Accelerated Tin Whisker Test -...

Accelerated Tin Whisker Test Project Overview

Phases 1 to 5

Heidi L. Reynolds, Ph.D.Former Project Chair

iNEMI WebinarJune 10, 2009

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H.L. Reynolds 6/10/09

Tin whisker test committee is a microcosm of the electronics industry • ITRI Soldertec

• Micro Semi• Soldering Tech.

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iNEMI Whisker-related Projects• 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

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Tin Whisker Test Project• Project Objective • To develop industry standard test methods for predicting

tin whiskers

• Current StructureRichard Parker (Chair) – Delphi Electronics & SafetyPeng Su (Co-Chair) – Cisco Systems

• Weekly teleconferencesDate: ThursdaysTime: 8am PST

• Contacts • Jim Arnold at [email protected]• Richard Parker at [email protected]

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Accelerated Tin Whisker Test Project Objective

• To identify accelerated test methods and to develop industry standard test methods for predicting tin whiskers.

R. Parker/iNEMI Phase 5/March 2007

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Renewed Interest in Tin Whisker Studies

19481951

1956

20002001

20042005

2006

Bell Telephone experienced failures on channel filters due to Cd whiskers

Bell Labs found whisker growth from Cd, Sn, Zn, Al, and Ag (in H2S)

Small Pb addition to Sn was found to mitigate tin whiskers

First draft of EU RoHS Directive

Industry rekindled the interest in Sn whisker study. NEMI formed Testing, User, and Model groups.

iNEMI published the first whisker test guideline document

JEDEC/IPC passed testing standard JEDEC22A121

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

Phase1& 2

Phase3

Ongoing & Future

Phase 5

Phase4

iNEMI Whisker Test Group

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Summary of Past Evaluation PhasesTest Samples Stresses Duration Results Industry adoption

1 Lab scale bright tin on brass coupons and SOIC packages

Temp/Humidity storage, and thermal cycling


3 Production components and lab samples of various metallurgy


10000 hrs

Longer term whisker growth behaviors, such as incubation time, length saturation, whisker density, etc., were monitored.

Inputs were provided to JEDEC. JEDEC released standard tin whisker test methods and acceptance criteria.

4 Assembled production components w/ various plating finishes and solder pastes

Temp/Humidity storage, and electrical bias.

3000 hrs Plating finish dependent wetting behavior. No apparent bias effects.

4 wks Whiskers on brass coupons only. Few whiskers formed. Results inconclusive.

2 Production matte tin plated SOIC leadframes

4 wks Whiskers can be effectively induced by environmental stresses. Plating chemistry and processes are most significant to whisker growth.

iNEMI proposed Tin Whisker Test Documents in 2003, which was adopted by JEDEC and released as JEDEC-22A121.

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Summary

Test Samples Test Methods Duration Objectives Results

5 Production matte tin plated components

Various temp/humidity storage

4000 to >26,280hours

Investigate the effects of temperature and humidity over a wide range of conditions to develop the optimal test conditions and correlation between accelerated test conditions and actual service conditions.

Development of Acceleration Model, Publication of complete data set over wide range of conditions

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Tin Whisker Test Project Evaluation History

• Phase 1: [Experimental] Bright Tin Plating – Brass Coupons & SOIC packages

– PreconditioningThermal Cycling (500 cycles) -40C to 90CAmbient 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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Tin Whisker Test Project Evaluation History• Phase 2: [Production] Matte Tin Plating

– Brass Coupons, SOIC packages, Chip Components

– 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.

Legs

Temp Cycle (°C)

Temp (°C) & Relative

Humidity (%)

Supplier

Plating Site

Remarks

6 - 60, 95 A Temp & Humidity7 - 60, 95 B Temp & Humidity8 - 30, 90 A Humidity9 - 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

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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

Environmental condition

Inspection interval

Total Duration

1000 to 3000 h 10,000 hours

Irregular(@2 kh &10

kh)3 kh for N

7 kh for L,M

10,000 hours

1000 h 9000 hours

2000 h 9000 hours

-55 °C (+0, -10) to + 85 °C (+10, -0) air-to-air temperature cycle (20 min per

cycle)

500 cycles 3000 cycles

60 °C (+5)93% RH (+2, -3)

Uncontrolled20 °C to 25 °C20 to 60 % RH

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A number of metallurgies proposed for industry use were evaluated in Phase 3

• 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 – on C1020 – plating B– on Alloy 42 – plating B– on C194 – plating B

• Sn/Ni underlay/BeCu substrate• Matte Sn

• Phase 2 DOE parts

Started later, fewer inspection intervals, and no thermal cycling

Note: Unless otherwise indicated Sn plating is 10 µm-thick (target)

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Note regarding samples for Phase 3

• 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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Examples of Data from Phase 3

• 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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Explanation of data presentation

0

50

100

150

200

250

300

Sn-Ag Sn-Bi Sn-Cu Hot-dipSn

BrightSn onA42

Sn on Nion BeCu

SnPb

Metallurgy

Whi

sker

leng

th [m

icro

ns]

0

50

100

150

200

250

300

Den

sity

[#]

Absolute maximum whisker length of all whiskers measured

Average maximum whisker length of up to 9 non-zero values of whisker length

Density (plotted relative to right axis) = total number of whiskers counted in 9 fields of view (0.56 mm2 of area)

Scale of plot held constant for comparison at 300 µm max and 300 whisker max

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0

50

100

150

200

250

300

SnDOE2 BrightSn

BrightSn onC1020

Sn 3-5mic

Sn Sn onC7025

245Creflow

Sn

150C1hr Sn

Metallurgy

Whi

sker

leng

th [m

icro

ns]

0

50

100

150

200

250

300

Den

sity

[#]

Performance in high temperature humidity testing depends on plating

8000 hr results60C/93%RH

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Performance in high temperature humidity testing depends on plating

0

50

100

150

200

250

300

Sn-Ag Sn-Bi Sn-Cu Hot-dipSn

BrightSn onA42

Sn on Nion BeCu

SnPb

Metallurgy

Whi

sker

leng

th [m

icro

ns]

0

50

100

150

200

250

300

Den

sity

[#]

8000 hr results60C/93%RH

Note: SnPb grew whiskers at 7000 hrs

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Phase 3 Conclusions regarding test conditions(See IEEE Journal October 2006 for more details.)

• 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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• Further optimization needed for true accelerated test.

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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Bias voltage between adjacent leads

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

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Whiskers limited to three package/assembly combinationsPhase 4 Evaluation Comments

Environmental Storage Conditions 30C/60% RH 60C/85% RH

No bias relationship for leads with whiskers.

Assembly Solder Paste SnPb SnAgCu SnPb SnAgCu

[1] Whiskers first observed at 1500 hours.

Sample[2] Whiskers first observed at 3000

hours.

32LQFP bright tin, C7025 None None NoneWhiskers

[2]

For SnPb paste: cracked/alloyed

For SnAgCu paste: cracking; whiskers on foot of lead; no bias relationship

32LQFP matte tin, C7025 None None NoneWhiskers

[1]

For SnPb paste: most leads wetted, flux residue

For SnAgCu paste: whiskers on 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, O194 None

Whiskers [1]

Leads wetted to shoulder;no bias relationship

16SOIC matte tin, O194 None NoneLeads wetted to shoulder, flux residue;

Some corrosion but no whiskers.

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Phase 4 - 3000 hours at 60˚C/87% RH

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

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FIB Cross-section

Surface SEM

FIB Cross-section

Base of whisker

Increasingmagnification

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

Cracking in plating

Phase 4

Courtesy P. Su, Freescale

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Phase 4 - 32LQFP, bright Sn, Sn/Ag/Cu solderFIB Cross-section - Magnified view

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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Phase 4 - 3000 hours at 60˚C/87% RH

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

No cracking of the plating observed. Some longer

whiskers also observed

Lead edge~70µm whisker

Courtesy P. Bush, SUNY, Buffalo

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Phase 4 Evaluation

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

All leads completely alloyed with solder.

Courtesy P. Bush, SUNY Buffalo

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Phase 4 Evaluation - General Observations

•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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Phase 4 Evaluation - General Observations(P.2)

• Whiskers found on 32LQFP with bright and matte Sn plating, assembled with SnAgCu paste and on 64LQFP with semi-bright Snplating 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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PHASE 4 Evaluation Summary

• 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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• Further optimization was needed for true accelerated test.

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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Phase 5 Evaluation● (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:

Optimal whisker test condition(s)Whether whisker behavior measured at accelerated testing conditions can be related to actual storage and/or customer service conditions.

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Questions to answer in this experiment

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 factor7) 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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Phase 5 Evaluation Test MatrixX shows JEDEC Std JESD201 Conditions

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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Component used for Phase 5 Evaluation

Plating Thickness

16L – SOIC Package

•Matte Sn over Cu (C194) leadframe•Post-plate heat treatment of 150C within 24 hours of plating

Generic Supplier Designation (A,B,C)

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Phase 5 Evaluation

Sample Labeling ConventionSample Labeling Convention

A - X - X - a

SupplierA,B or C

Reflowed ConditionR – reflowedN – non reflowed (as received)

Nominal Plating Thickness3 µm

10 µm

Lot #(if more than one tested)

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Phase 5 Evaluation(Approximate Total of hours in storage)

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

8 C-10-N-a

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

temp/humidityconditions

~800

0 ho

urs

~655

0 ho

urs

~989

0 ho

urs

~11,

080

hour

s

~10,

440

hour

s

~400

0 ho

urs

~800

0 ho

urs

~10,

080

hour

s

~10,

128

hour

s

+26,

280

hour

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Phase 5 Evaluation – Assumptions (Schroeder, Osenbach 5/6/04)

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 andhumidity 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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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 functionalrelationship, 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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Surface Appearance (As Received)

B-3-NA-10-N

Courtesy J. Osenbach/2005

B-10-NC-10-N-a

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Surface Morphology (As Received)Courtesy J. Osenbach/2005

B-3-N A-10-N

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

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Surface Morphology (As Received)Courtesy J. Osenbach/2005

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

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

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Phase 5 Evaluation Inspection ProtocolNotes: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

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Observations of Whiskers in Corroded vs. Non-corroded Regions

• 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 X200µm

X

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Phase 5 – 7488 hours @ 45C/60%RH

100 µm

Corrosion

Courtesy G. Henshall, 2006

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Phase 5 Evaluation – Data Measured

• Incubation Timewhisker growthcorrosion

• Maximum whisker lengths

• # of leads with some whiskers present

• # of leads some corrosion present

Used to develop Acceleration Model

Used for Comparison & AnalysisComplicated by variations in storage timeData analysis is ongoing

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Phase 5 Test Cells exhibiting Corrosion and/or Whisker Growth during the allowed storage time

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.

C = Corrosion observedW = Whisker growth observedN = No corrosion or whiskers

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30C/60%RH Test Condition• 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 hoursdoes 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.

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Acceleration Model Development from Phase 5 Evaluation

Whisker Growth/Corrosion Incubation Time Data

Acknowledgement – John Osenbach, LSI Corporation

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Data Analysis – for Acceleration Model

• 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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3um Thick Film

Linear Regression y = 0.968x + 150.91

R2 = 0.9134

0

2000

4000

6000

8000

10000

12000

0 2000 4000 6000 8000 10000 12000

Experimentally Measured Time to First Observation of Corrosion (hrs)

Empe

rical

Mod

el P

redi

ctio

n: T

ime

to C

orro

sion

(hrs

)

1 pt., 60C/60%RH 2 pts., 60C/60%RH

2 pts., 30C/90%RH 1 pt., 30C/90%RH

2 pts., 45C/60%RH

3 pts., 85C/85%RH

2 pts., 60C/87%RH 1 pt., 60C/87%RH

Emperical Data Fit Model TTC = A*exp(Ea/kT)*exp(C*RH) A = 0.00587hrs Ea = 0.38eV C = -0.0294

Corrosion Incubation Time

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3um Thick FilmNon-Corroded Regions

Linear Regressiony = 0.9377x + 480.16

R2 = 0.93750

2000

4000

6000

8000

10000

12000

0 2000 4000 6000 8000 10000 12000

Experimentally Measured Time to First Observation of Whiskers (hrs)

Empe

rical

Mod

el P

redi

ctio

n: T

ime

to W

hisk

er (h

rs)

1 pt., 60C/60%RH 2 pts., 60C/60%RH

3 pts., 30C/90%RH

3 pts., 85C/85%RH

2 pts., 60C/87%RH

1 pt., 60C/87%RH

Emperical Data Fit Model TTW = A*exp(Ea/kT)*exp(C*RH) A = 1.15hrs Ea = 0.31eV C = -0.031

Whisker Incubation Time

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Summary of fitting parameters for acceleration functions

Film Type A (hrs) Ea (eV) C (%RH) R2

3µm-N 0.0587 0.38 -0.0294-0.0294-0.015

0.9110µm-N 0.117 (2xA3um) 0.38 0.7410µm-R 1.31 0.28 0.79

Incubation time for corrosion = A*exp(Ea/KT)*exp(C(%RH))

Film Type Corrosion A (hrs) Ea (eV) C (%RH)

N -0.031-0.017-0.012-0.018-0.017-0.031

N10µm-R N 0.0014 0.41 0.693µm-N Y 5.16 0.23 0.8610µm-N Y 1.16 0.28 0.72

Y

R2

3µm-N 1.15 0.31 0.9410µm-N 1.16 0.28 0.72

10µm-R 1.97 0.3 0.9

For

Mat

te S

n ov

er C

u1

hr @

150

C Incubation time for whiskers = A*exp(Ea/KT)*exp(C(%RH))

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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Temperature Effect- non-corroded regions

050

100150200250300

0 2000 4000 6000 8000 10000 12000Storage T ime (hrs)

Max

imum

Whi

sker

Le

ngth

(um

)

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

050

100150200250300

0 2000 4000 6000 8000 10000 12000

Storage Time (hrs)

Max

imum

Whi

sker

Le

ngth

(um

)

A3 A10 B3 C3 B10 C1-10 C2-10 C3-10 A10-RB10-R C1-10-R C2-10-R C3-10-R

60C/87%RH

30C/87%RH Approximately 5X longer incubation time than 60C/87%RH

050

100150200250300

0 2000 4000 6000 8000 10000 12000Storage T ime (hrs)

Max

imum

Whi

sker

Le

ngth

(um

)


050

100150200250300

0 2000 4000 6000 8000 10000 12000

Storage Time (hrs)

Max

imum

Whi

sker

Le

ngth

(um

)

A3 A10 B3 C3 B10 C1-10 C2-10 C3-10 A10-RB10-R C1-10-R C2-10-R C3-10-R

60C/87%RH

30C/87%RH Approximately 5X longer incubation time than 60C/87%RH

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Relative Humidity Effect-non corroded regions

Approximately 4X longer incubation time than 60C/87%RH

050

100150200250300

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

Max

imum

Whi

sker

Le

ngth

(um

)

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

60C/60%RH

050

100150200250300

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

Max

imum

Whi

sker

Le

ngth

(um

)


60C/87%RH

050

100150200250300

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

Max

imum

Whi

sker

Le

ngth

(um

)

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

60C/60%RH

050

100150200250300

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

Max

imum

Whi

sker

Le

ngth

(um

)


60C/87%RH

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Phase 5 Evaluation – 8000 hours @ 100C/60%RH

Courtesy R.D. Parker/March 2007

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

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Tin whiskers with “classic” features observedPhase 5 Evaluation: 8000 hours at 100C/60%RH


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…….and also some unique whisker features observed


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

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Acceleration Factors

• 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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Whisker Incubation Time Acceleration FactorNormalized to 60C/87%RH

0.1

1

10

100

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

Test Condition

AF (t

ime@

60C

/87%

RH

/tim

e@T/

%R

H)

average-N Aver -C 3-N 3-C 10-N 10-C 10-R 10-R-C*Note: Data does NOT reflect information about whisker length or density

Data used to fit ModelExtrapolated from Model

Use CAUTIONin data interpretation for these test conditions

See next slide

Typically find t ~ 3-6 months @ 60C/87%RHModel predicts t ~ 15-30 months @ 30C/60%RH

Incubation time distribution is experimentally found to vary by approx. 1.5 to2X, thus prediction may be off by a factor of 2

Matte Sn over Cu; 1hr @150C

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Use CAUTION when interpreting AF (whisker incubation time)data for 85C/85%RH and 100C/60%RH Test Conditions

• 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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Modeling of maximum whisker lengths?

• 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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Phase 5 - Conclusions • Whisker presence and the initiation of corrosion can be

represented by a function of temperature and humidity.

• 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 bemodeled.

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iNEMI Test Group Summary (Evaluation Phases 1-5)• Phase 1 & 2 Evaluations: iNEMI proposed Tin Whisker Test

Document in 2003 based on results from these experiments.

• 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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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

© Copyright 2009

www.inemi.orgEmail contacts:

Jim [email protected]

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