Power Transistor Insulation

[Audiocrase]

Alumina is a remarkably strong ceramic and not easy to break or crack. It does need to mount on a flat surface, but really, the surface needs to be flat on any heatsink if its going to work decently. Ive just used the as-received surface on black anodized heatsinks.

That's where the Sil-Pad shines, It can take up a little bit of unevenness of the surface as it is compressible.

I think 0.35deg/W of the SP600 is very hard to beat after you add the grease.

 

[djk]

" It can take up a little bit of unevenness of the surface as it is compressible."

That's what the grease is for, white for rough surfaces, clear for flat.

If you repair a clear grease piece, you must re-surface or use white grease.

 

[SamAnytime]

If you have a lot of heat to dissipate, consider mounting the transistor without insulation, just grease, on a metal plate, and then bolt that plate onto the heatsink with a silicone pad. The larger contact area between the metal plate and the heatsink will bring down the thermal resistance.

You also get ISO packages for certain transistors that are insulated from the case - no insulating pad needed. The published thermal resistance is higher than for the non-insulated version, but the overall thermal resistance is often better than with the conventional approach, especially in a production environment where this kind of work is often done by unskilled/semi-skilled labour.