JPH0423341Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Purpose of the invention] (1) Industrial application field The present invention relates to a flexible printed circuit board having an excellent moisture-resistant conductor pattern. (2) Conventional technology Conventionally, flexible printed circuit boards are made by attaching aluminum or copper to a thickness of 500 to 2000 Å on flexible polyethylene terephthalate film (PET) using a vacuum evaporation method. A layer with a carbon coating layered on top is generally used. (3) Problems to be Solved by the Invention The above-mentioned conventional products have the disadvantage that the metal conductor layer has insufficient moisture resistance and is easily corroded, resulting in loss of electrical conductivity over time. The present invention consists of alternately laminating multiple layers of highly conductive metals with poor corrosion resistance, such as aluminum, copper, and silver, and thin films of chromium or corrosion-resistant metals containing chromium, as metal conductor thin film layers, and then applying a carbon coating on top. By having a laminated structure, the surface resistance of the conductor is 1Ω/□ or less, and an inexpensive and practically good flexible printed circuit board with superior corrosion resistance than conventional ones is provided. [Structure of the invention] In the present invention, flexible films include polyolefins such as polyethylene and polypropylene, polyamides such as nylon 6, nylon 66, and nylon 12, polyethylene terephthalate, and polybutylene terephthalate. Examples include films made of organic resins such as polyester-based, cellulose-based such as polynitrocellulose and polycellulose acetate, polyvinyl alcohol, trifluorinated polyethylene, polycarbonate, polymethyl methacrylate, and polyimide. may be a single layer or two or more layers bonded together. but,
The flexible film needs to have no heat shrinkage and high dimensional stability in order to improve pattern accuracy, so it is preferably biaxially stretched and further annealed. The thickness of the film is preferably 5 μm or more and 300 μm or less, and particularly preferably 25 μm or more and 100 μm or less in terms of ease of handling and durability against external impact. That is, if the thickness is 25 μm or less, the durability is poor, and if the thickness is 100 μm or more, the flexibility is poor. In addition, in this invention, highly conductive metals include copper,
This refers to aluminum, silver, and their alloys, etc., and thin films of these highly conductive metals and chromium or corrosion-resistant metals containing chromium are generally produced by vacuum evaporation, sputtering, ion plating, etc. The film is vacuum-deposited uniformly onto the surface of the flexible film base material. More specifically 10 ^-2
Metals are heated and vapor-deposited using resistance heating ^, induction heating, or high-frequency heating in a high vacuum atmosphere of ~ ^{10 -7} mmHg, or vapor deposition is performed using an inert gas such as argon gas. A thin film of metal target material is sputtered in a high vacuum to deposit it onto the flexible film of the substrate. The thickness of the metal varies depending on the current carrying capacity of the circuit and the width and length of the conductor in the circuit, but in order to obtain stable electrical conductivity, a film of 0.005 μm or more of highly conductive metal such as copper, aluminum, or silver is required. Requires thickness. In addition, the corrosion-resistant chromium or chromium-containing metal thin film is 0.005 μm in thickness to protect against the lack of corrosion resistance of highly conductive metals such as copper, aluminum, and silver.
The film thickness is preferably in the range of 0.05 to 0.039 μm. In this case, chromium has excellent corrosion resistance but poor malleability, so it is preferable to use an alloy with nickel or the like as necessary. There is no particular limit to the number of times these two types of metals with different electrical conductivity and corrosion resistance can be laminated, but the total thickness of the metal thin film lamination must be in the range of 0.01 to 0.1 μm, and should be in the range of 0.02 to 0.09 μm. is preferred. If the total thickness of the metal thin film stack is less than 0.01 μm,
Deterioration of electrical conductivity or corrosion resistance occurs. If the total thickness exceeds 0.1 μm, cracks will appear on the surface of the laminated metal thin film, impairing its continuous electrical conductivity as a conductor. Further, there is no particular restriction on the order in which the two types of metals are laminated on the surface of the flexible film, but a film having a corrosion-resistant metal layer on the surface has a more remarkable effect on corrosion resistance. In addition, the carbon layer in the present invention is a layer laminated by printing or other methods on top of a multilayer stack of metal thin films for the purpose of improving conductivity and reinforcing the strength of the pattern, and has a thickness of 0.1 μm or more and is made up of continuous fine particles. An electrically conductive coating with a thickness of less than 30 μm is preferred. [Effects of the invention] Examples of the flexible printed circuit board according to the invention will be described below with reference to the drawings together with conventional comparative examples. 1, 2, and 3 are cross-sectional views of embodiments of the present invention, in which 1 is a flexible film as a base material, 2, 3,
4 indicates a laminated conductor portion. 2 is electrically conductive 500Å
3 is a sputtered film of corrosion-resistant chromium or nickel-chromium alloy (alloy weight ratio 80/20) with a thickness of 400 Å, 4 is a 1 μm thick sputtered film
The carbon coating film has a thickness of . In these figures, a plurality of layers may be alternately laminated in parts 2 and 3. Figure 4 is a cross-sectional view of a conventional flexible printed circuit board.Since the metal conductor part is composed only of this electrically conductive metal, its corrosion resistance is insufficient and the metal layer is prone to corrosion in a high humidity atmosphere. A problem occurs. On the other hand, in the case of a conductor made only of corrosion-resistant chromium or a metal containing chromium, the electrical conductivity is insufficient, and the surface resistance value is limited to 10Ω/□ at most even in the case of thick film deposition. That is, only by using a conductor in which the two types of metal thin film layers described above are alternately laminated as in the present invention can a flexible printed circuit board with excellent electrical conductivity and moisture resistance be obtained. Examples and comparative examples will be described in more detail below. One side of a 50 μm thick biaxially stretched polyethylene terephthalate film (PET) was coated with Al or Cu to a thickness of 400 Å using a Bergier type vacuum evaporator at a vacuum level of 2 × 10 ^-4 mmHg. weight ratio 80/20) or chromium 5
It was deposited to a thickness of 400 Å using a magnetron type sputtering device with a vacuum level of ×10 ^-3 mmHg.
On top of that, a continuous comb-like conductor pattern with a width of 2 μm and a total length of 1 m was laminated using carbon paint to a thickness of 1 μm using the screen printing method. Then, the parts other than the carbon printed parts were immersed and dissolved in an etching solution containing 5% ferric chloride and 5% hydrofluoric acid to produce flexible printed circuit boards having the configurations shown in Tables 1 and 2. The conductor resistance values were measured before and after immersion in boiling water. The results are shown in Tables 1 and 2.

【table】

【table】 [Brief explanation of the drawing]

1 to 3 are cross-sectional views of an embodiment of a flexible printed circuit board according to the present invention, and FIG. 4 is a cross-sectional view of a conventional flexible printed circuit board. 1... Flexible film, 2... Vapor deposited thin film of a metal with excellent electrical conductivity, 3... Vapor deposited thin film of chromium or a corrosion-resistant metal containing chromium, 4... Coating film made of carbon powder.

Claims (1)

[Scope of utility model registration request] In a flexible printed circuit board in which a metal thin film conductor is provided on a flexible film, the conductor is an alternating multilayer laminate of two or more layers of a highly conductive metal and chromium or a corrosion-resistant metal containing chromium. The total thickness of the conductor is
1. A flexible printed circuit board having a moisture-resistant conductor pattern having a thickness of 0.01 to 0.1 μm and further laminated thereon with a carbon layer having a thickness of 0.1 μm or more.