Heat sink materials
Thermal conductivity of a heat sink is governed by its material composition, the conductive area, and the ambient temperature. Aluminum is the ubiquitous choice of material for LED heat sinks, despite the fact that copper has nearly twice the thermal conductivity of aluminum. In addition to its cost-effectiveness, moderately high thermal conductivity and high corrosion resistance, aluminum is also easily workable in mass volume using common casting, forging, extrusion and machining processes.
Aluminum heat sinks are not always made using the purest material. Aluminum alloys have been developed to address the processability issues or to enhance a specific characteristic, although the existence of most impurities will inevitably compromise the thermal conductivity. For example, magnesium is generally added the aluminum alloy for the purpose of increasing the tensile strength. The addition of copper can enhance the strength and thermal conductivity of the aluminum heat sink. Adding silicon enhances the fluidity of molten aluminum alloy at the time of die casting. A small amount of iron helps prevent dies from being fusion-bonded with the aluminum alloy.
Some heat sinks come with a ceramic or steel construction. Ceramics have thermal conductivities similar to aluminum and its alloys. What appeal to the lighting industry are their high dielectric constant and low manufacturing cost. The challenge of using ceramics is that they're brittle and require extra handling precautions. Steel heat sinks are typically found on fixture-as-heat-sink LED lighting systems such as troffers and linear high bay fixtures. The housing of these fixtures are typically fabricated from die formed cold rolled steel. Stainless steel, which provides a very stylish aesthetic and is corrosion resistant, also finds its application in fixture-as-heat-sink lighting systems. However, both cold rolled steel sheets and stainless steel are less conductive than ceramic and aluminum (16-24 W/mK for stainless steel, 30-67 W/mK for carbon steel).
