Multilayer films, metal-clad laminates and circuit boards

Abstract

To improve dielectric characteristics while securing dimensional stability and adhesion with an outer metal layer, in a multilayer film having an outer layer part made of multiple polyimide layers on both sides of an inner layer part made of an adhesion layer.SOLUTION: A multilayer film has a layer structure of thermoplastic polyimide layer / non-thermoplastic polyimide layer / adhesive layer / non-thermoplastic polyimide layer / thermoplastic polyimide layer, wherein a) a total thickness of the thermoplastic polyimide layer and the non-thermoplastic polyimide layer laminated on one side of the adhesive layer is within a range of 2 to 20 μm, b) a ratio of the total thickness of the thermoplastic polyimide layers to the total thickness of the thermoplastic and non-thermoplastic polyimide layers in the entire multilayer film is 0.1 to 0.6, c) a ratio of the thickness of the adhesive layer to the total thickness satisfies 0.60 to 0.99, d) the storage modulus of the adhesive layer at 100°C is less than 130 MPa, and the storage modulus at 200°C is 40 MPa or less, and e) the dielectric loss tangent of the entire multilayer film at 20 GHz is less than 0.0029.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a multilayer film, a metal-clad laminate, and a circuit board that are useful as materials for electronic components. [Background technology]

[0002] In recent years, with the progress in miniaturization, weight reduction, and space-saving of electronic devices, there has been an increasing demand for flexible printed circuits (FPCs), which are thin, lightweight, flexible, and have excellent durability even when repeatedly bent. Because FPCs allow for three-dimensional, high-density packaging even in limited spaces, their applications are expanding to include wiring for electronic devices such as hard disk drives, DVDs, and smartphones, as well as components such as cables and connectors.

[0003] In addition to increasing density, the advancement of device performance has necessitated the need to accommodate increasingly higher transmission signal frequencies. When transmitting high-frequency signals, high transmission loss along the transmission path can result in inconveniences such as electrical signal loss and long signal delay times. To accommodate increasingly higher transmission signal frequencies, a proposal has been made to improve dielectric properties by interposing a thick adhesive layer between the insulating resin layers of a pair of single-sided metal-clad laminates and using a thermoplastic polyimide derived from dimer acid diamine (DDA), in which the two terminal carboxylic acid groups of a dimer acid are substituted with primary aminomethyl or amino groups, as the adhesive layer (Patent Document 1). Patent Document 1 specifically discloses a layer structure for 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 order to further improve the dielectric properties in a layer structure such as that of Patent Document 1, it is effective to increase the thickness of the inner layer portion consisting of an adhesive layer with excellent dielectric properties and to reduce the thickness of the outer layer portion consisting of a thermoplastic polyimide layer / non-thermoplastic polyimide layer / thermoplastic polyimide layer. However, reducing the thickness of the non-thermoplastic polyimide layer in the outer layer portion reduces the coefficient of thermal expansion (CTE) of the outer layer portion, impairing dimensional accuracy, and also creating problems such as difficulty in ensuring adhesion with a metal layer when it is laminated on the outside, which has been a bottleneck in further improving the dielectric properties. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-170417 Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the present invention is to further improve the dielectric properties of a multilayer film having outer layers made of multiple polyimide layers on both sides of an inner layer made of an adhesive layer, while ensuring dimensional stability and adhesion when a metal layer is laminated on the outside. [Means for solving the problem]

[0007] As a result of extensive research, the inventors have discovered that for the outer layer portion, by consolidating the thermoplastic polyimide layer into a single layer on one side and increasing its thickness ratio, it is possible to reduce the overall thickness of the outer layer portion while ensuring dimensional stability and adhesion to the metal layer; and for the inner layer portion, by increasing the relative thickness ratio to reduce the dielectric tangent of the entire multilayer film while reducing the storage modulus at high temperatures, it is possible to mitigate the effect of the inner layer portion on dimensional change, thereby completing the present invention.

[0008] That is, the multilayer film of the present invention comprises a plurality of polyimide layers and an adhesive layer. The multilayer film of the present invention has a layer structure of thermoplastic polyimide layer / non-thermoplastic polyimide layer / adhesive layer / non-thermoplastic polyimide layer / thermoplastic polyimide layer. The multilayer film of the present invention satisfies the following conditions a) to e): a) The total thickness of the thermoplastic polyimide layer and the non-thermoplastic polyimide layer laminated on one side of the adhesive layer is within the range of 2 μm to 20 μm, b) The total thickness of the thermoplastic polyimide layers in the entire multilayer film is T A , the total thickness of the non-thermoplastic polyimide layers is T B When 0.1 ≦ (T A ) / (T A +T B ) ≦ 0.6 (i) c) The thickness of the adhesive layer is T C When 0.60 ≦ T C / (T A +T B +T C ) ≦ 0.99 (ii) d) The adhesive layer has a storage modulus of less than 130 MPa at 100°C and a storage modulus of 40 MPa or less at 200°C; e) The dielectric loss tangent of the entire multilayer film at 20 GHz measured using an SPDR resonator is less than 0.0029; It satisfies the following.

[0009] In the multilayer film of the present invention, the polyimide layer, which is a combination of a thermoplastic polyimide layer and a non-thermoplastic polyimide layer laminated on one side of the adhesive layer, may have a storage modulus of 1.0 GPa or more at 100°C, or a storage modulus of 0.1 GPa or more at 200°C. In the multilayer film of the present invention, the polyimide layer, which is a combination of the thermoplastic polyimide layer and the non-thermoplastic polyimide layer laminated on one side of the adhesive layer, may have a thermal expansion coefficient in the range of 5 to 35 ppm / K.

[0010] In the multilayer film of the present invention, the adhesive layer may contain a thermoplastic polyimide and a polystyrene elastomer resin, in which case the content of the polystyrene elastomer resin per 100 parts by weight of the thermoplastic polyimide may be in the range of 10 parts by weight to 150 parts by weight.

[0011] In the multilayer film of the present invention, the thermoplastic polyimide contained in the adhesive layer may contain acid dianhydride residues derived from an acid dianhydride component and diamine residues derived from a diamine component. In this case, the content of diamine residues derived from a dimer diamine composition mainly composed of a dimer diamine formed by substituting the two terminal carboxylic acid groups of a dimer acid with primary aminomethyl groups or amino groups may be 20 mol % or more relative to the total diamine residues, and the content of diamine residues derived from diamine compounds represented by the following general formula (1) may be in the range of 5 to 50 mol % in total:

[0012] [ka]

[0013] In general formula (1), R independently represents a halogen atom, an alkyl group or alkoxy group having 1 to 6 carbon atoms which may be substituted with a halogen atom, or a phenyl group or phenoxy group which may be substituted with 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 of 0 to 4; and m2 independently represents an integer of 0 to 2.

[0014] In the multilayer film of the present invention, the thermoplastic polyimide contained in the adhesive layer may be a crosslinked polyimide in which a ketone group contained in the molecular chain and an amino group of an amino compound having at least two primary amino groups as functional groups form a crosslinked structure via a C=N bond.

[0015] In the multilayer film of the present invention, the thermoplastic polyimide constituting the thermoplastic polyimide layer may contain acid dianhydride residues derived from the acid dianhydride component and diamine residues derived from the diamine component. In this case, the proportion of BPDA residues derived from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) relative to all acid dianhydride residues may be 40 mol % or more, and the proportion of diamine residues derived from the diamine compound represented by the above general formula (1) may be 30 mol % or more relative to all diamine residues.

[0016] In the multilayer film of the present invention, the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer may contain acid dianhydride residues derived from the acid dianhydride component and diamine residues derived from the diamine component. In this case, the proportion of acid dianhydride residues having a biphenyl skeleton to all acid dianhydride residues may be 40 mol % or more, and the proportion of diamine residues having a biphenyl skeleton to all diamine residues may be 40 mol % or more.

[0017] The metal-clad laminate of the present invention comprises any of the multilayer films described above and a metal layer laminated on one or both sides of the multilayer film. Furthermore, 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 may be within ±0.10% based on the multilayer film before etching, and the dimensional change rate after heating at 150°C for 30 minutes may be within ±0.10% based on the multilayer film after etching. The metal-clad laminate of the present invention is obtained by processing the metal layer of the above-mentioned metal-clad laminate into wiring. [Effects of the Invention]

[0018] The multilayer film of the present invention has a two-layer structure of outer layers, consisting of a thermoplastic polyimide layer and a non-thermoplastic polyimide layer, on each side, by consolidating the thermoplastic polyimide layers to one layer on each side and increasing their thickness ratio. This allows the entire outer layer to be thin, while ensuring dimensional stability and adhesion to the metal layer when laminated on the outside. Furthermore, by using a resin with excellent dielectric properties and a low storage modulus at high temperatures as the inner layer, dimensional stability is maintained while the relative thickness ratio of the inner layer is increased, allowing the entire multilayer film to have a low dielectric loss tangent. The effects of the present invention are particularly effective in layer structures in which the total thickness or thickness ratio of the outer polyimide layers is relatively small and the thickness or thickness ratio of the adhesive layers is relatively large. Therefore, when used in circuit boards transmitting high-frequency signals in the GHz band, metal-clad laminates using the multilayer film of the present invention can achieve reduced transmission loss and improved reliability due to their excellent dimensional stability. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a schematic cross-sectional view showing the layer structure of a multilayer film according to a preferred embodiment of the present invention. [Figure 2] 1 is a schematic cross-sectional view showing the layer structure of a metal-clad laminate according to a preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the accompanying drawings.

[0021] [Multi-layer film] FIG. 1 shows a cross-sectional structure of a multilayer film 100 according to one 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 laminated in this order. Here, the thermoplastic polyimide layer 10A and the non-thermoplastic polyimide layer 20A, which are the outer layer portions on one side, constitute a first insulating resin layer 40A, and the thermoplastic polyimide layer 10B and the non-thermoplastic polyimide layer 20B, which are the outer layer portions on the other side, constitute a second insulating resin layer 40B. Thus, the multilayer film 100 has a structure in which the first insulating resin layer 40A, which is the outer layer portion, the adhesive layer BS, which is the inner layer portion, and the second insulating resin layer 40B, which is also the outer layer portion, are laminated in this order.

[0022] Unlike the layer configuration of the prior art, the multilayer film 100 has a layer configuration in which only one thermoplastic polyimide layer is laminated in each of the outer layer portions, the first insulating resin layer 40A and the second insulating resin layer 40B. In this way, by making the outer layer portion on one side of the adhesive layer BS a two-layer configuration and concentrating the thermoplastic polyimide layer (thermoplastic polyimide layer 10A or thermoplastic polyimide layer 10B) on each side to one layer, it is possible to reduce the thickness of the outer layer portion while ensuring adhesion to the metal layer when it is laminated on the outside.

[0023] 1, the thermoplastic polyimide layer 10A and the thermoplastic polyimide layer 10B may be made of the same or different types of thermoplastic polyimides. The non-thermoplastic polyimide layer 20A and the non-thermoplastic polyimide layer 20B may also be made of the same or different types of non-thermoplastic polyimides. Details of the preferred polyimides used for the first insulating resin layer 40A and the second insulating resin layer 40B will be described later. The first insulating resin layer 40A and the second insulating resin layer 40B may contain, as appropriate, plasticizers, curable resin components such as epoxy resins, curing agents, curing accelerators, organic or inorganic fillers, coupling agents, flame retardants, etc.

[0024] The multilayer film 100 satisfies the following conditions a) to e). a) The total thickness of the thermoplastic polyimide layer and the non-thermoplastic polyimide layer laminated on one side of the adhesive layer is within the range of 2 μm to 20 μm. Condition a specifies that the total thickness of the thermoplastic polyimide layer 10A and the non-thermoplastic polyimide layer 20A, and the total thickness of the thermoplastic polyimide layer 10B and the non-thermoplastic polyimide layer 20B, which are laminated on one side of the adhesive layer BS, are both within the range of 2 μm to 20 μm inclusive in the configuration example shown in Fig. 1. In other words, 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 2 μm to 20 μm inclusive. By setting the thicknesses of the first insulating resin layer 40A and the second insulating resin layer 40B, which are the outer layers, within a predetermined range, it is possible to maximize the thickness and thickness ratio of the adhesive layer BS, which has relatively excellent dielectric properties, thereby improving the dielectric properties of the entire multilayer film 100. If the thickness of the first insulating resin layer 40A or the second insulating resin layer 40B is less than 2 μm, adhesion to the metal layer when a metal layer is laminated on the outside may be impaired. If the thickness exceeds 20 μm, this restricts the increase in the thickness and thickness ratio of the adhesive layer BS, making it difficult to achieve a low dielectric tangent for the entire multilayer film 100. From this perspective, the thickness of the first insulating resin layer 40A and the second insulating resin layer 40B are both preferably in the range of 2 μm to 12 μm, more preferably in the range of 2 μm to 8 μm, and most preferably in the range of 2 μm to 5 μm.

[0025] Here, the thickness of the thermoplastic polyimide layers 10A and 10B is preferably in the range of, for example, 0.5 μm or more and 2.0 μm or less, and more preferably 1.0 μm or more and 1.8 μm or less, from the viewpoint of ensuring sufficient adhesion with a metal layer when the metal layer is laminated on the outside. Furthermore, the thickness of the non-thermoplastic polyimide layers 20A, 20B is preferably in the range of 1.0 μm or more and 4.0 μm or less, and more preferably 1.5 μm or more and 3.0 μm or less, from the viewpoint of preventing an excessive decrease in the coefficient of thermal expansion (CTE) while ensuring the self-supporting properties of the entire multilayer film 100. The thermoplastic polyimide layers 10A and 10B may have the same or different thicknesses, and the non-thermoplastic polyimide layers 20A and 20B may have the same or different thicknesses. Furthermore, the first insulating resin layer 40A and the second insulating resin layer 40B may have the same or different thicknesses.

[0026] b) The total thickness of the thermoplastic polyimide layers in the entire multilayer film is T A , the total thickness of the non-thermoplastic polyimide layers is T B When 0.1 ≦ (T A ) / (T A +T B ) ≦ 0.6 (i) Condition b is the total thickness T A and the total thickness T of the non-thermoplastic polyimide layer 20A and the non-thermoplastic polyimide layer 20B. B and the sum of (T A +T B ) the total thickness T of the thermoplastic polyimide layer 10A and the thermoplastic polyimide layer 10B A The ratio of (T A +T B ) is the total thickness of the outer layer portions provided 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, the thickness ratio (T A ) / (T A +T B ) satisfies formula (i), so that even if the thicknesses of the first insulating resin layer 40A and the second insulating resin layer 40B, which are the outer layer portions, are made thinner in accordance with condition a than in the prior art, it is possible to prevent the CTE of the outer layer portions from becoming excessively low, and it is possible to sufficiently ensure adhesion to a metal layer when a metal layer is laminated on the outside.

[0027] The coefficient of thermal expansion (CTE) of the non-thermoplastic polyimide layers 20A, 20B included in the outer layer portion tends to decrease as the thickness decreases. This tendency is particularly noticeable when the non-thermoplastic polyimide layers 20A, 20B are formed by a casting method. The reason for this is thought to be that the thinner the thickness of the coating film is during the heat treatment, the more the solvent volatilizes, and the more the molecules are oriented. Therefore, the thickness ratio (T A ) / (T A +T B If the thickness ratio (T A ) / (T A +T B The lower limit of ) is preferably selected from, for example, 0.17, 0.20, 0.25, 0.30, or 0.40. On the other hand, the thickness ratio (T A ) / (T A +T B If the thickness ratio (T ) exceeds 0.60, the proportion of the high CTE thermoplastic polyimide layers 10A, 10B increases excessively, and it may become difficult to maintain the dimensional stability of the entire multilayer film 100, for example, when a metal layer is laminated on the outside and then etched or heat-treated. A ) / (T A +T B The upper limit of ) is preferably 0.55 or less, more preferably 0.50 or less.

[0028] c) The thickness of the adhesive layer is T C When 0.60 ≦ T C / (T A +T B +T C ) ≦ 0.99 (ii) Condition c is the total thickness of the multilayer film 100 (T A +T B +T C ) the thickness T of the adhesive layer BS C The ratio T C / (T A +T B +T C The thickness ratio T C / (T A +T B +T C By making the thickness ratio T satisfy the formula (ii), it is possible to achieve a balance between a low dielectric loss tangent of the entire multilayer film 100 and dimensional stability. C / (T A +T B +T C If the thickness ratio T C / (T A +T B +T C The lower limit of ) is preferably 0.70 or more, more preferably 0.80 or more, and most preferably 0.85 or more. On the other hand, the thickness ratio T C / (T A +T B +T C If the thickness ratio T ) exceeds 0.99, the thickness ratio of the adhesive layer BS becomes too large relatively, making it difficult to ensure adhesion with the metal layer and also making it difficult to maintain the dimensional stability of the entire multilayer film 100. C / (T A +T B +T C The upper limit of ) is preferably 0.96 or less, more preferably 0.94 or less.

[0029] The total thickness of the multilayer film 100 (T A +T B +T CThe thickness (T) of the entire multilayer film 100 is preferably in the range of 70 to 500 μm, and more preferably in the range of 100 to 300 μm. A +T B +T C If the thickness is less than 70 μm, the effect of suppressing transmission loss of high frequency signals when used in a circuit board will be insufficient, and if it exceeds 500 μm, there is a risk of a decrease in productivity.

[0030] In addition, the thickness T of the adhesive layer BS C The effect of the present invention of achieving both excellent dielectric properties and dimensional stability is obtained by the thickness T of the adhesive layer BS. C From this viewpoint, the thickness T of the adhesive layer BS is particularly effective. C The thickness T of the adhesive layer BS is preferably in the range of more than 50 μm to 450 μm, more preferably in the range of 60 to 250 μm, and even more preferably in the range of 80 to 200 μm. C If the thickness T of the adhesive layer BS is less than the above lower limit, the dielectric loss tangent will be insufficient, and problems such as insufficient dielectric properties will occur. C If the value exceeds the upper limit, problems such as a decrease in dimensional stability may occur.

[0031] d) The adhesive layer has a storage modulus of less than 130 MPa at 100°C and a storage modulus of 40 MPa or less at 200°C. Condition d specifies the storage modulus of the thermoplastic polyimide (hereinafter sometimes referred to as "adhesive polyimide") constituting the adhesive layer BS in the thermocompression temperature range (100°C to 200°C). Satisfying condition d means that the storage modulus is below 130 MPa and not excessively high in the temperature range from 100°C to less than 200°C. The residual stress after thermocompression bonding, which causes dimensional changes due to etching or heating of the metal layer after laminating an outer metal layer, increases with the storage modulus of the adhesive layer BS at the thermocompression temperature and is also thought to increase with the thickness and thickness ratio of the adhesive layer BS. Therefore, by using a resin whose storage modulus does not increase excessively in the thermocompression temperature range, the residual stress after thermocompression bonding can be reduced and dimensional stability can be ensured even if the thickness and thickness ratio of the adhesive layer BS is increased to a certain extent. From this perspective, the storage modulus of the adhesive layer BS at 100°C is preferably in the range of 0.01 MPa to 100 MPa, and more preferably in the range of 0.1 MPa to 50 MPa. The storage modulus at 200° C. is preferably in the range of 0.01 MPa or more and 30 MPa or less, and more preferably in the range of 0.1 MPa or more and 20 MPa or less.

[0032] e) The dielectric loss tangent of the entire multilayer film at 20 GHz measured using an SPDR resonator is less than 0.0029. Condition e stipulates that the dielectric loss tangent of the entire multilayer film 100 must be significantly lower than that of conventional technology. If the dielectric loss tangent of the entire multilayer film 100 at 20 GHz is less than 0.0029, it is possible to effectively reduce electrical signal loss in the transmission path of high-frequency signals in the GHz band, for example, from 1 GHz to 60 GHz, making it possible to apply the film to circuit boards used in high-speed communications such as 5G communications and beyond. From this perspective, the dielectric loss tangent of the entire multilayer film 100 at 20 GHz is preferably 0.0025 or less, and more preferably 0.0020 or less. From the same viewpoint, the relative dielectric constant of the entire multilayer film 100 at 20 GHz measured using an SPDR resonator is preferably 3.0 or less, and more preferably within the range of 2.9 to 1.5.

[0033] The multilayer film 100 satisfies conditions a to e, and further satisfies condition f; f) The polyimide layer, which is a combination of the thermoplastic polyimide layer and the non-thermoplastic polyimide layer laminated on one side of the adhesive layer, has a storage modulus of 1.0 GPa or more at 100°C and a storage modulus of 0.1 GPa or more at 200°C; It is preferable that the following is satisfied. Condition f specifies that the first insulating resin layer 40A and the second insulating resin layer 40B each have a storage modulus of 1.0 GPa or greater at 100°C and a storage modulus of 0.1 GPa or greater at 200°C. Satisfying condition f means that the storage modulus of the outer layer portion is higher than that of the adhesive layer BS, which is the inner layer portion, in the thermocompression bonding temperature range (100°C to 200°C). It is believed that increasing the spring constant of the outer layer portion by a certain amount relative to that of the inner layer portion is effective in suppressing dimensional changes due to residual stress after thermocompression bonding. Therefore, by taking condition d above into consideration and controlling the storage modulus of the outer layer portion to be higher than that of the inner layer portion, the dimensional stability of the entire multilayer film 100 can be improved. From this perspective, the storage modulus of the first insulating resin layer 40A and the second insulating resin layer 40B at 100°C is preferably in the range of 2 GPa to 10 GPa, more preferably 3 GPa to 8 GPa. The storage modulus 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. The storage modulus of the first insulating resin layer 40A and the second insulating resin layer 40B may be the same or different, but is preferably the same from the viewpoint of suppressing warpage.

[0034] When the multilayer film 100 is used as, for example, an insulating resin layer of a circuit board, in order to prevent warpage and a decrease in dimensional stability, the coefficient of thermal expansion (CTE) of the entire film is preferably in the range of 10 to 30 ppm / K, more preferably in the range of 10 to 25 ppm / K, and most preferably in the range of 10 to 20 ppm / K. If the CTE is less than 10 ppm / K or more than 30 ppm / K, warpage may occur or dimensional stability may decrease.

[0035] Furthermore, when applied as an insulating resin layer of a circuit board, for example, in order to prevent warping and 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 laminated on one side of the adhesive layer BS is preferably in the range of 5 to 35 ppm / K, more preferably in the range of 8 to 30 ppm / K, and most preferably in the range of 10 to 25 ppm / K. The coefficient 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 is preferably the same from the viewpoint of suppressing warpage.

[0036] [Polyimide] Next, the polyimide constituting the first insulating resin layer 40A, the second insulating resin layer 40B, and the adhesive layer BS will be described. In the present invention, the term "polyimide" refers to a resin made of a polymer having an imide group in its molecular structure, such as polyimide, polyamideimide, polyetherimide, polyesterimide, polysiloxaneimide, polybenzimidazoleimide, etc. When a polyimide has a plurality of structural units, they may exist as blocks or randomly, but random existence is preferred. Furthermore, the term "thermoplastic polyimide" generally refers to a polyimide whose glass transition temperature (Tg) can be clearly confirmed. In the present invention, however, the term "thermoplastic polyimide" refers to a polyimide whose storage modulus at 30°C measured using a dynamic viscoelasticity measuring device (DMA) is 1.0 × 10 9 Pa or more, and the storage modulus at 300°C is 1.0 × 10 8In addition, "non-thermoplastic polyimide" generally refers to a polyimide that does not soften or exhibit adhesiveness even when heated. In the present invention, however, the "non-thermoplastic polyimide" refers to a polyimide having a storage modulus of 1.0 × 10 Pa at 30°C as measured using a dynamic viscoelasticity measuring device (DMA). 9 Pa or more, and the storage modulus at 300°C is 1.0 × 10 8 This refers to polyimides with a modulus of tensile strength of 100 Pa or more.

[0037] <Thermoplastic polyimide> The thermoplastic polyimide used to form the thermoplastic polyimide layers 10A and 10B in the first insulating resin layer 40A and the second insulating resin layer 40B is obtained by reacting an acid dianhydride component with a diamine component containing an aliphatic diamine and / or an aromatic diamine, and contains an acid dianhydride residue derived from the acid dianhydride component and a diamine residue derived from the diamine component. By selecting the types of acid dianhydride component and diamine component, or by selecting the respective molar ratios when two or more types of acid anhydrides or diamines are used, the thermal expansion, adhesiveness, glass transition temperature, and other properties of the thermoplastic polyimide can be controlled. In the present invention, the term "acid dianhydride residue" refers to a tetravalent group derived from an acid dianhydride, and the term "diamine residue" refers to a divalent group derived from a diamine compound.

[0038] The thermoplastic polyimide used to form the thermoplastic polyimide layers 10A and 10B can be made using monomers commonly used in the synthesis of thermoplastic polyimides as the raw acid dianhydride and diamine components, but it is preferable to use aromatic acid dianhydrides and aromatic diamines. Examples of aromatic acid dianhydrides that can be preferably used include pyromellitic dianhydride (PMDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,3',3,4'-biphenyltetracarboxylic dianhydride, p-phenylenebis(trimellitate 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. In order to reduce the polar group concentration and improve the dielectric properties while ensuring adhesion to the substrate, the thermoplastic polyimide layers 10A and 10B preferably contain BPDA residues derived from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) in an amount of 40 mol % or more, and more preferably in the range of 45 to 80 mol %, relative to the total acid dianhydride residues.

[0039] As the aromatic diamine, it is preferable to use a diamine compound represented by the following general formula (1) from the viewpoint of ensuring appropriate flexibility and adhesion to the substrate.

[0040] [ka]

[0041] In general formula (1), R independently represents a halogen atom, an alkyl group or alkoxy group having 1 to 6 carbon atoms which may be substituted with a halogen atom, or a phenyl group or phenoxy group which may be substituted with 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 of 0 to 4; and m2 independently represents an integer of 0 to 2.

[0042] Examples of the diamine compound 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), 2,2-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), and 4,4'-diaminodiphenyl ether (DAPE).

[0043] In order to ensure adhesion to a metal layer when a metal layer is laminated even when the thickness of the thermoplastic polyimide layers 10A and 10B is thin, the content 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 within the range of 70 to 90 mol %, relative to all diamine residues.

[0044] <Non-thermoplastic polyimide> The non-thermoplastic polyimide used to form the non-thermoplastic polyimide layers 20A, 20B in the first insulating resin layer 40A and the second insulating resin layer 40B is obtained by reacting an acid dianhydride component with a diamine component containing an aliphatic diamine and / or an aromatic diamine, and contains an acid dianhydride residue derived from the acid dianhydride component and a diamine residue derived from the diamine component. By selecting the types of the acid dianhydride component and the diamine component, or by selecting the respective molar ratios when two or more types of acid anhydrides or diamines are used, the thermal expansion properties, dielectric properties, and the like of the non-thermoplastic polyimide can be controlled.

[0045] The non-thermoplastic polyimide used to form the non-thermoplastic polyimide layers 20A and 20B can be made from monomers commonly used in the synthesis of non-thermoplastic polyimides as the raw acid dianhydride and diamine components. However, from the viewpoint of controlling the coefficient of thermal expansion (CTE) of the outer layer portion and ensuring dimensional stability, it is preferable to use an aromatic acid dianhydride having a biphenyl skeleton or an aromatic diamine having a biphenyl skeleton. As the aromatic acid dianhydride having a biphenyl skeleton, for example, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,3',3,4'-biphenyltetracarboxylic dianhydride, etc. are preferred, with 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) being particularly preferred. The non-thermoplastic polyimide layers 20A, 20B control the coefficient of thermal expansion (CTE) of the outer layer portions to ensure the dimensional stability of the entire multilayer film 100, and also increase the storage modulus of the outer layer portions to satisfy condition f. To this end, the content of dianhydride residues having a biphenyl skeleton is preferably 40 mol % or more, and more preferably within the range of 45 to 70 mol %, of the total dianhydride residues.

[0046] Furthermore, examples of aromatic diamines having a biphenyl skeleton 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), 2,2'-di-n-propyl-4,4'-diaminobiphenyl (m-NPB), 2,2'-divinyl-4,4'-diaminobiphenyl (VAB), 4,4'-diaminobiphenyl, and 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl (TFMB), with 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB) being particularly preferred. It can be used.

[0047] The non-thermoplastic polyimide layers 20A, 20B control the coefficient of thermal expansion (CTE) of the outer layer portions to ensure the dimensional stability of the entire multilayer film 100, and also increase the storage modulus of the outer layer portions to satisfy condition f. To this end, the content of diamine residues having a biphenyl skeleton relative to all diamine residues is preferably 40 mol % or more, and more preferably within the range of 70 to 100 mol %.

[0048] <Adhesive polyimide> The adhesive polyimide, which is a preferred resin constituting the adhesive layer BS, is a thermoplastic polyimide obtained by reacting an acid dianhydride component with a diamine component containing an aliphatic diamine. As the acid dianhydride component serving as the raw material for adhesive polyimide, monomers generally used in the synthesis of thermoplastic polyimides can be used, such as 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA), 4,4'-oxydiphthalic anhydride (ODPA), 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), p-phenylenebis(trimellitic acid monoester anhydride) (TAHQ), and ethylene glycol. Aromatic acid dianhydrides such as bisanhydrotrimellitate (TMEG), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), and 2,3',3,4'-biphenyltetracarboxylic dianhydride are preferred, with 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) being more preferred. The adhesive polyimide preferably contains 40 to 100 mol %, and more preferably 50 to 90 mol %, of acid dianhydride residues derived from one or more of the above aromatic acid dianhydrides relative to the total acid dianhydride residues. More preferably, the total amount of acid dianhydride residues derived from the two aromatic acid dianhydrides is within a range of 40 to 100 mol % relative to the total amount of acid dianhydride residues. Most preferably, the amount of 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride (BTDA) is within a range of 50 to 90 mol %, and the amount of the aromatic acid dianhydrides excluding BTDA is within a range of 10 to 50 mol %.

[0049] As the diamine component serving as the raw material for the adhesive polyimide, a monomer commonly used in the synthesis of thermoplastic polyimides can be used, but it is preferable to use a dimer diamine composition from the viewpoint of controlling the storage modulus of the adhesive layer BS to satisfy condition d, lowering the dielectric tangent, improving the dielectric properties of the entire multilayer film 100, and satisfying condition e. That is, the adhesive polyimide preferably contains 20 mol% or more, more preferably 50 mol% or more, and most preferably 70 to 100 mol% of diamine residues derived from the dimer diamine composition relative to the total diamine residues. By including the diamine residues derived from the dimer diamine composition in the above amounts, the adhesive layer BS can have a lower glass transition temperature (lower Tg) to improve thermocompression bonding properties, and can also have a lower elastic modulus to alleviate internal stress and improve the dielectric properties of the adhesive layer BS. If the content of diamine residues derived from the dimer diamine composition relative to the total diamine residues is less than 20 mol%, transmission loss during high-frequency transmission may increase, or the adhesive layer BS interposed between the first insulating resin layer 40A and the second insulating resin layer 40B may not have sufficient adhesiveness.

[0050] The dimer diamine composition is a mixture containing the following component (a) as a main component and optionally containing components (b) and (c), and is a purified product in which the amounts of components (b) and (c) are controlled. (a) Dimer diamine (b) Monoamine compounds obtained by substituting the terminal carboxylic acid group of a monobasic acid compound having 10 to 40 carbon atoms with a primary aminomethyl group or an amino group. (c) Amine compounds obtained by substituting the terminal carboxylic acid group of a polybasic acid compound having a hydrocarbon group having 41 to 80 carbon atoms with a primary aminomethyl group or an amino group (excluding the dimer diamine).

[0051] The dimer diamine of component (a) refers to a diamine in which the two terminal carboxylic acid groups (—COOH) of a dimer acid are replaced with primary aminomethyl groups (—CH—NH) or amino groups (—NH). Dimer acids are known dibasic acids obtained by the intermolecular polymerization of unsaturated fatty acids. Their industrial production process is largely standardized in the industry, and they are obtained by dimerizing unsaturated fatty acids with 11 to 22 carbon atoms using a clay catalyst or the like. Industrially obtained dimer acids are primarily composed of a 36-carbon dibasic acid obtained by dimerizing 18-carbon unsaturated fatty acids such as oleic acid, linoleic acid, and linolenic acid. However, depending on the degree of purification, they may contain arbitrary amounts of monomer acid (18 carbon atoms), trimer acid (54 carbon atoms), and other polymerized fatty acids with 20 to 54 carbon atoms. Although double bonds remain after the dimerization reaction, in the present invention, dimer acids that have been further hydrogenated to reduce the degree of unsaturation are also included in the definition of dimer acids. The dimer diamine of component (a) can be defined as a diamine compound obtained by substituting the terminal carboxylic acid group of a dibasic acid compound having 18 to 54 carbon atoms, preferably 22 to 44 carbon atoms, with a primary aminomethyl group or an amino group.

[0052] Dimer diamine is characterized by its ability to impart properties derived from the dimer acid skeleton. Specifically, because dimer diamine is a macromolecular aliphatic molecule with a molecular weight of approximately 560 to 620, it can increase the molecular molar volume and relatively reduce the polar groups in polyimides. These characteristics of dimer diamine are believed to contribute to improving the dielectric properties of polyimides by reducing their relative dielectric constant and dielectric dissipation factor while suppressing a decrease in their heat resistance. Furthermore, because dimer diamine contains two freely movable hydrophobic chains with 7 to 9 carbon atoms and two linear aliphatic amino groups with a length approaching 18 carbon atoms, it not only imparts flexibility to polyimides but also allows them to have asymmetric or nonplanar chemical structures, thereby potentially lowering the dielectric constant of polyimides.

[0053] The dimer diamine composition used should be one in which the dimer diamine content of component (a) has been increased to 96% by weight or more, preferably 97% by weight or more, and more preferably 98% by weight or more, by a purification method such as molecular distillation. By increasing the dimer diamine content of component (a) to 96% by weight or more, the broadening of the molecular weight distribution of the polyimide can be suppressed. If technically possible, it is best for the entire dimer diamine composition (100% by weight) to be composed of component (a) dimer diamine. In addition, the dimer diamine composition preferably has a total area percentage of components (b) and (c) of 4% or less, preferably less than 4%, in a chromatogram obtained by GPC measurement. The area percentage of the chromatogram of component (b) is preferably 3% or less, more preferably 2% or less, and even more preferably 1% or less, and the area percentage of the chromatogram of component (c) is preferably 2% or less, more preferably 1.8% or less, and even more preferably 1.5% or less. By achieving these ranges, a rapid increase in the molecular weight of the polyimide can be suppressed, and an increase in the dielectric loss tangent of the resin film over a wide frequency range can be suppressed. Note that components (b) and (c) do not necessarily need to be present in the dimer diamine composition.

[0054] Commercially available dimer diamine compositions are available, 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, they are preferably purified to reduce the amount of components other than dimer diamine, and for example, it is preferable to make the dimer diamine content 96% by weight or more. The purification method is not particularly limited, but known methods such as distillation and precipitation purification are suitable.

[0055] The adhesive polyimide may be made from a diamine compound other than the dimer diamine composition as long as the effect of the invention is not impaired. Preferred examples of diamine compounds that can be used for the adhesive polyimide include the diamine compounds represented by the general formula (1).

[0056] Among the diamine compounds represented by general formula (1), the adhesive polyimide preferably contains, for example, 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), or the like.

[0057] In order to increase the flexibility of the adhesive layer BS and alleviate residual stress after thermocompression bonding due to the low elastic modulus, the adhesive polyimide preferably contains diamine residues derived from the diamine compound represented by general formula (1) in the range of 5 to 50 mol %, more preferably 10 to 30 mol %, of all diamine residues.

[0058] In adhesive polyimides, the thermal expansion coefficient, glass transition temperature, dielectric properties, etc. can be controlled by selecting the types of acid dianhydride components and diamine components, and when two or more types of acid dianhydrides or diamines are used, by selecting their respective molar ratios.

[0059] The weight-average molecular weight of the adhesive polyimide is preferably in the range of 10,000 to 400,000, more preferably in the range of 20,000 to 350,000. If the weight-average molecular weight is less than 10,000, the strength of the adhesive layer BS tends to decrease and the adhesive layer BS tends to become brittle. On the other hand, if the weight-average molecular weight exceeds 400,000, the viscosity increases excessively, and the adhesive layer BS tends to have defects such as uneven thickness and streaks during coating.

[0060] The adhesive polyimide is most preferably a completely imidized structure. However, a portion of the polyimide may be an amic acid. The imidization rate can be determined by measuring the infrared absorption spectrum of the polyimide thin film by the single-reflection ATR method using a Fourier transform infrared spectrophotometer (commercially available: FT / IR620 manufactured by JASCO Corporation) at 1015 cm -1Based on the benzene ring absorber near 1780cm -1 It can be calculated from the absorbance of the C=O stretching derived from the imide group.

[0061] The adhesive polyimide preferably has a glass transition temperature (Tg) of 250°C or less, more preferably in the range of 40°C to 200°C. A Tg of 250°C or less allows thermocompression bonding at low temperatures, thereby alleviating internal stress generated during lamination and suppressing dimensional changes after circuit processing. If the Tg of the adhesive polyimide exceeds 250°C, the temperature required for bonding between the first insulating resin layer 40A and the second insulating resin layer 40B becomes too high, which may impair dimensional stability after circuit processing.

[0062] By using the adhesive polyimide described above, the adhesive layer BS has excellent flexibility and dielectric properties (low dielectric constant and low dielectric loss tangent).

[0063] The adhesive layer BS preferably contains a polystyrene elastomer resin in addition to the adhesive polyimide. The polystyrene elastomer resin is a copolymer of styrene or a derivative thereof with a conjugated diene compound, including its hydrogenated derivative. Examples of styrene or a derivative thereof include, but are not limited to, styrene, methylstyrene, butylstyrene, divinylbenzene, and vinyltoluene. Examples of conjugated diene compounds include, but are not limited to, butadiene, isoprene, and 1,3-pentadiene. The polystyrene elastomer resin is preferably hydrogenated, which further improves its thermal stability and makes it less susceptible to changes such as decomposition and polymerization, and also enhances its aliphatic properties, thereby improving its compatibility with the adhesive polyimide.

[0064] The copolymer structure of the polystyrene elastomer resin may be a block structure or a random structure. Preferred examples of the polystyrene elastomer resin include styrene-butadiene-styrene block copolymer (SBS), styrene-butadiene-butylene-styrene block copolymer (SBBS), styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-ethylene-propylene-styrene block copolymer (SEPS), and styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS), but are not limited to these.

[0065] The weight-average molecular weight of the polystyrene elastomer resin is, for example, preferably in the range of 50,000 to 300,000, and more preferably in the range of 80,000 to 270,000.If the weight-average molecular weight is lower than the above range, the effect of improving the dielectric properties may be insufficient, while if it is higher, the viscosity of a composition containing an adhesive polyimide and a solvent may become high, making it difficult to produce a resin film. Furthermore, from the viewpoint of significantly lowering the dielectric loss tangent of the resin film, the weight-average molecular weight of the polystyrene elastomer resin 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 ensuring that the weight-average molecular weight of the polystyrene elastomer resin is 100,000 or less, it is possible to significantly improve the dielectric properties of the resin film.

[0066] The acid value of the polystyrene elastomer resin is preferably 10 mgKOH / g or less, more preferably 1 mgKOH / g or less, and even more preferably 0 mgKOH / g. By incorporating a polystyrene elastomer resin with an acid value of 10 mgKOH / g or less, the dielectric loss tangent of the formed resin film can be reduced and good peel strength can be maintained. On the other hand, if the acid value exceeds 10 mgKOH / g, the increase in polar groups deteriorates the dielectric properties, and compatibility with the adhesive polyimide deteriorates, resulting in poor adhesion when the resin film is formed. Therefore, the lower the acid value, the better, and a polystyrene elastomer that is not acid-modified (i.e., one with an acid value of 0 mgKOH / g) is most suitable. In the present invention, excellent adhesion can be achieved when the adhesive polyimide contains residues derived from aliphatic diamines. Therefore, even when a polystyrene elastomer resin that is not acid-modified (i.e., has strong aliphatic properties) is used, a decrease in adhesive strength can be avoided.

[0067] The polystyrene elastomer resin preferably has a content of styrene units [—CH2CH(C6H5)—] in the range of 10 to 65% by weight, more preferably 20 to 65% by weight, and most preferably 30 to 60% by weight. If the content of styrene units in the polystyrene elastomer resin is less than 10% by weight, the elastic modulus of the resin decreases, making it difficult to handle as a film. If the content exceeds 65% by weight, the resin becomes rigid, making it difficult to use as an adhesive, and the reduced rubber content in the polystyrene elastomer resin leads to poor dielectric properties. Furthermore, by having the styrene unit content within the above range, the proportion of aromatic rings in the resin film is increased, which makes it possible to increase the absorbency in the ultraviolet region when forming via holes (through holes) and blind via holes by laser processing during the process of manufacturing a circuit board using the resin film, thereby further improving laser processability.

[0068] As the polystyrene elastomer resin, commercially available products can be appropriately selected and used. Examples of commercially available polystyrene elastomer resins that can be preferably used include A1535HU (trade name), A1536HU (trade name), G1652MU (trade name), G1726VS (trade name), G1645VS (trade name), FG1901GT (trade name), G1650MU (trade name), G1654HU (trade name), G1730VO (trade name), and MD1653MO (trade name), manufactured by KRATON. Among these, MD1653MO (trade name), G1726VS (trade name), and the like, manufactured by KRATON, are more preferably used, as they have a weight-average molecular weight of 100,000 or less.

[0069] The content of the polystyrene elastomer resin per 100 parts by weight of adhesive polyimide is preferably in the range of 10 to 150 parts by weight, more preferably in the range of 50 to 120 parts by weight. If the content of the polystyrene elastomer resin per 100 parts by weight of adhesive polyimide is less than 10 parts by weight, the effect of reducing the dielectric tangent may not be fully achieved. On the other hand, if the weight ratio of the polystyrene elastomer resin exceeds 150 parts by weight, the adhesiveness of the formed resin film may decrease, and the solids concentration of the composition containing the adhesive polyimide and a solvent may become too high, increasing the viscosity and making it difficult to handle.

[0070] The total content of adhesive polyimide and polystyrene elastomer resin is preferably 60 to 100% by weight, more preferably 80 to 100% by weight, of the total resin components constituting the adhesive layer BS.

[0071] In addition to the polystyrene elastomer resin, the adhesive layer BS may contain, as appropriate, plasticizers, curable resin components such as epoxy resins, curing agents, curing accelerators, organic or inorganic fillers, coupling agents, flame retardants, etc.

[0072] <Synthesis of Polyimide> The thermoplastic polyimides and non-thermoplastic polyimides 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 produced by reacting the above-mentioned acid dianhydride and diamine compound in a solvent to produce polyamic acid, which is then subjected to thermal ring closure. For example, polyamic acid, a polyimide precursor, can be obtained by dissolving approximately equimolar amounts of the acid dianhydride and diamine compound in an organic solvent and stirring at a temperature in the range of 0 to 100°C for 30 minutes to 24 hours to cause a polymerization reaction. During the reaction, the reaction components are dissolved in the organic solvent so that the resulting precursor is in the range of 5 to 50 wt %, preferably 10 to 40 wt %, of the organic solvent. Examples of organic solvents used in the polymerization reaction include N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), 2-butanone, dimethyl sulfoxide (DMSO), hexamethylphosphoramide, N-methylcaprolactam, dimethyl sulfate, cyclohexanone, dioxane, tetrahydrofuran, diglyme, triglyme, and cresol. Two or more of these solvents can be used in combination, and aromatic hydrocarbons such as xylene and toluene can also be used in combination. The amount of such organic solvents is not particularly limited, but it is preferable to adjust the amount so that the concentration of the polyamic acid solution obtained by the polymerization reaction is about 5 to 50% by weight.

[0073] The synthesized polyamic acid is usually advantageously used as a solution in a reaction solvent, but it can be concentrated, diluted, or replaced with another organic solvent if necessary. Polyamic acid is also advantageously used because it generally has excellent solvent solubility. The viscosity of the polyamic acid solution is preferably within the range of 500 mPa·s to 100,000 mPa·s. If the viscosity is outside this range, defects such as uneven thickness and streaks are likely to occur in the film during coating using a coater or the like.

[0074] The method for imidizing the polyamic acid to form the adhesive polyimide is not particularly limited, and a suitable method is, for example, heat treatment in which the polyamic acid is heated at a temperature in the range of 80 to 400° C. for 0.1 to 24 hours.

[0075] <Crosslinking of adhesive polyimide> When an adhesive polyimide has a ketone group, the ketone group can be reacted with the amino group of an amino compound having at least two primary amino groups as functional groups to form a C=N bond, thereby forming a crosslinked structure. The formation of a crosslinked structure can improve the heat resistance of the adhesive polyimide. Examples of tetracarboxylic acid anhydrides suitable for forming adhesive polyimides having ketone groups include 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride (BTDA), and examples of diamine compounds include aromatic diamines such as 4,4'-bis(3-aminophenoxy)benzophenone (BABP) and 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene (BABB).

[0076] Examples of amino compounds that can be used to crosslink adhesive polyimides include dihydrazide compounds, aromatic diamines, and aliphatic amines. Among these, dihydrazide compounds are preferred. Aliphatic amines other than dihydrazide compounds tend to form crosslinked structures even at room temperature, raising concerns about the storage stability of the varnish. On the other hand, aromatic diamines require high temperatures to form crosslinked structures. When a dihydrazide compound is used, it is possible to achieve both the storage stability of the varnish and a shortened curing time. Examples of dihydrazide compounds include oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, pimelic acid dihydrazide, suberic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, dodecanedioic acid dihydrazide, maleic acid dihydrazide, fumaric acid dihydrazide, and diglycerides. Preferred dihydrazide compounds include cholic acid dihydrazide, tartaric acid dihydrazide, malic acid dihydrazide, phthalic acid dihydrazide, isophthalic acid dihydrazide, terephthalic acid dihydrazide, 2,6-naphthoic acid dihydrazide, 4,4-bisbenzenedihydrazide, 1,4-naphthoic acid dihydrazide, 2,6-pyridine dioic acid dihydrazide, itaconic acid dihydrazide, etc. The above dihydrazide compounds may be used alone or in combination of two or more.

[0077] When crosslinking an adhesive polyimide, the amino compound is added to a resin solution containing an adhesive polyimide having a ketone group, and a condensation reaction is caused between the ketone group in the adhesive polyimide and the primary amino group of the amino compound. This condensation reaction hardens the resin solution to form a cured product. In this case, the amino compound can be added in such an amount that the total number of primary amino groups per mole of ketone group is 0.004 to 1.5 moles, preferably 0.005 to 1.2 moles, more preferably 0.03 to 0.9 moles, and most preferably 0.04 to 0.5 moles. If the amount of amino compound added is such that the total number of primary amino groups per mole of ketone group is less than 0.004 moles, the crosslinking of the adhesive polyimide by the amino compound will be insufficient, and the adhesive layer BS will tend not to exhibit heat resistance after curing. If the amount of amino compound added is such that the total number of primary amino groups per mole of ketone group is more than 1.5 moles, the unreacted amino compound will act as a thermoplasticizer, tending to reduce the heat resistance of the adhesive layer BS.

[0078] The conditions for the condensation reaction for crosslinking are not particularly limited, as long as they are conditions under which 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). The temperature for the thermal condensation is preferably within the range of, for example, 120 to 220°C, more preferably within the range of 140 to 200°C, for reasons such as discharging water produced by the condensation outside the system or simplifying the condensation step when the thermal condensation reaction is carried out subsequently to the synthesis of the adhesive polyimide. The reaction time is preferably about 30 minutes to 24 hours, and the end point of the reaction can be determined by measuring the infrared absorption spectrum using, for example, a Fourier transform infrared spectrophotometer (commercially available: FT / IR620 manufactured by JASCO Corporation) at 1670 cm -1 The decrease or disappearance of the absorption peak due to the ketone group in the polyimide resin near 1635 cm -1 This can be confirmed by the appearance of an absorption peak derived from a nearby imine group.

[0079] 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 (a) adding an amino compound and heating the mixture following the synthesis (imidization) of the adhesive polyimide, (b) charging an excess amount of an amino compound as a diamine component in advance, and then heating the adhesive polyimide together with the remaining amino compound that is not involved in the imidization or amidation following the synthesis (imidization) of the adhesive polyimide, or (c) processing the adhesive polyimide composition to which the amino compound has been added into a predetermined shape (for example, after applying it to any substrate or forming it into a film) and then heating it.

[0080] The formation of imine bonds has been described as a method for forming a crosslinked structure to impart heat resistance to adhesive polyimides, but the present invention is not limited to this. For example, an adhesive polyimide can be cured by blending an epoxy resin, an epoxy resin curing agent, or the like.

[0081] [Metal-clad laminate] The metal-clad laminate of this embodiment has a multilayer film 100 and a metal layer laminated on one or both sides of this multilayer film 100. FIG. 2 shows a cross-sectional configuration 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 a metal layer 110A and a metal layer 110B are laminated on both sides of a multilayer film 100. Therefore, the metal-clad laminate 200 has a structure in which the metal layer 110A, the first insulating resin layer 40A, the adhesive layer BS, the second insulating resin layer 40B, and the metal layer 110B are laminated in this order. The metal layer 110A and the metal layer 110B are located on the outermost sides, respectively, with the first insulating resin layer 40A and the second insulating resin layer 40B disposed inside them, and the adhesive layer BS is further disposed between the first insulating resin layer 40A and the second insulating resin layer 40B. A metal-clad laminate 200 having such a layer structure can also be considered to have a structure in which a first single-sided metal-clad laminate (C1) having a metal layer 110A, a thermoplastic polyimide layer 10A, and a non-thermoplastic polyimide layer 20A laminated in that order is bonded to a second single-sided metal-clad laminate (C2) having a metal layer 110B, a thermoplastic polyimide layer 10B, and a non-thermoplastic polyimide layer 20B laminated in that order is bonded together with an adhesive layer BS so that the insulating layer sides face each other.

[0082] The material of the metal layer 110A and the metal layer 110B is not particularly limited, but examples thereof include copper, stainless steel, iron, nickel, beryllium, aluminum, zinc, indium, silver, gold, tin, zirconium, tantalum, titanium, lead, magnesium, manganese, and alloys thereof. Among these, copper or a copper alloy is particularly preferable. The material of the wiring layer in the circuit board of this embodiment, which will be described later, is also the same as that of the metal layer 110A and the metal layer 110B.

[0083] The thickness of the metal layer 110A and the metal layer 110B is not particularly limited, but when a metal foil such as copper foil is used, it is preferably 35 μm or less, and more preferably in the range of 5 to 25 μm. From the viewpoint of production stability and handling, the lower limit of the thickness of the metal foil is preferably 5 μm. When copper foil is used, it may be rolled copper foil or electrolytic copper foil. Furthermore, commercially available copper foil may be used as the copper foil.

[0084] Furthermore, the metal foil may be subjected to a surface treatment using, for example, siding, aluminum alcoholate, aluminum chelate, or a silane coupling agent, for the purpose of, for example, rust prevention or improving adhesive strength.

[0085] When metal layers 110A and 110B are removed by etching, it is preferable that the dimensional change rate of multilayer film 100 after etching is within ±0.10% based on multilayer film 100 before etching, and it is also preferable that the dimensional change rate after heating at 150°C for 30 minutes is within ±0.10% based on multilayer film 100 after etching. A dimensional change rate of within ±0.10% after etching and heating means that dimensional change during circuit processing is small, which can improve the reliability of circuit boards such as FPCs. Here, the dimensional change rate can be measured by the following procedure. First, a 150 mm square test piece made from a metal-clad laminate 200 is exposed to and developed at 100 mm intervals to form position measurement targets. After measuring the pre-etching (normal) dimensions in an atmosphere of 23±2°C and 50±5% relative humidity, the copper on the test piece other than the target is removed by etching (liquid temperature 40°C or less, time 10 minutes or less). After leaving the test piece in an atmosphere of 23±2°C and 50±5% relative humidity for 24±4 hours, the post-etching dimensions are measured. The dimensional change rate relative to the normal state at three locations in the MD (longitudinal direction) and TD (transverse direction) directions is calculated, and the average of these values ​​is used as the post-etching dimensional change rate. The post-etching dimensional change rate can be calculated using the following formula: Dimensional change rate after etching (%) = (BA) / A x 100 A: Target distance before etching B: Target distance after etching Next, the test piece is heated in an oven at 150°C for 30 minutes, and the distance between the target positions is measured after that. The dimensional change rate after etching is calculated at three locations in each of the MD (longitudinal direction) and TD (transverse direction), and the average value of these values ​​is used as the dimensional change rate after heat treatment. The dimensional change rate due to heat can be calculated using the following formula. Heat dimensional change rate (%) = (C-B) / B x 100 B: Target distance after etching C: Target distance after heating

[0086] [Manufacturing of metal-clad laminates] The metal-clad laminate 200 can be produced, for example, by the following method 1 or method 2. The adhesive polyimide that forms the adhesive layer BS may be crosslinked as described above. [Method 1] First, a first single-sided metal-clad laminate (C1) and a second single-sided metal-clad laminate (C2) having the layer structure described above are prepared. Next, the adhesive polyimide or its precursor, which will become the adhesive layer BS, is formed into a sheet to form an adhesive sheet. This adhesive sheet is 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 they are bonded together by thermocompression. [Method 2] 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 its precursor, which will form the adhesive layer BS, is applied to a predetermined thickness on either the first insulating resin layer 40A of the first single-sided metal-clad laminate (C1) or the second insulating resin layer 40B of the second single-sided metal-clad laminate (C2), or both, and dried 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 thermocompression on the side of the coating film.

[0087] The first single-sided metal-clad laminate (C1) and the second single-sided metal-clad laminate (C2) used in methods 1 and 2 can be produced, for example, by repeatedly applying and drying a solution of a polyamic acid, which is a precursor of a thermoplastic polyimide or a non-thermoplastic polyimide, onto a metal foil that will become the metal layers 110A and 110B, and then heat-treating it to imidize it. The adhesive sheet used in Method 1 can be produced, for example, by (1) applying a solution of polyamic acid to a supporting substrate, drying the solution, heat-treating it to form an imidization product, and then peeling it off from the supporting substrate to form an adhesive sheet; (2) applying a solution of polyamic acid to a supporting substrate, drying the solution, peeling the polyamic acid gel film from the supporting substrate, and heat-treating it to form an imidization product to form an adhesive sheet; or (3) applying a solution of the adhesive polyimide to a supporting substrate, drying the solution, and then peeling it off from the supporting substrate to form an adhesive sheet. In the above, the method for applying the polyimide solution (or polyamic acid solution) onto the metal foil, supporting substrate, or insulating resin layer is not particularly limited, and it can be applied using, for example, a coater such as a comma, die, knife, or lip coater.

[0088] The metal-clad laminate 200 of this embodiment obtained as described above can be used to manufacture circuit boards such as single-sided FPCs or double-sided FPCs by processing the metal layers 110A and / or 110B into wiring circuits, for example by etching them.

[0089] [Circuit board] Metal-clad laminate 200 of the present embodiment is useful primarily as a circuit board material for FPCs, rigid-flex circuit boards, etc. That is, by processing one or both of two metal layers 110A, 110B of metal-clad laminate 200 of the present embodiment into a pattern by a conventional method to form a wiring layer, a circuit board such as an FPC, which is an embodiment of the present invention, can be manufactured. [Example]

[0090] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the following examples, various measurements and evaluations were carried out according to the following methods unless otherwise specified.

[0091] [Measurement of thermal expansion coefficient] A 3mm x 20mm polyimide film was heated at a constant rate of 20°C / min from 30°C to 210°C while applying a 5.0g load using a TMA (trade name: TMA / SS6000, manufactured by Hitachi High-Technologies Corporation). After holding the film at that temperature for 10 minutes, the film was cooled at a rate of 5°C / min to determine the average thermal expansion coefficient (thermal expansion coefficient) from 200°C to 100°C.

[0092] [Storage modulus measurement] The storage modulus was measured on a sample film measuring 5 mm x 20 mm using a dynamic viscoelasticity measuring device (DMA: manufactured by TA Instruments Japan, product name: RSA-G2) at a heating rate of 10°C / min from 25°C to 300°C and a frequency of 1 Hz. The temperature at which the change in modulus (tan δ) was maximum was taken as the glass transition temperature. Note that the storage modulus at 30°C measured using DMA was 1.0 x 10 9 Pa or more, and the storage modulus at 300°C is 1.0 × 10 8 Those showing a storage modulus of less than 1.0 x 10 Pa are considered "thermoplastic" and have a storage modulus of 1.0 x 10 Pa at 30°C. 9 Pa or more, and the storage modulus at 300°C is 1.0 × 10 8 Those showing a thermal expansion coefficient of 100 Pa or more were categorized as "non-thermoplastic."

[0093] [Peel strength measurement] The copper foil from the copper-clad laminate sample was processed into a line-and-space circuit with a width of 1.0 mm and a spacing of 5.0 mm, and then cut into a measurement sample with a width of 8 cm and a length of 4 cm. Using a Tensilon tester (manufactured by Toyo Seiki Seisakusho, product name: Strograph VE-1D), the resin layer side of the measurement sample was fixed to an aluminum plate with double-sided tape, and the copper foil was peeled off in a 180° direction at a rate of 50 mm / min. The central strength was measured when the copper foil had peeled off 10 mm from the resin layer using a Tensilon tester (manufactured by Toyo Seiki Seisakusho, product name: Strograph VE-1D).

[0094] [Measurement of relative permittivity and dielectric loss tangent] The dielectric constant and dielectric loss tangent of the resin sheet at 20 GHz were measured using a vector network analyzer (Agilent, product name E8363C) and an SPDR resonator. The material used for the measurement was left for 24 hours under the conditions of temperature: 24 to 26°C and humidity: 45°C to 55%RH.

[0095] [Viscosity measurement] The viscosity was measured at 25°C using an E-type viscometer (Brookfield, product name: DV-II+Pro). The rotation speed was set so that the torque was 10% to 90%, and the viscosity was read when the viscosity stabilized 2 minutes after the start of measurement.

[0096] [Measurement of weight average molecular weight (Mw)] The weight-average molecular weight was measured by gel permeation chromatography (HLC-8220GPC manufactured by Tosoh Corporation). Polystyrene was used as a standard substance, and tetrahydrofuran (THF) was used as a developing solvent.

[0097] [Measurement of dimensional change rate after etching] First, a 150mm square test piece made from a metal-clad laminate is exposed to and developed at 100mm intervals to form a position measurement target. The pre-etching (normal) dimensions are measured in an atmosphere of 23±2°C and 50±5% relative humidity, after which the copper on the test piece other than the target is removed by etching (liquid temperature 40°C or less, time 10 minutes or less). After leaving the test piece in an atmosphere of 23±2°C and 50±5% relative humidity for 24±4 hours, the post-etching dimensions are measured. The dimensional change rate relative to the normal state at three locations in the MD (longitudinal) direction is calculated, and the average of these values ​​is used as the post-etching dimensional change rate. The post-etching dimensional change rate can be calculated using the following formula: Dimensional change rate after etching (%) = (BA) / A x 100 A: Target distance before etching B: Target distance after etching

[0098] [Measurement of dimensional change rate after heating] Next, the test piece whose dimensional change rate after etching was measured was heat-treated in an oven at 150°C for 30 minutes, and the distance between the target positions was then measured. The dimensional change rate after etching was calculated at three locations in the MD (longitudinal) direction, and the average value of these values ​​was used as the dimensional change rate after heat treatment. The dimensional change rate after heating can be calculated using the following formula. Heat dimensional change rate (%) = (C-B) / B x 100 B: Target distance after etching C: Target distance after heating

[0099] The abbreviations used in the examples represent the following compounds. BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride PMDA: Pyromellitic dianhydride m-TB: 2,2'-dimethyl-4,4'-diaminobiphenyl TPE-R: 1,3-bis(4-aminophenoxy)benzene Bisaniline-M: 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene NMP: N-methyl-2-pyrrolidone DMAc: N,N-dimethylacetamide BTDA: 3,3',4,4'-benzophenonetetracarboxylic dianhydride DDA: aliphatic diamine having 36 carbon atoms (manufactured by Croda Japan Co., Ltd., trade name: PRIAMINE 1074, amine value: 205 mg KOH / g, mixture of dimer diamines with cyclic and chain structures, dimer content: 95% by weight or more) BAPP: 2,2-bis[4-(4-aminophenoxy)phenyl]propane N-12: Dodecanedioic acid dihydrazide OP935: organic phosphinic acid aluminum salt (manufactured by Clariant Japan, trade name: Exolit OP935) Polystyrene elastomer resin: Kraton, product name: MD1653MO (hydrogenated polystyrene elastomer, styrene unit content: 30% by weight, Mw: 80,499, acid value: none)

[0100] (Synthesis Example 1) <Preparation of polyamic acid solution for insulating resin layer> Under a nitrogen atmosphere, 69.56 g of m-TB (0.328 mol), 542.75 g of TPE-R (1.857 mol), and DMAc (to a solids concentration of 12 wt%) were added to a reactor and stirred at room temperature. 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 with stirring at room temperature for 3 hours to prepare polyamic acid solution 1 (viscosity: 2,700 mPa s). The storage modulus of the polyimide film prepared using polyamic acid solution 1 was 4.3 × 10 at 30 °C. 9 Pa, 9.4 × 10 at 300 °C 7 Pa and was thermoplastic.

[0101] (Synthesis Example 2) <Preparation of polyamic acid solution for insulating resin layer> Under a nitrogen atmosphere, 64.20 g of m-TB (0.302 mol), 5.48 g of bisaniline-M (0.016 mol), and DMAc (to a solids concentration of 15 wt%) were added to a reactor and stirred at room temperature. 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 with stirring at room temperature for 3 hours to prepare polyamic acid solution 2 (viscosity: 28,000 mPa s). The storage modulus of the polyamic acid solution 2 was 7.0 × 10 at 30 °C. 9 Pa, 5.4 × 10 at 300 °C 8 Pa and was non-thermoplastic.

[0102] (Synthesis Example 3) <Preparation of resin solution for adhesive layer> A 500 mL separable flask was charged with 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, and mixed thoroughly at 40 °C for 1 hour to prepare a polyamic acid solution. This polyamic acid solution was heated to 190 °C and stirred for 5 hours. 65 g of xylene was added to complete the imidization, preparing Polyimide Solution 1 (solids content: 31 wt%, weight average molecular weight: 35,886, viscosity: 2.580 mPa s).

[0103] (Production Example 1) <Preparation of Resin Sheet for Adhesive Layer> Polyimide varnish 1 was prepared by blending 0.46 g of N-12, 2.54 g of OP935, and 7.62 g of polystyrene elastomer resin with 40.97 g of polyimide solution 1 (12.7 g as solid content), and diluting with 45.23 g of xylene.

[0104] Polyimide varnish 1 was applied to the silicone-treated surface of a release substrate (length × width × thickness = 320 mm × 240 mm × 25 μm) so that the thickness after drying would be 50 μm, and then the coating was dried by heating at 80°C for 15 minutes and peeled off from the release substrate to prepare resin sheet 1. The storage modulus properties of resin sheet 1 are as follows: Storage modulus (25°C): 901 x MPa Storage modulus (100°C): 5.0 x MPa Storage modulus (200°C): 2.0 x MPa

[0105] (Production Example 2) <Preparation of single-sided metal-clad laminate> Polyamic acid solution 1 was uniformly applied to copper foil 1 (electrolytic copper foil, thickness: 12 μm, surface roughness Rz on the resin layer side: 0.6 μm) to a thickness of approximately 1.6 μm after curing, and then heated and dried at 120°C to remove the solvent. Next, polyamic acid solution 2 was uniformly applied thereon to a thickness of approximately 2.4 μm after curing, and then heated and dried at 120°C to remove the solvent. Further, stepwise heat treatment from 120°C to 360°C was performed to complete the imidization, and a single-sided metal-clad laminate 1 was prepared. (Examples 3-4) Single-sided metal-clad laminates 2 and 3 were prepared in the same manner as in Preparation Example 2, except that the thicknesses of polyamic acid solution 1 and polyamic acid solution 2 after curing were changed as shown in Table 1 below.

[0106] [Table 1]

[0107] (Production Example 5) Polyamic acid solution 1 was uniformly applied to copper foil 1 (electrolytic copper foil, thickness: 12 μm, surface roughness Rz on the resin layer side: 0.6 μm) to a thickness of approximately 2 μm after curing, and then heated and dried at 120 ° C to remove the solvent. Next, polyamic acid solution 2 was uniformly applied thereon to a thickness of approximately 21 μm after curing, and then heated and dried at 120 ° C to remove the solvent. Further, polyamic acid solution 1 was uniformly applied thereon to a thickness of approximately 2 μm after curing, and then heated and dried at 120 ° C to remove the solvent. Further, stepwise heat treatment from 120 ° C to 360 ° C was performed to complete the imidization, and a single-sided metal-clad laminate 4 was prepared.

[0108] <Preparation of Polyimide Film> The copper foil layers of single-sided metal-clad laminates 1 to 4 were etched away using an aqueous ferric chloride solution to prepare polyimide films 1 to 4. The thermal expansion coefficients and storage moduli of the prepared polyimide films 1 to 4 were measured. The results are shown in Table 2 or Table 3.

[0109] [Example 1] Polyimide varnish 1 was applied to the insulating resin layer side of single-sided metal-clad laminate 1 so that the thickness after drying was 46 μm, and then the coating was dried using stepwise heat treatment from 80°C to 200°C to prepare single-sided metal-clad laminate 1 with an adhesive layer. Two single-sided metal-clad laminates 1 with adhesive layers were prepared, laminated with the adhesive layer sides facing each other, and pressed together at 180°C for 2 hours under a pressure of 3.5 MPa to prepare metal-clad laminate 1. The copper foil layer of metal-clad laminate 1 was also etched away to obtain multilayer film 1. Dimensional change rate and peel strength were measured using metal-clad laminate 1, and dielectric properties and thermal expansion coefficient were measured using multilayer film 1.

[0110] [Examples 2 to 3] Metal-clad laminates 2 to 3 and multilayer films 2 to 3 were prepared in the same manner as in Example 1, except that the dried thickness of polyimide varnish 1 was changed to 37.5 μm and single-sided metal-clad laminate 1 was changed to single-sided metal-clad laminate 2 or 3.

[0111] The configurations of the metal-clad laminate and multilayer film produced as described above and the evaluation results are shown in Table 2. The total thickness of the thermoplastic polyimide layers is T A , the total thickness of the non-thermoplastic polyimide layers is T B、 The thickness of the adhesive layer is T C It states that:

[0112] [Table 2]

[0113] (Comparative Example 1) Fluororesin sheets (manufactured by Asahi Glass Co., Ltd., product name: Adhesive Perfluororesin EA-2000) with thicknesses of 50 μm and 25 μm and two single-sided metal-clad laminates 2 were prepared, and the two fluororesin sheets were laminated so as to be sandwiched between the insulating resin layer sides of the two single-sided metal-clad laminates 2, and pressed together at 320°C for 5 minutes under a pressure of 3.5 MPa to prepare metal-clad laminate 4. The evaluation results of metal-clad laminate 4 and multilayer film 4 after removing the copper foil are shown in Table 3.

[0114] (Comparative Example 2) Two single-sided metal-clad laminates 4 were prepared, and the insulating resin layer side of each was overlapped on both sides of resin sheet 1, and the laminates were pressed together at 180°C for 2 hours under a pressure of 3.5 MPa to prepare metal-clad laminate 5. Table 3 shows the evaluation results of metal-clad laminate 5 and multilayer film 5 after copper foil removal.

[0115] (Comparative Example 3) Metal-clad laminate 6 was prepared in the same manner as in Comparative Example 2, except that a fluororesin sheet (manufactured by Asahi Glass Co., Ltd., product name: adhesive perfluororesin EA-2000, thickness: 50 μm) was used instead of resin sheet 1 and pressure-bonded at 320° C. for 5 minutes under a pressure of 3.5 MPa. The evaluation results of metal-clad laminate 6 and multilayer film 6 after copper foil removal are shown in Table 3.

[0116] [Table 3]

[0117] (Reference example 1) Polyamic acid solution 1 was uniformly applied to copper foil 1 (electrolytic copper foil, thickness: 12 μm, surface roughness Rz on the resin layer side: 0.6 μm) to a thickness of approximately 0.8 μm after curing, and then heated and dried at 120 ° C to remove the solvent. Next, polyamic acid solution 2 was uniformly applied thereon to a thickness of approximately 2.9 μm after curing, and then heated and dried at 120 ° C to remove the solvent. Polyamic acid solution 1 was further uniformly applied thereon to a thickness of approximately 0.8 μm after curing, and then heated and dried at 120 ° C to remove the solvent. Further, stepwise heat treatment was performed from 120 ° C to 360 ° C to complete imidization, and single-sided metal-clad laminate 5 was prepared. The peel strength of this single-sided metal-clad laminate 5 was measured and found to be 0.6 [kN / m].

[0118] In both Comparative Example 2 and Example 1, the CTE of the polyimide layer was approximately 20 ppm / K, which was within a suitable range. A ) / (T A +T BWhen forming a polyimide layer using the casting method, the thinner the thickness, the lower the CTE. Therefore, in order to achieve appropriate dimensional stability, (T A ) / (T A +T B ) must be kept within a specified range.

[0119] Furthermore, if the polyimide layer is made thinner while maintaining the conventional design of two layers of thermoplastic polyimide and one layer of non-thermoplastic polyimide, as in Reference Example 1, the peel strength decreases. On the other hand, sufficient peel strength is achieved in a design in which the thermoplastic polyimide layer is concentrated on the substrate side and the outer layer portion has a two-layer structure on one side, as in Example 1. Therefore, when designing a thinner polyimide layer, a two-layer structure of thermoplastic polyimide and non-thermoplastic polyimide is effective from the viewpoint of adhesion to copper foil.

[0120] Furthermore, a comparison of Comparative Examples 1 and 3 shows that when the inner layer is made of a resin with a high storage modulus at high temperatures, the thinner the polyimide layer in the outer layer, the more significantly the dimensional stability deteriorates. Also, a comparison of Comparative Example 1 and Example 2 shows that the dimensional stability deteriorates further when an adhesive layer with a low storage modulus at room temperature is used, and that the storage modulus at the process temperature range, rather than at room temperature, is important for ensuring dimensional stability.

[0121] From the above results, in a configuration in which a dimension control layer is provided in the outer layer portion and a low dielectric layer is provided in the inner layer portion, in order to make the outer layer portion thin and reduce the dielectric constant of the laminated film, it is important to control the thickness balance of each layer and the storage modulus of the inner layer portion in the process temperature range within a predetermined range so as to satisfy conditions a to d.

[0122] Although the embodiments of the present invention have been described in detail above for the purpose of illustration, the present invention is not limited to the above-described embodiments and various modifications are possible. [Explanation of symbols]

[0123] 10A, 10B...thermoplastic polyimide layers, 20A, 20B...non-thermoplastic polyimide layers, 100...multilayer film, 110A, 110B...metal layers, 200...metal-clad laminate, BS...adhesive layer

Claims

1. A multilayer film comprising a plurality of polyimide layers and an adhesive layer, A laminate having a layer structure of a thermoplastic polyimide layer / a non-thermoplastic polyimide layer / an adhesive layer / a non-thermoplastic polyimide layer / a thermoplastic polyimide layer, and satisfying the following conditions a) to e): a) the total thickness of the thermoplastic polyimide layer and the non-thermoplastic polyimide layer laminated on one side of the adhesive layer is in the range of 2 μm to 20 μm; b) The total thickness of the thermoplastic polyimide layers in the entire multilayer film is T Ａ , the total thickness of the non-thermoplastic polyimide layer is T Ｂ When 0.1 ≦ (T Ａ ) / (T Ａ +T Ｂ ) ≦ 0.6 ・・・ (i) c) The thickness of the adhesive layer is T Ｃ When .. ≦ ≴ Ｃ / () Ａ )) Ｂ )) Ｃ (ii) d) the adhesive layer has a storage modulus of less than 130 MPa at 100°C and a storage modulus of 40 MPa or less at 200°C; e) the multilayer film as a whole has a dielectric loss tangent at 20 GHz measured using an SPDR resonator of less than 0.0029; A multilayer film characterized by satisfying the above.

2. 2. The multilayer film according to claim 1, wherein the polyimide layer, which is a combination of the thermoplastic polyimide layer and the non-thermoplastic polyimide layer laminated on one side of the adhesive layer, has a storage modulus of 1.0 GPa or more at 100°C and a storage modulus of 0.1 GPa or more at 200°C.

3. 3. The multilayer film according to claim 1, wherein the thermal expansion coefficient of the polyimide layer, which is a combination of the thermoplastic polyimide layer and the non-thermoplastic polyimide layer laminated on one side of the adhesive layer, is in the range of 5 to 35 ppm / K.

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

5. 5. The multilayer film according to claim 4, wherein the thermoplastic polyimide contained in the adhesive layer contains acid dianhydride residues derived from an acid dianhydride component and diamine residues derived from a diamine component, and the content of diamine residues derived from a dimer diamine composition mainly composed of a dimer diamine obtained by substituting two terminal carboxylic acid groups of a dimer acid with primary aminomethyl groups or amino groups is 20 mol % or more relative to the total diamine residues, and the content of diamine residues derived from diamine compounds represented by the following general formula (1) is within the range of 5 to 50 mol % in total: 【Chemistry 1】 [In formula (1), R independently represents a halogen atom, an alkyl group or alkoxy group having 1 to 6 carbon atoms which may be substituted with a halogen atom, or a phenyl group or phenoxy group which may be substituted with a monovalent hydrocarbon group or alkoxy group having 1 to 6 carbon atoms; Z independently represents -O-, -S-, -CH ２ -, -CH(CH ３ )-, -C(CH ３ ) ２ -, -CO-, -COO-, -SO ２ represents a divalent group selected from -, -NH-, or -NHCO-, m １ are independently integers from 0 to 4, m ２ represents an integer of 0 to 2.]

6. The multilayer film according to claim 4 or 5, wherein the thermoplastic polyimide contained in the adhesive layer is a crosslinked polyimide in which a ketone group contained in the molecular chain and an amino group of an amino compound having at least two primary amino groups as functional groups form a crosslinked structure via a C=N bond.

7. 7. The multilayer film according to claim 1, wherein the thermoplastic polyimide constituting the thermoplastic polyimide layer contains acid dianhydride residues derived from an acid dianhydride component and diamine residues derived from a diamine component, and the proportion of BPDA residues derived from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) relative to all acid dianhydride residues is 40 mol % or more, and the proportion of diamine residues derived from a diamine compound represented by the following general formula (1) relative to all diamine residues is 30 mol % or more: 【Chemistry 2】 [In formula (1), R independently represents a halogen atom, an alkyl group or alkoxy group having 1 to 6 carbon atoms which may be substituted with a halogen atom, or a phenyl group or phenoxy group which may be substituted with a monovalent hydrocarbon group or alkoxy group having 1 to 6 carbon atoms; Z independently represents -O-, -S-, -CH ２ -, -CH(CH ３ )-, -C(CH ３ ) ２ -, -CO-, -COO-, -SO ２ represents a divalent group selected from -, -NH-, or -NHCO-, m １ are independently integers from 0 to 4, m ２ represents an integer of 0 to 2.]

8. 8. The multilayer film according to claim 1, wherein the non-thermoplastic polyimide constituting the non-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 acid dianhydride residues having a biphenyl skeleton relative to all acid dianhydride residues is 40 mol % or more, and the proportion of diamine residues having a biphenyl skeleton relative to all diamine residues is 40 mol % or more.

9. A metal-clad laminate comprising the multilayer film according to any one of claims 1 to 8 and a metal layer laminated on one or both sides of the multilayer film.

10. A metal-clad laminate as described in claim 9, wherein when the metal layer is etched and removed, 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.

11. A circuit board obtained by processing the metal layer of the metal-clad laminate according to claim 9 or 10 into wiring.

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