Abstract:
A circuit device comprises a circuit board and a plurality of leads each comprising an island portion, a bonding portion elevated from the island portion, and an oblique slope portion connecting the island portion and the bonding portion, and a plurality of circuit elements mounted on the island portions so as to be connected to corresponding bonding portions through wirings. Two leads are adapted to be connected to positive and negative electrodes of a direct-current power source, and yet another lead is an output lead adapted to output alternating-current power. One electrode provided on a transistor mounted on an island portion of the second input lead is connected to a bonding portion of the output lead through a wiring, and another electrode provided on a transistor mounted on an island portion of the output lead is connected to a bonding portion of the first input lead through a wiring.

Description:
This application is a continuation of U.S. patent application Ser. No. 13/242,202, filed Sep. 23, 2011, entitled “Circuit Device and Method of Manufacturing the Same,” and claims priority from Japanese Patent Application No. JP 2010-213694, filed Sep. 24, 2010, the content of which is incorporated herein by reference in its entirety. 
     CROSS REFERENCE TO RELATED, COPENDING APPLICATION 
     Related subject matter is found in copending U.S. patent application Ser. No. 15/003,958, filed Jan. 22, 2016, entitled “Method of Manufacturing a Circuit Device,” invented Shigeaki Mashimo et al., and assigned to the assignee hereof. 
    
    
     BACKGROUND 
     1. Field 
     The present disclosure relates to a circuit device and a method of manufacturing the same, and more particularly relates to a circuit device incorporating a power semiconductor element that performs switching of a large current and to a method of manufacturing the same. 
     2. Description of the Related Art 
     A structure of a conventional hybrid integrated circuit device  100  is described with reference to  FIG. 9 . This technology is described for instance in Japanese Patent Application Publication No. Hei 5-102645. A conductive pattern  103  is formed on a surface of a rectangular substrate  101  with an insulative layer  102  interposed therebetween. A certain electrical circuit is formed by fixedly attaching circuit elements on the conductive pattern  103 . Here, a semiconductor element  105 A and a chip element  105 B as the circuit elements are connected to the conductive pattern  103 . Leads  104  are connected to pads  109  each formed of a part of the conductive pattern  103  at a peripheral portion of the substrate  101  and function as external terminals. An encapsulating resin  108  has a function of encapsulating the electrical circuit formed on the surface of the substrate  101 . 
     The semiconductor element  105 A is a power element through which a large current of about several to several hundreds of amperes flows for example and thus generates an extremely large amount of heat. Thus, the semiconductor element  105 A has been placed on an upper portion of a heat sink  110  placed on the conductive pattern  103 . The heat sink  110  is made of a piece of metal such as copper having a size of about length×width×thickness=10 mm×10 mm×1 mm for example. 
     However, in the hybrid integrated circuit device  100  having the structure, to form a circuit such as an inverter circuit for converting a large current on the upper surface of the substrate  101 , the conductive pattern  103  needs to be wide to secure a current capacity. Thus, downsizing of the hybrid integrated circuit device  100  is hindered. Moreover, a heat sink needs to be prepared for each semiconductor element to secure heat dissipation, whereby the cost is increased. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view and  FIG. 1B  is a cross-sectional view showing a circuit device according to a preferred embodiment of the invention. 
         FIG. 2  is a plan view of the circuit device according to the preferred embodiment of the invention. 
         FIGS. 3A and 3B  are cross-sectional views partially showing the circuit device according to the preferred embodiment of the invention. 
         FIG. 4A  is a circuit diagram of an inverter circuit to be incorporated.  FIG. 4B  is an extracted plan view of the leads.  FIG. 4C  is a cross-sectional view showing the lead. 
         FIG. 5  is a cross-sectional view of a circuit device according to another preferred embodiment of the invention. 
         FIG. 6A  is a plan view and  FIG. 6B  is a cross-sectional view showing a method of manufacturing the circuit device according to the preferred embodiment of the invention. 
         FIG. 7A  is a plan view and  FIG. 7B  is a cross-sectional view showing the method of manufacturing the circuit device according to the preferred embodiment of the invention. 
         FIG. 8A  is a plan view and  FIG. 8B  is a cross-sectional view showing the method of manufacturing the circuit device according to the preferred embodiment of the invention. 
         FIG. 9  is a cross-sectional view of a hybrid integrated circuit device described in Description of the Related Art. 
     
    
    
     The use of the same reference symbols in different drawings indicates similar or identical items. 
     DETAILED DESCRIPTION 
     First of all, a structure of a hybrid integrated circuit device  10  as an example of a circuit device is described with reference to  FIGS. 1A through 5 . 
     The structure of the hybrid integrated circuit device  10  according to this embodiment is described with reference to  FIGS. 1A and 1B .  FIG. 1A  is a perspective view showing the hybrid integrated circuit device  10  as viewed from an obliquely upper direction.  FIG. 1B  is a cross-sectional view of the hybrid integrated circuit device  10 . 
     Referring to  FIGS. 1A and 1B , the hybrid integrated circuit device  10  includes a circuit board  12 , leads  18  and  20  disposed on the upper surface of the circuit board  12 , a transistor  22  and a diode  24  (circuit elements) disposed on an island portion  28  of the lead  18 , and an encapsulating resin  16  integrally covering the components. 
     The circuit board  12  is a metal substrate mainly made of metal such as aluminum (Al) or copper (Cu). Specifically, the circuit board  12  has a size of about length×width×thickness=30 mm×15 mm×1.5 mm for example. When a substrate made of aluminum is used as the circuit board  12 , both main surfaces of the circuit board  12  are subjected to alumite treatment. Here, the upper and the side surfaces of the circuit board  12  are covered with the encapsulating resin  16  and the lower surface is exposed to the outside. Thus, a heat sink can be brought into contact with the exposed lower surface of the circuit board  12 , whereby the heat dissipation is improved. Alternatively, the lower surface of the circuit board  12  may be covered with the encapsulating resin  16  to secure moisture resistance and withstand voltage. 
     Referring to  FIG. 1B , the leads  18  and  20  are respectively provided on the left and the right sides in the drawing. Here, a large number of leads  18  and  20  are disposed along two opposite sides of the circuit board  12 . Instead, only the leads  18  may be disposed along one side, or the leads may be disposed along four sides. 
     A plurality of the leads  18  are provided along one side of the circuit board  12 . The lead  18  includes the island portion  28 , a slope portion  30 , a bonding portion  34 , and a lead portion  32  in this order from the inner side. The transistor  22  and a diode  24  are fixedly attached on the upper surface of the island portion  28  with a conductive adhesive such as solder. The lower surface of the island portion  28  is fixedly attached on the upper surface of the circuit board  12 . Thus, the heat generated by the transistor  22  and the diode  24  during operation is favorably radiated outside through the island portion  28  and the circuit board  12 . Providing the slope portion  30  in an intermediate portion of the lead  18  separates the left upper end of the circuit board  12  from the lead  18  and thus prevents short circuiting of the circuit board  12  and the lead  18 . The bonding portion  34  is a portion connected to the transistor  22  and the diode  24  through a fine metal wire  26  (an aluminum wire having a diameter in a range from 20 μm to 500 μm, for example). A connection structure through the metal wire  26  is described later with reference to  FIG. 4B . The lead portion  32  is a terminal portion that is led out from the encapsulating resin  16  to be used for insert mounting and the like. 
     A plurality of the leads  20  are provided at positions opposite to those of the leads  18 . The lead  20  includes a bonding portion  36 , a slope portion  39 , and a lead portion  38  in this order from the inner side. The bonding portion  36  is fixedly attached on the upper surface of the circuit board  12  and is electrically connected to a control electrode of the transistor  22  mounted on the island portion  28 . The lead portion  38  is led out from the encapsulating resin  16  through the slope portion  39 . 
     The leads  18  and the leads  20  have different functions. Specifically, on the leads  18 , the transistors  22  and the diodes  24  are mounted to form an inverter circuit. Thus, the leads  18  also serve as paths through which direct-current power to be converted by the inverter circuit and alternate-current power obtained by the conversion pass. Moreover, the leads  18  are each formed of a thick piece of metal such as copper having a thickness of about 500 μm and thus also functions as a heat sink. Meanwhile, the lead  20  is connected to the control electrode of the transistor  22  and thus serves as a connection terminal through which a control signal passes. 
     Here, the transistor  22  and the like are connected through one fine metal wire  26  in the figure. Instead, the electrical connection of the transistor  22  may be achieved through multiple (two or three for example) fine metal wires  26 . As connecting means connecting the transistor  22  and the like, a metal foil formed by ribbon bonding may be employed in place of the fine metal wire. 
     Structures of the leads  18  and  20  are described with reference to  FIG. 2 . Referring to the figure, leads  18 A to  18 H and leads  20 A to  20 H are disposed opposite to each other. 
     Of the leads  18 A to  18 H, the leads  18 A and  18 H respectively disposed on the left and the right ends are leads through which a direct current is supplied from the outside, and the leads  18   c ,  18 D and  18 E are leads through which alternate-current power of three phases obtained by the conversion in the incorporated inverter circuit is outputted. A resistor  45  for detecting a current value is disposed between the leads  18 A and  18 B. 
     On the upper surfaces of the leads  18 C to  18 E, the transistors and the diodes that form the three phase inverter circuit are mounted. This is described in detail later with reference to  FIG. 4 . 
     Of the leads  20 A to  20 H, the leads  20 A and  20 B are respectively connected to the leads  18 A and  18 B through the fine metal wires  26  and are used for detecting the current value. The leads  20 C to  20 H are connected to the control electrodes of the transistors mounted on the leads  18 C to  18 H. Specifically, when the transistor is an IGBT, the leads  18 C to  18 H are connected to gate electrodes of the IGBTs. 
     Structures in which the island portion  28  of the lead is fixedly attached on the upper surface of the circuit board  12  is described with reference to cross-sectional views of  FIG. 3A  and  FIG. 3B . 
     Referring to  FIG. 3A , the upper surface of the circuit board  12  made of metal such as aluminum is covered with an insulative layer  44 . The insulative layer  44  is made of epoxy resin or the like highly filled with filler such as AL 2 O 3  in an amount of about 60% by weight to 80% by weight, for example. A conductive pattern  46  made of metal such as copper and having a thickness of about 50 μm is formed on the upper surface of the insulative layer  44 . The island portion  28  of the lead is fixedly attached on the upper surface of the conductive pattern  46  with an adhesive  48  such as solder provided therebetween. Thus, the heat generated by the transistor  22  during operation is radiated outside through the island portion  28 , the adhesive  48 , the conductive pattern  46 , and the circuit board  12 . 
     In  FIG. 3B  no conductive pattern is formed on the upper surface of the insulative layer  44 . The lower surface of the island portion  28  is fixedly attached on the upper surface of the insulative layer  44  with the conductive or insulative adhesive  48  provided therebetween. 
     The bonding portion  36  of the lead  20  shown in  FIG. 1B  is fixedly attached on the upper surface of the circuit board  12  in a structure similar to that described above. 
     Referring to  FIGS. 4A, 4B, and 4C , a structure in a case where the three phase inverter circuit is incorporated in the hybrid integrated circuit device  10  is described.  FIG. 4A  is a circuit diagram of the inverter circuit,  FIG. 4B  is a plan view showing a configuration of the leads, and  FIG. 4C  is a cross-sectional view of the lead  18 . 
     Referring to  FIG. 4A , the inverter circuit  56  includes six IGBTs (Q 1  to Q 6 ) and six diodes (D 1  to D 6 ). The IGBTs Q 1  to Q 3  are high side transistors while the IGBTs Q 4  to Q 6  are low side transistors. The flywheel diodes (D 1  to D 6 ) are connected to the collector electrode and the emitter electrode of the respective IGBTs (Q 1  to Q 6 ) in inverse parallel. By thus connecting the flywheel diodes with the IGBTs in inverse parallel, the IGBTs are prevented from being broken by an over voltage due to counter electromotive force generated in an inductive load. Here, other transistors such as a MOS and like may be used in place of the IGBT. 
     The IGBTs (Q 1 ) and (Q 4 ) are serially connected and exclusively ON/OFF controlled. The alternate-current power of U phase is outputted to the outside from the midpoint of the IGBTs (Q 1 ) and (Q 4 ) through the lead. The IGBTs (Q 2 ) and (Q 5 ) are serially connected and the alternate-current power of V phase is outputted to the outside from the midpoint of the IGBTs (Q 2 ) and (Q 5 ) that are exclusively ON/OFF controlled. The IGBTs (Q 3 ) and (Q 6 ) are serially connected and the alternate-current power of W phase is outputted to the outside from the midpoint of the IGBTs (Q 3 ) and (Q 6 ) that are exclusively ON/OFF controlled. Switching of the IGBTs is controlled by the control element positioned outside the device. 
     With this structure, the inverter circuit  56  converts received direct-current power into alternate-current power of three phases (U, V, W) which rotationally drives a motor M as a load. 
     Referring to  FIG. 4B , the IGBTs and the diodes are fixedly attached on the upper surfaces of the island portions  28 C to  28 H of the leads  18 C to  18 H with a conductive adhesive such as solder. Specifically, the IGBT (Q 1 ) and the diode D 1  are mounted on the island portion  28 C of the lead  18 C, while the IGBT (Q 2 ) and the diode D 2  are mounted on the island portion  28 D of the lead  18 D. The IGBT (Q 3 ) and the diode D 3  are mounted on the island portion  28 E of the lead  18 E, while three IGBTs (Q 4  to Q 6 ) and three diodes D 4  to D 6  are mounted on the island portion  28 H of the lead  18 H. A collector electrode formed on the back surface of each IGBT and a cathode electrode of each diode are connected to the upper surface of a corresponding island portion with a conductive adhesive such as solder. 
     The transistors and the diodes mounted on the island portions are connected with each other through the fine metal wires to form the inverter circuit. In this embodiment, the transistor and the diode mounted on each island are connected with a bonding portion of an adjacent lead through a fine metal wire. 
     Specifically, the IGBT (Q 1 ) and the diode D 1  mounted on the island portion  28 C of the lead  18 C respectively have an emitter electrode and an anode electrode connected to a bonding portion  34 B of the lead  18 B through the fine metal wire  26 . The IGBT (Q 2 ) and the diode D 2  mounted on the island portion  28 D of the lead  18 D respectively have an emitter electrode and an anode electrode connected to a bonding portion  34 C of the lead  18 C through the fine metal wire  26 . The IGBT (Q 3 ) and the diode D 3  mounted on the island portion  28 E of the lead  18 E respectively have an emitter electrode and an anode electrode connected to a bonding portion  34 D of the lead  18 D through the fine metal wire  26 . 
     Moreover, the IGBTs (Q 4  to Q 6 ) and the diodes D 4  to D 6  mounted on the island portion  28 H connected to the negative side of a direct-current power source are connected to the respective bonding portions  34 C to  34 E of the leads  18 D to  18 F. Specifically, an emitter electrode of the IGBT (Q 4 ) and an anode electrode of the diode D 4  are connected to the bonding portion  34 C of the lead  18 C through the fine metal wire  26 . An emitter electrode of the IGBT (Q 5 ) and an anode electrode of the diode D 5  are connected to the bonding portion  34 D of the lead  18 D through the fine metal wire  26 . An emitter electrode of the IGBT (Q 6 ) and an anode electrode of the diode D 6  are connected to the bonding portion  34 E of the lead  18 E through the fine metal wire  26 . 
     In this embodiment, the adjacent leads are connected with each other through the fine metal wires. The fine metal wire  26  connecting the IGBT (Q 4 ) and the diode D 4  with the bonding portion  34 C of the lead  18 C is formed to pass above the leads  18 D and  18 E. If the leads  18 B to  18 H are entirely flat, the fine metal wires  26  formed in such a complex manner may contact with each other and cause short circuiting. In this embodiment, the bonding portion  34  to which the fine metal wire is connected is positioned above the island portion  28  with the slope portion  30  provided therebetween as shown in  FIG. 4C . Thus, the fine metal wires formed in a complex manner to form the inverter circuit are prevented from being in contact and causing short circuiting. 
     Furthermore, in this embodiment, no conductive pattern is formed on the upper surface of the circuit board  12  and the transistor  22  and the diode  24  are mounted on the island portion  28  of the lead  18  placed on the upper surface of the circuit board  12  as shown in  FIG. 1B . Thus, the leads  18  of the present embodiment not only serve as external output terminals but also serve as the conductive pattern in Description of the Related Art. The island portion  28  of the lead  18  has a thickness of about 500 for example, and thus is formed to have a thickness larger than that (50 μm) of the conductive pattern formed on the upper surface of the circuit board described in Description of the Related Art. The thin conductive pattern is formed over a wide area to deal with a large current of about several tens of amperes in the conventional case. In the present embodiment however, the lead  18  is thick and thus has a large cross-sectional area. Thus the area occupied by the lead  18  can be made smaller compared with the conventional conductive pattern. This contributes to the downsizing of the device as a whole. 
     A structure of a hybrid integrated circuit device  10 A of another preferred embodiment is described with reference to  FIG. 5 . A basic structure of the hybrid integrated circuit device  10 A shown in this figure is same as that of the device shown in  FIGS. 1A and 1B . The difference from the structure in  FIG. 1  is that a control board  14  is fixedly attached on the upper surface of the circuit board  12 . 
     Specifically, the island portion  28  of the lead  18  is fixedly attached on left side in the drawing of the upper surface of the circuit board  12  as in the structure described above. 
     The control board  14  having a control element  42  mounted on its upper surface is fixedly attached on the right side in the drawing of the upper surface of the circuit board. The control board  14  is formed of an inexpensive insulative substrate such as a glass epoxy substrate. A conductive pattern is formed on the upper surface of the control board  14 . The control element  42  in a form of a resin encapsulated package is connected to the conductive pattern. The control element  42  is connected to the control electrode of the transistor  22  through the conductive pattern formed on the upper surface of the control board  14  and the fine metal wire. Thus, the transistor  22  in the inverter circuit is controlled by a control signal supplied from the control element  42 . The control element  42  is connected to the lead  20  on the right side of the drawing through the conductive pattern on the control board  14  and the fine metal wire  26 . 
     By providing the control element  42  in the hybrid integrated circuit device  10 A, a module in which the inverter circuit and the control circuit are integrated is formed, whereby the device as a whole can have a high performance. Moreover, the control element  42  is mounted on the control board  14  placed on the upper surface of the circuit board  12  made of a metal material, whereby the control element  42  is prevented from being over heated. Specifically, even when the heat generated by the transistor  22  during operation is transmitted to the circuit board  12  made of metal, the transmission of the heat to the control element  42  is prevented by the control board  14  made of an insulative material such as a resin material. 
     The control element  42  may be mounted on the conductive pattern formed directly on the upper surface of the circuit board  12  without disposing the control board  14  on the upper surface of the circuit board  12 . 
     Next, a method of manufacturing the hybrid integrated circuit device  10  having the above described structure is described with reference to  FIG. 6  to  FIG. 8 . 
     Referring to  FIGS. 6A and 6B , first of all, a lead frame  58  including multiple leads  18  and  20  are prepared.  FIG. 6A  is a plan view showing one unit  60  to be provided in the lead frame  58 .  FIG. 6B  is a cross-sectional view of the unit  60 . 
     Referring to  FIG. 6A , the unit  60  includes a large number of leads  18  and  20  forming a single hybrid integrated circuit device. Each of the leads  18  and  20  has one end positioned in an area on which the circuit board  12  is to be placed. The leads  18  are disposed on the left side of the unit  60  in the drawing and are provided with the island portions  28  on which the transistors and the diodes are mounted as described above. The leads  20  are disposed on the right side in the drawing and serve as external connection terminals and also are responsible for the connection of the control electrode of the transistor and mechanically supporting the control board. An outer end of each of the leads  18  and  20  is integrally supported by a tie bar  62  continuous with an outer frame  64 . 
     As shown in  FIG. 6B , the lead  18  on the left side in the drawing includes the island portion  28 , the slope portion  30 , the bonding portion  34 , and the lead portion  32 . Here, the island portion  28  is a portion on which a circuit element such as the transistor is mounted. The bonding portion  34  is a portion to which the fine metal wire is connected. The lead  20  on the right side of the drawing includes the bonding portion  36 , the slope portion  39 , and the lead portion  38 . 
     The lead frame  58  includes a plurality of the units  60  having the structure within the frame-shaped outer frame  64 . The following steps are collectively performed on the units  60 . 
     Referring to  FIGS. 7A and 7B , the circuit elements and the circuit board are fixedly attached on the leads.  FIG. 7A  is a plan view showing the present step and  FIG. 7B  is a cross-sectional view. 
     Specifically, the back surface electrode of the transistor  22  is fixedly attached on the island portion  28  of the lead  18  with a conductive adhesive such as solder. The back surface electrode of the diode  24  is fixedly attached in a similar manner. Then, the electrode of the transistor  22  is connected to the bonding portion  34  provided at the intermediate portion of the lead  18  through the fine metal wire  26 . Similarly, the control electrode (gate electrode) of the transistor  22  is connected to the bonding portion  36  of the lead  20  through the fine metal wire  26 . 
     Referring to  FIG. 7B , the island portion  28  of the lead  18  is fixedly attached on the upper surface of the circuit board  12 . The lower surface of the island portion  28  may be fixedly attached on the upper surface of the circuit board  12  as follows. Specifically, the island portion  28  may be fixedly attached on the conductive pattern  46  formed on the upper surface of the circuit board  12  as shown in  FIG. 3A  or may be directly fixedly attached on the upper surface of the insulative layer  44  covering the upper surface of the circuit board  12  as shown in  FIG. 3B . 
     In this step, the transistors  22  and the diodes  24  mounted on the island portions  28  of the leads  18  are connected to the bonding portions  34  through the fine metal wires  26  so that the inverter circuit is formed in each unit  60 . The connection structure using the fine metal wires  26  is as described with reference to  FIG. 4 . In this embodiment, the fine metal wires  26  are formed in a complex manner to form the inverter circuit. Accordingly, when the leads  18  have a flat shape, the fine metal wires  26  may be in contact with each other and cause short circuiting. In this embodiment, the bonding portion  34  to which the fine metal wire  26  is connected is disposed at a higher position than the island portion  28  so that the fine metal wires  26  are separated from one another to prevent short circuiting. 
     Here, to manufacture the hybrid integrated circuit device  10 A shown in  FIG. 5 , the control board  14  on which the control element  42  is mounted is disposed on the upper surface of the circuit board  12  and the control board  14 , the transistor  22 , and the lead  20  are connected to each other through the fine metal wires  26 . 
     Referring to  FIGS. 8A and 8B , next, an encapsulating resin is formed to cover the circuit board  12 .  FIG. 8A  is a cross-sectional view showing the step of molding the circuit board  12  using a mold and  FIG. 8B  is a plan view showing the lead frame  58  after the molding. 
     Referring to  FIG. 8A , the circuit board  12  fixed to the lead frame is placed in a cavity  72  defined by an upper mold  68  and a lower mold  70 . Here, the position of the circuit board  12  in the cavity  72  is fixed by clamping the leads  18  and  20  with the upper mold  68  and the lower mold  70 . Then, the circuit board  12  and the circuit elements and the like are encapsulated by injecting resin into the cavity  72  through a gate provided to the mold. In this step, transfer molding using a thermosetting resin or injection molding using a thermoplastic resin is performed. The encapsulating structure of the circuit board  12  is not limited to the resin encapsulation and an encapsulation by potting or an encapsulation using a case member may also be employed. 
     Referring to  FIG. 8B , after the molding step is completed, the leads  18  and  20  are separated from the lead frame  58  by press work. Specifically, the leads  18  and  20  are individually separated at a portion at which the tie bar  62  is provided. Thus, the hybrid integrated circuit device as shown in  FIG. 1  is separated from the lead frame  58 . 
     According to the disclosed embodiments, the lead is provided with the island portion and the bonding portion that are continuous through the slope portion. The island portion is fixedly attached on the upper surface of the circuit board while the bonding portion is disposed at a higher position than the upper surface of the circuit board to be separated therefrom. The circuit element mounted on the island portion and the bonding portion are connected with each other through connecting means. Thus, the connecting means made of a fine metal wire, for example, is prevented from contacting another connecting means and thus the short circuiting is prevented. Thus, a relatively complex circuit such as an inverter circuit can be formed with a plurality of leads and connecting means. 
     The above-disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments that fall within the true scope of the claims. Thus, to the maximum extent allowed by law, the scope of the present invention is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.