JPH04352494A - Method of forming adhesion layer for additive printed wiring board - Google Patents

Abstract

PURPOSE:To provide a method of forming an adhesion layer for additive wiring board which is superb in heat resistance, electrical characteristics, and adhesion property between a substrate and an electroless plating film and prevents generation of a pin hole positively. CONSTITUTION:A non-cured layer 7 of a heat-resistance resin liquid which becomes solution-retardant for a dissolution liquid by a curing treatment is formed on a surface of a substrate 1 and a non-cured layer 3 of an adhesive where a fine powder 8 which is difficult to be dissolved to the heat-resistance resin liquid and is soluble to a dissolution liquid at least partially is dispersed to the heat-resistance resin is formed on a non-cured layer 7 of the heat- resistance resin liquid. The non-cured layer 7 of the heat-resistance resin liquid and the non-cured layer 3 of the adhesive are subjected to curing treatment in that state for forming an adhesion layer 2, dissolution treatment of a surface portion of the adhesive layer 2 is performed by the dissolution liquid, and a soluble portion of the fine powder 8 near the surface of the adhesive layer 2 is dissolved and eliminated, thus forming a number of recessed portions 5.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an adhesive layer for additive printed wiring boards used in the manufacture of printed wiring boards.

0002

[Background Art] In recent years, electronic equipment has become smaller, more sophisticated, and more multifunctional, and the printed wiring boards used in these equipment are also required to have higher density and higher reliability due to fine patterns. There is. Conventionally, as a method for forming a conductor circuit on a printed wiring board, a subtractive method has been widely used in which a conductor circuit is formed by laminating copper foil on an insulating substrate and then photo-etching it. According to this method, it is possible to form a conductor circuit with excellent adhesion to the insulating substrate, but due to the thickness of the copper foil, so-called undercuts occur during etching, making it difficult to obtain fine patterns with high precision and high density. The problem is that it is difficult to respond to changes.

Therefore, as an alternative to the subtractive method, an adhesive is applied to an insulating substrate to form an adhesive layer, the surface of this adhesive layer is roughened, and then electroless plating is applied to form a conductor circuit. Additive methods are attracting attention. However, since the adhesives commonly used in additive methods contain synthetic rubber, they may have low heat resistance, such as the adhesion strength decreasing significantly at high temperatures or the electroless plating film blistering during soldering. However, it has the disadvantage that its electrical characteristics are insufficient in high humidity conditions, and its range of use is quite limited.

[0004] In order to solve the problems of the conventional adhesives, Japanese Patent Application Laid-Open No. 61-276875 discloses that a heat-resistant resin fine powder that is soluble in oxidizing agents and that has been hardened in advance is
An adhesive that is dispersed in an uncured heat-resistant resin liquid that has the property of becoming poorly soluble in oxidizing agents through curing treatment, and a method for manufacturing printed wiring boards using this adhesive have been proposed. There is.

In this method, the adhesive is applied to the surface of the substrate, dried and hardened to form an adhesive layer, and the surface of the adhesive layer is immersed in an oxidizing agent to dissolve and remove a portion of the heat-resistant resin fine powder. By doing this, an adhesive layer with a roughened surface is obtained.
An electroless plating layer is formed on the adhesive layer. That is, as shown in FIG. 3, the adhesive layer 2 formed on the surface of the substrate 1 includes fine powder 8 of a heat-resistant resin that is soluble in oxidizing agents in a matrix 3 that is made of a heat-resistant resin that is hardly soluble in oxidizing agents. It has a dispersed structure, and a large number of fine recesses 5 formed by dissolving and removing the fine powder 8 are formed on the surface portion.

[0006]

[Problems to be Solved by the Invention] The adhesive for forming the adhesive layer 2 made of the heat-resistant resin is
Since the composition is a mixture of a liquid heat-resistant resin and a solid fine powder 8, it has a high viscosity and is difficult to mix uniformly. If the uniform mixing is insufficient, when the adhesive is applied to the substrate 1, a part of the matrix 3 where the fine powder 8 has aggregated appears as shown in FIG. 4(a).

[0007] If the substrate is immersed in an etching solution in this state, a short pass of etching occurs, and a pinhole 6 is generated as shown in FIG. 4(b). If the pinhole 6 exists, the pinhole will occur in the plating resist film when forming the conductor circuit, and problems will arise in the insulation due to pattern shorts and the like. Another problem is that during immersion in the etching solution, the etching solution enters the interface between the substrate 1 and the adhesive layer 2 through the pinhole 6, creating a gap between the substrate 1 and the adhesive layer 2.

Furthermore, since the fine powder 8 is distributed throughout the adhesive layer 2, if the electrical properties of the fine powder 8 are poor, the physical properties of the adhesive layer as a whole will also be poor, so the materials that can be used as the fine powder 8 are limited. The present invention has been made in view of the above-mentioned problems, and its purpose is to provide excellent heat resistance, electrical properties, and adhesion between the substrate and the electroless plating film, and to reliably prevent the occurrence of pinholes. An object of the present invention is to provide a method for forming an adhesive layer for an additive printed wiring board.

[0009]

[Means for Solving the Problems] In order to achieve the above object, in the first invention, an uncured layer of a heat-resistant resin liquid that becomes hardly soluble in a solution by a curing treatment is formed on the surface of a substrate, On the uncured layer of the heat-resistant resin liquid, an adhesive is formed by dispersing in the heat-resistant resin a fine powder that is hardly soluble in the heat-resistant resin liquid and at least partially soluble in the solution. An uncured layer is formed, and in that state, the uncured layer of the heat-resistant resin liquid and the uncured layer of the adhesive are cured to form an adhesive layer, and then the surface portion of the adhesive layer is cured with a solution. A dissolution treatment was performed to dissolve and remove the soluble portion of the fine powder near the surface of the adhesive layer, thereby forming a large number of recesses.

[0010] Furthermore, in the second invention, an uncured film layer of a heat-resistant resin liquid that becomes poorly soluble in the solution is formed on the surface of the substrate by a curing treatment, and the uncured film layer of the heat-resistant resin liquid is formed on the surface of the substrate. An uncured film layer of an adhesive is formed on top of the heat-resistant resin by dispersing fine powder that is sparingly soluble in the heat-resistant resin liquid and at least partially soluble in the solution. Curing the uncured film layer of the heat-resistant resin liquid and the uncured film layer of the adhesive in the state to form an adhesive layer, and then dissolving the surface portion of the adhesive layer with the dissolving solution, A large number of recesses were formed by dissolving and removing the soluble portion of the fine powder near the surface of the adhesive layer.

[0011] The heat-resistant resin constituting the adhesive layer has excellent heat resistance, electrical insulation, chemical stability, and adhesion, and can be cured to dissolve in a solution (for example, an oxidizing agent such as an aqueous chromic acid solution). Any resin can be used as long as it has the property of being poorly soluble in water. In particular, epoxy resin,
It is preferably at least one selected from epoxy-modified polyimide resins, polyimide resins, and phenol resins, and in some cases, these resins may be imparted with photosensitivity (particularly ultraviolet curing properties).

As the heat-resistant resin liquid applied to the substrate, an uncured heat-resistant resin liquid containing no solvent can be used as is, but a heat-resistant resin liquid prepared by dissolving a heat-resistant resin in a solvent has a low It becomes viscous and becomes easier to apply to the substrate. As the solvent, methyl ethyl ketone, methyl cellosolve, ethyl cellosolve, tetralin, dimethylformamide, etc. are used.

The material of the fine powder dispersed in the adhesive layer may be any material as long as it is at least partially soluble in the dissolving liquid and slightly soluble or insoluble in the uncured heat-resistant resin liquid; It is not necessary to particularly have excellent heat resistance and electrical insulation. However, since the fine powder needs to be kept floating near the surface of the uncured heat-resistant resin liquid, it is preferable to use a material whose specific gravity is approximately equal to that of the heat-resistant resin liquid. Examples of such materials include hardened epoxy resins, polyester resins, bismaleimide triazine resins, and the like.

[0014] The particle size of the fine powder is an average particle size of 10
It is preferably less than μm, particularly preferably less than 5 μm. The reason for this is that when the average particle size is larger than 10 μm, the density of the recesses formed by dissolving and removing the fine powder decreases, the adhesion strength and reliability of the electroless plating film decreases, and the adhesive layer surface This is because the unevenness becomes severe, making it difficult to obtain a fine conductor pattern, and also unfavorable for mounting components. Such fine resin powders can be obtained by thermally curing the heat-resistant resin and then pulverizing it using a jet mill, freeze-pulverizer, etc., or directly by spray-drying and heat-hardening a heat-resistant resin solution before hardening. It can be obtained by various means such as pulverizing.

[0015] Instead of each fine powder consisting of a single particle, the fine powder has a structure in which a large number of particles are attached to each other, and particles having a diameter far smaller than that of the fine powder are present at least on the outside ( (hereinafter referred to as pseudo particles) may also be used. Pseudo-particles are soluble in the solution and are soluble in the solution on the surface of base particles made of hardened heat-resistant resin fine powder with an average particle size of 10 μm or less. heat-resistant resin fine powder or inorganic fine powder that has been hardened and adhered to the surface of the base particle, or heat-resistant resin fine powder that has an average particle size of 1 μm or less and is insoluble in the solution and has been hardened. Or those to which inorganic fine powder is attached, or those made by agglomerating fine particles of heat-resistant resin fine powder with an average particle size of 2 μm or less that is soluble in a solution and hardened, and whose diameter is 10 μm or less. etc. are used.

[0016] The dissolving solution is appropriately selected depending on the materials of the heat-resistant resin and fine powder that will become the adhesive layer, but generally an aqueous solution of an oxidizing agent such as chromic acid, chromate, permanganate, or ozone is used. In particular, a mixed acid aqueous solution of chromic acid and sulfuric acid is preferred.

[0017]

[Operation] In the first invention, an uncured layer of heat-resistant resin liquid is formed on the surface of the substrate, and on this uncured layer, there is a layer that is poorly soluble in the heat-resistant resin liquid and at least a part of which is dissolved in the liquid. An adhesive prepared by dispersing soluble fine powder in the heat-resistant resin is applied thereto to form an adhesive layer. When the uncured layer and the adhesive layer are cured in this state, the uncured layer and the adhesive layer turn into a cured heat-resistant resin layer that is hardly soluble in the solution, thereby forming an adhesive layer.

Next, the surface portion of the adhesive layer is subjected to a dissolution treatment using a dissolving solution, and the soluble portion of the fine powder existing near the surface is selectively dissolved and removed, resulting in a large number of fine depressions on the surface of the adhesive layer. It is formed. Since the fine powder exists only in the adhesive layer on the surface side of the adhesive layer and does not exist in the uncured layer on the substrate side, unlike conventional methods, the generation of pinholes during the melting process is reliably prevented. Ru.

In the second invention, an uncured film layer of the heat-resistant resin liquid is formed on the surface of the substrate, and an adhesive made of the fine powder dispersed in the heat-resistant resin is placed on the film layer. An adhesive layer is formed by forming an uncured film layer, and in that state, performing a curing treatment on the uncured film layer of the heat-resistant resin liquid and the uncured film layer of the adhesive. Then, by the same operation as in the first invention, many fine recesses are formed on the surface of the adhesive layer.

[0020]

[Examples] The present invention will be explained in more detail with reference to Examples below. (Example 1) Epoxy resin (Yuka Shell Epoxy Co., Ltd.)
Product name: E-807), curing agent (Shikoku Kasei Kogyo Co., Ltd.)
Product name: 2PZ) and solvent (dimethylformamide)
was stirred with a mixer to prepare a heat-resistant resin liquid (viscosity 20
0cps). This heat-resistant resin liquid is applied onto the substrate 1 using a roller coater so that the coating thickness is about 15 to 20 μm, and as shown in FIG. 1(a), an uncured layer 7 of the heat-resistant resin liquid is applied to the substrate It was formed on the surface of 1.

[0021] In addition, epoxy resin (manufactured by Mitsui Petrochemical Industries, trade name: TA-1800) was heated to 160% in a hot air dryer.
It was cured by drying at 180°C for 1 hour, followed by 4 hours at 180°C. After coarsely pulverizing this cured epoxy resin, it is finely pulverized using a supersonic jet pulverizer (manufactured by Nippon Pneumatic Industries, trade name: Labojet) while being frozen with liquid nitrogen, and then classified using a wind classifier to obtain an average particle size. Epoxy resin fine powder with a diameter of 4 μm was prepared. This fine powder is poorly soluble in the heat-resistant resin liquid.

[0022] The epoxy resin fine powder 8 is blended at a ratio of 120 parts by weight to 100 parts by weight of the solid content of the epoxy resin dissolved in the dimethylformamide, and then homogenized while adding the curing agent and dimethylformamide. The viscosity was adjusted to 200 cps using a dispersion machine, and then kneaded using three rolls to obtain an adhesive. And Figure 1
As shown in (b), the above adhesive is applied to the surface of the substrate 1 on which the uncured layer 7 of the heat-resistant resin liquid is formed using a roller coater, so that the adhesive has a thickness of 5 to 15 μm. An uncured layer 3 was formed. In the uncured adhesive layer 3, the epoxy resin fine powder 8 is almost uniformly dispersed.

[0023] In this state, at 120°C for 5 hours, and then for 15 hours.
The uncured layer 7 of the heat-resistant resin liquid and the uncured layer 3 of the adhesive were cured by heating and drying at 0° C. for 3 hours. As a result, as shown in FIG. 1(c), an uncured layer 7 of the heat-resistant resin liquid is formed.
The uncured adhesive layer 3 becomes a heat-resistant resin layer that is hardly soluble in the solution, and an adhesive layer 2 is formed on the surface of the substrate 1. At this time, the uncured layer 7 of the heat-resistant resin liquid and the uncured layer 3 of the adhesive
Since all of the components other than the fine powder 8 are made of uncured epoxy resin, they mix and harden at the interface between them, so that after curing, the interface between the two disappears. Therefore, there is no possibility that a solution, which will be described later, will enter the interface between the uncured layer 7 of the heat-resistant resin liquid and the uncured layer 3 of the adhesive, thereby creating a gap.

[0024] Since both the layer formed by curing the uncured layer 7 of the heat-resistant resin liquid and the substrate 1 are made of epoxy resin, the adhesion between them is good. The substrate 1 on which the adhesive layer 2 was formed was immersed in a solution consisting of an aqueous chromic acid solution (400 g/l of chromic acid) at 90° C. for 12 minutes to roughen the surface of the adhesive layer 2. The heat-resistant resin layer constituting the adhesive layer 2 is hardly soluble in this solution, and the fine powder 8 present near its surface is soluble in the solution, so the fine powder 8 is selectively removed from the adhesive layer 2 by the solution. It is dissolved and removed.

Then, as shown in FIG. 1(d), the adhesive layer 2
A large number of fine recesses 5 are formed on the surface after the fine powder 8 is removed. The fine powder 8 exists only near the surface of the adhesive layer 2 corresponding to the uncured layer 3 of the adhesive, and does not exist near the substrate 1. Therefore, even if the plurality of fine powders 8 that have come into contact with each other are melted and the recesses 5 are connected, there is no risk that the recesses 5 will reach the substrate 1. As a result, unlike the conventional method, pinholes are reliably prevented from forming during melting.

A palladium catalyst (manufactured by Shipley, trade name: Cataposit 44) was applied to the substrate 1 on which the surface of the adhesive layer 2 obtained as described above was roughened to activate the surface of the adhesive layer 2. Then, an electroless plating solution for additive method having the composition shown below (pH: 12.4, plating temperature: 70~
72℃) for 11 hours, the thickness of the plating film was 25 μm.
Electroless copper plating was applied.

[0027] Copper sulfate...0.06 mol/l, formalin...
0.30 mol/l, caustic soda...0.35/l, EDT
A: 0.12/l, additives: a little The wiring board produced as described above was further plated with copper to a thickness of 35 μm by electroplating in a copper sulfate plating bath. Regarding the printed wiring board manufactured in this way, the adhesion strength between the substrate 1 and the copper plating film was determined according to JIS-C-64.
It was measured by the method of 81. As a result, the peel strength was 1.6
It was found that the adhesion between the adhesive layer 2 and the electroless plating film was good. (Embodiment 2) Next, another embodiment embodying the present invention will be described with reference to FIGS. 2(a) to 2(d). In this example, the adhesive layer 2 was formed by forming the heat-resistant resin liquid and the adhesive into a film, laminating it onto a substrate, and performing a curing process.

As shown in FIG. 2(a), the heat-resistant resin liquid is applied onto a polyethylene terephthalate (hereinafter referred to as PET) film 9 to form an uncured film layer 10 of the heat-resistant resin liquid with a thickness of 20 to 50 μm. was formed. Also, Figure 2
As shown in (b), an adhesive in which the fine powder 8 is dispersed is applied onto the same PET film 9 to a thickness of 20 to 5.
An uncured film layer 11 of 0 μm adhesive was formed.

Next, first, an uncured film layer 10 of a heat-resistant resin liquid is pasted on the surface of the substrate 1, and then the PET film 9 is peeled off, and an uncured film layer 1 of an adhesive is applied thereon.
After pasting 1 in the same manner, the PET film 9 is peeled off. In this state, the uncured film layer 10 of the heat-resistant resin liquid was cured by heating at 120°C for 5 hours and then at 150°C for 3 hours.
and the uncured film layer 11 of the adhesive was cured. As a result, as shown in FIG. 2(c), the uncured film layer 10 of the heat-resistant resin liquid and the uncured film layer 1 of the adhesive are formed.
1 becomes a heat-resistant resin layer that is hardly soluble in the solution, and an adhesive layer 2 is formed on the surface of the substrate 1. At this time, an uncured film layer 10 of heat-resistant resin liquid and an uncured film layer 11 of adhesive
Since all of the components other than the fine powder 8 are made of uncured epoxy resin, they mix and harden at the interface between them, so that after curing, the interface between the two disappears. As a result, there is no fear that a solution, which will be described later, will enter the interface between the uncured film layer 10 of the heat-resistant resin liquid and the uncured film layer 11 of the adhesive, thereby creating a gap.

The surface of the adhesive layer 2 is roughened by immersing the substrate 1 on which the adhesive layer 2 is formed in a solution consisting of an aqueous chromic acid solution in the same manner as in Example 1, as shown in FIG. 2(d).
), a large number of fine recesses 5 are formed on the surface of the adhesive layer 2. It should be noted that the present invention is not limited to the above-described embodiments; for example, the fine powder 8 may have different particle sizes, or the fine powder 8 may have a large number of fine particles much smaller than the particle size aggregated on the surface. The above-mentioned pseudo particles (secondary particles) may be used. As for particles having different particle sizes, fine powders of epoxy resin having an average particle size of 4 μm and 1 μm may be prepared by classification. As pseudo particles, for example, an average particle size of 3
．． It is also possible to use one obtained by dispersing 9 μm epoxy resin powder in acetone and dropping a suspension of 0.5 μm average particle size epoxy resin powder dispersed in acetone while stirring. Furthermore, in place of the hardened resin powder, the fine particles can be replaced with an inorganic powder (
For example, calcium carbonate) may be used.

[0031]

Effects of the Invention As detailed above, according to the first and second inventions, an adhesive layer for additive method having excellent heat resistance, electrical properties, and adhesion between a substrate and an electroless plating film can be made into a pin. It can be formed in a state where the generation of holes is reliably prevented, and the reliability in the fully additive method is improved, which is an excellent effect.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view schematically showing a procedure for forming an adhesive layer in Example 1 of the present invention.

FIG. 2 is a cross-sectional view schematically showing the adhesive layer forming procedure of Example 2.

FIG. 3 is a cross-sectional view schematically showing a conventional adhesive layer.

FIG. 4 is a cross-sectional view schematically showing a conventional adhesive layer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Substrate, 2... Adhesive layer, 3... Uncured layer of adhesive, 5... Recessed part, 7... Uncured layer of heat-resistant resin liquid, 8... Fine powder, 10...
Uncured film layer of heat-resistant resin liquid, 11... uncured film layer of adhesive.

Claims (2)

[Claims] 1. An uncured layer (7) of a heat-resistant resin liquid that becomes poorly soluble in a solution by hardening treatment is formed on the surface of a substrate (1), and the uncured layer (7) of the heat-resistant resin liquid is formed on the surface of a substrate (1). ), an uncured layer (3) of an adhesive in which fine powder (8), which is sparingly soluble in the heat-resistant resin liquid and at least partially soluble in the heat-resistant resin, is dispersed in the heat-resistant resin. ), and in that state, the uncured layer (7) of the heat-resistant resin liquid and the uncured layer (3) of the adhesive are cured to form an adhesive layer (2), and then the adhesive layer (2) is formed using a solution. The surface portion of the adhesive layer (2) is subjected to a dissolution treatment to dissolve the fine powder (8) near the surface of the adhesive layer (2).
1. A method for forming an adhesive layer for an additive printed wiring board, the method comprising: forming a large number of recesses (5) by dissolving and removing the soluble portions of (5). 2. Forming an uncured film layer (10) of a heat-resistant resin liquid on the surface of the substrate (1), which becomes poorly soluble in the solution through a curing treatment, (10) On top is a fine powder (
8) is dispersed in the heat-resistant resin to form an uncured film layer (11) of the adhesive, and in this state, the uncured film layer (10) of the heat-resistant resin liquid and the uncured film layer (11) of the adhesive are formed. 11) to form an adhesive layer (2), and then perform a dissolution treatment on the surface of the adhesive layer (2) using the dissolving solution to remove fine powder near the surface of the adhesive layer (2). 8
1. A method for forming an adhesive layer for an additive printed wiring board, the method comprising: forming a large number of recesses (5) by dissolving and removing the soluble portions of (5).