for Low and No-Ag Alloys Pb-Free Alloy Characterization...

Thermal Fatigue Results for Low and

No-Ag Alloys Pb-Free Alloy

Characterization Project

Speaker: Keith Sweatman Nihon Superior Co., Ltd

iNEMI Session, IEMT 2012

Ipoh, Perak, Malaysia

November 7, 2012 © 2012 iNEMI

2

Project Team Members

Solder alloy suppliers, Component suppliers, EMS providers, OEMs

19 companies;

66 individuals

© 2012 iNEMI

3

Authors Keith Sweatman1, Keith Howell1, Richard Coyle2, Richard Parker3, Gregory

Henshall4, Joseph Smetana5, Elizabeth Benedetto6, Weiping Lui7, Ranjit S.

Pandher8, Derek Daily9, Mark Currie10, Jennifer Nguyen11, Tae-Kyu Lee12,

Michael Osterman13, Jian Miremadi4, Aileen Allen4, Joelle Arnold14,

Donald Moore10, and Graver Chang15 1Nihon Superior Co., Ltd., Osaka, Japan

2Alcatel-Lucent, Murray Hill, NJ, USA 3Delphi, Kokomo, IN, USA

4Hewlett-Packard Co., Palo Alto, CA, USA 5Alcatel-Lucent, Plano, TX, USA

6Hewlett-Packard Co., Houston, TX, USA 7Indium Corp., Utica, NY, USA

8Cookson Electronics, South Plainfield, NJ, USA 9Senju Comtek Corp., Cupertino, CA, USA

10Henkel Corp., Irvine, CA, USA 11Flextronics Milpitas, CA, USA

12Cisco Systems, San Jose, CA, USA 13CALCE, College Park, MD, USA

14DFR Solutions, College Park, MD, USA 15IST Inc., HsinChu, Taiwan, R.O.C.

© 2012 iNEMI

Thermal Fatigue Results for Low and No-Ag Alloys

The effect of Ag level and microalloying additions

4

© 2012 iNEMI

Agenda

• Background

• Alloys

• Test Vehicle

• Assembly

• Thermal Cycles

• Microstructures

• Results

– Effect of Composition

– Effect of Temperature Range

– Effect of Peak Temperature

– Effect of Component Type

– Characteristic Life Rankings

– Acceleration Factors

• Conclusions

5

Background

The Total Project

Concern about the reliability in thermal cycling of Pb-free

solder alloys that were being introduced to area array

packages because of problems with failure in drop impact of

high-Ag solders and the high cost of Ag.

This Part of the Project (Part III)

How is the performance in thermal cycling affected by the

• Ag level

− To improve resistance to drop impact and reduce cost Ag levels

were reduced

• Microalloying additions

− Introduced to improve performance and properties of solders

including resistance to drop impact

6

The Knowledge Gap

Lack of thermal cycling test data obtained under controlled identical

conditions for:

• New and established low Ag and microalloyed solders

• Benchmarking against Sn-37Pb and SAC305

• Creating life prediction models

© 2012 iNEMI

Data Objectives • Dependence of thermal fatigue

resistance on Ag concentration

• Effect on thermal fatigue

resistance of common

microalloying additions

• Performance of low Ag and

microalloyed solders relative to

Sn-37Pb and SAC305

• Effect of alloy composition on thermal

cycling acceleration factors

• Effect of two package designs.

• Impact of elevated temperature aging on

performance in thermal cycling

• Effect of dwell time on performance in

thermal cycling

• Effect of dwell time on performance in

thermal cycling Still in Progress

7

Solder Ball and Paste Alloys

Ball Alloy Selection

– Sn-37Pb control

– SN100C chosen as a 0% Ag Pb-free

alloy

– Two other established proprietary

alloys

– Two JEITA 2nd Generation

Recommendation alloys

– Various levels of silver (nominal 0-4%)

– Two microalloying additions (Ni and

Mn+Ce)

© 2012 iNEMI

No. BGA Ball Alloy

Trade Name or

Designation

Solder

Paste Comments

1 Sn-37Pb Eutectic Sn-Pb Sn-37Pb Control

2 Sn-0.7Cu+0.05Ni+Ge SN100C SN100C 0% Ag joint

3 Sn-0.7Cu+0.05Ni+Ge SN100C SAC305 Impact of [Ag]

4 Sn-0.3Ag-0.7Cu SAC0307 SAC305 Impact of [Ag]




8 Sn-4.0Ag-0.5cu SAC405 SAC305 Impact of [Ag]

9 Sn-1.0Ag-0.5Cu+0.05Ni SAC105+Ni SAC305

Impact of

dopant

10 Sn-2.0Ag-0.5Cu+0.05Ni SAC205+Ni SAC305

Impact of

dopant

11 Sn-1.0Ag-0.5Cu+0.03Mn SAC105+Mn+Ce SAC305

Impact of

dopant

12 Sn-0.3Ag-0.7Cu + Bi SACX0307 SAC305

Doped

commercial

alloy

13 Sn-1.0Ag-0.5Cu SAC105 aged SAC305 Effect of aging

14 Sn-3.0Ag-0.5Cu SAC305 aged SAC305 Effect of aging

15 Sn-1.0Ag-0.7Cu SAC107 SAC305 Impact of [Cu]

16 Sn-1.7Ag-0.7Cu-0.4Sb SACi SAC305

Doped

commercial

alloy

Paste Alloy

− SAC 305 except for SN100C in one

case to get 0% Ag alloy

− Recognition that in most cases today

the paste alloy will be SAC305 with

potentially multiple BGA ball alloys

being used on the same board Reported in

this paper

8

Sn-Ag-Cu Phase Diagram

• First stage of solidification is

growth of primary Sn

dendrites

© 2012 iNEMI

In Equilibrium Conditions

K.-W. Moon, W.J. Boettinger, U.R. Kattner, F.S.

Biancaniello, and C.A. Handwerker, J.

Elec. Mater. Vol. 29, (2000), p. 1122.

Final stage for all alloys is

ternary Sn-Ag3Sn-Cu6Sn5

eutectic

For other alloys next stage is

pseudobinary Sn-Cu6Sn5

eutectic

For SAC305 next stage is

pseudobinary Sn-Ag3Sn

eutectic

SAC305

SAC105 SAC107

SAC0307

Proportions of phases and their

morphology vary with the alloy

9

SAC107/Cu Interface

SN100C/Ni Interface

Examples of Microstructures

Copper Substrate

Cu6Sn5 intermetallic Layer

Primary Sn dendrite arms

Ag3Sn in interdendritic regions

Ni3Sn4 intermetallic

Some dispersed Cu6Sn5 in Sn matrix

10

Test Vehicle

11

Board Assembly

• Assembled by Flextronics, San Jose

– 16 test cells

– 13 PCAs per cell

– 5-mil thick stencil

– 14-mil-diameter round apertures 192-I/O CABGA

– 12-mil x 12-mil square apertures 84-I/O CTBGA

© 2012 iNEMI

PCA

Group

Number of PCAs

per Cell Allocations 1 8 Core DOE

2 2 Two additional profiles

3 1 Aging studies

4 1 Spares

5 1 Witness set

12

Assembly Reflow Profile

•All lead-free alloys assembled

with same profile

© 2012 iNEMI

13

Calculated Ag Content

© 2012 iNEMI

CTBGA84 CABGA192

Sn-37Pb/Sn-37Pb 0 0

SN100C/SN100C 0 0

SN100C/SAC305 0.79% 0.29%

SAC0307/SAC305 1.00% 0.57%

SAC0307+Bi+X/SAC305 1.00% 0.54%

SAC105/SAC305 1.50% 1.20%

SAC105+Ni/SAC305 1.46% 1.13%

SAC105+Mn+Ce/SAC305 1.48% 1.14%

SAC107/SAC305 1.50% 1.19%

SAC305/SAC305 2.94% 2.95%

Calculated AgBall Alloy/Paste Alloy

Note the effect of

solder ball size on

Ag content of

alloys reflowed

with SAC305

paste

Higher Final Ag

content in

smaller ball

14

Establishing Procedures for

Producing Comparable Data

• Great care was taken to ensure

traceability and consistency

– Three checklists

1. Unification of materials, tools &

instruments

2. Unification on methods of ATC setup

3. Checklist before start of ATC (profile,

ramp rate, failure definition, etc.)

– Tracking of the alloys throughout

each process

• Individual LGA substrate lots

• Ink dot pattern on every package per lot

allowed tracking throughout each

process

© 2012 iNEMI

15

Thermal Cycles

Profile Selection

– Goal 1: Impact and

interactions of: temperature

range, maximum

temperature, and dwell time

(core DOE profiles 1-4)

– Goal 2: Performance for

the most commonly used

profiles: 0/100 °C and -

40/125 °C (profiles 1 and 10)

– Goal 3: Impact of long

dwells (profiles 5, 6, 7, 8, 9)

– Goal 4: Select thermal

cycles that generate data

that can be used in life

modelling

© 2012 iNEMI

Profile No.

Testing Company

Cycle (Min/Max/Dwell) Comment

1 ALU 0/100/10

Core DOE

2 IST 25/125/10

3 Henkel -40/100/10

4 Nihon -15/125/10

5 ALU 0/100/60

6 HP 25/125/60

7 HP -40/100/60

8 CALCE -15/125/60

9 CALCE -40/100/120 Long Dwell

10 Delphi -40/125/10

Common; Auto

Profile No.

Testing Company

Cycle (Min/Max/Dwell) Comment

1 ALU 0/100/10

Core DOE

2 IST 25/125/10

3 Henkel -40/100/10

4 Nihon -15/125/10

5 ALU 0/100/60

6 HP 25/125/60

7 HP -40/100/60

8 CALCE -15/125/60

9 CALCE -40/100/120 Long Dwell

10 Delphi -40/125/10

Common; Auto

ΔT=100

ΔT=140

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Thermal Cycling Standardization

Checklist #3 compared profiles site to site

– Criteria to ensure profiles were within tolerances

– Profiles presented to team prior to start of test

© 2012 iNEMI

Thermocouple

Attachment

Failure definition (IPC9701A)

– Event Detector vs. Data Logger

– Unified failure definition using IPC definition

for event detectors (usable by data loggers)

– Failure: 10 “events” (measurements of resistance

above the threshold value of 1000Ω) take place within

10% of cycles from the first “event.” The first event

meeting this criterion is defined as the point of failure.

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Weibull Plots

63.2% Failure

Characteristic Life

η

Slope

β

Quality of Fit

ρ

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Effect of Ag Levels on Sn-0.7Cu 0-100°C, 10 minute dwells – CABGA192

© 2012 iNEMI

Hardening effect

of Ag is apparent

19

Low-Ag Alloys cf Reference Alloys 0-100°C, 10 minute dwells – CABGA192

© 2012 iNEMI

Even low Ag alloys

significantly longer

life than Sn-37Pb

20

Effect of Microalloying Additions 0-100°C, 10 minute dwells – CABGA192

© 2012 iNEMI

No significant effect of

Ni on SAC105 in this

test condition

Significant reduction

of characteristic life

and spread of failures

with Mn + Ce addition

21

Effect of Microalloying – Bi & Rare Earths 0-100°C, 10 minute dwells – CABGA192

© 2012 iNEMI

No significant

effect in this

test condition

22

Effect of Cu Level 0-100°C, 10 minute dwells – CABGA192

© 2012 iNEMI

No significant effect

in this test condition

23

Effect of Thermal Cycle – Ag-free Alloy CABGA192 Component

© 2012 iNEMI

84% reduction in

characteristic life

24

Effect of Thermal Cycle – Very Low-Ag Alloy CABGA192 Component

© 2012 iNEMI

79% reduction in

characteristic life

25

Effect of Thermal Cycle Microalloyed Very Low-Ag Alloy CABGA192 Component

© 2012 iNEMI

69% reduction in

characteristic life

26

Effect of Thermal Cycle - Low-Ag Alloy CABGA192 Component

© 2012 iNEMI

80% reduction in

characteristic life

27

Effect of Thermal Cycle Ni-doped Low-Ag Alloy CABGA192 Component

© 2012 iNEMI

70% reduction in

characteristic life

But lower

characteristic life

than without

microalloy

28

Summary of Effect of Temperature Range

© 2012 iNEMI

η β η β

Sn-37Pb/Sn-37Pb 1477 12.3 658 6.5

SAC305/SAC305 5718 7.0 1612 5.2

No-Ag SN100C/SN100C 3101 8.7 623 5.5

SN100C/SAC305 3067 10.0 826 7.0

SAC0307/SAC305 4071 9.2 846 14.2

SAC105/SAC305 4910 5.4 940 6.8

SAC107/SAC305 5000 5.2 1196 7.6

SACX0307/SAC305 4194 7.0 1079 5.6

SAC105+Ni/SAC305 4707 6.6 1245 7.0

SAC105+Mn/SAC305 3396 4.1 1040 7.8

Reference

Alloys 3.5

5.0

3.7

4.8

5.2

-40/125/10

CABGA192

Acceleration

Factor

0/100/10 to

-40/125/10

Alloy/PasteCategory

2.2

Very Low-Ag

Low Ag

Microalloyed

0/100/10

CABA192

4.2

3.9

3.8

3.3

Pb-free solders

up to 2.3 times

more sensitive

to temperature

range than

Sn-37Pb

29

Effect of Peak Thermal Cycle Temperature Ag-free Alloy CABGA192 Component

© 2012 iNEMI

32% reduction in

characteristic life

30

Effect of Peak Thermal Cycle Temperature Very Low-Ag Alloy CABGA192 Component

© 2012 iNEMI

32% reduction in

characteristic life

31

Effect of Peak Thermal Cycle Temperature Microalloyed Very Low-Ag Alloy

CABGA192 Component

© 2012 iNEMI

32% reduction in

characteristic life

32

Effect of Peak Thermal Cycle Temperature Low-Ag Alloy CABGA192 Component

© 2012 iNEMI

32% reduction in

characteristic life

Significantly

increased spread

of failures

33

Effect of Peak Thermal Cycle Temperature Ni-doped Low-Ag Alloy

CABGA192 Component

© 2012 iNEMI

27% reduction in

characteristic life

34

Summary of Effect of Peak Temperature

© 2012 iNEMI

η β η β

Sn-37Pb/Sn-37Pb 1477 12.3 1527 9.7

SAC305/SAC305 5718 7.0 4632 7.4

No-Ag SN100C/SN100C 3101 8.7 2087 10.6

SN100C/SAC305 3067 10.0 3197 3.4

SAC0307/SAC305 4071 9.2 2607 7.2

SAC105/SAC305 4910 5.4 3144 3.5

SAC107/SAC305 5000 5.2 2660 7.1

SACX0307/SAC305 4194 7.0 3205 5.5

SAC105+Ni/SAC305 4707 6.6 3413 4.1

SAC105+Mn/SAC305 3396 4.1 2873 2.7

Alloy/PasteCategory

1.2

0/100/10

CABGA192

25/125/10

CABGA192

Acceleration

Factor

0/100/10 to

25/125/10

Microalloyed

Low-Ag

Very Low-Ag

Reference

Alloys

1

1.2

1.5

1

1.6

1.6

1.9

1.3

1.4

Characteristic

life reduced

by as much

as 46% by

25°C

increase in

peak

temperature

with same ΔT.

No effect on

Sn-37Pb

35

Component Size Effect – Ag-free Alloy 0-100°C, 10 minute dwells

© 2012 iNEMI

50% Reduction in

characteristic life

resulting from

difference in ball

diameter and DNP

36

Component Size Effect – Very Low-Ag Alloy 0-100°C, 10 minute dwells

© 2012 iNEMI

1% Ag 0.57% Ag

Combined effect of

DNP, ball size and

the effect of ball

size on Ag content

when reflowed with

SAC305

37

Component Size Effect- Microalloyed Very Low-Ag Alloy 0-100°C, 10 minute dwells

© 2012 iNEMI

Combined effect of DNP,

ball size and the effect of

ball size on Ag content

when reflowed with

SAC305

1% Ag 0.54% Ag

38

Component Size Effect – Low-Ag Alloy 0-100°C, 10 minute dwells

© 2012 iNEMI

Combined effect of

DNP, ball size and the

effect of ball size on

Ag content when

reflowed with SAC305

1.5% Ag 1.2% Ag

39

Summary of Effect of Component Type

© 2012 iNEMI

η β η Β

Sn-37Pb/Sn-37Pb 1477 12.3 2310 11.0 1.6

SAC305/SAC305 5718 7.0 9819 7.0 1.7

No-Ag SN100C/SN100C 3101 8.7 5306 7.7 1.7

SN100C/SAC305 3067 10.0 6625 8.0 2.2

SAC0307/SAC305 4071 9.2 5577 11.6 1.4

SAC105/SAC305 4910 5.4 6826 7.9 1.4

SAC107/SAC305 5000 5.2 7255 7.4 1.5

SACX0307/SAC305 4194 7.0 7183 10.0 1.7

SAC105+Ni/SAC305 4707 6.6 7683 7.0 1.6

SAC105+Mn/SAC305 3396 4.1 6514 8.3 1.9

0/100/10

CTBGA84

Component Effect

0/100/10

CABGA192η Ratio

Reference

Alloys

Microalloyed

Very Low-Ag

Category Alloy/Paste

Low-Ag

Differences

in ball size,

DNP and Ag

content can

reduce life

by at least a

third.

Pb-free

similar to Sn-

37Pb

45

© 2012 iNEMI

Sn37Pb/Sn37Pb

SN100C/SN100C

SAC0307/SAC305

SAC105+Mn/SAC305

SN100C/SAC305

SACX0307/SAC305

SAC105/SAC305

SAC107/SAC305

SAC105+Ni/SAC305 SAC305/SAC305

0

1

2

3

4

5

6

7

8

9

1 2

3 4

5 6

7 8

9 10

Fre

qu

en

cy o

f R

an

kin

g

Ranking (Shortest to Longest Characteristic Life)

Sn37Pb/Sn37Pb

SN100C/SN100C

SAC0307/SAC305

SAC105+Mn/SAC305

SN100C/SAC305

SACX0307/SAC305

SAC105/SAC305

SAC107/SAC305

SAC105+Ni/SAC305

SAC305/SAC305

Distribution of Ranking Over All Test Conditions

51

Summary of Acceleration Factors

Thermal Cycle -40-125°C/10 25-125°C/10 -40-100°C/10 -15-125°C/10

0/100°C/10 Average 4.23 1.41

Std Dev 0.7 0.29

-40-125°C/10 Average 2.62

Std Dev 0.36

-40-100°C/10 Average 1.03

Std Dev 0.13

Acceleration Factor

© 2012 iNEMI

52

Conclusions

• In short dwell (10 minute) thermal cycles there is a

correlation between characteristic life and Ag content

• All of the Pb-free alloys perform better than

Sn-37Pb under the tested conditions

• Pb-free alloys have high acceleration factors (0-100°C

vs -40-125°C) which suggests low-Ag alloys will

perform better than Sn-37Pb in office or similarly

controlled environments

© 2012 iNEMI

53

Conclusions (continued)

• As the strain and exposure to elevated temperature

increases, the differences between Pb-free alloys

collapses and performance appears to converge towards

that of Sn-37Pb.

© 2012 iNEMI

Results of thermal

cycling with longer

dwells will confirm

whether the trend

to convergence

holds

54

Questions Raised by These Results!

• Why do characteristic life rankings vary with test

conditions?

• Why do acceleration factors vary so much with alloy?

• Why do β values (the range of cycles over which failures

are spread) vary so much with the alloy and the test

conditions?.

• Are all the observed differences significant or are some

the result of experimental factors?.

• What is the failure mechanics and how do they differ

between alloys and conditions?

• ???

55

Future Work

• Completion of all thermal cycles

• Detailed failure analysis to understand the

evolution of the microstructure to failure

• Development of life prediction models based on the

results of this test program.

• Generation of a portable test protocol for solder

alloys

© 2012 iNEMI

Thank You for Your Attention

www.inemi.org Email contacts:

Bill Bader

[email protected]

Haley Fu - Asia

[email protected]

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