Composition for tin or tin alloy electroplating comprising a pyrazole-type antioxidant

1 . An aqueous composition for electrodepositing tin or tin alloys, the composition comprising tin ions, optionally alloy metal ions selected from the group consisting of silver, indium, and bismuth, and at least one antioxidant

of formula X1a

or of formula X1b

or of formula X1c

or of formula X1d

or of formula X1e

or the tautomeric forms of formulas X1a, X1b, X1c, X1d, and X1e,

wherein

R X1 , R X1a are independently selected from the group consisting of:

(a) H,

(b) C 1 to C 6 alkyl, C 1 to C 6 alkenyl, C 5 to C 12 aryl, C 6 to C 15 alkylaryl, C 6 to C 15 arylalkyl, all of which are unsubstituted or substituted by OH, OR X3 , —CO—R X3 , —CO—OR X3 , —SO 2 —OR X3 , CN, halogen, and a combination thereof,

with the proviso that if the antioxidant is of formula X1b then R X1 is not C 5 to C 12 aryl or C 6 to C 15 alkylaryl;

R X2 is selected from the group consisting of:

(a) H, OH, OR X3 , —CO—R X3 , —CO—OR X3 , —SO 2 —OR X3 ,

(b) C 1 to C 6 alkyl, C 1 to C 6 alkenyl, C 5 to C 12 aryl, C 6 to C 15 alkylaryl, C 6 to C 15 arylalkyl, all of which are unsubstituted or substituted by OH, OR X3 , —CO—R X3 , —CO—OR X3 , —SO 2 —OR X3 , CN, halogen, and a combination thereof,

wherein in formula X1a at least one of R X2 is OH, and with the proviso that if in formula X1a R X1 is t-butyl then R X2 2 is not C 5 to C 12 aryl or substituted by —CO—R X3 ;

R X3 is H or C 1 to C 6 alkyl; and

n is the number of groups R X2 ;

wherein no further alloying metal ions are present in the composition besides the tin ions and the optional alloy metal ions selected from the group consisting of silver, indium, and bismuth; and

wherein the composition does not comprise any reducing agents besides the compounds of formulas X1a to X1e.

2 . The composition according to claim 1 , wherein R X1 is selected from the group consisting of (a) H, (b) C 1 to C 6 alkyl, phenyl, and C 1 to C 4 alkylphenyl, all of which are unsubstituted or substituted by —CO—OR X3 or —SO 2 —OR X3 .

3 . The composition according to claim 1 , wherein R X2 is selected from the group consisting of H, OH, OR X3 , —CO—R X3 , —CO—OR X3 , —SO 2 —OR X3 , C 1 to C 4 alkyl, phenyl, and C 1 to C 4 alkylphenyl, all of which are unsubstituted or substituted by OH, OR X3 , —CO—R X3 , —CO—OR X3 , or —SO 2 —OR X3 .

4 . The composition according to claim 1 , wherein R X2 is selected from the group consisting of H, OH, —CO—R X3 , methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2 butyl, t-butyl, and phenyl, which may be unsubstituted or substituted by OH.

5 . The composition according to claim 1 , wherein at least one antioxidant is a compound of formula X1a.

6 . The composition according to claim 5 , wherein R X1 is selected from the group consisting of a C 1 to C 4 alkyl and either R X2 1 or R X2 2 are OH and the other R X2 1 , R X2 1 , and R X2 1 are H, methyl ethyl, propyl or butyl, or substituted by —CO—R X3 .

7 . The composition according to claim 1 , wherein the antioxidant is selected from the group consisting of antipyrine, 5-pyrazolone, 1,3-dimethyl-1H-pyrazol-5-ol, 1-phenylpyrazolidine-3,5-dione, 2-tert-butyl-4,5-dimethyl-pyrazol-3-ol, 1-(4-hydroxy-1,5-dimethyl-pyrazol-3-yl)-ethanone, 1,5-dimethyl-3-phenyl-pyrazol-4-ol, 3-ethyl-1,5-dimethyl-pyrazol-4-ol, and 1-tert-butyl-3-ethyl-5-methyl-pyrazol-4-ol.

8 . The composition according to claim 1 , comprising the alloy metal ions, wherein the alloy metal ions comprise silver ions.

9 . The composition according to claim 1 , wherein the pH of the composition is below 4.

10 . The composition according to claim 1 , further comprising a further additive selected from the group consisting of one or more surfactants, one or more levelers, and one or more grain refiners.

11 . The composition according to claim 1 , wherein the only alloy metal ions consists of silver ions.

12 . The composition according to claim 1 , wherein the pH of the composition is below 3.

13 . The composition according to claim 1 , wherein the pH of the composition is below 2.

14 . A process for depositing a tin or tin alloy layer on a substrate comprising the steps of:

a) contacting a tin or tin alloy electroplating bath comprising the composition according to claim 1 with the substrate, and

b) applying a current density to the substrate for a time sufficient to deposit the tin or tin alloy layer onto the substrate.

15 . The process according to claim 14 , wherein the tin alloy layer is deposited, and a alloy metal content of the deposited tin alloy layer is in a range of from 0.01 to 10% by weight.

16 . The process according to claim 14 , wherein the substrate comprises recessed features having an aperture size in a range of from 1 to 1000 micrometers, and the deposition is performed to at least partially fill the micrometer sized recessed features.

17 . The process according to claim 14 , wherein the substrate comprises recessed features having an aperture size in a range of from 1 to 200 micrometers and the deposition is performed to at least partially fill the micrometer sized recessed features.

18 . The process according to claim 14 , wherein the substrate comprises recessed features having an aperture size in a range of from 3 to 100 micrometers, and the deposition is performed to at least partially fill the micrometer sized recessed features.