Abstract: Two-color and four-color detectors have been emerged as the development of Infrared Focal Plane Array technology. Millions of pixels have arisen on the chips and the spot pitch is even less than 13 micron. So high I/O density makes the fabrication more critical. This is beyond the ability of traditional micro-interconnection technology such as wire bonding (WB) technology and tape automated bonding (TAB) technology. Flip chip hybridization offers numbers of advantages over the widely used wire bonding technique such as small package size, high interconnect density and low cost. It consists of procedures: Under Bump Metallization deposition, indium deposition, reflowing, flip-chip bonding and inserting the underfill. Development of every procedure was performed. And the indium bumps were also emphasized for that indium bumping was a critical technology in the application of high-density interconnection between a focal plane array and a Si read-out integrated circuit (ROIC) by flip chip bonding.