Immersion tin or tin alloy plating bath with improved removal of cuprous ions

1. An aqueous immersion tin or tin alloy plating bath comprising

(i) Sn(II) ions,

(ii) optionally ions of an alloying metal,

(iii) at least one aromatic sulfonic acid or salt thereof,

(iv) at least one complexant selected from the group consisting of thiourea and derivatives thereof and

(v) a mixture of at least one first precipitation additive and at least one second precipitation additive,

wherein the at least one first precipitation additive is selected from the group consisting of aliphatic poly-alcohol compounds, ethers thereof and polymers derived thereof having an average molecular weight in the range of 62 g/mol and 600 g/mol and

wherein the at least one second precipitation additive is selected from the group consisting of polyalkylene glycol compounds having an average molecular weight in the range of 750 to 10,000 g/mol.

2. An immersion tin or tin alloy plating bath according to claim 1 wherein the concentration of the at least one second precipitation additive ranges from 1 to 10 wt.-% based on the total amount of the at least one first precipitation additive and the at least one second precipitation additive.

3. An immersion tin or tin alloy plating bath according to claim 1 wherein the at least one first precipitation additive is selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropyleneglycol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monopropyl ether and tripropylene glycol monobutyl ether, polyethylene glycol, polypropylene glycol, polyethylene glycol dimethylether, polyethylene glycol diethylether, polyethylene glycol dipropylether, polypropylene glycol dimethylether, polypropylene glycol diethylether, polypropylene glycol dipropyl ether, stearic acid polyglycol ester, oleic acid polyglycol ester, stearic alcohol polyglycol ether, nonylphenol polyglycol ether, octanol polyalkylene glycol ether, octane diol-bis-(polyalkylene glycol ether), poly(ethylene glycol-ran-propylene glycol), poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) and poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol.

4. An immersion tin or tin alloy plating bath according to claim 1 wherein the at least one first precipitation additive is selected from the group consisting of polyethylene glycol and polypropylene glycol.

5. An immersion tin or tin alloy plating bath according to claim 1 wherein the at least one second precipitation additive is selected from the group consisting of polyethylene glycol, polypropylene glycol, polyethylene glycol dimethylether, polyethylene glycol diethylether, polyethylene glycol dipropylether, polypropylene glycol dimethylether, polypropylene glycol diethylether, polypropylene glycol dipropyl ether, stearic acid polyglycol ester, oleic acid polyglycol ester, stearic alcohol polyglycol ether, nonylphenol polyglycol ether, octanol polyalkylene glycol ether, octane diol-bis-(polyalkylene glycol ether), poly(ethylene glycol-ran-propylene glycol), poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) and poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol).

6. An immersion tin or tin alloy plating bath according to claim 1 wherein the at least one second precipitation additive is selected from the group consisting of polyethylene glycol and polypropylene glycol.

7. An immersion tin or tin alloy plating bath according to claim 1 wherein the total concentration of the mixture of the at least one first precipitation additive and the at least one second precipitation additive ranges from 0.01 g/l to 200 g/l.

8. An immersion tin or tin alloy plating bath according to claim 1 wherein the at least one aromatic sulfonic acid is characterized by the formula R—SO 3 X, wherein R is selected from the group consisting of substituted and unsubstituted phenyl, substituted and unsubstituted benzyl and substituted and unsubstituted naphthyl and X is selected from the group consisting of H + , Li + , Na + , NH 4 + and K + .

9. An immersion tin or tin alloy plating bath according to claim 1 wherein the at least one aromatic sulfonic acid or salt thereof is selected from the group consisting of benzene sulfonic acid, benzyl sulfonic acid, o-toluene sulfonic acid, m-toluene sulfonic acid, p-toluene sulfonic acid, xylene sulfonic acid, naphthyl sulphonic acid and their salts with a counter ion selected from the group consisting of Li + , Na + , NH 4 + , K + .

10. An immersion tin or tin alloy plating bath according to claim 1 wherein the overall concentration of the at least one aromatic sulfonic acid or salt thereof ranges from 0.1 to 1.5 mol/l.

11. An immersion tin or tin alloy plating bath according to claim 1 wherein the immersion tin plating bath further comprises at least one non-aromatic sulfonic acid or salt thereof selected from the group consisting of methane sulfonic acid, methane disulfonic acid, methane trisulfonic acid, ethane sulfonic acid, propane sulfonic acid, 2-propane sulfonic acid, 1,3-propane disulfonic acid, butane sulfonic acid, 2-butane sulfonic acid, pentane sulfonic acid and their salts with a counter ion selected from the group consisting of Li + , Na + , NH 4 + , K + .

12. An immersion tin or tin alloy plating bath according to claim 1 wherein the concentration of the at least one aromatic sulfonic acid or salt thereof is at least 25 wt.-% based on the total amount of the at least one aromatic sulfonic acid and the at least one non-aromatic sulfonic acid.

13. An immersion tin or tin alloy plating bath according to claim 1 wherein the concentration of Sn(II) ions ranges from 1 to 50 g/l.

14. An immersion tin or tin alloy plating bath according to claim 1 wherein the plating bath further contains Ag(I) ions.

15. A process for depositing a tin or tin alloy layer onto copper surfaces comprising the steps of

(i) Providing a copper surface,

(ii) Contacting the copper surface with an immersion tin or tin alloy plating bath according to claim 1 .