Simulation analysis of the fine pitch micro-bump formation with solder injection method

In this paper, a new micro-bump formation process was investigated by simulation method. In detail, a solder filling fixture was fabricated to hold the solder paste or alloy over the photoresist openings. As the fixture moves along the wafer surface, the solder paste or alloy was heated up to liquid status to fill in the photoresist openings under pressure force and vacuum circumstance. Then cooled down the temperature and solidified the molten solder to form the desired bumps. Before conduct the new bumping formation process, simulation work should be done to evaluate the process practicability and validation. Emphasis was placed on the simulation process construction to demonstrate the feasibility of the new bumping technology. Different influencing factors that may affect the bumping quality were studied such as the wall thickness of the filling fixture, gap between the wafer and the filling fixture, filling pressure, movement velocity of the filling fixture, and so on. In conclusion, an optimal filling parameter was obtained based on the simulation result. Future work will concentrate on the filling tests to verify the simulation results.