Thermal interface, Pad vs. Paste, What to choose for large surface area?

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The MeanWell UHP-500R-48 power supply is passively cooled through coupling with the chassis it is mounted in.

I could use thermal paste, but it can be messy and hard to apply in a thin even layer over a large surface, I am leaning towards using a large thermal pad.

The thermal pad should be ~232mm x 81mm for the power supply,

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And I am going to need one for the amplifier board heat sink to couple it to the chassis heat sink, 3e Audio TPA3255 TPA3251 480-1-29A, 120mm x 85mm,

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Suggestions on what brand and series thermal pad would be a good choice?

Thank you, David.
 
Did you do a quick thermal assessment of that module? The devise report identifies individual part temp rise above two ambient temps. Did you identify which parts are internally bolted/heatsunk to the modules frame, and where on the frame? It looks like the max thermal dissipation is circa 48x10x0.05=25W, and a reasonable percentage of that has to convect though the top. With such a large psuedo-contact surface area, even without any thermal interface modification, you may find a negligible change when adding a full area interface. Have you characterised your local temperature operating conditions and how heat then flows to a room ambient?