Heat Sink-CPU Cooler Manufacturing Process and Principle

Heat emanating from the CPU core to the surface of the heatsink is a heat conduction process. For the base of the heatsink, since it is in direct contact with a small heat source with high heat, it requires the base to be able to conduct the heat away quickly. The use of materials with higher thermal conductivity for heat sinks is helpful in improving the efficiency of thermal conduction. Through the heat conduction system comparison table can be seen, such as the thermal conductivity of aluminum 237W/mK, the thermal conductivity of copper is 401W/mK, while comparing the same volume of the radiator, the weight of copper is three times that of aluminum, while the specific heat of aluminum is only 2.3 times that of copper, so the same volume, copper radiator can hold more heat than aluminum radiator, warming up more slowly. With the same thickness of the radiator base, copper can not only quickly draw away the heat source such as CPU Die temperature, but also its own temperature rise is slower than the aluminum heat sink. Therefore, copper is more suitable for the base of a heat sink.

However, the combination of these two metals is more difficult, the affinity between copper and aluminum is poor, if the joint is not handled well, it will produce a large interface thermal resistance (i.e., the thermal resistance between the two metals due to insufficient contact). In the actual design and manufacturing, manufacturers always try to reduce the interface thermal resistance as much as possible, to avoid the shortcomings, which often also reflects the manufacturer's design capabilities and manufacturing process.

Common copper and aluminum bonding processes include:

Skewer bonding

Stick welding is the use of the melting point than the melting point of the base material of the metal material as a solder, in the lower than the melting point of the base material and higher than the melting point of the solder temperature, the use of liquid solder to wet the base material, fill the gap between the joints, and then condense to form a solid joint interface of the welding method. The main processes are: pre-treatment of materials, assembly, heating and welding, cooling, post-treatment and so on. Commonly used skewer welding is tin skewer welding, aluminum surface in the air will form a very stable layer of oxide (AL2O3), so that the copper and aluminum welding difficulty is higher, which is the biggest obstacle to welding. It must be removed or chemically removed and plated with a layer of nickel or other easy to weld metal, so that copper and aluminum can be welded together smoothly.

The copper base on the heatsink is for heat conduction, which requires not only mechanical strength, but more importantly, a large soldering area (soldering rate should be high) in order to effectively enhance the heat dissipation performance, otherwise it will not only not enhance the heat dissipation performance, but also make it even worse than the all-aluminum alloy heatsink.

SMD and screw-locking

Patch process is a thin copper sheet through the screws and aluminum bottom surface combination, the main purpose of doing so is to increase the heat sink's instantaneous heat absorption capacity, to extend the life cycle of some of its own mature design of pure aluminum heat sink. After testing found that: the use of high-performance thermal conductive medium between the bottom of the aluminum heatsink and the copper block, applying a force of 80Kgf compression with screws to lock it, the heat dissipation effect and the effect of copper-aluminum soldering is comparable to that of the same to achieve the expected magnitude of the thermal efficiency of the enhancement of the magnitude of the heat dissipation.

This method is simpler than welding, and stable quality, process simplicity, investment in equipment costs lower than welding, but only as an improvement, so the performance improvement is not obvious. Although filled with Thermal Paste, the incomplete contact between the copper sheet and the aluminum base is still the biggest obstacle to heat transfer.

The main processes of manufacturing are: copper sheet cutting, calibration (flatness less than 0.1mm, drilling, applying thermal conductive medium drilling, tapping, cleaning, strong pre-pressure program, two-stage locking operation, fixed torque lock screws.

The focus of the patch process is to control the copper, aluminum flatness and roughness and the torque of the locking screw and other factors, you can get a certain degree of efficiency, is a good way to combine copper and aluminum. If the performance of the thermal conductive medium used is poor, or the flatness of the copper block is poor, the heat will not be smoothly conducted to the surface of the aluminum heat sink, so that the heat dissipation effect is greatly reduced. In addition, the locking force of the screws and the lack of purity of the copper material are undesirable influencing factors.

Copper plugging Copper embedded

There are two main ways to insert copper, one is to embed the copper into the aluminum base plate, which is common in radiators made with aluminum extrusion process. Due to the limited thickness of the aluminum radiator bottom, the volume of embedded copper is limited. The main purpose of increasing the copper sheet is to strengthen the instantaneous heat-absorbing ability of the radiator, and the contact with the aluminum radiator is also very limited, so most of the time, this kind of copper-aluminum radiator is not much better than the aluminum radiator, and in the case of poor contact, it will even prevent heat dissipation. There is also an aluminum radiator with copper posts embedded in radial fins, which is the design of Intel's original radiator. The copper posts are larger and have more contact with the radiator. With the use of copper pillars, the heat capacity and instantaneous heat absorption of the heat sink can be enhanced. This design is also used more by OEMs.