JP7539708B2 - Shielded thin flat cable and its manufacturing method - Google Patents

Description

The present invention relates to a shielded thin flat cable used for communication and wiring in devices that require high-density mounting, and a manufacturing method thereof. Applications of the shielded thin flat cable include communication devices that require high-density mounting, devices that use high-frequency and high-speed signals, and more specifically, smartphones, IoT devices, ADAS-related devices, and the like.

Coaxial cables, which have a core material covered with a shielding layer, are widely used for power supply lines connecting television sets or radio sets to antennas, for connecting measuring instruments, for transmitting audio and video signals, and for wiring high-frequency and high-speed transmission lines such as RF circuits inside electronic devices and their surrounding areas.

A typical coaxial cable is constructed with a core wire made of copper or the like wrapped in an insulator such as polyethylene, which is then wrapped in a shielding layer called a braided wire made of thin conductors woven together, and finally covered on the outside with a protective coating such as polyvinyl chloride. The braided wire blocks electromagnetic waves from the outside, suppressing noise and attenuation, and also reducing the leakage of electromagnetic waves from the inside. It has a wide transmission frequency range, from direct current to millimeter waves (see non-patent document 1).

On the other hand, in mobile devices and the like, triplate lines as shown in Fig. 9 are sometimes provided as signal transmission lines for transmitting high-frequency signals in resin multilayer boards made of thermoplastic resin, such as flexible boards for high-density mounting of components in electronic devices and flat cables for wiring through narrow gaps inside devices. A triplate line is a signal transmission line in which line conductors and ground conductors are provided in a resin multilayer board, and ground conductors that are wider than the line conductors are arranged opposite both sides of the line conductors (see, for example, Patent Documents 1 and 2). Since ground conductors are provided on both sides of the triplate line, it has the characteristic of suppressing noise from outside and making it less likely to generate unwanted radiation (unwanted radiation).

It has also been proposed to provide a resin multilayer board and electronic device that are easy to bend even when a triplate line is provided and that are less likely to experience degradation in transmission characteristics when bent (see, for example, Patent Document 3).

On the other hand, in order to improve the shielding effect, a method has been used in which a metal foil tape is attached to the flat cable to encase the flat cable (see, for example, Patent Document 4). However, the short side of such a flat cable exposes the insulator to the outside air, and the exposed insulator is exposed to water vapor, which penetrates into the interior of the insulator and causes the insulator to absorb moisture. The absorbed water affects the transmission characteristics. Insulators with a high moisture absorption rate are easily affected by water vapor, and this effect is particularly noticeable in the high frequency range, causing changes in the transmission characteristics.

There is also a method of wrapping shielding tape to strengthen the shielding in the longitudinal direction (see, for example, Patent Documents 5 and 6), but this involves wrapping a shielding film as a shielding layer, and gaps and contact resistance occur where the shielding film overlaps or comes into contact, so the shielding is not complete. Also, where the shielding film overlaps or comes into contact, organic matter such as the adhesive layer or bonding layer is exposed to the outside air, so the insulator absorbs moisture.

As mentioned above, moisture absorption causes the electrical properties of the insulator to change, which in turn changes the transmission properties of the cable. The effect of moisture absorption on transmission properties is particularly noticeable when handling high frequency or high speed signals.

Flat cables have also been proposed in which a seamless shielding film is formed in the longitudinal direction using copper plating (for example, Patent Document 7). However, the short side is cut into individual pieces, so the cross section is not plated and the conductor and insulator are exposed. In other words, the end faces in the short side are affected by humidity, allowing water vapor to penetrate through them. Therefore, in this case, for flat cables that require stable transmission characteristics, there are restrictions on the use of highly hygroscopic resins as insulators. Also, in order to connect to other components, new terminals must be formed.

In addition, due to the recent trend towards higher frequencies in communication, as typified by 5G communication, and the increased transmission speed of semiconductors, there is a demand for low loss in transmission lines. Insulators with low transmission loss are therefore required. For example, general-purpose hydrocarbon resins such as polyethylene, polystyrene and polypropylene have low transmission loss, are easy to process and are inexpensive, making them suitable materials for the above-mentioned higher frequencies and faster transmission speeds. However, in portable devices and in-vehicle devices, which require heat resistance and flame retardancy, these materials are difficult to use because they lack heat resistance and flame retardancy. For this reason, currently, highly heat-resistant insulators such as heat-resistant fluororesins and liquid crystal polymers are used for high-frequency and high-speed transmission applications.

Furthermore, flat cables that use copper wires as conductors can only be formed into the same shape in the longitudinal direction, and flat cables with multiple conductors have difficulty forming bent shapes while maintaining their flatness. Today's mobile devices, such as smartphones, require flat cables that can be curved while remaining flat.

JP 2011-71403 A JP 2017-188307 A International Publication No. WO2014/156422 JP 2010-182576 A Japanese Patent Application Publication No. 5-242736 International Publication No. WO2016/104066 Japanese Unexamined Patent Publication No. 131306/1986

Diatrend Corporation, Glossary, Coaxial Cable

In recent years, mobile devices such as smartphones have become more sophisticated with displays, cameras, and other features, while application processors have become larger in circuit scale as applications evolve, and batteries have become larger as transmission speeds increase, making it difficult to fit all of these functions and components into the limited space available inside the device. On the other hand, the number of wireless types used by smartphones is also increasing, resulting in an increase in the amount of wiring connecting antennas to devices and wiring connecting components to main boards.

Currently, flexible wiring boards are often used to wire the main board to the internal components of mobile devices, including smartphones, such as cameras and displays. On the other hand, coaxial cables are generally used for the RF part. In devices equipped with displays, such as smartphones, displays tend to get larger, so thinning in the thickness direction is important to make smartphones smaller and lighter. However, it is difficult to make coaxial cables thin, and recently it has become the case that the thickness of coaxial cables becomes an obstacle to the mounting design of devices. In other words, in order to mount them in devices with thickness restrictions, it is necessary to make the cable thinner.

To address this issue, thin wiring boards with triplate lines and microstrip lines using low-loss resins such as liquid crystal polymers have been proposed (see, for example, Patent Document 3). These wiring boards allow for the same circuit formation as flexible wiring boards, making it possible to process multiple signal lines on a single wiring board, and are therefore expected to contribute to future mobile devices.

On the other hand, thin wiring boards with triplate lines or microstrip lines that use low transmission loss resins such as liquid crystal polymers are not completely shielded compared to coaxial cables, and there are limitations to ground stability as the top and bottom grounds are connected with vias. As higher frequencies and speeds are sought, there are concerns about low transmission loss and EMI shielding.

Furthermore, even resins with low transmission loss are affected by the outside air; for example, low dielectric polyimide resin has excellent transmission characteristics, but has a high moisture absorption rate and its transmission characteristics are affected by humidity, making it unsuitable for use in current RF components. In other words, for thin wiring boards with the above-mentioned triplate lines or microstrip lines, it is necessary to select a resin that is less affected by humidity, and there are significant limitations on the resins that can be used. Furthermore, as use of high frequencies increases in the future, further stabilization of transmission characteristics will be required, so it will be necessary to minimize the effects of water vapor from the outside air.

In particular, low dielectric polyimide resins and resins that contain air absorb moisture due to the penetration of water vapor in the air, causing a significant change in electrical properties. For this reason, it is difficult to use them in current FFCs (flat flexible cables), and PTFE or LCP are used exclusively. However, these resins are expensive, require high-temperature processing, and have poor adhesion, making them difficult to produce and limiting their range of use.

On the other hand, polyethylene and its copolymers, polypropylene and its copolymers, and polystyrene and its copolymers are resins with low dielectric loss, are thermoplastic and have excellent processability, but they have low heat resistance and cannot be used as insulation for conventional flat cables as a resin alone.

It is possible to improve heat resistance and obtain a low transmission loss material by blending and dispersing a filler with low dielectric loss into a resin with low dielectric loss such as polyethylene and its copolymers, polypropylene and its copolymers, or polystyrene and its copolymers as an insulator for high frequency cables, but in this case, water vapor will penetrate into the resin and powder, affecting the electrical characteristics. In other words, if a filler with low dielectric loss is blended and dispersed into a resin with low dielectric loss to be used as an insulator for high frequency cables, a flat cable structure and manufacturing method that is not affected by moisture absorption by water vapor from the outside air is required.

The insulation on the short side of the flat cable is exposed to the outside air, and water vapor penetrates through the exposed insulation, causing moisture absorption into the interior of the insulation and affecting transmission characteristics. Insulation with a high moisture absorption rate is easily affected by water vapor, and this effect is particularly noticeable in the high frequency range, causing changes in transmission characteristics.

In addition, there is a method of wrapping shielding tape to strengthen the shielding in the longitudinal direction (see, for example, Patent Documents 5 and 6), but this involves wrapping a shielding film as a shielding layer, and gaps and contact resistance occur in the overlapping or contacting parts of the shielding film, making it impossible to achieve complete shielding. In addition, organic matter such as adhesive and bonding layers are exposed to the outside air in the overlapping or contacting parts of the shielding film, so moisture absorption occurs in the insulator due to the penetration of water vapor.

As mentioned above, the electrical properties of the insulator change due to moisture absorption caused by the penetration of water vapor from the outside air. This changes the transmission properties of the cable, so insulators that absorb moisture are not recommended for use in flat cables, particularly for high-speed or high-frequency transmission applications. Insulators that cover conductors must be free from the effects of water vapor. The impact of moisture absorption on transmission properties is particularly noticeable when handling high-frequency or high-speed signals.

Flat cables have also been proposed in which a seamless shielding film is formed in the longitudinal direction using copper plating (for example, Patent Document 7). However, the short sides are cut into individual pieces, so the cross sections are not plated and the conductors and insulators are exposed. In other words, water vapor penetrates from the short end faces, so highly hygroscopic resins cannot be used. Also, in order to connect to other components, new terminals must be formed.

Flat cables that use copper wires as the conductor can only be formed into the same shape in the longitudinal direction, and flat cables with multiple conductors have difficulty forming bent shapes while maintaining their flatness. Today's mobile devices, such as smartphones, require flat cables that can be curved while remaining flat.

When a product is mounted, flat cables are subject to heat from soldering, etc. Flat cables are usually exposed to heat of around 250°C, so the insulation of the flat cable must be heat resistant. However, if the insulation is designed so that it is not likely to melt, or does not deform even when softened, it is possible to use insulation with lower heat resistance, which also broadens the material options for the insulation.

Furthermore, flat cables are generally required to be flame retardant. General-purpose resins such as polyethylene, polypropylene, and polystyrene, which have low dielectric loss, have poor flame retardancy and cannot be used as is for applications that require flame retardancy. For this reason, currently, highly flame-retardant, heat-resistant insulators such as fluororesin and liquid crystal polymers are used for high-frequency, high-speed transmission applications, but they are expensive and difficult to process. For this reason, there is a demand for the use of inexpensive resins that are easy to process.

A method has been used to improve shielding by applying a shielding tape such as metal foil tape to a flat cable, but this method makes it difficult to completely cover the flat cable, and the mating parts and the adhesive end surface of the shielding tape are exposed, making it susceptible to the effects of outside air. In addition, the dimensions in the thickness direction and on the wall surface are not stable, which affects the transmission characteristics. Furthermore, mobile devices may require flat cables with complex shapes, such as those that are forked into two, but using the method of applying metal foil tape makes it difficult to manufacture flat cables with complex shapes, such as those shown in Figure 8.

For these reasons, there is a demand for a cable capable of high-frequency and high-speed communication that can be mounted on devices with limited mounting space in the thickness direction. In order to solve the above problems, the present invention provides a flat cable with a stable transmission line, a thin shape that is easy to mount, and excellent shielding properties, and a manufacturing method thereof. Furthermore, there is a demand for a wider range of insulator choices. The present invention provides a flat cable with a structure that is less susceptible to the external environment, thereby significantly widening the range of insulator choices.

There is also a need for a flat cable and a manufacturing method thereof that can be made thinner, has stable transmission characteristics, and has excellent shielding properties, and can be adapted to complex shapes rather than using methods that involve bonding metal tapes.

In recent years, a method of using conductive paste to connect layers has been proposed for the manufacture of flat cables. Although it is possible to stack multiple layers at once, for high-speed transmission, an appropriate distance is required between the conductor signal line and the metal shielding layer, and multiple sheets or a single thick film is required as an insulator between the conductor signal line and the metal shielding layer. When manufacturing flat cables with conductive paste, the insulator and metal shielding layer are connected at once using the conductive paste that is integrated with the metal shielding layer, making it difficult to ensure reliability of conduction and requiring advanced technology. This method of using conductive paste to connect layers also has the same issues as mentioned above due to the triplate structure.

In other words, flat cables for high-speed and high-frequency transmission are required to have the following in addition to the inherent flat cable properties of being thin and flexible: A transmission line with stable transmission characteristics that is not affected by moisture absorption from the outside air. High electromagnetic shielding effect. Heat resistance that can withstand soldering, etc. Flame retardancy. Easy to produce and can use inexpensive materials.

The present invention relates to a shielded thin flat cable that has stable transmission characteristics unaffected by moisture absorption from the outside air, has a high electromagnetic wave shielding effect, is heat resistant to soldering and the like, is flame retardant, is highly productive and can use inexpensive materials, and can be adapted to complex shapes, and a method for manufacturing the same.

The shielded thin flat cable of the present invention is characterized by having a conductor made of metal, an insulator that is in close contact with the conductor except for the terminal portion, and a metal film that is continuous over the entire outer surface of the insulator, including the short end faces .

In addition, in the shielded thin flat cable of the present invention, it is preferable that the insulator contains one or more resins selected from the group consisting of high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, polystyrene, polypropylene, and polyphenylene ether, and that the insulator contains 10 to 900 parts by weight of one or more of quartz glass, aluminum oxide, hollow glass balloons, magnesium oxide, and silica as a filler per 100 parts by weight of the resin.

In addition, in the shielded thin flat cable of the present invention, it is preferable that the insulator is made of a hardened photosensitive material.

In addition, in the shielded thin flat cable of the present invention, it is preferable that the dielectric constant of the insulator is 3.5 or less, the dielectric tangent is 0.003 or less, and the water absorption rate is 0.05% or more.

In addition, in the shielded thin flat cable of the present invention, it is preferable that the conductor is multi-layered.

In addition, in the shielded thin flat cable of the present invention, it is preferable that the thickness of the shielded thin flat cable is 10 μm to 500 μm per layer of the multi-layered conductor.

In addition, in the shielded thin flat cable of the present invention, it is preferable that the metal film is a film made of one or more of gold, silver, copper, and aluminum.

Furthermore, in the shielded thin flat cable of the present invention, it is preferable that the area of the portion of the outer surface of the insulator having the metal film is 95% or more of the area of the outer surface of the insulator.

In addition, in the shielded thin flat cable of the present invention, it is preferable that the metal film continuously covers the entire outer surface of the insulator except around the terminals of the conductor.

In addition, in the shielded thin flat cable of the present invention, it is preferable that the outer surface of the insulator around the terminal portion of the conductor has a moisture-proof film without having the metal film.

In addition, in the shielded thin flat cable of the present invention, it is preferable to provide a moisture-proof film layer between the insulator and the metal film.

In addition, in the shielded thin flat cable of the present invention, it is preferable that the moisture-proof film is made of one or more of high-density polyethylene, medium-density polyethylene, linear low-density polyethylene, polypropylene, and polyvinylidene chloride.

In addition, in the shielded thin flat cable of the present invention, it is preferable that the metal film is formed on the wall surface of a groove provided on the surface of the insulator.

The manufacturing method of the shielded thin flat cable of the present invention is characterized in that an insulator is provided in close contact with the periphery of a metal conductor other than the terminal portion, and a metal film is provided continuously over at least a portion of the outer surface of the insulator, including the short end faces .

In addition, in the manufacturing method of the shielded thin flat cable according to the present invention, it is preferable that the insulator contains one or more resins selected from the group consisting of high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, polystyrene, polypropylene, and polyphenylene ether, and that the insulator contains 10 to 900 parts by weight of one or more of quartz glass, aluminum oxide, hollow glass balloons, magnesium oxide, and silica as a filler per 100 parts by weight of the resin.

In addition, in the manufacturing method of the shielded thin flat cable of the present invention, it is preferable that the insulator is a photosensitive material.

In addition, in the manufacturing method of the shielded thin flat cable according to the present invention, it is preferable that the water absorption rate of the insulator is 0.05% or more or that the thermal deformation temperature of the insulator is between 60°C and 250°C.

In addition, in the manufacturing method of the shielded thin flat cable according to the present invention, it is preferable that the conductor is multi-layered.

In addition, in the manufacturing method of the shielded thin flat cable according to the present invention, it is preferable that the thickness of the shielded thin flat cable is 10 μm to 500 μm per layer of the multi-layered conductor.

In addition, in the manufacturing method of the shielded thin flat cable of the present invention, it is preferable that the metal film is a film of one or more of gold, silver, copper, and aluminum.

In addition, in the manufacturing method of the shielded thin flat cable of the present invention, it is preferable to form the metal film on more than 95% of the area of the outer surface of the insulator.

In addition, in the manufacturing method of the shielded thin flat cable of the present invention, it is preferable that the metal film continuously covers the outer surface of the conductor other than the area around the terminal portion.

In addition, in the manufacturing method of the shielded thin flat cable of the present invention, it is preferable to form a moisture-proof film rather than forming the metal film on the outer surface of the insulator around the terminal portion of the conductor.

In addition, in the manufacturing method of the shielded thin flat cable of the present invention, it is preferable to form a moisture-proof film layer between the insulator and the metal film.

In addition, in the manufacturing method of the shielded thin flat cable according to the present invention, it is preferable that the moisture-proof film is formed from at least one of high-density polyethylene, medium-density polyethylene, linear low-density polyethylene, polypropylene, and polyvinylidene chloride.

In addition, in the manufacturing method of the shielded thin flat cable of the present invention, it is preferable that the metal film is formed on the wall surface of a groove provided on the surface of the insulator.

In addition, in the manufacturing method of the shielded thin flat cable according to the present invention, it is preferable that the groove is formed by laser light and the metal film is formed on the wall surface of the formed groove by plating.

In addition, in the manufacturing method of the shielded thin flat cable according to the present invention, it is preferable that the grooves are formed by exposure and resin etching.

In addition, in the manufacturing method of the shielded thin flat cable according to the present invention, it is preferable to form the metal film in multiple rows parallel to the conductor on the outer surface of the insulator, which is provided in close contact with the conductor except for the multiple terminal portions, and then cut the insulator into individual pieces parallel to the conductor.

The shielded thin flat cable of the present invention enables low transmission loss in transmission lines requiring high frequency and high speed transmission. In addition, the shielded thin flat cable of the present invention has a structure in which the outer surface of the insulator is covered with metal, so that the barrier properties of the metal reduce the penetration of water vapor from the outside air into the insulator. Furthermore, by blending a filler into the insulator, heat resistance such as solder heat resistance and flame retardancy are improved. Therefore, the shielded thin flat cable of the present invention is less susceptible to the external environment, has improved transmission performance, and can be manufactured at a lower price due to the wider selection of resins used.

1 shows a shielded thin flat cable according to a first embodiment of the present invention, in which (A) is an oblique view, (B) is an oblique cross-sectional view of a portion of the shielded thin flat cable where a conductor is present, (C), (D), and (E) are views of the terminal portion of the conductor, and (AW) is an enlarged oblique view of the end of the shielded thin flat cable. 3 shows a manufacturing process for a thin shielded flat cable according to a first embodiment of the present invention. 5 shows a manufacturing process for a thin shielded flat cable according to a second embodiment of the present invention. 1 shows the structure of a shielded thin flat cable according to a third embodiment of the present invention. 1 shows the structure of a thin shielded flat cable according to an embodiment of the present invention. 1 shows the structure of a shielded thin flat cable according to a fourth embodiment of the present invention. 1 shows a stack structure of a shielded thin flat cable according to an embodiment of the present invention. 1 shows the structure of a thin shielded flat cable according to an embodiment of the present invention. 1 shows the structure of a thin, shielded flat cable having a triplate structure according to a comparative example. 4 shows a manufacturing process according to a second embodiment of the present invention. 4 shows a manufacturing process according to Example 4 of the present invention. 1 shows the structure of a thin shielded flat cable according to a fourth embodiment of the present invention.

The shielded thin flat cable of the present invention has a conductor made of metal, an insulator that is in close contact with the conductor except for the terminal portion, and a metal film on at least a part of the outer surface of the insulator. The insulator protects the conductor, and the metal layer shields the conductor.

In addition, the manufacturing method of the shielded thin flat cable of the present invention includes providing an insulator in close contact with the periphery of the metal conductor other than the terminal portion, and providing a metal film on at least a portion of the outer surface of the insulator.

In addition to the inherent flat cable characteristics of being thin and flexible, flat cables for high-frequency and high-speed transmission are required to have the following: A transmission line that is immune to the effects of outside air such as moisture absorption and has stable physical and electrical characteristics. High electromagnetic shielding effect. Heat resistance that can withstand soldering, etc. Flame retardancy. Easy to produce and can use inexpensive materials.

Figure 9 shows the structure of a typical flat cable today, and is a comparative example of the present invention. Since the insulator 106 is exposed to the outside air, the resin itself needs to be moisture-proof, heat-resistant, and flame-retardant.

The present invention significantly improves the above-mentioned required performance of conventional flat cables. That is, the shielded thin flat cable of the present invention has a metal shielding film continuously formed on the entire outer surface of the insulator except for the area around the terminals of the conductor, so that it is not affected by the outside air due to moisture absorption by the insulator, and is a transmission line with stable electrical characteristics and high electromagnetic wave shielding effect.

In addition, the barrier properties of the metal film formed on the outer surface of the insulator reduce the penetration of water vapor into the insulator, making it possible to use resins with high moisture absorption rates for the insulator. At the same time, heat resistance, including solder heat resistance, and flame retardancy are also improved. In other words, the range of resins to be used as insulators is broadened.

Transmission lines that require low transmission loss are required to have low dielectric constants and dielectric tangents, as well as a low water absorption rate that causes drift. However, because the structure of the present invention is such that it absorbs little moisture even if the water absorption rate of the insulator is high, it can also be used in applications that require low loss.

For low transmission loss applications, the insulator preferably has a dielectric constant of 3.5 or less and a dielectric dissipation factor of 0.003 or less. The water absorption rate may be 0.05% or more. In the conventional flat cables mentioned above, a water absorption rate of less than 0.05% is required, but the present invention can be used well even if the water absorption rate is 0.05% or more.

The present invention improves the heat resistance of the insulator by blending a filler without a dispersing aid into a resin with low heat resistance as an insulator, and improves the solder heat resistance of the resin with low heat resistance. When dispersing a filler in a resin, a dispersing aid such as a metal soap is usually blended to disperse the filler, but there is a problem that the dispersion aid reduces the transmission characteristics. Furthermore, if a dispersion aid is not used, tiny gaps occur between the resin and the filler, and if the insulator of the flat cable is exposed to the outside air, water vapor will penetrate into the gap between the resin and the filler through the exposed part, causing a change in the transmission characteristics over time.

In the present invention, even if a filler is blended without a dispersing agent into a resin with relatively low heat resistance, there is little penetration of water vapor from the outside air, so a filler is blended without a dispersing agent for the purpose of improving heat resistance, and the resin blend with improved heat resistance can be used as an insulator. In other words, the range of resins and fillers to be used as insulators is expanded, making it possible to select resins and fillers that are inexpensive and have good productivity.

In addition, by forming a moisture-proof film on the portion of the conductor terminal that does not have a metal film, it is almost completely unaffected by water vapor, making it possible to use highly hygroscopic insulators or insulators that contain air. This invention makes it possible to obtain stable transmission characteristics even in the high frequency range without being affected by the outside air, and to obtain a thin, shielded flat cable that has a high shielding effect and is heat-resistant and flame-retardant enough for practical use.

In particular, low-dielectric polyimide and resins that contain air are difficult to use in current FFCs (flat flexible cables) because their electrical properties change significantly when they absorb water vapor. Instead, PTFE or LCP is used instead, but these resins are expensive, require high-temperature processing, and have poor adhesive properties, making them difficult to produce and limiting their uses.

On the other hand, for example, high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, polystyrene, polypropylene, and polyphenylene ether, which are types of low dielectric loss materials, are thermoplastic and have excellent processability, but they have low heat resistance and cannot be used as resin alone as insulation for conventional flat cables in applications that require heat resistance, such as soldering.

It is possible to combine a resin with low dielectric loss as an insulator for high-frequency cables with a filler that also has low dielectric loss to improve heat resistance and obtain an insulator with low transmission loss; however, in this case, water vapor will penetrate the resin and filler, affecting the electrical characteristics.

That is, when a resin with low dielectric loss is mixed with a filler with low transmission loss and used as an insulator for a high-frequency cable without using a dispersion aid that affects transmission loss, a structure and manufacturing method for a flat cable that is not affected by moisture absorption from the outside air is required. As described above, the present invention is hardly affected by moisture absorption from the outside air due to the barrier properties of the metal film formed on the outer surface of the insulator, so that a combination of resin and filler can be selected without worrying about moisture absorption. As resins with low dielectric loss, high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, polystyrene, polypropylene, and polyphenylene ether are suitable, and it is preferable to include one or more of these. In addition, as fillers with low dielectric loss, quartz glass, aluminum oxide, hollow glass balloons, magnesium oxide, and silica are suitable, and it is preferable to include one or more of these.

It is preferable that the insulator contains 10 to 900 parts by weight of filler per 100 parts by weight of resin contained in the insulator of the present invention. If the filler exceeds 900 parts by weight, the dispersion of the resin and filler is poor and shape retention is also poor, making it difficult to process the insulator. If the total amount of filler is less than 10 parts by weight, the filler does not sufficiently improve heat resistance.

In addition, the resin and filler can be selected from a plurality of types and blended. In addition to the resin and filler, additives such as viscosity modifiers, lubricants, and flame retardants can be appropriately blended within the range that does not deteriorate the dielectric properties.
(Embodiment 1)

The configuration of the first embodiment of the shielded thin flat cable according to the present invention will be described. FIG. 1 shows a shielded thin flat cable 101 according to the first embodiment of the present invention, where (A) is a perspective view, (B) is a perspective cross-sectional view of the part of the shielded thin flat cable 101 where the conductor exists, (C), (D), and (E) are terminal parts of the conductor 204, and (AW) is an enlarged perspective view of the end of the shielded thin flat cable 101. As shown in FIG. 1(A), the shielded thin flat cable 101 is composed of a terminal exposed part 103 where the terminal part of the conductor 204 is exposed and a conductor part 102 where the conductor 204 exists. As shown in FIG. 1(B), the insulator 106 is in close contact with the conductor 204 around the conductor 204 made of metal other than the terminal part. The shielded thin flat cable 101 is covered with a metal film 202 except for the terminal part of the conductor 204. 1 (AW), the short end face of the shielded thin flat cable 101 also has a metal film 202. The conductor 204 is wrapped in the insulator 106 except for the terminal exposed portion 103, and the insulator 106 is also continuously covered with the metal film 202, which is a shield layer, except for the terminal exposed portion 103 of the conductor 204.

The thickness of the shielded thin flat cable 101 is preferably 10 μm to 500 μm. If it is less than 10 μm, the transmission loss will be large, and if it exceeds 500 μm, the advantage of its thinness as a thin flat cable will be lost and its mountability will be poor.

1(C), (D), and (E) show the terminal portion of the terminal exposed portion 103. In the terminal portion, the conductor 204 is connected to the conductor electrode 105 through a via hole. The conductor electrode 105 is for connection to an external element, etc., and is used as a connector connection terminal, a soldering terminal for fixing the connector, or a terminal for ACF connection. In order to achieve the above purpose, the surface of the conductor electrode 105 may be subjected to surface treatment such as soldering, gold plating, or OSP as necessary. The periphery of the conductor electrode 105 is structured so that it is not conductive from the conductor electrode 105 by the insulator 106 on which the metal film 202 is not formed. The shape of the conductor electrode 105 serving as the terminal may be any shape, such as a circle or a square. In addition, the number of conductor electrodes 105 may be multiple.

The manufacturing process of the shielded thin flat cable according to the first embodiment of the present invention is described with reference to FIG. 2. FIG. 2(F) shows a laminate in which metal films 202A and 202B are formed on both sides of the insulator 106. The metal forming the metal film 202 is one with good electrical conductivity, and gold, silver, copper, and aluminum are particularly preferred, with copper being the most suitable. Considering flexibility and electrical conductivity, rolled copper is the most suitable. The electrical resistivity of the metal film 202 is preferably 1 μΩ·m or less. The thickness of the metal film 202 is preferably 3 μm to 75 μm. If the thickness is less than 3 μm, pinholes and scratches will occur, and the barrier properties of the insulator 106 will not be maintained. Furthermore, if the thickness exceeds 75 μm, it will be difficult to make grooves and holes, causing problems in the flat cable manufacturing process.

The insulator 106 can be made of commercially available resins such as thermosetting or thermoplastic resins, but for high-frequency line applications in particular, examples include fluororesins, liquid crystal polymers, polyimide, PET, PEEK, COC, COB, high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, polystyrene, polypropylene, and polyphenylene ether. High-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, polystyrene, polypropylene, and polyphenylene ether are preferred.

The thickness of the insulator 106 is preferably 20 μm to 480 μm. If it is less than 20 μm, the transmission loss of the transmission line will be large, and if it exceeds 480 μm, the advantage of the thinness as a flat cable will be lost and mounting will become difficult.

Furthermore, the insulator 106 can also use the ABF series manufactured by Ajinomoto Co., Ltd., the AS series manufactured by Hitachi Chemical Co., Ltd., insulating films manufactured by Sekisui Chemical Co., Ltd., etc.

In addition, the insulator 106 may be a compound containing inorganic or organic fillers in the thermosetting or thermoplastic resin to adjust the electrical and physical properties. Suitable inorganic fillers include barium sulfate, quartz glass, silica, talc, aluminum oxide, aluminum hydroxide, calcium carbonate, magnesium oxide, magnesium carbonate, titanium oxide, barium titanate, silica balloons, hollow glass balloons, and aluminum nitride. Suitable organic fillers include PP powder, PE powder, PPE powder, epoxy powder, and acrylic powder. Suitable low transmission loss fillers include quartz glass, aluminum oxide, hollow glass balloons, magnesium oxide, and silica, as described above.

As the laminate shown in FIG. 2(F), for example, commercially available FCCL (Flexible Copper Clad Laminate) and CCL (Copper Clad Laminate) can be used. For example, ESPANEX manufactured by Nippon Steel & Sumikin Chemical Co., Ltd. and FELIOSU manufactured by Panasonic Corporation can be used.

The laminate is obtained by applying an insulating paste to the insulator 106A or by attaching an insulating film, and then laminating the paste surface or insulating film surface with, for example, copper foil as the metal film 202. Alternatively, it can be obtained by thermocompression bonding copper foil to both sides of the insulator 106A. As the insulating film, the AS series made by Hitachi Chemical Co., Ltd., the ABF series made by Ajinomoto Co., Inc., insulating film made by Sekisui Chemical Co., Ltd., etc. can also be used. To further improve the transmission characteristics, it is preferable that the surface roughness of the metal film 202B, which will later become the conductor 204, is small. A surface roughness Rz of 3.0 μ or less is preferable in terms of transmission characteristics.

Figure 2 (G) shows the process of forming the conductor 204. A method commonly used for printed wiring boards can be used. Conductor 204 can be formed by removing all parts of metal film 202B other than the conductor 204 through procedures such as forming a resist layer, forming an etching mask, exposing, developing, etching, and peeling off the etching mask. Since the width of conductor 204 has a large effect on the transmission characteristics, it is necessary to precisely manage the width. In addition, in order to improve the line width accuracy of conductor 204, it is also possible to use the MSAP method (Modified Semi Additive Process). To further improve the transmission characteristics, conductor 204 may be gold-plated or silver-plated.

Since the transmission line according to the present invention has a strip line structure, the characteristic impedance of the conductor 204 is determined by the conductor width, conductor thickness, insulator thickness, dielectric constant of the insulator, etc. That is, in order to obtain the desired impedance, the conductor width is usually adjusted. The width of the conductor 204 of the present invention is preferably 0.01 mm to 10 mm, and more preferably 0.2 mm to 5 mm. If the conductor width is less than 0.01 mm, it is difficult to control the finished dimensional accuracy of the conductor width. Therefore, it is difficult to match the impedance, and it is not preferable as a conductor. In addition, if the conductor width is less than 0.01 mm, the conductor loss becomes large, which is also not preferable as a transmission line. Conversely, if the conductor width exceeds 10 mm, the thickness of the insulator 106 to obtain the desired characteristic impedance becomes large, and it is not suitable for a flat cable that pursues thinness.

The thickness of the conductor 204 is preferably 1 μm to 75 μm. Due to conductor loss and the skin effect, electrical signals are not transmitted efficiently at a thickness of less than 1 μm. Furthermore, at a thickness of less than 1 μm, there is a high possibility that the conductor will break when bent. Conversely, if the thickness exceeds 75 μm, it becomes difficult to achieve a precise conductor width during conductor manufacturing, and the insulator 106 used to encase the conductor becomes thicker, making it unsuitable for a flat cable that pursues thinness.

Figure 2 (H) shows insulator 106B and metal film 202C formed in sequence on insulator 106A and conductor 204. The material of insulator 106B may be the same as that of insulator 106A. Alternatively, an insulator made of a different material may be used. Insulator 106B can be formed by thermocompression bonding a thermoplastic resin film or B-stage resin, or by applying a thermosetting resin and then thermally curing it.

It is preferable to use the same metal as that of the metal film 202A for the metal film 202C. The method of forming the metal film 202C may be to form the insulator 106B first and then the metal film 202C, or to form the insulator 106B and the metal film 202C simultaneously.

Figure 2 (I) shows the process of forming linear grooves 206 parallel to the conductor 204 along both side sides of the conductor 204.

The linear groove 206 is formed by a device capable of cutting the metal film 202C and the insulator 106 linearly without penetrating the metal film 202A on the underside of the insulator 106. For example, the cutting is performed by irradiating the metal film 202 and the insulator 106 with a laser, irradiating with plasma, sandblasting, etc., and a device equipped with a laser processing machine such as an excimer laser, carbon dioxide laser, or YAG laser, a plasma processing machine, or a sandblaster can be used. A laser processing machine is preferable because of its fast processing speed. Alternatively, the metal film 202C may be removed in advance by etching, and then the groove 206 may be formed using the above-mentioned laser processing machine, etc.

As shown in Figure 2(J), at the same time as forming groove 206, hole 207 can be formed as a via hole for connecting conductor 204 to the outside of metal film 202C. Figure 2(J) is a cross-sectional view of the terminal portion, and at the same time as forming groove 206, hole 207 for electrode extraction can be formed by a method similar to that for forming groove 206, such as laser processing. Figure 7 is a top view of Figure 2(J) and shows the general positional relationship when forming groove 206 and hole 207. The formation of groove 206 is an important process in the present invention, as it determines the outer peripheral shape of shielded thin flat cable 101 and forms all end faces including the long and short ends.

Figure 2(K) shows the process of forming a metal film 202D in the groove 206 in the state of Figure 2(I). Figure 2(L) shows the process of simultaneously forming a metal body in the hole 207 in Figure 2(J) and providing a via hole 208 to draw out conductivity from the conductor 204.

The metal film 202D and the metal body of the via hole 208 are suitably formed by a metal plating method, which is usually performed in the following order: cleaning the metal film 202, making the surface other than the insulator 106 conductive, and metal plating. The metal plating that forms the metal film 202D of the present invention forms the metal film 202 that continuously covers the entire outer surface of the shielded thin flat cable 101 of the present invention.

Metal plating is carried out by methods such as desmearing, catalyst formation, electroless plating, and electrolytic plating. Desmearing is necessary when foreign matter such as smears remain on the metal film surface, but is not necessary if the metal film surface is clean. Desmearing can be done by dry methods using plasma or wet methods using oxidizing agents such as permanganate, but in the present invention, the dry method is superior from the viewpoint of preventing water absorption.

The catalyst formation, electroless plating, and electrolytic plating methods can be performed using chemical systems from, for example, ATOTECH, JCU Corporation, Dow Chemical, Uemura Industries, Ltd., Okuno Chemical Industries, Ltd., MacDermid Enthone, etc. In order to minimize moisture absorption, a metal film 202 may be provided on the insulator surface by a dry method such as sputtering instead of wet catalyst formation.

Figures 2(M) and 2(N) show the process of removing a portion of the metal film 202 of the laminate shown in Figures 2(K) and 2(L). The metal film 202 is removed in order to form the conductor electrode 105 and cut off unnecessary insulator 106. The metal film 202 can be removed in the same manner as the formation of the conductor 204 in Figure 2(G). That is, the unnecessary portions of the metal film 202 can be removed by a procedure of forming an etching mask, forming a resist layer, exposing, developing, etching, and peeling off the etching mask, to form the desired shape.

The metal film 202 is preferably gold, silver, copper, or aluminum, with copper being more preferable. The thickness of the metal film 202 formed by plating is preferably 3 μm to 100 μm. If it is less than 3 μm, pinholes and scratches will occur and the internal barrier properties will not be maintained. Furthermore, if it exceeds 100 μm, the plating time will be longer, causing problems in the manufacturing process such as warping of the work plate.

The periphery of the conductor electrode 105 is the portion of the insulator 106 exposed to the outside air. In the present invention, it is important to minimize the area of the exposed portion of the insulator 106 around the conductor electrode 105. If the area of the exposed portion is large, the insulator will absorb moisture due to the water vapor in the outside air, and the transmission characteristics will be easily affected by moisture absorption. The exposed portion of the insulator 106 on which the metal film 202 is not formed must be 5% or less of the total surface area of the insulator 106. In other words, 95% or more of the total surface area of the insulator 106 has the metal film 202. If it is less than 95%, the transmission characteristics will be easily affected by moisture absorption due to water vapor in the outside air.

2(O) and 2(P) show the process of forming a solder mask 211, which serves as an insulating layer, on the surface of the metal film 202 of the laminate shown in FIG. 2(M) and FIG. 2(N). The solder mask 211 can be provided with openings as necessary to expose the conductor electrode 105 and the ground electrode 107, etc. The method of forming the solder mask can be a method commonly used in the manufacture of printed wiring boards. Specifically, a method of forming a solder mask ink by a photographic method or silk screen printing, a method of forming a film-like solder mask by a lamination method, etc. can be used. Examples of solder mask inks that can be used include the PSR series manufactured by Taiyo Ink Mfg. Co., Ltd., the PAF series and DSR series manufactured by Tamura Mfg. Co., Ltd., the SPSR series manufactured by Sanwa Chemical Industry Co., Ltd., etc., and examples of film-like solder masks that can be used include the Raytec manufactured by Hitachi Chemical Co., Ltd. and the PSR series manufactured by Taiyo Ink Mfg. Co., Ltd.

Figures 2(Q) and 2(R) show the process of cutting and individualizing Figures 2(O) and 2(P). By cutting and individualizing Figures 2(O) and 2(P), the shielded thin flat cable 101 of the present invention can be obtained. For cutting into individual pieces, a cutting method for flexible wiring boards can be used, and cutting with a mold, cutting with a router, or cutting with a laser processing machine are common. The present invention produces a shielded thin flat cable as an assembly and then cuts into individual pieces, resulting in good work efficiency.

In other words, the metal film 202 is formed in multiple rows parallel to the conductor 204 on the outer surface of the insulator 106, which is provided in close contact with the periphery of the conductor 204 other than the multiple terminal portions, and then the insulator 106 is cut into individual pieces parallel to the conductor 204, thereby improving production efficiency.

The shielded thin flat cable 101 of the present invention is capable of maintaining a high shielding effect and barrier properties because a metal film 202 is formed on the outer surface of the insulator 106, which continuously covers not only the top, bottom, and longitudinal end faces of the insulator 106 that is in close contact with the periphery of the conductor 204 other than the terminal portion, but also the short end face in the width direction.

In addition, since the conductive electrode 105 can be formed on the surface of the shielded thin flat cable 101 through the via hole 208, it can be directly soldered to other electronic components or connected to an ACF without forming a new electrode. It can also be used as a terminal for an FPC/FFC connector. The conductive electrode 105 can also be subjected to surface treatments commonly used in the printed wiring board manufacturing process, such as OSP, ENIG, and solder.

By forming the groove 206 and plating the inner surface of the groove 206 with metal, a metal film 202 having a continuous shielding function can be formed on the entire outer surface of the shielded thin flat cable 101, including the short end faces of the shielded thin flat cable 101. The shielded thin flat cable 101 of the present invention can be formed into a bent shape or a complex shape while remaining thin and flat in multiple wiring.

In addition, the manufacturing method of the present invention can use many flexible printed wiring board devices and processes, making it possible to produce large-sized flexible printed wiring boards and roll-to-roll manufacturing, and it is also good in productivity. Examples are shown below, but the present invention is not limited to these examples.
(Embodiment 2)

The manufacturing method of embodiment 2 is explained with reference to Figure 3. Although embodiment 2 differs from embodiment 1 in the manufacturing method, other shapes, structures, additional processing, etc. are similar to embodiment 1. The manufacturing method differs from embodiment 1 in that a photosensitive resin is used for the insulator 106. By using a photosensitive resin for the insulator 106, the groove 206 and the hole 207 for the via hole of the terminal portion can be formed without using a laser drilling machine.

The through-hole plating method used in printed circuit boards can be used to plate the groove 206 and the via hole 208 for electrical connection to the conductor electrode 105.

The laminate shown in FIG. 3(S) is a diagram in which a photosensitive resin insulator 106A is formed on a metal film 202A. The photosensitive resin may be a liquid photoresist or a photosensitive build-up film. Examples of liquid photoresists include the PSR series manufactured by Taiyo Ink Mfg. Co., Ltd., the PAF series and DSR series manufactured by Tamura Mfg. Co., Ltd., the SPSR series manufactured by Sanwa Chemical Industry Co., Ltd., and the SR series manufactured by Hitachi Chemical Co., Ltd., while examples of photosensitive build-up films include the Raytec series, PV-F series, and PX series manufactured by Hitachi Chemical Co., Ltd., and the PSR series manufactured by Taiyo Ink Mfg. Co., Ltd.

Figure 3 (T) shows the process of forming grooves 206 in the longitudinal direction along the short edge of the portion that will become the shield surface by a photography method. A photosensitive resin layer is formed on metal film 202A, and is exposed to light using an exposure machine so that the portions that will become grooves 206 are developed. After development with a developer, the undeveloped portions are cured with heat or UV light to obtain a laminate in which insulator 106 is formed on metal layer 202.

When the photosensitive resin is liquid photoresist, the method for forming the photosensitive resin insulator 106A on the metal film 202A is to apply the liquid photoresist onto the metal film 202A, dry it, expose it with an exposure machine, develop it, and harden it to form the insulator. When the photosensitive resin is a photosensitive build-up film, the method is to laminate it, expose it with an exposure machine, develop it, and harden it to form the insulator.

Figure 3(U) shows a process for forming metal film 202B, which will become a conductor in the next etching process, and metal film 202E in groove 206, so as to cover the entire surface of the laminate shown in Figure 3(T). Metal plating is a suitable method for forming metal film 202B and metal film 202E in groove 206, and a method similar to that of the process of Figure 2(K) in embodiment 1 of the present invention can be used.

Figure 3(V) shows the process of forming a conductor 204 in the laminate shown in Figure 3(T). This process can use a method commonly used for printed wiring boards, and can be the same as the process of forming the conductor 204 in Figure 2(G) according to embodiment 1 of the present invention. In the manufacturing method according to embodiment 2 of the present invention, which uses a photosensitive resin for the insulator 106, the SAP method (Semi Additive Process) can be used to form the conductor 204.

202B is removed by etching, leaving only the portion that becomes the conductor 204 of 202B in Figure 3 (U) and the upper part of the metal film 202E formed in the groove 206.

Figure 3 (W) shows the process of forming the insulator 106B from a photosensitive resin on the insulator 106A and the conductor 204. The formation of the insulator 106B from a photosensitive resin can be performed using the same material and method as the formation of the insulator 106A from a photosensitive resin of the laminate 106A in Figure 3 (A).

Figure 3(X) shows the process of forming groove 206B in the longitudinal direction along the short edge of the portion that will become the shield surface by a photography method. At the same time, Figure 3(Y) shows the process of forming hole 207 for a via hole to pull conductor 204 to the outside of the shield layer. At the same time as forming groove 206B in Figure 3(X), hole 207 for electrode pull-out can be formed. The method of forming groove 206B and hole 207 can be the same as the method of forming groove 206 in Figure 3(T).

3(Z) and 3(AA) show a metal film 202C that covers the entire surface of the laminate shown in Fig. 3(X) and 3(Y), and a metal film 202F and a via hole 208 are formed inside the groove 206B. The method of forming the metal film 202C, the metal film 202F and the via hole 208 can be the same plating method as in the process shown in Fig. 2(L).

Figures 3(Z) and 3(AA) have the same structures as Figures 2(K) and 2(L) according to embodiment 1 of the present invention, respectively, so that from this point on, the shielded thin flat cable 101 can be manufactured in a similar process to that of Figure 2, which shows the manufacturing process according to embodiment 1 of the present invention. That is, the metal film 202 is removed for forming and cutting the conductor electrode 105 in a similar manner to Figures 2(M) and 2(N). Furthermore, a solder mask 211 is formed as an insulating film on the surface of the laminate in a similar manner to Figures 2(O) and 2(P).

2(Q) and 2(R), the laminate is cut to form individual pieces. Through the above steps, the shielded thin flat cable 101 of the present invention can be obtained by the manufacturing method according to the second embodiment of the present invention.
(Embodiment 3)

FIG. 4 shows a shielded thin flat cable according to a third embodiment of the present invention. The third embodiment is characterized in that a moisture-proof film 203 is provided on the exposed portion of the insulator 106 that does not have the metal film 202 around the conductor electrode 105. As shown in FIG. 4(AB), in order to minimize the influence of moisture absorption of the insulator 106 inside the shielded thin flat cable 101, the moisture-proof film 203 is formed on the portion of the insulator 106 that is exposed to the outside. In particular, when a resin with high moisture absorption is used as the insulator 106, it is desirable to form the moisture-proof film 203. As the moisture-proof film 203, a film having a water vapor permeability of 15 g/m ² 2/24 h or less is preferable, and it is preferable to form the film from a resin such as high density polyethylene, medium density polyethylene, linear low density polyethylene, polypropylene, or polyvinylidene chloride. The thickness of the moisture-proof film 203 is preferably 5 μm to 500 μm. If it is less than 5 μm, sufficient moisture-proof effect cannot be obtained. If it exceeds 500 μm, the convex surface becomes an obstacle during mounting such as soldering.

In Fig. 4 (AB), the moisture-proof film 203 is formed directly on the surface of the insulator 106, while in Fig. 4 (AC), it is formed on the surface of the solder mask 211. In order to ensure moisture-proofing, Fig. 4 (AB), in which it is in contact with the metal layer 202, is preferable.
(Embodiment 4)

In the shielded thin flat cable 101 of the present invention, the number of built-in conductors 204 can be selected arbitrarily, and as shown in FIG. 5 (AD), there may be only an insulator 106 between the conductors 204, or a metal film 202 may be formed between the conductors 204. In FIG. 5 (AE), the solder mask 211 is not formed around the conductor electrode 105, but it is not necessary to form the solder mask 211 around the conductor electrode 105. The shielded thin flat cable 101 shown in FIG. 5 has multiple conductors 204 in the horizontal direction of the shielded thin flat cable 101.

Figure 6 shows a cross section of the conductor portion 102 of the shielded thin flat cable 101 according to embodiment 4 of the present invention. As shown in Figures 6 (AF), (AG) and (AH), the shielded thin flat cable 101 may have a plurality of conductors 204 in the vertical direction of the shielded thin flat cable 101. Figure 6 (AF) has two conductors 204 in the vertical direction. Figure 6 (AG) shows the shielded thin flat cable 101 having two vertical stages of Figure 5 (AD) having four conductors 204 in the horizontal direction. Figure 6 (AH) shows the shielded thin flat cable 101 having two vertical stages of Figure 5 (AE) having four conductors 204 in the horizontal direction. The shielded thin flat cable 101 of the present invention may have multiple layers of conductors 204 in the horizontal or vertical direction, or in both the horizontal and vertical directions.

When having two layers of conductor 204 in the vertical direction as shown in Figure 6 (AF), it is preferable that the thickness of the shielded thin flat cable 101 is 10 μm to 500 μm per layer of conductor 204. The thickness of the shielded thin flat cable 101 per layer of conductor 204 is the value obtained by dividing the thickness of the shielded thin flat cable 101 by the number of layers of conductor 204. If it is too thin, the transmission loss will be large, and if it is too thick, the advantage of its thinness as a flat cable will be lost and mounting will be poor. Even if the conductor 204 is a single layer, it is preferable that the thickness of the shielded thin flat cable 101 is 10 μm to 500 μm.

The following is an example of the most suitable embodiment of the present invention.

A specific example of constructing a shielded thin flat cable 101 according to embodiment 1 of the present invention is shown. The conductor 204 and metal film 202 are made of copper, the insulator 106 is made of an LCP resin film, and the shielded thin flat cable 101 of the present invention has a thickness of 140 μm.

Figure 2(F) is a cross-sectional view of the FCCL. Panasonic Corporation's FELIOS LCP R-F705T (copper foil 12 μm, resin film thickness 25 μm, dimensions 250 mm × 250 mm) was used as the FCCL.

2(G), the copper foil surface treatment, DFR attachment, exposure, development, etching, and DFR peeling were performed in sequence to form the conductor 204. A dry film (also called DFR) manufactured by Hitachi Chemical Co., Ltd. was attached to the metal films 202A and 202B with clean surfaces, and exposed to light using a manual exposure machine manufactured by ORC using a high-pressure mercury lamp with the desired exposure tool. The protective film of the DFR was peeled off, development was performed using a spray-type developer containing a weakly alkaline sodium carbonate solution, etching was performed using an etching device using a ferric chloride solution, and the DFR was peeled off in a tank containing a strongly alkaline sodium hydroxide solution, thereby forming the desired conductor 204.

2(H), the insulator 106B and copper foil as the metal film 202C were thermocompression bonded. The insulator 106B was made of an insulating adhesive film Adflema NC207 (film thickness 25 μm) manufactured by Namics, and the copper foil was made of copper foil GTS-MP (film thickness 12 μm) manufactured by Furukawa Electric Co., Ltd. The insulators were bonded at 200°C for 60 minutes using a press machine KVHC manufactured by Kitagawa Seiki Co., Ltd.

In the process of Fig. 2(J), grooves 206 and holes 207 are formed. The copper foil in the areas that will become grooves 206 and holes 207 is removed by etching. Openings are provided in the copper foil in the same manner as for conductor 204. Next, grooves 206 and holes 207 are formed using a carbon dioxide laser processing machine. After desmearing, copper plating is performed to obtain the laminate shown in Fig. 2(L).

Next, the conductor electrode 105 was formed in the same manner as the conductor 204, and then the solder mask 211 was formed and cut into individual pieces to obtain the desired shielded thin flat cable 101 of the present invention. The above-mentioned circuit formation, lamination method, drilling method, copper plating, solder mask formation method, and cutting method of the conductor 204, etc. are known to those skilled in the art.

A specific example of manufacturing the shielded thin flat cable 101 according to the first embodiment of the present invention is shown in Figure 10 as Example 2. In Example 2, the shielded thin flat cable 101 of the present invention is illustrated, in which the conductor 204 and the metal film 202 are made of copper, the insulator 106 is made of a polyimide resin film, and the thickness is 140 μm.

Figure 10 (AL) is a cross-sectional view of the FCCL. Panasonic Corporation's R-F775 (copper foil 12 μm, resin film thickness 25 μm, dimensions 250 mm × 250 mm) was used as the FCCL.

Figure 10 (AN) shows the lay-up state, and uses insulator 106B made by melt-kneading 100 parts by weight of polypropylene (-blende manufactured by Sumitomo Chemical Co., Ltd.) with 100 parts by weight of magnesium oxide (Starmag manufactured by Konoshima Chemical Co., Ltd.) having an average particle size of 3.5 μm, and then extrusion molding.

Figure 10 (AO) shows the formation of a laminate corresponding to the laminate shown in Figure 2 (H).

The subsequent steps in this embodiment were carried out using a manufacturing method similar to that of Example 1.

As a fifth embodiment of the present invention, a process for manufacturing a shielded thin flat cable 101 characterized by providing a moisture-proof film layer 210 between the insulator 106 and the metal layer 202 is shown in FIG. 12. A specific example using a moisture-proof film as the moisture-proof film layer 210 is shown in FIG. 11 and FIG. 12 as Example 3. In this Example 3, a moisture-proof film as the moisture-proof film layer 210 is inserted between the metal film 202C made of copper foil and the insulator 106B to form a shielded thin flat cable. Polyvinylidene chloride (Saran, Asahi Chemical Industry Co., Ltd.) was used as the moisture-proof film film. As the moisture-proof film layer 210 of the present invention, a film having a water vapor permeability of 15 g/m ² 2/24 h or less is preferable, and high density polyethylene, medium density polyethylene, linear low density polyethylene, polypropylene, and polyvinylidene chloride are suitable. A film having a water vapor permeability of 15 g/m ² 2/24 h or more has a small moisture-proof effect, and the insulator absorbs moisture under high temperature and high humidity conditions, resulting in large dielectric loss, making it difficult to use. The thickness of the moisture-proof film layer 210 is preferably 3 μm to 100 μm. If it is less than 3 μm, sufficient moisture-proofing effect cannot be obtained. If it exceeds 100 μm, the flat cable becomes too thick, and the advantage of the thinness of the flat cable of the present invention is lost.

It is also possible to form the insulator 106B and the moisture-proof film layer 210 as a single unit in advance.

Figure 12 is a cross-sectional structure diagram of a shielded thin flat cable of Example 3.

Figure 8 shows an example of a shielded thin flat cable according to the present invention having a complex shape, in which the insulator 106 is not exposed except for the insulator 106 around the conductor electrode 105, and the other parts are covered with a metal film 202. One method for strengthening the shielding in the longitudinal direction is to wrap a shielding tape around it (see, for example, Patent Documents 5 and 6), but this method does not provide shielding in a branched structure such as that shown in Figure 8, and moisture absorption occurs in the insulator 106 due to the penetration of water vapor.

DESCRIPTION OF SYMBOLS 101: Flat cable 102: Conductor portion 103: Exposed terminal portion 105: Conductor electrode 106: Insulator 202: Metal film 203: Moisture-proof film 204: Conductor 206: Groove 207: Hole 208: Via hole 210: Moisture-proof film layer 211: Solder mask

Claims (29)

A shielded thin flat cable,
A conductor made of a metal,
A shielded thin flat cable comprising an insulator that is in close contact with the periphery of the conductor other than the terminal portion, and a metal film that is continuous over the entire outer surface of the insulator, including the short end faces . 2. The shielded thin flat cable according to claim 1,
A shielded thin flat cable, characterized in that the insulator contains one or more resins selected from the group consisting of high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, polystyrene, polypropylene, and polyphenylene ether, and contains, as a filler contained in the insulator, 10 to 900 parts by weight of one or more of quartz glass, aluminum oxide, hollow glass balloons, magnesium oxide, and silica, per 100 parts by weight of the resin. 3. The shielded thin flat cable according to claim 1,
1. A shielded thin flat cable, wherein the insulation is made of a cured photosensitive material. 4. The shielded thin flat cable according to claim 1,
A shielded thin flat cable, characterized in that the insulator has a dielectric constant of 3.5 or less, a dielectric loss tangent of 0.003 or less, and a water absorption rate of 0.05% or more. 5. The shielded thin flat cable according to claim 1,
A shielded thin flat cable, characterized in that the conductor is multi-layered. 6. The shielded thin flat cable according to claim 5,
A shielded thin flat cable, characterized in that the thickness of each of the multi-layered conductor layers is 10 μm to 500 μm. 7. The shielded thin flat cable according to claim 1,
1. A shielded thin flat cable, wherein the metal film is made of at least one of gold, silver, copper, and aluminum. 8. The shielded thin flat cable according to claim 1,
1. A shielded thin flat cable, characterized in that an area of a portion of the outer surface of the insulator having the metal film thereon is 95% or more of an area of the outer surface of the insulator. 9. The shielded thin flat cable according to claim 1,
A shielded thin flat cable, characterized in that the metal film continuously covers the entire outer surface of the insulator except for the periphery of the terminal portion of the conductor. 10. The shielded thin flat cable according to claim 1,
13. A shielded thin flat cable, comprising: a moisture-proof film on the outer surface of the insulator around the terminal portion of the conductor, but not on the metal film. 11. The shielded thin flat cable according to claim 1,
A shielded thin flat cable, characterized in that a moisture-proof film layer is provided between the insulator and the metal film. 11. The shielded thin flat cable according to claim 10 ,
1. A shielded thin flat cable, wherein the moisture-proof film is made of at least one of high density polyethylene, medium density polyethylene, linear low density polyethylene, polypropylene, and polyvinylidene chloride. 13. The shielded thin flat cable according to claim 1,
A shielded thin flat cable, characterized in that the metal film is formed on the wall surface of a groove provided on the surface of the insulator. A method for manufacturing a shielded thin flat cable, comprising the steps of:
An insulator is provided in close contact with the periphery of the metal conductor other than the terminal portion,
A method for manufacturing a shielded thin flat cable, characterized in that a metal film is provided continuously over the entire outer surface of the insulator, including its short end faces . 15. The method for producing a shielded thin flat cable according to claim 14,
A method for manufacturing a shielded thin flat cable, characterized in that the insulator contains one or more resins selected from the group consisting of high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, polystyrene, polypropylene, and polyphenylene ether, and the insulator contains, as a filler, 10 to 900 parts by weight of one or more of quartz glass, aluminum oxide, hollow glass balloons, magnesium oxide, and silica per 100 parts by weight of the resin. 16. The method for producing a shielded thin flat cable according to claim 14 or 15,
A method for producing a shielded thin flat cable, characterized in that the insulation is a photosensitive material. 17. A method for producing a shielded thin flat cable according to any one of claims 14 to 16, comprising the steps of:
A method for manufacturing a shielded thin flat cable, characterized in that the water absorption rate of the insulator is 0.05% or more or the heat distortion temperature of the insulator is between 60°C and 250°C. 18. A method for producing a shielded thin flat cable according to any one of claims 14 to 17,
A method for producing a shielded thin flat cable, characterized in that the conductor is multi-layered. 20. The method of claim 18, further comprising the steps of:
A method for producing a shielded thin flat cable, characterized in that the thickness of the shielded thin flat cable is set to 10 μm to 500 μm per one layer of the conductor which is multi-layered. 20. A method for producing a shielded thin flat cable according to any one of claims 14 to 19, further comprising the steps of:
The method for producing a shielded thin flat cable, wherein the metal film is one or more of gold, silver, copper, and aluminum. A method for producing a shielded thin flat cable according to any one of claims 14 to 20, further comprising the steps of:
A method for manufacturing a shielded thin flat cable, comprising forming the metal film on 95% or more of the area of the outer surface of the insulator. 22. A method for producing a shielded thin flat cable according to any one of claims 14 to 21, comprising the steps of:
A method for manufacturing a shielded thin flat cable, characterized in that the metal film continuously covers the outer peripheral surface of the conductor except for the periphery of the terminal portion. A method for producing a shielded thin flat cable according to any one of claims 14 to 22, further comprising the steps of:
A method for manufacturing a shielded thin flat cable, characterized in that the metal film is not formed on the outer surface of the insulator around the terminal portion of the conductor, but a moisture-proof film is formed. A method for producing a shielded thin flat cable according to any one of claims 14 to 23, comprising the steps of:
A method for manufacturing a shielded thin flat cable, comprising forming a moisture-proof film layer between the insulator and the metal film. 24. The method of claim 23 for producing a shielded thin flat cable,
A method for producing a shielded thin flat cable, characterized in that the moisture-proof film is formed from at least one of high density polyethylene, medium density polyethylene, linear low density polyethylene, polypropylene, and polyvinylidene chloride. 26. A method for producing a shielded thin flat cable according to any one of claims 14 to 25, comprising the steps of:
A method for manufacturing a shielded thin flat cable, comprising forming the metal film on a wall surface of a groove provided on the surface of the insulator. 27. The method of claim 26 for producing a shielded thin flat cable, comprising:
A method for manufacturing a shielded thin flat cable, comprising the steps of: forming the groove by laser light; and forming the metal film on the wall surface of the formed groove by plating. 27. The method of claim 26 for producing a shielded thin flat cable, comprising:
The method for producing a shielded thin flat cable is characterized in that the grooves are formed by exposure to light and resin etching. 29. A method for producing a shielded thin flat cable according to any one of claims 14 to 28, comprising the steps of:
A method for manufacturing a shielded thin flat cable, characterized in that the metal film is formed in multiple rows parallel to the conductor on the outer surface of the insulator, which is provided in close contact with the conductor except for the multiple terminal portions, and then the insulator is cut into individual pieces parallel to the conductor.

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