Electronic control unit and method of manufacturing the same

An electronic control unit is disclosed. The electronic control unit includes: a resin board; a power device that is surface-mounted on the resin board; a microcomputer that is configured to control the power device; first heat radiation means for radiating heat, the first heat radiation means being disposed on an opposite side of the resin board from the power device; and first heat conduction means for conducting the heat generated by the power device to the first heat radiation means.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electronic control unit and a manufacturing method of the same. The present invention is applicable to an electronic control unit used in an electric power-assisted steering system.

2. Description of Related Art

There is known an electric power-assisted steering system for assisting a driver in steering. In a typical electric power-assisted steering system, a motor is rotated only when a force for steering assistance is needed. Thus, compared to a hydraulic power-assisted steering system, a typical electric power-assisted steering system is fuel-saving and environmentally friendly because of no waste oil.

A typical electric power-assisted steering system requires a large current of, for example, about 100 A to drive a motor when a vehicle has a low speed and a large steering angle, e.g., when a vehicle is moved into a garage. Thus, a power MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) used in an ECU (electronic control unit) for drive control of the motor can instantaneously have a junction temperature between, for example, about 150 degrees C. and about 170 degrees C.

In recent years, an engine room of a vehicle or an engine room side of an instrument panel, in which the ECU is typically disposed, has become a small space because of an increase in space of a vehicle compartment and an increase in the number of other ECUs for controlling various parts of the vehicle. If the ECU is downsized in view of the above, the ECU may have a high-density circuit, which disadvantageously lowers a heat radiation performance.

According to JP-H6-3832A, a molybdenum sheet is disposed between a heat sink and a board having a nickel-plated silicon-carbide, so that the heat generated by an electronic component mounted to the board is conducted to the heat sink. However, when the board uses such a high-priced material, the manufacturing cost becomes disadvantageously large.

SUMMARY OF THE INVENTION

In view of the above and other points, it is an objective of the present invention to provide an electronic control unit that can have a small size and a high heat radiation performance. It is also an objective of the present invention to provide a method of manufacturing such an electronic control unit. It is further an objective of the present invention to provide an electronic control unit and a manufacturing method of an electronic control unit that can reduce man-hours in manufacturing.

According to a first aspect of the present invention, an electronic control unit is provided. The electronic control unit includes: a resin board; a power device that is surface-mounted on the resin board; a microcomputer that is configured to control the power device; first heat radiation means for radiating heat, the first heat radiation means being disposed on an opposite side of the resin board from the power device; and first heat conduction means for conducting the heat generated by the power device to the first heat radiation means.

According to the above electronic control unit, since a heat radiation path for conducting and radiation the heat generated by the power device is formed by the first heat conduction means and the first heat radiation means, it is possible to improve a heat radiation performance of the electronic control unit. Moreover, the above configuration can simplify a structure of the electronic control unit, can reduce the size of the electronic control unit and reduce man-hour in assembling or manufacturing the electronic control unit.

According to a second aspect of the present invention, a method of manufacturing an electronic control unit is provided. The method includes: mounting an electronic component on a surface of a resin board, the electronic component including a power device; testing an operating condition of the electronic component at a predetermined high temperature or a predetermined low temperature after mounting the electronic component on the surface of the resin board, wherein the predetermined low temperature is lower than the predetermined high temperature; and providing heat conduction means and heat radiation means on an opposite side of the resin board from the power device after testing the operating condition of the electronic component.

According to the above method, since the operating conduction of the electronic component is tested before the heat radiation means is provided, a heat energy is not applied to the heat radiation means when the electronic component is tested. It is thus possible to perform a high/low temperature test in a short time of period and in an energy-saving manner. It is therefore possible to reduce man-hour in assembling or manufacturing the electronic control unit.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

An electronic control unit according exemplary embodiments will be described below with reference to the accompanying drawings. In the exemplary embodiments, like reference numerals may be used to refer to like parts, and explanation on like parts described in the preceding embodiment may not be given in the succeeding embodiment.

First Embodiment

An electronic control unit1of a first embodiment is illustrated below. As shown inFIGS. 1 and 2, the electronic control unit1is used in an electric power-assisted steering system100, and performs drive control of a motor101for generating a steering assistance force, based on a steering torque signal and a vehicle speed signal.

The electronic control unit1includes a resin board20, a heat sink40, and a cover60. On the resin board20, multiple electronic components are mounted. The resin board20is fixed to the heat sink40. The cover60covers the resin board20fixed to the heat sink40. The resin board20is, for example, a printed wiring board such as a FR-4 printed wiring board and the like. The heat sink40is an example of first heat radiation means and a first heat radiator.

The FR-4 printed wiring board is composed of a fiberglass cloth and an epoxy resin binder. The electronic components surface-mounted on the resin board20includes a power MOSFET31(also referred to as a power MOS31for simplicity) as a power device. The power MOS31switches a current that is supplied from a buttery102to the motor101via a connector36.

An IC (integrated circuit)35detects rotation direction and rotation torque of the motor101and outputs a signal from a driver to control the switch of the power MOS31, based on the steering torque signal and the vehicle speed signal inputted via the connector36. The IC35monitors the heat generated by the power MOS31or temperature of the power MOS31. The electronic components mounted on the resin board20include an electronic component34. The electronic component34has a capacitor, a coil and the like for smoothing the current that is switched by the power MOS31. The IC35is an example of a microcomputer

The power MOS31is provided with a terminal32and a metal base33. The power MOS31, the terminal32and the metal base33are integrated. The terminal32is electrically connected with a land of the resin board20. The metal base33is soldered to the resin board20, and decreases a thermal resistance of the power MOS31. The heat sink40is made of aluminum, copper or the like, and formed into a plate shape. The heat sink40has a projection part41projecting toward the resin board20and a base part42extending generally parallel to the resin board20. The projection part41is located across the resin board20from the power MOS31. More specifically, the projection part41may be just across the resin board20from the power MOS31. A insulating heat-radiation sheet51is disposed between the projection part41and the resin board20. The insulating heat-radiation sheet51has a small thermal resistance and contains, for example, silicon or the like. A heat radiation grease in a gel state whose base material is for example silicon may be applied to between the insulating heat-radiation sheet51and the heat sink40, so that the heat radiation grease fills a fine gap at a connection portion between the insulating heat-radiation sheet51and the heat sink40to increase a thermal conductivity. The resin board20, the insulating heat-radiation sheet51and the heat sink40form a heat radiation path (which may be also referred to as a first heat radiation path) for radiating the heat generated by the power MOS31. The cover60is connected with an end of the heat sink40and protects the electronic components mounted on the resin board20. The insulating heat-radiation sheet51is an example of first heat conduction means and a first heat conductor.

When the power MOS31is in a conductive state due to a driving current of the IC35, the large current for driving the motor101flows from the battery102through the power MOS31. In this case, as shown by the arrow “A” inFIG. 3, the heat generated by the power MOS31is conducted from the metal base33of the power MOS31to the resin board20, the insulating heat-radiation sheet51and the heat sink40, and the heat is radiated to air.

An assembling structure of the electronic control unit1is illustrated below with reference toFIG. 4. Cylindrical members451to454each having a screw hole are disposed at corner parts of the heat sink40. A cylindrical member455having a screw hole is further disposed at a center part of the heat sink40. The resin board20is attached to the cylindrical members451to455by using the cylindrical members451to455and screws251to254. In attaching the resin board20to the cylindrical members451to455, the insulating heat-radiation sheet51and the heat radiation grease52, which are disposed on the same side of the resin board20as the projection part41is, are fixed between the projection part41and the resin board20. The screw255penetrating the center part of the resin board20is used to minimize a position gap of the insulating heat-radiation sheet51and to suppress distortion of the resin board20. The cover60has a claw (hook) part63at an end of the cover60so that the claw part63is located on a heat sink side. The cover60and the heat sink40are assembled by crimping the claw part63around an end of the heat sink40. Through the above processes, the electronic control unit1can be assembled.

Manufacturing processes of the electronic control unit1is illustrated below with reference toFIG. 5. At S10, a solder paste is applied to a front surface of the resin board20, and an electronic component including the power MOS31(SMD: Surface Mount Device) is placed on the front surface of the resin board20. At S11, the electronic component is soldered to the front surface of the resin board20by using, for example, a reflow process. At S12, a solder paste is applied to a rear surface of the resin board20, and an electronic component including a SMD is placed on the rear surface of the resin board20. At S13, the electronic component is soldered to the rear surface of the resin board20by, for example, a reflow process. At S14, the resin board20on which the electronic components are mounted is heated or cooled in a constant temperature bath, and thereby high-lower temperature test is performed to test a function of the electronic component.

At S15, a moisture-proof material such as acrylate resin and the like is applied to the resin board20to protect the resin board20from moisture and the like. At S16, the heat radiation grease52is applied. At S17, the resin board20and the heat sink40are fixed to each other by using the screws251to255, and the insulating heat-radiation sheet51is attached between the resin board20and the heat sink40. At S18, the cover60is attached to the heat sink40. The manufacturing of the electronic control unit1is finished.

Comparison Example

An electronic control unit17according to a comparison example is illustrated below with reference toFIGS. 21 to 24. As shown inFIG. 21, the electronic control unit17includes a metal board480, a resin board200and a heat sink400. The metal board480and the resin board200are fixed to the heat sink400. A circuit of the metal board480and a circuit of the resin board200are electrically connected with each other via bus bars380,381. The metal board480is a printed wiring board, which includes a metal part made of aluminum or the like and an insulating layer490made of, for example, epoxy resin or the like. A power MOS310is mounted on the metal board480. The resin board is a printed wiring board such as FR-4 printed wiring board and the like. On the resin board200, an electronic component such as a coil, a capacitor and the like, an IC350and a connector360are mounted.

The heat sink400is made of, for example, aluminum, copper or the like. The heat sink400has a projection part410projecting toward the resin board200and a base part extending generally parallel to the resin board200. Four cylindrical members451to454are disposed at corner parts of the heat sink400. The metal board480is disposed on a cover side of the projection part410. In other words, the metal board480and a cover600are located on the same side of the projection part410. The resin board200is disposed on a cover side of the cylindrical members451to454. In other words, the resin board200and the cover60are located on the same side of the cylindrical member451to454. A heat radiation grease520is applied between the projection part410and the metal board480, and fills a clearance at a connection portion between the projection part410and the metal board480. When the power MOS310is in a conductive state due to a driving current of the IC350, a large current for driving the motor flows from a battery through the power MOS310. In this case, as shown by the arrow “M” inFIG. 22, the heat generated by the power MOS310is conducted from the power MOS310, the metal board480, the heat radiation grease520and the heat sink400, and radiated to the air.

An assembling structure of the electronic control unit17is illustrated below with reference toFIG. 23. The metal board480is attached to the projection part410of the heat sink400by using screws256,257. The resin board200is attached to the cylindrical members451to454of the heat sink400by using screws251to254. The cover600is fixed to the heat sink400by crimping a claw part610around an end of the heat sink400. Through the above processes, the assembling of the electronic control unit17is finished.

Manufacturing processes of the electronic control unit17is illustrated below with reference toFIG. 24. At S20, the electronic component such as the power MOS310and the like is mounted on the metal board480, and the multiple bus bars380,381are mounted to the circuit of the metal board480. In the above, the multiple bus bars are fixed by a guide (not shown). At S21, a surface mount device (SMD) such as an IC350and the like is mounted to the resin board200. At S22, a through-hole device (THD) such as a connector360and the like is mounted. At S23, a heat radiation grease520is applied to the projection part410of the heat sink400. At S24, the metal board480is fixed to the projection part410of the heat sink400by using screws256,257.

At S25, the resin board200is fixed to the cylindrical members451to454of the heat sink400by using the screws251to254. In the above, the multiple bus bars380,381are inserted into a through-hole vias210,211of the resin board200. At S26, the multiple bus bars380,381are soldered to a rear surface of the resin board200. At S27, a moisture-proof material is applied to the metal board480and the resin board200. At S28, the cover600is attached to the heat sink400. At S29, a high-low temperature test on the electronic component is performed. Then, the manufacturing of the electronic control unit17is finished.

The first embodiment involves the following unpredictable advantage over the comparison example.

In the first embodiment, the power MOS31and another electronic component are mounted on the single resin board20. In the comparison example, by contract, the power MOS310is mounted on the metal board480and another electronic component is mounted on the resin board200. Moreover, the circuit of the metal board480and the circuit of the resin board200are connected with each other by the multiple bus bars380,381, which are through-hole-mounted. As can be seen from the above, the electronic control unit1of the first embodiment can have a small size compared to the comparison example, because the electronic control unit1of the first embodiment uses the single resin board. Furthermore, the first embodiment can reduce man-hours in manufacturing or assembling because the process of mounting the bus bar to the resin board by through-hole mounting is omissible. Furthermore, the first embodiment can reduce the number of parts, because the metal board and the bus bar are omissible.

In connection with the first embodiment, let Tp, Tz, Th be thermal resistances of the resin board20, the insulating heat-radiation sheet and the heat sink, respectively. Then, a thermal resistance of the heat radiation path for conducting and radiating the heat generated by the power MOS31is given as “Tp+Tz+Th”. In connection with the comparison example, let Tz, Tm, Tg, Tn be thermal resistances of an insulating layer of the metal board, a metal part the metal board, the heat radiation grease, and the heat sink, respectively. Then a thermal resistance of the heat radiation path for conducting and radiating the heat generated by the power MOS310is given as “Tz+Tm+Tg+Th”. As can be seen from the above, the electronic control unit1of the first embodiment has the short heat radiation path and improves the heat radiation performance, compared to the comparison example. It is therefore possible to increase an output of the electronic control unit1.

In the first embodiment, when the resin board20and the heat sink40are assembled by using the screws251to255, the insulating heat-radiation sheet51is placed between the resin board20and the heat sink40, and the heat radiation path for conducting and radiation the heat generated by the power MOS31is formed. In the comparison example, by contrast, the assembling of the metal board480and the heat sink400by using the screws256,257leads to the formation of the heat radiation path for conducting and radiation the heat generated by the power MOS310, and then the resin board200and the heat sink400are assembled by using the screws251to254. As can be seen from the above, the first embodiment can reduce man-hours in assembling or manufacturing compared to the comparison example, because the assembling of the resin board20and the heat sink40and the forming of the heat radiation path for heat generated by the power MOS can be carried out at the same time.

In the first embodiment, after the electronic components are mounted on the front surface and the rear surface of the resin board20, the high-low temperature test is performed. In the comparison example, by contrast, after the metal board480and the resin board200are fixed to the heat sink400, and after the circuit of the metal board480and the circuit of the resin board200are connected by the bus bars380,381, the high-low temperature test is performed. As can seen from the above, in the electronic control unit1of the first embodiment, since an operating condition of the electronic component is tested before the resin board20and the heat sink40are assembled, the high-low temperature test does not involve application of thermal energy to the heat sink40. Therefore, compared to the comparison example, the first embodiment can use a constant temperature bath having a small heat capacity and can perform a high-low temperature test in a short period of time.

Second Embodiment

An electronic control unit2according to a second embodiment is illustrated below with reference toFIG. 6. In the second embodiment, the resin board20has an opening21. The projection part41of the heat sink40is inserted into the opening21. An insulating heat-radiation sheet51is disposed between the projection part41and the resin board20. The insulating heat-radiation sheet51is in direct contact with the metal base33of the power MOS31and the heat sink40. When a large current for driving the motor101flows through the power MOS31, the heat generated by the power MOS31is conducted from the power MOS31to the insulating heat-radiation sheet51and the heat sink40and is radiated to the air, as shown by the arrow “B” inFIG. 6.

In the second embodiment, a thermal resistance of the heat radiation path for conducting and radiation the heat generated by the power MOS31is given as “Tz+Th”. Thus, the electronic control unit2of the second embodiment has a small thermal resistance and improves the heat radiation performance, compared to the first embodiment. Moreover, since the projection part41is inserted into the opening21of the resin board20, it is possible to reduce size of the electronic control unit2.

Third Embodiment

An electronic control unit3according to a third embodiment is illustrated below with reference toFIG. 7. The electronic control unit3of the third embodiment includes a second heat sink66and a heat radiation grease71in addition to a first heat sink40. The second heat sink66is located on an opposite side of the power MOS31from the resin board20. The heat radiation grease71fills a gap between the second heat sink66and the power MOS31, thereby forming a second heat radiation path for conducting and radiation the heat generated by the power MOS31. Distance of the gap between the second heat sink66and the power MOS31is set to a predetermined distance that causes substantially no stress on the power MOS. The second heat sink66is an example of second heat radiation means and a second heat radiator. The heat radiation grease71is an example of second heat conduction means and a second heat conductor.

When a large current for driving the motor flows through the power MOS31, the heat generated by the power MOS31is conducted from the power MOS31to the resin board20, the insulating heat-radiation sheet51and the first heat sink40, and the heat is radiated to the air, as shown by the arrow “A” inFIG. 7. At the same time, as shown by the arrow “C” inFIG. 7, the heat can also be conducted from the metal base33of the power MOS31to the heat radiation grease71and the second heat sink66, and the heat is radiated to the air. In connection with the above, a heat path between the power MOS31, the resin board20, the insulating heat-radiation sheet51and the first heat sink40may be called a first heat radiation path. A heat path between the metal base33of the power MOS31, the heat radiation grease71and the second heat sink66may be called a second heat radiation path.

In connection with the third embodiment, let Tg be a thermal resistance of the heat radiation grease71. A thermal resistance of the heat radiation paths for conducting and radiating the heat generated by the power MOS31is given as “(Tp+Tz+Tz)//(Tg+Th)” where // denotes that the two heat radiation paths are formed parallel. Since the electronic control unit3of the third embodiment has two heat radiation paths for conducting and radiating the heat generated by the power MOS31, the third embodiment can improve the heat radiation performance compared to the first embodiment. Moreover, in the third embodiment, the metal base33of the power MOS31faces the second heat sink66and faces away from the resin board20. Thus, the third embodiment can further improve the heat radiation performance in such way that the metal base33faces the second heat radiation path whose thermal resistance is smaller than the first heat radiation path. In the present disclosure, the first heat radiation path may be also referred to a heat radiation path on a resin board side.

Fourth Embodiment

An electronic control unit4according to a fourth embodiment is illustrated below with reference toFIG. 8. The fourth embodiment can be a combination of the second and third embodiments. In the electronic control unit4of the fourth embodiment, the projection part41of the heat sink40is inserted into the opening21of the resin board20. The second heat sink66and the heat radiation grease71are located on an opposite side of the power MOS31from the resin board20. When the large current for driving the motor flows through the power MOS31, the heat generated by the power MOS31is conducted from the power MOS31to the insulating heat-radiation sheet51and the first heat sink40, and radiated to the air, as shown by the arrow “B” inFIG. 8. At the same time, as shown by the arrow “C” inFIG. 9, the heat generated by the power MOS31is conducted from the power MOS31to the heat radiation grease71and the second heat sink66, and radiated to the air.

In the fourth embodiment, a thermal resistance of the heat radiation paths for conducting and radiating the heat generated by the power MOS31is given as “(Tz+Th)//(Tg+Th)”. Therefore, the fourth embodiment has a small thermal resistance and improves the heat radiation performance, compared to the third embodiment.

Fifth Embodiment

An electronic control unit5according to a fifth embodiment is illustrated below with reference toFIG. 9. In the fifth embodiment, the resin board20has a through-hole via81, which extends in a thickness direction of the resin board20. An outerlayer copper foil82is located on a front side, on which the power MOS31is mounted, of the resin board20. An outerlayer copper foil83is located on a rear side, on which the heat sink40is located, of the resin board20. The through-hole via81is located just below the power MOS31, and connects the outerlayer copper foil82and the outerlayer copper foil83. A large-hardness insulating heat-radiation sheet53and a heat radiation grease52are disposed between the resin board20and the heat sink40. The large-hardness insulating heat-radiation sheet53causes a high insulation and a small thermal resistance. The heat radiation grease52fills a gap between the large-hardness insulating heat-radiation sheet53and the heat sink40, thereby enhancing heat conductivity between the large-hardness insulating heat-radiation sheet53and the heat sink40. The through-hole via81is an example of heat conduction path means and a heat conduction path provider. The outerlayer copper foil82,83is an example of a heat conduction layer, heat conduction path means, and a heat conduction path provider. The heat radiation grease52is an example of first heat conduction means and a first heat conductor.

When the large current for driving the motor flows through the power MOS31, the power MOS31generates the heat. As shown by the arrow “D” inFIG. 9, the heat is conducted from the power MOS31to the resin board20, the large-hardness insulating heat-radiation sheet53, the heat radiation grease52and the heat sink40, and radiated to the air.

In connection with the fifth embodiment, let Tp1 be a thermal resistance of the resin board having the through-hole via and the outerlayer copper foils. Let Tz, Tg, Th be thermal resistances of the large-hardness insulating heat-radiation sheet, the heat radiation grease, and the heat sink. In the fifth embodiment, the heat radiation path for conducting and radiating the heat generated by the power MOS31is given as “Tp1+Tz+Tg+Th” where the thermal resistance Tp1 has a relationship “Tp1<Tp” to the terminal resistance Tp of the first embodiment. As can be seen from the above, since the resin board20of the electronic control unit5has the through-hole via81and the outerlayer copper foils82,83, the fifth embodiment has a large heat radiation performance compared to the first embodiment.

Sixth Embodiment

An electronic control unit6of a sixth embodiment is illustrated below with reference toFIG. 10. In the sixth embodiment, a heat radiation grease52is disposed between the high-hardness insulating heat-radiation sheet53and the resin board20. The heat radiation grease52fills an inside of the through-hole via81and is in contact with the power MOS31. When the large current for driving the motor flows through the power MOS31, the power MOS31generates the heat. As shown by the arrow “E” inFIG. 10, the heat is conducted from the power MOS31to the resin board20, the large-hardness insulating heat-radiation sheet53, the heat radiation grease52and the heat sink40, and radiated to the air.

In the sixth embodiment, the heat radiation path for conducting and radiating the heat generated by the power MOS31is given as “(Tp1+Tg)+Tz+Th” where a relationship between the terminal resistance (Tp1+Tg) of the resin board of the sixth embodiment and the thermal resistance Tp1 of the resin board of the fifth embodiment is (Tp1+Tz)<Tp1. Therefore, the sixth embodiment improves a heat radiation performance compared to the fifth embodiment because the through-hole via81is filled with the heat radiation grease52in the sixth embodiment. Moreover, the sixth embodiment can provide low-cost processing, by using the heat radiation grease52to decrease the thermal resistance of the heat radiation path.

Seventh Embodiment

An electronic control unit7of a seventh embodiment is illustrated below with reference toFIG. 11. In the seventh embodiment, the resin board20includes innerlayer copper foils84,85. The innerlayer copper foil84,85extends in an extension direction of the resin board20, the extension direction being perpendicular to the thickness direction of the resin board20. An end of the innerlayer cupper foil84is connected with an outer wall of the through-hole via81so that that heat is conductable between the innerlayer cupper foil84and the through-hole via81. Another end of the innerlayer cupper foil84is connected with the screw25fixing the resin board20and the heat sink40so that heat is conductable between the innerlayer cupper foil84and the screw25. The innerlayer copper foil84radiates the heat generated by the power MOS31in the extension direction of the resin board20, and causes the heat radiation from an outer wall of the screw25. When the large current for driving the motor flows in the power MOS31, the power MOS31generates the heat. The heat is conducted from the power MOS31to the resin board20, the heat radiation grease52, the large-hardness insulating heat-radiation sheet53and the heat sink40, and is radiated to the air, as shown by the arrow “F” inFIG. 11. Each innerlayer copper foil84,85is an example of a heat conduction layer, heat conduction path means, and a heat conduction path provider.

In connection with the seventh embodiment, let Tp denote a thermal resistance of the resin board having the through-hole via, the outerlayer copper foil and the innerlayer copper foil. In the seventh embodiment, the heat radiation path for conducting and radiating the heat generated by the power MOS31is given as “(Tp2+Tg)+Tz+Th” where a relationship “(Tp2+Tg)<(Tp1+Tg)” is satisfied. In the above, (Tp2+Tg) is the terminal resistance of the resin board of the seventh embodiment, and (Tp1+Tg) is the thermal resistance of the resin board of the sixth embodiment. As can be seen from above, since the resin board20of the electronic control unit7of the seventh embodiment has the innerlayer copper foils84,85, the seventh embodiment can improve the heat radiation performance compared to the sixth embodiment.

Eighth Embodiment

An electronic control unit8of an eighth embodiment is illustrated below with reference toFIG. 12. In the eighth embodiment, a heat conduction chip91is mounted on the front surface of the resin board20and a heat conduction chip92is mounted on the rear surface of the resin board20. The heat conduction chips91,92are made of, for example, copper, solder or the like. The heat conduction chips91,92are respectively protruded from the front surface and the rear surface of the resin board20toward the air. The resin board20has a through-hole via86located just below the heat conduction chips91,92. The through-hole via86is connected with the innerlayer copper foils84,85so that heat is conductable between the through-hole via86and the innerlayer copper foils84,85. The heat conduction chips91,92are positioned so as to efficiently use a space of the surface of the resin board20. The heat conduction chips91,92efficiently radiate the heat conducting through the innerlayer copper foils84,85.

When the large current for driving the motor flows through the power MOS31, the power MOS31generates the heat. The heat is conducted from the power MOS31to the resin board20, the heat radiation grease52, the large-hardness insulating heat-radiation sheet53and the heat sink40, and radiated to the air, as shown by the arrow “G” inFIG. 12. At the same time, as shown by the arrows “H”, “I”, “J” inFIG. 12, the heat generated by the power MOS31is also conducted from the power MOS31to the through-hole via81, the outerlayer copper foils82,83, the innerlayer copper foils84,85, the through-hole via86and the heat conduction chips91,92, and radiated to the air.

In connection with the eighth embodiment, let Td denote a thermal resistance of the heat condition chip. In the eighth embodiment, the thermal resistance of the heat radiation paths for conducting and radiating the heat generated by the power MOS31is given as “(Tp2+Tg)+Tz+Th//Tp2+Td”. Therefore, the eighth embodiment improves the heat radiation performance compared to the seventh embodiment, because the electronic control unit8of the eighth embodiment has two heat radiation paths for radiating the heat generated by the power MOS31.

Ninth Embodiment

An electronic control unit9of a ninth embodiment is illustrated below with reference toFIG. 13. In the ninth embodiment, a cover60is attached to the resin board20. A heat radiation grease71fills a space between the cover60and the resin board20. Moreover, a heat radiation grease52fills a space between the resin board20and the heat sink40. The heat radiation grease71located between the cover60and the resin board20forms a heat radiation path between the power MOS31and the cover60, and another heat radiation path between the heat conduction chip91and the cover. The heat radiation grease52located between the resin board20and the heat sink40forms a heat radiation path between the heat conduction chip92and the heat sink40. The cover60is an example of second heat radiation means and a second heat radiator.

When the large current for driving the motor flows in the power MOS31, the power MOS31generates the heat. The heat is conducted from the power MOS31to the resin board20, the heat radiation grease52, the large-hardness insulating heat-radiation sheet53and the heat sink40, and radiated to the air, as shown by the arrow “G” inFIG. 13. At the same time, the heat is also conducted from the power MOS31, the through-hole via81, the outerlayer copper foils82,83, the innerlayer copper foils84,85, the heat conduction chips91,92, and the cover60or the heat sink40, and is radiated to the air.

In connection with the ninth embodiment, let Tk denote a thermal resistance of the cover. In the ninth embodiment, the thermal resistance of the heat radiation paths for radiating the heat generated by the power MOS31is given as “(Tp2+Tg2)+Tz+Th//Tp2+Td//Td+Tg+Tk”. Therefore, the ninth embodiment improves the heat radiation performance compared to the eighth embodiment, because the electronic control unit9of the ninth embodiment has three heat radiation paths for radiating the heat generated by the power MOS31.

Tenth Embodiment

An electronic control unit10of a tenth embodiment is illustrated below with reference toFIG. 14. In the tenth embodiment, the rear surface (i.e., a heat sink side) of the resin board20has a concave depression22concaved toward the power MOS31. The concave depression22is filled with a heat radiation grease52. The concave depression22creates a space between the resin board20and the heat sink40, and insulates the resin board20and the heat sink40from each other. Hence, the insulating heat-radiation sheet is omissible in the electronic control unit10of the tenth embodiment. When the large current for driving the motor flows in the power MOS31, the heat generated by the power MOS31is conducted from the power MOS31to the resin board20, the heat radiation grease52and the heat sink40, and radiated to the air, as shown by the arrow “K” inFIG. 14.

In the tenth embodiment, the heat radiation path for conducting and radiating the heat generated by the power MOS31is given as “Tp+Tz+Th”. The electronic control unit10of the tenth embodiment has a short heat radiation path for radiating the heat generated by the power MOS31, and thus improves the heat radiation performance, compared to the sixth embodiment. Moreover, since an insulating heat-radiation sheet for preventing electrical connection between the resin board20and the heat sink40is omissible in the tenth embodiment, the tenth embodiment can reduce man-hours in manufacturing or assembling.

Eleventh Embodiment

An electronic control unit11of an eleventh embodiment is illustrated below with reference toFIG. 15. In the eleventh embodiment, an small-hardness insulating heat-radiation sheet54is disposed between the resin board20and the heat sink40. For example, the small-hardness insulating heat-radiation sheet54contains silicon, has high flexibility, causes a high insulation and has and a small thermal resistance. Due to the use of the small-hardness insulating heat-radiation sheet54, the resin board20, the low-hardness insulating heat-radiation sheet54and the heat sink40are tightly attached to each other. Hence, a heat radiation grease is omissible in the eleventh embodiment. When the large current for driving the motor flows through the power MOS31, the heat generated by the power MOS31is conducted from the power MOS31to the resin board20, the small-hardness insulating heat-radiation sheet54and the heat sink40, and radiated to the air, as shown by the arrow “L” inFIG. 15. The small-hardness heat-radiation sheet54is an example of first heat conduction means or a first heat conductor.

In the eleventh embodiment, the heat radiation path for conducting and radiating the heat generated by the power MOS31is given as “Tp+Tz+Th”. In the electronic control unit11of the eleventh embodiment, the heat radiation path for conducting and radiating the heat generated by the power MOS31can be shortened, and the heat radiation performance can be improved. Moreover, since a heat radiation grease is omissible in the eleventh embodiment, it is possible to reduce man-hours in manufacturing and assembling.

Twelfth Embodiment

An electronic control unit12according to a twelfth embodiment is illustrated below with reference toFIG. 16. In the twelfth embodiment, the cover60has a lock part62defining an opening at a heat sink side end part of the cover60. The heat sink side end part is an end part to be connected with the heat sink40when the cover60and the heat sink40are assembled together. An end part of the heat sink40has a projection46corresponding to the lock part62. When the projection46of the heat sink40is fit into the opening of the lock part62, the cover60and the heat sink40are fixed to each other by elastic force of the lock part62.

In the electronic control unit12of the twelfth embodiment, the cover60and the heat sink40are fixed to each other by snap-fitting. Thus, a crimping process, which is employed in the first embodiment, is omissible in the twelfth embodiment. The twelfth embodiment can reduce man-hour in manufacturing or assembling. Moreover, since the heat sink40and the cover are connected with each other, it is possible to improve the heat radiation performance.

Thirteenth Embodiment

An electronic control unit13of a thirteenth embodiment is illustrated below with reference toFIG. 17. In the thirteenth embodiment, the cover60includes a flange63defining therein a hole. The flange63is located at an end part of the cover60. The heat sink40also has a flange47defining therein a hole so that the flange47corresponds to the flange63. The flange47is located at an end of the heat sink40. The electronic control unit13is attached to a body103of a vehicle equipped with the electric power-assisted steering system, in such way that: the flange63of the cover60is fitted to the flange47of the heat sink40; and a bolt105or a screw105is inserted into an attachment opening104of the body103of the vehicle.

In the thirteenth embodiment, the cover60, the heat sink40and the body103of the vehicle are fastened together when the electronic control unit13is attached to the body103of the vehicle. Thus, the thirteenth embodiment can reduce man-hour for connection of the cover60and the heat sink40, compared to the twelfth embodiment.

Fourteenth Embodiment

An electronic control unit14of a fourteenth embodiment is illustrated below with reference toFIG. 18. In the fourteenth embodiment, the cover60, the resin board20and the heat sink40are fixed by using screws251to255. The cover60has screw holes651to655, and touch parts661to665. The touch parts661to665are located in the vicinity of the screw holes651to655and are concaved toward the resin board20.

In the fourteenth embodiment, the cover60, the resin board20, the insulating heat-radiation sheet51, the heat radiation grease52and the heat sink40can be assembled at one time. Thus, the fourteenth embodiment can reduce man-hour compared to the twelfth embodiment. Moreover, since a heat radiation path between the cover60, the resin board20and the heat sink40is formed by the screws251to255, it is possible to improve the heat radiation performance.

A structure of the seventh embodiment is applicable to the present embodiment. For example, as shown inFIG. 25, the resin board20may include the innerlayer copper foil84,85, which an example of a heat conduction layer, heat conduction path means, and a heat conduction path provider. The innerlayer copper foil84,85may extend in a direction perpendicular to a thickness direction of the resin board20. The innerlayer copper foil84,85is connected to the screw252and the screw255, so that the heat is conductable between the innerlayer copper foil84,85and the screws252,255. It is noted that, as can be understood fromFIGS. 18 and 25, a corner part of the cover60, a corner part of the resin board20and a corner part of the heat sink40are screwed together with the screw252, and a center part of the cover60, a center part of the resin board20and a center part of the heat sink40are screwed together with the screw255.

In similar ways, a structure of the seventh embodiment is also applicable to the below fifteenth and sixteenth embodiments.

Fifteenth Embodiment

An electronic control unit15of a fifteenth embodiment is illustrated below with reference toFIG. 19. In the fifteenth embodiment, a heat radiation grease71is applied to the power MOS31and a part of the front surface of the resin board20. This structure increases an area of the part for radiating the heat generated by the power MOS31, and thus improves the heat radiation performance. The heat radiation grease may be further applied to an electronic component other than the power MOS and the vicinity of the electronic component that is mounted on the resin board and configured to generate heat when being energized. According to this structure, it is possible to further improve the heat radiation performance.

Sixteenth Embodiment

An electronic control unit16of a sixteenth embodiment is illustrated below with reference toFIG. 20. In the sixteenth embodiment, a heat radiation grease71and a small-hardness insulating heat-radiation sheet72are disposed between the cover60and the power MOS31. The heat radiation grease and the small-hardness insulating heat-radiation sheet72absorb a tolerance of a clearance between the cover60and the power MOS31, and form a heat radiation path for conducting the heat generated by the power MOS31to the cover60. Therefore, in the sixteenth embodiment, it is possible to radiate the heat generated by the power MOS31in a high efficient manner. As a result, it is possible to improve the heat radiation performance of the electronic control unit16.

Other Embodiments

The above-described embodiments can be modified in various ways, examples of which are described below.

In the above embodiments, explanation is given on an electronic control unit for controlling a motor of an electric power-assisted steering system. However, the present invention may be applied to, for example, an electronic control unit for controlling timing of opening and closing a valve of a VVT (Variable Valve Timing) apparatus or the like. In the above embodiments, a FR-4 wiring board is described as an example of the resin board containing resin. Alternatively, the resin board may be a rigid wiring board such as FR-5, CEM-3 and the like, a flexible wiring board, or the like. In the above embodiments, a power MOS is described as an example of a power device. Alternatively, a power device may be a FET (Field Effect Transistor), a SBD (Schottky Barrier Diode), an IGBT (Insulated Gate Bipolar Transistor) or the like

According to a first aspect of the present disclosure, there is provided an electronic control unit including: a resin board; a power device that is surface-mounted on the resin board; a microcomputer that is configured to control the power device; first heat radiation means for radiating heat, the first heat radiation means being disposed on an opposite side of the resin board from the power device; and first heat conduction means for conducting the heat generated by the power device to the first heat radiation means.

According to the above electronic control unit, since a heat radiation path for conducting and radiation the heat generated by the power device is formed by the first heat conduction means and the first heat radiation means, it is possible to improve a heat radiation performance of the electronic control unit. Moreover, the above configuration can simplify a structure of the electronic control unit, can reduce the size of the electronic control unit, and can reduce man-hour in assembling or manufacturing the electronic control unit.

The above electronic control unit may be configured such that: the first heat conduction means includes at least one of an insulating heat-radiation sheet and a heat radiation grease. According to this configuration, since the heat radiation grease can fill a space between the insulating heat-radiation sheet and the first heat radiation means, it is possible to decrease a thermal resistance of a heat radiation path for conducting the heat generated by the power device to the first heat radiation means.

The above electronic control unit may be configured such that: the resin board has an opening; the first heat conduction means is disposed in the opening of the resin board; and the first heat conduction means is in direct connect with the power device and the first heat radiation means. According to this configuration, the heat generated by the power device can be conducted to the first heat radiation means without passing through the resin board. Therefore, it is possible to shorten the heat radiation path, improve the heat radiation performance and reduce the size of the electronic control unit.

The above electronic control unit may further include: second heat radiation means for radiating the heat generated by the power device, the second heat radiation means being disposed on an opposite side of the power device from the resin board; and second heat conduction means for conducting the heat generated by the power device to the second heat radiation means. According to this configuration, the heat generated by the power device can be connected to the first heat radiation means and the second heat radiation means. Therefore, it is possible to form two heat radiation paths and thus improve the heat radiation performance.

The above electronic control unit may be configured such that: the second heat conduction means includes at least one of a heat radiation grease and a small-hardness insulating heat radiation sheet; and the at least one of the heat radiation grease and the small-hardness insulating heat-radiation sheet is disposed between the second heat radiation means and the power device. According to this configuration, the heat radiation grease and the small-hardness insulating heat-radiation sheet can advantageously absorb a tolerance of a clearance between the power device and the second heat radiation means, and can advantageously conduct the heat generated by the power device to the second heat radiation means.

The above electronic control unit may further include heat conduction path means for providing a heat conduction path in an inside of the resin board, the heat conduction path conducting the heat generated by the power device. According to this configuration, it is possible to decrease a thermal resistance of the resin board and improve the heat radiation performance.

The above electronic control unit may be configured such that: the heat conduction path means includes a through-hole via of the resin board; and the through-hole via penetrates the resin board in a thickness direction of the resin board, and is located directly below the power device. According to this configuration, a path for conducting the heat generated by the power device can be formed in the resin board at low cost.

The above electronic control unit may be configured such that: the first heat conduction means includes the heat radiation grease; and the through-hole via is filled with the heat radiation grease. According to this configuration, the heat radiation grease can be in contact with the power device. Therefore, it is possible to advantageously reduce a thermal resistance of a heat radiation path between the power device and the first heat radiation means.

The above electronic control unit may be configured such that: the heat conduction path means further includes a heat conduction layer; the heat conduction layer is connected with an outer wall of the through-hole via and extends in an extension direction of the resin board. According to this configuration, it is possible to advantageously conduct the heat generated by the power device in the extension direction of the resin board.

The above electronic control unit may be configured such that: the heat conduction layer is connected with a screw that fixes the resin board and the first heat radiation means. According to this configuration, it is possible to advantageously radiate the heat, the heat conducting through the heat conduction layer, from the outer wall of the screw to air.

The above electronic control unit may further include a heat conduction chip that is disposed on the resin board, wherein: the heat conduction chip has a first end and a second end; the first end of the heat conduction chip is connected with the heat conduction layer; and the second end of the heat conduction chip is protruded from a surface of the resin board in the thickness direction of the resin board. According to this configuration, it is possible to radiate the heat, the heat conducting thorough the heat conduction layer, to an outside of the resin board in a high efficient manner.

The above electronic control unit may be configured such that: the first heat conduction means includes a heat radiation grease that fills a space between the heat conduction chip and the first heat radiation means. According to this configuration, the heat generated by the power device can be conducted from the resin board to the first heat radiation means via the heat radiation chip and the heat radiation grease. The above electronic control unit may be configured such that: the second heat conduction means includes a heat radiation grease that fills a space between the heat conduction chip and the second heat radiation means. According to this configuration, the heat generated by the power device can be conducted from resin board to the second heat radiation means via the heat conduction chip and the heat radiation grease. Therefore, it is possible to decrease a thermal resistance of a heat radiation path between the power device and the first heat radiation means, and it is possible to improve the heat radiation performance.

The above electronic control unit may be configured such that: the resin board has a concave depression that is disposed on a same side of the resin board as the first heat radiation means is; the first heat conduction means includes the heat radiation grease; and the concave depression of the resin board is filled with the heat radiation grease. According to this configuration, because of the concave depression on the resin board, it is possible to insulate the resin board and the first heat radiation means from each other. Therefore, attachment of the insulating heat radiation sheet is omissible, and it is possible to reduce man-hour in assembling or manufacturing.

The above electronic control unit may be configured such that: the second heat radiation means includes a cover constructed to protect the power device; the first heat radiation means includes a heat sink; and the cover is connected with an end of the heat sink. According to this configuration, the heat is conductable between the first heat radiation means and the second heat radiation means. It is therefore possible to improve the heat radiation performance.

The above electronic control unit may be configured such that: the cover is connected with the end of the heat sink by snap-fitting. According to this configuration, it is possible to advantageously reduce man-hour in connecting between the first heat radiation means and the second heat radiation means.

The above electronic control unit may be configured such that: the electronic control unit is a component of an electric power-assisted steering system equipped in a vehicle; and the cover, the heat sink and a body of the vehicle are tighten together by using a screw. According to this configuration, it is possible to advantageously reduce man-hour in connecting between the first heat radiation means and the second heat radiation means.

The above electronic control unit may be configured such that: the cover, the resin board and the heat sink are tighten together by using a screw. According to this configuration, it is possible to advantageously reduce man-hour in connecting between the first heat radiation means and the second heat radiation means. Moreover, it is possible to reduce a thermal resistance of the first heat radiation means, the resin board and the second heat radiation means, and it is possible to improve the heat radiation performance.

The above electronic control unit may further include a heat generating component mounted on the resin board, wherein the second heat radiation means is disposed on an opposite side of the heat generating component from the resin board. According to this configuration, it is possible to form a heat radiation path for the heat generating component other than the power device, and it is possible to improve a performance of output of the electronic control unit.

According to a second aspect of the present disclosure, a method of manufacturing an electronic control unit is provided. The method includes: mounting an electronic component on a surface of a resin board, the electronic component including a power device; testing an operating condition of the electronic component at a predetermined high temperature or a predetermined low temperature after mounting the electronic component on the surface of the resin board, wherein the predetermined low temperature is lower than the predetermined high temperature; and providing heat conduction means and heat radiation means on an opposite side of the resin board from the power device after testing the operating condition of the electronic component.

According to the above method, since the operating condition of the electronic component is tested before the first heat radiation means is attached, an heat energy is not applied to the heat radiation means in testing the electronic component. It is thus possible to perform a high/low temperature test in a short time of period and in an energy-saving manner. It is therefore possible to reduce man-hour in assembling or manufacturing the electronic control unit.

While the invention has been described above with reference to various embodiments thereof, it is to be understood that the invention is not limited to the above described embodiments and constructions. The invention is intended to cover various modifications and equivalent arrangements. In addition, while the various combinations and configurations described above are contemplated as embodying the invention, other combinations and configurations, including more, less or only a single element, are also contemplated as being within the scope of embodiments.