JPH0316255Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention relates to a ceramic varistor, particularly the shape of a lead wire connected to an electrode formed on a varistor element, thereby improving thermal shock resistance.

[Technical background of the invention and its problems]

Conventionally, lead wires connected by soldering or the like to the electrodes of ceramic varistor elements containing zinc oxide as a main component have generally been used as they are, that is, having a circular cross section. However, when the entire varistor element is sheathed with resin after the lead wires are soldered, the thickness of the resin at the top of the lead wires becomes very thin compared to other parts.
When used in automobiles that require severe thermal shock resistance, that is, an operating temperature range of -55 to +150°C, cracks occur in the exterior resin, causing a decline in properties. Also, for example, JP-A-59-
It is also known that the lead wire portion to be soldered to the electrode of an electronic component is processed into a flat plate, such as the technique described in Japanese Patent No. 210631. Although this configuration has improved thermal shock resistance, it is difficult for solder to enter between the electrodes and the lead wires, resulting in weak soldering strength, and long-term thermal shock may cause the lead wires to peel off or cause the lead wires to break. It is difficult to completely remove the flux that has entered between the electrodes and when used at high temperatures, the residual flux decomposes and exposes the varistor element to a reducing atmosphere through the electrodes, causing characteristic deterioration. There were other problems. Furthermore, as shown in Figures 8 to 11, it is also possible to form the contact surface with the electrode in an elliptical, approximately semicircular, rhombus, or triangular cross section along the length of the lead wire, but these In this case, the contact with the electrode is unstable due to the wire contact, so it tends to tilt, and as shown in the figure, the thickness of the lead wire becomes thicker, and the outer resin layer becomes thinner, which has the drawback that cracks are more likely to occur.

[Purpose of invention]

This idea aims to improve thermal shock resistance by improving the shape of the lead wires connected to the electrodes of the varistor element.

[Summary of the invention] The varistor of this invention is a varistor that has a resin-sheathed varistor element in which lead wires are soldered to electrodes provided on the front and back surfaces, and the lead wires are wider than the thickness and are connected to the electrodes. The contact surface of the lead wire is characterized in that it has an unevenness provided in the length direction of the lead wire.

[Example of idea]

As shown in the cross-sectional view in Fig. 1, a silver electrode 2 with a diameter of 16 mm is baked on a ceramic varistor element 1 (diameter 20 mm x thickness 1 mm) whose main component is zinc oxide, and the contact surface with the silver electrode 2 is Lead wires 3 having a diameter of 1 mm and having a diameter of 0.5 mm and serrated in the length direction of the lead wires 3 were soldered to each other and covered with epoxy resin 4 to a maximum thickness of 4 mm. Figure 2 shows the cumulative number of cracks that occurred in the exterior resin when this varistor was subjected to a thermal shock test, and Figure 3 shows the cumulative number of peelings that occurred in the varistor electrode. rising voltage of
Figure 4 shows the rate of change in V1mA. In Figures 2 to 4, curve A shows the case of the above-mentioned embodiment of the present invention, curve B shows the conventional example (1) in which the 1 mmφ lead wire is used as is, and curve C shows the case with the electrode of the 1 mmφ lead wire. This shows a conventional example (2) in which the contact part was processed into a flat plate with a thickness of 0.5 mm, and the sample was otherwise prepared under the same conditions as the example of the present invention. Thermal shock test and high temperature load life test were conducted under the following conditions.

Thermal shock test: 50 minutes at -50°C → 50 minutes at +150°C, with a transfer time of 1 minute, and this is regarded as one cycle, and the relationship between the number of repetitions, the cumulative number of cracks generated, and the cumulative number of electrodes peeled off is shown.

High-temperature load life test The relationship between the application time and the rate of change in the rise voltage when the maximum allowable circuit voltage is applied at +150°C is shown.

As is clear from FIGS. 2 to 4, the number of cracks it takes to produce the same number of cracks in the exterior resin 4 of the varistor according to the embodiment of the present invention is approximately the same as that of the conventional example (2) which is processed into a flat plate. There is a difference of 20 to 30 times in the number of times until the same number of electrodes 2 are peeled off, and it is clear that they have excellent characteristics. Further, the rate of change in the rising voltage shown in FIG. 4 shows a characteristic that is much better than that of the conventional example (2), which is equivalent to the conventional example (1). The difference in these characteristics is that in the present invention, when the varistor electrode and the lead wire come into contact, the lead wire is in close contact with the electrode, and there is no instability like in the conventional example shown in Figs. 8 to 11, so it is stable. It can be soldered in a closed state, and since the space between the electrode and the lead wire is completely filled with solder, there is no residual flux. Furthermore, since the contact area is large, the soldering strength is high and the electrodes have a structure that is difficult to peel off.
Furthermore, since the thickness of the lead wire is reduced, a sufficient thickness of the exterior resin can be ensured and the occurrence of clutches can be suppressed. On the other hand, in conventional example (1), the lead wire is used as is, so cracks tend to occur in a short time.
In addition, the conventional example (2) in which the contact part with the electrode is processed into a flat plate has the disadvantage that peeling tends to occur due to residual flux between the electrode and the lead wire, and these are clear from Figures 2 to 4. .

In the above embodiment, a case was described in which the lead wire was processed into a sawtooth shape, but the lead wire 13 having a sine curve shape as shown in FIG. Exactly the same effect can be obtained by using the lead wire 33 made of a continuous circular arc as shown in the figure, or by using a combination of these.

[Effect of idea]

According to the present invention, it is possible to improve the thermal shock resistance of the varistor, and it is possible to provide a varistor whose characteristics are less deteriorated even when used at high to low temperatures.

[Brief explanation of the drawing]

1 to 7 show embodiments of the present invention.
Figure 2 is a cross-sectional view of the varistor, Figure 2 is a curve diagram showing the relationship between thermal shock cycles and the number of cracks in the exterior resin, Figure 3 is a curve diagram showing the relationship between thermal shock cycles and the number of electrodes peeled off, and Figure 4 is a curve diagram showing the relationship between thermal shock cycles and the number of electrode peelings. The figure is a curve diagram showing the relationship between the energization time and the rate of change of the rising voltage in a high temperature load test, Figure 5 is a cross-sectional view showing a state in which a lead wire according to another embodiment is placed on an electrode, and Figure 6 and FIG. 7 is a sectional view of another embodiment showing a state in which the lead wire is similarly placed on the electrode, and FIGS. 8 to 11.
The figure is a cross-sectional view showing a conventional lead wire placed on an electrode. 1... Varistor element, 2... Silver electrode, 3... Lead wire, 4... Epoxy resin.

Claims (1)

[Claims for Utility Model Registration] (1) A varistor in which a varistor element is coated with a resin and lead wires are soldered to electrodes provided on the front and back surfaces, and the lead wire is wider than the thickness thereof and is connected to the electrode. A varistor characterized in that a contact surface has unevenness provided in the length direction of a lead wire. (2) The unevenness provided in the length direction of the lead wire is serrated,
The varistor according to claim (1) of the utility model registration, characterized in that it has a sine curve shape, a continuous rectangular shape, a circular arc, or a combination thereof.