JP7452230B2 - Electromagnetic shielding sheet, printed wiring board and manufacturing method thereof - Google Patents

Description

The present invention relates to an electromagnetic shielding sheet, a printed wiring board, and a method for manufacturing the same. For example, the present invention relates to an electromagnetic shielding sheet suitable for use by being bonded to a part of a component that emits electromagnetic waves, a printed wiring board, and a method for manufacturing the same.

Various electronic devices including mobile terminals, PCs, servers, etc. have built-in substrates such as printed wiring boards. These boards are provided with electromagnetic shielding structures to prevent malfunctions caused by external magnetic fields and radio waves, and to reduce unnecessary radiation from electrical signals.

For example, Patent Document 1 discloses a structure in which a metal layer with a thickness of 0.5 to 12 μm and an anisotropically conductive adhesive layer are laminated. Furthermore, in Patent Document 2, a conductive adhesive layer, a shield layer which is a metal foil film layer in which a plurality of openings for escaping volatile components are formed, and an insulating layer are laminated in this order, and the delamination characteristics are An electromagnetic shielding film with excellent properties has been disclosed.

International Publication No. 2013/077108 International Publication No. 2018/147299

BACKGROUND ART In electronic devices such as mobile terminals, there has recently been a demand for higher quality electromagnetic shielding layers on printed circuit boards built into the electronic devices. For example, printed wiring boards in which an electromagnetic shielding layer is bonded to a printed wiring board are subjected to high-temperature processing such as solder reflow during the manufacturing process, but volatile components generated by the high-temperature processing can cause quality deterioration inside the printed wiring board. There is. Specifically, floating, peeling, or blistering may occur between the layers of the electromagnetic shielding layer laminate or at the interface between the electromagnetic shielding layer and the printed circuit board, or the appearance may be defective or the shielding properties may deteriorate. Yes (hereinafter referred to as solder reflow resistance).
In addition, with the recent increase in the speed of transmission of transmission signals, there is a strong demand for excellent transmission characteristics, particularly in the high frequency region.
Furthermore, there is a need for technology that increases the manufacturing yield of printed wiring boards. In the manufacturing process of printed wiring boards, an electromagnetic shielding sheet is usually temporarily attached to a wiring board and bonded by thermocompression bonding. If removability (reworkability) can be ensured at the stage of temporary attachment to the wiring board, manufacturing yield can be increased, but re-peeling may leave adhesive residue on the adherend, making rework impossible. Further, as the wiring board becomes thinner, the wiring board itself tends to be easily damaged, and there is also the problem that it is not easy to ensure removability (reworkability) at the stage of temporary attachment.

Note that, although the problems with printed wiring boards have been described above, similar problems may occur in general applications where an electromagnetic shielding layer is bonded to an adherend.

The present invention has been made in view of the above background, and its purpose is to provide an electromagnetic shielding sheet and printed material that has excellent solder reflow resistance, excellent transmission characteristics in the high frequency range, and excellent reworkability. An object of the present invention is to provide a wiring board and a method for manufacturing the same.

As a result of extensive studies, the present inventors have found that the problems of the present invention can be solved in the following embodiments, and have completed the present invention.
[1]: A laminate including a protective layer, a metal layer, and an adhesive layer in this order,
The adhesive layer is an electromagnetic shielding sheet having a plurality of communicating voids extending to at least one side.
[2]: The communicating gap is a groove that penetrates from the first main surface of the adhesive layer to the second main surface opposite to the first main surface, or a groove that penetrates the first main surface or the second main surface of the adhesive layer. a slit formed in a concave shape from one side to the inside of the adhesive layer, a pore formed inside the adhesive layer and not exposed to the first main surface and the second main surface, and the groove; The electromagnetic shielding sheet according to [1], which includes at least one of a slit and an opening formed by arbitrarily combining the pores.
[3]: The electromagnetic shielding sheet according to [2], wherein the adhesive layer is divided into a plurality of island parts by the grooves.
[4]: The electromagnetic shielding sheet according to any one of [1] to [3], wherein the adhesive layer exhibits conductivity.
[5]: A wiring board in which signal wiring is formed on an insulating base material,
an insulating cover coat layer formed on the wiring board;
an electromagnetic shielding layer formed on the cover coat layer,
Any one of [1] to [4], wherein the electromagnetic shielding layer has a laminate including, in this order, a protective layer, a metal layer, and an adhesive layer having a plurality of communicating voids extending to at least one side. A printed wiring board formed from the electromagnetic shielding sheet described above.
[6]: The electromagnetic wave shielding layer has communicating voids originating from the communicating voids of the electromagnetic shielding sheet,
The printed wiring board according to [5], wherein the communicating void extends to at least one side.
[7]: Step A of forming an electromagnetic shielding sheet having a laminate including a protective layer, a metal layer, and an adhesive layer in this order;
Step B of forming an insulating cover coat layer on a wiring board with signal wiring formed on an insulating base material;
Step C of placing the electromagnetic shielding sheet on the cover coat layer and forming an electromagnetic shielding layer by thermocompression bonding,
The step A includes a step of forming a plurality of communicating voids extending to at least one side in the adhesive layer,
A method for manufacturing a printed wiring board, comprising forming a communicating gap derived from the communicating gap in the electromagnetic shielding layer.

According to the present invention, it is possible to provide an electromagnetic shielding sheet, a printed wiring board, and a method for manufacturing the same, which have excellent solder reflow resistance, excellent transmission characteristics in a high frequency region, and excellent reworkability.

FIG. 1 is a schematic side view showing an example of an electromagnetic shielding sheet according to a first embodiment. FIG. 2 is a partially enlarged perspective view of region II in FIG. 1; FIG. 1 is a schematic perspective view showing an example of an adherend with an electromagnetic shielding layer according to the first embodiment. FIG. 1 is a schematic cross-sectional view showing an example of a printed wiring board according to the first embodiment. FIG. 7 is a schematic top view showing an example of an electromagnetic shielding sheet according to Modification 1. FIG. 7 is a schematic top view showing an example of an electromagnetic shielding sheet according to Modification Example 2. FIG. 7 is a schematic side view showing an example of an electromagnetic shielding sheet according to Modification 3. FIG. 7 is a schematic side view showing an example of an electromagnetic shielding sheet according to a second embodiment. FIG. 7 is a schematic perspective view showing an example of an electromagnetic shielding sheet according to a third embodiment. FIG. 3 is a schematic plan view of the main surface side of a printed circuit board having a coplanar circuit according to an example and a comparative example. FIG. 3 is a schematic plan view of the back side of a wiring board having a coplanar circuit according to an example and a comparative example. FIG. 3 is a schematic plan view of the main surface side of a wiring board having a coplanar circuit with an electromagnetic shielding sheet according to an example and a comparative example.

An example of an embodiment to which the present invention is applied will be described below. However, the present invention is not limited to the above-described embodiments and modifications, and other embodiments may also belong to the scope of the present invention as long as they meet the spirit of the present invention. Moreover, each embodiment and modification example can be suitably combined with each other. Note that the numerical values specified in this specification are values determined by the methods disclosed in the embodiments or examples. Further, the term "sheet" as used herein has the same meaning as "film" or "tape". For clarity of explanation, the following description and drawings have been simplified where appropriate. Unless otherwise noted, the various components appearing in this specification may be used individually or in combination of two or more.

The electromagnetic shielding sheet according to this embodiment has a laminate including at least an adhesive layer, a metal layer, and a protective layer in this order. The adhesive layer has a plurality of communicating voids extending to at least one side. As long as it extends to at least one side, its shape and the position of its starting point do not matter. Macroscopically, the communicating gap section extends in a direction toward the side surface of the substrate surface, but microscopically, it may extend in any direction. In this specification, the adhesive layer includes not only the portion where the adhesive actually exists, but also the communicating void portion. Note that the adhesive layer may have a void that does not extend to one side.

The adhesive layer is used as a layer for contacting and bonding the adherend. The adhesive layer functions as a bonding layer in the electromagnetic shielding layer after bonding the electromagnetic shielding sheet to the adherend. The metal layer mainly plays the role of providing shielding properties, and the protective layer plays the role of at least protecting the metal layer.

The electromagnetic wave shielding sheet can be used in all applications where it is desired to shield electromagnetic waves from the inside and/or the outside. Typically, the adhesive layer of the electromagnetic shielding sheet is bonded to an adherend and can be used as an adherend with an electromagnetic shielding sheet layer. A suitable example is a printed wiring board in which an electromagnetic shielding sheet is attached to a printed circuit board, and the electromagnetic shielding layer is bonded to the printed circuit board by a bonding process.

[First embodiment]
FIG. 1 is a schematic side view showing an example of the electromagnetic shielding sheet according to the first embodiment, and FIG. 2 is a partially enlarged perspective view of the area surrounded by the dotted line in FIG. 1 as seen from the adhesive layer 1 side. . As shown in these figures, the electromagnetic shielding sheet 10 has a laminate including an adhesive layer 1, a metal layer 2, and a protective layer 3 in this order. The electromagnetic shielding sheet 10 may have layers other than these.

The adhesive layer 1 is provided with a plurality of communicating voids 4 extending to the side surface 7 thereof. The communication gap 4 is formed by a groove penetrating from the first main surface 5 of the adhesive layer 1 to the second main surface 6 on the opposite side, and extends in the X direction and the Y direction in FIG. There is. The adhesive layer 1 has a plurality of islands formed in an array by communicating voids 4 . In the first embodiment, a collection of individual island portions (i.e., locations with adhesive) separated by communication voids 4 and a collection of communication voids 4 (i.e., locations where no adhesive is formed) are described. The body is adhesive layer 1.

FIG. 3 shows an example of a schematic partially enlarged perspective view of an adherend with an electromagnetic shielding layer. The electromagnetic shielding layer-attached adherend 30 is formed by bonding the electromagnetic shielding layer 15 to the adherend 31. The electromagnetic shielding layer 15 is obtained through a process of temporarily attaching the first principal surface 5 (see FIGS. 1 and 2) of the adhesive layer 1 of the electromagnetic shielding sheet 10 to the adherend 31 and then bonding. The adhesive layer 1 of the electromagnetic shielding sheet 10 is bonded to the adherend 31 through a temporary bonding and bonding process, and functions as a bonding layer 9. The communicating void 4 (see FIGS. 1 and 2) of the adhesive layer 1 undergoes a temporary attachment and bonding process, and a communicating void 8 originating from the communicating void 4 is formed. Preferred examples of the bonding process include thermocompression bonding treatment, heat treatment, pressure bonding treatment, and photocuring treatment. From the viewpoint of simplicity, thermocompression bonding processing is suitable for the joining process. The communicating gap hole 8 usually has an opening diameter smaller than that of the communicating gap part 4.

The size (average opening diameter (average minor axis), average major axis) of the communicating voids 8 is not particularly limited as long as it can discharge volatile components generated during high temperature processing in the manufacturing process of the printed wiring board 20. The size may be such that the communicating void holes 8 are not visually recognized, and it is sufficient that they have a function as an outgas evaporation path. The size of the communicating voids 8 may vary depending on manufacturing conditions such as the shape and position of the communicating voids 4 of the electromagnetic shielding sheet 10, the composition of the adhesive layer 1, and bonding conditions. In other words, these various conditions may be appropriately designed so that the communicating void hole 8 has a desired size and shape. Therefore, the conditions of the communication gap 4 of the electromagnetic shielding sheet 10 are not particularly limited.

FIG. 4 shows a schematic cross-sectional view showing an example of the printed wiring board according to the first embodiment. The printed wiring board 20 includes a wiring board 25 having a circuit pattern having a signal wiring 23 and a ground wiring 24 on an insulating base material 22, and a wiring circuit having an insulating cover coat layer 26 formed on the wiring board 25. It has a substrate 27. The printed wiring board 20 having the electromagnetic shielding layer 15 is formed by temporarily pasting the electromagnetic shielding sheet 10 (see FIG. 1) on the printed circuit board 27 having such a configuration and thermocompression bonding.

In the example of FIG. 4, the electromagnetic shielding layer 15 is formed using an electromagnetic shielding sheet having an adhesive layer exhibiting conductivity. A via 28 is formed in the cover coat layer 26 so that at least a portion of the ground wiring 24 is exposed. Then, the bonding layer 9 (adhesive layer 1 (see FIG. 1)) flows into the via 28 to establish electrical continuity between the ground wiring 24 and the metal layer 2.

The cover coat layer 26 is an insulating material that covers the signal wiring 23 and protects it from the external environment. The cover coat layer is preferably a polyimide film with a thermosetting adhesive, a thermosetting or ultraviolet curing solder resist, or a photosensitive coverlay film, and a photosensitive coverlay film is more preferable for microfabrication. For the cover coat layer, a known resin having heat resistance and flexibility, such as polyimide, is generally used. The thickness of the cover coat layer is usually about 10 to 100 μm.

The circuit pattern includes a ground wire 24 for grounding, and a signal wire 23 for sending electrical signals to electronic components. Both are generally formed by etching copper foil. The thickness of the circuit pattern is usually about 1 to 50 μm.

The insulating base material 22 is a support for a circuit pattern, and is preferably made of bendable plastic such as polyester, polycarbonate, polyimide, polyphenylene sulfide, fluororesin, liquid crystal polymer, and more preferably liquid crystal polymer and polyimide. Among these, liquid crystal polymers with low dielectric constants and low dielectric loss tangents are more preferable, considering the use of printed circuit boards that transmit high-frequency signals.
When the printed circuit board is a rigid wiring board, the constituent material of the insulating base material is preferably glass epoxy. By including the insulating base material as described above, the printed circuit board can have high heat resistance.

The conditions for carrying out the bonding process by thermocompression bonding are arbitrary, but for example, the bonding process is carried out at a temperature of about 150 to 190°C, a pressure of about 1 to 3 MPa, and a time of about 1 to 60 minutes. The adhesive layer 1 and the cover coat layer 26 are brought into close contact with each other by hot pressing, and the adhesive layer 1 flows and fills the vias 28 formed in the cover coat layer 26, thereby establishing conduction with the ground wiring 24. When a thermosetting resin is used as the adhesive layer, it is reacted and cured by heat pressing to become the electromagnetic shielding layer 15. In this case, post-curing may be performed at 150 to 190° C. for 30 to 90 minutes after hot pressing to accelerate curing.

The opening area of the via 28 is preferably 2.5 mm ² or less, and preferably 0.008 mm ² or more. By setting it within the above range, the area of the ground wiring can be narrowed, and the size of the printed wiring board can be reduced. The shape of the via is not particularly limited, and any shape such as a circle, square, rectangle, triangle, or irregular shape can be used depending on the purpose.

It is preferable that the electromagnetic shielding layer be laminated on both sides of the printed circuit board, since leakage of electromagnetic waves can be more effectively suppressed. Further, the electromagnetic shield layer 15 in the printed wiring board 20 can be used as a ground circuit in addition to shielding electromagnetic waves. This makes it possible to reduce costs by omitting a part of the ground circuit and reducing the area of the printed circuit board, allowing it to be incorporated into a narrow area within the housing.

Further, the signal wiring 23 can have various circuit configurations, such as a single-end circuit consisting of one signal wiring, or a differential circuit consisting of two signal wirings, but a differential circuit is more preferable. If the circuit pattern area of the printed circuit board 27 is limited and it is difficult to form a ground circuit in parallel, the electromagnetic shielding layer 15 may be used as a ground circuit without providing a ground circuit next to the signal circuit. . In this case, the printed wiring board structure has a ground in the thickness direction.

The printed wiring board of the present invention is suitable for mounting on electronic devices such as liquid crystal displays, touch panels, etc., as well as notebook PCs, mobile phones, smartphones, and tablet terminals.

By using an electromagnetic shielding layer in which a connecting layer is formed with communicating pores originating from the communicating pores, outgas generated during high-temperature processing can escape to the outside through the communicating pores. As a result, peeling at the interface between the electromagnetic shielding layer and the adherend and swelling due to gas retention can be effectively prevented. In addition, oxidation of the metal layer due to retention of generated water vapor and other gas components can be prevented. Furthermore, since the water vapor generated by providing the communication gap can be discharged to the outside, it is possible to effectively prevent problems such as short circuits caused by water and other foreign substances originating from the water vapor remaining. Furthermore, poor bonding between the layers of the electromagnetic shielding layer made of a laminate, such as interfacial peeling between the metal layer and the bonding layer, can be effectively prevented. As a result, a high-quality electromagnetic shielding sheet and printed wiring board with excellent shielding properties can be provided. That is, it is possible to provide a printed wiring board with improved solder reflow resistance and excellent shielding characteristics with high reliability. In addition, dielectric loss can be reduced by providing holes with a low dielectric constant in the bonding layer located closest to the signal wiring, making it possible to create an electromagnetic shielding layer with excellent transmission characteristics (particularly in reducing transmission loss in the high frequency range). Can be provided. In particular, excellent transmission characteristics can be achieved in an electromagnetic shielding layer bonded to a printed circuit board that transmits high-frequency signals (for example, 100 MHz to 50 GHz).

2. Description of the Related Art There has been a demand for technology that increases the manufacturing yield of printed wiring boards. In the manufacturing process of printed wiring boards, an electromagnetic shielding sheet is usually temporarily attached to a printed circuit board and formed by a bonding process. If the temporary attachment position is not the originally intended position, the production yield of printed wiring boards can be increased if the adhesive can be peeled off again. However, when the printed circuit board is peeled off again, adhesive residue originating from the adhesive layer is generated on the printed circuit board side, and rework may not be possible due to the large amount of adhesive residue. Further, depending on the adherend, as various substrates become thinner, the substrate itself may be easily damaged by re-peeling off the electromagnetic shielding sheet.

According to the electromagnetic shielding sheet according to the first embodiment, by providing the communication gap, the contact area during temporary attachment with the printed circuit board is reduced, so that the electromagnetic shielding sheet and the adherend during temporary attachment are reduced. can weaken the adhesive strength of As a result, it becomes possible to improve reworkability, and the manufacturing yield can be significantly increased.

Each member of the electromagnetic shielding sheet will be described in detail below.
<Adhesive layer>
As described above, the adhesive layer 1 is provided with a plurality of communicating voids 4 extending in the X and Y directions of FIG. 2 and extending to the opposing side surfaces 7, respectively. The communication gap 4 can take various forms as shown in modified examples and embodiments to be described later. In addition to being groove-shaped like the communicating void 4 of the first embodiment, it may also be a slit or a pore like the embodiment described later. Alternatively, the opening may be any combination of grooves, slits, and pores. From the viewpoint of manufacturing cost, it is preferable that the shape of the communicating gap is a groove and/or a slit. One or more types of communicating voids can be used in combination.

The shape of the opening seen from the side of the adhesive layer may be rectangular as shown in FIG. 1, or any other shape may be selected. For example, a circle, an ellipse, and a polygon can be used. Moreover, it may be amorphous. Among these, polygons such as triangles, rectangles, and trapezoids are preferred. Further, the extending direction may be any one direction, and may also be branched, bent, random, or a combination thereof.

The preferred size of the communicating gap may vary depending on the method of joining the electromagnetic shielding sheet. When bonding the electromagnetic shielding sheet to the adherend by thermocompression bonding, from the viewpoint of easily forming the communicating voids 8, it is preferable that the communicating voids 4 account for 20 to 85% by volume of the adhesive layer 1. . This proportion is more preferably 35% by volume or more, and even more preferably 40% by volume or more.

The gaps W1, W2 (see FIG. 2) between adjacent island portions of the adhesive layer 1, that is, the short diameters W1, W2 of the communicating gap portions are not limited as described above, but as a suitable range for thermocompression bonding, An example of each independently is 100 to 1500 μm. The thickness is more preferably 150 to 900 μm, even more preferably 200 to 600 μm, particularly preferably 250 to 300 μm. It is not essential that the short diameter be the same in the extending direction, and it can be any width.

Although the lengths of the island portions of the adhesive layer 1 in the X direction and Y direction in FIG. 2 are not limited as described above, a suitable range for thermocompression bonding can be independently exemplified as 100 to 1250 μm. Such lengths are each independently more preferably from 150 to 870 μm, even more preferably from 200 to 600 μm, particularly preferably from 230 to 290 μm. The area of the island portion is preferably 10,000 to 1,600,000 μm ² , more preferably 30,000 to 800,000 μm ² , and even more preferably 40,000 to 400,000 μm ² preferable. By setting the area of the island portion to 10,000 to 1,600,000 μm ² , reworkability can be improved more effectively.

The adhesive layer 1 is a layer formed from an adhesive composition containing a binder resin, and may be a non-conductive adhesive layer or a conductive adhesive layer. From the viewpoint of improving transmission characteristics in a high frequency region, a conductive adhesive layer is preferable. Note that the conductive adhesive layer referred to here only needs to exhibit conductivity after being bonded to an adherend, and does not need to exhibit conductivity at the stage of adhesive layer 1.

The binder resin includes at least a thermosoftening resin. Examples of thermoplastic resins include thermoplastic resins, thermosetting resins, and actinic light-curable resins. Thermosetting resins and actinic light-curable resins usually have reactive functional groups. When using a thermosetting resin, a curable compound and a thermosetting aid can be used together. Further, when using an actinic light-curable resin, a photopolymerization initiator, a sensitizer, etc. can be used in combination. In view of the simplicity of the manufacturing process, a thermosetting type that hardens during thermocompression bonding is preferred.
Further, a self-crosslinking resin or a plurality of resins that crosslink with each other may be used. Moreover, in addition to these resins, a thermoplastic resin may be mixed. The blending components such as resin and curable compound can be used individually or in combination.
Note that some crosslinking may be formed at the adhesive layer 1 stage, resulting in a B stage (semi-cured state). For example, a part of the thermosetting resin and the curable compound may react and be in a semi-cured state.

The weight average molecular weight Mw of the binder resin is not particularly limited, but is preferably from 10,000 to 500,000 from the viewpoint of solder reflow resistance. Mw is more preferably 30,000 or more, and even more preferably 50,000 or more.

Suitable examples of thermoplastic resins include polyurethane resins, polycarbonate resins, styrene elastomer resins, phenoxy resins, polyurethane urea resins, polyimide resins, polyamide resins, polycarbonate imide resins, polyamideimide resins, epoxy resins, epoxy ester resins, Acrylic resin, polyester resin, polystyrene, polyesteramide resin, acrylic resin, polyether resin, styrene elastomer, butadiene rubber, polyisoprene, cellulose, polyether ester resin, maleic acid resin, oxetane resin, phenolic resin, alkyd resin, Examples include amino resins, polylactic acid resins, oxazoline resins, benzoxazine resins, silicone resins, fluororesins, and liquid crystal polymers. Among these, polyurethane resins, polycarbonate resins, styrene elastomer resins, phenoxy resins, polyamide resins, and polyimide resins are preferred. The thermosoftening resin can be used alone or in a mixture of two or more in any ratio.
Further, from the viewpoint of suppressing transmission loss, it is preferable that the binder resin is a material with a low dielectric constant and a low dielectric loss tangent, and from the viewpoint of characteristic impedance, a material with a low dielectric constant is preferable. Suitable examples include liquid crystal polymers and fluororesins. The binder resin can be used alone or in combination of two or more.

Further, a conductive polymer may be used as the binder resin. Examples of the conductive polymer include polyethylene dioxythiophene, polyacetylene, polypyrrole, polythiophene, and polyaniline.

When used under severe conditions during reflow, it is preferable to include a thermosetting resin. The thermosetting resin has a functional group that can undergo a crosslinking reaction when heated. Examples of the functional group include a hydroxyl group, a phenolic hydroxyl group, a carboxyl group, an amino group, an epoxy group, an oxetanyl group, an oxazoline group, an oxazine group, an aziridine group, a thiol group, an isocyanate group, a blocked isocyanate group, and a silanol group.

The curable compound has a functional group that can crosslink with the reactive functional group of the thermosetting resin. Curable compounds include epoxy compounds, acid anhydride group-containing compounds, isocyanate compounds, polycarbodiimide compounds, aziridine compounds, dicyandiamide compounds, amine compounds such as aromatic diamine compounds, phenolic compounds such as phenol novolac resins, organometallic compounds, etc. preferable. Among these, it is more preferable to include an epoxy compound. Further, a combination in which an epoxy compound and an aziridine compound are used together as the curable compound is also suitable. The curable compound may be a resin. In this case, the thermosetting resin and the curable compound are distinguished as the thermosetting resin having a higher content and the curable compound having a lower content.

The curable compound is preferably contained in 1 to 50 parts by weight, more preferably 3 to 40 parts by weight, and even more preferably 3 to 30 parts by weight, based on 100 parts by weight of the thermosetting resin. The curable compounds can be used alone or in combination.

The conductive adhesive layer can be easily formed by using an adhesive composition containing a conductive filler. Examples of the conductive filler include metal fillers, conductive ceramic particles, conductive polymers, and mixtures thereof. Examples of the metal filler include metal powders such as gold, silver, copper, and nickel, alloy powders such as solder, core-shell type particles such as silver-coated copper powder, gold-coated copper powder, silver-coated nickel powder, and gold-coated nickel powder. From the viewpoint of obtaining excellent conductive properties, a conductive filler containing silver is preferred. From the viewpoint of cost, silver-coated copper powder, which is copper powder coated with silver, is particularly preferred. Examples of the conductive polymer include polyaniline and polyacetylene.

Furthermore, an electromagnetic wave absorbing filler may be used as the conductive filler. For example, iron, Fe-Ni alloy, Fe-Co alloy, Fe-Cr alloy, Fe-Si alloy, Fe-Al alloy, Fe-Cr-Si alloy, Fe-Cr-Al alloy, Fe-Si-Al alloy, etc. Examples include iron alloys such as Mg--Zn ferrite, Mn--Zn ferrite, Mn--Mg ferrite, Cu--Zn ferrite, Mg--Mn--Sr ferrite, Ni--Zn ferrite, and other ferrite-based materials, as well as carbon fillers. Examples of the carbon filler include acetylene black, Ketjen black, furnace black, carbon black, carbon fiber, particles made of carbon nanotubes, graphene particles, graphite particles, and carbon nanowalls. The conductive filler can be used alone or in combination of two or more types.

The shape of the conductive filler is not limited as long as desired conductivity can be obtained. Examples include spherical, flake-like, leaf-like, dendritic, plate-like, needle-like, rod-like, and grape-like shapes. In addition to using a filler of a single shape, conductive fillers of different shapes may be used in combination.

The D50 average particle diameter of the conductive filler is preferably 2 μm or more, more preferably 5 μm or more, and even more preferably 7 μm or more from the viewpoint of ensuring sufficient conductivity. On the other hand, from the viewpoint of making the conductive adhesive layer thinner, the thickness is preferably 30 μm or less, more preferably 20 μm or less, and even more preferably 15 μm or less. The D50 average particle diameter can be determined using a laser diffraction/scattering method particle size distribution analyzer or the like.

The content of the conductive filler is preferably 10 to 90% by mass in the adhesive layer excluding voids such as communicating voids, that is, in the region where the adhesive is present. It is more preferably 15 to 70% by weight, even more preferably 20 to 50% by weight. When the content is 10% by mass or more, the conductive connection between the adhesive layer and the ground wiring on the printed wiring board described later becomes good, and high frequency shielding properties are improved. On the other hand, when the content is 90% by mass or less, solder reflow resistance and transmission characteristics are improved.

The conductive adhesive layer can be an isotropic conductive adhesive layer or an anisotropic conductive adhesive layer. An isotropically conductive adhesive layer is a layer that is isotropically conductive, and an anisotropically conductive adhesive layer is an anisotropically conductive layer that is generally conductive in the thickness direction of the electromagnetic shielding sheet. This refers to the layer that has gender. From the viewpoint of cost reduction, an anisotropic conductive adhesive layer is preferable.

For the purpose of improving desired physical properties and imparting functions, the adhesive composition contains optional ingredients such as a silane coupling agent, a rust preventive agent, a reducing agent, an antioxidant, a pigment, a dye, a tackifying resin, a plasticizer, and ultraviolet rays. Absorbents, antifoaming agents, leveling agents, fillers, flame retardants, etc. can be added. For example, carbon particles can be added for the purpose of adjusting the viscoelasticity of the adhesive layer. Examples of the carbon particles include carbon black, Ketjen black, acetylene black, carbon nanotubes, and graphene.

The adhesive composition can be obtained by mixing and stirring the ingredients. For stirring, a known stirring device such as a dispermat or a homogenizer can be used.

A known method can be used to prepare the adhesive layer. For example, an adhesive layer may be formed by coating an adhesive composition on a releasable sheet and drying, or an extrusion molding machine such as a T-die may be used to form an adhesive composition into a sheet. It can also be formed by extrusion.

Coating methods include, for example, gravure coating, kiss coating, die coating, lip coating, comma coating, blade coating, roll coating, knife coating, spray coating, bar coating, spin coating, and dip coating. A known coating method such as a coating method can be used. It is preferable to perform a drying step during coating. In the drying step, for example, a known drying device such as a hot air dryer or an infrared heater can be used.

The thickness of the adhesive layer can be set appropriately depending on the application, and can be, for example, about 2 to 30 μm. The thickness is preferably 3 to 15 μm, more preferably 4 to 9 μm. When the thickness is in the range of 2 to 30 μm, solder reflow resistance can be improved.

<Metal layer>
The metal layer 2 is a layer sandwiched between the adhesive layer 1 and the protective layer 3, and is formed of, for example, metal foil, a metal vapor deposited film, a metal sputtered film, or a metal plating film.
The type of metal is preferably a conductive metal such as aluminum, copper, silver, or gold, and either one type of metal or an alloy of multiple metals can be used. Copper, silver, and aluminum are more preferred in terms of high frequency shielding properties and cost, and copper is even more preferred. Suitable examples of the metal foil include, for example, rolled copper foil and electrolytic copper foil. One or both surfaces of the metal layer 2 may be coated with another metal or an organic substance such as a rust preventive.

The thickness of the metal layer is not particularly limited, and is appropriately selected depending on the application. When flexibility is required, the thickness is preferably about 0.3 to 10 μm in consideration of electromagnetic shielding properties. By setting the thickness of the metal layer to 0.3 μm or more, transmission of the wavelength of electromagnetic noise generated from the printed circuit board can be suppressed, and sufficient high frequency shielding properties can be exhibited. More preferably, the thickness of the metal layer is 0.5 μm or more.

In the printed wiring board on which the electromagnetic shielding layer is formed, when the transmission signal flowing through the signal wiring formed on the printed circuit board becomes a high frequency, a current starts to flow through the metal layer 2. The transmission characteristics of signal wiring in a printed circuit board are affected by the current flowing through nearby conductors, so if the surface of the metal layer 2 adjacent to the signal wiring is rough, the distance between the current flowing through the metal surface and This causes the transmission characteristics to become unstable. Therefore, from the viewpoint of improving the transmission characteristics in the high frequency range, it is preferable that the arithmetic mean height Sa of the surface of the metal layer 2 in contact with the adhesive layer 1 is 0.01 to 2.5 μm. The arithmetic mean height Sa is more preferably 1.25 μm or less, and even more preferably 0.5 μm or less. Furthermore, from the viewpoint of improving reworkability, the root mean square slope Sdq of the surface of the metal layer 2 in contact with the adhesive layer 1 is preferably 0.0001 to 1.5, and more preferably 0.7 or less. It is preferably 0.3 or less, and more preferably 0.3 or less. By setting the root mean square slope Sdq of the surface of the metal layer on the adhesive layer side in the range of 0.0001 to 1.5, the angle of the unevenness formed on the surface of the metal layer can be made appropriately acute, and the adhesive The adhesion of the agent layer to the metal layer is improved. As a result, the adhesion between the metal layer and the adhesive layer can be further increased, so that when the adhesive layer at the temporary attachment stage is peeled off from the adherend, it is possible to reduce the amount of adhesive left on the adherend. Note that the arithmetic mean height Sa and the root mean square slope Sdq refer to values determined by an example described later.

Ｓｄｑは、触針式表面粗さ測定機などを用いた接触式表面粗さ測定、あるいは、レーザー顕微鏡などを用いた非接触式表面粗さ測定から得られた表面形状データを、適宜解析ソフトによって処理することにより算出することができる。Ｓｄｑは、表面における凹凸の険しさを表現するパラメータである。Ｓｄｑの数値が大きい程、表面凹凸はより険しくなる。即ち、Ｓｄｑの数値によって、表面凹凸険しさの程度を判断することができる。 Here, the arithmetic mean height Sa is defined in the ISO 25178-2:2012 standard, and is a parameter that extends the arithmetic mean height (Ra) of a line to a surface, and is , is a value calculated by averaging the absolute values of the heights of each point.
The root mean square slope Sdq is also defined in the ISO 25178-2:2012 standard, is the root mean square of the local slope dz/dx at the reference length, and is expressed by the following equation (1). A is the area of the defined surface, ∂x is the x-axis direction, ∂y is the y-axis direction, and ∂z(x, y) is the minute displacement in the z-axis direction.

Sdq uses analysis software to analyze surface shape data obtained from contact surface roughness measurement using a stylus surface roughness measuring device or from non-contact surface roughness measurement using a laser microscope. It can be calculated by processing. Sdq is a parameter expressing the steepness of the unevenness on the surface. The larger the value of Sdq, the steeper the surface unevenness. That is, the degree of roughness of the surface unevenness can be determined by the numerical value of Sdq.

Note that the value of the root mean square slope Sdq of this metal layer does not substantially change due to the formation process of the electromagnetic shielding layer, such as hot pressing. Therefore, the preferred range of the arithmetic mean height Sa of the interface of the metal layer in contact with the bonding layer in the electromagnetic shielding layer is 0.01 to 2.5 μm, and the preferred range of the root mean square slope Sdq is 0.0001 to 1. It is .5.

A method for controlling the arithmetic mean height Sa and root mean square slope Sdq of the metal layer surface is, for example, a method of attaching roughening particles on the surface of a copper foil to form a roughened surface, JP 2017-13473A. A method of polishing a metal surface using a buff described in the publication, a method of polishing a metal surface using coated abrasive paper, and a method of forming a metal layer on a carrier material having desired unevenness by a method such as plating. Examples include a method of transferring the unevenness of a carrier material, and a shot blasting method of spraying an abrasive onto a metal surface using compressed air.

The metal layer may have multiple openings. The opening here refers to a hole that penetrates the metal layer in the thickness direction. The porosity of the openings is not particularly limited, but may be, for example, 0.1 to 20%. A more preferred range is 0.3 to 15%, and an even more preferred range is 0.5 to 6.5%. This porosity can be determined by the following formula.
(Open area ratio [%]) = (Area of open areas per unit area) / (Area of open areas per unit area + Area of non-open areas per unit area) x 100

<Protective layer>
The protective layer 3 only needs to cover at least a portion of the metal layer 2 . From the viewpoint of shielding properties, a configuration in which the entire surface of the metal layer is covered is preferable. Although FIG. 1 shows an example in which the metal layer 2 is laminated directly above the metal layer 2, other layers may be laminated between the metal layer 2 and the protective layer 3. The protective layer 3 is a layer formed from a resin or a resin composition containing a binder resin, and has insulation properties. The resin composition can be formed using a conventionally known resin composition. Suitable examples include the binder resins (thermoplastic resins, actinic radiation-curable resins, and thermosetting resins) described in the adhesive composition forming the adhesive layer. The protective layer may be a single layer or a laminate of two or more layers. When a thermosetting resin or the like is used as the binder resin, the crosslinked structure etc. differ depending on the manufacturing stage of the protective layer, but in this specification, these will not be distinguished and will be referred to as the protective layer.

The weight average molecular weight of the binder resin (in the case of a thermosetting resin or actinic radiation curable resin, the weight average molecular weight of the resin until curing) is not particularly limited, but is preferably from 10,000 to 500,000. More preferably 30,000 or more, and even more preferably 50,000 or more. When the weight average molecular weight of the thermosetting resin is 10,000 or more, decomposition and dissolution of the coating film upon exposure to cleaning chemicals can be suppressed, and chemical resistance is improved. The weight average molecular weight of the thermosetting resin is more preferably 30,000 or more, and even more preferably 50,000 or more.

The protective layer 3 can be manufactured by a known method. For example, a protective layer can be formed by coating a resin composition on a removable sheet and drying it, or by extruding the resin composition into a sheet using an extrusion molding machine such as a T-die. It can also be formed. Further, the protective layer may be a film formed from an insulating resin such as polyester, polycarbonate, polyimide, polyamideimide, polyamide, polyphenylene sulfide, polyether ether ketone, or the like.

Suitable examples of the curable compound include the compounds exemplified in the adhesive composition. Among these, it is more preferable to include an epoxy compound. Also suitable is a combination of an epoxy compound and an aziridine compound.

Non-conductive particles can be added to the resin composition as an optional component. By adding non-conductive particles, surface roughness (unevenness) can be adjusted appropriately. Non-conductive particles include talc, mica, clay, calcium carbonate, barium titanate, carbon black, glass beads, glass hollow spheres, magnesium fluoride, aluminum dioxide (alumina), zirconium dioxide (zirconia), and silicon dioxide (silica). ), boron carbide, aluminum nitride, boron nitride, magnesium oxide (magnesia), titanium oxide, and other ceramics. The non-conductive fine particles may be used alone or in combination of two or more. The average particle diameter of the non-conductive fine particles is not particularly limited, and may be, for example, 0.01 μm or more and 10 μm or less, and may be 0.5 μm or more and 3 μm or less.

The thickness of the protective layer can be designed depending on the application, and can be, for example, 2 to 20 μm. When the thickness of the protective layer is 2 to 20 μm, dissolution of the protective layer and peeling from the metal layer after exposure to cleaning chemicals can be suppressed. The protective layer may have any one or a combination of hard coat properties, water vapor barrier properties, oxygen barrier properties, thermal conductivity, low dielectric constant properties, high dielectric constant properties, and heat resistance.

[Manufacturing method of electromagnetic shielding sheet and printed wiring board]
An example of a method for manufacturing an electromagnetic shielding sheet and a printed wiring board will be described below. However, the manufacturing method of the present invention is not limited to the following manufacturing method.
First, a pre-adhesive layer is formed on a releasable sheet, and the metal foil having a carrier material and the pre-adhesive layer are laminated and then the carrier material is peeled off. Then, a pre-laminated body is obtained by laminating the surface from which the carrier material has been peeled off and a protective layer separately formed on a releasable sheet. Thereafter, a laser beam is irradiated onto the pre-adhesive layer at a position where a communicating gap is to be formed, and a communicating gap is formed by ablation. Examples of types of laser light include, but are not limited to, YAG laser, carbon dioxide laser, and excimer laser. After irradiating with laser light, desmear treatment is performed as necessary. Alternatively, it may be formed by mechanical cutting using a drill or the like. Further, the communicating void portion may be formed by plasma treatment, nanoimprinting, embossing, printing, or the like.

The above method is an example, and an adhesive layer having a pattern such that communicating voids are formed on the metal layer may be obtained by screen printing or the like. Alternatively, a patterned adhesive layer may be obtained by photolithography.

The printed wiring board is obtained by placing the electromagnetic shielding sheet obtained as described above on a cover coat layer and subjecting the sheet to a bonding process. By the bonding process, a printed wiring board having an electromagnetic shielding layer in which communicating voids originating from the communicating voids of the electromagnetic shielding sheet are formed is obtained.

<Modified example>
In the above embodiment, an example is given of an electromagnetic shielding sheet having an adhesive layer in which communicating voids extending to opposing side surfaces are formed in each of the X direction and the Y direction, and island parts are formed in an array. The form of the communicating gap is not limited to this, and can be designed in various ways.
The electromagnetic shielding sheets according to Modifications 1 to 3 are different from the first embodiment in the communication gap portions, but the other basic configurations are the same as in the first embodiment. Note that in the following examples, descriptions that overlap with those of the first embodiment will be omitted as appropriate. In addition, the same element members will be given the same reference numerals as appropriate, and their explanation will be omitted.

FIG. 5 is a schematic top view of the electromagnetic shielding sheet according to Modification Example 1, viewed from the adhesive layer side. In the adhesive layer 1a of the electromagnetic shielding sheet 10a shown in the figure, a plurality of communicating voids 4a are formed at predetermined intervals, extending from one side surface in the Y direction to the opposite side surface. The short axis W1 of the communication gap 4a may be changed depending on the position, or may be the same. The interval between the communicating gaps 4a can be set arbitrarily.

FIG. 6 is a schematic top view of the electromagnetic shielding sheet according to Modification Example 2, viewed from the adhesive layer side. The adhesive layer 1b of the electromagnetic shielding sheet 10b in the figure has a communicating gap 4b extending in the Y direction in the figure from one side 7s1 to the inside, and a communicating gap 4b extending in the Y direction from the other side 7s2 opposite to the one side 7s1 to the inside. A plurality of communicating voids 4b are formed alternately at predetermined intervals. The short axis W1 of the communication gap 4b may be changed depending on the position, or may be the same. The interval between the communicating voids 4b can be set arbitrarily.
According to the electromagnetic shielding sheets according to Modifications 1 and 2, by forming the communicating gap in one arbitrary direction, the gas evaporation path can be concentrated in one direction, and a large number of bonding surfaces with the adherend can be obtained. It has the advantage of

In the electromagnetic shielding layer bonded to the adherend, the extending length of the communicating voids is preferably 10% or more, and preferably 20% or more, of the width of the outside diameter of the electromagnetic shielding layer. is more preferred, still more preferably 30% or more, particularly preferably 50% or more. Note that the extending length refers to the length passing through the center of the opening diameter (breadth diameter), and may be a straight line or a curved line.

FIG. 7 is a schematic side view of an electromagnetic shielding sheet according to modification 3. The adhesive layer 1c of the electromagnetic shielding sheet 10c shown in the figure is provided with communication voids 4c having different widths in the short axis in the thickness direction. Such a communicating gap 4c is created by, for example, forming a communicating gap using a laser beam or the like after laminating a pre-adhesive layer on the metal layer 2, and then bonding the second pre-adhesive layer to the first adhesive. It can be formed by laminating the adhesive layer on the adhesive layer and then providing a communicating gap in the second pre-adhesive layer using laser light or the like. The adhesive layer may be a laminate of three or more layers. Alternatively, it may be produced using a 3D printer. The electromagnetic shielding sheet according to Modification 3 is suitable for applications where it is desired to secure a communicating gap and to have a large bonding surface with an adherend.

[Second embodiment]
The electromagnetic shielding sheet according to the second embodiment is different from the first embodiment using an electromagnetic shielding sheet having an adhesive layer in which the communicating voids are grooves in that the communicating voids in the adhesive layer are slits. . However, other basic configurations and manufacturing methods are the same as those of the first embodiment except for the points specifically mentioned.

FIG. 8 is a schematic side view showing an example of a main part of the electromagnetic shielding sheet according to the second embodiment. As shown in the figure, the electromagnetic shielding sheet 10e has a laminate including an adhesive layer 1e, a metal layer 2, and a protective layer 3 in this order. The adhesive layer 1e is provided with a plurality of communicating voids 4e extending to the side surface 7 thereof. The communication gap 4e is formed by a slit forming a recess from the first main surface 5 of the adhesive layer 1e, and extends in the X direction and the Y direction. Concave portions are formed in the adhesive layer 1e by the communicating voids 4e, and in this example, convex portions are formed in an array.

In the example of FIG. 8, the shape of the communication gap 4e in side view is a trapezoid, but as in the first embodiment, it can take various shapes. The size of the slit may be designed in various ways depending on the bonding method and the like. In the case of thermocompression bonding, from the viewpoint of easily forming a communicating gap, the preferred range of the width W in the short direction of the opening when the communicating gap is rectangular is the same as in the first embodiment. In the case of a trapezoidal shape, the preferable range for the length of the top surface and the length of the bottom surface of the slit is independently 100 to 1500 μm, more preferably 150 to 900 μm, and preferably 200 to 600 μm. The thickness is more preferably 250 to 300 μm. As shown in FIG. 8, the length of the bottom part of the shape of the communicating gap in side view<the length of the top part, or vice versa.

Although the ratio of the length of the slit bottom, which is the communicating gap 4e, to the length of the slit top surface (in this example, the first principal surface of the adhesive layer), that is, the ratio of the length of the bottom surface/the length of the top surface, is not particularly limited. From the viewpoint of achieving both adhesion between the metal layer and the adhesive layer and ensuring an outgas evaporation path, it is preferably 0.9 or less. Further, the shape of the communication gap in side view may be changed to a trapezoid, and a triangular slit may be formed.

The depth (height) of the slit relative to the thickness of the adhesive layer, that is, the ratio of slit depth/thickness of the adhesive layer, is not limited, but it is important to ensure adhesion between the metal layer and the adhesive layer and a path for outgas evaporation. From the viewpoint of achieving both, it is preferably 0.2 or more and less than 1, more preferably 0.4 to 0.8, and even more preferably 0.4 to 0.6. The suitable thickness of the adhesive layer is as described in the first embodiment.

The communicating void portion 4e of the adhesive layer 1e can be formed by, for example, laser light irradiation, imprinting, embossing, or the like. The electromagnetic shielding sheet according to the second embodiment has the advantage that an outgas evaporation path can be reliably secured while securing the bonding area between the metal layer and the adhesive layer.

<Modified example>
In the second embodiment, an example was given in which a slit is formed on the side of the adhesive layer that is bonded to the adherend, but it is also possible to form a slit on the side of the adhesive layer that is bonded to the metal layer. good. Furthermore, slits may be formed on both the metal layer side and the adherend side. Furthermore, instead of the adhesive layer having communicating voids extending in the X and Y directions, for example, border-like communicating voids or comb-shaped communicating voids may be used, as exemplified in the modification of the first embodiment. It can also be a communicating void.

[Third embodiment]
The electromagnetic shielding sheet according to the third embodiment differs from the first embodiment in that the communicating voids in the adhesive layer are pores, in that the communicating voids are grooves. However, other basic configurations and manufacturing methods are the same as those of the first embodiment except for the points specifically mentioned.

FIG. 9 is a schematic perspective view showing an example of a main part of an electromagnetic shielding sheet according to a third embodiment. As shown in the figure, the electromagnetic shielding sheet 10f has a laminate including an adhesive layer 1f, a metal layer 2, and a protective layer 3 in this order. The adhesive layer 1f is provided with a plurality of communicating voids 4f extending to the side surface 7 at predetermined intervals. The communicating void portion 4f is formed with pores extending in the X direction and the Y direction inside the adhesive layer 1f.

The communicating voids 4f of the adhesive layer 1f may be formed, for example, by forming an intermediate layer in which a communicating void is formed in a releasable base material, and sandwiching this intermediate layer between a pair of surface layers that do not have communicating voids. It can be formed by The method described in the above embodiment can be applied as appropriate to the method for forming the communicating gap in the intermediate layer. Alternatively, it may be manufactured using a 3D printer.
According to the electromagnetic shielding sheet according to the third embodiment, the advantage is that an outgas evaporation path can be secured while securing the bonding area between the metal layer and the adhesive layer and the bonding area between the adhesive layer and the adherend. have

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples. Further, in the examples, "parts" and "%" mean "parts by mass" and "% by mass," respectively.
The acid value, weight average molecular weight (Mw), glass transition temperature (Tg) of the resin, and average particle diameter of the conductive filler were measured by the following methods.

《Measurement of acid value of binder resin》
The acid value was measured according to JIS K0070. Approximately 1 g of the sample was accurately weighed into a stoppered Erlenmeyer flask, and 100 mL of a mixed solution of tetrahydrofuran/ethanol (volume ratio: tetrahydrofuran/ethanol = 2/1) was added to dissolve it. To this, a phenolphthalein test solution was added as an indicator and titrated with 0.1N alcoholic potassium hydroxide solution, and the end point was defined as when the indicator remained pale pink for 30 seconds. The acid value was determined by the following formula.
Acid value (mgKOH/g) = (5.611 x a x F)/S
however,
S: Amount of sample collected (g)
a: Consumption amount (mL) of 0.1N alcoholic potassium hydroxide solution
F: Titer of 0.1N alcoholic potassium hydroxide solution

《Measurement of weight average molecular weight (Mw) of binder resin》
The weight average molecular weight (Mw) was measured using GPC (gel permeation chromatography) "HPC-8020" manufactured by Tosoh Corporation. GPC is liquid chromatography that separates and quantifies substances dissolved in a solvent (THF; tetrahydrofuran) based on the difference in molecular size. In this measurement, two columns of "LF-604" (manufactured by Showa Denko Co., Ltd.: GPC column for rapid analysis: 6 mm ID x 150 mm size) were connected in series, the flow rate was 0.6 mL/min, and the column temperature was 40°C. The weight average molecular weight (Mw) was determined in terms of polystyrene.

《Glass transition temperature (Tg) of binder resin》
The Tg was measured by differential scanning calorimetry (“DSC-1” manufactured by Mettler Toledo).

《Measurement of average particle diameter of conductive filler》
The D50 average particle diameter is a value obtained by measuring the conductive filler with a Tornado Dry Powder Sample Module using a laser diffraction/scattering method particle size distribution analyzer LS13320 (manufactured by Beckman Coulter). The cumulative value in the cumulative distribution is the particle size of 50%. Note that the refractive index was set to 1.6.

Next, the raw materials used in the examples are shown below.
"material"
・Binder resin: polyurethane urea resin (manufactured by Toyochem), acid value: 5 mgKOH/g, Mw: 54,000, Tg: -7°C,
・Epoxy compound: Bisphenol A type epoxy resin (“JER828”, manufactured by Mitsubishi Chemical Corporation), epoxy equivalent = 189 g/eq
・Aziridine compound: "Chemitite PZ-33" manufactured by Nippon Shokubai Co., Ltd. ・Conductive filler: Composite fine particles (dendritic fine particles coated with 10 parts by mass of silver per 100 parts by mass of copper in the core), average particle size D50 :11.0μm (manufactured by Fukuda Metal Foil and Powder Industries Co., Ltd.)
・Non-conductive particles: Sunsphere NP-100 (D50 average particle diameter: 8.0 μm, SiO ₂ ; volume resistivity 1.0×10 ¹⁴ Ω・cm content 99%. Manufactured by AGC SI Tech)
- Copper foil with carrier material: Copper foil with carrier material in which copper foil with a thickness of 2.5 μm is formed on a copper carrier material with a thickness of 12 μm by electrolytic smelting.

[Example 1]
A resin composition was obtained by adding 100 parts of a binder resin, 30 parts of an epoxy compound, and 7.5 parts of an aziridine curing agent in terms of solid content, and stirring with a disper for 10 minutes. The obtained resin composition was coated on the copper foil with carrier material to a dry thickness of 11 μm using a bar coater, and dried in an electric oven at 100° C. for 2 minutes to form a protective layer. . A pre-laminate was then obtained by laminating a slightly adhesive releasable sheet to the protective layer.

Next, the carrier material of the copper foil with carrier material was peeled off, the copper foil surface was buffed, and the arithmetic mean height Sa and root mean square slope Sdq of the copper foil surface were adjusted to the values shown in Table 1.

Thereafter, 100 parts of binder resin, 80 parts of conductive filler, 20 parts of epoxy compound, and 0.5 part of aziridine compound were charged into a container in terms of solid content, and a mixed solvent (toluene : isopropyl alcohol=2:1 (mass ratio)) and stirred with a disper for 10 minutes to prepare an adhesive composition. The obtained adhesive composition was coated on the copper foil surface of the pre-laminated body described above so that the dry thickness was 8 μm using a bar coater, and the laminated body was obtained by drying in an electric oven at 100 ° C. for 2 minutes. Ta.

Laser light irradiation (UV-YAG laser, irradiation wavelength 355 nm, Model 5330, manufactured by ESI) was performed from the pre-adhesive layer side of the produced laminate to form an array of island portions as shown in the first embodiment. , an adhesive layer having communicating voids extending in the X direction and the Y direction was obtained. In FIG. 2, the minor axis W1 of the gap between adjacent island portions in the X direction was 1500 μm, and the minor axis W2 of the gap between adjacent island portions in the Y direction was 1500 μm. Further, the length L1 of the island portion in the X direction and the length L2 of the island portion in the Y direction were both 1250 μm. It was confirmed that the copper foil was exposed in the area where the communicating gap was formed. 75% by volume of the adhesive layer is a communicating void. Through these steps, an electromagnetic shielding sheet having the structure of "slightly adhesive releasable sheet/protective layer/copper foil/adhesive layer" was obtained.

[Examples 2 to 8, 10 to 14, 19 to 21, Comparative Example 1]
Electromagnetic shielding sheets according to Examples 2 to 8, 10 to 14, 19 to 21, and Comparative Example 1 were obtained in the same manner as in Example 1, except that the conditions were changed to those shown in Tables 1 to 3.

[Example 9]
A resin composition was obtained by adding 100 parts of a binder resin, 30 parts of an epoxy compound, 7.5 parts of an aziridine compound, and 31.4 parts of non-conductive particles in terms of solid content, and stirring with a disper for 10 minutes. The obtained resin composition was coated on a releasable sheet using a bar coater to a dry thickness of 11 μm, and dried in an electric oven at 100° C. for 2 minutes to form a protective layer.

Next, a copper plating layer (2.5 μm), which is a metal layer, was formed on the surface of the obtained “peelable sheet/protective layer” where the protective layer was exposed. The copper plating layer was formed by electrolytic plating. The electrolytic solution used was copper sulfate, and a current was applied for 7 minutes at 25°C.

A pre-adhesive layer was attached to the surface of the formed metal layer, and then laser light was irradiated in the same manner as in Example 1 to form an adhesive layer having communicating voids. Through these steps, an electromagnetic shielding sheet consisting of "releasable sheet/protective layer/metal layer (plating layer)/adhesive layer/releasable sheet" was obtained. The metal layer and the pre-adhesive layer were bonded together using a thermal laminator at a temperature of 90° C. and a pressure of 3 kgf/cm ² . The other methods were the same as in Example 1.

[Example 15]
Example 15 differs from Example 1, etc., in that the shape of the communicating void is a pore, which is a groove. The adhesive layer was obtained by laminating a 1.0 μm pre-adhesive layer, a 6.0 μm opening diameter pre-adhesive layer, and a 1.0 μm pre-adhesive layer in this order. The pore diameter was 6.0 μm, and the distance between adjacent pores was 0.5 μm in each of the X and Y directions. 74.5% by volume of the adhesive layer was a continuous void.

[Example 16]
Example 16 differs from Example 1 and the like in that the shape of the communicating gap is a slit, which is a groove. The shape of the slit in a side view is trapezoidal as shown in FIG. 8, and the slit is formed in a concave shape from the first main surface 5 (the surface to be bonded to the adherend) of the adhesive layer. A similar communication gap is also formed in the X direction. By using the same method as in the above example except that ablation was performed at a lower power than when forming the groove, a connection was made in which the minor axis W1 (bottom) of the slit bottom was 200 μm and the minor axis W1 (top) of the top of the slit opening was 300 μm. A void was obtained. A similar slit-shaped communicating gap was also formed in the X direction in FIG. The lengths of the island portions in the X and Y directions were each 290 μm. 75.3% by volume of the adhesive layer was a continuous void.

[Example 17]
Example 17 differs from Example 1 and the like in which grooves were formed in the X and Y directions in that the communication gap was formed in one direction. The groove-shaped communication gap extends in the Y direction, as shown in FIG. The short axis W1 of the groove-shaped communicating gap was 300 μm, and the length of the island portion in the L1 direction was 103 μm. 74.0% by volume of the adhesive layer was a continuous void.

[Example 18]
In Example 18, the communication gap is formed as a groove in one direction, and as shown in FIG. It is different from Example 17 in that it is formed. The groove-shaped communication gap extends in the Y direction, as shown in FIG. The short axis W1 of the groove-shaped communicating gap was 300 μm, and the long axis of the communicating gap was 14,000 μm. Further, the length of the island portion in the L1 direction was set to 290 μm. 75.0% by volume of the adhesive layer was a continuous void.

Regarding the obtained electromagnetic shielding sheet, the thickness of each layer, the arithmetic mean height Sa of the metal layer, and the root mean square slope Sdq were measured by the following method.
In addition, in the above Examples and Comparative Examples, if the target values of the arithmetic mean height Sa and root mean square slope Sdq of the copper foil surface are different from the values of the carrier material, the surface may be polished or roughened by buffing as appropriate. The arithmetic mean height Sa and the root mean square slope Sdq were adjusted by performing the following as appropriate.

《Measurement of each layer thickness》
The thicknesses of the adhesive layer, metal layer, and protective layer of the electromagnetic shielding sheet were measured by the following method.
The releasable sheet on the adhesive layer side of the electromagnetic shielding sheet was peeled off, and the exposed adhesive layer and polyimide film (Kapton 200EN, manufactured by DuPont-Toray) were bonded together and heat pressed at 2 MPa and 170°C for 30 minutes. . After cutting this into a size of about 5 mm in width and 5 mm in length, 0.05 g of epoxy resin (Petropoxy 154, manufactured by Marto) was dropped onto a slide glass, an electromagnetic shield sheet was attached, and the slide glass/electromagnetic shield A laminate having a sheet/polyimide film configuration was obtained. The obtained laminate was cut by ion beam irradiation from the polyimide film side using a cross-section polisher (manufactured by JEOL Ltd., SM-09010) to obtain a measurement sample of a heat-pressed electromagnetic shielding sheet.

The cross section of the obtained measurement sample was observed using a laser microscope (manufactured by Keyence Corporation, VK-X100), and the thickness of each layer was measured from the enlarged image. The magnification was 500 to 2000 times.

<<Measurement of arithmetic mean height Sa and root mean square slope Sdq of metal layer>>
The arithmetic mean height Sa and root mean square slope Sdq of the metal layer of the electromagnetic shielding sheet were measured by the following method.
Adhesive tape ("CT1835" manufactured by Nichiban Co., Ltd.) is pasted on the exposed adhesive layer of the electromagnetic shielding sheet, leaving the edges of the adhesive tape intact, and the adhesive layer/adhesive tape is peeled off from the edge of the adhesive tape. Peel off. The adhesive layer was removed and the surface of the exposed metal layer was measured using a laser microscope (manufactured by Keyence Corporation, VK-X100) to obtain measurement data.
The acquired measurement data was imported into analysis software (analysis application "VK-H1XA" equipped with ISO 25178 surface texture measurement module "VK-H1XR", both manufactured by Keyence Corporation), and ISO 25178 surface texture measurement was performed (conditions were as follows: S-filter: 1 μm, L-filter: 0.2 mm). Note that for metal layers having openings on the surface, the openings were excluded from the measurement range when performing ISO 25178 surface texture measurement.

The following evaluations were performed using the obtained electromagnetic shield sheet. The results are shown in Tables 1 to 3.

<Solder reflow resistance>
Solder reflow resistance was evaluated based on the presence or absence of a change in appearance after the electromagnetic shielding sheet was brought into contact with molten solder. An electromagnetic shielding sheet with high resistance to solder reflow does not change its appearance, but an electromagnetic shielding sheet with low resistance to solder reflow causes appearance defects such as blistering and peeling.
First, peel off the removable sheet of the adhesive layer of the electromagnetic shielding sheet with a width of 25 mm and a length of 70 mm, and remove the exposed adhesive layer and the gold-plated copper clad laminate with a total thickness of 64 μm (gold plating 0.3 μm/nickel plating). The gold-plated surfaces of 1 μm/copper foil 18 μm/adhesive 20 μm/polyimide film 25 μm were pressed together under conditions of 170° C., 2.0 MPa, and 30 minutes, and then thermosetted to obtain a laminate. The obtained laminate was cut to a size of 10 mm in width and 65 mm in length to prepare a sample. The obtained sample was left in an atmosphere of 40° C. and 90% RH for 72 hours. After that, the sample was floated on molten solder at 250°C for 1 minute with the polyimide film side facing down, and then the sample was taken out and the appearance of the sample protective layer surface was visually observed to check for appearance defects such as blistering, lifting, and peeling. Evaluation was made based on the following criteria.
+++: No defective change in appearance is visually observed. Very good.
++: The extent of appearance defects is 10% or less of the area of the protective layer in the sample. In good condition.
+: The range of appearance defects is wider than 10% and 30% or less of the area of the protective layer in the sample. Practical.
NG: The range of appearance defects is wider than 30% of the area of the protective layer in the sample.
Not practical.

<Transmission characteristics>
The transmission characteristics were evaluated using a flexible printed wiring board 20g having a coplanar circuit with an electromagnetic shielding sheet shown in FIG.

FIG. 10 shows a schematic plan view of the main surface of 20 g of a flexible printed wiring board with a coplanar circuit (hereinafter also referred to as a wiring board with a coplanar circuit) used in the measurement, and FIG. 11 shows a schematic plan view of the back side. shows. First, a double-sided CCL "R-F775" (manufactured by Panasonic) was prepared, in which rolled copper foil with a thickness of 12 μm was laminated on both sides of a polyimide film 50 with a thickness of 50 μm. Then, six through holes 51 (diameter 0.1 mm) were provided near each of the four corners of the rectangle. In addition, in the figure, for convenience of illustration, only two through holes 51 are shown at each corner portion. Next, after performing an electroless plating process, an electrolytic plating process is performed to form a 10 μm copper plating film 52 to ensure conduction between the main surface and the back surface via the copper plating film formed in the through hole 51. did. Thereafter, as shown in FIG. 10, two signal wires 53 each having a length of 10 cm are formed on the main surface of the polyimide film 50, and a ground wire 54 parallel to the signal wires 53 extends from the ground wire 54 on the outside thereof. A ground pattern (i) 55 was formed in the region including the through hole 51 in the transverse direction of the polyimide film 50.

Thereafter, the copper foil formed on the back surface of the polyimide film 50 was etched to obtain a back ground pattern (ii) 56 as shown in FIG. 11 at a position corresponding to the ground pattern (i) 55. The circuit appearance and tolerance inspection specifications were based on the JPCA standard (JPCA-DG02). Next, on the main surface side of the polyimide film 50, a cover coat layer 26g "CISV1215 (manufactured by Nikkan Kogyo Co., Ltd.)" consisting of a polyimide film (thickness 12.5 μm) and an insulating adhesive layer (thickness 15 μm) is applied. pasted. In addition, in FIG. 10, the cover coat layer 26g is shown in a perspective view so that the structure of the signal wiring 53 and the like can be seen. Thereafter, the copper foil pattern exposed from the cover coat layer 26g was nickel plated (not shown), and then gold plated (not shown).

Next, as shown in FIG. 12, 10 g of an electromagnetic shielding sheet made of a laminate of an adhesive layer 1, a metal layer 2, and a protective layer 3 is prepared, and a release treatment sheet provided on the adhesive layer of the electromagnetic shielding sheet 10g is prepared. (not shown) was removed. Then, a coplanar circuit with an electromagnetic shielding layer is formed by pressing the adhesive layer of 10 g of the electromagnetic shielding sheet on the back surface side of the wiring board 25 having the coplanar circuit under the conditions of 170° C., 2.0 MPa, and 30 minutes. 20 g of a flexible printed wiring board was obtained. In FIG. 12, the back side ground pattern (ii) 56 is shown in a perspective view.

Note that the L/S (line/space) of the signal wiring 53 was appropriately adjusted so that the characteristic impedance was within ±10Ω. The width of the ground wiring 54 was 100 μm, and the distance between the ground wiring 54 and the signal wiring 53 was 1 mm.

Connect network analyzer E5071C (manufactured by Agilent Japan) to the exposed signal wiring 53 of the flexible printed wiring board 20g that has a coplanar circuit with an electromagnetic shielding sheet, input a 15 GHz sine wave, and measure the transmission loss. Characteristics were evaluated. The measured transmission characteristics were evaluated based on the following criteria.
+++: Transmission loss at 15 GHz is less than 7.0 dB. Very good.
++: Transmission loss at 15 GHz is 7.0 dB or more and less than 7.5 dB. In good condition.
+: Transmission loss at 15 GHz is 7.5 dB or more and less than 8.0 dB. Practical.
NG: Transmission loss at 15 GHz is 8.0 dB or more. Not practical.

<Reworkability>
Reworkability was evaluated based on the remaining area of the adhesive layer and the arithmetic average height when the electromagnetic shielding sheet temporarily attached to polyimide was peeled off. The adhesive layer of the electromagnetic shielding sheet cut out to a width of 50 mm and a length of 50 mm was laminated to a polyimide film (Kapton 300H) cut out to a width of 70 mm and a length of 70 mm, and then laminated using a roll laminator (conveying speed: 1 m/min, temperature: 90 mm). ℃ and pressure: 3 kgf/cm ² ) for temporary pasting. The electromagnetic shielding sheet in the obtained temporarily pasted laminate was peeled off from the end, and the adhesive residue rate was calculated by dividing the area of the adhesive remaining on the polyimide by the area of the adhesive before lamination. Next, select five arbitrary points from the remaining adhesive area, use a laser microscope (manufactured by Keyence Corporation, VK-X100) to acquire measurement data on the surface, and analyze the acquired measurement data using analysis software (ISO 25178 surface texture). It was imported into the analysis application "VK-H1XA" equipped with the measurement module "VK-H1XR" (both manufactured by Keyence Corporation), the ISO25178 surface texture measurement was performed, and the arithmetic mean height was calculated (the conditions were S-filter; 1 μm, L-filter; 0.2 mm). Using the adhesive residue rate and arithmetic average height thus obtained, evaluation was made according to the following criteria.
+++: If the adhesive residue rate is 5% or less, and if there is a portion with adhesive residue, the arithmetic mean height thereof is less than 20% of the adhesive layer thickness. Very good.
++: The adhesive residue rate is more than 5% and less than 15%, and the arithmetic average height is less than 20% of the adhesive layer thickness. In good condition.
+: The adhesive residue rate is 15% or less, and the arithmetic average height of the adhesive remaining portion is 20 to 50% of the adhesive layer thickness. Practical.
NG: The adhesive residue rate is greater than 15%, and/or the arithmetic mean height of the adhesive remaining portion is greater than 50% of the adhesive layer thickness. Not practical.

1 Adhesive layer 2 Metal layer 3 Protective layer 4 Communication gap 5 First main surface 6 Second main surface 7 Side surface 8 Communication gap 9 Bonding layer 10 Electromagnetic shielding sheet 15 Electromagnetic shielding layer 20 Printed wiring board 22 Insulating base material 23 Signal wiring 24 Ground wiring 25 Wiring board 26 Cover coat layer 27 Wired circuit board 28 Via 30 Adherent with electromagnetic shielding layer 31 Adherent 50 Polyimide film 51 Through hole 52 Copper plating film 53 Signal wiring 54 Ground wiring 55 Ground pattern (i)
56 Back side ground pattern (ii)

Claims (6)

It has a laminate including a protective layer, a metal layer, and an adhesive layer in this order,
The adhesive layer has a plurality of communicating voids ,
The communicating gap extends to one side of the adhesive layer, and the short axis, which is the opening diameter of the communicating gap, is 100 to 1500 μm . The communication gap is a groove that penetrates from the first main surface of the adhesive layer to a second main surface opposite to the first main surface, and is formed inside the adhesive layer, and is formed in the first main surface or A slit formed in a concave shape from either one of the second main surfaces to the inside of the adhesive layer, a pore that is not exposed to the first main surface and the second main surface, and the groove, the slit, and the narrow pore. The electromagnetic shielding sheet according to claim 1, characterized in that it includes at least one of an opening formed by an arbitrary combination of holes. The electromagnetic shielding sheet according to claim 2, wherein the adhesive layer is divided into a plurality of island parts by the grooves. The electromagnetic shielding sheet according to claim 1, wherein the adhesive layer exhibits conductivity. A wiring board with signal wiring formed on an insulating base material,
an insulating cover coat layer formed on the wiring board;
an electromagnetic shielding layer formed on the cover coat layer,
The electromagnetic shielding layer is formed from the electromagnetic shielding sheet according to any one of claims 1 to 4 ,
The electromagnetic wave shielding layer has communicating voids originating from the communicating voids of the electromagnetic shielding sheet,
In the printed wiring board, the communicating void extends to at least one side of the electromagnetic shielding layer . Step A of forming an electromagnetic shielding sheet having a laminate including a protective layer, a metal layer, and an adhesive layer in this order;
Step B of forming an insulating cover coat layer on a wiring board with signal wiring formed on an insulating base material;
Step C of placing the electromagnetic shielding sheet on the cover coat layer and forming an electromagnetic shielding layer by thermocompression bonding,
The step A includes a step of forming a plurality of communicating voids extending to at least one side in the adhesive layer,
A method for manufacturing a printed wiring board, comprising forming a communicating gap derived from the communicating gap in the electromagnetic shielding layer.

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