Optimization Of Flux For Sn-Cu Hypoeutectic Solder And Interfacial IMC In Solder Joints

In the process of application for the lead-free electronic packaging, because the lead-free solder have high melting temperature, the molten solder have low wetting ability on the sbustrate and poor solder joint reliability etc., it make the flux for lead solder in terms of lead-free solder is no longer applicabel. In addition, in the interface of micro-electronic packaging interconnect solder joints, because of the high levels tin metal in lead-free solders, it accelerated formation, growth and evolution of intermetallic compounds (IMC), making a very negative impact for the reliability of solder joints in service. At the same time, as geometry of micro-electronic packaging interconnect solder joints become smaller and smaller, the IMC which are brittle have a increasing proportion in the micro-solder joints, resulting in the IMC plays a key role for the reliability of micro solder joint and even electronic products. So make a flux match with the lead-free solder, and investigate formation, growth and evolution of interface intermetallic compound IMC is an important study.Our recent studies find that, a flux match with the sub-eutectic solder Sn-0.65Cu has good wetting, but it has larger residue after welding and more corrosive. To solve these problems, This paper studies the optimization of flux for Sn-Cu hypoeutectic Solder, at the same time, studies brazing time, brazing temperature, aging time and different flux effect on the thickness of interface IMC, and did a thorough analysis and discussion.The research paper get the main conclusions are as follows:(1) To reduce the larger residue after welding and more corrosive in this study reduced the content of hydrogenated rosin and active agent, and through select and add an appropriate amount of surfactant, to enhance their wetting performance and increase the resistivity of aqueous extract.(2) As the index to residues after welding, expansion rate, resistivity of aqueous extract and corrosion, carried out the releted experiments, in-depth analysis and study find two better flux formulas as follow: flux matrix is hydrogenated rosin 10%, selected the organic acids as active agents, glutaric acid 5%, lauric acid 0.7%, succinic acid 0.7%; nonylphenol ethoxylates 0.5% or dibromo butene diol 2%; margin for the isopropyl alcohol.(3) When the flux and sub-eutectic Sn-0.65Cu together used in soldering, the soldering temperature, soldering time and thermal aging time, and the activity of flux have an important effect on the growth of IMC interface, the law of impact are as follows:Improve the brazing temperature will accelerate the growth of IMC, makes the interface IMC grew thicker. The interface IMC layer of Sn-0.65Cu/Cu thickens with the brazing time extend, the growth thickness of interfacial IMC and brazing tim e is proportional to the 0.4 power. The thickness of the interfacial IMC in Sn-0.65Cu/Cu increases with aging time, the thickness of the interface IMC and aging time is proportional to the square root, indicating that their growth controlled by diffusion mechanism.Under certain conditions, when the active of the flux is higher, the solder spreading is better, the phase reaction between the solder and substrate become more intense, the interfacial IMC become thicker.