Influence of Fe-nanoparticle doped flux on electromigration effects in SAC305 solder joints

This study investigates the impact of incorporating iron nanoparticles (Fe-NPs) into SAC305 solder joints via flux doping on electromigration under prolonged high-current stressing. Chip-sized surface-mount devices (SMDs) solder joints were produced using flux with Fe-NP concentrations of 0.5, 1.0 and 2.0 wt%. The joints were subjected to 4 A for up to 4000 h. Enhancing electromigration (EM), localized high current densities were generated by track-to-pad angles of 90 and 135°. Secondary ion mass spectroscopy (SIMS) proved that flux doping successfully kept the Fe-NPs at the solder pad region, where they could affect electromigration. Shear tests evaluated mechanical reliability, while microstructure analysis, including intermetallic compound (IMC) layer thickness measurements, provided insight into material behaviour. After 2000 and 4000 h of loading, 0402 joints exhibited copper dissolution from the pad at the cathode, a phenomenon absent in joints prepared with 0.5 wt% Fe-NPs. The interfacial IMC layer in reference samples grew ∼1.1 μm (66 %) at the anode. In contrast, samples with Fe-NPs showed reduced IMC thickness increase of around 0–0.5 μm (0–28 %). This reduction is attributed to the diffusion-inhibiting effects of the metal nanoparticles. Fe-NPs segregate in front of the Cu 6 Sn 5 IMC layer, form FeSn 2 nanophases via in situ reactions, and partially substitute Cu in Cu 6 Sn 5 to create (Cu,Fe) 6 Sn 5 . These effects increase the activation energy of interfacial diffusion and thereby suppress Cu atom transport into the solder bulk. After 4000 h, shear performance of joints with 0402 components decreased by 2.1–5.6 MPa (12–27 %).