Bandwidth demand drives connector design

March 10, 2016 // By Brian Vicich, Samtec
Meeting today's bandwidth needs is often defined in terms of performance requirements and what can or can't be achieved with current technology options. Many engineers are currently struggling to design 28 Gbps communications channels while others say they are well on their way to 32 Gbps. Some are now reaching for 56 Gbps and a few are looking into the technology to achieve 112 Gbps data rate.

Connectors form an important link in a signal's transmission chain. Therefore, when designing high-speed systems, don't overlook them. With the right parts, proper PCB materials, and proper design, you can meet the demand for high data rates.


Mechanical vs. electrical interconnects

Prior to today’s high speed design requirements, the issues of concern for interconnects were the physical aspects of their designs and factors that influenced those designs. These aspects and factors include:


Physical aspects;

- Stack height or distance between boards

- Pitch

- Power

- Termination types required (through-hole, press-fit, SMT)

- Latches or locks

- Supports/Constraints such as standoffs, brackets, chassis slots or frames


Influential elements;

- Processing and operating temperature

- Humidity ranges

- Shock and vibration requirements

- Safety issues and specifications

- Adherence to environmental standards such as RoHS compliance, lead-free standards

- Packaging and auto placement requirements


As system speeds have increased, interconnect design is no longer based solely on mechanical requirements. Designers now have to take into account electrical performance issues such as insertion loss, return loss, crosstalk, skew, and propagation delay, to name a few. As with every aspect of high-speed product development, the successful design of any interconnect involves achieving the right balance between maximising the physical and mechanical strength of the interconnect while optimising SI (signal integrity). Interconnect design and manufacture has to be approached as part of the overall system level design process.


It's all about the footprint

The essence of any interconnect design is the footprint, which is sometimes defined by mechanical considerations and other times by SI considerations. Specifically, the factors that affect SI performance include footprint configuration, size, spacing of the pads, PTH (plated through hole) vias, and BOR (breakout region). A graphic of footprint/routing design is shown in Figure 1. Additional factors to consider include maintaining signal integrity through the space/trace relationship and determining via diameters, tolerance stack-ups, number of