JPH0644667B2 - Flexible printed circuit board with shield - Google Patents

Description

TECHNICAL FIELD The present invention relates to a flexible printed circuit board with a shield.

[Problems with conventional technology] Flexible printed circuit boards (hereinafter referred to as "FPCs") that have polyester or polyimide film coated with an adhesive and bonded to a copper foil, after which the copper foil is etched to form a circuit. However, as a substrate that requires heat resistance, flame retardancy, and solderability, it is mostly based on a polyimide film, and a substrate that is extruded and coated with a part of fluorine resin, such as FEP, PFA, ETFE. It is used.

By the way, a circuit used as a high frequency circuit of 1 MHz or more requires a shield layer for the FPC, but a polyimide film cannot obtain an excellent shield effect because the dielectric constant of the insulating layer is as high as 3.5.

Therefore, in a high frequency range of 10 GHz or more, a hard tetrafluoroethylene resin substrate is used, and a method of shielding with a metal plate is used.

In order to obtain the electrostatic shield and electromagnetic shield effects, it is necessary to reduce the capacity of the insulating layer. A polyimide film or a tetrafluoride resin film becomes inflexible and expensive when the layer is thickened. In particular, in the case of a tetrafluoride resin, it is difficult to bond the resin to the copper foil or the shield layer, and the surface treatment requires a great deal of labor and cost.

[Object of the Invention] The present invention is a flexible printed circuit board with a shield that has heat resistance, flame retardancy, solder heat resistance, retains flexibility, is excellent in processability, and can sufficiently maintain a high-frequency shielding effect. It is intended to provide.

[Structure of the Invention] The present invention is a method in which a tetrafluoroethylene resin is stretched by 100 to 500%, and a metal is physically applied to one side of a porous tetrafluoroethylene resin film in which the porosity in the stretched film is 30 to 80% Vapor deposition,
A porous tetrafluoroethylene resin film with an electrical circuit formed by exposure, development, etching, copper plating, and a shield layer with physical vapor deposition of metal on the other side, and physical vapor deposition of metal on one side as described above, and exposure , A porous tetrafluoroethylene resin film provided with an electric circuit formed by development, etching and copper plating and a shield layer formed by physically vapor-depositing a metal on one side, or a porous layer formed by physically vapor-depositing a metal on one side only With a tetrafluoroethylene resin film,
Another object of the present invention is to provide a flexible printed circuit board with a shield, characterized in that the shield layers of both films are bonded to each other. When the porosity is 30% or more, the dielectric constant does not decrease and the adhesive strength is low. When it is 80% or more, the physical vapor deposition of the metal layer on the surface cannot be obtained uniformly, and the mechanical strength is low and it cannot be practically used.

As described above, a porous tetrafluoroethylene resin film that is obtained by stretching a tetrafluoroethylene resin and also having micropores on the surface is
Copper and other metals can be uniformly coated by physical vapor deposition on the concavo-convex surface formed by the micropores on the surface, and the vapor-deposited metal enters the porous interior through the micropores and is mechanically and strongly bonded.

FIG. 2 shows an enlarged view of a metal vapor deposited on a porous tetrafluoroethylene film. As is already known, the tetrafluoroethylene resin is stretched (including biaxial stretching) into a porous film. What is used in the present invention, a pore diameter of about 0.1 to 5 μ and a thickness of 50 to 500 μ are suitable. In the figure, 1 indicates a porous tetrafluoroethylene resin film, 2 indicates micropores, and 3 indicates a physical vapor-deposited metal layer. Deposition of copper for circuit construction is performed, copper is on the opposite side,
The shield layer is formed by physical vapor deposition of a metal such as nickel or iron.

As a physical vapor deposition means for metals such as copper, nickel and iron, vacuum vapor deposition, sputtering, cluster ion vapor deposition and the like are used, and the thickness thereof is about 0.1 to 5 μm.

On the vapor-deposited surface of copper for circuit construction, the required circuit is exposed by exposure, development, and etching, and then only the circuit is electroplated to a thickness of approximately 10μ.

1 (a) and 1 (b) show an embodiment of the present invention. (A) In the figure, 1 is a porous tetrafluoroethylene resin film, and 4
Indicates a shield layer formed by metal deposition. As shown in the figure, a metal vapor deposition circuit 5 and an electric circuit 6 by copper plating on the surface thereof are formed on one surface of one of the two porous tetrafluoroethylene resin films 1 by the method already described. The polytetrafluoroethylene resin film 1 has the shield layer 4 as the outer side, and an adhesive is attached to the inner surface to be integrated.

In the figure (b), two porous tetrafluoroethylene resin films 1 are vertically symmetrically arranged on the two metal vapor deposition circuits 5 having the same pattern.
And an electric circuit was formed on the surface by copper electroplating, a shield layer was formed on the other side by metal deposition, and two porous tetrafluoroethylene resin films were formed symmetrically. The electric circuits 6 are combined and integrated by the solder layer 7.

The above is for exciting the configuration of the present invention. Next, a prototype example according to the present invention will be described.

Copper was vapor-deposited on a porous tetrafluoroethylene resin film (pore size: 0.3 to 2 μm) having a porosity of 40% and a thickness of 120 μm by a thickness of 0.5 μm in a sputtering apparatus. After that, an electric circuit was exposed on only one side by exposure, development, and etching, and then only the circuit was electroplated to a thickness of 10 μm.

Further, a thermosetting film adhesive was laminated on the back surface of the porous tetrafluoroethylene film having only one surface sputtered with copper, and was laminated on the circuit surface and pressure-bonded at 150 ° C.

The adhesive strength of the obtained circuit and shield layer was 400 g / cm, and peel strength was obtained, and the porous film was broken.

Moreover, as a result of measuring the shielding effect, the electrostatic capacity was reduced to 1/4 compared with the general FPC, and the good shielding property was shown.

The present invention can be applied to a high frequency substrate and a shielded FPC.

[Effect] As described above, in the past, a sheet made of tetrafluororesin was simply used, whereas in the present invention, a porous tetrafluoroethylene resin (thickness 50 to 500 μ) is used. Therefore, FPC exhibiting solder heat resistance, low dielectric constant (ε: 1.4 to 2.1) and flexibility can be obtained.

The metal vapor deposition layer penetrates to the depth of 1 to 10μ on the surface of the porous body and is in an anchored state, the metal is integrated on the porous surface without an adhesive, it is heat resistant, and the printed circuit is not affected by temperature and humidity. A substrate is obtained.

[Brief description of drawings]

1 (a) and 1 (b) are each an embodiment of the present invention and are enlarged sectional views. FIG. 2 is an illustration of metal physical vapor deposition on a porous tetrafluoroethylene resin film. 1 ... Porous tetrafluoroethylene resin film, 2 ... Micropores,
3 ... vapor deposition metal layer, 4 ... shield layer, 5 ... metal vapor deposition circuit,
6 ... Electric circuit, 7 ... Solder layer.

Claims (1)

[Claims] 1. A porous tetrafluoroethylene resin film having an electric circuit formed by physical vapor deposition of metal on one side and exposing, developing, etching, and copper plating, and a shield layer having physical vapor deposition of metal on the other side. Similarly to the above, physical vapor deposition of metal on one side, exposure, development, etching, a porous tetrafluoroethylene resin film provided with an electrical circuit formed by copper plating, and a shield layer on the other side of which physical vapor deposited metal, or A flexible printed circuit board with a shield, characterized in that a porous tetrafluoroethylene resin film having a shield layer in which metal is physically vapor-deposited on only one surface is joined to the shield layers of both films with the shield layers facing up.