Thermal strain measurements of solder joints in electronic packaging using moire interferometry

Abstract

Thermal strains are the major cause of low cycle fatigue failures of solder interconnections in an electronic package. The strains are created by a coefficient of thermal expansion (CTE) mismatch that occurs between two levels of packaging. As the package approaches smaller dimensions, the measurements of strain concentrations in the solder interconnection become very difficult. In this paper, Moiré interferometry technique was applied to evaluate the thermal strains in the second level interconnections for both conventional pin-in-hole (PIH) packages and surface mount components. The coefficient of thermal expansion of each component was measured. The thermal strains distributions in the solder interconnections (typical dimensions are 10 - 100 micrometers) were determined, and the reliability issues were discussed. The strains in solder joints of the PIH components were much higher than those of the stacked surface mount component. Even though the surface mount component had a lower inherent strength, the overall mechanical reliability was much higher since there were practically no localized strain concentrations.