# How to find temperature rise for Trace Width?

Hi Folks…Beginner here
When I look up tables or trace width calculator to find trace width I need to use…there’s always something called temperature rise…like 10 degree , 20 degree etc…
The trace width for a given current varies with the temperature rise
So how actually do you guys measure this…or do you guys just ignore this?
BTW how much do you guys care about trace width anyway…in my case I am having some Stepper motors…which kind of take 1.2-1.5A per phase…any recommandations for trace width?..
Sorry for too many questions at once and any help is highly appreciated!!
Thank You.

You don’t measure temperature rise but you assume what is temperature rise you can accept.
The higher temperature rise you can accept the thinner tracks you can use.
Many years ago I have read that 1mm track can be used for 1A current. But if I have at our output relay that we specify that output is 1A I use 2mm tracks at top and at bottom (so 4mm in total) to connect relay pins to terminal block. I believe it is more than enough.

Oh…thanks Piotr!
So having two traces between two point ,on front and back would kind of half the trace needed through one side is it?..
Again, thank you for taking your time to answer my silly doubts! Have a great day…

If you have one track than it is cooled mainly by air at one PCB side. If you have two traces with half the width of that one but at both PCB sides than you have the same power dissipated in those wires but they are cooled by air at both PCB sides. I think it is little better situation, but it is only my intuition.

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If you have one trace on one side of the PCB, and there are no other traces generating heat nearby, part of the heat from the one trace will be rejected to the surrounding air on the same side as the trace, part through radiation on that same side, and part will be conducted through the PCB core material, possible ground and power planes in inner layers if present, and to the other side of the PCB where it is rejected by radiation and convection on that side. The PCB core material will have a certain thermal resistance, but it is not infinite, that is, it will have some contribution to cooling the trace.

If you have traces on both sides, you only have heat rejection on one side per trace. So you have to take that into account when calculating the temperature rise.

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Piotr is knowledgeable and I agree with what he is saying. Also:

I will say what I said recently in another thread on this forum. Unless your board is squeezed for space (that certainly can be) or if you are using controlled impedance (not true for driving stepper motors) there is no reason to make traces much narrower than the pads to which they are connecting. You do not get any money back for etching more copper, and it will not help the board performance unless capacitance is an issue. This is very unlikely for anything under 50V.

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Temperature rise is often restricted by a product standard applying to the equipment.
A safe rule of thumb is that a rise of 10C is OK.

OH ok…Thank you so much mate!

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