Page 38 - 2020 Interconnect Innovations eBook

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In a typical mid-board application, a cable connector is located next to an FPGA or ASIC. The signal launches through discrete or ribbon twinax cable, over minimal trace length through the lossy PCB, to another location on the board or to an I/O connector, such as a QSFP.
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» Figure 4: Flyover Cable Systems can be used for mid-board-to-front- or back-panel applications.
High-performance Flyover cable systems allow designers to establish flexible board-to-board backplane architectures within a rack, as well as rack-to-rack interconnections. These solutions retain the traditional backplane architecture but achieve lower PCB complexity and higher performance targets. This approach also achieves higher data rates of 56Gb/s, 112Gb/s, and beyond, simplifies board design, and allows for more flexible and modular architectures. Another advantage is that it aids thermal dissipation by eliminating retimers and increasing airflow. As such, expensive PCB material usage is minimized along with higher layer counts. Ultimately, the total applied cost of the system is reduced by the Flyover approach.
An Innovation in Flyover Technology: Direct Connect to the Silicon Package
Achieving consistent, reliable 112Gb/s and 224Gb/s PAM4 performance requires removing as much loss from the signal channel as possible. Besides the high-speed cable strategy previously discussed, can other lossy signal channel components be removed?
Current system ASIC designs support 256 lanes/512 dynamic paths (DP) of 112Gb/s, offering 25.6TB aggregate data throughput while next-gen ASIC designs double that. Routing hundreds of DPs from larger ASIC packages and BGA breakouts cause nightmares for SI engineers and PCB designers. Isolation concerns contribute to the challenge as robust grounding schemes are required. ASIC packaging and BGA breakouts remain a key source of loss in the signal path.
A new interconnect system uses Direct Connect technology to integrate the connector in the silicon package. Its signals elude the BGA and route directly from the silicon package through a long-reach twinax cable.
However, integrating the connector within the package also presents challenges. High-speed interconnect design and advanced IC package and assembly collaboration is a must. The solution must also be small enough to avoid interfering with any thermal mitigation techniques like heatsinks, thermal interface materials, or liquid cooling.
Samtec’s new Si-FlyTM 112Gb/s PAM4 Low-Profile High-Density Cable System connects high-speed signals directly to the silicon package, which eliminates signal distortion by routing the signal from the IC package through long- reach cable. This ultra-high-density design also enables an aggregate data rate of 25.6TB with a path to 51.2TB.