JP3075491B2 - Multilayer circuit board and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer circuit board and a method for manufacturing the same, and more particularly, to a multilayer circuit board having an optical semiconductor layer in a multilayer structure and a simple method for manufacturing the same.

[0002]

2. Description of the Related Art A basic method of manufacturing a circuit board on which two or more electric circuits are formed is to form a circuit network of metal or the like on both sides of an electrically insulating substrate by etching or printing, and form a hole in the insulating substrate. After processing, the hole is filled with electroless plating of metal or conductive paste to form through holes that electrically connect the circuits that are independent on both sides to form a double-sided circuit board. It has become. In the case of further forming three layers, an insulating layer and a third circuit are formed again on one circuit surface, and through-hole processing is performed to form a three-layer substrate. By repeating this operation, an arbitrary multilayer substrate can be obtained.

In the above-mentioned manufacturing method, through-hole processing is generally performed by mechanically squeezing (drilling, punching or the like) when the insulating layer is thick (for example, a glass epoxy substrate), and when the insulating layer is thin, insulating by chemical etching or the like. Layers are opened or optically exposed and developed using an insulative photosensitive resin to form holes, and electroless plating of metal or the like is used to provide conductivity and make through holes. Normal.

[0004]

As electronic components have become finer, there has been a demand for a finer and thinner circuit network for a circuit board on which the electronic components are mounted. It is in the method of forming holes. The above-mentioned general through-hole forming method has a limit for the purpose of miniaturizing a circuit network.

For example, in mechanical drilling of an insulating substrate, considering the strength and the like of a drill and other processing jigs, there is naturally a limit to miniaturization, the accuracy of the drilling position, the state of the hole side wall, and the like. I am dissatisfied. The same applies to non-mechanical processing such as laser processing.

[0006] An etching method or the like which can be used for a thin substrate has an advantage that it can be made finer than a mechanical processing. However, in any of the processing methods, an ordinary metal-free method is used as a means for conducting an opening. Electrolytic plating is commonly used.
However, there is a problem in manufacturing control, such as a series of processes for conducting treatment being complicated and an electroless plating solution being unstable.

At present, it is difficult for these manufacturing methods to meet demands for high-precision, thin, and precise multilayer circuit boards and a reduction in manufacturing costs.

An object of the present invention is to solve the above-mentioned problems and to provide a high-precision, thin and precise multilayer circuit board and a method for manufacturing the same.

[0009]

Means for achieving the above object are as follows.

In some types of optical semiconductors, the exposed portion lowers the electrical resistance and maintains the state for a long time after exposure (exposure effect or optical memory property), while the unexposed portion has a high electrical resistance and serves as a resistor. It is known to perform well.
However, the exposure effect of the low-resistance
There are features such as the reversibility for thermally restoring the original high resistance state and the conductivity of the low resistance part are much worse than those of metals and other general conductive members.

However, it has been discovered that a low electric resistance portion can be permanently formed in a specific optical semiconductor layer exposed portion by a method described later, and by using this method, it is possible to form a through hole easily and adaptable to a fine circuit. Was found.

Among the optical semiconductors, N-type optical semiconductors such as zinc oxide, titanium oxide, and cadmium sulfide have an exposure effect (optical memory effect) in which the phenomenon of lowering the electrical resistance is maintained after exposure.
In particular, it is known that zinc oxide and titanium oxide have long and stable stability. Furthermore, in these metal oxide optical semiconductors, the exposed surface has a reducing property (the non-exposed part is oxidizing), and the metal is reduced and precipitated from a metal salt solution having a low reduction potential, or an easily reducing organic solution (for example, dye (A leuco solution). Furthermore, when electrolysis is performed in a solution containing an easily reducible substance using these optical semiconductors as cathodes, even a substance having a higher reduction potential is easily reduced and deposited on the exposed portion of the optical semiconductor electrode.
Generally, this phenomenon is regarded as a surface phenomenon of the exposed portion of the optical semiconductor, and is known as one image forming method called an electrolytic phenomenon method in electrophotography.

Further, there has been proposed a method of forming a blackened image by causing a self-reduction of a metal oxide photosemiconductor when no easily reducible substance is present and depositing a metal on the surface.

The present inventors have found that when sufficient development is performed under special development conditions, development of some optical semiconductors proceeds further, and the self-reduction of the metal oxide proceeds to the depth of the optical semiconductor, and It was found that it reached the opposite side of the layer. That is,
It was confirmed that a metal oxide layer as a high-resistance layer and a metal layer as a permanent low-resistance layer could be formed by exposing and developing the optical semiconductor layer. The formed metal layer, unlike the decrease in electric resistance due to the exposure of the oxide layer, is a laminate of the metal itself, so that the electric resistance is remarkably low and exhibits the properties of an electric conductor.

Therefore, a metal oxide optical semiconductor layer is formed on the surface of a conductive substrate or a conductive circuit, and is exposed and developed to form a metal conductive portion locally. A double-sided circuit board having an oxide insulating layer interposed therebetween can be produced. Further, by repeating the operation, a multilayer circuit board can be formed.

The method of forming a through hole according to the present invention is capable of forming a multilayer circuit board by a simple operation of only exposure and development, and high resolution at an optical level because no mechanical or other perforation processing is required only by exposure and development. Therefore, it can be used as a through hole of a multilayer substrate having an extremely fine circuit, and the initial purpose can be easily achieved.

Next, the method of the present invention will be described in detail with reference to the drawings.

As shown in FIG. 1A, the metal layer formed on the electrically insulating support 1 is circuit-etched by ordinary lithography or printed with a conductive ink to form a first-layer circuit 2. . The insulating support 1 is a plastic film, insulating paper, a composite substrate of glass epoxy or the like, or other general circuit substrates.

Next, an optical memory metal oxide optical semiconductor layer 3 is formed on the surface of the first layer circuit 2. The metal oxide that can be used is, for example, zinc oxide fine powder for electrophotography, which is dispersed in an insulating polymer binder using a suitable solvent, applied as a paste, and dried. As the polymer binder, alkyd resin, styrene-butadiene copolymer resin, acrylic resin, epoxy resin, polyimide resin and others,
Generally, a styrene-butadiene copolymer resin or an acrylic resin is easy to use. There are various coating methods such as Myrbar coating, roller coating, and screen coating, which can be appropriately selected and used depending on the purpose. The film thickness is between 5 and 30 microns, preferably between 10 and 20 microns. Optical sensitization is also possible, and general dye sensitizers (Rose Bengal,
Bromophenol blue, patent blue, etc.) can be used in a conventional manner similar to electrophotography, and the wavelength of light can be controlled.

The formation of the optical semiconductor layer is stored in a dark place, and a through-hole photographic pattern 4 (film or glass dry plate) which has been prepared in advance is aligned and exposed in close contact with the optical semiconductor layer. Is formed.

After exposure, the substrate is placed in a solution obtained by adding a slight amount of a surfactant to an aqueous solution of alkali sodium carbonate to form a cathode,
An insoluble metal, for example, a platinum plate is arranged as a counter electrode, and 5
When electrolysis is performed at １５15 V for several seconds to tens of seconds, zinc oxide is reduced and black zinc metal appears. The fact that zinc metal is black is due to the fine particles and the effect of the organic binder. As shown in FIG. 1B, the deposited metal penetrates the optical semiconductor coating layer, and the zinc fine particles are laminated to form a through hole 5. Since the through hole is a stack of fine metal particles,
The portion is an electrically conductive portion, and the non-exposed portion is a high resistance portion as it is.

Next, a metal film, for example, a Cu film is formed on the entire surface to a required thickness by a vacuum deposition method or an electroless plating method, and an arbitrary circuit 6 is etched by a photo etching method. Alternatively, the conductive ink may be circuit printed.
At this stage, the circuits 2 and 6 are electrically connected through the through hole 5, and a two-layer circuit board (FIG. 1C) is obtained.

The circuit formation of the third layer is the same as that of the second layer.
By coating the same optical semiconductor layer on the circuit surface of the layer, exposing using a photographic pattern having a required through-hole pattern, and performing electrolytic development in the same manner, the second through-hole 8 shown in FIG. Obtained by forming a circuit 9 on the surface.

Although a three-layer circuit is completed at this stage in form, the zinc oxide layer outside the circuit is exposed and the electric resistance is reduced by external light, so that the circuit board is unstable as it is. It is. Therefore, it is desirable to form the light-shielding film 10 by dispersing the black pigment in the electrically insulating photosensitive resin, applying and drying by a bar coat or the like, exposing an area other than the third circuit portion, and developing and drying. Similarly, the light-shielding film 10 may be formed by screen printing or another printing method using an electrically insulating black ink.

FIG. 2 shows a method of forming a light shielding film in advance and then forming a second layer circuit.

In FIG. 2A, as described above, the insulating substrate 1
An optical semiconductor layer 3 is formed on the surface of the first layer circuit 2 formed above, and then an electrically insulating light-shielding film 11 made of a light-shielding photosensitive resin film from which a through-hole portion has been removed is optically formed in advance, Exposure is performed using this to obtain a corresponding through-hole latent image. If the development is performed in the same manner as described above, a through hole 5 formed of a stack of fine metal zinc particles is formed in the latent image portion. Furthermore, if the circuit 6 is formed by forming a metal film and etching or printing the circuit, a two-layer circuit board having a structure in which the optical semiconductor is completely shielded from light is completed.

A multilayer circuit board having three or more layers can be easily obtained by repeating this process.

In the method in which the light-shielding film is pre-attached in FIG. 2, the electrical insulation of the light-shielding film can be effectively used. A highly reliable multilayer circuit board can be obtained.

In this case, there is an advantage that a fine circuit board having a narrower space between circuit lines can be stably obtained.

Further, when higher conductivity is required than through holes made of fine metal zinc particles, Cu, Ag, A
Since a heavy metal having good conductivity such as u can be replaced with zinc by a normal displacement plating method, a lower-resistance through hole can be obtained by replacing all or part of the metal zinc with these heavy metals.

By using the technology of the present invention, it is possible to create a fine precision circuit and to make it thinner, which cannot be achieved by the conventional multilayer circuit board manufacturing technology. It can be used effectively for multi-layer boards.

[0032]

According to the present invention, a metal oxide optical semiconductor layer is formed on a conductive substrate surface or a conductive circuit surface, and exposed and developed to locally form a metal conductive portion, and a metal layer or a metal circuit is provided on the surface. The metal conducting portion can function as a through hole, and a double-sided circuit board with a metal oxide insulating layer interposed can be formed. Further, by repeating the operation, a multilayer circuit board can be formed. Is only exposure and development, a multilayer circuit board can be formed by a simple operation, and high resolution can be provided at the optical level because no mechanical or other perforation processing is required only by exposure and development. It can be used as a through hole of a multilayer substrate having a fine circuit.

Further, according to the present invention, thin high-density fine wiring can be realized, so that a small and precise camera or other electro-optical devices, a small radio, a television, a handy personal computer,
It can be effectively applied to fine circuit boards in sensor devices, various precision electronic devices, and the like.

In addition, there are many uses, such as being suitable for use in the production of an electrodeposited substrate in the method of electrodepositing a multicolor filter for a liquid crystal display.

[0035]

EXAMPLES Example 1 As a manufacturing test of a fine multilayer circuit board, the possibility of wiring line width and the effect of through hole conduction in a three-layer circuit were examined. The configuration pattern of the test board is as follows.

First pattern wiring line width: 70 μm, line spacing: 70 μm, through hole diameter: 50 μm Second pattern wiring line width: 50 μm, line spacing: 50 μm, through hole diameter: 40 μm Third pattern wiring line width: 30 μm Line spacing: 30 μm, through-hole diameter: 20 μm Number of lines of each wiring: 15 each, Line length of each wiring: about 10
0 mm Three types of wiring blocks are arranged (including alignment marks) in a plane of about 100 mm square.

Using a flexible substrate having a 10 μm copper foil adhered to a polyester film surface having a thickness of 0.1 mm,
A negative photosensitive resin (OMR: trade name of Tokyo Ohka Kogyo Co., Ltd.) is applied to the entire surface of the copper foil to a thickness of 1 μm with a spinner and dried, and the above three types of wiring patterns (excluding through-hole patterns) Were exposed in close contact with each other and developed, dried and heat-treated in accordance with the designated prescription. Then, the layer was etched with an aqueous ferric chloride solution, washed with water and dried to form a first layer circuit.

Next, an optical semiconductor layer made of zinc oxide was uniformly applied to a thickness of 10 μm on the circuit surface of the first layer, dried and cured, and stored in a dark place. The composition of the optical semiconductor was as follows, and the paste was formed by an ultrasonic dispersion method.

(Composition of optical semiconductor coating solution) Fine powder of zinc oxide for electrophotography 80 g Epoxy resin (one-pack type) 20 g Sensitizer (rose bengal) Trace amount of solvent 100 ml A photographic pattern whose light-shielding portion is adhered to the portion was exposed to light for 10 seconds using a 100 W tungsten lamp. Next, electrolytic development was performed in the following electrolytic solution.

(Electrolyte solution) Sodium carbonate 150 g Sodium dodecyl sulfate 16 g Water 10,000 ml (Electrolysis conditions) Counter electrode Platinum plate Electrode distance 3 cm Electrolysis voltage 5 V Electrolysis temperature 20 ° C. Electrolysis time Approx. A zinc metal layer formed by reducing zinc was formed, and a through hole between the first and second layers was obtained.

Next, Cu is vapor-deposited on the entire surface to a thickness of about 1 μm, a photosensitive resin OMR is again applied and dried, a circuit pattern photographic master is exposed in close contact, developed, dried, etched, and the remaining photosensitive resin is designated. The film was removed with a solvent to form a second layer circuit.

Next, the zinc oxide paste is applied to a thickness of 10 μm and dried, and the through-hole pattern is aligned with the first-layer circuit (using alignment marks), and is closely adhered and developed similarly to the second and third layers. Was formed.

The third-layer circuit was formed in the same manner as in the preparation of the second-layer circuit, and a three-layer circuit board was formed.

When the conductivity between the first layer circuit and the third layer circuit was measured, the results obtained were sufficiently practical. However, there was no problem in a dark place, but under room light, current leakage was observed in a portion where the line interval of the circuit was small. This is thought to be due to the photoconductivity of the zinc oxide layer under indoor light, so a light-shielding film was applied to the exposed zinc oxide layer to shield the light, and a multilayer circuit board with no current leakage between circuits . For the formation of the light-shielding film, a black or red colored OMR is applied over the entire surface to a thickness of 2 μm, and then the photographic original having the circuit pattern reversed in black and white is accurately positioned so that the OMR does not adhere to the third layer circuit portion. And then exposed to light and developed and dried. The opposite side of the support, the polyester film, was painted black to prevent light from entering from the back.

As a result, a reliable multilayer circuit board could be manufactured.

Example 2 A three-layer circuit board was prepared in the same manner as in Example 1 except that a light-shielding polyester film (black or red) was used.

However, immediately after the zinc oxide layer was formed on the circuit, the light-shielding photosensitive resin (OMR) was
And dried, and the through-hole pattern was aligned, exposed in close contact, developed, dried and heat-treated to expose zinc oxide only in the through-hole.

Next, the zinc oxide layer was exposed to light using the formed photosensitive resin film as a mask, and was electrolytically developed to form a metal zinc laminated portion, thereby forming a through-hole portion.

Next, a Cu film having a thickness of 10 μm was formed on the surface of the photosensitive resin film while the photosensitive resin film was left, and circuit etching was performed by the above-described method, followed by washing with water and drying. That is, the circuit has a structure formed in the through-hole portion and the photosensitive resin film surface. The 10 μm Cu film was formed by using both ordinary electroless method and electrolytic method.

Example of prescription for electroless Cu plating (Sensitizer) Stannous chloride (SnCl ₂ .2H ₂ O) 10 to 40 g / 1 Hydrochloric acid (HCl, 35%) 10 to 40 m1 / 1 Water 1 (1) in total amount Liquid temperature 25 to 35 ° C (activator) Palladium chloride (PdCl) 0.1 to 0.3 g / 1 Hydrochloric acid (HCl, 35%) 1 to 3 m1 / 1 Water Total amount is 1 (1) Liquid temperature 30 to 40 ° C. (electroless Cu plating bath) copper sulfate _{(CuSO 4 · 5H 2 O)} 5g / 1 Rochelle salt _{(KNaC 4 H 4 O 6)} 25g / 1 formalin (HCHO) 10 g / 1 sodium hydroxide (NaOH) 7 g / 1 water total volume 1 (1) to liquid temperature 18 to 22 ° C. (electrolytic Cu plating bath) copper sulfate _{(CuSO 4 · 5H 2 O)} 240~250g / 1 sulfuric acid (H ₂ SO _4, specific gravity 1.83) 24～75G / 1 Liquid temperature 2 0 to 50 ° C. Current density 5 to 40 A / dm ² After forming a Cu film as described above, exposure, development and etching of a circuit pattern are performed using a photosensitive resin in the same manner as in the previous example to remove the residual resist and form the second layer. A circuit was formed.

After the zinc oxide layer was formed on the third layer in the same manner, a through-hole forming process using a light-shielding resist, a Cu film forming process, and an etching process were performed to complete a three-layer multilayer circuit board.

In this substrate, a light-shielding film is formed for each layer, and light from a space without a circuit is also shielded. Therefore, there is no influence of light on the zinc oxide layer, and an insulating light-shielding film is laminated. Therefore, the electrical insulation between the layers and between the circuits was high, and the reliability was higher than that of the product of Example 1.

[0053]

As described above, according to the present invention, since the through hole forming method is only exposure and development, a multilayer circuit board can be formed by a simple operation, and mechanical and other holes are formed only by exposure and development. Since no processing is required, high resolution at the optical level can be provided, so that it can be used as a through hole for a multilayer substrate having an extremely fine circuit, and it is possible to obtain a high-precision, thin and precise multilayer circuit substrate. Become.

Further, according to the present invention, thin high-density fine wiring can be realized, so that small and precise cameras and other electronic optical devices, small radios, televisions, handy personal computers,
It can be effectively applied to fine circuit boards in sensor devices, various precision electronic devices, and the like, and can also be suitably used in the production of electrodeposited substrates in a method of electrodepositing a multicolor filter for a liquid crystal display. .

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a method for producing a multilayer circuit board of the present invention.

FIG. 2 is a view showing another embodiment of the method for producing a multilayer circuit board of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Insulating support, 2 ... 1st layer circuit, 3 ... 7 Optical memory metal oxide optical semiconductor layer, 4 ... Photo pattern for through hole, 5, 8 ... Through hole, 6 ... 2nd layer circuit, 9 ... third-layer circuit, 10 ... light-shielding film.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H05K 3/46

Claims (12)

(57) [Claims] 1. A multi-layer circuit board in which a circuit is formed three-dimensionally by a through hole, a metal having a through hole formed of a metal conduction path formed by selective reduction on a circuit pattern formed on the surface of an insulating support. A multilayer circuit board, comprising a structure in which an oxide optical semiconductor layer and a circuit pattern are sequentially formed as one constituent unit, and at least one or more constituent units are sequentially laminated. 2. The multilayer circuit board according to claim 1, further comprising a light-shielding layer provided on an outer surface of the multilayer circuit board. 3. A multi-layer circuit board in which a circuit is formed three-dimensionally by through holes, a metal having a through hole formed of a metal conduction path formed by selective reduction on a circuit pattern formed on the surface of an insulating support. A structure in which an oxide optical semiconductor layer, an electrically insulating resin layer from which a through-hole portion has been removed, and a circuit pattern are sequentially formed as one constituent unit, and at least one or more constituent units are sequentially laminated. Multi-layer circuit board. 4. The multilayer circuit board according to claim 3, wherein the electrically insulating resin layer is colored so as to be light-shielding with respect to the photosensitive wavelength of the optical semiconductor. 5. The multilayer circuit board according to claim 1, wherein the metal oxide optical semiconductor layer is a zinc oxide layer using an electrically insulating resin as a binder. 6. A method of manufacturing a multi-layer circuit board in which a circuit is formed three-dimensionally by through holes, wherein a metal oxide optical semiconductor layer using an electrically insulating resin as a binder is formed on a surface of a support on which a circuit pattern is formed. Forming, exposing the metal oxide photo-semiconductor layer in the through-hole forming portion by photolithography, and using a circuit pattern forming support as a cathode in an alkaline solution, arranging a counter electrode and energizing the metal by applying a current. A step of selectively reducing a metal oxide in an exposed portion of the semiconductor layer to form a conductive portion, forming a through hole, a step of forming a metal layer on the entire surface, and forming a circuit pattern by etching the metal layer A multi-layer circuit board characterized in that an arbitrary multi-layer circuit board is manufactured by repeating the process step as one manufacturing process unit and repeating the manufacturing process unit. Plate manufacturing method. 7. The method of claim 6, further comprising:
A method for manufacturing a multilayer circuit board, comprising a step of providing a light shielding layer on an outer surface. 8. A method for manufacturing a multilayer circuit board in which a circuit is formed three-dimensionally by through holes, wherein a metal oxide optical semiconductor layer using an electrically insulating resin as a binder is formed on a surface of a support on which a circuit pattern is formed. Forming, applying and drying the insulating photosensitive resin, developing and removing the insulating photosensitive resin in the through-hole forming portion by photolithography, and exposing the metal oxide optical semiconductor layer in the through-hole forming portion to light. Step: In a alkaline solution, a circuit pattern forming support is used as a cathode, a counter electrode is arranged, and electricity is applied to selectively reduce the metal oxide in the exposed portion of the metal oxide photo-semiconductor layer to form a conductive portion and a through portion. The step of forming a hole, the step of forming a metal layer on the entire surface, and the step of forming a circuit pattern by etching the metal layer are defined as one manufacturing process unit. And a method of manufacturing a multilayer circuit board by manufacturing an arbitrary multilayer circuit board by repeating the manufacturing process unit. 9. The method according to claim 8, wherein an insulating coating is formed on portions other than the through-hole forming portions by using an insulating ink instead of the insulating photosensitive resin, and the through-hole forming portions are exposed. A method for manufacturing a multilayer circuit board, which is characterized in that: 10. A method for manufacturing a multilayer circuit board, wherein the insulating photosensitive resin according to claim 8 or 9 is colored so as to be light-shielding at the photosensitive wavelength of the optical semiconductor. 11. The method according to claim 6, wherein the metal oxide optical semiconductor layer is a zinc oxide layer using an electrically insulating resin as a binder. 12. The method according to claim 6, further comprising chemically replacing a part or all of the metal of the conductive part formed by the selective reduction with a heavy metal to form a heavy metal through hole. Manufacturing method of a multilayer circuit board.