Page 18 - Chip Scale Review_November December_2022-digital

Figure 6: 112Gbps PAM4 signal loopback design in a 150µm-probe head.
simulation result at the boundary
cond it ion, we u sed a si mplif ied
test jig in our lab environment with
a fou r-probe double-sided probe
station and a 110GHz performance
network analyzer (PNA), the results
of which show good correlation of
insertion loss between simulation and
measurement up to 85GHz (Figure
7). The simulation boundary condition
is also proven to be a reasonable
setting for such a high bandwidth.
To align with customers’ thermal
test requirements, we designed the
water heatsink channel and performed
t her mal si mu lat ion, f rom wh ich
we obtained the expected results.
After achieving satisfactory thermal
performance, a prototype thermal
head was manufactured to conduct the
lab test and compare the difference
between the simulation and actual
measurement (Figure 8), which is
a procedure similar to elect rical
verification and that internally proves
the capability of our product. Another
checkpoint of thermal simulation is to
achieve thermal distribution, which
will affect the fine-pitch probing
stability. Distinct material selection
and structural design lead to dramatic
differences in thermal expansion.

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