What's the purpose of a large thermal pad without a heatsink?

Question

I found this thermal pad on a controller board for SATA to USB enclosure. It's stuck on the SATA to USB bridge ICs. You can see 2 ICs to the left of it. There was an identical thermal pad adhered which I removed to inspect.

I've never seen a thermal pad without a heatsink before. Typically a thermal pad transfers heat into a heatsink. I'm trying to understand what its purpose is here. There's nothing that comes in contact with it opposite from the IC. I have a feeling it acts as a thermal mass itself, similar to a piece of copper without fins. I guess it still increases the surface area of the ICs by quite a bit given its size. Is this an inappropriate use of a thermal pad or is it perhaps a clever one?

Thank you!

Answer 1

That foam thermal interface material is meant to be compressed to give reasonable thermal transfer between non-plane surfaces either at a slight angle or to accommodate variances in height between the source(s) - multiple chips to a single heatsink or a single chip to an uneven surface, or both - foam is mostly air so in its uncompressed state it's pretty low thermal conductivity. Apparently it's good enough in this application that they decided to roll with it to, as you said, increase the surface area. It's probably cheaper than a heatsink, doesn't require any mounting hardware, won't cause problems if it falls off, and they might have just had a bunch lying around.