1. The rosin in the solder wire is able to enhance the smoothness of welding. It can make the tin droplets stick to the circuit board quickly during soldering. The liquid tin droplets make the solder joints very full and excellent because the poor fluidity makes the liquid tin droplets stay well around the electronic pin after cooled down. Thus when it solidifies, it will not change much, so as to ensure the quality of the soldered product.
2. As a solder flux, rosin has a lower melting point than solder. And the specific gravity, viscosity, and surface tension of rosin are smaller than that of solder wire. When soldering, the flux melts firstly, and quickly flows and covers the surface of the solder to isolate the air and prevent it from oxidation of the metal surface. Also it is able to react with solder tin and the oxide film on the metal surface under a high welding temperature, so as to melt it and restore a pure and clean metal surface. Quilty rosin core helps form a satisfactory solder joint shape and keep solder joints to be full and bright.
3. Rosin core enable solder wire to play a strong role in connecting parts in with high quality solder joints, heat dissipation during welding.
4. Rosin core is commonly used as flux in electronic soldering. It is neutral and will not corrode circuit components and soldering iron head. it is much better than the solid tin solder without rosin core when soldering.