JPS6318601A - Resistance circuit board - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of manufacturing a resistive circuit board in which a resistor is formed by printing carbon resistive paste between electrodes formed on an insulating substrate.

[Conventional technology]

In recent years, the production of resistive circuit boards using a printing method using copper foil electrodes has become popular. The production of circuit boards in which a resistor is formed by printing carbon resistance paste between rear electrodes is gaining prominence. However, as shown in FIG. 1, the difference in level between the insulating substrate 1 and the copper foil electrode 2 is usually as thin as 18 μm and as thick as 35 μm, especially when using copper through-holes.

In the case of the blank, the copper foil is thicker by the amount of plating, so the step difference between the sides is 45 to 60 μm larger. Therefore, if the resistor 4 is formed by printing a resistor paste between a pair of electrodes, only a resistive film with large variations will be obtained, and a resistor with excellent heat resistance, moisture resistance, etc. will not be obtained. In addition, even if you carefully print the resistor paste on a steel through-hole plated board, large depressions will occur at the interface between the electrode end and the insulating board, causing cracks to form during the hardening reaction process due to heating and causing a large change in resistance value. , sometimes causing wire breakage.

In order to form a resistive element with excellent electrical characteristics on an insulating substrate using the printing method, it is necessary to eliminate the level difference between the opposing electrodes on which the resistive paste is printed and the insulating substrate in the gap, so that the surface is smooth and uniform. This is an essential condition.

Various studies have been conducted to solve these problems. For example, if the conductor is thin, such as 17.5 μm, it is possible to easily form an almost identical insulating layer between the electrodes by printing once, but because the conductor is thin, its mechanical strength is low. Disconnection easily occurs, and 35μ
For thick copper foil electrodes such as those shown in Fig. 1, it is possible to form a thick insulating layer between the electrodes by repeatedly printing several times and eliminate the difference in level, but the productivity is low and it is difficult to say that this is a preferable method from an industrial perspective. . Therefore, as shown in Fig. 2, a resin layer 3 thinner than the electrode thickness is provided between the electrodes 2, and a ching resist 5 is provided between the electrodes.
A known method is to form a resistor by printing a resistor, etching it so that a part of the electrode on the opposing side is almost on the same surface as the insulating resin layer, and then connecting both electrodes.

However, it is not necessarily practical to re-notch the circuit electrodes that have already been formed by etching to make them flush with the insulating resin layer because of the difficulty in controlling the etching conditions and the complexity of the masking process. do not have. Also the third
As shown in the figure, there is also a method of printing an insulating resin layer 3 in the gap between the electrodes 2 so that it is on the same surface as the electrodes 2, and then forming the resistor 4 on it, but it is possible to Forming an insulating layer is difficult due to the accuracy of screen printing and technically, and in fact, sagging or bleeding of the paste may cause depressions at the boundary between the electrode and the insulating layer, and the insulating resin may adhere to the electrode due to the bleeding. Therefore, it cannot be put to practical use. As shown in FIG. 4, a method is also known in which an insulating resin layer 3 is provided overlapping the end of the electrode 2, and a resistor 4 is formed between the electrodes beyond this insulating layer 3. Although the difference in level between the electrode 2 and the resistor 4 becomes smaller, the part where the insulating resin layer 3 overlaps with the end of the electrode 2 is not smooth, and the resistor 4 formed thereon is not smooth. The thickness becomes uneven. In addition, when printing the insulating resin layer 3, sagging or bleeding is likely to occur in the area where it overlaps with the end of the electrode, and the resistor 4 that is formed beyond the insulating resin layer 3 has a narrow contact area with the electrode, resulting in a lower resistance value. This causes variations in the properties and tends to make the characteristics unstable.

[Purpose of the invention]

The purpose of the present invention is to improve the above-mentioned drawbacks of the conventional technology, provide an insulating layer between opposing electrodes and the gap between them, eliminate step differences, and form resistors on the same smooth surface, thereby reducing variations in resistance value and electrical characteristics. The present invention provides a resistor circuit board with excellent printing.

[Structure of the invention]

In order to eliminate the level difference between the electrode circuit pattern and the insulating substrate formed by the etching method of copper-clad laminates or the fully additive method on the insulating substrate, the condensation polymer resin is applied between the opposing electrodes to make the resin thicker than the electrodes. After forming an insulating layer by printing or coating it so that it overlaps a part or the entire area of the electrode, the insulating resin layer in the part that overlapped with the electrode is removed by puff polishing the surface of the insulating layer. Make the resin layer the same smooth surface as the electrode. Next, carbon resistance paste is printed on this smooth insulating resin layer so as to span between the opposing electrodes to form a resistor. Furthermore, by coating the resistor with an insulating resin, a highly reliable resistor circuit board can be obtained.

In order to remove the insulating resin adhering to the electrode and the excess insulating layer by polishing, it is important to select a polishing puff suitable for this purpose. In the present invention, we have discovered the fact that by using a brush containing an inorganic abrasive in the polishing process, the insulating resin adhering to the electrodes and the excess inter-electrode insulating layer can be removed by puff polishing, resulting in a smooth and uniform surface. It is something. Furthermore, since the condensation conditions of the resin greatly affect the hardness of the surface of the insulating resin layer, polishing is possible even if the condensation reaction is sufficiently completed, but polishing is easier if the condensation reaction is stopped before the step.

When implementing this application, it is important to select the condensation conditions of the resin used for the insulating layer and the polishing agent. When using an epoxy-based insulating resin, polishing puffs containing carborundum or metal oxide powder are important. preferable. In addition, when using a copper foil electrode, the reliability of the electrode portion can be further increased by printing and overlapping a part of the copper electrode with silver paste and printing a resistor paste thereon to form a resistor.

〔Example〕

Examples of the present invention will be described below. As shown in FIG. 5A, a copper foil pattern electrode 2 was formed on an insulating substrate 1 by etching the copper-clad laminate.

Next, as shown in FIG. 4 (b), a condensation polymer resin (Shikokukaki, FC-
- After printing C830), baking was performed for 10 minutes at 135C, which is lower than normal baking conditions, to form an insulating resin layer in a state before being completely cured. Thereafter, puff polishing (using Tsunoda brush No. 320) was performed over the entire surface of the substrate. During polishing, wet polishing was performed while running water. If the puff pressing pressure during polishing is too low, the insulating resin layer remains on the electrode, and if the pressure is too high, the insulating resin layer [3] tends to be polished too thin at the center far from both electrodes, so the puff By adjusting the pressure and polishing under optimum conditions, the insulating resin layer overlapping the electrode 2 was removed to obtain the same smooth surface as the electrode, as shown in FIG. Furthermore, as shown in Fig. 3(d), carbon resistance paste is printed on the insulating resin layer 3 across both electrodes so as to connect the opposing electrodes, and a resistor 4 is formed.
was formed, and a protective film 6 was further formed thereon to produce a resistive circuit board. In the resistor circuit board obtained in this way, the resistor is printed on a smooth insulating resin layer with large steps in the gap between the electrode and the insulating substrate, so sagging or fading may occur during printing. Therefore, the variation in resistance value was extremely small.

Hypurino) I C! using this resistor circuit board. When we performed solder reflow, which involves high temperatures during the manufacturing process, the rate of change in resistance was as small as -0.4 to -1.3 inches, compared to conventional resistance circuits manufactured using a method without an undercoat insulating resin layer. The board changed significantly from +5 to +10. Furthermore, even when an ultraviolet curable resin (Mitsui Toatsu MTUV 8033LV) was used as the undercoat, there was almost no difference in the rate of change in resistance value compared to a thermosetting resin (FC Hard 0830). 0 In carrying out the present invention, powders such as alumina, titanium oxide, boron nitride, and tetrafluoroethylene are added to the undercoat material as additives in order to improve various properties such as printability and polishability of the undercoat material. It is also possible to use a mixture.

〔Effect of the invention〕

As can be seen from the above examples, according to the present invention, the step of forming a smooth undercoat resin layer on the same surface as the electrode does not require complicated work, and the electrode and the insulating resin layer are formed on the same surface by facing each other. Since the surface is made smooth and then a resistive ink is printed across both electrodes to form a resistor, the depressions at the connection between the electrode part and the resistor disappear completely, and there is almost no difference in level. do not have. Also, since the resistive film thickness is constant, there is little variation in resistance value, making it a highly reliable hybrid IC with stable characteristics even under sudden changes in temperature and humidity.
It is possible to obtain a resistor circuit board for use in industrial applications, and the industrial effect is great.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional pattern without an undercoat insulating resin layer, Figures 2 and 3 are cross-sectional views of a conventional pattern with an undercoat insulating resin layer, and Figure 1 is a cross-sectional view of a conventional pattern with an undercoat insulating resin layer. 5(a), (b), (c), and (d) are sectional views showing the process according to the present invention. be. In the figure, 1 is an insulating resin substrate, 2 is a copper electrode, 3 is an undercoat insulating resin layer, 4 is a resistor, 5 is a protective film for etching,
6 is a resistor protective film. Patent applicant: Tokyo Cosmos Electric Co., Ltd.

Claims (1)

[Claims] An insulating layer is formed by printing an insulating resin slightly thicker than the electrodes in the gap between opposing electrodes formed on an insulating substrate, and then the electrodes and the insulating layer are polished so that they are on the same smooth surface. A method for manufacturing a resistor circuit board, characterized in that a resistor is formed by printing carbon resistor paste to connect opposing electrodes.