Printed circuit surface finish, method of use, and assemblies made therefrom

Abstract

A surface finish for a printed circuit board (PCB) and semiconductor wafer includes a nickel disposed over an aluminum or copper conductive metal surface. A barrier layer including all or fractions of a nitrogen-containing molecule is deposited on the surface of the nickel layer to make a barrier layer/electroless nickel (BLEN) surface finish. The barrier layer allows solder to be reflowed over the surface finish. Optionally, gold (e.g., immersion gold) may be coated over the barrier layer to create a nickel/barrier layer/gold (NBG) surface treatment. Presence of the barrier layer causes the surface treatment to be smoother than a conventional electroless nickel/immersion gold (ENIG) surface finish. Presence of the barrier layer causes a subsequently applied solder joint to be stronger and less subject to brittle failure than conventional ENIG.

1 . A method for making an electrical circuit assembly, comprising:
 receiving a substrate, at least a portion of the substrate including a conductive material layer that defines one or more electrical conductors;   applying nickel onto at least a portion of one of the one or more electrical conductors;   
       and
 applying a barrier layer onto the nickel, the barrier layer comprising at least a portion of a nitrogen-containing molecule. 
 
     
     
         2 . The method of  claim 1  further comprising applying immersion gold subsequent to the applying the barrier layer. 
     
     
         3 . The method of  claim 1  wherein the barrier layer is applied using a solution comprising an amine. 
     
     
         4 . The method of  claim 1  wherein the nitrogen-containing molecule includes from one to six carbon atoms. 
     
     
         5 . The method of  claim 1  wherein the barrier layer is applied using a solution comprising a diamine or a triamine. 
     
     
         6 . The method of  claim 1  wherein the barrier layer is applied using a solution comprising diethylene triamine. 
     
     
         7 . The method of  claim 1  wherein the barrier layer impedes oxidation of the nickel. 
     
     
         8 . A method of plating one or more metallic regions of a substrate, the method comprising:
 forming a nickel layer on at least a portion of the one or more metallic regions; and   performing a surface treatment on the nickel layer by exposing the nickel layer to a solution comprising nitrogen-containing molecules.   
     
     
         9 . The method of  claim 8  further comprising forming a gold layer on at least a portion of the one or more metallic regions after the performing the surface treatment. 
     
     
         10 . The method of  claim 8  wherein the surface treatment impedes oxidation of the nickel layer. 
     
     
         11 . The method of  claim 8  wherein the solution comprises an amine. 
     
     
         12 . The method of  claim 8  wherein the solution comprises a diamine or a triamine. 
     
     
         13 . The method of  claim 8  wherein the solution comprises siloxane. 
     
     
         14 . The method of  claim 8  wherein the substrate comprises a fiberglass reinforced epoxy. 
     
     
         15 . The method of  claim 8  wherein the substrate comprises a semiconductor material. 
     
     
         16 . A method of plating a terminal of a substrate, the method comprising:
 immersing the substrate in a first solution that forms a nickel layer on at least a portion of the terminal; and   immersing the substrate in a second solution comprising nitrogen-containing molecules that forms a conversion layer on at least a portion of the nickel layer.   
     
     
         17 . The method of  claim 16  further comprising immersing the substrate in a third solution after the immersing the substrate in the second solution, wherein the third solution forms a gold layer on at least a portion of an outermost surface of the terminal. 
     
     
         18 . The method of  claim 16  wherein the second solution comprises an amine. 
     
     
         19 . The method of  claim 16  wherein the nitrogen-containing molecules include from one to six carbon atoms. 
     
     
         20 . The method of  claim 16  wherein the second solution comprises a diamine or a triamine.