The case for nanoceramic PCBs in UV LEDs

October 23, 2017 //By John Cafferkey
UVA-based curing has been used in industrial applications for many years. However, the use of high-intensity discharge (HID) mercury vapour lamps as the UV source has limited the range of applications they were suitable for because the lamps, while effective, were large, fragile and slow to warm up.

Advances in technology have seen the rise of UV LEDs as an alternative to HIDs. LEDs use less power, run considerably cooler and operate at a specific wavelength and power cycle instantly. These characteristics are transforming the UV curing industry, from driving efficiency to offering new solutions such as hand-held curing applications that would not have been conceivable with HID lamps.

Yet LEDs are still relatively inefficient. Only around 40% of the power that goes into a UVA LED is converted into light with the remaining 60% converted into waste heat. This heat needs removing from the LED as quickly as possible to prevent the LED from overheating and exceeding its maximum operating temperature. Failure to remove this heat can lead to the light quality deteriorating and ultimately to catastrophic failure of the LED.

Unlike HID lamps, the small surface area and relatively low temperature of LEDs mean the amount of heat they can convect and radiate away is negligible. The only way to remove the heat is to conduct it out the back of the die, through the PCB, to a heatsink and to the ambient atmosphere. To keep the LED die under its maximum operating temperature, the substrate material used for the PCB needs to be highly thermally efficient. With UVA applications, the module substrate tends to be either a thermally effective metal-clad PCB (MCPCB) or electronics-grade ceramics, particularly high-performance aluminium nitride (AlN). In higher-power density applications epoxy-based MCPCBs simply don’t have the requisite thermal performance (<100W/mK vs 170W/mK for AlN) making AlN the substrate of choice where heat is a significant issue.