Solder particles, method for producing solder particles, and conductive composition

Abstract

To provide a solder particle that can avoid the risk of a short circuit and can suppress a deterioration of insulation properties, a method for producing a solder particle, and a conductive composition.SOLUTION: Provided are solder particles that have oxidized films on the surfaces thereof. The oxidized films have an average film thickness of at least 3 nm and an average surface roughness Ra of at least 10 nm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to solder particles, a method for producing solder particles, and a conductive composition. [Background technology]

[0002] Compared to metal-coated resin particles, which are commonly used as conductive particles, currently commercially available solder particles are not uniform in particle size (the particle size distribution is wide) and contain a certain amount of coarse solder particles. Therefore, when wiring patterns are connected using conductive compositions containing currently available solder particles, there is a risk of short circuits occurring due to coarse solder particles 11 present in the non-pressure-applied areas between wiring patterns 10 during thermocompression mounting, as shown in Figure 1. In Figure 1, 12 represents solder particles.

[0003] Furthermore, when wiring patterns are connected using a conductive composition containing metal-coated resin particles as conductive particles, the insulating binder present around the metal-coated resin particles ensures insulation between the wiring patterns. However, when wiring patterns are connected using a conductive composition containing solder particles as conductive particles, as shown in Figure 2, solder particles 12 between wiring patterns 10 melt during thermocompression bonding and self-aggregate to form large metal bodies 13, which may cause short circuits due to the large metal bodies present in the non-pressurized areas between the wiring patterns during thermocompression mounting.

[0004] To avoid the risk of such short circuits, it is conceivable to form an insulating film on the surface of solder particles. For example, a solder powder for solder paste 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 median particle size of 20 μm to 40 μm (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4084657 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the purpose of forming an oxide film with an average thickness of 2.5 nm to 6 nm in Patent Document 1 is to suppress an increase in viscosity of the paste over time after paste preparation, not to avoid the risk of short circuits, to prevent the melting and self-aggregation and coarsening of solder particles present between wiring patterns, or to suppress a decrease in insulation properties. Furthermore, Patent Document 1 does not mention or suggest that the average surface roughness Ra is 15 nm to 110 nm, or that the oxide film is formed by forced air classification in an oxygen atmosphere.

[0007] On the other hand, it is difficult to form an insulating film using the mechanochemical method with currently available solder particles. This is because, as mentioned above, the particle sizes of currently available solder particles are not uniform, making it difficult to form a uniform insulating film, and because the solder particles are relatively soft, they cannot withstand the physical impact force of the mechanochemical method and are therefore deformed.

[0008] The present invention aims to solve the above-mentioned problems in the prior art and to achieve the following objectives: That is, the present invention aims to provide solder particles, a method for manufacturing solder particles, and a conductive composition that can avoid the risk of short circuits and suppress deterioration of insulation properties. [Means for solving the problem]

[0009] The means for solving the above problems are as follows: <1> The solder particles have an oxide film on the surface, the oxide film having an average thickness of 3 nm or more and an average surface roughness Ra of 10 nm or more. <2> The oxide film has an average thickness of 5 nm or more and 100 nm or less, and an average surface roughness Ra of 15 nm or more and 110 nm or less. <1> The solder particles are as described in <3> The number average particle size is 1 μm or more. <1> from <2> The solder particles are any of the above. <4> the proportion of coarse solder particles having a number particle size 1.25 times or more larger than the number average particle size of the solder particles is 0.5% or less; <3> The solder particles are as described in <5> Sn and at least one selected from Bi, Ag, Cu, and In. <1> from <4> The solder particles are any of the above. <6> The above-mentioned is produced by a forced air classification treatment under an oxygen-containing atmosphere. <1> from <5> The solder particles are any of the above. <7> The method for manufacturing solder particles is characterized by including a classification step in which solder particles are classified by forcibly generating an air flow using a classification device in an oxygen-containing atmosphere. <8> The classifying device is a device that generates an airflow by suction with a blower, causes the solder particles to swirl and collide with a sieve surface, and classifies the solder particles. <7> This is a method for producing solder particles described in . <9> The classifying device is a device in which an air vortex swirls together with solder particles in a classification chamber, and classifies the solder particles by controlling the swirling centrifugal force generated by the rotation of the rotor and the air flow flowing toward the center of the rotor due to blower suction. <7> This is a method for producing solder particles described in . <10> The aforementioned <1> from <6> The present invention provides a conductive composition comprising the solder particles according to any one of the above items. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide solder particles, a method for manufacturing solder particles, and a conductive composition that can solve the above-mentioned problems in the past, achieve the above-mentioned objectives, avoid the risk of short circuits, and suppress a decrease in insulation properties. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram showing that when commercially available solder particles are used as conductive particles, short circuits occur due to large solder particles. [Figure 2] FIG. 2 is a schematic diagram showing that when a conductive film containing solder particles is heated and pressed between wiring patterns, the solder particles melt and self-aggregate to form large metal bodies. [Figure 3] Figures 3(a) and (b) are schematic diagrams showing that by increasing the average surface roughness of the classified solder particles, the contact area between the solder particles can be reduced compared to the solder particles before classification, which have a smaller average surface roughness. [Figure 4] Figures 4(a) and (b) are schematic diagrams showing that by increasing the average surface roughness of classified solder particles, the average thickness of the oxide film can be increased in a pseudo manner compared to solder particles before classification, which have a small average surface roughness. DETAILED DESCRIPTION OF THE INVENTION

[0012] (solder particles) The solder particles of the present invention have an oxide film on the surface, the oxide film having an average film thickness of 3 nm or more and an average surface roughness Ra of 10 nm or more. The oxide film preferably has an average thickness of 5 nm or more and 100 nm or less, and an average surface roughness Ra of 15 nm or more and 110 nm or less.

[0013] In the present invention, by classifying solder particles using a forced air classifier in an oxygen-containing atmosphere, coarse solder particles contained in commercially available solder particles can be removed, avoiding the risk of short circuits between wiring patterns due to coarse solder particles, and by roughening the solder particle surface and forming an oxide film on the surface, it is possible to prevent the solder particles present between the wiring patterns from melting and self-aggregating to become coarse, thereby suppressing a decrease in insulation properties.

[0014] The solder particles of the present invention have an oxide film on their surface with an average thickness of 3 nm or more. Therefore, when solder particles are mounted by thermocompression bonding, solder particles present in non-pressurized areas, such as between wiring patterns, do not melt and coalesce even when the solder particles reach their melting point, thereby preventing a decrease in insulation properties. The average thickness of the oxide film on currently commercially available solder particles (solder particles before classification) is about 1 nm, so the above-mentioned effects cannot be obtained. There is no particular upper limit to the thickness of the oxide film, but if the oxide film of the solder particles is too thick, the oxide film of the solder particles sandwiched between the upper and lower electrodes may not break during thermocompression mounting, resulting in an increase in electrical resistance, so it is preferable that the average thickness of the oxide film is 100 nm or less. Here, the average thickness of the oxide film was measured using, for example, a transmission electron microscope (TEM) (JEM-2100plus, manufactured by JEOL Ltd.) to measure the thickness of the oxide film from the surface toward the center of the solder particle in a cross-sectional photograph of the solder particle. The average oxide film thickness is calculated by measuring the oxide film thickness at three points on each solder particle, calculating the oxide film thickness for 10 solder particles, and averaging these oxide film thicknesses.

[0015] The solder particles of the present invention have an average surface roughness Ra of 10 nm or more, that is, by roughening the surface of the solder particles to form irregularities, an oxide film can be further formed in the depth direction of the solder particles.

[0016] 3(a) and 3(b) are schematic diagrams showing that by increasing the average surface roughness of classified solder particles 21, the contact area between solder particles can be reduced compared to unclassified solder particles 20, which have a small average surface roughness. As shown in FIG. 3(b), classified solder particles 21 of the present invention have a large average surface roughness Ra, which allows the contact area between solder particles to be reduced compared to unclassified solder particles 20 shown in FIG. 3(a). In FIG. 3, 22 is an oxide film.

[0017] 4(a) and 4(b) are schematic diagrams showing that by increasing the average surface roughness of classified solder particles 21, the average thickness of the oxide film can be increased in a pseudo manner compared to unclassified solder particles 20, which have a small average surface roughness. As shown in FIG. 4(b), classified solder particles 21 of the present invention have a large average surface roughness Ra, so that the thickness L1 of the oxide film of the unclassified solder particles can be increased in a pseudo manner to the thickness L2 of the oxide film of the classified solder particles, compared to unclassified solder particles 20 shown in FIG. 4(a). In FIG. 4, 22 denotes an oxide film.

[0018] As shown in Figures 3 and 4, the solder particles of the present invention, which are present in non-pressurized areas such as between wiring patterns during thermocompression mounting, do not melt and coalesce even when the contacting solder particles reach their melting point, thereby preventing a decrease in insulation properties. The average surface roughness Ra of solder particles currently available on the market (solder particles before classification) is about 1 nm, so the above-mentioned effects cannot be obtained.

[0019] The solder particles of the present invention can achieve the above-mentioned effects by having an average surface roughness Ra of 10 nm or more. While there is no particular upper limit for the average surface roughness Ra, if the average surface roughness Ra is too large, the classification process will cause significant damage not only to the solder particle surface but also to the entire solder particle, resulting in cracking and chipping of the solder particle. Furthermore, if the average surface roughness Ra of the solder particle is too large, it is equivalent to having an oxide film that is too thick, and the oxide film of the solder particle sandwiched between the upper and lower electrodes may not break during thermocompression mounting, resulting in increased conduction resistance. For this reason, the average surface roughness Ra is preferably 500 nm or less. The average surface roughness Ra of the solder particles is, for example, measured using an AFM (SPA400 NanoNaviII, manufactured by Hitachi High-Tech Corporation) at five locations per solder particle, and the surface roughness of 10 solder particles is calculated and averaged to obtain the average value of these surface roughnesses.

[0020] Examples of the solder particles include Sn-Pb, Pb-Sn-Sb, Sn-Sb, Sn-Pb-Bi, Bi-Sn, Sn-Cu, Sn-Pb-Cu, Sn-In, Sn-Ag, Sn-Pb-Ag, and Pb-Ag systems as specified in JIS Z3282-1999, and preferably contain Sn and at least one selected from Bi, Ag, Cu, and In, and specific examples include SnBi, SnBiAg, SnAgCu, and SnIn. The melting point of the solder particles is preferably 110°C or higher and 240°C or lower, and more preferably 120°C or higher and 200°C or lower.

[0021] The number 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 number 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. The number-average particle size of the solder particles can be expressed as a number frequency by measuring approximately 10,000 particles using, for example, a dry imaging particle size distribution analyzer (Morphologi G3, manufactured by Malvern). The proportion of coarse solder particles having a number particle size 1.25 times or more larger than the number average particle size in the solder particles 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%. When the proportion of coarse solder particles having a number particle size 1.25 times or more larger than the number average particle size in the solder particles is 0.5% or less, it is possible to avoid the occurrence of short circuits between wiring patterns due to the coarse solder particles.

[0022] (Method for manufacturing solder particles) The method for producing solder particles of the present invention includes a classification step in which solder particles are classified by forcibly generating an airflow using a classifier in an oxygen-containing atmosphere, and may further include other steps as necessary.

[0023] The classification device uses a device that generates a forced airflow to disperse particles and roughen their surfaces while classifying them. The classification device may be (1) a device that uses a sieve to spin particles with an airflow, causing them to collide with the sieve and pass through the sieve for classification, or (2) a device that does not use a sieve but uses a rotor that generates a spinning centrifugal force, and classifies solder particles by balancing the centrifugal force generated when the solder particles collide with the rotor and the drag of the air.

[0024] The classification device (1) mentioned above includes a device that generates an airflow by suction with a blower, causing the particles to rotate and collide repeatedly against a sieve surface for classification. With this classification device, the solder particle surfaces are roughened by the collisions between the solder particles and the sieve surface, and at the same time, an oxide film is formed while the solder particles are classified. An example of such a classification device is the Spin Air Sieve (manufactured by Seishin Enterprise Co., Ltd.). The blower suction pressure is preferably 0.1 MPa or more and 1.5 MPa or less, and more preferably 0.5 MPa or more and 1.0 MPa or less.

[0025] The classification device used in (2) above is a device in which an air vortex swirls with the solder particles in a classification chamber, and the rotor rotation generates a centrifugal force that balances with the airflow toward the center of the rotor due to blower suction, separating the solder particles into coarse and fine powders. The collisions between the solder particles and the rotor surface roughen the solder particle surfaces, forming an oxide film while the particles are classified. An example of such a classification device is the Cruseal (manufactured by Seishin Enterprise Co., Ltd.). The rotor rotation speed is preferably 500 rpm or more and 2,000 rpm or less, and more preferably 900 rpm or more and 1,800 rpm or less.

[0026] The classification 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. When the oxygen concentration is 15 vol% or more, a strong 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%.

[0027] (Conductive composition) The conductive composition of the present invention contains the solder particles of the present invention, and preferably contains a binder, a monofunctional polymerizable monomer, an elastomer, a curing agent, and a silane coupling agent, and may further contain other components as necessary.

[0028] The conductive composition may be either a film-like conductive film or a paste-like conductive paste. A conductive film is preferred in terms of ease of handling, and a conductive paste is preferred in terms of cost. When the conductive composition is a conductive film, a film not containing solder particles may be laminated on the conductive film containing solder particles.

[0029] -Solder particles- As the solder particles, the above-described solder particles of the present invention are used. The content of the solder particles in the conductive composition is not particularly limited, and can be adjusted appropriately depending on the wiring pitch and connection area of ​​the connection structure.

[0030] -binder- The binder is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include phenoxy resin, epoxy resin, unsaturated polyester resin, saturated polyester resin, urethane resin, butadiene resin, polyimide resin, polyamide resin, polyolefin resin, etc. These may be used alone or in combination of two or more. Among these, phenoxy resin is particularly preferred in terms of film-forming ability, processability, and connection reliability. The phenoxy resin is a resin synthesized from bisphenol A and epichlorohydrin, and may be either a suitably synthesized product or a commercially available product, such as YP-50 (manufactured by Tohto Kasei Co., Ltd.), YP-70 (manufactured by Tohto Kasei Co., Ltd.), or EP1256 (manufactured by Japan Epoxy Resins Co., Ltd.). The content of the binder in the conductive composition is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 20% by mass to 70% by mass, and more preferably 35% by mass to 55% by mass, for example.

[0031] -Monofunctional polymerizable monomer- The monofunctional polymerizable monomer is not particularly limited as long as it has one polymerizable group in the molecule and can be appropriately selected depending on the purpose. Examples include monofunctional (meth)acrylic monomers, styrene monomers, butadiene monomers, and other olefin-based monomers having double bonds. These may be used alone or in combination of two or more. Among these, monofunctional (meth)acrylic monomers are particularly preferred in terms of adhesive strength and connection reliability. The monofunctional (meth)acrylic monomer is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include acrylic acid or esters thereof, such as 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, and phenyl acrylate; and methacrylic acid or esters thereof, such as 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, and diethylaminoethyl methacrylate. These may be used alone or in combination of two or more.

[0032] The content of the monofunctional polymerizable monomer in the conductive composition is not particularly limited and can be appropriately selected depending on the purpose, and is preferably 2% by mass to 30% by mass, and more preferably 5% by mass to 20% by mass.

[0033] - Hardener - The curing agent is not particularly limited as long as it can cure the binder, and can be appropriately selected depending on the purpose. For example, organic peroxides are suitable. Examples of the organic peroxide include lauroyl peroxide, butyl peroxide, benzyl peroxide, dilauroyl peroxide, dibutyl peroxide, benzyl peroxide, peroxydicarbonate, benzoyl peroxide, etc. These may be used alone or in combination of two or more. The content of the curing agent in the conductive composition is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 1% by mass to 15% by mass, more preferably 3% by mass to 10% by mass.

[0034] -Elastomer- The elastomer is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include polyurethane elastomers, acrylic rubbers, silicone rubbers, butadiene rubbers, etc. These may be used alone or in combination of two or more.

[0035] -Silane coupling agent- The silane coupling agent is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include epoxy-based silane coupling agents, acrylic-based silane coupling agents, thiol-based silane coupling agents, and amine-based silane coupling agents. The content of the silane coupling agent in the conductive composition is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 0.5% by mass to 10% by mass, more preferably 1% by mass to 5% by mass.

[0036] -Other ingredients- The other components are not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include organic solvents, fillers, softeners, accelerators, antioxidants, colorants (pigments, dyes), ion catcher agents, etc. The amount of the other components added is not particularly limited and can be appropriately selected depending on the purpose.

[0037] <Application> The solder particles and conductive composition of the present invention can avoid the risk of short circuits and suppress a decrease in insulation properties, and can therefore be used to electrically connect the electrodes of various connection target components, such as connecting a flexible printed circuit board to a glass substrate (FOG (Film on Glass)), connecting a semiconductor chip to a flexible printed circuit board (COF (Chip on Film)), connecting a semiconductor chip to a glass substrate (COG (Chip on Glass)), and connecting a flexible printed circuit board to a glass epoxy substrate (FOB (Film on Board)). [Example]

[0038] Examples of the present invention will be described below, but the present invention is not limited to these examples in any way.

[0039] <Particle size distribution measurement> Approximately 10,000 particles were measured using a dry imaging particle size distribution analyzer (Morphologi G3, manufactured by Malvern), and the particle size distribution was expressed as a number frequency.

[0040] <Measurement of the average oxide film thickness> The thickness of the oxide film from the surface toward the center of the solder particle in a cross-sectional photograph of the solder particle was measured using a transmission electron microscope (TEM) (JEM-2100plus, manufactured by JEOL Ltd.). The average oxide film thickness is calculated by measuring the oxide film thickness at three points on each solder particle, calculating the oxide film thickness for 10 solder particles, and averaging these oxide film thicknesses.

[0041] <Measurement of average surface roughness Ra> Using an atomic force microscope (AFM) (SPA400 NanoNaviII, manufactured by Hitachi High-Tech Corporation), the surface roughness at five locations of each solder particle was measured. The surface roughness of 10 solder particles was determined, and the average value obtained by averaging these surface roughnesses was used.

[0042] <Measurement of the endothermic peak of solder particles by DSC> The endothermic peak of the solder particles by DSC was measured using a differential scanning calorimeter (DSC) (EXSTAR DSC6200, manufactured by Seiko Instruments Inc.).

[0043] <SEM observation of the surface of solder particles> The SEM observation of the surface of the solder particles was performed using a scanning electron microscope (SEM) (JSM-6510A, manufactured by JEOL Ltd.).

[0044] (Example 1) <Classification of solder particles> Sn was used as the solder particle 42 Bi 58 -Type5 (manufactured by Mitsui Mining & Smelting Co., Ltd.) was prepared. Sn 42 Bi 58 -Type5 was measured with a dry imaging type particle size distribution analyzer (Morphologi G3, manufactured by Malvern). As a result, the particle size distribution was 15 μm to 25 μm, the cumulative 50% number particle size (D 50 ) was 20 μm, and the ratio of coarse solder particles with a number particle size of 25 μm or more was 5%. A woven wire mesh sieve (manufactured by Tokyo Screen Co., Ltd.) with a diameter of φ200 mm and a mesh size of opening 20 μm was set on a spin air sieve (manufactured by Seishin Enterprise Co., Ltd.), and suction was performed with a blower so that the suction pressure was 0.5 kPa. 50 g of solder particles were introduced from the raw material supply port. The operation was carried out for 5 minutes in the air from the raw material introduction to the end of classification, and the particles on the fine powder side that passed through the sieve were recovered by forced air flow type classification treatment with one classification cycle to obtain classified solder particles. The resulting classified solder particles were measured using a dry imaging particle size distribution analyzer (Morphologi G3, manufactured by Malvern), and the proportion of coarse solder particles with a number particle size of 25 μm or more was found to be 0.01%. Scanning electron microscope (SEM) observation of the resulting classified solder particles revealed that they had uneven surfaces. Differential scanning calorimetry (DSC) measurements of the classified solder particles revealed an endothermic peak of 141°C. SEM observation of the classified solder particles after DSC measurement revealed that, compared to the solder particles before classification, the classified solder particles showed almost no aggregation due to particle melting. In addition, the thickness of the oxide film from the surface toward the center of the classified solder particles was measured using a transmission electron microscope (TEM), and it was confirmed that the average thickness of the oxide film was 5 nm, which was thicker than that of the solder particles before classification. In addition, the average surface roughness Ra of the classified solder particles was measured using an atomic force microscope (AFM), and it was found to be 15 nm, which was greater than the average surface roughness Ra of the solder particles before classification.

[0045] <Preparation of conductive film> Five parts by mass of the prepared solder particles of Example 1 and 95 parts by mass of the insulating binder described below were placed in a planetary stirrer and stirred for one minute to prepare a conductive composition. Next, the conductive composition was applied to a 50 μm thick PET film and dried in an oven at 80°C for 5 minutes, forming a 25 μm thick adhesive layer made of the conductive composition on the PET film, and producing a conductive film 2.0 mm wide.

[0046] -Insulating binder- The insulating binder was a mixed solution of ethyl acetate and toluene containing 47 parts by mass of phenoxy resin (trade name: YP-50, manufactured by Shin-Nichika Epoxy Manufacturing Co., Ltd.), 3 parts by mass of monofunctional monomer (trade name: M-5300, manufactured by Toagosei Co., Ltd.), 25 parts by mass of urethane resin (trade name: UR-1400, manufactured by Toyobo Co., Ltd.), 15 parts by mass of rubber component (trade name: SG80H, manufactured by Nagase ChemteX Corporation), 2 parts by mass of silane coupling agent (trade name: A-187, manufactured by Momentive Performance Materials Japan), and 3 parts by mass of organic peroxide (trade name: Nyper BW, manufactured by NOF Corporation) so that the solid content was 50% by mass.

[0047] <Fabrication of connection structure> A connection structure was produced by thermocompression bonding an evaluation substrate (glass epoxy substrate (FR4), 200 μm pitch, line:space=1:1, terminal thickness 10 μm, Cu (undercoat) / Ni / Au plating) and an FPC (polyimide film, 200 μm pitch, line:space=1:1, terminal thickness 12 μm, Cu (undercoat) / Ni / Au plating) via the conductive film. Thermocompression bonding was performed by pressing a tool down through a 200 μm thick silicone rubber on the FPC under the conditions of temperature: 150°C, pressure: 2 MPa, and time: 20 seconds.

[0048] <Evaluation of conduction characteristics> The initial conduction resistance of the produced connection structure was measured using a digital multimeter (manufactured by Yokogawa Electric Corporation) by the four-terminal method when a current of 1 mA was passed through it, and the results were evaluated according to the following criteria. In addition, a voltage was applied between the patterns of the connection structure, and the initial insulation resistance was measured to check for the presence or absence of a short circuit. 5 Ω or less was evaluated as NG for short circuit occurrence. [Evaluation criteria] ○: When the conduction resistance is 1Ω or less △: When the conduction resistance exceeds 1Ω ×: Conduction resistance is open

[0049] Example 2 <Solder particle classification> Solder particles of Example 2 were produced by carrying out forced airflow classification in the same manner as in Example 1, except that the number of classifications in the classification conditions was changed to three.

[0050] <Preparation of conductive film, preparation of connection structure, and evaluation> Using the prepared solder particles of Example 2, a conductive film and a connection structure were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0051] Example 3 <Solder particle classification> Solder particles of Example 3 were produced by carrying out forced airflow classification in the same manner as in Example 1, except that the suction pressure in the classification conditions was changed to 1 MPa.

[0052] <Preparation of conductive film, preparation of connection structure, and evaluation> Using the prepared solder particles of Example 3, a conductive film and a connection structure were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0053] Example 4 <Solder particle classification> In Example 1, Sn 42 Bi 58 -Type5, Sn 42 Bi 58 Solder particles of Example 4 were produced by performing forced airflow classification in the same manner as in Example 1, except that Ag1-Type5 (manufactured by Senju Metal Co., Ltd.) was used instead. Sn 42 Bi 58 Ag1-Type5 was measured using a dry imaging particle size distribution analyzer (Morphologi G3, manufactured by Malvern). The particle size distribution was 15 μm to 25 μm, and the cumulative 50% number particle size (D 50 ) 20 μm, and the proportion of coarse particles with a number diameter of 25 μm or more was 6%.

[0054] <Preparation of conductive film, preparation of connection structure, and evaluation> Using the prepared solder particles of Example 4, a conductive film and a connection structure were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0055] Example 5 <Solder particle classification> Sn as solder particles 42 Bi 58 -Using Type 5 (manufactured by Mitsui Mining & Smelting Co., Ltd.), the attached rotor of Cruseal (manufactured by Seishin Enterprise Co., Ltd.) was rotated at 900 rpm, and then blown for 3 m. 3 The machine was suctioned at a strength of 1 / min. 50g of solder particles were added through the raw material supply port. It was operated in air for 5 minutes from the time the raw material was added until the end of classification, and the fine particles were collected through a single forced air classification process to obtain classified solder particles. The resulting classified solder particles were measured using a particle size distribution analyzer, and the proportion of coarse solder particles with a number particle size of 25 μm or more was found to be 0%. SEM observation revealed that the surfaces of the resulting classified solder particles were uneven. When the classified solder particles were measured using a differential scanning calorimeter (DSC), they showed an endothermic peak of 141°C, and scanning electron microscope (SEM) observation of the particles after DSC measurement revealed that there was almost no aggregation of particles due to particle melting in the classified solder particles compared to the particles before classification. In addition, the thickness of the oxide film from the surface toward the center of the classified solder particles was measured using a transmission electron microscope (TEM), and it was confirmed that the average thickness of the oxide film was 8 nm, which was thicker than that of the solder particles before classification. In addition, the average surface roughness Ra of the classified solder particles was measured using an atomic force microscope (AFM), and it was found to be 20 nm, which was greater than that of the solder particles before classification.

[0056] <Preparation of conductive film, preparation of connection structure, and evaluation> Using the prepared solder particles of Example 5, a conductive film and a connection structure were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0057] Example 6 <Solder particle classification> Solder particles of Example 6 were produced by carrying out forced airflow classification in the same manner as in Example 1, except that in Example 5, the rotor rotation speed in the classification conditions was changed to 1200 rpm.

[0058] <Preparation of conductive film, preparation of connection structure, and evaluation> Using the prepared solder particles of Example 6, a conductive film and a connection structure were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0059] Example 7 <Solder particle classification> Solder particles of Example 7 were produced by carrying out forced airflow classification in the same manner as in Example 1, except that in Example 5, the rotor rotation speed in the classification conditions was changed to 1800 rpm.

[0060] <Preparation of conductive film, preparation of connection structure, and evaluation> Using the prepared solder particles of Example 7, a conductive film and a connection structure were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0061] (Comparative Example 1) Sn as solder particles 42 Bi 58 Type 5 (manufactured by Mitsui Mining & Smelting Co., Ltd.) was used as is without classification. When the solder particles were measured using a differential scanning calorimeter (DSC), the endothermic peak was 141°C. After the DSC measurement, the particles were observed under a scanning electron microscope (SEM), and it was found that numerous agglomerations of particles had formed due to particle melting. Furthermore, the thickness of the oxide film from the surface toward the center of the classified solder particles was measured using a transmission electron microscope (TEM), and it was found that the average thickness of the oxide film was 1 nm, which was thinner than the average thickness of the oxide film of the classified solder particles of Examples 1 to 7. Furthermore, the average surface roughness Ra of the solder particles was measured using an atomic force microscope (AFM), and it was found that the average surface roughness Ra was 5 nm, which was smaller than the average surface roughness Ra of the classified solder particles of Examples 1 to 7.

[0062] <Preparation of conductive film, preparation of connection structure, and evaluation> A conductive film and a connection structure were produced and evaluated using the solder particles of Comparative Example 1 in the same manner as in Example 1. The results are shown in Table 3.

[0063] (Comparative Example 2) <Solder particle classification> Sn as solder particles 42 Bi 58 -Type 5 (manufactured by Mitsui Mining & Smelting Co., Ltd.) 42 Bi 58 -Type 5 was classified using a sieve shaker (VUD-80, manufactured by Tsutsui Rikagaku Kiki Co., Ltd.) with a sieve having openings of #20 μm to remove coarse solder particles. Measurement of the resulting classified solder particles using a particle size distribution analyzer revealed that the proportion of coarse solder particles with a number particle size of 25 μm or more was 0%. Observation with a scanning electron microscope (SEM) confirmed that the surfaces of the resulting classified solder particles were virtually unchanged from before classification. Measurement of the endothermic peak of the classified solder particles using a differential scanning calorimeter (DSC) showed a value of 141°C, and SEM observation of the particles after the DSC measurement revealed that numerous agglomerations of particles had formed due to particle melting. In addition, the average thickness of the oxide film from the surface toward the center of the classified solder particles was measured using a transmission electron microscope (TEM), and it was found that the average thickness of the oxide film was 2 nm, which was thinner than that of the classified solder particles of Examples 1 to 7. Furthermore, the average surface roughness Ra of the classified solder particles was measured using an atomic force microscope (AFM), and it was found that the average surface roughness Ra was 8 nm, which was smaller than the average surface roughness Ra of the classified solder particles of Examples 1 to 7.

[0064] <Preparation of conductive film, preparation of connection structure, and evaluation> Using the prepared solder particles of Comparative Example 2, a conductive film and a connection structure were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0065] [Table 1]

[0066] [Table 2]

[0067] [Table 3]

[0068] The results in Tables 1 to 3 show that in all of Examples 1 to 7, good values ​​were obtained for both the initial conduction resistance and the initial insulation resistance. In addition, in Comparative Example 1, the initial conduction resistance was good, but a short circuit occurred during the measurement of the initial insulation resistance. When the channel patterns where the short circuit occurred were observed, areas where spherical solder particles with a diameter of about φ30 μm were sandwiched, or areas where irregularly shaped solder particles existed, where solder particles had melted and grown into coarse solder particles, were observed. In addition, in Comparative Example 2, the initial conduction resistance was good, but a short circuit occurred during the measurement of the initial insulation resistance. When the area between the patterns of the channel where the short circuit occurred was observed, there were areas where irregularly shaped solder particles, which had melted and grown into coarse solder particles, were present. [Industrial Applicability]

[0069] The solder particles and conductive composition of the present invention can avoid the risk of short circuits and suppress deterioration of insulation properties, and are therefore suitable for use, for example, in connecting flexible printed circuit boards (FPCs) or terminals of IC chips to ITO (Indium Tin Oxide) electrodes formed on the glass substrate of an LCD panel, connecting COFs to PWBs, connecting TCPs to PWBs, connecting COFs to glass substrates, connecting COFs to COFs, connecting IC substrates to glass substrates, and connecting IC substrates to PWBs. [Explanation of symbols]

[0070] 10 Wiring Pattern 11 Large solder particles 12 Solder particles 13 Metal body 20 Solder particles before classification 21 Solder particles after classification 22 Oxide film L1 Thickness of the oxide film on the solder particles before classification L2 Thickness of oxide film on solder particles after classification

Claims

1. Solder particles having an oxide film on the surface, the oxide film having an average film thickness of 5 nm or more and 100 nm or less, and an average surface roughness Ra of 15 nm or more and 110 nm or less, characterized in that the number-average particle diameter is 1 μm or more, and the proportion of coarse solder particles having a number-average particle diameter 1.25 times or more larger than the number-average particle diameter of the solder particles is 0.5% or less.

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

3. A method for manufacturing solder particles as described in any one of claims 1 to 2, characterized in that it includes a classification step in which an airflow is forcibly generated by a classification device in an oxygen-containing atmosphere to classify the solder particles.

4. A method for manufacturing solder particles as described in claim 3, characterized in that in the classification process, the average surface roughness of the solder particles is increased and an oxide film is formed on the surface of the solder particles.

5. 5. The method for manufacturing solder particles according to claim 3, wherein the classifying device is a device that generates an airflow by suction with a blower to cause the solder particles to swirl and collide with a sieve surface, thereby classifying the solder particles.

6. 5. A method for manufacturing solder particles according to claim 3, wherein the classification device is a device in which an air vortex swirls together with the solder particles in a classification chamber, and classifies the solder particles by controlling the swirling centrifugal force generated by the rotation of the rotor and the air flow flowing toward the center of the rotor due to blower suction.

7. A conductive composition comprising the solder particles according to claim 1 or 2.

Images