JPH047596B2 - - Google Patents

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 a resistor whose main component is indium oxide on a flexible substrate consisting of two layers of heat-resistant film such as polyimide film or metal foil coated with heat-resistant resin. The present invention relates to a printed circuit board with a resistive layer, which is characterized in that a conductive layer is provided as a second layer. Conventionally, printed circuit boards with resistive layers have been formed on substrates by printing methods, electroless plating methods, vapor deposition methods, etc., but all of them are formed on hard substrates such as glass ceramics. There is. Therefore, when mounting using these boards, a uniformly flat location is required, and uneven surfaces,
It is impossible to implement it in narrow spaces on flat surfaces and curved surfaces. Therefore, in order to compensate for the above drawbacks, it is necessary to use a thin substrate with excellent flexibility. However, the problem with providing a resistance layer on such a flexible substrate is that all conventionally used resistors, such as nichrome, have high hardness, so they do not easily deform as the substrate deforms. A crack occurred, making it impossible to use it as a resistor. The present invention solves the above problems,
When a flexible board is deformed, the resistance layer itself suppresses clock generation by elongating, withstands use in a variety of mounting conditions, and has a resistance layer with better performance than Nichrome as a resistor. This is how we discovered the substrate. Conventionally, the required performance of a resistor is 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. It has been found that in the case of the low antibody containing indium oxide as a main component according to the present invention, the elongation is approximately 20 times greater than that of nichrome (nickel:chromium weight ratio 80%:20%). 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 value deformation 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. Also, it has become easier to downsize the resistor. Furthermore, it was discovered that it has performance equivalent to or better than nichrome in terms of aging and temperature coefficient of resistance, which are required performances. 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 wires are joined directly to the resistor layer, which is mainly composed of indium oxide, using solder, which is widely used in electronic materials, the resistor layer will crack due to the sudden stress after solder adhesion, and the resistor layer will become unusable. 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 a crack near the interface. In this regard, according to the present invention, a conductive layer is formed on the resistive layer and soldered to the resistive layer, so that the resistive layer can be protected and a stable flexible resistor can be obtained. In addition, in order to use it as an electronic component, long-term stability under various boundaries is required, so when attaching electrodes using conductive paste or conductive rubber,
Becomes unstable. 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 of these materials is bonded onto a metal foil. In particular, when a transparent polyetherimide or polyether sulfone film is used as the substrate, it becomes a transparent flexible resistor that can be used in surface switches, etc., and is expected to have many applications. Next, as the resistance layer, it is preferable to use a material mainly composed of indium oxide, which is flexible and chemically stable. Here, components other than indium oxide vary depending on the target resistivity, but include tin, antimony, cadmium, indium, aluminum,
Titanium or the like or oxides thereof are preferred.
Further, the weight ratio of indium oxide is preferably 70 to 98%. This is because when it exceeds 98%, it approaches an insulator and its resistivity increases so much that it cannot be used 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 μ so that the resistivity is stable.
Further, the conductor layer formed on the resistance layer is preferably made of copper in terms of conductivity and workability. The present invention will be explained in more detail with reference to Examples below. Examples 1 and 2 A resistive layer was formed on a resin coating of a board made of a 50μ polyimide film and a 7.5μ thick copper foil coated with 10μ of polyimide resin, with 84wt% of indium oxide as the main component and oxidation as other components. tin
A compound containing 16wt% was formed to a thickness of 0.1μ by sputtering, and a conductive layer of 5μ of copper was further formed.
A thin film resistor with a circuit width of 100 μm and a length of 8 cm was formed using a chemical etching method using a printed circuit board with a resistive layer formed to a thickness of 100 μm by a sputtering method. Table 1 shows the flexibility of this thin film resistor and the specific resistance relative to nichrome. In addition, flexibility in Table 1 is indicated by the presence or absence of abnormalities due to deformation during processing and the presence or absence of resistance value changes when mounted so as to wrap around a curvature surface with a radius of 1.5 mm. . Comparative Example 1 An alloy consisting of 80% and 20% nickel and chromium by weight was formed as a resistive layer on a 50μ polyimide film to a thickness of 0.1μ, and a conductive layer of 5μ of copper was formed continuously. Table 1 shows the results of forming a similar thin film resistor using a printed circuit board with a resistive layer formed by sputtering.

[Table] 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 resistivity than nichrome, and has excellent flexibility. It can be seen that this shows that

Claims (1)

[Claims] 1. A resistive layer whose main component is indium oxide is provided as a first layer on a flexible substrate, and a conductive layer is further provided as a second layer thereon. Printed circuit board with flexible resistive layer. 2. The printed circuit board with a resistance layer according to claim 1, wherein the flexible substrate is a heat-resistant resin film such as polyimide. 3. The printed circuit board with a resistive layer according to claim 1, wherein the flexible substrate is composed of two layers of metal foil coated with heat-resistant resin.