JP6161293B2 - Manufacturing method of flexible wiring board - Google Patents

Description

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

  In recent years, in the field of mobile phone terminals and the like, in order to improve component mounting density, finer wiring circuits and multilayers (both sides or multilayers) have been demanded. Ratio of double-sided flexible wiring boards and multilayer flexible wiring boards Has increased. The double-sided flexible wiring board and the multilayer flexible wiring board use via holes (plating holes) for interlayer connection, and a plurality of conductive layers are electrically connected by performing copper plating on the via holes.

  Conventionally, manufacturing a multilayer flexible wiring board that forms a via hole by dissolving and removing a resin layer containing an alkali-soluble adhesive resin with an alkaline solution, and electrically connecting a plurality of conductive layers by copper plating on the via hole A method has been proposed (see, for example, Patent Document 1). According to this multilayer flexible wiring board manufacturing method, the manufacturing process can be simplified and continuous production can be achieved as compared with the case of forming a via hole by a drilling machine or a laser processing machine that is a drilling facility. It is possible to reduce the manufacturing cost and improve the productivity.

JP 2012-169346 A

  However, in the conventional method for manufacturing a multilayer flexible wiring board as described above, it is desired to reduce the diameter of the via hole and to stabilize the productivity accompanying the demand for further higher density. Further, in the dissolution removal using an alkaline solution, the resin layer is dissolved not only in the depth direction but also in the side surface direction inside the via hole. This is called side etching of the via hole. If this side etching is large, the copper plating may not be sufficiently covered, and the reliability of interlayer connection may be reduced.

  The present invention has been made in view of the above-described problems, and provides a method for manufacturing a flexible wiring board that has good productivity even when the via hole has a small diameter and that has excellent interlayer connection reliability. For the purpose.

  As a result of intensive studies to solve the above-mentioned problems, the inventor performs spray injection treatment under predetermined conditions for etching using an alkali solution of an uncured adhesive resin layer having alkali solubility, and then It has been found that by performing the water washing treatment by spraying under a predetermined condition, it is possible to suppress the occurrence of smear and to suppress the side etching of the via hole, and the present invention has been made based on this finding. That is, the present invention is as follows.

  The method for producing a flexible wiring board of the present invention includes a step of providing an uncured adhesive resin layer having alkali solubility on the surface of the first conductive layer, and a second conductive material on the surface of the uncured adhesive resin layer. A step of forming a layer, a step of forming a conformal mask by removing a part of the second conductive layer, and an uncured adhesive resin layer exposed in the opening of the conformal mask by using an alkaline solution. And a step of forming via holes reaching the first conductive layer by etching used, and the etching takes 0.1 times to a time required to remove the uncured adhesive resin layer The alkali solution is sprayed from the second conductive layer side by a spray at a treatment time corresponding to 0.6 times, and then the second conductive layer side at a water pressure of 0.10 MPa to 1.0 MPa by spraying. And performing by al rinsing.

  With this configuration, (a) the occurrence of smear associated with via hole formation can be suppressed, so desmear processing can be omitted, and the cost for forming via holes can be greatly reduced. In addition, (b) since the side etching of the via hole can be suppressed, a small-diameter via hole can be stably formed, and therefore, a flexible wiring board excellent in the fine patterning of the wiring circuit and the reliability of interlayer connection is manufactured. Is possible.

  In the method for manufacturing a flexible wiring board according to the present invention, the first conductive layer is preferably a conductive layer provided on a surface of a core substrate having at least one conductive layer.

  Further, in the method for manufacturing a flexible wiring board of the present invention, the step of curing the uncured adhesive resin layer by heating to obtain an insulating resin layer, and plating on the surface of the second conductive layer including the inside of the via hole It is preferable to further comprise a step of electrically connecting the first conductive layer and the second conductive layer.

  Further, in the method for manufacturing a flexible wiring board according to the present invention, at the same time as forming the conformal mask on the second conductive layer, a predetermined portion of the second conductive layer is removed, It is preferable to simultaneously remove the uncured adhesive resin layer exposed at the predetermined portion simultaneously with the formation of the via hole.

  In the method for producing a flexible wiring board of the present invention, it is preferable that the liquid pressure is 0.15 MPa or more and 0.3 MPa or less in the spray injection of the alkaline solution.

  In the method for producing a flexible wiring board of the present invention, it is preferable that the washing with water is performed for 60 seconds to 120 seconds.

  In the method for producing a flexible wiring board according to the present invention, in the spraying of the alkaline solution, the flow rate distribution in the effective processing surface is preferably within ± 20% of the liquid amount ratio compared to the center of the effective processing surface. .

  In the method for producing a flexible wiring board of the present invention, the uncured adhesive resin layer preferably contains an alkali-soluble resin having a carboxyl group or a phenolic hydroxyl group in the molecular chain.

  In the method for producing a flexible wiring board of the present invention, it is preferable that the alkali-soluble resin has at least a phenolic hydroxyl group and a polyimide structure.

  In the method for producing a flexible wiring board of the present invention, the uncured adhesive resin layer comprises (a) a polyimide containing a structure represented by the following general formulas (1) and (2), and (b) 2 or more. And an oxazoline compound having an oxazoline group.

（一般式（１）中、Ｘは単結合、−Ｏ−、−ＳＯ_２−、−Ｃ（＝Ｏ）−又はシリコーン含有基を表す。）

(In the general formula (1), X represents a single bond, —O—, —SO ₂ —, —C (═O) — or a silicone-containing group.)

（一般式（２）中、Ｚは単結合又は−Ｃ（−ＣＦ_３）_２−を表し、ｌは１から４の整数を表す。）

(In General Formula (2), Z represents a single bond or —C (—CF ₃ ) ₂ —, and 1 represents an integer of 1 to 4.)

  In the method for producing a flexible wiring board of the present invention, the uncured adhesive resin layer preferably contains a flame retardant.

  In the method for producing a flexible wiring board of the present invention, it is preferable that the uncured adhesive resin layer contains an adhesive.

  ADVANTAGE OF THE INVENTION According to this invention, even if a via hole is small diameter, productivity is favorable and the manufacturing method of the flexible wiring board excellent in the reliability of interlayer connection can be provided.

It is a cross-sectional schematic diagram which shows each process of the manufacturing method of the flexible wiring board which concerns on 1st Embodiment. It is a cross-sectional schematic diagram which shows each process of the manufacturing method of the flexible wiring board which concerns on 1st Embodiment. It is a cross-sectional schematic diagram which shows each process of the manufacturing method of the flexible wiring board which concerns on 2nd Embodiment.

  Hereinafter, an embodiment of the present invention (hereinafter abbreviated as “embodiment”) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.

  The method for manufacturing a flexible wiring board according to the present embodiment includes a step of providing an uncured adhesive resin layer having alkali solubility on the surface of the first conductive layer, and a step of forming on the surface of the uncured adhesive resin layer. A step of providing a conductive layer, a step of forming a conformal mask by removing a part of the second conductive layer, and the uncured adhesive resin layer exposed in the opening of the conformal mask, And a step of forming a via hole that reaches the first conductive layer by etching using an alkaline solution, and the etching is performed at a time required to remove the uncured adhesive resin layer by 0. The alkaline solution is sprayed from the second conductive layer side by a spray at a treatment time corresponding to 1 to 0.6 times, and then the second pressure is sprayed at a water pressure of 0.10 MPa to 1.0 MPa. And performing by washing from the conductive layer side.

  In the method for manufacturing a flexible substrate according to the present embodiment, the flexible wiring board includes at least two conductive layers, an interlayer insulating layer is disposed between the conductive layers, and penetrates the interlayer insulating layer. A via hole is formed, and the inside of the via hole is subjected to a plating process to enable electrical conduction and interlayer connection. Here, the via hole may be either a through via or a blind via.

  In the method for manufacturing a flexible wiring board according to the present embodiment, first, an uncured adhesive resin layer having alkali solubility is provided on the surface of the first conductive layer. The first conductive layer is made of a metal foil such as a copper foil, for example.

  Further, the first conductive layer may be a conductive layer already formed on the surface of the core substrate. The core substrate is a substrate having at least one conductive layer, for example, a single-layer flexible wiring board in which a conductive layer is provided on one or both sides of an interlayer insulating layer, or a multilayer in which conductive layers and interlayer insulating layers are alternately stacked. It is a flexible wiring board.

  The first conductive layer provided on the surface of the core substrate may be patterned for circuit formation.

  The uncured adhesive resin layer having alkali solubility has adhesiveness to the metal foil constituting the first conductive layer and the second conductive layer in the uncured state, and has alkali solubility for forming a via hole. . Further, in the cured state, it functions as an interlayer insulating layer that insulates between the first conductive layer and the second conductive layer, and has an insulating property, and also has a resiliency for imparting flexibility to the flexible wiring board. . Details of the resin composition constituting the uncured adhesive resin layer will be described later.

  The uncured adhesive resin layer can be formed, for example, by dissolving the resin composition in an organic solvent, and applying and drying on the surface of the core substrate including the first conductive layer. Alternatively, the resin composition may be formed into a film and laminated on a metal foil as the first conductive layer.

  Next, a second conductive layer is provided on the surface of the uncured adhesive resin layer. The second conductive layer is, for example, a metal foil such as a copper foil, and the second conductive layer is bonded to the surface of the uncured adhesive resin layer on the side opposite to the first conductive layer side. A conductive layer can be provided.

  Next, a part of the second conductive layer is removed, a part of the uncured adhesive resin layer is exposed, and a comfort mask having an opening corresponding to the via hole is formed. The removal of the second conductive layer can be performed, for example, by forming a resist mask on the second conductive layer and etching the second conductive layer through the resist mask.

  Next, via the conformal mask, the uncured adhesive resin layer exposed in the opening is removed by etching using an alkaline solution to form a via hole.

  Etching using an alkaline solution is performed in (1) a processing time corresponding to 0.1 to 0.6 times the time required to remove the uncured adhesive resin layer, and (2) the alkaline solution is subjected to the second treatment. Spraying from the conductive layer side, and (3) spraying the alkaline solution followed by washing with water from the second conductive layer side at a water pressure of 0.10 MPa to 1.0 MPa by spraying. .

  The alkali solution used here is not particularly limited as long as it can dissolve the alkali-soluble resin contained in the uncured adhesive resin layer. Examples of such an alkaline solution include a sodium carbonate aqueous solution, a potassium carbonate aqueous solution, a sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, and a tetramethylammonium hydroxide aqueous solution. Among these, it is preferable to use sodium carbonate aqueous solution, sodium hydroxide aqueous solution, etc. which are used in the manufacturing process of a general flexible wiring board.

  For spraying the alkaline solution, for example, a commercially available etching device, developing device or peeling device (hereinafter referred to as an alkaline solution developing device) having a spray nozzle can be used. An alkali solution having an injection amount of a certain amount or more is injected into the effective treatment surface. The effective treatment surface refers to a surface having a uniform spray pattern and flow rate distribution of the alkaline solution sprayed for a predetermined time.

  The alkaline solution developing device is not particularly limited, but it is preferable that the injection amount of the alkaline solution within the effective processing surface is balanced, and that liquid pool and retention can be reduced. As a suitable alkaline solution developing apparatus, an apparatus having an oscillation function can be mentioned.

  In spray spraying, the alkaline solution is continuously sprayed with a temperature-controlled alkali solution in order to prevent the accumulation and retention of the alkali solution, and the alkali solution is returned to the thermostat and circulated. The in-plane alkaline solution is always renewed, which is preferable from the viewpoint of reducing side etching of via holes. Side etching is the expansion of the etched part toward the inside of the uncured adhesive resin layer rather than the diameter of the conformal mask formed in the conductive layer. And the connection reliability between the first conductive layer and the second conductive layer may deteriorate.

  Also, from the viewpoint of suppressing side etching and removing smear on the side wall and bottom of the via hole, that is, removing the residue of the uncured adhesive resin layer, spraying is performed with a pressure of 0.2 L / min or more. Is preferred. For this reason, in the alkaline solution developing device, it is preferable that the spray nozzles are arranged at high density.

  A spray nozzle with a slit shape increases the impact of spray injection, and the droplet size of the spray droplets is reduced, so that the alkaline solution can easily enter the via hole and suppress side etching. To preferred.

  In the case of the slit shape, the liquid pressure is preferably 0.15 MPa or more because the injection amount decreases. From the viewpoint of suppressing side etching of via holes and removing smear, the liquid pressure is more preferably 0.2 MPa or more.

  Further, regarding the in-plane balance of the injection flow rate of the alkali solution, in order to make the etching rate uniform in the effective treatment surface where the alkali solution is injected, the variation in the liquid amount ratio compared to the center of the effective treatment surface is ± 20. % Or less, and more preferably within ± 10% from the viewpoint of suppressing variation in the formation of the blind vias to be formed. When a slit-shaped spray nozzle is used, the spray pattern is fan-shaped, and therefore it is particularly preferable that the alkaline solution developing device has an oscillation function from the viewpoint of in-plane balance and retention prevention.

  The treatment time for spraying is preferably 0.1 to 0.6 times the time required for removing the uncured adhesive resin layer from the viewpoint of suppressing side etching of the via hole, and preferably 0.1 to 0. More preferably, it is 5 times. From the viewpoint of the via hole having an inverted trapezoidal shape and good plating coverage, the ratio is more preferably 0.15 to 0.3 times.

  The “required time until the uncured adhesive resin layer is removed” is the time taken from the start of injection until the uncured adhesive resin layer is completely removed. Whether or not the uncured adhesive resin layer has been completely removed is confirmed using, for example, an appearance inspection apparatus.

  Following the spraying of the alkaline solution described above, washing with water removes the dry film peeling pieces and resin residues adhering to the surface of the second conductive layer forming the conformal mask, and the alkaline solution. From the viewpoint of removing smear in the via hole. In particular, from the viewpoint of removing the via hole sidewall and bottom smear in the small-diameter via hole and improving the coverage of the subsequent plating, the water pressure is 0.10 MPa or more and 0.3 MPa or less, and the washing time is 30 seconds or more and 120 seconds or less. It is preferable to carry out. Further, from the viewpoint of suppressing the peeling of the resin functioning as an interlayer insulating layer from the conductive layer included in the core substrate, the water pressure is 0.15 MPa or more and 0.3 MPa or less, and the water is washed with a treatment time of 60 seconds or more and 120 seconds or less. It is particularly preferable to do this.

  Although the water washing apparatus may be continuous with the alkali developing apparatus or separated from the alkali developing apparatus, the water washing process is preferably performed without taking any time from the etching process with the alkaline solution. Moreover, although the water washing process is generally performed by spraying, it is not particularly limited as long as it is an apparatus that can process the effective processing surface under the above-described conditions. The washing water may be purified water or city water.

  In the method for manufacturing a flexible wiring board according to the present embodiment, after forming the above-described via hole, the uncured adhesive resin layer is cured by heating to obtain an insulating resin layer.

  It is preferable that the thermosetting process performed here performs heat curing at the temperature of 120 to 400 degreeC from a viewpoint of reaction of a hardening | curing agent. More preferably, heating temperature is 150 degreeC or more and 200 degrees C or less.

  The reaction atmosphere in heat curing can be carried out in an air atmosphere or an inert gas atmosphere. Although the time required for heat curing varies depending on the reaction conditions, it is usually within 24 hours, particularly preferably in the range of 1 hour to 8 hours.

  Furthermore, the surface of the second conductive layer including the inside of the via hole is plated to electrically connect the first conductive layer and the second conductive layer. Thereby, a flexible wiring board can be obtained.

  The plating process performed here is formed by first depositing a general electroless copper plating process or a carbon fine particle layer and then plating to a predetermined thickness by electrolytic copper plating.

(Uncured adhesive layer)
In the present embodiment, the uncured adhesive resin layer has a dissolution rate in an aqueous sodium hydroxide solution of 0.22 μm in the state of an uncured layer formed by coating and drying on a substrate to a film thickness of 40 μm. In the state of the cured resin layer obtained by heating at 160 ° C. or higher for 1 hour or longer, the dissolution rate in the aqueous sodium hydroxide solution is preferably 0.02 μm / second or lower. If the alkali dissolution rate after uncured and cured is within the above range, it becomes easy to control the alkali solubility of the uncured adhesive resin layer, and the alkali solution development generally used in the manufacturing process of flexible wiring boards. The device can be used.

  In addition, the elastic modulus of the above-mentioned cured resin layer is such that the warp of the flexible wiring board is small and excellent in flexibility, and from the viewpoint of enabling molding by a roll-to-roll method, from 0.05 GPa to 3.0 GPa is preferable, and 0.05 GPa to 2.0 GPa is more preferable.

(Resin composition)
Next, the resin composition used for the method for manufacturing a flexible wiring board according to the present embodiment will be described. The resin composition contains an alkali-soluble resin and a reactive compound for thermosetting. In addition, a flame retardant, an adhesion material, and a solvent can be contained.

(Alkali-soluble resin)
The alkali-soluble resin is preferably a resin having a carboxyl group or a phenolic hydroxyl group in the molecular chain in order to have alkali solubility. More preferred is a phenolic hydroxyl group. In this case, it is because the reactivity at the time of hardening with a crosslinking agent etc. is excellent.

  Examples of the alkali-soluble resin include novolak resin, acrylic resin, copolymer of styrene and acrylic acid, polymer of hydroxystyrene, polyvinylphenol, poly α-methylvinylphenol, polyimide resin, polybenzoxazole Examples thereof include resins, polyvinylphenol resins, resol resins, copolymers of acrylic acid derivatives having phenolic hydroxyl groups, and polyvinyl acetal resins having phenolic hydroxyl groups. Of these, polyvinylphenol resins, novolak resins, and polyimide resins having phenolic hydroxyl groups are preferred.

  Examples of the polyvinylphenol resin include o-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene, dihydroxystyrene, trihydroxystyrene, tetrahydroxystyrene, pentahydroxystyrene, 2- (o-hydroxyphenyl) propylene, 2- Examples thereof include resins obtained by polymerizing hydroxystyrenes such as (m-hydroxyphenyl) propylene and 2- (p-hydroxyphenyl) propylene alone or in the presence of a radical polymerization initiator or a cationic polymerization initiator. . The polyvinyl phenol resin preferably has a polystyrene-equivalent weight average molecular weight (MW) of 500 to 100,000 as measured by gel permeation chromatography, and more preferably 1,000 to 50,000.

  Examples of novolak resins include phenol, o-cresol, m-cresol, p-cresol, 2,5-xylenol, 3,5-xylenol, o-ethylphenol, m-ethylphenol, p-ethylphenol, propylphenol. , N-butylphenol, t-butylphenol, 1-naphthol, 2-naphthol, 4,4′-biphenyldiol, bisphenol-A, pyrocatechol, resorcinol, hydroquinone, pyrogallol, 1,2,4-benzenetriol, phloroglucinol At least one phenol such as formaldehyde, acetaldehyde, propionaldehyde, benzaldehyde, furfural and the like (in addition to formaldehyde, paraformaldehyde) And the paraldehyde instead of acetaldehyde, may be used.), Or, acetone, methyl ethyl ketone, ketones such as methyl isobutyl ketone, and at least one and polycondensation resin obtained by the. Among them, the weight of phenol as phenols, o-cresol, m-cresol, p-cresol, 2,5-xylenol, 3,5-xylenol, resorcinol and formaldehyde, acetaldehyde, propionaldehyde as aldehydes or ketones. Condensates are preferred. In particular, the mixing ratio of m-cresol: p-cresol: 2,5-xylenol: 3,5-xylenol: resorcinol is 40 to 100: 0 to 50: 0 to 20: 0 to 20: 0 to 20 in molar ratio. A polycondensate of mixed phenols or mixed phenols of phenol: m-cresol: p-cresol with a molar ratio of 1-100: 0 to 70: 0-60 and formaldehyde is preferable.

  In order to improve the embedding property by lowering the melt viscosity, the novolak resin has 4,4′-biphenylylene group, 2,4′-biphenylylene group, 2,2′-biphenylylene group and / or 1,4 in the molecule. Use a novolak resin having both a phenol resin containing a cross-linking group such as a xylylene group, a 1,2-xylylene group, or a 1,3-xylylene group, and a phenol resin containing a methylene cross-linking group. Is also preferable.

  The novolak resin preferably has a polystyrene-reduced weight average molecular weight (MW) of 500 to 15,000 as measured by gel permeation chromatography, and more preferably 1,000 to 10,000.

  Furthermore, from the viewpoint of heat resistance and flexibility of the cured layer obtained after heating at 200 ° C. or less, a polyimide or a polyimide precursor having a carboxyl group or a phenolic hydroxyl group in the molecule, or a poly having a carboxyl group in the molecule Benzoxazole or polybenzoxazole precursors are preferred. More preferred is a polyimide having a phenolic hydroxyl group.

  A polyimide can be obtained by reacting an acid dianhydride and a diamine to synthesize a polyamic acid and then heating (heating imidization). It can also be obtained by reacting an acid dianhydride and a diamine to synthesize a polyamic acid and subsequently imidizing (chemical imidization) after adding a catalyst. Among these, chemical imidation is preferable in that imidization can be completed at a lower temperature.

  The polyimide used in the method for manufacturing a flexible wiring board according to the present embodiment is preferably an alkali-soluble polyimide having a structure represented by the following general formulas (1) and (2).

（一般式（１）中、Ｘは単結合、−Ｏ−、−ＳＯ_２−、−Ｃ（＝Ｏ）−又はシリコーン含有基を表す。）

(In the general formula (1), X represents a single bond, —O—, —SO ₂ —, —C (═O) — or a silicone-containing group.)

（一般式（２）中、Ｚは単結合又は−Ｃ（−ＣＦ_３）_２−を表し、ｌは１から４の整数を表す。）

(In General Formula (2), Z represents a single bond or —C (—CF ₃ ) ₂ —, and 1 represents an integer of 1 to 4.)

  The alkali-soluble polyimide having such a structure has, for example, an acid dianhydride component containing a tetracarboxylic dianhydride represented by the following general formula (3), and a residue from which an amino group is removed has the general formula (2 It is obtained by reacting a diamine component containing a diamine represented by

（一般式（３）中、Ｘは単結合、−Ｏ−、−ＳＯ_２−、−Ｃ（＝Ｏ）−又はシリコーン含有基を表す。）

(In general formula (3), X represents a single bond, —O—, —SO ₂ —, —C (═O) — or a silicone-containing group.)

  The tetracarboxylic dianhydride represented by the general formula (3) is 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,3,3 ′, 4′-biphenyltetracarboxylic acid. Dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride, 2,2 ′, 3,3′- Benzophenone tetracarboxylic dianhydride, 3,3′-oxydiphthalic dianhydride, 4,4′-oxydiphthalic dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, polydimethylsiloxane-containing acid A dianhydride etc. are mentioned. These tetracarboxylic dianhydrides may be used alone or in combination of two or more.

  The diamine in which the residue from which the amino group has been removed is represented by the above general formula (2) is 4,4′-diaminobiphenyl-3,3′-diol, 3,3′-diaminobiphenyl-4,4′-diol. 4,3′-diaminobiphenyl-3,4′-diol, 4,4′-diaminobiphenyl-3,3 ′, 5,5′-tetraol, 3,3′-diaminobiphenyl-4,4 ′, 5,5′-tetraol, 2,2′-bis (3-amino-4-hydroxyphenyl) hexafluoropropane, 2,2′-bis (3-amino-2,4-dihydroxyphenyl) hexafluoropropane, 2,2′-bis (4-amino-3,5-dihydroxyphenyl) hexafluoropropane and the like can be mentioned. These diamines may be used alone or in combination of two or more. Among these diamines, 4,4′-diaminobiphenyl-3,3′-diol and 2,2′-bis (3-amino) are considered from the viewpoints of solubility, insulation reliability, polymerization rate, and availability of polyimide. -4-Hydroxyphenyl) hexafluoropropane is preferred.

  The content of the diamine in which the residue from which the amino group has been removed is represented by the general formula (2) is preferably 5 mol% to 30 mol% with respect to the total diamine. More preferably, it is 10 mol%-25 mol%. If it is 5 mol% or more, it shows alkali solubility, and if it is 30 mol% or less, it is excellent in solvent solubility.

  As the acid dianhydride component other than the tetracarboxylic dianhydride represented by the general formula (3), a known tetracarboxylic dianhydride can be used without departing from the object of the present invention. Specific examples of tetracarboxylic dianhydrides include aromatic tetracarboxylic acids such as pyromellitic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, and 2,2-bis. (2,3-dicarboxyphenyl) propane dianhydride, 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride Bis (3,4-dicarboxyphenyl) methane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, 2,2-bis (4- (4-aminophenoxy) phenyl) propane, 1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylic acid-1,4-phenylene ester, 4- (2,5-dioxotetrahydrofuran-3-yl) -1,2,3 4-tetrahydronaphthalene-1,2-dicarboxylic anhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 2,3, 5,6-pyridinetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride, 2 , 2-bis (4- (3,4-dicarboxyphenoxy) phenyl) hexafluoropropane dianhydride, 2,2-bis (4- (3,4-dicarboxybenzoyloxy) phenyl) hexafluoropropane dianhydride Products, 2,2′-bis (trifluoromethyl) -4,4′-bis (3,4-dicarboxyphenoxy) biphenyl dianhydride, etc. Examples of the boronic acid dianhydride include cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 2,3,5,6-cyclohexanetetracarboxylic dianhydride, 5 -(2,5-dioxotetrahydro-3-furanyl) -3-methyl-3-cyclohexene-1,2-dicarboxylic dianhydride, bicyclo [2,2,2] oct-7-ene-2,3 , 5,6 tetracarboxylic dianhydride, 1,2,3,4-butanetetracarboxylic dianhydride and the like. These tetracarboxylic dianhydrides may be used alone or in admixture of two or more.

  Among these tetracarboxylic dianhydrides, 4,4′-oxydiphthalic dianhydride is preferable from the viewpoint of flexibility, solubility, insulation reliability, and polymerization rate of polyimide.

  Moreover, a well-known diamine can be used in the range which does not deviate from the objective of this invention as a diamine component other than the diamine which the residue remove | excluding the amino group is represented by the said General formula (2). Specific examples of diamines include, for example, 3,3′-diaminobenzophenone, 4,4′-diaminobenzophenone, 3,3′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ether, 1,3-bis (3-aminophenoxy ) Benzene, 1,4-bis (4-aminophenoxy) benzene, bis (3- (3-aminophenoxy) phenyl) ether, bis (4- (4-aminophenoxy) phenyl) ether, 1,3-bis ( 3- (3-aminophenoxy) phenoxy) benzene, 1,4-bis (4- (4-aminophenoxy) phenoxy) benzene, bis (3- (3- (3-aminophenoxy) phenoxy) phenyl) ether, bis (4- (4- (4-Aminophenoxy) phenoxy) phenyl) ether, 1,3-bis (3- (3 (3-Aminophenoxy) phenoxy) phenoxy) benzene, 1,4-bis (4- (4- (4-aminophenoxy) phenoxy) phenoxy) benzene, 4,4′-bis (3-aminophenoxy) biphenyl, 4 , 4′-bis (4-aminophenoxy) biphenyl, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2, , 2-bis [4- (3-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 2,2-bis [4- (4-aminophenoxy) phenyl] -1 , 1,1,3,3,3-hexafluoropropane, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, bis (3-aminophenyl Sulfide, bis (4-aminophenyl) sulfide, bis (3-aminophenyl) sulfoxide, bis (4-aminophenyl) sulfoxide, bis (3-aminophenyl) sulfone, bis (4-aminophenyl) sulfone, 2,2 -Bis [4- (3-aminophenoxy) phenyl] butane, α, ω-bis (2-aminoethyl) polydimethylsiloxane, α, ω-bis (3-aminopropyl) polydimethylsiloxane, α, ω-bis (4-aminobutyl) polydimethylsiloxane, α, ω-bis (4-aminophenyl) polydimethylsiloxane, α, ω-bis (3-aminopropyl) polydiphenylsiloxane, and the like.

  Among these diamines, when reducing the elastic modulus of the cured adhesive resin, use of polyoxyethylene diamine, polyoxypropylene diamine, and other polyoxyalkylene diamines containing oxyalkylene groups having different numbers of carbon chains may be used. preferable. Examples of polyoxyalkylene diamines include polyoxyethylene diamines such as Jeffamine ED-600, ED-900, ED-2003, EDR-148, and HK-511 manufactured by Huntsman, Inc., and Jeffamine D-230 and D-400. , D-2000, D-4000, polyamine propylene diamine such as polyetheramine D-230, D-400, D-2000 manufactured by BASF Germany, and polytetramethylene such as Jeffamine XTJ-542, XTJ533, XTJ536 Those having an ethylene group are listed as examples of use. Further, in order to improve the solubility of the uncured adhesive resin, α, ω-bis (2-aminoethyl) polydimethylsiloxane, α, ω-bis ( 3-aminopropyl) polydimethylsiloxane, α, ω-bis (4-aminobutyl) Polydimethylsiloxane, α, ω-bis (4-aminophenyl) polydimethylsiloxane, α, ω-bis (3-aminopropyl) polydiphenylsiloxane, α- (2-aminopropyl) -ω-aminopoly (oxypropylene) Etc. are mentioned as usage examples.

  The content of diamine for the purpose of reducing these elastic moduli is preferably 25 mol% to 65 mol% with respect to the total diamine. More preferably, it is 40 mol%-65 mol%. If it is 25 mol% or more, it is excellent in a softness | flexibility and solvent solubility. If it is 65 mol% or less, it is excellent in alkali solubility.

  Further, a diamine containing a hydroxyl group or / and a carboxyl group can be introduced into the polyimide. Such diamines include 2,5-diaminophenol, 3,5-diaminophenol, 4,4 ′-(3,3′-dihydroxy) diaminobiphenyl, 4,4 ′-(2,2 '-Dihydroxy) diaminobiphenyl, 2,2'-bis (3-amino-4-hydroxyphenyl) hexafluoropropane, 3-hydroxy-4-aminobiphenyl (HAB), 4,4'-(3,3'- Dicarboxy) diphenylamine, methylenebisaminobenzoic acid (MBAA), 2,5-diaminobenzoic acid (DABA), 3,3′-dicarboxy-4,4′-diaminodiphenyl ether, and the like.

  Next, a method for producing polyimide will be described. As a method for producing polyimide according to the present embodiment, all methods capable of producing polyimide, including known methods, can be applied. Among these, it is preferable to perform the reaction in an organic solvent. Examples of the solvent used in such a reaction include N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, γ-butyrolactone, triglyme, 1,2-dimethoxyethane, tetrahydrofuran, 1 , 3-dioxane, 1,4-dioxane, dimethyl sulfoxide, benzene, toluene, xylene, mesitylene, phenol, cresol, methyl benzoate, and ethyl benzoate. These may be used alone or in combination of two or more.

  In this embodiment, in the thermosetting process after forming the via hole, it is required that the shape of the via hole is maintained and there is no swelling due to outgas, and there is no swelling due to outgas during solder reflow during component mounting. And reliability in a thermal cycle test is required. For this reason, it is preferable that the residual solvent after hardening is 0.5 mass% or less in the hardened | cured material layer of a resin composition. More preferably, it is 0.2 mass% or less, More preferably, it is 0.1 mass% or less, Most preferably, it is 0.05 mass% or less.

  Therefore, the solvent used for the reaction is preferably a solvent having excellent drying properties, and is a solvent not containing an amide structure and having excellent volatility, such as γ-butyrolactone, triglyme, 1,2-dimethoxyethane, tetrahydrofuran, 1,3- Dioxane, 1,4-dioxane, dimethyl sulfoxide, benzene, toluene, xylene, mesitylene, phenol, cresol, methyl benzoate, ethyl benzoate and the like are preferable.

  When using a solvent having an amide structure such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, etc., because of hydrogen bonding with the polyimide of this embodiment even under reduced pressure conditions It is difficult to reduce the solvent residual amount to 0.5% by mass or less. When polymerization is performed using a solvent having an amide structure, a poor solvent is added after the polymerization to precipitate the polymer, After recovering and drying, it is preferable to use it by re-dissolving in a volatile solvent.

  The density | concentration of the reaction raw material in this polymerization reaction is 2 mass%-80 mass% normally, Preferably it is 20 mass%-50 mass%.

  The molar ratio of the tetracarboxylic dianhydride to be reacted and the diamine is in the range of 0.8 to 1.2. Within this range, the molecular weight can be increased, and the elongation and the like are excellent. Preferably it is 0.9-1.1, More preferably, it is 0.92-1.07.

  It is preferable that the weight average molecular weight of a polyimide precursor is 5000-150,000. Here, the weight average molecular weight refers to a molecular weight measured by gel permeation chromatography using polystyrene having a known number average molecular weight as a standard. The weight average molecular weight is more preferably from 10,000 to 60,000, and most preferably from 15,000 to 50,000. When the weight average molecular weight is 5,000 or more and 100,000 or less, the strength and elongation of the protective film obtained using the cured adhesive resin is improved, and the mechanical properties are excellent. Furthermore, it can be applied without bleeding at a desired film thickness during coating.

  Polyimide is obtained by the following method. First, a polyimide precursor having a polyamic acid structure is produced by subjecting a reaction raw material to a polycondensation reaction from room temperature to 80 ° C. Next, this polyimide precursor is preferably heated to 100 ° C. to 400 ° C. to imidize, or chemically imidized using an imidizing agent such as acetic anhydride, thereby repeating unit structure corresponding to polyamic acid. Is obtained. In the case of imidization by heating, in order to remove by-product water, dehydration is carried out under reflux using a Dean-Stark type dehydrator in the presence of an azeotropic agent (preferably toluene or xylene). Is also preferable.

  Moreover, it is also preferable to obtain a polyimide by carrying out the reaction at 80 ° C. to 220 ° C. to advance both the generation of the polyimide precursor and the thermal imidization reaction. That is, the diamine component and the acid dianhydride component are suspended or dissolved in an organic solvent and reacted under heating at 80 ° C. to 220 ° C. to cause both generation of a polyimide precursor and dehydration imidization. It is also preferable to obtain polyimide.

  Moreover, the terminal of the polymer main chain of the polyimide precursor can be end-capped with an end-capping agent made of a monoamine derivative or a carboxylic acid derivative. By sealing the terminal of the polymer main chain of polyimide, the storage stability derived from the terminal functional group is excellent.

  Examples of the end capping agent comprising a monoamine derivative include aniline, o-toluidine, m-toluidine, p-toluidine, 2,3-xylidine, 2,6-xylidine, 3,4-xylidine, and 3,5-xylidine. O-chloroaniline, m-chloroaniline, p-chloroaniline, o-bromoaniline, m-bromoaniline, p-bromoaniline, o-nitroaniline, p-nitroaniline, m-nitroaniline, o-aminophenol P-aminophenol, m-aminophenol, o-anisidine, m-anisidine, p-anisidine, o-phenetidine, m-phenetidine, p-phenetidine, o-aminobenzaldehyde, p-aminobenzaldehyde, m-aminobenzaldehyde, o-aminobenzonitrile, p-aminobenzonitrile Ryl, m-aminobenzonitrile, 2-aminobiphenyl, 3-aminobiphenyl, 4-aminobiphenyl, 2-aminophenylphenyl ether, 3-aminophenylphenyl ether, 4-aminophenylphenyl ether, 2-aminobenzophenone, 3 -Aminobenzophenone, 4-aminobenzophenone, 2-aminophenyl phenyl sulfide, 3-aminophenyl phenyl sulfide, 4-aminophenyl phenyl sulfide, 2-aminophenyl phenyl sulfone, 3-aminophenyl phenyl sulfone, 4-aminophenyl phenyl sulfone , Α-naphthylamine, β-naphthylamine, 1-amino-2-naphthol, 5-amino-1-naphthol, 2-amino-1-naphthol, 4-amino-1-naphthol, 5-amino Aromatic monoamines such as 2-naphthol, 7-amino-2-naphthol, 8-amino-1-naphthol, 8-amino-2-naphthol, 1-aminoanthracene, 2-aminoanthracene and 9-aminoanthracene Of these, derivatives of aniline are preferably used. These may be used alone or in combination of two or more.

  Examples of the end-capping agent comprising a carboxylic acid derivative mainly include carboxylic anhydride derivatives, such as phthalic anhydride, 2,3-benzophenone dicarboxylic acid anhydride, 3,4-benzophenone dicarboxylic acid anhydride, 2, 3-dicarboxyphenyl phenyl ether anhydride, 3,4-dicarboxyphenyl phenyl ether anhydride, 2,3-biphenyl dicarboxylic acid anhydride, 3,4-biphenyl dicarboxylic acid anhydride, 2,3-dicarboxyphenyl phenyl Sulfone anhydride, 3,4-dicarboxyphenyl phenyl sulfone anhydride, 2,3-dicarboxyphenyl phenyl sulfide anhydride, 3,4-dicarboxyphenyl phenyl sulfide anhydride, 1,2-naphthalenedicarboxylic acid anhydride, 2,3-naphthalenedicarboxylic anhydride, 1,8-naphth Dicarboxylic acid anhydride, 1,2-anthracene dicarboxylic acid anhydride, 2,3-anthracene dicarboxylic acid anhydride, 1,9-aromatic dicarboxylic acid anhydrides such as anthracene dicarboxylic acid anhydride. Of these aromatic dicarboxylic acid anhydrides, phthalic anhydride is preferably used. These may be used alone or in combination of two or more.

  Without removing the solvent, the obtained polyimide solution can be used as it is or further by adding necessary solvents, additives and the like to form the uncured adhesive resin layer of the flexible wiring board according to the present embodiment. It can also be used.

(Reactive compounds)
In the resin composition according to the present embodiment, the reactive compound reacts with the phenolic hydroxyl group in the alkali-soluble resin by heating to cause thermosetting.

  While maintaining a sufficient alkali solubility in the step of forming a via hole by etching the uncured adhesive resin layer with an alkali solution, it is preferable to have an alkali resistance by reducing the alkali solubility after the thermosetting treatment. . Since the cured product layer after the thermosetting treatment has alkali resistance, good insulation reliability required for the interlayer insulating film can be obtained. In addition, the cured product layer is dissolved by alkali when the dry film formed on the conductive layer is peeled off by alkali when the circuit is formed on the outer conductive layer by etching, such as when multilayering is sequentially performed by the build-up method. Not.

  For this reason, the reactive compound is a compound that exhibits alkali resistance by reacting with the phenolic hydroxyl group of the above-described alkali-soluble resin without reacting before the thermosetting treatment and reacting during the thermosetting treatment. desirable. Therefore, the reactive compound is preferably such that the reaction proceeds slowly at 120 ° C. or lower, preferably 100 ° C. or lower, and sufficiently proceeds at 150 ° C. or higher, preferably 170 ° C. or higher.

  Examples of such reactive compounds include oxazoline compounds, benzoxazine compounds, epoxy compounds, and oxetane compounds. Preferable examples include oxazoline compounds, benzoxazine compounds, and oxetane compounds. Particularly preferred are oxazoline compounds that do not by-produce hydroxyl groups by reaction.

  An oxazoline compound is a compound having one or more oxazoline groups in the molecule. As a compound containing an oxazoline group, a compound having two or more oxazoline groups in the molecule is preferable when the hydroxyl group of polyimide is sealed and further formed between polyimides.

  Specific examples of the oxazoline compound include 1,3-bis (4,5-dihydro-2-oxazolyl) benzene, K-2010E, K-2020E, K-2030E, 2,6-bis (4 -Isopropyl-2-oxazolin-2-yl) pyridine, 2,6-bis (4-phenyl-2-oxazolin-2-yl) pyridine, 2,2'-isopropylidenebis (4-phenyl-2-oxazoline) 2,2′-isopropylidenebis (4-tertiarybutyl-2-oxazoline) and the like. These oxazoline compounds may be used alone or in combination of two or more.

  The amount of the oxazoline compound added is preferably such that the molar amount of the oxazoline group is hydroxyl group / oxazoline group = 4 to 0.5 as a molar ratio, assuming that the molar amount of the hydroxyl group of the polyimide having a hydroxyl group is 1. 0.7 is more preferable. When the hydroxyl group / oxazoline group = 4 or less, the alkali processability of the resin composition is improved, and when the hydroxyl group / oxazoline group = 0.5 or more, the flexibility and heat resistance of the cured adhesive resin are improved.

  The resin composition containing the above oxazoline compound sufficiently removes volatile components such as a solvent and residual monomer and makes it soluble in an alkaline solution. It is preferable to heat and dry for a minute to form an uncured adhesive resin layer.

  Since this uncured adhesive resin layer is soluble in an alkaline solution, via holes can be formed by etching using an alkaline solution, and laser drilling or the like used in the production of a flexible wiring board is not required.

  Moreover, a hardened | cured material layer can be obtained by heating an uncured adhesive resin layer after via-hole formation. The heating method is not particularly limited, but for example, heating at 160 ° C. to 200 ° C. mainly causes hydroxyl group sealing and crosslinking reaction, and the obtained cured product layer becomes insoluble in an alkaline solution.

  The resin composition according to the present embodiment may further contain a compound having a thermally crosslinkable functional group as the reactive compound. Examples of the compound having a thermally crosslinkable functional group include triazine compounds, benzoxazine compounds, and epoxy compounds.

  As the triazine compound, melamines and cyanuric acid melamines are preferable. Examples of melamines include melamine derivatives, compounds having a structure similar to melamine, and melamine condensates. Specific examples of melamines include, for example, methylolated melamine, ammelide, ammelin, formoguanamine, guanylmelamine, cyanomelamine, arylguanamine, melam, melem and melon.

  Examples of the melamine cyanurate include an equimolar reaction product of cyanuric acid and melamine. Moreover, some of the amino groups or hydroxyl groups in melamine cyanurate may be substituted with other substituents. Among these, melamine cyanurate can be obtained by, for example, mixing an aqueous solution of cyanuric acid and an aqueous solution of melamine, reacting at 90 to 100 ° C. with stirring, and filtering the generated precipitate, and is a white solid. A commercially available product can be used as it is or after being pulverized into a fine powder.

  The benzoxazine compound may be composed only of monomers, or several molecules may be polymerized into an oligomer state. Moreover, you may use the benzoxazine compound which has a different structure simultaneously. Specifically, bisphenol benzoxazine is preferably used.

  As the epoxy compound, those containing at least two epoxy groups in the molecule are more preferred, and phenol glycidyl ether type epoxy resins are particularly preferred from the viewpoint of curability and cured product characteristics. Specifically, bisphenol A type (or AD type, S type, F type) glycidyl ether, phenol novolac resin glycidyl ether, naphthalene resin glycidyl ether, and the like are preferably used.

  Moreover, when using an epoxy resin, a hardening | curing agent can also be used as needed.

(Flame retardants)
Moreover, the resin composition which concerns on this Embodiment may contain a flame retardant from a viewpoint of improving a flame retardance. The type of flame retardant is not particularly limited, and examples thereof include halogen-containing compounds, phosphorus-containing compounds, and inorganic flame retardants. One kind of these flame retardants may be used, or two or more kinds may be mixed and used.

  The addition amount of the flame retardant is not particularly limited, and may be appropriately changed according to the type of the flame retardant used. Generally, it is preferably used in the range of 5% by mass to 50% based on the content of the alkali-soluble resin.

  Examples of the halogen-containing compound flame retardant include an organic compound containing chlorine and a compound containing bromine. Specific examples include pentabromodiphenyl ether, octabromodiphenyl ether, decabromodiphenyl ether, tetrabromobisphenol A, hexabromocyclododecane tetrabromobisphenol A, and the like.

  Examples of the phosphorus-containing compound flame retardant include phosphorus compounds such as phosphazene, phosphine, phosphine oxide, phosphate ester, and phosphite ester. In particular, from the viewpoint of compatibility with the polyimide composition, phosphazene, phosphioxide, or phosphate ester is preferably used.

  Examples of inorganic flame retardants include antimony compounds and metal hydroxides. Examples of the antimony compound include antimony trioxide and antimony pentoxide. Combined use of antimony compounds and the above halogen-containing flame retardants, the antimony oxide pulls out halogen atoms from the flame retardants to produce antimony halides in the thermal decomposition temperature range of plastics, thus synergistically increasing the flame retardancy. Can do. Examples of the metal hydroxide include aluminum hydroxide and magnesium hydroxide.

  When an inorganic flame retardant is used, it is not dissolved in an organic solvent, so the particle size of the powder is preferably 100 μm or less. If the particle diameter of the powder is 100 μm or less, it is preferable that the powder is easily mixed into the alkali-soluble resin composition without impairing the transparency of the cured resin. In order to further increase the flame retardancy, the particle size of the powder is preferably 50 μm or less, particularly preferably 10 μm or less.

(Adhesive material)
In addition, the resin composition according to the present embodiment may contain an adhesion material from the viewpoint of improving adhesion with the metal foil. Although it does not specifically limit as an adhesive material, A phenol compound, a nitrogen-containing organic compound, an acetylacetone metal complex etc. can be mentioned. A phenol compound is particularly preferable.

(solvent)
The resin composition according to the present embodiment may contain an organic solvent. By making it the state melt | dissolved in the organic solvent, it can be preferably used as a varnish.

  Examples of such organic solvents include amide solvents such as N, N-dimethylacetamide, N, N-diethylacetamide, N, N-dimethylformamide, N, N-diethylformamide, N-methyl-2-pyrrolidone, Lactone solvents such as γ-butyrolactone and γ-valerolactone, sulfur-containing solvents such as dimethyl sulfoxide, diethyl sulfoxide and hexamethyl sulfoxide, phenol solvents such as cresol and phenol, diethylene glycol dimethyl ether (diglyme), triethylene glycol dimethyl ether (triglyme) ), Tetraglyme, dioxane, tetrahydrofuran, butyl benzoate, ethyl benzoate, methyl benzoate and the like. These organic solvents may be used alone or in combination.

(Other)
When the resin composition according to the present embodiment is further made into a coating film, the viscosity and thixotropy are adjusted according to the coating method, so that a filler or a thixotropic agent is added as necessary. Can also be used. Moreover, it is also possible to add additives, such as a well-known antifoamer, a leveling agent, and a pigment.

  Hereinafter, a method for manufacturing a multilayer flexible wiring board to which the method for manufacturing a flexible wiring board according to the present embodiment is applicable will be described. Here, first, a laminated body in which an uncured adhesive resin layer is formed on a base material is produced, and this base material is laminated from both sides of a double-sided flexible board as a core board to produce a multilayer flexible wiring board.

(Production of laminate)
The laminate is produced by applying a varnish obtained by dissolving the resin composition in an organic solvent to the surface of the base material and drying it.

  It is preferable that the base material used here corresponds to a coating and drying facility capable of continuous production by a roll-to-roll method. Examples of such a substrate include a conductive substrate, a glass cloth, and a carrier film. Among these, a conductive substrate is preferable from the viewpoint of continuous productivity and handling. Examples of the conductive base material include electrolytic copper foil, rolled copper foil, electrodeposition film, film with conductive paste, aluminum foil film, stainless steel foil film, etc., from the viewpoint of wiring workability and adhesion after substrate pressure bonding. Electrolytic copper foil or rolled copper foil is particularly preferred.

  Examples of the coating method include bar coating, roller coating, die coating, blade coating, dip coating, doctor knife, spray coating, flow coating, spin coating, slit coating, and brush coating.

  After coating, if necessary, a heat treatment called pre-baking may be performed with a hot plate or the like.

  Although it does not specifically limit about the aspect as a drying method, In order to make it soluble in an alkaline solution, it is preferable to heat at 50 degreeC-140 degreeC for 1 minute-30 minutes. Further, heating in a high temperature region (for example, 160 ° C. to 200 ° C.) mainly causes hydroxyl group sealing and crosslinking reaction, and becomes insoluble in an alkaline solution.

  At least one cover film may be provided on the uncured adhesive resin layer of the laminate for protection from dirt and the like. In the laminate according to the present embodiment, the cover film is not limited as long as it is a film that can protect the uncured adhesive resin layer, such as low-density polyethylene.

(Production of multilayer flexible wiring board)
Next, the laminated body is laminated by thermocompression bonding from both sides of the double-sided flexible wiring board to be the core substrate to produce a multilayer flexible wiring board.

  A double-sided flexible wiring board is prepared as a core substrate. In the double-sided flexible wiring, conductive layers are provided on both sides of an insulating resin layer. The conductive layer is, for example, a line circuit. The material of the conductive layer is, for example, copper. For example, the circuit formation is performed by patterning a copper foil by a known subtractive method.

  First, a laminated body is arrange | positioned so that an unhardened adhesive resin layer may contact a conductive layer on both sides of a double-sided flexible substrate. In this state, thermocompression bonding is performed for lamination.

  Examples of the pressure bonding method include hot pressing, thermal laminating, thermal vacuum pressing, and thermal vacuum laminating. Among these, from the viewpoints of adhesion between the uncured adhesive resin layer and the wiring layer, and resin embedding properties in the through-holes and copper wiring circuits formed in the double-sided flexible wiring board, thermal vacuum pressing, thermal vacuum laminating Is preferred. Furthermore, from the viewpoint of productivity by the roll-to-roll method, the thermal vacuum lamination is particularly preferable.

  In a vacuum laminating apparatus capable of performing thermal vacuum laminating, a rubber base material including a reinforcing material is provided between a press surface plate and a laminated body when vacuum laminating. The rubber substrate may be fixed to the vacuum laminator or may be independent.

  The rubber substrate is not particularly limited as long as it has heat resistance up to about 200 ° C., but is preferably silicone or urethane material. The rubber has a surface hardness of preferably 30 degrees or more and 70 degrees or less, and more preferably 30 degrees or more and 50 degrees or less. Further, from the viewpoint of continuous productivity by a roll-to-roll manufacturing apparatus or the like, it is more preferable that the rubber base material is embossed with a fine uneven structure.

  Also, the size of the rubber substrate is larger than the laminate, and the uncured adhesive resin flows unnecessarily from the end of the double-sided flexible wiring board, so-called resin flow suppression, heat conduction of the press surface plate, This is preferable in view of the fact that there is no need to change the pressure uniformity and the size of any laminate and the size does not depend on the size of the press device.

  It is preferable to use cloth or non-woven fabric as the reinforcing material from the viewpoint of suppressing deformation of the rubber base material, suppressing pressure variation in the press surface, and uniform lamination. The material of the reinforcing material is not particularly limited as long as it has heat resistance, whether it is glass fiber or steel fiber.

  The lamination conditions for press lamination are uncured adhesive resin that is heated and pressurized for 0.5 to 10 minutes at a temperature of 80 to 180 ° C. and a pressure of 0.1 to 3 MPa. From the viewpoint of suppressing the progress of the curing reaction. From the viewpoint of improving the resin embedding property and the surface smoothness between the wirings of the double-sided flexible wiring board and in the through hole of the inner layer, the temperature is 100 ° C. to 180 ° C., the pressure is 0.5 MPa to 3 MPa, and the crimping time is 1 It is particularly preferable that the time be from 5 minutes to 5 minutes.

  Since the above lamination conditions do not particularly depend on the vacuum press or the vacuum laminator apparatus, they can be suitably used for a vacuum laminator, a quick press apparatus or the like in order to shorten the production time.

  According to the manufacturing method of the flexible wiring board according to the present embodiment described above, the etching using the alkaline solution of the uncured adhesive resin layer is performed in the time required for removing the uncured adhesive resin layer by 0. By spraying the alkaline solution with a spray at a treatment time corresponding to 1 to 0.6 times, and then washing with water at a water pressure of 0.10 MPa to 1.0 MPa by spraying, (a) smear caused by via hole formation Since generation can be suppressed, for example, a desmear process for decomposing and removing the resin using an aqueous potassium permanganate solution, an ashing process using plasma, UV irradiation, or the like can be omitted, and the via hole formation cost can be greatly reduced. Further, (b) side etching of the via hole can be suppressed, so that by performing alkali etching and water washing treatment through a conformal mask formed in the conductive layer, a small-diameter via hole whose inner shape is an inverted trapezoid can be stably formed. Can be formed. As a result, the copper plating coverage inside the via is excellent, and the copper plating thickness can be reduced, so that it becomes possible to manufacture a flexible wiring board with fine wiring circuit and excellent reliability of interlayer connection. .

  In addition to the effects as described above, since the uncured adhesive resin layer contains an alkali-soluble resin, it is possible to form a via hole by dissolving and removing it with an alkaline solution. Compared to the formation of a via hole by laser processing and drilling. The manufacturing process can be simplified and the manufacturing cost can be reduced.

  In addition, by dissolving and removing the uncured adhesive resin layer using an alkaline solution, via holes can be formed in a shorter time compared to laser processing and drilling processing, so that continuous production of flexible wiring boards is also possible. Thereby, the flexible wiring board excellent in circuit quality can be manufactured with high production efficiency.

  The manufacturing method of a flexible wiring board according to the present embodiment is an alkaline solution that is commonly used for manufacturing a flexible wiring board, and has a spray such as a commercially available etching apparatus, developing apparatus, and laminating equipment. Since the developing device can be used, no additional capital investment is required.

  Hereinafter, a method for manufacturing a multilayer flexible wiring board to which the method for manufacturing a flexible wiring board according to the present embodiment is applied will be described in detail with reference to the drawings.

  Hereinafter, a method for manufacturing the flexible wiring board according to the first embodiment will be described. First, a double-sided flexible wiring board as a core substrate is produced. FIG. 1 is a schematic cross-sectional view showing each step of the method for manufacturing a flexible wiring board according to the first embodiment. As shown in FIG. 1A, a laminate 11 is used. The laminated body 11 includes a copper foil 12a (for example, copper foil F2-WS (12 μm)), an uncured adhesive resin layer 14 that is provided on the copper foil 12a and includes the resin composition according to the above embodiment. .

  The laminate 11 is included in the uncured adhesive resin layer 14 by applying the resin composition according to the present embodiment dissolved in an organic solvent on the copper foil 12a and then heating at 95 ° C. for 12 minutes. It is produced by removing the organic solvent by drying.

  Next, as shown in FIG. 1B, the uncured adhesive resin layer 14 of the laminate 11 is stacked on the copper foil 12b and laminated by, for example, vacuum pressing at 100 ° C. for 1 minute at 4 MPa. As a result, a laminate 13 composed of the copper foil 12a, the uncured adhesive resin layer 14, and the copper foil 12b is obtained.

  Next, as shown in FIG. 1C, a photosensitive resist layer is formed on one copper foil 12b of the laminate 13, and a part of the copper foil 12b is formed by exposing and developing the resist layer and etching the copper foil 12b. A conformal mask is formed by removing 12b-1 (hereinafter referred to as an etching site). The photosensitive resist layer is removed during etching using an alkaline solution for forming a via hole described later.

  Next, as shown in FIG. 1D, the uncured adhesive resin layer 14 exposed at the etching site 12b-1 of the copper foil 12b through the conformal mask is removed by etching using an alkaline solution, and the via hole 15 Form. The etching using the alkaline solution performed here is performed by the alkali solution spraying treatment and the water washing treatment under the conditions as described above.

  Next, the uncured adhesive resin layer 14 is thermally cured to form the insulating resin layer 16 by heating at 180 ° C. for 1 hour using a curing and drying furnace, for example.

  Next, electroless copper plating or electrolytic copper plating after carbon fine particles are attached is performed to form a plating layer on the surfaces of the insulating resin layer 16 and the copper foils 12a and 12b constituting the inner wall of the via hole 15. By this plating layer, the copper foils 12a and 12b are electrically connected.

  Next, as shown in FIG. 1E, the double-sided flexible wiring board 10 is obtained by patterning the copper foils 12a and 12b by a subtractive method or the like to form a circuit.

  Next, using the double-sided flexible wiring board 10 obtained as described above as a core substrate, a multilayer flexible wiring board using blind vias is produced.

  FIG. 2 is a schematic cross-sectional view showing each step of the method of manufacturing the flexible wiring board according to the first embodiment. In the first embodiment, a multilayer flexible wiring board is manufactured using the above-described double-sided flexible wiring board (hereinafter referred to as a core board) 10 as a core board. In the core substrate 10, in addition to the double-sided flexible wiring board on which the above-described blind via is formed, a substrate on which a through via is formed may be used.

  First, as shown in FIG. 2A, the above-mentioned uncured adhesive resin layers 21a and 21b and copper foils 22a and 22b are sequentially laminated on the copper foils 12a and 12b of the core substrate 10, respectively.

  In this lamination step, as described above, a method of laminating a laminate composed of an uncured adhesive resin layer and a conductive layer on both sides of the double-sided flexible wiring board can be employed. That is, the varnish which melt | dissolved the resin composition in the organic solvent on the surface of copper foil 22a, 22b is applied and dried, uncured adhesive resin layer 21a, 21b is formed, and laminated body 23a, 23b is produced. These laminates 23 a and 23 b are arranged on both sides of the core substrate 10, sandwiched between the rubber base materials 100, and compressed by pressure.

  Next, after laminating a dry film resist on the copper foils 22a and 22b, exposure and development of the dry film resist and etching of the copper foils 22a and 22b, as shown in FIG. A conformal mask is formed by removing a part (hereinafter referred to as etching site) 22a-1 and 22b-1.

  Next, as shown in FIG. 2C, the uncured adhesive resin layers 21a and 21b exposed at the etching portions 22a-1 and 22b-1 of the copper foils 22a and 22b through the conformal mask were used with an alkaline solution. The blind via 24 is formed by etching. The etching using the alkaline solution performed here is performed by the alkali solution spraying treatment and the water washing treatment under the conditions as described above.

  Next, the uncured adhesive resin layers 21a and 21b are cured by, for example, heating at 60 ° C. to 200 ° C. for 10 minutes to 5 hours using a curing and drying furnace, and as shown in FIG. Resin layers 25a and 25b are formed. The reaction atmosphere in heat curing can be carried out in an air atmosphere or an inert gas atmosphere. A laminate of the insulating resin layers 25a and 25b formed in this manner and the copper foils 22a and 22b is referred to as external substrates 26a and 26b.

  Next, the electroless copper plating or the electrolytic copper plating after carbon fine particles are attached is performed, and the plating layers are formed on the surfaces of the insulating resin layers 25a and 25b and the copper foils 12a and 12b constituting the inner wall of the blind via 24. Form. Thus, the copper foil 12a on one main surface side of the core substrate 10 and the copper foil 22a on the other main surface side of the core substrate 10, and the copper foil 12b on the other main surface side of the core substrate 10 and the copper of the external substrate 26b. The foil 22b is electrically connected to each other.

  Next, as shown in FIG. 2D, circuit formation is performed by patterning the copper foils 22a and 22b of the external substrates 26a and 26b by a subtractive method. Next, in the same manner as in the conventional method for manufacturing a flexible wiring board, as shown in FIG. 2E, insulation treatment such as formation of a cover coat 27 is performed to obtain the multilayer flexible wiring board 20.

  According to the manufacturing method of the multilayer flexible wiring board 20 according to the first embodiment described above, the etching using the alkaline solution of the uncured adhesive resin layers 21a and 22b is performed with the uncured adhesive resin layers 21a and 22b. By spraying the alkaline solution with a spray at a processing time corresponding to 0.1 to 0.6 times the time required to remove the water, and then washing with water at a water pressure of 0.10 MPa to 1.0 MPa by spraying. (A) Since the occurrence of smear associated with the formation of the blind via 24 can be suppressed, the desmear process or the like can be omitted, and the blind via formation cost can be greatly reduced. Further, (b) since the side etching of the blind via 24 and the overhang from the conformal mask can be suppressed, the blind via 24 having a small diameter can be stably formed. It becomes possible to manufacture the multilayer flexible wiring board 20 excellent in reliability.

  In addition to the effects as described above, since the uncured adhesive resin layers 21a and 21b contain an alkali-soluble resin, the blind via 24 can be formed by dissolving and removing with an alkali solution. As a result, the manufacturing process can be simplified and the manufacturing cost can be reduced as compared to blind via formation by laser processing and drilling.

  In addition, by dissolving and removing the uncured adhesive resin layers 21a and 21b using an alkaline solution, the blind via 24 can be formed in a shorter time compared to laser processing and drilling. Production is also possible. Thereby, the multilayer flexible wiring board 20 excellent in circuit quality can be manufactured with high production efficiency.

  Moreover, according to the method for manufacturing the multilayer flexible wiring board 20 according to the first embodiment, the multilayer flexible wiring board 20 is configured without providing a cover coat between the core substrate 10 and the external substrates 26a and 26b. be able to. For this reason, the configuration can be simplified as compared with the multilayer flexible wiring board manufactured by the conventional method, and the manufacturing process can be greatly simplified. That is, in the conventional method for producing a multilayer flexible wiring board, the double-sided flexible wiring board is laminated via a bonding sheet (adhesive) or the like. A double-sided flexible wiring board has a cover coat layer for a wiring circuit, usually called a coverlay. In the manufacturing method of the multilayer flexible wiring board 20 according to the present embodiment, the uncured adhesive resin layers 21a and 21b serve as the cover coat layer and the bonding sheet by the conventional coverlay by the build-up method. The configuration can be simplified.

  In addition, the manufacturing method of the multilayer flexible wiring board 20 according to the first embodiment includes an etching apparatus, a developing apparatus, and an alkaline solution developing apparatus such as a laminating equipment that are generally used for manufacturing a flexible wiring board. Since it can be used, no additional capital investment is required.

  Next, the manufacturing method of the multilayer flexible wiring board using the blind via which has the flexible part to which the manufacturing method of the flexible wiring board which concerns on this Embodiment is applied is demonstrated.

  The flexible part is a part that has flexibility and bendability and is desired to have a small repulsive force after being bent. Therefore, thinning and flexibility are required. Conventionally, this part is manufactured by mechanically cutting it using a router or the like. However, in the method of manufacturing a flexible wiring board according to the present embodiment, the via hole can be easily manufactured by alkali etching and simultaneously removing this portion by alkali etching.

  FIG. 3 is a schematic cross-sectional view showing each step of the method for manufacturing a flexible wiring board according to the second embodiment. Since the process up to the fabrication of the core substrate 10 and the laminations 23a and 23b on both sides of the core substrate 10 are the same as those described in the first embodiment, the description thereof is omitted. Moreover, in the following description, the same code | symbol is attached | subjected about the structure similar to 1st Embodiment, and description is abbreviate | omitted.

  As shown in FIG. 3A, a part of the copper foils 22a and 22b (etching sites) 22a-1 and 22b-1 is removed by etching to form a conformal mask, and an etching site 22b- corresponding to the flexible portion is formed. Remove 2 simultaneously.

  Next, the uncured adhesive resin layers 21a and 21b exposed at the etching sites 22a-1, 22b-1 and 22b-2 are removed by etching using an alkaline solution through a conformal mask. As shown in FIG. 3B, the flexible portion 31 is formed simultaneously with the blind via 24.

  Thereafter, as described in the first embodiment, the uncured adhesive resin layers 21a and 21b are cured to form insulating resin layers 25a and 25b as shown in FIG. 3C. Next, a plating layer is formed on the surfaces of the insulating resin layers 25a and 25b and the copper foils 12a and 12b constituting the inner wall of the blind via 24. Thereafter, as shown in FIG. 3C, the copper foils 22a and 22b of the external substrates 26a and 26b are patterned by the subtractive method to form a circuit. Next, as shown in FIG. 3D, insulation processing such as formation of a cover coat 27 is performed in the same manner as in the conventional flexible substrate wiring board method, and the multilayer flexible wiring board 30 is obtained.

  According to the method for manufacturing the multilayer flexible wiring board 30 according to the second embodiment, in addition to the same effects as those described in the first embodiment, the following effects can be obtained.

  By providing the etching sites 22a-1 and 22b-1 on the copper foils 22a and 22b and at the same time providing the etching sites 22b-2 corresponding to the flexible portion 31, the uncured adhesive resin layers 21a and 21b can be formed with an alkaline solution. Since the flexible via 31 can be formed by dissolving and removing the uncured adhesive resin layers 21a and 21b exposed at the etching portion 22b-2 at the same time as forming the blind via 24 by dissolving and removing, The multilayer flexible wiring board 30 having the flexible portion 31 can be manufactured in a shorter time and at a lower cost.

  Hereinafter, although the Example performed in order to clarify the effect of this invention is described concretely, this invention is not limited at all by these examples.

  First, adjustment of the varnish of the resin composition containing the alkali-soluble resin used in Examples and Comparative Examples will be described.

[Sample S1]
A three-necked separable flask was equipped with a nitrogen condenser, a thermometer, and a ball condenser equipped with a moisture separation trap. At oil bath room temperature, 175.7 g of γ-butyrolactone, 50.0 g of toluene, 21.02 g of 2,2′-bis (3-amino-4-hydroxyphenyl) hexafluoropropane (6FAP), polyalkyl ether diamine (trade name) : Jeffamine (XTJ-542), manufactured by Huntsman) 42.60 g was added and stirred at 60 ° C. until uniform. Furthermore, 30.09 g of 4,4′-oxydiphthalic dianhydride (hereinafter referred to as ODPA) was added little by little. After 30 minutes, 0.89 g of phthalic anhydride was added, and then the temperature was raised to 180 ° C. and heated for 2 hours. During the reaction, by-product water was azeotroped with toluene and dehydrated under reflux using a ball-mounted condenser equipped with a water separation trap. After draining by-product water, the reflux was stopped, toluene was completely drained, and the mixture was cooled to room temperature. Next, the product was pressure filtered through a 5 μm filter to obtain a polyimide A varnish. The weight average molecular weight of the polyimide A varnish was 83,000.

  The obtained polyimide A varnish was used as it was, and diluted with γ-butyrolactone so that the solid content was 45% by mass. The solid content in the polyimide A varnish was 51.1% by mass, 1,3-bis (4,5-dihydro-2-oxazolyl) benzene (PBO) was 6.9% by mass as a compound containing two oxazoline groups, Compound magnesium hydroxide MGZ-5R (manufactured by Sakai Chemical Industry Co., Ltd.) is 40.0% by mass, and Irganox 245 (IRG245) (manufactured by BASF Co.) is 2.0% by mass as an antioxidant, A varnish of sample S1 was obtained.

[Sample S2]
The amount of ODPA was changed from 30.09 g to 31.02 g, and it was processed in the same way as Sample S1 except that phthalate anhydride was added, ODPA was added, the temperature was raised to 180 ° C. and heated for 2 hours. As a result, polyimide B varnish was obtained. The weight average molecular weight of the polyimide B varnish was 114,000.

  A sample S2 varnish having the same composition as the sample S1 was prepared except that the obtained polyimide B varnish was used instead of the polyimide A varnish.

[Sample S3]
In a separable flask under a nitrogen atmosphere, 42.0 g of γ-butyrolactone, 18.0 g of triethylene glycol dimethyl ether, 20.0 g of toluene, 19.54 mmol of silicone diamine (hereinafter referred to as KF-8010) (manufactured by Shin-Etsu Chemical Co., Ltd.) Then, 40.00 mmol of ethylene glycol-bis-trimellitic anhydride (TMEG) (manufactured by Shin Nippon Rika Co., Ltd.) was added, and a Dean-Stark apparatus and a reflux were attached, followed by heating and stirring at 180 ° C. for 30 minutes. After removing toluene as an azeotropic solvent, the mixture was cooled to 25 ° C., followed by 4.89 mmol of KF-8010, 1,3-bis (3-aminophenoxy) benzene (APB-N) (manufactured by Mitsui Chemicals) 15 .56 mmol was added and stirred at 25 ° C. for 5 hours. After stirring, a mixed solvent of γ-butyrolactone / triethylene glycol dimethyl ether was added so that the concentration of the solid content of the polymer was 30% by weight to obtain a polyimide precursor solution. Furthermore, 10 parts by mass of tris (butoxyethyl) phosphate (TBXP) (manufactured by Daihachi Chemical Co., Ltd.) and 7 parts by mass of a phosphazene compound (FP-100) (manufactured by Fushimi Pharmaceutical Co., Ltd.) are mixed with 100 parts by mass of the polyimide precursor. As a result, a varnish of sample S3 was obtained.

[Etching time]
Evaluation of the alkali etching property of the uncured adhesive resin layer containing the alkali-soluble resin was performed by the following procedure.

  A rough surface side of electrolytic copper foil (F2-WS) (manufactured by Furukawa Electric Co., Ltd.) was laid on a coating table (manufactured by Tester Sangyo Co., Ltd.) capable of vacuum adsorption, and the electrolytic copper foil was attached by vacuum adsorption. Using an applicator (manufactured by Tester Sangyo Co., Ltd.) on the electrolytic copper foil, any of the varnishes of the samples S1 to S3 described above was applied. Then, it dried by heating with a dryer (SPH-201) (manufactured by Espec) to remove the solvent, and a copper foil with an uncured adhesive resin having a resin thickness of 40 μm was produced.

  The resin layer side of the obtained copper foil with an uncured adhesive resin is placed on the copper foil surface of a single-sided flexible copper-clad plate (Espanex (registered trademark) M) (manufactured by Nippon Steel Chemical Co., Ltd.), and a vacuum press (Kitakawa Seiki) Was used for pressure bonding at 100 ° C. and 1.0 MPa for 2 minutes. Furthermore, after laminating a dry film resist (Sunfort (registered trademark) AQ2578) (manufactured by Asahi Kasei E-Materials) to form a conformal mask pattern having a diameter of 3 mm, a hole is formed with a ferric chloride etching solution. The copper foil of the forming part was removed by etching to expose the uncured adhesive resin layer.

  Thereafter, a 3% by mass sodium hydroxide aqueous solution heated to 45 ° C. was spray-injected at a pressure of 0.18 MPa (injection amount 0.92 L / min) using a full cone type nozzle (ISJJX8010) (manufactured by Ikeuchi Co., Ltd.) The time required until the uncured adhesive resin layer was completely removed was defined as the etching time (seconds).

[Blind via shape evaluation]
About the blind via of the flexible wiring board produced by the Example and the comparative example, it implemented by the optical microscope observation of the shape of an opening part and a cross section. Immediately after alkali etching, 50 arbitrary blind vias are observed from the upper part of the inner layer core substrate with an optical microscope, and are formed on the copper foil of the inner layer side copper foil surface exposed at the bottom side of the blind via, that is, the bottom part. The area ratio of the formed conformal mask to the etching site was evaluated. Evaluation was made on 50 arbitrary blind vias, and the average value was taken as the measured value. An area ratio of 90% or more was evaluated as ◎, 75% or more and less than 90% as 〇, 50% or more and less than 75% as Δ, and less than 50% as ×.

  As for the cross-sectional shape, a flexible wiring board having a blind via is embedded in an epoxy resin, and a vertical position of the blind via diameter is perpendicular to the embedded flexible wiring board using a polishing apparatus (manufactured by Marumoto Stratos). After performing the cross-section polishing process, it was observed with an optical microscope. Moreover, evaluation was performed for 10 arbitrary blind vias, and the average value was used as a measured value. In the cross-sectional shape of the blind via, when the overhang amount of the cured resin layer from the end of the conformal mask is 15 μm or less, ◎, more than 15 μm to 25 μm or less, ◯, more than 25 μm to 30 μm or less, and over 30 μm Is x.

[Cooling cycle test]
In the multilayer flexible wiring board manufactured in Examples 7 to 11 and Comparative Example 4 described below, a wiring circuit in which an inner layer wiring circuit and an outer layer wiring circuit are daisy chain-connected by copper plating through a blind via having a diameter of 100 μm. Each of the constant temperature baths of 125 ° C. and −40 ° C. was alternately reciprocated every 15 minutes, and the connection resistance value at that time was measured. When the number of cycles in which the fluctuation range from the initial value of the connection resistance value at each temperature (hereinafter referred to as “resistance variation rate”) is within 10% is 1000 cycles or more, ◎, 500 cycles or more and less than 1000 cycles The case was marked with ○, and the case with less than 500 cycles was marked with ×.

[Example 1]
The varnish of sample S1 was applied on one side of a 12 μm thick electrolytic copper foil (F2-WS) (manufactured by Furukawa Electric) using a bar coater. Then, it dried for 15 minutes in the oven heated at 95 degreeC, the solvent was removed, and the copper foil with uncured adhesive resin used as an outer layer material was obtained. The resin layer side of the copper foil with non-thermosetting adhesive resin is placed on the copper foil of a single-sided flexible wiring board (Espanex (registered trademark) M) (manufactured by Nippon Steel Chemical Co., Ltd.) having a copper foil thickness of 12 μm. The laminate A was prepared by sandwiching with a release film.

  Next, a vacuum press apparatus (manufactured by Kitagawa Seiki Co., Ltd.) in which heat-resistant silicon rubber having a hardness of 50 degrees was bonded to both upper and lower surface plates was heated to a vacuum press temperature of 120 ° C. in advance. The laminated body A is put in this vacuum press apparatus, and after evacuation is performed in a state where no pressure is applied for 2 minutes, the pressure is applied at a pressure of 1 MPa for 2 minutes, and the copper foil with an uncured adhesive resin as the outer layer material and the inner layer core substrate The laminate B was obtained by crimping the single-sided flexible wiring board.

  Next, a dry film resist (Sanfort (registered trademark) AQ2578) (manufactured by Asahi Kasei E-Materials Co., Ltd.) is bonded onto the outer layer copper foil of the laminate B by a roll laminator, and then exposed and developed. A mask was formed. Using this resist mask, the copper foil at a predetermined position was removed by etching to form a conformal mask on the copper foil. Here, the conformal mask has a plurality of etching parts with a diameter of 100 μm at a pitch interval of 300 μm and a circular hole with a diameter of 3 mm for forming a blind via.

  Next, about the laminated body B which etched the copper foil, melt | dissolution removal (alkali etching) of the uncured adhesive resin layer using an alkaline solution was performed.

  The time required for etching until the uncured adhesive resin layer exposed in the 3 mm diameter circular hole of the conformal mask formed on the copper foil of the laminate B is completely removed is referred to as the “time required for etching” described above. ”And measured as described above. The time required for etching was 124 seconds.

  A 3 mass% sodium hydroxide aqueous solution heated to 45 ° C. was added to an uncured adhesive resin layer exposed inside an etching site having a diameter of 100 μm of a conformal mask formed on the copper foil of the laminate B. Using a full cone spray nozzle of 18 MPa (spray rate 0.92 L / min), spraying is performed for 20 seconds, and then 0.12 MPa (spray amount 0.75 L / min) of spray is washed with water for 120 seconds to be uncured. The adhesive resin layer was removed by etching to form a plurality of blind vias.

  Regarding the formed blind via, as described in the above “Blind via shape evaluation”, the area ratio of the opening on the bottom side of the blind via to the etching portion of the conformal mask was determined to be 75% or more and less than 90%. Met.

  Next, the uncured adhesive resin layer was cured by heating the layered product B on which the blind via was formed at 180 ° C. for 1 hour using a curing / drying furnace to form a cured resin layer. Furthermore, an electroless copper / electrolytic copper plating process was performed inside the blind via to obtain a flexible wiring board.

  With respect to the obtained blind via of the flexible wiring board, the cross-sectional shape was observed with an optical microscope as described in the above “Blind via shape evaluation”. As a result, the inner layer core substrate and the outer layer material were copper-plated and the overhang amount of the cured resin layer from the end of the conformal mask was 12 μm at the maximum.

  Thus, the blind via cross-sectional shape of the flexible substrate produced in Example 1 had a small overhang amount and good copper plating properties.

[Comparative Example 1]
A layered product B on which a conformal mask was formed was produced under the same method and conditions as in Example 1.

  Etching the uncured adhesive resin layer exposed from the etching site of the conformal mask with an aqueous sodium hydroxide solution using the same method and conditions as in Example 1 except that the spraying time was changed from 11 seconds to 20 seconds. To form a blind via.

  Regarding the formed blind via, as described in the above “Blind via shape evaluation”, the area ratio of the bottom side opening of the blind via to the etching portion of the conformal mask was found to be 10% or less. .

  Moreover, when the cross-sectional shape of the blind via was observed for the flexible wiring board obtained by performing the thermosetting treatment and the plating treatment under the same method and conditions as in Example 1, smear was observed at the bottom of the blind via. In other words, the inner layer core substrate and the outer layer material were not connected by copper plating.

[Example 2]
A laminate B in which a conformal mask and a circular hole with a diameter of 3 mm were formed on a copper foil was produced in the same manner as in Example 1 except that the vacuum press temperature was 140 ° C.

  The time required for etching until the uncured adhesive resin layer exposed in the 3 mm diameter circular hole of the conformal mask formed on the copper foil of the laminate B is completely removed is referred to as the “time required for etching” described above. ”And measured as described above. The time required for etching was 119 seconds.

  Except for changing the washing time from 120 seconds to 60 seconds, the uncured adhesive resin layer exposed from the etching site of the conformal mask of the laminate B was treated with an aqueous sodium hydroxide solution under the same method and conditions as in Example 1. It removed by the etching using.

  Regarding the formed blind via, as described in the above “Blind via shape evaluation”, the area ratio of the opening on the bottom side of the blind via to the etching portion of the conformal mask was determined to be 75% or more and less than 90%. Met.

  Moreover, when the cross-sectional shape of the blind via was observed for the flexible wiring board obtained by performing the thermosetting treatment and the plating treatment under the same method and conditions as in Example 1, the inner core substrate and the outer layer material were found to be Copper plating was connected, and side etching of the cured resin layer from the end of the conformal mask was a maximum of 15 μm.

  Thus, the cross-sectional shape of the blind via of the flexible substrate produced in Example 2 had a small overhang amount and good copper plating properties.

Example 3
A layered product B on which a conformal mask was formed was produced in the same manner as in Example 2.

  The time required for etching until the uncured adhesive resin layer exposed in the 3 mm diameter circular hole of the conformal mask formed on the copper foil of the laminate B is completely removed is referred to as the “time required for etching” described above. ”And measured as described above. The time required for etching was 119 seconds.

  Using a slit type spray nozzle of 0.20 MPa (injection amount 0.82 L / min), the spray nozzle was oscillated so that the distribution of the amount of liquid injected to the effective treatment surface was within 10% in the liquid amount ratio. And the conformal of layered product B under the same method and conditions as in Example 1 except that the washing pressure was changed to 0.18 Mpa (injection amount 0.82 L / min) and the washing time was changed to 60 seconds. The uncured adhesive resin layer exposed from the etching portion of the mask was removed by etching using an aqueous sodium hydroxide solution to form a blind via.

  Regarding the formed blind via, as described in the above “Blind Via Shape Evaluation”, the area ratio of the bottom side opening of the blind via to the etching site of the conformal mask was 90% or more. .

  Moreover, when the cross-sectional shape of the blind via was observed for the flexible wiring board obtained by performing the thermosetting treatment and the plating treatment under the same method and conditions as in Example 1, the inner core substrate and the outer layer material were found to be Copper plating was connected, and side etching of the resin layer from the end of the conformal mask was 13 μm at maximum.

  Thus, the cross-sectional shape of the blind via of the flexible substrate produced in Example 3 had a small overhang amount and good copper plating properties.

[Comparative Example 2]
A layered product B on which a conformal mask was formed was produced in the same manner as in Example 2.

  An uncured adhesive resin exposed from the etching site of the conformal mask of the laminate B under the same method and conditions as in Example 1 except that the water washing pressure was changed to 0.05 Mpa and the water washing time was changed to 60 seconds. The layer was removed by etching with aqueous sodium hydroxide to form a blind via.

  Regarding the formed blind via, as described in the above “Blind Via Shape Evaluation”, the area ratio of the opening on the bottom side of the blind via to the etched portion of the conformal mask was about 20%. .

  Moreover, when the cross-sectional shape of the blind via was observed for the flexible wiring board obtained by performing the thermosetting treatment and the plating treatment under the same method and conditions as in Example 1, smear was observed at the bottom of the blind via. Therefore, the copper plating between the inner layer core substrate and the outer layer material was not sufficiently connected. The side etching of the cured resin layer from the end of the conformal mask was 15 μm at the maximum.

Example 4
A layered product B on which a conformal mask was formed was produced by the same method and conditions as in Example 1 except that the vacuum press temperature was 160 ° C.

  The time required for etching until the uncured adhesive resin layer exposed in the 3 mm diameter circular hole of the conformal mask formed on the copper foil of the laminate B is completely removed is referred to as the “time required for etching” described above. ”And measured as described above. The time required for etching was 128 seconds.

  Using a slit type spray nozzle of 0.25 MPa (spray amount 0.82 L / min), the spray nozzle is oscillated so that the liquid amount distribution sprayed to the effective treatment surface is within 10% in the liquid amount ratio, The same method as in Example 1 except that the spraying time was changed to 25 seconds, the washing pressure was changed to 0.18 Mpa (injection amount 0.88 L / min), and the washing time was changed to 60 seconds. Under conditions, the uncured adhesive resin layer exposed from the etching site of the conformal mask of the laminate B was removed by etching using an aqueous sodium hydroxide solution to form a blind via.

  Regarding the formed blind via, as described in the above “Blind Via Shape Evaluation”, the area ratio of the bottom side opening of the blind via to the etching site of the conformal mask was 90% or more. .

  Moreover, when the cross-sectional shape of the blind via was observed for the flexible wiring board obtained by performing the thermosetting treatment and the plating treatment under the same method and conditions as in Example 1, the inner core substrate and the outer layer material were found to be Copper plating was connected, and side etching of the resin layer from the end of the conformal mask was 10 μm at maximum.

  Thus, the cross-sectional shape of the blind via of the flexible substrate produced in Example 4 had a small overhang amount and good copper plating properties.

Example 5
A laminate B on which a conformal mask was formed was produced in the same manner as in Example 1 except that the vacuum press temperature was 180 ° C.

  The time required for etching until the uncured adhesive resin layer exposed in the 3 mm diameter circular hole of the conformal mask formed on the copper foil of the laminate B is completely removed is referred to as the “time required for etching” described above. ”And measured as described above. The etching time was 134 seconds.

  Conformal of layered product B under the same method and conditions as in Example 1 except that the spraying time was changed to 70 seconds, the washing pressure was changed to 0.18 Mpa, and the washing time was changed to 120 seconds. The uncured adhesive resin layer exposed from the etching portion of the mask was removed by etching using an aqueous sodium hydroxide solution to form a blind via.

  Regarding the formed blind via, as described in the above “Blind via shape evaluation”, the area ratio of the opening on the bottom side of the blind via to the etching portion of the conformal mask was determined to be 75% or more and less than 90%. Met.

  Moreover, when the cross-sectional shape of the blind via was observed for the flexible wiring board obtained by performing the thermosetting treatment and the plating treatment under the same method and conditions as in Example 1, the inner core substrate and the outer layer material were found to be Copper plating was connected, and side etching of the resin layer from the end of the conformal mask was 30 μm at maximum.

  Thus, the cross-sectional shape of the blind via of the flexible substrate produced in Example 5 had a small overhang amount and good copper plating properties.

Example 6
A laminate B on which a conformal mask was formed was produced by the same method and conditions as in Example 1 except that the varnish of sample S2 was used and the vacuum press temperature was 160 ° C.

  The time required for etching until the uncured adhesive resin layer exposed in the 3 mm diameter circular hole of the conformal mask formed on the copper foil of the laminate B is completely removed is referred to as the “time required for etching” described above. ”And measured as described above. The time required for etching was 145 seconds.

  Using a slit type spray nozzle of 0.20 MPa (spray amount 0.82 L / min), the spray nozzle is oscillated so that the liquid amount distribution sprayed to the effective treatment surface is within 10% in the liquid amount ratio, The same method as in Example 1 except that the spray spraying time was changed to 36 seconds, the water washing pressure was changed to 0.18 Mpa (injection amount 0.82 L / min), and the water washing time was changed to 60 seconds. Under conditions, the uncured adhesive resin layer exposed from the etching site of the conformal mask of the laminate B was removed by etching using an aqueous sodium hydroxide solution to form a blind via.

  Regarding the formed blind via, as described in the above “Blind via shape evaluation”, the area ratio of the opening on the bottom side of the blind via to the etching portion of the conformal mask was determined to be 75% or more and less than 90%. Met.

  Moreover, when the cross-sectional shape of the blind via was observed for the flexible wiring board obtained by performing the thermosetting treatment and the plating treatment under the same method and conditions as in Example 1, the inner core substrate and the outer layer material were found to be Copper plating was connected, and the side etching of the resin layer from the end of the conformal mask was 7 μm at maximum.

  Thus, the blind via cross-sectional shape of the flexible substrate produced in Example 6 had a small overhang amount and good copper plating properties.

[Comparative Example 3]
A layered product B on which a conformal mask was formed was produced in the same manner as in Example 1 except that the varnish of Sample 3 was used.

  The time required for etching until the uncured adhesive resin layer exposed in the 3 mm diameter circular hole of the conformal mask formed on the copper foil of the laminate B is completely removed is referred to as the “time required for etching” described above. ”And measured as described above. The etching time was 22 seconds.

  The uncured adhesive resin layer exposed from the etching part of the conformal mask of the laminate B was subjected to the same method and conditions as in Example 1 except that the spraying time was changed from 11 seconds to 15 seconds. A blind via was formed by removing by etching using an aqueous solution.

  Regarding the formed blind via, as described in the above “Blind Via Shape Evaluation”, the area ratio of the bottom side opening of the blind via to the etching site of the conformal mask was 90% or more. .

  Moreover, when the cross-sectional shape of the blind via was observed for the flexible wiring board obtained by performing the thermosetting process and the plating process under the same method and conditions as in Example 1, the resin from the end of the conformal mask The layer overhang was a minimum of 45 μm, and the copper plating property to the side wall of the blind via was poor.

Example 7
The inner layer core substrate was produced as follows. First, Espanex M (manufactured by Nippon Steel Chemical Co., Ltd., copper foil thickness 12 μm, insulating resin layer thickness 20 μm) was prepared as a double-sided flexible wiring board. A blind via having a diameter of 100 μm was formed on this double-sided flexible wiring board by drilling and copper plating. In addition, after laminating the outer layer material with a copper land portion having a diameter of 300 μm at a predetermined position where the outer layer material blind via is formed, the inner layer and the outer layer are formed with an electroless copper / electrolytic copper plating layer via the blind via. A copper wiring circuit (28 μm thick) having a width of 100 μm and alternately connecting lands was formed so that a circuit connected by a daisy chain could be formed.

  Next, the varnish of sample S1 was applied onto a 12 μm thick electrolytic copper foil (F2-WS, manufactured by Furukawa Electric) using a bar coater, and then dried in an oven heated to 95 ° C. for 15 minutes. Then, an uncured adhesive resin layer having a thickness of 40 μm was formed to obtain a copper foil with an uncured adhesive resin as an outer layer material.

  This uncured adhesive resin-coated copper foil was placed on the upper and lower surfaces of the inner layer core substrate, and a laminate C was prepared by sandwiching it with release films from both sides.

  A diaphragm type vacuum laminator (manufactured by Meiki Seisakusho) that can be laminated by the roll-to-roll method was used as the laminating apparatus. As a lamination method, the silicon rubber surface temperature of the diaphragm was set to 120 ° C., and after the laminate C was conveyed into the vacuum laminator, vacuuming was performed for 2 minutes without laminating pressure, and then 2 MPa at a pressure of 0.9 MPa. The outer layer material and the inner layer core substrate were pressure-bonded by pressurizing for a minute.

  Next, after laminating a dry film resist (Sunfort (registered trademark) AQ2578) (manufactured by Asahi Kasei E-Materials Co., Ltd.) on the copper foil of the outer layer with a roll laminator, exposure, development, and etching The copper foil was removed by etching, and a conformal mask was formed so as to be positioned above the copper land portion formed on the inner layer core substrate. The conformal mask has a plurality of etching portions with a diameter of 100 μm at a pitch of 300 μm and has circular holes with a diameter of 3 mm. Thereby, the laminated body D which has a conformal mask was obtained.

  The time required for etching until the uncured adhesive resin layer exposed in the 3 mm diameter circular hole of the conformal mask formed on the copper foil of the laminate D is completely removed is referred to as the “time required for etching” described above. ”And measured as described above. The time required for etching was 121 seconds.

  Further, the uncured adhesive resin layer exposed from the etching portion of the conformal mask having a diameter of 100 μm of the laminate D was etched away as follows to form a plurality of blind vias. For the etching, a developing device YCE-85 III manufactured by Yamagata Kikai was used. In the developing device, slit type spray nozzles are arranged above and below the layered product D, and are shaken 40 times per minute so that the distribution of the amount of liquid sprayed to the effective processing surface is within 10% in terms of the liquid amount ratio. Oscillation of motion.

  A 3% by weight sodium hydroxide aqueous solution heated to 45 ° C., 25 seconds at a pressure of 0.25 MPa (injection amount 0.92 L / min) on the upper side and 0.25 MPa (injection amount 0.92 L / min) on the lower side The spray fountain treatment was carried out, followed by a water washing treatment with a spray of 0.18 MPa (spray amount 0.88 L / min) for 60 seconds.

  Regarding the formed blind via, as described in the above “Blind Via Shape Evaluation”, the area ratio of the bottom side opening of the blind via to the etching site of the conformal mask was 90% or more. .

  Next, the uncured adhesive resin layer was cured by heating at 180 ° C. for 1 hour using a curing and drying furnace to form a cured resin layer. After that, when the cross-sectional shape of the blind via was observed, no smear was observed on the wall surface or bottom of the blind via, the formation of the blind via was good, and the desmear process using an aqueous potassium permanganate solution or the like was unnecessary. .

  Next, in order to establish an electrical connection with the inner layer core substrate, a plating process was performed on the blind via. First, a palladium catalyst was attached to the resin cured material layer on the inner wall of the blind via and activated, and then an electroless copper plating layer was formed while aeration was performed in an electroless copper plating bath. Thereafter, electrolytic copper plating was performed to complete the electrical connection between the conductive layer of the inner core and the outer conductive layer.

  Next, a circuit forming process was performed on the outer layer material in the same manner as in the conventional multilayer flexible wiring board. Further, a copper land portion having a diameter of 300 μm was formed around the blind via. In addition, a wiring circuit was formed in which lands that are not connected on the inner layer material side were connected by a wiring circuit having a width of 100 μm and the inner layer and the outer layer were connected in a daisy chain. The subsequent steps were performed in the same manner as the conventional method for manufacturing a flexible wiring board. Thereby, a multilayer flexible wiring board was obtained.

  With respect to the obtained blind via of the multilayer flexible wiring board, the cross-sectional shape was observed with an optical microscope as described in the above “Blind via shape evaluation”. As a result, the inner layer core substrate and the outer layer material were copper-plated and the side etching of the resin layer from the end of the conformal mask was 15 μm at the top and bottom. In addition, no smear was observed at the bottom of the blind via without desmear treatment.

  Further, the above-mentioned “cooling cycle test” was performed on the obtained multilayer flexible wiring board. As a result, the resistance fluctuation rate was 10% or less up to 1000 cycles, and the evaluation of the reliability of the interlayer connection was good.

  Thus, the multilayer flexible wiring board produced in Example 7 was excellent in the blind via formation property and the reliability of interlayer connection.

Example 8
A laminate D having a conformal mask was produced under the same method and conditions as in Example 7.

  The time required for etching until the uncured adhesive resin layer exposed in the 3 mm diameter circular hole of the conformal mask formed on the copper foil of the laminate D is completely removed is referred to as the “time required for etching” described above. ”And measured as described above. The time required for etching was 121 seconds.

  The laminated body D was etched under the same conditions as in Example 7 except that the spraying time was changed from 25 seconds to 40 seconds to form blind vias.

  Regarding the formed blind via, as described in the above “Blind Via Shape Evaluation”, the area ratio of the bottom side opening of the blind via to the etching site of the conformal mask was 90% or more. .

  Subsequent steps were performed under the same conditions as in Example 7 to obtain a multilayer flexible wiring board.

  With respect to the obtained blind via of the multilayer flexible wiring board, the cross-sectional shape was observed with an optical microscope as described in the above “Blind via shape evaluation”. As a result, the inner layer core substrate and the outer layer material were copper-plated and the side etching of the resin layer from the end of the conformal mask was 25 μm at the top and bottom.

  Further, the above-mentioned “cooling cycle test” was performed on the obtained multilayer flexible wiring board. As a result, the resistance fluctuation rate was 10% or less until 880 cycles, and the reliability of the interlayer connection was evaluated well.

  Thus, the multilayer flexible wiring board produced in Example 8 was excellent in blind via formation property and interlayer connection reliability.

Example 9
A laminate D having a conformal mask was produced under the same method and conditions as in Example 7.

  The time required for etching until the uncured adhesive resin layer exposed in the 3 mm diameter circular hole of the conformal mask formed on the copper foil of the laminate D is completely removed is referred to as the “time required for etching” described above. ”And measured as described above. The time required for etching was 121 seconds.

  The laminated body D was etched under the same conditions as in Example 7 except that an alkali peeling device without an oscillation function was used and the spray spraying time was changed from 25 seconds to 40 seconds to form blind vias. . At this time, the distribution of the amount of liquid injected to the effective treatment surface was 50% or more in terms of the liquid amount ratio.

  As for the formed blind via, as described in the above “Blind via shape evaluation”, the area ratio of the bottom side opening of the blind via to the etching portion of the conformal mask was 70% or more. .

  Subsequent steps were performed under the same conditions as in Example 7 to obtain a multilayer flexible wiring board.

  With respect to the obtained blind via of the multilayer flexible wiring board, the cross-sectional shape was observed with an optical microscope as described in the above “Blind via shape evaluation”. As a result, the inner layer core substrate and the outer layer material were copper-plated and the side etching of the resin layer from the end of the conformal mask was 25 μm at the top and bottom.

  Further, the above-mentioned “cooling cycle test” was performed on the obtained multilayer flexible wiring board. As a result, the resistance fluctuation rate was 10% or less up to 600 cycles, and the evaluation of the reliability of the interlayer connection was good.

  As described above, the multilayer flexible wiring board produced in Example 9 was excellent in blind via formation and interlayer connection reliability.

Example 10
A laminate D having a conformal mask was produced under the same method and conditions as in Example 7.

  The time required for etching until the uncured adhesive resin layer exposed in the 3 mm diameter circular hole of the conformal mask formed on the copper foil of the laminate D is completely removed is referred to as the “time required for etching” described above. ”And measured as described above. The time required for etching was 121 seconds.

  The laminated body D was etched under the same conditions as in Example 7 except that the water washing pressure was changed to 0.30 MPa to form blind vias.

  Regarding the formed blind via, as described in the above “Blind Via Shape Evaluation”, the area ratio of the bottom side opening of the blind via to the etching site of the conformal mask was 90% or more. .

  Subsequent steps were performed under the same conditions as in Example 7 to obtain a multilayer flexible wiring board.

  With respect to the obtained blind via of the multilayer flexible wiring board, the cross-sectional shape was observed with an optical microscope as described in the above “Blind via shape evaluation”. As a result, the inner layer core substrate and the outer layer material were connected by copper plating, and the side etching of the resin layer from the end of the conformal mask was 20 μm at the top and bottom.

  Further, the above-mentioned “cooling cycle test” was performed on the obtained multilayer flexible wiring board. As a result, the resistance fluctuation rate was 10% or less up to 1000 cycles, and the evaluation of the reliability of the interlayer connection was good.

  Thus, the multilayer flexible wiring board produced in Example 10 was excellent in blind via formation property and interlayer connection reliability.

[Comparative Example 4]
A laminate D having a conformal mask was produced under the same method and conditions as in Example 7.

  The time required for etching until the uncured adhesive resin layer exposed in the 3 mm diameter circular hole of the conformal mask formed on the copper foil of the laminate D is completely removed is referred to as the “time required for etching” described above. ”And measured as described above. The time required for etching was 121 seconds.

  The laminated body D is etched under the same conditions as in Example 7 except that the water washing treatment is performed at 1.2 MPa for 60 seconds using a high-pressure washing apparatus with an increased ability of the liquid feed pump to form a blind via. did.

  Regarding the formed blind via, as described in the above “Blind Via Shape Evaluation”, the area ratio of the bottom side opening of the blind via to the etching site of the conformal mask was 90% or more. .

  Subsequent steps were performed under the same conditions as in Example 7 to obtain a multilayer flexible wiring board.

  With respect to the obtained blind via of the multilayer flexible wiring board, the cross-sectional shape was observed with an optical microscope as described in the above “Blind via shape evaluation”. As a result, the side etching of the resin layer from the end of the conformal mask is 35 μm at the top and bottom, the resin at the bottom of the blind via is peeled off from the inner core substrate, and the copper plating is partially disconnected. Was confirmed.

Example 11
A layered product C was produced under the same method and conditions as in Example 7. A dry film resist (Sunfort (registered trademark) AQ2578) (manufactured by Asahi Kasei E-Materials Co., Ltd.) was bonded onto the copper foil of the outer layer of the laminate C using a roll laminator. Thereafter, the copper foil at a predetermined position is removed by exposure / development and etching, and a plurality of etching portions having a diameter of 100 μm are provided so as to be located above the copper land portion formed on the inner layer core substrate, and the diameter is 3 mm. A conformal mask having a circular hole was formed. At the same time, the copper foil was removed in the same process for the part to be the flexible part. Thereby, the laminated body E which has an etching site | part corresponding to a conformal mask and a flexible part was obtained.

  The time required for etching until the uncured adhesive resin layer exposed inside the circular hole having a diameter of 3 mm of the conformal mask formed on the copper foil of the laminate E is completely removed. ”And measured as described above. The time required for etching was 121 seconds.

  In addition, the uncured adhesive resin layer exposed from the etching part of the conformal mask having a diameter of 100 μm and the etching part corresponding to the flexible part of the laminate E is etched and removed as follows. Blind vias and flexible parts were formed. For the etching, a developing device YCE-85 III manufactured by Yamagata Kikai was used. In the developing device, slit type spray nozzles are arranged above and below the laminate E, and swung 40 times per minute so that the distribution of the amount of liquid sprayed to the effective processing surface is within 10% in terms of the liquid volume ratio. Oscillation was performed.

  A 3% by mass sodium hydroxide aqueous solution heated to 45 ° C., with an upper pressure of 0.2 MPa (injection amount 0.88 L / min) and a lower side of 0.25 MPa (injection amount 0.92 L / min) for 25 seconds. The spray fountain treatment was carried out, followed by a water washing treatment with a spray of 0.18 MPa (spray amount 0.88 L / min) for 60 seconds.

  Regarding the formed blind via, as described in the above “Blind Via Shape Evaluation”, the area ratio of the bottom side opening of the blind via to the etching site of the conformal mask was 90% or more. .

  Next, the uncured adhesive resin layer was cured by heating at 180 ° C. for 1 hour using a curing and drying furnace to form a cured resin layer. After that, when the cross-sectional shape of the blind via was observed, no smear was observed on the wall surface or bottom of the blind via, the formation of the blind via was good, and the desmear process using an aqueous potassium permanganate solution or the like was unnecessary. .

  Next, in order to establish an electrical connection with the inner layer core substrate, a plating process was performed on the blind via. First, a palladium catalyst was attached to the resin cured material layer on the inner wall of the blind via and activated, and then an electroless copper plating layer was formed while aeration was performed in an electroless copper plating bath. Thereafter, electrolytic copper plating was performed to complete the electrical connection between the conductive layer of the inner core and the outer conductive layer.

  Next, a circuit forming process was performed on the outer layer material in the same manner as in the conventional multilayer flexible wiring board. Further, a copper land portion having a diameter of 300 μm was formed around the blind via. In addition, a wiring circuit was formed in which lands that are not connected on the inner layer material side were connected by a wiring circuit having a width of 100 μm and the inner layer and the outer layer were connected in a daisy chain. The subsequent steps were performed in the same manner as the conventional method for manufacturing a flexible wiring board. Thereby, a multilayer flexible wiring board was obtained.

  With respect to the obtained blind via of the multilayer flexible wiring board, the cross-sectional shape was observed with an optical microscope as described in the above “Blind via shape evaluation”. As a result, the inner layer core substrate and the outer layer material were copper-plated and the side etching of the resin layer from the end of the conformal mask was 17 μm at the top and bottom. In addition, no smear was observed at the bottom of the blind via without desmear treatment.

  Further, the above-mentioned “cooling cycle test” was performed on the obtained multilayer flexible wiring board. As a result, the resistance fluctuation rate was 10% or less up to 1000 cycles, and the evaluation of the reliability of the interlayer connection was good.

  Thus, the multilayer flexible wiring board produced in Example 11 was excellent in blind via formation property and interlayer connection reliability.

  In Tables 1 and 2, the varnish, the vacuum press temperature, the time required for etching (referred to as “etching” in Tables 1 and 2), and the spray injection time (Table 1) in Examples 1 to 11 and Comparative Examples 1 to 4 And in Table 2, “injection”), ratio of injection time to required etching time (indicated in “Injection / etching” in Tables 1 and 2), nozzle type, presence / absence of oscillation, liquid volume distribution The results of the water washing pressure and treatment time, the blind via opening and cross-sectional shape evaluation, and the thermal cycle test are shown.

  In addition, this invention is not limited to the said embodiment, It can change and implement variously. In the above-described embodiment, the size, shape, and the like illustrated in the accompanying drawings are not limited to this, and can be appropriately changed within a range in which the effects of the present invention are exhibited.

  The present invention can be applied to the manufacture of a flexible wiring board, for example, can be suitably applied to the manufacture of a flexible wiring board for various electronic components that are required to be mounted at a high density. .

10 Double-sided flexible wiring board (core substrate)
11, 13, 23a, 23b Laminated body 12a, 12b, 22a, 22b Copper foil 14, 21a, 21b Uncured adhesive resin layer 15 Via hole 16, 25a, 25b Insulating resin layer 20, 30 Multilayer flexible wiring board 24 Blind via 26a 26b External substrate 31 Flexible part

Claims (12)

A step of providing an alkali-soluble uncured adhesive resin layer on the surface of the first conductive layer, a step of providing a second conductive layer on the surface of the uncured adhesive resin layer, and the second conductivity Forming a conformal mask by removing a part of the layer; and removing the uncured adhesive resin layer exposed in the opening of the conformal mask by etching using an alkaline solution. Forming a via hole reaching the conductive layer,
The etching is performed by spraying the alkaline solution from the second conductive layer side with a treatment time corresponding to 0.1 to 0.6 times the time required to remove the uncured adhesive resin layer, Then, the method of manufacturing a flexible wiring board is performed by washing with water from the second conductive layer side at a water pressure of 0.10 MPa to 1.0 MPa by spraying.   2. The method for manufacturing a flexible wiring board according to claim 1, wherein the first conductive layer is a conductive layer provided on a surface of a core substrate provided with at least one conductive layer.   A step of curing the uncured adhesive resin layer by heating to obtain an insulating resin layer; and plating the surface of the second conductive layer including the inside of the via hole to thereby form the first conductive layer and the first conductive layer. The method for manufacturing a flexible wiring board according to claim 2, further comprising a step of electrically connecting the two conductive layers.   At the same time as forming the conformal mask on the second conductive layer, a predetermined portion of the second conductive layer is removed, and at the same time as forming the via hole by the etching, The method for producing a flexible wiring board according to claim 2 or 3, wherein the exposed uncured adhesive resin layer is removed simultaneously.   The method for producing a flexible wiring board according to any one of claims 1 to 4, wherein in the spraying of the alkaline solution, the liquid pressure is 0.15 MPa or more and 0.3 MPa or less.   The method for producing a flexible wiring board according to any one of claims 1 to 5, wherein the washing with water is performed for 60 seconds to 120 seconds.   7. The spraying of the alkali solution according to any one of claims 1 to 6, wherein the flow rate distribution in the effective processing surface is within ± 20% of a variation in liquid volume ratio compared to the center of the effective processing surface. The manufacturing method of the flexible wiring board of crab.   The said uncured adhesive resin layer contains alkali-soluble resin which has a carboxyl group or a phenolic hydroxyl group in a molecular chain, The manufacturing of the flexible wiring board in any one of Claims 1-7 characterized by the above-mentioned. Method.   The method for producing a flexible wiring board according to claim 8, wherein the alkali-soluble resin has at least a phenolic hydroxyl group and a polyimide structure. The uncured adhesive resin layer contains (a) a polyimide containing a structure represented by the following general formulas (1) and (2), and (b) an oxazoline compound having two or more oxazoline groups. The manufacturing method of the flexible wiring board in any one of Claim 1 to 7 characterized by the above-mentioned.

(In the general formula (1), X represents a single bond, —O—, —SO ₂ —, —C (═O) — or a silicone-containing group.)

(In General Formula (2), Z represents a single bond or —C (—CF ₃ ) ₂ —, and 1 represents an integer of 1 to 4.)   The said uncured adhesive resin layer contains a flame retardant, The manufacturing method of the flexible wiring board in any one of Claims 1-10 characterized by the above-mentioned.   The method for producing a flexible wiring board according to any one of claims 1 to 11, wherein the uncured adhesive resin layer contains an adhesion material.

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