| Wavebourn |
| I traditionally use mica pads, but more and more I see silicone pads under transistors. What are resulting thermal resistances, if to compare? |
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| Netlist |
Here's an interesting thread about the subject.
/Hugo |
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| Wavebourn |
| quote: | Originally posted by Netlist
Here's an interesting thread about the subject.
/Hugo |
Thanks Hugo, great topic!!! |
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| XEAGLEKEEPER |
| 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 ? |
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| EUVL |
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 |
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| Wavebourn |
| quote: | Originally posted by XEAGLEKEEPER
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 ? |
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. |
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| john_ellis |
Hi all
see my note on the Pass Labs thread, mentioned "here" by Hugo.
John |
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| AndrewT |
Hi Wave,
they are not silicone pads.
Try using some other names in your searching. |
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| Stocker |
| quote: | Originally posted by EUVL
But then diamond is even better, isn't it ?
Patrick |
:D hey can I borrow your CVD chamber to lay a coat of diamond on my anodized heatsink? ;) |
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| BlackCatSound |
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. |
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| Wavebourn |
| quote: | Originally posted by BlackCatSound
Bergquist make kapton and also Boron nitride loaded silicon pre-cut transistor insulators.
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How do they look? |
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| XEAGLEKEEPER |
| 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 . |
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| Wavebourn |
| quote: | Originally posted by XEAGLEKEEPER
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 . |
They look to me attrcative too, because of the same reason, but what about thermal conductivity, is it the same? |
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| XEAGLEKEEPER |
| 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. |
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| EUVL |
> 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 |
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| AndrewT |
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. |
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| peranders |
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. |
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| BlackCatSound |
| Sil-pads are berquists cheapest. |
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| EchoWars |
| I use the K10's from Bergquist from time to time. Kinda $pendy, but they do a great job. |
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| P.Lacombe |
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 ;-) |
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| EUVL |
> 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 ?
I just checked with a friend in the ceramic business.
According to him, no one in the trade will touch Beryllium Oxide these days. The powder is more toxic than asbestos; there are companies who are still paying off millions of compensations to workers exposed to the stuff, and the buildings formerly used to manufacture the substrates had to be torned down with toxic disposal.
So I guess that leaves us only Aluminium nitirde, like I mentioned in the Pass forum.
http://www.diyaudio.com/forums/show...023#post1032023
Patrick |
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| Workhorse |
Hi Folks,
I have several KAPTON sheets measuring about 22 X 22 inches, Could they be used as insulators for Semiconductors and is it fine to replace the MICA or SILPAD, with my Kapton alternatives...
K a n w a r:) |
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| AndrewT |
Hi Workhorse,
Kapton is just perfect as an electrical insulator. I believe it is a special hi temp version of polyethylene but please correct me if this is wrong.
The Kapton sheet should be 0.002inch or less. Some sheet is thinner than the adhesive they apply to one face.
If thicker Kapton is used the thermal resistance is too high for high heat flow duties. Use thinner (0.001inch) if available.
Due to the smooth and fairly hard surface of Kapton it must be used with thermal compound on both sides (just like Mica) or on the clean side if adhesive is applied to the other side. |
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