Characterization of micro bump formed by Injection Molded Solder (IMS) technology

Injection Molded Solder (IMS) is an advanced solder bumping technology that the solder bumps can be made by injected pure molten solder through the masks. In this study, 3 different sizes of bumps were fabricated by IMS with PI film mask. 3 different solder types, Sn-Ag-Cu, Sn-Bi, and In-Sn were selected for this study. Firstly, effects of IMS stage temperature on bump mechanical integrity for Sn-Ag-Cu were evaluated by bump shear and cross-sectional IMC observation. It was found that higher temperature produced scalloped Cu₆Sn₅ IMC at the interface, however lower temperatures produced planar Cu₆Sn₅ IMC. The bumps fabricated with a lower temperature were subjected to thermal aging, and characterized by shear test and cross-sectional IMC observation. No interfacial failure was observed before and after aging, and shear fracture modes for all bumps were ductile. In addition, lower melting point solders Sn-Bi and In-Sn were subjected to aging, and no interfacial failure was found. Changes in shear strength after aging are dependent on the microstructure at the shear height.