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Update on lead-free solder joint reliability
Most of these accelerated tests were In Figure 6, Sn3.4Ag1.0Cu3.3Bi solder iNEMI results show the SAC solder joints
run as per IPC-9701, with any deviations joints outperform both Sn3.9Ag0.6Cu outperforming SnPb with the ‘mixed’
clearly stated. In one case the SAC-data and Sn37Pb solder joints in accelerated solder joints essentially between them.
had to be corrected because the SAC testing, whereas the data in Figure 7 show In Figures 12 and 13, results from tests
solder joints had a thickness dimension little difference in the accelerated fatigue performed to gain an understanding of
9% larger than the comparison SnPb- lives of Sn37Pb, Sn3.9Ag0.6Cu and the impact of the dwells at the cyclic
solder joints. Sn3.5Ag solder joints. temperature regimes are shown. The
In almost all cases a direct comparison In Figure 8, a comparison is made data in Figure 12 are performed with
is made to SnPb, even though such a between five SAC solders, some with asymmetric cycles with different dwell
comparison is meaningless in terms of additions, showing a decrease in fatigue times at the high and low temperature
product reliability for these short dwells live with decreasing Ag content. dwells. While, of course, longer dwells
given the significantly slower creep rates Unfortunately, it proved impossible to result in fewer cycles to failure, the
of SAC-solders. determine the test details. data that include ‘mixed’ solder alloys
In Figures 1 and 2, Sn37Pb outperforms The comparison between Sn37Pb, is not clear-cut. These data are further
SAC405 and SAC305, respectively, SAC305and 90Pb10Sn in Figure 9 shows confounded with the fact that all failures
with the SAC-solder data showing a that 90Pb10Sn outperforms the other occurred on the component sides,
much wider failure distribution. The solder alloys in terms of mean cyclic lives, making the results for the ‘mixed’ solder
later observation is commonly, but not but is about equivalent at lower failure meaningless.
universally reported. probabilities. Asymmetric cycles are ill-advised,
In Figures 3 through 5, SAC305 and In Figures 10 and 11, iNEMI data because they essentially make further
SAC405 solder joints show accelerated of ‘mixed’ SnPb/SAC solder joints analysis impossible.
fatigue lives essentially equivalent are compared with solder joints The results in Figure 13 clearly show the
with Sn37Pb and show similar failure exclusively made of either SnPb or SAC. importance of understanding the impact
d
Fig. 1
Fig. 5
istribution


s

. Interestingly, and uncharacteristically
Fig. 1 
 Fig. 7 
, the of different dwell times on the outcome


90
90
90











90

75


75
75







 


75











50


 





















 




50






 

 50


50




















 







25











 25 








25

 







25







15 mm

FCBGA on




93-mil-thick FR-4, 


% Failed
 
% Failed
10 



CSP Components on FR-4, 60 I/O 16x10 mm CSP on
% Failed



10  
CSP Components on FR-4, ATC: per IPC-9701 ATC: per IPC-9701
10 




% Failed
ATC: per IPC-9701 0100°C, 

1 m-thick FR-4,
10 



5

-55+125°C, 10°C/min ramps, 500 m  balls
5
 -55+125°C, 10°C/min ramps, 10°C/min ramps, 10 minute dwells @ -55°C & ATC: -65+150°C,
5

10 minute dwells @ -55°C & 15 minute dwells

5

30 minute dwells @ +125°C 10 minute dwells, 20% R
 
30 minute dwells @ +125°C Event Detector
2
  Sn37Pb Sn37Pb
Fig. 1 
2
  Sn37Pb Sn37Pb
2

 SAC 405
  SAC 405
 SAC405 1
2
 Sn3.5Ag0.7Cu
 Sn3.5Ag
1
1
10
2
1
200 500 10
3
2,000 5,000 10
4
10
2
10
3
2,000
200
5,000
500 10
3
10
4 2,000
2,000 50,000
5,000 10
4
10
5
10
2
200
Cycles-to-Failure
1
 Cycles-to-Failure
1
500 10
3
2,000 5,000 10
4
Cycles-to-Failure
5
Cycles-to-Failure
7
90






75





Figure





5. Weibull plots of Sn37Pb and SAC405 Figure 7. Weibull plots of Sn37Pb, Sn3.5Ag0.7Cu and Sn3.5Ag [Source: S. Yoon,
50
[Source:












J. Radhakrishnan, Intel, USA]. Hyundai, Japan].

Fig. 6



25 
 

 Fig. 8





% Failed
 
10  
CSP Components on FR-4, 1206 Resistors on FR-4, ??? on ???
ATC: per IPC-9701
 
90
ATC: per IPC-9701
90
ATC: -?? ???°C, Dwell: ??
-55+125°C, 10°C/min ramps, , = 3.0
5
-55+125°C, 10°C/min ramps,
10 minute dwells @ -55°C &
75
10 minute dwells @ -55°C &
75
SAC205 = 5.1
 
30 minute dwells @ +125°C 30 minute dwells @ +125°C
SAC305, , = 3.8
2

50
 Sn37Pb Sn37Pb
50
 SAC 405 Sn3.9Ag0.6Cu

SAC405, = 2.9
SAC387+Zn, = 3.0
1
l
e
d

10
2
200 500 10
3
25
Sn3.4Ag1.0Cu3.3Bi



a
i
2,000 5,000 10
4
25

 

 
Cycles-to-Failure
F 
1
 
%
10
 
% Failed
10
 
5 5
  
2 2
Lower Ag content
1 1
10
3
2,000 3,000 5,000 7,000 10
4
10
0
2 5 10
1
20 50 10
2
200 500 10
3
Cycles-to-Failure
6
Cycles-to-Failure
8
Figure 6. Weibull plots of Sn37Pb, Sn3.9Ag0.6Cu and Sn3.4Ag1.0Cu3.3Bi Figure 8. Weibull plots of Sn37Pb, Sn3.5Ag0.7Cu and Sn3.5Ag [Source: Linda
[Source: Dave Hillman, Rockwell Collins, USA]. Scala, Celestica, USA].
www.globalsmt.net Global SMT & Packaging - August 2008 – 47
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