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

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
• RX1, RX1a are independently selected from the group consisting of:
• (a) H,
• (b) C1 to C6 alkyl, C1 to C6 alkenyl, C5 to C12 aryl, C6 to C15 alkylaryl, C6 to C15 arylalkyl, all of which are unsubstituted or substituted by OH, ORX3, —CO—RX3, —CO—ORX3, —SO2—ORX3, CN, halogen, and a combination thereof,
• with the proviso that if the antioxidant is of formula X1b then RX1 is not C5 to C12 aryl or C6 to C15 alkylaryl;
• RX2 is selected from the group consisting of:
• (a) H, OH, ORX3, —CO—RX3, —CO—ORX3, —SO2—ORX3,
• (b) C1 to C6 alkyl, C1 to C6 alkenyl, C5 to C12 aryl, C6 to C15 alkylaryl, C6 to C15 arylalkyl, all of which are unsubstituted or substituted by OH, ORX3, —CO—RX3, —CO—ORX3, —SO2—ORX3, CN, halogen, and a combination thereof,
• wherein in formula X1a at least one of RX2 is OH, and with the proviso that if in formula X1a RX1 is t-butyl then RX22 is not C5 to C12 aryl or substituted by —CO—RX3;
• RX3 is H or C1 to C6 alkyl;
• and
• n is the number of groups RX2;
• 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.