JPWO2007122708A1 - Release sheet for hot press and method for producing flexible printed wiring board using the same - Google Patents

Abstract

A release sheet for hot press having a film made of a heat-resistant plastic and a resin layer having a glass transition temperature (Tg) of -50 to 20 ° C and having releasability on at least one surface of the film. . It does not damage the substrate after hot pressing, does not cause contamination such as resin adhesion, and further, the gold plating surface by terminal plating is discolored. It can be easily peeled from the body.

Description

  The present invention relates to a release sheet, in particular, a release sheet that is disposed between a workpiece and a hot plate when performing hot press processing, and can uniformly apply heat and pressure to the workpiece, and the release sheet The present invention relates to a method for manufacturing a flexible printed wiring board using the above.

  2. Description of the Related Art Conventionally, a reinforcing material, a decorative article, or the like is attached to the surface of an article for the purpose of reinforcement or decoration. For example, a transparent protective film is affixed for the purpose of protecting the IC surface of the IC card, a manufacturing process of a flexible printed wiring board, and the like. In these processes, there are many cases where heat press is mainly performed, and particularly when an adhesive made of a thermosetting resin is used at the time of bonding, the heat press is performed at a high temperature, for example, 180 ° C. or more. Further, the heating press is performed not only at the time of pasting, but also when processing into a specific shape such as mold forming using a mold or the like.

  In the hot pressing step, a release sheet is usually arranged between the workpiece and the hot plate. This release sheet can easily peel the work piece from the mold or hot plate, prevents the work piece from being damaged by the mold or hot plate, and applies uniform heating and pressure to the work piece. For example, paper or plastic film is used (see Patent Documents 1 to 8).

  As described above, the main use of the release sheet includes a printed wiring board manufacturing process, and is particularly used in a flexible printed wiring board manufacturing process. A flexible printed wiring board is a wiring board in which a wiring pattern made of a metal thin film is formed on one surface of a flexible insulating board. Unlike conventional rigid printed circuit boards, flexible printed wiring boards have excellent characteristics such as flexibility, flexibility, easy deformation, and storage in narrow spaces. It is widely used as a circuit board for small electronic devices that require miniaturization and high density such as terminals, notebook computers, and digital video cameras.

  A method for manufacturing such a flexible printed wiring board is called a so-called pre-process. For example, a metal-clad laminate (copper-clad laminate) in which a metal thin film is formed on one surface of a flexible insulating substrate. By using a laminated plate (CCL: Copper Clad Laminated) or the like as a starting material and subjecting this to a selective etching process, unnecessary portions of the metal thin film are removed to form a wiring pattern.

  Next, although referred to as a post-process, processing with a coverlay film is performed to prevent cutting and peeling of the wiring pattern formed in the pre-process and to ensure insulation. Thereafter, the edge connector terminal to be inserted for connection to the outside of the printed wiring board or the contact surface of the contact portion is plated. This treatment is referred to as terminal plating, and is generally performed by a method using electrolytic plating because it is easy to control the thickness and various metals can be plated.

  Conventionally, electrolytic plating of eutectic solder having a low melting point has been performed, but a method not using lead has been proposed in consideration of environmental problems. When high reliability is required, hard gold electrolytic plating with nickel as a base is performed.

  However, since the metal-clad laminate is rich in flexibility and flexibility, the handling strength is not sufficient in the state as it is, and it is difficult to perform a selective etching process or the like. Therefore, a sheet made of a resin such as polyester is attached as a backing material to the surface of the metal-clad laminate on which the metal thin film is not formed, and the wiring pattern is selectively etched by temporarily improving the handling strength. Many methods are used to obtain a flexible printed wiring board by peeling the backing material from the metal-clad laminate after forming, coverlay processing, and terminal plating.

  Because flexible printed wiring boards are thin and soft, it is not possible to mount heavy components as they are or insert a reinforcing plate with adhesive because it cannot be inserted into a card edge connector for printed circuit boards. . For this adhesive, a pressure-sensitive adhesive type and a thermosetting adhesive type are used depending on the purpose of use. The pressure-sensitive adhesive type has poor solvent resistance and cannot be used when high connection reliability is required due to creep characteristics. For this reason, when high reliability is required, a thermosetting adhesive type is used.

  When a reinforcing plate with a thermosetting adhesive is attached to a flexible printed wiring board, a method of curing a thermosetting resin by hot pressing is usually performed. In order to absorb the unevenness of the circuit pattern and the reinforcing plate and to complete the adhesion, a sheet with unevenness followability (release sheet for hot press) is used.

  Conventionally, as a sheet having unevenness followability, a sheet obtained by laminating and bonding a thin heat-resistant film on both sides of paper, a fiber reinforced silicone rubber sheet, and a thick film made of a low-temperature heat-fusible thermoplastic resin (Patent Document 1) Reference), a film in which polypropylene or polymethylpentene is used for the upper and lower layers of an intermediate layer made of a copolymer resin of ethylene and methyl methacrylate (see Patent Document 2), and layers made of polymethylpentene resin are formed on both sides of the polyolefin A film (see Patent Documents 3 and 7), a release sheet (see Patent Documents 4 and 5) using a poly-4-methyl-1-pentene film, and the like are used. However, these release sheets do not have sufficient releasability from the flexible printed circuit board after hot pressing, or circuit surfaces and terminal plating formed by a conductor such as copper due to elution from the sheet during hot pressing. As a result, the gold-plated surface caused by the discoloration caused a problem that the connection reliability was lowered. In order to solve these problems, a release film for printed circuit board lamination (see Patent Document 6) formed by coating polysiloxane on the surface of a metal plate or a release film made of a specific alicyclic olefin resin is used as a resin film. A release sheet (see Patent Document 8) made of a laminate laminated on at least one side of the above has been proposed, but has not yet been satisfied.

JP-A-1-276694 Japanese Patent Laid-Open No. 2-24139 JP-A-2-175247 JP-A-2-238911 Japanese Patent Laid-Open No. 3-73588 Japanese Patent Laid-Open No. 5-147055 JP 2000-263724 A JP 2001-233968 A

  The present invention relates to a release sheet, in particular, a release sheet that is disposed between a workpiece and a hot plate when performing hot press processing, and can uniformly apply heat and pressure to the workpiece, and the release sheet A flexible printed wiring board manufacturing method using heat release, which provides a release sheet for hot press with less discoloration of the gold-plated surface of the flexible printed wiring board after hot pressing due to elution from the sheet, especially during hot pressing It was made for the purpose of doing.

  In addition, as a result of intensive research to develop a release sheet for hot press having excellent performance as described above, the present invention has been disclosed that at least one surface of a heat-resistant plastic film is eluted from the sheet during hot press. In order to protect things, it has been found that the object is achieved by a release sheet provided with a resin layer having specific properties, and the present invention has been made based on this finding. That is, according to the present invention, the following release sheet for hot pressing is provided.

  [1] A release sheet for hot press comprising a film made of a heat resistant plastic and a resin layer having a glass transition temperature (Tg) of −50 to 20 ° C. on at least one surface of the film.

  [2] The release sheet for hot press as described in [1], wherein the resin layer has a thickness of 0.1 to 10 μm.

  [3] The release sheet for hot press according to [1] or [2], wherein the resin layer is a reaction product of an acrylic resin and a crosslinking agent.

[4] The release sheet for hot press according to any one of [1] to [3], wherein the color change degree in the following color change degree test is in the range of 0 to 3.0.
Discoloration test:
(1) L ^* a ^* of the gold plating surface of the gold plating sheet (the surface of the gold plating layer having a thickness of 0.15 μm laminated on the nickel underlayer having a thickness of 3 μm, surface roughness Ra = 0.24 μm) b ^* Measure the brightness index and chromatinex index according to the color system.
(2) A release sheet for hot pressing is placed on the gold-plated sheet so that the resin layer side is in contact with the gold-plated surface, and thermocompression bonding is performed for 1 hour at a temperature of 180 ° C. and a pressure of 30 kg / cm ² . After standing to cool, the release sheet for hot press is separated from the gold-plated sheet, and the lightness index and chromatinex index of the gold-plated surface are measured.
(3) Discoloration degree of gold-plated surface before and after hot pressing Calculated according to the color difference according to L ^* a ^* b ^* color system specified in JIS Z 8730.

  [5] A method for producing a flexible printed wiring board, wherein a reinforcing plate with a thermosetting adhesive is attached to the surface opposite to the wiring forming surface of the flexible printed wiring board by hot pressing using a hot plate. Flexible printing in which the release sheet for hot pressing according to any one of [1] to [4] is interposed between at least the hot plate and the wiring forming surface of the flexible printed wiring board A method for manufacturing a wiring board.

  [6] A method for producing a flexible printed wiring board, wherein in the attaching step of attaching a coverlay film to the wiring forming surface of the flexible printed wiring board by hot pressing using a hot plate, [1] to [ 4] The manufacturing method of the flexible printed wiring board which interposes the mold release sheet for hot press in any one between the said hot plate and the said cover-lay film.

  The release sheet for hot pressing according to the present invention is a release sheet that can be easily peeled after hot pressing, and provides a sheet with little discoloration on the gold-plated surface even when laminated on the gold-plated surface and processed by hot pressing or the like. Is. That is, a circuit formed from a conductor such as copper by the eluate from the sheet during hot pressing without causing damage to the flexible printed wiring board after hot pressing and without causing contamination such as resin adhesion. The gold-plated surface by pattern or terminal plating is discolored, and there is an effect that it can be easily peeled off from the adherend without lowering the connection reliability.

  BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the present invention will be described below, but the present invention is not limited to the following embodiment, and is based on the ordinary knowledge of those skilled in the art without departing from the gist of the present invention. It should be understood that modifications and improvements as appropriate to the following embodiments also fall within the scope of the present invention.

  The release sheet for hot pressing of the present invention is a sheet having a film made of a heat resistant plastic and a resin layer having a glass transition temperature (Tg) of −50 to 20 ° C. on at least one surface of the film. The details will be described below.

  The film made of heat-resistant plastic constituting the release sheet for hot press of the present invention has a handling property, a cushioning property, and a surface of the workpiece to have followability with the unevenness when hot pressing is performed. is necessary. In particular, the followability enables uniform heating and pressurization on the workpiece, which enables high-precision processing, for example, affixing a coverlay film to the surface irregularities without bubbles, and no misalignment or float. A reinforcing plate can be attached. Such a film preferably has a melting point of 210 ° C. or higher. Examples of such a film include synthetic resins (heat resistant, such as polyethylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polycarbonate, triacetyl cellulose, polyimide, polyamide, polyethersulfone, aromatic polyamide, and polysulfone. (Plastic) film. Among them, polybutylene terephthalate is preferable from the viewpoints of heat resistance, chemical resistance, and unevenness followability. The film may be transparent, or may be colored by blending various pigments and dyes with the material constituting the film, and the surface thereof may be processed into a mat shape. The thickness of the film can be used within a range that does not impair the cushioning property during hot pressing, and is usually in the range of 10 to 150 μm. If handling property is taken into consideration, it is more preferable that it is 25-100 micrometers.

  In addition, the film constituting the release sheet for hot press of the present invention contains known additives, specifically heat resistance stabilizers, oxidation resistance stabilizers, weather resistance stabilizers, ultraviolet absorbers, antistatic agents and the like. It can be included. Moreover, in order to improve the adhesiveness of a film and a resin layer, it is preferable to surface-treat a film and / or to provide the intermediate layer which has adhesiveness between a film and a resin layer. Examples of the surface treatment applied to the film include discharge treatment such as corona discharge treatment and glow discharge treatment, plasma treatment, flame treatment, ozone treatment, ionizing active ray treatment such as ultraviolet treatment, electron beam treatment and radiation treatment, and sand mat treatment. -Roughening treatment such as hairline treatment, chemical treatment, easy adhesion layer coating treatment and the like can be mentioned.

  The release sheet for hot pressing according to the present invention is a sheet having a so-called laminated structure having at least a film made of the above heat-resistant plastic and a resin layer directly on the film or via an intermediate layer provided as desired. It is. The glass transition temperature (Tg) of the resin layer is −50 ° C. to 20 ° C. When the glass transition temperature is lower than −50 ° C., resin adhesion tends to occur when the sheet is peeled off after hot pressing, which is one cause of discoloration of the gold-plated surface. On the other hand, if the glass transition temperature is higher than 20 ° C., the release sheet for hot pressing adheres to the flexible printed wiring board after hot pressing, which is not preferable because it becomes difficult to peel off. In addition, when separating the release sheet and the flexible printed wiring board after hot pressing, the resin layer of the release sheet for hot pressing according to the present invention is formed in consideration of resin adhesion to the flexible printed wiring board and release properties. The Tg of the resin is preferably -30 to 15 ° C, more preferably -10 to 10 ° C.

  The “glass transition temperature” in the present invention refers to a value (° C.) obtained by differential scanning calorimetry (DSC) of the resin layer peeled from the release sheet for hot press. Details of the glass transition temperature measurement method will be described later.

  In the present invention, the resin layer of the release sheet for hot pressing is not particularly limited as long as it has the glass transition temperature, and various types can be used. However, from the viewpoint of releasability from the flexible printed wiring board, a reaction product of an acrylic resin and a crosslinking agent is preferable.

  An acrylic resin that may be used as a resin for forming the resin layer is capable of reacting with a crosslinking agent. Specific examples include a copolymer of an acrylic acid alkyl ester and / or a methacrylic acid alkyl ester and a monomer having a functional group capable of reacting with a crosslinking agent. Examples of the alkyl ester constituting the acrylic acid alkyl ester and methacrylic acid alkyl ester include, for example, methyl ester, ethyl ester, propyl ester, isopropyl ester, butyl ester, isobutyl ester, s-butyl ester, t-butyl ester, and pentyl. Examples include esters, hexyl esters, heptyl esters, octyl esters, isooctyl esters, 2-ethylhexyl esters, isodecyl esters, dodecyl esters, tridecyl esters, pentadecyl esters, octadecyl esters, nonadecyl esters, eicosyl esters, and the like. Monomers having a functional group capable of reacting with a crosslinking agent include acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid whose functional group is a carboxyl group. In addition, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, hydroxyhexyl acrylate, methacrylic acid whose functional groups are hydroxyl groups. Hydroxyhexyl acid, hydroxyoctyl acrylate, hydroxyoctyl methacrylate, hydroxydecyl acrylate, hydroxydecyl methacrylate, hydroxylauryl acrylate, and methacrylate Le hydroxyethyl lauryl and the like.

  Further, if desired, monomers other than those described above may be used in combination. Specific examples include styrene, vinyl acetate, acrylonitrile, acrylamide, polyethylene glycol acrylate, N-vinyl pyrrolidone, and tetrafurfuryl acrylate.

  The resin forming this resin layer is obtained by radical copolymerization of the aforementioned acrylic acid alkyl ester and / or methacrylic acid alkyl ester monomer and a monomer having a functional group capable of reacting with a crosslinking agent. be able to. The copolymerization method in this case is well known, and examples thereof include an emulsion polymerization method, a solution polymerization method, a bulk polymerization method, a suspension polymerization method, and a photopolymerization method.

  In the release sheet for hot presses of the present invention, the resin forming the resin layer is preferably crosslinked with a crosslinking agent. Here, the crosslinking agent may be appropriately selected according to the resin used, and an isocyanate-based crosslinking agent, a metal chelate crosslinking agent, an epoxy-based crosslinking agent, or the like is preferably used. It is preferable to use an isocyanate-based cross-linking agent from the viewpoint of mold release from the resin and prevention of resin adhesion. Examples of the isocyanate crosslinking agent include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylene diisocyanate, diphenylmethane-4,4′-diisocyanate, diphenylmethane. Examples include -2,4-diisocyanate, 3-methyldiphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, dicyclohexylmethane-2,4-diisocyanate, and lysine isocyanate. Among these, a trimer of hexamethylene diisocyanate (for example, trade name: Takenate D-170N, manufactured by Mitsui Chemicals Polyurethane Co., Ltd.) can be preferably used. This cross-linking agent is preferable in that it has an effect of imparting excellent release properties and heat resistance. In addition, a "crosslinking agent" may be used independently and may be used in combination of 2 or more type.

  In the release sheet for hot pressing of the present invention, the resin and the crosslinking agent are appropriately blended so that the glass transition temperature (Tg) of the reaction product of the resin and the crosslinking agent is −50 to 20 ° C. Usually, it is preferable to add 0.1 to 5.0 parts by mass of a crosslinking agent to 100 parts by mass of the resin. If the blending amount of the crosslinking agent with respect to 100 parts by mass of the resin is less than 0.1 parts by mass, resin adhesion or the like may occur on the flexible printed wiring board, or the releasability from the flexible printed wiring board may be impaired. There is a case. On the other hand, when it exceeds 5.0 mass parts, the adhesiveness with the flexible printed wiring board around normal temperature may fall. From the viewpoint of preventing contamination of the flexible printed wiring board and releasing properties, the blending ratio of the crosslinking agent is more preferably 0.2 to 3.0 parts by mass with respect to 100 parts by mass of the resin.

  Next, the method for producing the release sheet for hot press of the present invention will be outlined. First, in order to form a resin layer on the surface of a film made of a heat-resistant plastic, the above-mentioned components are dissolved or dispersed in an appropriate solvent, and a resin layer forming coating having a solid content concentration of about 20 to 50% by mass is performed. Prepare the solution. Subsequently, after applying this resin layer forming coating liquid directly on the surface of the film according to a conventional method and then drying it to form a resin layer, a release sheet for hot pressing can be produced. The thickness of the resin layer to be formed is preferably 0.1 to 10 μm. If the resin layer is thicker than 10 μm, cohesive failure is likely to occur at the time of separation of the release sheet from the flexible printed wiring board after hot pressing, so that good releasability may not be obtained. On the other hand, if it is thinner than 0.1 μm, it becomes difficult to prevent the elution from the sheet during hot pressing, and therefore it is difficult to prevent discoloration of the circuit pattern made of a conductor such as copper or the gold plating surface. Considering releasability from the flexible printed wiring board and a circuit pattern formed from a conductor such as copper or a discoloration degree of the gold plating surface, the thickness of the resin layer is more preferably 0.5 to 8 μm.

  Various conventionally used additives such as a crosslinking accelerator, an antioxidant, a stabilizer, a viscosity modifier, or an organic or inorganic filler may be added to the resin layer forming coating solution. Examples of the crosslinking accelerator include triethylamine-based, cobalt naphthenate-based, and tin-based crosslinking accelerators, and in particular, stannous chloride, tetra-n-butyltin, trimethyltin hydroxide, dimethyltin chloride, dilaurate. It is preferable to use a tin-based crosslinking accelerator such as -n-butyltin. In addition, as an antioxidant, a phenolic antioxidant, etc., as a tackifier resin, a terpene resin, etc., as an organic filler, an acrylic or urethane spherical fine particle, etc., as an inorganic filler Silica, calcium carbonate, alumina and the like can be preferably used.

  In addition, as described above, the release sheet of the present invention is provided with an intermediate layer as desired on one or both sides of the heat-resistant film, and a resin layer having a glass transition temperature (Tg) in the range of −50 to 20 ° C. However, in addition to the conventional release sheet, the resin layer of the release sheet of the present invention is laminated on both sides of an intermediate resin layer made of a resin such as polyolefin or polyethylene. A release sheet is laminated so that the resin layer is on the outer side of the laminated body or the intermediate resin layer, and a conventional resin film made of polypropylene or polymethylpentene is used on the other side, or the heat resistance of the present invention. A laminate obtained by laminating films used for the adhesive film can also be used as the release sheet. These can obtain more cushioning properties than a release sheet that does not use an intermediate resin layer.

  Next, the manufacturing method of the flexible printed wiring board of this invention using the above-mentioned release sheet for hot presses is demonstrated. The method for producing a flexible printed wiring board according to the present invention includes a step of attaching a reinforcing plate with a thermosetting adhesive to a surface opposite to the wiring forming surface of the flexible printed wiring board by hot pressing using a hot plate. In the manufacturing method, the release sheet for hot press is interposed between at least the hot plate and the wiring forming surface of the flexible printed wiring board. The details will be described below.

  The reinforcing plate with a thermosetting adhesive is appropriately selected according to the intended use, and comprises a reinforcing plate and a thermosetting adhesive disposed on at least one surface of the reinforcing plate. It has a layer. Examples of the material constituting the reinforcing plate include paper phenol, glass epoxy resin, polyimide resin, and polyester resin. The reinforcing plate with a thermosetting adhesive can be obtained by laminating a thermosetting adhesive on the reinforcing plate.

  The reinforcing plate with a thermosetting adhesive is cut into a predetermined size and placed at a predetermined position on the opposite surface (back surface) of the wiring forming surface of the flexible printed wiring board. Here, in order to use a thick reinforcing plate with a thermosetting adhesive, when the level difference cannot be absorbed, a dummy plate (a plate in which a portion corresponding to the predetermined position described above is hollowed out) may be used. Usually done.

  Next, the release sheet for hot press of the present invention is interposed between the hot plate and the wiring forming surface of the flexible printed wiring board, and if necessary, between the hot plate and the reinforcing plate with a thermosetting adhesive. Let However, in the case where the release sheet for hot pressing has a structure in which a resin layer is provided only on one side of the heat resistant film, it is necessary to interpose the resin layer side in contact with the wiring forming surface. In addition, when a release sheet for hot pressing is interposed between the hot plate and the reinforcing plate with thermosetting adhesive, as in the case of the release sheet having a resin layer only on one side, The resin layer side of the release sheet for press is interposed in a state where it is in contact with the reinforcing plate with a thermosetting adhesive. Next, the thermosetting adhesive is cured using a hot press machine to bond the reinforcing plate. When the dummy board is used, the flexible printed wiring board with the reinforcing plate attached is manufactured by removing the dummy board after cooling to room temperature.

In order to cure the thermosetting resin, it is usually sufficient to heat press for about 30 minutes to 2 hours under the temperature and pressure conditions of 160 to 200 ° C. and 15 to 40 kg / cm ² .

  Next, another method for producing a flexible printed wiring board using the release sheet of the present invention will be described. In the manufacture of flexible printed wiring boards, after a conductive layer made of a conductive material such as copper is selectively etched, a cover lay film made of a thermosetting resin is applied so as to cover the formed circuit pattern The wiring protective layer is formed by pressurizing with a hot plate under a high temperature condition of 160 ° C. or higher to thermally cure the adhesive of the coverlay film. At this time, the release sheet is laminated between the hot plate and the cover lay film so that at least the resin layer is on the cover lay side, and then heated and pressurized. Since this cover lay film needs to follow unevenness such as a circuit pattern and is attached so as not to contain bubbles, the release sheet used at this time preferably has good followability to surface unevenness. .

The degree of color change in this specification means a color difference according to the L ^* a ^* b ^* color system defined in JISZ8730. In the release sheet for hot presses in the present invention, the discoloration degree is preferably 0 to 3.0 or less. Considering the connection reliability of the flexible printed wiring board, it is preferably 0 to 1.5.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples. In addition, the measuring method of the physical-property value of the release sheet for hot presses, and an evaluation method are shown below.

[Glass-transition temperature]
The “glass transition temperature” in the present invention refers to a value (° C.) obtained by differential scanning calorimetry (DSC) after peeling only the resin layer of the release sheet for hot press. The measurement was performed using a differential scanning calorimeter (Bruker AXS Co., Ltd., product name DSC3200S) at a heating rate of 10 ° C./min.

[Peelability]
Use a gold-plated sheet (with a gold-plated layer of 0.15 μm on a nickel underlayer 3 μm, surface roughness Ra = 0.24 μm), and place the resin layer side of the release sheet for hot press on the gold-plated surface. After pasting, whether the release sheet for hot pressing is peeled off from the adherend at room temperature (23 ° C.) after being hot-pressed for 1 hour under conditions of 180 ° C. and 30 Kg / cm ² . Evaluated whether or not. Evaluation criteria are ○ when the release sheet for hot press is easily peeled from the gold-plated sheet, Δ when applying force to the release sheet for hot press and peeling, and × when it is difficult to peel from the gold-plated sheet. did.

[Contamination]
In the above-described evaluation of “peelability”, the contamination of the gold-plated surface of the gold-plated sheet from which the release sheet for hot press has been peeled is 50 times with a microscope (manufactured by Keyence Corporation, product name VH-80-000). It was expanded and evaluated. As the evaluation criteria, a case where resin adhesion was not recognized was evaluated as ◯, and a case where adhesive residue was observed on the gold-plated surface was evaluated as ×.

[Discoloration]
L ^* a ^* b ^* color index of the gold-plated surface of the gold-plated sheet (with a gold-plated layer of 0.15 μm on a nickel underlayer 3 μm, surface roughness Ra = 0.24) Measure the nex index. Next, the release sheet for hot pressing of the present invention is placed so that the resin layer side is in contact with the gold-plated surface of the gold-plated sheet, and heat-pressed for 1 hour under the conditions of a temperature of 180 ° C. and a pressure of 30 kg / cm ² . After standing to cool, the release sheet for hot press is peeled off, and the lightness index and chromatinex index of the gold-plated surface are measured. The discoloration degree of the gold-plated surface before and after hot pressing is calculated based on the formula difference according to L ^* a ^* b ^* color system specified in JIS Z 8730.

(Example 1)
Acrylic resin A (glass transition temperature -8 ° C., weight average molecular weight 320,000, containing as constituent monomers methyl methacrylate, ethyl acrylate, butyl acrylate and 2-hydroxyethyl methacrylate) 60 parts by mass, acrylic resin B (glass transition temperature -60 ° C., weight average molecular weight 900,000, containing as constituent monomers 2-ethylhexyl acrylate and 2-hydroxyethyl methacrylate) 10 parts by mass, acrylic resin C (glass transition temperature 18 ° C., weight) Average molecular weight of 400,000, 40 parts by mass of methyl methacrylate, ethyl acrylate and 2-hydroxyethyl methacrylate as constituent monomers, isocyanate cross-linking agent (trade name: Takenate D-170N, nonvolatile content 20%, Mitsui Chemicals) 5 parts by mass of polyurethane, etc., antioxidant (trade name) Decasstab AO-330, 10% nonvolatile content, manufactured by Asahi Denka Kogyo Co., Ltd.) 2 parts by mass, 2 parts by mass of di-n-butyltin laurate (1% nonvolatile content, manufactured by Wako Pure Chemical Industries, Ltd.) and methyl ethyl ketone 300 parts by mass were uniformly mixed and dissolved to prepare a resin-forming coating solution. This resin-forming coating solution was applied onto a polybutylene terephthalate sheet having a thickness of 50 μm by a baker type applicator and sufficiently dried at 130 ° C., whereby a 1 μm-thick resin layer was formed. A mold sheet was prepared. Table 1 shows the measurement results of the physical properties of the release sheet for hot pressing and the evaluation results of various properties.

(Example 2)
A release sheet for hot pressing was prepared in the same manner as in Example 1 except that 2 parts by mass of the acrylic resin B was used. Table 1 shows the measurement results of the physical properties of the release sheet for hot pressing and the evaluation results of various properties.

(Example 3)
Acrylic resin C 30 parts by mass, acrylic resin D (glass transition temperature -42 ° C., weight average molecular weight 400,000, including 2-ethylhexyl acrylate, 2-hydroxyethyl methacrylate and vinyl acetate as constituent units), A release sheet for hot pressing was prepared in the same manner as in Example 1 except that the crosslinking agent used in Example 1 was changed to 15 parts by mass. Table 1 shows the measurement results of the physical properties of the release sheet for hot pressing and the evaluation results of various properties.

(Example 4)
A hot press sheet was produced in the same manner as in Example 1 except that the base material was changed to polyethylene terephthalate. Table 1 shows the measurement results of the physical properties of the release sheet for hot pressing and the evaluation results of various properties.

(Example 5)
A release sheet for hot pressing was produced in the same manner as in Example 1 except that the thickness of the resin layer was changed to 3 μm. Table 1 shows the measurement results of the physical properties of the release sheet for hot pressing and the evaluation results of various properties.

(Example 6)
A release sheet for hot pressing was produced in the same manner as in Example 1 except that the film thickness of the resin layer was changed to 7 μm. Table 1 shows the measurement results of the physical properties of the release sheet for hot pressing and the evaluation results of various properties.

(Comparative Example 1)
A release sheet for hot pressing was prepared in the same manner as in Example 1 except that 100 parts by mass of acrylic resin B was used without using acrylic resin A and acrylic resin C. Table 1 shows the measurement results of the physical properties of the release sheet for hot pressing and the evaluation results of various properties.

(Comparative Example 2)
Except for using an acrylic resin E (glass transition temperature 22 ° C., weight average molecular weight 300,000, including methyl methacrylate and butyl acrylate as constituents), the release for hot press was performed in the same manner as in Comparative Example 1. A mold sheet was prepared. Table 1 shows the measurement results of the physical properties of the release sheet for hot pressing and the evaluation results of various properties.

(Comparative Example 3)
A film obtained by co-extruding polymethylpentene on both surfaces of a polyolefin is used as a release sheet for hot press. Table 2 shows the evaluation results of various properties of this release sheet for hot press.

(Comparative Example 4)
A 50 μm polyethylene terephthalate film was used as the release sheet for hot press, and Table 2 shows the evaluation results of various properties of the release sheet for hot press.

(Comparative Example 5)
A polybutylene terephthalate film having a thickness of 50 μm was used as the release sheet for hot press. Table 2 shows the evaluation results of various properties of the release sheet for hot press.

  From the results of Tables 1 and 2, all of Examples 1 to 6 have low discoloration of 1.8 or less, excellent peelability from the gold-plated surface, and are hardly contaminated. I understand. Compared with it, it turns out that the thing of Comparative Examples 1-5 is not what can satisfy the performance of any one or both of the peelability from a gold plating surface, contamination | pollution property, and a discoloration degree. As shown in Table 2, it is understood that the conventionally used polyethylene terephthalate film and polybutylene terephthalate film are inferior in mold release or contamination than the heat press release sheet of the present invention. From this result, it can be considered that Examples 1 to 6 are materials that replace the release sheet conventionally used in the manufacturing process of flexible printed wiring boards.

[Contamination (Cu)]
After affixing a backing sheet (Somatack PS-105WA manufactured by SOMAR Co., Ltd.) to a polyimide surface of a copper-clad laminate by a method in accordance with JIS Z0237, each of the copper surface is described in Example 1 and Comparative Examples 3-5. The resin surface of the release sheet for hot press is bonded together. This sheet was hot-pressed at 180 ° C. and 30 kg / cm ² for 1 hour, allowed to cool, and then separated from the copper-clad laminate and the heat-release release sheet at room temperature (23 ° C.). The surface contamination was evaluated by a 50-fold magnification with a microscope (manufactured by Keyence Corporation, product name VH-8000). As the evaluation criteria, a case where resin adhesion was not recognized was evaluated as ◯, and a case where resin component adhesion was observed on the copper surface was evaluated as x.

  From the results of Table 3, it can be seen that the release sheet of Example 1 does not contaminate the copper surface as compared with Comparative Examples 3-5. From this, it can be seen that the release sheet of the present invention can be effectively used without contaminating the copper surface even when used in place of the release sheet conventionally used in the production process of flexible printed wiring boards.

  The release sheet for hot pressing of the present invention can be peeled off without causing resin adhesion after hot pressing in the step of applying the thermosetting adhesive-attached reinforcing plate of the flexible printed wiring board. Since the degree of color change is smaller than the conventional one, it can contribute to the improvement of the connection reliability of the flexible printed wiring board.

Claims (6)

A film made of heat-resistant plastic,
A release sheet for hot pressing, having a resin layer having a glass transition temperature (Tg) of -50 to 20 ° C and having releasability on at least one surface of the film.   The release sheet for hot press according to claim 1, wherein the resin layer has a thickness of 0.1 to 10 μm.   The release sheet for hot press according to claim 1 or 2, wherein the resin layer is a reaction product of an acrylic resin and a crosslinking agent. The release sheet for hot press according to any one of claims 1 to 3, wherein the discoloration degree according to the following discoloration degree test is in the range of 0 to 3.0.
Discoloration test:
(1) L ^* a ^* of the gold plating surface of the gold plating sheet (the surface of the gold plating layer having a thickness of 0.15 μm laminated on the nickel underlayer having a thickness of 3 μm, surface roughness Ra = 0.24 μm) b ^* Measure the brightness index and chromatinex index according to the color system.
(2) A release sheet for hot pressing is placed on the gold-plated sheet so that the resin layer side is in contact with the gold-plated surface, and thermocompression bonding is performed for 1 hour at a temperature of 180 ° C. and a pressure of 30 kg / cm ² . After standing to cool, the release sheet for hot press is separated from the gold-plated sheet, and the lightness index and chromatinex index of the gold-plated surface are measured.
(3) Discoloration degree of gold-plated surface before and after hot pressing Calculated according to the color difference according to L ^* a ^* b ^* color system specified in JIS Z 8730. A method of manufacturing a flexible printed wiring board,
In the sticking process of sticking a reinforcing plate with a thermosetting adhesive on the surface opposite to the wiring forming surface of the flexible printed wiring board by hot pressing using a hot plate, any one of claims 1 to 4. The manufacturing method of the flexible printed wiring board which interposes the release sheet for hot press described in 1 between the said hot plate and the said wiring formation surface of the said flexible printed wiring board. A method of manufacturing a flexible printed wiring board,
In the attaching step of attaching the coverlay film to the wiring forming surface of the flexible printed wiring board by hot pressing using a hot plate, the release sheet for hot pressing according to any one of claims 1 to 4, A method for producing a flexible printed wiring board interposed between at least the hot plate and the coverlay film.