JP2007313854A - Copper-clad laminated sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a copper-clad laminated sheet which can be used for suitably manufacturing FPC (Flexible Printed Circuit) for a bending use, for example, in an α or z winding form, etc. <P>SOLUTION: The copper-clad laminated sheet comprises a copper foil 3 provided on both surfaces of an insulating layer 2 containing at least a polyimide layer, and is characterized by having a loop stiffness value of 0.30 N/cm or less. Preferably, the insulating layer has a multi-layer structure wherein a thermoplastic polyimide layer is provided on both surfaces of the high heat resistant polyimide layer. The copper-clad laminated sheet can be manufactured by laminating the copper foil on both surfaces of the insulating layer by the heat roll laminate method. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an insulating layer containing at least one polyimide layer and a copper-clad laminate obtained by providing metal foil on both surfaces of the insulating layer.

  In recent years, the demand for various printed circuit boards has increased with the reduction in weight, size and density of electronic products, and in particular, the demand for flexible laminates (also referred to as flexible printed wiring boards (FPC), etc.) has increased. ing. The FPC has a structure in which a circuit made of a metal foil is formed on an insulating film.

  The FPC is generally made of various insulating materials, and is manufactured by a method in which a flexible insulating film is used as a substrate, and a metal foil is bonded to the surface of the substrate by heating and pressure bonding through various adhesive materials. Is done. A polyimide film or the like is preferably used as the insulating film. As the adhesive material, a thermosetting adhesive such as epoxy or acrylic is generally used (FPC using these thermosetting adhesives is hereinafter also referred to as three-layer FPC).

  The thermosetting adhesive used for the three-layer FPC has an advantage that it can be bonded at a relatively low temperature. However, in the future, in addition to stricter requirements for various characteristics such as heat resistance, flexibility, and electrical reliability for FPC, halogen-containing flame retardants contained in many thermosetting adhesives are environmentally unfavorable. Therefore, the current situation is that it is difficult to cope with the three-layer FPC using the thermosetting adhesive. Therefore, there is an increasing demand for so-called two-layer FPC that does not use a thermosetting adhesive. As a method for producing a flexible copper clad laminate for use in a two-layer FPC, a polyamic acid, which is a polyimide precursor, is cast on a metal foil, applied, and then casted directly onto a polyimide film by sputtering or plating. Examples thereof include a metallizing method for providing a metal layer and a laminating method for bonding a polyimide film and a metal foil through a thermoplastic polyimide.

  One of the uses of these two-layer FPCs is a wiring use at a bent portion such as a hinge portion of a mobile phone. However, due to the recent trend of downsizing and thinning electronic devices such as mobile phones and personal computers, there is an increasing demand for FPC with higher flexibility, and it has become difficult to cope with conventional FPC. Is the current situation.

  This invention is made in view of said subject, Comprising: For example, it is providing the copper clad laminated board which can produce suitably FPC used for a bending use in forms, such as alpha winding and z winding use. .

As a result of intensive studies in view of the above problems, the present inventors have uniquely found the configuration of a copper-clad laminate capable of suitably producing an FPC used for bending, and have completed the present invention.
That is, the present invention is a copper clad laminate in which copper foil is provided on both surfaces of an insulating layer containing at least one polyimide layer, and the loop stiffness value is 0.30 N / cm or less. The present invention relates to a copper clad laminate.

  A preferred embodiment relates to the copper clad laminate, wherein the insulating layer has a multi-layer structure in which a thermoplastic polyimide layer is provided on both surfaces of a high heat resistant polyimide layer.

 In a more preferred embodiment, the copper-clad laminate is characterized in that the high heat-resistant polyimide layer has a thickness of 7.5 to 13 μm, and each thickness of the thermoplastic polyimide layer is 1.2 to 2.5 μm. Regarding the board.

 A further preferred embodiment relates to the copper clad laminate, wherein the insulating layer has a thickness of 16 μm or less.

 A further preferred embodiment relates to the above copper clad laminate, wherein the insulating layer has a linear expansion coefficient of 20 to 24 ppm.

 Furthermore, a preferable embodiment relates to the copper clad laminate, wherein the total thickness of the copper foil is 20 μm or less.

 A further preferred embodiment relates to the copper clad laminate, wherein copper foil is laminated on both surfaces of the insulating layer by a hot roll laminating method.

 A further preferred embodiment relates to the copper-clad laminate as described above, wherein the copper-clad laminate is used in bending applications in the form of α winding or z winding.

  ADVANTAGE OF THE INVENTION According to this invention, the copper clad laminated board which can manufacture suitably FPC applied to a bending use can be provided.

Embodiments of the present invention will be described below.
<Stiffness of copper clad laminate>
The copper-clad laminate according to the present invention is a copper-clad laminate obtained by providing metal foil on both surfaces of an insulating layer containing at least one polyimide layer, and has a loop stiffness value of 0.30 N / cm or less. It is characterized by being.

  Conventional copper clad laminates that have been widely used have a loop stiffness value exceeding 0.30 N / cm. In the present invention, it is important that the loop stiffness value of the copper clad laminate is 0.30 N / cm or less. In order to improve the flexibility of the copper-clad laminate, there are methods such as reducing the elastic modulus of the insulating layer and reducing the thickness of the copper layer by vapor deposition, sputtering, etc. There are problems such as poor dimensional stability and high cost. The present inventors are the first to find that by controlling the stiffness value of the entire copper-clad laminate, a copper-clad laminate that does not break or break even in a folded state can be obtained. Thereby, there is an advantage that the selection range of the insulating layer and the copper foil is widened, and the degree of freedom in design is increased. A copper clad laminate is arranged in a folded state such as an α-winding or a z-winding at a jinge portion of a mobile phone. By controlling the loop stiffness of the entire metal laminate, it is possible to provide a metal laminate that does not break due to repeated bending even when used in a bent state.

  The loop stiffness can be measured using a loop stiffness tester manufactured by Toyo Seiki at a sample width of 5 to 10 mm, a loop length of 50 mm, and a crushing distance of 10 mm. What is necessary is just to set a sample width suitably so that a measured value may be set to 5-15g according to film thickness. The loop stiffness value of the copper clad laminate thus measured is 0.30 N / cm or less, preferably 0.25 N / cm or less.

  As a method for producing a copper clad laminate according to the present invention, a polyamic acid, which is a precursor of polyimide, is cast on a metal foil, casted after imidization, and directly applied onto a polyimide film by sputtering or plating. The metallizing method which provides a metal layer, the lamination method which bonds a polyimide film and metal foil through a thermoplastic polyimide are illustrated, and any method may be used. Among them, the laminating method is particularly preferable because the thickness range of the metal foil that can be handled is wider than the casting method, the width for selecting the copper foil is widened, and the apparatus cost is lower than that of the metalizing method. However, when a copper clad laminate is manufactured by a laminating method using a thin copper foil, there may be a problem such as wrinkles.

  Therefore, it is preferable that the insulating layer has a multi-layer structure in which a thermoplastic polyimide layer is provided on both surfaces of a high heat resistant polyimide layer.

Specific methods for setting the loop stiffness value of the copper-clad laminate to 30 N / cm or less include reducing the thickness of the insulating layer, reducing the thickness of the metal foil, etc. More specifically, the thickness of the insulating layer Is 16 μm or less, and the total thickness of the metal foil is 20 μm.
An example for obtaining the copper clad laminate of the present invention is shown below.

<Insulating layer>
The insulating layer has at least one polyimide layer. The insulating layer has a multi-layer structure in which a thermoplastic polyimide layer is provided on both sides of a high heat-resistant polyimide layer. This increases the density of the flexible printed board obtained by processing the copper-clad laminate according to the present invention. This is desirable because it is possible. Hereinafter, the structure will be described as an example.

  The insulating layer according to the present invention preferably has a multi-layer structure in which a thermoplastic polyimide layer is provided on both surfaces of a high heat resistant polyimide layer and a high heat resistant polyimide layer.

  The high heat resistant polyimide layer according to the present invention is not particularly limited in its molecular structure and thickness as long as it contains 90 wt% or more of a non-thermoplastic polyimide resin. The non-thermoplastic polyimide used for the high heat resistant polyimide layer is manufactured using polyamic acid as a precursor. Any known method can be used as a method for producing the polyamic acid, and usually, the aromatic tetracarboxylic dianhydride and the aromatic diamine are controlled by dissolving substantially equimolar amounts in an organic solvent. It is produced by stirring under temperature conditions until the polymerization of the acid dianhydride and diamine is completed. These polyamic acid solutions are usually obtained at a concentration of 5 to 35 wt%, preferably 10 to 30 wt%. When the concentration is in this range, an appropriate molecular weight and solution viscosity are obtained.

As the polymerization method, any known method and a combination thereof can be used. The characteristic of the polymerization method in the polymerization of polyamic acid is the order of addition of the monomers, and the physical properties of the polyimide obtained can be controlled by controlling the order of addition of the monomers. Therefore, in the present invention, any method of adding monomers may be used for the polymerization of polyamic acid. The following method is mentioned as a typical polymerization method. That is,
1) A method in which an aromatic diamine is dissolved in an organic polar solvent and this is reacted with a substantially equimolar amount of an aromatic tetracarboxylic dianhydride for polymerization.
2) An aromatic tetracarboxylic dianhydride is reacted with a small molar amount of an aromatic diamine compound in an organic polar solvent to obtain a prepolymer having acid anhydride groups at both ends. Then, the method of superposing | polymerizing using an aromatic diamine compound so that an aromatic tetracarboxylic dianhydride and an aromatic diamine compound may become substantially equimolar in all the processes.
3) An aromatic tetracarboxylic dianhydride and an excess molar amount of the aromatic diamine compound are reacted in an organic polar solvent to obtain a prepolymer having amino groups at both ends. Subsequently, after adding an aromatic diamine compound here, using the aromatic tetracarboxylic dianhydride so that the aromatic tetracarboxylic dianhydride and the aromatic diamine compound are substantially equimolar in all steps. How to polymerize.
4) A method in which an aromatic tetracarboxylic dianhydride is dissolved and / or dispersed in an organic polar solvent and then polymerized using an aromatic diamine compound so as to be substantially equimolar.
5) A method in which a substantially equimolar mixture of aromatic tetracarboxylic dianhydride and aromatic diamine is reacted in an organic polar solvent for polymerization.
And so on. These methods may be used singly or in combination.

  In the present invention, the polyamic acid obtained by using any of the above polymerization methods may be used, and the polymerization method is not particularly limited.

  In this invention, it is also preferable to use the polymerization method which obtains a prepolymer using the diamine component which has a rigid structure mentioned later. By using this method, a polyimide film having a high elastic modulus and a small hygroscopic expansion coefficient tends to be easily obtained. The molar ratio of the diamine having a rigid structure and the acid dianhydride used in preparing the prepolymer in the present method is 100: 70 to 100: 99 or 70: 100 to 99: 100, and further 100: 75 to 100: 90 or 75: 100-90: 100 is preferable. When this ratio is less than the above range, it is difficult to obtain the effect of improving the elastic modulus and the hygroscopic expansion coefficient, and when it exceeds the above range, there are cases where the linear expansion coefficient becomes too small or the tensile elongation becomes small.

  Here, the material used for the polyamic acid composition concerning this invention is demonstrated.

  Suitable tetracarboxylic dianhydrides that can be used in the present invention are pyromellitic dianhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyltetra. Carboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,3,3 ′, 4′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′- Benzophenone tetracarboxylic dianhydride, 4,4′-oxyphthalic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 3,4,9,10-perylenetetracarboxylic acid Dianhydride, bis (3,4-dicarboxyphenyl) propane dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,1-bis (3,4-dicarboxy) Phenyl) eta Dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) ethane dianhydride, oxydiphthalic dianhydride, bis (3,4-dicarboxyphenyl) Sulfone dianhydride, p-phenylenebis (trimellitic acid monoester acid anhydride), ethylene bis (trimellitic acid monoester acid anhydride), bisphenol A bis (trimellitic acid monoester acid anhydride) and the like These can be used alone or in a mixture of any proportion.

  Suitable diamines that can be used in the polyamic acid composition that is a precursor of the high heat-resistant polyimide according to the present invention include 4,4′-diaminodiphenylpropane, 4,4′-diaminodiphenylmethane, benzidine, and 3,3 ′. -Dichlorobenzidine, 3,3'-dimethylbenzidine, 2,2'-dimethylbenzidine, 3,3'-dimethoxybenzidine, 2,2'-dimethoxybenzidine, 4,4'-diaminodiphenyl sulfide, 3,3'- Diaminodiphenylsulfone, 4,4′-diaminodiphenylsulfone, 4,4′-oxydianiline, 3,3′-oxydianiline, 3,4′-oxydianiline, 1,5-diaminonaphthalene, 4,4 '-Diaminodiphenyldiethylsilane, 4,4'-diaminodiphenylsilane, 4,4'-di Minodiphenylethylphosphine oxide, 4,4′-diaminodiphenyl N-methylamine, 4,4′-diaminodiphenyl N-phenylamine, 1,4-diaminobenzene (p-phenylenediamine), 1,3-diaminobenzene, 1,2-diaminobenzene, bis {4- (4-aminophenoxy) phenyl} sulfone, bis {4- (4-aminophenoxy) phenyl} propane, bis {4- (3-aminophenoxy) phenyl} sulfone, 4 , 4′-bis (4-aminophenoxy) biphenyl, 4,4′-bis (3-aminophenoxy) biphenyl, 1,3-bis (3-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) ) Benzene, 1,3-bis (4-aminophenoxy) benzene, 1,3-bis (3-aminophenyl) Enoxy) benzene, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone and the like.

  As the diamine component, a diamine having a rigid structure and an amine having a flexible structure can be used in combination. In the present invention, the diamine having a rigid structure is

一般式（１）

式中のＲ２は

General formula (1)

R2 in the formula is

一般式群（１）
で表される２価の芳香族基からなる群から選択される基であり、式中のＲ₃は同一または異なってＨ−，ＣＨ₃−、−ＯＨ、−ＣＦ₃、−ＳＯ₄、−ＣＯＯＨ、−ＣＯ-ＮＨ₂、Ｃｌ−、Ｂｒ−、Ｆ−、及びＣＨ₃Ｏ−からなる群より選択される何れかの１つの基である）
で表されるものをいう。

General formula group (1)
And R _{3 in} the formula is the same or different and is H—, CH ₃ —, —OH, —CF ₃ , —SO ₄ , —, or a group selected from the group consisting of divalent aromatic groups. Any one group selected from the group consisting of COOH, —CO—NH ₂ , Cl—, Br—, F—, and CH ₃ O—)
The one represented by

  The diamine having a flexible structure is a diamine having a flexible structure such as an ether group, a sulfone group, a ketone group, or a sulfide group, and is preferably represented by the following general formula (2).

一般式（２）
（式中のＲ₄は、

General formula (2)
(R ₄ in the formula is

で表される２価の有機基からなる群から選択される基であり、式中のＲ₅は同一または異なって、Ｈ−，ＣＨ₃−、−ＯＨ、−ＣＦ₃、−ＳＯ₄、−ＣＯＯＨ、−ＣＯ-ＮＨ₂、Ｃｌ−、Ｂｒ−、Ｆ−、及びＣＨ₃Ｏ−からなる群より選択される１つの基である。）
本発明において用いられる高耐熱性ポリイミド層は、上記の範囲の中で所望の特性を有するなるように適宜芳香族酸二無水物および芳香族ジアミンの種類、配合比を決定して用いることにより得ることができる。

R _{5 in} the formula is the same or different and is H—, CH ₃ —, —OH, —CF ₃ , —SO ₄ , —, or a group selected from the group consisting of divalent organic groups represented by One group selected from the group consisting of COOH, —CO—NH ₂ , Cl—, Br—, F—, and CH ₃ O—. )
The high heat-resistant polyimide layer used in the present invention is obtained by appropriately determining the types and blending ratios of aromatic dianhydride and aromatic diamine so as to have desired characteristics within the above range. be able to.

  As the preferred solvent for synthesizing the polyamic acid, any solvent can be used as long as it dissolves the polyamic acid. However, amide solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, N- Examples thereof include methyl-2-pyrrolidone, and N, N-dimethylformamide and N, N-dimethylacetamide can be particularly preferably used.

  In addition, a filler can be added for the purpose of improving various film properties such as slidability, thermal conductivity, conductivity, corona resistance, and loop stiffness. Any filler may be used, but preferred examples include silica, titanium oxide, alumina, silicon nitride, boron nitride, calcium hydrogen phosphate, calcium phosphate, mica and the like.

The particle size of the filler is not particularly limited because it is determined by the film characteristics to be modified and the kind of filler to be added, but generally the average particle size is 0.05 to 100 μm, preferably 0.1. It is -75 micrometers, More preferably, it is 0.1-50 micrometers, Most preferably, it is 0.1-25 micrometers. If the particle size is below this range, the modification effect is less likely to appear. If the particle size is above this range, the surface properties may be greatly impaired or the mechanical properties may be greatly deteriorated. Further, the number of added parts of the filler is not particularly limited because it is determined by the film properties to be modified, the filler particle diameter, and the like. Generally, the addition amount of the filler is 0.01 to 100 parts by weight, preferably 0.01 to 90 parts by weight, and more preferably 0.02 to 80 parts by weight with respect to 100 parts by weight of the polyimide. If the amount of filler added is less than this range, the effect of modification by the filler hardly appears, and if it exceeds this range, the mechanical properties of the film may be greatly impaired. Addition of filler
1. 1. A method of adding to a polymerization reaction solution before or during polymerization 2. A method of kneading fillers using three rolls after the completion of polymerization. Any method such as preparing a dispersion containing filler and mixing it with a polyamic acid organic solvent solution may be used, but a method of mixing a dispersion containing filler with a polyamic acid solution, particularly immediately before film formation. This method is preferable because the contamination by the filler in the production line is minimized. When preparing a dispersion containing a filler, it is preferable to use the same solvent as the polymerization solvent for the polyamic acid. Further, in order to disperse the filler satisfactorily and stabilize the dispersion state, a dispersant, a thickener and the like can be used within a range not affecting the film physical properties.

  The solution containing the precursor of the non-thermoplastic polyimide resin thus obtained is also referred to as a solution containing a precursor of high heat resistant polyimide.

  The thermoplastic polyimide layer according to the present invention has a thermoplastic polyimide resin content and molecular structure contained in the layer as long as desired properties such as a significant adhesive force with a conductor and a suitable linear expansion coefficient are expressed. The thickness is not particularly limited. However, it is preferable that substantially 50 wt% or more of the thermoplastic polyimide resin is substantially contained in order to exhibit desired properties such as a significant adhesive force and a suitable linear expansion coefficient.

  As the thermoplastic polyimide contained in the thermoplastic polyimide layer, thermoplastic polyimide, thermoplastic polyamideimide, thermoplastic polyetherimide, thermoplastic polyesterimide and the like can be suitably used.

  The thermoplastic polyimide contained in the thermoplastic polyimide layer according to the present invention is obtained by a conversion reaction from the precursor polyamic acid. As the method for producing the polyamic acid, any known method can be used as in the precursor of the high heat resistant polyimide layer.

  Also, considering that it exhibits a significant adhesive force with the conductor layer and does not impair the heat resistance of the resulting copper-clad laminate, the thermoplastic polyimide in the present invention is glass in the range of 150 to 300 ° C. It preferably has a transition temperature (Tg). In addition, Tg can be calculated | required from the value of the inflexion point of the storage elastic modulus measured with the dynamic viscoelasticity measuring apparatus (DMA).

  The polyamic acid that is a precursor of the thermoplastic polyimide used in the present invention is not particularly limited, and any known polyamic acid can be used. Regarding the production of the polyamic acid solution, the raw materials and the production conditions can be used in exactly the same manner.

  The properties of thermoplastic polyimide can be adjusted by combining various raw materials to be used, but generally the glass transition temperature becomes higher and / or the storage elastic modulus during heat when the ratio of rigid diamine is increased. Is unfavorable because it increases the adhesion and processability. The diamine ratio of the rigid structure is preferably 40 mol% or less, more preferably 30 mol% or less, and particularly preferably 20 mol% or less.

  Specific examples of preferable thermoplastic polyimide resins include those obtained by polymerization reaction of acid dianhydrides including biphenyltetracarboxylic dianhydrides and diamines having aminophenoxy groups.

  Furthermore, for the purpose of controlling the characteristics of the insulating layer according to the present invention, inorganic or organic fillers, and other resins may be added as necessary.

  The method for obtaining an insulating layer according to the present invention is not particularly limited, but a multi-layer liquid film is formed into an endless drum or endless using two or more types of solutions containing a polyimide resin-containing solution and / or a precursor thereof. It is preferably produced by a production method comprising a step of forming on a smooth support such as a belt and then allowing drying and imidization to proceed. The method of forming a multi-layer liquid film on a smooth support is a method using a multilayer die, a method using a slide die, a method of arranging a plurality of single-layer dies, a method of combining a single-layer die with spray coating or gravure coating, etc. Conventionally known methods can be used. However, in consideration of productivity, maintainability, etc., a coextrusion-cast coating method using a multilayer die is particularly preferable. In particular, by producing an insulating layer in which a thermoplastic polyimide layer is provided on both sides of a high heat-resistant polyimide layer by a coextrusion-casting method using a multilayer die, the interface of each layer is not clarified, It becomes possible to disperse the stress when the copper-clad laminate using this is bent. As a result, the bending resistance is improved, which is a preferred embodiment in the present invention.

  Hereinafter, a coextrusion-casting method using a multilayer die will be described as an example.

  First, a solution containing a precursor of a high heat-resistant polyimide and a solution containing a thermoplastic polyimide or a solution containing a precursor of a thermoplastic polyimide are supplied to a multilayer die having three or more layers, from the outlet of the multilayer die Both solutions are extruded as a multi-layer liquid film. Next, a plurality of liquid films extruded from the multilayer die are cast onto a substrate, and at least a part of the solvent of the plurality of liquid films on the support is volatilized. A multilayer film having self-supporting properties is obtained. Further, the multilayer film is peeled off from the support, and finally the dried liquid film is sufficiently heated at a high temperature (250 to 600 ° C.) to substantially remove the solvent and advance imidization. Thus, the target insulating layer is obtained. In order to improve the melt fluidity of the thermoplastic polyimide layer, the imidization rate may be intentionally lowered and / or the solvent may be left.

  Particularly limited with respect to the method of volatilization of the solvent in the precursor solution of the high heat resistant polyimide extruded from the die for extrusion molding of three or more layers and the solution containing the thermoplastic polyimide or the precursor of the thermoplastic polyimide Although not, the method by heating and / or blowing is the simplest method. If the temperature at the time of heating is too high, the solvent will be volatilized rapidly, and the trace of the volatilization will cause micro defects to form in the insulating layer that is finally obtained. Preferably there is.

  As for the imidization time, it suffices to take a sufficient time for the imidization and drying to be substantially completed, and it is not uniquely limited, but generally it is appropriately set within a range of about 10 to 1800 seconds. Is done.

  As the above-mentioned three or more layers of extrusion forming dies, those having various structures can be used. For example, a die for forming a film for plural layers can be used. In addition, any conventionally known structure can be suitably used, but feed block dies and multi-manifold dies are exemplified as particularly suitable ones.

  In general, polyimide is obtained by a dehydration conversion reaction from a polyimide precursor, that is, a polyamic acid. As a method for performing the conversion reaction, a thermal curing method that is performed only by heat, and a chemical curing that includes a chemical dehydrating agent and a catalyst. Two methods of chemical curing using an agent are most widely known. However, considering the production efficiency, the chemical curing method is more preferable.

  As the chemical dehydrating agent according to the present invention, dehydrating ring-closing agents for various polyamic acids can be used, but aliphatic acid anhydrides, aromatic acid anhydrides, N, N′-dialkylcarbodiimides, lower aliphatic halides, halogenated compounds. Lower aliphatic acid anhydrides, aryl sulfonic acid dihalides, thionyl halides or mixtures of two or more thereof can be preferably used. Of these, aliphatic acid anhydrides and aromatic acid anhydrides work particularly well. In addition, the term “catalyst” refers to a component that has an effect of promoting the dehydration ring-closing action of a chemical dehydrating agent on polyamic acid. For example, an aliphatic tertiary amine, an aromatic tertiary amine, or a heterocyclic tertiary amine is used. be able to. Of these, nitrogen-containing heterocyclic compounds such as imidazole, benzimidazole, isoquinoline, quinoline, and β-picoline are particularly preferable. Furthermore, introduction of an organic polar solvent into a solution composed of a dehydrating agent and a catalyst can be appropriately selected.

  The preferable amount of the chemical dehydrating agent is 0.5 to 5 mol, preferably 0.7 to 4 mol, based on 1 mol of the amic acid unit in the polyamic acid contained in the solution containing the chemical dehydrating agent and the catalyst. . Moreover, the preferable amount of a catalyst is 0.05-3 mol with respect to 1 mol of amic acid units in the polyamic acid contained in the solution which contains a chemical dehydrating agent and a catalyst, Preferably it is 0.2-2 mol. . If the dehydrating agent and the catalyst are below the above ranges, chemical imidization may be insufficient, and may break during firing or mechanical strength may decrease. Moreover, when these amounts exceed the above range, the progress of imidization becomes too fast, and it may be difficult to cast into a film, which is not preferable.

  The insulating layer according to the present invention is integrated with a metal foil to form a copper clad laminate. In consideration of dimensional stability when processed into a copper-clad laminate, it is preferable to control the thermal expansion coefficient of the insulating layer as follows.

  The thermal expansion coefficient at 50 to 200 ° C. is preferably 20 to 24 ppm / ° C., more preferably 21 to 23 ppm / ° C.

  When the thermal expansion coefficient of the insulating layer exceeds the above range, the thermal expansion coefficient becomes too larger than that of the metal foil, so the difference in thermal behavior between the insulating layer and the metal foil during lamination becomes large, and the resulting flexible copper clad laminate In some cases, the dimensional change may be large. When the thermal expansion coefficient is below the above range, the thermal expansion coefficient of the insulating layer is too small compared to the metal foil, so the difference in thermal behavior during lamination is also large, and the dimensional change of the resulting flexible copper clad laminate May become larger.

  As a method of controlling the thermal expansion coefficient of the insulating layer, a method of adjusting drying conditions and baking conditions, a method of adjusting the amount of the chemical curing agent, a method of adjusting the thickness ratio of the high heat-resistant polyimide layer and the thermoplastic polyimide layer, etc. Any of them may be used, or a plurality of methods may be mixed and used.

  The preferable combination of thickness of each layer of the insulating layer is 7.5 to 13 μm for the high heat-resistant polyimide layer and 1.2 to 2.5 μm for the thermoplastic polyimide layer. When it exists in this range, the bending resistance of the obtained copper clad laminated board will become favorable.

  The coefficient of thermal expansion can be measured using, for example, TMA120C manufactured by Seiko Electronics Co., Ltd. After the sample temperature is raised from 10 ° C. to 400 ° C. at 10 ° C./min with a width of 3 mm, a length of 10 mm, and a load of 3 g. It is a value calculated as an average value from the coefficient of thermal expansion from 100 ° C. to 200 ° C. during the second temperature increase after cooling to 10 ° C. and further raising the temperature at 10 ° C./min.

  In order to improve the bending resistance of the obtained copper-clad laminate, the thickness of the insulating layer is preferably 16 μm or less. More preferably, it is 10-16 micrometers.

<Copper foil>
The copper foil used in the present invention is preferably a copper foil having a thickness of 20 μm or less from the viewpoint of improving the bending resistance of the obtained copper-clad laminate. More preferably, it is 8-20 micrometers. A copper foil with a carrier may be used. Examples of the copper foil include rolled copper foil and electrolytic copper foil. In consideration of the production cost of the copper clad laminate, electrolytic copper foil is preferably used.

<Method for producing copper-clad laminate>
As described above, the method for producing the copper clad laminate according to the present invention includes casting, coating and sputtering of polyamic acid which is a precursor of polyimide on a metal foil, followed by imidization, sputtering, and plating. The metallizing method which provides a metal layer directly on a polyimide film and the laminating method which bonds a polyimide film and metal foil through a thermoplastic polyimide are illustrated, and any method may be used. Among these, the laminating method is particularly preferable because the thickness range of the corresponding metal foil is wider than that of the casting method and the apparatus cost is lower than that of the metalizing method. Hereinafter, a laminating method in which an insulating layer and a metal foil are laminated will be described.

  Examples of the laminating apparatus include a hot roll laminating apparatus having a pair of metal rolls or a double belt press (DBP). Among these, it is preferable to use a hot roll laminating apparatus having a pair of metal rolls because the apparatus configuration is simple and advantageous in terms of maintenance cost. The “heat roll laminating apparatus having a pair of metal rolls” herein may be an apparatus having a metal roll for heating and pressurizing a material, and the specific apparatus configuration is particularly limited. It is not a thing.

  It is preferable that the flexible copper clad laminated board concerning this invention uses the laminating method using the continuous process by the hot roll laminating apparatus which has a pair or more metal roll. However, when a copper clad laminate is manufactured by a laminating method using a thin copper foil, there may be a problem such as wrinkles.

  That is, when using a hot roll laminating apparatus having a pair of metal rolls, lamination is performed at a high temperature. Moreover, since the heating roll with which a hot roll laminating apparatus is equipped and a laminated material are line-contacted, a pressure is applied locally to a laminated material. In particular, when the thickness of the film-like joining member is thin, it is difficult to uniformly apply pressure to the material to be laminated at the time of lamination.

  However, by appropriately selecting a method for producing a copper clad laminate, it is possible to easily produce a copper clad laminate having a desired stiffness value with no appearance abnormality.

  Therefore, it is preferable that the tension applied to the insulating layer during heat lamination when manufacturing a copper clad laminate is within a specific range, thereby effectively suppressing abnormal appearance such as wrinkles in the obtained copper clad laminate. be able to. Specifically, it is in the range of 0.01 to 1 N / cm, preferably in the range of 0.1 to 1 N / cm, and more preferably in the range of 0.3 to 1 N / cm. In order to ensure the transportability of the insulating layer, it is difficult to reduce the tension applied to the insulating layer during thermal lamination, and this method is not a method usually employed, but it is intended to reduce the tension applied to the insulating layer. Thus, a copper clad laminate having no appearance abnormality can be obtained. The tension applied to the insulating layer refers to the tension applied to the insulating layer immediately before entering the laminate roll, and can be detected by the tension pickup roll.

  In this invention, it is preferable that the process (process (2)) by which the said insulating layer is conveyed through an expander roll is included before the process (process (1)) of carrying out heat lamination.

  In the step (1), the heating method of the material to be laminated at the time of heat lamination (step of heat lamination) is not particularly limited. For example, it is possible to use a heating means employing a conventionally known method that can heat at a predetermined temperature, such as a heat circulation method, a hot air heating method, an induction heating method, or the like. Similarly, the method for pressurizing the material to be laminated at the time of thermal lamination is not particularly limited. For example, it is possible to use a pressurizing means that employs a conventionally known method that can apply a predetermined pressure, such as a hydraulic method, a pneumatic method, or a gap pressure method.

  The heating temperature at the time of thermal lamination (hereinafter also referred to as “laminate temperature”) is preferably a glass transition temperature (Tg) of the insulating layer + 50 ° C. or higher, and more preferably Tg + 100 ° C. or higher of the insulating layer. If it is Tg + 50 degreeC or more, an insulating layer and metal foil can be heat-laminated favorably. Moreover, if it is Tg + 100 degreeC or more, the lamination speed can be raised and the productivity of a flexible metal-clad laminated board can be improved more. In general, the laminating temperature is preferably 300 ° C to 500 ° C. The laminating speed during thermal lamination is preferably 0.5 to 10 m / min, more preferably 1.0 to 10 m / min. If it is 0.5 m / min or more, sufficient thermal lamination is possible, and if it is 1.0 m / min or more, productivity can be further improved.

  Furthermore, the higher the pressure at the time of thermal lamination, that is, the lamination pressure, there is an advantage that the lamination temperature can be lowered and the lamination speed can be increased. However, generally, when the laminating pressure is too high, the dimensional change of the obtained laminate tends to deteriorate. On the other hand, when the lamination pressure is too low, the adhesive strength of the copper foil of the resulting laminate is reduced. Therefore, the laminating pressure is preferably in the range of 49 to 490 N / cm 2 (5 to 50 kgf / cm 2), and more preferably in the range of 98 to 294 N / cm 2 (10 to 30 kgf / cm 2). Within this range, the three conditions of laminating temperature, laminating speed, and laminating pressure can be improved, and productivity can be further improved.

By having a process in which the insulating layer is transported through the expander roll, sagging and undulation of the insulating layer can be eliminated to ensure transportability, and a copper-clad laminate having the desired stiffness can be obtained. As shown in FIG. 1, the expander roll is preferably combined with other rolls so that the film is conveyed in an S shape, which is effective and preferable. It is preferable to install the expander roll at a distance as close as possible to the heat laminating roll as far as the apparatus is possible, preferably within 1.5 m immediately before the heat laminating roll, and more preferably within 1.0 m. Is good. Most preferably, it should be installed within 0.5 m immediately before thermal lamination.
Known expander rolls can be used. The size and material of the insulating layer to be thermally laminated can take an optimum form, but the material is low surface friction that prevents the joining member from meandering from the viewpoint of transportability of the insulating layer, and effectively It is preferable to have frictional properties that can eliminate sagging and waviness. Moreover, it is preferable that the edge of the expander roll has rubber properties so as not to damage the insulating layer. The size is preferably the minimum size that can eliminate sagging and undulations.

  Further, in the present invention, the specific configuration of the means for carrying out the thermal lamination is not particularly limited, but in order to improve the appearance of the resulting laminate, the space between the pressing surface and the metal foil is not limited. It is preferable to arrange a protective film.

  The protective film may be any film that can withstand the heating temperature during thermal lamination, and examples thereof include heat-resistant plastics such as non-thermoplastic polyimide films, copper foils, aluminum foils, and metal foils such as SUS foils. It is done. Among these, a non-thermoplastic polyimide film can be suitably used from the viewpoint of excellent balance between heat resistance and reusability.

  Moreover, when the thickness of the protective film is thin, the role of buffering and protection during lamination cannot be sufficiently achieved. Therefore, when a non-thermoplastic polyimide film is used as the protective film, the thickness is preferably 75 μm or more.

  The protective film is not necessarily a single layer, and may have a multilayer structure of two or more layers having different characteristics.

  Further, since the adhesive layer contains thermoplastic polyimide, the lamination temperature becomes very high. Therefore, if the protective film is used as it is for the laminate, the appearance and dimensional stability of the resulting flexible metal-clad laminate may be deteriorated due to rapid thermal expansion. Therefore, it is preferable to preheat the protective film before lamination.

  Examples of the preheating means include a method in which the protective film is brought into contact with a heat roll. Whichever method is employed, it is preferable that the surface temperature of the protective film is within the range of “the surface temperature of the hot roll−10 ° C. to the surface temperature of the hot roll” during lamination. Here, the “surface temperature of the protective film” refers to the temperature of the surface in contact with the metal foil during lamination.

  By setting the surface temperature of the protective film within the above range, since the thermal expansion of the protective film is completed at the time of lamination, it is possible to suppress the appearance and dimensional change of the flexible metal-clad laminate. If the surface temperature of the protective film deviates from the above range, lamination is performed without completing the thermal expansion of the protective film, so rapid thermal expansion occurs during lamination, and the appearance and dimensional changes of the resulting laminate may deteriorate. There is sex.

  The distance and time for holding the protective film on the hot roll are not particularly limited, and may be appropriately adjusted from the thickness of the protective film, the diameter of the hot roll, the lamination speed, and the like. About the surface temperature of a protective film and a heat roll, it can measure by well-known methods, such as a contact-type thermometer and a thermocouple.

  Moreover, it is preferable that the tension | tensile_strength concerning the said protective film in the range of 600-2000 N / m at the time of a thermal lamination. By setting it as the said structure, generation | occurrence | production of the sagging of a protective film, wrinkles, etc. can be suppressed, without cut | disconnecting a film. Therefore, there is an effect that a metal-clad laminate having a good appearance can be obtained.

  Further, in the present invention, before the step of heat laminating (the above step (1)), the insulating layer is heat laminated via a herringbone roll instead of the step of transporting via an expander roll. A feature step (step (3)) may be included.

  The insulating layer has a step of being conveyed through a herringbone roll, but is performed prior to the thermal laminating step, thereby eliminating slack and undulation that occurs in the insulating layer, ensuring transportability, and a desired stiffness value. A copper clad laminate having the following is obtained. As shown in FIG. 1, the herringbone roll is preferably combined with other rolls so that the film is conveyed in an S-shape, which is effective and preferable. The installation place of the herringbone roll is preferably installed as close to the heat laminating roll as possible in terms of equipment, preferably within 1.5 m immediately before the heat laminating roll, more preferably within 1.0 m. Is good. Most preferably, it should be installed within 0.5 m immediately before thermal lamination.

  Known herringbone rolls can be used. Its size and material can take the optimum form depending on the insulating layer to be heat-laminated, but the material is low surface friction that prevents the insulating layer from meandering from the viewpoint of the transportability of the insulating layer, and effectively It is preferable to have frictional properties that can eliminate sagging and waviness. Further, the surface irregularities of the herringbone roll are preferably those having no edge, and specifically, a rubber herringbone roll having an appropriate elastic modulus and hardness can effectively reduce sagging and undulation. The size is preferably the minimum size that can eliminate sagging and undulations. The angle of the spiral groove on the surface is preferably 45 ° or less, more preferably 30 ° or less when the roll axis is 0 °.

  In the flexible copper-clad laminate obtained by the manufacturing method according to the present invention, the dimensional change rate before and after removing the metal foil, and the total value of the dimensional change rate before and after heating at 250 ° C. for 30 minutes after removing the metal foil. However, it is very preferable that both the MD direction and the TD direction are in the range of -0.08 to +0.08. The rate of dimensional change before and after removal of the metal foil is expressed as a ratio between a difference between a predetermined dimension in the flexible copper-clad laminate before the etching process and a predetermined dimension after the etching process, and a predetermined dimension before the etching process. . The dimensional change rate before and after heating is represented by a ratio between a difference between a predetermined dimension in the flexible copper-clad laminate after the etching process and a predetermined dimension after the heating process and a predetermined dimension after the etching process.

  If the dimensional change rate is out of this range, the dimensional change at the time of component mounting will become large after forming fine wiring in the flexible copper clad laminate, and it will deviate from the component mounting position at the design stage. Become. As a result, there is a possibility that the component to be mounted and the board are not connected well. In other words, if the rate of dimensional change is within the above range, it can be considered that there is no problem in component mounting.

  The method for measuring the dimensional change rate is not particularly limited, and any method known in the art can be used as long as it is a method capable of measuring increase / decrease in dimensions before and after the etching or heating process in the flexible copper-clad laminate. Can be used.

  Here, it is essential to measure the dimensional change rate in both the MD direction and the TD direction. In the case of continuous imidization and lamination, since the method of applying tension differs in the MD direction and the TD direction, a difference appears in the degree of thermal expansion / contraction and the dimensional change rate also differs. Therefore, a material having a small dimensional change rate is required to have a low change rate in both the MD direction and the TD direction. In the present invention, the dimensional change rate before and after removing the metal foil of the flexible copper-clad laminate, and the total value of the dimensional change rate before and after heating at 250 ° C. for 30 minutes after removing the metal foil are MD direction, It is very preferable that the TD direction is in the range of -0.08 to +0.08.

  In addition, the specific conditions of the etching process at the time of measuring a dimensional change rate are not specifically limited. That is, since the etching conditions differ depending on the type of metal foil and the shape of the pattern wiring to be formed, the etching process conditions for measuring the dimensional change rate in the present invention are any conventionally known conditions. Also good. Similarly, in the heating process, it is sufficient that heating is performed at 250 ° C. for 30 minutes, and specific conditions are not particularly limited.

  The copper-clad laminate according to the present invention can be used as an FPC on which various miniaturized and high-density components are mounted if a desired pattern wiring is formed by etching a metal foil. Of course, the application of the present invention is not limited to this, and it goes without saying that it can be used for various applications as long as it is a laminate including a metal foil.

Examples of the method of the present invention will be specifically described below, but the present invention is not limited to these examples.

In addition, the evaluation method of the various characteristics in a synthesis example, an Example, and a comparative example is as follows.
[Loop stiffness]
Using a loop stiffness tester manufactured by Toyo Seiki, the sample width was 5 to 10 mm, the loop length was 50 mm, and the crushing distance was 10 mm. The sample width was appropriately set so that the measured value was 5 to 15 g depending on the film thickness. A five-point sample was taken so that the long axis of the sample was randomly oriented with respect to the plane of the copper-clad laminate, and the average value of the measured values at the five points was taken as the loop stiffness value of the sample.
[Bending resistance]
A pattern of a bending resistance test sample disclosed in JISC6471 was prepared on the prepared copper-clad laminate, and a 1.5 cm × 15 cm bending resistance test sample was prepared. Using this, the number of times until conduction was interrupted was measured under the conditions of a load of 750 g and a bending diameter of 0.38 mm in accordance with JISC5016. A 5-point sample was taken so that the long axis of the sample was randomly oriented with respect to the plane of the copper-clad laminate, and the average value of the measured values at the 5 points was taken as the bending resistance value of the sample. Is 350 times or more, and less than that is x.

(Synthesis Example 1: Synthesis of polyamic acid as a precursor of high heat-resistant polyimide)
In a reaction vessel with a capacity of 350 L, 234 kg of DMF and 19.9 kg of BAPP were added and stirred. 3.9 kg of 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride (BTDA) was added and dissolved, and then 6.9 kg of PMDA was added and stirred for 30 minutes to give a thermoplastic polyimide precursor. A body block component was formed.

  After 7.9 kg of p-phenylenediamine (p-PDA) was dissolved in this solution, 16.1 kg of PMDA was added and stirred for 1 hour to dissolve. Furthermore, a DMF solution of PMDA (PMDA 0.8 kg / DMF 10.5 kg) prepared separately was added carefully to this solution, and the addition was stopped when the viscosity reached about 3000 poise, and a precursor solution of high heat resistant polyimide was added. Obtained.

(Synthesis Example 2: Synthesis of polyamide acid precursor of thermoplastic polyimide)
To a reaction vessel having a capacity of 350 L, 248 kg of dimethylformamide (DMF) and 17.5 kg of 3,3′4,4′-biphenyltetracarboxylic dianhydride (BPDA) were added and stirred under a nitrogen atmosphere. To the solution, 41.4 g of 10% DMF dispersion of calcium hydrogenphosphate particles having a particle size distribution with a median average diameter of 2 μm and a particle size ratio of 7 μm or more is 0.05%, and sufficiently stirred. did. Then, 24.0 kg of 2,2-bis [4- (4-aminophenoxy) phenyl] propane (BAPP) was gradually added. A solution in which 0.5 kg of BPDA was dissolved in 10 kg of DMF was separately prepared, and this was gradually added to the reaction solution while being careful of the viscosity and stirred. When the viscosity reached 400 poise, the addition and stirring were stopped to obtain a thermoplastic polyimide precursor solution.
Example 1
The following chemical dehydrating agent and catalyst were contained in the polyamic acid solution of the precursor of the high heat-resistant polyimide obtained in Synthesis Example 1.
Chemical dehydrating agent: 2.0 mol per 1 mol of polyamic acid amic acid unit of acetic anhydride as precursor of high heat resistant polyimide Catalyst: 1 mol of amic acid unit of polyamic acid as precursor of high heat resistant polyimide Next, from the multi-manifold type three-layer coextrusion multilayer die having a lip width of 650 mm, the outer layer is a precursor of thermoplastic polyimide on the SUS endless belt running 15 mm below the die. Extrusion casting was carried out in the order in which the polyamic acid solution of the body and the inner layer became the polyamic acid solution of the precursor of the highly heat-resistant polyimide solution. Next, the multilayer film was heated at 130 ° C. for 100 seconds to be converted into a self-supporting gel film. Furthermore, the self-supporting gel film peeled off from the endless belt is fixed to a tenter clip, and dried and imidized at 300 ° C. × 16 seconds, 400 ° C. × 29 seconds, 500 ° C. × 17 seconds, and a thermoplastic polyimide layer Thus, an insulating layer with good appearance was obtained in which the thicknesses of the high heat-resistant polyimide layer and the thermoplastic polyimide layer were 2 μm, 10 μm, 2 μm, and 14 μm in total.

  Using a 9 μm rolled copper foil (BHY-22B, manufactured by Japan Energy) on both sides of the obtained insulating layer and a protective material (Apical 125 NPI: manufactured by Kaneka Corporation) on both sides of the copper foil, the tension of the polyimide film is 0. A copper-clad laminate was produced by continuous thermal lamination under the conditions of .4 N / cm, laminating temperature 380 ° C., laminating pressure 196 N / cm (20 kgf / cm), laminating speed 1.5 m / min. Note that an expander roll is inserted immediately before the thermal laminator to carry out lamination. When lamination is performed in this configuration, the total thickness of the copper foil is 18 μm.

The loop stiffness value of the produced copper clad laminate was measured and found to be 0.20 N / cm. Moreover, it was (circle) since it was 512 times as a result of the bending resistance test.
(Example 2)
A copper clad laminate was prepared in the same manner as in Example 1 except that 9 μm electrolytic copper foil (USLP-SE, manufactured by Nippon Electrolytic Co., Ltd.) was used instead of 9 μm electrolytic copper foil. When lamination is performed in this configuration, the total thickness of the copper foil is 18 μm.

The loop stiffness value of the produced copper-clad laminate was measured and found to be 0.21 N / cm. Moreover, since it was 487 times as a result of the bending resistance test, it was (circle).
(Example 3)
A copper clad laminate was prepared in the same manner as in Example 1 except that 12 μm electrolytic copper foil (USLP-SE, manufactured by Nippon Electrolytic Co., Ltd.) was used instead of 9 μm electrolytic copper foil. When lamination is performed in this configuration, the total thickness of the copper foil is 24 μm.

It was 0.29 N / cm when the loop stiffness value of the produced copper clad laminated board was measured. Moreover, it was (circle) since it was 412 times as a result of the bending resistance test.
(Comparative Example 1)
A copper clad laminate was prepared in the same manner as in Example 1 except that 18 μm rolled copper foil (BHY-22B, manufactured by Japan Energy Co., Ltd.) was used instead of 9 μm electrolytic copper foil. When lamination is performed in this configuration, the total thickness of the copper foil is 36 μm.

It was 0.48 N / cm when the loop stiffness value of the produced copper clad laminated board was measured. Moreover, since it was 307 times as a result of the bending resistance test, it was x.
(Comparative Example 2)
A copper-clad laminate was prepared in the same manner as in Example 1 except that the thickness of the insulating layer was 4 μm, 17 μm, 4 μm, and the total thickness of the thermoplastic polyimide layer, high heat-resistant polyimide layer, and thermoplastic polyimide layer was 25 μm. did.

  The loop stiffness value of the produced copper clad laminate was measured and found to be 0.33 N / cm. Moreover, since it was 332 times as a result of the bending resistance test, it was x.

  Although the insulating layer according to the present invention has been described above, the present invention is not limited to the above-described embodiment. Needless to say, the present invention can be implemented in a mode in which various modifications are made within the scope described above.

It is a side surface schematic diagram of one specific example of the lamination process which manufactures the copper clad laminated board of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1; Expander roll 2; Insulating layer 3; Copper foil 4;

Claims (8)

A copper-clad laminate comprising a copper foil on both surfaces of an insulating layer containing at least one polyimide layer, wherein the loop stiffness value is 0.30 N / cm or less. . The copper-clad laminate according to claim 1, wherein the insulating layer has a multi-layer structure in which a thermoplastic polyimide layer is provided on both surfaces of a high heat-resistant polyimide layer. The copper-clad laminate according to claim 2, wherein the high heat-resistant polyimide layer has a thickness of 7.5 to 13 µm, and the thermoplastic polyimide layer has a thickness of 1.2 to 2.5 µm. The copper clad laminate according to claim 1, wherein the insulating layer has a thickness of 16 μm or less. The copper-clad laminate according to claim 3, wherein a linear expansion coefficient of the insulating layer is 20 to 24 ppm. The copper-clad laminate according to claim 1, wherein the total thickness of the copper foil is 20 μm or less. The copper clad laminate according to claim 1, wherein a copper foil is laminated on both surfaces of the insulating layer by a hot roll laminating method. The copper-clad laminate according to claim 1, wherein the copper-clad laminate is used for bending in an α-winding or z-winding form.

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