Saw singulated leadless plastic chip carrier

Abstract

Leadless plastic chip carriers are formed from a matrix of lead frames provided in a section of a metal strip. Each lead frame in the matrix includes a die-attach pad and multiple leads disposed in close proximity to the die-attach pad. After a semiconductor die is attached to each of the die-attach pad and wire-bonded, the leadless plastic chip carriers are formed by providing a plastic encapsulation which exposes the bottom sides of the die-attach pad and the leads. The bottom sides of the leads serve as solder pads to be used for attaching the leadless plastic chip carrier to a printed circuit board.

We claim:  
     
         1 . A plastic chip carrier, comprising: 
 a semiconductor die having bonding pads formed thereon;    a die-attach pad having a bottom surface and a top surface on which said semiconductor die is attached;    a plurality of leads, each having a bottom surface and a top surface, said leads disposed in close proximity to said die-attach pad;    a plurality of wires each bonded to a selected one of said bonding pads and a corresponding one of said leads; and    an encapsulation encapsulating said semiconductor die, said top surface of said die attach-pad, said wires, and said top surfaces of said leads, and exposing said bottom surface of said die-attach pad and said bottom surfaces of said leads.    
     
     
         2 . A plastic chip carrier as in  claim 1 , wherein said die-attach pad is provided an interlocking lip at a portion of said die-attach pad, said interlocking lip engaging said die-attach pad to said encapsulation.  
     
     
         3 . A plastic chip carrier as in  claim 1 , further comprising a plurality of tie bars, each tie bar being attached to said die-attach pad and extending from said die-attach pad to form a peripheral heat pad for dissipating heat to the outside of said encapsulation.  
     
     
         4 . A plastic chip carrier as in  claim 3 , wherein one of said heat pads has an appearance distinctive from other heat pads of said chip carrier.  
     
     
         5 . A plastic carrier as in  claim 1 , wherein said die-attach pad and said leads are formed out of an array of lead frames integrally formed on a portion of a metal strip.  
     
     
         6 . A plastic carrier as in  claim 1 , wherein said die-attach pad is plated with palladium.  
     
     
         7 . A plastic carrier as in  claim 1 , wherein a distinctive pattern is formed on said encapsulation.  
     
     
         8 . A plastic carrier as in  claim 1 , further comprising solder balls each attached to a bottom side of a corresponding one of said leads.  
     
     
         9 . A plastic carrier as in  claim 1 , wherein a soft solder attaches said semiconductor die to said die-attach pad.  
     
     
         10 . A plastic carrier as in  claim 1 , wherein said plurality of leads are arranged as an annular row of inner leads and an annular row of outer leads.  
     
     
         11 . A process for forming a plastic carrier, comprising: 
 forming a matrix of lead frames out of a metal strip, each lead frame including a die-attach pad and a plurality of leads disposed in close proximity to said die-attach pad, said die-attach pad and said leads each having a bottom surface and a top surface;    attaching to the top surface of each die-attach pad a semiconductor die, said semiconductor die having a plurality of bonding pads formed thereon;    providing bond wires to electrically connect each of said bonding pads to the top surface of a corresponding lead; and    encapsulating said die-attach pad, said semiconductor die, said bond wires and said leads in a resin material such that said bottom surface of said die-attach pad and said bottom surfaces of said leads are exposed.    
     
     
         12 . A process as in  claim 11 , wherein said die-attach pad is provided an interlocking lip at the periphery such that said resin material engages interlocking lip of said die-attach pad.  
     
     
         13 . A process as in  claim 11 , wherein each of said lead frames includes tie bars, said matrix of lead frames being formed with each tie bar being attached to said die-attach pad and extending from said die-attach pad to form a peripheral heat pad for dissipating heat.  
     
     
         14 . A process as in  claim 13 , wherein one of said heat pads has an appearance distinctive from other heat pads in said lead frame.  
     
     
         15 . A process as in  claim 11 , further comprising the operation of plating said die-attach pad with palladium.  
     
     
         16 . A process as in  claim 11 , wherein a distinctive pattern is formed on said resin material by said encapsulating step.  
     
     
         17 . A process as in  claim 11 , further comprising the operation of attaching solder balls to the bottom sides of corresponding leads.  
     
     
         18 . A process as in  claim 11 , wherein said attaching step provides a soft solder to attach said semiconductor die to said die-attach pad.  
     
     
         19 . A lead frame, comprising: 
 a die-attach pad;    an annular row of inner leads;    an annular row of outer leads connected to said annular row of inner leads by a connecting portion, wherein said die-attach pad is connected is to said annular row of inner leads and said annular row of outer leads by a plurality of tie bars.    
     
     
         20 . A lead frame as in  claim 19 , wherein said connecting portion has a thickness which is half the thickness of a lead in said annular row of inner leads.  
     
     
         21 . A lead frame as in  claim 19 , wherein leads in said annular row of inner leads and said annular row of outer leads are arranged in an alternating fashion.  
     
     
         22 . A lead frame as in  claim 19 , wherein said lead frame is a lead frame within a matrix of substantially identical lead frames, and said matrix being one of multiple matrices of lead frames formed in a metal strip.