Effects of α-Fe₂O₃ Additions on Assembly Reliability of Electroplated Sn-Based Solder Cap on Cu Pillar Bump During Thermal Cycling

Composite solder alloys reinforced by different nominal concentrations of α-Fe₂O₃ nanoparticles are examined and the performance of corresponding copper (Cu) pillar bumps during thermal cycling (TC) tests is investigated. Firstly, the spherical α- Fe₂O₃ nanoparticles (50 nm in diameter) were successfully prepared by a chemical method. Then, the Sn-xFe₂O₃ composite solders with different concentrations of α-Fe₂O₃ were deposited on the surface of Cu pillar bumps by electroplating. During electroplating, the concentration of α-Fe₂O₃ nanoparticles in the plating solution ranged from 0 g/L to 0.04 g/L. TC tests of fabricated joints were conducted from − 65°C to 150°C for different numbers of cycles. The microstructure, evolution of interfacial intermetallic compounds (IMCs) and the shear strength of the solder joints were investigated following TC tests. Cross-sectional analysis indicates that adding α-Fe₂O₃ nanoparticles can remarkably suppress the overgrowth of the interfacial IMCs. Compared to the strength of joint without nanoparticles after the TC test, the strength of joints increases with the addition of α-Fe₂O₃ and an optimum nominal concentration of 0.032 g/L in the electroplating solution was identified.