JPH0312476B2 - - Google Patents

Description

[Detailed description of the invention]

(A) Industrial Application Field The present invention relates to electronic board materials, and relates to a functional sheet that serves as a substrate for flexible wiring boards among a wide range of board materials. (B) Prior art At present, flexible wiring boards in the field of electrical board materials include (a) those based on polyimide film sheets, (b) those based on polyester film sheets, and (c) those based on nonwoven fabric and resin. There is a product on the market that is based on a combination of films. The field of use for each varies depending on quality characteristics, price, etc., but in particular, products based on polyimide film sheets (a) secure a market share of approximately 70% due to their superior quality (solder heat resistance). This is the current situation. (C) Problems to be solved The problems of materials (a), (b), and (c) above are listed in Table 1.

[Table] ○: Good, ×: Bad, △: Moderately bad As described above, solder heat resistance and dimensional stability are essential requirements as electronic materials become more dense in the future. Currently, there are products that are mainly based on polyimide film bases (a), which are expensive and have some drawbacks in terms of hygroscopicity (some factors include solder heat resistance and down). An object of the present invention is to provide a flexible wiring board material with excellent insulating properties by using the present functional sheet as a base material, which has solved the above-mentioned drawbacks, in combination with various resins. (D) Means for Solving the Problems In order to solve the drawbacks of the above-mentioned base product based on the combination of nonwoven fabric and resin, solving the problem of the nonwoven fabric part is essential for solving the problem of quality based on the combination of nonwoven fabric and resin. We focused on the fact that this was the cause of the problem and resolved it after careful consideration. That is, the functional sheet of the present invention contains 75 to 90% by weight of para-aramid fibers, 10 to 25% by weight of synthetic thermal adhesive fibers (including moist heat fused fibers), and 0 to 10% by weight of non-adhesive synthetic fibers. Mix each fiber into a slurry, make paper into the desired thickness using a circular wire paper machine, Fourdrinier paper machine, etc., dry it with a dryer (90 to 130 °C), and uniformly process it with a super calender or heat calender. This is a functional sheet for printed circuit boards that has a certain thickness and is impregnated with heat-resistant resin. The nonwoven fabric of the present invention is produced by a papermaking method (there are various methods for producing nonwoven fabrics, but the papermaking method is preferable from the viewpoint of sheet uniformity), and 75% by weight or more, preferably 85% by weight or more, of para-process aramid fibers and synthetic fibers as an adhesive. By forming a sheet with a blending ratio of 25% by weight or less, preferably 15% by weight or less of heat-adhesive fibers (including moist heat-adhesive fibers), dimensional stability, which is the biggest drawback of nonwoven fabric and resin-based flexible substrate materials, can be improved. It is a solution to gender. Examples of the synthetic thermal bonding fibers (including moist heat bonding fibers) include PVA-based (e.g., Fibril Bond manufactured by Kuraray Co., Ltd.), PET-based (e.g., Tetron Binder 4080 manufactured by Unitika Co., Ltd.), Each of them may be used alone or in a mixture, and multiple synthetic fiber-based heat-adhesive fibers (for example, SWP synthetic pulp manufactured by Mitsui Petrochemical Co., Ltd.) may be used. Furthermore, of the 25% to 10% by weight of the above heat-adhesive fibers, 10% by weight of synthetic fibers that do not have adhesive properties.
The following can be used in place of: However, it is necessary to ensure a minimum blending amount of 10% by weight of thermal adhesive fibers. Examples of synthetic fibers without adhesive properties include fibers such as PET, acrylic, nylon, vinylon, and PE. This is because the strength of the functional sheet cannot be maintained if the thermoadhesive fiber is less than 10% by weight. Also, since the amount of para-aramid fibers is 75% by weight or more, bases using functional sheets (non-woven fabric + resin) with less than that amount will have somewhat poor solder resistance and problems will occur. . Examples of the heat-resistant resin used in the present invention include thermosetting resins such as epoxy resins, thermosetting polyesteramide resins, phenol resins, and polyimide resins. These can be used alone or in combination of two or more. Furthermore, in order to improve the adhesion of these resins, polyvinyl butyral resin, heat-resistant elastomer, phenoxy resin, etc. may be mixed, and in order to improve heat dissipation, alumina, silica, etc. may be mixed as an inorganic filler. It is possible to mix powders of , magnesia, zirconia, boron nitride, etc. Among these resins, epoxy resins are preferred from the viewpoint of adhesive properties. The thickness of the functional sheet for printed circuit boards is 30~
100μm is preferable, and if it is less than 30μm, the strength will be weak.
If the thickness exceeds 100 μm, flexibility will be impaired when used as a printed circuit board. (E) Examples The present invention will be explained by examples, but is not limited thereto. Example 1 and Comparative Examples 1 to 5 85% by weight of various heat-resistant fibers shown in Table 1 and 15% by weight of PVA fiber (Fibribond manufactured by Kuraray Co., Ltd., 1 denier, 3 mm) as a synthetic thermal adhesive fiber.
A mixed slurry was made, hand-sheeted into a sheet, dried with a dryer, and then supercalendered to obtain a sheet. The obtained sheet was impregnated with epoxy resin Epicoat 1001 (manufactured by Yuka Ciel Co., Ltd.) and cured to obtain a functional sheet of a composite sheet-like film having a thickness of 40 μm. Table 2 shows the characteristics of each functional sheet obtained. As is clear from Table 2, only Kevlar 29 (para-aramid fiber, manufactured by DuPont) had excellent properties.

【table】

[Table] Examples 2 to 10 and Comparative Examples 6 to 11 A mixed slurry was made of para-aramid fibers, thermally bonded fibers, and synthetic fibers according to the formulation shown in Table 3, and the slurry was hand-sheeted and dried with a dryer. , and supercalendered to obtain a sheet with uniform thickness. The obtained sheet was impregnated with epoxy resin Epicote 1001 (manufactured by Yuka Ciel Co., Ltd.) and cured, and the thickness
A 40 μm composite sheet-like film functional sheet for printed circuit boards was fabricated. Table 4 shows the properties of the functional sheet. This fourth
As is clear from the results in the table, the solder heat resistance is insufficient when the Kepler fiber content is less than 70% by weight, and it is preferably at least 75% by weight.
It can be seen that 85% by weight or more is required. Regarding the blended types of thermally bonded fibers, please refer to PVA fibers,
There was no significant difference between PET fibers. Further, there is no problem in terms of quality even if synthetic fibers that do not have adhesive properties are blended, but if there is a shortage of heat-adhesive fibers, there is a problem in strength as shown in Comparative Example 6. Comparative Examples 9 to 10 are commercially available polyimide films,
Shows the characteristic values of PET film. Comparative Example 11 shows the characteristic values of a nonwoven fabric made of meta fibers and PET fibers impregnated with the epoxy resin of this example.

【table】

【table】

[Table] (F) Effects of the invention The functional sheet for printed circuit boards using para-aramid fibers of the present invention improves dimensional stability, which was the biggest quality defect, in nonwoven fabric + resin flexible circuit board bases. However, it can sufficiently compete with a polyimide film substrate base, and depending on the processing method, it can be made lower in cost than a polyimide film substrate base.

Claims (1)

[Claims] 1 75 to 90% by weight of para-aramid fibers, 10 to 25% by weight of synthetic thermal adhesive fibers, 0 non-adhesive synthetic fibers
A functional sheet for printed circuit boards that is characterized by being made from a mixed paper containing ~10% by weight and impregnated with a heat-resistant resin. 2. The functional sheet for a printed circuit board according to claim 1, wherein the heat-adhesive fiber is one or more of PVA-based fibers and PET-based fibers. 3. The functional sheet for printed circuit boards according to claims 1 and 2, wherein the functional sheet has a thickness of 30 to 100 μm.