Sputtered nanoceramic (direct metallisation) as an alternative
Cambridge Nanotherm has come up with a solution that manages to overcome the limitations demonstrated by both MCPCBs and ceramics, resulting in an inorganic PCB with a thermal conductivity of 150W/mK, enough for all but the most aggressive UVC LED applications. This approach cleverly weds the best of both worlds; the robustness of aluminium with the thermal efficiency of ceramics.
Using a patented electro-chemical oxidation (ECO) process, Nanotherm converts the surface of an aluminium board into a layer of alumina (Al2O3) ceramic that is just microns thick. This acts as an electrically-isolating dielectric layer, preventing the circuit from shorting out against the aluminium heat spreader. Alumina isn’t the most thermally-effective substance, but because the layer is extraordinarily thin it conducts heat extremely effectively.
The circuit layer is attached to the nanoceramic using a direct plated copper process that bonds the copper to the ceramic dielectric at a molecular level without using any organic epoxy. This minimises impedance along the thermal path and ensures that heat is transferred between the layers as efficiently as possible. And as there’s no epoxy it makes the whole stack 100% inorganic so there’s nothing for UVC light to degrade.
The result is a board that demonstrates thermal qualities close to those of AlN while retaining the machineability and robustness of aluminium. Furthermore, this approach allows for much larger tile sizes to be manufactured which in turn means that designers can start to bring some of the economies of scale found in the MCPCB industry to bear on the UVC market.
Nanoceramic is enabling UV LED designers to overcome one of the key challenges they face in designing small, portable and low-cost UVC disinfection devices and helping this nascent industry to reach its full potential.
About the author:
John Cafferkey is marketing manager at Cambridge Nanotherm - www.camnano.com