This is the second time I was contracted to machine heat spreaders. The first time I thought the person sent me a model that wasn't importing correctly because it loaded into my CADCAM system as 20mm x 15mm. Turned out that was the size. After being anodized to make it nonconductive, it was clamped to a PC board and used to spread heat across several surface mount components on an RF board. I've made small parts before but usually the things I'm machining involve hammers and 8,000lb clamping force vises. I've done a lot of precision work though, like making gears for old clocks, etc.
The guy contracted again for heat spreaders and this one pushed the limits. The outside dimensions are 7.5mm x 7.6mm. The small step on the right channel is .2mm high (.0079"). I used a 1/32" end mill to rough out the channels and then finished them with a .015" end mill. To put that in perspective, a lead on a typical ceramic capacitor is .024". For miniature machining, this type of work wouldn't even get me in the contest. I've seen people make working machines that sit on a dime.
The picture doesn't do it justice as the tool marks that are visible could be buffed out just by rubbing the part on a piece of paper. I'll leave the finishing to the customer as even 2000 grit sandpaper would quickly spoil the edges.