JP6883400B2 - Coverlay film - Google Patents

Description

The present invention relates to a coverlay film. More specifically, the coverlay of a thin film having good processing suitability in the process of manufacturing a base material and good bonding workability and excellent followability to irregularities and steps of a flexible printed circuit board (hereinafter referred to as FPC). Regarding film.

In portable electronic devices such as mobile phones, electronic components are integrated on a printed circuit board in order to keep the external dimensions of the housing small and thin so that it is easy to carry. Further, in order to reduce the external dimensions of the housing, the printed circuit board is divided into a plurality of parts, and the printed circuit board is folded or folded by using a flexible FPC for the connection wiring between the divided printed circuit boards. It is being slid.

In addition, recent mobile information terminals (smartphones, tablets, etc.) consume more power than conventional mobile phones, resulting in poor battery life. Therefore, it is necessary to increase the volume and capacity of the battery as much as possible, and there is a strong demand for miniaturization and thinning of members and parts other than the battery. There is. Further, in recent years, the light-shielding property and the design property have been emphasized, and the coverlay film is required to be colored.

Conventionally, as a coverlay film used for the purpose of thinning the entire FPC, a thin polyimide film coated with an adhesive has been used (Patent Document 1). However, the thin polyimide film has a problem that the processability in the manufacturing process is inferior and the workability is inferior when it is attached to the FPC.
In addition, the conventional coverlay film lacks flexibility due to the difficulty in reducing the thickness, so that the FPC does not have sufficient followability to the step, and a gap is created, which is used in the heating process. It was the cause of problems such as swelling. Therefore, it has been difficult to sufficiently reduce the thickness of the entire FPC to which the coverlay film is attached.

Japanese Unexamined Patent Publication No. 9-13507

In view of the above background technology, it is an object of the present invention to provide a coverlay film which has good processability and workability at the time of manufacturing an FPC even if it is a thin film and has excellent followability to a step of the FPC.

In order to improve workability when the coverlay film is attached to the FPC, in the coverlay film of the present invention, an insulating layer and a thermosetting adhesive layer are sequentially laminated on one side of the support film. .. Further, the coverlay film can be transferred from the support film to the FPC by laminating the coverlay film of the present invention on the FPC via an adhesive layer and thermocompression bonding, and then peeling off the support film.
Further, in order to withstand harsh bending operations and improve the followability to FPC, in the present invention, the tensile elongation of the laminate composed of the insulating layer and the adhesive layer is increased.

Further, in order to solve the above problems, the present invention comprises laminating a first insulating layer, a second insulating layer, and a heat-curable adhesive layer on one side of the support film in this order. The tensile elongation of the laminate composed of the first insulating layer, the second insulating layer, and the thermosetting adhesive layer, in which the first insulating layer contains a flame retardant and the support film is removed, is Provided is a coverlay film characterized by being 100% or more.

It is preferable that the second insulating layer contains a flame retardant having a lower concentration than that of the first insulating layer, or does not contain a flame retardant.
It is preferable that the thickness of the first insulating layer is thinner than the thickness of the second insulating layer.

The thermosetting adhesive layer preferably contains a polyurethane resin and an epoxy resin.
The polyurethane resin is preferably a phosphorus-containing polyurethane resin.

It is preferable that at least one of the first insulating layer, the second insulating layer, and the thermosetting adhesive layer contains a light absorber.

The present invention also provides a mobile phone in which the coverlay film is used as a member for protecting an FPC.
The present invention also provides an electronic device in which the coverlay film is used as a member for protecting an FPC.

According to the coverlay film of the present invention described above, when a wiring plate or the like having a step is coated, it follows without a gap, and in the subsequent steps such as the solder reflow process and the plating process, there is a problem due to swelling or penetration of the plating solution. A thin film coverlay film that does not occur can be manufactured.
Further, when the insulating layer or the adhesive layer contains a light absorbing material, a specific coloring can be performed on one side of the coverlay film.

From the above, according to the present invention, it is highly flexible and thin, which can reduce the occurrence of problems due to swelling and penetration of the plating solution in the heating process such as the solder reflow process after coating the wiring board or the like. It is possible to provide a coverlay film having excellent bending characteristics, which does not cause a decrease in FPC protection performance even if a severe bending operation is repeatedly performed.

It is the schematic sectional drawing which shows the embodiment of the coverlay film of this invention.

Hereinafter, preferred embodiments of the present invention will be described. The present invention is not limited to the present embodiment, and various modifications can be made without departing from the gist of the present invention.

As shown in FIG. 1, a first insulating layer 12, a second insulating layer 13, and a thermosetting adhesive layer 14 are laminated in this order on one side of the support film 11. The laminate 15 composed of the first insulating layer 12, the second insulating layer 13, and the thermosetting adhesive layer 14 can be integrally peeled from the support film 11 and attached to FPC or the like. ..
When the coverlay film 10 of the present embodiment is attached to an FPC or the like as an adherend, the outer surface is a dielectric material, and the wiring and circuit parts of the FPC can be protected by electrical insulation. .. Further, the coverlay film of the present embodiment can reduce the overall thickness in order to improve the bending characteristics with respect to the bending operation.

(Support film)
Examples of the base material of the support film 11 used in the coverlay film 10 of the present embodiment include polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, and polyolefin films such as polypropylene and polyethylene.
When the base material of the support film 11 has a certain degree of peelability on the base material itself, such as polyethylene terephthalate, the support film 11 is directly peeled off without being subjected to a peeling treatment. , The laminated body 15 may be laminated, or the surface of the support film 11 may be subjected to a peeling treatment for facilitating the peeling of the laminated body 15 from the support film 11.

When the base film used as the support film 11 does not have peelability, the peeling treatment is performed by applying a peeling agent such as an amino alkyd resin or a silicone resin and then heating and drying. Be given. When the coverlay film 10 of the present embodiment is used for FPC, it is desirable not to use a silicone resin as the release agent. When the silicone resin is used as the release agent, a part of the silicone resin is transferred to the surfaces of the insulating layers 12 and 13 in contact with the surface of the support film 11, and further, the thermosetting adhesive layer 14 passes through the inside of the laminate 15. There is a risk of migrating to the surface of. The silicone resin transferred to the surface of the thermosetting adhesive layer 14 may weaken the adhesive force of the thermosetting adhesive layer 14.

The thickness of the support film 11 is not particularly limited because it is excluded from the total thickness of the laminated body 15 when it is used by coating it on the FPC, but it is usually about 12 to 150 μm. By using the support film 11, it is possible to improve the workability when forming the insulating layers 12 and 13 and the thermosetting adhesive layer 14 and the workability when attaching to the FPC.

The color of the support film 11 may be colorless (uncolored) or colored. When the support film 11 is colored, it is preferable that the color has a large contrast with the color of the laminated body 15 excluding the support film 11. For example, when the laminate 15 is a dark color such as black, the support film 11 is preferably a light color such as white or yellow. This makes it possible to improve the handleability such as peeling the laminated body 15 from the support film 11 and the confirmability of whether or not the support film 11 is peeled off. The support film 11 can be colored by using a known pigment, dye or the like. Examples of the support film 11 include a white PET film having a thickness of 30 μm or more and 60 μm or less.

(Insulation layer)
The insulating layers 12 and 13 of the coverlay film 10 are insulating layers made of a dielectric thin film resin layer or the like. The thin film resin film of the polyimide film formed by using the solvent-soluble polyimide has high mechanical strength, heat resistance, insulating property, and solvent resistance, which are the characteristics of the polyimide resin, and is chemically stable up to about 260 ° C. Therefore, it is suitable as the insulating layers 12 and 13.

Examples of the polyimide include a thermosetting polyimide produced by a dehydration condensation reaction by heating a polyamic acid, and a solvent-soluble polyimide which is a non-dehydration condensation type and is soluble in a solvent.
A general method for producing a polyimide film is to synthesize a polyamic acid, which is an imide precursor, by reacting a diamine with a carboxylic acid dianhydride in a polar solvent, and convert the polyamic acid into a polyimide by dehydration cyclization. is there. However, the temperature of the heat treatment in this imidization step is preferably in the temperature range of 200 ° C. to 300 ° C., and if the heating temperature is lower than this temperature, imidization may not proceed, which is not preferable. If the heating temperature is higher than the above temperature, thermal decomposition of the compound may occur, which is not preferable.

In the coverlay film 10 of the present embodiment, an extremely thin polyimide film having a total thickness of the insulating layers 12 and 13 of less than 10 μm is used with the intention of further improving the flexibility of the insulating layers 12 and 13. Can be done. When the thickness of the polyimide film used is thinner than about 7 μm, it is preferable to form a thin polyimide film laminated on one side of the support film 11 used as a reinforcing material for strength. For example, a coating liquid containing a polyamic acid can be cast on one side of the support film 11 and heated to form a polyimide film.

However, although the polyimide film itself has heat resistance to heat treatment at a heating temperature of 200 ° C to 250 ° C, the support film 11 is a general-purpose heat-resistant resin in terms of price and heat-resistant temperature performance. When a film, for example, a film having low heat resistance such as a polyethylene terephthalate (PET) resin film, is used, a method of forming polyimide from a conventional imide precursor, polyamic acid, cannot be adopted.
Since the solvent-soluble polyimide is completely imidized and is soluble in the solvent, the solvent is volatilized at a low temperature of less than 200 ° C. after applying the coating liquid dissolved in the solvent. A film can be formed. Therefore, the insulating layers 12 and 13 are coated with a coating liquid of a non-dehydration condensation type solvent-soluble polyimide on one side of the support film 11, and then dried at a heating temperature of less than 200 ° C. It is preferable to form a thin film of polyimide resin. By doing so, an extremely thin polyimide film having a thickness of 1 to 9 μm can be laminated on one side of the support film 11 made of a general-purpose heat-resistant resin film. Similar to the thermosetting adhesive layer 14, the insulating layers 12 and 13 are formed by coating, so that the support film 11 is conveyed along the longitudinal direction thereof, and the insulating layers 12 and 13 are conveyed on the support film 11. Since the thermosetting adhesive layer 14 and the like can be continuously formed, roll-to-roll production is also possible, and the processability and productivity are excellent.

The non-dehydration condensation type solvent-soluble polyimide that can be used for the insulating layers 12 and 13 of the present embodiment is not particularly limited, but a commercially available solvent-soluble polyimide coating solution can be used. Specific examples of commercially available solvent-soluble polyimide coating liquids include Solpy 6,6-PI (Solpy Industries), Q-IP-0895D (PI Giken), PIQ (Hitachi Kasei Kogyo), and SPI-200N (New Japan Chemical). ), Rikacoat SN-20, Rikacoat PN-20 (New Japan Chemical) and the like. The method of applying the solvent-soluble polyimide coating liquid onto the support film 11 is not particularly limited, and for example, it can be applied with a coater such as a die coater, a knife coater, or a lip coater.

The total thickness of the insulating layers 12 and 13 of the present embodiment (for example, the thickness of the polyimide film) is preferably 1 to 9 μm. It is technically difficult to form a polyimide film with a thickness of less than 0.8 μm because the mechanical strength of the formed film is weak. Further, if the thicknesses of the insulating layers 12 and 13 such as the polyimide film exceed 10 μm, it becomes difficult to obtain the laminated body 15 which is thin and has excellent bending performance. Further, when the total thickness of the insulating layers 12 and 13 is thinner than about 7 μm, it is difficult to adjust the tension when winding the insulating layers 12 and 13, so it is preferable to use the support film 11 as a reinforcing material in terms of strength.

Further, the insulating layers 12 and 13 of the present embodiment preferably have a large tensile elongation in order to improve the followability of the FPC to the step. The tensile elongation of one or both of the insulating layers 12 and 13 is preferably 100% or more, and more preferably 250% or less. Here, the tensile elongation is expressed in% at the time when the film is cut by constant velocity tension, and the larger the tensile elongation is, the more flexible the film is with respect to the tensile force. Therefore, in order for the laminated body 15 to have sufficient flexibility and to exhibit excellent followability to irregularities and steps of the FPC, it is preferable that the tensile elongation is 100% or more.
When the insulating layers 12 and 13 having high tensile elongation are composed of a polyimide film, for example, it is preferable to use a polyimide material having an aliphatic unit having 3 or more carbon atoms between the aromatic units. Further, the aliphatic unit preferably contains a polyalkyleneoxy group having an alkylene group having about 1 to 10 carbon atoms.

Further, the water vapor permeability of polyimide films available in the insulating layers 12 and 13 of the present embodiment is preferably 500g ^/ m 2 · day or more. If the water vapor permeability is lower than this, the residual solvent in each layer, the outgas from the adhesive, and the moisture in the film are rapidly heated in the heating process such as solder reflow after coating the FPC. There is a possibility that each layer will be separated by the generated water vapor. There is no particular upper limit on the water vapor transmission rate, but as long as the same material is used, the water vapor transmission rate is inversely proportional to the thickness. Therefore, when the thickness is reduced to increase the water vapor transmission rate, the thickness falls within the above-mentioned range. Is preferable.

(Flame retardants)
In order to ensure the flame retardancy of the laminated body 15, the insulating layers 12 and 13 can contain a flame retardant. Examples of the flame retardant include inorganic flame retardants such as metal hydroxide, antimony and red phosphorus, and organic flame retardants such as halogen (chlorine and bromine), phosphorus and guanidine. Phosphorus-based and bromine-based organic flame retardants are preferable in terms of excellent dispersibility with insulating resins such as polyimide. Examples of the phosphorus-based flame retardant include aliphatic phosphoric acid ester, aromatic phosphoric acid ester, aromatic condensed phosphoric acid ester, bisphenol phosphoric acid ester, halogen-containing phosphoric acid ester, halogen-containing condensed phosphoric acid ester, and phosphazene compound. ..

When the flame retardant is an additive type flame retardant that does not react with the resin, the tensile elongation of the insulating layers 12 and 13 may decrease depending on the amount of the flame retardant added. Therefore, the first insulating layer 12, which becomes the outermost layer when the laminated body 15 is bonded to FPC or the like, contains a flame retardant, and the second insulating layer 13 has a lower concentration than that of the first insulating layer 12. It is preferable that the second insulating layer 13 contains a flame retardant or does not contain a flame retardant. Further, it is preferable that the thickness of the first insulating layer 12 is thinner than the thickness of the second insulating layer 13. The thickness of the first insulating layer 12 is, for example, 0.5 to 5 μm. The thickness of the second insulating layer 13 is, for example, 2 to 9 μm.

The ratio of the resin contained in the insulating layers 12 and 13 to the flame retardant can be appropriately set. In the first insulating layer 12, the flame retardant is preferably 20 to 200 parts by weight with respect to 100 parts by weight of the resin. In the second insulating layer 13, the flame retardant is preferably 0 to 100 parts by weight with respect to 100 parts by weight of the resin. Here, the ratio of the flame retardant to 100 parts by weight of the resin is 0 parts by weight, which means that the flame retardant is not contained. The flame retardant may have a concentration distribution in the thickness direction of the insulating layer.
The first insulating layer 12 and the second insulating layer 13 may show an interface due to a difference in the composition of the resin or the additive, and do not show a clear interface due to continuous changes in the composition or the like. In some cases.
The first insulating layer 12 may be a flame retardant layer in which an electrically insulating flame retardant is separated from the second insulating layer 13 by coating, aggregation, precipitation or the like. In this case, the first insulating layer 12 may have a structure that does not contain a resin, or may have a structure that includes a resin or the like as a binder for the flame retardant.

(Thermosetting adhesive layer)
The thermosetting adhesive layer 14 is preferable as the adhesive layer used for adhering the laminate 15 of the coverlay film 10 to the FPC. The thermosetting adhesive used for the thermosetting adhesive layer 14 may be an electrically insulating adhesive layer, and specific examples thereof include acrylic adhesives, polyurethane adhesives, epoxy adhesives, and rubbers. Examples thereof include commonly used thermosetting adhesives such as adhesives and silicone adhesives. Further, a thermosetting adhesive which is made flame-retardant by mixing a flame retardant such as phosphorus or bromine is preferably used, but is not particularly limited. A phosphorus-containing compound can be used as the polyol compound or polyisocyanate compound as a raw material for polyurethane, and a polyurethane resin containing phosphorus in the molecular structure of the resin can also be used as a thermosetting adhesive. The thermosetting adhesive layer 14 preferably contains a polyurethane resin and an epoxy resin, and the polyurethane resin is more preferably a phosphorus-containing polyurethane resin.

The thickness of the thermosetting adhesive layer 14 is preferably 1 to 8 μm, for example. The thermosetting adhesive layer 14 can be formed, for example, by coating.
The adhesive strength of the thermosetting adhesive layer 14 is not particularly limited, but the measuring method is Method A of 8.1.1 of JIS-C-6471 "Copper-clad laminate test method for flexible printed wiring board". (Peeling in the 90 ° direction), a range of 5 to 30 N / inch is suitable. If the adhesive strength is less than 5 N / inch, for example, the laminate 15 bonded to the FPC may be peeled off or floated due to heat or bending.

If the thermosetting adhesive layer 14 is not a pressure-sensitive adhesive that exhibits pressure-sensitive adhesiveness at room temperature, but an adhesive layer that exhibits adhesiveness by heating and pressurizing, the adhesive strength is less likely to decrease with repeated bending. preferable. The conditions for heat-pressurization adhesion to the FPC are not particularly limited, and examples thereof include conditions for heat-pressing for 60 minutes at a temperature of 160 ° C. and a pressing force of 4.5 MPa.
When the laminated body 15 is heated and pressed against the FPC, the support film 11 may be peeled off and removed from the laminated body 15 in advance. Further, it is also possible to heat and pressurize the FPC while the support film 11 is laminated on the laminated body 15. In this case, the support film 11 may be peeled off and removed from the laminate 15 after the heat-pressurization adhesion treatment to the FPC.

(Anchor layer)
Between the second insulating layer 13 and the thermosetting adhesive layer 14 in order to improve the adhesion between the insulating layers 12 and 13 which are the base materials of the laminate 15 and the thermosetting adhesive layer 14. May be provided with an anchor layer (not shown). As the anchor layer, it is preferable to use an adhesive having excellent heat resistance because it can withstand even if the bonding temperature of the thermosetting adhesive layer 14 due to heating and pressurizing is 150 to 250 ° C. Further, an anchor layer having excellent adhesive force to the insulating layers 12 and 13 and the thermosetting adhesive layer 14 is preferable. If the adhesive force is sufficient, the anchor layer may be omitted and the second insulating layer 13 and the thermosetting adhesive layer 14 may be in direct contact with each other.

As the adhesive resin composition used for the anchor layer, a thermoplastic resin such as a polyester resin, a polyurethane resin, a (meth) acrylic resin, a polyethylene resin, a polystyrene resin, or a polyamide resin is preferably used. Further, it may be a thermosetting type such as an epoxy resin, an amino resin, a polyimide resin, and a (meth) acrylic resin.
Particularly preferable as the adhesive resin composition for the anchor layer are an adhesive resin composition for cross-linking a polyester resin composition having an epoxy group, and an adhesive resin composition obtained by mixing an epoxy resin as a curing agent with a polyurethane resin. Is. Therefore, the anchor layer has harder physical properties than the insulating layers 12 and 13 made of a thin film such as a polyimide film. The polyester-based resin composition having an epoxy group is not particularly limited, but for example, an epoxy resin having two or more epoxy groups in one molecule (the uncured resin thereof) and two or more carboxyls in one molecule. It can be obtained by reaction with a polyvalent carboxylic acid having a group or the like. For cross-linking of the polyester resin composition having an epoxy group, a cross-linking agent for an epoxy resin that reacts with the epoxy group can be used.

The thickness of the anchor layer is preferably about 0.05 to 1 μm, and if it is about this thickness, sufficient adhesion to the thermosetting adhesive layer 14 can be obtained. When the thickness of the anchor layer is 0.05 μm or less, the adhesive force between the insulating layers 12 and 13 and the thermosetting adhesive layer 14 may decrease. Further, even if the thickness of the anchor layer exceeds 1 μm, it is not effective in increasing the adhesive force between the insulating layers 12 and 13 and the thermosetting adhesive layer 14, and the thickness and cost of the laminated body 15 are increased, which is preferable. Absent. The anchor layer can be formed, for example, by coating.

(Light absorber)
A light absorbing material may be contained in any of the layers constituting the laminated body 15 in order to impart light-shielding property to the laminated body 15 or improve the design property in a state of being bonded to the FPC. The layer that can contain the light absorber for this purpose is one or both of the insulating layers 12 and 13, the thermosetting adhesive layer 14, or between the insulating layers 12 and 13 and the thermosetting adhesive layer 14. Any layer that can be provided, and examples thereof include at least one layer or two or more layers such as insulating layers 12, 13, for example, a thermosetting adhesive layer 14, an anchor layer, and the like. The thermosetting adhesive layer 14 may contain a light absorber, and the insulating layers 12 and 13 made of solvent-soluble polyimide may contain a light absorber. When the layer containing the light absorbing agent (light absorbing layer) also serves as at least one or more of the insulating layers 12 and 13 or the thermosetting adhesive layer 14, the laminated body is compared with the case where the light absorbing layers are separately laminated. It is preferable because the thickness increase of 15 can be suppressed.

Examples of the light absorber include one or more black pigments or coloring pigments selected from the group consisting of non-conductive carbon black, graphite, aniline black, cyanine black, titanium black, black iron oxide, chromium oxide, and manganese oxide. Be done. The type and amount of the light absorber are preferably selected so that the light absorption layer maintains electrical insulation.
The light absorbing material composed of a black pigment or a coloring pigment is preferably contained in any of the layers in an amount of 0.1 to 30% by weight. The black pigment or the coloring pigment preferably has an average particle size of primary particles of about 0.02 to 0.1 μm as observed by SEM. The thickness of the light absorbing layer is preferably thicker than the particle size of the light absorbing agent so that the fine particles of the light absorbing material are not exposed.
The light transmittance of the laminated body 15 excluding the support film 11 is preferably 5% or less. Examples of the light transmittance include visible light transmittance, total light transmittance and the like.

Among the light absorbers, a black pigment such as carbon black is preferable in order to effectively reduce the light transmittance and improve the light blocking effect. As the black pigment, silica particles or the like may be immersed in a black coloring material to make only the surface layer portion black, or the black pigment may be formed from a black coloring resin or the like so as to be entirely black. Further, the black pigment contains particles having a color similar to black such as gray, blackish brown, or blackish green in addition to pure black, and can be used as long as it is a dark color that does not easily reflect light.

(Release film)
In order to protect the thermosetting adhesive layer 14, the coverlay film 10 can attach the release film 19 on the thermosetting adhesive layer 14. Examples of the base material of the release film 19 include polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, and polyolefin films such as polypropylene and polyethylene. A release agent such as an aminoalkyd resin or a silicone resin is applied to these base films, and then the film is heat-dried to perform a release treatment. Since the coverlay film 10 of the present embodiment is attached to the FPC with the release film 19 removed, it is desirable not to use a silicone resin as the release agent. This is because when the silicone resin is used as the release agent, a part of the silicone resin is transferred to the surface of the thermosetting adhesive layer 14 in contact with the surface of the release film 19, and the adhesive force of the thermosetting adhesive layer 14 is weakened. Because there is a risk.
The thickness of the release film 19 is not particularly limited because it is excluded from the total thickness of the laminated body 15 when it is used by coating it on the FPC, but it is usually about 12 to 150 μm.

(Coverlay film)
The coverlay film 10 of the present embodiment can be suitably used as a coverlay film having excellent bending characteristics, which can be used by being bonded to an FPC that undergoes repeated bending operations. Further, the FPC to which the coverlay film of the present embodiment is attached can be used for various electronic devices such as mobile phones, notebook personal computers, and mobile terminals.
As a method for producing the coverlay film 10 of the present embodiment, the insulating layers 12 and 13 and the thermosetting adhesive layer 14 are sequentially applied on the support film 11 from the side closer to the support film 11. A method of laminating can be mentioned. Further, as described above, the release film 19 may be attached onto the thermosetting adhesive layer 14.
When the FPC bends, the coverlay film 10 of the present embodiment is preferably used by being bonded to the FPC in the state of the laminated body 15. Here, the laminate 15 is a laminate obtained by removing the support film 11 and the release film 19 from the coverlay film 10 when the coverlay film 10 has the release film 19, and the coverlay film 10 is peeled off. When it does not have the film 19, it is a laminated body excluding the support film 11. The laminated body 15 may include the above-mentioned anchor layer, light absorption layer, and the like.
The overall thickness of the laminate 15 is preferably 15 μm or less, and examples thereof include 5 to 15 μm and 12 μm or less. The tensile elongation of the laminated body 15 is preferably 100% or more, and may be 150% or more or 150% or less.

Hereinafter, the present invention will be specifically described with reference to Examples.

(Example 1)
A polyethylene terephthalate (PET) film having a thickness of 50 μm, which had been peeled off on one side, was used as the support film 11.
A coating liquid of a solvent-soluble polyimide resin containing 50 parts by weight of a phosphorus-based flame retardant with respect to 100 parts by weight of the resin is cast-coated and dried on one side of the support film 11 so that the thickness after drying becomes 1 μm. The first insulating layer 12 was formed.
On the first insulating layer 12, a coating liquid of a solvent-soluble polyimide resin containing no flame retardant and having a tensile elongation after drying of 170% is cast and dried so as to have a thickness of 3 μm after drying. The second insulating layer 13 was formed.
On the second insulating layer 13, 100 parts by weight of a phosphorus-containing polyurethane resin solution (Toyo Spinning Co., Ltd .: UR3575), 2.4 parts by weight of a polyfunctional epoxy resin (Toyo Spinning Co., Ltd .: HY-30), and fumed silica (manufactured by Nippon Aerosil) : R972) 4.7 parts by weight of the thermosetting adhesive was sequentially added and stirred, and the thermosetting adhesive was applied and dried so as to have a thickness of 8 μm after drying to form the thermosetting adhesive layer 14. , A coverlay film of Example 1 was obtained.

(Examples 2 and 3)
Examples 2 and 3 are the same as in Example 1 except that the proportion of the phosphorus-based flame retardant contained in the first insulating layer 12 is 100 parts by weight in Example 2 and 150 parts by weight in Example 3. I got a coverlay film.
(Examples 4 to 6)
Examples 1 to 3 except that the coating liquid for forming the second insulating layer 13 is a solvent-soluble polyimide resin containing 20 parts by weight of a phosphorus-based flame retardant with respect to 100 parts by weight of the resin. Similarly, coverlay films of Examples 4 to 6 were obtained.
(Example 7)
A coverlay film of Example 7 was obtained in the same manner as in Example 2 except that the thickness of the first insulating layer 12 was 2 μm and the thickness of the second insulating layer 13 was 7 μm.

(Comparative Example 1)
The coating liquid for forming the first insulating layer 12 is a coating liquid of a solvent-soluble polyimide resin containing no flame retardant, and the coating liquid for forming the second insulating layer 13 is applied to 100 parts by weight of the resin. A coverlay film of Comparative Example 1 was obtained in the same manner as in Example 1 except that the coating liquid was a solvent-soluble polyimide resin containing 100 parts by weight of a phosphorus-based flame retardant.
(Comparative Example 2)
As the solvent-soluble polyimide resin used to form the insulating layers 12 and 13, the coverlay of Comparative Example 2 is used in the same manner as in Example 2 except that the solvent-soluble polyimide resin having a lower tensile elongation after coating and drying is used. I got a film.

(Measurement method of tensile elongation)
Based on IPC-TM-650 2.4.19, the sample size was measured at a width of 15 mm, the distance between chucks was 100 mm, and the measurement speed was measured at 50 mm / min (measurement was performed with the number of samples N = 5 and the average value was taken. T).
The tensile elongation of the laminate was measured using the laminate excluding the support film as a sample.
The tensile elongation of the second insulating layer is obtained by applying a coating liquid for forming the second insulating layer on one side of a release film similar to the support film, and then peeling and removing the release film after drying. A single unit of the second insulating layer was measured as a sample.

(Evaluation method of followability)
A thermosetting adhesive surface of a coverlay film is superposed on a test pattern in which a copper wiring pattern having a thickness of 75 μm and L / S = 75 μm / 75 μm is formed on a polyimide film having a thickness of 12.5 μm, and the temperature is 140 ° C. and the speed is 1 m. Laminated by thermal lamination at / min. After peeling off the support film 11, heat pressing was performed at 160 ° C., 4.5 MPa, and 65 minutes to obtain an evaluation sample of followability.
Observe the cross section of the obtained sample, and if it follows the wiring pattern very well and has a good appearance, it is "◎". If it follows the wiring pattern well but the wiring edge is thin, it is "○". , The case where the wiring pattern is not followed and the coating film is cut off at the wiring edge is marked with "x".

(Evaluation method of flame retardancy)
The obtained coverlay film was hot-pressed on a polyimide film having a thickness of 12.5 μm by the above-mentioned method (see the method for evaluating followability) to obtain a sample for evaluating flame retardancy. Evaluate the flame retardancy according to the method of UL-94 thin material vertical combustion test (ASTM D4804). In the case, it was marked with "○", when it was burned up to the marked line, it was marked with "Δ", and when it burned above the marked line and had no flame retardancy, it was marked with "x".

(Test results)
For Examples 1 to 7 and Comparative Examples 1 and 2, the coverlay film was evaluated by the above evaluation method, and the obtained evaluation results are shown in Table 1.
In the columns of the first insulating layer and the second insulating layer, "parts by weight" means the parts by weight of the flame retardant with respect to 100 parts by weight of the resin. “PI1” means the solvent-soluble polyimide resin used in Example 1, and “PI2” means the solvent-soluble polyimide resin used in Comparative Example 2.
In the column of the material of the heat-adhesive adhesive layer, "PU1" means the heat-adhesive adhesive containing the flame-retardant polyurethane used in Example 1.
The thickness of the laminate means the thickness of the entire coverlay film excluding the support film, and the "total thickness" means the thickness of the entire coverlay film including the support film.
The phosphorus-based flame retardant is an aromatic condensed phosphoric acid ester [(CH ₃ ) ₂ C ₆ H ₃ O] ₂ P (O) OC ₆ H ₄ OP (O) [OC ₆ H ₃ (CH _3). ) ₂ ] ₂ was used.

According to the evaluation results shown in Table 1, it can be seen that when the tensile elongation of the laminated body is 100% or more, the followability is good. That is, when the tensile elongation of the laminated body is low, the followability to the step is deteriorated. When the tensile elongation of the second insulating layer was low, the tensile elongation of the laminated body also tended to decrease.
Further, in Comparative Example 1 in which the flame retardant was not added to the first insulating layer and the flame retardant was added to the second insulating layer, the total amount of the flame retardants contained in the first and second insulating layers was implemented. Although the number is higher than that of Examples 1 to 7, the flame retardancy of the first insulating layer, which is the outermost layer in the sample from which the support film has been peeled off, is low, so that the flame retardancy of the entire laminate is deteriorated.

10 ... Coverlay film, 11 ... Support film, 12 ... First insulating layer, 13 ... Second insulating layer, 14 ... Thermosetting adhesive layer, 15 ... Laminated body, 19 ... Release film.

Claims (9)

A first insulating layer, a second insulating layer, and a thermosetting adhesive layer are laminated in this order on one side of the support film, and the first insulating layer contains a flame retardant.
A coverlay characterized in that the tensile elongation of the laminate composed of the first insulating layer, the second insulating layer, and the thermosetting adhesive layer excluding the support film is 100% or more. the film. The coverlay film according to claim 1, wherein the second insulating layer contains a flame retardant having a lower concentration than that of the first insulating layer, or does not contain a flame retardant. The coverlay film according to claim 1 or 2, wherein the thickness of the first insulating layer is thinner than the thickness of the second insulating layer. The coverlay film according to claim 3, wherein the thickness of the first insulating layer is 0.5 to 5 μm, and the thickness of the second insulating layer is 2 to 9 μm. The coverlay film according to any one of claims 1 to 4 , wherein the thermosetting adhesive layer contains a polyurethane resin and an epoxy resin. The coverlay film according to claim 5 , wherein the polyurethane resin is a phosphorus-containing polyurethane resin. The cover according to any one of claims 1 to 6 , wherein at least one of the first insulating layer, the second insulating layer, and the thermosetting adhesive layer contains a light absorber. Ray film. A mobile phone in which the coverlay film according to any one of claims 1 to 7 is used as a member for protecting an FPC. An electronic device in which the coverlay film according to any one of claims 1 to 7 is used as a member for protecting an FPC.

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