Ultraviolet LED multi-chip module based on ceramic substrate
A high power ultraviolet (UV) light emitting diode (LED) multi-chip module package based on aluminum nitride (AIN) and alumina (Al203) is presented. The AIN subsrate with a high thermal conductivity of up to 180W/(mK) and LED chips based on copper alloy provide superb thermal management and heat extraction. Efficient cooling is an important prerequisite for the increase of extractable optical power and decrease of thermally induced wavelength shift. A design of a stackable module featuring arrays of 7x2 indium-gallium-aluminum-nitride UV LED ships at 395 nm is developed. This configuration of sub-modules allows for the scalable assembly of line sources with different lengths. Applications using UV LEDs cover market segments such as curing of adhesives, inks and coatings, sterilization of medical equipment and treatment of potable water, as well as various uses in chemical detection, biochemical analytics and spectroscopy. Thermal and thermo-mechanical modeling of the sub-mount is conducted using finite elements analysis. Die attach using eutectic gold-tin solder, lower melting tin-lead solder and silver-filled adhesive are compared with respect to optical output power and wavelength drift. Mechanical strength and structure of the resulting joints are investigated using shear force measurements, cross-sectioning and micro-tomography. An optical output power of 7.7 W is achieved using a cluster of 14 LED chips at 1050 mA resulting in a peak irradiance of 30.8 W/cm² at the LED surface with respect to the footprint and pitch of the attached chips.