JP5021806B2 - Method for producing flexible circuit board using high-temperature foam sheet - Google Patents

Description

  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. More specifically, an adhesive copolymer resin is used in the adhesive layer to provide excellent adhesive strength, and a foamed sheet for a flexible circuit board that can be easily peeled off from an adherend by high-temperature heat treatment, and the same And a method of manufacturing a flexible circuit board.

  Recently, the demand for flexible circuit boards has rapidly increased in response to downsizing and weight reduction of electronic device products such as mobile phones, digital cameras, MP3, DMB, and composite devices that integrate these functions. .

  The conventional process of manufacturing a flexible circuit board has been proceeded after being fixed on a substrate called a carrier or backup board using an adhesive tape due to the flexible characteristics of the flexible circuit board that bends or stagnates. A method of manufacturing a flexible circuit board using a foamed sheet for smooth peeling of the adhesive tape and the flexible circuit board after the process has been studied has been studied.

In general, foam sheets are mainly used as a support for bonding and cutting when manufacturing multilayer chip capacitors (MLCC) and inductor chips. At this time, the conditions for losing the adhesive force are set in a temperature range of 120 to 130 ° C. and normal pressure. In this case, important physical properties are an adhesive force and a foaming force. However, in the case of the production of a flexible circuit board, the foamed sheet does not tear in the cover layer adhesion process (hot press lamination) conditions of 150 to 160 ° C. and 40 kg / cm ² for 40 minutes or more. After the processing process is completed, it must be foamed at a temperature higher than that, approximately 180 ° C. to cause peeling, and during the manufacturing process of the flexible circuit board, the transfer of the adhesive resin causes contamination of the flexible circuit board. The condition that it must occur is necessary.

  However, even if a conventional foamed sheet has a high foaming temperature, foaming starts at about 150 ° C., and therefore there is a limit to use it for high temperature use.

  On the other hand, not only a method for manufacturing a flexible circuit board using a foam sheet that is foamed at a high temperature as described above, but also a double-sided flexible circuit board using a double-sided foam sheet in consideration of the profitability of the manufacturer of the flexible circuit board. There has been proposed a method of manufacturing. This uses a double-sided foam sheet for fixing when processing in the manufacturing process of a flexible circuit board, and if this is used, two products are produced simultaneously through a single process without changing the existing process. Thus, productivity within a unit time can be doubled during the manufacturing process of the flexible circuit board. In order to provide flexibility in the process of producing a multilayered flexible circuit board or a rigid-soft circuit board, there is no choice but to manufacture it with a single-sided flexible circuit board. Some manufacturers can work (process) both sides at the same time, but there is a limit to improving productivity because only one side can be processed. However, currently, in the process of producing a flexible circuit board, a double-sided adhesive foam sheet is used to attach a single-sided flexible circuit board to both sides of the foamed sheet, and both sides can be processed simultaneously, thereby improving productivity twice. In addition, the foam sheet can serve as a cushion film during the carrier film and molding process instead, reducing the use of secondary materials used in the manufacturing process of flexible circuit boards There is also.

The foam sheet used to advance the single-sided flexible circuit board in the double-sided process must foam or undergo thermal deformation at a temperature of 160 ° C. and a pressure of 40 kg / cm ² for 40 minutes or more. Chemical resistance is required for chemicals that come into contact during the manufacturing process, and foaming easily occurs at 170 to 190 ° C. after completion of the manufacturing process of the flexible circuit board. Resin transfer should cause contamination of the flexible circuit board.

  Conventionally, most of the pressure-sensitive adhesives used for processed foam sheets are acrylic pressure-sensitive adhesives and cross-linking agents containing cross-linkable functional groups, and these pressure-sensitive adhesives act to agglomerate microspheres. In order to suppress the expansion of the microspheres and increase the foaming temperature, the ratio of the cross-linking functional group must be large, and a large amount of cross-linking agent must be used. Therefore, when the time passes, the crosslinking proceeds and the viscosity changes greatly, or the gelation progresses and the coating operation is continued for 4 hours or more, the physical properties of the coated part at the beginning and the end become different. .

Korean Published Patent Publication No. 2002-0060659, Korean Published Patent Publication No. 2002-0060656, Korean Published Patent Publication No. 2002-0060657, Korean Registered Patent Publication No. 10-0514611 include a double-sided exposed flexible circuit board and a single-sided flexible circuit. It has been proposed that foam sheets can be used to reduce the process of substrates, thin film flexible circuit boards. However, the manufacturing process of flexible circuit board is refining-D / F adhesion-Exposure-D / F development-Cu corrosion-Drying-Winding-Roll cutting-Temporary bonding-Hot press-Refining-Surface treatment- In the electroless plating-punching process, especially in the case of the coverlay molding process, the process proceeds under conditions of 150 to 160 ° C. and 40 kg / cm ² for 40 minutes or more. Since the foamed sheet is foamed during the lay molding process, the existing foam sheet can be used only up to the previous stage of the cover lay molding process.

  In addition, it is known in Japanese Published Patent Application No. 2003-338678, filed by Nitto Denko, Japan, that a double-sided foam sheet is used as a carrier film in the double-sided process of a single-sided flexible circuit board. It can only be partially applied early in the manufacturing process using a foam sheet.

  In order to solve the above-described problems, the present invention is excellent in adhesive strength by using an interactive copolymer resin as an adhesive, and can be easily peeled off from an adherend by heat treatment at 180 ° C. or higher. The present invention provides a method for producing a high-temperature foam sheet that can be manufactured and using this to produce an FPCB.

Further, another object of the present invention is a condition of 160 ° C., 40 kg / cm ² , high temperature and high pressure for 40 minutes or more during the manufacturing process of FPCB (Flexible printed circuit board) and hot press process. By using a double-sided foam sheet that retains adhesive strength even underneath and has chemical resistance that prevents the penetration of the etchant in the etching process, it is a single-sided FPCB in a single process compared to the conventional single-sided FPCB production process. It is to provide a method for manufacturing FPCB that can improve the productivity of the manufacturing process of FPCB by making it possible to produce the two at the same time.

  The present invention employs an inter-reactive copolymer resin as an adhesive layer to provide excellent adhesive strength and a flexible circuit board that can be used in a high-temperature process that can be easily peeled off from an adherend by heat treatment at 180 ° C. or higher. And a method for producing a flexible circuit board using the foamed sheet for a flexible circuit board.

  Hereinafter, the method for producing a foamed sheet for a flexible circuit board that can be used in the high-temperature process used in the present invention and the method for producing a flexible circuit board using the same will be described above. The method for manufacturing a flexible circuit board will be sequentially described 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 foam sheet for high temperature used in the present invention forms an adhesive layer by using an adhesive resin mixed with an interreactive copolymer containing thermally expandable microspheres, and the adhesive layer is foamed or expanded by heating to increase the temperature. It is an adhesive sheet that can be peeled off.

  FIG. 1 is a cross-sectional view showing a single-sided foam sheet used for single-sided PCB production, and FIG. 2 is a cross-sectional view showing a double-sided foamed sheet used for double-sided PCB production.

  As shown in FIG. 1, the single-sided foam sheet according to the present invention is laminated in the order of a substrate 1, a surface treatment layer 2, an adhesive layer 3, and a release film 4, and the adhesive layer 3 is a thermally expandable microsphere. And an interactive copolymer.

  The substrate 1 can be an appropriate thin commercialized film such as PET, and the thickness is preferably 250 μm or less, and most preferably 25 to 100 μm, but is not limited thereto. The surface treatment layer 2 that makes a strong chemical bond between the base material and the adhesive layer is obtained by oxidizing the surface of the base material 1 by chromic acid treatment, ozone treatment, corona treatment, flame treatment, ion radiation treatment or the like. It is a layer in which a highly polar polymer such as polyester, hydrolyzed ethylene-vinyl acetate, and polyvinyl butyral is treated. The surface treatment layer 2 must not contaminate the adherend during peeling after the heat treatment, and should not be changed in particular in the chemicals and molding process conditions used during the manufacturing process of the flexible circuit board. The surface treatment layer has a thickness of 5 μm or less, desirably 1 μm or less. When the thickness of the surface treatment layer is large, the degree of deformation of the adhesive layer is small after the heat treatment of the foamed sheet, and the adhesive force is less reduced. When sticking a heat-peelable pressure-sensitive adhesive sheet to an adherend, the surface shape is well maintained, providing a large pressure-sensitive adhesive surface, and at the same time, foaming sheet when the pressure-sensitive adhesive layer is heated to foam or expand to peel from the adherend This reduces the restriction of foaming or expansion in the surface direction, and improves the deformation of the corrugated structure when the adhesive layer is foamed. When a foamed adhesive layer is coated on a base material, if there is no bonding force between the adhesive layer and the base material during foaming, peeling occurs between the foam layer and the base material during foam expansion. The predetermined purpose cannot be achieved.

  The pressure-sensitive adhesive layer 3 contains thermally expandable microspheres so that the pressure-sensitive 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 adhesion area where the foam pulls out the pressure-sensitive adhesive layer and contacts the adherend. Become.

  The heat-expandable microsphere is a material that is easily gasified, such as isobutane, propane, or pentane, and exhibits thermal expansion, and its skin is thermally soluble, for example, vinylidene chloride, acrylonitrile copolymer, etc. It consists of materials and suitable materials that can be destroyed by thermal expansion.

  The above-mentioned microspheres having an average particle size of 10 to 25 μm are easily dispersed in the adhesive resin by heat treatment, and the adhesive layer is greatly deformed and the adhesive force is clearly reduced. The adhesive layer is preferably a layer thicker than the average particle diameter of the thermally expandable microspheres and thicker than the maximum particle diameter of the final thermally expandable microsphere, and the surface of the adhesive layer is smoothed and stabilized before heat treatment. Those that achieve high adhesion are desirable. In order to reduce the adhesive strength of the pressure-sensitive adhesive layer by heat treatment, the microspheres should have a strength that causes foam expansion with a volume expansion rate of 10 times or more during heating, and the film is not ruptured at that time.

  In addition, since the high temperature condition of 160 ° C. is essential for the manufacturing process of the flexible circuit board, it is desirable to use the one having the highest foaming start temperature as much as possible. The amount of thermally expandable microspheres is appropriately selected according to the required degree of the adhesive layer, such as expansion rate and adhesive strength reduction, but is generally 50 parts by weight or less per 100 parts by weight of the adhesive forming the adhesive layer. Yes, preferably 5 to 20 parts by weight.

  In order to be able to apply thermally expandable microspheres where foaming starts around 140 ° C. so that the adhesive layer is heated at a temperature range of 170-190 ° C. that can withstand the manufacturing process of the flexible circuit board, It is necessary to restrain the expansion of the foam and raise the foaming temperature.

  A first copolymer obtained by copolymerizing a vinyl monomer, a vinyl comonomer, and a vinyl monomer containing a carboxy group as an interreactive copolymer constituting the adhesive layer; It is an adhesive resin obtained by mixing a vinyl comonomer and a second copolymer obtained by copolymerizing a vinyl monomer containing an oxazoline group.

  The vinyl monomer and the vinyl comonomer forming the first copolymer and the second copolymer are, as necessary, the tackiness, cohesive force, heat resistance, flexibility, holding power, elasticity, etc. of the pressure-sensitive adhesive. Which are used for the purpose of providing methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, hexyl acrylate, hexyl methacrylate, octyl acrylate, -Any one or more alkyl group-containing vinyl monomers selected from ethylhexyl acrylate; hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl One or more hydroxyl group-containing vinyl monomers selected from polyacrylate, hydroxybutyl methacrylate, hydroxyhexyl acrylate, and hydroxyhexyl methacrylate; selected from N, N-dimethylacrylamide and N, N-dimethylmethacrylamide Any one or more N-substituted amide vinyl monomers; any one or more alkoxyalkyl acrylate vinyl monomers selected from methoxyethyl acrylate, methoxyethyl methacrylate, ethoxyethyl acrylate, ethoxyethyl methacrylate; Vinyl acetate, vinyl propionate, N-vinyl pyrrolidone, methyl vinyl pyrrolidone, vinyl pyridine, vinyl piperidone, vinyl pyrimidine, vinyl piperazine, vinyl pyrazine, vinyl pyro At least one vinyl monomer selected from the group consisting of alcohol, vinyl imidazole, vinyl oxazole, vinyl morpholine, N-vinyl carboxamide, styrene, α-methyl styrene, and N-vinyl caprolactam; acrylonitrile, methacrylo Any one or more cyanoacrylate vinyl monomers selected from nitriles; 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, methoxyethylene glycol acrylate, methoxypolyethylene glycol methacrylate, methoxypolypropylene glycol One or more glycol acrylic ester monomers selected from acrylate and methoxypolypropylene glycol methacrylate; One or more acrylics selected from tetrahydroperpril acrylate, tetrahydroperpril methacrylate, and 2-methoxyethyl acrylate The acid ester monomer may be one or more monomers selected from isoprene, butadiene, isobutylene and vinyl ether; or one selected from the group consisting of a mixture of two or more thereof.

  The vinyl monomer containing a carboxy group of the first copolymer is used for the purpose of imparting crosslinkability by radical polymerization, and includes acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, Any one or more carboxyl group-containing monomers selected from maleic acid, fumaric acid, and crotonic acid; and any one or more acid anhydride monomers selected from maleic anhydride and itaconic anhydride Examples thereof include two or three or more kinds of copolymers selected from functional monomers.

  The first copolymer is produced with a vinyl monomer, a vinyl comonomer, and a vinyl monomer containing a carboxy group in a weight ratio of 1: 0.5 to 1.5: 0.05 to 0.3. What is done is desirable.

  The vinyl monomer containing the oxazoline group of the second copolymer is used for the purpose of imparting crosslinkability by radical polymerization. Examples of the vinyl monomer containing the oxazoline group include 2-vinyl-2-oxazoline and 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-isopropenyl-5-methyl-2-oxazoline, 2- (vinylbenzyloxy-1-methylethyl) -2-oxazoline, 2- (2-hydroxy-1-methylethyl) acrylate, 2- (2-hydroxy-1-methylethyl) methacrylate, or a mixture of two or more of these. Those selected from the group can be used.

  The second copolymer is produced with a vinyl monomer, a vinyl comonomer, and a vinyl monomer containing an oxazoline group in a weight ratio of 1: 0.5 to 1.5: 0.05 to 0.3. What was done is desirable.

  The foam sheet adhesive layer coating solution used for the adhesive layer of the flexible circuit board foam sheet according to the present invention produced a first copolymer containing a carboxy group and a second copolymer containing an oxazoline group. Thereafter, the microspheres are dispersed in an adhesive obtained by mixing the first copolymer and the second copolymer. The produced coating solution for the adhesive layer is stable with no change even during long-term storage at room temperature, and the foaming temperature can be further increased to 10 to 30 ° C. from the foaming temperature of the conventional foamed sheet.

The pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive layer coating liquid is resistant to chemicals that do not foam or undergo thermal deformation within 40 minutes at a temperature of 160 ° C. and a pressure of 40 kg / cm ² , and come into contact during the manufacturing process of the flexible circuit board. It must have chemical resistance, and the flexible circuit board must not be contaminated by the transfer of the adhesive resin during the manufacturing process of the flexible circuit board. Also, the heat treatment conditions of 170 to 190 ° C. for enabling easy peeling from the adherend after completion of the manufacturing process of the flexible circuit board, 10 seconds to 3 minutes with a hot plate or 5 minutes to 5 minutes with a hot air dryer Foaming must occur easily within 10 minutes.

  On the other hand, as shown in FIG. 2, the double-sided foam sheet for a flexible circuit board according to the present invention comprises a release film 4 ', an adhesive layer 3', a surface treatment layer 2 ', a substrate 1, a surface treatment layer. 2, the adhesive layer 3, and the release film 4 are laminated in this order, and the adhesive layers 2, 2 'include thermally expandable microspheres and an inter-reactive copolymer. The same as described above for the single-sided foam sheet for a flexible circuit board.

  Hereinafter, a method for producing a flexible circuit board using the foamed sheet for a flexible circuit board according to the present invention will be described.

  A method for producing a single-sided flexible circuit board using a single-sided foam sheet is a laminated paper (lamination) of FCCL and a foam sheet-front treatment-dry film line-exposure-development process-etching process-dry film peeling-temporary process- Manufactured through a hot pressing step-surface treatment-punching step-foaming sheet peeling step.

  On the other hand, the method for producing a double-sided flexible circuit board using a double-sided foamed sheet is as described above: Laminated paper (lamination) of FCCL and foamed sheet-front treatment-dry film line-exposure-development process-etching process-dry film Peeling-Tacking process-Hot pressing process-Surface treatment-Punching process-Manufactured through foam sheet peeling stage, FCCL and double-sided foam sheet are used in the laminated paper (lamination) stage of FCCL and FCCL The two sides are laminated and bonded so that one-sided FCCL can be worked on both sides, and the above-mentioned steps are followed. After the foam sheet peeling stage, two single-sided flexible circuit boards are produced simultaneously in one step be able to.

  In the manufacturing process of the flexible circuit board, the present invention has chemical resistance that keeps the adhesive force even under high temperature and high pressure conditions in the hot pressing process and does not cause the penetration of the etching solution in the etching process, and is a heat treatment at normal high temperature. A method for producing FPCB using a foam sheet that can be easily peeled off from an adherend is provided.

It is sectional drawing of the single-sided foam sheet used for this invention. It is sectional drawing of the double-sided foam sheet used for this invention. It is a graph which shows the working conditions of the hot press employ | adopted in this invention. It is a graph which shows the dimensional change rate at the time of the operation | work using the foam sheet by this invention. It is a graph which shows the dimensional change rate at the time of the single-sided operation | work using the conventional foam sheet.

  The present invention produces a high-temperature foam sheet that can be easily peeled off from an adherend by heat treatment at 180 ° C. or higher while using a reactive copolymer resin as a pressure-sensitive adhesive and is soft. A method for manufacturing a circuit board will be described in more detail through examples. However, these examples are presented only for the purpose of understanding the contents of the present invention, and the scope of rights of the present invention should not be construed as being limited to these examples.

<Production Example 1>

(Production of first copolymer)

  Mix 2L glass reactor equipped with stirrer, condenser, dropping funnel, thermometer, jacket (JACKET) with 45g ethyl acrylate, 45g comonomer n-butyl acrylate and 10g acrylic acid. Here, 0.01 g of initiator α, α′-azobisisobutyronitrile, 100 g of ethyl acetate and 20 g of toluene were added, and a radical polymerization reaction was performed at 70 ° C. About 30 minutes later, 135 g of ethyl acrylate, 135 g of comonomer n-butyl acrylate, and 30 g of acrylic acid were mixed, and 0.5 g of initiator α, α′-azobisisobutyronitrile was mixed with 100 g of ethyl acetate. It melt | dissolved in 40g of toluene, and dripping was advanced about 90 minutes using the dropping funnel. At the time of dropping, the temperature is adjusted to be constant, 1 g of a radical initiator is dissolved in 50 g of ethyl acetate and 50 g of ethanol so that no unreacted monomer remains after the reaction is completed, and dropped for 60 minutes, and further reacted for 3 hours. Then, a first copolymer was produced.

(Production of second copolymer)

  To a 2 L glass reactor equipped with a stirrer, condenser, dropping funnel, thermometer, jacket (JACKET) 45 g of ethyl acrylate, 45 g of comonomer n-butyl acrylate, and 2-isopropyl-2- 10 g of oxazoline was mixed. The initiator α, α'-azobisisobutyronitrile (0.01 g) was added thereto after dissolving 100 g of ethyl acetate and 20 g of toluene, and then proceeded at 70 ° C. in the same manner as the copolymer polymerization containing a carboxy group. . A radical polymerization reaction was performed. About 30 minutes later, 135 g of ethyl acrylate, 135 g of comonomer n-butyl acrylate, and 30 g of acrylic acid were mixed, and 0.5 g of initiator α, α′-azobisisobutyronitrile was mixed with 100 g of ethyl acetate. It melt | dissolved in 40g of toluene, and dripping was advanced about 90 minutes using the dropping funnel. After the reaction is completed, the temperature is kept constant and 1 g of a radical initiator is dissolved in 50 g of ethyl acetate and 50 g of ethanol so that no unreacted monomer remains after the reaction is completed, and further reacted for 3 hours for 60 minutes. A second copolymer was produced.

(Manufacture of adhesive resin)

  The prepared first copolymer and second copolymer were mixed at a weight ratio of 1: 1. To 100 g of this mixed resin, 10 g of microsphere F-80VSD (trade name, manufactured by Matsu headquarters, 150 to 160 ° C., beginning of foaming) was added and dispersed to produce an adhesive resin.

<Production Example 2>

  The weight ratio of the monomers used in the production of the first copolymer and the second copolymer in Production Example 1 was defined as ethyl acrylate / n-butyl acrylate / acrylic acid = 4.5 / 4.5 / 1.5. A pressure-sensitive adhesive resin was produced in the same manner as in Production Example 1, except that ethyl acrylate / n-butyl acrylate / 2-isopropyl-2-oxazoline = 4.5 / 4.5 / 1.5, respectively. .

<Production Example 3>

  The weight ratio of the monomers used in the production of the first copolymer and the second copolymer in Production Example 1 was defined as ethyl acrylate / n-butyl acrylate / acrylic acid = 4.5 / 4.5 / 0.6. A pressure-sensitive adhesive resin was produced in the same manner as in Production Example 1, except that ethyl acrylate / n-butyl acrylate / 2-isopropyl-2-oxazoline = 4.5 / 4.5 / 0.6, respectively. .

<Production Example 4>

  The type of monomer used in the production of the second copolymer of Production Example 1 was 2-ethylhexyl acrylate / methyl methacrylate / n-butyl acrylate / 2-isopropyl-2-oxazoline = 2.0 / 2.5 / An adhesive resin was produced in the same manner as in Production Example 1 except that each was used at 4.5 / 1.0.

<Production Example 5>

  The weight ratio of monomers used in the production of the second copolymer of Production Example 4 was 2-ethylhexyl acrylate / methyl methacrylate / n-butyl acrylate / 2-isopropyl-2-oxazoline = 2.0 / 2.5. A pressure-sensitive adhesive resin was produced in the same manner as in Production Example 4 except that each was used at /4.5/1.5.

<Example 1 to Example 5>

  After the adhesive resin produced in Production Example 1 to Production Example 5 was applied to a 50 μm PET film, a 37 μm foamed adhesive layer was formed, and a 36 μm release paper was adhered to produce the foamed sheet produced. Aged for days. The entire process of making both sides of a single-sided flexible circuit board was performed in the following order. Laminated paper of FCCL and foamed sheet (lamination)-Front treatment-Dry film liner-Exposure-Development process-Etching process-Dry film peeling-Tacking process-Hot press process-Surface treatment-Punching process-Foam sheet peeling The stage was advanced and the performance was evaluated in each process.

      A. Selection of FCCL (Flexible Copper Clad Laminate)

  Generally, FCCL for single-sided flexible circuit boards is classified according to the thickness of copper foil, adhesive, and polyimide film and according to the type of copper foil. In this example, copper foil having specifications as shown in Table 1 was used. The thickness of the coverlay film used for manufacturing the product is 25 μm of the pressure-sensitive adhesive layer, and the thickness of the polyimide layer is 25 μm.

      B. Lamination (FCCL and foam sheet laminate paper)

  This is the step of laminating the foam sheet and FCCL to bond the FCCL. Lamination was performed by using a general laminator so that the copper foil of the single-sided FCCL was directed outward and the polyimide surface was adhered to the foam sheet. It was carried out so that bubbles and polyimide tears did not occur in the product adhered during the lamination process, and in the subsequent process, the adhesion state of the outer part was confirmed so that various chemicals could not penetrate due to a decrease in the adhesive force of the outer part.

      C. Front treatment

The front treatment is treated with a rust inhibitor to prevent corrosion of the copper foil surface of FCCL. However, this rust preventive component is removed to give unevenness to the copper foil surface, increasing the surface area and increasing the surface area. This is a step of improving the adhesion of the photosensitive resin. This process was performed as a method of weakly corroding the copper surface by a chemical method. As a chemical used, a mixed solution of sulfuric acid (H ₂ SO ₄ ) and hydrogen peroxide (H ₂ O ₂ ) was used.

    D. Dry film laminate

  Dry film lamination is the process of bonding a photosensitive resin to form a circuit on copper foil. When manufacturing a single-sided flexible circuit board, the copper foil side is laminated with dry film, and the opposite polyimide side is FCCL. Since it is thin, it was attached to a carrier film in order to prevent tearing and tearing in subsequent processes.

      E. exposure

  In the exposure process, if the photosensitive resin is attached to the FCCL and the mask film is applied to irradiate the mask film with UV light, the black part on the mask film cannot pass the UV light and only the transparent part is exposed to UV light. And the dry film was subjected to crosslinking so as to be cross-linked only at the portion where it received ultraviolet rays.

      F. Development process

  The dry film is exposed with 3% sodium carbonate solution, and the part that is cross-linked by light is not dissolved, and the part that is not cross-linked by light is dissolved and copper is exposed. As given.

      G. Etching process

The part where the circuit is formed by the development process covers the copper foil with the role of the resist as a dry film, and the part other than the circuit is an etching solution that corrodes copper with the copper foil exposed (CuCl ₂ , HCl, H ₂ O ₂ ) was passed through to corrode the copper surface.

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

      H. Tacking process

  If 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 part soldered for mounting the component is bonded with a coverlay film to protect the circuit. It becomes like this. This cover lay film is a film to which a thermosetting adhesive is applied, so the adhesive strength is weak at room temperature, and before FCC on which the cover lay film and circuit are formed is cured by hot press (Hot Press) Temporary fixing was performed using a shochu partially so that the cover lay film was not misaligned.

      Li. Hot press process

  The hot press process was a process for bonding the circuit protection film to the coverlay film by thermosetting, and the operation was performed under the conditions shown in Table 3. This step is a step in which the coverlay film adhesive is heat-cured for a certain period of time using a hot press in a heated and pressurized state. In order to use a foamed sheet, the foamed sheet must be foamed under the working conditions of this process, and there should be no external deformation or change in dimensions of the foamed sheet and the flexible circuit board.

      Nu. surface treatment

  The surface treatment generally uses an electroless metal plating method, but the electroless metal plating was a batch type and was processed under the conditions shown in Table 4. Gold plating is a detailed process, and it has undergone a pretreatment process using chemicals as shown in the following table.

      Le. Outline processing (punching) process

  A flexible circuit board that has been installed with a foam sheet is subjected to a punching process for outline processing in order to be completed as a final product. However, the guide hole on the flexible circuit board is precisely aligned with the mold position. The outer shape was processed.

      Wow. Foam sheet peeling

  The flexible circuit board attached on both sides is peeled off at this stage. The characteristic of the foam sheet comes to be separated by the weakening of the adhesive force due to the expansion of the foam cell at the already designed temperature. The foaming temperature is designed so that foaming is performed at least at 170 ° C. or higher. The product on which the surface treatment work was completed was peeled off using a heating device such as a hot air circulation oven.

<Comparative Production Example 1>

  A 2 L glass reactor equipped with a stirrer, condenser, dropping funnel, thermometer, jacket (JACKET) was added to 48.5 g of n-butyl acrylate, 48.5 g of ethyl acrylate, 2 g of acrylic acid, 1 g of hydroxypropyl acrylate, and α, 0.01 g of α′-azobisisobutyronitrile was dissolved in 160 g of ethyl acetate and 270 g of toluene, placed in a dropping funnel, purged with nitrogen, and then dropped at 80 ° C. in a state where the flow continued, After proceeding with radical polymerization for 8 hours and adding an excessive amount of radical initiator at the end of the reaction so that no unreacted monomer remains, the microsphere F-80VSD (trade name, manufactured by Matsu head office, 150 to 160 ° C) 10 g of the foaming start) was added and dispersed, and the isocyanate cross-linking agent AK-75 (trade name, Aikei Chemical) was added in an amount twice the hydroxyl functional group of the adhesive resin. Was prepared an adhesive resin was.

<Comparative Production Example 2>

  A pressure-sensitive adhesive resin was produced in the same manner as in Comparative Example 1, except that the amount of 2 g of hydroxypropyl acrylate having a crosslinking functional group was increased from Comparative Production Example 1.

<Comparative Production Example 3>

  Adhesive in the same manner as Comparative Example 1 except that the isocyanate cross-linking agent AK-75 (trade name, Aikei Chemical) was used by adding 4 times the hydroxyl functional group of the adhesive resin from Comparative Production Example 1. A resin was produced.

<Comparative Production Example 4>

  Adhesive in the same manner as Comparative Example 2 except that the isocyanate crosslinking agent AK-75 (trade name, Aikei Chemical) was added in an amount four times the hydroxyl functional group of the adhesive resin. A resin was produced.

<Comparative Examples 1 to 4>

  Each of the adhesive resins manufactured in Comparative Production Examples 1 to 4 was applied to a PET film of 50 μm, and then a 37 μm foamed adhesive layer was formed, and a 36 μm release paper was adhered to produce a foamed sheet. The foamed sheet thus produced was aged for 7 days and used for the final test. The entire process of making both sides of a single-sided flexible circuit board was performed in the following order. Laminated paper of FCCL and foamed sheet (lamination)-Front treatment-Dry film liner-Exposure-Development process-Etching process-Dry film peeling-Tacking process-Hot press process-Surface treatment-Punching process-Foam sheet peeling The process was advanced and the performance was evaluated in each process.

  Adopting the following materials and process conditions as a high-temperature foam sheet for the double-sided test of the single-sided flexible circuit board for the adhesive resin and the foam sheet produced according to the above production examples, comparative production examples and examples and comparative examples. Reliability was investigated in all processes of flexible circuit boards.

      1. Selection of raw materials

  In order to use the foam sheet base sheet for the process of flexible circuit boards, the foaming agent is designed to be foamed at an optimal volume of at least 180 ° C. Yes, PET film between 25 and 100 μm was used because it should have flexibility in consideration of workability and roll to roll method. Furthermore, since heating and cooling at room temperature are repeated, dimensional deformation due to heat should not occur. In order to satisfy these conditions, the substrate was used at a thickness of 50 μm and the release film at a thickness of 36 μm.

      2. Foaming conditions and methods

  In general, the foamed sheet was peeled off using a convection oven or a hot plate. In the process of the flexible circuit board, a foam sheet having a minimum width of 250 mm or more is used, and it is necessary to have a precondition that it must withstand the hot pressing process, and the foaming temperature of the physical properties of the foaming agent must be high. Therefore, the foam peeling device was selected in consideration of the heat conduction efficiency by the necessary foaming force and the dimensional deformation of the flexible circuit board.

      3. Reliability assessment

  Is foam sheet applied to the construction method of single-sided flexible circuit boards to double the efficiency of the manufacturing process by double-sided and reduce defects such as tears and tears in the manufacturing process caused by the thin product characteristics of the flexible circuit board? Reduced productivity due to additional negative factors in the manufacturing process of the flexible circuit board, especially whether the foamed sheet itself additionally affects the quality of the flexible circuit board product during work using the foam sheet In addition, an experiment was conducted to determine whether the product itself was defective.

Lamination of FCCL was carried out on both sides of the foam sheet while maintaining 70 ° C. No air bubbles or tearing of the polyimide film occurred in the product adhered during the lamination process. In particular, in the process, the adhesion state of the outer part was confirmed so that various chemicals could not penetrate due to a decrease in the adhesive force of the outer part, but a strong adhesive force was revealed. No detachment phenomenon between the foam sheet and the copper foil was found even in the state of being wound around the roll and bent. The chemical used in the front treatment process is a mixed solution of sulfuric acid (H ₂ SO ₄ ) and hydrogen peroxide (H ₂ O ₂ ), and there should be no liquid penetration into the surface bonded to the foam sheet in this process. I was able to confirm. In this process, the foam sheet and FCCL are attached to both sides and the thickness is kept thick, so there is no need to use a secondary carrier film. If dry film is laminated on both sides simultaneously, karate is reduced by 50%. I was able to confirm. The exposure machine is irradiated with ultraviolet rays at the top and bottom so that both sides can be exposed at the same time in the exposure process, but when producing using a foam sheet in the exposure process, double-sided simultaneous exposure is possible and productivity is doubled. It can be confirmed that there is no factor that the double-sided work of FCCL affects the product quality separately, and it can be confirmed that the product became thicker during production and the ease of work increased. did it. In the development process, no separation phenomenon due to the penetration of the developer (Na ₂ CO ₃ ) was found on the adhesive surface between the foam sheet and FCCL. In the etching process, the possibility of separation from the contact surface of the FCCL and the foamed sheet due to the penetration of the liquid may be a problem in the solution having a strong acidity as in the development process, but the separation phenomenon could not be found in the actual test. The tacking process uses shochu, but the same work is required when working with foam sheets, and there is a requirement that foaming of foam sheets by shochu must not occur. It was confirmed that no foaming occurred.

  In order to confirm the dimensional stability in the hot pressing process, the dimensions of the product worked using the foam sheet and the product not using the foam sheet were measured using a three-dimensional measuring device. The target value of dimensional stability was set within 0.03%.

  An important matter in the electroless metal plating process of the surface treatment process is the separation of the foamed sheet due to the penetration of chemicals. As a result of checking the penetration of the chemicals with the naked eye, it was confirmed that the liquid did not penetrate.

  The flexible circuit board attached to both sides must be peeled off at this stage. The characteristic of the foam sheet comes to be separated by the weakening of the adhesive force due to the expansion of the foam cell at the already designed temperature. The foaming temperature is designed so that foaming is performed at least at 170 ° C. or higher. The product for which the surface treatment work was completed was peeled off using a heating device such as a hot air circulation oven. The required quality factor of the flexible circuit board that has been peeled off is that the adhesive of the foam sheet should not be transferred to the rear surface of the flexible circuit board. Should not occur. Thirdly, there should be no stain due to liquid penetration in the entire process in which the foam sheet uses chemicals. In fact, the product tears after foaming due to non-uniform particle size of the foam cells in the foam sheet, but the product with the same quality as the existing single-sided work is produced from the final product through uniformizing the particle size and particle size distribution of the foam sheet Table 5 shows the results of applying the samples obtained from the examples and comparative examples in the process of the flexible circuit board.

  In order to confirm the dimensional stability after hot pressing, the dimensional stability was measured using a three-dimensional measuring device for the dimensions of the product produced using the foam sheet and the product advanced by the existing single-side work. As shown in FIGS. 4 and 5, the measurement results show a change within 0.03% of the target of dimensional stability in the dimensional change rate when working with the foam sheet, which is the result of using the foam sheet. When working, it is a dimensional problem that does not affect the production of the product.

  When a flexible circuit board is manufactured using double-faced foam sheet, many kinds of chemicals come into contact with the manufacturing process. In this process, the foam sheet adhesive dissolves in the chemical used. It was confirmed whether it penetrated. At the time of dissolution and penetration, work cannot be performed in the process of separating the foamed sheet and FCCL due to the adhesive strength reduction of the adhesive, and the FCCL is contaminated by liquid penetration. There is no quality problem due to the penetration of chemicals used in many chemicals such as etchants. By using a foam sheet as a single-sided work, the productivity has been increased by the process actually confirmed in the process. The effect can be confirmed as shown in Table 6.

  As described above, the present invention has chemical resistance that keeps adhesive force even in the hot press process even under high temperature and high pressure conditions in the manufacturing process of the flexible circuit board and does not cause the penetration of the etching solution in the etching process. It is possible to provide a method for producing FPCB using a foam sheet that can be easily peeled off from an adherend by heat treatment at ordinary temperature.

  In addition, by adopting the double-sided foam sheet, compared to the conventional single-sided flexible circuit board production process, two single-sided flexible circuit boards can be produced simultaneously in a single process. There is an advantage that productivity can be improved.

1: Base material 2: Surface treatment layer 3: Foam pressure-sensitive adhesive sheet using a mutual-reactive copolymer mixture 4: Release film

Claims (11)

In the manufacturing method of the flexible circuit board,
Adhering a foam sheet comprising thermally expandable microspheres and an inter-reactive copolymer to one or both sides of a flexible circuit board;
Foaming the foam sheet and separating the foam sheet from the flexible circuit board;
Only including,
The interreactive copolymer includes a vinyl monomer, a vinyl comonomer, and a first copolymer obtained by copolymerizing a vinyl monomer containing a carboxy group, a vinyl monomer, and a vinyl copolymer. And a second copolymer obtained by copolymerizing a vinyl monomer containing an oxazoline group, and a method for producing a flexible circuit board. The foam sheet is laminated in the order of a substrate, a surface treatment layer, an adhesive layer, and a release film,
The method for producing a flexible circuit board according to claim 1, wherein the adhesive layer includes thermally expandable microspheres and an interactive copolymer. The foam sheet is laminated in the order of a release film, an adhesive layer, a surface treatment layer, a substrate, a surface treatment layer, an adhesive layer, and a release film,
The method for producing a flexible circuit board according to claim 1, wherein the adhesive layer includes thermally expandable microspheres and an interactive copolymer. The 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 methacrylate, hexyl acrylate, Hexyl methacrylate, octyl acrylate, 2-ethylhexyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, hydroxyhexyl acrylate, hydroxyhexyl methacrylate, N, N-dimethylacrylamide, N, N-dimethylmethacrylamide, methoxyethyla Relate, methoxyethyl methacrylate, ethoxyethyl acrylate, ethoxyethyl methacrylate, vinyl acetate, vinyl propionate, N-vinyl pyrrolidone, methyl vinyl pyrrolidone, vinyl pyridine, vinyl piperidone, vinyl pyrimidine, vinyl piperazine, vinyl pyrazine, vinyl pyrrole, vinyl imidazo , Vinyl oxazole, vinyl morpholine, N-vinyl carboxamide, styrene, α-methyl styrene, N-vinyl caprolactam, acrylonitrile, methacrylonitrile, glycidyl acrylate, glycidyl methacrylate, polyethylene glycol acrylate, polyethylene glycol methacrylate, polypropylene glycol acrylate , Polypropylene glycol methacrylate, Metoki Any one selected from polyethylene glycol acrylate, methoxypolyethylene glycol methacrylate, methoxypolypropylene glycol acrylate, methoxypolypropylene glycol methacrylate, tetrahydroperpril acrylate, tetrahydroperpril methacrylate, 2-methoxyethyl acrylate, isoprene, butadiene, isobutylene, and vinyl ether The method for producing a flexible circuit board according to claim 1, which is selected from one or a mixture of two or more thereof. The vinyl monomer containing a carboxy group of the first copolymer is any one or more selected from acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid. 2. The production of a flexible circuit board according to claim 1 , wherein the monomer is selected from one or more acid anhydride monomers selected from maleic anhydride and itaconic anhydride; Method. The first copolymer has a vinyl monomer, a vinyl comonomer, and a vinyl monomer containing a carboxy group in a weight ratio of 1: 0.5 to 1.5: 0.05 to 0.3. The method of manufacturing a flexible circuit board according to claim 1 , wherein the method is manufactured. The vinyl monomer containing 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-isopropenyl-5-methyl-2-oxazoline, 2- ( Any one selected from vinylbenzyloxy-1-methylethyl) -2-oxazoline, 2- (2-hydroxy-1-methylethyl) acrylate, and 2- (2-hydroxy-1-methylethyl) methacrylate, The method for producing a flexible circuit board according to claim 1, which is selected from a mixture of two or more of these. The second copolymer has a vinyl monomer, a vinyl comonomer, and a vinyl monomer containing an oxazoline group in a weight ratio of 1: 0.5 to 1.5: 0.05 to 0.3. The method of manufacturing a flexible circuit board according to claim 1 , wherein the method is manufactured. The adhesive layer does not foam or undergo thermal deformation within 40 minutes at a temperature of 160 ° C. and a pressure of 40 kg / cm ² , and within a temperature range of 170 ° C. to 190 ° C. with a hot plate within 10 seconds to 3 minutes. The method for producing a flexible circuit board according to claim 2, wherein the foaming is performed within 5 to 10 minutes by a hot air dryer.   The adhesive copolymer of the adhesive layer includes a first copolymer obtained by copolymerizing a vinyl monomer, a vinyl comonomer, and a vinyl monomer containing a carboxy group, a vinyl monomer, a vinyl The method for producing a flexible circuit board according to claim 2 or 3, wherein a comonomer and a second copolymer obtained by copolymerizing a vinyl monomer containing an oxazoline group are mixed. . The method for manufacturing a flexible circuit board according to claim 10 , wherein the adhesive layer is formed by mixing the first copolymer and the second copolymer and then dispersing microspheres.