A motherboard heatsink is a cooling device used on certain chips found on system boards. The main chip or computer processing unit (CPU) requires a heatsink, and chipsets also use heatsinks. The size and design of these devices varies, as do materials and method of attachment.
When a computer is in use, electrical activity within the CPU and chipset generates considerable heat, which if not dissipated, will damage or even melt the chips, making them inoperable. A motherboard heatsink is secured to the top of a chip, providing an efficient path for heat to escape, first into the heatsink, then from the heatsink into the environment.
A motherboard heatsink is typically made of aluminum alloys or of copper. Aluminum alloys are good thermal conductors, and also have the advantages of being both lightweight and inexpensive. Copper is triple the weight and several times more expensive, but has twice the thermal conductivity of aluminum for even better heat dissipation. (Price-prohibitive diamond has the highest level of thermal conductivity, beating copper by a factor of five.)
In addition to materials, physical design also plays a major part in how well the device dissipates heat. Heatsinks feature rows of fins or pins extending up from the base. These fins or pins provide maximum surface area to dissipate heat while still allowing airflow between the rows to carry that heat away. This cools the surfaces, creating a dynamic path for continued dissipation.
An active heatsink comes with a small fan attached to the top of the fin or pin area, used to cool the surface. A passive heatsink lacks a fan, but is usually designed with a larger surface area. Some passive heatsinks are quite tall, and clearance can be an issue. The advantage of a passive model, however, is lack of noise.
Since the motherboard heatsink is responsible for keeping the chip cool, the chip face and base of the heatsink must be pressed together squarely and very tightly. This is accomplished through a locking mechanism that varies according to design. The heatsink might come with z-clip retainers, a clip-on spring-loaded mechanism, or a swing-down plastic arm to lock the heatsink down on to the CPU or chipset. Some types of attachment methods require the motherboard to have holes or a plastic retaining frame in place.
While the retaining method will press the chip surface against the base of the heatsink, there will still be minute voids between the two surfaces due to irregularities, imperfections and the roughness of the surfaces. Trapped air introduces resistance or gaps in the thermal path, which hampers cooling. To address this, a motherboard heatsink is always used in conjunction with a thermal compound that sits between the two surfaces, filling these gaps. Thermal tape is the least expensive type of compound, but is generally considered the least efficient. Thermal pads and tubed compounds made of various materials from silver to micronized diamonds are more popular among enthusiasts and still quite affordable.
Some chip manufacturers recommend particular types of compounds and heatsinks to use with their CPUs. CPUs that are packaged for retail sale typically come with a heatsink and thermal compound. In some cases, the CPU warranty is voided if the chip is used with a different heatsink or compound.
Heatsinks and compounds are readily available from computer and electronics outlets. Prior to purchasing a motherboard heatsink, be sure the attaching mechanism and footprint are compatible with your motherboard and computer case. Refer to the chip manufacturer for recommendations and warranty information.