Which of the following is NOT a use of rosin flux?

Rosin flux is primarily used in soldering processes, specifically in electronics, to assist in the joining of metal parts. One of its key functions is preventing oxidation; it creates a protective barrier on metal surfaces to ensure effective soldering. Additionally, rosin flux improves electrical connectivity by ensuring that the surfaces being soldered are clean, which promotes better adhesion of the solder to the metal surfaces. Furthermore, it enhances solder flow by reducing the viscosity of the molten solder, allowing it to spread more easily over the surfaces being joined.

However, acting as a thermal insulator is not one of the functions of rosin flux. While it may have some minimal insulating properties due to its physical nature, its primary role is not to provide thermal insulation but to facilitate the soldering process. This distinction makes the choice of acting as a thermal insulator the one that does not align with the primary uses of rosin flux in electronic soldering.