JP4253933B2 - Optical / electrical wiring board and mounting board - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical / electrical wiring board in which optical wiring and electrical wiring are mixed, and a mounting board on which optical components and electrical parts are mounted on the board.
[0002]
[Prior art]
In order to make a computer that can perform arithmetic processing faster, the clock frequency of the CPU tends to increase more and more, and about 1 GHz now appears. As a result, there are parts where high-frequency signals flow in the copper electrical wiring on the printed circuit board in the computer, so that malfunctions may occur due to the generation of noise, and electromagnetic waves may be generated and the surrounding electronic equipment. It will also affect.
[0003]
In order to solve such a problem, a part of the copper electrical wiring on the printed circuit board is replaced with an optical fiber or optical waveguide optical wiring, and an optical signal is used instead of the electrical signal. This is because the generation of noise and electromagnetic waves can be suppressed in the case of optical signals.
[0004]
From the viewpoint of high-density mounting or downsizing, it is desirable to produce an optical / electrical wiring board in which electrical wiring and optical wiring are stacked on the same substrate. In particular, it is important to laminate optical substrates and electrical substrates in multiple layers and freely transmit electrical signals and optical signals between the substrates.
[0005]
In an electric board, through holes are formed between stacked electric wirings in the vertical direction, and conduction is achieved by covering an inner wall surface with metal. In an optical wiring board, an optical signal can be transmitted by crossing or bending the waveguide within a range in which transmission loss can be suppressed within the same board. However, it is difficult to increase the density of the optical wiring by this means.
[0006]
Another problem is that since it is difficult to bend the optical waveguide in the thickness direction of the optical substrate, it becomes difficult to transmit an optical signal between the stacked optical substrates. In general, a mirror that rotates the direction of light by 90 degrees is formed on an optical waveguide, an optical signal is taken out in a direction perpendicular to the substrate surface, and the extracted optical signal is received by a mirror on another optical substrate. No. 5-313027.
[0007]
In this method, it is necessary to form a plurality of mirrors in individual optical substrates and accurately align the optical axes. Also, it may be necessary to form through holes through a plurality of optical substrates. This lowers the reliability of the performance of the multi-layered high-density optical / electrical substrate and leads to an increase in cost.
[0008]
[Problems to be solved by the invention]
The present invention has been made in view of the drawbacks of the related art, and provides a structure of an optical / electrical wiring board that can be mounted with high density or miniaturized and that easily and reliably transmits an optical signal to a plurality of optical boards. That is.
[0009]
[Means for Solving the Problems]
In order to achieve the above object in the present invention, first, the invention of claim 1 is an optical / electrical device in which an optical substrate in which an optical waveguide for optical signal transmission is embedded is laminated on an electrical wiring substrate in which electrical wiring is embedded. In the wiring board, an optical member for changing an optical path is provided on a side surface of the optical substrate, the optical substrate is stacked in plural via a dummy substrate, and a plurality of columnar conductive guides are stacked in the optical substrate and the dummy substrate. One end of the columnar conductive guide is electrically connected to the electrical wiring on the electrical wiring board, and the other end of the columnar conductive guide becomes a recess for mounting an optical component. The optical / electrical wiring board is characterized in that a lens is provided between the optical board and the optical member for changing an optical path.
[0012]
According to a second aspect of the present invention, there is provided a mounting substrate in which an optical component and / or an electric component is mounted on the optical / electrical substrate according to the first aspect.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
1. Optical / Electrical Wiring Board FIG. 1 is a plan view of a portion where an optical component is mounted in a general optical / electrical wiring board, and FIG. 2 is a cross-sectional view taken along an optical waveguide 2 which is an optical wiring. . FIG. 2 shows a case where two layers of the optical wiring substrates 9 and 9 ′ are stacked via the dummy substrate 15.
[0014]
The optical / electrical wiring board has a structure in which a plurality (two in the drawing) of optical substrates 9 and 9 ′ are stacked on a substrate 8 having electrical wirings 10, 11, 12, and 13. The optical substrate may be laminated in three or more layers, and the substrate 8 may be a single-layer insulating substrate or a multilayer wiring substrate in which electrical wiring and insulating layers are alternately laminated. The constituent material may be an insulating substrate in which a glass cloth is impregnated with a resin, a polyimide film, a ceramic substrate, or the like.
[0015]
In the optical substrates 9 and 9 ′, core layers 2 and 2 ′ are embedded in cladding layers 1 and 1 ′ having a lower refractive index than the core material as optical waveguides (also referred to as optical wirings) for transmitting optical signals. . Since the patterning of the core layer is formed by a photolithography technique, the position can be determined by an alignment mark (not shown) formed on the support substrate.
[0016]
On the optical substrate 9 ′, a mirror 3 is formed which reflects a laser beam as an optical signal and changes the transmission direction to 90 °. This mirror inserts an optical signal emitted from a laser light emitting element mounted on an optical / electrical wiring board in a vertical direction toward the substrate into an optical wiring arranged in parallel with the substrate surface, or conversely It plays the role of changing the optical signal transmission direction vertically toward the light receiving element installed on the optical / electrical wiring board for the transmitted optical signal. Form.
[0017]
Since the mirror can be formed by drilling using an etching method based on a metal mask formed on the optical substrate by photolithography technology or by drilling by laser, the position of the mirror is the alignment formed on the substrate 8. It can be determined by a mark (not shown).
[0018]
The columnar conductive guides 5 and 7 serve as guides when laminating the optical substrate 9 and the dummy substrate 15 to be described later, and one end thereof is electrically connected to the electrical wirings 11 and 13 on the substrate 8. The end is a recess for mounting an optical component (a laser light emitting device lead). The optical substrate 9 and the substrate 8 are bonded with an adhesive 14.
[0019]
In the optical / electrical wiring board according to the present invention, an optical member for changing an optical path is provided on the side surface of the optical board in order to transmit an optical signal to another optical board. Hereinafter, the installation method will be described with reference to FIGS. 3 and 4 (note that description of mirrors and the like is omitted).
[0020]
As shown in FIG. 3, the side surface of the optical substrate on which the cladding layer 1 and the core layer 2 are formed (the side surface of the cladding layer is 1a and the side surface of the core layer is 2a) is optically polished. An optical member for changing the optical path is used to once extract the laser beam 21 as an optical signal from the side surface of the optical substrate and transmit the optical signal to another optical substrate. Specific examples of the optical member for changing an optical path include a prism 17 and an optical fiber. The prism or the like can be bonded to the side surface of the optical substrate with an optical adhesive. If the side surface of the optical substrate is thin and there is no room for bonding the prism 17 or the like, a dummy substrate 15 of the same material as the cladding layer can be inserted between the optical substrates with a suitable thickness. it can. Further, as shown in the right side of FIG. 3, a plurality of optical signals can be simultaneously processed by one prism.
[0021]
In the present invention, the optical wiring layer may be in the same optical substrate, or may be an optical wiring layer of a separate optical substrate. FIG. 4 shows a case where transmission is performed within the same substrate. In FIG. 4, a minute lens 19 is inserted to facilitate alignment of the optical axis of the laser light 21 that is an optical signal input and output to and from the optical fiber 18 and the core layers 2 and 2 ′. . Further, an optical signal can be transmitted to an arbitrary optical wiring layer by combining a plurality of prisms or changing the shape of the side surface of the optical fiber.
[0022]
2. Method for Manufacturing Optical / Electrical Wiring Board A method for manufacturing an optical / electrical wiring board according to the present invention will be described in detail with reference to the drawings.
(1) Manufacturing method of optical substrate A film-shaped optical substrate is formed by the following procedure (see FIG. 5). Resin 31 (which plays the role of a cladding layer in a support medium for an optical substrate that guides light and is a precursor of a fluorinated polyimide resin, a fluorinated polyamic acid, a fluorinated epoxy resin, etc.) on a silicon wafer 30 (Selection) is applied to a thickness of about 20 to 50 microns (step (a)). In the case of a polyamic acid solution, heating is performed at 350 degrees for 1 to 2 hours in order to imidize. If it is an epoxy resin, it is cured by UV curing or 100 to 200 degrees.
[0023]
Next, a resin 32 serving as an optical waveguide, for example, a resin having a refractive index suitable for the wavelength to be guided, such as a fluorine-based polyamic acid solution or a polymethylmethacrylate resin solution, is selected, and uniformly coated with 8 microns by an appropriate method (process) (b)). If there is photosensitivity, it is patterned by a conventional photolithography method to form the optical waveguide 33, and then a curing reaction according to the material is performed. If there is no photosensitivity, a metal mask having a predetermined pattern is formed after curing, and a waveguide pattern is formed by RIE dry etching (step (c)). Further, the same material as that of the previously formed clad layer is similarly applied to a thickness of about 20 to 50 microns to complete the optical substrate 34 (step (d)).
[0024]
Two optical substrates prepared in the same procedure were laminated using an adhesive (step (e)) to obtain multilayer optical substrates 34 and 34 '. The portion where the optical signal is input / output was cut linearly along the dotted line 36, and then the side surface 37 was optically polished to expose the core layer 38 (step (f)).
[0025]
Next, a through hole 35 was formed at a desired position of the multilayer optical substrate (step (g)). A hole is formed by irradiating an excimer laser through a mask having a predetermined pattern. Next, when the film is peeled off from the silicon wafer, a film-like multilayer optical substrate 39 including through holes can be formed (step (h)).
[0026]
(2) Manufacturing method of electric wiring board Next, a manufacturing method of the electric wiring board will be described (see FIG. 6). A copper thin film of about 20 microns is formed on a suitable insulating substrate 40 such as a glass epoxy substrate by plating, sputtering or vapor deposition. A desired metal wiring 41 is formed by a regular photolithography method. In order to form a columnar conductive guide, a metal thin film 42 is formed by sputtering (step (i)), and a resist 43 is applied and developed thereon to form an opening 44 (step (j)).
[0027]
Next, copper plating is performed using the metal thin film 42 as a cathode, and the inside of the opening is buried with copper as much as possible (step (k)). When the resist is removed (step (l)) and the metal thin film is removed by etching, the columnar conductive guide 45 can be formed on the metal wiring (step (m)). As for the shape of the via, it is desirable to use a mask having a shape corresponding to the terminal of an optical component such as a cylindrical shape or a quadrangular prism shape. The height is controlled by the resist film thickness or plating time. In general, the diameter is preferably 30 to 100 microns and the height is preferably about 20 to 100 microns.
[0028]
(3) Manufacturing Method of Optical / Electric Wiring Board The optical board and the electric wiring board are laminated using the conductive guide 45 (see FIG. 7). That is, the film is laminated so that a pillar made of a conductive metal or the like penetrates through the through-hole of the film to the middle of the film (step (n)). It is desirable that the adhesive 14 is applied to the side of the optical substrate that contacts the electric substrate to completely bond and fix the optical substrate and the electric substrate.
[0029]
One or both of the film thickness of the optical substrate and the height of the metal guide are adjusted so that the recess from the film surface is a depth necessary to accommodate the terminal of the optical component, preferably 20 to 100 microns.
[0030]
Further, a metal thin film 46 is formed on the surface of the laminated substrate by sputtering (step (o)), and a photoresist 47 is applied. An exposure / development process is performed to form a photoresist opening 48 for forming a mirror (step (p)).
[0031]
An opening 49 is formed in the metal thin film 46 by etching, and a metal mask for forming a mirror is formed. Further, the substrate is inclined at 45 °, the mirror 50 is formed by RIE dry etching (step (q)), and the metal mask is dissolved and removed to complete the mirror only on the uppermost portion of the optical / electrical wiring substrate ( Step (r)).
[0032]
3. Next, a method for manufacturing a mounting substrate will be described (see FIG. 8). Solder balls were mounted in the recesses 15 of the optical / electrical wiring board, and the terminals 24 of the optical component 22 (laser light emitting element, photodiode) were lightly inserted. The shape of the recess was a circle with a radius of 80 microns and the depth was 50 microns. The number of conducting terminals 24 of the optical component was four and the shape was a circle with a radius of 75 microns. Terminals for electrical components (CPU, memory) were placed on thin soldered metal pads.
[0033]
After cooling for 10 seconds in a reflow oven at a temperature of 250 degrees, the terminals of the optical components are fixed at an equilibrium position determined by the shape of the recess and the surface tension of the molten solder, and the optical axis of the laser is the center position of the mirror ± 3 microns. It was confirmed that it was within the range. Since the top of the columnar conductive guide is directly connected to the optical component by solder as a pad, the connection reliability is also improved.
[0034]
Finally, a prism 17 for optically connecting the necessary portions of the optical wiring layers on the side surfaces 9 and 9 'of the optical substrate is mounted using an optical adhesive so that the optical axis is aligned, and as shown in FIG. The mounting board was completed.
[0035]
Hereinafter, the operation of the mounting substrate will be described. The laser beam 21 irradiated from the laser irradiation unit 23 of the optical component 22 passes through the cladding layer 1 ′ of the optical substrate 9 ′, is reflected by the mirror 3 formed on the core layer 2 ′, and passes through the core layer 2 ′. To transmit. Then, the light is transmitted from the side surface of the optical substrate 9 ′ into the prism 17, reflected by the two sides of the prism, and transmitted from the side surface of the optical substrate 9 to the core layer. Thereafter, the light is reflected by a mirror (not shown) and reaches a light receiving portion of a photodiode (not shown).
[0036]
The mounting substrate according to the present invention was good because no noise was generated even when a signal of about 1 GHz was transmitted.
[0037]
【The invention's effect】
The present invention has the following effects.
First, since a plurality of optical wiring layers are provided on a substrate having electrical wiring, there is an effect that high-density mounting or miniaturization is possible.
[0038]
Second, an optical signal can be transmitted to a plurality of waveguides on different optical substrates by the same optical member.
[0039]
Third, it is possible to transmit an optical signal to different optical waveguides in the same optical substrate by the same optical member.
[0040]
Fourthly, even a thin optical substrate can be thickened with a dummy substrate interposed therebetween, so that a large optical member can be used to facilitate alignment of the optical axis.
[0041]
Fifth, the need for forming a through hole is reduced, and an optical member is externally attached. Therefore, reliability is improved and cost can be reduced.
[0042]
[Brief description of the drawings]
FIG. 1 is a plan view of a portion where an optical component is mounted on an optical / electrical wiring board.
FIG. 2 is a cross-sectional view of an optical / electrical wiring board.
FIG. 3 is an explanatory diagram showing an example of transmitting an optical signal to different optical wirings using the optical member for changing an optical path (prism) according to the present invention.
FIG. 4 is an explanatory diagram showing an example in which an optical signal is transmitted to an optical wiring existing in the same plane by using the optical member for changing an optical path (prism) according to the present invention.
FIG. 5 is an explanatory view showing an example of a method for manufacturing an optical substrate.
FIG. 6 is an explanatory view showing an example of a method for manufacturing an electrical wiring board.
FIG. 7 is an explanatory diagram showing an example in which an optical substrate and an electrical wiring substrate are stacked using a conductive guide.
FIG. 8 is an explanatory diagram of a mounting board according to the present invention.
[Explanation of symbols]
1, 1 'Clad layer 1a Clad layer side surface 2 Optical waveguide (core layer)
2a Optical waveguide (core layer) side surface 3 Mirror 4a Pad 5 Columnar conductive guide 5a Pad 6a Pad 7 Columnar conductive guide 7a Pad 8 Substrate 9, 9 'Optical substrate 10 Electrical wiring 11 Electrical wiring 12 Electrical wiring 13 Electrical wiring 14 Adhesion Agent 15 Dummy substrate 16 Recess 17 Prism 18 Optical fiber 19 Lens 21 Laser light 22 Optical component 23 Laser emission surface 24 Lead 25 Solder 30 Silicon substrate 31 Clad layer 32 Core layer 33 Waveguide 34, 34 'Optical wiring layer 35 Through hole 36 Polishing Part 37 Optically polished optical wiring layer side surface 38 Optically polished core side surface 39 Optical substrate 40 Insulating substrate 41 Electrical wiring 42 Metal thin film 43 Photoresist 44 Photoresist opening 45 Columnar metal guide 46 Metal thin film 47 Photoresist 48 Photoresist Opening 49 Metal thin film opening 50 Mira

Claims (2)

In an optical / electrical wiring board in which an optical board with an optical waveguide for optical signal transmission embedded in an electrical wiring board with an embedded electrical wiring,
An optical member for changing the optical path is provided on the side surface of the optical substrate ,
A plurality of the optical substrates are stacked via a dummy substrate,
A columnar conductive guide serves as a guide when the optical substrate and the dummy substrate are stacked, and one end of the columnar conductive guide is electrically connected to the electrical wiring on the electrical wiring substrate. The other end of the guide is a recess for mounting optical components,
A lens is provided between the optical substrate and the optical member for changing an optical path;
Optical and electrical wiring board characterized by A mounting substrate comprising an optical component and / or an electrical component mounted on the optical / electrical substrate according to claim 1 .

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