A substantially
cyanide-free plating solution for depositing
copper from the monovalent ionic state, which includes a source of
copper ions, a
reducing agent capable of reducing
divalent copper ions to monovalent copper ions, an alkali material in an amount sufficient to maintain the pH of the solution in the range of about 7 to about 10, and a complexing agent of an
imide, such as
succinimide, 3-methyl-3-ethyl
succinimide, 3-methyl
succinimide, 3-ethyl succinimide, 3,3,4,4-tetramethyl succinimide, or 3,3,4-trimethyl succinimide, or a
hydantoin, such as dimethyl
hydantoin. The substantially
cyanide-free plating solutions may also include at least one of a
conductivity salt, an additive to promote brightness, or an alloying
metal. The
reducing agent may be an alkali
sulfite, alkali
bisulfite,
hydroxylamine, or hydrazine. The copper is typically provided in the form of CuC1, CuC12, CuSO4, or Cu20 in an amount sufficient to provide a copper
ion concentration of from about 2 to about 30 grams per
liter of solution, and the complexing agent is present in an amount sufficient to provide a
molar ratio of copper ions to complexing agent of from about 1:1 to about 1:5, preferably about 1:4. The alkali material is typically NaOH, KOH, NH4OH, or Na2CO3, and the
conductivity salt is typically NaC1, KC1, Na2SO4, K4P2O7, Na3PO4, C6H5Na3O7, C6H11NaO7, NH4C1, or KNaC4H4O6. Useful additives include organic amines or oxyalkyl polyamines, such as triethylene
tetramine, tetraethylene
pentamine, and polyoxypropyl-triamine. Methods for preparing such a solution for plating copper onto a substrate, and of plating copper onto a substrate with such a solution are also disclosed.