JPS618342A - Printed circuit substrate with flexible resistance layer - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a printed circuit board with a resistance layer, which has a resistance layer as a first layer and a conductor layer as a second layer on a flexible substrate. More specifically, the first layer is made of a heat-resistant film such as a polyimide film, or a flexible substrate consisting of two layers of heat-resistant resin coated on a metal foil, and the main component is indium oxide. The present invention relates to a printed circuit board with a resistive layer, characterized in that a certain resistive layer is provided, and a conductor layer is further provided as a second layer.

Conventionally, printed circuit boards with resistive layers are produced using printing methods,
There are products that are formed on a substrate by an electroless plating method, a vapor deposition method, etc., but all of them are formed on a hard substrate typified by glass ceramics or the like. Therefore, when mounting using these substrates, a uniformly flat location is required, and it is impossible to mount on an uneven surface, a narrow flat surface, or a gap on a curved surface. Therefore, in order to compensate for the above drawbacks, it is necessary to use a thin substrate with excellent flexibility. However, on a flexible substrate like this.

The problem with providing a resistive layer is that conventionally used resistors, such as nichrome, have a high degree of hardness, so cracks occur as the substrate deforms, making them unsuitable for use as resistors. It was possible.

The present invention solves the above-mentioned problems.The present invention suppresses the occurrence of cracks due to the elongation of the resistor itself when the flexible substrate is deformed. We have discovered a printed circuit board with a resistive layer that has better physical performance than Nichrome.

Conventionally, the required performance of a resistor has been to have a high specific resistance, little change over time, and a small temperature coefficient of resistance, and many compositions have been studied up to the present.

In the case of the resistor based on indium oxide according to the present invention, the weight ratio of nichrome:nickel:chromium is 80%:2
It was found that the elongation increased approximately 20 times compared to 0%).

Therefore, in order to obtain the desired resistance value, a resistor pattern with no abnormality in resistance value can be formed even after undergoing etching processes that involve various deformations of the board, and even in various mounting states. It was possible to obtain a printed circuit board with an extremely flexible resistive layer in which no change in value was observed. Furthermore, since the resistive layer of the present invention whose main component is indium oxide has a specific resistance more than five times that of nichrome, it is possible to form a resistor with a wider resistance value range than nichrome through pattern processing. In addition, it has become easier to miniaturize the resistor.

Furthermore, it was found that the required performance, such as change over time and temperature coefficient of resistance, is equivalent to or better than that of nichrome.

Furthermore, with the recent increase in the density of electronic components, the number of resistors to be mounted has also increased, and therefore the number of man-hours required for bonding to the electrode portions has a significant impact on cost. However, in the printed circuit board with a resistive layer according to the present invention, since the resistor part and the electrode part are integrated, the process can be omitted and processing costs can be significantly reduced.

If the lead wire is connected directly to a resistive layer made of indium oxide as a main component using solder, which is widely used in electronic materials, cracks will occur in the resistive layer due to the sudden stress after the solder is attached, and the resistive layer will not be used. I can't do it.

This is because the stress generated when the solder cools is equal to the breaking strength of the solder and is directly applied to the resistance layer, and the stress is relaxed in the form of cracks near the interface.

In this regard, according to the present invention, a conductive layer is formed on the resistive layer and solder is applied to the conductive layer, so that the resistive layer can be protected and a stable flexible resistor can be obtained. In addition, since long-term stability under various environments is required for use as an electronic component, electrode attachment using conductive paste or conductive rubber will result in instability. In particular, when used as a resistor, which is the object of the present invention, it cannot withstand use in a high temperature and humidity environment or from the viewpoint of the temperature coefficient of resistance.

The present invention will be described in more detail below.

There are no particular restrictions on the substrate used in the present invention as long as it has sufficient flexibility, but for high-temperature use, polyimide, polyetherimide, or polyethersal, which have excellent heat resistance that can withstand soldering, may be used. The most desirable material is a composite substrate in which a film such as fluorine or a resin thereof is adhered onto a metal foil.

In particular, when a transparent polyetherimide or polyethersulfone film is used as a substrate, many applications can be expected, such as a transparent flexible resistor that can be used for surface switches and the like.

Next, as the resistance layer, it is preferable to use a material whose main component is indium oxide, which is flexible and chemically stable.

Here, as components other than indium oxide, tin, antimony, cadmium, indium, aluminum, titanium, etc., or oxides thereof are preferable, although they vary depending on the intended resistivity. Further, it is preferable that the weight ratio of ileidium acid is 70 to 98%. This is because when it becomes 98- or more, it becomes close to an insulator and the resistivity increases too much, making it impossible to use it as a general resistor.

Further, the thickness of the resistive layer containing indium oxide as a main component varies depending on the desired resistance value and area limitations, but it is preferably 0.03 to 0.2 μm, which stabilizes the resistivity. Further, the conductor layer formed on the resistance layer is preferably made of copper from the viewpoint of conductivity.

The present invention will be explained in detail below with reference to Examples.

Example 1.2 84w of indium oxide as the main component was applied as a resistive layer on the resin coating of a board made of 10^ of polyimide resin on a 50μ polyimide film and a 7.5μ thick copper foil.
t5 A resistive layer in which a compound containing 16 wt% of tin oxide as other components is formed by sputtering to a thickness of 0.1 μm, and copper is continuously formed as a conductor layer to a thickness of 5 μm by sputtering. 10 in the circuit using a printed circuit board with
A thin film resistor with a diameter of 0 μm and a length of 8 On was formed by chemical etching. Table 1 shows the flexibility of this thin film resistor and the specific resistance relative to nichrome. The flexibility in Table 1 is indicated by the presence or absence of abnormal parts due to deformation during processing and the presence or absence of resistance value change when mounted so as to wrap around a curvature surface of radius L5+w.

Comparative Example 1 An alloy consisting of 20 nickel and chromium with a weight ratio of 80% was formed as one resistance layer on a 50μ polyimide film to a thickness of J 0.1μ by sputtering, and copper was further continuously formed as a conductor layer. Table 1 shows the results of forming a similar thin film resistor using a printed circuit board with a resistive layer formed by sputtering to a thickness of 5 μm.

As is clear from Table 1, the thin film resistor fabricated using the printed circuit board with a resistive layer according to this example has a higher specific resistance than nichrome and exhibits extremely excellent flexibility. I understand.

Claims (3)

[Claims] (1) With a flexible resistance layer characterized by providing a resistance layer mainly composed of indium oxide as a first layer on a flexible substrate, and further providing a conductor layer as a second layer on top of the resistance layer. printed circuit board. (2) A printed circuit board with a resistive layer according to claim (1), wherein the flexible substrate is a heat-resistant resin film such as polyimide. (3) A printed circuit board with a resistive layer according to claim (1), wherein the flexible substrate is made of two layers of metal foil coated with heat-resistant resin.