Popular Post Chriull Posted June 10, 2022 Popular Post Share Posted June 10, 2022 (edited) ... for power mosfets mounted with thermal pads on a heatsink as done with EUCs. TLDR: Don't use it! Better use too little than too much! (see my next post here for details) It hinders thermal conductivity. It's just a mess. All those little syringes sold for CPUs are just overpriced. Especially the super duper silver enriched pastes ... If one likes to play with sticky gooey overpriced stuff - do it, but spare the poor EUCs How to mount a mosfet to a heatsink if one needs them electricly insulated: What insulators are normally used/available: aluminium oxide ceramics, mica plates or thermal pads. The ceramics are the best, mica is second and thermal pads afaik are the worst, some competing with mica. But all three have worse thermal condictivity than metal, so one uses them as thin as possible. If one uses "hard" materials like the ceramic or mica, there always will be some microvoluminas filled with air where the surfaces do not touch. No matter how precise the materials are produced and polished. Air is a real great thermal insulator - so one uses some paste to just fill this micro gaps! These pastes are sold under the name "thermal paste", but they do not deserve this name - they have shitty thermal conductivity, just better than air! But every little bit too much thermal paste, that comes between the metal and the insulator hinders the heat transfer to the heatsink! If one uses a thermal pad, they are made from elastic materials like some silicone mixtures. They are "squeezed" between the mosfet and heatsink so they by themselves fill these little microgaps so no air is anymore trapped in there. Every, as minimal amount of thermal paste, which always has worse conducitivity than the pad will hinder heat transfer again! And it can cancel an imortant advantage of the thermal pads - they stay elastic, thermal paste sometimes gets hard and crumbles within the gaps... But what if there is a visible gap between the power mosfet and the heatsink? Don't one need to fill this with some thermal grease? No - if there is a visible gap it's a grave design/manufacturing fault! No thermal pad/grease can repair this - this mosfet cannot perform powerwise as the heat cannot be efficiently transfered to the heatsink. Never. There still are some special products, like thermal pads which melt at first use and by this fill all gaps. And who knows what not - but afaik these three are the most common used materials. Comments, additions and corrections are heartly welcome! Edited July 13, 2022 by Chriull 6 1 Quote Link to comment Share on other sites More sharing options...
Chriull Posted July 13, 2022 Author Share Posted July 13, 2022 (edited) On 6/10/2022 at 5:14 PM, Chriull said: ... for power mosfets mounted with thermal pads on a heatsink as done with EUCs. TLDR: Don't use it! An update since @RagingGrandpajust posted a link to @EcoDrift's teardown of the V12HT in Some of the manufacturer application notes imply that the use of a minimal amount of thermal paste with thermal pads can improve the thermal conductivity a little bit. This pictures of the V12HT can be taken as perfect example of thermal paste dosage! For thermal paste dosage with some hard insulator like mica, kapton, aluminium oxide ceramic plates it would be a little too less, as not the whole surface is covered, but for thermal pads it's really lovely! As used here in case it does not help it for sure will not make it worse! Edit: PS: Still better to use no thermal paste than put a huge blob as unfortionately shown in many assembly video guides... ;( Edited July 13, 2022 by Chriull 1 Quote Link to comment Share on other sites More sharing options...
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