Direct bonding of alumina substrate with copper heat sink in air assisted by ultrasonic vibrations for high power LEDs devices

With the trend of high power, high luminance in the industries of solid-state lighting, the difficulty of heat dissipation gets remarkable. Thermal interfaces in packages are usually the drawbacks or hinders for heat dissipation due to the wide use of high-thermal-conductivity materials. Ceramics, such as alumina, AlN et al. are the cases. In this paper, the copper heat sink was directly bonded with the alumina substrate by a Zn-Al filler with an ultrasonic-assisted bonding method. Different from a DBC (direct bonded copper) substrate process, robust bonds were fabricated through such a direct and simple bonding method. The interfaces at both the alumina/filler and the filler/Cu are good and with no obvious defects under scanning electron microscope (SEM). The bond ratio was above 95%. Wetting and reacting at the two interfaces were verified. Shear tests showed that the strength reaches above 65 MPa. Compared with traditional methods for interconnections of thermal interfaces, here we proposed a robust and rapid bonding one.