Electroless nickel plating bath composition

Abstract

The present invention relates to an aqueous plating bath composition for depositing a nickel phosphorous alloy having a phosphorous content in the range of 5 to 12 wt. %. The plating bath comprises a sulfur-containing organic stabilizing agent.

1 . An aqueous plating bath composition for electroless plating of a nickel phosphorous alloy, the plating bath comprising
 (i) a water soluble source of nickel ions   (ii) a hypophosphite compound   (iii) at least one complexing agent selected from the group comprising carboxylic acids, polyamines, sulfonic acids and mixtures thereof and   (iv) a stabilizing agent selected from the group consisting of compounds according to formulae (1) and (2):
   R 1 S—(CH 2 ) n —SO 3 R 2    (1)
 
   R 3 SO 3 —(CH 2 ) m —S—S—(CH 2 ) m —SO 3 R 3    (2)
 
   wherein   R 1 , R 2  and R 3  are independently selected from the group consisting of hydrogen, methyl, ethyl, propyl, butyl, lithium, sodium, potassium and ammonium,   n ranges from 1 to  6 and      m ranges from 1 to 6   and having a pH value in the range of 3.5 to 6.5.   
     
     
         2 . The aqueous plating bath according to  claim 1  wherein the concentration of nickel ions ranges from 1 to 18 g/l. 
     
     
         3 . The aqueous plating bath composition according to  claim 1  wherein the hypophosphite compound is selected from the group comprising phosphorous acid, sodium hypophosphite, potassium hypophosphite and ammonium hypophosphite. 
     
     
         4 . The aqueous plating bath composition according to  claim 1  wherein the concentration of the hypophosphite compound ranges from 2 to 60 g/l. 
     
     
         5 . The aqueous plating bath composition according to  claim 1  wherein the concentration of the at least one complexing agent ranges from 1 to 200 g/l. 
     
     
         6 . The aqueous plating bath composition according to  claim 1  wherein the concentration of the stabilizing agent according to formulae (1) and (2) ranges from 1 to 100 ppm. 
     
     
         7 . The aqueous plating bath composition according to  claim 1  wherein the plating bath composition is essentially free of heavy metal ions selected from cadmium, thallium, lead and antimony. 
     
     
         8 . The aqueous plating bath composition according to  claim 1  having a pH value in the range of 4 to 6. 
     
     
         9 . Method for depositing a nickel phosphorous alloy having a phosphorous concentration in the range of 5 to 12 wt. %, the method comprising the steps of 
       (i) providing a substrate 
       (ii) contacting said substrate with an aqueous plating bath according to  claim 1 .