Isolation for heatsink..looking for advise.

[tallerseverino]

Hi there.

I'm finally on the stage of installing the output trt's on my p101 project and now I'm having trouble with the heatsink/trt's isolation.

I have micas, sil-pads, something called "elastomeros" in spanish and about this one I cannot find information, the seller told me the "elastomeros" don't need silicon grease and should work fine.

It's the High power version, and Rod elliot doesn't recommend sil-pads, but I don't know the english word for "elastomeros".

I have the three of them, the "elastomeros" are gray-ish in colour and not rigid at all. Since the p101 attach the amp to the heatsink pretty hard, and almost impossible to put the fingers on the trt's once installed (bad idea, i know since the mosfets are sensitive to this "brute" testing), I always used micas, but recently I had a mica deffective and burnt the output trt's along with the driver.

Should I try these "Elastomeros"? Or go old-fashioned with micas?

[jacco vermeulen]

Go for Mica and grease.

Elastomer insulators have pretty good thermal conductivity, unfortunately they are rather thick, which makes the C/W number inferior to Mica.

[Bazukaz]

"Elastomeros" is likely a "silicone rubber washer" in English.
It is not the best for thermal conductivity.
As far as I know mica+thermal compound outperforms silicone washers if not too thick.

Lukas.

[Tekko]

Sil-Pad as the trade name for silicon rubber insulators is, is about the worst.
Mica is better but aluminum oxide insulators are the best, but they are also the priciest wheres mica is among the cheapest.

[jacco vermeulen]

Originally Posted by Tekko

aluminum oxide insulators are the best

I've used AlO2 insulators from the mid '80s (thick ones) till a few years ago (thin ones from Avid Thermalloy).
There's better nowadays, and it's pretty in pink

(compliments go to EUVL)

[Tekko]

I've never seen pink AlO insulators, only bluetac color and white, but then again i only used them once.

[jacco vermeulen]

The Pink refers to Kerafol 86/82, the sheets which are on all sides of the text i posted.

(would have thought they were hard to miss)

[Tekko]

*d'oh*

[effebi]

Originally Posted by jacco vermeulen

I've used AlO2 insulators from the mid '80s (thick ones) till a few years ago (thin ones from Avid Thermalloy).
There's better nowadays, and it's pretty in pink

(compliments go to EUVL)

Very intereresting, Jacco.
So this means this time ESP is wrong recommending Kapton ( I believe they also sell a tape of that material).
BTW what about the source of your numbers?
a) Scientific paper subjet to peer review (i.e. IEEE)
b) Commercial (then, most probably biased)
c) Own measurements

Personally I have mixed experience about insulators.
I believe the mounting is of the max importance, insulators come second. I mean a hex socket screw with a large washer and or better a large plate ensures very good results on modern plastic flats.
I have very good experience with the sili pads (3M) for series production stuff, since the result is very repeatable.
Mica is good if you do it carefully one by one with a good compound, but prone to mistakes and random bad pieces. BTW I could never find precut micas for nothing else that old TO3 or TO 220 / 126 and is difficult to cut by hand.
Kapton I used only once for hobby where I could not find nothing else and it is working so far. It didn´t feel so bad as your numbers would show, but, again, the mounting was accurate. I am thinking to make some measurements and tests, now that I know.

[tallerseverino]

I didn't know Rod sells the Kepton isolators. I sent him an e-mail, It was stupid of me not to ask when i purchased the p101 pcb.

Anyways, most of the isolators you recommend are not available in Spain, If anyone knows where to find them in the EU, please let me know.

Thanks again.