Reflow Solder Oven
October 8, 2013
Team #55
F13-55-RFLO
Project Manager:
Patrick Selzer
ME
pselzer@siu.edu
Project Members:
Michael Ladd
ME
michaelladd@siu.edu
Corey Seidel
EE
coreyseidel@siu.edu
Patrick Mooney
CE
Client: Joe Lenox [lofh@siu.ed]
FTA: Dr. Sareh Taebi [staebi@siu.edu]
Transmittal Letter
pbenmooney@siu.edu
November 21, 2013
Dr. A Harackiewicz
Southern Illinois University Carbondale
College of Engineering – Mail Code 6603
Carbondale, IL 62901
Dear Dr. Harackiewicz,
We have received your request for a proposal for a solder reflow oven. Attached you will
find a proposal for a design that implements the high standard of quality offered in a commercial
oven mixed with the low cost and design specifications known to be needed at the hobbyist level.
We would like to thank you for giving us the opportunity to bid on this project and we are
grateful for your interest in our system’s design.
Our method of using technology that is already found in widely available toaster ovens
keeps the product cheap and easily attainable for low cost. While we have put much effort into
simplicity, through effective designing, this reflow oven will compete with commercially
available ovens on the market while having cost of lower end ovens.
Through research and testing we have attained what we have found to be, optimal
performance goals. We thank you again for the chance to bid our design on the project. Great
expectations lie ahead in working with your business; we look forward to our groups’
collaboration in putting together a great product. If there are any concerns or questions regarding
the attached documents please feel free to contact us.
Sincerely,
Patrick Selzer
Project Manager
F13-55-RFLO
Saluki Engineering Company
pselzser@siu.edu
2
Executive Summary (PS)
A Reflow Soldering oven is a device that solders electronic components to their
respective contact pads on a printed circuit board. Unlike regular hand soldering, reflow methods
allow for circuit boards and motherboards to be soldered as a whole; opposed to each surface
mount device being soldered individually. Proper reflow offers the advantages of uniform,
precise heat flux to the components at a quick rate. This greatly decreases manufacturing time
per board.
The majority of commercial grade reflow ovens range in price of several thousands of
dollars and require technically experienced personnel to utilize. This forces small businesses and
electronic enthusiasts to use rudimentary, inaccurate methods of reflow to perform their desired
task. The proposed design will retrofit a consumer-grade convection toaster oven into a highly
controlled reflow oven at the fraction of the cost of commercial ovens. The oven will be
configured with a computer that is responsible for controlling the heating elements and
convection fan to match the desired temperature profile of the board. Stock temperature profiles
are built in to account for a multitude of different solders. In conjunction with the stock profiles,
the user interface will allow further customization of the profile after experimentation due to
potential board defects. These user interface features in tandem with dynamic heat flux control
will ensure precise reflow for smaller businesses and hobbyists regardless of experience.
The project is expected to be completed by March 14, 2014 allowing for considerable
amount of time for library experimentation and testing. The total cost of the project will be no
more than $300.00. It will be constructed at an in-house facility.
3
Non-Disclosure Statement (PS)
RESTRICTION ON DISCLOSURE OF INFORMATION
The information provided in or for this proposal is the confidential, proprietary property of the
Saluki Engineering Company of Carbondale, Illinois, USA. Such information may be used solely
by the party to whom the proposal has been submitted by the Saluki Engineering Company and
solely for the purpose of evaluating this proposal. The submittal of this proposal confers no right
in, or license to use, or right to disclose to others for any purpose, the subject matter, or such
information or data, nor confers the right to reproduce or offer such information for sale. All
drawings, specifications, and other writings supplied with this proposal are to be returned to
Saluki Engineering Company promptly upon request. The use of this information, other than for
evaluating this proposal, is subject to the terms of agreement under which services are to be
performed pursuant to this proposal.
4
Table of Contents
Transmittal Letter...........................................................................Error! Bookmark not defined.
Executive Summary (PS) ...............................................................Error! Bookmark not defined.
Non-Disclosure Statement (PS) ...................................................................................................... 4
Table of Contents ............................................................................................................................ 5
Introduction (CS) ...........................................................................Error! Bookmark not defined.
Literature Survey ...........................................................................Error! Bookmark not defined.
Project Description........................................................................................................................ 18
Design Basis (PM) ........................................................................................................................ 19
Project Deliverables (PS) .............................................................................................................. 20
Project Organization (ML) ............................................................................................................ 21
Block Diagram (ML) .....................................................................Error! Bookmark not defined.
Action Item List (PS) .....................................................................Error! Bookmark not defined.
Time Line (PS).............................................................................................................................. 24
Resources (PM) ............................................................................................................................. 25
Appendix A: Resumes .................................................................................................................. 26
Appendix B: References (ML)...................................................................................................... 30
Appendix C: Specifications ..........................................................Error! Bookmark not defined.
5
Introduction (CS)
Competitive modern electronics design employs extensive use of surface-mount
components. The physical package size of these devices is kept to a minimum, enabling
sophisticated embedded devices while reducing power consumption. To the small business or
home hobbyist, however, the small size of these components often renders them unusable, as
traditional circuit board soldering methods are both quite difficult and often damaging to the
component.
The common solution is to first place all components on the circuit board using solder in
paste form, then raise the temperature of the entire assembly in a precisely controlled manner to
exactly the correct temperature required to activate the solder. Given a margin of error of only a
few degrees Celsius, potential difficulties become quite clear. High-capacity assembly line
soldering ovens, while quite capable, consume vast amounts of electricity, require floor space
large enough to park a small car, and cost upwards of $40,000, rendering them well out of reach
for small volume producers.
The answer to this dilemma is a small oven-like device, which would solder only a few
boards per run. There have been only a handful of manufactures to offer a similar product, and
nearly all still carry hefty price tags. Additionally, many of these ovens' ability to maintain
uniform temperature is reputed to be questionable at best. Our design will employ a more
accurate method of heat transfer (convection), and will be constructed with the goal of reduced
cost foremost in mind.
6
Literature Review
This review will outline the current professional models of reflow ovens as well as the
Do-It-Yourself (DIY) build plans easily found on the internet to determine the market gap
currently in place. Solder quality being paramount in any reflow oven: the effects of temperature,
heating speed, cooling speed, and heating method will all be analyzed on the basis of solder
quality. The method for controlling the majority of these elements will revolve around several
key components, the controller and the temperature sensor. Temperature sensors, and the error
typically involved with them will be critiqued, and common solutions to the problems they pose
will be presented. Control systems themselves depend greatly on the system being controlled.
Due to the nature of this project it is highly likely that a resistive heating element will be utilized,
and control methods for a resistive heating element will be explored.
Professional Model Evaluation
Table 1 lists a variety of low volume professional reflow ovens. Most of the low cost
suppliers are in China; the cheapest model from an American manufacturer is the $800 GF-C^2HT from Novastar, this is also the cheapest convection model. Both DIY and the professional
models listed are for low volume hobbyists or small businesses; large scale, belt fed, high
volume reflow ovens cost a minimum of $12,000 and can cost as much as $40,000 and higher.
Table 1: Professional Model Comparison
Model
Cost
T962A
$369.99
Cycle
Time
8 min
User Interface
Control Unit
B/W with function
Micro-processor
buttons
T962
$429.49
8 min
LCD display with
Micro-processor
function buttons
(Self-Contained)
T962C
$799.00
8 min
LCD display with
Micro-processor
function buttons
(Self-Contained)
AS-5060
$850.00
N/A
B/W with function
Micro-processor
buttons
2011 D.A
$2950.00
5 min
B/W with function
Control Unit with
buttons
EPROM
BT300CP
$1249.99
6 min
B/W with function
PID control
buttons
850
$1499.99
5.5 min B/W with function
PID control
buttons
GF-B-HT
$999.99
7 min
B/W with function
Micro-processor
buttons
GF-C^2-HT $799.99
7 min
Computer out
Outside Computer
HHL3000
$1059.00
6 min
B/W with function
Micro-processor
buttons
*Values obtained from manufacturer websites and web merchants such as Amazon
Solder Area
300 x320 mm
Heating
Element
Infrared
180 x 235 mm
Infrared
400 x 600 mm
Infrared
460 x 275 mm
Infrared
400 x 350 mm
Convection
230 x 370 mm
Convection
340 x 430 mm
Convection
305 x305 mm
Convection
305 x 305 mm
360 x 385 mm
Convection
Convection
DIY Design Evaluation
7
Many hobbyist or small business that have need for a reflow soldering oven, but without
the means to purchase one, have elected to make one themselves. There are many methods and
varying levels of expertise and cost involved with, briefly examined in Table 2. Table 2 outlines
five popular DIY builds and grades them based on various key performance criteria.
Table 2: DIY Oven Performance [1-5]
Build
After Oven
Automatic Control Temperature Ease
Ease of
Cost ($)
Uniformity
of Use Build
Spectrum
154.00
Yes
Good
Fair
Good
Fair
Freetronics
70.00
No
Poor
Poor
Poor
Very Good
Instructables
120.00
Yes
Good
Poor
Good
Fair
Die4laser
148.00
Yes
Good
Poor
Good
Good
Mad-science
85.00
Yes
Fair
Poor
Good
Very Good
*Due to the lack of empirical data on the performance and use of these ovens, the comparisons
have been made based on the quality of the materials, the design of the control system, and
reasonable judgment based on professional models.
Table 3: Weighted Performance
Build
Automatic
Control
Spectrum
Freetronics
Instructables
Die4laser
Mad-science
0.4
0
0.4
0.4
0.4
1.08
0.36
1.08
1.08
0.72
Temperature
Uniformity
0.56
0.28
0.28
0.28
0.28
Ease of
use
0.36
0.12
0.36
0.36
0.36
Ease of
Build
0.08
0.16
0.08
0.12
0.16
Weighted
Score
2.48
0.92
2.2
2.24
1.92
Table 3 contains the same performance data as Table 2, but each of the key performance
attribute was given a weight and each of the rankings from poor to very good were given a
proportional numerical value. These weighted scores were added and compared to their after
oven prices in Figure 1.
8
Figure 1: DIY Performance vs Cost
Performance vs Cost
3
Weighted Total
2.5
2
Build 1
Build 2
1.5
Build 3
1
Build 4
Build 5
0.5
0
60.00
70.00
80.00
90.00
100.00
110.00
120.00
130.00
140.00
150.00
160.00
Cost ($)
Figure 1 shows that there is a definite correlation between build quality and cost, but that
there is a large deviation. The consumer wants an affordable, high performance oven, but the
DIY builds currently available are either too expensive or don’t perform well enough.
Market Gap
The reflow market is expanding; users are changing from traditional wave soldering
equipment to reflow [6]. The market is devoid of low cost low volume ovens, this gap has been
attempted to be filled by DIY builds. However the low reproducibility and lack of adequate data
on performance makes DIY builds unsuitable for most small business needs. By making a
reliable, easy to reproduce, affordable oven with wide solder capabilities accompanied by testing
data and preset temperature profiles for common solders, this market gap can be filled.
Solder Overview
Lead-free Solder
In July 2006 the European Union began prohibiting the use of six substances deemed to
be hazardous; among these was lead. Lead-based solders have been the preferred solder for
years, largely due to their low melting point and other mechanical properties. The European ban
on lead increased the current shift in the solder industry to lead-free solders. Lead-based solders
typically have better mechanical properties than their lead-free counterparts; this is largely due to
their Young’s moduli, wettability, and creep properties; in addition to their drastically lowered
melting points [7].
9
Table 4: List of Lead-Free Solders [8]
Alloy
In52/Sn48
Sn42/Bi58
Sn42/Bi47/Ag1
In97/Ag3
Sn91/Zn9
Sn/Ag2.5/Cu8/Sb0.5
Sn/Ag3/Cu0.5
Sn/Ag3.5/Cu0.5
Sn96/Ag3.5
Sn99.3/Cu0.7
Sn95/Ag5
Sn97/Sb3
Sn95/Sb5
Au80/Sn20
Sn97/Cu3
Sn/Ag25/Sb10
Au88/Gel12
Melting
Point °C
118
138
138
143
199
217
217-218
217-218
221
227
221-240
232-238
232-240
281
227-300
260-300
356
Young’s moduli, wettability, and creep properties
are mechanical properties that are critical to the quality of
the solder. Young’s modulus, also known as modulus of
elasticity, is the measure of how ductile a material is.
Young’s modulus is closely linked to wettability, which is
the ability of a liquid to spread out over a surface;
something needed in solders. Creep is a problem of
physical deformation over time, this can lead to part failure
well after it has been put in place. Lead based solders have
high wettability, and low creep compared to lead-free
solders.
Table 4 lists a variety of lead-free solders and their
melting points. Many of these solders are not useable for
common boards; due to their high melting point which
would risk board damage. Among the most popular alloys
for lead-free soldering is a Sn-Ag-Cu (SAC) composite [9];
these solders have a moderately low melting point and
good mechanical properties. However, there is research being done constantly to discover new
solders with improved qualities; many newer and less tested alloys are not currently on the
market. The addition of iron to tin based alloys, an alloy not currently being marketed, has been
shown to increase wetting and shear strength in solders [9].
Solder Flux
A significant portion of the solder paste is flux. Flux is a chemical composition typically
composed of inorganic acid-bases that, along with the solvent and solder powder, act as a nonsolid solution that is unanimous with “solder paste” [10]. Flux has two primary concerns; it acts
as a vehicle for the solder and to remove oxides at higher temperatures. The flux ensures that the
wetted solder succeeds in proper intermetallic bonds with the metal base.
The flux’s technical specifications must be coupled effectively with the given solder.
Typically, flux activation should be 30 degrees lower then solder solidus temperature in order to
keep viscosity level’s desirable. The vaporization of flux increases viscosity while thermal
agitation decreases viscosity. Without a properly paired flux-solder, the non-ideal viscosity could
lead to defects such as bridging and slumping, these are demonstrated in figure 2.
10
Figure 2: Temperature’s Effect on Viscosity in Flux [10]
The use of inert gases as the working fluid has many advantages over typical air.
Oxidation rarely occurs under inert atmosphere and improves the solder quality tremendously.
Under experimental conditions, it has been shown that inert-soldered joints can display strengths
of 20-40% more than its peer [10]; this is primarily because oxidation doesn’t cause voids so the
material is more structurally sound. Among the strength increases, it also produces shinier solder
joints, improved wetting angle, and increases the margin of error for poorly optimized processes.
A reflow atmosphere of 10ppm of oxygen versus 100ppm demonstrates no solder quality
difference, which indicates a non-pure inert atmosphere isn’t necessary [11].
Temperature Profiles
Reflow ovens typically have four main zones: preheating zone, activating (or soak) zone,
heating zone, and cooling zone [12]. The purpose of the soak zone is to ensure uniform
temperature distribution throughout the board, but the soak zone is unnecessary in newer, more
efficient ovens where temperatures are at a virtual equilibrium [13]. A Ramp-Soak-Spike (RSS)
process can be used for all chemistries and ovens, but the Ramp-to-Spike, which eliminates the
soak zone, (RTS) yields better results. RTS profiles, shown in figure 3, grant increased control to
the ramp rate, prevents thermal shock, and better wetting [13]. If voiding is a continuing concern,
a Long-Soak-Profile (LSP) may be used. LSP profiles have a large soak zone and very short
preheating and heating zones [14]. Besides the oven parameters, the profile also relies on solder
composition, flux applications, and the potential of imperfections occurring.
Figure 3: Ramp to Spike Profile [14]
One study aimed at determining the optimal profile conditions for Sn-Ag-Cu solders. The
experiment concluded that for a RSS profile the largest determining factor was reflow time, and
11
that the optimal conditions for the solder were: peak temperature of 245°C; reflow time of 60s;
cooling slope of -4°C/s; and soak time of 90s [12]. This RSS profile can be used for the other
SAC alloys due to their small difference in melting temperature, and the peak temperature and
reflow time can be applied to the RTS profiles successfully.
Common Solder Defects
Figure 4: Effects of Profile on Defects [10]
There are over 20 well
recorded defects that can be broken
into three categories in relation to
the phase it occurred: ramp-up rate,
peak, and ramp-down [15].
Deterring these defects contributes
significantly to the calibration of a
thermal profile. Figure 4 concisely
explains the bias of defects and
how they relate to high or low
ramp up rate, peak, and ramp down
rates.
One particular flaw in the soldering process is ‘tombstoning’ which occurs because a
paste’s temperature differential on a given component produces surface tension; this surface
tension results in a torque that lifts up the component off the board [16]. To prevent this
deficiency, it is suggested that the heat transfer rate from 5 degrees before solidus to 5 degrees
after liquidus be lowered below 1 degree/s [10].
It is apparent from figure 4 that having a ‘base’ profile that incorporates a low ramp-up
rate, low peak, and high ramp-down rate can discourage most solder defects; some instances may
require other methods in order to keep failures rare.
Almost all sources say cooling rate should be about 3-4 °C/s [17]. Achieving this rate
means that the solder cannot simply be exposed to open air. The desired profile can be
accomplished by introducing a portion of room temperature fluid via bypass fans, and averaging
the hot air with incoming cool air until the desired temperature is encountered.
Heating Methods
Three major methods are used in reflow solder ovens: vapor phase, infrared radiation
(IR), and convection. Vapor phase ovens utilize heating elements to boil an inert liquid creating
vapor that will condensate on the board at a desired temperature; utilizing the high and even heat
transfers that condensation offers; these high heat transfer rates are often detrimental to the
solder properties [18]. Convection ovens force air past a heating element; increased air velocity
greatly increases thermal conductivity and uniformity. IR elements use radiation as their means
of heat transfer, varying energy densities and wavelengths can provide greater flexibility in heat
up rates and temperatures [19].
12
Figure 5: Flow Characteristics [20]
The heat transfer coefficient for
convection (H) is a coefficient that
relies on parameters such as density,
mass flow, roughness of surface and
incidence angle [20]. The inlet
velocity can be generated by either
nozzles or fan. In many reflow set
ups, this is accomplished with air
nozzles on the ceiling that jettison
the gas perpendicular to the board.
As shown in figure 5, the stream of
gases can be accurately modeled and
broken into three distinct
components: laminar, transitional,
and radial.
Figure 6: Phase Streams [20]
With only one
nozzle, the outside board
would be much cooler than
the center board and could
cause chronic soldering
defects. To account for this
in design, multiple nozzles
with proper spacing could be
introduced to ‘average’ out
heat transfer rates. This uneven thermal distribution can be concisely explained with the
following figure. Assuming these are the only two applicable nozzles, it is not surprising that
component 1 would have a higher temperature than component 2 because of the combined
stream flows interacting with it [20].
It is important to note that just because the heating application is of convective nature,
does not mean other heat transfer methods do not interfere. In design, the minimization of
radiative energy is necessary to calculate accurately the energy transfer. This can be relieved by
placing low emissive insulation on the walls such as polished stainless steel which has an
emissivity of .08 [16].
“Infrared is a more complex system, but it also offers many advantages, including a
smaller footprint, less power consumption, zoning, closed loop control, and quick startup and
shutdown.” [19]. Benefits of IR ovens are clear, but two inherent design problems must be
accounted for in infrared reflow ovens. The first issue arises from the geometry, which can lead
13
to shadowing of components and possible hotspots. The additional concern involves varying
emissivity of the individual components, due to finishing and color.
Table 5: PCB Component Emissivity [21]
Component
ε [-]
Dispersion
Metal Q
0.67
0
No. of
Items
1
CLCC
0.75
0.01
2
SAW
0.79
0.32
2
Variable C
0.8
0.02
5
Variable R
0.84
0.25
3
Electrolytic
C
R
0.88
0.29
11
0.88
0.41
13
LED
0.89
0.01
2
D
0.91
0
2
Trimmer C
0.92
0
2
QFP
0.92
0.04
3
Ceramic C
0.94
0.09
18
IC
0.95
0.01
2
Glass Q
0.95
0
1
SOT
0.95
0.12
3
PLCC
0.96
0
1
SOIC
0.96
0.04
6
Ferrite
0.98
0
1
Paul Svasta presented basic PCB components and
their emissive power (Table 5) which expounds this
unfortunate phenomenon. He evaluated each individually
by taking the ratio of the temperature of the component by
thermocouple and compared it to IR thermo sensor [21].
The largest differential of emissivity is .31; which can
lead to a power transfer gradient up to 68% using typical
reflow temperatures. Proper selection of lamps (Table 11)
can help mitigate these downsides. A “soak” stage is
frequently introduced with IR ovens; which maintains the
temperature right before the soldier solidus stage to create
thermal equilibrium between all components; this can take
anywhere from 0.5 minutes to 2.5 minutes [16].
Table 6: Infrared Radiation Method Comparison [10]
Emitter type
Focused tungsten
tube filament lamp
Emission
Near-IR
Diffuse array of
tungsten tube
filament lamps
Diffuse array of
nichrome tube
filament lamps
Area source
secondary emitter
Near-IR
Wattage Suitability
300
Shadowing by components. Thermal
W/cm
degradation: board delamination, board
warping, charring, Color selectivity
50-100 Color selectivity
W/cm
Near-to
middle-IR
15-50
W/cm
Greater component densities are possible.
Little color selectivity problem.
Middle-to
far-IR
1-4
W/cm
No shadowing. No color selectivity.
Thermal Measurement
Since a resistive heating element is planned to be used, at first glance, it may seem as
though the control system design should be incredibly simple, since the oven will not have any
significant inductive or capacitive time-variance effects. However, the system must regulate a
14
specific physical property (temperature), not directly linked to the method of variance (electrical
signal), of a small circuit board located some distance away from the heating element. Further,
since the plan is to use a convection oven to maintain a uniform temperature, the entire enclosed
air mass must be heated or cooled to effect a temperature change on the board itself.
For all of these reasons, some amount of time will elapse between varying the electrical
input to the heating element and the circuit board being soldered changing temperature; during
which time, the heating element temperature will continue to change. For example, during a
typical reflow soak cycle, with the board temperature needing to be 230°C, the heating element
may have to increase to 500°C while the oven's internal temperature is climbing, and then
quickly cool down to 230°C to maintain the set value. Hence, a closed loop proportionalintegral-differential (PID) control is an obvious design choice.
Proportional control corrects steady-state constant errors, whereas integral and
differential controls focus on transients, such as overshoot and rise time corrections [34]. Rise
time is typically used with regard to the amount of time required to change from one value to
another value. However, reflow soldering uses variable user-input temperature profiles that
specify the overall process rise and fall times. These user-defined values are not to be confused
with rise time in the sense of control. [25]. Overshoot is the amount that a system overshoots its
final value when transitioning from one value to another, and is specified as (amount of
overshoot)/(final value) . To give a reasonable safety margin of 5°C, we will require a
maximum overshoot for the heating element control subsystem to be 2%.
Figure 7: Control System Flowchart
The primary input to this control system will be a temperature output of a sensor. A
thermistor is a thermal sensitive resistor. It is a general use temperature sensor that is used in a
wide variety of DIY projects. With the price of a single sensor below $5 and the accuracy being
within an acceptable range of error, it is an extremely suitable sensor. "Thermistors are either
NTC (negative temperature coefficient) or PTC (positive temperature coefficient). NTC
15
thermistors best suit precision temperature measurement, and PTC devices best suit switching
applications" [22]. For the reflow solder application the NTC will be used.
1
= 𝐴0 + 𝐴1 ln(𝑅𝑇 ) + 𝐴3 ln(𝑅𝑇 3 )
𝑇
T = Temp in Kelvin
𝐴0 , 𝐴1 , 𝐴3 = Manufacture reference points [0, 20, 70 respectively]
𝑅𝑇 = thermocouple resistance at T.
Figure 8: Thermistor Resistance vs. Temperature [23]
All resistive elements will give
off heat as a byproduct. This
extra heat can impact the
accuracy of the thermistor. To
counter act this effect, the error
must be accounted for. To do this
the standard practice is to put the
thermistor in series with a
standard resistor to minimize
error [22],[23].
Figure 12: [22]
The new resistor helps linearize the circuit. The error of
the thermistor is also decreased and can be modified using control
system techniques to optimize. To do this the 𝑅𝑢𝑠𝑒𝑟 must equal the
magnitude of the thermistor at the midpoint of the temperature
range of interest. Typically, in most NTC's, the error is the least is
within ±25 degrees C. [24]
16
Figure 13: Temperature vs. Error [23]
The differential resistance
change for 10 degrees C is
significantly smaller than the
resistance at low temperatures.
[23]
Control System
A known voltage will be applied to the Ruser, before passing through the sensor on its way to
ground. The voltage present at the center node can then be used as the input to an operational
amplifier or microcontroller, the output of which will correspond to a temperature level. The
accuracy of the sensor within a useful operating range is largely determined by the choice of the
value of the Ruser resistor. It will need to be sized appropriately so as to give the greatest
accuracy at oven's critical temperature operating point near the temperature limit of components
(around 240°C-250°C).
The control system must take the desired temperature as its input and compare its value
to that of the temperature sensor before applying PID corrections. The temperature sensor value
will be subtracted from the given input; the result is the amount of correction needed at that
particular instant.[25] The PID controller will then make the correction while minimizing
overshoot and rise time. Traditionally, this is accomplished through the use of discrete
components, especially operational amplifiers (opamps). Opamp circuits are designed using
appropriately-sized resistors and capacitors to provide the functions of amplification
(proportional control), integration, and differentiation. The primary goal is selecting correct
component ratios, which are determined based on commonly available component values, or by
using common components in series, parallel, or a combination of the two in the event that an
off-the-shelf solution does not exist.
Modern microcontrollers are quite capable of performing the function of the entire
opamp circuit. Rather than varying discrete components to meet control specifications, the
designer needs only to reprogram the microcontroller, usually by simply changing values within
lines of code. A great benefit is that on-the-fly changes during testing are very simple to
implement [26]. A microcontroller already will be required for the user interface anyway;
therefore the simplest and least expensive method of control will be to further utilize the
existing component. Any controller that is chosen will be capable of outputting a wide range of
pulse width modulated frequencies, which can correspond to specific internal oven
temperatures. Resolution can easily be made much more precise than will be necessary [25].
The frequency, in turn, can be used to drive a high-amperage power MOSFET circuit to
energize and de-energize the resistive heating element.
17
Project Description
Upon project completion, a fully functional, variable-input reflow solder oven prototype
will be delivered. We require it to be able to successfully use all common solder pastes currently
on the market, as well as to be capable of adjusting its temperature profile based on a wide
range of manual user inputs. The oven will adhere to the temperature profile within a small
acceptable margin of error, resulting in ideal mechanical properties and high electrical
conductivity within the newly soldered circuit board. Given the lack of technical
training/expertise expected from the operator, the oven will be an exercise in simplicity; a small
number of definite choices, such as solder type, will be presented to the user. Ground-up design
with simplicity foremost in mind is a facet unique to our proposed design. Conveniently,
complexity is also related to the final cost of the unit, which will be low in comparison to
competing designs within the targeted market sector.
Convection (PS)
Convection is wholly responsible for heat flux to the individual board; this requires
minimization of other methods of heat transfer for precision. This subsystem is comprised of the
120 millimeter fan and stock heating element. Modeled in Newton's Law of Cooling, the fan and
heating element will work in tandem to manipulate the fluid temperature and air velocity to
achieve highly reactive control of the temperature profile. During reflow, the convection
subsystem is constantly responding to input from the PWM control subsystem for error
correction. Modification of the 'Black and Decker' oven entails the mounting of the aftermarket
fan. The internals of the oven will be fitted with highly reflective material in order to minimize
radiation. Similarly, contact between the board and the tray will be kept negligible to decrease
heat transfer by conduction
Cooling System (ML)
The literature review demonstrated that the ideal cooling slope is -4°C/s. To achieve this
goal, a series of vents in combination with the internal convection fan. There will be two vents,
one in the back and one on the left side, to maximize their flow. The vents will be comprised of
a small piece of scrap metal covering the hole and being moved by a solenoid. When the
temperature is at the desired peak a signal from the control system and the vents will be opened.
The increased cold air flowing into the system will be monitored and the fans voltage may be cut
18
to ensure the proper cooling rate. The solenoid and the brackets for the vents will be mounted
using heat resistant super glue.
Control System (CS)
The task of the control system is to maintain a set temperature within the allowable
margin of error. The subsystem consists of the Arduino microcontroller, temperature sensor, and
a high-amperage heating element driver. The temperature sensor will consist of a thermistor and
a resistor to minimize sensor error near the maximum soldering temperature. The Arduino
controller will take the user input, subtract the actual value given by the thermistor, and apply
PID corrections. It will then output a pulse width modulated frequency, which the heating
element driver circuit will take as an input. The driver circuit will consist of several power
MOSFET transistors, arranged in bridge configuration, which will provide both high-current
switching and DC rectification. As implemented by our design, the Arduino board has a wide
margin of expandability for additional outputs that may be needed, such as those required for an
additional fan and vent control solenoids.
Thermistor (PM)
Temperature subsystem will have two functions: to change the resistance of the closed
circuit in proportion with the temperature and to minimize error. The first will be accomplished
using a thermistor as a temperature sensor. To minimize the error of the system, the thermistor
must be in parallel with another resistor. The resistance of the added resistor should be
proportional to the thermistor's resistance at room temperature.
User Interface (PM)
The computer subsystem will have three main functions: to output a digital signal to the
heat source from an analog input from a temperature sensor and to take user input and apply it to
the system. Finally, to have values stored into a library that a user can access for temperature
profiles. The digital signal modulation will be done with an Arduino Duo board. The board will
take an analog input from up to 12 independent temperature sensors. These values will be
averaged and linearized by programming. Then the board will digitize that signal at 84 MHz and
send a frequency modulated power signal to the heating elements and logic.
The user input will be done by an Arduino TFT LCD screen. The position of the text on
the screen will correspond to the button that is associated with it. These will be standard I/O to
the board and there are more than enough ports than needed. The temperature library will be
stored in the 512Kb of memory that the unit has installed on it. The values will be taken from test
runs.
19
Design Basis (PM)
The basis of design work to be carried out by F13-55-RFLOW can be found in this list of
documents:
Document
Request for Proposal
Literature Review
Block Diagram
In the Block diagram the various goals of each team member are described and shown
how they are interrelated. The standard temperature profile will be for a standard lead free solder
and a unit that was at a hobbit price. The literature review outlines the research and market gaps
of this product.
Project Deliverables(PS)
Project deliverables to be included are as follows:






Instruction Manual
Documentation of stock library profiles
CAD model of finished reflow oven
Limited access to control system code
Overview of solder defect analysis and troubleshooting
Typical thermal properties derived from FEA for reference
What is required for deliverables:




Experimental testing to determine limits of operation
FEA program FLUENT for heat transfer optimization
All caution and warning labels placed in accessible areas on the oven
Calibration of thermal measurement devices specific to reflow temperature ranges for
precision
 Assortment of test solder for experimental purposes
20
Project Organization
21
Block Diagram(ML)
22
Action Item List(PS)
Team Members
Patrick Selzer, ME (PM)
Cory Seidel, EE/CE
Patrick Mooney, EE
Michael Ladd, ME
#
1
2
3
4
5
6
7
8
Activity
Acquire B&D oven
Find knowledgeable staff to help FEA
Order Arduino board and related materials
Order interface, measurement devices, and
related UI materials
Perform stock thermal testing
Begin stock thermal measurement testing
Arrange meeting with client
Begin psuedo coding control devices
Date: 11/18/2013
Person Assigned Due
New Due Status Comments
ML
01/13/14 01/20/14
PS
01/13/14 01/20/14
CS
01/13/14 01/20/14
PM
PS
ML
PM
CS
01/13/14
01/13/14
01/20/14
01/20/14
01/20/14
01/20/14
01/20/14
01/27/14
01/27/14
01/27/14
23
Activity
Activity:
Milestone:
Document design
Perfect device
Compile temp profiles
Solder Testing
1st System Test
FEA heat flux analysis
Synchronize subsystems
Mngt meeting
Install User Interface
Implement control
Design Reviews
Install vent and fan
Stock experimentation
Acquire Oven
As bid:
1/13
1/27
As worked:
1/20
2/3
Revised:
2/10
2/17
2/24
3/3
3/10
3/17
Schedule for SEC Projct #: S13-55-RFLO
3/24
3/31
4/7
4/14
4/21
4/28
5/5
5/12
Timeline(PS)
24
Resources(PM)
Part
1
2
3
4
5
6
7
8
9
10
11
12
13
Item
Black and Decker Toaster Oven
Arduino Duo
Arduino TFT
Solenoid
Computer Fan
Wire
Buttons
Solder
Thermistor
Super Glue
Metal Sheeting
Arduino Software
Contingency
Quantity
1
1
1
2
1
10
1
1
Price
$40.00
$43.00
$26.00
$7.00
$8.00
On Hand
On Hand
On Hand
$1.00
$2.00
On Hand
On Hand
$57.00
Cost
$40.00
$43.00
$26.00
$14.00
$8.00
$10.00
$2.00
Total
$40.00
$83.00
$109.00
$123.00
$131.00
$131.00
$131.00
$131.00
$141.00
$143.00
$57.00
Total:
$200.00
$200.00
25
Appendix A: Resumes
26
Patrick Selzer
Pselzer@siu.edu
Permanent Address
506 Edgewood Drive
Minooka, Il 60447
(815) 600-0894
College Address
912 West Mill Street
Carbondale, Il 62901
(815) 600-0894
Objective: An entry-level mechanical engineering position.
Education
Bachelor of Science in Mechanical Engineering and Energy Processes
Date of Graduation: Spring 2014
Southern Illinois University Carbondale, IL 62901
GPA :3.3/4.0
Relavent Coursework





Manufacturing Methods
o Design and analysis
o Injection Molding, Pressing, Mold casting
o Lean manufacturing and Six Sigma philosophies
Internal Engine Combustion
o Gas exchange process
o Charge motion within the cylinder
o Combustion in spark, compression ignition engines
o Engine friction and lubrication
Thermodynamics
o Brayton, Diesel, Otto cycles
o Vapor, gas power systems
o Refrigeration, heat pump systems
Heat Transfer
o Conduction, convection, radiation
o Fins, efficacy
o Lumped system analysis
Material Science
o Analysis of material properties at microscopic level
o Heat treatment, alloying, composite materials
o Non-destructive Testing
Experience:
Intern, The Plastics Group, Inc.
 Designed numerous assembly fixtures for incoming contracts
 Performed various thermal calibrations on moisture analyzer
 Dimensioned and drafted 40+ unique head toolings for injection molding
 Designed and implemented burst chamber for non-destructive testing purposes
27
Skills






Thermal measurement calibration and modeling
Experience in steady-state fluid analysis
Numerical analysis via Matlab and spreadsheets
Proficient in AutoCAD
Experience in C# and C++ programming languages.
Experience in modeling of viscoelastic systems
Honors/Awards
-Dean's List for majority of college career.
References:
Harold Cunningham
Corporate Engineer | The Plastics Group, Inc.
Email: hcunningham@theplasticsgroup.net
Phone: (630) 803-1922
Dr. James Mathias
Associate Professor | Mechanical Engineering and Energy Processes
email: mathias@engr.siu.edu
Phone: 618-453-7016
Dr. Asghar Esmaeeli
Associate Professor | Mechanical Engineering and Energy Processes
email: esmaeeli@engr.siu.edu
Phone: 618-453-7001
28
505 S. Hays St, Carbondale, IL 62901(217)-417-3737MichaelLadd@siu.edu
Michael Ladd
Education
August 2011-Present
Southern Illinois University
Carbondale, IL
Bachelor of Science in Mechanical Engineering
Anticipated May 2014
Experience
March 2008-August
2012
Family Video
Urbana/Carbondale,
IL
Shift Leader
Customer service
Employee management
Task management
June 2010-August 2011
New Covenant Fellowship
Champaign, IL
Kohl’s
Carbondale, IL
Youth Coordinator
Teaching
Organizing activities
Planning trips
August 2012-Present
Customer Service Representative
Customer service
Inventory management
Cash handling
Additional Skills
Proficient with Creo Design Software
Comfortable with C++
References
References are available on request.
29
Patrick Benjamin Mooney
Home: 630-665-2159
Personal: 630-917-2159
25w665 Prairie Rose Cir
Carol Stream, IL 60188
pbenmooney@siu.edu
Objective
Looking for a position as an Electrical Engineer in a multinational organization where my engineering, managing
and supervising skills will support to provide quality services and also a golden chance to explore my career in this
field.
•
•
•
•
•
•
•
•
•
•
Summary of Qualifications
I have sound experience of more than 8 years in this filed and learnt a lot of new techniques to the things in a
better way.
Designed installation procedures, focusing on safety, reliability and efficiency, received special recognition due
to company-wide adoption of procedures.
Conducted environmental tests of potential installation sites including noise levels, vibration effects, ventilation
requirements and earthquake vulnerability.
Conducted regular sales training sessions to ensure thorough understanding of products.
Organized and monitored simulated disaster tests and reviewed results with customers to identify potential
issues.
Developed and instituted thorough safety procedures, resulting in a perfect safety record.
Mapped and labeled every installation to provide customer with detailed schematics of backup system.
Improved customer confidence, commitment and satisfaction through bimonthly customer visits.
Identified new and innovative approaches to enhance business development through the implementation of
machine programming.
Instituted rigorous site preparation process to eliminate costly modifications during installation.
Employment History
(None)
Education
Electrical Engineering
Southern Illinois University Carbondale
2014
Carbondale, IL
Skills
• Engineering Graphics & Design
• Supervising Skills
• Presentation Skills
• Wire Line Coring
• Team Work Ability
• Quality Control
References
Available upon request
30
Corey J. Seidel
1341 N. Wayward St.
Marion, IL 62959
618-239-4186
coreyseidel@siu.edu
OBJECTIVE:
To obtain Master’s degree enrollment within a world-renown university.
SUMMARY:
•
•
•
2014 graduate with B.S. in Electrical Engineering, B.S. in Computer Engineering.
CNC robotic systems design and production experience.
Proven financial leadership.
EDUCATION:
Bachelor of Science in Electrical Engineering, May 2014
Bachelor of Science in Computer Engineering, May 2014
Southern Illinois University. Carbondale, Illinois, United States of America
Will graduate with estimated GPA of 3.3 on a 4.0 scale, while self employed
full-time to support family of three.
Courses taken include:
Analog Electronics
Embedded Systems
VLSI design
Advanced Computer Architecture
Networking
ASIC design
Control Systems
EXPERIENCE:
Owner & CEO: Lauren Seidel Photography, June 2010-Present.
Marion, IL
•
•
Designed and produced production-level 3-axis CNC vertical mill, resulting in an
upfront acquisition savings of over 800%, while reducing recurring production costs
by half.
Designed patent-pending camera lens targeted for first-quarter 2015 production.
31
•
Responsible for all executive financial decisions.
United States Army, June 2003-September 2009.
Infantry Mortarman, Artillery Fire Direction Control
•
•
•
•
•
Combat experience: OEF-Afghanistan 2008-2009.
Organized and maintained sole long-range indirect-fire capability for defense of
entire U.S.-Italian joint combat operations base, provincial-level Afghan government,
and of Farah city, pop. 150,000.
Directly responsible for ensuring daily squad-level mission readiness.
Provided long-range precision rifle and mobile mortar offensive-engagement
capabilities during nearly 200 combat missions.
Numerous decorations include Army Achievement Medal for training squad of rifle
infantry as expert-qualified mortarmen in three days; Army standard is two weeks.
32
Appendix B: References
References
[1] http://spectrum.ieee.org/geek-life/hands-on/the-poor-mans-solder-reflow-oven (Accessed: 16
September 2013)
[2] http://www.freetronics.com/pages/surface-mount-soldering-with-a-toasteroven#.UlBgX1Csh8E (Accessed: 16 September 2013)
[3] http://www.instructables.com/id/DIY-Soldering-Reflow-Oven/?ALLSTEPS (Accessed: 18
September 2013)
[4] http://www.die4laser.com/toaster/index.html (Accessed: 18 September 2013)
[5] http://mad-science.wonderhowto.com/how-to/diy-lab-equipment-build-your-own-reflow(Accessed: 23 September 2013)
[6] http://www.researchandmarkets.com/research/6xvcpl/analysis_of_the
[7] Guang Zeng, Stuart McDonald, Kazuhiro Nogita, “Development of high-temperature solders:
Review,” Microelectronics Reliability, vol. 52, 2012.
[8] AIM Incorperated, “Lead-Free Soldering Guide,” Manufacturing & Distribution Worldwide,
2002.
[9] H. Fallahi, M. S. Nurulakmal, A. Fallahi, Jamaluddin Abdullah “Modifying the mechanical
properties of lead-free solder by adding iron and indium and using a lap joint test,” Journal of
Materials Science: Materials in Electronics, vol. 23, pp.1739-1749, 2012.
[10] N.C. Lee, “Reflow Soldering Processes and Troubleshooting”, Burlington, Newnes, 2002
[11] Marc Peo, “How challenging conventional wisdom can optimize solder reflow,”
(hellerindustries), [online] http://www.hellerindustries.com/00600-248.pdf (Accessed: 20
September 2013)
[12] Ming-Hung Shu, Bi-Min Hsu, Min-Chuan Hua. “Optimal combination of soldering
conditions of BGA for halogen-free and lead-free SMT-green processes,” Microelectronics
Reliability, vol. 52, 2012.
[13] AIM Incorperated,“AIM Tech-Sheet: Reflow Profiling”
advprecision.com/pdf/Reflow_Profiling.pdf
[14] Karl Seelig, David Suraski. “A Practical Guide to Achieving Lead-Free Electronics
Assembly” aimsolder.com
[15] Lee, N. “Optimizing Reflow Profile Via Defect Mechanisms Analysis,” EmeraldInsight,
[online] 1999. http://www.emeraldinsight.com/journals.htm?articleid=1455665&show=pdf.
(Accessed 30 September 2013)
34
[16] John Vivari, “First Principles of Solder Reflow,” (nordson.com), [online],
http://www.nordson.com/en-us/divisions/efd/Literature/White-Papers/Solder/Nordson-EFDFirst-Principles-Solder-Reflow.pdf (accessed: 15 September 2013)
[17] C.S Lau, M.Z Abdullah, F.C Ani, “ Optimization modeling of the cooling stage of reflow
soldering process for ball grid array package using the gray-based Taguchi method,” SciVerse
ScienceDirect, [online] 2012.
http://www.sciencedirect.com/science/article/pii/S002627141200008X. (Accessed 25 September
2013)
[18] Steve Fraser, Chris Munroe. “Lead-free: Using Vapor Phase Reflow in Lead-free
Processing.” SMT: Surface Mount Technology, Vol. 19 Issue 4, p48 April 2005.
[19] PCI Magazine, “Convection vs. Infrared” Finishing Today, August 2006.
[20] Illes, B. Krammer, O. ; Harsanyi, G. ; Illyefalvi-Vitez, Z. “Modelling Heat Transfer
Efficiency in Forced Convection Reflow Ovens,” in Electronics Technology, 2006. ISSE '06,
2006
[21] P. Svasta, “Components’ Emisivity in Reflow Soldering Process,” Electronic Components
and Technology Conference, 2004. Proceedings 54th. Vol. 2, 2004
[22]
Bonnie Baker, Bakers Best, New York: EDN, 2007
[23] C. L. Yuan, X. Y. Liu, X. W. Zhang, C. R. Zhou, Electrical properties of
SrxBa1−xFe0·6Sn0·4O3−ε NTC thermistors, India: Academy of Sciences, 2012
[24] J. Leskauskaite, A. Dumicus. Thermistors for the Temperature Measurement Gear,
Lithuania: Department of Electronics Engineering, 2011
[25] G. Franklin, J.D. Powell, A. Emami-Naeini. Feedback Control of Dynamic Systems.
Reading, MA: Addison-Wesley, 1994.
[26] J. Septon, Occupational Safety & Health Administration. “ICP Backup Data Report for
Soldering & Brazing Matrices (ARL 3560).” Internet:
https://www.osha.gov/dts/sltc/methods/inorganic/id206arl3560icp/id206arl3560icp.html, [29
Sep. 2013]
35
Appendix C: Specifications
36
Project Specifications






Oven Requirements:
+ Minimum temperature of 300 degree Celsius
+Uniform thermal transfer rate
+Low Maintenance/Low Budget
+ >0.45 𝑓𝑡 3 reflow space
Solder
+Lead-Free
+Bias against reflow defects
Flux Methods
+Relies on solder choice
+NoClean flux if oven and defects permit
User Interface
+ <$30 CPU
+ Digital Display
+Profile Library
Control System
+10% overshoot
Thermal Profile
+Base profile of low ramp-up rate, low peak, high ramp-down rate
+Calibrated with respect to solder, flux, oven
37