Abstract: A water soluble, thermally stable, solder flux for use in forming a water soluble, thermally stable, solder paste is provided. The water soluble, thermally stable, solder flux contains an acidic ester component having about 50% to about 60% monoesters by weight based on total weight, about 40% to about 50% diesters by weight based on total weight, and about 0% to about 1.5% phosphoric acid by weight based on total weight. This ester component is combined with triethanolamine to form a flux vehicle having a molar ratio of triethanolamine to the ester component of about 0.6 to about 1.2. This vehicle is present in the solder flux in an amount from about 68% to about 79% by weight based on total weight of solder flux. The flux also contains rheology adjusting components in an amount ranging from about 17% to about 26% by weight based on total weight of solder flux. Citric acid included in the flux in an amount ranging from about 4% to about 6% by weight based on total weight of solder flux.