CN108848609B - Electromagnetic wave shielding film, flexible printed wiring board, and method for producing same - Google Patents
Electromagnetic wave shielding film, flexible printed wiring board, and method for producing same Download PDFInfo
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Classifications
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K1/00—Printed circuits
- H05K1/02—Details
- H05K1/0213—Electrical arrangements not otherwise provided for
- H05K1/0216—Reduction of cross-talk, noise or electromagnetic interference
- H05K1/023—Reduction of cross-talk, noise or electromagnetic interference using auxiliary mounted passive components or auxiliary substances
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B15/00—Layered products comprising a layer of metal
- B32B15/04—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B3/00—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar shape; Layered products comprising a layer having particular features of form
- B32B3/26—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar shape; Layered products comprising a layer having particular features of form characterised by a particular shape of the outline of the cross-section of a continuous layer; characterised by a layer with cavities or internal voids ; characterised by an apertured layer
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B33/00—Layered products characterised by particular properties or particular surface features, e.g. particular surface coatings; Layered products designed for particular purposes not covered by another single class
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
- B32B7/04—Interconnection of layers
- B32B7/06—Interconnection of layers permitting easy separation
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
- B32B7/04—Interconnection of layers
- B32B7/10—Interconnection of layers at least one layer having inter-reactive properties
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K3/00—Apparatus or processes for manufacturing printed circuits
- H05K3/0058—Laminating printed circuit boards onto other substrates, e.g. metallic substrates
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2307/00—Properties of the layers or laminate
- B32B2307/20—Properties of the layers or laminate having particular electrical or magnetic properties, e.g. piezoelectric
- B32B2307/212—Electromagnetic interference shielding
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2457/00—Electrical equipment
- B32B2457/08—PCBs, i.e. printed circuit boards
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
- H05K2201/07—Electric details
- H05K2201/0707—Shielding
- H05K2201/0715—Shielding provided by an outer layer of PCB
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
- H05K2203/01—Tools for processing; Objects used during processing
- H05K2203/0195—Tool for a process not provided for in H05K3/00, e.g. tool for handling objects using suction, for deforming objects, for applying local pressure
Landscapes
- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Manufacturing & Machinery (AREA)
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Shielding Devices Or Components To Electric Or Magnetic Fields (AREA)
- Structure Of Printed Boards (AREA)
Abstract
The present invention relates to an electromagnetic wave shielding film, a flexible printed wiring board, and methods for manufacturing the same. Specifically, an electromagnetic wave shielding film and a flexible printed wiring board with the electromagnetic wave shielding film, which can maintain the shielding effect of electromagnetic wave noise even if a crack is generated in a metal thin film layer, and a method for manufacturing the same are provided. The electromagnetic wave shielding film (10) comprises an insulating protective layer (12), an electromagnetic wave shielding layer, a metal thin film layer (14) having a surface resistance of 0.01-0.3 omega, and an isotropic conductive adhesive layer (16) containing a conductive filler and having a surface resistance of 1-100 omega in this order, and the increase in the resistance of the electromagnetic wave shielding layer due to the occurrence of cracks in the metal thin film layer is suppressed to 10 times or less.
Description
This application is a divisional application of a patent application having an application date of 2015, 9/2, application number of 201510557975.9, entitled "electromagnetic wave shielding film, flexible printed wiring board, and method for producing the same", and the entire contents thereof are incorporated herein by reference.
Technical Field
The present invention relates to an electromagnetic wave shielding film, a flexible printed wiring board provided with the electromagnetic wave shielding film, and a method for manufacturing the same.
Background
In order to shield electromagnetic wave noise generated from the flexible printed wiring board or electromagnetic wave noise from the outside, an electromagnetic wave shielding film may be provided on the surface of the flexible printed wiring board (for example, see patent document 1).
Fig. 9 is a sectional view showing an example of a conventional process for manufacturing a flexible printed wiring board with an electromagnetic wave shielding film.
The electromagnetic wave shielding film-equipped flexible printed wiring board 101 includes a flexible printed wiring board 130, an insulating film 140, and an electromagnetic wave shielding film 110 from which a release film 118 is peeled.
The flexible printed wiring board 130 has a printed circuit 134 on one surface of a base film 132.
The insulating film 140 is provided on the surface of the flexible printed wiring board 130 on the side where the printed circuit 134 is provided.
The electromagnetic wave shielding film 110 includes: an insulating protective layer 112, a metal thin film layer 114 covering a first surface of the insulating protective layer 112, an anisotropic conductive adhesive layer 116 covering a surface of the metal thin film layer 114, and a release film 118 (carrier film) covering a second surface of the insulating protective layer 112.
The anisotropic conductive adhesive layer 116 of the electromagnetic wave shielding film 110 is adhered to the surface of the insulating film 140 and cured. The anisotropic conductive adhesive layer 116 is electrically connected to the printed circuit 134 through a through hole 142 formed in the insulating film 140.
As shown in fig. 9, for example, the flexible printed wiring board with an electromagnetic wave shielding film 101 is manufactured through the following steps.
(i) An insulating film 140 having a through hole 142 formed at a position corresponding to the ground of the printed circuit 134 is provided on the surface of the flexible printed wiring board 130 on the side where the printed circuit 134 is provided.
(ii) The electromagnetic wave shielding film 110 is stacked such that the anisotropic conductive adhesive layer 116 of the electromagnetic wave shielding film 110 is in contact with the surface of the insulating film 140, and hot-pressed, whereby the anisotropic conductive adhesive layer 116 is adhered to the surface of the insulating film 140, and the anisotropic conductive adhesive layer 116 is electrically connected to the ground of the printed circuit 134 through the through hole 142.
(iii) After the hot pressing, the release film 118, which has finished its task as a carrier film, is peeled and removed from the insulating protective layer 112, and the electromagnetic wave shielding film-attached flexible printed wiring board 101 is obtained.
However, in the flexible printed wiring board with an electromagnetic wave shielding film 101, the electromagnetic wave shielding film 110 is bent and deformed along the shape of the unevenness, such as the portion of the through hole 142, and thus cracks are easily generated in the metal thin film layer 114. Since the anisotropic conductive adhesive layer 116 has conductivity in the thickness direction and does not have conductivity in the surface direction, when a crack occurs in the metal thin film layer 114, the resistance of the electromagnetic wave shielding layer composed of the metal thin film layer 114 and the anisotropic conductive adhesive layer 116 increases, and the electromagnetic wave noise shielding effect of the electromagnetic wave shielding layer decreases.
[ Prior art documents ]
[ patent document ]
[ patent document 1] Japanese patent application laid-open No. 2014-112576
Disclosure of Invention
The invention provides an electromagnetic wave shielding film capable of maintaining the shielding effect of electromagnetic wave noise even if a crack is generated in a metal thin film layer, a flexible printed wiring board with the electromagnetic wave shielding film, and a manufacturing method thereof.
The present invention has the following aspects.
(1) An electromagnetic wave shielding film, comprising in order: an insulating protective layer; a metal thin film layer having a surface resistance of 0.01 Ω to 0.3 Ω; contains a conductive filler and an isotropic conductive adhesive layer having a surface resistance of 1-100 omega.
(2) In the electromagnetic wave shielding film of (1), the proportion of the conductive filler is 30 vol% or more and 80 vol% or less of 100 vol% of the isotropic conductive adhesive layer.
(3) In the electromagnetic wave-shielding film of (1) or (2), the isotropic conductive adhesive layer contains conductive particles and conductive fibers as the conductive filler.
(4) The electromagnetic wave shielding film according to any one of (1) to (3) further comprises a first release film provided on a surface of the insulating protective layer.
(5) The electromagnetic wave-shielding film of (4) further comprises a second release film provided on the surface of the isotropic conductive adhesive layer.
(6) A method for producing the electromagnetic wave shielding film of (5), comprising the following steps (a) to (d):
(a) forming an insulating protective layer on one side of the first release film;
(b) forming a metal thin film layer on the surface of the insulating protective layer to obtain a first laminate sequentially comprising a first release film, the insulating protective layer and the metal thin film layer;
(c) forming an isotropic conductive adhesive layer on one surface of the second release film to obtain a second laminated body sequentially comprising the second release film and the isotropic conductive adhesive layer;
(d) the first laminate and the second laminate are bonded together so that the metal thin film layer and the isotropic conductive adhesive layer are in contact with each other.
(7) A flexible printed wiring board with an electromagnetic wave shielding film, comprising: a flexible printed wiring board having a printed circuit on at least one surface of a base film; an insulating film provided on a surface of the flexible printed wiring board on which the printed circuit is provided; and the electromagnetic wave shielding film of any one of (1) to (3) in which the isotropic conductive adhesive layer is adhered to the surface of the insulating film, wherein the isotropic conductive adhesive layer is electrically connected to the printed circuit through a through hole formed in the insulating film.
(8) A method for manufacturing a flexible printed wiring board with an electromagnetic wave shielding film, comprising the following steps (e) to (g):
(e) providing an insulating film having a through hole formed at a position corresponding to a printed circuit on a surface of a flexible printed wiring board having the printed circuit on at least one surface of a base film, the surface being provided with the printed circuit, to obtain a flexible printed wiring board with the insulating film;
(f) after the step (e), laminating the flexible printed wiring board with an insulating film and the electromagnetic wave shielding film of any one of (1) to (4) such that the isotropic conductive adhesive layer is in contact with the surface of the insulating film, and hot-pressing the laminated layers, whereby the isotropic conductive adhesive layer is adhered to the surface of the insulating film and the isotropic conductive adhesive layer is electrically connected to the printed circuit through the through hole;
(g) when the electromagnetic wave shielding film has the first release film, the first release film is peeled off after the step (f).
The electromagnetic wave shielding film of the present invention can maintain the shielding effect of electromagnetic wave noise even if cracks are generated in the metal thin film layer.
According to the method for manufacturing an electromagnetic wave shielding film of the present invention, an electromagnetic wave shielding film can be manufactured which can maintain the shielding effect of electromagnetic wave noise even if a crack is generated in the metal thin film layer.
The flexible printed wiring board with an electromagnetic wave shielding film of the present invention can maintain the shielding effect of electromagnetic wave noise even if a crack is generated in the metal thin film layer.
According to the method for manufacturing a flexible printed wiring board with an electromagnetic wave shielding film of the present invention, it is possible to manufacture a flexible printed wiring board with an electromagnetic wave shielding film capable of maintaining the shielding effect of electromagnetic wave noise even if a crack is generated in the metal thin film layer.
Drawings
Fig. 1 is a sectional view showing an example of an electromagnetic wave shielding film of the present invention.
Fig. 2 is a cross-sectional view showing an example of steps (a) to (b) in the method for producing an electromagnetic wave shielding film of the present invention.
Fig. 3 is a sectional view showing an example of the step (c) in the method for producing an electromagnetic wave shielding film of the present invention.
Fig. 4 is a sectional view showing an example of the step (d) in the method for producing an electromagnetic wave shielding film of the present invention.
Fig. 5 is a perspective view showing a typical example of an electromagnetic wave-shielding layer for estimating the overall resistance of the electromagnetic wave-shielding layer before cracks are generated in the metal thin film layer.
Fig. 6 is a perspective view showing a typical example of an electromagnetic wave-shielding layer for estimating the overall resistance of the electromagnetic wave-shielding layer after cracks are generated in the metal thin film layer.
Fig. 7 is a sectional view showing an example of the flexible printed wiring board with an electromagnetic wave shielding film of the present invention.
Fig. 8 is a sectional view showing an example of steps (e) to (g) in the method for manufacturing a flexible printed wiring board with an electromagnetic wave shielding film according to the present invention.
Fig. 9 is a sectional view showing an example of a conventional process for manufacturing a flexible printed wiring board with an electromagnetic wave shielding film.
Detailed Description
The following definitions of terms apply to the present description and claims.
The average particle diameter of the conductive particles is a value obtained as follows: the method includes the steps of randomly selecting 30 conductive particles from an electron microscope image of the conductive particles, measuring a minimum diameter and a maximum diameter of each conductive particle, and arithmetically averaging the measured particle diameters of the 30 conductive particles by using a central value of the minimum diameter and the maximum diameter as a particle diameter of one particle.
The average fiber length of the conductive fiber is a value obtained as follows: 30 conductive fibers were randomly selected from the electron microscope image of the conductive fibers, and the fiber length was measured for each conductive fiber, and the arithmetic average was taken of the measured fiber lengths of the 30 conductive fibers.
The average fiber diameter of the conductive fiber is a value obtained as follows: the method comprises the steps of randomly selecting 30 conductive fibers from an electron microscope image of the conductive fibers, measuring the minimum diameter and the maximum diameter of each conductive fiber, setting the central value of the minimum diameter and the maximum diameter as the fiber diameter of one fiber, and arithmetically averaging the measured fiber diameters of the 30 conductive fibers.
The specific surface area of the conductive particles and the conductive fibers is a value calculated from the amount of nitrogen adsorbed by measuring the amount of nitrogen by immersing degassed particles in liquid nitrogen.
The thicknesses of the film (release film, insulating film, etc.), coating film (insulating protective layer, conductive adhesive layer, etc.), metal thin film layer, etc. are values obtained by observing the cross section of the measurement object using a transmission electron microscope, measuring the thicknesses of 5 sites, and averaging the thicknesses.
The storage modulus of elasticity is measured as one of viscoelastic characteristics using a dynamic viscoelasticity measuring apparatus which calculates from a stress applied to a measurement object and a detected strain and outputs the calculated value as a function of temperature or time.
The surface resistance is the resistance between the electrodes and is measured as follows: using 2 thin film metal electrodes (length 10mm, width 5mm, inter-electrode distance 10mm) formed by vapor plating gold on quartz glass, the object to be measured was placed on the electrodes, and a region of 10mm × 20mm of the object to be measured was pressed from above the object to be measured with a load of 0.049N, and the measurement was performed at a measurement current of 1mA or less.
< electromagnetic wave shielding film >
Fig. 1 is a sectional view showing an example of an electromagnetic wave shielding film of the present invention.
The electromagnetic wave shielding film 10 has: an insulating protective layer 12, a metal thin film layer 14 covering a first surface of the insulating protective layer 12, an isotropic conductive adhesive layer 16 covering a surface of the metal thin film layer 14, a first release film 18 covering a second surface of the insulating protective layer 12, and a second release film 20 covering a surface of the isotropic conductive adhesive layer 16.
(insulating protective layer)
The insulating protective layer 12 is a base (foundation) for forming the metal thin film layer 14, and protects the metal thin film layer 14 after the electromagnetic wave shielding film 10 is attached to the surface of the insulating film provided on the surface of the flexible printed wiring board.
The surface resistance of the insulating protective layer 12 is preferably 1 × 10 from the viewpoint of electrical insulation6Omega or more. The surface resistance of the insulating protective layer 12 is preferably 1X 10 from the viewpoint of practical use19Omega is less than or equal to.
Examples of the insulating protective layer 12 include a coating film formed by applying and curing a paint containing a thermosetting resin and a curing agent, a coating film formed by applying a paint containing a thermoplastic resin, and a layer formed of a film obtained by melt-molding a thermoplastic resin. From the viewpoint of heat resistance when welding or the like is performed, a coating film formed by applying and curing a coating material containing a thermosetting resin and a curing agent is preferable.
The thermosetting resin may, for example, be an amide resin, an epoxy resin, a phenol resin, an amino resin, an alkyd resin, a urethane resin, a synthetic rubber, a UV-curable acrylate resin, or the like, and an amide resin or an epoxy resin is preferable in terms of excellent heat resistance.
The storage modulus of elasticity of the insulating protective layer 12 at 160 ℃ is preferably 5X 106 1X 10 above Pa8Pa or less, more preferably 8X 106Pa above 2X 107Pa or less. In general, a cured product of a thermosetting resin is hard, and thus a coating film formed therefrom lacks flexibility, and is very brittle particularly when the thickness is reduced, and does not have a strength enough to be present as an independent film. The insulating protective layer 12 preferably has sufficient strength at the temperature when the first release film 18 is peeled off (the temperature at which the conductive adhesive is cured, typically 150 ℃ to 200 ℃). If the storage elastic modulus of the insulating protective layer 12 at 160 ℃ is 5X 106Pa or more, the insulating protective layer 12 does not soften. If the storage elastic modulus of the insulating protective layer 12 at 160 ℃ is 1X 108When Pa or less, the flexibility and strength are sufficient. As a result, the insulating protective layer 12 makes the electromagnetic wave shielding film 10 less likely to break when the first release film 18 is peeled off than before.
The insulating protective layer 12 may be colored to give a design feeling to the flexible printed wiring board with the electromagnetic wave shielding film.
The insulating protective layer 12 may be composed of 2 or more kinds of layers having different properties such as storage modulus of elasticity and materials.
The thickness of the insulating protective layer 12 is preferably 1 μm to 10 μm, and more preferably 1 μm to 5 μm. The insulating protective layer 12 has good heat resistance if it has a thickness of 1 μm or more. If the thickness of the insulating protective layer 12 is 10 μm or less, the electromagnetic wave shielding film 10 can be made thin.
(Metal film layer)
The metal thin film layer 14 is a layer made of a metal thin film. The metal thin film layer 14 is formed to extend in the plane direction, and therefore has conductivity in the plane direction, and functions as an electromagnetic wave shielding layer or the like.
The metal thin film layer 14 may be a metal thin film or a metal foil formed by physical vapor deposition (vacuum vapor deposition, sputtering, ion beam vapor deposition, electron beam vapor deposition, or the like), CVD, plating, or the like, and is preferably a metal thin film (vapor deposited film) by physical vapor deposition, because the metal thin film can be made thin, has excellent conductivity in the plane direction even if the thickness is thin, and can be formed simply by a dry process.
Examples of the metal thin film material constituting the metal thin film layer 14 include aluminum, silver, copper, gold, and conductive ceramics. Copper is preferred from the viewpoint of electrical conductivity, and conductive ceramics is preferred from the viewpoint of chemical stability.
The thickness of the metal thin film layer 14 is preferably 0.01 μm to 1 μm, and more preferably 0.05 μm to 1 μm. When the thickness of the metal thin film layer 14 is 0.01 μm or more, the electrical conductivity in the in-plane direction is further improved. When the thickness of the metal thin film layer 14 is 0.05 μm or more, the electromagnetic wave noise shielding effect is further improved. When the thickness of the metal thin film layer 14 is 1 μm or less, the electromagnetic wave shielding film 10 can be made thin. In addition, the productivity and flexibility of the electromagnetic wave shielding film 10 are improved.
The surface resistance of the metal thin film layer 14 is 0.01 Ω to 0.3 Ω, preferably 0.02 Ω to 0.2 Ω, and more preferably 0.05 Ω to 0.1 Ω. When the surface resistance of the metal thin film layer 14 is 0.01 Ω or more, the metal thin film layer 14 can be sufficiently thinned. The metal thin film layer 14 has a surface resistance of 0.3 Ω or less, and can sufficiently function as an electromagnetic wave shielding layer.
(Isotropic conductive adhesive layer)
The isotropic conductive adhesive layer 16 is conductive in the thickness direction and the surface direction, and has adhesiveness.
The isotropic conductive adhesive layer 16 can sufficiently function as an electromagnetic wave shielding layer as compared with an anisotropic conductive adhesive layer having conductivity in the thickness direction and no conductivity in the surface direction.
The isotropic conductive adhesive layer 16 contains a conductive filler. The isotropic conductive adhesive layer 16 preferably contains the conductive particles 22 as a conductive filler from the viewpoint of conductivity in the thickness direction and the surface direction, and more preferably contains the conductive particles 22 and the conductive fibers 24 as conductive fillers from the viewpoint of better conductivity in the surface direction and lower surface resistance, and from the viewpoint of higher strength and less occurrence of cracks in the isotropic conductive adhesive layer 16.
In addition, in the isotropic conductive adhesive layer 16, it is preferable that the orientation of the fiber direction of the conductive fibers 24 is more biased toward the surface direction of the isotropic conductive adhesive layer 16 than the thickness direction of the isotropic conductive adhesive layer 16, that is, the conductive fibers 24 are oriented in the surface direction of the isotropic conductive adhesive layer 16, from the viewpoint that the conductivity in the surface direction becomes better and the surface resistance becomes low, and from the viewpoint that the strength of the isotropic conductive adhesive layer 16 becomes high and cracks are less likely to occur.
As the isotropic conductive adhesive layer 16, a thermosetting isotropic conductive adhesive layer is preferable from the viewpoint of exhibiting heat resistance after curing.
The thermosetting isotropic conductive adhesive layer 16 includes, for example, a thermosetting adhesive, conductive particles 22, and conductive fibers 24. The isotropic conductive adhesive layer 16 may be in an uncured state or in a B-stage state.
Examples of the thermosetting adhesive include epoxy resin, phenol resin, amino resin, alkyd resin, urethane resin, synthetic rubber, and UV-curable acrylate resin. From the viewpoint of excellent heat resistance, an epoxy resin is preferable. The epoxy resin may contain a rubber component (carboxyl-modified nitrile rubber or the like) for imparting flexibility, an adhesion-imparting agent, and the like.
The thermosetting adhesive may contain a cellulose resin or microfibers (e.g., glass fibers) in order to improve the strength of the isotropic conductive adhesive layer 16 and improve punching characteristics.
Examples of the conductive particles 22 include graphite powder, sintered carbon particles, particles of a metal (silver, platinum, gold, copper, nickel, palladium, aluminum, solder, or the like), and electrodeposited sintered carbon particles. Hard spherical fired carbon particles are preferred from the viewpoint of fluidity of the isotropic conductive adhesive layer 16.
The average particle diameter of the conductive particles 22 is preferably 0.1 μm to 10 μm, more preferably 0.2 μm to 1 μm. If the average particle diameter of the conductive particles 22 is 0.1 μm or more, the conductivity in the 3-dimensional direction can be stably improved by increasing the number of contact points of the conductive particles 22. If the average particle diameter of the conductive particles 22 is 10 μm or less, the flowability of the isotropic conductive adhesive layer 16 (the ability of the insulating film to follow the shape of the through-hole) can be ensured, and the through-hole of the insulating film can be sufficiently filled with the conductive adhesive.
The specific surface area of the conductive particles 22 is preferably 0.2m2More than 50 m/g2A value of less than or equal to g, more preferably 0.5m2More than 20 m/g2The ratio of the carbon atoms to the carbon atoms is less than g. If the specific surface area of the conductive particles 22 is 0.2m2When the ratio is more than g, the conductive particles 22 can be easily obtained. If the specific surface area of the conductive particles 22 is 50m2If the amount of oil absorbed by the conductive particles 22 is not too large,/g or less, the viscosity of the conductive adhesive is not too high, and the coating property is more excellent. In addition, the fluidity of the isotropic conductive adhesive layer 16 (the ability of the insulating film to follow the shape of the through-hole) can be further ensured.
When the conductive filler is only the conductive particles 22, the proportion of the conductive particles 22 is preferably 30 vol% to 80 vol%, more preferably 50 vol% to 70 vol%, of 100 vol% of the isotropic conductive adhesive layer 16. If the proportion of the conductive particles 22 is 30 vol% or more, the conductivity of the isotropic conductive adhesive layer 16 is stabilized. When the proportion of the conductive particles 22 is 80 vol% or less, the adhesiveness and fluidity (the ability of the insulating film to follow the shape of the through-hole) of the isotropic conductive adhesive layer 16 are improved. In addition, the flexibility of the electromagnetic wave shielding film 10 is improved.
The conductive fiber 24 may be, for example, a carbon nanofiber, a metal (copper, platinum, gold, silver, nickel, or the like) nano-wiring, or the like, and a carbon nanofiber having a small fiber diameter is preferable since the thickness of the isotropic conductive adhesive layer 16 is as small as a micrometer. The carbon nanofibers are preferably vapor-phase carbon fibers from the viewpoint of ensuring the fluidity of the isotropic conductive adhesive layer 16 (the ability of the insulating film to follow the shape of the through-holes) from the viewpoint of excellent dispersibility.
The average fiber length of the conductive fibers 24 is preferably 0.5 μm to 5 μm, and more preferably 1 μm to 3 μm. If the average fiber length of the conductive fibers 24 is 0.5 μm or more, the conductivity and strength of the isotropic conductive adhesive layer 16 are further improved. When the average fiber length of the conductive fibers 24 is 5 μm or less, the adhesiveness and fluidity (the ability of the insulating film to follow the shape of the through-hole) of the isotropic conductive adhesive layer 16 are improved.
The average fiber diameter of the conductive fibers 24 is preferably 0.01 μm to 0.5 μm, and more preferably 0.05 μm to 0.3 μm. When the average fiber diameter of the conductive fibers is 0.01 μm or more, the conductivity and strength of the isotropic conductive adhesive layer 16 become better. When the average fiber diameter of the conductive fibers 24 is 0.5 μm or less, the adhesiveness and fluidity (the ability of the insulating film to follow the shape of the through-hole) of the isotropic conductive adhesive layer 16 are improved.
The aspect ratio of the conductive fibers 24 is preferably 5 to 300, and more preferably 10 to 100. If the aspect ratio of the conductive fiber is 5 or more, the conductivity and strength of the isotropic conductive adhesive layer 16 become better. When the aspect ratio of the conductive fibers is 300 or less, the adhesiveness and fluidity (the ability of the insulating film to follow the shape of the through-hole) of the isotropic conductive adhesive layer 16 are improved.
The specific surface area of the conductive fibers 24 is preferably 2m2More than 50 m/g2A ratio of 2m or less per gram, more preferably240m above g2The ratio of the carbon atoms to the carbon atoms is less than g. If the specific surface area of the conductive fiber 24 is 2m2When the ratio is more than g, the conductive particles 20 can be easily obtained. If the specific surface area of the conductive fiber 24 is 50m2If the oil absorption amount is not too large, the viscosity of the conductive adhesive is not too high, and the applicability is better. In addition, the fluidity of the isotropic conductive adhesive layer 16 (the ability of the insulating film to follow the shape of the through-hole) can be further ensured.
When the conductive filler is the conductive particles 22 and the conductive fibers 24, the proportion of the conductive fibers 24 is preferably 3 vol% to 30 vol%, more preferably 5 vol% to 20 vol%, of 100 vol% of the isotropic conductive adhesive layer 16. However, the total of the conductive particles 22 and the conductive fibers 24 is 30 vol% to 80 vol% (preferably 50 vol% to 70 vol%). When the ratio of the conductive fibers 24 is 3 vol% or more, the conductivity and strength of the isotropic conductive adhesive layer 16 become better. If the proportion of the conductive fibers 24 is 30 vol% or less, the viscosity of the conductive adhesive is not excessively high, and the applicability is improved. Further, the flowability of the isotropic conductive adhesive layer 16 (the ability of the insulating film to follow the shape of the through-hole) can be ensured, and the through-hole of the insulating film can be sufficiently filled with the isotropic conductive adhesive layer 16.
The thickness of the isotropic conductive adhesive layer 16 is preferably 5 μm to 20 μm, and more preferably 7 μm to 17 μm. If the thickness of the isotropic conductive adhesive layer 16 is 5 μm or more, the conductivity of the isotropic conductive adhesive layer 16 becomes better, and the layer can sufficiently function as an electromagnetic wave shielding layer. Further, the flowability of the isotropic conductive adhesive layer 16 (the ability of the insulating film to follow the shape of the through-hole) can be ensured, the through-hole of the insulating film can be sufficiently filled with the conductive adhesive, the folding endurance can be ensured, and the conductive adhesive layer 16 does not break even when repeatedly bent. If the thickness of the isotropic conductive adhesive layer 16 is 20 μm or less, the electromagnetic wave shielding film 10 can be made thin. In addition, the flexibility of the electromagnetic wave shielding film 10 is improved.
The surface resistance of the isotropic conductive adhesive layer 16 is preferably 1 Ω to 100 Ω, preferably 1 Ω to 50 Ω, and more preferably 1 Ω to 10 Ω. When the surface resistance of the isotropic conductive adhesive layer 16 is 1 Ω or more, the isotropic conductive adhesive layer 16 also has high fluidity, high strength, and high toughness. If the surface resistance of the isotropic conductive adhesive layer 16 is 100 Ω or less, even if a crack occurs in the metal thin film layer 14, an increase in the resistance of the electromagnetic wave shielding layer composed of the metal thin film layer 14 and the isotropic conductive adhesive layer 16 can be suppressed, and as a result, the electromagnetic wave shielding film 10 can maintain the shielding effect of electromagnetic wave noise.
(first Release film)
The first release film 18 is a carrier film when the insulating protective layer 12 and the metal thin film layer 14 are formed, and improves the workability of the electromagnetic wave shielding film 10. The first release film 18 is peeled from the insulating protective layer 12 after the electromagnetic wave shielding film 10 is attached to a flexible printed wiring board or the like.
The resin material of the first release film 18 may, for example, be polyethylene terephthalate, polyethylene naphthalate, polyethylene isophthalate, polybutylene terephthalate, polyolefin, polyacetate, polycarbonate, polyphenylene sulfide, polyamide, ethylene-vinyl acetate copolymer, polyvinyl chloride, polyvinylidene chloride, synthetic rubber, liquid crystal polymer, etc., and polyethylene terephthalate is preferred from the viewpoint of heat resistance (dimensional stability) and cost in the production of the electromagnetic wave shielding film 10.
The storage elastic modulus of the first release film 18 at 160 ℃ is preferably 0.8X 108 4X 10 above Pa8Pa or less, more preferably 0.8X 108Pa or above 3X 108Pa or less. If the first release film 18 has a storage modulus of elasticity of 0.8X 10 at 160 DEG C8Pa or more improves the workability of the electromagnetic wave shielding film 10. If the first release film 18 has a storage modulus of elasticity of 4X 10 at 160 DEG C8When Pa is smaller, the flexibility of the first release film 18 becomes better.
The thickness of the first release film 18 is preferably 5 μm to 500 μm, more preferably 10 μm to 150 μm, and still more preferably 25 μm to 100 μm. If the thickness of the first release film 18 is 5 μm or more, the workability of the electromagnetic wave shielding film 10 becomes good. In addition, the first release film 18 sufficiently operates as a spacer material, and when the isotropic conductive adhesive layer 16 of the electromagnetic wave shielding film 10 is attached to the surface of the insulating film provided on the surface of the flexible printed wiring board by hot pressing, the isotropic conductive adhesive layer 16 easily follows the uneven shape of the surface of the insulating film. When the thickness of the first release film 18 is 500 μm or less, heat is easily transferred to the isotropic conductive adhesive layer 16 of the electromagnetic wave shielding film 10 when the isotropic conductive adhesive layer 16 is thermally pressed on the surface of the insulating film.
(Release agent layer)
The surface of the insulating protective layer 12 side of the release film main body 18a is subjected to a release treatment with release agent (duty), thereby forming a release agent layer 18 b. Since the first release film 18 has the release agent layer 18b, when the first release film 18 is peeled from the insulating protective layer 12 in the step (g) described later, the first release film 18 is easily peeled, and the insulating protective layer 12 and the cured isotropic conductive adhesive layer 16 are not easily broken.
Known release agents can be used as the release agent.
The thickness of the release agent layer 18b is preferably 0.05 μm to 2.0 μm, and more preferably 0.1 μm to 1.5 μm. If the thickness of the release agent layer 18b is within the above range, the first release film 18 is more easily peeled in the step (g) described later.
(second release film)
The second release film 20 protects the isotropic conductive adhesive layer 16 and improves the handling properties of the electromagnetic wave shielding film 10. The second release film 20 is peeled from the isotropic conductive adhesive layer 16 before the electromagnetic wave shielding film 10 is attached to a flexible printed wiring board or the like.
As the resin material of the second release film 20, the same resin material as that of the first release film 18 can be exemplified.
The thickness of the second release film 20 is preferably 5 μm to 500 μm, more preferably 10 μm to 150 μm, and still more preferably 25 μm to 100 μm.
(Release agent layer)
The surface of the release film main body 20a on the isotropic conductive adhesive layer 16 side is subjected to release treatment using a release agent to form a release agent layer 20 b. Since the second release film 20 has the release agent layer 20b, the second release film 20 is easily peeled and the isotropic conductive adhesive layer 16 is not easily broken when the second release film 20 is peeled from the isotropic conductive adhesive layer 16 in the step (g) described later.
Known release agents can be used as the release agent.
The thickness of the release agent layer 20b is preferably 0.05 μm to 2.0 μm, and more preferably 0.1 μm to 1.5 μm. If the thickness of the release agent layer 20b is within the above range, the second release film 20 is more easily peeled in the step (g) described later.
(thickness of electromagnetic wave shielding film)
The thickness of the electromagnetic wave shielding film 10 (excluding the release film) is preferably 10 μm to 45 μm, and more preferably 10 μm to 30 μm. If the thickness of the electromagnetic wave-shielding film 10 (excluding the release film) is 10 μm or more, the first release film 18 is not easily broken when peeled. If the thickness of the electromagnetic wave shielding film 10 (excluding the release film) is 45 μm or less, the flexible printed wiring board with the electromagnetic wave shielding film can be thinned.
(method for producing electromagnetic wave shielding film)
The electromagnetic wave shielding film of the present invention can be produced by a method having, for example, the following steps (a) to (d).
(a) An insulating protective layer is formed on one side of the first release film.
(b) By forming the metal thin film layer on the surface of the insulating protective layer, a first laminate having the first release film, the insulating protective layer, and the metal thin film layer in this order is obtained.
(c) The second laminate having the second release film and the isotropic conductive adhesive layer in this order is obtained by forming the isotropic conductive adhesive layer on one surface of the second release film.
(d) The first laminate and the second laminate are bonded so that the metal thin film layer and the isotropic conductive adhesive layer are in contact with each other.
Hereinafter, a method for manufacturing the electromagnetic wave shielding film 10 shown in fig. 1 will be described with reference to fig. 2 to 4.
(Process (a))
As shown in fig. 2, the insulating protective layer 12 is formed on the surface of the release agent layer 18b of the first release film 18.
Examples of the method of forming the insulating protective layer 12 include a method of applying a paint containing a thermosetting resin and a curing agent and curing the paint, a method of applying a paint containing a thermoplastic resin, and a method of attaching a film obtained by melt-molding a thermoplastic resin. From the viewpoint of heat resistance at the time of welding or the like, a method of applying a coating material containing a thermosetting resin and a curing agent and curing the coating material is preferable.
The coating material containing the thermosetting resin and the curing agent may contain a solvent and other components as necessary.
When the insulating protective layer 12 is formed by coating with paint, the insulating protective layer 12 can be made relatively thin. Further, the cured product of the thermosetting resin is hard, and when the insulating protective layer 12 is made thin, the strength is insufficient. As described above, the storage modulus of elasticity of the insulating protective layer 12 at 160 ℃ is 5X 106 1X 10 above Pa8Pa or less, the balance among flexibility, strength and heat resistance becomes good.
The storage elastic modulus of the insulating protective layer 12 is preferably controlled by selecting the kind and composition of the thermosetting resin, the curing agent, and the like and adjusting the storage elastic modulus of the cured thermosetting resin, from the viewpoint of the toughness obtained from the crosslinking density and the crosslinked structure.
The storage elastic modulus can be adjusted by adjusting the curing conditions such as temperature and time for curing the thermosetting resin, or by adding a thermoplastic resin such as a thermoplastic elastomer as a component having no thermosetting property.
(Process (b))
As shown in fig. 2, a metal thin film layer 14 is formed on the surface of the insulating protective layer 12 to obtain a first laminate 10 a.
Examples of the method for forming the metal thin film layer 14 include a method for forming a metal thin film by physical vapor deposition, CVD, plating, or the like, and a method for attaching a metal foil. The method of forming a metal thin film by physical vapor deposition, CVD, plating, or the like is preferable from the viewpoint of enabling the formation of the metal thin film layer 14 having excellent conductivity in the in-plane direction, and the method of physical vapor deposition is more preferable from the viewpoint of enabling the formation of the metal thin film layer 14 having a small thickness and having excellent conductivity in the in-plane direction even if the thickness is small, and enabling the formation of the metal thin film layer 14 by a dry process in a simple manner.
(step (c))
As shown in fig. 3, the isotropic conductive adhesive layer 16 is formed on the surface of the release agent layer 20b of the second release film 20, and the second laminate 10b is obtained.
As a method for forming the isotropic conductive adhesive layer 16, a method of applying a conductive adhesive composition may be mentioned.
As the conductive adhesive composition, a composition containing the thermosetting adhesive, the conductive particles 22, and the conductive fibers 24 is used.
(Process (d))
As shown in fig. 4, the first laminate 10a and the second laminate 10b are bonded so that the metal thin film layer 14 and the isotropic conductive adhesive layer 16 are in contact with each other.
The first laminate 10a and the second laminate 10b are preferably bonded by hot pressing using a press (not shown) or the like, from the viewpoint of facilitating orientation of the conductive fibers 24 in the surface direction of the isotropic conductive adhesive layer 16.
(Effect)
In the electromagnetic wave shielding film 10 described above, the surface resistance of the metal thin film layer 14 is 0.3 Ω or less and the surface resistance of the isotropic conductive adhesive layer 16 is 10 Ω or less, and therefore, as described below, even if cracks occur in the metal thin film layer 14, the electromagnetic wave noise shielding effect can be maintained.
Fig. 5 is a perspective view showing a typical example of the electromagnetic wave shielding layer composed of the metal thin film layer 14 and the isotropic conductive adhesive layer 16 before the occurrence of cracks in the metal thin film layer 14.
The electromagnetic wave shielding layer in the typical example is a laminate of a metal thin film layer 14 having a width of 10mm and a length of 20mm and an isotropic conductive adhesive layer 16 having a width of 10mm and a length of 20 mm.
Since the surface resistance Rms of the metal thin film layer 14 is the resistance between 2 electrodes having a length of 10mm and an inter-electrode distance of 10mm, the total resistance in the longitudinal direction (20mm) of the metal thin film layer 14, that is, the resistance of the circuit is 2Rms which is 2 times the surface resistance Rms.
The surface resistance Rcs of the isotropic conductive adhesive layer 16 is the resistance between 2 electrodes having a length of 10mm and an inter-electrode distance of 10mm, and therefore the overall resistance in the longitudinal direction (20mm) of the isotropic conductive adhesive layer 16 is similarly 2 Rcs.
When the electromagnetic wave shielding layer is a parallel circuit of the thin metal film layer 14 and the isotropic conductive adhesive layer 16, the overall resistance R1 in the longitudinal direction of the electromagnetic wave shielding layer before the occurrence of cracks is expressed by the following formula (1).
R1＝2×Rms·Rcs/(Rms+Rcs)···(1)
Fig. 6 is a perspective view showing a typical example of the electromagnetic wave shielding layer composed of the thin metal film layer 14 and the isotropic conductive adhesive layer 16 after the thin metal film layer 14 has been cracked.
It is assumed that a crack with a gap of 0.2mm is generated across the width direction at the center in the longitudinal direction of the metal thin film layer 14.
When the electromagnetic wave shielding layer is regarded as a parallel circuit in which a metal thin film layer 14 having a width of 10mm and a length of 9.9mm and an isotropic conductive adhesive layer 16 are connected in series, a circuit in which the isotropic conductive adhesive layer 16 having a width of 10mm and a length of 0.2mm is connected, and a parallel circuit in which the metal thin film layer 14 having a width of 10mm and a length of 9.9mm and the isotropic conductive adhesive layer 16 are connected in series, the overall resistance R2 in the longitudinal direction of the electromagnetic wave shielding layer after occurrence of a crack is expressed by the following formula (2).
R2＝2×0.99×Rms·Rcs/(Rms+Rcs)+0.02×Rcs···(2)
When the surface resistance Rms of the metal thin film layer 14 is 0.3 Ω as a maximum value and the surface resistance Rcs of the isotropic conductive adhesive layer 16 is 100 Ω as a maximum value, the overall resistance R1 in the longitudinal direction of the electromagnetic wave-shielding layer before occurrence of cracks is 0.598 Ω, and the overall resistance R2 in the longitudinal direction of the electromagnetic wave-shielding layer after occurrence of cracks is 2.538 Ω. Thus, the increase in the electrical resistance of the electromagnetic wave shielding layer due to the occurrence of cracks in the metal thin film layer 14 is suppressed to 10 times or less, and the electromagnetic wave noise shielding effect can be maintained.
On the other hand, when the surface resistance Rms of the metal thin film layer 14 is 0.3 Ω, and the surface resistance Rcs of the isotropic conductive adhesive layer 16 is 1000 Ω exceeding the maximum value, the total resistance R1 in the longitudinal direction of the electromagnetic wave shielding layer before the occurrence of cracks is 0.600 Ω, and the total resistance R2 in the longitudinal direction of the electromagnetic wave shielding layer after the occurrence of cracks is 20.540 Ω. When the surface resistance Rcs of the isotropic conductive adhesive layer 16 exceeds the maximum value, the electrical resistance of the electromagnetic wave shielding layer is greatly increased due to the occurrence of cracks in the metal thin film layer 14, and as a result, the electromagnetic wave noise shielding effect is reduced.
(other embodiments)
The electromagnetic wave shielding film of the present invention is not limited to the embodiment of fig. 1 as long as it has an insulating protective layer, a metal thin film layer having a specific surface resistance, and an isotropic conductive adhesive layer having a specific surface resistance in this order.
For example, when the adhesiveness of the surface of the isotropic conductive adhesive layer 16 is small, the second release film 20 may be omitted.
When the insulating protective layer 12 has sufficient flexibility and strength, the first release film 18 may be omitted.
When the release film has sufficient releasability (releasability) only from the film body, the release film may not have a release agent layer.
< Flexible printed Wiring Board with electromagnetic wave Shielding film >
Fig. 7 is a sectional view showing an example of the flexible printed wiring board with an electromagnetic wave shielding film of the present invention.
The electromagnetic wave shielding film-equipped flexible printed wiring board 1 has a flexible printed wiring board 30, an insulating film 40, and an electromagnetic wave shielding film 10 from which a release film is peeled.
The flexible printed wiring board 30 has a printed circuit 34 provided on at least one surface of a base film 32.
The insulating film 40 is provided on the surface of the flexible printed wiring board 30 on the side where the printed circuit 34 is provided.
The isotropic conductive adhesive layer 16 of the electromagnetic wave shielding film 10 is adhered to the surface of the insulating film 40 and cured. The isotropic conductive adhesive layer 16 is electrically connected to the printed circuit 34 through a through hole (not shown) formed in the insulating film 40.
The metal thin film layer 14 of the electromagnetic wave shielding film 10 is disposed facing the printed circuit 34 (signal circuit, ground layer, etc.) except for the portion having the through-hole, with the insulating film 40 and the isotropic conductive adhesive layer 16 interposed therebetween.
The distance between the printed circuit 34 and the metal thin film layer 14 excluding the portion having the through-hole is the sum of the thickness of the insulating film 40 and the thickness of the isotropic conductive adhesive layer 16. The separation distance is preferably 30 μm to 200 μm, and more preferably 60 μm to 200 μm. When the separation distance is smaller than 30 μm, the impedance of the signal circuit becomes low, and in order to have a characteristic impedance of 100 Ω or the like, the line width of the signal circuit must be reduced, and the line width variation becomes the variation of the characteristic impedance, and the reflection resonance noise due to the impedance mismatch easily enters the electric signal. When the spacing distance is larger than 200 μm, the flexible printed wiring board 1 with the electromagnetic wave shielding film becomes thick and the flexibility is insufficient.
When the separation distance is 30 μm or more, the impedance of the signal circuit increases, the characteristic impedance does not vary, and the reflection resonance noise due to the mismatch of the impedance hardly enters the electric signal. When the distance is 200 μm or less, the flexible printed wiring board 1 with an electromagnetic wave shielding film does not become thick and has excellent flexibility.
(Flexible printed Wiring Board)
The flexible printed wiring board 30 is formed by processing the copper foil of the copper clad laminate into a desired pattern by a known etching method to form a printed circuit 34 (a power supply circuit, a ground layer, and the like).
Examples of the copper-clad laminate include a copper foil-clad laminate obtained by bonding a copper foil to one or both surfaces of a base film 32 with an adhesive layer (not shown) interposed therebetween; a plate formed by casting a resin solution or the like for forming the base film 32 on the surface of the copper foil.
Examples of the material of the adhesive layer include epoxy resin, polyester, polyimide, polyamide-imide, polyamide, phenol resin, polyurethane, acrylic resin, and melamine resin.
The thickness of the adhesive layer is preferably 0.5 μm to 30 μm.
(base film)
The base film 32 is preferably a film having heat resistance, more preferably a polyimide film or a liquid crystal polymer film, and still more preferably a polyimide film.
The surface resistance of the base film 32 is preferably 1 × 10 from the viewpoint of electrical insulation6Omega or more. From the viewpoint of practical use, the surface resistance of the base film 32 is preferably 1 × 1019Omega is less than or equal to.
The thickness of the base film 32 is preferably 5 μm to 200 μm, more preferably 6 μm to 25 μm, and still more preferably 10 μm to 25 μm in view of flexibility.
(printed Circuit)
The copper foil constituting the printed circuit 34 (signal circuit, ground layer, etc.) may be a rolled copper foil, an electrolytic copper foil, or the like, and a rolled copper foil is preferable from the viewpoint of bendability.
The thickness of the copper foil is preferably 1 μm to 50 μm, more preferably 18 μm to 35 μm.
The end portions (terminals) in the longitudinal direction of the printed circuit 34 are not covered with the insulating film 40 and the electromagnetic wave shielding film 10 due to solder connection, connector connection, component mounting, and the like.
(insulating film)
The insulating film 40 forms an adhesive layer (not shown) on one surface of a base material film (not shown) by application of an adhesive, adhesion of an adhesive sheet, or the like.
From the viewpoint of electrical insulation, the surface resistance of the base material film is preferably 1X 106Omega or more. From the viewpoint of practical use, the surface resistance of the base material film is preferably 1X 1019Omega is less than or equal to.
The base material film is preferably a film having heat resistance, more preferably a polyimide film or a liquid crystal polymer film, and further preferably a polyimide film.
The thickness of the base material film is preferably 1 μm to 100 μm, and more preferably 3 μm to 25 μm from the viewpoint of flexibility.
Examples of the material of the adhesive layer include epoxy resin, polyester, polyimide, polyamide-imide, polyamide, phenol resin, polyurethane, acrylic resin, melamine resin, polystyrene, and polyolefin. The epoxy resin may contain a rubber component (carboxyl-modified nitrile rubber or the like) imparting flexibility.
The thickness of the adhesive layer is preferably 1 μm to 100 μm, more preferably 1.5 μm to 60 μm.
The shape of the opening of the through hole is not particularly limited. Examples of the shape of the opening of the through hole include a circle, an ellipse, and a quadrangle.
(method of manufacturing Flexible printed Wiring Board with electromagnetic wave-shielding film)
The flexible printed wiring board with an electromagnetic wave shielding film of the present invention can be produced, for example, by a method having the following steps (e) to (g).
(e) An insulating film having a through hole formed at a position corresponding to a printed circuit is provided on a surface of a flexible printed wiring board having a printed circuit on at least one surface of a base film, the surface being provided with the printed circuit, thereby obtaining a flexible printed wiring board with the insulating film.
(f) After the step (e), the flexible printed wiring board with the insulating film and the electromagnetic wave shielding film of the present invention are stacked so that the isotropic conductive adhesive layer is in contact with the surface of the insulating film, and the isotropic conductive adhesive layer is bonded to the surface of the insulating film by hot pressing the stacked layers, and the isotropic conductive adhesive layer is electrically connected to the printed circuit through the through hole.
(g) After the step (f), the first release film is peeled off to obtain the flexible printed wiring board with the electromagnetic wave shielding film.
Hereinafter, a method for manufacturing a flexible printed wiring board with an electromagnetic wave shielding film will be described with reference to fig. 8.
(step (e))
As shown in fig. 8, an insulating film 40 having a through hole 42 formed at a position corresponding to the printed circuit 34 is stacked on the flexible printed wiring board 30, an adhesive layer (not shown) of the insulating film 40 is adhered to the surface of the flexible printed wiring board 30, and the adhesive layer is cured to obtain the flexible printed wiring board 2 with the insulating film. The adhesive layer of the insulating film 40 may be temporarily adhered to the surface of the flexible printed wiring board 30, and the adhesive layer may be completely cured in the step (f).
The adhesive layer is bonded and cured by, for example, hot pressing with a press (not shown) or the like.
(step (f))
As shown in fig. 8, the electromagnetic wave shielding film 10 obtained by peeling the second release film 20 is stacked on the flexible printed wiring board with insulating film 2, and hot-pressed to obtain the precursor 3 of the flexible printed wiring board with electromagnetic wave shielding film, in which the isotropic conductive adhesive layer 16 is adhered to the surface of the insulating film 40, and the isotropic conductive adhesive layer 16 is electrically connected to the printed circuit 34 through the through hole 42.
The isotropic conductive adhesive layer 16 is bonded and cured by, for example, hot pressing using a press (not shown) or the like.
The time for hot pressing is 20 seconds to 60 minutes, and more preferably 30 seconds to 30 minutes. When the hot pressing time is 20 seconds or more, the isotropic conductive adhesive layer 16 is adhered to the surface of the insulating film 40. If the time for the hot pressing is 60 minutes or less, the time for manufacturing the flexible printed wiring board 1 with the electromagnetic wave shielding film can be shortened.
The temperature of hot pressing (temperature of the press platens) is preferably 140 ℃ to 190 ℃, more preferably 150 ℃ to 175 ℃. When the hot press temperature is 140 ℃ or higher, the isotropic conductive adhesive layer 16 adheres to the surface of the insulating film 40. In addition, the time for hot pressing can be shortened. When the temperature of the hot press is 190 ℃ or lower, deterioration of the electromagnetic wave shielding film 10, the flexible printed wiring board 30, and the like can be suppressed.
The pressure of the hot pressing is preferably 10MPa to 20MPa, more preferably 10MPa to 16 MPa. When the pressure of the hot pressing is 10MPa or more, the isotropic conductive adhesive layer 16 is adhered to the surface of the insulating film 40. In addition, the time for hot pressing can be shortened. When the pressure of the hot pressing is 20MPa or less, the electromagnetic wave shielding film 10, the flexible printed wiring board 30, and the like can be prevented from being damaged.
(step (g))
As shown in fig. 8, the first release film 18 is peeled from the insulating protective layer 12, and the electromagnetic wave shielding film-equipped flexible printed wiring board 1 is obtained.
When the hot press time in the step (f) is short, such as 20 seconds to 10 minutes, it is preferable to completely cure the isotropic conductive adhesive layer 16 before or after peeling the first release film 18.
The isotropic conductive adhesive layer 16 is completely cured using a heating device such as an oven, for example.
The heating time is preferably 15 to 120 minutes, and more preferably 30 to 60 minutes. If the heating time is 15 minutes or more, the isotropic conductive adhesive layer 16 can be sufficiently cured. If the heating time is 120 minutes or less, the time required for manufacturing the flexible printed wiring board 1 with an electromagnetic wave shielding film can be shortened.
The heating temperature (the temperature of the atmosphere in the oven) is preferably 120 ℃ to 180 ℃ inclusive, and more preferably 120 ℃ to 150 ℃ inclusive. If the heating temperature is 120 ℃ or higher, the heating time can be shortened. If the heating temperature is 180 ℃ or lower, deterioration of the electromagnetic wave shielding film 10, the flexible printed wiring board 30, and the like can be suppressed.
From the viewpoint that a special apparatus may not be used, it is preferable to heat without applying pressure.
(Effect)
In the flexible printed wiring board with an electromagnetic wave shielding film 1 described above, the surface resistance of the metal thin film layer 14 is 0.3 Ω or less, and the surface resistance of the isotropic conductive adhesive layer 16 is 10 Ω or less, so that the electromagnetic wave noise shielding effect can be maintained even if a crack occurs in the metal thin film layer 14.
(other embodiments)
The electromagnetic wave shielding film-attached flexible printed wiring board of the present invention may include a flexible printed wiring board, an insulating film, and the electromagnetic wave shielding film of the present invention, and is not limited to the embodiment illustrated in the drawings.
For example, the flexible printed wiring board may have a ground layer on the back surface side. The flexible printed wiring board may have printed circuits on both surfaces, or may have an insulating film and an electromagnetic shielding film bonded to both surfaces.
[ examples ]
Hereinafter, examples are shown. Further, the present invention is not limited to the embodiments.
(storage modulus of elasticity)
The storage modulus of elasticity was measured using a dynamic viscoelasticity measuring apparatus (manufactured by Rheometric Scientific, inc., RSAII).
(example 1)
As the first release film 18 and the second release film 20, polyethylene terephthalate films (T157, manufactured by Lintec Co., Ltd., thickness: 50 μm, storage modulus of elasticity at 160 ℃ C.: 6X 10) which were subjected to single-side release treatment with a non-silicone release agent were prepared8Pa)。
A step (a):
a solvent-soluble amide resin (T) is applied to the surface of the release agent layer 18b of the first release film 18&TPAE-617C) and a curing agent (toluene diisocyanate) were dissolved in N, N-dimethylformamide, and the resultant was heated at 150 ℃ for 0.4 hour to cure the amide resin, thereby forming an insulating protective layer 12 (thickness: 5 μm, storage modulus of elasticity at 160 ℃: 8X 106Pa, surface resistance: 8X 1012Ω)。
A step (b):
a first laminate 10a was obtained by physically evaporating copper on the surface of the insulating protective layer 12 by an electron beam evaporation method to form a deposited film (metal thin film layer 14) having a thickness of 0.07 μm and a surface resistance of 0.3 Ω.
A step (c):
a mixture of an epoxy resin (EXA-4816, manufactured by DIC) as a curable epoxy resin and a curing agent (PN-23, manufactured by MIKOKAI Fine technologies Co., Ltd.) and silver particles (AG 6-11, average particle diameter: 3.6 μm, specific surface area: 0.21m, manufactured by DOWA electronics Co., Ltd.) as conductive particles 22 were applied to the surface of the release agent layer 20b of the second release film 20 by a film coater2(iv)/g, true density: 10.5g/cm3) And carbon nanofibers (manufactured by showa electrical engineering corporation, VGCF, average fiber length: 6 μm, average fiber diameter: 0.15 μm, aspect ratio: 60, specific surface area: 13m2(iv)/g, true density: 2.1g/cm3) The conductive adhesive composition dissolved or dispersed in the solvent (methyl ethyl ketone) is evaporated to form the isotropic conductive adhesive layer 16 (thickness: 10 μm, silver particles: 58 vol%, carbon nanofiber: 15 vol%, surface resistance: 80 Ω) to obtain a second laminate 10 b.
Step (d):
the first laminate 10a and the second laminate 10b were stacked so that the metal thin film layer 14 and the isotropic conductive adhesive layer 16 were in contact with each other, and hot-pressed at a temperature of 90 ℃ and a pressure of 2MPa for 3 seconds using a hot press (VFPC-05R, manufactured by VIGOR corporation) to obtain the electromagnetic wave shielding film 10.
A step (e):
in a polyimide film (surface resistance: 1X 10) having a thickness of 25 μm17Ω) (substrate film) was coated with an insulating adhesive composition composed of a nitrile rubber-modified epoxy resin so that the dry film thickness was 25 μm, and an adhesive layer was formed to obtain an insulating film 40 (thickness: 50 μm).
A polyimide film (surface resistance: 1X 10) having a thickness of 12 μm was prepared17Ω) (base film 32) and a printed circuit 34 formed on the surface thereof.
The insulating film 40 is attached to the flexible printed wiring board 30 by hot pressing, and the flexible printed wiring board 2 with the insulating film is obtained.
A step (f):
the electromagnetic wave shielding film 10 from which the second release film 20 was peeled was stacked on the flexible printed wiring board 30, and hot-pressed at a temperature of 170 ℃ and a pressure of 15MPa for 30 seconds using a hot press (VFPC-05R, manufactured by VIGOR corporation) to bond the isotropic conductive adhesive layer 16 to the surface of the insulating film 40, thereby obtaining a precursor 3 of the electromagnetic wave shielding film-equipped flexible printed wiring board.
The precursor 3 of the flexible printed wiring board with the electromagnetic wave shielding film was heated at 170 ℃ for 30 minutes using a high temperature thermostat (HT 210, manufactured by nanba chemicals corporation) to completely cure the isotropic conductive adhesive layer 16 (this curing).
Step (g):
the first release film 18 is peeled from the insulating protective layer 12, and the electromagnetic wave shielding film-equipped flexible printed wiring board 1 is obtained.
Comparative example 1
Steps (a) to (b):
a first laminate was obtained in the same manner as in example 1.
A step (c):
a mixture of an epoxy resin (EXA-4816, manufactured by DIC) and a curing agent (PN-23, manufactured by Ajinomoto Kogyo Co., Ltd.) as a curing epoxy resin and calcined carbon particles (CR 2-800SR, average particle diameter: 5.0 μm, specific surface area: 0.8m, manufactured by Air Water Bell Pearl Co., Ltd.) as the conductive particles 22 were coated on the surface of the release agent layer of the second release film by a film coater2(iv)/g, true density: 1.34g/cm3) The conductive adhesive composition dissolved or dispersed in the solvent (methyl ethyl ketone) is evaporated to form an isotropic conductive adhesive layer (thickness: 10 μm, fired carbon particles: 75 vol%, carbon nanofiber: 10 vol%, surface resistance: 620 Ω) to obtain a second laminate.
Step (d):
an electromagnetic wave-shielding film was obtained in the same manner as in example 1, except that the second laminate obtained in the step (c) of comparative example 1 was used as the second laminate.
Steps (e) to (g):
a flexible printed wiring board with an electromagnetic wave-shielding film was obtained in the same manner as in example 1, except that the electromagnetic wave-shielding film obtained in step (d) of comparative example 1 was used as the electromagnetic wave-shielding film. Industrial applicability of the invention
The electromagnetic wave shielding film of the present invention is used as an electromagnetic wave shielding member for a flexible printed wiring board used in electronic devices such as smart phones, mobile phones, optical modules, digital cameras, game machines, notebook computers, and medical instruments.
[ description of symbols ]
Flexible printed wiring board with electromagnetic wave shielding film
2 Flexible printed Wiring Board with insulating film
3 precursor of flexible printed wiring board with electromagnetic wave shielding film
10 electromagnetic wave shielding film
10a first laminate
10b second laminate
12 insulating protective layer
14 metal film layer
16 Isotropic conductive adhesive layer
18 first release film
18a Release film body
18b Release agent layer
20 second release film
20a Release film body
20b Release agent layer
22 conductive particles
24 conductive fiber
30 flexible printed wiring board
32 base film
34 printed circuit
40 insulating film
42 through hole
101 flexible printed wiring board with electromagnetic wave shielding film
110 electromagnetic wave shielding film
112 insulating protective layer
114 metal thin film layer
116 Anisotropic conductive adhesive layer
118 release film
130 flexible printed wiring board
132 base film
134 printed circuit
140 insulating film
142 through the hole.
Claims (8)
1. An electromagnetic wave shielding film, comprising:
an insulating protective layer;
a metal thin film layer having a surface resistance of 0.01 Ω to 0.3 Ω; and
comprises a conductive filler and an isotropic conductive adhesive layer having a surface resistance of 1 to 100 omega,
the metal thin film layer and the isotropic conductive adhesive layer constitute an electromagnetic wave shielding layer,
the increase in the electrical resistance of the electromagnetic wave-shielding layer due to the occurrence of cracks in the metal thin film layer is 10 times or less,
wherein when the overall resistance of the electromagnetic wave-shielding layer in the longitudinal direction before occurrence of cracks is R1 and the overall resistance of the electromagnetic wave-shielding layer in the longitudinal direction after occurrence of cracks is R2,
r1 is represented by the following formula (1),
R1＝2×Rms·Rcs/(Rms+Rcs)……(1)
r2 is represented by the following formula (2),
R2＝2×0.99×Rms·Rcs/(Rms+Rcs)+0.02×Rcs……(2)
in the formulas (1) and (2), Rms is the surface resistance of the metal thin film layer, and Rcs is the surface resistance of the isotropic conductive adhesive layer.
2. The electromagnetic wave-shielding film according to claim 1,
the proportion of the conductive filler is 30 vol% or more and 80 vol% or less of 100 vol% of the isotropic conductive adhesive layer.
3. The electromagnetic wave shielding film according to claim 1 or 2,
the isotropic conductive adhesive layer contains conductive particles and conductive fibers as the conductive filler.
4. The electromagnetic wave shielding film according to claim 1 or 2,
the first release film is arranged on the surface of the insulating protective layer.
5. The electromagnetic wave-shielding film according to claim 4,
further comprising: and a second release film provided on a surface of the isotropic conductive adhesive layer.
6. A method for producing an electromagnetic wave shielding film according to claim 5, comprising the following steps (a) to (d):
(a) forming an insulating protective layer on one side of the first release film;
(b) forming a metal thin film layer on the surface of the insulating protective layer to obtain a first laminate sequentially comprising a first release film, the insulating protective layer and the metal thin film layer;
(c) forming an isotropic conductive adhesive layer on one surface of the second release film to obtain a second laminated body sequentially comprising the second release film and the isotropic conductive adhesive layer;
(d) the first laminate and the second laminate are bonded together so that the metal thin film layer and the isotropic conductive adhesive layer are in contact with each other.
7. A flexible printed wiring board with an electromagnetic wave shielding film, comprising:
a flexible printed wiring board having a printed circuit on at least one surface of a base film;
an insulating film provided on a surface of the flexible printed wiring board on which the printed circuit is provided; and
the electromagnetic wave shielding film according to any one of claims 1 to 3, wherein the isotropic conductive adhesive layer is adhered to the surface of the insulating film,
the isotropic conductive adhesive layer is electrically connected to the printed circuit through a through hole formed in the insulating film.
8. A method for manufacturing a flexible printed wiring board having an electromagnetic wave shielding film, comprising the following steps (e) to (g):
(e) providing an insulating film having a through hole formed at a position corresponding to a printed circuit on a surface of a flexible printed wiring board having the printed circuit on at least one surface of a base film, the surface being provided with the printed circuit, to obtain a flexible printed wiring board with the insulating film;
(f) after the step (e), laminating the flexible printed wiring board with an insulating film and the electromagnetic wave shielding film according to any one of claims 1 to 4 so that the isotropic conductive adhesive layer is in contact with the surface of the insulating film, and hot-pressing the laminated layers, whereby the isotropic conductive adhesive layer is adhered to the surface of the insulating film and the isotropic conductive adhesive layer is electrically connected to the printed circuit through the through-hole;
(g) when the electromagnetic wave shielding film has the first release film, the first release film is peeled off after the step (f).
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2014219422A JP6467701B2 (en) | 2014-10-28 | 2014-10-28 | Electromagnetic wave shielding film, flexible printed wiring board with electromagnetic wave shielding film, and manufacturing method thereof |
| JP2014-219422 | 2014-10-28 | ||
| CN201510557975.9A CN105555010B (en) | 2014-10-28 | 2015-09-02 | Electromagnetic shielding film, flexible printing wiring board and their manufacturing method |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
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| CN201510557975.9A Division CN105555010B (en) | 2014-10-28 | 2015-09-02 | Electromagnetic shielding film, flexible printing wiring board and their manufacturing method |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN108848609A CN108848609A (en) | 2018-11-20 |
| CN108848609B true CN108848609B (en) | 2021-02-26 |
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| Application Number | Title | Priority Date | Filing Date |
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| CN201910950714.1A Active CN110662347B (en) | 2014-10-28 | 2015-09-02 | Electromagnetic wave shielding film, flexible printed wiring board, and method for producing same |
| CN201510557975.9A Active CN105555010B (en) | 2014-10-28 | 2015-09-02 | Electromagnetic shielding film, flexible printing wiring board and their manufacturing method |
| CN201810993409.6A Active CN108848609B (en) | 2014-10-28 | 2015-09-02 | Electromagnetic wave shielding film, flexible printed wiring board, and method for producing same |
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| CN201910950714.1A Active CN110662347B (en) | 2014-10-28 | 2015-09-02 | Electromagnetic wave shielding film, flexible printed wiring board, and method for producing same |
| CN201510557975.9A Active CN105555010B (en) | 2014-10-28 | 2015-09-02 | Electromagnetic shielding film, flexible printing wiring board and their manufacturing method |
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| CN (3) | CN110662347B (en) |
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| CN203225988U (en) * | 2011-11-24 | 2013-10-02 | 大自达电线股份有限公司 | Shielding film and shielding printed circuit board |
| CN103857268A (en) * | 2012-11-28 | 2014-06-11 | 大自达电线股份有限公司 | Shield film, shield printed wiring board and method of manufacturing shield printed wiring board |
Also Published As
| Publication number | Publication date |
|---|---|
| JP6467701B2 (en) | 2019-02-13 |
| CN108848609A (en) | 2018-11-20 |
| CN110662347B (en) | 2022-12-13 |
| CN110662347A (en) | 2020-01-07 |
| JP2016086120A (en) | 2016-05-19 |
| CN105555010A (en) | 2016-05-04 |
| CN105555010B (en) | 2019-10-22 |
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