Hardware Reference
In-Depth Information
Installing a Heatsink
To accomplish the best possible transfer of heat from the processor to the heatsink, most
heatsink manufacturers specify some type of thermal interface material to be placed
between the processor and heatsink. This typically consists of a ceramic, alumina, or
silver-based grease but can also be in the form of a special pad or even a type of double-
stick tape. Some are called
phase-change
material because they change viscosity (be-
come thinner) above certain temperatures, enabling them to better flow into minute gaps
between the chip and heatsink. In general, thermal greases offer higher performance than
phase-change materials, but because they always have a lower viscosity, they flow more
easily, can be messy to apply, and (if too much is used) can spill from the sides onto the
socket and motherboard.
No matter what type you use, a thermal interface aid such as thermal grease or phase-
change material can improve heatsink performance dramatically compared to installing
the heatsink dry. Thermal interface materials are rated by thermal conductance (in which
case higher is better) or thermal resistance (in which case lower is better). Unfortunately,
several industry-standard rating scales measure performance, often making product com-
parisonsdifficult.Somemeasurethethermalconductivity;othersmeasurethethermalres-
istance;andthescalesusedcanvarygreatly.Themostcommonlyreportedspecificationis
thermal resistance in degrees centigrade per watt (°C/W) for an interface layer 0.001-inch
thick and 1 square inch in size. For a given material, the thinner the interface layer or the
larger the area, the lower the resistance. In addition, due to other variables such as surface
roughness and pressure, it is often impossible to directly compare different materials even
if they appear to use the same ratings scale.
I've seen actual tests of multiple brands of thermal greases, and in most cases the differ-
ences in temperature readings between different brands are insignificant. For that reas-
on, I generally don't get too excited about different brands of thermal grease; most of the
premium products on the market have surprisingly similar performance.
Liquid Cooling
One of the more extreme methods for cooling a PC is to use some form of liquid cooling.
Liquidshaveamuchgreaterthermalcarryingcapacity thanair,andasprocessorsrunhot-
ter and hotter, it can be advantageous or even necessary to use a form of liquid cooling
to dissipate the extreme levels of heat generated, especially in smaller or more confined
spaces.
Several forms of liquid cooling are available, including the following:
• Heat pipes
• Water cooling
