Electroless nickel coatings and compositions and methods for forming the coatings

Abstract

An aqueous electroless nickel plating bath for forming electroless nickel coatings includes nickel, a hypophosphorous reducing agent, zinc, a bismuth stabilizer, and at least one of a complexing agent, a chelating agent, or a pH buffer, and is free of a sulfur compound.

1 - 50 . (canceled) 
     
     
         51 . A method of forming a multilayer electroless metal coating on a substrate, the method comprising:
 i. contacting the substrate with a first electroless nickel plating bath to form a first eletroless nickel coating on the substrate, the first electroless nickel coating having a phosphorus content of 7% to 13% by weight   ii. contacting the substrate coated with the first electroless coating with a second aqueous electroless nickel plating bath to form a second electroless nickel coating over the first electroless coating, the second electroless coating having a phosphorous content of 8% to 11%, the second bath including nickel, a hypophosphorous reducing agent, 40 ppm to 100 ppm zinc, at least one of a complexing agent, chelating agent, and/or pH buffer, and 5 ppm to 30 ppm bismuth stabilizer, wherein the bath is free of an organic sulfur compound;   iii. etching the second electroless nickel coating with an etchant agent to provide the coated substrate with a black surface or contacting the substrate coated with the first and second electroless nickel coatings with an electroless copper plating bath to provide a copper top coat.   
     
     
         52 . The method of  claim 51 , wherein hypophosphorous reducing agent is selected from the group consisting of sodium hypophosphite, potassium hypophosphite, ammonium hypophosphite, and combinations thereof. 
     
     
         53 . The method of  claim 51 , wherein the second electroless nickel plating bath includes at least one pH buffer, complexing agent, or chelating agent is selected from the group consisting of acetic acid, formic acid, succinic acid, malonic acid, an ammonium salt, lactic acid, malic acid, citric acid, glycine, alanine, glycolic acid, lysine, aspartic acid, ethylene diamine tetraacetic acid (EDTA), and combinations thereof. 
     
     
         54 . The method of  claim 53 , comprising at least two of a pH buffer, complexing agent, and/or chelating agent. 
     
     
         55 . The method of  claim 51 , wherein the nickel is provided in the second electroless plating bath in the form of a water soluble nickel salt. 
     
     
         56 . The method of  claim 55 , the nickel salt being selected from the group consisting of nickel chloride, nickel bromide, nickel iodide, nickel acetate, nickel malate, and nickel hypophosphite. 
     
     
         57 . The method of  claim 51 , wherein the pH of the second electroless nickel plating bath is maintained at 4.5 to 5.0 and the temperature at 79° C. to 93° C. 
     
     
         58 . The method of  claim 51 , the second electroless nickel plating bath comprising 2 g/1 to 10 g/1 nickel, 20 g/1 to 35 g/1 of the hypophosphorous reducing agent, 1 g/1 to 75 g/1 each of the complexing agent, chelating agent, and/or pH buffer. 
     
     
         59 . The method of  claim 51 , the second electroless nickel plating bath comprising lactic acid, acetic acid, malic acid, succinic acid, sodium hypophosphite, ammonium hydroxide, nickel, zinc, and ethylenediamine tetraacetic acid. 
     
     
         60 . The method of  claim 51 , the etchant agent comprising ferric sulfate and hydrochloric acid. 
     
     
         61 . The method of  claim 51 , contacting the substrate coated with the first and second electroless nickel coatings with an acid solution prior to contacting the substrate with the electroless copper plating bath.