16 Processing and Reliability of Solder Interconnections …
523
Although the computational model predictions do not rely upon acceleration
factors, the model can calculate those factors in order to correlate accelerated test
results to long-term performance in the service environment. Acceleration factors can
be as high as 200–300 between the two environments shown in Fig. 16.29. Therefore,
TMF lifetime predictions that differ by 500, 1000, or even 2000 cycles, which appear
significant in accelerated aging tests, may not impact service lifetimes when the
latter predictions correlate to failures in several hundreds of thousands of years.
Conversely, these predictions can be used to select an accelerated aging test parameter
for qualification or acceptance evaluations that correlate to end-of-life or verify that
“used-up” TMF lifetime is minimized, respectively, thereby preventing the risk of
either undertesting or overtesting assemblies having PoP or PoPoP components.
16.4 Summary and Future Trends
16.4.1 Summary
The development of stacked packaging technology—materials, assembly processes,
and reliability—has led to significant advances in the miniaturization and
functionality of consumer electronics. Certainly, these advancements can provide
a springboard for enabling PoP and PoPoP components in high-reliability military,
space, and satellite systems. Empirical studies have clearly demonstrated the
robustness of first-level, package-to-package and second-level, package-to-PCB
interconnections based on Pb-free solders as well as mixed Sn–Pb/Pb-free, secondlevel solder joints. Conformal coatings have a negligible effect on solder joint TMF
because they do not bridge the gap. However, underfills can significantly alter the
failure behavior of PoP and PoPoP, first-level and second-level interconnections, but
not in an intuitively obvious manner. Computational modeling is indispensable for
predicting the response of first-level and second-level solder joints, particularly in
the case of temperature cycling environments. These models can readily account
for, not only different use conditions, but also, the complex construction of PoP
and PoPoP components. As the fidelity of these models improves, fewer accelerated
aging tests will be required at the design and process development stages of PWAs
using stacked packages. Rather, such experiments will transition to the lesser role of
model validation.
16.4.2 Future Trends
Stacked packages—PoP and PoPoP components—are considered to be a relatively
mature technology from the point-of-view of consumer electronics. The quest for
further miniaturization, especially reduced package heights, will place a greater
523
Although the computational model predictions do not rely upon acceleration
factors, the model can calculate those factors in order to correlate accelerated test
results to long-term performance in the service environment. Acceleration factors can
be as high as 200–300 between the two environments shown in Fig. 16.29. Therefore,
TMF lifetime predictions that differ by 500, 1000, or even 2000 cycles, which appear
significant in accelerated aging tests, may not impact service lifetimes when the
latter predictions correlate to failures in several hundreds of thousands of years.
Conversely, these predictions can be used to select an accelerated aging test parameter
for qualification or acceptance evaluations that correlate to end-of-life or verify that
“used-up” TMF lifetime is minimized, respectively, thereby preventing the risk of
either undertesting or overtesting assemblies having PoP or PoPoP components.
16.4 Summary and Future Trends
16.4.1 Summary
The development of stacked packaging technology—materials, assembly processes,
and reliability—has led to significant advances in the miniaturization and
functionality of consumer electronics. Certainly, these advancements can provide
a springboard for enabling PoP and PoPoP components in high-reliability military,
space, and satellite systems. Empirical studies have clearly demonstrated the
robustness of first-level, package-to-package and second-level, package-to-PCB
interconnections based on Pb-free solders as well as mixed Sn–Pb/Pb-free, secondlevel solder joints. Conformal coatings have a negligible effect on solder joint TMF
because they do not bridge the gap. However, underfills can significantly alter the
failure behavior of PoP and PoPoP, first-level and second-level interconnections, but
not in an intuitively obvious manner. Computational modeling is indispensable for
predicting the response of first-level and second-level solder joints, particularly in
the case of temperature cycling environments. These models can readily account
for, not only different use conditions, but also, the complex construction of PoP
and PoPoP components. As the fidelity of these models improves, fewer accelerated
aging tests will be required at the design and process development stages of PWAs
using stacked packages. Rather, such experiments will transition to the lesser role of
model validation.
16.4.2 Future Trends
Stacked packages—PoP and PoPoP components—are considered to be a relatively
mature technology from the point-of-view of consumer electronics. The quest for
further miniaturization, especially reduced package heights, will place a greater