Soft solder joints in power hybrid microcircuits

Lead-based soft solder alloys are used in the field of power hybrid microcircuits to provide low-stress component bonds. In this study solder joints were thermally aged and cycled in order to investigate the mechanisms of solder degradation. The samples were shear tested and examined by scanning electron microscopy. The cause of solder joint degradation was determined to be the segregation of intermetallic compounds from the lead-rich solder matrix. The application of plastic shear strain during thermal cycling formed severe microcracks between the lead-depleted compounds and the lead-rich matrix, resulting in a weak or fractured bond.