1 clech, apex 2004 - copyright © epsi inc., 2004 lead-free and mixed assembly solder joint...

1Clech, APEX 2004 - Copyright © EPSI Inc., 2004

LEAD-FREE AND MIXED ASSEMBLY SOLDER JOINT RELIABILITY

TRENDS

by Jean-Paul Clech, EPSI Inc.Montclair, NJ, USA

Tel: +1 (973)746-3796, fax: +1 (973)655-0815

E-mail: [email protected], URL: http://jpclech.com

Presented at

IPC / SMEMA Council APEX Conference

Anaheim, CA, February 26, 2004


Introduction Objective: Compare lead-free vs. SnPb solder joint

reliability over a wide range of circumstances Preliminary study limited to thermal cycling data

Where are we on the learning curve?

METRIC SNPB RELIABILITY SAC RELIABILITY RATIO (“SAC” COLUMN / “SNPB” COLUMN)

1. AUTHOR’S REFERENCE LIST

~ 2500 PUBLICATIONS ~ 250 PUBLICATIONS 10%

2. YEARS OF INDUSTRY EXPERIENCE

~ 50 YEARS ~ 12 YEARS 24%


SAC Test Data

Coffin-Manson approach: Correlation coefficient: R2 ~ 0.6

1.E+02

1.E+03

1.E+04

1.E+05

1.E-03 1.E-02 1.E-01 1.E+00

CYCLIC SHEAR STRAIN RANGE

CH

AR

AC

TE

RIS

TIC

LIF

E:

com

po

nen

t (cy

cles

)

ResistorsCBGAsLCCCPBGACSP

Thermal Conditions:0/100C-40/125C-55/125C

0.7

1

3.5 X

3.5 X

27 data points (100% SAC)

1%

Not much data for < 1%


First Order Correlation of SAC Test Data

First-order correlation obtained by: Scaling characteristic life for solder joint crack area Using characteristic life for population of critical solder joints

Do not use for life predictions or AF calculations– Dwell time, frequency effects etc… not included

R2 = 0.9649

1.E+05

1.E+06

1.E+07

1.E+08

1.E+09

1.E-03 1.E-02 1.E-01 1.E+00


CH

AR

AC

TE

RIS

TIC

LIF

E /

SO

LD

ER

CR

AC

K A

RE

A

join

t /

A (

CY

CL

ES

/IN

2 )

CSP

PBGA

CBGA

RES. 0603

RES. 1206

LCCC

RES. 2512

Thermal Conditions:0/100C, -40/125C-55/125C

1

1.7

2 X

1%


Correlation of SAC Test Data: Sorted by Board Finish

First-order correlation does not show significant board finish effect Slide # 4 data re-plotted by board finish type

1.E+05

1.E+06

1.E+07

1.E+08

1.E+09

1.E-03 1.E-02 1.E-01 1.E+00


CH

AR

AC

TE

RIS

TIC

LIF

E /

SO

LD

ER

CR

AC

K A

RE

A

join

t /

A (

CY

CL

ES

/IN

2 )

na

Ag

NiAu

OSP

(na = Not Available)


Correlation of SAC Test Data: Sorted by Alloy

1.E+05

1.E+06

1.E+07

1.E+08

1.E+09

1.E-03 1.E-02 1.E-01 1.E+00


CH

AR

AC

TE

RIS

TIC

LIF

E /

SO

LD

ER

CR

AC

K A

RE

A:

join

t / A

(C

YC

LE

S/IN

2 )Sn3.8Ag0.7Cu

Sn3.9Ag0.6Cu


SAC versus SnPb Test Data Correlation (Leadless Assemblies)

Difference in slopes suggests opposite reliability under low and high stress conditions

Do not use for life predictions or AF calculations– Dwell time, frequency effects etc… not included

1.E+05

1.E+06

1.E+07

1.E+08

1.E+09

1.E+10

1.E-04 1.E-03 1.E-02 1.E-01 1.E+00


CH

AR

AC

TE

RIS

TIC

LIF

E /

CR

AC

K A

RE

A (

cycl

es/i

n2 ) SnPb

SAC3.5 X

"HIGH STRESS":SN-PB > SAC

"LOWER STRESS":SAC > SN-PB

SAC

SnPb

6.2%


SAC vs. SnPb: Creep Rate Comparison

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1 10 100

SHEAR STRESS (MPa)

ST

RA

IN R

AT

E (

/SE

C)

Darveaux, Sn40Pb, 27C

Zhang, SAC 3906, 25C

Dusek, SAC 3807, 21C

Pang, SAC 3807, 25C

21-27C DATA(294-300K, = 2.0%)

SnPb

SAC & SnPb

18.1 MPa

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1 10 100

SHEAR STRESS (MPa)

ST

RA

IN R

AT

E (

/SE

C)

Darveaux, Sn40Pb, 67C

Zhang, SAC 3906, 75C

Pang, SAC 3807, 75C

67-75C DATA(340-348K, = 2.3%)

SnPb

SAC & SnPb

13.8 MPa

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1.0 10.0 100.0

SHEAR STRESS (MPa)

ST

RA

IN R

AT

E (

/SE

C)

Darveaux, Sn40Pb,132CZhang, SAC 3906,125CPang, SAC 3807,125C

125-132C DATA(398-405K, = 1.8%)

SnPb

SAC

9.2 MPa

Under high stress conditions, SAC creeps as fast as SnPb regardless of temperature

~ 25°C ~ 75°C

~ 125°C


SAC vs. SnPb: Creep Rate Comparison (2)

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1 10 100

TENSILE STRESS (MPa)

ST

RA

IN R

AT

E (

MP

a)

Whitelaw, Sn40Pb, -55C

Neu, Sn4.0Ag, -55C

Neu, Sn2.5Ag0.8Cu0.5Sb, -55C

SAC

-55C Data(218K)

SnPb

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1 10 100


ST

RA

IN R

AT

E (

MP

a)

Shi, Sn37Pb, 25C

Whitelaw, Sn40Pb, 23C

Raeder, Sn52Bi, 30C

Takahashi, Sn3.5Ag0.5Cu, 25C

Neu, Sn4.0Ag, 25C

Neu, Sn2.5Ag0.8Cu0.5Sb, 25C

Huang, Sn3.5Ag

Data at 23C-30C(296-303K, = 2.4%)

Sn3.5Ag

SnPb

SnBi

SAC

SnPb

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1 10 100


ST

RA

IN R

AT

E (

MP

a)

Shi, Sn37Pb

Whitelaw, Sn40Pb, 75C

Takahashi, Sn3.5Ag0.5Cu

Neu, Sn4.0Ag

Neu, Sn2.5Ag0.8Cu0.5Sb

Power (Whitelaw, Sn40Pb,75C)

Data at 75C (348K)

SnPb

SAC

-55°C ~ 25°C

75°C1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1 10 100


ST

RA

IN R

AT

E (

MP

a)

Amagai, Sn1.0Ag0.75Cu, 125CShi, Sn37Pb, 125CWhitelaw, Sn40Pb, 125CRaeder, Sn52Bi, 120CTakahashi, Sn3.5Ag0.5Cu, 125CNeu, Sn4.0Ag, 125CNeu, Sn2.5Ag0.8Cu0.5Sb, 125C

Data at 120-125C(393-398K, = 1.3%)

SnBi

SAC

SnPb

Sn1.0Ag0.75Cu

~ 125°C


Sn0.7Cu vs. SnPb

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E-02 1.E-01 1.E+00


CH

AR

AC

TE

RIS

TIC

LIF

E (

CY

CLE

S)

SAC

Sn0.7Cu

SnPb

6.2%

Correlations based on Bare Flip-Chip Thermal Cycling Data (references in paper)

Fatigue Testing Data at 20C (ITRI Pub. # 656 ).

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

10 100

SHEAR STRESS (MPa)

CY

CL

ES

TO

FA

ILU

RE

Sn1Cu

Sn3.5Ag

Sn-40Pb

Compared to SnPb, SnCu fatigue trend appears opposite that of SnAg / SAC trend


SAC vs. SnPb: Alloy 42 TSOPs

Alloy 42 TSOPs assembled with SAC have shorter test lives than when assembled with SnPb Sn2Bi finish provides for 31% life improvement over SnPb finish

1.E+02

1.E+03

1.E+04

10 100 1000T (deg. C)

CH

AR

AC

TE

RIS

TIC

LIF

E (

CY

CL

ES

)

Sn37Pb / SnPbSn37Pb / Sn10PbSn3.9Ag0.6Cu / SnPb

Sn3.0Ag0.7Cu / Sn10PbSn3.0Ag0.7Cu / Sn2Bi

2.02

1

1

1.90

1.63X

1.36X

1.31X

PASTE / LEAD FINISH:

Intersect at T = 9°C


SAC vs. SnPb: Summary

Reversed trends under high vs. low to medium stress conditions Situation requires accurate life prediction models or acceleration

factors for reliability assessment under service conditions.

Need to consider data over a wide range of conditions before conclusions can be drawn. Lack of data at cyclic strain ranges < 1%


Leadless SMT: with or without Pb contaminant SnPb balls: SAC or SnPb paste SAC balls: SAC or SnPb paste

Mixed Assembly Test Results


Leadless SMT with Pb Contamination

-55 to 125°C and -40 to 125°C data Pb contamination (< 1% wt.) is from component (R1206) or board finish

(HASL SnPb).

1

0

200

400

600

800

1000

0 200 400 600 800 1000

100% SAC (no Pb): Cycles to 1% Failure

SA

C +

Pb

Co

nta

min

ant:

Cyc

les

to 1

% F

ailu

re

R0603 (-55 to 125C)Board finish: SnPb HASL or Cu / OSP

1

1

R2512 (-55 to 125C)Board finish: SnPb HASL or Cu / OSP

LCCC 20 (-40 to 125C)Board finish: SnPb HASL or Immersion Ag

R1206 (-55 to 125C)Board finish: Immersion AgComponent finish: Sn0.7Cu or SnPb

R1206 (-55 to 125C): Board finish: NiAuComponent: Sn0.7Cu or SnPb finish

Low Failure Countfor SAC + Pb contaminant


Area Array Assemblies with SnPb Paste

“Backward compatibility”: mixed record. Limited data under 0/100°C conditions

SAC Ballsvs. SnPb Balls

0

1000

2000

3000

0 1000 2000 3000

SnPb Balls / SnPb Paste: Cycles to Low % Fails

SA

C B

all

s / S

nP

b P

aste

: C

yc

les

to

Lo

w %

Fa

ils

-40 to 125C data

0 to 100C data

-55 to 125C data 1

1

FC-PBGA*OSP

PBGANiAu or OSP

CSP**NiAu

CSP**Cu

fleXPBGANi/Au

TABGANi/Au

* : Cycles to First Fail between 1% and 5%**: Cycles to 0.1% FailureOthers: Cycles to 1% Failure

0.74X

0.68X

wbPBGAOSP

0.77X


Area Array Assemblies with SAC Balls

Under stated conditions, assemblies with SAC paste have similar or longer life than with SnPb paste.

SAC Pastevs. SnPb Paste

0

1000

2000

3000

0 1000 2000 3000

SAC Balls / SnPb Paste: Cycles to Low % Fails

SA

C B

all

s /

SA

C P

aste

: C

yc

les

to

Lo

w %

Fa

ils

-40 to 125C data0 to 100C data

-55 to 125C data 1

1

FC-PBGA*OSP

WCSP*OSP

PBGANiAu or OSP

CSP**NiAu

CSP**Cu

fleXPBGANi/Au

TABGANi/Au

* : Cycles to First Fail between 1% and 5%**: Cycles to 0.1% FailureOthers: Cycles to 1% Failure


Area Array Assemblies with SnPb Balls

“Forward compatibility”: opposite trends depending on thermal cycling conditions (-40/125°C vs. 0/100°C)

Test conditions matter, possible issue under milder conditions

0

1000

2000

3000

0 1000 2000 3000

SnPb Balls / SnPb Paste: Cycles to 1% Failure

Sn

Pb

Ba

lls /

SA

C P

aste

: Cyc

les

to 1

% F

ailu

re

PBGA 388

PBGA 357

CSP 169

CSP 151

1

1

-40 to 125C Data

SAC Pastevs. SnPb Paste

0

1000

2000

3000

4000

5000

6000

7000

8000

0 1000 2000 3000 4000 5000 6000 7000 8000

SnPb Balls / SnPb Paste: Cycles to 1% Failure

Sn

Pb

Bal

ls /

SA

C P

ast

e: C

ycl

es

to 1

% F

ailu

re

PBGA

CSP

FCPBGA

WCSPs

1

0.84

0 to 100C Data

1

1

PBGA 144 (15 to 95C)

2 data points


Lead-free Assembly Reliability - Conclusions

Lead-free assembly reliability is dependent on package, assembly and test conditions Reliability rank-ordering is strongly dependent on test conditions:

– SnPb test standards may have to be optimized for Pb-free assemblies

Need accurate life prediction model(s) and acceleration factors to extrapolate to use conditions

Mixed assemblies Both “backward” and “forward” compatibility situations require

further attention.


Speaker’s Bio Jean-Paul Clech is the founder of EPSI Inc. in Montclair, New-Jersey. His activities at EPSI include technical

consulting with clients across the electronics industry, software development and professional training. He is the principal developer of the Solder Reliability Solutions model and application software. His research interests cover multi-disciplinary aspects of electronics packaging, Surface Mount Technology (SMT) and circuit board assemblies, with emphasis on materials characterization and the application of materials and mechanical engineering fundamentals to sound product design. He has consulted on the physical design of small and large circuit boards and is constantly challenged by design and reliability problems brought about by emerging packaging and soldering technologies, and the application of SMT in harsh environments. His current research interests are in the areas of flip-chip assemblies, chip scale packages, mechanical flexing and vibration of board assemblies, lead-free material properties and lead-free reliability assessment.

Jean-Paul previously was a member of the technical staff at AT&T Bell Laboratories and manager of electronic packaging at a European super-computer start-up. He was trained as a metallurgist and received the "Diplôme d’ Ingénieur" degree (Materials Science major) from Ecole Centrale de Paris, France. He then received the M.S. and Ph.D. degrees in mechanical engineering from Northwestern University, Evanston, Illinois, where he worked on the mechanics and failures of hip and knee joint replacements. His interest in soldering and solder fatigue started during a post-doctoral assignment in the Materials Science department at Northwestern. He is a recognized expert in the field of surface mount assembly quality and reliability and has assisted law firms as an expert witness on packaging, board and soldering related issues. Jean-Paul is an active member of ASME, IEEE, IMAPS, SMTA and TMS, has published over thirty five papers and a book chapter, and has chaired numerous workshops and technical sessions at international conferences. He has been an invited speaker, lecturer and seminar leader at corporations, universities and R&D institutions in Asia, Europe and North America.

Contact information: Home page URL: http://jpclech.com E-mail: [email protected] Tel.: +1 (973)746-3796; fax: +1 (973)655-0815

1 clech, apex 2004 - copyright © epsi inc., 2004 lead-free and mixed assembly solder joint...

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