Method and apparatus for electrolytic plating of surface metals

Abstract

A method and apparatus for electrolytic plating of selected areas of printed circuit board traces is disclosed. The method is characterized by its elimination of the need for plating bus bars and plating contacts on the printed circuit board to facilitate a spot-plating process. In one embodiment, a printed circuit board substrate is provided which is at least partially conductive, such that a plating voltage may be applied to any one or more points on the substrate during a spot plating operation. In another embodiment, the substrate material is initially partially conductive, but following the spot-plating operation, is subjected to a curing treatment or the like to cause degeneration of the substrate's conductivity. Carbon-impregnated polimid, partially-cured polyimid, FR4 or FR5, with appropriate contaminants introduced therein are contemplated as materials suitable for a printed circuit board substrate in accordance with the invention. In another embodiment, the traces are first applied to the partially conductive substrate by an electroplating operation wherein an electroplating voltage is applied to the substrate such that the substrate itself serves as one terminal of the electroplating system.

What is claimed is:  
     
         1 . A method of spot-plating selected areas of metal traces on a printed circuit board, comprising: 
 (a) providing a partially-conductive printed circuit board substrate having said metal traces formed thereon;    (b) applying a plating voltage to said substrate; and    (c) performing an electrolytic plating operation on said substrate;    
     
     
         2 . A method in accordance with  claim 1 , wherein said partially-conductive printed circuit board substrate has a conductivity in a range between 10 6  and 10 8  Ω per square centimeter.  
     
     
         3 . A method in accordance with  claim 1 , further comprising: 
 (d) heat-treating said substrate after said step (c) of electroplating, thereby reducing said conductivity of said substrate.    
     
     
         4 . A method in accordance with  claim 1 , further comprising: 
 (d) curing said substrate with ultraviolet light after said step (c) of electroplating, thereby reducing said conductivity of said substrate.    
     
     
         5 . A printed circuit board, comprising: 
 a substrate composed of a partially conductive material;    at least one metal trace formed on said substrate;    wherein said substrate is adapted have a plating voltage applied thereto to facilitate a spot-plating operation on said at least one metal trace.    
     
     
         6 . A printed circuit board in accordance with  claim 5 , wherein said substrate is composed of a partially-cured material and is adapted to be subjected to a curing operation subsequent to said spot-plating operation.  
     
     
         7 . A printed circuit board in accordance with  claim 5 , wherein said partially conductive material has a conductivity in a range between 10 6  and 10 8  Ω per square centimeter.  
     
     
         8 . A method of applying metal traces to a printed circuit board substrate, comprising: 
 (a) providing a partially conductive substrate;    (b) applying an electroplating voltage to said substrate;    (c) electroplating said metal traces to said substrate using said electroplating voltage.    
     
     
         9 . A method in accordance with  claim 8 , further comprising: 
 (d) heat-treating said substrate, thereby reducing said partial conductivity thereof.    
     
     
         10 . A method in accordance with  claim 8 , further comprising: 
 (d) curing said substrate, thereby reducing said partial conductivity thereof.    
     
     
         11 . A method in accordance with  claim 8 , further comprising: 
 (d) while said electroplating voltage is applied to said substrate, performing an electrolytic spot-plating operation on said traces.