Page 48 - ChipScale_Mar-Apr_2021-digital

Summary
As bandwidth requirements in
high-performance applications
keep increasing, robust and reliable
2.5D packages have become
pertinent technology to address the
needs. The JEDEC standard TC-J
test is a standard test to evaluate
BGA solder fatigue reliability in
thermal cycling. But the results
need to be bridged to the end
application use conditions. Using
Figure 6: Normalized characteristic life in TC-J cycling obtained the coupled thermal-mechanical
from model and test data.
Figure 5: Equivalent plastic strain distribution simulation technique, field lifetime
in corner BGAs in global model showing critical for a product can be evaluated
BGA location. using the accelerated testing
lifetime. In this study we review
the highest strain BGA at the end of the
last cycle in the global model. Figure 5 a simplified method of modeling
shows the location of the highest strain field cycles. Further work in this
BGA in TC-J thermal cycling for the case area needs to be carried out to
where heat sink is used. This matches the model actual field cycles, which
fail location determined using the dye and can be more complex.
pry technique. The critical BGA location
for both of the configurations – with and Acknowledgment
without heat sink – is observed to be at the This article was revised from
package corner, which matches the fail Figure 7: Normalized lifetime in field cycle with different Tj max . its original version, which was
data. This corner failing BGA indicates a originally presented at the IEEE
shear dominant failure mode because of determined from test data (<10%) Electronic Components and
the higher CTE mismatch between organic indicating good model-data correlation. Technology Conference (ECTC) 2020
laminate and PCB and high DNP as a The combination of heat sink load and (virtual conference).
result of the large package size. Once the backing plate is observed to significantly
critical BGA is identified, the local model degrade BGA lifetime as it constrains the References
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