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CPU thermal paste for MOSFET?

nyhifihead

nyhifihead

Well-Known Member
Hey all I've noticed the hafler p7000 class a/b MOSFET I've had on duty powering the 2 12" low end in my NHT 3.3s has been running very hot.

The thermal protection light hasn't gone on even under heavy load but I know it can run cooler. Its 8x MOSFET transistors per channel that run in an atypical actively cooled setup.

Air is pushed back to front from the rear fans and the hot air blows out the front. The mosfets share a pseudo aluminum heatsink next to some case vents.

Under the aluminum strip there's some white caked up thermal paste due for a refresh, I'm wondering if CPU liquid silver paste would work on these between the MOSFET and aluminium

Here's a pic for reference.
I also ordered some Korean 60mm silent fans to replace the stock ones that are pretty noisey

P7000.jpg
 
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No conductive paste should go near any devices that rely on insulators to keep their metal cases electrically isolated while thermally conductive. Its a recipe for disaster.

If you need to refresh the thermal paste, use non-conductive thermal paste or, better yet, silicon pads to replace the mica and paste combo. Here's an AK thread on the topic.

Cheers,

David
 
dshoaf said:
No conductive paste should go near any devices that rely on insulators to keep their metal cases electrically isolated while thermally conductive. Its a recipe for disaster.

If you need to refresh the thermal paste, use non-conductive thermal paste or, better yet, silicon pads to replace the mica and paste combo. Here's an AK thread on the topic.

Cheers,

David
Click to expand...

thanks. I will look into the sil pads appropriate for my amp. Its nice having this thing as a space heater in the winter but I want it to last!
 
Do you have the SM and an infrared temp gun? If yes, see if there's a running temp range in it. Mosfets can run hotter than other transistor types.
 
I like the better grades of Sil-Pads for medium power amps, but if the unit runs hot and/or is capable of big dissipation, I still go with grease. Also go with grease on fully insulated plastic transistors, as they need all the help they can get.
 
Ds2000 said:
Do you have the SM and an infrared temp gun? If yes, see if there's a running temp range in it. Mosfets can run hotter than other transistor types.
Click to expand...

I do have the SM. N channel are 2SK2221 and P channel are 2SJ352. hitachi transsitors. operating temp according to digikey is 150C. I will be able to pick up a IR temp gun froma friend tomorrow and poke around inside to see what im dealing with..
 
In the past I was using silver based heat sink compound for NON computer ELECTRONIC uses and had even tested fresh past for conductive tendencies and found it to be (at first) non conductive.
Over time it caused short circuits on the output stages attached to ground (possibly due to evaporation of the silicon-like fluid keeping the paste "spreadable").
It seems like when the silver based paste dries out it becomes conductive (not an issue with non-energised cpu heat sink situations).

Bottom line- Don't use silver paste on powered output stages amplifiers!

Mark T.
 
Someone here recommended Avvid Thermalcote I for this purpose (thermally conductive but electrically non-conductive) and I've been very pleased with the results. The big tip, in my mind, is the 2oz tube (part number 250G) is only $1 more expensive than the 1oz tube.

Thermalcote™ Thermal Grease
Thermalcote (Part #: 249, 250G, 251G, 252G, and 253G)
Thermalcote™ is a superior silicone-based thermal joint compound uniquely developed to increase heat transfer to all heat sinks. Thermalcote’s thermal conductivity is more than 15 times that of air and more than 4 times the conductivity of typical silicone-based greases. It is non-toxic and extremely stable; it neither cakes nor runs between -40°C to 204°C.​
 
I've used Arctic Silver MX-4 paste on a amp, it's none conductive and worked pretty well, just expensive.
 
They carry the overpriced 1oz tube, part number 249G. A search with 250G comes up with a bunch of results from partial part numbers, none of which are heatsink grease.
 
Enter '250G', Aavid's part number, and you get gibberish back. Best to show Mouser's PN: 532-250

I only showed the 1oz tube because I could NOT find the other. And I'm generally pretty adept at wading through Digikey's and Mouser's website.
 
EchoWars said:
Enter '250G', Aavid's part number, and you get gibberish back. Best to show Mouser's PN: 532-250

I only showed the 1oz tube because I could NOT find the other. And I'm generally pretty adept at wading through Digikey's and Mouser's website.
Click to expand...

You're right; I was trying to avoid making a direct link so as to not trip over any AK rules about commercial sites, but it would have been more clear if I had used the Mouser part number 532-250 instead of the Aavid one.

If you use the 250G Aavid part number in the Mouser search box, it does show up when you click through on the Chemicals section.

The points I was trying to make were: Mouser does carry it, the 1oz version is indeed overpriced, but the 2oz version is a good value. I would have mistakenly bought the overpriced one if someone hadn't overtly pointed this out to me last year, so I was trying to pass the tip along to others.
 
I agree with Conrad.. sil pads are okay but limited to heat long term. Unless a device is say ground okay like a voltage ic and the type you might see with a mini heat sink? or someone added one.. the conductive stuff is okay like use for cpu heat transfer.. artic silver was used by many for overclocking and probably still is. But I have seen that silver' brand go hard or not applied well, too.
 
dlucy said:
I was trying to avoid making a direct link so as to not trip over any AK rules about commercial sites,
Click to expand...
No problem with posting a link or a part number for such a thing. The only issue is with eBay and Craigslist links (and other similar consumer oriented selling venues).
 
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