JPS648443B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a voltage nonlinear resistance element using a sintered body containing titanium oxide (TiO ₂ ) as a main component.

A voltage nonlinear resistance element has a resistance value that changes nonlinearly depending on the applied voltage applied between the electrodes provided on the sintered body, and the resistance value rapidly decreases in the range where the applied voltage exceeds the varistor voltage. It has the unique property of Taking note of this characteristic, voltage nonlinear resistance elements are widely used as a means for noise prevention in small DC motors associated with audio equipment, protection of relay contacts, and discharge absorption in color television cathode ray tube circuits.

Depending on the structure, shape, etc. of the equipment to which the voltage nonlinear resistance element is attached, for example, as shown in FIG. 1, electrodes 2, 3, and lead wires 4 and 5 are soldered onto the electrodes 2 and 3, or as shown in FIGS. A common electrode 8 and divided electrodes 9 are provided on both sides of the sintered body 7 formed in an annular shape.
a, 9b, and 9c are provided, respectively, and divided electrodes 9a,
9b and 9c are electrically connected to a commutator piece or the like of a small DC motor through lead wires.

By the way, conventional voltage nonlinear resistance elements include tin oxide (SnO ₂ )-based, iron oxide (Fe ₂ O ₃ )-based,
Silicon carbide (SiC)-based materials are known. Among these, the sintered body of the SnO _2- based and Fe ₂ O _3- based ones is a linear resistor, and by adding a special electrode to it, a potential barrier is formed between the sintered body and the electrode. , thereby obtaining varistor characteristics. In addition, SiC-based materials have varistor properties at the contact surfaces between SiC particles, so any electrodes are not particularly important.

However, the above-mentioned conventional voltage nonlinear resistance element has manufacturing difficulties such as electrode formation and sintered compact molding, which increases the price and tends to cause deterioration of nonlinearity over time. Moreover, the varistor voltage is high, making it unsuitable for applications such as noise prevention in small, low-voltage DC motors.

In order to improve these conventional drawbacks,
A titanium oxide-based voltage nonlinear resistance element has been proposed, which is made of titanium oxide (TiO ₂ ) as its main component, with trace amounts of oxides of semiconductor elements (antimony, niobium, tantalum, etc.) and bismuth oxide added and sintered. I want to. This titanium oxide-based voltage nonlinear resistance element has a sintered body itself that exhibits excellent voltage nonlinearity as shown by curve _L1 in Figure 3, and a varistor voltage
V _T is also low, so as long as we pay attention to the voltage nonlinearity of the sintered body itself, it is ideal for low voltage applications such as noise prevention in small DC motors.

However, when the contact between the sintered body and the electrode becomes non-ohmic, a rectification characteristic as shown in curve _L2 in Figure 3 occurs between the sintered body and the electrode, and the voltage non-stable between the electrodes. The linearity becomes a blunt characteristic like the curve L ₃ which is a combination of the curve L ₁ and the curve L ₂ ,
This results in the disadvantage that the excellent voltage nonlinearity of the sintered body itself, shown by the curve _L1 , cannot be effectively utilized.

Therefore, the present invention provides a titanium oxide-based voltage nonlinear resistance element that can fully utilize the excellent varistor properties of the sintered body itself, has strong adhesive strength to the sintered body, is highly corrosion resistant, and has low material cost. A voltage nonlinear resistance element with an inexpensive electrode structure of
It is an object of the present invention to provide a manufacturing method that can easily produce a highly accurate pattern without damaging the sintered body base.

In order to achieve the above object, the present invention provides a method for manufacturing a voltage nonlinear resistance element having an ohmic contact electrode mainly composed of nickel on a sintered body mainly composed of titanium oxide. a step of applying electroless plating containing nickel as a main component to substantially the entire surface of the electrode, a step of applying an etching resist to the electrode formation area on the surface of the electroless plating to specify an electrode pattern, and a step of applying the etching resist. It is characterized by comprising a step of etching away the electroless plating outside the area, a step of removing the etching resist, and a heat treatment step of converting the electroless plating remaining on the sintered body into an ohmic contact electrode. .

That is, the present invention provides a voltage nonlinear resistance element having the structure shown in FIGS. 1 and 2, for example, in which titanium oxide is the main component and oxides of semiconductor elements (antimony, niobium, tantalum, etc.) and If a normal electrode is applied to a sintered body containing a small amount of bismuth, the electrode will become a non-ohmic contact and the excellent varistor properties of the sintered body itself cannot be fully demonstrated, so an ohmic contact electrode is used as the electrode. This gives the sintered body sufficient varistor properties.

The ohmic contact electrode may also be made of an In-Ga alloy. However, In-Ga alloy is very expensive and not suitable for mass production. Furthermore, in order to attach the In-Ga alloy to the sintered body, rubbing or ultrasonic brazing must be performed, and the adhesion of the electrode to the sintered body is weak and accidents such as electrode peeling are likely to occur. Furthermore, the In--Ga alloy has a low melting point, which causes many problems when soldering lead wires.

Therefore, in the present invention, when providing an ohmic contact electrode on a sintered body mainly composed of titanium oxide, electroless plating is used to provide an ohmic contact electrode mainly composed of nickel on the sintered body. will be established.

Ohmic contact electrodes whose main component is nickel.
It is significantly cheaper than conventional IN-Ga alloys and is highly suitable for mass production. Therefore, according to the present invention, the adhesion between the sintered body and the electrode is very high, the interface peeling of the electrode is difficult to occur, the deterioration over time is small, and the highly reliable and inexpensive titanium oxide-based material is used. voltage nonlinear resistance elements can be manufactured.

Next, with reference to FIGS. 4 a ₁ to _{a 4} and b ₁ to b ₄ , a method for manufacturing a voltage nonlinear resistance element according to the present invention will be specifically described. This example shows a specific example of obtaining a titanium oxide-based voltage nonlinear resistance element having the split electrode structure shown in FIGS. 2A and B, but other shapes and structures may also be used. The same can be applied.

First, a composition containing titanium oxide (TiO ₂ ) as the main component, to which small amounts of niobium oxide (Nb ₂ O ₅ ) and bismuth oxide (Bi ₂ O ₃ ) were added, was fired at a temperature of 1380°C to form holes 6. After creating an annular sintered body 7 having the following properties, the entire surface of this sintered body 7 is electroless plated with nickel as the main component, as shown in FIG. 4 a ₁ and b ₁ . For electroless plating of nickel, the sintered body 7 is immersed in a tin chloride solution and a palladium chloride solution to activate the electrode forming regions 10a to 10d, and then nickel chloride, sodium hypophosphite,
It is immersed in a plating solution consisting of sodium citrate and subjected to nickel-phosphorus electroless plating at a temperature of 80 to 90°C.

Next, as shown in FIG. 4 a ₂ and b ₂ , etching resists 11 a to 11 d are applied to the electrode forming regions 10 a to 10 d on the surface of the electroless plating by means such as screen printing, and Thus, the electrode pattern is specified. Etching resist 11a~
Protocoat (trade name) is effective as 11d.

Next, this sintered body 7 is immersed in an etching solution,
The electroless plating in areas other than those coated with the etching resists 11a to 11d is removed by etching. As the etching solution, use a mixture of acetic acid, nitric acid, and acetone in a ratio of 1:1:1.
Etching treatment is performed at a temperature of ℃. As a result, as shown in FIG. 4 a ₃ and b ₃ , the electrode 8, the divided electrode 9a,
A layer having electroless plating layers 9b and 9c and etching resists 11a to 11d is obtained.

Next, _the etching resists _11a to 11d are removed using an alkaline solution or an organic solvent, and as shown in FIG. , divided electrode 9
Those having a to 9c are obtained. Then do this
Electrodes 8 and split electrodes 9a to 9c with stable ohmic contact are formed by heat treatment at a temperature of around 300°C.
A voltage nonlinear resistance element having a voltage nonlinearity is obtained.

The ohmic contact electrode 8 thus obtained,
9a to 9c have very strong adhesion to the sintered body 7 and excellent corrosion resistance. Also,
Compared to those using In-Ga alloy, electrode material costs are much lower and mass production is possible.

In addition, by applying electroless plating to almost the entire surface of the sintered body and then applying an etching resist to the surface of the electroless plating to specify the electrode pattern, there is no possibility of damaging the base of the sintered body. do not have.

Furthermore, since the etching resist can be easily applied in a highly accurate pattern using a screen printing method or the like, even a complicated electrode pattern can be easily formed with high accuracy.

In addition, in order to obtain a stable ohmic contact electrode, it is necessary to provide an electrode consisting of 98 to 80% by weight of nickel and 2 to 20% by weight of phosphorus, but the composition ratio of nickel and phosphorus is It is controlled by the hydrogen ion concentration (PH) of the solution, and in solutions with a pH of 10 or higher, the proportion of phosphorus is 2% by weight or less, and in solutions with a pH of 2 or less, the proportion of phosphorus is 20% by weight or more. Therefore, in order to obtain a good ohmic contact electrode, it is necessary to set the hydrogen ion concentration PH of the plating solution in the range of PH=2 to 10.

As described above, the present invention provides a method for manufacturing a voltage nonlinear resistance element having an ohmic contact electrode mainly composed of nickel on a sintered body mainly composed of titanium oxide. A step of applying electroless plating mainly composed of nickel to almost the entire surface, a step of applying an etching resist to the electrode formation area on the surface of the electroless plating to specify an electrode pattern, and a step of applying the etching resist to the area where the etching resist is applied. The present invention is characterized by comprising a step of etching away electroless plating other than the above, a step of removing the etching resist, and a heat treatment step of converting the electroless plating remaining on the sintered body into an ohmic contact electrode. , the following effects can be obtained.

(a) The voltage nonlinearity of the sintered body itself can be fully utilized, and the adhesive force between the sintered body and the ohmic contact electrode is extremely strong, making it difficult for electrode peeling to occur. Furthermore, a voltage nonlinear resistance element having electrodes with excellent corrosion resistance and less deterioration over time can be manufactured with good mass productivity.

(b) After applying electroless plating to almost the entire surface of the sintered body,
By going through the manufacturing process of applying an etching resist to the surface of the electroless plating to specify the electrode pattern, the base of the sintered body is not damaged by the etching resist.

(c) Etching resist can be easily applied in a highly accurate pattern by screen printing or the like, so even complex electrode patterns can be easily formed with high accuracy.

[Brief explanation of drawings]

Figure 1 is a front view showing the basic structure of a voltage nonlinear resistance element, Figures 2A and B are front and rear views of other examples, and Figure 3 is a sintered body mainly composed of titanium oxide. Varistor characteristic diagrams illustrating problems when configuring a voltage nonlinear resistance element using varistor characteristics, Figures 4 a ₁ to a ₄ are diagrams illustrating the manufacturing method according to the present invention, and Figures 4 b ₁ to b ₄ is D ₁ −D ₁ to D ₄ in Figure ₄ a 1 to _{a 4}
-D It is each cross-sectional view on the _4th line. 7... Sintered body, 8... Electrode, 9a, 9b, 9c
...Divided electrode.

Claims (1)

[Claims] 1. In a method for manufacturing a voltage nonlinear resistance element having an ohmic contact electrode mainly composed of nickel on a sintered body mainly composed of titanium oxide, substantially the entire surface of the sintered body is coated with nickel as the main component. a step of applying an etching resist to the electrode formation area on the surface of the electroless plating to specify an electrode pattern; and a step of etching away the electroless plating other than the area to which the etching resist has been applied. A method for manufacturing a voltage nonlinear resistance element, comprising: a step of removing the etching resist; and a heat treatment step of converting the electroless plating remaining on the sintered body into an ohmic contact electrode.