The influence of voids in solder joints on thermal performance and reliability investigated with transient thermal analysis

The thermal management of modern high power LEDs is essential for their life time. An important aspect is the thermal path from the heat generated in the LED die and phosphor, over the printed circuit board (PCB) to the heat sink. The temperature of the LED die depends on the quality of the solder joint between the LED package and the copper pads on the PCB. To evaluate the quality of the solder joint the transient thermal analysis is a powerful tool. In this paper the relative thermal resistance method is applied to detect the initial increase of the thermal resistance by voids in the solder joint and furthermore the impact of the initial voids on the reliability of the ceramic LED packages. The investigation in this paper reveals that the samples with voids have initially solely a slightly higher thermal resistance but the voids cause a significant faster thermal degradation during temperature shock test due to increased crack growth in the solder joint.