Mosfet heat sink- good contact or not?

[crazedm11]

Alright, kind of an odd question here. So I decided to replace the thermal pad on my mosfets with some thermal adhesive, but after further inspection of the mosfets, some are more elevated than others. Meaning that the heat sink will only make contact with half of them, being the shorter ones. But, I'd already modified the heat sink for the adhesive, so I couldn't put it back on with a thermal pad. So after I glued the heat sink on, according to hw monitor, the temps are still 10 degrees lower. I don't believe it at all. Or maybe it's correct? Are the shorter "mosfets" really mosfets? It seems kind of odd to have some taller than others. My motherboard is an MSI 970 Gaming. Any thoughts?

 

[BFG-9000]

Thermal epoxy transfers heat better than any thermal pad. And if you think about it, even the large gap it's filling now is no worse than it was with the pad.

The only trouble is if one Mosfet ever burns out, you'll end up destroying many of them to get that heatsink back off in order to even test them. Your mosfets are these 32 squares, right?

Heatsink and pad:

 

[crazedm11]

Thermal epoxy transfers heat better than any thermal pad. And if you think about it, even the large gap it's filling now is no worse than it was with the pad.

The only trouble is if one Mosfet ever burns out, you'll end up destroying many of them to get that heatsink back off in order to even test them. Your mosfets are these 32 squares, right?

Heatsink and pad:

Yes, but every other mosfet is a lot taller than the last, So only half of them have contact with the heatsink. I just thought it was weird to have them designed like that, because of the problem I'm having. Even with the thermal pad, the shorter ones weren't covered well, judging by the indentments on the pad. odd how in the picture they all had contact.

 

[Karadjgne]

You assume they are all the same mosfets. Msi probably has a mixed bunch in there, 2 different sizes, and was relying on the heatsink to be tight enough to make contact with all of them. Contact doesn't necessarily have to be uber firm, just slightly firm works.

I had to pull the heatsink off a gpu once, what was underneath was more like double sided sticky tape than any kind of thermal pad.

 

[crazedm11]

You assume they are all the same mosfets. Msi probably has a mixed bunch in there, 2 different sizes, and was relying on the heatsink to be tight enough to make contact with all of them. Contact doesn't necessarily have to be uber firm, just slightly firm works.

I had to pull the heatsink off a gpu once, what was underneath was more like double sided sticky tape than any kind of thermal pad.

Yeah, that's kind of a dumb design to be honest. And the big thing is, the shorter ones aren't making contact at all. I guess I need to either find the stock heatsink and use a thermal pad, or buy some new ones.

 

[Karadjgne]

Well the mosfets have certain spec ranges, so to cover the necessary voltages will require specific mosfets. Also back then, 3.3v and 5v were more prevalent in pc usage, so you'll have mosfets for cpu 3.3v and it's higher amps, mosfets for 5v and it's higher amps and mosfets for 12v and it's lower amps. Can't run all that through the same mosfets. But real estate around the cpu is at a premium, so you cram all the mosfets together, under the same heatsink and use a thicker thermal pad to contact all, vrs separately, requiring 2x heatsinks, more space, different trace routing etc. It's a major undertaking to re-trace a mobo design. All for the sake of better mosfet heatsink contact.

Depends. If you are any good with working metal, you could get a larger heatsink and shave off the areas where the screws are, and where the taller mosfets sit, leaving stock height where the shorter mosfets are. This would have the net affect of having crenelations that would fit the various drops when screwed down.

 

[crazedm11]

Well the mosfets have certain spec ranges, so to cover the necessary voltages will require specific mosfets. Also back then, 3.3v and 5v were more prevalent in pc usage, so you'll have mosfets for cpu 3.3v and it's higher amps, mosfets for 5v and it's higher amps and mosfets for 12v and it's lower amps. Can't run all that through the same mosfets. But real estate around the cpu is at a premium, so you cram all the mosfets together, under the same heatsink and use a thicker thermal pad to contact all, vrs separately, requiring 2x heatsinks, more space, different trace routing etc. It's a major undertaking to re-trace a mobo design. All for the sake of better mosfet heatsink contact.

Depends. If you are any good with working metal, you could get a larger heatsink and shave off the areas where the screws are, and where the taller mosfets sit, leaving stock height where the shorter mosfets are. This would have the net affect of having crenelations that would fit the various drops when screwed down.

Okay, that makes sense. I don't really have the tools necessary to do what you described, though. And the only mosfet heatsinks I've found are dinky little copper ones that are way too expensive for what they are.