Should a trace be connected through multiple pins on a pin header?

Question

I'm designing a modular board, where the two modules are connected through pin headers. For mechanical stability I have more pins than traces and my question is that which is the better: route each trace through one pin and leave the remaining pins free or route the traces through multiple pins?

In the case of power traces (e.g. ground) I think it shouldn't be a problem, but what about high frequency signals (e.g. gate drive signal)? Does splitting them on the pin header cause any problem (noise, signal integrity, EMI, etc.)?

Answer 1

This is quite common on power traces, not just "because there are enough headers" but it loweres contact resistance and current capability.

When done on high speed signals it can reduce the inductance, and increase the capacitance to other traces. In other words, it could impact the impedance and risetimes. However, if you don't need it, there is no point to do so - just having some unconnected copper pad on unused pins will be fine.

Answer 2

The stability as you clearly know is related to how many total pins you allocated for your pin header interface. So the question is really related with what to do with the spare pins.

I would leave one pin per "signal". But for "power" and "ground" delivery I would allocate the remaining pins to allow for more connections. When you allocate the additional power and ground pins make sure to take advantage of the additional pins to connect into the power and ground on the two circuits in a more robust way. For example it would be better if those header pins connect into the power and ground pours/planes on each end than to just run a thin trace up to the pins that are hooked together.

Answer 3

You don't need traces for mechanical strength. The copper inside and around the hole make up all of the mechanical strength. Adding a trace will not make any difference.

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I don't know what you are going to 'hang off' your connector but even a 2x5 header is amazingly strong. Just try to pry one off board: you will need a set of strong pliers. Going to e.g. 20 or 25 pins does not add much. For mechanical stability it would be better to use two, e.g. a small one on each side of the board.

Signal integrity depends very much on frequency. If you have high frequency signals you should use connectors with the right impedance. In that case you should not route those signals through multiple pins. Also route direct from the source to the connector. Avoid T-junctions.

Where multiple pins help, is when you want to void cross-talk. Keep them apart. If your connector goes to a flat-cable you might want to use signals on all even pins and ground on all odd pins. On your cable you then get signal-ground-signal-ground.