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Fabrication of high aspect ratio bumps for focal plane arrays applications
Author(s): Wei Zhang; Paul Bereznycky; Manuel Morales; Wei Huang; Doug Malchow; John Liobe; Scott Endicter; Michael Caro; Michael J. Evans; Sean Houlihan
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Paper Abstract

For ultra-fine pixel pitch focal plane array (FPA) applications, flip-chip hybridization has advantages including high I/O density and short distance between the photodiode array (PDA) and the readout integrated circuit (ROIC). Indium has become the primary interconnect material because of its high ductility at low temperature. Successful mating of large format die becomes increasingly difficult, however, for finer pitch applications where bumps are shorter, as tolerance for bowing is low. Simultaneously, the epoxy filling process for large image format, hybridized focal planes becomes more challenging. These constraints call for tall indium bumps with high aspect ratio to accommodate die bowing and provide larger openings for the flow of fill epoxy. A process for the fabrication of highly uniform, high aspect ratio (height:diameter) indium bumps has been developed by Sensors Unlimited Inc. (SUI), a Collins Aerospace Company. The grain size of the deposited indium metal is minimized by optimizing process parameters as well as introducing intermediate metal layers underneath the indium bumps. Anisotropic deposition has been achieved by optimizing deposition rate and controlling substrate parameters. Indium bumps with aspect ratios over 2:1 and flat bump heads have been achieved. The developed bump process has been successfully applied to the fabrication of high resolution indium gallium arsenide (InGaAs) FPAs. Key control parameters for bump formation will be discussed in this paper.

Paper Details

Date Published: 7 May 2019
PDF: 10 pages
Proc. SPIE 11002, Infrared Technology and Applications XLV, 110022F (7 May 2019); doi: 10.1117/12.2519202
Show Author Affiliations
Wei Zhang, Sensors Unlimited, a Collins Aerospace Co. (United States)
Paul Bereznycky, Sensors Unlimited, a Collins Aerospace Co. (United States)
Manuel Morales, Sensors Unlimited, a Collins Aerospace Co. (United States)
Wei Huang, Sensors Unlimited, a Collins Aerospace Co. (United States)
Doug Malchow, Sensors Unlimited, a Collins Aerospace Co. (United States)
John Liobe, Sensors Unlimited, a Collins Aerospace Co. (United States)
Scott Endicter, Sensors Unlimited, a Collins Aerospace Co. (United States)
Michael Caro, Sensors Unlimited, a Collins Aerospace Co. (United States)
Michael J. Evans, Sensors Unlimited, a Collins Aerospace Co. (United States)
Sean Houlihan, Sensors Unlimited, a Collins Aerospace Co. (United States)


Published in SPIE Proceedings Vol. 11002:
Infrared Technology and Applications XLV
Bjørn F. Andresen; Gabor F. Fulop; Charles M. Hanson, Editor(s)

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