Papers by Author: Li Meng Yin

Abstract: A lead-free hypoeutectic solder Sn-0.3Ag-0.68Cu-X with low sliver content was prepared by a new process. By the method of skimming surface oxidation film at static state, the growing behaviors of oxidation film on the surface of liquid solder alloy were studied. The experimental results show that the growth rate of oxidation film on the surface of liquid solder decreases greatly after surface modification process. Before the surface modification process, the growth behaviors of oxidation film on the surface of liquid solder obey parabolic law which changes with variation of time. After surface modification, the growth behavior of oxidation film of liquid solder is transformed into obeying logarithmic law. The formation rate of oxidation slag on the surface of liquid Sn-0.3Ag-0.68Cu-X solder can be reduced to 0.36 mg/cm².min at 260 °C under standard test conditions. Conceptually, the atomic-doping X (X=Ga, In, Bi, Ge, Sb, Ni and P) was absorbed to the surface of liquid solder according to Gibbs absorption equation and entered into oxidation film, which is prone to form more compact oxidation film to prevent the oxidation on the surface of liquid solder.

Abstract: As solder joints become increasingly miniaturized to meet the severe demands of future electronic packaging, the thickness of intermetallic compounds (IMC) in solder joint continuously decreases, while, the IMC proportion to the whole solder joint increases. So IMC plays a more and more important role in the reliability of microelectronic structure and microsystems. In this paper, the formation and growth behavior, along with the composition of IMC at the interface of Sn-based solders/Cu substrate in soldering were reviewed comprehensively. The effect of isothermal aging, thermal-shearing cycling and electromigration on the interfacial IMC growth and evolution were also presented. Furthermore, the formation mechanism of Kirkendall voids during thermal aging was introduced. In addition, the effect of the interfacial IMC on mechanical properties of solder joints was in-depth summarized. Adopting an appropriate flux to control the thickness of the IMC to improve the reliability of solder joints and electronic products was proposed in the end of this paper.

Abstract: The wetting properties of four typical Sn-based solders, i.e., Sn-37Pb, Sn-3.0Ag-0.5Cu, Sn-0.7Cu and Sn-9Zn, on copper (Cu) and aluminum (Al) substrates at 250 °C, 260 °C and 270 °C were evaluated and compared by wetting balance method. The experimental results show that the wetting time of all solders on Cu substrate is shorter than that on Al substrate, but the wetting force of the solders with Cu substrate is bigger than that with Al substrate except Sn-9Zn solder. In addition, the wettability of the solders on Al substrate increases with increasing soldering temperature, and the wetting force of Sn-9Zn increases most obviously among four solders and reach 3.68 mN at 270 °C. The results also show that the wettability of the solders on Cu substrate mainly depends on surface tension of solder alloy, however, it depends on both surface tension and interaction with Al on Al substrate. Due to the active element Zn riches on the surface of Sn-9Zn solder, and Zn solid solutes into Al more easily, the wettability of Sn-9Zn solder on Al substrate is better than other three solders.

Abstract: The (Sn-9Zn0.05Ce)xBi solders with different Bi contents were prepared by a new process. The characteristics of solders about microstructure, tensile strength, elongation and microhardness were studied. The results showed that addition Bi can induce acicular or granular Zn-rich precipitated phase in Sn-9Zn0.05Ce solder. To increasing Bi content caused more Zn-rich phase distributed disorderly. When the Bi content was added to 4%, the granular Bi precipitated phase was observable. The tensile strength and hardness of (Sn-9Zn0.05Ce)xBi solder will raise, but elongation descend significantly due to the Bi content increasing. It can be funded that there was a more obvious turning point as w(Bi)=2wt﹪.