JP2943231B2 - Method of forming conductive pattern - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for forming a conductive pattern.

The conductive pattern is used as a printed wiring board, an electrode, a heating element, and the like.

2. Description of the Related Art Conventional methods for forming a conductive pattern include: (1) a method of printing a conductive paste, and (2) a copper-clad laminate as a starting material, an unnecessary portion being removed by etching or the like to leave a conductive pattern. Typical examples include an active method and (3) an additive method in which a plating resist (negative) is formed on a substrate and other portions are selectively plated.

However, the method (1) has low conductivity, low paste adhesion, low pattern accuracy, and high cost, and is not practical for conducting through holes in the field of printed circuit boards. And the solder heat resistance of the paste is poor.

In addition, the method (2) has a problem that the process is complicated, is not suitable for forming a fine pattern, and has a problem of plating adhesion at a through-hole portion, and the rationalization thereof has already reached the limit.

The method (3) eliminates the waste of removing unnecessary portions by etching, and responds to the demand for higher wiring density and higher wiring reliability. Since the layer is not patterned, the insulating property is low and it is difficult to obtain a fine pattern.Because the catalyst is also contained in the substrate, the insulating property is further low, the physical properties such as strength are inferior, the catalyst cost is low. There are problems such as high plating resistance, low plating adhesion, and need for roughening before plating.

SUMMARY OF THE INVENTION An object of the present invention is to improve the additive method, and to improve the adhesion of plating, simplify the process, and improve the pattern accuracy without roughening.

Means for Solving the Problems The method for forming a conductive pattern according to the present invention comprises applying a solution in which a photosensitive resin and a metal salt are dissolved in a common solvent to a substrate having a desired shape, pre-baking, exposing, developing, and post-baking sequentially. In forming a desired pattern by performing, in a step after pre-baking, a metal salt is treated with a reducing agent, and the reduced metal is used as a catalyst to form a conductive pattern by electroless plating. .

 This will be described in detail below.

The substrate of the present invention is selected depending on the application and is not particularly limited. For example, a copper-clad laminate, a metal plate, a plastic plate, a plastic film, a ceramic plate and the like can be mentioned.

The photosensitive resin used in the present invention may be of any type and type (negative type or positive type) as long as it is soluble in a common solvent with the metal salt and has an affinity for the metal salt. Examples of the photosensitive resin used include those generally used as a photosensitive resin, such as photosensitive polyimide, novolak resin with a photosensitive agent added, cyclized natural rubber, cyclized synthetic rubber, and polyvinyl cinnamate. , Polymethylisopropenyl ketone, polyvinylphenol, polyvinyl-p-azidobenzoate, polymethacryloyloxybenzalacetophenone, polyvinyl alcohol and the like.

The metal salt used in the present invention is one which exhibits plating catalytic activity by being reduced to a metal by a reducing agent as described below, and which is soluble in a common solvent with the photosensitive resin as described above. Or inorganic, especially inorganic metal salts are preferred. It is desirable that such a metal salt be stable to the atmosphere or moisture. Specific examples of metal salts that can be used in the present invention include iron, cobalt, nickel, copper, rhodium, palladium, silver, platinum, and sulfuric acid of metals of Group Ib and Group VIII of the periodic table of elements such as gold. Salts, nitrates, chlorides, organic salts (eg, acetates) and the like can be mentioned. These metal salts can be used alone or in combination of two or more.

The ratio of the metal salt to the photosensitive resin can be varied over a wide range depending on the physical properties required for the plating base coat and the type of the metal salt.
5 to 100 parts by weight per 100 parts by weight is preferred.

Examples of the common solvent for both the photosensitive resin and the metal salt include chloroform, methylene chloride, trichloroethylene, tetrachloroethylene, benzene, toluene, xylene, acetone, ethyl acetate, dimethylformamide, dimethylsulfoxide, dimethylacetamide, N-methylpyrrolidone, and the like. Singly or in a mixed solvent. It is appropriately selected according to the combination of the photosensitive resin and the metal salt used. The amount of the solvent to be used for the photosensitive resin is selected so as to have appropriate viscosity and fluidity and to be suitable for applying to a molded article.

A coating containing a metal salt is formed by applying a solution comprising a photosensitive resin, a metal salt, and a solvent to a substrate (upper) having an arbitrary shape. For application, a normal application method such as brush coating, spray coating, immersion and the like is selected according to the shape of the substrate.

The conditions (temperature, time) for forming the coating film are determined according to the type, concentration, thickness of the coating film and the like of the photosensitive resin. It is usually applied with a nonvolatile content of 5 to 20% by weight.

A mask (negative or positive film) is brought into close contact with the coating film thus obtained and irradiated with light. The amount of exposure at this time is a predetermined amount necessary for patterning according to the photosensitive resin composition used. And the amount can be appropriately determined according to the purpose.

The exposed coating film is patterned by developing using a dedicated developer, but unnecessary portions (unexposed portions in the case of a negative type) do not necessarily need to be dissolved and removed together with the resin. The target conductive pattern can also be formed by removing only the diffusion.

The reduction treatment is usually performed after post-baking (curing), but may be performed after each of the pre-baking, exposure, and development steps. By treating with a reducing agent, the metal salt in the coating film is intensively deposited on the surface, and an integrated reduced metal (plating catalyst) layer partially embedded in the coating film is formed. Since it is integrated in the coating film, the plating adhesion is very good, and since the metal is deposited and protruded on the surface, it is not necessary to particularly roughen it unlike the conventional additive method.

As the reducing agent used in the present invention, those which can reduce a metal salt to a metal, for example, FeSO ₄ , sodium hypophosphite, sodium borohydride, aminoborane, dimethylamine borane, hydroxylamine sulfate, hydrosulfite Etc. can be used.

These reducing agents are usually used as an aqueous solution, but are not limited as long as the solvent system can dissolve the reducing agent. The concentration of the reducing agent in the reducing agent solution can be appropriately changed depending on the purpose of use, but is about 0.01 to 20% by weight, preferably 0.05 to 10% by weight, more preferably 0.1 to 7% by weight.

This reduction can be easily carried out by immersing the substrate having the coating film containing the metal salt in the reducing solution for an appropriate time or spraying the reducing solution.

The reduction temperature is preferably about room temperature to 90 ° C., and the contact time with the reducing agent solution is suitably about several tens of seconds to about ten and several minutes. The coating may be preheated before reduction.

The solvent in the coating film may be completely removed before reduction, or may partially remain. In the case of a coating film from which the solvent has been completely removed, it is preferable to slightly raise the temperature of the reducing solution or preheat the coating film before reduction. Preheating improves the efficiency of reduction.

The reduction is usually performed until at least the metal salt present in the surface layer is almost completely reduced, but may be stopped halfway if necessary.

The pattern that has been plated is transferred to an electroless plating step to become a desired metal conductive pattern. As the electroless plating, a commonly used method may be selected according to the purpose, and for example, Ni plating, Cu plating and the like are typical.

In the method of the present invention, it can be obtained by appropriately selecting the type of the photosensitive resin and the metal salt to be used, and by changing operating conditions such as patterning (exposure and development) conditions, processing conditions with a reducing agent, and the like. The adhesion strength, hardness, plating catalyst activity and the like of the plating base coat can be adjusted according to the purpose.

 Next, the present invention will be described specifically with reference to examples.

EXAMPLES Example 1 Negative photosensitive polyimide “Lisocoat PI” manufactured by Ube Industries, Ltd.
−400 ”(100 parts by weight), CoCl ₂・ 6H ₂
O. 24.75 parts and PdCl ₂ 0.25 parts were N-methylpyrrolidone (NM
P) It was added and dissolved in the form of a solution to obtain a mixed solution (resin concentration 5 wt%).

This mixed solution was formed on a glass plate by “San Ever B4
After coating on a film of "10" (Nissan Chemical Industries polyimide varnish), the film was prebaked (dried) at 65 ° C for 2 hours. A stainless steel mask was brought into close contact with the pre-baked coating film (5 μ) and exposed with a mercury lamp (ultraviolet light) (exposure amount 1 J / c).
m ^2).

After the exposure, the film is immersed in a dedicated developer (organic solvent system, 25 ° C.) for 5 minutes to obtain a developed pattern.
Stage: ethanol solution containing 5% N-methyl-2-pyrrolidone, second stage: ethanol) for 1 minute each.

The obtained pattern was heat-treated at 160 ° C. for 30 minutes and 230 ° C. for 30 minutes, immersed in a 0.5% aqueous sodium borohydride solution for 5 minutes, reduced, washed with water, and washed with Nihon Kanigen Ni plating solution “S6
80 "(50 ° C) for 5 minutes.

Nickel began to gradually precipitate in about 30 seconds after immersion in the plating solution, and after 5 minutes, a conductive pattern having a metallic luster was obtained.
The surface resistance of the conductive portion was 100Ω / □, and the mask portion showed insulation. Adhesion and pattern accuracy were also good.

Example 2 In Example 1, except that the reduction treatment was performed after the development rinse,
A pattern (plating underlayer) was obtained under the same conditions. This was similarly immersed in a Ni plating solution for 3 minutes. About 5 seconds after the immersion, nickel began to be precipitated from the entire surface of the pattern at the same time, and after 3 minutes, the same electric power pattern was obtained. The surface resistance of the conductive part was 10Ω / □, and the mask part showed insulation. Adhesion and pattern accuracy were also good.

Example 3 The plating base pattern obtained in Example 2 was applied to a copper plating solution manufactured by Meltex (room temperature) "Enplate Cu-406".
Soak for minutes. Copper begins to precipitate in about 5 seconds after immersion.
Minutes later, a copper-gloss conductive pattern was obtained. The surface resistance of the conductive part was 1Ω / □, and the mask part showed insulation. Adhesion and pattern accuracy were also good.

Example 4 A mask (negative film) made of convex plate printing was adhered to the same prebaked coating film as in Example 1, sandwiched between Pyrex glass plates, and exposed with a metal halide lamp (exposure amount 2J).
/ cm ² ). After the exposure, the pattern was obtained by performing an ultrasonic development process in a dedicated developer for 3 minutes. Thereafter, the pattern was nickel-plated under the same conditions as in Example 2. A clear conductive pattern was obtained in a pattern having a line width of 50 μ or more, and the conductivity was good.

Example 5 NiCl ₂ .6H ₂ O 25PHR was added to and dissolved in an acrylic resin-based negative etching resist “PMER N-D40P” manufactured by Tokyo Ohka in the form of a dimethylformamide (DMF) solution. This mixture is applied on a glass epoxy substrate and
Prebaked at 30 ° C for 30 minutes to form a coating film.

A mask was brought into close contact with this coating film and exposed with a mercury lamp (exposure amount: 1 J / cm ₂ ). After exposure, the film was developed for 3 minutes by immersion rocking method in a dedicated developer "N-A5" (alkali aqueous solution, 25 ° C.).

After rinsing (washing) the obtained pattern, it was post-baked at 120 ° C. for 30 minutes, and subsequently immersed in a 0.5% aqueous sodium borohydride solution for 3 minutes to reduce metal salts to form a plating base. Thereafter, nickel plating was performed under the same conditions as in Example 1 to obtain a conductive pattern. Adhesion and pattern accuracy were also good.

Example 6 Tokyo Ohka Kogyo Co., Ltd. of novolak resin based positive type etching resist "PMER P-DF40S" was CoCl ₂ · 6H ₂ O 25PHR, and added dissolved mixture with DMF solution. This mixed solution was applied on a glass plate and prebaked at 90 ° C. for 30 minutes to form a coating film. A mask was brought into close contact with this coating film and exposed with a mercury lamp (exposure amount: 1 J / cm ² ).

Post-exposure dedicated developer "P-1S" (alkali aqueous solution, 25
C.) for 3 minutes by the immersion rocking method. After rinsing (washing) the obtained pattern, it was post-baked at 140 ° C. for 10 minutes, and immersed in a 0.5% sodium borohydride aqueous solution for 3 minutes to reduce metal salts, thereby forming a plating base. Thereafter, copper plating was performed under the same conditions as in Example 3 to obtain a conductive pattern. Adhesion and pattern accuracy were also good.

The present invention makes it possible to obtain a conductive pattern by a simple method. The conductive (plating) layer is easily peeled off like a conventional electroless plating layer, even though the base material is not roughened, because the catalyst layer integrated with the photosensitive resin coating film is used as a base for plating. There is no fear. The application, development, reduction, and plating can be performed by immersion, and the shape and size of the substrate to be treated are not limited, and a conductive pattern can be formed on any substrate according to the purpose.

In addition, since it is easy to adjust the adhesion strength, hardness, plating catalyst activity, and the like of the plating base coating film according to the purpose, various metal platings are possible. In addition, since reduction and plating can be performed by treatment at a relatively low temperature (normal temperature to 90 ° C.), there is little possibility that the original physical properties of the coating film will be adversely affected.

Further, a negative photosensitive resin (eg, photosensitive polyimide)
In the above, when only the metal salt is removed from the unexposed portion during development, the metal salt can be used as it is as an insulating coating film. This is also effective for forming a (ultra) fine pattern and for maintaining the coating film adhesion.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-37196 (JP, A) JP-A-60-120589 (JP, A) JP-A-60-120590 (JP, A) JP-A-60-120 165787 (JP, A) JP-A-63-304693 (JP, A) JP-A-63-304694 (JP, A) JP-A-2-10362 (JP, A) JP-A-2-260691 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) G03F 7/40 H05K 3/18

Claims (3)

(57) [Claims] 1. A photosensitive resin composition obtained by dissolving a photosensitive resin and a metal salt in a common solvent is applied to a substrate by (a) coating, (b) prebaking, (c) exposure, (d) development, and (e) post. In forming a desired pattern by sequentially performing baking, a reduction treatment is performed after any one of the steps (b), (c), (d), and (e), and thereafter, electroless plating is performed. Characteristic conductive pattern forming method. 2. The method according to claim 1, wherein the reduction treatment is performed after the developing step (d), and is performed by immersion in an aqueous solution in which a reducing agent is dissolved. 3. The method according to claim 1, wherein the metal salt is selected from groups Ib and VII of the periodic table.
The method according to claim 1 or 2, wherein the method is a salt of a metal selected from Group I.