JPS6343876B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a voltage nonlinear resistance element, and more particularly to an electrode structure of a voltage nonlinear resistance element.

Basically, a voltage nonlinear resistance element is made by forming electrodes 2 and 3 on both sides of a sintered body 1 and soldering lead wires 4 and 5 to each electrode 2 and 3, as shown in FIG. As illustrated in FIG. 2, the resistance value changes non-linearly depending on the applied voltage V applied between the electrodes 2 and 3, and the applied voltage changes depending on the varistor voltage.
It has the unique characteristic that the resistance value decreases dramatically in the range exceeding Vt. Focusing on this characteristic, voltage nonlinear resistance elements are widely used as a means for noise prevention in small DC motors related to audio equipment, protection of relay contacts, protection against static electricity in semiconductor devices, and discharge absorption in color TV cathode ray tube circuits. has been done.

Conventionally, tin oxide (SnO ₂ )-based, iron oxide (Fe ₂ O ₃ )-based, and silicon carbide-based (SiC)-based devices are widely known as voltage nonlinear resistance elements.
Among these, the SnO ₂ type and Fe ₂ O ₃ type are those in which the sintered body 1 itself exhibits varistor characteristics, and the sintered body 1 itself is a linear resistor, but special electrodes are formed on it. By doing so, a potential barrier is formed between the electrode and the sintered body 1, thereby obtaining varistor characteristics. Also, SiC-based ones
By adding a binder to SiC particles and sintering them, varistor properties are obtained at the contact surfaces between the SiC particles.

However, the above-mentioned conventional voltage nonlinear resistance elements are difficult to manufacture, such as electrodes and sintered body molding, resulting in high costs, and the nonlinearity characteristics tend to deteriorate over time. However, the varistor voltage is high, and it has disadvantages such as being unsuitable for noise prevention in small low-voltage DC motors, which is an important application for voltage nonlinear resistance elements. Also, SnO ₂ series,
Among the Fe ₂ O ₃ series, those whose sintered bodies themselves exhibit varistor properties have low withstand voltages, such as small DC motors, where the peak value of the noise voltage to be removed is 20 to 100 times higher than the power supply voltage. Although it is about twice as effective, it is not suitable for noise prevention.

In order to improve these conventional drawbacks,
A titanium oxide-based voltage nonlinear resistance element has been proposed, which has titanium oxide (TiO ₂ ) as its main component and sintered it with the addition of a trace amount of one or more of niobium oxide, bismuth oxide, antimony oxide, or tantalum oxide. ing.

This titanium oxide (TiO ₂ )-based voltage nonlinear resistance element utilizes the voltage nonlinearity of the sintered body 1 itself, and has a low varistor voltage, making it ideal as a noise prevention means for small DC motors. It is.

In this case, in order to fully utilize the varistor properties of the sintered body 1 itself, the electrodes 2 and 3 shown in FIG. 1 are formed as ohmic contact electrodes. The method for forming an ohmic contact electrode is to use indium on silver.
Methods include printing a conductive paste containing a small amount of In or gallium Ga, applying heat treatment after electroless plating with nickel, or thermally spraying a metal such as aluminum. However, no matter which method is used to form the electrode, the electrode material itself has poor oxidation resistance and a thin oxide film is likely to form on the surface of the ohmic contact electrode, so the lead wires 4 and 5 are soldered to this. It has disadvantages such as poor solderability and failure to obtain sufficient soldering strength, and oxidation destroys ohmic contact, leading to changes in varistor characteristics over time.

The present invention eliminates the above-mentioned drawbacks, has excellent solderability and oxidation resistance, has little deterioration over time, does not cause characteristic fluctuations due to electrode position deviation, is highly reliable, and is inexpensive in terms of cost. It is an object of the present invention to provide a voltage nonlinear resistance element having electrodes.

In order to achieve the above object, the voltage nonlinear resistance element according to the present invention forms an electrode layer that makes ohmic contact on a sintered body that itself has varistor characteristics, and solders on the surface of the electrode layer. A voltage non-linear resistance element coated with a metal layer with good adhesion properties, wherein the metal layer is formed within its plane with a smaller planar area than the electrode layer so that a gap is generated around the entire circumference. It is characterized by

DESCRIPTION OF THE PREFERRED EMBODIMENTS The content of the present invention will be specifically explained in detail below with reference to the accompanying drawings which are examples. 3 and 4 show examples of voltage nonlinear resistance elements according to the present invention. First, the one shown in FIG. 3 has ohmic contact electrodes 2 and 3 on both sides of a sintered body 1 made of titanium oxide (TiO ₂ ) and formed into a disk shape, for example.
In addition, metal layers 6 and 7 made of high-purity silver are deposited on the ohmic contact electrodes 2 and 3. the ohmic contact electrode 2;
3 is formed by a well-known method such as silver alloy paste printing, aluminum thermal spraying, or nickel electroless plating, as described above. Further, the metal layers 6 and 7 are formed by printing a high-purity silver paste using a screen printing method or the like and then baking the same. The metal layers 6 and 7 are formed of ohmic contact electrodes such that a gap g ₁ is created between the metal layers 6 and 7 and the outer peripheries of the ohmic contact electrodes 2 and 3 so that they do not protrude outside the ohmic contact electrode layers 2 and 3. Printing is performed within the plane with a plane area smaller than 2.3.

As described above, if the metal layers 6 and 7 with good solderability, such as silver, are deposited on the ohmic contact electrodes 2 and 3, the lead wires 4 and 5 can be soldered to the metal layers 6 and 7. Since it can be fixed, the lead wires 4 and 5
The solderability and soldering strength are significantly improved.

Furthermore, since the ohmic contact electrodes 2 and 3 are covered with the metal layers 6 and 7, oxidation of the ohmic contact electrodes 2 and 3 is prevented, and the varistor characteristics are maintained stably for a long period of time. Become.

Furthermore, the metal layers 6, 7 are connected to the ohmic contact electrode layer 2,
The contact electrodes 2 and 3 are formed in a plane with a smaller planar area than the ohmic contact electrodes 2 and 3 so that a gap g ₁ is created between the ohmic contact electrodes 2 and the outer periphery of the ohmic contact electrodes 2 and 3 so as not to protrude outside of the ohmic contact electrodes 2 and 3. Because there is a gap g ₁
Even if the printing position shifts within the ohmic contact electrodes 2 and 3, it will not protrude outside the ohmic contact electrodes 2 and 3. For this reason,
The following effects can be obtained.

(b) The electrode area relative to the sintered body 1 is kept constant,
A varistor with stable characteristics can be obtained.

(b) When the metal layers 6 and 7 are made of silver, if the metal layers 6 and 7 protrude outside the ohmic contact electrodes 2 and 3 due to misalignment of the printing position, silver migration is likely to occur, reducing reliability. Sexuality decreases. On the other hand, in the present invention, since the metal layers 6 and 7 do not protrude due to misalignment of printing positions, it is possible to prevent silver migration from occurring and improve reliability.

(c) The amount of silver used to form the metal layers 6 and 7 is reduced, resulting in lower costs.

(d) Printing and forming the metal layers 6 and 7 becomes easier;
Mass productivity improves.

Note that the metal layers 6 and 7 can also be formed by tin electrolytic plating, solder plating, or nickel electrolytic plating.

Next, in the case shown in FIG. 4, the metal layers 10 and 11 of FIG. 1 are formed on the ohmic contact electrodes 2 and 3 by silver paste printing similar to that of FIG. Furthermore, on the surfaces of the ohmic contact electrodes 2 and 3 where the metal layers 10 and 11 are not present, metal layers 12 and 13 are deposited by electrolytic plating or solder plating.

With such a structure, the first metal layer 10,
The gap g ₁ caused by printing 11 can be filled with the metal layers 12 and 13, the soldering area can be expanded, and oxidation of the ohmic contact electrodes 2 and 3 can be more completely prevented.

5A and 5B show a plan view and a bottom view of a voltage nonlinear resistance element according to the present invention, which is configured to prevent noise in a general small DC motor having a three-pole structure. In general, in small DC motors, the width of the commutator pieces or brushes is small, and the rate of change in armature coil current over time and the value of the reactance voltage that depends on this become large. At the moment of movement, sparks are likely to occur between the commutator surface and the brush. These sparks not only cause wear on the commutator and brushes, shortening the life of the motor, but also cause spike-like noise voltage generation. This spike-like noise voltage is a bipolar voltage with a peak value several tens of times higher than the power supply voltage, and has a negative impact on audio equipment that uses small DC motors, so it must be removed. There must be. As such noise prevention means, voltage nonlinear resistance elements shown in FIGS. 5A and 5B are used.

In this example, on both sides of a sintered body 1 formed into an annular shape mainly composed of titanium oxide (TiO ₂ ),
Electrode 2 formed into a sector shape with approximately equal area
Gap g for a~2c and 3a~3c, respectively.
2 and g3 are arranged at three equal intervals. In this case, the electrodes 2a to 2c and 3a3c are formed to be shifted from each other, and there are overlapped portions S 1 , S 2 , S 3 between the electrodes 2a and 3a, 2b and 3a, 2c and 3b, 2c and _3c , and _2a and _3c, respectively. , S ₄ , S ₅ and S ₆ are formed. The electrodes 2a to 2c or 3a
At least one of electrodes 2a to 3c, for example electrodes 2a to 2c, is formed as an ohmic contact electrode. As described above, methods for forming the ohmic contact electrodes 2a to 2c include a method of printing and applying a silver alloy paste containing a small amount of indium and gallium, an aluminum thermal spraying method, and a nickel electroless plating method.

Furthermore, metal layers 14a to 14c with good solderability are provided on the surfaces of the ohmic contact electrodes 2a to 2c.
It is covered with In this embodiment, high-purity silver paste is printed on the ohmic contact electrodes 2a-2c to form the metal layers 14a-14c, but as shown in FIGS. 4 and 5, tin etc. Of course, it is also possible to form it as a metal layer including an electrolytically plated layer. The metal layers 14a to 14c are formed to have a smaller area than the ohmic contact electrodes 2a to 2c for the reason described above.

As described above, the metal layers 14a to 14 with good solderability are formed on the surfaces of the ohmic contact electrodes 2a to 2c.
c, the connection lead wire 1 is connected to the commutator piece.
5a to 15c are metal layers 14a to 14a with good solderability.
14c, it can be efficiently and reliably soldered and fixed. Also, ohmic contact electrodes 2a to 2c
are covered with the metal layers 14a to 14c, oxidation is prevented, the varistor characteristics are maintained stably for a long period of time, and the noise prevention effect is maintained constant for a long period of time.

Note that the voltage nonlinear resistance element in this embodiment includes ohmic contact electrodes 2a to 2c and electrodes 3a to 3c.
_3a , the sintered body ₁
Varistor characteristics appear in the thickness direction.

FIG. 6 is a diagram schematically showing the structure of a small DC motor equipped with the voltage nonlinear resistance element shown in FIG. 17, and its lead wires 15a to 15c are connected to each piece of the commutator 17 in a corresponding manner. 1
9a and 19b are brushes, and 20a and 20b are field magnets.

FIG. ₇ shows _an equivalent circuit of the small DC motor shown in FIG. Layers A to H are connected in series, two each, through commutator pieces 17a to 17c,
The armature coils 16a to 16c have a triangularly connected circuit configuration. Therefore, since the noise cutting effect of all of the varistor layers A to B is applied to the noise cutting voltage, an excellent noise reduction effect can be obtained even in a large current range.

Although the armature coils 16a to 16c are connected in a triangular manner, they may also be connected in a star shape.

As explained in detail above, the voltage nonlinear resistance element according to the present invention forms an electrode layer that makes ohmic contact on a sintered body that itself has varistor characteristics, and has a solderable surface on the surface of the electrode layer. A voltage non-linear resistance element coated with a metal layer having good properties, characterized in that the metal layer is formed within its plane to have a smaller planar area than the electrode layer so that a gap is generated around the entire circumference. Because of this, it has excellent solderability and oxidation resistance, has little deterioration over time, and does not cause characteristic fluctuations due to electrode position deviation, and is highly reliable.
A voltage nonlinear resistance element having an electrode that is inexpensive in cost can be provided. Furthermore, as shown in the example, when a titanium oxide-based sintered body is used and an ohmic contact electrode is provided on it, the poor solderability of the ohmic contact electrode is covered by the metal layer. At the same time, it prevents deterioration over time,
It is possible to provide a voltage nonlinear resistance element that has high mechanical strength, exhibits stable varistor characteristics over a long period of time in a low voltage range, and is ideal for noise prevention in small DC motors.

[Brief explanation of the drawing]

Figure 1 is a front view of the voltage nonlinear resistance element, Figure 2
The figure also shows the voltage-current characteristic diagram, Figures 3 and 4.
The figures are cross-sectional views of each embodiment of the voltage non-linear resistance element according to the present invention, and FIGS. 5A and 5B are plan and bottom views of the voltage non-linear resistance element according to the present invention configured as a small DC motor. , Fig. 6 is a diagram schematically showing a small DC motor equipped with the voltage nonlinear resistance element shown in Fig. 5, and Fig. 7 is an equivalent circuit diagram of the small DC motor shown in Fig. 6. It shows. 1... Sintered body, 2, 3, 2a-2c, 3a-3
c... Electrode, 6, 7, 10, 11, 12, 13,
14a to 14c...metal layer.

Claims (1)

[Claims] 1. A voltage source in which an electrode layer that makes ohmic contact is formed on a sintered body that itself has varistor characteristics, and a metal layer with good solderability is deposited on the surface of the electrode layer. 1. A voltage non-linear resistance element, characterized in that the metal layer is formed in a plane with a smaller planar area than the electrode layer so that a gap is generated around the entire circumference. 2. The voltage nonlinear resistance element according to claim 1, wherein the sintered body is made of a material whose main component is titanium oxide. 3. The voltage nonlinear resistance element according to claim 1 or 2, wherein the electrode layer is made of silver. 4. The voltage nonlinear resistance element according to claim 3, wherein the metal layer is formed by printing silver paste in an inner region of the electrode layer. 5. The voltage nonlinear resistance element according to claim 1 or 2, wherein the metal layer is an electroplated layer. 6. The metal layer is formed by depositing a silver layer on a part of the electrode layer, and depositing an electroplated layer on the silver layer and the electrode layer where the silver layer does not exist. A voltage nonlinear resistance element according to claim 1 or 2. 7. The sintered body is formed in an annular shape, and the electrode layer is arranged around the axis on at least one surface of the sintered body.
Claims 1, 2, 3, and 4 are characterized in that a plurality of them are provided via a gap.
6. The voltage nonlinear resistance element according to item 6. 8. The electrode layer is provided on both surfaces of the sintered body to face each other, and at least one electrode layer has the metal layer on its surface. Voltage nonlinear resistance element as described.