Extruded Heat Sinks
Extruded heat sinks are the most common heat sinks used for thermal management. Extruded heat sinks are generally used in medium power systems both in natural and forced convection. The extrusion process, pushing hot raw aluminium through a steel extrusion die to create the desired profile allows for innumerable complex shapes to be manufactured. Many standard shapes are available but modifying the profile shape changes the surface in contact with the air and consequently the heat dissipation capability. Columbia-Staver can supply standard profiles or engineer a heat sink shape to achieve optimal performance in the space available. After cooling and ageing, the material is cut to the final heat sink length and any additional features such as holes or pockets can be added.
Extruded heat sinks can be supplied raw or with a finish, such as anodizing, electrophoresis or powder coating. Certain finishes can alter the emissivity, which can enhance thermal performance.
Cold forging is a cold working process. Aluminium is squeezed by a press into the closed die, the resultant heat sink taking on the shape of the void in the die. This process is also known as cold heading. Cold forged heat sinks often have high performance compared with other technologies, mainly because any increase to the surface area of a heat sink will almost always result in improved thermal performance. Forged fins can be made almost perfectly straight, allowing for more fins per square inch than in an extruded product. The part is formed under high pressure which controls the grain structure and results in improved thermal performance The fins can also be formed into an elliptical or circular shape enabling airflow from any direction – a big advantage in some applications.
Stacked, Zipper, Folded Fin Heat Sinks
Stacked or zipper fin heat sinks can be an alternative to both extrusion and skived when looking for high density structure. Unlike the one piece skived fin heat sink, a zipper fin heat sink is an assembly of a base and a separate fin stack. The fin stack is created using a set of individually stamped fins, these fins are stacked or “zipped” together to form a block of fins. The finished fin stack is then soldered or bonded to the heat sink base. Zipper fins are most often used with a base plate but they can also be used with heat pipes. A hole or holes are stamped into the fins and the fin stack set is placed on a series of heat pipes to form the heat sink. Zipper fins can be manufactured from either copper or aluminium. Zipper fin heat sinks can also be customized with heat pipes embedded into the base plate to enhance performance.
Skived Heat Sinks
Skived fin heat sinks can be used as an alternative to extruded heat sinks when looking for a fin density which can’t be achieved by extrusion technology. Skived heat sinks can be manufactured from either copper or aluminium and usually have 0.5mm thick fins, although fins as thin as 0.2mm are achievable. In this manufacturing technology the heat sink fins are literally carved out of the base of the Heat sink. In the machine, specially designed blades slice the surface cutting very fine and thin fins into the raw metal block at a shallow angle, the fins are then folded vertically and aligned with the previous fin. As the fins and the heat sink base are part of the same block of material, skived fin heat sinks give excellent thermal conductivity between fin and base. Skived heat sinks can also be customized with embedded heat pipes to enhance performance if required.
Die-Cast Heat Sinks
Die casting is the process of injecting liquid metal under high pressure into a high precision mould created using two hardened tool steel dies. One of the big advantages of die casting is that it is an effective method of forming complex shapes of high tolerance with little need for post moulding machining. Mounting holes, slots, pins etc can be added with little cost penalty.
Heat sinks can be die-cast in both aluminium and zinc materials, however the thermal conductivity of the Die Cast material is not as good as that used in extruded heat sinks and die casting tooling is generally more expensive than extrusion tooling. A variety of surface treatment options are available depending on the casting material these include anodising, electrophoresis and powder coating.