[BrianG]

Well, I removed the heatshrink from my ESC last night and they are indeed stacked with a layer of PCB in between. There is even heatsink grease between the top of the FET and the bottom of the PCB, but I noticed there is about a 1mm thermal grease-filled gap between the top of the FET and the board above it. Heatsink grease does help reduce thermal resistance, but only if used VERY thinly. It's only designed to fill in the microscopic inconsistencies between the mating surfaces, otherwise it really is useless when filling gaps. MOSFETs by nature conduct less with increased temperature, so they tend to sorta self-regulate to a degree, but this would explain why some people burn out one of the layers since the tops of the FETs don't mate closely with the PCB above it so they retain the heat until they ignite. As a matter of fact, that globbed thermal grease actually retains some heat. :(

All in all, I like the design of the BK ESCs, but I really wish a little more attention would have been made to some of these types of details. A small slab of aluminum between layers would help sink/spread the heat, and fill in the gap. Personally, I'd make this slab bigger so it can be extended out the sides to allow a larger heatsink to be attached. But that's just me.