NDLI: Influences of pad shape and solder microstructure on shear force of low cost flip chip bumps

Content Provider	IEEE Xplore Digital Library
Author	Jian Cai Law, S. Teng, A. Chan, P.C.H.
Copyright Year	2000
Description	Author affiliation: Computer Aided Design & Manuf. Facility, Hong Kong Univ. of Sci. & Technol., China (Jian Cai)
Abstract	The bumping process plays a critical role in flip chip technology. A low cost bumping process has been developed using electroless nickel and immersion gold followed by stencil printing. The process flow is described in this paper. The Al pad size is about 100 /spl mu/m in diameter with a pitch of 400 /spl mu/m. Different electroless plating solutions were evaluated and different solder pastes were used to evaluate the stencil printing process. Different pad shapes were also tested for shear strength. Ni studs with no bump material were fabricated to evaluate the electroless process. The shear force test result shows a strength value of 230 MPa for Ni studs. The solder bump after reflow has a diameter of 160 /spl mu/m and a height of 120 /spl mu/m. There is some difference in the shear force test results for different pad shapes. SEM and EDAX results of the fracture surface indicate that the fracture was cohesive or inside the solder. Cross sections showed some intermetallic layers at the interface. A Ni-Sn intermetallic layer and a phosphorus rich layer formed during reflow, which have compositions of Ni/sub 3/Sn/sub 4/ and Ni/sub 3/P respectively. The low cost flip chip samples were subjected to multiple reflows and shear force tests were performed. Fracture surfaces were analysed and failure modes were differentiated.
Starting Page	91
Ending Page	98
File Size	1666553
Page Count	8
File Format	PDF
ISBN	0780366549
DOI	10.1109/EMAP.2000.904138
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2000-11-30
Publisher Place	China
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Shape Microstructure Nickel Testing Flip chip Costs Printing Surface cracks Intermetallic Gold
Content Type	Text
Resource Type	Article

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