Heatsinks can be classified in terms of manufacturing methods and their final form shapes. The most common types of air-cooled heatsinks include stampings, extrusions, forging, bonded/fabricated fins, die castings and folded fins. Following is an explanation of each technique.
Stampings - Copper or aluminium sheet metals are stamped into desired shapes. They offer a low cost solution to low density thermal problems. They are suitable for high volume production, because advanced tooling with high speed stamping would lower costs. Additional labour-saving options, such as clips and interface materials, can be factory applied to help to reduce assembly costs.
Extrusions - This is the most popular method of manufacturing heatsinks. Extrusion is the process by which long straight metal parts can be produced. It is done by squeezing metal in a closed cavity through a tool, known as a die, using either a mechanical or hydraulic press. After the metal has cooled, it is cut to the size you want the heatsink to be, based on motherboard standard sizes.
Forging - This is the process whereby metal is heated and shaped by plastic deformation by suitably applying compressive force. Usually the compressive force is in the form of hammer blows using a power hammer or a press. Heatsink manufacturers rarely use this method but it is used occasionally, and is definitely worth mentioning.
Bonded/Fabricated Fins - Most air cooled heatsinks are convection limited, and the overall thermal performance of an air cooled heatsink can often be improved significantly if more surface area can be exposed to the air stream. These high performance heatsinks utilise thermally conductive aluminium-filled epoxy to bond planar fins onto a grooved extrusion base plate.
Die Castings - Die casting is where the metal is injected into the mould under high pressure of 1,450-30,500psi. This results in a more uniform part, generally good surface finish and good dimensional accuracy, as good as 0.2% of casting dimension. In other words, you can make more complex shapes using die casting than you can using other methods such as extrusion.
Folded Fins - Corrugated sheet metal in either aluminium or copper increases surface area, hence the volumetric performance. The heatsink is then attached to either a base plate or directly to the heating surface via epoxying or brazing. It is not suitable for high profile heatsinks on account of the availability and fin efficiency.