JPH09129404A - Chip-type varistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a chip-type varistor to be surely kept in an open state when it is broken down by a method wherein a groove is provided to the upper surface of a molding resin along the outer circumference of a lead terminal. SOLUTION: When an abnormal high voltage which a ceramic varistor device 21 is not able to withstand is applied to it, it is broken down. The varistor device 21 grows high in temperature, its composition is partially vaporized to produce gas of high pressure and temperature. The pressure of the gas acts on a molding resin 25 so as to break it, a fissure is opened along a groove 26, and the molding resin 25 is sheared off. The molding resin 25 on the upside of the ceramic varistor device 21 is separated off together with a lead terminal 23b by the pressure of gas just as a lid is opened, whereby the ceramic varistor device 21 is kept in an electrically opened state. By this setup, a chip-type varistor which is surely kept in an open state when it gets out of order can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chip type varistor used as a countermeasure against an abnormal voltage that absorbs a surge voltage generated in a power supply circuit of a television receiver, a washing machine, an automobile electrical equipment and the like.

[0002]

2. Description of the Related Art In FIG. 15 and FIG. 16, 11 is a varistor element. 12a and 12b are electrodes provided on the main plane of the varistor element 11, 13a and 13b are lead terminals, 14
a and 14b are electrodes 12a and 12b and lead terminals 13a,
It is a conductive adhesive that connects 13b. Reference numeral 15 is a mold resin. The operation of the chip-type varistor having the above structure will be described below.

First, when an abnormally high voltage that the varistor element 11 itself cannot withstand is loaded, the varistor element 11 is
Causes penetration failure.

[0004]

In the above conventional structure, the mold resin 15 is covered, and when the varistor element 11 breaks through, the high pressure gas generated therewith breaks the mold resin 15 and the varistor is generated. The conduction between the element 11 and the lead terminals 13a and 13b is cut off. However, depending on where the mold resin 15 is destroyed, the varistor element 1
1 had a problem that it might not be in an open state.

The present invention solves the conventional problems, and an object of the present invention is to ensure that the varistor element 11 will be in an open state when it is broken through.

[0006]

In order to achieve this object, the chip type varistor of the present invention achieves the initial purpose by providing a groove on the upper surface of the mold resin along the outer circumference of the lead terminal. is there.

[0007]

According to the invention described in claim 1 of the present invention, the mechanical strength of the groove portion provided on the upper surface of the mold resin is weaker than that of the portion having no groove. Therefore, when the varistor element breaks through, it is sheared from the groove portion by the pressure of the generated gas, and the mold resin on the upper surface of the lead terminal is peeled off so that the lid opens together with the lead terminal. Therefore, the electrode and the lead terminal are electrically opened.

(Embodiment 1) FIG. 1 is a top view of a chip type varistor in an embodiment of the present invention, FIG. 2 is a top perspective view, and FIG. 3 is a sectional view taken along line AA of FIG. In FIG. 3, reference numeral 21 is a zinc oxide-based ceramic varistor element. Reference numeral 22 is an electrode provided on the main plane of the ceramic varistor element 21, and 23a and 23b are lead terminals. Reference numeral 24 is a conductive adhesive that electrically connects the electrode 22 and the lead terminals 23a and 23b. Reference numeral 25 is a molding resin made of epoxy insulating resin which covers the entire varistor, and 26 is a groove provided on the upper surface of the molding resin 25 along the outer periphery of the lead terminal 23b. The operation of the varistor configured as above will be described with reference to the drawings.

Although the ceramic varistor element 21 is a good insulator in the steady state, the ceramic varistor element 21 is
When an abnormally high voltage that cannot be endured by itself is applied, the ceramic varistor element 21 causes breakthrough. At this time, the destroyed ceramic varistor element 21 becomes high in temperature and a part of the composition evaporates. Along with this, high temperature and high pressure gas is generated. The pressure of this gas acts to destroy the mold resin 25, causes a crack along the groove 26 having weak mechanical strength, and causes shearing, and the pressure of the gas causes the mold resin on the upper surface of the ceramic varistor element 21 together with the lead terminal 23b. 25 is peeled off so that the lid is opened, and is electrically opened. FIG. 4 and FIG. 5 show a state in which the mold resin 25 on the upper surface is peeled off so that the lid is opened together with the lead terminal 23b in the present embodiment. FIG. 6 is a top view of the lead terminals 23a and 23b used in this embodiment, and FIG. 7 is a side view of the same. The resistance value of the chip-type varistor in this example after the through-breakage is compared with the resistance value of the conventional chip-type varistor after the break-through in (Table 1). It should be noted that the ceramic varistor element 21 is applied with a voltage twice the maximum allowable voltage to cause overvoltage breakdown.

[0010]

[Table 1]

As is clear from this (Table 1), it can be seen that the chip-type varistor according to the present invention has an open resistance value after breakage. As described above, in the present embodiment, the groove 26 is provided on the upper surface of the mold resin 25 along the outer periphery of the lead terminal 23b.
The failure mode of the chip type varistor when 1 is pierced and broken can be set to an open state.

(Second Embodiment) In FIGS. 8 to 10, 3
1 is a ceramic varistor element, 32 is an electrode, 33a, 3
3b is a lead terminal, 34 is a conductive adhesive, 35 is a mold resin, and 36 is a groove on the upper surface of the mold resin 35, which has the same configuration as in the first embodiment. The difference from the first embodiment is that the ceramic varistor element 3 is connected to the lead terminal 33b.
This is the point that 1 has a spring property so that it is easy to separate when it breaks through. FIG. 13 shows the lead terminal 3 used in this embodiment.
3a and 33b are top views and FIG. 14 is a side view thereof. 45 from the middle of the lead terminal 33b used in this embodiment.
Since it is bent at an angle of °, when it is pressed toward the ceramic varistor element 31 side and covered with the mold resin 35, spring properties are exhibited. 11 and 12, when the ceramic varistor element 31 in this embodiment is pierced and broken, the mold resin 35 on the upper surface of the electrode 32 of the ceramic varistor element 31 is peeled off along with the groove 36 so that the lid opens along with the lead terminal 33b. A state diagram is shown.

The operation of the chip type varistor constructed as described above will be described with reference to the drawings. The process until the lead terminal 33b shears the mold resin 35 due to the through breakage of the ceramic varistor element 31 is the same as in the first embodiment.
The same as the lead terminal 3 used in the second embodiment.
Since 3b has a spring property, the opening angle of the lead terminal 33b peeled off due to the pressure of gas is large.
It is shown that the open state can be achieved more reliably than in the case of.

Table 1 shows the resistance value of the chip type varistor in the second embodiment after the breakthrough and the resistance value of the conventional chip type varistor after the breakthrough. As is clear from this (Table 1), the chip-type varistor according to the second embodiment is more reliable in the failure mode of the chip-type varistor after the ceramic varistor element 31 is pierced by breaking the lead terminal 33b used. You can see that it can be opened.

[0015]

As described above, according to the present invention, it is possible to provide a chip type varistor that is reliably opened when a failure occurs.

[Brief description of the drawings]

FIG. 1 is a top view of a chip type varistor according to a first embodiment of the present invention.

FIG. 2 is a top perspective view of the chip varistor according to the first embodiment.

FIG. 3 is a sectional view taken along line AA of FIG. 1;

FIG. 4 is a top view showing a broken state of the chip type varistor according to the first embodiment.

FIG. 5 is a sectional view taken along line AA of FIG. 4;

FIG. 6 is a top view of the lead terminal according to the first embodiment.

FIG. 7 is a side view of the lead terminal according to the first embodiment.

FIG. 8 is a top view of a chip type varistor according to Embodiment 2 of the present invention.

FIG. 9 is a top perspective view of the chip type varistor according to the second embodiment.

10 is a cross-sectional view taken along the line AA of FIG.

FIG. 11 is a top view showing a broken state of the chip type varistor according to the second embodiment.

FIG. 12 is a sectional view taken along line AA of FIG. 11;

FIG. 13 is a top view of the lead terminal according to the second embodiment.

FIG. 14 is a side view of the lead terminal according to the second embodiment.

FIG. 15 is a top perspective view of a conventional chip-type varistor.

16 is a cross-sectional view taken along the line AA of FIG.

[Explanation of symbols]

 21 Ceramic Varistor Element 22 Electrode 23b Lead Terminal 25 Mold Resin 26 Groove

Claims (2)

[Claims] 1. A resin mold which covers a varistor element, an electrode provided on the main plane, a lead terminal electrically connected to the electrode, and a connection portion between the varistor element and the electrode and at least the electrode of the lead terminal. And a groove provided on the upper surface of the mold resin along the outer periphery of the lead terminal. 2. The chip type varistor according to claim 1, wherein the lead terminal has a spring property.