JP2007129208A - Substrate for flexible printed wiring board and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate for a flexible printed wiring board capable of both reducing water-absorbing properties of a resin layer and achieving electrical property of the resin layer with a high level by using a resin material replaced by polyimide, and to provide a method of manufacturing the same. <P>SOLUTION: The substrate for the flexible printed wiring board is provided with the resin layer containing a liquid crystal polyester layer on an extremely thin copper foil with a thickness of ≤5 μm. The substrate is manufactured by removing a support after applying solution containing the liquid crystal polyester and solvent on the extremely thin copper foil of ≤5 μm fixed on the support and by removing the solvent. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a flexible printed wiring board substrate and a method for manufacturing the same.

  A copper-clad laminate produced by forming a resin layer on a copper foil is known as a flexible printed wiring board substrate. Such a copper clad laminate is used as a flexible printed wiring board (hereinafter sometimes referred to as “FPC”) by processing a copper foil by etching or the like to form a wiring pattern.

  In recent years, a copper-clad laminate including an ultrathin copper foil having a thickness of 1 to 5 μm has attracted attention among copper-clad laminates. Copper-clad laminates with ultra-thin copper foil are expected for use in FPCs built into mobile phones, notebook computers, mobile TVs, and the like that require further downsizing.

On the other hand, as an insulating resin used for a copper clad laminate having an ultrathin copper foil, polyimide having both excellent wear resistance and heat resistance is widely used. The laminated board which consists of an ultra-thin copper foil and a polyimide layer is normally manufactured by the following methods. That is, polyimide is thermocompression-bonded to an ultrathin copper foil (hereinafter referred to as “ultrathin copper foil with carrier”) held on an supporting copper foil (carrier) having a thickness of about 35 μm via an adhesive layer. This method is a method in which a solution containing a polyamic acid that is a polyimide precursor is applied to an ultrathin copper foil with a carrier, followed by heat treatment to simultaneously perform drying and imidization (see, for example, Patent Documents 1 and 2). .
Japanese Patent Laid-Open No. 2003-340963 JP 2004-42579 A

  However, in Patent Documents 1 and 2, since the resin laminated on the copper foil is polyimide, the following problems are sufficiently solved when the flexible printed wiring board substrate is laminated on the copper foil. I couldn't.

  That is, as described above, polyimide has both excellent wear resistance and heat resistance, but when polyimide is used for the resin layer, it can be processed with sufficient accuracy when forming a fine wiring pattern. In particular, the demand for fine pitches such as a multi-pin and narrow pitch could not be satisfied. This is because polyimide generally has high water absorption and the following problems may occur in various processes for producing FPC.

  For example, in a step of obtaining a laminate by a method of thermocompression bonding a polyimide film on a copper foil or a method of applying a heat treatment by applying a polyimide precursor (polyamic acid or the like) solution on a copper foil, drying the polyimide film or the polyimide precursor solution If this is insufficient, there arises a problem that bubbles are generated or wrinkles are formed between the copper foil and the polyimide layer. In addition, in the heat treatment process for coating the protective film on the circuit formed by processing the copper foil, when moisture absorbed by the polyimide is vaporized, a void (void) is formed between the protective film and the adjacent layer. ) Occurs. Furthermore, in the process of forming a circuit on the copper foil, there is a problem that when the polyimide is immersed in an etching solution (for example, ferric chloride aqueous solution) used for etching the copper foil, the polyimide absorbs water and swells. In addition, the flexible printed wiring board made of polyimide is swelled by absorbing moisture in the environment, and the processed circuit pattern is likely to fluctuate over time, resulting in poor storage stability of the circuit pattern. It was.

  Furthermore, polyimide has insufficient electrical characteristics in the high frequency band of several hundreds of MHz to several tens of GHz. Especially, since the value of the dielectric loss tangent is relatively large, the electric signal flowing through the wiring is lost as heat and attenuates. was there. Furthermore, as described above, polyimide absorbs moisture over time, and thus has a drawback that its electrical characteristics are also unstable.

  Then, an object of this invention is to provide the board | substrate for flexible printed wiring boards which can achieve both the reduction of the water absorption of a resin layer, and the electrical property of a resin layer at a high level, and its manufacturing method.

  The board | substrate for flexible printed wiring boards by this invention is equipped with the resin layer containing liquid crystalline polyester on the ultra-thin copper foil of thickness 5 micrometers or less.

  Polyimide has been widely used so far as the resin constituting the resin layer provided in the flexible printed wiring board substrate. However, as described above, polyimide has problems in terms of water absorption and electrical characteristics. For this reason, the present inventors diligently studied about a resin material that can replace polyimide. As a result, it has been found that the use of liquid crystalline polyester as the resin constituting the resin layer can solve problems relating to the water absorption and electrical characteristics of the resin layer.

  Based on this knowledge, the resin layer which consists of liquid crystalline polyester was laminated | stacked on ultra-thin copper foil, and the board | substrate for flexible printed wiring boards was manufactured. Specifically, after applying the solution in which the liquid crystal polyester is dissolved on the ultrathin copper foil with a carrier, a primary heating process for removing the solvent in the coating liquid and a secondary heating process for aligning the liquid crystal polyester are performed. A flexible printed wiring board substrate was manufactured. As a result, the present inventors have found that a flexible printed wiring board substrate can be produced without causing wrinkles or the like in the ultrathin copper foil.

  Since liquid crystal polyester has lower water absorption than polyimide, it can prevent the formation of voids in the resin layer in the process of laminating the resin layer on the copper foil and form a fine wiring pattern. However, since it can be processed with sufficient accuracy and is less hygroscopic than polyimide, the circuit pattern does not vary with time, and a flexible printed wiring board having excellent storage stability can be obtained. In addition, liquid crystal polyester has a smaller dielectric loss tangent value in a high frequency band from several hundred MHz to several tens GHz compared to polyimide. That is, according to the substrate for a flexible printed wiring board of the present invention, both the water absorption reduction of the resin layer and the electrical characteristics of the resin layer can be achieved at a high level.

  Moreover, the flexible printed wiring board substrate of the present invention includes an ultrathin copper foil having a thickness of 5 μm or less, and the copper foil is easy to process, so that the flexible printed wiring board on which a fine wiring pattern is formed is provided. Easy to manufacture.

  The substrate for a flexible printed wiring board of the present invention is preferably a substrate having a 180 ° peel strength of 7 N / cm or more from a resin layer of an ultrathin copper foil at 23 ° C. When manufacturing the flexible printed wiring board substrate of the present invention as described later, from the viewpoint of improving the operability, the ultrathin copper foil is fixed to a support (carrier) on the ultrathin copper foil. It is preferable to form a resin layer on the substrate and then peel the support. When the 180 ° peel strength is 7 N / cm or more, the adhesion between the ultrathin copper foil and the layer adjacent thereto is sufficiently secured, so that there is a defect such as peeling between the copper foil and the resin layer due to the support peeling. It is preferable because it is difficult to occur.

The resin layer of such a flexible printed wiring board substrate can be formed by applying a solution containing liquid crystal polyester and a solvent on an ultrathin copper foil and removing the solvent.
When the resin layer is formed in this manner, the adhesion between the adjacent layer such as an ultrathin copper foil and the resin layer can be sufficiently improved.

  The resin layer may contain an inorganic filler as long as the electrical properties such as the relative dielectric constant and the hygroscopicity are not deteriorated. When the resin layer contains an inorganic filler, mechanical properties such as elastic modulus and dimensional accuracy of the resin layer can be further enhanced.

  The above-mentioned flexible printed wiring board substrate typically has a bending radius of curvature of 0.38 mm and a tension of 4.9 N in a folding resistance test defined by 100 or more (JIS C6471 (1995)). Refers to folding resistance measured under conditions.). Along with the high density mounting of electronic components in the housing of an electronic device, the number of bent portions of the flexible printed wiring board increases, and the angle formed between the two surfaces forming the bent portions has decreased. For this reason, if the ultrathin copper foil breaks in less than 100 repetitions in the bending resistance test of the flexible printed wiring board substrate, the wiring is likely to break due to the ductile fatigue of the ultrathin copper foil, and the electrical reliability Tends to decrease.

式（１）中、Ａｒ^０はフェニレン又はナフチレン；ＺはＯ，Ｓ，ＣＯ、ＳＯ_２、炭素数１〜４のアルキレン基、Ｏ（ＣＨ_２）_ｍＯ［ｍは１〜４の整数を表す。］又は単結合；ｎは０以上３以下の整数をそれぞれ表し、Ａｒ^０が複数ある場合、それらは互いに同一でも異なっていてもよい。 As the liquid crystal polyester, a liquid crystal polyester in which structural units of —Ar ¹ —, —Ar ² —, and —Ar ³ — are linked by —COO— (or —OCO—), —CONH— (or —NHCO—) is used. Can be used. In particular, the structural unit represented by the following formulas (i), (ii), and (iii) is included, and the structural unit represented by the formula (i) is 30 to 80 mol% with respect to the total structural units, and the formula (ii) ) Is preferably 10 to 35 mol% and the structural unit represented by formula (iii) is 10 to 35 mol%.
(I) —O—Ar ¹ —CO—
(Ii) —CO—Ar ² —CO—
(Iii) ^-X-Ar 3 -Y-
Here, in the above formula, Ar ¹ is phenylene, naphthylene, or biphenylene; Ar ² and Ar ³ are each independently a divalent group represented by the following formula (1); and X and Y are the same or different Each represents O or NH; In Ar ¹ , Ar ² and Ar ³ , the hydrogen atom bonded to the aromatic ring may be substituted with a halogen atom, an alkyl group or an aryl group.

In formula (1), Ar ⁰ is phenylene or naphthylene; Z is O, S, CO, SO ₂ , an alkylene group having 1 to 4 carbon atoms, O (CH ₂ ) _m O [m represents an integer of 1 to 4; . Or a single bond; n represents an integer of 0 or more and 3 or less, and when there are a plurality of Ar ^{0 s} , they may be the same or different.

  The liquid crystalline polyester contains 10 to 35 mol% of a structural unit derived from an aromatic diamine and / or a structural unit derived from an aromatic amine having a hydroxyl group, that is, a structure represented by the above formula (iii). What contains 10-35 mol% of structural units whose unit X and / or Y is NH with respect to all the structural units is preferable.

  Since the liquid crystalline polyester has good solubility in a solvent, a solution of the liquid crystalline polyester can be easily prepared by dissolving the liquid crystalline polyester in the solvent. A resin layer containing liquid crystal polyester can be easily formed by removing the solvent after applying the solution to a predetermined location.

  In addition, the resin layer containing the above-mentioned liquid crystalline polyester can achieve both a reduction in water absorption and electrical properties at a high level, and has practically sufficient adhesion to an adjacent layer such as an ultrathin copper foil. Can be obtained.

  The flexible printed wiring board substrate described above is applied, for example, by applying a solution containing liquid crystal polyester and a solvent onto an ultrathin copper foil having a thickness of 5 μm or less fixed on a support, removing the solvent, and then supporting the substrate. It can be manufactured by a manufacturing method for removing the body.

  Since the said solution contains liquid crystalline polyester as a solute, a resin layer can be easily formed by apply | coating and drying the said solution on the surface of the layer which should form a resin layer.

  On the other hand, since the ultra-thin copper foil is fixed to a support (carrier), the handling of the ultra-thin copper foil becomes easy in a process of forming a resin layer on the ultra-thin copper foil. And the board | substrate for flexible printed wiring boards can be obtained by removing a support body after formation of a resin layer.

  In the above production method, the support is preferably a metal. When the support is a metal, it is easy to select a material close to the thermal expansion coefficient of the ultrathin copper foil as the support, compared to a case where the support is made of a material other than metal.

The ultrathin copper foil is fixed to the support via a heat diffusion preventing layer (which means a layer that prevents ions in the ultrathin copper foil from diffusing into the adjacent layer by heating). preferable. If there is a thermal diffusion prevention layer between the ultrathin copper foil and the support, copper ions (Cu ²⁺ ) that can be generated when heated in the process of forming a resin layer on the ultrathin copper foil, etc. Transition is sufficiently suppressed. Therefore, excessive adhesion between the ultrathin copper foil and the support due to the migration of copper ions can be prevented, and the ultrathin copper foil can be easily separated from the support to obtain a flexible printed wiring board substrate.

  ADVANTAGE OF THE INVENTION According to this invention, the board | substrate for flexible printed wiring boards which can achieve both the reduction | decrease in the water absorption of a resin layer and the electrical property of a resin layer at a high level using the resin material which replaces a polyimide is provided, and its manufacturing method. The The flexible printed wiring board is not only excellent in flexibility, but also easily forms a flexible printed wiring board because the resin layer is not deteriorated by the etching liquid when the wiring pattern is formed on the copper foil using the etching liquid. Can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail. FIG. 1 is a schematic partial sectional view showing an embodiment of a flexible printed wiring board substrate of the present invention. A substrate (flexible printed wiring board substrate) 10 shown in FIG. 1 has a liquid crystal polyester layer (resin layer) 2 containing a liquid crystal polyester formed on one surface of an ultrathin copper foil 1 having a thickness of 5 μm or less.

<Ultra thin copper foil>
First, the ultrathin copper foil 1 will be described. FIG. 2 is a schematic partial cross-sectional view showing the state of the ultrathin copper foil 1 in a state of being fixed to the carrier layer (support) 12. In the ultrathin copper foil 50 with a carrier shown in FIG. 2, the ultrathin copper foil 1 is fixed to the carrier layer 12 via an adhesive layer (heat diffusion prevention layer) 14.

  The thickness of the ultrathin copper foil 1 is 5 μm or less, but the lower limit of the thickness of the ultrathin copper foil 1 is preferably 1 μm from a practical point of view. A copper foil having a thickness of 6 μm or more may be used in a state where it is not fixed to the carrier layer. However, the ultrathin copper foil 1 having a thickness of 5 μm or less is easily wrinkled and difficult to handle by itself. Therefore, it is generally used in a state of being fixed to the carrier layer 12. In addition, you may use the ultra-thin copper foil by which surface treatment was given as the ultra-thin copper foil 1. FIG. Examples of the surface treatment include roughening treatment, thermal discoloration prevention treatment, and rust prevention treatment. The surface roughness of the ultrathin copper foil 1 is preferably 0.5 to 2.0 μm from the viewpoint of securing the anchoring property of the liquid crystal polyester layer 2.

  As the carrier layer 12, a material made of a material capable of holding the ultrathin copper foil 1 can be used, but the material of the carrier layer 12 is preferably a metal. This is because, when the carrier layer 12 is a metal, a material close to the thermal expansion coefficient of the ultrathin copper foil 1 can be used as compared with a case where the carrier layer 12 is made of a material other than metal. From the viewpoint of the thermal expansion coefficient, it is more preferable that the carrier layer 12 be made of copper like the ultrathin copper foil 1. When using copper foil as the carrier layer 12, it is preferable that the thickness of the said copper foil is 12-70 micrometers from a practical viewpoint. As the copper foil having a thickness in this range, a rolled copper foil or an electrolytic copper foil can be used.

  As the adhesive layer 14, a layer made of an organic adhesive or an inorganic adhesive can be used. The adhesive layer 14 is preferably made of an inorganic adhesive from the viewpoint of maintaining adhesiveness when heated and suppressing gas generation. As the inorganic adhesive, for example, an adhesive having silica or mica as a main component and water as a dispersion medium can be used.

The adhesive layer 14 includes an ultrathin copper foil 1 and a carrier layer 1 formed by the transfer of copper ions (Cu ²⁺ ).
2 plays a role as a heat diffusion preventing layer of copper ions for preventing adhesion to the substrate 2. In the process of manufacturing the substrate for a flexible printed wiring board, when the ultrathin copper foil 1 is heated in a state of being fixed to the carrier layer 12, the adhesive layer 14 is interposed between the ultrathin copper foil 1 and the substrate. The migration of copper ions to the carrier layer 12 is sufficiently suppressed. In the case where the carrier layer 12 is made of a copper foil, the copper ions are sufficiently suppressed from moving between the ultrathin copper foil 1 and the carrier layer 12. Due to the presence of the adhesive layer 14, excessive adhesion between the ultrathin copper foil 1 and the carrier layer 12 due to migration of copper ions can be prevented, and in the process of finally obtaining a flexible printed wiring board substrate, the carrier layer 12 is extremely thin. The copper foil 1 can be easily separated.

<Liquid crystal polyester layer>
Next, the liquid crystal polyester layer (resin layer) 2 will be described. The liquid crystal polyester contained in the liquid crystal polyester layer 1 is a polyester called a thermotropic liquid crystal polymer, and forms a melt exhibiting optical anisotropy at a temperature of 450 ° C. or lower.

Specifically, when liquid crystal polyester is exemplified,
(1) What is obtained by polymerizing aromatic hydroxycarboxylic acid, aromatic dicarboxylic acid, and aromatic diol,
(2) those obtained by polymerizing the same or different aromatic hydroxycarboxylic acids,
(3) those obtained by polymerizing aromatic dicarboxylic acids and aromatic diols,
(4) those obtained by polymerizing aromatic hydroxycarboxylic acid, aromatic dicarboxylic acid and aromatic diol, and aromatic amine and / or aromatic diamine having a phenolic hydroxyl group,
(5) those obtained by polymerizing aromatic hydroxycarboxylic acids, aromatic dicarboxylic acids, and aromatic amines having phenolic hydroxyl groups,
(6) What is obtained by polymerizing an aromatic amine having an aromatic dicarboxylic acid and a phenolic hydroxyl group,
(7) What is obtained by polymerizing aromatic hydroxycarboxylic acid, aromatic dicarboxylic acid, and aromatic diamine,
(8) Products obtained by polymerizing aromatic dicarboxylic acid and aromatic diamine (however, polymer containing a liquid crystalline polyester moiety in the molecule)
Is mentioned.

式（１）中、Ａｒ^０はフェニレン又はナフチレン；ＺはＯ，Ｓ，ＣＯ、ＳＯ_２、炭素数１〜４のアルキレン基、Ｏ（ＣＨ_２）_ｍＯ［ｍは１〜４の整数を表す。］又は単結合；ｎは０以上３以下の整数をそれぞれ表し、Ａｒ^０が複数ある場合、それらは互いに同一でも異なっていてもよい。 Suitable liquid crystal polyesters include structural units represented by the following formulas (i), (ii) and (iii), the structural unit represented by the formula (i) is 30 to 80 mol%, and in the formula (ii) It is preferable that the structural unit shown is 10 to 35 mol% and the structural unit represented by the formula (iii) is 10 to 35 mol%.
(I) —O—Ar ¹ —CO—
(Ii) -CO-Ar ² -CO-
(Iii) -X-Ar ³ -Y-
Here, in the above formula, Ar ¹ is phenylene, naphthylene, or biphenylene; Ar ² and Ar ³ are each independently a divalent group represented by the following formula (1); and X and Y are the same or different Each represents O or NH; In addition, the hydrogen atom couple | bonded with the aromatic ring of Ar < ¹ >, Ar < ² > and Ar < ³ > may be substituted by the halogen atom, the alkyl group, or the aryl group.

In formula (1), Ar ⁰ is phenylene or naphthylene; Z is O, S, CO, SO ₂ , an alkylene group having 1 to 4 carbon atoms, O (CH ₂ ) _m O [m represents an integer of 1 to 4; . Or a single bond; n represents an integer of 0 or more and 3 or less, and when there are a plurality of Ar ^{0 s} , they may be the same or different.

  The liquid crystal polyester contained in the liquid crystal polyester layer 2 contains 10 to 35 mol% of structural units derived from aromatic diamines and / or structural units derived from aromatic amines having a phenolic hydroxyl group. Is preferred.

  Examples of such a liquid crystal polyester include the liquid crystal polyester of the above (5), (6), (7) or (8), and it is preferable to use a liquid crystal polyester selected from these. This is because a resin layer excellent in heat resistance and dimensional stability can be obtained by using these liquid crystal polyesters.

  Instead of the above aromatic hydroxycarboxylic acid, aromatic dicarboxylic acid, aromatic diol and aromatic amine having a phenolic hydroxyl group, these ester-forming derivatives or amide-forming derivatives may be used.

  Examples of the ester-forming derivative or amide-forming derivative of carboxylic acid include derivatives that promote a polyester-forming reaction or a polyamide-forming reaction, such as derivatives such as acid chlorides and acid anhydrides with improved reaction activity, transesterification reactions, or Examples thereof include esters or amide derivatives (carboxyl groups formed by reaction with alcohols, ethylene glycol, amines, etc.) capable of producing polyester or polyamide by an amide exchange reaction.

  Examples of the ester-forming derivative of a phenolic hydroxyl group include those in which a phenolic hydroxyl group forms an ester with a carboxylic acid so that a polyester is produced by a transesterification reaction.

  Examples of amide-forming derivatives of amino groups include those that form amides with carboxylic acids that form polyamides through amide exchange reactions.

  In addition, aromatic hydroxycarboxylic acids, aromatic dicarboxylic acids, aromatic diols, aromatic amines having phenolic hydroxyl groups, and aromatic diamines are chlorine atoms, fluorine atoms, as long as they do not inhibit ester formation or amide formation. It may be substituted with a halogen atom such as an atom, an alkyl group such as a methyl group or an ethyl group, or an aryl group such as a phenyl group.

  Examples of the repeating structural unit of the liquid crystalline polyester used in the present invention include the following, but are not limited thereto.

Examples of the structural unit represented by formula (i) (a structural unit derived from an aromatic hydroxy acid) include those represented by the following chemical formulas (A ¹ ) to (A ⁵ ). In the following structural units, the hydrogen atom bonded to the aromatic ring may be substituted with a halogen atom, an alkyl group or an aryl group. In addition, (A ¹ ), (A ² ), (A ³ ) or (A ⁵ ) is preferable from the viewpoint of availability of aromatic hydroxycarboxylic acids from which these structural units are derived.

  The structural unit (i) is preferably from 30 to 80 mol%, more preferably from 40 to 70 mol%, still more preferably from 45 to 65 mol%, based on all structural units. If the structural unit (i) exceeds 80 mol%, the solubility tends to be remarkably lowered, and if it is less than 30 mol%, the liquid crystallinity tends not to be exhibited.

Examples of the structural unit represented by formula (ii) (the structural unit derived from aromatic dicarboxylic acid) include those represented by the following chemical formulas (B ¹ ) to (B ⁸ ). In the following structural units, the hydrogen atom bonded to the aromatic ring may be substituted with a halogen atom, an alkyl group or an aryl group. In addition, (B ¹ ), (B ² ), (B ³ ), (B ⁵ ), or (B ⁶ ) is preferable from the viewpoint of easy availability of the aromatic dicarboxylic acid from which these structural units are derived.

  The structural unit (ii) is preferably from 35 to 10 mol%, more preferably from 30 to 15 mol%, further preferably from 27.5 to 17.5 mol%, based on all structural units. preferable. When the structural unit (ii) exceeds 35 mol%, the liquid crystallinity tends to be reduced, and when it is less than 10 mol%, the solubility tends to decrease.

  Examples of the structural unit represented by the formula (iii) include a structural unit derived from an aromatic diol, a structural unit derived from an aromatic amine having a phenolic hydroxyl group, and a structural unit derived from an aromatic diamine.

Examples of the structural unit derived from the aromatic diol include those represented by the following chemical formulas (C ¹ ) to (C ¹⁰ ). In the following structural units, the hydrogen atom bonded to the aromatic ring may be substituted with a halogen atom, an alkyl group or an aryl group. From the availability of aromatic diols that derive these structural units, (C ¹ ), (C ² ), (C ³ ), (C ⁵ ), (C ⁸ ), or (C ⁹ ) preferable.

Examples of the structural unit derived from an aromatic amine having a phenolic hydroxyl group include those represented by the following chemical formulas (D ¹ ) to (D ⁶ ). In the following structural units, the hydrogen atom bonded to the aromatic ring may be substituted with a halogen atom, an alkyl group or an aryl group. In addition, (D ¹ ) or (D ² ) is preferable from the viewpoint of availability of an aromatic amine having a phenolic hydroxyl group for deriving these structural units.

Examples of the structural unit derived from the aromatic diamine include those represented by the following chemical formulas (E ¹ ) to (E ⁶ ). In the following structural units, the hydrogen atom bonded to the aromatic ring may be substituted with a halogen atom, an alkyl group or an aryl group. In addition, (E ¹ ), (E ² ), or (E ⁴ ) is preferable because of the availability of aromatic diamines that derive these structural units.

  As the alkyl group which may be substituted with the above structural unit, for example, an alkyl group having 1 to 10 carbon atoms is usually used, and among them, a methyl group, an ethyl group, a propyl group or a butyl group is preferable. As the aryl group which may be substituted on the structural unit, for example, an aryl group having 6 to 20 carbon atoms is usually used, and among them, a phenyl group is preferable.

  The structural unit (iii) is preferably from 35 to 10 mol%, more preferably from 30 to 15 mol%, and more preferably from 27.5 to 17.5 mol%, based on all structural units. Further preferred. If the structural unit (iii) exceeds 35 mol%, the liquid crystallinity tends to be reduced, and if it is less than 10 mol%, the solubility tends to decrease.

In order to achieve both the heat resistance and dimensional stability of the liquid crystal polyester layer at a high level, the liquid crystal polyester is derived from the aromatic hydroxycarboxylic acid represented by the above (A ¹ ) and / or (A ³ ). It is preferable to include a structural unit and a structural unit derived from an aromatic dicarboxylic acid selected from (B ¹ ), (B ² ), (B ³ ) and (B ⁶ ). Examples of preferable combinations of these structural units include the following (P1) to (P11).
(P1): a combination of structural units (A ¹ ), (B ² ) and (D ¹ ),
(P2): combination of structural units (A ³ ), (B ² ) and (D ¹ ),
(P3): a combination of structural units (A ¹ ), (B ¹ ) and (D ¹ ),
(P4): combination of structural units (A ³ ), (B ³ ) and (D ¹ ), or (P5): structural units (B ¹ ), (B ² ) or (B ³ ) and (D ¹ ) combination.
(P6) in: the (P1) each combination of the ~ (P5), combined by substituting a part or all of ^{(D 1)} to ^{(D 2).}
(P6): In each of the combinations of the above (P1) or (P3), combined by substituting a part or all of ^{(A 1)} to ^{(A 3).}
(P7): A combination in which a part or all of (D ¹ ) is replaced with (E ¹ ) or (E ⁵ ) in each of the combinations (P1) to (P5).
(P8): A combination in which (D ¹ ) is partially substituted with (C ¹ ) or (C ² ) in each of the combinations (P1) to (P5).
(P9): In each of the combinations of the above (P1) or (P2), combined by substituting a part or all of ^{(B 2)} to ^{(B 6).}
(P10): in the combination of the above (P3), combined by substituting a part or all of ^{(B 1)} to ^{(B 6).}
(P11): in the combination of the above (P4), combined by substituting a part or all of ^{(B 3)} to ^{(B 6).}

  As a more preferable combination of the structural units, 30 to 80 mol% of structural units derived from at least one compound selected from the group consisting of p-hydroxybenzoic acid and 2-hydroxy-6-naphthoic acid, 4-aminophenol and 4 , 4′-diaminodiphenyl ether, 10 to 35 mol% of structural units derived from at least one compound selected from the group consisting of, and 10 to 35 structural units derived from at least one compound selected from the group consisting of terephthalic acid and isophthalic acid. Examples of particularly preferred combinations include 30 to 80 mol% of structural units derived from 2-hydroxy-6-naphthoic acid, 10 to 35 mol% of structural units derived from 4-hydroxyaniline, and isophthalic acid. What consists of 10-35 mol% of structural units derived from an acid is mentioned. It is.

  The method for producing the liquid crystal polyester used in the present invention is not particularly limited. For example, an aromatic hydroxy acid corresponding to the structural unit (i), an aromatic amine having a hydroxyl group corresponding to the structural unit (iii), and aromatic Acylation is obtained by acylating phenolic hydroxyl group or amino group of diamine with an excess amount of fatty acid anhydride, and transesterification (polycondensation) of the obtained acylation product and aromatic dicarboxylic acid corresponding to structural unit (ii) ) And then melt polymerization.

  In the acylation reaction, the amount of fatty acid anhydride added is preferably 1.0 to 1.2 times equivalent to the total of the phenolic hydroxyl group and amino group, more preferably 1.05 to 1. 1 equivalent. When the amount of fatty acid anhydride added is less than 1.0 times equivalent, acylated products, aromatic hydroxycarboxylic acids, aromatic dicarboxylic acids and the like tend to sublimate during polycondensation due to transesterification / amide exchange, and the reaction system tends to block. In addition, when the amount exceeds 1.2 times equivalent, the resulting liquid crystal polyester tends to be remarkably colored.

  The acylation reaction is preferably performed at 130 to 180 ° C. for 5 minutes to 10 hours, more preferably at 140 to 160 ° C. for 10 minutes to 3 hours.

  The fatty acid anhydride used in the acylation reaction is not particularly limited, and examples thereof include acetic anhydride, propionic anhydride, butyric anhydride, isobutyric anhydride, valeric anhydride, pivalic anhydride, anhydrous 2-ethylhexanoic acid, and monochloroacetic anhydride. , Dichloroacetic anhydride, trichloroacetic anhydride, monobromoacetic anhydride, dibromoacetic anhydride, tribromoacetic anhydride, monofluoroacetic anhydride, difluoroacetic anhydride, trifluoroacetic anhydride, glutaric anhydride, maleic anhydride, succinic anhydride, β- Examples thereof include bromopropionic acid, and two or more of these may be used in combination. From the viewpoint of price and handleability, acetic anhydride, propionic anhydride, butyric anhydride, and isobutyric anhydride are preferable, and acetic anhydride is more preferable.

  In the polymerization by transesterification / amide exchange, the acyl group of the acylated product is preferably 0.8 to 1.2 times equivalent to the carboxyl group.

  Polymerization by transesterification and amide exchange is preferably performed at 130 to 400 ° C. while raising the temperature at a rate of 0.1 to 50 ° C./min, and at 150 to 350 ° C. at a rate of 0.3 to 5 ° C./min. More preferably, the temperature is raised. At this time, in order to move the equilibrium, it is preferable to distill out the by-product fatty acid and the unreacted fatty acid anhydride, for example, by evaporating.

  The polymerization by acylation reaction or transesterification / amide exchange may be performed in the presence of a catalyst. As the catalyst, those conventionally known as polyester polymerization catalysts can be used, such as magnesium acetate, stannous acetate, tetrabutyl titanate, lead acetate, sodium acetate, potassium acetate, antimony trioxide and the like. And organic compound catalysts such as N, N-dimethylaminopyridine and N-methylimidazole. The catalyst is usually present during the acylation reaction, and it is not always necessary to remove it after acylation. If the catalyst is not removed, the next treatment can be carried out as it is. Moreover, you may add the above catalysts when performing the next process.

  Polymerization by transesterification / amide exchange is usually performed by melt polymerization, but melt polymerization and solid phase polymerization may be used in combination. The solid phase polymerization can be performed by a known solid phase polymerization method after the polymer is extracted from the melt polymerization step, solidified, pulverized into powder or flakes. Specifically, for example, a method of heat treatment in a solid state at 20 to 350 ° C. for 1 to 30 hours under an inert atmosphere such as nitrogen can be used. Solid phase polymerization may be carried out while stirring or in a state of standing without stirring. In addition, by providing an appropriate stirring mechanism, the melt polymerization tank and the solid phase polymerization tank can be made the same reaction tank. After the solid phase polymerization, the obtained liquid crystal polyester may be used after being pelletized by a known method.

  Manufacture of liquid crystalline polyester can be performed using a batch apparatus, a continuous apparatus, etc., for example. The weight average molecular weight of the liquid crystal polyester is usually about 100,000 to 500,000.

  A liquid crystal polyester having a sufficiently low water absorption can be obtained by appropriately selecting the structural unit and producing the structural unit. The water absorption rate of the liquid crystal polyester (after leaving for 24 hours at a temperature of 23 ° C. and a humidity of 50%) is preferably 1.0% by mass or less, and more preferably 0.3% by mass or less. When the water absorption rate exceeds 1.0% by mass, voids and the like tend to be generated in the liquid crystal polyester layer 2 in the manufacturing process of the flexible printed wiring board. Here, the water absorption rate is a value obtained by dividing the increase in the mass of the sample to be measured by the water absorption treatment by the mass of the sample before the water absorption treatment. The water absorption treatment means that the sample to be measured is allowed to stand for 24 hours under the condition of a temperature of 23 ° C. and a humidity of 50%. The sample to be measured is left as a pretreatment in a constant temperature bath maintained at a temperature of 50 ± 2 ° C. for 24 hours. Use what you did.

  Further, according to the liquid crystal polyester having low water absorption, the value of the dielectric loss tangent in the high frequency band can be sufficiently reduced. Specifically, the dielectric loss tangent value is preferably 0.005 or less. If the value of the dielectric loss tangent exceeds 0.005, the electric signal flowing through the wiring tends to be lost as heat and attenuate.

  The resin layer 2 containing liquid crystal polyester is made of the liquid crystal polyester produced as described above, but may contain an inorganic filler in addition to the liquid crystal polyester as long as the electrical characteristics and hygroscopicity are not deteriorated. When the liquid crystal polyester layer 2 contains an inorganic filler, mechanical properties such as elastic modulus or dimensional accuracy of the liquid crystal polyester layer 2 can be further improved.

  As the inorganic filler, aluminum borate, potassium titanate, magnesium sulfate, zinc oxide, silicon carbide, silicon nitride, glass fiber, alumina fiber, and the like can be used. When the resin layer 2 containing a liquid crystal polyester contains an inorganic filler, the content is preferably 5 to 30 parts by mass, with the liquid crystal polyester contained in the resin layer 2 being 100 parts by mass, More preferably, it is part by mass. When the content of the inorganic filler is within the above range, the mechanical properties can be improved while maintaining good electrical properties and hygroscopicity.

  The thickness of the resin layer 2 containing liquid crystal polyester is preferably 0.5 to 500 μm from the viewpoint of film forming properties and mechanical properties, and more preferably 1 to 100 μm from the viewpoint of handleability. In addition, the thickness of the liquid crystal polyester layer 2 can be adjusted by the number of coatings at the time of forming the layer or the viscosity of the coating solution.

<Method for manufacturing substrate for flexible printed wiring board>
Hereinafter, the manufacturing method of the board | substrate for flexible printed wiring boards is demonstrated. The substrate for a flexible printed wiring board of the present invention is obtained by forming a resin layer containing liquid crystal polyester on an ultrathin copper foil or on a surface to which a carrier layer of an ultrathin copper foil with a carrier layer is not attached. can get.

  Here, since the higher adhesiveness between the resin layer and the ultrathin copper foil is preferable, surface treatment of the ultrathin copper foil may be performed before forming the resin layer. As the surface treatment, an adhesion improver such as a silane coupling agent is usually used. That is, the silane coupling agent solution prepared at a concentration of about 0.1 to 10% by mass is applied to the surface on which the resin layer is formed on the surface of the ultrathin copper foil. Thereafter, the solvent contained in the silane coupling agent is removed by ventilation or heat treatment at about 50 to 100 ° C. The solvent of the silane coupling agent solution is not limited as long as it does not deactivate the silane coupling agent to be used and does not damage the ultrathin copper foil surface, but the solvent is easy to remove after coating. From the viewpoint, alcohol solvents such as methanol, ethanol and n-butanol, ketones such as acetone and methyl isobutyl ketone, esters such as propyl acetate and butyl acetate, aromatic hydrocarbons such as toluene and xylene, and mixed solvents thereof Is preferred.

As the silane coupling agent, those easily available from the market can be used, and examples thereof include compounds represented by the following (F ¹ ) to (F ⁷ ). These silane coupling agents may be partially oligomerized with moisture in the air, but when used as an adhesion improver, oligomerized by-products may be removed or removed. You don't have to.

  The resin layer can be formed by heating and melting the liquid crystalline polyester and extruding it onto the ultrathin copper foil surface, or by dissolving the liquid crystalline polyester in a suitable solvent to prepare a coating solution, which is then applied to the copper foil surface. And a method of forming a resin layer by casting. Among these forming methods, the latter method is particularly preferable because the operation is simple and a resin layer having a uniform film thickness can be easily obtained. Moreover, in order to improve the adhesiveness of a resin layer and an ultra-thin copper foil, you may use the coating liquid with which the said adhesive improvement agent was added.

  In addition, the structural unit derived from the aromatic diamine and / or the structural unit derived from the aromatic amine having a hydroxyl group with respect to all the structural units also in terms of ensuring sufficient adhesion between the resin layer and the ultrathin copper foil. It is preferable to use a liquid crystal polyester containing 10 to 35 mol%. When such a liquid crystal polyester is used, sufficient adhesion between the resin layer and the ultrathin copper foil can be secured without using a copper foil surface treatment with an adhesion improver or a coating solution to which an adhesion improver is added.

  Next, the preparation method of the coating liquid for resin layers containing liquid crystalline polyester is demonstrated.

  The coating solution can be obtained by dissolving liquid crystal polyester in a solvent. The solvent is not particularly limited as long as it dissolves the liquid crystalline polyester. For example, N, N′-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam, N, N′-dimethylformamide, N , N′-diethylformamide, N, N′-diethylacetamide, N-methylpropionamide, dimethyl sulfoxide, γ-butyrolactone, dimethylimidazolidinone, tetramethylphosphoric amide and ethyl cellosolve acetate, and parafluorophenol, para And halogenated phenols such as chlorophenol and perfluorophenol. These solvents can be used alone or in combination.

  Although the usage-amount of a solvent can be suitably selected according to a use, it is preferable that it is 0.5-50 mass parts of liquid crystal polyester with respect to 100 mass parts of solvent, and it is more preferable that it is 10-20 mass parts. preferable. If the liquid crystalline polyester is less than 0.5 parts by mass, the solution viscosity tends to be too low to uniformly coat, and if it exceeds 50 parts by mass, the viscosity tends to increase.

  In addition, although the solution which melt | dissolved liquid crystalline polyester in said solvent may be used as a coating liquid, it is preferable to pass the filter etc. and to remove the fine foreign material contained in a solution.

  Moreover, when forming the liquid crystalline polyester layer 2 containing an inorganic filler, what added the predetermined amount of inorganic fillers to the solution in which the liquid crystalline polyester is dissolved may be used as the coating liquid. In this case, the addition amount of the inorganic filler may be adjusted so that the content of the inorganic filler in the liquid crystal polyester layer 2 becomes a desired value after removing the solvent.

  Thus, when forming a resin layer using the coating liquid containing liquid crystalline polyester, the thickness of this resin layer should be adjusted with the frequency | count of application | coating liquid at the time of the said resin layer formation, or the viscosity of a coating liquid. Can do.

  Next, a method for manufacturing the substrate 10 using the coating solution prepared as described above will be described with reference to FIG.

  FIG. 3A is a schematic cross-sectional view showing a state in which a coating liquid containing liquid crystal polyester is applied to the surface of the ultrathin copper foil 1 to form a coating film 2a. Examples of the method for applying the coating liquid include various means such as a roller coating method, a dip coating method, a spray coating method, a spinner coating method, a curtain coating method, a slot coating method, and a screen printing method. By these means, the coating solution is cast flat and uniformly to form the coating film 2a.

  FIG. 3B is a schematic cross-sectional view showing a state in which the solvent in the coating film 2 a is removed and the non-oriented liquid crystal polyester layer 2 b is formed on the surface of the ultrathin copper foil 1. The solvent removal method is preferably performed by evaporation of the solvent. Examples of the method for evaporating the solvent include methods such as heating, reduced pressure, and ventilation. Among them, it is preferable to evaporate by heating from the viewpoint of production efficiency and handleability, and it is more preferable to evaporate by heating while ventilating. preferable. What is necessary is just to hold | maintain for 10 to 120 minutes at the temperature of 80-200 degreeC, when removing a solvent by heating.

  FIG. 3C is a schematic cross-sectional view showing a state in which the liquid crystal polyester layer 2 is formed by aligning the molecules of the non-aligned liquid crystal polyester by heating. What is necessary is just to hold | maintain for 30 to 180 minutes at the temperature of 250-350 degreeC, when aligning the molecule | numerator of liquid crystalline polyester. In addition, you may implement the process of orienting the molecule | numerator of liquid crystal polyester, without implementing the process of removing a solvent. In this case, from the viewpoint of preventing the occurrence of voids and the like due to the rapid evaporation of the solvent in the coating film 2a, the rate of temperature increase should be made slower than when the step of removing the solvent is performed. Is preferred.

  FIG. 3D is a schematic cross-sectional view showing a process of peeling the adhesive layer 14 and the carrier layer 12 from the ultrathin copper foil 1. In this way, the substrate 10 can be manufactured.

  The substrate 10 has sufficient adhesion between the ultrathin copper foil 1 and the liquid crystal polyester layer 2. As an adhesive evaluation test, there is a 180 ° peel strength test specified in JIS C6471 (1995), and the 180 ° peel strength from the resin layer 2 at 23 ° C. is preferably 7 N / cm or more, and 8N / Cm or more is more preferable. In addition, since the ultrathin copper foil of the object of the evaluation test is very thin and has insufficient strength, the obtained copper-clad laminate is made of copper until the thickness of the copper thin film reaches a predetermined thickness (for example, 12 μm). After plating, the adhesion evaluation test is performed.

  Further, the substrate 10 has excellent folding resistance. As an evaluation test of such folding resistance, there is a folding resistance test defined in JIS C6471 (1995), which is repeated 100 times or more in the test under the conditions of a curvature radius of 0.38 mm and a tension of 4.9 N. It is preferable that the ultrathin copper foil does not break even when bent.

  The flexible printed wiring board substrate of the present invention may be another embodiment as described below. FIG. 4 is a schematic partial cross-sectional view showing another embodiment of the flexible printed wiring board substrate of the present invention. The substrate 20 shown in FIG. 4 has an intermediate layer 3 between the ultrathin copper foil 1 and the liquid crystal polyester layer 2. In the flexible printed wiring board of the present invention, as long as the liquid crystal polyester layer 2 is formed on the ultrathin copper foil 1, the ultrathin copper foil 1 and the liquid crystal polyester layer 2 are not necessarily adjacent to each other. Good. In addition, as the intermediate | middle layer 3, you may provide the rust prevention layer and the primer layer one layer or two layers or more. Such an intermediate layer 3 can be formed by any conventionally known method.

  The flexible printed wiring board substrate of the present invention has high folding resistance and high heat resistance, and has excellent properties such as low water absorption. Therefore, its use is not limited to flexible printed wiring boards, and has attracted attention in recent years. It is suitably used for a semiconductor package obtained by a build-up method or the like, a multilayer printed board for a mother board, a film for tape automated bonding, or the like.

  EXAMPLES Hereinafter, although this invention is demonstrated using an Example, it cannot be overemphasized that this invention is not what is limited by an Example.

(Production Example 1)
<Synthesis of liquid crystal polyester A>
In a reactor equipped with a stirrer, a torque meter, a nitrogen gas inlet tube, a thermometer and a reflux condenser, 941 g (5.0 mol) of 2-hydroxy-6-naphthoic acid and 273 g (2.5 mol) of 4-aminophenol were added. ), 415.3 g (2.5 mol) of isophthalic acid and 1123 g (11 mol) of acetic anhydride. After sufficiently replacing the inside of the reactor with nitrogen gas, the temperature was raised to 150 ° C. over 15 minutes under a nitrogen gas stream, and the temperature was maintained and refluxed for 3 hours.

  Thereafter, the temperature was raised to 320 ° C. over 170 minutes while distilling off the by-product acetic acid and unreacted acetic anhydride, and the time when an increase in torque was observed was regarded as the completion of the reaction, and the contents were taken out. The obtained resin was pulverized with a coarse pulverizer and then heated at 10 ° C./min while observing a part of the powder with a polarizing microscope. As a result, a schlieren pattern peculiar to the liquid crystal phase was exhibited at 200 ° C. The resin thus obtained is designated as liquid crystal polyester A.

(Production Example 2)
<Synthesis of liquid crystal polyester B>
In a reactor equipped with a stirrer, a torque meter, a nitrogen gas inlet tube, a thermometer, and a reflux condenser, 658.6 g (3.5 mol) of 2-hydroxy-6-naphthoic acid and 354.7 g of 4-aminophenol ( 3.25 mol), 539.9 g (3.25 mol) of isophthalic acid, and 1123.0 g (11 mol) of acetic anhydride. After sufficiently replacing the inside of the reactor with nitrogen gas, the temperature was raised to 150 ° C. over 15 minutes under a nitrogen gas stream, and the temperature was maintained and refluxed for 3 hours.

  Thereafter, the temperature was raised to 300 ° C. over 170 minutes while distilling off the by-product acetic acid and unreacted acetic anhydride, and the time when an increase in torque was observed was regarded as the completion of the reaction, and the contents were taken out. Next, this was cooled to room temperature, pulverized with a coarse pulverizer, held at 250 ° C. for 10 hours in a nitrogen atmosphere, cooled to room temperature, pulverized again with a coarse pulverizer, and then held at 240 ° C. for 3 hours under a nitrogen atmosphere. The polymerization reaction proceeded in the solid phase to obtain an aromatic polyester powder. The resin thus obtained is designated as liquid crystal polyester B.

Example 1
<Manufacture of flexible printed wiring board substrates>
8 g of the liquid crystal polyester A powder obtained in Production Example 1 is added to 92 g of N-methyl-2-pyrrolidone (hereinafter referred to as “NMP”) and heated to 160 ° C., whereby the liquid crystal polyester is completely dissolved and brown transparent Solution was obtained. This solution was stirred and degassed to obtain a liquid crystal polyester solution. Aluminum borate (trade name: Arborex M20C, manufactured by Shikoku Kasei Co., Ltd., specific gravity 3.0 g / cm ³ ) was added as an inorganic filler to this solution. The amount of aluminum borate added was 10 parts by volume with respect to 100 parts by volume of the liquid crystalline polyester. After the addition of aluminum borate, dispersion and defoaming were performed to obtain a coating liquid for a liquid crystal polyester layer.

  This coating solution is applied onto a very thin copper foil with a carrier (trade name: Y-SNAP, manufactured by Nippon Electrolytic Co., Ltd., carrier layer thickness 18 μm / ultra thin copper foil thickness 3 μm) using a film applicator, and on a hot plate And dried at 80 ° C. for 1 hour. Thereafter, heat treatment was performed in a hot air oven in a nitrogen atmosphere at a temperature increase rate of 5 ° C./min from 30 ° C. to 300 ° C. and held at 300 ° C. for 1 hour. After cooling to room temperature, the carrier layer was peeled off to obtain a flexible printed wiring board substrate.

<Evaluation test>
In order to evaluate the characteristics of the substrate for a flexible printed wiring board thus obtained, the following evaluation test was performed. In addition, the test method followed the method prescribed | regulated to JISC6471 (1995).

(Measurement of 180 ° peel strength)
The 180 ° peel strength of the flexible printed wiring board substrate manufactured in Example 1 was measured as follows using a tensile tester. That is, first, copper plating was performed on the copper foil side of the flexible printed wiring board substrate until the thickness of the copper foil became 12 μm. After that, a reinforcing plate is attached to the surface of the flexible printed wiring board substrate on the liquid crystal polyester layer side with a double-sided adhesive tape, so that the ultrathin copper foil can be reliably peeled off from the liquid crystal polyester layer in the direction of 180 °. did. Then, a part of the ultrathin copper foil is peeled off from the liquid crystal polyester layer, one end of the flexible printed wiring board substrate from which the ultrathin copper foil is peeled is fixed to one clamp of a tensile tester, and the peeled ultrathin copper The foil was fixed to another clamp. From this state, the ultrathin copper foil was continuously peeled in the direction of 180 °, and the load during that time was measured. The measurement was performed by adjusting the room temperature to 23 ° C. The measurement results of 180 ° peel strength are shown in Table 1.

(Folding resistance test)
The folding resistance of the flexible printed wiring board substrate manufactured in Example 1 was measured based on JIS C6471 using a folding resistance tester (MITO-D, manufactured by Toyo Seiki Co., Ltd.). The bending radius of the bent surface was 0.38 mm, the bending angle was 135 °, bending was performed at a speed of 175 times per minute at a tension of 4.9 N, and the number of times until the flexible printed wiring board substrate was disconnected was measured. The results of the folding resistance test are shown in Table 1.

(Example 2)
Instead of the ultrathin copper foil with carrier (carrier layer thickness 18 μm / ultra thin copper foil thickness 3 μm) used in Example 1, the carrier layer ultrathin copper with carrier layer thickness 35 μm / ultra thin copper foil thickness 5 μm A flexible printed wiring board was produced in the same manner as in Example 1 except that the foil (trade name: XTF, manufactured by Nippon Olympus Co., Ltd.) was used, and various evaluation tests were conducted in the same manner. The evaluation results are shown in Table 1.

(Example 3)
A flexible printed wiring board substrate was produced in the same manner as in Example 1 except that the liquid crystal polyester B prepared in Production Example 2 was used instead of Liquid Crystalline Polyester A, and various evaluation tests were carried out in the same manner. When a flexible printed wiring board substrate is manufactured, a flexible printed wiring board substrate having 180 ° peel strength and folding resistance similar to those manufactured in Examples 1 and 2 is obtained.

Example 4
As a coating liquid for the liquid crystal polyester layer, a solution obtained by adding 8 g of liquid crystal polyester A powder to 92 g of NMP and heating to 160 ° C., that is, using a solution to which no inorganic filler is added is used. Otherwise, when the flexible printed wiring board substrate is manufactured in the same manner as in Example 1, the flexible printed wiring board has the same 180 ° peel strength and folding resistance as those manufactured in Examples 1 and 2. A substrate is obtained.

(Comparative Example 1)
Instead of the ultrathin copper foil with carrier (carrier layer thickness 18 μm / ultra thin copper foil thickness 3 μm) used in Example 1, a 9 μm thick copper foil (trade name: SQ-) not fixed to the carrier layer A liquid crystal polyester layer was formed in the same manner as in Example 1 except that VLP (manufactured by Mitsui Metal Mining Co., Ltd.) was used. However, in Comparative Example 1, the copper foil was wrinkled in the heat treatment step, and a substrate that could be used as a flexible printed wiring board could not be obtained.

(Characteristic evaluation of liquid crystal polyester and polyimide)
<Manufacture of liquid crystal polyester film>
A liquid crystal polyester A solution was prepared by adding 8 g of liquid crystal polyester A powder to 92 g of NMP and heating to 160 ° C. The solution was applied by casting on a copper foil (thickness: 18 μm) and dried on a hot plate at 80 ° C. for 1 hour. Then, it heat-processed at 300 degreeC for 1 hour in the hot-air oven of nitrogen atmosphere, and formed into a film. After cooling to room temperature, the copper foil was etched by dipping in a ferric chloride aqueous solution (Baume degree 40 °, manufactured by Kida Co., Ltd.) to obtain a liquid crystal polyester film (liquid crystal polyester film A).

  A liquid crystal polyester film (liquid crystal polyester film B) was obtained in the same manner as liquid crystal polyester film A, except that 8 g of liquid crystal polyester B powder was used instead of 8 g of liquid crystal polyester A powder.

<Manufacture of polyimide film>
Based on the literature (Polymer 1998, vol 39, pages 2963-2972), a polyamic acid was synthesized as follows. That is, the inside of a 100 ml four-necked flask equipped with a nitrogen introduction tube, a thermometer and a stirring rod was purged with nitrogen, and then charged with 4.45 g (22.2 mmol) of 4,4′-diaminodiphenyl ether, and 106.84 g of NMP was added. In addition, it was completely dissolved. Further, 4.84 g (22.2 mmol) of pyromellitic dianhydride was added and stirred at a reaction temperature of 25 ° C. for 15 hours to obtain a brown and viscous polyamic acid solution.
The polyamic acid solution thus obtained was applied to a copper foil (thickness: 18 μm) using a film applicator, heated at 80 ° C. for 1 hour and dried, and then heated at 350 ° C. for 1 hour. After cooling to room temperature, the copper foil was etched by immersion in a ferric chloride aqueous solution (Baume degree 40 °, manufactured by Kida Co., Ltd.) to obtain a polyimide film.

<Evaluation of film properties>
The characteristics of the liquid crystal polyester films A and B produced by the above method and the polyimide film were evaluated. Table 2 shows measured values of dielectric constant and dielectric loss tangent at 1 GHz at a temperature of 23 ° C., and water absorption (after being left for 24 hours at a temperature of 23 ° C. and a humidity of 50%) using an HP impedance analyzer.

It is a typical fragmentary sectional view showing one embodiment of a substrate for flexible printed wiring boards of the present invention. It is a model fragmentary sectional view which shows the mode of the ultra-thin copper foil of the state fixed to the support body. It is process sectional drawing of the manufacturing method of the board | substrate for flexible printed wiring boards of this invention. It is a typical fragmentary sectional view which shows other embodiment of the board | substrate for flexible printed wiring boards of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Ultra-thin copper foil, 2 ... Liquid crystal polyester layer (resin layer), 3 ... Intermediate layer, 10, 20 ... Board | substrate (substrate for flexible printed wiring boards), 12 ... Carrier layer (support body), 14 ... Adhesive layer (Heat diffusion prevention layer).

Claims (11)

  A substrate for a flexible printed wiring board, comprising a resin layer containing liquid crystalline polyester on an ultrathin copper foil having a thickness of 5 μm or less.   The substrate for flexible printed wiring boards according to claim 1, wherein 180 ° peel strength from the resin layer of the ultrathin copper foil at 23 ° C is 7 N / cm or more.   The flexible printed wiring board substrate according to claim 1 or 2, wherein the resin layer is obtained by removing the solvent from a solution containing liquid crystal polyester and a solvent applied on the ultrathin copper foil.   The board | substrate for flexible printed wiring boards as described in any one of Claims 1-3 in which the said resin layer contains an inorganic filler.   In the folding resistance test defined by JIS C6471 (1995), the folding resistance measured under the conditions of a curvature radius of 0.38 mm and a tension of 4.9 N is 100 or more. The substrate for flexible printed wiring boards according to any one of 4. The liquid crystalline polyester includes structural units represented by the following formulas (i), (ii) and (iii), and the structural unit represented by the formula (i) is 30 to 80 mol% with respect to all structural units, The flexible printed wiring board according to any one of claims 1 to 5, wherein the structural unit represented by the formula (ii) is 10 to 35 mol% and the structural unit represented by the formula (iii) is 10 to 35 mol%. Substrate.
(I) —O—Ar ¹ —CO—
(Ii) -CO-Ar ² -CO-
(Iii) -X-Ar ³ -Y-
(Wherein Ar ¹ is phenylene, naphthylene or biphenylene; Ar ² and Ar ³ are each independently a divalent group represented by the following formula (1); X and Y are the same or different, and O or NH In addition, the hydrogen atom bonded to the aromatic ring of Ar ¹ , Ar ² and Ar ³ may be substituted with a halogen atom, an alkyl group or an aryl group.

In formula (1), Ar ⁰ is phenylene or naphthylene; Z is O, S, CO, SO ₂ , an alkylene group having 1 to 4 carbon atoms, O (CH ₂ ) _m O [m represents an integer of 1 to 4; . Or a single bond; n represents an integer of 0 or more and 3 or less, and when there are a plurality of Ar ^{0 s} , they may be the same or different. )   The said liquid crystalline polyester contains 10-35 mol% of structural units derived from the aromatic diamine origin structural unit and / or the aromatic amine which has a hydroxyl group with respect to all the structural units. Flexible printed wiring board substrate.   For a flexible printed wiring board, a solution containing liquid crystal polyester and a solvent is applied onto an ultrathin copper foil having a thickness of 5 μm or less fixed on a support, and after removing the solvent, the support is removed. A method for manufacturing a substrate.   The manufacturing method of the board | substrate for flexible printed wiring boards of Claim 8 provided with the process of orientating the molecule | numerator of liquid crystalline polyester by heating after the said solvent is removed or in the state which does not remove the said solvent.   The manufacturing method of the board | substrate for flexible printed wiring boards of Claim 8 or 9 whose said support body is a metal.   The said ultra-thin copper foil is a manufacturing method of the board | substrate for flexible printed wiring boards as described in any one of Claims 8-10 currently fixed to the said support body through the thermal-diffusion prevention layer.

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