Improvement in Flip-Chip Bonding by Reduction of Oxides Using Hydrogen Radicals

The demand for high-density mounting increased because of the miniaturizing of a variety of electronic equipment such as personal computers and cellular phones. In response, the use of packaging methods such as flip-chip bonding has also increased to meet this demand. However, during the soldering process, the presence of oxides on the solder bump surface can obstruct the interconnections because oxides with a high melting point do not melt during the process. Methods for removing oxides from the solder bump surface have been developed. In this paper, we propose a novel oxide reduction method for the solder bump surface. This method uses hydrogen radicals generated by a heated catalyzer consisting of a tungsten wire. We have successfully demonstrated that the removal of oxides from the solder bump surface is possible by this treatment. Furthermore, we have verified that this method is effective in improving the reliability of flip-chip bonding without flux.