TW202521346A - Conductive film and manufacturing method thereof - Google Patents

Abstract

Provided is a conductive film that has a fluororesin film as a base material and a conductive coating applied thereon by plating. The conductive coating formed by plating on the fluororesin film has a peel strength of 5 to 15 N/cm. Therefore, it is possible to prevent the conductive coating from peeling off from the fluororesin film due to heat in usage environment, so that it can be used as a variety of substrate materials, such as layer components for build-up substrates. In addition, since the conductive coating is plated directly onto the fluororesin film, it is possible to take advantage of a low dielectric tangent of less than 0.001, a characteristic possessed by the fluororesin film, whereby the conductive film is a useful material for next-generation mobile communication systems represented by 5G/6G.

Description

Conductive film and method for manufacturing the same

The present invention relates to a conductive film formed by coating a conductive coating on a fluororesin film and a method for manufacturing the same.

The applicant of this case has proposed patent document 1, which is a technology related to a flexible circuit film formed by coating a functional resin film as a substrate and forming a conductive film. Patent document 1 also proposes using a flexible circuit film with a fluororesin film as a substrate as a flexible circuit substrate for high-speed transmission, a flexible circuit substrate for antenna cables, a flexible circuit substrate for semiconductors, and an actuator.

In addition, the bonding property of fluororesin film to other materials is extremely low. Therefore, when using fluororesin film as a substrate, it is difficult to bond the conductive film with high strength by plating, and from the perspective of practicality, there is still room for improvement. In addition to plating, it is also known that a conductive film is formed by impregnating glass cloth, polyimide varnish, epoxy resin, etc. into a fluororesin film to suppress thermal expansion or improve the bonding property with other substances, and then laminating copper foil by heat pressing. However, if impurities such as glass cloth or polyimide varnish are mixed in, the extremely low dielectric loss tangent characteristic of the fluororesin film itself will be offset. In addition, the back of the copper foil that is laminated by heat pressing has been roughened. Due to the skin effect, the unevenness will cause loss in transmission characteristics. Furthermore, the thermal stress applied to the substrate during heat pressing is large.

In addition, in recent years, semiconductor packaging and the like have adopted a semi-additive process due to high functionality and miniaturization. The semi-additive process is to stack insulating layers in an incremental manner and to stack circuits only in the required parts by electroplating copper. Such an insulating layer, as shown in non-patent document 1, uses an insulating resin film with a thermosetting resin such as epoxy resin as the main component. This insulating resin film is formed on a PET film and provided in a three-layer structure together with a protective film. After the protective film and the PET film are peeled off and thermally cured, through holes are formed, and then a coating process is performed to form a predetermined conductive film.

[Prior Art Literature]

[Patent Literature]

[Patent document 1] WO2018/225760

[Non-patent literature]

[Non-patent document 1] "Current status and trends of interlayer insulation materials for semiconductor package substrates", Hirohisa Narahashi, Shigeo Nakamura, Journal of the Society of Electronics Implementation Voi.14 No.5 (2011)

In addition, materials used in next-generation mobile communication systems represented by 5G/6G require excellent dielectric properties in high frequency bands such as millimeter wave bands (above 28GHz), and substrate materials with low dielectric loss tangent are particularly valued. In the case of insulating resin films with thermosetting resins such as epoxy resins as the main component shown in non-patent document 1, for example, the commercially available "Ajinomoto Build-up Film (registered trademark)" (Ajinomoto Fine-Techno Co., Ltd.), the lowest dielectric loss tangent is about 0.005. On the other hand, the dielectric loss tangent of fluororesin films is less than 0.001 if the purity is high, which is advantageous. However, as mentioned above, the adhesion of the fluororesin film is not good, so it must be mixed with impurities for practical use. The dielectric loss tangent of the fluororesin film used in the currently practical build-up substrate exceeds 0.001 when the copper foil is stacked.

The present invention is made in view of the above situation, and its subject is to provide a conductive film and a manufacturing method thereof, wherein the conductive film has a fluororesin film as a base material, and the coating layer is firmly attached, has excellent dielectric properties, and is suitable for use as a layer constituent material of a build-up substrate with a conductive film as a conductive layer.

In order to solve the above-mentioned problem, the present invention provides a conductive film, which is formed with a conductive coating on at least one side of a fluororesin film by plating treatment.

The peeling strength of the conductive film relative to the fluororesin film is in the range of 5 to 15 N/cm.

It is preferably used as a layer constituent material of a build-up substrate using the aforementioned fluororesin film as an insulating layer and the aforementioned conductive film as a conductive layer.

The aforementioned conductive film can be formed on one side of the aforementioned fluororesin film, and the other side is a surface that has undergone surface modification treatment to provide the aforementioned layer constituent material.

The conductive film can be provided as the layer constituent material in a form in which the conductive film is formed on both sides of the fluororesin film.

The aforementioned layer constituent material can be provided in a form in which the aforementioned conductive film is formed on one surface of the aforementioned fluororesin film, and a bonding sheet and a protective film are sequentially laminated on the other surface.

The fluororesin forming the aforementioned fluororesin film is preferably selected from polytetrafluoroethylene (4-fluorinated) (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (4.6-fluorinated) (FEP), tetrafluoroethylene-ethylene copolymer (ETFE), polyvinylidene fluoride (2-fluorinated) (PVDF), polychlorotrifluoroethylene (3-fluorinated) (PCTFE) or chlorotrifluoroethylene-ethylene copolymer (ECTFE).

In this case, the dielectric loss tangent is preferably less than 0.001.

The aforementioned fluororesin film preferably does not contain impurities useful for improving adhesion.

The conductive film of the present invention can be applied to flexible circuit substrates for high-frequency antenna modules, flexible cables for high-speed transmission, substrates for semiconductor packaging, multi-layer substrates, substrate-like printed circuit boards (hereinafter referred to as SLP (Substrate-Like PCB)), and actuators.

In addition, the present invention provides a method for manufacturing a conductive film, which is a method for manufacturing a conductive film by forming a conductive coating on at least one side of a fluororesin film by plating treatment, wherein the plating treatment is performed in the order of surface modification treatment of the fluororesin film, catalyst application treatment, acceleration treatment, electroless copper plating or electroless nickel plating, and electrolytic copper plating or electrolytic nickel plating.

The accelerator used in the aforementioned accelerated treatment is preferably a hot sulfuric acid solution.

The aforementioned hot sulfuric acid solution is preferably a sulfuric acid solution with a concentration of 10 to 30% by volume heated to 40 to 80°C.

The immersion time in the aforementioned sulfuric acid solution is preferably 1 to 5 minutes.

In the aforementioned manufacturing method, the fluororesin forming the aforementioned fluororesin film is preferably selected from polytetrafluoroethylene (4 fluorinated) (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (4.6 fluorinated) (FEP), tetrafluoroethylene-ethylene copolymer (ETFE), polyvinylidene fluoride (2 fluorinated) (PVDF), polychlorotrifluoroethylene (3 fluorinated) (PCTFE) or chlorotrifluoroethylene-ethylene copolymer (ECTFE).

According to the present invention, the peeling strength of the conductive film formed on the fluororesin film by plating is 5 to 15 N/cm. As a result, the peeling of the conductive film from the fluororesin film due to heat in the use environment can be suppressed, and various substrate materials such as layer components of build-up substrates can be used. In addition, because the conductive film is directly plated on the fluororesin film, the low dielectric loss tangent of less than 0.001 that the fluororesin film has can be produced, and it can be used as a material for next-generation mobile communication systems represented by 5G/6G. In addition, because the conductive film is formed by plating, both the plated surface and the plated surface are smooth, unlike the previous method of hot pressing the copper foil, which will not cause the transmission loss to increase due to the unevenness of the back of the copper foil. In addition, in the plating step, it is better to use hot sulfuric acid to accelerate the treatment, which helps to suppress the thermal stress of the conductive film.

Figures 1(a) to (c) are diagrams schematically showing examples of the uses and structures of the conductive film of the present invention.

Figures 2(a) to (c) are diagrams schematically showing another example of the structure of the conductive film of the present invention.

Figures 3(a) to (d) are diagrams used to illustrate an example of the manufacturing steps of a layered structural material having a single surface subjected to surface bonding treatment.

Figures 4(a) to (e) are diagrams for explaining another example of the manufacturing steps of a layered structural material having a single surface subjected to surface bonding treatment.

Figures 5(a) to (c) are diagrams showing an example of the manufacturing steps of a layered material having a copper-plated coating formed on both sides.

Figures 6(a) to (c) show examples of flexible circuit substrates used in high-frequency transmission cables.

Figures 7(a) to (c) are used to illustrate the manufacturing steps of the build-up substrate.

FIG8 is a diagram showing an image of a semiconductor package.

The present invention is described in more detail below based on the implementation shown in the drawings.

Figures 1(a) to (c) are diagrams schematically showing the use and configuration examples of the conductive film of the present invention. As an example, polytetrafluoroethylene (PTFE) is used as the substrate. Among them, Figures 1(a) and (b) show configuration examples of materials for flexible printed wiring boards (FPCs (Flexible printed circuits)) for high-frequency (RF) modules. Figure 1(a) shows copper plating on one side of PTFE, and Figure 1(b) shows copper plating on both sides of PTFE. Figure 1(c) shows a configuration example of a metal-attached bonding film suitable for build-up substrates and an impedance-integrated shielding film for flexible flat cables (FFCs). In Figure 1(c), copper plating is applied to one side, and a bonding sheet and a protective film are sequentially laminated on the other side.

Figures 2(a) to (c) are diagrams schematically showing another example of the structure of the conductive film of the present invention. Therein is shown an example of the structure of a layered component (type A to C) suitable for use as a build-up substrate. The build-up substrate is used, for example, as a semiconductor package substrate (Substrate) as shown in Figure 8. Such a build-up substrate is described in detail in the following section, but as shown in Figures 7(a) to (c), it is manufactured by the following method: The layered component composed of a laminated structure of a bonding sheet, a fluororesin film (such as PTFE) and copper plating is sandwiched with a core substrate for lamination, and through holes are formed, and then a conductive circuit is formed by etching. In addition, FIG. 8 shows a PCB equipped with a semiconductor package, but in recent years, an SLP (Substrate-Like PCB) having a fine conductor circuit is used as the PCB, and the conductive film of this embodiment that can form a fine circuit by plating is also suitable for use as a material for forming the SLP.

The layered material of type A shown in FIG2(a) is a fluororesin film (such as PTFE or tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA)) as a base material, and a copper-plated coating is formed on one side thereof. The other side is a surface that has been treated with a bonding layer such as a laminated bonding sheet (referred to as "surface bonding treatment" in this manual) when a build-up substrate is made using a fluororesin film with extremely poor bonding properties.

Figures 3(a) to (d) are an example of the manufacturing steps of a layered material in which a single side is subjected to a surface bonding treatment. First, the surface of both sides of a substrate (e.g., PTFE) is modified by plasma treatment and sodium treatment described later (Figure 3(a)). Then, electroless copper plating is performed on both sides (Figure 3(b)), the electroless copper plating on one side is masked, and the other side is etched (Figure 3(c)). Then, the mask is peeled off, and electrolytic copper plating is performed on a single side (Figure 3(d)). Thereby, on the other side, the electroless copper plating layer is etched, so that the surface modified by plasma treatment and sodium treatment is exposed. The exposed surface that has undergone surface modification becomes a surface that has undergone surface bonding treatment, and the bonding layer can be deposited.

Figures 4(a) to (e) are another example of the manufacturing steps of a layered material with one side subjected to surface bonding treatment. The steps of surface modification treatment on both sides of the substrate and electroless copper plating on both sides (Figures 4(a) and (b)) are the same as the steps of Figures 3(a) to (b). As shown in Figure 4(c), the steps of masking the electroless copper plating on one side and etching the electroless copper plating on the other side are basically the same as Figure 3(c). However, Figure 4(c) assumes that the etching result does not remain on the surface that has been subjected to surface modification treatment in step (a). In this case, after electroplating copper on one side (Figure 4(d)), the other side is subjected to surface modification treatment again (Figure 4(e)). In this way, the next layer can be deposited on the other side.

The layered material of type B shown in FIG2(b) is formed by using a fluororesin film (such as PTFE or PFA) as a substrate and forming a copper-plated coating on both sides thereof. FIG5(a) to (c) show the manufacturing steps, which are to perform surface modification treatment on both sides of the substrate (FIG5(a)), then perform electroless copper plating on both sides (FIG5(b)), and then perform electrolytic copper plating on both sides (FIG5(c)).

Type C shown in FIG2(c) is a structure in which a bonding sheet is laminated on the other side of a fluororesin film (such as PTFE or PFA) with a copper-plated coating formed on one side, which is equivalent to Type A in FIG2(a), and a protective film is laminated on the surface. As shown in FIG3 and FIG4, the opposite side of the copper-plated coating of Type A in FIG2(a) is a surface that has been subjected to surface bonding treatment to which the bonding sheet can be bonded. Therefore, if a bonding sheet and a protective film are pre-laminated on a surface subjected to surface bonding treatment, it can be easily used for a build-up substrate. Although the linear expansion coefficient of the fluororesin film is high, the type in which the bonding sheet is laminated also has the advantage of suppressing the thermal expansion of the fluororesin film.

Figures 6(a) to (c) show examples of configurations used as flexible circuit substrates for high-frequency transmission cables and flexible circuit substrates for high-frequency antenna modules. Figure 6(a) is an example of using type A in Figure 2(a), Figure 6(b) is an example of using type B in Figure 2(b), and Figure 6(c) is an example of layering type C in Figure 2(c) on type B in Figure 2(b).

In the case of the build-up substrate shown in Figures 7(a) to (c), for example, a layered material of type A (see Figure 2(a)) or type C (see Figure 2(c)) formed by single-sided copper plating on PTFE is bonded to a core board (Figure 7(a)). Then, through holes are formed by laser processing, and electroless copper plating is performed on the through holes to make the core board and the single-sided copper plating of PTFE conductive (Figure 7(b)).

Since the copper layer is formed on PTFE by plating, the thickness of the copper plating on PTFE can be set to less than 0.5μm, for example, and a more precise pitch circuit can be supported by the semi-additive process (Figure 7(c)).

In the past, RCC was made by coating epoxy resin (adhesive) on copper foil. However, in the case of copper foil, no matter how thin it is, it is still 1 to 2μm, which is thicker than the copper plating layer formed in this embodiment, and it is very expensive. Therefore, even if this material is used for semi-additive processing, when the Cu (1 to 2μm) of the seed layer is finally dissolved by etching, the circuit part is also reduced by about 2μm, and it cannot be used for precise patterns. This point is applicable to the formation of precise patterns in this embodiment as described above. In addition, the fluororesin film used in this embodiment does not contain impurities such as glass cloth mentioned in the previous technical paragraph, so it is also easy to open holes with laser.

The fluororesin used to form the fluororesin film used as the substrate is preferably selected from polytetrafluoroethylene (4 fluorinated) (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (4.6 fluorinated) (FEP), tetrafluoroethylene-ethylene copolymer (ETFE), polyvinylidene fluoride (2 fluorinated) (PVDF), polychlorotrifluoroethylene (3 fluorinated) (PCTFE) or chlorotrifluoroethylene-ethylene copolymer (ECTFE). In addition, the fluororesin film preferably does not contain impurities such as glass cloth or polyimide varnish for improving adhesion. If such impurities are contained, the dielectric loss tangent increases. In particular, polytetrafluoroethylene (4 fluorinated) (PTFE) and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) having a dielectric loss tangent of less than 0.001 are more preferred.

The manufacturing steps of the layered component shown in Figures 2 to 5 are roughly as described above. Although some of the descriptions are repeated, in more detail, the conductive film of this embodiment used in this layered component is manufactured by the following method. First, the fluororesin film as the substrate is degreased and then subjected to surface modification. Then, after ion-based or colloidal catalyst treatment and acceleration treatment, reduction precipitation is performed by electroless copper plating or electroless nickel plating, and then copper or nickel is electroplated to form a conductive film of a predetermined thickness, thereby manufacturing.

Here, the surface modification treatment may include plasma treatment, UV treatment, sodium treatment, chemical treatment, etc. Plasma treatment may use low-temperature plasma, but the types of vacuum plasma and atmospheric pressure plasma are not limited, and the type of gas used for plasma treatment is also not limited, and oxygen, nitrogen, helium, argon, ammonia, etc. may be used. Chemical treatment may include treatment that uses surfactants to make the surface potential cationic or anionic.

In addition, the catalyst treatment is carried out, for example, by immersing the fluororesin film that has undergone surface modification treatment in a catalyst solution (preferably a palladium-based catalyst solution), and then performing an accelerated treatment. In the accelerated treatment, it is preferred to use a hot sulfuric acid solution as an accelerator. The accelerator is preferably a sulfuric acid solution with a concentration of 10 to 30% by volume heated to 40 to 80°C. The immersion time in the sulfuric acid solution is preferably in the range of 1 to 5 minutes. By performing such a catalyst treatment and accelerated treatment, the adhesion and activation of the catalyst on the surface of the fluororesin film can be improved. In addition, by performing an accelerated treatment with hot sulfuric acid, the thermal stress of the conductive film can also be suppressed.

(Peel-off test)

The fluororesin film surface modified by plasma treatment was treated with palladium as a catalyst, and then a sulfuric acid solution with a concentration of 20% by volume heated to 55°C was used as an accelerator. The accelerated treatment was performed with an immersion time of 1 minute, and electroless plating and electroplating were performed to form a conductive film on the surface of the fluororesin film to produce conductive film samples. The thickness of the conductive film of each sample was 5 to 12μm. The peel strength of the conductive film formed by plating relative to the substrate (fluororesin film) was measured for each sample. The peel strength is measured by a 180-degree peel test (chuck speed 50 mm/min, stroke 10 mm) in accordance with JIS C 6471. Although the fluororesin film is used as the substrate, the peel strength is still in the range of 5 to 15 N/cm.

The details are as follows.

If the peeling strength is 5N/cm or more, there will be almost no problems such as thermal peeling in practice, but it is preferably 6N/cm or more, and more preferably 8N/cm or more.

In addition, among fluororesins, as mentioned above, it is better to use perfluoroalkoxy fluorine resin (PFA) and polytetrafluoroethylene (PTFE) with a dielectric loss tangent of less than 0.001 for flexible circuit substrates for high-frequency antenna modules, flexible cables for high-speed transmission, substrates for semiconductor packaging, multi-layer substrates, and SLP (Substrate-Like PCB). Although the dielectric loss tangent of polyvinylidene fluoride resin (PVDF) is higher than 0.01, it has piezoelectric function and is suitable for various actuators that utilize piezoelectric function.

Claims (14)

A conductive film is formed by plating at least one side of a fluororesin film to form a conductive coating. The peeling strength of the conductive film relative to the fluororesin film is in the range of 5 to 15 N/cm. The conductive film as described in claim 1 is used as a layer constituent material of a build-up substrate having the aforementioned fluororesin film as an insulating layer and the aforementioned conductive coating as a conductive layer. The conductive film as described in claim 2 is provided as the aforementioned layer constituent material in a form in which the aforementioned conductive coating is formed on one side of the aforementioned fluororesin film and the other side is a surface that has undergone surface modification treatment. The conductive film as described in claim 2 is provided as the aforementioned layer constituent material in the form of the aforementioned conductive coating formed on both sides of the aforementioned fluororesin film. The conductive film as described in claim 2 is provided as the aforementioned layer constituent material in the form of forming the aforementioned conductive coating on one surface of the aforementioned fluororesin film and sequentially laminating a bonding sheet and a protective film on the other surface. The conductive film as described in claim 1, wherein the fluororesin forming the aforementioned fluororesin film is selected from polytetrafluoroethylene (4-fluorinated) (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (4.6-fluorinated) (FEP), tetrafluoroethylene-ethylene copolymer (ETFE), polyvinylidene fluoride (2-fluorinated) (PVDF), polychlorotrifluoroethylene (3-fluorinated) (PCTFE) or chlorotrifluoroethylene-ethylene copolymer (ECTFE). The dielectric loss tangent of the conductive film described in claim 6 is less than 0.001. The conductive film as described in claim 6, wherein the fluororesin film does not contain impurities useful for improving adhesion. The conductive film as described in any one of claims 1 to 8 is used for a flexible circuit substrate for a high-frequency antenna module, a flexible cable for high-speed transmission, a substrate for semiconductor packaging, a multi-layer substrate, a substrate-like printed circuit board, and an actuator. A method for manufacturing a conductive film is a method for manufacturing a conductive film by forming a conductive coating on at least one side of a fluororesin film through a plating process, wherein the plating process is performed in the following order: Surface modification treatment of the aforementioned fluororesin film; The catalyst is handled; Accelerate processing; Electroless copper or electroless nickel; and Electroplated copper or electroplated nickel. The method for manufacturing a conductive film as described in claim 10, wherein the accelerator used in the aforementioned acceleration treatment is a hot sulfuric acid solution. The method for manufacturing a conductive film as described in claim 11, wherein the hot sulfuric acid solution is a sulfuric acid solution with a concentration of 10 to 30 volume % heated to 40 to 80°C. The method for manufacturing a conductive film as described in claim 12, wherein the immersion time in the aforementioned sulfuric acid solution is 1 to 5 minutes. A method for manufacturing a conductive film as described in claim 10, wherein the fluororesin forming the aforementioned fluororesin film is selected from polytetrafluoroethylene (4-fluorinated) (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (4.6-fluorinated) (FEP), tetrafluoroethylene-ethylene copolymer (ETFE), polyvinylidene fluoride (2-fluorinated) (PVDF), polychlorotrifluoroethylene (3-fluorinated) (PCTFE) or chlorotrifluoroethylene-ethylene copolymer (ECTFE).