Solder particles, method for manufacturing solder particles, and electrically conductive composition

Abstract

Provided is a solder particle having an oxide film on the surface thereof, the oxide film having an average film thickness of 3 nm or more and an average surface roughness Ra of 10 nm or more.

Description

Technical Field

[0001] This invention relates to solder particles, a method for manufacturing solder particles, and a conductive composition. Background Technology

[0002] Currently available solder particles have a wider particle size distribution than metal-coated resin particles, which are generally conductive particles, and contain a certain amount of coarse solder particles. Therefore, if a conductive composition containing currently available solder particles is used for wiring pattern connections, then… Figure 1 As shown, there is a concern that during heat-pressed installation, a short circuit may occur due to coarse solder particles 11 present in the unpressurized portion between the wiring patterns 10. Figure 1 In the text, 12 represents solder particles.

[0003] Furthermore, if a conductive composition containing metal-coated resin particles as conductive particles is used to connect wiring patterns, the insulation between the wiring patterns can be ensured by the insulating adhesive present around the metal-coated resin particles. However, if a conductive composition containing solder particles as conductive particles is used to connect wiring patterns, then... Figure 2 As shown, the solder particles 12 between the wiring patterns 10 melt during heating and pressing and agglomerate to form large metal bodies 13. During heating and pressing installation, there is a concern about short circuits due to the large metal bodies present in the unpressurized parts between the wiring patterns.

[0004] To avoid the risk of such short circuits, it is considered to form an insulating film on the surface of the solder particles. For example, a solder paste powder has been proposed, in which an oxide film with an average thickness of 2.5 nm to 6 nm is formed on the surface of solder particles with a central particle size of 20 μm to 40 μm. (For example, see Patent Document 1).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent No. 4084657 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] However, in the aforementioned Patent Document 1, the purpose of forming an oxide film with an average thickness of 2.5 nm to 6 nm is to suppress the viscosity increase of the paste after preparation, rather than to avoid short circuit risks, prevent the melting and coarsening of solder particles between wiring patterns, and suppress the reduction of insulation. Furthermore, Patent Document 1 neither describes nor implies the formation of an oxide film with an average surface roughness Ra of 15 nm to 110 nm through forced airflow staged processing in an oxygen atmosphere.

[0010] On the other hand, it is difficult to form an insulating film using commercially available solder particles through mechanochemical methods. The reasons are as mentioned above: the particle size of commercially available solder particles is inconsistent, making it difficult to form a uniform insulating film. In addition, solder particles are relatively soft and therefore cannot withstand the physical impact of mechanochemical methods, and will deform.

[0011] The objective of this invention is to solve the aforementioned problems and achieve the following: that is, to provide solder particles capable of avoiding short-circuit risks and suppressing insulation degradation, a method for manufacturing solder particles, and a conductive composition.

[0012] Methods for solving problems

[0013] The method for solving the above-mentioned problem is as follows. That is,

[0014] <1> A solder particle, characterized in that it has an oxide film on its surface, the average thickness of the oxide film being 3 nm or more, and the average surface roughness Ra being 10 nm or more.

[0015] <2> According to the solder particles described in <1> above, the average thickness of the oxide film is 5 nm or more and 100 nm or less, and the average surface roughness Ra is 15 nm or more and 110 nm or less.

[0016] <3> The solder particles according to any one of <1> to <2> above have an average particle size of 1 μm or more.

[0017] <4> According to the solder particles described in <3> above, the proportion of coarse solder particles with a number average particle size of more than 1.25 times is less than 0.5%.

[0018] <5> The solder particles according to any one of <1> to <4> above comprise: Sn, and at least one selected from Bi, Ag, Cu and In.

[0019] <6> The solder particles according to any one of <1> to <5> above are manufactured by forced airflow classification processing in an oxygen-containing atmosphere.

[0020] <7> A method for manufacturing solder particles, characterized in that it includes a grading process: in an oxygen-containing atmosphere, a grading device is used to force the airflow to be generated to grade the solder particles.

[0021] <8> According to the method for manufacturing solder particles described in <7> above, the grading device is a device that generates airflow by drawing in air with a blower, and grading the solder particles by causing them to rotate and collide with the screen surface.

[0022] <9> According to the solder particle manufacturing method described in <7> above, the above-mentioned grading device is a device in which air vortex rotates together with solder particles in a grading chamber, and grading is performed by controlling the rotational centrifugal force generated by the rotation of the rotor and the air flow drawn by the blower towards the center of the rotor.

[0023] <10> A conductive composition, characterized in that it contains solder particles as described in any one of <1> to <6> above.

[0024] The effects of the invention

[0025] According to the present invention, the aforementioned problems can be solved and the above-mentioned objectives can be achieved. Solder particles that can avoid short-circuit risks and suppress the reduction of insulation, a method for manufacturing solder particles, and a conductive composition are provided. Attached Figure Description

[0026] Figure 1 This is a schematic diagram illustrating a short circuit caused by coarse solder particles when commercially available solder particles are used as conductive particles.

[0027] Figure 2 This is a schematic diagram illustrating how, when a conductive film containing solder particles is heated and pressed between wiring patterns, the solder particles melt and self-aggregate to form a large metal body.

[0028] Figure 3 (a) and (b) are schematic diagrams illustrating that the solder particles after grading can reduce the contact area between each other by increasing the average surface roughness, compared with the solder particles before grading which had a small average surface roughness.

[0029] Figure 4 (a) and (b) are schematic diagrams illustrating how graded solder particles can approximately increase the average thickness of the oxide film compared to ungraded solder particles with smaller average surface roughness by increasing the average surface roughness. Detailed Implementation

[0030] (Solder particles)

[0031] The solder particles of the present invention have an oxide film on their surface, the average thickness of which is 3 nm or more, and the average surface roughness Ra is 10 nm or more.

[0032] The average thickness of the oxide film is preferably 5 nm or more and 100 nm or less, and the average surface roughness Ra is preferably 15 nm or more and 110 nm or less.

[0033] In this invention, solder particles are classified using a forced airflow classifier in an oxygen-containing atmosphere. This removes coarse solder particles from commercially available solder particles, avoiding the risk of short circuits between wiring patterns caused by coarse solder particles. At the same time, the surface of the solder particles is damaged while an oxide film is formed on the surface. This prevents the solder particles between wiring patterns from melting, self-coagulating, and coarsening, thus suppressing the reduction of insulation.

[0034] The solder particles of the present invention have an oxide film on their surface, the average thickness of which is 3 nm or more. Thus, during heat-pressing installation, the solder particles in the unpressurized areas such as between wiring patterns melt together even when they reach the melting point of the solder particles, and do not become fused together. Therefore, it is possible to prevent a decrease in insulation.

[0035] The average thickness of the oxide film of commercially available solder particles (solder particles before grading) is about 1 nm, so the above effect cannot be obtained.

[0036] There is no particular limit to the upper limit of the thickness of the oxide film. If the oxide film of the solder particles is too thick, there may be a situation where the oxide film of the solder particles clamped between the upper and lower electrodes does not break during heat pressing installation, resulting in an increase in conduction resistance. Therefore, the average thickness of the oxide film is preferably below 100 nm.

[0037] Here, the average thickness of the oxide film is measured, for example, from the surface of the solder particles in a cross-sectional photograph of the solder particles using a transmission electron microscope (TEM) (JEM-2100plus, manufactured by Nippon Electron Ltd.). The thickness of the oxide film in the center direction is measured.

[0038] The average thickness of the oxide film was determined by measuring the thickness of the oxide film at 3 locations for 1 solder particle, and then calculating the thickness of the oxide film for 10 solder particles. The average thickness of these oxide films was then calculated.

[0039] The solder particles of the present invention have an average surface roughness Ra of 10 nm or more, that is, they can form an uneven surface by damaging the surface of the solder particles, thereby further forming an oxide film in the depth direction of the solder particles.

[0040] here, Figure 3(a) and (b) are schematic diagrams showing that the solder particles 21 after grading can reduce the contact area between each other by increasing the average surface roughness, compared with the solder particles 20 before grading which have a small average surface roughness. Figure 3 As shown in (b), the graded solder particles 21 of the present invention increase the average surface roughness Ra, thereby improving their interaction with the solder particles. Figure 3 Compared to the solder particles 20 before grading shown in (a), the contact area between solder particles can be reduced. Figure 3 In the image, 22 represents the oxide film.

[0041] also, Figure 4 (a) and (b) are schematic diagrams showing that the average thickness of the oxide film can be approximately increased by the graded solder particles 21 by increasing the average surface roughness, compared with the ungraded solder particles 20 which have a small average surface roughness. Figure 4 As shown in (b), the graded solder particles 21 of the present invention have a large average surface roughness Ra, thereby interacting with... Figure 4 Compared to the solder particles 20 before grading shown in (a), the thickness L1 of the oxide film of the solder particles before grading can be approximately increased to the thickness L2 of the oxide film of the solder particles after grading. Figure 4 In the image, 22 represents the oxide film.

[0042] Figure 3 and Figure 4 As shown, when the solder particles of the present invention are installed by heat pressing, the solder particles present in the non-pressurized parts such as between wiring patterns melt and do not become fused together even if the solder particles in contact reach each other's melting point, thus preventing the reduction of insulation.

[0043] The average surface roughness Ra of commercially available solder particles (solder particles before grading) is about 1 nm, so the above effect cannot be obtained.

[0044] The solder particles of this invention have an average surface roughness Ra of 10 nm or more, thereby achieving the aforementioned effects. There is no particular upper limit to the average surface roughness Ra. However, if the average surface roughness Ra is too large, the grading process will cause greater damage not only to the surface of the solder particles but also to the solder particles as a whole, resulting in cracks and defects in the solder particles. Furthermore, if the average surface roughness Ra of the solder particles is too large, it has the same effect as an excessively thick oxide film, thus leading to a situation where, during heat-press bonding, the oxide film of the solder particles clamped between the upper and lower electrodes does not rupture, resulting in increased conductivity. Therefore, the average surface roughness Ra is preferably 500 nm or less.

[0045] The average surface roughness Ra of the above solder particles was measured, for example, using an AFM (SPA400 NanoNaviII, manufactured by Hitachi High Tech Co., Ltd.), the surface roughness at 5 locations was measured for 1 solder particle, and the surface roughness was calculated for 10 solder particles. The average surface roughness of these particles was then averaged.

[0046] Examples of the aforementioned solder particles include Sn-Pb system, Pb-Sn-Sb system, Sn-Sb system, Sn-Pb-Bi system, Bi-Sn system, Sn-Cu system, Sn-Pb-Cu system, Sn-In system, Sn-Ag system, Sn-Pb-Ag system, Pb-Ag system, etc., as specified in JIS Z3282-1999. Preferably, it includes Sn and at least one selected from Bi, Ag, Cu and In. Specifically, SnBi, SnBiAg, SnAgCu, SnIn, etc., are examples.

[0047] The melting point of the aforementioned solder particles is preferably 110°C to 240°C, and more preferably 120°C to 200°C.

[0048] The average particle size of the solder particles is preferably 1 μm or more, more preferably 5 μm or more, even more preferably 10 μm or more, and particularly preferably 15 μm or more. The upper limit of the average particle size of the solder particles is preferably 30 μm or less, more preferably 25 μm or less, and even more preferably 20 μm or less.

[0049] The average particle size of the aforementioned solder particles can be measured, for example, using a dry-type camera particle size analyzer (Morphologi G3, Malvern), with approximately 10,000 particles, and the particle size distribution expressed as a number frequency.

[0050] The proportion of coarse solder particles with a number average particle size of 1.25 times or more is preferably 0.5% or less, more preferably 0.1% or less, even more preferably 0.05% or less, particularly preferably 0.01% or less, and most preferably 0%.

[0051] If the proportion of coarse solder particles with a number average particle size of more than 1.25 times the number average particle size is less than 0.5%, then short circuits between wiring patterns caused by coarse solder particles can be avoided.

[0052] (Method for manufacturing solder particles)

[0053] The method for manufacturing solder particles according to the present invention includes a grading process: in an oxygen-containing atmosphere, a grading device is used to force the airflow to be generated to grade the solder particles, and further includes other processes as needed.

[0054] The aforementioned grading device uses a device that forcibly generates airflow to disperse particles and grading them while damaging the particle surface. As the aforementioned grading device, (1) it can be a device that uses a sieve to collide with the sieve and grading them by passing the particles rotating by airflow through the sieve, and (2) it can be a device that does not use a sieve but uses a rotor that generates centrifugal force to grading the solder particles by colliding with the rotor and balancing the generated centrifugal force with the air resistance.

[0055] As a grading device as described in (1) above, there exists a device that generates airflow by drawing in air with a blower, and grading the particles while they rotate and collide arbitrarily with the screen surface. According to this grading device, the surface of the solder particles is damaged into an uneven surface due to the collision between the solder particles and the screen surface, and an oxide film is formed while the particles are being graded. Examples of such grading devices include, for example, Spin Air Shave (manufactured by Seiko Corporation).

[0056] The suction pressure of the blower is preferably 0.1 MPa to 1.5 MPa, and more preferably 0.5 MPa to 1.0 MPa.

[0057] As described in (2) above, the grading device is used in a grading chamber where an air vortex rotates together with the solder particles. The centrifugal force generated by the rotation of the rotor and the airflow drawn towards the center of the rotor by a blower are balanced to grade the particles into coarse and fine powders. Due to the collision between the solder particles and the rotor surface, the surface of the solder particles becomes uneven, and an oxide film is formed while they are being graded. Examples of such grading devices include, for example, Classiel (manufactured by Seiko Corporation).

[0058] The rotor speed is preferably 500 rpm to 2,000 rpm, more preferably 900 rpm to 1,800 rpm.

[0059] The above-mentioned grading is carried out in an oxygen-containing atmosphere. The oxygen concentration in the oxygen-containing atmosphere is preferably 15 vol% or more, more preferably 20 vol% or more. If the above-mentioned oxygen concentration is 15 vol% or more, a robust oxide film can be formed on the surface of the solder particles. Air can be used as the oxygen-containing atmosphere with an oxygen concentration of 21 vol%.

[0060] (Conductive composition)

[0061] The conductive composition of the present invention contains the solder particles of the present invention, preferably containing a binder, a monofunctional polymeric monomer, an elastomer, a curing agent and a silane coupling agent, and further containing other components as needed.

[0062] The conductive composition described above can be either a conductive film or a conductive paste. From the perspective of ease of operation, a conductive film is preferred, while from the perspective of cost, a conductive paste is preferred. Furthermore, when the conductive composition is a conductive film, a film without solder particles can be laminated on top of a conductive film containing the aforementioned solder particles.

[0063] -Solder particles-

[0064] The solder particles of the present invention described above are used as solder particles.

[0065] The content of the conductive composition, which is the solder particle mentioned above, is not particularly limited and can be appropriately adjusted according to the wiring spacing, connection area, etc. of the connection structure.

[0066] -Adhesive-

[0067] There are no particular limitations on the adhesives used, and appropriate selection can be made according to the purpose. Examples include phenoxy resins, epoxy resins, unsaturated polyester resins, saturated polyester resins, urethane resins, butadiene resins, polyimide resins, polyamide resins, and polyolefin resins. One of these can be used alone, or two or more can be used in combination. Among these, phenoxy resins are particularly preferred from the perspectives of film-forming properties, processability, and bonding reliability.

[0068] The aforementioned phenoxy resin is a resin synthesized from bisphenol A and epichlorohydrin. Appropriately synthesized resins can be used, and commercially available products can be employed. Examples of such commercially available products include: YP-50 (manufactured by Toto Chemical Co., Ltd.), YP-70 (manufactured by Toto Chemical Co., Ltd.), and EP1256 (manufactured by Japan Epoxy Resin Co., Ltd.).

[0069] The content of the above-mentioned adhesive in the conductive composition is not particularly limited and can be appropriately selected according to the purpose. For example, it is preferably 20% to 70% by mass, and more preferably 35% to 55% by mass.

[0070] -Monofunctional polymerizable monomers-

[0071] As for the aforementioned monofunctional polymerizable monomers, there are no particular restrictions on monomers having a single polymerizable group within the molecule; they can be appropriately selected according to the purpose. Examples include monofunctional (meth)acrylic acid monomers, styrene monomers, butadiene monomers, and other olefin monomers with double bonds. One of these can be used alone, or two or more can be used in combination. Among these, monofunctional (meth)acrylic acid monomers are particularly preferred from the perspective of adhesive strength and bonding reliability.

[0072] There are no particular limitations on the monofunctional (meth)acrylic acid monomers mentioned above, and they can be appropriately selected according to the purpose. Examples include acrylic acid, methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, n-octyl acrylate, n-dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, and other acrylic acid or their esters; methacrylic acid, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, n-dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, and other methacrylic acid or their esters. They can be used alone or in combination of two or more.

[0073] The content of the above-mentioned monofunctional polymerizable monomer in the conductive composition is not particularly limited and can be appropriately selected according to the purpose, preferably 2% to 30% by mass, more preferably 5% to 20% by mass.

[0074] -Curing agent-

[0075] As for the aforementioned curing agent, there are no particular limitations as long as it can cure the adhesive, and it can be appropriately selected according to the purpose. For example, organic peroxides are suitable.

[0076] Examples of the aforementioned organic peroxides include lauroyl peroxide, butyl peroxide, benzyl peroxide, dilauryl peroxide, dibutyl peroxide, benzyl peroxide, dicarbonate peroxide, and benzoyl peroxide. They can be used individually or in combination of two or more.

[0077] The content of the curing agent in the conductive composition is not particularly limited and can be appropriately selected according to the purpose. It is preferably 1% to 15% by mass, and more preferably 3% to 10% by mass.

[0078] -Elastomer-

[0079] As elastomers, there are no particular restrictions, and they can be appropriately selected according to the purpose. Examples include polyurethane elastomers, acrylic rubbers, silicone rubbers, and butadiene rubbers. They can be used alone or in combination of two or more.

[0080] -Silane coupling agent-

[0081] There are no particular limitations on the silane coupling agents mentioned above, and they can be appropriately selected according to the purpose. Examples include epoxy silane coupling agents, acrylic silane coupling agents, thiol silane coupling agents, and amine silane coupling agents.

[0082] The content of the silane coupling agent in the conductive composition is not particularly limited and can be appropriately selected according to the purpose. It is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 5% by mass or less.

[0083] -Other ingredients-

[0084] There are no particular restrictions on the other components mentioned above, and they can be appropriately selected according to the purpose. Examples include organic solvents, fillers, softeners, accelerators, antioxidants, colorants (pigments, dyes), and ion scavengers. There are no particular restrictions on the amount of these other components added, and they can be appropriately selected according to the purpose.

[0085] <Uses>

[0086] The solder particles and conductive composition of the present invention can avoid the risk of short circuits and suppress the reduction of insulation. Therefore, for example, they can be used to make electrical connections between electrodes of various connection objects such as the connection between flexible printed circuit boards and glass substrates (FOG (Film on Glass)), the connection between semiconductor chips and flexible printed circuit boards (COF (Chip on Film)), the connection between semiconductor chips and glass substrates (COG (Chipon Glass)), and the connection between flexible printed circuit boards and glass epoxy boards (FOB (Film on Board)).

[0087] Example

[0088] The following describes embodiments of the present invention, but the present invention is not limited by these embodiments.

[0089] <Particle Size Distribution Determination>

[0090] Approximately 10,000 particles were measured using a dry-type camera particle size analyzer (Morphologi G3, Malvern). The particle size distribution is expressed as a number frequency.

[0091] <Determination of the average thickness of the oxide film>

[0092] The thickness of the oxide film in the center direction was determined from the surface of the solder particles in a cross-sectional photograph of the solder particles using a transmission electron microscope (TEM) (JEM-2100plus, manufactured by Nippon Electron Ltd.).

[0093] The average thickness of the oxide film is the average value obtained by measuring the thickness of the oxide film at 3 locations for 1 solder particle and calculating the thickness of the oxide film for 10 solder particles.

[0094] <Determination of average surface roughness Ra>

[0095] Using an atomic force microscope (AFM) (SPA400 NanoNaviII, manufactured by Hitachi High Tech Co., Ltd.), the surface roughness at 5 locations was measured for one solder particle. For 10 solder particles, the surface roughness was calculated as the average value obtained by averaging these surface roughnesses.

[0096] <Determination of the endothermic peak of solder particles using DSC>

[0097] The endothermic peak of solder particles was measured using a differential scanning calorimeter (DSC) (EXSTAR DSC6200, manufactured by Seiko Instruments (SII) Co., Ltd.) for DSC analysis.

[0098] <SEM observation of solder particle surface>

[0099] SEM observation of the solder particle surface was performed using a scanning electron microscope (SEM) (JSM-6510A, manufactured by Nippon Electron Ltd.).

[0100] (Example 1)

[0101] <Classification of Solder Particles>

[0102] As solder particles, prepare Sn 42 Bi 58 -Type5 (Made by Mitsui Metals & Mining Co., Ltd.). Sn 42 Bi 58 -Type 5 particle size distribution was measured using a dry-type camera particle size analyzer (Morphologi G3, Malvern). The results showed a particle size distribution of 15 μm to 25 μm, with a cumulative 50% number particle size (D). 50 The proportion of coarse solder particles with a diameter of 20μm or larger than 25μm is 5%.

[0103] A 200mm diameter twill fabric metal mesh screen (manufactured by Tokyo SCREEN Co., Ltd.) with 20μm apertures was installed on a spin air shave (manufactured by Seiko Corporation). A blower was used to apply suction at a pressure of 0.5 kPa. 50g of solder particles were fed into the raw material supply port. The system was run in air for 5 minutes from the time of raw material input until the end of the grading process. Using a forced airflow grading process with one grading cycle, particles passing through the sieve on the micronized side were recovered, resulting in graded solder particles.

[0104] The obtained graded solder particles were measured using a dry-type camera particle size analyzer (Morphologi G3, Malvern). The results showed that the proportion of coarse solder particles with a diameter greater than 25 μm was 0.01%. Scanning electron microscopy (SEM) revealed an uneven surface on the graded solder particles. Differential scanning calorimetry (DSC) was used to determine the endothermic peak of the graded solder particles, which was 141 °C. SEM observations of the graded solder particles after DSC measurement showed almost no particle aggregation due to melting compared to the ungraded solder particles.

[0105] In addition, the thickness of the oxide film in the center direction was measured from the surface of the graded solder particles using transmission electron microscopy (TEM). The results confirmed that the average thickness of the oxide film was 5 nm, which is thicker than that of the solder particles before grading.

[0106] In addition, the average surface roughness Ra of the graded solder particles was measured using atomic force microscopy (AFM), and the results confirmed that the average surface roughness Ra was 15 nm, which is larger than that of the solder particles before grading.

[0107] <Fabrication of Conductive Films>

[0108] Five parts by mass of the solder particles prepared in Example 1 and 95 parts by mass of the insulating adhesive described below were added to a planetary mixer and stirred for 1 minute to prepare a conductive composition.

[0109] Next, the conductive composition is coated onto a 50 μm thick PET film and dried in an oven at 80°C for 5 minutes to form a 25 μm thick adhesive layer on the PET film, thus producing a 2.0 mm wide conductive film.

[0110] -Insulating adhesive-

[0111] The insulating adhesive comprises a mixture of ethyl acetate and toluene containing 47 parts by weight of phenoxy resin (trade name: YP-50, manufactured by Shin-Nippon Chemical Epoxy Manufacturing Co., Ltd.), 3 parts by weight of monofunctional monomer (trade name: M-5300, manufactured by Toa Synthetic Co., Ltd.), 25 parts by weight of urethane resin (trade name: UR-1400, manufactured by Toyobo Corporation), 15 parts by weight of rubber component (trade name: SG80H, manufactured by Nagase ChemteX Co., Ltd.), 2 parts by weight of silane coupling agent (trade name: A-187, manufactured by Momentive Performance Materials Japan Co., Ltd.), and 3 parts by weight of organic peroxide (trade name: NYPER BW, manufactured by Nippon Oil Co., Ltd.) in such a manner that the solid components constitute 50% by weight.

[0112] <Construction of Connecting Structures>

[0113] Using the aforementioned conductive film, an evaluation substrate (glass epoxy board (FR4), 200 μm pitch, line:gap = 1:1, terminal thickness 10 μm, Cu (substrate) / Ni / Au plating) is thermo-pressed with an FPC (polyimide film, 200 μm pitch, line:gap = 1:1, terminal thickness 12 μm, Cu (substrate) / Ni / Au plating) to fabricate a connection structure.

[0114] Hot pressing is performed using a tool made of 200μm thick silicone rubber on an FPC, under the conditions of temperature: 150℃, pressure: 2MPa, and time: 20sec.

[0115] <Evaluation of conduction characteristics>

[0116] Regarding the manufactured connection structure, the initial on-resistance when a current of 1mA flows was measured using a digital multimeter (manufactured by Yokogawa Electric Corporation) using the 4-terminal method, and evaluated according to the following criteria.

[0117] In addition, a voltage is applied between the patterns of the connecting structures, and the initial insulation resistance is measured to confirm the presence or absence of short circuits. Furthermore, the initial insulation resistance is set to 1×10⁻⁶. 5 The rating below Ω is considered an NG (Not Acceptable) short circuit.

[0118] [Evaluation Criteria]

[0119] 〇: Case where the on-resistance is less than 1Ω

[0120] △: Case where the on-resistance exceeds 1Ω

[0121] ×: On-resistance is OPEN

[0122] (Example 2)

[0123] <Classification of Solder Particles>

[0124] In Example 1, the number of grading conditions was changed to 3 times. Otherwise, the same operation as in Example 1 was performed to carry out forced airflow grading process to produce solder particles of Example 2.

[0125] <Fabrication of conductive films, fabrication of interconnect structures, and evaluation>

[0126] Using the solder particles prepared in Example 2, conductive films and connection structures were fabricated in the same manner as in Example 1, and evaluated. The results are shown in Table 1.

[0127] (Example 3)

[0128] <Classification of Solder Particles>

[0129] In Example 1, the suction pressure in the grading conditions was changed to 1 MPa. Otherwise, the same operation as in Example 1 was performed to carry out forced airflow grading to produce solder particles of Example 3.

[0130] <Fabrication of conductive films, fabrication of interconnect structures, and evaluation>

[0131] Using the solder particles prepared in Example 3, conductive films and connection structures were fabricated in the same manner as in Example 1, and evaluated. The results are shown in Table 1.

[0132] (Example 4)

[0133] <Classification of Solder Particles>

[0134] In Example 1, Sn 42 Bi 58 -Type5 is replaced with Sn 42 Bi 58 Ag1-Type5 (manufactured by Senju Metals Co., Ltd.), except that, the same operation as in Example 1 was performed, and forced airflow classification processing was carried out to produce solder particles of Example 4.

[0135] Sn 42 Bi 58 Ag1-Type 5 was measured using a dry-type camera particle size analyzer (Morphologi G3, Malvern). The results showed a particle size distribution of 15 μm to 25 μm, with a cumulative 50% number particle size (D). 50 The proportion of coarse particles with a diameter of 20μm or larger is 6%.

[0136] <Fabrication of conductive films, fabrication of interconnect structures, and evaluation>

[0137] Using the solder particles prepared in Example 4, conductive films and connection structures were fabricated in the same manner as in Example 1, and evaluated. The results are shown in Table 2.

[0138] (Example 5)

[0139] <Classification of Solder Particles>

[0140] Sn is used as solder particles. 42 Bi 58 -Type5 (manufactured by Mitsui Metals & Minerals Co., Ltd.), for Classiel (manufactured by Seiko Corporation), the attached rotor rotates at 900 rpm, further utilizing a blower at 3m 3The suction intensity is / min. 50g of solder particles are fed into the raw material supply port. The process is carried out in the air for 5 minutes from the time the raw material is fed until the end of the classification. Through forced airflow classification with one classification cycle, the particles on the micro powder side are recovered, and classified solder particles are obtained.

[0141] The obtained graded solder particles were measured using a particle size analyzer, and the proportion of coarse solder particles with a diameter greater than 25 μm was 0%. SEM observation revealed an uneven surface on the graded solder particles. The endothermic peak of the graded solder particles was measured using differential scanning calorimetry (DSC), showing a peak temperature of 141℃. SEM observation of the particles after DSC measurement showed almost no particle aggregation due to melting compared to the ungraded particles.

[0142] In addition, the thickness of the oxide film in the center direction was measured from the surface of the graded solder particles using transmission electron microscopy (TEM). The results confirmed that the average thickness of the oxide film was 8 nm, which is significantly thicker than that of the solder particles before grading.

[0143] In addition, the average surface roughness Ra of the graded solder particles was measured using atomic force microscopy (AFM), and the results confirmed that the average surface roughness Ra was 20 nm, which was larger than that of the solder particles before grading.

[0144] <Fabrication of conductive films, fabrication of interconnect structures, and evaluation>

[0145] Using the solder particles prepared in Example 5, conductive films and connection structures were fabricated in the same manner as in Example 1, and evaluated. The results are shown in Table 2.

[0146] (Example 6)

[0147] <Classification of Solder Particles>

[0148] In Example 5, the rotor speed in the grading conditions was changed to 1200 rpm. Otherwise, the same operation as in Example 1 was performed to carry out forced airflow grading to produce the solder particles of Example 6.

[0149] <Fabrication of conductive films, fabrication of interconnect structures, and evaluation>

[0150] Using the solder particles prepared in Example 6, conductive films and connection structures were fabricated in the same manner as in Example 1, and evaluated. The results are shown in Table 2.

[0151] (Example 7)

[0152] <Classification of Solder Particles>

[0153] In Example 5, the rotor speed in the grading conditions was changed to 1800 rpm. Otherwise, the same operation as in Example 1 was performed to conduct forced airflow grading to produce the solder particles of Example 7.

[0154] <Fabrication of conductive films, fabrication of interconnect structures, and evaluation>

[0155] Using the solder particles prepared in Example 7, conductive films and connection structures were fabricated in the same manner as in Example 1, and evaluated. The results are shown in Table 3.

[0156] (Comparative Example 1)

[0157] As solder particles, Sn 42 Bi 58 -Type5 (Mitsui Metals & Minerals Co., Ltd.) is used directly without classification.

[0158] The endothermic peak of the solder particles was determined by differential scanning calorimetry (DSC), and the result showed 141℃. The results of scanning electron microscopy (SEM) observation of the particles after DSC measurement showed that the particles could agglomerate in large quantities through melting.

[0159] Furthermore, the thickness of the oxide film in the center direction was measured using transmission electron microscopy (TEM) on the surface of the solder particles. The results confirmed that the average thickness of the oxide film was 1 nm, which is thinner than that of the graded solder particles in Examples 1-7. Additionally, the average surface roughness Ra of the solder particles was measured using atomic force microscopy (AFM). The results confirmed that the average surface roughness Ra was 5 nm, which is smaller than that of the graded solder particles in Examples 1-7.

[0160] <Fabrication of conductive films, fabrication of interconnect structures, and evaluation>

[0161] Using the solder particles of Comparative Example 1, conductive films and connection structures were fabricated in the same manner as in Example 1, and evaluated. The results are shown in Table 3.

[0162] (Comparative Example 2)

[0163] <Classification of Solder Particles>

[0164] Sn is used as solder particles. 42 Bi 58 -Type5 (Made by Mitsui Metals & Minerals Co., Ltd.), Sn 42 Bi 58 -Type5 uses a sieve vibrator (VUD-80, manufactured by Tsutsui Rikenki Co., Ltd.) with a #20μm mesh sieve to classify and remove coarse solder particles.

[0165] The obtained graded solder particles were measured using a particle size analyzer, and the proportion of coarse solder particles with a diameter greater than 25 μm was 0%. The surface of the obtained graded solder particles was almost unchanged from that before grading, which could be confirmed by scanning electron microscopy (SEM). The endothermic peak of the graded solder particles was measured using differential scanning calorimetry (DSC), and the results showed that the peak was 141℃. SEM observation of the particles after DSC measurement showed that the particles could agglomerate extensively due to melting.

[0166] Furthermore, the average thickness of the oxide film in the central direction was measured using a transmission electron microscope (TEM) on the surface of the graded solder particles. The results confirmed that the average thickness of the oxide film was 2 nm, which is thinner than that of the graded solder particles in Examples 1 to 7.

[0167] In addition, the average surface roughness Ra of the graded solder particles was measured using atomic force microscopy (AFM), and the results confirmed that the average surface roughness Ra was 8 nm, which was smaller than that of the graded solder particles in Examples 1 to 7.

[0168] <Fabrication of conductive films, fabrication of interconnect structures, and evaluation>

[0169] Using the solder particles prepared in Comparative Example 2, conductive films and connection structures were fabricated in the same manner as in Example 1, and evaluated. The results are shown in Table 3.

[0170] [Table 1]

[0171]

[0172] [Table 2]

[0173]

[0174] [Table 3]

[0175]

[0176] As can be seen from the results in Tables 1 to 3, in Examples 1 to 7, the initial conduction resistance and the initial insulation resistance all obtained good values.

[0177] Furthermore, in Comparative Example 1, the initial conduction resistance was good, but a short circuit occurred during the initial insulation resistance measurement. Observation of the patterns of the short circuit channels revealed areas where large spherical solder particles with a diameter of approximately φ30μm were trapped, or areas where irregularly shaped solder grew from the melted and coarse solder particles.

[0178] Furthermore, in Comparative Example 2, the initial conduction resistance was good, but a short circuit occurred during the initial insulation resistance measurement. Observation of the patterns of the short-circuit channels revealed areas where irregularly shaped solder particles grew from the molten solder particles and coarse solder particles.

[0179] Industry availability

[0180] The solder particles and conductive composition of the present invention can avoid the risk of short circuits and suppress the reduction of insulation. Therefore, they are suitable for, for example, the connection of ITO (Indium Tin Oxide) electrodes formed on the glass substrate of flexible printed circuit boards (FPCs), IC chip terminals and LCD panels, the connection of COF to PWB, the connection of TCP to PWB, the connection of COF to glass substrates, the connection of COF to COF, the connection of IC substrates to glass substrates, and the connection of IC substrates to PWB.

[0181] This international application claims priority based on Japanese Patent Application No. 2021-138864, filed on August 27, 2021, and incorporates the entire contents of Japanese Patent Application No. 2021-138864 into this international application.

[0182] Explanation of symbols

[0183] 10 Wiring Pattern

[0184] 11. Coarse solder particles

[0185] 12 solder particles

[0186] 13 Metallic bodies

[0187] 20 Solder particles before grading

[0188] 21. Graded solder particles

[0189] 22 Oxide film

[0190] Thickness of oxide film on solder particles before L1 grading

[0191] The thickness of the oxide film on solder particles after L2 grading

Claims

1. A type of solder particle, characterized in that, The surface has an oxide film with an average thickness of 5 nm to 100 nm, and the solder particles have an average surface roughness Ra of 15 nm to 110 nm and a number average particle size of 1 μm or more. The proportion of coarse solder particles with a number average particle size of 1.25 times or more is 0.5% or less.

2. The solder particles according to claim 1, comprising: Sn, and at least one selected from Bi, Ag, Cu and In.

3. The solder particles according to claim 1 or 2, It is manufactured through a forced airflow staged process in an oxygen-containing atmosphere.

4. A method for manufacturing solder particles, which is the method for manufacturing solder particles as described in claim 1 or 2, characterized in that it includes a grading step: In an oxygen-containing atmosphere, a classifying device forces the airflow to be generated, classifying the solder particles.

5. The method for manufacturing solder particles according to claim 4, The grading device is a device that uses a blower to draw in airflow, causing solder particles to rotate and collide with the screen surface for grading.

6. The method for manufacturing solder particles according to claim 4, The grading device is a device in which air vortexes rotate together with solder particles in a grading chamber, and grading is performed by controlling the rotational centrifugal force generated by the rotation of the rotor and the air flow drawn towards the center of the rotor by a blower.

7. A conductive composition, characterized in that, It contains solder particles as described in any one of claims 1 to 3.

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