JP3058882B2 - Composition for temporary surface coating - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a temporary surface coating composition for forming a solder mask for manufacturing a printed wiring board.

(Prior art)

In recent years, in mounting a printed wiring board having components mounted on the printed wiring board, the density of mounting has been rapidly increasing. In particular, the spread of printed wiring boards equipped with VLSIs, which have recently attracted attention, and the use of surface-mounting boards with surface-mounting technology, has led to the progress of thinner wiring patterns on printed wiring boards and the reduction in the area of soldering lands. .

Further, these high-density printed wiring boards have been increased in size, and the mounting of components or the efficiency of devices have been promoted.

However, as such printed wiring boards have become finer and larger, there has been a great problem in forming solder mask patterns. This is because even if the solder mask ink (solder resist ink) is printed and applied on the printed wiring board by the conventional screen printing method, the ink does not enter between the patterns due to the narrow pattern interval, and the screen openings If the ink is inserted between the patterns by increasing the size of the ink, the solder mask ink will adhere to the through holes and solder lands that require soldering. In the latter case, soldering defects and the like occur, and many of these defects occur due to the increase in the density of the pattern and the size of the printed wiring board.

As a method of solving these problems, a solder mask pattern forming method using a photographic method (photolithography method) which has been employed in the circuit pattern forming method of a multilayer printed wiring board since about 1976 instead of the above screen printing method. Came to be adopted. A method of forming a solder mask pattern by photolithography involves forming a photosensitive film with a protective film called a cover film having a thickness of 25 μm on a printed wiring board, and then forming a negative (or positive) film having a thickness of 170 μm on the protective film. ) Adhesion of the film in a vacuum, exposure and development (using EIdu Pont dry film solder resist "Bacrel") and liquid photosensitive film formed on the printed wiring board and the liquid coating When
A method of exposing and developing by placing a negative (or positive) film at an interval of 300 μm to 1000 μm (Accutrace method of WRGrace, USA) and forming a photosensitive film on printed wiring, and then forming a 170 μm thick film on the photosensitive film A negative (or positive) film is adhered in a vacuum and exposed and developed (Provimer method of Ciba Geigy, Switzerland).

However, the solder mask forming method using these photographic methods requires low exposure of light used for exposure and takes a long time for exposure, and uses an exposure machine that improves the parallelism of light beams to improve pattern resolution. This has become a major problem in terms of productivity and capital investment costs.

〔Purpose〕

The present invention is based on the conventional screen printing method and high resolution PCB.
This is a temporary surface coating composition that enables the formation of a manufacturing solder mask pattern.

〔Constitution〕

The present inventor has conducted intensive studies to achieve the above object, and as a result, has found a temporary surface coating solution composition mainly composed of an alkali-soluble or solvent-soluble resin (a), a polymerization inhibitor (b) and a solvent (c). It has been confirmed that a high-resolution solder mask for manufacturing a PCB can be easily formed by a conventional screen printing method.

That is, a reverse pattern image of a solder mask is formed in advance on the soldering portion on the printed wiring board on which the conductive circuit is formed with the temporary surface coating composition of the present invention, and then the photocurable solder mask composition is coated A method in which a solder mask pattern is formed on a printed wiring board by directly applying light to the entire surface or a required portion of the printed wiring board including a pattern, irradiating light from above, and then performing development processing with a solvent or an aqueous alkali solution. It can be provided.

By using the composition for temporary surface coating of the present invention, productivity equal to or higher than screen printing can be obtained, and resolution is better than conventional screen printing. There is no need to invest in a huge amount of equipment just by adding facilities.

The resin component in the temporary surface coating composition of the present invention has such a property that the coating film formed by the composition is dissolved or swelled by a solvent or a low-concentration aqueous alkaline solution and the coating film can be removed cleanly. If so, any resin component can be used. Solvent-soluble resins include phenolic, xylene, urea, melamine, epoxy, alkyd, vinyl, acrylic, chloride rubber, cyclized rubber, polyamide, terpene, butyral, ketone and Cellulose derivatives and the like can be mentioned, but thermoplastic resins such as vinyl-based, rubber-based and cellulose derivatives are preferred.

Examples of the alkali-soluble resin include a novolak resin, a rosin resin, a rosin-modified resin, and a carboxyl-containing polymer. These resins are simultaneously solvent-soluble and are all preferred.

The rosin-modified resin is a resin represented by a rosin-modified maleic resin, and is usually a resin modified by reacting rosin with an acid or alcohol.

Carboxyl group-containing polymer is a polymer containing a carboxyl group in the polymer chain, acrylic acid, methacrylic acid, a polymer or copolymer of monomers such as maleic acid, acrylic acid ester, polymer of methacrylic acid ester Or a copolymer. Commercially available products include JONCRYL (styrene-acrylate copolymer) manufactured by Johnson Corporation and SMA (styrene-maleic acid copolymer) manufactured by Alco Chemical Company.

The novolak resin refers to a phenol resin, a crezone resin, and an alkylphenol resin that are soluble in an aqueous alkaline solution.

Next, typical examples of the polymerization inhibitor (b) include hydroquinone pt-butylcatechol or mono-t.
Hydroquinones such as -butylhydroquinone, phenols such as hydroquinone monomethyl ether or di-t-butyl-p-cresol, quinones such as p-benzoquinane, naphthoquinone or p-toluquinone, or ammonium N-nitrosophenylhydroxylamine Salts and chelates thereof, such as aluminum, copper and zinc, and copper salts such as copper naphthenate, can be mentioned. The mixing ratio of the resin (a) and the polymerization inhibitor (b) is 95: 5 to 5:95 by weight, preferably 65:35 to 35:65, and particularly preferably 50:50. When the amount of the resin (a) is large, the polymerization inhibiting effect is poor and an image needs to be formed by using strong mechanical polishing in developing the solder mask. Therefore, the surface of the solder mask is deeply scratched and the reliability of the coating film is reduced. When the amount of the resin is too small, the suitability for screen printing is lost, and at the same time, it takes time to dissolve the alkali in the temporary surface coating composition, resulting in poor productivity.

The solvent (c) dissolves the resin (a), and a known organic solvent corresponding to the resin to be used is used. Typically, toluene, aromatic hydrocarbons such as xylene, methanol, alcohols such as ethanol, ethyl acetate,
Examples include esters such as butyl acetate, ethers such as 1,4 dioxane and tetrahydrofuran, ketones such as methyl ethyl ketone, and glycol derivatives such as cellosolve, cellosolve acetate and carbitol.
The content of these organic solvents is not particularly limited, but 10 to 40
% Is preferred.

Further, as a filler for imparting screen printability of the temporary surface coating composition of the present invention, those used as general resin fillers such as silicon dioxide, silicon aluminum, magnesium silicate, aluminum hydroxide, and barium sulfate. use. The amount used is (a) (b)
3 to 90%, preferably 10 to 30%, based on the total amount of (c)
And the average particle size is preferably 15 μm or less.

In addition to the composition of the present invention, various additives usually used for screen printing resists, for example, fillers, chiquity agents, leveling agents, coloring agents, defoaming agents (for example, fluorine-based surfactants) may be added. Can be.

Next, examples of the present invention will be described. The examples shown here illustrate embodiments of the present invention and are not intended to be limiting. [%] In the examples is [% by weight].

〔Example〕

Example 1 Rosin-Modified Maleic Resin 34.0% Hydroquinone 20.0 Butyl Cellosolve 22.0 Colloidal Silica (Aerilil # 300, manufactured by Nippon Aerosil Co., Ltd.) 4.0 Varifast Blue (colorant) 3.0 Talc (average particle diameter 10μ) 15.0 Fluorosurfactant (Sumitomo) 3M Florard FC
-430) 2.0 A temporary surface coating composition was prepared with the above formulation.

The composition of the present invention is screen-printed on an etched copper foil of a printed wiring board with a reverse pattern of a solder mask and dried. Next, a solder mask (epoxy acrylate based Tamura Kaken USR-2G) using a conventionally known radical polymerizable ethylenic double bond as a photosensitive component is formed using a screen printing method for forming the solder mask. Print directly on the entire surface. After printing, the solder mask is cured by exposing for 3 seconds with an ultraviolet irradiation device (illuminance: 300 mW / cm ² ) operated by screen printing. Since the photosensitive film of the solder mask formed here contains an unsaturated group having an ethylenic double bond, the portion in contact with the pattern of the temporary surface coating composition does not cure even when exposed.

Next, when developed with a 5% aqueous sodium hydroxide solution, the solder mask in contact with the temporary surface coating composition and the temporary surface coating composition were removed at room temperature in about 15 seconds, and an image of the solder mask was obtained. After development, post-curing is not required, but ultraviolet curing or heat curing may be used in combination.

COMPARATIVE EXAMPLE 1 A temporary surface coating composition was prepared in the same manner as in Example 1 except that hydroquinone was changed from 20% to 1%, and similarly developed with a 5% aqueous sodium hydroxide solution, but no solder mask image was formed.

Example 2 Styrene-acrylate resin 38.0% Paramethoxyphenol 15.0 Phthalocyanine blue 2.0 Aeriel # 300 10.0 Silicone defoamer 2.0 Tetraline 10.0 Butyl cellosolve 23.0 A composition for temporary surface coating was prepared with the above composition.

After printing the present invention on a copper foil in the same manner as in Example 1, a solder mask was spray-coated and applied over the entire surface. UV after coating
Exposure was performed in a furnace for 3 seconds to cure the solder mask. Next, it was developed with methylene chloride and an image of the solder mask was obtained in 12 seconds.

〔effect〕

As described above, by using the composition for temporary surface coating of the present invention, it is possible to form a solder mask which is equivalent in productivity to a conventional screen printing method but has much higher resolution.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-264783 (JP, A) JP-A-62-45677 (JP, A) JP-B-60-30243 (JP, B2) (58) Field (Int.Cl. ⁷ , DB name) H05K 3/28 C09D 5/20

Claims (1)

(57) [Claims] 1. A composition for temporary surface coating comprising as a main component an alkali-soluble or solvent-soluble resin (a), a polymerization inhibitor (b) and a solvent (c).