JP4279161B2 - Ultra-thin flexible wiring board - Google Patents

Description

  The present invention relates to an ultra-thin flexible wiring board used for wiring of electrical equipment, electronic equipment, etc., and in particular, the thickness is thin and the pole has excellent reliability against bending during use. The present invention relates to a thin flexible wiring board.

  Conventionally, flexible wiring boards have been highly flexible and thus have been used as wiring for electrical equipment, electronic equipment, and the like. In particular, in recent years, it has been frequently used as a wiring for movable members of computer peripheral devices such as HDDs and CD-ROMs.

  For example, a flexible wiring board has a predetermined circuit pattern formed by laminating a copper foil on an adhesive composition made of a component resin or the like on a plastic film, for example, and performing a process such as etching on the copper foil. Then, a plastic film or the like is further laminated on the copper foil with an adhesive composition as necessary.

  Such a flexible wiring board is required to be thinner than ever because of high density arrangement in the housing space of the device. Therefore, for example, it is known to reduce the thickness of the flexible wiring board by laminating an ultrathin copper foil having a thickness of 1 to 5 μm and a polyimide film via an adhesive layer (for example, Patent Document 1). reference.).

Further, a polyimide or polyamic acid solution having a degree equal to or less than that of the metal foil is directly cast and applied onto an ultrathin metal foil having a thickness of 10 μm or less, and a polyimide film is heated and pressure-bonded on the applied side, thereby forming a flexible wiring board. It is known to reduce the thickness (see, for example, Patent Document 2).
JP 2001-102693 A JP-A-6-190967

  The flexible wiring board is required to be thinner than ever for high-density arrangement in the housing space of the device. As described above, the thickness of the flexible wiring board is becoming thinner by using the ultrathin metal foil, but the thickness is still over 25 μm, and the thickness can be reduced. It has been demanded. In addition, the flexible wiring board is required not only to have a small thickness but also to have excellent reliability against bending during use.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide an ultrathin flexible wiring board having an extremely thin thickness and sufficient bendability and bend reliability. It is said.

The ultrathin flexible wiring board of the present invention is an ultrathin flexible wiring board having a portion in which at least a base film and an ultrathin copper foil are laminated via a cured product of an adhesive composition , The thickness is 3 μm or more and 6 μm or less, the tensile strength which is the film physical property is 300 MPa or more, and the thickness of the laminated portion composed of the base film, the cured product of the adhesive composition and the ultrathin copper foil is 20 μm or less. It is characterized by being.

The base film is preferably a polyparaphenylene terephthalamide film. The adhesive composition preferably contains an elastomer in an amount of 5 wt% to 80 wt%, and the cured product of the adhesive composition preferably has a tensile modulus of 200 MPa to 2000 MPa.

The ultra-thin copper foil is not less 3μm or more 9μm or less thick, it is not preferable tensile strength is its copper property is not less than 400 MPa.

  The adhesive composition contains (A) a polyepoxide compound, (B) a curing agent for epoxy, (C) a curing accelerator for epoxy, (D) an inorganic filler, and (E) an elastomer as essential components. It is preferable.

According to the present invention, in an ultrathin flexible wiring board having a laminated portion formed by bonding at least a base film and an ultrathin copper foil through a cured product of an adhesive composition, the thickness of the base film is 3 μm or more. 6 μm or less, and the tensile strength, which is a physical property of the film, is 300 MPa or more, so that the thickness of the laminated portion made of the base film, the cured product of the adhesive composition and the ultrathin copper foil is 20 μm or less, and the bending sex, the bending songs reliability can be made sufficient.

  Hereinafter, the ultrathin flexible wiring board of the present invention will be described in detail. The ultrathin flexible wiring board of the present invention is an ultrathin flexible wiring board having a portion in which at least a base film and an ultrathin copper foil are laminated via a cured product of an adhesive composition, the base film, The thickness of the laminated part consisting of the cured product of the adhesive composition and the ultrathin copper foil is 20 μm or less.

  The ultrathin flexible wiring board of the present invention may have a single-sided structure in which an ultrathin copper foil is laminated on only one surface of the base film via a cured product of the adhesive composition. It may have a double-sided structure in which ultrathin copper foils are laminated on each of both sides via a cured product of the adhesive composition. In such a double-sided structure, the thickness of the laminated portion may be 20 μm or less on at least one surface side of the base film, but if the thickness of the portion is 20 μm or less on each surface side, More preferred.

The base film used in the ultrathin flexible wiring board of the present invention as described above, the thickness is not more 6 [mu] m or less than 3 [mu] m, the film properties in a tensile strength is not lower than 300 MPa.

If the thickness of the base film is less than 3 μm, reliability for pinholes, strength, etc. cannot be ensured. If the thickness exceeds 6 μm, the total thickness of the ultra-thin flexible wiring board increases, resulting in a narrow housing It is not preferable because it is difficult to bend and mount in the space and the bending reliability may be lowered. Moreover, it is not preferable that the tensile strength, which is the physical property of the film in the thickness range, is less than 300 MPa because the bending reliability in the thickness range cannot be ensured.

  More preferable thickness and tensile strength of the base film in the present invention are 4 μm or more and 6 μm or less and 350 MPa or more. Moreover, it is more preferable if the tensile elasticity modulus which is a film physical property in the said thickness range is 10 GPa or more and 20 GPa or less.

  The material of the base film is not particularly limited as long as it has the above-described tensile strength in the above thickness range. For example, polyimide film, polyparaphenylene terephthalamide film, polyether nitrile film, polyether sulfone film, polyethylene Examples thereof include plastic films such as a terephthalate film, a polyethylene naphthalate film, and a polyvinyl chloride film.

  Among these plastic films, a polyparaphenylene terephthalamide film and the like are preferable from the viewpoints of heat resistance, dimensional stability, electrical characteristics, mechanical characteristics, chemical resistance, cost, and the like.

  The ultrathin copper foil used for the ultrathin flexible wiring board of the present invention has a thickness of 3 μm or more and 9 μm or less, and preferably has a tensile strength of 400 MPa or more, which is a physical property of the copper foil.

  If the thickness of the ultra-thin copper foil is less than 3 μm, reliability against pinholes cannot be ensured. If the thickness exceeds 9 μm, the thickness of the entire ultra-thin flexible wiring board increases, resulting in a narrow housing space. It is not preferable because it is difficult to bend and mount, and the bending reliability may be lowered. Further, if the tensile strength in the thickness range is less than 400 MPa, it is not preferable because the bending reliability in the thickness range cannot be secured. More preferable thickness and tensile strength of the ultrathin copper foil in the present invention are 3 μm or more and 6 μm or less and 430 MPa or more.

  The cured product of the adhesive composition that bonds the base film and the ultrathin copper foil in the ultrathin flexible wiring board of the present invention preferably has a thickness of 5 μm or more and less than 20 μm. If it is less than 5 μm, heat resistance such as solder heat resistance of the flexible wiring board may be lowered, and if it is 20 μm or more, the bending resistance is remarkably lowered.

  The cured product of the adhesive composition used in the present invention is more preferable if the tensile elastic modulus in the above thickness range is 200 MPa or more and 2000 MPa or less. If the tensile modulus is less than 200 MPa, a sufficient bending life may not be obtained, which is not preferable. This is not preferable because it may cause

  The adhesive composition for obtaining such a cured product preferably contains at least an elastomer, and more preferably contains 5% by weight or more and 80% by weight or less of the elastomer in the entire adhesive composition.

  If the elastomer content in the entire adhesive composition is less than 5% by weight, the tensile elastic modulus of the cured product of the adhesive composition in the above thickness range exceeds 2000 MPa, and the flexibility of the flexible wiring board due to brittleness This is not preferable because the properties may be lowered and the folding resistance may be significantly lowered, and if it exceeds 80% by weight, the tensile elastic modulus in the above thickness range is less than 200 MPa, and a sufficient bending life may not be obtained. This is not preferable. The more preferable tensile elastic modulus of the cured product of the adhesive composition is 500 MPa to 1500 MPa with a thickness of 5 μm to 10 μm. Further, the more preferable content of the elastomer in the entire adhesive composition is 10% by weight or more and 60% by weight or less.

  Examples of elastomers include various synthetic rubbers such as acrylic rubber, acrylonitrile butadiene rubber, carboxy-containing acrylonitrile butadiene rubber, rubber-modified polymer compounds, polymer epoxy resins, phenoxy resins, modified polyimides, modified polyamideimides, etc. It can be used alone or in combination of two or more. Preferably, synthetic rubber, rubber-modified polymer compound, and polymer epoxy resin are used.

  More preferably, the adhesive composition used in the present invention comprises (A) a polyepoxide compound, (B) an epoxy curing agent, (C) an epoxy curing accelerator, (D) an inorganic filler, and (E) an elastomer. It is contained as a component.

  (A) As a polyepoxide compound, a glycidyl ether epoxy resin is preferably used. Examples of such a resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, and novolac type epoxy resin. These can be used alone or in combination of two or more.

  The glycidyl ether-based epoxy resin also includes a glycidyl ether-based modified epoxy resin. As the modified epoxy resin, for example, a BT resin (bismaleimide triazine resin), a urethane-modified resin, a phosphorus-modified epoxy resin, or the like can be used.

  (B) The epoxy curing agent can be used without particular limitation as long as it is a compound usually used for curing an epoxy resin. Examples of amine curing systems include dicyandiamide and aromatic diamine. A phenol novolak resin, a cresol novolak resin, a bisphenol A type novolak resin, a triazine-modified phenol novolak resin, and the like can be used, and these can be used alone or in combination.

  The content of the (B) epoxy curing agent is preferably 0.5 to 1.5 in terms of an equivalent ratio to the (A) polyepoxide compound. When the content of the (B) epoxy curing agent is less than 0.5 or more than 1.5 in terms of the equivalent ratio to the (A) polyepoxide compound, the tensile modulus of the cured product of the adhesive composition may not be a predetermined value. This is not preferable.

  (C) The curing accelerator for epoxy may be any one that is usually used as a curing accelerator for epoxy resins, and imidazole compounds such as 2-ethyl-4-methylimidazole and 1-benzyl-2-methylimidazole. , Boron trifluoride amine complex, triphenylphosphine and the like. These curing accelerators can be used alone or in combination of two or more. (C) The epoxy curing accelerator is preferably 0.01 parts by weight or more and 5 parts by weight or less with respect to 100 parts by weight of the (A) polyepoxide compound.

  (D) There is no restriction | limiting in particular as an inorganic filler, A talc, an alumina, aluminum hydroxide, magnesium hydroxide, a fused silica, a synthetic silica etc. are mentioned, These can be used individually or in mixture of 2 or more types. .

  (E) The elastomer is preferably the kind and content as described above. That is, as the elastomer (E), various synthetic rubbers such as acrylic rubber, acrylonitrile butadiene rubber and carboxy-containing acrylonitrile butadiene rubber, rubber-modified polymer compounds, polymer epoxy resins, phenoxy resins, modified polyimides, modified polyamideimides, etc. These may be used alone or in combination of two or more. Preferably, synthetic rubber, rubber-modified polymer compound, and polymer epoxy resin are used.

  Moreover, it is preferable that content of (E) elastomer is 5 to 80 weight% of the whole adhesive composition. When the content of the elastomer (E) in the adhesive composition is less than 5% by weight, the tensile elastic modulus of the cured product of the adhesive composition exceeds 2000 MPa, and the flexibility of the flexible wiring board decreases due to the brittleness. This is not preferable because folding resistance is remarkably lowered. Moreover, when the content of the elastomer in the adhesive composition exceeds 80% by weight, the tensile elastic modulus of the cured product of the adhesive composition becomes less than 200 MPa, which is not preferable because a sufficient bending life cannot be obtained.

  The adhesive composition used for the ultra-thin flexible wiring board of the present invention comprises (A) a polyepoxide compound, (B) an epoxy curing agent, (C) an epoxy curing accelerator, (D) an inorganic filler, and (E ) Elastomer is contained as an essential component, but other fine powder inorganic or organic fillers, pigments, deterioration inhibitors and the like can be added and blended as necessary and within the limits not violating the object of the present invention. .

  The preparation of such an adhesive composition includes the above (A) polyepoxide compound, (B) epoxy curing agent, (C) epoxy curing accelerator, (D) inorganic filler and (E) elastomer, as required. The other additives can be easily added by adding them to a solvent such as NMP (N-methylpyrrolidone), methyl ethyl ketone or toluene, and mixing and dissolving them uniformly.

  The ultrathin flexible wiring board of the present invention can be manufactured, for example, by the following method. In addition, the manufacturing method of the ultra-thin flexible wiring board of this invention is not limited to the following.

  First, an adhesive composition as described above is applied and dried on a base film having a predetermined thickness and tensile strength with a roll coater or the like so that the thickness after drying is 5 μm or more and 20 μm or less. And the processing surface of the ultrathin copper foil which has predetermined thickness and tensile strength is piled up on the surface which applied and dried adhesive composition, and both are pasted up applying pressure with a 60-200 ° C laminating roll. In combination, the adhesive composition is cured by heating at a temperature of 80 to 180 ° C. for 1 to 30 hours. Thereafter, for example, after pattern formation, a coverlay may be attached or a solder resist may be applied, and then terminal surface treatment such as plating may be performed.

  Hereinafter, the present invention will be described with reference to examples. In addition, this invention is not limited by these Examples.

(Example 1)
Bisphenol A type epoxy resin Epicoat 1001 (trade name, epoxy equivalent 475, manufactured by Japan Epoxy Resin Co., Ltd.) 43.5 parts by weight, 4,4′-diaminodiphenylsulfone (amine equivalent 62) 5.7 parts by weight, 2-ethyl-4 -0.2 parts by weight of methylimidazole, 10 parts by weight of aluminum hydroxide, 40.5 parts by weight of carboxy-containing acrylonitrile butadiene rubber Nipol 1072 (trade name, manufactured by Nippon Zeon), 10 parts by weight of cyclophenoxyphosphazene oligomer (melting point: 100 ° C) And 1 part by weight of N, N′-di-2-naphthyl-p-phenylenediamine as an anti-aging agent was dissolved and diluted in 250 parts by weight of a mixed solvent of methyl ethyl ketone / toluene = 6/4 to obtain an adhesive composition.

  This adhesive composition is a roll coater such that PPTA aramid film Aramika TM (trade name, thickness 4 μm, tensile strength 400 MPa, tensile elastic modulus 15 GPa, manufactured by Teijin Advanced Film) is 8 μm after drying. The coated surface is coated with an electrolytic copper foil micro thin (trade name, thickness 5 μm, tensile strength 450 MPa), and thermocompression bonded with a 170 ° C. laminating roll. It processed at 130 degreeC, 3 hours, 180 degreeC, and 3 hours, the adhesive composition was hardened, and the flexible copper clad laminated board with the whole thickness of 17 micrometers was obtained.

  The tensile modulus of the cured adhesive composition was 1200 MP. The tensile modulus of the cured product of the adhesive composition is determined based on ASTM D-882 by curing the adhesive composition into a film having the same thickness separately from the production of the flexible copper-clad laminate. It is a thing. Moreover, the measurement of the tensile strength of a base film and an ultra-thin copper foil was performed based on IPC-TM-650.

(Comparative Example 1)
A flexible copper clad laminate having a total thickness of 30 μm was obtained in the same manner as in Example 1 except that a general-purpose copper foil having a thickness of 18 μm and a tensile strength of 350 MPa was used as the copper foil.

(Comparative Example 2)
As a base film, a polyimide film Kapton (trade name, manufactured by Toray DuPont Co., Ltd.) having a thickness of 12 μm, a tensile strength of 250 MPa, and a tensile elastic modulus of 3.5 GPa is used. A flexible copper-clad laminate having a total thickness of 25 μm was obtained in the same manner as in Example 1 except that the tensile elastic modulus of the cured product of the adhesive composition was 150 MPa.

(Comparative Example 3)
A polyimide film Kapton (trade name, manufactured by Toray DuPont) with a thickness of 12 μm, a tensile strength of 250 MPa, and a tensile elastic modulus of 3.5 GPa is used as the base film, and a general-purpose copper foil with a thickness of 18 μm and a tensile strength of 350 MPa is used as the copper foil. In the same manner as in Example 1 except that the content of nipol 1072 of the carboxy-containing acrylonitrile butadiene rubber in the adhesive composition is 90% by weight and the tensile elastic modulus of the cured product of the adhesive composition is 150 MPa. Thus, a flexible copper clad laminate having a total thickness of 38 μm was obtained.

(Comparative Example 4)
As a base film, a polyimide film Kapton (trade name, manufactured by Toray DuPont Co., Ltd.) having a thickness of 12 μm, a tensile strength of 250 MPa, and a tensile elastic modulus of 3.5 GPa is used, and the content of carboxy-containing acrylonitrile butadiene rubber Nipol 1072 in the adhesive composition is A flexible copper-clad laminate having a total thickness of 25 μm was obtained in the same manner as in Example 1 except that the amount was 1% by weight and the tensile elastic modulus of the cured product of the adhesive composition was 2500 MPa.

(Comparative Example 5)
A polyimide film Kapton (trade name, manufactured by Toray DuPont) with a thickness of 12 μm, a tensile strength of 250 MPa, and a tensile elastic modulus of 3.5 GPa is used as the base film, and a general-purpose copper foil with a thickness of 18 μm and a tensile strength of 350 MPa is used as the copper foil. In the same manner as in Example 1 except that the content of nipole 1072 of the carboxy-containing acrylonitrile butadiene rubber in the adhesive composition is 1% by weight and the tensile elastic modulus of the cured product of the adhesive composition is 2500 MPa. Thus, a flexible copper clad laminate having a total thickness of 38 μm was obtained.

  The flexible copper clad laminates of Examples and Comparative Examples thus obtained were subjected to a bending test and a folding resistance test. The results are shown in Table 1.

  The bending test was performed by repeating the operation of bending the test piece 180 degrees five times and observing the occurrence of cracks in the copper foil at the folded portion. In Table 1, “◯” indicates that no crack was generated in the folded portion of the copper foil, “Δ” indicates that the crack was slightly generated in the folded portion of the copper foil, and “×” indicates that the folded portion of the copper foil was It shows the one where cracks occurred as a whole.

  The folding resistance test was performed according to JIS P 8115 (R = 2 mm). In Table 1, “◯” has a folding resistance of 1,000,000 times or more, “Δ” has a folding resistance of less than 1,000,000 times, and 100,000 times or more, and “X” is less than 100,000 times, 10,000 or more. The one with foldability is shown.

  As is apparent from Table 1, it was confirmed that the flexible copper clad laminates of the examples had sufficient bendability and fold resistance even though the thickness was as thin as 17 μm.

Claims (5)

An ultrathin flexible wiring board having a portion in which at least a base film and an ultrathin copper foil are laminated via a cured product of an adhesive composition, wherein the base film has a thickness of 3 μm to 6 μm. Ultra-thin flexible wiring, characterized in that the tensile strength, which is a physical property, is 300 MPa or more, and the thickness of the laminated portion composed of the base film, the cured product of the adhesive composition and the ultra-thin copper foil is 20 μm or less Board. 2. The ultrathin flexible wiring board according to claim 1, wherein the base film is a polyparaphenylene terephthalamide film. 3. The adhesive composition according to claim 1, wherein the adhesive composition contains an elastomer in an amount of 5 wt% to 80 wt%, and the cured product of the adhesive composition has a tensile modulus of 200 MPa to 2000 MPa. Ultra-thin flexible wiring board. The ultrathin flexible wiring according to any one of claims 1 to 3, wherein the ultrathin copper foil has a thickness of 3 µm or more and 9 µm or less, and a tensile strength that is a physical property of the copper foil is 400 MPa or more. Board. The adhesive composition contains (A) a polyepoxide compound, (B) an epoxy curing agent, (C) an epoxy curing accelerator, (D) an inorganic filler, and (E) an elastomer as essential components. The ultrathin flexible wiring board according to any one of claims 1 to 4.