I was looking at the PCB layout last night… There are thermal vias on these, too.
10x10mm heatsinks are about the right size to be placed on the underside.
Thanks for the reply man.
http://i.imgur.com/WDJyvQM.jpg You can see on the bottom of the image where the labels for the steppers and such are, I assume just above that are the thermal vias, those little pin hole looking spots/pattern. https://youtu.be/mYuZqx8xwTg?t=163 You can see the thermal vias here in this video clearly, shiny copper looking rectangle, the difference that I see is that whatever PCB laminate that is covering the TMC2660s thermal vias isn't covering the TMC2130s thermal vias. Think this is accurate? It's probably likely best to place heatsinks over the 2660s thermal vias, but I wonder why the thermal vias might be left covered.
What can help if you are pushing 2.4A is to blow a fan over the bottom of the board.
All around more cooling seems better to me than less, even if not entirely necessary, more surface area is good. I am not really sure what 2.4A really means (I know it's current), the datasheet says 2.8A RMS and I guess 4A maybe with proper cooling? I probably don't understand the datasheet very well.
Update: this older thermal testing post actually shows pictures of the heat spreading on the back of the board:
Thanks. I am guessing that the current limit could be blown away by some decent heatsinks placed over those hotspots, assuming the thermal pathway is good.