JPH0851272A - Method for manufacture flexible printed wiring board - Google Patents

Abstract

PURPOSE:To provide a flexible printed wiring board improved in adhesion for laminating a coverlay film, solder heat resistance, circuit burial property, and flex property. CONSTITUTION:After a low-temperature plasma treatment or a corona discharge treatment is performed to the circuit surface of a flexible printed wiring board formed in a circuit in advance, the flexible printed wiring board is heated to perform contact bonding of a coverlay film to the treatment surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a flexible printed wiring board having excellent adhesiveness between a flexible printed wiring board and a coverlay film and excellent soldering characteristics.

[0002]

2. Description of the Related Art In recent years, as electronic products have become lighter in weight, thinner in thickness, and higher in functionality, the demand for printed circuits has increased,
Among them, the flexible printed wiring board is expanding its range of use, and its demand is increasing more and more. Recently, as the performance of flexible printed wiring boards has become higher, fine patterns have been implemented, and components are being mounted on circuits, the use of coverlay films for protection of flexible printed wiring boards has increased. It is required to improve adhesiveness, solder heat resistance, and flexibility.

However, conventionally, development of an adhesive for a coverlay film has been studied as a countermeasure against the above. As the adhesive for the coverlay film, NBR / phenol resin,
Epoxy phenol / NBR, NBR / epoxy resin, epoxy / polyester resin, epoxy / acrylic resin and the like can be mentioned, but there are advantages and disadvantages depending on the conditions to be used, and they are not always satisfactory. N
The BR type has a large thermal deterioration, the epoxy type has a low peel strength, and the polyester type and the acrylic type also have low heat resistance, and the adhesive cannot be freely selected. Therefore, when the adhesiveness of the coverlay film is increased, there is a problem in that the solder heat resistance and the flexibility cannot be satisfied.

Further, conventionally, a coverlay film or a base film of a flexible printed wiring board is chemically treated,
Physical treatment, for example, low temperature plasma treatment, sandblasting method, alkali treatment, etc. were performed, but since the activation treatment is directly applied to the base film surface and the adhesive is applied to the treated surface of the base film respectively, Although the adhesiveness with the metal layer was good, the adhesiveness between the circuit and the coverlay film was poor, and when it was used as a flexible printed circuit board, the circuit embedding property and heat resistance were poor, which caused problems.

[0005]

The present invention solves the above problems and improves the adhesion between the circuit of the flexible printed wiring board and the protective coverlay film without limiting the adhesive for the coverlay film, At the same time, it is intended to provide a flexible printed wiring board having excellent solder heat resistance and circuit embedding property.

[0006]

The inventors of the present invention have made intensive studies to solve the above problems, and as a result, have reached the present invention. The gist of the present invention is to provide a circuit-formed flexible printed wiring. Heat the substrate and coverlay film
In a flexible printed wiring board formed by pressure bonding, the circuit surface of the flexible printed wiring board on which a circuit is formed in advance is subjected to low-temperature plasma treatment or corona discharge treatment, and then a cover lay film is heated and pressure-bonded to the treated surface. And a method for manufacturing a flexible printed wiring board.

The present invention will be described in detail below. According to the present invention, by performing low-temperature plasma treatment or corona discharge treatment on the circuit surface of a flexible printed wiring board on which a circuit is formed in advance, the adhesive layer of the coverlay film is well adhered to the circuit surface, that is, the conductor portion, and the peel strength is improved. The purpose is to improve. Further, by improving the embedding property and the adhesiveness of the adhesive in the circuit, the protection property of the circuit is improved, and the solder heat resistance, heat deterioration resistance and bendability are improved. In the present invention, the conductor surface of the flexible printed wiring board is subjected to low-temperature plasma treatment or corona discharge treatment in advance, and the conductor surface of the circuit surface and the adhesive surface from which the conductor portion is removed are surface-modified and surface-cleaned by the treatment. , The wettability and the affinity of the coverlay film with the adhesive are improved, and the adhesive of the coverlay film is evenly and strongly adhered to the circuit surface, which is related to the improvement of various characteristics.

The circuit-forming flexible printed wiring board used in the present invention may be a heat-resistant insulating plastic film laminated with a metal layer, or a heat-resistant insulating plastic film and a metal foil laminated via a heat-resistant adhesive. Alternatively, a metal foil may be directly coated with a heat resistant resin without an adhesive layer. The method of laminating the heat-resistant insulating plastic film and the metal foil with the heat-resistant adhesive is as follows. Examples of the heat-resistant insulating plastic film for the substrate include polyester, polyimide, polyparabanic acid, polyethersulfone, and polyetherketone, but polyimide film is particularly preferable. The thickness of the heat-resistant insulating plastic film is usually in the range of 12.5 to 125 μm, but an appropriate thickness can be used if necessary. Further, in the flexible printed wiring board, a low temperature plasma treatment, a corona discharge treatment or the like may be applied to the surface of the heat resistant insulating plastic film which is adhered to the metal layer.

The metal foil used in the present invention can be arbitrarily selected from those conventionally used such as copper foil (electrolytic copper foil, rolled copper foil), aluminum foil or stainless steel foil. Generally, copper foil is preferably used, and the thickness is usually preferably 8 to 70 μm. Since the circuit surface is activated, it is preferably 18 to 70 μm.

The heat-resistant adhesive used when laminating the heat-resistant insulating plastic film, the metal foil, and the adhesive layer on each other is nylon / epoxy type, NBR / phenol type, carboxyl group-containing NBR / epoxy type. ,
Examples thereof include polyester / epoxy type, acrylic resin type and modified polyimide resin type. As the solvent, an organic solvent such as alcohol such as methyl ethyl ketone, toluene and methanol is used. Adhesive coating thickness is 5 when dry
It is preferable to apply the coating so that the thickness becomes about 30 μm.

The structure is such that a heat resistant adhesive dissolved in a solvent at a desired concentration is applied to one side or both sides of a heat resistant insulating plastic film by a roll coater or the like, and the adhesive is heated at 50 to 150 ° C. with an in-line dryer. Dry at temperature for 2-20 minutes to evaporate the solvent to a semi-cured state. The metal foil is thermolaminated on one side or both sides of the heat-resistant insulating plastic film with a hot roll to continuously laminate. As pressure bonding conditions, a temperature of 80 to 200 ° C. and a linear pressure of 1 to
A range of 50 Kg / cm and a speed of 0.5 to 10 m / min is preferable. After cure 0.5 ~ 10 at 80 ~ 200 ℃
It is preferable to carry out in two steps within a range of time.

A flexible printed wiring board without an adhesive layer is a polyimide resin (polyamic acid) on a metal foil.
Insulation, which is a method of coating a heat-resistant resin such as the above to form a film, and directly laminating the resin on a metal foil, or a method of directly forming a metal layer (copper, etc.) on the above-mentioned insulating film by plating or vapor deposition. A flexible printed circuit board having a two-layer structure of a film-metal layer is also included. When the metal layer is coated with the heat-resistant resin, the heat-resistant resin may be coated so as to have a thickness of 10 to 100 μm in a dry state. In addition, the heat-resistant insulating plastic film is laminated so that the thickness of the metal layer in the plating method or the vapor deposition method is 3 to 35 μm.

Circuit formation using the above flexible printed circuit board can be carried out by a known method.
Specifically, after manufacturing the flexible printed circuit board, the following steps 1) to 5) are performed. 1) Perform a surface cleaning / polishing process on the substrate surface (particularly the metal foil surface). 2) In the circuit printing process, a circuit is written on the metal surface by a screen printing method, a photoresist method, or the like. 3) A circuit is formed by etching the written circuit. 4) Laminate the coverlay film on the circuit surface. 5) External mold processing and inspection of the circuit. In the present invention, after the above step 3) is finished, before the coverlay film is laminated 4), the low temperature plasma treatment or the corona discharge treatment is performed on the circuit surface of the circuit-formed flexible printed wiring board. Is. The circuit surface on which a circuit is formed on the flexible printed wiring board through the etching process has both a circuit portion (conductor portion) and an adhesive exposed portion (conductor removed portion). After the circuit is formed, the circuit surface (conductor portion and conductor removed portion) of the flexible printed wiring board is continuously faced up, and the circuit surface is subjected to a low temperature plasma treatment or a corona discharge treatment. The circuit surface, that is, the conductor portion and the conductor removed portion, is cleaned by low temperature plasma treatment or corona discharge treatment to clean the conductor surface such as dirt and the like, which makes it easier for the adhesive of the cover film to adhere evenly. The embedding property is improved, and the exposed surface of the adhesive has minute irregularities on the surface due to the activation treatment, and OH groups are partially generated to make the surface hydrophilic and the adhesiveness of the coverlay film with the adhesive is improved. It is expected to improve. Low temperature plasma treatment is effective for further improving the hydrophilicity of the exposed portion of the adhesive.

As a low temperature plasma treatment method, the circuit-formed flexible printed wiring board is placed in a low pressure plasma treatment apparatus capable of depressurizing, the apparatus is kept under an atmosphere of inorganic gas, and the pressure is 0.001 to 10 torr. Preferably 0.
0.1 to 10k between electrodes while holding at 01 to 1 torr
A low-temperature plasma of an inorganic gas is generated by applying a direct current or an alternating current of about V to cause glow discharge, and one or both surfaces having a circuit surface are continuously plasma-treated while sequentially moving the flexible printed wiring board. The plasma processing time is preferably about 0.1 to 100 seconds. The gas used for the low-temperature plasma treatment is an inorganic gas, and as the inorganic gas, helium, neon, an inert gas such as argon and oxygen, nitrogen, carbon monoxide, carbon dioxide, ammonia, air, etc. are used. Not only one kind but also a mixture of two or more kinds is used.

In the corona discharge treatment method, a high voltage is applied between a roller supporting a circuit-formed flexible printed wiring board and an electrode arranged opposite to the roller to cause corona discharge and move the wiring board between them. A method of sequentially treating the surface while performing the above is preferable. Specifically, it consists of a high-frequency oscillator body, a high-voltage transformer, and a discharge electrode,
Before and after that, a base material is sent out and a winding device is incorporated. The frequency of the high-frequency oscillator is 1 to 150
kHz, preferably 30-130 kHz, maximum output 0.
5 to 40 kW, preferably 1 to 10 kW is good. Since the installed electrode also treats a metal surface, a fixed type of ceramic coating, a roll type electrode or a roll type electrode of heat resistant silicone rubber coating is preferable. Processing speed is 1-100m / mi
n, preferably 5 to 50 m / min.

Next, the cover lay film used in the present invention comprises a heat-resistant insulating plastic film having a heat-resistant adhesive layer in a semi-cured state on one side, and a release paper or release film laminated on the adhesive side. is there. The heat-resistant insulating plastic film used for the coverlay film may be the same as the heat-resistant insulating plastic film used for the flexible printed wiring board. Among them, the polyimide film is preferable. As heat-resistant adhesives, polyester / epoxy type, epoxy / phenol / polyester type, nylon / epoxy type, carboxyl group-containing NBR / epoxy type, epoxy / phenol /
Carboxyl group-containing NBR type, epoxy / acrylic type,
Various synthetic adhesives such as acrylic adhesives can be used, and these are used alone or in combination of two or more. As the solvent, an organic solvent such as methyl ethyl ketone, toluene or methanol may be used. The release paper and release film are polyethylene coated paper, TPX coated paper, TPX film, polyethylene film, polypropylene film, polyester film with release agent (silicone release agent, etc.), polyethylene film, polypropylene film, etc.
Examples include, but are not limited to, release papers and release films having a thickness of μm.

As a method of manufacturing the coverlay film,
The heat-resistant adhesive dissolved in a solvent to a desired concentration is applied to a heat-resistant insulating plastic film by a coater so as to have a dry state of 10 to 50 μm, and dried at 50 to 150 ° C. to evaporate the solvent and adhere. The release agent is semi-cured and a release paper or release film is overlaid on the adhesive surface of the heat-resistant insulating film with the adhesive, and heat-pressed under the conditions of 60 to 120 ° C. and 5 to 20 kg / cm by a roll laminator. Manufactured by.

The cover lay film thus produced is subjected to a desired perforating process using a die or an NC drill, and the release paper or the cover lay film from which the release film has been removed is used to activate the flexible printed wiring board. Laminated on the circuit surface by a press machine, 120-180 ℃, 1
A flexible printed wiring board can be prepared by thermocompression bonding at 0 to 100 Kg / cm ² .

[0019]

According to the present invention, the adhesiveness between the circuit of the flexible printed wiring board and the coverlay film is increased, and it is possible to supply the flexible printed wiring board excellent in solder heat resistance, circuit embedding property and flexibility. became.

[0020]

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited thereto. (Example 1) A sample was prepared according to the following method and its physical properties were measured. The results are shown in Table 1. 1. Manufacture of a substrate for flexible printed wiring circuit A polyimide film having a thickness of 25 μm and a width of 508 mm (Kapton 100H manufactured by Toray DuPont) is coated with an epoxy-polyester adhesive by a roll coater so that the thickness after drying is 18 μm, After passing through an in-line dryer to remove the methyl ethyl ketone solvent at 120 ° C to semi-cure the adhesive, a rolled copper foil of 35 µm (BHN manufactured by Japan Energy) and a heating roll temperature of 120
The mixture was heat-pressed at a temperature of 20 ° C. and a linear pressure of 20 Kg / cm, and wound into a roll. This in a curing oven at 80 ℃ for 5 hours, 1
It was heated and cured at 50 ° C. for 5 hours to produce a flexible printed circuit board.

2. Production of coverlay film Polyimide film thickness 25 μm, width 508 mm (product name Kapton 100H) is coated with an epoxy-NBR adhesive with a roll coater so that the thickness after drying is 35 μm, and 80 ° C. × 2 After heating and drying at 120 ° C. for 5 minutes, the adhesive was semi-cured, and the release paper was heated and pressure-bonded with a roll laminator at a temperature of 50 ° C. and a linear pressure of 5 Kg / cm to obtain a coverlay film. The polyimide film used in the production of the flexible printed circuit board and the coverlay film was one on which the adhesive-coated surface was previously subjected to continuous low-temperature plasma treatment under the following conditions. Processing conditions are vacuum 0.1 torr, oxygen 1.0L
/ Min, the applied voltage was 2 kV, the input was 30 kW at 110 kHz, and the film was moved along the outside of the electrode at a speed of 30 m / min at a distance of 40 mm outside the electrode for processing.

3. Manufacturing of flexible printed wiring board A test circuit was prepared by the following method. 1) The following evaluation circuits (A) to (C) were printed on the above-mentioned substrate with a screen, etched, washed with water, and dried to prepare. The evaluation circuit (A) shape W = 240 mm × L = 300 mm was used for a flexible printed circuit board sample, and a line width of 0.2 mm shown in FIG.
A parallel pattern copper circuit having a line spacing of 0.3 mm is formed. A 10 mmφ copper circuit shown in FIG. 2 is formed on a flexible printed circuit board sample having an evaluation circuit (B) shape W = 240 mm × L = 300 mm. Evaluation circuit (C) shape W = 200 mm × L = 200 mm flexible printed circuit board sample, copper circuit width 0.2 m shown in FIG.
m, line spacing 0.3 mm, number of circuits 8 and circuit length 100 mm
To form a circuit.

[0023] 4. Circuits for activation treatment evaluation (A) to (C) of the circuit surface were formed on a flexible printed circuit board and subjected to low-temperature plasma treatment. Low - temperature plasma treatment conditions Oxygen is supplied at 1.0 L / min at a vacuum degree of 0.1 torr, input voltage is 2 kV, frequency is 110 kHz, and input is 30 k.
W, the apparatus has four electrodes arranged in a cylindrical shape, and the evaluation circuits A to C are moved along the outside of the electrode at a processing speed of 10 m / min at a distance of 40 mm outside the electrode, and the circuit surface is cooled to a low temperature. Plasma treatment was performed.

5. Laminated coverlay film (Flexi
Manufacture of a Bull Printed Wiring Board) Next, the cover lay film was laminated under the following conditions on the circuit surface subjected to the low temperature plasma treatment. Evaluation circuit (A ′) 240 × 28 in the evaluation circuit (A) that has been subjected to low temperature plasma treatment
The cover lay film cut to 0 mm is thermocompression bonded by a pressing method at a temperature of 160 ° C., a pressure of 30 Kg / cm, and a time of 60 minutes. Evaluation circuit (B ′) A coverlay film having a hole of 5 mmφ formed in the evaluation circuit (B) subjected to low-temperature plasma is positioned so that the hole of 5 mmφ is located at the center of the copper circuit of 10 mmφ, and the evaluation circuit (A ′ ) And press-bonding under the same conditions. Evaluation circuit (C ') The coverlay film is removed from the terminal for the evaluation circuit (C) subjected to the low temperature plasma treatment, and press molding is performed under the same conditions as those of the evaluation circuit (A').

6. Measurement of physical properties 5. The following physical properties were measured for the evaluation samples A ', B', and C'created in 1. (1) Coverlay film circuit embeddability The evaluation circuit (A ') is examined with a 30x magnifying glass for the embeddability of the copper circuit coverlay film adhesive in the circuit. This measurement is repeated and 20 sheets are inspected to count the number of embedded defects. (2) Solder heat resistance (normal state, moisture absorbing solder) The evaluation circuit (A ′) is cut into 25 × 25 mm, the sample is flowed in the solder bath for 30 seconds, and then the temperature at which no blistering occurs is measured. Moisture absorption solder sample 40 ℃ × 9
After absorbing moisture under the condition of 0% RH × 1hr, apply 3% to the solder bath.
Flow the sample for 0 seconds, and visually check the appearance, blisters and the like. (3) Peel strength The evaluation circuit (A ') was cut in parallel with the pattern to a width of 10 mm, and the sample was peeled from the circuit in the 90 ° direction at a speed of 20 mm / min. For the peel strength after heat deterioration, the peel strength is similarly measured after heat-treating the evaluation circuit (A ′) at 150 ° C. for 10 days. (4) Solder gouging property Apply solder paste to the exposed portion of the copper foil in the 5 mmφ hole of the evaluation circuit (B '), allow the solder to flow at the prescribed temperature, and visually measure the gouging of solder to the coverlay film. To do. ◯: No solder chipping ×: Solder chipping (5) MIT heat resistance The test circuit (C ') was cut to a width of 10 mm according to JIS
It measures according to P8115. Tip bending diameter 0.38mmR, load 500g

[0026]

Examples 2 to 3 Table 1 shows the processing speeds in Example 1.
A low-temperature plasma treatment was performed under the same conditions as in Example 1 except that the conditions shown in (1) were changed to prepare a flexible printed wiring board.
The results are shown in Table 1.

[0027]

Comparative Example 1 A flexible printed wiring board was prepared in the same manner as in Example 1 except that the circuit in Example 1 was not subjected to the low temperature plasma treatment.

[0028]

Examples 4 to 8 Flexible printed wiring boards were prepared in the same manner as in Example 1 except that the corona discharge treatment was performed under the following conditions instead of the low temperature plasma treatment in Example 1.・Corona discharge treatment conditions Kasuga Electric Co., Ltd. HFS- with different maximum oscillation frequency output
A 201 type (30 kHz, 2 kW) and HF-403 type (110 kHz, 4 kW) dual high-frequency power supply device was used, and a silicone rubber sleeve type roller electrode having a diameter of 100 mm and a length of 60 mm was used as a discharge electrode. The evaluation circuits A to C were subjected to corona discharge treatment under the conditions shown in Table 2.

[0029]

[Table 1]

[0030]

[Table 2]

[Brief description of drawings]

FIG. 1 is a plan view of an evaluation circuit (A) on a wiring board according to a first embodiment of the present invention.

FIG. 2 is a plan view of an evaluation circuit (B) on the wiring board according to the first embodiment of the present invention.

FIG. 3 is a plan view of an evaluation circuit (C) on the wiring board according to the first embodiment of the present invention.

[Explanation of Codes] W: Vertical axis of wiring board L: Horizontal axis of wiring board w1: Distance from board end to circuit on vertical axis of evaluation circuit (B) w2: Vertical axis of evaluation circuit (B) Distance between circuits 11: Distance between circuits on the horizontal axis of the evaluation circuit (B) 12: Length of the circuit at the bent portion of the evaluation circuit (C) 13: Length of the terminal portion of the circuit of the evaluation circuit (C)

Claims (1)

[Claims] 1. A flexible printed wiring board comprising a circuit-formed flexible printed wiring board and a coverlay film which are heated and pressure-bonded to each other. Low-temperature plasma treatment or corona discharge treatment is applied to a circuit surface of the flexible printed wiring board on which a circuit is previously formed. After applying the heat treatment, a cover lay film is heated and pressure-bonded to the treated surface, which is a method for manufacturing a flexible printed wiring board.