Circuit unit

Abstract

Disclosed is a circuit unit capable of suppressing or preventing deformation of a circuit board due to molding pressure of a mold resin.　A circuit unit 10 includes: a circuit board 12; a first electronic component 14 mounted on one surface 20 side of the circuit board 12; a first hollow case 18 mounted on the one surface 20 side of the circuit board and constituting a first hollow part 21 around the first electronic component 14 to cover the first electronic component 14; a deformation suppression member 24 mounted on the other surface 22 side of the circuit board 12 and arranged opposite to the first hollow part 21 across the circuit board 12 to suppress deformation of the circuit board 12; and a mold resin 16 for embedding, inside, the circuit board 12 and the first electronic component 14, the first hollow case 18, and the deformation suppression member 24 that are mounted on the circuit board 12.

Description

Circuit Unit

[0001] The present disclosure relates to a circuit unit.

[0002] Patent Document 1 proposes a structure in which a hollow case with a hollow interior is placed around the electronic components in a circuit unit in which a circuit board on which electronic components are mounted is embedded inside molded resin. In the structure of Patent Document 1, the top and side surfaces of the electronic components are covered by the hollow case placed across a gap, so that the electronic components can be protected from the adverse effects of molding pressure and heat of the resin when molding the molded resin around the circuit board.

[0003] Japanese Patent Application Laid-Open No. 2023-171548

[0004] However, in a circuit unit such as that disclosed in Patent Document 1, in the mounting portion of the circuit board where the electronic components are mounted and its surrounding area, the molding pressure of the resin acting on one side of the circuit board is absorbed or buffered by the hollow portion of the hollow case, while the molding pressure of the resin is directly acting on the other side of the circuit board. Therefore, if the molding temperature in the molding process of the molded resin exceeds the glass transition temperature of the circuit board, the rigidity of the circuit board decreases, and there is a risk that the circuit board will be deformed as if it is pressed toward the hollow case.

[0005] Therefore, a circuit unit is disclosed that can suppress or prevent deformation of the circuit board due to the molding pressure of the molding resin.

[0006] The circuit unit of the present disclosure comprises a circuit board, a first electronic component mounted on one side of the circuit board, a first hollow case mounted on the one side of the circuit board to form a first hollow portion around the first electronic component and cover the first electronic component, a deformation suppression member mounted on the other side of the circuit board and positioned opposite the first hollow portion with the circuit board in between to suppress deformation of the circuit board, and a molded resin that embeds the circuit board, the first electronic component mounted on the circuit board, the first hollow case, and the deformation suppression member inside.

[0007] According to the circuit unit of the present disclosure, deformation of the circuit board due to the molding pressure of the molding resin can be suppressed or prevented.

[0008] Fig. 1 is a longitudinal cross-sectional view showing a circuit unit according to a first embodiment. Fig. 2 is a perspective view from the top side showing the circuit unit shown in Fig. 1 with the molding resin removed. Fig. 3 is a perspective view from the bottom side of the circuit unit shown in Fig. 2. Fig. 4 is a longitudinal cross-sectional view showing a circuit unit according to a second embodiment. Fig. 5 is a longitudinal cross-sectional view showing a circuit unit according to a third embodiment. Fig. 6 is a longitudinal cross-sectional view showing a circuit unit according to a fourth embodiment. Fig. 7 is a longitudinal cross-sectional view showing a circuit unit according to another aspect of the present disclosure.

[0009] <Description of Embodiments of the Present Disclosure> First, embodiments of the present disclosure will be described. A circuit unit of the present disclosure includes: (1) a circuit board, a first electronic component mounted on one surface of the circuit board, a first hollow case mounted on the one surface of the circuit board to define a first hollow portion around the first electronic component and cover the first electronic component, a deformation suppressing member mounted on the other surface of the circuit board to face the first hollow portion with the circuit board therebetween and suppress deformation of the circuit board, and a molded resin in which the circuit board, the first electronic component mounted on the circuit board, the first hollow case, and the deformation suppressing member are embedded.

[0010] According to the circuit unit of the present disclosure, a first electronic component and a first hollow case that surrounds the first electronic component are mounted on one side of a circuit board, and a first hollow portion is formed between the first electronic component and the first hollow case and the first electronic component. Furthermore, a deformation suppressing member is mounted on the other side of the circuit board, facing the first hollow portion with the circuit board sandwiched therebetween. As a result, during a molding process in which a molded resin is molded around the circuit board with the first electronic component, the first hollow case, and the deformation suppressing member mounted thereon, the molding pressure of the resin applied to the one side of the circuit board is absorbed or buffered by the first hollow portion. Furthermore, during this molding process, deformation of the circuit board due to the molding pressure of the molded resin, which could not be suppressed in conventional structures in which a hollow case is provided only on one side of the circuit board, can be suppressed by the deformation suppressing member mounted on the other side of the circuit board. As a result, even if the molding temperature in the molding process of the mold resin exceeds the glass transition temperature of the circuit board and the rigidity of the circuit board decreases, deformation of the circuit board due to the molding pressure of the mold resin can be suppressed or prevented.

[0011] The first electronic component mounted on one surface of the circuit board may be mounted directly on the conductive path of the circuit board, or may be mounted on one surface of the circuit board by being mounted on another circuit body such as a bus bar or a flexible printed circuit board placed on one surface of the circuit board. The first hollow case mounted on one surface of the circuit board and the second hollow case mounted on the other surface of the circuit board may also be mounted directly on the circuit board, or may be mounted on the circuit board via another circuit body.

[0012] (2) In the above (1), it is preferable that the deformation suppressing member includes a second hollow case mounted on the other surface of the circuit board and defining a second hollow portion facing the first hollow portion with the circuit board sandwiched therebetween. The second hollow case, which is the deformation suppressing member, is mounted on the other surface of the circuit board, defining a second hollow portion facing the first hollow portion with the circuit board sandwiched therebetween. This allows the first hollow portion to absorb or buffer the molding pressure of the resin applied to one surface of the circuit board during a molding process of molding a molded resin around the circuit board on which the first electronic component, the first hollow case, and the second hollow case are mounted, while the second hollow portion, which faces the first hollow portion with the circuit board sandwiched therebetween, similarly absorbs or buffers the molding pressure of the resin applied to the other surface of the circuit board. Therefore, compared to conventional structures in which a hollow case is provided only on one side of the circuit board, it is possible to prevent the molding pressure of the resin from being applied unevenly to one side and the other side of the circuit board, and as a result, even if the molding temperature in the molding process of the mold resin exceeds the glass transition temperature of the circuit board and the rigidity of the circuit board decreases, it is possible to suppress or prevent deformation of the circuit board due to the molding pressure of the mold resin.

[0013] (3) In the above (2), it is preferable that the first hollow portion and the second hollow portion coincide with each other when projected in the thickness direction of the circuit board. Since the first hollow portion and the second hollow portion coincide with each other when projected in the thickness direction of the circuit board, the molding pressure applied to the circuit board can be similarly absorbed or buffered by the hollow portions, and deformation of the circuit board can be more effectively prevented or suppressed.

[0014] (4) In the above (2) or (3), it is preferable that the device further includes a second electronic component mounted on the other surface of the circuit board, and the second electronic component is covered by the second hollow case via the second hollow portion. The second hollow case can cover the second electronic component mounted on the other surface of the circuit board via the second hollow portion, and the second hollow case can have the function of protecting the second electronic component in addition to absorbing the molding pressure of the resin.

[0015] (5) In any one of (2) to (4) above, it is preferable that the protrusion dimension of the second hollow case from the other surface of the circuit board is smaller than the protrusion dimension of the first hollow case from the one surface of the circuit board. In cases where the purpose of providing the second hollow case is simply to provide a second hollow portion opposite the first hollow portion, or where the second hollow case also serves the function of covering electronic components that are smaller than the electronic components enclosed by the first hollow case, the protrusion height of the second hollow case can be made smaller than the protrusion height of the first hollow case, thereby achieving a compact circuit unit.

[0016] (6) In any one of (2) to (5) above, it is preferable that the first hollow case and the second hollow case are formed of a material having a glass transition temperature equal to or higher than the molding temperature of the mold resin. Since the first hollow case and the second hollow case are formed of a material having a glass transition temperature equal to or higher than the molding temperature of the mold resin, deformation of the first hollow case and the second hollow case during molding of the mold resin is advantageously prevented, and the first hollow portion and the second hollow portion are reliably maintained, thereby more advantageously suppressing or preventing deformation of the substrate.

[0017] (7) In any one of (2) to (5) above, it is preferable that at least one of the first hollow case and the second hollow case be made of metal. The first hollow case or the second hollow case made of metal is less likely to deform due to the molding temperature of the molded resin, so deformation of the hollow case is advantageously prevented. Therefore, the first hollow portion of the first hollow case made of metal or the second hollow portion of the second hollow case made of metal can be reliably maintained, thereby more advantageously suppressing or preventing deformation of the substrate.

[0018] (8) In the above (1), it is preferable that the deformation suppression member includes a plate member mounted on the other surface of the circuit board and arranged opposite the first hollow portion with the circuit board sandwiched therebetween, the plate member being formed of a material having a glass transition temperature equal to or higher than the molding temperature of the mold resin. Because the plate member constituting the deformation suppression member is formed of a material having a glass transition temperature equal to or higher than the molding temperature of the mold resin, deformation of the plate member during molding of the mold resin is advantageously prevented. Furthermore, because the plate member is arranged opposite the first hollow portion with the circuit board sandwiched therebetween, molding pressure of the mold resin from the other surface of the circuit board where the first hollow portion is located on one surface can be received by the plate member and prevented from being directly transmitted to the circuit board. As a result, deformation of the circuit board toward the first hollow portion, which was a problem in conventional structures, can be advantageously suppressed or prevented.

[0019] <Details of the Embodiments of the Present Disclosure> Specific examples of the resin-sealed unit of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0020] First Embodiment A circuit unit 10 according to a first embodiment of the present disclosure will be described below with reference to FIGS. 1 to 3. The circuit unit 10 has a structure in which a circuit board 12 and a first electronic component (a capacitor 14, as a specific example) are encapsulated within a molded resin 16. The molded resin 16 protects the circuit board 12 and the capacitor 14 from exposure to water or external forces and improves heat dissipation when the circuit board 12 or the capacitor 14 generate heat. Within the molded resin 16, the capacitor 14 is covered by a first hollow case 18, preventing the capacitor 14 from being subjected to heat, pressure, and the like that occurs during molding of the molded resin 16. While the circuit unit 10 can be positioned in any orientation, in the following description, the upper side will be referred to as the upper side in FIG. 1, the lower side will be referred to as the lower side in FIG. 1, the left side will be referred to as the left side in FIG. 1, the right side will be referred to as the right side in FIG. 1, the front side will be referred to as the front side of the page in FIG. 1, and the rear side will be referred to as the rear side of the page in FIG. 1. In the following description, when multiple identical components are used, only some of the components may be designated by reference numerals, and the reference numerals may be omitted for the other components.

[0021] <Circuit Unit 10> The circuit unit 10 includes a circuit board 12, a capacitor 14 as a first electronic component mounted on an upper surface 20, which is one surface of the circuit board 12, and a first hollow case 18 mounted on the upper surface 20 of the circuit board 12 to define a first hollow portion 21 around the capacitor 14 and cover the capacitor 14. The circuit unit 10 also includes a deformation suppressing member mounted on a lower surface 22, which is the other surface of the circuit board 12, and disposed opposite the first hollow portion 21 with the circuit board 12 therebetween to suppress deformation of the circuit board 12. The circuit unit 10 also includes a molded resin 16 that embeds the circuit board 12, the capacitor 14 mounted on the circuit board 12, the first hollow case 18, and the deformation suppressing member therein. In embodiment 1, the deformation suppression member is composed of a second hollow case 24 having a second hollow portion 23, and inside the second hollow case 24 (second hollow portion 23), a field effect transistor (FET) 26 as a second electronic component is mounted on the underside 22 of the circuit board 12.

[0022] <Circuit Board 12> The circuit board 12 of the first embodiment is, for example, a known rigid printed circuit board (PCB) that extends in the horizontal direction (a direction perpendicular to the up-down direction). An electric circuit (not shown) is printed on at least one surface (e.g., the upper surface 20) of the circuit board 12, and in the first embodiment, the electric circuit is printed on both surfaces (the upper surface 20 and the lower surface 22) of the circuit board 12.

[0023] The base plate portion constituting the circuit board 12 is formed of, for example, a known synthetic resin. The glass transition temperature (Tg) of this base plate portion is determined by the material of the synthetic resin constituting the base plate portion, and is not limited thereto. However, when a general synthetic resin is used as the material of the base plate portion, the glass transition temperature of the base plate portion is, for example, about 140°C.

[0024] Although the first electronic component mounted on the upper surface 20 of the circuit board 12 is not limited to a specific one, in the first embodiment it is a capacitor 14. As a known capacitor 14 is used, detailed description thereof will be omitted.

[0025] <Molded Resin 16> As described above, the circuit board 12, which includes the first hollow case 18 on the upper surface 20 and the second hollow case 24 on the lower surface 22, is covered with molded resin 16. The external shape of the molded resin 16 is not limited, but in embodiment 1, it has a substantially rectangular cross section as shown in FIG. 1 and is generally shaped like a rectangular parallelepiped. This molded resin 16 is made of, for example, a thermosetting resin. The temperature of heat applied when curing the thermosetting resin is determined by the type of thermosetting resin and is not limited, but in embodiment 1, the temperature applied when curing the thermosetting resin constituting the molded resin 16 is approximately 170°C. Therefore, the molding temperature when curing the molded resin 16 is set higher than the glass transition temperature of the circuit board 12 (base plate portion).

[0026] <First hollow case 18> The first hollow case 18 has an overall generally box-like shape that opens downward or a generally cylindrical shape that opens downward and has a bottom. In the first embodiment, the first hollow case 18 has a generally cylindrical shape that has a bottom. Note that the first hollow case 18 is shown in a transparent state in FIG. 2. The first hollow case 18 is formed, for example, from a thermosetting resin or a thermoplastic resin that has a high glass transition temperature. The synthetic resin material that constitutes the first hollow case 18 has a glass transition temperature that is equal to or higher than the temperature at which the mold resin 16 is formed.

[0027] Specifically, the first hollow case 18 includes a circular upper bottom wall portion 28 and an upper peripheral wall portion 30 that protrudes downward from the outer periphery of the upper bottom wall portion 28. The upper bottom wall portion 28 and the upper peripheral wall portion 30 each have a predetermined thickness. Although not limited thereto, the upper bottom wall portion 28 and the upper peripheral wall portion 30 are formed with, for example, a substantially constant thickness. The area surrounded by the upper bottom wall portion 28 and the upper peripheral wall portion 30 is a first hollow portion 21, and a first electronic component (capacitor 14) is housed within this first hollow portion 21. In other words, the first hollow portion 21 is formed around the capacitor 14 inside the first hollow case 18. Therefore, the size and shape of the first hollow case 18 can be appropriately changed depending on the size and shape of the electronic component to be housed in the first hollow portion 21.

[0028] In the first embodiment, a flange-shaped portion 34 is provided at the lower opening at the lower end of the upper peripheral wall portion 30, expanding outward like a flange. That is, the flange-shaped portion 34 expands in a horizontal annular shape, and in the first embodiment, the outer shape of the flange-shaped portion 34 is substantially rectangular in plan view. The lower surface of the flange-shaped portion 34 extends flat, and the lower surface of the flange-shaped portion 34 is superimposed on the portion of the upper surface 20 of the circuit board 12 surrounding the capacitor 14, thereby fixing the circuit board 12 and the first hollow case 18 to each other. In the first embodiment, the circuit board 12 and the first hollow case 18 are fixed by adhesive, and the overlapping surfaces of the flange-shaped portion 34 and the circuit board 12 are hermetically sealed. By fixing the circuit board 12 and the first hollow case 18 in this manner, air is sealed inside the first hollow case 18 (first hollow portion 21).

[0029] <Deformation Suppression Member (Second Hollow Case 24)> In the first embodiment, the deformation suppression member includes a second hollow case 24 mounted on the underside 22 of the circuit board 12 and defining a second hollow section 23 facing the first hollow section 21 with the circuit board 12 sandwiched therebetween. The second hollow case 24 has an overall generally box-like shape that opens upward or a generally cylindrical shape with a bottom that opens upward. In the first embodiment, the second hollow case 24 has a generally cylindrical shape with a bottom. Note that the second hollow case 24 is shown transparent in FIG. 3 . The second hollow case 24 is made of, for example, the same material as the first hollow case 18, and the synthetic resin material used for the second hollow case 24 has a glass transition temperature that is equal to or higher than the temperature at which the mold resin 16 is molded.

[0030] Specifically, the second hollow case 24 includes a circular bottom wall 36 and a lower peripheral wall 38 that protrudes upward from the outer periphery of the bottom wall 36. The bottom wall 36 and the lower peripheral wall 38 each have a predetermined thickness. While not limited to this, the bottom wall 36 and the lower peripheral wall 38 are formed with, for example, a substantially constant thickness. The area surrounded by the bottom wall 36 and the lower peripheral wall 38 is the second hollow portion 23. In the first embodiment, the second hollow portion 23 accommodates a second electronic component (FET 26) mounted on the lower surface 22 of the circuit board 12. In other words, the circuit unit 10 includes the FET 26 as the second electronic component mounted on the lower surface 22 of the circuit board 12. The second hollow portion 23 is formed around the FET 26 inside the second hollow case 24, and the FET 26 is covered by the second hollow case 24 via the second hollow portion 23. Since a known FET is used as the FET 26, detailed description thereof will be omitted. The size, shape, etc. of the second hollow case 24 can also be appropriately changed depending on the size, shape, etc. of the electronic component to be housed in the second hollow portion 23.

[0031] In the first embodiment, as described above, the first electronic component mounted on the upper surface 20 of the circuit board 12 is the capacitor 14, and the second electronic component mounted on the lower surface 22 of the circuit board 12 is the FET 26. Generally, the FET 26 has a smaller height than the capacitor 14. Therefore, in the first embodiment, the height (vertical dimension) of the second hollow case 24 is smaller than the height (vertical dimension) of the first hollow case 18. Specifically, the protrusion dimension of the second hollow case 24 from the lower surface 22 of the circuit board 12 is smaller than the protrusion dimension of the first hollow case 18 from the upper surface 20 of the circuit board 12.

[0032] Furthermore, in the first embodiment, a flange-shaped portion 42 similar to that of the first hollow case 18 is also provided at the upper opening at the upper end of the lower peripheral wall portion 38. The flange-shaped portion 42 of the second hollow case 24 is also overlapped with the portion of the lower surface 22 of the circuit board 12 surrounding the FET 26, and the circuit board 12 and the second hollow case 24 are fixed by adhesive. As a result, in the first embodiment, the overlapping surfaces of the flange-shaped portion 42 and the circuit board 12 are hermetically sealed. Furthermore, by fixing the circuit board 12 and the second hollow case 24 in this manner, air is sealed inside the second hollow case 24 (second hollow portion 23).

[0033] In particular, in the first embodiment, the first hollow portion 21 and the second hollow portion 23 coincide when projected in the thickness direction (vertical direction) of the circuit board 12. Specifically, the second hollow case 24, including the flange-shaped portion 42, is formed to have the same shape and size as the first hollow case 18 in a plan view, and the thickness dimension (left-right dimension) of the upper peripheral wall portion 30 of the first hollow case 18 and the thickness dimension (left-right dimension) of the lower peripheral wall portion 38 of the second hollow case 24 are substantially equal. Furthermore, the first hollow case 18 and the second hollow case 24 are fixed in positions where they entirely overlap in a plan view on both the upper and lower sides of the circuit board 12. As a result, the first hollow portion 21 formed on the inner periphery of the upper peripheral wall portion 30 of the first hollow case 18 and the second hollow portion 23 formed on the inner periphery of the lower peripheral wall portion 38 of the second hollow case 24 are positioned to coincide when projected in the vertical direction.

[0034] The circuit unit 10 having the above-described shape can be manufactured, for example, by the following method: First, the capacitor 14 is mounted on the upper surface 20 of the circuit board 12, and the FET 26 is mounted on the lower surface 22 of the circuit board 12. Then, the flange portion 34 of the first hollow case 18 is superimposed and adhered around the capacitor 14 on the upper surface 20 of the circuit board 12, and the flange portion 42 of the second hollow case 24 is superimposed and adhered around the FET 26 on the lower surface 22 of the circuit board 12.

[0035] Then, the circuit board 12 to which the first hollow case 18 and the second hollow case 24 are fixed is set in a mold for molding the molded resin 16, and the mold is filled with resin material for the molded resin 16, followed by heating and pressurization to form the molded resin 16. Note that, for example, conductive members (not shown) made of electric wires, bus bars, etc. for supplying power to the circuit board 12 are connected to the circuit board 12, and the conductive members are exposed on the outer surface of the molded resin 16 when the molded resin 16 is molded. In this way, the circuit unit 10 of embodiment 1 is completed.

[0036] In the circuit unit 10 formed in this manner, the circuit board 12, to which the first hollow case 18 and the second hollow case 24 are fixed on both the upper and lower surfaces 20, 22, is surrounded by the molded resin 16, thereby protecting the circuit board 12 from exposure to water or external forces. Furthermore, the capacitors 14 and FETs 26 mounted on the circuit board 12 generate heat when current is applied to them, but by using a material with good thermal conductivity for the molded resin 16, the heat generated in the capacitors 14 and FETs 26 can be stably dissipated via the molded resin 16.

[0037] According to the circuit unit 10 of the first embodiment having the above-described structure, by providing a deformation suppressing member (second hollow case 24) on the opposite side of the first hollow case 18 (first hollow portion 21) that surrounds the capacitor 14, sandwiching the circuit board 12 in the vertical direction, deformation of the circuit board 12 can be suppressed even when heating and pressure are applied during molding of the molded resin 16. That is, the glass transition temperature of the circuit board 12 (base plate portion) is generally lower than the molding temperature of the molded resin 16, and the first hollow case is merely filled with air. Therefore, in the case where a deformation suppressing member is not provided on the underside of the circuit board as in the conventional structure, when heating and pressure are applied during molding of the molded resin, the molding pressure is applied from below, which tends to cause deformation of the portion of the circuit board located below the first hollow case into the first hollow case.

[0038] In contrast, by providing the second hollow case 24 as a deformation suppression member on the lower surface 22 side, which is the opposite side in the vertical direction to the first hollow case 18 with the circuit board 12 sandwiched therebetween, as in the first embodiment, the molded resin 16 does not come into direct contact with the portion of the circuit board 12 located below the first hollow case 18, and this prevents the circuit board 12 from being adversely affected by heat or pressure when the molded resin 16 is molded. As a result, deformation of the circuit board 12 when the molded resin 16 is molded can be suppressed.

[0039] In the first embodiment, as described above, the deformation suppressing member is configured by the second hollow case 24 having the second hollow portion 23. That is, the heat and pressure generated during molding of the molded resin 16 are exerted on the circuit board 12 via the deformation suppressing member, but the heat and pressure are exerted not only through the second hollow case 24 made of synthetic resin, but also through the second hollow portion 23 formed of air sealed inside the second hollow case 24. Therefore, the effect of the heat and pressure generated during molding of the molded resin 16 on the circuit board 12 is reduced, and deformation of the circuit board 12 can be more reliably prevented.

[0040] The first hollow portion 21 and the second hollow portion 23 coincide when projected in the thickness direction (vertical direction) of the circuit board 12. In particular, in the first embodiment, the first hollow case 18 and the second hollow case 24 constituting the first hollow portion 21 and the second hollow portion 23, respectively, are provided in positions that overlap when projected in the vertical direction. This prevents deformation of the portions of the circuit board 12 that do not overlap when projected in the vertical direction due to heat or pressure during molding of the molded resin 16, for example, when one of the first hollow portion (first hollow case) and the second hollow portion (second hollow case) is larger than the other when projected in the vertical direction. In other words, by providing the first hollow portion 21 (first hollow case 18) and the second hollow portion 23 (second hollow case 24) in positions that overlap when projected in the vertical direction, deformation of the portion of the circuit board 12 sandwiched between the first hollow case 18 and the second hollow case 24 can be more reliably suppressed.

[0041] A second electronic component, a FET 26, is mounted on the underside 22 of the circuit board 12, and the FET 26 is covered by the second hollow case 24 via the second hollow portion 23. In other words, the second electronic component, the FET 26, can be disposed by making good use of the internal space (second hollow portion 23) of the second hollow case 24, which functions as a deformation suppression member. This allows not only the first electronic component (capacitor 14) but also the second electronic component (FET 26) to be mounted on the circuit board 12, thereby providing a circuit unit 10 that can perform a greater number of functions.

[0042] In particular, the protrusion dimension of the first hollow case 18 from the upper surface 20 of the circuit board 12 is set to be larger than the protrusion dimension of the second hollow case 24 from the lower surface 22 of the circuit board 12. Therefore, it is possible to place a first electrical component (e.g., capacitor 14) that has a larger vertical dimension than a second electronic component (e.g., FET 26) placed in the second hollow case 24 (second hollow portion 23) inside the first hollow case 18 (first hollow portion 21).

[0043] The first hollow case 18 and the second hollow case 24 are formed from a material having a glass transition temperature equal to or higher than the molding temperature of the molded resin 16. This prevents the heat and pressure generated during molding of the molded resin 16 from being applied to the circuit board 12 via the first hollow case 18 or the second hollow case 24, thereby more reliably preventing deformation of the circuit board 12 between the first hollow case 18 and the second hollow case 24.

[0044] Second Embodiment A circuit unit 50 according to a second embodiment of the present disclosure will be described below with reference to Fig. 4. The circuit unit 50 according to the second embodiment has a similar basic structure to the circuit unit 10 according to the first embodiment, but further includes a bus bar 52. In the second embodiment, the same members and parts as those in the first embodiment are denoted by the same reference numerals in the drawings, and detailed description thereof will be omitted.

[0045] As shown in Fig. 4 , in the second embodiment, the capacitor 14 is mounted on a bus bar 52, and the FET 26 is mounted on the circuit board 12. Specifically, the bus bar 52 is placed on the upper surface 20 of the circuit board 12 with an insulating sheet 54 interposed therebetween, and the capacitor 14 is mounted on the upper surface of the bus bar 52. As a result, the capacitor 14 as a first electronic component is mounted on one surface (the upper surface 20) of the circuit board 12. A first hollow case 18 is placed on the upper surface of the bus bar 52 around the capacitor 14 and fixed (for example, by adhesive). For ease of understanding, the thickness of the FET 26 is exaggerated in Fig. 4 .

[0046] The bus bar 52 has, for example, a flat plate shape that is substantially rectangular in plan view, and in the second embodiment, the bus bar 52 is smaller than the circuit board 12. The insulating sheet 54 has a substantially rectangular shape in plan view and is larger than the bus bar 52. Therefore, the bus bar 52 is superimposed on the circuit board 12 with the insulating sheet 54 interposed therebetween, so that the circuit board 12 and the bus bar 52 are superimposed in a non-conductive state. Therefore, conductive members (not shown) for supplying power extend from the circuit board 12 and the bus bar 52 separately, and when the molded resin 16 is molded to form the circuit unit 50, the conductive members extending from each are exposed on the outer surface of the molded resin 16.

[0047] Furthermore, the FET 26 is mounted on the lower surface 22 of the circuit board 12, as in the first embodiment, and a second hollow case 24 serving as a deformation suppression member is fixed around the FET 26 on the lower surface 22 of the circuit board 12. The first hollow case 18 and the second hollow case 24 have the same shapes as in the first embodiment, and the first hollow case 18 and the second hollow case 24 are fixed in positions where they entirely overlap in a plan view on both the upper and lower sides of the bus bar 52 and the circuit board 12.

[0048] The second embodiment, which has the above-described structure, also has the same basic structure as the first embodiment, and therefore can achieve the same effects as the first embodiment. Furthermore, in the second embodiment, the capacitor 14 is mounted on the bus bar 52. As a result, when the capacitor 14 generates heat due to the passage of current through the bus bar 52, which is made of metal and has good thermal conductivity, the heat is dissipated to the outside through the bus bar 52 and the molded resin 16 provided around the bus bar 52. Therefore, in the second embodiment, the bus bar 52 can also function as a heat sink. In particular, in the second embodiment, if the insulating sheet 54 has thermal conductivity, heat generated when the FET 26 is passed through the bus bar 52 is transferred to the bus bar 52 through the circuit board 12 and the insulating sheet 54. This allows dissipation of heat generated not only by the capacitor 14 but also by the FET 26. Furthermore, because the melting point of the metal bus bar 52 is higher than the temperature at which the molded resin 16 is formed, the metal bus bar 52 can prevent deformation of the circuit board 12 by being placed over the circuit board 12, thereby functioning as a deformation suppression member.

[0049] Third Embodiment A circuit unit 60 according to a third embodiment of the present disclosure will be described below with reference to Fig. 5 . The circuit unit 60 according to the third embodiment has the same basic structure as the circuit unit 10 according to the first embodiment, but further includes a flexible printed circuit board (FPC) 62. A known flexible printed circuit board may be used as the FPC 62, and in the third embodiment, an electrical circuit (not shown) is printed on both the top and bottom surfaces of the FPC 62. Note that the thickness of the FPC 62 is exaggerated in Fig. 5 for ease of understanding.

[0050] 5 , in the third embodiment, the capacitor 14 is mounted on the FPC 62, and the FET 26 is mounted on the circuit board 12. Specifically, the FPC 62 is overlaid on the top surface 20 of the circuit board 12, and the capacitor 14 is mounted on the top surface of the FPC 62. As a result, the capacitor 14 as a first electronic component is mounted on one surface (top surface 20) of the circuit board 12. Then, the first hollow case 18 is overlaid on the top surface of the FPC 62 around the capacitor 14 and fixed (for example, by adhesive).

[0051] Furthermore, the FET 26 is mounted on the underside 22 of the circuit board 12, as in the first embodiment, and a second hollow case 24 is fixed around the FET 26 on the underside 22 of the circuit board 12 as a deformation suppression member. The FPC 62 and the circuit board 12, which are stacked one on top of the other in the vertical direction, are electrically connected through electrical circuits provided on their respective overlapping surfaces. At least one of the circuit board 12 and the FPC 62 has a conductive member (not shown) extending therefrom for supplying power to the circuit board 12 and the FPC 62. When the molded resin 16 is molded to form the circuit unit 60, the conductive member is exposed on the outer surface of the molded resin 16. Note that the FPC 62 and the circuit board 12 may be stacked with an insulating sheet 54 interposed therebetween, as described in the second embodiment, and may not be electrically connected.

[0052] In addition, the first hollow case 18 and the second hollow case 24 have the same shape as in embodiment 1, and the first hollow case 18 and the second hollow case 24 are fixed in a position where they completely overlap in a planar view on both the upper and lower sides of the bus bar 52 and the circuit board 12.

[0053] In the third embodiment having the above-described structure, the basic structure is the same as that of the first embodiment, and therefore the same effect as that of the first embodiment is achieved, and the second hollow case 24 as a deformation suppression member can prevent deformation of the circuit board 12 and the FPC 62.

[0054] Fourth Embodiment A circuit unit 70 according to a fourth embodiment of the present disclosure will be described below with reference to Fig. 6. The circuit unit 70 according to the fourth embodiment has the same basic structure as the circuit unit 10 according to the first embodiment, but includes a plate member 72 as a deformation suppression member. The plate member 72 is mounted on the underside 22 of the circuit board 12 and is disposed opposite the first hollow portion 21 (first hollow case 18) with the circuit board 12 sandwiched therebetween.

[0055] The plate member 72 can be made of synthetic resin or metal, but if it is made of synthetic resin, it is preferably made of a material having a glass transition temperature equal to or higher than the molding temperature of the mold resin 16. The plate member 72 is formed as a polygonal member, including a circle or a rectangle, having an area equal to or larger than that of the first hollow case 18 in a plan view (up-down projection). The plate member 72 is fixed (for example, glued) to the underside 22 of the circuit board 12 so that the plate member 72 and the first hollow case 18 entirely overlap each other in a top-down projection, or so that the first hollow case 18 overlaps the inside of the plate member 72.

[0056] In the fourth embodiment having the above-described structure, the basic structure is the same as that of the first embodiment, and therefore the same effect as that of the first embodiment is achieved, and the plate member 72 as a deformation suppression member can prevent deformation of the circuit board 12.

[0057] <Modifications> Although Embodiments 1 to 4 have been described above in detail as specific examples of the present disclosure, the present disclosure is not limited to these specific descriptions. Modifications, improvements, etc. within the scope of achieving the object of the present disclosure are included in the present disclosure. For example, the following modifications of the embodiments are also included in the technical scope of the present disclosure.

[0058] (1) In the first embodiment, the capacitor 14 and the FET 26 are described as the first and second electronic components mounted on the circuit board 12. However, these are merely examples, and the types, shapes, etc. of the first and second electronic components are not limited, and known electronic components may be mounted. That is, in the first embodiment, the first electronic component (capacitor 14) has a larger vertical dimension than the second electronic component (FET 26). However, the second electronic component may be larger, or the vertical dimension of the second hollow case may be larger than the vertical dimension of the first hollow case. The same applies to the second and third embodiments in which the first electronic component is mounted on a bus bar or an FPC.

[0059] (2) In the above embodiment, one hollow case (hollow portion) accommodates one electronic component. However, one hollow case (hollow portion) may accommodate multiple electronic components. Furthermore, when multiple electronic components are mounted on one surface (e.g., the top surface) of a circuit board, the multiple electronic components may be accommodated in one hollow case as described above, or the multiple electronic components may be individually accommodated in the same number of hollow cases. Note that when multiple hollow cases (first hollow cases) are provided on one surface (e.g., the top surface) of a circuit board in this manner, hollow cases (second hollow cases) may be provided on the other surface (e.g., the bottom surface) of the circuit board at the same positions as the hollow cases (first hollow cases) on one surface, or a plate member such as that described in embodiment 4 may be provided so as to span the entire hollow cases (first hollow cases) on one surface.

[0060] (3) In the first to third embodiments, the second electronic component (FET 26) is provided in the second hollow case 24 (second hollow portion 23) and mounted on the lower surface 22 of the circuit board 12. However, this is not limiting. That is, the second hollow case does not have to accommodate the second electronic component. When hollow cases are provided on both the top and bottom surfaces of the circuit board, it is sufficient that an electronic component is accommodated in at least one of the hollow cases. For example, an electronic component may be accommodated in the second hollow case on the lower side, and no electronic component may be accommodated in the first hollow case on the upper side. In this case, a plate member such as that described in the fourth embodiment may be provided superimposed on the upper surface of the circuit board.

[0061] (4) In the above embodiment, the bus bar 52, which is smaller than the circuit board 12, is placed above the circuit board 12 with the insulating sheet 54 interposed therebetween. However, the positions of the circuit board and bus bar may be reversed, or a circuit board smaller than the bus bar may be placed above the bus bar with the insulating sheet interposed therebetween.

[0062] (5) In the first embodiment, the first hollow casing 18 was formed from synthetic resin. However, as in the circuit unit 80 shown in FIG. 7 , the first hollow casing 82 may be formed from metal. In this case, the first hollow casing 82 may be fixed to the circuit board 12 by adhesive or soldering. When the first hollow casing 82 is fixed to the circuit board 12 by soldering, the first hollow casing 82 can be fixed to the circuit board 12 simultaneously with mounting the first electronic component (e.g., a capacitor) on the circuit board 12. This eliminates the need for a bonding process for bonding the first hollow casing 82 to the circuit board 12, facilitating the manufacture of the circuit unit 80. The same applies to the second to fourth embodiments.

[0063] (6) In the first embodiment, the second hollow case 24 was formed from synthetic resin. However, as in the circuit unit 80 shown in FIG. 7 , the second hollow case 84 may be formed from metal. In this case, as described above, the same effect as when the first hollow case 82 is formed from metal can be achieved. The same applies to the second or third embodiment. Note that both the first hollow case 82 and the second hollow case 84 may be formed from metal, or only the first hollow case 82 or only the second hollow case 84 may be formed from metal.

[0064] REFERENCE SIGNS LIST 10 Circuit unit (first embodiment) 12 Circuit board 14 Capacitor (first electronic component) 16 Molded resin 18 First hollow case (case) 20 Upper surface (one surface) 21 First hollow portion 22 Lower surface (other surface) 23 Second hollow portion 24 Second hollow case (deformation suppressing member) 26 FET (second electronic component) 28 Upper bottom wall portion 30 Upper peripheral wall portion 34 Flange-shaped portion 36 Bottom wall portion 38 Lower peripheral wall portion 42 Flange-shaped portion 50 Circuit unit (second embodiment) 52 Bus bar (deformation suppressing member) 54 Insulating sheet 60 Circuit unit (third embodiment) 62 FPC 70 Circuit unit (fourth embodiment) 72 Plate member 80 Circuit unit (FIG. 7) 82 First hollow case 84 Second hollow case

Claims

1. A circuit unit comprising: a circuit board; a first electronic component mounted on one side of the circuit board; a first hollow case mounted on the one side of the circuit board to define a first hollow section around the first electronic component and cover the first electronic component; a deformation suppression member mounted on the other side of the circuit board and positioned opposite the first hollow section with the circuit board in between to suppress deformation of the circuit board; and a molded resin that embeds the circuit board, the first electronic component mounted on the circuit board, the first hollow case, and the deformation suppression member inside.

2. The circuit unit described in claim 1, wherein the deformation suppression member includes a second hollow case mounted on the other surface side of the circuit board and defining a second hollow portion facing the first hollow portion with the circuit board sandwiched therebetween.

3. The circuit unit according to claim 2, wherein the first hollow portion and the second hollow portion coincide with each other when projected in the thickness direction of the circuit board.

4. A circuit unit as described in claim 2 or claim 3, further comprising a second electronic component mounted on the other surface side of the circuit board, the second electronic component being covered by the second hollow case via the second hollow portion.

5. A circuit unit as described in claim 2 or claim 3, wherein the protruding dimension of the second hollow case from the other surface of the circuit board is smaller than the protruding dimension of the first hollow case from the one surface of the circuit board.

6. A circuit unit according to claim 2 or 3, wherein the first hollow case and the second hollow case are formed from a material having a glass transition temperature equal to or higher than the molding temperature of the molding resin.

7. The circuit unit according to claim 2 or 3, wherein at least one of the first hollow case and the second hollow case is made of metal.

8. The circuit unit described in claim 1, wherein the deformation suppression member includes a plate member mounted on the other surface side of the circuit board and positioned opposite the first hollow portion with the circuit board sandwiched therebetween, and the plate member is formed of a material having a glass transition temperature higher than the molding temperature of the molding resin.

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