Electronic control device

Abstract

Disclosed is an electronic control device in which the occurrence of shorting between lands that occurs along with scattering of solder during production is suppressed. The electronic control device comprises a circuit board in which an electronic circuit is formed and on which is mounted an electronic component that has a heat transfer part for heat dissipation, on the bottom surface thereof. The circuit board has: a heat dissipation land 210 to which the heat transfer part is connected; a terminal land 200 which is disposed in the surroundings of the heat dissipation land 210; and a solder resist 220 which is formed between the heat dissipation land 210 and the terminal land 200. Formed at an outer peripheral edge part of the heat dissipation land 210 are a plurality of openings 300 which sandwich therebetween closed parts 310 having solder resists formed on the upper surfaces thereof and at which the upper surface of the heat dissipation land 210 is exposed.

Description

Electronic control device

[0001] The present invention relates to an electronic control device used in a vehicle such as an automobile, and particularly to an electronic control device provided with a semiconductor device having a heat transfer portion for heat dissipation provided on the bottom surface.

[0002] In recent years, electronic control devices used in vehicles such as automobiles have become more highly functional with the spread of advanced driving assistance systems and autonomous driving systems. Under such circumstances, semiconductor devices used in electronic control devices have also become more highly functional, and the amount of heat generated during their operation has been increasing. Since a semiconductor device may cause operational failures such as thermal runaway when its temperature reaches a certain level or higher during operation, it is necessary to release the generated heat.

[0003] Conventionally, some semiconductor devices are configured to dissipate heat generated by semiconductor elements through a heat transfer portion called a heat spreader provided on their bottom surface and via lands formed on a circuit board on which the semiconductor devices are arranged (hereinafter referred to as heat dissipation lands in this specification). Generally, the heat spreader and the heat dissipation land are connected by solder. The heat dissipation land has a larger area than the land to which the terminals of the semiconductor device are connected (hereinafter referred to as terminal lands in this specification), and the amount of solder paste used during connection is also larger. Therefore, when the solder melts, the melted solder may spread from the heat dissipation land to the terminal land side, and there is a possibility that the heat dissipation land and the terminal land may be short-circuited.

[0004] Regarding such problems, for example, Patent Document 1 discloses that by providing another land to which no solder material is supplied between the land to which the heat dissipation portion on the bottom surface of the semiconductor device is connected and the land to which the terminals are connected, when the solder melts, the solder that spreads outside the land to which the heat dissipation portion is connected is joined to another land to prevent a short circuit between the lands.

[0005] Japanese Patent Application Laid-Open No. 2006-303392

[0006] On the other hand, there is a desire for miniaturization of electronic control devices installed in vehicles such as automobiles, from the standpoint of greater flexibility in placement within the vehicle and effective use of the limited space within the vehicle, and smaller electronic components such as semiconductor devices are increasingly being adopted. In miniaturized semiconductor devices, the distance between the heat spreader and the signal terminals is also decreasing, and as disclosed in Patent Document 1, it is becoming difficult to provide another land between the land to which the heat spreader is connected and the land to which the terminals are connected.

[0007] Therefore, in order to prevent short circuits between the heat dissipation land and the terminal land caused by the spread of solder from the heat dissipation land to the terminal land, it is conceivable to form solder resist on the outer periphery of the heat dissipation land (the end on the terminal land side), or on the heat dissipation land side of the terminal land.

[0008] According to the former method, the outer periphery of the heat dissipation land is covered with solder resist, which can prevent solder from flowing out to the terminal land. However, this makes it difficult for gas generated from the solder paste during the melting of the solder on the heat dissipation land to be released, making it easier for large-diameter voids to form. When large-diameter voids are formed in the solder paste, there is a concern that the solder paste may scatter as the gas inside the void is released from the solder paste, potentially leading to a short circuit between the lands. In addition, even if the solder that scatters during the melting of the solder does not cause a short circuit between the lands during manufacturing, it may adhere to the solder resist or electronic components on the circuit board as excess solder, and there is a risk that it may detach during operation and cause a short circuit between terminals in the future, which can reduce the reliability of products such as electronic control devices.

[0009] Furthermore, in the latter case, there is a concern that cracks may easily form at the joints in contact with the solder resist due to the mounting environment of electronic control devices, temperature changes, etc., which would reduce the reliability of the joints and thus reduce the reliability of the product.

[0010] The object of the present invention is to solve the problems of the prior art described above and to provide a highly reliable electronic control device that suppresses the occurrence of short circuits between lands caused by solder flowing out or scattering from the heat dissipation lands during solder melting in the manufacturing process, even when electronic components such as small semiconductor devices are used.

[0011] In one preferred embodiment, the electronic control device according to the present invention comprises an electronic component having a heat transfer section on its bottom surface and a plurality of terminals formed around the heat transfer section, and a circuit board on which the electronic component is mounted and an electronic circuit for controlling equipment installed in a vehicle is formed. The circuit board has a heat dissipation land to which the heat transfer section is connected via a bonding material, a plurality of terminal lands formed around the heat dissipation land to which a plurality of terminals are connected via a bonding material, a solder resist formed on the circuit board between the heat dissipation land and the plurality of terminal lands, a closed portion at the outer peripheral end of the heat dissipation land to which solder resist is formed so as to extend from the terminal land side toward the portion where a bonding material connecting the heat dissipation land and the heat transfer section is present on the upper surface of the heat dissipation land, and an opening at the outer peripheral end of the heat dissipation land to which a gap larger than the distance between the bottom surface of the electronic component and the solder resist in the closed portion is formed between the electronic component and the heat dissipation land in the thickness direction of the circuit board.

[0012] According to the present invention, even if the electronic components such as semiconductor devices constituting the electronic control device are small, it is possible to suppress the occurrence of short circuits between lands caused by solder that flows out or scatters during solder melting in the manufacturing stage, thereby suppressing a decrease in the reliability of the electronic control device. Other problems solved by the present invention and novel features will become clear from the description and drawings herein.

[0013] This is a schematic exploded perspective view showing the structure of one embodiment of an electronic control device. This is a schematic partial top view showing the portion of the circuit board on which the communication LSI is mounted, as seen from the side where the communication LSI is mounted. This is a magnified partial view of the portion enclosed by the dashed line A in Figure 2. This is a graph showing the relationship between the width of the opening and the maximum diameter of the void generated during solder melting. This is a schematic diagram showing the structure of the cross section X1-X1 in Figure 3. This is a schematic diagram showing the structure of the cross section X2-X2 in Figure 3.

[0014] Hereinafter, representative embodiments of the present invention will be described with reference to the drawings. The embodiments and drawings described below are illustrative examples for explaining the present invention, and have been omitted or simplified as appropriate for clarity of explanation. Furthermore, please note that in order to facilitate understanding of the invention, the position, size, shape, and extent of each component shown in the drawings may not necessarily represent them precisely. In each drawing, parts having the same configuration and / or function are denoted by the same reference numeral. In addition, in the following description, unless particularly necessary, redundant explanations of parts having the same configuration and / or function will be omitted.

[0015] Figure 1 is a schematic exploded perspective view showing the structure of one embodiment of the electronic control unit (ECU) according to the present invention.

[0016] The ECU 10 is an electronic control unit used in advanced driver-assistance systems, such as those that perform autonomous driving or assist the driver's driving operations. The ECU 10 does not necessarily have to be an ECU for autonomous driving or advanced driver-assistance systems; for example, it could be an ECU that controls sensing devices such as cameras or radar, or equipment such as the engine, brakes, and steering. Here, we will explain using an ECU used in an advanced driver-assistance system as an example.

[0017] The ECU 10 includes a circuit board 20 on which electronic circuits for realizing functions as an advanced driver assistance system are formed. The circuit board 20 is housed in a casing that is, for example, made of a metal base housing 30 and a cover 40. The casing in which the circuit board 20 is housed does not necessarily have to be made of metal, and may be made of a resin material, for example.

[0018] The circuit board 20 is equipped with various electronic components, including semiconductor devices such as a microcontroller unit (MCU) 100 that implements the functions controlled by the ECU 10 by executing a program stored in memory, and a communication LSI 110 for communicating with other ECUs via the in-vehicle network, as well as resistors and capacitors (not shown). These electronic components are interconnected via power supply wiring and signal wiring (not shown) formed on the circuit board 20, forming an electronic circuit.

[0019] The circuit board 20 is also provided with one or more connectors 120 to which cables connecting to the in-vehicle network are connected. The ECU 10 can communicate with other ECUs and other devices in the vehicle via the network to which the connectors 120 are connected.

[0020] The communication LSI 110 is a QFN (Quad Flat Non-leaded) type semiconductor device, for example, having power and signal terminals on all four sides of the flattened surface of a flattened cube-shaped package. These terminals are connected to lands that connect to power or signal wiring formed on the circuit board by, for example, a metal bonding material. In this embodiment, solder is used as the bonding material. The communication LSI 110 also has a heat spreader on its bottom surface facing the circuit board 20 when mounted on the circuit board 20, which is a heat transfer member for dissipating the generated heat through the lands formed on the circuit board 20.

[0021] The semiconductor device mounting structure in this embodiment will be described below, using the communication LSI 110 as an example. In this specification, the side of the circuit board 20 on which the communication LSI 110 is mounted will be referred to as the top surface.

[0022] Figure 2 is a schematic partial top view showing the portion of the circuit board 20 on which the communication LSI 110 is mounted, as seen from the side where the communication LSI 110 is mounted. In Figure 2, the external shape of the communication LSI 110 mounted on the circuit board 20 is shown by a dashed line. Also, the solder connecting the communication LSI 110 to the circuit board 20 is omitted from the illustration in Figure 2.

[0023] On the circuit board surface of the circuit board 20 corresponding to the outer periphery of the communication LSI 110, a plurality of terminal lands 200 are formed, to which power wiring or signal wiring formed on the circuit board 20 is connected, at positions corresponding to the power terminals and signal terminals of the communication LSI 110, respectively. In addition, a heat dissipation land 210 is formed on the circuit board 20 in the portion facing the heat spreader of the communication LSI 110, which is used to dissipate the heat generated by the communication LSI 110.

[0024] On the mounting surface of the electronic components on the circuit board 20, solder resist 220 is formed so that terminal lands 200 and heat dissipation lands 210 are exposed. However, as will be described later, the outer periphery of the heat dissipation lands 210 is formed with a portion where solder resist 220 is partially formed and a portion where the heat dissipation lands 210 are exposed. The exposed area of ​​the heat dissipation lands 210 that is exposed from the solder resist 220, where solder resist 220 is not formed on the upper surface, may be divided into multiple exposed areas by the solder resist 220. In the example shown in Figure 2, the exposed area of ​​the heat dissipation lands 210 is divided into four exposed areas 211, 212, 213, and 214 by a cross-shaped solder resist 220. By dividing the exposed area of ​​the heat dissipation lands 210 into small areas in this way, heat can be more evenly distributed, preventing excessive concentration of heat in specific areas, and preventing damage to the circuit board due to mechanical stress caused by thermal expansion and contraction of the substrate.

[0025] The power terminals and signal terminals of the communication LSI 110 are connected to the terminal lands 200 on the circuit board 20 by soldering. Similarly, the heat spreader is connected by soldering to the respective exposed areas 211, 212, 213, and 214 of the heat dissipation lands 210.

[0026] Figure 3 is a magnified view of the area enclosed by the dashed line A in Figure 2. Figure 3 shows the exposed area 211, which is one of the exposed areas of the heat dissipation land 210, and the surrounding terminal land 200.

[0027] As shown in Figure 3, the heat dissipation land 210 has an opening 300 at its terminal land 200 side where the outer periphery of the heat dissipation land 210 is exposed, and a closed portion 310 where solder resist 220 is formed on the land on the outer periphery of the heat dissipation land 210. Multiple openings 300 and closed portions 310 are formed alternately along the outer periphery of the heat dissipation land 210 (the terminal land 200 side end of the exposed area 211). Note that the closed portion 310 is not to be completely sealed by the solder resist 220, but rather to have a gap narrower than the gap formed in the opening in the thickness direction of the circuit board 20, as will be described later.

[0028] The width W2 of the opening 300 is formed to be sufficiently narrow compared to the opening width W1 of the exposed area 211 along the outer circumference of the heat dissipation land 210. Preferably, the width W2 of the opening 300 is formed to be narrow enough to prevent molten solder from flowing out to the terminal land 200 side during solder melting in the manufacturing stage, relative to the opening width W1.

[0029] On the other hand, if the width W2 of the opening is too narrow, it becomes difficult for the gas generated during solder melting to be discharged, and large-diameter voids tend to form near the outer periphery of the heat dissipation land 210. When large-diameter voids form near the outer periphery of the heat dissipation land 210, the gas inside the voids draws in the surrounding solder when it is discharged to the outside of the heat dissipation land 210, making solder splatter more likely.

[0030] Figure 4 is a graph showing the relationship between the width W2 of the opening 300 and the maximum diameter of voids generated during solder melting. As shown in Figure 4, if the width W2 of the opening is 0.1 mm or more, large-diameter voids are less likely to occur, and solder scattering caused by the inclusion of solder when gas inside the void is discharged is suppressed.

[0031] In Figure 3, the openings 300 are arranged at equal intervals in the width direction of the exposed area 211, with the closing portion 310 in between. However, the openings 300 do not necessarily need to be arranged at equal intervals. However, it is preferable that the openings 300 are formed to be dispersed in the width direction of the exposed area 211 (along the outer circumference of the heat dissipation land 210) so that the gas generated during solder melting can be effectively discharged.

[0032] Solder resist 220 is formed on the outermost layer of the circuit board 20 to prevent solder from adhering to unwanted areas when electronic components are mounted to the circuit board 20 using solder after circuit patterns such as terminal lands 200, heat dissipation lands 210, power wiring, and signal wiring have been formed on the circuit board 20. Solder resist 220 can be formed, for example, using a liquid photoresist method. In the photoresist method, solder resist ink is first applied to the surface of the circuit board 20 on which the circuit patterns have been formed. Next, a negative film is used to mask the areas where solder resist will not be formed so that they are shielded from light, and ultraviolet light is irradiated to expose the areas where solder resist will be formed and harden the solder resist ink. After that, the solder resist ink in the unexposed areas that were not exposed to ultraviolet light is removed to form the solder resist 220.

[0033] In this embodiment, solder resist is formed using a negative film in which the portion where the opening 300 is formed is rectangular, as shown in Figure 3. In the photoresist method, ultraviolet light can penetrate even the parts that are shielded during ultraviolet irradiation, so it should be noted that in reality the edges will be rounded and will not be a clean rectangle as shown in Figure 3. Also, the shape of the opening 300 does not have to be rectangular as shown in Figure 3; solder resist may be formed using a negative film with a wavy or triangular shape.

[0034] Figure 5 is a schematic diagram showing the structure of the cross-section X1-X1 in Figure 3 with the communication LSI 110 mounted on the circuit board 20, that is, the structure of the closed portion 310 in the thickness direction of the circuit board 20.

[0035] The power or signal terminal (terminal 111) of the communication LSI 110 is fixed to a terminal land 200 formed on the circuit board 20 at a position corresponding to terminal 111 by solder 500a. Solder resist 220a is formed on the end of the terminal land 200 opposite to the communication LSI 110, such that a portion of it overlaps the terminal land 200.

[0036] The heat spreader 112 is fixed to the exposed area of ​​the heat dissipation land 210 formed on the circuit board 20 at a position corresponding to the heat spreader 112 by solder 500b. Solder resist 220b is formed between the heat dissipation land 210 and the terminal land 200, and the heat resist on the heat dissipation land 210 side extends toward the area where solder 500b is present on the upper surface of the end of the heat dissipation land 210, and is formed to cover the end of the heat dissipation land 210.

[0037] The thickness T1 of the solder resist 220b formed on the upper end surface of the heat dissipation land 210 is greater than the thickness T2 of the solder resist 220a formed on the terminal land 200. Furthermore, the distance T3 between the solder resist 220b formed on the heat dissipation land 210 and the bottom surface of the communication LSI 110 is smaller than the width W2 of the opening 300. This makes it possible to more effectively prevent the solder 500b connecting the heat spreader 112 and the heat dissipation land 210 from flowing out to the terminal land 200 side during solder melting in the manufacturing process.

[0038] In Figure 5, the solder 500b and solder resist 220b connecting the heat spreader 112 and the heat dissipation land 210 are in contact with each other on the heat dissipation land 210. However, the solder 500b and solder resist 220b may be formed to be separated from each other and not in contact.

[0039] Figure 6 is a schematic diagram showing the structure of the cross-section X2-X2 in Figure 3 with the communication LSI 110 mounted on the circuit board 20, that is, the structure of the opening 300 in the thickness direction of the circuit board 20.

[0040] In this embodiment, the solder resist 220b formed between the heat dissipation land 210 and the terminal land 200 is formed so as not to overlap the heat dissipation land 210 at the opening 300. Therefore, the size of the gap formed below the bottom surface of the communication LSI 110 (the distance between the bottom surface of the communication LSI 110 and the end of the heat dissipation land 210) T4 is formed to be sufficiently larger than the distance T3 between the bottom surface of the communication LSI 110 and the solder resist 220b at the closed portion 310. Gas generated during solder melting in the manufacturing process is easily discharged into the space between the heat dissipation land 210 and the terminal land 200 through this gap formed below the bottom surface of the communication LSI 110. As a result, the formation of large voids in the solder 500b during solder melting is suppressed, and the scattering of solder due to gas release in the voids is also suppressed.

[0041] In Figure 6, the solder resist 220b is formed spaced apart from the heat dissipation land 210, but the solder resist 220b may be in contact with the heat dissipation land 210. Also, the edges of the heat dissipation land 210 do not necessarily need to be exposed, and a large amount of solder resist 220b may cover them. Even in such cases, it is sufficient that the size of the gap formed below the bottom surface of the communication LSI 110, between the communication LSI 110 and the heat dissipation land 210, is sufficiently larger than the distance T3 between the bottom surface of the communication LSI 110 and the solder resist 220b in the closed portion 310.

[0042] Here, we have used the mounting section of a communication LSI as an example of an electronic component having a heat spreader on its bottom surface facing the circuit board, but this can be similarly applied to the mounting of semiconductor devices and other electronic components that have a heat conduction section on their bottom surface, not just communication LSIs.

[0043] According to this embodiment, when mounting electronic components having a heat conduction part on the bottom surface, the scattering of solder caused by gas being drawn in from voids that form in the molten solder is suppressed, thereby preventing short circuits between terminals caused by scattered solder and enabling the realization of a highly reliable electronic control device.

[0044] As described above, the present invention has been described by taking its representative embodiments as examples. However, the present invention is not limited thereto, and can be implemented in various modes without departing from the gist of the invention described in the claims. Further, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described.

[0045] 10... Electronic control unit (ECU), 20... Circuit board, 30... Base housing, 40... Cover, 100... MCU, 110... Communication LSI, 120... Connector, 200... Terminal land, 210... Heat dissipation land, 220, 220a, 220b... Solder resist, 211, 222, 223, 224... Exposed area, 300... Opening, 310... Closing portion, 500a, 500b... Solder

Claims

1. An electronic control device comprising: an electronic component having a heat transfer section on its bottom surface and a plurality of terminals formed around the heat transfer section; and a circuit board on which the electronic component is mounted and an electronic circuit for controlling equipment installed in a vehicle is formed, wherein the circuit board has: a heat dissipation land to which the heat transfer section is connected via a bonding material; a plurality of terminal lands formed around the heat dissipation land to which the plurality of terminals are connected via a bonding material; a solder resist formed on the circuit board between the heat dissipation land and the plurality of terminal lands; a closure portion formed at the outer peripheral end of the heat dissipation land such that the solder resist extends from the terminal land side toward the portion where the bonding material connecting the heat dissipation land and the heat transfer section is located on the upper surface of the heat dissipation land; and an opening at the outer peripheral end of the heat dissipation land between the electronic component and the heat dissipation land such that a gap larger than the distance between the bottom surface of the electronic component and the solder resist in the closure portion is formed in the thickness direction of the circuit board.

2. The electronic control device according to claim 1, wherein a plurality of openings are formed along the outer circumference of the heat dissipation land with the closing portion in between.

3. The electronic control device according to claim 2, wherein the opening is formed such that its width in the direction along the outer circumference of the heat dissipation land is 0.1 mm or more.

4. The electronic control device according to claim 3, wherein the distance between the bottom surface of the electronic component and the upper surface of the solder resist formed in the closure portion is smaller than the width of the opening.

5. The electronic control device according to claim 2, wherein the terminal land has solder resist formed on the upper surface of the end opposite to the heat dissipation land, and the thickness of the solder resist formed on the heat dissipation land in the closed portion is greater than the thickness of the solder resist formed on the terminal land.

6. The electronic control device according to claim 2, wherein the outer peripheral end of the heat dissipation land in the opening is exposed without solder resist being formed thereon.

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