Page 54 - Chip Scale Review_November December_2021-digital

effect as the coaxial spring socket, as well
as superior transmission characteristics
and low manufacturing cost.
High-frequency electrical
simulation analysis and verification
In order to check the crosstalk according
to the structure, high-frequency analysis of
the spring, elastomer, coaxial spring, and
coaxial elastomer sockets was performed
in the frequency and time domains.
Insertion loss, return loss, and crosstalk
were analyzed in the frequency domain,
and an eye diagram was used for the time
domain analysis [4].
Crosstalk is divided into near-end and
far-end crosstalk. In general, near-end
crosstalk has a greater loss than far-end
crosstalk. Therefore, the analysis was
performed based on near-end crosstalk
for purposes of this article. The ball pitch
applied to the analysis is 0.80mm pitch,
and the ball array is shown in Figure 4.
Frequency domain analysis. As for
the analysis conditions in the frequency
domain, the solution frequency was set
to 20GHz and frequency sweep was set

Figure 4: A ball array.

from 10MHz to 20GHz, and the analysis
frequency point was set to 8GHz and
16GHz based on data rates of 16Gbps
and 32Gbps. The results are shown in
Table 1. The insertion loss characteristic
of the elastomeric socket is 17% better
than the spring socket, and the return
loss characteristic is 13% better based on
16GHz. This means that the elastomer
socket has a shorter signal length than
the spring socket and the characteristic
impedance is matched to nearly 50 ohms.
Crosstalk, however, which is a factor
that interferes with the transmission
of high-quality signals, is occurring at
16GHz and -34.79dB for the spring socket,
and at -41.40dB for the elastomer socket
as shown in Figure 5. To prevent such
crosstalk, we have proposed a coaxial
spring socket with metal housing, which
improves crosstalk to -44.66dB (about
Figure 5: Graphs showing: a) insertion loss, b) return loss, and c) crosstalk of spring and rubber socket materials.

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