JP7478679B2 - Low dielectric constant metal-clad fluororesin substrate and its manufacturing method - Google Patents

Description

The present invention relates to a low-dielectric metal-clad fluororesin substrate used in printed wiring boards for high-speed communications using high frequencies such as millimeter waves and microwaves.

Currently, with the advent of high-speed communications such as 5G, there is a strong demand for high-speed communication boards and antenna boards that have low transmission loss even when using high frequencies such as millimeter waves. In addition, there has been a remarkable trend toward high-density mounting and extremely thin wiring boards in information terminals such as smartphones.

For high-speed communications such as 5G, printed circuit boards are widely used, which are made by laminating prepregs obtained by impregnating low-dielectric glass cloth such as D glass, NE glass, or L glass with thermoplastic resins such as fluororesin or polyphenylene ether, or even thermosetting resins such as low-dielectric epoxy resin or low-dielectric maleimide resin, and then curing them under heat and pressure. However, the dielectric tangent of each board is large, about 0.002 to 0.005 in the high-frequency range of 10G or more for each type of glass, and when high frequencies such as millimeter waves are used for communication, the transmission loss is large and accurate information cannot be sent.

It is known that signal transmission loss is improved as the dielectric constant (ε) and dielectric tangent (tan δ) of the material decrease, as shown by the Edward A. Wolff formula: transmission loss ∝√ε × tan δ.

Generally, when it comes to the millimeter wave band, fluororesin substrates such as polytetrafluoroethylene (PTFE), which has a low dielectric tangent and small transmission loss, are used.

Here, the formation of copper foil on a copper-clad laminate used in a printed circuit board is carried out by laminating copper foil, a polytetrafluoroethylene (PTFE) substrate containing glass cloth, and copper foil in that order, and then thermocompression bonding (Patent Document 1). However, in Patent Document 1, the dielectric tangent is 0.001 or more, and quartz glass cloth is not used for the glass cloth.

A low-dielectric resin substrate made of quartz glass cloth and thermosetting resin (Patent Document 2) has been developed, but it does not use thermoplastic fluororesins such as PTFE, and the dielectric tangent measured at 10 GHz is limited to 0.0009, so a resin substrate with an even lower dielectric tangent is required.

As the wavelengths used in future high-speed communications move into the 70 to 100 GHz range, the interface between the resin surface and the copper wiring will need to be flat.

However, since fluororesins are generally water-repellent and the adhesive strength of the copper foil cannot be ensured, methods have been proposed to improve the adhesiveness of thin films by physically or chemically modifying the PTFE surface (Patent Documents 3 to 5). For example, a method of hydrophilizing a fluororesin film by irradiating it with an excimer laser in an atmosphere containing water (Patent Document 3) and a method of hydrophilizing it by irradiating it with an excimer laser using a dilute ammonia aqueous solution instead of water (Non-Patent Document 1) have been reported, but they have not been evaluated as metal-clad resin substrates. In addition, a method of hydrophilizing the fluororesin by causing an amino group addition reaction on the surface of the fluororesin by plasma generation in an amino group-containing gas atmosphere (Patent Document 4) is known. In addition, there is a method of improving adhesiveness by combining a process of introducing polar groups into the PTFE surface with a process of forming irregularities on the surface by subsequent etching (Patent Document 5).

Although hydrophilicity can be imparted by chemically modifying the surface, adhesion is still not sufficient due to the decrease in hydrophilicity over time and the variation in hydrophilicity. In either case, it is essential to create irregularities on the modified surface and ensure reliable adhesion between the copper foil and the fluororesin substrate through the anchor effect.

On the other hand, due to the skin effect, the higher the frequency of the transmission signal, such as millimeter waves, the more it propagates along the conductor surface, and the rougher the conductor surface, the greater the transmission loss. For this reason, several surface modification methods have been proposed to increase the adhesive strength of the thin film on PTFE (Patent Document 6), but the effect is not sufficient.

JP 2008-307825 A JP 2009-263569 A Japanese Patent Application Laid-Open No. 5-306346 JP 2005-343949 A JP 2003-201571 A International Publication No. 2018/212345

Polymer Review, Vol. 52, No. 1 (1995), pp. 66-68, "Surface Modification of Tetrafluoroethylene-Perfluoroalkyl Vinyl Ether Copolymers Using Excimer Laser"

In view of the above, the present invention aims to provide a low dielectric metal-clad fluororesin substrate that is excellent in dielectric properties and tensile strength and has improved peel strength from metal foils such as copper foil, and is optimal for high frequencies such as millimeter waves, and a method for manufacturing the same. Note that the "peel strength" referred to in the present invention refers to the peel strength value measured by the method described in JIS C 6481:1996. In the following, "peel strength" is sometimes referred to as "adhesion strength."

In order to solve the above problems, the present invention provides
A low dielectric metal-clad fluororesin substrate in which a metal foil is laminated on the surface of a fluororesin substrate,
The present invention provides a low dielectric metal-clad fluororesin substrate, characterized in that the surface of the fluororesin substrate is a hydrophilically treated surface having amino groups and hydroxyl groups, and the peel strength between the metal foil and the fluororesin substrate is 0.5 kN/m or more.

Such low-dielectric metal-clad fluororesin substrates have excellent dielectric properties and improved peel strength from metal foils such as copper foil, making them ideal for high-frequency applications such as millimeter waves.

In the present invention, it is preferable that the contact angle of the surface of the fluororesin substrate with pure water is 100° or less.

This will improve the adhesive strength with the metal foil.

In the present invention, the fluororesin substrate may further contain quartz glass cloth alone, or both quartz glass cloth and silica powder.

This will result in a low-dielectric metal-clad fluororesin substrate with excellent strength, durability, and reliability.

In this case, it is preferable that the dielectric tangent of the quartz glass cloth measured at 10 GHz is less than 0.0010.

A low-dielectric metal-clad fluororesin substrate containing this type of quartz glass cloth has superior dielectric properties.

It is also preferable that the quartz glass cloth has a tensile strength of at least 2.1 N/25 mm per cloth weight (g/m ² ).

A low-dielectric metal-clad fluororesin substrate containing this type of quartz glass cloth has superior strength and improved resistance to external forces applied during substrate manufacturing.

It is also preferable that the dielectric tangent of the silica powder measured at 10 GHz is less than 0.0010.

When a fluororesin substrate contains both quartz glass cloth and silica powder, the inclusion of such silica powder gives the low-dielectric metal-clad fluororesin substrate excellent dielectric properties, a low coefficient of thermal expansion, and high strength.

It is also preferable that the quartz glass cloth is surface-treated with a silane coupling agent.

In this way, coating the surface of the quartz glass cloth with a silane coupling agent (surface treatment) increases the slipperiness and wettability of the quartz glass cloth, and has the effect of increasing the tensile strength of the glass cloth.

In this case, it is preferable that the quartz glass cloth has a dielectric loss tangent of 0.0008 or less at 10 GHz and a tensile strength of 2.7 N/25 mm or more per cloth weight (g/m ² ).

If the substrate contains this type of quartz glass cloth, it will have excellent dielectric properties and strength, making it a metal-clad fluororesin substrate with even greater reliability.

The silane coupling agent is preferably an amino-based silane coupling agent, an unsaturated group-containing silane coupling agent, or an oligomer consisting of an amino-based silane coupling agent and an unsaturated group-containing silane coupling agent, or a combination of two or more of these.

By surface treating the quartz glass cloth with such a silane coupling agent, the slipperiness and wettability of the quartz glass cloth can be further improved, and the tensile strength of the glass cloth can be further increased.

In addition, in the present invention, it is preferable that the dielectric tangent of the fluororesin in the fluororesin substrate is 0.0008 or less at 10 GHz.

Such fluororesins have a low dielectric tangent and are particularly suitable for use at high frequencies such as millimeter waves.

The present invention also provides a method for producing a low dielectric metal-clad fluororesin substrate having a metal foil laminated on a surface of a fluororesin substrate, comprising the steps of:
The present invention provides a method for producing a low dielectric metal-clad fluororesin substrate, comprising: introducing an amino group and a hydroxyl group into a surface of the fluororesin substrate to hydrophilize the surface of the fluororesin substrate; and thermocompression bonding the metal foil to the hydrophilically treated surface at a temperature equal to or higher than the melting temperature of the fluororesin in the fluororesin substrate, thereby setting the peel strength between the metal foil and the fluororesin substrate to 0.5 kN/m or more.

This manufacturing method for low-dielectric metal-clad fluororesin substrates has excellent dielectric properties and tensile strength, and has improved adhesion strength with metal foils such as copper foil, making it possible to obtain low-dielectric metal-clad fluororesin substrates that are ideal for high-frequency applications such as millimeter waves.

In the present invention, in the hydrophilization treatment, it is preferable to introduce amino groups and hydroxyl groups onto the surface of the fluororesin substrate by irradiating the fluororesin substrate with an excimer laser in an atmosphere in which ammonia water is also present.

By carrying out the hydrophilic treatment in this manner, the surface of the fluororesin substrate can be efficiently made into a hydrophilic surface having amino groups and hydroxyl groups.

In the present invention, it is preferable that in the hydrophilization treatment, the contact angle of the surface of the fluororesin substrate with pure water is set to 100° or less.

This improves the adhesion strength between the metal foil and the fluororesin substrate.

The fluororesin substrate can be made of quartz glass cloth alone, or a fluororesin substrate containing both quartz glass cloth and silica powder.

By using such materials, it is possible to manufacture low-dielectric metal-clad fluororesin substrates that are strong, durable, and reliable.

In addition, it is preferable to use a quartz glass cloth having a dielectric tangent measured at 10 GHz of less than 0.0010.

By using this type of quartz glass cloth, it is possible to obtain a low-dielectric metal-clad fluororesin substrate with superior dielectric properties.

It is preferable to use, as the quartz glass cloth, a quartz glass cloth having a tensile strength per cloth weight (g/m ² ) of 2.1 N/25 mm or more.

By using such quartz glass cloth, it is possible to obtain a low-dielectric metal-clad fluororesin substrate that is stronger and has improved resistance to the external forces applied during substrate manufacturing.

It is preferable to use silica powder having a dielectric tangent measured at 10 GHz of less than 0.0010.

When using a fluororesin substrate containing both quartz glass cloth and silica powder, the use of such silica powder makes it possible to obtain a low-dielectric metal-clad fluororesin substrate with superior dielectric properties.

It is also preferable to use a quartz glass cloth that has been surface-treated with a silane coupling agent as the quartz glass cloth.

By coating the surface of the quartz glass cloth with a silane coupling agent (surface treatment) in this way, the slipperiness and wettability of the quartz glass cloth can be improved, and the tensile strength of the glass cloth can be increased.

In this case, it is preferable to use a quartz glass cloth having a dielectric loss tangent of 0.0008 or less at 10 GHz and a tensile strength of 2.7 N/25 mm or more per cloth weight (g/m ² ).

By using this type of quartz glass cloth, it is possible to manufacture metal-clad fluororesin substrates that have excellent dielectric properties and strength, and are even more reliable.

As the silane coupling agent, it is preferable to use any one of an amino-based silane coupling agent, an unsaturated group-containing silane coupling agent, or an oligomer consisting of an amino-based silane coupling agent and an unsaturated group-containing silane coupling agent, or a combination of two or more of these.

By surface treating the quartz glass cloth with such a silane coupling agent, the slipperiness and wettability of the quartz glass cloth can be further improved, and the tensile strength of the glass cloth can be further increased.

It is preferable to use a fluororesin substrate containing a fluororesin having a dielectric tangent of 0.0008 or less at 10 GHz as the fluororesin substrate.

By using such a fluororesin substrate, the dielectric tangent is low, making it particularly suitable for high frequency applications such as millimeter waves.

In addition, in the present invention, it is preferable to further perform the hydrophilization treatment and treat the surface of the fluororesin substrate having amino groups and hydroxyl groups with an alkoxysilane-containing primer.

By treating (applying) the substrate with an alkoxysilane-containing primer in this way, the adhesive strength with the metal foil, such as copper, is further increased, making it possible to obtain a metal-clad fluororesin substrate that is even more durable and reliable.

As described above, the low dielectric metal-clad fluororesin substrate of the present invention has excellent dielectric properties and tensile strength, and has improved adhesion strength with metal foils such as copper foil, making it ideal for high frequency applications such as millimeter waves. Furthermore, according to the manufacturing method of the low dielectric metal-clad fluororesin substrate of the present invention, the adhesion strength with metal foils such as copper foil can be efficiently improved by simultaneously introducing amino groups and hydroxyl groups into the surface of the fluororesin constituting the substrate, and a low dielectric metal-clad fluororesin substrate ideal for high frequency applications such as millimeter waves can be efficiently manufactured. In particular, the inclusion of quartz glass cloth with excellent dimensional accuracy, dielectric properties and tensile strength makes it highly useful for the above applications.

Furthermore, the low dielectric metal-clad fluororesin substrate produced by the method of the present invention can be used for printed circuit boards and the like. In particular, since the surface has been hydrophilized, strong adhesion can be obtained to metals such as copper foil having a smooth surface, and therefore transmission loss due to the skin effect is small, making this a low dielectric metal-clad fluororesin substrate that is optimal for high-speed communications using high frequencies such as millimeter waves.
Furthermore, the fluororesin substrate usable in the present invention may further contain quartz glass cloth or silica powder, which have low dielectric tangent properties even at high frequencies. By using such materials, a low dielectric metal-clad fluororesin substrate with excellent strength, durability, and reliability can be obtained.

As mentioned above, there was a need to develop a low-dielectric metal-clad fluororesin substrate that has excellent dielectric properties and tensile strength, and has improved adhesive strength with metal foil, making it ideal for high-frequency applications.

As a result of the intensive efforts made by the inventors to achieve the above object, they discovered that a surface treatment for fluororesin can be performed by irradiating the surface with an excimer laser in an ammonia water atmosphere to generate amino groups and hydroxyl groups on the surface of the fluororesin, thereby making the surface hydrophilic and allowing it to adhere to a metal foil, thus completing the present invention.

That is, the present invention is a low-dielectric metal-clad fluororesin substrate in which a metal foil is laminated on the surface of a fluororesin substrate, the surface of the fluororesin substrate is a hydrophilic surface having amino groups and hydroxyl groups, and the peel strength between the metal foil and the fluororesin substrate is 0.5 kN/m or more.

The present invention is described in detail below, but is not limited to these.

-Low dielectric metal-clad fluororesin substrate-
The low dielectric metal-clad fluororesin substrate of the present invention is a fluororesin substrate having a metal foil laminated on the surface thereof, the surface of the fluororesin substrate on which the metal foil is laminated is a hydrophilic surface having amino groups and hydroxyl groups, and is characterized in that the peel strength between the metal foil and the fluororesin substrate is 0.5 kN/m or more.

- Fluorine resin substrate -
The fluororesin substrate is not particularly limited as long as it is a substrate made of fluororesin, and may be a substrate made of fluororesin alone, but may contain a reinforcing material in the fluororesin substrate. The reinforcing material is not particularly limited in material, shape, etc., as long as it improves the mechanical strength, such as the tensile strength, of the fluororesin substrate and has excellent low dielectric properties, but silicon oxide-based reinforcing materials are preferred in consideration of the balance between the dielectric properties and strength. For example, the fluororesin substrate usable in the present invention may contain quartz glass cloth or silica powder, which has low dielectric tangent properties even at high frequencies such as millimeter waves and microwaves.

A metal foil is laminated on one or both surfaces of the fluororesin substrate. The surface of the fluororesin substrate on which the metal foil is laminated (the surface where the fluororesin substrate and the metal foil come into contact) is a hydrophilically treated surface, and this surface has amino groups and hydroxyl groups. In other words, the surface of the fluororesin substrate is a hydrophilically treated surface having amino groups and hydroxyl groups. The hydrophilically treated surface is not particularly limited as long as it has been hydrophilically treated and has amino groups and hydroxyl groups. Specifically, amino groups and hydroxyl groups are introduced onto the surface by, for example, the hydrophilic treatment described below.

In the present invention, the peel strength between the metal foil and the fluororesin substrate is 0.5 kN/m or more, and preferably 0.8 kN/m or more. If the peel strength is less than 0.5 kN/m, the peel strength between the low dielectric metal-clad fluororesin substrate and the metal foil is insufficient, and the adhesion reliability between the fluororesin substrate and the metal foil cannot be ensured.

-Fluorine resin-
Here, the term "fluororesin" refers to a polymer chain in which at least one hydrogen atom bonded to a carbon atom constituting a repeating unit is replaced with a fluorine atom or an organic group having a fluorine atom (hereinafter also referred to as a "fluorine atom-containing group"). The fluorine atom-containing group is a straight-chain or branched organic group in which at least one hydrogen atom is replaced with a fluorine atom, and examples of the fluorine atom-containing group include a fluoroalkyl group, a fluoroalkoxy group, and a fluoropolyether group.

A "fluoroalkyl group" refers to an alkyl group in which at least one hydrogen atom has been replaced with a fluorine atom, including a "perfluoroalkyl group." Specifically, a "fluoroalkyl group" includes groups in which all hydrogen atoms of an alkyl group have been replaced with fluorine atoms, groups in which all hydrogen atoms except for one hydrogen atom at the end of the alkyl group have been replaced with fluorine atoms, etc.

"Fluoroalkoxy group" means an alkoxy group in which at least one hydrogen atom is replaced with a fluorine atom, and includes "perfluoroalkoxy group". Specifically, "fluoroalkoxy group" includes groups in which all hydrogen atoms of an alkoxy group are replaced with fluorine atoms, groups in which all hydrogen atoms except for one hydrogen atom at the terminal of an alkoxy group are replaced with fluorine atoms, etc.

"Fluoropolyether group" means a monovalent group having oxyalkylene units as repeating units and having an alkyl group or a hydrogen atom at the end, in which at least one hydrogen atom of the alkylene oxide chain or the terminal alkyl group is replaced with a fluorine atom. "Fluoropolyether group" includes "perfluoropolyether groups" having multiple perfluoroalkylene oxide chains as repeating units.

Examples of fluororesins include polytetrafluoroethylene (PTFE), polytetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), chlorotrifluoroethylene-ethylene copolymer (ECTFE), polyvinyl fluoride (PVF), and thermoplastic fluororesins (THV) and fluoroelastomers made of three types of monomers: tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride. Mixtures and copolymers containing these compounds can also be used as fluororesins.

Among these, polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and polytetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA) have low dielectric tangents and are preferred fluororesins for this application.

The dielectric loss tangent of the fluororesin in the fluororesin substrate is preferably 0.0008 or less at 10 GHz.
Such fluororesins have a low dielectric tangent and are particularly suitable for use at high frequencies such as millimeter waves.

- Metal foil -
The metal foil used in the present invention is not particularly limited, and may be copper, nickel, tin, gold, silver, or an alloy thereof, but copper foil is preferably used from the viewpoints of electrical and economical aspects.

As mentioned above, in the 70 to 100 GHz wavelength band used in high-speed communications, the interface between the fluororesin surface and the copper wiring needs to be flat. On the other hand, if the interface is normally made flat, the anchor effect cannot be obtained and the adhesion reliability between the two cannot be ensured. However, in the present invention, the surface of the fluororesin substrate is a hydrophilic treated surface that has amino groups and hydroxyl groups, so the adhesion reliability between the two can be ensured even if the roughness of the metal foil is low.

Due to the skin effect, the higher the frequency of the transmission signal, such as millimeter waves, the more it propagates along the conductor surface, and the greater the roughness of the conductor (metal foil) surface, the greater the transmission loss. However, in the present invention, the roughness of the metal foil can be reduced, making it possible to suppress the transmission loss caused by the roughness of the metal foil surface. Therefore, in the present invention, the roughness (Rx) of the metal foil can be set to 0.8 μm. Note that in the present invention, the roughness (Rx) of the metal foil is a value measured in accordance with JIS-C-6481:1996.

-Quartz glass cloth-
As described above, the fluororesin substrate may contain a reinforcing material, but when the balance between the dielectric properties and strength is taken into consideration overall, the reinforcing material is preferably quartz glass cloth.
The quartz glass cloth that can be used in the present invention is, for example, a quartz glass cloth having a dielectric tangent of less than 0.0010 at 10 GHz and a tensile strength of 2.1 N/25 mm or more per cloth weight (g/ ^m2 ). The quartz glass cloth preferably has a dielectric tangent of 0.0008 or less, more preferably 0.0005 or less. The tensile strength is measured in accordance with "7.4 Tensile strength" of JIS R 3420:2013 "General test method for glass fibers".

To obtain this type of high-performance quartz glass cloth, the quartz glass is heated at high temperatures to remove the hydroxyl groups (silanol groups) present in the quartz glass, and then the distorted layer that has developed on the quartz glass surface is dissolved and removed (etched), and the quartz glass surface can be further treated with a coupling agent or the like as necessary.

This process makes it possible to reduce the dielectric tangent to the original level of quartz, which is less than 0.0010, more preferably 0.0008 or less, and even 0.0005 or less.

In the present invention, it is further preferable to treat the surface of the quartz glass cloth with a coupling agent. By coating the surface of the quartz glass cloth with a silane coupling agent in this way, the slipperiness and wettability of the glass cloth and yarn are improved, and the tensile strength of the quartz glass cloth is increased. By appropriately treating the surface, the tensile strength of the quartz glass cloth is 2.7 N/25 mm or more per cloth weight (g/m ² ), and by selecting an optimal silane coupling agent, it is 3.5 N/25 mm or more.

In particular, it is preferable to use a quartz glass cloth having a dielectric tangent of 0.0008 or less at 10 GHz and a tensile strength of 2.7 N/25 mm or more per cloth weight (g/ ^m2 ). By using such a quartz glass cloth, it is possible to obtain a metal-clad fluororesin substrate having excellent dielectric properties and strength and further excellent reliability.

As described below, when manufacturing prepregs, etc., surface treatment with a silane coupling agent can be performed to strengthen the adhesion between the fluororesin and the surface of the quartz glass cloth.

As the silane coupling agent, a known silane coupling agent can be used, but alkoxysilanes are preferred. Representative silane coupling agents include amino-based silane coupling agents such as 3-aminopropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.; product name: KBM-903), 3-aminopropyltriethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.; product name: KBE-903), N-2-(aminoethyl)-3-aminopropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.; product name: KBM-603), and N-2-(aminoethyl)-3-aminopropyltriethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.; product name: KBE-603), vinyltrimethysilane, etc. Examples of silane coupling agents that contain an unsaturated group include silane coupling agents such as vinyltriethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.; product name: KBM-1003), vinyltriethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.; product name: KBE-1003), 3-methacryloxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.; product name: KBM-503), 3-methacryloxypropyltriethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.; product name: KBE-503), and p-styryltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.; product name: KBM-1403); trifluoropropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.; product name: KBM-7103); fluorine atom-containing silane coupling agents such as glycidoxypropyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd.; trade name: KBM-403), glycidoxypropyltriethoxysilane (Shin-Etsu Chemical Co., Ltd.; trade name: KBE-403), 3-mercaptopropyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd.; trade name: KBM-803), 3-isocyanatepropyltriethoxysilane (Shin-Etsu Chemical Co., Ltd.; trade name: KBE-9007), 3-trimethoxysilylpropylsuccinic anhydride (Shin-Etsu Chemical Co., Ltd.; trade name: X-12-967C), benzotrimethoxysilane (Shin-Etsu Chemical Co., Ltd.; trade name: KBE-9007 ... One or more selected from the group consisting of functional groups other than those mentioned above, such as azo-group-containing trimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.; product name: X-12-1214A), silane coupling agents containing organic groups, or oligomers consisting of the amino-based silane coupling agents and unsaturated-group-containing silane coupling agents, are preferred, and any one of amino-based silane coupling agents, unsaturated-group-containing silane coupling agents, or oligomers consisting of amino-based silane coupling agents and unsaturated-group-containing silane coupling agents, or a combination of two or more of these, is more preferred, and amino-based silane coupling agents and unsaturated-group-containing silane coupling agents are particularly preferred.

The silane coupling agent is usually used in a dilute aqueous solution with a concentration between 0.1% and 5% by mass, but it is particularly effective to use it between 0.1% and 1% by mass. By using the quartz glass cloth of the present invention, the silane coupling agent adheres uniformly to the glass cloth surface, providing a more uniform protective effect and making it easier to handle, while also improving the tensile strength of the quartz glass cloth and enabling a uniform and consistent application to the resin used in producing the prepreg.

-Silica powder-
In the present invention, silica powder can also be used as a reinforcing material. In other words, the fluororesin substrate can further contain quartz glass cloth alone, or both quartz glass cloth and silica powder. This can provide a low-dielectric metal-clad fluororesin substrate with excellent strength, durability, and reliability.

The silica powder that can be used in the present invention is not particularly limited, but may have an average particle size of 30 μm or less, and a dielectric loss tangent of 0.0010 or less at 10 GHz, preferably less than 0.0010. More preferably, it is 0.0008 or less.

The silica powder is a low dielectric silica powder characterized in that it contains metals selected from aluminum, magnesium and titanium and/or their oxides in an amount of 200 ppm or less in terms of metal, and alkali metals and alkaline earth metals in an amount of 10 ppm or less, inside and partially or entirely on the surface.

Furthermore, silica powders in which the B content is 1 ppm or less, the P content is 1 ppm or less, and the U and Th contents are each 0.1 ppb or less can also be used as low dielectric silica powders. Like the quartz glass cloth, the silica powder used in the present invention is also heat-treated at a temperature of 500°C to 1500°C to reduce its dielectric constant, and it is further preferable that the silica powder surface is etched to reduce its dielectric constant.

In the present invention, the preferred silica powder has a hydroxyl group (Si-OH) content of 300 ppm or less; if the content is greater than this, a low dielectric tangent cannot be obtained. By the above heat treatment, the amount of hydroxyl groups contained in the silica powder becomes 300 ppm or less, preferably 280 ppm or less, and more preferably 150 ppm or less, resulting in a silica powder with low dielectric tangent characteristics.

The low dielectric silica powder used in the present invention is, for example, a silica powder with an average particle size of 0.1 to 30 μm, and preferably a maximum particle size of 100 μm or less. When used as a filler for high-speed communication boards and antenna boards, the average particle size is 0.1 to 5 μm and the maximum particle size is 20 μm, and more preferably 0.1 to 3 μm and the maximum particle size is 10 μm or less.

When silica powder is heat-treated at a temperature of 500°C or higher, a distorted layer may form on the particle surface, reducing its strength. For this reason, it is preferable to use silica powder from which this distorted layer has been removed for use in the present invention. The distorted layer of silica powder can be easily removed by immersing the silica powder in an etching solution, as with the quartz glass cloth described above.

By coating the surface of the silica powder with a silane coupling agent, it is possible to strengthen the adhesion between the resin and the glass cloth or the silica powder surface when producing prepregs.
As the silane coupling agent, the known silane coupling agents used in the above-mentioned quartz glass cloth can be used.

The amount of silica powder added is 0 to 1000 parts by mass, preferably 10 to 950 parts by mass, and more preferably 50 to 850 parts by mass, per 100 parts by mass of the total resin components. Depending on the type and application of the fluororesin, it may not be added, but adding it reduces the coefficient of thermal expansion (CTE) of the cured product and allows sufficient strength to be obtained. If it is 1000 parts by mass or less, there is no loss of flexibility during prepreg production and no poor appearance. The silica powder is preferably contained in the range of 10 to 90% by mass, and more preferably 35 to 85% by mass, of the total resin.

This silica powder is suitable as a filler for substrates such as high speed communication substrates and antenna substrates when used in combination with the above-mentioned quartz glass cloth.
The silica powder may be blended with silica powders having different average particle sizes in order to improve properties such as flowability and processability.

- Fluororesin substrate manufacturing method -
The method for producing the fluororesin substrate is not particularly limited. For example, the substrate can be produced by a conventional method using the above-mentioned fluororesin and, if necessary, a reinforcing material such as quartz glass cloth or silica powder, and other components.
When the fluororesin (matrix resin) cannot be dissolved or dispersed in a solvent, or is difficult to dissolve, a fluororesin substrate can be produced by heating and pressing a thin fluororesin film and, if necessary, a quartz glass cloth or the like (Production Method 1). When the fluororesin can be dissolved or dispersed in a solvent, a fluororesin substrate can be produced by preparing a fluororesin composition, using this to obtain a prepreg, and then pressurizing and heating the prepreg to harden it (Production Method 2). These production methods will be described below with examples.

(Production Method 1)
A fluororesin substrate can be produced by heating and pressing a thin fluororesin film and a quartz glass cloth. The fluororesin film may contain silica powder or the like in advance. For example, a fluororesin film/quartz glass cloth/fluororesin film can be laminated and pressed under heat to produce a fluororesin substrate. Thermocompression under heat is usually performed at a temperature in the range of 250 to 400°C for 1 to 20 minutes at a pressure of 0.1 to 10 MPa to produce a fluororesin substrate containing fluororesin and quartz glass cloth or silica powder.

The thermocompression temperature depends on the softening temperature of the fluororesin, but at high temperatures there is concern that the resin may bleed out or the thickness may become uneven, so in general it is preferable that the temperature is less than 340°C, and more preferably 330°C or less. Thermocompression can be performed in a batch manner using a press, or continuously using a high-temperature laminator. When using a press, it is preferable to use a vacuum press to prevent air from being trapped and to make it easier for the fluororesin to penetrate into the glass cloth.

(Production Method 2)
The fluororesin substrate can also be manufactured using an aqueous solution or dispersion (hereinafter also referred to as "dispersion, etc.") of a fluororesin such as polytetrafluoroethylene (PTFE) and a surfactant. In this case, a predetermined amount of silica powder or the like is mixed in advance with the dispersion, etc., as necessary, to form a slurry, which is then impregnated into a quartz glass cloth and dried to obtain a prepreg of the quartz glass cloth containing the fluororesin and, as necessary, the silica powder.

Since the dispersion liquid containing the fluororesin fine powder contains organic surfactants, the surfactants can be removed by heat treatment at a temperature of 350°C or higher, resulting in the low dielectric tangent characteristics of the fluororesin substrate.
The above-described manufacturing method makes it possible to prepare the fluororesin substrate, which is the starting material of the present invention.

- Hydrophilization process for fluororesin substrates -
The hydrophilic treatment of the fluororesin substrate is not particularly limited, but it is necessary that the surface of the fluororesin substrate is made into a hydrophilic treated surface having amino groups and hydroxyl groups. By such hydrophilic treatment, it is possible to make the peel strength between the metal foil and the fluororesin substrate 0.5 kN/m or more. The present inventors were the first to discover that the hydrophilic treatment improves the peel strength between the metal foil and the fluororesin substrate, i.e., the adhesion reliability.

The reason why the peel strength between the metal foil and the fluororesin substrate is improved as described above on a hydrophilic treated surface having amino groups and hydroxyl groups is believed to be due to the synergistic effect of both the amino groups and hydroxyl groups being hydrophilic and the stronger affinity between the amino groups and the metal foil than between the hydroxyl groups and the metal foil.

Examples of such treatments include hydrophilization of fluororesin such as PTFE by treating it with radio frequency low pressure non-equilibrium plasma of a mixed gas of argon, ammonia and water vapor, and treatment to hydrophilize the surface of fluororesin by irradiating it with ultraviolet laser light of wavelengths of 250 nm or less, such as an ArF excimer laser or KrF excimer laser, in the presence of an amino group and hydroxyl group source such as ammonia water (see, for example, Non-Patent Document 1).

In particular, the hydrophilization treatment of the present invention can easily generate amino groups and hydroxyl groups simultaneously on the fluororesin surface by irradiating an excimer laser to a fluororesin substrate in an atmosphere in which ammonia water coexists (ammonia water atmosphere). Here, the atmosphere in which ammonia water coexists means an environment in which both ammonia (NH ₃ ) and water (H ₂ O) exist as an atmosphere, and these may exist as liquids or gases in the atmosphere above the surface of the fluororesin substrate. In the hydrophilization treatment of the present invention, it is preferable to irradiate the laser light in an environment in which both ammonia and water exist as gases, rather than irradiating the laser light in a state in which ammonia water (liquid) is in contact with the fluororesin substrate, because this increases the degree of hydrophilization and simplifies the structure of the treatment device.
As the excimer laser, an ArF excimer laser (193 nm) or a KrF excimer laser (248 nm) can be used. However, since ammonia water has an absorption peak at about 190 nm, it is preferable to use an ArF excimer laser since hydrophilization occurs more efficiently.

In this way, amino groups and hydroxyl groups can be easily generated on the fluororesin surface by irradiating the excimer laser in an atmosphere coexisting with ammonia water, and the amount of amino groups and hydroxyl groups generated varies depending on the irradiation time of the laser light, and the amount of amino groups and hydroxyl groups generated can be increased by extending the irradiation time. As a result, the fluororesin surface becomes more hydrophilic. For example, the contact angle of the hydrophilized fluororesin substrate with pure water is preferably 100° or less, more preferably 90° or less, and even more preferably 80° or less, as measured by the sessile drop method of JIS R 3257:1999. In addition, the amount of amino groups and hydroxyl groups generated on the surface of the fluororesin substrate can be easily estimated by measuring the dielectric tangent.

The presence of amino groups and hydroxyl groups on the surface of the fluororesin substrate can be confirmed by known surface analysis methods. Examples include X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (particularly ATR-IR), static secondary ion mass spectrometry (Static-SIMS), and sum frequency generation (SPG) spectroscopy. In the present invention, the presence of amino groups and hydroxyl groups was confirmed by XPS.

<Surface treatment with primer>
In the present invention, it is preferable to further treat the hydrophilically treated surface with an alkoxysilane-containing primer.
By treating (coating) with an alkoxysilane-containing primer in this manner, the adhesive strength with the metal foil is further increased, making it possible to suitably obtain a metal-clad fluororesin substrate that is even more excellent in durability and reliability.

For example, hydrophilic treated products in which fluororesin is combined with quartz glass cloth or silica powder have a sufficiently reduced linear expansion coefficient, reduced resin seepage, and excellent adhesion and high adhesion even to metal foils such as copper with a surface roughness Ra of less than 0.2 μm. In addition, since hydrophilic treated fluororesin substrates contain amino groups and hydroxyl groups on the fluororesin surface, applying an alkoxysilane-containing primer further increases the adhesive strength with metal foils such as copper, resulting in a metal-clad fluororesin substrate with excellent durability and reliability.

- Manufacturing method for low dielectric metal-clad fluororesin substrate -
The low dielectric metal-clad fluororesin substrate of the present invention, in which a metal foil is laminated on the surface of a fluororesin substrate, is produced by hydrophilizing the surface of the fluororesin substrate by introducing amino groups and hydroxyl groups into the surface of the fluororesin substrate, and then thermocompressing the metal foil to the hydrophilically treated surface at a temperature equal to or higher than the melting temperature of the fluororesin in the fluororesin substrate, thereby making the peel strength between the metal foil and the fluororesin substrate 0.5 kN/m or more.
As described above, a fluororesin substrate is produced and subjected to hydrophilization treatment and the like. Then, the metal foil is thermocompression-bonded to the hydrophilized surface at a temperature equal to or higher than the melting temperature of the fluororesin in the fluororesin substrate to form a low dielectric metal-clad fluororesin substrate.

The composition of the low dielectric metal-clad fluororesin substrate (laminate substrate) is not particularly limited, but for example, when it is made of fluororesin and quartz glass cloth alternately laminated between two sheets of metal foil such as copper, the number of laminated sheets is preferably 8 or less, more preferably 6 or less. The linear expansion coefficient of the fluororesin substrate in the X-Y direction can be changed by changing the fluororesin content in the fluororesin substrate, the type of quartz glass cloth, the silica powder content, and the number of laminated sheets, but the value of the linear expansion coefficient is preferably in the range of 5 to 50 ppm/°C, more preferably in the range of 10 to 40 ppm/°C. If the linear expansion coefficient of the fluororesin substrate is 50 ppm/°C or less, the adhesion between the copper foil and the fluororesin substrate is sufficient, and defects such as warping or waving of the substrate do not occur after copper foil etching.

A printed wiring board can be obtained by processing the low dielectric metal-clad fluororesin substrate of the present invention using commonly used methods such as subtractive processing or drilling. The electrode pattern of the laminated substrate can be prepared by a known method, for example, by etching a metal-clad laminated substrate having the low dielectric metal-clad fluororesin substrate of the present invention and a metal foil such as copper provided on one or both sides of the laminated substrate.

The low-dielectric metal-clad fluororesin substrate of the present invention is a substrate that has excellent adhesion between the fluororesin and metal foil such as copper, i.e., excellent peel strength, and also has low dielectric constant and low dielectric loss tangent properties that provide excellent transmission characteristics for high-frequency signals such as millimeter waves.

Therefore, it is ideal for use in boards that require high reliability, such as mounting boards and antenna boards that transmit signals in areas related to safety, such as autonomous driving and remote medical treatment, which use high frequencies of 70 GHz or more.

The present invention will be specifically described below with reference to examples, comparative examples, and preparation examples, but the present invention is not limited to the following examples.
The following measurements of the dielectric loss tangent (10 GHz), peel strength, pure water contact angle, and copper foil roughness, and the analysis of the hydrophilized fluororesin substrate surface were carried out by the following methods.

1. Measurement of Dielectric Tangent Unless otherwise specified, a network analyzer (E5063A manufactured by Keysight Technologies) was connected to an SPDR dielectric resonator (manufactured by Keysight Technologies) to measure the dielectric tangent at 10 GHz.
2. Measurement of peel strength The measurement was performed in accordance with JIS C 6481:1996.
3. Measurement of contact angle with pure water Measurement was performed in accordance with JIS R 3257:1999.
4. Copper foil roughness (Rx)
Measurement was performed in accordance with JIS C 6481:1996.
5. Analysis of the Hydrophilized Fluororesin Substrate Surface It was confirmed by X-ray photoelectron spectroscopy (XPS) that the hydrophilized fluororesin substrate surface had amino groups and hydroxyl groups.
6. Measurement of tensile strength The measurement was performed in accordance with "7.4 Tensile strength" of JIS R 3420:2013 "General test method for glass fibers".

(Preparation Example 1) Example of manufacturing quartz glass cloth A quartz glass strand consisting of 200 quartz glass filaments with a diameter of 5.0 μm was produced by applying a sizing agent to a quartz glass thread while drawing it at a high temperature. Next, the obtained quartz glass strand was twisted 0.4 times per 25 mm to produce a quartz glass yarn.
The obtained quartz glass yarn was set in an air jet loom to weave a plain weave quartz glass cloth with a warp density of 54 threads/25 mm and a weft density of 54 threads/25 mm. The quartz glass cloth had a thickness of 0.045 mm and a cloth weight of 42.5 g/ ^m2 .
The quartz glass cloth was heat-treated at 400° C. for 10 hours to remove the fiber sizing agent, and a quartz glass cloth having a width of 1.3 m and a length of 2,000 m was produced. Next, the quartz glass cloth having a width of 1.3 m and a length of 2,000 m produced above was placed in an electric furnace set at 700° C. and heated for 5 hours. After heating, it was cooled to room temperature over 8 hours.
The cooled quartz glass cloth was then immersed in alkaline electrolytic water of pH 13 heated to 40° C. for 48 hours for etching. After etching, the cloth was washed with ion-exchanged water and dried to produce a low-dielectric, high-strength quartz glass cloth.
The heated and etched quartz glass cloth was then immersed in a 0.5% by mass aqueous solution of KBM-903 (product name: 3-aminopropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.) for 10 minutes, and then heated and dried for 20 minutes at 110°C for surface treatment. The dielectric tangent of this quartz glass cloth was 0.0002, and the tensile strength was 120 N/25 mm, with a value of 2.82 N/25 mm per cloth weight (g/ ^m2 ).

(Preparation Example 2) Preparation Example of Low Dielectric Silica Powder 5 kg of silica (SO-E5 manufactured by Admatechs Co., Ltd.) with an average particle size of 1.5 μm and a dielectric loss tangent of 0.0011 (10 GHz) was placed in an alumina container, heated in a muffle furnace (manufactured by AS ONE Co., Ltd.) in air at 900° C. for 12 hours, and then cooled to room temperature over 6 hours to obtain silica. The silica after the heat treatment was placed in a plastic container containing 20 liters of alkaline electrolytic water with a pH of 13 and stirred for 2 hours while heating to 60° C. to remove the strained layer on the silica powder surface. After that, the silica was separated using a centrifugal separator, washed with methanol and dried. The dried silica was crushed in a ball mill, and the resulting silica had a dielectric loss tangent of 0.0002 (10 GHz). The low dielectric silica powder obtained here was surface-treated with a silane coupling agent, KBM-503 (manufactured by Shin-Etsu Chemical Co., Ltd., 3-methacryloxypropyltrimethoxysilane), and used to manufacture a fluororesin substrate.

(Preparation Example 3) Fluorine resin substrate (1)
Polytetraethylene fine particle aqueous dispersion (PTFE aqueous dispersion) consisting of 60 mass% polytetrafluoroethylene (PTFE) fine particles with a dielectric loss tangent of 0.0002 at 10 GHz, 6 mass% nonionic surfactant, and 34 mass% water was adjusted to an adhesion amount of 46 mass% on the quartz glass cloth shown in Preparation Example 1, impregnated and applied, and then dried for 10 minutes in a drying oven at 100°C to remove moisture. Next, the prepared prepreg was molded for 5 minutes at 380°C and 1.5 MPa in a vacuum decompression press. It was further left for 5 minutes in a dryer at 380°C to prepare a fluororesin substrate (1).
The fluororesin substrate (1) had no molding defects and was a good fluororesin substrate. The dielectric loss tangent at 10 GHz was 0.0002, which was an excellent dielectric property.

(Preparation Example 4) Fluorine resin substrate (2)
Two sheets of 50 μm-thick tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) films (manufactured by Daikin, dielectric dissipation factor: 0.0008) and one sheet of the quartz glass cloth shown in Preparation Example 1 were prepared, and the PFA film/quartz glass cloth/PFA film were laminated in this order, and the laminate was hot-pressed for 30 minutes at 325° C. and 1.5 MPa using a vacuum pressure press to produce a fluororesin substrate (2) made of fluororesin.
The fluororesin substrate (2) had no molding defects and was a good fluororesin substrate. The dielectric loss tangent at 10 GHz was 0.0005, which was an excellent dielectric property.

(Preparation Example 5) Silica-containing fluororesin substrate (3)
40 parts by mass of the low dielectric silica powder prepared in Preparation Example 2 was added to 100 parts by mass of the PTFE aqueous dispersion of Preparation Example 3 to prepare a silica-containing PTFE dispersion. The dispersion was adjusted to an adhesion amount of 46% by mass on the quartz glass cloth shown in Preparation Example 1, impregnated and applied, and then dried for 10 minutes in a drying oven at 100°C to remove moisture. The prepared prepreg was then molded for 5 minutes at 380°C and 1.5 MPa in a vacuum decompression press. It was then left for 5 minutes in a dryer at 380°C to prepare a fluororesin substrate (3).
The fluororesin substrate (3) had no molding defects, a small thermal expansion coefficient, and high strength. The dielectric loss tangent at 10 GHz was 0.0003, which was an excellent dielectric property.

Preparation Example 6 Preparation Example of Primer Composition 1 Primer composition 1 was prepared by dissolving and mixing 1 part by mass of 3-aminopropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.; product name: KBM-903), 1 part by mass of 3-mercaptopropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.; product name: KBM-803), and 0.5 parts by mass of tetra-n-butoxytitanium in 97.5 parts by mass of n-hexane.

Preparation Example 7 Preparation Example of Primer Composition 2 Primer composition 2 was prepared by dissolving and mixing 2 parts by mass of benzotriazole group-containing trimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.; product name: X-12-1214A) in 98.0 parts by mass of n-hexane.

<Preparation of copper-clad fluororesin substrate>
(Examples 1 to 3, Comparative Example 1)
A container containing about 20 ml of 28-30% aqueous ammonia solution was placed in the irradiation area of an excimer irradiation device (MEIRA-M-1-152-H3 manufactured by M.D.COM Co., Ltd.) and a 10 cm square fluororesin substrate (1) was placed in a position in the container that did not touch the ammonia water. The irradiation area was sealed and irradiated with an excimer laser (wavelength: 172 nm, illuminance: 80 mW/cm ² ) for different times of 2 minutes, 5 minutes, and 10 minutes as shown in Table 1 to produce fluororesin substrates F11, F21, and F31 with hydrophilic surfaces. The fluororesin substrate that was not irradiated with the excimer laser and had a non-hydrophilic surface was designated F01. After irradiation, the fluororesin substrate was removed, the surface was washed with pure water, and dried at room temperature, and the contact angle with pure water was measured by the sessile drop method of JIS-R-3257:1999. It was confirmed by XPS that the surfaces of the hydrophilically treated fluororesin substrates F11, F21, and F31 had amino groups and hydroxyl groups.
Furthermore, using the substrates F01, F11, F21, and F31, low-roughness copper foil (roughness (Rx): 1.5 μm, thickness: 35 μm) was laminated on one side, and then hot-pressed for 30 minutes at 325° C. and 1.5 MPa using a vacuum pressure press to laminate the copper foil onto the fluororesin substrate, thereby producing copper-clad fluororesin substrates.
The copper foil was laminated at 325° C., and the dielectric loss tangent was measured at 10 GHz using the surface that had been removed by etching the copper foil from the fluororesin substrate, washed with pure water, and dried.
To measure the peel strength between the copper foil of a copper-clad fluororesin substrate and the fluororesin substrate, the copper foil was etched to a width of 1 cm and a length of 5 cm to prepare a test piece for measuring peel strength.
The measurement was performed by 90° peel measurement, and the results are shown in Table 1.

＊１ 銅箔積層後の誘電正接

*1 Dielectric tangent after copper foil lamination

As is clear from Table 1, the water contact angle is reduced by the hydrophilic treatment, and the longer the hydrophilic treatment time, the smaller the water contact angle becomes. In other words, the amount of amino groups and hydroxyl groups generated varies depending on the laser light irradiation time, and the amount of amino groups and hydroxyl groups generated can be increased by extending the irradiation time. As a result, the fluororesin surface becomes more hydrophilic.
Furthermore, the dielectric loss tangent tends to increase as the amount of polar groups, such as amino groups and hydroxyl groups, introduced increases. Therefore, the amount of amino groups and hydroxyl groups generated on the surface of the fluororesin substrate can be easily estimated by measuring the dielectric loss tangent.
Furthermore, the peel strength from the copper foil in Examples 1 to 3, in which the surface of the fluororesin substrate was a hydrophilically treated surface having amino groups and hydroxyl groups, was superior to that of Comparative Example 1, in which no hydrophilic treatment was performed (i.e., the surface of the fluororesin substrate did not have amino groups or hydroxyl groups).

(Examples 4 to 5, Comparative Examples 2 to 3)
A container containing 20 ml of 28-30% aqueous ammonia was placed in the irradiation area of an excimer irradiation device (manufactured by M.D.COM Co., Ltd.), and the 10 cm square fluororesin substrates (2) and (3) prepared in Preparation Examples 4 and 5 were placed in a position in the container that did not touch the ammonia water. The irradiation area was sealed and irradiated with an excimer laser (wavelength: 172 nm, illuminance: 80 mW/cm ² ) for 5 minutes to prepare fluororesin substrates F22 and F32 with hydrophilic surfaces. Note that fluororesin substrates without hydrophilic surfaces were designated F02 and F03. After irradiation, the fluororesin substrates were taken out, the surfaces were washed with pure water, and dried at room temperature, and the contact angle with pure water was measured by the sessile drop method of JIS-R-3257:1999. It was confirmed by XPS that the surfaces of the hydrophilic fluororesin substrates F22 and F32 had amino groups and hydroxyl groups.

Furthermore, low-roughness copper foil (roughness (Rx): 1.5 μm, thickness: 35 μm) was laminated on one side of the substrates F02, F03, F22, and F32, and then hot-pressed for 30 minutes at 325° C. and 1.5 MPa using a vacuum pressure press to prepare copper-clad fluororesin substrates in which copper foil was laminated on a fluororesin substrate.
The dielectric loss tangent after laminating the copper foil at 325° C. was also measured at 10 GHz using the surface that had been cleaned with pure water and dried after removing the copper foil from the fluororesin substrate by etching.
To measure the peel strength between the copper foil of a copper-clad fluororesin substrate and the fluororesin substrate, the copper foil was etched to a width of 1 cm and a length of 5 cm to prepare a test piece for measuring peel strength.
The measurement was performed by 90° peel measurement, and the results are shown in Table 2.

＊１ 銅箔積層後の誘電正接

*1 Dielectric tangent after copper foil lamination

As is clear from Tables 1 and 2, the water contact angle is reduced by the hydrophilic treatment, and the peel strength from the copper foil in Examples 1 to 5, in which the surface of the fluororesin substrate is a hydrophilic treated surface having amino groups and hydroxyl groups, is superior to that of Comparative Examples 1 to 3, in which no hydrophilic treatment is performed (i.e., the surface of the fluororesin substrate does not have amino groups or hydroxyl groups). Thus, without the hydrophilic treatment, the peel strength from the copper foil is weak, and the substrate lacks reliability as a low-dielectric substrate for high-speed communication for millimeter waves. In particular, in the present invention, even if a low-roughness metal foil is used, a metal-clad fluororesin substrate with sufficient adhesion can be produced by simply thermocompression bonding without the use of an adhesive such as an adhesive sheet, and the entire substrate can be made thin, making it highly useful as a high-speed communication low-dielectric substrate for millimeter waves, etc.

<Effects of primer treatment>
Example 6
The primer composition 1 prepared in Preparation Example 6 was applied to the surface of the fluororesin substrate F11 with a hydrophilic surface prepared in Example 1. The primer-treated fluororesin substrate was then air-dried at 25° C. for 30 minutes to remove the solvent, producing a primer-treated fluororesin substrate. A copper-clad fluororesin substrate was produced using this primer-treated fluororesin substrate in the same manner as in Example 1. The dielectric loss tangent (10 GHz) measured in the same manner as in Example 1 was 0.0003, and the peel strength from the copper foil was 1.0 kN/m.

(Example 7)
In the same manner as in Example 1, the primer composition 2 prepared in Preparation Example 7 was applied to the surface of the fluororesin substrate F11 with hydrophilic surface prepared in Example 1 and the surface of the copper foil. The primer-treated copper foil was then air-dried at 25° C. for 30 minutes to remove the solvent, thereby preparing a primer-treated copper foil. A copper-clad fluororesin substrate was prepared in the same manner as in Example 1 using this primer-treated copper foil. The dielectric loss tangent (10 GHz) measured in the same manner as in Example 1 was 0.0003, and the peel strength from the copper foil was 1.2 kN/m.

As is clear from Examples 1, 6, and 7, the peel strength from the copper foil is improved by further treating at least one of the surfaces of the hydrophilized fluororesin substrate and the copper foil with a primer.

The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included within the technical scope of the present invention.

Claims (16)

A low dielectric metal-clad fluororesin substrate in which a metal foil is laminated on the surface of a fluororesin substrate,
the fluororesin substrate contains either a quartz glass cloth alone having a dielectric loss tangent measured at 10 GHz of less than 0.0010, or both the quartz glass cloth and silica powder having a dielectric loss tangent measured at 10 GHz of less than 0.0010;
A low dielectric metal-clad fluororesin substrate, characterized in that the surface of the fluororesin substrate is a hydrophilically treated surface having an amino group and a hydroxyl group, and the peel strength between the metal foil and the fluororesin substrate is 0.5 kN/m or more. The low dielectric metal-clad fluororesin substrate according to claim 1, characterized in that the contact angle of the surface of the fluororesin substrate with pure water is 100° or less. 3. The low dielectric metal-clad fluororesin substrate according to claim 1 , wherein the quartz glass cloth has a tensile strength of at least 2.1 N/25 mm per cloth weight (g/m ² ). 4. The low dielectric metal-clad fluororesin substrate according to claim 1 , wherein the quartz glass cloth is surface-treated with a silane coupling agent. 5. The low dielectric metal-clad fluororesin substrate according to claim 4, wherein the quartz glass cloth has a dielectric loss tangent of 0.0008 or less at 10 GHz and a tensile strength of 2.7 N/25 mm or more per cloth weight (g/m ² ). The low dielectric metal-clad fluororesin substrate according to claim 4 or 5, characterized in that the silane coupling agent is any one of an amino-based silane coupling agent, an unsaturated group-containing silane coupling agent, and an oligomer consisting of an amino-based silane coupling agent and an unsaturated group - containing silane coupling agent, or a combination of two or more of these. 7. The low dielectric metal-clad fluororesin substrate according to claim 1, wherein the dielectric loss tangent of the fluororesin in the fluororesin substrate is 0.0008 or less at 10 GHz. A method for manufacturing a low dielectric metal-clad fluororesin substrate in which a metal foil is laminated on a surface of a fluororesin substrate, comprising the steps of:
The fluororesin substrate includes a quartz glass cloth having a dielectric loss tangent of less than 0.0010 measured at 10 GHz, or includes both the quartz glass cloth and silica powder having a dielectric loss tangent of less than 0.0010 measured at 10 GHz;
A method for producing a low dielectric metal-clad fluororesin substrate, comprising: introducing an amino group and a hydroxyl group into a surface of the fluororesin substrate to hydrophilize the surface of the fluororesin substrate; and thermocompression bonding the metal foil to the hydrophilically treated surface at a temperature equal to or higher than the melting temperature of the fluororesin in the fluororesin substrate, thereby setting the peel strength between the metal foil and the fluororesin substrate to 0.5 kN/m or more. 9. The method for producing a low dielectric metal-clad fluororesin substrate according to claim 8 , characterized in that in the hydrophilization treatment, an amino group and a hydroxyl group are introduced into the surface of the fluororesin substrate by irradiating the fluororesin substrate with an excimer laser in an atmosphere containing ammonia water. 10. The method for producing a low dielectric metal-clad fluororesin substrate according to claim 8 , wherein in the hydrophilization treatment, the contact angle of the surface of the fluororesin substrate with pure water is set to 100[deg.] or less. 11. The method for manufacturing a low dielectric metal-clad fluororesin substrate according to claim 8, wherein the quartz glass cloth has a tensile strength of 2.1 N/25 mm or more per cloth weight (g/ ^m2 ). 12. The method for producing a low dielectric metal-clad fluororesin substrate according to claim 8 , wherein the quartz glass cloth is a quartz glass cloth whose surface has been treated with a silane coupling agent. The method for manufacturing a low dielectric metal-clad fluororesin substrate according to claim 12, characterized in that the quartz glass cloth used has a dielectric tangent of 0.0008 or less at 10 GHz and a tensile strength of 2.7 N/25 mm or more per cloth weight (g/ ^m2 ). The method for producing a low dielectric metal-clad fluororesin substrate according to claim 12 or 13, characterized in that the silane coupling agent is any one of an amino-based silane coupling agent, an unsaturated group-containing silane coupling agent, and an oligomer consisting of an amino-based silane coupling agent and an unsaturated group - containing silane coupling agent, or a combination of two or more of these. 15. The method for producing a low dielectric metal-clad fluororesin substrate according to claim 8, wherein a fluororesin substrate containing a fluororesin having a dielectric loss tangent of 0.0008 or less at 10 GHz is used as the fluororesin substrate. 16. The method for producing a low dielectric metal-clad fluororesin substrate according to claim 8 , further comprising treating the hydrophilically treated surface with an alkoxysilane-containing primer.