The fabrication of electroplated gold and gold-tin bumps is well established world-wide to metallize chip 10s for Tape Automated Bonding (TAB) and Flip Chip Technology (FC). The method is predestined to realize smallest bump structures and highest 10 counts. Such a bumping process will be presented and characterized in this paper. The single process steps as sputtering, lithographic printing, electrochemical metal deposition and differential etching will be treated in detail. Possibilities, uncertainties and limits of the process will be demonstrated from a practical point of view. To guarantee the reliability of the process in the long term, the kind and effects of possible influencing factors must be known, which is particularly difficult with the electroplating of gold. The used sulfitic electrolytes are subjected to permanent changes of their bath chemistry and require a stringent analytical monitoring. Besides the choice of the right electrolyte the use of specially developed microelectroplating equipment is decisive for the attainable results. For assessing the bump quality, typical features like structural accuracy, roughness, ductility and others are used. To investigate the reliability of bumped ICs electrical measurements and shear tests after thermal cycling were carried out.
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