JP7344067B2 - Manufacturing method of flexible printed wiring board - Google Patents

Description

The present invention relates to a method for manufacturing a flexible printed wiring board.

As substrates for mounting electronic components to form electronic circuits, there are two types: rigid printed wiring boards, which are hard plate-like, and flexible printed wiring boards, which are film-like and flexible and can be bent freely. In addition, the demand for flexible printed wiring boards is increasing because their flexibility allows them to be used in places where flexibility is required, such as wiring inside a camera lens or the head of a printer.
Furthermore, in recent years, high-definition pattern formation is required also in flexible printed wiring boards. Since it is difficult to form a high-definition pattern using the subtractive method, wiring formation using a semi-additive method has been proposed (see, for example, Patent Document 1).

Japanese Patent Application Publication No. 2010-141216

However, when wiring is formed by a semi-additive method as in the flexible printed wiring board described in Patent Document 1, the copper wiring and the base material are joined by electroless copper plating. And, in such bonding by electroless copper plating, there is a problem that it is difficult to increase the adhesive strength between the copper wiring and the base material.

Therefore, an object of the present invention is to provide a method for manufacturing a flexible printed wiring board that can sufficiently increase the adhesive strength between wiring and a base material.

In order to solve the above problems, the present invention provides the following method for manufacturing a flexible printed wiring board.
The method for manufacturing a flexible printed wiring board of the present invention includes a step of applying an adhesive to at least one side of a base material layer made of a heat-resistant resin film and having a thickness of 8 μm or less to form an adhesive layer having a thickness of 3 μm or less. a step of laminating a metal foil on the adhesive layer to form a metal layer with a thickness of 4 μm or less; a step of forming a patterned plating resist layer on the metal layer; a step of electrolytically plating the laminate on which the plating resist layer has been formed to form a plating layer; a step of peeling the plating resist layer from the laminate on which the plating layer has been formed; and a step of peeling the plating resist layer. etching the laminate from which the layers have been peeled off to remove the metal layer and a portion of the plating layer; a base resin containing at least one of the above, (B) an epoxy resin, (C) a curing agent, and (D) a solvent, and the blending amount of (A) is the total solids of the adhesive. This method is characterized in that the content is 5% by mass or more and 30% by mass or less based on 100% by mass.

In the method for manufacturing a flexible printed wiring board of the present invention, it is preferable that the metal layer has a surface roughness Rz (maximum height) of 1 μm or more and 2.5 μm or less.
In the method for manufacturing a flexible printed wiring board of the present invention, it is preferable that the heat-resistant resin film is subjected to plasma treatment.
The method for manufacturing a flexible printed wiring board of the present invention preferably further includes a step of thermosetting the adhesive layer.

According to the present invention, it is possible to provide a method for manufacturing a flexible printed wiring board that can sufficiently increase the adhesive strength between wiring and a base material.

FIG. 3 is a diagram for explaining a method for manufacturing a flexible printed wiring board according to an embodiment of the present invention.

Embodiments of the present invention will be described below based on the drawings. The present invention is not limited to the contents of the embodiments. Note that in the drawings, some parts are shown enlarged or reduced for ease of explanation.

[Method for manufacturing flexible printed wiring board]
First, a method for manufacturing a flexible printed wiring board according to this embodiment will be explained.
The method for manufacturing a flexible printed wiring board of the present embodiment is a method for manufacturing a flexible printed wiring board using an adhesive described below, which includes an adhesive layer forming step, a metal layer forming step, a thermosetting step, described below. This method includes a plating resist layer forming step, a plating layer forming step, a plating resist peeling step, and an etching treatment step.

In the adhesive layer forming step, first, a heat-resistant resin film as shown in FIG. 1(A) is prepared, and this is used as the base material layer 1.
The thickness of the base material layer 1 needs to be 8 μm or less in order to make the flexible printed wiring board 100 sufficiently thin. Moreover, from the same viewpoint, the thickness of the base material layer 1 is preferably 1 μm or more and 7 μm or less, and more preferably 2 μm or more and 6 μm or less.
Examples of the material for the heat-resistant resin film include polyimide resin, polyamideimide resin, allyl resin, polyethylene terephthalate resin, and polyethylene naphthalate resin. Among these, polyimide resin is preferred from the viewpoint of heat resistance.
Moreover, it is preferable to subject the heat-resistant resin film to plasma treatment. Thereby, the surface of the heat-resistant resin film can be modified to further improve the adhesive strength between the wiring and the base material.

In the adhesive layer forming step, next, as shown in FIG. 1(B), an adhesive is applied to both surfaces of the base layer 1 to form an adhesive layer 2. Note that the adhesive layer 2 may be provided on at least one side of the base layer 1.
The thickness of the adhesive layer 2 needs to be 3 μm or less. If the thickness of the adhesive layer 2 exceeds 3 μm, the bending durability of the flexible printed wiring board will be insufficient. Further, from the viewpoint of adhesive properties, the thickness of the adhesive layer 2 is preferably 1 μm or more and 3 μm or less, and more preferably 1.5 μm or more and 2.5 μm or less.
As the adhesive, it is necessary to use the adhesive of this embodiment described later. With such an adhesive, the adhesive strength between the wiring and the base material can be sufficiently increased.
Examples of the adhesive coating device include a screen printer, a spray coater, a roll coater, a spin coater, a gravure coater, a comma coater, a rod coater, and a lip coater.

In the metal layer forming step, a metal foil 3 is laminated on the adhesive layer 2 as shown in FIG. 1(C) to form a metal layer 31 as shown in FIG. 1(D).
The thickness of the metal layer 31 needs to be 4 μm or less. When the thickness of the metal layer 31 exceeds 4 μm, it becomes difficult to completely etch the metal layer 31 in the etching process described below. Further, from the same viewpoint, the thickness of the metal layer 31 is preferably 1 μm or more and 3 μm or less, and more preferably 1.5 μm or more and 2.5 μm or less.
Examples of the material for the metal layer 31 include copper, silver, and aluminum. Among these, copper is preferred from the viewpoint of cost.
The surface roughness Rz (maximum height) of the metal layer 31 is preferably 1 μm or more and 2.5 μm or less. If the surface roughness Rz is within the above range, the adhesive strength between the wiring and the base material can be further improved.

Note that since it is difficult to laminate something as thin as the metal layer 31, first, the metal foil 3 including the metal layer 31 and the peelable metal layer 32 is laminated on the adhesive layer 2. . Then, by peeling off the peelable metal layer 32 from the metal layer 31, the metal layer 31 can be formed on the adhesive layer 2, as shown in FIG. 1(D).
The conditions for lamination are not particularly limited. For example, the heating temperature of the roll during lamination is preferably 70°C or more and 150°C or less, more preferably 80°C or more and 120°C or less. The pressure of the roll during lamination is preferably 0.4 MPa or more and 0.9 MPa or less.

In the thermosetting step, as shown in FIG. 1(D), after forming the metal layer 31 on the adhesive layer 2, the adhesive layer 2 is thermocured.
Thereby, the adhesive strength between the adhesive layer 2 and the metal layer 31 can be further increased.
The conditions for thermosetting are not particularly limited. For example, the thermosetting temperature is preferably 60°C or higher and 200°C or lower. The heat curing time is preferably 1 hour or more and 15 hours or less.
Further, in the thermosetting step, it is preferable to heat the material in stages while changing the temperature. For example, first-stage heating, second-stage heating, and third-stage heating can be performed. In this case, for the first stage heating, the heating time is 50°C or more and 90°C or less (more preferably 60°C or more and 80°C or less), and the heating time is 5 hours or more and 9 hours or less (more preferably 7 hours or more and 90°C or less). (hours or less) is preferable. In the second stage heating, the heating temperature is 80°C or more and 120°C or less (more preferably 90°C or more and 110°C or less), and the heating time is 1 hour or more and 3 hours or less (more preferably 1.5 hours or more and 2.5 hours or more). 5 hours or less) is preferable. In the third stage heating, the heating temperature is 160°C or more and 210°C or less (more preferably 180°C or more and 200°C or less), and the heating time is 1 hour or more and 3 hours or less (more preferably 1.5 hours or more and 2. 5 hours or less) is preferable.

In the plating resist layer forming step, a plating resist film is formed on the metal layer 31, exposed to light, and developed to form a patterned plating resist layer 4 as shown in FIG. 1(E).
The plating resist film can be formed using a plating resist. The plating resist is not particularly limited, and any known plating resist can be used as appropriate. Furthermore, the plating resist may be in the form of a film or in the form of an ink. In the case of a film-like plating resist, a laminator may be used. In the case of an ink-like plating resist, the coating device is not particularly limited, and examples include devices similar to adhesive coating devices. Furthermore, lamination conditions, coating film thickness, exposure conditions, and development conditions can be appropriately set according to the specifications of the plating resist used.

In the plating layer forming step, electrolytic plating is applied to the laminate on which the plating resist layer 4 has been formed, to form a plating layer 5 as shown in FIG. 1(F).
As the plating solution used for electrolytic plating, any known plating solution can be used as appropriate. The conditions for electrolytic plating are not particularly limited and can be set as appropriate depending on the specifications of the plating solution used.
Examples of the material of the plating layer 5 include copper and silver. Among these, copper is preferred from the viewpoint of cost.

In the plating resist peeling step, the plating resist layer 4 is peeled off from the laminate on which the plating layer 5 is formed, as shown in FIG. 1(G).
The conditions for peeling off the plating resist layer 4 are not particularly limited, and can be set as appropriate depending on the specifications of the plating resist to be used.

In the etching process, the laminate from which the plating resist layer 4 has been removed is subjected to an etching process to remove the metal layer 31 and part of the plating layer 5, as shown in FIG. 1(H). And in this way, flexible printed wiring board 100 is obtained.
The etching solution is not particularly limited, and any known etching solution can be used as appropriate. For example, when etching copper, an aqueous solution containing sulfuric acid and hydrogen peroxide can be used. Furthermore, the conditions for the etching process are not particularly limited and can be set as appropriate depending on the specifications of the etching solution used.

In the flexible printed wiring board 100, the adhesive strength between the wiring and the base material is sufficiently high. For example, the adhesive strength can be evaluated by measuring the 90 degree peel strength (50 mm/min) between the wiring and the base material (unit: N/mm) according to JIS6471. The 90 degree peel strength between the wiring and the base material is preferably 0.8 N/mm or more, more preferably 1.0 N/mm or more, and particularly preferably 1.2 N/mm or more.

[glue]
Next, the adhesive used in this embodiment will be explained.
The adhesive used in this embodiment contains (A) a base resin, (B) an epoxy resin, (C) a curing agent, and (D) a solvent.

[(A) Component]
The base resin (A) used in this embodiment is a resin containing at least one of a polyamideimide resin and a polyimide resin.
The type of polyamide-imide resin is not particularly limited, and may include a reaction product obtained by imidizing a tricarboxylic anhydride and a diisocyanate compound, a reaction product obtained by imidizing a tricarboxylic anhydride chloride and a diamine compound, etc. can be mentioned.

The tricarboxylic anhydride is not particularly limited, and examples include trimellitic anhydride.
The diisocyanate compound is not particularly limited, and examples include aromatic diisocyanates. Examples of the aromatic diisocyanate include biphenyl diisocyanate, dimethylbiphenyl diisocyanate, diethylbiphenyl diisocyanate, and dimethoxybiphenyl diisocyanate.
The diamine compound is not particularly limited, and examples include aromatic diamine compounds. Examples of the aromatic diamine compound include diaminobenzophenone, phenylenediamine, diaminodiphenyl, diaminodiphenyl ether, diaminodiphenylamide, diaminodiphenylmethane, and bis(aminophenoxy)biphenyl.

The weight average molecular weight of the polyamide-imide resin is not particularly limited, but the lower limit thereof is preferably 10,000 and more preferably 30,000 from the viewpoint of heat resistance. On the other hand, the upper limit of the weight average molecular weight of the polyamide-imide resin is preferably 100,000, more preferably 70,000, from the viewpoint of compatibility. These polyamideimide resins may be used alone or in combination of two or more.

The type of polyimide resin is not particularly limited, and examples include those having a phenylindane structure. Among these, a completely imidized soluble polyimide resin obtained by reacting a diaminotrialkylindane with a tetracarboxylic dianhydride or a derivative thereof is preferred. Here, examples of the diaminotrialkylindane include diaminotrimethylindane and diaminotriethylindane. Examples of derivatives of tetracarboxylic dianhydride include benzophenone tetracarboxylic dianhydride.

The weight average molecular weight of the polyimide resin is not particularly limited, but the lower limit thereof is preferably 10,000 and more preferably 20,000 from the viewpoint of heat resistance. On the other hand, the upper limit of the weight average molecular weight of the polyimide resin is preferably 50,000, more preferably 40,000, from the viewpoint of compatibility. These polyimide resins may be used alone or in combination of two or more.

The blending amount of component (A) needs to be 5% by mass or more and 30% by mass or less based on 100% by mass of the total solid content of the adhesive. If the amount of component (A) is less than 5% by mass, the bending durability of the flexible printed wiring board will be insufficient. On the other hand, if the amount of component (A) exceeds 30% by mass, voids will occur in the adhesive layer. Moreover, from the same viewpoint, the blending amount of component (A) is preferably 7% by mass or more and 20% by mass or less, and more preferably 8% by mass or more and 15% by mass or less.

[(B) Component]
The (B) epoxy resin used in this embodiment includes biphenyl novolak epoxy resin, biphenylaralkyl epoxy resin, phenylaralkyl epoxy resin, biphenyl epoxy resin, naphthalene epoxy resin, dicyclopentadiene epoxy resin, and bisphenol A. phenol novolac type epoxy resins such as bisphenol F type and bisphenol AD type, rubber modified epoxy resins such as silicone modified epoxy resins, epsilon-caprolactone modified epoxy resins, cresol novolac type epoxy resins such as ortho-cresol novolac type, bisphenol A Novolac type epoxy resin, cycloaliphatic polyfunctional epoxy resin, glycidyl ester type polyfunctional epoxy resin, glycidylamine type polyfunctional epoxy resin, heterocyclic polyfunctional epoxy resin, bisphenol modified novolac type epoxy resin, and polyfunctional modified novolac type Examples include epoxy resin.

The epoxy equivalent of the epoxy resin is not particularly limited, but its upper limit is preferably 2000 g/eq, more preferably 1000 g/eq, particularly preferably 500 g/eq. On the other hand, the lower limit of the epoxy equivalent is preferably 100 g/eq, more preferably 200 g/eq. These epoxy resins may be used alone or in combination of two or more.

The blending amount of component (B) is preferably 30% by mass or more and 80% by mass or less, more preferably 40% by mass or more and 70% by mass or less, based on 100% by mass of the total solid content of the adhesive. . If the blending amount of component (B) is at least the above-mentioned lower limit, the curability of the adhesive can be improved, and on the other hand, when it is below the above-mentioned upper limit, the bending durability of the flexible printed wiring board can be further improved.

[(C) Component]
Examples of the curing agent (C) used in this embodiment include amine compounds, phenol compounds, and acid anhydrides. These curing agents may be used alone or in combination of two or more.
As the amine compound, an aromatic diamine compound is preferable from the viewpoint of flexibility of the adhesive layer 2. An aromatic diamine compound is a compound having an aromatic group and two amino groups. Aromatic diamine compounds include trimethylene bis(4-aminobenzoate), poly(tetra/3-methyltetramethylene ether) glycol bis(4-aminobenzoate), polytetramethylene oxide di-p-aminobenzoate , and polytetramethylene oxide aminobenzoate.

As the phenol compound, a phenol resin is preferable from the viewpoint of flexibility of the adhesive layer 2. Examples of the phenol resin include novolac type phenol resin and novolac type bisphenol A resin. Specific examples include triphenylmethane novolac phenolic resin, xylylene novolac phenolic resin, biphenyl novolac phenolic resin, dicyclopentadiene novolak phenolic resin, and terpene novolac phenolic resin.

Examples of acid anhydrides include aromatic carboxylic anhydrides (phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, etc.), aliphatic carboxylic acid anhydrides (sebacic acid, dodecanedioic acid, etc.), and , alicyclic carboxylic anhydrides (tetrahydrophthalic anhydride, hexahydrophthalic anhydride, etc.).

The blending amount of component (C) is preferably 5% by mass or more and 50% by mass or less, more preferably 10% by mass or more and 40% by mass or less, based on 100% by mass of the total solid content of the adhesive. , it is particularly preferable that the amount is 15% by mass or more and 40% by mass or less. If the amount of component (C) is at least the above-mentioned lower limit, the curability of the adhesive can be improved, while if it is below the above-mentioned upper limit, the bending durability of the flexible printed wiring board can be further improved.

[(D) Component]
The solvent (D) used in this embodiment needs to be capable of dissolving the component (A). From the viewpoint of dissolving component (A), component (D) preferably contains N-methyl-2-pyrrolidone, γ-butyrolactone, and the like. Furthermore, component (D) may contain other solvents in addition to these solvents.
Other solvents include ketones (methyl ethyl ketone, cyclohexanone, etc.), aromatic hydrocarbons (toluene, xylene, etc.), alcohols (methanol, isopropanol, cyclohexanol, etc.), and alicyclic hydrocarbons (cyclohexane, methylcyclohexane, etc.). ), petroleum solvents (petroleum ether, petroleum naphtha, etc.), cellosolves (cellosolve, butyl cellosolve, etc.), carbitols (carbitol, butyl carbitol, etc.), and esters (ethyl acetate, butyl acetate, cellosolve, etc.) acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, ethyl diglycol acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, etc.).

The amount of component (D) to be blended is not particularly limited, and can be adjusted as appropriate from the viewpoint of coatability of the adhesive.

In addition to the above-mentioned components (A) to (D), the adhesive used in this embodiment may optionally contain various additive components, such as a curing accelerator, a flame retardant, a filler, a thixotropic agent, and Antioxidants and the like may be added as appropriate.

Examples of the curing accelerator include amine curing accelerators. Examples of the amine curing accelerator include 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-methylimidazole, 2-phenyl-4-methylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2 Examples include imidazole compounds such as -undecylimidazole and 2-phenyl-4,5-dihydroxymethylimidazole.

Examples of the flame retardant include phosphazene-based flame retardants and phosphorus-based flame retardants. Examples of phosphazene-based flame retardants include cyclic phosphazene-based flame retardants. Phosphorus-based flame retardants include non-halogen aliphatic phosphate esters (trimethyl phosphate, triethyl phosphate, tributyl phosphate, trioctyl phosphate, tributoxyethyl phosphate, etc.), non-halogen aromatic phosphate esters (triphenyl phosphate, Cresyl diphenyl phosphate, dicresyl phenyl phosphate, tricresyl phosphate, trixylenyl phosphate, xylenyl diphenyl phosphate, tris (isopropylphenyl) phosphate, isopropylphenyl diphenyl phosphate, diisopropylphenyl phenyl phosphate, tris (trimethylphenyl) phosphate, tris(t-butylphenyl) phosphate, hydroxyphenyl diphenyl phosphate, octyldiphenyl phosphate, etc.), metal salts of phosphinic acids (aluminum tris-diethylphosphinate, aluminum tris-methylethylphosphinate, aluminum tris-diphenylphosphinate, zinc bis-diethylphosphinate) , zinc bismethylethylphosphinate, zinc bisdiphenylphosphinate, titanyl bisdiethylphosphinate, titanium tetrakisdiethylphosphinate, titanyl bismethylethylphosphinate, titanium tetrakismethylethylphosphinate, titanyl bisdiphenylphosphinate, tetrakisdiphenylphosphinic acid titanium, etc.), and phosphine oxide compounds (diphenylvinylphosphine oxide, triphenylphosphine oxide, trialkylphosphine oxide, tris(hydroxyalkyl)phosphine oxide, etc.).

[Adhesive manufacturing method]
The method for producing the adhesive used in this embodiment described above is not limited to a specific method. For example, it can be produced by blending the above components in a predetermined ratio and then kneading or mixing at room temperature using a kneading means such as a three-roll mill, a ball mill, or a sand mill, or a stirring means such as a super mixer or a planetary mixer. Further, before kneading or mixing, preliminary kneading or premixing may be performed as necessary.

[Actions and effects of this embodiment]
According to the above embodiment, the following effects can be obtained.
In the flexible printed wiring board 100 obtained in this embodiment, the base material layer 1 and the wiring (metal layer 31 and plating layer 5) are bonded via the adhesive layer 2. Therefore, by electroless plating, it is easier to adjust the bonding strength, and it is also possible to further increase the bonding strength, compared to the case where wiring is formed. Furthermore, by subjecting the adhesive layer 2 to a heat curing process, the adhesive strength between the adhesive layer 2 and the metal layer 31 is further increased. In this way, the adhesive strength between the wiring (metal layer 31 and plating layer 5) and base layer 1 can be sufficiently increased.

[Modification of embodiment]
The present invention is not limited to the above-described embodiments, and the present invention includes modifications, improvements, etc. within the scope that can achieve the purpose of the present invention.
For example, in the embodiment described above, wiring (metal layer 31 and plating layer 5) was formed on both sides of base layer 1, but the present invention is not limited thereto. For example, wiring (metal layer 31 and plating layer 5) may be formed on one side of base layer 1.
Further, in the above-described embodiment, the resulting flexible printed wiring board 100 is a double-sided wiring board, but is not limited to this. For example, an insulating layer and wiring can be further provided on the obtained flexible printed wiring board 100, which is a double-sided wiring board, by performing the same method as in the above-described embodiment. In this way, it is also possible to produce a multilayered flexible printed wiring board.

Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples in any way. The materials used in the examples are shown below.
((A) component)
Polyimide resin: weight average molecular weight 30,000, solid content 20% by mass, product name "Q-VR-0163", manufactured by PI Technology Institute Polyamide-imide resin: weight average molecular weight 50,000, solid content 26% by mass (solvent: N-methyl pyrrolidone/xylene = 80% by mass/20% by mass), trade name "HPC-6000-26", manufactured by Hitachi Chemical (component (B))
Epoxy resin: Bisphenol A type resin, liquid, product name "Epicron 850-S", manufactured by DIC (component (C))
Curing agent: aromatic diamine compound, trimethylene-bis(4-aminobenzoate), trade name "CUA-4", manufactured by Kumiai Kogyo Co., Ltd. (component (D))
Solvent: N-methylpyrrolidone, manufactured by Mitsubishi Chemical (other ingredients)
Phenoxy resin: Phenoxy resin, weight average molecular weight 50,000, product name "YP-70", manufactured by Nippon Steel Chemical & Materials Flame retardant: phosphazene flame retardant, product name "Rabitor FP-110", manufactured by Fushimi Pharmaceutical Co., Ltd.

[Example 1]
50 parts by mass of polyimide resin (10 parts by mass in terms of solid content), 60 parts by mass of epoxy resin, 25 parts by mass of curing agent, and 5 parts by mass of flame retardant were put into a container, premixed with a stirrer, and then mixed with a planetary mixer. The mixture was mixed and dispersed at room temperature to obtain an adhesive. Furthermore, the viscosity of the obtained adhesive was adjusted using a solvent to obtain a coating adhesive.
On the other hand, a heat-resistant resin film (trade name "Kapton (registered trademark) 20EN", manufactured by DuPont-Toray, thickness: 5 μm substrate) was subjected to plasma treatment. In addition, for plasma treatment, after reducing the pressure to 0.1 Pa or less, Ar gas was introduced (Ar gas 100% by volume), the pressure was 13.3 Pa, the output was 5 KW (40 KHz), and the treatment time was 2 minutes. I went there.
Then, on one side of the heat-resistant resin film after the plasma treatment, a coating adhesive was applied using a gravure coater so that the thickness after drying was 2 μm, and dried to form an adhesive layer. . Thereafter, an ultra-thin copper foil with carrier copper foil (product name "MT18FL", manufactured by Mitsui Mining & Mining Co., Ltd., copper thickness: 2 μm, surface roughness After laminating the carrier copper foil (Rz: 1.3 μm), the carrier copper foil was peeled off to form a metal layer. Next, a first heat treatment at a temperature of 70°C for 8 hours, a second heat treatment at a temperature of 100°C for 2 hours, and a third heat treatment at a temperature of 190°C for 2 hours were performed to form the adhesive layer. Heat cured.
Next, after performing a soft etching treatment (sulfuric acid/hydrogen peroxide aqueous solution, treatment thickness: 0.2 μm) on the laminate including the base material layer, adhesive layer, and metal layer, a photosensitive film (product name: Photec RY-5319'' (manufactured by Hitachi Chemical Co., Ltd.) was laminated (dry thickness: 19 μm), exposed and developed to form a patterned plating resist layer. Thereafter, the laminate on which the plating resist layer was formed was subjected to electrolytic plating to form a plating layer (metal: copper, thickness: 9 μm), and then the plating resist layer was peeled off. Note that the RS-81 process manufactured by JCU was used to peel off the plating resist layer.
Next, the laminate including the base material layer, adhesive layer, metal layer, and plating layer is subjected to an etching treatment (sulfuric acid/hydrogen peroxide aqueous solution, trade name "FE-830II", manufactured by JCU) to remove the metal layer. and a part of the plating layer were removed to form wiring on the base material. After that, a solder resist (product name "NPR-3400", manufactured by Nippon Polytec Co., Ltd.) was applied to the laminate on which the wiring was formed (dry thickness: 20 μm), and cured at a temperature of 120°C for 60 minutes to solder. A resist layer was formed to produce a flexible printed wiring board.

[Example 2]
An adhesive was obtained in the same manner as in Example 1 except that each material was blended according to the composition shown in Table 1.
Further, a flexible printed wiring board was produced in the same manner as in Example 1 except that the obtained adhesive was used.

[Example 3]
A flexible printed wiring board was produced in the same manner as in Example 1 except that the heat-resistant resin film was not subjected to plasma treatment.

[Example 4]
Same as Example 1 except that a different ultra-thin copper foil with carrier copper foil (product name "MT18SD-H", manufactured by Mitsui Kinzoku Mining Co., Ltd., copper thickness: 3 μm, surface roughness Rz: 3.0 μm) was used. A flexible printed wiring board was fabricated.

[Example 5]
Flexible printed wiring was produced in the same manner as in Example 1, except that a different ultra-thin copper foil with carrier copper foil (manufactured by Fukuda Metal Foil and Powder Industries Co., Ltd., copper thickness: 3 μm, surface roughness Rz: 0.6 μm) was used. A substrate was prepared.

[Comparative Examples 1 to 3]
An adhesive was obtained in the same manner as in Example 1 except that each material was blended according to the composition shown in Table 1.
Further, a flexible printed wiring board was produced in the same manner as in Example 1 except that the obtained adhesive was used.

<Evaluation of flexible printed wiring board>
Evaluation of the flexible printed wiring board (voids, folding durability, initial peel strength, peel strength after thermal deterioration, and insulation reliability) was performed using the following method. The results obtained are shown in Table 1. Further, Table 1 shows the copper thickness and surface roughness Rz of the ultra-thin copper foils with carrier copper foils in Examples 1 to 5 and Comparative Examples 1 to 3, as well as the presence or absence of plasma treatment on the base material.
(1) Void A conductor portion of a flexible printed wiring board was etched, and the conductor portion was observed with a 50x objective lens to confirm the number of voids of 1 μm or more within a 30 cm square. Then, voids were evaluated according to the following criteria.
○: The number of voids is 0.
Δ: The number of voids is 1 or more and 9 or less.
×: The number of voids is 10 or more.
(2) Folding Durability A flexible printed wiring board cut into 25 mm width was used as a test plate. This test plate was folded, a weight of 1 kgf was placed on the fold for 5 seconds, the test plate was unfolded, a weight of 1 kgf was placed on the fold for 5 seconds, and the crease was confirmed using a magnifying glass. This process was repeated until cracks appeared, and the number of cycles was measured. Then, folding durability was evaluated according to the following criteria.
○: The number of cycles is 10 or more.
×: The number of cycles is less than 10 times.
(3) Initial Peel Strength A flexible printed wiring board before forming a solder resist layer was used as a sample, and a wiring having a width of 3 mm and a length of 100 mm was formed by etching to form a test board. Regarding this test board, the 90 degree peel strength (50 mm/min) between the wiring and the base material was measured according to the description in JIS6471 (unit: N/mm).
(4) Peel strength after thermal deterioration A flexible printed wiring board before forming a solder resist layer was used as a sample, and a wiring having a width of 3 mm and a length of 100 mm was formed by etching to form a test board. This test plate was subjected to heat treatment at a temperature of 150° C. for 168 hours. Regarding the heat-treated test plate, the 90 degree peel strength (50 mm/min) between the wiring and the base material was measured according to the description in JIS6471 (unit: N/mm).
(5) Insulation Reliability A comb-shaped pattern (L/S=20 μm/20 μm) was cut out from a flexible printed wiring board and used as a test board. A voltage of 50 V was applied to this test plate under an environment of a temperature of 85° C. and 85% RH (relative humidity), and the insulation resistance value was measured after 1000 hours. Then, the insulation reliability was evaluated according to the following criteria.
○: Insulation resistance value is 1×10 ¹⁰ Ω or more.
Δ: Insulation resistance value is 1×10 ⁸ Ω or more and less than 1×10 ¹⁰ Ω.
×: Insulation resistance value is less than 1×10 ⁸ Ω.

As is clear from the results shown in Table 1, when the method for manufacturing a flexible printed wiring board of the present invention (Examples 1 to 5) was used, the voids, folding durability, initial peel strength, and peel strength after thermal deterioration were Good results were obtained for both strength and insulation reliability. Therefore, it was confirmed that the method for manufacturing a flexible printed wiring board of the present invention can sufficiently increase the adhesive strength between the wiring and the base material.

1...Base material layer 2...Adhesive layer 3...Metal foil 31...Metal layer 32...Peelable metal layer 4...Plating resist layer 5...Plating layer 100...Flexible printed wiring board

Claims (4)

A step of applying an adhesive to at least one side of a base layer made of a heat-resistant resin film and having a thickness of 8 μm or less to form an adhesive layer having a thickness of 3 μm or less;
a step of laminating a metal foil on the adhesive layer to form a metal layer with a thickness of 4 μm or less;
forming a patterned plating resist layer on the metal layer;
performing electrolytic plating on the laminate on which the plating resist layer is formed to form a plating layer;
Peeling the plating resist layer from the laminate on which the plating layer is formed;
a step of performing an etching treatment on the laminate from which the plating resist layer has been peeled off to remove the metal layer and a part of the plating layer;
The adhesive contains (A) a base resin containing at least one of a polyamide-imide resin and a polyimide resin, (B) an epoxy resin, (C) a curing agent, and (D) a solvent,
A method for manufacturing a flexible printed wiring board, characterized in that the amount of (A) is 5% by mass or more and 30% by mass or less based on 100% by mass of the total solid content of the adhesive. The method for manufacturing a flexible printed wiring board according to claim 1,
A method for manufacturing a flexible printed wiring board, characterized in that the metal layer has a surface roughness Rz (maximum height) of 1 μm or more and 2.5 μm or less. In the method for manufacturing a flexible printed wiring board according to claim 1 or 2,
A method for manufacturing a flexible printed wiring board, comprising subjecting the heat-resistant resin film to plasma treatment. In the method for manufacturing a flexible printed wiring board according to any one of claims 1 to 3,
A method for manufacturing a flexible printed wiring board, further comprising the step of thermosetting the adhesive layer.

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