Sn-Ag alloys are currently especially interesting as the replacement material for toxic tin-lead solders hence the possibility of obtain of Sn-Ag alloy coatings by the electrolytic non-cyanide method is very important [1-13]. The fundamental problems in preparing of electrolytic bath for electrodeposition of Sn-Ag alloy are following: a great difference of the normal potentials between silver and tin, formation of sparingly soluble precipitates, presence of Sn(II)/Sn(IV) system which can cause reduction of silver (I) ions, electroless deposition of silver from solution on the copper base. All above problems can be solved by addition to solution of the suitable complexing ligands. Thermodynamical analysis of several models of non-cyanide Ag-Sn alloy plating baths was conducted and criteria of their stability was presented. Ag(I)-Sn(II,IV)-X-H2O, Ag(I)-Sn(II,IV)-Y-H2O, Ag(I)-Sn(II,IV)-X-Y-H2O and Ag(I)-Sn(II,IV)-X1-X2-Y-H2O systems were analyzed for selected strong complexing agents of silver (X) : thiourea, succinimide and for selected complexing agents of tin (Y): pyrophosphate, citrate. The potentiometric titration experiments were performed for determination of conditional stability constants of complex species. There are possible the stable solutions in acidic and in strong basic mediums on the base of one organic ligand which complexing Ag(I) ions (cationic ligands - thiourea in acidic mediums of Sn(II) and anionic ligands - succinimide in strong basic solution of Sn(IV)). In mediums with intermediate pH two ligands (succinimide-citrate, succinimide-pyrophosphate) and three ligands (succinimide-citrate-thiourea, succinimide-pyrophosphate-thiourea) systems are necessary for obtaining the stable solutions. There is only kinetic stability possible in case of non-cyanide poliligands solutions containing tin (II) ions.
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E-mail: nmozga@imim-pan.krakow.pl