I have very successfully done this kind of thing with careful via-in-pad to conduct heat through the PCB. I used a grid of vias underneath the tab of the SMD device (it was D2PAK in my case). The vias often need to be plugged to prevent their acting like solder wick but I've gotten down to about a 2.5 degree C/Watt total thermal resistance stackup from FET package to heatsink (under the board). The heatsink to ambient is on TOP of this figure. On Tue, Jul 29, 2014 at 4:42 AM, wrote: > > Which is why it baffles me that they have an SMD version that can > allegedly > > handle 5A. I do have a 2 sq-in pad on the board to dissipate heat, but > it's no > > where near enough. > > This is where you start going to aluminium core PCB with umpteen vias in > the tab mounting pad and very thin laminate layers. Aluminium core at edg= e > of PCB solidly attached to big piece of aluminium radiator, and chip > mounted as near the edge of the PCB as practical. > > Been there, done similar things, not quite that level of dissipation, but > had to take such things into account. > -- > Scanned by iCritical. > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .