Microstructure and morphology of the soldering interface of Sn–2.0Ag–1.5Zn low Ag content lead-free solder ball and different substrates

Eutectic Sn-Ag-Cu lead-free solder has limited applications due to cost and reliability issues. Sn-Ag-Zn solder has the advantages of low melting point, good mechanical properties and reliable welding interface. However, the research system of low silver content Sn-Ag-Zn solder is incomplete. In this paper, Sn-2.0Ag-1.5Zn low silver content alloy solder is soldered to different substrates. The interfacial reaction after soldering and the microstructure and reliability under different aging treatment conditions are studied. Sn-2.0Ag-1.5Zn solder is made into solder balls by direct melting method. The solder balls are placed in a solder strength tester to be heated and welded to the substrate, and then the solder joints are placed in a heating furnace for aging treatment. The results show that the solder is soldered to the bare Cu substrate, and a dense double-layer Intermetallic Compound (IMC) structure of Cu5Zn8 and Ag3Sn is formed at the interface after aging treatment. The double-layer structure blocks each other, limiting the development of copper-tin IMCs. The solder is soldered with the Cu substrate electroplated with Ni barrier layer, and the soldering interface forms a thin layer of Ni3Sn4 metal compound. After aging for 1000 h, the thickness of Ni3Sn4 is about 1 μm, the thickness of Ni barrier layer is kept at 2-3 μm, and the barrier effect of Ni barrier layer is stable. Sn-2.0Ag-1.5Zn solder has excellent loss performance in long aging treatment. It has good heat-resistance aging treatment, good quality of solder connection, high interface reliability and less environmental pollution. The low silver content in Sn-2.0Ag-1.5Zn solder results in a significant cost reduction. Coarse IMC Ag3Sn is not easily formed. The optimized ratio of Ag and Zn in Sn-2.0Ag-1.5Zn solder improves the strength and toughness of the solder joint. The performance has been improved, and it is a very promising alloy solder.