T
treez
Guest
TO247 FET mounted in "SMD" fashion and pressurized against heatsink with "foam"
We have a 4 layer PCB on which we have our offline , all surface mount, LED driver. This PCB sits on a thin thermal pad and this all lies against a big flat heatsink surface. The big flat heatsink is earthed.
Currently we use a D2PAK power FET and have thermal vias going through the PCB to bottom layer thermal copper pour…but this doesn’t give great heat conduction…therefore….
We wish instead to have a TO247 FET lying horizontally, with bent leads, so that it can be soldered as a “SMD” FET…….the TO247 tab will be screwed to a small rectanguloid of aluminium (a heatsink), which, through a small cutout in the PCB, will lie against the thermal pad, and thus give good thermal contact of the FET to the big flat heatsink.
The problem is, we cannot have a threaded hole in the heatsink, so how then will we get sufficient pressure with which to hold the rectanguloid heatsink against the big flat heatsink?….
…well, there is a flat perspex enclosure some 3mm above the top of the TO247 case (its above the whole PCB) ….and this perspex enclosure gets firmly screwed down…so yes, we are thinking we can put some kind of foam in between the TO247 case and the perspex cover, and then as the Perspex cover gets screwed down, it will pressurize the TO247 FET against the big flat heatsink……and that will do the job nicely...we hope...
But what materials can we use for the “foam pad”?
Preferably it will be non electrically conducting, and with a firm springiness so that it can really pressurize the TO247 against the big flat heatsink. Do you know of any such materials?
We have a 4 layer PCB on which we have our offline , all surface mount, LED driver. This PCB sits on a thin thermal pad and this all lies against a big flat heatsink surface. The big flat heatsink is earthed.
Currently we use a D2PAK power FET and have thermal vias going through the PCB to bottom layer thermal copper pour…but this doesn’t give great heat conduction…therefore….
We wish instead to have a TO247 FET lying horizontally, with bent leads, so that it can be soldered as a “SMD” FET…….the TO247 tab will be screwed to a small rectanguloid of aluminium (a heatsink), which, through a small cutout in the PCB, will lie against the thermal pad, and thus give good thermal contact of the FET to the big flat heatsink.
The problem is, we cannot have a threaded hole in the heatsink, so how then will we get sufficient pressure with which to hold the rectanguloid heatsink against the big flat heatsink?….
…well, there is a flat perspex enclosure some 3mm above the top of the TO247 case (its above the whole PCB) ….and this perspex enclosure gets firmly screwed down…so yes, we are thinking we can put some kind of foam in between the TO247 case and the perspex cover, and then as the Perspex cover gets screwed down, it will pressurize the TO247 FET against the big flat heatsink……and that will do the job nicely...we hope...
But what materials can we use for the “foam pad”?
Preferably it will be non electrically conducting, and with a firm springiness so that it can really pressurize the TO247 against the big flat heatsink. Do you know of any such materials?