JP7515299B2 - Glass cloth, prepreg, and printed wiring boards - Google Patents

Description

The present invention relates to glass cloth, prepregs, and printed wiring boards.

In many printed wiring boards, a transmission line is formed of copper foil on an insulating layer made of a glass cloth and a matrix resin composition.
Glass cloth used in printed wiring boards is formed by plain weaving glass yarns in the warp and weft directions. Therefore, in an insulator layer composed of glass cloth and a resin composition, the proportion of glass is high at the sites where the yarns cross, and the proportion of resin is high in areas where the yarns do not overlap or where there are no yarns.
Normally, since there is a difference between the dielectric constant of the glass of the glass cloth and the dielectric constant of the resin composition, it is known that a difference occurs between the signal propagation speed in a transmission line passing through a portion where the glass is abundant and the signal propagation speed in a transmission line passing through a portion where the resin composition is abundant. Therefore, in an electronic circuit that needs to synchronize multiple signals, when a difference occurs in the arrival time of the signals, there is a possibility that inconvenience will occur in signal processing.

With the recent development of the information and communications society, data communication and/or signal processing has become large-volume and high-speed, and the speed of signals transmitted on electronic circuit boards is increasing. Signal speeds have exceeded 10 Gbps and are now reaching speeds in the gigabit range, such as 28 Gbps and 56 Gbps. The higher the signal speeds, the greater the effect of the signal propagation speed difference described above, and there is an increasing demand to reduce the signal propagation speed difference.

The following Patent Documents 1 to 3 propose techniques for reducing the change in propagation speed caused by the relative positions of the glass cloth and the transmission line. Patent Document 1 discloses a technique for making the line width 75% to 95% of the spacing between the glass cloth threads. Patent Document 2 discloses a technique for matching the spacing between the glass threads and the spacing between the signal lines. Patent Document 3 discloses a technique for making the distance between the glass threads and the wiring width 50%.

In addition, the following Patent Documents 4 to 8 propose glass cloths with improved uniformity of glass distribution in the surface direction. As described in Patent Document 8 and the like, in order to reduce the difference in dielectric constant between a region with a high glass content and a region with a high resin content, many attempts have been proposed to reduce the dielectric constant of the glass cloth and reduce the difference with the dielectric constant of the resin. For example, the glass cloth disclosed in Patent Document 8 achieves a low dielectric constant by blending a large amount of B ₂ O ₃ in the glass composition and simultaneously adjusting the blending amount of other components such as SiO ₂ , compared to the E-glass cloth that has been generally used in the past.

JP 2014-130860 A International Publication No. 2016/117320 International Publication No. 2017/159649 WO 00/60153 Japanese Patent Application Laid-Open No. 11-61596 JP 2003-89967 A Japanese Patent No. 5195232 Japanese Patent Application Laid-Open No. 11-292567

The electronic circuit boards disclosed in Patent Documents 1 to 3 optimize the arrangement of the transmission lines, the glass cloth threads, and the spacing between the threads (areas without glass) to equalize the ratio of resin and glass through which the transmission lines pass. However, commercially available glass cloth has variations in the width of the warp and weft threads, and the weft threads are bent, making it substantially difficult to equalize the ratio of resin and glass through which the transmission lines pass.

The glass cloths disclosed in Patent Documents 4 to 8 have a high weft occupancy rate and high distribution uniformity in the plane direction of the glass cloth.
In the examples of Patent Document 4, glass cloths are disclosed which are woven using glass yarns of C1200 (Example 1), C900 (Example 2), D900 (Example 3) and D450 (Example 4) as warp and weft yarns, and then subjected to flattening processing, fiber-opening processing and surface treatment. The weft occupancy rates of these glass cloths are 97.2%, 97.7%, 98.3% and 100.2%, respectively.

The examples in Patent Document 5 disclose glass cloths that are woven using G75 (Examples 1 and 2) and E225 (Examples 3 and 4) glass yarns for the warp and weft, and then flattened, surface-treated, and opened; the weft occupancy rates of these glass cloths are 88.0%, 100.1%, 76.8%, and 100.8, respectively.

The examples of Patent Document 6 disclose glass cloths that are woven using D450 (Examples 1 to 4) glass yarns for the warp and weft, then impregnated with colloidal silica, opened with a vibro washer, and surface-treated. The weft occupancy rate of these glass cloths is 95.4% to 98.6%.

The examples in Patent Document 7 disclose glass cloths that are woven using glass yarns of C1200 (Example 1), D450 (Examples 2 and 3), and DE300 (Example 4) for the warp and weft, and then subjected to a surface treatment and fiber opening process. The weft occupancy rates of these glass cloths are 89.0%, 94.6%, 92.9%, and 87.8%, respectively.

The examples of Patent Document 8 disclose glass cloths that are woven using D450 (Example 1), E255 (Example 2), and G75 (Example 3) glass yarns for the warp and weft, and then the glass cloths are made to contain moisture and dried in a cylinder dryer. The weft occupancy rates of these glass cloths are 68.6%, 90.2%, and 79.5%, respectively.

However, commercially available glass cloths have the following problems: 1) warp and weft yarns have twist pools, which cause the yarns to become significantly thinner at the twist pools, resulting in localized areas where no glass is present; 2) weft yarns have bends and openings, resulting in localized areas where no glass is present; and 3) warp and weft yarns are not necessarily evenly arranged, resulting in areas where there are large gaps between adjacent glass yarns. For these reasons, even with the glass cloths disclosed in Patent Documents 4 to 8, it is difficult to obtain a glass cloth with uniform glass distribution in the surface direction, and further improvements are required.

In view of these problems with glass cloth of the prior art, the problem that the present invention aims to solve is to provide a glass cloth with improved uniformity of glass distribution in the surface direction, a prepreg using said glass cloth in which the difference in signal propagation speed between multiple transmission lines is reduced, and a printed wiring board having said prepreg.

As a result of intensive research and repeated experiments to solve the above problems, the inventors unexpectedly discovered that by using a glass cloth with a small elastic modulus within a specified range and a soft texture, and by controlling the weft occupancy rate, which indicates the overlap of the weft threads, within a specific range to avoid large distortion in the crimp structure, it is possible to obtain a glass cloth with excellent uniformity of glass distribution in the surface direction without impairing the interlayer adhesion with low dielectric resins and low roughness copper foils, which are useful for increasing the signal speed, and thus completed the present invention.

That is, the present invention is as follows.
[1] A glass cloth having a thickness of 50 μm to 100 μm and composed of glass yarns having an elastic modulus of 50 GPa to 70 GPa, the thickness being determined by the following formula (1):
Y=F/(25000/G)×100 Formula (1)
{wherein F is the weft width (μm), and G is the weaving density of the weft (pieces/25 mm).}, and the weft occupancy Y (%), which indicates the ratio of the area in which the weft is present in the MD direction, is 101.5% or more and 106.0% or less.
[2] The glass cloth according to the above [1], wherein the ratio of the weft width to the warp width of the glass cloth (weft width/warp width ratio) is 1.15 or more and 1.32 or less.
[3] The glass cloth according to [1] or [2], wherein the elastic modulus of the glass yarn is 50 GPa or more and 63 GPa or less.
[4] The glass cloth according to any one of [1] to [3], wherein the glass cloth is surface-treated with a silane coupling agent having an unsaturated double bond.
[5] The glass cloth according to any one of [1] to [4], wherein the glass cloth has a dielectric constant of 5.0 or less at a frequency of 10 GHz.
[6] A prepreg which is a composite of the glass cloth according to any one of [1] to [5] above and a matrix resin.
[7] A printed wiring board obtained by molding the prepreg according to [6] above.

The glass cloth according to the present invention has excellent uniformity of glass distribution in the surface direction, and can be used to provide a prepreg that has excellent heat resistance and serves as an insulating layer that reduces the difference in signal propagation speed between multiple transmission lines, as well as a printed wiring board made by molding the prepreg.

The following describes in detail an embodiment of the present invention (hereinafter referred to as the "present embodiment"); however, the present invention is not limited to this embodiment, and various modifications are possible without departing from the gist of the present invention.

One embodiment of the present invention is a glass cloth having a thickness of 50 μm or more and 100 μm or less and made of glass yarns having an elastic modulus of 50 GPa or more and 70 GPa or less, the glass cloth satisfying the following formula (1):
Y=F/(25000/G)×100 Formula (1)
{wherein F is the weft width (μm) and G is the weaving density of the weft (pieces/25 mm).}, and the weft occupancy coefficient Y (%), which indicates the ratio of the area in the MD where the weft is present, is 101.5% or more and 106.0% or less.

The glass cloth of this embodiment uses glass yarns with a soft texture, and the weft yarns are filled at an occupancy rate of more than 100%, so it has excellent surface smoothness, and when made into a prepreg, it has excellent in-plane distribution uniformity of glass while maintaining high impregnation and adhesion of low dielectric resin. As a result, it becomes an insulator layer with excellent heat resistance and reduced differences in signal propagation speed between multiple transmission lines.

[Elastic modulus]
The elastic modulus of the glass yarn constituting the glass cloth of the present embodiment is 50 GPa or more, preferably 51 GPa or more, and more preferably 52 GPa or more. If the elastic modulus is 50 GPa or more, the rigidity of the glass yarn is improved, and the glass cloth tends to be less likely to break or fluff during the manufacturing process.
On the other hand, the elastic modulus of the glass yarn is 70 GPa or less, preferably 65 GPa or less, more preferably 63 GPa or less. If the elastic modulus is 70 GPa or less, the glass yarn has a moderate flexibility, so that even if the weft occupancy rate described below becomes 101.5 or more and the weft yarns overlap each other, the crimp structure does not suffer from significant distortion, and both the warp and weft yarns can maintain a uniform wavy structure, resulting in a structure with good surface smoothness. As a result, in the prepreg and substrate composed of glass cloth and resin, the thickness of the resin layer can be uniformly configured, so that the interlayer adhesion between the glass cloth/resin in the laminate and the adhesion between the resin and the copper foil can be uniformly increased, resulting in high heat resistance.

[thickness]
The thickness of the glass cloth in this embodiment is 50 μm or more and 100 μm or less, preferably 60 μm or more and 98 μm or less, more preferably 65 μm or more and 96 μm or less. If the thickness of the glass cloth is 100 μm or less, it is possible to increase the density and multi-layer of the printed wiring board. The above thickness is preferably thin from the viewpoint of making the printed wiring board thin and high-density, but the lower limit of the thickness is 50 μm from the viewpoint of achieving the weft occupancy rate described below while maintaining the commonly used configuration (warp and weft yarn counts, weaving density) listed in the IPC registration list.

[Weft Yarn Occupancy Rate]
The weft occupancy rate of the glass cloth of the present embodiment is 101.5% or more, preferably 101.8% or more, more preferably 102.2% or more, and even more preferably 102.5% or more. On the other hand, the weft occupancy rate is 106.0% or less, preferably 105.7% or less, more preferably 105.4% or less, and even more preferably 105.0% or less.
In this specification, the weft occupation ratio Y (%) is a value indicating the ratio of the portion where the weft exists in the MD direction (machine direction, warp direction in weaving) of the glass cloth. Specifically, the weft occupation ratio Y (%) is calculated by the following formula (1): using the weaving density (lines/25 mm) of the weft measured in accordance with JIS R3420 and the weft width (μm) obtained by observing a glass cloth sample having a size of 100 mm×100 mm from the surface with a microscope, determining the width of all the wefts, and dividing the sum by the number of wefts to obtain the average value. In the case where the weft width varies within the sample, the width at the widest point is used.
Y=F/(25000/G)×100 Formula (1)
This is the value calculated using the formula:

The state where the weft occupation ratio exceeds 100% means a state where adjacent wefts overlap each other in the MD cross section of the glass cloth. The inventors of the present application have discovered that, in the conventional technology, when an attempt is made to increase the weft occupation ratio by widening the weft width, the crimp (waviness) structure in the warp direction becomes cramped, distortion occurs, the surface shape becomes non-uniform, and the in-plane uniformity (uniformity of glass distribution in the plane normal direction) and surface smoothness of the glass cloth decrease. In order to solve this problem, the inventors have found that by setting the weft occupation ratio within a predetermined range, it is possible to suppress the distortion of the crimp structure and thereby to increase the in-plane uniformity and surface smoothness of the glass cloth.
If the weft occupancy rate is 101.5% or more, the glass cloth has excellent in-plane uniformity, so that the ratio of glass to resin in the insulator layer composed of glass cloth and resin becomes more uniform, and the signal propagation speeds of multiple transmission lines formed on the insulator layer tend to be equal, resulting in small deviations in signal arrival times and enabling stable signal processing.

The glass cloth of this embodiment is composed of glass yarns having a soft and pliable texture with an elastic modulus of 70 GPa or less, and therefore even if the weft occupancy rate is 101.5% or more, no distortion occurs in the crimp structure of the weft and warp yarns, and a uniform woven structure can be obtained. Therefore, when a composite body is formed with resin or copper foil, the interface between the glass cloth and the resin becomes geometrically uniform in-plane, and the layer thickness of the resin also becomes uniform in-plane, so that the interlayer adhesion between the glass cloth/resin and the adhesion between the resin and the copper foil can be uniformly increased, thereby obtaining high heat resistance.
On the other hand, from the viewpoint of forming a uniform woven structure without causing distortion in the crimp structure of the weft and warp yarns, the upper limit of the weft occupancy rate is 106.0% or less.

The weft occupancy rate can be appropriately adjusted by designing the warp and weft weave densities in the warping and weaving processes, and by the degree of warp and weft width expansion in the spreading process described below. In the spreading process, tension is applied to the warp threads to spread the glass filaments in the planar direction while transporting the glass cloth, so the degree of width expansion can also be adjusted by adjusting the strength of the tension acting on the warp threads. In addition, it is preferable for the tension acting on the warp threads to be uniform in the width direction (weft direction), as this will result in uniform width expansion of the warp and weft threads, and therefore the in-plane uniformity of the glass cloth can be made uniform throughout the width direction of the glass cloth.

In the glass cloth of the present embodiment, the ratio of the weft width to the warp width (weft width/warp width ratio) is preferably 1.32 or less, more preferably 1.31 or less, and even more preferably 1.30 or less.
On the other hand, the weft width/warp width (weft width/warp width ratio) is preferably 1.01 or more, more preferably 1.05 or more, even more preferably 1.1 or more, and particularly preferably 1.15 or more.
If the weft width/warp width ratio is within this range, when a woven structure is formed with a weft occupancy rate of 101.5% or more using glass yarns with a soft and pliable texture and an elastic modulus of 70 GPa or less, the crimp amplitude of the weft yarn tends to be kept smaller, and the distortion of the crimp structure of the warp yarns and the weft yarns also tends to be kept smaller, which is preferable because it is easy to obtain a glass cloth with excellent in-plane glass uniformity and surface smoothness. As a result, the glass cloth has excellent surface smoothness while maintaining a high in-plane uniformity of the glass cloth, so that it is easy to achieve both the in-plane glass uniformity and the interlayer adhesion between the glass cloth and the resin, the interlayer adhesion between the resin and the copper foil, and heat resistance.

[Silane coupling agent]
The glass cloth of the present embodiment is preferably surface-treated with a silane coupling agent having an unsaturated double bond.
In order to achieve high-speed signals, the matrix resin used in the insulating layer of an electronic circuit board is also required to have a low dielectric constant and a low dielectric loss tangent. Therefore, low-dielectric resins such as polyphenylene ether resins having radically polymerizable functional groups such as vinyl groups, acrylate groups, methacrylate groups, and allyl groups are useful as matrix resins instead of the epoxy resins that have been widely used in electronic circuit boards.
The glass cloth is surface-treated with a silane coupling agent having an unsaturated double bond, which improves the interlayer adhesion with the low dielectric resin, and improves the insulation reliability, heat resistance, and mechanical durability.

The silane coupling agent having an unsaturated double bond is not particularly limited, but for example, a silane coupling agent represented by the following formula (2) is preferable.
X(R) _{SiY ...} (2)
In formula (2), X contains an organic functional group having at least one unsaturated double bond group, from the viewpoint of strengthening adhesion to the matrix resin. Suitable examples of the unsaturated double bond group include a vinyl group and an allyl group.
Each Y is independently an alkoxy group, n is an integer of 1 to 3, and each R is independently a group selected from the group consisting of a methyl group, an ethyl group, and a phenyl group.
The organic functional group of X may include an amino group. The amino group may be a primary amine group ( _-NH2 ), a secondary amine group (-NH-), or a tertiary amine group (-N<), and includes all of these primary to tertiary amine groups.
The alkoxy group Y may be in any form, but for the purpose of stabilizing the treatment of glass cloth, an alkoxy group having 5 or less carbon atoms is preferred.

Examples of silane coupling agents include, but are not limited to, 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, vinyltrimethoxysilane, vinyltriethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, and the like. These may be used alone or in combination of two or more.

[Dielectric constant]
The glass cloth of the present embodiment preferably has a relative dielectric constant of 5.0 or less at a frequency of 10 GHz. A relative dielectric constant of 5.0 or less at a frequency of 10 GHz is preferable because the difference in dielectric properties between a region having a high glass content and a region having a high resin content in an insulator layer made of glass cloth and resin is kept small, thereby reducing a change in the propagation speed.

<Method of manufacturing glass cloth>
The manufacturing method of the glass cloth of the present embodiment is not particularly limited, but may be a method in which glass yarns are used as warp and weft yarns, woven by a conventional method, and then post-processed by treating the green glass cloth with a silane coupling agent. The weaving structure of the glass cloth is not particularly limited, but may be, for example, a plain weave, a sash weave, a satin weave, or a twill weave. Furthermore, a mixed weave structure using different types of glass yarns may be used. Among these, a plain weave structure is preferred.

The method for producing the glass cloth of the present embodiment is not particularly limited, but a suitable example is a method having a coating process in which a treatment liquid having a silane coupling agent concentration of 0.1 to 3.0 wt % is applied to the glass cloth to almost completely cover the surfaces of the glass filaments with the silane coupling agent, a fixing process in which the silane coupling agent is fixed to the surfaces of the glass filaments by heating and drying, and a fiber-opening process in which the glass threads of the glass cloth are opened.
As the solvent for dissolving or dispersing silane coupling agent, water or organic solvent can be used, but from the viewpoint of safety and global environmental protection, it is preferable to use water as the main solvent.As the method for obtaining the treatment liquid with water as the main solvent, it is preferable to directly put silane coupling agent into water, or to dissolve silane coupling agent in a water-soluble organic solvent to make an organic solvent solution, and then put the organic solvent solution into water.In order to improve the water dispersibility and stability of silane coupling agent in the treatment liquid, it is also possible to use surfactant in combination.

Methods for applying the treatment solution of the silane coupling agent to the glass cloth include (a) a method in which the treatment solution of the silane coupling agent is stored in a bath and the glass cloth is immersed and passed through the solution (hereinafter referred to as the "immersion method"), and (b) a method in which the treatment solution of the silane coupling agent is directly applied to the glass cloth using a roll coater, a die coater, a gravure coater, etc. When applying the treatment solution by the immersion method (a) above, it is preferable to set the immersion time of the glass cloth in the treatment solution to 0.5 seconds or more and 1 minute or less.
As a method for heating and drying the solvent after applying the treatment liquid to the glass cloth, known methods such as hot air and electromagnetic waves can be used.

The heating and drying temperature is preferably 90°C or higher, more preferably 100°C or higher, so that the reaction between the silane coupling agent and the glass is sufficiently carried out. In addition, the heating and drying temperature is preferably 300°C or lower, more preferably 200°C or lower, to prevent deterioration of the organic functional groups of the silane coupling agent.

The method for opening the fibers in the opening step is not particularly limited, but examples thereof include a method for opening the glass cloth with spray water (high pressure water opening), a vibro washer, ultrasonic water, a mangle, etc. In order to keep the total area of the basket holes within a certain range, it is preferable to carry out the opening step with spray water.
When the fibers are spread using spray water, the water pressure may be appropriately set, and it is preferable to keep the water pressure constant in order to adjust the total area of the basket holes present in the glass cloth. Keeping the water pressure constant here means reducing the difference between the spray water pressure set for spreading and the maximum and minimum values of the actual water pressure. A heat drying step may also be included before or after the spreading step.

Another embodiment of the present invention is a prepreg which is a composite of the above-mentioned glass cloth and a matrix resin.
The glass cloth is impregnated with the matrix resin.
The prepreg can be produced by a conventional method, for example, by impregnating a glass cloth with a varnish prepared by diluting a matrix resin with an organic solvent, and then volatilizing the organic solvent in a drying furnace to produce a resin-impregnated prepreg.

As the matrix resin, either a thermosetting resin or a thermoplastic resin can be used.
The thermosetting resin is not particularly limited, but examples thereof include: a) an epoxy resin in which a compound having an epoxy group is reacted with a compound having at least one of an amino group, a phenol group, an acid anhydride group, a hydrazide group, an isocyanate group, a cyanate group, and a hydroxyl group that reacts with the epoxy group, without a catalyst or by adding a catalyst having a reaction catalytic ability, such as an imidazole compound, a tertiary amine compound, a urea compound, or a phosphorus compound, to be cured; b) a radical polymerization type curing resin in which a compound having at least one of a vinyl group, an allyl group, a methacryl group, and an acrylic group is cured using a thermal decomposition type catalyst or a photodecomposition type catalyst as a reaction initiator; c) a maleimide triazine resin in which a compound having a cyanate group is reacted with a compound having a maleimide group to be cured; d) a thermosetting polyimide resin in which a maleimide compound is reacted with an amine compound to be cured; and e) a benzoxazine resin in which a compound having a benzoxazine ring is crosslinked and cured by thermal polymerization.

The thermoplastic resin is not particularly limited, but examples thereof include polyphenylene ether, modified polyphenylene ether, polyphenylene sulfide, polysulfone, polyether sulfone, polyarylate, aromatic polyamide, polyether ether ketone, thermoplastic polyimide, insoluble polyimide, polyamide imide, and fluororesin.
Moreover, a thermosetting resin and a thermoplastic resin may be used in combination.

The matrix resin in the prepreg composed of glass cloth and a matrix resin, which is one of the present embodiments, is preferably a polyphenylene ether resin. More preferably, it is a polyphenylene ether resin having 1.5 to 5 functional groups containing a carbon-carbon double bond, such as vinyl groups, allyl groups, methacrylic groups, and acrylic groups, at the main chain terminal per molecule. Also, it is preferably a polyphenylene ether having a number average molecular weight of 500 to 8,000.
The matrix resin is preferably a polyphenylene ether resin, since it has excellent dielectric properties.
Furthermore, since the matrix resin has the above-mentioned functional groups and number average molecular weight, it is presumed that the resin composition easily penetrates into the interior of the glass cloth in the prepreg production process and press molding process, and many bonding points with the glass cloth are secured, resulting in excellent dielectric properties. However, even in a system such as this embodiment in which the in-plane uniformity of the glass is high and the air permeability is low, resulting in a reduced number of direct bonding points between the resin matrix layers formed above and below the glass cloth, strong adhesion is expressed at the interface between the glass cloth and the resin composition, thereby improving heat resistance and insulation reliability.

Yet another embodiment of the present invention is a printed wiring board manufactured using the prepreg described above, i.e., a printed wiring board formed by molding the prepreg of this embodiment. By manufacturing a printed wiring board using the prepreg of this embodiment, it is possible to provide a high-quality printed wiring board in which the difference in signal propagation speed between multiple transmission lines is reduced.

The present invention will be specifically described below using examples and comparative examples, but the present invention is not limited to the following examples.
First, the methods for evaluating various physical properties and characteristics used in the examples will be described.

(1) Elastic modulus of glass yarn (GPa)
The elastic modulus of the glass yarns constituting the glass cloth was measured by the pulse echo overlap method using a glass bulk obtained by melting and cooling the glass yarns as a test piece.

(2) Thickness of glass cloth (μm)
The thickness of the glass cloth was measured in accordance with JIS R3420 (7.10 cloth and mat thickness). Using Method A, the thickness was measured with a micrometer at five equal points 150 mm inside from the edge, and the arithmetic average of the measured values was calculated.

(3) Weave density of warp and weft threads constituting the glass cloth (threads/25 mm)
The weave density was measured in accordance with JIS standard R3420 (7.9 weave density). The number of threads at 50 mm intervals was measured at three locations 150 mm inside from the edge of the fabric. The number of threads per 25 mm was calculated for each measurement, and the average value of the three measurements was calculated.

(4) Width (μm) of warp and weft yarns constituting the glass cloth, and weft width/warp width ratio The width of the warp and weft yarns constituting the glass cloth was determined by observing a glass cloth sample measuring 100 mm×100 mm from the surface with a microscope, determining the width of all warp and weft yarns, and dividing the sum by the number of warp and weft yarns, to obtain the average value. In this case, when the width of the weft or warp yarn varies within the sample, the width of the widest part was regarded as the width of the weft or warp yarn. Using these, the weft width/warp width ratio was calculated.

(5) Weft Yarn Occupancy Rate Y (%)
Using the weaving density (counts/25 mm) and the width (μm) of the weft yarn as described above, the following formula (1):
Y=F/(25000/G)×100 Formula (1)
was calculated.

(6) Dielectric constant of glass yarn A bulk glass test piece with a length of about 50 mm and a width of about 1.5 mm was prepared by melting the glass yarn, and the dielectric constant was measured using a cavity resonator. The test piece was placed in an oven at 105°C ± 2°C and dried for 2 hours, and then left to stand in a thermostatic chamber at 23 ± 2°C and a relative humidity of 50 ± 5% for 96 hours, after which the dielectric constant at 10 GHz was measured.
The measurement was performed using a network analyzer (N5230A, manufactured by Agilent Technologies) and a cavity resonator (Cavity Resonator CP series) manufactured by Kanto Electronics Application Development Co., Ltd. under an environment of 23±2° C. and a relative humidity of 50±5%.

(7) Evaluation of Uniformity of Air Permeability of Glass Cloth The air permeability of the glass cloth was measured at 12 equally spaced points in the width direction and evaluated on a 5-point scale according to the following criteria: The air permeability was measured using an air permeability meter (FX3300LabAir Mark4, manufactured by TEXTEST AG).
5: Both the average and maximum air permeability are 3.0 or less. 4: The average air permeability is 3 or less, and the maximum value is greater than 3.0 and less than 3.3. 3: The average air permeability is 3 or less, and the maximum value is greater than 3.3 and less than 3.6. 2: The average air permeability is 3 or less, and the maximum value is greater than 3.6 and less than 5.0. 1: The average air permeability is greater than 3.

(8) Evaluation of Heat Resistance of Glass Cloth The glass cloths A to O obtained in the Examples and Comparative Examples were impregnated with the varnish of the polyphenylene ether-containing resin composition shown in Table 1 below, and then passed through a predetermined slit to scrape off excess varnish. The glass cloths were then dried for a predetermined time in a drying oven at 105° C. to remove the solvent, thereby obtaining prepregs.
Four sheets of the obtained prepreg were stacked, and copper foil (FV-WS foil, manufactured by Furukawa Electric Co., Ltd.) with a thickness of 12 μm and a surface roughness Rz of 2.0 μm was stacked on both sides of the stack. A copper-clad laminate was produced by vacuum pressing for 60 minutes under conditions of a temperature of 200° C. and a pressure of 40 kg/ ^cm2 .
The copper foil on only one side was removed by etching, and a heat resistance test was performed. The heat resistance test was performed by cutting test pieces into 50 mm squares, placing them in an oven at 105°C and drying them for 2 hours, and then performing a pressure cooker test (PCT) (condition 1: 3 atm, 72 hours, condition 2: 3 atm, 4 hours, condition 3: 2 atm, 4 hours). Then, a heat resistance test was performed in which the test pieces were dipped in a solder bath at 260°C or 288°C for 20 seconds, and this was repeated 30 times. The dip interval was 20 seconds.
The heat resistance was evaluated by visual observation according to the following evaluation criteria.
5: Laminate in which no blistering, peeling, or whitening was observed under soldering test conditions of 288°C (PCT 3 atmospheres, 72 hours) 4: Laminate in which no blistering, peeling, or whitening was observed under soldering test conditions of 288°C (PCT 3 atmospheres, 4 hours) 3: Laminate in which no blistering, peeling, or whitening was observed under soldering test conditions of 288°C (PCT 2 atmospheres, 4 hours) 2: Laminate in which no blistering, peeling, or whitening was observed under soldering test conditions of 260°C (PCT 2 atmospheres, 4 hours) (blistering, peeling, or whitening occurred under the 288°C condition)
1: A laminate that exhibited swelling, peeling, or whitening under the conditions of a solder test at 260°C (PCT 2 atmospheres, 4 hours).

<Materials used in matrix resin (polyphenylene ether-containing resin composition, see Table 1)>
PPE
Modified polyphenylene ether 1 (modified PPE1, Mn: 1600) obtained in Production Example 1 below
- Terminal methacrylic group modified PPE "Product name SA9000" (Sabic Innovative Plastics, Mn: 2756)
Polyphenylene ether "Product name S201A" (manufactured by Asahi Kasei Corporation, Mn: 22,000)
Thermoplastic resin: Hydrogenated styrene-based thermoplastic resin "Product name: Tuftec H1051" (manufactured by Asahi Kasei Corporation)
- Hydrogenated styrene-based thermoplastic resin "Product name: Tuftec N504" (manufactured by Asahi Kasei Corporation)
Other components: Crosslinking agent: TAIC (manufactured by Nippon Kasei Co., Ltd.)
Organic peroxide: di(2-t-butylperoxyisopropyl)benzene "Product name: Perbutyl P" (manufactured by NOF Corporation)
Flame retardant: Decabromodiphenylethane "Product name SAYTEX 8010" (manufactured by Albemarle Corporation)
Additive: Spherical silica (Tatsumori Co., Ltd.)

｛式中、ｌ、ｍ、及びｎは、下記数平均分子量を満たすように任意に選択される数である｝
で表される構造を有するＰＰＥ（以下、ＰＰＥ１という）であると確認できた。ＧＰＣ測定の結果、得られたＰＰＥ１のポリスチレン換算での分子量はＭｎ＝１，５００であった。また、ＰＰＥ１の２０％メチルエチルケトン溶媒中での溶液粘度は１２５ｃＰｏｉｓｅであった。 (Production Example 1)
Synthesis of PPE1 (PPE1) A 500 ml three-neck flask was fitted with a three-way cock, and further fitted with a Dimroth valve and a pressure equalizing dropping funnel. After replacing the atmosphere in the flask with nitrogen, 100 g of raw material PPE S202A, 200 g of toluene, and 12.8 g of 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane as a polyfunctional phenol were added. A thermometer was placed in the flask, and the flask was heated to 90° C. in an oil bath while stirring with a magnetic stirrer to dissolve the raw material PPE. As an initiator, 37.5 g of a 40% meta-xylene solution of a mixture of benzoyl peroxide, benzoyl m-methylbenzoyl peroxide, and m-toluyl peroxide (manufactured by NOF Corp.: Niper BMT) was diluted with 87.5 g of toluene and charged into a pressure equalizing dropping funnel. After the temperature inside the flask was lowered to 80°C, the initiator solution was started to be dropped into the flask to start the reaction. The initiator was dropped over 2 hours, and after the dropwise addition, the temperature was raised again to 90°C and stirring was continued for 4 hours. After the reaction, the polymer solution was dropped into methanol and reprecipitated, and then the solution was separated by filtration to recover the polymer. This was then dried at 100°C under vacuum for 3 hours. It was confirmed by ^1H -NMR that the low molecular weight phenol had been incorporated into the polymer and the peak of the hydroxyl group had disappeared. From the ^1H -NMR measurement results, the obtained polymer had the following formula:

{wherein l, m, and n are numbers arbitrarily selected to satisfy the number average molecular weight below}
As a result of GPC measurement, the molecular weight of the obtained PPE1 in terms of polystyrene was Mn=1,500. The solution viscosity of PPE1 in a 20% methyl ethyl ketone solvent was 125 cPoise.

｛式中、ｌ、ｍ、及びｎは、下記数平均分子量を満たすように任意に選択される数である｝で表される構造を有する変性ＰＰＥ（以下、変性ＰＰＥ１という）であると確認できた。
また、ＧＰＣ測定の結果、得られた変性ＰＰＥ１のポリスチレン換算での分子量はＭｎ＝１，６００であった。また、変性ＰＰＥ１の平均末端官能基数は、上記数式（２）に従って、２．０以上であることが算出された。更に、変性ＰＰＥ１の２０％メチルエチルケトン溶媒中での溶液粘度は１３１ｃＰｏｉｓｅであった。 (Synthesis of modified PPE1)
80 g of toluene and 26 g of PPE1 synthesized above were mixed and heated to approximately 85° C. 0.55 g of dimethylaminopyridine was added to the heated mixture. Once all solids appeared to have dissolved, 4.9 g of methacrylic anhydride was slowly added to the melt. The resulting solution was maintained at 85° C. for 3 hours with continuous mixing. The solution was then cooled to room temperature to provide a toluene solution of methacrylate modified PPE.
A part of the solution was collected, dried, and then ¹ H-NMR measurement was carried out. Since the peaks derived from the hydroxyl groups of the PPE had disappeared, it was judged that the reaction was proceeding, and the purification operation was started. 120 g of the above toluene solution of methacrylate-modified PPE was dropped over 30 minutes into 360 g of methanol in a 1 L beaker that was vigorously stirred with a magnetic stirrer. The resulting precipitate was filtered under reduced pressure with a membrane filter and then dried to obtain 38 g of polymer. The result of ¹ H-NMR measurement of the dried polymer is shown in FIG. 1. It was confirmed that the peak derived from the hydroxyl groups of PPE at around 4.5 ppm had disappeared, and that a peak derived from the olefin of the methacryl group had appeared at around 5.75 ppm. In addition, since the peaks derived from dimethylaminopyridine, methacrylic anhydride, and methacrylic acid had almost disappeared by GC measurement, it was judged that the peak derived from the methacryl group in NMR was that of the methacryl group bonded to the PPE terminal. From this result, the obtained polymer was a compound represented by the following formula:

It was confirmed that the modified PPE was a modified PPE (hereinafter referred to as modified PPE1) having a structure represented by the formula: {wherein l, m, and n are numbers arbitrarily selected so as to satisfy the number average molecular weight below}.
As a result of GPC measurement, the molecular weight of the modified PPE1 obtained was Mn=1,600 in terms of polystyrene. The average number of terminal functional groups of the modified PPE1 was calculated to be 2.0 or more according to the above formula (2). Furthermore, the solution viscosity of the modified PPE1 in a 20% methyl ethyl ketone solvent was 131 cPoise.

[Examples 1 to 7, Comparative Examples 1 to 3]
For both the warp and weft, low dielectric glass yarns (L glass LCDE340, elastic modulus 61 GPa, relative dielectric constant 4.8) having an average filament diameter of 6.0 μm and 200 filaments were used, and a glass cloth (grey) was woven using an air jet loom with a warp pick density of 59.0 yarns/25 mm and a weft pick density of 61.5 yarns/25 mm.
The grey fabric was heat-treated at 400°C for 24 hours to remove the size, and then the glass cloth was immersed in a treatment solution using a silane coupling agent, 3-methacryloxypropylmethyldimethoxysilane; KBM502 (manufactured by Shin-Etsu Silicones), as a surface treatment agent. After squeezing out the liquid, the glass cloth was dried at 120°C for 1 minute, and then subjected to a width-widening process and a fiber-opening process using a high-pressure water spray, to obtain glass cloths A to I shown in Table 1 below.
During the above-mentioned widening and opening processes, the tension and spray pressure acting in the MD were adjusted to adjust the warp width and weft width.

[Comparative Examples 4 to 6]
Glass cloths J to L were obtained in the same manner as in Example 1, except that a general-purpose glass yarn (E glass ECDE300, elastic modulus 74 GPa, relative dielectric constant 6.8) having an average filament diameter of 6.0 μm and 200 filaments was used for both the warp and weft.

[Example 8, Comparative Example 7]
For both the warp and weft yarns, low dielectric type glass yarns (L glass LCE255, elastic modulus 61 GPa, relative dielectric constant 4.8) consisting of 200 filaments with an average filament diameter of 7.0 μm were used, and the warp yarn packing density was 60.0 yarns/25 mm and the weft yarn packing density was 57.0 yarns/25 mm. Except for this, glass cloths M and N were obtained in the same manner as in Example 1.

Comparative Example 8
A glass cloth O was obtained in the same manner as in Example 8, except that a general-purpose glass yarn (E glass ECE225, elastic modulus 74 GPa, relative dielectric constant 6.8) having an average filament diameter of 7.0 μm and 200 filaments was used for both the warp and weft.

The various physical properties and characteristics of the glass cloths A to O obtained in Examples 1 to 8 and Comparative Examples 1 to 8, as well as the heat resistance of the copper-clad laminates formed by molding prepregs in which the glass cloths are compounded with a matrix resin, are shown in Table 1 below.

As disclosed in Examples 1 to 8, the glass cloth of the present embodiment had excellent uniformity in air permeability and heat resistance.
In Comparative Examples 1, 2, 4, and 7, the weft occupancy rate was small, so there were areas with large basket holes, and the air permeability was high and the uniformity of the air permeability was poor.
In Comparative Example 3, the weft occupancy rate was large, so the breathability was highly uniform. However, the large weft occupancy rate caused significant distortion in the crimp structure of the weft and warp yarns, resulting in poor heat resistance.
In Comparative Examples 5, 6, and 8, the weft occupancy rate was high, and a certain degree of uniformity in air permeability was obtained, but because E-glass with a high elastic modulus was used, the distortion of the crimp structure of the weft and warp yarns was large, and the heat resistance was poor.

The glass cloth according to the present invention has excellent uniformity of glass distribution in the surface direction, and can be used to provide a prepreg that has excellent heat resistance and serves as an insulating layer that reduces the difference in signal propagation speed between multiple transmission lines, as well as a printed wiring board made by molding the prepreg.

Claims (6)

A glass cloth having a thickness of 50 μm or more and 100 μm or less and made of glass yarns having an elastic modulus of 50 GPa or more and 70 GPa or less, the thickness of which satisfies the following formula (1):
Y=F/(25000/G)×100 Formula (1)
{wherein F is the weft width (μm), and G is the weaving density of the weft (lines/25 mm)}, and indicates the ratio of the area in which the weft is present in the MD direction , and is 101.5% or more and 106.0% or less, and the ratio of the weft width to the warp width (weft width/warp width ratio) of the glass cloth is 1.15 or more and 1.32 or less . The glass cloth according to claim 1 , wherein the elastic modulus of the glass yarn is 50 GPa or more and 63 GPa or less. 3. The glass cloth according to claim 1 , wherein the glass cloth is surface-treated with a silane coupling agent having an unsaturated double bond. The glass cloth according to any one of claims 1 to 3 , which has a relative dielectric constant of 5.0 or less at a frequency of 10 GHz. A prepreg which is a composite of the glass cloth according to any one of claims 1 to 4 and a matrix resin. A printed wiring board produced by molding the prepreg according to claim 5 .