A question regarding thermal adhesives

[neil_kaye]

I am planning on using Artic Silver Thermal Adhesive to attach my Mosfets and Jfets to their appropriate heatsinks.
The chips need to be electrically isolated from the heatsinks, so i have the following questions:
1. Would a thin layer of Thermal adhesive (which is non conductive) plus the anodizing on the chassis be enough to stop the Fets from shorting?
I have silicone pads which i can use to further isolate the FETS but Artic Silver recommends against this; the theory being, why add more thermal resistance if you don't need it.

Any experience in regards to this?

[Geek]

Hi,

Originally posted by neil_kaye
1. Would a thin layer of Thermal adhesive (which is non conductive) plus the anodizing on the chassis be enough to stop the Fets from shorting?

Probably not, unless it specifies this.

Originally posted by neil_kaye
I have silicone pads which i can use to further isolate the FETS but Artic Silver recommends against this; the theory being, why add more thermal resistance if you don't need it.

Yeah, thermal pads are crummy for higher power applications. Mixing any grease or adhesive and thermal pads is a no-no. Has to be either or.

Thin sheet of mica would be what I'd use.

[neil_kaye]

Thanks.
Do you have an online source for Mica?

[pinkmouse]

Any load on the mica and it will shear. I'd stick to bolts.

[neil_kaye]

I am going to give Artic Alumina a try: http://www.arcticsilver.com/arctic_a...l_adhesive.htm

It is completely non conductive so it should eliminate the need to additional thermal taps or pads

[Pit Hinder]

Al,
mica was b****y good when nothing else was available. I'm 53 and my grandfather told me to keep away from that oldfashioned *beep* from his appreticeship days.

Pit

[pinkmouse]

Yup. Mica is pretty good as an insulator. It's pretty strong in compression, but tension or lateral shear will delaminate it very easily. Glue on each side will lead to exactly this situation, which is why bolts, that hold it in compression, are the best bet.

[theAnonymous1]

www.mcmaster.com carries all kinds of mica. I bought some from them a few years ago for an amp. It can get a bit messy putting heat goop on both sides though.

[AndrewT]

Hi,
mica with thermal compound on both sides performs very well and even better if you can get 0.001inch thick insulators. Many are 0.004 to 0.006inch.
A few of the self adhesive dry insulators perform better than mica but tend to be at the expensive end of the range.
The cheaper dry insulators usually perform worse than mica.
Compare the numbers/prices.

All anodise is a good insulator IF UNDAMAGED.
Some of the softer and thinner anodised surfaces scratch very easily. Be prepared for a few failures if you do not use insulators.
You can test before making the semis live. An elevated voltage between collector/drain and sink will prove it.

[Geek]

Originally posted by pinkmouse
Yup. Mica is pretty good as an insulator. It's pretty strong in compression, but tension or lateral shear will delaminate it very easily.

Yes, indeed!

Don't pick up the device by the heatsink