text: With the recent advancement of the electronics industry, electronic components are being developed to have high performance and thus there is a demand for miniaturized and highly-densified packages. Accordingly, interposers which functions to connect ICs to a main board must be packed more densely. The high densification of packages is attributable to an increase of the number of I/Os of ICs, and the method for the connection with the interposers has also been made more efficient
  The growing popularity of one of the interposer technology is flip-chip bonding. Flip-chip assembly in the fabrication process flow of silicon integrated circuit (IC) devices is driven by several facts. First, the electrical performance of the semiconductor devices can be improved when the parasitic inductances correlated with conventional wire bonding interconnection techniques are reduced. Second, flip-chip assembly provides higher interconnection densities between chip and package than wire bonding. Third, flip-chip assembly consumes less silicon “real estate” than wire bonding, and thus helps to conserve silicon area and reduce device cost. And fourth, the fabrication cost can be reduced, when concurrent gang-bonding techniques are employed rather than consecutive individual bonding steps.
  In order to reduce interposer's size and its pitch, efforts were undertaken to replace the earlier solder-based interconnecting balls in flip-chip bonding with metal bumps, especially by an effort to create metal bumps by a modified wire ball technique. Typically, the metal bumps are created on an aluminum layer of the contact pads of semiconductor chips. Subsequently, the chips are attached to substrates using solder. The metal bumps are used for flip chip packaging with applications for LCDs, memories, microprocessors and microwave RFICs.