Improvement in the reliability of AlGaInP-based light-emitting diode package using optimal silicone and leadframe structure

We investigated how the reliability of red light-emitting diode (LED) packages was affected by the types of silicones and package structures. The tensile strengths of different types of silicones varied from 3.2 to 8.1 MPa and their elongations were in the range of 40-150%. To characterize the output maintenance of packaged LEDs, the packages were kept under an 85°C/85% relative humidity (RH) condition for 72 h, which was then reflow-processed at 260°C three times. The output powers of the samples were degraded by 1.27-21.2% after the process, depending on the types of silicones. Only the sample LD-B experienced cracking. The effect of four different leadframe structures on the reliability of the sample LD-B was characterized. After the thermal treatments, the sample with 4 leads (circular window) suffered cracking. Simulations showed that unlike the others, the sample LD-B displayed additional stress concentrator at the centre of the silicone encapsulant. The spray-coating test revealed that moisture was permeated mainly through the Polyphthalamide (PPA)/silicone interfaces. These results show that use of silicone with high tensile strength, spray-coating, and optimized leadframe structure can be effective in achieving the high moisture reliability of red-LED packages.