Phosphor concentration in silicone and its effect on the mechanical and interfacial properties of phosphor-filled silicone

The phenomenon that phosphor particles tend to settle in silicone is widely known. Recent researchers have discussed the effects of phosphor concentration on luminous efficacy of LED packaging. But to produce reliable products, mechanical and interfacial considerations are also essential. In this paper, the mechanical behaviors and interfacial strength of silicone with different levels of phosphor concentration are studied. In our experiments, four groups of silicone samples with different levels of phosphor concentration are prepared and are subjected to the uniaxial tensile loads. The results of tensile tests indicate that, for the same level of phosphor addition, higher phosphor concentration will result in lower tensile strength of the phosphor-filled silicone. SEM cross-section images show that the phosphor particles concentrate in the bottom area of the silicone layer. The fractograph of the material indicates that the crack initiates among the bottom area where phosphor particles settle. Interfacial tests of phosphor-filled silicone and GaN substrate are also conducted. The results demonstrate that phosphor concentration has negative effect on interfacial strength of materials. Therefore, for LED package, uniformly distributed phosphor in silicone is extremely demanded for mechanical and interfacial considerations.