Quote:
Originally Posted by tw
Thermal compound must be applied so sparingly so that most of a CPU makes direct contact with the heatsink. Thermal compound has higher thermal resistance - means less heat transfer.
Best thermal interface is when most of the CPU makes direct contact with a heatsink. Some microscopic holes will exist. A CPU to air pocket to heatsink has even higher thermal resistance (also called an insulator). Only enough thermal compound must be applies to fill these fewer air pockets. Thermal resistance that is higher than the direct 'CPU to heatsink' interface, but more conductive than air.
How sparingly? No thermal compound should spread out to the outer edges of the CPU to heatsink interface for numerous reasons. One is because most all heat transfers occur in the center. Another is that thermal compound outside that interface can create electrical problems and computer instability. Apply only enough thermal compound so that is spreads out in the center half of that interface.
How to discover the quality of a heatsink. All computers must work just fine with the heatsink attached using no thermal compound. Some manufacturers make heatsinks so poorly machined that thermal compound is necessary. The experiment is quite simple. First operate the computer with a heatsink and no thermal compound. Then repeat the experiment with thermal compound. If the heatsink was properly machines, then thermal compound should only create a less than 10 degree temperature reduction. Trivial. But some heatsinks (especially those without the necessary degree C per watt parameter) are not properly machined.
We tell everyone to always use thermal compound. Trying to explain reality to a majority of computer assemblers is virtually impossible. Trying to get them to even ask for the degree per watt numbers is futile. They only understand sound bytes. So they are told to always use thermal compound.
Then Arctic Silver gets them to spend massively for the same compound. People who fear numbers love to be scammed; even believed that Saddam had WMDs.
Bottom line – use as little thermal compound as possible so that only the center half of a CPU to heatsink interface is coated. If thermal compound squeezes out to the edge, then a *worse* (less) thermal conductivity exists.
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You're right. I didn't intend to say "more is better" I just thought it could have become, for lack of a more specific description, "messed-up" somehow once it was confirmed that the heatsick wasn't actually making a good physical connection.
Incidentally,
Quote:
Originally Posted by richlevy
I finally tried pushing down very hard on the heat sink. I heard a click...
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If you have Socket 775 you should be confirming FOUR CLICKS. Furthermore: each damn click could possibly UN-CLICK one of the previous clicks. I've had a hell of a time getting one of these bastards to get all the way attached. It can take two sets of hands.