I have a 100x100mm board that is directly attached to a same sized heatsink on one side (touching heat producing IC packages). The board is 4 layer, with a large ground middle layer. Is there any reason I should NOT be connecting the heatsink screw hole mount pads to this middle ground layer?
Electronic – Electrically Grounding a Large Heatsink to PCB Layer Ground
groundingheatsinkpcb-design
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Best Answer
One reason not to is that you may turn the heatsink into an antenna and unintentional radiator if your ground is especially noisy.
This is an unlikely scenario though and is very much dependent on the design. In most cases grounding the heatsink electrically will help cut back on noise.
The other reason is if the heatsink could bleed heat back into the PCB in an area you may not want it.
Something to think about and design for.