Copper is the oldest cooling material for LED chips. In the beginning, LED Street Light chips are fixed on copper bases. Since copper has very good thermal conductivity, heat generated by chips can rapidly transfer into cooling devices. Even now it is still the best packaging material for chips. However, in the early stage of LED lighting, copper bases cannot be well connected with cooling devices directly. Most heat generated by LED chips gathered on copper bases, cannot be further transferred into cooling devices. In order to solve this problem, aluminum plates were set between copper bases and cooling devices. Due to this problem, aluminum was wildly used later in LED Tubes packaging. Then designers installed LED chips directly on aluminum plates. This packaging method is the prototype of COB.
In next few years, a new cooling material for LED chips started to emerge: ceramic. Ceramic used for LED packaging should have better insulating capability and higher thermal conductivity. Currently, there are three types of ceramic material are competent: alumina, aluminium nitride and beryllia. Beryllia is toxic. Aluminium nitride has a very high thermal conductivity in theory but is not. In practice, the measured maximum thermal conductivity value of aluminium nitride is approximately 150-200 W/(m oC), very closed to the thermal conductivity of aluminum alloy. Since aluminium nitride is much more expensive than aluminum alloy, this material is also unsuitable for LED lighting. The thermal conductivity of alumina can be various depending on the constitutions of them. 95% purity has a thermal conductivity of 21.8 W/(m oC) and 36 W/(m oC) for 99% purity. It is much lower than aluminum alloy, not mention copper. But ceramic is isolated. In order to realize the function of cooling along with isolation, designers have to utilize this kind of material at the cost of thermal conductivity. Ceramic are fragile. When LED products subject to strong vibrations and pressures, they will be easily destroyed. Meanwhile, ceramic has much lower coefficient of thermal expansion than copper and aluminum. When there is a large change in temperature, ceramic base will generate a stress to destroy LED chips.
Above all, copper is the most suitable material for cooling system, then aluminum alloy. Only when insulation needs to be concerned, ceramic material and will be used.