With the development of the lead-free solder process in electronic packaging, the main challenge in the development of lead-free solder alloys is to obtain a suitable melt point, optimal wettability, well alloy structure stability, admirable oxidation resistance, and the raw material supply are sufficient to meet the needs of industrialization. Tin-zinc (Sn-Zn) alloys with excellent mechanical properties creep resistance and melting point which is closer to eutectic Sn-Pb solder have been considered as the most promising candidates for replacing the traditional Sn-Pb solder alloy. However, the solder wettability and oxidation resistance of Sn-Zn lead-free solder are not as good as expected. Wettability is an important index to evaluate the performance of lead-free solder and the key to form reliable solder joint and oxidation resistance is closely related to the service life of solder. Therefore, improving the wettability and oxidation resistance properties of Sn-Zn lead-free solder alloy is extremely necessary. A 16-channel swing furnace was used to prepare Sn-9Zn-In solder alloy with different In content. The microstructure and properties, characterization and analysis systematically were analyzed by differential scanning thermal analyzer (DSC), solderability tester, universal testing machine, scanning electron microscope(SEM), energy dispersive analysis (EDS) and thermal gravimetric analyze (TG). The melting characteristics and the microstructure of Sn-9Zn solder with different In elements were compared, the feasibility of Sn-Zn alternate Sn-Pb solder was discussed. In addition, In element was doped into Sn-9Zn to investigate the wettability, oxidation resistance, and mechanical properties of Sn-9Zn lead-free solder alloy. The effect of In on the wettability and oxidation property of Sn-Zn solder was emphatically discussed. The oxidation resistance of solder was judged by the method of oxidative weight gain, X-ray photoelectron spectroscopy (XPS) was used for qualitative analysis of the components of the solder oxidation products. The results showed that the addition of In element promoted the formation of a low melting point alloy with Sn and Zn. The melting point and solidus temperature of the solder alloys were significantly reduced with the increase of In content. The addition of In element reduced the surface tension of the solder alloy, which resulted in improved wettability. When the In content reached 2%, the spreading rate of the alloy was the highest, reaching 67.99%, which as 6.31% higher than that of Sn-9Zn. Besides, when the amount of In was 2%, the minimum wetting angle was 28°, the spread area reached 64.04 mm2, which was 9.39 mm2 larger than that of Sn-9Zn (54.65 mm2). The wetting force of the solder reached the maximum value of 0.857 mN, wetting time was 0.542 s when the In content was 3%, which compared with the addition of 2% In, the wetting force reached 0.821 mN in 0.531 s, and the wetting force increased by 0.036 mN when the time was only extended by 0.011 s. The matrix of Sn-Zn solder was mainly β-Sn phase, and Zn mainly existed in the form of needle rod. The addition of In was mainly distributed uniformly in the whole matrix, and a small part of the solution was in Sn and Sn-Zn matrix. The addition of In made the phase transformation of Zn rich fine, additionally, the tensile strength was first increased and then decreased and the elongation after fracture decreased gradually due to the effects of solution strengthening and precipitation strengthening after adding In into alloys. When In content as 2%, the tensile strength of the alloy about 57.81 MPa. After the addition of In, the elongated needle rod-like Zn-rich phase was broken and the elongation gradually decreased. When the addition amount of In was more than 3%, the strength of the solder alloy did not increase significantly, but the elongation decreased sharply, and the elongation of the solder alloy was less than 15%. Adding In element into the alloy mainly gained more weight at the heating stage, and then the mass changed tend to be flat, according to XPS results, the oxidation product In2O3 was generated in the oxidation process, which protected the melt and helped to enhance the oxidation resistance of the alloy. Through alloying, the wettability, oxidation resistance, creep resistance and other properties of Sn-Zn solder were improved to varying degrees, and a series of Sn-Zn solders with good performance were developed. At present, the research on the alloying of Sn-Zn solders was mainly limited to the ternary system, and the research on the multi-alloy system of the quaternary system and above was relatively small, and the mechanism of the alloying elements on the Sn-Zn solders lack of understanding made the development of new Sn-Zn brazing fillers blind to a certain extent. In addition, the "trial and error method" was mainly used for the research of multi-system soldiers, which was time-consuming, labor-intensive, and inefficient, and could not meet the rapid industrial development's demand for new lead-free soldiers. Therefore, a new material research and development model was urgently needed to accelerate new types of soldiers. The research and development speed of soldiers further improved the related properties of soldiers, and developed more new lead-free soldiers to achieve the purpose of improving the reliability of soldering, thereby improving the research and development efficiency and comprehensive performance of Sn-Zn soldiers. Eventually, the large-scale industrial application of Sn-Zn brazing filler metal in production practice should be promoted. © 2022, Youke Publishing Co., Ltd. All right reserved.
