Electronic control device

Abstract

The purpose of the present invention is to provide an electronic control device configured so that it is possible to suppress cracking of a solder resist in a board area having no land for signal transmission. This electronic control device (20) comprises: a circuit board (300) on which a conductor to which an electronic component is connected is disposed; and a solder resist (3105) formed on the surface of the circuit board. A dummy land (3111) is disposed between a substrate (3104) and a resist re-entrant angle section (3106) where two linear portions of a resist open end (3117) of the solder resist mutually intersect so as to have an interior angle greater than 180°, said dummy land having a thermal expansion coefficient between the thermal expansion coefficient of the circuit board and that of the solder resist.

Description

Electronic control unit

[0001] The present invention relates to an electronic control device that can prevent cracks in solder resist caused by changes in the environmental temperature of an electronic circuit board.

[0002] In internal combustion engines, the mixture ratio of air and gasoline inside the engine is important for improving fuel efficiency. The ECU controls the mixture ratio based on the intake air volume measured by a thermal air flow meter. We are currently investigating ways to reduce the cost of such air flow meters. For example, we are considering using a standard four-layer electronic circuit board or an inexpensive consumer solder resist (e.g., with a glass transition temperature of 100°C or less). However, on-board measuring instruments must be resistant to changes in environmental temperature. This means that there must be no deviations in the output characteristics of the measuring instruments due to changes in environmental temperature, and no communication problems due to signal disconnections caused by corrosion of the conductors on the circuit boards used in the measuring instruments over long periods of use.

[0003] However, with current low-cost boards, there is a problem where cracks occur in the solder resist during durability tests under environmental temperature changes.

[0004] Japanese Patent Application Laid-Open No. 2006-124462 (Patent Document 1) describes a technique for suppressing cracks in solder resist. The technique describes the following: "An electronic device includes a circuit board on which a plurality of electronic components are mounted and on which a solder resist is provided on a surface, and terminals passing through through holes in the circuit board are soldered to annular lands surrounding the through holes, the lands having an over-resist area including at least the periphery of the land and overlaid with the solder resist, and an exposed land area located closer to the through hole than the over-resist area and exposing the land surface around the through hole, the outer edge of the exposed land area being shaped so that it is not similar to the outer edge of the land area due to the over-resist area."

[0005] JP 2023-11102 A

[0006] The technology described in Patent Document 1 provides a method for preventing cracks in solder resist that open up in the land area during soldering to lands connected to signal wiring via through-holes. However, in electronic circuit boards, not only do solder resists open up in areas where there are no lands, but openings in the solder resist can also occur in areas where there are no lands. If cracks occur in the solder resist in these areas, they can reach nearby signal conductors, causing corrosion and disconnection. Therefore, it is believed that the technology described in this document has room for improvement in preventing cracks in solder resist in areas where there are no lands.

[0007] In view of the above circumstances, an object of the present invention is to provide an electronic control device that can suppress the occurrence of cracks in the solder resist in areas where there are no lands for signal transmission.

[0008] A brief summary of representative aspects of the inventions of the present disclosure is as follows.

[0009] One idea of ​​the present invention is that a solder resist for protecting the conductors is placed on a circuit board on which electronic components are arranged and the components are connected by conductors, and the solder resist also covers the surface of the circuit board in areas where there are no conductors, and also has a resist recessed corner, which is a part where two straight lines at the open end of the resist intersect and form an interior angle greater than 180 degrees, and a dummy land of a conductor that does not connect to other conductors in signals is placed between the resist recessed corner and the base material of the circuit board, and the thermal expansion coefficient of the dummy land is between the thermal expansion coefficients of the base material and the solder resist, and the resist recessed corner and the dummy land are overlapped.

[0010] According to the electronic control device of the present invention, in a resist recessed corner, which is a portion where two straight lines at the open end of the solder resist formed on the substrate of an electronic circuit board intersect to form an interior angle greater than 180 degrees, a dummy land is disposed between the solder resist and the substrate of the circuit board, thereby reducing thermal stress generated in the resist recessed corner and preventing cracks from occurring in the solder resist. In other words, durability against environmental temperature changes can be improved, and the use of inexpensive consumer solder resist can reduce the cost of the air flow measuring device.

[0011] 1 is a schematic diagram of an internal combustion engine control system using an electronic control device according to a first embodiment. FIG. 1 is a front view of an electronic control device according to a first embodiment. FIG. 2 is a right side view of an electronic control device according to a first embodiment. FIG. 3 is a rear view of an electronic control device according to a first embodiment with the cover removed. FIG. 4 is a front view of a circuit board of an electronic control device according to a first embodiment. FIG. 5 is a diagram of a solder resist configuration of a circuit board of an electronic control device according to a first embodiment. FIG. 6 is a plan view of a conventional resist recessed corner portion. FIG. 7 is a cross-sectional view of a resist recessed corner portion of a conventional circuit board. FIG. 8 is a diagram showing the results of a thermal stress analysis of a resist recessed corner portion of a conventional circuit board. FIG. 9 is a diagram showing the thermal expansion coefficient difference sensitivity of thermal stress for a conventional circuit board and a resist. FIG. 10 is a plan view of a resist recessed corner portion of an electronic control device according to a first embodiment. FIG. 11 is a cross-sectional view of a resist recessed corner portion of an electronic control device according to a first embodiment. FIG. 12 is a diagram showing the results of a thermal stress analysis of a resist recessed corner portion of an electronic control device according to a second embodiment. FIG. 13 is a diagram showing the results of a thermal stress analysis of a resist recessed corner portion of an electronic control device according to a third embodiment. FIG. 14 is a diagram showing the results of a thermal stress analysis of a resist recessed corner portion of an electronic control device according to a third embodiment.

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In all drawings used to explain the embodiments, the same components are generally designated by the same reference numerals, and repeated explanations thereof will be omitted. The present invention should not be interpreted as being limited to the description of the embodiments shown below. Those skilled in the art will readily understand that the specific configuration can be changed within the scope of the idea or intent of the present invention.

[0013] The designations "first," "second," "third," etc. in this specification are used to identify components and do not necessarily limit the number or order. Furthermore, numbers used to identify components are used in different contexts, and numbers used in one context do not necessarily indicate the same configuration in another context. Furthermore, this does not prevent a component identified by a certain number from also serving the function of a component identified by another number.

[0014] The position, size, shape, range, etc. of each component shown in the drawings, etc. may not represent the actual position, size, shape, range, etc. in order to facilitate understanding of the invention. Therefore, the present invention is not necessarily limited to the position, size, shape, range, etc. disclosed in the drawings, etc. In this specification, components expressed in the singular include the plural unless otherwise clearly indicated in the context.

[0015] In the following embodiment, the circuit board of the electronic control device is described as a sensor board, but the present invention is not limited to this configuration and other boards may be used. The electronic control device of this embodiment is used in a thermal air flow meter 20 of an automobile, but it can be particularly effective in environments where temperatures are severe, such as automobiles.

[0016] 1 is a schematic diagram of an internal combustion engine control system using an electronic control device according to Embodiment 1. The internal combustion engine control system 1 is a control system for an internal combustion engine in which air, which is a measurement target gas 2, is drawn in through an air cleaner 21 based on the operation of an internal combustion engine 10 including an engine cylinder 11 and an engine piston 12.

[0017] The measurement target gas 2 drawn in from the air cleaner 21 is guided to the combustion chamber 11 a of the engine cylinder 11 via the intake body 22 , the throttle body 23 and the intake manifold 24 .

[0018] The measurement gas 2 introduced into the combustion chamber 11a has a physical quantity detected by the thermal air flow meter 20 in the main flow path 22a, and is mixed with fuel supplied from the fuel injection valve 14 based on the detected physical quantity to form an air-fuel mixture, which is then introduced into the combustion chamber 11a. The thermal air flow meter 20 in this embodiment corresponds to an electronic control device in the claims.

[0019] The air-fuel mixture introduced into the combustion chamber 11a is combusted explosively by the spark ignition of the spark plug 13, generating mechanical energy. The gas after combustion is then introduced into the exhaust pipe 16a through the exhaust valve 16, and is discharged as exhaust gas 3 from the exhaust pipe 16a to the outside of the vehicle.

[0020] The flow rate of the measurement gas 2 introduced into the combustion chamber 11a is controlled by a throttle valve 25, the opening of which changes based on the operation of an accelerator pedal. Furthermore, the amount of fuel supply is controlled based on the flow rate of the measurement gas 2 introduced into the combustion chamber 11a. Therefore, the driver can change the opening of the throttle valve 25 by operating the accelerator pedal, thereby controlling the flow rate of the measurement gas 2 introduced into the combustion chamber 11a and changing the mechanical energy generated in the internal combustion engine.

[0021] The thermal air flow meter 20 is a sensor device that detects the air flow rate of the internal combustion engine. The thermal air flow meter 20 detects physical quantities such as the flow rate, temperature, humidity, and pressure of the measurement target gas 2 that is taken in from the air cleaner 21 and flows through the main flow path 22a (in this embodiment, the flow path inside the intake body 22), and outputs these physical quantities as electrical signals to the control device 4.

[0022] The throttle angle sensor 26 is a sensor that detects the opening of the throttle valve 25 and inputs the detected value as an electric signal to the control device 4. The rotation angle sensor 17 is a sensor that detects the positions and states of the engine piston 12, intake valve 15, and exhaust valve 16 of the internal combustion engine, as well as the rotation speed of the internal combustion engine, and inputs the detected value as an electric signal to the control device 4. The oxygen sensor 28 is a sensor that detects the mixture ratio of the fuel amount and the air amount from the state of the exhaust gas 3 and inputs the detected value as an electric signal to the control device 4.

[0023] The control device 4 is a device that calculates the fuel injection amount and ignition timing based on the detection values ​​of the thermal air flow meter 20, the throttle angle sensor 26, the rotation angle sensor 17, and the oxygen sensor 28. The amount of fuel supplied from the fuel injection valve 14 and the ignition timing of ignition by the spark plug 13 are controlled based on the calculation results of the control device 4. Furthermore, in order to control the rotation speed of the internal combustion engine in an idle operating state, the control device 4 controls the amount of air bypassing the throttle valve 25 using the idle air control valve 27 when the internal combustion engine is in an idle operating state. Therefore, the fuel supply amount and ignition timing, which are the main control variables of the internal combustion engine, are calculated based on the detection values ​​of the thermal air flow meter 20.

[0024] <Thermal air flow meter 20> Fig. 2 is a front view of the thermal air flow meter 20 according to this embodiment. Fig. 3 is a right side view of the thermal air flow meter 20 according to this embodiment. Fig. 4 is a rear view of the thermal air flow meter according to this embodiment with the cover 120 removed. Note that, hereinafter, the measurement target gas 2 flows through the main flow path 22a in one direction indicated by an arrow, and the description will be made regarding the upstream side and downstream side based on the direction of the arrow.

[0025] The thermal air flow meter 20 has a flange portion 111 which is a portion for fixing to the intake body 22, a connector portion 112 which is a portion for electrically connecting to an external device, and a measuring portion 113 which is a portion for measuring the physical quantity of the measured gas 2.

[0026] The flange portion 111 is, for example, a plate-like portion having a predetermined thickness and a generally rectangular shape in a plan view, and has a pair of fixing holes formed at diagonally opposite corners. A through-hole is formed in the center of the fixing holes, and the thermal air flow meter 20 is fixed to the intake body 22 by a screw inserted into the through-hole.

[0027] 3, the connector portion 112 is provided on the upper part of the flange portion 111 and includes, for example, a plurality of (four in this embodiment) external input / output terminals 147 and a correction terminal 148. The plurality of external input / output terminals 147 include terminals for outputting physical quantities such as flow rate and temperature, which are measurement results of the thermal air flow meter 20, and power supply terminals for supplying DC power for operating the thermal air flow meter 20. The correction terminal 148 is a terminal used for storing a correction value in the thermal air flow meter 20.

[0028] 4, the housing 100 is provided with a sub-flow passage groove 150 that connects the sub-flow passage inlet 131, the first outlet 132, and the second outlet 133, and a circuit chamber 101. The circuit chamber 101 also contains a circuit board 300 that is fixed to the recess 135.

[0029] The sub-flow groove 150 is a groove for passing the measurement target gas 2 through the measuring unit 113 to detect the physical quantity. The sub-flow groove 150 includes a first sub-flow groove 151 that connects the sub-flow inlet 131 and the first outlet 132, and a second sub-flow groove 152 that branches off from the first sub-flow groove 151, makes a detour upward, then bends downward, and connects to the second outlet 133.

[0030] <Circuit Board Mounting> Figure 5 is a front view of a circuit board 300 according to this embodiment. The thermal air flow meter 20 includes a circuit board 300 on which conductors to which electronic components are connected are arranged, and a solder resist 3000 formed on the surface of the circuit board 300. Electronic components mounted on the circuit board 300 include, for example, a flow sensor 140, a temperature sensor 160, a pressure sensor 170, and a humidity sensor 180. The flow sensor 140 has a chip package equipped with a sensor device that detects the air flow rate of an internal combustion engine.

[0031] The temperature sensor 160 is, for example, a chip-type temperature sensor mounted on the circuit board 300. For example, as shown in Fig. 5 , the temperature sensor 160 is disposed at the tip of an extension portion 301 of the circuit board 300 that extends toward the tip of the measurement portion 113 in the protruding direction of the measurement portion 113. The temperature sensor 160 is disposed in the temperature measurement passage 190 of the measurement portion 113 shown in Figs. 2 and 4 , and measures the temperature of the measurement target gas 2 taken into the temperature measurement passage 190 from the main passage 22.

[0032] 4 and 5 , the pressure sensor 170 is mounted on the surface of the circuit board 300 and disposed in the circuit chamber 101. The circuit chamber 101 is connected to a folded portion of the second sub-passage 134e that curves in a U-shape near the flange portion 111. This makes it possible to measure the pressure of the measurement target gas 2 taken into the sub-passage 134 by the pressure sensor 170 disposed in the circuit chamber 101.

[0033] 4, the humidity sensor 180 is mounted on the surface of the circuit board 300 and disposed in a partitioned area closer to the tip end of the measuring unit 113 than the circuit chamber 101. This partitioned area is in communication with, for example, the second sub-passage 134e of the sub-passage 134. This allows the humidity sensor 180 to detect the humidity of the measurement target gas 2 taken into the sub-passage 134.

[0034] 6 is a diagram showing the configuration of a circuit board 300 and the solder resist covering the surface of the board. The solder resist 3000 is a protective film that covers the surface of the board to protect the signal wiring from external factors (scratches and oxidation) and to prevent electrical shorts between adjacent signal lines, and is formed, for example, by a coating film.

[0035] Lands (conductors) for soldering the flow sensor (chip package) 140, temperature sensor 160, pressure sensor 170, humidity sensor 180, etc., and signal wiring (conductors) connected to the lands are provided on the surface of the circuit board 300. The solder resist 3000 is formed in a layer so as to cover a wider area of ​​the surface of the circuit board 300, including the lands and signal wiring. In other words, it is provided so as to cover even the board areas where there are no lands for signal transmission.

[0036] The solder resist 3000 is formed over almost the entire surface of the circuit board 300, and has a polygonal shape in plan view that follows the outline of the circuit board 300. On the surface of the circuit board 300, there are formed a solder resist protected portion 311, which is an area that is covered and protected by the solder resist 3000, and a solder resist unprotected portion 312, which is an area that is not covered by the solder resist 3000 and in which the base material is exposed on the surface of the circuit board 300.

[0037] Solder resist openings 3001 are provided in the solder resist protection portion 311 of the solder resist 3000 so that the lands (conductors) for solder connection are exposed on the surface. The solder resist unprotected portion 312 is an area where no sensors or signal wiring are arranged, and does not need to be protected by the solder resist 3000, so it is not covered with the solder resist 3000.

[0038] At the boundary between solder resist protected portion 311 and solder resist unprotected portion 312, two straight line portions of resist open end 3117 of solder resist 3000 intersect to form resist recessed corner portion 3003 having an interior angle greater than 180 degrees. Resist open end 3117 constitutes part of the outer edge of solder resist 3000, and does not include any portion that constitutes a closed curve such as solder resist opening 3001.

[0039] In this embodiment, the resist recessed corner 3003 has an interior angle of 270 degrees. The resist recessed corner 3003 is chamfered into an arc shape with a predetermined curvature. Thermal stress caused by changes in the environmental temperature is concentrated in the resist recessed corner 3003, which may cause cracks in the solder resist 3000.

[0040] <Structure for Countering Resist Cracks> Before describing the configuration of this embodiment for preventing the above-described resist cracks, a conventional configuration of a resist recessed corner where resist cracks occur and the mechanism by which resist cracks occur will be described.

[0041] Fig. 7 is a diagram of a conventional configuration. Fig. 8 is its cross-sectional view. Circuit board 300' is a typical four-layer board, and has conductor 3007, substrates 3004 and 3009, and solder resists 3005 and 3010 arranged symmetrically above and below core 3008. Note that circuit board 300' also has signal wiring (not shown) arranged between substrate 3004 and solder resist 3005, and between substrate 3009 and solder resist 3010, but Fig. 7 shows areas on the top and bottom layers where there are no conductor wiring signals.

[0042] Changes in the environmental temperature cause thermal stress to concentrate in resist recessed corner 3006. Due to the difference in thermal expansion coefficient (45 ppm / °C) between the thermal expansion coefficient of substrate 3004 (11 ppm / °C) and the thermal expansion coefficient of solder resist 3005 (57 ppm / °C), base material 3004 and solder resist 3005 are thermally deformed in directions along the two linear portions of resist open end 3117 (X direction and Y direction shown in FIG. 7 ), respectively, and stress is thought to concentrate in resist recessed corner 3006.

[0043] Considering that the cause of cracks occurring in the solder resist 3005 is thermal stress acting on the resist recessed corner 3006, the thermal stress value for the conventional structure was determined by thermal stress analysis. Figure 9 shows the results of a thermal stress analysis using a conventional structure model of the resist recessed corner 3006. As a result of the analysis, the maximum thermal stress occurring in the resist recessed corner 3006 was 133.6 MPa.

[0044] 10 is a diagram showing the sensitivity of concentrated thermal stress at a resist recessed corner to the difference in thermal expansion coefficient. As shown in FIG. 10, it can be seen that the smaller the difference in thermal expansion coefficients between the substrate 3004 and the solder resist 3005, the smaller the thermal stress acting on the resist recessed corner 3006. In other words, a method for reducing the thermal stress at the resist recessed corner 3006 is to reduce the difference in thermal expansion coefficients between the substrate 3004 or another component and the solder resist 3005.

[0045] For example, one solution would be to select a resist material for solder resist 3000 with a thermal expansion coefficient smaller than the current 57 ppm / °C. However, resist materials with a small thermal expansion coefficient are generally called high-durability resists and have the disadvantage of being expensive. Therefore, this disclosure proposes a method from a different perspective, in which a separate material, which replaces the substrate, is inserted between solder resist 3005 and substrate 3004.

[0046] FIG. 11 is a plan view showing the configuration of a resist recessed corner portion of the electronic control device according to the first embodiment, and FIG. 12 is a cross-sectional view thereof.

[0047] Circuit board 300 of this embodiment is a general four-layer board similar to the conventional structure shown in Fig. 8, and has conductor 3107, substrates 3104 and 3109, and solder resists 3105 and 3110 arranged symmetrically above and below core 3108. In circuit board 300, signal wiring (not shown) is also arranged between substrate 3104 and solder resist 3105, and between substrate 3109 and solder resist 3110, but Fig. 12 shows the configuration of the circuit board in areas where there are no conductor wiring signals on the top and bottom layers.

[0048] In this embodiment, as in the conventional structure, the surface of the substrate 3104 is partitioned into a solder resist protected portion 311 where the surface of the substrate 3104 is covered with solder resist 3105, and a solder resist unprotected portion 312 where the surface of the substrate 3004 is exposed and not covered with solder resist 3005. At the boundary between the solder resist protected portion 311 and the solder resist unprotected portion 312, there is a resist recessed corner portion 3106 where two straight line portions of the resist open end 3117 intersect.

[0049] In this resist recessed corner 3106, a dummy land (conductor) 3111 exists between the solder resist 3105 and the substrate 3104. In other words, the dummy land (conductor) 3111 is provided on the surface of the substrate 3104 so as to be interposed between the resist recessed corner 3106 of the solder resist 3105 and the substrate 3104. The dummy land 3111 is not connected to any sensor, signal wiring, or the like, and is independently disposed on the surface of the substrate 3004. The dummy land 3111 is made of the same material as the lands and signal wiring connected to, for example, a sensor, and is formed simultaneously when the lands and signal wiring are formed on the substrate 3104. The dummy land 3111 has the same thermal expansion coefficient as the lands and signal wiring, and has a value between the thermal expansion coefficients of the substrate 3004 and the solder resist 3005.

[0050] The dummy land 3111 has an L-shape and has a structure (overlap structure) in which it overlaps with the solder resist 3105 at the resist recessed corner 3106. At the resist recessed corner 3106, the overlap amount (overlapping amount) between the dummy land 3111 and the resist open end 3117 of the solder resist 3105 is preferably 25 μm or more and 500 μm or less, and more preferably about 50 μm. One side of the L-shape of the dummy land 3111 along the resist open end has a length (e.g., 200 μm) that is equal to or greater than the radius of curvature of the recessed corner 3106 where two straight line portions of the resist open end 3117 intersect.

[0051] The solder resist 3105 is configured to overlap the dummy land 3111 at the resist recessed corner 3106, so that it comes into contact with the dummy land 3111. This allows the difference in thermal expansion between the solder resist 3105's thermal expansion coefficient (57 ppm / °C) and the dummy land 3111's thermal expansion coefficient (17 ppm / °C) to be kept to 39 ppm / °C, lower than the conventional 45 ppm / °C, thereby reducing thermal stress due to changes in environmental temperature.

[0052] 13 shows the results of a thermal stress analysis of the resist recessed corner 3106 using the structural model of this embodiment. The analysis results show that the maximum thermal stress generated in the resist recessed corner 3106 is 101.5 MPa, a significant reduction from the conventional 133.6 MPa. In other words, compared to the conventional structure, it is possible to reduce the thermal stress in the resist recessed corner 3106, and it can be said that it is possible to prevent cracks from occurring in the solder resist 3105.

[0053] 10 shows the sensitivity of the thermal expansion coefficient difference to the concentrated thermal stress on the resist recessed corner 3016, and it can be seen that the dummy land configuration of this embodiment is more effective in reducing thermal stress than a method using a solder resist with a small thermal expansion coefficient. This is thought to be because, with the dummy land configuration, the area of ​​contact with the solder resist 3105 is smaller for the dummy land 3111 than for the base material 3004 of the conventional method, and the amount of displacement at the contact point between the solder resist 3105 and the dummy land 3111 in response to changes in environmental temperature is smaller, which in turn reduces the thermal stress.

[0054] <Effects> As described above, dummy land (conductor) 3111 is disposed and interposed between resist recessed corner 3106 of solder resist 3105 and base material 3104, dummy land 3111 is L-shaped to fit the shape of resist recessed corner 3106, and a structure (overlap structure) is formed in which the peripheral region including recessed corner 3106 where two straight line portions of resist open end 3117 intersect overlaps with solder resist 3105, thereby achieving the effect of reducing thermal stress generated in resist recessed corner 3106. In other words, the effect of preventing resist cracks from occurring in solder resist 3105 is achieved.

[0055] Second Embodiment A second embodiment will be described below. In this embodiment, an electronic control device in which the shape of the dummy land in the first embodiment is modified will be described. In addition, since the same internal combustion engine control system configuration as in the first embodiment is assumed, a description thereof will be omitted.

[0056] 14 is a plan view showing the configuration of a resist recessed corner portion of an electronic control device according to a second embodiment. A cross-sectional view is omitted. As with the first embodiment, this is a general four-layer board, and details are omitted.

[0057] As in the first embodiment, the surface of the substrate 3204 is partitioned into a solder resist protected portion 311 where the surface of the substrate 3204 is covered with solder resist 3205, and a solder resist unprotected portion 312 where the surface of the substrate 3204 is exposed and not covered with solder resist 3105. At the boundary between the solder resist protected portion 311 and the solder resist unprotected portion 312, there is a resist recessed corner portion 3206 where two straight line portions of a resist open end 3217 intersect.

[0058] In this resist recessed corner 3206, a dummy land (conductor) 3211 exists between the solder resist 3205 and the substrate 3204. In other words, the dummy land (conductor) 3211 is provided on the surface of the substrate 3204 so as to be interposed between the resist recessed corner 3206 of the solder resist 3205 and the substrate 3204. The dummy land (conductor) 3211 has a square shape in a plan view, and has a structure (overlap structure) in which its surrounding area including the resist recessed corner 3206 overlaps with the solder resist 3205. The dummy land (conductor) 3211 has the same configuration as in the first embodiment except for its shape, so a detailed description thereof will be omitted.

[0059] At the resist recessed corner 3206, the overlap amount between the dummy land 3211 and the resist open end 3217 of the solder resist 3205 is about 100 μm. Half the length of one side of the dummy land 3211 is equal to or greater than the radius of curvature of the resist recessed corner 3206 (for example, 100 μm).

[0060] The solder resist 3205 is in contact with the dummy land 3211 by having an overlap structure with the dummy land 3211 at the resist recessed corner portion 3206, so that the thermal stress caused by changes in the ambient temperature can be suppressed to 39 ppm / °C, which is lower than the conventional 45 ppm / °C, as the difference in thermal expansion between the solder resist 3205 (57 ppm / °C) and the dummy land 3211 (17 ppm / °C) is 39 ppm / °C.

[0061] 15 shows the results of a thermal stress analysis of the resist recessed corner 3206 using the structural model of this embodiment. The analysis results show that the maximum thermal stress generated in the resist recessed corner 3206 is 109.9 MPa, a significant reduction from the conventional 133.6 MPa. In other words, it is possible to reduce the thermal stress in the resist recessed corner 3206 compared to the conventional structure, and it can be said that it is possible to prevent cracks from occurring in the solder resist 3105.

[0062] <Effects> As described above, dummy land (conductor) 3211 is formed between resist recessed corner 3206 of solder resist 3205 and base material 3204, and dummy land 3211 is made square-shaped, and a structure (overlap structure) is formed in which the peripheral region including recessed corner 3206 where two straight line portions of resist open end 3217 intersect overlaps with solder resist 3205. This has the effect of reducing thermal stress generated in resist recessed corner 3206, as in the first embodiment. In other words, it has the effect of preventing resist cracks from occurring in solder resist 3205.

[0063] In this embodiment, the dummy land 3211 is described as being square in shape, but it may have any shape that is interposed between the resist recessed corner portion 3206 of the solder resist 3205 and the substrate 3204, and may be circular, for example.

[0064] Third Embodiment A third embodiment will be described below. In this embodiment, the arrangement of the dummy lands in the first embodiment is changed, and the purpose is changed from preventing resist cracks to preventing crack progression. Furthermore, since the third embodiment is based on the same internal combustion engine control system configuration as the first embodiment, a description thereof will be omitted.

[0065] 16 is a plan view showing the configuration of a resist recessed corner portion of an electronic control device according to the third embodiment. A cross-sectional view is omitted. As with the first embodiment, this is a general four-layer board, and details are omitted.

[0066] 16, the solder resist protection portion 311 is shown extended to the signal wiring area to show its effect of preventing crack propagation. As in the first embodiment, the surface of the substrate 3304 is covered with a resist 3305, and there is a resist recessed corner 3306 where two straight lines of a resist open end 3317 intersect. In the solder resist protection portion 311, lands 3312 for signal connection and signal wiring 3314 connected to the lands 3312 are provided on the surface of the substrate 3304, and solder resist openings 3313 are provided in the solder resist 3305 to expose the lands 3312.

[0067] In this embodiment, a dummy land (conductor) 3311 is interposed between the resist 3305 and the substrate 3304 at an intermediate position between the resist recessed corner 3306 and the signal wiring 3314. The dummy land 3311 has a structure (overlap structure) in which the entire surface of the dummy land 3311 is covered with the solder resist 3305.

[0068] The dummy land 3311 has an L-shape so as to fit the shape of the resist recessed corner 3306. The lengths L1 and L2 of one side of the L-shape are set to be equal to or greater than the radius of curvature of the recessed corner 3306 (for example, 100 μm).

[0069] The solder resist 3305 is in contact with the dummy land 3311 by being configured to overlap the dummy land 3311 at the intermediate position between the resist recessed corner portion 3306 and the signal wiring 3314. Therefore, the difference in thermal expansion between the solder resist 3305 and the dummy land 3311 can be kept low, and thermal stress due to changes in the environmental temperature can be reduced.

[0070] The thermal stress caused by changes in the environmental temperature of the dummy land 3311 and the solder resist 3305 can be kept lower than the conventional 45 ppm / °C by reducing the difference in thermal expansion between the solder resist 3305 (57 ppm / °C) and the dummy land 3311 (17 ppm / °C) to 39 ppm / °C.

[0071] Therefore, even if a crack occurs from the resist recessed corner 3306 toward a conductor such as the signal wiring 3314 or the land 3312, the dummy land 3311 is arranged in the direction of the crack's progression, and therefore acts as a barrier to prevent the crack from progressing.

[0072] 17 shows the results of a thermal stress analysis using a structural model of the resist recessed corner 3306. As a result of the analysis, the maximum thermal stress generated in the resist recessed corner 3306 was 125.7 MPa, a slight reduction from the conventional 133.6 MPa. Even if a crack occurs in the resist recessed corner 3306, the thermal stress is kept low around the dummy land 3311. In other words, it can be said that it is possible to reduce the thermal stress in the crack propagation direction from the resist recessed corner 3306 compared to the conventional structure, and therefore possible to prevent crack propagation.

[0073] <Effects> As described above, by forming dummy land 3311 between solder resist 3305 and base material 3304 at an intermediate position between resist recessed corner 3306 and conductors such as signal wiring 3314 and land 3312, and by making the dummy land L-shaped and by using a structure in which the dummy land is completely covered with resist (overlap structure), it is possible to reduce the thermal stress between solder resist 3305 and dummy land 3311 located in the crack propagation direction when a crack occurs in resist recessed corner 3306. In other words, it is possible to prevent the propagation of resist cracks.

[0074] The present invention is not limited to the above-described embodiments, and includes various modifications. For example, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with the configuration of another embodiment.

[0075] 1...Internal combustion engine control system, 20...Thermal air flow meter (electronic control device), 300...Circuit board, 311...Solder resist protected portion, 312...Solder resist unprotected portion, 3104, 3204, 3304...Base material, 3105, 3205, 3305...Resist, 3003, 3006, 3106, 3206, 3306...Resist recessed corner portion, 3117, 3217, 3317...Resist open end, 3111, 3211...Dummy land, 3312...Land, 3313...Solder resist opening, 3314...Signal wiring

Claims

1. An electronic control device having a circuit board on which conductors to which electronic components are connected are disposed, and a solder resist formed on the surface of the circuit board, wherein a dummy land having a coefficient of thermal expansion between that of the circuit board and that of the solder resist is disposed between a resist concave corner portion where two straight portions of the resist opening end of the solder resist intersect and the surface of the circuit board.

2. The electronic control device according to claim 1, wherein the dummy land is made of the same material as the conductor and is disposed independently without being signal-connected to the conductor.

3. The electronic control device according to claim 1, wherein one piece along the resist opening end of the dummy land has a length equal to or greater than the radius of curvature of the resist concave corner portion.

4. The electronic control device according to claim 1, wherein the overlapping amount between the dummy land and the resist opening end is 25 μm or more and 500 μm or less.

5. The electronic control device according to claim 1, wherein the resist opening end constitutes a part of the outer edge of the solder resist.

6. The electronic control device according to claim 1, wherein the resist concave corner portion is chamfered in an arc shape so as to have a predetermined curvature.

7. The electronic control device according to claim 1, wherein the dummy land has an L shape.

8. The electronic control device according to claim 1, wherein the dummy land has a square shape.

9. The electronic control device according to claim 1, wherein the dummy land has a circular shape.

10. The electronic control device according to claim 1, wherein the circuit board has a package on which a sensor device for detecting the air flow rate of an internal combustion engine is mounted.

11. An electronic control device having a circuit board on which conductors to which electronic components are connected are disposed, and a solder resist formed on the surface of the circuit board, wherein a dummy land having a coefficient of thermal expansion between that of the circuit board and that of the solder resist is disposed at an intermediate position between a resist concave corner portion where two straight portions of the resist opening end of the solder resist intersect and the conductor.

Images