An innovative Si package for high-performance UV LEDs

Abstract

Deep ultraviolet (UV) light emitting diodes (LEDs) have a wide range of applications such as water treatment, medical diagnostics, medical device sterilization and gas sensing. The internal quantum efficiency of UVB and UVC LEDs is extremely low. Added to this is the high refractive index of the sapphire substrate. The electrical input power is converted to more than 95% to heat. Typically, ceramic packages of alumina with metal core or aluminum nitride are used. These promise a minimized thermal resistance. Comparative thermal simulations show that even Si with slightly lower thermal conductivity of 150 W / mK compared to aluminum nitride with 180 to 200 W / mK does not necessarily impair thermal management. From the thermal and optical calculations, basic information was extracted that forms the basis of the Si package layout. The advantage of the Si packing due to the possibility of integrating functional components has been worked out. An optimized Si package is presented that meets in particular the requirements of the assembly and packaging technology of UVB and UVC LEDs. The process technology was designed and implemented. The first samples with integrated protection diode, an optimized reflector and an optically adjusted single Fresnel lens are presented. The Si packages are designed for the flip-chip technology of UV LEDs with SnAg soldering, thermo-compression or thermosonic bonding and silver sintering. Furthermore, an outlook is given on the possibilities of an encapsulating technology to improve the light extraction.