Patent Publication Number: US-2006012034-A1

Title: Engine control circuit device

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a circuit device comprising a circuit board on which a plurality of packaged electronic parts are mounted, and a connector mounted on the circuit board for connection to an external circuit. More particularly, the present invention relates to an engine control circuit device for use in automobiles, ships, agricultural machines, engineering machines, and so on.  
      2. Description of the Related Art  
      Recently, thermal environments of a module for controlling engines used in automobiles, ships, agricultural machines, engineering machines, etc. (hereinafter such a module is referred to as an “engine control circuit device”) have become increasingly severe year by year. In other words, the installation place of the engine control circuit device has changed from a compartment to an engine room and then to a location on an engine itself (called “on-engine mounting”). Correspondingly, the engine control circuit device has been exposed to higher temperatures. Further, the amount of generated heat has increased with a larger current supplied to a control load, and the amount of heat generated per unit volume has also increased with downsizing of the device.  
      Generally, an engine control circuit device had a waterproof structure comprising a circuit board on which a plurality of packaged electronic parts are mounted, and a housing covering the circuit board. To be adapted for the above-mentioned mounting of the circuit device in the engine room, however, it has become more prevail to use a housing with both a heat radiating structure and a waterproof structure. Further, in the case of the on-engine mounting where the engine control circuit device is subjected to severer thermal environments, the circuit device is required to have thermal resistance against temperatures of not lower than 130° C.  
      As one example of the related art, an electronic circuit device is disclosed which comprises a metal substrate including electronic parts mounted on one surface of the metal substrate, a case provided with heat radiating fins and accommodating the electronic parts therein with the metal substrate serving as a cover, and a resin filled between the metal substrate and the case (see, e.g., Patent Reference 1; JP,A 11-354956). According to the disclosed electronic circuit device, heat is radiated from both of the heat radiating fins of the case and the other surface of the metal substrate on which no electronic parts are mounted (i.e., an installation surface of the electronic circuit device).  
     SUMMARY OF THE INVENTION  
      However, the related art has the following problem.  
      In the disclosed electronic circuit device, though not clearly stated in Patent Reference 1, the resin filled between the metal substrate and the case is presumably a thermoplastic resin (for the reason that, if a thermo-setting resin is filled, the resin must be injected under high pressure and the case may be damaged). A versatile thermoplastic resin has a linear thermal expansion coefficient of about 50 ppm/° C., for example, and therefore causes a large difference in linear thermal expansion coefficient relative to a circuit board (metal substrate), the electronic parts, and other structural members. Because of such a large difference, the electronic parts may be damaged with thermal expansion under actual environments. On the other hand, an attempt of reducing the linear thermal expansion coefficient of the thermoplastic resin pushes up the cost.  
      Accordingly, it is an object of the present invention to provide an engine control circuit device that has higher heat resistance and can be installed in a place exposed to severe thermal environments.  
      (1) To achieve the above object, the present invention provides an engine control circuit device comprising a circuit board on which a plurality of packaged electronic parts are mounted, and a connector mounted on the circuit board for connection to an external circuit, wherein the engine control circuit device further comprises a resin portion formed of a thermo-setting resin and covering the connector except for a connecting portion thereof and the circuit board; and a cooling means integrally molded in the resin portion and cooling the resin portion.  
      According to the present invention, since the circuit board including the plurality of electronic parts and the connector mounted thereon is covered with the thermo-setting resin having good heat conductance, heat radiation from the electronic parts can be increased. Further, since the resin portion is cooled by the cooling means that is integrally molded in the resin portion, the entirety of the engine control circuit device including the electronic parts can be efficiently cooled. In addition, the linear thermal expansion coefficient of the thermo-setting resin is generally lower than that of a thermoplastic resin, and can be set closer to the linear thermal expansion coefficient of the circuit board, the electronic parts and other structural members. This is effective in suppressing damages of the electronic parts, which is attributable to thermal expansion. It is therefore possible to increase heat resistance of the engine control circuit device and to install the device in a place exposed to severe thermal environments.  
      (2) In above (1), preferably, the cooling means is a cooling pipe through which a coolant flows.  
      (3) In above (2), preferably, the cooling pipe is bonded to the circuit board using an adhesive and is integrally molded in the resin portion.  
      (4) In above (2), preferably, the cooling pipe is arranged such that engine cooling water flows as the coolant through the cooling pipe.  
      (5) To achieve the above object, the present invention also provides an engine control circuit device comprising a circuit board on which a plurality of packaged electronic parts are mounted, and a connector mounted on the circuit board for connection to an external circuit, wherein the engine control circuit device further comprises a resin portion formed of a thermo-setting resin and covering the connector except for a connecting portion thereof and the circuit board; and a cooling passage formed in the resin portion and allowing a coolant to flow through the cooling passage, thereby cooling the resin portion.  
      (6) To achieve the above object, the present invention further provides an engine control circuit device comprising a circuit board on which a plurality of packaged electronic parts are mounted, and a connector mounted on the circuit board for connection to an external circuit, wherein the engine control circuit device further comprises a resin portion formed of a thermo-setting resin and covering the connector except for a connecting portion thereof and the circuit board; and a metal-made heat sink integrally molded in the resin portion.  
      (7) In above (6), preferably, the heat sink is bonded to the circuit board using an adhesive and is integrally molded in the resin portion.  
      (8) In above (6), preferably, the heat sink has mount holes formed therein for fixing in place.  
      (9) In above (1), preferably, the circuit board has one or more thermal vias formed therein for radiating heat from one to the other side of the circuit board.  
      (10) In above (1), preferably, the circuit board is formed of a flexible substrate.  
      (11) In above (1), preferably, the resin portion is molded such that an illuminating electronic part is surrounded by a transparent thermo-setting resin.  
      According to the present invention, it is possible to increase heat resistance of the engine control circuit device, and to install the device in a place exposed to severe thermal environments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a vertical sectional view showing an overall structure of an engine control circuit device according to a first embodiment of the present invention;  
       FIG. 2  is a vertical sectional view for explaining a method of manufacturing the engine control circuit device according to the first embodiment of the present invention;  
       FIG. 3  is a vertical sectional view showing an overall structure of one modification of the engine control circuit device according to the first embodiment of the present invention;  
       FIG. 4  is a horizontal sectional view taken along the line IV-IV in  FIG. 3 ;  
       FIG. 5  is a vertical sectional view showing an overall structure of an engine control circuit device according to a second embodiment of the present invention;  
       FIG. 6  is a vertical sectional view for explaining a method of manufacturing the engine control circuit device according to the second embodiment of the present invention;  
       FIG. 7  is a partial enlarged vertical sectional view showing a detailed structure of a connector in one modification of the engine control circuit device according to the second embodiment of the present invention;  
       FIG. 8  is a partial enlarged vertical sectional view showing a detailed structure of a connector in another modification of the engine control circuit device according to the second embodiment of the present invention;  
       FIG. 9  is a vertical sectional view showing an overall structure of an engine control circuit device according to a third embodiment of the present invention;  
       FIG. 10  is a partial enlarged vertical sectional view showing a detailed structure of one modification of the engine control circuit device according to the present invention;  
       FIG. 11  is a partial enlarged vertical sectional view showing a detailed structure of another modification of the engine control circuit device according to the present invention;  
       FIG. 12  is a partial enlarged vertical sectional view showing a detailed structure of still another modification of the engine control circuit device according to the present invention;  
       FIG. 13  is a partial enlarged vertical sectional view showing a detailed structure of still another modification of the engine control circuit device according to the present invention;  
       FIG. 14  is a partial enlarged vertical sectional view showing a detailed structure of still another modification of the engine control circuit device according to the present invention;  
       FIG. 15  is a partial enlarged vertical sectional view showing a detailed structure of still another modification of the engine control circuit device according to the present invention;  
       FIG. 16  is a partial enlarged vertical sectional view showing a detailed structure of still another modification of the engine control circuit device according to the present invention;  
       FIG. 17  is a partial enlarged vertical sectional view showing a detailed structure of still another modification of the engine control circuit device according to the present invention;  
       FIG. 18  is a vertical sectional view showing an overall structure of an engine control circuit device according to a fourth embodiment of the present invention;  
       FIG. 19  is a vertical sectional view for explaining a method of manufacturing the engine control circuit device according to the fourth embodiment of the present invention;  
       FIG. 20  is a vertical sectional view showing an overall structure of one modification of the engine control circuit device according to the fourth embodiment of the present invention;  
       FIG. 21  is a vertical sectional view showing an overall structure of an engine control circuit device according to a fifth embodiment of the present invention;  
       FIG. 22  is a vertical sectional view showing an overall structure of an engine control circuit device according to a sixth embodiment of the present invention; and  
       FIG. 23  is a vertical sectional view showing an overall structure of one modification of the engine control circuit device according to the sixth embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Embodiments of the present invention will be described below with reference to the drawings.  
      A first embodiment of the present invention will be described with reference to  FIGS. 1 and 2 .  
       FIG. 1  is a vertical sectional view showing an overall structure of an engine control circuit device according to the first embodiment of the present invention.  
      In  FIG. 1 , the engine control circuit device comprises a circuit board  2  including a plurality of packaged electronic parts  1  mounted on, e.g., both surfaces thereof, a connector  3  for connection to an external circuit (not shown), a resin portion  4  formed of a thermo-setting resin and covering the connector  3  except for a connecting portion  3   a  thereof and the entirety of the circuit board  2 , and a cooling pipe  5  (cooling means) disposed below the circuit board  2  (on the lower side as viewed in  FIG. 1 ) and integrally molded in the resin portion  4 . A coolant flows through the cooling pipe  5  to cool the resin portion  4 .  
      The electronic parts  1  include, for example, board-inserted electronic parts  1 A (such as a resistor, a capacitor, a coil, a crystal, a diode, an IC, a FET, and a transistor), surface-mounted large-sized electronic parts  1 B (such as a microcomputer, a capacitor, a coil, a crystal, a diode, a transistor, and an IC), highly heating electronic parts  1 C (such as a power FET, a power transistor, a power diode, a power Zener diode, a power IC, a power IPD (Intelligent Power Device), and a microcomputer each provided with a metal-made heat sink or fins), and chip-type electronic parts iD (such as a capacitor, a resistor, a diode, a coil, an IC, a transistor, a FET, and a crystal).  
      The circuit board  2  is a resin-type printed wiring board made of, e.g., an epoxy resin or a polyimide resin mixed with glass fibers, and has a linear thermal expansion coefficient of about 14 ppm/° C. Also, the glass-transition temperature of the circuit board  2  is set to a high value so that the board has increased heat resistance.  
      The resin portion  4  is formed of a thermo-setting resin, such as an epoxy resin or a phenol resin, and has a linear thermal expansion coefficient of 8-24 ppm/° C., the coefficient of elasticity of 8-39 GPa, and the glass-transition temperature of 80-200° C.  
      The cooling pipe  5  has open ends  5   a  formed at opposite pipe ends (on the left and right sides as viewed in  FIG. 1 ) for connection to external piping (not shown). For example, an engine coolant flows through the cooling pipe  5  in a state where the cooling pipe  5  is connected to the external piping. To efficiently cool, e.g., the highly heating electronic parts  1 C mounted on the upper surface of the circuit board  2  (i.e., the surface of the circuit board  2  opposed to the cooling pipe  5 ), the cooling pipe  5  has section-enlarged areas  5   b  where a channel section is enlarged so as to make a pipe wall position closer to the circuit board  2  (i.e., offset upward as viewed in  FIG. 1 ). More specifically, the cooling pipe  5  is arranged close to the circuit board  2  to such an extent that the distance between the pipe wall and the electronic parts  1  mounted to the lower surface of the circuit board  2  is, e.g., about 1 mm.  
      A method of manufacturing the engine control circuit device according to the first embodiment will be described below.  FIG. 2  is a vertical sectional view for explaining the method of manufacturing the engine control circuit device according to the first embodiment.  
      In  FIG. 2 , a die used for molding the resin portion  4  is of, e.g., a two-split structure comprising an upper die  6 A and a lower die  6 B. When the upper die  6 A and the lower die  6 B are mated with each other, the cooling pipe  5  is supported in place in a state where the open ends  5   a  at the opposite ends of the cooling pipe  5  are closed. Though not shown in detail, the circuit board  2  including the plurality of electronic parts  1  and the connector  3  mounted thereon is supported by the upper die  6 A. Then, the thermo-setting resin is injected under pressure into a cavity  8  defined inside both the dies  6 A,  6 B through an injection port  7  of the upper die  6 A, thereby forming the resin portion  4  in which the circuit board  2  and the cooling pipe  5  are integrally molded using the thermo-setting resin.  
      With this first embodiment thus constructed, since the circuit board  2  including the plurality of electronic parts  1  and the connector  3  mounted thereon is covered with the resin portion  4  made of the thermo-setting resin having good heat conductance, heat radiation from the electronic parts  1  can be increased. Further, since the resin portion  4  is cooled through the cooling pipe  5  which is integrally molded in the resin portion  4 , the entirety of the engine control circuit device including the highly heating electronic parts  1 C, etc. can be efficiently cooled. Stated another way, the electronic parts  1  having an operational temperature range of, e.g., 125° C. or below can be efficiently cooled, and the engine control circuit device is further adaptable even for the on-engine mounting that causes the device to be exposed to severe thermal environments at 130° C. or higher. In addition, the linear thermal expansion coefficient of the thermo-setting resin is generally lower than that of the thermoplastic resin, and can be set closer to the linear thermal expansion coefficient of the circuit board  2  (for example, the linear thermal expansion coefficient of the resin-made printed wiring board is about 14 ppm/° C.). This is effective in suppressing damages of the electronic parts  1 , which is attributable to thermal expansion. It is therefore possible to increase heat resistance of the engine control circuit device and to install the device in a place exposed to severe thermal environments.  
      Also, with this first embodiment, since the resin-made printed wiring board is employed as the circuit board  2 , the engine control circuit device can be manufactured at a lower cost and higher productivity than the case of employing, e.g., a ceramic substrate having high heat resistance, while ensuring high durability based on high flexibility. Another advantage is that the known electronic part mounting techniques are available in production steps. Incidentally, if a ceramic substrate is used to form the circuit board  2 , a difficulty rises in enlarging the device size because of a limitation in substrate size and an increase of the cost.  
      Further, with this first embodiment, since the plurality of electronic parts  1  (and the cooling pipe  5 ) are fixedly molded in the resin portion  4 , influences of engine vibrations can be reduced and durability can be increased. Additionally, advantageous characteristics of the resin portion  4 , such as insulation and water tightness, can be given to the engine control circuit device. In other words, because of the circuit board  2  being covered with the resin portion  4 , even if, for example, the cooling pipe  5  is damaged, it is possible to prevent malfunctions, damages and other troubles of the electronic circuits, which are otherwise caused by leakage of the coolant. Moreover, since the resin portion  4  is made of the thermo-setting resin, the resin setting time can be cut and productivity can be increased as compared with the case of using a thermoplastic resin to form the resin portion  4 .  
      In this first embodiment, for the purpose of increasing the cooling efficiency, various contrivances can be easily practiced, as given in detail below, to increase the amount of heat transferred between the electronic parts  1  and the cooling pipe  5 .  
      (1) Coefficient of Thermal Conductivity of Resin Portion  
      The coefficient of thermal conductivity of the thermo-setting resin is preferably in the range of 0.2-3 W/m·K to avoid such a possibility that the coefficient of thermal conductivity of the resin portion  4  causes a bottleneck in heat transfer and restricts the transfer of heat from the highly heating electronic parts  1 C, etc. to the cooling pipe  5 . Also, by arranging the cooling pipe  5  so as to position closer to the highly heating electronic parts  1 C, etc., the cooling efficiency can be increased. Thus, since the thermo-setting resin and the cooling pipe are adjustable in practical layout, an optimum cooling structure can be provided without undergoing any restrictions in mount positions of the highly heating electronic parts  1 C in the stage of board design.  
      (2) Cooling Pipe  
      Preferable materials of the cooling pipe  5  are plastics, rubbers, and metals. Among those materials, metals having good heat conductance, such as copper, iron, aluminum and alloys thereof, are especially preferable from the viewpoint of increasing the cooling efficiency. Also, by forming the cooling pipe  5  such that its channel section is partly modified to have an enlarged heat-radiating area, the cooling efficiency can be increased without changing the overall size of the cooling pipe  5 .  
      (3) Coolant  
      By using the coolant flowing through the cooling pipe  5  in common with any of coolants (such as air, engine cooling water, and engine oil) used in ordinary cooling units provided in a vehicle, the cost required for the overall system can be cut. Generally, the cooling effect is obtained at the highest level with forced water-cooling, and then decreases in the order of forced air-cooling and natural air-cooling. Accordingly, when air is used as the coolant, a cooling fan is preferably installed to perform forced cooling. If natural convection of air must be utilized for some reason, relatively high cooling efficiency can be obtained by arranging the cooling pipe  5 , for example, such that air flows through the cooling pipe  5  in the vertical direction to allow easier air convection. When water is used as the coolant, a temperature range of the cooling water is preferably −40° C. to 110° C. When a corrosive coolant, e.g., saline water, is used as the coolant, an inner wall of the cooling pipe  5  is preferably coated with plating to increase corrosion resistance. Further, in the case of using the cooling water in common with the engine cooling unit, the engine cooling water before being used to cool an engine is preferably introduced to the cooling pipe  5  because the temperature of the cooling water after cooling the engine rises to about 130° C. To prevent the cooling water at high temperature from being introduced to the cooling pipe  5 , it is preferable to mount a temperature detecting means, e.g., a chip-type thermistor, on the circuit board  2 , to detect the inlet temperature of the cooling pipe  5 , and to control detection of a high-temperature abnormality of the cooling water and a system shutdown under control of a microcomputer.  
      Although layout of the cooling pipe  5  in a horizontal plane is not described in the foregoing first embodiment, the cooling pipe  5  may be arranged in the horizontal plane, by way of example, as shown in  FIGS. 3 and 4 .  FIG. 3  is a vertical sectional view showing an overall structure of one modification of the engine control circuit device according to the first embodiment, and  FIG. 4  is a horizontal sectional view taken along the line IV-IV in  FIG. 3  (note that  FIG. 4  shows only a part of the electronic parts  1 , i.e., the surface-mounted large-sized electronic parts  1 B and the highly heating electronic parts  1 C). To more efficiently cool the electronic parts  1  mounted on the circuit board  2 , a cooling pipe  5 ′ in this modification is arranged in a zigzag pattern over an entire area of the circuit board  2  with a predetermined spacing left between adjacent parallel pipe portions. This modification can also provide the same advantages as those obtained with the first embodiment. Additionally, the open ends  5   a  (inlet and outlet) of the cooling pipe  5  may be located at positions close to each other. This layout enables the cooling pipe  5  to be more easily connected to the external piping.  
      A second embodiment of the present invention will be described below with reference to  FIGS. 5 and 6 . In this second embodiment, a cooling passage is formed in the resin portion.  
       FIG. 5  is a vertical sectional view showing an overall structure of an engine control circuit device according to the second embodiment, and  FIG. 6  is a vertical sectional view for explaining a method of manufacturing the engine control circuit device according to the second embodiment. Identical components in  FIGS. 5 and 6  to those in the first embodiment are denoted by the same symbols and a description of those components is omitted here.  
      The engine control circuit device according to the second embodiment includes a resin portion  9  formed of a thermo-setting resin and covering a connector  3  except for a connecting portion  3   a  thereof and the entirety of a circuit board  2 , and a cooling passage  10  formed in the resin portion  9  to extend, for example, below the circuit board  2  (on the lower side as viewed in  FIG. 5 ). A coolant flows through the cooling passage  10  to cool the resin portion  9 . The cooling passage  10  has open ends  10   a  formed of a thermo-setting resin and positioned at opposite passage ends (on the left and right sides as viewed in  FIG. 5 ) for connection to external piping.  
      A die used for molding the resin portion  9  is made up of, by way of example, an upper die  11 A, a lower die  11 B, and a rod-shaped core  11 C made of a material that is easily releasable from the dies. When the upper die  11 A and the lower die  11 B are mated with each other, the rod-shaped core  11 C is supported between both the dies. Though not shown in detail, the circuit board  2  including a plurality of electronic parts  1  and the connector  3  mounted thereon is supported by the upper die  11 A. Then, the thermo-setting resin is injected under pressure into a cavity  13  defined inside both the dies  11 A,  11 B through an injection port  12  of the upper die  11 A, thereby molding the resin portion  9  so as to cover the whole of the circuit board  2 . By removing the rod-shaped core  11 C from the resin portion  9 , the cooling passage  10  is formed.  
      As with the first embodiment, this second embodiment constructed as described above can also realize an engine control circuit device that has higher heat resistance and can be installed in a place exposed to severe thermal environments. As compared with the first embodiment, since the cooling pipe  5  is not required, the number of parts and the assembly work can be lessened, thus resulting in a lower cost.  
      While the second embodiment has been described, by way of example, in connection with the structure where the open ends  10   a  at the opposite ends of the cooling passage  10  are formed of a thermo-setting resin, the present invention is not limited to that structure. More specifically, to avoid the open ends  10   a  from being subjected to stresses in a concentrated way and from being damaged when the open ends  10   a  are forcibly connected to the external piping in piping connection work, the opposite ends of the cooling passage  10  may be modified so as to include connectors made of, e.g., a metal (or a highly strong resin).  FIGS. 7 and 8  are each a partial enlarged vertical sectional view showing a detailed structure of the connector in such a modification.  
      In the modification shown in  FIG. 7 , the resin portion  9  is molded such that a connector  14  is embedded in the resin portion  9  and coupled to the cooling passage  10 . In the modification shown in  FIG. 8 , after molding the resin portion  9 , a connector  15  is attached to the cooling passage  10  by an adhesive  16  (or laser welding, etc.). These modifications can also provide the same advantages as those described above.  
      A third embodiment of the present invention will be described below with reference to  FIG. 9 . In this third embodiment, the cooling pipe  5  in the first embodiment is bonded to the circuit board  2 , etc. by an adhesive.  
       FIG. 9  is a vertical sectional view showing an overall structure of an engine control circuit device according to the third embodiment. Identical components in  FIG. 9  to those in the above-mentioned embodiments are denoted by the same symbols and a description of those components is omitted here.  
      In this third embodiment, the cooling pipe  5  disposed below the circuit board  2  (on the lower side as viewed in  FIG. 9 ) is bonded, using an insulating adhesive  17 , to not only the lower surface of the circuit board  2  in areas corresponding to the highly heating electronic parts  1 C mounted on the upper surface of the circuit board  2 , but also to some of electronic parts  1  mounted on the lower surface of the circuit board  2  (e.g., the surface-mounted large-sized electronic part  1 B in  FIG. 9 ). In such a state, the resin portion  4  is molded integrally with the cooling pipe  5 . Stated another way, the adhesive  17  serves to tentatively fix the cooling pipe  5  to the circuit board  2  until the resin portion  4  is molded, and also serves to insulate the cooling pipe  5  from the circuit board  2 . From the viewpoint of easiness in application, the adhesive  17  is preferably in the form of a liquid or in the other easily applicable form such as a double-coated adhesive tape or sheet. Further, the adhesive  17  having a high coefficient of thermal conductivity is preferably used to avoid such a possibility that a low coefficient of thermal conductivity of the adhesive  17  causes a bottleneck in heat transfer and restricts the transfer of heat from the highly heating electronic parts  1 C, etc. to the cooling pipe  5 .  
      As with the first embodiment, this third embodiment constructed as described above can also realize an engine control circuit device that has higher heat resistance and can be installed in a place exposed to severe thermal environments.  
      Although not specifically described in the forgoing first to third embodiments, the circuit board  2  may be provided with a thermal via (via hole) formed therein to release heat from one to the other surface of the circuit board  2 . FIGS.  10  to  12  are each a partial enlarged vertical sectional view showing a detailed structure of the engine control circuit device according to such a modification.  
      In the modification shown in  FIG. 10 , the cooling pipe  5  is bonded to the lower surface of the circuit board  2  using the adhesive  17  and is integrally molded in the resin portion  4 . The highly heating electronic part  1 C is mounted on the upper surface of the circuit board  2 , and a plurality of thermal vias  18  are formed through the circuit board  2  in an area close to the highly heating electronic part  1 C. With such an arrangement, heat generated from the highly heating electronic part  1 C is released toward the lower side of the circuit board  2  through the thermal vias  18  and is cooled by the cooling pipe  5  through the adhesive  17 .  
      In the modification shown in  FIG. 11 , the cooling pipe  5  is bonded, using the adhesive  17 , to the highly heating electronic part  1 C mounted on the lower surface of the circuit board  2 , and is integrally molded in the resin portion  4 . A plurality of thermal vias  18  are formed through the circuit board  2  in an area close to the highly heating electronic part  1 C. With such an arrangement, heat generated from the highly heating electronic part  1 C is cooled by the cooling pipe  5  through the adhesive  17  and is released toward the upper side of the circuit board  2  through the thermal vias  18 .  
      In the modification shown in  FIG. 12 , the highly heating electronic part  1 C is mounted on the upper surface of the circuit board  2 , and a thermal via  19  is formed through the circuit board  2  in an area close to the highly heating electronic part  1 C. The cooling pipe  5  is disposed below the circuit board  2  and has a projection  5   c  that is projected toward the circuit board side (upward as viewed in  FIG. 12 ) and inserted into the thermal via  19  of the circuit board  2 . Further, the cooling pipe  5  is bonded to the highly heating electronic part  1 C and the circuit board  2  using the adhesive  17 . With such an arrangement, heat generated from the highly heating electronic part  1 C is released toward the lower side of the circuit board  2  through the adhesive  17  and is cooled by the cooling pipe  5 .  
      With the modifications shown in FIGS.  10  to  12 , heat radiation efficiency can be further increased by forming the thermal vias  18  or via  19  in the circuit board  2 .  
      Although the foregoing embodiments and modifications have been described, by way of example, in connection with the structure where the cooling pipe  5  (or the cooling passage  10 ) is disposed only on one side, i.e., on the lower side of the circuit board  2 , it may be disposed only on the upper side of the circuit board  2 . As an alternative, it may be disposed on each of the upper and lower sides of the circuit board  2 . Such a modification will be described with reference to FIGS.  13  to  15 .  
      In the modification shown in  FIG. 13 , the highly heating electronic part  1 C is mounted on the upper surface of the circuit board  2 , and a plurality of thermal vias  18  are formed through the circuit board  2  in an area close to the highly heating electronic part  1 C. A cooling pipe  5 A disposed on the lower side of the circuit board  2  is bonded to the circuit board  2  using the adhesive  17  and is integrally molded in the resin portion  4 . On the other hand, a cooling pipe  5 B disposed on the upper side of the circuit board  2  is bonded to the highly heating electronic part  1 C using the adhesive  17  and is also integrally molded in the resin portion  4 . With such an arrangement, heat generated from the highly heating electronic part  1 C is released toward the lower side of the circuit board  2  through the thermal vias  18  and is cooled by the cooling pipe  5 A through the adhesive  17 , while the heat is further cooled by the cooling pipe  5 B through the adhesive  17 .  
      In the modification shown in  FIG. 14 , in addition to the construction of the modification shown in  FIG. 13 , the cooling pipe  5 A is formed to have projections  5   d  in channel section thereof. As a result, the surface area of the cooling pipe  5 A is increased and the cooling efficiency is enhanced.  
      In the modification shown in  FIG. 15 , the highly heating electronic part  1 C is mounted on the upper surface of the circuit board  2 , and a thermal via  19  is formed through the circuit board  2  in an area close to the highly heating electronic part  1 C. A cooling pipe  5 A disposed on the lower side of the circuit board  2  has a projection  5   c  that is projected toward the circuit board  2  (upward as viewed in  FIG. 15 ) and inserted into the thermal via  19  of the circuit board  2 . Further, the cooling pipe  5 A is bonded to the highly heating electronic part  1 C and the circuit board  2  using the adhesive  17 , and is integrally molded in the resin portion  4 . On the other hand, a cooling pipe  5 B disposed on the upper side of the circuit board  2  is bonded to the highly heating electronic part  1 C using the adhesive  17 , and is also integrally molded in the resin portion  4 . With such an arrangement, the highly heating electronic part  1 C is cooled by both the cooling pipes  5 A,  5 B through the adhesives  17 .  
      In the modification shown in  FIG. 16 , a semiconductor module  1 E (e.g., a BGA (Ball Grid Array) package), a flip-chip, or a multi-chip-module (MCM)) is mounted on the upper surface of the circuit board  2 . The semiconductor module  1 E comprises a bare chip  20 , a ball grid array (BGA)  21  serving as a portion for connection to an external circuit, a substrate  22  for connecting the bare chip  20  and the BGA  21 , and a resin  23  molded to package all of those components therein. A thermal via  19  is formed through the circuit board  2  in an area close to the semiconductor module  1 E. A cooling pipe  5 A disposed on the lower side of the circuit board  2  has a projection  5   c  that is projected toward the circuit board  2  (upward as viewed in  FIG. 16 ) and inserted into the thermal via  19  of the circuit board  2 . Further, the cooling pipe  5 A is bonded to the semiconductor module  1 E and the circuit board  2  using the adhesive  17 , and is integrally molded in the resin portion  4 . A cooling pipe  5 B disposed on the upper side of the circuit board  2  is bonded to the semiconductor module  1 E using the adhesive  17 , and is integrally molded in the resin portion  4 . With such an arrangement, the semiconductor module  1 E is cooled by both the cooling pipes  5 A,  5 B through the adhesives  17 .  
      With the modifications shown in FIGS.  13  to  16 , the electronic parts are cooled by both the cooling pipes  5 A,  5 B disposed on the upper and lower sides of the circuit board  2 , thus resulting higher cooling efficiency.  
      Although not specifically described in the forgoing embodiments and modifications, a resin portion  4 A may be molded such that, as shown in  FIG. 17  by way of example, a transparent thermo-setting resin is used as a part of the resin portion  4 A in an area surrounding an illuminating electronic part  1 F (e.g., a LED, namely a means for informing a user of an abnormality alarm, confirmation of normal conditions, or any other check item).  
      A fourth embodiment of the present invention will be described below with reference to  FIGS. 18 and 19 . In this fourth embodiment, a metal-made heat sink is integrally molded in the resin portion.  
       FIG. 18  is a vertical sectional view showing an overall structure of an engine control circuit device according to the fourth embodiment, and  FIG. 19  is a vertical sectional view for explaining a method of manufacturing the engine control circuit device according to the fourth embodiment. Identical components in  FIGS. 18 and 19  to those in the foregoing embodiments are denoted by the same symbols and a description of those components is omitted here.  
      The engine control circuit device according to the fourth embodiment includes a metal-made heat sink  24  (cooling means) disposed below a circuit board  2  (on the lower side as viewed in  FIG. 18 ), and a resin portion  25  formed of a thermo-setting resin and covering the heat sink  24  on the side facing the circuit board  2  (on the upper side as viewed in  FIG. 18 ), a connector  3  except for a connecting portion  3   a  thereof, and the entirety of the circuit board  2 .  
      The heat sink  24  has connecting portions  24   a  connected to the circuit board  2  with intent to enhance noise immunity of the circuit board  2  and to increase heat conductance, and also has projections  24   b  projected so as to approach the circuit board  2  with intent to increase the effect of cooling the electronic parts  1 . The projections  24   b  are bonded to the electronic parts  1 , the circuit board  2 , etc. by insulating adhesives  17 . Further, the heat sink  24  has a plurality of mount holes  24   c  formed in areas where the resin portion  25  is not molded, and bolts  26  are inserted through the mount holes  24   c  for mounting the heat sink  24  to a fixed wall  27  (such as an engine room sidewall, an engine block sidewall, an engine head, a radiator, or an intake manifold). As materials of the heat sink  24 , metals having good heat conductance, such as copper, iron, aluminum and alloys thereof, are preferable from the viewpoint of increasing the cooling effect. Also, the heat sink  24  is arranged close to the circuit board  2  to such an extent that the distance between the heat sink and the electronic parts  1  mounted to the lower surface of the circuit board  2  is, e.g., about 1 mm.  
      A die used for molding the resin portion  25  is of, e.g., a two-split structure comprising an upper die  28 A and a lower die  28 B. The heat sink  24  is supported by the lower die  28 B in a state where the mount holes  24   c  of the heat sink  24  are closed. The circuit board  2  including the plurality of electronic parts  1  and the connector  3  mounted thereon is supported by the upper die  28 A. Then, the thermo-setting resin is injected under pressure into a cavity  30  defined inside both the dies  28 A,  28 B through an injection port  29  of the upper die  28 A, thereby forming the resin portion  25  in which the circuit board  2  and the heat sink  24  are integrally molded using the thermo-setting resin.  
      As with the foregoing embodiments, this fourth embodiment constructed as described above can also realize an engine control circuit device that has higher heat resistance and can be installed in a place exposed to severe thermal environments. Further, since the heat sink  24  serves also as a fixture for fixing the device, the number of parts and the assembly work can be lessened, thus resulting in a lower cost.  
      While the fourth embodiment has been described, by way of example, in connection with the structure where the heat sink  24  is bonded to the circuit board  2 , etc. using the adhesives  17 , the present invention is not limited to that structure. It is needless to say that, as shown in  FIG. 20 , a similar structure can also be realized without using the adhesive  17 .  
      A fifth embodiment of the present invention will be described below with reference to  FIG. 21 . In this fifth embodiment, the circuit board is formed of a flexible substrate and the cooling pipe is integrally molded in the resin portion.  
       FIG. 21  is a vertical sectional view showing an overall structure of an engine control circuit device according to the fifth embodiment. Identical components in  FIG. 21  to those in the above-mentioned embodiments are denoted by the same symbols and a description of those components is omitted here.  
      In this fifth embodiment, a circuit board  31  is formed of a flexible substrate made of, e.g., a polyimide resin or a liquid crystal polymer (or a composite substrate comprising a rigid portion and a flexible portion, in which only a bent portion is formed of a flexible substrate). The circuit board  31  is bent at a midpoint into the U-form so that a projection area of the circuit board is halved. The electronic parts  1  (such as the surface-mounted large-sized electronic parts  1 B, the highly heating electronic parts  1 C, and the chip-type electronic part  1 D) are mounted on an inner surface of the circuit board  31  in areas where the board is not bent, and the connector  3  is mounted on an outer surface of the circuit board  31  in an area where the board is not bent. The engine control circuit device according to this fifth embodiment includes a resin portion  32  formed of a thermo-setting resin and covering the entirety of the circuit board  31 , and a cooling pipe  33  disposed inside the circuit board  31  to be out of interference with the electronic parts  1  and integrally molded in the resin portion  32 . A coolant flows through the cooling pipe  33  to cool the resin portion  32 . Though not shown in detail, the cooling pipe  33  is connected to external piping and, for example, engine cooling water flows through the cooling pipe  33  in a direction perpendicular to the drawing sheet of  FIG. 21 .  
      As with the foregoing embodiments, this fifth embodiment constructed as described above can also realize an engine control circuit device that has higher heat resistance and can be installed in a place exposed to severe thermal environments. Further, since the circuit board  31  is formed of a flexible substrate and bent into the U-form, the device size can be reduced.  
      A sixth embodiment of the present invention will be described below with reference to  FIG. 22 . In this sixth embodiment, the circuit board is formed of a flexible substrate and a metal-made heat sink is integrally molded in the resin portion.  
       FIG. 22  is a vertical sectional view showing an overall structure of an engine control circuit device according to the sixth embodiment. Identical components in  FIG. 22  to those in the above-mentioned embodiments are denoted by the same symbols and a description of those components is omitted here.  
      The engine control circuit device according to this sixth embodiment includes a resin portion  34  formed of a thermo-setting resin and covering the entirety of the circuit board  31 , and a metal-made heat sink  35  disposed inside the circuit board  31  to be out of interference with the electronic parts  1  and integrally molded in the resin portion  34 . A part of the heat sink  35  (right end part as viewed in  FIG. 22 ), which is exposed to the outside from the resin portion  34 , is of a fin structure for increasing a heat radiating area.  
      As with the foregoing embodiments, this sixth embodiment constructed as described above can also realize an engine control circuit device that has higher heat resistance and can be installed in a place exposed to severe thermal environments. Further, since the circuit board  31  is formed of a flexible substrate and bent into the U-form, the device size can be reduced.  
      While the sixth embodiment has been described, by way of example, in connection with the structure where the heat sink  35  is disposed inside the circuit board  31 , the present invention is not limited to that structure, and the heat sink  35  may be disposed outside the circuit board  31 .  FIG. 23  is a vertical sectional view showing an overall structure of an engine control circuit device according to such a modification.  
      In the modification shown in  FIG. 23 , a metal-made heat sink  36  is integrally molded in the resin portion  34  such that the heat sink  36  is disposed to be out of interference with the connector  3  in contact with an outer surface of the circuit board  31 . As an alternative, the heat sink  36  may be bonded to the circuit board  31  by an adhesive having a high coefficient of elasticity. Either modification can also provide the same advantages as those mentioned above.