Laminates, single-sided metal-clad laminates and multilayer printed circuit boards

Abstract

The 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 a thermoplastic polyimide layer (12) on one side of the multilayer polyimide film. The surface layer is preferably an inorganic layer with a thickness of 1 to 200 nm or a resin layer with a thickness of 0.1 to 5 μm. A single-sided metal-coated laminate (105) is formed by laminating a metal layer (5) onto the thermoplastic resin layer (11) on the non-forming side of the surface layer of the laminate.

Description

Technical Field

[0001] This invention relates to a laminate having a surface layer on one side of a multilayer polyimide film, and a single-sided metal-coated laminate. Furthermore, this invention relates to a multilayer printed circuit board manufactured using this single-sided metal-coated laminate. Background Technology

[0002] Various printed circuit boards are used in electronic devices. Printed circuit boards have metal wiring patterned on an insulating substrate, consisting of metal layers such as copper. Flexible printed circuit boards (FPCs) using heat-resistant resin films such as polyimide films as insulating substrates are becoming practical. With the increasing performance and miniaturization of electronic devices, multilayer flexible printed circuit boards are being developed, which are formed by laminating multiple wiring layers with insulating layers sandwiched between them.

[0003] In the manufacture of FPCs, double-sided metal-clad laminates are used, in which metal foils such as copper are laminated on both the front and back sides of a polyimide film, and single-sided metal-clad laminates are used, in which metal foils are laminated on one side of a polyimide film. As a method for manufacturing double-sided metal-clad laminates, a method is known to use a multilayer polyimide film in which thermoplastic resin layers function as adhesive layers are provided on both sides of a non-thermoplastic polyimide film (core layer), and metal foils are laminated on both sides of the multilayer polyimide film by heat lamination.

[0004] In the manufacturing of multilayer flexible printed circuit boards (FPCs), if double-sided metal-clad laminates are overlapped to create multiple layers, the metal foils come into contact with each other and are laminated. Therefore, single-sided metal-clad laminates are mainly used in the manufacturing of multilayer FPCs. The metal foils (metal layers) of the single-sided metal-clad laminate are patterned to form wiring, and a substrate with a wiring layer on one side of a polyimide film serving as an insulating layer is laminated with adhesive sheets such as bonding sheets, thereby achieving multilayering.

[0005] If a single-sided metal-clad laminate is formed by laminating a multilayer polyimide film with thermoplastic resin layers on both sides of the core layer with a metal foil, during the lamination process and the manufacturing process of the printed circuit board, sometimes the thermoplastic resin layer on the side without the metal foil lamination may experience defects such as welding with hot rollers.

[0006] Patent Document 1 describes a method for manufacturing a single-sided metal-coated laminate by using a polyimide film with thermoplastic resin layers on both sides of the core layer and a metal foil laminated on one side. This method utilizes a polyimide with a specific structure as the material for the thermoplastic resin layer on the side where the metal foil is not laminated, thus preventing welding to metal rollers or the like. Patent Document 2 proposes a method for manufacturing a single-sided metal-coated laminate by hot lamination with a metal foil on one side of the multilayer polyimide film and a release film on the other side.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2013-176931

[0010] Patent Document 2: Japanese Patent Application Publication No. 2007-109694 Summary of the Invention

[0011] The problem the invention aims to solve

[0012] As in Patent Document 1, multilayer polyimide films with thermoplastic polyimide layers of different compositions on the front and back sides of the core layer may warp due to differences in the heating dimensional changes (e.g., coefficient of thermal expansion) of the thermoplastic resin layers on the front and back sides. Sometimes, the multilayer polyimide film itself, or a single-sided metal-clad laminate with metal foil pressed on one side, may warp.

[0013] As proposed in Patent Document 2, if a release film is temporarily laminated on the side without the metal foil, it can prevent the thermoplastic resin from fusing to hot rollers or the like during the hot lamination of the metal foil onto the multilayer polyimide film. However, when the release film is attached, warping sometimes occurs in the single-sided metal-clad laminate due to differences in stress balance between the front and back sides. Furthermore, when manufacturing printed circuit boards using a single-sided metal-clad laminate, the release film is peeled off, exposing the thermoplastic resin layer, which sometimes causes fusing of the thermoplastic resin layer during the process.

[0014] In the manufacturing process of multilayer printed circuit boards, before and after multilayering, drilling, mechanical drilling, and laser processing are performed to ensure conductivity between metal traces. When the thermoplastic resin layer of the multilayer polyimide film is exposed, or when the bonding tabs are directly bonded to the thermoplastic resin layer, defects such as poor processing or difficulty in removing the cutting tabs may sometimes occur during drilling.

[0015] In view of the above, the object of the present invention is to provide a laminate that is used as a thin film substrate for a single-sided metal-coated laminate, which can suppress defects such as welding of the thermoplastic resin layer on the non-laminated side of the metal foil and suppress warping during the manufacturing process of the single-sided metal-coated laminate and the multilayer printed circuit board.

[0016] Solution for solving the problem

[0017] One embodiment of the present invention is a laminate having a surface layer on one side of a multilayer polyimide film, wherein a surface laminated metal layer is formed on the surface layer of the laminate, thereby forming a single-sided metal-coated laminate.

[0018] The multilayer polyimide film has thermoplastic polyimide layers on both sides of the core layer, which is a non-thermoplastic polyimide film. The thermoplastic polyimide layers on the front and back sides of the core layer can have the same composition. In the laminate, a surface layer is in contact with the thermoplastic polyimide layer on one side of the multilayer polyimide film. The surface layer can be an inorganic layer or an organic layer (resin layer).

[0019] When the surface layer is inorganic, ceramic materials such as silicon oxide are preferred. The thickness of the inorganic surface layer is preferably 1–200 nm.

[0020] When the surface layer is a resin layer, its thickness is preferably 0.1 to 5 μm. Examples of resin materials for the surface layer include thermoplastic or non-thermoplastic resin materials. When the surface layer is a thermoplastic resin layer, it is preferable to have a higher glass transition temperature than the thermoplastic resin layer of the multilayer polyimide film. The resin material can be polyimide. The resin material can also be a thermosetting resin such as an epoxy resin.

[0021] Single-sided metal-clad laminates are used in the formation of flexible printed circuit boards (PCBs). A PCB can be a multilayer PCB where multiple wiring layers are laminated with insulating layers sandwiched between them. The metal layers of the single-sided metal-clad laminate are patterned to form wiring layers, and the surface layer (the non-metal-forming surface) of this substrate is bonded to the wiring layers of other substrates, thereby achieving multilayering. The surface layer can be bonded to the wiring layers of other substrates using adhesive tabs such as bonding pads.

[0022] The effects of the invention

[0023] A single-sided metal-clad laminate with a metal layer on one side and the aforementioned surface layer on the other side of a multilayer polyimide film suppresses warping. Furthermore, since the surface layer is provided on the thermoplastic resin layer of the multilayer polyimide film, defects caused by the welding of the thermoplastic resin layer can be suppressed not only during the lamination of the metal layer onto the multilayer polyimide film but also during the printed circuit board manufacturing process. Attached Figure Description

[0024] Figure 1 This is a cross-sectional view of a laminate according to one embodiment.

[0025] Figure 2 This is a cross-sectional view of a single-sided metal-coated laminate according to one embodiment. Detailed Implementation

[0026] Figure 1This is a cross-sectional view of a laminate according to an embodiment of the present invention. A surface layer 2 is provided on one side of the multilayer polyimide film 1. The multilayer polyimide film 1 has thermoplastic resin layers 11 and 12 on both sides of the core layer 10. The laminate 101 has a surface layer 2 in contact with the thermoplastic resin layer 12 of the multilayer polyimide film 1.

[0027] Figure 2 This is a cross-sectional view of a single-sided metal-coated laminate according to an embodiment of the present invention. A metal layer 5 is laminated on the thermoplastic resin layer 11 of the laminate 101. That is, the single-sided metal-coated 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 where the metal layer 5 is not laminated).

[0028] [Composition of Laminates]

[0029] <Multilayer polyimide film>

[0030] In one embodiment of the present invention, the laminate 101 is a thin film substrate for forming a single-sided metal-coated laminate, and a surface layer 2 is provided on the non-metal-forming side of the multilayer polyimide film 1. The multilayer polyimide film 1 is composed of three layers, in which thermoplastic resin layers 11 and 12 are provided on both sides of a non-thermoplastic polyimide core layer 10.

[0031] (Core layer)

[0032] The core layer 10 is required to withstand the heating temperatures during thermal lamination in the manufacturing process of the printed circuit board. Therefore, a non-thermoplastic polyimide is used as the material for the core layer 10. The core layer 10 preferably contains 80% by weight or more of non-thermoplastic polyimide, more preferably 90% by weight or more.

[0033] "Non-thermoplastic polyimide" refers to polyimide that does not soften or exhibit adhesiveness even when heated. Specifically, it includes polyimide that maintains its shape without wrinkling or elongating when a single layer of polyimide is heated at 450°C for 2 minutes, and polyimide that substantially does not exhibit a glass transition temperature. It should be noted that the glass transition temperature is the temperature at which the storage modulus reaches its inflection point, as measured by a dynamic viscoelasticity measuring device (DMA). Resin materials that "substantially do not have a glass transition temperature" refer to materials that begin thermal decomposition before reaching the glass transition state.

[0034] Polyimides are typically obtained as follows: a polyimide precursor (polyamic acid) is prepared by polymerizing a diamine with a tetracarboxylic dianhydride, followed by imidization through dehydration and ring closure of the polyamic acid. In the preparation of non-thermoplastic polyimides, a combination of aromatic diamines and aromatic tetracarboxylic dianhydrides is suitable as the monomer.

[0035] 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'-dichlorobenzophenone. 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'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 9,9-bis(4-aminophenyl)fluorene, 4,4'-(1,4-phenylenebis(1-methylethylene))bisaniline, 4,4'-(1,3-phenylenebis(1-methylethylene))bisaniline, 4,4'-diaminobenzoylaniline, 2,2'-dimethylbiphenyl-4,4'-diamine, etc. Two or more aromatic diamines may be used.

[0036] Examples of aromatic tetracarboxylic dianhydrides include 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 2,2',3,3'-benzophenone tetracarboxylic dianhydride, 4,4'-oxobisphthalic dianhydride, 3,4'-oxobisphthalic dianhydride, ethylene bis(triphenylamine monoester anhydride), bisphenol A bis(triphenylamine monoester anhydride), pyromellitic dianhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, 3, Aromatic tetracarboxylic anhydrides such as 3',4,4'-dimethyldiphenylsilanetetracarboxylic dianhydride, 3,3',4,4'-tetraphenylsilanetetracarboxylic dianhydride, 1,2,3,4-furantetracarboxylic dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenylpropane dianhydride, 4,4'-hexafluoroisopropylidene phthalic anhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, p-phenylenebis(trimethoxymethyl phthalate anhydride), and p-phenylene diphthalic anhydride can be used. Two or more aromatic tetracarboxylic dianhydrides can be used.

[0037] Polyamic acid is obtained by reacting a diamine with a 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 in the polymerization of polyamic acid is not particularly limited as long as it can dissolve the diamine, tetracarboxylic dianhydride, and polyamic acid. Preferably, amide solvents such as N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone are preferred. The polymerization temperature is preferably -10°C to 50°C. The reaction time is not particularly limited and is typically from a few minutes to several hours. The solids concentration of the polyamic acid solution is typically 5% to 35% by weight, preferably 10% to 30% by weight.

[0038] Polyimide is obtained by imidizing (dehydrating and ring-closing) polyamic acid, which is a precursor of polyimide. During imidization, a curing agent can be added to the polyamic acid solution. Examples of curing agents include dehydrating agents and imidization catalysts. Examples of dehydrating agents include aliphatic anhydrides, aromatic anhydrides, N,N'-dialkylcarbodiimides, lower aliphatic halides, halogenated lower aliphatic anhydrides, arylsulfonic acid dihalides, and thionyl halides. Examples of imidization catalysts include aliphatic tertiary amines, aromatic tertiary amines, and heterocyclic tertiary amines.

[0039] In addition to non-thermoplastic polyimide resin, the core layer may also contain fillers. Examples of filler materials include silica, titanium dioxide, alumina, silicon nitride, boron nitride, dicalcium phosphate, calcium phosphate, and mica.

[0040] (Thermoplastic resin layer)

[0041] Examples of materials for the thermoplastic resin layers 11 and 12 disposed on both sides of the core layer 10 include polycarbonate resins, acrylonitrile-styrene copolymer resins, and thermoplastic polyimide resins. From the viewpoint of heat resistance and adhesion to the core layer, thermoplastic polyimide resins are preferred. The thermoplastic resin layers 11 and 12 preferably contain 50% by weight or more of thermoplastic polyimide resin.

[0042] From the viewpoint of matching the coefficient of linear expansion of the multilayer polyimide film 1 as a whole to suppress warping, and from the viewpoint of simplifying the manufacturing process, it is preferable that the thermoplastic resin layer 11 provided on one side (first main side) of the core layer 10 and the thermoplastic resin layer 12 provided on the other side (second main side) of the core layer 10 have the same composition.

[0043] 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 can be 200°C to 300°C.

[0044] Like non-thermosetting polyimides, thermoplastic polyimides are obtained through the dehydration and ring-closure of polyamic acid, which serves as a polyimide precursor. In the preparation of thermoplastic polyimides, combinations of aromatic diamines and aromatic tetracarboxylic dianhydrides are also suitable monomers. The properties of the polyimide can be adjusted by selecting the appropriate diamine and tetracarboxylic dianhydride.

[0045] Generally, if the proportion of a rigid aromatic diamine increases, the glass transition temperature increases, and consequently, the storage modulus at high temperatures increases, tending to decrease adhesion and processability. Examples of thermoplastic polyimide resin compositions include using benzophenone tetracarboxylic dianhydride, biphenyl tetracarboxylic dianhydride, oxydiphthalic dianhydride, and biphenyl sulfone tetracarboxylic dianhydride as the tetracarboxylic dianhydride, and using an aromatic diamine having an aminophenoxy group as the diamine. The proportion of a rigid aromatic diamine in the diamine used in the preparation of thermoplastic polyimide is preferably 40 mol% or less, more preferably 30 mol% or less, and even more preferably 20 mol% or less.

[0046] (Fabrication of multilayer polyimide films)

[0047] There is no particular limitation on the method for manufacturing the multilayer polyimide film 1 having thermoplastic resin layers 11 and 12 on both sides of the core layer 10. Examples include: a method of forming thermoplastic resin layers sequentially or simultaneously on the two main surfaces of the core layer 10; and a method of co-extruding the material of the core layer 10 and the material of the thermoplastic resin layers 11 and 12 in multiple layers from a multilayer mold.

[0048] Polyimides obtained by imidizing polyamic acid obtained by polymerization of aromatic diamines and aromatic tetracarboxylic dianhydrides have low solubility in organic solvents after imidization. Therefore, in the formation of the core layer 10 and the thermoplastic resin layers 11 and 12, it is preferable to perform imidization after forming the polyamic acid solution (polyimide precursor) into a film.

[0049] In the case of producing multilayer polyimide films by multilayer co-extrusion, it is preferable to: co-extrude three layers, applying a polyamic acid solution as a precursor of the non-thermoplastic polyimide constituting the core layer 10 and a polyamic acid solution as a precursor of the thermoplastic polyimide constituting the thermoplastic resin layers 11 and 12 in a film form onto a support substrate, removing the solvent by heating as needed, and then heating again to perform imidization. As mentioned above, a curing agent can be added to the polyamic acid solution to promote imidization. In the case of three-layer co-extrusion, the curing agent can be added only to the polyimide precursor of the core layer 10, or it can 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 polyimide of the core layer 10 and the thermoplastic resin layers 11 and 12 can be completely imidized, or it can contain a portion of unimidized structures (open-ring polyamic acid).

[0050] The thickness of the core layer 10 and the thickness of the thermoplastic resin layers 11 and 12 are not particularly limited. Preferably, the thickness is adjusted to balance the thickness, taking into account the coefficient of linear expansion of each layer, in a way that does not cause warping in the state of the multilayer polyimide film 1.

[0051] The thickness of the core layer 10 is preferably 3–50 μm, more preferably 5–40 μm. The thickness of each of the thermoplastic resin layers 11 and 12 is preferably 0.5–15 μm, more preferably 1–10 μm. The thicknesses of the thermoplastic resin layers 11 and 12 disposed 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 between the thickness of the thermoplastic resin layer 11 and the thickness of 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 0.7–1.3, more preferably 0.8–1.2, and even more preferably 0.9–1.1.

[0052] The thickness of each of the thermoplastic resin layers 11 and 12 is preferably 0.05 to 0.5 times the thickness of the core layer 10, and can be about 0.1 to 0.4 times. The overall thickness of the multilayer polyimide film 1 is preferably 4 to 65 μm, and more preferably 5 to 55 μm.

[0053] Commercially available products can be used as multilayer polyimide films with thermoplastic resin layers on both sides of the core layer. Examples of three-layer polyimide films, such as the "Pixeo" series manufactured by Kaneka Corporation, are also available.

[0054] <Surface Layer>

[0055] A laminate 101 is obtained by forming a surface layer 2 on a thermoplastic resin layer 12 on one surface of a multilayer polyimide film 1. By providing the surface layer 2, the thermoplastic resin layer 12 is not exposed to the surface, so that during thermal lamination when laminating a metal layer 5 on the thermoplastic resin layer 11 and during heating in the manufacturing process of a printed circuit board, defects caused by welding of the thermoplastic resin layer 12 can be suppressed.

[0056] The surface layer 2 preferably does not soften and does not exhibit adhesiveness during thermal lamination of a metal foil, during thermal lamination when laminating a metal layer 5 on the thermoplastic resin layer 11, and during heating in the manufacturing process of a printed circuit board. As long as the surface layer 2 has the above heat resistance, it can be an inorganic layer or an organic layer (resin layer). 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.

[0057] (Inorganic surface layer)

[0058] Examples of the inorganic material 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, Cd, and their alloys, as well as ceramic materials such as metal nitrides, oxides, and oxynitrides.

[0059] In a single-sided metal-clad laminate and a printed circuit board using the same, the surface layer 2 is in a state of being directly laminated and integrated on the thermoplastic resin layer 12. Therefore, the surface layer 2 is preferably an insulating material, and as the material for the inorganic surface layer, a ceramic material is preferred. In addition, from the viewpoints of chemical stability and mechanical strength, a ceramic material is also preferred.

[0060] Among ceramic materials, from the viewpoints of insulation, heat resistance, and chemical stability, oxides are preferred, and silicon oxide is particularly preferred. The silicon oxide can be silicon dioxide (SiO2) having a stoichiometric composition, or SiOx (0 < x < 2) with oxygen deficiency compared to the stoichiometric composition. From the aspect of excellent toughness, non-stoichiometric silicon oxide is preferred. In non-stoichiometric silicon oxide: SiOx, x is preferably around 1.2 to 1.95, can be 1.2 to 1.9, or 1.3 to 1.8.

[0061] As described above, the thickness of the inorganic surface layer is preferably 1 to 200 nm. When the thickness is 1 nm or more, it can uniformly cover the entire surface of the thermoplastic resin layer 12. When the thickness is 200 nm or less, warping is suppressed, and the inorganic surface layer has excellent flexibility, thus suppressing the generation of cracks or fissures. 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 can be 5 nm or more or 10 nm or more. From the viewpoint of suppressing cracks or fissures, the thickness of the inorganic surface layer is preferably 150 nm or less, more preferably 100 nm or less, and can be 80 nm or less or 50 nm or less.

[0062] There are no particular limitations on the method for forming the inorganic surface layer. From the perspective of easily forming a uniform film, dry coating methods such as sputtering, vacuum evaporation, ion plating, and CVD are preferred.

[0063] (Resin surface layer)

[0064] The resin material of surface layer 2 is not particularly limited as long as it possesses the aforementioned heat resistance; it can be any thermoplastic resin or non-thermoplastic resin, or a mixture of thermoplastic and non-thermoplastic resins. The resin surface layer can be formed by thermosetting or photosetting.

[0065] When the surface layer 2 is a thermoplastic resin layer, from the viewpoint of suppressing softening and welding caused by heating, the surface layer 2 preferably has a higher glass transition temperature than the thermoplastic resin layer 12 of the multilayer polyimide film 1. The glass transition temperature of the surface layer 2 is preferably 10°C or more, more preferably 15°C or more, higher than the glass transition temperature of the thermoplastic resin layer 12. The glass transition temperature of the surface layer as a thermoplastic resin layer is preferably 200°C or more, more preferably 250°C or more, and can be 280°C or more, or 300°C or more.

[0066] Polyimide is suitable as a thermoplastic resin with a high glass transition temperature, as described above. When the surface layer 2 is a thermoplastic polyimide resin layer, a thermoplastic polyimide with a higher glass transition temperature can be prepared by increasing the ratio of aromatic monomers that are more rigid than the polyimide constituting the thermoplastic resin layer 12 of the multilayer polyimide film 1.

[0067] When the surface layer 2 is a non-thermoplastic resin layer, non-thermoplastic polyimide is suitable due to its high heat resistance. Non-thermoplastic polyimide is used as the material for the core layer 10 as previously described. When the surface layer 2 is a non-thermoplastic polyimide resin layer, the composition of the core layer 10 may be the same as or different from the composition of the surface layer 2.

[0068] As described above, the resin material of surface layer 2 can be a mixture of thermoplastic resin and non-thermoplastic resin. The mixing ratio of thermoplastic resin and non-thermoplastic resin can be adjusted by considering factors such as the heat resistance of the surface layer.

[0069] The resin material of surface layer 2 can be a thermosetting resin such as epoxy or acrylic. From the viewpoint of heat resistance, the thermosetting resin of surface layer 2 is preferably in a cured state (the state after heat curing).

[0070] For the surface layer 2, which is a resin layer, from the viewpoint of inhibiting welding and adhesion, it can be formed by adding inorganic or organic fillers to create a surface with unevenness.

[0071] As described above, the thickness of the resin surface layer is preferably 0.1 to 5 μm. When the thickness is 0.1 μm or more, it can uniformly cover the entire surface of the thermoplastic resin layer 12. When 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 can 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 can be 2 μm or less, 1.5 μm or less, or 1 μm or less.

[0072] There is no particular limitation on the method for forming the resin surface layer. For example, a resin solution can be coated onto the thermoplastic resin layer 12 of the multilayer polyimide film 1, and the solvent can be removed by heating as needed, thereby forming the resin surface layer 2. When manufacturing the multilayer polyimide film, a laminate having the resin surface layer 2 can be formed by multilayer co-extrusion of three layers: the thermoplastic resin layer 11, the core layer 10, and the thermoplastic resin layer 12, plus the surface layer 2, to obtain a four-layer laminate.

[0073] When the resin material is polyimide, imidization can be performed based on heating after coating with a polyamic acid solution (polyimide precursor) as the resin solution. When the resin material is a thermosetting resin or a photocurable resin, the resin material can be cured by heating or irradiation with active light.

[0074] After laminating the metal layer 5 onto the thermoplastic resin layer 11 of the multilayer polyimide film 1, a surface layer 2 can be formed on the thermoplastic resin layer 12. For example, if the surface layer 2 has surface irregularities caused by fillers, the surface layer 2 can be formed by hot laminating the metal layer 5, thereby maintaining the irregular shape. When using a single-sided metal-clad laminate to manufacture a printed circuit board, this can help suppress the welding and adhesion of the non-forming surfaces of the metal layer.

[0075] (The role of the surface layer)

[0076] For surface layer 2, whether it is an inorganic layer or a resin layer, it is a layer directly laminated onto the thermoplastic resin layer 12 in the printed circuit board. In multilayer printed circuit boards, other wiring substrates (wiring layers) are attached to the surface of surface layer 2 by means of adhesive sheets such as bonding tabs. That is, after the metal layer 5 is laminated onto the thermoplastic resin layer 11, surface layer 2 is not peeled off from the thermoplastic resin layer 12, but is included in the printed circuit board as is. From the viewpoint of making the printed circuit board thinner, surface layer 2 is preferably as thin as possible within a range that can protect the surface of thermoplastic resin layer 12 and thus suppress welding, etc.

[0077] If surface layer 2 is provided, when fabricating a multilayer printed circuit board using a single-sided metal-clad laminate, the thermoplastic resin layer 12 does not come into contact with adhesive sheets such as bonding sheets. Therefore, even if the thermoplastic resin layer 12 softens due to heating such as hot pressing and becomes adhesive, fusion between the thermoplastic resin layer 12 and the adhesive sheets can be prevented. Therefore, the removal of the processing sheet (cutting sheet) is easy during drilling and other processing.

[0078] Single-sided metal-coated laminate

[0079] A metal layer 5 is laminated onto the thermoplastic resin layer 11 on the side of the laminate 101 where the surface layer 2 is not provided, thereby forming a single-sided metal-coated laminate 105. As mentioned above, the surface layer 2 can be laminated onto the thermoplastic resin layer 12 after the metal layer 5 is laminated onto the thermoplastic resin layer 11.

[0080] For the metal material of metal layer 5, copper or copper alloys, stainless steel or its alloys, nickel or nickel alloys (including alloy 42), aluminum or aluminum alloys are preferred from the perspective of high conductivity. From the perspective of ease of lamination, metal foil is preferred for metal layer 5; similar to conventional flexible printed circuit boards, rolled copper foil, electrolytic copper foil, etc., are preferred. A rust-preventive layer, a heat-resistant layer, an adhesive layer, etc., can be provided on the surface of the metal foil. The thickness of metal layer 5 is not particularly limited and can be selected according to the structure of the printed circuit board and the required conductivity. The thickness of metal layer 5 is, for example, 3 to 30 μm, preferably 5 to 20 μm.

[0081] The method for laminating the metal layer 5 onto the thermoplastic resin layer 11 is not particularly limited, but hot pressing is preferred from the perspective of suppressing wrinkles during lamination. Examples of hot pressing include intermittent hot pressing based on single-sheet pressing, continuous processing using a double-belt press (DBP) device, and hot lamination based on hot rollers. From the viewpoint of productivity, it is preferable to use a hot roller laminator equipped with metal rollers for heating and pressurizing the material to laminate the metal foil onto the thermoplastic resin layer 11 in a roll-to-roll manner.

[0082] During hot lamination, a protective film can be inserted between the pressure body (such as the hot roller) and the laminated material to prevent wrinkles and the fusion of resin material with the hot roller. When the metal layer 5 is laminated onto the thermoplastic resin layer 11 of the laminate 101 via hot lamination, the protective film can be inserted between the metal layer 5 (metal foil) and the hot roller, or between the surface layer 2 of the laminate 101 and the hot roller. The protective film can be inserted between the metal layer 5 and the hot roller, and between the laminate 101 and the hot roller. Since the surface layer 2 is pre-formed on the thermoplastic resin layer 12 in the laminate 101, fusion of the thermoplastic resin layer 12 with the protective film can be prevented, and the protective film is easy to peel off after hot lamination.

[0083] There are no particular limitations on the protective film as long as it can withstand the heating temperature during hot lamination. Heat-resistant resin films such as non-thermoplastic polyimide films, copper foil, aluminum foil, and SUS foil are suitable. Among these, non-thermoplastic polyimide films are particularly preferred from the viewpoints of heat resistance and recyclability. From the viewpoints of processability and wrinkle prevention during lamination, the thickness of the protective film is preferably 25–300 μm, more preferably 50–250 μm, and can be 75–200 μm.

[0084] When using non-thermoplastic polyimide film as a protective film, various known films can be used, such as commercially available polyimide films such as the "Apical" series manufactured by Kaneka Corporation, the "Upilex" series manufactured by Ube Industries, Ltd., and the "Kapton" series manufactured by DU PONT-TORAY CO.,LTD.

[0085] Printed Circuit Board

[0086] The aforementioned single-sided metal-clad laminate is suitable for the fabrication of flexible printed circuit boards (FPCs). An FPC can be a multilayer printed circuit board with multiple wiring layers laminated together, sandwiching insulating layers between them. In a multilayer printed circuit board, a multilayer polyimide film 1 with thermoplastic resin layers 11 and 12 on both sides of the core layer 10, and a surface layer 2, serve as insulating layers between the multiple wiring layers.

[0087] The metal layer 5 of the single-sided metal-clad laminate 105 is patterned to form a wiring layer (first wiring layer). Multilayering is achieved by laminating this single-sided wiring substrate with a substrate containing other wiring layers (second wiring layers). For example, multilayering is achieved by bonding the surface layer 3 side (the non-wiring layer side) of the single-sided metal-clad laminate having the 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 layers of the other substrate can be bonded together using adhesive sheets such as bonding tabs.

[0088] In the manufacturing process of multilayer printed circuit boards, interlayer lamination is performed, for example, by hot pressing. In the manufacturing process of multilayer printed circuit boards, before and after multilayering, drilling, mechanical drilling, laser processing, etc., are sometimes performed for the purpose of making the metal wiring conductive. During these processes, the processing part and its surrounding area are sometimes at high temperatures, and the thermoplastic resin layer 12 provided on the surface of the core layer 10 softens and thus exhibits adhesion.

[0089] In the single-sided metal-clad laminate 105, since a surface layer 3 is provided in contact with the thermoplastic resin layer 12, even if the thermoplastic resin layer 12 softens due to heat, it can prevent the thermoplastic resin layer 12 from fusing to the bonding sheet or the wiring layer of other substrates. Therefore, defects such as processing defects caused by the fusing of the thermoplastic resin layer 12 and poor removal of the drilling cutting sheet are suppressed, improving processability and handling, and also contributing to a higher yield.

[0090] Example

[0091] The present invention will be described in more detail below with examples, but the present invention is not limited to the following examples.

[0092] <Example 1>

[0093] (Formation of the surface layer)

[0094] As a multilayer polyimide film, a three-layer multilayer polyimide film (manufactured by Kaneka Corporation, "Pixeo SR") is used, consisting of a non-thermoplastic polyimide layer (34 μm thick) and two thermoplastic polyimide layers (8 μm thick) with a glass transition temperature of 290°C on both sides. A 20 nm thick SiOx layer (x≈1.5) is formed as a surface layer on the thermoplastic polyimide layer of one side of the multilayer polyimide film by sputtering, resulting in a laminate.

[0095] (Lamination of copper foil)

[0096] A 12 μm thick rolled copper foil (JX Metal "GHY5-82F-HA") is overlapped on a non-formable thermoplastic polyimide layer on the surface of the aforementioned laminate. A 125 μm thick non-thermoplastic polyimide film (Kaneka Corporation "Apical125NPI") is placed on both sides of the sample as a protective film. Hot lamination is 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 has the following structure: copper foil is laminated on one side of a three-layer polyimide film, and a surface layer is present on the other side.

[0097] <Example 2>

[0098] The thickness of the SiOx layer, which serves as the surface layer, was changed to 80 nm. Otherwise, the same procedure as in Example 1 was followed to obtain a single-sided copper-clad laminate.

[0099] <Example 3>

[0100] (Preparation of precursors for thermoplastic polyimide)

[0101] While maintaining the reaction system 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, and 10.63 g of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) was slowly added. After visually confirming the dissolution of BPDA, 30.48 g of pyromellitic dianhydride (PMDA) was added, and the mixture was stirred for 30 minutes. Next, 6.51 g of 1,4-phenylenediamine (PDA) was added, and 12.09 g of PMDA was added while stirring for 30 minutes. Then, a solution of 2.1 g of PMDA dissolved in DMF at a solid concentration of 7% was slowly added to the above reaction solution. Subsequently, stirring was continued until the viscosity reached 800 poise, yielding the precursor of thermoplastic polyimide (polyamic acid solution).

[0102] (Formation of the surface layer)

[0103] The above-mentioned thermoplastic polyimide precursor was coated onto a thermoplastic polyimide layer on one side of a three-layer multilayer polyimide film ("Pixeo SR" manufactured by Kaneka Corporation) using a spin coater. After removing the solvent by heating, imidization was performed by heating at 330°C for 3 minutes to form a surface layer of thermoplastic polyimide resin with a thickness of 0.5 μm (glass transition temperature: 305°C).

[0104] (Lamination of copper foil)

[0105] On the non-forming thermoplastic polyimide layer of the surface layer of the above-mentioned laminate, the same operation as in Example 1 is performed to laminate a rolled copper foil with a thickness of 12 μm to produce a single-sided copper-clad laminate.

[0106] <Example 4>

[0107] (Preparation of precursors for non-thermoplastic polyimides)

[0108] While maintaining the reaction system at 20°C, 25.1 g of 4,4'-oxodiamine (4,4'-ODA) and 5.8 g of PDA were added to 930.07 g of DMF. After stirring for 40 minutes under a nitrogen atmosphere, a solution of 1.3 g of PMDA dissolved in DMF at a solids concentration of 7% was slowly added to the above reaction solution. Stirring continued until the viscosity reached 800 poise, yielding a precursor of non-thermoplastic polyimide (polyamic acid solution).

[0109] (Surface layer formation and copper foil lamination)

[0110] Using the aforementioned non-thermoplastic polyimide precursor, except as described in Example 3, a surface layer of non-thermoplastic polyimide resin with a thickness of 0.5 μm is formed on one side of a multilayer polyimide film, and a rolled copper foil is laminated onto the non-forming side of the surface layer to produce a single-sided copper-clad laminate.

[0111] <Example 5>

[0112] The thermoplastic polyimide precursor prepared in Example 3 and the non-thermoplastic polyimide precursor prepared in Example 4 were mixed at a weight ratio of 1:1 to prepare a mixed solution of polyimide precursors. Using this mixed solution as the polyimide precursor, except that, the same procedure as in Example 3 was followed to form a 0.5 μm thick polyimide resin surface layer on one side of a multilayer polyimide film, and a calendered copper foil was laminated onto the non-forming side of the surface layer to fabricate a single-sided copper-clad laminate.

[0113] <Example 6>

[0114] A thermosetting epoxy resin composition containing a phenolic resin curing agent was coated onto a thermoplastic polyimide layer on one side of a three-layer multilayer polyimide film ("Pixeo SR" manufactured by Kaneka Corporation) using a spin coater. After removing the solvent by heating, the film was thermocured at 180°C for 30 minutes to form a 0.5 μm thick epoxy resin layer (surface layer). A 12 μm thick rolled copper foil was laminated onto the non-surface thermoplastic polyimide layer of this laminate, following the same procedure as in Example 1, to produce a single-sided copper-clad laminate.

[0115] <Comparative Example 1>

[0116] A copper foil was overlapped on one side of a three-layer multilayer polyimide film (Kaneka Corporation's "Pixeo SR"), and a 125 μm thick non-thermoplastic polyimide film (Kaneka Corporation's "Apical125NPI") was placed on both sides of the sample as a protective film. The copper foil was then thermally laminated under the same conditions as in Example 1 to produce a single-sided copper-clad laminate.

[0117] <Comparative Example 2>

[0118] The thickness of the SiOx layer, which serves as the surface layer, was changed to 220 nm. Otherwise, the same procedure as in Example 1 was followed to obtain a single-sided copper-clad laminate.

[0119] <Comparative Example 3>

[0120] The thickness of the surface layer (thermoplastic polyimide resin layer) was set to 7 μm. Otherwise, the same procedure as in Example 3 was followed to fabricate a single-sided copper-clad laminate with a 7 μm thick thermoplastic polyimide resin surface layer on one side of a multilayer polyimide film and copper foil laminated on the other side.

[0121] [evaluate]

[0122] <Seamlessness>

[0123] (Adhesion between the surface layer and the protective film)

[0124] The single-sided metal-coated laminates with protective films on both sides obtained in Examples 1-6 and Comparative Examples 1-3 were cut into pieces with a width of 1cm and a length of 10cm. The peel strength of the protective film (polyimide film) on the side without copper foil (the surface layer forming side) was measured using a tensile testing machine at a peel speed of 100mm / min.

[0125] (The adhesion of the copper foil hot-pressed onto the surface layer)

[0126] On the side of a single-sided copper-clad laminate without copper foil after the protective films on both sides have been peeled off, a 12 μm thick rolled copper foil (JX Metal GHY5-82F-HA) is overlapped and hot-pressed for 60 minutes at 250°C and 3 MPa. The sample is then cut into pieces 1 cm wide and 10 cm long, and the peel strength of the copper foil laminated to the surface layer is measured under the same conditions.

[0127] <Warp>

[0128] The laminate before copper foil bonding (a laminate consisting of three layers of multilayer polyimide film with a surface layer formed on one side) is cut into 5cm × 5cm squares. The surface layer side is placed on a horizontal table with the surface layer facing up. The distances (lifting amounts) from each of the four vertices of the square to the table are measured, and the average value is taken as the warpage. The same evaluation is performed on a single-sided copper-clad laminate with the copper foil bonding side facing up, placed on a horizontal table.

[0129] <Surface layer cracking>

[0130] The surface of the single-sided copper-clad laminate was observed using an optical microscope (magnification: 200x) to confirm the presence or absence of cracks in the surface layer.

[0131] Table 1 shows the material and thickness of the surface layer of the embodiments and comparative examples, as well as the evaluation results of the single-sided copper-clad laminate.

[0132] [Table 1]

[0133]

[0134] Compared to other examples, Comparative Example 1, which has copper foil laminated without a surface layer, exhibits high adhesion of the protective film but poor peelability. Furthermore, the high adhesion between the thermoplastic resin layer of the three-layer multilayer polyimide film and the copper foil raises concerns about potential defects during the printing circuit board manufacturing process, such as adhesion and drilling.

[0135] In contrast, in Examples 1-6, where a surface layer is provided on one side of a three-layer multilayer polyimide film with a thermoplastic resin layer and a copper foil is laminated on the other side, the surface layer exhibits poor adhesion to the protective film, is easy to peel off, and also shows poor adhesion to the copper foil. Furthermore, in Comparative Example 1, warping (curling) occurred with the copper foil side as the inner side after the copper foil was laminated, while in Examples 1-6, the single-sided copper-clad laminate exhibited less warping and better characteristics.

[0136] In Comparative Example 2, where a 220 nm thick SiOx layer was formed as the surface layer, the SiOx layer cracked. Based on the comparison between Examples 1 and 2 and Comparative Example 2, it can be seen that reducing the thickness of the inorganic surface layer can suppress surface layer cracking.

[0137] In Comparative Example 3, where a 7 μm thick thermoplastic polyimide layer was formed as the surface layer, curling occurred with the surface layer side as the inside after the surface layer was formed. Similarly, after copper foil was bonded to the non-surface surface of the surface layer, warping occurred with the copper foil side as the inside, as in Comparative Example 1. A comparison between Example 3 and Comparative Example 3 shows that by reducing the thickness of the resin surface layer, warping of the substrate (single-sided copper-clad laminate) after the surface layer was formed and after the copper foil was bonded can be reduced.

[0138] Explanation of reference numerals in the attached figures

[0139] 1. Multilayer polyimide film

[0140] 10-core layer (non-thermoplastic polyimide film)

[0141] 11, 12 Thermoplastic resin layers

[0142] 2 Surface layer

[0143] 101 laminate

[0144] 5 Metal Layers

[0145] 105 Single-sided metal-coated laminate

Claims

1. A laminate comprising: 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 disposed on the first main surface of the non-thermoplastic polyimide film; and a second thermoplastic polyimide layer disposed on the second main surface of the non-thermoplastic polyimide film; and A surface layer that is in contact with the second thermoplastic polyimide layer of the multilayer polyimide film. The surface layer is a silicon oxide layer with a thickness of 3~150nm.

2. The laminate according to claim 1, wherein, The silicon oxide in the silicon oxide layer is a non-stoichiometric silicon oxide represented by SiOx, where x is 1.2 to 1.

95.

3. The laminate according to claim 1 or 2, wherein, The thickness of the silicon oxide layer is 10~100nm.

4. The laminate according to claim 1 or 2, wherein, The first thermoplastic polyimide layer and the second thermoplastic polyimide layer have the same composition.

5. The laminate according to claim 1 or 2, wherein, The glass transition temperatures of the first thermoplastic polyimide layer and the second thermoplastic polyimide layer are 150~320℃.

6. The laminate according to claim 1 or 2, wherein, The glass transition temperatures of the first thermoplastic polyimide layer and the second thermoplastic polyimide layer are 200~300℃.

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

8. The single-sided metal-coated laminate according to claim 7, wherein, The metal foil is copper foil.

9. The single-sided metal-coated laminate according to claim 7 or 8, wherein, The thickness of the metal foil is 3~30μm.

10. A multilayer printed circuit board, comprising multiple wiring layers laminated with insulating layers sandwiched between them, the multilayer printed circuit board having a first wiring layer formed by patterning the metal foil of the single-sided metal-clad laminate according to any one of claims 7 to 9. The single-sided metal-coated laminate is multi-layered by bonding other layers to the surface layer.

11. The multilayer printed circuit board according to claim 10, wherein, A second wiring layer is attached to the surface layer by means of an adhesive sheet.

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