Effects of Cracks on Interfacial Thermal Properties of LED Packages by Entropy Generation

Entropy generation is a kind of available energy loss. Evolution of the thermodynamic entropy during accelerated test of die attach in LED is studied with transient analysis. The existing models on the study of heat transfer in the solder layer, mainly including the effect of voids on the mechanical properties and the heat transfer performance. However, there are few investigations that relating the second law of thermodynamics to the voids in the DA layer, transient heat distribution is less considered. In this work, based on the temperature distribution, the convection entropy rate of the chip to the ambient and the conduction entropy of the DA layer are studied. The results show that, as the length of the crack increases, both the convection entropy rate and the conduction entropy increase. Particularly, when the crack length was increased from 30% to 40%, the normalized conduction entropy of the DA layer showed a sharp increase, which indicates that the large crack (more than 30%) will pose a serious challenge to the quality of the LED packaging.