What is the function of rosin flux in soldering?

Rosin flux plays a critical role in the soldering process primarily by protecting the joint from oxidation. When metals are heated during soldering, they can easily oxidize, which creates a barrier that hinders the flow of solder and can result in a weak joint. The rosin flux acts as a barrier against oxygen, thereby preventing oxidation on the surfaces being joined. This protection ensures that the metals remain clean and ready for bonding when the solder is applied.

While rosin flux can also help in cleaning the surface, the primary purpose during the actual soldering process is to provide that protective environment, allowing for better adhesion and a stronger joint. The abilities to enhance solder flow or reduce melting point may stem from the presence of flux, but the primary function attributed to rosin flux focuses on its protective characteristics against oxidation.