Semiconductor device and method for producing the same

Abstract

A high-reliability power semiconductor device uses a lead-free solder layer to connect a semiconductor chip such as an IGBT to an insulating substrate having a ceramic board and conductor layers, and a lead-free solder layer to connect the insulating substrate to a radiating base. Before the insulating substrate and the radiating base are solder-connected, the radiating base is warped such that the surface of the radiating base on the side opposite to the insulating substrate is convex. The insulating substrate is solder-connected onto the warped radiating base with the lead-free solder so as to provide a substantially flat solder-connected radiating base. When the radiating base is attached to a cooling fin, the thermal resistances are lower, and heat from the semiconductor chip is effectively dissipated so as to prevent abnormal temperature rise.

1 . A semiconductor device comprising: 
 an insulating substrate comprising a ceramic board and having conductor layers disposed on two surfaces of the ceramic board, a radiating base solder-connected to the insulating substrate, and a semiconductor chip solder-connected to the insulating substrate,    wherein a solder connecting the insulating substrate to each of the semiconductor chip and the radiating base is a lead-free solder, and the connected radiating base is present in a substantially flat state.    
     
     
         2 . The semiconductor device according to  claim 1 , wherein the lead-free solder has a melting point of 250° C. or lower.  
     
     
         3 . The semiconductor device according to  claim 1 , wherein the lead-free solder comprises tin and at least one element selected from the group consisting of silver, bismuth, indium, antimony, zinc, aluminum, and copper.  
     
     
         4 . The semiconductor device according to  claim 1 , wherein, in the insulating substrate, the conductor layer connected to the semiconductor chip has a thickness equal to or smaller than that of the conductor layer connected to the radiating base.  
     
     
         5 . The semiconductor device according to  claim 1 , wherein, in the insulating substrate, the volume ratio of the conductor layer connected to the radiating base to the conductor layer connected to the semiconductor chip is 1 or more.  
     
     
         6 . The semiconductor device according to  claim 1 , wherein, in the insulating substrate, the conductor layers comprise a copper foil, and the ceramic board comprises alumina as a main component.  
     
     
         7 . The semiconductor device according to  claim 1 , wherein the insulating substrate is connected to each of the radiating base and the semiconductor chip such that the insulating substrate is divided into a plurality of portions.  
     
     
         8 . The semiconductor device according to  claim 1 , wherein, in the insulating substrate, the conductor layers have a thickness of 0.4 mm or more.  
     
     
         9 . The semiconductor device according to  claim 1 , wherein, in the insulating substrate, the ceramic board has a thickness of 0.2 to 0.635 mm.  
     
     
         10 . The semiconductor device according to  claim 1 , wherein the radiating base comprises copper.  
     
     
         11 . The semiconductor device according to  claim 1 , wherein the radiating base has a thickness of 2 to 4 mm.  
     
     
         12 . A method for producing a semiconductor device comprising: 
 solder-connecting a semiconductor chip, onto an insulating substrate comprising a ceramic board and having conductor layers on two surfaces thereof, with a lead-free solder,    warping a radiating base such that a surface of the radiating base on a side opposite to the insulating substrate is convex, and    solder-connecting the insulating substrate onto the warped radiating base with the lead-free solder so as to provide a substantially flat solder-connected radiating base.    
     
     
         13 . The method for producing a semiconductor device according to  claim 12 , wherein the lead-free solder has a melting point of 250° C. or lower.  
     
     
         14 . The method for producing a semiconductor device according to  claim 12 , wherein the lead-free solder comprises tin and at least one element selected from the group consisting of silver, bismuth, indium, antimony, zinc, aluminum, and copper.  
     
     
         15 . The method for producing a semiconductor device according to  claim 12 , wherein the radiating base is warped to an extent determined by properties of the insulating substrate.  
     
     
         16 . The method for producing a semiconductor device according to  claim 15 , wherein the radiating base is warped to an extent determined by a connection area between the radiating base and the insulating substrate.  
     
     
         17 . The method for producing a semiconductor device according to  claim 16 , wherein the insulating substrate is divided into a plurality of portions, and the radiating base is warped to an extent determined by a connection area between the radiating base and the divided insulating substrate.  
     
     
         18 . The method for producing a semiconductor device according to  claim 15 , wherein the radiating base is warped to an extent determined by a thickness of the conductor layer in the insulating substrate.  
     
     
         19 . The method for producing a semiconductor device according to  claim 15 , wherein the radiating base is warped to an extent determined by a volume ratio between the conductor layers disposed on both surfaces of the ceramic board in the insulating substrate.  
     
     
         20 . The method for producing a semiconductor device according to  claim 15 , wherein the radiating base is warped to an extent determined by a thickness of the ceramic board in the insulating substrate.  
     
     
         21 . The method for producing a semiconductor device according to  claim 12 , wherein the radiating base is warped to an extent determined by a thickness of the radiating base.  
     
     
         22 . The method for producing a semiconductor device according to  claim 12 , wherein, in the insulating substrate, the conductor layers comprise a copper foil, and the ceramic board comprises alumina as a main component.  
     
     
         23 . The method for producing a semiconductor device according to  claim 12 , wherein the radiating base comprises copper.