Status of JAXA Lead Free Study and Evaluation of Surface Treatment

Technology for Printed Wiring Board for Space Applications

October 16, 2009

○ Kazuhiro Aoyama, Norio Nemoto, JAXA S&MA○Shunji Sano, Yamanashi Avionics Co., Ltd.

Tsuyoshi Nakagawa, Nippon Avionics Co., Ltd.

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ContentsContentsI. Status of JAXA Lead Free Study

1. Background2. The Japanese Community to Study

RoHS Issues3. Major Technical Issues of LF parts

usage4. Schedule5. Conformal coating effects

II. Evaluation of Surface Treatment Technology for Printed Wiring Board for Space Applications

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The EU has enacted two directives, RoHS and WEEE, that prohibit the use of Pb, Cd, Cr6+, Hg, PBB and PBDE in products for the EU consumer market since July 2006. One of the key element in thesedirectives is Pb, which had been widely used in electric components such as solder and parts terminations. Although theseregulations only affect products for sale in the EU, many manufacturers in the world have shifted to lead-free products.

*1:RoHS(Restriction of the use of certain Hazardous Substance in electrical and electronic equipment)：http://europa.eu.int/eur-lex/pri/en/oj/dat/2003/l_037/l_03720030213en00190023.pdf

WEEE(Waste Electrical and Electronic Equipment)：http://europa.eu.int/eur-lex/pri/en/oj/dat/2003/l_037/l_03720030213en00240038.pdf

1．Background

1.JAXA continues to use parts containing SnPb for space applications.2.Purchase of the parts and materials that contain lead is becoming

difficult.3.Reliability problems of lead-free parts and materials may surface in

space applications.4.JAXA established Japanese community to study RoHS issues.

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CoreCoreMembersMembers

CommunityCommunity

Other membersOther members Parts and other manufacturersParts and other manufacturers

•Osaka Univ. •JEITA(Japan Electronics and Information

Technology Industries Association)•SJAC(The Society of Japanese

Aerospace Companies)

•HIREC•muRata•JAE•OKI

•IHI•IHIAerospace•KHI•JAXA

JAXA, Satellite or Rockets system companies

JAXA, Satellite or Rockets system companies

University and AssociationsUniversity and Associations

•MPC•MEISEI•SHINKO•EEE parts subcommittee member

2. The Japanese community to Study RoHS Issues

•MHI •Melco •NEC(NEC/TOSHIBA Space)

•Gunma Univ.

•Hitachi-Chemical•NEC Electronics•Nippon Avionics

•Sharing information about RoHS issues• Investigation and examination for technical issues•Establish lead free parts control guideline

PurposePurposePurpose

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Tin whisker is one of the most serious issues for Lead Free parts usage.

3. Major Technical Issues of LF parts usage

1.Whisker mitigation method

2.Whisker evaluation method

【Whisker】

•Conformal coating effects test*

•Several Acceleration environment tests

•Vacuum condition test

First step of lead free parts usage is mixed assemblies ( Lead free parts assembled using SnPb solder).

【Integrity of solder joint】

1.Solder joint reliability evaluation of lead free parts (includes NiPdAu plating)

•Tensile/Elongation properties test

•Shear strength test* •Wetting test•Thermal shock test*Explain later

4. ScheduleSeveral evaluation tests for whisker and solder joint are in progress. After these evaluation tests, lead free parts control guideline will be established in this fiscal year.

FY 2008 FY 2009 FY 2010Guide Line

1.1 Conformal Coating Effects

2.1 Acceleration environment test

2.2 Vacuum exposure test

3.1 Tensile/Elongation properties test

3.2 Shear properties test

3.3 Wetting test

3.4 Solder joint reliability test

3. Solder joint reliability evaluation of LF

2. Whisker evaluation method

1.Whisker mitigation method

Technical IssueEssence Draft/Establish Revise

Major 5 kind of materials

RT, HH, TC

10‐4 Pa

Another type coating

Initial High temp. storage

Plating: Sn/NiPdAu, Solder:SnPb

Initial

storage

Initial Vibration, Shock, TC5

5. Conformal coating effects(1/3)【Whisker mitigation test】

To evaluate whisker mitigation effects, major 5 conformal coating materials were selected. Upper and lower temperature of temperature cycling test condition is -40 to +85 deg. C, respectively with 30 minutes soaking time. The Thickness of each sample is based on normal application of each material for space use.

Type Urethane Silicone para-xylylene

Sample Coating A Coating Ｂ Coating Ｃ Coating Ｄ Coating Ｅ

Coefficient of linear thermal expansion

76×10-6/℃<Tg170×10-6/℃>Tg

126×10-6/℃ 3.5×10-6/℃@25℃

Tensile Strength 24.6kgf/cm2 28kgf/cm2 35kgf/cm2 700kgf/cm2

Specific gravity 1.15 1.07 1.08 1.11 1.289

Ｔｈｉｃｋｎｅｓｓ（Ave.） 130um 570um 50um 70um 15um

Application Method Brush Spray Brush Brush Deposition

table 1. conformal coating characteristics

Conformal coating（optional thickness）Tin plate（4um）

Base metal（42alloy/Cu, 500um）thickness

cross-sectionview

Conformalcoating

top-view6

5. Conformal coating effects(2/3)

【Test results】Penetrated whisker was not observed in every sample up to 1000 cycles. The test will be continued up to 2,000 cycles.

Fig.1 Temperature cycling test result (-40 to +85 deg. C)

0

2

4

6

8

10

12

14

16

18

20

0 500 1000 1500 2000

Temperature ｃｙｃｌｅ

Ｔｉｎ

　ｗ

ｈｉｓ

ｋｅｒ　

lengt

h（μ

ｍ）

Non-coating Coating A(130um)

Coating B(570um) Coating Ｃ(50um)

Coating Ｄ(70um) Coating Ｅ(15um)

Con

form

al c

oatin

g

whisker

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Photo.1 SEM image of conformal coated test peace cross-section

5. Conformal coating effects(3/3)【Discussion】

Compare with each conformal coating characteristics and whisker growth rate (500cycle to 1,000cycle), low whisker growth rate was observed in higher hardness and Young’s modulus respectively. From these results, hard conformal coating will mitigate whisker growth better than soft one.More detailed whisker mitigate effects will be discussed after the test.

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0.1 1 10 100 1000

Hardness(GPa)

Whis

ker

grow

th r

ate(μ

m)

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

1 10 100 1000 10000

Young's modulus(GPa)

Whis

ker

grow

th r

ate

（μm

）

Fig. 2 Comparison of coating hardness and whisker growth rate

Fig. 3 Comparison of coating Young’s modulus and whisker growth rate

Coating A

Coating B

Coating DCoating C

Coating E

Coating A

Coating B

Coating D Coating C

Coating E

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Contents

I. Status of JAXA Lead Free Study

II.Evaluation of Surface Treatment Technologyfor Printed Wiring Board for Space Applications

1. Technical issues2. Purpose of evaluation3. Approach4. Test results

4.1 Fracture mode4.2 Shear Strength4.3 NiSn IMC and AuSn IMC

5. Discussion6. Summary and future works

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1. Technical issues (1/2)

Keeping solderability well for long term (for more than 12month).

CGAColumSn90Pb

Ball(Sn37Pb/Sn90Pb)

Fig.5. Surface mountingFig 4. Through hole mounting

DIPBGA

Long term storageLong term storage

Solder joint strengthSolder joint strength

JAXA standard requires to remove Au before soldering because of JAXA standard requires to remove Au before soldering because of brittle brittle solder joint. But it is difficult to remove plated Au on PWB. solder joint. But it is difficult to remove plated Au on PWB.

Through holeSMD

SMT pad

NiPdAu plated PWB has been applied to high reliability commercial applications. NiPdAu plating is also used in lead free PWB.

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1. Technical issues (2/2)

Test piece.

* I.Shouji, et.al. , Effect of Impurities of Au and Pd on Tensile Properties of Eutectic Sn-Pb Solder for Aerospace Application, ICEP2009

decrease

Fig. 6 Tensile strength test result Fig. 7 Elongation test result

Solder joint strength of Au adding SnPb solder was already evaluated. Au content rate in SnPb solder assembly should be less than 3% as required in several standards.After adding Au/Pd to SnPb eutectic solder, elongation was decreased although Au content was less than 3% . This result shows that the solder joint strength will depend on each Au/Pd content rate in SnPb solder.

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2. Purpose of evaluation

Cu（Ｐａｄ）

Solder (Sn37Pb)

Surface treatment definedin JAXA specification.

(Solder coating)

NiPdAu

Solder coating(SnPb)

Lead free surface treatment.(Electroless NiPdAu plating)

We evaluated solder joint strength of the electroless NiPdAu plating with different Au/Pd thickness.

Electrode

Parts

Electroless plating

Solder (Sn37Pb)

Solder (SnAgCu)

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3. Approach (1/2)

PlatingPlating

Ball mountingBall mounting

Accelerated testAccelerated test

Ball shear testBall shear test

Electroless NiPdAu plating (15 test conditions)

SnPb eutectic solder balls are mounted by reflow.

High temperature storage150deg.C 0h/250h/500h/1000h

Test flowTest flow

Solder Ball(Sn37Pb)Φ0.76mm

Shear speed : 0.2mm/sec

Hig

ht :

50μ

m

Shea

r too

l

Evaluate the shear strength and fracture modes.

Fracture mode “A” (fracture in solder).

Fracture mode “B~E” (interfacial fracture). Solder remaining rate75~99% → B mode : 50~74% → C mode25~49% → D mode : 0~24% → E mode

OK

NGSolder resist BGA pad

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3. Approach (2/2)

No.Ni Pd Au

1 0.05μｍ2 0.1μｍ3 0.5μｍ4 0.05μｍ5 0.1μｍ6 0.5μｍ7 0.05μｍ8 0.1μｍ9 0.5μｍ10 0.05μｍ11 0.1μｍ12 0.5μｍ13 0.05μｍ14 0.1μｍ15 0.5μｍ

Thickness of Plating

3μｍ

0.03μｍ

0.05μｍ

0.1μｍ

0.2μｍ

Diameter of pad ：Φ0.75mm Diameter of S/R： Φ 0.6mm

BGA design Test Condition of NiPdAu plating

Sample SpecificationsSample Specifications

Cu PadSolder resist（S/R）

Printed Circuit Board Cu NiPdAu

Fig. 8 Cross section image Electroless NiPdAu plating

Pad pitch：1.27mm

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0%20%40%60%80%

100%

0H 250H 500H 1000H 0H 250H 500H 1000H 0H 250H 500H 1000H

Incid

ence

E

D

C

B

A

4. Test results 4.1 Fracture mode (1/2)

Au0.05μｍ Au0.5μｍAu0.1μｍ

PdNone

Pd0.03μｍ

Pd0.05μｍ

Pd0.1μｍ

Pd0.2μｍ

ピンクはアニメーション

0%20%40%60%80%

100%

0H 250H 500H 1000H 0H 250H 500H 1000H 0H 250H 500H 1000H

Incid

ence

E

D

C

B

A

0%20%40%60%80%

100%

0H 250H 500H 1000H 0H 250H 500H 1000H 0H 250H 500H 1000H

Incid

ence

E

D

C

B

A

0%20%40%60%80%

100%

0H 250H 500H 1000H 0H 250H 500H 1000H 0H 250H 500H 1000H

Incid

ence

E

D

C

B

A

0%20%40%60%80%

100%

0H 250H 500H 1000H 0H 250H 500H 1000H 0H 250H 500H 1000H

Incid

ence

E

D

C

B

A

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4. Test results4.1 Fracture mode (2/2)

Au：0.05μｍ

Cu

NiCu

Ni

Pb

Ni3Sn4

※Yellow arrows indicate shear direction.

Pd：0.2μｍ Au0.5μmPd：none

Ni3Sn4

Pb

Photo 2.Appearance offracture sitex100(SEM)

Photo 3.Cross section offracture sitex5000(SEM)

SnAuNiSn

D-mode D-mode

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4. Test results4.2 Shear Strength

下限分布データ解析

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0

実測データ

累積

確率

指標

（σ

）

Pd=N/A

Pd=0.03um

Pd=0.05um

Pd=0.10um

Pd=0.20um

下限分布データ解析

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0

実測データ

累積確

率指

標（

σ）

Pd=N/A

Pd=0.03um

Pd=0.05um

Pd=0.10um

Pd=0.20um

Au 0.5μmAu 0.05μm

下限分布データ解析

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0

実測データ

累積確

率指

標（

σ）

Pd=N/A

Pd=0.03um

Pd=0.05um

Pd=0.10um

Pd=0.20um

下限分布データ解析

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0

実測データ

累積確

率指

標（

σ）

Pd=N/A

Pd=0.03um

Pd=0.05um

Pd=0.10um

Pd=0.20um

Shear Strength(N)

◆◆▲▲■■●●◆◆

◆◆▲▲■■●●◆◆

Shear Strength(N)

Initial

150deg.C1000H

Fig. 9 Shear Strength test result

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4. Test results4.3 Ni-Sn IMC and Au-Sn IMC (1/3)

CuNi Cu

Solder

Ni3Sn4

Cu

ＯＫ

Ni3Sn4

Ni3Sn4

Initial

150deg.C1000H

Fracture Line

ＯＫ ＯＫ

ＯＫＯＫ

NG

Solder

Solder

NiNi

Fig. 10. Cross section of SEM observation result (Au:0.05um) ※Yellow arrows indicate “Flake type” NiSn IMC.

Pd:0.2μm Au:0.05μmPd:0.03μm Au:0.05μmPd:none Au:0.05μm

Pd content rate dependence was evaluated.Flake type NiSn IMC density was increased by increasing of Pd content rate.

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4. Test results4.3 Ni-Sn IMC and Au-Sn IMC(2/3)

ＯＫSolder

Cu

NiCu

ＯＫ

Solder

Ni

Initial

PbSn

Ni3Sn4

AuxSny

ＯＫ

150deg.C/1000H

※Yellow arrows indicate AuSn IMC.

AuxSny

PbSn

Ni3Sn4

NG

Fracture Line

Pd:none Au:0.5μm Pd:0.05μm Au:0.5μm

Initial

150deg.C/1000H

Pd content rate dependence was evaluated in higher Au content rate.Density of AuSn IMC was decreased by increasing of Pd content rate.

Fig. 11. Cross section of SEM observation result (Au:0.5um)

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4. Test results 4.3 Ni-Sn IMC and Au-Sn IMC(3/3)

Initial Initial

1000H

Initial

Initial

150deg.C1000H

Pd:0.2μm Au:0.5μmPd:0.05μm Au:0.5μmPd:none Au:0.5μm

AuxSny Pb

Sn

Ni3Sn4

NG

Fracture Line

PbSn

Ni3Sn4

AuxSny

ＯＫ1000H 1000H

Pb

Sn

Ni3Sn4

AuxSny

Fracture Line

※Yellow arrows indicate AuSn IMC.

Focused on Pd content rate, NiSn IMC was observed.Flake type NiSn IMC density was increased by increasing of Pd content rate.

Fig. 12. Cross section of SEM observation result (Au:0.5um)

NiSn

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5. Discussion(1/3)

CuNi

Less Au/Pd Au content “Much”

Ni3Sn4 IMC(layer)

Solder Ball(Sn-37Pb)

Pd content “Much”

Flake type NiSn IMCAuSn IMC

From these test results, we focused on the differences of IMC type.

We also evaluate in the case of high temperature solder ball BGA.

CuNi

Solder Ball(Sn90Pb)

Solder paste(Sn37Pb)

Solder colum(Sn90Pb)

PdAu

BGA CGA

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5. Discussion(2/3)

Pd:0.03μm Au:0.05μm Sn90Pb solder ball (Φ 0.76mm).Initial

Pd:0.03μm Au:0.05μm Sn37Pb solder ball(Φ0.76mm)

Initial 150deg.C/250H

SEM observation (cross section)

150deg.C/250H

Flake type NiSn IMC was observed at interface. Pd/Au content rate in SnPb solder will be increased.

Observation point

Solder Ball(Sn90Pb)

Observation point

Solder Ball(Sn37Pb)

Flake type NiSn IMC was not observed at interface.

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From ball share test and SEM cross-section image results, the relationship of solder joint strength and NiSn/AuSn IMC was observed. By increasing of NiSn/AuSn IMC, solder joint strength was decreased.

NiSn/AuSn IMC was increased by increasing the Au/Pd content rate in SnPb solder. But suitable amount of Pd content rate, AuSn IMC was decreased. Pd might suppress AuSn IMC formation in SnPb solder. But Pd might contribute to NiSn IMC formation.

5. Discussion(3/3)

Au/Pd content rate in SnPb solder joint should be controlled in the mixed assemblies.

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6. Summary and future works

We evaluated electroless NiPdAu plated PWB, the following results were obtained.

1.By increasing of Au/Pd content rate, solder joint strength was decreased although Au content rate was less than 3%.

2.In the high temperature storage test, NiSn/AuSn IMC was generated at SnPb solder and PWB plate interface.

3.NiSn/AuSn IMC was increased by increasing the Au/Pd content rate.

4.The relationship of solder joint strength and NiSn/AuSn IMC was observed.

In the case of mixed assembly (solder:SnPb, plate:NiPdAu),Au/Pd content rate in SnPb solder was one of the key

parameters for solder joint reliability.We are going to continue these evaluation. With the evaluation,we will acquire more detailed data confirming solderabilitiy hasa close relation to NiSn/AuSn IMC.

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Acknowledgement

・The Institute of Scientific and Industrial Research (ISIR), Osaka University

・Department of Mechanical System Engineering Graduate School of Engineering, Gunma University

・C.Uyemura & CO.,LTD・High-Reliability Engineering & Components Corporation・Avionics Fukushima Co.,Ltd