The 23rd Microelectronics Workshop

Tin Whisker Evaluation Status for Space Application

November 11, 2010Norio Nemoto, Japan Aerospace Exploration Agency (JAXA)

Tsuyoshi Nakagawa, Nippon Avionics co.,ltdT hi ki Y d A i i F k hi l dToshiyuki Yamada, Avionics Fukushima co., ltd

Katsuaki Suganuma, Osaka University

ContentsContents

1. The community to Discuss RoHS Issues2. Space Environment2. Space Environment3. Whiskers Evaluation Test Method4. Experimental Condition5 Test Result5. Test Result6. Discussion7. Summary

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1. The Japanese community to Discuss Pb-free Issues1.1 Purpose of this community

RoHS issue Discussing Community was established in FY2007. Lead free issue’s is discussed and evaluated in this community.

•Sharing information about Pb-free issues and other RoHS prohibit materials issue.

• Investigation and examination for Pb-free technical issues.

JAXA, Satellite and Rockets system companies

JAXA, Satellite and Rockets system companies

CoreCoreMembersMembers

•IHI•IHIAerospace•KHI•JAXA

•MHI •Melco •NEC(NEC/TOSHIBA Space)•HIREC (secretariat)

CommunityCommunity •Osaka Univ. •JEITA(Japan Electronics and Information

Technology Industries Association)

University and AssociationsUniversity and Associations•Gunma Univ.

Other membersOther members Parts and other manufacturersParts and other manufacturers

gy )•SJAC(The Society of Japanese

Aerospace Companies)

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•HIREC•muRata•JAE•OKI

•MPC•MEISEI•SINFONIA•EEE parts subcommittee member

•NEC Electronics•Nippon Avionics•Yamanashi Avionics

1.2. Working Group

Mixed Assemble tech. (solder: SnPb eutectic, Parts :LF parts)NEC/T hib S S t

Community

WG- A

Pb-free trend survey and lead apply tech. : HIREC

NEC/Toshiba Space SystemsWG A

WG- B

Pb-free parts, material, assembly techniquesWG- C Pb-Free Assemble tech. : Melco

Whiskers growth mechanism, evaluation and accelerated test WG- D Whiskers evaluation : Osaka Univ. Prof. Suganuma

method, mitigation method1. Difference in test condition between consumer and Space

system: Air and Vacuum condition test2 T t diti l ti f hi k l ti t t2. Test condition evaluation for whisker acceleration test :

Temperature range of temperature cycle test.3. Whiskers mitigation method : conformal coating

3Lead, Cadmium, Hexavalent ChromiumOther prohibited materials : MHI

WG- E

2.Space Environment

S di ti

【【GEOGEO】】

･Space radiation(Solar proton) 〔〔MagnetosphereMagnetosphere〕〕･Radiation belt

(Outer belt)

･Ultraviolet rays

･Vacuum･Microgravity

･Space debris

・Vacuum・Micro gravity

【【LEOLEO】】

･Radiation belt(Inner belt)

Micro gravity・Extreme temperature cycling

(90 minutes /cycle, 6000 cycle/ year)

・Vacuum・Micro gravity・Extreme temperature cycling

El t ifi ti El t i l di h

vibration and･High energy

･High energy(Electron)

・Electrification, Electrical discharge

vibration and shock, at launch

･High energy(Electron)(Proton)

･Atomic oxygen･Cosmic rays

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〔〔The atmosphereThe atmosphere〕〕

3. Whiskers Evaluation Test Method

• Ambient Temperature/ Humidity Storage30 d C d 60%RH

【for consumer application 】Test conditions is b d30 deg.C and 60%RH

• High Temperature/ Humidity Storage55 deg.C and 85%RH

based on storage, and whether or not operating forg

• Temperature Cycling-55/-40 to +85 deg.C, Air to Air

f S li i ?

operating for consumer system

for Space application?

• Ambient Temperature/ Humidity Storage Ground storage( ll d

y g30 deg.C and 60%RH

• High Temperature/ Humidity Storage55 deg C and 85%RH

(more controlled condition for space application)55 deg.C and 85%RH

• Temperature Cycling-55/-40 to +85 deg.C, Air to Air

• Vacuumed Temperature Cycling

space application)

What’s difference f hi k h

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• Vacuumed Temperature Cycling-40 to +125 deg. C Vacuum condition

of whisker growth in space?

4. Experimental ConditionTest Sample : Chip ceramic capacitor

(Electrode: Sn(8um) on Ni barrier metal)Temperature cycling :-40 to +125 deg. CSoak time : 60 minutesT t li t 3 000 lTemperature cycling : up to 3,000 cycleAtmosphere : Air, Vacuum(10-4Pa)VVacuumpump Chip

capacitor

6Figure 1 Test equipmentFigure 2 Temperature controlled

profile of test equipment

5.Test Result5.1 Tin Whisker Growth in 500cycle

Air Vacuum

7There is a difference in whisker shape between Air and Vacuum.

5.2 Whisker Length and Diameter

AirVacuum

Air Vacuum

Whisker Length : Vacuum > Air

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Whisker Length : Vacuum AirWhisker Diameter : Vacuum < Air

5.3 Striation on Whisker(1/2)

(A)(B)

(C) Ambience : Air(A) (C)Cycle : 200cycleLength : 32.8μmDiameter : 7.1μm

(A) (B) (C)(A) (B) (C)Groove

I t l 330 I t l 167 I t l 138Interval:330nm Interval:167nm Interval:138nm

•Striation maybe indicate each thermal cycle

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Striation maybe indicate each thermal cycle.•Top region grows faster than root maybe due to Sn supply amount.•Striation for axial direction was clearly observed.

5.3 Striation on Whisker(2/2)

Ambience : Vacuum(a) (b) (c)

Cycle : 200cycleLength : 52.7μm

( ) ( ) ( )

Diameter : 3~3.9μm

(a) (b) ( )(a) (b) (c)

Interval:1000nm Interval:375nm Interval:180nmInterval:1000nm Interval:375nm Interval:180nm

•Top region grows faster than the root maybe due to Sn supply amount

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Top region grows faster than the root maybe due to Sn supply amount.•The striation for axial direction was not clearly observed unlike in air.•The longer intervals indicate whiskers in vacuum grow faster than in air.

5.5 EBSD of Surface Cross-section

20m 20m 20m

a Fr

actio

n

a Fr

actio

n

a Fr

actio

n Inverse Pole Figure MapNormal Direction

Grain size (Diameter) [m] Grain size (Diameter) [m] Grain size (Diameter) [m]

Are

a

Are

a

Are

a

Surface Cross-section of Sn layer was evaluated using Electron BackScatter Diffraction (EBSD)

(c) After 200 cycle in Vacuum(a) Initial cross-section (b) After 200 cycle in Air

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( )• Grain size : Miniaturization was observed in Vacuum

: Coarsening was observed in Air

5.6 Sn Layer Surface Roughness

Ra=0 43m Ra=0 92m Ra=0 50mRa=0.43mRy=7.65m

Ra=0.92mRy=21.37m

Ra=0.50mRy=8.61m

(c) After 200 cycles in Vacuum(a) Initial surface (b) After 200 cycles in Air •Along with temperature cycling surface roughness was increased

no-whisker area no-whisker area

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Along with temperature cycling, surface roughness was increased.•Surface morphology in air condition was rougher than in vacuum.

5.7 Cross-section of Air Condition Whisker

Direction of observation

Cross section line

Focused Ion Beam

Cross-section line

25Stripe 25nm

34nm

p

groove groove

•Groove was observed around the root of a whisker

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Groove was observed around the root of a whisker.•Thin oxide layer was observed at the surface of groove and around grain.•Oxide layer stripe was observed at the surface of grain.

5.8 Cross-section of Vacuum Condition Whisker

Cross-section line

Focused Ion BeamDirection of observation

22nm25nm

groovegroove groove

•Groove was also observed around the root of a whisker

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•Groove was also observed around the root of a whisker.•Thin oxide layer was also observed at the surface of groove and around grain.

6. Discussion6.1 Sn Supplied Amount

Initial 200 cycles in vacuum1500 cycles in vacuum

1500 cycles in vacuum

405nm

Top regionroot region

•Sn whisker length and amo nt increase

143nm

CTE mismatch caused Sn

whisker growth

amount increase•Surface roughness increase•Compression stress decrease•Sn supplied amount decrease Whisker length saturated

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whisker growth in

thermal cycle test

•Sn supplied amount decrease•Interval of whisker striation decrease

Whisker length saturated

6.2 Difference of Air/ Vacuum Whisker

(A) (B) (C)

(A) (B) (C)

Interval:330nm Interval:167nm Interval:138nm

AirVolume of internode(m3)

Diameter : 7.1m13.1 6.61 5.46

(a) (b) (c)

(a) (b) (c)

VacuumInterval:1000nm Interval:375nm Interval:180nm

VacuumVolume of internode(m3)

Diameter : 3~3.9m7.10 4.48 2.15

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•Internode volume of vacuum whisker is lower than that of air.=> Driving force of Sn in Vacuum whisker maybe lower than Air one.

6.3 Impact of air/ vacuum on whisker growth

1. Sn oxide layer

Air whisker needs higher stress

Vacuum whisker grows

In air In vacuumstress thin & longer

Sn oxideSn oxideSnSnSnSn

2.Grain size during thermal cycle test.

17(b) After 200 cycle in Vacuum(a) After 200 cycle in Air

6.4 Winding Growth

Friction caused by root groove makes whisker winding.Striation of axial direction maybe related with groove and friction.y g

Sn oxideSn oxideSnSn

Sn Supply Sn Supplygroove

SnSn

Sn Supply pp y

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7. SummaryJAXA established the community to discuss and evaluate the Pb-free issue. Whisker evaluation test was started for space applicationapplication.1. Thin and straight whisker was observed in vacuumed

condition test.2. Groove was observed at the root of a whisker.3. Striation was observed at the side surface of whiskers. The

interval of striation at the top of whisker was longer than atinterval of striation at the top of whisker was longer than at the root.

4. Whisker growth in vacuum is faster than in air.5 S i i i i ll th th t f i i5. Sn grain size in vacuum is smaller than that of in air.6. Saturation of whisker length maybe caused by Sn depletion.7. Difference between air and vacuum whisker shape maybe p y

caused by Sn oxide layer and/or Sn grain size.Whisker evaluation test will be continued to estimate the vacuum environment effects for space applications Whisker mitigation

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environment effects for space applications. Whisker mitigation method such as conformal coating will also be continue to be evaluated.

Acknowledgement KOBELCO RESARCH INSTITUTE, INC.

Mr. Shunsuke HiranoMr. Kenichi Inokuchi

High-Reliability Engineering & Components CorporationMr Fusao IwaseMr. Fusao IwaseMr. Mikihiko Urano

Yamanashi Avionics Co Ltd Yamanashi Avionics Co., Ltd.Mr. Syunji Sano

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Thank you for your attention!!