The property of flow characteristics is connected with the concept of viscosity. It indicates with what viscosity a liquid flows – very fluidly or less fluidly. The higher the viscosity, the less fluid is the liquid, the smaller the viscosity, the more fluid. For soldering, the term flow characteristic refers to the ability of the solder to spread. This ability can be influenced by temperature and by the type of flux. Flux reduces the viscosity by removing the oxides on the surfaces. Oxidized surfaces impair the flow characteristics.