TW202424142A - Electromagnetic wave-shielding film and manufacturing method for electromagnetic wave-shielding film - Google Patents

Abstract

The present invention provides: an electromagnetic wave-shielding film in which the interlayer adhesion between an adhesive layer and a shield layer is unlikely to be destroyed even if the film is heated through reflow or the like; and a manufacturing method for the electromagnetic wave-shielding film. The present invention pertains to an electromagnetic wave-shielding film comprising a conductive adhesive layer, and a shield layer laminated on the conductive adhesive layer, the film being characterized in that the conductive adhesive layer contains at most 50 wt% of a conductive filler, and the specific surface area of the conductive filler is at most 0.9 m2/g.

Description

Electromagnetic wave shielding film and method for producing the same

The present invention relates to an electromagnetic wave shielding film and a method for manufacturing the electromagnetic wave shielding film.

Background technology In the past, electromagnetic wave shielding films were pasted on printed wiring boards such as flexible printed wiring boards (FPC) to shield electromagnetic waves from the outside.

The electromagnetic wave shielding film usually has a structure in which an adhesive layer, a shielding layer composed of a metal thin film, etc., and an insulating layer are sequentially laminated. When the electromagnetic wave shielding film is superimposed on a printed wiring board and heated and pressurized, the electromagnetic wave shielding film is bonded to the printed wiring board via the adhesive layer, thereby manufacturing a shielded printed wiring board. After the above bonding, the parts are mounted on the shielded printed wiring board by solder reflow. In addition, the printed wiring board becomes a structure in which the printed pattern on the base film is covered with an insulating film.

Regarding such an electromagnetic wave shielding film, Patent Document 1 discloses a shielding film characterized by having a metal layer with a thickness of 0.5 μm to 12 μm and an anisotropic conductive adhesive layer in a laminated state. Prior Art Document Patent Document

[Patent Document 1] International Publication No. 2013/077108

Summary of the invention Problems to be solved by the invention If such an electromagnetic wave shielding film is placed on a printed wiring board and then parts are mounted by reflow, there is a problem that the interlayer adhesion between the adhesive layer and the metal layer of the electromagnetic wave shielding film is destroyed, resulting in interlayer peeling.

The above-mentioned interlayer peeling is believed to be caused by the following mechanism. Figures 3A and 3B are explanatory diagrams, which schematically show the mechanism of interlayer peeling between the adhesive layer and the metal layer when a shielded printed wiring board is manufactured using a conventional electromagnetic wave shielding film. As shown in Figure 3A, when manufacturing a shielded printed wiring board, an electromagnetic wave shielding film 510 having an adhesive layer 520 and a shielding layer 530 composed of a metal layer stacked in sequence is heated by heating and pressing or solder reflow. Due to the heating, volatile components (mainly water) 560 are generated from the adhesive layer 520 of the electromagnetic wave shielding film 510, etc., and are accumulated between the adhesive layer 520 and the shielding layer 530.

In such a state, if rapid heating such as reflow is performed for mounting parts, as shown in FIG. 3B , the volatile components 560 accumulated between the adhesive layer 520 and the shielding layer 530 expand and destroy the interlayer adhesion between the adhesive layer 520 and the shielding layer 530, resulting in interlayer peeling.

The present invention is completed to solve the above-mentioned problem. The purpose of the present invention is to provide an electromagnetic wave shielding film and a method for manufacturing an electromagnetic wave shielding film, which is not easy to damage the interlayer adhesion between the adhesive layer and the shielding layer even if it is subjected to heating such as reflow. Means for solving the problem

The inventors of the present invention have found that the reason why volatile components are accumulated between the adhesive layer and the shielding layer is that the adhesive layer absorbs moisture in the air when the electromagnetic wave shielding film is stored. The above problem can be solved by reducing the hygroscopicity of the adhesive layer, and thus the present invention was conceived.

That is, the electromagnetic wave shielding film of the present invention is characterized by comprising: a conductive adhesive layer; and a shielding layer laminated on the conductive adhesive layer; the conductive adhesive layer contains 50 wt % or less of a conductive filler, and the specific surface area of the conductive filler is 0.9 m ² /g or less.

In the electromagnetic wave shielding film of the present invention, the conductive adhesive layer contains less than 50% by weight of a conductive filler, so that conductivity can be imparted to the conductive adhesive layer and the bonding strength of the conductive adhesive can be improved. In addition, as described later, in the electromagnetic wave shielding film of the present invention, volatile components are not easy to enter the surroundings of the conductive filler. Therefore, by including the conductive filler, the hygroscopicity of the adhesive layer as a whole is reduced. Therefore, for the electromagnetic wave shielding film of the present invention, even if it is subjected to heating such as reflow, it is not easy to destroy the interlayer adhesion between the conductive adhesive layer as the adhesive layer and the shielding layer.

The reason why the volatile components in the electromagnetic wave shielding film of the present invention are not easy to enter the surroundings of the conductive filler is explained. In the electromagnetic wave shielding film of the present invention, the specific surface area of the conductive filler is 0.9 ^m2 /g or less. If the specific surface area of the conductive filler is within the above range, the angle of the surface of the conductive filler will become smaller (for example, close to a perfect sphere), and volatile components such as moisture will not easily accumulate around the conductive filler. If the above specific surface area is greater than 0.9 ^m2 /g, the surface of the conductive filler will become uneven, and branches will increase on the surface, and volatile components such as moisture will easily accumulate between the branches. Therefore, the hygroscopicity of the conductive adhesive layer as a whole is likely to increase.

In the electromagnetic wave shielding film of the present invention, the tap density of the conductive filler is preferably 1 g/cm ³ or more. If the tap density is 1 g/cm ³ or more, since the volume of the conductive filler is small, the number of contact points between the conductive fillers is small, and the volatile components are not easily accumulated between the conductive fillers, and the above-mentioned interlayer damage caused by heating is even less likely to occur. If the tap density is less than 1 g/cm ³ or more, since the volume of the conductive filler is large, the number of contact points between the conductive fillers is large, and the volatile components are easily accumulated between the conductive fillers, and it is difficult to suppress the above-mentioned interlayer damage caused by heating. The tap density of the conductive filler is the powder density obtained by tapping a container under specified conditions, and refers to a value measured in accordance with JIS Z 2512:2012 (Metal powder-Tap density measurement method).

In the electromagnetic wave shielding film of the present invention, an insulating layer is preferably further laminated on the above-mentioned shielding layer. By forming the insulating layer, the shielding layer and the adhesive layer can be protected. In addition, by the existence of the insulating layer, the shielding layer can be prevented from contacting other conductive components.

The manufacturing method of the electromagnetic wave shielding film of the present invention is characterized by comprising the following steps: mixing a conductive filler with a resin to prepare a conductive adhesive containing 50 wt % or less of the conductive filler; and coating the conductive adhesive on a shielding layer to form a conductive adhesive layer; the specific surface area of the conductive filler is 0.9 m ² /g or less.

In the method for producing an electromagnetic wave shielding film of the present invention, since the conductive adhesive contains 50% by weight or less of the conductive filler, the conductive adhesive layer can be given conductivity and the bonding strength of the conductive adhesive can be improved. In addition, in the method for producing an electromagnetic wave shielding film of the present invention, since the specific surface area of the conductive filler is 0.9 m ² /g or less, the interlayer adhesion between the conductive adhesive layer as the adhesive layer and the shielding layer is not easily destroyed even when subjected to heat such as reflow, as in the case of the electromagnetic wave shielding film of the present invention.

In the method for manufacturing the electromagnetic wave shielding film of the present invention, the tap density of the conductive filler is preferably 1 g/cm ³ or more. If the tap density is 1 g/cm ³ or more, the interlayer damage caused by heating is less likely to occur, as in the case of the electromagnetic wave shielding film of the present invention. If the tap density is less than 1 g/cm ³ or more, the interlayer damage caused by heating is difficult to suppress, as in the case of the electromagnetic wave shielding film of the present invention. Effect of the Invention

According to the present invention, an electromagnetic wave shielding film and a method for manufacturing the electromagnetic wave shielding film can be provided, wherein the interlayer adhesion between the adhesive layer and the shielding layer is not easily damaged even when subjected to heating such as reflow.

Forms for implementing the invention The electromagnetic wave shielding film and the method for manufacturing the electromagnetic wave shielding film of the present invention are specifically described below. However, the present invention is not limited to the following implementation forms, and can be appropriately modified and applied within the scope of not changing the main purpose of the present invention.

FIG1 is a cross-sectional view schematically showing an example of the electromagnetic wave shielding film of the present invention. The electromagnetic wave shielding film 10 shown in FIG1 has a conductive adhesive layer 20, and a shielding layer 30 laminated on the conductive adhesive layer 20, and an insulating layer 40 is further laminated on the shielding layer 30. In addition, the conductive adhesive layer 20 contains a resin and a conductive filler.

In the electromagnetic wave shielding film 10, since the conductive adhesive layer 20 contains 50 wt % or less of the conductive filler, the conductive adhesive layer 20 can be provided with conductivity and the bonding strength of the conductive adhesive can be improved.

In the electromagnetic wave shielding film 10, the specific surface area of the conductive filler is less than 0.9 ^m2 /g. Since the conductive filler has the above-mentioned characteristics, volatile components are not easy to enter the surroundings of the conductive filler. Therefore, by including the conductive filler, the hygroscopicity of the conductive adhesive layer 20 as a whole is reduced. Therefore, in the electromagnetic wave shielding film 10, even if it is subjected to heat such as reflow, the interlayer adhesion between the conductive adhesive layer 20 and the shielding layer 30 is not easily destroyed.

The reason why volatile components are less likely to enter the vicinity of the conductive filler when the conductive filler has the above characteristics is explained as follows.

If the specific surface area of the conductive filler is 0.9 m ² /g or less, the angle of the conductive filler surface will be reduced (for example, close to a perfect sphere), and volatile components such as water will not easily accumulate around the conductive filler. If the above-mentioned specific surface area is greater than 0.9 m ² /g, the surface of the conductive filler will become uneven, and branches will increase on the surface, and volatile components such as water will easily accumulate between the branches. Therefore, the hygroscopicity of the conductive adhesive layer as a whole is likely to increase. In addition, the specific surface area of the conductive filler is preferably 0.25 m ² /g or more and 0.9 m ² /g or less, more preferably 0.25 m ² /g or more and less than 0.8 m ² /g, and more preferably 0.25 m ² /g or more and 0.5 m ² /g or less. The specific surface area of the conductive filler can be measured by a nitrogen adsorption method using an elemental analysis device: Vari EL III (manufactured by Elementar).

In the electromagnetic wave shielding film 10, the tap density of the conductive filler is preferably 1 g/cm ³ or more, more preferably 1.5 g/cm ³ or more and 5.0 g/cm ³ or less, and more preferably 2.0 g/cm ³ or more and 5.0 g/cm ³ or less. If the tap density is 1 g/cm ³ or more, since the volume of the conductive filler is small, the number of contact points between the conductive fillers is small, so the volatile components are not easy to accumulate between the conductive fillers, and the above-mentioned interlayer damage caused by heating is even less likely to occur. If the tap density is less than 1 g/cm ³ or more, since the volume of the conductive filler is large, the number of contact points between the conductive fillers is large, so the volatile components are easy to accumulate between the conductive fillers, and it is difficult to suppress the above-mentioned interlayer damage caused by heating. Conductive fillers with a tap density of 5.0 g/cm ³ or less are easy to produce.

In the electromagnetic wave shielding film 10, the conductive adhesive layer 20 contains 50% by weight or less of the conductive filler, but preferably contains 3% by weight or more and 39% by weight or less of the conductive filler, preferably contains 3% by weight or more and 35% by weight or less of the conductive filler, and more preferably contains 3% by weight or more and 30% by weight or less of the conductive filler. If the ratio of the conductive filler is greater than 50% by weight, the ratio of the resin in the conductive adhesive layer becomes relatively small, and the bonding strength of the conductive adhesive layer is easy to decrease. In addition, because the conductive fillers are easy to contact each other (the current is easy to flow in the planar direction), the electrical characteristics such as the transmission characteristics are easy to decrease. In addition, if the ratio of the conductive filler is 3% by weight or more and 39% by weight or less, anisotropic conductivity can be given to the conductive adhesive layer 20. When the ratio of the conductive filler is less than 3% by weight, no conductivity will be exhibited.

In this way, the conductive adhesive layer 20 may have isotropic conductivity that ensures electrical conductivity in all three-dimensional directions consisting of the thickness direction, the width direction, and the length direction, or may have anisotropic conductivity that ensures electrical conductivity only in the thickness direction, but it is preferable to have anisotropic conductivity. As described later, the electromagnetic wave shielding film 10 will be arranged on a printed wiring board. When the conductive adhesive layer 20 has anisotropic conductivity, the transmission characteristics of high-frequency signals transmitted through the signal circuit of the printed wiring board are further improved compared to when it has isotropic conductivity.

In the electromagnetic wave shielding film 10, the particle size ( _D50 ) of the conductive filler is preferably 3.0 μm or more and 15 μm or less, more preferably 5.0 μm or more and 11 μm or less, and more preferably 5.0 μm or more and 8.0 μm or less. When the particle size ( _D50 ) of the conductive filler is less than 3 μm, the conductive adhesive layer 20 is thicker than the conductive filler, and the conductive filler cannot contact the ground circuit, and conductivity may not be obtained. If the particle size ( _D50 ) of the conductive filler is greater than 15 μm, the conductive filler may pierce the insulating layer 40 (which may cause poor appearance).

In the electromagnetic wave shielding film 10, the conductive filler is not particularly limited, and may be metal fine particles, carbon nanotubes, carbon fibers, metal fibers, and the like.

When the conductive filler is a metal particle, there is no particular limitation on the metal particle, and the metal particles may be silver powder, copper powder, nickel powder, solder powder, aluminum powder, silver-coated copper powder obtained by silver-plating copper powder, metal-coated polymer particles or glass beads, etc. Among them, copper powder or silver-coated copper powder that can be obtained at a low price is preferred from the perspective of economy.

The shape of the conductive filler is not particularly limited, and can be appropriately selected from spherical, flat, scaly, dendrite, rod, fiber, and the like.

In the electromagnetic wave shielding film 10, the thickness of the conductive adhesive layer 20 is preferably 5 to 50 μm, preferably 5 to 30 μm. If the thickness of the conductive adhesive layer is less than 5 μm, the adhesiveness is reduced because it is very thin. If the thickness of the conductive adhesive layer is greater than 50 μm, the conductive adhesive layer becomes thicker, making it difficult to miniaturize the electromagnetic wave shielding film.

In the electromagnetic wave shielding film 10, the resin material of the conductive adhesive layer 20 is not particularly limited, and thermoplastic resin compositions such as styrene resin compositions, vinyl acetate resin compositions, polyester resin compositions, polyethylene resin compositions, polypropylene resin compositions, imide resin compositions, amide resin compositions, and acrylic resin compositions can be used; or thermosetting resin compositions such as phenol resin compositions, epoxy resin compositions, urethane resin compositions, melamine resin compositions, and alkyd resin compositions can be used. The resin material may be a single one of these, or a combination of two or more.

In the electromagnetic wave shielding film 10, the conductive adhesive layer 20 may contain, in addition to the resin and the conductive filler, a curing accelerator, a tackifier, an antioxidant, a pigment, a dye, a plasticizer, an ultraviolet absorber, a defoaming agent, a leveling agent, a filler, a flame retardant, a viscosity regulator, etc. as needed.

In the electromagnetic wave shielding film 10, the shielding layer 30 is preferably composed of a metal layer. In addition, the metal layer preferably includes at least one metal selected from the group consisting of copper, silver, gold, aluminum, nickel, tin, palladium, chromium, titanium and zinc. In addition, the metal layer can also be composed of at least two alloys selected from the above group. The shielding layer 30 composed of these metals can properly shield electromagnetic waves.

In the electromagnetic wave shielding film 10, when the shielding layer 30 is composed of a metal layer, the metal layer can be a rolled metal foil, a metal coating layer, or a metal vapor deposition layer.

In the electromagnetic wave shielding film 10, when the shielding layer 30 is composed of a metal layer, its thickness is preferably 0.1~10μm, preferably 0.5~6μm. If the thickness of the shielding layer is less than 0.1μm, the strength of the shielding layer will be reduced because the shielding layer is too thin. Therefore, the anti-bending property will be reduced. In addition, since it will be difficult to fully reflect and absorb electromagnetic waves, the electromagnetic wave shielding characteristics are easily reduced. If the thickness of the shielding layer is greater than 10μm, the thickness of the entire electromagnetic wave shielding film becomes thicker and becomes difficult to handle.

In the electromagnetic wave shielding film 10, the insulating layer 40 is not particularly limited as long as it has sufficient insulation and can protect the shielding layer 30 and the conductive adhesive layer 20, but it is preferably composed of, for example, a thermoplastic resin composition, a thermosetting resin composition, an active energy ray-curable composition, etc. Regarding the above-mentioned thermoplastic resin composition, there is no particular limitation, and examples thereof include: styrene resin composition, vinyl acetate resin composition, polyester resin composition, polyethylene resin composition, polypropylene resin composition, imide resin composition, acrylic resin composition, etc.

The thermosetting resin composition is not particularly limited, and examples thereof include phenolic resin compositions, epoxy resin compositions, urethane resin compositions, melamine resin compositions, alkyd resin compositions, and the like.

The active energy ray-curable composition is not particularly limited, and examples thereof include a polymerizable compound having at least two (meth)acryloyloxy groups in a molecule.

The insulating layer 40 may be made of a single material or may be made of two or more materials.

The insulating layer 40 may also contain, as needed: a hardening accelerator, a tackifier, an antioxidant, a pigment, a dye, a plasticizer, an ultraviolet absorber, a defoaming agent, a leveling agent, a filler, a flame retardant, a viscosity regulator, an anti-caking agent, etc.

The pigment is not particularly limited, and black pigments such as carbon black can be cited as examples.

The thickness of the insulating layer 40 is not particularly limited and can be appropriately set as needed, but is preferably 1 to 15 μm, preferably 3 to 10 μm. If the thickness of the insulating layer 40 is less than 1 μm, it is too thin and difficult to fully protect the shielding layer 30 and the conductive adhesive layer 20. If the thickness of the insulating layer 40 is greater than 15 μm, it is too thick, so the electromagnetic wave shielding film 10 is difficult to bend and the toughness of the insulating layer 40 is reduced. Therefore, it is difficult to apply to components that require resistance to bending.

Furthermore, in the electromagnetic wave shielding film of the present invention, an insulating layer may be formed as needed, or may not be formed.

Next, a method for manufacturing the electromagnetic wave shielding film of the present invention is described.

The method for manufacturing an electromagnetic wave shielding film of the present invention comprises the following steps: preparing a conductive adhesive containing 50 wt % or less of the conductive filler by mixing the conductive filler with a resin; and coating the conductive adhesive on a shielding layer to form a conductive adhesive layer; the specific surface area of the conductive filler is 0.9 m ² /g or less.

In the method for manufacturing the electromagnetic wave shielding film of the present invention, a step of forming the shielding layer on the insulating layer may be performed before the step of forming the conductive adhesive layer, thereby manufacturing the electromagnetic wave shielding film 10.

The following is a detailed description of each step.

(Conductive Adhesive Preparation Step) In this step, a conductive filler is mixed with a resin to prepare a conductive adhesive containing 50 wt % or less of the conductive filler. The specific surface area of the conductive filler is 0.9 m ² /g or less.

Since the conductive adhesive contains 50% by weight or less of the conductive filler, the conductive adhesive layer can be given conductivity and the bonding strength of the conductive adhesive can be improved. In addition, since the specific surface area of the conductive filler is 0.9 ^m2 /g or less, the interlayer adhesion between the conductive adhesive layer and the shielding layer is not easily destroyed even when subjected to heat such as reflow.

As described above, the specific surface area of the conductive filler is preferably 0.25 m ² /g to 0.9 m ² /g, more preferably 0.25 m ² /g to less than 0.8 m ² /g, and even more preferably 0.25 m ² /g to 0.5 m ² /g.

As described above, the conductive adhesive preferably contains 3 wt % to 39 wt % of the conductive filler, more preferably 3 wt % to 35 wt % of the conductive filler, and even more preferably 3 wt % to 30 wt % of the conductive filler.

As described above, the tap density of the conductive filler is preferably 1 g/cm ³ or more, more preferably 1.5 g/cm ³ or more and 5.0 g/cm ³ or less, and more preferably 2.0 g/cm ³ or more and 5.0 g/cm ³ or less.

The preferred materials of the conductive filler and resin have already been explained and are therefore omitted here.

(Shielding layer formation step) In this step, a shielding layer is formed on the insulating layer. At this time, regarding the shielding layer, a metal evaporation layer can be formed on the insulating layer by evaporation, a rolled metal foil can be attached to the insulating layer, or a metal coating layer can be formed on the insulating layer by electrolytic plating.

The preferred materials for the insulation layer and the shielding layer have already been explained and are therefore omitted here.

(Conductive adhesive layer forming step) After the above-mentioned shielding layer forming step, in this step, a conductive adhesive is applied on the shielding layer to form a conductive adhesive layer. Regarding the method of configuring the conductive adhesive layer, conventionally known coating methods can be listed, for example, gravure coating method, contact coating method (kiss coat) method, die coating method, lip coating method, notch wheel coating method, blade coating method, roller coating method, knife coating method, spray coating method, rod coating method, rotary coating method, dip coating method, etc.

Through the above steps, the electromagnetic wave shielding film 10 can be manufactured.

Next, a shielded printed wiring board using the electromagnetic wave shielding film of the present invention will be described. FIG. 2 is a cross-sectional view schematically showing an example of a shielded printed wiring board using the electromagnetic wave shielding film of the present invention.

The shielded printed wiring board 1 shown in FIG2 is composed of a printed wiring board 50 and an electromagnetic wave shielding film 10. The printed wiring board 50 includes a base film 51, a printed circuit 52 arranged on the base film 51, and a cover film 53 arranged to cover the printed circuit 52. In the printed wiring board 50, the printed circuit 52 includes a grounding circuit 52a, and an opening 53a is formed in the cover film 53 to expose the grounding circuit 52a.

In the shielded printed wiring board 1, the electromagnetic wave shielding film 10 is disposed on the printed wiring board 50 in such a manner that the cover film 53 is in contact with the conductive adhesive layer 20.

In the shielded printed wiring board 1, the conductive adhesive layer 20 fills the opening 53a of the cover film 53 and contacts the ground circuit 52a. By forming such a structure, the shielding characteristics of the electromagnetic wave shielding film 10 can be improved. [Example]

The following shows embodiments of the present invention in more detail, but the present invention is not limited to these embodiments.

(Example 1) An insulating layer composed of an epoxy resin with a thickness of 5 μm is prepared as an insulating layer. Next, electrolytic plating is performed to form a copper layer with a thickness of 2.0 μm on the insulating layer. Furthermore, the copper layer functions as a shielding layer.

Next, a polyester-based thermosetting resin as a resin and silver powder (particle size D ₅₀ : 10.8 μm) as a conductive filler were mixed so that the conductive filler was 20% by weight relative to the total amount of the conductive adhesive, thereby producing the conductive adhesive of Example 1. Parameters such as the specific surface area of the conductive filler used and the conductivity of the produced conductive adhesive are shown in Table 1. Next, the conductive adhesive was applied to the shielding layer to a thickness of 20 μm, thereby producing the electromagnetic wave shielding film of Example 1.

[Table 1]

(Example 2) to (Example 6) and (Comparative Example 1) to (Comparative Example 9) Except that the conductive fillers shown in Table 1 were used and the ratio of the conductive fillers was changed, the electromagnetic wave shielding films of Examples 2 to 6 and Comparative Examples 1 to 9 were manufactured in the same manner as in Example 1.

(Evaluation of interlayer delamination) The electromagnetic wave shielding films of each embodiment and each comparative example were bonded to a printed wiring board by hot pressing. Then, the printed wiring board was placed in a constant temperature and humidity tank at 30°C and 60%RH for 1 day, and then exposed to the temperature conditions during reflow to evaluate the presence of interlayer delamination. Furthermore, regarding the temperature conditions during solder float, the maximum temperature was set to 260°C. In addition, the printed wiring board with the shielding film bonded was floated in the solder tank 3 times, and the presence of expansion was visually observed to evaluate the presence of interlayer delamination. Here, the shielding film that did not expand at all was marked as "◎", the shielding film that only partially expanded was marked as "○", and the shielding film that expanded significantly on the entire surface was marked as "╳". The results are shown in Table 1.

(Evaluation of the strength of the film) The electromagnetic wave shielding films of each embodiment and each comparative example were used to evaluate the strength of the film according to the following procedure.

FIG4A is a schematic cross-sectional view of a sample used for bonding strength evaluation test. As shown in FIG4A , first, each electromagnetic wave shielding film 10 having an insulating layer 40, a shielding layer 30 and a conductive adhesive layer 20 laminated in sequence is pressed against the polyimide film substrate side of a copper-clad laminate (polyimide film substrate/adhesive layer/electrolessly plated copper foil) as a base material 61 under the conditions of 2MPa, 170°C, 10sec and 180sec. Next, the electromagnetic wave shielding film 10 adhered to the base material 61 is pressed on the adhesive film 62b side of the reinforcing film 62 (polyimide film substrate 62a/adhesive film 62b) at 3MPa, 170°C, and 3min. Then, the laminate is heated at 150°C and 60min for post-hardening. Finally, the reinforcing film 62 of the laminate is adhered to the double-sided tape 63b side of the fixing plate 63 (glass epoxy substrate 63a/double-sided tape 63b) to prepare a sample 60 with a width of 10mm.

FIG4B is a schematic cross-sectional view of the sample in the subsequent strength evaluation test. Then, as shown in FIG4B, the base material 61 is stretched at a stretching speed of 50 mm/min and a stretching angle of 180° while the sample 60 is fixed, thereby peeling the base material 61 and the electromagnetic wave shielding film 10, and measuring the average peeling force at this time. The evaluation test was performed 5 times. The results are shown in Table 1. Furthermore, the evaluation criteria are as follows. If the average peeling force is 4N/10mm or more, the electromagnetic wave shielding film is suitable for practical use, and if the average peeling force is less than 4N/10mm, the electromagnetic wave shielding film is not suitable for practical use. ◎: Average peeling force is 5N/10mm or more ○: Average peeling force is 4N/10mm or more and less than 5N/10mm ╳: Average peeling force is less than 4N/10mm

As shown in Table 1, it can be seen that the electromagnetic wave shielding films of each embodiment have almost no interlayer peeling.

1: Shielded printed wiring board 10,510: Electromagnetic wave shielding film 20,520: Conductive adhesive layer 30,530: Shielding layer 40,540: Insulating layer 50: Printed wiring board 51: Base film 52: Printed circuit 52a: Ground circuit 53: Cover film 53a: Opening 60: Sample 61: Base material 62: Reinforcement film 62a: Polyimide film base material 62b: Adhesive film 63: Fixing plate 63a: Glass epoxy substrate 63b: Double-sided tape 560: Volatile components

FIG. 1 is a cross-sectional view schematically showing an example of the electromagnetic wave shielding film of the present invention. FIG. 2 is a cross-sectional view schematically showing an example of a shielded printed wiring board using the electromagnetic wave shielding film of the present invention. FIG. 3A is an explanatory view schematically showing a mechanism of interlayer peeling between an adhesive layer and a metal layer when a shielded printed wiring board is manufactured using a conventional electromagnetic wave shielding film. FIG. 3B is an explanatory view schematically showing a mechanism of interlayer peeling between an adhesive layer and a metal layer when a shielded printed wiring board is manufactured using a conventional electromagnetic wave shielding film. FIG. 4A is a cross-sectional view schematically showing a sample used for a bonding strength evaluation test. FIG. 4B is a cross-sectional view schematically showing a sample used for a bonding strength evaluation test.

10: Electromagnetic wave shielding film

20: Conductive adhesive layer

30: Shielding layer

40: Insulation layer

Claims (5)

An electromagnetic wave shielding film is characterized by comprising: a conductive adhesive layer; and a shielding layer laminated on the conductive adhesive layer; the conductive adhesive layer contains 50 wt % or less of a conductive filler, and the specific surface area of the conductive filler is 0.9 m ² /g or less. The electromagnetic wave shielding film of claim 1, wherein the tap density of the conductive filler is greater than 1 g/cm ³ . The electromagnetic wave shielding film of claim 1 or 2, wherein an insulating layer is further laminated on the shielding layer. A method for manufacturing an electromagnetic wave shielding film comprises the following steps: preparing a conductive adhesive containing less than 50 wt % of the conductive filler by mixing the conductive filler with a resin; and coating the conductive adhesive on a shielding layer to form a conductive adhesive layer; the conductive filler has a specific surface area of less than 0.9 m ² /g. A method for producing an electromagnetic wave shielding film as claimed in claim 4, wherein the tap density of the conductive filler is greater than 1 g/cm ³ .

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