Patent Application
20150028992
There is a conventionally known chip thermistor in which external electrodes are formed at both ends of a thermistor element body containing, for example, metal oxides of Mn, Co, and Ni as major ingredients (see, for example Patent Literature 1). In the chip thermistor of this kind, the overall resistance of the chip thermistor is determined by the specific resistance of the thermistor element body and the distance between the external electrodes formed at the both ends thereof,
The present invention relates to a chip thermistor and a method for manufacturing it.
There is a conventionally known chip thermistor in which external electrodes are formed at both ends of a thermistor element body containing, for example, metal oxides of Mn, Co, and Ni as major ingredients (see, for example Patent Literature 1). In the chip thermistor of this kind, the overall resistance of the chip thermistor is determined by the specific resistance of the thermistor element body and the distance between the external electrodes formed at the both ends thereof.
Incidentally, in the chip thermistor of this configuration, the overall resistance of the chip thermistor varies depending upon a plurality of factors such as the specific resistance of the thermistor element body, the distance between the external electrodes, and the shape thereof, and, therefore, consideration must be given to the plurality of factors, for achieving a desired value of resistance of the chip thermistor; it was thus sometimes difficult to adjust the resistance of the chip thermistor to a desired value. Particularly, in the case where the chip thermistor had an extremely small size like the 0402 type (0.4 mm long×0.2 mm high×0.2 mm wide), there was the problem that it became difficult to control the distance between the external electrodes or the like to a desired value and it was further difficult to adjust the resistance of the chip thermistor to a desired value.
It is an object of the present invention to provide a chip thermistor allowing easy adjustment of resistance and a method for manufacturing it.
To resolve the above problem, a chip thermistor according to the present invention comprises: a thermistor portion comprised of a ceramic material containing a metal oxide as a major ingredient; a pair of composite portions comprised of a composite material including a metal and a metal oxide and arranged on both sides of the thermistor portion so as to sandwich in the thermistor portion between the composite portions; and external electrodes arranged at both ends in a longitudinal direction of an substantially rectangular parallelepiped shaped element body which includes the thermistor portion and the pair of composite portions, the external electrodes are connected to the pair of composite portions respectively.
The chip thermistor according to the present invention is configured that the pair of composite portions are arranged on both sides of the thermistor portion so as to sandwich in the thermistor portion between them and that the external electrodes are connected to the pair of composite portions. For this reason, the resistance of the chip thermistor can be adjusted mainly with consideration to the resistance in the thermistor portion, without need for much consideration to, for example, the distance between the external electrodes, the shape thereof, and so on. Therefore, this chip thermistor allows easy adjustment of the resistance. The chip thermistor is configured that the composite portions sandwich in the thermistor portion between them in the longitudinal direction of the substantially rectangular parallelepiped shaped element body. For this reason, a design range of the thickness of the thermistor portion is relatively widened, thereby the chip thermistor allows easy adjustment of the resistance in this point.
The chip thermistor according to the present invention is configured that the pair of composite portions sandwich in the thermistor portion between them and that the external electrodes are connected to the pair of composite portions (e.g., cf.
In the chip thermistor according to the present invention, the composite portions are arranged between the thermistor portion and the external electrodes and the composite portions are comprised of the composite material of the metal and the metal oxide. For this reason, heat in the chip thermistor can be readily dissipated through the composite portions, whereby the chip thermistor can be obtained with excellent heat dissipation. Particularly, the thermistor originally has a property of varying its resistance with heat, and thus the excellent heat dissipation leads to improvement in thermal responsiveness, so as to allow more accurate detection. Since the chip thermistor has the excellent heat dissipation, it is also feasible to increase the rated power of the chip thermistor and thus to apply the chip thermistor to usage in various fields.
In the chip thermistor according to the present invention, each of the external electrodes may be configured to cover respective end faces in the longitudinal direction of the element body. In this case, connection strength between the external electrodes and the composite portions which constitute a part of the element body is made firm.
In the chip thermistor according to the present invention, each of the external electrodes may be configured to oppose to each other on at least one side face which extends along the longitudinal direction of the element body. In this case, connection strength between the external electrodes and the composite portions which constitute a part of the element body is made further firm. Since the external electrodes are formed on the side face of the element body, it is feasible to easily mount the chip thermistor on a surface of a substrate or the like
In the chip thermistor according to the present invention, the thermistor portion may be configured in a layered structure such that a direction in which the pair of composite portions are opposed to each other is a laminated direction. In this case, the thickness of the thermistor portion (thickness in the direction in which the composite portions are opposed to each other) can be adjusted by the number of laminated thermistor layers. This allows easy adjustment of the resistance of the chip thermistor which bears a proportional relation to the thickness of the thermistor portion. Since the resistance of the chip thermistor is adjusted by the number of laminated thermistor layers, it is feasible to readily suppress variation in resistance in each chip thermistor and, particularly, in the case of the chip thermistor of an extremely small size, the variation can be drastically suppressed. Namely, this configuration allows the chip thermistor to be readily obtained in an extremely small size and with high detection accuracy.
In the chip thermistor according to the present invention, each of the pair of composite portions may be configured in a layered structure such that a direction in which the pair of composite portions are opposed to each other is a laminated direction. In this case, the length of each composite portion (length in the direction in which the composite portions are opposed to each other) can be readily adjusted by the number of laminated composite layers. If both of the thermistor portion and the composite portions are configured in the layered structure, the overall length of the chip thermistor or the like can be readily adjusted and, even in the case of the chip thermistor of an extremely small size, the chip thermistor can be readily obtained with high dimensional accuracy.
In the chip thermistor according to the present invention, the thermistor portion may be substantially totally connected to the pair of composite portions, on both sides thereof. In this case, secure coupling is made between the thermistor portion and the composite portions.
In the chip thermistor according to the present invention, the thermistor portion may be composed of a thermistor element having a negative characteristic, and a thickness of the thermistor portion in the direction in which the pair of composite portions are opposed to each other may be any length in the range of 0.01 times to 0.8 times a longitudinal length of the element body. In this case, the resistance of the chip thermistor as an NTC (Negative Temperature Coefficient) thermistor can be set rather smaller. Particularly, in terms of reduction in resistance, the thickness of the thermistor portion is preferably not more than 0.1 times the longitudinal length of the element body.
In the chip thermistor according to the present invention, the composite material may be a material in which the metal is dispersed in the metal oxide or in which the metal oxide is dispersed in the metal. Furthermore, in each of the pair of composite portions, the metal in the composite material may form an electrical conduction path between the external electrode and the thermistor portion.
In the chip thermistor according to the present invention, an insulating layer may be formed at least over a region across the thermistor portion out of an exterior surface of the element body. In this case, it is feasible to more eliminate the influence of the distance between the external electrodes and other factors on the resistance of the chip thermistor. When the insulating layer is formed on the exterior surface of the element body, the external electrodes may be formed by electroplating.
In the chip thermistor according to the present invention, the external electrodes may be formed by directly plating the composite portions which constitutes a part of the element body. In the case, processes such as printing and burning one electrode layer that forms part of the external electrodes become unnecessary, and the thermal influence of burning on the chip thermistor can be reduced. Furthermore, since one electrode layer that forms part of the external electrodes is no longer required, a further reduction in the size of the chip thermistor becomes possible. Also, the plating is coated along the shape of the element, and thus the flatness of the exterior of the chip thermistor can be enhanced, thereby preventing the chip thermistor from tumbling in a housing for a series of electronic components, and making it possible to reduce faults in installing the chip thermistor onto a substrate or the like.
In the chip thermistor according to the present invention, the external electrodes are configured to cover substantially all of outer surfaces of the composite portions which constitute a part of the element body. In this case, since the thicknesses of the composite portions directly correspond to the widths of the external electrodes, variations of the width measurements in both external electrodes can be suppressed. As a result of this, it is possible to reduce phenomena such as tombstoning upon installation, which is caused by differences in the melting time of solder due to variations in the width measurements of the external electrodes.
In the chip thermistor according to the present invention, the external electrodes are configured not to cover the thermistor portion which constitutes a part of the element body. In the case, it is feasible to reduce the influence to the resistance if the thickness of the thermistor portion is thin.
To resolve the above problem, a method for manufacturing a chip thermistor according to the present invention, comprises preparing thermistor layers comprised of a ceramic material containing a metal oxide as a major ingredient, preparing composite layers comprised of a composite material including a metal and a metal oxide, laminating the thermistor layers and the composite layers to obtain a multilayer body such that a predetermined number of thermistor layers are sandwiched in between the composite layers, cutting the multilayer body to obtain a plurality of element bodies, and forming external electrodes at both ends of the element bodies in such a manner that a laminated direction of the thermistor layers and the composite layers is a direction in which the external electrodes are opposed to each other.
In the manufacturing method of the chip thermistor according to the present invention, the chip thermistor is manufactured by preparing the thermistor layers comprised of the ceramic material containing the metal oxide as a major ingredient and the composite layers comprised of the composite material including the metal and the metal oxide, laminating the thermistor layers and the composite layers so as to sandwich in the predetermined number of thermistor layers between the composite layers, and so on. In this case, the resistance of the chip thermistor manufactured can be adjusted mainly with consideration to the number of laminated thermistor layers, without need for much consideration to, for example, the distance between the external electrodes and other factors. Therefore, this manufacturing method of the chip thermistor allows the chip thermistor to be manufactured with easy adjustment of the resistance of the chip thermistor.
Since the manufacturing method of the chip thermistor according to the present invention allows the adjustment of the resistance of the chip thermistor by the number of laminated thermistor layers, the chip thermistor can be manufactured with suppression of variation in resistance, and, particularly, in the case of the chip thermistor of an extremely small size, it can be manufactured with suppression of variation. Since the chip thermistor is manufactured by laminating the thermistor layers and the composite layers, the overall length of the chip thermistor or the like can also be readily adjusted and, even in manufacturing the chip thermistor in an extremely small size, the chip thermistor can be readily manufactured with high dimensional accuracy.
According to the present invention, it is feasible to provide the chip thermistor allowing easy adjustment of the resistance and the method for manufacturing it.
Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the description, the same elements or elements with the same functionality will be denoted by the same reference signs, without redundant description.
A chip thermistor 1 is an NTC thermistor and, as shown in
The element body 3 is configured to include a thermistor portion 7 and a pair of composite portions 9. The element body 3 has square end faces 3a, 3b opposed to each other, and four side faces 3c to 3f perpendicular to the end faces 3a, 3b as outer surfaces. The four side faces 3c to 3f extend so as to interconnect the end faces 3a, 3b. The end faces 3a, 3b may form rectangular shape.
The thermistor portion 7, as shown in
The thermistor layers 7a constituting the thermistor portion 7 are made, for example, of a ceramic material containing respective metal oxides of Mn, Ni, and Co as major ingredients. The thermistor layers 7a may contain minor ingredients of Fe, Cu, Al, Zr, etc. to adjust characteristics, in addition to the respective metal oxides of Mn, Ni, and Co as major ingredients. The thermistor portion 7 may be made of respective metal oxides of Mn and Ni or respective metal oxides of Mn and Co, instead of the respective metal oxides of Mn, Ni, and Co.
The composite portions 9, as shown in
In the composite material making up the composite portions 9, Ag—Pd is in a state in which Ag—Pd is dispersed in the aforementioned metal oxides and, as shown in
As shown in
The pair of external electrodes 5, 5 are formed in a multilayer structure so as to cover the respective end faces 3a, 3b of the element body 3. The external electrode 5 includes: a first electrode layer 5a directly connected to the composite portion 9 of the element body 3 and containing an electroconductive powder containing Ag or the like as a major ingredient, and a glass frit; a second electrode layer 5b formed so as to cover the first electrode layer 5a and containing Ni as a major ingredient; and a third electrode layer 5c formed so as to cover the second electrode layer 5b and containing Sn as a major ingredient.
Next, a method for manufacturing the chip thermistor 1 will be described with reference to
First, a well-known method is employed to prepare a thermistor material by mixing respective metal oxides of Mn, Ni, and Co as major ingredients of the thermistor layers 7a, and Fe, Cu, Al, Zr, etc. as minor ingredients at a predetermined ratio. Then an organic binder and other matter are added in this thermistor material to obtain a slurry P1 (step S01). Similarly, a composite material is prepared by mixing Ag—Pd and respective metal oxides of Mn, Ni, and Co to be contained in the composite material making up the composite layers 9a, at a predetermined ratio. Then an organic binder and other matter are added in this composite material to obtain a slurry P2 (step S01).
Next, each of the slurries P1, P2 prepared is applied onto film to form green sheets corresponding to the thermistor layers 7a or green sheets corresponding to the composite layers 9a, respectively (step S02). Thereafter, the respective green sheets corresponding to the thermistor layers 7a and the composite layers 9a are laminated in such a manner that a predetermined number of green sheets corresponding to the thermistor layers 7a are sandwiched in between the green sheets corresponding to the composite layers 9a (cf.
After that, the plurality of green bodies 30 are thermally treated at the temperature of 180° C. to 400° C. for about 0.5 to 24 hours to be subjected to debindering. After the debindering process, the green bodies 30 are heated at the temperature of not less than 800° C. in an air or oxygen ambience to fire the thermistor portion 7 and the composite portions 9 together (step S05). This step results in forming the element bodies 3. It is optional to perform barrel polishing on an as-needed basis, after the firing. Then the insulating layer 11 consisting of SiO2 or the like is formed on the outer surface of each element body by sputtering or the like so as to cover the side faces 3c to 3f of the element body (step S06).
The next step is to prepare an electroconductive paste by mixing an organic binder and an organic solvent into a metal powder containing Ag, Cu, or Ni as a major ingredient, and a glass frit. Then this electroconductive paste is applied by a transfer method so as to cover the both end faces 3a, 3b of each element body 3 and is then baked to form the first electrode layer 5a. Subsequently, electroplating processes such as Ni plating and Sn plating are carried out so as to cover the first electrode layer 5a, thereby forming the second and third electrode layers 5b, 5c. This forms the external electrodes 5 at both ends of the element body 3 so that the laminated direction of the thermistor layers 7a and the composite layers 9a is a direction in which the external electrodes 5 are opposed to each other (step S07), thereby completing the chip thermistor 1.
As described above, the chip thermistor 1 of the present embodiment is configured, as shown in
The chip thermistor 1, having the above-described configuration, can also have the resistance lower than that of the conventional configuration wherein the external electrodes are connected directly to the thermistor element body (cf.
In the chip thermistor 1, the composite portions 9, 9 are arranged between the thermistor portion 7 and the external electrodes 5, 5 and the composite portions 9, 9 are made of the composite material of the metal and metal oxides. For this reason, heat in the chip thermistor 1 can be readily dissipated through the composite portions 9, 9, whereby the chip thermistor 1 can be obtained with excellent heat dissipation. Particularly, the thermistor originally has a property of varying its resistance with heat, and thus the excellent heat dissipation leads to improvement in thermal responsiveness, so as to make the chip thermistor 1 capable of more accurate detection. Since the chip thermistor 1 is provided with the excellent heat dissipation, the rated power of the chip thermistor can also be increased, allowing the chip thermistor to be applied to usage in various fields.
In the chip thermistor 1, the thermistor portion 7 is formed in the layered structure such that the direction in which the pair of composite portions 9, 9 are opposed to each other is the laminated direction. For this reason, the thickness of the thermistor portion 7 (thickness in the direction in which the composite portions 9, 9 are opposed to each other) can be adjusted by the number of laminated thermistor layers 7a, which allows easy adjustment of the resistance of the chip thermistor 1 bearing a proportional relation to the thickness of the thermistor portion 7. Since the resistance of the chip thermistor 1 is adjusted by the number of laminated thermistor layers 7a, it is easy to suppress variation in resistance of the chip thermistor 1 and, particularly, in the case of the chip thermistor 1 of an extremely small size, the variation can be significantly suppressed. In other words, the configuration in the present embodiment allows the chip thermistor 1 to be readily obtained in an extremely small size and with high detection accuracy.
In the chip thermistor 1, each of the pair of composite portions 9, 9 is formed in the layered structure such that the direction in which the pair of composite portions 9, 9 are opposed to each other is the laminated direction. For this reason, the length of each composite portion 9, 9 (length in the direction in which the composite portions 9, 9 are opposed to each other) can be readily adjusted by the number of laminated composite layers. Particularly, since both of the thermistor portion 7 and the composite portions 9, 9 are formed in the layered structure in the chip thermistor 1, it is easy to adjust the overall length of the chip thermistor 1 and even if the chip thermistor has an extremely small size (0402 type) like the chip thermistor 1, the chip thermistor can be readily obtained with high dimensional accuracy.
In the chip thermistor 1, the thermistor portion 7 is substantially totally connected to the pair of composite portions 9, 9, on both sides thereof. Since they are connected across the wide region, secure coupling is achieved between the thermistor portion 7 and the composite portions 9, 9. In addition, since the thermistor portion 7 and the composite portions 9 are configured to contain the metal oxides of the same kinds in the present embodiment, the coupling between them can be made firmer.
In the chip thermistor 1, the element body 3 of the substantially rectangular parallelepiped shape is formed of the thermistor portion 7 and the pair of composite portions 9, 9 and the insulating layer 11 is formed on the side faces 3c to 3f of the element body 3 including the region across the thermistor portion 7. This insulating layer 11 prevents the external electrodes 5 from being connected directly to the thermistor portion 7, so as to more eliminate the influence of the distance between the external electrodes 5, 5 and other factors on the resistance of the chip thermistor 1.
In the chip thermistor 1, the external electrodes 5, 5 are formed to cover respective end faces 3a, 3b in the longitudinal direction of the element body 3. For this reason, connection strength between the external electrodes 5, 5 and the composite portions 9, 9 which constitute a part of the element body 3 is made firm.
In the chip thermistor 1, the external electrodes 5, 5 are formed to oppose to each other on the side faces 3c to 3f which extend along the longitudinal direction of the element body 3. For this reason, connection strength between the external electrodes 5, 5 and the composite portions 9, 9 which constitute a part of the element body 3 is made further firm. Since the external electrodes 5, 5 are formed on the side face 3d (a mounting surface) of the element body 3, it is feasible to easily mount the chip thermistor 1 on a surface of a substrate or the like.
In the chip thermistor 1, the external electrodes 5, 5 are formed not to cover the thermistor portion 7 which constitutes a part of the element body 3. In the case, it is feasible to reduce the influence to the resistance if the thickness of the thermistor portion 7 is thin.
Next, a chip thermistor 21 of the second embodiment will be described. The chip thermistor 21 is an NTC thermistor as well as the first embodiment and, as shown in
The element body 23 is configured to include a thermistor portion 27 and a pair of composite portions 29, as showed in
The thermistor portion 27, as shown in
The composite portions 29, as shown in
The pair of external electrodes 25, 25 are formed so as to cover substantially all of outer surfaces of the composite portions 29, 29, which includes the respective end faces 23a, 23b of the element body 23. The external electrode 25 is formed by directly plating the composite portion 29 which constitutes a part of the element body 23 and includes: a second electrode layer 25b directly formed on the composite portion 29 and containing Ni as a major ingredient; and a third electrode layer 25c formed so as to cover the second electrode layer 25b and containing Sn as a major ingredient. In this embodiment, the external electrode 25 does not include the first electrode layer formed from an electroconductive paste, unlike the first embodiment. Thickness in the longitudinal direction (Y-direction) of the external electrode 25, which is formed so as to approximately cover the entire surface of the composite portion 29, is 100 μm, yielding a thickness of an extent that enables surface installation of the substrate or the like (enables adherence to the substrate land or the like with solder).
The chip thermistor 21 provided with such a configuration can be produced using approximately the same production method as the first embodiment. However, the second embodiment differs from the first embodiment in that, since the insulating layer 11 is not formed, step S06 shown in
As mentioned above, the chip thermistor 21 according to the present embodiment is configured, as shown in
The working effect of the chip thermistor 21 mentioned above will now be described on the basis of a comparative experiment with conventional chip thermistors. The comparative experiment was performed by comparing CV values of the chip thermistor 21, and the CV values of the conventional type of chip thermistor, wherein a resistance value is yielded by a portion comprising a typical capacitor structure and an overlapping pair of internal electrodes (internal electrode layered structure type), in each of four different chip configuration size types.
Chip configurations used in the comparative example:
1) 1608 (length: 1.6 mm; height and width: 0.8 mm)
2) 1005 (length: 1.0 mm; height and width: 0.5 mm)
3) 0603 (length: 0.6 mm; height and width: 0.3 mm)
4) 0402 (length: 0.4 mm; height and width: 0.2 mm)
The CV values used in this comparative example are indices showing the extent of variations in element resistance values at 25° C., and are shown in formula (1) below. In the present comparative example, the number N of each sample was 30.
CV value=(standard deviation/mean resistance value)×100% (1)
The results of the comparative experiment mentioned above are shown in Table 1 below.
As shown in Table 1, the chip thermistor 21 made it possible to lower the CV value over the conventional chip component in all four chip configuration types. That is, the chip thermistor 21 enables variation in resistance value to be suppressed. Specifically, in the chip thermistor 21, there was a tendency for the CV value to be significantly reduced compared to the conventional component for the smaller chip configurations (e.g. 0603 and 0402). The reason for this is considered to be that, in a component with an internal electrode layered structure such as the conventional component, smaller chip configurations cause printing variations upon printing the internal electrodes and layering variations upon layering occur, and increases the influence on the resistance value, whereas the chip thermistor 21 shown in the second embodiment enables the influence of such variations to be reduced.
Furthermore, in addition to the working effect mentioned above, the chip thermistor 21 also enables the resistance to be lowered and the range of resistance value adjustment to be widened. Moreover, the heat in the chip thermistor 21 can be easily dissipated via the composite portions 29, 29, enabling the chip thermistor 21 with excellent heat dissipation to be obtained. Specifically, thermistors are originally characterized in that their resistance values change due to heat, and thus the excellent heat dissipation of the chip thermistor 21 increases its thermal responsiveness, allowing more accurate detection.
Furthermore, in the chip thermistor 21, the external electrodes 25, 25 are formed by directly plating onto the composite portions 29, 29. As such, processes such as printing and firing the first electrode layer formed from an electroconductive paste or the like become unnecessary, and the thermal influence of firing on the chip thermistor can be reduced. Furthermore, in this way, since the first electrode layer is no longer required, a further reduction in the size of the chip thermistor becomes possible. Also, the plating is coated along the shape of the element 23, and thus the flatness of the exterior of the chip thermistor 21 can be enhanced, thereby preventing the chip thermistor 21 from tumbling in a housing for a series of electronic components, and making it possible to reduce faults in installing the chip thermistor 21 onto a substrate or the like.
In the chip thermistor 21, furthermore, the external electrodes 25, 25 are configured so as to cover substantially all of the external surfaces of the composite portions 29, 29, and thus the thicknesses of the composite portions 29, 29 directly correspond to the widths of the external electrodes 25, 25, and variations of the width measurements in both external electrodes 25, 25 can be suppressed. As a result of this, it is possible to reduce phenomena such as tombstoning upon installation, which is caused by differences in the melting time of solder due to variations in the width measurements of the external electrodes 25, 25. In the present embodiment, since external electrodes 25, 25 are formed so as to cover substantially all of the external surfaces of the composite portions 29, 29, in some cases the external electrodes 25, 25 may cover part of the surface of thermistor portion 27. However, even in such cases, the plating of which the external electrodes 25, 25 are composed does not completely adhere to the thermistor portion 27, and thus barely influences the resistance value of the chip thermistor 21.
The embodiments of the present invention were described above in detail, but it should be noted that the present invention is not limited solely to the above embodiments and can be modified in many ways. For example, the first embodiment showed the case where the thickness of the thermistor portion 7 was 100 μm and the second embodiment showed the case where the thickness of the thermistor portion 27 was 200 μm, but, in order to further decrease the resistance of the chip thermistor, as shown in
In order to further decrease the resistance of the chip thermistor, as shown in
The above embodiments showed the example in which the chip thermistor 1 was the NTC thermistor, but the present invention is not limited only to it; it is a matter of course that the present invention may also be applied to other chip thermistors such as a PTC (Positive Temperature Coefficient) thermistor.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-144015 | Jun 2010 | JP | national |
This is a continuation application of U.S. application Ser. No. 13/805,043 filed Dec. 18, 2012, which in turn is a U.S. National Stage of PCT/JP2011/064171 filed Jun. 21, 2011, which claims foreign priority to JPA 2010-144015 filed Jun. 24, 2010. The disclosures of the prior applications are hereby incorporated by reference herein in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13805043 | Dec 2012 | US |
| Child | 14514738 | US |
