Microstructure, kinetic analysis and hardness of Sn-Ag-Cu-1 wt% nano-ZrO2 composite solder on OSP-Cu pads

Nano-sized, nonreacting, noncoarsening ZrO2 particle-reinforced Sn-Ag-Cu composite solders were prepared by mechanically dispersing ZrO2 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 Cu6Sn5 and Cu3Sn intermetallic compound (IMC) layers were found in solder joints with and without the ZrO2 particles and the IMC layer thickness was substantially increased with reaction time and temperature. In the solder ball region, needle-shaped Ag3Sn and spherically-shaped Cu6Sn5 IMC particles were found to be uniformly distributed in the beta-Sn matrix. However, after the addition of ZrO2 nano-particles, Ag3Sn and Cu6Sn5 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 (Cu6Sn5+Cu3Sn) IMC layers for Sn-Ag-Cu and Sn-Ag-Cu-1 wt% ZrO2 composite solder joints on OSP-Cu pads were about 53.2 and 59.5 kJ/mol, respectively. In addition, solder joints containing ZrO2 nano-particles displayed higher hardness due to the uniform distribution of ZrO2 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 ZrO2 nano-particles after 5 min reaction at 250 degrees 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. (C) 2010 Elsevier B.V. All rights reserved.