Mask-Less Selective Plating of Leadframes

Abstract

A method for selectively plating a leadframe ( 1100 ) by oxidizing selected areas ( 401, 402, 403, 404 ) of the leadframe made of a first metal ( 102 ) and then depositing a layer ( 901 ) of a second metal onto un-oxidized areas. The selective oxidations are achieved by selective active marking

1 . A method for selectively plating a leadframe comprising the steps of:
 oxidizing selected areas of a leadframe made of a first metal; and   depositing a layer of a second metal onto un-oxidized areas.   
     
     
         2 . The method of  claim 1  wherein the second metal layers have diffuse edges bordering the oxidized areas. 
     
     
         3 . The method of  claim 1  wherein the step of oxidizing includes the step of contacting the selected leadframe areas with a chemical agent suitable for oxidizing the first metal. 
     
     
         4 . The method of  claim 3  wherein the agent is sodium hypochlorite (NaOCl). 
     
     
         5 . The method of  claim 3  wherein the step of contacting includes a rubber stamp for pressing against the leadframe, the stamp having elevated mesas matching the selected leadframe areas, the mesas suitable to be dipped into the chemical agent. 
     
     
         6 . The method of  claim 3  wherein the step of contacting includes the movable jet of a printer. 
     
     
         7 . The method of  claim 1  wherein the step of oxidizing includes the step of transferring heat into the selected leadframe areas for accelerating oxidation of the first metal. 
     
     
         8 . The method of  claim 7  wherein the step of transferring heat includes a tool having elongated probes matching the selected leadframe areas, the probes suitable to be electrically heated. 
     
     
         9 . The method of  claim 7  wherein the step of transferring heat includes a movable laser beam. 
     
     
         10 . The method of  claim 1  wherein the first metal is selected from a group including copper, copper alloy, aluminum, iron-nickel alloy, and Kovar™. 
     
     
         11 . The method of  claim 1  wherein the step of depositing includes the step of immersing the leadframe into a plating bath, the deposited layer adhering to the un-oxidized leadframe areas while not adhering to the oxidized areas. 
     
     
         12 . The method of  claim 11  wherein the step of depositing includes the step of flood plating. 
     
     
         13 . The method of  claim 13  further including the step of peeling away the deposited layer not adhering to the oxidized leadframe areas. 
     
     
         14 . The method of  claim 13  wherein the second metal includes a layer of nickel in contact with the first metal, a layer of palladium in contact with the nickel, and a layer of gold in contact with the palladium. 
     
     
         15 . The method of  claim 13  wherein the second metal includes tin.