Tool and method for welding to IC frames

Abstract

A device for forming an encapsulated end of a wire bonded to a metal surface. The device includes a clamp being an end surface of a bar is pressed against a surface of a p[ate. The end surface has a ridge formed around its edge. so that when a clamping force is applied to the bar against the plate, the metal sheet clamped between the plate surface and end surface of the bar, the clamping force is concentrated at an interface between the metal surface and ridge. When encapsulant is injected into the contact region, the ridge prevents contaminating material from migranting over interface between bar and plate where the welding step is to be performed. The bar is then withdrawn leaving a tunned through which the wire is positioned with the end of the wire in contact bondable to the clean surfave of metal. The wire is positioned in the tunnel and bonded to the metal surface.

I claim:  
     
         1 . A device for forming an encapsulated circuit, said circuit including a wire with an end and a metal sheet having a metal surface, said circuit including said wire having an end contacting said metal surface, said device comprising: 
 a plate having a plate surface;    a bar having an end surface perpendicular to and meeting an elongated side surface of said bar, whereby a comer edge of said bar is defined;    a ridge formed on said end surface around said comer edge of said bar;    means for applying a clamping force to force said ridge toward said plate surface whereby said ridge abuts an area of said metal surface when said metal sheet is clamped between said plate surface and said end surface providing that said clamping force is concentrated at an interface between said metal surface and said ridge;    an enclosure arranged to form a molding by injecting an encapsulating medium into a region within said enclosure that includes said interface between said interface and said ridge;    said molding, after being separated from said plate and said bar, includes said encapsulating medium containing a portion of said metal sheet and a tunnel through said encapsulating medium left after withdrawing said metal bar from said enclosure;    said tunnel extending from one end coincident with said metal surface and a tunnel opening on a surface of said molding providing that said wire is positionable in said tunnel with an end of said wire in contact with said metal surface.    
     
     
         2 . The device of  claim 1  wherein said clamping force is sufficiently great to deform said metal surface.  
     
     
         3 . The device of  claim 1  further comprising means for bonding said end of said wire positioned in said tunnel to said metal surface;  
     
     
         4 . The device of  claim 1  further comprising means for backfilling said tunnel with encapsulating medium.  
     
     
         5 . The device of  claim 3  further comprising means for backfilling said tunnel with encapsulating medium.  
     
     
         6 . The device of  claim 3  wherein said metal surface is plated with a solder alloy and said means for bonding includes means for passing a current through said wire having an end in contact with said metal surface, said current being sufficient to solder said end of said wire to said metal surface.  
     
     
         7 . The device of  claim 1  wherein said bar is a tube providing that said ridge is an edge of said tube.  
     
     
         8 . The device of  claim 2  wherein said means for bonding comprises means for injecting ultra sonic energy into said interface.  
     
     
         9 . The device of  claim 8  wherein said wire is a rigid metal pin and said means for injecting ultrasonic energy comprises: 
 a source of ultrasonic energy;  
 means for coupling said source of ultrasonic energy to an end of said pin extending from said tunnel.  
 
     
     
         10 . The device of  claim 1  wherein said metal sheet is a lead of a lead frame.  
     
     
         11 . A method for forming an encapsulated circuit, said circuit Including a wire with an end making contact at a location on a metal surface of a metal sheet, said method including the steps in operable order: 
 providing a mold having a cavity containing a clamp, said clamp including a plate being one jaw, and a bar having an end clamping surface being an opposing jaw wherein said bar has a ridge extending around an edge of said clamping surface, said bar slidably supported to permit forcing said end clamping surface against said plate;    cleaning said metal surface sufficiently to permit forming a bond of said end of said wire to said metal surface;    clamping the metal sheet between said jaws with a clamping force at a location where said contact is required;    forming an encapsulation by injecting an encapsulating medium into said cavity wherein said encapsulating medium is prevented from covering said location by intimate contact between said ridge and said metal surface;    withdrawing said clamping bar from said mold, leaving said metal sheet encapsulated in a molding formed in said mold cavity, molding having a tunnel that extends from said location on said metal surface to a surface of the molding.    inserting a wire is inserted into said tunnel wherein one end of said wire is in contact with said metal surface and another end of said wire extends out of said open end of the tunnel;    applying at least one of ultrasonic and heat energy sufficient to weld a tip of said wire to said metal surface at said location;    severing said wire leaving an end of said wire extending out of said open end of said tunnel;    filling said tunnel in a second encapsulating step whereby said wire is secured in place.    
     
     
         12 . The method of  claim 11  wherein said clamping force is sufficient to form a depression at said location in said metal surface.