JPH0379343A - Metal-foiled laminated sheet and preparation thereof - Google Patents

Abstract

PURPOSE:To suppress the irregularity of a laminated sheet and to obtain the laminated sheet excellent in withstand voltage characteristics by using a high m.p. fluoroplastic in a base film and interposing a specific fusible insulating film between a metal foil and the base film to integrally fuse all of them. CONSTITUTION:A metal foil 7 whose bonding surface is roughened is laminated to an insulating base film 5 whose bonding surface is roughened through a thin fusible insulating film 6 composed of fluoroplastic having an m.p. lower than that of fluoroplastic constituting the insulating base film and having a chemically activated surface. In this case, the metal foil 7 and the films 6, 5 are pressed and heated at temp. near to the lower limit within the m.p. of the fluoroplastic constituting the fusible insulating film 6 at first and continuously heated at temp. near to the upper limit within said m.p. under pressure higher than the previous one to be fused and subsequently cooled to room temp. under pressure. By this method, the thickness irregularity as the whole of the insulating layer is reduced and withstand voltage characteristics are also enhanced.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a metal foil-clad laminate for use in printed wiring boards,
In particular, the present invention relates to a metal foil-clad laminate having a heat-resistant, low dielectric constant base film for flexible printed wiring boards, and a method for manufacturing the same.

(Prior technology) The basic structure of a typical printed wiring board is a so-called metal foil laminate in which a base film and conductive metal foil are bonded together using an insulating adhesive, and circuit patterns are etched using etching methods. The cross-sectional view is shown in FIG. 4, in which 1 is a base film, 2 is an insulating adhesive layer, 3 is a circuit pattern consisting of a metal foil formed by etching, The mainstream metal foil is copper foil, which has good conductivity.

In a printed wiring board having such a configuration, the characteristics of the insulating layer 4 made of the base film 1 and the insulating adhesive layer 2 often directly become the physical characteristics of the printed wiring board. For example, the typical characteristics of ceramic wiring boards include hardness, high insulation, and high dimensional stability.
This largely depends on the characteristics of the base ceramic itself. Furthermore, there are an increasing number of modern issues related to the functions of electronic components installed, such as heat dissipation issues, dimensional accuracy, signal transmission speed, etc., to ensure that the functions of electronic components are not impaired. It can be said to be a given characteristic. Recently, devices that operate in high frequency bands have become commonplace, and signal transmission delays due to wiring are becoming a problem for printed wiring boards as well. In other words, a wiring board for high-speed transmission is required.

In the printed wiring board having the general structure described above, the signal transmission speed is closely related to the dielectric constant of the insulating layer 4 made up of the base film 1 supporting the conductor circuit pattern and the insulating adhesive layer 2. Therefore, since fluororesin has a dielectric constant of 2.0 to 2.8, which is significantly lower than that of other organic resins, fluororesin is used as a base film for wiring boards for high-speed transmission. has been attempted, but
Because fluororesin requires high processing temperatures and has poor adhesion to metal, a thick fluororesin plate impregnated with filler such as glass fiber is bonded to copper using a resin material adhesive such as imide, which has a relatively low dielectric constant. There are those that are laminated to foil, and those that are made by heat-pressing a base film made of fluororesin impregnated with filler such as glass epoxy fiber cloth and copper foil at a temperature higher than the melting point of the fluororesin, but both are hard wiring. It is a board.

(Problems to be Solved by the Invention) Similar to the above, the demand for flexible wiring boards for high-speed transmission is increasing, and in order to lower the dielectric constant of flexible wiring boards, fluororesin is used as the base film, and the surface It has been proposed that a conductive metal thin film is formed by vapor deposition or sputtering, or that a fluororesin film and conductive metal foil are directly heat-sealed.

However, in the case of the former, even if a thin film of conductive metal is formed with a thickness of around 5 nm at most, it cannot be used as a general wiring circuit, so it is necessary to make the layer thickness around 10 nm. Furthermore, metal film layers formed by vapor deposition or sputtering methods have difficulty adhesion to the base film, and especially when the base film is made of fluororesin, the adhesion strength is insufficient. In addition, the conductor circuit is likely to peel off due to deformation of the wiring board or external stress such as soldering. Furthermore, variations in film thickness when the metal film layer is made thicker by plating,
Warpage and deflection of the substrate are likely to occur due to internal stress in the metal film layer.

In addition, as in the latter case, when the metal foil and the fluororesin film used as the base film are directly heat-sealed, the adhesive strength between them can be achieved at a level that does not pose any practical problems, but the fluororesin film After it melts and fuses with the metal foil, it becomes a film again after cooling.
Variations in the pressure distribution of the press plate cause variations in film thickness, which not only makes it difficult to manufacture large-area substrates, but also makes pinholes and withstand voltage failures more likely to occur.At the same time, the smoothness and dimensions of the substrate There are problems such as loss of accuracy.

(Means for Solving the Problems) The present invention has been made to solve the above-mentioned problems, and provides a metal foil-clad laminate in which metal foil and an insulating base film are laminated to form a circuit. As the plate, a fluororesin with a relatively high melting point is used for the base film, and between the metal foil and the base film, a thin film with a low melting point and a low thickness than the base film is used, and also has good adhesiveness with the metal foil. To provide a metal foil-clad laminate which is integrally fused by interposing an insulating film for fusion made of fluororesin.

The present invention also provides a method for obtaining the above-mentioned metal foil-clad laminate, in which the bonding surface of the metal foil is roughened. As a fusion material, a thin film made of fluororesin having a lower melting point than the fluororesin constituting the insulating base film is used.
Then, the insulating base film whose bonding surface has been roughened by sputter etching is laminated via the insulating film for fusion whose surface has been chemically activated by inert ion plasma treatment. The fluororesin constituting the insulating film for welding is heated under pressure at a temperature within the melting point and near its lower limit, and then in the second step, the upper limit of the fluororesin constituting the insulating film for fusing is heated. A method for producing a metal foil-clad laminate, which is characterized by heating under pressure at a nearby temperature and at a higher pressure than in the first step, thereby fusing the layers, and then cooling to room temperature under pressure. provide.

Note that the metal foil-clad laminate may be a single-sided laminate with metal foil on only one side, or a double-sided laminate with metal foil on both sides.

Next, to explain the fluororesin used in the present invention, tetrafluoroethylene resin (PTFE melting point 327°C),
Tetrafluoroethylene-perfluoroalkyl vinyl ether mJ11 (PFA melting point 300-310°C), tetrafluoroethylene-hexabutypropylene copolymer resin (F
Among these resins are A material with a relatively high melting point and a material with a relatively low melting point are combined, and the former is used as a base film and the latter is used as a fusion film.

(Function) Since the metal foil-clad laminate of the present invention uses fluororesin as the insulating layer, it is flexible and has a low dielectric constant. Since the resin maintains a constant thickness without changing physically or chemically during the lamination and fusing process, it suppresses variations in the laminate due to pressure variations within the press area.
At the same time, the present invention provides a laminate having excellent withstand voltage characteristics without the occurrence of pinholes penetrating the insulating layer.

In addition, in manufacturing the laminate of the present invention, the fusion bonding surfaces of the metal foil and the base film are roughened, and the surface of the fusion film is chemically activated to bond the fluororesin and the metal foil to each other. By increasing the adhesion with the fusion film and using specific pressure and heating conditions, it is possible to obtain a laminate with high reliability in interlayer fusion and excellent dimensional accuracy with very little variation in thickness. It will be done. Particularly in the cooling stage, since a pressure cooling method is used, a strain-free fused layer can be obtained.

(Example) FIG. 1 is a cross-sectional schematic diagram of a double-sided metal foil-clad laminate according to the present invention, and FIG. 2 is a cross-sectional schematic diagram of a single-sided metal foil-clad laminate. In these figures, 5 is an insulating base film and 100 is a fluororesin having a relatively high melting point.
n-thick PTFE (melting point 327°C) was used. 6 is an insulating film for heat fusion, which is a 50-thick FEP (melting point 2
50 to 282°C). Reference numeral 7 is made of copper foil, which are integrated by pressure heat fusion to form a double-sided or single-sided metal foil-clad laminate. A desired flexible printed wiring board is produced by removing unnecessary portions of the metal foil of this laminate using an etching method or the like.

An embodiment of the method for manufacturing the double-sided metal foil clad laminate shown in FIG. 1 will be described with reference to FIG. 3.

The copper foil 7 is a 35 pm thick electrolytic copper foil whose adhesive surface facing the base film 5 is roughened by sand matting, and the base film 5 is the above 100 μ thick PTFH film, which is sputtered. The adhesive surface is roughened to have an acicular structure of about 1 to 3 mm by etching treatment, and the insulating film 6 for heat fusion is the above-mentioned 5 On thick FEP film, which is coated with helium, argon, etc. A laminate 8 is created by laminating copper foil 7 on both sides of the base film 5 with an insulating film 6 interposed therebetween, using an inert gas plasma discharge treatment applied to both surfaces and chemically activated. The laminated plate 8 is sandwiched between the upper plate 10 and the lower plate 11 of the press machine with heat-resistant separators 9 on both sides of the plate, and the temperature is within the range of the melting point of FEP, from 250 to 250, which is close to its lower limit. Heat to 260℃,
A gentle pressure of 10 kg/cm2 was applied for about 60 minutes, and then the heating temperature was increased to 270°C, which is close to the upper limit of FEP's melting point.
Heat to ~290℃ and apply pressure to 25~50kg
/cs" and pressurized for about 30 minutes, then slowly lowered the temperature to 200 to 250 °C below the melting point of FEP over a period of about 120 degrees while keeping this pressure applied, and then to room temperature. After natural cooling, the pressure is released, the press is removed, and the separator is removed to obtain the desired metal foil-clad laminate. Note that a single-sided metal foil-clad laminate can also be manufactured by the same manufacturing method.

Note that the thickness of the insulating base film and the insulating film for fusion can be changed depending on the desired thickness of the metal foil clad laminate. However, in order to increase the dimensional accuracy of the layer thickness, The thickness of the insulating film for welding can be made thinner, but in order to ensure good, stable adhesion and smoothness over the entire surface of the laminate, the thickness of the insulating film for fusing used this time should be approximately the same as in the above example. It is preferable that the thickness is 1/2 or more.

The present invention is not limited to the combination of the two types of fluororesins shown in the above embodiments, and other combinations of fluororesins with a relatively high melting point and fluororesins with a low melting point may be used. , the second stage of heating, that is, heating near the upper limit of the melting point of the fluororesin, which has a relatively low melting point, is
It is necessary to carry out the process under conditions that do not melt the fluororesin, which has a relatively high melting point.

(Effects of the Invention) The metal foil-clad laminate of the present invention uses a fluororesin with a relatively high melting point and low dielectric constant as an insulating base film, and has good adhesion with metal foils with a low dielectric constant as an insulating film for fusion. Since fluororesin with good properties is used, the entire insulating layer formed by these is made of fluororesin with a low dielectric constant.
Since this insulating layer can be made extremely thin, it can be made into a thin, flexible, low dielectric constant metal foil laminate, which can be used to create a flexible printed wiring board for high-speed transmission. can do.

In addition, a fluororesin with a relatively high melting point is used as the base film, a fluororesin with a lower melting point than the fluororesin of the base film is used as the insulating film for fusion, and certain conditions are set within the range of the melting point of this low melting fluororesin. Since the base film is not melted, and the insulating film for heat fusion is thin, even if the thickness of this layer varies due to melting and solidification, the overall thickness of the insulating layer will remain the same. The variation is small and the dimensional accuracy is improved. At the same time, since the base film maintains a constant thickness and no pinholes occur, the withstand voltage characteristics are also improved. Moreover, the manufacturing unit area can be expanded. A fluororesin with a low melting point is used as the insulating film for heat fusion, but even though it is low melting point, it has a very high melting point compared to general organic resins, and can be used stably even in the high temperature range of around 230℃. can do.

[Brief explanation of drawings]

Figure 1 is a cross-sectional schematic diagram of a double-sided metal foil-clad laminate according to the present invention, Figure 2 is the same (cross-sectional schematic diagram of a single-sided metal foil-clad laminate, and Figure 3 is a method for manufacturing a metal foil-clad laminate according to the present invention). FIG. 4 is a cross-sectional schematic diagram of a printed wiring board made of a conventional metal foil-clad laminate. 5: M-edge base film, 6: Insulating film for fusion, 7: Metal foil .

Claims (2)

[Claims] 1. In a metal foil laminate in which a metal foil for forming a circuit and an insulating base film are laminated, the metal foil for forming a circuit and an insulating base film made of a fluororesin having a relatively high melting point. are laminated and fused together via an insulating fusion film made of a fluororesin having a lower melting point than the base film. 2. A bonding insulating film made of a fluororesin with a lower melting point than the fluororesin constituting the insulating base film is layered on the metal foil with a roughened joint surface, and then an insulating film made of a fluororesin with a relatively high melting point is layered on the metal foil with a roughened joint surface. After overlapping the adhesive base film, in the first step, the melting point of the fluororesin constituting the insulating film for fusion is heated under pressure at a temperature near the lower limit of the melting point, and then in the second step, the Heat and pressurize at a temperature close to the upper limit of the fluororesin that makes up the insulating film for fusion and at a higher pressure than in the first stage to fuse the layers, then cool under pressure to room temperature. A method for manufacturing a metal foil-clad laminate, characterized by: