An aqueous acidic copper plating bath for deposition of copper or copper alloys comprising at least one source of copper ions and at least one acid characterised in that it further comprises at least one guanidine compound which contains at least one unit according to formula wherein a is an integer ranging from 1 to 40 and A represents a unit derived from a monomer according to the following formulae and/or wherein - Y and Y' are each individually selected from the group consisting of CH 2, O and S; - R 1 is an organic residue selected from the group consisting of hydrogen, alkyl, aryl and alkaryl; - R 2 is an organic residue selected from the group consisting of hydrogen, alkyl, aryl and alkaryl; - R 3, R 4, R 5 and R 6 are each organic residues independently from each other selected from the group consisting of hydrogen, alkyl, aryl and alkaryl; - b and b' are integers each individually and independently from each other ranging from 0 to 6; - c and c' are integers each individually and independently from each other ranging from 1 to 6; - d and d' are integers each individually and independently from each other ranging from 0 to 6; - e and e' are integers each individually and independently from each other ranging from 0 to 6; - D is a divalent residue and is selected from the group consisting of -Z 1 -[Z 2 -O] g -Z 3 -, -[Z 4 -O] h -Z 5 -, -CH 2 -CH -Z 6 -[Z 7 -O] i -Z 8 -CH -CH 2 -,; wherein - Z 1 is an alkylene group with 1 to 6 carbon atoms; - Z 2 is selected from the group consisting of alkylene group with 1 to 6 carbon atoms, aryl-substituted alkylene groups whereby the alkylene group comprises 1 to 6 carbon atoms and mixtures of the aforementioned; - Z 3 is an alkylene group with 1 to 3 carbon atoms; - Z 4 is selected from the group consisting of alkylene group with 1 to 6 carbon atoms, aryl-substituted alkylene groups whereby the alkylene group comprises 1 to 6 carbon atoms and mixtures of the aforementioned; - Z 5 is an alkylene group with 1 to 3 carbon atoms; - Z 6 is an alkylene group with 1 to 6 carbon atoms; - Z 7 is selected from the group consisting of alkylene group with 1 to 6 carbon atoms, aryl-substituted alkylene groups whereby the alkylene group comprises 1 to 6 carbon atoms and mixtures of the aforementioned; - Z 8 is an alkylene group with 1 to 3 carbon atoms; - g is an integer ranging from 1 to 100; - h is an integer ranging from 1 to 100; - i is an integer ranging from 1 to 100; and - wherein the individual units A are selected independently from each other, and the individual units D are selected independently from each other and the guanidine compound is linear and/or cross-linked - and the aqueous acidic copper plating bath is free of zinc ions. - Y and Y' are each individually selected from the group consisting of CH 2, O and S; - R 1 is an organic residue selected from the group consisting of hydrogen, alkyl, aryl and alkaryl; - R 2 is an organic residue selected from the group consisting of hydrogen, alkyl, aryl and alkaryl; - R 3, R 4, R 5 and R 6 are each organic residues independently from each other selected from the group consisting of hydrogen, alkyl, aryl and alkaryl; - b and b' are integers each individually and independently from each other ranging from 0 to 6; - c and c' are integers each individually and independently from each other ranging from 1 to 6; - d and d' are integers each individually and independently from each other ranging from 0 to 6; - e and e' are integers each individually and independently from each other ranging from 0 to 6; - D is a divalent residue and is selected from the group consisting of -Z 1 -[Z 2 -O] g -Z 3 -, -[Z 4 -O] h -Z 5 -, -CH 2 -CH -Z 6 -[Z 7 -O] i -Z 8 -CH -CH 2 -,; - Z 1 is an alkylene group with 1 to 6 carbon atoms; - Z 2 is selected from the group consisting of alkylene group with 1 to 6 carbon atoms, aryl-substituted alkylene groups whereby the alkylene group comprises 1 to 6 carbon atoms and mixtures of the aforementioned; - Z 3 is an alkylene group with 1 to 3 carbon atoms; - Z 4 is selected from the group consisting of alkylene group with 1 to 6 carbon atoms, aryl-substituted alkylene groups whereby the alkylene group comprises 1 to 6 carbon atoms and mixtures of the aforementioned; - Z 5 is an alkylene group with 1 to 3 carbon atoms; - Z 6 is an alkylene group with 1 to 6 carbon atoms; - Z 7 is selected from the group consisting of alkylene group with 1 to 6 carbon atoms, aryl-substituted alkylene groups whereby the alkylene group comprises 1 to 6 carbon atoms and mixtures of the aforementioned; - Z 8 is an alkylene group with 1 to 3 carbon atoms; - g is an integer ranging from 1 to 100; - h is an integer ranging from 1 to 100; - i is an integer ranging from 1 to 100; and - wherein the individual units A are selected independently from each other, and the individual units D are selected independently from each other and the guanidine compound is linear and/or cross-linked - and the aqueous acidic copper plating bath is free of zinc ions.