JP6431998B1 - Conductive adhesive layer - Google Patents

Abstract

An object of the present invention is to provide a conductive adhesive layer that improves the adhesion of a conductive adhesive layer to an adherend after a temporary fixing step and does not cause a positional shift after the temporary fixing step.
The present invention is characterized by comprising a conductive adhesive containing a binder resin 110 and a conductive filler 120, and having a skewness Ssk on the surface of −3.5 or more and 2.7 or less. The maximum peak height Sp on the surface is 1.3 μm or more and 30 μm or less, the conductive filler has an average particle diameter D50 of 3 μm or more and 20 μm or less, and the content in the conductive adhesive is 10% by mass or more. 80% by mass or less is preferable.
[Selection] Figure 1

Description

  The present disclosure relates to a conductive adhesive layer, an electromagnetic wave shielding film, and a shield wiring board.

  A conductive adhesive is frequently used for printed wiring boards. This type of conductive adhesive is used, for example, as an electromagnetic shielding film as a raw material for the conductive adhesive layer formed on the surface of the insulating protective layer. This electromagnetic wave shielding film is bonded to, for example, a printed wiring board to conduct the conductive adhesive layer and the ground circuit of the printed wiring board.

  By the way, when the electromagnetic wave shielding film is bonded to a printed wiring board or the like, it is usually temporarily fixed at a predetermined position and then pressed under conditions of pressure and heating that are stricter than those when temporarily fixing.

  However, many conventional electromagnetic shielding films focus on improving the adhesive strength after pressure heating, and the adhesive strength after pressure heating is high, but the adhesive strength after temporary fixing is high. Inferior, if the substrate is moved even if temporarily fixed, the electromagnetic wave shielding film may be peeled off and the operation may be reworked.

  Therefore, in order to improve the adhesive strength with an adherend such as a printed wiring board, the surface property of the conductive adhesive layer is defined by the surface roughness Ra (for example, see Patent Document 1). .

JP 2017-25280 A

  However, even if the surface roughness Ra of the conductive adhesive layer is in a specific range, the adhesive strength after the temporary fixing process is inferior, and the conductive adhesive layer may be displaced after the temporary fixing process.

  This indication is made in view of this point, and the object of the present disclosure is to improve the adhesion after the temporary fixing process to the adherend, so that the conductive adhesive layer after the temporary fixing process is improved. The purpose is to prevent displacement.

  One aspect of the conductive adhesive layer of the present disclosure is composed of a conductive adhesive containing a binder resin and a conductive filler, and the skewness Ssk on the surface is −3.5 or more and 2.7 or less. Features.

  In one embodiment of the conductive adhesive layer of the present disclosure, the maximum peak height Sp on the surface can be set to 1.3 μm or more and 30 μm or less.

  In one embodiment of the conductive adhesive layer of the present disclosure, the average particle diameter D50 may be 3 μm or more and 20 μm or less, and the content in the conductive adhesive may be 10% by mass or more and 80% by mass or less. .

  One aspect of the electromagnetic shielding film of the present disclosure includes an insulating protective layer and the conductive adhesive layer of the present disclosure provided on the surface of the insulating protective layer.

  One aspect of the shielded wiring board of the present disclosure includes a printed wiring board provided with a ground circuit, and an electromagnetic wave shielding film of the present disclosure bonded to the printed wiring board so as to be electrically connected to the ground circuit. Features.

  According to this indication, it is excellent in the adhesiveness after the temporary fixing process with respect to a to-be-adhered body, and position shift of the conductive adhesive layer after a temporary fixing process can be prevented.

It is sectional drawing which shows one Embodiment of the conductive adhesive layer formed on the base layer. It is sectional drawing of the electromagnetic wave shielding film which concerns on one Embodiment. It is sectional drawing which shows other embodiment of an electromagnetic wave shield film. It is sectional drawing of the shield wiring board which concerns on one Embodiment.

  Hereinafter, embodiments of the present disclosure will be described in detail. The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the present disclosure, its application, or its application.

<Conductive adhesive layer>
(Skewness Ssk)
The conductive adhesive layer according to this embodiment is characterized in that the skewness Ssk on the surface thereof is −3.5 or more and 2.7 or less. As shown in FIG. 1, the conductive adhesive layer 100 according to the present embodiment has a concavo-convex surface composed of convex portions 100 a (mountains) and concave portions 100 b (valleys), and skewness is used as a parameter for specifying the surface properties. Since Ssk is controlled within a specific range, it has excellent adhesion after the temporary fixing process to the adherend (not shown), and can prevent displacement of the conductive adhesive layer 100 after the temporary fixing process. it can.

  The skewness Ssk indicates the symmetry of the height distribution with respect to the average surface of the concavo-convex surface. When the skewness Ssk is 0, the height distribution is a surface that is symmetrical in the vertical direction (normal distribution). When it is small, the surface has many fine valleys, and when it is larger than 0, the surface has many fine peaks.

  When the absolute value of the skewness Ssk on the surface of the conductive adhesive layer 100 is large, that is, an uneven surface with many peaks or troughs, the adhesion area with the adherend becomes small, and after the temporary fixing process to the adherend Adhesive strength is insufficient.

  Therefore, by making the surface of the conductive adhesive layer 100 a surface having a skewness Ssk in a specific range centered at 0 and having a relatively symmetrical height distribution, the adhesion area with the adherend is increased. The adhesion after the temporary fixing step to the adherend can be improved.

  Therefore, the skewness Ssk increases the adhesion area with the adherend and improves the adhesion after the temporary fixing process to the adherend by reducing the valleys and bringing the height distribution closer to a vertically symmetrical surface. From the viewpoint, it is −3.5 or more, preferably −3 or more, more preferably −2.5 or more, and further preferably −2 or more. Further, from the viewpoint of increasing the adhesion area with the adherend and improving the adhesion after the temporary fixing step to the adherend by reducing the ridges and bringing the height distribution closer to the surface symmetrical in the vertical direction, 2 0.7 or less, preferably 2.5 or less, more preferably 2 or less, and even more preferably 1.5 or less.

  In the present specification, the “adherent” means, for example, a resin film such as a polyimide film that forms a base layer of a printed wiring board, a metal layer such as a copper foil that forms a ground circuit, and the like.

  In the present specification, the “temporary fixing step” refers to the conductive adhesive layer 100 formed by, for example, two heating plates (not shown) heated to 120 ° C. before the final fixing step. And the adherend are sandwiched from above and below and pressed at a pressure of 0.5 MPa for 5 seconds.

  Further, in this specification, “excellent adhesion after the temporary fixing process to the adherend” means that the 180 ° peel strength between the conductive adhesive layer 100 and the adherend after the temporary fixing process is 0. It means 5 N / cm or more. In this case, displacement of the conductive adhesive layer 100 after the temporary fixing step can be prevented. In addition, the specific measuring method of peel strength is demonstrated in a following example.

(Maximum mountain height Sp)
In addition, the conductive adhesive layer 100 according to this embodiment preferably has a maximum peak height Sp on the surface of 1.3 μm or more and 30 μm or less. As described above, the conductive adhesive layer 100 according to the present embodiment controls the maximum peak height Sp to a specific range as a parameter for specifying the surface property, thereby allowing the adherend to adhere to the adherend after the temporary fixing step. The position of the conductive adhesive layer 100 after the temporary fixing step can be further prevented.

  The maximum peak height Sp indicates the maximum peak height from the average surface of the concavo-convex surface, and the larger the maximum peak height Sp, the higher the surface.

  When the maximum peak height Sp on the surface of the conductive adhesive layer 100 is large, that is, when the surface has a high peak, the high peak causes an obstacle and the adhesion area with the adherend is reduced. Adhesive strength after the temporary fixing process to the adherend becomes insufficient.

  Therefore, by making the surface of the conductive adhesive layer 100 a surface where the maximum peak height Sp is a specific range and the peak height of the highest peak is relatively low, the adhesion area with the adherend is further increased. The adhesion after the temporary fixing process to the adherend can be further improved.

  Therefore, the maximum peak height Sp is preferably 1.3 μm or more, more preferably 1. from the viewpoint of further increasing the adhesion area with the adherend and further improving the adhesion after the temporary fixing process to the adherend. 6 μm or more. Moreover, from the viewpoint of increasing the adhesion area with the adherend and further improving the adhesion after the temporary fixing step to the adherend by approaching the surface where the height of the highest mountain is relatively low, preferably It is 30 μm or less, more preferably 25 μm or less.

(Other parameters)
In addition to the skewness Ssk and the maximum peak height Sp, for example, the parameter for specifying the surface property of the conductive adhesive layer 100 is the sum of the maximum valley depth Sv, the maximum peak height Sp, and the maximum peak depth Sv. Although the maximum height Sz shown etc. are mentioned, this indication is not limited only to this illustration.

  On the other hand, the inventor of the present invention found that the arithmetic average Sa does not correlate with the adhesion after the temporary fixing process to the adherend as shown in Examples and Comparative Examples described later. The reason for this is that the arithmetic mean Sa represents the average of the height difference of each point (mountain and valley) with respect to the average surface of the concavo-convex surface, so even if the value is small, it is high. There may be a case where the uneven surface which the mountain and the deep valley have to the same extent is included. In this case, it is considered that the high peaks and deep valleys obstruct the adhesive area with the adherend, and the adhesive strength after the temporary fixing process to the adherend becomes insufficient. Therefore, the arithmetic average Sa is not suitable as a parameter for specifying the surface property of the conductive adhesive layer 100 in order to obtain an adhesive strength that can prevent the displacement of the conductive adhesive layer 100 after the temporary fixing step. Absent.

  In addition, the surface property in this indication is a value measured based on ISO 25178-6: 2010, and a specific measuring method is demonstrated in a following example.

  The conductive adhesive layer 100 according to this embodiment is formed of a conductive adhesive containing a binder resin 110 and a conductive filler 120.

(Binder resin)
The binder resin 110 is not particularly limited, and various resins used for conductive adhesives can be used. Examples of such resins include thermoplastic resins such as polystyrene, vinyl acetate, polyester, polyethylene, polypropylene, polyamide, rubber, and acrylic; phenol, epoxy, urethane, and melamine Alternatively, an alkyd-based thermosetting resin or the like can be used. These binder resins 110 may be used alone or in combination of two or more.

  In addition, the binder resin 110 includes resin fine particles or a resin fine particle from the viewpoint of adjusting the surface properties (skewness Ssk and maximum peak height Sp) of the conductive adhesive layer 100 to a predetermined state within a range that does not impair the effects of the present invention. Inorganic fine particles can be added. Examples of the resin fine particles include acrylic resin fine particles, polyacrylonitrile fine particles, polyurethane fine particles, polyamide fine particles, and polyimide fine particles. Examples of the inorganic fine particles include calcium carbonate fine particles, calcium silicate fine particles, clay, kaolin, talc, silica fine particles, glass fine particles, diatomaceous earth, mica powder, alumina fine particles, magnesium oxide fine particles, zinc oxide fine particles, barium sulfate fine particles, sulfuric acid. Examples include aluminum fine particles, calcium sulfate fine particles, and magnesium carbonate fine particles. These resin fine particles and inorganic fine particles may be used alone or in combination of two or more.

(Conductive filler)
The conductive filler 120 is not particularly limited, and a metal filler, a metal-coated resin filler, a carbon filler, a mixture thereof, and the like used for the conductive adhesive can be used. Examples of the metal filler include copper powder, silver powder, nickel powder, silver-coated copper powder, gold-coated copper powder, silver-coated nickel powder, and gold-coated nickel powder. These metal powders can be produced by, for example, an electrolytic method, an atomizing method, or a reducing method. These conductive fillers 120 may be used alone or in combination of two or more. Among these, silver powder, silver-coated copper powder and copper powder are preferable, and silver-coated copper powder is more preferable.

  Examples of the shape of the conductive filler 120 include a spherical shape, an elliptical shape, a flake shape, a fiber shape, and a dendritic shape (dendritic shape). Moreover, it can also be set as a metal nanoparticle. Examples of the metal nanoparticles include silver nanoparticles and gold nanoparticles.

  The average particle diameter D50 (median diameter) of the conductive filler 120 is preferably 3 μm or more, more preferably 5 μm or more, and preferably 20 μm or less, more preferably 15 μm or less. The average particle diameter D50 of the conductive filler 120 can be measured by a generally used method such as a laser diffraction type particle size distribution measuring device or a flow type particle image analyzer.

  In addition, the average particle diameter D50 of the conductive filler 120 may be appropriately set according to the thickness of the conductive adhesive layer 100 and the like. Specifically, when the thickness of the conductive adhesive layer 100 is about 5 μm, it is preferably about 3 μm, more preferably about 5 μm. Moreover, when the thickness of the conductive adhesive layer 100 is about 15 to 60 μm, it is preferably about 20 μm, more preferably about 15 μm.

  The content of the conductive filler 120 in the conductive adhesive is not particularly limited, but may be appropriately set according to the use of the conductive adhesive, preferably 10% by mass or more, and preferably 80% by mass or less. More preferably, it is 75 mass% or less, More preferably, it is 70 mass% or less. The conductive adhesive layer 100 may be either an anisotropic conductive adhesive layer or an isotropic conductive adhesive layer. When used as an anisotropic conductive adhesive layer, the conductive adhesive layer 100 The content of the conductive filler 120 in the agent is preferably 10% by mass or more, more preferably 15% by mass or more, further preferably 20% by mass or more, and preferably 45% by mass or less, more preferably 40% by mass. Hereinafter, it is more preferably 35% by mass or less. When used as an isotropic conductive adhesive layer, the content of the conductive filler 120 in the conductive adhesive is preferably 50% by mass or more, more preferably 55% by mass or more, and further preferably 60% by mass or more. It is preferably 80% by mass or less, more preferably 75% by mass or less, and still more preferably 70% by mass or less.

  By setting the average particle diameter D50 of the conductive filler 120 and the content of the conductive filler 120 in the conductive adhesive to the specific ranges described above, the position of the conductive adhesive layer 100 after the temporary fixing step The conductive adhesive layer 100 having the skewness Ssk suitable for preventing the shift can be realized.

(Optional component)
For the conductive adhesive, for example, an antifoaming agent, an antioxidant, a viscosity modifier, a diluent, an anti-settling agent, a leveling agent, a coupling agent, a coloring agent, or a difficult agent, as long as the effects of the present invention are not impaired. A flame retardant etc. can be added. These optional components may be used alone or in combination of two or more. Among these, it is particularly preferable to add a flame retardant from the viewpoint of imparting flame retardancy to the conductive adhesive.

  Examples of such a flame retardant include nitrogen-based flame retardants such as melamine cyanurate or melamine polyphosphate; metal hydrates such as magnesium hydroxide or aluminum hydroxide; phosphate esters, red phosphorus, or phosphate compounds. And phosphorus-based flame retardants. Of these flame retardants, phosphate compounds are preferred.

  When adding a flame retardant to the conductive adhesive, it is preferable to add 10 parts by mass to 60 parts by mass with respect to 100 parts by mass of the binder resin 110.

<Method for forming conductive adhesive layer>
Next, a method of forming the conductive adhesive layer 100 according to this embodiment using a conductive adhesive containing the binder resin 110 and the conductive filler 120 will be described.

(Process for preparing conductive adhesive)
First, a binder resin solution in which the binder resin 110 is dissolved in a solvent so as to have a predetermined concentration is prepared. Examples of the solvent include toluene, acetone, methyl ethyl ketone, methanol, ethanol, propanol, and dimethylformamide, but the present disclosure is not limited to such examples. Note that the concentration of the binder resin 110 in the solution may be set as appropriate according to the thickness of the conductive adhesive layer 100 and the like.

  Next, the conductive adhesive 120 is prepared by stirring and mixing the conductive filler 120 and, if necessary, a mixed suspension added to the binder resin solution prepared above.

(Coating process for conductive adhesive)
Next, the conductive adhesive prepared above is applied onto the base layer 130. As the base layer 130, for example, a resin sheet or film can be used. As a material constituting the sheet or film, for example, a thermoplastic resin such as a polyester resin, a polyethylene resin, a polypropylene resin, a polyamide resin, an acrylic resin, and / or a thermosetting resin can be used. . The surface of the base layer 130 may be provided with an uneven fine pattern by embossing that is generally used. In addition, when forming an electromagnetic wave shield film, a conductive adhesive is applied on the insulating protective layer or shield layer described later.

  A release treatment may be performed on the surface of the base layer 130 as necessary. As the release treatment, for example, a layer made of a silicon release agent, a non-silicon release agent, a melamine release agent, or the like can be formed on the surface of the base layer 130. By performing a mold release treatment on the surface of the base layer 130, the base layer 130 can be easily peeled off after the conductive adhesive layer 100 formed on the base layer 130 is attached to the adherend.

  Moreover, the adhesive layer may be provided in the surface of the base layer 130 as needed. By providing the pressure-sensitive adhesive layer on the surface of the base layer 130, it is possible to prevent the base layer 130 from being unintentionally peeled off from the conductive adhesive layer 100. As such an adhesive, for example, a known adhesive such as an acrylic adhesive or a polyester adhesive can be used.

  Note that the thickness of the base layer 130 is not particularly limited, and can be appropriately determined in consideration of ease of use.

  The method for applying the conductive adhesive on the base layer 130 is not particularly limited, and for example, a method such as lip coating, comma coating, gravure coating, or slot die coating can be used.

(Drying process of conductive adhesive)
Finally, the conductive adhesive layer 100 according to this embodiment can be formed by heating and drying the conductive adhesive applied on the base layer 130 to remove the solvent. Examples of the drying method include hot air drying, infrared drying, oven drying, hot plate drying, and vacuum drying.

  The thickness of the conductive adhesive layer 100 according to this embodiment obtained as described above may be adjusted according to the particle size of the conductive filler 120. From the viewpoint of realizing good conductivity, the thickness of the conductive adhesive layer 100 is preferably not more than 5.5 times the average particle diameter D50 of the conductive filler 120, more preferably not more than 3.5 times. The average particle diameter D50 of the conductive filler 120 is preferably +70 μm or less (that is, d + 70 μm or less when the average particle diameter D50 of the conductive filler 120 is d μm), more preferably +60 μm or less (d + 60 μm or less). . From the viewpoint of good coating, the thickness of the conductive adhesive layer 100 is preferably 0.6 times or more, more preferably 0.7 times or more the average particle diameter D50 of the conductive filler 120. The average particle size D50 of the conductive filler 120 is preferably −7 μm or more (d−7 μm or more), more preferably −5 μm or more (d−5 μm or more).

  If necessary, a peeling substrate (separate film) (not shown) may be bonded to the surface of the conductive adhesive layer 100 opposite to the surface to which the base layer 130 is bonded. As the peeling substrate, for example, a silicon-based or non-silicon-based release agent or an acrylic-based or polyester-based pressure-sensitive adhesive on a base film such as polyethylene terephthalate or polyethylene naphthalate is used as the conductive adhesive layer 100. And the like coated on the surface to be bonded to the surface. By attaching a release substrate to the surface of the conductive adhesive layer 100, it is possible to prevent the surface of the conductive adhesive layer 100 from being scratched or foreign matter from adhering. Note that the thickness of the release substrate is not particularly limited, and can be appropriately determined in consideration of ease of use.

  In the above description, an example in which the conductive adhesive layer 100 having a predetermined skewness Ssk is formed by applying and drying a conductive adhesive on the base layer 130 has been described. It can also be formed. In this case, the surface property of the conductive adhesive layer 100 can be set to a predetermined state by using a release substrate having a fine pattern and transferring the fine pattern to the surface of the conductive adhesive layer 100.

  As described above, since the conductive adhesive layer 100 of the present disclosure has a skewness Ssk of −3.5 or more and 2.7 or less on the surface thereof, it has excellent adhesion after the temporary fixing process to the adherend. . Thus, since the conductive adhesive layer 100 of the present disclosure can prevent displacement of the conductive adhesive layer 100 after the temporary fixing step, it can be suitably used for, for example, an electromagnetic shielding film. it can.

<Electromagnetic wave shielding film>
As shown in FIG. 2, the electromagnetic wave shielding film 200 according to this embodiment includes an insulating protective layer 210 and a conductive adhesive layer 100 provided on the surface of the insulating protective layer 210. Thus, since the electromagnetic wave shielding film 200 according to the present embodiment has the conductive adhesive layer 100 according to the present embodiment as the conductive adhesive layer, the electromagnetic wave shielding film 200 according to the present embodiment is applied to an adherend (not shown) such as a printed wiring board. The adhesiveness after the temporary fixing process is excellent, and displacement of the conductive adhesive layer 100 after the temporary fixing process, that is, the electromagnetic wave shielding film 200 can be prevented.

  Further, the electromagnetic wave shielding film 200 according to the present embodiment is bonded to the conductive adhesive layer 100 according to the present embodiment so as to be electrically connected to a ground circuit of a printed wiring board (not shown). The adhesive layer 100 can function as a shield against electromagnetic waves. As shown in FIG. 3, the electromagnetic wave shielding film 200 according to this embodiment can also be provided with a shielding layer 220 between the insulating protective layer 210 and the conductive adhesive layer 100.

(Insulation protective layer)
The insulating protective layer 210 is not particularly limited as long as it has sufficient insulating properties and can protect the conductive adhesive layer 100 and the shield layer 220. For example, a thermoplastic resin, a thermosetting resin, an active energy ray curable resin, and the like. Can be used.

  The insulating protective layer 210 may have a laminated structure of two or more layers having different materials or physical properties such as hardness or elastic modulus. For example, if the outer layer having a low hardness and the inner layer having a high hardness have a laminated structure, the outer layer has a cushioning effect. it can. For this reason, it can suppress that the shield layer 220 is destroyed by the level | step difference provided in the printed wiring board.

  The thickness of the insulating protective layer 210 is not particularly limited and can be appropriately set as necessary, but is preferably 1 μm or more, more preferably 4 μm or more, and preferably 20 μm or less, more preferably 10 μm or less. More preferably, it is 5 μm or less. By setting the thickness of the insulating protective layer 210 to 1 μm or more, the conductive adhesive layer 100 and the shield layer 220 can be sufficiently protected. In addition, by setting the thickness of the insulating protective layer 210 to 20 μm or less, the flexibility of the electromagnetic wave shielding film 200 can be ensured, and this embodiment is also applied to a member that requires flexibility, such as a flexible printed wiring board. It becomes easy to apply the electromagnetic wave shielding film 200 according to the embodiment.

(Shield layer)
The shield layer 220 only needs to have conductivity, and can be constituted by, for example, a metal thin film, a conductive filler, a metal vapor deposition film, or the like. The metal thin film can be made of, for example, nickel, copper, silver, tin, gold, palladium, aluminum, chromium, titanium, zinc, or an alloy containing two or more. The metal thin film can be manufactured, for example, by using a metal foil or depositing a metal by an additive method. As the additive method, for example, an electrolytic plating method, an electroless plating method, a sputtering method, an electron beam evaporation method, a vacuum evaporation method, a chemical vapor deposition (CVD) method, a metal organic deposition (MOCVD) method, or the like is used. it can.

  When the shield layer 220 is composed of a conductive filler, for example, a metal filler, a metal-coated resin filler, a carbon filler, a mixture thereof, or the like can be used. Examples of the metal filler include copper powder, silver powder, nickel powder, silver-coated copper powder, gold-coated copper powder, silver-coated nickel powder, and gold-coated nickel powder. It can be created by the method and the reduction method. Examples of the shape of the metal powder include a spherical shape, a flake shape, a fiber shape, and a dendritic shape. Moreover, it can also be set as a metal nanoparticle. Examples of the metal nanoparticles include silver nanoparticles and gold nanoparticles.

  The metal material and thickness of the shield layer 220 may be appropriately selected according to the required electromagnetic shielding effect and repeated bending / sliding resistance, but the thickness can be about 0.1 μm to 12 μm.

  In addition, it can also be set as the electromagnetic wave shielding film 200 which does not have the shield layer 220 but the conductive adhesive layer 100 which concerns on this embodiment functions as a shield layer.

<Method for forming electromagnetic wave shielding film>
Next, a method for forming the electromagnetic wave shielding film 200 according to this embodiment will be described. First, an insulating protective layer 210 and, if necessary, a shield layer 220 are sequentially formed on a support film (not shown) using a generally used method to obtain a laminate. As the support film, a resin sheet or film similar to the base layer 130 described above can be used. Moreover, you may use the support body film (transfer film) which has a fine pattern on the surface as a support film. In this case, the surface property of the insulating protective layer 210 can be set to a predetermined state by transferring the fine pattern onto the surface of the insulating protective layer 210.

  Next, by using the laminate formed above as a base layer, the conductive adhesive layer 100 according to the present embodiment is formed on the base layer in the same manner as the method for forming the conductive adhesive layer 100 described above. The electromagnetic wave shielding film 200 according to this embodiment can be obtained.

  As described above, the electromagnetic wave shielding film 200 of the present disclosure has the conductive adhesive layer 100 of the present disclosure as the conductive adhesive layer, and thus has excellent adhesion after the temporary fixing process to the adherend. The position shift of the conductive adhesive layer 100 after the stopping step, that is, the electromagnetic wave shielding film 200 can be prevented. For this reason, the electromagnetic wave shielding film 200 of the present disclosure is a shield wiring board in which the conductive adhesive layer 100 is electrically connected to the ground circuit of the printed wiring board and the conductive adhesive layer 100 functions as a shield against electromagnetic waves. Can do.

<Shield wiring board>
As shown in FIG. 4, a shield wiring board 400 according to the present embodiment relates to a printed wiring board 300 having a ground circuit 320a, and the printed wiring board 300 bonded to the printed wiring board 300 so as to be electrically connected to the ground circuit 320a. And an electromagnetic wave shielding film 200. The electromagnetic wave shielding film 200 may have a shield layer 220.

  The printed wiring board 300 includes, for example, a base layer 310, a printed circuit 320 including a ground circuit 320a and a signal circuit 320b formed on the base layer 310, and a base layer so as to expose at least a part of the ground circuit 320a. And an insulating layer 330 covering 310. The printed wiring board 300 may be a flexible board or a rigid board.

  The base layer 310 and the insulating layer 330 may be any material, but may be, for example, a resin film. In this case, it can be formed of a resin such as polypropylene, crosslinked polyethylene, polyester, polybenzimidazole, polyimide, polyimide amide, polyether imide, or polyphenylene sulfide. The printed circuit 320 can be, for example, a copper wiring pattern formed on the base layer 310.

  When the electromagnetic wave shielding film 200 according to the present embodiment is bonded to the printed wiring board 300, the electromagnetic wave shielding film 200 is disposed so as to be electrically connected to the ground circuit 320a. Specifically, the conductive adhesive layer 100 of the electromagnetic wave shielding film 200 is disposed on the ground circuit 320a. Then, the electromagnetic wave shielding film 200 and the printed wiring board 300 are sandwiched from above and below by two heating plates (not shown) heated to a predetermined temperature (for example, 120 ° C.). ) For a short time (for example, 5 seconds). Thereby, the electromagnetic wave shielding film 200 is temporarily fixed to the printed wiring board 300.

  At this time, in the shield wiring board 400 according to this embodiment, the printed wiring board 300 and the electromagnetic wave shielding film 200 according to this embodiment are bonded via the conductive adhesive layer 100 according to this embodiment. Therefore, it is excellent in the adhesiveness after the temporary fixing process with respect to the printed wiring board 300 (adhered body), and the position shift of the electromagnetic wave shielding film 200 after the temporary fixing process can be prevented. For this reason, the shielded wiring board 400 in a state where the electromagnetic wave shielding film 200 is temporarily fixed to the printed wiring board 300 can be stored, for example, by overlapping the shielded wiring boards 400 until final fixing.

  Next, the temperature of the two heating plates is set to a predetermined temperature (for example, 170 ° C.) higher than that at the time of temporarily fixing, and is pressurized at a predetermined pressure (for example, 3 MPa) for a predetermined time (for example, 30 minutes). Thereby, the electromagnetic wave shielding film 200 can be reliably fixed to the printed wiring board 300.

<Other embodiments>
The conductive adhesive layer 100 according to the present embodiment is not limited to the electromagnetic wave shielding film and the shield wiring board. For example, a conductive (metal) reinforcing plate made of stainless steel or the like is attached to the flexible printed wiring board. It can also be used for the attachment. In this case, the conductive (metal) reinforcing plate can function as a shield against electromagnetic waves.

  Hereinafter, the present invention will be described in detail by way of examples. The following examples are illustrative and are not intended to limit the present invention.

<Preparation process of conductive adhesive>
A binder resin solution in which a predetermined binder resin was dissolved in toluene or methyl ethyl ketone as a solvent was prepared so as to have a predetermined solid content concentration. A predetermined adhesive filler and optional components were added to the obtained binder resin solution, and mixed and stirred using a planetary stirring / defoaming device to prepare a conductive adhesive.

<Preparation of electromagnetic shielding film>
As the support film, a PET film having a thickness of 60 μm and a surface subjected to a release treatment was used. On the support film, the composition for protective layers (solid content 30 mass%) containing silica particles, bisphenol A type epoxy resin and methyl ethyl ketone was applied and dried by heating to form an insulating protective layer. Subsequently, a laminated body (base layer) was obtained by forming a copper foil having a thickness of 0.5 μm as a shield layer on the surface of the insulating protective layer. Next, an electromagnetic wave shielding film was obtained by applying the conductive adhesive prepared above to the surface of the shield layer of the obtained laminate and drying to form a conductive adhesive layer having a predetermined thickness. .

  Using the electromagnetic shielding film obtained above, the thickness, surface properties, and adhesion after the temporary fixing step to the adherend were evaluated by the following methods.

<Thickness of conductive adhesive layer>
The value obtained by subtracting the thickness of the laminate before forming the conductive adhesive layer from the thickness of the electromagnetic wave shielding film after forming the conductive adhesive layer was taken as the thickness of the conductive adhesive layer. In addition, each thickness was measured based on JIS C2151 using the micrometer [Mittoyo Co., Ltd. make, brand name: MDH-25].

<Surface properties of the conductive adhesive layer>
Using a confocal microscope (Lasertec, OPTELICS HYBRID, objective lens 20 times), five arbitrary positions on the surface of the conductive adhesive layer were measured. Thereafter, the inclination of the surface was corrected using data analysis software (LMey7), and the skewness Ssk, the maximum peak height Sp, and the arithmetic mean Sa were obtained in accordance with ISO 25178-6: 2010. Note that the cutoff wavelength of the S filter was 0.0025 mm, and the cutoff wavelength of the L filter was 0.8 mm. Moreover, each numerical value was made into the average value of the value which measured 5 places.

<Adhesion after temporary fixing process to adherend>
The adhesion of the conductive adhesive layer to the adherend after the temporary fixing step was measured by a 180 ° peel test. Specifically, first, a conductive adhesive layer of an electromagnetic wave shielding film and a polyimide surface of a single-sided copper-clad laminate [product name: F30VC1 25RC1 1/2 (H)] manufactured by Nikkan Kogyo Co., Ltd. as an adherend. Was temporarily fixed using a press machine under the conditions of temperature: 120 ° C., time: 5 seconds, pressure: 0.5 MPa, to obtain a test sample.

  Next, the test sample obtained above was subjected to a tensile tester [manufactured by Shimadzu Corporation, trade name: AGS-X50S] at room temperature at a peeling angle of 180 ° and a pulling speed of 50 mm. / Minute peeled from the single-sided copper-clad laminate, measured 180 ° peel strength (maximum value) at the time of breakage, and evaluated the adhesion after the temporary fixing process to the adherend based on the following evaluation criteria did.

(Evaluation criteria)
◯: Even when the 180 ° peel strength was 0.5 N / cm, no peeling occurred at the interface between the conductive adhesive layer and the adherend (180 ° peel between the conductive adhesive layer and the adherend after the temporary fixing step) Strength is 0.5 N / cm or more).
×: 180 ° peel strength was less than 0.5 N / cm, and peeling occurred at the interface between the conductive adhesive layer and the adherend.

(Example 1)
An epoxy resin was used as the binder resin, and silver-coated copper powder having an average particle diameter D50 of 12 μm and a dendritic shape was used as the conductive filler. The content of the conductive filler in the conductive adhesive was 10% by mass.

  The conductive adhesive layer (anisotropic) obtained in Example 1 has a thickness of 17 μm, a skewness Ssk on the surface of 1.10, a maximum peak height Sp of 11.87, and an arithmetic average Sa Was 2.30.

  In addition, the conductive adhesive layer obtained in Example 1 did not peel at the interface with the adherend even when the 180 ° peel strength was 3.23 N / cm (evaluation result: ◯). The adhesion after the temporary fixing process was very good.

( Reference Example 1 )
Epoxy resin was used as the binder resin, and silver-coated copper powder having an average particle diameter D50 of 5 μm and spherical and elliptical shapes was used as the conductive filler. The content of the conductive filler in the conductive adhesive was 30% by mass.

The conductive adhesive layer (anisotropic) obtained in Reference Example 1 has a thickness of 5 μm, a skewness Ssk on the surface of 1.50, a maximum peak height Sp of 9.38, and an arithmetic average Sa Was 0.55.

In addition, the conductive adhesive layer obtained in Reference Example 1 did not peel at the interface with the adherend even when the 180 ° peel strength was 5.74 N / cm (evaluation result: ◯). The adhesion after the temporary fixing process was very good.

Example 3
An epoxy resin was used as the binder resin, and silver-coated copper powder having an average particle diameter D50 of 12 μm and a dendritic shape was used as the conductive filler. The content of the conductive filler in the conductive adhesive was 15% by mass.

  The conductive adhesive layer (anisotropy) obtained in Example 3 has a thickness of 15 μm, a skewness Ssk of 2.31, a maximum peak height Sp of 12.05, and an arithmetic average Sa Was 1.40.

  In addition, the conductive adhesive layer obtained in Example 3 did not peel at the interface with the adherend even when the 180 ° peel strength was 2.91 N / cm (evaluation result: ◯). The adhesion after the temporary fixing process was very good.

( Reference Example 2 )
Epoxy resin was used as the binder resin, and silver-coated copper powder having an average particle diameter D50 of 6 μm and a dendritic shape was used as the conductive filler. The content of the conductive filler in the conductive adhesive was 65% by mass.

The conductive adhesive layer (isotropic) obtained in Reference Example 2 has a thickness of 15 μm, a skewness Ssk on the surface thereof of −0.31, a maximum peak height Sp of 1.67, and an arithmetic average Sa was 0.17.

Moreover, since the conductive adhesive layer obtained in Reference Example 2 did not peel at the interface with the adherend even when the 180 ° peel strength was 4.50 N / cm (evaluation result: ◯), the adherend The adhesion after the temporary fixing process was very good.

( Reference Example 3 )
Epoxy resin was used as the binder resin, and silver-coated copper powder having an average particle diameter D50 of 6 μm and a dendritic shape was used as the conductive filler. The content of the conductive filler in the conductive adhesive was 70% by mass.

The conductive adhesive layer (isotropic) obtained in Reference Example 3 has a thickness of 15 μm, a skewness Ssk on the surface of −2.47, a maximum peak height Sp of 1.66, and an arithmetic average Sa was 0.15.

Moreover, since the conductive adhesive layer obtained in Reference Example 3 did not peel at the interface with the adherend even when the 180 ° peel strength was 1.93 N / cm (evaluation result: ◯), The adhesion after the temporary fixing process was very good.

( Reference Example 4 )
An epoxy resin was used as the binder resin, and silver-coated copper powder having an average particle diameter D50 of 15 μm and a dendritic shape was used as the conductive filler. The content of the conductive filler in the conductive adhesive was 70% by mass.

The conductive adhesive layer (isotropic) obtained in Reference Example 4 has a thickness of 60 μm, a skewness Ssk on the surface thereof of −0.18, a maximum peak height Sp of 11.21, and an arithmetic average Sa was 2.82.

In addition, the conductive adhesive layer obtained in Reference Example 4 was peeled off at the interface with the adherend, but the 180 ° peel strength at break was 1.03 N / cm, which is 0.5 N / cm or more. (Evaluation result: ◯), the adhesion after the temporary fixing process to the adherend was good.

( Reference Example 5 )
An epoxy resin was used as the binder resin, and silver-coated copper powder having an average particle diameter D50 of 8 μm and a dendritic shape was used as the conductive filler. The content rate of the conductive filler in the conductive adhesive was 60% by mass.

The conductive adhesive layer (isotropic) obtained in Reference Example 5 has a thickness of 15 μm, a skewness Ssk on the surface thereof of −2.83, a maximum peak height Sp of 3.94, and an arithmetic average. Sa was 1.25.

Further, the conductive adhesive layer obtained in Reference Example 5 did not peel off at the interface with the adherend even when the 180 ° peel strength was 1.85 N / cm (evaluation result: ◯). The adhesion after the temporary fixing process was very good.

( Reference Example 6 )
An epoxy resin was used as the binder resin, and silver-coated copper powder having an average particle diameter D50 of 12 μm and a dendritic shape was used as the conductive filler. The content of the conductive filler in the conductive adhesive was 70% by mass.

The conductive adhesive layer (isotropic) obtained in Reference Example 6 has a thickness of 60 μm, a skewness Ssk on the surface thereof of −0.55, a maximum peak height Sp of 17.27, and an arithmetic average. Sa was 5.26.

Further, the conductive adhesive layer obtained in Reference Example 6 did not peel off at the interface with the adherend even when the 180 ° peel strength was 4.23 N / cm (evaluation result: ◯). The adhesion after the temporary fixing process was very good.

Example 9
An epoxy resin containing 1% by mass of silica particles having an average particle diameter D50 of 22 μm was used as the binder resin, and silver-coated copper powder having an average particle diameter D50 of 12 μm and a dendritic shape was used as the conductive filler. The content of the conductive filler in the conductive adhesive was 15% by mass.

  The conductive adhesive layer (anisotropy) obtained in Example 9 has a thickness of 36 μm, a skewness Ssk on its surface of 1.36, a maximum peak height Sp of 16.37, and an arithmetic average Sa Was 2.15.

  Further, the conductive adhesive layer obtained in Example 9 did not peel off at the interface with the adherend even when the 180 ° peel strength was 4.28 N / cm (evaluation result: ◯). The adhesion after the temporary fixing process was very good.

(Example 10)
An epoxy resin containing 2% by mass of silica particles having an average particle diameter D50 of 22 μm was used as the binder resin, and silver-coated copper powder having an average particle diameter D50 of 12 μm and a dendritic shape was used as the conductive filler. The content of the conductive filler in the conductive adhesive was 15% by mass.

  The conductive adhesive layer (anisotropy) obtained in Example 10 has a thickness of 40 μm, a skewness Ssk of 1.65, a maximum peak height Sp of 22.94, and an arithmetic average Sa Was 2.44.

  In addition, the conductive adhesive layer obtained in Example 10 did not peel at the interface with the adherend even when the 180 ° peel strength was 4.51 N / cm (evaluation result: ◯). The adhesion after the temporary fixing process was very good.

(Comparative Example 1)
Epoxy resin was used as the binder resin, and silver-coated copper powder having an average particle diameter D50 of 15 μm and spherical and elliptical shapes was used as the conductive filler. The content of the conductive filler in the conductive adhesive was 5% by mass.

  The conductive adhesive layer (anisotropy) obtained in Comparative Example 1 has a thickness of 15 μm, a skewness Ssk on its surface of 4.05, a maximum peak height Sp of 17.81, and an arithmetic average Sa Was 0.98.

  Further, the conductive adhesive layer obtained in Comparative Example 1 was peeled off at the interface with the adherend at 0.01 N / cm with a 180 ° peel strength of less than 0.5 N / cm (evaluation result: × ), The adhesion after the temporary fixing process to the adherend was poor.

(Comparative Example 2)
Epoxy resin was used as the binder resin, and silver-coated nickel powder having an average particle diameter D50 of 23 μm and an elliptical shape was used as the conductive filler. The content of the conductive filler in the conductive adhesive was 35% by mass.

  The conductive adhesive layer (anisotropy) obtained in Comparative Example 2 has a thickness of 30 μm, a skewness Ssk on the surface thereof of 4.01, a maximum peak height Sp of 29.54, and an arithmetic average Sa Was 1.63.

  Further, the conductive adhesive layer obtained in Comparative Example 2 was peeled off at the interface with the adherend at 0.13 N / cm having a 180 ° peel strength of less than 0.5 N / cm (evaluation result: × ), The adhesion after the temporary fixing process to the adherend was poor.

  Table 1 shows the composition of the conductive filler and the physical properties of the conductive adhesive layer used in each example and each comparative example.

  The conductive adhesive layer of the present disclosure is extremely useful because it has excellent adhesion to the adherend after the temporary fixing step and can prevent displacement of the conductive adhesive layer after the temporary fixing step.

DESCRIPTION OF SYMBOLS 100 Conductive adhesive layer 100a Convex part 100b Concave part 110 Binder resin 120 Conductive filler 130 Base layer 200 Electromagnetic wave shield film 210 Insulation protective layer 220 Shield layer 300 Printed wiring board 310 Base layer 320 Print circuit 320a Ground circuit 320b Signal circuit 330 Insulation layer 400 Shield printed wiring board

Claims (3)

It consists of a conductive adhesive containing a binder resin and a conductive filler,
Skewness Ssk is -3.5 or more in the surface state, and are 2.7 or less,
The maximum peak height Sp on the surface is 1.3 μm or more and 30 μm or less,
The conductive filler is at least one selected from the group consisting of copper powder, silver powder, silver-coated copper powder and gold-coated copper powder, the shape is dendritic, and the average particle diameter D50 is 3 μm or more, 20 μm or less,
The conductive filler content is 10 mass% or more, the conductive adhesive layer, wherein less der Rukoto 35 wt% in the conductive adhesive. Electromagnetic wave shielding film, wherein the insulating protective layer, provided on the surface of the insulating protective layer, that a conductive adhesive layer according to claim 1. A printed wiring board provided with a ground circuit;
A shield wiring board comprising: the electromagnetic shielding film according to claim 2 bonded to the printed wiring board so as to be electrically connected to the ground circuit.