The study of thermal cycling performance of enacpasulant material in SMD LEDs application

Evaluation platform of high efficient LED package material have been set up for studying the relationship between material properties and LED performance. PLCC 5050 SMD LEDs were used as test vehicle in this study. Three kinds of encapsulant material were encapsulated to evaluate the performance of thermal cycling test (TCT). The encapsulant materials are including a hard type silicone epoxy hybrid encapsulat, a soft type silicone epoxy hybrid encapsulat and commercial silicone encapsulant. It was found that the soft type silicone epoxy encapsulant and commercial siliocone encapsulant can pass the thermal cycling test; however, the hard one was failed. In failure analysis, delaminating between LED chip and lead frame electrode was observed through optical microscopic cross-section analysis of failed sample, which indicates the large thermal stress results in the delamination of the hard type material during the thermal cycling test. Dynamic mechanical analysis (DMA) was used to study the behavior of the hard type, the soft type silicone epoxy hybrid resin and the commercial silicone encapsulant from -80°C ramping to 250°C. The TCT temperature condition is within the analyzed temperature range of DMA measurement. The results show that storage modulus of the soft silicone epoxy hybrid encapsulant and commercial silipocne is lower than the hard one; furthermore, storage modulus of the soft silicone epoxy hybrid encapsulant and commercial silipocne are decreasing significantly at around 50°C, while, the hard material keeps high modulus till 150°C. From DMA study, it is supposed that the soft type silicone epoxy hybrid resin and the commercial silicone encapsulated SMD LEDs show better stress relaxation ability than the hard type encapsulation. Therefore, designing of the proper mechanical properties of encapsulant is important to meet the thermal cycling test of SMD LED package.