Glass cloth, prepreg and printed circuit board

Abstract

The purpose of this application is to provide a quartz glass cloth composed of glass yarn with a high silica (SiO2) content, which can improve the insulation reliability of laminates, as well as prepregs and printed circuit boards containing the same. According to this application, a glass cloth composed of glass yarn containing multiple filaments as warp and weft yarns can be provided. The silicon (Si) content in the glass yarn, converted from silica (SiO2), is 95.0% to 100% by mass, and the average single filament diameter (D) of the filaments is in the range of 4.5 μm to 9.0 μm. The relationship between the thickness (T) of the glass cloth and the average single filament diameter (D) of the filaments satisfies the following formula: 24.0 × D - T > 96.0. Furthermore, the product of the thickness and air permeability of the glass cloth (μm·cm) is... 3 / cm 2 The range of / s is 2500 to 6000.

Description

Technical Field

[0001] This application relates to glass cloth, prepregs, and printed circuit boards, etc. This international application claims priority to Japanese Patent Application No. 2023-023775, filed on February 17, 2023, the entire contents of which are incorporated herein by reference. Background Technology

[0002] Currently, the high performance of information terminals such as smartphones and the high-speed communication represented by 5G are developing. Against this backdrop, especially for printed circuit boards (PCBs) used in high-speed communication, there is a desire not only to improve the long-sought-after heat resistance, but also to further improve the dielectric properties of the insulating materials (e.g., lower dielectric loss tangent). Similarly, there is a desire to improve the dielectric properties of the prepregs used in the insulating materials of PCBs, the glass cloth contained in the prepregs, and the glass yarns constituting the glass cloth.

[0003] Patent documents 1 and 2 describe how, for the purpose of reducing the dielectric properties of insulating materials, a prepreg made by impregnating glass cloth with a low-dielectric resin is used as the matrix resin to construct the insulating material. Patent documents 1 and 2 also describe how polyphenylene ethers with end-modified vinyl or methacryloyloxy groups are advantageous in terms of low dielectric properties and heat resistance, and how such modified polyphenylene ethers are used as the matrix resin.

[0004] Patent document 3 describes how the dielectric properties of prepreg and printed circuit boards are improved by using glass cloth with a SiO2 content of 98% to 100% by mass.

[0005] For printed circuit boards (PCBs), in addition to dielectric properties, insulation reliability is also required. Various methods are known to suppress one mode of insulation failure in PCBs: the formation of conductive anodic filaments (CAFs). For example, Patent Document 4 describes a method for improving the insulation reliability of PCBs by removing alkali metal and alkaline earth metal compounds from the surface of glass cloth. Furthermore, Patent Document 5 describes a method for suppressing CAF formation by reducing the aggregation of modified phenol compounds and smoothing the inner walls of vias.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: International Publication No. 2019 / 065940

[0009] Patent Document 2: International Publication No. 2019 / 065941

[0010] Patent Document 3: Japanese Patent Application Publication No. 2021-63320

[0011] Patent Document 4: Japanese Patent Application Publication No. 2005-42245

[0012] Patent Document 5: Japanese Patent Application Publication No. 2006-63114 Summary of the Invention

[0013] The problem the invention aims to solve

[0014] According to the research results of the inventors, when using quartz glass with a high silica (SiO2) content, the conventional glass cloth described in Patent Documents 1 to 4 has room for further improvement in the insulation reliability of the resulting laminate.

[0015] The purpose of this application is to provide a quartz glass cloth composed of glass yarn with a high silica (SiO2) content, which can improve the insulation reliability of the laminate, as well as prepregs and printed circuit boards containing the same.

[0016] Solution for solving the problem

[0017] Some aspects of this application are illustrated in the following items[1] to

[17] .

[0018] [1] A glass cloth is made of glass yarn containing multiple filaments as warp and weft yarns, wherein the silicon (Si) content in the glass yarn is 95.0% to 100% by mass (based on silicon dioxide (SiO2) conversion), the average monofilament diameter (D) of the filaments is in the range of 4.5 μm to 9.0 μm, and the relationship between the thickness (T) of the glass cloth and the average monofilament diameter (D) of the filaments satisfies the following formula (A1).

[0019] 24.0 × DT > 96.0…(A1)

[0020] The product of the thickness and air permeability of the above-mentioned glass cloth (μm·cm) 3 / cm 2 The range of / s is 2500 to 6000.

[0021] [2] According to the glass cloth of Project 1, when the glass cloth is immersed in a cleaning solution and heated at 80°C for 2 hours, the cleaning reduction rate of the average monofilament diameter (D) of the filaments expressed by the following formula is 25% or less.

[0022] Stain reduction rate = (monofilament diameter before stain removal - monofilament diameter after stain removal) ÷ ​​monofilament diameter before stain removal × 100

[0023] [3] The glass cloth according to item 1 or 2, wherein the air permeability of the glass cloth is 25cm. 3 / cm 2 / s~350cm 3 / cm 2 The range of / s.

[0024] [4] The glass cloth according to any one of items 1 to 3, wherein the glass yarn is surface treated with a surface treatment agent.

[0025] [5] The glass cloth according to item 4, wherein the surface treatment agent comprises a silane coupling agent having the structure shown in the following general formula (1).

[0026] X(R) 3-n SiY n …(1)

[0027] {In formula (1), X is an organic group having one or more unsaturated double bond groups with free radical reactivity, Y is each independently an alkoxy group, n is an integer from 1 to 3, and R is each independently at least one group selected from the group consisting of methyl, ethyl, and phenyl.}

[0028] [6] The glass cloth according to item 5, wherein X in the above general formula (1) has (meth)acryloyloxy group.

[0029] [7] The glass cloth according to any one of items 1 to 6, wherein the loss on ignition of the glass cloth is in the range of 0.01% to 0.50% by mass.

[0030] [8] The glass cloth according to any one of items 1 to 7, wherein the average number of filaments of the glass yarn is in the range of 20 to 200.

[0031] [9] The glass cloth according to any one of items 1 to 8, wherein the coefficient of variation of the total carbon content obtained by gas chromatography of the glass cloth is in the range of 15% or less.

[0032]

[10] The glass cloth according to any one of items 1 to 9, wherein the nitrogen content of the glass cloth obtained by gas chromatography is less than 0.004% by mass.

[0033]

[11] A prepreg containing glass cloth as described in any one of items 1 to 10, and a matrix resin impregnated into the glass cloth.

[0034]

[12] The prepreg according to item 11 also contains an inorganic filler.

[0035]

[13] A printed circuit board comprising the prepreg described in item 11.

[0036]

[14] An integrated circuit comprising the printed circuit board described in item 13.

[0037]

[15] An electronic device comprising the printed circuit board described in item 13.

[0038]

[16] A method for manufacturing glass cloth, wherein the method includes:

[0039] The process of weaving glass yarn, which contains multiple long filaments and has a Si content ranging from 95.0% to 100% by mass (calculated as SiO2), as both warp and weft yarns to obtain glass cloth, is as follows:

[0040] The above method, prior to the weaving process, further includes flattening the glass yarn bundles, followed by a sizing and warping process.

[0041] After the aforementioned warping process and before, during, or after the aforementioned weaving process, the following processes are also included:

[0042] The process of cleaning the glass yarn using water at a temperature of 50°C or higher;

[0043] The process of reducing the amount of adhesive adhering to the aforementioned glass yarn by heating and degreasing; and

[0044] The glass yarn, which has undergone the above-mentioned heating and degreasing process, is subjected to ultrasonic waves in a liquid to split at least a portion of the glass filaments that are bonded together by the residue of the binder after heating and degreasing.

[0045] The average monofilament diameter (D) of the aforementioned filaments ranges from 4.5 μm to 9.0 μm, and the relationship between the thickness (T) of the aforementioned glass cloth and the average monofilament diameter (D) of the aforementioned filaments satisfies the following equation (A1):

[0046] 24.0×DT>96.0…(A1).

[0047]

[17] The method according to item 16 further includes:

[0048] The surface treatment process involves multiple operations as follows: applying a surface treatment agent to the surface of the fiber-opened glass cloth, and fixing the surface treatment agent to the surface of the glass cloth by heating and drying; and

[0049] A fiber-opening process is performed on at least a portion of the glass filaments bonded by the surface treatment agent.

[0050] The effects of the invention

[0051] According to this application, quartz glass cloth composed of glass yarn with high silica (SiO2) content, which can improve the insulation reliability of laminates, as well as prepregs and printed circuit boards containing it, can be provided. Detailed Implementation

[0052] The following describes the implementation of this application, but this application is not limited thereto and various modifications can be made without departing from its spirit.

[0053] In this application, the numerical range recorded using "~" indicates a range of values ​​including the values ​​before and after "~" as both lower and upper limits. Furthermore, within a range of values ​​recorded in stages, the upper or lower limit of a certain numerical range can be replaced by the upper or lower limit of other numerical ranges recorded in stages. Moreover, the upper or lower limit of a certain numerical range can also be replaced by the values ​​shown in the embodiments. Furthermore, the term "process" not only includes independent processes, but also includes processes that achieve their function, even when they cannot be clearly distinguished from other processes.

[0054] Glass cloth

[0055] The glass cloth of this application comprises glass yarn containing multiple filaments as warp and weft yarns. The silicon (Si) content in the glass yarn, calculated as silicon dioxide (SiO2), is 95.0% by mass or more and 100% by mass or less, and the average single filament diameter (D) of the filaments is in the range of 4.5 μm or more and 9.0 μm or less. The relationship between the thickness (T) of the glass cloth and the average single filament diameter (D) of the filaments satisfies the following formula (A1).

[0056] 24.0 × DT > 96.0…(A1)

[0057] In addition, the thickness (μm) and air permeability (cm) of the glass cloth... 3 / cm 2 The product of ( / s) is 2500~6000 (μm·(cm)). 3 / cm 2 The range of / s)).

[0058] The conventional glass cloths described in Patent Documents 1 and 2 did not take into account the use of low-dielectric glass, leaving room for further improvement in dielectric properties. Regarding this, Patent Document 3 describes improving the dielectric properties of prepregs and printed wiring substrates by using glass cloth formed from glass filaments with a high SiO2 content. However, research results from the inventors of this application indicate that there is room for further improvement in the insulation reliability of printed wiring substrates.

[0059] As an improvement to glass cloth aimed at enhancing insulation reliability (hereinafter also referred to as "CAF resistance"), improvements to the fiber-opening process of the glass cloth can be cited, as described in Patent Document 4. However, research results from the inventors of this application indicate that quartz glass has a higher hardness than other types of glass. Therefore, when using glass cloth made of quartz glass yarn, the conventional fiber-opening process described in Patent Document 4 is insufficient to adequately improve CAF resistance.

[0060] In contrast, according to this application, a quartz glass cloth capable of improving the insulation reliability of a laminate, as well as prepregs and printed circuit boards containing the cloth, can be provided. There are no limitations on the theory or specific manufacturing method. By using quartz glass with an average filament diameter (D) satisfying a specified relationship with respect to the thickness (T) of the glass cloth as the glass yarn, eliminating adhesion between the filaments of the glass yarn caused by adhesive residue, and performing a process that results in a higher fiber opening compared to conventional methods, the product of the glass cloth's thickness and air permeability can be adjusted to a specified range. Furthermore, by ensuring that the product of the thickness and air permeability of the glass cloth using quartz glass with an average filament diameter (D) satisfying a specified relationship with respect to the thickness (T) of the glass cloth is within a specified range, a glass cloth with excellent CAF resistance can be provided, as detailed below.

[0061] [Glass yarn]

[0062] The glass yarn constituting the glass cloth can be obtained from quartz glass. Specifically, the Si content in the glass yarn, converted from SiO2, is in the range of 95.0% to 100% by mass, preferably 99.0% to 100% by mass, more preferably 99.5% to 100% by mass, and particularly preferably 99.9% to 100% by mass. By using this glass yarn, the dielectric properties and CAF resistance of the resulting glass cloth can be improved.

[0063] The average monofilament diameter of the glass filaments constituting the glass cloth is 4.5 μm to 9.0 μm. More preferably, it is 5.0 μm to 9.0 μm, even more preferably, it is 5.5 μm to 8.5 μm, even more preferably, it is 5.8 μm to 8.2 μm, and particularly preferably, it is 6.0 μm to 8.0 μm. If the average monofilament diameter is above the lower limit mentioned above, the breaking strength of the filaments is improved, thus suppressing fuzzing of the resulting glass cloth. If the average monofilament diameter is below the upper limit mentioned above, the glass cloth is less prone to breakage (fracture) due to bending deformation, thus improving the mass production of the glass cloth. If the average monofilament diameter of the glass filaments is within the above range, it is easy to adjust the product of thickness and air permeability and the stain reduction rate to the specified range, thereby achieving the effect of improved CAF resistance.

[0064] The average number of glass filaments constituting the glass yarn is preferably in the range of 20 to 200. The upper limit of the average number of filaments is more preferably 180 or less, even more preferably 160 or less, and particularly preferably 150, 140, 130, 120, 110, or 100 or less. The lower limit, any combination of these upper limits, is more preferably 30 or more, more preferably 35 or more, and particularly preferably 40 or more or 45 or more. If the average number of filaments is above the aforementioned lower limit, the glass yarn is less prone to breakage, and the resulting glass cloth is less prone to pilling. If the average number of filaments is below the aforementioned upper limit, adhesion between filaments caused by adhesive residue is easily eliminated, and the glass yarn is easily opened. Detergent is less likely to penetrate into the glass yarn bundle, thus easily obtaining a glass cloth with excellent CAF resistance. Therefore, if the average number of filaments is within the above range, CAF resistance is easily achieved.

[0065] [Weaving structure, etc.]

[0066] Glass cloth is constructed using glass yarn (e.g., glass yarn formed from multiple glass filaments) as both warp and weft yarns. Examples of weaving structures for glass cloth include plain weave, square weave, satin weave, and twill weave. Plain weave is preferred.

[0067] The drive density of the warp and weft yarns constituting the glass cloth is preferably 10 yarns / inch to 120 yarns / inch (= 10 to 120 yarns / 25.4 mm), and more preferably 40 yarns / inch to 100 yarns / inch. If the drive density is within the above range, it is easy to adjust the product of thickness and air permeability to the specified range, and it is easy to obtain the effect of CAF resistance.

[0068] The preferred unit area weight (mass of the glass cloth) is 8 g / m². 2 ~250g / m 2 More preferably 8g / m 2 ~100g / m 2 Further preferred is 8g / m 2 ~80g / m 2 The preferred value is 8g / m 2 ~50g / m 2 If the weight per unit area of ​​the glass cloth is within the above range, it is easy to adjust the product of thickness and air permeability and the stain reduction rate to the specified range, and it is easy to obtain the effect of CAF resistance.

[0069] [Surface treatment agent]

[0070] From the viewpoint of improving adhesion to the resin used in the prepreg, the glass yarn of the glass cloth is preferably surface-treated with a surface treatment agent. It should be noted that in this application, both surface treatment of the glass filaments during the manufacturing process of the glass cloth and surface treatment of the glass cloth itself are included within the concept of "the glass yarn being surface-treated with a surface treatment agent." The glass yarn can be surface-treated using, for example, titanate-based coupling agents or silane coupling agents. From the viewpoint of easily modifying each resin of the prepreg with suitable functional groups, the surface treatment agent preferably contains a silane coupling agent.

[0071] The silane coupling agent preferably has the structure shown in the following general formula (1).

[0072] X(R) 3-n SiY n …(1)

[0073] {In formula (1), X is an organic group having one or more unsaturated double bonds with free radical reactivity, Y is each independently an alkoxy group, n is an integer from 1 to 3, and R is each independently a group selected from the group consisting of methyl, ethyl, and phenyl.}

[0074] By using a silane coupling agent of general formula (1) to treat the surface of glass cloth, there is a tendency to improve the insulation reliability and heat resistance of printed circuit boards.

[0075] In the molecular structure of the silane coupling agent of general formula (1), X preferably has a (meth)acryloyloxy group. X is more preferably an amino-free (meth)acryloyloxy group. Silane coupling agents containing amino components in extremely small amounts or without amino components have high hydrophobicity. By using such a highly hydrophobic silane coupling agent to surface treat the glass cloth used as quartz glass, peeling at the interface between the resulting glass cloth and the matrix resin can be suppressed, thereby improving CAF resistance. As a method for evaluating whether a silane coupling agent contains amino components, there are no particular limitations, but the method of using gas chromatography is known. By using gas chromatography to determine the amount of nitrogen dioxide produced due to thermal decomposition, it is possible to determine whether the silane coupling agent contains amino components. Specifically, if the nitrogen content per unit mass of the glass cloth is less than 0.004% by mass, it can be determined that the silane coupling agent does not contain amino components. This nitrogen content is more preferably less than 0.0035%, further preferably less than 0.003%, and particularly preferably less than 0.0025%. It should be noted that the nitrogen content per unit mass of glass cloth can be 0% by mass or more than 0% by mass. However, in silane coupling agents where the amino-containing component is extremely small or absent, according to this determination method, there are sometimes cases where the "content of the amino-containing component in the silane coupling agent," and consequently the "nitrogen content per unit mass of glass cloth," is derived as a negative value due to baseline disturbances. In such cases, it still conforms to the principle that the nitrogen content per unit mass of glass cloth is trace, and therefore is included in the range of "0% by mass or more but less than 0.004% by mass" or "more than 0% by mass but less than 0.004% by mass."

[0076] In general formula (1), X preferably does not contain amino groups. For example, X in general formula (1) preferably does not contain amines such as primary amines, secondary amines, tertiary amines, or ammonium cations such as quaternary ammonium cations. As a result, the amount of silane coupling agent that is chemically bonded to the surface of the glass cloth can be suitably controlled, and the resistance of the glass cloth to CAF can be further improved.

[0077] For the purpose of stabilizing the glass cloth, in general formula (1), at least one of the plurality of Y atoms is preferably an alkoxy group having 1 to 5 carbon atoms (an alkoxy group having 1, 2, 3, 4 or 5 carbon atoms). More preferably, more than half or all of the plurality of Y atoms are alkoxy groups having 1 or more carbon atoms and less than 5 carbon atoms.

[0078] The silane coupling agent shown in general formula (1) can be used alone or in combination with two or more silane coupling agents. For example, two or more silane coupling agents in general formula (1) whose X values ​​are different from each other can be used in combination. In addition, two or more silane coupling agents in general formula (1) whose R values ​​are different from each other can be used in combination.

[0079] The content of the silane coupling agent derived from general formula (1) in the surface treatment agent for surface treatment of glass cloth is preferably 95.0% to 100% by mass, more preferably 96.5% to 100% by mass, further preferably 98.0% to 100% by mass, even more preferably 99.0% to 100% by mass, and particularly preferably 99.9% to 100% by mass. Accordingly, various properties, including CAF resistance, are further improved for the resulting glass cloth. The silane coupling agent may contain silane coupling agents other than those shown in general formula (1) (other silane coupling agents), or may contain components other than silane coupling agents.

[0080] The molecular weight of the silane coupling agent represented by general formula (1) is preferably 100 to 600, more preferably 150 to 500, and even more preferably 200 to 450. It is preferable to use a combination of multiple silane coupling agents within the above range and with different molecular weights as the silane coupling agent. Accordingly, glass yarn can be appropriately surface-treated using different types of silane coupling agents, resulting in a higher density of silane coupling agents on the glass surface. This tends to further enhance the reactivity with the matrix resin. When using a combination of multiple silane coupling agents with different molecular weights, it is preferable that at least two of the silane coupling agents are represented by general formula (1) and are within the above molecular weight range.

[0081] The silane coupling agent represented by general formula (1) is preferably nonionic. For example, X in general formula (1) preferably has at least one group selected from the group consisting of vinyl and (meth)acryloyloxy, more preferably (meth)acryloyloxy. Accordingly, suitable reactivity with the matrix resin can be ensured, and the heat resistance and reliability of the printed circuit board can be easily improved. It should be noted that (meth)acryloyloxy includes at least one of methacryloyloxy and acryloyloxy.

[0082] As the silane coupling agent represented by general formula (1), preferred options include, for example, vinyltrimethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, 5-hexenyltrimethoxysilane, and acryloyloxypropyltrimethoxysilane. With these silane coupling agents, resistance to CAF is readily achieved. Including the substances described above, the following silane coupling agents can be listed as silane coupling agents represented by general formula (1).

[0083] [Table 1]

[0084] X Y n R vinyl Carbon atoms 1 to 5 1 At least one of methyl, ethyl and phenyl vinyl Carbon atoms 1 to 5 2 At least one of methyl, ethyl and phenyl vinyl Carbon atoms 1 to 5 3 At least one of methyl, ethyl and phenyl Methacryloyloxy Carbon atoms 1 to 5 1 At least one of methyl, ethyl and phenyl Methacryloyloxy Carbon atoms 1 to 5 2 At least one of methyl, ethyl and phenyl Methacryloyloxy Carbon atoms 1 to 5 3 At least one of methyl, ethyl and phenyl Acryloyloxy Carbon atoms 1 to 5 1 At least one of methyl, ethyl and phenyl Acryloyloxy Carbon atoms 1 to 5 2 At least one of methyl, ethyl and phenyl Acryloyloxy Carbon atoms 1 to 5 3 At least one of methyl, ethyl and phenyl

[0085] [Loss on Ignition]

[0086] The weight loss on ignition of the glass cloth is preferably in the range of 0.01 to 0.50% by mass. The upper limit of the weight loss on ignition is more preferably 0.25% by mass or less, further preferably 0.20% by mass or less, even more preferably 0.18% by mass or less, and particularly preferably 0.16%, 0.15%, 0.14%, or 0.13% by mass or less, respectively. The lower limit, in any combination of these upper limits, is more preferably 0.02% by mass or more, further preferably 0.03% by mass or more, even more preferably 0.04% by mass or more, and particularly preferably 0.05% by mass or more. If the weight loss on ignition is below the aforementioned upper limit, the amount of surface treatment agents such as silane coupling agents chemically bonded to the surface of the glass cloth will not be excessive, thus increasing the dielectric loss tangent of the glass cloth and consequently the dielectric loss tangent of the resulting printed circuit board. On the other hand, if the weight loss on ignition is above the lower limit mentioned above, the amount of surface treatment agent bonded to the surface of the glass yarn will not be too little, and the heat resistance and insulation reliability of the resulting printed circuit board will be improved.

[0087] As described above, it is preferable to use low-dielectric glass as the glass cloth, and the nitrogen content, based on the total mass of the glass cloth, is less than 0.004% by mass. There is no lower limit for the nitrogen content; for example, it can be 0% or more, or even greater than 0%. Generally, due to the high hardness of quartz glass, glass cloth made using quartz glass is prone to brittle fracture. However, by ensuring good compatibility between quartz glass and surface treatment agents such as silane coupling agents with low nitrogen content, and by achieving a weight loss on ignition of the glass cloth within the aforementioned range, the risk of brittle fracture can be reduced.

[0088] [Coefficient of variation of total carbon content in glass cloth]

[0089] As described in the embodiments of this application, the total carbon content of the glass cloth obtained by the evaluation method using gas chromatography is preferably 0.01 to 0.50% by mass. The upper limit of the total carbon content of the glass cloth is more preferably 0.25% by mass or less, and even more preferably 0.20% by mass or less. The lower limit, in any combination with these upper limits, is more preferably 0.03% by mass or more, even more preferably 0.04% by mass or more, and particularly preferably 0.05% by mass or more. The total carbon content of the glass cloth reflects the amount of surface treatment agents such as silane coupling agents attached to the glass yarn; the more surface treatment agents are attached, the higher the total carbon content of the glass cloth. Furthermore, the evaluation method using gas chromatography allows for evaluation using small-area test pieces, and is therefore suitable for evaluating deviations in the dosage of surface treatment agents attached to the glass cloth. To improve the CAF resistance of printed circuit boards, reducing the area on the glass yarn surface where no surface treatment agent is attached is effective. By ensuring that the surface treatment agent is present throughout the glass filaments of the glass cloth, the dissolution of the glass filaments can be suppressed during the cleaning process, thus improving the CAF resistance of the printed circuit board. In other words, the smaller the area on the surface of the glass filament that is not covered with surface treatment agent, the smaller the rate of decontamination reduction of the average single filament diameter of the glass filament tends to be.

[0090] The inventors have discovered that determining the characteristic of uniform adhesion of the surface treatment agent to the glass filaments using the coefficient of variation of the total carbon content of the glass cloth is effective. Regarding the total carbon content obtained using gas chromatography, samples with a larger area where the surface treatment agent is not adhered tend to have a larger coefficient of variation for the total carbon content. Therefore, to improve the CAF resistance of printed circuit boards, glass cloth with a smaller coefficient of variation of the total carbon content after surface treatment is preferred. The upper limit of the range of the coefficient of variation of the total carbon content of the glass cloth is preferably 15% or less, more preferably 12% or less, further preferably 10% or less, even more preferably 8%, and particularly preferably 6% or less. The lower limit, which can be any combination of these upper limits, is not limited; for example, it can be 0% or more, more than 0%, or 1% or more. If the coefficient of variation of the total carbon content of the glass cloth is 15% or less, the amount of surface treatment agent adhered to the surface of the glass yarn becomes more uniform, the area of ​​the glass yarn where the surface treatment agent is not adhered becomes smaller, and the rate of reduction in the average monofilament diameter of the glass filaments decreases. As described below, performing multiple surface treatment processes is an effective way to reduce the coefficient of variation of the total carbon content in glass cloth. By performing multiple surface treatment processes, the areas on the glass yarn surface without surface treatment agent can be reduced.

[0091] [The relationship between the thickness of the glass cloth and the average monofilament diameter of the glass filaments]

[0092] Regarding the glass cloth, the relationship between the thickness (T) of the glass cloth and the average monofilament diameter (D) of the glass yarn satisfies the following formula (A1), preferably satisfies the following formula (A2), further preferably satisfies the following formula (A3), even more preferably satisfies (A4), and particularly preferably satisfies (A5).

[0093] 24.0 × DT > 96.0…(A1)

[0094] 24.0 × DT > 98.0…(A2)

[0095] 24.0 × DT > 100.0…(A3)

[0096] 24.0 × DT > 104.0…(A4)

[0097] 24.0 × DT > 108.0…(A5)

[0098] By satisfying the above formula (A1), the capillary force within the glass fiber bundle is reduced, thus suppressing the seepage of liquids into the glass fiber bundle during the treatment of the printed circuit board using cleaning and plating solutions. This improves the CAF resistance of the printed circuit board.

[0099] [Stain reduction rate based on average monofilament diameter of glass filament]

[0100] The stain reduction rate of the average monofilament diameter of the glass filaments in the glass cloth is preferably 25% or less. If the stain reduction rate is below the aforementioned upper limit, the damage to the glass cloth caused by the cleaning solution during the cleaning treatment of the printed circuit board is reduced, and the CAF resistance of the printed circuit board is improved. The stain reduction rate is preferably 24% or less, more preferably 23% or less, and even more preferably 22% or less. The lower limit of the stain reduction rate that can be combined with these upper limits can be 0% or more, for example, more than 0%. The stain reduction rate is measured using the method described in the embodiments of this application.

[0101] There is no specific manufacturing method. In the manufacturing method of glass cloth described later, by, for example, flattening the yarn bundles during warping before sizing (applying sizing), washing the glass cloth with water at a specified temperature or above before heating and degreasing, performing fiber opening treatment during the period after heating and degreasing and before surface treatment, and performing multiple surface treatments of the glass cloth, it is easier to control the stain reduction rate of the average monofilament diameter of the glass filaments in the glass cloth.

[0102] [Air permeability of glass cloth]

[0103] The air permeability of the glass cloth is preferably 25-350 cm. 3 / cm 2 The range of / s is more preferably 30–330 cm.3 / cm 2 / s, further preferably 35–300cm 3 / cm 2 / s, preferably 40–250cm 3 / cm 2 / s, 40~200cm 3 / cm 2 / s or 40~150cm 3 / cm 2 / s. If the air permeability is below the upper limit mentioned above, air bubbles, known as voids, are less likely to remain between the glass filaments in the prepreg, thus reducing the risk of poor insulation on the printed circuit board. If the air permeability is above the lower limit mentioned above, the inner walls of the drilled holes become smooth during the formation of the printed circuit board, further reducing the risk of poor insulation. It should be noted that the air permeability of the glass cloth can be adjusted through a fiber-opening process. The fiber-opening process, described later, makes it easier to adjust the air permeability of the glass cloth to the aforementioned range.

[0104] [The product of the thickness and air permeability of the glass cloth]

[0105] The thickness (μm) and air permeability (cm) of the glass cloth 3 / cm 2 The product of thickness and air permeability is in the range of 2500 to 6000. This product of thickness and air permeability is preferably in the range of 2800 to 5800, more preferably in the range of 2900 to 5600, further preferably in the range of 3000 to 5400, and particularly preferably in the range of 3200 to 5200. To ensure that the relationship between the thickness (T) of the glass cloth and the average monofilament diameter (D) of the glass yarn satisfies the above formula (A1), it is important to use glass yarn with a relatively large monofilament diameter and to evenly open the yarn bundle. When the opening of the glass cloth is insufficient, there is a tendency for the glass cloth to become thicker and for the air permeability to be higher (i.e., the product of thickness and air permeability to become larger). Glass cloth with a product of thickness and air permeability exceeding 6000 is prone to retaining air bubbles, known as voids, between the glass filaments in the prepreg, which can easily lead to poor insulation of the printed circuit board. Furthermore, if the thickness of the glass cloth becomes too thick, drill bit wear is more likely to occur during drilling, and the inner wall of the drilled hole is more likely to become rough. In addition, glass cloth that meets the above formula (A1) and is fully open can easily adjust the product of thickness and air permeability to more than 2500, which can easily improve the CAF resistance of printed circuit boards.

[0106] There is no specific manufacturing method. In the manufacturing method of glass cloth described later, by, for example, flattening the yarn bundles during warping before sizing (applying sizing), washing the glass cloth with water at a specified temperature or above before heating and degreasing, performing multiple surface treatments on the glass cloth, and performing fiber opening treatment during the period after heating and degreasing and before surface treatment, it is easier to control the product of the thickness and air permeability of the yarn glass cloth, as well as the stain reduction rate of the average monofilament diameter of the glass filaments.

[0107] [Thickness of the glass cloth]

[0108] The thickness of the glass cloth is preferably 10 to 100 μm. From the viewpoint of easily controlling the fiber opening of the glass cloth, the upper limit of the glass cloth thickness is preferably 80 μm or less, more preferably 60 μm or less, and particularly preferably 50 μm or less. Furthermore, from the viewpoint of excellent operability when conveying the glass cloth, the lower limit value, which can be combined with these upper limits, is preferably 15 μm or more, more preferably 20 μm or more, and particularly preferably 30 μm or more.

[0109] Manufacturing Method of Fiberglass Cloth

[0110] The method for manufacturing glass cloth according to this application includes: a step of weaving glass yarn containing multiple filaments and having a Si content in the range of 95.0% to 100% by mass (calculated as SiO2) as warp and weft yarns to obtain glass cloth (weaving step: B). Before the weaving step, the method further includes: a warping step (A) of straightening and flattening the glass yarn and then applying a sizing agent; a step of cleaning the glass yarn before heating and degreasing with water at 50°C or higher after the warping step and before, during, or after the weaving step (cleaning step before heating and degreasing: C); a step of reducing the amount of adhesive adhering to the glass yarn by heating and degreasing (heating and degreasing step: D); and a step of opening at least a portion of the glass filaments bonded by the residue of the adhesive after heating and degreasing (cleaning and opening step: E). The method optionally includes: a surface treatment step (F) of uniformly coating a surface treatment agent onto glass filaments; and a step (G) of splitting at least a portion of the glass filaments bonded by the surface treatment agent. Thus, glass cloths and prepregs capable of improving the CAF resistance of printed circuit boards can be provided.

[0111] The aforementioned glass processing method (steps (C) to (G)) can be applied to quartz glass yarn before weaving, and also to the woven glass cloth. In other words, the step of weaving quartz glass yarn to obtain glass cloth can be set before, during, or after the glass processing method. Hereinafter, an example will be given including steps (A) to (G) in sequence, but the manufacturing method of the glass cloth in this application is not limited to this.

[0112] [Warping process of glass yarn (A)]

[0113] The warping process of glass yarn includes: using glass yarn with a Si content ranging from 95.0% to 100% by mass (calculated as SiO2), flattening the yarn bundle, and then sizing the glass yarn. This treatment allows for sizing while the yarn width is increased, thus facilitating the widening of the yarn width in the woven glass cloth state, and enabling control by ensuring the product of the glass cloth thickness and air permeability meets specified ranges. The method for flattening the glass yarn bundle is not particularly limited; examples include processing under roller pressure. From the viewpoint of suppressing fuzzing and flattening the yarn bundle, a pressure of 1.0 kg / cm is preferred. 2 ~6.0kg / cm 2 More preferably 2.0 kg / cm 2 ~5.0kg / cm 2 A further preferred value is 2.5 kg / cm². 2 ~5.5kg / cm 2 In addition, this warping process makes it easier to remove the paste from the subsequent cleaning process before heating and degreasing.

[0114] [Weaving process of glass cloth blank (B)]

[0115] The preparation process for glass cloth prefabricated fabric includes weaving glass yarn containing multiple filaments and having a Si content in the range of 95.0% to 100% by mass (calculated as SiO2) as both warp and weft yarns. The glass yarn used in this process has a filament diameter that satisfies at least one of the above formulas (A1) to (A3) relative to the thickness of the resulting glass cloth. This allows for the preparation of glass cloth prefabricated fabric. To suppress fuzzing of the glass yarn during spinning and warping, the glass yarn is preferably surface-treated with a sizing agent whose main components are starch, polyvinyl alcohol, etc. The sizing agent treatment can be performed simultaneously with the spinning and warping processes of the glass yarn. The glass cloth prefabricated fabric is woven by weaving the warp yarn obtained in the warping process into the weft yarn. It should be noted that in this application, "glass cloth prefabricated fabric" refers to glass cloth before heat degreasing.

[0116] The glass yarn used in the above processes (A) to (B) is glass yarn with a filament diameter that satisfies at least one of the above formulas (A1) to (A5). This improves the CAF resistance of the printed circuit board.

[0117] [C) Cleaning process before heating and degreasing]

[0118] The pre-heat degreasing cleaning process includes cleaning the glass cloth before heat degreasing with water at 50°C or higher, thereby reducing the amount of paste used. This reduces adhesion caused by the paste from the filaments and the combustion residue of the paste during heat degreasing, allowing control to be achieved by ensuring the product of the glass cloth's thickness and air permeability meets a specified range. From the viewpoint of cleaning efficiency, water is preferably used as the cleaning solvent, and the temperature is preferably 50°C or higher. By using water at 50°C or higher, the amount of paste necessary for protecting the glass cloth up to the heat degreasing process is retained, while excess paste is washed away. The water temperature is preferably 50°C or higher and lower than 100°C. The lower limit of the water temperature is more preferably 55°C or higher, further preferably 60°C or higher, and even more preferably 65°C or higher. The upper limit of the water temperature that can be combined with these lower limits is more preferably 95°C or lower, and further preferably 90°C or lower. The solvent used for cleaning is not particularly limited; from the viewpoints of safety and cost, cleaning with water, reverse osmosis (RO) water, or ion-exchange water is preferred. There are no particular limitations on the cleaning method for glass cloth blanks. Methods such as ultrasonic cleaning (e.g., using an ultrasonic transducer), spray-based spraying (e.g., high-pressure spraying), and steam spraying can be considered. From the viewpoint of cost-effective processing, the following method is preferred: immersing the glass cloth blank in a tank containing a cleaning solution, removing excess cleaning solution using a squeeze roller or similar device, and then drying the glass cloth blank. In this case, the immersion time can be, for example, 2 seconds or more, 5 seconds or more, 10 seconds or more, or 15 seconds or more but less than 120 seconds, less than 90 seconds, less than 60 seconds, or less than 45 seconds.

[0119] [Reducing the steps of applying sizing agents (D)]

[0120] The process (D) of heating and degreasing the adhesive attached to the glass cloth blank can include, for example, a degreasing process (heating and degreasing process) in which the glass cloth blank is heated at a temperature of 650°C to 1000°C. This makes it easier to reduce the amount of adhesive removed from the glass.

[0121] The heating of the glass cloth blank can be carried out sequentially or continuously in a closed or open system, or a combination of closed and open systems. From a productivity point of view, it is particularly preferred to use a device with a winding mechanism and a take-up mechanism to heat the glass cloth blank in a roller-to-roll manner.

[0122] In a closed system, from the viewpoint of heating means, it is preferable to place the glass cloth blank inside the heating furnace, and / or, from the viewpoint of storage space and heating range, it is preferable to store and heat the glass cloth blank while it is in a wound state. Furthermore, from the viewpoint of improving the removal efficiency of organic matter or shortening the removal time of organic matter, it is also preferable to heat the glass cloth blank while it is being conveyed inside the heating furnace.

[0123] In an open system, from the viewpoint of the heated area, it is preferable to heat the glass cloth blank while it is being conveyed. The conveying of the glass cloth blank can be carried out using, for example, a roll-up mechanism and a take-up mechanism.

[0124] (Heating furnace)

[0125] As for the heating method in the heating furnace, any method that can heat the glass cloth blank to a temperature higher than 650°C can be considered, such as electric heaters or burners, and is not limited to a specific method. In addition, multiple methods can be combined for heating. It is preferable to heat the glass cloth blank in an atmosphere with an oxygen concentration of 10% or higher. For this purpose, a gas-type single radiant tube burner or an electric heater is preferred.

[0126] From the perspective of heating efficiency, the heating furnace preferably has means for venting the gas generated inside the furnace and / or means for air circulation. Gas venting means can be, for example, nozzles, gas pipes, orifices, degassing valves, etc. Air circulation means can be, for example, blades, air conditioning equipment, etc.

[0127] In order to efficiently remove organic matter adhering to the surface of glass cloth blank, a continuous method that allows the edge of the glass cloth blank to be continuously fed into the heating furnace for heating is preferred over an intermittent method of winding the glass fiber fabric into a core and heating the glass cloth blank at a specified atmosphere temperature.

[0128] To thoroughly remove organic matter adhering to the surface of the glass cloth blank, the preferred heating temperature is a surface temperature of the glass cloth blank above 650°C, more preferably above 700°C, even more preferably above 750°C, and particularly preferably above 800°C. The surface temperature of the glass cloth blank can be measured using, for example, a thermocouple or a non-contact thermometer.

[0129] (Contact component used to heat glass cloth blank)

[0130] As a method for heating glass cloth blanks, the aforementioned heating furnace can be used. From the viewpoint of low operating costs, the glass cloth blanks can be heated by bringing a component heated to a specified temperature into contact with the glass cloth blanks.

[0131] If heating can be performed in a manner that allows the surface temperature of the glass cloth blank to exceed 650°C, the shape of the contact member is not particularly limited; however, a roller shape is preferred for ease of conveying the glass cloth blank. As a member capable of heating the glass cloth blank in a roller shape, a roller that can be used in high-temperature regions and exhibits minimal temperature deviation in the width direction, and which heats by induction heating, is preferred. When heating the glass cloth blank using the contact member, it can be assumed that the temperature of the contact member is approximately equal to the surface temperature of the glass cloth blank.

[0132] As the glass cloth blank is continuously heated, in order to remove the carbon deposits adhering to the heating roller, the heating roller method is preferably equipped with a mechanism for removing dirt or foreign matter adhering to the roller, such as a scraper mechanism.

[0133] [Cleaning and fiber opening process of glass cloth (E)]

[0134] Preferably, the glass cloth after heat degreasing is subjected to a step (E) to separate the glass filaments that are stuck together due to adhesive residue, thereby obtaining the glass cloth of this application. The fiber separation step (E) preferably includes a fiber separation step of irradiating the glass cloth with ultrasound in a liquid to separate the fibers.

[0135] By performing a fiber-opening treatment on the glass cloth after heat degreasing, the adhesive residue present between the glass filaments can be impacted, thereby eliminating adhesion between the glass filaments. For effective elimination of adhesion between glass filaments, it is preferable to perform the fiber-opening treatment during the period after heat degreasing and before surface treatment, rather than after surface treatment. By performing sufficient fiber-opening treatment before surface treatment, adhesion between glass filaments is eliminated, allowing for uniform coating of the surface treatment agent on each glass filament, resulting in glass cloth and prepreg with excellent CAF resistance.

[0136] In the fiber-opening process after heating and degreasing, in addition to the process of opening fibers by irradiating the glass cloth with ultrasound in a liquid, other fiber-opening processes can be included. Other fiber-opening methods include: immersing the glass cloth in a liquid; immersing the glass cloth in a liquid and applying force to the glass cloth through the liquid (e.g., vibration cleaning, ultrasonic cleaning); and forcefully spraying the glass cloth with liquid (e.g., high-pressure spraying). From the viewpoint of being able to immerse the glass cloth in a liquid while it is in a wound state and perform fiber opening, or from the viewpoint of increasing productivity, it is preferable to use a device with a take-up mechanism and a roll-up mechanism, in which the glass cloth is conveyed and opened simultaneously in a roller-to-roll manner.

[0137] Water or organic solvents can be used as the liquid for fiber opening, but from the perspective of safety and environmental protection, liquids with water as the main component are preferred. To improve the efficiency of fiber opening, surfactants and pH adjusters can also be added to the liquid used for washing.

[0138] There is no particular limitation on the temperature of the liquid used in fiber opening, but from the viewpoint of improving efficiency, it is preferably 5°C or higher. Furthermore, from a safety perspective, the temperature of the liquid used in fiber opening is preferably 60°C or lower.

[0139] It is preferable to feed the glass cloth into the surface treatment process after removing as much adhesive residue as possible after heating and degreasing. Therefore, from the viewpoint of improving cleaning power, it is preferable to use a method of opening the fiber by irradiating the glass cloth with ultrasonic waves in water.

[0140] By immersing the glass cloth in a liquid irradiated with ultrasound using an ultrasonic oscillator, the glass cloth can be opened by irradiating it with ultrasound in the liquid. The preferred tension applied to the warp yarns during the opening process is 30N to 500N per 1m of glass cloth width. When the tension applied to the warp yarns is 30N or more per 1m of glass cloth width, the glass cloth will not slack, and the warp yarns will not slack, but will be uniformly tensioned. Therefore, the ultrasound-based opening process can be performed uniformly.

[0141] Fiber opening based on ultrasonic irradiation can use ultrasonic waves with a frequency of 20 kHz or higher and 200 kHz or lower. The frequency of the ultrasonic wave is preferably 20 kHz or higher and 50 kHz or lower, more preferably 20 kHz or higher and 30 kHz or lower. Using ultrasonic waves with a frequency of 20 kHz or higher and 200 kHz or lower allows for fiber opening without significant defects such as coil bending in the glass cloth, and is therefore preferred.

[0142] Ultrasonic cleaning is preferably performed using an output power of 0.07 W / cm². 2 Above and 3.60W / cm 2The following ultrasound. A more preferred range for ultrasound output power is 0.14 W / cm. 2 Above and 2.16W / cm 2 The preferred range is 0.21 W / cm². 2 Above and 1.44W / cm 2 The ultrasonic output power is 0.07W / cm. 2 At the above levels, fiber opening can be performed effectively, with an ultrasonic output power of 3.60 W / cm. 2 The following conditions prevent coil bending and allow for uniform fiber opening, making it the preferred choice.

[0143] The preferred ultrasonic treatment time is 0.5 seconds or more and 60 seconds or less. An ultrasonic treatment time of 0.5 seconds or more is preferred because it effectively opens the fiber in the glass cloth or its intermediate material. A longer ultrasonic treatment time results in a greater fiber-opening effect, which is also preferred. Even if the treatment exceeds 60 seconds, there is almost no further fiber opening; therefore, 60 seconds is sufficient.

[0144] The liquid used in ultrasonic cleaning typically contains dissolved air, primarily composed of nitrogen and oxygen. The dissolved oxygen content (by weight) is preferably 1 ppm to 20 ppm, more preferably 3 ppm to 17 ppm, and even more preferably 4 ppm to 14 ppm. By managing the dissolved oxygen content, the amount of dissolved gas can be indirectly controlled, thereby controlling the degree of ultrasonic attenuation due to the dissolved gas. A dissolved oxygen content of 1 ppm or higher allows for uniform fiber opening, and is therefore preferred. A dissolved oxygen content of 20 ppm or lower provides good fiber opening for fibrous fabrics, and is therefore preferred. A dissolved oxygen content in the range of 1 ppm to 20 ppm provides a uniform and good fiber opening effect, and is therefore preferred.

[0145] [Surface treatment process of glass cloth (F)]

[0146] The surface treatment process (F) of uniformly coating the glass filament with a surface treatment agent preferably involves multiple operations, such as adhering the surface treatment agent to the surface of the glass cloth and fixing the surface treatment agent to the surface of the glass cloth by heating and drying. This facilitates uniform coating of the surface treatment agent onto each glass filament, providing glass cloth and prepreg with excellent CAF resistance. Furthermore, to reduce residues and modifiers of surface treatment agents, such as silane coupling agents, that cannot be reduced by water, a cleaning process (fine cleaning step) based on a highly hydrophobic organic solvent or based on an organic solvent with high affinity for hydroxyl-containing silane coupling agent residues and modifiers is performed after the fixing process, thereby easily and appropriately surface treating the glass cloth.

[0147] By eliminating adhesion between filaments through a heat-induced degreasing and fiber-opening process, and by performing multiple surface treatments on the glass cloth, a surface treatment agent can be uniformly coated on each filament, unlike previous methods. The surface treatment agent chemically bonds the glass cloth in the prepreg to the matrix resin; therefore, the more uniformly the surface treatment is applied to the filaments, the better the glass cloth and prepreg can be provided with CAF resistance.

[0148] Methods for adhering surface treatment agents include: coating a glass cloth with a treatment solution containing a surface treatment agent, or immersing the glass cloth in the treatment solution. As a method of coating the glass with the treatment solution through a surface treatment process, it can be: (a) immersing the glass in or passing it through a treatment solution contained in a bath (hereinafter referred to as the "immersion method"); (b) coating the glass with the treatment solution using a roller coater, die coater, or gravure coater, etc. When using the immersion method, it is preferable to select an immersion time of the glass in the treatment solution within a range of 0.5 seconds to 1 minute. Furthermore, after coating the glass with the treatment solution, the solvent contained in the treatment solution can be heated and dried using methods such as hot air or electromagnetic waves. From the viewpoint of easily controlling the amount of treatment solution adhering to the glass cloth, it is preferable to remove excess treatment solution by pressing the glass cloth with a squeeze roller or the like after immersion in the treatment solution.

[0149] The concentration of the surface treatment agent contained in the treatment solution is preferably 0.05% to 0.4% by mass, more preferably 0.07% to 0.35% by mass, and even more preferably 0.09% to 0.3% by mass. Accordingly, it is easier and more suitable to perform surface treatment on glass.

[0150] In the fixing process of the surface treatment agent, in order to fully allow the surface treatment agent, such as a silane coupling agent, to react with the glass, the heating and drying temperature is preferably 80°C or higher, more preferably 90°C or higher. Furthermore, in order to prevent the deterioration of the organic groups present in the surface treatment agent, such as the silane coupling agent, the heating and drying temperature is preferably 300°C or lower, and more preferably 180°C or lower.

[0151] After the glass cloth is impregnated with the treatment solution, from the time it is pressed using extrusion rollers until it is heated and dried, the treatment solution sometimes repels the glass surface, resulting in very little or no surface treatment agent adhering to that area. Therefore, from the viewpoint of achieving a uniform surface treatment, it is preferable to perform the covering and fixing processes multiple times, for example, 2 to 5 times. From the viewpoint of balancing productivity and achieving a uniform surface treatment on the glass surface, it is more preferable to perform the covering and fixing processes 2 to 3 times.

[0152] In the fine cleaning process, known methods such as immersion and spraying can be used to remove silane coupling agent residues and modifiers, and heating and cooling can be applied as needed. To prevent re-adhesion of dissolved glass cloth deposits, the cleaned glass cloth is preferably dried using a pressure roller or similar method to reduce excess solvent. The organic solvent used is not particularly limited; for example, highly hydrophobic organic solvents include:

[0153] Saturated chain aliphatic hydrocarbons such as n-pentane, isopentane, n-hexane, isohexane, n-heptane, isoheptane, n-octane, isooctane, 2,2,4-trimethylpentane (isooctane), n-nonane, isononane, n-decane, isodecanane, 2,2,4,6,6-pentamethylheptane (isododecane);

[0154] Cyclopentane, cyclohexane, methylcyclohexane, dimethylcyclohexane, ethylcyclohexane, and other saturated cyclic aliphatic hydrocarbons;

[0155] Aromatic hydrocarbons such as benzene, toluene, xylene, ethylbenzene, diethylbenzene, trimethylbenzene, and triethylbenzene;

[0156] Halogen-containing solvents such as chloroform, dichloromethane, and dichloroethane.

[0157] Organic solvents with high affinity for silane coupling agent modifiers include alcohols such as methanol, ethanol, and butanol; ketones such as acetone and methyl ethyl ketone; and ethers such as methyl ethyl ether and diethyl ether.

[0158] Amides such as N,N-dimethylformamide and N,N-dimethylacetamide;

[0159] Dimethyl sulfoxide, etc.

[0160] Among these, from the viewpoint of making the dielectric loss tangent of the obtained glass cloth close to the dielectric loss tangent of the bulk phase, aromatic hydrocarbons, alcohols, or ketones are preferred, and methanol is more preferred. Therefore, as the cleaning fluid in the fine cleaning process, a cleaning fluid with methanol as the main component (more than 50% or 60% by mass relative to 100% by mass of the cleaning fluid) is preferred.

[0161] The drying process reduces the amount of cleaning fluid used in the aforementioned washing process. To facilitate reducing the amount of cleaning fluid through drying, the boiling point of the cleaning fluid used in the washing process is preferably below 120°C. Drying can be performed by heating or by blowing air. It should be noted that, when using an organic solvent as the cleaning fluid, from a safety perspective, heating drying using hot air with low-pressure steam or hot oil as the heat source is preferred. The drying temperature is preferably above the boiling point of the cleaning fluid, and from the viewpoint of suppressing the deterioration of the silane coupling agent, it is preferably below 180°C.

[0162] [Surface treatment followed by fiber opening process (G)]

[0163] Preferably, a fiber-opening process (G) is performed to open at least a portion of the glass filaments bonded by the surface treatment agent. As the fiber-opening process (G), methods such as using water spray (high-pressure water fiber opening), a vibratory cleaner, ultrasonic water, or a liquid rolling mill can be employed to open the glass cloth. During this fiber-opening process, there is a tendency to further reduce air permeability by reducing the tension applied to the glass cloth. It should be noted that, in order to suppress the reduction in tensile strength of the glass cloth caused by the fiber-opening process, it is preferable to implement measures such as low friction with the contact components during glass yarn weaving, and optimization and high adhesion of the sizing agent.

[0164] The processes described above do not necessarily need to be performed in separate processes; multiple processes can be combined into one. For example, if a cleaning process is performed after the weaving process, the cleaning process can also serve as a fiber-opening process by using high-pressure water spray. The composition of the glass cloth usually remains largely unchanged before and after fiber opening. Furthermore, the manufacturing method of glass cloth may include optional processes in addition to those described above. For example, a slit-forming process may be performed after the fiber-opening process. Additionally, the order of the above processes can be changed if possible.

[0165] According to the glass cloth manufacturing method described above, after eliminating the adhesion between glass filaments, a surface treatment agent can be uniformly coated on the glass surface, providing glass cloth and prepreg with excellent CAF resistance.

[0166] Prepreg

[0167] The prepreg of this application contains the glass cloth of this application and a matrix resin impregnated into the glass cloth. Thus, a prepreg with fewer pores can be provided.

[0168] Thermosetting or thermoplastic resins can be used as the base resin. If possible, a combination of both can be used, and other resins may also be included.

[0169] Examples of thermosetting resins include:

[0170] (a) An epoxy resin formed by reacting a compound having an epoxy group with a compound having at least one group selected from the group consisting of an amino group, a phenolic group, an anhydride group, an acylhydrazine group, an isocyanate group, a cyanate group and a hydroxyl group that react with the epoxy group, and then curing the compound.

[0171] (b) A free radical polymeric cured resin formed by curing a compound having at least one group selected from the group consisting of allyl, methacryl, and acryloyl;

[0172] (c) Maleimide triazine resin formed by reacting a compound having a cyanate ester group with a compound having a maleimide group and then curing the mixture.

[0173] (d) A thermosetting polyimide resin formed by reacting maleimide compounds with amine compounds and then curing them;

[0174] (e) Benzoxazine resins, etc., which are formed by cross-linking and curing compounds with benzoxazine rings through heating polymerization.

[0175] It should be noted that, in obtaining (a) the epoxy resin, the compound can react under catalyst-free conditions. Alternatively, catalysts with reaction catalytic capabilities, such as imidazole compounds, tertiary amine compounds, urea compounds, and phosphorus compounds, can be added to induce the reaction. Furthermore, in obtaining (b) the free radical polymerization type curing resin, thermally decomposable catalysts or photodecomposable catalysts can be used as reaction initiators.

[0176] Examples of thermoplastic resins include polyphenylene ether, modified polyphenylene ether, polyphenylene sulfide, polysulfone, polyethersulfone, polyarylate, aromatic polyamide, polyetheretherketone, thermoplastic polyimide, insoluble polyimide, polyamide-imide, and fluoropolymers. For use as an insulating material in printed circuit boards for high-speed communication, polyphenylene ether or modified polyphenylene ether with high free radical reactivity is preferred.

[0177] When the matrix resin used in printed circuit boards for high-speed communication has vinyl or methacryloyl groups, silane coupling agents with high hydrophobicity and functional groups such as methacryloyl groups that participate in free radical reactions have good compatibility with the matrix resin.

[0178] As mentioned above, thermosetting resins and thermoplastic resins can be used in combination. Additionally, the prepreg may also contain inorganic fillers. Inorganic fillers are preferably used in combination with thermosetting resins, and examples include aluminum hydroxide, zirconium oxide, calcium carbonate, alumina, mica, aluminum carbonate, magnesium silicate, aluminum silicate, silica, talc, short glass fibers, aluminum borate, and silicon carbide. Inorganic fillers can be used alone or in combination of two or more.

[0179] Printed Circuit Boards

[0180] The printed circuit board of this application contains one or more of the aforementioned prepregs. This provides a printed circuit board with excellent insulation reliability.

[0181] Integrated Circuits and Electronic Devices

[0182] According to this application, integrated circuits and electronic devices incorporating the aforementioned printed circuit board can also be provided. Integrated circuits and electronic devices obtained using the printed circuit board of this application exhibit excellent characteristics.

[0183] Example

[0184] The embodiments and comparative examples of this application are described in detail below, but this application is not limited to the following embodiments and comparative examples.

[0185] Determination Method

[0186] [Methods for determining the weight loss on ignition and air permeability of glass cloth]

[0187] According to JIS R3420, calculate the weight loss on ignition and air permeability of the glass cloth.

[0188] [Evaluation method for the thickness of glass cloth]

[0189] According to JIS R3420 7.10, using a micrometer, rotate the spindle smoothly until it gently contacts the measuring surface parallel to it, and read the scale after the ratchet makes three clicks.

[0190] [The product of the thickness and air permeability of the glass cloth]

[0191] The calculation is performed based on the product of the glass cloth thickness and air permeability obtained through the above method.

[0192] The product of fiberglass cloth thickness and air permeability = fiberglass cloth thickness (μm) × fiberglass cloth air permeability (cm) 3 / cm 2 / s)

[0193] [Coefficient of variation of total carbon content in glass cloth]

[0194] The surface-treated glass cloth was cut to a mass of 80–100 mg. The cut glass cloth was heated at approximately 800°C for 1 minute, and the amount of carbon dioxide in the generated gas was determined using gas chromatography. The total carbon content per unit mass of the surface-treated glass cloth was determined by comparing it to the amount of carbon dioxide generated when a predetermined amount of acetanilide (C8H9NO) was similarly heated at approximately 800°C for 1 minute. The determination was performed using a SUMIGRAPH NC-TR22 (manufactured by Sumitomo Chemical Analysis Center).

[0195] The molecular weight of acetanilide is 135.17.

[0196] The carbon content of acetanilide is 71.09%.

[0197] That is, the total carbon content per unit mass of glass cloth is calculated according to the following formula.

[0198] The total carbon content per unit mass of glass cloth = [{mass of acetanilide × (carbon ratio of acetanilide / 100)} / peak area of ​​carbon dioxide produced from acetanilide] × {(peak area of ​​carbon dioxide produced by glass cloth / mass of glass cloth) × 100}

[0199] While changing the cutting position of the glass cloth, this operation was performed at a total of 10 locations, and the total carbon content at each location was measured. The average value and standard deviation were then calculated. The coefficient of variation of the total carbon content of the glass cloth was calculated using the following formula.

[0200] Coefficient of variation (%) of total carbon content in glass cloth = Standard deviation of total carbon content ÷ Average of total carbon content × 100

[0201] [Methods for determining nitrogen content]

[0202] The surface-treated glass cloth was cut to a mass of 80–100 mg. The cut glass cloth was heated at approximately 800°C for 1 minute, and the amount of nitrogen dioxide in the resulting gas was determined using gas chromatography. The nitrogen content (mass%) per unit mass of the surface-treated glass cloth was determined by comparing it to the amount of nitrogen dioxide produced when a predetermined amount of acetanilide (C8H9NO) was similarly heated at approximately 800°C for 1 minute. A SUMIGRAPH NC-TR22 (manufactured by Sumitomo Chemical Analysis Center) was used in the determination.

[0203] The molecular weight of acetanilide is 135.17.

[0204] The nitrogen content of acetanilide is 10.36%.

[0205] That is, the nitrogen content per unit mass of glass cloth is calculated according to the following formula.

[0206] The nitrogen content per unit mass of glass cloth = [{mass of acetanilide × (nitrogen ratio of acetanilide / 100)} / peak area of ​​nitrogen dioxide produced from acetanilide] × {(peak area of ​​nitrogen dioxide produced by glass cloth / mass of glass cloth) × 100}

[0207] [Stain reduction rate of glass filaments]

[0208] The swelling solution and the cleaning solution are prepared by stirring at room temperature according to the proportions shown in Table 2 below.

[0209] [Table 2]

[0210]

[0211] Follow the steps below to clean the glass cloth. It should be noted that "after cleaning" refers to the state after being immersed in both the swelling solution and the cleaning solution, while "before cleaning" refers to the state before immersion in the swelling solution.

[0212] (1) Cut the glass cloth into 4cm squares. Put the obtained glass cloth into a container made of perfluoroalkoxyalkane (PFA) and add swelling solution until the glass cloth is impregnated.

[0213] (2) To prevent the swelling solution from evaporating, the container was capped and heated at 80°C for 2 hours. The glass cloth, after being treated with the swelling solution, was thoroughly washed with ion-exchanged water and then dried.

[0214] (3) Put the glass cloth obtained by operation (2) back into the container made of PFA and add cleaning solution until the glass cloth is soaked.

[0215] (4) To prevent the cleaning solution from evaporating, the container is covered and heated at 80°C for 2 hours. After thoroughly cleaning the glass cloth with deionized water, it is dried to complete the cleaning treatment of the glass cloth.

[0216] (5) Using a microscope (HRX-1 manufactured by HIROX), observe the average diameter of the glass filaments that make up the glass cloth before and after the cleaning treatment of 20 glass filaments, and calculate the average single filament diameter of the glass filaments.

[0217] (6) Based on the diameter of the monofilament before and after the decontamination treatment, the decontamination reduction rate is calculated using the following formula.

[0218] Stain reduction rate = (monofilament diameter before stain removal - monofilament diameter after stain removal) ÷ ​​monofilament diameter before stain removal × 100

[0219] Manufacturing Examples

[0220] (Example 1)

[0221] The warp yarn is prepared using silica glass yarn with a SiO2 content greater than 99.9% by mass, an average filament diameter of 7.5 μm, a filament count of 44, and a twist rate of 1.0 Z (process (A)). At this time, the yarn is conveyed at a speed of 60 m / min using rollers at a speed of 3.0 kg / cm². 2The load clamps the aligned warp yarns, thereby flattening the glass yarn. Then, a sizing agent with polyvinyl alcohol (PVA) resin as the main component is applied according to the following steps: A 5% aqueous solution of PVA (trade name: PVA403, manufactured by Kuraray Co., Ltd.) is prepared, and 2% hydrogenated castor oil as a lubricant is mixed into this aqueous solution to obtain the sizing agent. The sizing agent, which has been kept at 60°C, is applied to the glass yarn and then dried, thereby performing the sizing treatment. Subsequently, a glass cloth fabric is woven using an air-jet loom with a warp density of 66 ends / inch and a weft density of 68 ends / inch (step (B)). As the weft yarn, a silica glass yarn with an average filament diameter of 7.5 μm, a filament count of 44, and a twist count of 1.0 Z is used.

[0222] The obtained glass cloth blank is conveyed at a linear speed while being immersed in a water tank containing ion-exchange water at 60°C for 15 seconds, and the sizing agent adhering to the glass surface is cleaned (step (C)). Subsequently, it undergoes heat degreasing treatment by being heated at 1000°C for 30 seconds in an atmospheric atmosphere using a roller-to-roll method in a furnace located on the same production line (step (D)). The heat-degreased glass cloth is then continuously processed through the following steps on the same production line: (E) heat-degreased fiber opening, (F) surface treatment, and (G) surface treatment fiber opening. At this time, the linear speed is set to 20 m / min, and the conveying tension of the glass cloth is set to 200 N. In the (E) heat-degreased fiber opening process, the glass cloth is irradiated with a frequency of 25 GHz and an output power of 0.72 W / cm² while moving through water. 2 The glass cloth is subjected to ultrasonic treatment, followed by heating and drying at 130°C for 30 seconds to eliminate adhesion between the filaments. Next, in the surface treatment step (F), the glass cloth is immersed in a treatment solution containing 0.3% by mass of 3-methacryloyloxypropyltrimethoxysilane Z6030 (manufactured by DOW·TORAY) dispersed in pure water adjusted to pH=3 with acetic acid, and then squeezed out, followed by drying at 125°C for 30 seconds. By performing the above series of processes of immersion, squeezing, and drying twice, a surface treatment agent is uniformly coated onto the glass filaments. Next, in the fiber-opening step (G) after surface treatment, the glass cloth is opened using a columnar stream sprayed from a 1.4 MPa high-pressure water sprayer, followed by drying at 130°C for 30 seconds, thereby obtaining the glass cloth.

[0223] (Example 2)

[0224] (A) warp yarns are prepared using silica glass yarn with a SiO2 content greater than 99.9% by mass, an average filament diameter of 7.5 μm, 89 filaments, and a twist rate of 1.0 Z. At this time, the yarn is fed at a speed of 60 m / min using rollers at a speed of 3.5 kg / cm². 2 The load clamps the aligned warp yarns, thereby flattening the glass yarn. Then, a sizing agent with polyvinyl alcohol (PVA) resin as the main component is applied according to the following steps: A 5% aqueous solution of PVA (trade name: PVA403, manufactured by Kuraray Co., Ltd.) is prepared, and 2% hydrogenated castor oil as a lubricant is mixed into this aqueous solution to obtain the sizing agent. The sizing agent, which has been kept at 60°C, is applied to the glass yarn and then dried, thereby performing the sizing treatment. Subsequently, a fabric is woven using an air-jet loom with a warp density of 54 ends / inch and a weft density of 54 ends / inch. As the weft yarn, silica glass yarn with an average filament diameter of 7.5 μm, a filament count of 89, and a twist count of 1.0 Z is used. The resulting glass cloth fabric is processed with a conveying tension of 300 N, otherwise, the glass cloth is processed using the same method as in Example 1.

[0225] (Example 3)

[0226] (A) warp yarns are prepared using silica glass yarn with a SiO2 content greater than 99.9% by mass, an average filament diameter of 6.0 μm, 22 filaments, and a twist rate of 0.6 Z. At this time, the yarn is fed at a speed of 60 m / min using rollers at a speed of 3.0 kg / cm². 2 The load clamps the aligned warp yarns, thereby flattening the glass yarn. Then, a sizing agent with polyvinyl alcohol (PVA) resin as the main component is applied according to the following steps: A 5% aqueous solution of PVA (trade name: PVA403, manufactured by Kuraray Co., Ltd.) is prepared, and 2% hydrogenated castor oil as a lubricant is mixed into this aqueous solution to obtain the sizing agent. The sizing agent, which has been kept at 60°C, is applied to the glass yarn and then dried, thereby performing the sizing treatment. Subsequently, a fabric is woven using an air-jet loom with a warp density of 95 ends / inch and a weft density of 95 ends / inch. As the weft yarn, silica glass yarn with an average filament diameter of 6.0 μm, a filament count of 22, and a twist count of 0.6 Z is used. The resulting glass cloth fabric is processed with a conveying tension of 100 N, otherwise, the glass cloth is processed using the same method as in Example 1.

[0227] (Example 4)

[0228] As warp and weft yarns, silica glass yarns with an average monofilament diameter of 6.0 μm, 69 filaments, and a twist of 1.0 Z are used. Otherwise, the glass cloth is processed using the same method as in Example 1.

[0229] (Example 5)

[0230] The series of processes in the (F) surface treatment step, including impregnation, squeezing and drying, are performed only once. Otherwise, the glass cloth is processed using the same method as in Example 4.

[0231] (Example 6)

[0232] As warp and weft yarns, silica glass yarns with an average monofilament diameter of 5.7 μm, 78 filaments, and a twist of 1.0 Z are used. Otherwise, the glass cloth is processed using the same method as in Example 1.

[0233] (Comparative Example 1)

[0234] As warp and weft yarns, silica glass yarns with an average monofilament diameter of 5.0 μm, 100 filaments, and a twist of 1.0 Z are used. Furthermore, the fiber opening process after heating and degreasing (E) is not performed. Otherwise, the glass cloth is processed using the same method as in Example 1.

[0235] (Comparative Example 2)

[0236] As warp and weft yarns, silica glass yarns with an average monofilament diameter of 5.0 μm, 200 filaments, and a twist of 1.0 Z are used. Furthermore, the fiber opening process after heating and degreasing (E) is not performed. Otherwise, the glass cloth is processed using the same method as in Example 2.

[0237] (Comparative Example 3)

[0238] After performing the (E) heating and degreasing fiber opening process, the glass cloth was processed using the same method as in Comparative Example 1.

[0239] (Comparative Example 4)

[0240] The fiber opening process after heating and degreasing (E) is omitted. Otherwise, the glass cloth is processed using the same method as in Example 1.

[0241] (Comparative Example 5)

[0242] (F) The surface treatment process is performed once. Otherwise, the glass cloth is processed using the same method as in Comparative Example 4.

[0243] (Comparative Example 6)

[0244] In (A) the warp yarns are not clamped during warping, but the glass cloth is processed using the same method as in Example 1.

[0245] (Comparative Example 7)

[0246] Without cleaning the sizing agent (C), the glass cloth is processed using the same method as in Example 1.

[0247] (Comparative Example 8)

[0248] As the glass cloth, E glass (SiO2 composition of 55% by mass) was used, and the glass cloth was processed using the same method as in Comparative Example 4.

[0249] Evaluation Methods

[0250] [Evaluation method for insulation reliability (CAF resistance) of laminated boards]

[0251] For 210 parts by weight of toluene, add 9 parts by weight of TUFTEC H1041 (registered trademark, hydrogenated styrene thermoplastic elastomer, manufactured by Asahi Kasei Corporation) and stir until dissolved. Next, add 24.5 parts by weight, 66 parts by weight, and 80 parts by weight of SAYTEX 8010 (registered trademark, ethylene bis(pentabromobenzene), manufactured by Albemarle Corporation), spherical silica SC2500-SVJ (registered trademark, manufactured by ADMATECHS Corporation), and NorylSA9000 (trade name, polyphenylene ether, manufactured by SABIC Corporation), respectively, and continue stirring until NorylSA9000 is dissolved. Next, add 20 parts by weight and 0.5 parts by weight of TAIC (registered trademark, triallyl isocyanurate, manufactured by Mitsubishi Chemical Corporation) and PERBUTYL P (registered trademark, α,α'-di(tert-butylperoxide)diisopropylbenzene, manufactured by Nippon Oil Company), respectively, and stir thoroughly to obtain a varnish. After impregnating the glass cloth obtained in the examples and comparative examples with the varnish, it was dried at 115°C for 1 minute to obtain a prepreg. The obtained prepreg was then overlapped, and copper foil with a thickness of 12 μm was further overlapped on top and bottom, and the mixture was dried at 200°C and 40 kg / cm². 2 The laminate was heated and pressurized for 120 minutes to obtain a 1.0 mm thick layer. A wiring pattern with through-holes spaced at 0.30 mm intervals was fabricated on the copper foil on both sides of the laminate to obtain a sample for insulation reliability evaluation. For the obtained sample, a voltage of 50 V was applied in an atmosphere of 85°C and 85% RH, and the change in resistance was measured. If the resistance was less than 1 MΩ within 500 hours of the start of the test, it was counted as insulation failure. The same measurement was performed on 10 samples, and the number of samples exhibiting insulation failure was determined.

[0252] The manufacturing conditions and evaluation results of the examples and comparative examples are shown in Tables 3 and 4.

[0253] [Table 3]

[0254]

[0255] [Table 4]

[0256]

Claims

1. A glass cloth comprising glass yarn containing multiple filaments as warp and weft yarns, wherein the silicon (Si) content in the glass yarn is 95.0% to 100% by mass (calculated as silicon dioxide, SiO2), the average monofilament diameter (D) of the filaments is in the range of 5.0 μm to 8.5 μm, and the relationship between the thickness (T) of the glass cloth and the average monofilament diameter (D) of the filaments satisfies the following formula (A4). 24.0 × DT > 104.0 … (A4) The thickness of the glass cloth is 15μm or more and 80μm or less, and The product of the thickness and air permeability of the glass cloth is in the range of 2500 μm-cm 3 / cm 2 / s 3 / cm 2 / s is in the range of 6000 μm-cm 2. The glass cloth of claim 1, wherein, When the glass cloth is subjected to a decontamination treatment, the decontamination reduction rate of the average monofilament diameter D of the filaments, expressed by the following formula, is 25% or less. Decontamination reduction rate = (monofilament diameter before decontamination treatment - monofilament diameter after decontamination treatment) ÷ monofilament diameter before decontamination treatment × 100 The decontamination treatment is carried out through the following operations: (1) Cut the glass cloth into 4cm squares, put the obtained glass cloth into a container made of perfluoroalkoxyalkane (PFA), and add swelling solution until the glass cloth is impregnated. (2) To prevent the swelling solution from evaporating, the container is covered and heated at 80°C for 2 hours. The glass cloth, after being treated with the swelling solution, is thoroughly cleaned with ion-exchanged water and then dried. (3) The glass cloth obtained by operation (2) is put back into the PFA container and a cleaning solution is added until the glass cloth is soaked. (4) In order to prevent the cleaning solution from evaporating, the container is covered and heated at 80°C for 2 hours. The glass cloth that has been treated with the cleaning solution is thoroughly cleaned with ion-exchanged water and then dried to complete the cleaning treatment of the glass cloth. (5) Using a microscope, observe the average diameter of the glass filaments that make up the glass cloth before and after the cleaning treatment for 20 glass filaments, and calculate the average single filament diameter of the glass filaments. (6) Based on the monofilament diameters before and after the decontamination treatment, the decontamination reduction rate is calculated using the above formula. The swelling solution comprises 5 volumes of a 40% by weight sodium hydroxide aqueous solution, 15 volumes of a 20% by weight to 30% by weight 2-(2-butoxyethoxy)ethanol aqueous solution, and 80 volumes of deionized water. The cleaning solution contains 8 volumes of 40% sodium hydroxide aqueous solution, 10 volumes of 40% sodium permanganate aqueous solution, and 82 volumes of ion-exchanged water.

3. The glass cloth of claim 1 or 2, wherein, The glass cloth has an air permeability of 25 cm 3 / cm 2 / s~350 cm 3 / cm 2 / s.

4. The glass cloth of claim 1 or 2, wherein, The glass yarn was surface-treated using a surface treatment agent.

5. The glass cloth of claim 4, wherein, The surface treatment agent comprises a silane coupling agent having the structure shown in the following general formula (1). X (R) 3-n SiY n … (1) In formula (1), X is an organic group having one or more unsaturated double bond groups with free radical reactivity, Y is an alkoxy group, n is an integer from 1 to 3, and R is at least one group selected from the group consisting of methyl, ethyl and phenyl.

6. The glass cloth according to claim 5, wherein, X in the general formula (1) has a (meth)acryloyloxy group.

7. The glass cloth according to claim 1 or 2, wherein, The loss on ignition of the glass cloth is in the range of 0.01% to 0.50% by mass.

8. The glass cloth according to claim 1 or 2, wherein, The average number of filaments in the glass yarn is in the range of 20 to 200.

9. The glass cloth according to claim 1 or 2, wherein, The coefficient of variation of the total carbon content of the glass cloth obtained by gas chromatography is less than 15%.

10. The glass cloth according to claim 1 or 2, wherein, The nitrogen content of the glass cloth obtained by gas chromatography is less than 0.004% by mass.

11. A prepreg comprising the glass cloth of claim 1 or 2, and a matrix resin impregnated into the glass cloth.

12. The prepreg according to claim 11, further comprising an inorganic filler.

13. A printed circuit board comprising the prepreg of claim 11.

14. An integrated circuit comprising the printed circuit board of claim 13.

15. An electronic device comprising the printed circuit board of claim 13.

16. A method for manufacturing glass cloth, wherein, The method includes: The process of weaving glass yarn, which contains multiple long filaments and has a Si content (calculated as SiO2) ranging from 95.0% to 100% by mass, as both warp and weft yarns, to obtain glass cloth. The method further includes flattening the glass yarn bundles before the weaving process, followed by a sizing and warping process. The following processes are included after the warping process and before, during, or after the weaving process: The process of cleaning the glass yarn with water at a temperature of 50°C or higher; The process of reducing the amount of adhesive adhering to the glass yarn by heating and degreasing; and The glass yarn, after being heated and degreased, is subjected to ultrasonic waves in a liquid to open at least a portion of the glass filaments that are bonded together by the residue of the binder after heating and degreasing. The average monofilament diameter D of the filament is in the range of 5.0 μm to 8.5 μm, and the relationship between the thickness T of the glass cloth and the average monofilament diameter D of the filament satisfies the following equation (A4): 24.0×DT>104.0 …(A4) The thickness of the glass cloth is 15μm or more and 80μm or less, and The product of the thickness and air permeability of the glass cloth is in the range of 2500 μm-cm 3 / cm 2 / s 3 / cm 2 / s 17. The method of claim 16, further comprising: The surface treatment process involves multiple operations as follows: applying a surface treatment agent to the surface of the fiber-opened glass cloth, and fixing the surface treatment agent to the surface of the glass cloth by heating and drying. as well as A process of opening at least a portion of the glass filaments bonded by the surface treatment agent.

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