The lead-free solder paste is mainly composed of tin/silver/copper, with silver and copper replacing the original lead.
Fundamental characteristics and phenomena In the tin/silver/copper system, the metallurgical reaction between tin and secondary elements (silver and copper) is the main factor determining the application temperature, curing mechanism and mechanical efficiency. According to the binary phase diagram, there are three possible binary eutectic reactions between the three elements. A reaction between silver and tin forms the eutectic structure of tin matrix phase at 221 ° C and ε Combined phase between metals (Ag3Sn). Copper reacts with tin to form eutectic structure of tin matrix phase at 227 ° C η The combining phase between metals (Cu6Sn5).
Silver can also react with copper to form rich silver at 779 ° C α Xianghe is rich in copper α Phase of eutectic alloy. However, in the current study, no phase transition was found at 779 ° C in the measurement of the curing temperature of the tin/silver/copper triple compound. This means that it is likely that silver and copper will react directly in the triple compound. In terms of temperature kinetics, it is more suitable for the reaction of silver or copper with tin to form intermetallic compounds of Ag3Sn or Cu6Sn5. In this case, the tin/silver/copper triple reaction can be expected to include tin matrix phase ε The combined phase (Ag3Sn) and η The combining phase between metals (Cu6Sn5).
As confirmed by the dual phase tin/silver and tin/copper systems, relatively hard Ag3Sn and Cu6Sn5 particles in the tin matrix tin/silver/copper triple alloy can effectively strengthen the alloy by establishing a long-term internal stress. These hard particles can also effectively prevent the propagation of fatigue cracks. The formation of Ag3Sn and Cu6Sn5 particles can separate smaller tin matrix particles. The finer the Ag3Sn and Cu6Sn5 particles are, the more effectively they can separate the tin matrix particles, resulting in a finer overall microstructure. This contributes to the sliding mechanism of the particle boundary, which extends the fatigue life at elevated temperatures.
Hongqiao Technology Co., Ltd. is a high-tech enterprise specializing in the research, development and production of cutting fluid, electronic hardware cleaner, surface treatment agent, welding materials: solder paste, tin rod, tin wire, BGA solder ball, SMT tin, electronic flux and thinner, electronic welding equipment and accessories, electroplating anode plate (rod), semi tin ball and other products.