Joining sheet

Abstract

The bonding sheet (1) contains a resin component and solder particles (5). The average primary particle diameter of the solder particles (5) and the average secondary particle diameter of the solder particles (5) are both 7 [mu] m or less.

Description

Technical Field

[0001] The present invention relates to a joining sheet. Background Art

[0002] Conventionally, a bonding sheet has been used to bond terminals of two wired circuit boards that are arranged at a distance in the thickness direction.

[0003] Specifically, first, prepare a first wiring circuit substrate having a plurality of first electrodes arranged in a surface direction, and a second wiring circuit substrate having a plurality of second electrodes arranged in a surface direction. Next, arrange a bonding sheet in a manner that covers the surface of the first wiring circuit substrate provided with the first electrode, and further arrange the second wiring circuit substrate on the surface of the bonding sheet in a manner that covers the surface of the second wiring circuit substrate provided with the second electrode. That is, the first electrode and the second electrode are arranged relative to each other in the thickness direction. Next, heat the bonding sheet. As a result, the solder particles contained in the bonding sheet melt, gather (self-aggregate) between the first electrode and the second electrode, and form a solder portion that electrically connects the first electrode and the second electrode.

[0004] As such a bonding sheet, for example, an anisotropic conductive bonding film containing a solid epoxy resin, a liquid epoxy resin, a flux compound, and solder particles having an average particle size of 7.1 μm has been proposed (for example, see Example 1 of Patent Document 1).

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2021-68842 Summary of the invention

[0008] Problems to be solved by the invention

[0009] On the other hand, the average particle size of the solder particles of Patent Document 1 is as large as 7.1 μm, so the above-mentioned self-aggregation may be uneven, which may cause a problem of reduced reliability.

[0010] The present invention provides a bonding sheet having excellent reliability.

[0011] Means for solving problems

[0012] The present invention [1] is a bonding sheet comprising a resin component and solder particles, wherein the average primary particle size of the solder particles and the average secondary particle size of the solder particles are both 7 μm or less.

[0013] The present invention [2] comprises the bonding sheet described in the above [1], further comprising a soldering flux.

[0014] The present invention [3] comprises the joining sheet described in the above [1], wherein the resin component comprises a thermoplastic resin, and the softening point of the thermoplastic resin is 110° C. or higher.

[0015] The present invention [4] comprises the bonding sheet according to any one of [1] to [3], wherein the viscosity of the resin component at the melting point of the solder particles is 5000 mPa·s or less.

[0016] The present invention [5] comprises the joining sheet described in [1] above, wherein the resin component comprises a thermoplastic resin and a thermosetting resin, the thermoplastic resin is solid at 25°C, and the thermosetting resin is liquid at 25°C.

[0017] The present invention [6] includes the bonding sheet described in the above [1], wherein the average primary particle size of the solder particles and the average secondary particle size of the solder particles are both 5 μm or less.

[0018] The present invention [7] comprises the joining sheet according to any one of [1] to [6] above, wherein the thickness of the joining sheet is 15 μm or less.

[0019] Effects of the Invention

[0020] The bonding sheet of the present invention includes solder particles, and both the average primary particle size and the average secondary particle size of the solder particles are 7 μm or less. Therefore, the reliability can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] [ Figure 1 ] Figure 1 A and Figure 1 B shows an embodiment of a method for producing a joining sheet. Figure 1 A shows a preparation step of preparing a release liner. Figure 1 B shows a placement step of placing the bonding sheet on one surface in the thickness direction of the release liner.

[0022] [ Figure 2 ] Figure 2 A~ Figure 2 E shows one embodiment of a method of using the joining sheet. Figure 2 A shows a first step of preparing a first substrate and a second substrate. Figure 2 B shows the second step of preparing the bonding sheet. Figure 2 C shows the third step of laminating the first substrate, the bonding sheet, and the second substrate. Figure 2 D shows a fourth step of thermocompression bonding the first substrate and the second substrate to the bonding sheet. Figure 2 E shows a fifth step of forming an adhesive layer for solder-bonding the first substrate and the second substrate to the bonding sheet.

[0023] [ Figure 3 ] Figure 3 A and Figure 3 B is a schematic diagram showing a columnar solder portion in the adhesive layer. Figure 3 A shows a mode of electrically connecting columnar solder portions adjacent to each other in the plane direction. Figure 3 B shows a state where the columnar solder portion does not form an electrical connection.

[0024] [ Figure 4 ] Figure 4 A digital microscope observation photograph of the bonding sheet of Example 1 is shown.

[0025] [ Figure 5 ] Figure 5 A digital microscope observation photograph of the bonding sheet of Example 2 is shown.

[0026] [ Figure 6 ] Figure 6 A digital microscope observation photograph of the bonding sheet of Example 3 is shown.

[0027] [ Figure 7 ] Figure 7 A digital microscope observation photograph of the bonding sheet of Comparative Example 1 is shown.

[0028] [ Figure 8 ] Figure 8 A digital microscope observation photograph of the bonding sheet of Comparative Example 2 is shown. DETAILED DESCRIPTION

[0029] The joining sheet is formed into a sheet shape from the joining sheet composition.

[0030] The bonding sheet composition contains a resin component and solder particles. That is, the bonding sheet contains a resin component and solder particles.

[0031] <Resin ingredients>

[0032] The resin component includes a thermoplastic resin and a curable resin.

[0033] [Thermoplastic resin]

[0034] Examples of the thermoplastic resin include thermoplastic epoxy resins, thermoplastic phenolic resins, phenoxy resins, polyolefins (e.g., polyethylene, polypropylene, ethylene-propylene copolymers, etc.), thermoplastic acrylic resins, thermoplastic polyesters, polyvinyl acetate, ethylene-vinyl acetate copolymers, polyvinyl chloride, polystyrene, polyacrylonitrile, polyamide (nylon (registered trademark)), polycarbonate, polyacetal, polyethylene terephthalate, polyphenylene ether, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polyarylsulfone, thermoplastic polyimide, thermoplastic polyurethane, polyaminobismaleimide, polyamideimide, polyetherimide, bismaleimide triazine resin, polymethylpentene, fluorinated resins, liquid crystal polymers, olefin-vinyl alcohol copolymers, ionomers, polyarylates, acrylonitrile-ethylene-styrene copolymers, acrylonitrile-butadiene-styrene copolymers, acrylonitrile-styrene copolymers, and butadiene-styrene copolymers. Preferred examples of the thermoplastic resin include thermoplastic epoxy resins and thermoplastic phenol resins.

[0035] Examples of the thermoplastic epoxy resin include thermoplastic bisphenol epoxy resins (e.g., thermoplastic bisphenol A epoxy resins, thermoplastic bisphenol F epoxy resins, and thermoplastic bisphenol S epoxy resins), thermoplastic Novolac epoxy resins (e.g., thermoplastic phenol Novolac epoxy resins, thermoplastic cresol Novolac epoxy resins, and thermoplastic biphenyl epoxy resins), thermoplastic naphthalene epoxy resins, thermoplastic fluorene epoxy resins (e.g., diarylfluorene epoxy resins), and thermoplastic triphenylmethane epoxy resins (e.g., trihydroxyphenylmethane epoxy resins). Examples of the thermoplastic epoxy resin include preferably thermoplastic bisphenol epoxy resins. Examples of the thermoplastic epoxy resin include more preferably thermoplastic bisphenol A epoxy resins.

[0036] In addition, these thermoplastic resins may be in any form of solid, semi-solid or liquid at room temperature (25° C.).

[0037] Note that being solid at 25° C. means not flowing and having no viscosity at 25° C. Also, being liquid at 25° C. means having viscosity at 25° C., including liquids and fluids (the same applies hereinafter).

[0038] As the thermoplastic resin, preferably, a solid thermoplastic resin is used.

[0039] The softening point of the thermoplastic resin is, for example, 110°C or higher, preferably 120°C or higher, more preferably more than 120°C, further preferably 125°C or higher, and is, for example, 230°C or lower, preferably 200°C or lower, more preferably less than 150°C, further preferably 140°C or lower.

[0040] When the softening point is equal to or higher than the lower limit, both the average primary particle size and the average secondary particle size of solder particles described below can be more reliably set to 7 μm or less.

[0041] Specifically, when the softening point is equal to or greater than the lower limit, the thermoplastic resin can suppress aggregation of solder particles in the arrangement step of the bonding sheet manufacturing method described below. As a result, the average primary particle size and average secondary particle size of the solder particles described below can be more reliably set to 7 μm or less.

[0042] In addition, the said softening point can be measured using a thermomechanical analyzer.

[0043] The thermoplastic resins can be used alone or in combination of two or more.

[0044] The content ratio of the thermoplastic resin relative to 100 parts by mass of the resin component is, for example, 30 parts by mass or more, preferably 40 parts by mass or more, and, for example, 70 parts by mass or less, preferably 60 parts by mass or less.

[0045] [Curing resin]

[0046] As the curable resin, for example, a thermosetting resin can be cited. As the thermosetting resin, for example, a thermosetting epoxy resin, a urea resin, a melamine resin, a diallyl phthalate resin, a silicone resin, a phenolic resin, a thermosetting acrylic resin, a thermosetting polyester, a thermosetting polyimide, and a thermosetting polyurethane can be cited. As the curable resin, preferably, a thermosetting epoxy resin can be cited.

[0047] As the thermosetting epoxy resin, for example, thermosetting bisphenol epoxy resin (for example, thermosetting bisphenol A epoxy resin, thermosetting bisphenol F epoxy resin and thermosetting bisphenol S epoxy resin), thermosetting Novolac epoxy resin (for example, thermosetting phenol Novolac epoxy resin, thermosetting cresol Novolac epoxy resin and thermosetting biphenyl epoxy resin), thermosetting naphthalene epoxy resin, thermosetting fluorene epoxy resin (for example, thermosetting diaryl fluorene epoxy resin), and thermosetting triphenylmethane epoxy resin (for example, thermosetting trihydroxyphenylmethane epoxy resin) can be mentioned. As the thermosetting epoxy resin, preferably, thermosetting bisphenol epoxy resin can be mentioned. As the thermosetting epoxy resin, more preferably, thermosetting bisphenol A epoxy resin can be mentioned.

[0048] In addition, these thermosetting resins may be in any form of solid, semi-solid or liquid at room temperature (25° C.).

[0049] As the thermosetting resin, preferably, a liquid thermosetting resin is used.

[0050] Furthermore, the resin component preferably contains a solid thermoplastic resin and a liquid thermosetting resin. When the resin component contains a solid thermoplastic resin and a liquid thermosetting resin, the adhesive sheet has excellent moldability and adhesive strength.

[0051] The resin component is more preferably formed of a solid thermoplastic resin and a liquid thermosetting resin.

[0052] The curable resins may be used alone or in combination of two or more.

[0053] The content ratio of the curable resin relative to 100 parts by mass of the resin component is, for example, 30 parts by mass or more, preferably 40 parts by mass or more, and, for example, 70 parts by mass or less, preferably 60 parts by mass or less.

[0054] Furthermore, the viscosity of the resin component at the melting point of the solder particles described later is, for example, 1 mPa·s or more, preferably 100 mPa·s or more, and, for example, 5000 mPa·s or less, preferably 2000 mPa·s or less, more preferably 1000 mPa·s or less, and further preferably 500 mPa·s or less.

[0055] When the viscosity is not less than the lower limit and not more than the upper limit, unaggregated solder particles (described later) can be reduced. As a result, productivity can be improved.

[0056] It should be noted that the viscosity can be measured using a rheometer. The measurement of the viscosity will be described in detail in the Examples described below.

[0057] The content ratio of the resin component relative to the joining sheet composition (joining sheet) is, for example, 20 mass % or more, preferably 30 mass % or more, and, for example, 60 mass % or less, preferably 40 mass % or less.

[0058] In the resin component, the mass ratio of the curable resin to the thermoplastic resin is, for example, 0.6 or more, preferably 0.9 or more, and for example, 1.5 or less, preferably 1.1 or less.

[0059] <Solder particles>

[0060] From the perspective of environmental friendliness, the solder material forming the solder particles may include a lead-free solder material (lead-free solder material). Specifically, as the solder material, for example, tin and tin alloys may be included. As the tin alloy, for example, tin-bismuth alloy (Sn-Bi), tin-silver-copper alloy (Sn-Ag-Cu) and tin-silver alloy (Sn-Ag) may be included.

[0061] The content of tin in the tin-silver alloy is, for example, 90% by mass or more, preferably 95% by mass or more. The content of silver in the tin-silver alloy is, for example, 10% by mass or less, preferably 5% by mass or less.

[0062] In addition, the content ratio of tin in the tin-silver-copper alloy is, for example, 90% by mass or more, preferably 95% by mass or more. In addition, the content ratio of silver in the tin-silver-copper alloy is, for example, 10% by mass or less, preferably 5% by mass or less. In addition, the content ratio of copper in the tin-silver-copper alloy is, for example, 1% by mass or less, preferably 0.5% by mass or less.

[0063] The tin content in the tin-bismuth alloy is, for example, 30 mass % or more, preferably 40 mass % or more, and the bismuth content in the tin-bismuth alloy is, for example, 70 mass % or less, preferably 60 mass % or less.

[0064] Preferred examples of the solder material include tin-silver alloy (Sn—Ag) and tin-silver-copper alloy (Sn—Ag—Cu).

[0065] The melting point of the solder material (ie, the melting point of the solder particles) is, for example, 260° C. or less, preferably 235° C. or less, and, for example, 100° C. or more, preferably 130° C. or more. The melting point is determined by differential scanning calorimetry (DSC) (the same applies hereinafter).

[0066] The shape of the solder particles is not particularly limited, and examples thereof include spherical shapes, plate shapes, and needle shapes. As the shape of the solder particles, a spherical shape is preferred. Figure 1 B. Figure 2 B. Figure 2 C and Figure 2 In D, the shape of the solder particles is shown as a sphere, but the shape of the solder particles is not limited to this.

[0067] The surface of the solder particle is usually covered with an oxide film formed of an oxide of the solder material. The thickness of the oxide film is, for example, not less than 1 nm, and not more than 20 nm.

[0068] In addition, in the preparation of the bonding sheet composition described later and / or the arrangement step of the bonding sheet manufacturing method described later, some or all of the solder particles may aggregate to form secondary particles. That is, the bonding sheet contains primary particles of solder particles and / or secondary particles of solder particles.

[0069] Furthermore, the average primary particle size and the average secondary particle size of the solder particles are both 7 μm or less, preferably 5 μm or less from the viewpoint of miniaturization and reliability, and are, for example, 0.1 μm or more, preferably 0.5 μm or more.

[0070] In detail, the so-called primary particle is the smallest unit of a particle, and refers to an independent particle without aggregation. The average primary particle size of the solder particles is 7 μm or less, preferably 5 μm or less from the viewpoint of miniaturization and reliability, and is, for example, 0.1 μm or more, preferably 0.5 μm or more.

[0071] The secondary particles are particles formed by aggregation of primary particles. The average secondary particle size is larger than the average primary particle size, specifically, 7 μm or less, preferably 5 μm or less, and for example, 1 μm or more from the viewpoint of miniaturization and reliability.

[0072] As described above, the bonding sheet contains primary particles of solder particles and / or secondary particles of solder particles. That is, the bonding sheet contains only primary particles of solder particles, or only secondary particles of solder particles, or primary particles of solder particles and secondary particles of solder particles, and in any case, the average primary particle size of the solder particles and the average secondary particle size of the solder particles are both 7 μm or less.

[0073] When both the average primary particle size and the average secondary particle size are equal to or less than the upper limit, unevenness can be suppressed in the self-aggregation described later. As a result, reliability can be improved.

[0074] On the other hand, when at least any one of the average primary particle size and the average secondary particle size exceeds the upper limit, it is not possible to suppress unevenness in the self-aggregation described below, resulting in reduced reliability.

[0075] It should be noted that the above average primary particle size can be measured using a laser diffraction particle size distribution measuring device. In addition, the method for measuring the above average secondary particle size will be described in detail in the examples described below.

[0076] The solder particles can be used alone or in combination of two or more.

[0077] The content ratio of the solder particles relative to the joining sheet composition (joining sheet) is, for example, 50 mass % or more, preferably 55 mass % or more, and, for example, 80 mass % or less, preferably 60 mass % or less.

[0078] <Flux>

[0079] The bonding sheet composition preferably contains a soldering flux. That is, the bonding sheet preferably contains a soldering flux. The soldering flux is a component for removing an oxide film (an oxide film formed of an oxide of a solder material) on the surface of solder particles.

[0080] As the material of the soldering flux, for example, organic acid salts can be cited. As the organic acid salts, for example, organic acids, hydroxyquinoline derivatives and metal carbonyl acid salts can be cited. As the organic acid, for example, aliphatic carboxylic acids and aromatic carboxylic acids can be cited. As the aliphatic carboxylic acid, for example, aliphatic dicarboxylic acids can be cited. As the aliphatic dicarboxylic acids, specifically, adipic acid, malic acid, malonic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, and sebacic acid can be cited. As the aromatic carboxylic acid, for example, benzoic acid, 2-phenoxybenzoic acid, phthalic acid, diphenylacetic acid, trimellitic acid and pyromellitic acid can be cited. As the material of the soldering flux, preferably, organic acids can be cited. As the material of the soldering flux, more preferably, malic acid can be cited.

[0081] The melting point of the flux is, for example, 250° C. or lower, preferably 180° C. or lower, more preferably 160° C. or lower, and, for example, 100° C. or higher, preferably 120° C. or higher, more preferably 130° C. or higher.

[0082] The shape of the flux is not particularly limited, and examples thereof include a plate shape, a needle shape, and a spherical shape.

[0083] Alternatively, the flux may be dissolved in a known solvent to prepare a flux solution. The solid content concentration of the flux solution is, for example, 10% by mass or more and, for example, 40% by mass or less.

[0084] The flux may be used alone or in combination of two or more.

[0085] The content ratio of the flux relative to the bonding sheet composition (bonding sheet) is, for example, 1 mass % or more, preferably 5 mass % or more, and, for example, 20 mass % or less, preferably 10 mass % or less.

[0086] <Additives>

[0087] The bonding sheet composition may contain additives (eg, a curing agent, a curing accelerator, and a silane coupling agent) at appropriate ratios as necessary.

[0088] <Preparation of bonding sheet composition>

[0089] The bonding sheet composition is prepared by mixing the resin component, solder particles, a flux blended as required, and additives blended as required, and stirring as required.

[0090] In the above preparation, if the solder particles are mixed without stirring, most of the solder particles aggregate to form secondary particles. On the other hand, in the above preparation, if the solder particles are mixed with stirring, they exist in the state of primary particles.

[0091] Alternatively, the joining sheet composition may be mixed with a known solvent to prepare a varnish. The solid content concentration of the varnish of the joining sheet composition is, for example, 50% by mass or more, preferably 60% by mass or more, and, for example, 80% by mass or less.

[0092] <Method for producing bonding sheet>

[0093] In one embodiment of the method for manufacturing a bonding sheet, referring to Figure 1 A and Figure 1 B explains in detail.

[0094] exist Figure 1 A and Figure 1 In B, the up-down direction on the paper is the up-down direction (thickness direction). In addition, the upper side on the paper is the upper side (one side in the thickness direction), and the lower side on the paper is the lower side (the other side in the thickness direction). In addition, the left-right direction and the depth direction on the paper are the plane directions orthogonal to the up-down direction. Specifically, follow the direction arrows in each figure.

[0095] The method for producing a joining sheet comprises a preparation step of preparing the release liner 10 and a placement step of placing the joining sheet 1 on one surface of the release liner 10 in the thickness direction.

[0096] [Preparation process]

[0097] In the preparation process, Figure 1 As shown in A, a release liner 10 is prepared.

[0098] The release liner is a film for covering and protecting the joining sheet 1. The release liner 10 has a film shape.

[0099] The release liner 10 is, for example, a plastic substrate (plastic film). Examples of the plastic substrate include polyester sheets (polyethylene terephthalate (PET) sheets), polyolefin sheets (e.g., polyethylene sheets, polypropylene sheets), polyvinyl chloride sheets, polyimide sheets, and polyamide sheets (nylon sheets). The surface (one surface in the thickness direction) of the release liner 10 may be subjected to a surface treatment such as silicone treatment.

[0100] The thickness of the release liner 10 is, for example, not less than 1 μm, and not more than 100 μm.

[0101] [Configuration process]

[0102] In the configuration process, Figure 1 As shown in B, the joining sheet 1 is disposed on one surface of the release liner 10 in the thickness direction.

[0103] In order to arrange the joining sheet 1 on one surface of the release liner 10 in the thickness direction, the joining sheet composition (a varnish of the joining sheet composition) is applied to one surface of the release liner 10 in the thickness direction and then dried as necessary.

[0104] As drying conditions, the drying temperature is, for example, 40° C. or higher, and, for example, 100° C. or lower. The drying time is, for example, 1 minute or longer, and, for example, 60 minutes or less.

[0105] In addition, the resin component may flow due to the heating during the drying, and accordingly, the solder particles 5 may flow. In this case, part or all of the solder particles 5 aggregate to form secondary particles. The higher the drying temperature, the more the solder particles 5 tend to aggregate, but by increasing the softening point of the thermoplastic resin, the flow of the resin component can be suppressed, and even if the drying temperature is high, the aggregation of the solder particles 5 can be suppressed. Preferably, the drying temperature is adjusted so that the difference between the softening point of the thermoplastic resin and the drying temperature (softening point of the thermoplastic resin - drying temperature) is, for example, 50°C or more, preferably 60°C or more.

[0106] In the above manner, the joining sheet 1 arranged on one surface in the thickness direction of the release liner 10 can be manufactured.

[0107] Such a bonding sheet 1 includes a resin component and solder particles 5 (primary particles and secondary particles of the solder particles 5) dispersed in the resin component. Figure 1 In B, primary particles and secondary particles are not distinguished and are all described as solder particles 5 (the same applies hereinafter).

[0108] From the viewpoint of reducing size and height, the thickness of the joining sheet 1 is, for example, 15 μm or less, preferably 7 μm or less, more preferably 6 μm or less, and for example, 1 μm or more.

[0109] <How to use the bonding sheet>

[0110] For one embodiment of the method for using the bonding sheet (the method for manufacturing the bonding structure), refer to Figure 2 A~ Figure 2 E is described in detail.

[0111] The method for using a bonding sheet (a method for manufacturing a connection structure) comprises: a first step of preparing a first substrate 2 and a second substrate 4; a second step of preparing a bonding sheet 1; a third step of stacking the first substrate 2, the bonding sheet 1 and the second substrate 4; a fourth step of thermally pressing the first substrate 2 and the second substrate 4 to the bonding sheet 1; and a fifth step of forming an adhesive layer 3 for soldering the first substrate 2 and the second substrate 4 to the bonding sheet 1.

[0112] [1st step]

[0113] In the first step, if Figure 2 As shown in A, a first substrate 2 and a second substrate 4 are prepared.

[0114] The first substrate 2 has a flat plate shape.

[0115] The first substrate 2 includes: a first wired circuit board 11; and a plurality of first electrodes 12 arranged in the surface direction of the first wired circuit board 11. In other words, the first substrate 2 includes: the first wired circuit board 11; and a plurality of first electrodes 12 provided on the surface (one surface in the thickness direction) of the first wired circuit board 11.

[0116] The first wired circuit board 11 is formed of, for example, an insulating material and a semiconductor material.

[0117] The thickness of the first wired circuit board 11 is, for example, not less than 5 μm, and not more than 1000 μm.

[0118] The first electrode 12 is formed of metal.

[0119] The first electrode 12 is arranged in a dot pattern on the first substrate 2 .

[0120] Specifically, the first electrode 12 has a circular shape in a plan view. In addition, the plurality of first electrodes 12 are arranged evenly in the surface direction.

[0121] The thickness of the first electrode 12 is, for example, 0 μm or more, preferably 0.001 μm or more, and, for example, 5 μm or less. When the surface of the first substrate 2 coincides with the surface of the first electrode 12 , the thickness of the first electrode 12 is 0 μm.

[0122] The diameter of the first electrode 12 is, for example, 100 μm or less, preferably 20 μm or less, and, for example, 1 μm or more.

[0123] In the plane direction, the distance (pitch) between adjacent first electrodes 12 is, for example, 3 μm or more, preferably 5 μm or more, and, for example, 200 μm or less, preferably 100 μm or less, and more preferably 40 μm or less.

[0124] The second substrate 4 has a flat plate shape.

[0125] The second base material 4 includes: a second wiring circuit board 13; and a plurality of second electrodes 14 arranged in the surface direction of the second wiring circuit board 13. In other words, the second base material 4 includes: a second wiring circuit board 13; and a plurality of second electrodes 14 provided on the surface (the other surface in the thickness direction) of the second wiring circuit board 13.

[0126] The second wired circuit board 13 is formed of, for example, an insulating material or a semiconductor material.

[0127] The thickness of the second wired circuit board 13 is, for example, not less than 5 μm, and not more than 1000 μm.

[0128] The second electrode 14 is formed of metal.

[0129] The second electrode 14 is arranged in a dot pattern on the second substrate 4 .

[0130] Specifically, the second electrode 14 has a circular shape in a plan view. In addition, the plurality of second electrodes 14 are arranged evenly in the plane direction.

[0131] The thickness of the second electrode 14 is, for example, 0 μm or more, preferably 0.001 μm or more, and, for example, 5 μm or less. When the surface of the second substrate 4 coincides with the surface of the second electrode 14 , the thickness of the second electrode 14 is 0 μm.

[0132] The diameter of the second electrode 14 is, for example, 100 μm or less, preferably 20 μm or less, and, for example, 1 μm or more.

[0133] In addition, in the plane direction, the distance (pitch) between the adjacent second electrodes 14 is the same as the distance (pitch) between the adjacent first electrodes 12 in the plane direction.

[0134] [Step 2]

[0135] In the second step, if Figure 2 As shown in B, a joining sheet 1 is prepared. The joining sheet 1 includes solder particles 5. As described above, the solder particles 5 in the joining sheet 1 are primary particles or secondary particles.

[0136] [Step 3]

[0137] In the third step, if Figure 2 As shown in C, the first substrate 2, the bonding sheet 1, and the second substrate 4 are stacked.

[0138] Specifically, the first substrate 2 and the second substrate 4 are brought close to the bonding sheet 1, and the first substrate 2 and the second substrate 4 are brought into contact with the bonding sheet 1. More specifically, in the thickness direction, one surface of the first substrate 2 in the thickness direction is brought into contact with the other surface of the bonding sheet 1 in the thickness direction in such a manner that the first electrode 12 and the second electrode 14 are opposed to each other, and the other surface of the second substrate 4 in the thickness direction is brought into contact with one surface of the bonding sheet 1 in the thickness direction.

[0139] In this way, the first substrate 2 , the bonding sheet 1 , and the second substrate 4 are stacked, and a stacked body 6 is manufactured.

[0140] [Step 4]

[0141] In the fourth step, if Figure 2 As shown in D, the first substrate 2 and the second substrate 4 are thermally compressed and bonded to the bonding sheet 1 .

[0142] Specifically, while the laminated body 6 is heated, the first substrate 2 and the second substrate 4 are pressed toward the bonding sheet 1 (thermocompression bonding).

[0143] The temperature of the thermocompression bonding is a temperature lower than the melting point of the solder particles 5. Specifically, the temperature of the thermocompression bonding is, for example, lower than 100° C., preferably lower than 80° C., and, for example, higher than 40° C., preferably higher than 60° C. The pressure of the thermocompression bonding is, for example, higher than 0.001 MPa, preferably higher than 0.005 MPa, more preferably higher than 0.01 MPa, and, for example, lower than 10 MPa, preferably lower than 5 MPa, more preferably lower than 1 MPa.

[0144] Thus, the first electrode 12 of the first substrate 2 is embedded in the bonding sheet 1, and one surface of the first substrate 2 in the thickness direction is covered by the bonding sheet 1. In addition, the second electrode 14 of the second substrate 4 is embedded in the bonding sheet 1, and the other surface of the second substrate 4 in the thickness direction is covered by the bonding sheet 1.

[0145] [Step 5]

[0146] In the fifth step, if Figure 2 As shown in E, an adhesive layer 3 is formed for soldering the first substrate 2 and the second substrate 4 to the bonding sheet 1.

[0147] Specifically, the stacked body 6 is heated.

[0148] The heating temperature is a temperature equal to or higher than the melting point of the solder particles 5. Specifically, the heating temperature is, for example, 100°C or higher, preferably 130°C or higher, and, for example, 300°C or lower, preferably 280°C or lower, and more preferably 270°C or lower.

[0149] By such heating, the solder particles 5 melt. The melted solder particles 5 gather (self-aggregate) between the first electrode 12 and the second electrode 14 (the first electrode 12 and the second electrode 14 are opposed to each other in the thickness direction) to form a columnar solder portion 15. On the other hand, the resin component in the bonding sheet 1 is squeezed out by the self-aggregated solder particles 5 and moves to the periphery of the columnar solder portion 15. Then, in the case where the resin component includes a thermosetting resin, the thermosetting resin is thermally cured to become a cured resin 16 that bonds the first substrate 2 and the second substrate 4.

[0150] It should be noted that, as described above, most of the melted solder particles 5 are used to form the columnar solder portion 15, but there is also the following situation: a part of the melted solder particles 5 and / or the unmelted solder particles 5 are not used to form the columnar solder portion 15, but remain in a dispersed state in the resin component, becoming unaggregated solder particles.

[0151] Thus, the adhesive layer 3 including the columnar solder portion 15 and the cured resin 16 is formed.

[0152] From the viewpoint of miniaturization and low profile, the thickness of the adhesive layer 3 is less than 15 μm, preferably 10 μm or less, more preferably less than 10 μm, further preferably 5 μm or less, and for example, 1 μm or more.

[0153] In the above manner, the connection structure 20 is manufactured.

[0154] The connection structure 20 comprises: a first substrate 2; a second substrate 4 arranged at a distance in the thickness direction; and an adhesive layer 3 interposed between the first substrate 2 and the second substrate 4. In other words, the connection structure 1 comprises the first substrate 2, the adhesive layer 3, and the second substrate 4 in order toward one side in the thickness direction. More specifically, the connection structure 1 comprises: a first substrate 2; an adhesive layer 3 directly arranged on the upper surface (one surface in the thickness direction) of the first substrate 2; and a second substrate 4 directly arranged on the upper surface (one surface in the thickness direction) of the adhesive layer 3.

[0155] The adhesive layer 3 bonds the first substrate 2 and the second substrate 4. Specifically, the adhesive layer 3 is bonded to the surface of the first substrate 2 excluding the first electrode 12. In addition, the adhesive layer 3 is bonded to the surface of the second substrate 4 excluding the second electrode 14.

[0156] The columnar solder portion 15 electrically connects the first electrode 12 and the second electrode 14 facing each other in the thickness direction. The columnar solder portion 15 has a columnar shape (specifically, a cylindrical shape), is disposed between the first electrode 12 and the second electrode 14, and is in contact with them.

[0157] In the above-mentioned method of using the bonding sheet (method of manufacturing a connection structure), the above-mentioned bonding sheet is used. Therefore, the above-mentioned unevenness in the self-aggregation can be suppressed. As a result, the reliability can be improved.

[0158] <Effects>

[0159] The bonding sheet 1 includes the solder particles 5, and the average primary particle size and the average secondary particle size of the solder particles 5 are both 7 μm or less. Therefore, the above-mentioned non-uniformity in self-aggregation can be suppressed. As a result, the reliability can be improved.

[0160] Specifically, if at least one of the average primary particle size and the average secondary particle size of the solder particles 5 exceeds 7 μm, the self-aggregation of the solder particles 5 becomes uneven. In this case, when the interval between two adjacent first electrodes 12 in the plane direction is narrow, in the fifth step, Figure 3 As shown in A, the solder particles 5 are locally self-aggregated between two first electrodes 12 adjacent in the plane direction, thereby electrically connecting the columnar solder portions 15 adjacent in the plane direction (that is, the two adjacent first electrodes 12 are electrically connected (bridged).) Since the two adjacent first electrodes 12 are electrically connected, the two first electrodes 12 are short-circuited, and the reliability is reduced.

[0161] In addition, if the self-aggregation of the solder particles 5 is uneven, Figure 3 As shown in FIG. 1B , the solder particles 5 are partially self-aggregated between the first electrode 12 and the second electrode 14 on the left side, while the solder particles 5 are not self-aggregated between the first electrode 12 and the second electrode 14 on the right side, and there is a case where the columnar solder portion 15 cannot be formed. As a result, poor connection occurs, and reliability is reduced.

[0162] On the other hand, in the bonding sheet 1, the average primary particle size and the average secondary particle size of the solder particles 5 are both 7 μm or less, so that the above-mentioned non-uniformity in self-aggregation can be suppressed. Thus, the above-mentioned bridging and connection failure can be suppressed, and reliability is improved.

[0163] <Modification>

[0164] In the modification, the same reference numerals are used for the same components and processes as those in the first embodiment, and detailed description thereof is omitted. In addition, unless otherwise specified, the modification can exert the same effects as those in the first embodiment. In addition, the first embodiment and the modification can be appropriately combined.

[0165] In the above description, the first electrode 12 and the second electrode 14 are arranged in a dot pattern, but the arrangement of the first electrode 12 and the second electrode 14 is not limited thereto.

[0166] In the above description, the first electrode 12 and the second electrode 14 have circular shapes in plan view, but the shapes of the first electrode 12 and the second electrode 14 are not limited thereto, and may have, for example, a quadrilateral shape in plan view.

[0167] In the above description, the second substrate 4 has a flat plate shape, but the shape of the second substrate 4 is not limited thereto, and for example, it may be a shape of a chip component (eg, mini / microLED).

[0168] In the above description, in the third step, the first substrate 2 and the second substrate 4 are brought close to the bonding sheet 1, and the first substrate 2 and the second substrate 4 are brought into contact with the bonding sheet 1. However, the bonding sheet 1 may be first arranged on one surface in the thickness direction of the first substrate 2 (the surface provided with the first electrode 12), and then, the second substrate 4 may be arranged on one surface in the thickness direction of the bonding sheet 1 in such a manner that the first electrode 12 and the second electrode 14 are opposed. In addition, before the second substrate 4 is arranged, a surface treatment (for example, surface treatment by coating a silica filler) may be applied to one surface in the thickness direction of the bonding sheet 1.

[0169] In the above description, the fourth step and the fifth step are implemented as separate steps, but the fourth step and the fifth step may be implemented simultaneously. In this case, the pressure in the fourth step and the temperature in the fifth step are used for thermal compression bonding.

[0170] In the above description, in the fourth step, the first substrate 2 and the second substrate 4 are thermally pressed together with the bonding sheet 1. However, in particular when the second substrate 4 is a chip component, the connection structure 20 can be manufactured by reflow soldering or vacuum reflow soldering without performing thermal pressing.

[0171] Example

[0172] Next, the present invention is described based on examples and comparative examples, but the present invention is not limited to the following examples. It should be noted that, unless otherwise specified, "parts" and "%" are based on mass. In addition, the specific numerical values ​​such as the mixing ratio (containing ratio), physical property values, parameters, etc. used in the following description can be replaced by the upper limit value (defined as "below", "less than") or lower limit value (defined as "above", "exceeding") of the corresponding mixing ratio (containing ratio), physical property values, parameters, etc. recorded in the above-mentioned "Specific Implementation Method".

[0173] <Ingredients details>

[0174] The trade names and abbreviations of the components used in the respective Examples and Comparative Examples are described in detail.

[0175] jER1007: Bisphenol A epoxy resin, solid at 25°C, thermoplastic resin, softening point 128°C, manufactured by Mitsubishi Chemical Corporation

[0176] jER1009: Bisphenol A epoxy resin, solid at 25°C, thermoplastic resin, softening point 144°C, manufactured by Mitsubishi Chemical Corporation

[0177] jER1010: Bisphenol A epoxy resin, solid at 25°C, thermoplastic resin, softening point above 150°C, manufactured by Mitsubishi Chemical Corporation

[0178] UH2170: acrylic resin, solid at 25°C, thermoplastic resin, softening point 80-85°C, manufactured by Toa Gosei Co., Ltd.

[0179] jER1004: Bisphenol A epoxy resin, solid at 25°C, thermoplastic resin, softening point 97°C, manufactured by Mitsubishi Chemical Corporation

[0180] jER828: Bisphenol A epoxy resin, epoxy equivalent 184 ~ 194g / eq, liquid at 25 ℃, thermosetting resin, made by Mitsubishi Chemical Corporation

[0181] SnAg: solder particles (Sn 96.5 mass % Ag 3.5 mass %, melting point 221°C, spherical shape, average primary particle size 3 μm, oxygen concentration 1100 ppm)

[0182] SnAgCu: solder particles, (Sn 96.5 mass % Ag 3.0 mass % Cu 0.5 mass %, melting point 217-219°C, spherical shape, average primary particle size 3 μm, oxygen concentration 1100 ppm)

[0183] SnBi: solder particles, (Sn 42 mass %, Bi 58 mass %, melting point 139°C, spherical shape, average primary particle size 3 μm, oxygen concentration 1100 ppm)

[0184] <Joining sheet composition and preparation of joining sheet>

[0185] Examples 1 to 5, Comparative Examples 1 and 2

[0186] [Preparation of Joining Sheet Composition]

[0187] According to the formulation described in Table 1, the resin component, solder particles, and flux were mixed and added to methyl ethyl ketone (MEK) to prepare a bonding sheet composition (solid content concentration was 70% by mass). It should be noted that as the flux, a flux solution (solid content concentration was 30% by mass) prepared by adding malic acid to ethanol and dissolving it was used.

[0188] [Preparation of bonding sheet]

[0189] (Preparation process)

[0190] Prepare the release liner.

[0191] (Configuration process)

[0192] A bonding sheet was arranged on one side of the release liner in the thickness direction. Specifically, a varnish of a bonding sheet composition was applied to one side of the release liner in the thickness direction and dried. The drying temperature was set to 60° C. and the drying time was set to 5 minutes. Thus, a bonding sheet (thickness 5 μm) was prepared on one side of the release liner in the thickness direction.

[0193] <Production of Evaluation Electrodes>

[0194] The bonding sheets of each embodiment and each comparative example were attached to a substrate with multiple simulated electrodes (the electrodes were cylindrical, with a diameter of 15 μm, a height of 1 μm, and an electrode spacing (= center-to-center distance) of 30 μm), and the release liner was peeled off. Next, the substrate was placed on a heating plate preheated to 40°C, and then heated to 260°C (170°C in the case of Example 5) at a heating rate of 20°C / second, and the temperature was maintained for 5 seconds, and then cooled to 40°C by heat dissipation again. Thus, an electrode for evaluation was prepared.

[0195] <Evaluation>

[0196] [Viscosity of the resin component when the solder particles are melted]

[0197] For each embodiment and each comparative example, the viscosity of the resin component when the solder particles were melted was measured. Specifically, a rheometer (trade name "MCR302e", manufactured by Anton Paar) was used to measure the viscosity under the conditions of a heating rate of 10°C / min, a strain of 0.05%, and a frequency of 1 Hz. Sheets with a thickness of 300 μm containing only the resin components of embodiments 1 to 5 and comparative examples 1 and 2 were prepared and used. The results are shown in Table 1.

[0198] [Average secondary particle size of solder particles]

[0199] The bonding sheets of each example and each comparative example were observed using a digital microscope (trade name "VHX-8000", manufactured by KEYENCE) at a magnification of 1000 times, and still images were taken. A portion of the results are shown in FIG. Figures 4 to 8 Specifically, Figure 4 Showing Example 1, Figure 5 Showing Example 2, Figure 6 Showing Example 3, Figure 7 Comparative Example 1 is shown. Figure 8 Comparative Example 2 is shown.

[0200] Next, the obtained still image is binarized using the "Threshold" function of the image processing software "imageJ, developed by Wayne Rasband (NIH)". For the binarized image, draw an arbitrary straight line from one side of the captured image to the corresponding side, and display the pixels on the line in grayscale. For the parts of the grayscale mark that continuously display the value of 255, count the number of pixels respectively. The number of pixels of the length of the scale bar in the image (100μm) is counted and standardized, thereby determining the secondary particle size of the solder particles based on each part of the grayscale mark that continuously displays the value of 255, and averaging them to calculate the average secondary particle size of the solder particles. The results are shown in Table 1.

[0201] [Occurrence of bridging]

[0202] The evaluation electrodes of each embodiment and each comparative example were observed using a digital microscope (trade name "VHX-8000", manufactured by KEYENCE, 500 times magnification) to see if there was a bridge connecting adjacent electrodes. The occurrence of bridges was evaluated based on the following criteria. The results are shown in Table 1.

[0203] {Benchmark}

[0204] ○: The occurrence of bridging is less than 1% of the total.

[0205] ×: The occurrence of bridging exceeds 1% of the whole.

[0206] [Observation of solder part]

[0207] For the evaluation electrodes of each embodiment and each comparative example, a digital microscope (trade name "VHX-8000", manufactured by KEYENCE, 500-fold magnification) was used to observe the aggregation to the electrode. The aggregation to the electrode was evaluated based on the following criteria. The results are shown in Table 1.

[0208] {Benchmark}

[0209] ○: The proportion of more than half of the electrode not covered by solder particles is less than 1% of the whole.

[0210] ×: The ratio of more than half of the electrode not being covered with solder particles is 1% or more of the whole.

[0211] [Confirmation of unaggregated solder particles]

[0212] The number of solder particles that were not aggregated on the electrodes of the examples and comparative examples was measured using a digital microscope (trade name "VHX-8000", manufactured by KEYENCE, 500 times magnification). The solder particles that were not aggregated were evaluated based on the following criteria. The results are shown in Table 1.

[0213] {Benchmark}

[0214] Almost none: every 100×100μm 2 The number of unaggregated solder particles is 100 or less.

[0215] Slightly: Every 100×100μm 2 The number of solder particles that are not aggregated is more than 100 and is 200 or less.

[0216] Yes: Every 100×100μm 2 The number of unaggregated solder particles in the sample exceeded 200.

[0217] [Table 1]

[0218]

[0219] It should be noted that the above invention is provided as an exemplary embodiment of the present invention, but it is merely an example and is not to be construed as limiting. Modifications of the present invention that are obvious to those skilled in the art are included in the claims.

[0220] Industrial Applicability

[0221] The bonding sheet of the present invention can be suitably used for bonding between terminals of two wired circuit boards which are arranged at a distance in the thickness direction.

[0222] Description of Reference Numerals

[0223] 1 Joint piece

[0224] 5 Solder particles

Claims

1. A bonding sheet comprising a resin component and solder particles, The average primary particle size of the solder particles and the average secondary particle size of the solder particles are both 7 μm or less. The bonding sheet according to claim 1 , further comprising a soldering flux.

3. The bonding sheet according to claim 1, wherein: The resin component comprises a thermoplastic resin, The thermoplastic resin has a softening point of 110° C. or higher.

4. The bonding sheet according to claim 1, wherein: The resin component has a viscosity of 5000 mPa·s or less at the melting point of the solder particles.

5. The bonding sheet according to claim 1, wherein: The resin component includes a thermoplastic resin and a thermosetting resin. The thermoplastic resin is solid at 25°C. The thermosetting resin is in liquid state at 25°C.

6. The bonding sheet according to claim 1, wherein: The average primary particle size of the solder particles and the average secondary particle size of the solder particles are both 5 μm or less. 7 . The joining sheet according to claim 1 , which has a thickness of 15 μm or less.

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