New-Tech Europe Magazine | Aug 2018

and beyond with minimal loss. Since the high-speed signal is removed from the PCB you are now allowed to reduce the layer count, remove any re-timers that were in place and go to a more common PCB material and all of these will reduce the overall cost of the system. However, producing a high-speed cable assembly system to achieve these performance goals is difficult. Among the many pieces in the puzzle are the mating connectors, the transition boards in the cable assemblies, and the PCB routing strategies, and of course the cable itself. Samtec incorporates its ultra-low skew twinax cable technology in high-speed cable assemblies. Co- extruded twinax cable technology eliminates the performance limitations and inconsistencies of individually extruded dielectric twinax cabling. This improves signal integrity, bandwidth and reach for high-performance system architectures. Although the goals of miniaturization and higher data rates conflict, connector manufacturers can strike a balance in data rate performance and footprint size. Interconnect contacts can be designed to minimize size and maximize bandwidth. The plastic materials in the connector insulator also affect performance. And alternative strategies, like taking signals off-board with high- speed cable systems, can address the challenges of speed and cost.

Figure 2 shows bandwidth that can be achieved in traditional and high-speed materials.

Flyover™ Technology System architects are now using an alternate approach that reduces the use of PCB traces to conduct high-speed signals. Instead of increasing layer counts, using costly high-performance PCB materials, and dealing with long degrading trace lengths, the signals are taken out of the board and a cable is used to fly them over the PCB. We refer to this technique as Flyover™. Flyover™ improves signal integrity performance, it allows for a higher signal speed, and it reduces the overall cost of the system.

For the typical application a connector is positioned as close to the chip set as possible and then a discrete or ribbonized twinax cable is used to pass the signals to another location on the board or they can attach directly to an IO connector. Depending on the system layout there are multiple connector options to work around the available space, such as a low profile horizontal connector that would attach underneath the chip set heat sink. There are many advantages of Flyover. First, we can achieve those high data rates of 28, 56, 112 Gbps

Figure 3: Samtec Flyover™ QSFP-DD application

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