JPH06268339A - Flex-rigid multilayer printed wiring board and production thereof - Google Patents

Abstract

PURPOSE:To form a highly accurate fine pattern by providing a multilayer rigid part comprising a plurality of conductor layers and resin insulation layers and forming the resin insulation layer of a photosensitive insulating material. CONSTITUTION:A flexible substrate 1 formed with a conductor circuit is laminated with a coverlay film and a photosensitive resin insulating layer 2 is formed thereon. A via hole part and a flex part are then applied with a photoresist mask which is exposed by an ultrahigh pressure mercury lamp and heat treated thus curing the photosensitive resin insulation layer 2. The photosensitive resin insulation layer 2 is then subjected to surface activation and applied with a liquid photoresist 3 thus forming a plating film 6. Finally, an adhesive is applied and the entire process is repeated three times. Thereafter, the liquid photoresist 3 is removed thus forming a flex-rigid multilayer wiring board comprising four layers 4, 6, 8, 10. This method simplifies the production process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring board composed of a flex portion and a multilayer rigid portion, a so-called flex-rigid multilayer printed wiring board and a method for manufacturing the same.
In particular, we propose a flex-rigid multilayer printed wiring board in which a plurality of conductor circuits are formed on a flexible substrate by a build-up method, and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, as electronic equipment has become smaller and more sophisticated due to the progress of the electronic industry, there has been an increasing demand for a flexible printed wiring board which allows free three-dimensional wiring while mounting components.

A feature of this flexible printed wiring board is that it has not only a function as a component mounting board but also a harness function as an in-device wiring material. Therefore, according to such a flexible printed wiring board,
Connection components such as connectors can be omitted, wiring mistakes due to soldering, etc. can be reduced, the entire mounting board can be made compact, and wiring reliability can be greatly improved.

However, such a flexible printed wiring board has a problem that if the number of conductor layers is increased, the flexibility of the entire substrate is substantially lost even if the number of conductor layers is, for example, three. Therefore, the flexible printed wiring board having the characteristic of flexibility has a design defect that it cannot be multilayered.

On the other hand, conventionally, a partial multilayer flexible printed wiring board, so-called flex-rigid multilayer printed wiring board, has been proposed as a printed wiring board for high-density mounting in which the above-mentioned drawbacks of flexible printed wiring boards have been solved. According to this flex-rigid multilayer printed wiring board, high-density components can be mounted in the multi-layer part, and in the lead part that is freely pulled out from each layer, the so-called flex part, space is taken up as necessary for wiring inside the device. It has the characteristic that it can be turned around without any need.

FIG. 1 is a diagram of a typical flex-rigid multilayer printed wiring board, which has at least one or more flexible flex portions for mounting and fixing components. It has a basic structure including a rigid portion. FIG. 2 is a diagram showing a cross-sectional structure of this wiring board. The inner layer is composed of a double-sided flexible substrate protected by a coverlay film, and the rigid portion is formed by partially pressing and heating copper foil through a prepreg to bond them together, and the inner flex layer is called a cap. It has a sandwich structure sandwiched by hard materials (outermost layer) such as glass epoxy. And
Conduction between the layers is performed through the through holes. The flex section is of course composed of only flex layers, but basically each flex layer has a double-sided structure at the maximum, and the conductor layer does not have three or more layers. In addition, when wiring of three or more layers is required for the flex portion, a structure is adopted in which independent double-sided flexible substrates that are not bonded to each other are stacked (see FIG. 2).

Next, a typical manufacturing method of such a flex-rigid multilayer printed wiring board is shown in FIG. As is clear from this figure, a flex-rigid multilayer printed wiring board can be manufactured by, for example, stacking an outer layer copper-clad board, a prepreg, and an inner layer circuit board that has been pre-etched on a flexible board, heating and pressing with a press, and then punching. It is then manufactured by electroplating and then etching to form a conductor circuit.

As a method for forming a conductor circuit in a flex-rigid multilayer printed wiring board, heretofore, an etched foil method (subtrade method) for forming a conductor circuit by laminating a copper foil on a substrate and then photoetching it has been used. The active method) was common.

[0009]

However, in the flex-rigid multilayer wiring board as described above, the conductor layers and the resin insulating layers, which are different in material, are alternately laminated, and the laminated structure is different depending on the part. ,
The manufacturing process was complicated. Therefore, in the production of the above wiring board that handles a material that is thin and has strict dimensional accuracy, there is a problem in that the defect rate due to the pattern deviation is high and it is difficult to obtain the positional accuracy.

Further, the formation of the conductor circuit by the etched foil method has an advantage that the conductor circuit having excellent adhesion to the substrate can be formed, but the cost becomes high and the copper foil is thick so that the etching is performed. Therefore, there is a big drawback that it is difficult to obtain a high-precision fine pattern, and there is a problem that the manufacturing process is made more complicated and the efficiency is not good.

An object of the present invention is to advantageously solve the above-mentioned problems of the prior art. In particular, a flex-rigid multilayer printed wiring board having a high precision fine pattern and excellent reliability is provided. It is to establish the technology provided by a simple manufacturing process.

[0012]

In order to achieve the above object, the inventors of the present invention have conducted extensive studies mainly on a method of forming a conductor circuit on a flexible substrate, and as a result, have conducted a conductor circuit on the flexible substrate by an additive method. It has been found that high-precision and high-density circuit formation can be performed without complicated steps by forming a multi-layer structure by using a photosensitive insulating material as a resin insulating layer of a multi-layer rigid portion, I thought about it.

That is, according to the present invention, there is provided a flex-rigid multilayer printed wiring board comprising a multilayer rigid portion having a plurality of conductor layers and a resin insulating layer, and a flex portion connected to the multilayer rigid portion. The flexible rigid multilayer printed wiring board is characterized in that the resin insulating layer of the multilayer rigid portion is formed of a photosensitive insulating material. Then, the manufacturing method of the present invention provides a flex-rigid multilayer printed wiring board constituted by a multilayer rigid part having a plurality of conductor layers and a resin insulating layer, and a flex part continuous with the multilayer rigid part. In the manufacturing method, at least the following steps (a) to (d); namely, (a) a step of partially forming a photosensitive resin insulating layer on a flexible substrate having a conductor circuit on at least one surface thereof, (b) ) A step of roughening the surface portion of the photosensitive resin insulating layer by treating with an acid or an oxidant, (c) applying electroless plating on the roughened photosensitive resin insulating layer to form a conductor circuit. Forming process,
Is repeated once or more. Here, the photosensitive insulating material is pre-cured to be soluble in an acid or an oxidant in an uncured heat-resistant resin matrix that is hardly soluble in an acid or an oxidant when subjected to a curing treatment. The adhesive is preferably a dispersion of fine powder of heat resistant resin.

[0014]

Now, as a method for forming a conductor circuit on a hard multilayer substrate, conventionally, an adhesive containing diene-based synthetic rubber is applied to the surface of the substrate to form an adhesive layer, and the surface of this adhesive layer is roughened. After that, an additive method of forming a conductor by electroless plating is adopted. According to this method, since a conductor is formed by applying electroless plating after forming a resist, it is possible to provide wiring with higher density and higher pattern accuracy than the etched foil method (subtractive method) in which pattern formation is performed by etching. Is. However,
Since the adhesive that is commonly used in this method contains synthetic rubber, it has a low heat resistance, such as a significant decrease in adhesion strength at high temperatures, or swelling of the electroless plating film during soldering. There are problems such as insufficient electrical characteristics such as resistance, and the range of use is considerably limited.

On the other hand, the present inventors have solved the above-mentioned drawbacks of the adhesive for applying electroless plating, and have excellent heat resistance, electrical characteristics and adhesion to the electroless plated film. In addition, an adhesive which is relatively easy to carry out and a method for manufacturing a wiring board using this adhesive have been proposed (Japanese Patent Laid-Open No. Sho 61-61).
-276875 gazette). That is, the conventional technique proposed by the inventors is such that an uncured resin powder having a property that a pre-cured heat-resistant resin powder that is soluble in an oxidant is hardly soluble in the oxidant when subjected to a curing treatment. Of the heat-resistant resin liquid, and after applying the adhesive to a substrate, it is dried and cured to form an adhesive layer, and the above-mentioned fine particles dispersed on the surface portion of the adhesive layer. In this method, at least a part of the powder is dissolved and removed to roughen the surface of the adhesive layer, and then electroless plating is performed. According to the technique proposed by the present inventors, it is possible to obtain a wiring board which does not have the drawbacks of conventional adhesives, is easy to manufacture, has a large adhesion strength, and is highly reliable.

Under such background art, the inventors have
In particular, the present inventors have conducted intensive studies focusing on the application of the adhesive having the above-described characteristics to a flex-rigid multilayer printed wiring board. As a result, by specifying the adhesive as a photosensitive insulating material, and by forming the photosensitive insulating material only in the multilayer rigid portion on the flexible substrate to form a multilayer, it is possible to reliably achieve the above-mentioned object. I found it.

The feature of the present invention is, firstly, that the adhesive is made of a photosensitive insulating material. This makes it possible to use the photographic method without going through the lamination pressing process.
The flex portion or the multilayer rigid portion can be accurately formed at a predetermined position on the flexible substrate.

The second feature is that the conductor circuit is formed by the additive method, and the multilayer rigid portion on the flexible substrate is made into a multilayer structure by the build-up method. As a result, the connection reliability between the multilayer rigid portion and the flex portion is excellent, and the density can be increased. Moreover,
The manufacturing process can be remarkably simplified as compared with the conventional complicated process.

The third feature is that the heat-resistant resin fine powder is contained in the adhesive. As a result, the stress generated during the deformation of the flex part can be relaxed, even if micro cracks occur in the adhesive due to the deformation of the flex part, their growth can be suppressed and the function of the flex rigid plate can be fully utilized. Is possible.

As can be seen from the above description, according to the present invention, a flex-rigid multilayer printed wiring board which can be inserted arbitrarily according to the space of the equipment to be mounted and which can make the entire mounting board compact is easy. Can be manufactured. Furthermore, according to the present invention, it is possible to easily and inexpensively provide a flex-rigid multilayer printed wiring board having a highly precise fine pattern and excellent reliability.

Here, in the flex-rigid multilayer printed wiring board of the present invention, the uncured photosensitive resin matrix constituting the adhesive made of the photosensitive insulating material is heat resistance, electrical insulation, chemical stability and It is possible to use a photosensitive resin which has excellent adhesiveness and is hardly soluble in an acid or an oxidizing agent when cured.

As such a photosensitive resin, a photosensitive resin composition containing an acrylic polymer and a photopolymerizable monomer as main components, a photosensitive resin composition containing an epoxy resin having a photoreactive group as a main component, Any one or more of the photosensitive resin compositions containing a polyimide resin having a photoreactive group as a main component is preferably used. Among them, a photosensitive resin composition containing an epoxy resin having a photoreactive group as a main component is preferable.

If necessary, components such as an initiator, a sensitizer, a photopolymerizable monomer, and a curing agent for epoxy resin may be added to the photosensitive resin composition.

As the photosensitive resin matrix in the adhesive of the present invention, a heat-resistant photosensitive resin containing no solvent can be used as it is, but the one prepared by dissolving the photosensitive resin in a solvent does not have a viscosity control. Since it can be easily carried out, the fine powder can be uniformly dispersed, and since it is easy to apply, it can be advantageously used. The solvent used for dissolving the photosensitive resin is usually a solvent such as methyl ethyl ketone, methyl cellosolve, ethyl cellosolve, butyl cellosolve, butyl cellosolve acetate, butyl carbitol, butyl cellulose,
Examples thereof include tetralin, dimethylformamide, normal methylpyrrolidone and the like.

Further, in this photosensitive resin matrix,
For example, an additive such as a colorant (pigment), a leveling agent, a defoaming agent, an ultraviolet absorber, a flame retardant, or other filler may be appropriately mixed.

Next, the heat-resistant resin fine powder to be dispersed in such an uncured photosensitive resin matrix is excellent in heat resistance and electric insulation, and it is necessary to be stable to ordinary chemicals. It is preferably either a hardened heat-resistant resin fine powder or an inorganic fine powder coated with a heat-resistant resin. For example, as the pre-cured heat-resistant resin fine powder, epoxy resin, amino resin (melamine resin, urea resin, guanamine resin), polyester resin, bismaleimide triazine, phenol resin, etc. are used, and the inorganic fine powder to be coated is used. As such, silica and alumina are preferably used.

Such a heat-resistant resin fine powder is added in an amount of 5 to 5 parts by weight based on 100 parts by weight of the total solid content of the heat-resistant resin matrix.
It is desirable to mix a range of 80 parts by weight. The reason for this is that if the amount of the fine powder blended is less than 5 parts by weight, the anchor density is low and sufficient adhesion strength cannot be obtained. On the other hand, if the blending amount of the fine powder is more than 80 parts by weight, the adhesive layer is almost completely dissolved and removed, and a clear anchor cannot be formed.

The particle size of such heat-resistant resin fine powder is preferably 10 μm or less in average particle size, and particularly preferably 5 μm or less. The reason is that if the average particle size is larger than 10 μm, the density of the anchor formed by dissolution and removal tends to be low and the anchor tends to be non-uniform, so that the adhesion strength and its reliability decrease. Moreover, since the unevenness of the surface of the adhesive layer becomes severe, it is difficult to obtain a fine pattern of the conductor, and it is not preferable for mounting components and the like.

As such a pre-cured heat-resistant resin fine powder, those having an average particle diameter of 5 μm or less can be preferably used, but the heat-resistant resin fine powder having an average particle diameter of 2 μm or less is agglomerated. Aggregated particles having an average particle size of 2 to 10 μm, a particle mixture of a heat resistant resin powder having an average particle size of 2 to 10 μm and a heat resistant resin powder having an average particle size of 2 μm or less, or a heat resistance having an average particle size of 2 to 10 μm Average particle size 2 on the surface of resin powder
Pseudo particles obtained by adhering at least one of a heat resistant resin powder having a particle size of not more than μm and an inorganic fine powder can also be used.

In the present invention, an epoxy resin can be used as the thermosetting resin component of the heat-resistant resin matrix insoluble in an acid or an oxidizing agent, while an epoxy resin can be used as a heat-resistant resin powder soluble in an acid or an oxidizing agent. Resin can be used. This point will be described below by taking solubility in an oxidizing agent as an example. Epoxy resin can be prepared by controlling these prepolymers (polymers with a relatively low molecular weight of about 300-10000), the type of curing agent, and the crosslink density.
The physical properties can differ greatly. This difference in physical properties is not an exception even with respect to the solubility in an oxidizing agent, and can be adjusted to an arbitrary one by appropriately selecting the type of prepolymer, the type of curing agent, and the crosslinking density. For example, as the "oxidizing agent-soluble epoxy resin" that constitutes the heat-resistant resin powder, (A)
“Alicyclic epoxy is selected as the epoxy prepolymer, a chain aliphatic polyamine curing agent is used as the curing agent, and the molecular weight between cross-linking points (the molecular weight between cross-linking points. The larger the cross-linking density, the lower the cross-linking density). The value is about 700 and gently cross-linked "is used. On the other hand, the "hardly soluble (including insoluble) epoxy resin" that is a thermosetting resin component of the heat resistant resin matrix is
(B) "Bisphenol A as an epoxy prepolymer
Type epoxy resin was selected, and an aromatic diamine-based curing agent was used as the curing material, and the cross-linking point molecular weight was cross-linked to about 500. "or (C)" Phenol as an epoxy prepolymer having a lower solubility. " A novolac type epoxy resin is selected, an acid anhydride type curing agent is used as a curing agent, and the molecular weight between crosslinking points is crosslinked to about 400 ”. Further, the epoxy resin (B) can also be used as the "oxidizing agent-soluble epoxy resin". In this case, the epoxy resin (C) is adopted as the "oxidizing agent-insoluble epoxy resin". . As described above, the epoxy resin can be adjusted to have an arbitrary solubility by appropriately selecting the type of prepolymer, the type of curing agent, and the crosslinking density. Further, as understood from the above-mentioned examples, being soluble in an oxidant or sparingly soluble (or insoluble) in an oxidant means a relative dissolution rate in the oxidant. As the epoxy resin fine powder of (3), those having a difference in solubility may be arbitrarily selected. The means for imparting a solubility difference to the resin is not limited to the type of prepolymer, the type of curing agent, and the adjustment of the crosslink density,
Other means may be used. Table 1 shows the prepolymer, curing agent, crosslink density, and
The solubilities are listed.

[0031]

[Table 1]

In the present invention, the oxidation treatment is carried out for a certain period of time by utilizing the difference in the solubility of each epoxy resin as described above. By performing such a treatment, the soluble epoxy resin fine powder having the highest solubility in the oxidizing agent is vigorously dissolved, and a large recess is formed.
At the same time, the epoxy resin matrix, which is hardly soluble in the oxidizing agent, remains to form a roughened surface (anchor) as shown in FIG. 4 (4).

Next, a method of manufacturing the flex-rigid multilayer printed wiring board of the present invention will be described. In the manufacturing method of the present invention, first, a portion of a flexible substrate on which a conductor circuit is formed, which becomes a multilayer rigid portion, is in an uncured heat-resistant resin matrix that becomes hard to dissolve in an acid or an oxidizing agent when subjected to a curing treatment. A heat-resistant resin fine powder that is soluble in an acid or an oxidant and that has been previously cured is dispersed to form a photosensitive resin insulating layer.

As a method of forming the above-mentioned photosensitive resin insulating layer on the substrate on which the conductor circuit is formed, for example, an uncured photosensitive resin whose characteristics after curing are hardly soluble in acid or oxidant is used. A method of applying an adhesive in which fine powder of a heat-resistant resin soluble in an acid or an oxidizing agent is dispersed, or a resin film obtained by processing the adhesive into a film,
Alternatively, a method of applying a prepreg in which fibers such as glass cloth are impregnated with this adhesive can be applied.
As a method of forming this, for example, a roller coating method,
Various means such as a dip coating method, a spray coating method, a spinner coating method, a curtain coating method and a screen printing method can be applied.

The above-mentioned fine powder of heat-resistant resin soluble in acid or oxidizing agent is composed of a heat-resistant resin which has been hardened. The heat-resistant resin constituting this fine powder of heat-resistant resin is limited to the one that has been subjected to the curing treatment. If an uncured resin is used, the heat-resistant resin liquid that forms the matrix or the heat-resistant resin that forms this matrix is used. When the resin is added to a solution that is dissolved using a solvent, the heat-resistant resin that constitutes this heat-resistant resin fine powder also dissolves in the heat-resistant resin liquid or solution, and functions as a heat-resistant resin fine powder. This is because it will be impossible to make full use of it.

Such a heat-resistant resin fine powder is obtained by, for example, thermosetting the heat-resistant resin and then pulverizing it with a jet mill or freeze pulverizer, or spray-drying the heat-resistant resin solution before curing treatment. Particles obtained by curing treatment or addition of an aqueous solution curing agent to an uncured heat-resistant resin emulsion and stirring are classified by an air classifier or the like to produce.

Among the above heat-resistant resin fine powders, as a method for forming pseudo particles by adhering at least one of heat-resistant resin fine powders or inorganic fine powders to the surface of heat-resistant resin powders, for example, heat-resistant resin It is advantageous to apply a method in which the surface of the heat-resistant resin powder is sprinkled with the heat-resistant resin fine powder or the inorganic fine powder and then heated and fused or adhered via a binder.

Among the above-mentioned heat-resistant resin fine powders, the heat-resistant resin fine powders may be aggregated into agglomerated particles by, for example, simply heating the heat-resistant resin fine powders with a hot air dryer or the like. The binder is added, mixed and dried to aggregate. And then the ball mill,
It is advantageous to disintegrate using an ultrasonic disperser or the like, and further classify with an air classifier or the like to manufacture.

The shape of the heat-resistant resin fine powder thus obtained is not only spherical but also various complicated shapes, so that the shape of the anchor formed thereby also has a complicated shape accordingly. Therefore, it effectively acts to improve the adhesion strength of the plating film such as peel strength and pull strength.

The heat-resistant resin fine powder produced as described above is added uniformly to a heat-resistant resin liquid that forms a matrix or a solution in which the heat-resistant resin that forms the matrix is dissolved in a solvent to obtain a uniform mixture. Disperse.

The preferable thickness of the resin insulating layer in the present invention is about 20 to 100 μm, but it can be made thicker if a particularly high insulating property is required.

The substrate used in the present invention may be any one having appropriate flexibility, and for example, a plastic substrate, a metal substrate, a film substrate or the like can be used. Specifically, a glass epoxy substrate, a glass substrate or the like can be used. A polyimide substrate, an aluminum substrate, an iron substrate, a polyimide film substrate, a polyethylene film substrate, or the like can be used.

In the next step, a via hole portion (fine hole) for connecting the conductor layers of the photosensitive resin insulating layer at a position where a multilayer rigid portion is formed is formed by exposing and developing. As a method of forming a via hole portion in this step, a method of covering a predetermined portion with a photoresist mask and exposing and then developing is suitable, but in addition, a method of forming a via hole portion by laser processing is applied. You can also

The next step is a treatment for dissolving and removing the heat-resistant resin fine powder scattered on the surface portion of the photosensitive resin insulating layer by using an acid or an oxidizing agent. As a method of dissolving and removing in this step, the substrate on which the photosensitive resin insulating layer is formed is immersed in a solution of an acid or an oxidizing agent, or the surface of the photosensitive resin insulating layer is treated with an acid or an oxidizing agent. It can be carried out by means such as spraying the solution. As a result, the surface of this photosensitive resin insulating layer can be roughened. In order to effectively remove the heat-resistant resin fine powder by dissolving, the surface portion of the photosensitive resin insulating layer is lightly lightened by polishing or liquid honing using, for example, a fine powder abrasive. Roughening is extremely effective.

Chromic acid, chromate, permanganate, ozone, etc. are preferable as the oxidizing agent for roughening the photosensitive resin insulating layer. As the acid, hydrochloric acid, sulfuric acid, organic acid and the like are preferable.

Further, the next step is a treatment for roughening the surface of the photosensitive resin insulating layer and then subjecting the roughened surface to electroless plating to form a conductor circuit. Examples of this electroless plating method include electroless copper plating, electroless nickel plating, electroless tin plating, electroless gold plating and electroless silver plating, and in particular electroless copper plating, electroless copper / Nickel eutectic plating, electroless nickel plating, or electroless gold plating, at least 1
The seed is preferred. In addition, it is also possible to further perform different types of electroless plating or electroplating on the above-mentioned electroless plating, or to coat solder. Then, the flex-rigid multilayer printed wiring board of the present invention is manufactured by repeating the above-mentioned steps one or more times.

In the method of the present invention, the above-mentioned conductor circuit can be formed by another method which has been carried out for a known printed wiring board. For example, a method of subjecting a substrate to electroless plating and then etching the circuit. Alternatively, a method of directly forming a circuit when performing electroless plating may be applied.

[0048]

[Example] (Example 1) (1) Photosensitive polyimide resin (manufactured by Hitachi Chemical Co., Ltd.) Solid content 10
0 parts by weight of epoxy resin fine powder (manufactured by Toray)
The viscosity was adjusted to 5000 cp with a homodisper disperser while adding an N-methylpyrrolidone solvent, and then kneaded with three rolls to obtain an adhesive solution for a photosensitive resin insulating layer. . (2) Next, after laminating a coverlay film on the flexible substrate 1 on which the conductor circuit is formed, the adhesive solution for the photosensitive insulating layer is applied by using a spinner (1000 rpm), and it is kept horizontal in 60 After leaving it at room temperature for 10 minutes,
After being dried for a minute, a photosensitive resin insulating layer 2 having a thickness of 60 μm was formed (see FIG. 4 (2)). (3) Next, a photoresist mask was formed on the via hole part and the flex part, and exposed with an ultrahigh pressure mercury lamp for 30 seconds. This was N-methylpyrrolidone-methanol (3:
1) A via hole for connecting between conductors was formed by developing the mixed solvent for 1 minute. Then, the photosensitive resin insulating layer was completely cured by exposing it to an ultra-high pressure mercury lamp for 5 minutes and then heating it at 200 ° C. for 30 minutes (see FIG. 4 (3)). (4) The surface of the resin insulation layer 2 is roughened by immersing this substrate in an oxidizing agent consisting of an aqueous solution of chromic acid (CrO ₃ ) 800 g / l at 60 ° C. for 2 minutes, and then using a neutralizing solution (manufactured by Shipley). It was dipped and washed with water (see Fig. 4 (4)). (5) Palladium (manufactured by Shipley Co.) is applied to the printed wiring board having the surface of the resin insulating layer 2 roughened to activate the surface of the resin insulating layer 2, and then the liquid photoresist 3 is applied.
Immerse in electroless copper plating solution for additive for 10 hours,
The electroless copper plating having a thickness of 25 μm was applied to the plating film 6 (see FIG. 4 (5)). (6) Next, apply the adhesive prepared in (1), and (2), (3),
The steps (4) and (5) were repeated three times. (7) Finally, the liquid photoresist 3 applied in (5) was removed to form a 4-layer (4,6,8,10) flex-rigid multilayer printed wiring board (see FIG. 4 (6)).

Example 2 (1) Photosensitive polyimide resin (manufactured by Hitachi Chemical Co., Ltd.) Solid content 10
0 parts by weight of epoxy resin fine powder (manufactured by Toray)
The viscosity was adjusted to 5000 cp with a homodisper disperser while adding N-methylpyrrolidone solvent, and then kneaded with three rolls to obtain an adhesive solution for a photosensitive insulating layer. (2) Next, the adhesive solution for the photosensitive insulating layer is spun on a flexible substrate 1 having a conductor circuit formed thereon (1000
rpm), left at room temperature for 60 minutes in a horizontal state, and then dried at 80 ° C. for 10 minutes to form a photosensitive resin insulating layer 2 having a thickness of 60 μm. (3) Next, a photoresist mask was brought into close contact with the via hole portion and the flex portion, and exposed with an ultrahigh pressure mercury lamp for 30 seconds. By developing this with a mixed solvent of N-methylpyrrolidone-methanol (3: 1) for 1 minute,
Via holes for connecting conductors were formed. After that, the photosensitive resin insulating layer 2 was completely cured by exposing it to an ultra-high pressure mercury lamp for 5 minutes and then heating it at 200 ° C. for 30 minutes. (4) The surface of the resin insulation layer 2 is roughened by immersing this substrate in an oxidizing agent consisting of an aqueous solution of chromic acid (CrO ₃ ) 800 g / l at 60 ° C. for 2 minutes, and then using a neutralizing solution (manufactured by Shipley). It was dipped and washed with water. (5) Palladium (manufactured by Shipley Co.) is applied to the printed wiring board with the surface of the resin insulating layer 2 roughened to activate the surface of the resin insulating layer 2, and then the electroless copper plating solution for full additive is applied. After immersion for 10 hours, electroless copper plating with a thickness of 25 μm was applied to the plating film 6. (6) An acid-resistant negative photoresist was applied on the entire surface. (7) A photoresist mask was brought into close contact with the flex portion, and the photoresist coated in (6) was exposed. As a result, the resist was not placed on only the flex portion. (8) This substrate was immersed in dilute acid to remove the copper plating on the flex portion, and then washed with water. (9) Next, the adhesive prepared in (1) was applied, and the steps (2) to (8) were repeated three times. (10) Through the above steps, a 4-layer (4,6,8,10) flex-rigid multilayer printed wiring board was prepared.

Example 3 (1) An epoxy resin (manufactured by Mitsui Petrochemical Co., Ltd.) was dried in a hot air dryer at 160 ° C. for 1 hour and subsequently at 180 ° C. for 4 hours to be cured, and then cured. After the epoxy resin was roughly pulverized, it was further pulverized with a sonic jet pulverizer while being frozen with liquid nitrogen to obtain an epoxy resin fine powder having an average particle size of 1.6 μm. (2) Next, 1 part of the epoxy resin fine powder was added to 100 parts by weight of the solid content of the photosensitive polyimide resin (manufactured by Hitachi Chemical Co., Ltd.).
It is blended at a ratio of 00 parts by weight, and the viscosity is 5000 cp with a homodisper disperser while adding an N-methylpyrrolidone solvent
And then kneading with a three-roll mill to obtain an adhesive solution for the photosensitive insulating layer. (3) Next, the adhesive solution for the photosensitive insulating layer is applied on the flexible substrate 1 on which the conductor circuit is formed in the same manner as in Example 1 to form the photosensitive resin insulating layer 2 having a thickness of 60 μm. did. (4) Next, a photoresist mask was brought into close contact with the via hole portion and the flex portion, and exposed with an ultrahigh pressure mercury lamp for 30 seconds. By developing this with a mixed solvent of N-methylpyrrolidone-methanol (3: 1) for 1 minute,
Via holes for connecting conductors were formed. After that, the photosensitive resin insulating layer 2 was completely cured by exposing it to an ultra-high pressure mercury lamp for 5 minutes and then heating it at 200 ° C. for 30 minutes. (5) Next, the surface of the resin insulation layer 2 is roughened by immersing the substrate in an oxidizer composed of an aqueous solution of 800 g / l chromic acid (CrO ₃ ) at 60 ° C. for 2 minutes, and then a neutralizing solution (Shipley Company). Manufactured) and washed with water. (6) Palladium (manufactured by Shipley Co.) is applied to the printed wiring board having the surface of the resin insulating layer 2 roughened to activate the surface of the resin insulating layer 2, and then the liquid photoresist 3 is applied.
The electroless copper plating solution for full additive was immersed for 10 hours to perform electroless copper plating with a plating film 6 having a thickness of 25 μm. (7) Next, apply the adhesive created in (1), and (3), (4),
The steps (5) and (6) were repeated 3 times. (8) Finally, the liquid photoresist 3 applied in (6) was removed to obtain a 4-layer (4,6,8,10) flex-rigid multilayer printed wiring board.

Example 4 (1) 70 parts by weight of 50% acrylate of cresol novolac type epoxy resin (manufactured by Nippon Kayaku), 30 parts by weight of bisphenol A type epoxy resin (manufactured by Yuka Shell), as a photosensitive monomer , 7.5 parts by weight of dipentaerythritol hexaacrylate (made by Kyoeisha Yushi) and 3.75 parts by weight of neopentyl glycol-modified trimethylolpropane diacrylate (made by Nippon Kayaku), 5 parts by weight of benzophenone and 0.5 parts by weight of Michler's ketone as a photopolymerization initiator, 4 parts by weight of imidazole type curing agent (manufactured by Shikoku Kasei) and 25 parts by weight of epoxy resin filler (manufactured by Toray) of 5.5 μm and 0.5 parts by weight
After mixing 10 parts by weight of μm, the mixture was stirred with a homodisper stirrer while adding butyl cellosolve acetate, and 0.9 wt% of a leveling agent (manufactured by San Nopco, trade name: Dappo S-65) was further added to this mixture. The mixture was kneaded with three rolls to obtain an adhesive solution for a photosensitive resin insulating layer having a solid content of 70%. (2) In the same manner as in Example 1 below, a 4-layer flex-rigid multilayer printed wiring board was prepared.

Comparative Example 1 (1) An inner layer circuit and a conductor circuit corresponding to a flex portion were formed on a flexible substrate by a subtractive method, and then a punched coverlay film was placed on the conductor circuit. Combine and temporarily bond, then
By heating and pressurizing with a multi-stage press, a flexible substrate to be the inner layer circuit board and the flex portion was produced. (2) Another inner layer circuit is formed on one surface of the glass epoxy double-sided copper clad board by the subtractive method, and then,
By external processing, a rigid substrate for forming one conductor layer of the multilayer rigid portion was produced. (3) The flexible substrate prepared in (1) and (2) above and a plurality of rigid substrates were laminated and fixed via a prepreg, and heated and pressed by a press to be integrated. Next, after making holes in the obtained substrate, electroless plating is performed to connect and connect the inner layer circuit and the outer layer circuit through through holes, and to form a conductor circuit on the other surface of the rigid portion. As a result, a flex-rigid multilayer printed wiring board was obtained.

(Comparative Example 2) A printed wiring board with a double-sided circuit made of a glass epoxy substrate manufactured by a normal subtractive method was used as a rigid part, and this rigid part and the flexible substrate manufactured in (1) of the comparative example 1 were used. Were joined by a soldering method as shown in FIG. 5 to produce a flex-rigid multilayer printed wiring board.

Table 2 shows the results of evaluation of the inter-pattern insulation (connection reliability) and folding endurance (folding characteristics) of the flex-rigid multilayer printed wiring board manufactured as described above. As is clear from the results shown in this table, the flex-rigid multilayer printed wiring board of the present invention, as compared with the flex-rigid multilayer printed wiring board by the conventional method, without impairing the inter-pattern insulating property and the folding endurance, It was confirmed that a patterned circuit could be easily formed with high precision. Moreover, it was confirmed that the peel strength of 1.4 kg / cm or more could be secured.

[0055]

[Table 2]

A method for evaluating the inter-pattern insulating property and the folding endurance will be described. (1) Pattern insulation L / S = 80/85% at a comb pattern of 50/50 μm
The insulation resistance between the patterns after / 24 V and 1000 hours was measured. (2) Folding endurance was performed according to JIS-P-8115.

Furthermore, in the flex-rigid multilayer printed wiring board manufactured by the conventional method as described above,
At the time of deformation, stress is applied to the end portions of the multilayer rigid portion, and troubles such as peeling or cracking of the rigid portion and tearing of the flex portion are likely to occur. Therefore, in the conventional flex-rigid multilayer printed wiring board, as shown in FIG. 6, the end face of the rigid portion is sealed with silicone rubber or the like. In this respect, since the flex-rigid multilayer printed wiring board of the present invention uses the resin composition containing the heat-resistant fine powder as the resin insulating layer of the multilayer rigid portion, the adhesion strength between the conductor layer and the resin insulating layer is Since the rigid portion is high, peeling or cracking of the rigid portion does not occur at the time of deformation, and the radius of curvature after deformation can be reduced, so that the electronic device can be downsized. Moreover, in the manufacturing method of the present invention, the rigid portions are laminated by the exposure and development process to form a multilayer structure.
As shown in, the boundary between the multilayer rigid portion and the flex portion can be easily strengthened without sealing.

[0058]

As described above, according to the present invention, the manufacturing process of a flex-rigid multilayer printed wiring board can be simplified, and besides, a fine pattern with high precision can be easily formed and insulation between patterns can be achieved. It is possible to reliably and inexpensively provide a flex-rigid multilayer printed wiring board having excellent reliability such as properties.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a typical flex-rigid multilayer printed wiring board.

FIG. 2 is a diagram showing a cross-sectional structure of a typical flex-rigid multilayer printed wiring board.

FIG. 3 is a diagram showing a manufacturing process of a conventional flex-rigid multilayer printed wiring board.

FIG. 4 is a diagram showing a manufacturing process of the flex-rigid multilayer printed wiring board of the present invention.

FIG. 5 is a diagram showing a method of joining a rigid portion and a flex portion according to a conventional technique.

FIG. 6 is a view showing a reinforcing sealing of a rigid end surface portion according to a conventional technique.

FIG. 7 is a view showing one form of a rigid end face portion in the flex-rigid multilayer printed wiring board of the present invention.

[Explanation of symbols]

 1 flexible substrate 2 photosensitive resin insulating layer 3 liquid photoresist 4, 6, 8, 10 plating film (conductor layer) 5 via hole

Claims (4)

[Claims] 1. A flex-rigid multilayer printed wiring board, comprising: a multilayer rigid portion each having a plurality of conductor layers and a resin insulating layer; and a flex portion connected to the multilayer rigid portion. A flex-rigid multilayer printed wiring board, characterized in that the resin insulating layer of the part is formed of a photosensitive insulating material. 2. The photosensitive insulating material is pre-cured to be soluble in an acid or an oxidant in an uncured heat-resistant resin matrix that becomes hardly soluble in an acid or an oxidant when subjected to a curing treatment. The flex-rigid multilayer printed wiring board according to claim 1, which is an adhesive in which fine powder of heat-resistant resin is dispersed. 3. A method of manufacturing a flex-rigid multilayer printed wiring board, comprising: a multilayer rigid part having a plurality of conductor layers and a resin insulating layer; and a flex part continuous with the multilayer rigid part. , At least the following steps (a) to (d); that is, (a) a step of partially forming a photosensitive resin insulating layer on a flexible substrate having a conductor circuit on at least one surface, (b) the photosensitivity A step of roughening the surface portion of the resin insulating layer by treating with an acid or an oxidant, (c) a step of forming a conductor circuit by performing electroless plating on the roughened photosensitive resin insulating layer, The method for producing a flex-rigid multilayer printed wiring board is characterized in that the above is repeated once or more. 4. The photosensitive insulating material is pre-cured to be soluble in an acid or an oxidant in an uncured heat-resistant resin matrix that is hardly soluble in an acid or an oxidant when subjected to a curing treatment. The manufacturing method according to claim 3, which is an adhesive obtained by dispersing the heat-resistant resin fine powder.