Facile fabrication and low-temperature bonding of Cu@Sn-Bi core-shell particles for conductive pastes.

The rapid development of flexible wearable electronics arouses huge demand for low-temperature sintering metal inks applied to temperature-sensitive substrates. The high sintering temperature and easy oxidation limited the application of Cu-based pastes. A two-step method involving liquid co-reduction and heat ripening was developed to synthesize Cu@Sn-Bi core-shell particles. The thickness of Sn-Bi shells can be flexibly adjusted changing the mass ratio of Cu to Sn-Bi. The volume resistivity of printed circuits using Cu@Sn-Bi pastes solidified at 200 °C was as low as 481 μΩ cm, which increased by 11.8% after an aging process at 190 °C for 6 h. The outstanding stability in a harsh environment would attribute to the effective protection of Sn-Bi alloy shells. This work suggests a new pathway toward the low-temperature bonding and anti-oxidation of Cu particles as conductive fillers, which can be widely applied to the additive manufacturing of flexible wearable electronics.