JPH05191019A - Solder pattern forming method - Google Patents

Abstract

PURPOSE:To form a solder circuit pattern by a method wherein an adhesive resin pattern is formed, and soldering powder is selectively made to adhere to the necessary part only utilyzing the stickiness of the above-mentioned resin. CONSTITUTION:Polymethyl methacrylate/butyl acrylate copolymer resin, having the glass transition point of 100 deg.C and molecular weight of about 60,000, polymerized rosin, trimethylpropane triacrylate, benzophenone, ethyl Michler's ketone and benzil dimethyl ketal are dissolved into acetone, and a 30% solution is formed. This solution is applied to a glass epoxy board and dried up. Then, after 25-micron polyester film has been laminated, it is closely contacted in vacuum state with the original pattern film for formation of a solder circuit and exposed. A polyester film is peeled off, eutectic solder powder is splinkled on the surface of a photosensitive resin layer, and a solder grain pattern, which is stuck to the non-exposed part, is obtained. Subsequently, post flux is sprayed on the whole surface of the board, and after the board has been heated up, it is washed.

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 a solder pattern on a copper circuit of a printed circuit board or a ceramic substrate (hereinafter referred to as "circuit board").

[0002]

2. Description of the Related Art In recent years, various electronic components are mounted on electronic circuit boards, and the packaging density has been dramatically improved. As a method of mounting these electronic components, they are often connected to a copper circuit by soldering. As a method of forming a solder pattern on a conductor circuit of copper, silver, silver palladium, etc. of a conventional circuit board, using a solder paste in which solder particles are kneaded with a rosin resin or the like, a pattern is obtained by a screen printing method or the like, Furthermore, a method of melting the solder has been adopted. As another method, a method has been proposed in which lead organocarboxylate and tin particles are kneaded, coated on the entire surface of a circuit board, and then heated to deposit the solder only on the conductor circuit (Nikkei Electronics NO. 528, P. 2
45-250, 1991.5.27).

[0003]

The conventional method for forming a solder pattern on a conductor circuit has the following problems. That is, the solder paste method based on the screen printing method has a limit in the printing accuracy of the screen printing, and cannot meet the demand for high definition in the industrial world. According to this method, the limit is generally 300 μm pitch. Further, since the solder particles and the flux are integrated, deterioration with time tends to occur. Although it is said that the method of depositing solder by using the organic lead carboxylate and tin particle system can achieve high definition, the degree of freedom of the composition of the deposited solder is not so large and the solder composition is limited. The industry has various demands, for example, bismuth-containing and silver-containing solder as well as eutectic. Furthermore, it is necessary to strictly control the heating conditions, which makes management difficult in practice. Furthermore, there is a problem in that solder is generated in addition to the circuit, and there is much waste. The present invention provides an effective method for solving all of these problems.

[0004]

The substrate used in the present invention is for forming an electric circuit, and may be either a resin substrate or a ceramic substrate, but a substrate on which a conductor circuit is previously formed is used. To do. The method of forming the copper circuit may be any known method. The adhesive resin used in the present invention needs to have adhesiveness at room temperature, and in order to obtain an adhesive resin pattern, a method of using two kinds of photosensitive resin and non-photosensitive resin is provided. The photosensitive adhesive resin pattern forming method is a method in which the resin layer is formed on the entire substrate by coating or the like, and then the adhesiveness of the light irradiation portion is eliminated through pattern original image exposure. The non-photosensitive adhesive resin pattern forming method is a method in which the adhesive resin is formed into a so-called ink together with a liquid compound such as an organic solvent and a plasticizer and is obtained by a printing method such as screen printing or transfer printing. For the adhesive resin pattern obtained by any of the above methods, after attaching solder particles of a predetermined particle size, apply flux and solder in a heating furnace at a temperature sufficient to melt the solder particles. To obtain the desired solder pattern. The present invention will be clarified in detail below.

The photosensitive adhesive resin must have the property of losing its adhesiveness upon irradiation with actinic rays, and the compound is not particularly limited. As an example, it is possible to select a material having a film-forming resin as a basic compounding with a monomer having an unsaturated bond and a reactive group and a photoreaction initiator. As the resin, an acrylic resin, an epoxy resin or the like can be used. Acrylic monomers and epoxy monomers having a double bond are effective as the monomers. The photoreaction initiator can be selected from known materials, and examples thereof include benzophenone, benzoin and its derivatives, benzyldimethylketal, and triarylsulfone salt. Addition of other liquid components such as a plasticizer or a tackifier to impart tackiness is also effective. Addition of a component effective as a so-called solder flux to the adhesive photosensitive resin is extremely effective for adhesion to the underlying circuit metal when the solder is melted. For example, it can be selected from rosin resin, various amines and salts thereof, various carboxylic acids and salts thereof, and the like. It is effective to add 1% by weight or more of the flux component. If it is less than 1% by weight, its action becomes poor.

[0006] If the blending ratio of the photosensitive resin having tackiness used in the present invention is shown, a copolymer of polymethylmethacrylate and butylacrylate 35 to 45 parts by weight, polymerized rosin 15 to 25 parts by weight, trimethylolpropane triacrylate. 30-40 parts by weight, benzophenone 2-5 parts by weight, ethyl Michler's ketone 0.
An example is one in which 3 to 1 parts by weight and 1 to 2 parts by weight of benzyl dimethyl ketal are dissolved in acetone to form a 30% solution.

The above components are dissolved or dispersed in an organic solvent at an appropriate concentration according to the method of use, and then directly coated on a circuit board and dried, or previously coated and dried on a support such as a polyester film. The obtained product may be laminated on a circuit board. The adhesive photosensitive resin also includes those which are liquid at room temperature. In this case, of the above components, so-called solventless photosensitive resins mainly composed of monomers can be used. As a coating method, a known method such as a roller coater or various printing methods can be used. The thickness of the adhesive photosensitive resin needs to be appropriately increased or decreased depending on the solder particle size, the solder film thickness, and the solder circuit definition. In general, when the particle size is 1 micron or less, the photocurability is poor in a normal irradiation light source device, and irradiation with an inert atmosphere may be required.

It is desirable that the non-photosensitive adhesive resin contains a so-called flux component in the solid content of 1% by weight or more in the resin component exhibiting the adhesive property like the above-mentioned photosensitivity.
Examples of the flux component include rosin resin, various amines and salts thereof, and various carboxylic acids and salts thereof. The non-photosensitive adhesive resin is obtained by forming a component containing 1% by weight or more of at least one of these components together with a liquid compound such as an organic solvent or a plasticizer and, if necessary, a tackifier into a so-called ink. .. An adhesive resin pattern is obtained by a printing method such as screen printing or transfer printing using the ink thus obtained.

If the blending ratio of the non-photosensitive adhesive resin is shown,
An ink-like material is obtained using 20 to 50 parts by weight of a rosin resin, 1 to 10 parts by weight of an organic acid, 20 to 50 parts by weight of butyl cellosolve, and 1 to 5 parts of a cellulose derivative.

Solder particles having various compositions can be selected. For example, eutectic solder, bismuth-containing solder, silver-containing solder, or the like can be used. The shape can be selected from a wide range such as spherical and amorphous. The grain size is appropriately selected depending on the required solder film thickness and the circuit definition. Generally, a small particle size is used when high definition is required, and a large particle size is used when a thick film thickness is required, but solder particles having a minimum diameter of 5 microns and a maximum of 200 microns are used in terms of spherical diameter. When the thickness is 5 microns or less, the solder film thickness does not reach a practical level, which is not preferable, and when the thickness is 200 microns or more, it is not suitable for obtaining a high-definition pattern.

As a method of selectively attaching solder to the adhesive resin pattern, it suffices to place the solder powder on the substrate. By vibrating lightly, the solder powder other than the adhesive resin part can be easily removed. After applying solder powder only to the adhesive resin part, applying flux and heating to a temperature above the melting point of the solder,
It melts into a solder circuit pattern.

It is extremely important and essential to apply various fluxes onto the solder particles after the solder particles are attached and before the solder is melted. That is, the surface of the solder particles having the particle diameter of the present invention used for obtaining a high-definition pattern is easily covered with the oxide film and is necessary for preventing the melting trouble during heating. As the flux, a solder paste flux or a post flux can be used. As the light source used for the exposure of the solder pattern original image, a lamp suitable for the sensitivity of the photosensitive resin is used, and generally, a mercury lamp, a metal halide lamp, a xenon lamp and the like can be used. A commercially available general heating furnace can be used as the heating device used for melting the solder.

[0013]

The present invention is to form a solder circuit pattern by forming a resin pattern having an adhesive property and selectively adhering solder powder only to a necessary portion by utilizing the adhesive property of the resin.

[0014]

Embodiment 1 Next, an embodiment of the present invention will be described with reference to FIG. Adhesive photosensitive resin solution A having the following composition was prepared. Glass transition point 100
℃, polymethylmethacrylate with a molecular weight of about 60,000 /
Butyl acrylate copolymer resin 40 parts, softening point 135 ° C
Polymerized rosin (20 parts), trimethylolpropane triacrylate (35 parts), benzophenone (3 parts), ethyl Michler's ketone (0.5 parts) and benzyldimethyl ketal (1.5 parts) were dissolved in acetone to give a 30% solution. This solution A was applied onto a glass epoxy substrate on which a copper circuit was formed and dried to obtain an adhesive photosensitive resin layer of about 10 microns (Fig. 1).
(See (a)).

Next, in order to prevent adhesion between the pattern original image and the resin layer and laminate a 25 micron polyester film in order to enhance air curing, the film is vacuum-contacted with the solder circuit forming original image film, and it is about 25 at a distance of 90 cm by a 3 Kw mercury lamp.
Second exposure was performed (see FIG. 1 (b)). The polyester film was peeled off, and eutectic solder powder having an average particle size of about 20 microns was sprinkled on the surface of the photosensitive resin layer to obtain a solder particle pattern attached to the unexposed portion (see FIG. 1 (c)). Then, a commercially available post flux is sprayed on the entire surface of the substrate to make the substrate 25
After heating on a 0 ° C. hot plate for about 1 minute, cleaning was performed to obtain a highly precise solder pattern having a resolution of 80 μm pitch solder thickness of 20 μm (see FIG. 1D).

Example 2 50 parts by weight of a rosin resin having an acid value of 170 and a softening point of 135 ° C. was dissolved in 30 parts by weight of butyl cellosolve, and further 5 parts by weight of a fatty acid amide wax, 5 parts by weight of caprylic acid, and an acrylic resin were used as rheology adjusting agents. The mixture was kneaded with 1 part by weight of a foaming agent to obtain an adhesive resin ink for screen printing. The ink is screen-printed through a 300 mesh polyester gauze on a portion of the substrate where solder is required to form a film having a thickness of 10 to 15
A micron tacky resin pattern was obtained. After depositing a solder powder having an average spherical diameter of 100 microns on the pattern,
Apply commercially available post-flux and solder powder to 250
℃, 1 minute to melt on a hot plate, solder thickness 80
A solder pattern was obtained that resolved a ~ 300 micron pitch.

[0017]

The effects of the present invention will be described below. According to the present invention, an adhesive resin pattern can be obtained with high precision by a photosensitizing method and a printing method, and a solder pattern can be formed by attaching solder powder corresponding to the pattern. Solder particles can be used from small to large.
The use of large particles improves the manufacturing yield of solder particles and
Since its specific surface area is small, flux with weak activity can be used, which is good in terms of circuit corrosion. The conventional solder paste has a limit in particle size used for both large and small sizes. That is, the small particles are apt to be oxidized and deteriorated in the paste, and the large particles are poor in the removal property of the screen. Solder particles and flux are separate and can be used stably without deterioration over time.
A solder composition suitable for the purpose can be used. Not only eutectic but also bismuth-containing, silver-containing, etc. can be freely selected. After melting the solder, a solder pattern can be obtained without any special post-treatment.
According to the present invention, a solder pattern can be reliably formed on a fine conductor circuit. It is apparent that the effects of the above-described invention have advantages that cannot be obtained by other methods such as the conventional solder paste method.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a step of a pattern forming method according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Copper circuit 3, 3'Adhesive photosensitive resin layer 4 Polyester film 5 Solder pattern original image 6 Actinic ray 7,7 'Solder 8 Solder

Claims (4)

[Claims] 1. A resin layer pattern having adhesiveness is formed on a conductor circuit of a circuit board, solder particles are selectively adhered to the surface of the adhesive resin pattern, and flux is further applied to the surface of the solder particles before soldering. A method for forming a solder pattern, which comprises heating at a temperature sufficient for melting particles. 2. The solder pattern forming method according to claim 1, wherein the adhesive resin layer is a photosensitive adhesive resin. 3. The solder pattern forming method according to claim 1, wherein the adhesive resin layer pattern is formed by a printing method. 4. The solder pattern forming method according to claim 1, wherein the size of the solder particles is in the range of 5 μm to 200 μm in terms of spherical diameter.