Compressively Stressed Medium Phosphorus Electroless Nickel

Abstract

A method of producing compressive stressed, medium phosphorus nickel deposits from an electroless nickel plating solution is disclosed herein. It was previously believed that a compressively stressed nickel deposit could only be produced with nickel deposits having a high phosphorus nickel content. The inventors have surprisingly discovered that, through selection and concentration of the additives of an electroless nickel plating solution, a medium phosphorus nickel deposit may be produced exhibiting compressive stress.

What is claimed is: 
     
         1 . A method of producing a compressively-stressed medium-phosphorus electroless nickel deposit on a substrate, the method comprising the step of contacting the substrate with an electroless nickel plating solution, the electroless nickel plating solution comprising:
 i) nickel ions;   ii) hypophosphite ions;   iii) at least one chelator; and   iv) a molecule comprising divalent sulfur;   wherein the electroless nickel plating solution deposits on the substrate a compressively-stressed layer of nickel comprising between 4% and 9% phosphorus.   
     
     
         2 . The method according to  claim 1  wherein nickel ions are present in the electroless nickel plating solution at a concentration between 1 gram per liter and 5 grams per liter. 
     
     
         3 . The method according to  claim 1  wherein nickel ions are present in the electroless nickel plating solution at a concentration between 2 gram per liter and 3 grams per liter. 
     
     
         4 . The method according to  claim 1  wherein sodium hypophosphite is the source of hypophosphite ions and sodium hypophosphite is present in the electroless nickel plating solution at a concentration between 10 grams per liter and 25 grams per liter. 
     
     
         5 . The method according to  claim 1  wherein sodium hypophosphite is the source of hypophosphite ions and sodium hypophosphite is present in the electroless nickel plating solution at a concentration between 15 grams per liter and 20 grams per liter. 
     
     
         6 . The method according to  claim 1  wherein the molecule comprising divalent sulfur is selected from the group consisting of 2-aminothiazole and thiosalicylic acid. 
     
     
         7 . The method according to  claim 1  wherein the at least one chelator is selected from the group consisting of lactic acid, malic acid, glycine, and glacial acetic acid. 
     
     
         8 . The method according to  claim 1  wherein the electroless nickel plating solution comprises at least two chelators selected from the group consisting of lactic acid, malic acid, glycine, and glacial acetic acid. 
     
     
         9 . The method according to  claim 1  wherein the electroless nickel plating solution further comprises bismuth ions. 
     
     
         10 . The method according to  claim 1  wherein the electroless nickel plating solution deposits on the substrate a compressively-stressed layer of nickel comprising between 5% and 8% phosphorus. 
     
     
         11 . The method according to  claim 1  wherein the compressively-stressed layer of nickel has a compressive stress between 200 psi and 5000 psi. 
     
     
         12 . The method according to  claim 1  wherein nickel ions are present in the electroless nickel plating solution at a concentration between 2 gram per liter and 4 grams per liter, wherein sodium hypophosphite is the source of hypophosphite ions, wherein sodium hypophosphite is present in the electroless nickel plating solution at a concentration between 15 grams per liter and 25 grams per liter, and wherein the electroless nickel plating solution comprises at least two chelators selected from the group consisting of lactic acid, malic acid, glycine, and glacial acetic acid. 
     
     
         13 . The method according to  claim 12  wherein the electroless nickel plating solution further comprises bismuth ions. 
     
     
         14 . The method according to  claim 1  wherein the substrate is steel. 
     
     
         15 . The method according to  claim 1  wherein the electroless nickel plating solution is heated to a temperature between 175° F. and 200° F. 
     
     
         16 . The method according to  claim 1  wherein the molecule comprising divalent sulfur is thiosalicylic acid. 
     
     
         17 . The method according to  claim 1  wherein the pH of the electroless nickel plating solution is between 4 and 6. 
     
     
         18 . The method according to  claim 1  wherein the substrate is contacted with the electroless nickel plating solution for between 30 minutes and 2 hours.