Pan Pacific Symposium Conference Proceedings


Author: Kyung-Wook Paik
Company: Korea Advanced Institute
Date Published: 2/2/1999   Conference: Pan Pacific Symposium

Abstract: In flip chip interconnection on organic substrates using eutectic Pb/Sn solder bumps, a highly reliable Under Bump Metallurgy (UBM) is required to maintain adhesion and solder wettability. Various UBM systems, such as 1m Al/0.2m Ti/5m Cu, 1m Al/0.2m Ti/1m Cu, 1m Al/0.2m Ni/1m Cu, 1m Al /0.2m Ti /1m Cu /0.2m NiV, 1m Al/ 0.2m Pd/1m Cu, and 1m Al /0.2m Ti /1m Pd /1m Cu have been investigated with regard to their interfacial reactions and adhesion properties under eutectic Pb/Sn solder bumps. The effects of the number of solder reflow cycles and the aging time on the growth of intermetallic compounds (IMCs) and on the solder ball shear strength were investigated. Good ball shear strength was obtained with 1m Al/0.2m Ti/5m Cu, 1m Al/0.2m Ni/1m Cu, 1m Al /0.2m Ti /1m Cu /0.2m NiV, and 1m Al /0.2m Ti /1m Pd /1m Cu even after 4 solder reflows or 7 day aging at 150oC. In contrast, 1m Al/0.2m Ti/1m Cu and 1m Al/0.2m Pd/1m Cu showed poor ball shear strength. The decrease of the shear strength was mainly due to the direct contact between solder and nonwettable metals such as Ti and Al, resulting in a delamination. In this case, thin 1m Cu and 0.2 m Pd diffusion barrier layer were completely consumed by Cu-Sn and Pd-Sn reaction.

KEY WORDS UBM (Under Bump Metallurgy), flip-chip interconnection, eutectic Pb/Sn, organic substrate, intermetallic compound, bump shear strength, electroplating

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