Indium Bump Deposition for Flip-Chip Micro-Array Image Sensing and Display Applications

In the micro-array flip-chip fabrication process, the formation of solder bumps with small diameter and high aspect ratio is key for high pixel density and low noise detectors. Because of its cryogenic ability, good thermal and electrical conductivity, and ductile nature, indium is the ideal material for bump formation in low temperature sensing applications.

In this paper, we examine:

• Fill quality of micro-patterned arrays with thermally evaporated indium thin film
• The impact of indium evaporation rate, substrate temperature, bump aspect ratio and bump array pitch on bump formation in the via trenches
• How to achieve state-of-the-art indium bump size with high aspect ratio and small array pitch, along with high uniformity and low defect density

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