JP3528174B2 - Method for producing prepreg, and glass fiber nonwoven fabric - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a prepreg obtained by impregnating a glass fiber nonwoven fabric with a thermosetting resin, and particularly to a prepreg suitably used for a printed wiring board, a method for producing the same and a prepreg for the same. The present invention relates to a suitable glass fiber non-woven fabric.

[0002]

2. Description of the Related Art Conventionally, in manufacturing a printed wiring board, a prepreg obtained by impregnating a glass fiber nonwoven fabric with a thermosetting resin such as an epoxy resin has been used as an insulating reinforcing material. Explaining an example of a method for producing a printed wiring board, prepregs obtained by impregnating a glass woven cloth with a thermosetting resin are superposed on both surfaces of the prepreg, and metal foils such as copper foil are superposed on both surfaces. Then, the laminate is press-heated and molded to obtain a so-called laminated plate in which the thermosetting resin is cured. Further, the printed wiring board is completed by forming a circuit by subjecting this laminated board to etching, drilling, or the like.

[0003]

The prepreg and glass fiber non-woven fabric used for printed wiring boards and the like have the following problems. That is, for example, when performing a drilling process on the boundary portion between the glass fiber and the thermosetting resin in the laminated plate using the conventional glass fiber nonwoven fabric and the prepreg containing the same, the tip of the drill escapes to the soft resin side. As a result, there have often been problems such as breakage of the drill and inability to form a hole at an accurate position. Also, when performing laser processing, the laser output is usually adjusted according to the strength of the glass fiber, but since this output is too strong for the resin part,
There was also a problem that the resin portion was too melted and it was difficult to make the hole circular. Therefore, it is required to improve the drilling workability in the laminated board using the prepreg.

Further, the conventional prepreg in which a woven glass cloth is impregnated with a thermosetting resin has a large difference in permittivity between the glass fiber portion and the resin portion, so that there is a problem that the permittivity becomes uneven over the entire prepreg. there were. If the prepreg has a non-uniform dielectric constant, it becomes difficult to control the characteristic impedance of the printed wiring board using the prepreg.

Further, with the demand for thinning and downsizing of the printed wiring board, it is possible to improve the electric resistance characteristics of the printed wiring board, that is, to improve the electrical insulating property of the printed wiring board other than the circuit portion from the conventional one. Is desired.

The present invention has been made in view of the above circumstances, and has good drilling workability, high uniformity of permittivity, and high electrical insulation, and a method of manufacturing the same.
And a glass fiber nonwoven fabric suitable for use in the prepreg thereof.

[0007]

In order to solve the above problems, the present invention provides a prepreg obtained by impregnating a glass fiber nonwoven fabric with a thermosetting resin, wherein the glass fiber nonwoven fabric comprises:
The cross section has a minor axis of 2 to 7 μm and the cross section has a major axis of 6 to 40 μm.
In addition, the flattening ratio is 2 to 10 and the length is 1.5 to 25 mm. The thermosetting resin is formed of a plurality of flat glass fibers, and insulating powder having electrical insulation properties is distributed in the thermosetting resin. It is characterized by being.

According to the prepreg of the present invention, when flat glass fibers are made into a glass fiber non-woven fabric, most of the flat glass fibers forming the glass fiber non-woven fabric are overlapped with the major axis side being horizontal. The density of the glass fiber, which is an insulator, becomes higher than that when glass fiber having a circular cross section is used. In particular, since the flat glass fibers are thin fibers having a short diameter of 2 to 7 μm and a long diameter of 6 to 40 μm in cross section, the density of the flat glass fibers is further increased and the electrical insulation is improved. In addition, since the insulating powder having the electric insulating property is arranged in the thermosetting resin, the density of the substance having the electric insulating property in the prepreg is increased, and the electric insulating property is further enhanced. Further, as the density of the flat glass fiber and the insulating powder having the electric insulating property is increased in this way, as compared with the case where the prepreg is formed only with the flat glass fiber and the thermosetting resin, the entire material is uniform. As a result, the escape and breakage of a drill or the like can be prevented, the precision of the drilling position can be improved, and the holes can be easily made circular when laser processing is performed, which improves drilling workability. Furthermore, as described above, the entire prepreg is in a state close to a uniform material, so that the dielectric constant is uniform over the entire prepreg.

Further, in the prepreg according to the present invention,
The thickness is preferably 30 μm or less. By reducing the thickness in this way, it is possible to further improve the drilling workability of the prepreg. Further, as described above, in the present invention, the electric insulation is enhanced, so that the thickness is 30 μm.
Sufficient electric resistance can be secured even in the following cases.
Moreover, the surface on the minor axis side of most flat glass fibers is vertical, but since the minor axis is as small as 2 to 7 μm, a large number of flat glass fibers can be arranged in a prepreg having a thickness of 30 μm or less. This increases the strength of the prepreg.

The flat glass fiber and the insulating powder are preferably made of the same material. in this case,
Since the flat glass fiber and the insulating powder have the same characteristics such as strength and abrasion resistance, the drilling workability of the prepreg is further enhanced. Moreover, since the entire prepreg is closer to the uniform material, the uniformity of the dielectric constant can be further improved.

Further, the ratio of the insulating powder to the flat glass fibers forming the glass fiber nonwoven fabric is preferably 10 to 60% by weight. If the insulating powder is placed in the thermosetting resin in an amount within this range, the electrical insulation of the prepreg,
The drilling workability and the uniformity of the dielectric constant can be improved.

The method of manufacturing a prepreg of the present invention is
The cross section has a minor axis of 2 to 7 μm and the cross section has a major axis of 6 to 40 μm.
And a step of forming a glass fiber nonwoven fabric by paper-making a plurality of flat glass fibers having a flatness ratio of 2 to 10 and a length of 1.5 to 25 mm, and insulating powder having electrical insulation properties. And a step of forming a prepreg by impregnating a glass fiber non-woven fabric with a thermosetting resin.

In the prepreg obtained by the production method of the present invention, most of the flat glass fibers forming the glass fiber nonwoven fabric are overlapped with the major axis side being horizontal, so that a glass fiber having a circular cross section is used. As a result, the density of the glass fiber, which is an insulator, increases. In particular, since the flat glass fibers are thin fibers having a short diameter of 2 to 7 μm and a long diameter of 6 to 40 μm in cross section, the density of the flat glass fibers is further increased and the electrical insulation is improved. In addition, since the glass fiber non-woven fabric is formed by making the insulating powder having electrical insulation properties together with the flat glass fibers, the density of the electrically insulating substance in the prepreg is increased, and the electrical insulation properties are further enhanced. Further, as the density of the flat glass fiber and the insulating powder having the electric insulating property is increased in this way, as compared with the case where the prepreg is formed only with the flat glass fiber and the thermosetting resin, the entire material is uniform. As a result, the escape and breakage of a drill or the like can be prevented, the precision of the drilling position can be improved, and the holes can be easily made circular when laser processing is performed, which improves drilling workability. Further, since the entire prepreg is in a state close to a uniform material, the dielectric constant is uniform over the entire prepreg.

In the method for producing a prepreg according to the present invention, the density of the glass fiber nonwoven fabric is 0.3 to 0.5 g.
It is preferable that flat glass fiber and insulating powder are made into paper so that the amount becomes / cm ³ . By setting the density of the glass fiber nonwoven fabric composed of the flat glass fibers and the insulating powder in such a range, it is possible to further improve the electric insulation and the drilling workability.

Further, the glass fiber nonwoven fabric of the present invention has a cross-sectional short diameter of 2 to 7 μm and a cross-sectional long diameter of 6 to 40 μm.
It is characterized by comprising a plurality of flat glass fibers having a flatness ratio of 2 to 10 and a length of 1.5 to 25 mm, and an insulating powder that adheres to the flat glass fibers and has electrical insulation. .

For example, when the glass fiber nonwoven fabric according to the present invention is impregnated with a thermosetting resin to form a prepreg, the same effects as those of the above prepreg of the present invention are obtained, that is, drilling workability, uniform dielectric constant, and electrical insulation. Can be obtained.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of a prepreg, a method for producing the same, and a glass fiber nonwoven fabric according to the present invention will be described in detail below with reference to the accompanying drawings. The same elements will be denoted by the same reference symbols, without redundant description.

FIG. 1 is a sectional view showing a prepreg of this embodiment. As shown in the figure, the prepreg 1 of this embodiment has a glass fiber nonwoven fabric 10 formed by a plurality of flat glass fibers 2 having a flat cross section, and a thermosetting epoxy resin or the like impregnated in the flat glass fibers 2. Resin 20
And a plurality of glass powders (insulating powders) 30 arranged in the thermosetting resin 20. The flat glass fibers 2 are bonded to each other by a binder.

First, the flat glass fiber 2 will be described in detail. The flat glass fiber 2 has a short diameter of 2 to 7 μm, a long diameter of 6 to 40 μm, and an oblateness ratio of 2 to 10. The flat glass fiber 2 is formed of E glass and is a so-called chopped strand having a length of 1.5 to 25 mm. Here, with reference to FIG. 2, the definitions of the “major axis”, “minor axis”, and “flatness” of the flat glass fiber 2 will be described. As shown in FIG.
The “major axis” and the “minor axis” are the length A of the long side Ra of the rectangle R (corresponding to the longest dimension of the fiber cross section), and the rectangle R having the smallest area circumscribing the flat glass fiber 2, , And correspond to the length B of the short side Rb. The "flatness" is represented by the ratio of the length of the long side to the length of the short side, that is, A / B.

When the glass fiber nonwoven fabric 10 is formed by using the flat glass fibers 2 as in the prepreg 1 of this embodiment,
The following effects can be obtained. That is, as shown in FIG.
Since most of the flat glass fibers 2 overlap with each other with the surface on the major axis side being horizontal, the density of the glass fibers as an insulator is higher than that when glass fibers having a circular cross section are used. In particular, since the flat glass fibers 2 are thin fibers having a short diameter of 2 to 7 μm and a long diameter of 6 to 40 μm in cross section, the density of the flat glass fibers 2 is further increased and the electrical insulation is improved. In addition, since the content of the flat glass fibers 2 in the prepreg 1 becomes high, the flat glass fibers 2 are evenly arranged in the prepreg 1. For this reason, the dimensional stability of the prepreg 1 is improved and the surface smoothness is also improved, so that when manufacturing a printed wiring board using the prepreg 1, it is possible to suppress problems such as disconnection in the etching process of the metal foil.

Further, the minor axis of the cross section of the flat glass fiber 2 is set to 2
The reason why the length is set to ˜7 μm and the major axis is set to 6 to 40 μm is as follows. That is, the reason why the minor axis is set to 2 μm or more is that it is difficult to spin glass fibers if the minor axis is smaller than this. On the other hand, the minor axis is set to 7 μm or less because when the minor axis exceeds 7 μm, the gap between the flat glass fibers 2 becomes large, and as a result, the mechanical strength of the glass fiber nonwoven fabric 10 is reduced and the drilling processability is reduced. This is because it causes a decrease. Further, if the minor axis exceeds 7 μm, there arises a problem that the insulation resistance is lowered and the dielectric constant is difficult to be nonuniform. Further, if the major axis is less than 6 μm, it becomes difficult to spin the glass fiber, and if the major axis exceeds 40 μm, the flattening efficiency is poor and the rigidity becomes high.

Further, the flatness of the flat glass fiber 2 is set to 2-1.
The reason why the range is set to 0 is as follows. That is, when the oblateness is less than 2, the major axis is too short with respect to the minor axis, and the flat glass fibers deposited on the net when the flat glass fibers are made into paper stand with the end in the major axis direction facing downward. Easily occurs, the bulk density becomes low, and it is difficult to improve the electrical insulation. On the other hand, when the flatness ratio is larger than 10, there are problems that it takes too much draining time during papermaking, spinning is difficult, and the impregnation speed of the thermosetting resin 20 into the glass fiber nonwoven fabric 10 becomes slow. Moreover, the rate at which the bulk density increases decreases.

Further, the flat glass fiber 2 has a length of 1.5 to
The reason why the distance is 25 mm is as follows. That is, if the flat glass fiber 2 is shorter than 1.5 mm, the mechanical strength of the prepreg 1 cannot be obtained, while if it is longer than 25 mm, the glass fiber non-woven fabric 10 is uniformly formed. I can't.

The flat glass fiber 2 is formed of E glass, but the composition is not particularly limited, and glass fibers such as ECR glass, S glass, C glass, D glass, and low dielectric glass can be manufactured. If

Next, the glass powder 30 will be described in detail.
Glass powder 30 having electrical insulation as in the present embodiment
Is placed in the thermosetting resin 20, that is, in the gaps between the flat glass fibers 2, the density of the glass in the prepreg 1 is increased, and the electrical insulation is further improved. Further, the flat glass fiber 2 and the glass powder 30 having the electric insulation property as described above
As the density of the flat glass fiber 2 and the glass powder 30 increases, the flat glass fiber 2 and the glass powder 30 are uniformly distributed in the thermosetting resin 20. That is, as compared with the case where the glass powder 30 is not used, the amount of the thermosetting resin 20 in the prepreg 1 is reduced, and the prepreg 1 is in a state close to a uniform material. Therefore, when the prepreg 1 is drilled by a drill, a laser, or the like, it is possible to prevent the drill from escaping from the flat glass fiber 2 to the soft resin side, which may cause the drill to break or the drilling position to shift. Further, when laser processing is performed, the holes are easily made circular, and the drilling workability is improved. Further, as described above, the entire prepreg 1 is in a state close to a uniform material, so that the dielectric constant is uniform over the entire prepreg 1. When the dielectric constant of the prepreg 1 becomes uniform, it becomes easy to control the characteristic impedance of the printed wiring board formed using the prepreg 1.

Further, in this embodiment, as the glass powder 30, a lump of E glass is crushed by a ball mill. By thus forming the glass powder 30 with the same material as the flat glass fiber 2, the flat glass fiber 2 and the glass powder 30 have the same characteristics such as strength and abrasion resistance, and therefore the prepreg 1 has a drilling workability. Also, the uniformity of the dielectric constant can be further enhanced. Glass powder 3
The average particle size of 0 is 25 μm or less, preferably 10 μm or less. This is because if the particle size of the glass powder 30 is too large, the surface of the prepreg 1 will not be smooth, or it will be difficult to insert the glass powder 30 into the gaps between the flat glass fibers 2. Further, more preferably, the maximum particle size of the glass powder 30 is 24 μm or the maximum side is 24.
It is preferable that the thickness is about μm. Glass powder 30 in this case
Has an average particle size of 4 to 6 μm. The average particle diameter of the glass powder (insulating powder) 30 is obtained by dispersing the glass powder 30 in a solvent such as pure water or ethanol that does not affect the transmittance of the laser and taking a picture of the image measured by the laser analysis measuring device. , The average value of the diameter of a circle having an area equal to the cross-sectional area of the glass powder 30.

Furthermore, the ratio of the glass powder 30 to the flat glass fibers 2 forming the glass fiber nonwoven fabric 10 is 1
It is preferably from 0 to 60% by weight. This is because when the amount of the glass powder 30 is less than the lower limit of this range, the density of the glass in the prepreg 1 becomes small, and thus it becomes difficult to improve the electrical insulating property, the drilling workability, and the uniformity of the dielectric constant. On the other hand, when the amount of the glass powder 30 exceeds the upper limit of this range, the glass fiber nonwoven fabric 1
This is because the amount of the thermosetting resin 20 to be contained in 0 becomes small, resulting in a decrease in strength of the prepreg 1 and a decrease in efficiency of papermaking work and impregnation work.

The glass powder 30 may be crushed glass lumps, crushed glass fibers, crushed flat glass fibers, crushed glass balloons, or the like. In addition, since the crystallized glass of glass fiber or flat glass fiber crushed by a ball mill or the like is oriented, the strength of the prepreg 1 can be increased as compared with that of crushed glass balloon. Further, the powder contained in the thermosetting resin 20 is
The material is not limited to glass as long as it has electrical insulation, and powder of silica, mica, or the like may be used.

The thickness of the prepreg 1 of this embodiment is 30 μm or less. This thickness is JIS-
It measures based on the thickness measuring method of P-8118. By reducing the thickness in this way, the drilling workability of the prepreg 1 can be further improved. Further, as described above, in this embodiment, the electric insulation is enhanced, so that even if the thickness is 30 μm or less, sufficient electric resistance can be secured. Moreover, the surface on the minor axis side of most of the flat glass fibers 2 is vertical, but since the minor axis is as small as 2 to 7 μm,
Flat glass fibers 2 in a prepreg 1 having a thickness of 30 μm or less
Can be distributed in large numbers. With this, the strength is high,
It is possible to form an extremely thin prepreg 1 having high electric insulation and good drilling workability.

In this embodiment, the glass powder 30 is not contained in the glass fiber nonwoven fabric 10 but contained in the thermosetting resin 20, but the glass powder 30 is also contained in the glass fiber nonwoven fabric during papermaking. It is also possible to use a mode in which paper is made at the same time, that is, a mode in which the glass fiber nonwoven fabric 10 contains the glass powder 30. Also in this case, when the glass fiber nonwoven fabric is impregnated with the thermosetting resin, the glass powder is placed in the thermosetting resin. When the latter glass fiber nonwoven fabric 10 is made to contain the glass powder 30, the density of the glass fiber nonwoven fabric is 0.3 to 0.
It is preferably 5 g / cm ³ . If the density of the glass fiber non-woven fabric is smaller than the lower limit of this range, it becomes difficult to improve the electrical insulating property and the drilling workability of the prepreg 1, while if the density of the glass fiber non-woven fabric is larger than the upper limit of this range. This is because the amount of the thermosetting resin 20 contained in the glass fiber non-woven fabric is reduced, resulting in a decrease in strength of the prepreg 1 and a decrease in efficiency of papermaking work and impregnation work. The density of the glass fiber nonwoven fabric is JIS-P.
It is measured by the density measuring method of -8118.

Next, a method of manufacturing the prepreg 1 of this embodiment will be described. First, the molten glass is pulled out from the bushing at a high speed, and is cooled and solidified while maintaining the above flat shape, and then those coated with a sizing agent for protecting the glass fibers are collected to form a strand. Then, the flat glass fiber 2 can be obtained by cutting this strand into a chopped strand by cutting it into a length of 1.5 to 25 mm.

Subsequently, the flat glass fiber 2 is made into a paper by a wet non-woven fabric forming method to produce a glass fiber non-woven fabric 10. A known method for producing a glass fiber non-woven fabric can be used in this wet papermaking step, and the details are as follows. For example, the flat glass fibers 2 can be put into a large amount of water to which a dispersant or the like has been added, and can be dispersed in water in the state of glass single fibers by a dispersing mechanism such as a pulper. Then, the liquid in which the flat glass fibers 2 are dispersed is dehydrated by a paper machine, and a binder such as an epoxy resin is applied by a spray device. Thereafter, the adhesion is adjusted and the glass fiber nonwoven fabric 10 is completed by drying.

Next, the glass fiber nonwoven fabric 10 thus obtained is impregnated with the thermosetting resin 20. Specifically, the glass fiber non-woven fabric is passed through a resin tank in which the thermosetting resin 20 mixed with the glass powder 30 is stored, or the thermosetting resin 2 mixed with the glass powder 30 is used.
The glass fiber non-woven fabric is impregnated with the thermosetting resin 20 by contacting a roller coated with 0 on the surface. As a result, the prepreg 1 of this embodiment is completed.

Here, the method of impregnating the glass fiber nonwoven fabric with the thermosetting resin 20 mixed with the glass powder 30 has been described, but when the flat glass fiber is made, the glass powder 30 is also made at the same time. After forming the fibrous nonwoven fabric, the thermosetting resin 20 may be impregnated.

[Embodiment] Next, the present invention will be described more specifically based on an embodiment.

As shown in Table 1, in Example 1, the flat glass fiber has a short diameter of 6 μm, a long diameter of 24 μm and a fiber length of 1.
It was set to 2 mm. The insulating powder used was flat glass fibers crushed, and the average particle size was 24 μm. Also,
The ratio (blending amount) of insulating powder to flat glass fiber is 4
It was set to 3 wt%. Then, the flat glass fiber and the insulating powder were paper-made to form a glass fiber non-woven fabric, and the density thereof was measured and found to be 0.42 g / cm ³ . In the case of prepregs using high-density glass fiber non-woven fabric, the insulating powder is evenly distributed and the whole becomes close to a uniform material, improving electrical insulation, drilling workability, and even dielectric constant. Can be achieved.

The above glass fiber nonwoven fabric was impregnated with the following resin and dried at 130 ° C. for 7 minutes to obtain gel time 10
A 0 second prepreg was prepared. Epicoat 5046-B-80 (made by Yuka Shell Epoxy Co., Ltd.) 100 parts by weight Epicoat 154 (made by Yuka Shell Epoxy Co., Ltd.) 20 parts by weight Dicyandiamide 4 parts by weight Benzyldimethylamine 0.2 parts by weight Dimethylformamide 30 parts by weight Methyl ethyl ketone 15 parts by weight Department

Further, after 16 sheets of this prepreg were laminated, copper foil having a thickness of 18 μm was laminated on both sides of the prepreg at a temperature of 1
It was pressed at 70 ° C. and a pressure of 50 kg / cm ² for 60 minutes.
After this press-heating molding, the copper foil was removed by etching to obtain a laminated board. Then, the surface roughness of this laminated plate is J
When measured based on IS-R-3420-5.4, it was about 1.5 μm, and it was found that the surface smoothness was excellent.

[Table 1]

In Example 2, the ratio (blending amount) of insulating powder to flat glass fiber was set to 25 wt%. The other conditions are the same as in Example 1. Then, the density of the glass fiber non-woven fabric was measured and found to be 0.40 g / cm ³
It turns out that the density is high. In addition, Example 1
When a laminate similar to the above was prepared and the surface roughness was measured,
It was about 1.8 μm, which proved to be excellent in surface smoothness.

For comparison, the minor axis is 8 μm and the major axis is 3 μm.
A similar experiment was conducted using flat glass fibers of 2 μm. The other conditions are the same as in Example 1. Then, when the density of the glass fiber non-woven fabric was measured, it was 0.28 g /
It was found that the density was as low as cm ³ . In a prepreg using such a glass fiber nonwoven fabric having a low density, improvement in electrical insulation, drilling workability, and uniformity of dielectric constant cannot be expected. Moreover, the surface roughness of the laminated plate produced using this glass fiber nonwoven fabric was about 2.2 μm. As described above, when flat glass fibers having a short diameter and a long diameter as in Examples 1 and 2 are used, the electrical insulation of the prepreg, the drilling workability, the uniformity of the dielectric constant, and the surface smoothness are improved. It has become clear that

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments.

[0042]

As described above, according to the prepreg and the method for producing the same according to the present invention, most flat glass fibers forming the glass fiber nonwoven fabric are overlapped with their major-diameter side surfaces horizontal, and thus have a circular cross section. The density of the glass fiber, which is an insulator, is higher than that in the case where the glass fiber is used. In particular, the flat glass fiber has a cross-sectional minor axis of 2 to 7 μm.
Since a long fiber with a long diameter of 6 to 40 μm is used,
The density of the flat glass fiber is further increased, and the electric insulation is improved. In addition, since the insulating powder having the electric insulating property is arranged in the thermosetting resin, the density of the substance having the electric insulating property in the prepreg is increased, and the electric insulating property is further enhanced. Further, as the density of the flat glass fiber and the insulating powder having the electric insulating property is increased in this way, as compared with the case where the prepreg is formed only with the flat glass fiber and the thermosetting resin, the entire material is uniform. As a result, the escape and breakage of a drill or the like can be prevented, the precision of the drilling position can be improved, and the holes can be easily made circular when laser processing is performed, which improves drilling workability. Furthermore, as described above, the entire prepreg is in a state close to a uniform material, so that the dielectric constant can be made uniform over the entire prepreg.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a prepreg of the present invention.

FIG. 2 is a view used for explaining a major axis and a minor axis of a flat glass fiber.

[Explanation of symbols]

1 ... Prepreg, 2 ... Flat glass fiber, 10 ... Glass fiber nonwoven fabric, 20 ... Thermosetting resin, 30 ... Glass powder (insulating powder).

Continuation of front page (51) Int.Cl. ⁷ Identification code FI D21H 13/40 D21H 13/40 19/16 19/16 H05K 1/03 610 H05K 1/03 610T // C08L 101: 00 C08L 101: 00 ( 56) References JP-A-6-257042 (JP, A) JP-A-4-370257 (JP, A) JP-A-7-162149 (JP, A) JP-A-2001-196712 (JP, A) JP-A-2001 -196711 (JP, A) JP 2001-156460 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08J 5/04-5/10 C08J 5/24 B29B 11/16 B29B 15/08-15/14 D21H 13 / 40,19 / 16 H05K 1/03

Claims (3)

(57) [Claims] 1. A cross-section has a minor axis of 2 to 7 μm, a cross-sectional major axis of 6 to 40 μm, an oblateness of 2 to 10 and a length of 1.5 to.
A plurality of flat glass fibers satisfying the condition of 25 mm and insulating powder having electric insulation are made into paper to have a density of 0.3.
A step of forming a glass fiber non-woven fabric of 0.5 g / cm ^{3 or} less, and a step of forming a prepreg by impregnating the glass fiber non-woven fabric with a thermosetting resin. And a glass powder having an average particle size of 25 μm or less. 2. A cross-section has a minor axis of 2 to 7 μm, a cross-sectional major axis of 6 to 40 μm, an oblateness of 2 to 10, and a length of 1.5 to.
A plurality of flat glass fibers satisfying a condition of 25 mm, and a glass powder having an average particle size of 25 μm or less formed by adhering to the plurality of flat glass fibers and crushing the glass fibers, and having a density of 0. A glass fiber non-woven fabric, which is ³ to 0.5 g / cm ³ . 3. The glass fiber non-woven fabric according to claim 2, which has a thickness of 30 μm or less.