PCB manufacturing lead-free flux main problems and countermeasures

(1) There is a chemical reaction between the flux and the surface of the alloy, so different flux components should be selected for different alloy compositions.

(2) The wettability of lead-free alloys is poor, so it is required to have high activity for pcb manufacturing flux.

(3) The lead-free alloy has poor wettability and needs to increase the amount of flux. Therefore, it requires less post-weld residue and is non-corrosive to meet ICT probe capability and electromigration.

(4) Lead-free alloys have a high melting point, so it is required to increase the activation temperature of the flux to suit the high temperature of lead-free soldering.

(5) Lead-free flux is a water-based solvent-based flux. If the water does not complete volatilization during welding, it will cause solder splash, pores and voids. Therefore, it is required to increase the preheating time, and the soldering time of the manual soldered pcb manufacturing is longer than that of the lead solder.

(6) The key to printability and solderability lies in the flux. After the lead-free alloy is determined, the key is the flux. Solder paste with poor wettability has a lot of resistance and capacitance shift after soldering; solder paste with good wettability is not tomb after soldering, so choose solder paste to do process test to see if printing can meet the requirements,how is post-soldering quality?

(7) Lead-free solder must be specially formulated. The no-clean solder paste has been used for many years and is a mature technology. The chemical reaction between the flux and the solder alloy in the solder paste affects the rheological properties of the solder paste (it’s important to the print performance). Therefore, lead-free solder must be specially formulated.

Develop new fluxes with stronger activity and better wettability, matching preheating temperature and soldering temperature, and meeting environmental protection requirements. Actual tests have proved that no-clean flux is better for lead-free soldering.

Similarly, no VOC no-clean flux in wave soldering requires special formulation. Lead-free solder pastes and wave soldered water soluble fluxes are also required for certain pcb manufacturing products.