Contact Resistance and Thermal Cycling Reliability of the Flip-Chip Joints Processed with Cu-Sn Mushroom Bumps

Abstract

Flip-chip bonding using Cu-Sn mushroom bumps composed of Cu pillar and Sn cap was accomplished, and the contact resistance and the thermal cycling reliability of the Cu-Sn mushroom bump joints were compared with those of the Sn planar bump joints. With flip-chip process at a same bonding stress, both the Cu-Sn mushroom bump joints and the Sn planar bump joints exhibited an almost identical average contact resistance. With increasing a bonding stress from 32 MPa to 44 MPa, the average contact resistances of the Cu-Sn mushroom bump joints and the Sn planar bump joints became reduced from 30 m Omega/bump to 25 m Omega/bump due to heavier plastic deformation of the bumps. The Cu-Sn mushroom bump joints exhibited a superior thermal cycling reliability to that of the Sn planar bump joints at a bonding stress of 32 MPa. While the contact resistance characteristics of the Cu-Sn mushroom bump joints were not deteriorated even after 1000 thermal cycles ranging between -40 degrees C and 80 degrees C, the contact resistance of the Sn planar bump joints substantially increased with thermal cycling.