Flexible wiring board and method of manufacturing the same

Abstract

To provide a flexible wiring board which has proper adhesion between a base material and wiring and which can restrain volume resistivity from increasing due to corrosion of a metallic material constituting the wiring, and a method of manufacturing the same.SOLUTION: A flexible wiring board comprises a rubber base material that has a first surface and a second surface positioned on the opposite side of the first surface, and wiring that is provided on at least the first surface. The rubber base material, in which a rubber composition not containing sulfur is cross-linked, contains at least one kind of an ethylene propylene diene rubber and an ethylene butene diene rubber, or a butyl rubber.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a flexible printed circuit board and a method for manufacturing the same.

Background Art

[0002] As a wiring board used for curved surfaces, joint parts, etc. in medical devices such as iontophoresis, wearable devices, robots, etc., a flexible printed circuit board having stretchability, flexibility, etc. is used. A flexible printed circuit board generally has a base material having stretchability, flexibility, etc. and wiring formed on one surface of the base material. The wiring in the flexible board is required to have stretchability to the extent that it can follow the expansion and contraction of the base material. Conventionally, a wiring board having a stretchable resin layer containing a rubber component and a conductor foil or a conductor plating film provided on the stretchable resin layer and forming a wiring pattern is known (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Since the stretchable resin layer in the above wiring board contains a rubber component, sufficient stretchability can be obtained. However, the adhesion between the stretchable resin layer and the conductor foil or the like forming the wiring pattern decreases, and the conductor foil or the like peels off from the stretchable resin layer, or cracks occur in the stretchable resin layer. There is also a risk that the metal material constituting the conductor foil or the like corrodes over time, increasing the volume resistivity of the wiring.

[0005] In view of the above problems, an object of the present invention is to provide a flexible printed circuit board and a method for manufacturing the same, which have good adhesion between a base material and a wiring and can suppress an increase in volume resistivity due to corrosion of a metal material constituting the wiring.

Means for Solving the Problems

[0006] In order to solve the above problems, the present invention provides a rubber base material having a first surface and a second surface located on the opposite side of the first surface, and a wiring provided at least on the first surface. The rubber base material is formed by crosslinking a rubber composition containing at least one of ethylene propylene diene rubber and ethylene butene diene rubber, or butyl rubber and not containing sulfur. A flexible printed circuit board is provided.

[0007] The present invention is a method for manufacturing a flexible printed circuit board, which crosslinks and molds a rubber composition containing at least one of ethylene propylene diene rubber and ethylene butene diene rubber, or butyl rubber and not containing sulfur to produce a rubber base material having a first surface and a second surface located on the opposite side of the first surface. And a step of forming a wiring by printing a conductive paste on at least the first surface of the rubber base material. A method for manufacturing a flexible printed circuit board is provided.

Effects of the Invention

[0008] According to the present invention, it is possible to provide a flexible printed circuit board and a method for manufacturing the same, which have good adhesion between a base material and a wiring and can suppress an increase in volume resistivity due to corrosion of a metal material constituting the wiring.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0010] An embodiment of the present invention will be described. Aspect 1 in this embodiment includes a rubber base material having a first surface and a second surface located on the opposite side of the first surface, and wiring provided at least on the first surface. The rubber base material is a flexible printed circuit board formed by crosslinking a rubber composition containing at least one of ethylene propylene diene rubber and ethylene butene diene rubber, or butyl rubber, and not containing sulfur.

[0011] Aspect 2 in this embodiment is a flexible printed circuit board in which, in the above Aspect 1, the rubber composition contains inorganic particles. Aspect 3 in this embodiment is a flexible printed circuit board in which, in the above Aspect 1 or Aspect 2, the wiring is provided by printing a conductive paste on at least the first surface of the rubber base material.

[0012] Aspect 4 in this embodiment is a flexible printed circuit board in which, in any of the above Aspects 1 to 3, the volume resistivity of the wiring is 0.8×10 -5 ~2.0×10 -4 Ω·cm. Aspect 5 in this embodiment is a flexible printed circuit board in which, in any of the above Aspects 1 to 4, the thickness of the rubber base material is 0.1 to 0.3 mm.

[0013] Aspect 6 in this embodiment is a method for manufacturing a flexible printed circuit board, which includes a step of producing a rubber base material having a first surface and a second surface located on the opposite side of the first surface by crosslinking and molding a rubber composition containing at least one of ethylene propylene diene rubber and ethylene butene diene rubber, or butyl rubber, and not containing sulfur, and a step of forming wiring by printing a conductive paste on at least the first surface of the rubber base material.

[0014] Aspect 7 in this embodiment is a method for manufacturing a flexible printed circuit board in which the rubber composition contains inorganic particles in the above Aspect 6. Aspect 8 in this embodiment is a method for manufacturing a flexible printed circuit board in which, in the above Aspect 6 or Aspect 7, the volume resistivity of the wiring is 0.8×10 -5 ~2.0×10 -4 Ω·cm, and the conductive paste is printed on at least the first surface.

[0015] Aspect 9 in this embodiment is a method for manufacturing a flexible printed circuit board in which, in any of the above Aspects 6 to 8, the rubber base material with a thickness of 0.1 to 0.3 mm is produced. Aspect 10 in this embodiment is a method for manufacturing a flexible printed circuit board in which, in any of the above Aspects 6 to 9, the step of forming the wiring includes a step of forming a wiring pattern by printing the conductive paste on at least the first surface, and a step of heating the rubber base material on which the wiring pattern is formed under temperature conditions of 80 to 150°C to form the wiring.

[0016] FIG. 1 is a perspective view showing a schematic configuration of a flexible printed circuit board according to this embodiment. The flexible printed circuit board 1 according to this embodiment includes a rubber base material 2 having a first surface 21 and a second surface 22 located on the opposite side of the first surface 21, and a wiring 3 provided on the first surface 21. In FIG. 1, only the first surface 21 of the rubber base material 2, that is, an aspect in which the wiring 3 is provided only on one surface of the rubber base material 2 is shown, but the present invention is not limited to this aspect. For example, the wiring 3 may be provided on the second surface 22 of the rubber base material 2, that is, on both surfaces of the rubber base material 2. In this aspect, through holes for electrically connecting the wirings 3 provided on the first surface 21 and the second surface 22 in the thickness direction of the rubber base material 2 may be provided in the rubber base material 2.

[0017] The rubber material constituting the rubber base material 2 is formed by crosslinking a sulfur-free rubber composition. If the rubber base material 2 is composed of a rubber material formed by crosslinking (vulcanizing) a rubber composition containing sulfur, the adhesion of the wiring 3 to the first surface 21 and the second surface 22 of the rubber base material 2 will decrease, and the followability of the wiring 3 to the elastic deformation of the rubber base material 2 will decrease. As a result, problems such as at least a part of the wiring 3 peeling off from the rubber base material 2 may occur, and oxidation corrosion of the conductive material constituting the wiring 3 may easily occur, and the volume resistivity of the conductive material constituting the wiring 3 may increase. In the present embodiment, since the rubber material constituting the rubber base material 2 is formed by crosslinking a sulfur-free rubber composition, it is possible to prevent the occurrence of the above problems. In the present embodiment, "sulfur-free" means not only that sulfur is not completely contained in the rubber composition, but also that sulfur is contained in an amount less than the detection limit in the quantitative analysis method of sulfur in the rubber composition (for example, JIS K 6234: 1998), or sulfur is contained to such an extent that the above problems do not occur.

[0018] In the present embodiment, as the rubber composition, it may contain at least one of ethylene propylene diene rubber (EPDM) and ethylene butene diene rubber, or butyl rubber. Since the rubber base material 2 in the present embodiment is composed of a rubber material formed by crosslinking at least one of EPDM and ethylene butene diene rubber, or butyl rubber, it has the effect that the adhesion of the wiring 3 is good and a relatively thin rubber base material 2 can be easily produced. When a rubber composition containing a mixture of EPDM and ethylene butene diene rubber is used as the above rubber composition, the blending ratio of the two is not particularly limited.

[0019] The rubber base material 2 in the present embodiment may be formed by crosslinking the rubber composition using a resin such as an organic peroxide or an alkylphenol resin. When the rubber composition contains at least one of EPDM and ethylene-butene-diene rubber, the rubber base material 2 is preferably formed by crosslinking the rubber composition using an organic peroxide. When the rubber composition contains butyl rubber, the rubber base material 2 is preferably formed by crosslinking the rubber composition using a resin.

[0020] The rubber composition may contain a filler or the like having a relatively high volume resistivity. By including a filler or the like having a relatively high volume resistivity, the insulating property of the rubber base material 2 can be relatively enhanced. As the filler or the like, for example, inorganic particles are preferable, and those containing silicon such as silica (silicon dioxide), talc, mica, kaolinite (kaolin), wollastonite are particularly preferable. Further, the filler or the like may be a material having a volume resistivity of 10 10 Ω·cm or more, and preferably a material having a volume resistivity of 10 15 Ω·cm or more. For example, the rubber composition may contain inorganic particles having a volume resistivity of about 10 15 Ω·cm or more as the filler or the like.

[0021] In addition, the rubber composition may contain, for example, an antioxidant, a processing aid, a filler, a crosslinking aid, a crosslinking agent, etc., as long as the properties required for the rubber base material 2 in the present embodiment, that is, the insulating property (the volume resistivity of the rubber base material 2 is 10 7 Ω·cm or more), the rubber elasticity (stretchability), etc. are not hindered.

[0022] The volume resistivity of the rubber base material 2 in the present embodiment may be, for example, about 10 7 Ω·cm or more, preferably 10 10 Ω·cm or more, and particularly preferably 10 14 Ω·cm or more. If the volume resistivity is less than 10 7 Ω·cm, there is a risk of dielectric breakdown of the rubber base material 2.

[0023] In this embodiment, the thickness T2 of the rubber base material 2 may be, for example, 0.1 to 0.3 mm. If the thickness T2 of the rubber base material 2 is less than 0.1 mm, there is a possibility that the desired rubber elasticity cannot be obtained. If it exceeds 0.3 mm, it becomes difficult to contribute to the thinning of the flexible printed circuit board 1.

[0024] In this embodiment, the wiring 3 is provided by printing a conductive paste on the first surface 21 of the rubber base material 2. The conductive paste used to form the wiring 3 may be, for example, a conductive material such as metals such as gold, silver, copper, nickel, tin, stainless steel, iron, palladium, and compounds of these metals (for example, metal oxides, metal chlorides, etc.), and a binder resin component composed of a thermosetting resin such as an acrylic resin, a urethane resin, or an epoxy resin, and an organic solvent capable of dissolving the binder resin component.

[0025] The particle diameter of the conductive material is not particularly limited and can be appropriately set to such an extent that the formation of thin lines and smoothing of the wiring 3 formed by printing the conductive paste on the first surface 21 of the rubber base material 2 are not difficult.

[0026] The viscosity of the conductive paste is not particularly limited and may be appropriately set within a range in which the wiring 3 can be formed by printing on the first surface 21 of the rubber base material 2. For example, the viscosity of the conductive paste may be appropriately set within the range of 150 to 350 dPa·s. Note that the viscosity of the conductive paste may be a value measured, for example, using an EHD type viscometer in an environment of a 3-degree cone, 5 rpm, and 23°C.

[0027] As the above conductive paste, for example, DOTITE XA-9613, DOTITE XA-9605, DOTITE XA-9587 (all manufactured by Fujikura Kasei Co., Ltd.) are preferably used. According to the wiring 3 formed using these conductive pastes, it can preferably follow the elastic deformation of the rubber base material 2, and it is difficult to cause peeling from the rubber base material 2 and deterioration (increase in volume resistivity) due to the elastic deformation of the rubber base material 2.

[0028] The volume resistivity of the wiring 3 in this embodiment may be appropriately set according to the use of the flexible wiring board 1 according to this embodiment, etc. For example, 0.8×10 -5 ~2.0×10 -4 Ω·cm or so is sufficient.

[0029] The width of the wiring 3, the structure (circuit structure) of the wiring 3, etc. in this embodiment may be appropriately set according to the use of the flexible wiring board 1 according to this embodiment, etc., and is not limited to the example shown in FIG. 1.

[0030] A method for manufacturing the flexible wiring board 1 according to this embodiment will be described. The method for manufacturing the flexible wiring board 1 according to this embodiment includes a step of producing a rubber base material 2 having a first surface 21 and a second surface 22 located on the opposite side of the first surface 21 by crosslinking and molding a rubber composition, and a step of forming a wiring 3 by printing a conductive paste on the first surface 21 of the rubber base material 2.

[0031] In the step of producing the rubber base material 2, at least one of ethylene propylene diene rubber (EPDM) and ethylene butene diene rubber, or butyl rubber, and a filler having a relatively high volume resistivity such as silica are included, sulfur is not included, and an organic peroxide or a resin is included as a vulcanizing agent (crosslinking agent). After molding the rubber composition to a film thickness of about 0.1 to 0.3 mm, it is vulcanized (crosslinked) with the above vulcanizing agent (crosslinking agent). Thereby, a rubber base material 2 having a first surface 21 and a second surface 22 located on the opposite side thereof is produced.

[0032] Subsequently, a wiring pattern is formed by printing a conductive paste on the first surface 21 of the rubber base material 2. Examples of the printing method of the conductive paste include offset printing, gravure printing, screen printing, inkjet printing, etc., and preferably screen printing. By heating the rubber base material 2 on which the wiring pattern is formed under temperature conditions of 80 to 150 ° C, preferably 100 to 130 ° C, a wiring 3 is formed on the first surface 21 of the rubber base material 2. The lower the temperature condition for heating the rubber base material 2 on which the wiring pattern is formed, the less likely the rubber base material 2 is to deteriorate.

[0033] The embodiments described above are described to facilitate the understanding of the present invention and are not described to limit the present invention. Therefore, each element disclosed in the above embodiments is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

Example

[0034] Hereinafter, the present invention will be described in more detail with reference to examples and the like, but the present invention is not limited to the following examples and the like.

[0035] [Example 1] A rubber base material 2 (250 mm × 250 mm) was produced using a rubber composition containing ethylene-butene-diene rubber, an antioxidant, a filler (silicon dioxide), a plasticizer, and a peroxide crosslinking agent and not containing sulfur (containing 60 parts by mass of the filler and 7 parts by mass of the peroxide crosslinking agent with respect to 100 parts by mass of ethylene-butene-diene rubber). Then, a conductive paste (DOTITE XA-9613, manufactured by Fujikura Kasei Co., Ltd.) was applied to the first surface 21 of the rubber base material 2, and a baking treatment was performed at a temperature of 130 ° C for 5 minutes to form a conductive film on the first surface 21 of the rubber base material 2.

[0036] The volume resistivity of the conductive film formed on the first surface 21 of the rubber base material 2 was measured using a resistivity measuring device (product name: Digital Ultra High Resistance / Microammeter, manufactured by Advantest Corporation). As a result, the volume resistivity was 0.9×10 -4 Ω·cm.

[0037] Cuts were made at 2 mm intervals in the conductive film formed on the first surface 21 of the rubber base material 2 in each of one direction and the direction orthogonal thereto, and cellophane tape (registered trademark) was attached to the cut conductive film, and a tape test was conducted to peel off the cellophane tape (registered trademark). As a result, it was confirmed that there was no peeling of the conductive film and the adhesion of the conductive film was good.

[0038] Both ends in the vicinity of two opposite sides of the rubber base material 2 having the conductive film formed on the first surface 21 were fixed, and the rubber base material 2 was pulled so that the displacement amount (displacement amount = 50 mm) was 20% of the length (250 mm) of one side of the rubber base material 2, and a stretching and shrinking characteristic test was conducted to measure the volume resistivity of the conductive film while repeating the stretching and shrinking of the rubber base material 2 for 100 times, and the change rate of the volume resistivity of the conductive film was obtained by the following formula. The results of the stretching and shrinking characteristic test are as shown in FIG. 2. Further, when the rubber base material 2 after the stretching and shrinking characteristic test was visually confirmed, there was no peeling of the conductive film and the adhesion of the conductive film was good. Change rate of volume resistivity of conductive film = (A - B) / B In the above formula, A represents "the measured value of the volume resistivity of the conductive film during the stretching and shrinking characteristic test", and B represents "the volume resistivity of the conductive film before the stretching and shrinking characteristic test".

[0039] [Example 2] A conductive film was formed on the first surface 21 of the rubber base material 2 in the same manner as in Example 1 except that the rubber base material 2 coated with the conductive paste was subjected to a baking treatment at a temperature of 100 °C for 30 minutes, the volume resistivity of the conductive film was measured, and a tape test and a stretching and shrinking characteristic test were conducted. As a result, the volume resistivity of the conductive film was 0.8×10 -4 Ω·cm, and there was no peeling of the conductive film by the tape test. Also, there was no peeling of the conductive film by the stretching and shrinking characteristic test.

[0040] [Example 3] A rubber composition containing butyl rubber (Bayer bromobutyl X2), zinc oxide, carbon black, filler (kaolin), plasticizer, and resin crosslinking agent (Takkirol 250-I) and not containing sulfur (containing 50 parts by mass of filler and 10 parts by mass of crosslinking agent per 100 parts by mass of butyl rubber) was used to produce the rubber substrate 2. Except for this, a conductive film was formed on the first surface 21 of the rubber substrate 2 in the same manner as in Example 1, the volume resistivity of the conductive film was measured, and a tape test and a stretch and shrink characteristics test were conducted. As a result, the volume resistivity of the conductive film was 1.6×10 -4 Ω·cm, and there was no peeling of the conductive film. The results of the stretch and shrink characteristics test are as shown in Figure 2. Also, there was no peeling of the conductive film due to the stretch and shrink characteristics test.

[0041] [Example 4] A conductive film was formed on the first surface 21 of the rubber substrate 2 in the same manner as in Example 3, except that the rubber substrate 2 coated with the conductive paste was subjected to a firing treatment at a temperature of 100°C for 30 minutes. The volume resistivity of the conductive film was measured, and a tape test and a stretch and shrink characteristics test were conducted. As a result, the volume resistivity of the conductive film was 1.3×10 -4 Ω·cm, and there was no peeling of the conductive film. Also, there was no peeling of the conductive film due to the stretch and shrink characteristics test.

[0042] [Reference Example] A conductive film was formed on the first surface (one surface) of a film made of thermoplastic polyurethane resin (TPU) in the same manner as in Example 1. The volume resistivity of the conductive film was measured, and a tape test and a stretch and shrink characteristics test were conducted. As a result, the volume resistivity of the conductive film was 0.9×10 -4 Ω·cm, and there was no peeling of the conductive film. The results of the stretch and shrink characteristics test are as shown in Figure 2. Also, there was no peeling of the conductive film due to the stretch and shrink characteristics test.

[0043] As is clear from the above results and the results of the expansion and contraction property test shown in FIG. 2, the conductive film formed on the rubber base material produced using the rubber compositions containing ethylene-butene-diene rubber of Example 1 and Example 2 has the same conductivity as the conductive film formed on the thermoplastic polyurethane resin (TPU) generally used as a flexible printed circuit board, and also showed the same results in the expansion and contraction property test. Further, the conductive film formed on the rubber base material produced using the rubber compositions containing butyl rubber of Example 3 and Example 4 has the same conductivity as the conductive film formed on the thermoplastic polyurethane resin (TPU), and also showed excellent results in the expansion and contraction property test.

Explanation of Signs

[0044] 1... Flexible printed circuit board 2... Rubber base material 21... First surface 22... Second surface 3... Wiring

Claims

1. A rubber base material having a first surface and a second surface located on the opposite side of the first surface, and wiring provided at least on the first surface are provided, The rubber base material is made of a rubber material containing at least one of ethylene propylene diene rubber and ethylene butene diene rubber, or butyl rubber, The rubber material is formed by crosslinking a sulfur-free rubber composition, and a flexible printed circuit board characterized by this.

2. The flexible printed circuit board according to claim 1, wherein the rubber composition contains inorganic particles.

3. The flexible printed circuit board according to claim 1 or 2, wherein the wiring is provided by printing a conductive paste on at least the first surface of the rubber base material.

4. The volume resistivity of the wiring is 0.8×10 －５ to 2.0×10 －４ Ω·cm, and the flexible printed wiring board according to claim 1 or 2, characterized in that.

5. The flexible printed circuit board according to claim 1 or 2, wherein the thickness of the rubber base material is 0.1 to 0.3 mm.

6. A method for manufacturing a flexible printed circuit board, By crosslinking and molding a rubber composition containing at least one of ethylene propylene diene rubber and ethylene butene diene rubber, or butyl rubber, and not containing sulfur, a rubber base material having a first surface and a second surface located on the opposite side of the first surface is produced. Process, A process of forming wiring by printing a conductive paste on at least the first surface of the rubber base material A method for manufacturing a flexible printed circuit board, characterized by having.

7. The method for manufacturing a flexible printed circuit board according to claim 6, wherein the rubber composition contains inorganic particles.

8. The volume resistivity of the wiring is 0.8 × 10 －５ ~2.0 × 10 －４ Ω·cm, and the conductive paste is printed on at least the first surface, and the method for manufacturing a flexible printed circuit board according to claim 6 or 7 is characterized in that.

9. The method for manufacturing a flexible printed circuit board according to claim 6 or 7, characterized by producing the rubber base material having a thickness of 0.1 to 0.3 mm.

10. The step of forming the wiring includes a step of forming a wiring pattern by printing the conductive paste on at least the first surface, and heating the rubber base material on which the wiring pattern is formed under a temperature condition of 80 to 150 ° C. The method for manufacturing a flexible printed circuit board according to claim 6 or 7, characterized by including a step of forming the wiring.

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