JPH06260302A - Chip-type ptc thermistor - Google Patents

Abstract

PURPOSE:To provide the structure, wherein the dispersion of the resistance values caused by the contact between outer electrodes and the element body of a thermistor and the deterioration of characteristics in the elapse of time are hard to occur, in a chip-type PTC thermistor having internal electrodes. CONSTITUTION:Insulating coat layers 15 and 16 are formed on both edges of a thermistor element body 12 having first and second inner electrodes 13 and 14 other than parts from which the inner electrodes 13 and 14 are led out. First and second outer electrodes 17 and 18 are formed on the insulating coat layers 15 and 16 so that the electrodes 17 and 18 are electrically connected to the first and second inner electrodes 13 and 14. A chip-type PTC thermistor 11 is constituted by forming these parts.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chip PTC (positive characteristic) thermistor, and more particularly to a chip PTC thermistor having a structure in which internal electrodes are embedded in a thermistor body made of semiconductor ceramics.

[0002]

2. Description of the Related Art A PTC thermistor is required to be used as a chip type component that can be surface-mounted on a substrate, like other electronic components. An example of a conventional surface mountable PTC thermistor is shown in FIGS. 4 (a) and 4 (b).

In the chip type PTC thermistor 1, as shown in FIG.
As shown in (b), ohmic electrodes 3 that are in ohmic contact with the thermistor element body 2 are formed on both end surfaces of the plate-shaped thermistor element body 2. Also, FIG.
As shown in (a), protective electrodes 4 and 4 are formed so as to cover the ohmic electrodes 3 and 3. The protective electrodes 4 and 4 are formed so as to reach not only the end surface of the thermistor element body 2 but also the upper and lower surfaces of the thermistor element body 2.

In the chip type PTC thermistor 1, the resistance value is adjusted by reducing the thickness of the thermistor element body 2 by polishing or changing the thickness of the wafer to be used. However, there has been a problem that the element thickness fluctuates considerably between manufacturing lots, which tends to cause variations in resistance.

Further, since the protective electrode 4 is exposed on the surface, there is a problem that the characteristics are likely to change with time and the life characteristics are not sufficient. In addition, due to dimensional variation of the thermistor element body 2 and dimensional variation of the protective electrode 4,
Since the resistance value is greatly affected, there is also a problem that the accuracy of the resistance value is not sufficient.

[0006]

As a solution to the above-mentioned problems of the conventional chip type PTC thermistor, a chip type P in which internal electrodes are arranged in the thermistor body is provided.
TC thermistors have been proposed. This chip type PTC
The thermistor is shown in FIGS. 5 (a) and 5 (b).

In the chip type PTC thermistor 5, internal electrodes 7 and 8 are embedded in a thermistor element body 6 made of semiconductor ceramics. The internal electrodes 7 and 8 are arranged so as to overlap each other in the thickness direction with the semiconductor ceramic layer interposed therebetween. One internal electrode 7 is drawn out to one end face 6a of the thermistor element body 6, and the other internal electrode 8 is drawn out to the other end face 6b. External electrodes 9 and 10 are formed to cover both end surfaces 6a and 6b of the thermistor element body 6 so as to be electrically connected to the internal electrodes 7 and 8, respectively.

In the chip type PTC thermistor 5, the resistance value is determined by the overlapping area between the internal electrodes 7 and 8 and the distance R (see FIG. 5) between the internal electrodes 7 and 8 shown in a plan sectional view in FIG. Therefore, it is possible to reduce variations in resistance value and the influence of the external environment. Therefore, it is possible to obtain a chip-type PTC thermistor having a small variation in resistance value and excellent reliability.

By the way, the chip PTC thermistor 5 as described above is manufactured by laminating ceramic green sheets together with the material forming the internal electrodes and firing them integrally. However, when a base metal is used as the internal electrode material, the firing temperature of the thermistor element is 1300.
Since it is as high as around ℃, there is a problem that the metal of the internal electrode material is oxidized.

When noble metals such as Pt and Pd are used as the internal electrode material, they are not oxidized during firing, but their work function is higher than the electron affinity of the semiconductor. There is a problem that a barrier is formed between the body and it is difficult to obtain ohmic contact.

Therefore, by applying a pulse voltage between the internal electrodes in the thermistor body, the barrier between the internal electrodes and the thermistor body is removed, whereby a good voltage is provided between the internal electrodes and the thermistor body. A method of providing ohmic contact has been proposed (Japanese Patent Application No. 4-109909).
issue).

However, it has been found that the following problems occur when the barrier voltage is broken by applying the above pulse voltage. That is, when a pulse voltage is applied between the external electrodes 9 and 10 in the chip type PTC thermistor 5 to break the barrier, the barrier is regenerated between the external electrodes 9 and 10 and the thermistor element body 6 over time, and as a result, , The obtained chip type PTC thermistor 5
There was a problem that the variation of the resistance value in 1 was increased again.

Further, the external electrodes 9, 10 are in direct contact with the end surfaces 6a, 6b of the thermistor element body 6, and the ohmic contact between the external electrodes 9, 10 and the thermistor element body 6 changes the external environment. There is also a problem that the life characteristics are deteriorated due to the influence of

The object of the present invention is to provide good ohmic contact between the internal electrode and the thermistor element body even when the internal electrode is formed by using a material made of a noble metal, and to provide a high resistance value. An object of the present invention is to provide a chip PTC thermistor that has a small variation and is less likely to deteriorate in characteristics over time, and has excellent reliability.

[0015]

According to the present invention, there are provided a thermistor element body made of semiconductor ceramics, and first and second elements formed in the thermistor element body and arranged so as to overlap each other with a semiconductor ceramic layer interposed therebetween. And the first internal electrode on one end face of the thermistor body,
A second inner electrode is drawn out to the other end face, and first and second end faces are formed on both end faces of the thermistor body so as to be electrically connected to the first and second inner electrodes, respectively.
And an insulating coating layer disposed so as to be interposed in at least a part of a region between the first and second external electrodes and the end face of the thermistor body. Is a chip type PTC thermistor.

[0016]

In the chip type PTC thermistor of the present invention, the insulating coating layer is interposed in at least a part of the area between the external electrode and the thermistor element body. Therefore, in the part where the direct contact of the external electrode with the thermistor element body is blocked by the insulating coating layer, the barrier is not regenerated between the external electrode and the thermistor element body, and the influence of the external environment change Is also hard to receive.

That is, the present invention focuses on the fact that in the conventional chip type PTC thermistor having the internal electrode, the portion where the external electrode is in direct contact with the thermistor element body causes the above-mentioned problems. The direct contact between the external electrode and the thermistor element body is interrupted by interposing an insulating coating layer, thereby reducing the influence of variations in resistance value and changes in the external environment.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be clarified by explaining embodiments of the present invention with reference to the drawings. Figure 1
(A), (b) is a perspective view and a longitudinal section showing a chip type PTC thermistor concerning one example of the present invention.

The chip type PTC thermistor 11 of this embodiment
Has a structure in which a first internal electrode 13 and a second internal electrode 14 are arranged in a thermistor element body 12 made of semiconductor ceramics. The 1st internal electrode 13 and the 2nd internal electrode 14 are arrange | positioned so that it may overlap via a semiconductor ceramic layer. The first internal electrode 13 is drawn out to the one end surface 12a of the thermistor element body 12, and the second internal electrode 14 is drawn to the other end surface 12b.

Further, the end surface 12a of the thermistor body 12 is
In 12b, insulating coating layers 15 and 16 are formed except for the portions where the internal electrodes 13 and 14 are drawn out. The insulating coating layers 15 and 16 are formed not only on the end surfaces 12a and 12b but also on the upper and lower surfaces of the thermistor element body 12 and both side surfaces.

Further, first and second external electrodes 17 and 18 are formed on the insulating coating layers 15 and 16, respectively. The first and second outer electrodes 17 and 18 are electrically connected to the first and second inner electrodes 13 and 14 exposed on the end faces 12a and 12b, respectively.

The chip type PTC thermistor 11 of this embodiment
Is manufactured by the following steps. First, a ceramic green sheet on which an internal electrode material is printed is laminated, and the ceramic green sheet and the internal electrode material are integrally fired to obtain the thermistor element body 12. next,
The insulating coating layers 15 and 16 and the first and second external electrodes 17 and 18 are formed on both end surfaces of the obtained thermistor body 12. Then, in order to provide a good ohmic contact between the first and second internal electrodes 13 and 14 and the thermistor element body 12, by applying a pulse voltage between the external electrodes 17 and 18, the internal electrodes 13 and 14 and thermistor body 12
Break the barrier between.

In the chip type PTC thermistor of this embodiment, the external electrodes 17 and 18 are not in direct contact with the thermistor element body 12 in regions other than the portions connected to the internal electrodes 13 and 14. Therefore, the barrier is not regenerated between the external electrodes 17 and 18 and the thermistor body 12, and the external electrodes 17 and 18 are not changed due to the change of the external environment.
The characteristic variation due to the change in the contact portion between the thermistor body 12 and the thermistor body 12 is unlikely to occur.

Any insulating material can be used for the insulating coating layers 15 and 16 as long as it is an insulating material capable of preventing direct contact between the external electrodes 17 and 18 and the thermistor body 12. Can be formed by baking a glass frit or applying / baking an insulating ceramic paste. Next, a specific experimental example will be described.

First, BaTiO ₃ as a main component, Y ₂ O ₃ as a semiconducting agent, and SiO ₂ and A as a mineralizing agent.
l ₂ O ₃ and MnO ₂ as a property improving agent were mixed, mixed, pulverized and then calcined. An acrylic organic binder was mixed with the obtained calcined powder to prepare a ceramic slurry. Using the prepared ceramic slurry, a ceramic green sheet having a predetermined uniform thickness was formed.

On the other hand, a powder containing Pt as a main component was mixed with a varnish and a binder to prepare a conductive paste. This conductive paste was printed on the ceramic green sheet punched into a predetermined size to obtain a ceramic green sheet on which the internal electrodes 13 and 14 were printed. The first and second ceramic green sheets printed with internal electrodes
Of the internal electrodes 13 and 14 are laminated, and a plurality of ceramic green sheets on which the internal electrode material is not printed are laminated on the upper and lower sides thereof, and pressure-bonded in the thickness direction to form a laminate having a thickness of 1.1 mm. Got the body

The obtained laminate was cut into a size of 2.4 × 1.5 × thickness 1.1 mm and fired at a temperature of 1200 to 1350 ° C. for 2 hours. Then, the fired chips were barrel-polished to obtain the thermistor element body 12.

Next, as shown in FIG. 2, a glass frit containing SiO ₂ as a main component and having a softening point of 650 ° C. was formed so as to reach from the both end surfaces of the obtained thermistor element body 12 to the upper and lower surfaces and both side surfaces. The coating was applied and baked at a temperature of 680 ° C. for 10 minutes to form insulating coating layers 15 and 16. When applying the glass frit, the internal electrodes 13, 14 were
The exposed portion is covered with a mask,
An insulating coating layer made of glass frit was not formed on the exposed portion of 14.

Next, an Ag paste containing a glass frit having a softening point of 500 ° C. is applied on the insulating coating layers 15 and 16 and baked at 530 ° C. for 10 minutes to form the first and second external electrodes 17 and 18. Formed. As described above, the first and second
After forming the external electrodes 17 and 18 of the above, a DC pulse voltage of 300 V is applied between the first and second external electrodes 17 and 18 to connect the first and second internal electrodes 13 and 14 to the thermistor element body. I broke the barrier between them.

For comparison, the insulating coating layers 15 and 16 are used.
A chip type PTC thermistor obtained in the same manner as described above was prepared except that the above was not formed. The chip type PTC thermistor of the above embodiment and the chip type PTC of the comparative example
100 thermistors were prepared and left in the atmosphere for 500 hours. Then, the resistance value of each chip type PTC thermistor was measured. The results are shown in Table 1 below.

[0031]

[Table 1]

As is clear from Table 1, the chip-type PTC of the embodiment is compared with the chip-type PTC thermistor of the comparative example.
It can be seen that the thermistor has a higher resistance value and the 3CV showing the variation in the resistance value is also very small.

Further, 10 chips each of the chip type PTC thermistor of the above-mentioned example and 10 chips of the chip type PTC thermistor of the comparative example were left in an atmosphere of 90 ° C. and a relative humidity of 95%, respectively,
The resistance values were measured after 0 hours, 300 hours, 500 hours and 1000 hours, respectively. The change in the measured resistance value is shown in FIG. As is clear from FIG. 3, the chip-type PTC thermistor of the example in which the insulating coating layer is formed has a resistance change rate reduced to ½ or less as compared with the chip-type PTC thermistor of the comparative example. .

In the chip-type PTC thermistor described above, the insulating coating layer was formed on the entire area of the end surface of the thermistor element body excluding the portion where the internal electrodes were exposed, but the insulating coating layer remained. It may be formed in a part of the region. That is, at the end face of the thermistor element,
As long as the insulating coating layer is provided between the external electrode and the thermistor element body in at least a part of the remaining region except the portion where the internal electrode is electrically connected, the external electrode and the thermistor element body It is possible to reduce various problems caused by the contact between the two compared to a chip type PTC thermistor in which the insulating coating layer is not formed.

Further, in the illustrated embodiment, one first internal electrode 13 and one second internal electrode 14 are formed, but a plurality of first and second internal electrodes are arranged respectively. The present invention can be applied to a chip type PTC thermistor.

[0036]

According to the present invention, since the insulating coating layer is provided in at least a part of the region between the thermistor element body and the external electrode, the external electrode is provided in the portion where the insulating coating layer is provided. The electrical contact between the and the thermistor body is cut off. Therefore, since ohmic contact does not occur between the external electrode and the thermistor element in the portion where the insulating coating layer is interposed, the barrier is regenerated in the area, or the contact situation changes due to changes in the external environment. Never. Therefore, variations in resistance value can be reduced and life characteristics can be improved.

Further, in the chip type PTC thermistor of the present invention, since the characteristics are determined by the overlapping area and the distance between the first and second internal electrodes, compared to the conventional surface mountable chip type PTC thermistor, It is possible to reduce variations in resistance value and variations in characteristics between manufacturing lots. Therefore, according to the present invention, it is possible to provide a surface mountable chip type PTC thermistor with less variation in resistance value.

[Brief description of drawings]

1A and 1B are a perspective view and a vertical cross-sectional view of a chip type PTC thermistor of an embodiment, respectively.

FIG. 2 is a perspective view showing a state in which an insulating coating layer is formed on the thermistor element body in the example.

FIG. 3 is a diagram showing the results of the life characteristic test of chip PTC thermistors of Examples and Comparative Examples.

FIG. 4A and FIG. 4B are perspective views for explaining a conventional chip type PTC thermistor.

5A and 5B are a perspective view and a vertical cross-sectional view of a chip type PTC thermistor having internal electrodes that triggers the present invention.

6 is a plan sectional view for explaining the shape of internal electrodes in the chip PTC thermistor shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Chip type PTC thermistor 12 ... Thermistor element body 12a, 12b ... End face 13 ... 1st internal electrode 14 ... 2nd internal electrode 15, 16 ... Insulation coating layer 17 ... 1st external electrode 18 ... 2nd external electrode

Claims (1)

[Claims] 1. A thermistor element body made of semiconductor ceramics, and a first and a first formed in the thermistor element body and arranged so as to overlap with each other with the semiconductor ceramics interposed therebetween.
A second internal electrode, the first internal electrode is drawn out to one end face of the thermistor element body, the second internal electrode is drawn out to the other end face of the thermistor element body, and the first and second internal electrodes are provided. Between the first and second external electrodes formed on the end surface of the thermistor element body so as to be electrically connected to the electrodes, respectively, and between the end surface of the thermistor element body and the first and second external electrodes. A chip-type PTC thermistor, further comprising an insulating coating layer arranged so as to be interposed in at least a part of the region.