JPS5813005B2 - How to form a resistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a resistor that suppresses the effects of heating and power application to form a stable resistor.

Multilayer wiring boards have been developed in which not only a conductive foil but also a resistor is formed on a printed wiring board by printing or the like, or a multilayer wiring board is formed by printing a second layer of conductive foil.

Traditionally, resistors formed on these printed wiring boards have been
A printed resistor is known in which a suitable amount of a powder of a conductive substance such as carbon, a filler made of an inorganic material, etc. is mixed into a resin, and the mixture is made into a paste, printed and solidified.

However, it has been pointed out that the resistor formed in this manner has a defect in that the resistance value changes over time, for example, in the direction of lowering, due to heating during soldering or when electric power is applied.

Therefore, it could not be used in equipment that required accurate circuit constants.

This invention aims to improve these drawbacks by using a resin carbon-based resistance ink containing an inorganic filler, and forming a protective coat mainly made of a heat-resistant, low-humidity resin on the resistor. The purpose of the present invention is to provide a method for forming a resistor that can physically strengthen the resistor, suppress the effects of heating and power application, and make the resistor stable.

This invention will be explained below.

In this invention, after printing on a substrate using a resin carbon-based resistance ink containing 5 to 100 parts by weight of an inorganic filler with a size of 1μ or less based on 100 parts by weight of a resin and baking it, the ink is printed on the resistor. This method of forming a resistor is characterized by printing and firing using a protective coating ink mainly made of a heat-resistant and moisture-resistant resin such as a novolak type epoxy resin.

Since the resistor contains a relatively large amount of fine insulating inorganic matter, fine irregularities or voids are formed on the surface and inner layers of the resistor after firing.

In this state, a heat-resistant and moisture-resistant resin such as a novolak type epoxy resin is coated in a solution, and then baked and solidified.
Due to the physical lead effect, the resistor and the protective coat are strongly bonded, and as a result, the resistor is firmly fixed by the protective coat.

In addition, the thermal and moisture characteristics of the resistor are improved by forming a resin layer on the upper surface of the resistor. It has been known that thermal and moisture-resistant epoxy resins are greatly affected by heat and humidity, but when a heat-resistant and moisture-resistant novolak-type epoxy resin is used for printing as in this invention, It now depends on the visibility of the novolak resin on the top surface, and its thermal and moisture resistance has been significantly improved.

Furthermore, cured products of heat-resistant and moisture-resistant resins have extremely good thermal stability and are also excellent in humidity, so the resistor also has excellent thermal stability.
Becomes moisture stable.

The insulating inorganic substance contained in the resistor is not limited to % as long as it is not water-soluble or hydrolyzable, does not react with the composition of the resistance ink, and is thermally stable up to about 200C. However, those that give the best results for that purpose include ions, alumina, titanium dioxide, and the like.

The reason for limiting the insulating inorganic fine powder to 5 to 100 parts by weight per 100 parts by weight of the resin in the resistance ink is that if it is less than 5 parts by weight, it will have a poor stabilizing effect on the resistor, and if it is more than 100 parts by weight, it will resist the resistance. This is because cracks occur during firing of the body, making it impossible to obtain a predetermined resistance value.

The reason why the size of the insulating inorganic fine powder is limited to 1 μm or less is because if the size is 1 μm or more, the stabilizing effect of the resistor becomes poor.

On the other hand, the protective coating layer formed on the upper surface of the resistor is made of a heat-resistant and moisture-resistant resin, for example, a composition mainly composed of a novolak type epoxy resin, and a composition consisting of a phenol condensate or cresol condensate and shrimp chlorolyhydrin. Obtained by reaction.

R:H or CH3 is the composition of the formula.

When this resin is coated on the upper surface of the resistor containing insulating inorganic fine powder, it exhibits a remarkable effect on stabilizing the resistor.

Note that the above-mentioned effects cannot be obtained with bisphenol-based epoxy resins, phenol resins, epoxy melamine resins, etc. that are commonly used as protective coatings.

Furthermore, if a novolak type epoxy resin is used as the resin component of the resistance ink and the protective coat is removed, it is expected that a good printed resistor will be obtained due to the novolak type epoxy resin's excellent heat resistance and moisture resistance. As a result of the experiment, there was almost no difference from ordinary resol type phenolic resin.

This is thought to be because a relatively large amount of carbon or inorganic insulating material is mixed in compared to the amount of resin, making it difficult to form a continuous resin layer, and therefore unable to exhibit the characteristics of the resin.

Next, a specific example will be explained.

100 parts by weight of resol type phenolic resin, 10 parts by weight of acetylene black, and the inorganic filler shown in Table 1 were collected in the parts by weight shown in Table 1, and 130 parts by weight of butyl carpitol acetate were taken and kneaded with a paint roll. The printing resistance ink was adjusted by

A resistor was formed by screen printing on NEMA standard, XXXPC grade paper and a phenol substrate, and heated to 150°C.
After baking for a period of time, 100 parts by weight of a novolac type epoxy resin (trade name: Araldite ECN1280), 15 parts by weight of m-phenylenediamine, and 50 parts by weight of tetralin were placed on the resistor.
Parts by weight were added, and a homogeneous ink was coated by screen printing to a thickness of about 30 μm, and baked at 150 C for 30 minutes.

Table 1 shows the results of the heat resistance load test and the humidity resistance load test for Examples (4 examples) of the present invention and Comparative Examples (3 examples) not of the present invention.

The conditions for the heat resistance load test are a 70C atmosphere and a rated voltage of 90C.
After a cycle of applying for 30 minutes and shutting off for 30 minutes was continued for 1000 hours, measurements were taken at room temperature, and the rate of change from the initial value was shown.

In addition, the humidity load test showed results similar to the high temperature load test in a 40C95% atmosphere.

Looking at the examples and comparative examples of this invention from Table 1,
It is clearly seen that the thermal stability of the printed resistor, which is obtained by coating the resistor containing insulating fine inorganic powder with a particle size of 1 μm or less with a novolac type epoxy resin, is improved.

As described above, according to the present invention, it is possible to provide a method for forming a resistor in which the resistor is firmly fixed by a protective coat, has very little influence even when heated or electric power is applied, and has excellent stability. can.

Claims (1)

[Claims] 1. A resin carbon-based resistance ink containing 5 to 100 parts by weight of an inorganic filler of 1 μm or less per 100 parts by weight of resin is printed on a printed wiring board, and after baking, novolak type epoxy is applied on top of this. A method for forming a resistor by printing and firing a protective coating ink mainly composed of resin.