TW201940627A - Conductive adhesive layer conductive adhesive containing a binder resin and a conductive filler, and the surface skewness Ssk being between -3.5 and 2.7 - Google Patents

Abstract

An object of the present invention is to improve the adhesion after the temporary positioning step of the adherend, and to prevent misalignment of the conductive adhesive layer after the temporary positioning step. The conductive adhesive layer is a solution of the present invention. The conductive adhesive layer is composed of a conductive adhesive containing a binder resin and a conductive filler, and the surface skewness Ssk is between -3.5 and 2.7.

Description

Conductive adhesive layer

FIELD OF THE INVENTION The present invention relates to a conductive adhesive layer, an electromagnetic wave shielding film, and a shielded wiring board.

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

However, when an electromagnetic wave shielding film is attached to a printed wiring board or the like, it is usually pressed under a more severe pressure and heating condition after temporarily positioning and fixing at a predetermined position than when temporarily positioning and fixing.

However, most of the conventional electromagnetic shielding films focus on improving the bonding strength after pressure heating. Although the bonding strength after pressure heating is high, the bonding strength after temporary positioning and fixing is poor. Even if the positioning is temporarily temporary, when moving the substrate In some cases, the electromagnetic wave shielding film may be peeled off and the operation may be restarted.

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

Prior Art Literature Patent Literature Patent Literature 1: Japanese Patent Laid-Open No. 2017-25280

SUMMARY OF THE INVENTION Problems to be Solved by the Invention However, even if the surface roughness Ra of the conductive adhesive layer is within a specific range, there is a possibility that the bonding strength after the temporary positioning step is poor and the conductive adhesive layer is dislocated after the temporary positioning step .

The present invention has been made in view of this point, and an object thereof is to improve adhesion after a temporary positioning step to an adherend, thereby preventing misalignment of the conductive adhesive layer after the temporary positioning step.

Means for Solving the Problem One aspect of the conductive adhesive layer of the present invention is that it is composed of a conductive adhesive containing a binder resin and a conductive filler, and the surface skewness Ssk is -3.5 or more and 2.7 or less.

In one aspect of the conductive adhesive layer of the present invention, the maximum peak height Sp of the surface may be 1.3 μm or more and 30 μm or less.

In one aspect 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 rate in the conductive adhesive may be 10% by mass or more and 80% by mass. %the following.

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

One aspect of the shielded wiring substrate of the present disclosure includes: a printed wiring substrate provided with a ground circuit; and an electromagnetic wave shielding film of the disclosed invention which is connected to the printed wiring substrate in a manner of conducting with the ground circuit. .

ADVANTAGE OF THE INVENTION According to this invention, it is excellent in the adhesiveness after a temporary positioning process with respect to an adherend, and the dislocation of the conductive adhesive layer after a temporary positioning process can be prevented.

Embodiments for Carrying Out the Invention Embodiments of the present invention will be described in detail below. The following descriptions of the preferred embodiments are merely examples in nature, and are not intended to limit the disclosed invention, its application, or its use.

<Conductive Adhesive Layer>
(Skew Ssk)
The conductive adhesive layer of this embodiment is characterized in that the surface skewness Ssk is -3.5 or more and 2.7 or less. As shown in FIG. 1, the conductive adhesive layer 100 of this embodiment has a concave-convex surface composed of a convex portion 100 a (peak portion) and a concave portion 100 b (valley portion). Since it is controlled in a specific range, it has excellent adhesion to the adherend (not shown) after the temporary positioning step, and prevents the conductive adhesive layer 100 from being displaced after the temporary positioning step.

Skewness Ssk shows the symmetry of the height distribution based on the average surface of the uneven surface. When Skewness Ssk is 0, the height distribution is a symmetrical surface (regular distribution). On the other hand, when it is less than When it is 0, it is a surface with many fine valleys. When it is greater than 0, it is a surface with many fine peaks.

When the absolute value of the skewness Ssk on the surface of the conductive adhesive layer 100 is large, that is, if the surface has a large number of peaks or valleys, the area of contact with the adherend will be reduced. The bonding strength after the temporary positioning step becomes insufficient.

Therefore, the surface of the conductive adhesive layer 100 is made to have a skewness Ssk in a specific range centered at 0, that is, the height distribution is a symmetrical surface up and down, thereby increasing the bonding area with the adherend, and Adhesion after the temporary positioning step to the adherend can be improved.

Therefore, by reducing the valleys and approaching a vertically symmetrical surface with a height distribution, the bonding area with the adherend will be increased, and the adhesion after the temporary positioning step for the adherend will be improved. , The skewness Ssk is -3.5 or more, preferably -3 or more, more preferably -2.5 or more, and even more preferably -2 or more. In addition, by reducing the peaks and approaching the surface whose height distribution is symmetrical up and down, it will increase the bonding area with the adherend, and improve the adhesion after the temporary positioning step for the adherend. From this point of view, , It is 2.7 or less, preferably 2.5 or less, more preferably 2 or less, and even more preferably 1.5 or less.

In this specification, the "adhered body" 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 this specification, the "temporary positioning step" means a step performed before the final fixing step. For example, a conductive adhesive is held from above and below by two heating plates (not shown) heated to 120 ° C. The layer 100 and the adherend were pressed at a pressure of 0.5 MPa for 5 seconds.

In addition, in this specification, "excellent adhesion after the temporary positioning step to the adherend" means that the 180 ° peel strength of the conductive adhesive layer 100 and the adherend after the temporary positioning step is 0.5 N / cm or more. In this case, the conductive adhesive layer 100 can be prevented from being displaced after the temporary positioning step. In addition, the specific measurement method of peeling strength is demonstrated by the following example.

(Maximum peak height Sp)
The maximum peak height Sp of the surface of the conductive adhesive layer 100 of this embodiment is preferably 1.3 μm or more and 30 μm or less. Accordingly, by controlling the maximum peak height Sp as a specific surface property parameter of the conductive adhesive layer 100 of this embodiment in a specific range, the adhesion after the temporary positioning step for the adherend can be further improved. Thereby, the dislocation of the conductive adhesive layer 100 after the temporary positioning step is further prevented.

The maximum peak height Sp shows the maximum value of the peak height from the average surface of the uneven surface. The larger the maximum peak height Sp, the more a surface having a peak is formed.

When the maximum peak height Sp of the surface of the conductive adhesive layer 100 is large, that is, if the surface has a peak, the peak becomes an obstacle and the area of contact with the adherend is reduced. The bonding strength after the temporary positioning step becomes insufficient.

Therefore, the surface of the conductive adhesive layer 100 is a surface having a maximum peak height Sp in a specific range, that is, a surface with a lower peak height of the highest peak, thereby further increasing the bonding area with the adherend, thereby further improving the alignment. Adhesion after the temporary positioning step of the adherend.

Therefore, from the viewpoint of further increasing the area of contact with the adherend to further improve the adhesion after the temporary positioning step for the adherend, the maximum peak height Sp is preferably 1.3 μm or more, which is ideal. It is 1.6 μm or more. In addition, the surface close to the lower peak height of the highest peak will further increase the bonding area with the adherend, thereby further improving the adhesion after the temporary positioning step for the adherend. In view of this, the thickness is preferably 30 μm or less, and more preferably 25 μm or less.

(Other parameters)
In addition, as the parameters of the surface properties of the specific conductive adhesive layer 100, in addition to the skewness Ssk and the maximum peak height Sp, for example, the maximum valley depth Sv, the sum of the maximum peak height Sp and the maximum valley depth Sv may be exemplified. The maximum height Sz and the like are not limited to the foregoing examples.

On the other hand, the inventors of the present invention have found that, as shown in the examples and comparative examples described later, the arithmetic mean Sa has nothing to do with the adhesion after the temporary positioning step for the adherend. The reason is that the arithmetic mean Sa is an average of the absolute values of the height differences of the points (peaks and valleys) with respect to the average surface of the uneven surface. Therefore, even when the value is small, the same may be included. The uneven surface of the peaks and deep valleys. At this time, I think that the peaks and valleys will become obstacles so that the area of contact with the adherend will decrease, and the adhesion strength after the step of temporarily positioning the adherend will become insufficient. Therefore, the arithmetic mean Sa is not suitable as a parameter of the surface properties of the specific conductive adhesive layer 100, and this parameter is used to obtain a bonding strength that can prevent the dislocation of the conductive adhesive layer 100 after the temporary positioning step.

In addition, the surface properties of the present invention are measured according to ISO 25178-6: 2010, and specific measurement methods are described by the following examples.

The conductive adhesive layer 100 of 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 the conductive adhesive can be used. Examples of such resins include thermoplastic resins such as polystyrene, vinyl acetate, polyester, polyethylene, polypropylene, polyamide, rubber, or acrylic; phenol, epoxy, and amine. Thermosetting resins such as ethyl formate, melamine or alkyd. These binder resins 110 may be used alone or in combination of two or more kinds.

In addition, from the viewpoint of adjusting the surface properties (the skewness Ssk and the maximum peak height Sp) of the conductive adhesive layer 100 to a predetermined state, the adhesive resin 110 can be added to the adhesive resin 110 as long as the effect of the present invention is not hindered. Resin fine particles or inorganic fine particles. 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 particles, glass fine particles, diatomite, mica powder, alumina fine particles, magnesium oxide fine particles, zinc oxide fine particles, Barium sulfate fine particles, aluminum sulfate fine particles, calcium sulfate fine particles, magnesium carbonate fine particles, and the like. These resin fine particles and inorganic fine particles may be used alone, or two or more of them may be used in combination.

(Conductive filler)
The conductive filler 120 is not particularly limited, and metal fillers used for conductive adhesives, metal-coated resin fillers, carbon fillers, and mixtures thereof 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, or gold-coated nickel powder. These metal powders can be produced by, for example, an electrolytic method, an atomization method, or a reduction method. These conductive fillers 120 may be used alone or in combination of two or more kinds. Among these, silver powder, silver-coated copper powder, and copper powder are desirable, and silver-coated copper powder is more desirable.

Examples of the shape of the conductive filler 120 include a spherical shape, an oval shape, a small plate shape, a fibrous shape, and a dendritic shape (dendritic shape). Moreover, it can also be set as a metal nanoparticle. Examples of the metal nano particles include silver nano particles and gold nano particles.

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 more preferably 20 μm or less, and more preferably 15 μm or less. The average particle diameter D50 of the conductive filler 120 can be measured, for example, by a generally used method such as a laser diffraction particle size distribution measurement device or a flow-type particle image analysis device.

The average particle diameter D50 of the conductive filler 120 can be appropriately set in accordance with 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, and more preferably about 5 μm. When the thickness of the conductive adhesive layer 100 is about 15 to 60 μm, it is preferably about 20 μm, and more preferably about 15 μm.

The content of the conductive filler 120 in the conductive adhesive is not particularly limited, and 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, and more preferably 75 mass% or less, and more preferably 70 mass% or less. The conductive adhesive layer 100 may be any of an anisotropic conductive adhesive layer and an isotropic conductive adhesive layer. When the anisotropic conductive adhesive layer is used, the conductive adhesive layer is used. The content of the medium conductive filler 120 is preferably 10% by mass or more, more preferably 15% by mass or more, more preferably 20% by mass or more, and preferably 45% by mass or less, and more preferably 40% by mass or less. More preferably, it is 35 mass% or less. When an isotropic conductive adhesive layer is used, 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 more preferably 60% by mass or more. It should be 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less.

By setting the average particle diameter D50 of the conductive filler 120 and the content ratio of the conductive filler 120 in the conductive adhesive to the above specific ranges, respectively, it is possible to achieve a thickness sufficient to prevent the conductive adhesive layer 100 from being displaced after the temporary positioning step. The conductive adhesive layer 100 having the skewness Ssk.

(Optional ingredient)
As long as the effect of the present invention is not hindered, for example, a defoamer, an antioxidant, a viscosity modifier, a diluent, an anti-settling agent, a leveling agent, a coupling agent, a colorant, or a flame retardant may be added to the conductive adhesive. Wait. These arbitrary components can be used individually or in combination of 2 or more types. Among these, a flame retardant is preferably added from the viewpoint of imparting flame retardance to a conductive adhesive.

Examples of such flame retardants include nitrogen-based flame retardants such as melamine melamine and melamine polyphosphate; metal hydrates such as magnesium hydroxide and aluminum hydroxide; phosphorus-based compounds such as phosphate esters, red phosphorus, and phosphate compounds Flame retardants, etc. Among these flame retardants, phosphate compounds are desirable.

When the flame retardant is added to the conductive adhesive, it is preferable to add 10 to 60 parts by mass relative to 100 parts by mass of the amount of the binder resin 110.

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

(Step of preparing conductive adhesive)
First, a binder resin solution prepared by dissolving the binder resin 110 in a solvent to a predetermined concentration is prepared. Examples of the solvent include toluene, acetone, methyl ethyl ketone, methanol, ethanol, propanol, and dimethylformamide. However, the present invention is not limited to the foregoing examples. The concentration of the binder resin 110 in the solution can be appropriately set in accordance with the thickness of the conductive adhesive layer 100 and the like.

Next, a conductive suspension 120 is added to the prepared binder resin solution to obtain a mixed suspension as required, and a mixed suspension is obtained. The mixed suspension is stirred and mixed to prepare a conductive adhesive.

(Coating step of conductive adhesive)
Next, the conductive adhesive prepared as described above is coated on 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. On the surface of the base layer 130, a fine pattern of irregularities can also be applied by a commonly used embossing process. When an electromagnetic wave shielding film is formed, a conductive adhesive is applied to an insulating protective layer or a shielding layer described later.

On the surface of the base layer 130, a demolding treatment can also be performed as needed. The release treatment can form, for example, a layered body composed of a silicon-based release agent, a non-silicon-based release agent, or a melamine-based release agent 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 adhered to the adherend.

In addition, an adhesive layer may be provided on the surface of the base layer 130 as needed. Since an adhesive layer is provided on the surface of the base layer 130, the base layer 130 can be prevented from being accidentally 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.

In addition, the thickness of the base layer 130 is not particularly limited, and may be determined in consideration of ease of use as appropriate.

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

(Drying step of conductive adhesive)
Finally, the conductive adhesive layer coated on the base layer 130 is dried by heating to remove the solvent, so that the conductive adhesive layer 100 of this embodiment can be formed. Examples of the drying method include warm air drying, infrared drying, oven drying, hot plate drying, and vacuum drying.

The thickness of the conductive adhesive layer 100 of the present embodiment obtained as described above can be adjusted according to the particle diameter of the conductive filler 120. From the viewpoint of achieving good conductivity, the thickness of the conductive adhesive layer 100 is preferably 5.5 times or less the average particle diameter D50 of the conductive filler 120, and more preferably 3.5 times or less. The average particle diameter D50 of the conductive filler 120 is preferably +70 μm or less (that is, when the average particle diameter D50 of the conductive filler 120 is d μm, it is d + 70 μm or less), and 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, and more preferably 0.7 times or more, the average particle diameter D50 of the conductive filler 120. The average particle diameter D50 of the conductive filler 120 is preferably -7 μm or more (d-7 μm or more), and more preferably -5 μm or more (d-5 μm or more).

If necessary, a release substrate (separation film) (not shown) may be bonded to the surface of the conductive adhesive layer 100 on the surface opposite to the surface to be bonded to the base layer 130. Examples of the release substrate include a silicon-based coating on a surface of a base film such as polyethylene terephthalate or polyethylene naphthalate, and the surface to be bonded to the conductive adhesive layer 100. Or non-silicone release agents, or acrylic or polyester adhesives. By attaching the 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 damaged or from adhering foreign matter. In addition, the thickness of the release substrate is not particularly limited, and can be determined in consideration of ease of use as appropriate.

In the above description, an example is shown in which the conductive adhesive layer 100 having a predetermined skewness Ssk is formed by coating and drying the conductive adhesive on the base layer 130. However, peeling may be used. Substrate. At this time, by using a release substrate having a fine pattern and transferring the fine pattern on the surface of the conductive adhesive layer 100, the surface properties of the conductive adhesive layer 100 can also be made into a predetermined state.

As described above, since the deflection Ssk of the surface of the conductive adhesive layer 100 of the present disclosure is -3.5 or more and 2.7 or less, the adhesiveness after the temporary positioning step on the adherend is excellent. Accordingly, the conductive adhesive layer 100 of the present disclosure can prevent the displacement of the conductive adhesive layer 100 after the temporary positioning step. Therefore, the conductive adhesive layer 100 can be suitably used in, for example, an electromagnetic wave shielding film.

＜ Electromagnetic wave shielding film ＞
As shown in FIG. 2, the electromagnetic wave shielding film 200 of this embodiment is characterized by having an insulating protective layer 210 and a conductive adhesive layer 100 provided on the surface of the insulating protective layer 210. Accordingly, the electromagnetic wave shielding film 200 of this embodiment has the conductive adhesive layer 100 of this embodiment as a conductive adhesive layer. Therefore, after the temporary positioning step of the adherend (not shown) such as a printed wiring board, The adhesiveness is excellent, and the conductive adhesive layer 100 after the temporary positioning step, that is, the displacement of the electromagnetic wave shielding film 200 can be prevented.

In addition, the electromagnetic wave shielding film 200 of this embodiment is connected to the ground circuit of a printed wiring board (not shown), and then the conductive adhesive layer 100 of this embodiment is connected to the conductive adhesive layer. 100 functions as a shield for electromagnetic waves. In addition, as shown in FIG. 3, the electromagnetic wave shielding film 200 of this embodiment may be provided with a shielding layer 220 between the insulating protection 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 insulation and can protect the conductive adhesive layer 100 and the shielding layer 220. For example, the insulating protective layer 210 can be formed using a thermoplastic resin, a thermosetting resin, an active energy ray-curable resin, or the like.

The insulating protective layer 210 may have a multilayer structure of two or more layers having different physical properties such as material, hardness, or elastic modulus. For example, if a laminated structure with an outer layer having a low hardness and an inner layer having a high hardness is formed, the outer layer has a buffer effect. Therefore, the electromagnetic wave shielding film 200 can be gently applied to the shield during the step of heating and pressing the electromagnetic wave shielding film 200 on the printed wiring board. Layer 220 pressure. Therefore, it is possible to prevent the shield layer 220 from being damaged due to the height difference provided on the printed wiring board.

There is no particular limitation on the thickness of the insulating protective layer 210, and it can be appropriately set according to needs. It is preferably 1 μm or more, more preferably 4 μm or more, and ideally 20 μm or less, more preferably 10 μm or less, and even more preferably 5 μm. the following. By setting the thickness of the insulating protective layer 210 to 1 μm or more, the conductive adhesive layer 100 and the shielding 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 the electromagnetic wave shielding film 200 of this embodiment can be easily applied to members requiring flexibility, such as flexibility. Printed wiring boards, etc.

(Shield)
The shielding layer 220 is only required to have conductivity, and may be formed of, for example, a metal thin film, a conductive filler, a metal vapor-deposited film, or the like. The metal thin film may be formed of any one of nickel, copper, silver, tin, gold, palladium, aluminum, chromium, titanium, zinc, or the like, or an alloy containing two or more types. The metal thin film can be produced by, for example, using a metal foil or depositing a metal by an addition method. The addition method may be, for example, an electroplating method, an electroless plating method, a sputtering method, an electron beam evaporation method, a vacuum evaporation method, a chemical vapor deposition (CVD) method, or a metal organic vapor deposition (MOCVD) method.

When the shielding layer 220 is made of a conductive filler, for example, a metal filler, a metal-coated resin filler, a carbon filler, or a mixture thereof can be used. Metal fillers include, for example: copper powder, silver powder, nickel powder, silver-coated copper powder, gold-coated copper powder, silver-coated nickel powder, or gold-coated nickel powder, etc. These metal powders can be processed by electrolytic method, atomization method, and reduction method. To make. Examples of the shape of the metal powder include a spherical shape, a small plate shape, a fibrous shape, and a dendritic shape. Moreover, it can also be set as a metal nanoparticle. Examples of the metal nano particles include silver nano particles and gold nano particles.

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

In addition, an electromagnetic wave shielding film 200 may be prepared in which the conductive adhesive layer 100 of the present embodiment does not have the shielding layer 220 and functions as a shielding layer.

＜ Method of forming electromagnetic wave shielding film ＞
Next, a method of forming the electromagnetic wave shielding film 200 of this embodiment will be described. First, a generally used method is used to sequentially form an insulating protection layer 210 and an optional shielding layer 220 on a supporting film (not shown), thereby preparing a laminated body. As the supporting film, the same resin sheet or film as the base layer 130 can be used. As the support film, a support film (transfer film) having a fine pattern on its surface may be used. At this time, by transferring a fine pattern on the surface of the insulating protective layer 210, the surface properties of the insulating protective layer 210 can be made into a predetermined state.

Next, the laminated body formed as described above is used as a base layer, and the conductive adhesive layer 100 of this 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 of this embodiment is 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 a conductive adhesive layer, and therefore, it has excellent adhesion after the temporary positioning step for the adherend, and can prevent The conductive adhesive layer 100 after the temporary positioning step, that is, the dislocation of the electromagnetic wave shielding film 200. Therefore, the electromagnetic wave shielding film 200 of the present disclosure can be used as a shielded wiring substrate that conducts the grounding circuit between the conductive adhesive layer 100 and the printed wiring board, and causes the conductive adhesive layer 100 to function as a shield for electromagnetic waves.

<Shielded wiring board>
As shown in FIG. 4, a shielded wiring substrate 400 according to this embodiment includes a printed wiring board 300 having a ground circuit 320a; and an electromagnetic wave shielding film 200 according to this embodiment, which is connected to the printed circuit in a manner of conducting with the ground circuit 320a Substrate 300. The electromagnetic wave shielding film 200 may include a shielding 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 an insulating layer 330 that covers the substrate so as to expose at least a part of the ground circuit 320a. Layer 310. The printed wiring board 300 may be a flexible substrate or a rigid substrate.

Any of the base layer 310 and the insulating layer 330 may be used, and for example, a resin film or the like may be used. At this time, it can be formed from resins such as polypropylene, cross-linked polyethylene, polyester, polybenzimidazole, polyimide, polyimide, imide, polyetherimide, 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 of this embodiment is attached to the printed wiring board 300, the electromagnetic wave shielding film 200 is arranged so as to be in conduction with the ground circuit 320a. Specifically, the conductive adhesive layer 100 of the electromagnetic wave shielding film 200 is disposed on the ground circuit 320a. In addition, the electromagnetic wave shielding film 200 and the printed wiring board 300 are sandwiched from above and below by two heating plates (not shown) that have been heated to a predetermined temperature (for example, 120 ° C), and are shorted at a predetermined pressure (for example, 0.5 MPa). Time (for example, 5 seconds) to press. Thereby, the electromagnetic wave shielding film 200 can be temporarily positioned and fixed to the printed wiring board 300.

At this time, since the shielded wiring substrate 400 of this embodiment is bonded to the printed wiring substrate 300 and the electromagnetic wave shielding film 200 of this embodiment through the conductive adhesive layer 100 of this embodiment, the printed wiring substrate 300 (substrate) ) Is excellent in adhesion after the temporary positioning step, and can prevent misalignment of the electromagnetic wave shielding film 200 after the temporary positioning step. Therefore, the shielded wiring board 400 in a state where the electromagnetic wave shielding film 200 has been temporarily positioned and fixed to the printed wiring board 300 may be stored by overlapping the shielded wiring boards 400 with each other, for example, before final fixing.

Next, the temperature of the two heating plates is set to a predetermined temperature (for example, 170 ° C.) which is higher than that at the time of temporary positioning and 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 of this embodiment is not limited to an electromagnetic wave shielding film and a shielded wiring substrate. For example, when a conductive (metal) reinforcing plate made of stainless steel or the like is stuck on a flexible printed wiring substrate, Can be used for this application. In this case, the conductive (metal) reinforcing plate can be used to exhibit the function of shielding electromagnetic waves.

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

＜ Step of preparing conductive adhesive ＞
A predetermined binder resin is dissolved in toluene or methyl ethyl ketone as a solvent to have a predetermined solid content concentration to prepare a binder resin solution. A predetermined conductive filler and optional components are added to the obtained binder resin solution, and the mixture is stirred using a planetary stirring and defoaming device to prepare a conductive adhesive.

＜ Production of electromagnetic shielding film ＞
As a support film, a PET film having a thickness of 60 μm and having been subjected to a mold release treatment was used. On the support film, a composition for a protective layer (solid content: 30% by mass) containing silicon dioxide particles, a bisphenol A epoxy resin, and methyl ethyl ketone was applied and dried by heating. Insulating protective layer. Next, a copper foil having a thickness of 0.5 μm was formed on the surface of the insulating protective layer as a shielding layer, thereby obtaining a laminated body (base layer). Next, the surface of the shielding layer of the obtained laminated body is coated with the conductive adhesive prepared as described above and dried to form a conductive adhesive layer having a predetermined thickness, thereby preparing an electromagnetic wave shielding film.

The electromagnetic wave shielding film prepared as described above was used to evaluate the thickness, surface properties, and adhesion of the conductive adhesive layer after the temporary positioning step to the adherend by the following methods.

<Thickness of conductive adhesive layer>
The thickness of the electromagnetic wave shielding film after the conductive adhesive layer is formed is subtracted from the thickness of the laminated body before the conductive adhesive layer is formed, and is set to the thickness of the conductive adhesive layer. In addition, each thickness was measured using a micrometer [made by Mitutoyo Co., Ltd., trade name: MDH-25], in accordance with JIS C2151.

<Surface properties of conductive adhesive layer>
Using a confocal microscope (Lasertec Corporation, OPTELICS HYBRID, objective lens 20 times), any five points on the surface of the conductive adhesive layer were measured. Then, use the data analysis software (LMeye7) to correct the tilt of the surface, and obtain the skewness Ssk, the maximum peak height Sp, and the arithmetic mean Sa according to ISO 25178-6: 2010. In addition, the cut-off wavelength of the S-type filter is set to 0.0025 mm, and the cut-off wavelength of the L-type filter is set to 0.8 mm. In addition, each numerical value was made into the average value of the value obtained by measuring 5 places.

<Adhesion after the temporary positioning step for the adherend>
The 180 ° peel test was used to measure the adhesion of the conductive adhesive layer to the adherend after the temporary positioning step. Specifically, first, a conductive adhesive layer of an electromagnetic wave shielding film and a single-sided copper-clad laminated board as an adherend were formed using a press under conditions of temperature: 120 ° C, time: 5 seconds, and pressure: 0.5 MPa. The polyimide surface of [NIKKAN Industry Co., Ltd., product name: F30VC1 25RC1 1/2 (H)] was temporarily positioned and fixed, thereby preparing a test sample.

Next, a tensile tester [manufactured by Shimadzu Corporation, trade name: AGS-X50S] was used, at room temperature, at a peeling angle: 180 ° and at a tensile speed: 50 mm / min. The sample was peeled from the single-sided copper-clad laminated board side, and the 180 ° peel strength (maximum value) at the time of breaking was measured, and the adhesion after the temporary positioning step for the adherend was evaluated based on the following evaluation criteria.

(Evaluation criteria)
○: Even if the 180 ° peel strength is 0.5 N / cm, no peeling occurs at the interface between the conductive adhesive layer and the adherend (the 180 ° peel strength of the conductive adhesive layer and the adherend after the temporary positioning step is 0.5 N / cm or more).
×: The 180 ° peel strength is less than 0.5 N / cm, and peeling occurs at the interface between the conductive adhesive layer and the adherend.

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

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

The conductive adhesive layer prepared in Example 1 did not peel off at the interface with the adherend even at a 180 ° peel strength of 3.23 N / cm (evaluation result: ○). The adhesion after the temporary positioning step of the adherend is very good.

(Example 2)
The binder resin is an epoxy resin, and the conductive filler is a silver-clad copper powder having an average particle diameter D50 of 5 μm and a spherical and oval shape. The content of the conductive filler in the conductive adhesive is set to 30% by mass.

The conductive adhesive layer (anisotropic) prepared in Example 2 had a thickness of 5 μm, a surface skewness Ssk of 1.50, a maximum peak height Sp of 9.38, and an arithmetic average Sa of 0.55.

The conductive adhesive layer prepared in Example 2 did not peel off at the interface with the adherend even at a 180 ° peel strength of 5.74 N / cm (evaluation result: ○). The adhesion after the temporary positioning step of the adherend is very good.

(Example 3)
The binder resin is an epoxy resin, and the conductive filler is a silver-clad copper powder having an average particle diameter D50 of 12 μm and a dendritic shape. The content of the conductive filler in the conductive adhesive is set to 15% by mass.

The conductive adhesive layer (anisotropic) prepared in Example 3 had a thickness of 15 μm, a surface skewness Ssk of 2.31, a maximum peak height Sp of 12.05, and an arithmetic mean Sa of 1.40.

The conductive adhesive layer prepared in Example 3 did not peel off at the interface with the adherend even at a 180 ° peel strength of 2.91 N / cm (evaluation result: ○). The adhesion after the temporary positioning step of the adherend is very good.

(Example 4)
As the binder resin, an epoxy-based resin is used, and as the conductive filler, a silver-clad copper powder having an average particle diameter D50 of 6 μm and a dendritic shape is used. The content of the conductive filler in the conductive adhesive was set to 65% by mass.

The conductive adhesive layer (isotropic) prepared in Example 4 had a thickness of 15 μm, a surface skewness Ssk of −0.31, a maximum peak height Sp of 1.67, and an arithmetic average Sa of 0.17.

The conductive adhesive layer prepared in Example 4 did not peel off at the interface with the adherend even at a 180 ° peel strength of 4.50 N / cm (evaluation result: ○). The adhesion after the temporary positioning step of the adherend is very good.

(Example 5)
As the binder resin, an epoxy-based resin is used, and as the conductive filler, a silver-clad copper powder having an average particle diameter D50 of 6 μm and a dendritic shape is used. The content of the conductive filler in the conductive adhesive is set to 70% by mass.

The conductive adhesive layer (isotropic) prepared in Example 5 had a thickness of 15 μm, a surface skewness Ssk of −2.47, a maximum peak height Sp of 1.66, and an arithmetic average Sa of 0.15.

The conductive adhesive layer prepared in Example 5 did not peel off at the interface with the adherend even at a 180 ° peel strength of 1.93 N / cm (evaluation result: ○). The adhesion after the temporary positioning step of the adherend is very good.

(Example 6)
The binder resin is an epoxy resin, and the conductive filler is a silver-clad copper powder having an average particle diameter D50 of 15 μm and a dendritic shape. The content of the conductive filler in the conductive adhesive is set to 70% by mass.

The conductive adhesive layer (isotropic) prepared in Example 6 had a thickness of 60 μm, a surface skewness Ssk of −0.18, a maximum peak height Sp of 11.21, and an arithmetic average Sa of 2.82.

In addition, although the conductive adhesive layer prepared in Example 6 was peeled off at the interface with the adherend, the 180 ° peel strength at the time of breaking was 1.03 N / cm of 0.5 N / cm or more (evaluation result) :)). Therefore, the adhesion after the temporary positioning step for the adherend is good.

(Example 7)
The binder resin is an epoxy-based resin, and the conductive filler is a silver-clad copper powder having an average particle diameter D50 of 8 μm and a dendritic shape. The content of the conductive filler in the conductive adhesive is 60% by mass.

The conductive adhesive layer (isotropic) prepared in Example 7 had a thickness of 15 μm, a surface skewness Ssk of −2.83, a maximum peak height Sp of 3.94, and an arithmetic average Sa of 1.25.

The conductive adhesive layer prepared in Example 7 did not peel off at the interface with the adherend even at a 180 ° peel strength of 1.85 N / cm (evaluation result: ○). The adhesion after the temporary positioning step of the adherend is very good.

(Example 8)
The binder resin is an epoxy resin, and the conductive filler is a silver-clad copper powder having an average particle diameter D50 of 12 μm and a dendritic shape. The content of the conductive filler in the conductive adhesive is set to 70% by mass.

The conductive adhesive layer (isotropic) prepared in Example 8 had a thickness of 60 μm, a surface skewness Ssk of −0.55, a maximum peak height Sp of 17.27, and an arithmetic average Sa of 5.26.

The conductive adhesive layer prepared in Example 8 did not peel off at the interface with the adherend even at a 180 ° peel strength of 4.23 N / cm (evaluation result: ○). The adhesion after the temporary positioning step of the adherend is very good.

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

The conductive adhesive layer (anisotropic) prepared in Example 9 had a thickness of 36 μm, a surface skewness Ssk of 1.36, a maximum peak height Sp of 16.37, and an arithmetic average Sa of 2.15.

The conductive adhesive layer prepared in Example 9 did not peel off at the interface with the adherend even at a 180 ° peel strength of 4.28 N / cm (evaluation result: ○). The adhesion after the temporary positioning step of the adherend is very good.

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

The conductive adhesive layer (anisotropic) prepared in Example 10 had a thickness of 40 μm, a surface skewness Ssk of 1.65, a maximum peak height Sp of 22.94, and an arithmetic average Sa of 2.44.

The conductive adhesive layer prepared in Example 10 did not peel off at the interface with the adherend even at a 180 ° peel strength of 4.51 N / cm (evaluation result: ○). The adhesion after the temporary positioning step of the adherend is very good.

(Comparative example 1)
The binder resin is an epoxy resin, and the conductive filler is a silver-clad copper powder having an average particle diameter D50 of 15 μm and a spherical and oval shape. The content of the conductive filler in the conductive adhesive is 5% by mass.

The conductive adhesive layer (anisotropy) prepared in Comparative Example 1 had a thickness of 15 μm, a surface deflection Ssk of 4.05, a maximum peak height Sp of 17.81, and an arithmetic mean Sa of 0.98.

The conductive adhesive layer prepared in Comparative Example 1 was peeled off at the interface with the adherend at a 180 ° peel strength of 0.01 N / cm of less than 0.5 N / cm (evaluation result: ×). Therefore, the adhesion after the temporary positioning step for the adherend is poor.

(Comparative example 2)
As the binder resin, an epoxy-based resin is used, and as the conductive filler, an silver-clad nickel powder having an average particle diameter D50 of 23 μm and an oval shape is used. The content of the conductive filler in the conductive adhesive is 35% by mass.

The conductive adhesive layer (anisotropic) prepared in Comparative Example 2 had a thickness of 30 μm, a surface skewness Ssk of 4.01, a maximum peak height Sp of 29.54, and an arithmetic mean Sa of 1.63.

The conductive adhesive layer prepared in Comparative Example 2 had peeling at the interface with the adherend at a 180 ° peel strength of 0.13 N / cm of less than 0.5 N / cm (evaluation result: ×). Therefore, the adhesion after the temporary positioning step for the adherend is poor.

Table 1 shows the composition of the conductive fillers used in the examples and comparative examples, and the physical properties of the conductive adhesive layer.

[Table 1]

INDUSTRIAL APPLICABILITY The conductive adhesive layer of the present disclosure has excellent adhesion to the adherend after the temporary positioning step, and can prevent misalignment of the conductive adhesive layer after the temporary positioning step, which is extremely useful. .

100‧‧‧ conductive adhesive layer

100a‧‧‧ convex

100b‧‧‧ recess

110‧‧‧Binder Resin

120‧‧‧ conductive filler

130‧‧‧ Grassroots

200‧‧‧ electromagnetic shielding film

210‧‧‧Insulation protective layer

220‧‧‧Shield

300‧‧‧printed wiring board

310‧‧‧ basal layer

320‧‧‧printed circuit

320a‧‧‧ Ground Circuit

320b‧‧‧Signal Circuit

330‧‧‧ Insulation

400‧‧‧shielded wiring substrate

FIG. 1 is a cross-sectional view showing an embodiment of a conductive adhesive layer formed on a base layer.

Fig. 2 is a sectional view of an electromagnetic wave shielding film according to an embodiment.

FIG. 3 is a sectional view showing another embodiment of the electromagnetic wave shielding film.

FIG. 4 is a cross-sectional view of a shielded wiring substrate according to an embodiment.

Claims (5)

A conductive adhesive layer, which is composed of a conductive adhesive containing a binder resin and a conductive filler, and has a surface skewness Ssk of -3.5 or more and 2.7 or less. For example, in the conductive adhesive layer of claim 1, the maximum peak height Sp of the surface is 1.3 μm or more and 30 μm or less. The conductive adhesive layer according to claim 1 or 2, wherein the average particle diameter D50 of the conductive filler is 3 μm or more and 20 μm or less, and its content in the conductive adhesive is 10% by mass or more and 80% by mass %the following. An electromagnetic wave shielding film, comprising: Insulation protection; and The conductive adhesive layer according to any one of claims 1 to 3 is provided on the surface of the insulating protective layer. A shielded wiring substrate, comprising: A printed wiring board provided with a ground circuit; and The electromagnetic wave shielding film according to claim 4, which is connected to the printed wiring board in a manner to be conducted to the ground circuit.