TWI869385B - Metal-clad laminates and circuit boards - Google Patents

Abstract

The present invention provides a metal-clad laminate including an insulating resin layer having high dimensional stability and in-plane isotropy even when the insulating resin layer is thin and excellent adhesion to a metal layer, and also suppressing curling of the metal-clad laminate and a film after etching the metal layer. A metal-clad laminate includes an insulating resin layer and a metal layer laminated on one side of the insulating resin layer, wherein the insulating resin layer has a non-thermoplastic polyimide layer composed of non-thermoplastic polyimide and a thermoplastic polyimide layer composed of thermoplastic polyimide disposed in contact with at least one side of the non-thermoplastic polyimide layer. The thermoplastic polyimide layer is interposed between the metal layer and the non-thermoplastic polyimide layer, the thickness of the insulating resin layer is in the range of 2 μm or more and 15 μm or less, and the birefringence Δn (xy-z) in the thickness direction is in the range of 0.080 to 0.140.

Description

Metal-clad laminates and circuit boards

The present invention relates to a metal-clad laminate and a circuit substrate.

In recent years, with the development of miniaturization, lightness and space saving of electronic equipment, the demand for thin and light, flexible, and durable flexible printed circuits (FPC) is increasing. FPC can be installed in a three-dimensional and high-density manner even in a limited space, so its use is expanding to parts such as wiring or cables, connectors, etc. of movable parts of electronic equipment such as hard disk drives (HDD), digital versatile discs (DVD), mobile phones, and smart phones.

FPC is manufactured by etching the metal layer of a metal-clad laminate having a metal layer and an insulating resin layer and performing wiring processing. In the photolithography process of the metal-clad laminate or the process of mounting the FPC, various processes such as bonding, cutting, exposure, and etching are performed. The processing accuracy in these processes is important in maintaining the reliability of electronic devices equipped with FPC. However, metal-clad laminates have a structure in which metal layers and insulating resin layers with different coefficients of thermal expansion (hereinafter sometimes referred to as "CTE") are laminated. Therefore, due to the difference in the coefficient of thermal expansion (CTE) between the metal layer and the insulating resin layer, stress is generated between the layers. The stress is released when the metal layer is etched and wiring is performed, resulting in expansion and contraction, which is the main cause of changes in the dimensions of the wiring pattern. Therefore, dimensional changes ultimately occur at the FPC stage, causing poor connections between wiring or between wiring and terminals, thereby reducing the reliability or yield of the circuit board. Therefore, dimensional stability is a very important characteristic in metal-clad laminates as circuit board materials.

It is expected that electronic devices will become more functional and smaller in the future. Therefore, it is believed that the demand for using FPC in a multi-layered state will increase. In addition, in response to the thinning of the casing of electronic devices such as mobile phones and smart phones, the circuit board itself is also required to be thinner. In the circuit board, when the thickness of the insulating resin layer is reduced, in order to match the impedance, more fine wiring processing is required, so it is necessary to improve the dimensional stability to a higher level than before and suppress curling. In addition, when processing into fine wiring, in order to prevent the wiring from peeling off the substrate, close contact is also required. Therefore, for the insulating resin layer of the circuit board such as FPC, the following characteristics are required more strictly than before. ·Thinning, ·Low thermal expansion (high dimensional stability), ·Reduced in-plane anisotropy (isotropy), ·Low curling (both in the metal-clad laminate state and in the film state after etching), ·Adhesion to the metal layer, etc. If the thickness of the insulating resin layer is an extremely thin layer of 15 μm or less, especially 12 μm or less, the conventional design concept cannot be applied to satisfy the required characteristics other than thickness, and a different approach is required.

As a metal-clad laminate, a copper-clad laminate (CCL) formed by laminating copper foil and polyimide is widely used. A single-layer polyimide film with a thickness of 10 μm or less that can be applied to the insulating resin layer of the CCL has been proposed (Patent Documents 1 to 3). However, regarding the polyimide films proposed in Patent Documents 1 to 3, there is no description related to the reduction of in-plane anisotropy (isotropy). In addition, since it is a single-layer polyimide film, when an adhesive is used when laminating with a metal, the total thickness of the insulating resin layer becomes thicker. Therefore, there is room for improvement from the perspective of reducing the thickness.

In addition, as a metal-clad laminate without an adhesive layer, a metal-clad laminate having an insulating resin layer including a three-layer polyimide layer has been proposed (Patent Document 4). However, Patent Document 4 relates to the improvement of solder resistance after moisture absorption, and there is no disclosure or suggestion about the insulating resin layer having a total thickness of the three-layer polyimide layer of less than 12 μm, and there is room for improvement from the perspective of further thinning the thickness. Furthermore, there is no description about the warping (curling) of the metal-clad laminate or the film after etching. As a method for improving the curling of a metal-clad laminate or a film after etching, the following metal-clad laminate has been proposed: a high thermal expansion polyimide layer is provided on both sides of a low thermal expansion polyimide layer, and the curling of the film is controlled by controlling the thickness ratio of the high thermal expansion polyimide layer (Patent Document 5). However, the insulating resin layer is generally about 25 μm, and there is no record of the control technology when the thickness is reduced.

In addition, a polyimide film with a thickness of about 25 μm has been proposed that can reduce dimensional changes during high-temperature processing by controlling CTE and 0° retardation (Patent Document 6). However, regarding 0° retardation, the thinner the thickness, the more difficult it is to find a difference, and as an indicator of physical property evaluation, there is room for improvement. [Prior art document] [Patent document]

[Patent Document 1] Japanese Patent Publication No. 2016-186031 [Patent Document 2] Japanese Patent Publication No. 2014-196467 [Patent Document 3] Japanese Patent Publication No. 2017-145325 [Patent Document 4] Japanese Patent Publication No. 2016-141152 [Patent Document 5] Japanese Patent Publication No. 2006-306086 [Patent Document 6] Japanese Patent Publication No. 2017-200759

[Problem to be solved by the invention] The object of the present invention is to provide a metal-clad laminate, which includes an insulating resin layer having high dimensional stability and in-plane isotropy even when the thickness of the insulating resin layer is thin, and excellent adhesion to the metal layer, and the curling of the state of the metal-clad laminate and the state of the film after etching the metal layer is also suppressed. [Technical means for solving the problem]

The inventors of the present invention have conducted intensive research and found that the above-mentioned problem can be solved by controlling the birefringence Δn(xy-z) in the in-plane direction and the thickness direction of the insulating resin layer, thereby completing the present invention.

That is, the metal-clad laminate of the present invention is a metal-clad laminate including an insulating resin layer and a metal layer laminated on one side of the insulating resin layer. The insulating resin layer of the metal-clad laminate of the present invention has a non-thermoplastic polyimide layer composed of non-thermoplastic polyimide, and a thermoplastic polyimide layer composed of thermoplastic polyimide provided in contact with at least one side of the non-thermoplastic polyimide layer. Moreover, the metal-clad laminate of the present invention is characterized in that the thermoplastic polyimide layer is interposed between the metal layer and the non-thermoplastic polyimide layer, the thickness of the insulating resin layer is in the range of 2 μm or more and 15 μm or less, and the birefringence Δn (xy-z) in the thickness direction is in the range of 0.080 to 0.140.

In the metal-clad laminate of the present invention, the non-thermoplastic polyimide may contain tetracarboxylic acid residues and diamine residues, and contain 50 mol parts or more of diamine residues derived from a diamine compound represented by the following formula (1) relative to 100 mol parts of all diamine residues.

[Chemistry 1]

In formula (1), R independently represents a halogen atom, an alkyl or alkoxy group having 1 to 6 carbon atoms which may be substituted with a halogen atom, or a phenyl or phenoxy group which may be substituted with a monovalent alkyl group or alkoxy group having 1 to 6 carbon atoms, _n1 independently represents an integer of 0 to 4, and _n2 represents an integer of 0 to 1.

In the metal-clad laminate of the present invention, the insulating resin layer may also have a non-thermoplastic polyimide layer composed of the non-thermoplastic polyimide, and a thermoplastic polyimide layer composed of thermoplastic polyimide disposed in contact with both sides of the non-thermoplastic polyimide layer. Furthermore, in the metal-clad laminate of the present invention, when the thickness of the thermoplastic polyimide layer disposed on the side adjacent to the metal layer is set to T1, the thickness of the non-thermoplastic polyimide layer is set to T2, and the thickness of the thermoplastic polyimide layer disposed on the side opposite to the metal layer is set to T3, the thicknesses of T1, T2, and T3 satisfy the following relational expressions (1) and (2). (1) 0.8≦T3/T1＜1.4 (2) 0.20＜(T1+T3)/(T1+T2+T3)≦0.50

In the metal-clad laminate of the present invention, the CTE of the insulating resin layer may be in the range of 15 ppm/K or more and 30 ppm/K or less, and the CTE (CTE _MD ) in the longitudinal direction (machine direction, MD) and the CTE (CTE _TD ) in the transverse direction (transverse direction, TD) of the insulating resin layer may satisfy the relationship of the following formula (i). |(CTE _MD -CTE _TD )/(CTE _MD +CTE _TD )|≦0.05 …(i)

In the metal-clad laminate of the present invention, the width of the metal-clad laminate may be greater than or equal to 470 mm and the thickness deviation of the insulating resin layer may be within a range of ±0.5 μm.

In the metal-clad laminate of the present invention, in the insulating resin film obtained by etching away the metal layer, when the insulating resin film of 50 mm square is left to stand in a state where the convex surface in the center is in contact with the flat surface under the conditions of 23° C. and 50% RH for 24 hours, the curling amount obtained by calculating the average of the floating amounts at the four corners can be less than 10 mm.

In the metal-clad laminate of the present invention, the diamine residues derived from the diamine compound represented by the general formula (1) may be in the range of 50 to 99 mol parts relative to 100 mol parts of all diamine residues contained in the non-thermoplastic polyimide, and the diamine residues derived from the diamine compound represented by the following general formula (2) may be in the range of 1 to 50 mol parts.

[Chemistry 2]

In formula (2), R independently represents a halogen atom, an alkyl or alkoxy group having 1 to 6 carbon atoms which may be substituted with a halogen atom, or a phenyl or phenoxy group which may be substituted with a monovalent alkyl group or alkoxy group having 1 to 6 carbon atoms, _Z1 independently represents a single bond, a divalent group selected from -O-, -S-, _-CH2- , -CH( _CH3 )-, -C( _CH3 ) _2- , -CO-, _-SO2- , or -NH-, _n3 independently represents an integer of 0 to 4, and _n4 represents an integer of 0 to 2. At least one of _Z1 represents a divalent group selected from -O-, -S-, _-CH2- , -CH( _CH3 )-, -C( _CH3 ) _2- , -CO-, _-SO2- , or -NH-.

The metal-clad laminate of the present invention may also include another metal layer laminated on the insulating resin layer on the side opposite to the metal layer based on the insulating resin layer.

The circuit board of the present invention is formed by processing the metal layer of any of the metal-clad laminates into wiring. [Effect of the invention]

The metal-clad laminate of the present invention includes an insulating resin layer having a thin thickness, high dimensional stability, in-plane isotropy, excellent adhesion to the metal layer, and suppressed curling. Therefore, when performing circuit processing on FPC, etc., the insulating resin layer has excellent dimensional stability and curling is not easy to occur. In addition, since the insulating resin layer is thin, when applied to a multi-layer substrate, the total thickness can be reduced, and high-density mounting can be achieved. In addition, since the insulating resin layer is thin and has excellent adhesion to the metal layer, the heat dissipation from the power device or light-emitting diode (LED) element mounted on the circuit is also excellent, and adhesion can be ensured even in a high-temperature environment. Therefore, the metal-clad laminate of the present invention is also useful for applications that require heat dissipation.

Next, the implementation of the present invention is described.

<Metal-clad laminate> The metal-clad laminate of the present embodiment includes an insulating resin layer and a metal layer laminated on at least one side of the insulating resin layer. In addition, the metal-clad laminate of the present embodiment may be a single-sided metal-clad laminate having a metal layer on one side of the insulating resin layer, or may be a double-sided metal-clad laminate having a metal layer on both sides of the insulating resin layer.

<Insulating resin layer> In the metal-clad laminate of the present embodiment, the insulating resin layer has a thermoplastic polyimide layer on at least one side of the non-thermoplastic polyimide layer. That is, the thermoplastic polyimide layer can be provided on one side or both sides of the non-thermoplastic polyimide layer. In addition, the thermoplastic polyimide layer is interposed between the metal layer and the non-thermoplastic polyimide layer. That is, the metal layer and the thermoplastic polyimide layer are in contact with each other. Here, the non-thermoplastic polyimide is generally a polyimide that does not show adhesiveness even when softened by heating, and in the present invention refers to a polyimide having a storage elastic modulus of 1.0×10 ⁹ Pa or more at 30°C and a storage elastic modulus of 1.0×10 ⁸ Pa or more at 360°C as measured using a dynamic viscoelasticity measuring device (dynamic mechanical analyzer (DMA)). Thermoplastic polyimide is generally a polyimide with a clearly identified glass transition temperature (Tg), and in the present invention refers to a polyimide having a storage modulus of 1.0×10 ⁹ Pa or more at 30°C and less than 1.0×10 ⁸ Pa at 360°C as measured using DMA.

The insulating resin layer may be a two-layer structure of a thermoplastic polyimide layer and a non-thermoplastic polyimide layer, and preferably a three-layer structure of a thermoplastic polyimide layer, a non-thermoplastic polyimide layer and a thermoplastic polyimide layer sequentially stacked from the side in contact with the metal layer. For example, when the insulating resin layer is formed by casting, it may be a two-layer structure in which a thermoplastic polyimide layer and a non-thermoplastic polyimide layer are sequentially stacked from the casting surface side, or it may be a three-layer structure in which a thermoplastic polyimide layer, a non-thermoplastic polyimide layer, and a thermoplastic polyimide layer are sequentially stacked from the casting surface side, preferably a three-layer structure. The so-called "cast surface" mentioned here means the surface on the support side when the polyimide layer is formed. The support may be a metal layer of a metal laminate, or may be a support when a gel film is formed. In addition, in the insulating resin layer, the surface opposite to the cast surface is described as a "laminated surface", and unless otherwise specified, a metal layer may or may not be laminated on the laminated surface.

<Thickness of insulating resin layer and birefringence Δn (xy-z) in the thickness direction> In order to ensure dimensional stability, a low CTE non-thermoplastic polyimide layer is often included in the metal-clad laminate, but the CTE of the non-thermoplastic polyimide layer tends to decrease as the thickness becomes thinner. The above behavior is particularly evident in the casting method, and the reasons include: during the heat treatment, the thinner the thickness, the more the volatility of the solvent in the resin layer is promoted, and the more the molecular alignment is carried out. Accompanying the above behavior, it is believed that the thinner the thickness, the smaller the orientation difference in the thickness direction. Therefore, even if the thermoplastic layer/non-thermoplastic layer thickness ratio of the conventional polyimide layer with a thickness of about 25 μm is directly applied to the thin insulating resin layer, the CTE is lowered, resulting in a CTE mismatch between the metal layer and the resin layer, and deteriorating dimensional stability. Furthermore, in the case of a polyimide film including a thermoplastic layer/non-thermoplastic layer, the orientation distribution of the non-thermoplastic layer in the thickness direction changes, so if the thermoplastic layer/non-thermoplastic layer thickness ratio is the same as before, curling occurs in the film. That is, in an extremely thin insulating resin layer, a design concept different from that of conventional technologies is required from the viewpoint of improving dimensional stability after circuit processing and suppressing curling.

In order to improve the dimensional stability after circuit processing and suppress curling, it is necessary to control the thickness ratio of the thermoplastic layer/non-thermoplastic layer and strike a balance including the CTE of each layer, taking into account the low CTE caused by thinning and the change in the orientation distribution in the thickness direction. In particular, in thin areas, it becomes difficult to separate each layer, so it is difficult to grasp the CTE of each layer. Furthermore, when the insulating resin layer is made by casting, since the direction of solvent penetration is one direction, even if the material and thickness are the same, the CTE becomes a different value depending on the layering order. Therefore, the CTE of each insulating resin layer formed by casting is different from the CTE value obtained by measuring a polyimide film separately produced with the same material and the same thickness as the layers.

Therefore, we have made great efforts to study the balance of each layer. As a result, we found that by evaluating the molecular orientation and the thickness ratio of the thermoplastic layer/non-thermoplastic layer using the birefringence Δn (xy-z) in the thickness direction and controlling it within a specified range, dimensional stability and film curling can be suppressed. Here, the so-called "birefringence Δn (xy-z) in the thickness direction" is the difference between the refractive index Nxy in the in-plane direction (xy plane) and the refractive index Nz in the cross-sectional direction (z direction) orthogonal to the in-plane direction in the polyimide film. The more the molecular orientation is carried out, the stronger the tendency of the molecules to be arranged in the in-plane direction, so Δn (xy-z) becomes larger. When no orientation is carried out, Δn (xy-z) becomes smaller. In addition, the larger the proportion of the non-thermoplastic layer, the larger Δn (xy-z). Therefore, by using Δn (xy-z) to evaluate the degree of molecular orientation and the thickness ratio of the thermoplastic layer/non-thermoplastic layer and controlling them within a specified range, dimensional stability can be improved and film curling can be suppressed.

From this point of view, the thickness of the insulating resin layer of the metal-clad laminate of the present embodiment is within the range of 2 μm or more and 15 μm or less, and the birefringence Δn(xy-z) in the thickness direction is controlled within the range of 0.080 or more and 0.140 or less. The thickness of the insulating resin layer can be set to a thickness within a specified range according to the purpose of use. If the thickness of the insulating resin layer is less than the lower limit, problems such as failure to ensure electrical insulation or difficulty in handling in the manufacturing process due to reduced operability may occur. On the other hand, if the thickness of the insulating resin layer exceeds the upper limit, it becomes difficult to thin or high-density mount circuit boards such as FPCs. Since the application of existing designs becomes more difficult as the thickness decreases, the effect of the present invention is more effective when applied to thin areas. In addition, if the birefringence Δn (xy-z) in the thickness direction is less than 0.080, the orientation is not fully performed, which becomes a cause of deterioration of dimensional stability, and it is easy to produce orientation differences in the thickness direction, so as a film, it is also easy to produce curling. On the other hand, if the birefringence Δn (xy-z) in the thickness direction exceeds 0.140, the CTE is excessively reduced, and the dimensional stability after circuit processing is deteriorated due to the mismatch with the CTE of the metal foil.

The birefringence Δn(xy-z) in the thickness direction is preferably 0.090 or more and 0.140 or less, more preferably 0.090 or more and 0.130 or less, and most preferably 0.090 or more and 0.120 or less. By controlling the birefringence Δn(xy-z) within the prescribed range, the warping of the film and the reduction in dimensional stability caused by the mismatch between the metal layer and the resin layer can be suppressed, and even if the thickness of the insulating resin layer is 15 μm or less, for example, a thin film of 12 μm or less, good workability during circuit processing and dimensional accuracy of fine wiring can be ensured.

The thickness of the insulating resin layer is 15 μm or less, preferably 12 μm or less, more preferably 9 μm or less, and further preferably 5 μm or less. By making the thickness of the insulating resin layer 15 μm or less, preferably 12 μm or less, more preferably 9 μm or less, and further preferably 5 μm or less, an extremely thin circuit board can be manufactured. Therefore, the degree of freedom in application such as folded wiring or multi-layer wiring in a thin frame is increased, and high-density mounting can be achieved.

In this embodiment, when the average thickness is T μm, the thickness deviation of the insulating resin layer is preferably within the range of T ± 0.5 μm, more preferably within the range of T ± 0.3 μm. If the thickness deviation exceeds T ± 0.5 μm, it may be difficult to control the birefringence Δn (xy-z) in the thickness direction.

<Thickness ratio of thermoplastic layer and non-thermoplastic layer> In the previous design, the orientation on the lamination surface side is promoted by the orientation difference in the thickness direction. Therefore, as in Patent Document 5 (Japanese Patent Publication No. 2006-306086), when the thickness is about 25 μm, the thickness of the thermoplastic polyimide layer on the lamination surface side is slightly thickened to suppress the curling of the film. However, if the thickness of the polyimide layer is reduced to 15 μm or less, especially 12 μm or less, the distribution of the orientation is close to uniform, so compared with the previous design, it is necessary to increase the thickness ratio of the thermoplastic polyimide layer on the casting surface side. From this viewpoint, in order to suppress curling and improve dimensional stability after circuit processing, in a single-sided metal-clad laminate, when the thickness of the thermoplastic polyimide layer existing on the side in contact with the metal layer (casting surface side) is set to T1, the thickness of the non-thermoplastic polyimide layer is set to T2, and the thickness of the thermoplastic polyimide layer existing on the side opposite to the metal layer (laminated surface side) is set to T3, T3/T1 is preferably in the range of 0.8 or more and less than 1.4. In particular, when the thickness of the insulating resin layer exceeds 9 μm and is less than 12 μm, T3/T1 is more preferably in the range of 0.8 to 1.3, and when the thickness of the insulating resin layer is 2 μm to 9 μm, T3/T1 is most preferably in the range of 0.9 to 1.3. If the ratio T3/T1 is less than 0.8, the influence of the thermoplastic polyimide layer on the casting surface side becomes too large, so that the film curls toward the casting surface side. On the other hand, if the ratio T3/T1 is 1.4 or more, the influence of the thermoplastic polyimide layer on the laminated surface side becomes too large, so that the film curls toward the laminated surface side. In addition, in the case where the metal-clad laminate is a double-sided metal-clad laminate having a metal layer laminated on both sides of an insulating resin layer, when the metal layer on one side is removed by etching to form two types of single-sided metal-clad laminates, it is sufficient that any one of the single-sided metal-clad laminates satisfies the relationship of the ratio T3/T1.

Furthermore, as a balance between the non-thermoplastic polyimide layer and the thermoplastic polyimide layer, it is also necessary to make the thermoplastic polyimide layer thicker than in the conventional design by utilizing the thinned orientation promotion. Therefore, (T1+T3)/(T1+T2+T3) representing the ratio of the thermoplastic polyimide layer to the polyimide layer is set to a range of more than 0.20 and less than 0.50. In particular, when the thickness of the insulating resin layer exceeds 9 μm and is less than 12 μm, (T1+T3)/(T1+T2+T3) is more preferably in the range of 0.25 to 0.50, and when the thickness of the insulating resin layer is 2 μm to 9 μm, (T1+T3)/(T1+T2+T3) is most preferably in the range of 0.30 to 0.50. When (T1+T3)/(T1+T2+T3) exceeds 0.50, the thickness of the non-thermoplastic polyimide layer is too small, so there is a tendency that the CTE of the insulating resin layer becomes larger and exceeds 30 ppm/K. On the other hand, if (T1+T3)/(T1+T2+T3) is less than 0.20, the thickness of the non-thermoplastic polyimide layer is too large, so the CTE of the insulating resin layer tends to be smaller and lower than 15 ppm/K.

<CTE> Regarding the metal-clad laminate of the present embodiment, in order to suppress warping and improve dimensional stability after circuit processing, it is important that the CTE of the insulating resin layer is in the range of 15 ppm/K or more and 30 ppm/K or less, preferably in the range of 15 ppm/K or more and 25 ppm/K or less. If the CTE is less than 15 ppm/K or exceeds 30 ppm/K, undesirable conditions such as warping of the metal-clad laminate or reduction in dimensional stability after circuit processing may occur.

In addition, the CTE (CTE _MD ) in the MD direction (length direction/conveying direction) and the CTE (CTE _TD ) in the TD direction (width direction) of the insulating resin layer are preferably in a relationship that satisfies the following formula (i). Satisfying the following formula (i) means that the deviation of the CTE in the MD direction and the TD direction relative to the average value (CTE _AVE ) of the CTE in the MD direction and the TD direction is less than 5%, and the anisotropy is small. If the anisotropy in the MD direction and the TD direction of the insulating resin layer becomes larger, it will have an adverse effect on the dimensional stability. Therefore, the smaller the value on the left side of the formula (i), the better. In other words, when satisfying the formula (i), any one of the following formulas (iii) and (iv) is also satisfied. |(CTE _MD -CTE _TD )/(CTE _MD +CTE _TD )｜≦0.05 …(i) CTE _AVE =(CTE _MD +CTE _TD )/2 …(ii) |(CTE _MD -CTE _AVE )/(CTE _AVE )｜≦0.05 …(iii) |(CTE _TD -CTE _AVE )/(CTE _AVE )｜≦0.05…(iv)

In the insulating resin layer, the non-thermoplastic polyimide layer constitutes a low thermal expansion polyimide layer, and the thermoplastic polyimide layer constitutes a high thermal expansion polyimide layer. Here, the low thermal expansion polyimide layer refers to a polyimide layer having a CTE preferably in the range of 0 ppm/K or more and 20 ppm/K or less, and more preferably in the range of 0 ppm/K or more and 15 ppm/K or less. In addition, the high thermal expansion polyimide layer refers to a polyimide layer having a CTE preferably greater than 35 ppm/K, more preferably within the range of greater than 35 ppm/K and less than 80 ppm/K, and further preferably within the range of greater than 35 ppm/K and less than 70 ppm/K. The polyimide layer can be made into a polyimide layer having a desired CTE by appropriately changing the combination of raw materials used, thickness, and drying/curing conditions.

In the metal-clad laminate of the present embodiment, the insulating resin layer is preferably formed by a casting method in which a solution of a thermoplastic or non-thermoplastic polyimide or a solution of a precursor is sequentially applied. In the case of the casting method, it is easy to produce an extremely thin insulating resin layer having a thickness of 15 μm or less, especially 12 μm or less, including a plurality of polyimide layers. In contrast, in the case of the tenter method, for example, in order to produce an insulating resin layer having a thickness of 15 μm or less, especially 12 μm or less, it is necessary to stretch the film, so that cracks or tortoise cracks are easily generated, and the technical difficulty is high. Furthermore, the thickness or CTE in the plane is prone to deviation, and the CTE in the MD direction and the TD direction is also prone to anisotropy.

(Non-thermoplastic polyimide) In this embodiment, the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer preferably contains tetracarboxylic acid residues and diamine residues, and these residues all contain aromatic groups. It is believed that since the tetracarboxylic acid residues and diamine residues contained in the non-thermoplastic polyimide all contain aromatic groups, it is easy to form an ordered structure of the non-thermoplastic polyimide, thereby contributing to improving dimensional stability.

In the present invention, the tetracarboxylic acid residue refers to a tetravalent group derived from tetracarboxylic dianhydride, and the diamine residue refers to a divalent group derived from a diamine compound. In the "diamine compound", the hydrogen atoms in the two terminal amino groups may be substituted, for example, -NR ₃ R ₄ (wherein R ₃ and R ₄ independently represent any substituent such as an alkyl group).

The non-thermoplastic polyimide contained in the metal-clad laminate of the present embodiment preferably contains 50 mol parts or more of diamine residues derived from a diamine compound represented by the following general formula (1) relative to 100 mol parts of all diamine residues.

[Chemistry 1] [In formula (1), R independently represents a halogen atom, an alkyl or alkoxy group having 1 to 6 carbon atoms which may be substituted with a halogen atom, or a phenyl or phenoxy group which may be substituted with a monovalent alkyl group or alkoxy group having 1 to 6 carbon atoms, _n1 independently represents an integer of 0 to 4, and _n2 represents an integer of 0 to 1]

The diamine residue derived from the diamine compound represented by the general formula (1) can easily form an ordered structure and lower the CTE, thereby improving the dimensional stability. In addition, since it contains two or more benzene rings, it is also helpful to reduce the concentration of imide groups and reduce moisture absorption, which is also beneficial in improving the dimensional stability. From this point of view, the diamine residue derived from the diamine compound represented by the general formula (1) is preferably contained in an amount of 50 mol parts or more, and more preferably in a range of 60 mol parts to 100 mol parts, relative to 100 mol parts of all diamine residues contained in the non-thermoplastic polyimide. If it is less than 50 mol parts, the CTE increases and the dimensional stability deteriorates.

Preferred specific examples of the diamine residue derived from the diamine compound represented by the general formula (1) include diamine residues derived from the following diamine compounds: 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB), 2,2'-diethyl-4,4'-diaminobiphenyl (m-EB), 2,2'-diethoxy-4,4'-diaminobiphenyl (m-EOB), 2,2'-diprop ... 4,4'-diaminobiphenyl, 4,4'-diaminobiphenyl, 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 4,4'-diamino-p-terphenyl, 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl) ... Among these, 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB), 2,2'-diethyl-4,4'-diaminobiphenyl (m-EB), 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl (TFMB), and 4,4''-diamino-p-terphenyl (DATP) are preferred. In particular, 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB) is the most preferred because it easily forms an ordered structure and reduces the imide group concentration and moisture absorption rate.

In order to reduce the modulus of elasticity of the insulating resin layer and improve elongation and bending resistance, the non-thermoplastic polyimide preferably contains a diamine residue derived from a diamine compound represented by the following general formula (2).

[Chemistry 2]

In formula (2), R independently represents a halogen atom, an alkyl or alkoxy group having 1 to 6 carbon atoms which may be substituted with a halogen atom, or a phenyl or phenoxy group which may be substituted with a monovalent alkyl group or alkoxy group having 1 to 6 carbon atoms, _Z1 independently represents a single bond, a divalent group selected from -O-, -S-, _-CH2- , -CH( _CH3 )-, -C( _CH3 ) _2- , -CO-, _-SO2- , or -NH-, _n3 independently represents an integer of 0 to 4, and _n4 represents an integer of 0 to 2. At least one of _Z1 represents a divalent group selected from -O-, -S-, _-CH2- , -CH( _CH3 )-, -C( _CH3 ) _2- , -CO-, _-SO2- , or -NH-.

The diamine residue derived from the diamine compound represented by the general formula (2) has a flexible portion and can therefore impart flexibility to the insulating resin layer. From this viewpoint, the diamine residue derived from the diamine compound represented by the general formula (2) is preferably contained in the range of 1 mol to 50 mol, and most preferably contained in the range of 1 mol to 40 mol, relative to 100 mol of all diamine residues contained in the non-thermoplastic polyimide. If contained in an amount exceeding 50 mol, CTE increases and dimensional stability deteriorates. In addition, when the content is less than 1 mol, flexibility deteriorates, and thus bending characteristics deteriorate. When the non-thermoplastic polyimide contains both diamine residues derived from the diamine compound represented by the general formula (1) and diamine residues derived from the diamine compound represented by the general formula (2), the content of the diamine residues derived from the diamine compound represented by the general formula (1) is preferably in the range of 50 to 99 mol parts, and most preferably in the range of 60 to 99 mol parts, based on 100 mol parts of all diamine residues contained in the non-thermoplastic polyimide.

Preferred specific examples of the diamine compound represented by the general formula (2) include 3,3'-diaminodiphenylmethane, 3,3'-diaminodiphenylpropane, 3,3'-diaminodiphenyl sulfide, 3,3'-diaminodiphenylsulfone, 3,3-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylpropane, 3,4'-diaminodiphenyl sulfide, 3,4'-diaminobenzophenone, (3,3'-bisamino)diphenylamine, 1,4-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene (1,3- bis(4-aminophenoxy)benzene, TPE-R), 1,4-bis(4-aminophenoxy)benzene (1,4-bis(4-aminophenoxy)benzene, TPE-Q), 3-[4-(4-aminophenoxy)phenoxy]aniline, 3-[3-(4-aminophenoxy)phenoxy]aniline, 1,3-bis(3-aminophenoxy)benzene (1,3-bis(3-aminophenoxy)benzene, APB), 4,4'-[2-methyl-(1,3-phenylene)bisoxy]bisaniline, 4,4'-[4 bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(3-aminophenoxy)phenyl]propane, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)benzophenone, bis[4,4'-(3-aminophenoxy)benzanilide, 4-[3-[4-(4-aminophenoxy)phenoxy]phenoxy]aniline, 4,4'-[oxybis(3,1-phenyleneoxy)]bisaniline , bis[4-(4-aminophenoxy)phenyl]ether (BAPE), bis[4-(4-aminophenoxy)phenyl]ketone (BAPK), bis[4-(3-aminophenoxy)]biphenyl, bis[4-(4-aminophenoxy)]biphenyl, 2,2-bis(4-aminophenoxyphenyl)propane (BAPP), etc. Among these, preferred are those in which _n3 in the general formula (2) is 0, for example, 4,4'-diaminodiphenyl ether (4,4'-DAPE), 1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,3-bis(3-aminophenoxy)benzene (APB), 1,4-bis(4-aminophenoxy)benzene (TPE-Q), and 2,2-bis(4-aminophenoxyphenyl)propane (BAPP).

As long as the purpose of the present invention is not hindered, other commonly used diamines may be used as raw materials of polyimide. Examples of other diamines include p-phenylenediamine (p-PDA) and m-phenylenediamine (m-PDA).

The tetracarboxylic acid residue contained in the non-thermoplastic polyimide is not particularly limited, and for example, tetracarboxylic acid residues derived from pyromellitic dianhydride (PMDA) (hereinafter also referred to as PMDA residues) and tetracarboxylic acid residues derived from 3,3',4,4'-biphenyl tetracarboxylic dianhydride (BPDA) (hereinafter also referred to as BPDA residues) can be preferably listed. These tetracarboxylic acid residues can easily form an ordered structure. In addition, the PMDA residue is a residue that plays a role in controlling CTE and controlling the glass transition temperature. Furthermore, regarding the BPDA residue, since there is no polar group in the tetracarboxylic acid residue and the molecular weight is relatively large, it is also expected to reduce the imide group concentration of the non-thermoplastic polyimide and inhibit the moisture absorption of the insulating resin layer. From this point of view, the total amount of PMDA residues and/or BPDA residues is preferably 50 mol parts or more, more preferably in the range of 60 mol parts to 100 mol parts, and most preferably in the range of 80 mol parts to 100 mol parts, relative to 100 mol parts of all tetracarboxylic acid residues contained in the non-thermoplastic polyimide. If the content is less than 50 mol parts, the CTE increases and the dimensional stability deteriorates.

Examples of other tetracarboxylic acid residues contained in the non-thermoplastic polyimide include tetracarboxylic acid residues derived from the following aromatic tetracarboxylic acid dianhydrides: 2,3',3,4'-biphenyltetracarboxylic acid dianhydride, 2,2',3,3'-biphenyltetracarboxylic acid dianhydride, 3,3',4,4'-diphenylsulfonatetetracarboxylic acid dianhydride, 4,4'-oxydiphthalic acid anhydride, 2,2',3,3'-benzophenonetetracarboxylic acid dianhydride, 2,3,3',4'-benzophenonetetracarboxylic acid dianhydride or 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride, 2,3',3,4'-diphenylethertetracarboxylic acid dianhydride, bis(2,3-dicarboxyphenyl)ether dianhydride, 3,3',4,4'-diphenylsulfonatetetracarboxylic acid dianhydride, 4,4'-oxydiphthalic acid anhydride, ,4,4''-terphenyltetracarboxylic dianhydride, 2,3,3'',4''-terphenyltetracarboxylic dianhydride or 2,2'',3,3''-terphenyltetracarboxylic dianhydride, 2,2-bis(2,3-dicarboxyphenyl)-propane dianhydride or 2,2-bis(3,4-dicarboxyphenyl)-propane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride or bis(3,4-dicarboxyphenyl)methane dianhydride, bis(2,3-dicarboxyphenyl)sulfonate dianhydride or bis(3,4-dicarboxyphenyl)sulfonate dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride or 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, 1,2,7,8 1,2,6,7-phenanthrene-tetracarboxylic dianhydride, 1,2,6,7-phenanthrene-tetracarboxylic dianhydride or 1,2,9,10-phenanthrene-tetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)tetrafluoropropane dianhydride, 2,3,5,6-cyclohexane dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylic dianhydride, 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride or 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride anhydride, 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride or 1,4,5,8-tetrachloronaphthalene-2,3,6,7-tetracarboxylic dianhydride, 2,3,8,9-perylene-tetracarboxylic dianhydride, 3,4,9,10-perylene-tetracarboxylic dianhydride, 4,5,10,11-perylene-tetracarboxylic dianhydride or 5,6,11,12-perylene-tetracarboxylic dianhydride, cyclopentane-1,2,3,4-tetracarboxylic dianhydride, pyrazine-2,3,5,6-tetracarboxylic dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic dianhydride, thiophene-2,3,4,5-tetracarboxylic dianhydride, 4,4'-bis(2,3-dicarboxyphenoxy)diphenylmethane dianhydride, and the like.

By selecting the types of the acid anhydride and diamine or the molar ratio of each when two or more acid anhydrides or diamines are used, the CTE, toughness, thermal expansion, adhesion, glass transition temperature (Tg), etc. of the non-thermoplastic polyimide can be controlled. In addition, when the non-thermoplastic polyimide has a plurality of polyimide structural units, they may exist in the form of blocks or randomly, preferably randomly.

The imide group concentration of the non-thermoplastic polyimide is preferably 35 wt% or less. Here, "imide group concentration" refers to the value obtained by dividing the molecular weight of the imide group (-(CO) ₂ -N-) in the polyimide by the molecular weight of the entire structure of the polyimide. If the imide group concentration exceeds 35 wt%, the molecular weight of the resin itself becomes smaller, and the low hygroscopicity is also deteriorated due to the increase in polar groups. By selecting the combination of the acid anhydride and the diamine compound, the orientation of the molecules in the non-thermoplastic polyimide is controlled, thereby suppressing the increase in CTE accompanying the decrease in the imide group concentration, thereby ensuring low hygroscopicity.

The weight average molecular weight of the non-thermoplastic polyimide is preferably in the range of 10,000 to 400,000, more preferably in the range of 50,000 to 350,000. If the weight average molecular weight is less than 10,000, the strength of the insulating resin layer is reduced and the coating tends to be brittle. On the other hand, if the weight average molecular weight exceeds 400,000, the viscosity is excessively increased, and defects such as uneven thickness and streaks tend to occur during coating.

(Thermoplastic polyimide) In this embodiment, the thermoplastic polyimide constituting the thermoplastic polyimide layer preferably contains tetracarboxylic acid residues and diamine residues, and these residues all contain aromatic groups. Since the tetracarboxylic acid residues and diamine residues contained in the thermoplastic polyimide all contain aromatic groups, heat resistance can be ensured.

In the present embodiment, as the diamine residue contained in the thermoplastic polyimide, it is preferred to contain a diamine residue derived from a diamine compound represented by the general formula (2). The diamine residue derived from the diamine compound represented by the general formula (2) is preferably 50 mol parts or more, more preferably in the range of 70 mol parts to 100 mol parts, and most preferably in the range of 80 mol parts to 100 mol parts, relative to 100 mol parts of all diamine residues. By including 50 mol parts or more of the diamine residue derived from the diamine compound represented by the general formula (2) relative to 100 mol parts of all diamine residues, flexibility and adhesion can be imparted to the thermoplastic polyimide layer, thereby functioning as an adhesive layer relative to the metal layer. Among the diamine residues derived from the diamine compound represented by general formula (2), 4,4'-diaminodiphenyl ether (4,4'-DAPE), 1,3-bis(4-aminophenoxy)benzene (TPE-R), and 2,2-bis(4-aminophenoxyphenyl)propane (BAPP) are particularly preferred. The diamine residues derived from these diamine compounds have a flexible portion, and thus can reduce the elastic modulus of the insulating resin layer and impart flexibility.

In the present embodiment, the diamine residue derived from a diamine compound other than the diamine compound represented by the general formula (2) contained in the thermoplastic polyimide may be, for example, a diamine residue derived from the following diamine compounds: 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB), 2,2'-diethyl-4,4'-diaminobiphenyl (m-EB), 2,2'-diethoxy-4,4'-diaminobiphenyl (m-EOB), 2,2'-dipropoxy-4,4'-diaminobiphenyl (m-POB), 2,2'-n-propyl-4,4'-diaminobiphenyl (m-NPB), 2,2'-divinyl-4,4'-diaminobiphenyl (VAB), 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl (TFMB), p-phenylenediamine (p-PDA), m-phenylenediamine (m-PDA), etc.

The tetracarboxylic acid residues contained in the thermoplastic polyimide are not particularly limited, and preferably include tetracarboxylic acid residues derived from pyromellitic dianhydride (PMDA) (hereinafter also referred to as PMDA residues), tetracarboxylic acid residues derived from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) (hereinafter also referred to as BPDA residues), and tetracarboxylic acid residues derived from 3,3',4,4'-benzophenonetetracarboxylic dianhydride (hereinafter also referred to as BTDA residues). These tetracarboxylic acid residues can easily form an ordered structure and reduce the dimensional change rate in a high temperature environment. In addition, the PMDA residue is a residue that plays a role in controlling CTE and controlling the glass transition temperature. Furthermore, regarding the BPDA residue, since there is no polar group in the tetracarboxylic acid residue and the molecular weight is relatively large, it is also expected to reduce the imide group concentration of the thermoplastic polyimide and inhibit the moisture absorption of the insulating resin layer. Furthermore, the BTDA residue has a moderate degree of flexibility, so it can impart flexibility without significantly increasing the CTE. From this point of view, the total amount of PMDA residues, BPDA residues and/or BTDA residues is preferably 50 mol parts or more, more preferably in the range of 60 mol parts to 100 mol parts, and most preferably in the range of 80 mol parts to 100 mol parts, relative to 100 mol parts of all tetracarboxylic acid residues contained in the thermoplastic polyimide.

As other tetracarboxylic acid residues contained in the thermoplastic polyimide, there can be mentioned tetracarboxylic acid residues derived from the same aromatic tetracarboxylic dianhydride as exemplified in the above-mentioned non-thermoplastic polyimide.

In the thermoplastic polyimide, by selecting the types of the tetracarboxylic acid residues and diamine residues or the molar ratio of the tetracarboxylic acid residues or diamine residues when two or more tetracarboxylic acid residues or diamine residues are contained, CTE, tensile modulus, glass transition temperature, etc. can be controlled. In addition, when the thermoplastic polyimide has a plurality of structural units of polyimide, they may exist in the form of blocks or randomly, preferably randomly.

The imide group concentration of the thermoplastic polyimide is preferably 35 wt% or less. Here, "imide group concentration" refers to the value obtained by dividing the molecular weight of the imide group (-(CO) ₂ -N-) in the polyimide by the molecular weight of the entire structure of the polyimide. If the imide group concentration exceeds 35 wt%, the molecular weight of the resin itself becomes smaller, and the low hygroscopicity is also deteriorated due to the increase in polar groups. By selecting the combination of the acid anhydride and the diamine compound, the molecular orientation in the thermoplastic polyimide is controlled, thereby suppressing the increase in CTE accompanying the decrease in the imide group concentration, thereby ensuring low hygroscopicity.

The weight average molecular weight of the thermoplastic polyimide is preferably in the range of 10,000 to 600,000, more preferably in the range of 50,000 to 500,000. If the weight average molecular weight is less than 10,000, the strength of the insulating resin layer is reduced and the coating tends to be brittle. On the other hand, if the weight average molecular weight exceeds 600,000, the viscosity is excessively increased, and defects such as uneven thickness and streaks tend to occur during coating.

(Synthesis of non-thermoplastic polyimide and thermoplastic polyimide) Generally, polyimide can be produced by reacting tetracarboxylic dianhydride and diamine compound in a solvent to generate polyamide, and then heating and ring closing. For example, tetracarboxylic dianhydride and diamine compound are dissolved in an organic solvent in approximately equimolar amounts, and the mixture is stirred for 30 minutes to 24 hours at a temperature in the range of 0°C to 100°C to perform a polymerization reaction, thereby obtaining polyamide as a precursor of polyimide. During the reaction, the reaction components are dissolved in the organic solvent in such a manner that the generated precursor is in the range of 5% by weight to 30% by weight, preferably in the range of 6% by weight to 20% by weight. Examples of organic solvents used in the polymerization reaction include N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), 2-butanone, dimethyl sulfoxide (DMSO), hexamethylphosphatamide, N-methylcaprolactam, dimethyl sulfate, cyclohexanone, dioxane, tetrahydrofuran, diethylene glycol dimethyl ether (diglyme), triethylene glycol dimethyl ether (triglyme), cresol, etc. These solvents may be used in combination of two or more, and aromatic hydrocarbons such as xylene and toluene may be used in combination. The amount of the organic solvent used is not particularly limited, but is preferably used in an amount adjusted so that the concentration of the polyamide solution obtained by the polymerization reaction becomes about 5% by weight to 30% by weight.

The synthesized polyamine is usually advantageously used in the form of a reaction solvent solution, and can be concentrated, diluted or replaced with other organic solvents as needed. In addition, polyamine is generally excellent in solvent solubility, so it can be used advantageously. The viscosity of the polyamine solution is preferably in the range of 500 cps to 100,000 cps. If it deviates from the above range, when applying the film using a coating machine, etc., uneven thickness, streaks and other defects are likely to occur in the film. There is no particular limitation on the method for imidizing the polyamine. For example, it is preferably possible to use a heat treatment such as heating in the above solvent at a temperature condition in the range of 80°C to 400°C for 1 hour to 24 hours.

<Metal layer> Metals constituting the metal layer include, for example, metals selected from copper, aluminum, stainless steel, iron, silver, palladium, nickel, chromium, molybdenum, tungsten, zirconium, gold, cobalt, titanium, tantalum, zinc, lead, tin, silicon, bismuth, indium, or alloys thereof. The metal layer may be formed by, for example, sputtering, evaporation, plating, etc., but from the perspective of adhesion, it is preferred to use a metal foil. In terms of conductivity, copper foil is particularly preferred. The copper foil may be either an electrolytic copper foil or a rolled copper foil. When the metal-clad laminate of the present embodiment is continuously produced, a long metal foil having a predetermined thickness and wound in a roll is used as the metal foil.

The metal layer is preferably a copper foil having a rust-proof layer containing nickel, zinc and cobalt on at least the side of the surface in contact with the thermoplastic polyimide layer. In the above case, the surface roughness Rz of at least the side of the copper foil in contact with the thermoplastic polyimide layer is preferably 1.0 μm or less, and more preferably 0.6 μm or less. If the surface roughness Rz of the copper foil exceeds 1.0 μm, the thermoplastic polyimide layer in contact with the copper foil is damaged in the extremely thin insulating resin layer with an overall thickness of 15 μm or less, especially 12 μm or less, resulting in poor insulation, peel strength, etc.

In the metal-clad laminate of the present embodiment, when a 50 mm square insulating resin film is left to stand at 23° C. and 50% RH for 24 hours with the convex surface in the center in contact with the flat surface, the curling amount obtained by calculating the average of the floating amounts at the four corners is preferably 10 mm or less, more preferably 8 mm or less, and most preferably 5 mm or less. If the curling amount exceeds 10 mm, the workability is reduced and it is difficult to maintain the dimensional accuracy during circuit processing.

The width of the metal-clad laminate of the present embodiment (i.e., the length in the TD direction) is preferably 470 mm or more, and more preferably in the range of 470 mm to 1200 mm. Generally, the larger the width of the metal-clad laminate (i.e., the length in the TD direction), the more difficult it is to control the dimensional stability and in-plane isotropy, and the larger the deviation tends to be. Therefore, the present invention is particularly useful in the application of metal-clad laminates with a width of 470 mm or more, and the effect of the present invention can be greatly exerted. In addition, if the width exceeds 1200 mm, the deviation of the in-plane dimensional stability or thickness becomes larger, and for example, when processed into FPC, etc., it is easy to produce defects and there is a tendency for the yield to deteriorate.

Hereinafter, a copper-clad laminate having a copper layer will be described as a preferred embodiment of the metal-clad laminate.

<Copper-clad laminate> The copper-clad laminate of the present embodiment only needs to include an insulating resin layer and a copper layer such as copper foil located on at least one side of the insulating resin layer. In addition, in order to improve the adhesion between the insulating resin layer and the copper layer, the layer in the insulating resin layer that is in contact with the copper layer is a thermoplastic polyimide layer. The insulating resin layer has the same structure as that described for the metal-clad laminate. The copper layer is provided on one side or both sides of the insulating resin layer. That is, the copper-clad laminate of the present embodiment may be a single-sided copper-clad laminate (single-sided CCL) or a double-sided copper-clad laminate (double-sided CCL). In the case of a single-sided CCL, the single-sided copper layer laminated on the insulating resin layer is defined as the "first copper layer" in the present invention. In the case of a double-sided CCL, the copper layer laminated on one side of the insulating resin layer is set as the "first copper layer" in the present invention, and the copper layer laminated on the side of the insulating resin layer opposite to the side on which the first copper layer is laminated is set as the "second copper layer" in the present invention. In addition, the "second copper layer" is equivalent to the "other metal layer" laminated on the side opposite to the first copper layer based on the insulating resin layer. The copper-clad laminate of this embodiment is used as an FPC by performing wiring circuit processing on the copper layer by etching or the like to form copper wiring.

The copper-clad laminate can be manufactured, for example, by preparing a polyimide resin film, sputtering a metal thereon to form a seed layer, and then, for example, forming a copper layer by copper plating.

Alternatively, copper-clad laminates can be prepared by preparing a polyimide resin film and laminating the film with copper foil by hot pressing or the like.

Furthermore, a copper-clad laminate can also be prepared by casting a coating liquid containing polyamide acid as a precursor of polyimide on a copper foil, drying it to form a coating film, and then heat-treating and imidizing it to form a polyimide layer. When an insulating resin layer including a plurality of polyimide layers is formed by a casting method, a coating liquid of polyamide acid can be applied sequentially. For example, when the polyimide layer has a three-layer structure, the following method is preferably used: a coating liquid of polyamide acid is applied sequentially on a copper foil by sequentially laminating a precursor layer of thermoplastic polyimide, a precursor layer of non-thermoplastic polyimide, and a precursor layer of thermoplastic polyimide, and then heat-treating and imidizing the copper foil.

(First copper layer) In the copper-clad laminate of the present embodiment, the copper foil used in the first copper layer (hereinafter sometimes referred to as "first copper foil") is not particularly limited, and may be, for example, a rolled copper foil or an electrolytic copper foil.

For example, when high-density mounting or bendability is required, the thickness of the first copper foil is preferably less than 35 μm, more preferably in the range of 6 μm to 18 μm. If the thickness of the first copper foil exceeds 35 μm, the bending stress applied to the copper layer (or copper wiring) when the copper-clad laminate (or FPC) is bent becomes larger, thereby reducing the bending resistance. In addition, from the perspective of production stability and operability, the lower limit of the thickness of the first copper foil is preferably set to 6 μm. In addition, for applications such as power modules or LED substrates that require heat dissipation, the thickness of the first copper foil is preferably greater than 18 μm, more preferably in the range of 18 μm to 50 μm, and further preferably in the range of 35 μm to 50 μm. In applications requiring heat dissipation, a large current is often required depending on the power required by the mounted device, so it is preferable to increase the thickness of the metal layer. If the thickness of the metal layer is less than 18 μm, the supply current of the device is limited, and if it exceeds 50 μm, the processability tends to deteriorate.

In addition, the tensile modulus of the first copper foil is preferably in the range of 50 GPa to 300 GPa, and more preferably in the range of 70 GPa to 250 GPa. In the case of using a rolled copper foil as the first copper foil in the present embodiment, if annealing is performed by heat treatment, the flexibility tends to increase. Therefore, if the tensile modulus of the copper foil is less than the lower limit value, the rigidity of the first copper foil itself is reduced due to heating during the process of forming an insulating resin layer on the long first copper foil. On the other hand, if the tensile modulus of elasticity exceeds the upper limit value, a greater bending stress is applied to the copper wiring when the FPC is bent, and its bending resistance is reduced. In addition, the tensile modulus of the rolled copper foil tends to change depending on the heat treatment conditions when the insulating resin layer is formed on the copper foil, or the annealing treatment of the copper foil after the insulating resin layer is formed. Therefore, in the present embodiment, in the finally obtained copper-clad laminate, the tensile modulus of the first copper foil only needs to be within the above range.

The first copper foil is not particularly limited, and a commercially available rolled copper foil can be used.

(Second copper layer) The second copper layer is laminated on the surface of the insulating resin layer opposite to the first copper layer. The copper foil (second copper foil) used in the second copper layer is not particularly limited, and may be, for example, a rolled copper foil or an electrolytic copper foil. In addition, a commercially available copper foil may be used as the second copper foil. In addition, the same copper foil as the first copper foil may be used as the second copper foil.

As described above, the metal-clad laminate of the present embodiment includes an extremely thin insulating resin layer having high dimensional stability and in-plane isotropy, excellent adhesion to the metal layer, and suppressed warping, even though the thickness of the insulating resin layer is 15 μm or less, preferably 12 μm or less. Therefore, dimensional changes or warping caused by environmental changes (e.g., high temperature/high pressure environment, humidity changes, etc.) during the circuit processing process, substrate lamination process, and component mounting process can be effectively suppressed. In addition, since the thickness of the insulating resin layer is 15 μm or less, preferably 12 μm or less, high-density mounting of circuit boards such as FPCs obtained from the metal-clad laminate can be achieved. Therefore, by using the metal-clad laminate of this embodiment as a circuit board material, it is possible to cope with the miniaturization of electronic devices and improve the reliability and yield of the circuit board. In addition, since the insulating resin layer is thin and the adhesion to the metal layer is excellent, it is also useful in applications requiring heat dissipation, such as power module or LED substrates.

<Circuit board> The metal-clad laminate of the present embodiment is mainly useful as a material for a circuit board such as an FPC. For example, a circuit board such as an FPC which is an embodiment of the present invention can be manufactured by processing the copper layer of the copper-clad laminate described above into a pattern by a common method to form a wiring layer. In addition, a multi-layer circuit board or a rigid flexible substrate (rigid FPC) can be manufactured by laminating a circuit board such as an FPC which is an embodiment of the present invention in multiple layers.

In addition, since the insulating resin layer of the circuit substrate such as FPC which is one embodiment of the present invention is thin, it is also a useful material in applications requiring heat dissipation, such as the substrate of a power module or LED. In such applications, the thickness of the metal layer can be thickened to increase the supply current to the device. Furthermore, the thickness of the insulating resin layer can be reduced to improve the heat dissipation. When the insulating resin layer is thinned, the thickness of the insulating resin layer is preferably in the range of 2 μm to 9 μm, and more preferably in the range of 2 μm to 5 μm. If the thickness of the insulating resin layer exceeds 9 μm, the heat dissipation property will be impaired, and if it is less than 2 μm, there are concerns about damage during circuit processing or failure to ensure insulation after FPC processing. [Example]

The following examples are shown to more specifically illustrate the features of the present invention. However, the scope of the present invention is not limited to the examples. In addition, in the following examples, unless otherwise specified, various measurements and evaluations are performed using the following methods.

[Viscosity measurement] The viscosity at 25°C was measured using an E-type viscometer (Brookfield, trade name: DV-II+Pro). The rotation speed was set so that the torque was 10% to 90%, and the value when the viscosity stabilized was read 2 minutes after the start of the measurement.

[Measurement of weight average molecular weight] The weight average molecular weight was measured using a gel permeation chromatograph (manufactured by Tosoh Corporation, trade name: HLC-8220GPC). Polystyrene was used as a standard substance and N,N-dimethylacetamide was used as a developing solvent.

[Measurement of storage elastic coefficient] Using a dynamic viscoelasticity measuring apparatus (DMA: manufactured by UBM, trade name: E4000F), a polyimide film having a size of 5 mm × 20 mm was measured at a heating rate of 4°C/min and a frequency of 11 Hz from 30°C to 400°C. Those showing a storage elastic coefficient of 1.0×10 ⁹ Pa or more at 30°C and a storage elastic coefficient of less than 1.0×10 ⁸ Pa at 360°C were determined to be "thermoplastic", and those showing a storage elastic coefficient of 1.0×10 ⁹ Pa or more at 30°C and a storage elastic coefficient of 1.0×10 ⁸ Pa or more at 360°C were determined to be "non-thermoplastic".

[Measurement of coefficient of thermal expansion (CTE)] Using a thermomechanical analyzer (manufactured by Bruker, trade name: 4000SA), a 3 mm × 20 mm polyimide film was heated from 30°C to 265°C at a rate of 20°C/min while applying a load of 5.0 g. The film was then kept at the temperature for 10 minutes and then cooled at a rate of 5°C/min to determine the average coefficient of thermal expansion (CTE) from 250°C to 100°C.

[Measurement of surface roughness of copper foil] Regarding the surface roughness of copper foil, an atomic force microscope (AFM) (manufactured by Bruker AXS, trade name: Dimension Icon Scanning Probe Microscope (SPM)) and a probe (manufactured by Bruker AXS, trade name: TESPA (NCHV), tip curvature radius 10 nm, spring constant 42 N/m) were used to measure the surface of the copper foil in an area of 80 μm × 80 μm in tapping mode, and the ten-point average roughness (Rz) was calculated.

[Regarding retardation Re and birefringence Δn (xy-z) in the thickness direction] The birefringence Δn (xy-z) in the thickness direction is measured using a birefractive index meter (manufactured by Photonic-Lattice, trade name: wide range birefringence evaluation system WPA-100, measurement area: MD: 20 mm × TD: 15 mm). The retardation Re described later is measured using a known polarization state control device (for example, refer to Japanese Patent Laid-Open No. 2016-126804), and the birefringence Δn (xy-z) in the thickness direction is calculated based on the obtained measurement results.

First, the evaluation method of the delay Re is explained. FIG. 1 is an explanatory diagram showing a part of the evaluation system of the delay Re. The evaluation system of the delay Re includes a birefringence/phase difference evaluation device (manufactured by Photonic-Lattice Co., Ltd., WPA-100) and an unillustrated rotating device for rotating the sample in order to change the incident angle θ ₁ of the light incident on the sample. In FIG. 1 , symbol 20 represents the sample, symbol 21 represents the light source of the birefringence/phase difference evaluation device, and symbol 22 represents the light receiving part of the birefringence/phase difference evaluation device. The wavelength of the light emitted by the light source 21 is 543 nm. The sample 20 is fixed to the unillustrated rotating device in a state supported by a fixing frame.

The delay Re is measured by changing the incident angle _θ1 of the light incident on the sample 20 by changing the tilt angle of the sample 20 supported by the frame using a rotating device (not shown) (see FIG. 2 ). The incident angle _θ1 is changed to 0°, ±30°, ±45°, and ±60°, and the delay Re is measured at each angle.

Next, the calculation method of the birefringence Δn (xy-z) in the thickness direction is described. The birefringence Δn (xy-z) in the thickness direction is calculated using the measurement result of the retardation Re. When the polyimide film is evaluated using the retardation evaluation system, the incident angle θ ₁ and the refraction angle θ ₂ are as shown in FIG2 . In FIG2 , the symbol 2 represents the polyimide film, the symbol 2a represents the lamination surface of the polyimide film 2, the symbol 2b represents the casting surface of the polyimide film 2, and d represents the thickness of the polyimide film. Here, the symbol L ₁ represents the light before being incident on the lamination surface 2a, the symbol L ₂ represents the light in the polyimide film 2, and the symbol L ₃ represents the light emitted from the casting surface 2b. The X axis, Y axis, and Z axis are orthogonal to each other, the XY direction is an axis parallel to the laminated surface 2a of the polyimide film, and the Z direction is an axis orthogonal to the laminated surface 2a of the polyimide film 2 and is an axis in the thickness direction.

As shown in the following formula (A), the retardation Re depends on the thickness d, the birefringence Δn (xy-z) in the thickness direction, and the refraction angle θ ₂ . The refraction angle θ ₂ depends on the incident angle θ ₁ . Therefore, the birefringence Δn (xy-z) can be calculated from the measured values of the retardation Re obtained for multiple incident angles θ ₁ . Re=d·Δn(xy-z)·sin ² θ ₂ /cosθ ₂ …(A) Wherein, the refraction angle θ ₂ is the angle between the light beam inside the film and the normal to the film, and the incident angle θ ₁ is related to θ ₂ =sin ^-1 (sinθ ₁ /N) according to Snell's law. Here, d is the film thickness, and N is the refractive index of the measured sample. In addition, Δn(xy-z) is the difference between the refractive index in the in-plane direction and the refractive index in the thickness direction, and satisfies Δn(xy-z)= _nxy - _nz . _nxy : Refractive index in the in-plane direction _nz : Refractive index in the thickness direction

[Measurement of curling amount] The copper foil is etched off from the sample of the metal-clad laminate to obtain a polyimide film. Then, the polyimide film of 50 mm × 50 mm is placed on a smooth table with the curling direction set to the upper surface after humidification at 23°C and 50% RH for 24 hours. The curling amount at this time is measured using a vernier caliper. At this time, the curling of the film toward the etched surface of the substrate is recorded as positive (plus), and the curling toward the opposite side is recorded as negative (minus). The average of the measured values at the four corners of the film is set as the curling amount.

[Thickness measurement] The copper foil is etched away from the metal-clad laminate sample at five points about 90 mm apart in the width direction to obtain the polyimide film, and then the thickness is measured. The average value of the five-point thickness is set as the thickness, and the difference between the average value and each point is evaluated as the thickness deviation.

[Peeling strength measurement] The copper foil from the metal-clad laminate sample was processed with a circuit with lines and spaces of 1.0 mm in width and 5.0 mm in spacing, and then cut into pieces of 8 cm in width and 4 cm in length to prepare the measurement sample 1. The peeling strength of the cast surface side of the measurement sample 1 was measured using the following method. Using a Tensilon tester (manufactured by Toyo Seiki Seisaku-sho, trade name: Strograph VE-1D), the resin layer side of the test sample 1 was fixed to an aluminum plate with double-sided tape, and the copper foil was peeled off in a 180° direction at a speed of 50 mm/min. The central strength was determined when the copper foil was peeled off 10 mm from the resin layer.

The abbreviations used in the examples and comparative examples represent the following compounds. BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride PMDA: pyromellitic dianhydride BTDA: 3,3',4,4'-benzophenonetetracarboxylic dianhydride m-TB: 2,2'-dimethyl-4,4'-diaminobiphenyl TPE-R: 1,3-bis(4-aminophenoxy)benzene TPE-Q: 1,4-bis(4-aminophenoxy)benzene DAPE: 4,4'-diaminodiphenyl ether BAPP: 2,2-bis[4-(4-aminophenoxy)phenyl]propane DMAc: N,N-dimethylacetamide

(Synthesis Example 1) Under a nitrogen flow, 94.1 parts by weight of m-TB (0.40 mol) and 14.3 parts by weight of TPE-R (0.05 mol) and DMAc in an amount such that the solid content concentration after polymerization becomes 7.5 wt% were added to a reaction tank, and stirred at room temperature to dissolve. Then, 29.4 parts by weight of BPDA (0.10 mol) and 87.1 parts by weight of PMDA (0.4 mol) were added, and the polymerization reaction was continued at room temperature for 3 hours to obtain a polyimide precursor resin liquid a. The solution viscosity of the polyimide precursor resin liquid a was 12,000 cps, and the weight average molecular weight was 250,000.

(Synthesis Example 2) Under a nitrogen flow, 77.8 parts by weight of BAPP (0.19 mol) and DMAc in an amount such that the solid content concentration after polymerization becomes 6.0 wt% were added to a reaction tank, and stirred at room temperature to dissolve. Then, 2.8 parts by weight of BPDA (0.01 mol) and 39.4 parts by weight of PMDA (0.18 mol) were added, and the polymerization reaction was continued at room temperature for 3 hours to obtain a polyimide precursor resin liquid b. The solution viscosity of the polyimide precursor resin liquid b was 700 cps, and the weight average molecular weight was 261,000.

(Synthesis Example 3) Under a nitrogen flow, 53.5 parts by weight of DAPE (0.27 mol) and DMAc in an amount such that the solid content concentration after polymerization becomes 7.0 wt% were added to a reaction tank, and stirred at room temperature to dissolve. Then, 86.7 parts by weight of BTDA (0.27 mol) were added, and the polymerization reaction was continued at room temperature for 3 hours to obtain a polyimide precursor resin liquid c. The solution viscosity of the polyimide precursor resin liquid c was 1,200 cps, and the weight average molecular weight was 140,000.

(Synthesis Example 4) Under a nitrogen flow, 35.96 parts by weight of m-TB (0.1691 mol), 2.75 parts by weight of TPE-Q (0.0094 mol), 3.86 parts by weight of BAPP (0.0094 mol), and DMAc in an amount such that the solid content concentration after polymerization becomes 15.0 wt% were added to a reaction tank, and stirred at room temperature to dissolve. Then, 20.18 parts by weight of PMDA (0.0925 mol) and 27.26 parts by weight of BPDA (0.0925 mol) were added, and the polymerization reaction was carried out while continuing to stir at room temperature for 3 hours to obtain a polyimide precursor resin liquid d. The solution viscosity of the polyimide precursor resin solution d is 25,000 cps, and the weight average molecular weight is 220,000.

(Synthesis Example 5) Under a nitrogen flow, 5.63 parts by weight of m-TB (0.0265 mol) and 30.96 parts by weight of TPE-R (0.1059 mol) and DMAc in an amount such that the solid content concentration after polymerization becomes 15.0 wt% were added to a reaction tank, and stirred at room temperature to dissolve. Then, 8.53 parts by weight of PMDA (0.0391 mol) and 26.88 parts by weight of BPDA (0.0913 mol) were added, and the polymerization reaction was continued at room temperature for 3 hours to obtain a polyimide precursor resin liquid e. The solution viscosity of the polyimide precursor resin liquid e was 3,000 cps, and the weight average molecular weight was 120,000.

(Example 1) A polyimide precursor resin liquid b was uniformly applied to a roughened surface (Rz = 0.6 μm) of a copper foil 1 (electrolytic copper foil, manufactured by Futian Metal Foil Powder Industry Co., Ltd., trade name: T49-DS-HD2, thickness: 12 μm) using a die coater with a coating width of 500 mm, and then heated and dried at 130°C to remove the solvent. Subsequently, a polyimide precursor resin liquid a was uniformly applied to the obtained surface with a coating width of 500 mm using a die coater in a manner of layering, and heated and dried at 90°C to 125°C to remove the solvent. Furthermore, the polyimide precursor resin liquid c was uniformly applied on the polyimide precursor resin liquid a layer with a coating width of 500 mm using a die coater, and the solvent was removed by heat drying at 130°C. Then, heat treatment and imidization were performed in a stepwise temperature increase step from room temperature to 320°C for about 30 minutes, and a metal-clad laminate 1 was obtained in which an insulating resin layer including three polyimide resin layers with a total thickness of about 4.5 μm (thickness deviation within ±0.3 μm) was formed on the copper foil 1. The thickness of the polyimide precursor resin liquid applied on the copper foil 1 after curing is about 0.8 μm/about 2.9 μm/about 0.8 μm in the order of b/a/c. The evaluation results of the metal-clad laminate 1 are as follows. Birefringence Δn (xy-z) in the thickness direction: 0.113 CTE _MD : 20 ppm/K CTE _TD : 20 ppm/K Film curling: 1.8 mm Thickness ratio of the thermoplastic polyimide layer on the casting surface side and the lamination surface side: T3/T1=1.0 Ratio of the thermoplastic layer: (T1+T3)/(T1+T2+T3)=0.36 Peel strength: 0.6 kN/m

(Example 2) The polyimide precursor resin liquid b was uniformly applied to the roughened surface of the copper foil 1 with a coating width of 500 mm using a die coater, and then the solvent was removed by heating and drying at 130°C. Subsequently, the polyimide precursor resin liquid a was uniformly applied to the obtained surface with a coating width of 500 mm using a die coater in a manner of layering, and the solvent was removed by heating and drying at 90°C to 125°C. Furthermore, the polyimide precursor resin liquid b was uniformly applied on the polyimide precursor resin liquid a layer with a coating width of 500 mm using a die coater, and the solvent was removed by heat drying at 130°C. Then, heat treatment and imidization were performed in a stepwise temperature increase step from room temperature to 320°C for about 30 minutes, and a metal-clad laminate 2 was obtained in which an insulating resin layer including three polyimide resin layers with a total thickness of about 11.8 μm (thickness deviation within ±0.3 μm) was formed on the copper foil 1. The thickness of the polyimide precursor resin liquid applied to the copper foil 1 after curing is about 1.8 μm/about 8.0 μm/about 2.0 μm in the order of b/a/b. The evaluation results of the metal-clad laminate 2 are as follows. Birefringence Δn (xy-z) in the thickness direction: 0.131 CTE _MD : 23 ppm/K CTE _TD : 23 ppm/K Film curling: -1.0 mm Thickness ratio of the thermoplastic polyimide layer on the casting surface side and the lamination surface side: T3/T1=1.1 Ratio of the thermoplastic layer: (T1+T3)/(T1+T2+T3)=0.32 Peel strength: 0.9 kN/m

(Example 3) The polyimide precursor resin liquid b was uniformly applied to the roughened surface of the copper foil 1 with a coating width of 500 mm using a die coater, and then the solvent was removed by heating and drying at 130°C. Subsequently, the polyimide precursor resin liquid a was uniformly applied to the obtained surface with a coating width of 500 mm using a die coater in a manner of layering, and the solvent was removed by heating and drying at 90°C to 125°C. Furthermore, the polyimide precursor resin liquid b was uniformly applied on the polyimide precursor resin liquid a layer with a coating width of 500 mm using a die coater, and the solvent was removed by heat drying at 130°C. Then, heat treatment and imidization were performed in a stepwise temperature increase step from room temperature to 320°C for about 25 minutes, and a metal-clad laminate 3 having an insulating resin layer with a total thickness of about 11.1 μm (thickness deviation within ±0.3 μm) formed on the copper foil 1 was obtained. The thickness of the polyimide precursor resin liquid applied to the copper foil 1 after curing is about 2.1 μm/about 6.8 μm/about 2.2 μm in the order of b/a/b. The evaluation results of the metal-clad laminate 3 are as follows. Birefringence Δn (xy-z) in the thickness direction: 0.138 CTE _MD : 27 ppm/K CTE _TD : 27 ppm/K Film curling: 9.3 mm Thickness ratio of the thermoplastic polyimide layer on the casting surface side and the lamination surface side: T3/T1=1.0 Ratio of the thermoplastic layer: (T1+T3)/(T1+T2+T3)=0.39 Peel strength: 0.9 kN/m

(Reference Example 1) A polyimide precursor resin liquid e was uniformly applied to the roughened surface of the copper foil 1 with a coating width of 500 mm using a die coater, and then the solvent was removed by heating and drying at 130°C. Subsequently, a polyimide precursor resin liquid d was uniformly applied to the obtained surface with a coating width of 500 mm using a die coater in a manner of layering, and the solvent was removed by heating and drying at 90°C to 125°C. Furthermore, the polyimide precursor resin liquid e was uniformly applied on the polyimide precursor resin liquid d layer with a coating width of 500 mm using a die coater, and the solvent was removed by heat drying at 135°C. Then, heat treatment and imidization were performed in a stepwise temperature increase step from room temperature to 320°C for about 30 minutes, and a metal-clad laminate 4 having an insulating resin layer with a total thickness of about 24.1 μm (thickness deviation within ±0.3 μm) formed on the copper foil 1 was obtained. The thickness of the polyimide precursor resin liquid applied on the copper foil 1 after curing is about 2.0 μm/about 19.3 μm/about 2.8 μm in the order of e/d/e. The evaluation results of the metal-clad laminate 4 are as follows. Birefringence Δn (xy-z) in the thickness direction: 0.142 CTE _MD : 23 ppm/K CTE _TD : 23 ppm/K Film curling: 0.5 mm Thickness ratio of the thermoplastic polyimide layer on the casting surface side and the laminate surface side: T3/T1=1.4 Ratio of the thermoplastic layer: (T1+T3)/(T1+T2+T3)=0.20 Peel strength: >1.0 kN/m

(Comparative Example 1) The polyimide precursor resin liquid a was uniformly applied to the copper foil 1 with a coating width of 500 mm using a die coater, and the solvent was removed by heating and drying at 90°C to 125°C. Then, the temperature was gradually raised from room temperature to 280°C over a period of about 5 minutes and imidization was performed to obtain a metal-clad laminate 5 having an insulating resin layer with a thickness of about 5.2 μm (thickness deviation ±0.3 μm) formed on the copper foil 1. The evaluation results of the metal-clad laminate 5 are as follows. Birefringence Δn in the thickness direction (xy-z): 0.123 CTE _MD : 22 ppm/K CTE _TD : 21 ppm/K Film curling: 20 mm or more (film becomes round and cannot be measured) Peel strength: 0.2 kN/m

(Comparative Example 2) The polyimide precursor resin liquid a was uniformly applied to the copper foil 1 with a coating width of 500 mm using a die coater, and the solvent was removed by heating and drying at 90°C to 125°C. Then, the copper foil 1 was heat treated and imidized for about 30 minutes from room temperature to 320°C, and a metal-clad laminate 6 having an insulating resin layer with a thickness of about 4.1 μm (thickness deviation ±0.3 μm) was obtained on the copper foil 1. The evaluation results of the metal-clad laminate 6 are as follows. Birefringence in thickness direction Δn (xy-z): 0.140 CTE _MD : 1 ppm/K CTE _TD : 1 ppm/K Film curvature: 2 mm Peel strength: 0.3 kN/m

As mentioned above, although the embodiment of the present invention is described in detail for the purpose of illustration, the present invention is not limited to the embodiment described above, and various modifications can be made.

2: polyimide film 2a: laminated surface 2b: cast surface 20: sample 21: light source 22: light receiving part d: thickness θ ₁ : incident angle θ ₂ : refraction angle L ₁ , L ₂ , L ₃ : light

FIG. 1 is a diagram for explaining the delay evaluation system used in the embodiment and the comparative example. FIG. 2 is a principle diagram for explaining the delay measurement method used in the embodiment and the comparative example.

Claims (9)

A metal-clad laminate comprises an insulating resin layer and a metal layer laminated on one side of the insulating resin layer, wherein the insulating resin layer comprises a non-thermoplastic polyimide layer made of non-thermoplastic polyimide and a thermoplastic polyimide layer disposed in contact with at least one side of the non-thermoplastic polyimide layer. A thermoplastic polyimide layer composed of amine, the thermoplastic polyimide layer is interposed between the metal layer and the non-thermoplastic polyimide layer, the thickness of the insulating resin layer is within the range of 2 μm or more and 15 μm or less, and the birefringence △n (xy-z) in the thickness direction is within the range of 0.080~0.140. The metal-clad laminate as claimed in claim 1, wherein the non-thermoplastic polyimide comprises tetracarboxylic acid residues and diamine residues, and contains 50 mol parts or more of diamine residues derived from a diamine compound represented by the following formula (1) relative to 100 mol parts of all diamine residues;

[In formula (1), R independently represents a halogen atom, or an alkyl or alkoxy group having 1 to 6 carbon atoms which may be substituted by a halogen atom, or a phenyl or phenoxy group which may be substituted by a monovalent alkyl group or alkoxy group having 1 to 6 carbon atoms, _n1 independently represents an integer of 0 to 4, and _n2 represents an integer of 0 to 1]. The metal-clad laminate as claimed in claim 1, wherein the insulating resin layer comprises a non-thermoplastic polyimide layer composed of the non-thermoplastic polyimide and a thermoplastic polyimide layer composed of thermoplastic polyimide disposed on both sides of the non-thermoplastic polyimide layer, and when the thermoplastic polyimide layer disposed on the side in contact with the metal layer When the thickness of the polyimide layer is set to T1, the thickness of the non-thermoplastic polyimide layer is set to T2, and the thickness of the thermoplastic polyimide layer disposed on the side opposite to the metal layer is set to T3, the thicknesses of T1, T2, and T3 satisfy the following relations (1) and (2); (1) 0.8≦T3/T1<1.4 (2) 0.20<(T1+T3)/(T1+T2+T3)≦0.50. A metal-clad laminate as described in any one of claims 1 to 3, wherein the CTE of the insulating resin layer is in the range of 15 ppm/K or more and 30 ppm/K or less, and the CTE (CTE _MD ) in the longitudinal (MD) direction and the CTE (CTE _TD ) in the transverse (TD) direction of the insulating resin layer satisfy the relationship of the following formula (i); |(CTE _MD -CTE _TD )/(CTE _MD +CTE _TD )|≦0.05...(i). A metal-clad laminate as described in any one of claim 1 to claim 3, wherein the width of the metal-clad laminate is greater than 470 mm and the deviation of the thickness of the insulating resin layer is within the range of ±0.5 μm. A metal-clad laminate as described in any one of claim 1 to claim 3, wherein in the insulating resin film obtained by etching away the metal layer, when the insulating resin film of 50 mm square is left to stand at 23°C and 50%RH for 24 hours with the convex surface in the center in contact with the flat surface, the curling amount obtained by calculating the average of the floating amounts at the four corners is 10 mm or less. The metal-clad laminate according to any one of claims 1 to 3, wherein the diamine residues derived from the diamine compound represented by formula (1) are in the range of 50 to 99 mol parts relative to 100 mol parts of all diamine residues contained in the non-thermoplastic polyimide, and the diamine residues derived from the diamine compound represented by the following formula (2) are in the range of 1 to 50 mol parts;

[In formula (2), R independently represents a halogen atom, or an alkyl or alkoxy group having 1 to 6 carbon atoms which may be substituted by a halogen atom, or a phenyl or phenoxy group which may be substituted by a monovalent hydrocarbon or alkoxy group having 1 to 6 carbon atoms, _Z1 independently represents a single bond, a divalent group selected from -O-, -S-, _-CH2- , -CH( _CH3 )-, -C( _CH3 ) _2- , -CO-, _-SO2- , or -NH-, _n3 independently represents an integer of 0 to 4, and _n4 represents an integer of 0 to 2; wherein at least one of _Z1 represents a divalent group selected from -O-, -S-, _-CH2- , -CH( _CH3 )-, -C( _CH3 ) _2- , -CO-, _-SO2- , or -NH-]. The metal-clad laminate as described in any one of claim 1 to claim 3 further includes another metal layer laminated on the insulating resin layer on the side opposite to the metal layer based on the insulating resin layer. A circuit substrate, which is formed by processing the metal layer of the metal-clad laminate as described in any one of claims 1 to 8 into wiring.