KR20080113709A - Manufacturing method of fpcb - Google Patents

Abstract

A manufacturing method of the flexible printed circuit board is provided to produce one side flexible printed circuit board by one process, so improving the productivity of the flexible printed circuit board manufacturing process. A manufacturing method of the flexible printed circuit board is comprised of steps: After attaching a foam sheet to the one side or both sides of the flexible printed circuit board, foaming and separating them; laminating a material(1), a surface processing layer(2), an adhesion layer(3) and release film(4) in sequence. The adhesive layer includes the thermal expansibility microsphere and cross reactivity copolymers.

Description

Manufacturing method of flexible circuit board using high temperature foam sheet {Manufacturing method of FPCB}

1 is a cross-sectional view of the cross-section foam sheet used in the present invention

Figure 2 is a cross-sectional view of the double-sided foam sheet used in the present invention

Figure 3 is a graph showing the hot press working conditions employed in the present invention

Figure 4 is a graph showing the dimensional change rate when working with the foam sheet according to the present invention

Figure 5 is a graph showing the rate of change of the dimension of the cross section work using a conventional foam sheet

* Description of the main parts of the drawing

1: Base

2: surface treatment layer

3: Foam adhesive sheet using interreactive copolymer mixture

4: Release Film

The present invention relates to a method for manufacturing a flexible printed circuit board (FPCB) using a foam sheet that is foamed at a high temperature, and more particularly, by adopting an interreactive copolymer resin as a pressure-sensitive adhesive layer to excellent adhesive strength The present invention relates to a foam sheet for a flexible circuit board which can be easily peeled from an adherend by high temperature heat treatment, and a method of manufacturing the flexible circuit board using the same.

Recently, the demand for flexible circuit boards is rapidly increasing with the miniaturization and lightening of electronic device products such as mobile phones, digital cameras, MP3, DMB, or composite devices incorporating these functions.

The conventional manufacturing process of the flexible printed circuit board is performed by fixing it with adhesive tape on a substrate called a carrier or a backup board due to the flexural or creased ductility of the flexible printed circuit board. Afterwards, a method of manufacturing a flexible circuit board using a presentation sheet has been studied for smooth peeling of the adhesive tape and the flexible circuit board.

In general, foam sheets are mainly used as a support for bonding or cutting multilayer chip capacitors (MLCC) or inductor chips. At this time, the conditions for losing the adhesive force is made at a temperature range of 120 to 130 ℃ and atmospheric pressure and in this case, the important physical properties are adhesive force and foaming force. However, in the manufacturing of flexible circuit boards, the foam sheet does not burst in the foam cell under conditions of more than 40 minutes at 150 to 160 ° C. and 40 kg / cm 2, which is a hot press lamination condition. After completion, the foaming should be performed at a higher temperature, about 180 ° C., and peeling should occur. Also, a condition that the contamination of the flexible circuit board should not occur due to the transfer of the adhesive resin during the manufacturing process of the flexible circuit board.

However, the conventional foam sheet has a limit to use for high temperature because foaming starts at about 150 ℃ even if the foaming temperature is high.

On the other hand, as well as a method of manufacturing a flexible printed circuit board using a foam sheet foamed at a high temperature as described above, in order to improve the profitability of the flexible printed circuit board manufacturers propose a method of manufacturing a double-sided flexible printed circuit board using a double-sided foam sheet. It is becoming. This is a double-sided foam sheet for fixing during processing in the flexible circuit board manufacturing process. With this, two products are produced simultaneously through one process without changing the existing process. The productivity in time can be doubled. In order to give flexibility in the process of producing a multilayered flexible circuit board or a rigid-flex circuit board, it is inevitably manufactured as a single-sided flexible circuit board. Some manufacturers can work on both sides at the same time, but there is a limit to increase productivity because only one side can be processed. However, in the process of producing flexible circuit boards, by using double-sided adhesive foam sheets, double-sided flexible circuit boards can be attached to both sides of the foam sheet so that both sides can be processed at the same time, thus improving productivity twice. It can take the role of a cushion film (cushion film) in the carrier film or molding process, there is an advantage that can reduce the use of the material used in the flexible circuit board manufacturing process.

Foam sheets employed to advance single-sided flexible printed circuit boards into double-sided processes should not foam or thermally deform under conditions of more than 40 minutes at a temperature of 160 ° C and a pressure of 40 kg / cm 2. Chemical resistance is required, foaming occurs easily at 170 to 190 ° C after completion of the flexible circuit board manufacturing process, and contamination of the flexible circuit board does not occur due to the transfer of the adhesive resin during the manufacturing process of the flexible circuit board.

Conventionally, acrylic adhesives and crosslinking agents including crosslinking functional groups are mostly used as adhesives for foamed sheet processed products. In order to increase foaming temperature by suppressing expansion of the microspheres by cohesive action on the microspheres, the crosslinking functional groups may be used. The ratio must be high and a large amount of crosslinking agent must be used. Therefore, as time passes, the crosslinking progresses and the viscosity changes significantly, or when the coating process proceeds for 4 hours or more due to gelation, the physical properties of the starting part and the ending part of the coating are changed.

Republic of Korea Patent Publication No. 2002-0060659, Republic of Korea Patent Publication No. 2002-0060656, Republic of Korea Patent Publication No. 2002-0060657, Republic of Korea Patent Registration No. 10-0514611 double-sided exposure type flexible printed circuit board, single-sided flexible printed circuit board, It has been proposed that foam sheets can be used to reduce the process of thin film flexible circuit boards. However, the manufacturing process of flexible circuit boards is based on:-D / F adhesion-Exposure-D / F phenomena-Cu corrosion-Drying-Winding-Roll cutting-Welding-Coverlay hot press-Square-Surface treatment-Electroless Gold-It proceeds to the stage of punching process, in particular, in the case of the coverlay molding process is carried out in a condition of 40 minutes or more at 150 to 160 ℃, 40㎏ / ㎠, under this condition, the existing foam sheet is foamed during the coverlay molding process Since the existing foam sheet can be employed only up to the previous step of the coverlay forming process, there is a disadvantage that there is no practical use in the prior art.

In addition, Japanese Laid-Open Patent Application No. 2003-338678 filed by Nito Electric Co., Ltd., Japan, discloses that a double-sided foam sheet is used as a carrier film in the double-sided process of a single-sided flexible circuit board. The sheet may only be partially applied early in the manufacturing process.

In order to solve the above problems, the present invention is excellent in the adhesive strength by using the cross-linked copolymer resin as an adhesive, and at the same time to produce a high-temperature foam sheet that can be easily peeled from the adherend by heat treatment at 180 ℃ or more. And to provide a method for producing FPCB using this.

In addition, another object of the present invention is the adhesive force under the high temperature and high pressure conditions of 160 ℃, 40㎏ / ㎠, 40 minutes or more during the manufacturing process of the flexible printed circuit board (FPCB), hot press (hot press) process By using a double-sided foam sheet with chemical resistance that does not penetrate the etching liquid in the etching process, compared to the conventional single-sided FPCB production process, it is possible to produce two single-sided FPCB at the same time in one step of the FPCB manufacturing process It is to provide a method for producing FPCB that can improve productivity.

The present invention provides a flexible circuit board foam sheet that can be used in a high temperature process that can be easily peeled from the adherend by heat treatment at 180 ° C. or more by employing an interreactive copolymer resin as an adhesive layer. The present invention also relates to a method for manufacturing a flexible circuit board using the foam sheet for flexible circuit board.

Hereinafter, a method for manufacturing a flexible circuit board foam sheet usable in a high temperature process used in the present invention and a method for manufacturing a flexible circuit board using the same will be described in detail. In addition, the method of manufacturing a flexible printed circuit board will be described sequentially with respect to a method for manufacturing a single-sided flexible circuit board and a method for manufacturing a double-sided flexible circuit board.

The high-temperature foam sheet used in the present invention forms a pressure-sensitive adhesive layer by using a pressure-sensitive adhesive resin containing a mixture of thermally expandable microspheres, and the pressure-sensitive adhesive layer can be peeled at high temperatures by foaming or expanding by heating. It is an adhesive sheet. 1 is a cross-sectional view showing a single-sided foam sheet used in the manufacture of single-sided PCB, Figure 2 is a cross-sectional view showing a double-sided foam sheet used in the production of double-sided PCB.

As shown in FIG. 1, the single-sided foam sheet according to the present invention is laminated in the order of the substrate 1, the surface treatment layer 2, the adhesive layer 3, and the release film 4, and the adhesive layer 3. Is characterized by including thermally expandable microspheres and interreactive copolymers.

The substrate 1 may be a suitable thin film commercialized, such as PET, the thickness is preferably 250 μm or less, preferably 25 to 100 μm, but is not limited thereto. The surface treatment layer 2 for forming a strong chemical bond between the substrate and the adhesive layer is subjected to a chemical treatment in which the surface is oxidized by chromic acid treatment, ozone treatment, corona treatment, flame treatment, ion radiation treatment, or the like. It is a layer treated with highly polar polymer such as polyester, hydrolyzed ethylene-vinylacetate and polyvinyl butyral. The surface treatment layer 2 should not be contaminated with the adherend during peeling after heat treatment, and in particular should not be changed under chemical or molding processing conditions used during the flexible circuit board manufacturing process. The surface treatment layer has a thickness of 5 m or less, preferably 1 m or less. When the thickness of the surface treatment layer is large, the degree of deformation of the pressure-sensitive adhesive layer after heat treatment of the foam sheet is small, and the adhesion strength decreases. When the heat-peelable pressure-sensitive adhesive sheet is adhered to the adherend, the surface shape is maintained well, while providing a large adhesion area, and at the same time, foaming in the plane direction of the foam sheet when the pressure-sensitive adhesive layer is heated or foamed to peel from the adherend. Or it reduces the constraint of expansion and serves to improve the deformation of the corrugated structure when the adhesive layer is foamed. When the foamed adhesive layer is formed on the substrate by coating, if there is no bonding force between the adhesive layer and the substrate at the time of foaming, peeling occurs between the foamed layer and the substrate when the foaming and expansion is performed, and thus a predetermined purpose cannot be achieved.

The adhesive layer 3 contains thermally expandable microspheres so that the adhesive sheet adhered to the adherend can be easily peeled off from the adherend by heat treatment. By heating the pressure-sensitive adhesive layer and foaming and expanding the thermally expandable microspheres, the pressure-sensitive adhesive sheet can be peeled off by reducing the adhesive area in which the foam penetrates the pressure-sensitive adhesive layer and in contact with the adherend.

The thermally expandable microspheres are materials that easily gasify and exhibit thermal expansion properties such as isobutane, propane and pentane, and the shells are thermally soluble materials such as vinylidene chloride and acrylonitrile copolymers. Or a suitable material that is destroyed by thermal expansion.

The microspheres having an average particle diameter of 10 to 25 µm are easily dispersed in the adhesive resin by heat treatment, the deformation of the adhesive layer is large, and the drop in adhesive strength is obvious. In addition, the pressure-sensitive adhesive layer is preferably formed thicker than the average particle diameter of the thermally expandable microspheres, and thicker than the maximum particle diameter of the final thermally expandable microspheres, and it is preferable to smooth the surface of the pressure-sensitive adhesive layer and achieve a stable adhesion before heat treatment. Do. In order to reduce the adhesive strength of the adhesive layer by the heat treatment, the microspheres may have a strength of foam expansion and expansion at a volume expansion rate of 10 times or more upon heating and the film does not rupture at that time.

In addition, since a high temperature condition of 160 ° C. is mandatory for the flexible circuit board manufacturing process, it is preferable to use a foaming start temperature as high as possible. Although the compounding quantity of thermally expansible microsphere is suitably selected according to the required degree, such as the expansion ratio of an adhesive layer, the fall of adhesive force, etc., it is generally 50 weight part or less per 100 weight part of adhesive which forms an adhesive layer, Preferably it is 5-20 weight It is wealth.

In order to be able to apply thermally expandable microspheres in which foaming starts near 140 ° C. so that the adhesive layer is heated at a temperature range of 170 to 190 ° C. to withstand the flexible circuit board manufacturing process, it is necessary to increase the foaming temperature by restricting expansion of the micro spheres. need.

A first copolymer obtained by copolymerizing a vinyl monomer comprising a monomer, a vinyl comonomer and a carboxyl group, and a vinyl monomer including a vinyl monomer, a vinyl comonomer, and an oxazoline group. It is an adhesive resin mixed with a copolymer.

Vinyl monomers and vinyl comonomers constituting the first copolymer and the second copolymer are used for the purpose of imparting the adhesiveness, cohesion, heat resistance, flexibility, holding force, elasticity, etc. of the pressure-sensitive adhesive, if necessary, independently of each other Eate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, hexyl acrylate, hexyl methacrylate, octyl acrylate, 2-ethyl Any one or more alkyl group-containing vinyl monomers selected from hexyl acrylate; Hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, hydroxyhexyl acrylate, hydroxyhexyl methacrylate Any one or more hydroxyl group-containing vinyl monomers selected from rates; At least one N-substituted amide vinyl monomer selected from N, N-dimethyl acrylamide and N, N-dimethyl methacrylamide; Any one or more alkoxyalkyl acrylate vinyl monomers selected from methoxyethyl acrylate, methoxyethyl methacrylate, ethoxyethyl acrylate and ethoxyethyl methacrylate; Vinyl acetate, vinyl propionate, N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole At least one vinyl monomer selected from vinylmorpholine, N-vinylcarboxamide, styrene, α-methylstyrene, and N-vinylcaprolactam; Any one or more cyanoacrylate vinyl monomers selected from acrylonitrile and methacrylonitrile; Any one or more epoxy group-containing acrylic monomers selected from glycidyl acrylate and glycidyl methacrylate; Polyethylene glycol acrylate, polyethylene glycol methacrylate, polypropylene glycol acrylate, polypropylene glycol methacrylate, methoxy ethylene glycol acrylate, methoxy polyethylene glycol methacrylate, methoxy polypropylene glycol acrylate, methoxy poly Any one or more glycol-based acrylic ester monomers selected from propylene glycol methacrylates; Any one or more acrylic ester monomers selected from tetrahydroperpriryl acrylate, tetrahydrofurryl methacrylate, 2-methoxyethyl acrylate; Any one or more monomers selected from isoprene, butadiene, isobutylene and vinyl ether; Or a group selected from the group consisting of two or more kinds thereof.

The vinyl monomer containing the carboxyl group of the first copolymer is employed for the purpose of imparting crosslinking properties by radical polymerization. Acrylic acid, methacrylic acid, carboxy ethyl acrylate, carboxy pentyl acrylate, itaconic acid, maleic acid, Any one or more carboxyl group-containing monomers selected from malic acid and crotonic acid; Two or three or more copolymers selected from functional monomers such as any one or more acid anhydride monomers selected from maleic anhydride and itaconic anhydride can be exemplified.

The first copolymer is preferably prepared from 1: 0.5 to 1.5: 0.05 to 0.3 in a weight ratio of the vinyl monomer including the vinyl monomer, the vinyl comonomer and the carboxyl group. The vinyl monomer containing the oxazoline group of the second copolymer is used for the purpose of imparting crosslinkability by radical polymerization, and the vinyl monomer containing the oxazoline group is 2-vinyl-2-oxazoline, 2-vinyl- 4-vinyl-2-oxazoline, 2-vinyl-5-vinyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, 2- Isopropenyl-5-methyl-2-oxazoline, 2- (vinylbenzyloxy-1-methylethyl) -2-oxazoline, 2- (2-hydroxy-1-methylethyl) acrylate, 2- ( One selected from the group consisting of 2-hydroxy-1-methylethyl) methacrylate or a mixture of two or more thereof can be used.

The second copolymer is preferably prepared from 1: 0.5 to 1.5: 0.05 to 0.3 in weight ratio of the vinyl monomer including the vinyl monomer, the vinyl comonomer and the oxazoline group.

The coating liquid for foam sheet adhesive layer used in the pressure-sensitive adhesive layer of the foam sheet for flexible circuit board according to the present invention after preparing the first copolymer containing a carboxyl group and the second copolymer containing an oxazoline group, respectively, It is prepared by dispersing microspheres in the pressure-sensitive adhesive mixed with the copolymer and the second copolymer. The prepared coating liquid for the pressure-sensitive adhesive layer is stable with no change over time even at long-term storage at room temperature, it is possible to increase the foaming temperature up to 10 to 30 ℃ than the foaming temperature of the conventional foam sheet.

The pressure-sensitive adhesive layer formed of the coating liquid for the pressure-sensitive adhesive layer does not foam or heat deformation within 40 minutes at a temperature of 160 ° C. and a pressure of 40 kg / cm 2, and should have chemical resistance to chemicals encountered during the manufacturing process of the flexible circuit board. During the manufacturing process, the contamination of the flexible circuit board should not occur due to the transfer of the adhesive resin. In addition, it is easy to foam within 10 seconds to 3 minutes in a hot plate, or 5 to 10 minutes in a hot air dryer, at a temperature of 170 to 190 ° C., a heat treatment condition for easy peeling off the adherend after completion of the flexible circuit board manufacturing process. Should wake up.

On the other hand, as shown in Figure 2, the double-sided foam sheet for a flexible circuit board according to the present invention is the foam sheet is a release film (4 '), adhesive layer (3'), surface treatment layer (2 '), the substrate ( 1), the surface treatment layer (2), the adhesive layer (3) and the release film (4) are laminated in this order, the adhesive layer (2, 2 ') is characterized in that it comprises a thermally expandable microsphere and an interreactive copolymer Details of each component are as described above in the cross-section foam sheet for the flexible circuit board.

Hereinafter, a method of manufacturing a flexible circuit board of a foam sheet for a flexible circuit board according to the present invention will be described.

The method of manufacturing single-sided flexible printed circuit board using single-sided foam sheet is lamination of FCCL and foam sheet-front treatment-dry film laminate-exposure-development process-etching process-dry film peeling-welding process-hot press process -Surface treatment-Punching process-Manufactured through peeling of foam sheet.

On the other hand, the method of manufacturing a double-sided flexible printed circuit board using a double-sided foam sheet as described above, the laminated (lamination) of the FCCL and the foam sheet-front treatment-dry film laminate-exposure-development process-etching process-dry film peeling-temporary welding Process-Hot press process-Surface treatment-Punching process-Manufactured by peeling of foam sheet, Laminated FCCL on both sides using double-sided foam sheet in lamination stage of FCCL and foam sheet By adhering to be able to proceed to each of the above steps, and finally through the peeling step of the foam sheet can be produced at the same time two sheets of flexible printed circuit board in one process.

The present invention provides a high-temperature foam sheet that can be easily peeled from the adherend by heat treatment at 180 ° C or more while using the mutually reactive copolymer resin as an adhesive, and using the flexible circuit The method of manufacturing the substrate will be described in more detail with reference to the examples. However, these examples are only presented to understand the content of the present invention, and the scope of the present invention should not be construed as being limited to these embodiments.

[Production Example 1]

My Monocopolymer  Produce

Ethyl acrylate (45 g), comonomer n-butyl acrylate (45 g) and acrylic acid (10 g) are mixed in a 2 L glass reactor equipped with a stirrer, a condenser, a dropping funnel, a thermometer and a jacket. The initiator α, α'-azobisisobutyronitrile (0.01 g) was added to ethyl acetate (100 g) and toluene (20 g), and the radical polymerization reaction was carried out at 70 ° C. After about 30 minutes, ethyl acrylate (135 g), comonomer n-butyl acrylate (135 g), and acrylic acid (30 g) were mixed, and the initiator α, α'-azobisisobutyronitrile (0.5 g) was added thereto. Ethyl acetate (100 g) and toluene (40 g) were added dropwise using a dropping funnel for about 90 minutes. After dropping, the temperature is kept constant and the radical initiator (1 g) is dissolved in ethyl acetate (50 g) and ethanol (50 g) and added dropwise for 60 minutes to avoid unreacted monomer after the reaction is over. The first copolymer was prepared.

My Dipolymer  Produce

Ethyl acrylate (45 g) as a monomer, comonomer n-butyl acrylate (45 g) and 2-isopropyl-2-oxa in a 2 L glass reactor equipped with a stirrer, condenser, dropping funnel, thermometer, and jacket Sleepy (10 g) was mixed. An initiator α, α'-azobisisobutyronitrile (0.01 g) was added to the solution, which was dissolved in ethyl acetate (100 g) and toluene (20 g), and then proceeded to the same method as the polymerization of a copolymer containing a carboxyl group at 70 ° C. . A radical polymerization reaction was performed. After about 30 minutes, ethyl acrylate (135 g), comonomer n-butyl acrylate (135 g) and acrylic acid (30 g) were mixed, and the initiator α, α'-azobisisobutyronitrile (0.5 g) was added thereto. It was dissolved in ethyl acetate (100 g) and toluene (40 g), and the dropping was performed for about 90 minutes using a dropping funnel. After dropping, the temperature was constantly adjusted, and after the reaction was completed, the radical initiator (1 g) was dissolved in ethyl acetate (50 g) and ethanol (50 g) and reacted for an additional 3 hours to prevent unreacted monomers. Copolymers were prepared.

Adhesive  Produce

The prepared first copolymer and the second copolymer were mixed at a weight ratio of 1: 1. A microsphere F-80VSD (trade name, manufactured by Matsudodo Co., Ltd., 150-160 ° C. foaming start) (10 g) was added to the mixed resin (100 g) and dispersed to prepare an adhesive resin.

[Production Example 2]

The weight ratio of the monomers used in the preparation of the first copolymer and the second copolymer of Preparation Example 1 was determined as ethyl acrylate / n-butyl acrylate / acrylic acid = 4.5 / 4.5 / 1.5 and ethyl acrylate / n-butyl acrylate / A sticky resin was prepared in the same manner as in Preparation Example 1, except that 2-isopropyl-2-oxazoline = 4.5 / 4.5 / 1.5 was used.

[Production Example 3]

The weight ratio of the monomers used in the preparation of the first copolymer and the second copolymer of Preparation Example 1 was determined as ethyl acrylate / n-butyl acrylate / acrylic acid = 4.5 / 4.5 / 0.6 and ethyl acrylate / n-butyl acrylate / A sticky resin was prepared in the same manner as in Preparation Example 1, except that 2-isopropyl-2-oxazoline was used as 4.5 / 4.5 / 0.6.

[Production Example 4]

 The type of monomers used in the preparation of the second copolymer of Preparation Example 1 was 2-ethylhexyl acrylate / methyl methacrylate / n-butylacrylate / 2-isopropyl-2-oxazoline = 2.0 / 2.5 / 4.5 Adhesive resin was prepared in the same manner as in Preparation Example 1, except that each was used as /1.0.

Production Example 5

The weight ratio of monomers used in the preparation of the second copolymer of Preparation Example 4 was 2-ethylhexyl acrylate / methyl methacrylate / n-butylacrylate / 2-isopropyl-2-oxazoline = 2.0 / 2.5 / 4.5 Adhesive resin was prepared in the same manner as in Preparation Example 4, except that each was used as /1.5.

[Examples 1 to 5]

After applying the adhesive resin prepared in Preparation Examples 1 to 5 to the PET film (50㎛) to form a foam adhesive layer of 37㎛, and prepared by attaching a 36㎛ release paper, the prepared foam sheet Aged for 7 days. The whole process of double-sided flexible circuit board was carried out in the following order. Lamination of FCCL and Foam Sheet-Facade Treatment-Dry Film Lamination-Exposure-Development Process-Etching Process-Dry Film Peeling-Welding Process-Hot Press Process-Surface Treatment-Punching Process-Foam Sheet Peeling Process Performance was evaluated in each process.

end. FCCL ( Flexible Copper Clad Laminate Selection of)

In general, FCCL for single-sided flexible printed circuit boards is divided according to the thickness of copper foil, adhesive and polyimide film and according to the type of copper foil. In the present Example, the copper foil of the specification of Table 1 was used. The thickness of the coverlay film used for the production of the product was 25 μm of the adhesive layer and 25 μm of the polyimide layer.

TABLE 1

I. Lamination (Lamination of FCCL and Foam Sheet)

Laminating the foam sheet and FCCL is a step of adhering the FCCL. Using a general laminator, the copper foil of the cross-section FCCL was directed outward, and the surface of the polyimide was adhered to the foam sheet to perform lamination. In the lamination process, bubbles and polyimide were not wrinkled in the adhered product, and the adhesion state of the outer portion was confirmed so that various chemicals did not penetrate the adhesive force of the outer portion in the process.

All. Frontal treatment

In order to prevent corrosion of the copper foil surface of FCCL, the surface treatment is a rust preventive treatment. The rust preventive component is removed and irregularities are applied to the surface of the copper foil to increase the surface area to improve the adhesion of the dry film (photosensitive resin). This process is performed by chemically corroding the copper surface. The chemical used is a mixture of sulfuric acid (H ₂ SO ₄ ) and hydrogen peroxide (H ₂ O ₂ ).

la. Dry film  Laminate

Dry film lamination is a process of bonding photosensitive resin to form a circuit on copper foil. When manufacturing a single-sided flexible circuit board, the copper foil surface is laminated with dry film and the opposite polyimide surface is wrinkled or torn in subsequent processes. In order to prevent the adhesion to the carrier film.

hemp. Exposure

In the exposure process, when the photosensitive resin is irradiated with ultraviolet rays applied to the mask film to form a circuit in the state where FCCL is adhered, the black portion on the mask film does not pass through the ultraviolet rays but only the transparent portion passes through the ultraviolet rays, and the dry film Only crosslinking was made to the part.

bar. Developing process

The dry film was exposed to light in 3% sodium carbonate (Sodium Carbonate) solution so that the cross-linked part did not dissolve and did not receive light.

four. Etching process

The part where the circuit formation is made by the developing process, the dry film is heated on the copper foil as a resist, and the part outside the circuit passes through the etching solution (CuCl ₂ , HCl, H ₂ O ₂ ) to corrode the copper in the exposed copper foil. To corrode the copper surface.

The chemicals and the process conditions used in the above individual processes are as shown in Table 2.

TABLE 2

Ah. Temporary Process

When the FCCL forms a circuit through the etching process, the circuit part other than the part connected to the connector in the circuit part and the soldered part for mounting the part is bonded to the coverlay film to protect the circuit. Since this coverlay film is a film coated with a thermosetting adhesive, the adhesive strength is weak at room temperature, so that the coverlay film does not roll before curing the adhesive by hot press of the FCCL formed with the coverlay film and the circuit. Temporary fixation was done using the pharynx partially to prevent it.

character. Hot press  fair

The hot press process is a process for adhering the coverlay film by thermal curing the circuit protection film, and the work was performed under the conditions shown in Table 3. to be. This process is a process to heat the adhesive of the coverlay film for a certain time in a heated pressurized state using a hot press. In order to use the foam sheet, it is essential that the foam sheet should not be foamed under the working conditions of the process, and there should be no appearance deformation or dimension change of the foam sheet and the flexible circuit board.

TABLE 3

car. Surface treatment

Surface treatment is generally electroless gold plating method, electroless gold plating is a batch type was treated under the conditions of Table 4. Gold plating went through a pretreatment process using the chemicals listed in the table below.

TABLE 4

Ka. External Processing (Punching) Process

The flexible printed circuit board attached to the foam sheet has a punching process for external processing in order to finally complete the product. The external processing is performed by aligning the guide hole on the flexible circuit board with the mold position.

Get. Peeling of foam sheet

The flexible printed circuit boards attached on both sides should be peeled off in this step. Characteristics of the foam sheet is separated by the weakening of the adhesive force by the expansion of the foam cell at the pre-designed temperature. The design of this foaming temperature is such that foaming occurs at least 170 ° C or higher. The finished product was peeled off using a heating apparatus such as an oven of a hot air circulation system.

[Comparative Production Example 1]

In a 2 L glass reactor equipped with a stirrer, condenser, dropping funnel, thermometer, and jacket, n-butyl acrylate (48.5 g), ethyl acrylate (48.5 g), acrylic acid (2 g), and hydroxypropyl acrylate ( 1.0 g) and α, α'-azobisisobutyronitrile (0.01 g) is dissolved in ethyl acetate (160 g) and toluene (270 g), placed in a dropping funnel, replaced with nitrogen, and the flow continues. After radical polymerization was carried out at 80 ° C. for 8 hours and an excessive amount of radical initiator was added at the end of the reaction to prevent unreacted monomers from remaining. Then, microsphere F-80VSD (trade name, manufactured by Matsudodo, 150-160 ° C.) was used. (10 g) of foaming was added and dispersed, and an isocyanate crosslinking agent AK-75 (trade name, Aekyung Chemical) was added twice as much as the hydroxyl functional group of the adhesive resin, and stirred to prepare an adhesive resin.

[Comparative Production Example 2]

A pressure-sensitive adhesive resin was prepared in the same manner as in Comparative Example 1 except that the amount of hydroxypropyl acrylate (2.0 g) having a crosslinking functional group was increased in Comparative Preparation Example 1.

[Comparative Production Example 3]

In Comparative Preparation Example 1, an isocyanate crosslinking agent AK-75 (trade name, Aekyung Chemical) was prepared by adding 4 times the amount of the hydroxyl group functional group of the adhesive resin, to prepare an adhesive resin in the same manner as in Comparative Example 1.

[Comparative Production Example 4]

In Comparative Preparation Example 2, an isocyanate crosslinking agent AK-75 (trade name, Aekyung Chemical) was prepared by adding 4 times the amount of the hydroxyl group functional group of the adhesive resin, to prepare an adhesive resin in the same manner as in Comparative Example 2.

Comparative Example 1 to Comparative Example 4

After applying the adhesive resins prepared by Comparative Preparation Examples 1 to 4, respectively, on PET film (50㎛), and formed a foam adhesive layer of 37㎛ and attached a release sheet of 36㎛ foam sheet Prepared. The foam sheet thus prepared was aged for 7 days and used for the final test. The whole process of double-sided flexible circuit board was carried out in the following order. Lamination of FCCL and Foam Sheet-Facade Treatment-Dry Film Lamination-Exposure-Development Process-Etching Process-Dry Film Peeling-Welding Process-Hot Press Process-Surface Treatment-Punching Process-Foam Sheet Peeling Process Performance was evaluated in each process.

For the double-sided test of single-sided flexible circuit boards, the adhesive resin and foam sheet manufactured according to the above production examples, comparative manufacturing examples and comparative examples, adopting the following materials and process conditions as a high-temperature foam sheet The reliability was investigated in the previous process.

1. Selection of Fabric

The fabric for foam sheet is designed to be foamed in optimum volume at least 180 ℃ in order to use for flexible circuit board process. Therefore, it is necessary to maximize heat transfer during foaming and workability or roll-to-roll ( In order to have flexibility in consideration of the roll to roll) method, a PET film between 25 and 100 μm was used. Furthermore, heating to high temperatures and cooling to room temperature are repeated, so thermal dimensional deformation should not occur. In order to satisfy these conditions, the base material was used by 50 micrometers and 36 micrometers thickness as a release film.

2. Foaming condition and method

In general, the separation of the foam sheet was used, such as a hot air oven (convection oven) and hot plate (hot plate). In the flexible circuit board process, a foam sheet having a width of at least 250 mm is used, and a precondition for enduring the hot press process is required, and thus the foaming temperature of the foaming agent itself must be high. Therefore, the foam peeling device was selected in consideration of the thermal conductivity efficiency and the dimensional deformation of the flexible circuit board.

3. Reliability Assessment

The foam sheet is applied to the single-sided flexible circuit board process to double the efficiency of the manufacturing process by double-sided, and to reduce defects such as wrinkles and tears in the manufacturing process caused by thin product characteristics of the flexible circuit board. In particular, when the foam sheet is used, the foam sheet itself provides nutrition to the quality of the flexible circuit board product, and additional negative factors occur in the manufacturing process of the flexible circuit board. It was tested whether or not the occurrence of defects.

Maintaining 70 ℃ proceeded laminating the FCCL on both sides of the foam sheet. Bubbles and wrinkles of the polyimide film did not occur in the adhered product during the lamination process. In particular, the adhesion state of the outer part was checked so that various chemicals did not penetrate due to the deterioration of the adhesive force of the outer part, but it showed a firm adhesive force. Even in the state of winding and bending the roll, the detachment phenomenon of the foam sheet and the copper foil was not found. The chemical used in the frontal treatment process was a mixture of sulfuric acid (H ₂ SO ₄ ) and hydrogen peroxide (H ₂ O ₂ ), and it was confirmed that there was no liquid penetration into the surface bonded to the foam sheet. In this process, the foam sheet and FCCL are attached to both sides, so that the thickness is kept thick, so that the use of subsidiary carrier film is unnecessary. When laminating both sides of the dry film at the same time, it can be seen that the airflow is reduced by 50%. In the exposure process, the exposure machine is irradiated with ultraviolet rays from the top to the bottom so that it can be exposed at the same time, and when the foam sheet is used in the exposure process, it can be confirmed that the double-sided simultaneous exposure is possible and the productivity is doubled. No factor affecting the quality of the product was found, and it was confirmed that the ease of operation was increased due to the thickening of the product during production. In the development process, no separation phenomenon due to penetration of the developer (Na ₂ CO ₃ ) was found in the adhesion between the foam sheet and the FCCL. In the etching process, it is a strong acid solution. Like the developing process, the possibility of separation at the contact surface between the FCCL and the foam sheet due to the penetration of the liquid may be a problem, but in the actual test, the separation phenomenon was not found. In the welding process, the iron is used, and the same work is attempted by using the foam sheet, and there is a requirement that foaming of the foam sheet due to the iron does not occur, so that no partial foaming occurs after the welding process. Could.

In order to confirm the dimensional stability in the hot press process, the dimensions of the product worked with the foam sheet and the product without the foam sheet were measured using a three-dimensional measuring instrument. The target value of the dimensional stability was aimed at 0.03% or less.

In the electroless plating process, which is a surface treatment process, an important matter is whether the foam sheet is separated by the penetration of chemicals, and the electroless plating process of the present invention is a chemical treatment method in which the chemical treatment method of the adhesive sheet between the foam sheet and FCCL is deposited. Visually confirmed whether the solution did not penetrate.

The flexible printed circuit boards attached on both sides should be peeled off in this step. Characteristics of the foam sheet is separated by the weakening of the adhesive force by the expansion of the foam cell at the pre-designed temperature. The design of this foaming temperature is such that foaming occurs at least 170 ° C or higher. The finished product was peeled off using a heating apparatus such as an oven of a hot air circulation system. As a quality factor required for peeling completed, first, the adhesive of the foam sheet should not be transferred to the back of the flexible circuit board, and second, the product should not be wrinkled in the foam peeling step. In the entire process of using the chemical, there should be no stains caused by the penetration of the liquid. Although the wrinkles of the product occurred after foaming due to the particle size distribution of the foam cells of the foam sheet, the uniform quality of the foam sheet and the particle size distribution could be produced in the final product. , Table 5 shows the results obtained by applying the samples obtained in the Examples and Comparative Examples in the flexible circuit board process.

TABLE 5

In order to confirm the dimensional stability after hot pressing, the dimensions of the products produced by using foam sheets and products that have been processed by conventional cross-section were measured by using a three-dimensional measuring instrument. As shown in Figs. 4 and 5, the measurement results show a change within the dimensional stability of 0.03% in the dimensional change rate when the foam sheet is used, which is a dimension problem when working with the foam sheet. It does not affect the production of.

  When the flexible circuit board manufacturing process is carried out using double-sided foam sheet, the manufacturing process goes through various kinds of chemicals. In this process, it was confirmed whether the adhesive of the foam sheet dissolved into the chemical used. In the case of dissolution penetration, the operation of the foam sheet and the FCCL may be impossible due to the adhesive force of the adhesive deteriorated, and the contamination of the FCCL may occur due to the penetration of the liquid. There was no quality problem due to the penetration of chemicals used in various chemicals,

By double-sided work on the foam sheet using the double-sided work, the productivity increase effect of the process actually confirmed in the process can be confirmed as shown in Table 6.

TABLE 6

As described above, the present invention maintains the adhesive force even under high temperature and high pressure conditions in the hot press process in the manufacturing process of the flexible circuit board, has a chemical resistance that does not penetrate the etching liquid in the etching process, by heating at room temperature The method of manufacturing FPCB using the foam sheet which can be easily peeled from an adherend can be provided.

In addition, by adopting a double-sided foam sheet, compared to the conventional single-sided flexible printed circuit board production process, it is possible to produce two single-sided flexible printed circuit board at the same time in one process has the advantage of improving the productivity of the flexible printed circuit board manufacturing process.

Claims (11)

In the method of manufacturing a flexible circuit board, A method of manufacturing a flexible circuit board, comprising: adhering a foam sheet including thermally expandable microspheres and an interreactive copolymer to one or both sides of the flexible circuit board, and then foaming and separating the foam sheet. The method of claim 1, The foam sheet is laminated in the order of the substrate (1), the surface treatment layer (2), the adhesive layer (3) and the release film (4), the adhesive layer (3) comprises a thermally expandable microspheres and an interreactive copolymer Method of manufacturing a flexible circuit board, characterized in that. The method of claim 1, The foam sheet is a release film (4 '), adhesive layer (3'), surface treatment layer (2 '), substrate (1), surface treatment layer (2), adhesive layer (3) and release film (4) in order Stacked, The adhesive layer (2, 2 ') is a method of manufacturing a flexible circuit board, characterized in that it comprises a thermally expandable microspheres and an interreactive copolymer. The method of claim 1, The interreactive copolymer is a mixture of a first copolymer copolymerized with a vinyl monomer including a vinyl monomer, a vinyl comonomer and a carboxyl group, and a second copolymer copolymerized with a vinyl monomer including a vinyl monomer, a vinyl comonomer and an oxazoline group. Method of manufacturing a flexible circuit board, characterized in that. The method of claim 4, wherein Vinyl monomers of the first copolymer and the second copolymer are independently of each other methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacryl. Latex, hexyl acrylate, hexyl methacrylate, octyl acrylate, 2-ethylhexyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxy At least one N-substituted amide system selected from butyl acrylate, hydroxybutyl methacrylate, hydroxyhexyl acrylate, hydroxyhexyl methacrylate, N, N-dimethyl acrylamide, N, N-dimethyl methacrylamide Vinyl monomers; Methoxyethyl acrylate, methoxyethyl methacrylate, ethoxyethyl acrylate, ethoxyethyl methacrylate, vinyl acetate, vinyl propionate, N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, Vinylpiperidone, vinylpyrimidine, vinylpyrazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, N-vinylcarboxamide, styrene, α-methylstyrene, N-vinylcapro Lactam, acrylonitrile, methacrylonitrile, glycidyl acrylate, glycidyl methacrylate, polyethylene glycol acrylate, polyethylene glycol methacrylate, polypropylene glycol acrylate, polypropylene glycol methacrylate, meth Methoxyethylene glycol acrylate, methoxy polyethylene glycol methacrylate, methoxy polypropylene glycol acrylate, methoxy polypropylene glycol Other methacrylic any one or more glycol acryl ester monomer selected from acrylate; Tetrahydroperpriacrylate, tetrahydrofurryl methacrylate, 2-methoxyethyl acrylate, isoprene, butadiene, isobutylene and any one selected from vinyl ether, or a mixture of two or more thereof. Method of manufacturing a flexible circuit board. The method of claim 4, wherein The vinyl monomer including the carboxyl group of the first copolymer may be any one or more carboxyl group-containing monomers selected from acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxy pentyl acrylate, itaconic acid, maleic acid, fumaric acid and crotonic acid; A method for producing a flexible circuit board, characterized in that it is selected from two or three or more copolymers selected from functional monomers such as one or more acid anhydride monomers selected from maleic anhydride and itaconic anhydride. The method of claim 4, wherein The first copolymer is a vinyl monomer comprising a vinyl monomer, a vinyl comonomer and a carboxyl group in a weight ratio of 1: 0.5 to 1.5: 0.05 to 0.3, a method for producing a flexible circuit board. The method of claim 4, wherein The vinyl monomer including the oxazoline group of the second copolymer is 2-vinyl-2-oxazoline, 2-vinyl-4-vinyl-2-oxazoline, 2-vinyl-5-vinyl-2-oxazoline, 2 Isopropenyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, 2- (vinylbenzyloxy-1-methyl Any one selected from ethyl) -2-oxazoline, 2- (2-hydroxy-1-methylethyl) acrylate and 2- (2-hydroxy-1-methylethyl) methacrylate, or two or more thereof A method for manufacturing a flexible circuit board, characterized in that selected from the mixture. The method of claim 4, wherein The second copolymer is a vinyl monomer comprising a vinyl monomer, a vinyl comonomer, and an oxazoline group in a weight ratio of 1: 0.5 to 1.5: 0.05 to 0.3. The method of claim 4, wherein The adhesive layer is a method of manufacturing a flexible circuit board, characterized in that the microspheres are dispersed after mixing the first copolymer and the second copolymer. The method of claim 2, The pressure-sensitive adhesive layer is foamed within 40 minutes at a temperature of 160 ℃, pressure 40kg / ㎠ or heat deformation does not occur, foaming within 10 seconds to 3 minutes or hot air dryer 5 to 10 minutes hot plate in the temperature range of 170 to 190 ℃ Method of manufacturing a flexible circuit board, characterized in that happening.

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