Reconstruction and thermal performance analysis of die-bonding filling states for high-power light-emitting diode devices

This paper proposed a half-experimental model to reconstruct the die-bonding thermal path of high-power light-emitting diodes (HP-LEDs). In this model, the partially insufficient filling of bonding materials and their directional/random distributions (“filling state” for short) have been taken into consideration. Both the silver-paste structure and the Au/Sn-eutectic structure were analyzed and compared. Finite element analysis (FEA) indicated that qualified die-bonding with uniform filled areas would lead to much better thermal performance. Hotspots have been observed above the insufficiently filled regions. The simulated thermal resistances of the defective bonding were 5.4 times and 2.1 times higher than those of the qualified samples under conditions of Au/Sn-eutectic and silver-paste, respectively. Transient thermal resistance measurements further demonstrated that the devices with different filling states would result in distinct thermal resistances. Interestingly, it was noted that although the qualified silver-paste bonding had a larger filled area, the measured thermal resistance remained higher than that of the defective Au/Sn-eutectic bonding because of the high contact thermal resistance caused by poor wetting properties. Furthermore, defectively bonded LED devices revealed a poor maintenance of luminous flux after 500 h of aging, which was consistent with the results of thermal performance analysis on the reconstructed die-bonding models.