JPS637004B2 - - 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 means for noise prevention in small DC motors associated with audio equipment, protection of relay contacts, and discharge absorption in color TV 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 characteristics at the contact surfaces between SiC particles, so any electrode is 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 the 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 an electroless plating resist to the surface of the sintered body to specify an electrode pattern; a step of applying electroless plating mainly composed of nickel to the sintered body with the electroless plating resist still attached; A step of removing the electroless plating resist and unnecessary electroless plating while leaving the electroless plating attached to the sintered body in the electrode pattern specified by the electrolytic plating resist, and removing the electroless plating resist and unnecessary electroless plating remaining on the sintered body. It is characterized by a heat treatment process for converting electroless plating into an ohmic contact electrode.

That is, the present invention provides a voltage nonlinear resistance element having the structure shown in FIG. 1 or FIG. 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 its own excellent 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. A voltage nonlinear resistance element can be provided.

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, as shown in Figure 4 a ₁ and b ₁ , 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. is fired at a temperature of 1380° C. to form an annular sintered body 7 having holes 6.

Next, as shown in FIG. 4 a ₂ and b ₂ , electroless plating resists 11 a and 11 b are applied to areas other than the electrode forming areas 10 a to 10 c on the electrode forming surface of the sintered body 7 by means such as screen printing. The electrode pattern is specified by this method. Various organic substances can be used as the plating resist.

Next, this sintered body 7 is immersed in a tin chloride solution and a palladium chloride solution to form electrode forming regions 10a to 10.
After activating d, it is immersed in a plating solution consisting of nickel chloride, sodium hypophosphite, and sodium citrate, and subjected to electroless plating of nickel-monophosphorus at a temperature of 80 to 90°C. As shown in FIG. 4 a ₃ and b ₃ , this electroless plating of nickel monophosphorus is performed on the parts where the plating resists 11a and 11b are not present and the base of the sintered body 7 is exposed, that is, the electrode forming regions 10a to 10. 1
0d, applied to the outer circumferential surface 7a and the inner circumferential surface 7b.

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.

Next, using a suitable solvent, a plating resist 11 is applied.
a, 11b, and the electroless plating layer on the outer circumferential surface 7a and inner circumferential surface 7b by centerless polishing or sandblasting, etc., as shown in FIG.
As shown in a ₄ and b ₄ , electrodes 8 and divided electrodes 9a, 9b, and 9c each made of an electroless plating layer of nickel and phosphorus are provided on both sides of the sintered body 7, respectively.

In this way, before electroless plating, a plating resist made of an organic substance is applied to form an electrode forming area in advance, and after electroless plating is applied to this electrode forming area to form an electrode, the plating resist is removed. By employing this method, the plating resist can be removed using an organic solvent, and the base of the sintered body is not damaged when the plating resist is removed. However, since the plating 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.

Through the above steps, the voltage nonlinear resistance element having the structure shown in FIG. 2 is prepared, but the ohmic contact is incomplete.

Therefore, this is then heat treated at a temperature of around 300°C. As a result, a voltage nonlinear resistance element having ohmic contact electrodes 8, 9a to 9c mainly composed of nickel on the sintered body 7 is obtained.

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

As described above, the present invention includes a step of applying an electroless plating resist to the surface of a sintered body to specify an electrode pattern, and a step of applying nickel to the sintered body with the electrodeless plating resist still attached. A step of applying electroless plating as a component, and leaving the electroless plating attached to the sintered body in the electrode pattern specified by the electroless plating resist, and removing the electroless plating resist and unnecessary electroless plating. Since the present invention is characterized by comprising a removing step 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) Electroless plating resist is applied to form an electrode forming area in advance, and after electroless plating is applied to this electrode forming area to form an electrode, the plating resist is removed. can be removed using an organic solvent, and the base of the sintered body is not damaged when removing the plating resist.

(c) Since the plating 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.

[Brief explanation of the drawing]

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 c ₁ - c 1 - _{c 4} - in Figure ₄ a ₁ - a 4
c 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, the surface of the sintered body is coated with an electroless plating resist. a step of applying electroless plating mainly composed of nickel to the sintered body with the electroless plating resist still attached, and a step of specifying the electrode pattern with the electroless plating resist. a step of removing the electroless plating resist and unnecessary electroless plating while leaving the electroless plating attached to the sintered body; and converting the electroless plating remaining on the sintered body into an ohmic contact electrode. A method for manufacturing a voltage ratio linear resistance element, comprising a heat treatment step.