DESIGN FOR CLEANING AND RELIABILITY
DfR / KYZEN Webinar
10-8-15

1. Device Reliability Matters?
2. How Does the Assembler Reduce Contamination and Improve Cleaning Effects?
3. REAL TIME (RT) SIR
4. Conclusions

• Continue to shrink
• Performance capabilities grow
• Becoming more integrated into our daily lives https://www.mccrone.com/electronic-devices-industries

• Device Reliability
– Must demonstrate quantitative maximum failure rate
– Evidence of product and test capabilities
– Sound procedures for process control
– For field failures, review and corrective action http://www.digitaltrends.com/wearables/introducing-apex-homeland-securitysnext-generation-first-responder-suit/

• Complexity of Systems challenge
– Missions
– Environments
– Safety
– New technologies
– Life testing
Screen in Reliability
• Must perform
– Loss of life, aircraft
– Customers demand HiRel
– Lost revenue Design in Reliability

• Patient care monitoring
• Implantable devices
• Products must work on demand
– High impedance circuits demand cleanliness
• Move from leaded to lead-free products http://www.connector.com/2015/03/3d-medical-device-design-efficiency-and-simplicity-using-flexible-print-circuit-technology/

• Electronics are advancing
– Advanced Driver Assist
– Powertrain & Chassis
– Body & Comfort
– Driver Information
& Connectivity
• Smart Cars
– Failure is not an option
Source: Google

• Reliability Metrics
– Uptime service as required
– How long the electronics can perform without interruption
– How quickly service can be restored
– Contracted support commitments http://www.digitalartsonline.co.uk/features/creative-business/adobe-never-mind-products-heres-creative-services-opportunity/

• Harsh environments are a reliability challenge
– Health and Fitness
– Track merchandise
– Monitor your cognitive patterns
– Track GPS
– Continuous heart rate
– Sleep
– Distance walked
– Calories burned http://www.insidecounsel.com/2014/11/18/6-cutting-edge-ip-trends-to-look-for-in-2015?page=3

• On demand performance http://www.geglobalresearch.com/focus/silicon-carbide

• Equipment Performance Analysis
– Failure modes
– Cause / Effect
– Mechanisms
– Field Formats
– Other Performance
Indicators http://www.unidec.com/index.shtm

• What consumers say about customer loyalty
– 39% of customer loyalty attributed to supplier brand
– 9% attributed to price
– 53% of customer loyalty is purchase experience
• Product performance
• Service
• Warranty
• In respect to electronics
– Many products have an electronic component
– Reliability is more tilted to electronics than mechanical
– Product failure can lead to devastating consequences http://www.thenational.ae/business/the-life/reliability-matters-more-than-price-in-product-marketing

HOW DOES THE ASSEMBLER REDUCE
CONTAMINATION AND IMPROVE
CLEANING?

• QFN / MLF components
– Increased usage
– External metalized terminations
– Part of the component board
• Issues include
– Voids
– Entrapped contamination
– Cleaning

• Flux residue under BTC is a function of
– Attractive and repulsive capillary forces
• When the Z-Axis is less than 2 mils
– Flux residue capillary forces attract during reflow
– Heavy flux residue deposits accumulate in the
• Streets
• Interconnecting pads
• Attractive force renders
– Significant level of flux residue
– Underfills component with flux residue
– Flow channels closed

• High standoff gaps
– Flux outgases during reflow
– Capillary forces are negative
– Residues burn off with residue forming around solder pads
Air Flow and Exhaustion

• Residue trapped under BTC
– Flux has a channel to outgas
– Flux under component reduced
– Opens the cleaning process window

• Voiding
– Large voids form when flux does not have a channel to outgas
• Flux Activity
– No Clean flux residues must outgas
– Trapped residues are active and should be cleaned
Kummerl, S. (June, 2014). Texas Instruments Advanced Packaging Trends. SMS Emerging Technology Forum.

• Pad Finish
• Pad Elevation
• Solder Paste Thickness
• Solder Mask
• Solder Mask Definition
• Preforms
• Via holes to facilitate outgassing

Source: www.internationalcircuits.com

Source: www.maximintegrated.com

Source: www.maximintegrated.com
NoSM

Source: www.indium.com

S e e r t t s
Via Hole diameter 11-12 mils

NSMD NoSM NSMD NoSM
25 Holes
9 Holes
Solid with
Hole in
Streets

Research is a Joint Collaboration Between STI Electronics and KYZEN Corp.
Published at SMTAI, 2015
Bixenman, M., Lober, D., McMeen, M., & Tynes, J. (2015). Cleanliness Becomes More Important when Miniaturization Kicks In. SMTAI, 2015

• When ions are mobilized
– The corrosion process is initiated
• Oxidation and reduction of metal ions
• When biased, mobilized metal ions migrate
• Metallic fragments plate out until a dead short occurs
• Contamination Sources
– Components
– Printed Circuit Boards
– Flux residues
– Material handling
– Upstream / Downstream
– Touch up and Repair
– Environmental conditions

• Problem results from
– Active flux residues under BTC
– Environmental conditions
PCB
+ + + + + + + +
+ + + + + + + +
+ + + + + + + +
+ + + + + + + +
Board Terminations
Liquid Carrier
Metal Ions
Migrating Metal Ions
+
+ +
++ ++++++ ++
+++
++++
+++++
+ + + + + +
-
Applied Voltage
McMeen, M. (2014, Nov.). Complex Electronic Assembly
Cleanliness Requirements. Objectively Quantifying “Clean
Enough.” STI Electronics, Inc. IPC/SMTA Cleaning and
Coating Conference.

Parts Removed with Heat Only
Residue Pool Across Pads!!!
Looks Can Be Deceiving

• Key concerns
– Resistive and Capacitive effects
– Residue trapped between the part and the board
• Presence of mildly conductive residues
– Drop the resistance between adjacent pins
– Permit current leakage during operation
• The presence of mildly capacitive residues tend to
– Provide a potential source of charge storage
– Undermines the integrity of high frequency circuits
• Any foreign substance will have some
– Potentially measurable electrical property
– Deviates from that of air and/or PCB dielectric substrate material
– Real time SIR test vehicle seeks to isolate and illuminate

• The test vehicle utilizes
– QFN package with a large ground lead in the center
– Part is 7mm square with 0.5 mm pin pitch
– Ground lead serves as an
• Electrical reference
• Thermal path for the part
• Large volume of solder
– Flux devoid of ionic residue must
– Activate
– Vaporize
– Evacuate/outgas

Designed by STI Electronics, Inc.

• The influences of
– Humidity on resistance measurements
– No-clean flux types
• Halide-free vs. standard
– Propensity of test vehicles to return to baseline conditions after exposure to environmental accelerants (hysteresis)
– Effectiveness of flux outgassing
• Ground Lug
– Solid
– Via hole to outgas

• The boards were subjected to a
– Series of extended environmental stresses
– Induce any flux residue-related electrochemical changes
– 40°C and 95% relative humidity (non-condensing) for 168 hours (1 week)
– 5VDC voltage bias was applied between the ground terminal and perimeter leads
– Prolonged electromotive force to the residue
• The intent was to coax the alignment of ionic compounds using a persistent electric field
– High impedance measurements
– After the 168 hour exposure
• Boards were return to ambient conditions (25°C and 40% RH) to dry out
• Measurements were again taken at regular intervals to capture any subsequent recovery of electrical properties
• After stabilization, the boards were returned to the environmental chamber for a final round of identical stresses and regular measurements

• Miniaturization speeds up failure
– Highly dense interconnects
– environmental factors
• To build in quality
– Definition of the finished product performance expectations is the starting point
– What are the performance objectives in relation to size, speed, cost, mass, style and efficiency?
– By first screening in reliability the product can be designed for the end use environment
– It is critical to plan for the environment in which the device will be used

• Corrosion process is initiated through
– Oxidation and reduction of metal ions
• Ionic residues are mobilized based on
– The strength of the ion-dipole forces of attraction with water
– The intermolecular bond with water creates an electrolytic solution
– When the electrolyte solution comes in contact with solder alloy, component metallization and pad, metal oxides can dissolve into the electrolyte
– The metals mobilized within the electrolyte can plate out in the form of dendrites
– The leakage current from these dendrites reduces resistivity

– A fluid carrier system must be present in order to
• Mobilize ions
• Current leakage pathway
• Water is the most viable carrier system
– In dry conditions
• Ions will not migrate
• High levels of contamination lay dormant
• Minimal risk

• Site specific method
• Risk assessment under BTCs
– Evaluate the cleanliness levels
– Humidity is needed in order to coax electrochemical phenomenon to manifest in a measurable way
– The absence of moisture in samples can mask the presence of flux residue by rendering it immobile, allowing potentially innocuous compounds to lay dormant until sufficiently hydrated
– Outgassing flux residues under bottom terminations provides a channel to reduce active residues under the bottom termination

• Mike Bixenman
Kyzen Corp. mikeb@kyzen.com