Dynamic Mechanical Analysis of Solder and Reliability Implications for Surface Mount Interconnections

The thermo-viscoelastic material behavior of solder has important consequences in advanced electronics packaging technologies that use surface mount (SM) solder interconnections. The long-term integrity of SM connections is controlled by the response of solder to the cyclic loading induced by periodic temperature excursions under product use conditions. The SM connections undergo stress relaxation and/or creep during each operational thermal cycle, which over time results in accumulated internal fatigue demage and degraded solder joint reliability. The fatigue damage per thermal cycle is maximized for operational conditions of relatively high temperatures and slow cycling rates with extended dwell time. These temperature-frequency conditions are the same as those that appreciably degrade the complex modulus in thermo-viscoelastic materials. The reliability of SM solder connections can be estimated using models that account for the fatigue damage per thermal cycle and failure statistice representative of wear-out.