JP2014003053A - Thermistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermistor in a rectangular parallelepiped shape, capable of suppressing generation of cracking.SOLUTION: A thermistor matrix 12 has two end faces S1 and S2 facing each other and is in a rectangular parallelepiped shape. External electrodes 14a and 14b are respectively arranged at the end faces S1 and S2. The external electrodes 14a and 14b respectively include a Cr layer, a Ni/Cu layer, an Ag layer, and a Sn layer. The Cr layer is in ohmic contact with the thermistor matrix 12. The Ni/Cu layer is arranged on the Cr layer. The Ag layer is arranged on the Ni/Cu layer and has an average thickness of 0.7 μm or more and 2 μm or less. A chamfering process is executed to the thermistor matrix 12 and the external electrodes 14a and 14b.

Description

  The present invention relates to a thermistor, and more particularly to a rectangular parallelepiped thermistor.

  As a conventional thermistor, for example, a thermistor used in a motor starting component described in Patent Document 1 is known. The thermistor is composed of a thermistor base and two external electrodes. The thermistor base has a cylindrical shape. The external electrodes are provided on both end faces of the thermistor. The motor starting circuit described in Patent Document 1 achieves low power consumption by setting the thermistor volume or the like as a predetermined condition.

  By the way, a rectangular parallelepiped thermistor is known with respect to a cylindrical thermistor. The rectangular parallelepiped thermistor is excellent in that a large number of thermistors can be manufactured simultaneously as described below. More specifically, external electrodes are formed on both main surfaces of the plate-like mother element body by sputtering or plating. A plurality of thermistors are obtained by cutting the mother body with a dicer or the like. Finally, the thermistor is chamfered by barrel polishing to prevent chipping of the thermistor base.

  However, in the rectangular thermistor, as described below, the thermistor base may be damaged when a high voltage is applied. FIG. 10 is a cross-sectional view of a thermistor 500 having a rectangular parallelepiped shape.

  As shown in FIG. 10, the thermistor 500 includes a thermistor base 502 and external electrodes 504a and 504b. The thermistor base 502 has a rectangular parallelepiped shape. The external electrodes 504a and 504b are provided on two end faces of the thermistor base 502 located at both ends in the left-right direction in FIG. Further, since the thermistor 500 is chamfered by barrel polishing, the corners of the thermistor base 502 are rounded. The external electrodes 504 a and 504 b are cut by barrel polishing and are not formed at the corners of the thermistor base 502. Hereinafter, the lower end portion of the external electrode 504b is referred to as an end portion A, and the lower right corner of the thermistor base 502 is referred to as a corner B.

  Here, the end A of the external electrode 504 b is positioned above the corner B of the thermistor base 502. Therefore, current flows into the end A of the external electrode 504b from above, from the side, and from below. The end A of the external electrode 504b is very thin because it is cut by barrel polishing, and has a high resistance value. Therefore, when the current concentrates on the end A of the external electrode 504b, the end A of the external electrode 504b generates heat.

  On the other hand, since the external electrode 504b is not provided at the corner B of the thermistor base 502, almost no current flows. Therefore, the temperature at the corner B of the thermistor base 502 hardly rises. Therefore, the difference between the temperature of the thermistor base 502 at the end A and the temperature of the thermistor base 502 at the corner B becomes large. As a result, a crack may occur in the thermistor base 502 between the end A and the corner B.

JP 2006-60992 A

  Then, the objective of this invention is providing the rectangular parallelepiped thermistor which can suppress that a crack generate | occur | produces.

  A thermistor according to an embodiment of the present invention includes a rectangular parallelepiped thermistor base having two end faces facing each other, a first external electrode and a second external electrode provided on each of the two end faces. An external electrode, and each of the first external electrode and the second external electrode includes a first layer that is in ohmic contact with the thermistor base, Ag, and the first electrode. And a second layer having an average thickness of 0.7 μm or more and 2 μm or less, and the thermistor substrate and the first external electrode. Further, the second external electrode is chamfered.

  According to the present invention, the occurrence of cracks can be suppressed.

It is the figure which planarly viewed the thermistor which concerns on one Embodiment of this invention. FIG. 2 is a cross-sectional structure diagram of C in FIG. 1. It is the figure which showed the manufacturing process of the thermistor of FIG. It is the figure which showed the manufacturing process of the thermistor of FIG. It is the graph which showed the 2nd experiment result. FIG. 3 is a graph of Table 2. It is the figure which planarly viewed the thermistor which concerns on a modification from upper direction. (A) is an enlarged view of a cross section of a portion surrounded by a circle D in FIG. 7, and (b) is a diagram showing a heat conduction path in the thermistor in FIG. It is a figure which shows the change of Sn film thickness by Sn plating process. It is a cross-section figure of a rectangular parallelepiped thermistor.

  A thermistor according to one embodiment of the present invention will be described below with reference to the drawings.

(Thermistor configuration)
First, the structure of the thermistor will be described. FIG. 1 is a plan view of the thermistor 10. In FIG. 1, the longitudinal direction of the thermistor 10 is defined as the x-axis direction, the width direction of the thermistor 10 is defined as the y-axis direction, and the height direction of the thermistor 10 is defined as the z-axis direction.

  The thermistor 10 is used, for example, in a circuit for starting a motor used in a compressor of a refrigerator, and includes a thermistor base 12 and external electrodes 14a and 14b as shown in FIG. The thermistor base 12 is made of a semiconductor material having a positive resistance temperature characteristic (for example, barium titanate semiconductor ceramic). As shown in FIG. 1, the length L is 2.5 mm and the width W is 1. It has a rectangular parallelepiped shape with 2 mm and a height T of 1.2 mm. However, the length L should just be 2.30 mm or more and 2.70 mm or less. Moreover, the width W and the height T should just be 0.9 mm or more and 1.5 mm or less. Hereinafter, the surface on the positive direction side in the x-axis direction of the thermistor base 12 is referred to as an end surface S1, and the surface on the negative direction side in the x-axis direction of the thermistor base 12 is referred to as an end surface S2. The end surface S1 and the end surface S2 face each other. The length L means the distance between the end faces S1 and S2.

  The external electrodes 14a and 14b are provided on the end surfaces S1 and S2, respectively, and do not protrude from the end surfaces S1 and S2. Further, the thermistor base 12 and the external electrodes 14a and 14b are chamfered by barrel polishing. Therefore, as shown in FIG. 1, the corners of the thermistor base 12 are rounded. The corners of the thermistor base 12 are chamfered so as to have a radius of curvature of 45 μm or more and 76.6 μm or less. Further, the outer edges of the external electrodes 14 a and 14 b are scraped by barrel polishing and are located away from the corners of the thermistor base 12.

  Here, the external electrodes 14a and 14b are configured by overlapping a plurality of layers. Hereinafter, the external electrode 14a will be described as an example. FIG. 2 is a cross-sectional structure diagram of C in FIG.

  As shown in FIG. 2, the external electrode 14a includes a Cr layer 16a, a Ni / Cu (monel) layer 18a, an Ag layer 20a, and a Sn layer 22a. The Cr layer 16 a is in ohmic contact with the thermistor base 12. The Cr layer 16a is formed on the end surface S1 of the external electrode 14a by a method such as sputtering. The average thickness of the Cr layer 16a is 0.14 μm. However, the average thickness of the Cr layer 16a may be 0.05 μm or more and 0.40 μm or less. The average thickness means the average thickness of the region excluding the outer edge portion where the external electrode 14a is chamfered. An example of the region is a rectangular region having a height of 0.6 mm and a width of 0.6 mm at the central portion of the external electrode 14a.

  The Ni / Cu layer 18a is provided on the Cr layer 16a. The Ni / Cu layer 18a is formed on the Cr layer 16a by a method such as sputtering. The average thickness of the Ni / Cu layer 18a is 0.85 μm. However, the average thickness of the Ni / Cu layer 18a may be 0.35 μm or more and 1.0 μm or less.

  The Ag layer 20a is provided above the Cr layer 16a. Specifically, the Ag layer 20a is provided on the Ni / Cu layer 18a. The Ag layer 20a is formed on the Ni / Cu layer 18a by a method such as sputtering. The average thickness of the Ag layer 20a is 0.70 μm. However, the average thickness of the Ag layer 20a may be 0.70 μm or more and 2.0 μm or less.

  The Sn layer 22a is provided on the Ag layer 20a. The Sn layer 22a is formed on the Ag layer 20a by a method such as plating. The average thickness of the Sn layer 22a is 3.5 μm. However, the average thickness of the Sn layer 22a may be 1.4 μm or more and 14.5 μm or less.

(Thermistor manufacturing method)
Next, a method for manufacturing the thermistor 10 will be described with reference to the drawings. 3 and 4 are views showing the manufacturing process of the thermistor 10.

  First, as shown in FIG. 3A, a mother thermistor substrate 112 made of a barium titanate semiconductor ceramic is produced. Specifically, after a barium titanate-based semiconductor powder is molded to obtain a molded body, the molded body is fired and lapped to obtain the mother thermistor substrate 112.

  Next, as shown in FIG. 3B, Cr layers 116a and 116b, Ni / Cu layers 118a and 118b, and Ag layers 120a and 120b are sputtered on the principal surfaces on both sides in the z-axis direction of the mother thermistor base 112. Are formed in this order.

  Next, as shown in FIG. 3C, the mother thermistor base body 112 is cut along a dotted line with a dicer or the like to obtain a plurality of thermistor base bodies 12.

  Next, as shown in FIG. 4A, the thermistor base 12 is chamfered by barrel polishing. Thereby, the corners of the thermistor base 12 are rounded, and the outer edges of the Cr layers 16a and 16b, the Ni / Cu layers 18a and 18b, and the Ag layers 20a and 20b are scraped.

  Next, as shown in FIG. 4B, an Sn layer 22a is formed on the Ag layer 20a by plating. The thermistor 10 is completed through the above steps.

(effect)
According to the thermistor 10 configured as described above, it is possible to suppress the occurrence of cracks in the thermistor base 12 as described below. When a high voltage is applied to the thermistor 500 shown in FIG. 7, cracks may occur in the thermistor base 502 between the end A and the corner B. Specifically, the end A of the external electrode 504 b is located above the corner B of the thermistor base 502. Therefore, a current flows into the end portion of the external electrode 504b from above, from the side, and from below. The end A of the external electrode 504b is very thin because it is cut by barrel polishing. Therefore, when the current concentrates on the end A of the external electrode 504b, the end A of the external electrode 504b generates heat.

  On the other hand, since the external electrode 504b is not provided at the corner B of the thermistor base 502, almost no current flows. Therefore, the temperature at the corner B of the thermistor base 502 hardly rises. The difference between the temperature of the thermistor base 502 at the end A and the temperature of the thermistor base 502 at the corner B becomes large. As a result, a crack may occur in the thermistor base 502 between the end A and the corner B.

  Therefore, in the thermistor 10, the Ag layer 20a and the Sn layer 22a are formed thicker than usual. Specifically, the Ag layer 20 has an average thickness of 0.7 μm or more and 2 μm or less. Thereby, the surface resistance of the external electrodes 14a and 14b becomes lower than usual. As a result, the amount of heat generated in the external electrodes 14a and 14b is reduced, and an increase in the temperature of the external electrodes 14a and 14b is also suppressed. Therefore, the difference between the temperature in the vicinity of the outer edges of the external electrodes 14a and 14b in the thermistor base 12 and the temperature of the corners of the thermistor base 12 is suppressed. As a result, the occurrence of cracks in the thermistor base 12 is suppressed.

  In addition, the surface resistance of the external electrodes 14a and 14b is lower than usual even when the Sn layer 22 has an average thickness of 1.4 μm or more and 14.5 μm or less. As a result, the occurrence of cracks in the thermistor base 12 is suppressed.

  Further, since the Ag layer 20 and the Sn layer 22 are formed thicker than usual, the heat capacities of the external electrodes 14a and 14b become larger than usual. As a result, the temperature rise of the external electrodes 14a and 14b is suppressed. Therefore, the occurrence of cracks in the thermistor base 12 is suppressed.

(Experiment)
The inventor of the present application conducted an experiment described below in order to clarify the effect of the thermistor 10.

  First, as a first experiment, an experiment was performed to confirm that the average thickness of the Ag layer 20 is preferably 0.70 μm or more. Specifically, 20 first to fourth samples each having the following configuration of external electrodes were produced, and a voltage was applied to the first to fourth samples. The first sample corresponds to a comparative example, and the second to fourth samples correspond to examples. The difference between the first sample and the second to fourth samples is the thickness of the Ag layer. The first to fourth samples are chamfered so that the thermistor base has a radius of curvature of 76.6 μm, and no Sn layer is provided. And the voltage was increased and the number of the 1st-4th sample in which the crack did not generate | occur | produce was investigated. The voltage application method conforms to the JIS standard “JIS Z 8601”.

First sample Cr layer: 0.14 μm
Ni / Cu layer: 0.55 μm
Ag layer: 0.35 μm
Second sample Cr layer: 0.14 μm
Ni / Cu layer: 0.60 μm
Ag layer: 0.70 μm
Third sample Cr layer: 0.14 μm
Ni / Cu layer: 0.60 μm
Ag layer: 1.00 μm
Fourth sample Cr layer: 0.14 μm
Ni / Cu layer: 0.60 μm
Ag layer: 1.90 μm

  Table 1 is a table showing the experimental results of the first experiment.

  Here, the thermistor 10 is used, for example, in a motor starting circuit of a compressor of a refrigerator. Therefore, the AC voltage supplied by the power source is 200V to 220V. When an AC voltage of 200 V to 220 V is applied, variations occur in the AC voltage, and thus the thermistor 10 needs to be designed so that cracks do not occur even when an AC voltage of 350 V is applied. Therefore, referring to Table 1, when the average thickness of the Ag layer is 0.35 μm (that is, the first sample), it can be seen that there are many samples in which cracks occur when an AC voltage of 350 V is applied. On the other hand, when the average thickness of the Ag layer is 0.70 μm or more (that is, the second to fourth samples), it can be seen that there are almost no samples that generate cracks even when an AC voltage of 350 V or less is applied. . Therefore, it can be seen that if the average thickness of the Ag layer is 0.70 μm or more, the thermistor substrate 12 is prevented from being cracked.

  From the viewpoint of manufacturing cost, it has been found that the average thickness of the Ag layer is preferably 2 μm or less.

  Next, as a second experiment, an experiment was conducted to confirm that the corner radius of curvature of the thermistor substrate 12 is preferably 76.6 μm or less. Specifically, a plurality of types of samples in which the radius of curvature of the thermistor base was changed in the range of 45 μm to 76.6 μm were produced, and a voltage was applied to each sample. Then, the voltage was increased, and the upper limit voltage at which no crack occurred in each sample was examined.

  FIG. 5 is a graph showing the results of the second experiment. The vertical axis represents voltage, and the horizontal axis represents the radius of curvature of the thermistor base. In addition, “average” means the average value of the upper limit voltage at which cracks did not occur in each sample, and “minimum” means the minimum value of the upper limit voltage at which cracks did not occur in each sample. Means.

  As can be seen from FIG. 5, the voltage at which cracks occur decreases as the corner radius of curvature of the thermistor base increases. And when the curvature radius of the corner of the thermistor base is 76.6 μm, it can be seen that there is no sample in which cracks occur even when an AC voltage of about 350 V is applied.

  In addition, as shown in FIG. 5, the inventor of the present application manufactured a sample with a corner radius of curvature of 45 μm of the thermistor base 12, and confirmed that problems such as cracks did not occur in the thermistor base 12. Therefore, it can be seen that the corner radius of curvature of the thermistor substrate 12 is preferably 45 μm or more.

  Next, as a third experiment, an experiment was performed to confirm that the average thickness of the Sn layer 22 is preferably 1.4 μm or more. Specifically, 20 samples of the fifth to thirteenth samples each having the following configuration of the external electrode were produced, and a voltage was applied to the fifth sample to the thirteenth sample. The fifth sample corresponds to a comparative example, and the sixth to thirteenth samples correspond to examples. The fifth sample has the same specifications as the second sample. The difference from the fifth to thirteenth samples is the thickness of the Sn layer. Then, the voltage was increased, and the number of the fifth to thirteenth samples in which no crack was generated in the fifth to thirteenth samples was examined. The voltage application method conforms to the JIS standard “JIS Z 8601”.

Average thickness of the Sn layer of the fifth sample: 0 μm
Average thickness of the Sn layer of the sixth sample: 0.8 μm
Average thickness of Sn layer of seventh sample: 1.4 μm
Average thickness of Sn layer of eighth sample: 3.0 μm
Average thickness of Sn layer of the ninth sample: 4.8 μm
Average thickness of Sn layer of 10th sample: 6.7 μm
Average thickness of the Sn layer of the eleventh sample: 8.9 μm
Average thickness of Sn layer of 12th sample: 11.5 μm
Average thickness of Sn layer of 13th sample: 14.5 μm

  Table 2 is a table showing the results of the third experiment. FIG. 6 is a graph of Table 2. The vertical axis represents voltage, and the horizontal axis represents film thickness. In addition, “average” means the average value of the upper limit voltage at which cracks did not occur in each sample, and “minimum” means the minimum value of the upper limit voltage at which cracks did not occur in each sample. Means.

  Here, it is necessary to design the thermistor 10 so that cracks do not occur even when an AC voltage of 350 V is applied. Therefore, referring to Table 2 and FIG. 6, it can be seen that if the average thickness of the Sn layer is 1.4 μm or more, there is no sample in which cracks occur even when an AC voltage of 350 V is applied.

  From the viewpoint of manufacturing cost, it has been found that the average thickness of the Sn layer is preferably 14.5 μm or less.

(Thermistor variants)
Next, a modified example of the thermistor will be described. FIG. 7 is a plan view of the thermistor 40 according to the modification from above. In FIG. 7, the thermistor 40 is different from the thermistor 10 in that it includes external electrodes 44a and 44b instead of the external electrodes 14a and 14b. Since there is no difference other than this, in FIG. 7, the thing equivalent to the structure of FIG. 1 is attached with the same referential mark, and description of each is abbreviate | omitted.

  The external electrodes 44a and 44b are the same as the external electrodes 14a and 14b except for the following differences. Therefore, only differences from the external electrodes 14a and 14b will be described below, and description of common parts will be omitted.

  Each of the external electrodes 44a and 44b is configured by overlapping a plurality of layers. Since the external electrodes 44a and 44b have the same structure, the external electrode 44a will be representatively described below with reference to FIGS.

  FIG. 8A shows an enlarged cross section of a corner B (portion surrounded by a circle D) of the thermistor 40 in FIG. In FIG. 8A, the external electrode 44a includes a base electrode 46a and an Sn layer 48a.

  The base electrode 46a includes a Cr layer, a Ni / Cu (monel) layer, and an Ag layer. Since these three layers are described in detail in the above embodiment with reference to FIG. 2, the description thereof is omitted here.

  The Sn layer 48a is formed on the Ag layer constituting the base electrode 46a by a method such as plating. The average thickness of the Sn layer 48a is 6.7 μm in the illustrated example, but the average thickness of the Sn layer 48a may be 3.5 μm or more and 14.5 μm or less as described in the above embodiment. As described above, if the average thickness of the Sn layer 48a is relatively increased, the Sn layer 48a completely covers the base electrode 46a, and the outer edge of the Sn layer 48a reaches the corner B.

(Manufacturing method of thermistor of modification)
The method of manufacturing the thermistor 40 is different from that described above in that the Sn plating process is performed for a long time, thereby forming the Sn layer 48a having a large average thickness. Since there is no difference other than that, description about each common process is abbreviate | omitted. When the Sn plating process is performed for a long time, as shown in FIG. 9, the thickness of Sn gradually increases, and Sn is deposited so as to cover the base electrode 46a. When the plating process is further continued, the outer edge of Sn reaches the corner B of the thermistor base 12. Thus, the Sn layer 48a is formed.

(Effect of modification)
According to the thermistor 40 configured as described above, the occurrence of cracks in the thermistor base 12 can be further suppressed. The reason is described below. In FIG. 8B, the heat generated in the base electrode 46a is transmitted above the base electrode 46a (Sn layer 48a), and further transmitted to the outer edge of the Sn layer 48a (see the dotted arrow E). In this way, the heat of the base electrode 46a escapes to the Sn layer 48a, so that the temperature rise of the base electrode 46a is suppressed.

  Further, the temperature at the corner B of the thermistor base 12 rises due to the heat transferred to the outer edge of the Sn layer 48a. As a result, the temperature difference between the end A of the base electrode 46a and the corner B of the thermistor base 12 is reduced, and the flash withstand voltage is improved. Thereby, it is possible to suppress the occurrence of cracks in the thermistor base 12.

  As described above, the present invention is useful for a thermistor, and is particularly excellent in that it can suppress the occurrence of cracks.

S1, S2 End face 10, 40 Thermistor 12 Thermistor base 14a, 14b External electrode 16a Cr layer 18a Ni / Cu layer 20a Ag layer 22a, 48a Sn layer 112 Mother thermistor base 116a Cr layer 118a Ni / Cu layer 120a Ag layer 46a Base electrode

Claims (7)

A rectangular parallelepiped thermistor base having two end faces facing each other;
A first external electrode and a second external electrode provided on each of the two end faces;
With
The first external electrode and the second external electrode are respectively
A first layer in ohmic contact with the thermistor substrate;
A second layer containing Ag and provided above the first layer, the second layer having an average thickness of 0.7 μm or more and 2 μm or less;
Contains
The thermistor base, the first external electrode, and the second external electrode are chamfered,
Thermistor characterized by. The corner of the thermistor base has a radius of curvature of 45 μm or more and 76.6 μm or less,
The thermistor according to claim 1. The first external electrode and the second external electrode are respectively
A third layer containing Sn and provided on the second layer, the third layer having an average thickness of 1.4 μm or more and 14.5 μm or less;
Further including,
The thermistor in any one of Claim 1 or Claim 2 characterized by these. The third layer covers the entirety of the first and second layers, and an outer edge of the third layer reaches a corner of the thermistor base;
The thermistor according to claim 3. The first layer contains Cr;
The thermistor in any one of Claims 1 thru | or 4 characterized by these. The first external electrode and the second external electrode are respectively
A fourth layer containing Ni and Cu and provided on the first layer;
In addition,
The second layer is provided on the fourth layer;
The thermistor according to any one of claims 1 to 5, wherein The width and height of the end face of the thermistor base are 0.9 mm or more and 1.5 mm or less,
The length between the end faces of the thermistor base is 2.30 mm or more and 2.70 mm or less,
The thermistor according to claim 1, wherein: