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 Cu6Sn5 IMC layer, form FeSn2 nanophases via in situ reactions, and partially
substitute Cu in Cu6Sn5 to create (Cu,Fe)6Sn5. 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 %).
