JP3088485B2 - 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 method 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, a conductor circuit having excellent adhesion to an insulating substrate can be formed. However, a so-called undercut occurs due to etching due to the thickness of the copper foil, and it is difficult to obtain a high-precision fine pattern. 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 an insulating 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. Thereby, an adhesive layer having a roughened surface is obtained, and an electroless plating layer is formed on the adhesive layer. That is, as shown in FIG. 4, the adhesive layer 2 formed on the surface of the insulating substrate 1 is made of a heat-resistant resin fine powder 8 that is soluble in the oxidant in a matrix 3 made of a heat-resistant resin that is hardly soluble in the oxidant. 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.

[0005] The adhesive is applied to the insulating substrate by a method of directly applying to the surface of the insulating substrate by roll coating, or by forming an adhesive layer on the film surface to form a dry film and then applying the adhesive layer to the surface of the insulating substrate. There is a method of laminating.

[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. If the uniform mixing is insufficient, apply adhesive to the insulating substrate 1.
When applied to the matrix 3, as shown in FIG.
A portion in which the fine powder 8 is aggregated is generated in a part of. Then, when immersed in an etching solution in this state, a short path of etching occurs, and as shown in FIG.
Occurs. 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. Further, when immersed in the etching solution, the etching solution penetrates into the interface between the insulating substrate 1 and the adhesive layer 2 via the pinhole 6, and there is a problem that a gap is formed between the insulating substrate 1 and the adhesive layer 2.
Further, since the fine powder 8 is distributed throughout the adhesive layer 2, the fine powder 8
If the electrical properties are poor, the physical properties of the entire adhesive layer will also be poor, so the materials that can be used as the fine powder 8 are limited. Each of the above problems occurs regardless of whether the adhesive is applied by a roll coating method or a dry film forming method.

The insulating substrate has a thickness of 1.6 mm and a thickness of ± 0.20 mm due to variations in the thickness of the sheets constituting the insulating substrate.
There is a degree of thickness variation. Therefore, when the roll coating method is used for applying the adhesive, the applied thickness of the adhesive also varies. This variation adversely affects the control of the electrical characteristics (for example, impedance).

The present invention has been made in view of the above-mentioned 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 ensure the generation of pinholes. It is an object of the present invention to provide a method of forming an adhesive layer for an additive method, which can prevent the formation of the adhesive layer and can make the thickness of the adhesive layer uniform.

[0009]

In order to achieve the above-mentioned object, the present invention provides a heat-resistant film having a uniform thickness on a surface of a heat-resistant film, which is hardly soluble in a solution by a curing treatment.
Hardly soluble in the aqueous resin solution and at least
Partially disperse the soluble fine powder, and then apply the heat-resistant resin liquid thereon and dry the resin liquid to form an adhesive layer on the heat-resistant film. A heat-resistant film is laminated on the insulating substrate in a state corresponding to the surface of the insulating substrate, and then an adhesive layer is formed by peeling off the heat-resistant film from the adhesive layer and curing the adhesive layer, and then using the solution described above. A dissolution treatment was performed on the surface portion of the adhesive layer, 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.

The heat-resistant resin constituting the adhesive layer has heat resistance,
Use a resin that has excellent electrical insulation properties, chemical stability, and adhesiveness, and has properties that make it hardly soluble in a dissolving solution (for example, an oxidizing agent such as an aqueous solution of chromic acid) by curing. It is particularly preferable that the resin is at least one selected from an epoxy resin, an epoxy-modified polyimide resin, a polyimide resin, and a phenol resin, and in some cases, imparts photosensitivity (particularly, ultraviolet curability) to these resins. It may be made to be.

As the heat-resistant resin liquid applied to the heat-resistant film, 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 used. Has a low viscosity, which makes it easier to apply to a heat-resistant film. As the solvent, methyl ethyl ketone, methyl cellosolve, ethyl cellosolve,
Tetralin, dimethylformamide and the like are used.

The material of the fine powder only needs to be at least partially soluble in the dissolving solution and hardly soluble or insoluble in the uncured heat-resistant resin solution, and itself is particularly excellent in heat resistance and electrical insulation. You don't have to. However, since the fine powder needs to be held near the interface between the uncured heat-resistant resin liquid and the heat-resistant film, a material whose specific gravity is 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 fine powder has an average particle size of 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. Further, the dissolution solution is appropriately selected depending on the material of the heat-resistant resin and the fine powder to be the adhesive layer, but generally, an aqueous solution of an oxidizing agent such as chromate, chromate, permanganate, and ozone is used. Particularly, a mixed acid aqueous solution of chromic acid and sulfuric acid is preferable.

[0014]

[Function] A curing treatment is applied to the surface of a heat-resistant film having a uniform thickness.
Difficult to heat-resistant resin liquids
Soluble and at least part of the solution
The adhesive layer is formed on the heat resistant film by spraying the soluble fine powder and then applying the heat resistant resin liquid thereon and drying the resin liquid, so that the adhesive layer has a uniform thickness. The formed and fine powder is held near the interface between the uncured heat-resistant resin and the heat-resistant film. Next, a heat-resistant film is laminated on the insulating substrate with the adhesive layer side corresponding to the surface of the insulating substrate, and when the heat-resistant film is peeled off from the adhesive layer and the adhesive layer is cured, the surface becomes slightly fine. An adhesive layer in which the powder is dispersed is formed on the insulating substrate. Next, a dissolving treatment is performed on the surface portion of the adhesive layer with a dissolving solution, and the soluble portion of the fine powder is dissolved and removed, so that many fine concave portions are formed on the surface of the adhesive layer. Since the fine powder is present only in the vicinity of the surface of the adhesive layer, the occurrence of pinholes during the dissolution treatment is reliably prevented unlike the related art.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below more specifically based on embodiments. The epoxy resin (trade name: TA-1800, manufactured by Mitsui Petrochemical Industries, Ltd.) was dried and cured in a hot air dryer at 160 ° C. for 1 hour and subsequently at 180 ° C. for 4 hours.
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. Also, an epoxy resin (manufactured by Yuka Shell Epoxy Co., Ltd .; E-807), a curing agent (Shikoku Chemical Industry Co., Ltd.)
2PZ) and a solvent (dimethylformamide) were stirred with a mixer to prepare a heat-resistant resin solution (specific gravity: 1.1, viscosity: 200 cps).

Next, a 50 μm thick PET (polyethylene terephthalate) as a heat-resistant film having a uniform thickness.
The fine powder 8 was sprayed on the film 7 (FIG. 1).
(A)). The fine powder 8 is sprayed on the PET film 7 at the falling position of the fine powder 8 blown off by the pressure of the compressed air.
It is performed by installing. After uniformly dispersing the fine powder 8 on the PET film 7, the heat-resistant resin liquid is applied on the PET film 7 using a roller coater so that the applied thickness is about 20 to 50 μm, and FIG. b)
An uncured layer 9 of a heat-resistant resin liquid as an adhesive layer is formed on the surface of the PET film 7 and dried at 80 ° C. for 5 minutes to volatilize the solvent as shown in FIG. Was formed. The fine powder 8 is held near the interface between the uncured layer 9 of the heat-resistant resin liquid and the PET film 7.

Next, as shown in FIG. 1C, the PET film 7 is thermocompression-bonded on the insulating substrate 1 with the uncured layer 9 of the heat-resistant resin liquid on the insulating substrate 1 side. Peeled off at this temperature for 5 hours at 120 ° C.
The uncured layer 9 was cured by heating and curing at 50 ° C. for 3 hours. As a result, the uncured layer 9 becomes a heat-resistant resin layer that is hardly soluble in the solution, and the adhesive layer 2 is formed on the surface of the insulating substrate 1 (FIG. 1D).

The insulating substrate 1 on which the adhesive layer 2 is formed is
The surface of the adhesive layer 2 was roughened by immersing it in a solution of a chromic acid aqueous solution (chromic acid 400 g / l) at 90 ° C. for 12 minutes. The heat-resistant resin layer constituting the adhesive layer 2 is hardly soluble in the dissolving solution, and the fine powder 8 existing near the surface thereof is soluble in the dissolving solution. It is dissolved and removed. Then, as shown in FIG. 1 (e), a large number of fine concave portions 5 after the fine powder 8 is removed are formed on the surface of the adhesive layer 2. Since the fine powder 8 is present only in the vicinity of the surface of the adhesive layer 2, the occurrence of pinholes at the time of dissolution is reliably prevented unlike the related art.

The present invention is not limited to the above-described embodiment. For example, instead of the PET film 7, a 0.1 mm thick aluminum plate or another resin having a uniform thickness and heat resistance may be used as the heat resistant film. A film or a metal foil may be used. Further, as shown in FIG. 2 (a), as shown in FIG. 2 (a), a mother particle 8a made of a heat-resistant resin fine powder which is soluble in a solution and cured, and a large number of adhered particles 8b adhered to the surface of the mother particle 8a 2 (b), pseudo particles (secondary particles) formed by aggregating a large number of fine particles 8c having substantially the same particle size as shown in FIG. 2 (b), or the same as described above as shown in FIG. 3 (a). Although pseudo particles composed of base particles 8a and a large number of adhered particles 8b adhered to the surface of the base particles 8a, pseudo particles composed of fine powder in which the adhered particles 8b are insoluble in a solution may be used. The average particle size of the pseudo particles is 10 μm or less,
Preferably, it is 5 μm or less. These pseudo particles are disclosed in JP-A-1-301774 and JP-A-1-30177.
No. 5, JP-A-2-8281.

Since the pseudo particles shown in FIGS. 2A and 2B are all soluble in the dissolving solution, when the pseudo particles are used, the entire pseudo particles are selectively dissolved from the adhesive layer 2 by the dissolving solution. After being removed, a large number of concave portions 5 having a complicated surface structure corresponding to the external shape of the pseudo particle are formed on the surface of the adhesive layer 2 as shown in FIG. On the other hand, when the pseudo particles shown in FIG. 3A are used, only the base particles 8a are selectively dissolved and removed from the adhesive layer 2 by the dissolving solution, and as shown in FIG. Are formed with a large number of concave portions 5 having a complicated surface structure in which the attached particles 8b protrude from the surface.
Further, after two kinds of fine powders 8 having different particle diameters are sequentially sprayed on the heat resistant film, a heat resistant resin liquid may be applied. In this case, even if a fine powder having a complicated structure such as a pseudo particle is not used, a part of the fine powders 8 having different particle diameters is brought into contact with the other fine powders 8 in the uncured layer 9. The concave portion 5 having a complicated shape is formed by performing the curing treatment of the uncured layer 9 and the dissolving treatment of the adhesive layer 2.

[0021]

As described above in detail, according to the present invention, the adhesive layer for the additive method, which is excellent in heat resistance, electric characteristics and adhesion between the insulating substrate and the electroless plating film, is uniformly formed on the surface of the insulating substrate. It can be formed with a small thickness and in a state where the generation of pinholes is reliably prevented, and the reliability of the full additive method can be improved.

[Brief description of the drawings]

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

FIGS. 2A and 2B are cross-sectional views of pseudo particles used in a modified example, and FIG. 2C is a partial cross-sectional view schematically showing an adhesive layer.

FIG. 3A is a cross-sectional view of another pseudo particle used in a modified example, and FIG. 3B is a partial cross-sectional view schematically showing an adhesive layer.

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

FIG. 5 is a cross-sectional view schematically showing a conventional adhesive layer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Insulating substrate, 2 ... Adhesive layer, 5 ... Depressed part, 7 ... PET film as heat resistant film, 8 ... Fine powder, 9 ... Uncured layer.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-50-141535 (JP, A) JP-A-61-263189 (JP, A) JP-A-61-276875 (JP, A) JP-A-63-263 126297 (JP, A) JP-A-63-245993 (JP, A) JP-A-64-47095 (JP, A) JP-B-60-14515 (JP, B1) (58) Fields investigated (Int. ⁷ , DB name) H05K 3/38 H05K 3/18 H05K 1/03

Claims (1)

(57) [Claims] 1. A heat resistant film which becomes hardly soluble in a dissolving solution by a curing treatment on the surface of a heat resistant film (7) having a uniform thickness.
Hardly soluble in the aqueous resin solution and at least
A partly soluble fine powder (8) is sprayed, and then the heat-resistant resin liquid is applied thereon and the resin liquid is dried to form an adhesive layer (9) on the heat-resistant film (7). After formation, a heat-resistant film (7) is laminated on the insulating substrate (1) with the adhesive layer (9) side corresponding to the surface of the insulating substrate (1). The adhesive layer (2) is formed by peeling the conductive film (7) and curing the adhesive layer (9), and then dissolving the surface of the adhesive layer (2) with the dissolving solution. (2) A method for forming an adhesive layer for an additive printed wiring board, wherein a soluble portion of the fine powder (8) near the surface is dissolved and removed to form a large number of recesses (5).