Coil component

Abstract

To improve the strength of an adhesive layer until it breaks when external force is applied, and improve the tensile strength of a metal terminal relative to a core in a coil component in which the metal terminal is fixed to a core via the adhesive layer.SOLUTION: In order to reduce the stress remaining in an adhesive layer 27 when an adhesive hardens, the adhesive layer 27 for fixing a metal terminal 9 to a core 2 is configured to include an adhesive 28 and air bubbles 29. The size of the air bubbles 29 is preferably 300 μm or less in equivalent circle diameter, and the area ratio of the air bubbles 29 in the cross section of the adhesive layer 27 is preferably 2.9% or more and 27% or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to coil components, and more particularly to improvements in an adhesive layer for adhering a metal terminal to a core in a coil component having a core that holds a coil conductor and a metal terminal connected to the coil conductor. [Background technology]

[0002] An example of a technology that is of interest to the present disclosure is that described in Japanese Patent Application Laid-Open No. 2021-39961 (Patent Document 1). Patent Document 1 describes a coil component that includes a drum-shaped core having a winding core and flanges provided at opposite ends of the winding core in the axial direction, a wire as a coil conductor wound around the winding core, and a metal terminal made of a metal plate connected to the wire, the metal terminal being fixed to the flange of the core via an adhesive layer containing an adhesive.

[0003] Such a structure, which includes metal terminals for connection to the outside, is used, for example, in common mode choke coils for automobiles. In common mode choke coils for automobiles, cracks are likely to occur in the solder used for connection to the printed circuit board due to heat cycles in the operating environment, but if metal terminals made of metal plates are used as the terminals, it is possible to some extent to prevent cracks in the solder due to deformation of the metal terminals themselves. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-39961 Summary of the Invention [Problem to be solved by the invention]

[0005] In the coil component described in Patent Document 1, when the metal terminal is fixed to the core via an adhesive layer, residual stress remains in the adhesive layer when the adhesive hardens. In particular, the thicker the adhesive layer, the greater this residual stress becomes. When an external force is applied, the residual stress reduces the strength of the adhesive layer until it breaks.

[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 in the coil component. [Means for solving the problem]

[0007] The present disclosure is directed to a coil component including a coil conductor, a core 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. To solve the above-mentioned technical problem, the present disclosure is characterized in that the adhesive layer contains an adhesive and air bubbles. [Effects of the Invention]

[0008] According to the present disclosure, the adhesive layer contains gas bubbles, which have greater deformability than the adhesive before curing. As a result, the gas bubbles expand in response to the shrinkage of the adhesive that occurs during curing, resulting in a cured adhesive layer with reduced residual stress in the adhesive portion. Therefore, since the residual stress in the adhesive portion of the adhesive layer can be reduced, the adhesive layer can be made into a cured product with high strength, thereby improving the tensile strength against the core of the metal terminal. [Brief explanation of the drawings]

[0009] [Figure 1] 1A and 1B are perspective views showing the appearance of a coil device 1 according to an embodiment of the present disclosure, where (A) is a view seen from relatively above, and (B) is a view seen from relatively below. [Figure 2] 2 is an enlarged cross-sectional view taken along line II-II in FIG. 1, showing a portion where a metal terminal 9 is attached to a flange portion 5 in the coil device 1 shown in FIG. [Figure 3]FIG. 1 shows cross-sectional polished photographs of adhesive layers in four states A, B, C, and D, where the area ratio of bubbles is different. [Figure 4] 4 is a diagram showing the tensile strength of the metal terminal to the core in four states A, B, C and D, which are different in area ratio of the bubbles shown in FIG. 3. DETAILED DESCRIPTION OF THE INVENTION

[0010] A coil component 1 according to an embodiment of the present disclosure will be described with reference to Figures 1 and 2. The coil component 1 shown in Figure 1 constitutes, for example, a common mode choke coil.

[0011] The core 2 included in the coil device 1 is drum-shaped and includes a winding core 3 and flanges 5 provided at opposite ends of the winding core 3 in the axial direction AX. The core 2 is preferably made of ferrite. However, the core 2 may also be made of a non-conductive material other than ferrite, such as a non-magnetic material such as alumina, or a resin containing ferrite powder or metal magnetic powder.

[0012] Two wires 7 and 8 serving as coil conductors are wound around the winding core 3. In Fig. 1, the main parts of the wires 7 and 8 are not shown.

[0013] Each end of the wires 7 and 8 is connected to a metal terminal 9. As shown in FIG. 1 , the coil device 1 includes four metal terminals 9. The four metal terminals 9 have the same or symmetrical shapes. More specifically, two metal terminals 9 with symmetrical shapes are arranged side by side in the width direction on one flange 5, and similarly, two metal terminals 9 with symmetrical shapes are arranged side by side in the width direction on the other flange 5.

[0014] The winding core 3 provided in the core 2 has, for example, a quadrangular prism shape with a rectangular cross section. Note that the cross section of the winding core 3 may be a polygon such as a hexagon, a circle, an ellipse, or a combination thereof, in addition to a rectangle.

[0015] Each flange 5 provided on the core 2 has a bottom surface 11 that extends parallel to the axial direction AX and faces the mounting board during mounting, and a top surface 12 that faces in the opposite direction from the bottom surface 11. Each flange 5 also has a surface rising from the bottom surface 11 and extending in a direction perpendicular or nearly perpendicular to the mounting board, an inner end surface 13 on which the end of the winding core 3 is located, an outer end surface 14 that faces in the opposite direction from 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.

[0016] Metal terminal 9 is manufactured by processing a metal plate made of a copper alloy such as phosphor bronze or tough pitch copper. The metal plate from which metal terminal 9 is made is preferably tin-plated. The metal plate has a thickness of, for example, 0.10 mm or more and 0.15 mm or less.

[0017] Each of the metal terminals 9 has a base portion 20 extending along the bottom surface 11 of the flange 5, and a rising portion 23 connected to the base portion 20 via a bent portion 22 covering a ridge portion 21 where the bottom surface 11 and the outer end surface 14 of the flange 5 intersect, and extending along the outer end surface 14 of the flange 5. Furthermore, each of the metal terminals 9 has a connecting piece 24 extending from the base portion 20.

[0018] Each end of the wires 7 and 8 is connected to a connecting piece 24 of the metal terminal 9. This connection can be achieved, for example, by laser welding. FIG. 1 shows a hemispherical weld nub 25 formed by laser welding. Instead of laser welding, each end of the wires 7 and 8 may be connected to the connecting piece 24 of the metal terminal 9 by thermocompression bonding, or by other methods.

[0019] The wires 7 and 8 typically have a circular cross section and include a linear central conductor and an insulating coating made of an electrically insulating resin that covers the circumferential surface of the central conductor. The diameter of the central conductor is, for example, 28 μm or more and 50 μm or less. The thickness of the insulating coating is, for example, 3 μm or more and 6 μm or less. The central conductor is made of a highly conductive metal such as copper, silver, or gold. The insulating coating is made of, for example, polyurethane, polyamideimide, polyester, or polyimide.

[0020] 1, the two wires 7 and 8 are spirally wound in the same direction around the winding core 3. More specifically, the two wires 7 and 8 may be wound in two layers, with one on the inner layer and the other on the outer layer, or may be bifilar wound, with the turns of each wire alternately arranged in the axial direction of the winding core 3 and aligned in the same direction.

[0021] The attachment portion of the metal terminal 9 to the collar portion 5 is clearly shown in Fig. 2. The metal terminal 9 is bonded to the collar portion 5 via an adhesive layer 27. More specifically, the metal terminal 9 is fixed to the collar portion 5 at the outer end surface 14 of the collar portion 5 via the adhesive layer 27.

[0022] The adhesive constituting adhesive layer 27 is generally an epoxy resin containing a base agent and a curing agent. For example, a one-component epoxy resin is used, which uses bisphenol A or F as the base agent and amine or dicyandiamide as the curing agent. The adhesive may further contain carbon as a colorant, or an inorganic solid such as silica as a filler, or other appropriate additives.

[0023] It is known that adhesives shrink when thermally cured. This shrinkage increases residual stress within the adhesive layer 27, reducing the strength required for breakage when an external force is applied. Therefore, it is preferable that the residual stress within the adhesive layer 27 is small.

[0024] To reduce residual stress within the adhesive layer 27, the adhesive layer 27 contains air bubbles 29 in addition to the adhesive 28, as shown schematically in FIG. 2. This state in which the adhesive layer 27 contains both the adhesive 28 and the air bubbles 29 can be achieved, for example, by injecting gas into the adhesive 28 while stirring it in its liquid state before hardening. A planetary mixer, for example, is used as the stirring method. The injected gas, i.e., the gas filling the air bubbles 29, is preferably an inert gas such as nitrogen or argon, or alternatively, air, which is a mixture of primarily nitrogen, oxygen, argon, and carbon dioxide. Here, air refers to the gas that makes up the Earth's atmosphere. Inert gases such as nitrogen and argon have the advantage of suppressing oxidation of the adhesive. Air also has the advantage of being inexpensive.

[0025] The bubbles 29 preferably include bubbles having a flat shape like a squashed sphere. In particular, the major axis direction that gives the bubbles 29 their flat shape is more preferably oriented in a direction perpendicular to the thickness direction of the adhesive layer 27. In Fig. 3 described below, the bubbles 29 contained in the adhesive layer 27 are shown as whitish images, but because Fig. 3 shows a polished cross-sectional photograph perpendicular to the thickness direction, the flat shape of the bubbles 29 is difficult to see in the photograph.

[0026] The size of the bubbles 29 on the cross section that appears when the adhesive layer 27 is polished parallel to the adhesive surface is preferably 300 μm or less in equivalent circle diameter. If the diameter exceeds 300 μm, the degree of reduction in the adhesive area between the adhesive layer 27 and the metal terminal 9 and core 2 that contact it becomes significant, and there is a concern that the adhesive strength may decrease.

[0027] In a cross section obtained by polishing adhesive layer 27 parallel to the adhesive surface, the area ratio of bubbles 29 is preferably 2.9% or more and 27% or less. If the area ratio of bubbles 29 is less than 2.9%, the proportion occupied by bubbles 29 is too low, and residual stress may not be fully alleviated. On the other hand, if the area ratio of bubbles 29 exceeds 27%, the amount of expansion of bubbles 29 due to heat during the curing process of adhesive 28 becomes significant, making it difficult to control bubbles 29 and making it difficult to manufacture adhesive layer 27 with good reproducibility.

[0028] 1, the coil device 1 may further include a top plate 31 extending between the top surfaces 12 of the two flange portions 5. The top plate 31 is preferably made of ferrite, as in the case of the core 2. The top plate 31 may also be made of a non-conductive material other than ferrite, such as a non-magnetic material such as alumina, or a resin containing ferrite powder or metal magnetic powder.

[0029] The top plate 31 is adhered to each top surface 12 of the two flanges 5 with an adhesive (not shown). This allows the top plate 31 to form a closed magnetic circuit in cooperation with the core 2. The adhesive may be, for example, an epoxy resin or an epoxy resin containing silica filler.

[0030] Next, an example of an experiment conducted to confirm the effects of the present disclosure will be described.

[0031] The adhesive used was a one-component epoxy resin with bisphenol A as the base and amine as the curing agent. Before the adhesive hardened, it was in a liquid state and stirred with a planetary mixer while nitrogen gas was injected, thereby incorporating air bubbles into the adhesive. This resulted in the formation of an adhesive layer containing air bubbles and adhesive, yielding a sample with the structure shown in Figure 2. The adhesive layer in each sample had an adhesive surface area of 4.0 x 10 5 μm 2 The thickness was 30 μm.

[0032] Here, by changing the stirring conditions for obtaining an adhesive containing bubbles, samples were obtained in which the bubble area ratio, bubble diameter, and tensile strength of the adhesive layer to be formed by the adhesive were different.

[0033] The bubble area ratio and bubble diameter are the area ratio and diameter of bubbles on a cross section of the adhesive layer that is revealed by polishing the adhesive layer parallel to the adhesive surface. However, the samples used for measuring the bubble area ratio and bubble diameter were processed in a state in which the cross section of the adhesive layer was exposed, so the samples themselves could not be used for measuring tensile strength. Therefore, in this experimental example, adhesives processed under specified stirring conditions were prepared, and from these samples, samples used for measuring the bubble area ratio and bubble diameter and samples used for measuring tensile strength were selected. In other words, the samples used for measuring the bubble area ratio and bubble diameter and the samples used for measuring tensile strength were adhesives processed under the same stirring conditions, so it is assumed that the bubble area ratio, bubble diameter, and tensile strength are substantially the same.

[0034] The measured "cell area ratio," "cell diameter," and "tensile strength" are shown in Table 1. For each of "cell area ratio," "cell diameter," and "tensile strength," the number of samples was 10, and the average value is shown.

[0035] Figure 3 shows a cross-sectional polished photograph taken in a direction parallel to the adhesive surface, i.e., perpendicular to the thickness direction of the adhesive layer. In Figure 3, air bubbles contained in the adhesive layer are shown as whitish images, and the dark areas around them represent the adhesive. "State A," "State B," "State C," and "State D" in Figure 3 correspond to "State A," "State B," "State C," and "State D" in Table 1, respectively.

[0036] As shown in Table 1, the "bubble area ratio" was 0% for the adhesive layer in "Condition A", 2.9% for the adhesive layer in "Condition B", 14% for the adhesive layer in "Condition C", and 27% for the adhesive layer in "Condition D".

[0037] The "bubble area ratio" is the ratio of the area occupied by bubbles that appear on a cross section taken at the center of the adhesive layer's thickness direction and perpendicular to the thickness direction to the area of the adhesive surface of the adhesive layer, and was calculated by binarizing the brightness values of bubbles on the observation surface using image processing software. When photographing the cross-sectional image to determine the "bubble area ratio," bubbles with an area that could not be distinguished as bubbles were not considered to be bubbles. More specifically, bubbles with a diameter of less than 1% of the equivalent circle diameter of the adhesive surface of the adhesive layer were not considered to be bubbles. In this experimental example, when the area of the adhesive surface of the adhesive layer was 4.0 x 10 5 μm 2 Therefore, the circle equivalent diameter is 710 μm, and 1% of that is 7.1 μm. Therefore, bubbles with a diameter of less than 7.1 μm were not considered to be bubbles for the purpose of calculating the "bubble area ratio."

[0038] "Bubble diameter" is the average circle-equivalent diameter of bubbles with a diameter of 7.1 μm or more that appear in the same cross section as the cross section used to determine the "bubble area ratio," that is, the cross section taken at the center of the adhesive layer in the thickness direction and perpendicular to the thickness direction. Similarly, when determining "bubble diameter," bubbles with a diameter of less than 7.1 μm were not considered to be bubbles for the purpose of determining "bubble diameter."

[0039] The tensile strength of the metal terminal relative to the core was also measured in each of the conditions A to D. The results are shown in Table 1 under "Tensile Strength" and in Figure 4. Figure 4 shows the average tensile strength and distribution for 10 samples. Referring to Figure 2, the tensile strength is measured by applying a force to the metal terminal 9 in the direction indicated by arrow L while the core 2 is fixed in place with an appropriate holder (not shown). This force is gradually increased until the metal terminal 9 can no longer be held by the core 2. The phenomenon in which the metal terminal 9 can no longer be held by the core 2 can occur due to fracture within the thickness of the adhesive layer 27 itself (cohesive failure) or due to separation at the interface between the adhesive layer 27 and the core 2 or metal terminal 9 (interfacial failure). However, in this experimental example, a combination of both types of failure occurred.

[0040] [Table 1]

[0041] As can be seen from Table 1 and Figure 4, the adhesive layers in Conditions B, C, and D, which contain air bubbles, have improved tensile strength compared to the adhesive layer in Condition A, which does not contain air bubbles. This is because the adhesive layers in Conditions B, C, and D have smaller residual stress than the adhesive layer in Condition A.

[0042] Furthermore, when comparing the bubble-containing states B, C, and D, the larger the "bubble area ratio," the larger the "bubble diameter" and the higher the "tensile strength." Note that the "bubble area ratio" is not necessarily limited, and a larger value is not preferable; as will be described later, it is preferable that the "bubble area ratio" is 27% or less.

[0043] From the data shown in Table 1, it can be seen that the bubble size is preferably 300 μm or less in equivalent circle diameter, and that the bubble area ratio is preferably 2.9% or more and 27% or less.

[0044] While the coil component according to the present disclosure has been described above based on an embodiment relating to a common mode choke coil, this embodiment is merely illustrative and various other modifications are possible. Therefore, the number of wires and the winding direction of the wires provided in the coil component, as well as the number of metal terminals, can be changed depending on the function of the coil component.

[0045] Furthermore, in the above-described embodiment, the wires 7 and 8 are provided as coil conductors, but the present disclosure can also be applied to coil components that include coil conductors made of conductive films instead of wires.

[0046] Furthermore, in the above-described embodiment, the core was a drum-shaped core having the winding core portion 3 and the flange portions 5 provided at opposite ends of the winding core portion 3 in the axial direction, but the present disclosure can also be applied to coil components having cores of other shapes, such as simply plate-shaped cores, and further to coil components having a laminated structure.

[0047] Furthermore, in the above-described embodiment, an adhesive containing an epoxy resin was exemplified as the adhesive for fixing the metal terminal 9 to the core 2, but the present disclosure may be similarly applied to adhesives having other compositions.

[0048] Furthermore, each embodiment described in this specification is merely an example, and partial substitution or combination of configurations is possible between different embodiments.

[0049] Embodiments of the present disclosure include the following:

[0050] <1> A coil conductor; a core that holds the coil conductor; a metal terminal connected to the coil conductor; an adhesive layer for fixing the metal terminal to the core; Equipped with The adhesive layer includes an adhesive and air bubbles. Coil parts.

[0051] <2> The bubbles are filled with at least one gas selected from nitrogen, argon, and air. <1> The coil component according to claim 1.

[0052] <3> The bubbles include those with a flat shape. <1> or <2> The coil component according to claim 1.

[0053] <4> The average size of the bubbles is 300 μm or less in equivalent circle diameter. <1> Or <3> The coil component according to any one of the preceding claims.

[0054] <5> In the cross section of the adhesive layer, the area ratio of the air bubbles is 2.9% or more and 27% or less. <1> Or <4> The coil component according to any one of the preceding claims.

[0055] <6> the core has a winding core portion and flange portions provided at opposite ends of the winding core portion in the axial direction, the coil conductor includes a wire wound around the winding core, the wire is connected to the metal terminal; the metal terminal is bonded to the flange portion via the adhesive layer; · Or <5> The coil component according to any one of the preceding claims.

[0056] <7> the flange portion has an inner end surface on which an end of the winding core portion is positioned and an outer end surface facing in the opposite direction to the inner end surface, the metal terminal is bonded to the flange portion at the outer end surface of the flange portion via the adhesive layer; <6> The coil component according to claim 1. [Explanation of symbols]

[0057] 1 Coil parts 2 cores 3 Winding core 5. Tsuba 7,8 wires 9 Metal terminal 13 Inner end face 14 Outer end face 27 Adhesive layer 28 Adhesive 29 Bubbles AX Axial direction

Claims

1. A coil conductor; a core that holds the coil conductor; a metal terminal connected to the coil conductor; an adhesive layer for fixing the metal terminal to the core; Equipped with The adhesive layer includes an adhesive and air bubbles. Coil parts.

2. The coil component according to claim 1 , wherein the bubbles are filled with at least one gas selected from the group consisting of nitrogen, argon, and air.

3. The coil component according to claim 1 , wherein the bubbles include bubbles having a flat shape.

4. The coil component according to claim 1 , wherein the bubbles have an average equivalent circle diameter of 300 μm or less.

5. The coil component according to claim 1 , wherein an area ratio of the air bubbles in a cross section of the adhesive layer is 2.9% or more and 27% or less.

6. the core has a winding core portion and flange portions provided at opposite ends of the winding core portion in the axial direction, the coil conductor includes a wire wound around the winding core, the wire is connected to the metal terminal; the metal terminal is bonded to the flange portion via the adhesive layer; The coil component according to claim 1 .

7. the flange portion has an inner end surface on which an end of the winding core portion is positioned and an outer end surface facing in the opposite direction to the inner end surface, the metal terminal is bonded to the flange portion at the outer end surface of the flange portion via the adhesive layer; The coil component according to claim 6 .

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