Multilayer films, metal-clad laminates and circuit boards

Abstract

This invention provides a multilayer film, a metal-clad laminate, and a circuit board. The multilayer film has outer layers comprising multiple polyimide layers on both sides of an inner layer including an adhesive layer, ensuring dimensional stability while further improving dielectric properties. The multilayer film includes multiple polyimide layers and an adhesive layer, wherein the multilayer film satisfies: a) the total thickness of the thermoplastic polyimide layer and the non-thermoplastic polyimide layer stacked on one side of the adhesive layer is in the range of 2 μm or more and 20 μm or less; b) 65 < P P / P AD <1,550, by P P =P P1 +P P2 P P1 =(E' P100 +E' P200 )×thickness of polyimide layer [μm], P P2 =(E' P100 +E' P200 )×thickness of polyimide layer [μm], P AD =(E' AD100 +E' AD200 E' represents the thickness of the adhesive layer [μm]. P100 、E' P200 E' is the storage elastic modulus [GPa] of the polyimide layer at 100℃ and 200℃. AD100 、E' AD200 c) The storage elastic coefficient [GPa] of the adhesive layer at 100℃ and 200℃; c) As a whole multilayer film, the dielectric loss tangent at 20 GHz measured using an SPDR resonator is less than 0.0029.

Description

Technical Field

[0001] This invention relates to a multilayer film, a metal-clad laminate, and a circuit board that can be effectively used as materials for electronic components. Background Technology

[0002] In recent years, with the advancements in miniaturization, weight reduction, and space-saving of electronic devices, the demand for thin, lightweight, flexible, and highly durable flexible printed circuit boards (FPCs) that withstand repeated bending has increased. FPCs can achieve three-dimensional and high-density mounting even in limited spaces; therefore, their applications are gradually expanding in components such as wiring or cables and connectors for electronic devices like hard disk drives (HDDs), digital video discs (DVDs), and smartphones.

[0003] In addition to increasing density, the performance of equipment is also being promoted, thus requiring a response to the increasing frequency of transmitted signals. When transmitting high-frequency signals, significant transmission losses along the transmission path can lead to signal loss or longer signal delays. To address this, a method has been proposed to improve dielectric properties by placing a high-thickness adhesive layer between a pair of single-sided metal-clad laminates and insulating resin layers, using a thermoplastic polyimide (DDA) made from a dimer acid-type diamine with two terminal carboxylic acid groups substituted with primary aminomethyl or amino groups as the adhesive layer material (Patent Document 1). Specifically, Patent Document 1 discloses a layer structure as the resin portion: thermoplastic polyimide layer / non-thermoplastic polyimide layer / thermoplastic polyimide layer / adhesive layer / thermoplastic polyimide layer / non-thermoplastic polyimide layer / thermoplastic polyimide layer.

[0004] In the layer structure described in Patent Document 1, to further improve dielectric properties, it is effective to increase the thickness of the inner layer, which includes an adhesive layer with excellent dielectric properties, and to thin the outer layer, which includes a thermoplastic polyimide layer / a non-thermoplastic polyimide layer / a thermoplastic polyimide layer. However, when the thickness of the non-thermoplastic polyimide layer in the outer layer is reduced, the coefficient of thermal expansion (CTE) of the outer layer decreases, and dimensional accuracy is compromised, thus hindering further improvement of dielectric properties.

[0005] [Existing Technical Documents]

[0006] [Patent Literature]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2018-170417 Summary of the Invention

[0008] [The problem the invention aims to solve]

[0009] The object of the present invention is to further improve the dielectric properties of a multilayer film having an outer layer containing multiple polyimide layers on both sides of an inner layer including an adhesive layer.

[0010] [Technical means to solve the problem]

[0011] Through diligent research, the inventors discovered that by focusing on the storage elasticity coefficients of the inner and outer layers at a specified temperature and controlling the elasticity coefficient parameters derived from these storage elasticity coefficients to have a specific relationship, it is possible to increase the ratio of the inner layer while ensuring the dimensional stability of the multilayer film, thereby achieving low dielectric loss tangent. Furthermore, for the outer layer, by assembling the thermoplastic polyimide layers into a single layer on each side and increasing its thickness ratio, the outer layer can be made into a thin film while ensuring dimensional stability and adhesion to the metal layer. For the inner layer, by increasing the relative thickness ratio, low dielectric loss tangent is achieved for the entire multilayer film. On the other hand, by reducing the storage elasticity coefficient at high temperatures, the influence of the inner layer on dimensional changes can be mitigated, thus completing this invention.

[0012] That is, the present invention is a multilayer film comprising multiple polyimide layers and an adhesive layer, and having the following layer structure (1) or (2):

[0013] (1) Thermoplastic polyimide layer / non-thermoplastic polyimide layer / adhesive layer / non-thermoplastic polyimide layer / thermoplastic polyimide layer,

[0014] or,

[0015] (2) Thermoplastic polyimide layer / non-thermoplastic polyimide layer / thermoplastic polyimide layer / adhesive layer / thermoplastic polyimide layer / non-thermoplastic polyimide layer / thermoplastic polyimide layer. Furthermore, the multilayer film of the present invention satisfies the following conditions a) to c):

[0016] a) The combined thickness of the thermoplastic polyimide layer and the non-thermoplastic polyimide layer laminated on one side of the adhesive layer is between 2 μm and 20 μm;

[0017] b) Satisfies the following equation (i);

[0018] 65 < P P / P AD <1,550…(i)

[0019] {Here, PP It is the elastic modulus parameter of the polyimide layer, P AD The elastic coefficient parameter of the adhesive layer is expressed by the following equations (ii) to (v):

[0020] P P =P P1 +P P2 …(ii)

[0021] P P1 =(E' P100 +E' P200 )×t p1 …(iii)

[0022] P P2 =(E' P100 +E' P200 )×t p2 …(iv)

[0023] P AD =(E' AD100 +E' AD200 )×tad…(v)

[0024] E' P100 Storage elastic modulus of the polyimide layer at 100°C [GPa]

[0025] E' P200 Storage elastic modulus of the polyimide layer at 200°C [GPa]

[0026] E' AD100 Storage elastic modulus of the adhesive layer at 100°C [GPa]

[0027] E' AD200 Storage elastic modulus of the adhesive layer at 200°C [GPa]

[0028] t p1 The total thickness [μm] of the thermoplastic polyimide layer and the non-thermoplastic polyimide layer laminated on one side of the adhesive layer.

[0029] t p2 The total thickness [μm] of the thermoplastic polyimide layer and the non-thermoplastic polyimide layer laminated on the other side of the adhesive layer.

[0030] tad: Thickness of the adhesive layer [μm]

[0031] Here, the elastic modulus parameter P of the polyimide layer is... P To make the elastic coefficient parameter P P1 With elastic coefficient parameter P P2 The value obtained by adding them together is the elastic coefficient parameter P. P1The elastic modulus parameter P is calculated by equation (iii) by treating the thermoplastic polyimide layer and the non-thermoplastic polyimide layer stacked on one side of the adhesive layer as a single polyimide layer. P2 The thermoplastic polyimide layer and the non-thermoplastic polyimide layer stacked on the other side of the adhesive layer are considered as a single polyimide layer, and the result is calculated using equation (iv).

[0032] c) As a whole multilayer film, the dielectric loss tangent at 20 GHz, measured using split post dielectric resonators (SPDR), is less than 0.0029.

[0033] In the multilayer film of the present invention, the storage elasticity coefficient of the polyimide layer formed by combining a thermoplastic polyimide layer and a non-thermoplastic polyimide layer on one side of the adhesive layer can be 1.0 GPa or more at 100°C and 0.1 GPa or more at 200°C.

[0034] In addition, in the multilayer film of the present invention, the storage elasticity coefficient of the adhesive layer at 100°C can be less than 130 MPa, and the storage elasticity coefficient at 200°C can be less than 40 MPa.

[0035] For the multilayer film of the present invention, the total thickness of the thermoplastic polyimide layer in the entire multilayer film is set as T. A Let the total thickness of the non-thermoplastic polyimide layer be T. B When the thickness of the adhesive layer is set to tad, the following equation (vi) can be satisfied.

[0036] 0.60≦tad / (T A +T B +tad)≦0.99…(vi)

[0037] Furthermore, in the multilayer film of the present invention, the coefficient of thermal expansion of the polyimide layer formed by combining a thermoplastic polyimide layer and a non-thermoplastic polyimide layer stacked on one side of the adhesive layer can be in the range of 5ppm / K to 35ppm / K.

[0038] In the multilayer film of the present invention, the adhesive layer may contain thermoplastic polyimide and polystyrene elastomer resin, and the content of polystyrene elastomer resin relative to 100 parts by weight of thermoplastic polyimide may be in the range of 10 parts by weight or more and 150 parts by weight or less.

[0039] In the multilayer film of the present invention, the thermoplastic polyimide contained in the adhesive layer may contain dianhydride residues derived from the dianhydride component and diamine residues derived from the diamine component. In this case, the proportion of diamine residues derived from the dimer diamine composition relative to all diamine residues may be 20 mol% or more, wherein the dimer diamine composition is mainly composed of a dimer diamine formed by replacing the two terminal carboxylic acid groups of a dimer acid with primary aminomethyl or amino groups, and the proportion of diamine residues derived from the diamine compound represented by the following general formula (1) may be in the range of 5 mol% to 50 mol%.

[0040] [Chemistry 1]

[0041]

[0042] In formula (1), R independently represents a halogen atom, or an alkyl or alkoxy group that can be substituted by a halogen atom having 1 to 6 carbon atoms, or a phenyl or phenoxy group that can be substituted by a monovalent hydrocarbon group or alkoxy group having 1 to 6 carbon atoms, Z independently represents a divalent group selected from -O-, -S-, CH2-, -CH(CH3)-, -C(CH3)2-, -CO-, -COO-, -SO2-, -NH- or -NHCO-, m1 independently represents an integer from 0 to 4, and m2 represents an integer from 0 to 2.

[0043] In the multilayer film of the present invention, the thermoplastic polyimide contained in the adhesive layer may be a cross-linked polyimide in which the ketone group contained in the molecular chain and the amino group of an amino compound having at least two primary amino groups as functional groups are cross-linked through C=N bonds.

[0044] In the multilayer film of the present invention, the thermoplastic polyimide constituting the thermoplastic polyimide layer may contain dianhydride residues derived from an acid dianhydride component and diamine residues derived from a diamine component. In this case, the proportion of BPDA residues derived from 3,3',4,4'-biphenyl tetracarboxylic dianhydride (BPDA) may be 40 mol% or more relative to all acid dianhydride residues, and the proportion of diamine residues derived from the diamine compound represented by the general formula (1) may be 30 mol% or more relative to all diamine residues.

[0045] In the multilayer film of the present invention, the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer may contain dianhydride residues derived from the dianhydride component and diamine residues derived from the diamine component. In this case, the proportion of dianhydride residues having a biphenyl backbone relative to all dianhydride residues may be 40 mol% or more, and the proportion of diamine residues having a biphenyl backbone relative to all diamine residues may be 40 mol% or more.

[0046] The metal-clad laminate of the present invention has any of the multilayer films and a metal layer laminated on one or both sides of the multilayer film.

[0047] When the metal layer of the metal-clad laminate of the present invention is etched away, the dimensional change rate of the multilayer film after etching can be within ±0.10% based on the multilayer film before etching, or the dimensional change rate after heating at 150°C for 30 minutes can be within ±0.10% based on the multilayer film after etching.

[0048] The circuit board of the present invention is formed by processing the metal layer of any of the aforementioned metal-clad laminates into wiring.

[0049] A circuit board includes an insulating resin layer and a wiring layer disposed on at least one side of the insulating resin layer, wherein the insulating resin layer is any of the multilayer films.

[0050] [The effects of the invention]

[0051] The multilayer film of the present invention, by satisfying conditions a) to c), enables the outer layer to be integrally thinned, while ensuring dimensional stability and improving the overall dielectric properties of the multilayer film. In particular, by achieving a ratio (P) under condition b... P / P AD Satisfying equation (i), the elastic coefficient parameter (P) of the outer layer P ) and the elastic coefficient parameter of the inner layer (P) AD Compared to controlling the thickness within a specified range, this invention improves the overall dimensional stability of the multilayer film. This effect is particularly effective in layer structures where the total thickness or thickness ratio of the polyimide layer (outer layer) is relatively small, while the thickness or thickness ratio of the adhesive layer is relatively large. Furthermore, by using a resin with excellent dielectric properties and a low storage elasticity coefficient at high temperatures as the resin constituting the inner layer, dimensional stability can be maintained while increasing the relative thickness ratio of the inner layer, achieving low dielectric loss tangent for the entire multilayer film. Therefore, when a metal-clad laminate using the multilayer film of this invention is applied to a circuit board transmitting high-frequency signals in the GHz band, it can reduce transmission loss and improve reliability based on excellent dimensional stability. Attached Figure Description

[0052] Figure 1 This is a schematic cross-sectional view showing the layer structure of a multilayer film according to a preferred embodiment of the present invention.

[0053] Figure 2 This is a schematic cross-sectional view showing the layer structure of a multilayer film according to another preferred embodiment of the present invention.

[0054] Figure 3This is a schematic cross-sectional view showing the layer structure of a metal-clad laminate according to a preferred embodiment of the present invention.

[0055] Figure 4 This is a schematic cross-sectional view illustrating the layer structure of a metal-clad laminate according to another preferred embodiment of the present invention.

[0056] [Explanation of Symbols]

[0057] 10A, 10B, 30A, 30B: Thermoplastic polyimide layers

[0058] 20A, 20B: Non-thermoplastic polyimide layers

[0059] 40A: First insulating resin layer

[0060] 40B: Second insulating resin layer

[0061] 100, 101: Multilayer film

[0062] 110A, 110B: Metal layers

[0063] 200, 201: Metal-clad laminates

[0064] BS: Adhesive layer Detailed Implementation

[0065] The embodiments of the present invention will be described with appropriate reference to the accompanying drawings.

[0066] [Multilayer film]

[0067] The multilayer film of the present invention comprises a plurality of polyimide layers and an adhesive layer, and has the following layer structure (1) or (2):

[0068] (1) Thermoplastic polyimide layer / non-thermoplastic polyimide layer / adhesive layer / non-thermoplastic polyimide layer / thermoplastic polyimide layer,

[0069] or,

[0070] (2) Thermoplastic polyimide layer / non-thermoplastic polyimide layer / thermoplastic polyimide layer / adhesive layer / thermoplastic polyimide layer / non-thermoplastic polyimide layer / thermoplastic polyimide layer.

[0071] Figure 1This diagram shows a cross-sectional structure of a multilayer film 100 according to an embodiment of the present invention. The multilayer film 100 has a layer structure in which a thermoplastic polyimide layer 10A, a non-thermoplastic polyimide layer 20A, an adhesive layer BS, a non-thermoplastic polyimide layer 20B, and a thermoplastic polyimide layer 10B are sequentially stacked. Here, the thermoplastic polyimide layer 10A and the non-thermoplastic polyimide layer 20A on one side of the outer layer constitute a first insulating resin layer 40A, and the thermoplastic polyimide layer 10B and the non-thermoplastic polyimide layer 20B on the other side of the outer layer constitute a second insulating resin layer 40B. Therefore, the multilayer film 100 has a structure obtained by sequentially stacking the first insulating resin layer 40A as the outer layer, the adhesive layer BS as the inner layer, and the second insulating resin layer 40B as the outer layer.

[0072] Unlike existing layer structures, in the multilayer film 100, the first insulating resin layer 40A and the second insulating resin layer 40B, which serve as the outer layers, each have a layer structure in which only one thermoplastic polyimide layer is stacked. Thus, by forming the outer layer on one side of the adhesive layer BS into a two-layer structure and by assembling one thermoplastic polyimide layer (thermoplastic polyimide layer 10A or thermoplastic polyimide layer 10B) on each side, the thickness of the outer layer can be reduced while ensuring a tight bond with the metal layer when it is stacked on the outside.

[0073] Figure 2 The cross-sectional structure of the multilayer film 101 according to another preferred embodiment of the present invention is shown. The multilayer film 101 has a layer structure obtained by sequentially stacking a thermoplastic polyimide layer 10A, a non-thermoplastic polyimide layer 20A, a thermoplastic polyimide layer 30A, an adhesive layer BS, a thermoplastic polyimide layer 30B, a non-thermoplastic polyimide layer 20B, and a thermoplastic polyimide layer 10B.

[0074] Here, the thermoplastic polyimide layer 10A, the non-thermoplastic polyimide layer 20A, and the thermoplastic polyimide layer 30A constitute the first insulating resin layer 40A, and the thermoplastic polyimide layer 10B, the non-thermoplastic polyimide layer 20B, and the thermoplastic polyimide layer 30B constitute the second insulating resin layer 40B. Therefore, the multilayer film 101 has a structure obtained by sequentially stacking the first insulating resin layer 40A, the adhesive layer BS, and the second insulating resin layer 40B.

[0075] exist Figure 1 and Figure 2In the structural example shown, thermoplastic polyimide layers 10A, 10B, 30A, and 30B can be composed of the same or different types of thermoplastic polyimide. Similarly, non-thermoplastic polyimide layers 20A and 20B can also be composed of the same or different types of non-thermoplastic polyimide. Details regarding the preferred polyimides used in the first insulating resin layer 40A and the second insulating resin layer 40B will be explained later.

[0076] In addition, the first insulating resin layer 40A and the second insulating resin layer 40B may be appropriately formulated with, for example, plasticizers, epoxy resin and other curing resin components, curing agents, curing accelerators, organic or inorganic fillers, coupling agents, flame retardants, etc.

[0077] Multilayer film 100 and multilayer film 101 satisfy the following conditions a) to c).

[0078] a) The combined thickness of the thermoplastic polyimide layer and the non-thermoplastic polyimide layer laminated on one side of the adhesive layer is between 2 μm and 20 μm.

[0079] Condition a stipulates that, Figure 1 In the structural example shown, the combined thickness of the thermoplastic polyimide layer 10A and the non-thermoplastic polyimide layer 20A, and the combined thickness of the thermoplastic polyimide layer 10B and the non-thermoplastic polyimide layer 20B, both laminated on one side of the adhesive layer BS, are within the range of 2 μm or more and 20 μm or less. Furthermore, condition a specifies that... Figure 2 In the structural example shown, the combined thickness of the thermoplastic polyimide layer 10A, the non-thermoplastic polyimide layer 20A, and the thermoplastic polyimide layer 30A, all laminated on one side of the adhesive layer BS, as well as the combined thickness of the thermoplastic polyimide layer 10B, the non-thermoplastic polyimide layer 20B, and the thermoplastic polyimide layer 30B, are all within the range of 2 μm or more and 20 μm or less. That is, in Figure 1 and Figure 2 In the process, the thickness of the first insulating resin layer 40A and the thickness of the second insulating resin layer 40B are both within the range of 2μm or more and 20μm or less.

[0080] Thus, by keeping the first insulating resin layer 40A and the second insulating resin layer 40B, which are the outer layers, within a specified thickness range, the thickness / thickness ratio of the adhesive layer BS, which has relatively excellent dielectric properties, can be maximized, thereby improving the overall dielectric properties of the multilayer film 100 and the multilayer film 101. If the thickness of the first insulating resin layer 40A or the second insulating resin layer 40B is less than 2 μm, the adhesion to the metal layer when it is laminated on the outside may be compromised. If it exceeds 20 μm, it becomes a constraint when increasing the thickness / thickness ratio of the adhesive layer BS, making it difficult to achieve a low dielectric loss tangent for the multilayer film 100 and the multilayer film 101 as a whole. From the above perspective, the thickness of both the first insulating resin layer 40A and the second insulating resin layer 40B is preferably in the range of 2 μm or more and 12 μm or less, more preferably in the range of 2 μm or more and 8 μm or less, and most preferably in the range of 2 μm or more and 5 μm or less.

[0081] exist Figure 1 and Figure 2 In this context, regarding the thickness of the thermoplastic polyimide layer 10A and the thermoplastic polyimide layer 10B, from the viewpoint of ensuring sufficient adhesion to the metal layer when it is laminated on the outside, it is preferably, for example, in the range of 0.5 μm or more and 3 μm or less, more preferably in the range of 1 μm or more and 2 μm or less, and even more preferably in the range of 1 μm or more and 1.8 μm or less. Furthermore, from the viewpoint of ensuring the overall self-support of the multilayer film 100 and the multilayer film 101 and suppressing excessive reduction of the coefficient of thermal expansion (CTE), the thickness of the non-thermoplastic polyimide layer 20A and the non-thermoplastic polyimide layer 20B is preferably, for example, in the range of 1 μm or more and 10 μm or less, more preferably in the range of 1 μm or more and 4 μm or less, even more preferably in the range of 1.5 μm or more and 5 μm or less, and most preferably in the range of 1.5 μm or more and 3 μm or less.

[0082] In addition, Figure 2 In view of the adhesion and dielectric properties of the adhesive layer BS, the thicknesses of the thermoplastic polyimide layer 30A and the thermoplastic polyimide layer 30B are preferably in the range of 0.5 μm or more and 3 μm or less, and more preferably in the range of 1 μm or more and 2 μm or less.

[0083] Furthermore, the thermoplastic polyimide layers 10A, 10B, 30A, and 30B can be of the same or different thicknesses, and the non-thermoplastic polyimide layers 20A and 20B can also be of the same or different thicknesses. Moreover, the first insulating resin layer 40A and the second insulating resin layer 40B can be of the same or different thicknesses.

[0084] b) Satisfies the following equation (i).

[0085] 65 < P P / P AD <1,550…(i)

[0086] {Here, P P It is the elastic modulus parameter of the polyimide layer, P AD It is the elastic coefficient parameter of the adhesive layer, expressed by the following equations (ii) to (v):

[0087] P P =P P1 +P P2 …(ii)

[0088] P P1 =(E' P100 +E' P200 )×t p1 …(iii)

[0089] P P2 =(E' P100 +E' P200 )×t p2 …(iv)

[0090] P AD =(E' AD100 +E' AD200 )×tad…(v)

[0091] E' P100 Storage elastic modulus of the polyimide layer at 100°C [GPa]

[0092] E' P200 Storage elastic modulus of the polyimide layer at 200°C [GPa]

[0093] E' AD100 Storage elastic modulus of the adhesive layer at 100°C [GPa]

[0094] E' AD200 Storage elastic modulus of the adhesive layer at 200°C [GPa]

[0095] t p1 The total thickness [μm] of the thermoplastic polyimide layer and the non-thermoplastic polyimide layer laminated on one side of the adhesive layer.

[0096] t p2 The total thickness [μm] of the thermoplastic polyimide layer and the non-thermoplastic polyimide layer laminated on the other side of the adhesive layer.

[0097] tad: Thickness of the adhesive layer [μm]

[0098] Here, the elastic modulus parameter P of the polyimide layer is... P To make the elastic coefficient parameter P P1 With elastic coefficient parameter P P2 The value obtained by adding them together is the elastic coefficient parameter P. P1 The elastic modulus parameter P is calculated by equation (iii) by treating the thermoplastic polyimide layer and the non-thermoplastic polyimide layer stacked on one side of the adhesive layer as a single polyimide layer. P2 The thermoplastic polyimide layer and the non-thermoplastic polyimide layer stacked on the other side of the adhesive layer are considered as a single polyimide layer, and the result is calculated using equation (iv).

[0099] Condition b specifies the elastic modulus parameter (P) of the polyimide layer as a whole, which is the outer layer. P The elastic modulus parameter (P) of the adhesive layer BS, which is the inner layer, is relative to the elastic modulus parameter. AD The ratio of (P) P / P AD Within the specified range. Elasticity coefficient parameter (P) P (P) is, for example, the product of the storage elastic modulus of the first insulating resin layer 40A at 100°C and 200°C in the process temperature range during hot pressing and its thickness. P1 The product of the storage elastic modulus of the second insulating resin layer 40B at the stated temperature and its thickness (P) P2 The value is obtained by adding them together. Additionally, the elastic coefficient parameter (P) AD For example, it is the product of the storage elasticity coefficient of the adhesive layer BS at 100℃ and 200℃ in the process temperature range of hot pressing and its thickness.

[0100] Here, the ratio of the elastic coefficient parameter of the outer layer to that of the inner layer (P) is... P / P ADThe significance of this indicator is explained. It is believed that the residual stress in each layer after hot pressing, due to the dimensional changes before and after etching caused by the heat treatment during hot pressing and the etching process of the metal layers, is affected by the differences in the storage elasticity coefficient or thickness of each layer. That is, regarding the storage elasticity coefficient of each layer, the storage elasticity coefficient within the process temperature range is crucial. The storage elasticity coefficient varies significantly with temperature; therefore, the higher the storage elasticity coefficient, the greater the stress during thermal expansion or contraction. Furthermore, regarding thickness, it is believed that layers with a larger thickness ratio tend to have a greater impact on dimensional changes. Because the adhesive layer BS in the inner layer has superior dielectric properties compared to the polyimide layer, increasing the thickness ratio of the adhesive layer BS improves the overall dielectric properties of multilayer films 100 and 101. However, to achieve a high level of balance between dimensional stability and dielectric properties, methods for controlling the optimal balance between the storage elasticity coefficient and thickness of each layer were studied separately for the outer and inner layers. The results showed that calculating the following parameter—the product of the sum of the storage elasticity coefficients of each layer at 100°C and 200°C (representative values ​​within the process temperature band) and the thickness—and controlling the ratio of this parameter within a specified range, resulted in the desired dimensional stability. Based on this understanding, the overall elasticity coefficient parameter (P) of the polyimide layer... P The elastic modulus parameter (P) relative to the adhesive layer BS AD The ratio of (P) P / P AD The ratio of residual stress in the outer layer to that in the inner layer is a simplified representation of the residual stress using the storage elastic coefficient. This ratio (P) is used to suppress dimensional changes caused by residual stress after hot pressing. P / P AD Satisfying equation (i), the elastic coefficient parameter (P) of the outer layer P ) and the elastic coefficient parameter of the inner layer (P) AD Compared to controlling the increase within a specified range, this improves the overall dimensional stability of the multilayer film 100 and multilayer film 101.

[0101] Assuming the thickness of the outer layer satisfies condition a, in equation (i), if the ratio (P) P / P AD If the ratio (P) is below 65, the dimensional changes caused by residual stress after hot pressing become larger, potentially impairing dimensional stability. If it is above 1,550, while dimensional stability is maintained, low dielectric loss tangent cannot be achieved, making it difficult to satisfy condition c below. From this perspective, the ratio (P) P / P AD The lower limit value of (P) is preferably 70 or more, more preferably 80 or more, and most preferably 90 or more. Additionally, the ratio (P) P / P ADThe upper limit of ) is preferably 1200 or less, more preferably 900 or less, and most preferably 500 or less.

[0102] c) As a whole multilayer film, the dielectric loss tangent at 20 GHz, measured using an SPDR resonator, is less than 0.0029.

[0103] Condition c specifies that the dielectric loss tangent of the multilayer films 100 and 101 as a whole is a very low value compared to the prior art. As long as the dielectric loss tangent of the multilayer films 100 and 101 as a whole at 20 GHz is less than 0.0029, the loss of electrical signals can be effectively reduced in the transmission path of high-frequency signals in the GHz band of 1 GHz to 60 GHz, and therefore it can also be applied to circuit boards used in high-speed communications such as 5G. From this perspective, the dielectric loss tangent of the multilayer films 100 and 101 as a whole at 20 GHz is preferably 0.0025 or less, more preferably 0.0020 or less.

[0104] Furthermore, from the same point of view, the relative permittivity of the multilayer film 100 and the multilayer film 101 as a whole at 20 GHz, as measured using an SPDR resonator, is preferably 3.0 or less, and more preferably in the range of 2.9 to 1.5.

[0105] In addition to satisfying conditions a) to c), multilayer films 100 and 101 are preferably satisfied with one or more of conditions d) to g).

[0106] d) The polyimide layer, which is composed of a thermoplastic polyimide layer and a non-thermoplastic polyimide layer stacked on one side of the adhesive layer, has a storage elasticity coefficient of 1.0 GPa or higher at 100°C and a storage elasticity coefficient of 0.1 GPa or higher at 200°C.

[0107] Condition d specifies that for both the first insulating resin layer 40A and the second insulating resin layer 40B, the storage elasticity coefficient at 100°C is 1.0 GPa or more, and the storage elasticity coefficient at 200°C is 0.1 GPa or more. Meeting condition d means that in the hot-pressing temperature range (100°C to 200°C), the storage elasticity coefficient of the outer layer is higher than that of the adhesive layer BS, which is the inner layer. To suppress dimensional changes caused by residual stress after hot pressing, it is considered effective to increase the elasticity coefficient parameter of the outer layer by a certain amount relative to the inner layer. Therefore, by considering condition e as described below, and controlling the process to increase the storage elasticity coefficient of the outer layer compared to the inner layer, the overall dimensional stability of the multilayer film 100 and multilayer film 101 can be improved. From this perspective, the storage elasticity coefficients of the first insulating resin layer 40A and the second insulating resin layer 40B at 100°C are preferably in the range of 2 GPa or more and 10 GPa or less, more preferably in the range of 3 GPa or more and 8 GPa or less. In addition, the storage elasticity coefficient at 200°C is preferably in the range of 0.5 GPa or more and 8 GPa or less, and more preferably in the range of 1 GPa or more and 5 GPa or less.

[0108] Furthermore, the storage elastic coefficients of the first insulating resin layer 40A and the second insulating resin layer 40B may be the same or different, but from the viewpoint of suppressing warping, they are preferably the same.

[0109] e) The storage elasticity coefficient of the adhesive layer at 100°C is less than 130 MPa, and the storage elasticity coefficient at 200°C is less than 40 MPa.

[0110] Condition e specifies the storage elastic modulus of the thermoplastic polyimide (hereinafter sometimes referred to as "adhesive polyimide") constituting the adhesive layer BS in the hot-pressing temperature range (100°C to 200°C). Meeting condition e means that, within the temperature range of 100°C to 200°C, the storage elastic modulus is below 130 MPa and does not become excessively large. It can be considered that, after the outer metal layer is laminated, the residual stress after hot-pressing, which is due to dimensional changes caused by etching or heating of the metal layer, increases with a higher storage elastic modulus of the adhesive layer BS at the hot-pressing temperature, and further increases with a larger thickness / thickness ratio of the adhesive layer BS. Therefore, by using a resin whose storage elastic modulus does not become excessively large in the hot-pressing temperature range, even if the thickness / thickness ratio of the adhesive layer BS is increased to some extent, the residual stress after hot-pressing can be reduced, ensuring dimensional stability. From the aforementioned perspective, the storage elastic modulus of the adhesive layer BS at 100°C is preferably in the range of 0.01 MPa or more and 100 MPa or less, more preferably in the range of 0.1 MPa or more and 50 MPa or less. Furthermore, the storage elastic modulus at 200°C is preferably in the range of 0.01 MPa or more and 30 MPa or less, more preferably in the range of 0.1 MPa or more and 20 MPa or less.

[0111] f) When the total thickness of the thermoplastic polyimide layer in the entire multilayer film is set as T A Let the total thickness of the non-thermoplastic polyimide layer be T. B When the thickness of the adhesive layer is set to tad, the following equation (vi) is satisfied.

[0112] 0.60≦tad / (T A +T B +tad)≦0.99…(vi)

[0113] Condition f specifies that the thickness tad of the adhesive layer BS is relative to the overall thickness (T) of the multilayer film 100 and the multilayer film 101. A +T B +tad) ratio tad / (T A +T B +tad) is set to the specified range. Here, the thickness T A for Figure 1 The total thickness of the thermoplastic polyimide layer 10A and thermoplastic polyimide layer 10B, or Figure 2 The total thickness of thermoplastic polyimide layer 10A, thermoplastic polyimide layer 10B, thermoplastic polyimide layer 30A, and thermoplastic polyimide layer 30B in the mixture. Figure 1 and Figure 2 Thickness T in B It is the total thickness of the non-thermoplastic polyimide layer 20A and the non-thermoplastic polyimide layer 20B.

[0114] By making the thickness ratio tad / (T) A +T B +tad) satisfies equation (vi), which enables low dielectric loss tangent for the entire multilayer film 100 and multilayer film 101, while achieving a balance with dimensional stability. If the thickness ratio tad / (T A +T B If the thickness ratio tad / (T) is less than 0.60, the thickness ratio of the adhesive layer BS becomes relatively small. Therefore, achieving low dielectric loss tangent for the multilayer films 100 and 101 as a whole becomes difficult, leading to increased transmission loss during high-frequency signal transmission. From the aforementioned perspective, the thickness ratio tad / (T) A +T B The lower limit value of (+tad) is preferably 0.65 or higher, more preferably 0.70 or higher, even more preferably 0.80 or higher, and most preferably 0.85 or higher.

[0115] On the other hand, in the thickness ratio tad / (T) A +T B When the thickness ratio tad / (T) is higher than 0.99, the thickness ratio of the adhesive layer BS becomes relatively too large. Therefore, in addition to making it difficult to ensure adhesion to the metal layer, it is sometimes difficult to maintain the overall dimensional stability of the multilayer films 100 and 101. Therefore, the thickness ratio tad / (T) A +T B The upper limit of (+tad) is preferably 0.96 or less, more preferably 0.94 or less.

[0116] In addition, the overall thickness (T) of multilayer film 100 and multilayer film 101 A +T B +tad) is preferably in the range of 70μm to 500μm, more preferably in the range of 100μm to 300μm. If the overall thickness (T) of the multilayer film 100 and multilayer film 101 is... A +T B If the thickness (+tad) is less than 70μm, the effect of suppressing the transmission loss of high-frequency signals when making circuit boards is insufficient; if it exceeds 500μm, productivity may be reduced.

[0117] Furthermore, the thickness tad of the adhesive layer BS is preferably greater than 50 μm. The present invention effectively balances excellent dielectric properties and dimensional stability in laminated structures where the thickness tad of the adhesive layer BS is greater than 50 μm. From this perspective, the thickness tad of the adhesive layer BS is preferably in the range of 50 μm to 450 μm, and more preferably in the range of 60 μm to 250 μm. If the thickness tad of the adhesive layer BS is less than the lower limit, the low dielectric loss tangent is insufficient, sometimes resulting in problems such as the inability to obtain sufficient dielectric properties. On the other hand, if the thickness tad of the adhesive layer BS exceeds the upper limit, sometimes adverse conditions such as reduced dimensional stability may occur.

[0118] g) When the total thickness of the thermoplastic polyimide layer in the entire multilayer film is set as T A Let the total thickness of the non-thermoplastic polyimide layer be T. B When, the following equation (vii) is satisfied.

[0119] 0.1≦(T A ) / (T A +T B )≦0.6…(vii)

[0120] Condition g specifies that the total thickness T A Relative to the total (T) A +T B The ratio of (T) is set within a specified range. Here, (T) A +T B The total thickness of the outer layer portion (T) is the total thickness of the outer layer portion disposed on both sides of the adhesive layer BS (i.e., the total thickness of the first insulating resin layer 40A and the second insulating resin layer 40B). Thus, by adjusting the ratio of the total thickness of the thermoplastic polyimide layers in the outer layer portion to (T) A ) / (T A +T B If formula (vii) is satisfied, even if the thickness of the first insulating resin layer 40A and the second insulating resin layer 40B, which are the outer layers, is made thinner than in the prior art according to condition a, excessive low CTE of the outer layers can be suppressed, and the adhesion to the metal layer when the metal layer is laminated on the outside can be fully ensured.

[0121] Furthermore, the non-thermoplastic polyimide layers 20A and 20B in the outer layer tend to have a lower coefficient of thermal expansion (CTE) as their thickness increases. This tendency is particularly noticeable when the non-thermoplastic polyimide layers 20A and 20B are formed by casting. This is believed to be because, during heat treatment, a thinner coating accelerates solvent evaporation and molecular orientation. Therefore, if the thickness ratio (T...)... A ) / (TA +T B If the thickness ratio (T) is less than 0.1, excessive low CTE processing is carried out in the outer layer. Furthermore, when stacking metal layers on the outer side, it is sometimes difficult to ensure tight adhesion with the metal layers. From this perspective, the thickness ratio (T) A ) / (T A +T B The lower limit value is preferably selected from, for example, any one of 0.17, 0.20, 0.25, 0.30 or 0.40.

[0122] On the other hand, in the thickness ratio (T) A ) / (T A +T B When the thickness ratio (T) exceeds 0.6, such as in cases where the metal layer is etched after being stacked on the outside or in cases of heat treatment, it is sometimes difficult to maintain the overall dimensional stability of the multilayer films 100 and 101. Therefore, the thickness ratio (T) A ) / (T A +T B The upper limit of ) is preferably 0.55 or less, more preferably 0.50 or less.

[0123] For example, when multilayer films 100 and 101 are used as insulating resin layers in circuit boards, in order to prevent warping or a decrease in dimensional stability, the overall coefficient of thermal expansion (CTE) of the film is preferably in the range of 10 ppm / K to 30 ppm / K, more preferably in the range of 10 ppm / K to 25 ppm / K, and most preferably in the range of 10 ppm / K to 20 ppm / K. If the CTE is less than 10 ppm / K or exceeds 30 ppm / K, warping or a decrease in dimensional stability will occur.

[0124] In addition, for example, when the insulating resin layer is used as a circuit board, in order to prevent warping or a decrease in dimensional stability, the coefficient of thermal expansion (CTE) of the first insulating resin layer 40A or the second insulating resin layer 40B stacked on one side of the adhesive layer BS is preferably in the range of 5ppm / K to 35ppm / K, more preferably in the range of 8ppm / K to 30ppm / K, and most preferably in the range of 10ppm / K to 25ppm / K.

[0125] Furthermore, the coefficients of thermal expansion (CTE) of the first insulating resin layer 40A and the second insulating resin layer 40B may be the same or different, but from the viewpoint of suppressing warping, they are preferably the same.

[0126] [Polyimide]

[0127] Next, the polyimide constituting the first insulating resin layer 40A, the second insulating resin layer 40B, and the adhesive layer BS will be described.

[0128] Furthermore, when referred to as polyimide in this invention, it also refers to resins containing polymers having imide groups in their molecular structure, such as polyamide-imide, polyether-imide, polyester-imide, polysiloxane-imide, and polybenzimidazole-imide. Additionally, when a polyimide has multiple structural units, it can exist as a block or as a random unit, but a random form is preferred.

[0129] Furthermore, "thermoplastic polyimide" generally refers to polyimide whose glass transition temperature (Tg) can be definitively determined. In this invention, it refers to polyimide with a storage elastic modulus of 1.0 × 10⁻⁶ at 30°C, as measured using a dynamic viscoelasticity measuring device (Dynamic thermomechanical analyzer, DMA). 9 Above Pa, the storage elasticity coefficient at 300℃ is less than 1.0 × 10⁻⁶. 8 Pa of polyimide. Additionally, "non-thermoplastic polyimide" refers to polyimide that typically does not exhibit softening or stickiness even when heated; however, in this invention, it refers to a stored elastic modulus of 1.0 × 10⁻⁶ at 30°C, as measured using a dynamic viscoelasticity measuring device (DMA). 9 Above Pa, the storage elasticity coefficient at 300℃ is 1.0 × 10⁻⁶. 8 Polyimide with a strength of Pa or higher.

[0130] <Thermoplastic polyimide>

[0131] The thermoplastic polyimide layers 10A, 10B, 30A, and 30B used to form the first insulating resin layer 40A and the second insulating resin layer 40B are obtained by reacting an acid dianhydride component with a diamine component containing aliphatic diamines and / or aromatic diamines, etc., and contain acid dianhydride residues derived from the acid dianhydride component and diamine residues derived from the diamine component. By selecting the types of acid dianhydride components and diamine components, and the molar ratio of each when using two or more acid dianhydrides or diamines, the thermal expansion, adhesion, glass transition temperature, etc. of the thermoplastic polyimide can be controlled. Furthermore, in this invention, "acid dianhydride residue" refers to a tetravalent group derived from an acid dianhydride, and "diamine residue" refers to a divalent group derived from a diamine compound.

[0132] In the thermoplastic polyimide used to form thermoplastic polyimide layer 10A, thermoplastic polyimide layer 10B, thermoplastic polyimide layer 30A, and thermoplastic polyimide layer 30B, the acid dianhydride component and the diamine component, which are monomers commonly used in the synthesis of thermoplastic polyimide, can be used as raw materials, but aromatic acid dianhydrides or aromatic diamines are preferred.

[0133] As aromatic acid dianhydrides, preferred choices include, for example, pyromellitic dianhydride (PMDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,3',3,4'-biphenyltetracarboxylic dianhydride, p-phenylene bis(trimellitic acidmonoester) anhydride (TAHQ), and 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA). Among these, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) is the most preferred.

[0134] In order to reduce the concentration of polar groups and improve dielectric properties while ensuring adhesion to the substrate, the thermoplastic polyimide layer 10A, thermoplastic polyimide layer 10B, thermoplastic polyimide layer 30A, and thermoplastic polyimide layer 30B preferably contain BPDA residues derived from 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) at a rate of 40 mol% or more, more preferably in the range of 45 mol% to 80 mol%, relative to all acid dianhydride residues.

[0135] As an aromatic diamine, from the viewpoint of ensuring adequate flexibility and adhesion to the substrate, it is preferable to use a diamine compound represented by the following general formula (1).

[0136] [Chemistry 1]

[0137]

[0138] In general formula (1), R independently represents a halogen atom, or an alkyl or alkoxy group that can be substituted by a halogen atom having 1 to 6 carbon atoms, or a phenyl or phenoxy group that can be substituted by a monovalent hydrocarbon group or alkoxy group having 1 to 6 carbon atoms, Z independently represents a divalent group selected from -O-, -S-, -CH2-, -CH(CH3)-, -C(CH3)2-, -CO-, -COO-, -SO2-, -NH- or -NHCO-, m1 independently represents an integer from 0 to 4, and m2 represents an integer from 0 to 2.

[0139] Examples of diamine compounds represented by general formula (1) include: 1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,4-bis(4-aminophenoxy)benzene (TPE-Q), 1,3-bis(3-aminophenoxy)benzene (APB), and 2,2-bis[4-(4-aminophenoxy)benzene (APB). Examples of bis[4-(4-aminophenoxy)phenyl]propane (BAPP), bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS), 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene (bisaniline-M), 4,4'-diaminodiphenyl ether (DAPE), etc.

[0140] In thermoplastic polyimide layer 10A, thermoplastic polyimide layer 10B, thermoplastic polyimide layer 30A, and thermoplastic polyimide layer 30B, from the viewpoint that even with a thinning of the thickness, the adhesion between the metal layer and the metal layer can be ensured when the metal layer is laminated, the proportion of diamine residues derived from the diamine compound represented by general formula (1) is preferably 30 mol% or more, more preferably 50 mol% or more, and even more preferably in the range of 70 mol% to 90 mol% relative to all diamine residues.

[0141] <Non-thermoplastic polyimide>

[0142] The non-thermoplastic polyimide layers 20A and 20B used to form the first insulating resin layer 40A and the second insulating resin layer 40B are obtained by reacting an acid dianhydride component with a diamine component containing aliphatic diamines and / or aromatic diamines, etc., and contain acid dianhydride residues derived from the acid dianhydride component and diamine residues derived from the diamine component. By selecting the types of acid dianhydride components and diamine components, and the molar ratio of each when using two or more acid dianhydrides or diamines, the thermal expansion, dielectric properties, etc. of the non-thermoplastic polyimide can be controlled.

[0143] In the non-thermoplastic polyimide used to form the non-thermoplastic polyimide layer 20A and the non-thermoplastic polyimide layer 20B, acid dianhydride components and diamine components, which are monomers commonly used as raw materials in the synthesis of non-thermoplastic polyimides, can be used. However, from the viewpoint of controlling the coefficient of thermal expansion (CTE) of the outer layer and ensuring dimensional stability, it is preferable to use aromatic acid dianhydrides or aromatic diamines with a biphenyl backbone. As aromatic acid dianhydrides with a biphenyl backbone, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) and 2,3',3,4'-biphenyltetracarboxylic acid dianhydride are preferred, and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) is particularly preferred.

[0144] In the non-thermoplastic polyimide layer 20A and the non-thermoplastic polyimide layer 20B, in order to control the coefficient of thermal expansion (CTE) of the outer layer to ensure the overall dimensional stability of the multilayer film 100 and the multilayer film 101, and to improve the storage elasticity coefficient of the outer layer to meet condition d, the content of dianhydride residues having a biphenyl backbone is preferably 40 mol% or more, more preferably in the range of 45 mol% to 70 mol% relative to all dianhydride residues.

[0145] In addition, as aromatic diamines having a biphenyl skeleton, preferred examples include 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB), 2,2'-diethyl-4,4'-diaminobiphenyl (m-EB), 2,2'-diethoxy-4,4'-diaminobiphenyl (m-EOB), 2,2'-dipropoxy-4,4'-diaminobiphenyl (m-POB), and 2,2'-n-propyl-4,4'-diaminobiphenyl (m-POB). Biphenyl (m-NPB), 2,2'-divinyl-4,4'-diaminobiphenyl (VAB), 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl (TFMB), etc., with 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB) being particularly preferred.

[0146] In the non-thermoplastic polyimide layer 20A and the non-thermoplastic polyimide layer 20B, in order to control the coefficient of thermal expansion (CTE) of the outer layer to ensure the overall dimensional stability of the multilayer film 100 and the multilayer film 101, and to improve the storage elasticity coefficient of the outer layer to meet condition d, the content of diamine residues having a biphenyl backbone is preferably 40 mol% or more, more preferably in the range of 70 mol% to 100 mol% relative to all diamine residues.

[0147] <Adhesive Polyimide>

[0148] The adhesive polyimide that is the preferred resin for constituting the adhesive layer BS is a thermoplastic polyimide obtained by reacting an acid dianhydride component with a diamine component containing an aliphatic diamine.

[0149] As a raw material for adhesive polyimides, the acid dianhydride component can be a monomer commonly used in the synthesis of thermoplastic polyimides, such as preferably 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride (DSDA), 4,4'-oxydiphthalic dianhydride (ODPA), 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (2,2-bis[4-(3,4-dicarboxyphenoxy]propane) dianhydride (BPADA), p-phenylene bis(trimethacrylate) anhydride (TAHQ), ethylene glycol bis(trimethacrylate) anhydride (ethylene glycol bispramine) Aromatic acid dianhydrides such as TMEG, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA), and 2,3',3,4'-biphenyltetracarboxylic acid dianhydride, more preferably 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride (BTDA). The adhesive polyimide preferably contains, relative to all acid dianhydride residues, one or more acid dianhydride residues derived from the aromatic acid dianhydride in a total range of 40 mol% to 100 mol%, more preferably in a total range of 50 mol% to 90 mol%. Further preferably, it contains two acid dianhydride residues derived from the aromatic acid dianhydride in a total range of 40 mol% to 100 mol%, most preferably 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride (BTDA) in a range of 50 mol% to 90 mol%, and more preferably, the aromatic acid dianhydrides other than BTDA in a range of 10 mol% to 50 mol%.

[0150] As a diamine component that serves as a raw material for adhesive polyimide, monomers commonly used in the synthesis of thermoplastic polyimide can be used. However, from the viewpoint of controlling the storage elastic coefficient of the adhesive layer BS to satisfy conditions b and e, and reducing the dielectric loss tangent to improve the overall dielectric properties of the multilayer film 100 and multilayer film 101 to satisfy condition c, a dimer diamine composition is preferred.

[0151] That is, the adhesive polyimide preferably contains diamine residues derived from the dimer diamine composition in a range of preferably 20 mol% or more, more preferably 50 mol% or more, and most preferably 70 mol% to 100 mol% relative to all diamine residues. By containing diamine residues derived from the dimer diamine composition in the aforementioned amount, the thermocompression properties can be improved due to the lower glass transition temperature (lower Tg) of the adhesive layer BS, thereby alleviating internal stress due to the lower elastic coefficient, and improving the dielectric properties of the adhesive layer BS. If the content of diamine residues derived from the dimer diamine composition is less than 20 mol% relative to all diamine residues, the transmission loss during high-frequency transmission increases, or as an adhesive layer BS between the first insulating resin layer 40A and the second insulating resin layer 40B, sufficient adhesion may not be obtained.

[0152] The dimer diamine composition is a mixture containing (a) as the main component and may also contain (b) and (c) components, and is a refined product in which the amounts of (b) and (c) components are controlled.

[0153] (a) Dimeric diamine

[0154] (b) Monoamine compounds obtained by substituting the terminal carboxylic acid group of a monocarboxylic acid compound having 10 to 40 carbon atoms with a primary aminomethyl or amino group.

[0155] (c) An amine compound obtained by substituting the terminal carboxylic acid group of a polybasic acid compound having a hydrocarbon group in the range of 41 to 80 carbon atoms with a primary aminomethyl or amino group (except for the dimer diamine).

[0156] (a) The dimer diamine of component (a) refers to a diamine formed by replacing the two terminal carboxylic acid groups (-COOH) of a dimer acid with a primary aminomethyl group (-CH2-NH2) or an amino group (-NH2). Dimer acids are known dicarboxylic acids obtained through intermolecular polymerization of unsaturated fatty acids. Their industrial manufacturing process is largely standardized in the industry, and they can be obtained by dimerizing unsaturated fatty acids with 11 to 22 carbon atoms using clay catalysts, etc. Industrially obtained dimer acids are mainly composed of 36-carbon dicarboxylic acids obtained by dimerizing 18-carbon unsaturated fatty acids such as oleic acid, linoleic acid, and linolenic acid. Depending on the degree of purification, they contain arbitrary amounts of monomeric acids (18 carbon atoms), trimer acids (54 carbon atoms), and other polymeric fatty acids with 20 to 54 carbon atoms. In addition, double bonds remain after the dimerization reaction, but in this invention, the dimer acid also contains compounds that undergo hydrogenation to reduce the degree of unsaturation. (a) The dimer diamine of component (a) can be defined as a diamine compound obtained by replacing the terminal carboxylic acid group of a dicarboxylic acid compound with a carbon number in the range of 18 to 54, preferably in the range of 22 to 44, with a primary aminomethyl or amino group.

[0157] As a characteristic of dimerized diamines, they can impart properties derived from the backbone of dimer acids. Specifically, dimerized diamines are large aliphatic molecules with molecular weights of approximately 560–620, thus increasing the molar volume of the molecule and relatively reducing the polar groups in the polyimide. This characteristic of dimerized diamines is believed to help suppress the decrease in the heat resistance of polyimides and improve dielectric properties by reducing the relative dielectric constant and dielectric loss tangent. Furthermore, since they contain two freely moving hydrophobic chains with 7–9 carbon atoms and two chain-like aliphatic amino groups with a length close to 18 carbon atoms, not only can polyimides be endowed with flexibility, but they can also be configured with asymmetric or non-planar chemical structures, thus enabling the lower dielectric constant of polyimides.

[0158] The dimer diamine composition preferably uses a dimer diamine composition in which the content of dimer diamine in component (a) is increased to 96% by weight or more, preferably 97% by weight or more, and more preferably 98% by weight or more, by purification methods such as molecular distillation. By setting the content of dimer diamine in component (a) to 96% by weight or more, the expansion of the molecular weight distribution of the polyimide can be suppressed. Furthermore, if technically feasible, it is optimal that the dimer diamine composition is entirely (100% by weight) composed of dimer diamine in component (a).

[0159] Furthermore, based on the area percentage of the chromatogram obtained by gel permeation chromatography (GPC), the total of components (b) and (c) in the dimer diamine composition is 4% or less, preferably less than 4%. Additionally, the area percentage of the chromatogram for component (b) is preferably 3% or less, more preferably 2% or less, and even more preferably 1% or less; the area percentage of the chromatogram for component (c) is preferably 2% or less, more preferably 1.8% or less, and even more preferably 1.5% or less. By setting these ranges, the sharp increase in the molecular weight of the polyimide can be suppressed, thereby suppressing the increase in the dielectric loss tangent of the resin film over a wide frequency range. Furthermore, components (b) and (c) may not be included in the dimer diamine composition.

[0160] The dimer diamine composition can utilize commercially available products, such as PRIAMINE 1073 (trade name), PRIAMINE 1074 (trade name), and PRIAMINE 1075 (trade name) manufactured by Croda Japan. When using these commercially available products, purification is preferred to reduce components other than the dimer diamine; for example, it is preferable to set the dimer diamine to 96% by weight or more. There are no particular limitations on the purification method; known methods such as distillation or precipitation purification are preferred.

[0161] Adhesive polyimides may use diamine compounds other than the dimer diamine composition as raw materials without impairing the effects of the invention. Examples of preferred diamine compounds that can be used in adhesive polyimides include those represented by the general formula (1).

[0162] Among the diamine compounds represented by general formula (1), the adhesive polyimide is preferably, for example, containing 1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,4-bis(4-aminophenoxy)benzene (TPE-Q), 1,3-bis(3-aminophenoxy)benzene (APB), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS), etc.

[0163] In adhesive polyimide, in order to improve the flexibility of the adhesive layer BS and alleviate the residual stress after hot pressing caused by the low elastic coefficient, the proportion of diamine residues derived from the diamine compound represented by general formula (1) is preferably in the range of 5 mol% to 50 mol% relative to all diamine residues, more preferably in the range of 10 mol% to 30 mol%.

[0164] By selecting the types of acid dianhydride and diamine components in adhesive polyimides, or by using the molar ratio of two or more acid dianhydrides or diamines, the coefficient of thermal expansion, glass transition temperature, dielectric properties, etc., can be controlled.

[0165] The weight-average molecular weight of the adhesive polyimide is preferably in the range of 10,000 to 400,000, and more preferably in the range of 20,000 to 350,000. If the weight-average molecular weight is less than 10,000, the adhesive layer BS tends to become brittle due to reduced strength. On the other hand, if the weight-average molecular weight exceeds 400,000, the viscosity tends to increase excessively, which can easily lead to uneven thickness and streaks in the adhesive layer BS during coating.

[0166] The most preferred adhesive polyimide is a fully imidized structure. However, a portion of the polyimide may also be an amide acid. The imidization rate can be measured using a Fourier transform infrared spectrophotometer (commercially available: FT / IR620 manufactured by Nippon Spectrophotometer) and by using the single-reflection ATR method to determine the infrared absorption spectrum of the polyimide film at 10¹⁵ cm⁻¹. -1 Based on the nearby benzene ring absorber, according to 1780 cm -1 The absorbance is calculated from the C=O stretching of the imide group.

[0167] The glass transition temperature (Tg) of the adhesive polyimide is preferably below 250°C, more preferably in the range of 40°C to 200°C. By setting the Tg of the adhesive polyimide to below 250°C, hot pressing can be performed at low temperatures, thus mitigating internal stress generated during lamination and suppressing dimensional changes after circuit fabrication. If the Tg of the adhesive polyimide exceeds 250°C, the temperature during bonding between the first insulating resin layer 40A and the second insulating resin layer 40B becomes higher, potentially impairing the dimensional stability of the circuit after fabrication.

[0168] By using the above adhesive polyimide, the adhesive layer BS has excellent flexibility and dielectric properties (low dielectric constant and low dielectric loss tangent).

[0169] In the adhesive layer BS, polystyrene elastomer is preferably formulated together with adhesive polyimide. Polystyrene elastomer is a copolymer of styrene or its derivatives with a conjugated diene compound, including its hydride. Here, styrene or its derivatives are not particularly limited, and examples include: styrene, methylstyrene, butylstyrene, divinylbenzene, vinyltoluene, etc. Similarly, the conjugated diene compound is not particularly limited, and examples include: butadiene, isoprene, 1,3-pentadiene, etc.

[0170] Furthermore, the polystyrene elastomer is preferably hydrogenated. Hydrogenation further improves its thermal stability, making it less prone to decomposition or polymerization, and enhances its aliphatic properties and compatibility with adhesive polyimides.

[0171] The copolymer structure of polystyrene elastomers can be either block or random. Preferred specific examples of polystyrene elastomers include: styrene-butadiene-styrene block copolymers (SBS), styrene-butadiene-butylene-styrene block copolymers (SBBS), styrene-ethylene-butylene-styrene block copolymers (SEBS), styrene-ethylene-propylene-styrene block copolymers (SEPS), and styrene-ethylene-ethylene / propylene-styrene block copolymers (SEEPS), but are not limited to these specific examples.

[0172] The weight-average molecular weight of the polystyrene elastomer is preferably in the range of 50,000 to 300,000, more preferably in the range of 80,000 to 270,000. If the weight-average molecular weight is below this range, the improvement in dielectric properties may be insufficient. Conversely, if the weight-average molecular weight is above this range, the viscosity may increase when preparing a composition containing an adhesive polyimide and a solvent, making the preparation of the resin film difficult.

[0173] Furthermore, from the viewpoint of achieving a significantly low dielectric loss tangent in the resin film, the weight-average molecular weight of the polystyrene elastomer is preferably 100,000 or less, more preferably in the range of 50,000 to 100,000, and most preferably in the range of 70,000 to 100,000. By making the weight-average molecular weight of the polystyrene elastomer 100,000 or less, the dielectric properties of the resin film can be significantly improved.

[0174] The acid value of the polystyrene elastomer is preferably 10 mg KOH / g or less, more preferably 1 mg KOH / g or less, and even more preferably 0 mg KOH / g. By adjusting the polystyrene elastomer to an acid value of 10 mg KOH / g or less, the dielectric loss tangent during resin film formation can be reduced while maintaining good peel strength. Conversely, if the acid value exceeds 10 mg KOH / g and becomes too high, the dielectric properties deteriorate due to the increase in polar groups, and the compatibility with the adhesive polyimide deteriorates, resulting in reduced adhesion during resin film formation. Therefore, the lower the acid value, the better, and unmodified materials (i.e., resins with an acid value of 0 mg KOH / g) are most suitable. In this invention, excellent adhesion is exhibited when the adhesive polyimide contains residues derived from aliphatic diamines, so even when using unmodified (i.e., polystyrene elastomers with strong aliphatic properties), a decrease in adhesive strength can be avoided.

[0175] The polystyrene elastomer preferably contains styrene units [-CH2CH(C6H5)-] in a range of 10% by weight or more and 65% by weight or less, more preferably in a range of 20% by weight or more and 65% by weight or less, and most preferably in a range of 30% by weight or more and 60% by weight or less. When the styrene unit content in the polystyrene elastomer is less than 10% by weight, the elastic modulus of the resin decreases, resulting in deterioration of its operability as a film. If the content increases to more than 65% by weight, the resin becomes rigid and difficult to use as an adhesive. In addition, the rubber component in the polystyrene elastomer decreases, thus leading to deterioration of its dielectric properties.

[0176] Furthermore, by having a styrene unit content within the specified range, the proportion of aromatic rings in the resin film increases. Therefore, when forming through holes (through holes) and blind holes by laser processing during the manufacturing of circuit boards using resin films, the absorption in the ultraviolet region can be improved, further enhancing laser processability.

[0177] Commercially available polystyrene elastomers can be appropriately selected. Among these, KRATON's A1535HU, A1536HU, G1652MU, G1726VS, G1645VS, FG1901GT, G1650MU, G1654HU, G1730VO, and MD1653MO are preferred as polystyrene elastomers. Of these, KRATON's MD1653MO and G1726VS are more preferred as polystyrene elastomers with a weight average molecular weight of 100,000 or less.

[0178] The content of polystyrene elastomer relative to 100 parts by weight of adhesive polyimide is preferably in the range of 10 parts by weight or more and 150 parts by weight or less, more preferably in the range of 50 parts by weight or more and 120 parts by weight or less. When the content of polystyrene elastomer relative to 100 parts by weight of adhesive polyimide is less than 10 parts by weight, the effect of reducing the dielectric loss tangent may not be sufficiently achieved. On the other hand, if the weight ratio of polystyrene elastomer exceeds 150 parts by weight, the adhesion when forming the resin film decreases, and the concentration of solid components when forming a composition containing adhesive polyimide and solvent becomes too high, resulting in increased viscosity and sometimes reduced workability.

[0179] In addition, the total content of adhesive polyimide and polystyrene elastomer is preferably 60% to 100% by weight of all resin components constituting the adhesive layer BS, more preferably 80% to 100% by weight.

[0180] In addition to polystyrene elastomer, the adhesive layer BS can also contain appropriate amounts of plasticizers, epoxy resins and other curing resin components, curing agents, curing accelerators, organic or inorganic fillers, coupling agents, flame retardants, etc.

[0181] <Synthesis of Polyimide>

[0182] The thermoplastic polyimide and non-thermoplastic polyimide constituting the first insulating resin layer 40A and the second insulating resin layer 40B, and the adhesive polyimide constituting the adhesive layer BS, can be manufactured by reacting the acid dianhydride with a diamine compound in a solvent, and then heating to close the ring after the formation of polyamic acid. For example, the acid dianhydride component and the diamine compound are dissolved in an organic solvent at approximately equimolar amounts, and the polymerization reaction is carried out by stirring at a temperature in the range of 0°C to 100°C for 30 minutes to 24 hours, thereby obtaining polyamic acid as a precursor of polyimide. During the reaction, the reaction components are dissolved in an organic solvent at a concentration in the range of 5% to 50% by weight, preferably in the range of 10% to 40% by weight. Examples of organic solvents used in polymerization reactions include: N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), 2-butanone, dimethyl sulfoxide (DMSO), hexamethylphosphoramide, N-methylcaprolactam, dimethyl sulfate, cyclohexanone, dioxane, tetrahydrofuran, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and cresol. Two or more of these solvents may be used in combination, and aromatic hydrocarbons such as xylene and toluene may also be used. Furthermore, there are no particular limitations on the amount of this organic solvent used; it is preferable to adjust the concentration of the polyamic acid solution obtained through the polymerization reaction to approximately 5% to 50% by weight.

[0183] The synthesized polyamic acid is advantageous because it is commonly used as a reaction solvent solution, and can be concentrated, diluted, or replaced with other organic solvents as needed. Furthermore, polyamic acid generally has excellent solvent solubility, which is advantageous for its use. The viscosity of the polyamic acid solution is preferably in the range of 500 mPa·s to 100,000 mPa·s. If it deviates from this range, defects such as uneven thickness and streaks are easily generated in the film, for example, when performing coating operations using a coating machine.

[0184] There are no particular limitations on the method of imidizing polyamic acid to form adhesive polyimide. For example, heat treatment such as heating at a temperature range of 80°C to 400°C for 0.1 hours to 24 hours may be suitable.

[0185] <Crosslinking Formation of Adhesive Polyimide>

[0186] When adhesive polyimides have ketone groups, a cross-linked structure can be formed by reacting the ketone group with an amino group of an amino compound having at least two primary amino groups as functional groups to form a C=N bond. The heat resistance of the adhesive polyimide can be improved by forming a cross-linked structure. Preferred tetracarboxylic anhydrides for forming adhesive polyimides with ketone groups include, for example, 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA). As diamine compounds, examples include aromatic diamines such as 4,4'-bis(3-aminophenoxy)benzophenone (BABP) and 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene (BABB).

[0187] Examples of amino compounds that can be used for the crosslinking formation of adhesive polyimides include dihydrazide compounds, aromatic diamines, and aliphatic amines. Among these, dihydrazide compounds are preferred. Aliphatic amines other than dihydrazide compounds readily form crosslinked structures even at room temperature, raising concerns about the shelf life of the varnish. On the other hand, aromatic diamines require high temperatures to form crosslinked structures. By using dihydrazide compounds, both the shelf life of the varnish and the curing time can be shortened. Preferred diacylhydrazides include, for example, oxalate diacylhydrazide, malonate diacylhydrazide, succinate diacylhydrazide, glutarate diacylhydrazide, adipate diacylhydrazide, pimecrolate diacylhydrazide, octanoate diacylhydrazide, azelaate diacylhydrazide, sebacylhydrazide, dodecanoate diacylhydrazide, maleate diacylhydrazide, fumarate diacylhydrazide, diethylene glycol diacylhydrazide, tartrate diacylhydrazide, malate diacylhydrazide, phthalate diacylhydrazide, isophthalate diacylhydrazide, terephthalate diacylhydrazide, 2,6-naphthoic acid diacylhydrazide, 4,4-bisphenyl diacylhydrazide, 1,4-naphthoic acid diacylhydrazide, 2,6-pyridine diacylhydrazide, itaconic acid diacylhydrazide, etc. These diacylhydrazides can be used alone or in combination of two or more.

[0188] When crosslinking an adhesive polyimide, the amino compound is added to a resin solution containing an adhesive polyimide having ketone groups, causing the ketone groups in the adhesive polyimide to undergo a condensation reaction with the primary amino group of the amino compound. Through this condensation reaction, the resin solution is cured to form a cured product. In this case, the amount of amino compound added can be 0.004 mol to 1.5 mol, preferably 0.005 mol to 1.2 mol, more preferably 0.03 mol to 0.9 mol, and most preferably 0.04 mol to 0.5 mol, with the primary amino group accounting for 1 mol of the ketone group. If the amount of amino compound added is less than 0.004 moles (1 mole of primary amino group relative to ketone group), the crosslinking of polyimide using the adhesive properties of the amino compound is insufficient, and therefore the cured BS adhesive layer tends to have poor heat resistance. If the amount of amino compound added is more than 1.5 moles (1 mole of primary amino group relative to ketone group), the unreacted amino compound acts as a thermoplasticizer, which tends to reduce the heat resistance of the BS adhesive layer.

[0189] The conditions for the condensation reaction used to form crosslinks are not particularly limited if the ketone group in the adhesive polyimide reacts with the primary amino group of the amino compound to form an imine bond (C=N bond). Regarding the temperature of the heating condensation, for reasons such as releasing the water generated by the condensation to the outside of the system, or simplifying the condensation process by performing the heating condensation reaction after the synthesis of the adhesive polyimide, a range of 120°C to 220°C is preferred, and a range of 140°C to 200°C is more preferred. The reaction time is preferably about 30 minutes to 24 hours. The endpoint of the reaction can be determined, for example, by measuring the infrared absorption spectrum using a Fourier transform infrared spectrophotometer (commercially available: FT / IR620 manufactured by Nippon Spectrophotometer) and using a 1670 cm⁻¹ spectral density. -1 The absorption peaks originating from ketone groups in the nearby polyimide resin decrease or disappear, and at 1635 cm⁻¹ -1 This was confirmed by the presence of an absorption peak originating from an imine group nearby.

[0190] The thermal condensation of the ketone group of the adhesive polyimide with the primary amino group of the amino compound can be carried out, for example, by the following methods: (a) adding the amino compound and heating immediately after the synthesis (imidization) of the adhesive polyimide; (b) pre-adding an excess of the amino compound as a diamine component, then heating the remaining amino compound, which does not participate in imidization or amidation, together with the adhesive polyimide immediately after the synthesis (imidization) of the adhesive polyimide; or (c) heating the composition of the adhesive polyimide with the added amino compound after processing it into a predetermined shape (e.g., after coating it onto any substrate or after forming it into a film).

[0191] In order to impart heat resistance to adhesive polyimides, the formation of imine bonds is explained in the formation of cross-linked structures, but it is not limited to this. As a curing method for adhesive polyimides, epoxy resins, epoxy resin hardeners, etc. can also be formulated for curing.

[0192] [Metal-clad laminate]

[0193] The metal-clad laminate of this embodiment includes a multilayer film 100, a multilayer film 101, and a metal layer laminated on one or both sides of the multilayer film 100 and the multilayer film 101.

[0194] Figure 3 The diagram shows a cross-sectional structure of a metal-clad laminate 200 according to a preferred embodiment of the present invention. The metal-clad laminate 200 has a structure in which metal layers 110A and 110B are stacked on both sides of a multilayer film 100. Therefore, the metal-clad laminate 200 has a structure formed by stacking metal layer 110A, first insulating resin layer 40A, adhesive layer BS, second insulating resin layer 40B, and metal layer 110B in this order. Metal layers 110A and 110B are located on the outermost sides, and the first insulating resin layer 40A and the second insulating resin layer 40B are disposed on their inner sides. Furthermore, the adhesive layer BS is interposed between the first insulating resin layer 40A and the second insulating resin layer 40B. It can also be considered that the metal-clad laminate 200 with this layer structure has the following structure, namely, a first single-sided metal-clad laminate (C1) formed by stacking metal layer 110A, thermoplastic polyimide layer 10A and non-thermoplastic polyimide layer 20A in this order, and a second single-sided metal-clad laminate (C2) formed by stacking metal layer 110B, thermoplastic polyimide layer 10B and non-thermoplastic polyimide layer 20B in this order, are bonded together with the insulating layer side facing each other using an adhesive layer BS.

[0195] Figure 4The diagram shows a cross-sectional structure of a metal-clad laminate 201 according to another preferred embodiment of the present invention. The metal-clad laminate 201 has a structure in which metal layers 110A and 110B are stacked on both sides of a multilayer film 101. Therefore, the metal-clad laminate 201 has a structure formed by stacking metal layer 110A / first insulating resin layer 40A / adhesive layer BS / second insulating resin layer 40B / metal layer 110B in this order. Metal layers 110A and 110B are located on the outermost sides, and the first insulating resin layer 40A and the second insulating resin layer 40B are disposed on their inner sides. Furthermore, the adhesive layer BS is interposed between the first insulating resin layer 40A and the second insulating resin layer 40B. It can also be considered that the metal-clad laminate 201 with this layer structure has the following structure, namely, a first single-sided metal-clad laminate (C1) formed by stacking metal layer 110A, thermoplastic polyimide layer 10A, non-thermoplastic polyimide layer 20A and thermoplastic polyimide layer 30A in this order, and a second single-sided metal-clad laminate (C2) formed by stacking metal layer 110B, thermoplastic polyimide layer 10B, non-thermoplastic polyimide layer 20B and thermoplastic polyimide layer 30B in this order, are bonded together with the insulating layer side facing each other using an adhesive layer BS.

[0196] There are no particular limitations on the materials used for metal layers 110A and 110B. Examples include copper, stainless steel, iron, nickel, beryllium, aluminum, zinc, indium, silver, gold, tin, zirconium, tantalum, titanium, lead, magnesium, manganese, and their alloys. Copper or copper alloys are particularly preferred. Furthermore, the material of the wiring layer in the circuit board of this embodiment, described later, is the same as that of metal layers 110A and 110B.

[0197] The thickness of metal layers 110A and 110B is not particularly limited. For example, when using metal foil such as copper foil, it is preferably 35 μm or less, and more preferably in the range of 5 μm to 25 μm. From the viewpoint of production stability and processability, the lower limit of the metal foil thickness is preferably set to 5 μm. Furthermore, when using copper foil, rolled copper foil or electrolytic copper foil can be used. In addition, commercially available copper foil can be used as the copper foil.

[0198] In addition, for metal foils, for purposes such as rust prevention or improved adhesion, surface treatments using siding, aluminum alkoxides, aluminum chelates, silane coupling agents, etc., can be implemented.

[0199] When etching away metal layers 110A and 110B in metal-clad laminates 200 and 201, the dimensional change rate of the multilayer films 100 and 101 after etching is preferably within ±0.10%, based on the original multilayer films 100 and 101. Furthermore, the dimensional change rate after heating at 150°C for 30 minutes, based on the etched multilayer films 100 and 101, is preferably within ±0.10%. A dimensional change rate of ±0.10% after etching and heating indicates minimal dimensional change during circuit fabrication, which improves the reliability of circuit boards such as FPCs.

[0200] Here, the determination of the rate of dimensional change can be carried out in the following order.

[0201] First, a 150mm square test piece made of metal-clad laminate 200 and metal-clad laminate 201 is exposed and developed with dry film resist at 100mm intervals to form a target for position determination. After measuring the dimensions before etching (normal state) in an environment of 23±2℃ and 50±5% relative humidity, copper outside the target material of the test piece is removed by etching (liquid temperature below 40℃, time within 10 minutes). After standing for 24±4 hours in an environment of 23±2℃ and 50±5% relative humidity, the dimensions after etching are measured. The dimensional change rate relative to the normal state is calculated at three locations each in the MD direction (length direction) and TD direction (width direction), and the average value of each is taken as the dimensional change rate after etching. The dimensional change rate after etching can be calculated using the following formula.

[0202] Dimensional change rate after etching (%) = (BA) / A × 100

[0203] A: Distance between targets before etching

[0204] B: Distance between etched targets

[0205] Next, the test piece was heated in an oven at 150°C for 30 minutes, and the distance between the targets was measured afterward. The dimensional change rate relative to the etching was calculated at three locations each in the MD direction (length direction) and TD direction (width direction), and the average value of each was taken as the dimensional change rate after heat treatment. The dimensional change rate after heat treatment can be calculated using the following formula.

[0206] Dimensional change rate after heating (%) = (CB) / B × 100

[0207] B: Distance between etched targets

[0208] C: Distance between heated targets

[0209] [Manufacturing of metal-clad laminates]

[0210] Metal-clad laminate 200 and metal-clad laminate 201 can be manufactured, for example, using method 1 or method 2. Furthermore, the adhesive polyimide that forms the adhesive layer BS can be cross-linked as described above.

[0211] [Method 1]

[0212] First, a first single-sided metal-clad laminate (C1) and a second single-sided metal-clad laminate (C2) having the aforementioned layer structure are prepared. Next, the adhesive polyimide or its precursor, which will become the adhesive layer BS, is formed into a sheet to create an adhesive sheet. The adhesive sheet is then placed between the first insulating resin layer 40A of the first single-sided metal-clad laminate (C1) and the second insulating resin layer 40B of the second single-sided metal-clad laminate (C2) and bonded together using a heat press.

[0213] [Method 2]

[0214] First, a first single-sided metal-clad laminate (C1) and a second single-sided metal-clad laminate (C2) are prepared. Next, a solution of the adhesive polyimide, or a solution of its precursor, which will become the adhesive layer BS, is applied to either or both of the first insulating resin layer 40A of the first single-sided metal-clad laminate (C1) and the second insulating resin layer 40B of the second single-sided metal-clad laminate (C2) to a specified thickness, and allowed to dry to form a coating film. Then, the first single-sided metal-clad laminate (C1) and the second single-sided metal-clad laminate (C2) are bonded together by heat pressing on the coated film side.

[0215] The first single-sided metallized laminate (C1) and the second single-sided metallized laminate (C2) used in Method 1 and Method 2 can be manufactured, for example, by repeatedly coating a solution of polyamic acid, which is a precursor of thermoplastic polyimide or non-thermoplastic polyimide, onto metal foils that become metal layer 110A and metal layer 110B, drying it, and then performing heat treatment to imidize it.

[0216] In addition, the adhesive sheet used in Method 1 can be manufactured by, for example, the following methods: (1) coating a polyamic acid solution onto any support substrate and drying it, performing heat treatment to imidize it, and then peeling it off from the support substrate to form an adhesive sheet; (2) coating a polyamic acid solution onto any support substrate and drying it, peeling a polyamic acid gel film off from the support substrate, performing heat treatment to imidize it, and then forming an adhesive sheet; (3) coating a solution of the adhesive polyimide onto a support substrate and drying it, and then peeling it off from the support substrate to form an adhesive sheet.

[0217] In this context, there are no particular limitations on the method of coating a polyimide solution (or polyamic acid solution) onto a metal foil, a supporting substrate, or an insulating resin layer. For example, coating can be performed using a coating machine such as a doctor blade, a die, a knife, or a die lip.

[0218] The metal-clad laminate 200 and metal-clad laminate 201 of this embodiment obtained as described above can be used to process wiring circuits by etching metal layers 110A and / or metal layers 110B, and can be used to manufacture circuit boards such as single-sided FPCs or double-sided FPCs.

[0219] [Circuit board]

[0220] The metal-clad laminate 200 and 201 of this embodiment are primarily used as circuit board materials such as FPCs and rigid-flexible circuit boards. Specifically, by using conventional methods to process one or both of the two metal layers 110A and 110B of the metal-clad laminate 200 and 201 of this embodiment into a pattern to form a wiring layer, a circuit board such as an FPC, as an embodiment of the present invention, can be manufactured.

[0221] [Example]

[0222] The present invention will now be described in more detail through examples, but the invention is not limited to these examples in any way. Furthermore, in the following examples, unless otherwise specified, various measurements and evaluations are described below.

[0223] [Determination of the coefficient of thermal expansion]

[0224] For a 3mm × 20mm polyimide film, using a TMA (manufactured by Hitachi High-Tech, trade name: TMA / SS6000), a load of 5.0g was applied while the temperature was increased from 30°C to 210°C at a certain rate of 20°C / min. After holding at the temperature for 10 minutes, the film was cooled at a rate of 5°C / min. The average coefficient of thermal expansion (CTE) from 200°C to 100°C was then calculated.

[0225] [Determination of Storage Elasticity Coefficient]

[0226] For a 5mm × 20mm sample film, a dynamic viscoelasticity measuring device (DMA: manufactured by TA Instruments Japan, trade name: RSA-G2) was used to measure the temperature from 25℃ to 300℃ at a heating rate of 10℃ / min and a frequency of 1Hz. The temperature at which the change in elastic modulus (tanδ) is greatest is set as the glass transition temperature.

[0227] [Determination of relative permittivity and dielectric loss tangent]

[0228] The relative permittivity (Dk) and dielectric loss tangent (Df) of the resin sheet at 20 GHz were determined using a Vector Network Analyzer (Agilent Technologies, trade name: E8363C) and an SPDR resonator. Furthermore, the material used in the measurements was placed for 24 hours at a temperature of 24°C–26°C and a relative humidity of 45%–55% (RH).

[0229] [Viscosity Measurement]

[0230] Viscosity at 25°C was measured using an E-type viscometer (Brookfield, trade name: DV-II+Pro). The rotation speed was set to a torque of 10%–90%, and the viscosity was read after 2 minutes from the start of the measurement, when the viscosity stabilized.

[0231] [Determination of weight-average molecular weight (Mw)]

[0232] The weight-average molecular weight was determined using gel permeation chromatography (GPC) (manufactured by Tosoh Corporation, HLC-8220GPC). Polystyrene was used as the standard, and tetrahydrofuran (THF) was used as the developing solvent.

[0233] [Determination of dimensional change rate after etching]

[0234] First, a 150mm square test piece made of a metal-clad laminate was exposed and developed with dry film resist at 100mm intervals to form a target for position determination. After measuring the dimensions before etching (normal state) in an environment of 23±2℃ and 50±5% relative humidity, copper outside the target material was removed from the test piece by etching (liquid temperature below 40℃, time within 10 minutes). After standing for 24±4 hours in an environment of 23±2℃ and 50±5% relative humidity, the dimensions after etching were measured. The dimensional change rate relative to the normal state was calculated at three locations each in the MD direction (length direction) and TD direction (width direction), and the average value of these values ​​was taken as the dimensional change rate after etching. The dimensional change rate after etching can be calculated using the following formula.

[0235] Dimensional change rate after etching (%) = (BA) / A × 100

[0236] A: Distance between targets before etching

[0237] B: Distance between etched targets

[0238] [Determination of the rate of dimensional change after heating]

[0239] Next, the test piece with the measured dimensional change rate after etching was heated in an oven at 150°C for 30 minutes, and the distance between the targets at the subsequent locations was measured. The dimensional change rate relative to the etching was calculated at three locations each in the MD direction (length direction) and TD direction (width direction), and the average value of these values ​​was taken as the dimensional change rate after heat treatment. The dimensional change rate after heat treatment can be calculated using the following formula.

[0240] Dimensional change rate after heating (%) = (CB) / B × 100

[0241] B: Distance between etched targets

[0242] C: Distance between heated targets

[0243] [Determination of peel strength]

[0244] The copper foil on the copper-clad laminate sample was processed to form lines and spaces 1.0 mm wide and 5.0 mm apart. These were then cut into samples 8 cm wide and 4 cm long to prepare the test sample. Using a Tensilon tester (manufactured by Toyo Seiki Co., Ltd., trade name: Strograph VE-1D), the resin layer side of the test sample was fixed to an aluminum plate using double-sided tape. The copper foil was peeled off at a speed of 50 mm / min in a 180° direction. The central strength of the copper foil when it was peeled 10 mm from the resin layer was determined.

[0245] The abbreviations used in this embodiment refer to the following compounds.

[0246] BPDA: 3,3',4,4'-Biphenyltetracarboxylic acid dianhydride

[0247] PMDA: Pyromellitic dianhydride

[0248] m-TB: 2,2'-dimethyl-4,4'-diaminobiphenyl

[0249] TPE-R: 1,3-Bis(4-aminophenoxy)benzene

[0250] Bisaniline-M: 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene

[0251] NMP: N-methyl-2-pyrrolidone

[0252] DMAc: N,N-dimethylacetamide

[0253] BTDA: 3,3',4,4'-benzophenone tetracarboxylic dianhydride

[0254] DDA: An aliphatic diamine with 36 carbon atoms (manufactured by Croda Japan, trade name: PRIAMINE 1074, amine value: 205 mg KOH / g, a mixture of cyclic and chain-structured dimer diamines, with dimer content of 95% by weight or more).

[0255] BAPP: 2,2-bis[4-(4-aminophenoxy)phenyl]propane

[0256] N-12: Dodecanedioic acid dihydrazide

[0257] OP935: Aluminum organophosphonate (manufactured by Clariant Japan, trade name: Exolit OP935)

[0258] Polystyrene elastomer: Manufactured by KRATON, trade name: MD1653MO (hydrogenated polystyrene elastomer, styrene unit content: 30% by weight, Mw: 80,499, acid-free)

[0259] (Synthesis example 1)

[0260] <Preparation of polyamic acid solution for insulating resin layer>

[0261] Under a nitrogen atmosphere, 69.56 g of m-TB (0.328 mol), 542.75 g of TPE-R (1.857 mol), and DMAc with a post-polymerization solids concentration of 12% by weight were added to the reaction vessel and stirred at room temperature to dissolve them. Next, 194.39 g of PMDA (0.891 mol) and 393.31 g of BPDA (1.337 mol) were added, and the polymerization reaction was continued for 3 hours at room temperature to prepare polyamic acid solution 1 (viscosity: 2,700 mPa·s).

[0262] The storage elastic modulus of the polyimide film prepared using polyamic acid solution 1 is 4.3 × 10⁻⁶ at 30°C. 9 Pa at 300℃ is 9.4 × 10⁻⁶. 7 Pa is a thermoplastic.

[0263] (Synthesis example 2)

[0264] <Preparation of polyamic acid solution for insulating resin layer>

[0265] Under a nitrogen atmosphere, 64.20 g of m-TB (0.302 mol), 5.48 g of bisphenylamine-M (0.016 mol), and DMAc with a solid content of 15% by weight after polymerization were added to the reaction vessel and stirred at room temperature to dissolve them. Next, 34.20 g of PMDA (0.157 mol) and 46.13 g of BPDA (0.157 mol) were added, and the polymerization reaction was continued for 3 hours at room temperature to prepare polyamic acid solution 2 (viscosity: 28,000 mPa·s).

[0266] The storage elastic modulus of the polyimide film prepared using polyamic acid solution 2 is 7.0 × 10⁻⁶ at 30°C. 9 Pa at 300℃ is 5.4 × 10⁻⁶. 8 Pa is non-thermoplastic.

[0267] (Synthesis example 3)

[0268] <Preparation of Resin Solution for Adhesive Layer>

[0269] In a 500 ml detachable flask, 21.34 g of BTDA (0.06622 mol), 12.99 g of BPDA (0.04414 mol), 46.7042 g of DDA (0.08741 mol), 8.97104 g of BAPP (0.02185 mol), 126 g of NMP, and 84 g of xylene were added and mixed thoroughly at 40 °C for 1 hour to prepare a polyamic acid solution. The polyamic acid solution was then heated to 190 °C and stirred for 5 hours. 65 g of xylene was added to prepare imidized polyimide solution 1 (solid content: 31 wt%, weight average molecular weight: 35,886, viscosity: 2,580 mPa·s).

[0270] (Production example 1)

[0271] <Preparation of Resin Sheets for Adhesive Layers>

[0272] 0.46g of N-12, 2.54g of OP935, and 7.62g of polystyrene elastomer resin were prepared in 40.97g of polyimide solution 1 (12.7g as solid component), and 45.23g of xylene was added for dilution to prepare polyimide varnish 1.

[0273] Polyimide varnish 1 was applied to the polysiloxane-treated surface of a release substrate (length × width × thickness = 320 mm × 240 mm × 25 μm) to a thickness of 50 μm after drying. The substrate was then heated and dried at 80°C for 15 minutes and peeled off from the release substrate, thereby preparing resin sheet 1. Furthermore, the storage elastic modulus of resin sheet 1 is as follows.

[0274] Storage elasticity coefficient (25℃): 901MPa

[0275] Storage elasticity coefficient (100℃): 5.0MPa

[0276] Storage elasticity coefficient (200℃): 2.0MPa

[0277] (Production example 2)

[0278] <Preparation of single-sided metal-clad laminates>

[0279] Polyamic acid solution 1 was uniformly coated onto copper foil 1 (electrolytic copper foil, thickness: 12 μm, surface roughness Rz on the resin layer side: 0.6 μm) to a hardened thickness of approximately 1.6 μm, and then dried at 120 °C to remove the solvent. Next, polyamic acid solution 2 was uniformly coated onto it to a hardened thickness of approximately 2.4 μm, and dried at 120 °C to remove the solvent. Then, a staged heat treatment from 120 °C to 360 °C was performed to complete imidization, thus preparing a single-sided metal-coated laminate 1.

[0280] (Production Example 3 to Production Example 4)

[0281] Except for changing the cured thickness of polyamic acid solution 1 and polyamic acid solution 2 as shown in Table 1, single-sided metal-coated laminate 2 and single-sided metal-coated laminate 3 are prepared in the same manner as in Example 2.

[0282] [Table 1]

[0283]

[0284] (Production example 5)

[0285] Polyamic acid solution 1 is uniformly coated onto copper foil 1 to a hardened thickness of approximately 2 μm, and then dried at 120°C to remove the solvent. Next, polyamic acid solution 2 is uniformly coated onto it to a hardened thickness of approximately 21 μm, and dried at 120°C to remove the solvent. Then, polyamic acid solution 1 is uniformly coated onto it to a hardened thickness of approximately 2 μm, and dried at 120°C to remove the solvent. Finally, a staged heat treatment from 120°C to 360°C is performed to complete imidization, thus preparing a single-sided metal-clad laminate 4.

[0286] <Preparation of Polyimide Films>

[0287] Polyimide films 1 to 4 were prepared by etching away the copper foil layers of single-sided metal-coated laminates 1 to 4 using an aqueous ferric chloride solution. The coefficients of thermal expansion and storage elasticity of the polyimide layers were measured using the prepared polyimide films 1 to 4. The results are shown in Table 2 or Table 3.

[0288] [Example 1]

[0289] Polyimide varnish 1 was applied to the insulating resin layer side of the single-sided metal-coated laminate 1 with a dried thickness of 46 μm. The laminate was then dried in stages from 80°C to 200°C to prepare the single-sided metal-coated laminate 1 with an adhesive layer. Two single-sided metal-coated laminates 1 with adhesive layers were prepared, laminated with the adhesive layer sides joined together, and pressed together at 180°C with a pressure of 3.5 MPa for 2 hours to prepare the metal-coated laminate 1. Furthermore, the copper foil layer in the metal-coated laminate 1 was etched away to obtain a multilayer film 1. The dimensional change rate and peel strength were measured using the metal-coated laminate 1, and the dielectric properties and coefficient of thermal expansion were measured using the multilayer film 1.

[0290] [Example 2-Example 3]

[0291] The thickness of the dried polyimide varnish 1 was changed to 37.5 μm, and the single-sided metal-coated laminate 1 was changed to a single-sided metal-coated laminate 2 and a single-sided metal-coated laminate 3. Otherwise, the metal-coated laminate 2 to the metal-coated laminate 3 and the multilayer film 2 to the multilayer film 3 were prepared in the same manner as in Example 1.

[0292] Table 2 shows the layer structure and evaluation results of the fabricated metal-clad laminates 1 to 3 and multilayer films 1 to 3. Furthermore, in Table 2, the total thickness of the thermoplastic polyimide layers is set as T. A Let the total thickness of the non-thermoplastic polyimide layer be T. B Set the thickness of the adhesive layer to tad.

[0293] [Table 2]

[0294]

[0295] (Comparative Example 1)

[0296] Fluoropolymer sheets 1 (manufactured by Asahi Glass Co., Ltd., trade name: Adhesive Perfluoropolymer EA-2000) with thicknesses of 50 μm and 25 μm, and two single-sided metal-coated laminates 2 were prepared. The two fluoropolymer sheets were stacked by clamping them on the insulating resin layer side of the two single-sided metal-coated laminates 2, and then pressed together at 320°C with a pressure of 3.5 MPa for 5 minutes to prepare the metal-coated laminate 4. The evaluation results of the metal-coated laminate 4 and the multilayer film 4 after removing the copper foil are shown in Table 3.

[0297] (Comparative Example 2)

[0298] Two single-sided metal-coated laminates 4 were prepared, with their insulating resin layer sides overlapping the two sides of the resin sheet 1. They were then pressed together at 180°C under a pressure of 3.5 MPa for 2 hours to prepare the metal-coated laminate 5. The evaluation results of the metal-coated laminate 5 and the multilayer film 5 after removing the copper foil are shown in Table 3.

[0299] (Comparative Example 3)

[0300] Instead of resin sheet 1, fluororesin sheet 1 was used, and the metal-coated laminate 6 was prepared by applying a pressure of 3.5 MPa at 320°C for 5 minutes. Otherwise, the same procedure as in Comparative Example 2 was followed. The evaluation results of the metal-coated laminate 6 and the multilayer film 6 after removing the copper foil are shown in Table 3.

[0301] [Table 3]

[0302]

[0303] Comparing Comparative Example 1 and Comparative Example 3, it can be seen that in structures with a high storage elasticity coefficient at high temperatures in the inner layer, the thinner the outer polyimide layer, the more significantly the dimensional stability deteriorates. Furthermore, comparing Comparative Example 1 and Example 2, it can be seen that when a low-elasticity adhesive layer is used at room temperature, the dimensional stability deteriorates further. To ensure dimensional stability, a storage elasticity coefficient that falls within the process temperature range, rather than the ambient temperature range, is crucial.

[0304] Based on the above results, in a structure with a size control layer on the outer layer and a low-dielectric layer on the inner layer, in order to make the outer layer thinner and to make the laminated film low-dielectric, it is important to balance the thickness of each layer and control the storage elasticity coefficient of the inner layer's process temperature band within a specified range.

[0305] Specifically, the index (P) calculated from the storage elasticity coefficient at 100℃ and 200℃ and the thickness can be used. P / P AD In Comparative Example 1, since P P / P AD If the value is too small, the influence of the adhesive layer is more pronounced, leading to dimensional deterioration. To ensure sufficient dimensional stability, the value needs to be set to a level exceeding that of Comparative Example 3 and equivalent to or higher than that of Example 1 (P). P / P AD Additionally, in cases like Comparative Example 2 (P) P / P AD While excessively high dielectric strength can ensure dimensional stability, it also degrades dielectric properties due to the excessive thickness of the polyimide layer.

[0306] (Refer to Example 1)

[0307] Polyamic acid solution 1 was uniformly coated onto copper foil 1 to a hardened thickness of approximately 0.8 μm, and then dried at 120°C to remove the solvent. Next, polyamic acid solution 2 was uniformly coated onto it to a hardened thickness of approximately 2.9 μm, and dried at 120°C to remove the solvent. Then, polyamic acid solution 1 was uniformly coated onto it to a hardened thickness of approximately 0.8 μm, and dried at 120°C to remove the solvent. Subsequently, a staged heat treatment from 120°C to 360°C was performed to complete imidization, thus preparing a single-sided metal-coated laminate 5. The peel strength of the single-sided metal-coated laminate 5 was measured, and the result was 0.6 kN / m.

[0308] In Comparative Example 2 and Example 1, the CTE of the polyimide layer was preferably around 20 ppm / K, but the ratio of the thermoplastic polyimide layer to the non-thermoplastic polyimide layer (T) was different. A ) / (T A +T B The differences are significant. When forming a polyimide layer via casting, the thinner the layer, the lower the CTE (Continuous Tear Emission). Therefore, to exhibit appropriate dimensional stability, it is necessary to reduce the CTE by a certain amount (T). A ) / (T A +T B It should be suppressed within the prescribed range.

[0309] Furthermore, as in Reference Example 1, when the polyimide layer is thinned in a conventional design where two layers of thermoplastic polyimide and one layer of non-thermoplastic polyimide are maintained, the peel strength decreases. On the other hand, in a design where the thermoplastic polyimide layer is concentrated on the substrate side, as in Example 1, and the outer layer has a single-sided two-layer structure, sufficient peel strength is exhibited. Therefore, in a design where the polyimide layer is thinned, from the viewpoint of adhesion to the copper foil, a two-layer structure of thermoplastic polyimide and non-thermoplastic polyimide is effective.

[0310] The embodiments of the present invention have been described in detail above for illustrative purposes, but the present invention is not limited to the described embodiments and can be modified in various ways.

Claims

1. A multilayer film, characterized in that, The multilayer film comprises multiple polyimide layers and an adhesive layer, and has the following layer structure (1) or (2): (1) Thermoplastic polyimide layer / non-thermoplastic polyimide layer / adhesive layer / non-thermoplastic polyimide layer / thermoplastic polyimide layer, or, (2) Thermoplastic polyimide layer / non-thermoplastic polyimide layer / thermoplastic polyimide layer / adhesive layer / thermoplastic polyimide layer / non-thermoplastic polyimide layer / thermoplastic polyimide layer, and The following conditions (a) to (c) must be met: a) The combined thickness of the thermoplastic polyimide layer and the non-thermoplastic polyimide layer laminated on one side of the adhesive layer is between 2 μm and 20 μm. b) Satisfies the following equation (i); Here, P P is a coefficient of elasticity parameter of the polyimide layer, P AD is a coefficient of elasticity parameter of the adhesive layer, and is represented by the following equations (ii) to (v): Storage elastic modulus of the polyimide layer at 100°C, in GPa. Storage elastic modulus of the polyimide layer at 200°C, in GPa. Storage elastic modulus of the adhesive layer at 100°C, in GPa. Storage elastic modulus of the adhesive layer at 200°C, in GPa. The total thickness of the thermoplastic polyimide layer and the non-thermoplastic polyimide layer stacked on one side of the adhesive layer, in μm. The total thickness of the thermoplastic polyimide layer and the non-thermoplastic polyimide layer stacked on the other side of the adhesive layer, in μm. tad: Thickness of the adhesive layer, in μm Here, the elastic modulus parameter P of the polyimide layer is... P To make the elastic coefficient parameter P P1 With elastic coefficient parameter P P2 The value obtained by adding them together is the elastic coefficient parameter P. P1 The elastic modulus parameter P is calculated by equation (iii) by treating the thermoplastic polyimide layer and the non-thermoplastic polyimide layer stacked on one side of the adhesive layer as a single polyimide layer. P2 The thermoplastic polyimide layer and the non-thermoplastic polyimide layer stacked on the other side of the adhesive layer are considered as a single polyimide layer and calculated using equation (iv). c) As a whole multilayer film, the dielectric loss tangent at 20 GHz, measured using a split-column dielectric resonator, is less than 0.0029.

2. The multilayer film according to claim 1, wherein, The polyimide layer formed by combining a thermoplastic polyimide layer and a non-thermoplastic polyimide layer on one side of the adhesive layer has a storage elastic modulus of 1.0 GPa or higher at 100°C and a storage elastic modulus of 0.1 GPa or higher at 200°C.

3. The multilayer film according to claim 1, wherein, The storage elasticity coefficient of the adhesive layer at 100°C is less than 130 MPa, and the storage elasticity coefficient at 200°C is less than 40 MPa.

4. The multilayer film according to claim 1, wherein, Let the total thickness of the thermoplastic polyimide layer in the multilayer film be T. A Let the total thickness of the non-thermoplastic polyimide layer be T. B When the thickness of the adhesive layer is set to tad, the following equation (vi) is satisfied: 。 5. The multilayer film according to claim 1, wherein, The coefficient of thermal expansion of the polyimide layer formed by combining a thermoplastic polyimide layer and a non-thermoplastic polyimide layer on one side of the adhesive layer is in the range of 5 ppm / K to 35 ppm / K.

6. The multilayer film according to claim 1, wherein, The adhesive layer contains thermoplastic polyimide and polystyrene elastomer resin, wherein the content of polystyrene elastomer resin relative to 100 parts by weight of thermoplastic polyimide is in the range of 10 parts by weight or more and 150 parts by weight or less.

7. The multilayer film according to claim 6, wherein, The thermoplastic polyimide contained in the adhesive layer contains dianhydride residues derived from the dianhydride component and diamine residues derived from the diamine component, and the proportion of diamine residues derived from the dimer diamine composition relative to all diamine residues is 20 mol% or more. The dimer diamine composition is mainly composed of a dimer diamine formed by replacing the two terminal carboxylic acid groups of a dimer acid with primary aminomethyl or amino groups, and the total proportion of diamine residues derived from the diamine compound represented by the following general formula (1) is in the range of 5 mol% to 50 mol%. In formula (1), R independently represents a halogen atom, or an alkyl or alkoxy group substituted with or not substituted with a halogen atom having 1 to 6 carbon atoms, or a phenyl or phenoxy group substituted with or not substituted with a monovalent hydrocarbon group or alkoxy group having 1 to 6 carbon atoms, and Z independently represents a phenyl group selected from... or The binary base, m1 independently represents integers from 0 to 4, and m2 represents integers from 0 to 2.

8. The multilayer film according to claim 6, wherein, The thermoplastic polyimide contained in the adhesive layer is a cross-linked polyimide whose molecular chain contains ketone groups and amino compounds having at least two primary amino groups as functional groups, which form a cross-linked structure through C=N bonds.

9. The multilayer film according to claim 1, wherein, The thermoplastic polyimide constituting the thermoplastic polyimide layer contains acid dianhydride residues derived from the acid dianhydride component and diamine residues derived from the diamine component, and the proportion of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride residues derived from 3,3',4,4'-biphenyltetracarboxylic acid dianhydride residues is 40 mol% or more relative to all acid dianhydride residues, and the proportion of diamine residues derived from the diamine compound represented by the following general formula (1) is 30 mol% or more relative to all diamine residues. In formula (1), R independently represents a halogen atom, or an alkyl or alkoxy group substituted with or not substituted with a halogen atom having 1 to 6 carbon atoms, or a phenyl or phenoxy group substituted with or not substituted with a monovalent hydrocarbon group or alkoxy group having 1 to 6 carbon atoms, and Z independently represents a phenyl group selected from... or The binary base, m1 independently represents integers from 0 to 4, and m2 represents integers from 0 to 2.

10. The multilayer film according to claim 1, wherein, The non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer contains dianhydride residues derived from the dianhydride component and diamine residues derived from the diamine component, and the proportion of dianhydride residues having a biphenyl backbone is 40 mol% or more relative to all dianhydride residues, and the proportion of diamine residues having a biphenyl backbone is 40 mol% or more relative to all diamine residues.

11. A metal-clad laminate comprising a multilayer film according to any one of claims 1 to 10, and a metal layer laminated on one or both sides of the multilayer film.

12. The metal-clad laminate according to claim 11, wherein, When etching away the metal layer, the dimensional change rate of the multilayer film after etching is within ±0.10%, based on the multilayer film before etching, and the dimensional change rate after heating at 150°C for 30 minutes is within ±0.10%, based on the multilayer film after etching.

13. A circuit board, which is formed by processing the metal layer of the metal-clad laminate according to claim 11 into wiring.

14. A circuit board comprising an insulating resin layer and a wiring layer disposed on at least one side of the insulating resin layer, wherein in the circuit board, The insulating resin layer is a multilayer film according to any one of claims 1 to 10.

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