Comprehensive studies on interfacial properties and microstructures of silicone used in LED packaging

Light emitting diodes (LEDs) hold the promise for efficient, lightweight and environmental-friendly lighting sources, which is regarded as the next-generation lighting technology. Since so many problems still remain to be solved, this emerging technology has attracted the attention of a large number of researchers. Among several issues frequently discussed in the community, the long-time reliability of LED module is crucial. Since the packaging material and structure play an indispensable role on the reliability of LED, we are motivated to study the material properties of silicone and the interfacial strengths of silicone on various substrates. These properties are closely connected to the reliability of LED packaging, yet they have rarely been investigated. Uniaxial tensile test is adopted to obtain mechanical properties of silicone and interfacial shearing test is used to investigate the interfacial behavior of silicone on three different substrates. The results of tensile tests show that the ultimate tensile strength of tested silicone is around 0.4MPa at room temperature, exceeded stress will result in failure of the material. The fractograph analysis is conducted by scanning electron microscope (SEM) to provide micro-scale explanations of the fracture under tensile load. In the shearing test part, for the interface of silicone on copper substrate, the fracture force is 8.05N, while the fracture forces of silicone-ceramic and silicone-silicon interfaces are 7.34N and 6.87N, respectively. Since interfacial fracture force is an important indicator for interfacial delamination, it can be summarized that the interfacial strength of silicone-copper is the highest among the tested samples.