Packaging of High Power UV-LED Modules on Ceramic and Aluminum Substrates
M. Schneider, B. Leyrer, C. Herbold, S. Maikowske
- Datum: Proceedings 45th International Symposium on Microelectronics, IMAPS 2012, San Diego, California, September 2012, pp. 225-232, invited
Today UV light is used in many industrial applications e.g. to rapidly cure paints, lacquers, coatings, and adhesives. Currently these applications use high power, medium pressure gas discharge lamps. High power LED technology is gaining increased attention because it promises easier operation, lower power consumption, variable light output, faster switching, and longer lifetime. Lifetime, efficiency, and reliability of LED systems are closely associated with the junction temperature of every single LED. Thus the thermal properties of the packaging and the cooling system are crucial issues. We present an LED module consisting of 98 UV LEDs with an emission wavelength of 395 nm placed on a ceramic substrate of 211 mm². The module is cooled by a forced air heat sink and, to lower the thermal resistance, a high performance microstructured water cooler. For high thermal conductance we use a liquid metal as the thermal interface material between substrate and heat sink. With the forced air heat sink we achieve a maximum irradiance of 27.3 W/cm² at a forward current of 700 mA and 220 W electrical input power. The microstructured water cooler enables us to obtain almost twice the electrical input power (413 W) while maintaining the chip’s maximum temperature. In order to decrease further the module’s thermal resistance we started the development of a thick film process for aluminum sheet metal substrates. A prototype LED module with 25 UV LED chips on an area of 0.54 cm² achieved a maximum optical power density of 31.6 W/cm² at a forward current of 900 mA using a forced air heat sink. For improved cooling of the LED chips we currently develop a chip-on-heat sink-technology. Aluminum substrates with embedded water cooling channels eliminate the thermal interface between substrate and heat sink and therefore its thermal resistance.