Page 32 - Chip Scale Review_March April_2023-digital

annealing to achieve covalent bonding
between oxide layers and metallic
bonding between Cu-Cu contacts and the
diffusion of Cu atoms.
For the package substrate, the process
is to stencil print the solder paste on the
substrate and then reflow into C4 solder
bumps. For the final assembly, the bridge
+ chiplets module is picked and placed on
the package substrate, then the C4 bumps
are reflowed.
Hybrid bonding bridge with C4
bumps on the chiplet wafer. Figure
7 shows the process flow of the hybrid
bonding bridge with C4 bumps on
the chiplet wafer. It can be seen that,
compared with the C4 bumps for the
package substrate case, the process steps
for the bridge wafer and the chiplet wafer
are the same up to the bridge-to-chiplet
wafer bonding step. After that, the C4
bumps are fabricated by wafer bumping
Figure 5: Hybrid bonding bridge. SOURCE: Unimicron on the chiplet wafer. Then, the chiplet
wafer is diced into individual modules
(bridge + chiplets with C4 bumps). The
final assembly is accomplished by picking
and placing the individual module on the
package substrate and reflowing the C4
solder bumps.

Summary
S o m e i m p o r t a n t r e s u l t s a n d
recommendations are as follows:

• The key advantages of chiplet design
and heterogeneous integration
packaging are cost, cost, and cost.
• The key disadvantages of chiplet
design and heterogeneous integration
packaging are to increase package
size and package complexity, which
Figure 6: Hybrid bonding bridge with C4 bumps on the package substrate. SOURCE: Unimicron leads to higher cost.
• In general, the semiconductor cost
is a few times the packaging cost,
therefore, the savings that can be
achieved with chiplet design and
heterogeneous integration packaging
are worth pursuing.
• The patents for bridges embedded in
fan-out EMC with RDLs with chip
(bridge) first and chip face-up, chip
(bridge) first and chip face-down,
and chip-last or RDL-first, have been
provided.
• A new bridge with hybrid bonding
has been proposed. Its advantages
a r e : h i g h e r d e n s i t y, b e t t e r
performance, less process steps, and
lower cost.
Figure 7: Hybrid bonding bridge with C4 bumps on the chiplet wafer. SOURCE: Unimicron

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