Trace width for 0.35µm thickness of copper

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Hi everyone, in order to enhance our custom board (2 layer board of 35µm) (regarding to EMI, robustness…) I 'am wondering on to size the trace of some nets in my design.

In fact I am using relay (finder 32.21.7.005.2000) that accepts 6A max on commutation. Therefore I should be abble to size the trace width according to that. On some websites we found an empirical rule that says 1mm per Ampere. But I’ve found an other one: ANSI PCB Track Width Calculator that give me a result of 1.2mm for the 6 Ampere considering a Ambient T° about 60°C and a rising T° of 60 °C (I think that our pcb burn above 125-150°C).

The gap is huge between 1.2mm and 6 mm!!!

Any advice?

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A 60 degree rise for a trace is, in my opinion, absolutely unacceptable. I’m not an EE, but I certainly wouldn’t consider a design that had traces that hot sound. Your 6mm number would have a rise closer to 5 degrees.

I’d shoot for a 10 degree or less rise. That also means less wasted power.

Also, when it comes to trace size, a nice rule of thumb is (as long as we’re not talking RF design or anything crazy) “as big as you have room for”.