JPH09232105A - Thermistor element and thermistor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove stress caused by the cutting of a thermistor element and prevent chipping at the corners by rounding principal planes in which electrodes are formed and side faces of a thermistor element assembly which are adjacent to the principal planes. SOLUTION: Corners 28, 29 which are formed by principal planes in which electrodes 26, 27 are formed and side faces of a thermistor element assembly 25 which are adjacent to the principal planes are rounded. At that time, the ends of the electrodes are also rounded together with the corners 28, 29. Therefore, the electrodes 26, 27 are not formed in the rounded corners 28, 29. As a method for rounding, a barrel polishing method is used. By this method, residual stress near side faces 30, 31, 32 due to dicing is removed and microcracks generated in the interfaces between parts of the thermistor element assembly 25 which are near the corners 28, 29 and the electrodes 26, 27 are eliminated. Furthermore, the barrel-polished thermistor element 21 can have the increased adhesion between the thermistor element 25 and the electrodes 26, 27.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermistor element having a highly accurate resistance value and a thermistor using the element.

[0002]

2. Description of the Related Art A conventional thermistor element of this type will be described with reference to FIGS. Electrodes 3 and 4 are formed on both main surfaces of a large plate-shaped thermistor wafer 2 made of ceramic, and then the alternate long and short dash lines A and B shown in FIG.
Is diced along. Each piece divided by dicing is the thermistor element 1. Therefore, the thermistor element 1 has a hexahedral shape and is provided with a pair of electrodes 6 and 7 on both main surfaces of the thermistor element body 5.

[0003]

However, in the thermistor element 1, the corners 8 and 9 formed by the thermistor element body 5 and the end portions of the electrodes 6 and 7 are formed into a right angle and cut by dicing. The stress remains on the side surfaces 10, 11, 12, 13 of the thermistor element 1. Further, at the interfaces between the thermistor element body 5 and the electrodes 6 and 7 in the vicinity of the corners 8 and 9, microcracks are inherently present due to dicing, and the adhesion strength is lowered.

Therefore, the corners 8 and 9 of the thermistor element 1 are
Has a problem that when the thermistor element 1 is handled, it is likely to be chipped when it comes into contact with something, and the chipping reduces the area of the electrodes 6 and 7 and increases the resistance value of the thermistor element 1. Furthermore, the adhesion strength between the ceramic body 5 and the electrodes 6 and 7 at the corners 8 and 9 is low, the electrical connection is unstable, and the reliability of the load test such as the temperature cycle test is lowered. There was a point.

Further, a thermistor in which a lead terminal is connected to the electrode of the thermistor element 1 and the thermistor element 1 is covered with insulation also has the same problems as those of the thermistor element 1 described above.

The object of the present invention is to eliminate the above-mentioned problems, and it is difficult for the thermistor element to have the corners without chipping, the electrode adhesion strength is stable, and the resistance value is highly accurate and reliable. An object is to provide an element and a thermistor using the element.

[0007]

In order to achieve the above object, in a thermistor element of the present invention, a plate-like thermistor element body made of ceramic and a pair of thermistor element bodies formed on opposing main surfaces thereof. And the side surface of the thermistor element body adjacent to the main surface on which the electrode is formed is rounded.

Further, the thermistor of the present invention comprises the above-mentioned thermistor element and a lead terminal electrically connected to the electrode of the thermistor element, and the thermistor element is insulated and coated. As a result, the stress due to the cutting of the thermistor element can be eliminated, the chipping of the corner portion where contact and collision are likely to occur can be prevented, and the portion where the adhesion strength between the thermistor element body and the electrode is weak can be removed.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION One embodiment of a thermistor element according to the present invention will be described with reference to FIGS. The thermistor element 21 is, for example, Mn—Ni.
The conventional thermistor shown in FIG. 5 in which an electrode containing Ag as a main component is formed on a ceramic body 5 having negative characteristics and made of a ceramic raw material containing —Co as a main raw material and Al, Fe, Cu, etc. The corners 8 and 9 of the element 1 are rounded. That is, in the thermistor element 21, as shown in FIGS. 1 and 2, a pair of electrodes 26 and 27 are formed on both main surfaces of the thermistor element body 25 which face each other, and the electrode 2
Corners 28, 2 formed by the main surface on which 6 and 27 are formed and the side surface of the thermistor element body 25 adjacent to this main surface.
9 is integrally rounded including the ends of the electrodes 26 and 27. Therefore, as shown in FIG.
In the rounded portion 29, the thermistor element 21 does not include the electrodes 26 and 27.

Barrel polishing is preferably used as the rounding method, and the thermistor element 21 whose corners 28, 29 are rounded by barrel polishing cannot be shown in FIGS. 1 and 2, but the side surfaces 30, 31, Residual stress due to dicing near 32 and 33 is eliminated, and the thermistor element body 2 near corners 28 and 29 is removed.
The microcrack portion generated at the interface between the electrode 5 and the electrodes 26 and 27 is removed. Furthermore, the barrel-polished thermistor element 21 has the effect of further increasing the adhesion strength between the thermistor element body 25 and the electrodes 26, 27 due to the collision of the electrodes 26, 27 with a cobblestone or the like.

Next, one embodiment of the thermistor according to the present invention will be described in detail with reference to FIG.
The thermistor 41 includes the electrodes 26, 2 of the thermistor element 21.
7, the ends of lead terminals 42, 43 made of, for example, soldered annealed copper wires are electrically connected by solders 44, 45, etc., and the thermistor element 21 together with the connecting portions of the lead terminals 42, 43 is, for example, resin-molded. Insulation coating is carried out by 46.

An example of a method for obtaining the thermistor element 21 will be described below. The size shown in FIG. 5 is 1 × 1 ×
20,000 0.5mm thermistor elements 1 and φ3
~ Φ5mm boulder 600g and water 350g φ110
mm barrel × height 100 mm barrel, 22 barrel
The thermistor element 1 was polished by rotating at 0 rpm.

Table 1 shows the relationship between the barrel polishing time and the roundness of the corners 28 and 29 (represented by the radius R) of the thermistor element 21 obtained by changing the polishing time. It can be seen from Table 1 that the longer the barrel polishing time, the larger the roundness of the corners.

[0014]

[Table 1]

Table 2 shows the adhesion strength of the electrodes 26 and 27 of the thermistor element 21 obtained by the above-mentioned barrel polishing. As a comparative example, Table 2 shows the adhesion strength of the electrodes 6 and 7 in the conventional thermistor element 1. As is clear from Table 2, the adhesion strength of the electrode according to the present invention was 34% on average and 67% higher than the adhesion strength of the conventional example.

[0016]

[Table 2]

Next, Table 3 shows the chipping occurrence rate, the resistance value variation (R variation), and the room temperature resistance value change rate (working change rate) during processing of the thermistor element 21 into the thermistor 41. Further, Table 3 also shows the rate of change in resistance value by the temperature cycle test. The condition of the temperature cycle test (referred to as HCT) in Table 3 is −55 ± 3.
One cycle consists of holding each of the air at 30 ° C., room temperature and 125 ± 2 ° C. for 30 minutes, which is repeated 100 times. Further, 3CV in Table 3 is an index representing the degree of variation of the set, and is defined as 3CV = 3σ / X, where X is the average value of the set and σ is the standard deviation.

[0018]

[Table 3]

The rounded corners 28 and 29 of the thermistor element 21 shown in Tables 2 and 3 have similar effects as long as R is 0.02 mm or more. In addition, the amount of boulders to be put into the barrel is 600 ± 50g, and the amount of water is 350 ± 50.
g, if the rotation speed of the barrel is in the range of 220 ± 40 rpm, the corner portion 2 of the thermistor element 21 is the same as in the above-described embodiment.
It is possible to add roundness to 8 and 29.

Further, although the thermistor element 21 and the thermistor 41 have been described based on the negative characteristic thermistor, they may be applied to the positive characteristic thermistor, and even if they are electronic parts other than the thermistor, both main surfaces of the ceramic element are used. Any electronic component in which a pair of electrodes is formed can be applied.

[0021]

As described above, in the thermistor element according to the present invention, the corners between the main surface on which the electrode is formed and the side surface of the thermistor element body adjacent to this main surface are rounded. In addition, even if the thermistor elements are in contact with each other or other than the thermistor element, chipping such as chipping of the corners does not occur, handling of the thermistor element is easy and the area of the electrode formed on the thermistor element is reduced. Without doing so, the rate of change of resistance decreases.

Further, since the portion where the electrode adhesion strength near the corner of the thermistor element is weak is removed, the electrode adhesion strength becomes constant, and the rate of change in the resistance value of the thermistor element due to a load test or the like decreases, and the thermistor element is reduced. The reliability of the device is improved.

Further, in the thermistor according to the present invention, since the thermistor element having rounded corners is used, it is possible to obtain the same effect as that of the above-described thermistor element.

[Brief description of drawings]

FIG. 1 is a perspective view of an embodiment of a thermistor element 21 according to the present invention.

FIG. 2 is a sectional view of FIG.

FIG. 3 is a partial cross-sectional view of one embodiment of a thermistor 41 using the thermistor element 21 of FIG.

FIG. 4 is a perspective view of a conventional thermistor wafer 2 on which electrodes 3 and 4 before dicing are formed.

FIG. 5 is a perspective view of a conventional thermistor element 1.

[Explanation of symbols]

 21 thermistor element 25 thermistor element body 26, 27 electrode 28, 29 corner 41 thermistor 42, 43 lead terminal

Claims (2)

[Claims] 1. A plate-like thermistor element body made of ceramics and a pair of electrodes formed on opposing main surfaces of the thermistor element body, the main surface having the electrodes and the main surface A thermistor element having rounded corners with the side surface of the thermistor element body adjacent to the main surface. 2. A thermistor comprising the thermistor element according to claim 1 and a lead terminal electrically connected to an electrode of the thermistor element, wherein the thermistor element is insulation-coated.