Copper-zinc alloy electroplating bath and plating method using the copper-zinc alloy electroplating bath

Abstract

A cyanide-free copper-zinc alloy electroplating bath is provided which can form a uniform and glossy alloy layer having the desired composition even at a higher current density than that for a conventional electroplating bath, and which is excellent in productivity. The copper-zinc alloy electroplating bath comprises at least one selected from a copper salt, zinc salt, alkali metal pyrophosphate, and amino acid or a salt thereof, and has a pH of 8.5 to 14. The pH is preferably 10.5 to 11.8; and the concentration of the amino acid or a salt thereof is preferably 0.08 mol/L to 0.22 mol/L, more preferably 0.1 mol/L to 0.13 mol/L. As the amino acid or a salt thereof, histidine or a salt thereof may be preferably used.

1 . A copper-zinc alloy electroplating bath comprising at least one selected from a copper salt, zinc salt, alkali metal pyrophosphate, and amino acid or a salt thereof, said copper-zinc alloy electroplating bath having a pH of 8.5 to 14. 
     
     
         2 . The copper-zinc alloy electroplating bath according to  claim 1 , wherein said pH is 10.5 to 11.8. 
     
     
         3 . The copper-zinc alloy electroplating bath according to  claim 1 , wherein the concentration of said amino acid or a salt thereof is 0.08 mol/L to 0.22 mol/L. 
     
     
         4 . The copper-zinc alloy electroplating bath according to  claim 1 , wherein the concentration of said amino acid or a salt thereof is 0.1 mol/L to 0.13 mol/L. 
     
     
         5 . The copper-zinc alloy electroplating bath according to  claim 1 , wherein the sum of the concentrations of copper and zinc contained in said copper-zinc alloy electroplating bath is within the range of 0.03 to 0.3 mol/L. 
     
     
         6 . The copper-zinc alloy electroplating bath according to  claim 1 , comprising at least one selected from an alkali metal hydroxide and an alkaline earth metal hydroxide. 
     
     
         7 . The copper-zinc alloy electroplating bath according to  claim 1 , wherein said amino acid or a salt thereof is histidine or a salt thereof. 
     
     
         8 . A electroplating method of copper-zinc alloy using the copper-zinc alloy electroplating bath according to  claim 1 , wherein the cathode current density in the plating bath is more than 5 A/dm 2  and not more than 10 A/dm 2 .