Abstract
A high power UV light emitting diode (LED) multichip module package based on aluminum nitride (AlN) and alumina (Al2O3) is presented. The AlN substrate with a high thermal conductivity of up to 180 W/(m·K) and LED chips based on a copper alloy provide superb thermal management and heat extraction. Efficient cooling is an important prerequisite for the increase of extractable optical power and for the reduction of thermally induced wavelength shift. A design of a stackable module featuring arrays of 7×2 indium-gallium-aluminum-nitride UV LED chips at 395 nm is developed. This configuration of submodules 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 thermomechanical modeling of the submount is conducted using finite element 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 microtomography. 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 33.9 W/cm2 at the LED surface with respect to the footprint and pitch of the attached chips.
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