JPH06281831A - Electric wiring/optical wiring combined flexible printed circuit board and substrate therefor - Google Patents

Abstract

PURPOSE:To provide the electric wiring/optical wiring combined flexible printed circuit board formed by housing electric wiring and optical wiring in the same wiring board and the substrate for such circuit board. CONSTITUTION:This electric wiring/optical wiring combined flexible printed circuit board is formed by using a high-polymer film having optical waveguide and metallic wiring formed on it as main constituting elements. The electric wiring/optical wiring combined flexible printed circuit board is formed by using the high-polymer film having the optical waveguide and metallic foil formed on it as main constituting elements. The main base materials of the respective high-polymer films are polyimide and more particularly adequately polyimide of org. tetracarboxylic acid and 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl. Since the circuit boards have characteristics, such as resilience and lightness, the circuit board makes contribution for high advancement of future optical communication apparatus, optical information device, etc. The circuit boards are easily made from the substrates.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric wiring / optical wiring mixed flexible printed wiring board using a polymer film and its substrate.

[0002]

2. Description of the Related Art Flexible printed wiring boards are widely used for small electronic devices such as cameras, electronic timepieces, calculators, and electronic parts, taking advantage of the fact that they can be freely wired in a narrow space. It is expected that the applicable fields such as small computers, exchanges, and office automation equipment will further expand in the future. On the other hand, with the practical use of optical communication systems through the development of optical fibers, various optical communication parts have been developed. Further, it is desired to establish an optical wiring technology for mounting these optical components at a high density, particularly an optical waveguide technology. In general, the optical waveguide is required to have conditions such as small optical loss, easy manufacture, controllable difference in refractive index between core and clad, and excellent heat resistance. As a low-loss optical waveguide, silica has been mainly studied, and since quartz has an extremely good optical transparency as demonstrated in optical fibers, the wavelength is 1.3 μm even when used as a waveguide.
A low optical loss of 0.1 dB / cm or less has been achieved at m. However, it takes a long time to manufacture the optical waveguide,
There are problems in manufacturing, such as high temperature required at the time of manufacturing and difficulty in increasing the area. On the other hand, a polymer optical waveguide such as polymethylmethacrylate has advantages that it can be formed into a film and can be molded at a low temperature and that a low price can be expected, but it has a drawback that it is inferior in heat resistance. Therefore, polymer optical waveguides having excellent heat resistance have been expected.

By the way, polyimide having excellent heat resistance, which is used as a base film of a flexible printed wiring board, has hardly been applied to optical parts such as optical waveguides. Although the present inventors have been researching and developing polyimide optical materials applicable to optical waveguides,
In applying polyimide as an optical material, it is particularly important that it has excellent light transmittance and that the refractive index can be freely controlled. The inventors of the present invention disclosed in JP-A-3-725.
No. 28 discloses a transparent fluorinated polyimide,
Further, Japanese Patent Laid-Open No. 4-8734 discloses that copolymerization of this fluorinated polyimide can control the refractive index necessary for forming an optical waveguide. Further, JP-A-4-9807, 4-235505 and 4-2.
As disclosed in each publication of Japanese Patent No. 35506, an optical waveguide has been successfully produced by using these fluorinated polyimides. With the progress of optical communication technology and optical information processing technology,
It is considered that electric wiring and optical wiring will be required to be housed in the same wiring board. However, at present, there is no report on a flexible printed wiring board in which electric wiring and optical wiring are housed in the same wiring board.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electric wiring / optical wiring mixed flexible printed wiring board in which electric wiring and optical wiring are accommodated in the same wiring board, and a substrate thereof.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a flexible printed wiring board on which electric wiring and optical wiring are mixed to achieve the above-mentioned object, and a substrate thereof. The electric wiring and optical wiring mixed flexible of the first invention of the present invention. Printed wiring board
It is characterized in that a polymer film on which an optical waveguide is formed and a metal wiring are main components. The electric wiring / optical wiring mixed flexible printed wiring board substrate of the second invention of the present invention is characterized in that a polymer film having an optical waveguide formed thereon and a metal foil are main components.

A basic configuration example of a flexible printed wiring board on which electric wiring and optical wiring are mixed according to the present invention will be shown. 1 is a side view, FIG. 2 is a plan view, and FIG. 3 is a sectional view. In each figure, reference numeral 1 is metal wiring, 2 is an optical waveguide clad layer, 3
Indicates the core layer of the optical waveguide.

The metal wiring 1 includes, for example, copper, aluminum, gold, etc. Normally, copper, which is currently mainly used in flexible printed wiring boards, is generally used. The thickness of metal wiring is currently 35 μm or 19 μm, but
Other than this is acceptable. Also, the width of the metal wiring is not particularly limited, and may be the same as the current flexible printed wiring board. The metal wiring may be in direct contact with the polymer film as shown in the figure, or may be in contact with an adhesive.

The base material of the clad layer and core layer of the polymer film on which the optical waveguide is formed may be any polymer material,
Different polymer materials may be used. However, it is essential that the refractive index of the core layer is higher than that of the cladding layer.
Specific materials include polymethylmethacrylate, polystyrene, polyester, polyimide, and silicone resin. Polyimide is preferable from the viewpoints of flexible printed circuit boards and heat resistance. Furthermore, the following general formula (Formula 1) is being developed as an optical waveguide:

[0009]

[Chemical 1]

A polyimide containing a repeating unit represented by the formula (where X is a tetravalent organic group) is more preferable. However, if other polymer waveguides are developed in the future, the material can be used as a matter of course. The optical waveguide includes a multimode type and a single mode type, but both of them are applicable. The core shape may be a sphere, a square, a rectangle, or the like, and the dimensions of the core are limited to some extent depending on the waveguide type, but various dimensions are possible. For example, a square core shape with a core size of 1 to 100 μ
m is common. If the thickness of the clad layer is too thin as compared with the thickness of the core layer, it leads to a loss of light, which is not preferable. When the total thickness of the core layer and the clad layer is thin and the mechanical strength as a flexible printed wiring board cannot be obtained, a supporting film may be laminated.

The electric wiring / optical wiring mixed flexible printed wiring board illustrated in the figure has a basic structure.
For example, there are various types such as one having electric wiring on both sides, one having more layers, one having a plurality of core layers of an optical waveguide, and one having more layers.

A substrate for flexible printed wiring board on which electric wiring and optical wiring are mixed is a combination of an optical wiring-provided polymer film and a metal foil. It is in the previous state.

A flexible printed wiring board on which electric wiring and optical wiring are mixed is manufactured as follows. First, a polymer film having an optical waveguide is formed, and then a metal foil is attached with an adhesive or plating treatment is performed. A wiring process is performed on the thus obtained substrate for a flexible printed wiring board on which electric wiring and optical wiring are mixed to obtain a flexible printed wiring board on which electric wiring and optical wiring are mixed. The polymer film having the optical waveguide can be obtained by peeling the polymer optical waveguide prepared on a suitable substrate from the substrate.

[0014]

The present invention will be described in detail with reference to the following examples. The present invention is not limited to these examples.

Example 1 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl ( A polyamic acid solution with a concentration of 15 wt% was obtained from TFDB) and N, N-dimethylacetamide (DMAc). This polyamic acid solution was spin-coated on a silicon wafer and then heated in an oven at 70 ° C. for 2 hours, 160 ° C. for 1 hour, 250 ° C. for 30 minutes, 380 ° C. for 1 hour,
Imidization was performed to obtain a polyimide film having a thickness of 30 μm. Next, a mixture of TFDB and acid anhydride (6FDA: 9
From 0 mol%, pyromellitic dianhydride: 10 mol%) and DMAc, a 15 wt% solution of polyamic acid, which is a precursor of polyimide having a refractive index higher than that of the lower clad layer, was obtained. After spin-coating the polyamic acid solution on the lower clad layer, it is heated in an oven at 70 ° C. for 2 hours.
Imidization was performed by heating at 160 ° C. for 1 hour, 250 ° C. for 30 minutes, and 380 ° C. for 1 hour to form a core layer having a thickness of 10 μm. 0.3 μm on this core layer with a vapor deposition device
Of aluminum film was formed. Next, a normal positive resist was applied by spin coating and then prebaked. Next, ultraviolet rays were radiated using a super high pressure mercury lamp through a pattern forming mask having a line width of 10 μm and a length of 60 mm, and then development was performed using a developing solution. After that, it was afterbaked. Next, wet etching of aluminum not coated with resist was performed. After washing and drying, the polyimide was processed using a dry etching device. Then, aluminum on the upper layer of the polyimide was removed by the above-mentioned etching solution, and a ridge type optical waveguide having a core layer with a width of 10 μm was obtained. Further, the same polyamic acid solution as that for the lower clad layer was spin-coated on the ridge type optical waveguide and then in an oven at 70 ° C. for 2 hours and 160 ° C. for 1 hour.
The mixture was heated at 30 ° C. for 30 minutes and at 380 ° C. for 1 hour for imidization to form an upper clad having a thickness of 30 μm. The polyimide optical waveguide on the silicon wafer thus produced was immersed in water and left to stand, and the polyimide film on which the optical waveguide was formed was peeled off. Take this out and put it under vacuum 10
It was dried at 0 ° C. for 1 hour. Then, a polyimide film having an optical waveguide formed thereon was plated with copper by 18 μm by an electroless plating method to obtain a substrate for a flexible printed wiring board on which electric wiring and optical wiring were mixed. Further, electric wiring was formed by a usual patterning method to obtain a flexible printed wiring board on which electric wiring and optical wiring were mixed.

[0016]

EFFECTS OF THE INVENTION The flexible printed wiring board on which electric wiring and optical wiring are mixed according to the present invention is capable of simultaneously transmitting electric signals and optical signals, and is characterized by flexibility and light weight. There is an effect that it can contribute to the sophistication of the optical communication device and the optical information device. In addition, the flexible printed wiring board mixed with electric wiring / optical wiring has an effect that a flexible printed wiring board mixed with electric wiring / optical wiring can be easily manufactured.

[Brief description of drawings]

FIG. 1 is a side view of an example of a flexible printed wiring board on which electric wiring and optical wiring are mixed according to the present invention.

FIG. 2 is a plan view of the electric wiring / optical wiring mixed flexible printed wiring board of FIG. 1 of the present invention.

FIG. 3 is a cross-sectional view of the flexible printed wiring board on which electric wiring / optical wiring is mixed according to the present invention.

[Explanation of symbols]

 1: Metal wiring, 2: Cladding, 3: Core

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Toru Matsuura 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (6)

[Claims] 1. A flexible printed wiring board on which electric wiring and optical wiring are mixed, which comprises a polymer film having an optical waveguide and a metal wiring as main components. 2. An electrical wiring comprising a polymer film having an optical waveguide and a metal foil as main components.
Substrate for flexible printed wiring board with optical wiring mixed. 3. The flexible printed wiring board according to claim 1, wherein polyimide is used as a main base material of the polymer film on which the optical waveguide is formed. 4. The substrate for electric wiring / optical wiring mixed flexible printed wiring board according to claim 2, wherein polyimide is used as a main base material of the polymer film on which the optical waveguide is formed. 5. The following general formula (Formula 1) is used as a main base material of the polymer film on which the optical waveguide is formed: A flexible printed wiring board having electrical wiring and optical wiring mixed therein according to claim 1, wherein a polyimide containing a repeating unit represented by the formula (where X is a tetravalent organic group) is used. 6. The following general formula (Chemical formula 1) as a main base material of the polymer film having the optical waveguide formed thereon: The substrate for electric wiring / optical wiring mixed flexible printed wiring board according to claim 2, wherein a polyimide containing a repeating unit represented by the formula (where X is a tetravalent organic group) is used.