What is the main purpose of using flux when soldering?

Using flux when soldering is primarily to reduce oxidation. When metals are heated during the soldering process, they can oxidize, forming a layer of oxide on the surface. This oxidation can prevent a good bond between the solder and the surfaces being joined, leading to a weak or ineffective connection.

Flux acts as a cleaning agent by preventing the formation of this oxide layer. It helps to remove existing oxidation and creates a barrier that protects the metal surfaces during the heating process. By doing so, flux ensures that the solder can properly wet the metal surfaces, enabling a strong, reliable joint.

While other factors like heat flow and surface treatment are involved in the soldering process, the primary function of flux specifically relates to controlling oxidation.