Hi,
To attach an LM317 (for example) in the TO-220 format to the corresponding heat sink (see link below), is it useful to apply any thermal paste in addition to the flexible mat that comes with the heat sink?
Thanks.
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I would :-)
How much heat are you dissipating? (can you float the heat sink?) I usually don't use any thermal paste with a sil pad.
George H.
Me too. But only apply very, very sparingly.
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Agreed, also I missed the power dissipation angle. If it was only low power it's not worth the effort.
Good point. If the load is light enough he doesn't need an additional heat sink at all.
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I'd compare it to a real silpad and see. If the pad itself has poor thermal conductivity, grease won't help.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
I'd use paste only, unless an electrical connection between regulator and heatsink would cause problems. That rubber stuff is for when you need an insulator between the TO220 and the heatsink.
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That's why I prefer the old mica pads.
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Mica is OK, and so is hard anodized aluminum plus grease.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Not if you need electrical isolation.
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Works fine up to a few hundred volts--there are commercial thermal insulators made that way. YCLIU.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
The only reason I know of to use mica or the anoidized aluminum plus grease for them is when you need electrical isolation, otherwise just use the grease or one of the rubber type pads. The pads are good for isolation or heat transfer.
Hopefully both, but either way they're inferior to mica + good HS grease. A lot cleaner and more convenient though!
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
** The TO220 heatsinks in the pic are only good for a couple of watts in free air - so device dissipation is low.
Device temp will only vary a few degrees using different mounting interfaces.
... Phil
You are right of course, if it were I and there was sufficient clearance there is no need for the insulation but there is scant info on the power rating etc.
Is mica any better than a sil pad? I thought it was worse. I found this,
George H.
It may depend on the type of pad. The best pads seem to be slightly better than the mica/grease. They are almost the same,so I would guess that whoever does the testing and maybe the material makes the difference.
OK the only thing I ever tested was a sil pad versus Kapton tape. (TO-220) I didn't use any goop on the tape. (and it was tape with a layer of adhesive on one side.) The sil pad worked better. I think it was 1 mil tape (0.001"), but we have 2 mil tape too and it might have been that.
George H.
I thought Kapton was more of a heat insulator. I have only used it as a heat shield when using the hot air wand on surface mounted devices so don't know much about its properties.
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