Thermal Stability of Solder Joints of Epoxy-based Sn-Bi Solder Paste

To investigate the effect of the epoxy resin shell on the thermal stability of Sn-Bi solder joints, the temperature range of 130 - 170 ℃ was set and thermal cycling tests were carried out on solder joints formed by self-made epoxy-based Sn-Bi solder paste and commercial Sn-Bi solder paste (without curable resin). Results show that after 1 000 thermal cycles, the epoxy resin shell on the surface of the solder joints formed by the epoxy-based Sn-Bi paste remains intact and the thickness of the intermetallic compound between the solder joint and the copper substrate is also significantly lower than that of the commercial Sn-Bi solder pastes. The electrical conductivity of the solder joint formed by the epoxy-based Sn-Bi paste decreases from 1.90×10⁶ to 7.96×10⁵ s/m after 1 000 thermal cycles, and the shear strength decreases from 145.7 to 123.7 MPa. However, the electrical conductivity of the solder joint formed by the commercial Sn-Bi paste decreases from 1.94×10⁶ to 4.95×10⁵ s/m, and the shear strength decreases from 116.1 to 97.3 MPa. Therefore, compared with commercial Sn-Bi solder paste, the epoxy resin shell on the surface of the solder joint formed by epoxy-based Sn-Bi solder paste effectively improves the shear strength and thermal stability of the solder joint, and to some extent hinders the growth of intermetallic compounds.