Patent ID: 7431817

Claim:
A solution for use in connection with depositing of a eutectic gold-tin alloy on an electrically conductive substrate, the solution consisting essentially of: water, complexed gold ions, tin ions, a complexing compound to render the tin ions soluble in the solution, an alloy stabilization agent present in an amount sufficient to stabilize the eutectic gold-tin alloy that is deposited and to enable the eutectic gold-tin alloy to be provided over a usable current density range, wherein the solution has a pH of between about 3 and 5.5 and the gold ions and tin ions are present in relative amounts sufficient to ensure that the eutectic gold-tin alloy that is deposited has a gold content of between 75 and 85% by weight and a tin content of between 15 and 25% by weight, and, optionally, at least one of an anti-oxidation compound or a brightening agent; wherein the alloy stabilization agent is an anionic surfactant based on phosphate esters of general structural formula: wherein R is alkyl or alkyl aryl group; n is 7 to 10 moles of ethylene and/or propylene oxide; M is hydrogen, sodium, potassium or other counter ion; and R′ is ethyl and/or propyl group and the alloy stabilization agent contributes to brightening of the deposit.