The influence of a small amount of Al and Ni nano-particles on the microstructure, kinetics and hardness of Sn–Ag–Cu solder on OSP-Cu pads

In order to identify the effect of the addition of Al and Ni nano-particles to Sn–Ag–Cu solder, the interfacial microstructure between the composite solders and Organic Solderability Preservative (OSP)-Cu pads has been investigated as a function of reaction time at various temperatures as well as aging time. Also the hardness of the solder joints was evaluated with the reaction time. In Sn-Ag-Cu-0.5Ni composite solder joints, a scallop-shaped Sn–Ni–Cu intermetallic compound (IMC) layer was clearly observed at the interfaces. However, after long time aging, a very thin Cu3Sn IMC was formed between the Sn–Ni–Cu IMC layer and the OSP-Cu substrate. On the other hand, a layer type Cu6Sn5 and Cu3Sn IMC layers were found at the interfaces in the solder joints containing Al nano-particles. In addition, the Cu3Sn IMC layer thickness was substantially increased with an increase in the aging time. In solder ball regions, very fine Sn–Ni–Cu IMC particles in the Sn-Ag-Cu-0.5Ni composite solder and very fine Sn–Ag–Al IMC particles in the Sn-Ag-Cu-0.5Al composite solder joints were uniformly distributed in the β-Sn matrix as well as the Ag3Sn IMC particles. From kinetic analysis, the calculated activation energies for the Sn–Ni–Cu for the Sn-Ag-Cu-0.5Ni IMC and total (Cu6Sn5+Cu3Sn) IMC layers for Sn-Ag-Cu-0.5Al composite solder joints on OSP-Cu pads were 49.3 and 55.1 kJ/mol, respectively. In addition, solder joints containing Ni nano-particles displayed a higher hardness due to the uniform distribution of fine Sn–Ni–Cu IMC particles. The hardness values of Sn-Ag-Cu-0.5Ni and Sn-Ag-Cu-0.5Al composite solder joints after 5 min reaction at 250 °C were about 16.7 Hv and 16.1 Hv, respectively while, their hardness values after 30 min reaction were about 15.0 Hv and 14.7 Hv, respectively.