Method for producing polyimide film and method for producing metal-clad laminate

Abstract

To provide a manufacturing method of a polyimide film having low dielectric tangent without large deviation of a thermal expansion coefficient (CTE) by controlling manufacturing conditions for forming a polyimide film.SOLUTION: There is disclosed a manufacturing method of a polyimide film involving a non-thermoplastic polyimide layer having its one side or double sides laminated with a thermoplastic polyimide layer, and as a whole film, having a dielectric tangent at frequency of 10 GHz of 0.0045 or under and a CTE in a range of 10 ppm / K or over and 30 ppm / K or under, a CTE of the non-thermoplastic polyimide layer in a range of 1 ppm / K or over and 25 ppm / K, and a CTE of the thermoplastic polyimide layer of 35 ppm / K or over, wherein the maximum temperature in a heat treatment in an imidization step is +80°C or under of a glass transformation temperature (Tg) of the non-thermoplastic polyimide.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a polyimide film and a metal-clad laminate useful as materials for electronic components. [Background technology]

[0002] As electronic devices become smaller, lighter, and more space-saving, there is an increasing demand for flexible printed circuits (FPCs), which are thin, lightweight, flexible, and highly durable even when bent repeatedly. 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 cables, connectors, and other components.

[0003] One type of FPC is known to have a structure in which a circuit pattern is formed on an insulating resin layer of polyimide film, which has excellent heat resistance and flexibility. Polyimide film is widely used due to its characteristics such as high insulation, dimensional stability, easy formability, and light weight.

[0004] In recent years, there has been a demand for faster information transmission, such as with so-called 5G communications, and the components and materials used in these communications are also required to support high-speed transmission. Therefore, efforts have been made to lower the dielectric constant and dielectric dissipation factor of polyimide films to achieve electrical properties compatible with high-speed transmission. Most of the conventional techniques for lowering the dielectric constant and dielectric dissipation factor of polyimide films have mainly involved multilayering with low-dielectric-constant and low-dielectric-dissipation factor resins (e.g., fluororesins and liquid crystal polymers), compounding with different materials such as low-dielectric-constant and low-dielectric-dissipation factor fillers, making the film porous, or introducing an ester structure. However, compounding and porous structures have problems such as reduced processability, and the introduction of ester structures reduces film strength, limiting their use in large quantities.

[0005] Furthermore, Patent Documents 1 and 2 propose polyimide films that can be applied to high-frequency circuit boards by improving the dielectric properties through the use of innovative raw material monomer compositions for polyimide. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] WO2017 / 159274 [Patent Document 2] WO2018 / 061727 Summary of the Invention [Problem to be solved by the invention]

[0007] As mentioned above, conventional approaches to lowering the dielectric loss tangent of polyimide films have involved multilayering, compounding, and raw material monomer composition, but little research has been done on the effect of the manufacturing conditions used to form polyimide films on their dielectric properties.In addition, because the manufacturing conditions used to form polyimide films have a significant effect on, for example, the coefficient of thermal expansion (CTE), there was concern that changing the manufacturing conditions would make it difficult to control the CTE.

[0008] Therefore, an object of the present invention is to provide a method for producing a polyimide film having a low dielectric loss tangent without significantly varying the CTE by controlling the production conditions when forming the polyimide film. [Means for solving the problem]

[0009] As a result of extensive research, the present inventors have discovered that by controlling the heat treatment conditions for imidizing a polyimide precursor, it is possible to produce a polyimide film with a low dielectric loss tangent without significantly varying the CTE, and have thus completed the present invention.

[0010] The method for producing a polyimide film of the present invention is a method for producing a polyimide film in which a thermoplastic polyimide layer containing a thermoplastic polyimide is laminated on one or both sides of a non-thermoplastic polyimide layer containing a non-thermoplastic polyimide. The method for producing a polyimide film of the present invention comprises the following steps a and b: a) forming a precursor laminate including a first precursor layer containing a precursor of the thermoplastic polyimide and a second precursor layer containing a precursor of the non-thermoplastic polyimide; b) heat-treating the precursor laminate to imidize the precursor to form the thermoplastic polyimide layer and the non-thermoplastic polyimide layer; Contains: In the method for producing a polyimide film of the present invention, the polyimide film as a whole has a dielectric dissipation factor of 0.0045 or less at a frequency of 10 GHz and a CTE in the range of 10 ppm / K to 30 ppm / K, the CTE of the non-thermoplastic polyimide layer is in the range of 1 ppm / K to 25 ppm / K, and the CTE of the thermoplastic polyimide layer is 35 ppm / K or more. In the method for producing a polyimide film of the present invention, the maximum temperature of the heat treatment in the step b is the glass transition temperature (Tg) of the non-thermoplastic polyimide + 80° C. or less.

[0011] In the method for producing a polyimide film of the present invention, when the maximum temperature of the heat treatment in the step b is a temperature exceeding the glass transition temperature (Tg) of the non-thermoplastic polyimide, the heat treatment time at the temperature exceeding the glass transition temperature (Tg) may be 1 minute or more and 30 minutes or less.

[0012] In the method for producing a polyimide film of the present invention, the maximum temperature of the heat treatment in the step b may be equal to or lower than the glass transition temperature (Tg) of the non-thermoplastic polyimide.

[0013] In the method for producing a polyimide film of the present invention, the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer is obtained by reacting an acid anhydride component with a diamine component, and the proportion of the diamine component having a biphenyl skeleton to the total of all the diamine components may be 50 mol % or more.

[0014] In the method for producing a polyimide film of the present invention, the thickness ratio of the non-thermoplastic polyimide layer to the entire thickness of the film may be in the range of 70% to 97%.

[0015] The method for producing a metal-clad laminate of the present invention is a method for producing a metal-clad laminate comprising an insulating resin layer and a metal layer laminated on one or both sides of the insulating resin layer, The insulating resin layer is a polyimide film produced by any one of the above-described methods for producing a polyimide film.

[0016] In the method for producing a metal-clad laminate of the present invention, the step a may be such that the precursor laminate is formed by applying a solution containing a precursor of the thermoplastic polyimide and a solution containing a precursor of the non-thermoplastic polyimide onto a metal foil having a surface roughness Rzjis of 1.2 μm or less. [Effects of the Invention]

[0017] According to the method of the present invention, by controlling the heat treatment conditions, it is possible to produce a polyimide film having a low dielectric loss tangent while maintaining a CTE within a desired range. Therefore, when this polyimide film is used as an insulating resin layer in a circuit board, it is possible to reduce the transmission loss of high-frequency signals, thereby enabling high-speed transmission. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 2 is a schematic diagram showing an example of the relationship between time and temperature in heat treatment. [Figure 2] FIG. 10 is a schematic diagram showing another example of the relationship between time and temperature in heat treatment. DETAILED DESCRIPTION OF THE INVENTION

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the accompanying drawings.

[0020] [Manufacturing method of polyimide film] The method for producing a polyimide film according to the present embodiment includes the following steps a and b.

[0021] Step a) forming a precursor laminate comprising a first precursor layer comprising a precursor of a thermoplastic polyimide and a second precursor layer comprising a precursor of a non-thermoplastic polyimide; In step a, a precursor laminate is formed. The precursor laminate may have a two-layer structure of a first precursor layer / a second precursor layer, or a three-layer structure of a first precursor layer / a second precursor layer / a first precursor layer. In the case of a three-layer structure, the first precursor layers on both sides may have the same structure or different structures as long as they are precursors of thermoplastic polyimides. Specific structures of non-thermoplastic polyimides and thermoplastic polyimides will be described later.

[0022] The method for forming the precursor laminate is not particularly limited, and may be, for example, a casting method in which a solution containing a polyamic acid (precursor solution), which is a precursor of polyimide, is applied to an arbitrary substrate and dried multiple times; a multilayer extrusion method in which multiple types of precursor solutions are applied to an arbitrary substrate in a multilayer laminate state and dried; or a tenter method in which a gel film is formed using a tenter device. In the case of a two-layer structure, the precursor laminate may be laminated in the order of first precursor layer / second precursor layer, or second precursor layer / first precursor layer, from the substrate side. In the case of a three-layer structure, the precursor laminate may be laminated in the order of first precursor layer / second precursor layer / first precursor layer, from the substrate side. Note that the precursor laminate may be peeled from the substrate and subjected to the next step b in the form of a gel film, but it is preferable to perform the imidization in step b on the substrate, as this makes it easier to control the orientation of the polyimide.

[0023] Polyamic acid, a precursor of polyimide, can be synthesized by reacting a tetracarboxylic dianhydride with a diamine compound in a solvent. For example, polyamic acid can be obtained by dissolving approximately equimolar amounts of tetracarboxylic dianhydride and diamine compound in an organic solvent and stirring at a temperature ranging from 0 to 100°C for 30 minutes to 24 hours to polymerize the resulting mixture. The reaction components are dissolved in the organic solvent so that the resulting polyamic acid is in the range of 5 to 30% by weight, preferably 10 to 20% by weight. Examples of organic solvents used in the polymerization reaction include N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), 2-butanone, dimethyl sulfoxide (DMSO), 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 used is not particularly limited, but it is preferable to adjust the amount so that the concentration of the polyamic acid solution obtained by the polymerization reaction is about 5 to 30% by weight.

[0024] The synthesized polyamic acid reaction solvent solution can be used as the precursor solution as is. However, because polyamic acid has excellent solvent solubility, it can be concentrated, diluted, or replaced with another organic solvent as necessary. The viscosity of the precursor solution is preferably within the range of 500 cps to 100,000 cps. 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. The method for applying the precursor solution to the substrate is not particularly limited, and application can be performed using a coater such as a comma, die, knife, or lip. The substrate is not particularly limited, but metal foil is preferred because it allows the production of a metal-clad laminate without peeling the polyimide film. The method for producing a polyimide film or a metal-clad laminate by applying a precursor solution to a metal foil will be described later.

[0025] Step b) heat-treating the precursor laminate to imidize the precursor to form a thermoplastic polyimide layer and a non-thermoplastic polyimide layer; In step b, imidization is carried out by thermally cyclizing the polyamic acid in the precursor laminate to form a polyimide, thereby forming a polyimide film consisting of multiple layers including a thermoplastic polyimide layer and a non-thermoplastic polyimide layer. In this embodiment, since it is important to control the heat treatment conditions in the imidization step as described below, a method of imidizing the precursor laminate all at once is adopted.

[0026] Here, the heat treatment in step b will be described with reference to the drawings. Figures 1 and 2 are schematic diagrams showing the change in temperature (vertical axis) in the heat treatment including the imidization step in relation to time (horizontal axis). Stepwise temperature increases are indicated by thick dashed lines in Figures 1 and 2. The "temperature" in the heat treatment refers to the temperature of the precursor laminate.

[0027] In Figures 1 and 2, the heat treatment time for imidization in step b is, in principle, the time from t1 to t3 on the horizontal axis. That is, the sum (t1 to t3) of the temperature rise time from t1 to t2 and the heating time at the maximum temperature Tmax from t2 to t3 is the heat treatment time in step b. The drying step from t0 to before t1 on the horizontal axis is not included in the heat treatment in step b, but is included in step a. Because the purpose of the drying step is to remove the solvent, it has little effect on the control of the dielectric tangent and CTE. After the drying step is performed, the imidization step in step b may be started from t1 while the temperature is maintained, or the temperature may be lowered after the drying step and then raised again to start the imidization step in step b. In this case, there may be no temporal continuity between the drying step and the imidization step, and another process such as cooling may be interposed.

[0028] In addition, the temperature-reducing time t3 to t4 on the horizontal axis in Figures 1 and 2 is not, in principle, included in the heat treatment of step b. This is because when thermal imidization is performed at a high temperature where the maximum heat treatment temperature Tmax is near the glass transition temperature (Tg) of the non-thermoplastic polyimide, imidization of the polyamic acid is essentially complete at the maximum temperature Tmax (t2 to t3). Therefore, even if residual heat is added during the subsequent temperature-reducing time, the effect on the dielectric tangent and CTE of the polyimide film is almost negligible. However, as shown in Figure 1, when the maximum heat treatment temperature Tmax exceeds the Tg of the non-thermoplastic polyimide, the temperature-reducing time t3 to t6 at temperatures above Tg is exceptionally included in the heat treatment time. Therefore, in Figure 1, the horizontal axis t1 to t6 is considered to be the heat treatment time for imidization of step b.

[0029] FIG. 1 shows a case where the maximum heat treatment temperature Tmax in step b exceeds the Tg of the non-thermoplastic polyimide. In the production of polyimide films, it is preferable to proceed with imidization at as high a temperature as possible within the range in which dimensional stability can be controlled. Exposing a polyimide film to high temperatures and containing a large amount of polyamic acid structures, which have higher molecular chain mobility and greater flexibility than polyimide, to imidization facilitates regular alignment of the molecular chains. This is thought to result in the formation of an ordered structure of the polyimide molecular chains, reducing the dielectric loss tangent. Thus, in order to reduce the dielectric loss tangent while maintaining the CTE of the polyimide film, it is important to set the maximum heat treatment temperature Tmax in step b to a temperature above the Tg of the non-thermoplastic polyimide, but not higher than Tg + 80°C, preferably not higher than Tg + 50°C. Heat treatment at a temperature above Tg + 80°C increases the molecular chain mobility excessively, resulting in random orientation of the molecular chains regardless of the heat treatment time, potentially worsening the dielectric loss tangent or causing thermal decomposition.

[0030] Furthermore, as shown in FIG. 1, when the maximum temperature Tmax of the heat treatment in step b exceeds the Tg of the non-thermoplastic polyimide (i.e., when the maximum temperature Tmax exceeds the Tg and is within a range of Tg + 80°C), the heat treatment time at the temperature above Tg is preferably 1 minute to 30 minutes, more preferably more than 1 minute to 25 minutes. Here, "heat treatment time at a temperature above Tg" refers to the total time from t5 to t6 on the horizontal axis in FIG. 1. Heat treatment at a temperature above Tg for longer than 30 minutes can cause thermal degradation of the film or can cause excessive movement of the polyimide molecular chains, resulting in random orientation and loss of the regularly arranged structure, resulting in a deterioration in the dielectric loss tangent. On the other hand, if the heat treatment time at a temperature above Tg is less than 1 minute, and the difference between the maximum temperature Tmax and the Tg (Tmax - Tg) is 20°C or more, the rapid temperature rise can cause foaming due to the rapid evaporation of residual solvent in the film. However, even if the heat treatment time at a temperature above Tg is less than 1 minute, the problem of foaming does not occur as long as the difference between the maximum temperature Tmax and Tg (Tmax-Tg) is less than 20°C.

[0031] As described above, when heat treatment is performed at a temperature above Tg, by setting the heat treatment time t5 to t6 within the range of 1 minute to 30 minutes, a structure is formed in which molecular chains with increased molecular mobility above Tg are arranged in a moderately regular manner, and the dielectric loss tangent can be effectively reduced. Furthermore, when the maximum temperature Tmax of the heat treatment is a temperature exceeding the Tg of the non-thermoplastic polyimide, from the viewpoint of ensuring throughput and suppressing foaming due to rapid evaporation of the solvent, on the premise that an ordered structure advantageous for reducing the dielectric tangent is formed in the polyimide chain, the total heat treatment time is preferably within a range of, for example, 5 to 180 minutes, more preferably within a range of 7 to 150 minutes, and of this, the heat treatment time t5 to t6 at a temperature exceeding the Tg is preferably within a range of, for example, 1 to 30 minutes.

[0032] FIG. 2 shows a case where the maximum temperature Tmax of the heat treatment in step b is equal to or lower than the Tg of the non-thermoplastic polyimide. Thus, it is also preferable to set the maximum temperature Tmax of the heat treatment in step b equal to or lower than the Tg of the non-thermoplastic polyimide. As mentioned above, if the heat treatment is performed above the Tg, the polyimide molecular chains may adopt a random arrangement if the heat treatment time is extended, which may prevent the formation of a regular arrangement structure advantageous for achieving a low dielectric tangent. On the other hand, from the viewpoint of shortening the time of the imidization step, it is preferable to carry out the imidization at a temperature as high as possible within the range in which dimensional stability can be controlled. Therefore, when the maximum temperature Tmax of the heat treatment is set equal to or lower than the Tg of the non-thermoplastic polyimide, it is preferable to set the maximum temperature Tmax within the range of, for example, Tg-20°C or higher and Tg or lower, in order to ensure sufficient imidization while maintaining throughput. Furthermore, when the maximum temperature Tmax of the heat treatment is equal to or lower than the Tg of the non-thermoplastic polyimide, the heat treatment time is, on the premise that an ordered structure advantageous for reducing the dielectric tangent is formed in the polyimide chain, from the viewpoint of ensuring both throughput and suppressing foaming due to rapid evaporation of the solvent, preferably within a range of, for example, 5 to 180 minutes, more preferably within a range of 7 to 150 minutes, and of this, the heat treatment time at a temperature in the range of Tg-20°C or higher and Tg or lower is preferably within a range of, for example, 1 to 20 minutes.

[0033] In Figures 1 and 2, there is a clear period from t2 to t3 during which the temperature steadily changes at the maximum temperature Tmax, but this is not meant to be limiting. A temperature profile may also be one in which there is no steady temperature period, and the imidization process ends immediately after the maximum temperature Tmax is reached at t2 (i.e., t2 and t3 occur almost simultaneously), and the temperature starts to drop.

[0034] In step b), it is preferable to complete the imidization of the polyamic acid on the substrate. Since the polyamic acid-containing precursor layer is imidized while being fixed to the substrate, the expansion and contraction changes of the polyimide layer during the imidization process can be suppressed, and the thickness and dimensional changes of the polyimide film can be suppressed.

[0035] The polyimide film produced by the above method has a multi-layer laminate structure in which a thermoplastic polyimide layer containing a thermoplastic polyimide is laminated on one or both sides of a non-thermoplastic polyimide layer containing a non-thermoplastic polyimide. The resin component of the non-thermoplastic polyimide layer is preferably a non-thermoplastic polyimide. The resin component of the thermoplastic polyimide layer is preferably a thermoplastic polyimide. Here, "non-thermoplastic polyimide" generally refers to a polyimide that does not soften or exhibit adhesiveness even when heated. In the present invention, however, a non-thermoplastic polyimide having a storage modulus of 1.0 x 10 at 30°C measured using a dynamic viscoelasticity measuring apparatus (DMA) is used. 9 Pa or more, and the storage modulus at 300°C is 3.0 × 10 8 The term "thermoplastic polyimide" generally refers to a polyimide whose Tg can be clearly confirmed, but in the present invention, it refers to a polyimide whose storage modulus at 30°C measured by DMA is 1.0 × 10 9 Pa or more, and the storage modulus at 300°C is 3.0 × 10 8 Polyimides with a modulus of less than 1 Pa are also referred to as polyimides.

[0036] The polyimide film produced by the method of the present embodiment may be a single film (sheet), or may be laminated on a substrate such as a metal foil, a glass plate, or a resin sheet.

[0037] Furthermore, the polyimide film as a whole has a dielectric loss tangent (Tan δ) of 0.0045 or less, preferably 0.0040 or less, at 10 GHz, as measured using a split post dielectric resonator (SPDR). To improve the transmission loss of a circuit board, it is particularly important to control the dielectric loss tangent of the insulating resin layer. By controlling the dielectric loss tangent of a polyimide film used as an insulating resin layer within the above range, the effect of reducing transmission loss is enhanced. Therefore, when a polyimide film is used as an insulating resin layer of a high-frequency circuit board, for example, transmission loss can be efficiently reduced. If the dielectric loss tangent at 10 GHz exceeds 0.0045, when the polyimide film is used as an insulating resin layer of a circuit board, problems such as increased electrical signal loss in the transmission path of high-frequency signals are likely to occur. While there is no particular lower limit for the dielectric loss tangent at 10 GHz, consideration must be given to controlling the physical properties of the polyimide film when used as an insulating resin layer of a circuit board.

[0038] When the polyimide film is used as an insulating resin layer of a circuit board, for example, the film as a whole preferably has a relative dielectric constant of 4.0 or less at 10 GHz, more preferably 3.5 or less, in order to ensure impedance matching. If the relative dielectric constant at 10 GHz exceeds 4.0, when the polyimide film is used as an insulating resin layer of a circuit board, this leads to an increase in dielectric loss, which is likely to cause inconveniences such as an increase in the loss of electrical signals on the transmission path of high-frequency signals.

[0039] The thickness of the polyimide film to be produced can be set within a predetermined range depending on the purpose of use. The thickness of the polyimide film is preferably, for example, within the range of 8 to 75 μm, and more preferably within the range of 11 to 50 μm. If the thickness of the polyimide film is less than the above-mentioned lower limit, problems such as an inability to ensure electrical insulation or difficulty in handling during the production process due to reduced handleability may occur. On the other hand, if the thickness of the polyimide film exceeds the above-mentioned upper limit, problems such as reduced productivity may occur.

[0040] The thickness ratio of the non-thermoplastic polyimide layer to the entire polyimide film is preferably within the range of 70% to 97%, more preferably 75% to 95%. If this ratio is less than 70%, the thickness of the non-thermoplastic polyimide layer relative to the entire polyimide film will be too small, making it difficult to control the CTE and impairing dimensional stability. In addition, the difference in the progress of imidization and ordered structure formation between the non-thermoplastic polyimide layer and the thermoplastic polyimide layer will easily cause foaming due to the evaporation of residual solvent and condensed water accompanying the progress of imidization. If the ratio exceeds 97%, the thickness of the thermoplastic polyimide layer will be too small, easily reducing the reliability of adhesion between the polyimide film and the metal layer or circuit wiring layer.

[0041] The polyimide film has a CTE of 10 ppm / K or more and 30 ppm / K or less for the entire film. By keeping the CTE of the entire polyimide film within this range, it is possible to suppress warping and a decrease in dimensional stability when a metal-clad laminate is formed. Furthermore, if the CTE is less than 10 ppm / K or more than 30 ppm / K, warping and a decrease in dimensional stability may result in poor handling, which may lead to processing defects due to misalignment during wiring processing.

[0042] In the polyimide film, the non-thermoplastic polyimide layer constitutes a low-thermal expansion polyimide layer, and the thermoplastic polyimide layer constitutes a high-thermal expansion polyimide layer, where the low-thermal expansion polyimide layer preferably has a CTE in the range of 1 ppm / K to 25 ppm / K, more preferably 3 ppm / K to 25 ppm / K. The high thermal expansion polyimide layer preferably has a CTE of 35 ppm / K or more, more preferably in the range of 35 ppm / K to 80 ppm / K, and even more preferably in the range of 35 ppm / K to 70 ppm / K. The CTE of the polyimide layer can be controlled to a desired value by adjusting the combination of raw materials used, the thickness, the drying and curing conditions, etc., but in this embodiment, the CTE can be maintained within the above range while reducing the dielectric loss tangent by controlling the heat treatment conditions for imidization as described above.

[0043] The polyimide film obtained by the method of this embodiment may contain an inorganic filler or an organic filler in the non-thermoplastic polyimide layer or the thermoplastic polyimide layer, as necessary. Specific examples include inorganic fillers such as silicon dioxide, aluminum oxide, magnesium oxide, beryllium oxide, boron nitride, aluminum nitride, silicon nitride, aluminum fluoride, and calcium fluoride, and organic fillers such as fluorine-based polymer particles and liquid crystal polymer particles. These may be used alone or in combination of two or more.

[0044] Next, the polyimides constituting the non-thermoplastic polyimide layer and the thermoplastic polyimide layer will be described. As described above, polyimides are obtained by imidizing polyamic acid and are produced by reacting a specific acid anhydride with a diamine compound. Therefore, specific examples of non-thermoplastic polyimides and thermoplastic polyimides can be understood by explaining the acid anhydride and the diamine compound.

[0045] <Non-thermoplastic polyimide> (acid anhydride) The non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer preferably uses, as raw material acid anhydrides, at least one of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and 1,4-phenylenebis(trimellitic acid monoester) dianhydride (TAHQ), and at least one of pyromellitic dianhydride (PMDA) and 2,3,6,7-naphthalenetetracarboxylic dianhydride (NTCDA). In this case, the total amount of BPDA and TAHQ is preferably 20 mol% to 80 mol%, more preferably 20 mol% to 60 mol%, based on the total amount of all acid anhydrides, and the total amount of PMDA and NTCDA is preferably 20 mol% to 80 mol%, more preferably 40 mol% to 80 mol%, based on the total amount of all acid anhydrides.

[0046] Non-thermoplastic polyimides may contain acid anhydrides other than BPDA, TAHQ, PMDA, and NTCDA, such as 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 2,3',3,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-, 2,3,3',4'-, or 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,3',3,4'-diphenylethertetracarboxylic dianhydride, bis(2,3-dicarboxyphenyl)ether dianhydride, 3,3'',4,4''-, 2,3,3'',4''-, or 2,2'',3,3''-p-terphenyltetracarboxylic dianhydride, 2,2-bis(2,3- or 3,4-dicarboxyphenyl)propane dianhydride, bis(2,3- or 3,4-dicarboxyphenyl)propane dianhydride, and bis(2,3- or 3,4-dicarboxyphenyl)propane dianhydride.4-dicarboxyphenyl)methane dianhydride, bis(2,3- or 3,4-dicarboxyphenyl)sulfone dianhydride, 1,1-bis(2,3- or 3,4-dicarboxyphenyl)ethane dianhydride, 1,2,7,8-, 1,2,6,7- or 1,2,9,10-phenanthrenetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)tetrafluoropropane dianhydride, 2,3,5,6-cyclohexane dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylic acid Dianhydrides, 2,6- or 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,6,7-(or 1,4,5,8-)tetrachloronaphthalene-1,4,5,8-(or 2,3,6,7-)tetracarboxylic dianhydride, 2,3,8,9-, 3,4,9,10-, 4,5,10,11- or 5,6,11,12-perylene-tetracarboxylic dianhydride, cyclopentane-1,2,3,4-tetracarboxylic dianhydride, pyrazine-2,3,5,6-tetracarboxylic dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic dianhydride, thiophene-2,3,4,5-tetracarboxylic dianhydride, 4,4'-bis(2,3-dicarboxyphenoxy)diphenylmethane dianhydride, ethylene glycol Aromatic tetracarboxylic dianhydrides such as bisanhydrotrimellitate can be used as raw materials.

[0047] (diamine compounds) The non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer preferably contains 50 mol% or more, more preferably 70 mol% or more, and even more preferably 80 mol% or more of diamine components having a biphenyl skeleton in which two benzene rings are single-bonded, based on the total content of all diamine components in the raw materials. By including 50 mol% or more of biphenyl-type diamines in the total diamine content, the polyimide chains are more likely to have a regularly arranged structure, which is advantageous for achieving a low dielectric loss tangent. Furthermore, the CTE of the non-thermoplastic polyimide layer can be controlled within a range of 1 ppm / K to 25 ppm / K, achieving both a low dielectric loss tangent and high dimensional stability. If the biphenyl-type diamine content is less than 50 mol%, the CTE becomes too high, which can lead to warpage in the metal-clad laminate, resulting in poor handling during processing and reduced dimensional stability.

[0048] As the biphenyl type diamine, it is preferable to use a diamine compound represented by the general formula (A1).

[0049] [ka]

[0050] In general formula (A1), X independently represents an alkyl group having 1 to 3 carbon atoms which may be substituted with a fluorine atom, and n1 and n2 independently represent an integer of 1 to 4. In the above formula (A1), the hydrogen atoms in the two terminal amino groups may be substituted, for example, -NR2R3 (where R2 and R3 independently represent any substituent such as an alkyl group).

[0051] The diamine compound represented by general formula (A1) (hereinafter sometimes referred to as "diamine (A1)") is an aromatic diamine having a biphenyl skeleton, and because it has a rigid structure, it has the effect of imparting an ordered structure to the entire polymer. Examples of diamine (A1) include 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB), 2,2'-diethyl-4,4'-diaminobiphenyl (m-EB), 2,2'-n-propyl-4,4'-diaminobiphenyl (m-NPB), and 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl (TFMB).

[0052] The non-thermoplastic polyimide may be prepared by using, as a diamine compound other than the diamine (A1), for example, the diamine compounds represented by the general formulas (B1) to (B7) described later, as well as 1,4-diaminobenzene (p-PDA; paraphenylenediamine), 4,4'-diaminobiphenyl, 2,2'-diethoxy-4,4'-diaminobiphenyl (m-EOB), 2,2'-dipropoxy-4,4'-diaminobiphenyl (m-POB), 2,2'-divinyl-4,4'-diaminobiphenyl (VAB), 4-aminophenyl-4'-aminobenzoate (APAB), 4,4'- Diamino-p-terphenyl (DATP), 2,2-bis-[4-(3-aminophenoxy)phenyl]propane, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)biphenyl, bis[1-(3-aminophenoxy)]biphenyl, bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)]benzophenone, 9,9-bis[4-(3-aminophenoxy)phenyl]fluorene, 2,2-bis-[4-(4 -aminophenoxy)phenyl]hexafluoropropane, 2,2-bis-[4-(3-aminophenoxy)phenyl]hexafluoropropane, 3,3'-dimethyl-4,4'-diaminobiphenyl, 4,4'-methylenedi-o-toluidine, 4,4'-methylenedi-2,6-xylidine, 4,4'-methylene-2,6-diethylaniline, 3,3'-diaminodiphenylethane, 3,3'-diaminobiphenyl, 3,3'-dimethoxybenzidine, 3,3''-diamino-p-terphenyl, 4,4'-[1,4-phenylenebis(1-methylethyl) 4,4'-[1,3-phenylenebis(1-methylethylidene)]bisaniline, 4,4'-[1,3-phenylenebis(1-methylethylidene)]bisaniline, bis(p-aminocyclohexyl)methane, bis(p-β-amino-t-butylphenyl)ether, bis(p-β-methyl-δ-aminopentyl)benzene, p-bis(2-methyl-4-aminopentyl)benzene, p-bis(1,1-dimethyl-5-aminopentyl)benzene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2,4-bis(β-amino-t-butyl)toluene, 2,4-diaminotoluene, m-xylene-2,Aromatic diamine compounds such as 5-diamine, p-xylene-2,5-diamine, m-xylylenediamine, p-xylylenediamine, 2,6-diaminopyridine, 2,5-diaminopyridine, 2,5-diamino-1,3,4-oxadiazole, piperazine, 2'-methoxy-4,4'-diaminobenzanilide, 4,4'-diaminobenzanilide, 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene, and 6-amino-2-(4-aminophenoxy)benzoxazole, as well as aliphatic diamine compounds such as dimer acid-type diamines in which the two terminal carboxylic acid groups of a dimer acid are substituted with primary aminomethyl groups or amino groups, can be used as raw materials.

[0053] The CTE, storage modulus, tensile modulus, etc. of non-thermoplastic polyimides can be controlled by selecting the types of acid anhydrides and diamine compounds used as raw materials, or by selecting the molar ratios of the respective acid anhydrides and diamine compounds when two or more types of acid anhydrides and diamine compounds are used. Furthermore, when a non-thermoplastic polyimide has a plurality of polyimide structural units, they may be present as blocks or randomly, but are preferably present randomly.

[0054] The weight-average molecular weight of the non-thermoplastic polyimide is, for example, preferably in the range of 10,000 to 400,000, more preferably in the range of 50,000 to 350,000. If the weight-average molecular weight is less than 10,000, the film tends to have reduced strength and become brittle. On the other hand, if the weight-average molecular weight exceeds 400,000, the viscosity increases excessively, and defects such as uneven film thickness and streaks tend to occur during coating.

[0055] The non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer preferably has a Tg in the range of 280°C or more and 400°C or less, and more preferably in the range of 300°C or more and 380°C or less, in order to impart heat resistance and dimensional stability sufficient for mounting and to control the dielectric properties by the heat treatment temperature conditions.

[0056] <Thermoplastic polyimide> (acid anhydride) The thermoplastic polyimide constituting the thermoplastic polyimide layer can use, as the raw material acid anhydride, those exemplified as the acid anhydrides for the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer.

[0057] (Diamine compounds) The thermoplastic polyimide constituting the thermoplastic polyimide layer preferably uses, as a raw material diamine compound, diamine compounds represented by the general formulae (B1) to (B7).

[0058] [ka]

[0059] In formulas (B1) to (B7), R1 independently represents a monovalent hydrocarbon group or alkoxy group having 1 to 6 carbon atoms, linking groups A independently represent a divalent group selected from -O-, -S-, -CO-, -SO-, -SO2-, -COO-, -CH2-, -C(CH3)2-, -NH-, or -CONH-, and n1 independently represents an integer of 0 to 4. However, formula (B3) excluding those that overlap with formula (B2), and formula (B5) excluding those that overlap with formula (B4). Here, "independently" means that in one or more of formulas (B1) to (B7), multiple linking groups A, multiple R1s, or multiple n1s may be the same or different. In the above formulas (B1) to (B7), the hydrogen atoms in the two terminal amino groups may be substituted, for example, -NR2R3 (where R2 and R3 independently represent any substituent such as an alkyl group).

[0060] The diamine compounds represented by formulas (B1) to (B7) all have high flexibility and are thought to contribute to improving the flexibility of polyimide molecular chains. Therefore, the use of the diamine compounds represented by formulas (B1) to (B7) enhances the thermoplasticity of polyimide.

[0061] Examples of the diamine compound represented by formula (B1) include 3,3'-diaminodiphenylmethane, 3,3'-diaminodiphenylpropane, 3,3'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylpropane, 3,4'-diaminodiphenyl sulfide, 3,3'-diaminobenzophenone, and (3,3'-bisamino)diphenylamine.

[0062] Examples of the diamine compound represented by formula (B2) include 1,4-bis(3-aminophenoxy)benzene, 3-[4-(4-aminophenoxy)phenoxy]benzenamine, and 3-[3-(4-aminophenoxy)phenoxy]benzenamine.

[0063] Examples of the diamine compound represented by formula (B3) include 1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,3-bis(3-aminophenoxy)benzene (APB), 4,4'-[2-methyl-(1,3-phenylene)bisoxy]bisaniline, 4,4'-[4-methyl-(1,3-phenylene)bisoxy]bisaniline, and 4,4'-[5-methyl-(1,3-phenylene)bisoxy]bisaniline.

[0064] Examples of the diamine compound represented by formula (B4) include bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(3-aminophenoxy)phenyl]propane, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)]benzophenone, and bis[4,4'-(3-aminophenoxy)]benzanilide.

[0065] Examples of the diamine compound represented by formula (B5) include 4-[3-[4-(4-aminophenoxy)phenoxy]phenoxy]aniline, 4,4'-[oxybis(3,1-phenyleneoxy)]bisaniline, and the like.

[0066] Examples of the diamine compound represented by formula (B6) include 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), bis[4-(4-aminophenoxy)phenyl]ether (BAPE), bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS), and bis[4-(4-aminophenoxy)phenyl]ketone (BAPK).

[0067] Examples of the diamine compound represented by formula (B7) include bis[4-(3-aminophenoxy)]biphenyl, bis[4-(4-aminophenoxy)]biphenyl, and the like.

[0068] Thermoplastic polyimides are prepared by using at least one diamine compound selected from formulas (B1) to (B7) in an amount of at least 70 molar parts, preferably 70 to 99 molar parts, and more preferably 80 to 95 molar parts, per 100 molar parts of all diamine compounds. Because the diamine compounds represented by formulas (B1) to (B7) have flexible molecular structures, using at least one diamine compound selected from these compounds in an amount within the above range can improve the flexibility of the polyimide molecular chain and impart thermoplasticity. If the total amount of diamine compounds represented by formulas (B1) to (B7) is less than 70 molar parts per 100 molar parts of all diamine compounds, the polyimide will lack flexibility and will not exhibit sufficient thermoplasticity.

[0069] Furthermore, as a diamine compound used as a raw material for thermoplastic polyimides, a diamine compound represented by general formula (A1) is also preferred. The diamine compound represented by formula (A1) [diamine (A1)] is as described in the description of non-thermoplastic polyimides. For thermoplastic polyimides, diamine (A1) is preferably used in an amount ranging from 1 to 30 parts by mole, more preferably from 5 to 20 parts by mole. By using diamine (A1) in an amount within the above range, an ordered structure is formed throughout the polymer due to the rigid structure derived from the monomer, resulting in a polyimide that is thermoplastic yet has low gas permeability and moisture absorption and excellent long-term heat-resistant adhesiveness.

[0070] Diamine compounds other than those mentioned above can be used as raw materials for the thermoplastic polyimide as long as the effects of the invention are not impaired.

[0071] In thermoplastic polyimides, the CTE, tensile modulus, Tg, etc. can be controlled by selecting the types of acid anhydrides and diamine compounds used as raw materials, or by selecting the molar ratios of the respective acid anhydrides and diamine compounds when two or more types of acid anhydrides and diamine compounds are used. Furthermore, when a thermoplastic polyimide has a plurality of polyimide structural units, they may be present as blocks or randomly, but are preferably present randomly.

[0072] The weight-average molecular weight of the thermoplastic polyimide is preferably in the range of 10,000 to 400,000, and more preferably in the range of 50,000 to 350,000. If the weight-average molecular weight is less than 10,000, the film tends to have reduced strength and become brittle. On the other hand, if the weight-average molecular weight exceeds 400,000, the viscosity increases excessively, and defects such as uneven film thickness and streaks tend to occur during coating.

[0073] The thermoplastic polyimide constituting the thermoplastic polyimide layer preferably has a Tg in the range of 200°C or more and 350°C or less, more preferably in the range of 200°C or more and 320°C or less, in order to improve adhesion to the metal foil.

[0074] Furthermore, since thermoplastic polyimides are used as adhesive layers in insulating resins for circuit boards, for example, a completely imidized structure is most preferable in order to suppress copper diffusion. However, a portion of the polyimide may be in the form of an amic acid. The imidization rate can be determined by measuring the infrared absorption spectrum of a polyimide thin film using a Fourier transform infrared spectrophotometer (commercially available: FT / IR620 manufactured by JASCO) using the single-reflection ATR method, and determining the imidization rate at 1015 cm -1 Based on the benzene ring absorber near 1780cm -1 It is calculated from the absorbance of the C=O stretching derived from the imide group.

[0075] [Metal-clad laminate manufacturing method] The method for manufacturing a metal-clad laminate according to this embodiment is a method for manufacturing a metal-clad laminate comprising an insulating resin layer and a metal layer laminated on one or both sides of the insulating resin layer, wherein the insulating resin layer is a polyimide film manufactured by a method including the above-described steps a and b.

[0076] In the above step a, it is preferable to use a metal foil as a substrate and to form a precursor laminate by applying a solution containing a thermoplastic polyimide precursor and a solution containing a non-thermoplastic polyimide precursor onto the metal foil. The material of the metal foil is not particularly limited, but examples 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 copper alloys are particularly preferred.

[0077] Furthermore, the surface roughness Rzjis of the metal foil on the side to which the precursor solution is applied is preferably 1.2 μm or less, more preferably 1.0 μm or less. By making the surface roughness Rzjis of the metal foil 1.2 μm or less, fine wiring processing that corresponds to high-density mounting becomes possible, and conductor loss during high-frequency signal transmission can be reduced, making it applicable to circuit boards for high-frequency signal transmission. If the surface roughness Rzjis exceeds 1.2 μm, the wiring shape during fine wiring processing deteriorates, making processing difficult, and conductor loss increases, making it unsuitable for high-frequency signal transmission.

[0078] The thickness of the metal foil is not particularly limited, but when copper foil is used, it is preferably 35 μm or less, 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. Commercially available copper foil may be used as the copper foil. Furthermore, the metal foil may be surface-treated with, for example, siding, aluminum alcoholate, aluminum chelate, silane coupling agent, etc., for the purpose of, for example, rust prevention or improving adhesive strength.

[0079] [Circuit board manufacturing method] The method for manufacturing a circuit board according to this embodiment is a method for manufacturing a circuit board including an insulating resin layer and a wiring layer laminated on one or both sides of the insulating resin layer, in which the insulating resin layer is a polyimide film manufactured by a method including the above-described steps a and b. That is, the circuit board is obtained by wiring the metal layer of the metal-clad laminate. By processing the metal layer of the metal-clad laminate into a pattern by a conventional method to form a wiring layer (conductor circuit layer), a circuit board such as an FPC can be manufactured. [Example]

[0080] The features of the present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. In the following examples, various measurements and evaluations are as follows, unless otherwise specified.

[0081] [Viscosity measurement] The viscosity was measured at 25° C. using an E-type viscometer (manufactured by Brookfield, product name: DV-II+Pro). The rotation speed was set so that the torque was 10% to 90%, and the viscosity was read when the viscosity stabilized 2 minutes after the start of measurement.

[0082] [Measurement of relative permittivity and dielectric loss tangent] The resin sheet was left for 24 hours under conditions of a temperature of 23°C and a humidity of 50%, and then the relative permittivity (ε) and dielectric loss tangent (Tanδ) at a frequency of 10 GHz were measured using a vector network analyzer (manufactured by Agilent, product name: Vector Network Analyzer E8363C) and an SPDR resonator.

[0083] [Measurement of coefficient of thermal expansion (CTE)] Using a thermomechanical analyzer (manufactured by Bruker, product name: 4000SA), a 3 mm x 20 mm polyimide film was heated from 30°C to 265°C at a constant heating rate while applying a 5.0 g load, and then held at that temperature for 10 minutes. After that, the film was cooled at a rate of 5°C / min, and the average thermal expansion coefficient (linear thermal expansion coefficient) from 250°C to 100°C was determined. For polyimide films with a glass transition temperature lower than 250°C, the linear thermal expansion coefficient was determined from below the glass transition temperature to 100°C.

[0084] [Measurement of glass transition temperature] The glass transition temperature was determined by measuring a 5 mm x 20 mm polyimide film using a dynamic viscoelasticity measuring device (DMA: manufactured by UBM, product name: E4000F) from 30 °C to 400 °C at a heating rate of 4 °C / min and a frequency of 11 Hz. The temperature at which the change in elastic modulus (tan δ) reached a maximum was defined as the glass transition temperature. The storage modulus at 30 °C measured using DMA was 1.0 × 109 Pa or more, and the storage modulus at 300°C is 3.0 × 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 3.0 × 10 8 Those showing a thermal expansion coefficient of 100 Pa or more were categorized as "non-thermoplastic."

[0085] [Measurement of copper foil surface roughness] The ten-point average roughness (Rzjis) was measured using a stylus surface roughness meter (manufactured by Kosaka Laboratory Co., Ltd., product name: Surfcorder ET-3000) under the measurement conditions of Force: 100 μN, Speed: 20 μm, and Range: 800 μm. The surface roughness was calculated according to the method in accordance with JIS-B0601:1994.

[0086] The abbreviations used in the examples and comparative examples represent the following compounds. TPE-R: 1,3-bis(4-aminophenoxy)benzene TFMB: 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl m-TB: 2,2'-dimethyl-4,4'-diaminobiphenyl DAPE: 4,4'-diaminodiphenyl ether BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride PMDA: Pyromellitic dianhydride BTDA: 3,3',4,4'-benzophenonetetracarboxylic dianhydride DMAc: N,N-dimethylacetamide

[0087] (Synthesis Example 1) In a reaction vessel equipped with a stirrer and a nitrogen gas inlet tube, 178.010 parts by weight of TPE-R (0.609 mol), 32.318 parts by weight of m-TB (0.152 mol), and an amount of DMAc such that the solids concentration after polymerization was 12% by weight were added under nitrogen flow and stirred at room temperature to dissolve. Next, 159.117 parts by weight of BPDA (0.541 mol) and 50.555 parts by weight of PMDA (0.232 mol) were added, and the polymerization reaction was continued with stirring at room temperature for 24 hours to obtain polyamic acid solution a. The solution viscosity of polyamic acid solution a was 2,700 cps.

[0088] (Synthesis Example 2) Under a nitrogen stream, 139.923 parts by weight of TFMB (0.437 mol), 83.925 parts by weight of m-TB (0.395 mol), 60.825 parts by weight of TPE-R (0.208 mol), and an amount of DMAc such that the solids concentration after polymerization was 15% by weight were added to a reaction vessel similar to that of Synthesis Example 1, and the mixture was stirred at room temperature to dissolve. Next, 60.606 parts by weight of BPDA (0.206 mol) and 179.721 parts by weight of PMDA (0.824 mol) were added, and the mixture was stirred at room temperature for 24 hours to carry out the polymerization reaction, yielding polyamic acid solution b. The solution viscosity of polyamic acid solution b was 24,800 cps.

[0089] (Synthesis Example 3) Under a nitrogen stream, 164.240 parts by weight of DAPE (0.820 mol parts) and an amount of DMAc such that the solids concentration after polymerization was 12% by weight were added to a reaction vessel similar to that of Synthesis Example 1, and the mixture was stirred at room temperature to dissolve. Next, 237.869 parts by weight of BTDA (0.738 mol parts) and 17.891 parts by weight of PMDA (0.082 mol parts) were added, and the mixture was stirred at room temperature for 24 hours to carry out the polymerization reaction, yielding polyamic acid solution c. The solution viscosity of polyamic acid solution c was 4,200 cps.

[0090] (Production Example 1) Polyamic acid solution a was uniformly applied to copper foil and then heated to 120°C for 3 minutes to remove the solvent, resulting in a thickness of approximately 25 μm after heat treatment. The temperature was then raised stepwise from 130°C to 360°C to effect imidization, producing a single-sided copper-clad laminate. The copper foil of this single-sided copper-clad laminate was etched away using an aqueous ferric chloride solution to obtain a polyimide film with thermoplastic properties, a glass transition temperature of 244°C, and a CTE of 52.0 ppm / K from 230°C to 100°C.

[0091] (Production Example 2) A polyimide film was obtained in the same manner as in Preparation Example 1 except that polyamic acid solution b was used instead of polyamic acid solution a. The polyimide film was non-thermoplastic, had a glass transition temperature of 314°C, and a CTE of 17.1 ppm / K.

[0092] (Production Example 3) A polyimide film obtained in the same manner as in Preparation Example 1 except that polyamic acid solution c was used instead of polyamic acid solution a was thermoplastic, had a glass transition temperature of 282°C and a CTE of 55.1 ppm / K.

[0093] [Example 1] Polyamic acid solution a was uniformly applied to the surface of rolled copper foil (Rzjis; 0.4 μm) to a thickness of approximately 2 to 3 μm after curing, and then heated and dried at 140°C to remove the solvent. Next, polyamic acid solution b was uniformly applied thereon to a thickness of approximately 46 μm after curing, and then heated and dried at 90 to 120°C to remove the solvent. Polyamic acid solution a was further uniformly applied thereon to a thickness of approximately 2 to 3 μm after curing, and then heated and dried at 140°C to remove the solvent, yielding a metal laminate 1 provided with a polyamic acid film.

[0094] This metal laminate 1 with a polyamic acid film was subjected to heat treatment under the conditions shown in Table 1, including a stepwise temperature increase from 140°C to 360°C and a cooling process that began immediately after the maximum temperature was reached, for a total of 120.0 minutes to complete the imidization, thereby obtaining a single-sided metal-clad laminate 1 with a polyimide film. The heat treatment time at a temperature exceeding the glass transition temperature (314°C) of the non-thermoplastic polyimide obtained by heat-treating polyamic acid solution b was 25.0 minutes.

[0095] The copper foil of the obtained single-sided metal-clad laminate 1 was etched away using an aqueous ferric chloride solution to obtain a polyimide film 1. The obtained polyimide film 1 had a relative dielectric constant of 3.2, a dielectric dissipation factor of 0.0040, and a CTE of 21 ppm / K.

[0096] [Example 2] The metal laminate 1 provided with a polyamic acid film obtained in the same manner as in Example 1 was heated stepwise from 140°C to 300°C under the conditions shown in Table 1, and heat-treated for a total of 240.0 minutes to complete imidization, and then immediately cooled to obtain a single-sided metal-clad laminate 2 provided with a polyimide film. The heat treatment time at 294°C or higher, which is 20°C lower than the glass transition temperature (314°C) of non-thermoplastic polyimide, was 9.0 minutes.

[0097] The copper foil of the obtained single-sided metal-clad laminate 2 was etched away using an aqueous ferric chloride solution to obtain a polyimide film 2. The obtained polyimide film 2 had a relative dielectric constant of 3.2, a dielectric dissipation factor of 0.0042, and a CTE of 23 ppm / K.

[0098] [Example 3] Polyamic acid solution a was uniformly applied to the surface of rolled copper foil (Rzjis; 0.4 μm) to a thickness of approximately 2 to 3 μm after curing, and then heated and dried at 140°C to remove the solvent. Next, polyamic acid solution b was uniformly applied thereon to a thickness of approximately 46 μm after curing, and then heated and dried at 90 to 120°C to remove the solvent. Polyamic acid solution c was further uniformly applied thereon to a thickness of approximately 2 to 3 μm after curing, and then heated and dried at 140°C to remove the solvent, yielding a metal laminate 2 provided with a polyamic acid film.

[0099] This metal laminate 2 with a polyamic acid film was subjected to heat treatment under the conditions shown in Table 1, including a stepwise temperature increase from 140°C to 360°C and a cooling process that began immediately after the maximum temperature was reached, for a total of 120.0 minutes to complete the imidization, thereby obtaining a single-sided metal-clad laminate 3 with a polyimide film. The heat treatment time at temperatures above 314°C was 25.0 minutes.

[0100] The copper foil of the obtained single-sided metal-clad laminate 3 was etched away using an aqueous ferric chloride solution to obtain a polyimide film 3. The obtained polyimide film 3 had a relative dielectric constant of 3.2, a dielectric dissipation factor of 0.0042, and a CTE of 20 ppm / K.

[0101] [Example 4] The metal laminate 2 provided with a polyamic acid film obtained in the same manner as in Example 3 was subjected to a stepwise temperature increase from 140°C to 300°C under the conditions shown in Table 1, and heat treatment was carried out for a total of 240.0 minutes. After completing the imidization, the laminate was immediately cooled to obtain a single-sided metal-clad laminate 4 provided with a polyimide film. The heat treatment time at 294°C or higher, which is 20°C lower than the glass transition temperature (314°C) of the non-thermoplastic polyimide, was 9.0 minutes.

[0102] The copper foil of the obtained single-sided metal-clad laminate 4 was etched away using an aqueous ferric chloride solution to obtain a polyimide film 4. The obtained polyimide film 4 had a relative dielectric constant of 3.2, a dielectric dissipation factor of 0.0044, and a CTE of 21 ppm / K.

[0103] Comparative Example 1 The metal laminate 1 provided with a polyamic acid film obtained in the same manner as in Example 1 was subjected to a heat treatment for a total of 240.0 minutes under the conditions shown in Table 1, including a stepwise temperature increase from 140°C to 360°C and a part of a cooling process that started immediately after the maximum temperature was reached, to complete imidization and obtain a single-sided metal-clad laminate 5 provided with a polyimide film. The heat treatment time at a temperature above 314°C was 50.0 minutes.

[0104] The copper foil of the obtained single-sided metal-clad laminate 5 was etched away using an aqueous ferric chloride solution to obtain a polyimide film 5. The obtained polyimide film 5 had a relative dielectric constant of 3.2, a dielectric dissipation factor of 0.0099, and a CTE of 20 ppm / K.

[0105] Comparative Example 2 The metal laminate 2 provided with a polyamic acid film obtained in the same manner as in Example 3 was subjected to a heat treatment under the conditions shown in Table 1, which included a stepwise temperature increase from 140°C to 360°C and a cooling process that began immediately after the maximum temperature was reached, for a total of 240.0 minutes to complete the imidization, thereby obtaining a single-sided metal-clad laminate 6 provided with a polyimide film. The heat treatment time at a temperature exceeding 314°C was 50.0 minutes.

[0106] The copper foil of the obtained single-sided metal-clad laminate 6 was etched away using an aqueous ferric chloride solution to obtain a polyimide film 6. The obtained polyimide film 6 had a relative dielectric constant of 3.2, a dielectric dissipation factor of 0.0104, and a CTE of 18 ppm / K.

[0107] Comparative Example 3 Metal laminate 1 with a polyamic acid film obtained in the same manner as in Example 1 was subjected to a heat treatment for a total of 6.0 minutes under the conditions shown in Table 1, including a stepwise temperature increase from 140°C to 360°C and a cooling process that began immediately after the maximum temperature was reached, to complete imidization and obtain single-sided metal-clad laminate 7 with a polyimide film. The heat treatment time at a temperature exceeding 314°C was 0.4 minutes. The obtained single-sided metal-clad laminate 7 had bubbles on the entire surface, making it impossible to evaluate its characteristics.

[0108] The results of the above examples and comparative examples are shown in Table 1.

[0109] [Table 1]

[0110] The results of the Examples and Comparative Examples show that the dielectric loss tangent varies greatly depending on the glass transition temperature of the non-thermoplastic polyimide layer and the heat treatment temperature and time. Comparative Examples 1 and 2, in which heat treatment was performed for 50 minutes or longer at a temperature above the glass transition temperature, resulted in a significant deterioration in the dielectric loss tangent, and Comparative Example 3, in which heat treatment was performed for a short time of 0.4 minutes at a temperature above the glass transition temperature, resulted in foaming. Therefore, by applying the heat treatment conditions of the present invention, it is possible to produce a polyimide film with good appearance, a CTE of 10 to 30 ppm / K, and a dielectric loss tangent of 0.0045 or less.

[0111] 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.

Claims

1. A method for producing a polyimide film in which a thermoplastic polyimide layer containing a thermoplastic polyimide is laminated on one or both sides of a non-thermoplastic polyimide layer containing a non-thermoplastic polyimide, the method comprising: Steps a and b below: a) forming a precursor laminate including a first precursor layer containing a precursor of the thermoplastic polyimide and a second precursor layer containing a precursor of the non-thermoplastic polyimide; b) heat-treating the precursor laminate to imidize the precursor to form the thermoplastic polyimide layer and the non-thermoplastic polyimide layer; Including, the polyimide film as a whole has a dielectric loss tangent of 0.0045 or less at a frequency of 10 GHz and a CTE in the range of 10 ppm / K or more and 30 ppm / K or less; the CTE of the non-thermoplastic polyimide layer is in the range of 1 ppm / K or more and 25 ppm / K or more, and the CTE of the thermoplastic polyimide layer is 35 ppm / K or more; a maximum temperature of the heat treatment in the step (b) being 300°C or lower, a temperature within the range of not lower than the glass transition temperature (Tg) of the non-thermoplastic polyimide minus 20°C but not higher than the Tg, and a heat treatment time at the glass transition temperature (Tg) or higher minus 20°C being within the range of 1 to 20 minutes.

2. 2. The method for producing a polyimide film according to claim 1, wherein the non-thermoplastic polyimide constituting the non-thermoplastic polyimide layer is obtained by reacting an acid anhydride component with a diamine component, and the proportion of the diamine component having a biphenyl skeleton to the total of all the diamine components is 50 mol % or more.

3. 3. The method for producing a polyimide film according to claim 1, wherein the thickness ratio of the non-thermoplastic polyimide layer to the entire thickness of the film is in the range of 70% to 97%.

4. A method for manufacturing a metal-clad laminate comprising an insulating resin layer and a metal layer laminated on one or both sides of the insulating resin layer, A method for producing a metal-clad laminate, wherein the insulating resin layer is a polyimide film produced by the method for producing a polyimide film according to any one of claims 1 to 3.

5. 5. The method for producing a metal-clad laminate according to claim 4, wherein the step a) forms the precursor laminate by applying a solution containing a precursor of the thermoplastic polyimide and a solution containing a precursor of the non-thermoplastic polyimide onto a metal foil having a surface roughness Rzjis of 1.2 μm or less.

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