JP7321879B2 - Prepregs and printed wiring boards - Google Patents

Description

TECHNICAL FIELD The present invention relates to a silica glass cloth, a prepreg using the same, and a printed wiring board provided with the prepreg.

BACKGROUND ART At present, as information terminals such as smart phones have improved performance and high-speed communication, printed wiring boards used in them have been remarkably developed to have higher density and ultra-thin thickness, as well as to have low dielectric and low dielectric loss tangent.

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. While the dielectric constant of the matrix resin used in the above high-speed communication substrate is about 3, the dielectric constant of the general E-glass cloth is about 6.7, and the problem of high dielectric constant when laminated is It is becoming apparent. The signal transmission loss is described by Edward A. et al. Wolff formula: transmission loss ∝√ε×tan δ, it is known that the smaller the dielectric constant (ε) and dielectric loss tangent (tan δ) of the material, the better the improvement. It is known that the contribution of the dielectric loss tangent (tan δ) is large.

Therefore, there have been proposed glass cloths with improved dielectric properties, such as D-glass, NE-glass, and L-glass, which have glass compositions different from E-glass (see, for example, Patent Documents 1 to 3).

However, in future 5G communication applications, etc., these low dielectric constant glass cloths still have room for improvement from the viewpoint of achieving sufficient transmission speed performance. Here, it is conceivable to further reduce the dielectric constant and the dielectric loss tangent by setting the amount of SiO ₂ in the glass composition to approximately 100% by mass. As already described in Patent Document 4, a glass cloth with a SiO ₂ content of approximately 100% by mass has been developed.

However, although Patent Document 4 mentions the reduction of the dielectric constant, it does not mention the reduction of the dielectric loss tangent, which contributes more to the transmission loss.

In addition, Non-Patent Document 1 discloses that the amount of OH in silica glass is reduced by heating silica glass having a SiO ₂ content of approximately 100.0% by mass at a high temperature of 900° C. or higher. However, the dielectric properties (dielectric constant, dielectric loss tangent) of silica glass have not been studied at all.

JP-A-5-170483 JP 2009-263569 A Japanese Unexamined Patent Application Publication No. 2009-19150 JP 2018-197411 A

Changes in OH Group Concentration in Silica Glass Due to Heat Treatment Feb. 2011 Master's Program Thesis, Graduate School of Engineering, University of Fukui

The present invention has been made in view of the above problems, and a substrate with low dielectric loss tangent and low transmission loss (“substrate” is a concept including prepreg, printed wiring board, or laminates thereof, etc. ), a prepreg using the silica glass cloth, and a printed wiring board.

In order to solve the above problems, the present invention provides a heat-treated silica glass cloth made of glass filaments containing 96.0 to 100.0% by mass of SiO ₂ composition, wherein the dielectric loss tangent of the heat-treated silica glass cloth is tan δ1 is 0.0015 or less at a frequency of 9 GHz or higher, and the ratio tan δ1/tan δ2 of the dielectric loss tangent tan δ1 of the heat-treated silica glass cloth to the dielectric loss tangent tan δ2 of the non-heat-treated silica glass cloth at a frequency of 9 GHz or higher is 0.7 or lower. To provide a heat-treated silica glass cloth characterized by:

With such a heat-treated silica glass cloth, a substrate having a low dielectric loss tangent, a low transmission loss, and excellent interlayer insulation reliability can be produced.

In this case, the heat-treated silica glass cloth is preferably the non-heat-treated silica glass cloth heat-treated at 450° C. to 1650° C. for 1 minute to 72 hours.

With such a heat-treated silica glass cloth, the dielectric properties of the heat-treated silica glass cloth are more favorable.

In addition, the heat-treated silica glass cloth of the present invention is obtained by twisting 4 to 40 times per 1 m of a glass strand obtained by bundling 10 to 400 glass filaments having an average filament diameter of 3 μm to 20 μm. It is preferable that the yarn is woven from glass yarn with a count size of 0.5 to 40 tex.

By using such a heat-treated silica glass cloth, it is possible to obtain a prepreg that is thin, has a low dielectric loss tangent, and has a small transmission loss.

The present invention also provides a prepreg comprising the heat-treated silica glass cloth and a curable resin impregnated in the heat-treated silica glass cloth.
Furthermore, the present invention provides a printed wiring board comprising the prepreg.

The prepreg and printed wiring board using the above heat-treated silica glass cloth have a low dielectric loss tangent and low transmission loss, and are particularly useful as a substrate for suppressing transmission loss in high-speed communication such as 5G, which will increase in the future. .

The present invention also provides a method for producing a heat-treated silica glass cloth,
A step of preparing a non-heat-treated silica glass cloth made of glass filaments containing 96.0 to 100.0% by mass of SiO ₂ composition;
a step of heat-treating the non-heat-treated silica glass cloth at a temperature of 450° C. to 1650° C. for 1 minute to 72 hours to obtain a heat-treated silica glass cloth;
The heat-treated silica glass cloth has a dielectric loss tangent tan δ1 of 0.0015 or less at a frequency of 9 GHz or higher,
A heat-treated silica glass cloth characterized in that the ratio tan δ1/tan δ2 of the dielectric loss tangent tan δ1 of the heat-treated silica glass cloth to the dielectric loss tangent tan δ2 of the non-heat-treated silica glass cloth at a frequency of 9 GHz or higher is 0.7 or less. A manufacturing method is provided.

According to the method for manufacturing the heat-treated silica glass cloth of the present invention, the dielectric loss tangent can be reduced to about 1/10 or less and the transmission loss can be suppressed by a simple method of heating the silica glass cloth.

According to the present invention, as a method for suppressing transmission loss in high-speed communication such as 5G, which will increase in the future, a simple method of heating the silica glass cloth used for the substrate is used to reduce the dielectric loss tangent to 1/10. As described below, it is possible to suppress transmission loss and produce a substrate excellent in interlayer insulation reliability.

Even with the existing silica glass cloth with a SiO ₂ content of 96.0 to 100.0% by mass, the dielectric loss tangent is about 0.002 at a frequency of 9 GHz or higher, the transmission loss is small, and the interlayer insulation reliability is high. In order to obtain an excellent silica glass cloth for substrates, it is necessary to lower the dielectric loss tangent.

Here, regarding the reduction of the dielectric loss tangent, which greatly contributes to the transmission loss, it is known that the dielectric loss tangent decreases when the amount of OH in the glass decreases as in Patent Document 1.

On the other hand, Non-Patent Document 1 discloses that the amount of OH in silica glass is reduced by heating silica glass having a SiO ₂ content of approximately 100.0% by mass at a high temperature of 900° C. or higher. there is

However, the silica glass studied in Non-Patent Document 1 is a block or tubular bulk body, and is significantly different in physical shape from the silica glass cloth made of silica glass filaments (silica glass fibers) like the present invention. there is In addition, the decrease in the amount of OH in the silica glass is caused by the movement (diffusion) of water molecules in the silica glass, the dehydration of silanol groups (2Si-OH→2Si-O+H ₂ O), and the distribution of water molecules (OH groups). and so on, strongly depends on the form of silica glass (shape, length, thickness, surface area, etc.). Therefore, even if the amount of OH in the silica glass could be reduced by heat treatment of the silica glass cloth, it was not expected that the dielectric loss tangent of the silica glass cloth itself would be reduced.

As a result of intensive studies on the above-mentioned problems, the present inventors have found that silica glass cloth with a SiO ₂ content (composition amount) of 96.0 to 100.0% by mass is heat-treated to obtain silica glass cloth. A heat treatment in which the dielectric loss tangent is 0.0015 or less at a frequency of 9 GHz or higher, and the ratio tanδ1/tanδ2 of the dielectric loss tangent tanδ1 of the heat-treated glass cloth to the dielectric loss tangent tanδ2 of the unheated silica glass cloth is 0.7 or less. The present invention was completed by discovering that it becomes a silica glass cloth.

That is, the present invention provides a heat-treated silica glass cloth made of glass filaments containing 96.0 to 100.0% by mass of SiO ₂ , wherein the heat-treated silica glass cloth has a dielectric loss tangent tan δ1 of a frequency of 9 GHz or more. is 0.0015 or less, and the ratio tan δ1/tan δ2 of the dielectric loss tangent tan δ1 of the heat-treated silica glass cloth to the dielectric loss tangent tan δ2 of the non-heat-treated silica glass cloth at a frequency of 9 GHz or higher is 0.7 or less. A heat-treated silica glass cloth characterized by:

Although the present invention will be described in detail below, the present invention is not limited thereto.

In this specification, silica glass filament is a thin thread-like single fiber obtained by stretching silica glass, silica glass strand is a bundle of silica glass filaments, and silica is a bundle of silica glass filaments and further twisted. Defined as glass yarn.

[Silica glass cloth]
The heat-treated silica glass cloth of the present invention is a heat-treated non-heat-treated silica glass cloth made of silica glass filaments containing 96.0 to 100.0% by mass of SiO ₂ . The heat treatment for obtaining the heat-treated body is not particularly limited, but the non-heat-treated silica glass cloth is preferably heat-treated at 450° C. to 1650° C. for 1 minute to 72 hours.

The SiO ₂ content (composition amount) of the silica glass filaments is 96.0 to 100.0% by mass, preferably 98.0 to 100.0% by mass, and more preferably 99.0% by mass or more. If the SiO ₂ amount is less than 96.0% by mass, it becomes difficult to satisfy the target dielectric properties. A commercially available product having an SiO ₂ content within the above range can also be used. Note that the amount of SiO ₂ in the silica glass hardly changes before and after the heat treatment.

The raw material ingot of silica glass with a SiO ₂ content of 96.0 to 100.0% by mass can be produced by an electric melting method using crystal as a raw material, a flame melting method, or a direct synthesis method using silicon tetroxide as a raw material. Examples include a plasma synthesis method, a soot method, or a sol-gel method using alkyl silicate as a raw material, but are not limited to these production methods as long as the SiO ₂ content is 96.0 to 100.0% by mass. . In particular, the electric melting method using crystal as a raw material, the plasma synthesis method using silicon tetroxide as a raw material, the soot method, or the sol-gel method using alkyl silicate as a raw material are preferable because they are less likely to contain OH as an impurity.

The average filament diameter of the silica glass filaments is preferably 3 μm to 20 μm, more preferably 3.5 μm to 9 μm. There is no particular limitation on the method for producing silica glass filaments, and known spinning methods can be used. Examples thereof include electric melting and stretching using an oxyhydrogen flame, but the manufacturing method is not limited to these methods as long as the silica glass has an average filament diameter of 3 μm to 20 μm. For example, a desired filament diameter can be obtained by controlling the diameter of the silica glass rod, the feeding speed of the silica glass rod to be drawn, and the drawing speed of the silica glass filament.

The silica glass filaments are preferably bundled in numbers of 10 to 400 to form a silica glass strand, more preferably 100 to 200.

The silica glass cloth in the present invention can be produced by weaving silica glass yarn.
As the silica glass yarn, the silica glass filaments are bundled to form a silica glass strand, and the silica glass strand is twisted 4 to 40 times per 1 m, and the count size is 0.5 to 40 tex. A fused silica glass yarn can be used.

A silica glass strand obtained by bundling a predetermined number of silica glass filaments is preferably twisted using a twisting machine to form a silica glass yarn.

In the present invention, the number of twists of the silica glass yarn is not particularly limited. In addition, when the number of twists is large, the convergence of the yarn is enhanced, and breakage and fluffing are less likely to occur. For this reason, the twist number is preferably in the range of 4 turns/m to 40 turns/m, more preferably 5 turns/m to 30 turns/m.

In addition, when twisting the yarn, the yarn guide, traveler, and snail wire come into direct contact with the yarn at high speed in the yarn path for twisting, but since silica glass is very hard, these jigs are damaged by contact with the yarn. is likely to occur. Care must be taken because scratches on the jig may cause the filament to break. In particular, since the traveler is made of plastic, it is easily damaged, so it is important to check the surface condition and use a scratch-free jig before twisting.

As long as the dielectric properties required for the heat-treated silica glass cloth of the present invention are satisfied, the silica glass strand and silica glass yarn are not limited.

The method for producing the non-heat-treated silica glass cloth of the present invention is not particularly limited, and it can be produced by a known method.

The total number of filaments of the warp and weft constituting the silica glass cloth is not particularly limited, but is preferably 290,000 filaments/m ² or more and 400,000 filaments/m ² or less. Within this range, yarn breakage is less likely to occur against the tension and working pressure applied to the glass filaments in the weaving process, washing process, and opening process, and it is possible to suppress fluffing. Further, by setting the total number of glass filaments of the warp and weft to 400,000/m ² or less, the thickness of the glass cloth can be reduced, and a thin substrate can be obtained. As a result, it is possible to provide a glass cloth with which a substrate that is thinner and has a lower dielectric constant than the conventional one can be produced. The total number of glass filaments can be controlled by adjusting the implantation density and the number of glass filaments.

The aperture ratio of the silica glass cloth represents the area ratio of the portion where neither the warp nor the weft is distributed with respect to the area of the entire silica glass cloth, and from the viewpoint of suppressing uneven coating of the resin during prepreg coating, it is preferably 20% or less. , more preferably 18% or less.
The aperture ratio of the glass cloth can be adjusted by setting the density of the fibers, the degree of fiber opening, and the count of the glass yarn.

The average area of the openings of the silica glass cloth represents the average value of the area of a single portion where neither the warp nor the weft is distributed, and from the viewpoint of suppressing uneven resin coating during prepreg coating, it is preferably 20,000 μm ² /piece. or less, more preferably 15,000 μm ² /piece or less.
The average area of the openings of the glass cloth can be adjusted by the density of the fibers, the degree of fiber opening, and the count of the glass yarn.

The density of warps and wefts constituting silica glass cloth is independently preferably 50 to 140/inch, more preferably 80 to 130/inch.

From the viewpoint of thinning the silica glass cloth, it is preferable that the warp and weft counts (also referred to as tex) of the silica glass cloth are independently 0.5 g/1000 m or more and 40 g/1000 m or less.

The cloth weight (basis weight) of the silica glass cloth is preferably 4 to 10 g/m ² , more preferably 5 to 9 g/m ² , still more preferably 6 to 8 g/m ² .

The weave structure of silica glass cloth is not particularly limited, but examples thereof include plain weave, Nanako weave, satin weave, and twill weave, with plain weave structure being preferred.

[Heat-treated silica glass cloth]
The heat-treated silica glass cloth of the present invention comprises silica glass filaments containing 96.0 to 100.0% by mass of SiO ₂ composition. When the dielectric loss tangent of the heat-treated silica glass cloth at a frequency of 9 GHz or higher is tan δ1, and the dielectric loss tangent of the non-heat-treated silica glass cloth before heat treatment is tan δ2, tan δ1 is 0.0015 or less, and tan δ1/tan δ2 is 0.7 or less. If tan δ1 exceeds 0.0015 or tan δ1/tan δ2 exceeds 0.7, transmission loss is large in 5G communication applications and the like, and sufficient transmission speed performance cannot be achieved.
The dielectric loss tangent (tan δ) may be measured by a known method, for example, SPDR (Split post dielectric resonators) for permittivity measurement (manufactured by Keysight Technologies, Inc.).

In the present invention, a heat-treated silica glass cloth is obtained by heat-treating the silica glass cloth (non-heat-treated silica glass cloth).

[Heat treatment]
The heat treatment temperature of the non-heat-treated silica glass cloth is preferably 450°C to 1650°C, more preferably 500°C to 1100°C, even more preferably 700°C to 1100°C. With such a heat treatment temperature, the dielectric properties of the heat-treated body can be made favorable. As the heating method, heating with a furnace includes heating with an electric heating furnace, a muffle furnace, a tubular heating furnace, etc. If the heat treatment temperature is 450 ° C. to 1650 ° C., a heating method with a furnace, an electric heating furnace, and a muffle can be used. It is not limited to a heating method using a furnace or the like. However, the method using an oxyhydrogen flame produces H ₂ O, which causes OH, and is therefore not preferable.

The heat treatment time of the non-heat-treated silica glass cloth is preferably 1 minute to 72 hours, more preferably 1 hour to 10 hours. With such a heat treatment time, the dielectric properties of the heat-treated body can be made favorable.

The heat treatment of the non-heat-treated silica glass cloth is preferably performed in an inert gas atmosphere in order to avoid contamination with impurities, and can be performed in, for example, a nitrogen, argon, or helium atmosphere. Also, it is preferable that the inert gas contains as little moisture as possible, and it is more preferable that the inert gas contains substantially no moisture. Optionally, dry air can also be used.

The non-heat-treated silica glass cloth consists of silica glass filaments containing 96.0 to 100.0% by mass (composition amount) of SiO ₂ , and 10 to 400 silica glass filaments having an average filament diameter of 3 μm to 20 μm. The number of strands is bundled to form a silica glass strand, and the silica glass strand is twisted 4 to 40 times per 1 m to weave a silica glass yarn having a count size of 0.5 to 40 tex. Manufactured ones are preferred. By using the heat-treated silica glass cloth, which is a heat-treated body of the non-heat-treated silica glass cloth, it is possible to obtain a prepreg or a printed wiring board that is thin, has a low dielectric loss tangent, has a small transmission loss, and has excellent interlayer insulation reliability. can be done.

[Method for producing heat-treated silica glass cloth]
The method for producing the heat-treated silica glass cloth of the present invention comprises:
A step of preparing a non-heat-treated silica glass cloth made of glass filaments containing 96.0 to 100.0% by mass of SiO ₂ composition;
a step of heat-treating the non-heat-treated silica glass cloth at a temperature of 450° C. to 1650° C. for 1 minute to 72 hours to obtain a heat-treated silica glass cloth;
The heat-treated silica glass cloth has a dielectric loss tangent tan δ1 of 0.0015 or less at a frequency of 9 GHz or higher,
A ratio tan δ1/tan δ2 of the dielectric loss tangent tan δ1 of the heat-treated silica glass cloth to the dielectric loss tangent tan δ2 of the non-heat-treated silica glass cloth at a frequency of 9 GHz or higher is set to 0.7 or less.

First, the non-heat-treated silica glass cloth described above is prepared. Next, the non-heat-treated silica glass cloth is heat-treated at a temperature of 450° C. to 1650° C. for 1 minute to 72 hours to obtain a heat-treated silica glass cloth. The heat treatment of the non-heat-treated silica glass cloth may be performed as described above. Under such heat treatment conditions (temperature, time), a heat-treated silica glass cloth having the dielectric properties described above can be suitably obtained.

A heat-treated non-heat-treated silica glass cloth (heat-treated silica glass cloth) has a low dielectric loss tangent due to the heat treatment described above. In particular, even when the non-heat-treated silica glass cloth has a dielectric loss tangent tan δ2 of more than 0.0015 at a frequency of 9 GHz or higher, the heat-treated body can have a dielectric loss tangent tan δ1 of 0.0015 or less by adjusting the heat treatment conditions. and tan δ1/tan δ2 can be 0.7 or less, particularly 0.1 or less. As described above, according to the present invention, it is possible to reduce the dielectric loss tangent to 1/10 or less by a simple method of heating the silica glass cloth used for the substrate, thereby suppressing the transmission loss. .

[Prepreg]
The prepreg of the present invention comprises the heat-treated silica glass cloth and a curable resin (matrix resin) impregnated in the heat-treated silica glass cloth. This makes it possible to provide a prepreg that is thin, has a low dielectric constant, and has improved insulation reliability.
The matrix resin is not particularly limited, and both thermosetting resins and thermoplastic resins can be used.

If necessary, the silica glass yarn and silica glass cloth are preferably surface-treated with a known surface-treating agent such as a silane coupling agent.

[Printed wiring board]
A printed wiring board of the present invention includes the prepreg. Thereby, a printed wiring board having a low dielectric constant and improved insulation reliability can be provided. The prepreg in the printed wiring board of the present invention may be a laminate composed of two or more layers.

As described above, according to the present invention, as a method for suppressing transmission loss in high-speed communication such as 5G, which will increase in the future, a simple method of heating the silica glass cloth used for the substrate can be used to reduce the dielectric loss tangent is reduced to 1/10 or less and transmission loss can be suppressed. Therefore, it has a very high utility value in the field of high-speed communication.

EXAMPLES The present invention will be described in more detail with reference to the following examples, but it goes without saying that these examples are shown by way of illustration and should not be construed as limiting. In addition, below, the "non-heat-treated silica glass cloth" is also simply referred to as "silica glass cloth".

Measurements and calculation of dielectric loss tangent values in the following examples were carried out by the following methods.

1. Measurement of Dielectric Loss Tangent It was measured using SPDR (Split post dielectric resonators) for dielectric constant measurement with a dielectric resonator frequency of 9 GHz (manufactured by Keysight Technologies, Inc.).

2. Calculation of dielectric loss tangent value From the volume calculated from the area of the dielectric resonator and the thickness of the silica glass cloth, the silica glass cloth is a composite of silica glass (A) and air (B), and the following equation 1 is used. A dielectric loss tangent value of only silica glass was calculated.
tan δ=V _A ×tan δ _A +V _B ×tan δ _B (Equation 1)
(tan δ: dielectric loss tangent of the composite, VA: volume fraction of silica glass (A), tan _{δ A :} dielectric loss tangent of silica glass (A), V _B : volume fraction of air (B), tan δ _B : air Dielectric loss tangent of (B))
The dielectric loss tangents of the examples and comparative examples all indicate the dielectric loss tangent of the silica glass cloth alone obtained by the above formula 1.

(Example 1)
A silica glass cloth (2116) containing 99.9% by mass or more of SiO ₂ and having a tan δ2 of 0.0022 was placed in an electric heating furnace and heated at 500° C. for 10 minutes. After heating, the cross shape was maintained. The dielectric loss tangent (tan δ1) of the obtained heat-treated glass cloth was measured, and the value was calculated to be 0.0014. The ratio to before treatment was tan δ1/tan δ2=0.66, which was a good result.

(Example 2)
As in Example 1, a silica glass cloth (2116) containing 99.9% by mass or more of SiO ₂ and having a tan δ2 of 0.0022 was placed in an electric heating furnace and heated at 500° C. for 10 hours. After heating, the cross shape was maintained. The dielectric loss tangent of the obtained heat-treated glass cloth was measured and calculated, and tan δ1 was 0.0010. The ratio to before treatment was tan δ1/tan δ2=0.47, which was a good result.

(Example 3)
As in Example 1, a silica glass cloth (2116) containing 99.9% by mass or more of SiO ₂ and having a tan δ2 of 0.0022 was placed in an electric heating furnace and heated at 700° C. for 5 hours. After heating, the cross shape was maintained. The dielectric loss tangent of the obtained heat-treated glass cloth was measured and calculated, and tan δ1 was 0.0006. The ratio to before treatment was tan δ1/tan δ2=0.28, which was a better result than in Example 1.

(Example 4)
As in Example 1, a silica glass cloth (2116) containing 99.9% by mass or more of SiO ₂ and having a tan δ2 of 0.0022 was placed in an electric heating furnace and heated at 700° C. for 10 hours. After heating, the cross shape was maintained. The dielectric loss tangent of the obtained heat-treated glass cloth was measured and calculated to find that tan δ1 was 0.0002. The ratio to before treatment was tan δ1/tan δ2=0.10, which was a better result than in Example 2.

(Example 5)
As in Example 1, a silica glass cloth (2116) containing 99.9% by mass or more of SiO ₂ and having a tan δ2 of 0.0022 was placed in an electric heating furnace and heated at 1100° C. for 10 hours. After heating, the cross shape was maintained. The dielectric loss tangent of the obtained heat-treated glass cloth was measured and calculated to find that tan δ1 was 0.0002. The ratio before treatment was tan δ1/tan δ2=0.10, which was a good result similar to Example 4.

(Comparative example 1)
A silica glass cloth (2116) containing 99.9% by mass or more of SiO ₂ and having a tan δ2 of 0.0022 was placed in an electric heating furnace and heated at 400° C. for 10 hours. After heating, the cross shape was maintained. The dielectric loss tangent of the obtained heat-treated glass cloth was measured and calculated, and tan δ1 was 0.00218. The ratio to before treatment was tan δ1/tan δ2=1.00. Due to insufficient heating energy, tan δ1 after heating did not become 0.0015 or less.

(Comparative example 2)
A silica glass cloth (2116) containing 99.9% by mass or more of SiO ₂ and having a tan δ2 of 0.0022 was placed in an electric heating furnace and heated at 1700° C. for 10 hours. Due to the high temperature heat treatment, the cross shape could not be maintained. Therefore, the dielectric loss tangent tan δ1 could not be measured.

Table 1 shows the results of Reference Examples, Examples and Comparative Examples.

In Example 1-5 in which the silica glass cloth was heat-treated at 500 to 1100° C. for 0.17 to 10 hours, the dielectric loss tangent tan δ1 of the heat-treated silica glass cloth was 0.0015 or less at a frequency of 9 GHz or higher, and The tan δ1/tan δ2 was 0.7 or less. Especially in Examples 4 and 5, although the dielectric loss tangent tan δ2 of the non-heat-treated silica glass cloth exceeded 0.0015, tan δ1/tan δ2 was 1/10 or less, and the dielectric loss was greatly reduced. On the other hand, in Comparative Example 1 in which the heating energy was insufficient, tan δ1 did not become 0.0015 or less, and in Comparative Example 2 in which the heating energy was excessive, the cross shape could not be maintained.

As described above, according to the present invention, as a method for suppressing transmission loss in high-speed communication such as 5G, which will increase in the future, the dielectric loss tangent is measured by a simple method of heating the silica glass cloth used for the substrate. A significant effect is achieved in that the transmission loss can be suppressed by reducing the transmission loss to one-tenth or less.

In addition, this invention is not limited to the said embodiment. The above-described embodiment is an example, and any device having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same effect is the present invention. included in the technical scope of

Claims (3)

A prepreg made of a heat-treated silica glass cloth and a curable resin impregnated in the heat-treated silica glass cloth,
The heat-treated silica glass cloth is a heat-treated silica glass cloth made of glass filaments containing 96.0 to 100.0% by mass of SiO ₂ composition,
The ratio tan δ1/tan δ2 of the dielectric loss tangent tan δ1 at a frequency of 9 GHz of the heat-treated silica glass cloth alone to the dielectric loss tangent tan δ2 at a frequency of 9 GHz of the non-heat-treated silica glass cloth alone is 0.47 or less,
The heat-treated silica glass cloth has a dielectric loss tangent tan δ1 of 0.0010 or less at a frequency of 9 GHz,
The prepreg, wherein the dielectric loss tangent value is obtained by calculating a dielectric loss tangent value of silica glass alone as a composite of silica glass and air, measured at a dielectric resonator frequency of 9 GHz. The heat-treated silica glass cloth is a glass strand in which 10 to 400 glass filaments having an average filament diameter of 3 μm to 20 μm are bundled, and twisted 4 to 40 times per 1 m. The prepreg according to claim 1, wherein the prepreg is made by weaving glass yarn having a size of 0.5 to 40 tex. A printed wiring board comprising the prepreg according to claim 1 or 2.