Flexible printed wiring board, electronic device using flexible printed wiring board, and method for manufacturing flexible printed wiring board

Abstract

To provide a flexible printed wiring board which has no warp, has excellent flexibility (elastic behavior), and includes a conductive layer for shielding electromagnetic waves.SOLUTION: A flexible printed wiring board including a base material having a first surface and a second surface facing the first surface, and signal wiring and a conductive layer only on the first surface side includes the signal wiring provided on the first surface, a first insulating resin layer provided on the signal wiring, the conductive layer provided on the first insulating resin layer, and a second insulating resin layer provided on the conductive layer, and a third insulating resin layer is provided on the second surface.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a flexible printed wiring board, an electronic device using a flexible printed wiring board, and a method for manufacturing a flexible printed wiring board. [Background technology]

[0002] Digital signal data communication is performed between two semiconductor devices mounted on an electronic device and driven relative to each other via a flexible printed circuit board. In recent years, the miniaturization of electronic devices and the high density of component mounting have led to a demand for high flexibility in the flexible printed circuit boards mounted thereon. On the other hand, when data communication is performed, electromagnetic noise is generated from the flexible printed circuit board. If the electromagnetic noise is transmitted to surrounding electronic devices or semiconductor devices, it can cause a deterioration in the quality of digital signals and malfunction of the semiconductor devices. For this reason, Patent Document 1 discloses a flexible printed circuit board to which an electromagnetic wave shielding sheet having a function of shielding electromagnetic waves is attached. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2003-86907 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the electromagnetic shielding sheet that needs to be pressure-bonded to the flexible printed wiring board disclosed in Patent Document 1 is used, the flexibility (flexibility) of the flexible printed wiring board is often insufficient.

[0005] Furthermore, when the shielding layer is formed, warping may occur in the flexible printed wiring board. [Means for solving the problem]

[0006] A flexible printed wiring board for solving the above problem is a flexible printed wiring board having a base material having a first surface and a second surface opposite to the first surface, and a signal wiring and a conductive layer only on the first surface side, the flexible printed wiring board comprising: the signal wiring provided on the first surface, a first insulating resin layer provided on the signal wiring, the conductive layer provided on the first insulating resin layer, and a second insulating resin layer provided on the conductive layer, and a third insulating resin layer provided on the second surface.

[0007] In addition, a manufacturing method for a flexible printed wiring board to solve the above problem is a manufacturing method for a flexible printed wiring board having a base material having a first surface and a second surface opposite to the first surface, and a signal wiring and a conductive layer only on the first surface side, characterized in that it includes the steps of: preparing a member having the signal wiring on the first surface and a first insulating layer having the first insulating resin layer provided on the signal wiring; providing the conductive layer on the first insulating resin layer; providing a second insulating resin layer on the conductive layer; and providing a third insulating resin layer on the second surface. Effect of the Invention

[0008] According to the present invention, it is possible to provide a flexible printed wiring board which is free from warping, has excellent flexibility (pliability), and has a conductive layer that blocks electromagnetic waves. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of a digital camera as an example of an electronic device according to the present invention. [Diagram 2] 1 is a perspective view of an imaging unit according to the present invention; [Diagram 3] 2 is a cross-sectional view taken along line AA of the flexible wiring board according to the present invention. [Figure 4] 1A to 1C are diagrams illustrating a method for manufacturing a flexible wiring board according to the present invention. [Diagram 5]2 is a cross-sectional view taken along the line AA of a flexible printed wiring board when an adhesive layer according to the present invention is provided. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0011] (First embodiment) (electronic equipment) 1 is a schematic diagram of a digital camera 600 as an example of an electronic device according to the present invention. The digital camera 600 includes a camera body 601 and a detachable lens unit (lens barrel) 602. The camera body 601 includes a housing 611, and an imaging unit 100 and a wireless communication unit 150 housed inside the housing 611.

[0012] The imaging unit 100 is an electronic component unit including a first printed circuit board 101, a second printed circuit board 102, and a flexible printed wiring board 11 that is a wiring board that electrically connects the first printed circuit board 101 and the second printed circuit board 102. By using the flexible printed wiring board 11, the wiring structure can be made lighter than a coaxial cable.

[0013] The first printed circuit board 101 includes a first printed wiring board 110 and a first semiconductor device 111 mounted on the first printed wiring board 110. The second printed circuit board 102 includes a second printed wiring board 120 and a second semiconductor device 121 mounted on the second printed wiring board 120.

[0014] The first semiconductor device 111 is an image sensor serving as an imaging element. The image sensor is, for example, a CMOS (Complementary Metal Oxide Semiconductor) image sensor or a CCD (Charge Coupled Device) image sensor. The image sensor has a function of converting light incident via the lens unit 602 into an electrical signal. The second semiconductor device 121 is a digital signal processor serving as a processing circuit. The digital signal processor has a function of acquiring an electrical signal indicating image data from the image sensor, performing a process of correcting the acquired electrical signal, and generating corrected image data.

[0015] The wireless communication unit 150 is a modularized wireless communication module that performs wireless communication in the GHz band. The wireless communication unit 150 has a printed wiring board 151 provided with an antenna (not shown) and a wireless communication IC 152 mounted on the printed wiring board 151. The antenna is provided in the same plane as the wireless communication IC 152 and is disposed in a position close to the housing 611 so as to facilitate communication with the outside. The wireless communication IC 152 transmits and receives image data by performing wireless communication with an external device (such as a PC or a wireless router) via the antenna. That is, the wireless communication IC 152 modulates a digital signal indicating image data and transmits it from the antenna as radio waves of a communication frequency of a wireless standard. The wireless communication IC 152 also demodulates the radio waves received by the antenna into a digital signal indicating image data. The wireless communication IC 152 performs wireless communication with an external device in compliance with a standard such as WiFi (registered trademark) or Bluetooth (registered trademark).

[0016] Although the digital camera 600 has been shown above as an example of an electronic device according to the present invention, the present invention can also be used in other electronic devices, such as mobile phones, smartphones, tablets, notebook PCs, and video cameras.

[0017] (Flexible printed circuit board) Fig. 2 is a perspective view of an electronic component unit (imaging unit 100) in which a first substrate and a second substrate are connected using a flexible printed wiring board 11 according to the present invention. Fig. 3 is a cross-sectional view of the flexible printed wiring board 11 taken along line AA.

[0018] As shown in FIG. 2, the first printed wiring board 110, which is the first substrate, includes a first connector 112. The first connector 112 is electrically connected to the first semiconductor device 111 by a conductor formed on the first printed wiring board 110. The second printed wiring board 120, which is the second substrate, includes a second connector 122. The second connector 122 is electrically connected to the second semiconductor device 121 by a conductor formed on the second printed wiring board 120. That is, the first semiconductor device 111 and the second semiconductor device 121 are electrically connected via the first printed wiring board 110, the flexible printed wiring board 11, and the second printed wiring board 120, and can communicate with each other. The first substrate and the second substrate may be an organic wiring board using a glass epoxy substrate, a ceramic wiring board using ceramics, or a metal core wiring board having a metal core layer. The substrate is not limited to a printed wiring substrate, and may be a silicon substrate.

[0019] As shown in FIG. 3, the flexible printed wiring board 11 has a base material, and a signal wiring and a conductive layer only on one side of the base material. The flexible printed wiring board 11 includes a base material 21, a signal wiring 22, a first insulating resin layer 23, a conductive layer 24, a second insulating resin layer 25, and a third insulating resin layer 26. The base material 21 has a first surface 21A and a second surface 21B facing the first surface 21A. The signal wiring 22 is provided on the first surface 21A of the base material 21, and the first insulating resin layer 23 is provided on the first surface 21A of the base material 21 and the signal wiring 22. The conductive layer 24 is provided on the first insulating resin layer 23, and the second insulating resin layer 25 is provided on the conductive layer 24. The third insulating resin layer 26 is provided on the second surface 21B of the base material 21.

[0020] The total thickness of the flexible printed wiring board 11 formed in the above configuration is preferably 75 μm or less. More preferably, it is 70 μm or less. If the total thickness is 75 μm or less, the flexible printed wiring board has high flexibility. If the flexible printed wiring board 11 has high flexibility, the first printed circuit board 101 and the second printed circuit board 102 attached to both ends of the flexible printed wiring board 11 can be stored in a small space.

[0021] (base material) The material of the substrate 21 is a resin. Examples of the resin include polyimide-based resins such as polyimide, polyamide, and polyamideimide, thermosetting resins such as epoxy, and thermoplastic resins such as liquid crystal polymers. Among these, polyimide or liquid crystal polymer is preferable. Polyimide has excellent heat resistance and mechanical properties, and is easily available commercially. Liquid crystal polymers have a low relative dielectric constant, making them suitable for high-speed signal transmission applications, and have low moisture absorption and excellent dimensional stability. The thickness of the substrate 21 is not particularly limited, but is preferably in the range of 5 μm to 13 μm. If the thickness is less than 5 μm, handling may be difficult. In addition, since it is too thin, it may be vulnerable to impact and may easily break, exposing the signal wiring 22. On the other hand, if the thickness exceeds 13 μm, the rigidity of the resin may be high, and flexibility may be insufficient. More preferably, the thickness is in the range of 8 μm to 13 μm.

[0022] (Signal wiring) The signal wiring 22 is a wiring for transmitting a data signal between the first semiconductor device 111 and the second semiconductor device 121. In Fig. 2 and Fig. 3, an example is shown in which two pairs of differential signal wiring are used, each pair of which transmits a data signal. However, the number of wirings is not particularly limited, and any number of wirings may be used. In addition, the signal wiring 22 may be a wiring for transmitting a single-ended signal such as a control signal or a response signal, or a wiring for ground.

[0023] The thickness of the signal wiring 22 (thickness of the differential signal wiring) is not particularly limited, but is, for example, in the range of 1 μm to 12 μm.

[0024] (First insulating resin layer) The first insulating resin layer 23 contains a cured resin, and the resin may be so-called engineering plastic. Examples include polypropylene, cross-linked polyethylene, polyester, polybenzimidazole, polyamide, polyimide, polyimideamide, polyetherimide, polyphenylene sulfide (PPS), polyethylene naphthalate (PEN), and polyether ether ketone (PEEK). From the viewpoint of low cost, polyester film is preferable. From the viewpoint of excellent flame retardancy, it is preferable to use a polyphenylene sulfide film, and when heat resistance is required, an aramid film or a polyimide film is preferable.

[0025] The insulating resin may be any resin having insulating properties, such as a thermosetting resin or an ultraviolet curing resin. Examples of the thermosetting resin include phenolic resin, acrylic resin, epoxy resin, melamine resin, silicone resin, and acrylic modified silicone resin. Examples of the ultraviolet curing resin include epoxy acrylate resin, polyester acrylate resin, and their methacrylate modified products. The curing form may be any of heat curing, ultraviolet curing, and electron beam curing. In addition, other known additives such as coloring pigments, flame retardants, antioxidants, lubricants, dust prevention agents, and curing accelerators may be used as necessary.

[0026] The thickness of the first insulating resin layer 23 is not particularly limited, but is preferably in the range of 5 μm to 13 μm, and more preferably in the range of 8 μm to 13 μm. If the thickness is less than 5 μm, the strength may be insufficient. On the other hand, if the thickness exceeds 13 μm, the sliding property and bending property may be reduced. In addition, the volume resistivity is 1×10 9 A value of Ω·cm or more is preferable, and a value of 1×10 13 Ω·cm or more.

[0027] (Conductive layer) The conductive layer 24 is provided on the first insulating resin layer 23, and is a layer for shielding electromagnetic waves generated from the signal wiring 22. Therefore, it is preferable that the distance between the wireless communication unit 150 and the conductive layer 24 is shorter than the distance between the wireless communication unit 150 and the signal wiring 22. That is, it is preferable that the conductive layer 24 is disposed at a position closer to the wireless communication unit 150 than the signal wiring 22. Since the conductive layer 24 is located closer to the wireless communication unit 150 than the signal wiring 22, it is possible to suppress the electromagnetic waves generated from the signal wiring 22 from being superimposed on the radio waves of the external communication performed by the wireless communication unit 150. In addition, if an electronic device such as the wireless communication unit 150 is present around the flexible printed wiring board 11, the electromagnetic waves generated from the electronic device may cause a deterioration in the quality of the data signal transmitted by the signal wiring 22. However, since the conductive layer 24 is located closer to the electronic device than the signal wiring 22, it is expected that the conductive layer 24 can shield the electromagnetic waves generated from the electronic device and suppress the deterioration in the quality of the data signal transmitted by the signal wiring 22.

[0028] The form of the conductive layer 24 can be appropriately selected based on the balance between the electromagnetic noise shielding property and the impedance value. It may be formed uniformly over the entire surface of the printed wiring board, or may be formed partially over the entire surface. Alternatively, it may have regular or irregular openings.

[0029] Examples of materials include metal materials such as gold, silver, copper, aluminum, and nickel, conductive resin compositions in which conductive fillers such as metal particles, metal fibers, and carbon nanotubes are mixed with resin, and conductive polymers such as polythiophene and polypyrrole. Of these, silver paste consisting of silver particles with high conductivity and a resin binder is particularly suitable as a coating film forming means. In addition to silver paste, gold paste, copper paste, carbon paste, and the like may also be used.

[0030] From the viewpoint of the ability to block electromagnetic waves, the volume resistivity of the conductive layer 24 is set to 1×10 -6 Ω cm or more 5×10 -4 A range of Ω·cm or less is preferable.

[0031] The thickness of the conductive layer 24 is preferably in the range of 1 μm to 13 μm. If the thickness is less than 1 μm, the resistance value of the conductive layer 24 increases, making it difficult for a return current to flow when common mode noise occurs, and there is a risk of an increase in the amount of radiated noise. On the other hand, if the thickness of the conductive layer 24 is thicker than 13 μm, the second insulating resin layer 25 needs to be applied thickly, which may impair flexibility. More preferably, the thickness is in the range of 2 μm to 10 μm.

[0032] (Second insulating resin layer) The second insulating resin layer 25 is provided on the conductive layer 24, and serves as an insulating layer for suppressing electrical conduction to other components in the electronic device. For this reason, it is formed by coating an insulating resin that is insulating, heat-resistant, and flexible.

[0033] The insulating resin may be any resin having insulating properties, and may be an energy curable resin. Examples of the insulating resin include a thermosetting resin or an ultraviolet curable resin, and a coating agent made of a resin solution in which a cured film component is dispersed in a solvent. Examples of the thermosetting resin include phenolic resin, acrylic resin, epoxy resin, polyamide resin, polyamideimide resin, polyimide resin, melamine resin, silicone resin, and acrylic modified silicone resin. Examples of the ultraviolet curable resin include epoxy acrylate resin, polyester acrylate resin, and their methacrylate modified products. Examples of the resin solution include polyester urethane resin and polyamideimide resin dissolved in an organic solvent. In addition, if necessary, color pigments, flame retardants, antioxidants, lubricants, plasticizers, viscosity modifiers, dust prevention agents, curing accelerators, inorganic fillers such as silica and carbon black, organic fillers such as silicone particles and polyester particles, and other known additives may be blended. The formed coating film shrinks when cured. Therefore, a shrinking force acts on the surface of the flexible printed wiring board 11 on which the coating film is formed, and the flexible printed wiring board may warp. Therefore, a coating agent made of a resin solution in which hardened film components are dispersed in a solvent is preferable because it causes little shrinkage due to the hardening reaction and can suppress warping. Furthermore, a coating agent in which a flexible and heat-resistant polyamide-imide resin is dissolved in a solvent is even more preferable.

[0034] The thickness of the second insulating resin layer 25 is preferably in the range of 13 μm to 18 μm. If the thickness is less than 13 μm, the conductive layer 24 may be easily exposed. On the other hand, if the thickness is more than 18 μm, the rigidity of the resin may be high and the flexibility may be insufficient. More preferably, the thickness is in the range of 4 μm to 10 μm.

[0035] (Third insulating resin layer) The third insulating resin layer 26 is a layer provided on the second surface 21B of the substrate 21 in order to suppress warping of the flexible printed wiring board that occurs when the second insulating resin layer 25 is formed. The coating film formed as the second insulating resin layer 25 shrinks when cured. Therefore, if the coating film of the insulating resin layer is formed only on one surface of the flexible printed wiring board, the shrinkage force associated with curing acts only on one surface, causing warping of the flexible printed wiring board. However, since the flexible printed wiring board according to the present invention has the second insulating resin layer 25 and the third insulating resin layer 26 on both surfaces, the shrinkage forces associated with curing cancel each other out, suppressing the occurrence of warping.

[0036] The insulating resin of the third insulating resin layer 26 may be the same as that of the second insulating resin layer 25. However, a different material may be used as long as it can counteract the shrinkage force that occurs when the second insulating resin layer 25 hardens.

[0037] The thickness of the third insulating resin layer 26 is preferably such that T(T2 / T3), which is the value obtained by dividing T2 by T3, is in the range of 0.5 to 2.0, where T2 is the thickness of the second insulating resin layer 25 and T3 is the thickness of the third insulating resin layer 26. If T(T2 / T3) is less than 0.5 or more than 2.0, the difference in thickness between the second insulating resin layer 25 and the third insulating resin layer 26 becomes large, and there is a possibility that warping may occur during the formation of the resin layer. If warping occurs, flexibility may be lost and the attachment work to the electronic component may become difficult. More preferably, it is in the range of 0.7 to 1.4.

[0038] Furthermore, it is not necessary for the thickness to be uniform over the entire surface. For example, in a flexible printed wiring board, the insulating resin layer may be thinned to the extent that insulation protection is possible in the expected bending region, and T(T2 / T3) may be adjusted so that warping occurs in accordance with the expected bending direction.

[0039] (Manufacturing method) Here, the manufacturing method of the flexible wiring board of the present invention will be described with reference to FIG.

[0040] 4(a), a member is prepared that includes signal wiring 22 provided on a first surface 21A of a substrate 21, and a first insulating resin layer 23 provided on the first surface 21A and the signal wiring 22. Such a substrate is called a single-sided flexible wiring board, and is commercially available.

[0041] Next, as shown in FIG. 4(b), a conductive layer 24 is formed on the first insulating resin layer 23. The method for forming the conductive layer 24 is not particularly limited. For example, methods for forming the conductive layer 24 on the first insulating resin layer 23 include subtractive methods, electroless plating methods, electrolytic plating methods, and physical vapor deposition methods such as vacuum deposition and sputtering methods. Also, known coating film forming methods such as bar coating, slit coating, and screen printing methods can be used. Among these, a method for directly forming the conductive layer 24 on the first insulating resin layer 23 is preferably a method in which a conductive material that can be formed under normal temperature and pressure is applied and heated to form a dried coating film.

[0042] Next, as shown in FIG. 4(c), a solution of an uncured second insulating resin is applied onto the conductive layer, and the second insulating resin is cured to form the second insulating resin layer 25. Also, an uncured third insulating resin is applied onto the second surface 21B of the base material 21, and the third insulating resin is cured to form the third insulating resin layer. The second insulating resin layer 25 and the third insulating resin layer 26 may be formed simultaneously, or one may be formed after the other. If they are formed simultaneously, the shrinkage forces accompanying the curing are also canceled out by the surfaces of both the second insulating resin layer 25 and the third insulating resin layer 26, so that warping is suppressed. When one is formed after the other is formed, if the flexible printed wiring board is fixed until both are cured, warping is suppressed even if the fixing is released. A known method can be selected as a coating film formation method for the second insulating resin layer 25 and the third insulating resin layer 26. For example, bar coating, slit coating, spray coating, dot dispenser, screen printing, etc. can be mentioned. The method for forming a cured film after forming the coating film can be appropriately selected according to the material, such as heat curing, ultraviolet curing, electron beam curing, heat drying, vacuum drying, and the like.

[0043] 4(a) shows an example in which a commercially available member is prepared. However, the present manufacturing method is not limited to this process, and it is also possible to prepare a base material 21 having a first surface 21A and a second surface 21B, form a signal wiring 22 on the first surface 21A, and form a first insulating resin layer 23 on the first surface 21A and the signal wiring 22.

[0044] When forming the signal wiring 22 on the first surface 21A, the method for manufacturing the signal wiring 22 is not particularly limited, and the signal wiring 22 can be formed by a known method such as laminating metal foil, metal plating, inkjet process, etc. When using copper foil as the metal foil, a film laminated with an adhesive or the like can be used to form a required transmission line pattern by a photolithography / etching process. When using an inkjet process, a polymer ink containing conductive metal particles can be drawn in the required pattern and the pattern can be baked at a predetermined temperature to form the pattern.

[0045] When forming the first insulating resin layer 23 on the first surface 21A and the signal wiring 22, the method of forming the first insulating resin layer 23 is not particularly limited, and the insulating resin can be coated by a known method. A solution in which an insulating resin is dissolved in a solvent can be applied by a gravure coating method, a kiss coating method, a die coating method, a blade coating method, a roll coating method, a knife coating method, a spray coating method, a bar coating method, a spin coating method, or a dip coating method. The solvent can be appropriately selected depending on the type of resin used. For example, ketone-based solvents such as acetone, methyl ethyl ketone, and cyclohexanone, and alcohol-based solvents such as methanol, ethanol, propanol, ethylene glycol, glycerin, and propylene glycol monomethyl ether can be used. In addition, acids such as acetic acid, amide-based solvents such as formamide, dimethylacetamide, and N-methylpyrrolidone, nitrile-based solvents such as acetonitrile and propylonitrile, and ester-based solvents such as methyl acetate and ethyl acetate can be used. In addition, carbonate-based solvents such as dimethyl carbonate and diethyl carbonate can be used. During coating, a heating or drying step may be performed to volatilize the solvent, if necessary. For heating and drying, known heating and drying devices such as hot air dryers and infrared heaters can be used, and the heating and drying temperature and time can be appropriately selected.

[0046] Second embodiment The second embodiment will now be described with reference to Fig. 5, which is a cross-sectional view taken along line AA of the flexible printed wiring board 11. Explanations of the same points as in the first embodiment will be omitted, and only points that differ from the first embodiment will be described below.

[0047] The second embodiment differs from the first embodiment in that the first insulating resin layer 23 does not have a function of adhering to the base material 21 and the signal wiring 22. Therefore, an adhesive layer 31 is provided between the first insulating resin layer 23 and the base material 21 and the signal wiring 22. By providing the adhesive layer 31, it becomes possible to adhere the first insulating resin layer 23 to the base material 21 and the signal wiring 22.

[0048] It is preferable that the adhesive layer 31 has high electrical insulation. A cured product of a known adhesive can be used for the adhesive layer 31. Examples of the adhesive include an acrylonitrile butadiene rubber (NBR) adhesive, a polyamide adhesive, a polyester adhesive, an acrylic adhesive, a polyester polyurethane adhesive, and a silicone adhesive.

[0049] The thickness of the adhesive layer 31 is not particularly limited, but it is sufficient that the adhesive layer 31 is thicker than the signal wiring 22 so as to sufficiently cover the signal wiring 22 .

[0050] The manufacturing method of the flexible printed wiring board when the adhesive layer 31 is used is not particularly limited, and for example, the following method can be adopted. After forming the signal wiring 22 on the first surface 21A of the base material 21, an adhesive is applied onto the base material 21 and the signal wiring 22. A first insulating resin layer 23 that does not have an adhesive function is placed on the applied adhesive, and the adhesive is cured to form the adhesive layer 31 and the first insulating resin layer 23. The method of forming the adhesive is not particularly limited, and a method of laminating a sheet-like adhesive and curing it, a method of applying a liquid adhesive by a dispenser or printing method, etc., and curing it by heat or ultraviolet irradiation, etc. can be used. Other points are the same as those of the first embodiment.

[0051] (Example) Next, the present invention will be described in more detail with reference to examples and comparative examples.

[0052] In this embodiment, a single-sided flexible printed wiring board having dimensions of 20 mm width and 150 mm length and 20 pairs of differential signal wiring was used as the flexible printed wiring board.

[0053] In the examples and comparative examples, the flexible printed wiring boards were evaluated in terms of bending load and warpage.

[0054] First, the bending load will be described. The flexibility of the printed wiring board of the present invention was evaluated by the repulsive load when it was bent. The procedure was as follows. First, a flexible printed wiring board 11 with a width of 20 mm was placed horizontally. Next, it was bent 180 degrees in the longitudinal direction with a curvature of 3 mm. The vertical repulsive force at the end of the curvature was measured with a digital force gauge 32 ("ZTA-2N" manufactured by Imada Co., Ltd.). The bending load quantitatively determines the flexibility of the flexible printed wiring board of the present invention. If the bending load is large, the flexibility is low and the flexible printed wiring board becomes hard. If the flexibility is low, not only is it difficult to attach it to an electronic component, but if it is connected between two electronic components that are driven relatively, it may cause a disturbance in driving. The evaluation criteria are as follows, and B or higher was considered to be acceptable. A (Excellent): Bending load is less than 200 mN. B (Good): The bending load is 200 mN or more and less than 300 mN. C (Not acceptable): The bending load is 300 mN or more.

[0055] Next, the amount of warping will be described. The amount of warping on the flexible printed wiring board was evaluated by the height of the warping. The flexible printed wiring board was cut into a length of 50 mm in the longitudinal direction to form a test piece. The short side of this cut-out test piece was placed on a horizontal and smooth table and left to stand, and the maximum height of the cut-out test piece from the table was evaluated as the amount of warping. This amount of warping quantitatively judges the warping of the flexible printed wiring board of the present invention, and a small amount of warping means that the flexible printed wiring board itself also has a small amount of warping, and can be attached to electronic components in the subsequent process without any problems. On the other hand, if the amount of warping becomes large, the flexible printed wiring board itself warps significantly, making it difficult to store in an orderly manner and causing great problems in the attachment work to electronic components. The evaluation criteria are as follows, and B or higher was considered to be acceptable. A (Excellent): Warpage is less than 4.0 mm. B (Good): The amount of warpage is 4.0 mm or more and less than 5.0 mm. C (Unacceptable): The amount of warping is 5.0 mm or more.

[0056] Example 1 A flexible printed wiring board 11 having the shape shown in FIG. 5 was produced.

[0057] First, a single-sided flexible printed circuit board (hereinafter, referred to as single-sided FPC) manufactured by Nippon Mektron Co., Ltd. was prepared. The dimensions of the single-sided FPC were 20 mm wide and 150 mm long. The single-sided FPC was as follows. A 12.5 μm thick polyimide film was used as the base material 21, and 20 pairs of signal wiring 22 were formed as differential wiring pairs on the first surface 21A of the base material 21 using copper foil with a thickness of 12 μm. An adhesive layer 31 with a thickness of 15 μm was formed on the first surface 21A and the signal wiring 22, and a first insulating resin layer 23 made of a 12.5 μm thick polyimide film was formed on the adhesive layer 31. The thickness of the single-sided FPC was 52 μm.

[0058] Next, a conductive layer 24 was formed on the first insulating resin layer 23 of the single-sided FPC. The conductive layer 24 was formed to a thickness of 4 μm by using a silver paste (product name: DD-1630L-245) manufactured by Kyoto Elex Co., Ltd., with a screen printer (MT-320T manufactured by Micro-Tec Co., Ltd.).

[0059] Next, a second insulating resin layer 25 was formed on the conductive layer 24. For the second insulating resin layer 25, a polyamideimide resin soluble coating agent (product name: HR-16NN) manufactured by Toyobo Co., Ltd. was used. The second insulating resin layer 25 was formed using a coating device (product name: Control Valve MiniVal NCV-17) manufactured by Musashi Engineering Co., Ltd. with a slit nozzle having a width of 20 mm under conditions such that the wet film thickness was 30 to 40 μm. After coating, the substrate was heated at 80° C. for 15 minutes, and then further heated at 200° C. for 30 minutes to dry the solvent, and a hardened second insulating resin layer 25 was obtained. The thickness of the second insulating resin layer 25 at this time was 4 μm.

[0060] Furthermore, a third insulating resin layer 26 was formed on the second surface 21B of the base material 21 of the single-sided FPC. The third insulating resin layer 26 was also formed using the same material and under the same conditions as the second insulating resin layer 25.

[0061] The flexible printed wiring board in Example 1 had a total thickness of 64 μm.

[0062] Example 2 In the second embodiment, differences from the first embodiment will be described below. Other points are the same as those in the first embodiment.

[0063] The second insulating resin layer 25 and the third insulating resin layer 26 were each made by uniformly mixing a polyamideimide resin soluble coating agent (product name: HR-12N2) manufactured by Toyobo Co., Ltd. and an epoxy resin (product name: jER-828) manufactured by Mitsubishi Chemical. The mixing ratio was 100 parts by mass of the former and 10 parts by mass of the latter. The second insulating resin layer 25 was applied with a bar coater, and after application, the coating was heated at 80 degrees for 15 minutes, and then further heated at 200 degrees for 30 minutes to dry the solvent, thereby obtaining a cured film having a thickness of 5 μm.

[0064] The total thickness of the flexible printed wiring board in Example 2 was 66 μm.

[0065] Example 3 In the third embodiment, differences from the first embodiment will be described below. The other points are the same as those in the first embodiment.

[0066] The second insulating resin layer 25 and the third insulating resin layer 26 were made of UV-curable resin (product name: HA7975) manufactured by Showa Denko Materials Co., Ltd. The second insulating resin layer 25 was applied with a bar coater, and after application, the resin was heated and held at 50° C. for 15 minutes, and then further irradiated with UV energy of 500 mJ / cm 2 . 2 The mixture was cured under the above conditions to obtain a cured film having a thickness of 7 μm.

[0067] The total thickness of the flexible printed wiring board in Example 3 was 70 μm.

[0068] Example 4 Example 4 is similar to Example 1 except that the thickness of the cured film of second insulating resin layer 25 and third insulating resin layer 26 is set to 9 μm.

[0069] The total thickness of the flexible printed wiring board in Example 4 was 74 μm.

[0070] (Comparative Examples 1 to 3) Comparative Example 1 is a flexible printed wiring board having the configuration of Example 2, except that the third insulating resin layer 26 is not formed.

[0071] The total thickness of the flexible printed wiring board in Comparative Example 1 was 61 μm.

[0072] Comparative Example 2 is a flexible printed wiring board having the same configuration as in Example 3, except that the third insulating resin layer 26 is not formed.

[0073] The total thickness of the flexible printed wiring board in Comparative Example 2 was 63 μm.

[0074] In Comparative Example 3, an electromagnetic wave shielding film for FPC (product name: LIOELM TSS500Z-S, manufactured by Toyochem Co., Ltd.) was attached onto the first insulating resin layer of the single-sided FPC. The total thickness was 68 μm.

[0075] (Evaluation Results) Table 1 shows the evaluation results of the flexible printed wiring boards in the configurations of Examples 1 to 4 and Comparative Examples 1 to 3. As shown in Table 1, the bending load and warpage of the printed wiring board in which an electromagnetic noise shielding layer and a second insulating resin layer were formed on one side of a single-sided FPC and a third insulating resin layer was formed on the other side were small and good. In addition, in the configuration in which the second insulating resin layer was formed but the third insulating resin layer was not formed, the warpage at the time of forming the second insulating resin layer was not eliminated, so the warpage was uniformly large. In addition, in the configuration equipped with a commercially available adhesive shielding sheet, it was found that the bending load was large because the sheet was composed of three layers, an adhesive layer, a metal layer, and a resin layer, and therefore had high rigidity.

[0076] [Table 1] [Explanation of symbols]

[0077] 11 Flexible printed circuit board 21 Base material 21A 1st page 21B 2nd side 22 Signal wiring 23 First insulating resin layer 24 Conductive layer 25 Second insulating resin layer 26 Third insulating resin layer 31 Adhesive layer 600 Digital Camera (Electronic Device) 611 Case

Claims

1. a substrate having a first surface and a second surface opposite to the first surface; A flexible printed wiring board having a signal wiring and a conductive layer only on the first surface side, The signal wiring provided on the first surface; a first insulating resin layer provided on the signal wiring; the conductive layer provided on the first insulating resin layer; a second insulating resin layer provided on the conductive layer; a third insulating resin layer provided on the second surface, The flexible printed circuit board has a total thickness of 75 μm or less.

2. A substrate having a first surface and a second surface opposite the first surface; A flexible printed wiring board having a signal wiring and a conductive layer only on the first surface side, The signal wiring provided on the first surface; a first insulating resin layer provided on the signal wiring; the conductive layer provided on the first insulating resin layer; a second insulating resin layer provided on the conductive layer; a third insulating resin layer provided on the second surface, 2. A flexible printed circuit board, comprising: a first insulating layer and a second insulating layer; a second insulating layer and a third insulating layer, the second insulating layer and the third insulating layer being made of a polyamideimide.

3. A substrate having a first surface and a second surface opposite the first surface; A flexible printed wiring board having a signal wiring and a conductive layer only on the first surface side, The signal wiring provided on the first surface; a first insulating resin layer provided on the signal wiring; the conductive layer provided on the first insulating resin layer; a second insulating resin layer provided on the conductive layer; a third insulating resin layer provided on the second surface, The flexible printed circuit board is characterized in that the material of the substrate is polyimide or liquid crystal polymer.

4. A substrate having a first surface and a second surface opposite the first surface; A flexible printed wiring board having a signal wiring and a conductive layer only on the first surface side, The signal wiring provided on the first surface; a first insulating resin layer provided on the signal wiring; the conductive layer provided on the first insulating resin layer; a second insulating resin layer provided on the conductive layer; a third insulating resin layer provided on the second surface, 2. A flexible printed wiring board, wherein the resin of the first insulating resin layer is polyester, polyphenylene sulfide, aramid or polyimide.

5. 5. The flexible printed wiring board according to claim 2, wherein the total thickness of the flexible printed wiring board is 75 [mu]m or less.

6. A flexible printed wiring board as described in any one of claims 1 to 5, characterized in that the resin of the third insulating resin layer is different from the material of the substrate.

7. A flexible printed wiring board described in any one of claims 1 to 6, characterized in that the resin of the third insulating resin layer is the same as the resin of the second insulating resin layer.

8. 8. The flexible printed wiring board according to claim 1, wherein when the thickness of the second insulating resin layer is T2 and the thickness of the third insulating resin layer is T3, a value T (T2 / T3) obtained by dividing T2 by T3 is in the range of 0.5 or more and 2.0 or less.

9. An electronic component unit having a flexible printed wiring board, a first board and a second board, the first board and the second board being electrically connected using the flexible printed wiring board, The flexible printed wiring board is a substrate having a first surface and a second surface opposite to the first surface; signal wiring provided on the first surface; a first insulating resin layer provided on the signal wiring; a conductive layer provided on the first insulating resin layer; a second insulating resin layer provided on the conductive layer; a third insulating resin layer provided on the second surface, The material of the substrate is polyimide or liquid crystal polymer; The resin of the first insulating resin layer is polyester, polyphenylene sulfide, aramid or polyimide; the resin of the second insulating resin layer is polyamideimide; the resin of the third insulating resin layer is polyamideimide; The total thickness of the flexible printed circuit board is 75 μm or less; An electronic component unit characterized by at least one of the above.

10. the first substrate has an imaging element; 10. The electronic component unit according to claim 9, wherein the second substrate has a processing circuit for processing an electric signal transmitted from the image sensor.

11. The device has a housing, 11. An electronic device comprising the electronic component unit according to claim 9 or 10 housed in the housing.

12. An electronic device comprising a housing and an electronic component unit housed in the housing, the electronic component unit has a flexible printed wiring board, a first substrate, and a second substrate, the first substrate and the second substrate being electrically connected to each other using the flexible printed wiring board; The flexible printed wiring board is a substrate having a first surface and a second surface opposite to the first surface; signal wiring provided on the first surface; a first insulating resin layer provided on the signal wiring; a conductive layer provided on the first insulating resin layer; a second insulating resin layer provided on the conductive layer; a third insulating resin layer provided on the second surface, the housing further accommodates a wireless communication unit capable of wirelessly communicating with an external device; 2. An electronic device comprising: a flexible printed wiring board having a first conductive layer and a second conductive layer disposed in a position closer to the wireless communication unit than the signal wiring;

13. The material of the substrate is polyimide or liquid crystal polymer; The resin of the first insulating resin layer is polyester, polyphenylene sulfide, aramid or polyimide; the resin of the second insulating resin layer is polyamideimide; the resin of the third insulating resin layer is polyamideimide; The total thickness of the flexible printed circuit board is 75 μm or less; 13. The electronic device according to claim 12, characterized in that:

14. a substrate having a first surface and a second surface opposite to the first surface; A method for manufacturing a flexible printed wiring board having a signal wiring and a conductive layer only on the first surface side, preparing a member in which the signal wiring is provided on the first surface of the base material and a first insulating resin layer is provided on the signal wiring; providing the conductive layer on the first insulating resin layer; providing a second insulating resin layer on the conductive layer; providing a third insulating resin layer on the second surface; 2. A method for producing a flexible printed wiring board comprising the steps of:

15. In the step of providing the second insulating resin layer, an uncured second insulating resin is applied onto the conductive layer, and the second insulating resin is cured to provide the second insulating resin layer; 15. The method for manufacturing a flexible printed wiring board according to claim 14, characterized in that in the step of providing the third insulating resin layer, an uncured third insulating resin is applied onto the second surface, and the third insulating resin is cured to provide the third insulating resin layer.

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