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Study on non-uniformity of Through-Mask electroplated Ni thin-film

Through-mask electroplating has been widely used in the fabrication of chips, BGA substrates and PCBs etc. The uniformity of plating thin-film is the major factor contributed to the reliability of the products. Currently, it is usually by setting optimum plating parameters and adopting electrochemical method to achieve the uniformity of plating. However, the problem of non-uniform distribution of electric field, which is the major cause of the non-uniformity of the plating thin-film, has not been solved. In this paper, finite element method (FEM) was developed to analyze the non-uniform distribution of electric field under different conditions in the process of electroplating. The results show that different thickness of photo-resist and size of electroplating cell are two major factors contribute to the uniformity of plating thin-film. The uniform of electroplating cell can be improved by adding in-chip auxiliary electrode. Also better uniformity of the plating film in radial direction can achieved by setting a shield in the proper position of the plating solution and annular out-chip auxiliary electrode (Cu) around the wafer. The simulation results were consistent with experimental results, which proved that finite element method is an effect way to simulate the electroplating process.