I traditionally use mica pads, but more and more I see silicone pads under transistors. What are resulting thermal resistances, if to compare?
Has anyone ever used beryllium oxide isolators ? Beryllium oxide is carcinogenic and poses health risks if inhaled. I know it is used in traveling wave tubes TWT's for rapid heat transfer to cold plates in Hi-power RF amplifiers( mil-aircraft). Any thoughts ?
Beryllia is great stuff, even better than Aluminium Nitride. If you know a source to get thin substrates at affordable prices, please let us know.
But then diamond is even better, isn't it ?
Patrick
But then diamond is even better, isn't it ?
Patrick
XEAGLEKEEPER said:
I used berillium ceramic for hybrid ICs. Also, long time ago I had mil spec TO-3 pads made of berillium ceramic. But I don't remember details.
Why I started the thread, silicone pads look attractive, and I wandered, what if to use them instead of mica pads.
Bergquist make kapton and also Boron nitride loaded silicon pre-cut transistor insulators.
5-6x the thermal conductivity of the gray rubbery pads, but about the same increase in cost.
Still, FAR cleaner than any of the thermal goops.
5-6x the thermal conductivity of the gray rubbery pads, but about the same increase in cost.
Still, FAR cleaner than any of the thermal goops.
I've used both the mica/silicone compound and the sil-pads. I like the sil-pads due to ease of installation and no white silicone grease everywhere its not suppose to be .
XEAGLEKEEPER said:
They look to me attrcative too, because of the same reason, but what about thermal conductivity, is it the same?
I'm not sure. Of course the Sil-pad manufacturer claims they are. I haven't burnt-up any output devices yet. Thats what I used with my ESP P101's.
> hey can I borrow your CVD chamber to lay a coat of diamond on my anodized heatsink?
Actually since you mentioned, I do have access to one.
Thanks for the tip.
: )
Patrick
Actually since you mentioned, I do have access to one.
Thanks for the tip.
: )
Patrick
Hi,
the thermally conductive pads have a large variation in thermal performance.
A ratio of 3:1 is common from best to worst.
The worst is much worse than 0.002inch mica and thermal grease on both sides. But better than mica put in dry.
Choose carefully. Performance seems to be proportional to price.
the thermally conductive pads have a large variation in thermal performance.
A ratio of 3:1 is common from best to worst.
The worst is much worse than 0.002inch mica and thermal grease on both sides. But better than mica put in dry.
Choose carefully. Performance seems to be proportional to price.
I have used all types exepct for those white alumnium oxide and I must say I'll prefer silcone rubber, no mess with heat compound.
Wavebourn, what is your application? If it's medium duty any type will do.
Wavebourn, what is your application? If it's medium duty any type will do.
AndrewT is right !
I always use mica for audio amplifiers, because of the critical importance of the thermal transfer, in order to reduce thermal transient intermodulation distorsion (class B).
But silicon pads are more secure for high voltage, switching power supplies, video amplifiers, etc.
Mica pads necessite more precise surface machining than silicon pads, for both transistor and heatsink. Carefully inspection and cleaning are essential !
Apologies for mispelling and other barbarisms ;-)
I always use mica for audio amplifiers, because of the critical importance of the thermal transfer, in order to reduce thermal transient intermodulation distorsion (class B).
But silicon pads are more secure for high voltage, switching power supplies, video amplifiers, etc.
Mica pads necessite more precise surface machining than silicon pads, for both transistor and heatsink. Carefully inspection and cleaning are essential !
Apologies for mispelling and other barbarisms ;-)
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