JPS6057685B2 - Variable resistor extraction electrode formation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming lead electrodes of a variable resistor.

FIGS. 1 and 2 show an example of a variable resistor that serves as a background for explaining the conventional example of the present invention.
The figure is a plan view of the variable resistor, and FIG. 2 is a partially enlarged side sectional view thereof.

In the figure, 1 is an insulating substrate made of ceramic such as alumina, forsterite, zirconia, etc., 2 is a resistive coating formed on the insulating substrate 1, and a slider 3 slides on this resistive coating 2.

Reference numerals 4 and 5 denote lead-out electrodes electrically connected to both ends of the resistive coating 2, respectively, and lead-out terminals 6 and 7 are connected to the lead-out electrodes 4 and 5, respectively.

8 is a lead terminal on the slider 3 side.

In a variable resistor with such a conventional structure, especially the second
As is clear from the figure, the ends of the resistive coating 2 are formed to overlap the lead electrodes 4 and 5. As the extraction electrodes 4 and 5, baked silver electrodes have traditionally been used. For this reason, when sliding the slider to increase the resistance from the minimum resistance value, the change in resistance does not become smooth as shown in Figure 3, especially after the slider has moved. A phenomenon in which the resistance value jumped (hop-off) was observed on the extraction electrode side. This is because the baked silver electrode itself is a thick film, so the extraction electrode 4,
A difference in level occurs between the resistive coating 2 on the resistive coating 5 and the resistive coating 2 on the insulating substrate 1, and the slider 3 jumps due to the level difference in the resistive coating 2, making it impossible to obtain a smooth change in resistance value. Furthermore, if the extraction electrodes 4 and 5 are thick films as in the past, when forming the resistance coating 2, specifically when printing the resistance paste, the resistance paste The printing width has become wider, and this has become a factor in resistance value variations, especially in small variable resistors. Furthermore, since the thickness of the resistive coating 2 at the terminal edge portions of the extraction electrodes 4 and 5 becomes thinner, deterioration factors such as wire breakage during sliding, heat generation due to current concentration during load, and sliding noise may occur. I was getting used to it. Therefore, in place of this baked silver electrode, there is a desire for a variable resistor in which the step difference between the resistance coating on the extraction electrode and the resistance coating on the insulating substrate is small, and the resistance value changes smoothly from the minimum to the maximum. Ta.

The present invention provides a method for forming an extraction electrode of a variable resistor that can meet the above-mentioned requirements. More specifically, the present invention provides a method for forming an extraction electrode of a variable resistor that can exhibit a smooth change in resistance value.

Furthermore, the present invention provides a method by which extraction electrodes can be easily formed.

Furthermore, the present invention provides a significantly less expensive method than using conventional baked silver.

That is, the gist of the present invention is to provide a variable resistor in which a resistance coating on which a slider slides is formed on an insulating substrate, and extraction electrodes are formed at both ends of the resistance coating. In forming the
Activation paste is applied to the parts of the insulated substrate where the extraction electrodes are to be formed, and then activated by baking.
It is characterized by subsequently applying an electroless plating film.

The present invention will be explained below according to one embodiment.

Example A ceramic substrate made of alumina, forsterite, steatite, zirconia, etc. is used as the insulating substrate constituting the main body of the variable resistor, and active paste is applied through a desired mask to the corresponding parts of the ceramic substrate where the lead electrodes will be formed. It was applied by brush painting, printing, spraying, etc.

This activation page. For example, palladium, platinum,
A catalytic metal such as gold is made into a paste with resin, solvent, etc. After applying the activation paste, dry it,
Next, heat treatment was performed at a temperature of 550 to 650°C to perform activation treatment. Further, it was immersed in a known electroless plating bath of nickel, copper, etc., pulled out, washed with water, and dried to form an extraction electrode made of an electroless plating film. After this, in order to form a resistive film,
A resistor/resistance paste containing a resistive material such as carbon or cermet as a main component was applied onto a ceramic substrate and baked to form a resistive film, and both ends of the paste were laid over lead-out electrodes for electrical connection.

Next, the slider was rotatably attached to slide on the resistive coating on the ceramic substrate.

Next, a description will be given based on a specific example. An alumina substrate was used as the insulating substrate. 3% by weight of palladium was added to the areas on this alumina substrate where extraction electrodes were to be formed.
An activated paste containing ethyl cellulose resin diluted with a solvent was applied by screen printing, and then heat treatment was performed at each temperature shown in the table. Next, it was immersed in a nickel electroless plating bath, pulled out, washed with water, and further dried to form an extraction electrode.

For each lead-out electrode obtained, the electrode formation state was visually observed, and those with "unevenness" on the surface of the plating film were marked with an "X".
Those with a high proportion of "unevenness" are indicated by a Δ mark, and those with no "unevenness" are indicated by an O mark.

Further, a lead wire was vertically soldered onto the plating film, and a tensile test was conducted to measure the adhesive strength of the plating film.
Note that the area of the extraction electrode is 2×3T1g1&.
In addition, cases where the heat treatment temperature exceeds 650C are excluded from the heat treatment temperature range because there is no significant difference in effectiveness or there is no advantage in terms of energy cost from increasing the heat treatment temperature. According to the variable resistor obtained in the above-described embodiment, the extraction electrode is made of an electroless plating film that is thinner than the thick baked silver electrode, so the resistance value of the extraction electrode itself is lowered, and the resistance value of the extraction electrode itself is lowered, unlike the conventional one. The hop-off phenomenon in the resistance value change process is no longer observed.

In addition, when using an electroless plating film electrode instead of a baked silver electrode, according to the conventional electroless plating method, an electroless plating film is first formed on an insulating substrate, a resist film is applied, and then an etching process is performed. There is a method of leaving extraction electrodes only in the necessary locations, but according to the present invention, the extraction electrodes can be formed only in the necessary locations during the process of forming the electroless plating film, making it easy to form the extraction electrodes, and also leaving them in the desired locations. It can be formed at the following locations.

Furthermore, since the lead electrode made of the electroless plating film obtained by this invention has a thick catalytic metal, the adhesion strength of the plating film is higher and the resistance value is lower than that of the conventional electroless plating method. I can do it.

In addition to the above-mentioned examples, if the insulating substrate is subjected to pre-treatment such as degreasing, etching, or sensitization treatment as necessary before the activation treatment, a more uniform and high-quality plating film can be obtained. can be formed, and the adhesive strength can also be improved.

Furthermore, by heat-treating at 300 to 800[deg.] C. after forming the plating film, the adhesive strength of the layer can be increased. As described above, according to the method of the present invention, the lead electrode of the variable resistor can be formed at any location by electroless plating, and the conventional troublesome process of removing the plating film is not necessary.

Also, thick-film baked electrodes using nickel paste or copper paste are cheaper than baked silver electrodes, but they require special treatment such as a non-oxidizing atmosphere during the baking process. The present invention not only does not require any such treatment, but also has the advantage of being able to provide a variable resistor at a low cost that eliminates the resistance hop-off phenomenon that cannot be eliminated with baked electrodes.

[Brief explanation of drawings]

1 and 2 are a plan view and a partially enlarged side sectional view of a variable resistor, which serves as a background for explaining the method of this invention, and FIG.
The figure is a diagram showing the relationship between the rotation angle and the rate of change in resistance value. 1...Insulating substrate, 2...Resistive coating, 3
...Slider, 4,5...Extractor electrode.

Claims (1)

[Claims] 1. In a variable resistor in which a resistance coating on which a slider slides is formed on an insulating substrate, and extraction electrodes are formed on both sides of this resistance coating, when forming the extraction electrodes, the extraction electrodes of the insulating substrate are Activation paste is applied to the area where the
A method for forming lead electrodes of a variable resistor, which is characterized by performing activation treatment by baking and subsequently applying an electroless plating film.