TW201312602A - Thermal resistor - Google Patents

Abstract

The present invention provides a thermal resistor having cuboid-shape capable of suppressing generation of cracking. A thermal resistor matrix 12 of the present invention has two cuboid-shaped end faces S1, S2 facing to each other. External electrodes 14a, 14b are respectively arranged at the end faces S1, S2. The external electrodes 14a, 14b respectively include a Cr layer, a Ni/Cu layer, a Ag layer and a Sn layer. The Cr layer has an ohmic that is in contact with the thermal resistor 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 above 0.7 μm and below 2μm. The present invention performs chamfering process to the thermal resistor matrix 12 and the external electrodes 14a, 14b.

Description

Thermal resistor

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

As a thermal resistor of the prior art, for example, a thermal resistor for a component for starting a motor described in Patent Document 1 is known. The thermistor comprises a resistor body and two external electrodes. The base of the thermistor is cylindrical. The external electrodes are disposed on both end faces of the thermistor. The motor starting circuit described in Patent Document 1 achieves low power consumption by setting the volume of the thermistor to a specific condition.

Further, a rectangular parallelepiped heat resistor is known with respect to a cylindrical heat resistor. The rectangular parallelepiped thermal resistor is excellent in that it can be manufactured at the same time as described below. More specifically, the external electrodes are formed by sputtering, plating, or the like on both principal surfaces of the plate-shaped mother body. Then, the mother body is cut by a dicer or the like, thereby obtaining a plurality of thermistors. Finally, the thermal resistor is chamfered by barrel polishing to prevent the defect of the base of the thermistor.

However, in the case of a rectangular parallelepiped which has a high voltage applied as described below, the thermal resistor base is damaged. Fig. 10 is a cross-sectional structural view of a rectangular parallelepiped heat resistor 500.

As shown in FIG. 10, the thermistor 500 includes a thermistor substrate 502 and external electrodes 504a, 504b. The thermistor base 502 has a rectangular parallelepiped shape. The external electrodes 504a and 504b are respectively provided at the two end faces of the thermistor base 502 located at both ends in the left-right direction of FIG. Moreover, since the heat resistor 500 is used The chamfering of the barrel grinding is performed, so that the corner of the thermal resistor base 502 is rounded. Further, the external electrodes 504a and 504b are cut by the barrel polishing process, and are not formed at the corner of the thermistor base 502. Hereinafter, the end portion on the lower side 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 an angle B.

Here, the end portion A of the outer electrode 504b is located on the upper side with respect to the corner B of the thermistor base 502. Therefore, the current flows from the upper side, the side, and the lower side to the end portion A of the external electrode 504b. Since the end portion A of the external electrode 504b is cut by the barrel polishing process, it is extremely thin and has a high resistance value. Therefore, if the current concentrates on the end portion A of the external electrode 504b, the end portion 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 of the corner B of the thermistor base 502 hardly rises. Thereby, the difference between the temperature of the thermistor base 502 at the end A and the temperature of the thermistor base 502 at the angle B becomes large. As a result, there is a crack in the thermal resistor base 502 between the end portion A and the corner B.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2006-60992

Accordingly, it is an object of the present invention to provide a rectangular resistor which is capable of suppressing generation of cracks.

A thermal resistor according to an aspect of the present invention includes: a rectangular parallelepiped heat resistor base having two end faces facing each other; and a first outer electrode and a second outer electrode respectively provided in the two The first outer electrode and the second outer electrode each include: a first layer ohmically contacting the thermal resistor base; and a second layer containing Ag and disposed on the upper layer than the first layer, and An average thickness of 0.7 μm or more and 2 μm or less is provided, and chamfering is performed on the above-mentioned thermistor substrate, the first external electrode, and the second external electrode.

According to the present invention, crack generation can be suppressed.

Hereinafter, a thermal resistor according to one embodiment of the present invention will be described with reference to the drawings.

(Composition of thermistor)

First, the configuration of the thermal resistor will be described. FIG. 1 is a plan view of the thermal resistor 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, as a starting circuit for 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 substrate 12 is fabricated using a semiconductor material having a positive resistance temperature characteristic (for example, a barium titanate-based semiconductor ceramic), and has a length L of 2.5 mm, a width W of 1.2 mm, and a height T of 1.2 as shown in FIG. The rectangular shape of mm. Wherein, the length L is only 2.30 mm or more and 2.70 mm or less can. Further, the width W and the height T may be 0.9 mm or more and 1.5 mm or less. Hereinafter, the surface of the thermal resistor base 12 on the positive side in the x-axis direction is referred to as an end surface S1, and the surface of the thermistor base 12 on the negative side in the x-axis direction is referred to as an end surface S2. The end surface S1 and the end surface S2 oppose each other. The length L refers to the distance between the end faces S1 and S2.

The external electrodes 14a and 14b are provided on the end faces S1 and S2, respectively, and do not protrude from the end faces S1 and S2. Further, the thermistor base 12 and the external electrodes 14a and 14b are subjected to chamfering by barrel polishing. Therefore, as shown in FIG. 1, the corners of the resistor base 12 are rounded. The corner of the thermistor base 12 is 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 outer electrodes 14a and 14b are cut by the barrel polishing process, and are located at positions away from the corners of the thermal resistor base 12.

Here, the external electrodes 14a and 14b are formed by overlapping a plurality of layers. Hereinafter, the external electrode 14a will be described as an example. Figure 2 is a cross-sectional structural view of C of Figure 1.

As shown in FIG. 2, the external electrode 14a includes a Cr layer 16a, a Ni/Cu (monal) layer 18a, an Ag layer 20a, and an Sn layer 22a. The Cr layer 16a is in ohmic contact with respect to the thermistor substrate 12. The Cr layer 16a is formed on the end surface S1 of the external electrode 14a by a method such as sputtering. The Cr layer 16a has an average thickness of 0.14 μm. The average thickness of the Cr layer 16a may be 0.05 μm or more and 0.40 μm or less. In addition, the average thickness means the average thickness of the area of the external electrode 14a excluding the chamfering edge part. An example of this 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 was 0.85 μm. 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 on the upper layer than the Cr layer 16a, specifically, 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 Ag layer 20a has an average thickness of 0.70 μm. 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 Sn layer 22a has an average thickness of 3.5 μm. The average thickness of the Sn layer 22a may be 1.4 μm or more and 14.5 μm or less.

(Method of manufacturing thermistor)

Next, a description will be given of a method of manufacturing the thermistor 10 with reference to the drawings. 3 and 4 are views showing the manufacturing steps of the thermistor 10.

First, as shown in FIG. 3(a), a mother thermal resistor base 112 including a barium titanate-based semiconductor ceramic is produced. Specifically, after the powder of the barium titanate-based semiconductor is formed to obtain a molded body, the molded body is subjected to firing and lapping polishing to obtain a mother thermal resistor base 112.

Next, as shown in FIG. 3(b), Cr layers 116a, 116b and Ni/Cu layers 118a, 118b are sequentially formed by sputtering on the main faces on both sides in the z-axis direction of the mother thermistor substrate 112. And Ag layers 120a, 120b.

Then, as shown in FIG. 3(c), the mother thermistor substrate 112 is cut along a broken line by a dicer or the like, whereby a plurality of thermistor substrates 12 are obtained.

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

Then, as shown in FIG. 4(b), the 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, cracking of the thermistor base 12 can be suppressed as described below. If a higher voltage is applied to the thermistor 500 shown in FIG. 7, there is a flaw in the thermal resistor base 502 between the end portion A and the corner B. Specifically, the end portion A of the outer electrode 504b is located on the upper side with respect to the corner B of the thermistor base 502. Therefore, the current flows from the upper side, the side, and the lower side to the end of the external electrode 504b. The end portion A of the external electrode 504b is cut by the barrel polishing process, so that it is extremely thin. Therefore, if the current concentrates on the end portion A of the external electrode 504b, the end portion 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 of 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 angle B becomes large. As a result, there is a crack in the thermal resistor base 502 between the end portion 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, 14b becomes more common. Often lower. As a result, the amount of heat generated in the external electrodes 14a and 14b is reduced, and the rise in the temperature of the external electrodes 14a and 14b is also suppressed. Thereby, it is possible to suppress the difference in temperature between the temperature near the outer edge of the external electrodes 14a, 14b in the heat resistor base 12 and the angle of the corner of the thermistor base 12 from becoming large. As a result, cracking of the thermistor base 12 can be suppressed.

Further, the Sn layer 22 has an average thickness of 1.4 μm or more and 14.5 μm or less, and the surface resistance of the external electrodes 14a and 14b is made lower than usual. As a result, cracking of the thermistor base 12 can be suppressed.

Further, since the Ag layer 20 and the Sn layer 22 are formed thicker than usual, the heat capacity of the external electrodes 14a and 14b becomes larger than usual. As a result, the rise in the temperature of the external electrodes 14a and 14b is suppressed. Thereby, cracking of the thermistor base 12 can be suppressed.

(experiment)

In order to make the effect of the thermistor 10 more clear, the inventors of the present invention conducted the experiment described below.

First, as a first experiment, an experiment for confirming that the average thickness of the Ag layer 20 is 0.70 μm or more is performed. Specifically, the first to fourth samples having the following external electrodes were formed, and voltages were applied to the first to fourth samples, respectively. The first sample corresponds to a comparative example, and the second to fourth samples correspond to the examples. The difference between the first sample and the second to fourth samples is the thickness of the Ag layer. For the first to fourth samples, chamfering was performed so that the corner of the base of the thermistor had a radius of curvature of 76.6 μm, and the Sn layer was not provided. Further, the voltage was increased, and the number of the first to fourth samples in which no crack occurred was examined. The method of applying voltage is based on the JIS standard (Japanese Industrial Standards, day) This industry 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

Sample 3

Cr layer: 0.14 μm

Ni/Cu layer: 0.60 μm

Ag layer: 1.00 μm

Sample 4

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 supply is 200 V to 220 V. When an AC voltage of 200 V to 220 V is applied, since the AC voltage is uneven, it is necessary to design the thermistor 10 in such a manner that no crack is generated even if an AC voltage of 350 V is applied. Therefore, as can be seen from Table 1, when the average thickness of the Ag layer is 0.35 μm (that is, the first sample), if an AC voltage of 350 V is applied, a large number of cracked samples are generated. 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), even if an AC voltage of 350 V or less is applied, there is almost no crack-producing sample. Thereby, it is understood that when the average thickness of the Ag layer is 0.70 μm or more, cracking of the thermistor base 12 can be suppressed.

Further, from the viewpoint of the production cost, it is understood that the average thickness of the Ag layer is preferably 2 μm or less.

Next, as a second experiment, an experiment for confirming that the radius of curvature of the corner of the thermal resistor base 12 is 76.6 μm or less is preferably performed. Specifically, making A voltage is applied to each sample by a plurality of samples in which the radius of curvature of the corner of the base of the thermistor is varied from 45 μm to 76.6 μm. Further, 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 the voltage, and the horizontal axis represents the radius of curvature of the corner of the base of the thermistor. In addition, the "average" means the average value of the upper limit voltage which does not generate a crack in each sample, and the "lowest" means the minimum value of the upper limit voltage which does not generate a crack in each sample.

According to Fig. 5, it is understood that as the radius of curvature of the corner of the base of the thermistor becomes larger, the voltage at which the crack occurs is lowered. Further, it can be seen that when the radius of curvature of the corner of the base of the thermistor is 76.6 μm, there is no sample which is cracked even if an AC voltage of about 350 V is applied.

Further, the inventors of the present invention produced a sample having a radius of curvature of a corner of the base of the thermistor 12 as shown in Fig. 5, and confirmed that the thermal resistor base 12 did not cause cracks or the like. Thereby, it is understood that the radius of curvature of the corner of the heat resistor base 12 is preferably 45 μm or more.

Next, as a third experiment, an experiment for confirming that the average thickness of the Sn layer 22 is 1.4 μm or more is performed. Specifically, 20 external samples having the fifth sample to the thirteenth sample having the configuration shown below were produced, and voltages were applied to the fifth sample to the thirteenth sample. The fifth sample corresponds to the comparative example, and the sixth sample to the thirteenth sample correspond to the examples. The fifth sample and the second sample have the same specifications. The difference between the fifth and thirteenth samples is the thickness of the Sn layer. Further, the voltage was increased, and the number of the fifth to thirteenth samples in which no crack occurred was examined for the fifth sample to the thirteenth sample. The method of applying the voltage is based on 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 the Sn layer of the seventh sample: 1.4 μm

Average thickness of the Sn layer of the eighth sample: 3.0 μm

Average thickness of the Sn layer of the ninth sample: 4.8 μm

Average thickness of the Sn layer of the 10th sample: 6.7 μm

Average thickness of the Sn layer of the 11th sample: 8.9 μm

Average thickness of the Sn layer of the 12th sample: 11.5 μm

Average thickness of the Sn layer of the 13th sample: 14.5 μm

Table 2 is a table showing the results of the third experiment. Figure 6 is a diagram showing the graph of Table 2. The vertical axis represents voltage and the horizontal axis represents film thickness. In addition, the "average" means the average value of the upper limit voltage which does not generate a crack in each sample, and the "lowest" means the minimum value of the upper limit voltage which does not generate a crack in each sample.

Here, it is necessary to prevent cracking even if an AC voltage of 350 V is applied. The thermal resistor 10 is designed in such a manner. Therefore, as can be seen from Table 2 and FIG. 6, when the average thickness of the Sn layer is 1.4 μm or more, no crack is generated even if an AC voltage of 350 V is applied.

Further, from the viewpoint of the manufacturing cost, it is understood that the average thickness of the Sn layer is preferably 14.5 μm or less.

(Modification of thermistor)

Next, a modification of the thermistor will be described. Fig. 7 is a view of the thermal resistor 40 of the modified example as seen from above. In FIG. 7, the thermistor 40 differs from the above-described thermistor 10 in that it includes external electrodes 44a and 44b instead of the external electrodes 14a and 14b. In the following, the same reference numerals will be given to the components corresponding to those in FIG. 1 and the description of each will be omitted.

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

The external electrodes 44a and 44b are each formed by stacking 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. 8 and 9.

A cross section of the corner B (portion surrounded by the circle D) of the thermistor 40 of Fig. 7 is shown enlarged in Fig. 8(a). In Fig. 8(a), 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. These three layers have been described in detail in the above embodiment with reference to Fig. 2, and thus the description thereof is omitted here.

The Sn layer 48a is formed on the base electrode 46a by plating or the like. On the Ag layer. 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. If the average thickness of the Sn layer 48a is relatively increased in this manner, the Sn layer 48a completely covers the base electrode 46a, and further, the outer edge of the Sn layer 48a reaches the angle B.

(Method of Manufacturing Heat Resistor of Modification)

The method of manufacturing the thermistor 40 differs from the above in that the Sn layer 48a having a large average thickness is formed by performing the Sn plating treatment for a long period of time. There is no difference other than this, and therefore the description of each step is omitted for the common steps. When the Sn plating process is performed for a long period of time, as shown in FIG. 9, the film thickness of Sn gradually increases, and Sn is deposited so as to cover the base electrode 46a. If the plating process is further continued, the outer edge of Sn reaches the corner B of the thermal resistor base 12. The Sn layer 48a is thus formed.

(Effect of the modification)

According to the thermistor 40 configured as described above, cracking of the thermistor base 12 can be further suppressed. The reason is explained below. In Fig. 8(b), heat generated in the base electrode 46a is transmitted to the upper side of the base electrode 46a (Sn layer 48a), and further transmitted to the outer edge of the Sn layer 48a (refer to the broken line arrow E). Thus, 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 of the corner B of the thermistor substrate 12 is raised by the heat transmitted to the outer edge of the Sn layer 48a. As a result, the temperature difference between the end portion A of the base electrode 46a and the corner B of the thermistor base 12 becomes small, and the transient withstand voltage is increased. Thereby, the occurrence of cracks in the thermal resistor base 12 can be suppressed.

[Industrial availability]

As described above, the present invention is useful for a thermal resistor, and is particularly excellent in suppressing generation of cracks.

10‧‧‧Thermal resistance

12‧‧‧Thermal resistor base

14a‧‧‧External electrode

14b‧‧‧External electrode

16a‧‧‧Cr layer

18a‧‧‧Ni/Cu layer

20a‧‧‧Ag layer

22a‧‧‧Sn layer

40‧‧‧Thermistor

46a‧‧‧Base electrode

48a‧‧‧Sn layer

112‧‧‧Female thermal resistor base

116a‧‧‧Cr layer

118a‧‧‧Ni/Cu layer

120a‧‧‧Ag layer

L‧‧‧ length

S1‧‧‧ end face

S2‧‧‧ end face

T‧‧‧ Height

W‧‧‧Width

Fig. 1 (a) and Fig. 1 (b) are views showing a heat resistor according to an embodiment of the present invention.

Figure 2 is a cross-sectional structural view of C of Figure 1.

3(a) to (c) are views showing the manufacturing steps of the thermistor of Fig. 1.

4(a) and 4(b) are views showing the manufacturing steps of the thermistor of Fig. 1.

Fig. 5 is a graph showing the results of the second experiment.

Figure 6 is a diagram showing the graph of Table 2.

7(a) and 7(b) are views of the thermal resistor of the modified example as seen from above.

Fig. 8(a) is an enlarged view of a cross section of a portion surrounded by a circle D of Fig. 7, and Fig. 8(b) is a view showing a heat conduction path of the thermistor of Fig. 7.

Fig. 9 is a view showing a change in the film thickness of Sn based on the Sn plating treatment.

Fig. 10 is a cross-sectional structural view of a rectangular parallelepiped heat resistor.

10‧‧‧Thermal resistance

12‧‧‧Thermal resistor base

14a‧‧‧External electrode

14b‧‧‧External electrode

L‧‧‧ length

S1‧‧‧ end face

S2‧‧‧ end face

T‧‧‧ Height

W‧‧‧Width

Claims (10)

A thermistor comprising: a rectangular parallelepiped heat resistor base having two end faces facing each other; and a first outer electrode and a second outer electrode respectively disposed on the two end faces; Each of the external electrode and the second external electrode includes a first layer that is in ohmic contact with the thermal resistor base, and a second layer that contains Ag and is disposed on the upper layer than the first layer and has a thickness of 0.7 μm or more. And an average thickness of 2 μm or less; and the chamfering process is performed on the thermistor substrate, the first external electrode, and the second external electrode. The thermal resistor of claim 1, wherein the corner of the thermal resistor base has a radius of curvature of 45 μm or more and 76.6 μm or less. The thermal resistor according to any one of claims 1 to 2, wherein the first external electrode and the second external electrode further comprise: a third layer containing Sn and disposed on the second layer and having 1.4 An average thickness of μm or more and 14.5 μm or less. A thermal resistor according to claim 3, wherein said third layer covers the entirety of said first and said second layers, and said outer edge of said third layer reaches an angle of said heat resistor base. A heat resistor according to claim 3, wherein said first layer contains Cr. A thermistor according to any one of claims 1 to 2, wherein the first layer contains Cr. The thermal resistor according to claim 3, wherein the first external electrode and the second external electrode further comprise: a fourth layer containing Ni and Cu and provided on the first layer; and the second layer is disposed on On the fourth layer above. The thermal resistor according to claim 5, wherein the first external electrode and the second external electrode further comprise: a fourth layer containing Ni and Cu and provided on the first layer; and the second layer is disposed on On the fourth layer above. The thermal resistor according to any one of claims 1 to 2, wherein the first external electrode and the second external electrode further comprise: a fourth layer containing Ni and Cu and disposed on the first layer And the second layer is disposed on the fourth layer. The thermal resistor according to any one of claims 1 to 2, wherein the width and height of the end surface of the heat resistor base are 0.9 mm or more and 1.5 mm or less, and the length between the end faces of the heat resistor base It is 2.30 mm or more and 2.70 mm or less.