Method for manufacturing solder particles

Abstract

A method for manufacturing solder particles includes: a preparation step of preparing a substrate having a plurality of recesses and solder microparticles; a receiving step of receiving at least a portion of the solder microparticles in the recesses; and a fusion step of fusing the solder microparticles received in the recesses to form solder particles inside the recesses, wherein the average particle size of the solder particles is 1 μm to 30 μm and the CV value of the solder particles is less than 20%.

Description

Solder pellets and methods for manufacturing solder pellets This invention relates to a solder pellet and a method for manufacturing solder pellets. Previously, the use of solder particles as conductive particles incorporated into anisotropic conductive materials such as anisotropic conductive films and anisotropic conductive pastes has been studied. For example, Patent Document 1 describes a conductive paste containing thermosetting components and multiple solder particles with specific surface treatments. [Prior Art Documents][Patent Documents] [Patent Document 1] Japanese Patent Application Publication No. 2016-76494 [Problem to be Solved by the Invention] In recent years, with the increasing precision of circuit components and the continuous miniaturization of connection parts, the required conductivity and insulation reliability of anisotropic conductive materials have been continuously improving. In order to ensure conductivity and insulation reliability, it is necessary to miniaturize and homogenize the conductive particles in the anisotropic conductive material. However, in the previous solder particle manufacturing methods, it is difficult to manufacture solder particles that take into account both small average particle size and narrow particle size distribution. The present invention was made in view of the aforementioned problems, and its object is to provide a method for manufacturing solder particles that can easily produce solder particles that balance small average particle size and narrow particle size distribution. Furthermore, the object of the present invention is to provide solder particles that balance small average particle size and narrow particle size distribution using the aforementioned manufacturing method. [Means for Solving the Problem] One aspect of the present invention relates to a method for manufacturing solder particles, comprising: a preparation step of preparing a substrate having a plurality of recesses and solder microparticles; a receiving step of receiving at least a portion of the solder microparticles in the recesses; and a fusion step of fusing the solder microparticles received in the recesses to form solder particles inside the recesses. The solder particles manufactured using this method have an average particle size of 1 μm to 30 μm and a coefficient of variation (CV) value of 20% or less. In one embodiment, the CV value of the solder particles prepared in the preparation step can exceed 20%. By using such solder particles, the filling ability of the solder particles into the recesses is increased, making it easier to obtain more homogeneous solder particles. In one embodiment, the solder particles contained in the recess may be exposed to a reducing environment before the fusion step. In one embodiment, the fusion step may be a step of fusing the solder particles contained in the recess in a reducing environment. In one embodiment, the fusion step may be a step of fusing the solder particles contained in the recess in an environment above the melting point of the solder particles. In one embodiment, the solder particles prepared in the preparation step may be at least one selected from the group consisting of tin, tin alloys, indium, and indium alloys. In one embodiment, the solder particles prepared in the preparation step may be at least one selected from the group consisting of In-Bi alloy, In-Sn alloy, In-Sn-Ag alloy, Sn-Au alloy, Sn-Bi alloy, Sn-Bi-Ag alloy, Sn-Ag-Cu alloy and Sn-Cu alloy. Another aspect of the present invention relates to a solder particle with an average particle size of 1 μm to 30 μm and a CV value of less than 20%. One embodiment of the solder pellet can be achieved by forming a quadrilateral externally tangent to the projected image of the solder pellet using two pairs of parallel lines, wherein the distances between opposing sides are X and Y (where Y < X), and X and Y satisfy the following formula: 0.8 < Y / X < 1.0 The solder pellets in one embodiment may also include at least one selected from the group consisting of tin, tin alloys, indium and indium alloys. The solder particles of one embodiment may also include at least one selected from the group consisting of In-Bi alloy, In-Sn alloy, In-Sn-Ag alloy, Sn-Au alloy, Sn-Bi alloy, Sn-Bi-Ag alloy, Sn-Ag-Cu alloy and Sn-Cu alloy. [Effects of the Invention] According to the present invention, a method for manufacturing solder particles that can easily produce solder particles with both small average particle size and narrow particle size distribution can be provided. Furthermore, according to the present invention, solder particles that balance small average particle size and narrow particle size distribution can be provided. The following describes embodiments of the present invention. The present invention is not limited to the following embodiments. Furthermore, unless otherwise specified, any of the materials exemplified below may be used alone or in combination of two or more. Regarding the content of each component in the composition, in the case where multiple substances equivalent to each component exist in the composition, unless otherwise specified, it refers to the total amount of the multiple substances present in the composition. The numerical range indicated by "~" represents the range in which the values ​​before and after "~" are respectively the minimum and maximum values. In the numerical ranges described in stages in this specification, the upper or lower limit of a certain stage's numerical range may also be replaced by the upper or lower limit of the numerical ranges of other stages. In the numerical ranges described in this specification, the upper or lower limit of the numerical range may also be replaced by the values ​​shown in the embodiments. <Solder Particle Manufacturing Method> The solder particle manufacturing method of this embodiment is a method for manufacturing solder particles with an average particle size of 1 μm to 30 μm, and includes: a preparation step of preparing a substrate having multiple recesses and solder particles; a receiving step of receiving at least a portion of the solder particles in the recesses of the substrate; and a fusion step of fusing the solder particles received in the recesses to form solder particles inside the recesses. According to this manufacturing method, solder particles with an average particle size of 1 μm to 30 μm and a CV value of 20% or less can be manufactured. The manufacturing method of solder particles will be described below with reference to Figures 1(a) to 5. First, solder particles and a substrate 60 for housing the solder particles are prepared. Figure 1(a) is a plan view schematically showing an example of the substrate 60, and Figure 1(b) is a cross-sectional view along line Ib-Ib shown in Figure 1(a). The substrate 60 shown in Figure 1(a) has a plurality of recesses 62. The plurality of recesses 62 can be regularly arranged in a prescribed pattern. In this case, after solder particles are formed in the recesses 62, the solder particles in the recesses 62 are transferred to a resin material or the like, thereby allowing the solder particles to be arranged in a regular manner. The recess 62 of the substrate 60 is preferably formed as a cone shape, with the opening area expanding from the bottom 62a side of the recess 62 towards the surface 60a side of the substrate 60. That is, as shown in Figures 1(a) and 1(b), the width of the bottom 62a of the recess 62 (width a in Figures 1(a) and 1(b)) is preferably narrower than the width of the opening of the surface 60a of the recess 62 (width b in Figures 1(a) and 1(b)). Moreover, the dimensions of the recess 62 (width a, width b, volume, cone angle, and depth, etc.) can be set according to the size of the solder particles to be targeted. Furthermore, the shape of the recess 62 can be other than the shapes shown in Figure 1(a) and Figure 1(b). For example, the shape of the opening of the surface 60a of the recess 62 can be elliptical, triangular, quadrilateral, polygonal, etc., in addition to the circle shown in Figure 1(a) and Figure 1(b). Furthermore, the shape of the recess 62 in the cross-section perpendicular to the surface 60a can be, for example, the shape shown in Figures 2(a) to 2(h). Figures 2(a) to 2(h) are cross-sectional views schematically showing examples of the cross-sectional shapes of the recesses in the substrate. In any of the cross-sectional shapes shown in Figures 2(a) to 2(h), the width (width b) of the opening of the surface 60a of the recess 62 becomes the maximum width in the cross-sectional shape. This makes it easy to collect solder particles in the recess 62, and the solder particles formed in the recess 62 are easy to remove, improving workability. In addition, the shape of the recess 62 in the cross-section perpendicular to the surface 60a can also be, for example, the shape shown in Figure 9, which is formed by tilting the wall surface of the cross-sectional shape shown in Figures 2(a) to 2(h). Figure 9 can be referred to as the shape formed by tilting the wall surface of the cross-sectional shape shown in Figure 2(b). The materials constituting the substrate 60 can be inorganic materials such as silicon, various ceramics, glass, and stainless steel, as well as organic materials such as various resins. Preferably, the substrate 60 is a heat-resistant material that does not deteriorate at the melting temperature of the solder particles. Furthermore, the recesses 62 of the substrate 60 can be formed using known methods such as photolithography. The solder particles prepared in the preparation step only need to include particles whose particle size is smaller than the width (b) of the opening of the surface 60a of the recess 62, and preferably include more particles whose particle size is smaller than the width b. For example, the solder particles preferably have a particle size distribution with a D10 particle size smaller than the width b, more preferably a particle size distribution with a D30 particle size smaller than the width b, and even more preferably a particle size distribution with a D50 particle size smaller than the width b. The particle size distribution of solder particles can be determined using various methods consistent with their size. For example, methods such as dynamic light scattering, laser diffraction, centrifugal sedimentation, electrical detection banding, and resonant mass determination can be used. Furthermore, methods can be employed to determine particle size based on images obtained from optical microscopes, electron microscopes, etc. Specific devices include: flow-through particle image analyzers, Microtrac, and Coulter counters. There is no particular limitation on the CV value of the solder particles prepared in the preparation step, but from the viewpoint of improving the filling performance of the recess 62 by combining particles of different sizes, a higher CV value is preferable. For example, the CV value of the solder particles can exceed 20%, preferably 25% or more, and even more preferably 30% or more. The CV value of solder particles can be calculated by multiplying the value obtained by dividing the standard deviation of the particle size determined by the method by the average particle size (D50 particle size) by 100. The solder particles may contain tin or tin alloys. Examples of tin alloys include In-Sn alloys, In-Sn-Ag alloys, Sn-Au alloys, Sn-Bi alloys, Sn-Bi-Ag alloys, Sn-Ag-Cu alloys, and Sn-Cu alloys. Specific examples of these tin alloys are given below. • In-Sn (In 52% by mass, Sn 48% by mass, melting point 118℃) • In-Sn-Ag (In 20% by mass, Sn 77.2% by mass, Ag 2.8% by mass, melting point 175℃) • Sn-Bi (Sn 43% by mass, Bi 57% by mass, melting point 138℃) • Sn-Bi-Ag (Sn 42% by mass, Bi 57% by mass, Ag 1% by mass, melting point 139℃) • Sn-Ag-Cu (Sn 96.5% by mass, Ag 3% by mass, Cu 0.5% by mass, melting point 217℃) • Sn-Cu (Sn 99.3% by mass, Cu 0.7% by mass, melting point 227℃) • Sn-Au (Sn 21.0% by mass, Au 79.0% by mass, melting point 278℃) Solder particles may contain indium or indium alloys. Examples of indium alloys include In-Bi alloys and In-Ag alloys. Specific examples of these indium alloys are as follows: • In-Bi (In 66.3% by mass, Bi 33.7% by mass, melting point 72°C) • In-Bi (In 33.0% by mass, Bi 67.0% by mass, melting point 109°C) • In-Ag (In 97.0% by mass, Ag 3.0% by mass, melting point 145°C) The tin alloy or indium alloy can be selected depending on the intended use of the solder particles (temperature at which they are used). For example, if solder particles for low-temperature welding are desired, In-Sn alloys or Sn-Bi alloys can be used, resulting in solder particles capable of welding at temperatures below 150°C. Using materials with high melting points, such as Sn-Ag-Cu alloys or Sn-Cu alloys, solder particles that maintain high reliability even after being placed at high temperatures can be obtained. The solder particles may also contain one or more elements selected from Ag, Cu, Ni, Bi, Zn, Pd, Pb, Au, P, and B. Among these elements, Ag or Cu may also be included, as follows: By including Ag or Cu in the solder particles, the following effects can be achieved: solder particles with excellent bonding strength to the electrode can be obtained, resulting in a lower melting point of approximately 220°C, thereby achieving better conductivity reliability. The Cu content of the solder particles can be, for example, 0.05% to 10% by mass, or 0.1% to 5% by mass, or 0.2% to 3% by mass. If the Cu content is 0.05% by mass or higher, solder particles that achieve good solder joint reliability are easily obtained. Furthermore, if the Cu content is 10% by mass or lower, solder particles with low melting points and excellent wettability are easily obtained, resulting in better joint reliability due to the solder particles. The Ag content of the solder particles can be, for example, 0.05% to 10% by mass, or 0.1% to 5% by mass, or 0.2% to 3% by mass. If the Ag content is 0.05% by mass or higher, solder particles that achieve good solder joint reliability are easily obtained. Furthermore, if the Ag content is 10% by mass or lower, solder particles with low melting point and excellent wettability are easily obtained, resulting in better joint reliability due to the solder particles. In the receiving step, solder particles prepared in the preparation step are received in each of the recesses 62 of the substrate 60. The receiving step may be a step in which all the solder particles prepared in the preparation step are received in the recesses 62, or it may be a step in which a portion of the solder particles prepared in the preparation step (e.g., the solder particles smaller than the width b of the opening of the recess 62) is received in the recesses 62. Figure 3 is a schematic cross-sectional view showing the state in which solder particles 111 are contained in the recesses 62 of the substrate 60. As shown in Figure 3, multiple solder particles 111 are contained in each of the multiple recesses 62. The amount of solder particles 111 contained in the recess 62 is preferably 20% or more, more preferably 30% or more, more preferably 50% or more, and most preferably 60% or more, relative to the volume of the recess 62. This can suppress deviations in the amount contained and easily obtain solder particles with a smaller particle size distribution. There is no particular limitation on the method of collecting solder particles in the recess 62. The collection method can be either dry or wet. For example, the solder particles prepared in the preparation step can be placed on the substrate 60, and the surface 60a of the substrate 60 can be rubbed with a scraper to remove excess solder particles while simultaneously collecting sufficient solder particles in the recess 62. When the width b of the opening of the recess 62 is greater than the depth of the recess 62, solder particles may sometimes fly out from the opening of the recess 62. If a scraper is used, the solder particles flying out from the opening of the recess 62 are removed. Other methods for removing excess solder particles include blowing compressed air and rubbing the surface 60a of the substrate 60 with non-woven fabric or fiber bundles. These methods have weaker physical force compared to scrapers, and are therefore better for handling easily deformable solder particles. Furthermore, these methods may also leave solder particles flying out from the opening of the recess 62 within the recess. The fusion step involves fusing the solder particles 111 contained in the recess 62 to form solder grains 1 inside the recess 62. Figure 4 is a schematic cross-sectional view showing the state in which solder grains 1 are formed in the recess 62 of the substrate 60. The solder particles 111 contained in the recess 62 are integrated by melting and formed into spheres by surface tension. At this time, at the contact portion between the recess 62 and the bottom 62a, the molten solder follows the bottom 62a to form a planar portion 11. In this way, the formed solder grains 1 have a planar portion 11 on a part of their surface. Figure 5 is a view of the solder pellet 1 from the side opposite to the opening of the recess 62 in Figure 4. The solder pellet 1 has a shape in which a planar portion 11 of diameter A is formed on a part of the surface of a sphere having diameter B. Furthermore, the solder pellet 1 shown in Figures 4 and 5 has a planar portion 11 because the bottom 62a of the recess 62 is planar, but when the bottom 62a of the recess 62 has a shape other than planar, it has a surface with a different shape corresponding to the shape of the bottom 62a. As a method for melting the solder particles 111 housed in the recess 62, one possible method is to heat the solder particles 111 to a temperature above the melting point of the solder. Due to the influence of the oxide film, the solder particles 111 may not melt even when heated to a temperature above their melting point, may not wet and spread, or may not be integrated. Therefore, by exposing the solder particles 111 to a reducing environment to remove the surface oxide film, and then heating them to a temperature above their melting point, the solder particles 111 can be melted, wetted, and integrated. Furthermore, melting of the solder particles 111 is preferably performed in a reducing environment. By heating the solder particles 111 to a temperature above their melting point and setting the environment to a reducing state, the oxide film on the surface of the solder particles 111 is reduced, making melting, wettation, and integration of the solder particles 111 easier and more effective. The method of creating a reducing environment is not particularly limited as long as it achieves the desired effect; for example, methods using hydrogen gas, hydrogen radicals, formic acid gas, etc., can be employed. For instance, by using a hydrogen reduction furnace, a hydrogen radical reduction furnace, a formic acid reduction furnace, or a conveyor furnace or continuous furnace of these types, the solder particles 111 can be melted in a reducing environment. These devices may include a heating device, a chamber filled with an inert gas (nitrogen, argon, etc.), and a mechanism for creating a vacuum within the chamber, thereby making the control of the reducing gas easier. Furthermore, if a vacuum is created within the chamber, after the solder particles 111 have melted and integrated, voids can be removed by depressurization, resulting in solder particles 1 with superior bonding stability. The settings for reduction and melting conditions, temperature, and furnace environment adjustment of solder particles 111 can be appropriately set considering the melting point, particle size, recess size, and material of the substrate 60. For example, after inserting the substrate 60, which is filled with solder particles 111 in the recess, into the furnace and evacuating it, a reducing gas is introduced to fill the furnace and remove the surface oxide film of the solder particles 111. The reducing gas is then removed by evacuation, and the furnace is heated to above the melting point of the solder particles 111 to melt and integrate the solder particles, forming solder particles in the recess 62. After filling with nitrogen, the furnace temperature is restored to room temperature, thereby obtaining solder particles 1. Alternatively, for example, after inserting the substrate 60, which contains solder particles 111 in the recess, into a furnace and evacuating it, a reducing gas is introduced to fill the furnace. The solder particles 111 are then heated using a furnace heater to remove the surface oxide film. The reducing gas is then removed by evacuation, and the temperature is further increased to above the melting point of the solder particles 111, causing them to melt and integrate, forming solder grains within the recess 62. Nitrogen is then added, and the furnace temperature is restored to room temperature, thus obtaining solder grains 1. Heating the solder particles in a reducing environment has the following advantages: increased reducing power, and easier removal of the surface oxide film from the solder particles. Furthermore, for example, after inserting a substrate 60 filled with solder particles 111 into a furnace and evacuating it, a reducing gas is introduced to fill the furnace. The substrate 60 is then heated above the melting point of the solder particles 111 using a furnace heater. This reduction removes the surface oxide film of the solder particles 111, while simultaneously melting and integrating the solder particles to form solder grains within the recess 62. After removing the reducing gas by evacuating to reduce the voids within the solder grains, nitrogen is added, and the furnace temperature is restored to room temperature, thus obtaining solder grains 1. In this case, the temperature rise and fall within the furnace can be adjusted in one step, thus offering the advantage of short processing time. After solder particles are formed in the recess 62, a further step can be added to set the furnace to a reducing environment to remove any remaining surface oxide film. This reduces residues such as unfused solder particles or a portion of the unfused oxide film. In the case of a conveyor furnace using atmospheric pressure, a substrate 60 with solder particles 111 filling the recess can be placed on a conveyor and continuously passed through multiple zones to obtain solder particles 1. For example, the substrate 60 with solder particles 111 filling the recess can be placed on a conveyor set to a certain speed, passing through a zone filled with inert gases such as nitrogen or argon with a temperature lower than the melting point of the solder particles 111, then through a zone where reducing gases such as formic acid with a temperature lower than the melting point of the solder particles 111 are present, to remove the surface oxide film of the solder particles 111, then through a zone filled with inert gases such as nitrogen or argon with a temperature higher than the melting point of the solder particles 111, to melt and integrate the solder particles 111, and then through a cooling zone filled with inert gases such as nitrogen or argon, thereby obtaining solder particles 1. For example, a substrate 60 filled with solder particles 111 in its recesses is placed on a conveyor set to a certain speed. It passes through an area filled with inert gases such as nitrogen or argon at temperatures above the melting point of the solder particles 111, and then through an area containing reducing gases such as formic acid at temperatures above the melting point of the solder particles 111. This removes the oxide film on the surface of the solder particles 111, resulting in melting and integration. The substrate then passes through a cooling area filled with inert gases such as nitrogen or argon, thereby obtaining solder particles 1. Since the conveyor furnace can process at atmospheric pressure, it can also continuously process film-like materials roll-to-roll. For example, a continuous roll product made from a substrate 60 filled with solder particles 111 in its recesses is manufactured. A roll-out machine is installed at the inlet side of the conveyor furnace, and a winding machine is installed at the outlet side. The substrate 60 is conveyed at a certain speed, passing through various areas within the conveyor furnace, thereby fusing the solder particles 111 filled into the recesses. The formed solder particles 1 can be transported and stored in the recesses 62 of the substrate 60, or they can be removed from the recesses 62 for recycling. Alternatively, a resin material can be deposited on the surface 60a of the substrate 60, so that the solder particles 1 in the recesses 62 can be transferred to the resin material. In this case, if the recesses 62 are arranged in a regular manner, the solder particles 1 can be arranged in a regular manner on the resin material. In the manufacturing method of this embodiment, solder particles of uniform size can be formed regardless of the material and shape of the solder particles. For example, indium-based solder can be deposited by plating, but it is difficult to deposit in particle form, as it is soft and difficult to handle. However, in the manufacturing method of this embodiment, by using indium-based solder particles as raw materials, indium-based solder particles with uniform particle size can be easily manufactured. In addition, the formed solder particles 1 can be handled in a state where they are housed in the recess 62 of the substrate 60, so they can be handled and stored without deforming the solder particles. Furthermore, since the formed solder particles 1 are only housed in the recess 62 of the substrate 60, they are easy to remove, and can be recycled and surface-treated without deforming the solder particles. In addition, the solder particles 111 may have large deviations in particle size distribution and may also have distorted shapes. If they can be housed in the recess 62, they can be used as raw materials for the manufacturing method of this embodiment. Furthermore, regarding the manufacturing method of this embodiment, the shape of the recess 62 can be freely designed using photolithography, imprinting, machining, electron beam processing, or radiation processing. Since the size of the solder particles 1 depends on the amount of solder particles 111 housed in the recess 62, the size of the solder particles 1 can be freely designed by designing the recess 62 in the manufacturing method of this embodiment. (Solder Particles) The solder particles of this embodiment have an average particle size of 1 μm to 30 μm and a CV value of less than 20%. These solder particles combine a small average particle size with a narrow particle size distribution, making them well-suited for use as conductive particles in anisotropic conductive materials with high conductivity and insulation reliability. The solder particles of this embodiment can be manufactured using the described manufacturing method. The average particle size of the solder particles is not particularly limited as long as it falls within the aforementioned range, but is preferably 30 μm or less, more preferably 25 μm or less, and even more preferably 20 μm or less. Furthermore, the average particle size of the solder particles is preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 4 μm or more. The average particle size of solder particles can be determined using various methods consistent with particle size. For example, methods such as dynamic light scattering, laser diffraction, centrifugal sedimentation, electrical detection banding, and resonant mass determination can be used. Furthermore, particle size can be determined based on images obtained from optical microscopes, electron microscopes, etc. Specific devices include: flow-through particle image analyzers, Macchie counters, and Coulter counters. From the viewpoint of achieving superior conductivity and insulation reliability, the CV value of the solder particles is preferably 20% or less, more preferably 10% or less, further preferably 7% or less, and especially preferably 5% or less. Furthermore, there is no particular limitation on the lower limit of the CV value of the solder particles. For example, the CV value of the solder particles can be 1% or more, or even 2% or more. The CV value of solder particles can be calculated by multiplying the value obtained by dividing the standard deviation of the particle size determined by the method by the average particle size by 100. Solder particles can have a planar portion formed on a part of their surface, and the surface other than the planar portion is preferably spherical. That is, solder particles can have a planar portion and a spherical curved surface. Solder particle 1 shown in FIG5 can be cited as such a solder particle. The ratio (A / B) of the diameter A of the planar portion of solder particle 1 to its diameter B can, for example, exceed 0.01 and be less than 1.0 (0.01 < A / B < 1.0), or it can be 0.1 to 0.9. By having a planar portion, the stability of the solder particle is improved, and the operability is enhanced. Specifically, when solder particles are placed on objects such as electrodes that are to be connected by solder particles, the presence of the planar portion makes it easy to place them in a specified position, and has the effect of suppressing the movement of the solder particles from the specified position due to vibration, wind, external force, static electricity, etc. In addition, when the component on which the solder particles are placed is tilted, compared with solder particles that do not have a planar portion, such as spherical ones, the solder particles are less likely to move due to gravity. When a quadrilateral tangent to the projected image of a solder particle is formed using two pairs of parallel lines, and the distance between opposing sides is set as X and Y (where Y < X), the ratio of Y to X (Y / X) can exceed 0.8 but is less than 1.0 (0.8 < Y / X < 1.0), or it can be 0.9 or more but less than 1.0. Such solder particles can be described as particles that are closer to a true sphere. According to the manufacturing method of this embodiment, such solder particles can be easily obtained. Because the solder particles are close to a true sphere, for example, when multiple opposing electrodes are electrically connected via the solder particles, uneven contact between the solder particles and the electrodes is less likely to occur, and a stable connection is tended to be obtained. Furthermore, when manufacturing a conductive film or resin in which the solder particles are dispersed in a resin material, high dispersibility can be obtained, and dispersion stability during manufacturing is tended to be achieved. Furthermore, when a film or paste formed by dispersing solder particles in a resin material is used for electrode connection, even if the solder particles rotate in the resin, if the solder particles are spherical, the projected areas of the solder particles are close when observed in a projected image. Therefore, there is a tendency to easily obtain a stable electrical connection with minimal deviation when connecting electrodes. Figure 6 shows the distances X and Y (where Y < X) between opposing sides when a quadrilateral tangent to the projected image of a solder particle is formed using two pairs of parallel lines. For example, a projected image is obtained by observing an arbitrary particle using a scanning electron microscope. Two pairs of parallel lines are drawn for the obtained projected image. One pair of parallel lines is positioned at the point where the distance between the parallel lines is minimum, and the other pair is positioned at the point where the distance between the parallel lines is maximum. The Y / X of this particle is then calculated. This operation is performed on 300 solder particles, and the average value is calculated as the Y / X of the solder particle. Solder particles may contain tin or tin alloys. Examples of tin alloys include In-Sn alloys, In-Sn-Ag alloys, Sn-Au alloys, Sn-Bi alloys, Sn-Bi-Ag alloys, Sn-Ag-Cu alloys, and Sn-Cu alloys. Specific examples of these tin alloys are given below. • In-Sn (In 52% by mass, Sn 48% by mass, melting point 118℃) • In-Sn-Ag (In 20% by mass, Sn 77.2% by mass, Ag 2.8% by mass, melting point 175℃) • Sn-Bi (Sn 43% by mass, Bi 57% by mass, melting point 138℃) • Sn-Bi-Ag (Sn 42% by mass, Bi 57% by mass, Ag 1% by mass, melting point 139℃) • Sn-Ag-Cu (Sn 96.5% by mass, Ag 3% by mass, Cu 0.5% by mass, melting point 217℃) • Sn-Cu (Sn 99.3% by mass, Cu 0.7% by mass, melting point 227℃) • Sn-Au (Sn 21.0% by mass, Au 79.0% by mass, melting point 278℃) Solder particles may contain indium or indium alloys. Examples of indium alloys include In-Bi alloys and In-Ag alloys. Specific examples of these indium alloys are as follows: • In-Bi (In 66.3% by mass, Bi 33.7% by mass, melting point 72°C) • In-Bi (In 33.0% by mass, Bi 67.0% by mass, melting point 109°C) • In-Ag (In 97.0% by mass, Ag 3.0% by mass, melting point 145°C) The tin alloy or indium alloy can be selected depending on the intended use of the solder particles (temperature at which they are used). For example, when the solder particles are used for low-temperature welding, In-Sn alloys or Sn-Bi alloys can be used, and welding can be performed at temperatures below 150°C. When using materials with high melting points such as Sn-Ag-Cu alloys or Sn-Cu alloys, high reliability can be maintained even after being placed at high temperatures. The solder particles may also contain one or more elements selected from Ag, Cu, Ni, Bi, Zn, Pd, Pb, Au, P, and B. Among these elements, Ag or Cu may also be included, as follows: By including Ag or Cu in the solder particles, the melting point of the solder particles can be lowered to approximately 220°C, and the bonding strength with the electrode can be further improved, thus making it easier to obtain better conductivity reliability. The Cu content of the solder particles can be, for example, 0.05% to 10% by mass, or 0.1% to 5% by mass, or 0.2% to 3% by mass. If the Cu content is 0.05% by mass or higher, it is easier to achieve better solder joint reliability. In addition, if the Cu content is 10% by mass or lower, it is easier to form solder particles with low melting point and excellent wettability, resulting in better joint reliability due to the solder particles. The Ag content of the solder particles can be, for example, 0.05% to 10% by mass, or 0.1% to 5% by mass, or 0.2% to 3% by mass. If the Ag content is 0.05% by mass or higher, it is easier to achieve better solder joint reliability. In addition, if the Ag content is 10% by mass or lower, it is easier to form solder particles with low melting point and excellent wettability, resulting in better joint reliability due to the solder particles. The application of solder particles is not particularly limited. For example, they can be preferably used as conductive particles for anisotropic conductive materials. Additionally, they can be preferably used for electrically connecting electrodes to each other, such as in ball grid array (BGA) connections widely used in the mounting of semiconductor integrated circuits, or for sealing or sealing tubes, soldering, and height or gap control partitions in components such as microelectromechanical systems (MEMS). In other words, the solder particles can be used in the general applications previously used with solder. The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments. [Example] The present invention will be further described in detail below with reference to embodiments, but the present invention is not limited to these embodiments. <Example 1> (Step a1) Grading of solder particles: 100 g of Sn-Bi solder particles (manufactured by 5N Plus, melting point 139°C, Type 8) were immersed in distilled water for ultrasonic dispersion, then allowed to stand, and the solder particles suspended in the supernatant were recovered. This operation was repeated, and 10 g of solder particles were recovered. The average particle size of the obtained solder particles was 1.0 μm, and the CV value was 42%. (Step b1) Substrate configuration: A substrate (polyimide film, 100 μm thick) was prepared with multiple recesses having an opening diameter of 1.2 μmϕ, a bottom diameter of 1.0 μmϕ, and a depth of 1.0 μm (with respect to the bottom diameter of 1.0 μmϕ, the opening is located in the center of the opening diameter of 1.2 μmϕ when viewed from the top surface). The multiple recesses were arranged regularly at 1.0 μm intervals. The solder particles (average particle size 1.0 μm, CV value 42%) obtained in step a1 are disposed in the recesses of the substrate. Then, excess solder particles are removed by rubbing the recessed side of the substrate with a micro-adhesion roller, resulting in a substrate with solder particles disposed only in the recesses. (Step c1) Solder Particle Formation: The substrate with solder particles disposed in the recesses in step b1 is placed in a hydrogen reduction furnace (vacuum welding apparatus manufactured by Shin Kong Precision Machinery Co., Ltd.). After evacuation, hydrogen gas is introduced into the furnace to fill it. The furnace is then maintained at 280°C for 20 minutes, followed by evacuation again, introduction of nitrogen, and restoration to atmospheric pressure. The furnace temperature is then lowered to room temperature to form solder particles. (Step d1) Solder Particle Recovery: Solder particles are recovered from the recesses by tapping the substrate passed through the recesses from the back side. The obtained solder particles are evaluated using the following method. (Evaluation of Solder Particles) The obtained solder particles were placed on a conductive tape fixed to the surface of a SEM observation platform. The SEM observation platform was then tapped against a 5 mm thick stainless steel plate to allow the solder particles to spread uniformly on the conductive tape. Compressed nitrogen gas was then blown onto the conductive tape surface to fix the solder particles in a single layer. The diameter of 300 solder particles was measured using SEM, and the average particle size and CV value were calculated. The results are shown in Table 2. <Examples 2 to 12> The recess dimensions were changed as described in Table 1. Solder particles were fabricated in the same manner as in Example 1, and then recycled and evaluated. The results are shown in Table 2. <Example 13> Step c2 is performed instead of step c1, except that solder particles are prepared in the same manner as in Example 1, and then recovered and evaluated. The results are shown in Table 2. (Step c2) Formation of solder particles The substrate with solder particles arranged in the recess in step b1 is placed in a hydrogen free radical reduction furnace (plasma reflow device manufactured by Shin Kong Precision Machinery Co., Ltd.). After evacuation, hydrogen gas is introduced into the furnace to fill it with hydrogen. Then the furnace temperature is adjusted to 120°C and irradiated with hydrogen free radicals for 5 minutes. Afterwards, the hydrogen gas in the furnace is removed by evacuation, and the temperature is heated to 170°C. Nitrogen is introduced into the furnace and the pressure is restored to atmospheric pressure. The furnace temperature is then lowered to room temperature to form solder particles. <Examples 14 to 24> The recess dimensions were changed as described in Table 1. Solder particles were fabricated in the same manner as in Example 13, and then recycled and evaluated. The results are shown in Table 2. <Example 25> Step c3 is performed instead of step c1, except that solder particles are prepared in the same manner as in Example 1, and then recovered and evaluated. The results are shown in Table 2. (Step c3) Formation of solder particles The substrate with solder particles disposed in the recess in step b1 is placed into a formic acid reduction furnace. After evacuation, formic acid gas is introduced into the furnace to fill it with formic acid gas. Then the furnace temperature is adjusted to 130°C and maintained for 5 minutes. Afterward, the formic acid gas in the furnace is removed by evacuation, and the temperature is heated to 180°C. Nitrogen is introduced into the furnace and the pressure is restored to atmospheric pressure. The furnace temperature is then lowered to room temperature to form solder particles. <Examples 26 to 36> The recess dimensions were changed as described in Table 1. Solder particles were fabricated in the same manner as in Example 25, and then recycled and evaluated. The results are shown in Table 2. <Example 37> Step c4 is performed instead of step c1, except that solder particles are produced in the same manner as in Example 1, and then recycled and evaluated. The results are shown in Table 2. (Step c4) Formation of solder particles The substrate with solder particles arranged in the recess in step b1 is placed into a formic acid conveying reflow oven (1913MK manufactured by Heller Industries, Inc.), and conveyed by a conveyor, continuously passing through a nitrogen zone, a nitrogen and formic acid gas mixing zone, and a nitrogen zone. Solder particles are formed by passing through the nitrogen and formic acid gas mixing zone for 5 minutes. <Examples 38 to 48> The recess dimensions were changed as described in Table 1. Solder particles were fabricated in the same manner as in Example 37, and then recycled and evaluated. The results are shown in Table 2. [Table 1] [Table 2] <Example 1> (A) Fabrication of anisotropic conductive film (Step e1) Solder particles coated with flux were prepared using the same method as in Example 13. 200 g of the obtained solder particles, 40 g of adipic acid, and 70 g of acetone were weighed into a three-necked flask. Then, 0.3 g of dibutyltin oxide was added to catalyze the dehydration condensation reaction between the hydroxyl groups on the surface of the solder particles and the carboxyl groups of adipic acid. The reaction was carried out at 60°C for 4 hours. Afterward, the solder particles were filtered and recovered. The recovered solder particles, 50 g of adipic acid, 200 g of toluene, and 0.3 g of p-toluenesulfonic acid were weighed into a three-necked flask, and the mixture was evacuated and refluxed, and reacted at 120°C for 3 hours. At this time, a Dean-Stark extraction apparatus was used to remove the water generated by the dehydration condensation and to allow the reaction to proceed. Afterward, the solder particles were recovered by filtration, washed with hexane, and dried. The dried solder particles are pulverized using an air-jet pulverizer and passed through a mesh screen using an ultrasonic sieve to obtain flux-coated solder particles. (Step f1) Preparation of flux-coated solder particles: A transfer mold (polyimide film, 100 μm thick) is prepared, having multiple recesses with an opening diameter of 1.2 μm ϕ, a bottom diameter of 1.0 μm ϕ, and a depth of 1.0 μm (with respect to the bottom diameter of 1.0 μm ϕ, the opening is located at the center of the opening diameter of 1.2 μm ϕ when viewed from the top surface). Furthermore, the multiple recesses are arranged regularly at 1.0 μm intervals. The flux-coated solder particles obtained in step e1 are placed in the recesses of this transfer mold. (Step g1) Preparation of the adhesive film: 100 g of phenoxy resin (manufactured by Union Carbide, trade name "PKHC") and 75 g of acrylic rubber (a copolymer of 40 parts by weight of butyl acrylate, 30 parts by weight of ethyl acrylate, 30 parts by weight of acrylonitrile, and 3 parts by weight of glycidyl methacrylate, molecular weight: 850,000) were dissolved in 400 g of ethyl acetate to obtain a solution. 300 g of liquid epoxy resin (epoxy equivalent 185, manufactured by Asahi Kasei Epoxy Co., Ltd., trade name "Novacure HX-3941") containing a microencapsulated latent curing agent was added to this solution, and the mixture was stirred to obtain an adhesive solution. The obtained adhesive solution was applied to a release liner (silicone-treated polyethylene terephthalate film, 40 μm thick) using a roller coater and dried at 90°C for 10 minutes to form adhesive films (insulating resin films) with thicknesses of 4 μm, 6 μm, 8 μm, 12 μm, and 20 μm on the release liner. (Step h1) Transfer of flux-coated solder particles: The adhesive film formed on the release liner was positioned opposite the transfer mold containing the flux-coated solder particles from step f1, and the flux-coated solder particles were transferred onto the adhesive film.(Step i1) The anisotropic conductive film is fabricated by bringing the adhesive film fabricated using the same method as in step g1 into contact with the transfer surface of the adhesive film obtained in step h1 at 50°C and 0.1 MPa (1 kgf / cm). 2 Heating and pressurizing are applied to obtain an anisotropic conductive film in which flux-coated solder particles are arranged in layers in the cross-sectional view of the film. Furthermore, for a film with a thickness of 4 μm, 4 μm is overlapped; similarly, 6 μm is overlapped for 6 μm, 8 μm for 8 μm, 12 μm for 12 μm, and 20 μm for 20 μm, thereby producing anisotropic conductive films with thicknesses of 8 μm, 12 μm, 16 μm, 24 μm, and 40 μm. (B) Fabrication of the connecting structure (step j1) Preparation of the wafer with copper bumps Prepare the following 5 types of wafers with copper bumps (1.7 mm × 1.7 mm, thickness: 0.5 mm). • Wafer C1 • Area: 30 μm × 30 μm, Space: 30 μm, Height: 10 μm, Number of bumps: 362 • Wafer C2 • Area: 15 μm × 15 μm, Space: 10 μm, Height: 10 μm, Number of bumps: 362 • Wafer C3 • Area: 10 μm × 10 μm, Space: 10 μm, Height: 7 μm, Number of bumps: 362 • Wafer C4 • Area: 5 μm × 5 μm, Space: 6 μm, Height: 5 μm, Number of bumps: 362 • Wafer C5 • Area: 3 μm × 3 μm, Space: 3 μm, Height: 5 μm, Number of bumps: 362 (Step k1) Preparation of substrates with copper bumps Prepare the following 5 types of substrates with copper bumps (thickness: 0.7 mm). • Substrate D1 • Area: 30 μm × 30 μm, Space: 30 μm, Height: 10 μm, Number of bumps: 362 • Substrate D2 • Area: 15 μm × 15 μm, Space: 10 μm, Height: 10 μm, Number of bumps: 362 • Substrate D3 • Area: 10 μm × 10 μm, Space: 10 μm, Height: 7 μm, Number of bumps: 362 • Substrate D4 • Area: 5 μm × 5 μm, Space: 6 μm, Height: 5 μm, Number of bumps: 362 • Substrate D5 • Area: 3 μm × 3 μm, Space: 3 μm, Height: 5 μm, Number of bumps: 362 (Step l1) Next, using the anisotropic conductive film prepared in step i1, according to the order shown below i) to iii), a wafer (1.7 mm × 1.7 mm, thickness: 0.5 mm) with copper bumps and a substrate (thickness: 0.7 mm) with copper bumps are formed. A connection (mm) is formed to obtain the connection structure. i) The single-sided separator (silicone-treated polyethylene terephthalate film, 40 μm thick) of the anisotropic conductive film (2 mm × 19 mm) is peeled off, so that the anisotropic conductive film is in contact with the substrate with copper bumps, at 80°C and 0.98 MPa (10 kgf / cm²). 2ii) The separator is peeled off, and the bumps of the chip with copper bumps are aligned with the bumps of the substrate with copper bumps. iii) The chip is heated and pressurized from above at 180°C, 40 gf / bump, for 30 seconds to perform the formal connection. The following seven connection structures (1) to (7) are fabricated by combining the "chip / anisotropic conductive film / substrate" as described in (1) to (7). (1) Wafer C1 / 40 μm thick conductive film / substrate D1 (2) Wafer C1 / 24 μm thick conductive film / substrate D1 (3) Wafer C1 / 16 μm thick conductive film / substrate D1 (4) Wafer C2 / 16 μm thick conductive film / substrate D2 (5) Wafer C3 / 12 μm thick conductive film / substrate D3 (6) Wafer C4 / 8 μm thick conductive film / substrate D4 (7) Wafer C5 / 8 μm thick conductive film / substrate D5 <Preparation Examples 2 to 12> Solder particles prepared using the same method as in Examples 14 to 24, and a transfer mold with the same shape as the substrate used in the preparation of solder particles in Examples 14 to 24, were used as transfer molds. Otherwise, anisotropic conductive films and connecting structures were prepared using the same method as in Preparation Example 1. <Comparative Fabrication Example 1> Sn-Bi solder particles (Mitsui Metals Corporation's "Type-4", with an average particle size of 26 μm and a CV value of 25%) were used as solder particles. Otherwise, the anisotropic conductive film and the connection structure were fabricated using the same method as in Fabrication Example 1. <Comparative Preparation Example 2> Anisotropic conductive paste containing solder particles was prepared, comprising the following components in the following parts by weight: (Polymer): 12 parts by weight (Thermosetting compound): 29 parts by weight (High dielectric constant curing agent): 20 parts by weight (Thermosetting agent): 11.5 parts by weight (Fluoride): 2 parts by weight (Solder particles): 34 parts by weight (Polymer): 72 parts by weight of bisphenol F (containing 4,4'-methylenebisphenol, 2,4'-methylenebisphenol and 2,2'-methylenebisphenol in a mass ratio of 2:3:1), 70 parts by weight of 1,6-hexanediol diglycidyl ether, and 30 parts by weight of bisphenol F type epoxy resin (EPICLON EXA-830CRP manufactured by DIC) were placed in a three-necked flask and dissolved at 150°C under a nitrogen atmosphere. Subsequently, 0.1 parts by mass of tetrabutyl strontium bromide, which acts as a catalyst for the addition reaction of hydroxyl and epoxy groups, were added, and the addition polymerization reaction was carried out at 150°C for 6 hours under a nitrogen atmosphere to obtain the reaction product (polymer). (Thermosetting compound): Resorcinol-type epoxy compound, "EX-201" manufactured by Nagase ChemteX Co., Ltd. (High dielectric constant curing agent): Pentaerythritol tetra(3-mercaptobutyrate) ester (Thermosetting agent): "Karenz MT PE1" manufactured by Showa Denko Co., Ltd. (Fluoride): Adipic acid, manufactured by Wako Pure Chemical Industries Co., Ltd. (Solder particles): 200 g of SnBi solder particles ("ST-3" manufactured by Mitsui Metals Co., Ltd.), 40 g of adipic acid, and 70 g of acetone were weighed into a three-necked flask. Then, 0.3 g of dibutyltin oxide, which serves as a dehydration condensation catalyst for the hydroxyl groups on the surface of the solder particles and the carboxyl groups of adipic acid, was added. The reaction was carried out at 60°C for 4 hours. Afterward, the solder particles were filtered and recovered. In a three-necked flask, 50 g of recovered solder particles, 200 g of adipic acid, and 0.3 g of p-toluenesulfonic acid were weighed and subjected to vacuum and reflux, and reacted at 120°C for 3 hours. During this process, a Diane-Stark extraction apparatus was used to remove water generated by dehydration condensation and to allow the reaction to proceed. The solder particles were then recovered by filtration, washed with hexane, and dried. Finally, the obtained solder particles were pulverized using a ball mill. The average particle size of the obtained SnBi solder particles was 4 μm, and the CV value was 32%. Prepare a chip with copper bumps and a substrate with copper bumps, similar to those used in Example 1. Apply anisotropic conductive paste containing solder particles to the top of the substrate with copper bumps, and then place the chip with copper bumps on it. Align the bumps of the chip with copper bumps with the bumps of the substrate with copper bumps, and heat and pressurize from above the chip at 180°C, 4 gf / bump, for 30 seconds to perform the formal connection. Use the following combinations (1) to (7) to fabricate a total of 7 connection structures (1) to (7). Anisotropic conductive paste / substrate D1 containing solder particles with a thickness of (1) 40 μm on wafer C1 (on copper bumps), (2) 24 μm on wafer C1 (on copper bumps), (3) 16 μm on wafer C1 (on copper bumps), (4) 16 μm on wafer C2 (on copper bumps), (5) 12 μm on wafer C3 (on copper bumps), (6) 8 μm on wafer C4 (on copper bumps), (7) 8 μm on wafer C5 (on copper bumps) Anisotropic conductive paste / substrate D5 containing solder particles with a thickness of μm (on the copper bump) is combined and connected to obtain the connection structure of (1) to (7). [Evaluation of Connection Structure] For a portion of the obtained connection structure, conduct continuity resistance test and insulation resistance test as follows. (Conduction Resistance Test - Moisture Absorption and Heat Resistance Test) Regarding the conduction resistance between the wafer (bump) with copper bumps and the substrate (bump) with copper bumps, the initial value of the conduction resistance and the value after the moisture absorption and heat resistance test (placed at 85°C and 85% humidity for 100 hours, 500 hours, and 1000 hours) were measured for 20 samples, and the average value of these values ​​was calculated. The conduction resistance was evaluated based on the obtained average value and according to the following criteria. The results are shown in Table 3. Furthermore, if the following criteria A or B are met after 1000 hours of the moisture absorption and heat resistance test, the conduction resistance can be considered good. A: The average conduction resistance is less than 2 Ω B: The average conduction resistance is 2 Ω or more but less than 5 Ω C: The average conduction resistance is 5 Ω or more but less than 10 Ω D: The average conduction resistance is 10 Ω or more but less than 20 Ω E: The average conduction resistance is 20 Ω or more (Conduction Resistance Test - High Temperature Placement Test) The conduction resistance between the wafer (bump) and the substrate (bump) with copper bumps was measured before and after the high temperature placement test (placed at 100°C for 100 hours, 500 hours, and 1000 hours). Furthermore, after high temperature placement, a drop impact was applied, and the conduction resistance of the samples after the drop impact was measured. The drop impact involved fixing the connection structure to a metal plate with fastening screws and dropping it from a height of 50 cm. The DC resistance value was measured at the solder joint at the corner of the wafer with the greatest impact (4 locations). If the measured value increased by more than 5 times from the initial resistance, it was considered as a breakage and evaluated. Furthermore, measurements were performed on 20 samples at a total of 80 locations (4 locations). The results are shown in Table 4. Solder connection reliability was evaluated as good if the following criteria A or B were met after 20 drop impacts. A: After 20 drops, no solder joints with resistance more than 5 times that of the initial resistance were observed at any of the 80 locations. B: After 20 drops, solder joints with resistance more than 5 times that of the initial resistance were observed at 1 to 5 locations. C: After 20 drops, solder joints with resistance more than 5 times that of the initial resistance were observed at 6 to 20 locations. D: After 20 drops, solder joints with resistance more than 5 times that of the initial resistance were observed at 21 or more locations. (Insulation Resistance Test) Regarding the insulation resistance between wafer electrodes, the initial insulation resistance values ​​and the values ​​after migration tests (placed at 60°C, 90% humidity, and 20V for 100 hours, 500 hours, and 1000 hours) were measured for all 20 samples. The insulation resistance value for all 20 samples was calculated to be 10. 9 The proportion of samples with an Ω or higher. Insulation resistance is evaluated based on the obtained proportion and according to the following criteria. The results are shown in Table 5. Furthermore, if either criterion A or B is met after 1000 hours of moisture absorption and heat resistance testing, the insulation resistance can be considered good. A: Insulation resistance value 10 9 The proportion of Ω and above is 100% (B): Insulation resistance value 10 9 The proportion of insulation resistance values ​​above Ω is 90% or more but less than 100% (C): Insulation resistance value 10 9 The proportion of Ω and above is 80% or more but less than 90% (D): Insulation resistance value 10 9 The proportion of Ω and above is 50% or more but less than 80% E: Insulation resistance value 10 9 The proportion of Ω and above is less than 50%. [Table 3] [Table 4] [Table 5] <Evaluation of Solder Particles> Using the solder particles obtained in Example 1, except for the steps (e1) to (h1) of Example 1, an adhesive film with solder particles transferred was obtained. A 10 cm × 10 cm section of the adhesive film was cut, and Pt sputtering was performed on the surface with the solder particles, followed by SEM observation. 300 solder particles were observed, and the average diameter B (average particle size), average diameter A of the planar portion, roundness, A / B, and Y / X of the solder particles were calculated. The same measurements were performed using solder particles from Examples 2 to 12. The results are shown in Table 6. Roundness: The ratio r / R of the radii of the two concentric circles of the solder particle (radius r of the smallest circumscribed circle and radius R of the largest inscribed circle). A / B: The ratio of the diameter A of the planar portion of the solder particle to its diameter B. Y / X: When a quadrilateral tangent to the projection image of a solder particle is formed using two pairs of parallel lines, the ratio of Y to X is given when the distance between opposing sides is set as X and Y (where Y < X). [Table 6] Furthermore, Figures 7(a) and 7(b) are SEM images of the solder particles formed in Example 17, and Figures 8(a) and 8(b) are SEM images of the solder particles used in Comparative Production Example 1. <Example 49> In step b1, a substrate with a plurality of recesses having the cross-sectional shape shown in FIG9 (approximate to the recess shape in FIG2(b)), i.e., the bottom diameter a of the recess is 0.6 μm, the opening diameter b1 is 1.0 μm, and the opening diameter b2 is 1.2 μm (regarding the bottom diameter a: 0.6 μmϕ, the opening is located in the center of the opening diameter b2: 1.2 μmϕ when viewed from the top surface), is used instead of step c1 to perform the following step c2. Solder particles are prepared in the same manner as in Example 1, and are recovered and evaluated. The results are shown in Table 8. (Step c2) Formation of Solder Particles The substrate with solder particles arranged in the recesses in step b1 is placed in a hydrogen free radical reduction furnace (a plasma reflow device manufactured by Shin Kong Precision Machinery Co., Ltd.), and after evacuation, hydrogen gas is introduced into the furnace to fill the furnace with hydrogen gas. Then the furnace is adjusted to 120°C and irradiated with hydrogen free radicals for 5 minutes. Afterwards, hydrogen is removed from the furnace by vacuuming, and the furnace is heated to 170°C. Nitrogen is then introduced into the furnace and the pressure is restored to atmospheric pressure. The furnace temperature is then lowered to room temperature to form solder particles. <Examples 50-60> The recess dimensions were changed as described in Table 7. Solder particles were fabricated in the same manner as in Example 49, and then recycled and evaluated. The results are shown in Table 8. <Example 61> In step b1, a substrate with multiple recesses having the cross-sectional shape shown in Figure 2(e), i.e., the recesses having an opening of 1.2 μm and a diameter that tapers from the opening to the bottom, was used instead of step c1 to perform the following step c2. Solder particles were fabricated in the same manner as in Example 1, and were then recovered and evaluated. The results are shown in Table 8. (Step c2) Formation of Solder Particles The substrate with solder particles arranged in the recesses in step b1 was placed in a hydrogen free radical reduction furnace (a plasma reflow device manufactured by Shin Kong Precision Machinery Co., Ltd.). After evacuation, hydrogen gas was introduced into the furnace to fill it with hydrogen. The furnace temperature was then adjusted to 120°C and irradiated with hydrogen free radicals for 5 minutes. Afterward, the hydrogen gas in the furnace was removed by evacuation, and the temperature was heated to 170°C. Nitrogen was then introduced into the furnace and the pressure was restored to atmospheric pressure. The furnace temperature was then lowered to room temperature, thereby forming solder particles. <Examples 62-72> The recess dimensions were changed as described in Table 7. Otherwise, solder particles were fabricated in the same manner as in Example 61, and were recycled and evaluated. The results are shown in Table 8. <Example 73> In step b1, a substrate with multiple recesses having the cross-sectional shape shown in Figure 2(h), i.e., the opening of the recess is 1.2 μm, the bottom has a continuous curved surface that is convex from the opening towards the depth direction, is used instead of step c1 in step c2. Solder particles are fabricated in the same manner as in Example 1, and are then recycled and evaluated. The results are shown in Table 8. Furthermore, in this case, the depth is defined as the distance to the point where a vertical line drawn from a line parallel to the surface of the substrate where the opening is located intersects with the deepest point of the bottom continuous curved surface. (Step c2) Formation of Solder Particles The substrate with solder particles arranged in the recesses in step b1 is placed in a hydrogen free radical reduction furnace (a plasma reflow device manufactured by Shin Kong Precision Machinery Co., Ltd.), a vacuum is drawn, and hydrogen is introduced into the furnace to fill the furnace with hydrogen. The furnace is then adjusted to 120°C and irradiated with hydrogen free radicals for 5 minutes. Afterwards, hydrogen is removed from the furnace by vacuuming, and the furnace is heated to 170°C. Nitrogen is then introduced into the furnace and the pressure is restored to atmospheric pressure. The furnace temperature is then lowered to room temperature to form solder particles. <Examples 74 to 84> The recess dimensions were changed as described in Table 7. Solder particles were fabricated in the same manner as in Example 61, and then recycled and evaluated. The results are shown in Table 8. <Preparation Examples 13-24> Solder particles prepared using the same method as in Examples 49-60, and a transfer mold with the same substrate shape as used in the preparation of solder particles in Examples 49-60, were used as transfer molds. Otherwise, anisotropic conductive films and connecting structures were prepared using the same method as in Preparation Example 1. The results are shown in Tables 9-11. <Examples 25-36> Solder particles were fabricated using the same method as in Examples 61-72, and a transfer mold with the same substrate shape as that used in the solder particle fabrication of Examples 61-72 was used as a transfer mold. Otherwise, anisotropic conductive films and connecting structures were fabricated using the same method as in Example 1. The results are shown in Tables 12-14. <Preparation Examples 37-48> Solder particles prepared using the same method as in Examples 73-84, and a transfer mold with the same substrate shape as used in the preparation of solder particles in Examples 73-84, were used as transfer molds. Otherwise, anisotropic conductive films and connecting structures were prepared using the same method as in Preparation Example 1. The results are shown in Tables 15-17. It was confirmed that the solder particles obtained in Examples 49 to 60 exhibited the same performance as those obtained in Examples 13 to 24. Furthermore, the solder particles obtained in Examples 49 to 60, like those obtained in Examples 13 to 24, also had a shape with a partially planar portion. It was confirmed that the solder particles obtained in Examples 61 to 72 exhibited the same performance as those obtained in Examples 13 to 24. Furthermore, it was confirmed that the solder particles obtained in Examples 61 to 72 formed a shape resembling a conical shape with a continuously varying cross-sectional diameter. It was confirmed that the solder particles obtained in Examples 73 to 84 exhibited the same performance as those obtained in Examples 13 to 24. Furthermore, it was confirmed that the solder particles obtained in Examples 73 to 84 were resembling a spherical shape. Moreover, this shape has the advantage that when using a resin adhesive film to connect electrodes to each other, resin is easily expelled when pressure is applied, allowing for easy contact between the electrode and the solder particle, resulting in a stable connection. [Table 7] [Table 8] [Table 9] [Table 10] [Table 11] [Table 12] [Table 13] [Table 14] [Table 15] [Table 16] [Table 17] <Examples 85-87> In step a1, 10 g of Sn-Bi solder particles (manufactured by 5N Plus, melting point 139°C, Type 9, average particle size: 3.0 μm, CV value: 32%) were used. In step b1, the recess shown in Table 18 was used instead of step c1 to perform the following step c2. Solder particles were prepared in the same manner as in Example 1, and were recovered and evaluated. The results are shown in Table 19. (Step c2) Formation of solder particles The substrate with solder particles arranged in the recess in step b1 was placed in a hydrogen radical reduction furnace (plasma reflow device manufactured by Shin Kong Precision Machinery Co., Ltd.). After evacuation, hydrogen gas was introduced into the furnace to fill the furnace with hydrogen gas. Then the furnace temperature was adjusted to 120°C and irradiated with hydrogen radicals for 5 minutes. Afterwards, hydrogen is removed from the furnace by vacuuming, and the furnace is heated to 170°C. Nitrogen is then introduced into the furnace and the pressure is restored to atmospheric pressure. The furnace temperature is then lowered to room temperature to form solder particles. <Examples 88-90> In step a1, 10 g of Sn-Bi solder particles (manufactured by 5N Plus, melting point 139°C, Type 10, average particle size: 2.8 μm, CV value: 28%) were used. In step b1, the recess shown in Table 18 was used instead of step c1 to perform the following step c2. Solder particles were prepared in the same manner as in Example 1, and were recovered and evaluated. The results are shown in Table 19. (Step c2) Formation of solder particles The substrate with solder particles arranged in the recess in step b1 was placed in a hydrogen radical reduction furnace (plasma reflow device manufactured by Shin Kong Precision Machinery Co., Ltd.). After evacuation, hydrogen gas was introduced into the furnace to fill the furnace with hydrogen gas. Then the furnace temperature was adjusted to 120°C and irradiated with hydrogen radicals for 5 minutes. Afterwards, hydrogen is removed from the furnace by vacuuming, and the furnace is heated to 170°C. Nitrogen is then introduced into the furnace and the pressure is restored to atmospheric pressure. The furnace temperature is then lowered to room temperature to form solder particles. <Examples 91-93> 100 g of In-Sn solder particles (manufactured by 5N Plus, melting point 120°C, Type 8) were immersed in distilled water for ultrasonic dispersion, then allowed to stand, and the solder particles suspended in the supernatant were recovered to obtain solder particles with an average particle size of 1.0 μm and a CV value of 40%. In step a1, using the solder particles (average particle size 1.0 μm, CV value 40%), in step b1, the recess shown in Table 18 was used instead of step c1 to perform the following step c2. Otherwise, the solder particles were prepared in the same manner as in Example 1, and were recovered and evaluated. The results are shown in Table 19. (Step c2) Formation of solder particles The substrate with solder particles arranged in the recess in step b1 was placed in a hydrogen radical reduction furnace (plasma reflow device manufactured by Shin Kong Precision Machinery Co., Ltd.), and after evacuation, hydrogen gas was introduced into the furnace to fill the furnace with hydrogen gas. The furnace temperature was then adjusted to 110°C and irradiated with hydrogen free radicals for 5 minutes. After that, hydrogen was removed from the furnace by vacuuming, and the furnace was heated to 160°C. Nitrogen was then introduced into the furnace and the pressure was restored to atmospheric pressure. The furnace temperature was then lowered to room temperature to form solder particles. <Examples 94-96> 100 g of Sn-Ag-Cu solder particles (manufactured by 5N Plus, melting point 218°C, Type 8) were immersed in distilled water for ultrasonic dispersion, then allowed to stand and the solder particles suspended in the supernatant were recovered to obtain solder particles with an average particle size of 1.0 μm and a CV value of 41%. In step a1, using the solder particles (average particle size 1.0 μm, CV value 41%), in step b1, the recess shown in Table 18 was used instead of step c1 to perform the following step c2. Otherwise, the solder particles were prepared in the same manner as in Example 1, and were recovered and evaluated. The results are shown in Table 19. (Step c2) Formation of solder particles The substrate with solder particles arranged in the recess in step b1 was placed in a hydrogen radical reduction furnace (plasma reflow device manufactured by Shin Kong Precision Machinery Co., Ltd.), and after evacuation, hydrogen gas was introduced into the furnace to fill the furnace with hydrogen gas. The furnace temperature was then adjusted to 150°C and irradiated with hydrogen free radicals for 3 minutes. After that, the hydrogen gas in the furnace was removed by vacuuming, and the furnace was heated to 240°C. Nitrogen was then introduced into the furnace and the pressure was restored to atmospheric pressure. The furnace temperature was then lowered to room temperature to form solder particles. <Preparation Examples 49-51> Solder particles prepared using the same method as in Examples 85-87, and a transfer mold with the same substrate shape as used in the preparation of solder particles in Examples 85-87, were used as transfer molds. Otherwise, anisotropic conductive films and connecting structures were prepared using the same method as in Preparation Example 1. The results are shown in Tables 20-22. <Preparation Examples 52-54> Solder particles prepared using the same method as in Examples 88-90, and a transfer mold with the same substrate shape as used in the preparation of solder particles in Examples 88-90, were used as transfer molds. Otherwise, anisotropic conductive films and connecting structures were prepared using the same method as in Preparation Example 1. The results are shown in Tables 20-22. <Preparation Examples 55-57> Solder particles prepared using the same method as in Examples 91-93, and a transfer mold with the same substrate shape as used in the preparation of solder particles in Examples 91-93, were used as transfer molds. Otherwise, anisotropic conductive films and connecting structures were prepared using the same method as in Preparation Example 1. The results are shown in Tables 20-22. <Examples 58-60> Solder particles prepared using the same method as in Examples 94-96, and a transfer mold with the same substrate shape as used in the preparation of solder particles in Examples 94-96, were used as transfer molds. In step 11, the formal pressing temperature was set to 230°C. Otherwise, the anisotropic conductive film and the connecting structure were prepared using the same method as in Example 1. The results are shown in Tables 20-22. [Table 18] [Table 19] [Table 20] [Table 21] [Table 22] Regarding small recess sizes (e.g., 2 μm to 3 μm at the bottom), there is a tendency for lower CV values ​​to be obtained from solder particles with smaller center diameters. This is believed to be because smaller center diameters of solder particles lead to higher filling rates into the recesses and reduced filling deviations between multiple recesses. Based on the above embodiments, it has been confirmed that, if it is the method of the present invention, solder particles with uniform particle size and different melting points can be easily obtained simply by changing the composition of the solder particles. Furthermore, the cross-sectional shape of the recess can be varied. That is, the cross-sectional shape of the recess can be appropriately selected according to the final utilization method or shape of the solder particles. For example, when the solder particles are dispersed in resin to ensure fluidity like ink, it is considered that the surface of the solder particles preferably has a continuous curved surface. On the other hand, when the solder particles are dispersed in a film and brought into contact with the electrode through a pressing step, if the solder particles have a flat portion, it can sometimes mitigate the impact during contact and prevent electrode damage. In addition, sometimes the resin, whose viscosity is reduced by heating during the pressing step, flows and moves away from the electrode. However, with a flat portion, the contact area with the electrode is easily increased, and when the oxide film is removed using flux, the wetting of the electrode expands rapidly. Therefore, it also has the advantage of suppressing the movement caused by resin flow. The same phenomenon can also be seen in resin pastes. When the concave section has a conical shape towards the bottom as shown in Figure 2(e), the resulting solder particles, although lacking sharp corners due to the surface tension of the solder, become a pseudo-conical shape with a continuously changing cross-sectional diameter. Such particles can be configured, for example, in the thickness direction of the resin film, thus offering the following advantages: during crimping, the finer portion of the pseudo-conical cross-section improves resin rejection, allowing the solder particles to easily contact the electrode and achieving a stable connection. 1: Solder particle 11: Planar part 60: Substrate 60a: Surface 62: Recess 62a: Bottom 111: Solder particle A: Diameter a: Width (bottom diameter) B: Diameter b: Width b1: Opening diameter b2: Opening diameter Figure 1(a) is a plan view schematically showing an example of the substrate, and Figure 1(b) is a cross-sectional view of line Ib-Ib shown in Figure 1(a). Figures 2(a) to 2(h) are cross-sectional views schematically showing examples of the cross-sectional shape of the recess of the substrate. Figure 3 is a cross-sectional view schematically showing the state in which solder particles are contained in the recess of the substrate. Figure 4 is a cross-sectional view schematically showing the state in which solder particles are formed in the recess of the substrate. Figure 5 is a view of the solder particles viewed from the side opposite to the opening of the recess in Figure 4. Figure 6 is a diagram showing the distances X and Y (where Y≦X) between the opposing sides when a quadrilateral tangent to the projected image of the solder particles is formed using two pairs of parallel lines. Figures 7(a) and 7(b) are SEM images showing the solder particles formed in Example 17. Figures 8(a) and 8(b) are SEM images showing the solder particles used in Comparative Production Example 1. Figure 9 is a cross-sectional view schematically showing another example of the cross-sectional shape of a recess in the substrate. 60: Matrix 60a: Surface 62: concave part 62a: Bottom a: width b: width

Claims

1. A method for manufacturing solder particles, comprising: Preparation steps: Prepare a substrate with multiple recesses and powdered solder particles with a coefficient of variation value exceeding 20%; The storage step involves storing at least a portion of the powdered solder particles in the recess; The process includes a fusion step, in which the powdered solder particles contained in the recess are fused together to form solder particles inside the recess.

2. The method for manufacturing solder particles as claimed in claim 1, wherein the powdered solder particles housed in the recess are exposed to a reducing environment prior to the fusion step.

3. The method for manufacturing solder particles as claimed in claim 1, wherein in the fusion step, the powdered solder particles housed in the recess are fused in a reducing environment.

4. The method for manufacturing solder particles as claimed in claim 1, wherein the powdered solder particles prepared in the preparation step comprise at least one selected from the group consisting of tin, tin alloys, indium, and indium alloys.

5. The method for manufacturing solder particles as claimed in claim 4, wherein the powdered solder particles prepared in the preparation step comprise at least one selected from the group consisting of In-Bi alloy, In-Sn alloy, In-Sn-Ag alloy, Sn-Au alloy, Sn-Bi alloy, Sn-Bi-Ag alloy, Sn-Ag-Cu alloy, and Sn-Cu alloy.

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