Effect of multiple reflows on interfacial reaction and shear strength of Sn–Ag electroplated solder bumps for flip chip package

The effect of displacement rate and intermetallic compound (IMC) growth on the shear strength of electroplated Sn–2.5Ag (in wt.%) flip chip solder with Cu under-bump metallization (UBM) were investigated after multiple reflows. Cu6Sn5 IMC was formed at the interface after one reflow. After five reflows, two different IMC layers, consisting of a scallop-shaped Cu6Sn5 phase and a planar Cu3Sn phase, and their thicknesses increased with increasing reflow number up to 10. The shear strengths peaked after four reflows, and then decreased with increasing reflow number. Increasing displacement rate increased the shear force. The tendency toward brittle fracture characteristics was intensified with increasing displacement rate and reflow number.