Circuit board

Abstract

A circuit board 1 comprises: a flexible printed board (FPC) 2; a thermistor 3 mounted on the FPC 2; a frame component 4 fixed to a surface of the FPC 2 on which the thermistor 3 is mounted, and surrounding the thermistor 3; and a resin material 5 filled in a space 4C which is surrounded by an inner peripheral surface 4B of the frame component 4, and covering the thermistor 3. The presence of the frame component 4 can prevent the final shape of the resin material 5 from being haphazard. Therefore, the height dimension of the circuit board 1 and the spread dimension of the resin material 5 can be easily managed.

Description

Circuit board

[0001] The technology disclosed in this specification relates to a circuit board.

[0002] Conventionally, a circuit board including a printed circuit board, electronic components mounted on the printed circuit board, and a resin material covering the electronic components is known (see, for example, Patent Document 1). Specifically, the invention described in Patent Document 1 includes a flexible printed circuit board, a current limiting element mounted on the flexible printed circuit board, and an insulating resin overcoating the current limiting element. Patent Document 1 describes that since the current limiting element is overcoated with an insulating resin, the electrodes of the current limiting element will not be short-circuited by water droplets or the like formed due to condensation.

[0003] Japanese Patent No. 6894558 (paragraph 0008, FIG. 5)

[0004] The invention described in Patent Document 1 had room for improvement in covering electronic components with a resin material. This specification discloses a technique for facilitating the management of the height dimension of a circuit board in which an electronic component is covered with a resin material and the spread dimension of the resin material.

[0005] The circuit board according to the present disclosure includes a printed circuit board, electronic components mounted on the printed circuit board, a frame component fixed to the surface of the printed circuit board on which the electronic components are mounted, surrounding the electronic components, and a resin material filled in a space surrounded by the inner peripheral surface of the frame component and covering the electronic components.

[0006] According to the present disclosure, it becomes easier to manage the height dimension of a circuit board in which an electronic component is covered with a resin material and the spread dimension of the resin material.

[0007] FIG. 1 is a top view of a circuit board according to Embodiment 1. FIG. 2 is a cross-sectional view of the circuit board taken along line A - A shown in FIG. 1. FIG. 3 is a bottom view of the circuit board. FIG. 4 is a cross-sectional view schematically showing a cross-section of a circuit board according to Embodiment 2.

[0008] [Description of Embodiments of the Present Disclosure] First, the embodiments of the present disclosure will be listed and described.

[0009] (1) The circuit board according to the present disclosure comprises a printed circuit board, electronic components mounted on the printed circuit board, a frame component fixed to the surface of the printed circuit board on which the electronic components are mounted and surrounding the electronic components, and a resin material filling the space surrounded by the inner circumferential surface of the frame component and covering the electronic components.

[0010] In the invention described in Patent Document 1 mentioned above, there is a problem in that the final shape of the insulating resin is left to chance, making it difficult to control the dimensions. Specifically, as shown in Figure 5 of the same document, the insulating resin described in the document is thicker in the center and thinner towards the edges. For this reason, it is necessary to apply a thick overcoat to prevent the corners of electronic components from being exposed or to prevent the insulating resin from becoming thin at the corners of electronic components. However, applying a thick overcoat means that the final thickness of the circuit board is left to chance, which presents a problem in that it is difficult to control the height of the circuit board when there are strict constraints on the height of the circuit board. Furthermore, applying a thick overcoat also means that the spread of the insulating resin is left to chance, making it difficult to control the spread dimensions of the insulating resin. In contrast, with the circuit board described in (1) above, the presence of a frame component prevents the final shape of the resin material from being left to chance. Therefore, it becomes easier to control the height dimensions of the circuit board in which the electronic components are covered with the resin material, as well as the spread dimensions of the resin material.

[0011] (2) In the circuit board described in (1) above, the resin material may be contained within the space.

[0012] According to the circuit board described in (2) above, since the resin material is contained within the space (in other words, the resin material does not protrude from the space), the height of the circuit board can be controlled by the height of the frame component rather than the resin thickness. Therefore, it becomes easier to control the height dimension when there are strict constraints on the height of the circuit board.

[0013] (3) In the circuit board described in (2) above, the side of the resin material opposite to the printed circuit board may be a concave surface that is recessed toward the printed circuit board.

[0014] According to the circuit board described in (3) above, since the resin material is recessed in a concave shape, it is possible to more reliably suppress the resin material from protruding from the space.

[0015] (4) In the circuit board described in any one of (1) to (3) above, the inner circumferential surface of the frame component may be tapered, with the inner diameter narrowing from one side to the other in a direction perpendicular to the surface of the printed circuit board.

[0016] According to the circuit board described in (4) above, if one side is the printed circuit board side with respect to the frame component and the other side is the side away from the printed circuit board, the inner diameter narrows in the direction away from the printed circuit board. In this case, the resin material is held in place by the inner circumferential surface of the frame component, making it difficult for the resin material to come off. Conversely, if one side is the side away from the printed circuit board with respect to the frame component and the other side is the printed circuit board side, the inner diameter narrows toward the printed circuit board. In this case, the inner circumferential surface of the frame component is held in place by the resin material, making it difficult for the frame component to come off.

[0017] (5) In the circuit board described in any one of (1) to (4) above, the printed circuit board is a flexible printed circuit board, and a plate-shaped component may be attached to the surface of the flexible printed circuit board opposite to the surface on which the electronic components are mounted, in a range that includes the area obtained by projecting the electronic components onto the opposite surface.

[0018] According to the circuit board described in (5) above, the presence of plate-shaped components allows for physical protection of the flexible printed circuit board and improvement of its strength.

[0019] [Details of Embodiments of the Disclosure] Details of embodiments of the Disclosure are described below. The Disclosure is not limited to these examples and is intended to include all modifications within the meaning and scope equivalent to the claims, as indicated by the claims.

[0020] <Embodiment 1> Embodiment 1 will be described with reference to Figures 1 to 3. In the following description, the front-rear direction and left-right direction will be based on the front-rear direction and left-right direction shown in Figure 1, and the up-down direction will be based on the up-down direction shown in Figure 2.

[0021] [1] Circuit board diagram 1 will be used to describe the circuit board 1 according to Embodiment 1. The circuit board 1 is a temperature detection circuit board that is placed on the upper or lower surface of a predetermined device to detect the temperature of the device. The circuit board 1 comprises a flexible printed circuit board 2 (FPC) as a printed circuit board, a thermistor 3 as an electronic component, a frame component 4, a resin material 5 (see Figure 2), and a metal plate 6 (see Figure 2) as a plate-shaped component. In the following description, the flexible printed circuit board 2 will be referred to as FPC2.

[0022] [1-1] FPC As shown in Figure 2, the FPC 2 comprises a base layer 2A made of a thin insulating material such as a plastic film, a temperature detection line 2B formed by patterning copper foil formed on the base layer 2A, and a coverlay layer 2C made of a thin insulating material. An opening 2D is formed in the coverlay layer 2C where the thermistor 3 is mounted, and the temperature detection line 2B is exposed.

[0023] [1-2] Thermistor Thermistor 3 is an electronic component that detects temperature. A PTC (Positive Temperature Coefficient) thermistor or an NTC (Negative Temperature Coefficient) thermistor can be used as thermistor 3. The electrode 3A of thermistor 3 is soldered to the temperature detection line 2B with solder 7. If there are strict constraints on the height of the circuit board 1, it is preferable that thermistor 3 be thin.

[0024] [1-3] As shown in Figure 1 of the frame component, the frame component 4 is fixed to the surface on which the thermistor 3 is mounted in the FPC 2 and surrounds the thermistor 3. The frame component 4 is rectangular in top view and has a roughly circular through hole 4A that penetrates in the vertical direction (perpendicular to the plane of the paper in Figure 1). The shape of the frame component 4 is not limited to a rectangular shape and can be any suitable shape. The shape of the through hole 4A is also not limited to a roughly circular shape and can be any suitable shape.

[0025] The frame component 4 is made of an insulating resin material. The frame component 4 is fixed to the FPC 2 using double-sided tape or adhesive after the thermistor 3, which is mounted on the FPC 2 during the mounting process, is heated and soldered during the reflow process. The reason the frame component 4 is fixed after the reflow process is that, since the frame component 4 is made of resin, there is a risk that it will melt due to the heat of the reflow process if it is fixed before the reflow process.

[0026] As shown in Figure 2, the frame component 4 has a certain thickness. Specifically, the thickness of the frame component 4 (in other words, its width in the vertical direction) is greater than the thickness of the thermistor 3. Therefore, the thermistor 3 is housed within the space 4C enclosed by the inner circumferential surface 4B of the frame component 4. The inner circumferential surface 4B of the frame component 4 according to Embodiment 1 is tapered, with the inner diameter narrowing from the lower side (one example of one side) to the upper side (an example of the other side) in the vertical direction (an example of the direction perpendicular to the surface of the printed circuit board). Therefore, the inner diameter of the inner circumferential surface 4B narrows in the direction away from the FPC 2.

[0027] [1-4] The resin material 5 is provided to insulate and waterproof the thermistor 3. The resin material 5 is filled (potted) into the space 4C of the frame component 4 and covers the entire thermistor 3. The resin material 5 is, for example, an epoxy resin mixed with a hardening agent that has been cured with ultraviolet light, and has insulating and waterproof properties. The material of the resin material 5 is not limited to epoxy resin; other materials may be used as long as they can be filled into the space 4C and cured, and have insulating and waterproof properties. The resin material 5 is contained within the space 4C and does not protrude above the space 4C. More specifically, the upper surface 5A of the resin material 5 (in other words, the surface 5A of the resin material 5 opposite to the FPC 2) is concave towards the FPC 2 side.

[0028] [1-5] Metal Plate The metal plate 6 (an example of a plate-shaped component) is attached to the back surface of the FPC2 (in other words, the side of the FPC2 opposite to the side on which the thermistor 3 is mounted). The metal plate 6 is made of copper or aluminum, for example. Specifically, as shown in Figure 3, the metal plate 6 is attached to the area on the back surface of the FPC2 that includes the area on which the thermistor 3 is projected onto the back surface. In the example shown in Figure 3, the metal plate 6 is attached to an area that includes not only the area on which the thermistor 3 is projected onto the back surface, but also the area on which the frame component 4 is projected onto the back surface. The reason for attaching the metal plate 6 is to provide physical protection for the FPC2, improve its strength, and improve the temperature measurement accuracy of the thermistor 3.

[0029] [2] As shown in Figure 2 of the embodiment, the circuit board 1 according to embodiment 1 has a frame component 4 which prevents the final shape of the resin material 5 from being determined by chance. Therefore, it becomes easier to control the height dimension of the circuit board 1 in which the thermistor 3 is covered by the resin material 5 and the spread dimension of the resin material 5.

[0030] According to the circuit board 1, since the resin material 5 is contained within the space 4C (in other words, the resin material 5 does not protrude from the space 4C), the height of the circuit board 1 can be controlled by the height of the frame component 4 rather than the resin thickness. Therefore, it becomes easier to control the height dimension when there are strict constraints on the height of the circuit board 1.

[0031] According to the circuit board 1, the upper surface 5A of the resin material 5 is concave, which more reliably prevents the resin material 5 from protruding from the space 4C.

[0032] According to the circuit board 1, the inner diameter of the inner circumferential surface 4B of the frame component 4 narrows in the direction away from the FPC 2. In this way, the resin material 5 is held in place by the inner circumferential surface 4B of the frame component 4, making it difficult for the resin material 5 to come off.

[0033] According to the circuit board 1, the presence of the metal plate 6 provides physical protection and improves the strength of the FPC 2. If the electronic component is a thermistor 3, the metal plate 6 can also improve the accuracy of temperature measurement by receiving heat from the object being measured.

[0034] <Embodiment 2> Referring to Figure 4, the circuit board 201 according to Embodiment 2 will be described. The inner circumferential surface 204B of the frame component 204 of the circuit board 201 is tapered, with the inner diameter narrowing from the upper side (one example of one side) to the lower side (an example of the other side) in the vertical direction (an example of a direction perpendicular to the board surface of the printed circuit board). Therefore, the inner diameter of the inner circumferential surface 204B narrows toward the FPC2. In this way, the inner circumferential surface 204B of the frame component 204 is held in place by the resin material 5, making it difficult for the frame component 204 to come off.

[0035] <Other Embodiments> The technology disclosed herein is not limited to the embodiments described above in the description and drawings, and the following embodiments, for example, are also included in the technical scope disclosed herein.

[0036] (1) In the above embodiment, thermistor 3 was used as an example of an electronic component, but the electronic component is not limited to thermistor 3 and may be other electronic components. For example, the electronic component may be a chip fuse.

[0037] (2) In the above embodiment, the case in which the resin material 5 is contained within the space 4C was illustrated. In contrast, if, for example, there are no strict constraints on the height dimension of the circuit board 1 and only the spread dimension of the resin material 5 needs to be controlled, the resin material 5 may protrude above the space 4C.

[0038] (3) In the above embodiment, the upper surface 5A of the resin material 5 was shown as a concave shape, but the upper surface 5A does not have to be concave as long as the resin material 5 does not protrude above the space 4C. For example, the upper surface 5A may be a flat surface that is flush with the upper surface of the frame component 4.

[0039] (4) In the above embodiment, the resin material 5 was shown as having insulating and waterproof properties, but the resin material 5 may have only one of these properties. For example, if the circuit board 1 is located in a place where the possibility of short circuits is low, the resin material 5 does not need to have insulating properties. Alternatively, if the circuit board 1 is located in a place that is completely sealed and where condensation is unlikely to occur, the resin material 5 does not need to have waterproof properties.

[0040] (5) In the above embodiment, the case where the inner peripheral surface 4B of the frame component 4 is tapered has been exemplified. However, the inner peripheral surface 4B does not have to be tapered. That is, the inner diameter of the inner peripheral surface 4B of the frame component 4 may be constant from top to bottom.

[0041] (6) In the above embodiment, the case where the frame component 4 is made of resin has been exemplified. However, if the possibility of the circuit board 1 being short-circuited is low even when the frame component 4 is made of metal, the frame component 4 may be made of metal. However, in order to reliably protect the circuit board 1 from short-circuiting, it is preferable that the frame component 4 is made of resin.

[0042] (7) In the above embodiment, the case where the metal plate 6 is attached to the back surface of the FPC 2 has been exemplified. However, the metal plate 6 does not have to be attached.

[0043] (8) In the above embodiment, the metal plate 6 has been exemplified as the plate-like component. However, the material of the plate-like component is not limited to metal and may be resin.

[0044] (9) In the above embodiment, the FPC 2 has been exemplified as the printed circuit board. However, the printed circuit board may be a rigid printed circuit board (so-called rigid substrate). Examples of the rigid substrate include a so-called glass epoxy substrate in which glass fiber is impregnated with epoxy resin.

[0045] (10) As described above, the shape of the through-hole 4A of the frame component 4 is not limited to a substantially circular shape, and an appropriate shape can be adopted. For example, the through-hole 4A may be square, rectangular, elliptical, or a so-called racetrack shape composed of two parallel straight lines and two semi-circles. As the shape of the through-hole 4A, a shape that substantially matches the shape of the electronic component may be adopted. For example, when the shape of the electronic component is rectangular, if the shape of the through-hole 4A is also rectangular, the distance between the electronic component and the inner peripheral surface of the through-hole 4A can be made substantially constant over the entire circumference of the electronic component. By doing so, the creepage distance from an arbitrary position at a certain distance from the electronic component to the electronic component can be made substantially constant.

[0046] 1: Circuit board 2: FPC (Flexible Printed Circuit Board) 2A: Base layer 2B: Temperature detection line 2C: Coverlay layer 2D: Opening 3: Thermistor 3A: Electrode 4: Frame component 4A: Through hole 4B: Inner surface 4C: Space 5: Resin material 5A: Top surface 6: Metal plate 7: Solder 201: Circuit board 204: Frame component 204B: Inner surface

Claims

1. A circuit board comprising: a printed circuit board; electronic components mounted on the printed circuit board; a frame component fixed to the surface of the printed circuit board on which the electronic components are mounted and surrounding the electronic components; and a resin material filling the space surrounded by the inner circumferential surface of the frame component and covering the electronic components.

2. A circuit board according to claim 1, wherein the resin material is contained within the space.

3. A circuit board according to claim 2, wherein the side of the resin material opposite to the printed circuit board is a concave surface that is recessed toward the printed circuit board.

4. A circuit board according to any one of claims 1 to 3, wherein the inner circumferential surface of the frame component is tapered, with the inner diameter narrowing from one side to the other in a direction perpendicular to the surface of the printed circuit board.

5. A circuit board according to any one of claims 1 to 3, wherein the printed circuit board is a flexible printed circuit board, and a plate-shaped component is attached to the surface of the flexible printed circuit board opposite to the surface on which the electronic components are mounted, in a range that includes an area obtained by projecting the electronic components onto the opposite surface.

Images