When disassembling certain electronic devices, such as computer hosts or white goods, there is always a metal block within the internal structure. This metal block is the heat sink, and it is one of the most crucial components for the overall thermal dissipation of the electronic device. Without it, the accumulated heat would be unable to release or exchange with the external environment.
What is a Heat Sink?
A heat sink is a device engineered to transfer the operational heat of equipment away to maintain normal function, primarily applied to core components such as computer CPUs and GPUs (graphics cards). Based on the cooling method, they are categorized into various types, including air cooling, liquid cooling, and heat pipe technology. The primary materials are copper and aluminum alloys, though non-metallic materials such as graphene, thermally conductive plastics and ceramics (e.g., silicon carbide, boron nitride) are also utilized.
Heat dissipation is achieved through the synergistic action of thermal conduction, convection, and radiation. Manufacturing processes encompass techniques like aluminum extrusion and copper-aluminum bonding. The design and forming of the fins directly impact the thermal dissipation efficiency.
Heat Sink Types
Heat sinks come in numerous varieties due to differences in material and structural geometry. Below we introduce several common types of heat sinks.
Folded Fin Heat Sink
Folded fins are produced using a progressive stamping method. The fins are then bonded to the base to form the heat sink, utilizing thermally conductive epoxy, brazing, welding, or similar metallurgical bonds. An advantage of folded fin heat sinks is the ability to integrate aluminum and copper, allowing for the customization of the heat sink’s performance for a specific application. If heat must be spread across a large heat sink base, copper can be used for its high thermal conductivity, while the heat sink fins can be manufactured from aluminum due to its low weight and cost.
Skived Fin Heat Sink
Skived fin heat sinks utilize a single block of material (copper or aluminum) and employ a specialized skiving machine with a high-precision heat sink skiving process to cut out high-density, tall, and extra-long fin structures. Skived fin heat sinks overcome the limitations imposed by the thickness and aspect ratio of traditional heat sinks, enabling the creation of heat sinks with high-density fins. The fins and base are “monolithic” (one-piece). Since the base and fins are integrated into a single piece, there is no additional thermal resistance. Combined with the high purity of the skived material, the efficiency of skived fin heat sinks is significantly higher than that of soldered heat sinks, with thermal conductivity efficiency reaching a level comparable to that of extruded profiles.
The skiving process is also applied in the recently very popular micro-channel liquid cold plates, serving the purpose of increasing the specific surface area for heat exchange and enhancing the effect of convective heat transfer.
The manufacturing process flow for skived fin heat sinks is as follows:
- Raw Material Preparation: Profiles are typically selected based on the heat sink requirements to maximize raw material savings.
- Tooling/Molding: Molds are created according to product dimensions, allowing for one or multiple products per mold; operations can be continuous or piece-by-piece.
- CNC Machining: This includes milling away unwanted sections, milling grooves for sealing rings, etc.
- Skiving Process: The skiving process is executed using a CNC skiving machine.
- Hobbing (Leveling): This is completed using operations on a hobbing machine.
- Secondary Machining: Based on the product drawings, this involves milling off edge fins, drilling holes in the center, creating clearance spaces (avoidance cuts), fly-cutting surfaces, machining threaded holes, and creating fastener features (buckle seats), etc.
- Surface Treatment: Anodizing, electroplating and more.
Aluminum Extruded Heat Sink
Aluminum profile heat sinks are characterized by their aesthetic appearance, light weight, excellent thermal performance, and good energy-saving effects. The surface of finished aluminum profile heat sinks is treated with anodic oxidation to enhance the aluminum’s corrosion resistance, wear resistance, and visual appeal. Aluminum extruded heat sinks are generally used for high-power thermal components and systems. The technology allows for the realization of complex fin structures through molds. These complex fins significantly increase the heat dissipation surface area while simultaneously reducing the cost and time associated with machining aluminum blocks.
Bonded Fin Heat Sink
Bonded fin heat sinks are typically manufactured using an assembly process that involves bonding a layer of thin metal fins to a base or substrate.
The general process flow for manufacturing bonded fin heat sinks is as follows:
- Preparation: The base and fins, typically made of aluminum or copper, are carefully cleaned to ensure a successful bonding process.
- Bonding: The fins are then adhered to the base using an adhesive material, such as epoxy or a thermal transfer compound. The adhesive material is typically applied uniformly to the base, and the fins are placed on top, with pressure applied to ensure a firm bond.
- Curing: The adhesive material is then cured, typically through heating or ultraviolet (UV) light, to form a permanent bond between the fins and the base.
- Assembly: If the heat sink requires additional components, such as mounting hardware or interface materials, component adjustments are made at this stage.
Zipper Fin Heat Sink
This type of heat sink integrates aluminum fins with heat pipes. Holes are punched into the aluminum fins according to the structural design, and heat pipes of the specified dimensions are inserted, followed by bonding and welding. The advantage is utilizing the phase-change effect of the heat pipe to increase the overall heat transfer efficiency of the heat sink. Furthermore, the external aluminum fins significantly increase the heat exchange surface area per unit volume, rapidly dissipating heat to the external environment through air convective heat transfer.
Naturally, there are many other types of heat sinks not covered here. However, the common types mentioned above are those most frequently utilized in current electronic devices.
Applications of Heat Sinks
The application of heat sinks is ubiquitous, ranging from large-scale fields like aerospace, electric power, metallurgy, photovoltaics, rail transit, automotive, and communication base stations, down to small devices such as chips, servers, consumer electronics, and household appliances. Wherever there is electricity, the reinforcement of a heat sink is certainly required.
Particularly in the currently most critical AI computing servers, the heat sink is an extremely vital thermal component. In the context of overall system cooling, the heat sink’s structural integrity and thermal performance are essential factors determining the long-term stable operation of the server unit.
Liquid cold plates are considered an iterative and upgraded product form of heat sinks, utilizing the convective heat transfer effect of liquid to remove heat from the source more rapidly. The structure of the heat sink fins is continued in the popular micro-channel liquid cold plates, where the fin structure is significantly more precise. The gap between fins is typically less than 1mm, which imposes extremely high requirements on precision machining technology.
Heat Sink Materials
The main materials are copper and aluminum alloys, with copper dominating the high-end thermal management sector. Aluminum alloy heat sinks are primarily utilized in large-scale environmental applications where thermal requirements are relatively lower, but structural integrity and lightweighting requirements are higher, such as in electric power systems, photovoltaics, automotive applications, and communication base stations. Recently, new metal composite materials have emerged, including graphene-based aluminum, diamond/aluminum composites, and diamond/copper composites.
Heat Sink Manufacturing
The current core manufacturing methods are CNC machining and skiving. These methods offer significant advantages in terms of production efficiency and cost for medium-to-large-sized heat sinks. However, they struggle with the machining of high-precision micro heat sinks and complex structural heat sinks due to the excessively high mold requirements and very expensive tooling costs.
For ultra-thin fin heat sinks, such as micro-channel liquid cold plates, where channel gaps are less than 1mm or even reach 0.1mm, metal 3D printing technology must be employed. Metal 3D printing technology achieves breakthroughs in thermal performance due to its ability to realize complex structures specifically optimized for heat dissipation. For instance, in the thermal solutions for high-end AI computing accelerator cards, it can manufacture conformal, non-standard structures that closely fit the chip surface. By increasing the heat exchange area, optimizing the flow channel design, and strengthening fluid mixing, this technology achieves highly efficient heat dissipation, reduces pump power consumption, and effectively prevents localized overheating.
Furthermore, for heat sinks with highly complex structures, traditional machining methods result in cumbersome tooling and preparation, leading to low production efficiency and high costs. Metal 3D printing technology perfectly resolves this issue and has recently achieved significant breakthroughs in printing solutions for copper heat sinks.
