JPH0750570B2 - Flexible printed wiring board - Google Patents

Description

The present invention relates to a flexible printed wiring board having excellent high frequency characteristics.

(Prior Art) In recent years, the development of the electronics field has been remarkable, and especially electronic devices for communication, consumer use, etc. are becoming smaller, lighter and higher in density, and requirements for these performances are becoming more and more advanced. There is.

In response to such demands, the flexible printed wiring board has flexibility, so that it can be mounted in a narrow space with a three-dimensional high density, and can withstand repeated bending, and wiring to electronic equipment,
Its applications are expanding as composite parts with cable and connector functions.

A substrate for flexible printed wiring generally uses a film of polyimide or polyester resin as an electrically insulating substrate, and these substrates and a metal foil such as a copper foil or an aluminum foil are laminated and integrated via an adhesive. Based on, the circuit is formed on it and mounted on many devices such as cameras, calculators, and computers. With regard to this flexible printed wiring board, recently, with the spread of satellite broadcasting receivers, a flat type that can be miniaturized has been developed as an antenna used for the substrate, compared to a conventional parabolic type. Flexible printed wiring boards are mainly used for this flat type antenna,
Further, in order to realize further miniaturization and higher performance, it is desired to develop a flexible printed wiring board having excellent high frequency characteristics.

To date, studies have been conducted on power feeding methods and flexible printed wiring boards to improve high frequency characteristics. There are a microstrip line method, a triplate method, a suspended line method, and a waveguide array method as a power feeding method, and the triplate method and the suspended line method are predominant due to the balance between transmission loss and structure. As a substrate for flexible printed wiring, an aluminum foil is used as a conductor, a polyester film is used as an insulating film, and a urethane / epoxy adhesive having a thickness of 3 is used.
Those having a thickness of up to 8 μm have been proposed. However, in realizing further miniaturization and higher performance, satisfactory characteristics have not been obtained even with the above combination.

(Problem to be Solved by the Invention) An object of the present invention is to provide a flexible printed wiring board having excellent high frequency characteristics.

(Means for Solving the Problems) The inventors of the present invention have focused their attention on the constituent material of the flexible printed wiring board in order to satisfy the above characteristics, and as a result of diligent study,
Using oxygen-free copper foil with good conductivity as the copper foil that is a conductor,
By setting this surface roughness in the range of 1.5 to 5, the surface of the adhesive after removing the copper foil is made flat, and by further reducing the thickness of the adhesive, a flexible printed wiring board with excellent high frequency characteristics is obtained. That is, the present invention has been achieved.

The present invention will be described in detail below.

Examples of the electrically insulating film (hereinafter referred to as an insulating film) used in the present invention include a polyimide film, a polyparabanic acid film, a polyester film, a polyethersulfone film, a polyetheretherketone film, etc. If necessary, low temperature plasma treatment, corona discharge treatment, sand mat treatment and the like may be performed for the purpose of improving the strength.

As oxygen-free copper foil, the surface roughness is 1.5-5 (JISB0601)
If necessary, a silane coupling agent or the like may be used to improve the adhesive strength with the adhesive.

Although the kind of the adhesive is not particularly limited, it is preferable to use a urethane / epoxy type or a polyester / epoxy type having good adhesiveness and electrical insulation. The thickness of the adhesive needs to be 10 μm or less after drying, and if it exceeds 10 μm, the high frequency characteristics are adversely affected. At the time of applying the adhesive, the resin content concentration is appropriately adjusted using a solvent, if necessary, and flow coating, brush coating, bar coater coating is performed,
It may be finished to a desired thickness.

The flexible printed wiring board obtained by the present invention has excellent high-frequency characteristics, but particularly brings about an effect of reducing transmission loss in a frequency range of 10 to 14 GHz.

Next, specific embodiments of the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited thereto. The physical property measuring methods used in these specific examples are as follows.

High-frequency characteristics (transmission loss) measuring method Flexible printed wiring board with a length of 250 mm
A 1.5 mm pattern was created, this was set in the suspended line format as shown in Fig. 1, and the transmission loss (dB / m) at a frequency of 12 GHz was measured.

Example 1 A polyester / epoxy thermosetting adhesive was applied to a 25 μm-thick Kapton film (trade name of a polyimide film manufactured by DuPont) to a thickness of 8 μm and dried. An oxygen-free copper foil (surface roughness 3) having a thickness of 25 μm was heated and pressure-bonded thereto with a roll laminator, and further cured by heating to obtain a substrate for flexible printed wiring. When the transmission loss of this substrate was measured, it was 2.6 dB / m.

(Example 2) The thickness of the Kapton film having a thickness of 25 μm in Example 1
A substrate for flexible printed wiring was obtained under the same conditions except that a polyester film of 50 μm was used instead. When the transmission loss of this substrate was measured, it was 2.6 dB / m.

Comparative Example 1 A urethane / epoxy thermosetting adhesive was applied and dried on a polyester film having a thickness of 50 μm so as to have a thickness of 5 μm when dried. An aluminum foil having a thickness of 20 μm was heated and pressure-bonded thereto with a roll laminator, and further heat-cured to obtain a substrate for flexible printed wiring. When the transmission loss of this substrate was measured, it was 3.0 dB / m.

(Comparative Example 2) The same conditions were used except that the oxygen-free copper foil (surface roughness 3) in Example 1 was replaced with the oxygen-free copper foil (surface roughness 10),
A substrate for flexible printed wiring was obtained. When the transmission loss of this substrate was measured, it was 3.4 dB / m.

(Comparative Example 3) A flexible printed wiring board was obtained under the same conditions as in Example 1 except that the thickness of the adhesive was changed from 8 µm to 18 µm. When the transmission loss of this substrate was measured, it was 3.5 dB / m.

(Effect of the Invention) According to the present invention, the high-frequency characteristics are excellent by defining the material of the constituent material of the flexible printed wiring board, particularly the oxygen-free copper foil having a limited surface roughness and the thickness of the adhesive. It has a very high utility value in practice.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing the structure of the suspended line method of the high frequency characteristic (transmission loss) measuring methods. Symbol in the figure 1: Insulation film, 2: Conductor 3: Ground conductor plate

Claims (1)

[Claims] 1. An electrically insulating film having a surface roughness of 1.5 to 5
A flexible printed wiring board having excellent high-frequency characteristics, which is obtained by laminating and integrating an oxygen-free copper foil in the range of 1) via an adhesive having a thickness of 10 μm or less.