Asymmetric plating

Abstract

A method and apparatus are disclosed for forming a tapered contact structure over a contact pad. The tapered contact structure may be used to securely anchor an overlying solder bump or solder ball. Additionally, the tapered contact structure allows the use of either larger contact pads or, alternately, allows a greater density of contact pads to be achieved on an integrated circuit substrate.

What is claimed is:  
     
         1 . A solder ball contact comprising: 
 a substrate having a contact region; and    a tapered nickel contact formed over the contact region.    
     
     
         2 . The solder ball contact of  claim 1 , wherein the tapered nickel contact is substantially pyramidal.  
     
     
         3 . The solder ball contact of  claim 1 , wherein the tapered nickel contact is substantially conical.  
     
     
         4 . The solder ball contact of  claim 1 , wherein the contact region comprises aluminum.  
     
     
         5 . The solder ball contact of  claim 1 , wherein the contact region comprises copper.  
     
     
         6 . The solder ball contact of  claim 1 , wherein the contact region comprises an underbump metalization layer.  
     
     
         7 . The solder ball contact of  claim 1 , wherein the solder ball contact is formed by providing a nickel bath, controlling the temperature of the nickel bath to no more than 90 degrees Celsius, placing the substrate having the contact region to be plated in the nickel bath, and causing movement of the nickel bath relative to the contact region to cause nickel from the nickel bath to plate onto the contact region to form the tapered nickel contact.  
     
     
         8 . The solder ball contact of  claim 1 , comprising a solder ball disposed over the tapered nickel contact.