JP7712059B2 - Metal-clad laminates and circuit boards - Google Patents

Description

The present invention relates to metal-clad laminates and circuit boards that are useful as electronic components.

In recent years, with the progress of miniaturization, weight saving, and space saving of electronic devices, there is an increasing demand for flexible printed circuits (FPCs) that are thin, lightweight, flexible, and have excellent durability even when repeatedly bent. Because FPCs allow three-dimensional and high-density mounting even in a limited space, their applications are expanding to include wiring for moving parts of electronic devices such as HDDs, DVDs, and smartphones, as well as components such as cables and connectors.

In addition to the increased density mentioned above, the increasing performance of devices has also necessitated the need to accommodate higher frequencies for transmitted signals. When transmitting high-frequency signals, if there is a large transmission loss in the transmission path, problems such as loss of electrical signals and longer signal delay times will occur. For this reason, reducing transmission loss will also be important in the future for FPCs.

In order to improve high-frequency transmission characteristics, it has been proposed to use a laminate in which a film made of fluororesin is laminated on both sides of a polyimide film as an insulating resin layer (Patent Document 1). The insulating resin layer in Patent Document 1 uses a fluororesin, and therefore has excellent dielectric properties, but there are issues with dimensional stability. In particular, when applied to FPCs, there are concerns that dimensional changes before and after circuit processing by etching and before and after heat treatment will be significant.

In order to improve the high-frequency transmission characteristics, it has been proposed to laminate two single-sided metal-clad laminates together using an adhesive layer containing a specific diamine residue, while controlling the thickness of the entire resin layer and the adhesive layer (Patent Document 2). However, in Patent Document 2, the insulating layer of the single-sided metal-clad laminate separates the low dielectric tangent adhesive layer from the metal layer (wiring), leaving room for further improvement in the effect of reducing transmission loss.

JP 2004-216830 A JP 2018-170417 A

The object of the present invention is to provide a metal-clad laminate and a circuit board that can reduce transmission loss even in high-frequency transmission and have excellent dimensional stability.

As a result of intensive research, the inventors have found that by providing a transmission loss suppression layer with a low dielectric tangent in contact with each of a pair of metal layers (wiring), providing a structure in which multiple dimensional accuracy maintaining layers are stacked with intermediate transmission loss suppression layers between the transmission loss suppression layers, and setting the ratio of the total thickness of the dimensional accuracy maintaining layers to the overall thickness of the resin layer to a certain value or more, it is possible to suppress misalignment of the wiring even if the overall thickness of the resin layer is increased, thereby making it possible to achieve both reduced transmission loss and maintained dimensional accuracy.

The metal-clad laminate of the present invention comprises a first metal layer, a first transmission loss suppression layer provided in contact with one side of the first metal layer, a second metal layer, a second transmission loss suppression layer provided in contact with one side of the second metal layer, and a plurality of resin layers interposed between the first transmission loss suppression layer and the second transmission loss suppression layer.
In the metal-clad laminate of the present invention, a resin laminate is formed by the first transmission loss suppression layer, the second transmission loss suppression layer, and the multiple resin layers, and the resin laminate has at least two or more dimensional accuracy maintaining layers and an intermediate transmission loss suppression layer laminated between the dimensional accuracy maintaining layers.
The metal-clad laminate of the present invention satisfies the following conditions i and ii:
i) The dielectric loss tangent at 10 GHz measured by a split post dielectric resonator (SPDR) after 24 hours of conditioning under constant temperature and humidity conditions (normal state) of 23° C. and 50% RH, where Df ₁ is the dielectric loss tangent of the first transmission loss suppression layer and the second transmission loss suppression layer, and Df ₂ is the dielectric loss tangent of the dimensional accuracy maintaining layer, satisfies the relationship Df ₁ < Df ₂ ;
ii) the total thickness of the dimensional accuracy maintaining layer is within the range of 25 to 60% of the total thickness of the resin laminate;
It meets the following criteria.

The circuit board of the present invention comprises a first wiring layer, a first transmission loss suppression layer provided in contact with one side of the first wiring layer, a second wiring layer, a second transmission loss suppression layer provided in contact with one side of the second wiring layer, and a plurality of resin layers interposed between the first transmission loss suppression layer and the second transmission loss suppression layer.
The circuit board of the present invention includes a resin laminate formed by the first transmission loss suppression layer, the second transmission loss suppression layer, and the plurality of resin layers, and the resin laminate includes at least two or more dimensional accuracy maintaining layers, an intermediate transmission loss suppression layer laminated between the dimensional accuracy maintaining layers,
It has.
The circuit board of the present invention satisfies the following conditions i and ii:
i) The dielectric loss tangent at 10 GHz measured by a split post dielectric resonator (SPDR) after 24 hours of conditioning under constant temperature and humidity conditions (normal state) of 23° C. and 50% RH, where Df ₁ is the dielectric loss tangent of the first transmission loss suppression layer and the second transmission loss suppression layer, and Df ₂ is the dielectric loss tangent of the dimensional accuracy maintaining layer, satisfies the relationship Df ₁ < Df ₂ ;
ii) the total thickness of the dimensional accuracy maintaining layer is within the range of 25 to 60% of the total thickness of the resin laminate;
It meets the following criteria.

In the metal-clad laminate or circuit board of the present invention, the dimensional accuracy maintaining layer may be a low-thermal expansion polyimide layer whose minimum storage modulus in the temperature range of 100°C to 250°C is within the range of 1.0 to 8.0 GPa and whose thermal expansion coefficient is within the range of 15 to 25 ppm/K.

In the metal-clad laminate or circuit board of the present invention, the resin constituting the first transmission loss suppression layer and the second transmission loss suppression layer may be a polyimide obtained by reacting an acid anhydride component with a diamine component, and may contain 50 molar parts or more of a dimer diamine in which the two terminal carboxylic acid groups of a dimer acid are substituted with primary aminomethyl groups or amino groups per 100 molar parts of the total amount of the diamine component.

The metal-clad laminate of the present invention has a transmission loss suppression layer with a low dielectric tangent provided in contact with each of a pair of metal layers (wiring), so that the transmission loss in high-frequency signal transmission can be effectively suppressed. In addition, a structure in which multiple dimensional accuracy maintaining layers and intermediate transmission loss suppression layers are laminated between the transmission loss suppression layers is provided, and the total thickness ratio of the dimensional accuracy maintaining layers to the thickness of the entire resin layer is set to a certain value or more, so that low dielectric constant is achieved while maintaining high dimensional stability. Therefore, when the metal-clad laminate of the present invention is applied to a circuit board or the like that transmits high-frequency signals with a frequency of 10 GHz or more, for example, it becomes possible to effectively reduce transmission loss.

1 is a schematic diagram showing a configuration of a metal-clad laminate according to one embodiment of the present invention. FIG. FIG. 2 is a schematic cross-sectional view showing the configuration of a metal-clad laminate according to another embodiment of the present invention. FIG. 4 is a schematic cross-sectional view showing the configuration of a metal-clad laminate according to still another embodiment of the present invention. 4 is a schematic cross-sectional view showing one configuration example of a dimensional precision maintaining layer. FIG.

The embodiment of the present invention will be explained with reference to the drawings as appropriate.

[Metal-clad laminate]
FIG. 1 is a schematic diagram showing a configuration of a metal-clad laminate according to an embodiment of the present invention. The metal-clad laminate 10 according to the present embodiment includes:
a first metal layer M1;
a first transmission loss suppression layer BS1 provided in contact with one side of the first metal layer M1;
A second metal layer M2; and
a second transmission loss suppression layer BS2 provided in contact with one side of the second metal layer M2;
a plurality of resin layers interposed between the first transmission loss suppression layer BS1 and the second transmission loss suppression layer BS2;
Metal-clad laminate 10 has first transmission loss suppression layer BS1 and second transmission loss suppression layer BS2, which have low dielectric tangents, provided at positions closest to a pair of metal layers (first metal layer M1 and second metal layer M2 that form wiring), respectively, and therefore can effectively suppress transmission loss in high-frequency signal transmission.
Here, the first transmission loss suppression layer BS1, the second transmission loss suppression layer BS2, and a plurality of resin layers form a resin laminate 20. In addition to the first transmission loss suppression layer BS1 and the second transmission loss suppression layer BS2, the resin laminate 20 has at least two or more dimensional accuracy maintaining layers PL and an intermediate transmission loss suppression layer BS3 laminated between the dimensional accuracy maintaining layers PL.
In this way, by providing a laminated structure of a dimensional accuracy maintaining layer PL and an intermediate transmission loss suppression layer BS3 between the first transmission loss suppression layer BS1 and the second transmission loss suppression layer BS2, low dielectric constant is achieved while maintaining high dimensional stability.
The resin laminate 20 may have any resin layers other than those described above, but is preferably formed only from resin layers having the above functions.

As shown in FIG. 1, the first metal layer M1 and the second metal layer M2 are located on the outermost side, and the first transmission loss suppression layer BS1 and the second transmission loss suppression layer BS2 are arranged adjacent to the inner side of them, and further, between the first transmission loss suppression layer BS1 and the second transmission loss suppression layer BS2, a plurality of resin layers including a plurality of dimensional accuracy maintaining layers PL and an intermediate transmission loss suppression layer BS3 are interposed. Here, the first transmission loss suppression layer BS1 is adjacent to one dimensional accuracy maintaining layer PL, and the second transmission loss suppression layer BS2 is adjacent to another dimensional accuracy maintaining layer PL.

The metal-clad laminate 10 shown in FIG. 1 has two dimensional accuracy maintaining layers PL and one intermediate transmission loss suppression layer BS3, but there is no particular limit to the number of intermediate transmission loss suppression layers BS3 as long as there are two or more dimensional accuracy maintaining layers PL. For example, as shown in FIG. 2, it may have a configuration having three dimensional accuracy maintaining layers PL and two intermediate transmission loss suppression layers BS3, or as shown in FIG. 3, it may have a configuration having five dimensional accuracy maintaining layers PL and four intermediate transmission loss suppression layers BS3.

In the metal-clad laminate 10, the first metal layer M1 and the second metal layer M2 may have the same or different configurations, but it is preferable that they be made of the same material, have the same physical properties, and have the same thickness.

The first transmission loss suppression layer BS1 and the second transmission loss suppression layer BS2 may have the same or different configurations, but preferably have the same material, physical properties, and thickness. For example, by making the dielectric tangent and thickness of the first transmission loss suppression layer BS1 and the second transmission loss suppression layer BS2 the same, it becomes easier to design a high-frequency transmission circuit board to reduce transmission loss.

Furthermore, the configurations of the first transmission loss suppression layer BS1, the second transmission loss suppression layer BS2, and the intermediate transmission loss suppression layer BS3 may be the same or different, but are preferably made of the same material and have the same physical properties in order to improve the dielectric properties of the entire resin laminate 20 and effectively suppress the transmission loss of high-frequency signals.

The configuration of the multiple dimensional accuracy maintaining layers PL may be the same or different, but it is preferable that they be made of the same material, have the same physical properties, are the same thickness, and have the same layer structure, as this makes it easier to design the mechanical strength and dimensional accuracy when manufacturing the circuit board.

The metal-clad laminate 10 satisfies the following conditions i and ii.

Condition i:
When the dielectric tangent of the first transmission loss suppression layer BS1 and the second transmission loss suppression layer BS2 is Df ₁ and the dielectric tangent of the dimensional accuracy maintaining layer PL is Df ₂ , there is a relationship of Df ₁ <Df ₂ .
The dielectric loss tangent _Df1 of the first and second transmission loss suppression layers BS1 and BS2, which are in contact with the first and second metal layers M1 and M2, respectively, that are to become the circuit wiring that is the transmission path of the high-frequency signal, is designed to be lower than the dielectric loss tangent _Df2 of the dimensional accuracy maintaining layer PL, thereby effectively suppressing the transmission loss of the high-frequency signal. Even if the dielectric loss tangents of the first transmission loss suppression layer BS1 and the second transmission loss suppression layer BS2 are different, it is necessary that both satisfy the relationship _Df1 < _Df2 . Unless otherwise specified in the present invention, the dielectric constant and dielectric loss tangent refer to the dielectric constant and dielectric loss tangent at 10 GHz measured by a split post dielectric resonator (SPDR) after 24 hours of humidity control under constant temperature and humidity conditions (normal state) of 23°C and 50% RH.

From the viewpoint of suppressing transmission loss of high-frequency signals, the dielectric loss tangent _Df1 at 10 GHz of the first and second transmission loss suppression layers BS1, BS2 is preferably 0.005 or less, and more preferably 0.003 or less.

From the viewpoint of suppressing transmission loss of high-frequency signals, the dielectric loss tangent _Df3 of the intermediate transmission loss suppression layer BS3 at 10 GHz measured in the same manner as under condition i is preferably 0.005 or less, more preferably 0.003 or less, and most preferably the same as the dielectric loss tangent _Df1 of the first and second transmission loss suppression layers BS1, BS2.

In addition, it is desirable that the dielectric loss tangent _Df2 of the dimensional accuracy maintaining layer PL is as low as possible, but since the dimensional accuracy maintaining layer PL is a layer whose main purpose is to maintain dimensional accuracy and mechanical strength, it is preferably 0.012 or less, and more preferably 0.010 or less, provided that condition i is satisfied. Even if the dielectric loss tangent _Df2 of the dimensional accuracy maintaining layer PL is somewhat high, the low dielectric constant of the entire resin laminate 20 can be ensured by laminating it with the first and second transmission loss suppression layers BS1, BS2 and the intermediate transmission loss suppression layer BS3, which have lower dielectric loss tangents, and by taking into consideration the thickness ratios thereof.

Condition ii:
The total thickness T _PL of the dimensional accuracy maintaining layers PL is within the range of 25 to 60% of the total thickness T of the resin laminate 20 (i.e., the first and second transmission loss suppression layers BS1, BS2, one or more intermediate transmission loss suppression layers BS3, and the multiple dimensional accuracy maintaining layers PL).
By setting the ratio of the total thickness T _PL of the plurality of dimensional accuracy maintaining layers PL to the total thickness T of the resin laminate 20 within the above range, it is possible to reduce the transmission loss of high frequency signals while maintaining the dimensional accuracy and mechanical strength when the metal-clad laminate 10 is circuit-processed. From this viewpoint, the ratio of the thickness T _PL to the total thickness T is preferably within the range of 25 to 50%.

Here, the thickness of each layer in the resin laminate 20 is not particularly limited as it can be appropriately set depending on the intended use, but examples thereof include the following.
The thickness of each of the first and second transmission loss suppression layers BS1 and BS2 is preferably in the range of 2 to 100 μm, and more preferably in the range of 5 to 75 μm.
The thickness of each of the dimensional accuracy maintaining layers PL is preferably within a range of 10 to 100 μm, and more preferably within a range of 12 to 50 μm.
The thickness of each of the intermediate transmission loss suppression layers BS3 is preferably in the range of 12 to 150 μm, and more preferably in the range of 25 to 100 μm.
The total thickness T of the resin laminate 20 is preferably within a range of 50 to 300 μm, and more preferably within a range of 75 to 200 μm.

In addition, in order to reduce the dielectric constant of the entire resin laminate 20, the total thickness T _B of the first and second transmission loss suppression layers BS1, BS2 and the intermediate transmission loss suppression layer BS3 is preferably in the range of 40 to 75% of the total thickness T of the resin laminate 20, and more preferably in the range of 50 to 75%.

Below, we will explain each layer that makes up the metal-clad laminate 10.

[Metal layer]
The material of the first metal layer M1 and the second metal layer M2 is not particularly limited, but examples thereof include copper, stainless steel, iron, nickel, beryllium, aluminum, zinc, indium, silver, gold, tin, zirconium, tantalum, titanium, lead, magnesium, manganese, and alloys thereof. Among these, copper or a copper alloy is particularly preferable. The material of the wiring layer in the circuit board of this embodiment, which will be described later, is the same as that of the first metal layer M1 and the second metal layer M2.

The thickness of the first metal layer M1 and the second metal layer M2 is not particularly limited, but when a metal foil such as copper foil is used, it is preferably 35 μm or less, and more preferably in the range of 5 to 25 μm. From the viewpoint of production stability and handling, it is preferable that the lower limit of the thickness of the metal foil is 5 μm. When copper foil is used, it may be rolled copper foil or electrolytic copper foil. In addition, commercially available copper foil may be used as the copper foil.

The metal foil may also be surface-treated with, for example, siding, aluminum alcoholate, aluminum chelate, silane coupling agent, etc., for the purpose of, for example, rust prevention or improving adhesion.

[Transmission loss suppression layer]
The resins constituting the first and second transmission loss suppression layers BS1, BS2 and the intermediate transmission loss suppression layer BS3 (hereinafter sometimes collectively referred to as "transmission loss suppression layers BS1 to BS3") preferably have a glass transition temperature (Tg) of 180°C or less, more preferably 160°C or less. By setting the glass transition temperature of the transmission loss suppression layers BS1 to BS3 to 180°C or less, thermocompression bonding at low temperatures is possible, thereby alleviating internal stress generated during lamination and suppressing dimensional changes after circuit processing. If the Tg of the transmission loss suppression layers BS1 to BS3 exceeds 180°C, the temperature becomes high when they are interposed between the dimensional accuracy maintaining layers PL and bonded, which may impair dimensional stability after circuit processing.

The transmission loss suppression layers BS1 to BS3 preferably have a maximum storage modulus of 1.0 GPa or less in a temperature range of 100° C. to 250° C. Such a storage modulus can reduce internal stress during thermocompression bonding and maintain dimensional stability after circuit processing. In addition, warping is unlikely to occur even after a solder reflow process after circuit processing.

The resin constituting the first and second transmission loss suppression layers BS1, BS2 and the intermediate transmission loss suppression layer BS3 is preferably a polyimide, more preferably a thermoplastic polyimide (hereinafter sometimes referred to as "DDA-type polyimide") obtained by imidizing a precursor polyamic acid obtained by reacting an acid anhydride component with a diamine component containing 50 mol parts or more of a dimer diamine in which two terminal carboxylic acid groups of a dimer acid are substituted with primary aminomethyl groups or amino groups, relative to a total of 100 mol parts of the diamine component, or a crosslinked cured product thereof. In addition, when the term "polyimide" is used in the present invention, it means a resin made of a polymer having an imide group in the molecular structure, such as polyamideimide, polyetherimide, polyesterimide, polysiloxaneimide, polybenzimidazoleimide, etc., in addition to polyimide.

<DDA-based polyimide>
DDA-based polyimides are aliphatic thermoplastic polyimides that are highly flexible and have sufficient toughness even when a large amount of liquid crystalline polymer filler is added, and when a resin film is formed, it has a high ability to retain its shape.

DDA-based polyimides contain tetracarboxylic acid residues derived from the raw material tetracarboxylic acid anhydride and diamine residues derived from the raw material diamine compound. In the present invention, the tetracarboxylic acid residue refers to a tetravalent group derived from the tetracarboxylic acid dianhydride, and the diamine residue refers to a divalent group derived from the diamine compound. By reacting the raw materials tetracarboxylic acid anhydride and diamine compound in approximately equimolar amounts, the types and amounts of the tetracarboxylic acid residues and diamine residues contained in the DDA-based polyimide can be made to roughly correspond to the types and amounts of the raw materials.

(Acid anhydride component)
The DDA polyimide may use, as a raw material, any tetracarboxylic anhydride generally used in thermoplastic polyimides without any particular limitations, but it is preferable that the DDA polyimide contains tetracarboxylic anhydrides represented by the following general formula (1) and/or (2) in total at 90 mol% or more relative to the total acid anhydride components. In other words, the DDA polyimide preferably contains tetracarboxylic acid residues derived from tetracarboxylic anhydrides represented by the following general formula (1) and/or (2) in total at 90 mol% or more relative to 100 mol% of all tetracarboxylic acid residues. By containing tetracarboxylic acid residues derived from tetracarboxylic anhydrides represented by the following general formula (1) and/or (2) in total at 90 mol% or more relative to 100 mol% of tetracarboxylic acid residues, it is preferable that the DDA polyimide easily achieves both flexibility and heat resistance. If the total amount of tetracarboxylic acid residues derived from tetracarboxylic anhydrides represented by the following general formula (1) and/or (2) is less than 90 mol%, the solvent solubility of the DDA polyimide tends to decrease.

In general formula (1), X represents a single bond or a divalent group selected from the following formulas, and in general formula (2), the cyclic portion represented by Y represents a cyclic saturated hydrocarbon group selected from a 4-membered ring, a 5-membered ring, a 6-membered ring, a 7-membered ring, or an 8-membered ring.

In the above formula, Z represents —C ₆ H ₄ —, —(CH ₂ )n— or —CH ₂ —CH(—O—C(═O)—CH ₃ )—CH ₂ —, where n represents an integer of 1 to 20.

Examples of tetracarboxylic acid anhydrides represented by the above general formula (1) include 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA), 4,4'-oxydiphthalic anhydride (ODPA), 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), p-phenylenebis(trimellitic acid monoester anhydride) (TAHQ), and ethylene glycol bisanhydrotrimellitate (TMEG). Among these, 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) is particularly preferred. When BTDA is used, the carbonyl group (ketone group) contributes to adhesion, so the adhesion of the DDA-based polyimide can be improved. In addition, the ketone group present in the molecular skeleton of BTDA may react with the amino group of an amino compound for crosslinking (described later) to form a C=N bond, which is likely to produce an effect of improving heat resistance. From this perspective, it is preferable to contain 50 molar parts or more, more preferably 60 molar parts or more of tetracarboxylic acid residues derived from BTDA per 100 molar parts of tetracarboxylic acid residues.

Examples of tetracarboxylic acid anhydrides represented by general formula (2) include 1,2,3,4-cyclobutane tetracarboxylic acid dianhydride, 1,2,3,4-cyclopentane tetracarboxylic acid dianhydride, 1,2,4,5-cyclohexane tetracarboxylic acid dianhydride, 1,2,4,5-cycloheptane tetracarboxylic acid dianhydride, and 1,2,5,6-cyclooctane tetracarboxylic acid dianhydride.

DDA-based polyimides may contain tetracarboxylic acid residues derived from acid anhydrides other than the tetracarboxylic acid anhydrides represented by the above general formula (1) and general formula (2) within the scope of the invention. There are no particular limitations on such tetracarboxylic acid residues, and examples thereof include pyromellitic dianhydride, 2,3',3,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'- or 2,3,3',4'-benzophenonetetracarboxylic dianhydride, 2,3',3,4'-diphenylethertetracarboxylic dianhydride, bis(2,3-dicarboxyphenyl)ether dianhydride, 3,3'',4,4''-, 2,3,3'',4''- or 2,2'',3,3''-p-terphenyltetracarboxylic dianhydride, 2,3',3,4''- ... ,2-Bis(2,3- or 3,4-dicarboxyphenyl)-propane dianhydride, bis(2,3- or 3,4-dicarboxyphenyl)methane dianhydride, bis(2,3- or 3,4-dicarboxyphenyl)sulfone dianhydride, 1,1-bis(2,3- or 3,4-dicarboxyphenyl)ethane dianhydride, 1,2,7,8-, 1,2,6,7- or 1,2,9,10-phenanthrene tetracarboxylic dianhydride, 2,3,6,7-anthracene tetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl) ) tetrafluoropropane dianhydride, 1,2,5,6-naphthalene tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride, 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylic dianhydride, 2,6- or 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,6,7- (or 1,4,5,8-) tetrachloronaphthalene-1,4,5,8- (or 2, 3,6,7-) tetracarboxylic acid dianhydride, 2,3,8,9-, 3,4,9,10-, 4,5,10,11- or 5,6,11,12-perylene-tetracarboxylic acid dianhydride, pyrazine-2,3,5,6-tetracarboxylic acid dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic acid dianhydride, thiophene-2,3,4,5-tetracarboxylic acid dianhydride, 4,4'-bis(2,3-dicarboxyphenoxy)diphenylmethane dianhydride, and other aromatic tetracarboxylic acid dianhydrides are included.

(Diamine component)
DDA-based polyimides use, as a raw material, a diamine component containing 50 molar parts or more, more preferably 70 molar parts or more, of dimer diamine, which is formed by substituting two terminal carboxylic acid groups of a dimer acid with primary aminomethyl groups or amino groups, per 100 molar parts of the total amount of the diamine component. By containing the dimer diamine in the above amount, the dielectric properties of the polyimide can be improved, and the thermocompression bonding properties can be improved by lowering the glass transition temperature (lowering Tg) of the polyimide, and the internal stress can be alleviated by lowering the elastic modulus.

Dimer diamine means a diamine in which two terminal carboxylic acid groups (-COOH) of a dimer acid are replaced by primary aminomethyl groups (-CH ₂ -NH ₂ ) or amino groups (-NH ₂ ). Dimer acid is a known dibasic acid obtained by intermolecular polymerization reaction of unsaturated fatty acids, and its industrial production process is almost standardized in the industry, and is obtained by dimerizing unsaturated fatty acids having 11 to 22 carbon atoms using a clay catalyst or the like. Industrially obtained dimer acid is mainly composed of a dibasic acid having 36 carbon atoms obtained by dimerizing unsaturated fatty acids having 18 carbon atoms such as oleic acid, linoleic acid, and linolenic acid, but contains any amount of monomer acid (having 18 carbon atoms), trimer acid (having 54 carbon atoms), and other polymerized fatty acids having 20 to 54 carbon atoms depending on the degree of purification. In addition, although double bonds remain after the dimerization reaction, in the present invention, those which have been further subjected to a hydrogenation reaction to reduce the degree of unsaturation are also included in the dimer acid. A dimer diamine can be defined as a diamine compound obtained by substituting a terminal carboxylic acid group of a dibasic acid compound having a carbon number of 18 to 54, preferably 22 to 44, with a primary aminomethyl group or an amino group.

Dimer diamine has the characteristic of being able to impart properties derived from the dimer acid skeleton. In other words, since dimer diamine is an aliphatic macromolecule with a molecular weight of about 560 to 620, it can increase the molecular molar volume and relatively reduce the polar groups of DDA-based polyimide. It is believed that such characteristics of dimer acid type diamine contribute to improving the dielectric properties by reducing the dielectric constant and dielectric tangent while suppressing the deterioration of the heat resistance of DDA-based polyimide. In addition, since it has two freely moving hydrophobic chains with 7 to 9 carbon atoms and two chain-like aliphatic amino groups with a length close to 18 carbon atoms, it is not only able to impart flexibility to DDA-based polyimide, but also to give DDA-based polyimide an asymmetric chemical structure or a non-planar chemical structure, which is believed to be able to reduce the dielectric constant.

The dimer diamine used in the present invention is preferably purified in order to reduce components other than the dimer diamine. The purification method is not particularly limited, but known methods such as distillation and precipitation purification are suitable. Dimer diamine before purification is available as a commercially available product, such as PRIAMINE 1073 (trade name), PRIAMINE 1074 (trade name), and PRIAMINE 1075 (trade name) manufactured by Croda Japan.

Diamine compounds other than dimer diamine used in DDA-based polyimides include aromatic diamine compounds and aliphatic diamine compounds. Specific examples of these include 1,4-diaminobenzene (p-PDA; paraphenylenediamine), 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB), 2,2'-n-propyl-4,4'-diaminobiphenyl (m-NPB), 4-aminophenyl-4'-aminobenzoate (APAB), 2,2-bis-[4-(3-aminophenoxy)phenyl]propane, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)biphenyl, bis[1-(3-aminophenoxy)]biphenyl, bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(3 -aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)]benzophenone, 9,9-bis[4-(3-aminophenoxy)phenyl]fluorene, 2,2-bis-[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis-[4-(3-aminophenoxy)phenyl]hexafluoropropane, 3,3'-dimethyl-4,4'-diaminobiphenyl, 4,4'-methylenedi-o-toluidine, 4,4'-methylenedi-2,6-xylidine, 4,4'-methylene-2,6-diethylaniline, 3,3'-diaminodiphenylethane, 3,3'-diaminobiphenyl, 3 ,3'-Dimethoxybenzidine, 3,3''-Diamino-p-terphenyl, 4,4'-[1,4-phenylenebis(1-methylethylidene)]bisaniline, 4,4'-[1,3-phenylenebis(1-methylethylidene)]bisaniline, bis(p-aminocyclohexyl)methane, bis(p-β-amino-t-butylphenyl)ether, bis(p-β-methyl-δ-aminopentyl)benzene, p-bis(2-methyl-4-aminopentyl)benzene, p-bis(1,1-dimethyl-5-aminopentyl)benzene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2,4-bis(β-amino-t -butyl)toluene, 2,4-diaminotoluene, m-xylene-2,5-diamine, p-xylene-2,5-diamine, m-xylylenediamine, p-xylylenediamine, 2,6-diaminopyridine, 2,5-diaminopyridine, 2,5-diamino-1,3,4-oxadiazole, piperazine, 2'-methoxy-4,4'-diaminobenzanilide, 4,4'-diaminobenzanilide, 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene, 6-amino-2-(4-aminophenoxy)benzoxazole, 1,3-bis(3-aminophenoxy)benzene and other diamine compounds.

DDA-based polyimides can be produced by reacting the above-mentioned acid anhydride and diamine components in a solvent to produce polyamic acid, which is then heated to close the ring. For example, the acid anhydride and diamine components are dissolved in approximately equimolar amounts in an organic solvent, and the mixture is stirred at a temperature in the range of 0 to 100°C for 30 minutes to 24 hours to cause a polymerization reaction, thereby obtaining polyamic acid, which is a precursor of polyimide. In the reaction, the reaction components are dissolved so that the resulting precursor is in the range of 5 to 50% by weight, preferably 10 to 40% by weight, in the organic solvent. 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, dimethylsulfoxide (DMSO), hexamethylphosphoramide, N-methylcaprolactam, dimethyl sulfate, cyclohexanone, methylcyclohexane, dioxane, tetrahydrofuran, diglyme, triglyme, methanol, ethanol, benzyl alcohol, and cresol. Two or more of these solvents can be used in combination, and aromatic hydrocarbons such as xylene and toluene can also be used in combination. The amount of such organic solvents used is not particularly limited, but it is preferable to adjust the amount so that the concentration of the polyamic acid solution obtained by the polymerization reaction is about 5 to 50% by weight.

The synthesized polyamic acid is usually advantageously used as a reaction solvent solution, but it can be concentrated, diluted, or replaced with another organic solvent if necessary. Polyamic acid is also advantageously used because it generally has excellent solvent solubility. The viscosity of the polyamic acid solution is preferably within the range of 500 mPa·s to 100,000 mPa·s. If it is outside this range, defects such as uneven thickness and streaks are likely to occur in the film during coating operations using a coater, etc.

There are no particular limitations on the method for imidizing polyamic acid to form polyimide, and a suitable method is, for example, heat treatment in the solvent at a temperature in the range of 80 to 400°C for 1 to 24 hours. The temperature may be constant, or it may be changed during the process.

In DDA-based polyimides, the dielectric properties, thermal expansion coefficient, tensile modulus, glass transition temperature, etc. can be controlled by selecting the types of the acid anhydride components and diamine components, and the molar ratios of each when two or more types of acid anhydride components or diamine components are used. In addition, in DDA-based polyimides, when multiple polyimide structural units are present, they may be present as blocks or randomly, but it is preferable that they are present randomly.

The weight average molecular weight of the DDA polyimide is preferably in the range of 10,000 to 200,000, for example. If the weight average molecular weight is within this range, it is easy to control the weight average molecular weight of the polyimide. For example, when applied as an adhesive for FPCs, the weight average molecular weight of the DDA polyimide is more preferably in the range of 20,000 to 150,000, and even more preferably in the range of 40,000 to 150,000. When applied as an adhesive for FPCs, if the weight average molecular weight of the DDA polyimide is less than 20,000, the flow resistance tends to deteriorate. On the other hand, if the weight average molecular weight of the DDA polyimide exceeds 150,000, the viscosity increases excessively and the polyimide becomes insoluble in a solvent, and defects such as uneven thickness of the adhesive layer and streaks tend to occur during coating operations.

The imide group concentration of the DDA polyimide is preferably 22% by weight or less, more preferably 20% by weight or less. Here, "imide group concentration" means 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 polyimide structure. If the imide group concentration exceeds 22% by weight, the molecular weight of the resin itself decreases, and the low moisture absorption property deteriorates due to an increase in polar groups, and Tg and elastic modulus increase.

The DDA polyimide is most preferably a completely imidized structure. However, a part of the polyimide may be an amic acid. The imidization rate can be calculated from the absorbance of the C=O stretching derived from the imide group at 1780 cm ^- 1, based on the benzene ring absorber at about 1015 cm- ¹ , by measuring the infrared absorption spectrum of the polyimide thin film by the single reflection ATR method using a Fourier transform infrared spectrophotometer (commercial product: FT/IR620 manufactured by JASCO Corporation).

DDA-based polyimides can contain optional components such as plasticizers, other curable resin components such as epoxy resins, curing agents, curing accelerators, inorganic fillers, coupling agents, bulking agents, solvents, and flame retardants.

[Crosslinking of DDA-based polyimide]
When the DDA polyimide has a ketone group, the ketone group can be reacted with an amino group of an amino compound having at least two primary amino groups as functional groups (hereinafter, sometimes referred to as "amino compound for crosslinking") to form a C=N bond, thereby forming a crosslinked structure. The formation of the crosslinked structure can improve the heat resistance of the DDA polyimide. A preferred tetracarboxylic anhydride for forming a DDA polyimide having a ketone group is, for example, 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), and a preferred diamine compound is, for example, an aromatic diamine such as 4,4'-bis(3-aminophenoxy)benzophenone (BABP) or 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene (BABB).

For the purpose of forming a crosslinked structure, it is particularly preferable to include the above-mentioned DDA-based polyimide, which contains BTDA residues derived from BTDA in an amount of preferably 50 mol % or more, more preferably 60 mol % or more, relative to the total tetracarboxylic acid residues, and an amino compound for crosslinking. In the present invention, the "BTDA residue" means a tetravalent group derived from BTDA.

Examples of amino compounds for forming crosslinks include (I) dihydrazide compounds, (II) aromatic diamines, and (III) aliphatic amines. Among these, dihydrazide compounds are preferred. Aliphatic amines other than dihydrazide compounds are prone to form crosslinked structures even at room temperature, which raises concerns about the storage stability of the varnish, while aromatic diamines require high temperatures to form crosslinked structures. In this way, when a dihydrazide compound is used, it is possible to achieve both the storage stability of the varnish and a shortened curing time. Examples of dihydrazide compounds include oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, pimelic acid dihydrazide, suberic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, dodecanedioic acid dihydrazide, maleic acid dihydrazide, fumaric acid dihydrazide, diglyceryl ester dihydrazide, ... Dihydrazide compounds such as cholic acid dihydrazide, tartaric acid dihydrazide, malic acid dihydrazide, phthalic acid dihydrazide, isophthalic acid dihydrazide, terephthalic acid dihydrazide, 2,6-naphthoedioic acid dihydrazide, 4,4-bisbenzene dihydrazide, 1,4-naphthoic acid dihydrazide, 2,6-pyridine diacid dihydrazide, and itaconic acid dihydrazide are preferred. The above dihydrazide compounds may be used alone or in combination of two or more.

The above amino compounds, such as (I) dihydrazide compounds, (II) aromatic diamines, and (III) aliphatic amines, can also be used in combination of two or more types beyond the scope of the category, such as a combination of (I) and (II), a combination of (I) and (III), or a combination of (I), (II), and (III).

In order to make the mesh-like structure formed by the crosslinking with the crosslinking amino compound denser, the crosslinking amino compound used in the present invention preferably has a molecular weight (weight average molecular weight when the crosslinking amino compound is an oligomer) of 5,000 or less, more preferably 90 to 2,000, and even more preferably 100 to 1,500. Among these, crosslinking amino compounds having a molecular weight of 100 to 1,000 are particularly preferred. If the molecular weight of the crosslinking amino compound is less than 90, only one amino group of the crosslinking amino compound will form a C=N bond with a ketone group of the DDA polyimide, and the surroundings of the remaining amino groups will be three-dimensionally bulky, making it difficult for the remaining amino groups to form C=N bonds.

When crosslinking the ketone group in the DDA polyimide with the crosslinking amino compound, the crosslinking amino compound is added to a resin solution containing the DDA polyimide to cause a condensation reaction between the ketone group in the DDA polyimide and the primary amino group of the crosslinking amino compound. This condensation reaction hardens the resin solution to become a hardened product. In this case, the amount of the crosslinking amino compound added can be 0.004 to 1.5 moles, preferably 0.005 to 1.2 moles, more preferably 0.03 to 0.9 moles, and most preferably 0.04 to 0.6 moles of primary amino groups per mole of ketone group. If the amount of crosslinking amino compound added is such that the total number of primary amino groups per mole of ketone groups is less than 0.004 moles, crosslinking by the crosslinking amino compound is insufficient, and heat resistance after curing tends to be difficult to achieve. If the amount of crosslinking amino compound added exceeds 1.5 moles, the unreacted crosslinking amino compound acts as a thermoplasticizer, tending to reduce the heat resistance of the adhesive layer.

The conditions of the condensation reaction for forming crosslinks are not particularly limited as long as the ketone group in the DDA polyimide reacts with the primary amino group of the amino compound for forming crosslinks to form an imine bond (C=N bond). The temperature of the heat condensation is preferably in the range of, for example, 120 to 220°C, more preferably in the range of 140 to 200°C, for the purpose of releasing water produced by condensation out of the system, or for the purpose of simplifying the condensation step when the heat condensation reaction is carried out subsequently to the synthesis of the DDA polyimide. The reaction time is preferably about 30 minutes to 24 hours. The end point of the reaction can be confirmed by, for example, a Fourier transform infrared spectrophotometer (commercial product: FT/IR620 manufactured by JASCO) by measuring the infrared absorption spectrum, based on the decrease or disappearance of the absorption peak derived from the ketone group in the polyimide resin at around 1670 cm ^-1 , and the appearance of the absorption peak derived from the imine group at around 1635 cm ^-1 .

The thermal condensation of the ketone group of the DDA polyimide with the primary amino group of the crosslinking amino compound can be carried out, for example, by the following method:
(1) A method in which, following the synthesis (imidization) of a DDA-based polyimide, an amino compound for crosslinking is added and heated;
(2) A method in which an excess amount of an amino compound is charged in advance as a diamine component, and following the synthesis (imidization) of a DDA-based polyimide, the remaining amino compound that is not involved in imidization or amidation is used as an amino compound for crosslinking and heated together with the DDA-based polyimide;
Or,
(3) A method in which the DDA-based polyimide composition containing the above-mentioned amino compound for crosslinking is processed into a predetermined shape (for example, after being applied to a substrate or formed into a film), and then heated;
This can be done by, etc.

To impart heat resistance to DDA-based polyimides, the formation of imine bonds has been described as a method for forming crosslinked structures, but this is not limiting. For example, polyimides can be cured by blending and curing compounds with unsaturated bonds, such as epoxy resins, epoxy resin curing agents, maleimides, activated ester resins, and resins with styrene skeletons.

[Dimensional accuracy maintaining layer]
In order to maintain the mechanical strength of the metal-clad laminate 10, the dimensional accuracy maintaining layer PL preferably has a minimum storage modulus in the range of 1.0 to 8.0 GPa, more preferably 2.0 to 6.0 GPa , in the temperature range of 100° C. to 250° C. If the minimum storage modulus of the dimensional accuracy maintaining layer PL is less than 1.0 GPa, sufficient mechanical strength and dimensional accuracy after circuit processing cannot be obtained. If the minimum storage modulus exceeds 8.0 GPa, warping is likely to occur during lamination pressing.

In addition, in order to maintain the dimensional accuracy when the metal-clad laminate 10 is circuit-processed, the dimensional accuracy maintaining layer PL preferably has a coefficient of thermal expansion (CTE) in the range of 15 to 25 ppm/K, and more preferably in the range of 16 to 23 ppm/K. If the CTE of the dimensional accuracy maintaining layer PL is less than 15 ppm/K, the metal-clad laminate 10 is more likely to warp, and if it exceeds 25 ppm/K, dimensional accuracy after circuit processing cannot be obtained.

The dimensional accuracy maintaining layer PL is not particularly limited as long as it is made of a resin having electrical insulation properties, and examples thereof include polyimide, epoxy resin, phenolic resin, polyethylene, polypropylene, polytetrafluoroethylene, silicone, ETFE, etc., but it is preferable that it is made of polyimide. In other words, it is preferable that the dimensional accuracy maintaining layer PL is a low thermal expansion polyimide layer consisting of a single layer or multiple layers.

When the dimensional accuracy maintaining layer PL is a single polyimide layer, it can have the same configuration as the non-thermoplastic polyimide layer 31 described below. As the single polyimide layer, for example, commercially available products such as Kapton EN (product name; manufactured by DuPont Toray Co., Ltd.) and Apical NPI (product name; manufactured by Kaneka Corporation) can be used.

When the dimensional accuracy maintaining layer PL is composed of a plurality of polyimide layers, the dimensional accuracy maintaining layer PL may have a structure in which a thermoplastic polyimide layer 33 containing a thermoplastic polyimide as a resin component is laminated on both sides of a non-thermoplastic polyimide layer 31 containing a non-thermoplastic polyimide as a resin component, as shown in FIG. 4. In addition, the term "non-thermoplastic polyimide" generally refers to a polyimide that does not soften or exhibit adhesiveness even when heated, but in the present invention, it refers to a polyimide whose storage modulus at 30°C is 1.0×10 ⁹ Pa or more and whose storage modulus at 350°C is 1.0×10 ⁸ Pa or more, as measured using a dynamic viscoelasticity measuring device (DMA). In addition, the term "thermoplastic polyimide" generally refers to a polyimide whose glass transition temperature (Tg) can be clearly confirmed, but in the present invention, it refers to a polyimide whose storage modulus at 30°C is 1.0×10 ⁹ Pa or more and whose storage modulus at 350°C is less than 1.0×10 ⁸ Pa, as measured using a DMA.

Next, we will explain preferred configuration examples of the non-thermoplastic polyimide layer 31 and the thermoplastic polyimide layer 33 for forming the dimensional accuracy maintaining layer PL.

Non-thermoplastic polyimide layer:
The non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer 31 contains a tetracarboxylic acid residue and a diamine residue. The polyimide preferably contains an aromatic tetracarboxylic acid residue derived from an aromatic tetracarboxylic dianhydride and an aromatic diamine residue derived from an aromatic diamine.

(Tetracarboxylic acid residue)
The non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer 31 preferably contains, as the tetracarboxylic acid residue, a tetracarboxylic acid residue derived from at least one of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and 1,4-phenylenebis(trimellitic acid monoester) dianhydride (TAHQ), and a tetracarboxylic acid residue derived from at least one of pyromellitic dianhydride (PMDA) and 2,3,6,7-naphthalenetetracarboxylic dianhydride (NTCDA).

Tetracarboxylic acid residues derived from BPDA (hereinafter also referred to as "BPDA residues") and tetracarboxylic acid residues derived from TAHQ (hereinafter also referred to as "TAHQ residues") tend to form ordered polymer structures and can reduce dielectric tangent and hygroscopicity by suppressing molecular motion. BPDA residues can impart self-supporting properties to the gel film of the polyamic acid of the polyimide precursor, but at the same time, they tend to increase the CTE after imidization and lower the glass transition temperature, thereby reducing heat resistance.

From this viewpoint, the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer 31 is controlled so that the total of BPDA residues and TAHQ residues is preferably within the range of 30 to 60 molar parts, more preferably 40 to 50 molar parts, per 100 molar parts of all tetracarboxylic acid residues. If the total of BPDA residues and TAHQ residues is less than 30 molar parts, the formation of an ordered structure of the polymer will be insufficient, resulting in reduced moisture absorption resistance and insufficient reduction in dielectric tangent. If it exceeds 60 molar parts, there is a risk of an increase in CTE, an increase in the amount of change in in-plane retardation (RO), and reduced heat resistance.

In addition, the tetracarboxylic acid residue derived from pyromellitic dianhydride (hereinafter also referred to as "PMDA residue") and the tetracarboxylic acid residue derived from 2,3,6,7-naphthalenetetracarboxylic dianhydride (hereinafter also referred to as "NTCDA residue") are residues that have rigidity, and therefore increase the in-plane orientation, suppress the CTE low, and also play a role in controlling the in-plane retardation (RO) and the glass transition temperature. On the other hand, since the PMDA residue has a small molecular weight, if the amount of the PMDA residue becomes too large, the imide group concentration of the polymer increases, the polar groups increase, and the hygroscopicity increases, and the dielectric tangent increases due to the influence of moisture inside the molecular chain. In addition, the NTCDA residue tends to make the film brittle due to the highly rigid naphthalene skeleton, and tends to increase the elastic modulus.
Therefore, the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer preferably contains the total of PMDA residues and NTCDA residues in the range of 40 to 70 molar parts, more preferably in the range of 50 to 60 molar parts, and even more preferably in the range of 50 to 55 molar parts, relative to 100 molar parts of all tetracarboxylic acid residues. If the total of PMDA residues and NTCDA residues is less than 40 molar parts, the CTE may increase or the heat resistance may decrease, while if it exceeds 70 molar parts, the imide group concentration of the polymer increases, the polar groups increase, and the low moisture absorption property is impaired, the dielectric loss tangent may increase, or the film may become brittle and the self-supporting property of the film may decrease.

The total amount of at least one of BPDA residues and TAHQ residues and at least one of PMDA residues and NTCDA residues is preferably 80 molar parts or more, and more preferably 90 molar parts or more, per 100 molar parts of all tetracarboxylic acid residues.

In addition, the molar ratio of at least one of BPDA residues and TAHQ residues to at least one of PMDA residues and NTCDA residues {(BPDA residues + TAHQ residues)/(PMDA residues + NTCDA residues)} is set within the range of 0.4 to 1.5, preferably within the range of 0.6 to 1.3, and more preferably within the range of 0.8 to 1.2, to control the CTE and the formation of an ordered structure of the polymer.

PMDA and NTCDA have a rigid skeleton, so compared to other common acid anhydride components, it is possible to control the in-plane orientation of the molecules in the polyimide, suppressing the coefficient of thermal expansion (CTE) and improving the glass transition temperature (Tg). In addition, BPDA and TAHQ have a larger molecular weight than PMDA, so an increase in the charge ratio reduces the imide group concentration, which is effective in reducing the dielectric tangent and moisture absorption rate. On the other hand, if the charge ratio of BPDA and TAHQ is increased, the in-plane orientation of the molecules in the polyimide decreases, leading to an increase in CTE. Furthermore, the formation of an ordered structure in the molecule progresses, and the haze value increases. From this perspective, the total charge amount of PMDA and NTCDA is within the range of 40 to 70 mol parts, preferably within the range of 50 to 60 mol parts, and more preferably within the range of 50 to 55 mol parts, relative to 100 mol parts of the total acid anhydride components of the raw material. If the total amount of PMDA and NTCDA charged is less than 40 molar parts per 100 molar parts of the total acid anhydride components of the raw material, the in-plane orientation of the molecules decreases, making it difficult to achieve a low CTE, and the heat resistance and dimensional stability of the film when heated due to a decrease in Tg. On the other hand, if the total amount of PMDA and NTCDA charged exceeds 70 molar parts, the moisture absorption rate tends to deteriorate and the elastic modulus tends to increase due to an increase in the imide group concentration.

BPDA and TAHQ are also effective in suppressing molecular motion and lowering the dielectric tangent and moisture absorption rate by reducing the imide group concentration, but they also increase the CTE of the polyimide film after imidization. From this perspective, the combined amount of BPDA and TAHQ to be charged should be within the range of 30 to 60 molar parts, preferably 40 to 50 molar parts, per 100 molar parts of the total acid anhydride components of the raw material.

Examples of tetracarboxylic acid residues other than the BPDA residue, TAHQ residue, PMDA residue, and NTCDA residue contained in the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer 31 include 3,3',4,4'-diphenylsulfonetetracarboxylic acid dianhydride, 4,4'-oxydiphthalic anhydride, 2,3',3,4'-biphenyltetracarboxylic acid dianhydride, 2,2',3,3'-, 2,3,3',4'-, or 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride, 2,3',3,4'-diphenylethertetracarboxylic acid dianhydride, bis(2,3-dicarboxylic acid), bis(2,3-dicarboxylic ... 2,2-bis(2,3- or 3,4-dicarboxyphenyl)-propane dianhydride, bis(2,3- or 3,4-dicarboxyphenyl)methane dianhydride, bis(2,3- or 3,4-dicarboxyphenyl)sulfone dianhydride, 1,1-bis(2,3- or 3,4-dicarboxyphenyl)ethane dianhydride, 1,2,7,8-, 1,2,6,7- or 1,2,9,10-phenanthrene-tetracarboxylic acid dianhydride Acid dianhydrides, 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, 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylic dianhydride, 2,6- or 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,6,7-(or 1,4,5,8-) Examples of the tetracarboxylic acid residues include those derived from aromatic tetracarboxylic acid dianhydrides such as tetrachloronaphthalene-1,4,5,8-(or 2,3,6,7-)tetracarboxylic acid dianhydride, 2,3,8,9-, 3,4,9,10-, 4,5,10,11- or 5,6,11,12-perylene-tetracarboxylic acid dianhydride, cyclopentane-1,2,3,4-tetracarboxylic acid dianhydride, pyrazine-2,3,5,6-tetracarboxylic acid dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic acid dianhydride, thiophene-2,3,4,5-tetracarboxylic acid dianhydride, 4,4'-bis(2,3-dicarboxyphenoxy)diphenylmethane dianhydride, and ethylene glycol bisanhydrotrimellitate.

(Diamine residue)
The diamine residue contained in the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer 31 is preferably a diamine residue derived from a diamine compound represented by the general formula (A1).

In formula (A1), the linking group Z represents a single bond or -COO-, Y independently represents a monovalent hydrocarbon having 1 to 3 carbon atoms, which may be substituted with a halogen atom or a phenyl group, or an alkoxy group having 1 to 3 carbon atoms, or a perfluoroalkyl group having 1 to 3 carbon atoms, or an alkenyl group, n represents an integer of 0 to 2, and p and q independently represent integers of 0 to 4. Here, "independently" means that in formula (A1), the multiple substituents Y, and further the integers p and q, may be the same or different. In formula (A1), the hydrogen atoms in the two amino groups at the ends may be substituted, for example, -NR ₂ R ₃ (wherein R ₂ and R ₃ independently represent any substituent such as an alkyl group).

The diamine compound represented by the general formula (A1) (hereinafter sometimes referred to as "diamine (A1)") is an aromatic diamine having one to three benzene rings. Diamine (A1) has a rigid structure, and therefore has the effect of imparting an orderly structure to the entire polymer. As a result, a polyimide with low gas permeability and low moisture absorption can be obtained, and the moisture inside the molecular chain can be reduced, thereby lowering the dielectric tangent. Here, a single bond is preferable as the linking group Z.

Examples of diamines (A1) include 1,4-diaminobenzene (p-PDA; paraphenylenediamine), 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB), 2,2'-n-propyl-4,4'-diaminobiphenyl (m-NPB), and 4-aminophenyl-4'-aminobenzoate (APAB).

The non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer 31 preferably contains 80 molar parts or more, more preferably 85 molar parts or more, of diamine residues derived from diamine (A1) relative to 100 molar parts of all diamine residues. By using diamine (A1) in an amount within the above range, an ordered structure is easily formed throughout the polymer due to the rigid structure derived from the monomer, and a non-thermoplastic polyimide with low gas permeability, low moisture absorption, and low dielectric tangent is easily obtained.

When the diamine residues derived from diamine (A1) are within the range of 80 to 85 molar parts per 100 molar parts of all diamine residues in the non-thermoplastic polyimide, it is preferable to use 1,4-diaminobenzene as diamine (A1) from the viewpoint of a structure that is more rigid and has excellent in-plane orientation.

Other diamine residues contained in the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer 31 include, for example, 2,2-bis-[4-(3-aminophenoxy)phenyl]propane, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)biphenyl, bis[1-(3-aminophenoxy)]biphenyl, bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)]benzophenone, 9,9-bis[4-(3-aminophenoxy)phenyl]fluorene, 2,2-bis bis-[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis-[4-(3-aminophenoxy)phenyl]hexafluoropropane, 3,3'-dimethyl-4,4'-diaminobiphenyl, 4,4'-methylenedi-o-toluidine, 4,4'-methylenedi-2,6-xylidine, 4,4'-methylene-2,6-diethylaniline, 3,3'-diaminodiphenylethane, 3,3'-diaminobiphenyl, 3,3'-dimethoxybenzidine, 3,3''-diamino-p-terphenyl, 4,4'-[1,4-phenylenebis(1-methylethylidene)]bisaniline, 4,4'-[1 ,3-phenylenebis(1-methylethylidene)]bisaniline, bis(p-aminocyclohexyl)methane, bis(p-β-amino-t-butylphenyl)ether, bis(p-β-methyl-δ-aminopentyl)benzene, p-bis(2-methyl-4-aminopentyl)benzene, p-bis(1,1-dimethyl-5-aminopentyl)benzene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2,4-bis(β-amino-t-butyl)toluene, 2,4-diaminotoluene, m-xylene-2,5-diamine, p-xylene-2,5-diamine, m-xylylenediamine, p-xylylenediamine Examples of such diamine residues include diamine residues derived from aromatic diamine compounds such as amines, 2,6-diaminopyridine, 2,5-diaminopyridine, 2,5-diamino-1,3,4-oxadiazole, piperazine, 2'-methoxy-4,4'-diaminobenzanilide, 4,4'-diaminobenzanilide, 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene, and 6-amino-2-(4-aminophenoxy)benzoxazole, and diamine residues derived from aliphatic diamine compounds such as dimer acid type diamines in which the two terminal carboxylic acid groups of a dimer acid are replaced with primary aminomethyl groups or amino groups.

In non-thermoplastic polyimides, the thermal expansion coefficient, storage modulus, tensile modulus, etc. can be controlled by selecting the types of the tetracarboxylic acid residues and diamine residues, or the molar ratios of two or more types of tetracarboxylic acid residues or diamine residues. In addition, in non-thermoplastic polyimides, when multiple polyimide structural units are used, they may be present as blocks or randomly, but from the viewpoint of suppressing the variation in the in-plane retardation (RO), it is preferable that they are present randomly.

It is preferable that the tetracarboxylic acid residues and diamine residues contained in the non-thermoplastic polyimide are both aromatic groups, since this improves the dimensional accuracy of the polyimide film in a high-temperature environment and reduces the amount of change in the in-plane retardation (RO).

The imide group concentration of the non-thermoplastic polyimide is preferably 33% or less, more preferably 32% or less. Here, "imide group concentration" means 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 polyimide structure. When the imide group concentration exceeds 33%, the molecular weight of the resin itself decreases, and the low moisture absorption property also deteriorates due to the increase in polar groups. By selecting the combination of the acid anhydride and the diamine compound, the molecular orientation in the non-thermoplastic polyimide is controlled, thereby suppressing the increase in CTE associated with the decrease in the imide group concentration and ensuring low moisture absorption.

The weight-average molecular weight of the non-thermoplastic polyimide is preferably, for example, in the range of 10,000 to 400,000, and 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 film tends to decrease and it tends to become brittle. On the other hand, if the weight-average molecular weight exceeds 400,000, the viscosity increases excessively, and defects such as uneven film thickness and streaks tend to occur during the coating process.

The thickness of the non-thermoplastic polyimide layer 31 is preferably in the range of 6 μm to 100 μm, more preferably in the range of 9 μm to 50 μm, in order to ensure the function as a base layer and to facilitate transport during production and during thermoplastic polyimide coating. If the thickness of the non-thermoplastic polyimide layer 31 is less than the lower limit, electrical insulation and handling properties will be insufficient, and if the thickness exceeds the upper limit, productivity will decrease.

From the viewpoint of heat resistance, it is preferable that the non-thermoplastic polyimide layer 31 has a glass transition temperature (Tg) of 280°C or higher.

In addition, from the viewpoint of suppressing warping, the thermal expansion coefficient of the non-thermoplastic polyimide layer 31 is preferably in the range of 1 ppm/K to 30 ppm/K, more preferably in the range of 1 ppm/K to 25 ppm/K, and even more preferably in the range of 15 ppm/K to 25 ppm/K.

The non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer 31 may contain optional components such as plasticizers, other curable resin components such as epoxy resins, curing agents, curing accelerators, coupling agents, fillers, solvents, and flame retardants. However, some plasticizers contain many polar groups, which may promote the diffusion of copper from the copper wiring, so it is preferable to avoid using plasticizers as much as possible.

Thermoplastic polyimide layer:
The thermoplastic polyimide constituting the thermoplastic polyimide layer 33 contains a tetracarboxylic acid residue and a diamine residue, and preferably contains an aromatic tetracarboxylic acid residue derived from an aromatic tetracarboxylic dianhydride and an aromatic diamine residue derived from an aromatic diamine.

(Tetracarboxylic acid residue)
As the tetracarboxylic acid residue used in the thermoplastic polyimide constituting the thermoplastic polyimide layer 33, the same ones as those exemplified as the tetracarboxylic acid residue in the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer can be used.

(Diamine residue)
The diamine residue contained in the thermoplastic polyimide constituting the thermoplastic polyimide layer 33 is preferably a diamine residue derived from a diamine compound represented by any one of the general formulae (B1) to (B7).

In formulae (B1) to (B7), R ₁ independently represents a monovalent hydrocarbon group or alkoxy group having 1 to 6 carbon atoms, linking group A independently represents a divalent group selected from -O-, -S-, -CO-, -SO-, -SO ₂ -, -COO-, -CH ₂ -, -C(CH ₃ ) ₂ -, -NH- or -CONH-, and n ₁ independently represents an integer of 0 to 4. However, formula (B3) excluding those which overlap with formula (B2), and formula (B5) excluding those which overlap with formula (B4). Here, "independently" means that in one or two or more of formulae (B1) to (B7), multiple linking groups A, multiple R _1s or multiple n _1s may be the same or different. In the above formulas (B1) to (B7), the hydrogen atoms in the two terminal amino groups may be substituted, for example, -NR ₂ R ₃ (wherein R ₂ and R ₃ independently represent any substituent such as an alkyl group).

The diamine represented by formula (B1) (hereinafter sometimes referred to as "diamine (B1)") is an aromatic diamine having two benzene rings. In this diamine (B1), since an amino group directly bonded to at least one benzene ring and a divalent linking group A are at meta positions, the degree of freedom of the polyimide molecular chain is increased and the polyimide has high flexibility, which is considered to contribute to improving the flexibility of the polyimide molecular chain. Therefore, by using diamine (B1), the thermoplasticity of the polyimide is increased. Here, as the linking group A, -O-, -CH ₂ -, -C(CH ₃ ) ₂ -, -CO-, -SO ₂ -, and -S- are preferable.

Examples of diamines (B1) include 3,3'-diaminodiphenylmethane, 3,3'-diaminodiphenylpropane, 3,3'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylpropane, 3,4'-diaminodiphenyl sulfide, 3,3'-diaminobenzophenone, and (3,3'-bisamino)diphenylamine.

The diamine represented by formula (B2) (hereinafter sometimes referred to as "diamine (B2)") is an aromatic diamine having three benzene rings. In this diamine (B2), the amino group directly bonded to at least one benzene ring and the divalent linking group A are in the meta position, which increases the degree of freedom of the polyimide molecular chain and gives it high flexibility, which is thought to contribute to improving the flexibility of the polyimide molecular chain. Therefore, the use of diamine (B2) increases the thermoplasticity of the polyimide. Here, -O- is preferable as the linking group A.

Examples of diamines (B2) include 1,4-bis(3-aminophenoxy)benzene, 3-[4-(4-aminophenoxy)phenoxy]benzeneamine, and 3-[3-(4-aminophenoxy)phenoxy]benzeneamine.

The diamine represented by formula (B3) (hereinafter sometimes referred to as "diamine (B3)") is an aromatic diamine having three benzene rings. In this diamine (B3), two divalent linking groups A directly bonded to one benzene ring are in the meta position relative to each other, which increases the degree of freedom of the polyimide molecular chain and gives it high flexibility, which is thought to contribute to improving the flexibility of the polyimide molecular chain. Therefore, the use of diamine (B3) increases the thermoplasticity of the polyimide. Here, -O- is preferred as the linking group A.

Examples of diamines (B3) include 1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,3-bis(3-aminophenoxy)benzene (APB), 4,4'-[2-methyl-(1,3-phenylene)bisoxy]bisaniline, 4,4'-[4-methyl-(1,3-phenylene)bisoxy]bisaniline, and 4,4'-[5-methyl-(1,3-phenylene)bisoxy]bisaniline.

The diamine represented by formula (B4) (hereinafter sometimes referred to as "diamine (B4)") is an aromatic diamine having four benzene rings. This diamine (B4) has high flexibility due to the fact that the amino group directly bonded to at least one benzene ring and the divalent linking group A are at the meta position, and is considered to contribute to improving the flexibility of the polyimide molecular chain. Therefore, the use of diamine (B4) enhances the thermoplasticity of the polyimide. Here, the linking group A is preferably -O-, -CH ₂ -, -C(CH ₃ ) ₂ -, -SO ₂ -, -CO-, or -CONH-.

Examples of diamines (B4) include 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, and bis[4,4'-(3-aminophenoxy)]benzanilide.

The diamine represented by formula (B5) (hereinafter sometimes referred to as "diamine (B5)") is an aromatic diamine having four benzene rings. In this diamine (B5), two divalent linking groups A directly bonded to at least one benzene ring are mutually in meta positions, which increases the degree of freedom of the polyimide molecular chain and gives it high flexibility, which is thought to contribute to improving the flexibility of the polyimide molecular chain. Therefore, the use of diamine (B5) enhances the thermoplasticity of the polyimide. Here, -O- is preferred as the linking group A.

Examples of diamines (B5) include 4-[3-[4-(4-aminophenoxy)phenoxy]phenoxy]aniline, 4,4'-[oxybis(3,1-phenyleneoxy)]bisaniline, etc.

The diamine represented by formula (B6) (hereinafter sometimes referred to as "diamine (B6)") is an aromatic diamine having four benzene rings. This diamine (B6) has high flexibility due to having at least two ether bonds, and is considered to contribute to improving the flexibility of the polyimide molecular chain. Therefore, the use of diamine (B6) enhances the thermoplasticity of the polyimide. Here, the linking group A is preferably -C( _CH3 ) _2- , -O-, _-SO2- , or -CO-.

Examples of diamines (B6) include 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), bis[4-(4-aminophenoxy)phenyl]ether (BAPE), bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS), and bis[4-(4-aminophenoxy)phenyl]ketone (BAPK).

The diamine represented by formula (B7) (hereinafter sometimes referred to as "diamine (B7)") is an aromatic diamine having four benzene rings. This diamine (B7) has a highly flexible divalent linking group A on both sides of the diphenyl skeleton, and is therefore thought to contribute to improving the flexibility of the polyimide molecular chain. Therefore, the use of diamine (B7) enhances the thermoplasticity of the polyimide. Here, -O- is preferred as the linking group A.

Examples of diamines (B7) include bis[4-(3-aminophenoxy)]biphenyl, bis[4-(4-aminophenoxy)]biphenyl, etc.

The thermoplastic polyimide constituting the thermoplastic polyimide layer 33 contains 60 or more mol parts, preferably 60 or more 99 or less mol parts, more preferably 70 or more 95 or less mol parts of diamine residues derived from at least one diamine compound selected from diamine (B1) to diamine (B7) per 100 mol parts of all diamine residues. Since diamine (B1) to diamine (B7) have a molecular structure with flexibility, by using at least one diamine compound selected from these in an amount within the above range, the flexibility of the polyimide molecular chain can be improved and thermoplasticity can be imparted. If the total amount of diamine (B1) to diamine (B7) in the raw material is less than 60 mol parts per 100 mol parts of all diamine components, the flexibility of the polyimide resin is insufficient and sufficient thermoplasticity cannot be obtained.

As the diamine residue contained in the thermoplastic polyimide constituting the thermoplastic polyimide layer 33, a diamine residue derived from a diamine compound represented by general formula (A1) is also preferred. The diamine compound represented by formula (A1) [diamine (A1)] is as described in the explanation of non-thermoplastic polyimides. Diamine (A1) has a rigid structure and has the effect of imparting an ordered structure to the entire polymer, so that it is possible to reduce the dielectric tangent and moisture absorption by suppressing the movement of molecules. Furthermore, by using it as a raw material for thermoplastic polyimide, polyimide with low gas permeability and excellent long-term heat-resistant adhesion can be obtained.

The thermoplastic polyimide constituting the thermoplastic polyimide layer 33 may contain diamine residues derived from diamine (A1) in a range of preferably 1 to 40 molar parts, more preferably 5 to 30 molar parts. By using diamine (A1) in an amount within the above range, an ordered structure is formed throughout the polymer due to the rigid structure derived from the monomer, resulting in a polyimide that is thermoplastic, yet has low gas permeability and moisture absorption, and has excellent long-term heat-resistant adhesion.

The thermoplastic polyimide constituting the thermoplastic polyimide layer 33 may contain diamine residues derived from diamine compounds other than the diamines (A1) and (B1) to (B7) to the extent that the effect of the invention is not impaired.

In thermoplastic polyimides, the thermal expansion coefficient, tensile modulus, glass transition temperature, etc. can be controlled by selecting the types of the tetracarboxylic acid residues and diamine residues, or the molar ratios of two or more types of tetracarboxylic acid residues or diamine residues. In addition, in thermoplastic polyimides, when multiple polyimide structural units are present, they may be present as blocks or randomly, but it is preferable that they are present randomly.

In addition, by making the tetracarboxylic acid residues and diamine residues contained in the thermoplastic polyimide both aromatic groups, the dimensional accuracy of the polyimide film in a high-temperature environment can be improved and the amount of change in the in-plane retardation (RO) can be suppressed.

The imide group concentration of the thermoplastic polyimide is preferably 33% or less, more preferably 32% or less. Here, "imide group concentration" means 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 polyimide structure. If the imide group concentration exceeds 33%, the molecular weight of the resin itself decreases, and the low moisture absorption property also deteriorates due to an increase in polar groups. By selecting a combination of the above diamine compounds, the molecular orientation in the thermoplastic polyimide is controlled, thereby suppressing the increase in CTE associated with a decrease in the imide group concentration, and ensuring low moisture absorption.

The weight-average molecular weight of the thermoplastic polyimide is preferably, for example, in the range of 10,000 to 400,000, and 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 film tends to decrease and it tends to become brittle. On the other hand, if the weight-average molecular weight exceeds 400,000, the viscosity increases excessively, and defects such as uneven film thickness and streaks tend to occur during the coating process.

The thermoplastic polyimide constituting the thermoplastic polyimide layer 33 is most preferably a completely imidized structure in order to suppress the diffusion of copper, since it becomes, for example, an adhesive layer in the insulating resin of a circuit board. However, a part of the polyimide may be an amic acid. The imidization rate is calculated from the absorbance of the C=O stretching derived from the imide group at 1780 cm ^-1 , based on the benzene ring absorber at around 1015 cm- ¹ , by measuring the infrared absorption spectrum of the polyimide thin film by the single reflection ATR method using a Fourier transform infrared spectrophotometer (commercial product: FT/IR620 manufactured by JASCO).

From the viewpoint of ensuring adhesive function, the thickness of the thermoplastic polyimide layer 33 is preferably in the range of 1 μm to 10 μm, and more preferably in the range of 1 μm to 5 μm. If the thickness of the thermoplastic polyimide layer 33 is less than the lower limit value, the adhesiveness will be insufficient, and if it exceeds the upper limit value, the dimensional stability will tend to deteriorate.

From the viewpoint of suppressing warping, the thermoplastic polyimide layer 33 should have a thermal expansion coefficient of 30 ppm/K or more, preferably in the range of 30 ppm/K to 100 ppm/K, and more preferably in the range of 30 ppm/K to 80 ppm/K.

In addition to polyimide, the resin used for the thermoplastic polyimide layer 33 may contain optional components such as plasticizers, other curable resin components such as epoxy resins, curing agents, curing accelerators, inorganic fillers, coupling agents, bulking agents, solvents, and flame retardants.

The non-thermoplastic polyimide and thermoplastic polyimide for forming the non-thermoplastic polyimide layer 31 and thermoplastic polyimide layer 33 can be produced by reacting an acid anhydride component and a diamine component in a solvent to generate a polyamic acid, followed by heating to close the ring, as in the case of the DDA-based polyimide. In the synthesis of the non-thermoplastic polyimide and thermoplastic polyimide, the above-mentioned acid anhydrides and diamines can each be used alone or in combination of two or more kinds. By selecting the types of acid anhydrides and diamines, or the respective molar ratios when two or more types of acid anhydrides or diamines are used, the thermal expansion, adhesion, glass transition temperature, etc. can be controlled.

<Thermal expansion coefficient>
In the metal-clad laminate 10, the coefficient of thermal expansion (CTE) of the entire resin laminate 20 is preferably 10 ppm/K or more, preferably in the range of 10 ppm/K to 30 ppm/K, more preferably in the range of 15 ppm/K to 25 ppm/K. If the CTE is less than 10 ppm/K or more than 30 ppm/K, warping occurs or dimensional stability decreases. By appropriately changing the combination of raw materials used, the thickness, and the drying and curing conditions, a polyimide layer having a desired CTE can be obtained.

<Dielectric tangent>
In the metal-clad laminate 10, the dielectric loss tangent (Tan δ) at 10 GHz of the entire resin laminate 20 is preferably 0.02 or less, more preferably in the range of 0.0005 to 0.01, and even more preferably in the range of 0.001 to 0.008. If the dielectric loss tangent at 10 GHz of the entire resin laminate 20 exceeds 0.02, when applied to a circuit board, problems such as loss of electrical signals on the transmission path of high-frequency signals are likely to occur. On the other hand, the lower limit of the dielectric loss tangent at 10 GHz of the entire resin laminate 20 is not particularly limited, but the physical property control as an insulating resin layer of a circuit board is taken into consideration.

<Dielectric constant>
In the metal-clad laminate 10, when the resin laminate 20 is applied as, for example, an insulating resin layer of a circuit board, in order to ensure impedance matching, it is preferable that the dielectric constant at 10 GHz is 4.0 or less for the entire resin laminate 20. If the dielectric constant at 10 GHz for the entire resin laminate 20 exceeds 4.0, this leads to an increase in dielectric loss when applied to a circuit board, and is likely to cause inconveniences such as loss of electrical signals on the transmission path of high-frequency signals.

[Production of metal-clad laminate]
The metal-clad laminate 10 can be manufactured, for example, by preparing resin sheets corresponding to a first transmission loss suppression layer BS1, a second transmission loss suppression layer BS2, multiple dimensional accuracy maintaining layers PL, and one or more intermediate transmission loss suppression layers BS3, and placing these resin sheets between the first metal layer M1 and the second metal layer M2, bonding them together, and thermocompression bonding them.

The metal-clad laminate 10 of this embodiment obtained as described above can be used to manufacture circuit boards such as single-sided FPCs or double-sided FPCs by processing the wiring circuitry, for example by etching the first metal layer M1 and/or the second metal layer M2.

[Circuit board]
The metal-clad laminate 10 is useful mainly as a circuit board material for FPC, rigid-flex circuit boards, etc. One or both of the first metal layer M1 and the second metal layer M2 of the metal-clad laminate 10 are processed into a pattern by a conventional method to form a wiring layer, thereby manufacturing a circuit board such as an FPC, which is one embodiment of the present invention. Although not shown, this circuit board includes a resin laminate 20 and a wiring layer provided on one or both sides of the resin laminate 20, and is capable of reducing transmission loss even in high-frequency transmission and has excellent dimensional stability.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In the following examples, various measurements and evaluations are as follows, unless otherwise specified.

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

[Measurement of storage modulus]
A resin sheet measuring 5 mm x 20 mm was measured using a dynamic viscoelasticity measuring device (DMA: manufactured by UBM, product name: E4000F) at a heating rate of 4°C/min from 30°C to 400°C and a frequency of 11 Hz.

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

[Measurement of dielectric constant and dielectric tangent]
The dielectric constant (Dk) and dielectric loss tangent (Df) of the resin sheet at 10 GHz were measured using a vector network analyzer (manufactured by Agilent, product name: E8363C) and an SPDR resonator. The material used for the measurement was left for 24 hours under the conditions of temperature: 24 to 26°C and humidity: 45°C to 55% RH.

[Measurement of dimensional change rate]
The measurement of the dimensional change rate was carried out by the following procedure. First, a 150 mm square sample was used, and a dry film resist was exposed and developed at 100 mm intervals to form a position measurement target. After measuring the dimensions before etching (normal state) in an atmosphere of 23±2°C and 50±5% relative humidity, copper other than the target of the test piece was removed by etching (liquid temperature 40°C or less, time 10 minutes or less). After leaving the test piece in an atmosphere of 23±2°C and 50±5% relative humidity for 24±4 hours, the dimensions after etching were measured. The dimensional change rate was calculated for three locations in each of the vertical and horizontal directions with respect to the normal state, and the average value of each was used as the dimensional change rate after etching. The dimensional change rate after etching was calculated by the following formula.

Dimensional change rate after etching (%) = (B-A)/A x 100
A: Distance between targets before etching B: Distance between targets after etching

Next, the test piece is heat-treated in an oven at 250°C for one hour, and the distance between the position targets is then measured. The dimensional change rate after etching is calculated for three locations in each of the vertical and horizontal directions, and the average value of each is taken as the dimensional change rate after heat treatment. The dimensional change rate due to heating was calculated using the following formula.

Heat dimensional change rate (%) = (C-B)/B x 100
B: Target distance after etching C: Target distance after heating

[Measurement of copper foil surface roughness (Rz; ten-point average roughness)]
The surface roughness was measured using a stylus surface roughness meter (manufactured by Kosaka Laboratory Co., Ltd., product name: Surfcorder ET-3000) under the measurement conditions of Force: 100 μN, Speed: 20 μm, Range: 800 μm. The surface roughness was calculated according to the method in accordance with JIS-B0601:1994.

The abbreviations used in the synthesis examples represent the following compounds.
BTDA: 3,3',4,4'-benzophenonetetracarboxylic dianhydride PMDA: pyromellitic dianhydride BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride BPADA: 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride DAPE: 4,4'-diaminodiphenyl ether p-PDA: p-phenylenediamine BAPP: 2,2-bis[4-(4 m-TB: 2,2'-dimethyl-4,4'-diaminobiphenyl TPE-R: 1,3-bis(4-aminophenoxy)benzene DDA: aliphatic diamine having 36 carbon atoms (manufactured by Croda Japan Ltd., trade name: PRIAMINE 1074, amine value: 205 mg KOH/g, mixture of dimer diamines having cyclic and chain structures, dimer component content: 95% by weight or more)
OP935: organic phosphinic acid aluminum salt (manufactured by Clariant Japan, trade name: Exolit OP935)
N-12: Dodecanedioic acid dihydrazide DMAc: N,N-dimethylacetamide NMP: N-methyl-2-pyrrolidone

(Synthesis Example 1)
312g of DMAc was placed in a reaction vessel equipped with a thermocouple and a stirrer and capable of introducing nitrogen. 14.67g of DAPE (0.073 mol) was dissolved in the reaction vessel while stirring. Next, 23.13g of BTDA (0.072 mol) was added. Stirring was continued for 3 hours to prepare a polyamic acid resin solution a with a solution viscosity of 2,960 mPa·s.

(Synthesis Example 2)
200 g of DMAc was placed in a reaction vessel equipped with a thermocouple and a stirrer and capable of introducing nitrogen. 1.335 g of m-TB (0.0063 mol) and 10.414 g of TPE-R (0.0356 mol) were dissolved in the reaction vessel while stirring. Next, 0.932 g of PMDA (0.0043 mol) and 11.319 g of BPDA (0.0385 mol) were added. Stirring was then continued for 2 hours to prepare a polyamic acid resin solution b with a solution viscosity of 1,420 mPa·s.

(Synthesis Example 3)
250 g of DMAc was placed in a reaction vessel equipped with a thermocouple and a stirrer and capable of introducing nitrogen. 2.561 g of p-PDA (0.0237 mol) and 16.813 g of DAPE (0.0840 mol) were dissolved in the reaction vessel while stirring. Next, 18.501 g of PMDA (0.0848 mol) and 6.239 g of BPDA (0.0212 mol) were added. Stirring was continued for 3 hours to prepare a polyamic acid resin solution c with a solution viscosity of 29,500 mPa·s.

(Synthesis Example 4)
250 g of DMAc was placed in a reaction vessel equipped with a thermocouple and a stirrer and capable of introducing nitrogen. 12.323 g of m-TB (0.0580 mol) and 1.886 g of TPE-R (0.0064 mol) were dissolved in the reaction vessel while stirring. Next, 8.314 g of PMDA (0.0381 mol) and 7.477 g of BPDA (0.0254 mol) were added. Stirring was then continued for 3 hours to prepare a polyamic acid resin solution d with a solution viscosity of 31,500 mPa·s.

(Synthesis Example 5)
<Preparation of resin solution e for adhesive layer>
A 500mL four-neck flask equipped with a nitrogen inlet tube, a stirrer, a thermocouple, a Dean-Stark trap, and a cooling tube was charged with 44.92g of BTDA (0.139 mol), 75.08g of DDA (0.141 mol), 168g of NMP, and 112g of xylene, and mixed at 40°C for 30 minutes to prepare a polyamic acid solution. The polyamic acid solution was heated to 190°C, heated and stirred for 4 hours, and the distilled water and xylene were removed from the system. Thereafter, the solution was cooled to 100°C, 112g of xylene was added and stirred, and the solution was further cooled to 30°C to complete the imidization, and a resin solution e (solid content: 29.5% by weight) for the adhesive layer was obtained.

(Synthesis Example 6)
<Preparation of resin solution f for adhesive layer>
A polyamic acid solution was prepared in the same manner as in Synthesis Example 5, except that the raw material composition was 42.51 g of BPADA (0.082 mol), 34.30 g of DDA (0.066 mol), 6.56 g of BAPP (0.016 mol), 208 g of NMP, and 112 g of xylene. This polyamic acid solution was treated in the same manner as in Synthesis Example 5 to obtain a resin solution f (solid content: 30.0 wt%) for an adhesive layer.

(Preparation Example 1)
<Preparation of Polyimide Film>
A polyamic acid resin solution c was uniformly applied to one surface of an electrolytic copper foil 1 (thickness: 12 μm, Rz: 2.1 μm) so that the thickness after curing was about 25 μm, and then the solution was heated and dried at 120° C. to remove the solvent. Further, a stepwise heat treatment from 120° C. to 360° C. was performed within 30 minutes to complete the imidization. The copper foil was etched away using an aqueous ferric chloride solution to prepare a polyimide film 1 (thickness: 25 μm, Dk: 3.4, Df: 0.0085, CTE: 16 ppm/K, minimum storage modulus (100-250° C.): 2.9 GPa ).

(Preparation Example 2)
<Preparation of Polyimide Film>
A polyimide film 2 (thickness: 25 μm, Dk: 3.3, Df: 0.0034, CTE: 17 ppm/K, minimum storage modulus (100 to 250° C.): 3.0 GPa ) was prepared in the same manner as in Preparation Example 1, except that resin solution d was used.

(Preparation Example 3)
<Preparation of Polyimide Film>
Resin solution a was uniformly applied to one surface of electrolytic copper foil 1 (thickness 12 μm, Rz; 2.1 μm) so that the thickness after curing would be about 2 to 3 μm, and then heated and dried at 120 ° C to remove the solvent. Next, resin solution d was uniformly applied thereon so that the thickness after curing would be about 21 μm, and then heated and dried at 120 ° C to remove the solvent. Furthermore, resin solution a was uniformly applied thereon so that the thickness after curing would be about 2 to 3 μm, and then heated and dried at 120 ° C to remove the solvent. In this way, three polyamic acid layers were formed, and then stepwise heat treatment was performed from 120 ° C to 360 ° C to complete the imidization. The copper foil layer was etched away using an aqueous solution of ferric chloride to prepare a polyimide film 3 (thickness: 25 μm, Dk: 3.4, Df: 0.0052, CTE: 21 ppm/K, minimum storage modulus (100-250° C.): 2.8 GPa ).

(Preparation Example 4)
<Preparation of Polyimide Film>
Resin solution b was uniformly applied to one surface of electrolytic copper foil 1 (thickness 12 μm, Rz; 2.1 μm) so that the thickness after curing would be about 2 to 3 μm, and then heated and dried at 120 ° C to remove the solvent. Next, resin solution d was uniformly applied thereon so that the thickness after curing would be about 21 μm, and then heated and dried at 120 ° C to remove the solvent. Furthermore, resin solution b was uniformly applied thereon so that the thickness after curing would be about 2 to 3 μm, and then heated and dried at 120 ° C to remove the solvent. In this way, three polyamic acid layers were formed, and then stepwise heat treatment was performed from 120 ° C to 360 ° C to complete the imidization. The copper foil layer was etched away using an aqueous solution of ferric chloride to prepare a polyimide film 4 (thickness: 25 μm, Dk: 3.3, Df: 0.0032, CTE: 23 ppm/K, minimum storage modulus (100-250° C.): 2.7 GPa ).

(Preparation Example 5)
<Preparation of Resin Sheet>
Polyimide varnish 1 was prepared by mixing 1.8 g of N-12 (0.0036 mol) and 12.5 g of OP935 with 169.49 g of resin solution e (50 g as solid content), and diluting the mixture with 6.485 g of NMP and 19.345 g of xylene.

Polyimide varnish 1 was applied to the silicone-treated surface of a release substrate so that the thickness after drying was 25 μm, and then the coating was dried by heating at 80° C. and peeled off from the release substrate to prepare resin sheet 1. The dielectric constant (Dk) and dielectric loss tangent (Df) of resin sheet 1 were 2.7 and 0.0023, respectively.

(Preparation Example 6)
<Preparation of Resin Sheet>
Except for the fact that the thickness after drying was 50 μm, a resin sheet 2 was prepared in the same manner as in Preparation Example 6. The dielectric constant (Dk) and dielectric loss tangent (Df) of the resin sheet 2 were 2.7 and 0.0023, respectively.

(Preparation Example 7)
<Preparation of Resin Sheet>
Except for the fact that the thickness after drying was 75 μm, a resin sheet 3 was prepared in the same manner as in Preparation Example 6. The dielectric constant (Dk) and dielectric loss tangent (Df) of the resin sheet 3 were 2.7 and 0.0023, respectively.

(Preparation Example 8)
<Preparation of Resin Sheet>
Resin sheet 4 was prepared in the same manner as in Preparation Example 6, except that the thickness after drying was adjusted to 5 μm. The dielectric constant (Dk) and dielectric loss tangent (Df) of resin sheet 4 were 2.7 and 0.0023, respectively.

(Preparation Example 9)
<Preparation of Resin Sheet>
The resin solution f for the adhesive layer was applied to the silicone-treated surface of the release substrate so that the thickness after drying was 25 μm, and then the coating was dried by heating at 80° C. and peeled off from the release substrate to prepare a resin sheet 5. The dielectric constant (Dk) and dielectric loss tangent (Df) of the resin sheet 5 were 2.8 and 0.0028, respectively.

(Preparation Example 10)
<Preparation of Resin Sheet>
A resin sheet 6 was prepared in the same manner as in Preparation Example 10, except that the thickness after drying was adjusted to 50 μm. The dielectric constant (Dk) and dielectric loss tangent (Df) of the resin sheet 6 were 2.8 and 0.0028, respectively.

[Example 1]
Two electrolytic copper foils 1, two resin sheets 1, one resin sheet 2, and two polyimide films 4 were prepared, and laminated in the order of electrolytic copper foil 1/resin sheet 1/polyimide film 4/resin sheet 2/polyimide film 4/resin sheet 1/electrolytic copper foil 1, and then subjected to thermocompression bonding at 160° C. and 4 MPa for 60 minutes to prepare a double-sided metal-clad laminate 1. The evaluation results of the double-sided metal-clad laminate 1 are as follows.
Dimensional change rate after etching in MD direction: -0.05%
Dimensional change rate after etching in the TD direction: -0.04%
Dimensional change rate after heating in MD direction: -0.03%
Dimensional change rate after heating in TD direction: 0.03%
The dielectric constant (Dk) and the dielectric loss tangent (Df) of the resin laminate 1 (thickness: 150 μm) prepared by etching and removing the electrolytic copper foil 1 in the double-sided metal-clad laminate 1 were 2.9 and 0.0026, respectively. The total thickness of the dimensional accuracy maintaining layer was 33% of the total thickness of the resin laminate 1.

[Example 2]
Two electrolytic copper foils 1, two resin sheets 1, one resin sheet 3, and two polyimide films 4 were prepared, and laminated in the order of electrolytic copper foil 1/resin sheet 1/polyimide film 4/resin sheet 3/polyimide film 4/resin sheet 1/electrolytic copper foil 1, and then subjected to thermocompression bonding at 160° C. and 4 MPa for 60 minutes to prepare a double-sided metal-clad laminate 2. The evaluation results of the double-sided metal-clad laminate 2 are as follows.
Dimensional change rate after etching in MD direction: -0.06%
Dimensional change rate after etching in the TD direction: -0.04%
Dimensional change rate after heating in MD direction: -0.04%
Dimensional change rate after heating in TD direction: 0.04%
The dielectric constant (Dk) and the dielectric loss tangent (Df) of the resin laminate 2 (thickness: 175 μm) prepared by etching and removing the electrolytic copper foil 1 in the double-sided metal-clad laminate 2 were 2.92 and 0.0026, respectively. The total thickness of the dimensional accuracy maintaining layer was 29% of the total thickness of the resin laminate 2.

[Example 3]
Two electrolytic copper foils 1, one resin sheet 1, two resin sheets 2, and two polyimide films 4 were prepared, and the laminated layers were stacked in the order of electrolytic copper foil 1/resin sheet 2/polyimide film 4/resin sheet 1/polyimide film 4/resin sheet 2/electrolytic copper foil 1, and then subjected to thermocompression bonding at 160° C. and 4 MPa for 60 minutes to prepare a double-sided metal-clad laminate 3. The evaluation results of the double-sided metal-clad laminate 3 are as follows.
Dimensional change rate after etching in MD direction: -0.02%
Dimensional change rate after etching in the TD direction: 0.03%
Dimensional change rate after heating in MD direction: -0.06%
Dimensional change rate after heating in TD direction: -0.02%
The dielectric constant (Dk) and the dielectric loss tangent (Df) of the resin laminate 3 (thickness: 175 μm) prepared by etching and removing the electrolytic copper foil 1 in the double-sided metal-clad laminate 3 were 2.9 and 0.0026, respectively. The total thickness of the dimensional accuracy maintaining layers was 29% of the total thickness of the resin laminate 3.

[Example 4]
A double-sided metal-clad laminate 4 was prepared in the same manner as in Example 1, except that the polyimide film 1 was used instead of the polyimide film 4. The double-sided metal-clad laminate 4 was evaluated, and no problem was found with respect to dimensional change. The dielectric constant (Dk) and dielectric loss tangent (Df) of the resin laminate 4 (thickness: 150 μm) prepared by removing the electrolytic copper foil 1 in the double-sided metal-clad laminate 4 by etching were 2.9 and 0.0044, respectively. The total thickness of the dimensional accuracy maintaining layer was 33% of the total thickness of the resin laminate 4.

[Example 5]
A double-sided metal-clad laminate 5 was prepared in the same manner as in Example 1, except that the polyimide film 2 was used instead of the polyimide film 4. The double-sided metal-clad laminate 5 was evaluated, and no problem was found with respect to dimensional change. The dielectric constant (Dk) and dielectric loss tangent (Df) of the resin laminate 5 (thickness: 150 μm) prepared by removing the electrolytic copper foil 1 in the double-sided metal-clad laminate 5 by etching were 2.9 and 0.0027, respectively. The total thickness of the dimensional accuracy maintaining layer was 33% of the total thickness of the resin laminate 5.

[Example 6]
A double-sided metal-clad laminate 6 was prepared in the same manner as in Example 1, except that a polyimide film 3 was used instead of the polyimide film 4. The double-sided metal-clad laminate 6 was evaluated, and no problem was found with respect to dimensional change. The dielectric constant (Dk) and dielectric loss tangent (Df) of the resin laminate 6 (thickness: 150 μm) prepared by removing the electrolytic copper foil 1 in the double-sided metal-clad laminate 6 by etching were 2.9 and 0.0033, respectively. The total thickness of the dimensional accuracy maintaining layer was 33% of the total thickness of the resin laminate 6.

[Example 7]
A double-sided metal-clad laminate 7 was prepared in the same manner as in Example 1, except that resin sheet 5 was used instead of resin sheet 1 and resin sheet 6 was used instead of resin sheet 2. The double-sided metal-clad laminate 7 was evaluated and found to have no problem with dimensional change. The dielectric constant (Dk) and dielectric loss tangent (Df) of the resin laminate 7 (thickness: 150 μm) prepared by etching and removing the electrolytic copper foil 1 in the double-sided metal-clad laminate 7 were 3.0 and 0.0029, respectively. The total thickness of the dimensional accuracy maintaining layer was 33% of the total thickness of the resin laminate 7.

[Example 8]
A double-sided metal-clad laminate 8 was prepared in the same manner as in Example 1, except that a resin sheet 4 was used instead of the resin sheet 1. The double-sided metal-clad laminate 8 was evaluated, and no problem was found with respect to dimensional change. The dielectric constant (Dk) and dielectric loss tangent (Df) of the resin laminate 8 (thickness: 110 μm) prepared by removing the electrolytic copper foil 1 in the double-sided metal-clad laminate 8 by etching were 3.0 and 0.0027, respectively. The total thickness of the dimensional accuracy maintaining layer was 45% of the total thickness of the resin laminate 8.

[Comparative Example 1]
Two sheets of electrolytic copper foil 1, two sheets of resin sheet 2, and one sheet of polyimide film 1 were prepared, and the layers were laminated in the order of electrolytic copper foil 1/resin sheet 2/polyimide film 1/resin sheet 2/electrolytic copper foil 1, and then thermocompression bonded for 60 minutes under conditions of 160° C. and 4 MPa to prepare a double-sided metal-clad laminate 9. The evaluation results of the double-sided metal-clad laminate 9 are as follows.
Dimensional change rate after etching in MD direction: 0.02%
Dimensional change rate after etching in the TD direction: 0.08%
Dimensional change rate after heating in MD direction: -0.10%
Dimensional change rate after heating in TD direction: -0.05%
The dielectric constant (Dk) and the dielectric loss tangent (Df) of the resin laminate 9 (thickness: 125 μm) prepared by etching and removing the electrolytic copper foil 1 from the double-sided metal-clad laminate 9 were 2.8 and 0.0035, respectively. The total thickness of the dimensional accuracy maintaining layer was 20% of the total thickness of the resin laminate 9.

The above describes in detail the embodiment of the present invention for illustrative purposes, but the present invention is not limited to the above embodiment and various modifications are possible.

Reference Signs List 10...metal-clad laminate, 20...resin laminate, M1...first metal layer, M2...second metal layer, BS1...first transmission loss suppression layer, BS2...second transmission loss suppression layer, BS3...intermediate transmission loss suppression layer, PL...dimensional accuracy maintaining layer, 31...non-thermoplastic polyimide layer, 33...thermoplastic polyimide layer

Claims (4)

a first metal layer;
a first transmission loss suppression layer provided in contact with one side of the first metal layer;
a second metal layer; and
a second transmission loss suppression layer provided in contact with one side of the second metal layer;
a plurality of resin layers interposed between the first transmission loss suppression layer and the second transmission loss suppression layer;
Equipped with
the first transmission loss suppression layer, the second transmission loss suppression layer, and the plurality of resin layers form a resin laminate,
The resin laminate is
At least two or more dimensional accuracy maintaining layers;
an intermediate transmission loss suppression layer laminated between the dimensional accuracy maintaining layers;
It has
Conditions i and ii below:
i) The dielectric loss tangent at 10 GHz measured by a split post dielectric resonator (SPDR) after 24 hours of conditioning under constant temperature and humidity conditions (normal state) of 23° C. and 50% RH, where Df ₁ is the dielectric loss tangent of the first transmission loss suppression layer and the second transmission loss suppression layer, and Df ₂ is the dielectric loss tangent of the dimensional accuracy maintaining layer, satisfies the relationship Df ₁ < Df ₂ ;
ii) the total thickness of the dimensional accuracy maintaining layer is within the range of 29 to 45% of the total thickness of the resin laminate;
While satisfying the above,
The metal-clad laminate has a dielectric loss tangent (Tan δ) at 10 GHz of the entire resin laminate in the range of 0.0005 or more and 0.0033 or less. The metal-clad laminate according to claim 1, wherein the dimensional accuracy maintaining layer is a low-thermal expansion polyimide layer having a minimum storage modulus in the temperature range of 100°C to 250°C of 1.0 to 8.0 GPa and a thermal expansion coefficient in the range of 15 to 25 ppm/K. The metal-clad laminate according to claim 1 or 2, wherein the resin constituting the first transmission loss suppression layer and the second transmission loss suppression layer is a polyimide obtained by reacting an acid anhydride component with a diamine component, and contains 50 molar parts or more of a dimer diamine in which two terminal carboxylic acid groups of a dimer acid are substituted with primary aminomethyl groups or amino groups per 100 molar parts of the total amount of the diamine component. A first wiring layer;
a first transmission loss suppression layer provided in contact with one side of the first wiring layer;
A second wiring layer;
a second transmission loss suppression layer provided in contact with one side of the second wiring layer;
a plurality of resin layers interposed between the first transmission loss suppression layer and the second transmission loss suppression layer;
Equipped with
the first transmission loss suppression layer, the second transmission loss suppression layer, and the plurality of resin layers form a resin laminate,
The resin laminate is
At least two or more dimensional accuracy maintaining layers;
an intermediate transmission loss suppression layer laminated between the dimensional accuracy maintaining layers;
It has
Conditions i and ii below:
i) The dielectric loss tangent at 10 GHz measured by a split post dielectric resonator (SPDR) after 24 hours of conditioning under constant temperature and humidity conditions (normal state) of 23° C. and 50% RH, where Df ₁ is the dielectric loss tangent of the first transmission loss suppression layer and the second transmission loss suppression layer, and Df ₂ is the dielectric loss tangent of the dimensional accuracy maintaining layer, satisfies the relationship Df ₁ < Df ₂ ;
ii) the total thickness of the dimensional accuracy maintaining layer is within the range of 29 to 45% of the total thickness of the resin laminate;
While satisfying the above,
The circuit board has a dielectric loss tangent (Tan δ) at 10 GHz of the entire resin laminate in the range of 0.0005 or more and 0.0033 or less.