Influence of phosphor amount on microstructure and damage evolution of silicone/phosphor composite in light-emitting diodes packaging

Volume fraction of phosphor in silicone has strong impact on microstructure and damage evolution of silicone/phosphor composite, which eventually affect the performance and reliability of light-emitting diodes (LEDs) packaging. In this paper, mechanical response of silicone/phosphor composite under exterior loading is investigated experimentally and numerically. Test samples of silicone with various amount of phosphor are prepared and subjected to tensile loading. Micro-scale morphology and fracture surfaces of samples are observed by scanning electron microscopy (SEM) after tensile tests. Interphase debonding can be identified on fracture surface and cracks are initiated around debonded phosphor particles. In order to provide micro-scale illustrations of the macro-scale behavior, a three dimensional multi-sphere random unit cell (RUC) model is introduced. Silicone matrix is modeled as hyperelastic solid and interphase region is modeled with cohesive law. Both experiment and simulation results demonstrate that, increasing the amount of rigid phosphor stiffens the silicone composite. On the other hand, increasing phosphor amount also shortens the average distance between rigid phosphor particles and intensifies strain localization in silicone matrix, which consequently results in interphase debonding and crack growth in the composite. This effect is regarded as the main mechanism that controls mechanical degradation of the silicone/phosphor composite. (C) 2014 Elsevier Ltd. All rights reserved.