In-Situ Method for Fatigue Life Assessment subjected to Surface Strain

A methodology to assess the solder joint reliability of electronic components on Printed Circuit Boards (PCB) under different surface strains is presented. Since the solder fatigue life depends on surface strains and measuring by strain gauge contains different uncertainties, a two-sided fixed beam is assumed and both the bending line and the surface strain along the PCB are calculated. For the realisation of a vibration shape according to the bending line, a two-sided clamped PCB is excited with the first natural frequency. Additionally, an acceleration sensor is mounted on the PCB so that experiments can be conducted under varying ambient temperature. The investigation of the PCB vibration shape is conducted by laser scanning. For the lifetime analysis, an in-situ monitoring is realised by a four-terminal sensing for each component.The results show a very good correlation between the calculated bending line and the measured PCB displacements. Furthermore, the influence of the mounted accelerometer on the vibration behaviour is shown. Finally, restricted areas are defined which should be left out for the component placement.