JPH09130016A - Circuit formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent tipping defect at the time of circuit formation of a printed wiring board by a method wherein it is heated at a temperature in a specific range within a constant time period after the exposure to light and next developed. SOLUTION: After sensitive resist 3 is applied to a face of a metal part of a copper-clad laminated board, it is exposed to light and heated, and next the sensitive resist 3 in a portion on which UV lights, etc., are not irradiated by being screened by a mask film 1 is melted and developed, and thereafter it is washed with water and next etched to form a circuit. Heating after the exposure to light is performed within 5min after the exposure to light. Further, heating is performed at a temperature of 70 to 90 deg.C. Directly after the development, it is washed with water at a liquid temperature 25 to 32 deg.C for 1 to 5min, preferably. Further thereafter, it is washed with water at a liquid temperature 40 to 50 deg.C for 1 to 3min, more preferably.

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 circuit on a printed wiring board used in electric / electronic equipment.

[0002]

2. Description of the Related Art Printed wiring boards used for electric and electronic equipment are mainly formed into circuits by a so-called subtractive method. Specifically, a copper-clad laminate is used to form printed wiring boards as needed. After the copper foil on the surface of the copper foil is plated with copper, a photosensitive resist is applied to the surface of the copper foil or the copper-plated portion formed by the copper plating (hereinafter, both are collectively referred to as a metal portion). Then, after the mask film is brought into contact with the photosensitive resist, it is exposed to UV light or the like for exposure, and the mask film is released and stored at room temperature. Then, the photosensitive resist is shielded with a mask film and the portion of the photosensitive resist not exposed to UV light is dissolved and developed, and after washing with water, the metallic portion of the portion where the photosensitive resist is dissolved is dissolved and etched, and washed with water, Next, the remaining photosensitive resist is dissolved, peeled off, and washed with water to form a circuit.

However, in this circuit forming method, there may be a defect that a metal portion of a necessary portion is lost by etching and a defect of residual copper that remains without etching a metal portion of an unnecessary portion. In a printed wiring board that requires high precision and high density circuit formation, the circuit finish precision is not sufficient and needs to be improved.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems, and an object of the present invention is to form a circuit in which a defective chip is less likely to occur when forming a circuit on a printed wiring board. To provide a method. Also,
It is another object of the present invention to provide a circuit forming method that is less likely to cause residual copper defects.

[0005]

According to a first aspect of the present invention, there is provided a circuit forming method, wherein a surface of a copper-clad laminate is coated with a photosensitive resist, exposed, then developed, washed with water, and then etched. In the circuit forming method of forming a circuit by heating at a temperature of 70 to 90 ° C. within 5 minutes after exposure,
Then, development is performed.

A circuit forming method according to claim 2 of the present invention is
The circuit forming method according to claim 1, wherein the photosensitive resist is a negative type or an alkali developing type and has a thickness of 10 to 50 μm.
m sheet-shaped photosensitive resist.

The circuit forming method according to claim 3 of the present invention is
In the circuit forming method according to claim 1 or 2, the washing with water after development is performed with water having a liquid temperature of 25 to 32 ° C for 1 to 5 minutes.

The circuit forming method according to claim 4 of the present invention is
The circuit forming method according to any one of claims 1 to 3, wherein the water washing after development is performed by washing with water having a liquid temperature of 25 to 32 ° C for 1 to 5 minutes, and then water having a liquid temperature of 40 to 50 ° C. So 1
It is characterized by washing for 3 minutes.

In order to solve the above-mentioned problems, the inventors have conducted various studies, and as a result, when forming a circuit by a so-called subtractive method, the light-irradiated portion of the photosensitive resist and the light-irradiated portion are not irradiated. There is a semi-cured portion between the exposed portions, and the photosensitive resist in this semi-cured portion may or may not dissolve during development, which may cause defects such as chipping defects and residual copper defects. I found one. That is, as shown in FIG. 1, in the case of this method, in the layer of the carrier film 2 provided so that the light 8 irradiated at the time of exposure does not adhere to the photosensitive resist 3 and the mask film 1. Due to the diffusion, between the uncured portion 4 and the curing completed portion 7, a semi-cured portion 5 that is slightly cured by diffusion of the light 8 and a light amount of the light 8 that is slightly insufficient due to diffusion of the light 8 and is almost cured. The hardened part 6 is formed. The slightly cured semi-cured portion 5 and the substantially cured semi-cured portion 6 change in size and degree of curing depending on the intensity of the light 8 irradiated at the time of exposure, the sensitivity of the photosensitive resist 3, and the like. Since the dissolving power also varies depending on the amount of the dissolved photosensitive resist, the almost cured semi-cured portion 6 is dissolved, and the metal portion in that portion is excessively etched to cause a chipping defect or is slightly cured. The semi-cured portion 5 remains without being melted, the metal portion in that portion is not etched, and a residual copper defect occurs. Also, the semi-cured part 5 that has been slightly hardened easily adheres to other objects even if it is once melted, and again adheres to the metal part, hinders the etching of the metal part in that part, and causes a residual copper defect. Let

Therefore, the present inventors have found that even in the semi-cured portion 6 that is almost cured, the photosensitive resist is difficult to dissolve during development,
The inventors have found a method of forming a circuit in which the photosensitive resist is surely dissolved during development even in the slightly cured semi-cured portion 5, and solved the problem.

According to the circuit forming method of the present invention, by heating after exposure, the adhesion between the semi-cured photosensitive resist portion and the metal portion is improved, and the semi-cured photosensitive resist portion is less likely to dissolve. It is possible to obtain a circuit with less occurrence of chipping defects.

Further, according to the circuit forming method of the third and fourth aspects of the present invention, further, the semi-cured photosensitive resist remaining on the metal portion or the photosensitive resist which is once dissolved and then adhered to the metal portion again. The resist and the like can be washed well, and a circuit with less residual copper defects can be obtained.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The circuit forming method of the present invention comprises applying a photosensitive resist to the surface of a metal portion of a copper-clad laminate, exposing it to light, heating it, and then shielding it with a mask film to protect it from UV light and the like. After the photosensitive resist in the non-irradiated portion is dissolved and developed, it is washed with water and then etched to form a circuit. It is important to heat after exposure, and the heating improves the adhesion between the semi-cured part 6 and the metal part, which are almost cured,
Since the almost cured semi-cured portion 6 becomes difficult to dissolve, the metal portion in that portion is not excessively etched, and chip defects are reduced. It is important that the heating condition after exposure is heating within 5 minutes after exposure. When it is heated for more than 5 minutes after exposure, the semi-cured part 6 is almost cured.
The adhesion between the metal part and the metal part is not so improved, and chipping defects are difficult to reduce. This is because the curing reaction of the photosensitive resist started by light irradiation continues within 5 minutes after the exposure, and the heating reaction accelerates the curing reaction of the semi-cured photosensitive resist when heated, and the cured photosensitive resist is cured. It is considered that the characteristics are almost the same as those described above, and it becomes difficult to dissolve during development.
Further, it is important to heat at a temperature of 70 to 90 ° C. When the temperature is lower than 70 ° C., the adhesion with the metal part is not improved so much, and the chipping defect is difficult to reduce. If the temperature exceeds 90 ° C., the semi-cured part 5 that is slightly hardened or even the uncured part 4 may be hardened, and a copper residue problem is likely to occur. The post-exposure time of the present invention represents the elapsed time from the time when the light irradiation is completed. The heating temperature within the above range is appropriately selected depending on the thickness and size of the copper-clad laminate. The heating time is generally 30 to 120 seconds.

Immediately after development, the liquid temperature is 25 to 32 ° C.
It is preferable to wash with water for 1 to 5 minutes, and then,
It is more preferable to wash with water having a liquid temperature of 40 to 50 ° C. for 1 to 3 minutes. Immediately after development, use water with a liquid temperature of 25 to 32 ° C for 1 to 5
After washing for a minute, the remaining uncured photosensitive resist can be removed well.A little cured semi-cured photosensitive resist left on the metal part or a photosensitive resist that has once dissolved and then adhered to the metal part again can be used. Even if there is, it is washed well, and defects in residual copper are easy to reduce. If the temperature is lower than 25 ° C., the effect of the above cleaning becomes insufficient and the effect of reducing residual copper defects becomes small. If the temperature exceeds 32 ° C., the activity of the developer adhering to the surface during development and brought into the water washing section is reduced. And the semi-cured portion 6 that has been substantially cured prior to washing with water is attacked by the developer and dissolved, resulting in a chipping defect. After washing with water at a liquid temperature of 25 to 32 ° C., a liquid temperature of 40 to 5
Washing with water at 0 ° C. allows for better removal of the uncured photosensitive resist residue, which further reduces copper defects.

Examples of the photosensitive resist used in the present invention include solvent-developing type or alkali-developing type, sheet-like dry film, ink and the like. Thickness 10-50μ
The sheet-shaped photosensitive resist of m is preferable because it has a proper resolution and a proper adhesion to the metal part. Further, the solvent developing type is difficult to process because it uses a chlorine-based solvent, and an alkali developing type photosensitive resist is preferable.
The photosensitive resist is preferably a negative type. The positive type, in which the photosensitive resist in the portion irradiated with light is removed by development, has poor adhesion to metal and is likely to cause chipping defects.

The copper-clad laminate used in the present invention may be a plate having copper foil stretched on one or both sides, and examples thereof include inorganic fibers such as glass, polyester, polyamide, polyacryl, polyimide and the like. Organic fiber, cloth of natural fiber such as cotton, base material such as paper,
Adhesive with thermosetting resin such as epoxy resin type, phenol resin type, polyimide resin type, unsaturated polyester resin type, polyphenylene ether resin type, or thermoplastic resin such as polyvinyl chloride, polyethylene, etc., and copper foil on one or both sides And a sheet in which a copper foil is stretched on one side or both sides of the sheet of the thermosetting resin or the thermoplastic resin alone.

Examples of the copper foil of the copper-clad laminate used in the present invention include electrolytic copper foil and rolled copper foil. The thickness of the copper foil is preferably 5 to 70 μm. If it is less than 5 microns, it becomes difficult to obtain copper foil, and if it exceeds 70 microns, the accuracy of the circuit deteriorates.

The circuit forming method of the present invention is not limited to the circuit forming method of the circuit of the outer layer of the printed wiring board, but includes the circuit forming method of the inner layer circuit of the multilayer printed wiring board.

[0019]

【Example】

(Example 1) 30 μm thick, negative type on the surface of copper foil (thickness 35 μm) of a double-sided glass substrate epoxy resin copper-clad laminate (FR-4 type) having a size of 50 × 50 cm and a thickness of 0.2 mm excluding copper foil , Alkaline developing type, sheet-like photosensitive resist [Tokyo Ohka Kogyo Co., Ltd., product name AF-
730] was attached. Then, a mask film was brought into contact with the photosensitive resist, and then UV light having a light amount of 50 mJ / cm 2 was applied for exposure, and the mask film was released. Then, the mask film was put into a heater at 80 ° C. within 2 minutes. After heating for 60 seconds, it was cooled to room temperature. Then, at a temperature of 28 ° C., an aqueous solution of sodium carbonate having a concentration of 1% is sprayed for 2 minutes, shielded with a mask film to dissolve and develop the photosensitive resist in a portion not irradiated with UV light, and immediately after that, at 20 ° C.
Was sprayed for 2 minutes and washed with water. Then the second chloride
Using a copper etching solution, dissolve the metal part of the part where the photosensitive resist is dissolved, etch it, wash with water, and then 3%
An aqueous solution of sodium hydroxide was sprayed for 2 minutes to dissolve the remaining photosensitive resist, peeled off, and washed with water to form a circuit.

The pattern of the mask film has a conductor width of 150 and a conductor-to-conductor spacing of 150.
A pattern was used in which 2000 circuits each having a length of 200 μm and a length of 200 μm were used.

(Example 2) A circuit was formed in the same manner as in Example 1 except that, immediately after development, water at 30 ° C was sprayed for 2 minutes for washing.

(Example 3) A circuit was formed in the same manner as in Example 1 except that water at 30 ° C was sprayed for 2 minutes immediately after development and then water was further sprayed at 45 ° C for 1 minute for washing. did.

(Comparative Example 1) Example 1 was repeated except that after the exposure, the mask film was released, it was left at room temperature without heating.
A circuit was formed in the same manner as in.

(Comparative Example 2) A circuit was formed in the same manner as in Example 1 except that after exposure, the mask film was released, and after 7 minutes, it was placed in a heater at 80 ° C and heated for 60 seconds.

(Comparative Example 3) A circuit was formed in the same manner as in Example 1 except that the mask film was exposed, the film was placed in a heater at 65 ° C within 2 minutes, and heating was performed for 60 seconds.

(Comparative Example 4) A circuit was formed in the same manner as in Example 1 except that after exposing the mask film and releasing the mask film, the mask film was placed in a heater at 95 ° C within 2 minutes and heated for 60 seconds.

The numbers of occurrences of chipping defects and residual copper defects of the circuits obtained in Examples 1 to 3 and Comparative Examples 1 to 4 were evaluated with reference to the pattern shape of the mask film. As an evaluation method, an optical AOI inspector [manufactured by Dainippon Screen Co., Ltd., product name OPI-2600] was used, and a portion lacking 30 μm or more from the above criteria, and 3
The number of portions where copper remained at 0 μm or more was evaluated on both sides of each of 5 sheets.

The results are shown in Table 1.
It was confirmed that Nos. 3 to 3 had a smaller number of chipping defects than Comparative Examples 1 to 4. Further, Examples 2 and 3 are Comparative Examples 1
It was confirmed that the number of occurrences of residual copper defects was smaller than that of Nos. 4 to 4.

[0029]

[Table 1]

[0030]

According to the method of forming a circuit of the present invention, by heating after exposure, the adhesion between the substantially cured semi-cured photosensitive resist portion and the metal portion is improved, and the substantially cured semi-cured photosensitive resist portion is improved. Is less likely to dissolve, so that the circuit formation method of the present invention can provide a circuit with less defects.

By using the circuit forming method according to the third and fourth aspects of the present invention, in addition to the above-mentioned effects, a circuit with less residual copper defects can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view for explaining a circuit forming method of the present invention.

[Explanation of symbols]

 1 Mask film 2 Carrier film 3 Photosensitive resist

Claims (4)

[Claims] 1. A circuit forming method comprising forming a circuit by applying a photosensitive resist to the surface of a copper-clad laminate, exposing it, then developing it, washing it with water, and then etching it to form a circuit.
A method for forming a circuit, which comprises heating at a temperature of 70 to 90 ° C. within 5 minutes after exposure and then developing. 2. The method for forming a circuit according to claim 1, wherein the photosensitive resist is a negative type or alkali development type sheet-shaped photosensitive resist having a thickness of 10 to 50 μm. 3. The washing with water after development is performed at a liquid temperature of 25 to 32 ° C.
Washing with water for 1 to 5 minutes.
Alternatively, the circuit forming method according to claim 2. 4. A liquid temperature of 25 to 32 ° C. after washing with water after development.
The method for forming a circuit according to any one of claims 1 to 3, characterized in that after washing with water for 1 to 5 minutes, it is washed with water having a liquid temperature of 40 to 50 ° C for 1 to 3 minutes.