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 1m Al/0.2m Ti/5m Cu, 1m Al/0.2m Ti/1m Cu, 1m Al/0.2m Ni/1m Cu, 1m Al /0.2m Ti /1m Cu /0.2m NiV, 1m Al/ 0.2m Pd/1m Cu, and 1m Al /0.2m Ti /1m Pd /1m 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 1m Al/0.2m Ti/5m Cu, 1m Al/0.2m Ni/1m Cu, 1m Al /0.2m Ti /1m Cu /0.2m NiV, and 1m Al /0.2m Ti /1m Pd /1m Cu even after 4 solder reflows or 7 day aging at 150oC. In contrast, 1m Al/0.2m Ti/1m Cu and 1m Al/0.2m Pd/1m 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 1m 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