Composition for tin-silver alloy electroplating comprising a complexing agent

An aqueous composition comprising (a) metal ions comprising tin ions and silver ions and (b) at least one complexing agent of formula C11

• RC12-XC11- RC11 (C11)
• and their salts, wherein
• XC11 is selected from the group consisting of
• (a) a divalent 5 or 6 membered aromatic N-heterocyclic group comprising
• (i) a single N atom;
• or
• (ii) a first N atom and a second heteroatom selected from N and S, wherein the first N atom and the second heteroatom are separated by at least one C atom;
• or
• (iii) a triazole or a thiadiazole;
• (b) a divalent 6 membered aromatic carbocyclic group;
• and
• (c) a divalent 5 or 6 membered aliphatic N-heterocyclic group comprising one N atom and optionally a second heteroatom selected from the group consisting of N and O;
• all of which may be unsubstituted or substituted by one or more OH or one or more RC14;
• RC11 is selected from the group consisting of (a) -XC12-S[-XC13-DC11]n-RC13,
• RC12 is selected from the group consisting of RC11, XC11-RC11, H, OH, C1 to C10 alkyl, and C1 to C10 alkoxy, with the proviso that if XC11 is a divalent 6 membered aromatic carbocyclic group, then RC12 is selected from the group consisting of RC11, XC11-RC11, C1 to C10 alkyl, and C1 to C10 alkoxy;
• XC12 is a chemical bond or a linear, branched or cyclic C1-C6 alkanediyl, which may be unsubstituted or substituted by OH, with the proviso that if (a) XC11 is a divalent 5 or 6 membered aromatic N-heterocyclic group and (b) RC13 is substituted by one OH and (c) RC12 is not RC11, then XC12 is a chemical bond;
• XC13 is a linear, branched or cyclic C1-C6 alkanediyl, which may be unsubstituted or substituted by OH;
• XC14 is a chemical bond or a linear or branched C1-C4 alkanediyl;
• DC11 is selected from the group consisting of S and O;
• RC13 is selected from the group consisting of (a) a linear, branched or cyclic C1-C6 alkyl, which may be unsubstituted or substituted by one or more OH, (b) Ph or XC14-Ph, which may be substituted by OH or RC14, with Ph=phenyl, when XC11 is not the aromatic carbocyclic group, and (c) a C2 to C4 polyoxyalkylene group;
• with the proviso that if XC11 is a divalent 5 or 6 membered aromatic N- heterocyclic group, then RC13 is unsubstituted or substituted by one OH with the exception that if XC11 is a divalent 5 or 6 membered aromatic N-heterocyclic group comprising a first N atom and a second heteroatom that is N, then RC13 is unsubstituted;
• RC14 is selected from the group consisting of H and a linear, branched or cyclic C1-C6 alkyl;
• and
• n is 0 or an integer of from 1 to 5;
• wherein the composition is free of copper ions.