Definitely Ceramic (Alumina)
Alumina (aluminium oxide) is much better than mica and kapton in conducting heat, see page 25 in EUVL's article for a comparison with 1mm thick alumina.
I find Alumina much more reliable and easier to work with because they are very durable, almost impossible to damage them.
With the softer isolators there's a change to damage them if the edges of the transistor are sharp and the pressure is not evenly spread:
with the bolt on one end of the transistor that edge will get more pressure and will likely cut into the isolator.
I bought some Alumina on AliExpress.
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I deburr the mounting side of the transistor with a couple very light swipes across a fine grit (25 micron) diamond whetstone
before polishing heatsink and transistor with Flitz. Cleanup with isoproopyl & acetone, then mica and Wakefield goop.
Sounds like a great idea. Thank you.
The problem with splitting mica insulators is that you often get changes in levels which creates air gaps. Of course, you are also lowering the breakdown voltage, and you have to know what that is to start with. Why not just buy the correct ones from Keystone?
Kapton tape isn't that good either.
-Chris
Kapton tape isn't that good either.
-Chris
Hi Andrew,
Wanna bet? That would almost assure you of trapped air. There is no way a human can apply thermal compound with that perfect a surface flatness for one. The goal is to displace trapped air, but you'll still have some small air pockets. Add to this a rough surface like casually split mica (as opposed to machine split) and you will have greatly inferior surface conditions than just using the prepared mica you buy pre-cut into shapes.
Extra thermal compound adds it's own special problems and the fluid pressure can crack the attach adhesive or even the die. Over-tightening the hardware on a transistor compounds this problem. So it would see that we mortals should strive to use the best materials (within reason) and practices and accept that even that has imperfections.
If you're going to use Mica, buy the pre-cut forms and use them as they were manufactured. You can cut those down to fit odd shapes, but don't attempt to economise by attempting to split them further. The other issue is that the layers de-laminate throughout the thickness when you attempt to split them. You should see what I've pulled out of amplifiers over the years.
Finally, don't use the thermal compound that is already there. That's just being cheap and pretty silly. It's loaded with dust, dirt and whatever else was floating around in the air over the years. But another way, it doesn't work very well anymore. That stuff is a single use product for the amount you used.
-Chris
Wanna bet? That would almost assure you of trapped air. There is no way a human can apply thermal compound with that perfect a surface flatness for one. The goal is to displace trapped air, but you'll still have some small air pockets. Add to this a rough surface like casually split mica (as opposed to machine split) and you will have greatly inferior surface conditions than just using the prepared mica you buy pre-cut into shapes.
Extra thermal compound adds it's own special problems and the fluid pressure can crack the attach adhesive or even the die. Over-tightening the hardware on a transistor compounds this problem. So it would see that we mortals should strive to use the best materials (within reason) and practices and accept that even that has imperfections.
If you're going to use Mica, buy the pre-cut forms and use them as they were manufactured. You can cut those down to fit odd shapes, but don't attempt to economise by attempting to split them further. The other issue is that the layers de-laminate throughout the thickness when you attempt to split them. You should see what I've pulled out of amplifiers over the years.
Finally, don't use the thermal compound that is already there. That's just being cheap and pretty silly. It's loaded with dust, dirt and whatever else was floating around in the air over the years. But another way, it doesn't work very well anymore. That stuff is a single use product for the amount you used.
-Chris
Kapton is a MIRACLE MATERIAL take a look this link
Kapton: Miracle Material With A Tragic History | Hackaday
Kapton: Miracle Material With A Tragic History | Hackaday
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