Mechanical and electrical properties of reverse-offset printed Sn-Ag-Cu solder bumps

Solder pastes were formulated for reverse-offset printing using Sn-3.0Ag-0.5Cu alloy particles. Paste solderability was improved by increasing only a small amount of particle content without a change of flux amount in solder paste, which was affected by the improvement of paste printability. The electrical resistance of the printed solder bumps decreased from 6 MΩ to 0.05 mΩ as the particle content increased from 79 to 85 wt%. The shear strength of the printed solder bumps linearly increased from 46 to 61 MPa with the increase of particle content. Thermal and microstructural analysis revealed that the suppression of supercooling led to the growth of β-Sn aggregates surrounded by intermetallic compounds, which strengthened the mechanical properties.