Heat sinks keep CPUs and chipsets cool. Passive heat sinks lack a fan, but are larger and use extra surface area to improve thermal cooling. They are quieter and eliminate the possibility of catastrophic overheating due to fan failure. Material, surface area, and locking mechanisms affect efficiency. Thermal compounds fill gaps to improve heat sink efficiency. Passive heat sinks have advantages over active ones, but can be larger and harder to install. It’s important to choose a heatsink rated for your CPU or chipset.
Heat sinks are devices used to keep computer processing units (CPUs) and chipsets cool. Most heat sinks are active, which means the design includes a small fan powered by a connector on the motherboard or a cable from the power supply. A passive heat sink does not include a fan in the design and is typically larger than a standard model, using the extra surface area of the device to improve thermal cooling in compensation for the lack of a fan. Its purpose is to reduce system noise and eliminate the possibility of catastrophic overheating due to fan failure.
When chipsets and CPUs are running, a lot of heat is generated from electrical activity. These chips would quickly become damaged and unusable without cooling. A heat sink sits on top of the CPU or chipset, creating a path for heat to rise from the chip to the heat sink where it can dissipate. A passive heat sink accomplishes this without the benefit of a built-in fan.
Many elements contribute to the efficiency of a heat sink. The first consideration is the material used. Aluminum is an extremely light and cheap material with a high degree of thermal conductivity. Copper is three times heavier and a little more expensive than aluminum, but it’s also twice as efficient at conducting heat. A passive heat sink could be made of one or both of these materials in combination.
A heat sink has a flat base made to interface with the face of the chip. Rows of pins or “fins” extending from the base provide surface area for heat to dissipate. A passive heat sink typically has more surface area, and the pins or fins are often made of aluminum alloys to keep the weight down. Copper could be used strategically in the base and heat pipes or other design elements. Heat pipes are often used to more efficiently channel thermal buildup from the base of the heat sink to the fins or studs where circulating air within the computer case can carry the heat away.
The heat sinks attach to the chips via locking mechanisms that differ by model. Some locking mechanisms are easier to use than others, but the type of CPU socket will determine which models of heatsinks your motherboard can accommodate. A large and heavy passive cooler may require you to remove the motherboard to install a special bracket or locking mechanism.
As always, a thermal compound should be used between the base of the heat sink and the chip. Imperfections in these surfaces create voids that introduce resistance along the thermal conduction path. Applying a thermal compound will fill these gaps to improve heat sink efficiency and ensure cooler operation of the chip. Thermal tape is the least expensive type of compound, but in general, thermal pads or thermal grease are considered more efficient and are quite affordable.
While a passive heat sink may be great, it has advantages over an active heat sink. Active heat sinks, or those that rely on a built-in fan, can get by with a smaller surface area, but if the fan fails, the heat sink won’t be able to keep the chip cool and damage could occur. A passive heatsink, properly installed and rated for the chip it is cooling, cannot fail under normal operating conditions.
Another advantage of a passive heatsink is the absence of noise. Every system must include fans, but eliminating the chipset or CPU fan can help keep overall decibels down. Even a passive heatsink does not require power.
The main disadvantage is the size. Due to the larger surface area typically built into a passive heat sink, the footprint can be quite large and may not fit in every computer case. Installation can also be more difficult in some cases. However, the benefit is a quieter system without the possibility of heatsink failure, and these two factors are appealing to many enthusiasts.
It is important to choose a heatsink that is rated to cool your desired CPU or chipset. In some cases, chip manufacturers recommend particular heatsinks and even compounds, and using another model or compound may void the chip warranty. Check with the manufacturer’s website for details as required.
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