JPS6150301A - Variator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a varistor used in various electronic devices, and provides a high-performance varistor that protects the energy barrier between a silver electrode and a varistor element. be.

Conventional configurations and their problems In recent years, the use of semiconductors in the electric circuits of home appliances and industrial equipment has significantly progressed, and surge protection for semiconductor electronic components, which are the main components thereof, has become essential. Generally, metal oxide varistors with high voltage nonlinearity and high surge resistance are used to suppress surge voltages. However, currently, the driving voltage of semiconductor electronic components is decreasing, and most of them are below 10V. Along with this, the market is demanding varistors with high surge suppression performance for low voltage circuits.

The configuration of a conventional varistor will be described below with reference to the drawings.

FIG. 1 is a front view of a conventional varistor, and FIG. 2 is a sectional view thereof. In FIGS. 1 and 2, 1 is a varistor element made of a metal oxide, and the fl support is a sintered body containing zinc oxide as a main component. 2a and 2b are silver electrodes provided on the variable surface element 1, which are vapor deposited.

The burn-in is formed by processing or the like. 3a and 3b are lead wires taken out from the silver electrodes 2a and 2b. 4a,
4b connects the lead wires 3a and 3b to silver electrodes 2&, 2b
This is solder to fix it. Generally, the connection between the varistor element 1 and the lead wires 3a, 3b is made by sandwiching the silver electrodes 21L, 2b on the iZ+) star element 1 between U-shaped lead wires with crossed tips, and dipping the entire electrode surface in a solder bath. It is done by.

Incidentally, a metal oxide varistor and an electrode formed on its surface generally have an energy barrier due to a difference in work function. For example, the energy barrier between a metal oxide type varistor and a silver electrode is 3.0 to 4.0 V on both sides, and this value always remains constant regardless of the varistor voltage (vlmA). However,
This energy barrier is largely destroyed by soldering the entire surfaces of the silver electrodes 1a and 2b, resulting in deterioration of various characteristics of the varistor element 1. The variables most strongly affected by this are the varistor voltage (v1Tnm) and the limiting voltage ratio. By soldering the entire surface of the silver electrode, the varistor voltage is reduced by about 3 to 4 V at maximum.

This phenomenon occurs when the varistor voltage is high.
! ″″:e6″′ln;/+Z・(KtlEz' !J
2 z% [′< ! When the I, t, and p voltages are 30 V or less, variations in varistor voltage increase, which is the main cause of yield reduction.

Furthermore, the limiting voltage ratio, which is one of the most important characteristics of a varistor, also deteriorates significantly. The limiting voltage ratio is the value obtained by dividing the limiting voltage by the varistor voltage (v1□person), and when current is passed through the varistor, the voltage (limiting voltage) generated in varistor element 1 is V & , vaA/v11nA However, &A) +mA. Here, the varistor element 1 and the silver electrodes 21L, 2b
The reason for the deterioration of the limiting voltage specific voltage due to the energy barrier breakdown between the two will be explained. Now, the varistor voltage is vl, the limiting voltage is vl, and the energy barrier between the silver electrodes 2a, 2b and the varistor element 1 is V. (Assuming that it does not change depending on the current), the limiting voltage ratio of the conventional varistor is V, /V, ...... (
1). 0 in the presence of an energy barrier
) is expressed as the limiting voltage of an element with the same varistor voltage. Dividing equation (2) by equation (1) gives us the following.

By definition, V, > v+, so the formula 0) takes a value smaller than 1. From equation 0), it can be seen that the larger the energy barrier between the silver electrodes 21L, 2b and the varistor element 1, the better the limiting voltage ratio. In the conventional varistor, the energy barrier between the silver electrodes 2a, 2b and the varistor element 1 is lowered because the entire silver electrode is soldered, and the limiting voltage ratio is deteriorated.

Purpose of the Invention The present invention has been made in view of the above drawbacks, and involves forming an upper surface electrode of a metal other than silver over the entire silver electrode on a varistor element, and soldering a lead wire to this upper surface electrode. It is an object of the present invention to provide a varistor which can be manufactured with good yield and has a good limiting voltage ratio.

Structure of the Invention In order to achieve the above object, the varistor of the present invention provides an upper surface electrode made of at least one kind of metal other than silver on the entire upper surface of the silver electrode formed on both sides of a varistor element made of a metal oxide. A series lead wire is connected to the top electrode by solder, and this structure protects the energy barrier between the silver electrode and the varistor element, making it possible to obtain a high-performance varistor.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a sectional view of a varistor in one embodiment of the present invention. In FIG. 3, 5 is a varistor element, 61, eb
are silver electrodes and are the same as in the conventional example. 7a
, 7b are upper electrodes provided on the entire surface of the silver electrodes 6a and eb, and are made of one or more metals other than silver, such as kl, Cu.
, Ni, Pd, Mu, etc., and is provided by vapor deposition or spackling. a&, 8b are lead wires, and upper surface electrodes 7&, 7 are connected by soldering 9a, 9b.
It is fixed at b.

When manufacturing the varistor of the present invention as described above, after forming the upper surface electrodes 7a and 7b, similar to the conventional example, the lead wires 8N,
The element is sandwiched between 8b and dipped into a solder bath. Here, it is necessary that the upper surface electrodes 7a, 7b almost completely cover the silver electrodes 6a, 6b, and in the case of porous electrodes, when soldering, the solder 9&, 9b will cover the silver electrodes 6m, 6b.
penetrates into the environment and causes deterioration of properties. Therefore, electrode formation methods such as metallicon are inappropriate.

The effects of the present invention will be shown together with experimental results. The varistor element 5 used is a sample of the same type having a varistor voltage (V+.A) of 22v1 and an element diameter of 20φ.

The temperature of the solder bath was 230° C. and the dipping time was about 2 seconds. The value is the average value of n=10. Deterioration voltage value of vjmA and limiting voltage ratio (V, .A/v1.1llA)
is as shown in the table below.

(The following is a blank space) As can be seen from this table, compared to the conventional example, the varistor according to the present invention shows almost no deterioration in the varistor voltage and the limiting voltage ratio. Therefore, it is possible to eliminate variations in voltage deterioration caused by the soldering process as in the conventional example.

Effects of the Invention As described above, the risk of the present invention is that it is possible to prevent the energy barrier formed between the silver electrode and the varistor element from being destroyed by solder dip, thereby suppressing the drop in varistor voltage. , it is possible to prevent deterioration of the limiting voltage ratio and obtain a predetermined /〈risk with good yield, and its utility value is very high.

[Brief explanation of drawings]

FIG. 1 is a front view of a conventional varistor, FIG. 2 is a sectional view thereof, and FIG. 3 is a sectional view of a varistor according to an embodiment of the present invention. 5... Varistor element, sa, eb... Silver electrode, 7! L, 7b...Top electrode, 82L, 8b
...Lead wire, 9a, gb mark, solder. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
figure

Claims (2)

[Claims] (1) A varistor formed by providing a top electrode made of at least one metal other than silver on the entire top surface of a silver electrode formed on both sides of a varistor element made of a metal oxide, and connecting a lead wire to the top electrode by solder. . (2) The varistor according to claim 1, wherein the upper surface electrode is formed by either vapor deposition or sputtering.