Abstract
Silicone resin has recently attracted great attention as a high-power Light Emitting Diode (LED) encapsulant material due to its good thermal stability and optical properties. In general, the abrupt curing reaction of the silicone resin for the LED encapsulant during the curing process induces reduction in the mechanical and optical properties of the LED product due to the generation of residual void and moisture, birefringence, and residual stress in the final formation. In order to prevent such an abrupt curing reaction, the reduction of residual void and birefringence of the silicone resin was observed through experimentation by introducing the multi-step cure processes, while the residual stress was calculated by conducting finite element analysis that coupled the heat of cure reaction and cure shrinkage. The results of experiment and analysis showed that it was during the three-step curing process that the residual void, birefringence, and residual stress reduced the most in similar tendency. Through such experimentation and finite element analysis, the study was able to confirm that the optimization of the LED encapsulant packaging process was possible.
Highlights
Light Emitting Diode (LED) has attracted great attention as a next-generation light source due to its excellent characteristics such as high-energy efficiency, quick response, long life, and light weight
It is considered that internal voids are sufficiently removed when applying the step cure process from low temperature to high temperature since the viscosity is maintained at low enough state prior to curing, after which curing with almost no voids present would be possible during the reaction
Lai and Wang [20] predicted residual stress distribution by comparing injection molding analysis and birefringence for COP plastic lenses. They analyzed the effect of birefringence on the optical property of lenses by measuring the optical aberrations of lenses according to process conditions using design of experiment
Summary
Light Emitting Diode (LED) has attracted great attention as a next-generation light source due to its excellent characteristics such as high-energy efficiency, quick response, long life, and light weight. Abrupt temperature rise can cause various defects in the cured silicone resin; i.e., surface roughening, delamination from LED chip, residual void including air and water, and residual stress, which lead to the deterioration of mechanical and optical properties of LED lighting products. Bogetti and Gillespie [5] analyzed the development of residual stresses in the cured thick composite laminates by coupling the incremental laminated plate theory with the one-dimensional cure simulation, accounting for the chemical shrinkage based on the cure-dependent mechanical property of thermoset resin. Whether the step cure process was effective in terms of reducing the residual stress and birefringence was quantitatively studied by calculating the residual stress through the finite element analysis of the cure process and experimentally measuring the birefringence. The optimal cure process was derived by conducting an optimization analysis
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