Comparative study on the hourglass-like joint of electroplated Sn-base solder reinforced by adding Ag₃Sn nanoparticles and Ag micro-alloying elements

In this work, two types of tin (Sn)-based solder bumps reinforced by Ag₃Sn nanoparticles (nano-Ag₃Sn), and Ag microalloying elements were successfully deposited on copper-clad laminates (CCL) by electroplating. Hourglass-shaped Sn-based solder joints were formed by precise control of the solder volume and the joint height during the reflowing process in solder bonding. Results show that when shaping the solder joints during solder reflowing, Ag₃Sn nanoparticles would uniformly disperse in the Sn-nano-Ag₃Sn solder joint, while microalloying Ag preferentially binds to Sn elements enriching at Sn-Ag solder/CCL interfaces and producing large interfacial intermetallic compounds (IMCs). After the solder reflowing, the nano-Ag₃Sn will redistribute in the solder joints, where the nano-Ag₃Sn adjacent to the solder/CCL interface would advance and adhere to the IMC surface. Compared with the solder joints containing Ag microalloying elements, nano-Ag₃Sn can aggregate on the surface IMC surfaces and hinder the interdiffusion of Sn and Cu ions across the solder/CCL interface. Mechanical shear strength tests of solder joints illustrate the enhancement of mechanical robustness of nano- Ag₃Sn reinforced solder, which inherently correlates to the absorption of nano- Ag₃Sn at the interfaces. Thus, we conclude that the nano-Ag₃Sn will inhibit the overgrowth of the interfacial IMC, specifically Cu₆Sn₅, which ultimately improves the mechanical strength and interconnect reliability of the hourglass-shaped solder joints.