Laminate, single-sided metal-clad laminate, and multilayer printed wiring board

Abstract

This laminate (101) comprises: a multilayer polyimide film (1) having thermoplastic polyimide layers (11, 12) on both sides of a core layer (10) which is a non-thermoplastic polyimide film; and a surface layer (2) in contact with the plastic polyimide layer (12) on one surface side of the multilayer polyimide film. The surface layer is preferably an inorganic layer having a thickness of 1-200 nm or a resin layer having a thickness of 0.1-5 μm. This single-sided metal-clad laminated sheet (105) is formed by laminating a metal layer (5) on the thermoplastic resin layer (11) on the surface layer non-formed surface side of said laminate.

Description

[Technical Field]

[0001] The present invention relates to a laminate having a surface layer on one side of a multilayer polyimide film, and a single-sided metal-clad laminate.Furthermore, the present invention relates to a multilayer printed wiring board produced using the single-sided metal-clad laminate. [Background technology]

[0002] Various types of printed wiring boards are used in electronic devices. Printed wiring boards have metal wiring made by patterning metal layers such as copper on an insulating substrate, and flexible printed wiring boards (FPCs) that use heat-resistant resin films such as polyimide film as the insulating substrate have been put to practical use. As electronic devices become more powerful and smaller, progress is being made in the development of multilayer flexible printed wiring boards, which are made by stacking multiple wiring layers with insulating layers between them.

[0003] FPCs are manufactured using double-sided metal-clad laminates, in which metal foil such as copper is laminated on both sides of a polyimide film, and single-sided metal-clad laminates, in which metal foil is laminated on one side of a polyimide film.A known method for manufacturing double-sided metal-clad laminates is to use a multilayer polyimide film with thermoplastic resin layers that function as adhesive layers on both sides of a non-thermoplastic polyimide film (core layer), and then laminate metal foil on both sides of the multilayer polyimide film by thermal lamination.

[0004] In the manufacture of multilayer flexible printed wiring boards, when double-sided metal-clad laminates are stacked together to form a multilayer, the metal foils are laminated in contact with each other. For this reason, single-sided metal-clad laminates are mainly used to manufacture multilayer FPCs. Multilayering is achieved by patterning the metal foil (metal layer) of the single-sided metal-clad laminate to form wiring, and then laminating a substrate with a wiring layer on one side of a polyimide film insulating layer via an adhesive sheet such as a bonding sheet.

[0005] When a single-sided metal-clad laminate is formed by laminating a metal foil on one side of a multilayer polyimide film having a core layer with thermoplastic resin layers on both sides, problems such as the thermoplastic resin layer on the side not having the metal foil laminated thereon being fused to a heated roll or the like may occur during lamination or in the manufacturing process of a printed wiring board.

[0006] Patent Document 1 describes that in the production of a single-sided metal-clad laminate in which metal foil is laminated on one side of a multilayer polyimide film having thermoplastic resin layers on both sides of a core layer, the use of a polyimide having a specific structure as the material for the thermoplastic resin layer on the side not laminated with the metal foil can prevent fusion to a metal roll, etc. Patent Document 2 proposes a method for producing a single-sided metal-clad laminate in which metal foil is placed on one side of a multilayer polyimide film and a release film is placed on the other side, and then thermally laminated. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-176931 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-109694 Summary of the Invention [Problem to be solved by the invention]

[0008] As in Patent Document 1, in a multilayer polyimide film having thermoplastic polyimide layers of different compositions on the front and back of a core layer, warping may occur in the multilayer polyimide film itself or in a single-sided metal-clad laminate having a metal foil laminated on one side due to differences in the behavior of dimensional changes upon heating (e.g., coefficient of linear thermal expansion) of the thermoplastic resin layers on the front and back.

[0009] As proposed in Patent Document 2, temporarily laminating a release film on the side on which the metal foil is not laminated can prevent the thermoplastic resin from fusing to a heated roll or the like when thermally laminating the metal foil onto the multilayer polyimide film. However, with the release film attached, warping may occur in the single-sided metal-clad laminate due to differences in the stress balance between the front and back sides. Furthermore, when a printed wiring board is produced using the single-sided metal-clad laminate, the release film is peeled off to expose the thermoplastic resin layer, which may cause problems with fusing of the thermoplastic resin layer during the process.

[0010] In the manufacturing process of multilayer printed wiring boards, holes are made by punching, mechanical drilling, laser processing, etc. before and after multilayering in order to provide electrical continuity between metal wirings, etc. When the thermoplastic resin layer of a multilayer polyimide film is exposed or when a bonding sheet is directly attached to the thermoplastic resin layer, problems such as poor processing or difficulty in removing cut pieces may occur during drilling.

[0011] In view of the above, an object of the present invention is to provide a laminate that can be used as a film substrate for single-sided metal-clad laminates, and that can suppress defects such as fusion associated with the thermoplastic resin layer on the non-metal foil laminated surface and the occurrence of warping during the manufacturing process of single-sided metal-clad laminates and multilayer printed wiring boards. [Means for solving the problem]

[0012] One embodiment of the present invention is a laminate having a surface layer on one side of a multilayer polyimide film, and by laminating a metal layer on the surface-free side of this laminate, a single-sided metal-clad laminate is formed.

[0013] The multilayer polyimide film has a thermoplastic polyimide layer on both sides of a core layer which is a non-thermoplastic polyimide film. The thermoplastic polyimide layers on the front and back of the core layer may have the same composition. In the laminate, the surface layer is in contact with the thermoplastic polyimide layer on one side of the multilayer polyimide film. The surface layer may be an inorganic layer or an organic layer (resin layer).

[0014] When the surface layer is an inorganic layer, its material is preferably a ceramic material such as silicon oxide, etc. The thickness of the inorganic surface layer is preferably 1 to 200 nm.

[0015] When the surface layer is a resin layer, its thickness is preferably 0.1 to 5 μm. Examples of resin materials for the resin surface layer include thermoplastic and non-thermoplastic resin materials. When the resin surface layer is a thermoplastic resin layer, it preferably has a higher glass transition temperature than the thermoplastic resin layer of the multilayer polyimide film. The resin material may be polyimide. The resin material may be a thermosetting resin such as an epoxy resin.

[0016] Single-sided metal-clad laminates are used to form flexible printed wiring boards. The printed wiring board may be a multilayer printed wiring board in which multiple wiring layers are laminated with insulating layers interposed between them. The metal layer of the single-sided metal-clad laminate is patterned to form a wiring layer, and the surface layer of this board (the surface on which the metal layer is not formed) is bonded to the wiring layer of another board, thereby forming a multilayer board. The surface layer and the wiring layer of the other board may be bonded together via an adhesive sheet such as a bonding sheet. [Effects of the Invention]

[0017] A single-sided metal-clad laminate having a metal layer on one side of a multilayer polyimide film and the above-mentioned surface layer on the other side is suppressed in warping. Furthermore, because the surface layer is provided on the thermoplastic resin layer of the multilayer polyimide film, defects caused by fusion of the thermoplastic resin layer can be suppressed not only during lamination of the metal layer onto the multilayer polyimide film but also during the manufacturing process of a printed wiring board. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a cross-sectional view of a laminate according to one embodiment. [Figure 2] 1 is a cross-sectional view of a single-sided metal-clad laminate according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] 1 is a cross-sectional view of a laminate according to one embodiment of the present invention, which has a surface layer 2 on one side of a multilayer polyimide film 1. The multilayer polyimide film 1 has thermoplastic resin layers 11 and 12 on both sides of a core layer 10. The laminate 101 has the surface layer 2 in contact with the thermoplastic resin layer 12 of the multilayer polyimide film 1.

[0020] 2 is a cross-sectional view of a single-sided metal-clad laminate according to one embodiment of the present invention, in which a metal layer 5 is laminated on the thermoplastic resin layer 11 of the above-mentioned laminate 101. That is, the single-sided metal-clad laminate 105 has a metal layer 5 on the thermoplastic resin layer 11 on one side of the multilayer polyimide film 1, and a surface layer 2 on the thermoplastic resin layer 12 on the other side of the multilayer polyimide film 1 (the side on which the metal layer 5 is not laminated).

[0021] [Laminate structure] <Multi-layer polyimide film> Laminate 101 according to one embodiment of the present invention is a film substrate used to form a single-sided metal-clad laminate, and includes a surface layer 2 on the non-metal layer side of multilayer polyimide film 1. Multilayer polyimide film 1 has a three-layer structure, with thermoplastic resin layers 11 and 12 on both sides of non-thermoplastic polyimide core layer 10.

[0022] (core layer) The core layer 10 is required to be able to withstand the heating temperatures encountered during thermal lamination in the manufacturing process of a printed wiring board. For this reason, a polyimide that does not have thermoplastic properties (non-thermoplastic polyimide) is used as the material for the core layer 10. The core layer 10 preferably contains 80% by weight or more, and more preferably 90% by weight or more, of non-thermoplastic polyimide.

[0023] "Non-thermoplastic polyimides" are polyimides that do not soften or exhibit adhesive properties when heated. Specifically, "non-thermoplastic polyimides" include polyimides that retain their shape without wrinkling or stretching when a single layer of polyimide is heated at 450°C for 2 minutes, and polyimides that do not substantially exhibit a glass transition temperature. The glass transition temperature is the temperature at which the storage modulus measured using a dynamic mechanical analyzer (DMA) shows an inflection point. A resin material that "does not substantially have a glass transition temperature" refers to one that begins thermal decomposition before reaching a glass transition state.

[0024] Polyimides are generally obtained by preparing a polyimide precursor (polyamic acid) by polymerizing a diamine and a tetracarboxylic dianhydride, and then imidizing the polyamic acid by dehydration and ring closure. In preparing non-thermoplastic polyimides, a combination of an aromatic diamine and an aromatic tetracarboxylic dianhydride is preferably used as the monomer.

[0025] Examples of aromatic diamines include 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 2,2-bis{4-(4-aminophenoxy)phenyl}propane, 2,2-bis{4-(4-aminophenoxy)phenyl}hexafluoropropane, bis{4-(3-aminophenoxy)phenyl}sulfone, bis{4-(4-aminophenoxy)phenyl}sulfone, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, and 3,3'-dichlorobenzyl. Examples of aromatic diamines include benzidine, 3,3'-dimethylbenzidine, 2,2'-dimethylbenzidine, 3,3'-dimethoxybenzidine, 2,2'-dimethoxybenzidine, 1,4-diaminobenzene (p-phenylenediamine), 1,3-diaminobenzene (m-phenylenediamine), 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 9,9-bis(4-aminophenyl)fluorene, 4,4'-(1,4-phenylenebis(1-methylethylidene))bisaniline, 4,4'-(1,3-phenylenebis(1-methylethylidene))bisaniline, 4,4'-diaminobenzanilide, and 2,2'-dimethylbiphenyl-4,4'-diamine. Two or more aromatic diamines may be used.

[0026] Examples of aromatic tetracarboxylic dianhydrides include 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, 3,4'-oxyphthalic dianhydride, ethylene bis(trimellitic acid monoester acid anhydride), bisphenol A bis(trimellitic acid monoester acid anhydride), pyromellitic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 3,3',4,4 Examples of aromatic tetracarboxylic acid dianhydrides include 3,3',4,4'-dimethyldiphenylsilane tetracarboxylic acid dianhydride, 3,3',4,4'-tetraphenylsilane tetracarboxylic acid dianhydride, 1,2,3,4-furan tetracarboxylic acid dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenylpropane dianhydride, 4,4'-hexafluoroisopropylidenediphthalic anhydride, 3,3',4,4'-biphenyl tetracarboxylic acid dianhydride, 2,3,3',4'-biphenyl tetracarboxylic acid dianhydride, p-phenylene bis(trimellitic acid monoester anhydride), and p-phenylene diphthalic anhydride. Two or more aromatic tetracarboxylic acid dianhydrides may be used.

[0027] Polyamic acid can be obtained by reacting diamine and tetracarboxylic dianhydride in substantially equimolar amounts. The order of addition, the combination of monomers, and the composition are not particularly limited. The organic solvent used for the polymerization of polyamic acid is not particularly limited, as long as it dissolves diamine, tetracarboxylic dianhydride, and polyamic acid. Preferred organic solvents are amide solvents such as N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone. The polymerization temperature is preferably -10°C to 50°C. The reaction time is not particularly limited, but is usually several minutes to several hours. The solids concentration of the polyamic acid solution is usually 5 to 35% by weight, preferably 10 to 30% by weight.

[0028] Polyimides are obtained by imidizing (dehydrating and cyclizing) polyamic acid as a polyimide precursor. During imidization, a curing agent may be added to the polyamic acid solution. Examples of curing agents include dehydrating agents and imidization catalysts. Examples of dehydrating agents include aliphatic acid anhydrides, aromatic acid anhydrides, N,N'-dialkylcarbodiimides, lower aliphatic halides, halogenated lower aliphatic acid anhydrides, arylsulfonic acid dihalides, and thionyl halides. Examples of imidization catalysts include aliphatic tertiary amines, aromatic tertiary amines, and heterocyclic tertiary amines.

[0029] The core layer may contain a filler in addition to the non-thermoplastic polyimide resin, such as silica, titanium oxide, alumina, silicon nitride, boron nitride, calcium hydrogen phosphate, calcium phosphate, and mica.

[0030] (thermoplastic resin layer) Examples of materials for the thermoplastic resin layers 11 and 12 provided on both sides of the core layer 10 include polycarbonate resins, acrylonitrile-styrene copolymer resins, and thermoplastic polyimide resins. Among these, thermoplastic polyimide resins are preferred from the viewpoints of heat resistance and adhesion to the core layer. The thermoplastic resin layers 11 and 12 preferably contain 50% by weight or more of thermoplastic polyimide resin.

[0031] From the viewpoint of suppressing warping by matching the linear expansion coefficient of the entire multilayer polyimide film 1 and simplifying the manufacturing process, it is preferable that the thermoplastic resin layer 11 provided on one side (first main surface) of the core layer 10 and the thermoplastic resin layer 12 provided on the other side (second main surface) of the core layer 10 have the same composition.

[0032] From the viewpoint of adhesion to the metal layer 5 and heat resistance, the thermoplastic polyimide resin layers 11 and 12 preferably have a glass transition temperature in the range of 150°C to 320°C. The glass transition temperature of the thermoplastic polyimide resin layers 11 and 12 may be 200°C to 300°C.

[0033] Thermoplastic polyimides, like non-thermosetting polyimides, are obtained by dehydration ring closure of polyamic acid as a polyimide precursor. In preparing thermoplastic polyimides, a combination of aromatic diamines and aromatic tetracarboxylic dianhydrides is preferably used as monomers. The properties of the polyimide can be adjusted by selecting the diamine and tetracarboxylic dianhydride.

[0034] Generally, as the proportion of rigid aromatic diamine used increases, the glass transition temperature increases, which in turn increases the storage modulus at high temperatures and tends to result in poor adhesion and processability. Examples of thermoplastic polyimide resin compositions include those using tetracarboxylic dianhydrides such as benzophenone tetracarboxylic dianhydride, biphenyl tetracarboxylic dianhydride, oxydiphthalic dianhydride, and biphenyl sulfone tetracarboxylic dianhydride, and aromatic diamines having aminophenoxy groups as diamines. The proportion of rigid aromatic diamines in the diamines used to prepare thermoplastic polyimides is preferably 40 mol% or less, more preferably 30 mol% or less, and even more preferably 20 mol% or less.

[0035] (Preparation of multilayer polyimide film) There are no particular limitations on the method for producing the multilayer polyimide film 1 having the thermoplastic resin layers 11 and 12 on both sides of the core layer 10. Examples include a method of sequentially or simultaneously forming the thermoplastic resin layers on both main surfaces of the core layer 10, and a method of co-extruding the material for the core layer 10 and the materials for the thermoplastic resin layers 11 and 12 from a multilayer die.

[0036] Polyimides obtained by imidizing polyamic acids obtained by polymerization of aromatic diamines and aromatic tetracarboxylic dianhydrides have low solubility in organic solvents after imidization. Therefore, in forming the core layer 10 and the thermoplastic resin layers 11 and 12, it is preferable to form a polyamic acid solution (polyimide precursor) into a film and then perform imidization.

[0037] When preparing a multilayer polyimide film by multilayer coextrusion, it is preferable to apply a polyamic acid solution serving as a precursor of the non-thermoplastic polyimide constituting the core layer 10 and a polyamic acid solution serving as a precursor of the thermoplastic polyimide constituting the thermoplastic resin layers 11 and 12 to a support substrate in the form of a film by three-layer coextrusion, heat the film if necessary to remove the solvent, and then further heat the film to perform imidization. As described above, a curing agent may be added to the polyamic acid solution to promote imidization. In the case of three-layer coextrusion, the curing agent may be added only to the polyimide precursor of the core layer 10, or may be added to both the polyimide precursor of the core layer 10 and the polyimide precursor of the thermoplastic resin layers 11 and 12. The polyimides of the core layer 10 and the thermoplastic resin layers 11 and 12 may be completely imidized or may contain a portion of an unimidized structure (open-ring polyamic acid).

[0038] The thickness of the core layer 10 and the thermoplastic resin layers 11 and 12 are not particularly limited, but it is preferable to adjust the balance of the thicknesses taking into consideration the linear expansion coefficient of each layer, etc., so as to prevent warping in the state of the multilayer polyimide film 1.

[0039] The thickness of the core layer 10 is preferably 3 to 50 μm, more preferably 5 to 40 μm. The thickness of each of the thermoplastic resin layers 11 and 12 is preferably 0.5 to 15 μm, more preferably 1 to 10 μm. The thicknesses of the thermoplastic resin layers 11 and 12 provided on both sides of the core layer 10 may be the same or different. From the viewpoint of suppressing warping, it is preferable that the difference in thickness between the thermoplastic resin layer 11 and the thermoplastic resin layer 12 is small. The ratio of the thickness of the thermoplastic resin layer 11 to the thickness of the thermoplastic resin layer 12 is preferably 0.7 to 1.3, more preferably 0.8 to 1.2, and even more preferably 0.9 to 1.1.

[0040] The thickness of each of the thermoplastic resin layers 11, 12 is preferably 0.05 to 0.5 times, or may be about 0.1 to 0.4 times, the thickness of the core layer 10. The total thickness of the multilayer polyimide film 1 is preferably 4 to 65 μm, and more preferably 5 to 55 μm.

[0041] Commercially available multilayer polyimide films having thermoplastic resin layers on both sides of a core layer may also be used. Kaneka's "Pixio" series is an example of a three-layer polyimide film having a non-thermoplastic polyimide core layer and thermoplastic polyimide layers on both sides.

[0042] <Surface layer> A surface layer 2 is formed on the thermoplastic resin layer 12 on one side of the multilayer polyimide film 1 to obtain a laminate 101. By providing the surface layer 2, the thermoplastic resin layer 12 is not exposed on the surface, which can suppress problems caused by fusion of the thermoplastic resin layer 12 during thermal lamination when laminating the metal layer 5 on the thermoplastic resin layer 11 or during heating in the manufacturing process of a printed wiring board.

[0043] The surface layer 2 preferably does not soften or exhibit adhesiveness when heated during thermal lamination of metal foil, thermal lamination when laminating the metal layer 5 onto the thermoplastic resin layer 11, or during the manufacturing process of a printed wiring board. The surface layer 2 may be an inorganic layer or an organic layer (resin layer) as long as it has the above-mentioned heat resistance. From the viewpoint of suppressing warping of the laminate 101 and the single-sided metal-clad laminate 105, the thickness of the surface layer 2 is preferably 5 μm or less. When the surface layer 2 is an inorganic layer, the thickness is preferably 1 to 200 nm. When the surface layer is a resin layer, the thickness is preferably 0.1 to 5 μm.

[0044] (Inorganic surface layer) Inorganic materials for the surface layer 2 include metals such as Si, Ge, Sn, Pb, Al, Ga, In, Tl, As, Sb, Bi, Se, Te, Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, and Cd, as well as alloys thereof, and ceramic materials such as metal nitrides, oxides, and oxynitrides.

[0045] In a single-sided metal-clad laminate and a printed wiring board using the same, the surface layer 2 is laminated and integrated on the thermoplastic resin layer 12 as it is. Therefore, the surface layer 2 is preferably an insulating material, and as the material of the inorganic surface layer, a ceramic material is preferred. Also, a ceramic material is preferred from the viewpoints of chemical stability and mechanical strength.

[0046] Among ceramic materials, oxides are preferred from the viewpoints of insulation, heat resistance, and chemical stability, and silicon oxide is particularly preferred. The silicon oxide may be silicon dioxide (SiO2) having a stoichiometric composition, or may be SiOx (0 < x < 2) in which oxygen is deficient compared to the stoichiometric composition. Silicon oxide with a non-stoichiometric composition is preferred because of its excellent toughness. In the non-stoichiometric composition silicon oxide: SiOx, x is preferably about 1.2 to 1.95, and may also be about 1.2 to 1.9 or about 1.3 to 1.8.

[0047] As described above, the thickness of the inorganic surface layer is preferably 1 to 200 nm. If the thickness is 1 nm or more, the entire surface of the thermoplastic resin layer 12 can be uniformly covered. If the thickness is 200 nm or less, warping is suppressed, and the inorganic surface layer is excellent in flexibility, and the occurrence of cracks and fractures tends to be suppressed. From the viewpoint of reliably covering the entire surface of the thermoplastic resin layer 12, the thickness of the inorganic surface layer is preferably 2 nm or more, more preferably 3 nm or more, and may also be 5 nm or more or 10 nm or more. From the viewpoint of suppressing cracks and fractures, the thickness of the inorganic surface layer is preferably 150 nm or less, more preferably 100 nm or less, and may also be 80 nm or less or 50 nm or less.

[0048] The method for forming the inorganic surface layer is not particularly limited, but dry coating such as sputtering, vacuum evaporation, ion plating, CVD method, etc. is preferred because it is easy to form a uniform film.

[0049] [[ID=!5]] (Resin surface layer)[[ID=!7]] The resin material of the surface layer 2 is not particularly limited as long as it has the above-mentioned heat resistance, and may be either a thermoplastic resin or a non-thermoplastic resin, or may be a mixed resin material of a thermoplastic resin and a non-thermoplastic resin. The resin surface layer may be formed by heat curing or photocuring.

[0050] When the surface layer 2 is a thermoplastic resin layer, from the viewpoint of suppressing softening and fusion due to heating, the surface layer 2 preferably has a glass transition temperature higher than that of the thermoplastic resin layer 12 of the multilayer polyimide film 1. The glass transition temperature of the surface layer 2 is preferably at least 10°C higher, and more preferably at least 15°C higher, than the glass transition temperature of the thermoplastic resin layer 12. The glass transition temperature of the surface layer, which is a thermoplastic resin layer, is preferably at least 200°C, more preferably at least 250°C, and may be at least 280°C or at least 300°C.

[0051] Polyimide is preferably used as a thermoplastic resin having such a high glass transition temperature. When the surface layer 2 is a thermoplastic polyimide resin layer, a thermoplastic polyimide having a higher glass transition temperature can be prepared by, for example, increasing the proportion of an aromatic monomer that is more rigid than the polyimide that constitutes the thermoplastic resin layer 12 of the multilayer polyimide film 1.

[0052] When the surface layer 2 is a non-thermoplastic resin layer, a non-thermoplastic polyimide is preferably used because of its high heat resistance. Non-thermoplastic polyimide is as described above as the material for the core layer 10. When the surface layer 2 is a non-thermoplastic polyimide resin layer, the composition of the core layer 10 and the composition of the surface layer 2 may be the same or different.

[0053] As described above, the resin material of the surface layer 2 may be a mixed resin material of a thermoplastic resin and a non-thermoplastic resin. The mixing ratio of the thermoplastic resin and the non-thermoplastic resin may be adjusted taking into consideration the heat resistance of the surface layer, etc.

[0054] The resin material of the surface layer 2 may be a thermosetting resin such as an epoxy or acrylic resin. From the viewpoint of heat resistance, the thermosetting resin of the surface layer 2 is preferably in a cured state (a state after thermal curing).

[0055] The surface layer 2, which is a resin layer, may have surface irregularities formed by adding an inorganic or organic filler from the viewpoint of suppressing fusion and blocking.

[0056] As described above, the thickness of the resin surface layer is preferably 0.1 to 5 μm. If the thickness is 0.1 μm or more, the entire surface of the thermoplastic resin layer 12 can be uniformly covered. If the thickness is 5 μm or less, warping tends to be suppressed. From the viewpoint of reliably covering the entire surface of the thermoplastic resin layer 12, the thickness of the resin surface layer is preferably 0.2 μm or more, and may be 0.3 μm or more. From the viewpoint of suppressing warping, the thickness of the resin surface layer is preferably 4 μm or less, more preferably 3 μm or less, and may be 2 μm or less, 1.5 μm or less, or 1 μm or less.

[0057] The method for forming the resin surface layer is not particularly limited. For example, the resin surface layer 2 can be formed by coating a resin solution on the thermoplastic resin layer 12 of the multilayer polyimide film 1, and then heating it as necessary to remove the solvent. When producing the multilayer polyimide film, a laminate including the resin surface layer 2 may be formed by multilayer coextrusion of four layers, namely the thermoplastic resin layer 11, the core layer 10, and the thermoplastic resin layer 12, plus the surface layer 2.

[0058] When the resin material is polyimide, a polyamic acid solution (polyimide precursor) may be applied as a resin solution, and then imidized by heating, etc. When the resin material is a thermosetting resin or a photocurable resin, the resin material may be cured by heating or by irradiating with actinic rays.

[0059] After laminating the metal layer 5 on the thermoplastic resin layer 11 of the multilayer polyimide film 1, the surface layer 2 may be formed on the thermoplastic resin layer 12. For example, if the surface layer 2 has surface irregularities due to a filler, the surface irregularities can be maintained by forming the surface layer 2 after laminating the metal layer 5 by thermal lamination, which can contribute to suppressing fusion and blocking on the surface without the metal layer when a printed wiring board is produced using the single-sided metal-clad laminate.

[0060] (Function of the surface layer) Regardless of whether the surface layer 2 is an inorganic layer or a resin layer, the surface layer 2 is a layer that is laminated integrally onto the thermoplastic resin layer 12 as is in the printed wiring board. In a multilayer printed wiring board, another wiring board (a wiring layer thereof) is bonded to the surface of the surface layer 2 via an adhesive sheet such as a bonding sheet. That is, even after the metal layer 5 is laminated onto the thermoplastic resin layer 11, the surface layer 2 is not peeled off from the thermoplastic resin layer 12 and remains included in the printed wiring board as is. From the viewpoint of thinning the printed wiring board, it is preferable that the thickness of the surface layer 2 is as small as possible within a range that can protect the surface of the thermoplastic resin layer 12 and suppress fusion, etc.

[0061] If the surface layer 2 is provided, when a multilayer printed wiring board is produced using the single-sided metal-clad laminate, the thermoplastic resin layer 12 will not come into contact with an adhesive sheet such as a bonding sheet. Therefore, even if the thermoplastic resin layer 12 is softened and becomes adhesive by heating such as heat pressing, fusion between the thermoplastic resin layer 12 and the adhesive sheet can be prevented. Therefore, when processing such as drilling is performed, processed pieces (cut pieces) can be easily removed.

[0062] [Single-sided metal-clad laminate] A single-sided metal-clad laminate 105 is formed by laminating a metal layer 5 on the thermoplastic resin layer 11 on the side of the laminate 101 on which the surface layer 2 is not provided. As described above, the surface layer 2 may be formed on the thermoplastic resin layer 12 after laminating the metal layer 5 on the thermoplastic resin layer 11.

[0063] As the metal material for the metal layer 5, copper or copper alloy, stainless steel or its alloy, nickel or nickel alloy (including 42 alloy), aluminum or aluminum alloy, etc. are preferred because of their high conductivity. As the metal layer 5, a metal foil is preferred because of ease of lamination, and copper foil such as rolled copper foil or electrolytic copper foil, as in general flexible printed wiring boards, is preferred. An anti-corrosion layer, heat-resistant layer, adhesive layer, etc. may be provided on the surface of the metal foil. The thickness of the metal layer 5 is not particularly limited and may be selected depending on the configuration of the printed wiring board and the required conductivity. The thickness of the metal layer 5 is, for example, 3 to 30 μm, and preferably 5 to 20 μm.

[0064] The method for laminating the metal layer 5 on the thermoplastic resin layer 11 is not particularly limited, but thermocompression bonding is preferred because it can prevent wrinkles from occurring during lamination. Examples of thermocompression bonding include batch-type thermocompression bonding using a single plate press, continuous processing using a double belt press (DBP) device, and thermal lamination using a heated roll. From the viewpoint of productivity, a method in which a metal foil is laminated on the thermoplastic resin layer 11 by a roll-to-roll method using a heated roll laminator equipped with metal nip rolls for heating and pressurizing the material is preferred.

[0065] During thermocompression bonding, a protective film may be interposed between a pressure applying member such as a heated roll and the material to be laminated to prevent wrinkles and adhesion of the resin material to the heated roll. When a metal layer 5 is laminated onto the thermoplastic resin layer 11 of the laminate 101 by thermal lamination, the protective film may be interposed between the metal layer 5 (metal foil) and the heated roll, or between the surface layer 2 of the laminate 101 and the heated roll. A protective film may be interposed both between the metal layer 5 and the heated roll and between the laminate 101 and the heated roll. In the laminate 101, the surface layer 2 is previously provided on the thermoplastic resin layer 12, which prevents adhesion of the thermoplastic resin layer 12 to the protective film and makes it easy to peel off the protective film after thermal lamination.

[0066] The protective film is not particularly limited as long as it can withstand the heating temperature during thermocompression bonding, and heat-resistant resin films such as non-thermoplastic polyimide films, and metal foils such as copper foil, aluminum foil, and SUS foil are preferably used. Among these, non-thermoplastic polyimide films are particularly preferred from the viewpoints of heat resistance and recyclability. From the viewpoints of handleability and prevention of wrinkles during lamination, the thickness of the protective film is preferably 25 to 300 μm, more preferably 50 to 250 μm, and may be 75 to 200 μm.

[0067] When a non-thermoplastic polyimide film is used as the protective film, various known films can be used, and for example, commercially available polyimide films such as the "Apical" series manufactured by Kaneka, the "Upilex" series manufactured by Ube Industries, and the "Kapton" series manufactured by Toray DuPont may be used.

[0068] [Printed wiring board] The single-sided metal-clad laminate is suitable for use in the manufacture of flexible printed circuit boards (FPCs). The FPC may be a multilayer printed circuit board in which multiple wiring layers are laminated with insulating layers interposed therebetween. In the multilayer printed circuit board, a multilayer polyimide film 1 having thermoplastic resin layers 11 and 12 provided on both sides of a core layer 10, and a surface layer 2 serve as insulating layers between the multiple wiring layers.

[0069] A wiring layer (first wiring layer) is formed by patterning the metal layer 5 of the single-sided metal-clad laminate 105. This single-sided wiring board is laminated with a substrate including another wiring layer (second wiring layer) to form a multilayer structure. For example, multilayer structure is achieved by bonding the surface of the surface layer 3 side (the surface without the wiring layer) of a single-sided metal-clad laminate including a first wiring layer formed by patterning the metal layer 5 to the wiring layer (second wiring layer) of another substrate. The surface layer and the wiring layer of the other substrate may be bonded together via an adhesive sheet such as a bonding sheet.

[0070] In the manufacturing process of a multilayer printed wiring board, lamination between layers is performed, for example, by heat pressing. In the manufacturing process of a multilayer printed wiring board, holes may be made by punching, mechanical drilling, laser processing, etc. before and after multilayering in order to provide electrical continuity between metal wirings, and during these processes, the processed area and its surroundings may become hot, which may soften the thermoplastic resin layer 12 provided on the surface of the core layer 10 and cause it to become adhesive.

[0071] In the single-sided metal-clad laminate 105, the surface layer 3 is provided in contact with the thermoplastic resin layer 12, so that even if the thermoplastic resin layer 12 is softened by heat, the thermoplastic resin layer 12 can be prevented from fusing to a bonding sheet or a wiring layer of another substrate. This prevents defects such as processing defects caused by fusing of the thermoplastic resin layer 12 and insufficient removal of processed chips (cut chips) from drilling, improving processability and handling, and can also contribute to an increase in yield. [Example]

[0072] The present invention will be described in more detail below by showing examples, but the present invention is not limited to the following examples.

[0073] Example 1 (Formation of surface layer) The multilayer polyimide film used was a three-layer multilayer polyimide film ("Pixio SR" manufactured by Kaneka) with a non-thermoplastic polyimide layer (34 μm thick) and a thermoplastic polyimide layer (8 μm thick) with a glass transition temperature of 290°C on both sides. A 20 nm thick SiOx layer (x≒1.5) was formed as a surface layer on the thermoplastic polyimide layer on one side of the multilayer polyimide film by sputtering to obtain a laminate.

[0074] (copper foil lamination) A 12 μm-thick rolled copper foil (JX Metals "GHY5-82F-HA") was laminated onto the thermoplastic polyimide layer on the non-surface layer side of the laminate. A 125 μm-thick non-thermoplastic polyimide film (Kaneka "Apical 125NPI") was placed on both sides of the sample as a protective film. Thermal lamination was performed at a lamination temperature of 360°C, a lamination pressure of 245 N / cm, and a lamination speed of 1 m / min to produce a single-sided metal-clad laminate with protective films on both sides. The single-sided copper-clad laminate had a laminate structure in which copper foil was laminated on one side of a three-layer polyimide film and a surface layer was formed on the other side.

[0075] <Example 2> A single-sided copper-clad laminate was obtained in the same manner as in Example 1, except that the thickness of the SiOx layer serving as the surface layer was changed to 80 nm.

[0076] Example 3 (Preparation of Thermoplastic Polyimide Precursors) With the reaction system maintained at 20°C, 74.18 g of 2,2'-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) was added to 636.07 g of N,N-dimethylformamide (DMF). Under a nitrogen atmosphere, 10.63 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was slowly added while stirring. After visually confirming that the BPDA had dissolved, 30.48 g of pyromellitic dianhydride (PMDA) was added and stirred for 30 minutes. Next, 6.51 g of 1,4-phenylenediamine (PDA) was added, and while stirring, 12.09 g of PMDA was added and stirred for 30 minutes. Furthermore, a solution of 2.1 g of PMDA dissolved in DMF to a solids concentration of 7% was slowly added to the reaction solution. Stirring was continued until the viscosity reached 800 poise, yielding a thermoplastic polyimide precursor (polyamic acid solution).

[0077] (Formation of surface layer) The above thermoplastic polyimide precursor was applied to one side of a three-layer multilayer polyimide film (Kaneka's "Pixio SR") using a spin coater. After removing the solvent by heating, the film was heated at 330°C for 3 minutes to imidize it, forming a 0.5 μm-thick surface layer of thermoplastic polyimide resin (glass transition temperature: 305°C).

[0078] (copper foil lamination) A rolled copper foil having a thickness of 12 μm was laminated onto the thermoplastic polyimide layer on the surface of the laminate not having the surface layer in the same manner as in Example 1 to prepare a single-sided copper-clad laminate.

[0079] Example 4 (Preparation of Non-Thermoplastic Polyimide Precursors) With the reaction system maintained at 20°C, 25.1 g of 4,4'-oxydiamine (4,4'-ODA) and 5.8 g of PDA were added to 930.07 g of DMF and stirred for 40 minutes under a nitrogen atmosphere. Then, 1.3 g of PMDA dissolved in DMF to a solids concentration of 7% was slowly added to the reaction solution. Stirring was continued until the viscosity reached 800 poise, yielding a non-thermoplastic polyimide precursor (polyamic acid solution).

[0080] (Formation of surface layer and lamination of copper foil) A single-sided copper-clad laminate was produced in the same manner as in Example 3, except that the above-mentioned non-thermoplastic polyimide precursor was used. A surface layer of non-thermoplastic polyimide resin having a thickness of 0.5 μm was formed on one side of a multilayer polyimide film, and rolled copper foil was laminated on the side without the surface layer.

[0081] <Example 5> The thermoplastic polyimide precursor prepared in Example 3 and the non-thermoplastic polyimide precursor prepared in Example 4 were mixed in a weight ratio of 1:1 to prepare a mixed solution of polyimide precursors. A single-sided copper-clad laminate was produced in the same manner as in Example 3, except that this mixed solution was used as the polyimide precursor. A 0.5 μm-thick polyimide resin surface layer was formed on one side of a multilayer polyimide film, and rolled copper foil was laminated on the side without the surface layer.

[0082] Example 6 A thermosetting epoxy resin composition containing a phenolic resin curing agent was applied to the thermoplastic polyimide layer on one side of a three-layer multilayer polyimide film ("Pixio SR" manufactured by Kaneka) using a spin coater, and after removing the solvent by heating, the film was heated at 180°C for 30 minutes to perform thermal curing, forming an epoxy resin layer (surface layer) with a thickness of 0.5 μm. A rolled copper foil with a thickness of 12 μm was laminated on the thermoplastic polyimide layer on the side of this laminate where the surface layer was not formed, in the same manner as in Example 1, to produce a single-sided copper-clad laminate.

[0083] <Comparative Example 1> Copper foil was placed on one side of a three-layer multilayer polyimide film ("Pixio SR" manufactured by Kaneka), and a 125 μm-thick non-thermoplastic polyimide film ("Apical 125NPI" manufactured by Kaneka) was placed on both sides of this sample as a protective film. Copper foil was then thermally laminated under the same conditions as in Example 1 to produce a single-sided copper-clad laminate.

[0084] <Comparative Example 2> A single-sided copper-clad laminate was obtained in the same manner as in Example 1, except that the thickness of the SiOx layer serving as the surface layer was changed to 220 nm.

[0085] <Comparative Example 3> A single-sided copper-clad laminate was produced in the same manner as in Example 3, except that the thickness of the surface layer (thermoplastic polyimide resin layer) was 7 μm. The multilayer polyimide film had a 7 μm-thick surface layer of thermoplastic polyimide resin on one side and copper foil laminated on the other side.

[0086] [evaluation] <Adhesion> (Adhesion between the surface layer and the protective film) The single-sided metal-clad laminates having protective films on both sides obtained in Examples 1 to 6 and Comparative Examples 1 to 3 were cut into a width of 1 cm and a length of 10 cm, and the peel strength of the protective film (polyimide film) on the side not having the copper foil (the side on which the surface layer was formed) was measured using a tensile tester at a peel rate of 100 mm / min.

[0087] (Adhesion of copper foil hot-pressed onto the surface layer) After peeling and removing the protective films on both sides, a 12 μm thick rolled copper foil (GHY5-82F-HA manufactured by JX Metals) was placed on the side of the single-sided copper-clad laminate that did not have copper foil, and hot-pressed for 60 minutes at a temperature of 250°C and a pressure of 3 MPa. This sample was cut into a 1 cm wide x 10 cm long piece, and the peel strength of the copper foil that had been hot-pressed onto the surface layer was measured under the same conditions as above.

[0088] <Warping> The laminate before the copper foil was attached (a laminate with a surface layer formed on one side of a three-layer multilayer polyimide film) was cut into a 5 cm x 5 cm square and placed on a horizontal table with the surface layer side facing up. The distance from the table (amount of lift) was measured for each of the four vertices of the square, and the average value was taken as the amount of warpage. The single-sided copper-clad laminate was also placed on a horizontal table with the copper foil attached side facing up, and the same evaluation was performed.

[0089] <Cracks in the surface layer> The surface layer side of the single-sided copper-clad laminate was observed under an optical microscope (magnification: 200 times) to check for the presence or absence of cracks in the surface layer.

[0090] Table 1 shows the materials and thicknesses of the surface layers of the examples and comparative examples, as well as the evaluation results of the single-sided copper-clad laminates.

[0091] [Table 1]

[0092] In Comparative Example 1, in which copper foil was laminated without forming a surface layer, the adhesion of the protective film was high and the peelability of the protective film was poor compared to the other examples. In addition, the adhesion between the thermoplastic resin layer of the three-layer multilayer polyimide film and the copper foil was high, which raised concerns about blocking in the manufacturing process of printed wiring boards and processing defects during processing such as drilling.

[0093] In contrast, in Examples 1 to 6, in which a surface layer was provided on a thermoplastic resin layer on one side of a three-layer multilayer polyimide film and copper foil was laminated on the other side, the adhesion between the surface layer and the protective film was low, allowing for easy peeling, and the surface layer also showed little adhesion to the copper foil.Furthermore, in Comparative Example 1, warping (curling) occurred with the copper foil side facing inward after copper foil lamination, whereas in Examples 1 to 6, the single-sided copper-clad laminate showed little warping and exhibited good properties.

[0094] In Comparative Example 2, in which a 220 nm thick SiOx layer was formed as the surface layer, cracks occurred in the SiOx layer. Comparing Examples 1 and 2 with Comparative Example 2, it can be seen that cracks in the surface layer can be suppressed by reducing the thickness of the inorganic surface layer.

[0095] In Comparative Example 3, in which a 7 μm-thick thermoplastic polyimide layer was formed as the surface layer, curling occurred with the surface layer side facing inward after the surface layer was formed, and after copper foil was bonded to the surface on which the surface layer was not formed, warping occurred with the copper foil side facing inward, similar to Comparative Example 1. Comparing Example 3 and Comparative Example 3, it can be seen that by reducing the thickness of the resin surface layer, it is possible to reduce warping of the substrate (single-sided copper-clad laminate) after the surface layer is formed and after copper foil is bonded. [Explanation of symbols]

[0096] 1. Multilayer polyimide film 10 Core layer (non-thermoplastic polyimide film) 11,12 Thermoplastic resin layer 2 Surface layer 101 laminate 5 metal layer 105 Single-sided metal-clad laminate

Claims

1. a multilayer polyimide film comprising a non-thermoplastic polyimide film having a first main surface and a second main surface, a first thermoplastic polyimide layer provided on the first main surface of the non-thermoplastic polyimide film, and a second thermoplastic polyimide layer provided on the second main surface of the non-thermoplastic polyimide film; and a surface layer in contact with the second thermoplastic polyimide layer of the multilayer polyimide film, The surface layer is a ceramic layer having a thickness of 1 to 200 nm.

2. The laminate according to claim 1 , wherein the surface layer is a silicon oxide layer.

3. a multilayer polyimide film comprising a non-thermoplastic polyimide film having a first main surface and a second main surface, a first thermoplastic polyimide layer provided on the first main surface of the non-thermoplastic polyimide film, and a second thermoplastic polyimide layer provided on the second main surface of the non-thermoplastic polyimide film; and a surface layer in contact with the second thermoplastic polyimide layer of the multilayer polyimide film, The surface layer is a thermoplastic resin layer having a thickness of 0.1 to 5 μm.

4. The laminate of claim 3 , wherein the surface layer has a higher glass transition temperature than the second thermoplastic polyimide layer.

5. The laminate according to claim 3 or 4, wherein the surface layer is a polyimide layer.

6. 6. The laminate according to claim 1, wherein the first thermoplastic polyimide layer and the second thermoplastic polyimide layer have the same composition.

7. A single-sided metal-clad laminate comprising the laminate according to any one of claims 1 to 6 and a metal foil in contact with the first thermoplastic polyimide layer of the laminate.

8. A multilayer printed wiring board in which a plurality of wiring layers are laminated with insulating layers interposed therebetween, The single-sided metal-clad laminate according to claim 7 has a first wiring layer in which the metal foil is patterned, A multilayer printed wiring board, which is formed by laminating another layer to the surface layer of the single-sided metal-clad laminate according to claim 7.

9. The multilayer printed wiring board according to claim 8 , wherein a second wiring layer is attached to the surface layer via an adhesive sheet.

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