Microstructure, kinetic analysis and hardness of Sn–Ag–Cu–1 wt% nano-ZrO 2 composite solder on OSP-Cu pads

Abstract

Nano-sized, nonreacting, noncoarsening ZrO 2 particle-reinforced Sn–Ag–Cu composite solders were prepared by mechanically dispersing ZrO 2 nano-particles into Sn–Ag–Cu solder and the interfacial morphology between the solder and organic solderability preservative (OSP)-Cu pads were characterized metallographically. At their interfaces, island-shaped Cu 6Sn 5 and Cu 3Sn intermetallic compound (IMC) layers were found in solder joints with and without the ZrO 2 particles and the IMC layer thickness was substantially increased with reaction time and temperature. In the solder ball region, needle-shaped Ag 3Sn and spherically-shaped Cu 6Sn 5 IMC particles were found to be uniformly distributed in the β–Sn matrix. However, after the addition of ZrO 2 nano-particles, Ag 3Sn and Cu 6Sn 5 IMC particles appeared with a fine microstructure and retarded the growth rate of the IMC layers at their interfaces. From a kinetic analysis, the calculated activation energies for the total (Cu 6Sn 5 + Cu 3Sn) IMC layers for Sn–Ag–Cu and Sn–Ag–Cu–1 wt% ZrO 2 composite solder joints on OSP-Cu pads were about 53.2 and 59.5 kJ/mol, respectively. In addition, solder joints containing ZrO 2 nano-particles displayed higher hardness due to the uniform distribution of ZrO 2 nano-particles as well as the refined IMC particles. The hardness values of the plain Sn–Ag–Cu solder joint and solder joints containing 1 wt% of ZrO 2 nano-particles after 5 min reaction at 250 °C were about 15.0 Hv and 17.1 Hv, respectively. On the other hand, their hardness values after 30 min reaction were about 13.7 Hv and 15.5 Hv, respectively.