JP7321222B2 - Glass cloth, prepreg, and printed wiring board - Google Patents

Description

The present invention relates to glass cloth, prepreg, and printed wiring board.

BACKGROUND ART At present, as electronic devices become more sophisticated, the printed wiring boards used in them are remarkably becoming denser and thinner.
As an insulating material for this printed wiring board, a laminated board obtained by laminating prepregs obtained by impregnating glass cloth with thermosetting resin such as epoxy resin (hereinafter referred to as "matrix resin") and curing under heat and pressure. is widely used. In particular, in cutting-edge smartphones and wearable devices, printed wiring boards are being miniaturized, and glass cloth, which is a constituent material, is required to be of high quality, high performance, and ultra-thin.

The diameter of the glass filaments constituting the glass cloth is generally designed to have a minimum diameter of 3 μm or more from the viewpoint of safety and reduction of environmental load. For this reason, glass cloth manufacturers have applied various processes to achieve ultra-thin glass cloth (see Patent Documents 1 to 4, for example).

Japanese Patent No. 4446754 Japanese Patent No. 5905150 Japanese Patent No. 6020764 Japanese Patent No. 5936726

However, there is still room for improvement from the viewpoint of achieving sufficient quality and performance in future ultra-thin printed wiring boards. Specifically, in order to thin the insulating layer of the printed wiring board, ^a glass cloth having a thickness of 13 μm or less is used, and the mass of the resin (g /m ² ) is 65% by mass or less, pinholes occur at a constant frequency during prepreg production, and delamination occurs during mounting at high temperatures.

Actually, the glass cloth disclosed in Patent Document 2 has a problem that pinholes are generated when RC is set to 69% by mass or less.

Further, the glass cloth disclosed in Patent Document 4 has a problem that anisotropy tends to occur during mounting at high temperatures because glass fibers with different thicknesses are used for the warp and weft.

The present invention has been made in view of the above problems, and is a high-quality substrate that is resistant to delamination. ), a prepreg using the glass cloth, and a printed wiring board.

The present inventors have studied to solve the above problems, and as a result, have found that a predetermined glass cloth can solve the above problems, and have completed the present invention.

That is, the present invention is as follows.
[1]
A glass cloth made by weaving glass threads made of a plurality of glass filaments as warp and weft,
The average filament diameter of the glass filaments is 3.0 to 4.5 μm,
The number of the glass filaments is 20 to 50,
The warp yarns and weft yarns constituting the glass cloth have a density of 70 to 130 yarns/inch each independently,
The glass cloth has a thickness of 7 to 13 μm,
The maximum area of basket holes present in the glass cloth is 50,000 μm ² or less.
Glass cloth.
[2]
The glass cloth according to [1], having a maximum air permeability of 250 cm ³ /cm ² /sec or less.
[3]
The glass cloth according to [1] or [2], wherein the openness of the warp and the weft is independently 90% or more.
[4]
The glass cloth according to any one of [1] to [3], wherein the minimum yarn width of each of the warp yarns and weft yarns is independently 100 μm or more.
[5]
The glass cloth according to any one of [1] to [4], wherein the basket hole has a maximum width of 120 μm or less.
[6]
The glass cloth according to any one of [1] to [5], wherein the surface of the glass yarn is treated with a plurality of types of silane coupling agents.
[7]
A prepreg comprising the glass cloth according to any one of [1] to [6] and a matrix resin impregnated in the glass cloth.
[8]
A printed wiring board having the prepreg according to [7].

According to the present invention, it is possible to provide a glass cloth, a prepreg using the glass cloth, and a printed wiring board from which a high-quality, delamination-resistant substrate can be produced.

Hereinafter, an embodiment of the present invention (hereinafter referred to as "this embodiment") will be described in detail, but the present invention is not limited to this, and various modifications are possible without departing from the gist thereof. is.

〔Glass cloth〕
The glass cloth of the present embodiment is a glass cloth obtained by weaving glass yarns made of a plurality of glass filaments as warp yarns and weft yarns.
Further, in the glass cloth of the present embodiment, the average filament diameter of the glass filaments is 3.0 to 4.5 μm, the number of the glass filaments is 20 to 50, and the warp constituting the glass cloth and the weft yarn density is independently 70 to 130/inch, the thickness of the glass cloth is 7 to 13 μm, and the maximum area of the basket hole existing at any position on the glass cloth. is 50,000 μm ² or less.

If the maximum area of basket holes is 50,000 μm ² or less, pinholes are extremely unlikely to occur when a prepreg is produced by impregnating glass cloth with a resin. The maximum area of the basket holes is preferably 45,000 μm ² or less, more preferably 40,000 μm ² or less.
Also, the minimum area of the basket hole is preferably 3,000 μm ² or more, more preferably 4,000 μm ² or more, still more preferably 5,000 μm ² or more. When the minimum area of the basket holes is 3,000 μm ² or more, delamination tends to be less likely to occur.

Furthermore, the average area of the basket holes is preferably 5,000 μm ² or more and 20,000 μm ² or less, more preferably 6,000 μm ² or more and 19,000 μm ² or less, and still more preferably 7, 000 μm ² or more and 18,000 m ² or less. When the average area of basket holes is 5,000 μm ² or more and 20,000 μm ² or less, pinholes are less likely to occur and delamination tends to be less likely to occur.

The basket hole in this embodiment refers to a gap between the warp and the weft, and the pinhole refers to a void defect caused by the resin not filling the basket hole portion.
Generally, when the average area of basket holes is reduced, pinholes are less likely to occur, but the amount of resin applied is reduced, and delamination is more likely to occur during high-temperature mounting. In the present invention, it was found that the maximum area of the basket holes is the most important for the pinhole quality of the prepreg and the suppression of delamination of the substrate, rather than the size of the average area of the basket holes. The maximum area of the basket hole referred to here is obtained by pulling out the glass cloth roll, cutting out 100 mm × 100 mm from an arbitrary position, observing the surface of the glass cloth with a scanning electron microscope, measuring the area of all the basket holes, Refers to the area of the largest basketball hole among them.

Methods of reducing the maximum area of basket holes while maintaining a constant average area of basket holes include, for example, a method of controlling tension and processing conditions in the steps of warping, weaving, desizing, processing, and opening. is mentioned.
Specifically, the method of managing tension and processing conditions includes a method of monitoring the tension of all warp yarns that make up the glass cloth and removing warp yarns whose tension deviates from the control value, the amount of size adhered during warping, and weaving. Examples include a method of making constant the number of revolutions during the time, the rate of temperature rise during desizing, and the water pressure in the opening process.

By keeping the warp tension within a certain range, the bundled state of the warp can be controlled, and the yarn width can be kept constant. In addition, by keeping the size adhesion amount constant during warping, the spreading effect in the spreading process can be controlled, and the yarn widths of the warp and weft can be kept constant. Further, by keeping the number of rotations constant during weaving, the tension of the weft can be controlled, the spreading effect in the spreading process can be controlled, and the width of the weft can be kept constant. In addition, by setting the temperature rise rate during desizing within a certain range, it is possible to control the amount of residual size after the desizing process, control the opening effect in the opening process, and keep the warp and weft widths constant. can be kept in Further, by keeping the water pressure in the opening process constant, the opening effect can be controlled, and the yarn widths of the warp and weft can be kept constant.
By controlling these tensions and processing conditions, it is possible to reduce the maximum area of the basket holes while keeping the average area of the basket holes constant.

In this embodiment, the maximum air permeability of the glass cloth is preferably 250 cm ³ /cm ² /sec or less. When the maximum air permeability is 250 cm ³ /cm ² /sec or less, the pinhole quality of the prepreg can be greatly improved. The maximum air permeability is more preferably 240 cm ³ /cm ² /sec or less, and still more preferably 230 cm ³ /cm ² /sec or less.
Also, the minimum air permeability is preferably 50 cm ³ /cm ² /sec or more, more preferably 60 cm ³ /cm ² /sec or more, still more preferably 70 cm ³ /cm ² /sec or more. When the minimum air permeability is 50 cm ³ /cm ² /sec or more, the occurrence of delamination tends to be suppressed.

The air permeability in this embodiment is air permeability that can be measured according to the method described in JIS R 3420.
Specifically, as the testing equipment, a manual or automatic Franziel type testing machine is used. Place the glass cloth test piece on one end of the cylinder and hold it with a clamp. In the case of the manual type, air is sucked in by the rheostat so that the inclined oil pressure gauge indicates a pressure of 124.5 Pa, and the pressure indicated by the vertical oil pressure gauge when adjusting the suction fan and the air hole used The amount of air cm ³ /cm ² /sec that passes through the test piece is determined from the type of
Three points in the width direction of the glass cloth are measured by the same measurement method, and the maximum and minimum values of air permeability are obtained.
Methods for adjusting air permeability include, for example, a method of controlling tension and processing conditions in the steps of warping, weaving, desizing, processing, and opening.

In the present embodiment, the openness of the warp and weft widths of the glass cloth is preferably 90% or more independently. When the degree of openness of the warp and weft is 90% or more, it is possible to improve pinhole quality and occurrence of delamination, and increase the rigidity of the substrate. The openness of the warp and weft is more preferably 91% or more, and still more preferably 92% or more.
Also, the upper limit of the openness of the warp and weft is preferably 120% or less, more preferably 115% or less, and still more preferably 110% or less. When the upper limit of the openness of the warp and weft is 120% or less, the area of the basket hole can be kept constant, and the pinhole quality tends to be improved.

The opening degree [%] in the present embodiment is a value calculated from the yarn width [μm], the filament diameter [μm], and the number of filaments [lines], as shown in the following formula.
Openness [%] = yarn width [μm] ÷ (filament diameter [μm] x number of filaments [lines]) x 100

Methods for adjusting the degree of opening include, for example, a method of controlling tension and processing conditions in the steps of warping, weaving, desizing, processing, and opening.

In the present embodiment, the minimum yarn widths of the warp and weft are each independently preferably 100 μm or more, more preferably 110 μm or more, and still more preferably 120 μm or more, from the viewpoint of improving the pinhole quality. be.
In the present embodiment, the maximum yarn widths of the warp and weft are each independently preferably 240 μm or less, more preferably 230 μm or less, and even more preferably 220 μm or less, from the viewpoint of suppressing the occurrence of delamination. is.
The width of the warp and weft is adjusted by adjusting the average filament diameter and the number of glass filaments, or by controlling the tension and processing conditions in the processes of warping, weaving, desizing, processing, and opening. can be adjusted by

The maximum width of the basket holes in the weft direction (also referred to as the maximum lateral width of the basket holes) is preferably 120 μm or less, more preferably 115 μm or less, and even more preferably 110 μm or less.
By setting the maximum width of the basket holes in the weft direction to 120 μm or less, the pinhole quality can be improved.
The minimum width of the basket holes in the weft direction is preferably 50 μm or more, more preferably 60 μm or more, and even more preferably 70 μm or more. Delamination tends to be suppressed by setting the minimum width of the basket holes in the weft direction to 50 μm or more.
The width of the basket holes in the weft direction can be adjusted, for example, by methods of controlling tension and processing conditions in the steps of warping, weaving, desizing, treating, and opening.

The cloth weight (basis weight) of the glass cloth is preferably 5 to 12 g/m ² , more preferably 6 to 11 g/m ² , still more preferably 7 to 10 g/m ² . Within the above range, the obtained substrate can be made thinner, the pinhole quality can be improved, and the occurrence of delamination can be suppressed.

The woven structure of the glass cloth is not particularly limited, but examples thereof include woven structures such as plain weave, Nanako weave, satin weave, and twill weave. Among these, the plain weave structure is more preferable.

The glass threads (including glass filaments) forming the glass cloth are preferably surface-treated with a silane coupling agent. As the silane coupling agent, it is preferable to use, for example, a silane coupling agent represented by the following general formula (1).

X(R) _{3-nSiYn (} 1)

In formula (1), X is an organic functional group having at least one of an amino group and an unsaturated double bond group, Y is each independently an alkoxy group, and n is 1 or more and 3 or less. It is an integer and R is a group selected from the group consisting of methyl, ethyl and phenyl groups.

X is more preferably an organic functional group having at least three or more of an amino group and an unsaturated double bond group, and X has at least four or more of an amino group and an unsaturated double bond group. More preferably, it is an organic functional group.
Any form of the alkoxy group can be used, but an alkoxy group having 5 or less carbon atoms is preferable for stabilizing the glass cloth.

Specific usable silane coupling agents include, for example, N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane and its hydrochloride, N-β-(N-vinylbenzylaminoethyl )-γ-aminopropylmethyldimethoxysilane and its hydrochloride, N-β-(N-di(vinylbenzyl)aminoethyl)-γ-aminopropyltrimethoxysilane and its hydrochloride, N-β-(N-di (vinylbenzyl)aminoethyl)-N-γ-(N-vinylbenzyl)-γ-aminopropyltrimethoxysilane and its hydrochloride, N-β-(N-benzylaminoethyl)-γ-aminopropyltrimethoxysilane and its hydrochloride, N-β-(N-benzylaminoethyl)-γ-aminopropyltriethoxysilane and its hydrochloride, γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-(2-amino Ethyl)aminopropyltriethoxysilane, aminopropyltrimethoxysilane, vinyltrimethoxysilane, methacryloxypropyltrimethoxysilane, acryloxypropyltrimethoxysilane, etc., or mixtures thereof.

The molecular weight of the silane coupling agent is preferably 100-600, more preferably 150-500, still more preferably 200-450.
Among these, it is preferable to use two or more silane coupling agents having different molecular weights. By treating the glass fiber surface with two or more silane coupling agents having different molecular weights, the density of the treatment agent on the glass surface tends to increase and the reactivity with the matrix resin tends to be further improved.

The ignition loss value of the glass cloth is preferably 0.12% by mass or more and 1.0% by mass or less, more preferably 0.13% by mass or more and 0.90% by mass or less, and still more preferably 0.14. It is more than mass % and below 0.80 mass %.
When the ignition loss value is 0.12% by mass or more and 1.0% by mass or less, the transportability (handling ability) of the prepreg can be improved more than before. In addition, it is possible to suppress the deterioration of the insulation reliability of the substrate due to the fact that the resin and the glass cloth are easily peeled off at the interface, and it is possible to suppress the deterioration of the insulation reliability of the substrate due to the plating solution permeating the glass cloth. There is a tendency.

The "loss on ignition value" as used herein can be measured according to the method described in JIS R 3420. First, the glass cloth is placed in a drier at 110° C. and dried for 60 minutes. After drying, the glass cloth is transferred to a desiccator, left for 20 minutes, and allowed to cool to room temperature. After standing to cool, the glass cloth is weighed in units of 0.1 mg or less. Next, the glass cloth is heated in a muffle furnace at 625° C. for 20 minutes. After heating in a muffle furnace, the glass cloth is transferred to a desiccator, left for 20 minutes, and allowed to cool to room temperature. After standing to cool, the glass cloth is weighed in units of 0.1 mg or less. The amount of glass cloth treated with the silane coupling agent is defined by the ignition loss value determined by the above measuring method.

A glass called E glass (alkali-free glass) is usually used for the glass cloth used for the laminate. In the glass cloth of this embodiment, L glass, NE glass, D glass, S glass, T Glass, silica glass, quartz glass, high dielectric constant glass, etc. may be used. E-glass is most preferably used because it is inexpensive.

[Method for manufacturing glass cloth]
The method for producing the glass cloth of the present embodiment is not particularly limited. , a fixing step of fixing the silane coupling agent to the surface of the glass filaments by heat drying, and a fiber opening step of opening the glass fibers of the glass cloth.

As a solvent for dissolving or dispersing the silane coupling agent, either water or an organic solvent can be used, but from the viewpoint of safety and protection of the global environment, it is preferable to use water as the main solvent. Methods for obtaining a treatment liquid containing water as a main solvent include a method of directly adding a silane coupling agent to water, a method of dissolving a silane coupling agent in a water-soluble organic solvent to form an organic solvent solution, and then dissolving the organic solvent solution. A method of throwing into water is preferable. A surfactant may be used in combination to improve the water dispersibility and stability of the silane coupling agent in the treatment liquid.

Methods for applying the treatment liquid to the glass cloth include (a) a method in which the treatment liquid is stored in a bath and the glass cloth is immersed and passed through (hereinafter referred to as the "immersion method"), (b) a roll coater, a die coater, Alternatively, a method of applying the treatment liquid directly to a glass cloth by a gravure coater or the like can be used. When the coating is performed by the above-described dipping method (a), it is preferable to select the immersion time of the glass cloth in the treatment liquid to be 0.5 seconds or more and 1 minute or less.

Further, as a method for heating and drying the solvent after the treatment liquid is applied to the glass cloth, known methods such as hot air and electromagnetic waves can be used.
The heat-drying temperature is preferably 90° C. or higher, more preferably 100° C. or higher so that the silane coupling agent and the glass react sufficiently. The heat drying temperature is preferably 300° C. or lower, more preferably 200° C. or lower, in order to prevent deterioration of the organic functional group of the silane coupling agent.

The method of opening the fibers in the opening step is not particularly limited, but examples thereof include a method of opening the glass cloth with spray water (high-pressure water opening), vibro washer, ultrasonic water, mangle, or the like. . In order to reduce the maximum area of the basket holes while keeping the average area of the basket holes constant, it is preferable to perform the fiber opening step with spray water.
In the case of opening with spray water, the water pressure may be appropriately set, and it is preferable to keep the water pressure constant in order to adjust the maximum area of basket holes present in the glass cloth to 50,000 μm ² or less. Here, keeping the water pressure constant means reducing the difference between the water pressure of the spray set for opening the fibers and the actual maximum and minimum values of the water pressure.
The difference between the water pressure of the spray set for opening and the maximum and minimum values of the actual water pressure should be less than 6% of the water pressure of the spray set for opening. It is preferably within 5%, more preferably within 4%.
Even after the opening step, a step of drying by heating may be included.

[Prepreg]
The prepreg of this embodiment has the glass cloth and a matrix resin impregnated in the glass cloth. As a result, it is possible to provide a prepreg that is thin, has excellent pinhole quality, and suppresses the occurrence of delamination of the substrate.

Both thermosetting resins and thermoplastic resins can be used as the matrix resin. Although the thermosetting resin is not particularly limited, for example, a) a compound having an epoxy group and an amino group, a phenol group, an acid anhydride group, a hydrazide group, an isocyanate group, a cyanate group, and a hydroxyl group that react with the epoxy group and a compound having at least one such as, without a catalyst, or with the addition of a catalyst having a reaction catalytic ability such as an imidazole compound, a tertiary amine compound, a urea compound, a phosphorus compound, etc. Epoxy that is reacted and cured Resin; b) A radically polymerizable curable resin that cures a compound having at least one of an allyl group, a methacrylic group, and an acrylic group using a thermal decomposition catalyst or a photodecomposition catalyst as a reaction initiator; c ) a maleimide triazine resin cured by reacting a compound having a cyanate group with a compound having a maleimide group; d) a thermosetting polyimide resin cured by reacting a maleimide compound with an amine compound; e) benzo Examples include benzoxazine resins and the like in which a compound having an oxazine ring is crosslinked and cured by heat polymerization.

The thermoplastic resin is not particularly limited, but for example, polyphenylene ether, modified polyphenylene ether, polyphenylene sulfide, polysulfone, polyether sulfone, polyarylate, aromatic polyamide, polyether ether ketone, thermoplastic polyimide, insoluble polyimide, Polyamideimide, fluororesin and the like are exemplified. Also, a thermosetting resin and a thermoplastic resin may be used in combination.

[Printed wiring board]
The printed wiring board of this embodiment has the prepreg described above. As a result, it is possible to provide a high-quality printed wiring board in which the occurrence of delamination is suppressed.

Next, the present invention will be described in more detail with reference to examples and comparative examples. The present invention is by no means limited by the following examples.

(Example 1)
Glass cloth (average filament diameter of glass filaments: 4.0 μm, number of filaments: 40, warp density: 95/inch, weft density: 95/inch, mass: 10 g/m ² ) was added to N-β-(N -vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane hydrochloride (manufactured by Dow Corning Toray Co., Ltd.; Z6032) was immersed in a treatment liquid in which water was dispersed, and dried by heating. Next, the water pressure was adjusted to 5.0±0.1 kg/cm ² , followed by high-pressure water opening, followed by heat drying to obtain a product.

(Example 2)
Glass cloth (average filament diameter of glass filaments: 4.0 μm, number of filaments: 33, warp density: 105/inch, weft density: 105/inch, mass: 9 g/m ² ) was added to N-β-(N -vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane hydrochloride (manufactured by Dow Corning Toray Co., Ltd.; Z6032) was immersed in a treatment liquid in which water was dispersed, and dried by heating. Next, the water pressure was adjusted to 5.0±0.1 kg/cm ² , followed by high-pressure water opening, followed by heat drying to obtain a product.

(Example 3)
Glass cloth (average filament diameter of glass filaments: 3.5 μm, number of filaments: 40, warp density: 110/inch, weft density: 110/inch, mass: 7 g/m ² ) was added to N-β-(N -vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane hydrochloride (manufactured by Dow Corning Toray Co., Ltd.; Z6032) was immersed in a treatment liquid in which water was dispersed, and dried by heating. Next, the water pressure was adjusted to 5.0±0.1 kg/cm ² , followed by high-pressure water opening, followed by heat drying to obtain a product.

(Comparative example 1)
Glass cloth (average filament diameter of glass filaments: 4.0 μm, number of filaments: 40, warp density: 95/inch, weft density: 95/inch, mass: 10 g/m ² ) was added to N-β-(N -vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane hydrochloride (manufactured by Dow Corning Toray Co., Ltd.; Z6032) was immersed in a treatment liquid in which water was dispersed, and dried by heating. Next, the water pressure was adjusted to 5.0±0.3 kg/cm ² , followed by high-pressure water opening and drying by heating to obtain a product.

(Comparative example 2)
Glass cloth (average filament diameter of glass filaments: 4.0 μm, number of filaments: 33, warp density: 105/inch, weft density: 105/inch, mass: 9 g/m ² ) was added to N-β-(N -vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane hydrochloride (manufactured by Dow Corning Toray Co., Ltd.; Z6032) was immersed in a treatment liquid in which water was dispersed, and dried by heating. Next, the water pressure was adjusted to 5.0±0.3 kg/cm ² , followed by high-pressure water opening and drying by heating to obtain a product.

(Comparative Example 3)
Glass cloth (average filament diameter of glass filaments: 3.5 μm, number of filaments: 40, warp density: 110/inch, weft density: 110/inch, mass: 7 g/m ² ) was added to N-β-(N -vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane hydrochloride (manufactured by Dow Corning Toray Co., Ltd.; Z6032) was immersed in a treatment liquid in which water was dispersed, and dried by heating. Next, the water pressure was adjusted to 5.0±0.3 kg/cm ² , followed by high-pressure water opening and drying by heating to obtain a product.

<Evaluation method for glass cloth basket hole, warp width, and weft width>
An arbitrary position of 100 mm×100 mm on the glass cloth was observed with a scanning electron microscope, all warp widths, weft widths, and basket hole areas were measured, and each average value and maximum value were obtained.

<Method for evaluating filament diameter of glass cloth>
Cross sections of 30 glass fiber bundles at arbitrary positions on the glass cloth were observed with a scanning electron microscope, and the average value was calculated to determine the average filament diameter.

<Method for evaluating degree of opening>
Using the warp width, weft width, and filament diameter obtained above, the opening degree was obtained by the following formula.
Openness [%] = yarn width [μm] ÷ (filament diameter [μm] x number of filaments [lines]) x 100

<Method for evaluating thickness of glass cloth>
According to 7.10 of JIS R 3420, using a micrometer, the spindle was gently rotated and brought into light parallel contact with the measurement surface, and the scale was read after the ratchet sounded three times.

<Method for producing prepreg and method for evaluating pinhole quality of prepreg>
Epoxy resin varnish (40 parts by mass of low-brominated bisphenol A epoxy resin, 10 parts by mass of o-cresol novolak epoxy resin, 50 parts by mass of dimethylformamide, 1 part by mass of dicyandiamide and 0.1 part by mass of 2-ethyl-4-methylimidazole diluted with a methyl ethyl ketone solvent to 50 wt%), pulled up at a speed of 2 m / min, and adjusted the gap so that RC was 65%. Excess resin was scraped off through a slit and dried at 160° C. for 1 minute to obtain a prepreg. An arbitrary 500 mm×500 mm area of the produced prepreg was observed with a portable microscope to determine the number of pinholes. The smaller the number of pinholes, the higher the quality.

<Method for preparing substrate>
The prepregs obtained above were layered, and copper foils having a thickness of 12 μm were layered on the upper and lower sides, followed by heating and pressing at 175° C. and 40 kg/cm ² for 60 minutes to obtain a laminate.

<Method for evaluating delamination property of substrate>
A substrate was prepared so as to have a thickness of 0.1 mm as described above, and after removing the copper foil with an etchant, it was exposed to a temperature of 121 ° C. and a humidity of 100% (2 atm) for 1 week. The substrate was immersed in a solder bath at 288° C. for 20 seconds, and the presence or absence of blisters and cracks on the substrate was visually checked. In Table 1, ◯ means that no swelling or cracks were found on the substrate, and X means that swelling or cracks were found on the substrate.

Table 1 summarizes the evaluation results of the glass cloths shown in Examples and Comparative Examples.
It was found that by using the glass cloth of the example, the pinhole quality of the prepreg is excellent and the occurrence of delamination of the substrate can be suppressed.

The glass cloth of the present invention has industrial applicability as a base material for printed wiring boards used in the electronic and electrical fields.

Claims (8)

A glass cloth made by weaving glass threads made of a plurality of glass filaments as warp and weft,
The average filament diameter of the glass filaments is 3.0 to 4.5 μm,
The number of the glass filaments is 20 to 50,
The warp yarns and weft yarns constituting the glass cloth have a density of 70 to 130 yarns/inch each independently,
The glass cloth has a thickness of 7 to 13 μm,
The maximum area of basket holes present in the glass cloth is 50,000 μm ² or less.
Glass cloth. 2. The glass cloth according to claim 1, having a maximum air permeability of 250 cm ³ /cm ² /sec or less. 3. The glass cloth according to claim 1 or 2, wherein the warp and weft yarn width openness is independently 90% or more. The glass cloth according to any one of claims 1 to 3, wherein the minimum yarn width of each of the warp yarns and the weft yarns is independently 100 µm or more. The glass cloth according to any one of claims 1 to 4, wherein the basket hole has a maximum lateral width of 120 µm or less. The glass cloth according to any one of claims 1 to 5, wherein the surface of the glass yarn is treated with a plurality of types of silane coupling agents. A prepreg comprising the glass cloth according to any one of claims 1 to 6 and a matrix resin impregnated in the glass cloth. A printed wiring board comprising the prepreg according to claim 7 .