Soldering (see RoHS), has led to a change in formulation of both solders and fluxes. Water-soluble non-rosin-based fluxes have been increasingly used since the 1980s so that soldered boards can be cleaned with water or water-based cleaners. This eliminates hazardous solvents from the production environment, and from factory effluents. Those regulations have also reduced the use of lead based solders, and caused the melting temperatures of solders in use to increase by up to . "Hot-bar reflow" is a selective soldering process where two pre-fluxed, solder coated parts are heated with heating element (called a thermode) to a sufficient temperature to
Liquid metal (Fr)(estimated at 27 °C [81 °F]), and gallium (Ga)(30 °C [86 °F]). Alloy systems that are liquid at room temperature have thermal conductivity far superior to ordinary non-metallic liquids, allowing liquid metal to efficiently transfer energy from the heat source to the liquid. They also have a higher electrical conductivity that allows the liquid to be pumped by more efficient, electromagnetic pumps. This results in the use of these materials for specific heat conducting and/or dissipation applications. Another advantage of liquid alloy systems is their inherent high densities. Once oxides have been removed from the substrate surface, most liquid metals