Mica pads for TO22 devices - alternatives
- Thread starter chrisn
- Start date
No. It will go crispy/shrink if it gets warm for any length of time.
Not sure I understand - how is mica messy? How is the mica associated with heat-sinking, other than being an electrical insulator twixt component and sink?
Arkless Electronics
Trade: Amp design and repairs.
I think "messy" refers to the silicone thermal compound... Can't say I've ever found it an issue beyond a mild annoyance now and then... it cleans off hands easy enough with normal detergent. Just try and avoid getting it on clothes.
There are various "sil-pad" type solutions that don't require thermal compound. Look on the sites of the usual component suppliers etc.
There are various "sil-pad" type solutions that don't require thermal compound. Look on the sites of the usual component suppliers etc.
Something like these? (They are rubbery/floppy not solid items)
https://uk.rs-online.com/web/p/thermal-pads/7073361/?sra=pstk
https://uk.rs-online.com/web/p/thermal-pads/7073361/?sra=pstk
Arkless Electronics
Trade: Amp design and repairs.
yes
I’ve used something similar called Keratherm (I think) when I built my old Pass F5 amp. They were recommended over at DIYAudio but the one caveat was you should make sure the face of the transistor is flat. Some MOSFETs I used did have a little burr, but you can carefully sand it flat. Some people apparently had issues where the sharp part puncture the pads and shorted when tightened down. So if you use them maybe check for continuity between the heat sink and the three transistor legs.
When I rebuilt my Sansui I replaced the old flaky mica instead of using pads. It wasn’t hard to do or messy if you got the paste spread thinly and evenly.
When I rebuilt my Sansui I replaced the old flaky mica instead of using pads. It wasn’t hard to do or messy if you got the paste spread thinly and evenly.
The nice thing about mica pads is that they are harder to puncture than the silicone alternatives with slight burrs on transistors/heatsinks, and still very good thermal performance if you know just the right amount of thermal paste to apply (clue - if it seeps out the sides you used too much). Practice is the key, as usual. I find nothing about them fiddly (you're doing electronics, it's all fiddly!), and never had any crack on me - if one delaminates then just bin it and get another out of the bag, hell they're cheap enough. Get some decent ones from Rapid Electronics etc, and avoid cheap crap from Ebay/Amazon etc. Applies to many things in life really, doesn't it?
a.palfreyman
pfm Member
You just need a few 'dots' of compound. I like to apply just enough to get a very slight edge seepage. That way you know you're OK. If you get a lot oozing out then as S_J says, yes you have too much. Also, some are electrically (as well as thermally) conductive. Have a practice. I find that it is best to press in place first with a finger so you can see how much oozes out. Too much, remove clean with a tissue and try again. Two or three goes and you should get it.
Worst thing for me is 'fat finger syndrome' so just use tweezers, apply a few dots to the transistor, stick the pad in place, a few dots to the pad and then position the transistor roughly in place, pop a bolt (with insulator) through to align, then press in place with a finger. If all looks good, tighten up.
Worst thing for me is 'fat finger syndrome' so just use tweezers, apply a few dots to the transistor, stick the pad in place, a few dots to the pad and then position the transistor roughly in place, pop a bolt (with insulator) through to align, then press in place with a finger. If all looks good, tighten up.