An acidic aqueous composition for copper electroplating comprising (a) copper ions; (b) bromide ions; and (c) at least one additive of formula S1 wherein X S1 is selected from a linear, branched or cyclic C 1 -C 12 alkanediyl, which may be substituted or unsubstituted, and which may optionally be interrupted by O, S or NR S40; R S1 is a monovalent (a) poly(oxy(C 3 to C 6)alkylene)-block-poly(oxyethylene) group which is bound to the N-atom by the poly(oxy(C 3 to C 6)alkylene part, or (b) a poly(oxyethylene)-block-poly(oxy(C 3 to C 6)alkylene)-block-poly(oxyethylene), which groups both have a poly(oxyethylene) content of from 5 to 30 % by weight; R S2, R S3, R S4 are (a) selected from H, R S1, R S40, or (b) R S3 and an adjacent group R S4 or, if n>2, two adjacent groups R S4 may together form a divalent group X S3; R S40 is selected from (a) linear or branched C 1 -C 20 alkyl, which may optionally be substituted by hydroxyl, alkoxy or alkoxycarbonyl, and (b) linear or branched C 1 -C 20 alkenyl, which may optionally be substituted by hydroxyl, alkoxy or alkoxycarbonyl; X S3 is selected from a linear, branched or cyclic C 1 -C 12 alkanediyl, which may be substituted or unsubstituted, and which may optionally be interrupted by O, S or NR S40; and n is an integer of from 1 to 6. (a) copper ions; (b) bromide ions; and (c) at least one additive of formula S1 wherein X S1 is selected from a linear, branched or cyclic C 1 -C 12 alkanediyl, which may be substituted or unsubstituted, and which may optionally be interrupted by O, S or NR S40; R S1 is a monovalent (a) poly(oxy(C 3 to C 6)alkylene)-block-poly(oxyethylene) group which is bound to the N-atom by the poly(oxy(C 3 to C 6)alkylene part, or (b) a poly(oxyethylene)-block-poly(oxy(C 3 to C 6)alkylene)-block-poly(oxyethylene), which groups both have a poly(oxyethylene) content of from 5 to 30 % by weight; R S2, R S3, R S4 are (a) selected from H, R S1, R S40, or (b) R S3 and an adjacent group R S4 or, if n>2, two adjacent groups R S4 may together form a divalent group X S3; R S40 is selected from (a) linear or branched C 1 -C 20 alkyl, which may optionally be substituted by hydroxyl, alkoxy or alkoxycarbonyl, and (b) linear or branched C 1 -C 20 alkenyl, which may optionally be substituted by hydroxyl, alkoxy or alkoxycarbonyl; X S3 is selected from a linear, branched or cyclic C 1 -C 12 alkanediyl, which may be substituted or unsubstituted, and which may optionally be interrupted by O, S or NR S40; and n is an integer of from 1 to 6. X S1 is selected from a linear, branched or cyclic C 1 -C 12 alkanediyl, which may be substituted or unsubstituted, and which may optionally be interrupted by O, S or NR S40; R S1 is a monovalent (a) poly(oxy(C 3 to C 6)alkylene)-block-poly(oxyethylene) group which is bound to the N-atom by the poly(oxy(C 3 to C 6)alkylene part, or (b) a poly(oxyethylene)-block-poly(oxy(C 3 to C 6)alkylene)-block-poly(oxyethylene), which groups both have a poly(oxyethylene) content of from 5 to 30 % by weight; (a) poly(oxy(C 3 to C 6)alkylene)-block-poly(oxyethylene) group which is bound to the N-atom by the poly(oxy(C 3 to C 6)alkylene part, or (b) a poly(oxyethylene)-block-poly(oxy(C 3 to C 6)alkylene)-block-poly(oxyethylene), R S2, R S3, R S4 are (a) selected from H, R S1, R S40, or (b) R S3 and an adjacent group R S4 or, if n>2, two adjacent groups R S4 may together form a divalent group X S3; (a) selected from H, R S1, R S40, or (b) R S3 and an adjacent group R S4 or, if n>2, two adjacent groups R S4 may together form a divalent group X S3; R S40 is selected from (a) linear or branched C 1 -C 20 alkyl, which may optionally be substituted by hydroxyl, alkoxy or alkoxycarbonyl, and (b) linear or branched C 1 -C 20 alkenyl, which may optionally be substituted by hydroxyl, alkoxy or alkoxycarbonyl; X S3 is selected from a linear, branched or cyclic C 1 -C 12 alkanediyl, which may be substituted or unsubstituted, and which may optionally be interrupted by O, S or NR S40; and n is an integer of from 1 to 6.