OT - Question

Steve Etter

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Steve Etter
Join Date
Apr 2002
Location
Morristown, TN
Posts
965
Got a quick question - When mounting an SCR, there is a white "grease" they put in between it and its mount. Can someone tell me what this "grease" is called?

Thanks.

Steve
 
I call it 'Heatsink compound' - but i'm sure variations will follow...!! (y)

I also use a silicon based oil sometimes.

Rob.
 
APPLY IT SPARINGLY!

You want a very thin film on the device, and on the heatsink. If it 'oozes' out when you clamp them together, it's generally too much.
 
When the two metal pieces (SCR and heatsink) are touching they are only doing so at small points. Viewed on the microscopic level the face of the SCR and the heatsink appear to have massive hills and valleys. Only the 'peaks' of the hills of each device are touching and transferring heat. The purpose of the 'heat sink compound' is to fill in the 'valleys' and provide a better heat transfer path than the air. It only take an incredible thin film. Any more actually forces the 'peaks' apart and makes the heat transfer worse.
 
A little dab 'l do ya. You only want enough to fill the tool marks in the heat sink.

Also I recommend using disposable gloves. Even then it will probably end up on your nose, ears, elbows, and other unexpected places. (I have a much less polite way of explaining this to new techs, but posting it would probably get me spanked here). The stuff starts white but leaves dark gray marks everywhere, and I do mean everywhere.
 
Just to round the topic out, if you are using thermal compound on something like a microprocessor, the white compound is not what you want to use. Spend the extra money for a good silver based compound .

Also, before re-assembling anything that uses a heat transfer compound, REMOVE THE OLD COMPOUND COMPLETELY. Use a fast evaporating solvent if needed, but get rid of the old gunk.
 
An electrical joint compound like EJC #2 is actually better. Heat sink compound is great for heat transfering but is a lousy conductor of electricity.

Thoroughly clean the surfaces of the heat sink(s) and the mating surfaces of the SCR. After doing this, DO NOT TOUCH the surfaces. I have seen too many finger prints on hockey pucks and heat sinks after they failed.

I hope you have tested the snubber circuits.
 
Back when I used to do a lot of overclocking with my pc and really researched thermal compound a lot, the best I came across was Arctic Silver

http://www.frozencpu.com/thr-16.html


It always worked great, and made a noticeable difference in the operating temps. of my cpu.

Again, only put about a "rice grain size" amount on the bottom of the heatsink when attaching to the processor.
 

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