Apex

Not that it explains All the cost, but heatsinks like these do require the footprint area to be machined to a certain flatness and roughness (which then incurs QA work) So the added labor cost could be major. cheers, RS

In my experience, the big heat sink extrusions are not usually very flat. We often do our own secondary machining to get them flat.

Sure, I accept that. A former colleague of mine designed his audio amps to push the limits. (these were full production commercial units). the output devices ran as hot as possible, and to ensure adequate heat removal, he left out the insulators. Devices were mounted "metal -on-metal" - so flatness mattered. I assume they ordered the heatsinks already machined as needed. Yes, the heatsinks were electrified, one at +100V and the other -100V. Very tricky to work on...

Of course, the flatness need not be too low if we're using a thermal pad or compound to fill the small gaps.

Yeah, you squeeze a toothpaste tube, it's not straight. For the aluminum extrusions, each length is pulled (stretched) by a few percent while it's still hot.

A couple of passes with a flycutter after anodizing is not a hard task. Any good heatsink manufacturer could/would do that.