How tall can be cube, like MGM?
I can put 2 PCB's with 12 FET's on each (both sides). With 4 FET's I hope we do not need heatsink, it would be heavy enough with all that copper from D2Pak tabs. Or we can add 3d board - 6 FET's - getting expensive ($5.00 each).

Or 2 FET's per phase and heatsink to frame? What if there is no metal frame? Electrical isolation can be done with regular heatpad.

Artur

Personally, I'd use a metal case with small fins, kinda like the Quarks. IMO, shape or size isn't all that important as long as it's not gargantuan. However, a thin, rectangular case would probably be the easiest to mount. Even add some tapped screw holes for small fans. Using a metal case/heatsink, I would definitely use thermal pads like in your link. I've used something like those before and they work well as long as each device is not dissipating tons of heat, which these FETs shouldn't be since they're running in switch mode. This might be a nice kit or upgrade path for a smaller ESC like a 9920 to offer for those who want a high current ESC without the $500+ price - as long as they don't mind the size.

Rethinking the module idea; the brains of an ESC is probably concentrated only on one board. If the whole case is designed so the output FETs are mounted on the outside walls, the processing board might slide vertically in the center so it won't take up much room. Just another option I guess if running an umbilical between two units isn't wanted...