JPS636895A - Method of forming photo-solder resist film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method for forming a solder resist film on a printed wiring board for the purpose of protecting conductor circuits on the printed wiring board. It is something.

(Prior art) In order to protect the conductive circuit formed on the printed wiring board from peeling and oxidation, the conductive circuit is formed on the copper clad layer 8 and then Is it necessary to form a solder resist film on the upper side? In recent years, printed wiring boards need to have higher density conductor circuits, etc., in response to demands for smaller size, lighter weight, and higher performance. For this reason, in order to be able to form the above-mentioned solder resist film only on the required portions, a photo solder resist is often used to form the solder resist film.

The formation of this photo solder resist film basically involves applying a photo solder resist to a printed wiring board.
A method has been adopted in which a photo solder resist film is formed by exposing the photo solder resist to light through a photomask, developing the photo solder resist, and then hardening the photo solder resist.

This photo solder resist is cured by causing a photopolymerization reaction by irradiating it with light (ultraviolet light), but if oxygen is present around it during this photopolymerization, this oxygen This interferes with the photopolymerization action described above. That is, when photopolymerization of the photosolder resist is caused, oxygen is present around it.

This oxygen suppresses the photopolymerization effect of the photosolder resist. If such suppression occurs, the necessary copper layer of the photo solder resist coating will be peeled off at the same time as the unnecessary copper layer.

There are two possible materials for the photo solder resist that forms such a photo solder resist film: a film type and a liquid type. Although film-like photo solder resists have advantages such as simplifying the process of forming a film, as shown in Figure 4,
It is difficult to completely cover the conductor circuit, and a gap inevitably exists between the conductor circuit and the board.

As a method of forming a printed wiring board using such a film-like photo solder resist, for example, Japanese Patent Application Laid-Open No. 1018/1983 describes a method for forming a printed wiring board using a photosensitive resin composition that is coated on a support in advance and then dry-lit. A method of forming a resist by heating and pressurizing a film of a material onto a substrate, irradiating it with actinic light, and developing it. The invention proposed in JP-A-54-1018 itself is a photosensitive resin composition for solder resist (photo solder resist) suitable for such a method.
The present invention relates to a film-like photo solder resist.

However, when such a film-like photo solder resist is used, when it is formed as a film on a printed wiring board, the film W2 (usually a polyester cover) that protects the film-like photo solder resist is removed. (called a sheet) must be removed, which requires a process. Not only that, but in order to achieve high density printed wiring boards, many through holes are formed in this type of printed wiring boards, and a film-like photo solder is formed on these printed wiring boards. When a resist film is formed, as shown in Figure 3, this film-like photo solder resist becomes floating in the vicinity of the through hole, and depending on this film-like photo solder resist, it may not be possible to form it on a printed wiring board. This means that the inside of the through hole will not be protected.

In other words, the presence of air, that is, oxygen, which has an adverse effect on the photopolymerization action of the photosolder resist, is allowed to exist, especially within the through hole.

On the other hand, when a liquid photo solder resist is used, as shown in FIG. Printed wiring boards coated with solder resist are hardened by # elements in the air during transport or during storage, so printed wiring using materials in this form is difficult. There are some difficulties in manufacturing the board. Therefore, liquid photo solder resist materials must be protected in some way before use.

There is a point. Particularly when the printed wiring board has through holes, attention must be paid to the properties of the liquid photo solder resist.

Now, if we consider the role of a through hole, this through hole provides electrical continuity between the front and back sides of the printed wiring board through the conductor layer formed inside it, and also uses this through hole to connect electronic components. etc. will be implemented. In recent printed wiring boards, soldering is performed on the parts where electronic components are mounted, but if particles of this solder adhere to through holes (usually called bayer holes) that are not involved in mounting electronic components. and.

These solder particles peel off and cause short circuits in electronic components. Therefore, for such through holes, it is often necessary to sufficiently protect the portions exposed to the front side of the printed wiring board by covering them with a photo solder resist.

If that is the case, when the above-mentioned film-like photo solder resist is used to form a 7-photo solder resist film, air will remain in the through-hole as described above, so in this state. When the photo solder resist is photopolymerized, the photo solder resist film required in the vicinity of the through hole is not sufficiently photopolymerized by the m element in the souffle hole, and the required solder resist film is not sufficiently photopolymerized by the m element in the souffle hole. - It becomes difficult to form a solder resist film.

In addition, in the case of through-holes that are not involved in the mounting of components as mentioned above, for example, as shown in FIG. 2, in order to prevent solder from adhering to the inner surface thereof,
It may be necessary to protect the inner surface of the through hole with a photo solder resist.

In order to solve these problems and necessities in conventional methods, the uninvented inventor has conducted intensive research and developed a photo solder resist that protects conductor circuits and through holes with printed wiring boards and protects it from oxygen. The present invention was completed based on the new finding that by using a liquid material as a material, it is possible to form a film that completely avoids residual oxygen.

(Problems to be solved by the invention) The present invention has been made based on the above process,
The problems to be solved are the residual oxygen during the formation of the photo solder resist film, and the incompleteness of the formation of the photo solder resist film on the inner surface of the through hole.

The objective of Kiwazu's 1 H is to be able to reliably prevent oxygen from remaining when forming the photo solder resist film, and to ensure that the photo solder resist film is formed on the inner surface of the through hole. An object of the present invention is to provide a method for forming a photo solder resist film that can be easily applied.

(Means for solving the problems) The means taken by the present invention to solve the above problems are as follows:
To explain with reference to FIGS. 1 and 2 corresponding to the embodiment, ``After applying a liquid photo solder resist, a liquid transparent high resist is applied to a part or the entire surface of the printed wiring board including the through-hole portion. The method is characterized in that after forming a film made of a molecular polymer, the photo solder resist is exposed to light, then the film made of the high molecular polymer is peeled off, and then the photo solder resist is developed and cured. "Method for Forming Photosolder Resist Film".

That is, in the method for forming a photo solder resist film according to the present invention, a liquid material is used as the photo solder resist, and a film for protecting this photo solder resist is also formed using a liquid material. This is a method that can reliably form a photo solder resist film, especially in the vicinity of through holes.

The liquid photosolder resist that can be used in the method of the present invention is preferably an epoxy acrylate composition. The reason for this is that materials have been developed that have high sensitivity, high resolution, and good heat resistance when exposed to light with oxygen blocked. The viscosity of such liquid photo solder resist is 100 to 10
000 CP S is good, and in particular, 100 to 5000 CP S is optimal for penetrating the inside of the through hole (12) shown in FIGS. 1 and 2.

Application methods for such a liquid photo solder resist include dipping, spray coating, curtain coating, roll coating, and printing.

Various polymer solutions can be used as the polymer solution that can be used in the method of the present invention, and any one selected from bovinyl alcohol, gelatin, and water-soluble polyamide can be used. In addition, as for the water-soluble polyamide described in J:.

It is possible to use a copolymer of N, N'

Among the above-mentioned polymer solutions, polyvinyl alcohol is particularly suitable, and among them, a polyvinyl alcohol aqueous solution containing a surfactant is most suitable. In this case, the surfactants include C12-18 alkyl@,
or sodium sulfonate, polyoxyethylene glycol having a molecular weight of 1000 or less, and polyoxyethylene octylphenyl ether, sodium dioctyl sulfosuccinate can be used. The addition amount may be in the range of a, aat to 10% with respect to the aqueous solution, and in particular in the range of 0.1 to 1.0%, the poly and neal alcohol aqueous solution which is a high molecular weight polymer solution can be added. It is possible to improve the wettability of the photo solder resist (13). Polyvinyl alcohol has a degree of polymerization of 500 to 3000, preferably 1500.
A polymerization degree of ~2,000 is good, and the reason for this is that if the degree of polymerization is less than 500, there is no strength as a film;
This is because if it is larger, the solubility in water will deteriorate, which is not preferable. Regarding the degree of saponification, a degree of saponification greater than 90% is unfavorable because of low solubility in water, while a degree of less than 75 mo1% is unfavorable because the oxygen permeability increases and the effect as an oxygen barrier membrane decreases. Undesirable. The inventors found that the degree of saponification was 75 to 90%, particularly 86 to 89%, based on various tests.
It has been found that this material is suitable as a protective film.

In addition, it is desirable to add a plasticizer to this polyvinyl alcohol aqueous solution in order to maintain a dry polyvinyl alcohol coating that is constant and uniform, regardless of environmental temperature and humidity. Examples of plasticizers that can be added include glycerin. , trimethylolpropane, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, etc.
It can be used in the range of ~50%. The viscosity of the polyvinyl alcohol aqueous solution is preferably 100 OCPs or less, particularly 100 cPs or less, in order for the polyvinyl alcohol aqueous solution to sufficiently penetrate into the through-hole.The thickness of the film thus formed is , 0. A thickness thicker than i p, , m is the minimum required for an oxygen barrier film, or a thickness thicker than 10 gm is undesirable from a lower resolution and from an economical point of view. A range of lm to 10m is suitable.

Furthermore, when forming a film made of a high molecular polymer, it is more preferable to immerse a printed wiring board coated with a photo solder resist in a solution of the high molecular polymer; It is preferable to apply the polymer solution to the coated printed wiring board by any one of spray coating, curtain coating, brush coating, roll coating, and sealing. Are these methods current? This is because c2t can be used without much modification, and the high molecular weight polymer described in 1 can be sufficiently coated by this method as well.

(Operation of the invention) According to the method of the present invention configured as described below, first,
This is because the photo solder resist film (13) is formed from a liquid photo solder resist material.

This liquid photosolder resist material permeates well into each through hole (12). For this reason.

As shown in FIG. 2, this photo solder resist covers not only the surface of the substrate (11) but also the entire surface of the conductor layer (12a) formed in each through hole (2) of the substrate (11). will be completely covered by.

The surface of the photo solder resist film (13) thus formed is coated with a film (
14), the photo solder resist film (1) is formed.
(e) is completely cut off from air, that is, # elements. At this time, since the material of the covering 111u (14) is liquid, 1? such as immersion VX or the like? ! By the proper operation, it can sufficiently penetrate into the through hole (12), and this film (14) can reliably cover the surface of the photo solder resist H (13) inside the through hole (12). be.

After doing this, if necessary parts of the photo solder resist coating v(+3) are cured by photopolymerization through the photomask (15), the photo solder resist coating (
1) cures without being affected by the adverse effects of oxygen. A substrate (11) having the thus cured photo solder resist coating (13).

Even if immersed in the solder layer, the photo solder resist coating (
There is no unnecessary solder adhering to the inside of the 1 piece.

Next, the present invention will be explained in detail using examples.

(Example) Example 1 Double-sided through-hole printed wiring board (1
A liquid photosolder resist having the following composition was applied onto the surface of the substrate (11) of No. 0) by a printing method.

[Composition of photo solder resist] - Acrylic modified epoxy resin ... 45 parts by weight - Pentaerythritol triacrylate - 30 parts by weight - Epoxy resin -25 parts by weight - Dicyandiamide - 1.5 parts by weight - Benzophenone -2 ,7 parts by weight Michler's ketone...0.3 trace parts P-methoxyphenol -0.6 parts by weight Methyl ethyl ketone
-160 parts by weight of such a composition on a substrate (l
After coating, dry at 80°C for 15 minutes. wm
A photo solder resist layer was formed on the substrate (11).

Next, a photo solder resist was applied to the back surface of this substrate (11) in the same manner as above and dried.

Then, a liquid polymer having the following composition was applied onto the photo solder resist layer by a spray coating method.

[Composition of polymer] - Partially saponified polyvinyl alcohol (saponification degree 86
~89 olL degree of polymerization +700)... 6 proximal moieties, sodium dioctyl sulfosuccinate -0.1 parts by weight, water... total amount of 100 parts by weight Composition of such a high molecular weight polymer It was confirmed that a uniform film of 1 to 2 JLm was formed by coating the photo solder resist film on the surface of the photo solder resist film and drying it at 40° C. for 60 minutes. Then the board (+1)
By applying a similar polymer to the back side of the substrate, it was confirmed that a transparent polymer film (14) was formed on the entire surface of the substrate (11) including the through holes (12). did it.

Next, a photomask (15) is brought into close contact with this substrate (11), and a 300mJ/W high-pressure mercury lamp is used for
When exposed to light at a light intensity of crn', the number of steps of the 21 step tablet was 9 steps. and by spraying with warm water at 60°C for 60 seconds.

After peeling off the transparent polymer coating (14) and removing moisture with warm air at 50°C,
-) When spray development was carried out with dichloroethane for 60 seconds, the necessary parts of the photo solder resist remained corresponding to the photomask (15), and the unnecessary parts were removed. Finally, the photo solder resist-covered IFJ (13) was formed by drying at 150° C. for 60 minutes.

￥Example 2 Double-sided through-hole printed wiring board with cleaned surface (1
A liquid photosolder resist having the following composition was applied onto the surface of the substrate (11) of No. 0) by a curtain coating method.

[Composition of photo solder resist] - Acrylic modified epoxy resin...45 parts by weight - Pentaerythritol triacrylate -30 parts by weight -Epoxy resin -25! ! Amount: Dicyandiamide 1.5 parts by weight Benzophenone -2.7 parts by weight Michler's ketone -0.3 parts by weight P-methoxyphenol -0.6 parts by weight Methyl ethyl ketone
-200i mounting plate such a composition on a substrate (II
) and dried at 80'C for 15 minutes to form a 30 gm photo solder resist layer on the substrate (II).

Next, a photo solder resist was applied to the back surface of this substrate (II) in the same manner as above and dried.

Then, a liquid polymer having the following composition was applied to the photo solder resist layer by a dipping method.

[M1 composition of high molecular weight polymer] ・Partially saponified polyvinyl alcohol (saponification degree 86
~89 mol $, degree of polymerization 1700)...4 parts by weight Sodium dioctyl sulfosuccinate -o, i parts by weight Polyethylene glycol #400...1 part by weight Water...Amount to make a total of 100 parts by weight When the substrate (11) on which the photo solder resist film was formed was immersed in such a polymer composition and dried at 40°C for 60 minutes, the through holes (12) were removed. 1 to 24 on the entire surface of the substrate (11) containing
It was confirmed that a uniform film of m was formed.

Next, a photomask (15) is closely attached to this substrate (11), and a 300J/W high pressure mercury lamp is used for 4.
Exposure was performed at a light intensity of crrr'. Then, the transparent polymer coating (14) was peeled off by spraying with warm water at 60°C for 60 seconds, and the water was removed with warm air at 50°C, followed by 1.1. When spray-developed with l-trichloroethane for 60 seconds, a foot mask (1
Corresponding to 5), the necessary parts of the photo solder resist remained, and the unnecessary parts were removed. Finally, 150°
By drying at C for 60 minutes, a photo solder resist coating (13) was formed.

Example 3 A substrate (11) was immersed in the photo solder resist composition used in Example 2 to form a photo solder resist layer over the entire surface of the substrate (II).

Then, a high molecular weight polymer using gelatin instead of the polyvinyl alcohol used in Example 2 was applied to the substrate (+1) by a curtain coating method.

The rest was carried out in the same manner as in the above example.

A necessary photo solder resist film (ig) was formed on the resulting substrate (11).

example].

Double-sided through-hole printed wiring board with a smooth surface (l
On the surface of the substrate (II) of (O), a film-like 7-Oton Ruder resist (SR100OG-75, trade name manufactured by Hitachi Chemical) was laminated using a special laminator.

Next, the photo solder resist was exposed through a photomask (15) using a 4KW high pressure mercury lamp. The exposure amount at this time was 270 mj/cm'. Next, after peeling off the polyester cover sheet protecting the foot solder resist, 1.1.1-
) - Spray developed for 120 seconds with dichloroethane, then developed using three 8H/cs high pressure mercury lamps.
After irradiating with UV light of J/cm', the film was dried at 150° C. for 60 minutes to form a solder resist film.

Partial peeling was observed within this photo solder resist film, particularly within the through holes that would become Bayer holes.

Comparative Example 2 Double-sided through-hole printed wiring board (1
The liquid photo solder resist used in Example 2 was applied to the surface of the substrate (II) of No. 0) by a curtain coating method and dried at 80° C. for 15 minutes.

Subsequently, the back side was coated in the same manner and then dried.

Next, the photo solder resist was exposed to light through a photomask (15) using a W high pressure mercury lamp.

The exposure amount at this time was 700J/am', and the number of steps on the step tablet was 9 steps. (21 stages made by Stoffer) Next, 1.1 at 18°C. 60 in l-trichloroethane
Spray development was performed for seconds, and then dried at 150° C. for 60 minutes to form a photo solder resist film.

In this case as well, as in Comparative Example 1, 31 tl was partially observed in the photo solder resist film, particularly in the through holes that would become Bayer holes.

(Effects of the Invention) As explained above, according to the method for forming a photo solder resist film according to the present invention, as exemplified in the above embodiments.

After applying a liquid photo solder resist, a film made of a liquid transparent polymer is formed on a part or the entire surface of the printed wiring board including the through-hole portion, and then the photo solder resist is exposed to light. 1. Next, the coating made of the high molecular weight polymer is peeled off, and then the photo solder resist is developed and cured.'' This enables the photo solder resist coating to be applied to a printed wiring board with through holes. 7. A method for forming an Oton Ruder resist film that can reliably prevent oxygen from remaining not only on the surface but also in the through-holes described in 1 above, and simplify the process. can be provided.

That is, first, the substrate (11) is coated with a photo solder resist material using a liquid photo solder resist material.
Since (13) is formed, the surface of the substrate (!I) is of course
Through hole (I2) formed in this substrate (it)
) can also be covered with this photo solder resist film (13). Since the entire photo solder resist film formed in this way is formed, the surface of the photo solder resist film (1:l), especially the photo solder on the upper side of the conductor r:f (12a) in the through hole (12), The surface of the resist film (13) can also be completely covered with the liquid polymer film (14). Therefore, the photosonoresist coating (
13) is completely shielded from oxygen in the air, and the photo solder resist film (13) can be cured by photopolymerization without any hindrance.

As described above, if the photo solder resist film (13) is formed by the method of the present invention, the surface of the conductive layer (12a) of the through hole (12) (via hole) which is not involved in the mounting and mounting of electronic components can be completely covered. The through holes (12) can be covered with a photo solder resist film (13), and even if the printed wiring board (10) is immersed in a solder bath, unnecessary solder will not adhere to the through holes (12). It is. Therefore, in the printed wiring board (IO) manufactured according to the present invention as described above, there is no unnecessary solder, so problems such as short circuits caused by excess solder that conventionally occurred can be avoided. It is possible to avoid it.

[Brief explanation of the drawing]

Figure 1 is a partially enlarged vertical cross-sectional view showing a state in which a film made of a liquid polymer is formed on the surface of a photo solder resist film, and Figure 2 is a partially enlarged longitudinal cross-sectional view showing a state in which a film made of a liquid polymer is formed on the surface of a photo solder resist film. 3 is a partially enlarged vertical cross-sectional view corresponding to FIG. 1, centered on the through hole.
The figure is a partially enlarged longitudinal cross-sectional view for explaining the conventional method of forming a photo solder resist film, FIG. 4 is a partially enlarged longitudinal cross-sectional view showing a conductor circuit covered with a film-like photo solder resist, and FIG. 4 is a partially enlarged vertical cross-sectional view corresponding to FIG. 4 when a liquid photo solder resist is used. Explanation of symbols 10...Printed wiring board, 11...Substrate, 12.
・-Through hole, 12a... Conductor layer, 1:+-・
- Photo solder resist coating, 14... Coating made of high molecular polymer, I5... Photomask. 1i Figure 2, 12 Leg 3 Figure 4 Figure 5

Claims (1)

[Scope of Claims] 1) After applying a liquid photo solder resist to a printed wiring board having at least one through hole portion and exposing it to light through a photomask, the photo solder resist is developed, and then the photo solder resist is In a method of forming a photo solder resist film by curing a resist, after applying the liquid photo solder resist, a liquid transparent polymer is applied to a part or the entire surface of the printed wiring board including the through hole portions. The photo solder resist is characterized in that the photo solder resist is exposed to light after forming a film made of the above, and then the film made of the high molecular weight polymer is peeled off, and then the photo solder resist is developed and cured. How to form a film. 2) The method for forming a photosolder resist film according to claim 1, characterized in that the liquid photosolder resist is made of an epoxy acrylate composition. 3) As the film made of the high molecular weight polymer, one selected from polyvinyl alcohol, gelatin, and water-soluble polyamide is used. The method for forming a photo solder resist film according to item 2. 4) The film made of the high molecular weight polymer is formed by immersing the printed wiring board coated with the photo solder resist in a solution of the high molecular weight polymer. A method for forming a photo solder resist film according to claims 1 to 3. 5) Formation of a film made of the high molecular weight polymer by spraying a solution of the high molecular weight polymer on the printed wiring board coated with the photo solder resist, by spray painting, curtain painting, brush painting, roll painting, or printing. 4. A method for forming a photo solder resist film according to claims 1 to 3, characterized in that the method is carried out by any one method selected from the following.