JPH0748581B2 - Printed circuit board base sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to a substrate sheet for a printed circuit board used in various electronic devices, and particularly to a substrate sheet having a low dielectric constant.

<Prior Art> With the recent increase in the speed of arithmetic processing for communication and computers, it is required to develop a printed board having excellent high frequency characteristics, especially a printed board having a low dielectric constant.

Conventionally, a base material sheet made of paper or glass cloth is impregnated with a phenol resin, an epoxy resin, a polyimide resin, or a fluororesin and dried or heat-treated, and then the resin-impregnated base material is provided with a metal such as a copper foil or an aluminum foil. Substrates obtained by laminating and molding foils are used as various printed wiring boards for electric and electronic devices.

However, it has been impossible to obtain a sufficiently low dielectric constant with a printed circuit board using a base sheet made of the paper or glass cloth.

On the other hand, a prepreg obtained by impregnating and curing a thermosetting resin as a base sheet of a mixed woven fabric composed of polytetrafluoroethylene fiber (hereinafter referred to as PTFE fiber) that has been stretched recently and glass fiber. Laminate molding (Japanese Patent Laid-Open No.
No. 139629) or a silica fiber aggregate used as a base sheet and impregnated with a fluorine resin (JP-A-63-28).
No. 3181) has been proposed. However, in the former case
Since the PTFE fiber is stretched, shrinkage occurs during heat treatment in the manufacturing process of the printed circuit board, and in the latter case, it is still difficult to obtain a sufficiently low dielectric constant.

<Means for Solving the Problems> The present invention has been made in view of such circumstances, and the invention of claim 1 heat-sinters a sheet in which unstretched polytetrafluoroethylene fibers are formed by wet papermaking. A printed circuit board substrate sheet comprising: a polytetrafluoroethylene mixed sheet in which unstretched polytetrafluoroethylene fibers and inorganic fibers are mixed by a wet papermaking method; It is a base material sheet.

The unstretched polytetrafluoroethylene fiber referred to in the present invention is a dispersion of PTFE, viscose, carboxymethyl cellulose, constituted by a binder such as polyvinyl alcohol as a matrix, obtained by spinning into a coagulation bath from the pores. However, it does not go through a stretching step involving heat treatment.

To prepare the printed circuit board substrate sheet of the present invention, the unstretched PTFE fiber is cut into a length of 3 to 15 mm and dispersed in water together with a dispersant such as polyacrylamide to form a papermaking raw material. The raw material is applied to an existing paper machine such as a cylinder paper machine or a Fourdrinier paper machine to prepare a PTFE sheet without making a paper.

At this time, the matrix substance mixed in the PTFE fiber is
It exerts a binding function between fibers during papermaking, making it possible to make PTFE fiber sheets.

Then, the sheet is heated to a temperature above the melting point of PTFE (for example, 380
(° C) heat treatment to fuse the PTFE fibers, and
The printed circuit board sheet of the present invention can be obtained by subjecting the matrix such as viscose mixed between the PTFE fibers to a heat treatment at about 300 to 330 ° C. for thermal decomposition and removal.

The substrate sheet of the present invention obtained as described above is impregnated with a phenol resin or an epoxy resin in order to improve the stackability with a metal foil, and the metal foil is laminated to form a printed circuit board.

According to a second aspect of the present invention, a PTFE mixed paper sheet obtained by mixing inorganic fibers such as glass fibers, silica fibers, alumina fibers, and aluminum silicate with PTFE fibers is heat-sintered by a wet papermaking method to obtain a printed circuit board base sheet. That is what I got.

As a result, it is possible to control the compounding ratio of various inorganic fibers to the PTFE fiber according to the required characteristics, which improves the rigidity of the base sheet and stabilizes the dielectric constant of PTFE in a wide frequency range, resulting in a dielectric loss tangent. It is possible to obtain a printed circuit board base sheet which can maximize electric characteristics such as stable characteristics in a low and wide temperature range and has high flame retardancy.

<Examples> Examples will be described below.

Example 1 Unstretched PTFE fiber obtained from PTFE dispersion using viscose as a matrix (Toyoflon manufactured by Showa Kogyo Co., Ltd.)
Is cut into 6 mm length and dispersed in water at a concentration of 0.5% and a polyacrylamide synthetic dispersant is added to form a papermaking raw material into a sheet with a round net paper machine, and the basis weight is 243 g / m ² , 182 g / m ² , 131 g. / m
^2, to obtain a PTFE sheet of ^{87g / m 2, 70g / m} 2. This sheet is heated at 380 ° C for 3 minutes using an infrared heater, and P
The TFE particles were continuously fused and the entangled fibers were fused. Furthermore, in order to thermally decompose and remove viscose in the sheet, it was heat treated at 320 ° C for 20 hours and weighed 286 g / m ² (Sample No.
1), 220g / m ² (Sample No2), 195g / m ² (Sample No3), 107g / m ²
(Sample No. 4) and 83 g / m ² (Sample No. 5) were obtained as five types of white printed board substrate sheets of the present invention.

Example 2 80 parts by weight of fiber obtained by cutting unstretched PTFE fiber similar to that in Example 1 to a length of 6 mm, glass fiber (manufactured by Nippon Glass Fiber Co., Ltd.)
20 parts by weight of 6 mm long cut fiber (GP11W) is dispersed in water at a concentration of 0.5%, a polyacrylamide synthetic dispersant is added, and this is made into a sheet with a gauze paper machine.
A PTFE mixed sheet of / m ² was obtained.

This sheet is heated at 380 ° C for 3 minutes using an infrared heater, and further 320 for complete thermal decomposition and removal of viscose.
A heat treatment was performed at 20 ° C. for 20 hours to obtain a 99 g / m ² (Sample No. 6) white printed circuit board base sheet according to the present invention.

The dielectric constant of the printed circuit board base sheet according to the present invention obtained above was measured, and the results shown in Table 1 were obtained.

(Effects of the Invention) The printed circuit board base sheet of the present invention has the above-mentioned constitution, and it is possible to obtain a printed circuit board having excellent electrical characteristics which have not been obtained in the past.

Also, since the PTFE fibers that make up the base sheet are unstretched,
Shrinkage due to heat treatment is extremely small, which is preferable in the printed circuit board manufacturing process.

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location D04H 1/54 Q 7199-3B D21H 13/14

Claims (2)

[Claims] 1. A printed circuit board base sheet, wherein a polytetrafluoroethylene sheet formed by wet-making unstretched polytetrafluoroethylene fibers is heat-sintered. 2. A printed circuit board substrate sheet, wherein a wet-textured polytetrafluoroethylene mixed paper sheet obtained by mixing unstretched polytetrafluoroethylene fibers and inorganic fibers is heat-sintered.