CN1784110A - Electro-optic hybrid circuit board - Google Patents

Abstract

The present invention provides an electrical-optical hybrid circuit board having an optical waveguide stacked on a wiring circuit board, the electrical-optical hybrid circuit board comprising: an insulating layer; a conductor pattern formed on the insulating layer; A lower cover layer on an insulating layer having a conductor pattern to surround the conductor pattern; a core layer formed on the lower cover layer; and an upper cover layer formed to cover the core layer and the lower cover layer.

Description

Electro-optical hybrid circuit board

technical field

The present invention relates to an electro-optic hybrid circuit board, which includes a wiring circuit board part and an optical waveguide part.

Background technique

In recent information communication technologies, optical signals and electrical signals are converted into each other in conducting information communication. In this information communication, an electro-optical hybrid circuit board having a wiring circuit board for transmitting electric signals and an optical waveguide for transmitting light is used. For example, Patent Document 1 describes an electro-optical hybrid circuit board including a wiring circuit board and an optical waveguide stacked on each other via an adhesive layer.

Patent Document 1: JP 2001-166165A

In high-density information communication, it is necessary to reduce the size and thickness of communication equipment. Therefore, there is still a need for an electro-optical hybrid circuit board with a smaller thickness.

Contents of the invention

It is therefore an object of the present invention to provide an electro-optical hybrid circuit board which is thinner than that of the prior art.

Other objects and effects of the present invention will be apparent from the following description.

In order to achieve the stated object, the present invention provides an electro-optical hybrid circuit board having an optical waveguide stacked on a wiring circuit board, the electro-optic hybrid circuit board comprising:

Insulation;

a conductor pattern formed on the insulating layer;

a lower cover layer formed on the insulating layer having a conductor pattern to surround the conductor layer;

a core layer formed on the lower cladding layer; and

An upper cladding layer formed to cover the core layer and the lower cladding layer.

In the electro-optical hybrid circuit board of the present invention, the lower cover layer of the optical waveguide also serves as the insulating cover layer of the wiring circuit board. Therefore, compared with the electric-optical hybrid circuit board of the related art in which the optical waveguide and the wiring circuit board are stacked on each other through the adhesive layer, the total thickness of the hybrid circuit board of the present invention is reduced by the amount corresponding to the adhesive layer. and the total thickness of the insulation covering layer of the wiring board.

Description of drawings

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view of an essential part of an embodiment of an electro-optic hybrid circuit board of the present invention.

Fig. 2 (a) to 2 (d) are the sectional views of each step in the method for preparing the electric-optical hybrid circuit board shown in Fig. 1: Fig. 2 (a) is the step of forming wiring circuit board part; Fig. 2 (b ) is a step of forming a lower cover layer on the wiring circuit board part; FIG. 2(c) is a step of forming a core layer on the lower cover layer; and FIG. 2(d) is a step of forming an upper cover layer on the core layer layer steps.

The reference numerals used in the drawings are respectively indicated as follows.

1: insulating layer

2: Conductor pattern

3: Lower cover layer

4: core layer

5: Upper cover layer

6: Wiring circuit board part

7: Optical waveguide part

Detailed ways

The electro-optical hybrid circuit board of the present invention includes a wiring circuit board and an optical waveguide stacked thereon. As shown in FIG. 1, it includes a wiring circuit board portion 6 and an optical waveguide portion 7, and the lower cover layer 3 of the optical waveguide also serves as an insulating cover layer of the wiring circuit board.

The wiring circuit board section 6 and the optical waveguide section 7 will be explained in order below.

First, the wiring circuit board section 6 is explained with reference to FIG. 1 .

The material used to form the insulating layer 1 of the wiring circuit board portion 6 is not particularly limited as long as it has insulating properties. Examples thereof include, for example, synthetic resins such as polyimide resins, poly(amide-imide) resins, acrylic resins, polyethernitrile resins, polyethersulfone resins, poly(ethylene terephthalate) resins, Poly(ethylene naphthalate) resins, poly(vinyl chloride) resins, epoxy resins, and polyurethane resins. From the viewpoint of heat resistance, polyimide resin is preferably used.

The thickness of the insulating layer 1 is preferably 5 to 50 μm.

A conductor pattern 2 having a predetermined shape is formed on the insulating layer 1 . The material used to form the conductor pattern 2 is not particularly limited as long as it has conductivity. Examples thereof include, for example, metals such as copper, chromium, nickel, aluminum, stainless steel, copper-beryllium, phosphor bronze, iron-nickel, and alloys of these metals. Copper is preferably used.

The line width of the conductor pattern 2 is preferably 5 to 50 μm, and the line spacing is preferably 5 to 50 μm. The thickness of the conductive pattern 2 is preferably 3 to 50 μm.

Next, the optical waveguide section 7 is explained with reference to FIG. 1 .

The lower cover layer 3 is formed on the conductor pattern 2 of the wiring circuit board portion 6 . The material used to form the lower cover layer 3 is not particularly limited as long as it has transparency. Examples thereof include, for example, synthetic resins such as epoxy resins, poly(amic acid) resins, and polyimide resins.

The thickness of the lower cover layer 3 is preferably 5 to 100 μm.

A core layer 4 having a predetermined pattern is formed on the lower cover layer 3 . The material used to form the core layer 4 is not particularly limited as long as it has transparency. Examples thereof include, for example, epoxy resins, poly(amic acid) resins, polyimide resins, and the like. Generally, the core layer 4 is designed to have a higher refractive index than the lower cladding layer 3 and the upper cladding layer 5, which will be described below.

The line width of the pattern of the core layer 4 is preferably 5 to 100 μm, and the line pitch is preferably 5 to 500 μm. The thickness of the core layer 4 is preferably 5 to 100 μm.

An upper cladding layer 5 is formed on the core layer 4 . The material used to form the upper cover layer 5 is not particularly limited as long as it has transparency. Examples thereof include, for example, epoxy resins, poly(amic acid) resins, and polyimide resins. In general, the same materials are used as for the lower cover layer 3 .

The thickness of the upper cover layer 5 is preferably 5 to 100 μm.

The total thickness of the electro-optical hybrid circuit board of the present invention is preferably 15-250 μm.

Next, a method of manufacturing the electro-optical hybrid circuit board of the present invention will be explained with reference to FIG. 2 .

In preparing the electro-optical hybrid circuit board of the present invention, the wiring circuit board portion 6 is first formed. The optical waveguide portion 7 is then formed thereon so as to be superimposed on the portion 6, thereby producing a hybrid circuit board.

A method of forming the wiring circuit board portion 6 and the optical waveguide portion 7 will be explained in order below.

First, as shown in FIG. 2( a ), a conductor pattern 2 having a predetermined shape is formed on an insulating layer 1 . For forming the conductor pattern 2, for example, a known method such as a subtractive method, a semi-additive method or an additive method can be used.

In the subtractive technique, a conductor layer is formed on the entire surface of an insulating layer, and unnecessary portions of the conductor layer are removed by etching, thereby forming a conductor pattern having a predetermined shape. In the semi-phase additive method and the additive technique, a conductor pattern having a predetermined shape is formed by a method such as electroplating.

According to the method described above, the wiring circuit board portion 6 is formed.

Subsequently, as shown in FIG. 2( b ), the lower cover layer 3 is formed on the conductor pattern 2 . The lower cover layer 3 can be formed by applying and drying a solution prepared by dissolving a synthetic resin for forming the lower cover layer 3 in a solvent.

From the viewpoint of forming the lower cover layer 3 having a smooth surface, the resin concentration in the solution is preferably 50 to 90% by weight.

As shown in FIG. 2( c ), a core layer 4 having a predetermined pattern is then formed on the lower cladding layer 3 . The method of forming core layer 4 is not particularly limited. For example, the layer 4 can be formed using a photosensitive resin. Preferable examples of photosensitive resins include photosensitive epoxy resins, photosensitive poly(amic acid) resins, and photosensitive polyimide resins.

Subsequently, as shown in FIG. 2( d ), an upper cladding layer 5 is formed on the core layer 4 . The upper cladding layer 5 can be formed in the same manner as the lower cladding layer 3 is formed.

Thus, the electro-optical hybrid circuit board of the present invention can be obtained, which includes the wiring circuit board portion 6 and the optical waveguide portion 7 formed thereon.

Example

The present invention will be explained in more detail with reference to the following examples, but it should not be meant that the present invention is limited thereto.

Example 1

By the semi-additive method, a conductor pattern was formed on an insulating layer comprising a polyimide film having a thickness of 25 µm (see FIG. 2( a )) to thereby manufacture a wiring circuit board portion.

In the semi-phase additive method, a thin chromium layer with a thickness of 0.01 μm and a thin copper layer with a thickness of 0.15 μm are deposited successively by sputtering to form a thin metal film on the insulating layer. Thereafter, a plating resist is formed to have a pattern opposite to that of the conductor pattern to be formed. Copper plating was then performed to form metal wirings made of 20 μm-thick copper with a metal wiring line width of 25 μm and a metal wiring pitch of 25 μm as a conductor pattern. Thereafter, the plating resist is stripped, and the metal thin film not covered by the conductor pattern is removed by wet etching.

Subsequently, an optical waveguide portion was formed on the wiring circuit board portion obtained above in the following manner.

First, according to the formulation shown in Table 1, various ingredients were mixed together and dissolved using cyclohexanone as a solvent. Thus, varnishes A and B were prepared. For each varnish, the refractive index of the cured resin obtained by setting the varnish was measured at a wavelength of 633 nm, as also shown in Table 1.

Table 1 (parts by weight) varnish A B Fluorene Derivatives 1 83 67 Fluorene derivatives 2 - 33 Thinner 17 - photo-acid generator 1 1 Refractive index of cured resin (measurement wavelength 633nm) 1.585 1.615

Fluorene derivative 1: Bisphenoxyethanol fluorene diglycidyl ether (represented by the general formula (1), wherein R ₁ to R ₆ are each a hydrogen atom and n is 1)

Fluorene derivative 2: bisphenol fluorene diglycidyl ether (represented by the general formula (1), wherein R ₁ to R ₆ are each a hydrogen atom and n is 0)

Diluent: 3',4'-epoxycyclohexenyl carboxylic acid 3,4-epoxycyclohexenylmethyl ester (Celoxide 2021P, manufactured by Daicel Chemical Industries, Ltd.)

Photo-acid generator: 50% propylene carbonate solution of 4,4-bis[bis(β-hydroxyethoxy)phenylsulfinyl]diphenylsulfide bishexafluoroantimonate

The varnish A was applied to the conductor pattern side of the wiring circuit board portion by spin coating, and dried at 90° C. for 15 minutes to form a resin layer. Thereafter, the resin layer was entirely irradiated with ultraviolet rays at an irradiation dose of 2000 mJ/cm ² , and then heated at 100° C. for 30 minutes to form a lower cover layer having a smooth surface and a thickness of 30 μm (see FIG. 2( b ) ).

Subsequently, Varnish B was applied onto the lower cover layer by spin coating, and dried at 90° C. for 15 minutes to form a resin layer. The resin layer was irradiated with ultraviolet rays at an irradiation dose of 2000 mJ/ ^cm2 through a photomask (synthetic quartz-based chrome mask) having a linear light-waveguide pattern with a line width of 50 μm, and then by a contact exposure method.

Next, post-exposure heating was performed at 90° C. for 60 minutes. The resulting structure was immersed in an acetonitrile-based developer. The resin layer is thus developed to obtain a pattern there. Then, the resin layer was heated at 100° C. for 30 minutes. Thus, core layers having cross-sections at intervals of 250 µm, having a thickness of 50 µm and a width of 50 µm were formed (see FIG. 2(c)).

The varnish A was coated on the lower cover layer and the core layer by spin coating, and dried at 90° C. for 15 minutes to form a resin layer. Next, the resin layer was entirely irradiated with ultraviolet rays at an irradiation dose of 2000 mJ/cm ² , and then heated at 100° C. for 30 minutes to form an upper cladding layer with a thickness of 80 μm (see FIG. 2( d )). Thus, a multimode optical waveguide portion having a specific refractive index difference Δ of 1.8% was obtained.

Through the above process, an electro-optical hybrid circuit board as shown in FIG. 1 is produced.

The total thickness of the prepared electro-optic hybrid circuit board was 135 μm.

Although the present invention has been described in detail with reference to the specific embodiments thereof, it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

This application is based on Japanese Patent Application No. 2004-352545 filed on December 6, 2004, the contents of which are incorporated herein by reference.

Claims (2)

1. An electro-optic hybrid circuit board having an optical waveguide stacked on a wiring circuit board, the electro-optic hybrid circuit board comprising: Insulation; a conductor pattern formed on the insulating layer; a lower cover layer formed on the insulating layer having a conductor pattern to surround the conductor pattern; a core layer formed on the lower cladding layer; and An upper cladding layer formed to cover the core layer and the lower cladding layer. 2. The electro-optical hybrid circuit board according to claim 1, which has a total thickness of 15 to 250 [mu]m.

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