JP3090973B2 - Method of forming adhesive layer for additive printed wiring board - Google Patents

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 an additive printed wiring board used for manufacturing a printed wiring board.

[0002]

2. Description of the Related Art In recent years, miniaturization, high performance, and multifunctionality of electronic devices have been promoted, and high density and high reliability by fine patterns have been demanded for printed wiring boards used therein. I have. Conventionally, as a method of forming a conductive circuit on a printed wiring board, a subtractive method of forming a conductive circuit by laminating a copper foil on an insulating substrate and then performing photoetching has been widely performed. According to this method, it is possible to form a conductor circuit having excellent adhesion to an insulating substrate, but it is difficult to obtain a high-precision fine pattern due to so-called undercut due to etching due to the thickness of the copper foil. There is a problem that it is difficult to cope with this.

For this reason, as an alternative to the subtractive method, an adhesive is applied to an insulating substrate to form an adhesive layer, the surface of the adhesive layer is roughened, and electroless plating is applied to form a conductor circuit. Attention is being paid to the additive method. However, since the adhesive generally used in the additive method contains synthetic rubber, for example, the adhesive strength is greatly reduced at a high temperature, and the heat resistance is low, such as the electroless plating film being swollen at the time of soldering. However, there is a disadvantage that the electrical characteristics in a high humidity state are not sufficient, and the range of use is considerably restricted.

For the purpose of solving the problem of the conventional adhesive, Japanese Patent Application Laid-Open No. 61-276875 discloses a pre-cured heat-resistant resin fine powder which is soluble in an oxidizing agent.
An adhesive which is dispersed in an uncured heat-resistant resin liquid having a property of being hardly soluble in an oxidizing agent by curing treatment, and a method of manufacturing a printed wiring board using this adhesive have been proposed. I have.

In this method, the adhesive is applied to the surface of a substrate, dried and cured to form an adhesive layer, and the surface of the adhesive layer is immersed in an oxidizing agent to dissolve and remove a part of the heat-resistant resin fine powder. By doing, an adhesive layer having 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 is composed of a matrix 3 made of a heat-resistant resin that is hardly soluble in an oxidizing agent, and a fine powder 8 of a heat-resistant resin soluble in the oxidizing agent. It has a dispersed structure, and a large number of fine concave portions 5 formed by dissolving and removing the fine powder 8 are formed on the surface portion.

[0006]

The adhesive for forming the adhesive layer 2 made of the heat resistant resin is a matrix 3
Because of the composition in which the solid fine powder 8 is mixed with the liquid heat-resistant resin constituting the above, it is difficult to mix uniformly with high viscosity. When the uniform mixing is insufficient, when the adhesive is applied to the substrate 1, a portion where the fine powder 8 is agglomerated occurs in a part of the matrix 3 as shown in FIG.

[0007] When immersed in an etching solution in this state, a short path of etching occurs, and pinholes 6 are generated as shown in FIG. If there is the pinhole 6, a pinhole is generated in the coating film of the plating resist when the conductive circuit is formed, and a short circuit of the pattern causes a problem in insulation. In addition, there is a problem that the etchant penetrates into the interface between the substrate 1 and the adhesive layer 2 via the pinhole 6 when dipping in the etchant, and a gap is formed between the substrate 1 and the adhesive layer 2.

Further, 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 entire adhesive layer are also poor. Therefore, the materials that can be used as the fine powder 8 are limited. The present invention has been made in view of the above problems, and has as its object to provide excellent heat resistance, electrical characteristics, and excellent adhesion between a substrate and an electroless plating film, and to reliably prevent the occurrence of pinholes. It is an object of the present invention to provide a method for forming an adhesive layer for an additive printed wiring board that can be used.

[0009]

In order to achieve the above object, according to a first aspect of the present invention, an uncured layer of a heat-resistant resin liquid which becomes hardly soluble in a dissolving solution by a curing treatment is formed on a substrate having a conductive circuit. Formed on the surface of the plate, a fine powder that is hardly soluble in the heat-resistant resin liquid and at least a part thereof is soluble in the solution is formed on the uncured layer of the heat-resistant resin liquid. rESIN liquid uncured layer of adhesive material dispersed form in the adhesive layer was formed by performing the curing treatment of the uncured layer of the uncured layer and the adhesive of the heat-resistant resin solution in this state, then The surface portion of the adhesive layer was subjected to a dissolving treatment with a dissolving solution, and the soluble portion of the fine powder near the surface of the adhesive layer was dissolved and removed to form a large number of concave portions.

[0010] In the second invention, an uncured film layer of a heat-resistant resin liquid which becomes hardly soluble in a solution by a curing treatment is formed on the surface of a substrate having a conductive circuit, and An uncured film layer of an adhesive in which a fine powder that is hardly soluble in the heat-resistant resin liquid and at least a part of which is soluble in the solution is dispersed in the heat-resistant resin liquid on the uncured film layer. To form an adhesive layer by performing a curing treatment of the uncured film layer of the heat-resistant resin liquid and the uncured film layer of the adhesive in that state, and then the solution of the surface portion of the adhesive layer with the solution A dissolving treatment was performed to dissolve and remove the soluble portion of the fine powder near the surface of the adhesive layer to form a large number of concave portions.

The heat-resistant resin constituting the adhesive layer is excellent in heat resistance, electrical insulation, chemical stability and adhesiveness, and is a solution (eg, an oxidizing agent such as an aqueous solution of chromic acid) by being cured. Any resin can be used as long as it has the property of being hardly soluble in water. In particular, epoxy resin,
The resin is preferably at least one selected from an epoxy-modified polyimide resin, a polyimide resin, and a phenol resin. In some cases, these resins may be provided with photosensitivity (particularly, ultraviolet curability).

As the heat-resistant resin liquid applied to the substrate, an uncured heat-resistant resin liquid containing no solvent can be used as it is, but a heat-resistant resin liquid obtained by dissolving a heat-resistant resin in a solvent is low. The viscosity becomes high, and the coating operation on the substrate becomes easy. Examples of the solvent include methyl ethyl ketone, methyl cellosolve, ethyl cellosolve, tetralin, dimethylformamide and the like.

The material of the fine powder dispersed in the adhesive layer may be at least partially soluble in the solution and hardly soluble or insoluble in the uncured heat-resistant resin solution. In particular, it is not necessary to be excellent in heat resistance and electrical insulation. However, since the fine powder needs to be kept in a state of floating near the surface of the uncured heat-resistant resin liquid, a material having a specific gravity substantially equal to the specific gravity of the heat-resistant resin liquid is preferable. Examples of such a material include a cured epoxy resin, a polyester resin, and a bismaleimide / triazine resin.

The average particle size of the fine powder is 10
μm or less, and particularly preferably 5 μm or less. The reason is that, when the average particle size is larger than 10 μm, the density of the concave portion formed by dissolving and removing the fine powder decreases, the adhesion strength of the electroless plating film and its reliability decrease, and the surface of the adhesive layer further decreases. This is because it is difficult to obtain a fine conductor pattern due to severe irregularities, and it is not preferable for mounting components and the like. Such a resin fine powder is heat-cured to the heat-resistant resin and then finely pulverized using a jet mill or a freeze-pulverizer, or directly subjected to spray drying and heat curing of the heat-resistant resin solution before the curing treatment. It can be obtained by various means such as pulverization.

A structure in which a large number of particles adhere to each other in place of a fine powder consisting of a single particle as a fine powder, and a particle having a diameter much smaller than the diameter of the fine powder exists at least on the outside ( Hereinafter, what is called pseudo particles may be used. The pseudo particles are soluble in the dissolving solution and are soluble in the dissolving solution having an average particle size of 1 μm or less on the surface of the base particles made of a heat-resistant resin fine powder having an average particle size of 10 μm or less which has been cured. A heat-resistant resin fine powder or an inorganic fine powder which has been cured and adhered thereto, or a heat-resistant resin fine powder which has an average particle diameter of 1 μm or less on the surface of the base particles and is insoluble in a solution and which has been cured. Or, a fine particle of heat-resistant resin fine powder with an average particle diameter of 2 μm or less, which is soluble in a solution and has been cured and has a diameter of 10 μm or less. Etc. are used.

The dissolving solution is appropriately selected depending on the material of the heat-resistant resin to be the adhesive layer and the fine powder. In general, an aqueous solution of an oxidizing agent such as chromic acid, chromate, permanganate, or ozone is used. Particularly, a mixed acid aqueous solution of chromic acid and sulfuric acid is preferable.

[0017]

According to the first aspect of the invention, an uncured layer of a heat-resistant resin liquid is formed on the surface of the substrate, and the uncured layer is hardly soluble in the heat-resistant resin liquid and at least a part thereof is dissolved in the solution. On the other hand, an adhesive in which a soluble fine powder is dispersed in the heat resistant resin is applied to form an adhesive layer. When the curing treatment of the uncured layer and the adhesive layer is performed in this state, the uncured layer and the adhesive layer are combined with the cured heat-resistant resin layer that is hardly soluble in the solution to form the adhesive layer.

Next, the surface portion of the adhesive layer is subjected to a dissolving treatment with a dissolving solution, so that the soluble portion of the fine powder present near the surface is selectively dissolved and removed, and many fine concave portions are formed on the surface of the adhesive layer. It is formed. Since the fine powder is present only in the adhesive layer on the surface side of the adhesive layer and is not present in the uncured layer on the substrate side, unlike the related art, the occurrence of pinholes during the dissolution treatment is reliably prevented. You.

In the second invention, an uncured film layer of the above-mentioned heat-resistant resin liquid is formed on the surface of the substrate, and an adhesive made of an adhesive obtained by dispersing the fine powder in a heat-resistant resin is formed on the film layer. An uncured film layer is formed, and in this state, the uncured film layer of the heat-resistant resin liquid and the uncured film layer of the adhesive are cured to form an adhesive layer. Then, by the same operation as in the first invention, many fine concave portions are formed on the surface of the adhesive layer.

[0020]

The present invention will be described more specifically with reference to the following examples. (Example 1) Epoxy resin (Yuka Shell Epoxy Co., Ltd.)
Trade name; E-807), curing agent (Shikoku Chemicals Co., Ltd.)
Product name: 2PZ) and solvent (dimethylformamide)
Was stirred with a mixer to prepare a heat-resistant resin liquid (viscosity 20).
0 cps). This heat-resistant resin liquid is applied on the substrate 1 using a roller coater so that the coating thickness is about 15 to 20 μm, and as shown in FIG. 1 was formed on the surface.

An epoxy resin (trade name: TA-1800, manufactured by Mitsui Petrochemical Industries, Ltd.) was heated at 160 ° C. in a hot air dryer.
For 1 hour and subsequently at 180 ° C. for 4 hours for curing. After coarsely pulverizing the cured epoxy resin, it is finely pulverized using a supersonic jet pulverizer (trade name: Labjet, manufactured by Nippon Pneumatic Industries, Ltd.) while being frozen with liquid nitrogen, and classified by an air classifier to obtain an average particle size. An epoxy resin fine powder having a diameter of 4 μm was prepared. This fine powder is hardly soluble in the heat-resistant resin liquid.

The epoxy resin fine powder 8 is blended in a proportion of 120 parts by weight with respect to 100 parts by weight of the solid content of the epoxy resin dissolved in the dimethylformamide, and homogenized while adding the curing agent and dimethylformamide. The viscosity was adjusted to 200 cps by a disperser and then kneaded with three rolls to obtain an adhesive. And FIG.
As shown in (b), an adhesive having a thickness of 5 to 15 μm 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. An uncured layer 3 was formed. In the uncured layer 3 of the adhesive, the epoxy resin fine powder 8 is substantially uniformly dispersed.

In this state, at 120 ° C. for 5 hours, further 15
The film was cured by heating at 0 ° C. for 3 hours to cure the uncured layer 7 of the heat-resistant resin liquid and the uncured layer 3 of the adhesive. Thus, as shown in FIG. 1C, the uncured layer 7 of the heat-resistant resin liquid and the uncured layer 3 of the adhesive become a heat-resistant resin layer that is hardly soluble in the solution, and The adhesive layer 2 is formed. At this time, since the uncured layer 7 of the heat-resistant resin liquid and the uncured layer 3 of the adhesive are formed of an uncured epoxy resin except for the fine powder 8, they are mixed at the boundary surface thereof. After curing, there is no boundary between them. Therefore, there is no possibility that a solution to be described later will penetrate into the boundary surface between the uncured layer 7 of the heat-resistant resin liquid and the uncured layer 3 of the adhesive, and a gap will be generated.

Since the layer formed by curing the uncured layer 7 of the heat-resistant resin liquid and the substrate 1 are both formed 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 of a chromic acid aqueous solution (chromic acid 400 g / l) 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 existing near the surface thereof is soluble in the solution. Dissolved and removed.

Then, as shown in FIG.
Many fine concave portions 5 after the fine powder 8 is removed are formed on the surface of the substrate. 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 are in contact with each other are dissolved and the recesses 5 communicate with each other, there is no possibility that the recesses 5 reach the substrate 1. As a result, unlike the related art, the generation of pinholes during melting is reliably prevented.

A palladium catalyst (manufactured by Shipley Co., trade name: Cataposit 44) is applied to the substrate 1 obtained by roughening the surface of the adhesive layer 2 obtained as described above.
Is activated, and an electroless plating solution for an additive method having the following composition (pH: 12.4, plating temperature: 70)
７２72 ° C.) for 11 hours to obtain a plating film having a thickness of 25 μm.
m of electroless copper plating.

Copper sulfate: 0.06 mol / l, formalin:
0.30 mol / l, caustic soda ... 0.35 / l, EDT
A: 0.12 / l, additive: a little The wiring board produced as described above was further subjected to copper plating with a thickness of 35 μm by electroplating in a copper sulfate plating bath. For the printed wiring board thus manufactured, the adhesion strength between the substrate 1 and the copper plating film was measured according to JIS-C-6.
481. As a result, the peel strength was 1.
60 kg / cm, indicating that the adhesion between the adhesive layer 2 and the electroless plating film was good. (Embodiment 2) Next, another embodiment of the present invention will be described with reference to FIGS. In this example, the adhesive layer 2 was formed by forming the heat-resistant resin liquid and the adhesive in a film shape, laminating the film on a substrate, and performing a curing treatment.

As shown in FIG. 2A, the above-mentioned heat-resistant resin solution is applied on a polyethylene terephthalate (PET) film 9 to form an uncured film layer 10 of a heat-resistant resin solution having a thickness of 20 to 50 μm. Was formed. FIG.
As shown in (b), an adhesive in which the fine powder 8 is dispersed is applied on the PET film 9 and the thickness is 20 to 5.
An uncured film layer 11 of an adhesive having a thickness of 0 μm was formed.

Next, an uncured film layer 10 made of a heat-resistant resin liquid is first adhered to the surface of the substrate 1 and then the PET film 9 is peeled off.
After attaching 1 in the same manner, the PET film 9 is peeled off. In this state, the film is dried and cured by heating at 120 ° C. for 5 hours and further at 150 ° C. for 3 hours.
And the uncured film layer 11 of the adhesive was cured. Thereby, as shown in FIG. 2C, the uncured film layer 10 of the heat-resistant resin liquid and the uncured film layer 1 of the adhesive are formed.
Reference numeral 1 denotes a heat-resistant resin layer that is hardly soluble in a solution, and an adhesive layer 2 is formed on the surface of the substrate 1. At this time, the uncured film layer 10 of the heat-resistant resin liquid and the uncured film layer 11 of the adhesive are used.
Means that, except for the fine powder 8, both are formed of uncured epoxy resin, and are mixed and cured at their boundary surfaces, so that after curing, the boundary surfaces between the two disappear. As a result, there is no possibility that a solution to be described later penetrates a boundary surface between the uncured film layer 10 of the heat-resistant resin liquid and the uncured film layer 11 of the adhesive, and a gap is generated.

The substrate 1 on which the adhesive layer 2 is formed is immersed in a dissolving solution composed of an aqueous solution of chromic acid to roughen the surface of the adhesive layer 2 in the same manner as in the first embodiment.
As shown in (d), many fine concave portions 5 are formed on the surface of the adhesive layer 2. The present invention is not limited to the above-described embodiment. For example, the fine powder 8 may have a different particle diameter, and a large number of fine particles far smaller than the diameter are aggregated on the surface. The pseudo particles (secondary particles) described above may be used. As those having different particle diameters, fine powders of epoxy resin having an average particle diameter of 4 μm and 1 μm may be prepared by classification. As pseudo particles, for example, a suspension in which an epoxy resin powder having an average particle size of 0.5 μm is dispersed in acetone is dropped while dispersing an epoxy resin powder having an average particle size of 3.9 μm in acetone and stirring. May be used. Further, an inorganic powder (for example, calcium carbonate) soluble in a solution may be used as the fine particles instead of the cured resin powder.

[0031]

As described above in detail, according to the first and second aspects of the present invention, the adhesive layer for the additive method, which is excellent in heat resistance, electric characteristics, and adhesion between the substrate and the electroless plating film, is used as a pin. Holes can be formed in a state in which generation of holes is reliably prevented, and an excellent effect that reliability in a full additive method is improved is obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view schematically showing a procedure for forming an adhesive layer according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view schematically showing a procedure for forming an adhesive layer in 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 ... board | 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)

(57) [Claims] 1. A uncured layer of the heat-resistant resin solution becomes hardly soluble in solution by curing treatment to form the table <br/> surface of the base plate with a conductor circuit, only the heat-resistant resin solution the hardened layer forming an uncured layer of the heat-resistant resin solution to sparingly soluble at and at least partially adhesive prepared by dispersing soluble fine powder to the solution in the heat-resistant resin solution , an adhesive layer is formed in this state by performing the curing treatment of the uncured layer of uncured So及 beauty adhesive of the heat-resistant resin solution, by then dissolving liquid was dissolved treatment of the surface portion of the adhesive layer, the fine powder in the vicinity of the surface of the adhesive layer
The method of forming the additive printed wiring board adhesive layer, characterized in that by dissolving and removing the soluble portion of forming multiple concave portion. Wherein the uncured film layer of the heat-resistant resin solution becomes hardly soluble in solution by hardening is formed on the surface of the <br/> board with conductor circuits, only the heat-resistant resin solution the uncured film layer of the cured film layer on the heat-resistant resin solution to sparingly soluble at and at least partially adhesive prepared by dispersing soluble fine powder to the solution in the heat-resistant resin solution formed, the adhesive layer by performing a curing process of the uncured film layer of the uncured film So及 <br/> beauty adhesive of the heat-resistant resin solution in the state
It is formed and then subjected to dissolution treatment of the surface portion of the adhesive layer by the solution, and characterized by the formation of a large number of concave portions by dissolving and removing the fine powder of the meltable near the surface of the adhesive layer Of forming an adhesive layer for an additive printed wiring board.