JP4128341B2 - Flexible wiring board substrate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wiring board substrate.
[0002]
[Prior art]
Conventionally, a wiring board substrate in which a metal foil such as a copper foil is laminated on a substrate has been widely used. This wiring board substrate is used as a printed wiring board by a photolithography technique in which a wiring pattern is drawn on a metal foil portion and etching or the like is performed along the wiring pattern, and is used in various electric / electronic devices.
[0003]
In general, the printed wiring board may generate heat from a circuit with use. In that case, if heat accumulates in the vicinity of the circuit and the temperature rises, an unexpected failure such as thermal runaway may occur, and thus the generated heat needs to be quickly dissipated. However, many conventional printed wiring board substrates (that is, wiring board substrates) are made of synthetic resin such as phenol resin, and such synthetic resin is inferior in thermal conductivity, so that the generated heat is sufficient. There was a problem that could not be released.
[0004]
By the way, with recent downsizing and thinning of electronic devices, development of printed wiring boards that can be mounted in a narrower space is desired. On the other hand, for example, a flexible printed wiring board in which a metal circuit is formed on a polyimide film to give flexibility as a whole is known. However, this flexible printed wiring board also has the problem that the thermal conductivity is low and the heat dissipation is insufficient because the substrate is a resin film, as in the above example.
[0005]
[Problems to be solved by the invention]
Therefore, in view of the above-described conventional situation, the present invention is flexible as a whole and can be arbitrarily bent, has excellent thermal conductivity, and can quickly dissipate generated heat. It is an object of the present invention to provide a novel flexible wiring board substrate.
[0006]
To solve the above problems, a substrate for flexible wiring board of the present invention, the at least one surface of the sheet-like graphite having a flexibility which is 100 to 300 [mu] m, not impaired flexibility of the sheet-like graphite thickness The conductive metal layer is laminated through a woven or non-woven fabric impregnated with an adhesive and having an insulating property ,
The woven or non-woven fabric has a thickness of 50 to 200 μm, a tensile strength (according to the synthetic fiber nonwoven fabric test method of the Japan Chemical Fiber Association) of 20 to 400 N / 5 cm, and a basis weight of 10 g / m ² or more. and wherein the der Rukoto.
[0007]
According to the said structure, a sheet-like graphite and a conductive metal layer are integrated via an insulating woven fabric or a nonwoven fabric. And the heat | fever generate | occur | produced in the case of use is rapidly thermally radiated with the sheet-like graphite excellent in thermal conductivity. In addition, even if the manufactured wiring board substrate is bent, for example, the wiring board substrate flexibly follows the large deformation, and in particular, the sheet-like graphite is reinforced by a woven fabric or a non-woven fabric. Defects such as peeling do not occur. Furthermore, since the sheet-like graphite and the metal foil or the metal plating layer are reliably separated by the thickness of the woven or non-woven fabric, an accident such as a short circuit is prevented.
[0009]
According to the said structure, the thickness of a woven fabric or a nonwoven fabric is optimized from a viewpoint of fully exhibiting the reinforcement effect by a woven fabric or a nonwoven fabric, maintaining the high thermal conductivity of the whole board | substrate for flexible wiring boards.
[0011]
According to the above configuration, the tensile strength of the woven fabric or the non-woven fabric is optimized so that even if the wiring board substrate is arbitrarily bent and a large deformation is applied, the wiring board substrate is not defective. Moreover, if the tensile strength of the woven fabric or the nonwoven fabric is sufficiently high, the flexible wiring board substrate can be continuously manufactured by a winding tension device or the like.
[0013]
According to the said structure, the thickness of sheet-like graphite is optimized considering the heat dissipation of the board | substrate for flexible wiring boards, and the balance of flexibility.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
FIG. 1 schematically shows a cross section in the embodiment (1) of the substrate for flexible wiring board of the present invention. The flexible wiring board substrate 1 in FIG. 1 is generally configured by laminating a conductive metal layer 4 on one side of a sheet-like graphite 2 with an insulating woven or nonwoven fabric 3 interposed therebetween. In laminating, for example, the adhesive 5 can be used for attachment. In FIG. 1, for convenience, a three-layer structure in which a woven or non-woven fabric 3 is sandwiched between adhesives 5 between the sheet-like graphite 2 and the conductive metal layer 4 is depicted. In this case, the adhesive 5 is preferably cured while being impregnated in the woven or non-woven fabric 3, and in this case, the three-layer structure is overlapped to form one layer.
[0015]
As the sheet-like graphite 2, various conventionally known graphite sheets can be appropriately selected and used on condition that they are flexible. For example, those derived from natural graphite, those derived by graphitizing a polymer compound, and the like can be mentioned. Here, “having flexibility” means that the sheet-like graphite 2 is not cracked in appearance when it is bent 90 ° at R = 10 mm.
[0016]
If the thickness of the sheet-like graphite 2 is too thick, the flexibility is lowered. On the other hand, if the thickness is too thin, the influence of the thickness of the woven fabric or the nonwoven fabric 3 is increased, and sufficient heat dissipation cannot be obtained. It is set as appropriate in consideration of balance. Specifically, the thickness is preferably about 100 to 300 μm, but is not limited thereto.
[0017]
Moreover, in order to improve adhesiveness with the woven fabric or the nonwoven fabric 3, the primer can also be beforehand apply | coated to the surface of the sheet-like graphite 2 as needed. As an example of this primer, primer C (trade name: manufactured by Shin-Etsu Silicone), primer X (trade name: manufactured by Toray Dow Corning Silicone), primer Y (trade name: manufactured by Toray Dow Corning Silicone), ME151 (trade name: manufactured by Toshiba Silicone) and the like can be mentioned.
[0018]
Next, the woven or non-woven fabric 3 can be appropriately selected from woven or non-woven fabrics such as various synthetic fibers, natural fibers, and glass fibers on the condition that it has electrical insulation. As a suitable example of such a woven or non-woven fabric, there can be mentioned a non-woven fabric made of aramid fibers such as meta-aramid paper (trade name: manufactured by DuPont Teijin Advanced Paper). By laminating the woven fabric or the non-woven fabric 3, the safety when the entire flexible wiring board substrate 1 is bent is increased, and the sheet-like graphite 2 is not cracked against a large deformation. Further, by interposing the woven fabric or the non-woven fabric 3, the sheet-like graphite 2 and the conductive metal layer 4 can be reliably separated, and an accident such as a short circuit can be prevented.
[0019]
When the thickness of the woven fabric or the nonwoven fabric 3 is too thick, the thermal conductivity of the entire heat conductive sheet 1 is lowered, which is not preferable. On the other hand, when the thickness is too thin, a sufficient reinforcing effect on the sheet-like graphite 2 cannot be obtained. Since there is a possibility of short-circuiting, it is appropriately set in consideration of these balances. Specifically, about 50-200 micrometers is suitable, Preferably it is 50-100 micrometers.
[0020]
The woven fabric or non-woven fabric 3 may be a coarse mesh or the like, but if the mesh is too coarse, the sheet-like graphite 2 and the conductive metal layer 4 are short-circuited at the through-hole portion of the mesh. It is necessary to be careful. The specific roughness of the mesh is not unequivocally related to the thickness of the woven fabric or the nonwoven fabric 3, but it is preferable that the basis weight is at least 10 g / m ² or more.
[0021]
In consideration of the case where the flexible wiring board substrate 1 of the present invention is manufactured as a continuous sheet by a winding tension device, for example, the woven fabric or the nonwoven fabric 3 in the present invention is strong against external force. It is desirable to use it. Specifically, it is preferable to use a woven fabric or a nonwoven fabric 3 having a tensile strength of about 20 to 400 N / 5 cm. In addition, the said tensile strength is a value obtained by the synthetic fiber long-fiber nonwoven fabric test method of Japan Chemical Fiber Association.
[0022]
And the conductive metal layer 4 is comprised from the various metals conventionally used for the board | substrate for wiring boards, and has a softness | flexibility to the extent which can follow the deformation | transformation of the board | substrate for wiring boards. The example of FIG. 1 is a case where a metal foil 41 is used as the conductive metal layer 4. In general, a copper or nickel foil is preferably used as the metal layer 41. In addition, the thickness of the metal foil 41 is not particularly limited, but the present invention is one of the characteristics that is a flexible wiring board substrate, and therefore does not hinder the overall flexibility. A relatively thin layer is preferable. Here, the metal foil 41 includes not only a so-called metal foil before the circuit pattern is formed by means such as photolithography but also a lead frame produced by punching the circuit pattern in advance.
[0023]
Next, a method for manufacturing the flexible wiring board substrate 1 will be described. In manufacturing the flexible wiring board substrate 1, for example, when a metal foil 41 is used as the conductive metal layer 4, the woven or non-woven fabric 3 and the metal foil 41 are affixed to the sheet-like graphite 2 using the adhesive 5. It can be manufactured by wearing. Specifically, after applying the adhesive 5 to the sheet-like graphite 2, the woven fabric or the nonwoven fabric 3 is laminated, the adhesive 5 is applied thereon, and the metal foil 41 is further laminated and cured, Alternatively, a method in which a woven fabric or a nonwoven fabric 3 previously coated or impregnated with the adhesive 5 is sandwiched between the sheet-like graphite 2 and the metal foil 41 and cured can be appropriately employed.
[0024]
The adhesive 5 used in the production can be appropriately selected and used from various conventionally known adhesives on the condition that melting and deterioration do not occur at a temperature at which heat is generated from the circuit. Specific examples include adhesives such as rubber, acrylic resin, polyamide, polyimide, epoxy, ethylene-vinyl acetate copolymer, and silicone resin.
[0025]
As a method of applying or impregnating the adhesive 5 to the sheet-like graphite 2, the metal foil 41, or the woven or non-woven fabric 4, known means such as a spray method, a calendering method, a wire bar coating method, a dipping method, etc. Can be used as appropriate.
[0026]
When the sheet-like graphite 2, the woven or nonwoven fabric 3, and the metal foil 41 are laminated and cured, the entire process can be performed while applying pressure. As a method of pressurizing, various press machines, such as a roll and a flat plate press, are used suitably while heating as needed. The pressure at the time of pressurization is appropriately adjusted according to the curing temperature, the thickness of the sheet-like graphite 2, and the like. By applying pressure, curing proceeds while the sheet-like graphite 2, the woven or non-woven fabric 3, and the metal foil 41 are in close contact with each other, so that defects between layers that later cause separation and voids are removed, and high thermal conductivity is maintained. Is done.
[0027]
Next, FIG. 2 is Embodiment (2) of the board | substrate for flexible wiring boards of this invention. This embodiment is an example in which a metal plating layer 42 is provided instead of the metal foil 41 as the conductive metal layer 4. In this case, the manufacturing method is different from the case of the metal foil 41. Usually, the sheet-like graphite 2 and the woven or non-woven fabric 3 are first adhered and cured with the adhesive 5, and then the metal plating layer 42 is formed. To manufacture.
[0028]
The metal plating layer 42 can be formed by appropriately selecting and employing a conventionally known electroless plating method. The metal plating layer 42 in the present invention includes a metal layer formed by vapor deposition. Examples of the metal to be plated include copper and nickel.
[0029]
Other configurations, that is, specific configurations of the sheet-like graphite 2, the woven fabric, or the nonwoven fabric 3 are the same as those in the above embodiment (1).
[0030]
In the above embodiments (1) and (2), the case where the woven or non-woven fabric 3 and the metal foil 41 are provided on one side of the sheet-like graphite 2 has been described, but in addition to this, the woven or non-woven fabric 3 and the metal foil 41 etc. can also be provided on both surfaces of the sheet-like graphite 2. As another example, a woven or nonwoven fabric 3 and a metal foil 41 are sequentially laminated on one surface of the sheet-like graphite 2 and only the woven or nonwoven fabric 3 is laminated on the other surface. You can also. In this case, compared to the above embodiments (1) and (2), the thermal conductivity is slightly reduced by the amount of one woven fabric or nonwoven fabric 3, but the effect of reinforcing the sheet-like graphite 2 is increased. Flexibility is improved.
[0031]
The above-described flexible wiring board substrate forms a circuit according to a conventionally known photolithography technique to form a printed wiring board. This printed wiring board can be suitably used particularly for small and thin electronic devices and the like by taking advantage of its excellent flexibility and heat dissipation while having flexibility as a whole.
[0032]
【Example】
EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated further in detail, it is not limited to this.
(Example 1)
First, a 160 μm thick polyester nonwoven fabric (manufactured by Unitika; Love Sheet (trade name)) was immersed in a commercially available general silicone varnish, and the polyester nonwoven fabric was impregnated with the silicone varnish. The impregnation ratio was such that the polyester woven fabric was impregnated so that the silicone varnish was 120 wt% as a solid content. This is laminated on both sides of a 200 μm thick sheet-like graphite (manufactured by Nippon Carbon Co., Ltd .; Nika Film FL-401 (trade name)), and is heated under pressure using a flat plate press machine to form a silicone varnish as an adhesive. Was confirmed to be cured, and a base sheet was obtained. And, on one side of the base sheet, a copper foil having a thickness of 50 μm coated with a silicone adhesive (manufactured by Shin-Etsu Silicone; KE1800T (trade name)) is applied to one side of the base sheet. Lamination was done in contact. For lamination, primer treatment is performed by brushing primer A (trade name; manufactured by Toray Dow Corning Silicone) on one side of the base sheet and the copper foil before applying the adhesive. I gave it. Subsequently, air and excess adhesive are removed as a pressed state of 294 N / cm ^{2 by} a heat press at 120 ° C. for 3 minutes, and then the adhesive is released from the pressed state and heat-treated at 120 ° C. for 60 minutes. Curing was performed to obtain the desired flexible wiring board substrate.
[0033]
When the obtained flexible wiring board substrate was bent at a right angle along a 20 mm diameter round bar, its shape was maintained and no delamination between layers or cracks in sheet-like graphite were observed. Furthermore, when bending with a finger was repeated, no cracks, cleavage, etc. occurred in the sheet-like graphite portion, and no fragments were missing. The cracks were observed for the first time by bending the claws so that they were completely bent, but even in that case, it was confirmed that the cracks were not lost and that they were sufficiently resistant to use under severe conditions.
Moreover, about the sheet | seat of the base which remove | excluded copper foil from the board | substrate for flexible wiring boards, the thermal conductivity was measured using the thermal conductivity meter (Kyoto Electronics Industry Co., Ltd .; QTM500). As a result, the thermal conductivity was 5 W / mK, which was a sufficiently high value. Further, the volume resistivity was 6 × 10 ¹³ Ω · cm, and the dielectric breakdown strength was 1.0 kV, which was applicable as a substrate for a flexible wiring board.
[0034]
Furthermore, when the produced flexible wiring board substrate was etched with an appropriate circuit pattern, the circuit pattern could be sufficiently reproduced and formed. This flexible printed wiring board is excellent in heat dissipation while having the same or higher flexibility than the conventional one, and in particular, a circuit with heat generation is arranged in a bent portion of various electric and electronic devices. It can be suitably used for cases where a plurality of wiring boards are arranged at high density in a narrow place where heat is likely to accumulate.
[0035]
【The invention's effect】
As described above, the flexible wiring board substrate of the present invention has flexibility as a whole because the conductive metal layer and the flexible sheet-like graphite are laminated together via a woven fabric or a non-woven fabric. It can be bent arbitrarily, and in addition, sheet-shaped graphite has excellent thermal conductivity, so heat generated from the circuit can be quickly dissipated, and malfunction of the circuit due to heat accumulation can be prevented. it can. That is, since heat dissipation is improved while ensuring the overall flexibility, for example, it is possible to mount in a small electronic device in a folded state with high density.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a flexible wiring board substrate according to an embodiment (1) of the present invention.
FIG. 2 is a cross-sectional view of a flexible wiring board substrate according to an embodiment (2) of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Board | substrate for flexible wiring boards 2 Sheet-like graphite 3 Woven cloth or nonwoven fabric 4 Conductive metal layer 41 Metal foil 42 Metal plating layer 5 Adhesive

Claims (1)

A woven or non-woven fabric having insulating properties by impregnating at least one surface of a flexible sheet-like graphite having a thickness of 100 to 300 μm with an adhesive so as not to impair the flexibility of the sheet-like graphite. via a conductive metal layer is formed by laminating,
The woven or non-woven fabric has a thickness of 50 to 200 μm, a tensile strength (according to the synthetic fiber nonwoven fabric test method of the Japan Chemical Fiber Association) of 20 to 400 N / 5 cm, and a basis weight of 10 g / m ² or more. der Ru flexible wiring board substrate.

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