What is a passive heatsink?

Heat sinks are devices used to keep computer processing units (CPUs) and chipsets cool. Most heatsinks are active, which means the design includes a small fan powered by a header on the motherboard or a power supply cable. A passive heatsink 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.

Passive heat sinks are designed to move heat away from the computer’s central processing unit without using a fan.

When chipsets and CPUs are in operation, considerable heat is generated by electrical activity. These chips would quickly become damaged and inoperable without cooling. A heatsink sits on top of the CPU or chipset, creating a path for heat to rise from the chip to the heatsink, where it can dissipate. A passive heatsink does this without the benefit of a built-in fan.

Many elements influence the efficiency of a heat sink. The first consideration is the material used. Aluminum is an extremely light and inexpensive material with a high degree of thermal conductivity. Copper is three times heavier and slightly more expensive than aluminum, but it is also twice as efficient at conducting heat. A passive heat sink can be made from one or both of these materials combined.

A heatsink has a flat base made to interface with the face of the chip. Extending upward from the base are rows of pins or “fins” that provide surface area for heat dissipation. A passive heatsink typically has more surface area and the pins or fins are usually made of aluminum alloys to keep the weight down. Copper can be used strategically in the base and in 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 pins, where air circulating inside the computer case can carry heat away.

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The heat sinks attach to the chips by locking mechanisms that differ depending on the model. Some locking mechanisms are easier to work with than others, but the type of CPU socket will determine which heatsink models the motherboard can accommodate. A large, heavy passive heatsink may require removing the motherboard to install a special bracket or locking mechanism.

As always, thermal paste should be used between the heatsink base 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 heatsink efficiency and ensure a cooler running chip. Thermal tape is the cheapest type of compound, but in general thermal pads or thermal paste are considered more efficient and quite affordable.

While a passive heatsink can be large, it has advantages over an active heatsink. Active heatsinks—or those that rely on a built-in fan—may come out with a smaller surface area, but if the fan fails, the heatsink won’t be able to keep the chip cool and damage can 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 lack of noise. Every system should include fans, but eliminating the chipset or CPU fan can help keep overall decibels lower. A passive heatsink also requires no power.

The main disadvantage is size. Due to the larger surface area normally incorporated into a passive heatsink, the footprint can be quite tall and might not fit into all computer cases. Installation can also be more challenging in some instances. Nevertheless, the payoff is a quieter system with no chance for heatsink failure, and these two factors are appealing to many enthusiasts.

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It is important to choose a heatsink that is rated to cool the CPU or chipset desired. In some cases, chip manufacturers recommend particular heatsinks and even compounds, and using another model or compound might void the chip’s warranty. Check with the manufacturer’s website for details as required.

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