Method for forming a displacement tin alloy plated film, displacement tin alloy plating bath and method for maintaining a plating performance

Abstract

Disclosed herein is a method for forming a displacement tin alloy plated film, on a copper or a copper alloy on a substrate, a tin alloy plated film containing at least one additive metal selected from silver, bismuth, palladium, indium, zinc and antimony, the method including the steps of: forming an under layer on the copper or copper alloy in a low temperature displacement tin alloy plating bath at a temperature of 10 to 50° C.; and forming an upper layer on the under layer in a high temperature tin alloy plating bath at a temperature of 40 to 80° C. to form the displacement tin alloy plated film formed of the under layer and the upper layer.

1 . A method for forming a displacement tin alloy plated film consisting of an under-layer and an upper layer on a copper or a copper alloy of a substrate, wherein the displacement tin alloy plated film contains at least one additive metal selected from silver, bismuth, palladium, indium, zinc and antimony, and the method comprises the steps of:
 forming the under layer on the copper or copper alloy in a low temperature displacement tin alloy plating bath at a temperature of 10 to 50° C.; and   forming the upper layer on the under layer in a high temperature tin alloy plating bath at a temperature of 40 to 80° C.   
     
     
         2 . The method for forming the displacement tin alloy plated film of  claim 1 , wherein said displacement tin alloy plating bath comprises:
 (A) 1 to 50 g/L, based on tin, of a divalent tin compound;   (B) 0.1 to 5 mol/L of an acid capable of yielding the same anion as the anion generated from the divalent tin compound;   (C) 50 to 250 g/L of thiourea; and   (D) 1 to 1000 ppm, based on the additive metal, of a compound of the additive metal.   
     
     
         3 . The method for forming the displacement tin alloy plated film of  claim 2 , wherein a concentration of the component (D) is at 5 to 80 ppm based on the additive metal. 
     
     
         4 . A displacement tin alloy plating bath used in the method of  claim 1 , comprising:
 (A) 1 to 50 g/L, based on tin, of a divalent tin compound;   (B) 0.1 to 5 mol/L of an acid capable of yielding the same anion as the anion generated from the divalent tin compound;   (C) 50 to 250 g/L of thiourea; and   (D) 1 to 1000 ppm, based on the additive metal, of a compound of the additive metal.   
     
     
         5 . The displacement tin alloy plated bath of  claim 4 , wherein a concentration of the component (D) is at 5 to 80 ppm based on the additive metal. 
     
     
         6 . A method for maintaining a plating performance of the displacement tin plating bath used for plating in the method of  claim 2 , wherein the maintenance method comprises continuously or intermittently adding thiourea of the component (C) to said plating bath, in correspondence to an increasing concentration of copper in the plating bath dissolved out by the displacement, in such a way that the thiourea is made at a concentration higher than a concentration of the initial plating bath. 
     
     
         7 . The method for maintaining a plating performance of  claim 6 , wherein the maintenance method further comprises continuously or intermittently adding a compound of the additive metal of the component (D) to said plating bath with the thiourea of the component (C) in such a way that the compound of the additive metal is made at a concentration higher than a concentration of the initial plating bath.