Effect of die-attach materials and thickness on the reliability of HP-LED

Different materials and thickness of die-attach layers can directly affect the heat dissipation of LED devices, so the influencing mechanism of interconnect materials and thickness to the thermal performances and optical durability were studied respectively. In the experiments, chip-on-board LED devices interconnected by gold-tin(Au80Sn20), solder paste and silver paste were prepared and evaluated respectively in terms of thermal resistance and reliability under wet and temperature life test. First, finite element analysis software ANSYS was used to simulate the influence of the die-attach layer´s thermal conductivity and the thickness on the junction temperature. The results show the junction temperature becomes lower when the thermal conductivity of the interconnect layers become higher and the thickness become thinner. At the same time, the thermal stress of different die-attach layers were simulated. By the thermal resistance test with the T3Ster instrument, it was found that the thermal resistance of the Au80Sn20 interconnected LED device was the lowest. Finally, 12 pieces of LED devices of each die-attach material packaged HP-LED were selected and aged in 55°C/55% RH condition for 2200 hours. The HP-LED interconnected by Au80Sn20 got the highest luminous flux durability. During the aging period, the change of the thermal resistance of LED device interconnected by sliver paste was more obvious than those interconnected by Au80Sn20 and solder paste.