Conductive composition

Abstract

A conductive composition comprising an epoxy resin, a curing agent, and metal particles, wherein: a liquid epoxy resin and a solid epoxy resin are contained as the epoxy resin; high-melting-point metal particles that contain a metal having a melting point of not lower than 800°C and low-melting-point metal particles that contain a metal having a melting point of not higher than 240°C are contained as the metal particles; and, in the particle size distribution of the low-melting-point metal particles, D10 is 3-20 μm and D90 is 8-30 μm.

Description

conductive composition CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from Japanese Patent Application No. 2023-193360, the entire disclosure of which is incorporated herein by reference.

[0002] The present invention relates to an electrically conductive composition.

[0003] 2. Description of the Related Art Conventionally, as an EMC measure for electronic devices, a shield is formed to block electromagnetic waves that may become noise.

[0004] For example, semiconductor packages typically include a resin encapsulant that protects electronic elements such as ICs, and a shielding layer that covers the encapsulant. Some semiconductor packages are known to have a shielding layer that is electrically connected to a ground circuit exposed through the encapsulant. Such a shielding layer stabilizes the ground potential, facilitating the release of radiated noise and enhancing the shielding effect.

[0005] Meanwhile, a method using a conductive composition that is liquid at room temperature, such as a conductive paste containing metal particles and a resin that can be cured by heat or light, is known as a method that satisfies the recent demand for more compact electronic devices and can form a shielding layer more easily than methods that require vacuum conditions, such as sputtering. For example, Patent Document 1 describes a method in which a conductive composition containing epoxy resin, silver powder, and a curing agent is applied to the exposed end of a ground circuit together with a sealing material, and then the conductive composition is heated to harden, thereby forming a shielding layer that is electrically connected to the ground circuit.

[0006] International Publication No. 2019 / 198336

[0007] Such a shielding layer is required to have adhesion to an adherend having both a resinous portion and a metallic portion, that is, this type of conductive composition is required to provide not only a shielding effect but also adhesion to an adherend having both a resinous portion and a metallic portion.

[0008] In view of the above circumstances, an object of the present invention is to provide a conductive composition capable of forming a shielding layer that has sufficient shielding effect and adhesion to an adherend that has both a resinous portion and a metallic portion.

[0009] The conductive composition according to the present invention comprises an epoxy resin, a curing agent, and metal particles, the epoxy resin comprising a liquid epoxy resin and a solid epoxy resin, the metal particles comprising high-melting-point metal particles containing a metal having a melting point of 800°C or higher and low-melting-point metal particles containing a metal having a melting point of 240°C or lower, and the particle size distribution of the low-melting-point metal particles has a D10 of 3 μm or more and a D90 of 8 μm or more and a D90 of 8 μm or more and a 30 μm or less.

[0010] In the conductive composition according to one aspect of the present invention, the liquid epoxy resin is preferably a glycidylamine-type epoxy resin, the curing agent is preferably a blocked polyisocyanate, and the solid epoxy resin is more preferably a novolac-type epoxy resin.

[0011] In the conductive composition according to one aspect of the present invention, the mass ratio of the high-melting-point metal particles to the low-melting-point metal particles is 0.2 to 5.

[0012] In the conductive composition according to one aspect of the present invention, the high-melting-point metal particles are in a flake shape.

[0013] The conductive composition according to one embodiment of the present invention further includes a flux.

[0014] As described above, according to the present invention, it is possible to provide a conductive composition capable of forming a shielding layer that has sufficient shielding effect and adhesion to an adherend that has both a resinous portion and a metallic portion.

[0015] Although the use of the conductive composition of the present invention is not particularly limited, the following description will be given taking as an example a case where the adherend is a semiconductor package. That is, the conductive composition according to the embodiment of the present invention will be described by exemplifying a conductive composition for forming a shielding layer that imparts electromagnetic shielding function to a semiconductor package.

[0016] The conductive composition of this embodiment is used as a material for forming an electromagnetically shielded semiconductor package that includes a semiconductor package and a shielding layer that covers a part or all of the semiconductor package.

[0017] The semiconductor package may contain only a semiconductor chip, or may be called a semiconductor module containing a semiconductor chip and other elements. The semiconductor package may be, for example, a box-shaped, flat package having a first surface facing a substrate on which the semiconductor chip is mounted, a second surface opposite the first surface, and a side surface connecting the outer periphery of the second surface with the outer periphery of the first surface, and a thickness, which is the dimension from the first surface to the second surface, that is smaller than the dimensions (length and width) of the first surface and the second surface in the planar direction.

[0018] The semiconductor package according to this embodiment includes a package substrate, a semiconductor chip mounted on the package substrate, a resin encapsulant that encapsulates the semiconductor chip, a ground circuit whose leading edge is exposed from a side surface of the encapsulant, and a shielding layer that covers the encapsulant while conducting electrical conductivity with the ground circuit. The semiconductor package according to this embodiment includes an insulating region made of a resin composition and having electrical insulation properties, and a conductive region made of a metal material (conductive material) that constitutes the ground circuit and has electrical conductivity. The semiconductor package according to this embodiment includes, for example, a covered surface in which part or all of the second surface and part or all of the side surface are covered with a conductive composition (shielding layer), and the covered surface has the conductive region. The shielding layer has a top surface portion that covers the second surface along the extension direction of the package substrate, and a side surface portion that extends from the top surface portion to the package substrate. The side surface portion and the top surface portion are continuous via corners of the semiconductor package, and the side surface portion and the top surface portion are electrically connected. The electromagnetically shielded semiconductor package of this embodiment is configured to absorb electromagnetic waves by converting them into an induced potential in the shielding layer, and then release the resulting induced potential through the ground circuit, thereby providing a shielding effect.

[0019] The conductive composition of this embodiment is configured to be sprayable onto the sealing material, and after being applied to the sealing material, is cured to form the shielding layer. When the conductive composition of this embodiment is applied, a coating film for forming the upper surface portion of the shielding layer and a coating film for forming the side surface portion are formed.

[0020] The conductive composition of this embodiment includes a curable resin composition and metal particles. The curable resin composition is liquid before being cured. In this specification, the term "liquid" does not only mean a low-viscosity composition that exhibits fluidity under the action of gravity at room temperature (25°C), but also includes a semi-solid state such as a paste state.

[0021] The curable resin composition of the present embodiment includes an epoxy resin, a curing agent, a solvent, and any additives. The curable resin composition has reaction curing properties, and in this embodiment, has thermosetting properties.

[0022] The curable resin composition of the present embodiment contains, as the epoxy resin, a liquid epoxy resin and a solid epoxy resin.

[0023] The liquid epoxy resin is an epoxy resin that is liquid at room temperature (25°C). The mass average molecular weight of the liquid epoxy resin is, for example, 150 to 500. The epoxy equivalent of the liquid epoxy resin is preferably 90 to 500 g / eq, more preferably 90 to 250 g / eq. On the other hand, the solid epoxy resin is an epoxy resin that is solid at room temperature (25°C). The mass average molecular weight of the solid epoxy resin is, for example, 900 to 60,000. The epoxy equivalent of the solid epoxy resin is, for example, 150 to 10,000 g / eq, or may be 150 to 5,000 g / eq, 150 to 3,000 g / eq, 150 to 2,000 g / eq, or 150 to 1,000 g / eq. The solid epoxy resin preferably has a softening point of 50°C or higher.

[0024] Examples of the liquid epoxy resin include bisphenol-type epoxy resins such as bisphenol A-type epoxy resins and bisphenol F-type epoxy resins; glycidyl ether-type epoxy resins such as 4-hydroxybutyl acrylate glycidyl ether; glycidylamine-type epoxy resins such as N,N-diglycidyl-4-glycidyloxyaniline and 4,4'-methylenebis(N,N-diglycidylaniline); aliphatic epoxy resins, etc. The curable resin composition may also contain an epoxy resin as a reactive diluent that is liquid at room temperature (25°C), such as butyl glycidyl ether, 2-ethylhexyl glycidyl ether, or 1,6-hexanediol diglycidyl ether. The liquid epoxy resin is preferably a glycidylamine type epoxy resin, more preferably an aromatic glycidylamine type epoxy resin having a glycidyl group bonded to the amino group of an aromatic amine, such as N,N-diglycidyl-4-glycidyloxyaniline or 4,4'-methylenebis(N,N-diglycidylaniline), and even more preferably an aminophenol type epoxy resin having a glycidyl group bonded to the amino group and a glycidyl group bonded to the hydroxyl group of an aminophenol, such as N,N-diglycidyl-4-glycidyloxyaniline.

[0025] Examples of the solid epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, naphthalene type epoxy resin (specifically, naphthol type epoxy resin), biphenyl type epoxy resin (specifically, biphenol type epoxy resin), terpene type epoxy resin (specifically, terpenol type epoxy resin), brominated bisphenol A type epoxy resin, glycidyl ether type epoxy resin such as tris(glycidyloxyphenyl)methane and tetrakis(glycidyloxyphenyl)ethane; 5,12-dioxahexacyclo[7.6.1.0(2,8).0(4,6).0(10,15).0(11,13)]hexadecane, 5,12-dioxaheptacyclo[7.6.1.1(3,7).0(2,8).0(4,6).0(10,15). Examples of suitable epoxy resins include alicyclic epoxy resins such as 2-(2-(2-(2-(2-(2-(2-(2-(2-(2-(2-(2-(2-(2-(2-(2-(2-(2-(2-(2-(2-(2-(2-(2-(3 ...

[0026] The solid epoxy resin is preferably a novolac epoxy resin, and more preferably a bisphenol A novolac epoxy resin. The bisphenol A novolac epoxy resin preferably has the following repeating structure: R １ and R ２ is preferably a linear or branched alkyl group having 1 to 5 carbon atoms. １ and R ２are the same and are either a methyl group, an ethyl group, a propyl group, or a butyl group. ３ is a functional group containing an epoxy group, specifically a glycidyl group. n is an integer of 1 to 5, preferably 2 to 4. Furthermore, the bisphenol A novolac epoxy resin preferably has a softening point of 60°C or higher. The softening point can be measured by the method specified in JIS K 2531.

[0027] In the combination of the liquid epoxy resin and the solid epoxy resin, both preferably have an aromatic ring. More specifically, it is preferable that the liquid epoxy resin be an aromatic glycidyl amine-type epoxy resin, and the solid epoxy resin be the glycidyl ether-type epoxy resin or the novolac-type epoxy resin containing bisphenol. This combination of a solid epoxy resin and a liquid epoxy resin results in a shielding layer with a well-balanced electrical conductivity and adhesion, which is a cured product. Furthermore, warping of the shielding layer relative to the substrate is reduced, improving smoothness, and facilitating the production of a highly reliable shielding package with excellent heat resistance. It is believed that the improved heat resistance and adhesion of the shielding layer are primarily due to the novolac-type epoxy resin, which is the solid epoxy resin. It is also believed that the improved electrical conductivity and reduced warping of the shielding layer are primarily due to the glycidyl ether-type epoxy resin, which is the liquid epoxy resin.

[0028] The total content of the liquid epoxy resin and the solid epoxy resin is preferably 90% by mass or more, and more preferably 95% by mass or more, relative to the epoxy resin. The content of the liquid epoxy resin and the solid epoxy resin may be 100% by mass, relative to the epoxy resin. The mass ratio of the liquid epoxy resin to the solid epoxy resin is preferably 4:6 to 9.5:0.5, and more preferably 5:5 to 9.5:0.5. The inclusion of a predetermined amount of the liquid epoxy resin improves dischargeability from the nozzle of a spray gun, forming a coating film in which each component is uniformly dispersed, and the inclusion of a predetermined amount of the solid epoxy resin can impart sufficient adhesion to the shielding layer.

[0029] Examples of the curing agent include an isocyanate-based curing agent, a phenol-based curing agent, an imidazole-based curing agent, and an amine-based curing agent. The curing agent is preferably an isocyanate-based curing agent. The isocyanate-based curing agent is preferably an aliphatic diisocyanate that is liquid at room temperature, such as hexamethylene diisocyanate.

[0030] As described above, in this embodiment, a glycidylamine-type epoxy resin such as N,N-diglycidyl-4-glycidyloxyaniline is preferably used as a liquid epoxy resin. This type of epoxy resin has low viscosity, making it suitable as a constituent material for the conductive resin composition that constitutes the coating liquid sprayed onto the semiconductor package. It also has the advantage of being capable of low-temperature curing. However, this type of epoxy resin may undergo self-polymerization due to the presence of a tertiary amine in its molecular structure, which may shorten the pot life of the conductive resin composition. Therefore, a blocked polyisocyanate having two or more blocked isocyanate groups in its molecule is preferably used as the isocyanate-based curing agent. Blocked polyisocyanates (blocked HDIs) in which the isocyanate groups, such as hexamethylene diisocyanate, are more preferred.

[0031] Examples of the blocking agent for the blocked polyisocyanate include oxime compounds, alcohol compounds, acid amide compounds, acid imide compounds, phenol compounds, amine compounds, active methylene compounds, imidazole compounds, and pyrazole compounds.

[0032] Examples of the oxime compounds include formaldoxime, acetaldoxime, acetoxime, methyl ethyl ketoxime, and cyclohexanone oxime.

[0033] Examples of the alcohol compounds include methanol, ethanol, 2-propanol, n-butanol, sec-butanol, 2-ethyl-1-hexanol, 2-methoxyethanol, 2-ethoxyethanol, and 2-butoxyethanol.

[0034] Examples of the acid amide compounds include acetanilide, acetic acid amide, ε-caprolactam, δ-valerolactam, and γ-butyrolactam.

[0035] Examples of the acid imide compounds include succinimide and maleimide.

[0036] Examples of the phenolic compounds include phenol, cresol, ethylphenol, butylphenol, nonylphenol, dinonylphenol, styrenated phenol, and hydroxybenzoic acid esters.

[0037] Examples of the amine compounds include diphenylamine, aniline, carbazole, di-n-propylamine, diisopropylamine, and isopropylethylamine.

[0038] Examples of the active methylene compounds include dimethyl malonate, diethyl malonate, methyl acetoacetate, ethyl acetoacetate, and acetylacetone.

[0039] Examples of the imidazole compounds include imidazole and 2-methylimidazole.

[0040] Examples of the pyrazole compounds include pyrazole, 3-methylpyrazole, and 3,5-dimethylpyrazole.

[0041] The content of the curing agent is preferably 3 parts by mass or more and 150 parts by mass or less, and more preferably 4 parts by mass or more and 130 parts by mass or less, relative to 100 parts by mass of the epoxy resin. With such a content, electrical continuity between the ground circuit and the shielding layer is improved.

[0042] The curable resin composition may contain a cationic polymerization initiator. The cationic polymerization initiator generates a strong acid when heated, and this strong acid initiates the polymerization reaction of the epoxy resin. Examples of the cationic polymerization initiator include salts of aromatic sulfonium with inorganic anions such as tetrafluoroborate, hexafluoroantimonate, and hexafluorophosphate, and salts of aromatic sulfonium salts with borates having fluorophenyl groups, such as tetrafluoroborate in which some of the fluoro groups have been substituted with pentafluorophenyl groups. The content of the cationic polymerization initiator is preferably 0.5 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the epoxy resin.

[0043] Examples of the solvent include ketone-based solvents such as methyl ethyl ketone, acetone, and acetophenone, ether-based solvents such as tetrahydrofuran, methyl cellosolve, ethyl cellosolve, butyl cellosolve, methyl carbitol, ethyl carbitol, butyl carbitol, and ethylene glycol monomethyl ether, ester-based solvents such as methyl acetate, ethyl acetate, ethylene glycol monomethyl ether acetate, and 3-methoxy-3-methyl-1-butyl acetate, and alcohol-based solvents such as 1-methoxy-2-propanol and diethylene glycol dimethyl ether. The curable resin composition may contain only one type of solvent, or may contain multiple types of solvents.

[0044] The content of the solvent is preferably 100 parts by mass or more and 2000 parts by mass or less, more preferably 300 parts by mass or more and 1800 parts by mass or less, and even more preferably 500 parts by mass or more and 1500 parts by mass or less, relative to 100 parts by mass of the epoxy resin. The solvent is not particularly limited, but is preferably an aqueous solvent. Examples of the aqueous solvent include alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, n-amyl alcohol, isoamyl alcohol, sec-amyl alcohol, tert-amyl alcohol, 1-ethyl-1-propanol, 2-methyl-1-butanol, n-hexanol, and cyclohexanol; ketones such as methyl ethyl ketone, methyl isobutyl ketone, ethyl butyl ketone, and cyclohexanone; ethers such as tetrahydrofuran and dioxane; ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, sec-butyl acetate, and 3-methyl acetate. esters such as butyl ether, methyl propionate, ethyl propionate, diethyl carbonate, and dimethyl carbonate; glycol derivatives such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, and ethylene glycol ethyl ether acetate; 1-methoxy-2-propanol, 1-ethoxy-2-propanol, 3-methoxy-3-methyl-1-butanol, methoxybutanol, acetonitrile, dimethylformamide, dimethylacetamide, diacetone alcohol, ethyl acetoacetate, 1,2-dimethylglycerin, 1,3-dimethylglycerin, and trimethylglycerin.

[0045] In the curable resin composition, it is preferable that the solid epoxy resin is dissolved in the solvent, since this is preferable for spray applications and makes it easier for the shielding layer to exhibit its overall performance. Note that in the curable resin composition, the solid epoxy resin may be suspended in the solvent without being (completely) dissolved.

[0046] The curable resin composition of the present embodiment further includes a flux as the additive. The flux of the present embodiment includes an activator as an active ingredient. The flux can remove an oxide film from copper used to form the ground circuit and suppress oxidation at the joint between the ground circuit and the shielding layer.

[0047] Examples of the activator include carboxylic acids such as dicarboxylic acids such as sebacic acid, adipic acid, glutaric acid, succinic acid, malonic acid, 8-ethyloctadecanedioic acid, and pimelic acid, tricarboxylic acids such as citric acid, and aromatic carboxylic acids such as benzoic acid; alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine; and salts of the carboxylic acids and the alkanolamines.

[0048] The content of the activator is preferably 10 parts by mass or more and 200 parts by mass or less, more preferably 20 parts by mass or more and 180 parts by mass or less, and even more preferably 30 parts by mass or more and 150 parts by mass or less, relative to 100 parts by mass of the epoxy resin.

[0049] Examples of the other additives include colorants such as pigments, plasticizers, flame retardants, antioxidants, antifoaming agents, adhesion promoters, leveling agents, rheology control agents, fillers, etc. The content of the other additives is, for example, 0.5 to 20 parts by mass relative to 100 parts by mass of the epoxy resin.

[0050] The conductive composition of this embodiment contains, as the metal particles, high-melting-point metal particles containing a metal with a melting point of 800°C or higher, and low-melting-point metal particles containing an alloy of a metal with a melting point of 240°C or lower.

[0051] At least the surface layer of the high-melting-point metal particles is preferably made of a metal capable of forming an alloy with the molten low-melting-point metal. Examples of metals that form the surface layer include copper, silver, nickel, and gold. The high-melting-point metal particles may have core particles made of copper, nickel, or silver (which may contain unavoidable impurities). When the high-melting-point metal particles have core particles made of copper or nickel, the core particles are preferably coated with silver or gold. Examples of such high-melting-point metal particles include copper particles, nickel particles, silver particles, silver-coated copper particles, gold-coated copper particles, silver-coated nickel particles, and gold-coated nickel particles.

[0052] The high-melting-point metal particles are preferably in the form of flakes.

[0053] The median diameter (D50) of the high-melting point metal particles is preferably 0.5 μm or more and 30 μm or less. The median diameter (D50) of the high-melting point metal particles may be 1 μm or more, 2 μm or more, or 3 μm or more. The median diameter (D50) of the high-melting point metal particles may be 25 μm or less, 20 μm or less, or 15 μm or less.

[0054] The low-melting-point metal particles of this embodiment are made of a lead-free alloy containing Sn as the primary component (which may contain unavoidable impurities). Examples of the alloy include those containing Sn as the primary component and one or more elements selected from Bi, Ag, In, Ni, Cu, Zn, Ga, Sb, Au, Pa, Ge, Cr, Al, P, Cd, Tl, Si, Mg, and Pb. Examples of the alloy include Sn-Bi, Sn-Zn, Sn-Zn-Bi, Sn-In, Sn-Sb, Sn-Cu, Sn-Cu-Ni, Sn-Cu-Bi, Sn-Ag, and Sn-Ag-Cu alloys. The melting point of the alloy is preferably 200°C or lower, and more preferably 150°C or lower. When the phase diagram of the alloy shows both a solidus and a liquidus, the alloy preferably has a liquidus melting point of 200°C or less, more preferably a liquidus melting point of 150°C or less, even more preferably a solidus melting point of 200°C or less, and even more preferably a solidus melting point of 150°C or less. By having the alloy have a melting point of 200°C or less, even when used in combination with a resin composition that hardens upon heating at a relatively low temperature, such as the curable resin composition of this embodiment, the low-melting-point metal can melt and diffuse between the high-melting-point metal particles, forming an alloy with the high-melting-point metal so as to cover the high-melting-point metal particles. Furthermore, due to its excellent heat resistance, such an alloy can impart long-term reliability to the electrical conductivity between the shielding layer and the ground circuit.

[0055] The alloy is preferably a Sn—Bi alloy having a relatively low melting point. Among the Sn—Bi alloys, those having a mass ratio of Sn to Bi of 40:60 to 50:50 are more preferred. Because the melting point at the liquidus of such an Sn—Bi alloy is relatively low, it has excellent diffusibility between high-melting-point metal particles and can provide good electrical conductivity and long-term reliability.

[0056] The particle size distribution of the low-melting-point metal particles has a D10 of 3 μm or more and a D90 of 8 μm or more and a D90 of 8 μm or more and a D10 of 30 μm or less. The particle size distribution of the low-melting-point metal particles preferably has a D10 of 3 μm or more and a D90 of 8 μm or more and a D90 of 8 μm or more and a D10 of 3 μm or more and a D90 of 8 μm or more. When the particle size distribution of the low-melting-point metal particles has a D10 of 3 μm or more and a D90 of 8 μm or more, the conductivity of the shielding layer is increased and the ground potential can be stabilized, thereby improving the shielding effect of the shielding layer. Specifically, when the low-melting-point metal particles have a D10 of 3 μm or more and a D90 of 8 μm or more, an alloy layer is formed between the shielding layer and the ground circuit, which increases the conductivity, stabilizes the ground potential, and enhances the shielding effect of the shielding layer. Additionally, the formation of the alloy layer suppresses the occurrence of cracks due to heat cycles, thereby improving the reliability of the shielded package. Furthermore, by having a D10 of 30 μm or less and a D90 of 10 μm or less in the particle size distribution of the low-melting-point metal particles, the adhesion of the shielding layer, particularly the adhesion of the side portions of the shielding layer to the sealing material of the semiconductor package, can be improved. Specifically, by having a D10 of 20 μm or less and a D90 of 30 μm or less of the low-melting-point metal particles, it is believed that the occurrence of pinholes in the shielding layer is suppressed, conductivity is increased, the ground potential is stabilized, and the shielding effect of the shielding layer is enhanced. Note that D10, D50, and D90 refer to the particle diameters at which the cumulative values ​​on the particle size distribution curve reach 10%, 50%, and 90%, respectively. The particle diameters of the high-melting-point metal particles and the low-melting-point metal particles can be determined from the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method.

[0057] When the low-melting-point metal particles are metal particles mainly composed of Sn, those with a small specific surface area are advantageous in consideration of the formation of an oxide film on the surface. On the other hand, when the high-melting-point metal particles are metal particles whose surfaces are made of silver, gold, or the like, an oxide film is less likely to form. For this reason, when the median diameter (D50) of the low-melting-point metal particles is "D50L" and the median diameter (D50) of the high-melting-point metal particles is "D50H," the low-melting-point metal particles may be prepared so that the median diameter (D50L) is larger than the median diameter (D50) of the high-melting-point metal particles, for example, such that the relationship "(D50L) > (D50H)" holds between the two.

[0058] It is preferable that the particle sizes of the low-melting-point metal particles and the high-melting-point metal particles are not too different. Therefore, when the D90 of the high-melting-point metal particles is "D90H" and the D10 of the low-melting-point metal particles is "D10L", the two may be prepared so that the relationship "D90H≦D10L" holds. Furthermore, when the D90 of the low-melting-point metal particles is "D90L", the two may be prepared so that the relationship "(1.1×D50H)≦D90L≦(4.0×D50H)" holds, or the relationship "(1.1×D50H)≦D90L≦(3.0×D50H)" holds.

[0059] The content of the high-melting-point metal particles is preferably 100 to 10,000 parts by mass, more preferably 300 to 9,000 parts by mass, even more preferably 400 to 8,500 parts by mass, still more preferably 500 to 8,000 parts by mass, and particularly preferably 1,000 to 5,000 parts by mass, relative to 100 parts by mass of the epoxy resin. On the other hand, the content of the low-melting-point metal particles is preferably 400 to 25,000 parts by mass, more preferably 400 to 21,000 parts by mass, even more preferably 400 to 10,000 parts by mass, particularly preferably 400 to 5,000 parts by mass, and particularly preferably 500 to 5,000 parts by mass, relative to 100 parts by mass of the epoxy resin. The mass ratio of the high-melting-point metal particles to the low-melting-point metal particles is preferably 0.1 to 5, and more preferably 0.2 to 4. By including a predetermined amount of the high-melting-point metal particles and the low-melting-point metal particles, the conductivity of the shielding layer is improved, thereby improving the shielding effect and also ensuring long-term reliability.

[0060] The content of the metal particles is preferably 1,000 parts by mass or more and 10,000 parts by mass or less with respect to 100 parts by mass of the epoxy resin.

[0061] It is preferable that the content of the metal particles is 1,500 parts by mass or more and 10,000 parts by mass or less per 100 parts by mass of the epoxy resin, and the mass ratio of the high-melting-point metal particles to the low-melting-point metal particles is 1 to 4.

[0062] The viscosity of the conductive composition is preferably 0.1 to 5 Pa·s, more preferably 0.3 to 4 Pa·s, and even more preferably 0.5 to 3 Pa·s. When the viscosity is equal to or greater than a predetermined value, dripping of the uncured coating film in the sealing material is suppressed, thereby suppressing shielding unevenness. Furthermore, when the viscosity is equal to or less than a predetermined value, clogging of the nozzle during spraying is suppressed, allowing the formation of a coating film in which the solid components are uniformly dispersed, thereby resulting in a shielding layer with high shielding effect. Note that the viscosity can be measured using a cone-plate viscometer at 25°C and a shear rate of 10 (1 / sec).

[0063] Although one embodiment has been shown above as an example, the conductive composition according to the present invention is not limited to the configuration of the above embodiment. Furthermore, the conductive composition according to the present invention is not limited by the above-mentioned effects. The conductive composition according to the present invention can be modified in various ways without departing from the gist of the present invention.

[0064] The present disclosure includes the following: [1] A conductive composition comprising an epoxy resin, a curing agent, and metal particles, wherein the epoxy resin comprises a liquid epoxy resin and a solid epoxy resin, and the metal particles comprise high-melting-point metal particles containing a metal having a melting point of 800°C or higher and low-melting-point metal particles containing a metal having a melting point of 240°C or lower, and wherein the low-melting-point metal particles have a particle size distribution having a D10 of 3 μm or more and a D90 of 8 μm or more and a D90 of 8 μm or more and a D10 of 8 μm or more and a D90 of 8 μm or more and a D90 of 30 μm or more.

[0065] The shielding layer formed by curing such a conductive composition exhibits adhesion to the resinous portions of the adherend due to the binder formed from the liquid epoxy resin and the solid epoxy resin. Furthermore, this shielding layer exhibits adhesion to the metal portions of the adherend due to the low-melting-point metal particles melting and adhering to the metal portions of the adherend. Furthermore, this shielding layer has an enhanced shielding effect due to the high-melting-point metal particles being bonded by the molten low-melting-point metal particles, providing a good electrical connection. Furthermore, this shielding layer exhibits enhanced shielding effect and enhanced adhesion to adherends having both resinous and metal portions due to the low-melting-point metal particles having a D10 of 3 μm or more and a D90 of 8 μm or more and 30 μm or less.

[0066] [2] The conductive composition according to the above [1], wherein the liquid epoxy resin is a glycidyl amine type epoxy resin.

[0067] The shielding layer formed from such a conductive composition can fully exhibit the above-mentioned performance.

[0068] [3] The conductive composition according to the above [1] or [2], wherein the curing agent is a blocked polyisocyanate.

[0069] The shielding layer formed from such a conductive composition can fully exhibit the above-mentioned performance.

[0070] [4] The conductive composition according to any one of the above [1] to [3], wherein the solid epoxy resin is a novolac type epoxy resin.

[0071] The shielding layer formed from such a conductive composition can fully exhibit the above-mentioned performance.

[0072] [5] The conductive composition according to any one of the above [1] to [4], wherein the mass ratio of the high melting point metal particles to the low melting point metal particles is 0.2 to 5.

[0073] Such a conductive composition can provide the shielding layer with reliability against heat cycles.

[0074] [6] The conductive composition according to any one of the above [1] to [5], wherein the high-melting-point metal particles are in the form of flakes.

[0075] Such a conductive composition can provide the shielding layer with excellent adhesion and reliability against heat cycles.

[0076] [7] The conductive composition according to any one of the above [1] to [6], further comprising a flux.

[0077] Such a conductive composition can improve the adhesion of the shielding layer to the metal portion of the adherend.

[0078] The present invention will be further explained below with reference to examples, but the present invention is not limited to these examples.

[0079] [Raw materials used] Liquid epoxy resin: glycidylamine type epoxy resin (manufactured by ADEKA Corporation, EP-3950S, epoxy equivalent 95 g / eq, 650 mPa·s) Solid epoxy resin: bisphenol A novolac type epoxy resin (manufactured by Mitsubishi Chemical Corporation, JER157S70, consisting of the four above repeating units) １ and R ２is a methyl group and R ３ glycidyl group, epoxy resin, epoxy equivalent 200 to 220 g / eq) High melting point metal particle 1: silver-coated copper powder, flake-shaped, D50: 5 μm High melting point metal particle 2: silver powder, flake-shaped, D50: 5 μm High melting point metal particle 3: silver-coated copper alloy (Cu-Ni-Zn alloy), flake-shaped, D50: 5 μm High melting point metal particle 4: silver-coated copper powder, spherical, D50: 5 μm Low melting point metal particle 1: Sn-Bi alloy (Sn:Bi=42:58), D10: 5 μm, D90: 11.7 μm Low melting point metal particle 2: Sn-Bi alloy (Sn:Bi=42:58), D10: 3.8 μm, D90: 9 μm Low-melting point metal particles 3: Sn—Bi alloy (Sn:Bi=42:58), D10: 8.8 μm, D90: 17.5 μm Low-melting point metal particles 4: Sn—Bi alloy (Sn:Bi=42:58), D10: 2.1 μm, D90: 6.6 μm Low-melting point metal particles 5: Sn—Bi alloy (Sn:Bi=42:58), D10: 20.6 μm, D90: 40 μm Curing agent: hexamethylene diisocyanate (blocked polyisocyanate having diethyl malonate as a blocking agent, manufactured by Asahi Kasei Corporation, Duranate WM44-L70G) Flux activator: triethanolamine Solvent: 1-methoxy-2-propanol

[0080] [Production Examples] Conductive compositions were prepared by blending the components in the blending ratios shown in Tables 1 to 3.

[0081] [Evaluation 1: Electrical Conductivity] Each conductive composition was used to form a 20 μm thick coating film in an area of ​​150 mm x 150 mm on a polyimide sheet, and after pre-curing at 100°C for 10 minutes, the film was heated at 190°C for 50 minutes to prepare a cured product of the conductive composition. The resistance value of each cured product was measured using a surface resistance measuring tool (milliohm high tester) and evaluated according to the following evaluation criteria. The results are as shown in Tables 1 to 3. (Evaluation Criteria) Pass: Resistance value of the cured product is 500 mΩ or less

[0082] [Evaluation 2: Electric Field Shielding Effect] Each conductive composition was used to form a 20 μm thick coating film in an area of ​​150 mm × 150 mm on a polyimide sheet, and after pre-curing at 100° C. for 10 minutes, the film was heated at 190° C. for 50 minutes to prepare a cured product of the conductive composition. The electric field shielding effect per 1 GHz of each cured product was measured using the KEC method. (Evaluation Criteria) Pass: The electric field shielding effect of the cured product was 60 dB or more.

[0083] [Evaluation 3: Adhesion - Presence or absence of side pinholes] Using a spray coating device SL-940E (manufactured by Nordson Asymtek), the conductive composition was sprayed onto the sealing material of an IC package, and then temporarily cured at 100°C for 10 minutes, and then heated at 190°C for 50 minutes to cure, forming a shielding layer with a thickness of approximately 20 μm. The IC package on which the coating film was formed was cut and molded with acrylic resin. After molding, the cut surface was polished, and the thickness of the shielding layer on the top surface of the IC package (thickness of the top surface of the shielding layer) and the thickness of the shielding layer on the side surface (thickness of the side surface of the shielding layer) were measured using a microscope. (Evaluation criteria) Pass: Thickness of top surface / thickness of side surface is 3.0 or less

[0084] [Evaluation 4: Adhesion - Cross-Cut Method] Using a spray coating device SL-940E (manufactured by Nordson Asymtek), a conductive composition was sprayed onto the encapsulant of an IC package, pre-cured at 100°C for 10 minutes, and then heated at 190°C for 50 minutes to cure, forming a shielding layer approximately 20 μm thick. The adhesion of the shielding layer was evaluated based on ASTM D 3359 (cross-cut method). (Evaluation Criteria) 5B: The edges of the cuts were completely smooth, and there was no peeling at any of the grid squares. 4B: Small peeling of the coating occurred at the intersections of the cuts. The cross-cut area was clearly affected by no more than 5%. 3B: The coating peeled along the edges and / or at the intersections of the cuts. The cross-cut area was clearly affected by more than 5% but not more than 15%. 2B: The coating has partially or completely peeled off significantly along the edges of the cuts and / or various sections of the mesh have partially or completely peeled off. In the cross-cut areas, more than 15% but not more than 35% is clearly affected. 1B: The coating has partially or completely peeled off significantly along the edges of the cuts and / or several sections have partially or completely peeled off. In the cross-cut areas, not more than 35% is clearly affected. 0B: Any degree of peeling that cannot be classified into the above four categories.

[0085] [Evaluation 5: Reliability] As a heat cycle test, each sample obtained in Evaluation 3 was subjected to 1,000 cycles of heat cycles consisting of 30 minutes at -65°C and 30 minutes at 125°C. Resistance was measured on the PAD electrodes of the IC package before and after the heat cycle test using a surface resistance measuring tool (milliohm high tester). The resistance measured before the test was designated a and the resistance measured after the test was designated b, and the rate of change in resistance (rate of change in resistance) before and after the heat cycle test was calculated using the following formula: Rate of change in resistance (%) = (b - a) × 100 / a (Evaluation criteria) A rate of change in resistance within ±20% was evaluated as having excellent reliability.

[0086]

[0087]

[0088]

Claims

1. A conductive composition comprising an epoxy resin, a curing agent, and metal particles, the epoxy resin comprising a liquid epoxy resin and a solid epoxy resin, the metal particles comprising high-melting-point metal particles containing a metal having a melting point of 800°C or higher and low-melting-point metal particles containing a metal having a melting point of 240°C or lower, the particle size distribution of the low-melting-point metal particles having a D10 of 3 μm or more and a D90 of 8 μm or more and 30 μm or less.

2. The conductive composition according to claim 1, wherein the liquid epoxy resin is a glycidyl amine type epoxy resin.

3. The conductive composition of claim 2, wherein said curing agent is a blocked polyisocyanate.

4. The conductive composition according to any one of claims 1 to 3, wherein the solid epoxy resin is a novolac type epoxy resin.

5. The conductive composition according to any one of claims 1 to 3, wherein the mass ratio of said high melting point metal particles to said low melting point metal particles is 0.2 to 5.

6. The conductive composition according to any one of claims 1 to 3, wherein the high melting point metal particles are in the form of flakes.

7. The conductive composition according to any one of claims 1 to 3, further comprising a flux.

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