Mica newb question...

[monkeyevil]

Please excuse my ignorance, but I should be using a dab of heat transfer grease between both the mica and the case, and the mica and the transistor, correct?

Using this kit
4880MG Aavid Thermalloy Heatsinks

Should I put it between the case and the external sink as well?

Steel case and anodized sinks...
Standard Products Found

Thanks!

[mickeymoose]

With the Thermasil or the Thermafilm a thermal compound should not be needed.
With mica you would smear a thin film of the compound on each side of the mica pad to aid heat transfer. E

[BrianVG]

When you often heat the transistors and they go trough their 'thermal cycle' (ambient-operation-ambient temperatures)often, they will act as a bimetal with your heatsinks. It will create little gaps. After a while these gaps get bigger,so less heat is transferred and so on.
I use thermal paste which gets a bit fluid when it heats up=>fills gap

Anodized= isolated, so no need for mica if you use paste.

[jaycee]

4880MG is mica, so yes you need paste on both sides of the pad. BTW, 4880MG is TO-220 pads and your heatsinks are for TO-3 transistors.

Whether you should use paste between the case and the heatsink depends on whether the transistors are mounted on the heatsink, and then onto the case, or not.

[AndrewT]

If one wants to transfer heat quickly, then air must be excluded from all interfaces across which the heat needs to pass.

[HighTec]

Speaking of which, I bought this tube of crappy thermal grease. It's ok but the problem is that it has a high viscosity and starts to melt at a rather low temperatures. Actually, the damn thing begins to seep and collect under the heatsink. So, guys, which thermal grease do you use? Can you recommend me some real stuff?

Edit: what about Dow Corning 340 thermal compound?

[monkeyevil]

Originally Posted by jaycee

4880MG is mica, so yes you need paste on both sides of the pad. BTW, 4880MG is TO-220 pads and your heatsinks are for TO-3 transistors.

Whether you should use paste between the case and the heatsink depends on whether the transistors are mounted on the heatsink, and then onto the case, or not.

This is actually for a headphone hybrid (Starving Student) and my first forte into case design.

I have the transistors mounted to the underside of the case, and the sink mounted to the topside. So it goes transistor, mica, case, sink.

Not much heat is getting into the sinks currently, and I need to go back and introduce thermal paste.

Is it a poor design to assume the heat will transfer from the case into the sinks?





All finished.

[jaycee]

No that is fine, but yes you should have thermal paste between the heat sinks and the casing.

Are those transistors getting hot? If you can't keep your finger on them, then they're too hot. The case itself might be an adequate heat sink in itself. I couldn't say without seeing the design. You should have transistor, paste, mica, paste, case, paste, heatsink.

Looks nice BTW

[mickeymoose]

Ah, Blue Beauty! E