Strength evaluation of silicon die for 3D chip stacking packages using ABF as dielectric and barrier layer in through-silicon via

The objective of this study is to evaluate the strength of silicon dies covered with a polymer film – Ajinomoto Build-up Film (ABF) – through the four-point bending (4PB) test and finite element method (FEM) analysis. With the evaluated strength, the possibility of die-cracking in 3D packages, wherein the thinned stacking dies are covered with ABF, under a thermal cycle condition is further investigated. In this study, a sandwich structure composed of an ABF layer as the intermediate layer between two (1 0 0) silicon substrates is applied in the 4PB test. Additionally, two kinds of bonding pressure are applied in the fabrication of 4PB specimens: 1 and 5 MPa. The force–displacement relation of the specimen is first measured by the 4PB test. On the other hand, the corresponding FEM model is simulated to obtain the relation of the first principal stress and the applied displacement. By comparing the experimental data and simulation results, the strength of the silicon substrate covered with ABF can be evaluated. Moreover, the FEM analysis results of a 10-layered die stacking 3D package show that the stress distribution in each stacking die does not exceed the evaluated strength. In summary, this paper demonstrates that the strength of the silicon substrate covered with soft and elastic material, such as ABF, as dielectric and barrier layer in 3D die stacking packages can be enhanced.