JPS60142503A - Varistor - 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 Field of the Invention The present invention relates to a type of varistor, such as a chip-shaped or ring-shaped varistor, in which electrodes are directly soldered without applying an exterior resin mold or the like.

A varistor has a 41F characteristic in which the resistance value decreases dramatically in a range where the applied voltage exceeds the varistor voltage (limiting voltage) of the element. Taking note of this specificity, varistors are widely used as a means for noise prevention 11- of small DC motors related to audio equipment, protection of relay contacts, discharge absorption of color TV cathode ray tube circuits, and the like.

Prior Art In varistors in which the varistor body I'' has varistor properties, such as titanium oxide (TiOz)-based, strontium titanate (SrTi03)-based, and zinc oxide (ZnO)-based varistors S, the sintered body itself In order to fully exhibit the varistor characteristics of the varistor, as shown in FIG. 11, an electrode 2 is formed in ohmic contact with the varistor body 1. Such ohmic contact′
The electrode 2 generally has silver as a doping component, and a fine 1i1 gold + irj component 1, for example, Indium, to help form an ohmic contact.
, Ga, Sn, Sb, Cd, Zn, AI, etc., and apply these to the surface of the varistor element by means of screen printing, IJ, and burnout. It is formed.

In addition, in order to compensate for the solder contact of this ohmic contact (city pole 2) and to supplement the strength of the ohmic contact, as well as to prevent the deterioration of the ohmic contact due to oxidation, as shown in Figure 2, the ohmic contact is It has also been common practice to apply silver paste to 4- of the contact electrode 2 by means such as screen printing to form a protective electrode 3.

Disadvantages of the Prior Art However, conventional varistors have the following drawbacks.

(b) Since the ohmic contact electrode 2 and the protective electrode 3 also contain a large amount of silver, the silver contained in the electrode 2.3 diffuses into the solder during soldering. ] A chipping phenomenon occurs, leading to a decrease in the adhesive strength between the electrode and the varistor body and deterioration of the electrical characteristics.

(b) As a means of strengthening the adhesion of Ti and electrodes, it is possible to make the electrodes thicker. However, if the electrodes are made thicker, the amount of silver, which is a precious metal material, will be increased, resulting in higher costs.

(c) Another method to strengthen the adhesive force of the electrode is to increase the frit content, but in this case, the diffusion of the varistor element into the grain boundaries increases, making it impossible to maintain the varistor properties. Only extremely limited characteristics can be obtained, and reliability deteriorates.

Purpose of the tree invention The tree invention solves the conventional problems mentioned in -1;N6
1JI 4rI can prevent the decrease in adhesive strength of electrodes and the deterioration of electrical characteristics due to E1, and moreover, half +4
The purpose of this research is to provide an electrode with good performance and low cost.

DISCLOSURE OF THE INVENTION In order to achieve the object described above, the present invention is characterized in that it comprises an electrode having a paint layer with good solderability and corrosion resistance.

Embodiment FIG. 3 is an IE side view of a varistor according to the present invention. In the figure, 1 is a varistor element. In this embodiment, the varistor element l is a sintered body that exhibits varistor 4-v properties, such as a ZnO system, a TlO2 system, or a 5rTi03
It is composed of a sintered body.

Reference numeral 2 denotes a contact electrode of the ohm 1 formed flush with the varistor body 1. As described above, the ohmic contact electrode 2 has silver as its main component, and a trace amount of metal components that help make the ohmic contact, such as In, Ga, Sn, and Sb.
, Cd, Zn, AI, etc., are applied to the surface of the varistor body l together with a frit by means such as screen printing, and then baked.

3 is a plated layer having good solderability and corrosion resistance, and is formed on the surface of the ohmic contact electrode 2 so as to cover it. Such a plating layer 3 is made of, for example, Ni
, Cu, Sn, or chemical plating such as solder. In this embodiment, the plating layer 3 includes a first plating layer 31 having excellent semi-corrosion resistance and a first plating layer 31 formed to cover the surface of the ohmic contact electrode 2, and a first plating layer 31 formed on the surface of the plating layer 31. The second plating layer 3 has good soldering properties.
It is boiled in two layers. The plating layer 31 is made of Ni
Alternatively, the plating layer 32 is formed by chemical plating such as Cu, and has good solderability, and is formed by Cu, Sn or solder plating.

As described in , the varistor according to the present invention has an electrode structure that is
Since the structure has a plating layer 3 with good soldering properties and solder corrosion resistance, titanium oxide (Ti02), for example, can be used.
For varistors in which the varistor body itself has varistor characteristics, such as the risk of strontium titanate (SrTi03) and 11i lead oxide (Zn0) systems, it is necessary to fully utilize the varistor characteristics of the sintered body itself. Even when an ohmic contact conductor J412 made of a silver alloy is formed on the varistor element body in order to achieve the desired effect, the half-]]1-eating phenomenon does not occur.

Therefore, it is possible to prevent a decrease in the adhesive strength between the ohmic contact electrode 2 and the risk element 1 and to prevent deterioration of the electrical characteristics.

In addition, the plating layer 3 can be formed by chemical plating such as NI, Cu, Sn or semi-111.
Electrode formation cost is low. Moreover, since the plating layer 3 can be easily formed in mass production by chemical polishing, it is highly workable.

FIG. 4 shows another embodiment of the varistor according to the invention, in which a Ni coating layer 311 and a Cu coating layer 1- of the ohmic contact electrode 2 are shown.
A first plating layer 31 consisting of a plating layer 312 having excellent semi-UJ corrosion resistance is formed, and a second plating layer 31 having good solderability and being formed by chemical plating of Cu is formed on the surface of this plating layer 31. The electrode structure includes a plating layer 32. Although not shown, the first plating layer 31 includes a Cu plating layer provided on the ohmic contact electrode 812, and a Ni plating layer on the -1- side.
A structure including a plating layer may also be used. Further, the second plating layer 32 is also 9 mm.

It may be formed by Sn plating or solder plating instead.

In addition, in the embodiment described above, an electrode is provided on one side of the varistor body 1.
, 3, but on one or both sides of the ballista body l? The present invention can be similarly applied to other electrode structures, such as an electrode structure having a number of divided electrodes. Furthermore, the shape of the varistor body l is not limited to that shown in the embodiment. Furthermore, it is not limited to varistors in which the element body itself exhibits varistor properties, but also silicon type (Sin) type varistors that obtain varistor properties at the contact surfaces between the particles of the sintered body, and the sintered body itself is a linear resistor. It is also possible to apply the present invention to other types of varistors, such as those based on tin oxide (SnO→) and iron oxide (Fe, 203), which obtain varistor characteristics depending on the state of contact with the electrodes.

Figure 5 is a graph showing the relationship between soldering time and electrode adhesion strength. In Figure 6, curve A is the characteristic of the varistor according to the present invention having the structure shown in Figure 4, and curve B is the graph shown in Figure 2. This is a characteristic of conventional varistors.

As is clear from Fig. 5, in the conventional varistor,
In the case of half-day one, when the time becomes 1- every 5 seconds, the adhesive strength of the electrode decreases rapidly, and after 20 seconds, the adhesive strength becomes zero (JXt), but the varistor according to the present invention The adhesive strength of the electrode hardly deteriorates even after 30 seconds of attachment.

In view of the effects of the present invention (-), the varistor according to the present invention is equipped with an electrode having a plating layer with good scratch resistance and semi-corrosion resistance. Because of its characteristics, it is possible to prevent the low adhesion strength of the electrode and the deterioration of electrical characteristics caused by half-FH attachment, and the half-FH bonding has good properties and low cost I. A varistor having a flexible electrode can be provided.

[Brief explanation of drawings]

FIG. 1 is a front view of a conventional varistor, FIG. 2 is a hemostatic diagram in another conventional example, FIG. 3 is a front view of a varistor according to the present invention, and FIG. 4 is a front view in another embodiment.
FIG. 5 is a diagram showing the relationship between time and electrode bonding strength. l...Varistor element body 2φ...Ohmic contact electrode 3・ψ・Plating layer 31・Medium・Plating layer with solder corrosion resistance 32...Plating layer with good soldering properties Fig. 1 2 Figure 2 Figure 3 Figure 41.1 Figure 5 "Roshii?" r1 o'clock I! treetops

Claims (6)

[Claims] (1) A varistor characterized by comprising an electrode having a plating layer having good solder corrosion resistance and solder corrosion resistance. (2) The plating layer is characterized by having a multilayer structure of a plating layer having excellent -1J solder corrosion resistance and a plating layer having good solder resistance formed on the plating layer 1-. A varistor according to claim 1. (3) Ij: The plating layer I is made of N1, Cu, Sn or half IB plating. Barista. (4) /<The varistor according to claim 1, 2 or 3, wherein the ristor body itself exhibits varistor characteristics. (5) The varistor according to claim 4, wherein the varistor body is made of TiOz, 5rTi03, or ZnO-based sintered body. (6) Claim 4 or 5, characterized in that the varistor body has an ohmic contact electrode on its surface, and the coating layer is provided on L of the ohmic contact electrode.
Barista as described in section.