JPH0132322Y2 - - 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 × 20 × 10 ^-6 cm/cm/°C, which is significantly different. In such cases, there is no problem with high-pressure products with V1mA/mm of 100 to 300V because the crystal grains of the sintered body as the varistor element are very small at 5 to 50 μm, and the bond strength between the crystal grains is strong. V1mA/mm
For low pressure applications of 10 to 50 V, the crystal grains of the sintered body used as the varistor body are extremely large, measuring 50 to 200 microns, and the bonding strength between crystal grains is significantly reduced, resulting in rapid temperature changes. When used as an electronic component or an electronic component that generates heat due to high power use, such as a power supply for medical equipment X-rays, a switchboard, or an electronic component for dry electronic copying, the varistor body cannot follow the expansion and contraction of the electrode plate, resulting in cracks and cracks. It has the drawback of causing a fatal problem, and resolving this drawback was an urgent task. 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 Figs. 1 and 2, it is made by molding and sintering ceramic powder containing zinc oxide, tin oxide, barium titanate, strontium titanate, etc. as the main ingredients, mixed with several other metal oxides. Silver electrodes 2 are formed by coating and baking a silver base on both sides of the varistor body 1, leaving the outer periphery on both sides, and one of the silver electrodes 2 is coated with nickel, for example.
The main component is iron, cobalt is added as necessary, and trace amounts of manganese, silicon, carbon, etc. are added as impurities.The linear expansion coefficient in the temperature range of 30 to 300℃ is 7 x 10 ^-6 cm/cm/℃. The following alloy electrode plate 3 is attached with solder 4, and a lead terminal 5 is attached with solder 6 to the other side, and an exterior resin layer 7 is formed. 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
It has an excellent advantage of being able to reduce the tensile stress between the alloy electrode plate 3 and the alloy electrode plate 3, thereby eliminating damage to the varistor element body 1. Note that if the alloy electrode plate 3 is subjected to solder plating, nickel plating, copper plating, or tin plating, the solderability with the silver electrode 2 will be improved, and the efficiency of the soldering work can be greatly improved. Next, we will discuss the effects of the present invention based on the implementation results. That is, silver electrodes were formed on both sides of a zinc oxide-based varistor body that was molded and sintered to a diameter of 21 mm and a thickness of 0.8 mm, and the rising voltage (V1 mA) was set to 22 V. The electrode plates were soldered and a heat cycle test was conducted, with the results shown in Table 2. The dimensions of the electrode plates used were 66 mm x 8 mm and a thickness of 0.8 mm.

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【table】

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[Table] * Defect judgment = Baritas element cracked by visual inspection, products with cracks As is clear from Table 2, conventional examples E, F, G, H
In the case of the products of the present invention, all of them were defective after 2 to 8 times, and in the case of Reference Example D, defects occurred at the 6th time, and all of the products were defective after the 30th time, whereas the products of the present invention A, B, and C were defective after 100 times.
There were no defects at the time of testing, demonstrating its excellent effectiveness. As described above, according to the present invention, either one of the silver electrodes formed on both sides of a nonlinear metal oxide varistor body has a linear expansion coefficient of 7×10 ⁻ in the temperature range of 30 to 300°C. By soldering alloy electrode plates of ⁶ cm/cm/°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]

FIGS. 1 and 2 relate to one embodiment of the present invention, and FIG. 1 is a perspective view showing a high-power varistor before packaging;
FIG. 2 is a sectional view showing the high power varistor after being packaged. 1... Varistor element body, 2... Silver electrode, 3... Alloy electrode plate, 4, 6... Solder, 5... Output terminal,
7...Exterior resin layer.

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 peripheral edges left on both sides of the element, and one of the electrodes soldered to a temperature of 30 to 300°C. A high power varistor comprising an alloy electrode plate having a linear expansion coefficient of 7×10 ^-6 cm/cm/°C or less in a temperature range of .