Why UVC presents such a significant thermal challenge
UVC LEDs convert only 5% of the power put in to light, with the remaining 95% converted into heat. And UVC LEDs, like any electronic component, are extremely vulnerable to heat. This heat needs to be removed otherwise the LED die risks overheating and failing, which will impair its lifespan and light quality.
The size of UV LEDs is too small to allow for any significant loss of heat through ambient radiation or convection. The only way heat can be removed is through conduction through the back of the LED to the PCB and then to the ambient atmosphere via a heat sink. It stands to reason that the PCB on which the LED is mounted must have a high thermal conductivity.
raditional visible-light, high-power LEDs use metal-clad PCBs (MCPCBs) to provide the thermal performance required. However, most MCPCBs aren’t suited to UVC applications because of the way they’re manufactured. Most are manufactured from a sheet of metal (usually aluminium or copper) with the copper circuit layer attached with a layer of thermally conductive, but electrically insulating, dielectric. This dielectric poses the problem: Conventional MCPCBs use an organic epoxy to attach the copper circuit layer which aren’t suitable for UVC LEDs as UV degrades organic matter. This means the options are limited to inorganic ceramic PCBs.
One choice is aluminium nitride (AIN) which has excellent thermal conductivity (140–170 W/mK) but is also expensive. Alumina (Al2O3) is a cheaper alternative but has limited thermal conductivity (20–30 W/mK). And thermal conductivity and price aside, both materials are very brittle, which means they can’t easily be mounted with screws and risk breaking in applications that operate in harsher environments.