Conductive adhesive layer

Abstract

The present disclosure aims to provide an electrically conductive adhesive layer, which is excellent in connection stability of adherends of electrically conductive members to each other, and can maintain the connection stability even in the case of applying high temperature. The electrically conductive adhesive layer (1) is an electrically conductive adhesive layer including a binder component (11) and electrically conductive particles (12), the electrically conductive particles (12) containing electrically conductive particles A (12a) having a median diameter of 100% or more with respect to the thickness (T) of the electrically conductive adhesive layer (1), and electrically conductive particles B (12b) having a median diameter of 1 to 50% with respect to the median diameter of the electrically conductive particles A (12a), the content of the electrically conductive particles (12) being 110 to 900 parts by mass with respect to 100 parts by mass of the binder component (11), and the mass ratio [electrically conductive particles A / electrically conductive particles B] of the electrically conductive particles A (12a) and the electrically conductive particles B (12b) being 0.1 to 7.2.

Description

Technical Field

[0001] This invention relates to conductive adhesive layers. Background Technology

[0002] In electronic devices such as mobile phones, cameras, and laptops, printed circuit boards (PCBs) are primarily used for assembling circuits within mechanisms. They are also used to connect movable parts like printheads to control units. These electronic devices require electromagnetic shielding, and the PCBs used within these devices are shielded PCBs with implemented electromagnetic shielding measures.

[0003] As an example of the shielding printed circuit board, it has the following structure: on a substrate film containing printed circuits, the electromagnetic wave shielding film, on which an adhesive (adhesive layer), a metal film and an insulating layer are sequentially stacked, is placed in such a way that the adhesive surface of the electromagnetic wave shielding film is tightly sealed, and then the adhesive is bonded to the substrate film by heating and pressing (thermal bonding).

[0004] The aforementioned printed circuit boards are used to mount electronic components. Flexible printed circuit boards (FPCs) are known among printed circuit boards. Because electronic components can easily detach from FPCs due to bending at the mounting points, reinforcing members are sometimes provided on the printed circuit board to prevent this. Among these reinforcing members, those capable of grounding to an external potential are sometimes used to allow electromagnetic waves that intrude into or are generated within the printed circuit board to escape to the outside. For example, Patent Document 1 discloses a printed circuit board with reinforcing members, including conductive reinforcing members and a conductive adhesive.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2013-41869 Summary of the Invention

[0008] The conductive adhesive layer (conductive adhesive sheet) used in printed circuit boards with conductive reinforcing components is mostly an isotropic conductive adhesive layer.

[0009] However, isotropic conductive adhesive layers tend to have higher resistance in the thickness direction due to the large amount of contact resistance in the conductive particles. On the other hand, anisotropic conductive adhesive layers contain fewer conductive particles than isotropic conductive adhesive layers. This results in insufficient conductive particles filling the openings in the electromagnetic wave shielding film used to ensure continuity between the grounding circuit and the installation side. Consequently, the conductivity of the grounding circuit and the reinforcing components on the grounding side tends to decrease, leading to poorer connection stability. Since a smaller opening diameter results in fewer conductive particles filling the opening, the decrease in connection stability is more significant. Furthermore, even with good initial connection stability, conductivity may decrease when high temperatures are applied during processes such as reflow.

[0010] Therefore, the purpose of this disclosure is to provide a conductive adhesive layer that enables excellent bonding stability between adhered components that are conductive parts, and maintains bonding stability even under high temperature conditions.

[0011] This disclosure provides a conductive adhesive layer, which comprises adhesive components and conductive particles.

[0012] The aforementioned conductive particles include conductive particles A, whose median diameter is 100% or more of the thickness of the aforementioned conductive adhesive layer, and conductive particles B, whose median diameter is 1 to 50% of the median diameter of conductive particles A.

[0013] The content of the aforementioned conductive particles is 110 to 900 parts by mass relative to 100 parts by mass of the aforementioned binder component.

[0014] The mass ratio of the aforementioned conductive particle A to the aforementioned conductive particle B [conductive particle A / conductive particle B] is 0.1 to 7.2.

[0015] The conductive particle A is preferably a metal particle with a 20% compressive strength of 1.0 to 25 MPa at 170°C.

[0016] The shape of the aforementioned conductive particle A is preferably spherical.

[0017] The shape of the aforementioned conductive particles B is preferably sheet-like or dendritic.

[0018] The conductive adhesive layer disclosed herein provides excellent connection stability between the adhered components, which are conductive parts, even under high temperatures. Therefore, when used, for example, in bonding a grounding circuit to a reinforcing member on the grounding side, the connection stability between the grounding circuit and the reinforcing member on the grounding side is excellent, even with a small opening diameter. Attached Figure Description

[0019] Figure 1 This is a cross-sectional view showing one embodiment of the conductive adhesive layer of this disclosure.

[0020] Figure 2 This is a cross-sectional view showing one embodiment of a printed circuit board with reinforcing members in which the conductive adhesive layer of this disclosure is applied. Detailed Implementation

[0021] [Conductive adhesive layer]

[0022] The conductive adhesive layer disclosed herein includes at least an adhesive component and conductive particles. Furthermore, the conductive particles comprise conductive particles (conductive particle A) whose median diameter is 100% or more of the thickness of the conductive adhesive layer, and conductive particles (conductive particle B) whose median diameter is 1 to 50% of the median diameter of conductive particle A. Only one of the adhesive component, conductive particle A, and conductive particle B may be used, or two or more may be used.

[0023] Figure 1 This illustrates one embodiment of the conductive adhesive layer of the present disclosure. The conductive adhesive layer (1) is layered (sheet-like) and includes an adhesive component (11) and conductive particles (12). The conductive particles (12) contain conductive particles A (12a) and conductive particles B (12b). At least a portion of the conductive particles A (12a) protrudes from the surface of the adhesive portion composed of the adhesive component (11).

[0024] (Conductive particle A)

[0025] As described above, the conductive adhesive layer contains conductive particles A whose median diameter (D50) is 100% or more relative to the thickness of the conductive adhesive layer. It should be noted that the thickness of the conductive adhesive layer refers to the thickness in the region where the conductive particles of the adhesive portion constituted by the adhesive component do not protrude before the adhesive component flows (e.g., the thickness in the region where the conductive particles do not protrude). Figure 1 (The thickness T shown). Furthermore, in this specification, the median diameter of the conductive particle A refers to its median diameter in its uncompressed state when the conductive particle A is compressed. The median diameter of the conductive particle A is preferably 150% or more, more preferably 200% or more, and even more preferably 250% or more, relative to the thickness of the conductive adhesive layer. By making the median diameter of the conductive particle A 100% or more, the particle size of the conductive particle A is sufficiently thick relative to the thickness of the adhesive layer, and even when the conductive particle A penetrates the opening of the electromagnetic wave shielding film by causing the adhesive components to flow through heating or the like, the conductivity in the thickness direction of the conductive adhesive layer is excellent.

[0026] The median diameter of the conductive particle A is preferably 1000% or less, more preferably 900% or less, even more preferably 750% or less, and particularly preferably 500% or less, relative to the thickness of the conductive adhesive layer. If the median diameter of the conductive particle A is 1000% or less, the adhesion strength to the adhered objects is superior.

[0027] The median diameter of the conductive particle A is preferably 1–90 μm, more preferably 5–75 μm, and even more preferably 10–45 μm. If the median diameter is 1 μm or more, the conductivity in the thickness direction can be better utilized using the conductive particle A. In addition, the conductive particles have good dispersibility and can suppress agglomeration. If the median diameter is 90 μm or less, the adhesive strength of the conductive adhesive layer to the adhered object is even better.

[0028] Examples of conductive particles A include metal particles, metal-coated resin particles, metal fibers, carbon fillers, and carbon nanotubes.

[0029] Examples of metals constituting the coating portion of the aforementioned metal particles and the aforementioned metal-coated resin particles include gold, silver, copper, nickel, zinc, indium, tin, lead, bismuth, and alloys containing two or more of these. Only one of these metals may be used, or two or more may be used.

[0030] Specifically, examples of the aforementioned metal particles include, for instance, copper particles, silver particles, nickel particles, silver-coated copper particles, indium particles, tin particles, lead particles, bismuth particles, gold-coated copper particles, silver-coated nickel particles, gold-coated nickel particles, indium-coated copper particles, tin-coated copper particles, lead-coated copper particles, bismuth-coated copper particles, indium-coated nickel particles, tin-coated nickel particles, bismuth-coated nickel particles, and silver-coated alloy particles. For example, silver-coated copper alloy particles are formed by coating copper-containing alloy particles (e.g., copper alloy particles composed of an alloy of copper, nickel, and zinc) with silver. These metal particles can be produced by electrolysis, atomization, reduction, or other methods.

[0031] As the conductive particle A, it is preferably a metal particle with a 20% compressive strength of 1.0 to 25 MPa at 170°C. More preferably, the compressive strength is 5.0 to 23 MPa, and even more preferably 11 to 22 MPa. If the conductive particle A is a metal particle with a compressive strength within the above range, the particle can be moderately compressed while maintaining its shape when high pressure is applied at high temperatures, resulting in better conductivity in the thickness direction. The 20% compressive strength of the aforementioned metal particle was measured according to JIS Z 8844:2019. It should be noted that the aforementioned compressive strength refers to the compressive strength of the conductive particle A in its state before compression.

[0032] The conductive particles A preferably contain at least tin as a constituent metal. The proportion of tin in the conductive particles A relative to 100% by mass of the total amount of conductive particles A is preferably 80% by mass or more, more preferably 85% by mass or more, further preferably 90% by mass or more, and particularly preferably 94% by mass or more. It is presumed that the tin in the conductive particles A will form an alloy at the interface with the conductive adherends (grounding circuit, grounding side reinforcement, etc.) during hot pressing. Therefore, if the conductive particles A contain 80% by mass or more (especially 90% by mass or more) of tin, the connection stability between the adherends can be maintained even when high temperatures are applied in processes such as reflow. The above-mentioned content ratio is preferably 99.9% by mass or less, more preferably 99.6% by mass or less. If the above-mentioned content ratio is 99.9% by mass or less, the conductive particles A have a certain degree of hardness, and when high pressure is applied in a high-temperature environment, the conductive particles A are not excessively compressed, making it easy to ensure the conductivity between the adherends.

[0033] The constituent metals of the aforementioned tin-containing metal particles may also include other metals besides tin. Examples of these other metals include gold, silver, copper, platinum, nickel, zinc, lead, palladium, bismuth, antimony, and indium. From the viewpoint of superior bonding stability, it is preferable to include metals that are harder than tin, such as gold, silver, copper, platinum, nickel, and palladium. Each of these other metals may be contained in only one form or in two or more forms.

[0034] Examples of shapes for conductive particles A include spherical (perfect sphere, ellipsoid, etc.), plate-like (scale-like, flat), dendritic (dendritic), fibrous, and irregular shapes (polyhedrons). Among these, spherical shapes are preferred from the perspective of superior conductivity in the thickness direction.

[0035] The proportion of conductive particles A in the aforementioned conductive adhesive layer relative to 100% by mass of the total conductive adhesive layer is preferably 10-70% by mass, more preferably 15-60% by mass, and even more preferably 20-50% by mass. If the above-mentioned proportion is 10% by mass or more, the conductivity in the thickness direction becomes better. If the above-mentioned proportion is 70% by mass or less, the flexibility of the conductive adhesive layer is excellent.

[0036] (Conductive particle B)

[0037] As described above, the conductive adhesive layer contains conductive particles B whose median diameter is 1 to 50% of the median diameter of conductive particles A. The median diameter of conductive particles B relative to the median diameter of conductive particles A is preferably 5 to 30%, more preferably 8 to 20%. By ensuring the median diameter of conductive particles B is within the above range, the resistivity in the planar direction of the conductive adhesive layer can be reduced, achieving isotropic conductivity. By combining this isotropic conductivity with the anisotropic conductivity based on conductive particles A, excellent bonding stability between the adhered materials is achieved even under high temperatures.

[0038] The median diameter of the conductive particles B is preferably 0.5–25 μm, more preferably 3–10 μm. If the median diameter is 0.5 μm or more, the isotropic conductivity is better utilized. Furthermore, the conductive particles exhibit good dispersibility and can suppress agglomeration. If the median diameter is 25 μm or less, the adhesive strength of the conductive adhesive layer to the adhered objects is even more excellent.

[0039] As conductive particle B, examples such as metal particles, metal-coated resin particles, metal fibers, carbon fillers, and carbon nanotubes can be cited, similar to the examples and descriptions of conductive particle A described above.

[0040] As the conductive particle B, metal particles are preferred, and silver particles, silver-coated copper particles, and silver-coated copper alloy particles are particularly preferred. From the viewpoint of excellent conductivity, suppression of oxidation and aggregation of conductive particles, and reduction of the cost of conductive particles, silver-coated copper particles and silver-coated copper alloy particles are especially preferred.

[0041] Examples of shapes for conductive particles B include spherical (perfect sphere, ellipsoid, etc.), plate-like (scale-like, flat), dendritic (dendritic), fibrous, and irregular shapes (polyhedrons). Among these, plate-like and dendritic shapes are preferred. The reason is as follows: By making the conductive particles B plate-like or dendritic, it is easier to arrange the conductive particles B in an overlapping manner, thereby increasing the contact between the conductive particles B and improving the conductivity in the planar direction. If the conductivity in the planar direction is improved, the conductivity in the thickness direction of the conductive particles A is combined, and the overall conductivity (electrical stability) of the conductive adhesive layer is improved, further enhancing the bonding stability between the adhered materials.

[0042] The proportion of conductive particles B in the aforementioned conductive adhesive layer relative to 100% by mass of the total conductive adhesive layer is preferably 10-70% by mass, more preferably 15-60% by mass, and even more preferably 20-50% by mass. If the above-mentioned proportion is 10% by mass or more, isotropic conductivity is better utilized, and anisotropic conductivity is more fully utilized. If the above-mentioned proportion is 70% by mass or less, the conductive adhesive layer exhibits excellent flexibility.

[0043] The mass ratio of conductive particle A to conductive particle B [conductive particle A / conductive particle B] is 0.1 to 7.2, preferably 0.2 to 5.2, more preferably 0.3 to 4.0, and even more preferably 0.5 to 2.7. Since the mass is within the above range, the anisotropic conductivity of conductive particle A and the isotropic conductivity of conductive particle B can be balanced, resulting in excellent conductivity in the thickness direction of the conductive adhesive layer. Even under high temperatures, the connection resistance is unlikely to increase, and the bonding stability between the adhered components is excellent.

[0044] The content (total amount) of the conductive particles in the conductive adhesive layer is 110 to 900 parts by mass relative to 100 parts by mass of the total adhesive components, preferably 120 to 700 parts by mass, more preferably 150 to 500 parts by mass, and even more preferably 150 to 300 parts by mass. By setting the content to 110 parts by mass or more, the content of conductive particles becomes sufficient, and even under high temperatures, it is difficult for the connection resistance value to increase, resulting in excellent connection stability between the adhered components. By setting the content to 900 parts by mass or less, the contact opportunity between conductive particles can be suppressed, the increase in resistance value can be suppressed, and the conductivity in the thickness direction is excellent. Furthermore, the conductive adhesive layer exhibits excellent flexibility and formability.

[0045] (Adhesive components)

[0046] Examples of adhesive components include thermoplastic resins, thermosetting resins, and active energy line curing compounds. Examples of thermoplastic resins include polystyrene-based resins, vinyl acetate-based resins, polyester-based resins, polyolefin-based resins (e.g., polyethylene-based resins, polypropylene-based resin compositions, etc.), polyimide-based resins, and acrylic resins. Only one type of thermoplastic resin may be used, or two or more types may be used.

[0047] Examples of thermosetting resins include both thermosetting resins and resins obtained by curing the aforementioned thermosetting resins. Examples of thermosetting resins include phenolic resins, epoxy resins, polyurethane resins, melamine resins, and alkyd resins. Only one type of thermosetting resin may be used, or two or more types may be used.

[0048] Examples of epoxy resins mentioned above include bisphenol type epoxy resins, spirocyclic epoxy resins, naphthalene type epoxy resins, biphenyl type epoxy resins, terpene type epoxy resins, glycidyl ether type epoxy resins, glycidyl amine type epoxy resins, and phenolic varnish type epoxy resins.

[0049] Examples of bisphenol-type epoxy resins include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, and tetrabromobisphenol A type epoxy resin. Examples of glycidyl ether type epoxy resins include tris(glycidyloxyphenyl)methane and tetra(glycidyloxyphenyl)ethane. Examples of glycidylamine type epoxy resins include tetraglycidyldiaminodiphenylmethane. Examples of phenolic varnish type epoxy resins include cresol phenolic varnish type epoxy resin, phenolic varnish type epoxy resin, α-naphthol phenolic varnish type epoxy resin, and brominated phenolic varnish type epoxy resin.

[0050] Examples of active energy line curable compounds include compounds cured by irradiation with active energy lines (active energy line curable compounds) and compounds cured by curing the aforementioned active energy line curable compounds. There are no particular limitations on the active energy line curable compound; examples include polymeric compounds having one or more (preferably two or more) free radical reactive groups (e.g., (meth)acryloyl groups) in their molecules. Only one type of active energy line curable compound may be used, or two or more may be used.

[0051] Of the above-mentioned adhesive components, thermosetting resins are preferred. In this case, a conductive adhesive layer is applied to the substrate, such as a printed circuit board or a shielded printed circuit board with electromagnetic wave shielding measures, and then the adhesive component can be cured by applying pressure and heat, resulting in good adhesion of the bonded portion. For example, when the adhesive component is a thermosetting resin, the adhesive component after hot pressing is a thermosetting resin obtained by curing the aforementioned thermosetting resin.

[0052] When the above-mentioned adhesive components contain a thermosetting resin, they may also contain a curing agent for promoting the thermosetting reaction. The curing agent may be appropriately selected based on the type of thermosetting resin. Only one type of curing agent may be used, or two or more types may be used.

[0053] The proportion of the adhesive component in the aforementioned conductive adhesive layer is not particularly limited, but relative to 100% by mass of the total conductive adhesive layer, it is preferably 5 to 50% by mass, more preferably 10 to 45% by mass, and even more preferably 15 to 40% by mass. If the above-mentioned content percentage is 5% by mass or more, the adhesion to the adhered objects is better. If the above-mentioned content percentage is 50% by mass or less, the conductive particles can be fully mixed, and the conductivity in the thickness direction is more excellent.

[0054] To the extent that it does not impair the intended effect of this disclosure, the conductive adhesive layer may also contain other components besides those described above. Examples of these other components include those found in known and conventional adhesives. These other components include, for example, curing accelerators, plasticizers, flame retardants, defoamers, viscosity modifiers, antioxidants, diluents, anti-settling agents, fillers, colorants, leveling agents, coupling agents, UV absorbers, tackifying resins, and anti-blocking agents. Only one of these other components may be used, or two or more may be used. Furthermore, the conductive adhesive layer may also contain conductive particles other than conductive particles A and conductive particles B, but their proportion relative to the total of 100 parts by mass of conductive particles A and conductive particles B is, for example, 10 parts by mass or less, preferably 5 parts by mass or less, and more preferably 1 part by mass or less.

[0055] The thickness of the conductive adhesive layer is preferably 1 to 40 μm, more preferably 5 to 30 μm. If the thickness is 1 μm or more, the adhesion strength between the adhered objects is better. If the thickness is 40 μm or less, costs can be controlled, and products with the conductive adhesive layer can be designed to be thinner. It should be noted that the thickness of the conductive adhesive layer refers to the thickness in areas where conductive particles do not protrude (e.g.,...). Figure 1 The thickness T is shown. Furthermore, when the adhesive component (adhesive component) constituting the conductive adhesive layer flows and penetrates the opening formed in the adhered object through heating or the like, the thickness of the conductive adhesive layer is the thickness of the adhesive layer that does not penetrate the opening area.

[0056] For the aforementioned conductive adhesive layer, the resistance value (initial resistance value) obtained through the following conductivity test is not particularly limited, but is preferably 200 mΩ or less, more preferably 150 mΩ or less, and even more preferably 100 mΩ or less. If the aforementioned initial resistance value is 200 mΩ or less, the adhered objects through the aforementioned conductive adhesive layer have good conductivity with each other.

[0057] [Conductivity Test]

[0058] A conductive adhesive layer was bonded to an SUS board (thickness: 200 μm) by heating and pressurizing it for 5 seconds at 120°C and 0.5 MPa. The conductive adhesive layer side was then bonded to a printed circuit board for evaluation. After vacuuming for 60 seconds using a press, the board was heated and pressurized for 30 minutes at 170°C and 3.0 MPa to prepare the evaluation substrate. The printed circuit board used consisted of two copper foil patterns (thickness: 18 μm, line width: 3 mm) simulating a grounding circuit formed on a substrate component made of a 12.5 μm thick polyimide film. An insulating adhesive (thickness: 13 μm) and a cover layer made of a 25 μm thick polyimide film were formed on these patterns. A circular opening simulating a grounding connection with a diameter of 1 mm was formed on the cover layer. The resistance value between the copper foil patterns and the SUS board was measured using a ohmmeter and used as the resistance value for the evaluation substrate.

[0059] For the aforementioned conductive adhesive layer, after five cycles of a reflow process involving exposure to a 265°C hot air temperature curve for 5 seconds, the resistance value obtained through a conductivity test (reflow resistance value) is not particularly limited, but is preferably 200 mΩ or less, more preferably 150 mΩ or less, and even more preferably 100 mΩ or less. If the resistance value is 200 mΩ or less, the adhered materials through the aforementioned conductive adhesive layer have good conductivity. It should be noted that the reflow resistance value is measured by performing the same conductivity test on the evaluation substrate after five cycles of the aforementioned reflow process, using the same initial resistance value.

[0060] For the aforementioned conductive adhesive layer, the rate of change of its resistance value [(resistance value after reflow - initial resistance value) / initial resistance value × 100] is not particularly limited, but is preferably 50% or less, more preferably 10% or less, and even more preferably 0% or less. If the rate of change of resistance value is 50% or less, it is difficult for the connection resistance value to increase even when high temperatures are applied, and the connection stability between the adhered objects, which are conductive components, is more excellent.

[0061] In the aforementioned conductive adhesive layer, the adhesion strength (peel force) of the gold-plated copper foil laminate, determined by a peel test at room temperature, a tensile speed of 50 mm / min, and a peel angle of 90°, is not particularly limited, but is preferably 4.5 N / cm or higher, more preferably 10 N / cm or higher, and even more preferably 15 N / cm or higher. If the adhesion strength is 4.5 N / cm or higher, the adhesion to the adhered object of the aforementioned conductive adhesive layer is even better. The aforementioned gold-plated copper foil laminate can also be reinforced with a plastic film or the like to prevent it from breaking during the peel test. The specific method for the peel test is as described in the examples below.

[0062] The aforementioned conductive adhesive layer is preferably used in printed circuit boards, and particularly preferably in flexible printed circuit boards (FPCs). This conductive adhesive layer is economical and provides excellent bonding stability between the adhered components, maintaining stability even under high temperatures. Therefore, this conductive adhesive layer is preferably used as an electromagnetic wave shielding film or conductive bonding film for printed circuit boards (especially for FPCs). The aforementioned conductive bonding film is used to mount conductive (metallic) reinforcing plates on printed circuit boards; examples also include grounding connection lead-out films to allow electromagnetic waves intruding into or generated within the printed circuit board to escape to the outside.

[0063] The conductive adhesive layer described above can also be laminated with a separator film on at least one side. That is, the conductive adhesive layer can also be provided as a laminate containing a separator film and the conductive adhesive layer formed on the release surface of the separator film. The separator film is peeled off during use.

[0064] The aforementioned conductive adhesive layer can be manufactured using known and conventional manufacturing methods. For example, an adhesive composition forming the conductive adhesive layer can be coated (applied) onto a temporary substrate or substrate such as a separator membrane, and then, if necessary, desolvated and / or partially cured.

[0065] The adhesive composition described above contains, for example, a solvent in addition to the components included in the conductive adhesive layer. Examples of solvents include toluene, acetone, methyl ethyl ketone, methanol, ethanol, propanol, and dimethylformamide. The concentration of the solid components in the adhesive composition is appropriately set based on the thickness of the formed conductive adhesive layer.

[0066] The above-mentioned adhesive composition can be coated using known coating methods. For example, gravure roller coaters, reverse roller coaters, matching roller coaters, lip coaters, dip roller coaters, bar coaters, doctor blade coaters, spray coaters, comma coaters, direct coaters, slot die coaters, and other coating machines can be used.

[0067] [Printed circuit board with reinforcing components]

[0068] Figure 2 This illustrates an example of applying the aforementioned conductive adhesive layer to a printed circuit board with reinforcing components. For example... Figure 2 As shown, a printed circuit board (X) with a reinforcing member, as one embodiment of a printed circuit board with a reinforcing member, includes: a printed circuit board (3), a conductive adhesive layer (1') disposed on the printed circuit board (3), and a conductive reinforcing member (2) disposed on the conductive adhesive layer (1').

[0069] The printed circuit board (3) has a base component (31), a circuit pattern (32) partially disposed on the surface of the base component (31), an insulating protective layer (33) covering the circuit pattern (32) for insulating protection, and an adhesive (34) covering the circuit pattern (32) and used to bond the circuit pattern (32) and the base component (31) to the insulating protective layer (33). The circuit pattern (32) includes multiple signal circuits (32a) and ground circuits (32b). An opening (through hole) (3a) is formed in the adhesive (34) and the insulating protective layer (33) on the ground circuit (32b) and extends through the thickness direction of the adhesive (34) and the insulating protective layer (33).

[0070] A conductive adhesive layer (1') is bonded to the surface of the insulating protective layer (33) of the printed circuit board (3) in a manner that covers and blocks the opening (3a), and an adhesive component (adhesive component) (11') fills the opening (3a). The conductive adhesive layer (1') is formed by conductive particles A (12a), (12a'), conductive particles B (12b) and adhesive component (adhesive component) (11'). The conductive adhesive layer (1') has a thick film portion that is thicker than the adhesive layer and a thin film portion that is thinner than the adhesive layer. The thick film portion corresponds to the portion that fills the opening (3a), and the thin film portion corresponds to the portion located between the insulating protective layer (33) and the reinforcing member (2). The conductive particles A (12a) in the thick film portion are located between the reinforcing member (2) and the grounding circuit (32b), and preferably contact and conduct between the reinforcing member (2) and the grounding circuit (32b). The thickness of the adhesive layer in the thick film portion is, for example, 50% or more (preferably 70% or more, more preferably 90% or more) relative to the maximum particle size of the conductive particles A (12a) in the adhesive layer thickness direction of the thick film portion. The conductive particles A (12a') in the thin film portion are located between the reinforcing member (2) and the insulating protective layer (33), and are compressed and deformed due to pressure, preferably in contact with the reinforcing member (2) and the insulating protective layer (33). The thickness of the adhesive layer in the thin film portion is, for example, 50% or more (preferably 70% or more, more preferably 90% or more) relative to the maximum particle size of the conductive particles A (12a') in the adhesive layer thickness direction of the thin film portion. With such a structure, the grounding member (32b) and the reinforcing member (2) are connected via the conductive particles (12), the reinforcing member (2) acts as an external conductive layer, and the surface of the reinforcing member (2) is electrically connected to the external grounding member.

[0071] During hot pressing to form a conductive adhesive layer (1'), conductive particles A (12a) penetrate the opening (3a) and fully utilize their conductivity in the thickness direction (anisotropic conductivity). Conductive particles A (12a') that do not penetrate the opening (3a) but exist in the thin film portion also fully utilize their conductivity in the thickness direction (anisotropic conductivity), just like conductive particles A (12a). On the other hand, conductive particles B (12b) exhibit isotropic conductivity. Through this isotropic conductivity, conductive particles A (12a), A (12a'), and B (12b) can exhibit conductivity in both the planar and thickness directions between the particles. Therefore, in the conductive adhesive layer (1'), by combining the anisotropic conductivity of conductive particles A (12a) and (12a') and the isotropic conductivity of conductive particles B (12b), the conductive adhesive layer exhibits excellent conductivity in the thickness direction, resulting in excellent bonding stability between the adhered components and the conductive parts, even under high temperatures. Furthermore, this effect is maintained even when the diameter of the opening (3a) is small.

[0072] For example, the conductive adhesive layer (1) before flow or curing (1') is attached to the surface of the reinforcing member (2) as needed, and then attached to the insulating protective layer (33) in the printed circuit board (3). Then, the adhesive component (11) is heated to flow or cure and hot-pressed, so that the conductive particle A (12a) is sandwiched between the reinforcing member (2) and the insulating protective layer (33) and compressed and deformed to become the conductive particle A (12a'). At the same time, the adhesive component (adhesive component) (11) is bonded to the insulating protective layer (33), and the adhesive component (11) is flowed to fill the opening (3a) with the adhesive component (11), conductive particle A (12a) and conductive particle B (12b). The adhesive component (11') is cured as needed to form the adhesive component (11'). Thus, the conductive adhesive layer (1') can be obtained.

[0073] An electronic component (4) is connected to a mounting portion provided on the surface of the printed circuit board (3) opposite to the reinforcing member (2). The reinforcing member (2) is arranged opposite to the mounting portion of the electronic component (4). Thus, the reinforcing member (2) strengthens the mounting portion of the electronic component (4). The conductive reinforcing member (2) is electrically connected to the grounding circuit (32b) in the printed circuit board (3) via a conductive adhesive layer (1'). Thus, in order to keep the reinforcing member (2) and the grounding circuit (32) at the same potential, the influence of external electromagnetic waves and other noise on the mounting portion of the electronic component (4) is shielded.

[0074] Example

[0075] The conductive adhesive layer of this disclosure will now be described in more detail based on an embodiment, but the conductive adhesive layer of this disclosure is not limited to these embodiments.

[0076] Example 1

[0077] An adhesive composition was prepared by mixing 45.5 parts by weight of bisphenol A type epoxy resin (trade name "jER1256", manufactured by Mitsubishi Chemical Corporation), 0.05 parts by weight of curing agent (trade name "ST14", manufactured by Mitsubishi Chemical Corporation), 24.5 parts by weight of metal particles (composition: Ag3.5 / Cu0.75 / Sn95.75 (numerical values ​​represent mass ratios), 20% compressive strength at 170°C: 20.0 MPa, conductive particle 1, spherical), and 30.0 parts by weight of silver-coated copper powder (conductive particle 2, dendritic) in toluene, bringing the solid content to 20% by weight. The mixture was stirred to prepare the adhesive composition. It should be noted that the median diameter (D50) of conductive particles 1 and 2 used is shown in Table 1. The obtained adhesive composition was applied to the release surface of a PET film that had undergone a release treatment, and the solvent was removed by heating to form a conductive adhesive layer. It should be noted that in Example 1, conductive particle 1 is equivalent to conductive particle A, and conductive particle 2 is equivalent to conductive particle B.

[0078] Examples 2-7 and Comparative Examples 1-4

[0079] The median diameter of the conductive particles, the content of conductive particles, and the thickness of the conductive adhesive layer were varied as shown in Table 1. Otherwise, the conductive adhesive layer was fabricated in the same manner as in Example 1. It should be noted that the median diameter (D50) of the conductive particles used in each example is shown in Table 1. Furthermore, in Examples 2-7, conductive particle 1 corresponds to conductive particle A, and conductive particle 2 corresponds to conductive particle B.

[0080] (evaluate)

[0081] The conductive particles used in the examples and comparative examples, as well as the conductive adhesive layers obtained in the examples and comparative examples, were evaluated as follows. The evaluation results are recorded in Table 1.

[0082] (1) Median diameter

[0083] The median diameter of conductive particles was determined using a flow particle imaging analyzer (trade name "FPIA-3000", manufactured by Sysmex Corporation). Specifically, a conductive particle dispersion with a concentration adjusted to 4000–20000 particles / μl was measured using a 10x objective lens in a bright-field optical system in LPF measurement mode. The conductive particle dispersion was prepared by adding 0.1–0.5 ml of surfactant to a 0.2% (w / w) sodium hexametaphosphate aqueous solution, followed by 0.1 ± 0.01 g of conductive particles as the test sample. The resulting suspension was dispersed in an ultrasonic disperser for 1–3 minutes before measurement. The median diameters of the conductive particles obtained are shown in Table 1.

[0084] (2) Conductivity test

[0085] The conductive adhesive layer prepared in the examples and comparative examples was heated and pressurized for 5 seconds at a temperature of 120°C and a pressure of 0.5 MPa to be bonded to the SUS plate (thickness: 200 μm) of the reinforcing component. The PET film on the conductive adhesive layer was peeled off, and the side of the conductive adhesive layer was bonded to the printed circuit board for evaluation. After vacuuming for 60 seconds using a press, it was heated and pressurized for 30 minutes at a temperature of 170°C and a pressure of 3.0 MPa to prepare the substrate for evaluation. It should be noted that the aforementioned printed circuit board has two parallel copper foil patterns (thickness: 18 μm, line width: 3 mm) spaced apart on a substrate component made of a 12.5 μm thick polyimide film, an insulating adhesive (thickness: 13 μm) covering the copper foil patterns, and an insulating protective layer (thickness: 25 μm) made of a 25 μm thick polyimide film. A cylindrical opening exposing each copper foil pattern is provided on the insulating protective layer. When the conductive adhesive layer is overlapped with the printed circuit board, the opening is completely covered by the conductive adhesive layer. Furthermore, the resistance value between the copper foil patterns of the evaluation substrate and the SUS board, measured using a ohmmeter, is used as the resistance value between the printed circuit board and the SUS board before reflow (initial resistance value). It should be noted that the measurements were performed for four cases with opening diameters of 0.8 mm, 1 mm, 1.4 mm, and 1.8 mm.

[0086] Next, a heat treatment with a reflow design was performed, and the resistance value after reflow was measured. This heat treatment and resistance value measurement were repeated 5 times. The heat treatment was designed to use lead-free solder and set the temperature distribution of the conductive adhesive layer in the evaluation substrate exposed at 265°C for 5 seconds. Then, the initial resistance value was set as "connection resistance value (initial)" and the resistance value after reflow was set as "connection resistance value (5 reflows)", as shown in Table 1.

[0087] (3) Adhesion strength

[0088] Under the conditions of temperature: 120°C, time: 5 seconds, and pressure: 0.5 MPa, the conductive adhesive layer and the SUS metal reinforcing plate (thickness: 200 μm) prepared in the examples and comparative examples were heated and pressurized using a press. After being heated at 150°C for 1 hour, the PET film was peeled off to prepare a metal reinforcing plate with a conductive adhesive layer.

[0089] Next, under the same conditions as the hot-pressing described above, the gold-plated layer of the copper foil laminate was bonded to a metal reinforcing plate with a conductive adhesive layer. Then, the bonding was further performed using a press at a temperature of 170°C, a time of 30 minutes, and a pressure of 3 MPa to produce a copper foil laminate with a metal reinforcing plate. This copper foil laminate comprises a polyimide substrate, copper foil formed on the surface of the substrate, and a gold-plated layer formed on the surface of the copper foil. Next, the copper foil laminate with the metal reinforcing plate was fixed to a testing stage using a double-sided laminating sheet. At room temperature, the copper foil laminate was peeled from the conductive adhesive layer using a tensile testing machine (trade name "AGS-X50S", manufactured by Shimadzu Corporation) at a tensile speed of 50 mm / min and a peel angle of 90°. The maximum peel strength at break was measured. It should be noted that a peel strength of 4.5 N / cm or higher is considered excellent adhesion.

[0090]

[0091] The conductive adhesive layer of the embodiment has a low initial resistance value, indicating excellent connection stability between the adhered components and the conductive parts. Furthermore, its resistance value after reflow is also low, demonstrating good conductivity even under high temperatures. On the other hand, when the median diameter of conductive particle 1 is less than 100% of the thickness of the conductive adhesive layer (Comparative Examples 1 and 3), the resistance values ​​before and after reflow are high when the diameter of the opening is less than 1 mm, indicating poor connection stability. Moreover, even if the median diameter of conductive particle 1 is more than 100% of the thickness of the conductive adhesive layer, if the median diameter of conductive particle 2 is greater than 50% of the median diameter of conductive particle 1 (Comparative Examples 2 and 4), the resistivity after reflow remains high, indicating poor connection stability under high temperatures.

[0092] Industrial availability

[0093] The conductive adhesive layer disclosed herein can be used in the connection of conductive components in electronic components. Attached Figure Description

[0095] X Printed circuit board with reinforcing components

[0096] 1, 1' Conductive adhesive layer

[0097] 11, 11' Adhesive components (adhesive composition)

[0098] 12 conductive particles

[0099] 12a, 12a' conductive particles A

[0100] 12b conductive particles B

[0101] 2. Reinforcing components

[0102] 3 Printed Circuit Board

[0103] 31 Base components

[0104] 32 Circuit Pattern

[0105] 32a signal circuit

[0106] 32b Grounding circuit

[0107] 33 Insulation protective layer

[0108] 34 Adhesives

[0109] 4 Electronic components

Claims

1. A conductive adhesive layer, comprising adhesive components and conductive particles, The conductive particles include conductive particles A and conductive particles B. The median diameter of conductive particle A is more than 100% of the thickness of the conductive adhesive layer, and the median diameter of conductive particle B is 1-50% of the median diameter of conductive particle A. The content of the conductive particles is 110 to 900 parts by weight relative to 100 parts by weight of the binder component. The mass ratio of conductive particle A to conductive particle B [conductive particle A / conductive particle B] is 0.1 to 7.2; The conductive particle A is a metal particle with a compressive strength of 1.0 to 25 MPa at 20% of its weight at 170°C.

2. The conductive adhesive layer according to claim 1, wherein, The conductive particle A is spherical in shape.

3. The conductive adhesive layer according to claim 1 or 2, wherein, The conductive particles B are in the shape of sheets or dendrites.

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