JP6801422B2 - Electronic circuit with coil components - Google Patents

Description

The present invention relates to an electronic circuit including a coil component, and more particularly to an electronic circuit coated with a moisture-proof coating resin.

Surface mount type coil parts using a drum type core are used in many electronic devices as electronic parts for noise suppression. In recent years, in order to further improve the reliability of the entire electronic circuit including the coil parts, a moisture-proof coating resin may be applied to a substrate on which the coil parts and the like are mounted (see Patent Document 1). When the moisture-proof coating resin is applied, the electronic components mounted on the substrate are protected from moisture, so that the reliability of the entire electronic circuit is improved.

Japanese Unexamined Patent Publication No. 2008-159610

However, compared to ordinary electronic circuits, electronic circuits coated with a moisture-proof coating resin are more likely to crack the solder connecting the coil components due to repeated temperature changes, and in some cases the coil components themselves may fall off from the substrate. There was also.

Therefore, an object of the present invention is to prevent poor connection of coil parts in an electronic circuit coated with a moisture-proof coating resin.

The present inventors have diligently studied the reason why poor connection of coil parts is likely to occur in an electronic circuit coated with a moisture-proof coating resin. As a result, unlike electronic components such as capacitors in which circuit elements are covered with a body, coil parts are used with the wires exposed from the body, so it is necessary to secure a certain amount of clearance between them and the substrate. It was found that the cause of the poor connection is the thermal expansion of the moisture-proof coating resin that has entered this gap.

The present invention has been made based on such technical knowledge, and the electronic circuit according to the present invention is a substrate, a coil component mounted on the substrate, and a core having a winding core portion and a flange portion. A terminal electrode provided on the flange portion, a wire wound around the winding core portion and having an end connected to the terminal electrode, and a protective resin covering at least a part of the winding core portion. A coil component and a moisture-proof coating resin applied to the substrate so as to cover at least a part of the coil component are provided, and at least a part of the protective resin is formed by the substrate and the winding core portion of the coil component. It is located between them, and the thermal expansion coefficient of the protective resin is smaller than the thermal expansion coefficient of the moisture-proof coating resin.

According to the present invention, since the protective resin having a coefficient of thermal expansion smaller than that of the moisture-proof coating resin is provided in the space between the substrate and the winding core portion, there is less room for the moisture-proof coating resin to enter this space. As a result, it is possible to prevent the phenomenon that the coil parts are pushed up by the thermal expansion of the moisture-proof coating resin that has entered this space, and as a result, solder cracks and the coil parts fall off.

In the present invention, it is preferable that the coil component further includes a top plate connected to the collar portion, and another part of the protective resin is located between the winding core portion and the top plate. According to this, there is less room for the moisture-proof coating resin having a large coefficient of thermal expansion to enter the space sandwiched between the top plate and the core portion. As a result, the top plate is pushed up by the thermal expansion of the moisture-proof coating resin that has entered this space, and as a result, the phenomenon that the top plate is peeled off from the core can be prevented.

In this case, the collar portion is located on the inner side surface provided with the winding core portion, the outer surface located on the opposite side of the inner side surface, the upper surface facing the top plate, and the opposite side of the upper surface surface. The upper surface of the flange portion has a lower surface, and has an upper surface to which the top plate is connected and a lower surface which is set back from the upper surface and forms a space between the top plate. The terminal electrode is continuously formed over the lower surface, the outer surface, and the lower surface of the collar portion, and the joint wire portion of the terminal electrode is connected to the portion formed on the lower surface. Yet another part of the protective resin may be configured to be located on the upper surface of the top plate and the outer surface of the collar portion. As described above, if the structure is such that the wire is connected to the upper surface side of the flange portion, most of the coil parts can be covered with the protective resin.

In the present invention, the coefficient of thermal expansion of the protective resin is preferably 250 (1 / ° C.) or less. According to this, it is possible to surely prevent the occurrence of solder cracks due to thermal expansion and the falling off of coil parts.

In the present invention, the wire is located between the coil portion wound around the winding core portion, the joint wire portion in contact with the terminal electrode, and the coil portion and the joint wire portion, and is in contact with the core. It is preferable that the protective resin covers at least a part of the overhead wire portion and the joint wire portion, including an overhead wire portion that does not. According to this, the overhead wire part that is easily broken by stress and the joint wire part that is easily peeled by physical impact are protected, so that stress on the coil parts that may occur during or after mounting on the board Can be alleviated.

According to the present invention, it is possible to prevent poor connection of coil parts in an electronic circuit coated with a moisture-proof coating resin. This makes it possible to improve the reliability of the electronic circuit on which the coil component is mounted.

FIG. 1 is a cross-sectional view showing a part of an electronic circuit 200 according to a preferred embodiment of the present invention. FIG. 2 is a top view showing a part of the substrate 100 on which the coil component 10 is mounted. FIG. 3 is a schematic perspective view showing the appearance of the coil component 10. FIG. 4 is an exploded perspective view of the coil component 10. 5A and 5B are views for explaining a state in the vicinity of the ends of the wires W1 and W2, where FIG. 5A is a view seen from the y direction and FIG. 5B is a view seen from the z direction. FIG. 6 is a schematic cross-sectional view showing a modified example of the coil component 10.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view showing a part of an electronic circuit 200 according to a preferred embodiment of the present invention.

As shown in FIG. 1, the electronic circuit 200 according to the present embodiment includes a substrate 100, a coil component 10 mounted on the substrate 100, and a moisture-proof coating resin 70 applied to the substrate 100.

The coil component 10 is a surface mount type common mode filter, and its specific configuration will be described in detail later with reference to FIGS. 3 to 5. As shown in FIG. 2, a mounting region 10A of the coil component 10 is defined on the surface of the substrate 100. Land patterns P1 to P4 to be connected to the terminal electrodes 31 to 34 of the coil component 10 are provided in the mounting area 10A, respectively, and corresponding wiring patterns L1 to L4 are connected to the land patterns P1 to P4, respectively. There is. The wiring patterns L1 and L2 form a pair of differential signal lines IN, and the wiring patterns L3 and L4 form a pair of differential signal lines OUT. Then, if the coil component 10 is mounted in the mounting area 10A, the common mode filter is inserted between the differential signal line IN and the differential signal line OUT, so that common mode noise superimposed on the differential signal is generated. Can be removed.

As shown in FIG. 1, the surface of the substrate 100 is coated with a moisture-proof coating resin 70 that covers the coil component 10. As a result, the wires W1 and W2 and the terminal electrodes 31 to 34 constituting the coil component 10 are covered with the moisture-proof coating resin 70, so that corrosion due to moisture is less likely to occur, and the reliability of the electronic circuit 200 is enhanced.

However, when the moisture-proof coating resin 70 enters the space between the substrate 100 and the coil component 10, the coil component 10 is pushed up by the thermal expansion of the moisture-proof coating resin 70 at a high temperature, and the solder 60 is cracked. Depending on the situation, the coil component 10 itself may fall off from the substrate 100. This is because the coefficient of thermal expansion of the material generally used as the moisture-proof coating resin 70 is relatively large. Further, unlike an electronic component in which a circuit element is covered with an element body such as a capacitor, the coil component 10 is used in a state where the wires W1 and W2 are exposed from the element body, and thus is formed between the coil component 10 and the substrate 100. The gap is large. For this reason, solder cracks and parts falling off due to thermal expansion of the moisture-proof coating resin 70 occur remarkably in the coil parts 10 and hardly occur in other electronic parts.

In order to solve such a problem, in the electronic circuit 200 according to the present embodiment, the protective resin 50 is provided between the substrate 100 and the coil component 10. The material of the protective resin 50 is not particularly limited as long as it has a coefficient of thermal expansion smaller than that of the moisture-proof coating resin 70, and an epoxy resin or the like can be used. By providing such a protective resin 50, there is less room for the moisture-proof coating resin 70 to enter the space between the substrate 100 and the coil component 10, so that connection failure caused by thermal expansion of the moisture-proof coating resin 70 is prevented. be able to.

Further, in the present embodiment, the coil component 10 is provided with the top plate 40, and the protective resin 50 is also provided between the core 20 and the top plate 40. As a result, there is less room for the moisture-proof coating resin 70 to enter the space between the core 20 and the top plate 40, so that peeling of the top plate 40 caused by thermal expansion of the moisture-proof coating resin 70 can be prevented.

FIG. 3 is a schematic perspective view showing the appearance of the coil component 10. Further, FIG. 4 is an exploded perspective view of the coil component 10.

As shown in FIGS. 3 and 4, the coil component 10 includes a core 20 having a winding core portion 21 and flange portions 22, 23, four terminal electrodes 31 to 34 provided on the flange portion, and a winding of the core 20. It includes two wires W1 and W2 wound around a core portion 21 and connected to terminal electrodes 31 to 34 whose ends correspond to each other, and a top plate 40 covering the core 20.

The core 20 is a drum-shaped core having an integral structure made of a magnetic material such as ferrite, and the axial direction of the winding core portion 21 is the x direction. The collar portions 22 and 23 are provided on both sides of the winding core portion 21 in the x direction, respectively. The flange portions 22 and 23 include inner side surfaces 22i and 23i provided with a winding core portion 21, outer surfaces 22o and 23o located on opposite sides of the inner side surfaces 22i and 23i, and upper surfaces 22t and 23t having a stepped shape. , Has lower surfaces 22b, 23b located on opposite sides of the upper surfaces 22t, 23t. The inner side surfaces 22i and 23i and the outer side surfaces 22o and 23o all form a yz plane, and the upper surfaces 22t and 23t and the lower surfaces 22b and 23b all have an xy plane.

Upper surface 22t of the flange portion 22 includes an upper surface 22t ₁ positioned at the center of the y-direction, has a set-back two lower surface 22t ₂ from the top surface 22t _1, the upper surface 22t ₁ is lower surfaces It protrudes from 22t _{2 in the} z direction. Similarly, the upper surface 23t of the flange portion 23, an upper surface 23t ₁ positioned at the center of the y-direction, has two lower surface 23t ₂ which is set back from the upper surface 23t _1, the upper surface 23t ₁ Projects from the lower surface 23t _{2 in the} z direction. The upper surfaces 22t ₁ , 23t ₁ are surfaces to which the top plate 40 is connected.

The top plate 40 has a lower surface 41 facing the core 20 side and an upper surface 42 located on the opposite side of the lower surface 41. Both the lower surface 41 and the upper surface 42 of the top plate 40 form an xy plane, and when mounting on the substrate 100, the coil component 10 can be handled by using the upper surface 42 of the top plate 40 as a suction surface. .. Further, if a magnetic material is used as the material of the top plate 40, a closed magnetic path can be formed by the core 20 and the top plate 40. However, it is not essential that the top plate 40 is made of a magnetic material. The method of connecting the top plate 40 is not particularly limited, and for example, an adhesive may be used.

When the top plate 40 is connected to the core 20, a space S is formed between the lower surface 41 of the top plate 40 and the lower surfaces 22t ₂ , 23t ₂ of the flanges 22, 23. The height of the space S in the z direction is defined by the difference in height between the lower surfaces 22t ₂ , 23t ₂ and the upper surfaces 22t ₁ , 23t _{1 in} the z direction. As will be described later, this space S accommodates a part of the terminal electrodes 31 to 34 and the ends of the wires W1 and W2.

The terminal electrodes 31 to 34 have upper portions 31t to 34t, lower portions 31b to 34b, and side portions 31s to 34s, respectively. The upper portions 31t and 32t of the terminal electrodes 31 and 32 are portions that cover the lower surface 22t ₂ of the collar portion 22, and the upper portions 33t and 34t of the terminal electrodes 33 and 34 are portions that cover the lower surface 23t ₂ of the collar portion 23. is there. The lower portions 31b and 32b of the terminal electrodes 31 and 32 are portions that cover the lower surface 22b of the collar portion 22, and the lower portions 33b and 34b of the terminal electrodes 33 and 34 are portions that cover the lower surface 23b of the collar portion 23. The side portions 31s and 32s of the terminal electrodes 31 and 32 are portions that cover the outer surface 22o of the collar portion 22, and the side portions 33s and 34s of the terminal electrodes 33 and 34 are portions that cover the outer surface 23o of the collar portion 23. is there. As a result, the terminal electrodes 31 to 34 are continuously formed over the lower surfaces 22t ₂ , 23t ₂ of the flange portion 22 or 23, the outer surfaces 22o, 23o, and the lower surfaces 22b, 23b.

The wires W1 and W2 are coated conductive wires in which a core material such as copper is coated with insulation, and are wound around the core portion 21 of the core 20 in the same number of turns. One end of the wire W1 is connected to the upper 31t of the terminal electrode 31, and the other end of the wire W1 is connected to the upper 33t of the terminal electrode 33. Further, one end of the wire W2 is connected to the upper portion 32t of the terminal electrode 32, and the other end of the wire W2 is connected to the upper portion 34t of the terminal electrode 34. As a result, the ends of the wires W1 and W2 are both housed in the space S formed between the flanges 22 and 23 and the top plate 40, so that a physical impact from the outside is unlikely to be applied. There is. The wires W1 and W2 and the terminal electrodes 31 to 34 can be connected by welding, thermocompression bonding, or the like, but the coil component 10 used in this embodiment is on the side opposite to the lower surfaces 22b and 23b, which are the mounting surfaces. Since the wires W1 and W2 are joined on the upper surfaces 22t and 23t, it is not necessary to consider the interference between the substrate and the connecting portion, and therefore it is preferable to use welding having a higher connection strength.

With such a configuration, the coil component 10 can be used as a surface mount type common mode filter.

5A and 5B are views for explaining a state in the vicinity of the ends of the wires W1 and W2, where FIG. 5A is a view seen from the y direction and FIG. 5B is a view seen from the z direction. In consideration of the legibility of the drawings, the top plate 40 is omitted in both FIGS. 5A and 5B.

As shown in FIG. 5, the wires W1 and W2 have three portions including a joint wire portion A, an overhead wire portion B, and a coil portion C. The connecting wire portion A is a portion in contact with the terminal electrodes 31 to 34, and is a portion fixed to the terminal electrodes 31 to 34 by welding, thermocompression bonding, or the like. The coil portion C is a portion wound around the winding core portion 21. The overhead wire portion B is located between the joint wire portion A and the coil portion C, and is a portion that is overhead-wired in the air without contacting the core 20. In the coil component 10 used in the present embodiment, the entire overhead wire portion B is covered with the protective resin 50 so that the overhead wire portion B is not exposed. As a result, the overhead wire portion B, which is most likely to be disconnected, can be protected by the protective resin 50.

Further, in the present embodiment, the protective resin 50 also enters the space S, and a part of the connecting wire portion A is also covered with the protective resin 50 by the protective resin 50 that has entered the space S. As a result, the joint wire portion A, which is likely to be peeled off from the terminal electrodes 31 to 34, is protected by the protective resin 50.

The protective resin 50 preferably has a Young's modulus lower than that of the moisture-proof coating resin 70. According to this, after the coil component 10 is mounted on the substrate 100, the stress applied to the overhead wire portions B of the wires W1 and W2 from the moisture-proof coating resin 70 due to the temperature change is sufficiently relaxed, so that the overhead wire portion B It is possible to prevent disconnection of the wires W1 and W2.

As the material of the protective resin 50, an epoxy resin or the like can be used as described above, and the uncured protective resin 50 may be supplied by using a dispenser or the like and then thermoset. The uncured protective resin 50 needs to be supplied after the connection of the wires W1 and W2 is completed, and is particularly preferably performed after the connection of the top plate 40 is completed. If the protective resin 50 is supplied after the connection of the top plate 40 is completed, the protective resin 50 does not widen the gap between the core 20 and the top plate 40, and the surface tension of the lower surface 41 of the top plate 40 does not widen. This makes it possible to suppress the spread of the protective resin 50.

In the present invention, it is not essential that the protective resin 50 covers the entire overhead line portion B, and only a part of the overhead line portion B may be covered. However, since the overhead line portion B is the portion where the disconnection is most likely to occur, it is preferable to cover the entire overhead line portion B with the protective resin 50.

Further, although it is not essential that the coil component 10 according to the present invention includes the top plate 40, if the top plate 40 is used and the top plate 40 is connected to the core 20 and then the protective resin 50 is applied, excessive protection is provided. Since the resin 50 stays on the lower surface 41 of the top plate 40 due to surface tension, it becomes easy to control the coating position of the protective resin 50.

The coating range of the protective resin 50 is not particularly limited as long as it covers the lower part of the winding core portion 21. That is, it is sufficient that at least a part of the protective resin 50 is positioned between the substrate 100 and the winding core portion 21 in the state of being mounted on the substrate 100. Therefore, as shown in FIG. 6, most of the coil parts 10 except for the lower portions 31b to 34b of the terminal electrodes 31 to 34, that is, between the upper surface 42 of the top plate 40, the lower surface 41 of the top plate 40, and the winding core portion 21. , The outer surfaces 22o, 23o of the flange portions 22, 23 may be covered. The lower parts 31b to 34b of the terminal electrodes 31 to 34 are exposed from the protective resin 50 because the lower parts 31b to 34b of the terminal electrodes 31 to 34 are connected to the substrate.

As described above, the electronic circuit 200 according to the present embodiment can prevent the occurrence of solder cracks and the detachment of the coil component 10 due to the thermal expansion of the moisture-proof coating resin 70.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention, and these are also the present invention. It goes without saying that it is included in the range.

For example, in the above embodiment, the case where the coil component is a common mode filter has been described as an example, but the object of the present invention is not limited to this, and it can be applied to other types of coil components. Is.

10 Coil component 10A Mounting area 20 Core 21 Winding cores 22, 23 Collars 22b, 23b Bottom surface 22i, 23i Inner side surface 22o, 23o Outer side surface 22t, 23t Top surface 22t ₁ , 23t ₁ Upper surface 22t ₂ , 23t ₂ Lower surface 31 ~ 34 Terminal electrodes 31b ~ 34b Lower part 31s ~ 34s Side part 31t ~ 34t Upper part 40 Top plate 41 Lower surface 42 Upper surface 50 Protective resin 60 Solder 70 Moisture-proof coat resin 100 Substrate A Joint wire part B Overhead wire part C Coil part L1 to L4 Wiring Pattern P1 to P4 Land pattern S Space W1, W2 Wire

Claims (5)

With the board
A coil component mounted on the substrate, a core having a winding core portion and a flange portion, a terminal electrode provided on the flange portion, and a coil component wound around the winding core portion, and an end portion is wound on the terminal electrode. A coil component containing the connected wire and a protective resin covering at least a part of the winding core portion.
A moisture-proof coating resin coated on the substrate so as to cover at least a part of the coil component is provided.
At least a part of the protective resin and at least a part of the moisture-proof coating resin are located between the substrate and the core portion of the coil component.
An electronic circuit characterized in that the coefficient of thermal expansion of the protective resin is smaller than the coefficient of thermal expansion of the moisture-proof coating resin. The coil component further includes a top plate connected to the collar.
The electronic circuit according to claim 1, wherein another part of the protective resin and another part of the moisture-proof coating resin are located between the winding core portion and the top plate. The collar portion includes an inner surface provided with the winding core portion, an outer surface located on the opposite side of the inner side surface, an upper surface facing the top plate, and a lower surface located on the opposite side of the upper surface. Have and
The upper surface of the flange portion has an upper surface to which the top plate is connected and a lower surface which is set back from the upper surface and forms a space between the top plate.
The terminal electrode is continuously formed over the lower surface, the outer surface, and the lower surface of the collar portion, and the connecting portion of the wire is connected to the portion formed on the lower surface.
The electronic circuit according to claim 2, wherein still another part of the protective resin is located on the upper surface of the top plate and the outer surface of the collar portion. The electronic circuit according to any one of claims 1 to 3, wherein the coefficient of thermal expansion of the protective resin is 250 (1 / ° C.) or less. The wire includes a coil portion wound on the winding core portion, the said connecting wire portion in contact with the terminal electrode, positioned between the coil portion and the joint line section, the overhead wire not in contact with the core Including the part
The electronic circuit according to any one of claims 1 to 4, wherein the protective resin covers at least a part of the overhead wire portion and the joint wire portion.

Images