JP2013151638A - Coverlay film, flexible wiring board, and production method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coverlay film having excellent adhesion relative to a substrate material in a flexible wiring board and being excellent in transfer characteristics of an electric signal such as a high frequency wave.SOLUTION: A coverlay film is configured such that an adhesion layer 12 is formed on one side (for example, a rear side) of a cover film-shaped base material 11; the adhesion layer 12 is formed on the cover film-shaped base material 11 by adhering the layer to or applying the layer onto the cover film-shaped base material 11. Alternately, to a rear side of the adhesion layer 12, further a release material layer 13 is adhered; the cover film-shaped base material 11 has an elastic modulus larger than the adhesion layer 12 and preferably has a dielectric constant of 3.5 or less; the adhesion layer 12 contains a synthetic resin containing oligophenylene ether and a styrene-butadiene-based elastomer; and the release material layer 13 is not particularly limited so long as the release material layer 13 can be peeled without impairing the shape of the adhesion layer 12.

Description

  The present invention relates to a coverlay film used for a flexible wiring board on which transmission wiring, circuit wiring, and the like are disposed, a flexible wiring board having the coverlay film, and a method for manufacturing the same.

  BACKGROUND OF THE INVENTION Flexible printed wiring boards (hereinafter also referred to as FPC: Flexible Printed Circuit) are widely used in electronic devices such as portable devices, network devices, servers, and testers. And this FPC is expanding its application also as a composite part provided with a circuit, a cable, a connector function, etc. to an electronic device. In addition, taking advantage of its excellent flexibility, it can be used as a substitute for electrical signal wiring materials such as coaxial cables and wire harnesses in consumer and industrial equipment such as OA equipment, various computers, and automobiles. Promising and used.

  In the above-described equipment, miniaturization and high functionality are being developed in the development of finer, higher integration, higher speed, or multiple functions of semiconductor devices (hereinafter also simply referred to as high performance of semiconductor devices). It is remarkable. In general, FPCs are required to have high density wiring and light weight, and miniaturization of wirings arranged on a wiring board, reduction of wiring spacing, multilayering and thinning of insulating layers are performed. It has been broken.

  The FPC has, as its basic structure (single layer structure), a wiring disposed on the surface of the resin base film that is an insulator layer, and a resin cover lay film that is an insulator layer that covers and protects the wiring and the base film. Consists of. Here, for example, a single-sided metal-clad laminate having a copper metal foil, which is attached to one main surface of the base film, is used. Then, the metal foil is patterned into a desired wiring, and the coverlay film is integrally bonded to a substrate such as a wiring and a base film via the adhesive layer, thereby forming a single-sided flexible wiring board together with the substrate (for example, Patent Documents) 1 and 2).

  In the case of a multilayer wiring board, an interlayer insulating layer made of a resin such as a prepreg is laminated between multilayer wiring layers, and a multilayer flexible wiring board having a resin cover lay film formed on the surface layer is obtained. . For example, in an FPC having a two-layer structure, a double-sided metal-clad laminate having metal foils attached to both sides of a base film is used. Then, the metal foils on both sides are patterned into a desired wiring, and the coverlay film is integrally joined to the base material such as a two-layer wiring and a base film through the adhesive layer to form a double-sided flexible wiring board (for example, And Patent Document 3).

JP 2010-144081 A JP 2010-150437 A JP 2006-261383 A

  By the way, especially in an electronic apparatus equipped with a semiconductor device which is increased in speed, the operation speed is increased along with the miniaturization thereof. Accordingly, excellent transmission characteristics of high-frequency signals in FPC, stable low reactance, impedance, and excellent transmission / conduction characteristics of electrical signals due to transmission loss are required. For example, when a high-speed digital signal having a frequency of several GHz to several tens of GHz is used, high-speed transmission is required without impairing the high-frequency characteristics. Therefore, for the coverlay film as well as the FPC substrate material, a material having stable and excellent electrical characteristics (for example, low relative dielectric constant (ε), low dielectric loss tangent (tan δ)) in the high frequency region is required.

  However, in the conventional coverlay film having an adhesive layer, emphasis is placed on the adhesive strength or heat resistance with the substrate material of the FPC, and the realization of excellent transmission characteristics such as high-frequency signals in the FPC has not been studied much. It was. Therefore, the adhesive layer in the coverlay film has a high relative dielectric constant of about 4.0 and a relatively high dielectric loss tangent. Also, stable low water absorption and hygroscopicity in the adhesive are not considered. For these reasons, it has been difficult for the above-described conventional FPC to ensure stable and excellent characteristics in the transmission of the high-frequency signal.

  The present invention has been made in view of the above circumstances, and has a superior adhesiveness to a base material in a flexible wiring board such as a wiring and a base film, and an excellent transmission characteristic of an electric signal such as a high frequency. The main purpose is to provide a ray film. And the flexible wiring board by which the surface layer is coat | covered and protected by the said coverlay film, and its manufacturing method are provided.

  In order to achieve the above object, a cover lay film according to the present invention is a cover lay film that is formed on the surface layer of a flexible wiring board and protects the wiring of an inner layer. An adhesive layer provided on a main surface, and the film-like base material is made of a resin having a higher elastic modulus than the adhesive layer, and the adhesive layer contains an oligophenylene ether and a styrene-butadiene based elastomer. It consists of resin.

  Here, the film-like substrate is preferably a low dielectric resin film having a relative dielectric constant of 3.5 or less at a frequency of 1 GHz. The low dielectric resin film may be composed of a liquid crystal polymer, polyethylene naphthalate, syndiotactic polystyrene, polyphenylene sulfide, polyimide resin, polyetherimide, polyphenylene ether, or a composite resin thereof. Further preferred.

  In the flexible wiring board according to the present invention, wiring is formed on a main surface of a resin substrate made of a liquid crystal polymer or a composite resin containing a liquid crystal polymer, and the cover lay film is integrated with the resin substrate and the wiring. It is characterized by being joined.

  In the method for manufacturing a flexible wiring board according to the present invention, the cover lay film is thermocompression bonded to the resin substrate on which the wiring is formed by a hot roll laminating method, and then the wiring and the resin substrate are subjected to heat treatment. The coverlay film is bonded and integrated.

  According to the present invention, it is possible to provide a coverlay film that has excellent adhesion to a base material in a flexible wiring board such as a wiring and a base film, and is excellent in high-frequency signal transmission characteristics. Then, a flexible wiring board that is stable in high-frequency signals and has excellent transmission characteristics can be easily made.

Sectional drawing which showed two examples of the coverlay film concerning embodiment of this invention. The partial expanded sectional view which shows an example of the flexible wiring board concerning embodiment of this invention. Sectional drawing according to manufacturing process which shows an example of the manufacturing method of a flexible wiring board same as the above. The partially expanded sectional view which shows the other examples of the flexible wiring board concerning embodiment of this invention.

  A preferred embodiment of the present invention will be described below with reference to FIGS. Here, the drawings are schematic, and ratios of dimensions and the like are different from actual ones. In these drawings, the same or similar parts are denoted by the same reference numerals, and a duplicate description is partially omitted.

  As shown in FIG. 1 (a) or (b), the cover layer film of this embodiment has an adhesive layer 12 formed on one side (for example, the back side) of a cover film-like substrate 11. Here, the adhesive layer 12 is, for example, pasted or applied to the cover film substrate 11. And in FIG.1 (b), the mold release material layer 13 is further affixed on the back surface of the contact bonding layer 12. FIG. Here, as the film-like base material, a resin film having a large elastic modulus as compared with the adhesive layer 12 after thermosetting and excellent in its low water absorption or low water absorption is preferable. With such a coverlay film, the change over time in its electrical characteristics is small and stable. Moreover, the adhesiveness with the base film in a flexible wiring board becomes stable and becomes excellent.

  And it is preferable that the cover film-form base material 11 is a low dielectric resin film which has a low dielectric property. In this low dielectric property, the relative dielectric constant at a frequency of 1 MHz is preferably 3.5 or less. Such a relative permittivity facilitates high-speed transmission in high-speed digital signal transmission of, for example, several GHz to several tens GHz band. Further, in the low dielectric property, the dielectric loss tangent in the high frequency band is preferably 0.005 or less. Such a dielectric loss tangent, together with the adhesive layer 12 having the composition described later in the FPC, causes a small dielectric loss in a high-speed digital signal in a high frequency band of several GHz to several tens GHz, and impairs the high-frequency characteristics. High quality electrical signals can be transmitted without any problems.

  Here, the film thickness of the cover film-like substrate 11 is appropriately determined according to the FPC and the material to which it is applied, and is set to, for example, about 5 μm to 50 μm. As will be described later, when a ground layer is formed on the coverlay film in the FPC, for example, the cover film-like substrate 11 is set to be relatively thick. This is to reduce the parasitic capacitance between the FPC wiring and the ground layer formed with the coverlay film interposed therebetween.

  As such a cover film-like substrate 11, crystalline resins such as liquid crystal polymer, polyethylene naphthalate (PEN), syndiotactic polystyrene (SPS), polyphenylene sulfide (PPS), polyimide (PI) resin, poly Examples thereof include amorphous resins such as etherimide (PEI) and polyphenylene ether (PPE), and composite resins such as these. Alternatively, a thermosetting resin such as bismaleimide-triazine resin (BT resin) may be used.

  In particular, the liquid crystal polymer is preferable because it exhibits excellent transmission characteristics at high frequencies and flexibility. Here, the liquid crystal polymer is, for example, a multiaxially oriented thermoplastic polymer represented by xidar (trade name, manufactured by Dartco) or Vectra (trade name, manufactured by Clanese). Further, it may be modified by adding and blending another insulating resin. Examples thereof include Bexter FA type (melting point 285 ° C.), Bexter CT-X type (melting point 280 ° C. to 335 ° C.), BIAC film (melting point 335 ° C.), and the like. In addition, the glass transition point Tg of these liquid crystal polymers exhibits a high temperature of 205 ° C to 300 ° C.

  Examples of the polyimide resin include polyimide film “Kapton” (trade name, manufactured by Toray DuPont) and Aurum (trade name, manufactured by Mitsui Chemicals). And as a polyethylene naphthalate type-resin, the thermoplastic resin of Teonex (brand name. Product made by Teijin DuPont) is illustrated as a suitable thing, for example.

  The adhesive layer 12 is a thermosetting synthetic resin containing an oligophenylene ether and a styrene butadiene elastomer. For example, the ADFEMA OPE system (trade name, manufactured by NAMICS) is exemplified as the uncured film. Alternatively, an adhesive prepared by appropriately dissolving or dispersing a component containing an oligophenylene ether or styrene butadiene elastomer in an organic solvent such as toluene can also be used. And the film thickness of the adhesive layer 12 before thermosetting is appropriately determined according to the material of the cover film-like base material 11, the material of the base film in the FPC, the thickness of the wiring formed on the base film, etc. For example, it is set to about 10 μm to 50 μm. This oligophenylene ether (including derivatives) is also called, for example, OPE (bifunctional polyphenylene ether oligomer) and has a polymer structure in which polyphenylene ether is added to both ends of the bifunctional core. Here, the average molecular weight of OPE is about 500 to 5000, preferably 1000 to 3000. Examples of such commercially available products include OPE2St-1200 and OPE2St-2200 manufactured by Mitsubishi Gas Chemical Company, Inc. The OPE is produced by using, for example, a vinyl compound described in JP-A Nos. 2009-161725 and 2011-68713 as a composition.

  Here, the adhesive layer 12 may contain other components. For example, in order to adjust the curing temperature of the adhesive layer 12, a maleimide-based curing agent, a phenol-based curing agent, an amine-based curing agent, and the like are appropriately mixed. Or in order to adjust adhesiveness, an epoxy resin and its curing catalyst are added, for example. Here, as the curing catalyst, for example, an amine-based curing catalyst or an imidazole-based curing catalyst for shortening heat curing is used.

  In any case, the adhesive layer 12 is made of a resin whose curing temperature is lower than the glass transition point Tg or the melting point Tm of the cover film substrate 11. Here, the curing temperature is a temperature at which the uncured resin film or adhesive layer is cured by polymerization or crosslinking. The resin of the cover film-like substrate 11 may have a glass transition point and may not show a clear Tg. However, when the resin does not show a clear Tg, the thermosetting temperature is lower than the melting point Tm of the thermoplastic resin. It is good to do. And the elasticity modulus in the contact bonding layer 12 after thermosetting becomes smaller than the elasticity modulus of the cover film-like base material 11 or the base film mentioned later.

  The elastic modulus in the adhesive layer 12 can be appropriately adjusted by the amount of the elastomer component. For such an elastomer component, a resin having a small dielectric loss tangent, such as polyester resin, nitrile rubber (NBR), styrene butadiene rubber (SBR), is preferable. For example, the tensile elastic modulus of the adhesive layer 12 after thermosetting is set to be in the range of 100 MPa to 1 GPa. In addition, the tensile elasticity modulus of the cover film-like base material 11 or the base film described above is about 2 GPa to 20 GPa and larger than that of the adhesive layer 12.

  In addition, a glass transition point is normally calculated | required by two methods, TMA method and DMA method, by the glass transition temperature measuring method (it applies to JISC6493). Here, in the TMA method, the test piece is heated from room temperature at a rate of 10 ° C./min, the amount of thermal expansion in the thickness direction is measured with a thermal analyzer, and a tangent line is drawn on the curves before and after the glass transition point. Tg is obtained from the intersection of the tangent lines. In the DMA method (tensile method), the test piece is heated from room temperature at a rate of 2 ° C./min, the dynamic viscoelasticity and loss tangent of the test piece are measured with a viscoelasticity measuring device, and the peak temperature of the loss tangent is measured. Obtain Tg. As the elastic modulus, the tensile elastic modulus or bending elastic modulus of the resin film is used. The elastic modulus is measured according to JIS K 7127 or ASTM D882.

  The release material layer 13 is not particularly limited as long as it can be peeled without impairing the shape of the adhesive layer 12. Specific examples of the release material constituting the material include polypropylene (PP) film, polyethylene (PE) film, PP film with silicone release material, and PE film. Further, for example, a release paper having a plastic layer for preventing curling due to moisture absorption / release on both surfaces of a base paper such as high-quality paper and kraft paper. Examples of such a material include PP resin-coated paper and PE resin-coated paper. The release material layer 13 may have any thickness, but for example, the resin film has a thickness of 10 μm to 50 μm, and the release paper has a thickness of 50 μm to 100 μm, for example.

  Next, a flexible wiring board using the coverlay film of the present embodiment and a manufacturing method thereof will be described with reference to FIGS. Here, an FPC in which transmission wiring for transmitting a high-frequency signal is formed will be described. As shown in FIG. 2, in the FPC as an example, the inner layer signal wiring 15 and the ground wiring 16 which are a plurality of strip lines are arranged in a wiring pattern on one main surface of the base film 14 made of resin. Here, the signal wiring 15 is shown as two pairs of transmission wirings that can cope with LVDS (Low Voltage Differential Signaling).

  A cover film-like base material 11 is thermocompression bonded to the signal wiring 15, the ground wiring 16, and the base film 14 via the adhesive layer 12 as a surface layer of the FPC, and is integrally formed. Here, the cover film-like substrate 11 and the adhesive layer 12 constitute a cover lay film. The elastic modulus of the adhesive layer 12 is smaller than the elastic modulus of the cover film-like substrate 11 and the base film 14 as described above.

  Moreover, although not shown in figure, in the cover film-like base material 11, the ground layer may be stuck by the main surface facing the contact bonding layer 12 through another contact bonding layer. Here, the other adhesive layer is made of the same resin as the adhesive layer 12. These ground wirings 16 or ground layers act as electromagnetic shields to reduce signal interference due to electromagnetic interference between the signal wirings 15 or external electromagnetic waves.

  In the FPC, it is preferable to use a liquid crystal polymer as described above for the cover film-like substrate 11 and the base film 14 and use a synthetic resin containing oligophenylene ether and a styrene-butadiene elastomer for the adhesive layer 12. In this combination, the relative dielectric constants of the cover lay film made of the cover film-like substrate 11 and the adhesive layer 12 and the base film 14 become 3 or less. Further, their dielectric loss tangent is 0.003 or less. The signal wiring 15 in this FPC exhibits extremely excellent transmission / conduction characteristics of high-speed digital signals in the several GHz to several tens GHz band.

  In the FPC, as the base film 14, in addition to the liquid crystal polymer, other thermoplastic resins or thermosetting resins having low dielectric properties can be used. When the cover film and the base film are made of the same material, the above-described characteristics are exhibited, and the thermal expansion coefficient is the same, so that there is no inconvenience due to the coefficient difference.

  Next, an example of the manufacturing method of a flexible wiring board is demonstrated. As shown in FIG. 3A, for example, a single-sided copper-clad laminate in which a copper foil 17 is stuck to the surface of a base film 14 made of a liquid crystal polymer having a thickness of about 15 μm to 50 μm is prepared. Here, the thickness of the copper foil 17 is about 3 μm to 35 μm. The single-sided copper-clad laminate may be one obtained by sticking a copper foil to the surface of a resin film, or one obtained by electrolytic plating. Then, as shown in FIG. 3B, the copper foil 17 is patterned as a strip line by known etching to form the signal wiring 15 and the ground wiring 16.

  Next, as shown in FIG. 3 (c), for example, a cover film-like substrate made of an uncured film-like adhesive layer 12 having a thickness of about 15 μm to 50 μm and a liquid crystal polymer having a thickness of about 5 μm to 50 μm, for example. 11 are sequentially stacked from above the base film 14. Here, as shown in FIG. 1, a coverlay film composed of the adhesive layer 12 formed on one side of the cover film-like substrate 11 may be overlapped.

  And as shown in FIG.3 (d), the lamination | stacking cushion sheet | seat 18 is piled up on the cover film-like base material 11, and a cover film-like base material 11 is made into a base film through the contact bonding layer 12 by the well-known hot roll laminating method. 14 is thermocompression bonded. Here, the temperature in the hot roll laminate is a predetermined temperature at which the adhesive layer 12 in an uncured state is cured, and is a temperature lower than the glass transition point or the melting point of the cover film-like substrate 11. For example, the thermocompression bonding temperature is about 160 ° C. to 200 ° C., for example.

  And as shown in FIG.3 (e), the lamination | stacking cushion sheet | seat 18 is peeled and it heat-processes for a predetermined time at predetermined temperature, without pressing. This temperature is, for example, about 180 ° C. to 200 ° C. By this heat treatment, the cover film-like substrate 11 is joined and integrated with the base film 14, the signal wiring 15 and the ground wiring 16t via the adhesive layer 12. In this way, the flexible wiring board having the cross-sectional structure shown in FIG.

  In addition, in the said joint integration, you may use the hot press method which is a heat press process like the past. In this case, required pressurization is required for a predetermined time of about 1 to 2 hours, for example, by maintaining the predetermined temperature at which the adhesive layer 12 in an uncured state is cured.

  The base film 14, the signal wiring 15 and the ground wiring 16 and the coverlay film that are joined using the above-mentioned hot roll laminating method are joined together by roll-to-rolling using the flexibility of the base material in the manufacture of FPC. The roll (Roll to Roll) method is suitable for a production method using a long continuous substrate. In this method, for example, a flexible single-sided metal-clad laminate or a long-sided double-sided metal-clad laminate is used as a base material, and various processes are performed while being transported between a roll unwinder and a roll winder. It adds processing. The hot roll laminating method is suitable for the roll-to-roll method, while the hot press method is difficult to apply to the processing while transporting. The heat treatment for a predetermined time after the above-described hot roll laminating method is preferably performed separately from the roll-to-roll method in the final step.

  If this roll-to-roll manufacturing method can be applied, it is suitable for manufacturing a long FPC with a length of 1 m or more, such as a flat cable on which transmission wiring is formed. Becomes effective.

  As described above, the adhesive layer 12 of the present embodiment has an elastic modulus after thermosetting that is smaller than the elastic modulus of the cover film-like base material 11 or the base film 14, so that excellent bonding is possible. This is because the thermal stress generated when the temperature is lowered from the heated state to room temperature is absorbed and relaxed by the adhesive layer 12 regardless of the hot roll laminating method or the hot pressing method. That is, the adhesive layer 12 effectively functions as a cushioning material between the coverlay film and the base film to be joined because its elastic modulus is smaller than the surroundings.

  And the adhesive layer 12 after thermosetting has small hygroscopicity, and shows a stable value of relative dielectric constant 2.4-3.0 and dielectric loss tangent 0.0015-0.003. Moreover, the glass transition point shows a high value with 180 degreeC-230 degreeC, for example.

  Further, when the base film 14, the signal wiring 15 and the ground wiring 16 and the coverlay film are joined, the amount of the oozing of the adhesive layer 12 is greatly reduced as compared with the case of the conventional adhesive layer. For this reason, the workability | operativity in joining integration using the above-mentioned hot roll laminating method or the hot press method becomes excellent.

  Next, another example of the flexible wiring board will be described with reference to FIG. This is the case of an FPC in which circuit wiring having a two-layer structure is provided. Here, an FPC in which circuit wiring for transmitting a high-speed digital signal is formed will be described. In the same manner as described with reference to FIG. 2, a plurality of first circuit wirings 19 are arranged in a wiring pattern of, for example, a copper foil on one main surface of a base film 14 made of a resin such as a liquid crystal polymer. The first cover film-like substrate 20 is thermocompression bonded to the first circuit wiring 19 and the base film 14 via the first adhesive layer 21. Here, the 1st cover film-like base material 20 and the 1st contact bonding layer 21 comprise a 1st coverlay film.

  Similarly, as the inner layer of the FPC, a plurality of second circuit wirings 22 are arranged on another main surface of the base film 14 in another wiring pattern of copper foil, for example. Then, the second cover film-like base material 23 is thermocompression bonded to the second circuit wiring 19 and the base film 14 via the second adhesive layer 24. Here, the 2nd cover film-like base material 23 and the 2nd contact bonding layer 24 comprise the 2nd cover-lay film used as the surface layer of FPC. This second coverlay film is formed of the same or different material as the first coverlay film. In any case, the elastic modulus of the second adhesive layer 24 is set to be smaller than the elastic modulus of the second cover film-like base material 23 and the base film 14. In this way, the FPC has a two-layer structure which is joined and integrated.

  In the FPC having the two-layer structure, a liquid crystal polymer is used for the first cover film-like substrate 11, the second cover film-like substrate 23 and the base film 14, and an oligophenylene ether is used for the first adhesive layer 12 and the second adhesive layer 24. It is preferable to use a synthetic resin containing a styrene-butadiene elastomer. In this combination, as in the case of the FPC having the single layer structure shown in FIG. 2, the signal wiring 15 in this FPC exhibits extremely excellent transmission / conduction characteristics of high-speed digital signals in the band of several GHz to several tens of GHz. Then, for example, an FPC having a wiring circuit corresponding to a high-speed digital signal reaching the GHz band like a CPU clock of a computer is easily provided.

  For the base film 14 in the two-layer structure FPC, in addition to the liquid crystal polymer, a PI resin, a PEN resin, or a composite resin such as these is preferably used. Alternatively, other thermoplastic resins or thermosetting resins having low dielectric properties can be used.

  In the above embodiment, the case of an FPC in which a wiring having a single layer structure or a two layer structure is formed is described, but a multilayer wiring board having three or more layers of wiring can be formed in the same manner. For example, a multilayer wiring board can be very easily formed by laying up an FPC structure as shown in FIG. 1 or FIG. 4 with different adhesive layers between each other. Here, as another adhesive layer, a synthetic resin containing oligophenylene ether and a styrene-butadiene elastomer is used as in the case of the first adhesive layer 12 and the second adhesive layer 24. Alternatively, for example, a resin such as a prepreg may be laminated between the multilayer wiring layers, and a coverlay film may be covered on the outermost layer as a surface layer to protect the inner layer wiring.

  The coverlay film of this embodiment is composed of a cover film-like substrate, an adhesive layer made of a synthetic resin containing an oligophenylene ether and a styrene-butadiene elastomer. The adhesive layer has an elastic modulus smaller than that of the cover film-like substrate. Here, the cover film-like substrate has low dielectric properties, and the relative dielectric constant and dielectric loss tangent are preferably 3.5 or less and 0.005 or less, respectively.

  The adhesive layer used in the present embodiment can easily reduce the elastic modulus, and exhibits stable and excellent adhesion of the coverlay film to the base film. And in manufacture of a flexible wiring board, the outstanding joining with a base film and wiring becomes easy. This is because in the thermocompression bonding using the hot roll laminating method or the hot pressing method as described above, the thermal stress generated when the temperature is lowered from the heated state to room temperature is absorbed and relaxed by the adhesive layer. .

  Further, in the case of the cover lay film, it is not necessary to use an adhesive that increases the relative dielectric constant and the dielectric loss tangent as in the conventional case in joining and integrating the base film and wiring with the cover lay film. Further, as described above, the combination of the base film and the coverlay film enables stable adhesion. And it becomes easy to make small the relative dielectric constant of the board | substrate material in the flexible wiring board produced by joining and integrating a base film and a coverlay film, and those dielectric loss tangents. Therefore, such an FPC can easily increase the speed of high-frequency signals and reduce the dielectric loss, and can be a high-performance one having excellent transmission characteristics.

  Furthermore, the glass transition point of the adhesive layer is 180 ° C. or higher, and an FPC having high heat resistance and high bending resistance becomes possible. And it becomes possible to meet the demand for in-vehicle devices such as automobiles. In this case, the base film and the cover film-like substrate are preferably made of a liquid crystal polymer, a PI resin, or a PEN resin.

  In addition, the adhesive layer used in the present embodiment can have a glass transition point of 230 ° C. or higher by adjusting its composition. For this reason, in mounting components such as semiconductor elements on a flexible wiring board, it is possible to realize a high heat resistance FPC that can endure even in a severe environment where lead-free solder reflow is performed at about 230 ° C., for example.

  Although the preferred embodiments of the present invention have been described above, the above-described embodiments do not limit the present invention. Those skilled in the art can make various modifications and changes in specific embodiments without departing from the technical idea and technical scope of the present invention.

  The present invention is not limited to a flexible wiring board that transmits a high-frequency signal as described in the present embodiment. For example, it should be noted that the present invention is similarly effective even in the case of an FPC that transmits a low-frequency electrical signal of less than 1 MHz.

  DESCRIPTION OF SYMBOLS 11 ... Cover film-like base material, 12 ... Adhesive layer, 13 ... Release material layer, 14 ... Base film, 15 ... Signal wiring, 16 ... Ground wiring, 17 ... Copper foil, 18 ... Laminated cushion sheet, 19 ... First circuit Wiring, 20 ... first cover film-like substrate, 21 ... first adhesive layer, 22 ... second circuit wiring, 23 ... second cover film-like substrate, 24 ... second adhesive layer

Claims (6)

A coverlay film that is formed on the surface layer of the flexible wiring board and protects the inner layer wiring,
A film-like substrate;
An adhesive layer provided on the main surface of the substrate,
The base material is made of a resin having a larger elastic modulus than the adhesive layer,
The cover layer film is made of a synthetic resin containing an oligophenylene ether and a styrene butadiene elastomer.   The cover lay film according to claim 1, wherein the base material is a low dielectric resin film having a relative dielectric constant of 3.5 or less at a frequency of 1 GHz.   The low dielectric resin film is composed of a liquid crystal polymer, polyethylene naphthalate, syndiotactic polystyrene, polyphenylene sulfide, polyimide resin, polyetherimide, polyphenylene ether, or a composite resin thereof. The coverlay film according to claim 2.   A wiring is formed on a main surface of a resin substrate made of a liquid crystal polymer or a composite resin containing a liquid crystal polymer, and the coverlay film according to any one of claims 1 to 3 is provided for the resin substrate and the wiring. A flexible wiring board characterized by being integrally joined.   The flexible wiring board according to claim 4, wherein the resin substrate and the cover film are liquid crystal polymers. The cover lay film according to any one of claims 1 to 3 is thermocompression bonded to the resin substrate on which the wiring is formed by a hot roll laminating method, and the cover is applied to the wiring and the resin substrate through a subsequent heat treatment. A method for producing a flexible wiring board, wherein a lay film is joined and integrated.

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