A question about lapping the heatsink

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Wrathh

Limp Gawd
Joined
Oct 23, 2004
Messages
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I'm not sure I understand the purpose behind this. An unlapped or "rough" surface would provide more surface area for heat disipation (and assuming you are using some kind of thermal paste/grease/silver) for heat transmission between the cpu and the block.

Could someone clarify this for me please?
 
The heatsinks and waterblocks are made to transfer heat from the processor to the heatsink or waterblock. If you have less contact, you're getting less heat transfer. Thermal paste is just an extra precaution to take to make sure you're getting 100% contact since it fills in the microscopic holes and rivets you would have missed while lapping.

You want full contact, and you can't do that with a rough surface.
 
but rough surface with spikes and valleys (eg surface of moon) will minimalize the surface of contact between the cpu and the heatsink...

thermal paste no matter how good it is, is still an insulator compared to metal (heatsink). just that better thermal paste (eg. AS5) have better heat transfer properties than other generic thermal paste.

your theory of heat dissipation on true for heatsink design where rough surface have more surface area for heat dissipation through air, but not true for contact heat transfer between 2 solid objects.
 
no it doesnt give more surface area as even silver paste isnt 100% heat conductive the peaks and valleys between the hs and core cause pockets of air or paste in the solution of perfect flat not being able to be achieved. On some heatsinks the bottoms are concave even scratched some have machine grinding such as the sk-7 form thirmal right if you drag your fingernail over it it is not smooth at all. Some are so concave the bottoms only touch the corners of the processor some procesors are concave too those with the metal covers sometimes are and some people lap them...
 
Rough surface = less surface area contact. It's simple. You want the most contact, so you want the smoothest and flatest surface. You just use AS5 to fill in the valleys you can't see and can't get rid of.
 
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