JPS5824922B2 - Manufacturing method of variable resistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a variable resistor from a circuit board.

As a resistive circuit board, a resistive material and a highly conductive material are sequentially laminated on an insulating support to obtain a board. The highly conductive material and the resistive material in the areas related to the negative image are etched by masking the composite pattern part with a photoresist film, then masking with a photoresist film except for the resistor circuit pattern part, and etching the resistor material. Etching methods are known for etching highly conductive materials in circuit pattern areas.

However, in the above-mentioned resistor circuit board, in the conductor circuit,
When obtaining a variable resistor with a configuration in which a bottom electrode is selected by a brush, a resistor to be selected is interposed in the conductor circuit, and the circuit resistance value is changed by selecting the electrode by the brush, the electrode is Because it is formed in a stepped manner higher than the top surface of the support, a step is created at the electrode edge that is disadvantageous for brush sliding, and a considerable amount of torque is required to move the brush, resulting in noticeable wear of the brush and electrode. Unavoidable problems such as

The method for manufacturing a variable resistor according to the present invention is a method for manufacturing a variable resistor that does not have the above-mentioned difficulties. The highly conductive material and the resistive material in the portions that have a negative image relationship with the composite pattern of the conductor circuit pattern including the terminal and the resistor circuit pattern are removed, and then the remaining highly conductive material and resistor of the composite pattern are removed. The method is characterized by embedding a portion of the material in the support by applying pressure so that the surface of the highly conductive material is flush with the surface of the support, and then removing the highly conductive material in the pattern portion of the resistance circuit. It is something to do.

In the present invention, at the stage where the layers of the resistive material and the highly conductive material of the substrate are formed into a composite pattern of the conductor circuit pattern and the resistor circuit pattern, as shown in FIG.
Each layer of the resistive material A and the highly conductive material A is located at a higher level than the upper surface of the support C.

In the next pressurizing step, the resistive material a and the highly conductive material of the composite pattern are buried in the support C, and as shown in FIG. It is said that they are on the same level.

Therefore, at the stage shown in FIG. 3 in which the part corresponding to the resistor circuit part of the highly conductive material is removed from the composite pattern, a flush conductor circuit is formed on the upper surface of the support C. The electrode is flush with the support.

Therefore, the brush slides smoothly against the electrode without any hesitation.

In the present invention, a thermoplastic is usually used for the support plate, and the support plate is softened by heating during the above-mentioned pressurization.

Thermosetting plastics can also be used for the support plate, and in this case, in the steps up to the above-mentioned pressurization, it can be kept in a semi-hardened state, softened by heating during pressurization, and then hardened.

In addition, as shown in the following example, for conductor circuits, the copper foil to be formed in the conductor circuit is shielded from the etching solution, and the electrodes to which the lead wires are connected are soldered to improve performance. For this purpose, gold plating can be applied.

Examples of the present invention will be described below.

The circuit board of the example has a structure in which a resistance layer mainly composed of nickel is provided on one side of a glass-epoxy laminate having a thickness of 16 mm, and a copper foil is bonded thereon.

A dry photopolymer film (manufactured by DuPont, trade name, Riston 16S) is laminated on the copper foil surface of this circuit board, exposed and developed by a conventional method to expose the copper foil portion corresponding to the conductor circuit, and The surface is plated with gold to a thickness of 1 micron using a conventional method.

Next, the remaining dry photo film is peeled off according to a conventional method, the board is washed and dried, and the dry photo film is again laminated on the copper foil surface after smoothing, and this film is exposed and developed to form a conductor circuit. is removed, leaving a composite pattern portion of the pattern and the resistor circuit pattern.

The copper foil surface exposed by removing this dry photo film was etched and removed using the following compounded solution (temperature 50°C).
Further, the resistive material layer exposed by this etching is removed by etching with the following mixed solution (temperature: 90° C.).

copper foil etching liquid Cr 03 3009 Concentrated sulfuric acid 35g water 11 Etching solution for resistive material layer Fe2(S04)2 400g Concentrated sulfuric acid 368g water 11 Next, the remaining resist is peeled off, washed, and dried.

At this stage, the part to be formed into a conductor circuit (described later) consists of a gold plating layer, a copper foil layer, and a resistive material layer from the surface, and the part to be formed into a resistor circuit (to be described later) consists of a copper foil layer from the surface. The structure of the resistive material layer as well as the resistive material layer.

All of these parts are present on the upper surface of the support.

After drying, the circuit board is heated and pressurized using a lamination press under the conditions described above.

Pressing conditions Make-up Attach one mirror plate of stainless steel with a thickness of 2 mm to the front and back sides of the circuit board, and as cushioning material, attach 10 sheets each of cushion paper with a thickness of 2.00 mm on the top and bottom. Placement.

Temperature: 170℃ Pressure: 20Kg/i Pressure time: 40 minutes With this press, both the portion corresponding to the conductor circuit and the portion corresponding to the resistor circuit are press-fitted into the support plate, and these parts and the support plate are flush with each other. be made into

After pressing, the copper foil is removed from the portion corresponding to the resistor circuit pattern under the copper foil etching conditions described above.

By this removal, a resistor circuit is formed, and at the same time as this formation, a conductor circuit is formed.

Since the surface of the copper foil of the conductor circuit is coated with a gold plating layer, the copper foil of the conductor circuit is not removed during the above etching.

A photoresist film can also be used instead of this gold plating layer.

After the above etching, the resistor circuit is thoroughly washed and dried, and an epoxy cover coat is applied to the resistor circuit portion, thereby completing the manufacture of the variable resistor.

In the variable resistor thus obtained, the conductor surface of the conductor circuit is flush with the support plate, and the electrode surface that comes into contact with the brush and the support plate surface can be made flush.

Furthermore, when press-fitting the conductor material layer and the resistance material layer into the support plate, since the entire surface of the resistance material layer is covered with the conductor material layer, that is, copper foil, the resistance material layer may be partially There is no pressure-fitting (therefore, there is no cracking, breakage, etc. of the resistive material layer that occurs during this local press-fitting), and the properties of the resistive material layer can be maintained well.

[Brief explanation of drawings]

Figures 1, 2, and 3 are explanatory drawings to illustrate the present invention, with Figure 1 showing the stage before the press-fitting process, Figure 2 the stage after the press-fitting process, and Figure 3 the circuit. Each stage after molding is shown. In the figure, a is a resistive material, b is a highly conductive material, and C is a support.

Claims (1)

[Claims] 1. In a substrate in which a resistive material and a highly conductive material are sequentially laminated on an insulating support, the high conductivity of a portion that is in a negative image relationship with respect to a composite pattern of a conductive circuit pattern including an electrode terminal and a resistive circuit pattern material and the resistive material are removed, and then the remaining portions of the highly conductive material and the resistive material of the composite pattern are buried in the support by applying pressure,
A method for manufacturing a variable resistor, which comprises making the surface of the highly conductive material flush with the surface of the support, and then removing the highly conductive material from the patterned portion of the resistance circuit.