Solution and process for increasing the solderability and corrosion resistance of a metal or metal alloy surface

1. An aqueous solution having a pH in the range of 1 to 5 for treating a tin or tin alloy surface comprising

(a) at least one phosphorous compound or its salt represented by the following formulas I or II:

wherein R1 is selected from the group consisting of H, OH, methyl, ethyl, n-propyl, isopropyl, n-hexyl, isohexyl, n-heptyl, isoheptyl, n-octly, isooctyl, n-nonyl, isononyl, n-decyl, isodecyl, n-undecyl, isodecyl, n-dodecyl, isododecyl, R2 and R3 are the same or different and are selected independently from the group consisting of H, a counter ion, C 1 -C 20 -alkyl, substituted or unsubstituted, linear or branched, C 1 -C 6 -alkaryl, linear or branched, substituted or unsubstituted and aryl, substituted or unsubstituted and wherein n is an integer ranging from 2 to 10,

R4 is F(CF 2 CF 2 ) z , z ranges from 1 to 7, x is 1 or 2, y is 1 or 2 and x+y is 3 and

(b) at least one solderability-enhancing compound or its salt represented by the following formula

wherein m, n, o and p are integers ranging from 0 to 200 and are the same or different and m+n+o+p is at least 2

wherein R1 and R7 are the same or different and are selected independently from the group consisting of H, a counter ion, C 1 -C 20 -alkyl, substituted or unsubstituted, linear or branched, C 1 -C 6 -alkaryl, linear or branched, allyl, aryl, sulfate, phosphate, halide and sulfonate and wherein each of the R2, R3, R5 and R6 groups may be the same or different and are selected independently from the group consisting of H and C 1 -C 6 -alkyl, linear or branched, substituted or unsubstituted and wherein R4 is selected from the group consisting of C 1 -C 12 -alkylene, linear or branched, substituted or unsubstituted, arylene 1,2-, 1,3- and 1,4-substituted, naphthylene, 1,3-, 1,4- 1,5- 1,6- and 1,8-substituted, higher annulated arylene, cylcloalkylene, —O—(CH 2 (CH 2 ) n OR1, wherein R1 has the meaning defined above, and moieties represented by the following formula

wherein the substitution independently is 1,2-, 1,3- or 1,4 for each ring and wherein q and r are the same or different and range independently from 0 to 10 and R8 and R9 are selected independently from the group consisting of H and C 1 -C 6 -alkyl, linear or branched.

2. An aqueous solution according to claim 1 , wherein R2 and R3 of the phosphorous compound are selected independently from the group consisting of H, a counter ion, methyl, ethyl, n-propyl, isopropyl, n-hexyl, isohexyl, n-heptyl, isoheptyl, n-octyl, isooctyl, n-nonyl, isononyl, n-decyl, isodecyl, n-undecyl, isodecyl, n-dodecyl, and isododecyl.

3. An aqueous solution according to claim 1 , wherein R1 and R7 of the solderability-enhancing compound III are selected independently from the group consisting of H, methyl, sodium, potassium, halide, sulfate, phosphate and sulfonate.

4. An aqueous solution according to claim 1 , wherein R2, R3, R5 and R6 of the solderability-enhancing compound III are selected independently from the group consisting of H, methyl, ethyl, n-propyl and isopropyl.

5. An aqueous solution according to claim 1 , wherein R4 of the solderability-enhancing compound III is selected from the following formulas

and wherein R8 and R9 are selected from the group consisting of H, methyl, ethyl, n-propyl and isopropyl.

6. An aqueous solution according to claim 1 , wherein the solderability-enhancing compound III is selected from the group consisting of the following formulas

wherein n=1-20,

wherein n=1-20 and

wherein n=1-20.

7. An aqueous solution according to claim 1 , wherein the at least one phosphorous compound (a) represented by the formulas I-II is used in an amount of 0.0001 to 0.05 mol/l.

8. An aqueous solution according to claim 1 , wherein the at least one solderability-enhancing compound (b) represented by the formula III. is used in an amount of 0.0001 to 0.1 mol/l.

9. An aqueous solution according to claim 1 , wherein the pH value is between 2 and 5.

10. An aqueous solution according to claim 1 , wherein a buffer system selected from the group consisting of formic acid/formate, tartaric acid/tartrate, citric acid/citrate, acetic acid/acetate and oxalic acid /oxalate is contained.

11. An aqueous solution according to claim 1 , wherein

R1 and R7 of the solderability-enhancing compound III are selected independently from the group consisting of H, methyl, sodium, potassium, halide, sulfate, phosphate and sulfonate; and

R2, R3, R5 and R6 of the solderability-enhancing compound III are selected independently from the group consisting of H, methyl, ethyl, n-propyl and isopropyl.

12. An aqueous solution according to claim 1 , wherein

R1 and R7 of the solderability-enhancing compound III are selected independently from the group consisting of H, methyl, sodium, potassium, halide, sulfate, phosphate and sulfonate;

R2, R3, R5 and R6 of the solderability-enhancing compound III are selected independently from the group consisting of H, methyl, ethyl, n-propyl and isopropyl; and

R4 of the solderability-enhancing compound III is selected from the following formulas

and wherein R8 and R9 are selected from the group consisting of H, methyl, ethyl, n-propyl and isopropyl.

13. A process for increasing the solderability and corrosion resistance of a substrate having a tin or tin alloy surface wherein the surface is treated with an aqueous solution according to claim 1 .

14. The process according to claim 13 , wherein the tin alloy surface is selected from the group consisting of SnPb, SnCu, SnBi, SnAg and SnAgCu surfaces.

15. The process according to claim 13 further comprising reflowing the tin or tin alloy surface of the substrate prior or after treatment with the aqueous solution.

16. Substrate having a tin or tin alloy surface treated with the aqueous solution according to claim 1 .

17. Substrate according to claim 16 , wherein the substrate is a tin plated semi-finished good.

18. Substrate according to claim 17 , wherein the substrate is a tin plate or tin wire or a lead frame, a connector or a printed circuit board.