Four of the big things about an effective heat sink.
1. Mass. How much metal is in it?
2. Thermal conductivity. How fast does heat energy move through it?
3. Surface area. How much surface area in comparison to the mass?
4. Radiation. How well does heat escape the surface via infra-red energy?
Generally a more massive heat sink is better than a lighter one. But a lighter
sink with more total surface area can out perform a heavier one.
A massive cube of metal would work very well, until it's saturated with heat in
a few seconds. Remove half the mass but drastically increase the surface area
and it will work much better.
Copper has a much higher conductivity (thermal and electrical) than aluminum,
but how well it radiates is less than aluminum. This is why heat sinks with a
copper base topped by an aluminum plate and fins work better than an equivalent
mass/area all aluminum style.
The copper base spreads the heat sideways away from the CPU core more
efficiently while the aluminum on top radiates the heat more efficiently.
This is especially important for "flip chip" designs where all the heat must
transfer through a one square centimeter or smaller patch of the CPU die.
Airflow is also very important. The moving air molecules are directly heated by
the infra red radiant energy and also by conduction from direct contact with
the surface of the heat sink. The more surface area, the more efficient the
transfer of heat to the air.
Even a light coating of dust will reduce the conduction and radiation
efficiency.
What I do with heat sinks is remove the fan and other non-metal parts and mask
off a spot on the base just large enough to cover the chip contact area.
Ordinary masking tape works fine.
Then I put the heat sink in my glass bead blasting cabinet and rough up the
whole thing. The surface gets a smooth "satin" finish which increases the
surface area, especially on places that were originally shiny or very smooth
extruded aluminum. This also gently 'breaks' sharp corners which should allow
for smoother airflow and less catching of stuff like carpet fuzz and pet hair.
'Course I keep my computers off the floor and don't have pets in the house, nor
do I smoke, so I have no problems with the three major causes of computer
gunkification. ;) Opening a PC to find it all coated with yellow fur and
smelling like an ashtray is not fun.
I'd like to see somebody do a test of several CPU heat sinks, then do the bead
blasting and run the same tests again to see if that makes any significant
difference. Theoretically it should. Mass removal would be minimal for the
amount of surface area increase.
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