Page 20 - Chip Scale Review_January February_2023-digital

DRAM packages showed better timing
margin and enhanced HIFOM had
much improved results. At 6400Mbps,
PoP with enhanced HIFOM is only
available at over 20%. In addition to
the adoption of FOWLP to DRAM
packaging, its implementation in AP
packages can also provide a much
wider timing margin as shown in
Table 3: Far-end cross talk (FEXT) comparison of a normal W/B package and FOWLP at various frequencies.
Figure 12b. While the amount of
routing of power and ground lines. In SI timing margins of a PoP system improvements in the timing margin
addition, multiple power TSVs or fine were also investigated at various is not so much at low speeds (e.g.,
interconnects of TSV-bridged dies are clock speeds. The data eye window around 3,733Mbps or 4,266Mbps),
also able to provide the benefits of low- in the W/B package is very narrow, the timing margin at high speed can
power impedance. Crosstalk was also while it has a much wider window be greatly enhanced and its amount
evaluated as presented in Figure 10 in FOWLP with enhanced HIFOM, is almost up to 50% at 6,400Mbps.
a nd it showed a n ext remely low as shown in Figure 11. Figure 12 Based on our investigation, it can be
value compared with the nor mal shows the timing margins of the PoP concluded that co-adoption of fan-out
W/B package. As noted in Table 3, the system wit h va r ious DR A M a nd technologies to AP packages – and
crosstalk of the FOWLP is reduced AP packages. Figure 12a shows the DRAM packages as well – showed the
by 5~17dB as the frequency. As the timing margin for various DRAM best performance in timing margin.
frequency is higher, the improvement packages with a substrate-type AP In summary, the overall performance
of crosstalk is more dominant in package. Compared with nor mal difference as a function of clock speed
the FOWLP. W/B DRAM packages, FOWLP-type is presented in Figure 13. At low

Figure 11: Data eye diagrams for two different packages at four different frequencies.

Figure 12: Timing margin of a PoP system for various DRAM package types with a) a substrate-based AP package, and b) a FOWLP-based AP package.

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