Fabrication of Aluminum Nitride Thermal Substrate and Low-Temperature Die-Bonding Process for High Power LED

In this study, a low-cost aluminum nitride (AlN) sintering process to produce thick AlN film substrate with a high thermal conductivity is developed. The thermal conductivity of the present produced thick AlN film substrate is about 163.8 W/mK, which is very close to the reported thermal conductivity of the AlN material. Also, a Sn-Bi die-bonding system is developed to die-bond light emitting diodes (LEDs) on the present sintered AlN substrate with a relatively low die-bonding temperature (below 160°C). In this work, to enhance a better wetting at the die-bonding interface, three external forces (10 N, 15 N, and 20 N) were applied on LED chips during the die-bonding process. We found that the 15-N applied force can achieve a better die-bonding interface among three external forces (10 N, 15 N, and 20 N). The LED die-attached on the AlN substrates by 15 N normal force has the best shear strength (41.5 MPa), compared to the shear strength of 36.9 MPa and 31.5 MPa of the LED die-attached on AlN substrates by 20 N and 10 N normal force, respectively. The LED chips die-attached on the AlN substrate by 15-N normal force shows the best thermal resistance (7.3°C/W). The agreement between the thermal resistance tests and the shear strength tests implies that the better die-bonding interface produced a higher shear strength and a lower thermal resistance of the LED chips die-bonded on the AlN substrates.