Circuit board holding structure

Abstract

To provide a circuit board holding structure capable of suppressing occurrence of damage in a junction location caused by a junction material during thermal stress addition.SOLUTION: A circuit board holding structure 1 comprises: a housing 2 including a recess 8; a circuit board 3 disposed in the recess 8; a conductive member 4 including an abutment face 4b, which abuts on a one-side face of the circuit board 3 opposed to a bottom face 8a of the recess 8, and a connection part 9 which is inserted from one side of the circuit board 3 and connected to the other-side face of the circuit board 3 via a junction material 10; a filler 5 with which the recess 8 is to be filled; and an absorption layer 6 which is provided between the one-side face of the circuit board 3 and the filler 5 and has the Young's modulus smaller than that of the filler 5.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a circuit board retention structure. [Background technology]

[0002] A circuit board holding structure is known that includes a housing having a recess, a circuit board placed in the recess, a conductive member inserted from one surface of the circuit board facing the bottom surface of the recess and connected to the other surface of the circuit board via a bonding material, and a filler material filled in the recess (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-2039 Summary of the Invention [Problem to be solved by the invention]

[0004] In the circuit board holding structure described above, it is desirable to suppress the occurrence of damage at the joints of the joining material when thermal stress is applied, thereby achieving excellent reliability.

[0005] Therefore, an object of the present disclosure is to provide a circuit board holding structure that can suppress the occurrence of damage at the joints caused by the joining material when thermal stress is applied. [Means for solving the problem]

[0006] One aspect of the present disclosure is as follows.

[0007] [1] a housing having a recess; a circuit board disposed in the recess; a conductive member having a contact surface that contacts a surface on one side of the circuit board that faces the bottom surface of the recess, and a connection portion that is inserted from the one side of the circuit board and connected to a surface on the other side of the circuit board via a bonding material; A filler material filled in the recess; an absorption layer provided between the one surface of the circuit board and the filler, the absorption layer having a Young's modulus smaller than that of the filler.

[0008] With this configuration, when the filler between the bottom surface of the recess and one side of the circuit board thermally shrinks, the board can be prevented from moving relative to the connecting portion of the conductive member from the opening side to the bottom side by the abutment surface of the conductive member, while when the filler between the bottom surface of the recess and one side of the circuit board thermally expands, the absorption layer can be prevented from moving relative to the connecting portion of the conductive member from the bottom side to the opening side by the absorption layer, thereby preventing damage to the joint by the joining material when thermal stress is applied.

[0009] [2] The circuit board holding structure according to [1], wherein the absorption layer has a negative linear thermal expansion coefficient.

[0010] With this configuration, when the filler between the bottom surface of the recess and one side of the circuit board thermally expands, the board can be prevented from moving relative to the connection portion of the conductive member from the bottom surface of the recess toward the opening by the thermal contraction of the absorption layer having a negative linear thermal expansion coefficient, thereby preventing damage to the joint by the bonding material when thermal stress is applied.

[0011] [3] The circuit board holding structure according to [1] or [2], further comprising an adhesive layer that bonds the absorption layer to the one surface of the circuit board.

[0012] This configuration makes it easier to achieve stable placement of the absorption layer relative to the substrate. [Effects of the Invention]

[0013] According to the present disclosure, it is possible to provide a circuit board holding structure that can suppress the occurrence of damage at the joints caused by the joining material when thermal stress is applied. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view showing a circuit board holding structure according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

[0016] As shown in FIG. 1, a circuit board holding structure 1 according to one embodiment includes a housing 2, a circuit board 3, a conductive member 4, a filler material 5, an absorbent layer 6, and an adhesive layer .

[0017] The housing 2 constitutes a part of a temperature transmitter. A temperature transmitter converts an output signal from a temperature sensor such as a resistance thermometer or a thermocouple into a signal suitable for long-distance transmission and transmits the signal. The housing 2 may also constitute a part of a device other than a temperature transmitter, such as a field device. Field devices are devices used in plants, such as temperature measuring devices, pressure measuring devices, and flow measuring devices. Examples of plants include industrial plants such as chemical plants, plants that manage and control wellheads or surrounding areas of gas fields and oil fields, plants that manage and control power generation such as hydroelectric, thermal, and nuclear power plants, plants that manage and control environmental power generation such as solar and wind power plants, and plants that manage and control water supply and sewage systems, dams, etc.

[0018] The housing 2 has a recess 8. The recess 8 is formed by a bottom surface 8a, which is the end surface of the recess 8 in the depth direction, and an inner peripheral surface 8b that is continuous with the outer peripheral edge of the bottom surface 8a, and forms an opening 8c on the opposite side of the bottom surface 8a.

[0019] The circuit board 3 is placed in the recess 8. The circuit board 3 has a first main surface 3a which is one surface facing the bottom surface 8a of the recess 8, and a second main surface 3b which is the other surface of the circuit board 3.

[0020] For ease of explanation, the direction perpendicular to the circuit board 3 is also referred to as the board vertical direction D, the direction from the second main surface 3b side toward the first main surface 3a side along the board vertical direction D is also referred to as the first direction D1, and the direction from the first main surface 3a side toward the second main surface 3b side is also referred to as the second direction D2.

[0021] The conductive member 4 constitutes terminals such as input terminals, output terminals, and power supply terminals. However, the conductive member 4 is not limited to those constituting terminals. The conductive member 4 is formed of a metal such as brass, for example.

[0022] The conductive member 4 has an abutment surface 4b that abuts against the first main surface 3a of the circuit board 3, and a connection portion 9 that is inserted from the side of the first main surface 3a of the circuit board 3 and connected to the second main surface 3b of the circuit board 3 via a bonding material 10. The conductive member 4 has a shaft portion 4a that tapers in stages in the second direction D2. The shaft portion 4a tapers in stages from the abutment surface 4b. The abutment surface 4b has an annular shape when viewed in the board-perpendicular direction D, and the connection portion 9 protrudes from the inner peripheral edge of the abutment surface 4b in the second direction D2. The abutment surface 4b may have a circular ring shape or a ring shape other than a circular ring, such as a rectangular ring shape. The abutment surface 4b is not limited to having an annular shape when viewed in the board-perpendicular direction D.

[0023] The circuit board 3 has a through hole 3c that penetrates the circuit board 3 in the board vertical direction D. The abutment surface 4b of the conductive member 4 abuts against the periphery of the through hole 3c on the first main surface 3a of the circuit board 3. The connection portion 9 of the conductive member 4 is inserted into the through hole 3c in the second direction D2. The bonding material 10 adheres to the outer peripheral surface of the connection portion 9 on the second direction D2 side of the second main surface 3b of the circuit board 3, and also adheres to the periphery of the through hole 3c on the second main surface 3b of the circuit board 3, thereby electrically and mechanically connecting the connection portion 9 and the circuit board 3. The bonding material 10 is made of a conductive molten bonding material such as solder.

[0024] Furthermore, the shaft portion 4a of the conductive member 4 has a step surface 4c that abuts against the filler 5. The shaft portion 4a tapers in stages via the step surface 4c. The step surface 4c is located closer to the first direction D1 than the abutment surface 4b. The step surface 4c is annular when viewed in the substrate-perpendicular direction D. However, the step surface 4c is not limited to being annular when viewed in the substrate-perpendicular direction D. The shaft portion 4a has a protrusion 4d that protrudes in the second direction D2 from the inner peripheral edge of the step surface 4c to the outer peripheral edge of the abutment surface 4b.

[0025] The absorption layer 6 has a through hole 6a that penetrates the absorption layer 6 in the substrate perpendicular direction D. The protrusion 4d of the conductive member 4 is inserted into the through hole 6a in the second direction D2.

[0026] The adhesive layer 7 is disposed at the interface between the absorption layer 6 and the first main surface 3a of the circuit board 3, and bonds the absorption layer 6 to the first main surface 3a of the circuit board 3. This configuration makes it easier to achieve stable placement of the absorption layer 6 on the board.

[0027] The procedure for arranging the adhesive layer 7 is not particularly limited, but a step may be provided in which the adhesive layer 7 is arranged on the absorption layer 6 in advance, and the absorption layer 6 is then attached to the circuit board 3. Such a step allows for efficient assembly.

[0028] The protrusion 4d and the connection portion 9 of the conductive member 4 are disposed in the recess 8. The conductive member 4 is fixed to the housing 2 on the side of the stepped surface 4c in the first direction D1.

[0029] The filler 5 is made of, for example, a resin, and is filled into the recess 8. By covering the substrate, the absorption layer 6, and the shaft portion 4a of the conductive member 4 (preferably entirely) with the filler 5, waterproofing is improved, and excellent reliability can be achieved, particularly in high-temperature and high-humidity environments. The expansion and contraction deformation of the filler 5 due to temperature changes is restrained by the bottom surface 8a and inner circumferential surface 8b of the recess 8. In other words, deformation of the filler 5 is restrained in the portions facing the bottom surface 8a and inner circumferential surface 8b of the recess 8, but not in the portions facing the opening 8c of the recess 8.

[0030] The absorption layer 6 is provided between the first main surface 3a of the circuit board 3 and the filler 5, and has a smaller Young's modulus than the filler 5. With this configuration, when the filler 5 between the bottom surface 8a of the recess 8 and the first main surface 3a of the circuit board 3 thermally shrinks, the substrate can be prevented from moving relative to the connection portion 9 of the conductive member 4 in the first direction D1 by the abutment of the substrate against the abutment surface 4b of the conductive member 4, while when the filler 5 between the bottom surface 8a of the recess 8 and the first main surface 3a of the circuit board 3 thermally expands, the absorption layer 6 can prevent the substrate from moving relative to the connection portion 9 of the conductive member 4 in the second direction D2. Therefore, damage (such as cracks) at the joints formed by the bonding material 10 can be prevented when thermal stress is applied.

[0031] The absorption layer 6 may be configured to have a negative coefficient of linear thermal expansion. With this configuration, when the filler 5 between the bottom surface 8a of the recess 8 and the first main surface 3a of the circuit board 3 thermally expands, the substrate can be prevented from moving relative to the connection portion 9 of the conductive member 4 in the second direction D2 by the thermal contraction of the absorption layer 6 having a negative coefficient of linear thermal expansion. Therefore, damage to the joint portion formed by the bonding material 10 when thermal stress is applied can be prevented.

[0032] The material having a negative linear thermal expansion coefficient is not particularly limited, but for example, oxides such as β-eucryptite (LiAlSiO4) or zirconium tungstate (ZrW2O8) can be used, and it is particularly preferable to use β-eucryptite, which is inexpensive and environmentally friendly. Note that, because the absorbing layer 6 is covered with the filler 5, there is little need to consider weather resistance, chemical resistance, flame retardancy, etc. when selecting a material for the filler 5, and it is sufficient to consider the temperature range of use, etc.

[0033] The present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

[0034] Therefore, the circuit board holding structure 1 according to the above-described embodiment can be modified in various ways as long as it is a circuit board holding structure 1 having a housing 2 having a recess 8, a circuit board 3 placed in the recess 8, a conductive member 4 having an abutment surface 4b that abuts against one side of the circuit board 3 facing the bottom surface 8a of the recess 8 and a connection portion 9 that is inserted from one side of the circuit board 3 and connected to the other side of the circuit board 3 via a bonding material 10, a filler 5 that is filled in the recess 8, and an absorption layer 6 that is provided between one side of the circuit board 3 and the filler 5 and has a Young's modulus smaller than that of the filler 5.

[0035] For example, the circuit board 3 may have a cutout such as a slit instead of the through hole 3c. The absorption layer 6 may have a cutout such as a slit instead of the through opening 6a. The conductive member 4 may not have a stepped surface 4c. The adhesive layer 7 may not be provided. The conductive member 4 may not be fixed to the housing 2. The circuit board 3 may have a planar or curved shape. The circuit board holding structure 1 may have a configuration including a plurality of conductive members 4, each having a contact surface 4b that contacts one surface of the circuit board 3 facing the bottom surface 8a of the recess 8, and a connection portion 9 that is inserted from one side of the circuit board 3 and connected to the other surface of the circuit board 3 via a bonding material 10. [Explanation of symbols]

[0036] 1 Circuit board holding structure 2. Housing 3 Circuit Board 3a 1st principal surface 3b 2nd principal surface 3c through hole 4 Conductive materials 4a Shaft body part 4b Contact surface 4c Step surface 4d protrusion 5 Filling material 6 Absorbing layer 6a Through hole 7 Adhesive layer 8 recess 8a Bottom 8b Inner surface 8c aperture 9 Connection 10 Bonding material D Board vertical direction D1 1st direction D2 2nd direction

Claims

1. a housing having a recess; a circuit board disposed within the recess; a conductive member having a contact surface that contacts a surface on one side of the circuit board that faces the bottom surface of the recess, and a connection portion that is inserted from the one side of the circuit board and connected to a surface on the other side of the circuit board via a bonding material; A filler material filled in the recess; an absorption layer provided between the one surface of the circuit board and the filler, the absorption layer having a Young's modulus smaller than that of the filler.

2. The circuit board retention structure according to claim 1 , wherein the absorption layer has a negative coefficient of linear thermal expansion.

3. The circuit board holding structure according to claim 1 , further comprising an adhesive layer that bonds the absorption layer to the one surface of the circuit board.

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