Transient thermal strain measurements in electronic packages

Fractional fringe moire interferometry was successfully applied to monitor thermo/mechanical strain histories in a memory device as the temperature was changing from room temperature (25°C) to an arbitrarily chosen final temperature of 80°C. Full displacement fields were recorded at different temperatures and used to predict strains in a small region at the chip corner. Moreover, strains across the chip thickness along a line close to the chip corner were investigated. A dramatic change in the pattern of axial strain growth was observed for temperatures around 70°C and above. It is suggested that the development of severe compressive stains due to bending of the package is responsible for such a change. A minor deficiency in the data collection procedure affected the accuracy of strains predicted for the selected region. This necessitated the use of a least-squares curve fitting procedure to represent deformations based on experimentally collected values. This yielded smooth strain distributions giving a clear qualitative picture of strain histories, but is introduced some errors in the strain magnitudes (10-15% of actual values)