1. There is a chemical reaction between the flux and the surface of the alloy, so different flux components should be selected according to different alloy compositions.
2. Since the wettability of the lead-free alloy is poor, the flux activity is required to be high.
3. Due to the poor wettability of lead-free alloys, it is necessary to increase the amount of flux, so that less residue after soldering and no shield corrosion are required to meet ICT probe capability and electromigration.
4. Lead-free alloys have a high melting point, so it is required to appropriately increase the activation temperature of the flux to adapt to the high temperature of lead-free soldering.
5. Lead-free flux is a water-based solvent-based flux. If the water is not completely volatilized during soldering, it will cause solder splash, pores and voids. Therefore, it is required to increase the preheating time, and the welding time of manual welding is longer than that of leaded soldering.
6. Lead-free flux must be specially formulated. In the early days, the lead-free solder paste was simply a mixture of no-clean solder and lead-free alloy of Pb-Sn solder, and the results were very bad. The chemical reaction between the flux and the solder alloy in the solder paste affects the rheological properties of the solder paste (which is critical to print performance). Therefore, lead-free flux must be specially formulated.
Develop new types of fluxes with better activity and better wettability, matching preheating temperatures and soldering temperatures, and lead-free clean free fluxes that meet environmental requirements to meet the needs of lead-free soldering.