Page 26 - Chip Scale Review_March April_2022-digital

is getting worse when the number of RDL This indicates that the CL structure has Summary
layers is raised from 2L to 5L. This study the potential to show a better cost benefit F O - M C M u s i n g t h e c h i p - l a s t
shows that the CL design has the better than the CF structure once either the FO technique has been demonstrated as a
yield control capability in both the large size or the number of RDL layers exceed a robust package paradigm. It provides
module size and high RDL layers design. particular range. less stress effect, better warpage control
and high yield performance. Figure 7
shows the SEM cross-section image of
a FO-MCM with 6L RDL. The micro-
bump height and diameter are 8µm
and 25µm in this design, and the top
coplanarity is controlled within 4µm,
which ensures the quality of the micro-
bump joint after the reflow process. In
addition, the 6-via stacking structure
was demonstrated in this experiment
through the use of an optimized glass
design. The top total thickness variation
(TTV) was shown to be under control
such that excellent joint quality was
achieved in both the via stacking and
non-via stacking areas.
Additionally, reliability tests were
verified in this study. All reliability
conditions received a “pass” result for
MSL3, TCT1000, u-HAST192, and
HTSL1000 conditions. Furthermore, the
cross-section of the micro-bump joint
area (after completing the reliability
tests) as shown in Figure 8, indicates
perfect joint quality without any non-
wetting, void or solder creeping issues.
In this investigation, the FO-MCM
package not only provides an alternative
solution from a cost-benefit standpoint,
but also results in less warpage during
chiplet integration when using an
optimized glass carrier design. With the
advantages of being able to control the
warpage and have less internal stress,
FO-MCM is the proper platform to build
up a much larger package size for the
integration of even more dies.
Figure 6: a) Fan-out size versus yield performance; and b) Analysis of the RDL yield by different RDL layers.

Figure 7: SEM cross-section image of an FO-MCM structure with 6L RDLs. Figure 8: Micro-bump joint cross-section SEM result.

24
24 Chip Scale Review March • April • 2022 [ChipScaleReview.com]