The investigation of flip-chip eutectic bonding on the performance and lifetime of light emitting diodes

The present study investigated the eutectic bonding on the long-term performance of flip-chip LEDs under varying aging stresses. A direct eutectic bond was used to adhesive the power LED chip to the Al₂O₃ ceramic substrate. The flip-chip structure was capable to perform both high thermal conductance and good light extraction efficiency of the LED device. The varying sputtered copper thickness on the ceramic substrate was investigated to reduce junction temperature. The experimental results showed that flip-chip LEDs using eutectic bonding exhibited superior die shear strength and also performed good long-term reliability after applying 1000 h aging test under various ambient temperature and relative humidity (RH). Thermal resistance decreases as thickness of copper was decreased from 60 μm to 15 μm. The lumen maintenances were above 98.5% and 104% for the eutectic flip-chip LEDs under temperature of 298 K and 358 K, respectively. When the RH was increased from 50% to 90%, lumen maintenance was higher than 100% for all eutectic flip-chip LEDs. However, the luminous decay was at 31.6% for sliver pate LED sample at 90% RH after aging tests. The experimental results are applicable for optimizing the direct eutectic bonding process and for designing highly reliable LED devices.