Accelerated Tin Whisker Test Project Overview Phases 1 to 5

Heidi L. Reynolds, Ph.D. Former Project Chair iNEMI Webinar June 10, 2009

H.L. Reynolds 6/10/09

• Tin Whisker Fundamentals Project – Theory & Mechanisms for whisker growth

• Tin Whisker Users Group – Published recommended mitigation guidelines

• Tin Whisker Accelerated Test Project

• *Note – The Fundamentals & Test Projects were combined in June 2007

H.L. Reynolds 6/10/09

• Current Structure Richard Parker (Chair) – Delphi Electronics & Safety Peng Su (Co-Chair) – Cisco Systems

• Weekly teleconferences Date: Thursdays Time: 8am PST • Contacts • Jim Arnold at [email protected] • Richard Parker at [email protected]

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R. Parker/iNEMI Phase 5/March 2007

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JEDEC/IPC revised the testing standard, and passed the acceptance criteria, JESD-201

JEDEC/IPC passed testing standard JEDEC22A121 iNEMI Whisker 2006 2005 Test Group iNEMI published the first whisker 2004 test guideline document Ongoing & Future 2001 Industry rekindled the interest in 2000 Phase 5 Sn whisker study. NEMI formed Testing, User, and Model groups. Phase4 First draft of EU RoHS Directive Phase3

Phase1& 2 1956

1951 Small Pb addition to Sn was found to mitigate tin whiskers 1948 Bell Labs found whisker growth from Cd, Sn, Zn, Al, and Ag (in H2S) Bell Telephone experienced failures on channel filters due to Cd whiskers H.L. Reynolds 6/10/09

Test Samples Stresses Duration Results Industry adoption

1 Lab scale bright Temp/Humidity 4 wks Whiskers on brass tin on brass storage, and coupons only. Few coupons and thermal whiskers formed. SOIC packages cycling Results inconclusive. 2 Production Temp/Humidity 4 wks Whiskers can be iNEMI proposed Tin matte tin plated storage, and effectively induced by Whisker Test SOIC thermal environmental Documents in 2003, leadframes cycling stresses. Plating which was adopted chemistry and by JEDEC and processes are most released as JEDEC- significant to whisker 22A121. growth. 3 Production Temp/Humidity 10000 Longer term whisker Inputs were provided components and storage, and hrs growth behaviors, to JEDEC. JEDEC lab samples of thermal such as incubation released standard tin various cycling time, length saturation, whisker test methods metallurgy whisker density, etc., and acceptance were monitored. criteria. 4 Assembled Temp/Humidity 3000 hrs Plating finish production storage, and dependent wetting components w/ electrical bias. behavior. No apparent various plating bias effects. finishes and solder pastes H.L. Reynolds 6/10/09

Test Samples Test Methods Duration Objectives Results

5 Production matte Various 4000 to Investigate the effects Development of tin plated temp/humidity >26,280 of temperature and Acceleration components storage hours humidity over a wide Model, range of conditions to Publication of develop the optimal complete data set test conditions and over wide range correlation between of conditions accelerated test conditions and actual service conditions.

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• Phase 1: [Experimental] Bright Tin Plating

– Brass Coupons & SOIC packages

– Preconditioning Thermal Cycling (500 cycles) -40C to 90C Ambient Storage (1 week)

– Five Storage Environments (4 weeks) ➔ 55C/20%-60% RH ➔ 55C/85% RH ➔ 85C/20%-60% RH ➔ 85C/85% RH ➔ 20-25C/20%-60% RH

• Few whiskers formed – Experimental (laboratory) plating had low impurity level? – Incubation time for whisker formation not exceeded?

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• Phase 2: [Production] Matte Tin Plating – Brass Coupons, SOIC packages, Chip Components

Suppli Leg Temp Temp (°C) & er s Cycle Relative Plating Remarks (°C) Humidity (%) Site 6 - 60, 95 A Temp & Humidity 7 - 60, 95 B Temp & Humidity 8 - 30, 90 A Humidity 9 - 30, 90 B Humidity 10 -55 to 85 30, 90 A Temp Cycle + Humidity

11 -55 to 85 30, 90 B Temp Cycle + Humidity

12 -55 to 85 Ambient A Test Temp Cycle

13 -55 to 85 Ambient B Test Temp Cycle

14 Ambient Ambient A Ambient

15 Ambient Ambient B Ambient

– Environmental Stress Conditions sufficient to create whiskers – Thermal Cycling was most effective. – Addition of temperature and humidity exposure did not significantly add to whisker length or frequency when TC performed first. – Most significant effect was plating chemistry/plating process.

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© Copyright 2009 10 Tin Whisker Test Project Evaluation History • Phase 3: Results presented at ECTC/Orlando 2005 Published in IEEE Journal (October 2006) – Verify and Validate iNEMI recommended test conditions – Provide additional input to JEDEC

Inspection Total Environmental interval Duration condition Uncontrolled 1000 to 3000 h 10,000 20 °C to 25 °C hours 20 to 60 % RH Irregular 10,000 (@2 kh &10 hours kh) 3 kh for N 7 kh for L,M 60 °C (+5) 1000 h 9000 93% RH (+2, -3) hours 2000 h 9000 hours -55 °C (+0, -10) to + 500 cycles 3000 85 °C (+10, -0) air- cycles to-air temperature cycle (20 min per cycle)

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• Sn on Cu (C7025) • Matte Sn – plating A • Sn on Cu (C194) • Matte Sn – plating A – Annealed matte Sn (1 hr at 150C) – plating A – Reflowed matte Sn (245C peak) – plating A • Matte Sn 3-5 microns – plating A •Sn-Bi •Sn-Cu •Sn-Ag • Solder-dipped tin • JEITA samples bright Sn Started later, – on C1020 – plating B fewer inspection – on Alloy 42 – plating B intervals, and no – on C194 – plating B thermal cycling • Sn/Ni underlay/BeCu substrate •Matte Sn Note: Unless otherwise indicated Sn • Phase 2 DOE parts plating is 10 µm-thick (target) H.L. Reynolds 6/10/09

• Only one example of each surface finish/substrate combination was used. Hence, this study alone [Phase 3] cannot be used to prove or disprove the effectiveness of a particular surface finish, substrate, underplating or heat treatment.

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• The following slides show only a sampling of data collected in Phase 3. • For more details: – V. Schroeder, iNEMI Tin Whisker Workshop, ECTC, Orlando, May 2005 – V. Schroeder, P. Bush, M. Williams, N. Vo and H. L. Reynolds, “Tin Whisker Test Method Development”, IEEE Transactions on Electronics Packaging Manufacturing, 29(4): pp. 231 – 238, October 2006

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300 Absolute maximum 300 whisker length of all 250 whiskers measured 250

rons] Average maximum whisker 200 200

length of up to 9 non-zero ] #

values of whisker length [ y t 150 150 i Density (plotted relative to s r length [mic

right axis) = total number of Den 100 100

ke whiskers counted in 9 fields s of view (0.56 mm2 of area)

Whi 50 50

0 0 Sn-Ag Sn-Bi Sn-Cu Hot-dip Bright Sn on Ni SnPb Scale of plot held constant Sn Sn on on BeCu for comparison at 300 µm A42 max and 300 whisker max MeH.L.ta Reynoldsllurgy 6/10/09

] 250 60C/93%RH 250 ons r

ic 200 200 ]

150 150 ngth [m nsity [# e r le 100 100 D ke

Whis 50 50

0 0 SnDOE2 Bright Bright Sn 3-5 Sn Sn on 245C 150C Sn Sn on mic C7025 reflow 1hr Sn C1020 Sn Metallurgy H.L. Reynolds 6/10/09

300 300 8000 hr results

] 250 60C/93%RH 250 s

cron 200 200 y [#] 150 150 t ngth [mi e

100 100 Densi ker l s i h

W 50 50

0 0 Sn-Ag Sn-Bi Sn-Cu Hot-dip Bright Sn on Ni SnPb Sn Sn on on BeCu A42 Metallurgy Note: SnPb grew whiskers at 7000 hrs H.L. Reynolds 6/10/09

• Ambient isothermal – Uncontrolled ambient, especially humidity, may lead to conflict in data from different research groups – Results led to change in JEDEC tin whisker test method to control ambient condition

• 60C/93%RH isothermal – 90-95% relative humidity resulted in condensation and localized corrosion. – Better control of chamber, better shut down procedure, and reduced humidity can reduce or prevent condensation. – Results led to change in JEDEC tin whisker test method to reduce chamber humidity

• -55C to +85C thermal cycles – Significant damage occurred in plating during thermal cycling – Additional study of thermal cycle profiles, especially at lower delta T, may yield more information.

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Phase 4 Evaluation: Investigate the effects of electrical bias on the susceptibility of tin finishes to form and grow whiskers.

Phase 5 Evaluation: Investigate the effects of temperature and humidity over a wide range of conditions.

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Schematic must be followed to determine which leads are biased relative to neighbor.

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Phase 4 Evaluation Comments No bias relationship for Environmental Storage leads with whiskers. Conditions 30C/60% RH 60C/85% RH

Assembly Solder Paste SnPb SnAgCu SnPb SnAgCu

[1] Whiskers first observed at 1500 hours. [2] Whiskers first observed at 3000 Sample hours.

For SnPb paste: cracked/alloyed

Whiskers For SnAgCu paste: cracking; whiskers 32LQFP bright tin, C7025 None None None [2] on foot of lead; no bias relationship

For SnPb paste: most leads wetted, flux residue

Whiskers For SnAgCu paste: whiskers on 32LQFP matte tin, C7025 None None None [1] shoulder; no bias relationship

64LQFP matte tin, O194 None None None None All leads completely wetted. 32LQFP Sn/Pb, C7025 None None Sn/Pb Plating 64LQFP semi-bright tin, Whiskers Leads wetted to shoulder; O194 None [1] no bias relationship

Leads wetted to shoulder, flux residue; 16SOIC matte tin, O194 None H.L. NoneReynolds 6/10/09 Some corrosion but no whiskers.

32LQFP, bright Sn, Sn/Ag/Cu solder Whiskers growing in “wetted” or alloyed region of the lead.

Many leads with whiskers growing on foot area. Whiskers grow through flux residue. No apparent effect of bias. Courtesy P. Bush, SUNY Buffalo H.L. Reynolds 6/10/09

FIB Cross-section Inc m rea a sin gni g fica tion

Base of whisker

Surface SEM Courtesy P. Su, Freescale

32LQFP, bright Sn, Sn/Ag/Cu solder

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Peng Su, Freescale • The finish near the whisker does not have a columnar structure. • Grain sizes of the different phases vary greatly near the root of the whisker.

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32LQFP, matte Sn, Sn/Ag/Cu solder. 0v/0A, next to 0v/0A.

No cracking of the Some longer plating observed. whiskers also observed

Lead edge ~70µm whisker

Courtesy P. Bush, SUNY, Buffalo

H.L. Reynolds 6/10/09

64LQFP, matte Sn, Sn/Ag/Cu solder.

All leads completely alloyed with solder.

H.L. Reynolds 6/10/09 Courtesy P. Bush, SUNY Buffalo

•Wetting behavior of the bright tin plating was significantly different than the wetting behavior of the other platings. Extensive cracking and irregular wetting (de-wetted and non-wetted regions) were observed using both SnPb and SnAgCu paste.

•Small dimensions on 64LQFP leads allowed complete wetting on matte Sn but not on semi-bright Sn

•On components with complete wetting of the leads, whisker testing was conducted on the alloyed finish, NOT the Sn plating.

•Components with nearly complete wetting, resulted in a small sample size for whisker testing of the exposed, non-wetted regions of the plated leads.

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• Whiskers found on 32LQFP with bright and matte Sn plating, assembled with SnAgCu paste and on 64LQFP with semi-bright Sn plating assembled with SnPb paste.

•Whiskers growing on wetted regions of the leads. (Additional characterization of these components is still underway.)

•Corrosion and flux residue are present on many leads

•Flux residue does not hinder whisker growth.

•No apparent bias effect although results are not conclusive due to complete or nearly complete wetting of the leads.

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• Whiskers grow from thin wetted regions. Reflow or ”wetting” of the lead, alone, may not mitigate whisker formation and growth.

• No apparent bias effect on the acceleration of whisker growth for fully soldered (wetted) leadframes.

• Effect of applied bias on the susceptibility of exposed (non-wetted) tin finishes to form and grow whiskers could not be confirmed in this study due to complete or nearly complete wetting of the leads.

• Module assembly adds complication to the evaluation of tin whisker test results.

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Phase 4 Evaluation: Investigate the effects of electrical bias on the susceptibility of tin finishes to form and grow whiskers.

Phase 5 Evaluation: Investigate the effects of temperature and humidity over a wide range of conditions.

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● (Proposed by V. Schroeder, J. Osenbach & others to Test Group in 2004)

● Hypothesis

● Whisker presence and/or length, measured in isothermal environments, is a function of temperature and humidity. Whisker length could be discontinuous at a threshold point or could vary as a function of temperature and humidity over the entire tested range. If such a function exists and becomes known, this function can be used to determine:

¾ Optimal whisker test condition(s)

¾ Whether whisker behavior measured at accelerated testing conditions can be related to actual storage and/or customer service conditions.

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1) What is the relationship (if any exists) between whisker presence and/or length variables of temperature and humidity? 2) Are two temperature/humidity tests necessary? 3) Has the iNEMI Test Group chosen the optimal two temperature/humidity tests? 4) Can the iNEMI tests be used to indicate behavior at other temperature/humidity points that could be relevant storage or service conditions? 5) What is happening during the accelerated test? 6) Why is there a variation between companies results? Compressive stress may be a factor 7) If reflow is an equalizer, but still have a variation. Then this may be a process issue not a plating issue.

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Test Cell Conditions Humidity [% RH] Temperature [C] 10 40 60 85 (+/- 5) 30 X X X

45 X

60 X X X X

85 X

100 X

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Plating Thickness 16L – SOIC Package

Generic Supplier Designation (A,B,C) •Matte Sn over Cu (C194) leadframe •Post-plate heat treatment of 150C within 24 hours of plating

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SampleSample LabelingLabeling ConventionConvention A -X -X -a Lot # (if more than one tested) Supplier Nominal Reflowed Condition A,B or C Plating Thickness R – reflowed 3 µm N – non reflowed 10 µm (as received)

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Test Cells LSI LSI LSI LSI Freescale ON Semi HP HP HP Delphi

Agere Agere Agere Agere Freescale Microchip HP Intersil Anamet Delphi

Cell Sample 60/87 60/60 60/10 30/87 85/85 30/60 45/60 30/10 60/40 100/60

1 A-3-N

2 A-10-N

3 A-10-R

4 B-3-N

5 B-10-N

6 B-10-R

7 C-3-N ~4000 hours ~6550 hours ~8000 hours ~8000 hours ~9890 hours ~10,440 hours

8 C-10-N-a ~10,080 hours ~10,128 hours +26,280 hours ~11,080 hours 9 C-10-R-a

10 C-10-N-b

11 C-10-R-b

12 C-10-N-c

13 C-10-R-c

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Assumptions • C194 will be representative of the ability of a particular temp/humidity condition to accelerate whisker growth. (Only one substrate used)

•Some cells will form whiskers to be able to assess differences in behavior as a function of temperature and humidity

•Differences in whisker behavior as a function of temperature and humidity in 320 days will indicate differences between 1 yr and some longer time.

•Same mechanism is working for 3 microns and 10 micron thick Sn.

• Same mechanism at all temp/humidity conditions and there is some relationship between them.

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© Copyright 2009 37 Phase 5 Evaluation – Limitations (Schroeder, Osenbach 5/6/04) Limitations • Due to the length of the test, threshold behavior could be confused with incubation times in excess of 320 days.

• Whiskers may not grow in enough cells to establish a functional relationship, only threshold points.

• A non-monotonic relationship may exist that will limit conclusions

• Substrate dependence is not taken into account, however, substrate dependence at ambient and 60C/93%RH will be available from the phase 3 DOE

• It is not clear whether the whisker saturation point, the whisker growth rate over a certain period of time, or the maximum whisker length at a certain point in time should be used to compare between temp/humidity conditions. If saturation point is most important, then there is a limitation because the saturation point may not be reached in a 320 day test

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A-10-N B-3-N

C-10-N-a B-10-N

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B-10-N C-10-N-a

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C-10- N-c C-10- N-c

C-10- N-b C-10- N-b

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Notes: Used the JEDEC test method - 6 parts and 96 leads. Used Optical pre-screening to identify whiskers. Verified longest whiskers with SEM. If no whiskers present, checked 6 leads in SEM. Detailed inspection conducted on 18 leads if there were whiskers. Recorded whisker lengths optically. Verified longest 3 whiskers in SEM. Evaluated every ~2000 hours (varied depending on specific Test Cell). Used dry bag to avoid condensation in high humidity environments.

Inspection diagram courtesy of ST Microelectronics

H.L. Reynolds 6/10/09

• Where possible, whiskers growing in or near (< 200µm) corroded regions(X) were distinguished from whiskers growing in non-corroded regions(X). • This distinction was more difficult in the Test Cells with higher whisker densities.

Corrosion

X X 200µm

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100 µm

Corrosion

Courtesy G. Henshall, 2006

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• Incubation Time Used to develop whisker growth Acceleration Model corrosion

• Maximum whisker lengths

• # of leads with some whiskers present

• # of leads some corrosion present

9Used for Comparison & Analysis 9Complicated by variations in storage time 9Data analysis is ongoing

H.L. Reynolds 6/10/09

C = Corrosion observed W = Whisker growth observed N = No corrosion or whiskers Humidity [% RH] Temperature [C] 10 40 60 85 (+/- 5) 30 N N C,W

45 C,W

60 N N C,W C,W

85 C,W

100 C,W

Whiskers in corroded & non-corroded regions are not distinguished from each other. H.L. Reynolds 6/10/09

• New Sn plating chemistries/processes substantially improved over last 3-5 years – reflected in test samples

• No whisker growth or corrosion observed up to 8000 hours in Phase 5 Evaluation

• Essentially no whisker growth in any Phase 5 Test Cell with humidity <60%RH even for storage durations >9000 hours

• Based on industry tin whisker test data submitted over the previous two years, data from 30C/60% JEDEC test condition for 4000 hours does not grow whiskers.

• Recommend to JEDEC to remove the 30C/60%RH storage test condition from JESD201

• Do not remove the 30C/60%RH storage condition from JESD22A121.01 Long- term data (>9000 hours) adds to knowledge base.

H.L. Reynolds 6/10/09

Whisker Growth/Corrosion Incubation Time Data

Acknowledgement – John Osenbach, LSI Corporation

H.L. Reynolds 6/10/09

• The time to first observation of corrosion or whisker formation for each cell of devices, for each aging condition where corrosion or whisker growth took place (85C/85%RH, 45C/60%RH, 60C/87%RH, 60C/60%RH, and 30C/90%RH) in Phase 5 was fit to three different commonly used Temperature/Relative Humidity acceleration functions:

1. Time = A*exp(Ea/kT)*exp(C%RH) 2. Time = A*exp(Ea/kT)*exp(C/%RH) 3. Time = A*exp(Ea/kT)*(%RH) –F • The best fit, as determined both by R2 and by analysis of residual plots, was always equation 1.

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© Copyright 2009 49 3um Thick Film Corrosion Incubation Time 12000 Emperical Data Fit Model 2 pts., 45C/60%RH TTC = A*exp(Ea/kT)*exp(C*RH) 10000 A = 0.00587hrs Ea = 0.38eV C = -0.0294 on: rs) ti 2 pts., 30C/90%RH 1 pt., 30C/90%RH c

(h 8000 n edi sio Pr

rro 6000 1 pt., 60C/60%RH 2 pts., 60C/60%RH Co Model cal i 4000 me to i

T 2 pts., 60C/87%RH 1 pt., 60C/87%RH Emper 2000 Linear Regression y = 0.968x + 150.91 R2 = 0.9134 3 pts., 85C/85%RH 0 0 2000 4000 6000 8000 10000 12000 Experimentally Measured Time to First Observation of Corrosion (hrs)

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on: C = -0.031 ti c 1 pt., 60C/60%RH 2 pts., 60C/60%RH 8000 edi Pr 6000

Model 2 pts., 60C/87%RH cal i 4000

Time to Whisker (hrs) Time to Whisker 1 pt., 60C/87%RH Emper 2000 Linear Regression 3 pts., 85C/85%RH y = 0.9377x + 480.16 R2 = 0.9375 0 0 2000 4000 6000 8000 10000 12000 Experimentally Measured Time to First Observation of Whiskers (hrs)

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© Copyright 2009 51 Summary of fitting parameters for acceleration functions Incubation time for corrosion = A*exp(Ea/KT)*exp(C(%RH)) Film Type A (hrs) Ea (eV) C (%RH) R2 3µm-N 0.0587 0.38 -0.0294 0.91

10µm-N 0.117 (2xA3um) 0.38 -0.0294 0.74 10µm-R 1.31 0.28 -0.015 0.79

Incubation time for whiskers = A*exp(Ea/KT)*exp(C(%RH)) Film Type Corrosion A (hrs) Ea (eV) C (%RH) R2 For Matte Sn over Cu 1 hr @ 150C 3µm-N N 1.15 0.31 -0.031 0.94 10µm-N N 1.16 0.28 -0.017 0.72 10µm-R N 0.0014 0.41 -0.012 0.69 3µm-N Y 5.16 0.23 -0.018 0.86 10µm-N Y 1.16 0.28 -0.017 0.72 10µm-R Y 1.97 0.3 -0.031 0.9

Incubation time for whiskers = A*exp(Ea/KT)*exp(C(%RH)) Whisker prone films: ref: J. Osenbach et. al, J. Mater. Sci.: Mater. Electron, pp 283-305 (2007) A = 0.007hrs; Ea = 0.44eV; C = -0.044 (%RH)

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A3 A10 B3 C3 B10 C1-10 C2-10 C3-10 A10-R B10-R C1-10-R C2-10-R C3-10-R

300 ker ker ) ) 250 s s m m 200 60C/87%RH u u ( ( h h 150 t t 100 mum Whi mum Whi Leng Leng 50 Maxi Maxi 0 0 2000 4000 6000 8000 10000 12000 Storage Time (hrs)

A3 A10 B3 C3 B10 C1-10 C2-10 C3-10 A10-R B10-R C1-10-R C2-10-R C3-10-R

r r 300 e e k k ) ) s s 250 30C/87%RH i i m m Approximately 5X u u 200 ( ( longer incubation time h h 150 t t m Wh m Wh g g 100 than 60C/87%RH n n mu mu i i Le Le 50 x x 0 Ma Ma 0 2000 4000 6000 8000 10000 12000

Storage Time (hrs)

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A3 A10 B3 C3 B10 C1-10 C2-10 C3-10 A10-R B10-R C1-10-R C2-10-R C3-10-R

300 kerker

)) 250 ss ii mm hh uu 200 60C/87%RH ( ( W W

hh 150 mm uu

ngtngt 100 mm LeLe xixi 50 aa

MM 0 0 2000 4000 6000 8000 10000 12000 Storage Time (hrs)

A3 A10 B3 C3 B10 C1-10 C2-10 C3-10 A10-R B10-R C1-10-R

300 rr ee kk

)) 250 60C/60%RH ss ii mm hh uu 200 Approximately 4X

h (h ( 150

m Wm W longer incubation time

ngtngt 100

mumu than 60C/87%RH ii LeLe

xx 50 aa

MM 0 0 2000 4000 6000 8000 10000 12000 Storage Time (hrs) H.L. Reynolds 6/10/09

Whiskers with diverse morphologies within the same region “stout” & “needle-like”

Courtesy R.D. Parker/March 2007

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Phase 5 Evaluation: 8000 hours at 100C/60%RH

Courtesy R.D. Parker/March 2007

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Courtesy R.D. Parker/March 2007 H.L. Reynolds 6/10/09

• Assuming the Acceleration Model holds true, an Acceleration Factors (AF) can be calculated for different temperature and humidity conditions for both:

– Whisker Incubation Time (Example on next slide)

– Corrosion Incubation Time (See IEEE Publication 2009)

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Matte Sn over Cu; 1hr @150C Normalized to 60C/87%RH Data used to fit Model Extrapolated from Model *Note: Data does NOT reflect information about whisker length or density average-N Aver -C 3-N 3-C 10-N 10-C 10-R 10-R-C 100

) Incubation time distribution is experimentally found to vary by

H Use CAUTION approx. 1.5 to2X, thus prediction may be off by a factor of 2 R in data % / interpretation Typically find t ~ 3-6 months @ 60C/87%RH for these test Model predicts t ~ 15-30 months @ 30C/60%RH @T

e conditions 10 m i t / H

R See next slide 87% / 1 e@60C m i t ( F A 0.1 100/60 85/85 60/87 60/60 60/40 60/10 45/60 30/87 30/60 30/10 Test Condition

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• Caution based on Phase 5 results – Typically whiskers are found near corroded area – Typically whisker density is low in non corroded area – Whisker length is low in non-corroded area

• Caution also based on other literature and supplier data – Data at 85C/85%RH often does not show whiskers in non- corroded areas

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• Issue is still under technical debate • With respect to Phase 5 Evaluation, the ability to model maximum whisker lengths was limited by the length of the experiment itself – Some test cells had only just begun to growth whiskers • Some researchers believe that because, statistically the maximum whisker length is the “outlier” of the entire whisker population, it cannot be modeled as a function of temperature and humidity.

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• Two temperature/humidity conditions are not necessary.

• 60C/87%RH appears to be the optimal high temperature/high humidity test condition at this time for Sn over Cu substrates

• The iNEMI tests can be used to indicate behavior at other temperature/humidity points that could be relevant storage or service conditions within the limits of the whisker and corrosion (incubation) acceleration functions developed in this study.

• Whisker formation differs in corroded and non-corroded regions, but it appears that the incubation times for both regions can be modeled.

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• Phase 3 Evaluation (2003- 2004) – Validate and verify proposed test methods – Compare short-term (1 month) vs. long-term (1 year) testing. • Results of Phase 3 Evaluation & other Industry Studies provided input for JEDEC standards. – JEDEC standard JESD22A121/ Test Methods (May 2005) – JEDEC standard JESD201/ Acceptance Criteria (March 2006)

• Phase 4 Evaluation – No apparent effect of electrical bias, wetting behavior variability, highlighted issues related to assembly-level testing

• Phase 5 Evaluation – Acceleration Model Development, publication of complete data set for comparison and future analysis, temperature and humidity effects over a wide range of conditions

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© Copyright 2009 63 References • Phases 1 & 2 – I. Boguslavsky, P. Bush, E. Kam-Lum, M. Kwoka, J. McCullen and N. Vo, "Tin Whisker Project", Proc. of the 2002 APEX Conf., April 2002. – N. Vo, M. Kwoka and P. Bush, “Tin Whisker Test Standardization”, IEEE Transactions on Electronics Packaging Manufacturing, 28(1): pp. 3 - 9, January 2005.

• Phase 3 – V. Schroeder, iNEMI Tin Whisker Workshop, ECTC, Orlando, May 2005 – V. Schroeder, P. Bush, M. Williams, N. Vo and H. L. Reynolds, “Tin Whisker Test Method Development”, IEEE Transactions on Electronics Packaging Manufacturing, 29(4): pp. 231 – 238, October 2006

• Phases 4 & 5 – H.L. Reynolds, iNEMI Tin Whisker Workshop, ECTC, San Diego, May 2006 – H.L. Reynolds, iNEMI Tin Whisker Workshop, ECTC, Reno, May 2007 – H.L. Reynolds, J.W. Osenbach, G. Henshall, R.D. Parker, P. Su, “Tin Whisker Test Development – Temperature and Humidity Effects Part I: Experimental Design, Observations and Data Collection”, submitted to IEEE Transactions on Electronics Packaging Manufacturing, February 2009 – J.W. Osenbach, H.L. Reynolds, G. Henshall, R.D. Parker, P. Su, “Tin Whisker Test Development – Temperature and Humidity Effects Part II: Acceleration Model Development”, submitted to IEEE Transactions on Electronics Packaging Manufacturing, March 2009

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