Development Of The Solder Paste For Aluminum Soldering And Solder Wires For Automated Soldering In Electronic Packaging

With the rapid developments of electronic manufacturing industry in China, traditional soldering techniques such as wave soldering and manual soldering, which rely on high energy-consumption and cheap labor, are no longer favorable. The process of electronic packaging tends to automation, high accuracy, lower cost and lightweight. Surface mounting technology(SMT) is one of the electronic packaging processes with great potential to achieve automation and high accuracy. Solder paste is the essential material for SMT and attracts significant attentions both in industrial labs and research institutions; meanwhile, the use of aluminum in electronic products is increasing due its lightweight and low cost as compared to copper. Therefore, the solder paste for aluminum soldering becomes one of the bottlenecks which determine whether it can be widely used. On the other hand, the urgent needs to develop a high-performance solder wire and its corresponding flux for automated soldering is evident.The present work aims to develop a high-performance and low-residue solder paste for aluminum soldering, and the processing adaptability and properties of the solder paste have been evaluated and optimized. Meanwhile, a flux-cored solder wire for automated soldering has been developed, as well as a pilot product for further improvements.The development of solder paste for aluminum soldering stared with the preparation of the flux. The activators were prepared by concentration, which can wipe off the oxidation films on the aluminum surface. Film-forming agents were then added to improve the activity of the flux and to adjust the status of the flux. The effects of adding surfactants on the spreading area of solder joints were studied systematically, and then determining the proportion of the solder paste for aluminum soldering by selecting the optimized solder component and particle size. The microstructure and composition at the interface of solder joints were analyzed, the tensile strength of the Al/SAC0307/Al joints was measured by using the tensile test machine, it has been shown that all of the solder joints fractured inside the joints and shown typical ductile fracture characteristics. The tensile strength of the solder joints is reaching a maximum value at 84 MPa when the soldering temperature is 280℃ and holding for 30 s. A best corrosion resistance of the solder joints(about 92.5h) is achieved when the soldering temperature is 245℃ and holding time at 120 s.The development of the flux of solder wires used for automated soldering started with selecting organic acids. By mixing different organic acids to adjust the components of the activator, the wetting time and spreading area were improved. The effects of adding active reinforcers, carriers, addition agents and surfactants were then investigated systematically. The so-designed flux has been used to prepare a pilot product. In comparison with two commercial products, the present solder wire for automated soldering processes better spreading area, high surface insulation resistance, less spattering during soldering.