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to compensate for minor die shifts during
RDL patterning will also contribute to
overall panel yield.
CSAM inspection: mold voids
detection. Mold voids can occur because
of short gel time, short spiral flow length
of the mold compound, contamination on
the interface between silicon and mold
compound material, or an un-optimized
mold dispense profile and parameters,
to name a few causes. In the example
from Figure 8b, mold voids are normally
detected with a CSAM metrology tool
because a standard microscope will
not be able to detect voids at the mold
compound to the Si interface layer
(Figure 8a). Figure 8c confirms post-
Cu stud top grind that mold voids were
Figure 6: Die shift illustration from chip attach to post-mold cure.
custom adaptive pattern to each panel [1].
Utilizing this photolithography process
helps with mitigating issues encountered
during die shift (X, Y, Ɵ).
Key challenges in 600mm panel
processing
Some of the key challenges in 600mm
x 600mm PLP are die shift during the
panelization process, warpage control,
mold thickness variation, C-mode
scanning acoustic microscopy (CSAM) Figure 8: a) Example of CSAM defects: a) low magnification microscope; b) CSAM inspection; c) (four panels)
Mold void after panel top grind post-CSAM.
for defect detection, panel segmentation
and panel design to satisfy a >99.5% yield direction. This shift
requirement. Some of these challenges can be attributed to an
are addressed in the sections below. incorrect recipe set-up
Panelization. In Figure 6, an example or pick and place bond
of why die shift occurs is illustrated. heads that are not aligned
There are two major areas for die shift. to the center of the die, or
The first will occur at the chip attach to optical misalignment.
process and the second will occur during D u r i n g t h e m ol d
the mold compression process. During compression process,
the chip attach process, singulated die mold material tends to
may experience a shift in the x, y or Ɵ shrink and therefore
te n d s t o g r a v i t a te
towards the center of the
panel. Consequently, this
shrinkage also affects Figure 9: CSAM mechanism for checking mold voids.
die placement f rom present from CSAM inspection. In this
the previous process. An example of a example, the CSAM is performed prior to
600mm X 600mm panel that will require the Dielectric 1 process.
further improvements in mold dispense is In the example shown in Figure 9,
shown in Figure 7. Referencing Figure the entire panel is submerged in water.
7, die shift during mold compression can Ultrasonic waves cannot pass through air
be mitigated by applying a die position pockets and therefore, the waves reflects
compensation during the chip attach at different interfaces or defects. For
process. In addition, the mold dispense example, any air pockets or areas where
pattern can be optimized to ensure better the ultrasonic wave cannot pass through
coverage and the minimization of total will be reflected 100%. This, in turn,
thickness variation (TTV) within the
Figure 7: Die position compensation and mold panel. The use of laser directed imaging provides us with a mapping of what the
dispense need to be optimized.

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