Hybrid solder joints: the effect of nanosized ZrO₂ particles on morphology of as-reflowed and thermally aged Sn-3.5Ag solder joints

Abstract

The main number of current researches has been focused on the microstructure and mechanical properties of the Sn-based Sn-Ag-Cu-based solders, while various kinds of nanosized particles have been added. The synthesis and handling of ceramic nanosized powder are much easier than of metal nanoparticles. In addition, metal nanoparticles solved in solder joints during the soldering process or by thermal aging could behave as an alloying element similar to bulk metal additions, while ceramic nanoparticles retain their chemically inactive behavior in various thermal, thermo-mechanical, and electrical constraints. In some cases, the solved metal nanosized inclusions could increase the growth kinetics of the present intermetallic phases or even create new phases, which leads to more complexity in the predictions and simulations of chemical processes in the solder joints. Based on the assertions mentioned above, ceramic nanosized particles are industrially more favorable as reinforcing inclusions. On the other hand, there is no direct comparison in the literature between Sn-based Sn-Ag-Cu and Sn-Ag solder joints with similar ceramic nanoinclusions based on microstructural features and mechanical properties. In the present research, the Cu/flux + NPs/SAC/flux + NPs/Cu solder joints were produced with a nominal amount of 0.2 wt%, 0.5 wt%, and 1.0 wt% nanosized ZrO₂ powder. The solder joints prepared via the above-described method are called in the literature as hybrid solder joints. The microstructure of the as-reflowed and thermally aged samples has been studied, especially at the interface solder/substrate. It has been shown that the minor additions of ZrO₂ NPs lead to a decrease in the thickness of the Cu₆Sn₅ interfacial layer in the as-reflowed solder joints and a reduction in the growth kinetics of this layer, while the Cu₃Sn interfacial IMC layer remains practically unaffected. Similar investigations were performed in our previous study but for both the hybrid and nanocomposite Sn-3.0Ag-0.5Cu solder joints. A comparative analysis of the impact of the ZrO₂ nanoinclusions on the hybrid solder joints using Sn-3.5Ag and Sn-3.0Ag-0.5Cu has been performed.