Method for Plating Fine Grain Copper Deposit on Metal Substrate

Abstract

A method of depositing an oxygen-free electronic copper layer on a metal substrate is provided that includes cleaning a substrate surface, electropolishing the substrate surface activating the substrate surface, depositing nickel on the substrate; and depositing copper on the substrate using a cyanide copper strike bath and a cyanide copper plate bath, where a periodic pulse and a reverse periodic pulse current is applied using a pulse periodic reverse current power supply, where the deposited oxygen-free copper comprises a fine-grained, equiaxed structure having a uniform surface geometry and less than 10% thickness variation across all surfaces.

What is claimed: 
     
         1 . A method of depositing an oxygen-free electronic copper layer on a metal substrate, comprising:
 a. cleaning a surface of a substrate;   b. electropolishing said substrate surface;   c. activating said substrate surface;   d. depositing nickel on said substrate; and   e. depositing copper on said substrate using a cyanide copper strike bath and a cyanide copper plate bath, wherein a periodic pulse and a reverse periodic pulse current is applied using a pulse periodic reverse current power supply, wherein said deposited oxygen-free copper comprises a fine-grained, equiaxed structure having a uniform surface geometry and less than 10% thickness variation across all surfaces.   
     
     
         2 . The method according to  claim 1 , wherein said cleaning said substrate comprises using a solvent degreaser, a detergent cleaner, a potassium permanganate solution dip, and a combined nitric acid and hydrofluoric acid dip. 
     
     
         3 . The method according to  claim 2 , wherein said solvent degreaser comprises a liquid and vapor solvent degreaser capable of removing oil and soil from said substrate, wherein said vapor solvent comprises a hot vapor degreaser with temperature in a range of 100 to 140° F. and an ultrasonic cleaner. 
     
     
         4 . The method according to  claim 1 , wherein said electropolishing comprises using a phosphoric acid bath having a preset current density of 0.5 to 2 ampere per square inch of said substrate surface for a predetermined time. 
     
     
         5 . The method according to  claim 1 , wherein said activation of said substrate surface comprises a two part process having an anodic treatment in a sulfuric acid comprising a concentration in a range of 10 to 50% by volume, and a cathodic treatment in a sulfuric acid comprising a concentration in a range of 10 to 50% by volume for a predetermined duration. 
     
     
         6 . The method according to  claim 1 , wherein said deposition of nickel comprises a Watt nickel strike bath comprises nickel chloride, hydrochloric acid and water having a current density of more than 40 amperes per square foot. 
     
     
         7 . The method according to  claim 1 , wherein said cyanide copper strike bath comprises Rochelle salt, copper cyanide and potassium cyanide with controlled free cyanide concentration in a solution with a temperature range from 120 to 150° F. and a high current density between 30 to 60 ampere per square foot. 
     
     
         8 . The method according to  claim 1 , wherein said copper plate bath comprises controlled free cyanide, potassium hydroxide and potassium carbonate concentrations at predetermined levels, wherein said copper bath further comprises copper cyanide, potassium cyanide, potassium hydroxide, and potassium-sodium tartrate. 
     
     
         9 . The method according to  claim 1 , wherein said periodic pulse and reverse periodic pulse may each have durations ranging between 0 and 500 seconds. 
     
     
         10 . The method according to  claim 1 , wherein said metal substrate comprises a ferrous metal. 
     
     
         11 . The method according to  claim 10 , wherein said substrate comprises titanium, copper-based alloys, nickel, cobalt, zinc, tungsten, or aluminum, wherein said copper-based alloys comprises brass or Glidcop. 
     
     
         12 . The method according to  claim 1 , wherein said metal comprises a ferrous metal. 
     
     
         13 . The method according to  claim 12 , wherein said substrate comprises stainless steel or steel.