The effect of thermal stress on the reliability of low Ag solder joints in high-power LEDs

The reliability of solder joints of LED packages is very critical in ensuring the overall reliability of a LED lighting fixture. This study focuses on the influence of voids on the reliability of SAC105 solder joints of high-power LEDs. Therefore, the solder joints are characterized by the nondestructive test method of computer tomography (CT) before and after accelerated aging tests to document the development of failures. This three-dimensional method enables not only detection of cracks and voids in solder joints but also determination of their exact positions and volumes. The solder joints were first classified by their void percentage, followed by accelerated aging processes such as the air-to-air thermal shock, liquid-to-liquid thermal shock, and power cycle test. Based on the CT-data, the times of origin of failures as well as the differences of the failure modes of the various thermal load processes can be analyzed.