Patent Application
20160372255
This application claims benefit of priority to Japanese Patent Application 2015-120751 filed Jun. 16, 2015, and to Japanese Patent Application No. 2016-022323 filed Feb. 9, 2016, the entire content of which is incorporated herein by reference.
The present disclosure relates to a method for manufacturing a ceramic electronic component, and a ceramic electronic component, and particularly relates to formation of an electrode of a ceramic electronic component.
In the related art, it is common as a method for forming external electrodes of a ceramic electronic component to apply an electrode paste to both end surfaces of a sintered ceramic body, bake the paste to form base electrodes, and then form upper layer electrodes on the base electrodes by plating. However, this method has a problem of complicating the manufacturing steps and causing the cost increase, because the step of applying a paste and the heating step associated with the baking are necessary for the formation of the base electrodes.
Further, the method has a problem of an applied shape limited in applying a conductive paste in the formation of the base electrodes. For example, in the case of forming a conductive paste by a dip method at both ends of a ceramic body having a rectangular parallelepiped shape, the conductive paste is applied to not only both of the end surfaces of the ceramic body, but also four side surfaces adjacent to both of the end surfaces so as to wrap around the side surfaces. Therefore, finally formed external electrodes have shapes extending to both of the end surfaces and the four side surfaces adjacent to the end surfaces.
In place of such a method for forming electrodes in the related art, there is proposed a method for forming external electrodes just by plating (Japanese Patent Application Laid-Open No. 2004-40084). According to this method, a plurality of ends of internal electrodes is exposed on an end surface of a ceramic body with the ends in proximity to each other, dummy terminals referred to as anchor tabs are exposed in proximity on the same end surface as the ends of the internal electrodes, and the ceramic body is subjected to electroless plating to cause plated metals to grow with the ends of the internal electrodes and the anchor tabs as nuclei, thereby forming external electrodes.
However, according to this method, the ends of the plurality of internal electrodes and the anchor tabs have to be exposed in proximity in an external electrode formation part of the ceramic body, thus resulting in a disadvantage of complicating the manufacturing steps and of causing the cost increase. In addition, the surface on which the plated metals are formed is limited to the surface on which the ends of the internal electrodes and the anchor tabs are exposed, and thus it is not possible to form an external electrode on any part.
On the other hand, Japanese Patent Application Laid-Open Nos. 2000-223342, 2000-243629, and 11-176685 each disclose forming an electrode over the entire surface of ferrite constituting an inductor, and then burning off the electrode through laser irradiation, thereby forming a coil pattern. In that regard, these documents disclose the fact that heat of the laser spreads to not only the electrode but also the ferrite thereunder, thereby changing some of the ferrite properties to a conducting property or a lower resistance (see paragraph 0005 in Japanese Patent Application Laid-Open No. 2000-223342, paragraph 0004 in Japanese Patent Application Laid-Open No. 2000-243629, and paragraph 0005 in Japanese Patent Application Laid-5 No. 11-176685). However, these documents disclose only burning off the electrode through the laser irradiation, and in addition, describe the fact that the heat of the laser adversely affects characteristics as an inductor.
Therefore, an object of the present disclosure is to propose a manufacturing method that is capable of forming an electrode on any part of a surface of a sintered ceramic body in accordance with a simple approach, and a ceramic electronic component manufactured by the method.
In order to achieve the object described above, the present disclosure provides a method for manufacturing a ceramic electronic component, which includes the following steps of:
The present disclosure has focused on the locally heating of an electrode formation region on a surface of a sintered ceramic body, thereby lowering resistance of the heated part or making the heated part conducting, and subjecting the ceramic body to plating, thereby making it possible to use the low-resistance portion as a deposition starting point of a plated metal. The low-resistance portion (or conductor part) refers to a part where a metal oxide constituting a ceramic body is modified due to local heating, and a resistance value is lower than a resistance value of the metal oxide. When the locally heated ceramic body is subjected to plating, the plated metal is first deposited on the low-resistance portion, and the plated metal with the deposited plated metal as a nucleus rapidly grows, and thereby an electrode covering the entire electrode formation region can be formed efficiently. Therefore, the step of forming an electrode is simplified without need for any complicated step such as applying and baking a conductive paste in the related art. Further, since there is no need to expose a plurality of internal electrodes or anchor tabs in proximity on end surfaces of a ceramic body as in Japanese Patent Application Laid-Open No. 2004-40084, the electrode shape is not limited, and in addition, the manufacturing steps are simplified, and it is possible to reduce the cost.
The low-resistance portion may include a reduced layer obtained by partially reducing the metal oxide contained in the ceramic body. The metal oxide is partially reduced to make the metal oxide conducting or semiconducting, and the plated metal becomes more likely to be deposited. Further, a configuration may be adapted such that a surface layer of the reduced layer is partially or entirely covered with a reoxidized layer. In the case where the reoxidized layer is formed, there is an effect of enabling suppression of oxidation of the reduced layer present in the lower layer, and suppression of change of the reoxidized layer itself with time. Moreover, since the reoxidized layer is a type of semiconductor, and has a resistance value lower than a resistance value of the metal oxide as an insulator, the plated metal is likely to be deposited on the reoxidized layer. It is to be noted that since the reoxidized layer is formed, for example, in the form of a thin film on the order of nm, there is also a possibility that media balls used in electrolytic plating collide against the reoxidized layer, thereby partially peeling the reoxidized layer, or a plating solution cause erosion into the reoxidized layer, thereby resulting in plating attached onto the reduced layer present under the reoxidized layer.
The electrode according to the present disclosure is not limited to an external electrode as long as the electrode is formed on the surface of the ceramic body, but may be any electrode. For example, the electrode may be a coil-shaped electrode or a wiring electrode. As a method for the local heating, there are various methods such as, for example, laser irradiation, electron beam irradiation, or local heating with the use of an image furnace. Among them, the laser irradiation is advantageous in that a position of irradiating the ceramic body with the laser can be changed quickly.
According to the present disclosure, since the electrode formation region is just locally heated and subjected to plating, the electrode can be formed on any part. For example, a method in the related art using a conductive paste has difficulty in forming deformed electrodes, that is, external electrodes (L-shaped form as viewed from a side surface) on both end surfaces and one side surface adjacent to the end surfaces, or forming a plurality of external electrodes at an interval on one side surface, but according to the present disclosure, even such external electrodes in any shape can be formed easily. The local heating only needs to be applied to a surface layer part of the ceramic body, and thus has substantially no influence on characteristics as a ceramic electronic component (for example, inductor).
As a method for the plating, both electrolytic plating and electroless plating are possible, but an electrolytic plating method is preferred. That is, an object to be plated needs to be conductive in the electrolytic plating method. Since the low-resistance portion formed by the method according to the present disclosure has conductivity, the density of current flowing through the low-resistance portion during electrolytic plating becomes higher than that in the other part, and the plated metal is deposited rapidly on the low-resistance portion. In a plating method in the related art, in the case of wishing to leave a part of the ceramic body without being plated, it has been necessary to coat the part in advance with an anti-plating material. According to the present disclosure, a plated electrode extends rapidly over the electrode formation region with the low-resistance portion as a nucleus, while a growth rate of a plated electrode is low because a part other than the electrode formation region has an insulating property without any conductive part as a nucleus. Therefore, the plated metal can be grown selectively in the electrode formation region, without coating with the anti-plating material. Further, since the plated metal formed by electrolytic plating on the low-resistance portion is larger in thickness than that in another part, fixing strength of the plated electrode to the ceramic body advantageously increases.
The present disclosure can also be applied to electronic components including internal electrodes. For example, for a ceramic body having a rectangular parallelepiped shape, a low-resistance portion may be formed by laser irradiation or the like on a surface on which ends of internal electrodes are exposed, and an external electrode may be formed by plating so as to cover the ends of the internal electrodes. The electrode can be formed on any surface as long as the surface can be subjected to local heating such as laser processing. For example, it is also possible to form no electrode on either of width-direction side surfaces. As for an electronic component that has no external electrode formed on either of width-direction side surfaces, when this electronic component is mounted at a high density, the insulating distance to an electronic component adjacent in the width direction can be ensured, and it is possible to reduce the risk of short circuits. Therefore, further high-density mounting becomes possible. Further, when an external electrode is formed only on a lower surface (a bottom surface) of a ceramic body, it is possible to further reduce the risk of causing short circuits between the electrode and surrounding electronic components because of mounting only on the bottom surface.
The present disclosure can also be applied to, for example, wound coil components. That is, a configuration may be adopted such that the ceramic body is a ferrite core including flanges at both ends, and a winding core therebetween, the winding core of the ferrite core has a coil-shaped low-resistance portion formed by laser processing or the like, the flanges of the core have external electrode-shaped low-resistance portions formed by laser processing or the like, the coil-shaped low-resistance portion is connected to the external electrode-shaped low-resistance portions, and a plated electrode is continuously formed on the coil-shaped low-resistance portion and the external electrode-shaped low-resistance portions. In this case, since it is possible to form both the coil part and the external electrode part by laser processing or the like, the manufacture is further simplified. It is to be noted that the electrode on the coil part can be thicker than the external electrodes by a method such as adjusting laser intensity.
Further, a configuration may be adopted such that the ceramic body is a ferrite core including flanges at both ends, and a winding core therebetween, a wire is wound around a peripheral surface of the winding core, the low-resistance portion is formed on each of surfaces of the flanges, electrodes including a plated metal are formed on each of the low-resistance portions of the flanges, and the electrodes are connected to both ends of the wire. In this case, since the wound part is formed with the metal wire, a high magnetic efficiency is high, and since the external electrodes can be thin-wall electrodes according to the present disclosure, inductors with high Q values can be realized with a small eddy current loss.
When a laser is used as the method for the local heating, energy of the laser is concentrated in a narrow region, and thus the ceramic body is partially melted and solidified to form linear or dotted laser irradiation marks on the surface of the ceramic body, and low-resistance portions are formed around the marks. The depths and areas of the laser irradiation marks and low-resistance portions can be adjusted by the laser irradiation energy (wavelength, output, and the like). Since the plated metals deposited on the low-resistance portions are fixed along inner walls of the depressed laser irradiation marks, an anchor effect thereof can enhance the fixing strength of the plated metals (electrodes) to the ceramic body.
The electrode formation region may be densely irradiated with the laser such that low-resistance portions are present almost without any gap. In this case, since the low-resistance portions are also continuously formed, the plated metals are deposited and grown rapidly, and it is possible to reduce plating time. It is to be noted that the term “densely irradiating” refers to the fact that an interval between spot centers of laser irradiation is equal to or smaller than the area width of a low-resistance portion. That is, the term refers to D≦W when the interval between spot centers of laser irradiation is denoted by D, and the diameter of a spot (the area width of the low-resistance portion) is denoted by W.
When the electrode formation region is densely irradiated with the laser as described above, a large number of shots is required, which takes processing time. Therefore, the electrode formation region may be dispersedly irradiated with the laser at a predetermined distance, thereby dispersedly forming more than one low-resistance portion in the electrode formation region, and the plated metals deposited on the low-resistance portions are grown with the metals as nuclei, and the plating may be continued until the plated metals are connected to each other. Here, the term “dispersedly irradiating” refers to the fact that the interval between spot centers of laser irradiation is larger than the area width of a low-resistance portion. That is, the term refers to D>W when the interval between spot centers of laser irradiation is denoted by D, and the diameter of a spot (the area width of the low-resistance portion) is denoted by W. An advantage of the plating is that once the plated metal is deposited on a part, the plated metal rapidly grows around with the part as a nucleus. With the utilization of the advantage, a homogeneous electrode can be formed over the entire electrode formation region, because after the deposition of plated metals on the plurality of dispersed low-resistance portions, the plated metals grow over a region other than the low-resistance portions with the metals as nuclei. Therefore, high-quality electrodes can be formed without dense laser irradiation, and the laser processing time can be shortened.
An example of typical ceramic materials that can be lowered in resistance or made conducting by laser irradiation includes ferrite. Ferrite is ceramics containing an iron oxide as its main component, and examples thereof include spinel ferrite, hexagonal ferrite, and garnet ferrite. Irradiating the ferrite with a laser increases temperature of the irradiated part, and a surface layer part of the insulating ferrite is modified to be conductive. Examples of ferrite for use in inductors include Ni—Zn based ferrite and Ni—Cu—Zn based ferrite. In the case of the Ni—Zn based ferrite, some of Fe contained in the ferrite is believed to be reduced by the laser irradiation, and there is further a possibility that Ni and/or Zn be also reduced. In the case of the Ni—Cu—Zn based ferrite, Fe and/or Cu contained in the ferrite are believed to be reduced, and there is further a possibility that Ni and/or Zn be also reduced.
As described above, according to the present disclosure, the electrode formation region of the sintered ceramic body is locally heated to form the low-resistance portion, the ceramic body is subjected to plating to deposit the plated metal on the low-resistance portion, and the plated electrode is grown over the electrode formation region. Thus, electrodes can be formed by a simple method. Moreover, since the electrode can be formed on any part as long as the part is a region that can be locally heated, electrodes in any shape can be formed simply.
The ceramic body 10 is obtained by, as shown in
The external electrodes 30, 31 are, as shown in
An experimental example where an external electrode was actually formed will be described below.
As a result of carrying out the plating under the conditions as described above, a favorable Cu external electrode of 20 μm in average thickness was successfully formed on a surface of the ceramic body. It is to be noted that a similar result was obtained even in the case of using Ni—Zn based ferrite. Moreover, a copper sulfate plating solution, a copper cyanide plating solution, and the like can be use as the plating solution, besides the copper pyrophosphate plating solution.
—Evaluation—
A sample obtained by irradiating Ni—Cu—Zn based ferrite with the laser and a sample obtained without irradiating Ni—Cu—Zn based ferrite with laser were each evaluated for valences of Fe, Cu, and Zn on a sample surface by XPS (X-ray photoelectron spectroscopy) and K-edge XAFS (X-ray absorption fine structure) for Fe, Cu, and Zn using conversion electron yield. As a result of the XPS, no metal component was able to be detected on a surface layer part of the sample subjected to the laser irradiation, and the metal components were able to be detected on the lower layer thereof. Moreover, as a result of the XAFS, the metal component of Cu was able to be detected on the surface layer part of the sample subjected to the laser irradiation. On the other hand, as a result of the XAFS, the metal component of Fe was not able to be detected on the surface layer part of the sample subjected to the laser irradiation, but a semiconductor component of Fe and an insulator component thereof were able to be detected thereon. It was also found that a ratio of Fe2+ to Fe3+ in the lower layer was higher than a ratio in the whole ceramic body. From the foregoing, it is presumed that heat generated by the laser processing decomposed metal oxides contained in the ferrite to reduce metal elements of the ferrite in the lower layer of the ceramic body, and the remaining heat led to reoxidation of the surface layer part of the ceramic body.
When the reoxidized layer described above is formed, the following effects are conceivable. That is, Fe3O4 formed as the reoxidized layer has a property of being less likely to be reoxidized at normal temperature, and also has an effect of enabling suppression of oxidation of the reduced layer present in the lower layer, and suppression of change of the reoxidized layer itself with time. Moreover, the reoxidized layer is a type of semiconductor, and has a resistance value lower than a resistance value of ferrite as an insulator. Therefore, plated metals are likely to be deposited on the reoxidized layer.
In the present embodiment, the external electrodes 30, 31 are each formed in an L-shaped form as viewed from the side surface (when the ceramic body 10 is viewed from the Y direction). That is, the external electrodes 30, 31 are formed only on both end surfaces and a bottom surface (in mounting) of the inductor 1, and formed neither on an upper surface (in mounting) nor on either of side surfaces in the Y direction. Therefore, as shown in
In this case, as shown in
As shown in
According to this example, the coil-shaped low-resistance portion and the low-resistance portions for external electrodes can be formed continuously by laser processing. For example, a method of fixing a laser position and rotating and moving the core 50 in an axial direction can be used as the laser processing. Since the coil electrode 56 and the external electrodes 54, 55 can be formed simultaneously by the plating, the steps of manufacturing the inductor can be made more efficient, and it is possible to reduce the manufacturing cost. It is to be noted that a multilayer structure can be provided by subjecting the coil electrode 56 and the external electrodes 54, 55 to the plating a plurality of times. It is to be noted that the coil electrode 56 and the external electrodes 54, 55 are formed by the plating in this example, but in a wound inductor (ferrite core) with wire wound around a winding core, only external electrodes connected to the wire can also be formed by the plating.
As described above, when the coil electrode 56 and the external electrodes 54, 55 are formed by laser processing and plating, there is a possibility that the electrodes 56, 54, 55 substantially have an almost constant thickness. In particular, in the case of wishing to increase a generated magnetic flux of the coil electrode 56, it is desirable to make the thickness of the coil electrode 56 larger than the thicknesses of the external electrodes 54, 55. In such a case, for example, laser intensity of a laser with which the winding core 53 is irradiated may be made higher than laser intensity of a laser with which the external electrode regions are irradiated, or irradiation methods (for example, intermittent irradiation and continuous irradiation, scaling of irradiation range) for the laser with which the winding core 53 is irradiated and for the laser with which the external electrode regions are irradiated may be changed. The increased laser intensity makes a resistance value of the coil-shaped low-resistance portion lower than a resistance value of each of the low-resistance portions of the external electrode formation regions, or makes the depth of the coil-shaped low-resistance portion larger than the depth of each of the low-resistance portions of the external electrode formation regions. Thus, the thickness of the electrode 56 formed by plating on the coil-shaped low-resistance portion can be made larger than the thicknesses of the electrodes 54, 55 formed on the low-resistance portions of the external electrode formation regions.
In this example, since the external electrodes 54, 55 can be formed in a thin-fall fashion as compared with the wire 57, there is an effect of suppressing an eddy current loss. That is, interlinkage of magnetic fluxes (indicated by dashed arrows in
While the examples of applying the present disclosure to the formation of the external electrodes of the stacked inductor and the electrodes of the wound inductor (ferrite cores) have been provided, the present disclosure is not limited to these examples. The ceramic electronic components to which the present disclosure is directed are not limited to inductors, and the present disclosure is applicable to electronic components including a ceramic body that is modified by laser irradiation to form a low-resistance portion as deposition starting points for plated electrodes. That is, the material of the ceramic body is not limited to ferrite. Further, the structure of the electronic component is not limited to a structure including internal electrodes or a structure having a plurality of insulating layers stacked. While the examples of using electrolytic plating as a plating method have been provided, electroless plating may be used.
While the laser irradiation is used as a local heating method in the example described above, electron beam irradiation, heating with use of an image furnace, and the like are also applicable. In each case, since heat source energy can be focused to locally heat an external electrode formation region of a ceramic body, an electrical property in other regions are not impaired.
In the present disclosure, one laser may be divided, and a plurality of sites may be irradiated simultaneously with the laser.
Further, in the present disclosure, a focus of a laser may be shifted to widen the irradiation range of the laser, as compared with a case of a focused laser.
The present disclosure is not limited to the case of growing a lowermost layer of plated metal so as to extend over the entire electrode formation regions when a plurality of layers of plated metal is formed. The lowermost layer of plated metal may be grown so as to extend partially over electron formation regions, and an upper layer of plated metal may be grown so as to extend over the entire electrode formation regions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-120751 | Jun 2015 | JP | national |
| 2016-022323 | Feb 2016 | JP | national |
