Rosin Resins for Soldering Solution

In general, liquid soldering fluxes for electronics have the ability to remove the oxidizing materials on the PCB surface. Gum rosin, modified rosin resins are the key raw materials, have 1~45 %Wt. in the formulation of Rosin Fluxes, and have 2~8 %Wt. in the Low-Solids/No-Clean Fluxes. The actives of rosin acid remove the oxides and extending tin material on the PCB surface. Also forming a coating on the solder joints to prevent reoxidation.

But there is some weakness by using gum rosin as the raw material in the soldering flux formulation. Comparing with the modified resin system, the sticky residual substances of gum rosin will dirty the PCB surface, requires more machine maintenance, the residuals also can pose difficulty for downstream processes. By using modified rosin resin system for Rosin Fluxes and  Low-Solids/No-Clean Fluxes can improve the issues.

When PCB is stored for longer or deeper oxidation, the activating agent is needed to enhance rosin activity. The alkalinity of ammonium salt can be neutralized with acid. However, halogen compounds such as chlorine and bromine will cause corrosion and lead to a decline in insulation resistance. Halogen compounds are the key controlled pollutants, halogen free will become the industry standard (RoHS). In the halogen-free formulation, small molecular organic acids can satisfy the soldering requirements. Fluxes can be partially sublimated or vaporized at the soldering temperature. And the insulation resistance of the residues is relatively high.

Soldering paste is mixed by solder powder, flux, solvent, surfactant, and the thixotropic agent. The thixotropic agent is used for adjusting the adhesion and printing performance of soldering paste, to prevent trailing and sticking. The solvent makes the soldering paste more uniform while stirring, it also affecting the soldering paste’s storage life. The surfactant can remove oxidizing substances from the surface of PCB and parts, and reduce the surface tension of tin and lead. Flux can prevent PCB reoxidation after soldering, and improve the adhesion of solder paste, and paste electronic components.

Rosin free is the new composition of soldering pastes. Comparing with the rosin system products, the rosin free system results new features, such as a) Low solid content level; b) No corrosion on the surface of PCB; c) Soldering substances are easily decomposing, sublimation, or volatilization at soldering temperature; d) No residue after soldering. The features make soldering more easier to meet the requirements for ion cleanliness testing in some special industries.

Rosin free soldering paste is mixed by surfactants (0.5% to 3.0%), forming agents (0.2% to 2.0%), cosolvents (5% to 20%) and solvents (75% to 90%). In some cases, the formulators select fatty acid, aromatic acid, or amino acid to use for the surfactant. Select hydrocarbons, alcohols, or esters to use for forming agents. Select ethers, esters, or terpenes to used for cosolvents. The cosolvent is used for improving the solubility of surfactants and forming agents. Reduce deposition, and increases the wettability of the pastes.