Indium bump deposition for flip-chip micro-array image sensing and display applications

Solder bump array formation is a key step in micro-array flip-chip fabrication process. Fabrication of solder bumps with small diameter and high aspect ratio geometries is necessary for high pixel density and low noise detectors. Indium is an attractive material for low temperature sensing application due to its cryogenic stability, good thermal and electrical conductivity, and ductile nature. In this paper, fill quality of micro-patterned arrays with thermally evaporated indium thin film is studied. Impact of indium evaporation rate, substrate temperature, bump aspect ratio and bump array pitch on bump formation in the via trenches is investigated. The indium bump formation dynamics are discussed in detail. State-of-art indium bump size with high aspect ratio and small array pitch is achieved, along with high uniformity and low defect density.