Abstract:
Disclosed is a vehicle-mounted electronic device wherein heat generated from a heat-generating electronic device can be efficiently released without redesigning various kinds of components even if an input/output signal array for a terminal of a connector is changed. The vehicle-mounted electronic device is comprised of a lower housing ( 2   b ) having a bottom surface, a part of which is opened; a connector ( 3 ) which is projected from an opening ( 2   c ) of the lower housing ( 2   b ), and which can be connected to an outside device which inputs/outputs electric signals and an outside power source which supplies electric power; a circuit board ( 5 ) which is provided within the lower housing ( 2   b ), and is electrically connected to the connector ( 3 ) to process signals using electric signals and electric power; a metal wiring plate ( 7 ) composed of a plurality of metal wires, which is provided within the lower housing ( 2   b ) on the side adjacent to the bottom surface of the lower housing ( 2   b ), and has an end portion projected from the lower housing ( 2   b ) to electrically connect to the circuit board; and heat-generating electronic components ( 6 ), the bottom surfaces of which are coupled to a part of the metal wires in the metal wiring plate ( 7 ). The thickness of the metal wires coupled to the bottom surfaces of the heat-generating electronic components ( 6 ) in the metal wiring plate ( 7 ) is larger than the thickness of the terminal of the connector ( 3 ).

Description:
TECHNICAL FIELD 
     The present invention relates to a vehicle-mounted electronic apparatus such as a control unit that accommodates a circuit substrate in a resin case. 
     BACKGROUND ART 
     With a conventional vehicle-mounted electronic apparatus, in order to miniaturize and lower the cost of a control unit, a heating block and others are made unnecessary by connecting heat-generating electronic components to a metallic wiring board (see, for example, patent literature 1). Also, with a general vehicle-mounted electronic apparatus, in order to release the heat produced by heat-generating electronic components, a heat-sink plate is insert-molded in the bottom surface of a case, and heat-generating electronic components are placed on this heat-sink plate (see, for example, patent literature 2). 
     CITATION LIST 
     Patent Literature 
     PTL 1 
     
         
         Japanese Patent Application Laid-Open No. 1999-284370
 
PTL 2
 
         Japanese Patent Application Laid-Open No. 2006-179763 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, with the molding method disclosed in patent literature 1, there is a problem of difficulty components multifunctional. This is because, with the molding method disclosed in patent literature 1, the connector-signal arrangement is fixed by insert-molding connectors and a case as one, so that, when the method of inputting and outputting electrical signals to and from connectors changes, all components of a vehicle-mounted electronic apparatus, such as a case, heat-generating electronic components and metallic wiring board need to be redesigned. By contrast with this, if a molding method is used that does not insert-mold an mounting section of heat-generating electronic components in a case and that instead places heat-generating electronic components on a circuit substrate, a vehicle-mounted electronic apparatus suffers performance deterioration due to the heat produced by heat-generating electronic components. Also, with the molding method disclosed by patent literature 2, a step of insert-molding a heat-sink plate in the bottom surface of a case to release heat is necessary, and, although the heat produced by heat-generating electronic components can be released, there is a problem of poor productivity. 
     In view of the above problems, it is an object of the present invention to provide a vehicle-mounted electronic apparatus that, even when the method of inputting and outputting electrical signals to and from connectors changes, makes it possible to release heat from heat-generating electronic components efficiently and makes the components of the vehicle-mounted electronic apparatus multifunctional, without redesigning various components. 
     Solution to Problem 
     In order to achieve the above object, a vehicle-mounted electronic apparatus according to the present invention has: a case, in which part of a bottom surface or side surface has an opening; a connector that sticks out from the opening of the case and that can be connected to an external device that inputs and outputs an electrical signal and an external power supply that supplies power; a circuit substrate that is provided inside the case, and that, by electrically connecting with the connector, performs signal processing using the electrical signal received as input from the external device and the power supplied from the external power supply; a metallic wiring board that comprises a plurality of metallic wires, and that is provided on an inner section on the bottom surface of the case and electrically connects with the circuit substrate; and a heat-generating electronic component that has its bottom surface connected on part of metallic wires in the metallic wiring board, and, in this vehicle-mounted electronic apparatus, the thickness of a metallic wire in the metallic wiring board that connects with the bottom surface of the heat-generating electronic component is thicker than the thickness of the connector terminal. 
     Advantageous Effects of Invention 
     With the vehicle-mounted electronic apparatus of the present invention, even when the method of inputting and outputting electrical signals to and from connectors changes, it is possible to release heat from heat-generating electronic components efficiently, without redesigning component of the vehicle-mounted electronic apparatus such as the case and metallic wiring board, or adding additional processing steps. That is to say, according to the present invention, it is possible to provide a vehicle-mounted electronic apparatus that makes components multifunctional while maintaining heat-releasing characteristics. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a vehicle-mounted electronic apparatus according to an embodiment of the present invention; 
         FIG. 2  is a perspective view of a vehicle-mounted electronic apparatus according the embodiment; 
         FIG. 3  is an enlarged view of a lower case, which is a principle part of a vehicle-mounted electronic apparatus according to the embodiment; 
         FIG. 4  illustrates a metallic wiring board provided inside a lower case according to the embodiment; 
         FIG. 5  illustrates a metallic wiring board according to the embodiment; 
         FIG. 6  is a perspective view illustrating an area around heat-generating electronic components according to the embodiment; and 
         FIG. 7  is a cross-sectional view illustrating an area around heat-generating electronic components according to the embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An embodiment of a vehicle-mounted electronic apparatus of the present invention will be described now with reference to the accompanying drawings. 
       FIG. 1A  is a perspective view showing a vehicle-mounted electronic apparatus according to the present invention from above.  FIG. 1B  is a perspective view showing a vehicle-mounted electronic apparatus according to the present invention from below. 
       FIG. 2  is an exploded perspective view of a vehicle-mounted electronic apparatus according to the present invention from above; 
     As shown in  FIG. 1  and  FIG. 2 , a vehicle-mounted electronic apparatus has case  2 , connectors  3 , heat-sink plate  4 , circuit substrate  5 , heat-generating electronic components  6 , and metallic wiring board  7 . 
     Case  2  is comprised of upper case  2   a  and lower case  2   b , and is a structure to cover circuit substrate  5  in a state upper case  2   a  and lower case  2   b  are coupled. Also, case  2  is made of resin or metal. Lower case  2   h  has opening section  2   c . Upper case  2   a  has hook section  2   d  in each side. Lower case  2   b  has lock section  2   e  in each side. When these hook section  2   d  and lock section  2   e  are fitted together, upper case  2   a  and lower case  2   b  are fixed. With the present embodiment, opening section  2   c  is provided in the bottom surface  2   f  of lower case  2   b , but it is equally possible to provide opening section  2   c  on a side surface  2   g  of lower case  2   b . Also, case  2  may adopt a structure that does not provide hook section  2   d  and lock section  2   e  and that instead couples upper case  2   a  and lower case  2   b  by means of a screw, for example. 
     Connectors  3  each have metallic terminals  3   a  and protecting section  3   b  that protects metallic terminal  3   a . Metallic terminals  3   a  include an input terminal for receiving as input an electrical signal from an external electronic apparatus; an output terminal for outputting an electrical signal to an external electronic apparatus; a power supply terminal for connecting with a power supply and acquiring power; and a ground terminal to connect with the ground. As shown in  FIG. 1B  and  FIG. 2 , connectors  3  stick out from opening section  2   c  of lower case  2   b.    
     As shown in  FIG. 1B , heat-sink plate  4  is connected to the outer bottom surface of lower case  2   b . This heat-sink plate  4  is made of metal having a high heat-releasing effect, and is, for example, an aluminum plate or copper plate. 
     Circuit substrate  5  has a signal electronic component (not shown) that performs signal processing and that has a low calorific value. This circuit substrate  5  is made of, for example, glass epoxy. Also, in this circuit substrate  5 , connectors  3  and metallic terminals  3   a  are electrically connected by alloy-junctioning or press-fitting metallic terminals  3   a  in a through hole provided in one end section on the bottom surface of circuit substrate  5 . Then, circuit substrate  5  receives as input an electrical signal from an external device via metallic terminal  3   a  of an input terminal, is supplied power from an external power supply via metallic terminal  3   a  of a power supply terminal, and outputs an electrical signal to an external device via metallic terminal  3   a  of an output terminal. 
     Although circuit substrate  5  and connector  3  are electrically connected via a through hole according to the present embodiment, any method of connection is possible. For example, circuit substrate  5  and connector  3  may be connected by wire bonding and suchlike means, without using a through hole. 
     The inner structure of lower case  2   b  will be described next. 
       FIG. 3  is an enlarged perspective view of lower case  2   b  in  FIG. 2 . Heat-generating electronic components  6  and metallic wiring board  7  are provided in lower case  2   b.    
       FIG. 4  illustrates metallic wiring board  7  provided inside lower case  2   b , showing lower case  2   b  shown in  FIG. 3  from above. 
     Heat-generating electronic components  6  are comprised of power-related electronic components of a high calorific value, such as transistors. As shown in  FIG. 2  to  FIG. 4 , heat-generating electronic components  6  provided in lower case  2   b  are comprised of three heat-generating electronic components  6   a ,  6   b  and  6   c . Heat-sink plate  4  is provided on the back surface of lower case  2   b  in which heat-generating electronic components  6  are provided. 
       FIG. 5  is an enlarged view illustrating metallic wiring board  7  in part  10  enclosed by a dotted line in  FIG. 4 . In  FIG. 5 , electronic component  6   a  is removed from part  10  enclosed by a dotted line in  FIG. 4 , to explain metallic wiring board  7 . 
       FIG. 6  is a perspective view for explaining an area around heat-generating electronic component  6   a , showing  FIG. 3  from above. In  FIG. 6 , lower case  2   b  is removed in order to explain the positional relationships between heat-generating electronic components  6   a  and metallic wiring board  7 . 
       FIG. 7  is an A-A cross-sectional view of  FIG. 6 .  FIG. 7  will be described including lower case  2   b.    
       FIG. 5  to  FIG. 7  explain the positional relationships and connection relationships between heat-generating electronic component  6   a  and metallic wiring board  7 . As shown in  FIG. 6 , heat-generating electronic component  6   a  has two lead terminals wire-bonded with the inner circuitry of heat-generating component  6   a . The positional relationships and connection relationships between heat-generating electronic component  6   a  and metallic wiring board  7  shown in  FIG. 5  to  FIG. 7 , apply alike to heat-generating electronic components  6   b  and  6   c . Consequently, the positional relationships or connection relationships between heat-generating electronic components  6   b  and  6   c  and metallic wiring boar  7  will not be illustrated by way of drawing or explained. 
     Metallic wiring board  7  has a plurality of metallic wires  7   d . Each metallic wire  7   d  is formed L-shaped (see  FIG. 3 ). As shown in  FIG. 2  and  FIG. 3 , end section  7   a , which is one end of each metallic wire  7   d  formed in an L shape, sticks out nearly vertically from the bottom surface  2   f  of lower case  2   b . This end section  7   a  is electrically connected with circuit substrate  5 , by means of alloy-junctioning or press-fitting, in a through hole provide in the other end section on the bottom surface of circuit substrate  5 . 
     Incidentally, although metallic wiring board  7  and circuit substrate  5  are electrically connected via a through hole according to the present embodiment, any method of connection is possible. For example, metallic wiring board  7  and circuit substrate  5  may be connected by wire bonding and suchlike means without using a through hole. 
     Also, as shown in  FIG. 3  and  FIG. 4 , metallic wiring board  7  is insert-molded in lower case  2   b  except for end section  7   a.    
     Metallic wiring board  7  is formed with input section  7   b , output section  7   c  and power supplying section  7   d . Input section  7   b  provides metallic wiring for inputting a signal from circuit substrate  5  to heat-generating electronic component  6   a . Output section  7   c  provides metallic wiring for outputting a signal from heat-generating electronic components  6  to circuit substrate  5 . Power supplying section  7   d  provides metallic wiring for supplying power from circuit substrate  5  to heat-generating electronic component  6   a.    
     As shown in  FIG. 5  to  FIG. 7 , in the front end section of input section  7   b  and the front end section of output section  7   c —in other words, in end sections on the side of metallic wiring board  7  apart from end section  7   a —connecting section  7   e  that exposes from lower case  2   b  and electrically connects with heat-generating electronic components  6   a  is provided. This connecting section  7   e  electrically connects with lead terminal  8 , so that input section  7   b , output section  7   c  and heat-generating electronic components  6   a  are electrically connected. 
     In the front end section of power supplying section  7   d , mounting section  7   f , where heat-generating electronic component  6   a  is placed and installed, is provided. This mounting section  7   f  is part of the upper surface of power supplying section  7   d  exposing from lower case  2   b , as shown in  FIG. 7 . When the bottom surface of heat-generating electronic component  6   a  is placed upon the upper surface of this mounting section  7   f , power supplying section  7   d  and heat-generating electronic component  6   a  are electrically connected. 
     As shown in  FIG. 7 , mounting section  7   f  has a greater metal thickness than input section  7   b  and output section  7   c . The proportion of the weight of metallic wiring board  7  in a vehicle-mounted electronic apparatus is 10% or so, for example, and therefore the weight of metallic wiring board  7  cannot be ignored. Consequently, making the metal of power supplying section  7   d  including mounting section  7   f  thicker contradicts the demand for reducing the weight of a vehicle-mounted electronic apparatus. 
     With the present embodiment, the metal of power supplying section  7   d  including to which power of a high calorific value is supplied from a power supply, is made thick, and the metal of input section  7   b  and output section  7   c , to which electrical signals of a low calorific value is inputted from circuit substrate  5 , is made thinner. By this means, it is possible to improve the heat-releasing effect while maintaining the weight of metallic wiring board  7 . Consequently, with the present embodiment, it is possible to both improve heat-release performance and reduce the weight of a vehicle-mounted electronic apparatus. With the present embodiment, metallic wiring board  7  is formed an L shape, but may be formed in other shapes such as a U-shape as well. 
     Heretofore, when a metallic wiring board is provided inside a case forming a connector and a case as one, the thickness of the metallic wiring board depends upon the thickness of connector terminals and is usually the same thickness as the connector terminal. However, with the present embodiment, upon providing mounting section  7   f , the thickness of each metallic wire in metallic wiring board  7  does not depend upon the thickness of connector terminals and can be set freely. Consequently, it is possible to improve the heat releasing effect by making the thickness of power supplying section  7   d , which includes mounting section  7   f  where heat-generating electronic components  6  of high calorific values are mounted, thicker than metallic terminal  3   a  of connector  3 . 
     On the other hand, the thickness of metallic wiring in input section  7   b  and output section  7   c  connecting with circuit substrate  5  where signal electronic components of low calorific values are mounted, can be made equal to or thinner than the thickness of metallic terminal  3   a . Consequently, it is possible to improve the heat releasing effect without increasing the weight of a vehicle-mounted electronic apparatus, and reduce the weight of a vehicle-mounted electronic apparatus. 
     In particular, generally one hundred or more vehicle-mounted electronic apparatuses are mounted in a vehicle to control the vehicle electrically, weight reduction is possible on the order of kilograms per vehicle, so that significant improvement of mileage is possible. Also, the step if insert-molding a heat-sink plate inside a case cab be omitted, so that it is possible to improve the prevision of processing and reduce the time of processing to improve productivity. 
     With this structure of a vehicle-mounted electronic apparatus, an electrical signal that is received as input from an external electronic apparatus via an input terminal in metallic terminals  3   a  of connector  3  is subjected to signal processing using signal electronic component in circuit substrate  5 . An electrical signal having been subjected to signal processing is inputted in end section  7   a  of input section  7   b  in metallic wiring board  7 . An electrical signal that is inputted in input section  7   b  is subject to signal processing by power-supplied heat-generating electronic components  6 . This supply of power is given from power supplying section  7   d , via a power supply terminal in metallic terminals  3   a . An electrical signal having been subjected to signal processing in heat-generating electronic components  6  is inputted in output section  7   c  in metallic wiring board  7 . An electrical signal received as input in output section  7   c  is subjected to signal processing by signal electronic components in circuit substrate  5 . An electrical signal having been subjected to signal processing is outputted to an external electronic apparatus via an output terminal in metallic terminals  3   a  of connectors  3 . 
     The vehicle-mounted electronic apparatus of the present embodiment has a structure in which the metal thickness of a metallic wire connecting with the bottom surface of heat-generating electronic components  6  in metallic wiring board  7  of lower case  2   b  is thicker than the thickness of other metallic wires. Consequently, with the vehicle-mounted electronic apparatus of the present embodiment, it is possible to release heat efficiently while reducing the weight. 
     Furthermore, the vehicle-mounted electronic apparatus according to the present embodiment has a structure in which input and output signals to and from heat-generating electronic components  6  do not pass connectors  3  directly but instead are inputted to or outputted from connectors  3  via signal electronic components on circuit substrate  5 . Consequently, with the vehicle-mounted electronic apparatus of the present embodiment, it is possible to continue using lower case  2   b  in which metallic wiring board  7  is insert-molded and make the components multifunctional even when the specifications of connector input-output arrangement varies between vehicle types. 
     Although a vehicle-mounted electronic apparatus according to the present invention is provided with a heat-sink plate to improve the heat releasing effect of heat-generating electronic components  6 , it is possible to release heat as long as metallic wiring board  7  of the present invention is provided, so that it is not mandatory to provide heat-sink plate  4 . By this means, it is possible to reduce the weight of a vehicle-mounted electronic apparatus. Also, it is possible to reduce the labor of processing while maintaining the heat releasing effect by metallic wiring board  7 , and therefore it is possible to improve the productivity of a vehicle-mounted electronic apparatus. 
     Also, with the present embodiment, amongst a plurality of f metallic wires provided in metallic wiring board  7 , a metallic wire that connects with the bottom surface of heat-generating electronic components  6  is made power supplying section  7   d  and metallic wires that connect with heat-generating electronic components  6  via lead terminal  8  are made input section  7   b  and output section  7   c , but this is by no means limiting. 
     For example, it is possible to make a metallic wire that connects with the bottom surface of heat-generating electronic components  6  an input section. In this case, metallic wires connecting with heat-generating electronic components  6  via lead terminal  8  become an output section and power supplying section. Also, it is equally possible to make a metallic wire connecting with the bottom surface of heat-generating electronic component  6  an output section. In this case, metallic wires connecting with heat-generating electronic components  6  via lead terminal  8  become an input section and power supplying section. That is to say, heat-generating electronic component  6  is placed on the surface of one of an input section and an output section in metallic wiring board  7  and connects with the bottom surface. Then, in metallic wiring board  7 , the thickness of a metallic wire connecting with the bottom surface of heat-generating electronic component  6  is thicker than the thickness of metallic terminal  3   a  of connectors  3 . On the other hand, in metallic wiring board  7 , the thickness of a metallic wire connecting via lead terminal  8 , not connecting with the bottom surface of heat-generating electronic component  6 , is thinner than the thickness of metallic terminal  3   a  of connectors  3 . 
     Also, although the number of metallic wire terminals in metallic wiring board  7  to connect with one heat-generating electronic component  6  is three, this number may as well be greater than three. Also, this number of terminals may be less than three, and needs to be at least two or greater. In the event there are two terminals, metallic wiring board  7  has only an input section and an output section. 
     The disclosure of Japanese Patent Application No. 2009-75557, filed on Mar. 26, 2009, including the specification, drawings and abstract, is incorporated herein by reference in its entirety. 
     INDUSTRIAL APPLICABILITY 
     The vehicle-mounted electronic apparatus according to the present invention is suitable for use as a vehicle-mounted electronic apparatus having varying specifications per vehicle type. 
     REFERENCE SIGNS LIST 
     
         
           2  Case 
           2   a  Upper case 
           2   b  Lower case 
           2   b  Lower case 
           3   a  Metallic terminal 
           3   b  Protecting section 
           4  Heat-sink plate 
           5  Circuit substrate 
           6  Heat-generating electronic component 
           7  Metallic wiring board 
           7   a  End section 
           7   b  Input section 
           7   c  Output section 
           7   d  Power supplying section 
           7   e  Connecting section 
           7   f  Mounting section