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If you want the best thermal exchange with the air, is it preferable to leave a thermal/ground plane raw or to cover it with solder mask? And how important is the difference?

(Dave from EEVblog is pretty self-confident saying it's more efficient without solder mask: https://youtu.be/q3RhWuXFixU?t=782)

Motla
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    Try reading this q and a: https://electronics.stackexchange.com/questions/449224/heatsink-on-underside-of-pcb#:~:text=Typical%20solder%20mask%20has%2020,of%201%C2%B0C%2FW. – Andy aka Nov 14 '20 at 15:16
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    The PCB is such a bad heatsink anyways that the very slight improvement from no solder mask doesn't mean much. – DKNguyen Nov 14 '20 at 17:32

3 Answers3

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The short answer is no it won’t make a significant difference. The long answer is that conduction will be slightly worse with solder mask but radiation will be better, assuming that the bare metal is in good condition - the emissivity of a shiny metal surface is generally low, around 0.1 while that of a coated surface is 0.9 or more. Thus bare metal may paradoxically be a worse heat sink at higher temperatures. This assumes that the bare metal doesn’t oxidise or corrode, unlikely if it’s copper but possible if it’s tinned or gold plated.

Frog
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The solder mask coating is a very thin thermal and electrical insulator. However, "preferable" is a relative term. Exposed copper or solder plate will oxidize / corrode / whatever, and as above is uninsulated from accidental contact with a non-ground-potential conductor of some kind.

So, yes, there are several differences; but no, I've never seen a situation where the thermal difference is significant.

AnalogKid
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good thing to avoid solder mask, make sure copper is not exposed and surface finishes are applied. This exposed metal can be touched with a heat sink if required

NIKHILRAJ
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