The solder on rubber (SOR) interconnection design and its reliability assessment based on shear strength test and finite element analysis

A novel chip-on-metal structure of the advanced wafer level chip scale package (WLCSP) which has the capability of redistributing the electrical circuit is proposed in this study. In the WLCSP, the solder on rubber (SOR) design expands the chip area and also provides a buffer layer for the deformation energy from the coefficient of thermal expansion (CTE) mismatch. By using the solder ball shear test, the stress/strain-released behavior in the SOR structure is investigated in this research. On the other hand, a three-dimensional nonlinear finite element (FE) model for the ball shear test is established to assist the design of the package. The force-displacement curves from the FE analysis are compared with the experimental results to demonstrate the accuracy of the simulation. Likewise, the issue from element mesh density is also discussed herein. The investigation reveals that the SOR structure could highly decrease the damage in solder bumps from the ball shear test. Furthermore, the transferred stress/strain in the interconnect near the contact pad could be diminished through a suitable layout of redistribution lines.