Mechanical strength of thin Cu-TSV memory dies used in 3D IC packaging

The mechanical strength of the thin dies especially with copper through-silicon via (Cu-TSV), has to be determined for ensuring good yield during manufacture handling and packaging. In this study, three test methods: a line-load on elastic-foundation (LoEF) test, a 3-point bending (3PB) test and a 4-point bending (4PB) test are used for the strength determination of Cu-TSV thin memory dies. The results of displacement (deflection) versus applied load of TSV memory die and corresponding failure loads are presented. The maximum mechanical failure stress, so called apparent strength, of memory dies is determined from experimental failure loads associated with finite element analysis. In addition, the actual strength of memory dies, by the superposition of mechanical stress and thermal residual stress, is applied to predict the failure initiation point of memory dies. It is found that actual strengths of memory dies (controlled by Cu-TSV) obtained from these three tests are consistent, but with only 60% of the die strength without Cu TSV.