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Improvement study of solder bumped flip chip technologies

Authors Fu, Xiaochen
Issue Date 2005
Summary In recent years, a rapid advance in the electronic packaging and the growing market for faster, lighter, smaller, yet less expensive electronic products, the low cost stencil printing based on flip-chip has attracted attention. The low-cost stencil printing process consists of the electroless NickeI/Gold (Ni/Au) Under Bump Metallurgy (UBM), and the solder paste printing using the metal stencil mask on top of the UBM. The electroless plating replaces the expensive photolithograph and vaccum sputtering in the UBM formation process as a cost effectiveness consideration. In fine pitch stencil printing, uniformity and bridging have been the major issues. In order to improve the quality of the solder ball, the squeegee blade and printing parameters were optimized in the stencil printing process. The actual height of the solder ball achieved was closer our desired height of solder ball by the use of the new squeegee blade. In the solder reflow procedure, the bridging defect was eliminated by the optimization of the reflow process. After the soldering, the flux residues remained in the gap between the chip and the substrate. A proper cleaning process was performed to clean the flux residues. The electrical performance of the solder joint and the active level of the flux were considered in selecting the proper flux.
Note Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2005
Language English
Format Thesis
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