Coil component and coil-component-equipped mounting substrate

A coil component has an outer electrode include a bottom-surface electrode portion disposed along a bottom surface of a component body and an end-surface electrode portion disposed along an end surface of the component body so as to be continuous with the bottom-surface electrode portion. The adhesive strength of the bottom-surface electrode portion with respect to the component body is lower than that of the end-surface electrode portion with respect to the component body.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit of priority to Japanese Patent Application No. 2017-164099, filed Aug. 29, 2017, the entire content of which is incorporated herein by reference.

BACKGROUND

Technical Field

The present disclosure relates to a coil component and a coil-component-equipped mounting substrate, and more particularly to a coil component that includes a component body and an outer electrode formed on an outer surface of the component body and a coil-component-equipped mounting substrate that includes such a coil component.

Background Art

An example of a coil component related to the present disclosure is a coil component described in Japanese Unexamined Patent Application Publication No. 2011-77183. The coil component described in Japanese Unexamined Patent Application Publication No. 2011-77183 includes a drum core that includes a winding core portion and first and second flange portions, which are provided at the ends of the winding core portion. Wires are wound around the winding core portion of the drum core. Outer electrodes are formed on the first and second flange portions of the drum core, and ends of the wires are electrically connected to the outer electrodes.

The above-mentioned outer electrodes are formed by applying and baking an electrically conductive paste containing silver as an electrically conductive component and then performing nickel plating and tin plating. In addition, each of the outer electrodes is formed so as to extend from a bottom surface of a corresponding one of the flange portions, the bottom surface facing a mounting surface, to a top surface of the flange portion that faces in a direction opposite to the direction in which the bottom surface faces through an end surface of the flange portion, the end surface being located on the side opposite to the side on which the winding core portion is present.

SUMMARY

The coil component described in Japanese Unexamined Patent Application Publication No. 2011-77183 is usually put to practical use by being mounted onto a mounting substrate. A mounting structure of the coil component is realized by soldering the outer electrodes of the coil component to conductors included in the mounting substrate.

In the above-mentioned mounted state, stress generated as a result of temperature changes is most likely to concentrate at solder portions that connect the outer electrodes of the coil component to the conductors of the mounting substrate, and as a result, cracks are likely to be generated in the solder portions. In addition, in the mounted state, stress is also generated when deflection occurs in the mounting substrate, and the stress may sometimes cause fracturing of the drum core.

Accordingly, the present disclosure provides a coil component capable of reducing the probability of generation of a crack in a solder portion and a fracture in a component body such as a drum core, which have been described above. The present disclosure also provides a coil-component-equipped mounting substrate that includes the above-described coil component. Accordingly, the present disclosure has been made on the basis of a viewpoint that problems such as those described above occur in the technology described in Japanese Unexamined Patent Application Publication No. 2011-77183 because the outer electrodes are strongly fixed to the component body.

A coil component according to one embodiment of the present disclosure includes a component body and an outer electrode that is formed on an outer surface of the component body. The component body at least has a bottom surface facing a mounting surface and an end surface extending in a direction away from the mounting surface. The outer electrode includes a bottom-surface electrode portion that is disposed along the bottom surface of the component body and an end-surface electrode portion that is disposed along the end surface of the component body so as to be continuous with the bottom-surface electrode portion. An adhesive strength of the bottom-surface electrode portion with respect to the component body is lower than an adhesive strength of the end-surface electrode portion with respect to the component body. This configuration realizes a state where the bottom-surface electrode portion is capable of easily moving with respect to the component body when an external force acts on the outer electrode.

In the coil component, the adhesive strength of the bottom-surface electrode portion with respect to the component body may be about zero, as in a case where the bottom-surface electrode portion is separated from the component body. In the coil component, the component body preferably includes a round chamfered portion that is formed at a ridge line portion between the bottom surface and the end surface, and the bottom-surface electrode portion further includes a round electrode portion that is disposed along the round chamfered portion and that extends to the end-surface electrode portion. With this configuration, the round electrode portion can be included in the portion of the bottom-surface electrode portion that is capable of easily moving with respect to the component body.

Preferably, the component body included in the coil component according to the preferred embodiment of the present disclosure includes a core including a winding core portion, a first flange portion, which is formed at a first end of the winding core portion, and a second flange portion, which is formed at a second end of the winding core portion that is opposite to the first end of the winding core portion, and a wire that is wound around the winding core portion. In this case, the above-mentioned bottom surface includes flange-portion bottom surfaces of the first and second flange portions that face the mounting surface, and the above-mentioned end surface include flange-portion end surfaces of the first and second flange portions that are located on a side opposite to a side on which the winding core portion is present. In addition, the outer electrode is electrically connected to an end of the wire and is formed so as to extend from the flange-portion bottom surface to the flange-portion end surface of one of the first and second flange portions. This configuration is employed in a common wire-wound coil component.

In the case that each of the first and second flange portions has a flange-portion top surface facing in a direction opposite to the direction in which the corresponding flange-portion bottom surface faces, it is preferable that the end-surface electrode portion of the outer electrode is not formed on the flange-portion top surface and a portion of the flange-portion end surface adjacent to the flange-portion top surface. With this configuration, magnetic flux generated in the coil component can be prevented from being blocked by the outer electrode.

In addition, it is preferable that the flange-portion bottom surface has a low resistance portion having an electrical resistance lower than an electrical resistance of another portion of the core and that the bottom-surface electrode portion is an electroplated film precipitated on the low resistance portion. The electroplated film precipitated on the low resistance portion as mentioned above can have a relatively low adhesive strength with respect to the core. Also, instead of forming the bottom-surface electrode portion in a manner described in the above embodiment, even if the bottom-surface electrode portion is made of a resin that contains metal powder and that does not contain glass, the adhesive strength of the bottom-surface electrode portions with respect to the core can be relatively low.

In the coil component, the end-surface electrode portion is preferably a sputtered film. The end-surface electrode portion of a sputtered film can obtain a relatively high adhesive strength with respect to the core. Also, instead of forming the end-surface electrode portion in a manner described in the above embodiment, even if the end-surface electrode portion is a conductor containing a glass coupled to the core, the end-surface electrode portion can obtain a relatively high adhesive strength with respect to the core.

In the coil component, it is preferable that the outer electrode further includes an outer-layer plated film that coats the bottom-surface electrode portion and the end-surface electrode portion in a continuous manner. With this configuration, even if the bottom-surface electrode portion having a relatively low adhesive strength separate from the bottom surface of the component body, the bottom-surface electrode portion can be maintained in a state of being held by the end-surface electrode portion having a relatively high adhesive strength via the outer-layer plated film.

In the above case, it is further preferable that the outer-layer plated film has a thickness of about 10 μm or more. With this configuration, the outer-layer plated film can obtain a mechanical strength equal to or higher than a predetermined degree. As a result, the outer-layer plated film can more reliably exhibit its function of causing the bottom-surface electrode portion separated from the component body to be held by the end-surface electrode portion via the outer-layer plated film.

In the coil component, the adhesive strength of the bottom-surface electrode portion, which is lower than the adhesive strength of the end-surface electrode portion, may be about zero as mentioned above. In other words, the bottom-surface electrode portion may be in a state of being separated from the bottom surface of the component body. This state may occur after the coil component has been mounted on a mounting substrate. Therefore, the present disclosure is also directed to a mounting structure of a coil component such as that described below.

A coil-component-equipped mounting substrate according to another embodiment of the present disclosure includes the coil component according to the above-described preferred embodiment of the present disclosure and a mounting substrate onto which the coil component is mounted and that includes a conductor to which the outer electrode are soldered. At least a portion of the bottom-surface electrode portion has separated from the bottom surface of the component body.

In the coil component according to the present disclosure, the adhesive strength of the bottom-surface electrode portion of the outer electrode with respect to the component body is set to be lower than the adhesive strength of the end-surface electrode portion of the outer electrode with respect to the component body, and thus, when an external force acts on the outer electrode, first, the bottom-surface electrode portion can move with respect to the component body. Therefore, in a mounted state of the coil component, stress that causes cracks to be generated in solder portions and a fracture to occur in the component body can be favorably released, and a mounting structure that is highly resistant to temperature changes and to deflection that occurs in a mounting substrate can be realized.

Other features, elements, characteristics and advantages of the present disclosure will become more apparent from the following detailed description with reference to the attached drawings.

DETAILED DESCRIPTION

A coil component1according to an embodiment of the present disclosure will be described with reference toFIGS. 1 to 3. The coil component1illustrated inFIGS. 1 to 3is a wire-wound coil component.

The coil component1includes a component body2and first and second outer electrodes3and4that are formed on an outer surface of the component body2. The component body2at least has a bottom surface5facing a mounting surface, end surfaces6each extending in a direction away from the mounting surface, and a top surface7facing in a direction opposite to the direction in which the bottom surface5faces. Each of the outer electrodes3and4at least includes a bottom-surface electrode portion9that is disposed along the bottom surface5of the component body2and an end-surface electrode portion10that is disposed along one of the end surfaces6of the component body2so as to be continuous with the bottom-surface electrode portion9.

A feature of the present disclosure is that the adhesive strength of each of the bottom-surface electrode portions9with respect to the component body2is set to be lower than the adhesive strength of each of the end-surface electrode portions10with respect to the component body2. This configuration realizes a state where the bottom-surface electrode portions9, which are portions of the outer electrodes3and4, are capable of moving with respect to the component body2by, for example, separating from the component body2as illustrated inFIG. 3when an external force acts on the outer electrodes3and4.

In the present embodiment, the component body2includes round chamfered portions11formed at ridge line portions between the bottom surface5and the end surfaces6, and each of the above-mentioned bottom-surface electrode portions9includes a round electrode portion12that is disposed along a corresponding one of the round chamfered portions11and that extends to a corresponding one of the end-surface electrode portions10. With this configuration, the round electrode portions12can be included in the portions of the bottom-surface electrode portions9that are capable of moving with respect to the component body2. Therefore, the outer electrodes3and4can be more resistant to thermal fatigue at the time of soldering and to deflection.

As mentioned above, the coil component1illustrated inFIGS. 1 to 3is a wire-wound coil component. Accordingly, the component body2includes a core17including a winding core portion14, a first flange portion15that is formed at a first end of the winding core portion14, and a second flange portion16that is formed at a second end of the winding core portion14that is opposite to the first end of the winding core portion14, and a wire18that is wound around the winding core portion14. The core17is made of an electrical insulating property, and more specifically is made of a magnetic material such as ferrite, a non-magnetic material such as alumina, a curing resin, or the like. Note that, inFIG. 1andFIG. 3, the wire18is illustrated in a simplified manner. The wire18may be wound around the winding core portion14in a single-layer winding or may be wound around the winding core portion14in a double-layer winding.

In this case, the above-mentioned bottom surface5includes a flange-portion bottom surface5aof the first flange portion15and a flange-portion bottom surface5bof the second flange portion16, the flange-portion bottom surfaces5aand5bfacing the mounting surface. The above-mentioned end surfaces6include a flange-portion end surface6aof the first flange portion15and a flange-portion end surface6bof the second flange portion16, the flange-portion end surfaces6aand6bbeing located on the side opposite to the side on which the winding core portion14is present. The above-mentioned top surface7includes a flange-portion top surface7aof the first flange portion15and a flange-portion top surface7bof the second flange portion16.

The first outer electrode3is formed so as to extend at least from the flange-portion bottom surface5ato the flange-portion end surface6aof the first flange portion15, and the second outer electrode4is formed so as to extend at least from the flange-portion bottom surface5bto the flange-portion end surface6bof the second flange portion16. More specifically, the end-surface electrode portion10of the outer electrode3is not formed on a portion of the flange-portion end surface6aof the first flange portion15, the portion being adjacent to the flange-portion top surface7a, and the end-surface electrode portion10of the outer electrode4is not formed on a portion of the flange-portion end surface6bof the second flange portion16, the portion being adjacent to the flange-portion top surface7b. Accordingly, the outer electrode3is not formed on the flange-portion top surface7aof the first flange portion15, and the outer electrode4is not formed on the flange-portion top surface7bof the second flange portion16. With this configuration, the magnetic flux generated in the coil component1can be prevented from being blocked by the outer electrodes3and4.

The ends of the wire18are respectively connected to the first and second outer electrodes3and4by, for example, thermocompression bonding. In the present embodiment, as illustrated inFIG. 1, the ends of the wire18are respectively connected to the first and second outer electrodes3and4on the side on which the bottom surface5of the component body2is present. However, if it is desired to further stabilize the connection between the wire18and the outer electrodes3and4, although not illustrated, the ends of the wire18may be respectively connected to the first and second outer electrodes3and4on the side on which the end surfaces6of the component body2are present or on the side on which the top surface7of the component body2is present.

There are several embodiments to realize a characteristic configuration according to the present disclosure in which, as described above, the adhesive strength of each of the bottom-surface electrode portions9with respect to the component body2is lower than the adhesive strength of each of the end-surface electrode portions10with respect to the component body2. These embodiments include several embodiments related to the bottom-surface electrode portions9and several embodiments related to the end-surface electrode portions10. Usually, the embodiments related to the bottom-surface electrode portions9and the embodiments related to the end-surface electrode portions10can be suitably combined with one another.

The embodiments related to the bottom-surface electrode portions9include a first embodiment in which electroplated film that are formed by, for example, a laser plating method are used as the bottom-surface electrode portions9. More specifically, in this first embodiment, in the case where the core17is made of a ceramic, such as ferrite or alumina, the bottom-surface electrode portions9are formed by radiating a laser beam onto portions of a surface of the core17at which the bottom-surface electrode portions9are to be positioned so as to cause each of the portions to have electrical conductivity, that is, so as to reduce the resistance of each of the portions, and then performing electroplating on these low resistance portions. Each of the bottom-surface electrode portions9is formed of a plated film made of a conductive metal, such as silver or copper. The electroplated film formed by the above method are influenced by modification of the surface of the core17using the laser beam, and thus, each of the bottom-surface electrode portions9has a relatively low adhesive strength with respect to the component body2.

When making the portions of the core17become the low resistance portions each having an electrical resistance lower than that of the other portions of the core17in order to form the bottom-surface electrode portions9, a method other than laser beam radiation may be employed. In other words, in the portions of the core17to which the laser beam has been radiated, a metal oxide is reduced and becomes a metal which is not oxidized, and the low resistance portions each having electrical conductivity are formed. Therefore, a reduction method other than laser beam radiation may be applied.

Note that the low resistance portions are formed by laser beam radiation so as to have a predetermined depth from the surface of the core17, and there is a possibility that the surface of the low resistance portions of the core17will be oxidized again by being exposed to an atmosphere. Thus, there is a possibility that the resistances of portions of the surfaces of the low resistance portions will be increased. However, even in this case, the above-mentioned electroplating will not usually become completely impossible. On the contrary, in this case, it is assumed that the adhesive strength of each of the electroplated film is further decreased, which in turn leads to results that are preferable for the bottom-surface electrode portions9.

The embodiments related to the bottom-surface electrode portions9include a second embodiment in which the bottom-surface electrode portions9are made of a resin that contains metal powder and that does not contain glass. Since the bottom-surface electrode portions9according to this second embodiment do not contain glass that functions as an adhesive with respect to the core17, the bottom-surface electrode portions9each have a relatively low adhesive strength with respect to the component body2. As the metal powder included in the bottom-surface electrode portions9, for example, powder of a conductive metal, such as silver or copper, can be used. As the resin included in the bottom-surface electrode portions9, a curing resin, such as a thermosetting resin or an ultraviolet-ray-curing resin may be used, or a thermoplastic resin may be used.

The embodiments related to the end-surface electrode portions10include a first embodiment in which the end-surface electrode portions10are formed of sputtered films. Each of the end-surface electrode portions10, which are formed of sputtered films, can obtain a relatively high adhesive strength with respect to the core17. The sputtered films are formed by, for example, sputtering using a conductive metal, such as silver or copper, as a target.

The embodiments related to the end-surface electrode portions10include a second embodiment in which the end-surface electrode portions10are conductors containing glass coupled to the core17. In this case, the glass functions as an adhesive with respect to the core17, and each of the end-surface electrode portions10can have a relatively high adhesive strength with respect to the core17. The above-mentioned conductors forming the end-surface electrode portions10each contain, for example, silver or copper as an electrically conductive component.

Note that the above-described laser plating method, which is used for forming the above-mentioned bottom-surface electrode portions9or the above-mentioned end-surface electrode portions10, the glass-free resin electrodes, the glass electrodes, and the sputtered electrodes are not limited to being used in the above exemplary combination and may be freely combined with one another. Any combination can be employed as long as the adhesive strength of each of the bottom-surface electrode portions9with respect to the component body2is lower than the adhesive strength of each of the end-surface electrode portions10with respect to the component body2.

Although the order in which the process of forming the bottom-surface electrode portions9and the process of forming the end-surface electrode portions10are performed is not particularly limited, it is preferable that one of the processes that requires a higher temperature be performed before the other of the processes that can be performed at a lower temperature is performed in order to make the electrode portions formed through the process that is performed first less likely to be influenced by the subsequent process.

In the present embodiment, each of the first and second outer electrodes3and4further includes an outer-layer plated film19that coats a corresponding one of the bottom-surface electrode portions9and a corresponding one of the end-surface electrode portions10in a continuous manner. With this configuration, for example, even when the bottom-surface electrode portions9each having a relatively low adhesive strength separate from the bottom surface5of the component body2as illustrated inFIG. 3, the bottom-surface electrode portions9can be maintained in a state of being held by the end-surface electrode portions10each having a relatively high adhesive strength via the outer-layer plated films19. Thus, for example, even when the bottom-surface electrode portions9completely separate from the bottom surface5of the component body2, the bottom-surface electrode portions9will not fall off from the component body2. In addition, as illustrated inFIG. 3, in the case where the coil component1is mounted on a mounting substrate20, the probability that the component body2will be displaced with the end-surface electrode portions10on the mounting substrate20can be reduced, and the probability that the electrical connection state between the coil component1and the mounting substrate20will be less than ideal can be suppressed.

It is preferable that the thickness of each of the outer-layer plated films19be about 10 μm or more. When the thickness of each of the outer-layer plated films19is about 10 μm or more, each of the outer-layer plated films19can obtain a mechanical strength equal to or higher than a predetermined degree. As a result, the outer-layer plated films19can more reliably exhibit its function of causing the bottom-surface electrode portions9separated from the component body2to be held by the end-surface electrode portions10via the outer-layer plated films19.

As illustrated inFIGS. 2A to 2C, as each of the outer-layer plated films19, a plurality of plated layers are preferably formed, the plurality of plated layers including a nickel plated layer19a, a copper plated layer19bformed on the nickel plated layer19a, and a tin plated layer19cformed on the copper plated layer19b. In this case, as an example, the thickness of the nickel plated layer19ais set to about 3 μm. The thickness of the copper plated layer19bis set to about 30 μm or more and about 50 μm or less (i.e., from about 30 μm to about 50 μm). The thickness of the tin plated layer19cis set to about 10 μm.

Note that, in each of the outer-layer plated films19, there will be no problem as long as the tin plated layer19cis the outermost layer, and thus, a lamination order of Cu/Ni/Sn may be employed instead of the above-mentioned lamination order of Ni/Cu/Sn. In addition, the copper plated layer19bhas a function of improving the adhesion of plating, and thus, for example, the copper plated layer19bmay be divided into two layers and formed so as to have a thickness larger than the above-mentioned thickness.

The situation in which the adhesive strength of each of the bottom-surface electrode portions9is lower than the adhesive strength of each of the end-surface electrode portions10, which is the feature of the present disclosure, can be confirmed by, for example, conducting the following heat cycle test.

A sample is prepared by mounting a coil component that includes outer electrodes, each of which is formed in a recommended component shape by performing a method of forming bottom-surface electrode portions and a method of forming end-surface electrode portions, onto a substrate made of flame retardant type 4 (FR-4) with a solder paste portion having a recommended component thickness. Then, a combination of storing the sample at −40° C. for 30 minutes and storing the sample at +105° C. for 30 minutes is set as one cycle, and a heat cycle test in which this cycle is repeated several times is conducted. This heat cycle test is conducted until it is observed that at least one of the bottom-surface electrode portions and the end-surface electrode portions have separated from the coil component, and it can be evaluated that one of the bottom-surface electrode portions and the end-surface electrode portions that have separated from the coil component first each have a lower adhesive strength.

As described above, the adhesive strength of each of the bottom-surface electrode portions9with respect to the component body2may be about zero. In other words, the bottom-surface electrode portions9may be in a state of being separated from the bottom surface5of the component body2. This state may occur after the coil component1has been mounted on the mounting substrate20as illustrated inFIG. 3.

That is to say, in a state where the outer electrodes3and4of the coil component1are connected to conductors of the mounting substrate20with solder portions21and22, when stress is generated in the mounting substrate20in the directions of arrows23and24as a result of, for example, temperature changes or deflection occurred in the mounting substrate20, at least a portion of one of the bottom-surface electrode portions9is brought into a state of being separated from the bottom surface5of the component body2before cracks are generated in the solder portions21and22or before a fracture occurs in the component body2. As a result, cracks are prevented from being generated in the solder portions21and22, and a fracture is prevented from occurring in the component body2.

FIG. 3illustrates gaps25each of which is generated between one of the bottom-surface electrode portions9and the bottom surface5. It should be understood that the gaps25are exaggeratedly illustrated in order to clearly illustrate the state in which the bottom-surface electrode portions9have separated from the bottom surface5. Thus, in practice, such a situation in which the gaps25clearly appear rarely occurs, and on the contrary, the bottom-surface electrode portions9are often in contact with the bottom surface5even after the bottom-surface electrode portions9have separated from the bottom surface5.

The present disclosure is also directed to a mounting structure of the coil component1such as that described above. Note that, in the description of the mounting structure of the coil component1according to the present disclosure, it is stated that at least a portion of one of the bottom-surface electrode portions9separates from the bottom surface5of the component body2instead of simply stating that the bottom-surface electrode portions9separate from the bottom surface5of the component body2in order to include not only a case where both a portion of the bottom-surface electrode portion9of the first outer electrodes3and a portion of the bottom-surface electrode portion9of the second outer electrode4separate from the bottom surface5but also a case where a portion of only one of the bottom-surface electrode portions9of the first and second outer electrodes3and4separates from the bottom surface5.

FIG. 4is a photograph of a cross section obtained by grinding an outer electrode and a component body of a working product in order to confirm a state in which at least a portion of a bottom-surface electrode portion of the outer electrode has separated from the bottom surface of the component body in the working product.FIG. 4illustrates a portion in the vicinity of the flange-portion bottom surface5bof the second flange portion16that is illustrated at the lower right ofFIG. 3and, as a principal portion of the outer electrode4, the bottom-surface electrode portion9that is disposed so as to cover the bottom surface5b.

InFIG. 4, the gap25formed between the bottom-surface electrode portion9and the bottom surface5appears as a somewhat thick black line, and the presence of the gap25can be confirmed.

Although the coil component according to the present disclosure has been described above on the basis of the embodiments related to the wire-wound coil component1including, as the component body2, the core17that includes the winding core portion14, the first flange portion15, which is formed at the first end of the winding core portion14, and the second flange portion16, which is formed at the second end of the winding core portion14that is opposite to the first end of the winding core portion14, and the wire18that is wound around the winding core portion14, the embodiments are examples, and various other modifications can be made.

For example, the present disclosure can also be applied to a coil component that has a multilayer structure and whose component body is formed of a multilayer body including a plurality of insulator layers that are laminated together and a coil conductor that is disposed along the interface between the insulator layers in the multilayer body.

In addition, in the case of a wire-wound coil component, the number of wires included in the coil component, a wire winding direction, the number of outer electrodes, and so forth may be changed in accordance with a function of the coil component. In the case where a coil component includes a plurality of outer electrodes, the coil component may include an outer electrode that does not have the characteristic configuration according to the present disclosure as long as at least one of the outer electrodes included in the coil component has the characteristic configuration according to the present disclosure.