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When using CAD software to draw board layouts, is there any convention on how to represent heatsinks attached to, say, some power transistors? I want to make sure they don't interfere with one another, and representing them on the board layout makes it easier to spot problems when I am moving stuff around.

It seems to me the alternatives are:

  • represent heatsinks as a separate component
  • modify the transistor's footprint so that it includes the heatsink
  • just draw the heatsinks on some separate layer that's normally off, and turn it on when checking for interferences

So far, I am very partial to the first option, and have been making heatsink components on Eagle and adding them right next to the transistors:

custom heatsink footprint on Eagle

However, I've never seen anyone do it like this. Is this a bad idea? Is there any sort of convention on that?

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  • \$\begingroup\$ What program are you using? In Altium we can just add a 3D body to the design. \$\endgroup\$ – The Photon Jun 26 '19 at 14:34
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It is called the keepout layer. I would include it in the transistor footprint for positional accuracy but it might be useful to have it separate for a PCB assembler so they know they have two components there on the BOM and pick and place list.

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