Flip chip technology is widely used on the electronic packaging, and the market forces drive toward finer pitch interconnection. Cu pillar bump structure is a currently trend of the fine pitch flip chip package with less than 100μm bump pitch. But there is a solder volume limitation on solder capped Cu pillar bump structure. In addition, Cu may easily react with Sn-based solder into intermetallic compounds (IMCs). So it may be difficult for much finer pitch application with the structure. © 2012 IEEE.