Reliability of solder joints in High-power LED package in power cycling tests

In this paper, an improved method to investigate the reliability of solder joint between High-power LED chip and heat sink is presented. The power cycling is carried out through the switching on and off of the current stress. The optical and electrical characteristics do not degrade apparently. Electrical method is used to measure the thermal resistance of high-power LED which increases from 15.81°C/W to 43.95°C/W for typical one of three samples before and after power cycling. Furthermore, some voids are observed in solder joint after power cycling according to the result of scanning acoustic microscope (SAM). That is, the solder joint degrade significantly after power cycling. Our results indicate that this method can effectually evaluate the reliability of solder joint.