We are going to use GAP PAD HC 5.0 thermal pad to transfer the heat from a FPGA (XCKU040) to a heatsink. My question is regarding the thickness I should choose to obtain best performance.
On the one side, I understand that lower thickness = lower thermal resistance = higher heat transfer. On the other side, higher thickness allows it to absorb more deformations in the chip / heatsink surface, but it is worse in terms of heat transfer.
Is this correct? Any more ideas?
Thank you very much.
For that chip I'd go with the thinnest 20 mil.
The case is so smooth if they had a thinner one I'd use that.
The case top surface does not appear to deviate more than 1 mil.
I guess that's the quality you get when you pay over $2,000 for a chip.
I like the thermal pad you selected. Good choice.
On the other side, higher thickness allows it to absorb more deformations in the chip / heatsink surface, but it is worse in terms of heat transfer.
Yes, thicker is worse in terms of heat transfer.
Doubling the pad thickness doubles the thermal resistance.
Source: Gap Pad 5000S35 datasheet
Yes, that is correct.
It is unlikely that the surface of a chip or of a heatsink would be so rough that much needs to be taken up by a pad.
Where you might need to use a thicker pad is if you are using one heatsink for several components and some of those components have a different height, and the thermal dissipation does not warrant the cost of machining the base of the heatsink to varying heights. For example, on a PC GPU card.
