Circuit board

Abstract

To provide a circuit board which can ensure excellent detection accuracy while keeping moisture resistance.SOLUTION: A circuit board 10 comprises: a board body part 20 which has mounting surfaces 20a, 20b located opposite to each other; a MEMS sensor 30 mounted on the mounting surface 20b; an electronic component 41a which is mounted on the mounting surface 20a and is electrically connected to the MEMS sensor 30; a moisture-resistant coating agent 25 which is formed on the mounting surface 20a and is in a hardened state; a through-hole 22a which penetrates the board body part 20 in its thickness direction; and a solder part 24 which closes the through-hole 22a in order to prevent the moisture-resistant coating agent 25, in a fluid state before hardening, from reaching the MEMS sensor 30 via the through-hole 22a.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to circuit boards. [Background technology]

[0002] Patent Document 1 discloses a moisture-resistant coating method for coating a coating area of ​​a substrate with a moisture-resistant coating. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-168501 Summary of the Invention [Problem to be solved by the invention]

[0004] The moisture-resistant coating film described in Patent Document 1 prevents the substrate from shorting out due to water droplets, even when the substrate is exposed to an environment with drastic changes in ambient temperature or high humidity, thereby improving the moisture resistance of the substrate. On the other hand, if a moisture-resistant coating agent is applied to the first surface of the substrate, this moisture-resistant coating agent may reach the detection element on the second surface behind the first surface of the substrate through various holes (e.g., through holes) in the substrate, which may affect the detection accuracy of the detection element.

[0005] The present disclosure has been made in consideration of the above-described circumstances, and has an object to provide a circuit board that can maintain good detection accuracy while maintaining moisture resistance. [Means for solving the problem]

[0006] In order to achieve the above object, the circuit board according to the present disclosure comprises: a substrate main body having a first surface and a second surface that are mounting surfaces located on opposite sides of each other; an inertial force detection unit mounted on the first surface; an electronic component mounted on the second surface and electrically connected to the inertial force detection unit; a moisture-resistant coating agent formed on the second surface and in a cured state; a hole penetrating the substrate body in a thickness direction; and a hole closing portion that closes the hole to prevent the moisture-resistant coating agent, which has fluidity before hardening, from reaching the inertial force detection portion through the hole. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to maintain good detection accuracy while maintaining moisture resistance. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a schematic plan view showing a front mounting surface of a substrate according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic plan view showing a back mounting surface of a substrate according to an embodiment of the present disclosure. [Figure 3] FIG. 2 is a schematic cross-sectional view taken along line III-III in FIG. [Figure 4] 1 is an enlarged cross-sectional view of a portion of a circuit board on which a cream solder portion is printed according to an embodiment of the present disclosure. [Figure 5] FIG. 10 is a schematic cross-sectional view of a portion of a circuit board according to a comparative example. [Figure 6] FIG. 10 is a schematic cross-sectional view of a portion of a circuit board according to a modified example of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0009] A circuit board according to an embodiment of the present disclosure will be described with reference to the drawings. The circuit board is mounted on a vehicle and outputs a detection signal that detects the acceleration and / or angular velocity of the vehicle. The output detection signal is used for vehicle braking functions such as ABS (Abrupt Brake System), ESC (Electronic Stability Control), TCS (Traction Control System), LKAS (Lane Keep Assist System), and ACC (Adaptive Cruise Control).

[0010] 1 and 2, the circuit board 10 includes a board main body 20, a plurality of conductive patterns 21, a plurality of through holes 22a to 22c, a ground plane 27, a MEMS (Micro Electro Mechanical System) sensor 30, and a plurality of electronic components 41a to 41f, and, as shown in Fig. 3, a solder resist 23, a solder portion 24, and a moisture-resistant coating agent 25. The MEMS sensor 30 and the electronic components 41a to 41f are mounted on the circuit board 10.

[0011] The X and Y directions of the substrate main body 20 are defined as directions that are perpendicular to each other on the mounting surfaces 20a and 20b of the substrate main body 20, and the Z direction is defined as the thickness direction of the substrate main body 20. The X and Y directions each extend along two perpendicular sides of the rectangular substrate main body 20.

[0012] The substrate body 20 is an electrically insulating flat-plate base material made of glass epoxy resin, etc. The substrate body 20 has mounting surfaces 20a and 20b on both the front and back sides. The board main body 20 is made up of a total of four layers, namely, layers 1 to 4. The board main body 20 has a solid ground layer (not shown) as an inner layer (second or third layer) of the four layers. The first layer is the mounting surface 20a. As shown in Fig. 1, the conductive pattern 21 and the ground plane 27 are formed on the mounting surface 20a. The fourth layer is the mounting surface 20b. As shown in Fig. 2, the conductive pattern 21 and the ground plane 27 are formed on the mounting surface 20b.

[0013] The conductive pattern 21 is a wiring circuit through which control signals or electrical signals related to the mounted components (MEMS sensor 30 and electronic components 41a to 41f) flow. The conductive pattern 21 is formed by laminating a copper plate on the mounting surfaces 20a and 20b and patterning the copper plate using photoresist technology.

[0014] The plurality of through holes 22a to 22c are via holes that penetrate the board main body 20 in its thickness direction and are formed by cylindrical metal-plated conductive tubes. The plurality of through holes 22a, 22c are electrically connected to the conductive patterns 21 on the mounting surfaces 20a, 20b of the board main body 20. In other words, the through holes 22a, 22c constitute part of the circuit pattern on the circuit board 10. The plurality of through holes 22b are not electrically connected to the conductive patterns of the layers of the substrate body 20 and are therefore unused.

[0015] 3, the solder resist 23 is an electrical insulating film that is applied to areas other than those that need to be electrically connected to mounted components, etc. The solder resist 23 prevents oxidation or disconnection of the conductive pattern 21 made of copper wiring, and also has the function of preventing solder from adhering to unnecessary areas during soldering.

[0016] The MEMS sensor 30 is an inertial measurement unit (IMU) that detects physical motion parameters such as acceleration, rotation, or position change. The MEMS sensor 30 is a six-axis inertial sensor element. The MEMS sensor 30 combines an acceleration sensor and a gyro (yaw rate) sensor, and detects the acceleration and angular velocity of the vehicle. The detection results of the MEMS sensor 30 are used for vehicle braking, such as the ABS described above.

[0017] 2, the MEMS sensor 30 is mounted on the mounting surface 20b, in this example, at the center of the mounting surface 20b. The MEMS sensor 30 includes a plurality of terminals 31 (see FIG. 3) that are electrically connected to a plurality of conductive patterns 21 arranged around the MEMS sensor 30.

[0018] The through-holes 22a and 22b located around the MEMS sensor 30 are closed with solder portions 24. Specifically, a virtual hole-filling area A1 is set in an area including the MEMS sensor 30 when viewed from the Z direction. The hole-filling area A1 is rectangular and located at the center of the MEMS sensor 30. When viewed from the Z direction, the hole-filling area A1 is similar in shape to the MEMS sensor 30. The outline of the hole-filling area A1 is set at a position a certain distance L away from the outline of the MEMS sensor 30 (more precisely, the outer surface of its package 32). The certain distance L is set to be greater than the distance that a fluid moisture-resistant coating agent, when applied to the mounting surface 20a before hardening, can pass through the through-holes 22a and 22b without the solder portions 24 and spread onto the mounting surface 20b. The certain distance L is set to, for example, 2 mm to 5 mm, more preferably 3 mm to 4 mm, and as an example, 3.5 mm.

[0019] 3, a gap Sp is formed between the mounting surface 20b and the bottom surface (the upper surface in FIG. 3) of the package 32 of the MEMS sensor 30. The gap Sp prevents distortion from occurring in the MEMS sensor 30, thereby improving the detection accuracy of the MEMS sensor 30.

[0020] As shown in FIG. 1, electronic components 41a to 41d are mounted on the mounting surface 20a. As shown in FIG. 2, electronic components 41e and 41f are mounted on the mounting surface 20b. The plurality of electronic components 41a are resistors or ceramic capacitors that are smaller in size than the other electronic components 41b to 41f. The electronic components 41a are, for example, 1005 size (1 mm x 0.5 mm). The electronic components 41a are mounted for noise countermeasures and pull-down or pull-up purposes.

[0021] The electronic component 41c is a microcomputer that controls the circuit board 10, and converts the detection signal from the MEMS sensor 30 and outputs it to the electronic component 41e (communication section).

[0022] The electronic component 41b is a regulator that generates a voltage such as an LDO (Low Drop Out) etc. The electronic component 41b steps down an external voltage and supplies operating power to the microcomputer (electronic component 41c) via the conductive pattern 21. The electronic component 41d is a surge cut transistor.

[0023] Electronic components 41a to 41c are densely arranged on mounting surface 20a. The distance between the terminals of electronic components 41b and 41c is shorter than the distance between the terminals of electronic component 41d. As the distance between the terminals becomes shorter, the distance between conductive patterns 21 also becomes shorter. The moisture-resistant coating agent 25 is a coating that prevents leakage and is applied to a coating area A2 that includes the electronic components 41a to 41c. The coating area A2 is formed in an area that includes the electronic components 41a to 41c. In this example, the coating area A2 has a rectangular shape with one corner removed. The electronic component 41d is located outside the coating area A2. The area of ​​the coating area A2 is smaller than the area of ​​the hole filling area A1. The hole filling area A1 and the coating area A2 are arranged so that at least a portion of their areas (e.g., more than half of their areas) overlap on the front and back of the substrate main body 20. It should be noted that, without being limited to this example, the area of ​​the application area A2 may be larger than the area of ​​the hole filling area A1, or may be the same area as the area of ​​the hole filling area A1. Furthermore, the hole filling area A1 and the application area A2 may be formed in areas that completely coincide on the front and back of the substrate main body 20.

[0024] Electronic components 41e and 41f are arranged outside hole filling area A1 on mounting surface 20b, that is, on the outer periphery of mounting surface 20b. The electronic component 41e is a communication unit including a CAN (Controller Area Network) transceiver that transmits and receives detection signals to and from the outside, and outputs the detection signal from the electronic component 41c (microcomputer) to the outside. The electronic component 41f is an inductor for noise suppression, and is electrically connected to the electronic component 41e via the conductive pattern 21. The electronic components 41d, 41e, and 41f are arranged at positions other than directly behind the MEMS sensor 30 because noise generated by the electronic components 41d, 41e, and 41f is likely to affect the detection accuracy of the MEMS sensor 30.

[0025] As shown in Figures 1 and 3, moisture-resistant coating agent 25 is formed within application area A2. Moisture-resistant coating agent 25 is formed so as to cover electronic components 41a-41c and conductive pattern 21, and protects electronic components 41a-41c and conductive pattern 21 from condensation and the like. Moisture-resistant coating agent 25 is formed by applying a urethane-based solution or the like and allowing this solution to harden, resulting in a solidified state. The solution application process is performed after the process of forming solder portions 24, for example, at the end of the manufacturing process of circuit board 10.

[0026] The solder portion 24 is formed so as to block all of the through holes 22a, 22b located in the hole filling area A1. Blocking the through holes 22a, 22b means making the through holes 22a, 22b unable to pass liquid therethrough. As shown in FIG. 3, the solder portion 24 is located within the through holes 22a and 22b and is in close contact with the inner circumferential surfaces of the through holes 22a and 22b. The solder portion 24 is located closer to the mounting surface 20b than the center of the through holes 22a and 22b in the Z direction (the axial direction of the through holes 22a and 22b). The solder portion 24 becomes thicker in the Z direction as it approaches the inner circumferential surfaces of the through holes 22a and 22b. The solder portion 24 is provided only to fill the through holes 22a and 22b. Therefore, the solder portion 24 does not conduct electricity between the conductive pattern and other components or fix the components. Solder portions other than the solder portion 24 (not shown) conduct electricity between the conductive pattern and other components or fix the components. The solder portion 24 is an alloy mainly composed of lead and tin, but the solder portion 24 may also be lead-free solder. The through holes 22a and 22b are formed as bottomed holes by the solder portion 24. Therefore, the solution is collected in these bottomed holes, and dripping of the solution that would otherwise spread excessively over the mounting surface 20a can be suppressed.

[0027] The method for forming the solder portion 24 will now be described. As shown in Figure 4, with the mounting surface 20b facing upward, a solder printing device (not shown) applies cream solder 24a to the through-hole 22a so as to cover the upper opening on the mounting surface 20b side. At this time, cream solder other than cream solder 24a is also applied. After that, a reflow soldering device is used to heat and melt the applied cream solder on the board, performing reflow. At this time, cream solder 24a solidifies while entering through-hole 22a, becoming solder portion 24 (see Figure 3).

[0028] The solder portion 24 prevents the moisture-resistant coating agent 25 from passing through the through-holes 22a and 22b and reaching the MEMS sensor 30 when the moisture-resistant coating agent 25 is applied to the application range A2 including the electronic components 41a to 41c. 5 , which does not have the solder portions 24, the moisture-resistant coating agent 25 passes through the through-holes 22a and reaches the MEMS sensor 30, which may adversely affect the detection accuracy of the MEMS sensor 30. In this regard, in the present embodiment, the moisture-resistant coating agent 25 is used to maintain moisture resistance while preventing the moisture-resistant coating agent 25 from reaching the MEMS sensor 30, so that the detection accuracy of the MEMS sensor 30 can be maintained at a good level.

[0029] (effect) According to the embodiment described above, the following effects are achieved. (1) The circuit board 10 includes a substrate main body 20 having mounting surfaces 20a, 20b, which are examples of a first surface and a second surface located opposite each other; a MEMS sensor 30, which is an example of an inertial force detection unit, mounted on the mounting surface 20b (first surface); electronic components 41a to 41c, which are mounted on the mounting surface 20a (second surface) and electrically connected to the MEMS sensor 30; a moisture-resistant coating agent 25 formed on the mounting surface 20a and in a hardened state; through holes 22a, 22b, which are an example of holes penetrating the thickness direction of the substrate main body 20; and a solder portion 24, which is an example of a hole sealing portion that seals the through holes 22a, 22b to prevent the fluid moisture-resistant coating agent 25 before hardening from reaching the MEMS sensor 30 via the through holes 22a, 22b. According to this configuration, even if the moisture-resistant coating agent 25 is applied to the mounting surface 20a, the moisture-resistant coating agent 25 is prevented from reaching the MEMS sensor 30. Therefore, the moisture resistance of the circuit board 10 can be maintained, and the detection accuracy of the MEMS sensor 30 can be kept good. Furthermore, even if electronic components 41a to 41c are arranged on the back side of MEMS sensor 30, moisture-resistant coating agent 25 does not reach MEMS sensor 30, which also contributes to miniaturization of circuit board 10.

[0030] (2) The through-holes 22a that are closed with the solder portions 24 are made of a conductive material that constitutes part of the circuit that electrically connects the MEMS sensor 30 and the electronic components 41a to 41c. According to this configuration, the through holes 22 a located around the MEMS sensor 30 are closed by the solder portions 24 .

[0031] (3) Of the plurality of through holes 22a to 22c, one or more through holes 22a, 22b located within a hole filling area A1, which is an example of an area set around the MEMS sensor 30 so as to include the MEMS sensor 30, are formed in a state in which they are blocked by the solder portion 24. Of the plurality of through holes 22a to 22c, one or more through holes 22c located outside the hole filling area A1 are formed in an unblocked state. According to this configuration, of the through holes 22a to 22c, only the through holes 22a and 22b located near the MEMS sensor 30 are blocked with the solder portion 24. Therefore, the number of through holes 22a and 22b blocked with the solder portion 24 can be reduced.

[0032] (4) A gap Sp is formed between the bottom surface of the package 32 of the MEMS sensor 30 and the mounting surface 20b. The gap Sp prevents distortion of the MEMS sensor 30 and improves the detection accuracy of the MEMS sensor 30, but in the configuration of the comparative example (see FIG. 5 ), there is a risk of moisture-resistant coating agent entering the gap Sp. In this embodiment, the solder portion 24 prevents the moisture-resistant coating agent 25 from reaching the mounting surface 20b, so the moisture-resistant coating agent does not enter the gap Sp and the detection accuracy of the MEMS sensor 30 is maintained.

[0033] The present disclosure is not limited to the above-described embodiments and drawings. Modifications (including deletion of components) may be made as appropriate within the scope of the present disclosure. An example of such a modification is described below.

[0034] (Variation) In the above embodiment, the solder portions 24 are provided in the through holes 22a and 22b as hole closing portions, but the hole closing portions may be formed of an object other than the solder portions 24. For example, as shown in Fig. 6, the solder resist 23 may serve as the hole closing portion and close the openings of the through holes 22a and 22b in a manner that covers them.

[0035] In the above embodiment, the hole sealing portion such as the solder portion 24 is configured to seal the through holes 22a, 22b formed by the conductive material, but it may also be configured to seal holes other than the through holes 22a, 22b in the substrate main body portion 20, for example, positioning holes in the substrate main body portion 20.

[0036] The number or arrangement of the through holes 22a to 22c in the above embodiment can be changed as appropriate. The number and arrangement positions of the electronic components 41a to 41f in the above embodiment can be changed as appropriate.

[0037] In the above embodiment, the circuit board 10 is mounted on a vehicle, but it may be mounted on a device other than a vehicle. The MEMS sensor 30 may detect information other than acceleration and angular velocity, and may be configured to be able to detect, for example, atmospheric pressure or geomagnetism. Furthermore, the MEMS sensor 30 may be any kind and type of sensor, as long as the detection accuracy is not likely to be impaired by a moisture-resistant coating.

[0038] In the above embodiment, the solder portions 24 are located on the mounting surface 20b side of the through holes 22a and 22b, but this is not limiting, and the solder portions 24 may be located on the mounting surface 20a side of the through holes 22a and 22b. In the above embodiment, a portion of the solder portion 24 may be located on the mounting surface 20b. In the above embodiment, a plurality of solder portions 24 may be provided in each through hole 22 a, 22 b. For example, a first solder portion may be located on the mounting surface 20 a side of each through hole 22 a, 22 b, and a second solder portion may be located on the mounting surface 20 b side of each through hole 22 a, 22 b. The solder portions 24 may also be formed over the entire area inside the through holes 22a and 22b. [Explanation of symbols]

[0039] 10,10A circuit board 20 Main board part 20a, 20b Mounting surface 21 Conductive pattern 22a~22c through holes 23 Solder resist 24 Soldering part 24a Cream solder part 25 Moisture-resistant coating agent 27 Ground Betta 30 MEMS sensors 31 terminals 32 packages 41a~41f Electronic parts A1 Filling range A2 Coating area L fixed distance Sp Gap

Claims

1. a substrate main body portion having a first surface and a second surface which are mounting surfaces located on opposite sides of each other; an inertial force detection unit mounted on the first surface; an electronic component mounted on the second surface and electrically connected to the inertial force detection unit; a moisture-resistant coating agent formed on the second surface and in a cured state; a hole penetrating the substrate body in a thickness direction; a hole closing portion that closes the hole to prevent the moisture-resistant coating agent, which has fluidity before hardening, from reaching the inertial force detection unit through the hole. Circuit board.

2. the hole is a through-hole made of a conductive material that constitutes part of a circuit that electrically connects the inertial force detection unit and the electronic component. The circuit board according to claim 1 .

3. one or more of the holes located within a region set around the inertial force detection unit so as to include the inertial force detection unit are formed in a state of being blocked by the hole blocking portion, Among the plurality of holes, one or more holes located outside the region are formed in an unblocked state. The circuit board according to claim 1 or 2.

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