Mechanism and thermal effect of delamination in light-emitting diode packages

In this paper we report on the mechanism of delamination in light-emitting diode (LED) packages and its effects on thermal characteristics of LEDs. The LED samples were subjected to moisture preconditioning treatments followed by heat block testing. Transient thermal measurements were performed for the investigation of the thermal behavior of the delaminated LEDs. Increase of thermal resistance with the degree of delamination was observed from the transient measurement test. Thermomechanical stress and hygro-mechanical stress in the LED package were obtained by coupled-field analysis using FEA. The calculated thermo-mechanical and hygro-mechanical stress distributions agree well with the micrographical evidence. It was found that the thermomechanical stress plays more important role than the hygro-mechanical stress for the development of delamination in the LED packages. Moisture preconditioning for 3 hrs and 6 hrs under 85 ̊C/85RH conditions was found to make little contribution to the delamination between the chip and lead frame. Significant delamination was expected for the samples experienced the moisture preconditioning for 24 hrs.