In the process of PCB assembly, the use of lead-free flux will directly affect the soldering quality. Taking into account the high temperature and poor wettability of lead-free alloys, the production line technicians should correctly set the temperature curve according to the melting point of the solder joint alloy and the activation temperature of the flux. If improper control causes welding defects.
The main problems and countermeasures are as follows:
1. There is a chemical reaction between the flux and the alloy surface, so different fluxes should be selected for different alloy compositions.
2. Due to the poor wettability of lead-free alloys, high flux activity is required.
3. Due to the poor wettability of lead-free alloys, it is necessary to increase the amount of flux, so it requires less residue after soldering and non-corrosive.
4. Due to the high melting point of lead-free alloys, it is required to increase the activation temperature of the flux to adapt to the high temperature of lead-free soldering.
5. The lead-free flux is a water-based solvent flux. If the water is not completely volatilized during soldering, it will cause solder splashes, pores and voids. Therefore, it is required to increase the preheating time, and the welding time of manual welding is longer than that of lead.
6. The key to printability and solderability is flux. The flux should be specially formulated, because the chemical reaction between the flux and the solder alloy in the solder paste affects the rheological properties of the solder paste.
