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As data center equipment speeds continue to increase, traditional FR4 printed circuit board (PCB) substrates may no longer provide acceptable transmission performance, especially at 25 Gbps and beyond. Core switches and routers need maximum throughput with superior signal integrity, and as these systems achieve greater computational power, the backplanes and the number of daughter cards they support become greater in size, number, and complexity. Many equipment manufacturers are looking for connectivity alternatives to PCB substrates, and high-speed cabled backplane technology has emerged as a primary option. In this article, we will examine the need for high-speed cabled backplane connectivity, its advantages over PCB-based alternatives, its potential drawbacks, and key requirements for cabled backplane products that can provide maximum flexibility and throughput with exceptional signal integrity.
Why cabled backplanes?
Cabled backplane technology has been in existence for more than 10 years. Recent migration from the 10 Gbps backplane ecosystem to the 25 Gbps and beyond backplane ecosystem is making cabled backplane technology a more attractive solution for today’s system architects. A cabled backplane can solve three issues: it increases performance, enables low-loss communications across long channels, and allows routing flexibility.
* Higher performance – Using high-speed cabled backplanes significantly improves electrical performance at 25 Gbps and beyond. Other than using fiber optic technology, the cabled approach is one of the few alternatives for larger computing and switching systems. Leading PCB fabrication suppliers have developed HDI (high density interconnect) structures to help mitigate trace routing challenges, but it takes 20-30 fabrication process steps to build these very high layer count backplanes, and they are 5-10 times more expensive than traditional PCB substrates.
* Low-loss communications – Loss budgets for an entire channel are becoming tighter so designers need to reduce the insertion loss as much as possible in the physical connection. PCBs have insertion...