JP3202774B2 - Solder pattern transfer film and method of manufacturing the same - 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 transferring a solder pattern onto a conductive circuit such as a printed circuit board, a ceramic substrate or a metal substrate.

[0002]

2. Description of the Related Art In recent years, electronic circuit boards have various electronic components mounted thereon, and the mounting density has been dramatically increased. As a method of mounting these electronic components, a method of connecting the components by soldering mainly on a copper circuit has been widely adopted. Conventionally, as a method of forming a solder pattern on a conductor circuit such as copper, silver, silver palladium of a circuit board, using a solder paste obtained by kneading solder particles with a rosin resin or the like,
A method of obtaining a pattern by a screen printing method or the like and further melting the solder is employed. As another method, there has been proposed a method in which lead organic carboxylate and tin particles are kneaded, applied to the entire surface of a circuit board, and then heated to deposit solder only on a conductor circuit (Nikkei Electronics No. 528). , P.245-250, 1991.5.2.
7). Alternatively, a solder plating method or a preform soldering method in which a foil-like solder is formed in a predetermined shape is also used.

[0003]

The prior art method for forming a solder pattern on a conductive circuit has the following problems. That is, the thickness of the pattern formed by solder plating is usually 10 μm or less, which is insufficient for mounting components, tends to cause segregation of solder alloy components, and it is difficult to obtain a solder pattern having a predetermined solder alloy composition. is there. In the case of solder paste application by screen printing, there is a limit in terms of plate releasability, it is difficult to form a high-definition pattern with a pattern pitch of 300 μm or less, and the solder paste itself is easily deteriorated with time. It has the disadvantage of high screen manufacturing costs. It is difficult to adopt a free pattern shape for the preform solder due to the limitation of the forming method, and it is difficult to quickly and accurately mount a large number of preform solders at predetermined positions on the substrate. The present invention provides an effective means for solving all of these problems.

[0004]

The present invention employs a means for forming a film having a circuit pattern in which solder powder is adhered to the surface of a flexible film via an adhesive resin layer. The film of the present invention is a resin, rubber, paper, cloth, metal foil,
A thin film or a composite material of these or a material obtained by applying an adhesive resin to the surface of a flexible planar body (hereinafter, referred to as a "flexible film") reinforced with glass fibers or metal wires is used as a raw film. . It is desirable to form a thin film of a silicone resin or the like on the application surface side of the flexible film so that the flexible film can be easily peeled off in a later step.

The adhesive resin is not particularly limited, but it is necessary that the adhesive resin has adhesiveness at room temperature or has a property of exhibiting adhesiveness when heated. Further, a material that can form a fine pattern by printing or the like is selected. For example, photosensitive resin is convenient because a fine pattern can be formed by mask work. As the adhesive resin, for example, a resin obtained by appropriately mixing a rosin resin, an acrylic resin, a rubber resin, a plasticizer, and the like in a solvent is used. Further, it is preferable to contain an activator component effective for adhesion diffusion at the time of solder melting from the viewpoint of affinity with metal. For example, various amines or their salts, various carboxylic acids or their salts and the like can be mentioned. The flux component is 1 to 1 in the entire adhesive resin.
It is effective to add about 20% by weight. If one example of the composition of the adhesive resin is shown, rosin is 1 to 95 parts by weight,
Rosin ester 1 to 95 parts by weight, cyclohexylamine hydrochloride 1 part by weight, and propylene glycol monobutyl ether 5 to 50 parts by weight as a solvent.

[0006] As an example of a method of attaching the adhesive resin to the surface of the flexible film, a required pattern can be obtained by a printing method such as a screen printing method and an offset printing method.
The thickness of the adhesive resin can be made much smaller than the thickness of the cream solder, and is usually used in the range of 1 to 100 microns. The reason is that the solder particles adhere only to the resin surface. In general, the required resin film thickness increases as the solder particle diameter increases, and decreases as the particle diameter decreases. As described above, since only the resin pattern is formed first and the film thickness is small, a high-definition pattern can be formed as compared with the cream solder method. Therefore, various problems encountered with the cream solder at the time of printing, for example, problems such as sagging, bleeding, and plate missing during printing are remarkably improved.

[0007] The tacky photosensitive resin has tackiness at room temperature or when heated, and the property of eliminating the tackiness upon irradiation with actinic rays is essential, and the compound is not particularly limited. As an example, a material having a basic composition of a monomer having an unsaturated bond or a reactive group and a photoreaction initiator in a resin capable of forming a film is used. Acrylic resin, epoxy resin, or the like can be used as the resin. As monomers, acrylic monomers and epoxy monomers having a double bond are effective. Examples of the photoreaction initiator include benzophenone, benzoin and derivatives thereof, benzyldimethyl ketal, and triarylsulfonium salts. Alternatively, a modified rosin resin in which rosin is modified to give a photoreactive salt can also be used. The addition of other liquid components, such as plasticizers or tackifiers, is also effective for imparting tackiness. When a component effective as a so-called solder flux is added to the adhesive photosensitive resin, an action of removing the solder particles and an oxide film on the surface of the circuit metal at the time of melting of the solder works to enhance the solderability. As the flux, for example, there is a rosin-based resin,
Furthermore, various amines and salts thereof, various carboxylic acids and salts thereof, and the like may be added as an activator.

Preferred examples of the adhesive photosensitive resin are shown below. 35-45 parts by weight of copolymer of polymethyl methacrylate and butyl acrylate, polymerized rosin
15 to 25 parts by weight, trimethylolpropane triacrylate 30 to 40 parts by weight, benzophenone 2 to 2
5 parts by weight, 0.3 to 1 part by weight of ethyl Michler's ketone, and 1 to 2 parts by weight of cyclohexylamine hydrochloride are dissolved in acetone to prepare a 30% solution.

Using these materials, a flexible film is irradiated with actinic rays such as ultraviolet rays through an original pattern,
The adhesiveness of the exposed portion is eliminated, and solder particles are selectively attached to the adhesive portion of the non-exposed portion to form a solder pattern.
Then, a pressure-sensitive adhesive made of a mixture of polymerized rosin and isopropyl alcohol is sprayed thereon to impart adhesiveness to a circuit board. This is omitted when the adhesive layer of the circuit pattern is formed directly on the circuit board. It is desirable that a component effective as a solder flux is added to the pressure-sensitive adhesive used here similarly to the above-mentioned pressure-sensitive adhesive photosensitive resin.

The solder particles used have various compositions, shapes,
Particles having a particle size can be used. For example, it can be used for tin-lead solder, bismuth-containing solder, silver-containing solder, and the like. The shape can be used irrespective of the spherical shape and the irregular shape. The particle size is appropriately selected depending on the required solder film thickness and the definition of the circuit, but those having a particle size of 10 μm or less have poor solder wettability and are difficult to use.

[0011] The method of attaching the solder powder to the adhesive resin layer is to remove excess solder using vibration or the like after placing solder particles on the entire surface of the flexible film having the adhesive resin pattern. Or by using a mask or the like corresponding to the pattern to adhere solder particles only to necessary portions.

It is desirable that a protective film be laminated on the completed solder pattern transfer film in order to prevent contamination or damage to the pattern during transportation or other handling. It is desirable to form a thin film of a silicone resin or the like on the adhesive surface so that the protective film is easily peeled off when transferred to the circuit board. When transferring the solder pattern from the solder pattern transfer film onto the circuit board, the protective film is peeled off, the alignment is performed, and the solder pattern transfer film is brought into close contact with the circuit board, and then the support film is peeled off. The solder is melted in a reflow furnace to form a solder pattern. If predetermined components are mounted before reflow, soldering is performed.

[0013]

According to the present invention, a film in which solder powder is adhered only to a necessary portion of a circuit pattern via an adhesive resin layer is provided so that a solder pattern can be prepared in advance. By superimposing this film on the circuit pattern, the efficiency of the soldering operation is improved.

[0014]

FIG. 1 shows an embodiment of the present invention. (Example 1) An adhesive photosensitive resin solution was applied on a polyester film 1 having a thickness of 25 μm on which a thin film of a silicone resin was formed for peeling, and dried to form an adhesive photosensitive resin layer 2 having a thickness of about 3 μm. Was obtained. The composition of the adhesive photosensitive resin solution is as follows: a glass transition point of 100 ° C., a molecular weight of about 60,000, a polymethyl methacrylate / butyl acrylate copolymer resin of 40 parts, a softening point of 135 ° C., 20 parts of a polymerized rosin, and trimethylolpropanetriene. 35 parts of acrylate, 3 parts of benzophenone, 0.5 part of ethyl Michler's ketone and 1.5 parts of cyclohexylamine hydrochloride were dissolved in acetone to form a 30% solution (FIG. 1).
(A)).

Next, a polypropylene film 3 having a thickness of 12 μm, on which a thin film of a silicone resin is formed, is laminated to prevent adhesion between the pattern original 4 and the tacky photosensitive resin layer 2 and to enhance air curability. The original film of the solder pattern and the raw film were vacuum-adhered and exposed with a 3 kW mercury lamp at a distance of 90 cm for about 25 seconds (see FIG. 1B).

The polypropylene film 3 is peeled off, and a tin-lead eutectic solder powder having an average particle size of 80 μm is sprayed on the surface of the adhesive photosensitive resin layer to obtain a solder particle pattern adhered to the non-exposed portion, and an adhesive is formed thereon. The solution was sprayed and dried to form an adhesive layer 7 having a thickness of 3 microns. The composition of the pressure-sensitive adhesive solution was such that 70 parts by weight of polymerized rosin was
It is dissolved in parts by weight. A 12 μm thick polypropylene protective film 8 having a silicone resin thin film formed thereon was laminated on the adhesive layer to obtain a solder pattern transfer film (see FIG. 1C).

(Example 2) Adhesive resin solution B having the following composition
Was prepared. 60 parts by weight of rosin having an acid value of 170 and a melting point of 85 ° C.
20 parts by weight of rosin ester, 1 part by weight of cyclohexylamine hydrochloride, 20 parts by weight of propylene glycol monobutyl ether. This adhesive resin solution B is
By a screen printing method using a 50 mesh nylon screen, printing was performed on the surface of the polyester film having a thickness of 12 μm to obtain a resin layer having a thickness of 10 μm. next,
Eutectic solder particles having an average particle size of 80 μm were sprinkled over the entire surface of the adhesive resin pattern, and extra particles were removed by vibration to obtain a solder particle pattern. An adhesive layer was formed thereon in the same manner as in Example 1, and a polypropylene protective film was laminated thereon to obtain a pattern transfer film.

Next, an example of use of the solder pattern transfer film will be described. Example 1 and Example 2 as circuit boards
The protective film 8 of the solder pattern transfer film of Example 1 and Example 2 was peeled off from the glass-epoxy base printed wiring board having the same pattern (negative pattern) as the solder pattern transfer film obtained in the above. A predetermined portion of the pattern transfer film and the solder pattern position of the pattern transfer film are aligned and superimposed, lightly rolled with a rubber roller, and then the flexible film 1 is peeled off.
The solder was melted by heating at a temperature of 1 ° C. for 1 minute, and the resin residue was washed to obtain a solder layer having a thickness of about 40 μm on a predetermined portion of the copper foil of the printed wiring board. This solder pattern had a thickness that allowed component mounting, and a uniform thickness was obtained over the entire circuit. Also, no bridge was observed in the circuit using this solder pattern.

[0019]

According to the present invention, when an adhesive photosensitive resin is used, a high-definition adhesive or non-adhesive pattern can be obtained by pattern original image exposure, so that a high-definition solder pattern can be obtained. Since the solder particles do not have the limitations of the plate removal property unlike the solder paste, solder particles having a relatively large particle size, that is, a small specific surface area can be used, so that deterioration with time is small. A solder composition suitable for the purpose can be used. Eutectic, silver, bismuth etc.
You can choose freely. Since it can be used regardless of the size of the pattern area and the pattern shape, the degree of freedom in circuit design is high.
At the same time, a large number of patterns can be formed collectively. The solder pattern transfer film can be centrally manufactured and supplied to many remote mounting processes. According to the photographic method, the original pattern can be manufactured at a lower cost than a screen for printing solder paste.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a method for manufacturing a solder pattern transfer film of the present invention.

FIG. 2 is a view showing a structure of a solder pattern transfer film of Example 1. (A) is a plan view and (b) is A in (a).
It is -A 'sectional drawing.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 flexible film 2 adhesive photosensitive resin layer (uncured) 2 ′ adhesive photosensitive resin layer (cured) 3 polypropylene film 4 original solder pattern 5 actinic ray 6 solder particles 7 adhesive 8 protective film

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H05K 3/34 H05K 3/20 B23K 3/06

Claims (2)

(57) [Claims] 1. A solder pattern transfer film comprising: a photosensitive resin layer having an adhesive property corresponding to a circuit pattern on a surface of a flexible film; and solder powder adhered to the adhesive portion. . 2. A photosensitive resin layer having an adhesive property is formed on the surface of a flexible film, and the adhesive photosensitive resin layer is irradiated with actinic rays through a pattern original so as to eliminate the adhesive property of an exposed portion. A method for producing a solder pattern transfer film, characterized in that solder particles are selectively adhered only to the surface of the adhesive photosensitive resin layer in the non-exposed portion where the property remains.