JPS5885501A - Square 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 The present invention relates to a rectangular varistor, particularly a so-called chip-shaped varistor which is small and has no lead wires.

In recent years, a voltage nonlinear resistor (varistor) has been developed that is made by adding a small amount of metal oxide such as bismuth oxide to zinc oxide and sintering it. It is widely used to protect various electronic devices from abnormal voltages such as induced lightning.

On the other hand, looking at recent technological trends, electronic devices are becoming smaller and lighter, and the high-density packaging of components is rapidly progressing.

Therefore, there is a strong demand for miniaturization of various electronic components.
The trend is toward square chips and small rod-like melf-shaped chips.
It's moving in that direction.

In view of these technological trends, the present invention aims to provide a rectangular chip varistor with excellent performance.

Conventionally, attempts have been made to create a rectangular plate-shaped varistor using a voltage nonlinear resistor whose main component is zinc oxide (ZnO). As shown in FIG. 1, a pair of silver electrodes 2a and 2b are formed on faces facing each other from the end face of a rectangular plate-shaped voltage nonlinear resistor 1 whose main component is zinc oxide. Figure 2 is a cross-sectional view of this rectangular plate-shaped varistor.In general, a voltage nonlinear resistor whose main component is zinc oxide has a fine structure in which a grain boundary layer of low resistance is formed around the zinc oxide particles. The varistor voltage is proportional to the number of grain boundary layers in series between the electrodes. Therefore, in this square plate-shaped varistor, in order for the current to pass through the inside of the element instead of through the element surface, the element thickness tl must be smaller than the distance t2 between the electrodes 21L and 2b on the element surface 1- in Fig. 2. It needs to be small. If these conditions are not met, current will flow on the surface of the element, in which case the current density will be extremely high, and a small amount of current will cause deterioration. Moreover, even if t2>tl, the effective length of this square plate as a varistor is t3, which is very short, and most of the square plate does not function as a varistor. Furthermore, if there is a limit of t2)t+, when the shape of the square plate is limited, the element thickness tl will inevitably be limited, and an element with a very high varistor voltage cannot be produced.

Therefore, the present invention aims to solve these drawbacks and provide a rectangular chip varistor with excellent performance that is not constrained by the conventional concept of the distance between electrodes and the thickness of the element.

As a means for this purpose, the voltage nonlinear resistor is made of high resistance materials around both ends, and is composed of antibodies on the side between the electrodes, so that current flows inside the element.

Hereinafter, the present invention will be explained using FIGS. 3 and 4 showing one embodiment. In the figure, reference numeral 3 denotes a voltage nonlinear resistor whose main component is zinc oxide, and numerals 4a and 0.4b denote high resistance parts formed around both ends of the voltage nonlinear resistor 3. 5N and 6b are a pair of electrodes made of silver or the like and formed opposite to each other from the end faces.

Next, a method for manufacturing this rectangular varistor will be described. Hismuth oxide (B1203) in zinc oxide (ZnO)
, cobalt oxide (CO2O3), manganese oxide (MnO
2), antimony oxide (Sb203), silicon oxide (Sb203),
0.01 to 2.0 mol% of iO2) and 0.0001 to 0.01 of oxidized fluorine (A120s), respectively.
% by mole was added and mixed thoroughly. The mixture was then compression molded and calcined in air to a t crystallinity of 1100-1350'C. Next, this sintered body was cut into a square plate using a cutting machine.

The voltage nonlinear resistor 3 was thus obtained. Next, hismuth oxide (Bi20s) 65-70
wt%, boron oxide (B203) 10-20 wt%,
Silicon oxide (SiO2) 2~ewt%, silver oxide (Agz
O) 2-6 wt%, lithium oxide (Li20) 1-5 w
t%, melted at 1,000 to 12,000 G, vitrified by dropping into water, and added an organic binder to the free-glued material.
It was applied to the end face and the periphery of the end face of the voltage non-linear resistor 3) and baked at 800 to 9000C. There are four resistor parts 4&, 4b formed in this way. Next, apply it to the silver base (with ・ facing away from the end surface) and apply 800~
Baking was performed at 8600G to form electrodes 6a and 5b to create a rectangular varistor.

In the areas around both ends of the rectangular varistor thus obtained, lithium (Li) atoms diffuse into zinc oxide (ZnO) particles, and high resistance areas (''10+z~101) are formed by valence control.
5Ω1cm), and as shown in FIG. 4, even if the interelectrode distance t5 is shorter than the element thickness t4, the current does not flow on the element surface but inside the element.Moreover, in this case,
The effective length of the varistor is t6, which is much larger than t3 in FIG. 2, and the withstand strength when a surge current flows is also increased.

In this way, the rectangular varistor of the present invention breaks the constraint that the distance between the electrodes must be longer than the thickness of the cord, which is a fateful condition of voltage nonlinear resistors whose main component is zinc oxide. This will be extremely useful as elements become increasingly smaller in the future.

In addition, although lithium (Ll) was used to make the l@J resistance part in "Implementation V" described in "-," any material that can be used as a madder resistor under K1 valence control may be used. For example, copper (Cu)
But you can get the same effect. In addition, we used color paste baking as a forming means, but this is also lithium (Ll).
), or diffuses into zinc oxide (ZnO) particles to form a resistor.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a conventional square varistor, FIG. 2 is a sectional view thereof, FIG. 3 is a perspective view showing an embodiment of a square varistor according to the present invention, and FIG. 4 is a sectional view thereof. 3...-Voltage nonlinear resistor, 4a, 4b--High resistance part, 52L, 5b... Electrode. Name of agent Benyo 1st person Toshi Nakao Male Baka 1 person Figure 2 Figure 3 Figure 4 f 3-

Claims (2)

[Claims] (1) A rectangular varistor in which high resistance parts are formed around both ends of a rectangular plate-shaped voltage nonlinear resistor whose main component is zinc oxide (ZnO), and a pair of electrodes are formed on opposite sides of the end face. (2) A rectangular varistor according to claim 1, wherein the high resistance portion is formed by baking a bismuth borosilicate glass base containing lithium (Ll).