In the manual soldering iron soldering of lead-free flux-cored solder wire, the temperature setting of the soldering iron tip is above 300 C. The requirements of contemporary green electronics processes pose enormous challenges to flux cored fluxes:

1. The activation temperature of rosin is generally below 300 C, and there is almost no activity when the temperature exceeds 315 C. The widely used rosin-based lead-free flux cored flux has insufficient soldering activity;

2. There are many harmful residues after welding. The current rosin-based fluxes contain halogens. The halogen ions in the residues are easy to corrode circuit boards, solder joints and components in high-humidity and high-heat environments, resulting in poor insulation and circuit breakers. Poor contact, the waste liquid generated during the cleaning process of residues also seriously pollutes the environment;

3. The solder joints of rosin-based solid flux are easy to change color after welding, and rosin is easy to carbonize and change color under high temperature, which makes the solder joints black and affects the appearance, which limits its use in high-end electronic products.

The carrier component of the flux should have good solubility of the organic acid active ingredient and other ingredients, and be able to form a uniform liquid. Secondly, it is necessary to meet the actual flux-cored solder wire preparation process and welding temperature requirements. The extruding temperature of Sn- 0.7Cu lead-free flux-cored solder wire is 110 C ~ 130 C. It is required that the flux can be completely melted at 110 C, forming a uniform liquid with good fluidity, and can be smoothly pressed into the inside of the solder wire to form a continuous drug core. In addition, in order to prevent the flux-cored wire from flowing out during the wire drawing process, the flux is required to be solid below 80 C. The soldering temperature of lead-free solder manual soldering iron is above 300 C, the boiling point of the flux should be close to it, and it should not deviate too much. This is because the flux has a low boiling point. Higher levels will result in increased post-solder residue. Rosin is a typical carrier substance, it is neutral at room temperature, has no corrosion to metals, and can dissolve various organic substances, does not absorb moisture, is not conductive, is a good active agent and film-forming agent, and has been used as a carrier. The boiling point of octadecanoic acid is 376.1 C, and the boiling point can be adjusted by adding rosin. However, Sn-0.7Cu lead-free flux-cored solder wire has a high manual soldering iron temperature, rosin loses its activity, and carbonizes and discolors. Experimental research shows that reducing the amount of rosin added and adding other organic substances can achieve good soldering.