Lead frame, semiconductor device using the same and method of producing the semiconductor device

Abstract

A lead frame of the present invention includes a pair of base portions having a substantially flat bottom each. An island portion and electrode portions are partly connected to the tops of the base portions. The lead frame needs a minimum of production cost and promotes dense mounting of semiconductor devices to a circuit board.

What is claimed is:  
     
         1 . A lead frame comprising: 
 a base portion having a substantially flat bottom; and    an island portion and an electrode portion partly formed integrally with a top of said base portion.    
     
     
         2 . A lead frame comprising: 
 a pair of base portions each having a substantially flat bottom;    a pair of electrode portions each being at least partly integrally formed with a top of one of said pair of base portions; and    an island portion at least partly integrally formed with tops of said pair of base portions, connecting said tops to each other.    
     
     
         3 . The lead frame as claimed in  claim 1 , wherein said pair of base portions each consists of a portion beneath said island portion, a portion beneath associated one of said pair of electrode portions, and a portion connecting said portions.  
     
     
         4 . A semiconductor device comprising: 
 an island portion on which a semiconductor chip is mounted; and    electrode portions connected to electrodes formed on a surface of said semiconductor chip by bonding wires;    wherein said island portion and said electrode portions are sealed with seal resin while partly protruding from a bottom of said seal resin each.    
     
     
         5 . A method of producing a semiconductor device for causing a surface of a lead frame to partly appear on a bottom of said semiconductor device, said method comprising the steps of: 
 mounting a semiconductor chip to an island portion included in said lead frame;    connecting electrodes formed on a surface of said semiconductor chip and an electrode portion with bonding wires;    sealing part of a top and part of a bottom of said lead frame, which include said island portion, said semiconductor chip, said electrode portion and said bonding wire, with seal resin;    grinding an entire surface of said seal resin beneath said lead frame in parallel to the bottom of said lead frame; and    causing part of the bottom of said lead frame to appear on a bottom of said seal resin.    
     
     
         6 . The method as claimed in  claim 5 , wherein said lead frame comprises: 
 a base portion having a substantially flat bottom, and    said island portion and said electrode portion partly formed integrally with a top of said base portion.    
     
     
         7 . The method as claimed in  claim 5 , wherein said lead frame comprises: 
 a pair of base portions each having a substantially flat bottom;    a pair of electrode portions each being at least partly integrally formed with a top of one of said pair of base portions; and    said island portion at least partly integrally formed with tops of said pair of base portions, connecting said tops to each other.    
     
     
         8 . A method of producing a semiconductor device for causing a surface of a lead frame to partly appear on a bottom of said semiconductor device, said method comprising the steps of: 
 mounting a semiconductor chip to an island portion included in said lead frame;    connecting electrodes formed on a surface of said semiconductor chip and an electrode portion with bonding wires;    sealing part of a top and part of a bottom of said lead frame, which include said island portion, said semiconductor chip, said electrode portion and said bonding wire, with seal resin;    grinding an entire surface of said seal resin beneath said lead frame in parallel to the bottom of said lead frame;    causing part of the bottom, of said lead frame to appear on a bottom of said seal resin;    half-cut dicing a bottom of said island portion;    plating the bottom of said lead frame and the bottom of said island portion appeared on a bottom of said semiconductor device; and    cutting a connecting portion, which forms part of a base portion of said lead frame, by half-cut dicing.    
     
     
         9 . The method as claimed in  claim 8 , wherein said lead frame comprises: 
 said base portion having a substantially flat bottom, and    said island portion and said electrode portion partly formed integrally with a top of said base portion.    
     
     
         10 . The method as claimed in  claim 8 , wherein said lead frame comprises: 
 a pair of base portions each having a substantially flat bottom;    a pair of electrode portions each being at least partly integrally formed with a top of one of said pair of base portions; and    said island portion at least partly integrally formed with tops of said pair of base portions, connecting said tops to each other.