Turnigy Trackstar 150A GenII ESC

[BrianG]

From the looks of it, the bottom un-heatsunk PCB is the brains, so should generate little heat. I've seen lots of boards connected with pins like that, and as long as the case holds them together, there should be little concern even for off-road use.

And about the dual heatsink thing: FET packages are relatively poor at transferring heat, which is why they soldered the heatspreader to the PCB - which will pull heat from the FET faster than any HS on a plastic FET case. Then, they use the main large heatsink to dissipate the heat pulled from the heatspreaders. And even though the FETs on the underside of the PCB are not directly heatsinked, the large traces should be more than sufficient to transfer the heat upwards. IMO, not a bad design to be honest.

A better option to me would be to use FETs that have a low rdson and a high slew rate - those two factors alone can result in less heat to be generated in the first place. Those FETs have an rdson of ~3mohm and a rise/fall time of ~50ns. Not sure how those figures compare with FETs of other current generation ESCs, but that's something to look at.