Flip-Chip Process Using Interlocking-Bump Joints

A new flip-chip process using interlocking-bump joints, formed by inserting Cu bumps into Sn bumps, was investigated. Severe plastic deformation of Sn bumps occurred during formation of the interlocking-bump-joint structure. Contact resistance of the interlocking-bump joints was remarkably improved, compared to that of planar-bump joints. The average contact resistances below 17 mOmega/ bump were obtained for the interlocking-bump joints processed with bonding forces larger than 7 N. The interface resistance between a Cu bump and a Sn bump in the interlocking-bump joints processed with a bonding force of 15 N was evaluated as 11.2 mOmega/bump . Chip shear force was greatly improved from 0.14 N of the planar-bump joints up to 3.9 N for the interlocking-bump joints.