for low and no-ag alloys pb-free alloy characterization...
TRANSCRIPT
Thermal Fatigue Results for Low and
No-Ag Alloys Pb-Free Alloy
Characterization Project
Speaker: Keith Sweatman Nihon Superior Co., Ltd
iNEMI Session, IEMT 2012
Ipoh, Perak, Malaysia
November 7, 2012 © 2012 iNEMI
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Project Team Members
Solder alloy suppliers, Component suppliers, EMS providers, OEMs
19 companies;
66 individuals
© 2012 iNEMI
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Authors Keith Sweatman1, Keith Howell1, Richard Coyle2, Richard Parker3, Gregory
Henshall4, Joseph Smetana5, Elizabeth Benedetto6, Weiping Lui7, Ranjit S.
Pandher8, Derek Daily9, Mark Currie10, Jennifer Nguyen11, Tae-Kyu Lee12,
Michael Osterman13, Jian Miremadi4, Aileen Allen4, Joelle Arnold14,
Donald Moore10, and Graver Chang15 1Nihon Superior Co., Ltd., Osaka, Japan
2Alcatel-Lucent, Murray Hill, NJ, USA 3Delphi, Kokomo, IN, USA
4Hewlett-Packard Co., Palo Alto, CA, USA 5Alcatel-Lucent, Plano, TX, USA
6Hewlett-Packard Co., Houston, TX, USA 7Indium Corp., Utica, NY, USA
8Cookson Electronics, South Plainfield, NJ, USA 9Senju Comtek Corp., Cupertino, CA, USA
10Henkel Corp., Irvine, CA, USA 11Flextronics Milpitas, CA, USA
12Cisco Systems, San Jose, CA, USA 13CALCE, College Park, MD, USA
14DFR Solutions, College Park, MD, USA 15IST Inc., HsinChu, Taiwan, R.O.C.
© 2012 iNEMI
Thermal Fatigue Results for Low and No-Ag Alloys
The effect of Ag level and microalloying additions
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© 2012 iNEMI
Agenda
• Background
• Alloys
• Test Vehicle
• Assembly
• Thermal Cycles
• Microstructures
• Results
– Effect of Composition
– Effect of Temperature Range
– Effect of Peak Temperature
– Effect of Component Type
– Characteristic Life Rankings
– Acceleration Factors
• Conclusions
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Background
The Total Project
Concern about the reliability in thermal cycling of Pb-free
solder alloys that were being introduced to area array
packages because of problems with failure in drop impact of
high-Ag solders and the high cost of Ag.
This Part of the Project (Part III)
How is the performance in thermal cycling affected by the
• Ag level
− To improve resistance to drop impact and reduce cost Ag levels
were reduced
• Microalloying additions
− Introduced to improve performance and properties of solders
including resistance to drop impact
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The Knowledge Gap
Lack of thermal cycling test data obtained under controlled identical
conditions for:
• New and established low Ag and microalloyed solders
• Benchmarking against Sn-37Pb and SAC305
• Creating life prediction models
© 2012 iNEMI
Data Objectives • Dependence of thermal fatigue
resistance on Ag concentration
• Effect on thermal fatigue
resistance of common
microalloying additions
• Performance of low Ag and
microalloyed solders relative to
Sn-37Pb and SAC305
• Effect of alloy composition on thermal
cycling acceleration factors
• Effect of two package designs.
• Impact of elevated temperature aging on
performance in thermal cycling
• Effect of dwell time on performance in
thermal cycling
• Effect of dwell time on performance in
thermal cycling Still in Progress
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Solder Ball and Paste Alloys
Ball Alloy Selection
– Sn-37Pb control
– SN100C chosen as a 0% Ag Pb-free
alloy
– Two other established proprietary
alloys
– Two JEITA 2nd Generation
Recommendation alloys
– Various levels of silver (nominal 0-4%)
– Two microalloying additions (Ni and
Mn+Ce)
© 2012 iNEMI
No. BGA Ball Alloy
Trade Name or
Designation
Solder
Paste Comments
1 Sn-37Pb Eutectic Sn-Pb Sn-37Pb Control
2 Sn-0.7Cu+0.05Ni+Ge SN100C SN100C 0% Ag joint
3 Sn-0.7Cu+0.05Ni+Ge SN100C SAC305 Impact of [Ag]
4 Sn-0.3Ag-0.7Cu SAC0307 SAC305 Impact of [Ag]
5 Sn-1.0Ag-0.5Cu SAC105 SAC305 Impact of [Ag]
6 Sn-2.0Ag-0.5Cu SAC205 SAC305 Impact of [Ag]
7 Sn-3.0Ag-0.5Cu SAC305 SAC305 Impact of [Ag]
8 Sn-4.0Ag-0.5cu SAC405 SAC305 Impact of [Ag]
9 Sn-1.0Ag-0.5Cu+0.05Ni SAC105+Ni SAC305
Impact of
dopant
10 Sn-2.0Ag-0.5Cu+0.05Ni SAC205+Ni SAC305
Impact of
dopant
11 Sn-1.0Ag-0.5Cu+0.03Mn SAC105+Mn+Ce SAC305
Impact of
dopant
12 Sn-0.3Ag-0.7Cu + Bi SACX0307 SAC305
Doped
commercial
alloy
13 Sn-1.0Ag-0.5Cu SAC105 aged SAC305 Effect of aging
14 Sn-3.0Ag-0.5Cu SAC305 aged SAC305 Effect of aging
15 Sn-1.0Ag-0.7Cu SAC107 SAC305 Impact of [Cu]
16 Sn-1.7Ag-0.7Cu-0.4Sb SACi SAC305
Doped
commercial
alloy
Paste Alloy
− SAC 305 except for SN100C in one
case to get 0% Ag alloy
− Recognition that in most cases today
the paste alloy will be SAC305 with
potentially multiple BGA ball alloys
being used on the same board Reported in
this paper
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Sn-Ag-Cu Phase Diagram
• First stage of solidification is
growth of primary Sn
dendrites
© 2012 iNEMI
In Equilibrium Conditions
K.-W. Moon, W.J. Boettinger, U.R. Kattner, F.S.
Biancaniello, and C.A. Handwerker, J.
Elec. Mater. Vol. 29, (2000), p. 1122.
Final stage for all alloys is
ternary Sn-Ag3Sn-Cu6Sn5
eutectic
For other alloys next stage is
pseudobinary Sn-Cu6Sn5
eutectic
For SAC305 next stage is
pseudobinary Sn-Ag3Sn
eutectic
SAC305
SAC105 SAC107
SAC0307
Proportions of phases and their
morphology vary with the alloy
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SAC107/Cu Interface
SN100C/Ni Interface
Examples of Microstructures
Copper Substrate
Cu6Sn5 intermetallic Layer
Primary Sn dendrite arms
Ag3Sn in interdendritic regions
Ni3Sn4 intermetallic
Some dispersed Cu6Sn5 in Sn matrix
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Test Vehicle
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Board Assembly
• Assembled by Flextronics, San Jose
– 16 test cells
– 13 PCAs per cell
– 5-mil thick stencil
– 14-mil-diameter round apertures 192-I/O CABGA
– 12-mil x 12-mil square apertures 84-I/O CTBGA
© 2012 iNEMI
PCA
Group
Number of PCAs
per Cell Allocations 1 8 Core DOE
2 2 Two additional profiles
3 1 Aging studies
4 1 Spares
5 1 Witness set
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Assembly Reflow Profile
•All lead-free alloys assembled
with same profile
© 2012 iNEMI
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Calculated Ag Content
© 2012 iNEMI
CTBGA84 CABGA192
Sn-37Pb/Sn-37Pb 0 0
SN100C/SN100C 0 0
SN100C/SAC305 0.79% 0.29%
SAC0307/SAC305 1.00% 0.57%
SAC0307+Bi+X/SAC305 1.00% 0.54%
SAC105/SAC305 1.50% 1.20%
SAC105+Ni/SAC305 1.46% 1.13%
SAC105+Mn+Ce/SAC305 1.48% 1.14%
SAC107/SAC305 1.50% 1.19%
SAC305/SAC305 2.94% 2.95%
Calculated AgBall Alloy/Paste Alloy
Note the effect of
solder ball size on
Ag content of
alloys reflowed
with SAC305
paste
Higher Final Ag
content in
smaller ball
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Establishing Procedures for
Producing Comparable Data
• Great care was taken to ensure
traceability and consistency
– Three checklists
1. Unification of materials, tools &
instruments
2. Unification on methods of ATC setup
3. Checklist before start of ATC (profile,
ramp rate, failure definition, etc.)
– Tracking of the alloys throughout
each process
• Individual LGA substrate lots
• Ink dot pattern on every package per lot
allowed tracking throughout each
process
© 2012 iNEMI
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Thermal Cycles
Profile Selection
– Goal 1: Impact and
interactions of: temperature
range, maximum
temperature, and dwell time
(core DOE profiles 1-4)
– Goal 2: Performance for
the most commonly used
profiles: 0/100 °C and -
40/125 °C (profiles 1 and 10)
– Goal 3: Impact of long
dwells (profiles 5, 6, 7, 8, 9)
– Goal 4: Select thermal
cycles that generate data
that can be used in life
modelling
© 2012 iNEMI
Profile No.
Testing Company
Cycle (Min/Max/Dwell) Comment
1 ALU 0/100/10
Core DOE
2 IST 25/125/10
3 Henkel -40/100/10
4 Nihon -15/125/10
5 ALU 0/100/60
6 HP 25/125/60
7 HP -40/100/60
8 CALCE -15/125/60
9 CALCE -40/100/120 Long Dwell
10 Delphi -40/125/10
Common; Auto
Profile No.
Testing Company
Cycle (Min/Max/Dwell) Comment
1 ALU 0/100/10
Core DOE
2 IST 25/125/10
3 Henkel -40/100/10
4 Nihon -15/125/10
5 ALU 0/100/60
6 HP 25/125/60
7 HP -40/100/60
8 CALCE -15/125/60
9 CALCE -40/100/120 Long Dwell
10 Delphi -40/125/10
Common; Auto
ΔT=100
ΔT=140
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Thermal Cycling Standardization
Checklist #3 compared profiles site to site
– Criteria to ensure profiles were within tolerances
– Profiles presented to team prior to start of test
© 2012 iNEMI
Thermocouple
Attachment
Failure definition (IPC9701A)
– Event Detector vs. Data Logger
– Unified failure definition using IPC definition
for event detectors (usable by data loggers)
– Failure: 10 “events” (measurements of resistance
above the threshold value of 1000Ω) take place within
10% of cycles from the first “event.” The first event
meeting this criterion is defined as the point of failure.
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Weibull Plots
63.2% Failure
Characteristic Life
η
Slope
β
Quality of Fit
ρ
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Effect of Ag Levels on Sn-0.7Cu 0-100°C, 10 minute dwells – CABGA192
© 2012 iNEMI
Hardening effect
of Ag is apparent
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Low-Ag Alloys cf Reference Alloys 0-100°C, 10 minute dwells – CABGA192
© 2012 iNEMI
Even low Ag alloys
significantly longer
life than Sn-37Pb
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Effect of Microalloying Additions 0-100°C, 10 minute dwells – CABGA192
© 2012 iNEMI
No significant effect of
Ni on SAC105 in this
test condition
Significant reduction
of characteristic life
and spread of failures
with Mn + Ce addition
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Effect of Microalloying – Bi & Rare Earths 0-100°C, 10 minute dwells – CABGA192
© 2012 iNEMI
No significant
effect in this
test condition
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Effect of Cu Level 0-100°C, 10 minute dwells – CABGA192
© 2012 iNEMI
No significant effect
in this test condition
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Effect of Thermal Cycle – Ag-free Alloy CABGA192 Component
© 2012 iNEMI
84% reduction in
characteristic life
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Effect of Thermal Cycle – Very Low-Ag Alloy CABGA192 Component
© 2012 iNEMI
79% reduction in
characteristic life
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Effect of Thermal Cycle Microalloyed Very Low-Ag Alloy CABGA192 Component
© 2012 iNEMI
69% reduction in
characteristic life
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Effect of Thermal Cycle - Low-Ag Alloy CABGA192 Component
© 2012 iNEMI
80% reduction in
characteristic life
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Effect of Thermal Cycle Ni-doped Low-Ag Alloy CABGA192 Component
© 2012 iNEMI
70% reduction in
characteristic life
But lower
characteristic life
than without
microalloy
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Summary of Effect of Temperature Range
© 2012 iNEMI
η β η β
Sn-37Pb/Sn-37Pb 1477 12.3 658 6.5
SAC305/SAC305 5718 7.0 1612 5.2
No-Ag SN100C/SN100C 3101 8.7 623 5.5
SN100C/SAC305 3067 10.0 826 7.0
SAC0307/SAC305 4071 9.2 846 14.2
SAC105/SAC305 4910 5.4 940 6.8
SAC107/SAC305 5000 5.2 1196 7.6
SACX0307/SAC305 4194 7.0 1079 5.6
SAC105+Ni/SAC305 4707 6.6 1245 7.0
SAC105+Mn/SAC305 3396 4.1 1040 7.8
Reference
Alloys 3.5
5.0
3.7
4.8
5.2
-40/125/10
CABGA192
Acceleration
Factor
0/100/10 to
-40/125/10
Alloy/PasteCategory
2.2
Very Low-Ag
Low Ag
Microalloyed
0/100/10
CABA192
4.2
3.9
3.8
3.3
Pb-free solders
up to 2.3 times
more sensitive
to temperature
range than
Sn-37Pb
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Effect of Peak Thermal Cycle Temperature Ag-free Alloy CABGA192 Component
© 2012 iNEMI
32% reduction in
characteristic life
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Effect of Peak Thermal Cycle Temperature Very Low-Ag Alloy CABGA192 Component
© 2012 iNEMI
32% reduction in
characteristic life
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Effect of Peak Thermal Cycle Temperature Microalloyed Very Low-Ag Alloy
CABGA192 Component
© 2012 iNEMI
32% reduction in
characteristic life
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Effect of Peak Thermal Cycle Temperature Low-Ag Alloy CABGA192 Component
© 2012 iNEMI
32% reduction in
characteristic life
Significantly
increased spread
of failures
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Effect of Peak Thermal Cycle Temperature Ni-doped Low-Ag Alloy
CABGA192 Component
© 2012 iNEMI
27% reduction in
characteristic life
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Summary of Effect of Peak Temperature
© 2012 iNEMI
η β η β
Sn-37Pb/Sn-37Pb 1477 12.3 1527 9.7
SAC305/SAC305 5718 7.0 4632 7.4
No-Ag SN100C/SN100C 3101 8.7 2087 10.6
SN100C/SAC305 3067 10.0 3197 3.4
SAC0307/SAC305 4071 9.2 2607 7.2
SAC105/SAC305 4910 5.4 3144 3.5
SAC107/SAC305 5000 5.2 2660 7.1
SACX0307/SAC305 4194 7.0 3205 5.5
SAC105+Ni/SAC305 4707 6.6 3413 4.1
SAC105+Mn/SAC305 3396 4.1 2873 2.7
Alloy/PasteCategory
1.2
0/100/10
CABGA192
25/125/10
CABGA192
Acceleration
Factor
0/100/10 to
25/125/10
Microalloyed
Low-Ag
Very Low-Ag
Reference
Alloys
1
1.2
1.5
1
1.6
1.6
1.9
1.3
1.4
Characteristic
life reduced
by as much
as 46% by
25°C
increase in
peak
temperature
with same ΔT.
No effect on
Sn-37Pb
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Component Size Effect – Ag-free Alloy 0-100°C, 10 minute dwells
© 2012 iNEMI
50% Reduction in
characteristic life
resulting from
difference in ball
diameter and DNP
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Component Size Effect – Very Low-Ag Alloy 0-100°C, 10 minute dwells
© 2012 iNEMI
1% Ag 0.57% Ag
Combined effect of
DNP, ball size and
the effect of ball
size on Ag content
when reflowed with
SAC305
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Component Size Effect- Microalloyed Very Low-Ag Alloy 0-100°C, 10 minute dwells
© 2012 iNEMI
Combined effect of DNP,
ball size and the effect of
ball size on Ag content
when reflowed with
SAC305
1% Ag 0.54% Ag
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Component Size Effect – Low-Ag Alloy 0-100°C, 10 minute dwells
© 2012 iNEMI
Combined effect of
DNP, ball size and the
effect of ball size on
Ag content when
reflowed with SAC305
1.5% Ag 1.2% Ag
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Summary of Effect of Component Type
© 2012 iNEMI
η β η Β
Sn-37Pb/Sn-37Pb 1477 12.3 2310 11.0 1.6
SAC305/SAC305 5718 7.0 9819 7.0 1.7
No-Ag SN100C/SN100C 3101 8.7 5306 7.7 1.7
SN100C/SAC305 3067 10.0 6625 8.0 2.2
SAC0307/SAC305 4071 9.2 5577 11.6 1.4
SAC105/SAC305 4910 5.4 6826 7.9 1.4
SAC107/SAC305 5000 5.2 7255 7.4 1.5
SACX0307/SAC305 4194 7.0 7183 10.0 1.7
SAC105+Ni/SAC305 4707 6.6 7683 7.0 1.6
SAC105+Mn/SAC305 3396 4.1 6514 8.3 1.9
0/100/10
CTBGA84
Component Effect
0/100/10
CABGA192η Ratio
Reference
Alloys
Microalloyed
Very Low-Ag
Category Alloy/Paste
Low-Ag
Differences
in ball size,
DNP and Ag
content can
reduce life
by at least a
third.
Pb-free
similar to Sn-
37Pb
40
0-100°C 10 minute dwell Ranked by Characteristic Life
© 2012 iNEMI
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© 2012 iNEMI
-40-120°C 10 minute dwell Ranked by Characteristic Life
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© 2012 iNEMI
25-125°C 10 minute dwell Ranked by Characteristic Life
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© 2012 iNEMI
-40-100°C 10 minute dwell Ranked by Characteristic Life
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© 2012 iNEMI
-15-125°C 10 minute dwell Ranked by Characteristic Life
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© 2012 iNEMI
Sn37Pb/Sn37Pb
SN100C/SN100C
SAC0307/SAC305
SAC105+Mn/SAC305
SN100C/SAC305
SACX0307/SAC305
SAC105/SAC305
SAC107/SAC305
SAC105+Ni/SAC305 SAC305/SAC305
0
1
2
3
4
5
6
7
8
9
1 2
3 4
5 6
7 8
9 10
Fre
qu
en
cy o
f R
an
kin
g
Ranking (Shortest to Longest Characteristic Life)
Sn37Pb/Sn37Pb
SN100C/SN100C
SAC0307/SAC305
SAC105+Mn/SAC305
SN100C/SAC305
SACX0307/SAC305
SAC105/SAC305
SAC107/SAC305
SAC105+Ni/SAC305
SAC305/SAC305
Distribution of Ranking Over All Test Conditions
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Trends in Characteristic Life
© 2012 iNEMI
47
Trends in Characteristic Life
© 2012 iNEMI
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Acceleration factors between the -40-125°C profile
and the 0-100°C
© 2012 iNEMI
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Thermal Cycle Acceleration Factors
© 2012 iNEMI
50
Thermal Cycle Acceleration Factors
© 2012 iNEMI
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Summary of Acceleration Factors
Thermal Cycle -40-125°C/10 25-125°C/10 -40-100°C/10 -15-125°C/10
0/100°C/10 Average 4.23 1.41
Std Dev 0.7 0.29
-40-125°C/10 Average 2.62
Std Dev 0.36
-40-100°C/10 Average 1.03
Std Dev 0.13
Acceleration Factor
© 2012 iNEMI
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Conclusions
• In short dwell (10 minute) thermal cycles there is a
correlation between characteristic life and Ag content
• All of the Pb-free alloys perform better than
Sn-37Pb under the tested conditions
• Pb-free alloys have high acceleration factors (0-100°C
vs -40-125°C) which suggests low-Ag alloys will
perform better than Sn-37Pb in office or similarly
controlled environments
© 2012 iNEMI
53
Conclusions (continued)
• As the strain and exposure to elevated temperature
increases, the differences between Pb-free alloys
collapses and performance appears to converge towards
that of Sn-37Pb.
© 2012 iNEMI
Results of thermal
cycling with longer
dwells will confirm
whether the trend
to convergence
holds
54
Questions Raised by These Results!
• Why do characteristic life rankings vary with test
conditions?
• Why do acceleration factors vary so much with alloy?
• Why do β values (the range of cycles over which failures
are spread) vary so much with the alloy and the test
conditions?.
• Are all the observed differences significant or are some
the result of experimental factors?.
• What is the failure mechanics and how do they differ
between alloys and conditions?
• ???
55
Future Work
• Completion of all thermal cycles
• Detailed failure analysis to understand the
evolution of the microstructure to failure
• Development of life prediction models based on the
results of this test program.
• Generation of a portable test protocol for solder
alloys
© 2012 iNEMI
Thank You for Your Attention