This document summarizes research on achieving high reliability and low-cost lead-free solder joints using manganese or cerium doping of tin-silver-copper (SAC) solder. Experimental results show that SAC doped with 0.05% manganese (SACM) or 0.02% cerium (SACC) outperforms baseline SAC105 and SAC305 alloys in drop test reliability and thermal cycling performance. Specifically, SACM and SACC exhibit higher drop test lifetimes and allow packages to withstand higher dynamic bending strains compared to SAC105 and SAC305. This research demonstrates that minor manganese or cerium doping of SAC alloys can improve

1. Achieving High Reliability Low
Cost Lead-Free SAC Solder
Joints Via Mn Or Ce Doping
Dr. Weiping Liu1, Dr. Ning-Cheng Lee1, Adriana Porras2, Dr. Min
Ding2, Anthony Gallagher3, Austin Huang4, Scott Chen4, and
Jeffrey ChangBing Lee5
1 Indium Corporation; 2 Freescale Semiconductor
3 Motorola Inc; 4 Advanced Semiconductor Engineering Group;
5 IST-Integrated Service Technology Inc
1

2. Introduction
• SAC with high Ag good in thermal fatigue
performance, but poor in drop test
performance
• SAC with low Ag OK in drop test, but poor in
thermal fatigue performance
• A Pb-free alloy with improved drop test
performance, and good in thermal fatigue
performance badly needed.
• SAC105+Mn or Ce studied here
2

3. Experimental Design
• New Alloys
– SAC105+0.05Mn (SACM)
– SAC105+0.02Ce (SACC)
• DOE for JEDEC drop test & TCT
Package Daisy TFBGA244 12X12
Ball/pitch ( mm) 0.3/0.5 0.3/0.5 0.3/0.5 0.3/0.5 0.3/0.5 0.3/0.5
Solder ball SnPb SAC105 SAC305 SACM SACM SACC
Surface finish of substrate NiAu NiAu NiAu NiAu OSP NiAu
Solder paste SnPb SAC305 SAC305 SAC305 SAC305 SAC305
Reflow profile 220C 245C 245C 245C 245C 245C
PCB High Tg FR4/8 layer/NVIP/NSMD/OSP (ENIG, ImAg)
3

4. Test Design 1500G
• JEDEC Drop Test (JESD22-B111)
– Fail when > 1000 ohms
• Dynamic Bending Test
– Board strain at 1st fail
– Dye & pry
• Thermal Cycling Test
– - 40C/125C
– 42 min/cycle, ramp 11 min, dwell 10 min
– Fail when > 20% Resistance increase
• Cyclic Bending Test
– 1 Hz/2mm
– Paste SAC387
– Fail when > 1000 ohms
4

5. JEDEC Drop Test Results
SACM, SACC ≥ SnPb, 105 > 305
ReliaSoft's Weibull++ 6.0 - www.Weibull.com
Probability - Weibull
6.0
3.0
2.0
1.6
1.4
1.2
1.0
0.9
0.8
0.7
0.6
0.5
β
99.00
Weibull
SAC105
90.00 W2 RRX - SRM
F=10 / S=5
SnPb SAC305
300 η W2 RRX - SRM
150C/0 hr
F=10 / S=5
SACCe
150C/100 hrs 50.00
W2 RRX - SRM
Mn
150C/250 hrs
200 TCT 250 cycles F=10 / S=5
C-Life in Drop Test
SACMn
Unreliability, F(t)
W2 RRX - SRM
Ce F=11 / S=4
SnPb
100
105 W2 RRX - SRM
10.00 F=10 / S=5
305
0
SnPb SAC105 SAC305 SACM SACC 5.00
CK
Company
2009/2/23 09:4
1.00
5 1.00 10.00
Time, (t)
100.00 500.00

6. Dynamic Bending Test Result
SACM ≥ SACC > 105 > 305
Failure Criteria: 0.5% strain level
Package TFBGA ( Bravo)
ball/pitch ( mm) 0.3/0.5 0.3/0.5 0.3/0.5 0.3/0.5
surface finish (substrate) NiAu NiAu NiAu NiAu
solder ball SAC105 SAC305 SAC105Mn SAC105Ce
Solder paste SAC387
reflow profile Linear ramp profile, peak 235C
PCB (FR4/8 layer/NVIP/SMD) 80 80 80 80
Thermal aging 150C/0hr Failure Criteria( Strain ) 0.5049% 0.2406% 0.7490% 0.6963%
Thermal aging 150C/250hr Failure Criteria( Strain ) 0.0999% 0.1493% 0.3550% 0.2968%
*SACM is SAC105 + Mn dopant
SACC is SAC105 + Ce dopant
0.8%
150C/0 hr
150C/250 hrs
0.6%
Strain to failure
0.4%
0.2%
6 0.0%
SAC105 SAC305 SACM SACC

7. TCT (-40C/125C) Test Results TFBGA on PCB (OSP)
SACC, SACM, -305 > SAC105 > SnPb
ReliaSoft's Weibull++ 6.0 www.Weibull.com
Probability - Weibull
6.0
3.0
2.0
1.6
1.4
1.2
1.0
0.9
0.8
0.7
0.6
0.5
β
99.00
Weibull
150C/250 hr SAC105
90.00 Aging 105 W2 RRX - SRM M
F=13 / S=2
SAC305
η W2 RRX - SRM M
2500 F=15 / S=0
150C/0 hr
SACCe
50.00
2000 150C/100 hrs
150C/250 hrs
SnPb W2 RRX - SRM M
F=15 / S=0
SACMn
305
Unreliability, F(t)
C-Life in TCT
1500
W2 RRX - SRM M
F=14 / S=0
1000 Mn SnPb
W2 RRX - SRM M
10.00 F=14 / S=1
500
Ce
5.00
0
SnPb SAC105 SAC305 SACM SACC
CK
Company
2009/2/16 17:54
1.00
100.00 1000.00 5000.00
7 Time, (t)

8. CBT Test Results TFBGA on PCB (OSP)
305 > 105, SACM, SACC > SnPb
SAC305 exhibited the
Mn highest value in TS, YS,
105 Young's modulus, and
elongation (%).
All LF are better than
SnPb SnPb.
as reflowed
Ce 305
8

9. Effect of Surface Finish
Package: NiAu ≥ OSP (in general)
300 10000
150C/0 hr
150C/100 hrs JDT TCT 150C/0 hr CBT
150C/250 hrs 150C/100 hrs
7500 150C/250 hrs
TCT 250 cycles
C-Life in Bending Test
C-Life of Drop Test
200
TCT 250 cycles
5000
100
2500
0
0
NiAu BGA
SACM OSP BGA
SACM NiAu BGA SACM OSP BGA
PCB: Weak trend ImAg > OSP > ENIG (in general)
300 16000
150C/0 hr 150C/0 hr
150C/100 hrs JDT TCT CBT 150C/100 hrs
C-Life of Bending Test (cycles)
150C/250 hrs 12000 150C/250 hrs
C-Life of Drop Test
200 TCT 250 cycles TCT 250 cycles
8000
100
PCB:
4000
No obvious trend.
0 0
OSP ENIG ImAg OSP ENIG ImAg OSP ENIG ImAg OSP ENIG ImAg
9 PCB PCB
SACM
PCB PCB PCB
SACC
PCB PCB PCB
SACM
PCB PCB PCB
SACC
PCB

10. Results
SACM and SACC
displayed
(a) thinner and
smoother
interfacial IMC
layers
(b) finer IMC
particles
within bulk
solder
10

11. Mn & Ce Suppressed IMC Growth
On package side On PCB side
12 8
SnPb/NiAu
10
SAC105/NiAu
IMC Thickness (microns
6
IMC Thickness (microns
8 SAC305/NiAu
SACM/NiAu
6 SACM/OSP
4
SACC/NiAu
4
2 SnP b/NiA u B GA SA C105/NiA u B GA
2 SA C305/NiA u B GA SA CM /NiA u B GA
SA CM /OSP B GA SA CC/NiA u B GA
0 0
0 400 800 1200 0 400 800 1200
150C Aging Hrs 150C Time (hrs)
11

12. 150C
Mn & Ce suppressed
coarsening of IMC rods
at interface
12

13. Microstructure of solder joints of TFBGA
(NiAu) on PCB (OSP) after TCT
15
Vicker Hardness Number
10
Mn suppressed coarsening of IMC particles,
thus maintained hardness of joint
5
SAC105
SACM
0
0 100 200 300
13 150C Aging Time (hrs)

14. Mn & Ce suppressed IMC coarsening upon
thermal aging, hence stabilized microstructure.
IMC particle coarsened
14

15. Mn & Ce stabilized grain size upon thermal aging,
presumably through stabilizing IMC particles.
Grain boundary fading away Grain size stabilized Grain size stabilized
15

16. Discussion
• Drop Test
– Both SACM and SACC exhibit finer and thinner IMC
structure at interface.
– Inclusion of dopants in IMC may also alter the
crystallinity, hence reduce the brittleness of IMC layer.
• TCT Test
– A stable and fine IMC structure may be the primary
contributing factor, and the stabilized grain structure
resulted may be the secondary cause for SACM and SACC
to exhibit a high TCT reliability.
16

17. Conclusion
• The Mn or Ce doped low cost SAC105 alloys
– Achieved a higher drop test and dynamic bending test reliability than
SAC105 and SAC305, and exceeded SnPb for some test conditions.
– Matched high Ag SAC in thermal cycling performance
• The mechanism for high drop performance and high thermal
cycling reliability can be attributed to
– A stabilized microstructure, with uniform distribution of fine IMC
particles, presumably through the inclusion of Mn or Ce in the IMC.
– A thinner IMC layer
• The cyclic bending results showed SAC305 being the best,
and all lead-free alloys are equal or superior to SnPb.
• NiAu is preferred over OSP for BGA packages if assembled
on PCB (OSP).
• Weak trend on preference of PCB finishes: ImAg > OSP >
ENIG
17