Heat Sink ? I remember lots of discussions and trials on the now-defunct slice forum and in this forum
okichatan
as chewitt says it needs a bit of work and the CM3+ will need a slightly thinner heatsink (fatter CPU because of the silver top). The easy solution is as chewitt suggests, get a stick-on one. I found that it still did not really remove enough heat, especially when playing video, so I adopted the DIY approach. While the measurement of the sink needs to be fairly accurate, there is a slight bit of "give" if you press on the CPU so there is a small amount of lattitude when making one.
There were a lot of different designs using bits of copper, I recall one was using buss-bar from a consumer distribution unit.
I used a copper core from an old PC CPU cooler and while not the best at heat transfer, using an aluminium plate, fixing it to the case with epoxy resin glue and letting it sit on the CPU with some heatsink compound works fine. The combination of Cu and Al gave "just the right" size to bridge the gap. The plate is fixed so it prevents the sink being dislodged and doing damage inside.
I attach a picture of the parts. The kaptan tape was used to position the sink and the heatsink compound was used to check contact with the CPU before finalising the design. You can use heatsink compound to help measure the gap, when it transfers to the case or CPU you have it "just right".
I hope that gives you an idea of how to do it.
Roger