JPS642401Y2 - - Google Patents

Description

[Detailed explanation of the idea]

The present invention relates to a high power varistor with good heat dissipation and improved thermal shock resistance. In general, high-power varistors need to have good heat dissipation, and for this reason, conventionally, a varistor body made of ceramic powder is molded and sintered, and silver electrodes are formed on both sides of the varistor body, leaving an outer periphery on both sides. Electrode plates such as brass plates, copper plates, nickel plates, iron plates, etc., were soldered to provide a heat dissipation function. However, the 30~
Linear expansion coefficient is 3.5 to 5.0 in the temperature range of 300℃
×10 ^-6 cm/cm/°C, whereas the linear expansion coefficient of the electrode plate is 12 to 20 × 10 ^-6 cm/cm/°C, which is significantly different. In such cases, there is no problem with high-pressure products with VlmA/mm of 100 to 300 V because the crystal grains of the sintered body as the varistor body are very small at 5 to 50 μm, and the bond strength between crystal grains is strong. VlmA/mm is 10
For low pressure applications of ~50V, the crystal grains of the sintered body used as the varistor body are extremely large, measuring 50 to 200 μm, and the bond strength between crystal grains is significantly reduced, resulting in rapid temperature changes. When used as a component, the varistor body cannot follow the expansion and contraction of the electrode plate, causing a fatal problem of cracking and cracking, and it was an urgent task to resolve this defect. . The present invention was developed in view of the above points, and by using an alloy plate with a relatively small coefficient of linear expansion as the electrode plate, the varistor element can be stabilized for a long time without being destroyed even by thermal shock. The purpose is to provide a high power varistor that can exhibit its characteristics. An embodiment of the present invention will be described below. That is, as shown in the figure, a varistor element body 1 is formed by molding and sintering ceramic powder containing, for example, zinc oxide, tin oxide, barium titanate, strontium titanate, etc. as its main components, mixed with several other metal oxides.
A silver base is coated and baked on both sides, leaving an outer periphery, to form a silver electrode 2.The silver electrode 2 is made of, for example, nickel or iron as the main component, cobalt is added as needed, and further impurities such as manganese, silicon, or carbon are added to the silver electrode 2. The alloy electrode plate 3 has a linear expansion coefficient of 7×10 ⁻⁶ cm/cm/° C. or less in the temperature range of 30 to 300° C. and is bonded with solder 4. The high-power varistor constructed as described above uses an alloy electrode plate 3 having a coefficient of linear expansion of 7×10 ^-6 cm/cm/°C or less in the temperature range of 30 to 300°C as the electrode plate, and the varistor element 1 itself. Since the coefficient of linear expansion is set to be relatively similar to that of
This has the excellent advantage that the tensile stress between the alloy electrode plates 3 can be reduced and breakage of the varistor body 1 can be eliminated. Next, we will discuss the effects of the present invention based on experimental results. In other words, silver electrodes were formed on both sides of a zinc oxide varistor element body which was molded and sintered to a diameter of 21 mm and a thickness of 0.8 mm, with a rising voltage (VlmA) of 22 V, and each electrode plate shown in Table 1 was soldered to the silver electrodes. Table 2 shows the failure status of the varistor body as determined by the heat cycle test.

【table】

【table】

[Table] * Defect judgment: Visually inspected varistor body cracks, products with cracks As is clear from Table 2, conventional examples (E), (F), (G), (H)
In contrast, in the case of the present invention (A), (B), all of the products were defective after 2 to 10 times, and in the case of reference example (D), defects occurred after 10 times and all of the products were defective after 40 times. (C) is 100
There were no defects even during the initial cycle, demonstrating its excellent effectiveness. As described above, according to the present invention, the linear expansion coefficient of the silver electrodes formed on both sides of the nonlinear metal oxide varistor element body in the temperature range of 30 to 300°C is 7 × 10 ^-6 cm/cm. By soldering alloy electrode plates with a temperature of /°C or less, it is possible to obtain a high-power varistor that can exhibit stable characteristics for a long time without destroying the varistor element even when subjected to thermal shock.

[Brief explanation of the drawing]

The figure is a sectional view showing a high power varistor according to an embodiment of the present invention. 1... Varistor element body, 2... Silver electrode, 3... Alloy electrode plate, 4... Solder.

Claims (1)

[Scope of utility model registration request] A varistor element formed by molding and sintering a metal oxide, a silver electrode formed with outer edges left on both sides of the element, and a linear expansion coefficient in the temperature range of 30 to 300°C soldered to the electrode. High power varistor equipped with an alloy electrode plate of 7×10 ^-6 cm/cm/℃ or less.