potential – 0.7V
Avalanche breakdown voltage – 50V
Drain to source voltage – 5V
3.2.5 Virtual Reliability Assessment
Life-cycle assessment is used to identify potential failure sites, damage
mechanisms and failure modes, based on the product architecture and life-cycle loads.
This step includes a stress, damage, and life assessment.
Given the captured hardware and the life-cycle environmental profiles, a reliability
assessment can be completed based on the dominant failure mechanisms of the circuit
card assemblies. The calcePWA™ software tool was used to model each PCB,
perform thermal and vibration simulations, and conduct a damage and life assessment.
39
CADMP-II software was used to model the IC packages, perform thermal
simulations7, and conduct a damage and life assessment.
3.2.5.1 Stress Assessment
The stress assessment can be divided into two parts – component level stress
assessment and board level stress assessment. The stress assessment is done to
transform the environmental and operational loads into stress fields on the electronic
assembly/component, which can lead to failures.
3.2.5.1.1 Board level stress assessment
As there are three primary loads on the printed circuit boards – temperature,
vibration, and shock, the stress assessment is done in three steps:
1. Thermal analysis
2. Vibration analysis
3. Shock analysis
Thermal analysis
The thermal analysis for the circuit card assemblies was performed at temperatures
of 25°C and 150°C. The thermal analysis was done by finite difference method using a
10 X 10 mesh for PQG101 and 10 X 10 mesh for PQG202.
Boundary conditions – Assuming the boards are in equilibrium with the
surrounding, the temperatures on the sides, bottom and top of the boards was modeled
equal to the ambient. Combined conduction and natural convection analysis was
7
Vibration simulation was not done at the package level since vibration does not pose a reliability issue
for on-chip failure mechanisms
40
performed for a vertically oriented printed circuit board. Figure 21 shows the assembly
and modes of heat transfer from the boards.
Steel
PCB
Clamps
Insulator
Steel
Small standoff to protect
soldered leads
Hot oil surrounding
the tube
(isothermal 150ºC)
Figure 21: Thermal boundary conditions
The thermal analysis results for PQG101 and PQG202 at a temperature of 150°C
is shown in the Figure 22 and Figure 23. A maximum of 1.2°C temperature rise was
found on PQG101 while a maximum rise of 1.6°C was found on PQG202.
Figure 22: Thermal analysis of PQG101 at 150°C
150.001
–
150.138
150.138
–
150.271
150.271
–
150.406
150.406
–
150.541
150.541
–
150.676
150.676
–
150.811
150.811
–
150.946
150.946
–
151.081
151.081
–
151.216
151.216
–
151.351
151.351
–
151.486
151.486
–
151.620
Figure 23: Thermal analysis of PQG202 at 150°C
150.000
–
150.099
150.099
–
150.197
150.197
–
150.296
150.296
–
150.395
150.395
–
150.493
150.493
–
150.592
150.592
–
150.691
41
150.691
–
150.789
150.789
–
150.888
150.888
–
150.986
150.986
–
151.085
151.085
–
151.182
Vibration analysis
The vibration stress analysis is done for four different vibration profiles
corresponding to testing, transportation, installation and operation. The vibration
analysis is done using finite element analysis with a mesh of 12 X 8 for PQG101 and
20 X 10 for PQG202.
Boundary conditions - Since the boards are fixed to the steel chassis as shown in
Figure 21 the boards are modeled with clamped points supports. The ideal mechanical
model for the board assembly is shown in Figure 24. The boards are supported at the
clamping points by rigid clamps and everywhere else by non-linear springs. The
springs offer no resistance for deflection within the standoff distance. For deflections
more than the standoff distance, the resistance due to the springs increases with
deflection becoming infinite at the thickness of the insulating sheet. However due to
limitations of the software, the boards were modeled as supported only at the clamping
points. This is a worst case assumption and the will result in conservative estimates.
This is shown in Figure 25. PQG101 is clamped at six points as shown in Figure 26
and PQG202 is clamped at five points as shown in Figure 27.
42
Figure 25: Worst case model
Fixed
Can restrain free
clamps
deflection
Standoff - x
Figure 24: Ideal mechanical model
Figure 26: Vibration boundary conditions for PQG101
Figure 27: Vibration boundary conditions for PQG202
The first three frequency modes for each of the boards were determined. The
dynamic response of the boards to the PSD profile was found by superimposing the
response at these three frequency modes. PQG101 frequency modes were 313.6Hz,
314.7Hz and 472.8Hz while those for PQG202 were 575.5Hz, 728.8Hz and 1556.2Hz.
Figure 28 and Figure 29 show the first frequency mode and the displacement profile
for PQG101 while Figure 30 and Figure 31 show the first frequency mode and the
displacement profile for PQG202.
43
Figure 28: PQG101 Mode 1- 313.6Hz
Figure 29: PQG101 Vibration displacement profile
Figure 30: PQG202 Mode 1 - 575.5 Hz
Figure 31: PQG202 Vibration displacement profile
Minimum
Maximum
Displacement color map
Shock
Shock analysis was performed for a shock load of 500g (2 ms). The ability of the
interconnects to sustain the shock level was analyzed. The boundary conditions for the
shock analysis were similar to the vibration analysis. Figure 32 and Figure 33 show
the displacement profile for PQG101and PQG202.
44
Figure 32: Shock displacement of components on PQG101
Figure 33: Shock displacement of components on PQG202
Minimum
Maximum
Displacement color map
3.2.5.1.2 Component level stress analysis
The component level thermal stress analysis was performed using a finite
difference method. Assuming that the component has come in equilibrium with the
surrounding, the temperatures at the top, bottom and sides of the IC package were
modeled equal to the ambient temperature (150°C). Temperature rise in the
components was in the vicinity of 0.1 to 0.3°C owing to their low power dissipation
during operation.
45
Figure 34: Thermal profile - M27C256
3.2.5.2 Damage and Life Assessment
Damage and life assessments for the IC components and the printed circuit boards
were performed. In case of component level analysis the results are in terms of
percentage of life left while in case of board analysis the results are in terms of
damage ratio.
3.2.5.2.1 Component level damage and life assessment
CADMP-II was used to perform the component level reliability analysis. The
failure models used in the damage and life assessment of the six IC packages include:
•
Black’s model (electromigration)[49]
•
Hermetic metallization corrosion [32]
•
Fowler Nordheim tunnel model (time dependent dielectric breakdown)[52]
•
Hu Pecht Dasgupta’s model (wire fatigue)[50]
•
Bond pad fatigue model[50]
•
Wire shear fatigue model[50]
•
Wire bond pad shear fatigue model[50]
46
The two most dominant degradation failure mechanisms in each of the ICs
analysed are shown in Table 8 to Table 12. No failures are expected during the 5 year
operating life of the ICs. Electromigration and metallization corrosion are the
prominent degradation mechanisms in all the ICs.
Table 8: OP221
Table 9: M27C256
Failure model
% remaining life
Failure model
% remaining life
Electromigration
0.979
Electromigration
0.995
Met corrosion
0.988
Met corrosion
0.997
Table 11: DCM92
Table 10: 80C154
Failure model
% remaining life
Failure model
% remaining life
Electromigration
0.970
Electromigration
0.949
Met corrosion
0.994
Met corrosion
0.995
Table 12: VQ3001
Failure model
% remaining life
Electromigration
0.994
Met corrosion
0.995
Sensitivity analysis was performed for all the five devices to assess the variation in
the damage due to each of the dominant failure mechanism with temperature. It was
found that damage due to electromigration changed significantly due to temperature
while the damage due to metallization corrosion remained fairly the same. Figure 35
and Figure 36 show the sensitivity analysis data for DCM92 IC device.
47
Figure 35: DCM92 - electromigration
sensitivity analysis
Figure 36: DCM92 - metallization corrosion
sensitivity analysis
Table 13: % Remaining life - DCM92
125ºC
150ºC
175ºC
Electromigration
0.983
0.949
0.872
Metallization corrosion
0.995
0.995
0.995
3.2.5.2.2 Board level damage and life assessment
Board level damage assessment was performed using calcePWA. Solder joint
fatigue models for through-hole interconnects were used to evaluate board level
reliability. The failure models evaluated were as follows
•
Thermal fatigue for insertion mount packages
•
Random vibration fatigue
The results from board level vibration and temperature stress analysis were used as
inputs, along with the life cycle environment profile, to evaluate the damage occurring
during the life cycle of the printed circuit boards. After evaluating the damage due to
wear out mechanisms, the failures were ranked in the expected order of the occurrence
48
(earliest and most critical to the less critical ones). The first five predicted failures for
PQG101 and PQG202 are shown in Table 14 and Table 15. Figure 37 shows the two
leading components on the vibration displacement profile for PQG101. The damage
ratio along with the percentage of the total damage done by each of the failure
mechanisms is shown. Results show that no failures are expected in the 5 year
operating life of the boards due to these mechanisms. However, vibration is the
dominant degradation mechanism in the printed circuit boards.
Table 14: Ranking of failures in PQG101
Table 15: Ranking of failures in PQG202
Component Damage %Vibration %Thermal
ratio
C5
0.75
~100
~0
C4
0.40
~100
~0
CR2
0.37
~100
~0
C10
0.20
~100
~0
C2
0.18
~100
~0
Component Damage %Vibration %Thermal
ratio
R29
0.01
~100
~0
TP7
~0
C18
~0
C9
~0
C19
~0
-
C5
C4
Figure 37: Vibration displacement profile for PQG101 with C5 and C4
The damage assessment of the boards for shock intensity of 500 g (2 ms) was done
using calcePWA. The analysis was done taking shock failure as an overstress
mechanism. The ability of the interconnects to sustain the applied shock levels was
49
evaluated and the results were given in terms of success or failure of the interconnects
to survive the shock loads. Table 16 and
Table 17 show the potential failures identified in PQG101 and PQG202. It was
decided to conduct a shock test in order to verify the results. However it should be
noted that both vibration and shock analysis was performed considering an extremely
worst case of dynamic response from the boards because of only 5 or 6 fixed clamp
supports.
Table 16: Components showing potential failures due to shock in PQG101
Component ID
Component ID
Component ID
Component ID
CR7
R17
R6
R7
C17
CR1
CR2
C13
C16
R22
C1
C2
C4
C5
C10
C9
C12
C16
Table 17: Components showing potential failures due to shock in PQG202
Component ID
Component ID
Component ID
Component ID
R29
R17
CL1
TP8
TP9
R13
C13
R14
C23
C6
C1
R27
C20
R28
R1
R5
R6
C10
C7
C19
C16
C9
R4
R22
R24
R3
R10
C8
C14
C18
R9
C21
R25
R23
C17
R18
3.3 Accelerated thermal testing
Accelerated thermal testing of the printed circuit boards was performed in order to
assess reliable operation of the boards at high temperature. Specific objectives were to
assess high temperature reliability of all the components using sub-assembly level
50
testing, assess drift in the output from the boards to extended periods of operation at
high temperature and to assess degradation due to identified degradation mechanisms
like electromigration, intermetallic growth and hermetic metallization corrosion.
3.3.1 Accelerated test loads and acceleration factor
The stable operating limit for the boards was 175°C. In order to obtain maximum
time compression on the thermal testing, it was decided to test the boards at 175°C.
Table 18 gives a justification for usage upto 175°C from a materials standpoint.
Acceleration factors for different steady state temperature dependent failure
mechanisms were calculated. The values for DCM92 are shown in Table 19. Since the
temperature at the top of the die is similar in all the components the acceleration
factors for all of them no significant difference.
Table 18: Material Tg/melting points for stable operations upto 175°C
Polyimide/E-glass - 250°C
Copper - 1083°C
Aluminum - 660°C
Alloy 42 - 1425°C
HMP - 296°C
Alumina - 2054°C
Table 19: Acceleration factors for DCM-92
IC – DCM92
Electromigration
Met. Corrosion
TDDB
125°C to 175°C
7
~1
35
150°C to 175°C
2.5
~1
5.1
3.3.2 Accelerated test setup
Two sets of HPQG assemblies were prepared. The requirements for the setup were
as follows-
51
Two printed circuit boards PQG101
Solder equipment
Two printed circuit boards PQG202
Oscilloscope
4 Temperature crystals8 and 2 reference crystals
PC and a data collection software
Data acquisition unit
A gauge simulator
High temperature wires
A thermal chamber capable of going upto 175oC
The boards were baked at 125°C. Two temperature crystals and one reference
crystal were soldered to each PQG202 board which was then connected to PQG101
boards using high temperature wires. The two HPQG assemblies were placed in the
thermal chamber. Output from the two HPQG assemblies (from PQG101) and one
gauge simulator9 was connected to the data acquisition unit. The data acquisition unit
was connected to the serial port of a PC loaded with a real-time monitoring software.
3.3.3 Calibration
Since the boards were new, their electrical response was not calibrated to
surrounding conditions. So a temperature step test was conducted in order to calibrate
the boards. The boards were taken from 25°C to 175°C in steps of 25°C and back. At
each temperature the boards were kept for 12 hours. The ramp rate was about
3°C/min. Apart from calibrating the response, the test served to –
8
•
Check operation of the boards upto 175°C
•
Check if there is any hysteresis in the response of the boards
As a sub-objective, it was decided to test how compatible temperature crystals are on the pressure line
of the PQG electronic boards, considering that the frequency outputs from the pressure and temperature
crystal are very close to each other. Hence each PQG202 had two temperature crystal instead of one
pressure and one temperature crystal.
9
Gauge simulator sends dummy frequency signals corresponding to temperature and pressure values to
check if the data acquisition unit is working properly.
52
•
Check if output from the boards is stable at constant temperature
The boards worked fine upto 175°C without any hysteresis and had stable output
at constant temperature. The coefficients from the calibration profiles were input into
the software to give the exact temperature output on the monitor. Figure 38 - Figure 41
show the results of the calibration test. It is clear from the results that the temperature
line of the HPQGs have a linear response with increasing temperature while the
pressure line has a non-linear response. This is because of the mismatch in the
frequency between temperature crystal and frequency for which the pressure line
16000
180
14000
160
Temperature line response
Pressure line response
circuit is designed.
12000
10000
8000
6000
4000
2000
y =-88.467x + 17458
20
40
60
80
100
120
140
160
180
120
200
y =1.1537x - 38.599
100
80
60
40
20
0
-20 0
0
0
140
20
40
60
Actual temperature
160
12000
140
Temperature line response
Pressure line response
180
14000
10000
8000
6000
y =-89.317x + 17250
2000
0
20
40
60
80
100
120
120
140
160
180
200
Figure 39: HPQG-1 Temperature line response
16000
0
100
Actual temperature
Figure 38: HPQG-1 Pressure line response
4000
80
140
160
180
120
100
80
40
20
0
-20 0
200
Actual temperature
y =1.1524x - 42.738
60
20
40
60
80
100
120
140
160
180
200
Actual temperature
Figure 40: HPQG-2 Pressure line response
Figure 41: HPQG-2 Temperature line response
3.3.4 Failure criteria
The printed circuit boards were to be declared failed if
•
One or both output lines of either of the boards stop responding
53
•
If the frequency response of the crystals drifts away from the range of 10
KHz to 50KHz permanently or temporarily
This was translated into ±10% drift in the mean value of the outputs
from the boards
•
If there is ± 25% variation (a spike) in any measurement from the mean
value
Real time output from the boards was monitored and stored in order to detect any
failures occurring during the high temperature testing. Alarms were set at 135°C and
215°C (in the monitoring software) to point out any measurements beyond the +/-25%
limits.
3.3.5 Accelerated testing
After the calibration was done, the boards were tested at 175°C for 4500 hours.
Figure 42 - Figure 45 show the results of the testing. It is clear from the results that the
output from the pressure line has far more variations compared to the output from the
temperature line. It can be concluded from this that the temperature crystal on the
pressure line does not perform satisfactorily and thereby can’t be used as a substitute
on the pressure line of the HPQG. In order to calculate the drift in the circuit, linear
and non-linear trends were fit to the temperature line response. Figure 46 and Figure
47 show the trends in the output from the temperature line of the two HPQGs. The
linear fit shows a 0.06% drift in HPQG-1 and 0.11% drift in HPQG-2. The non-linear
fits show an asymptotic convergence at a temperature of about 175.2°C. Hence, the
linear fit is a more conservative estimate of the output trends from the HPQGs.
54
Individual readings stayed within +/- 25% of the mean value (~175°C). Both the
boards were working at the end of 4500 hours of testing and response was stable from
185
185
183
183
Temperature line response (
Pressure line response (ps
both the boards.
181
179
177
175
173
171
169
167
165
181
179
177
175
173
171
169
167
165
0
1000
2000
3000
4000
0
1000
2000
Time (hours)
4000
Figure 43: HPQG-1 Temperature line output
185
185
183
183
T em preature line response
Pressure line response (p
Figure 42: HPQG-1 Pressure line output
181
179
177
175
173
171
169
167
181
179
177
175
173
171
169
167
165
165
0
1000
2000
3000
0
4000
1000
2000
Figure 44: HPQG-2 Pressure line output
Tempreature line response
(C)
175.5
175
174.5
174
1000
2000
4000
Figure 45: HPQG-2 Temperature line output
176
0
3000
T im e (hours)
Time (hours)
Temperature line
response (C)
3000
Time (hours)
3000
4000
175.5
175
174.5
174
0
Time (hours)
Figure 46: HPQG-1 Drift in temperature line
response
176
1000
2000
3000
4000
Time (hours)
Figure 47: HPQG-2 Drift in temperature line
response
55
3.4 Visual Inspection
The boards were inspected under the microscope after thermal testing to see if
there is evidence of any incipient failures or severe degradation. No significant defects
or signs of degradation were observed in either of the boards. Benign cracks on the
solder joint and some of the traces were found, but they did not affect the functionality
of the boards. It was also concluded that the cracks won’t see any significant
degradation due to further high temperature testing. Figure 48 to Figure 51 show the
cracks on the solder joint and traces.
Figure 48: Cracks on capture pads
Figure 49: Solder joint on an axial leaded
component
Figure 51: Cracks on traces
Figure 50: Solder joints and via connections on
the back side of the PCB
56
PQG electronics
Functional Block Diagram
HPQG
1.0 PQG101
Board
• Regulate the
tool’s power
1.1 Power
regulation
• Protect against
current or voltage
overloads
1.2
Protection
Receive the
surface
communications
• Transmit the
gauge’s
measurements
•
•
Manage the
addresses and data
Check the card
working
• Contain the
µcontroller program
• Communicate the
program
• Provide the
µcontroller clock
Digitalize pressure
and temperature
frequencies
1.3
Telemetry
receiver
1.4 Telemetry
transmission
1.5
µController
2.0 PQG202
Board
2.1 Pressure
oscillator
• Oscillate the
pressure crystal
3.0 Quartzdyne
sensor
3.1 Pressure
Crystal
Provide pressure
frequency
2.2 Reference
Oscillator
3.2 Reference
Crystal
• Oscillate the
reference crystal
• Provide reference
frequency
2.3 Temperature
Oscillator
3.3 Temperature
Crystal
• Oscillate the
temperature crystal
Provide temperature
frequency
1.5 PROM
2.4 Mixers
1.6 Clock
oscillator
2.5 Wave
Shaping & filter
Combine reference and
• Pressure frequency
• Temperature frequency
1.7 Counter
Filter and amplify
the output signal
Figure 52: Functional block diagram of the HPQG electronics
57
Table 20: General description of a FMECA header
System
Component
System name and part number
Component name and part number
Mission Mode What is the state of the system during each of the steps below?
Key Function What does this component do? What is its purpose?
Table 21: General description of a FMECA chart
Item #
58
The
reference
number for
a specific
failure
mode of a
specific
component.
Component
name &
P/N
Operating
condition
The name &
part number
of the
component
in the
subsystem.
Operation
condition
under
which the
failure
occurs for
the
component
part listed.
Failure mode
1.
2.
3.
For each component’s
function and operational
mode failure modes are
identified and recorded.
A failure mode is defined
as the manner by which a
failure is revealed. All
units are designed to
fulfill one or more
functions; a failure is thus
defined as nonfulfillment of one or
more of these functions.
Failure Effect
Local
Next Higher
End system
Failure Effect:
The main effects
of the identified
failure modes on
the subsystems.
System Effect:
The main effects
of the identified
failure modes on
the primary
function of the
system and the
resulting
operational status
of the system after
the failure.
Cause of
Failure
Control Measures,
Follow-up
Corrective Action,
or Opportunity for
improvement (OFI)
The possible
failure
mechanisms
(corrosion,
erosion,
fatigue, etc.)
that may
produce the
identified
failure modes.
This is a statement of
possible actions to
prevent, or to correct
the failure and restore
the function or to
mitigate its serious
consequences. Also
recorded are actions
that are likely to
reduce the probability
of occurrence of the
failure.
OFIs may also be
described that are
recommendations for
improvements in
design or procedures.
Failure Classification
Criticality
Probability
Critical
High
Major
Medium
Nuisance
Low
See Section on
FMECA
See
Section
FMECA
Table 22: FMECA header for PQG101
System
Component
HPQG Electronics Digital / Regulator Board
PQG101
Mission Mode Powered on continuously making P/T measurements & transmitting
Key Function Count P & T Freqs, regulate pwr and transmit measurements
Table 23: FMECA chart for PQG101
Item #
see
Figure
52
1.11
PQG101
Compone
nt name
& P/N
PQG101
+5V Pwr
Regulator
LT1021A
_5
Operat
ing
conditi
on
Failure mode
Always
active
Loss of +5V
power
1.
2.
3.
1.
2.
59
3.
1.12
PQG101
+5V Pwr
Regulator
2N2905A
Always
active
Loss of +5V
power
1.
2.
3.
1.13
PQG101
Pwr Reg
2N2905A
& R15
Always
active
Loss of +5V
power
1.
2.
3.
Failure Effect
Local
Next Higher
End system
Failure Classification
Criticality
Probability
- Critical
- High
- Major
- Medium
- Nuisance
- Low
Critical
Low
Cause of Failure
Control Measures or Followup Corrective Action or
Opportunity for
improvement (OFI)
LT1021A_5 open
circuit output
Component was specially
qualified and is screened Hi
Rel Mil Spec
OFI: Add a 2nd, redundant part
Loss of +5V
output
No power to
boards
No P/T
measurement
Open circuit output
Component was specially
qualified and is screened Hi
Rel Mil Spec
OFI: Add a 2nd, redundant
regulator
Critical
Low
Loss of +5V
output
No power to
boards
No P/T
measurement
Open circuit of
connection
between
components
2N2905A & R15
due to bad
soldering or
broken path
1.
2.
3.
Critical
Low
Loss of +5V
output
No power to
boards
No P/T
measurement
Technology was qualified
Vendor was qualified
Process is qualified and
controlled
Item #
see
Figure
52
1.14
1.15
60
1.16
1.17
PQG101
Compone
nt name
& P/N
PQG101
Pwr Reg
printed
circuit
board
PQG101
Pwr Reg
CR7
Operat
ing
conditi
on
Failure mode
Always
active
Loss of +5V
power
1.
2.
3.
Always
active
PQG101
Pwr Reg
C3
Always
active
PQG101
Pwr Reg
C11
Always
active
Failure Classification
Criticality
Probability
- Critical
- High
- Major
- Medium
- Nuisance
- Low
Critical
Low
Fabricator was qualified
Process was qualified and
is controlled
ΜController rapidly
degrades (depends on
surface V & cable
config.)
1. Short circuit
of CR7 (0 V out)
2. Short circuit
between input &
output of
regulator
1.
Component was specially
qualified and is screened
Hi Rel Mil Spec
Power derating
Major
Low
V regulation
degraded (out
of spec)
1. Short life
2N2905A
2. V Reg out of spec
3. Loss of P/T
accuracy
Variation or open
circuit of R18
1)
Component is specially
qualified and screened
Power derating
Major
Medium
V regulation
degraded (out
of spec)
1)
2)
V Reg out of spec
Loss of P/T
accuracy
Short lifetme
Current leakage
through
capacitance
Changes in
capacitance value
1)
Component is specially
qualified and screened
Voltage derating
Major
Medium
1) V Reg out of spec
2) Loss of P/T
accuracy
3) Short Lifetime
Current leakage
through
capacitance
Changes in
capacitance value
1)
Component is specially
qualified and screened
Voltage derating
Major
Medium
Regulation
lost
3)
1.18
Control Measures or Followup Corrective Action or
Opportunity for
improvement (OFI)
1.
2.
3.
PQG101
Pwr Reg
R18
Cause of Failure
Open circuit of
connection in
board
1.
2.
Always
active
Failure Effect
Local
Next Higher
End system
V regulation
degraded (out
of spec)
Loss of +5V
output
No power to
boards
No P/T
measurement
2.
2)
2)
2)
Item #
see
Figure
52
1.21
1.22
1.31
PQG101
Compone
nt name
& P/N
Protection
Passive
mode
Protection
Active
mode
61
Telemetr
y receiver
U3 OP221
Operat
ing
conditi
on
Failure mode
Passive
mode
Active
mode
Passive
mode
Failure Effect
Local
Next Higher
End system
Cause of Failure
Transition
into active
mode
unjustified
Loss of P/T accuracy or
no measurements at all
Failure of VQ3001
Protection is
short circuited
1) No transmissions
2) Tool’s head
voltage too low (out of
spec low)
3) No P/T
measurements
1.
2.
3.
Loss of gauge
transmission
1)
2)
3)
U3 Pin 7 stays
high
Loss of
transmission
No P/T
measurements
Short-circuit
• OP221
• LT1021
Control Measures or Followup Corrective Action or
Opportunity for
improvement (OFI)
1)
Component is specially
qualified and screened
2) Fabrication process under
strict anti-electrostatic
conditions
Long term life qualification
made at high temperature
(150deg C)
Failure Classification
Criticality
Probability
- Critical
- High
- Major
- Medium
- Nuisance
- Low
Major
Medium
Major
Low
• Resistor R11
Short circuited
OP221
Component is specially
qualified and screened
Critical
Low
1.41
Telemetry
transmissi
on
U1
VQ3001
Transm
it gauge
signals
Loss of gauge
transmission
1) Constant head
volts
2) Loss of
transmission
3) No P/T
measurements
Open circuited R1,
VQ3001 or
µController
Component is specially
qualified and screened
Critical
Low
1.42
Telemetry
transmissi
on
U1
VQ3001
Transm
it gauge
signals
Loss of gauge
transmission
1)
Solder broken
Qualification of technology,
process, supplier
Critical
Medium
2)
3)
Constant head
volts
Loss of
transmission
No P/T
measurements
Item #
see
Figure
52
1.43
PQG101
Compone
nt name
& P/N
Telemetry
transmissi
on
U1
VQ3001
Operat
ing
conditi
on
Failure mode
Transm
it gauge
signals
Loss of gauge
transmission
1.
2.
3.
1)
1)
2)
Failure Effect
Local
Next Higher
End system
Cause of Failure
Control Measures or Followup Corrective Action or
Opportunity for
improvement (OFI)
Failure Classification
Criticality
Probability
- Critical
- High
- Major
- Medium
- Nuisance
- Low
Critical
Medium
Constant head
volts
Loss of
transmission
No P/T
measurements
PCB failure (path
opened)
Qualification of technology,
process, supplier
Constant head
volts
Loss of
transmission
No P/T
measurements
Variation of R1
out of spec
Component is specially
qualified and screened
Design derating
Critical
Medium
Telemetry
transmissi
on
U1
VQ3001
Transm
it gauge
signals
1.51
µControll
er U6
Manage
bus
address
es &
data
µC control
line failure
1)
Loss of gauge
functions
2) Loss of
transmission
3) No P/T
measurements
Solder failure
Bonding
failure
Silicon circuit
failure
PCB failure
Qualification of technology
Qualification of supplier
Qualification of process
Qualification test /shock &
vibration
Critical
Medium
1.52
µControll
er U6
Manage
bus
address
es &
data (17
pins of
bus)
µC I/O Pin
failure
1)
Solder failure
Bonding
failure
Silicon circuit
failure
PCB failure
Qualification of technology
Qualification of supplier
Qualification of process
Qualification test /shock &
vibration
Critical
Medium
1.44
Loss of gauge
transmission
1)
2)
3)
62
Loss of gauge
functions
2) Loss of
transmission
3) No P/T
measurements
Item #
see
Figure
52
1.53
PQG101
Compone
nt name
& P/N
µControll
er U6
Operat
ing
conditi
on
Failure mode
Control
noncritical
functio
ns
µC pin failure
of: REC_DIR,
REC_INT,
TXD, or RXD
1.
2.
3.
1)
2)
3)
Failure Effect
Local
Next Higher
End system
Multiple gauge
transmissions
overlap.
Board fails during
mfgr testing
No
communications
Cause of Failure
Control Measures or Followup Corrective Action or
Opportunity for
improvement (OFI)
Solder failure
Bonding
failure
Silicon circuit
failure
PCB failure
Qualification of technology
Qualification of supplier
Qualification of process
Qualification test /shock &
vibration
Failure Classification
Criticality
Probability
- Critical
- High
- Major
- Medium
- Nuisance
- Low
Nuisance
Low
63
1.54
PROM
Progra
m
content
Loss of
program
1)
2)
Program lost
Loss of gauge
functions
3) No P/T
measurements
Retention life
too short
Premature
aging
Component is specially
qualified and screened
Qualification life tested
Critical
Medium
1.55
PROM
Commu
nicate
content
Failure of
PROM
connection
1)
Solder failure
Bonding
failure
Silicon circuit
failure
PCB failure
Qualification of technology
Qualification of supplier
Qualification of process
Qualification test /T shock &
vibration
Critical
Medium
-
Qualification of quartz and
resistors
Qualification of supplier
Qualification of process
Qualification of DCM92
counter
Qualification test /T shock &
vibration
Critical
Medium
2)
3)
1.61
Clock
Oscillator
Y1, R14,
R15
Furnish
time
steps to
µContr
oller
Loss of
timing
frequency
1)
2)
Loss of one or
more PROM lines
Loss of all gauge
functions
No P/T
measurements
µController stops
Loss of all digital
board functions
3) No P/T
measurements
-
-
-
Failure of
quartz crystal Y1
Failure of
µController
power supply
Failure of
C14 or C15
(open or short)
Failure of
DCM92 oscout
Failure of
PCB
Item #
see
Figure
52
1.62
1.71
PQG101
Compone
nt name
& P/N
Clock
Oscillator
Y1, R14,
R15
Counter
DCM92
Operat
ing
conditi
on
Failure mode
Furnish
time
steps to
µContr
oller
Timing
frequency out
of spec
Digitize
the P/T
frequen
cies
Loss of count
or incorrect
count
1.
2.
3.
1)
2)
3)
1)
2)
3)
Failure Effect
Local
Next Higher
End system
µController stops
Loss of all digital
board functions
No P/T
measurements
Counts incorrect
No transmissions
or erratic
transmissions
No P/T
measurements
Cause of Failure
-
-
Degradation
of quartz
Xtal Y1
Failure of
C14 or C15
(out of spec)
Solder failure
Bonding
failure
Silicon circuit
failure
PCB failure
Control Measures or Followup Corrective Action or
Opportunity for
improvement (OFI)
Qualification of quartz and
resistors
Derating in voltage
Qualification of technology
Qualification of supplier
Qualification of process
Qualification test /T shock &
vibration
Failure Classification
Criticality
Probability
- Critical
- High
- Major
- Medium
- Nuisance
- Low
Critical
Medium
Critical
Medium
64
Table 24: PQG202 General description
System
Component
HPQG Oscillator Mixer Board
PQG002
Mission Mode Powered on continuously making P/T measurements & transmitting
Key Function Generate Pressure, Temperature and Reference Frequencies
Table 25: FMEA table for PQG202
Item #
see
Figure
52
2.11
PQG202
Component
name & P/N
Pressure
oscillator
Operating
condition
65
Oscillate
Quartz
Pressure
Xtal
Failure
mode
No
oscillation
Failure Effect
1. Local
2. Next Higher
3. End system
1)
2)
3)
2.12
Pressure
oscillator
Oscillate
Quartz
Pressure
Xtal
Frequency
out of spec
1)
2)
3)
Cause of Failure
Control Measures or
Follow-up Corrective
Action or Opportunity
for improvement (OFI)
No change
TP9
No P signal
out TP7
No P
measurement
Bad capacitor (out of spec)
Change in resistance value “
Change in 2N2857 “
Bad solder joint (open)
Component was
specially qualified and
is screened Hi Rel Mil
Spec
P Freq out of
spec
P output out
of spec (TP7)
Incorrect P
measurement
Change in capacitor (out of
spec)
Change in resistance value “
Change in 2N2857 “
Component was
specially qualified and
is screened Hi Rel Mil
Spec
Failure Classification
Criticality
Probability
- Critical
- High
- Major
- Medium
- Nuisance
Critical
- Low
Low
Critical
Low
Item #
see
Figure
52
2.21
PQG202
Component
name & P/N
Reference
oscillator
Operating
condition
Oscillate
the Quartz
Reference
Xtal
Failure
mode
No
oscillation
Failure Effect
1. Local
2. Next Higher
3. End system
1)
2)
3)
Cause of Failure
Control Measures or
Follow-up Corrective
Action or Opportunity
for improvement (OFI)
No V change
at TP3
No Ref signal
out TP3
No P or T
measurements
Bad capacitor (out of spec)
Change in resistance value “
Change in 2N2857 “
Bad solder joint (open)
Component was
specially qualified and
is screened Hi Rel Mil
Spec
Failure Classification
Criticality
Probability
- Critical
- High
- Major
- Medium
- Nuisance
Critical
- Low
Low
Reference
oscillator
Oscillate
the Quartz
Reference
Xtal
Frequency
out of spec
1)
Ref Freq out
of spec
2)
Ref output
out of spec
(TP3)
3)
Incorrect P &
T
measurements
Change in capacitor (out of
spec)
Change in resistance value “
Change in 2N2857 “
Component was
specially qualified and
is screened Hi Rel Mil
Spec
Critical
Low
2.31
Temperature
oscillator
Oscillate
Quartz
Temperatur
e Xtal
No
oscillation
4)
No change
TP8
No T signal
out TP6
No T
measurement
Bad capacitor (out of spec)
Change in resistance value “
Change in 2N2857 “
Bad solder joint (open)
Component was
specially qualified and
is screened Hi Rel Mil
Spec
Major
Low
T Freq out of
spec
T output out
of spec (TP6)
Incorrect T
measurement
Change in capacitor (out of
spec)
Change in resistance value “
Change in 2N2857 “
Component was
specially qualified and
is screened Hi Rel Mil
Spec
Major
Low
66
2.22
5)
6)
2.32
Temperature
oscillator
Oscillate
the Quartz
temperature
Xtal
Frequency
out of spec
1)
2)
3)
Item #
see
Figure
52
2.41
2.42
PQG202
Component
name & P/N
Pressure
Mixer
Temperature
Mixer
Operating
condition
Failure
mode
Combine
Ref & P
freqs
(Heterodyn
e)
Loss of
Mixer
function
Combine
Ref & T
freqs
(Heterodyn
e)
Loss of
Mixer
function
Filter T
signal
T Filtering
out of spec
Failure Effect
1. Local
2. Next Higher
3. End system
Loss of P
measurement
Shaping T
signal
(Q4 & Q7
ckt)
-
Loss of T
measurement
-
67
2.51
Cause of Failure
Loss of T
measurement
-
2.52
Shaping P
signal
(Q2 & U1
ckt)
Amplify T
out
T signal too
low
(Out of
spec)
Loss of P
measurement
-
Control Measures or
Follow-up Corrective
Action or Opportunity
for improvement (OFI)
Failure Classification
Criticality
Probability
- Critical
- High
- Major
- Medium
- Nuisance
Critical
- Low
Low
Qualification of
technology
Qualification of supplier
Qualification of process
Qualification test /T shock
& vibration
Major
Low
Solder failure
Bonding failure
Capacitor failure C12,
C9, C14
Silicon, circuit failure
(2N2907)
PCB failure
Qualification of
technology
Qualification of supplier
Qualification of process
Qualification test /T shock
& vibration
Major
Low
Solder failure
Bonding failure
Capacitor failure C5
Silicon, circuit failure
(2N2857 or HC14)
PCB failure
Qualification of
technology
Qualification of supplier
Qualification of process
Qualification test /T shock
& vibration
Major
Low
Solder failure
Bonding failure
Silicon circuit failure
( 2N2857 )
PCB failure
Qualification of
technology
Qualification of supplier
Qualification of process
Qualification test /T shock
& vibration
Solder failure
Bonding failure
Silicon circuit failure
( 2N2857 )
PCB failure
Item #
see
Figure
52
2.53
PQG202
Component
name & P/N
Shaping P
signal
(Q5, & Q6
ckt)
Operating
condition
Filter P
signal
Failure
mode
Filtering
out of spec
Failure Effect
1. Local
2. Next Higher
3. End system
Loss of P
measurement
Cause of Failure
-
Shaping P
signal
(Q3 & U1
ckt)
Amplify P
out
P signal too
low
(out of
spec)
Loss of P
measurement
3.11
Quartz
Pressure Xtal
Furnish P
freq
No
oscillation
Loss of P
measurement
68
2.54
-
Control Measures or
Follow-up Corrective
Action or Opportunity
for improvement (OFI)
Criticality
Probability
- Critical
- High
- Major
- Medium
- Nuisance
Critical
- Low
Low
Qualification of
technology
Qualification of supplier
Qualification of process
Qualification test /T shock
& vibration
Critical
Low
-
Critical
Low
Solder failure
Bonding failure
Capacitor failure C10,
C11, C13
Silicon, circuit failure
2N2907
PCB failure
Qualification of
technology
Qualification of supplier
Qualification of process
Qualification test /T shock
& vibration
Solder failure
Bonding failure
Capacitor failure C2
Silicon, circuit failure
2N2907
PCB failure
Failure of P Quartz :
Failure of Au plated
contacts
Twinning (abrupt
change in xtal structure)
Aging of Xtal
(increased motional
resistance)
Crack
Failure of Bellows seal
Failure Classification
Qualification of
Quartz component,
technology, process
& aging
- Individual motional
resistance test
- Qualification in
shock & vibration
- Qualification of
Bellows design,
process controls and
He leak inspections
Item #
see
Figure
52
PQG202
Component
name & P/N
Operating
condition
Failure
mode
Failure Effect
1. Local
2. Next Higher
3. End system
Cause of Failure
Control Measures or
Follow-up Corrective
Action or Opportunity
for improvement (OFI)
Failure Classification
Criticality
Probability
- Critical
- High
- Major
- Medium
69
3.21
Quartz
reference Xtal
Furnish ref
freq
No
oscillation
Loss of P & T
measurements
Failure of P Quartz :
Failure of Au plated
contacts
Twinning (abrupt
change in xtal structure)
Aging of Xtal
(increased motional
resistance)
Crack
-
- Nuisance
Critical
- Low
Low
3.31
Quartz
Temperature
Xtal
Furnish T
freq
No
oscillation
Loss of T
measurement
Failure of P Quartz :
Failure of Au plated
contacts
Twinning (abrupt
change in xtal structure)
Aging of Xtal
(increased motional
resistance)
Crack
-
Major
Low
Qualification of
Quartz component,
technology, process
& aging
- Individual motional
resistance test
- Qualification in
shock & vibration
Qualification of
Quartz component,
technology, process
& aging
- Individual motional
resistance test
- Qualification in
shock & vibration
Chapter 4
Results and Conclusions
A physics of failure based reliability assessment of the board interconnects and the
components was performed using numerical simulations (calcePWA and CADMP
software). Life cycle profile for the HPQG was developed using the methodology
described in Chapter 2. Thermal, vibration and shock analysis was performed for the
printed circuit board assemblies PQG101 and PQG202, using calcePWA. The thermal
analysis showed little temperature rise on the boards relative to the ambient
conditions. A maximum of 0.7°C was found on PQG101 and a maximum of 1.6°C
was found on PQG202. A worst-case mechanical model was used for vibration and
shock analysis. First three fundamental modes of oscillation of the boards were found.
PQG202 had higher frequency modes than PQG101 because it is a stiffer assembly.
Displacements of the components due to shock loads were calculated. FMECA for
PQG101 and PQG202 identified 38 failure modes. Critical IC devices were selected
from FMECA classification of medium or low probability of failure for on-chip and
package level reliability analysis. Thermal analysis was perfomed on these five
selected IC devices using CADMP. Due to low power dissipation during operation,
the rise in temperature at the die was in the vicinity of 0.1°C to 0.3°C. Stress analysis
at the interconnect (assembly) level and the component level helps assess the response
of the hardware elements to environmental loads.
Stress analysis results are used in failure models at the board interconnect level as
well as component level in order to perform damage and life analysis. Board level
70
damage and life analysis was performed using calcePWA. Solder joint fatigue models
– Thermal fatigue models for insertion mount interconnects and random vibration
fatigue models were used to assess the wear-out damage in the interconnects at the
board level. Life cycle profile developed was used to determine the loads at each stage
of the life cycle of the boards. Stress analysis results were used to determine the
response (stress values) at each stage due to these loads. Results show that solder joint
fatigue due to vibration the prime degradation mechanism in the interconnects at the
PCB level. No failures are expected in the board interconnects during the 5-year life of
the boards. Degradation due to vibration fatigue is much higher in PQG101 than in
PQG202. Thermal fatigue causes negligible degradation in the life of the board level
interconnects. This is expected since the life cycle of the boards predominantly has
steady state high temperature rather than thermal cycling. Steady state temperature
does not significantly affect the life of PCB level interconnections. Shock analysis was
performed as an overstress assessment. The ability of the component interconnects to
withstand the shock loads was evaluated and potential failures were predicted. The
results can be verified by drop tests (500g 2ms).
Component level damage and life analysis was performed using CADMP
software. Electromigration, metallization corrosion, time dependent dielectric
breakdown, wire fatigue, wirebond fatigue and pad fatigue failure models were used to
assess the time to failure due to each of these mechanisms. Results show that no
failures are expected during the 5-year life of the IC devices. Electromigration and
hermetic metallization corrosion are the two leading degradation mechanisms.
Sensitivity analysis was done to assess the variation in the damage at different
71
temperatures. Significant variation in damage due to electromigration is seen with
change in operating temperature, while the change in damage due to metallization
corrosion is negligible.
The acceleration factors corresponding to various steady state temperature
dependent failure mechanisms were calculated. Accelerated thermal testing was
performed at 175°C to further assess the reliability of the printed circuit boards using
two representative HPQG assemblies. The boards were operated at 175°C
uninterrupted for 4500 hours. The prime objectives were
1.
To check if any of the identified component level failure mechanisms show
signs of degradation
2.
To check the drift in the frequency output from the sensor crystals
Real time temperature output from the boards was monitored in order to determine
failure. No failures in the boards were observed in 4500 hours of testing. Plotting the
output trend from the boards show that there is very little drift in the measurements.
0.06% drift was observed in one of the HPQGs, while 0.11% drift was observed in the
other. 10% drift in the output was required for the boards to qualify as failed boards.
Extrapolation of the results proves that no failures are expected during 5- year
operation of the boards at 150°C due to the operating temperature. Post test visual
inspection of the boards indicated that there is no evidence of any incipient failure or
significant degradation on the boards. The printed circuit boards are reliable for high
temperature operation at 150°C.
72
4.1 Upratability of the printed circuit boards
Uprating is the process of assessing the ability of a part to meet the functionality
and performance requirements for the application in which the part is used outside the
manufacturer-specified temperature range. Uprating is considered when there are no
electronic parts rated to operate at the required application temperature and other
alternatives are found to be technically incompatible or inadequate. In our study on
the reliability assessment of printed circuit boards PQG101 and PQG202, we tested
the boards at a temperature of 175°C for 4500 hours monitoring the functionality of
the boards. The boards were typically rated for use upto 150°C. No failures were
observed in the 4500 hours of testing and the boards met the functionality required by
the application. Thereby, the testing also supports the upratability of the boards for
operation upto 175°C. The IC devices used in the printed circuit boards are rated in the
military range of -55°C to 125°C. The results of the test also support the upratability
of these military grade IC devices to extended temperatures upto 175°C. The IC
devices are listed in chapter 3 under component level testing.
4.2 IEEE 1413 analysis
IEEE Std. 1413-1998 [58] [59] identifies a framework for reliability prediction
processes for electronic systems (products) and equipment. In order to comply with
IEEE Std 1413-1998 a reliability prediction report should provide documentation of
the prediction results, the intended use of prediction results, the method(s) used for the
prediction, a list of inputs required to conduct the prediction, the extent to which each
73
input is known, sources f known input data, assumptions used for unknown input data,
figures of merit, confidence in the prediction, sources of uncertainty in the prediction
results, limitations of the results, and a measure of the repeatability of the prediction
results .
A list of criteria is provided in IEEE Std. 1413-1998. The criterion consists of
questions that concern inputs, assumptions, and uncertainties associated with each
methodology, enabling the risk associated with the methodology used. The list of
questions along with their answers corresponding to the methodology used in the
present study have been provided in Table 26.
Table 26: IEEE Std 1413 – Reliability prediction methodology questionnaire
Q
Does the methodology identify the source used to develop the prediction methodology and
describe the extent to which the source is known?
A
Yes. The methodology used for the prediction is the Physics of failure approach developed at
CALCE, University of Maryland. The methodology is well described and has been used
successfully in different cases for reliability prediction. Both the softwares calcePWATM and
CADMPTM have well documented software models and reference within their manuals.
Q
Are assumptions used to conduct the prediction according to the methodology identified,
including those used for any unknown data?
A
Yes. For example, it has been assumed that proper output from the boards implies proper
functioning of the components on the PCB. Values like breakdown voltage and junction voltage
for the IC devices have been assumed from the default values used by the software tool.
Q
Are limitations of the prediction results identified?
A
Yes. For example, the virtual reliability assessment is a point estimate. In reality, the time to
failure is a distribution. Moreover, the mechanical model used for vibration analysis is a worst-
74
case condition due to the limitation of the modeling software. Combined temperature and
vibration loads can lead to more damage than each of the loads individually. This combined effect
has not been analyzed in this study.
Q
Are sources of uncertainty in the prediction results identified?
A
Yes. For example, all the values used for the calculation have some form of distribution.
However, nominal values have been used for point estimates adding uncertainty to the
calculations. Similarly, the environmental conditions have been estimated based on generic data
and there is uncertainty associated with the validity of those values at a given period of time.
Q
Are failure modes identified?
A
Yes. For example, electromigration will lead to an open. Solder joint fatigue will lead to an open.
See FMECA chart in chapter 3 for a list of expected failure modes.
Q
Are failure mechanisms identified?
A
Yes. For example, thermal and vibration fatigue at the board interconnect level. Electromigration
and metallization corrosion at the die level. See chapter 3 for complete details.
Q
Are confidence levels for the prediction results identified?
A
No. Distributions for the input data were not available in order to form confidence intervals and
no distributions were assumed.
Q
Does the methodology account for life cycle environmental conditions, including those
encountered during a) product usage (including power and voltage conditions), b) packaging, c)
handling, d) storage e) transportation, and f) maintenance conditions?
A
Yes. Please refer chapter 2.
Q
Does the methodology account for materials, geometry, and architectures that comprise that part?
A
Yes. Please refer to chapter 3 – design capture
Q
Does the methodology account for part quality?
A
Yes. A screen test was performed on the new pair of HPQG assemblies used for this study. The
successful screen test is indicative of the good quality of the HPQG assemblies. It is also possible
to account for part quality by including variations in the part parameters. However, in this
75
assessment nominal values were taken for analysis.
Q
Does the methodology allow incorporation of reliability data and experience?
A
Yes. If field failures are known, root cause analysis can be used to find out causes of failures and
the results of the assessment can be validated. Improvements can be made in the assumptions and
constants used in the assessment process based on the actual data.
4.3 Contributions
A methodology to assess environmental considerations in electronics used in oil
and gas extraction and production applications was developed. Steps to develop a life
cycle profile were described. A list of environmental factors along with the associated
failures in electronic systems was developed. Emphasis was given on assessing the
effects of combined environmental. Combined environmental factors were classified
and their effects were listed for some example cases.
Failure mechanisms associated with electronics used in permanent monitoring
gauges were identified by a case study on reliability assessment of a downhole
permanent monitoring gauge using physics-of-failure approach. The gauge electronics
was tested for high temperature reliability. A case for uprating of the electronics
assembly was described.
76
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