Circuit device

Abstract

A circuit device having superior voltage resistance is provided. A structure is achieved that omits the resin layer that is normally provided to the top surface of a circuit board. Specifically, a ceramic substrate ( 22 ) is disposed on the top surface of a circuit board ( 12 ) comprising a metal, and a transistor ( 34 ) such as an IGBT is mounted to the top surface of the ceramic substrate ( 22 ). As a result, the transistor ( 34 ) and the circuit board ( 12 ) are insulated from each other by the ceramic substrate ( 22 ). The ceramic substrate ( 22 ), which comprises an inorganic material, has an extremely high voltage resistance compared to the conventionally used insulating layer comprising resin, and so even if a high voltage on the order of 1000V is applied to the transistor ( 34 ), short circuiting between the transistor ( 34 ) and the circuit board ( 12 ) is prevented.

The invention claimed is:  
     
       1. A semiconductor device, comprising:
 a circuit board made of a metal, the circuit board having an upper surface; 
 an oxide film directly on the upper surface; 
 an island made of a metal film directly on the oxide film; 
 a fixation substrate made of a ceramic and fixed to the island with a fixing material; and 
 a semiconductor element mounted on an upper surface of the fixation substrate. 
 
     
     
       2. The circuit device according to  claim 1 , wherein another metal film is provided on a lower surface of the fixation substrate, and the fixing material is in contact with the metal film of the island provided on the upper surface of the circuit board and is in contact with the another metal film provided on the lower surface of the fixation substrate. 
     
     
       3. The circuit device according to  claim 1 , wherein the upper surface of the circuit board is coated with an insulating layer made of a resin material, and
 the island is formed directly on an upper surface of the insulating layer. 
 
     
     
       4. The circuit device according to  claim 1 , wherein a plurality of the fixation substrates are disposed overlying the upper surface of the circuit board, and
 a transistor and a diode connected to a main electrode of the transistor are mounted on the upper surfaces of the plurality of fixation substrates. 
 
     
     
       5. The circuit device according to  claim 1 , further comprising:
 a case material abutting on a periphery part of the circuit board; and 
 a plurality of leads incorporated into the case material, the plurality of leads disposed on stepped portions of the case material provided at ends of the case material and wherein one end of each lead being exposed in an internal space of the case material, and the other end thereof being disposed outward of the case material, wherein an electrode of the semiconductor element is connected to any of the leads exposed in the internal space of the case material. 
 
     
     
       6. The circuit device according to  claim 5 , wherein the plurality of leads are disposed in the same plane. 
     
     
       7. The circuit device according to  claim 5 , further comprising;
 a sealing resin filled in the internal space of the case material, and coating the semiconductor element. 
 
     
     
       8. The circuit device according to  claim 1 , wherein a converter circuit configured to boost direct-current power inputted from the outside and an inverter circuit configured to convert the boosted direct-current power into alternating-current power are assembled on the upper surface of the circuit board, and
 the semiconductor element constitutes the converter or the inverter. 
 
     
     
       9. The circuit device according to  claim 5  wherein electrodes of the semiconductor element are not connected to a conductor on the circuit board. 
     
     
       10. The circuit device of  claim 1  wherein no conductor pattern is formed on the upper surface of the circuit board. 
     
     
       11. The circuit device of  claim 1  wherein the island is disposed between the fixation substrate and the circuit board. 
     
     
       12. The circuit board of  claim 1  further including a case material fixed to a periphery part of the upper surface and forming a cavity;
 another portion of case material internal to the cavity and extending across the circuit board; and 
 an output conductor integrally embedded into the another portion of the case material. 
 
     
     
       13. A semiconductor device, comprising:
 a circuit board made of a metal, the circuit board having an upper surface; 
 an insulating layer coating the upper surface; 
 an island made of a metal film directly on the insulating layer; 
 a fixation substrate made of a ceramic and fixed to the island with a fixing material; and 
 a semiconductor element mounted on an upper surface of the fixation substrate.