The basic heatsink is designed for one purpose, to increase the rate at which an
object can release heat. The basic principal is that heat transfers from your
component (say your CPU) into the air, and by increasing the amount of surface
area available to the air the amount of heat released is increased. That is all
heatsinks are designed to do, increase the surface area of a component and
allow heat to better transfer to the atmosphere.
There are many different types of heatsinks around. All have one common feature
though, a large surface that is positioned over the chip, harddrive or whatever you
are cooling.
This is how heat is first transfered to the heatsink, and it's important that
the connection made is good as heat travels badly through air and, in a sealed
environment, not at all through vacuum (no air).
Heatsinks must increase the surface area of the object to be cooled somehow. Looking
at CPU heatsinks, there are many different types available. Some use a flat layer
with spikes or "feet" sticking up like this one:
*** image here ***
Some use two layers with "honeycomb" between them and gaps to let a fan
pass air thru. There are many other designs as well. Often a heatsink will come
with a fan glued on as well (and vice versa, many fans have heatsinks on them)
because a fan can push air past the surface of a heatsink and the more cool air
that passes the better. In fact, a heatsink is almost useless unless there is
a constant supply of cool air (maybe from a case fan) because if the air next to
it is also very hot not much heat will be transfered. When the air and the
heatsink are exactly the same temperature heat transfer stops altogether.
Manufacturers have come up with a lot of ideas to improve the performance of
heatsinks over the years. Many heatsinks are made of aluminium, but more expensive
ones are made of copper. Copper costs more but conducts heat better too. Some
heatsinks come in different colours (most are either black or metallic silver
with no paint), although the benefits of this are extremely small. Okay, go ahead
and buy a blue heatsink but it won't make any noticeable difference to the
cooling power of the unit.
Speaking of cooling power, the performance of a heatsink is measured in degrees
centigrade per watt of energy. The lower the ratio the better. For instance,
Maplins sell a particular heatsink rated at 3°C/1W. This means that for every
watt of heat energy given off by the CPU, that heatsink will only get 3°C
hotter. This assumes reasonable ventilation etc, the performance can be
improved by using a fan blowing onto the heatsink. Some manufacturers (especially
computer manufacturers) quote the performance with a fan as they often ship the
unit with a fan glued on already.
When it comes to attaching things to your heatsink, it's important to get a
good connection. Most computer heatsinks come with a bit of glue to stick it
on with, but this tends to be low quality and if you are serious about cooling
is best replaced.
Thermal paste is a very important part of using a heatsink. In an ideal world
heatsinks would make perfect contact with the chip they were on and stay
firmly connected to it. In reality you need some kind of glue to keep the to
parts together, even if your heatsink clips on. The reason for this is that
any gaps between your heatsink and chip reduce it's efficiency. Even when pressed
down there will still be gaps as most heatsinks are not perfectly flat:
These minor imperfections make a big difference to how well a heatsink works.
In order to get around this people use thermal paste (also known as thermal
grease). It is made up of zinc oxide and silicone grease, and transfers heat
much better than air. Sometimes you will come across thermal tape (found often
on cheap heatsink/fan combos) which really isn't very good, stick to the paste.
In order to remove the old glue or tape you can use alcohol or one of the
near-pure cleaning fluids.
The quality of thermal paste also varies. The quality of paste is measured in
W/mK, which means watts of energy transferred by a 1 meter cube of the material
per degree of temperature difference on either side. Average thermal paste is
a little under 1W/mK, the best stuff is over 2W/mK but it's also very expensive.
To apply thermal paste first make sure that the heatsink and chip are both
clean. I mean completely clean, use cleaning fluid and a lint free cloth to
be sure. Put a very thin layer of paste on the heatsink, as thin as you can get
it while covering the entire surface area you are going to stick to the
chip. Be careful not to put too much on or the paste will insulate the chip and
obviously that's bad. Carefully stick the heatsink on and press it firmly down.
A tiny bit of lateral motion is okay, but don't move it from side to side too
much or you might not get even coverage of the paste.
Some people have taken to something called "lapping" to improve their
heatsinks. Lapping is a process where you scrape off the surface of the heatsink
in order to make it flatter. Obviously this needs incredible skill or even better
machining to improve performance, otherwise it tends to just trash the conductive
surface. Some people even use lapping on their CPUs, although this is not
recommended! On the Amiga, none of this should really be a big enough problem
to make lapping worth considering I should think, unless you have a heavily
overclocked CPU.
