Modal analysis of board vibration during mechanical reliability tests of lead-free solder joints

Complex studies on reliability of lead-free solder joints subjected to combined temperature cycles and vibration shown that the results obtained in two independent laboratories (Wroclaw University of Technology and Fraunhofer Institute for Electronic Nano Systems ENAS in Chemnitz) equipped in different equipment may differ more or less significantly depending on tested objects (SMD resistors, BGA daisy chains, one-sided PCB, multilayer PCB) despite the same testing condition. Controlled conditions in such case is a profile of temperature cycles and PSD level of vibration measured in the center of tested PCBs and on fixture. This can be problematic in the case of standardization and comparison of combined reliability tests performed in different laboratories. In order to determine the reason of observed differences, two kinds of PCBs (one sided and multilayer) as well as two kinds of tested objects (BGA - Ball Grid Array packages and SMD - Surface Mount Device chip resistors) were subjected to vibration using different vibration setups and scanned using scanning laser vibrometer. Within the frame of the paper conclusions of performed reliability tests as well as the results of comprehensive modal analysis using scanning laser vibrometer will be presented. The results of reliability tests include mean time to failure as well as X-Ray computed tomography of failed solder joints. The modal analysis enabled to assess deflection of tested PCBs during reliability tests and determine the possible reason of observed differences in fatigue process.