Coil component

Abstract

A coil component is provided. In a coil component in which a metal terminal is affixed to a core via an adhesive layer, the resistance until the adhesive layer breaks when an external force is applied is improved, and the tensile strength of the metal terminal with respect to the core is improved. In order to reduce the stress remaining on the adhesive layer (27) when the adhesive is cured, the adhesive layer (27) for affixing the metal terminal (9) to the core (2) has a structure containing an adhesive (28) and air bubbles (29). The size of the air bubbles (29) is preferably 300 [mu] m or less in terms of circle-equivalent diameter, and the area ratio of the air bubbles (29) in the cross section of the adhesive layer (27) is preferably 2.9%-27% (inclusive).

Description

Technical Field

[0001] The present disclosure relates to a coil component. In particular, it relates to an improvement in an adhesive layer for fixing a metal terminal to a core body in a coil component including a core body that holds a coil conductor and a metal terminal connected to the coil conductor. Background Art

[0002] As a technology of interest to the present disclosure, for example, there is the technology described in Japanese Unexamined Patent Application Publication No. 2021-39961 (Patent Document 1). Patent Document 1 describes a coil component including: a drum-shaped core body having a winding core portion and flange portions provided at opposite end portions in the axial direction of the winding core portion; a wire material as a coil conductor wound around the winding core portion; and a metal terminal connected to the wire material and made of a metal plate, the metal terminal being fixed to the flange portion of the core body via an adhesive layer containing an adhesive.

[0003] In this way, for a structure including a metal terminal as a terminal for forming a connection with the outside, it is adopted, for example, in a common mode choke coil for an automobile. In a common mode choke coil for an automobile, due to thermal cycling in the use environment, cracks are likely to occur in the solder for forming a connection to a printed circuit board. However, if a metal terminal made of a metal plate is used as the terminal, cracks in the solder can be suppressed to a certain extent by the deformation of the metal terminal itself.

[0004] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2021-39961

[0005] In the coil component described in Patent Document 1, when the metal terminal is fixed to the core body via the adhesive layer, stress remains in the adhesive layer when the adhesive cures. In particular, the thicker the adhesive layer, the greater the residual stress. The residual stress causes a reduction in the resistance until the adhesive layer breaks when an external force is applied. Summary of the Invention

[0006] Therefore, an object of the present disclosure is to reduce the stress remaining in the adhesive layer that joins the metal terminal to the core body in the coil component.

[0007] The present disclosure is a coil component including: a coil conductor; a core body that holds the coil conductor; a metal terminal connected to the coil conductor; and an adhesive layer containing an adhesive for fixing the metal terminal to the core body. To solve the above technical problem, the present disclosure is characterized in that the adhesive layer contains an adhesive and air bubbles.

[0008] According to the present disclosure, the adhesive layer contains air bubbles. Therefore, compared with the adhesive before curing, the air bubbles as gases have greater deformability. As a result, the air bubbles expand, counteracting the shrinkage generated during the curing of the adhesive, and an adhesive layer as a cured product with reduced residual stress in the adhesive portion can be obtained. Therefore, the residual stress in the adhesive portion of the adhesive layer can be reduced. Therefore, the adhesive layer can be made into a cured product with high strength. Therefore, the tensile strength of the metal terminal relative to the core can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 FIG. is a perspective view showing the appearance of a coil component 1 according to an embodiment of the present disclosure. Figure 1 (A) is a view observed from the relatively upper side. Figure 1 (B) is a view observed from the relatively lower side.

[0010] Figure 2 FIG. shows Figure 1 an enlarged cross-sectional view along line II-II of the mounting portion where the metal terminal 9 in the coil component 1 shown is mounted on the flange portion 5. Figure 1 FIG.

[0011] Figure 3 FIG. is a diagram showing cross-sectionally polished photographs of the adhesive layer in four states A, B, C, and D with different area ratios of air bubbles.

[0012] Figure 4 FIG. shows Figure 3 the tensile strength of the metal terminal relative to the core in four states A, B, C, and D with different area ratios of the air bubbles shown.

[0013] REFERENCE SIGNS LIST

[0014] 1... Coil component; 2... Core; 3... Spool portion; 5... Flange portion; 7, 8... Wire materials; 9... Metal terminal; 13... Inner end face; 14... Outer end face; 27... Adhesive layer; 28... Adhesive; 29... Air bubble; AX... Axis direction. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0015] With reference to Figure 1 and Figure 2 FIGS., a coil component 1 according to an embodiment of the present disclosure will be described. Figure 1 The coil component 1 shown in FIG. constitutes, for example, a common mode choke coil.

[0016] The core 2 included in the coil component 1 has a drum shape and includes: a bobbin portion 3; and flange portions 5 respectively provided at opposite ends of the bobbin portion 3 in the axial direction AX. Preferably, the core 2 is made of ferrite. Alternatively, the core 2 may be made of a non-conductive material other than ferrite, such as a non-magnetic material like alumina, or a resin containing ferrite powder or metal magnetic powder, etc.

[0017] Two wire materials 7 and 8, which are coil conductors, are wound around the bobbin portion 3. Figure 1 In the figure, the main portions of the wire materials 7 and 8 are not shown.

[0018] Each end of the wire materials 7 and 8 is connected to a metal terminal 9. As Figure 1 shown, the coil component 1 includes 4 metal terminals 9. The 4 metal terminals 9 have the same or symmetric shapes with each other. More specifically, two metal terminals 9 with symmetric shapes are arranged side by side in the width direction at one flange portion 5, and similarly, two metal terminals 9 with symmetric shapes are arranged side by side in the width direction at the other flange portion 5.

[0019] The bobbin portion 3 included in the core 2 has, for example, a quadrangular prism shape with a cross-sectional shape of a quadrilateral. In addition, the cross-sectional shape of the bobbin portion 3 may be a polygon such as a hexagon, a circle, an ellipse, or a combination of these shapes, in addition to being a quadrilateral.

[0020] Each flange portion 5 included in the core 2 has: a bottom surface 11 that extends parallel to the axis direction AX and faces the mounting substrate side during installation; and a top surface 12 that faces the direction opposite to the bottom surface 11. Each flange portion 5 further has: an inner end surface 13, which is a surface that rises from the bottom surface 11 and extends in a direction orthogonal or substantially orthogonal to the mounting substrate, and the end of the bobbin portion 3 is located at this inner end surface 13; an outer end surface 14 that faces the direction opposite to the inner end surface 13; and a first side surface 15 and a second side surface 16 that connect the inner end surface 13 and the outer end surface 14.

[0021] The metal terminal 9 is manufactured by processing a metal plate made of, for example, a copper-based alloy such as phosphor bronze or tough pitch copper. It is preferable to apply tin plating to the metal plate that constitutes the material of the metal terminal 9. The metal plate has a thickness of, for example, 0.10 mm or more and 0.15 mm or less.

[0022] Each of the metal terminals 9 has: a base portion 20 that extends along the bottom surface 11 of the flange portion 5; and a standing portion 23 that is connected to the base portion 20 via a bent portion 22 that covers a ridge line portion 21 formed by the intersection of the bottom surface 11 and the outer end surface 14 of the flange portion 5 and extends along the outer end surface 14 of the flange portion 5. And a connection piece 24 extending from the base portion 20 is formed on each of the metal terminals 9.

[0023] Each end of the wire rods 7 and 8 is connected to the connection piece 24 of the metal terminal 9. This connection is, for example, laser welding. Figure 1 The figure shows a welded block portion 25 that protrudes in a hemispherical shape formed by laser welding. In addition to laser welding, each end of the wire rods 7 and 8 can also be connected to the connection piece 24 of the metal terminal 9 by hot pressing, or the connection can be formed by other methods.

[0024] Generally, the cross-sections of the wire rods 7 and 8 are circular, and they have a linear center conductor and an insulating film that covers the circumferential surface of the center conductor and is made of an electrically insulating resin. The diameter of the center conductor is, for example, 28 μm or more and 50 μm or less. In addition, the thickness of the insulating film is, for example, 3 μm or more and 6 μm or less. The center conductor is made of a good conductor metal such as copper, silver, or gold. The insulating film is made of, for example, polyurethane, polyamideimide, polyester, or polyimide.

[0025] In Figure 1 Although not shown in the figure, the two wire rods 7 and 8 are wound around the core portion 3 in a spiral shape in the same direction. More specifically, the two wire rods 7 and 8 can also be wound in a double layer with one of them wound on the inner layer side and the other wound on the outer layer side, or they can be wound in a double wire winding, and the above double wire winding is performed in a state where the respective turns are alternately arranged in the axial direction of the core portion 3 and are arranged in the same direction as each other.

[0026] Figure 2 The installation portion of the metal terminal 9 installed on the flange portion 5 is clearly shown. The metal terminal 9 is joined to the flange portion 5 via an adhesive layer 27. More specifically, the metal terminal 9 is fixed to the flange portion 5 via the adhesive layer 27 at the outer end surface 14 of the flange portion 5.

[0027] The adhesive constituting the adhesive layer 27 is usually an epoxy resin containing a main agent and a curing agent. For example, a one-component epoxy resin using bisphenol A or bisphenol F as the main agent and amine or dicyandiamide as the curing agent is used. The adhesive can also contain carbon as a coloring agent, can also contain an inorganic solid such as silica as a filler, and can also contain appropriate additives in addition to this.

[0028] It is well-known that adhesives shrink during thermal curing. The shrinkage during thermal curing causes an increase in the residual stress inside the adhesive layer 27, and the resistance until fracture decreases when an external force is applied. Therefore, it is preferable that the residual stress inside the adhesive layer 27 is small.

[0029] In order to reduce the residual stress inside the adhesive layer 27, as Figure 2 schematically shown, the adhesive layer 27 contains, in addition to the adhesive 28, air bubbles 29. Thus, the state in which the adhesive layer 27 contains the adhesive 28 and the air bubbles 29 is obtained, for example, by injecting gas into the adhesive 28 and stirring it in the liquid phase before curing. As a stirring method, for example, a planetary mixer is used. As the gas injected, that is, the gas filling the air bubbles 29, for example, an inert gas such as nitrogen or argon is preferable, or air which is mainly a mixture of nitrogen, oxygen, argon, and carbon dioxide may also be used. The air mentioned here refers to the gas that constitutes the atmosphere of the earth. Inert gases such as nitrogen and argon have the advantage of being able to inhibit the oxidation of the adhesive. In addition, air has the advantage of being inexpensive.

[0030] Preferably, the air bubbles 29 have a flat shape like a flattened sphere. In particular, it is more preferable that the major axis direction of the flat shape given to the air bubbles 29 is perpendicular to the thickness direction of the adhesive layer 27. In the following Figure 3 the air bubbles 29 contained in the adhesive layer 27 are shown in the form of a white image, but Figure 3 a cross-sectional polished photograph in the direction perpendicular to the thickness direction is shown, and thus, the flat shape of the air bubbles 29 is not easily recognizable in this photograph.

[0031] The size of the air bubbles 29 on the cross-section obtained by grinding the adhesive layer 27 parallel to the bonding surface is preferably 300 μm or less in terms of the equivalent circle diameter. If it exceeds 300 μm, the degree of reduction in the bonding area where the adhesive layer 27 is bonded to the metal terminal 9 and the core 2 in contact with it becomes large, and a decrease in the bonding strength is feared.

[0032] Preferably, in the cross-section obtained by grinding the adhesive layer 27 parallel to the bonding surface, the area ratio (occupancy ratio) of the air bubbles 29 is 2.9% or more and 27% or less. This is because, on the one hand, if the area ratio of the air bubbles 29 is less than 2.9%, the proportion of the air bubbles 29 is too low, and thus, the residual stress may not be completely relieved. On the other hand, if the area ratio of the air bubbles 29 exceeds 27%, the amount of thermal expansion of the air bubbles 29 during the curing process of the adhesive 28 can be ignored, the control of the air bubbles 29 becomes difficult, and it is not easy to manufacture the adhesive layer 27 with good reproducibility.

[0033] It may also be, as Figure 1As shown, the coil component 1 further includes a top plate 31 between the top surfaces 12 of the two flange portions 5. Similar to the case of the core 2, the top plate 31 is preferably made of ferrite. In addition, the top plate 31 may be made of a non-conductive material other than ferrite, such as a non-magnetic material like alumina, or a resin containing ferrite powder or metal magnetic powder, etc.

[0034] The top plate 31 is bonded to the top surfaces 12 of the two flange portions 5 by an adhesive (not shown). Thus, the top plate 31 can form a closed magnetic circuit together with the core 2. As the adhesive, for example, an adhesive made of an epoxy resin or an adhesive containing silica filler therein is used.

[0035] Next, an experimental example implemented to confirm the effects of the present disclosure will be described.

[0036] As the adhesive, a one-component epoxy resin with bisphenol A as the main agent and an amine as the curing agent is used. While injecting nitrogen gas, stirring is performed by a planetary mixer in the liquid state before the adhesive cures, so that the adhesive contains bubbles. And a sample with a structure as shown having an adhesive layer formed with bubbles and the adhesive is obtained. In addition, in the sample, the area of the adhesive layer on the bonding surface is 4.0×10 Figure 2 As shown, and the thickness is 30 μm. 5 μm 2

[0037] Here, by changing the above stirring conditions for obtaining the adhesive containing bubbles, samples with different bubble area ratios, bubble diameters, and tensile strengths of the adhesive layer to be formed by the adhesive are obtained.

[0038] In addition, the bubble area ratio and the bubble diameter are respectively the area ratio and the diameter of the bubbles on the cross-section presented by grinding the adhesive layer parallel to the bonding surface. However, since the samples for measuring these bubble area ratios and bubble diameters are in a state where the cross-section of the adhesive layer is exposed, the samples themselves cannot be used for measuring the tensile strength. Therefore, in this experimental example, adhesives treated under predetermined stirring conditions are prepared, and samples for measuring the bubble area ratio and the bubble diameter and samples for measuring the tensile strength are selected from them. That is, the samples for measuring the bubble area ratio and the bubble diameter and the samples for measuring the tensile strength are adhesives treated under shared stirring conditions, so it is presumed that the bubble area ratio, the bubble diameter, and the tensile strength are substantially the same.

[0039] Table 1 shows the "bubble area ratio", "bubble diameter", and "tensile strength" obtained by measurement. For any one of the "bubble area ratio", "bubble diameter", and "tensile strength", the number of samples is 10, and the average value is shown.

[0040] ​Figure 3 A cross-sectional polished photograph is shown in a direction parallel to the bonding surface, i.e., in a direction perpendicular to the thickness direction of the adhesive layer. Figure 3 In it, the bubbles contained in the adhesive layer are shown as white images, and the black area around them represents the adhesive. Figure 3 "State A", "State B", "State C", and "State D" respectively correspond to "State A", "State B", "State C", and "State D" in Table 1.

[0041] As shown in Table 1, for the "bubble area ratio", it is 0% in the adhesive layer of "State A", 2.9% in the adhesive layer of "State B", 14% in the adhesive layer of "State C", and 27% in the adhesive layer of "State D".

[0042] The "bubble area ratio" is the ratio of the area occupied by the bubbles presented in the cross-section in the direction perpendicular to the thickness direction at the center in the thickness direction of the adhesive layer with respect to the area of the bonding surface of the adhesive layer. In the observation surface, the bubbles are calculated by binarization based on the luminance value of the image processing software. In addition, when photographing the cross-sectional image for solving the "bubble area ratio", the area that cannot be recognized as the area of the bubble is not regarded as a bubble. More specifically, bubbles with a diameter less than 1% of the equivalent circle diameter of the bonding surface of the adhesive layer are not regarded as bubbles. In the case of this experimental example, the area of the bonding surface of the adhesive layer is 4.0×10 5 μm 2 , so the equivalent circle diameter is 710 μm, and 1% of it is 7.1 μm. Therefore, bubbles with a diameter less than 7.1 μm are not regarded as bubbles for solving the "bubble area ratio".

[0043] The "bubble diameter" is the diameter obtained by solving the average value of the equivalent circle diameters of the bubbles with a diameter of 7.1 μm or more presented in the same cross-section as the cross-section for solving the "bubble area ratio", i.e., in the cross-section in the direction perpendicular to the thickness direction at the center in the thickness direction of the adhesive layer. When solving the "bubble diameter", similarly, bubbles with a diameter less than 7.1 μm are not regarded as bubbles for solving the "bubble diameter".

[0044] In addition, the tensile strength of each metal terminal with respect to the core body under States A to D was measured. The results are shown in "Tensile Strength" in Table 1 and Figure 4 as shown. Figure 4 In it, the average value and distribution state of the tensile strength for a sample number of 10 are shown. When referring to Figure 2When explaining, the tensile strength means the force in the direction shown by arrow L is applied to the metal terminal 9 while fixing the core 2 with an appropriate holder (not shown), and then this force is gradually increased until the moment when the metal terminal 9 can no longer be held by the core 2. In addition, the phenomenon that the metal terminal 9 can no longer be held by the core 2 can occur due to fracture within the range of the thickness of the adhesive layer 27 itself (cohesive failure) and due to disconnection at the interface between the adhesive layer 27 and the core 2 or the metal terminal 9 (interface failure), but in this experimental example, a mixed failure of both occurred.

[0045] [Table 1]

[0046] Table 1

[0047] Bubble area ratio (average value) Bubble diameter (average value) Tensile strength (average value) State A 0％ 0μm 1.18N State B 2.9％ 26.4um 1.38N State C 14％ 81.3um 1.57N State D 27％ 136um 1.70N

[0048] As can be seen from Table 1 and Figure 4 As can be known, according to the adhesive layers in states B, C, and D that contain bubbles, compared with the adhesive layer in state A that does not contain bubbles, the tensile strength is improved. This is because, compared with the adhesive layer in state A, the residual stress of the adhesive layers in states B, C, and D is smaller.

[0049] In addition, if a comparison is made among states B, C, and D that contain bubbles, the larger the "bubble area ratio", the larger the "bubble diameter" and the larger the "tensile strength". In addition, the "bubble area ratio" is not limited, and a relatively large value is not preferred. As will be described later, it is preferably 27% or less.

[0050] From the data shown in Table 1, it is read that the size of the bubbles is preferably 300 μm or less in terms of the equivalent circle diameter, and the bubble area ratio is preferably 2.9% or more and 27% or less.

[0051] Above, the coil component related to the present disclosure has been described based on the embodiment related to the common mode choke coil, but this embodiment is illustrative, and there can be various other modification examples. Therefore, the number of wire materials, the winding direction of the wire materials, the number of metal terminals, etc. included in the coil component can be changed according to the function of the coil component.

[0052] In addition, in the above embodiment, wire materials 7 and 8 are provided as the coil conductors, but the present disclosure can also be applied to a coil component that has a coil conductor composed of a conductor film instead of the wire materials.

[0053] In addition, in the above-described embodiment, as the core, a drum-shaped core is provided, and the drum-shaped core has a winding core portion 3 and flange portions 5 provided at opposite ends in the axial direction of the winding core portion 3. However, the present disclosure can also be applied to coil components having cores of other shapes such as simple plate shapes, and further can also be applied to coil components having a laminated structure.

[0054] In addition, in the above-described embodiment, as the adhesive for fixing the metal terminal 9 to the core 2, an adhesive containing epoxy resin is exemplified, and the present disclosure can be similarly applied to adhesives composed of other components.

[0055] In addition, each embodiment described in this specification is illustrative, and a part of the structure can be replaced or combined between different embodiments.

[0056] The embodiments of the present disclosure have the following contents.

[0057] <1> A coil component, comprising: a coil conductor; a core that holds the coil conductor; a metal terminal that is connected to the coil conductor; and an adhesive layer that fixes the metal terminal to the core, wherein the adhesive layer contains an adhesive and air bubbles.

[0058] <2> In the coil component according to <1>, at least one gas selected from nitrogen, argon, and air is filled in the air bubbles.

[0059] <3> In the coil component according to <1> or <2>, the air bubbles include flat-shaped air bubbles.

[0060] <4> In the coil component according to any one of <1> to <3>, the average value of the size of the air bubbles has an equivalent circle diameter of 300 μm or less.

[0061] <5> In the coil component according to any one of <1> to <4>, in the cross section of the adhesive layer, the area ratio of the air bubbles is 2.9% or more and 27% or less.

[0062] <6> In the coil component according to any one of <1> to <5>, the core has a winding core portion and flange portions provided at opposite ends in the axial direction of the winding core portion, the coil conductor includes a wire wound around the winding core portion, the wire is connected to the metal terminal, and the metal terminal is joined to the flange portion via the adhesive layer.

[0063] <7> In the coil component described in <6>, the flange portion has: an inner end face on which an end portion of the bobbin portion is located; and an outer end face facing a direction opposite to the inner end face, and the metal terminal is joined to the flange portion via the adhesive layer at the outer end face of the flange portion.

Claims

1. A coil component, characterized in that, Comprising: A coil conductor; A core that holds the coil conductor; Metal terminals that are connected to the coil conductor; and An adhesive layer for fixing the metal terminals to the core, wherein the adhesive layer contains an adhesive and air bubbles.

2. The coil component according to claim 1, characterized in that at least one gas selected from nitrogen, argon, and air is filled in the air bubbles.

3. The coil component according to claim 1 or 2, characterized in that the air bubbles include flat-shaped air bubbles.

4. The coil component according to any one of claims 1 to 3, characterized in that the average value of the size of the air bubbles has a diameter of 300 μm or less in terms of the equivalent circle diameter.

5. The coil component according to any one of claims 1 to 4, characterized in that in the cross-section of the adhesive layer, the area ratio of the air bubbles is 2.9% or more and 27% or less.

6. The coil component according to any one of claims 1 to 5, characterized in that the core has a wound core portion and flange portions respectively provided at opposite ends in the axial direction of the wound core portion, the coil conductor includes a wire wound around the wound core portion, the wire is connected to the metal terminals, and the metal terminals are joined to the flange portions via the adhesive layer.

7. The coil component according to claim 6, characterized in that the flange portion has: an inner end face where the end of the wound core portion is located; and an outer end face facing the direction opposite to the inner end face, and the metal terminals are joined to the flange portion via the adhesive layer at the outer end face of the flange portion.

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