Novel bumping material for stacking silicon chips

Bumping processes like the controlled collapse chip connect new process (C4NP) and the immersion solder bumping process for a fine pitch bumping have the disadvantages of the complicated series of process and the possibility of the reliability problems, respectively. To overcome the weak points of these processes, we developed a novel bumping material based on the rheological behavior of the molten droplets of solder in a resin. The novel resin was designed to have the properties of low viscosity for the rheological behavior of the droplets during the bumping process, the elimination of the oxide layer on the solder powder for the wetting on the pad near the melting point of the solder, and no major weight loss caused by the out-gassing. With this novel material, the bumps array of Sn-58Bi solder were formed, and the applicability of the resin to the Sn-3.0Ag-0.5Cu (SAC305) was, also, identified.