Reduction of surface oxidation during electroplating

Abstract

Methods of providing improved metal coatings or metal deposits on a substrate, improvements in plating solutions that are used to provide such metal deposits and articles of the metal-coated substrates. The solderability of the metal coating is enhanced by incorporating trace amounts of phosphorus in the metal coating to reduce surface oxide formation during subsequent heating and thus enhance long term solderability of the metal coating. The phosphorus is advantageously provided in the metal coating by incorporating a source of phosphorus in a solution that is used to provide the metal coating on the substrate, and the metal coating is then provided on the substrate from the solution.

1 . In an electroplating solution that includes metal ions for electroplating a metal deposit on a substrate, the improvement which comprises incorporating a source of phosphorus in the electroplating solution in an amount to provide trace amounts of phosphorus in the metal deposit to reduce surface oxide formation during subsequent heating of the deposit to thus enhance long term solderability or reflow properties of the metal deposit.  
   
   
       2 . The solution of  claim 1  wherein the source of phosphorus is a compound of phosphorus that is soluble in the solution and which provides ppm levels of phosphorus in the metal deposit.  
   
   
       3 . The solution of  claim 1  wherein the phosphorus is present in the metal deposit in a detectable amount but less than about 200 ppm.  
   
   
       4 . The solution of  claim 1  wherein the metal deposit is produced by electroplating at a current density of no greater than about 2000 ASF.  
   
   
       5 . The solution of  claim 1  wherein the metal ions and resulting deposits comprise nickel, cobalt, copper, tungsten, zinc, or tin.  
   
   
       6 . The solution of  claim 1  wherein the electroplated metal deposit is tin and the phosphorus is present in the coating in a detectable amount but less than about 50 ppm.  
   
   
       7 . The solution of  claim 1  wherein the electroplated metal deposit is nickel and the phosphorus is present in the coating in a detectable amount but less than about 200 ppm.  
   
   
       8 . The solution of  claim 1  wherein the phosphorus is provided in the metal deposit by incorporating a source of phosphorus in the electroplating solution that is used to provide the metal deposit on the substrate, wherein the phosphorus source comprises an organic or inorganic phosphorus compound that is at least partially soluble in the solution.  
   
   
       9 . The solution of  claim 8  wherein the source of phosphorus is a compound of phosphorus that is completely soluble in the solution and which provides the desired levels of phosphorus in the electroplated metal coating.  
   
   
       10 . The solution of  claim 8  wherein the phosphorus compound is an alkali or alkaline earth phosphite, hypophosphite, phosphate or pyrophosphide and is present in the solution at a concentration of between 0.5 to 15 g/l.  
   
   
       11 . The solution of  claim 1  wherein the substrate is an electronic component that, after being plated, is subjected to further processing steps which require multiple thermal excursions at temperatures as high as 175° C.  
   
   
       12 . The solution of  claim 11  wherein the electronic component comprises a circuit or lead frame.  
   
   
       13 . The solution of  claim 11  wherein the substrate is made of copper, steel or stainless steel.  
   
   
       14 . The solution of  claim 13  wherein the substrate is a composite substrate that includes conductive and non-conductive or electroplatable and non-electroplatable portions.  
   
   
       15 . The solution of  claim 1  wherein the metal deposit is tinplate having reflow properties that are enhanced compared to tinplate that does not contain phosphorus.  
   
   
       16 . The solution of  claim 15  wherein the tinplate is a bright tin deposit provided by a reflow operation.  
   
   
       17 . A method for enhancing solderability of an electroplated coating on a substrate, which comprises providing a nickel coating on the substrate by electroplating utilizing the electroplating solution of  claim 1  containing nickel ions, with the electroplated nickel coating being produced by electroplating at a current density of no greater than about 2000 ASF, the current density being controlled to achieve the desired quantity of phosphorus in the electroplated nickel coating, and the phosphorus being present in the electroplated metal coating in an amount sufficient to reduce surface oxide formation on exposed portions of the electroplated coating during subsequent heating or processing operations to thus enhance long term solderability or reflow properties of the electroplated coating.  
   
   
       18 . The method of  claim 17  which further comprises electroplating tin or a tin alloy upon the nickel coating to further enhance solderability of the electroplated coating.  
   
   
       19 . The method of  claim 17 , wherein the substrate is made of copper, steel or stainless steel and the phosphorus is present in the coating in a detectable amount but less than about 200 ppm.  
   
   
       20 . The method of  claim 19  which further comprises subjecting the electroplated coating to a reflow operation to provide a bright tin deposit.