Solder particles, method for manufacturing solder particles, and substrate with solder particles

Abstract

A production method for solder particles, the production method including a preparation step for preparing a substrate that has a plurality of protrusions, a solder layer formation step for forming a solder layer on at least a portion of the protrusions of the substrate, and a fusion step for fusing the solder layer that has been formed on the protrusions and thereby forming solder particles on the protrusions.

Description

[Technical Field]

[0001] The present invention relates to solder particles, a method for manufacturing solder particles, and a substrate with solder particles. [Background technology]

[0002] The use of solder particles has been studied as conductive particles to be blended into anisotropic conductive materials such as anisotropic conductive films, anisotropic conductive pastes, etc. For example, Patent Document 1 describes a conductive paste containing a thermosetting component and a plurality of solder particles that have been subjected to a specific surface treatment. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-76494 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, as circuit components have become increasingly finer, connection points have become smaller, and the electrical continuity and insulation reliability required of anisotropic conductive materials has increased. In order to ensure electrical continuity and insulation reliability, it is necessary to miniaturize and homogenize the conductive particles blended into the anisotropic conductive material. However, with conventional solder particle manufacturing methods, it has been difficult to manufacture solder particles that have both a small average particle diameter and a narrow particle size distribution.

[0005] The present invention has been made in view of the above-mentioned problems, and aims to provide a method for manufacturing solder particles that can manufacture solder particles that have both a small average particle diameter and a narrow particle size distribution. Another aim of the present invention is to provide solder particles that have both a small average particle diameter and a narrow particle size distribution using the manufacturing method. [Means for solving the problem]

[0006] One aspect of the present invention relates to a method for manufacturing solder particles, including a preparation step of preparing a base having a plurality of convex portions, a solder layer formation step of forming a solder layer on at least some of the convex portions of the base, and a fusion step of fusing the solder layer formed on the convex portions to form solder particles on the convex portions.

[0007] According to the above manufacturing method, by appropriately adjusting the shape of the protrusions and the thickness of the solder layer, solder particles of a desired particle size and a narrow particle size distribution can be obtained. In other words, according to the above manufacturing method, solder particles that have both a small average particle size and a narrow particle size distribution, which have been difficult to produce in the past, can be easily produced.

[0008] In one embodiment, the protrusions may be columnar or frustum-shaped.

[0009] In one embodiment, the base may have a first surface having a plurality of convex portions and bottom portions formed between the convex portions, and the ratio of the projected area of ​​the bottom portions to the projected area of ​​the first surface may be 8% or more.

[0010] In one embodiment of the manufacturing method, in the solder layer forming step, the solder layer may be formed on the protrusion by at least one method selected from the group consisting of plating, vapor deposition, sputtering, and spray coating.

[0011] The manufacturing method according to one aspect may further include a reduction step of exposing the solder layer formed on the protrusion to a reducing atmosphere before the fusing step.

[0012] In the manufacturing method according to one aspect, in the fusing step, the solder layer formed on the protrusion may be fused in a reducing atmosphere.

[0013] In one embodiment, the solder layer may contain at least one selected from the group consisting of tin, a tin alloy, indium, and an indium alloy.

[0014] In one aspect, the solder layer may contain 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.

[0015] Another aspect of the present invention relates to solder particles having an average particle diameter of 100 nm or more and less than 1 μm and a C.V. value of 20% or less.

[0016] In the case where a rectangle circumscribing the projection image of the solder particles according to one aspect is created by two pairs of parallel lines, when the distances between opposite sides are X and Y (where Y < X), X and Y may satisfy the following formula. 0.8 < Y / X < 1.0

[0017] The solder particles according to one aspect may contain at least one selected from the group consisting of tin, tin alloy, indium, and indium alloy.

[0018] The solder particles according to one aspect may contain 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.

[0019] Yet another aspect of the present invention relates to a substrate with solder particles, comprising a substrate having a plurality of convex portions and a plurality of solder particles disposed on the convex portions of the substrate. Such a substrate with solder particles can be easily manufactured by the fusion process in the above-described manufacturing method. According to such a substrate with solder particles, the transportation, storage, and management of the solder particles become easy.

[0020] In one aspect, the average particle diameter of the solder particles may be 100 nm or more and less than 1 μm, and the C.V. value of the solder particles may be 20% or less.

Advantages of the Invention

[0021] According to the present invention, there is provided a method for manufacturing solder particles capable of manufacturing solder particles having both a small average particle diameter and a narrow particle size distribution. Further, according to the present invention, there are provided solder particles having both a small average particle diameter and a narrow particle size distribution.

Brief Description of the Drawings

[0022] [Figure 1] FIG. 1(a) is a plan view schematically showing an example of a substrate, and FIG. 1(b) is a cross-sectional view taken along line Ib-Ib shown in FIG. 1(a). [Figure 2] FIG. 2(a) is a cross-sectional view schematically showing an example of a convex portion, and FIG. 2(b) is a cross-sectional view schematically showing another example of a convex portion. [Figure 3] FIGS. 3(a) to (e) are diagrams schematically showing examples of the shape of a cross-section perpendicular to the height direction of a convex portion. [Figure 4] FIG. 4 is a cross-sectional view schematically showing an example of a state in which a solder layer is formed on a convex portion of a substrate. [Figure 5] FIG. 5 is a cross-sectional view schematically showing an example of a state in which solder particles are formed on a convex portion of a substrate. [Figure 6] FIG. 6 is a cross-sectional view schematically showing another example of a state in which a solder layer is formed on a convex portion of a substrate. [[ID=ID=26]] [Figure 7] FIG. 7 is a cross-sectional view schematically showing another example of a state in which solder particles are formed on a convex portion of a substrate. [Figure 8] FIG. 8 is a diagram showing distances X and Y (where Y < X) between opposite sides when a quadrilateral circumscribing the projected image of solder particles is created by two pairs of parallel lines. [Figure 9] FIG. 9 is a SEM image of the substrate prepared in Example 13. [Figure 10] FIG. 10 is a SEM image of the state in which a solder layer is formed on a convex portion of the substrate in Example 13. [Figure 11] FIG. 11 is a SEM image of the state in which solder particles are formed on a convex portion of the substrate in Example 13. [Figure 12]FIG. 12 is an SEM image of the solder particles obtained in Example 2. [Figure 13] FIG. 13 is an SEM image of the solder particles obtained in Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0023] The following describes embodiments of the present invention. The present invention is not limited to the following embodiments. The materials exemplified below may be used singly or in combination, unless otherwise specified. When multiple substances corresponding to each component are present in the composition, the content of each component in the composition refers to the total amount of the multiple substances present in the composition, unless otherwise specified. Numerical ranges indicated using "to" indicate ranges that include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range may be replaced with the upper or lower limit of a numerical range of another stage. In the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with the values ​​shown in the examples.

[0024] <Method for manufacturing solder particles> The method for manufacturing solder particles according to this embodiment includes a preparation step of preparing a base having a plurality of convex portions, a solder layer formation step of forming a solder layer on at least some of the convex portions of the base, and a fusion step of fusing the solder layer formed on the convex portions to form solder particles on the convex portions.

[0025] According to the above manufacturing method, solder particles of a desired particle size and narrow particle size distribution can be obtained by appropriately adjusting the shape of the convex portions and the thickness of the solder layer. That is, according to the above manufacturing method, solder particles that have both a small average particle size and a narrow particle size distribution (for example, solder particles with an average particle size of 100 nm to 30 μm and a CV value of 20% or less), which have been difficult to manufacture in the past, can be easily manufactured.

[0026] Furthermore, the above manufacturing method can produce solder particles that are difficult to produce using conventional methods. For example, the above manufacturing method can produce extremely small solder particles with an average particle diameter of 100 nm or more and less than 1 μm, with a narrow particle size distribution (for example, a CV value of 20% or less).

[0027] The method for producing solder particles will be described below with reference to FIGS.

[0028] First, a substrate for forming a solder layer is prepared (preparation step). FIG. 1(a) is a diagram schematically illustrating an example of a substrate, and FIG. 1(b) is a cross-sectional view taken along line Ib-Ib in FIG. 1(a). The substrate 10 shown in FIG. 1(a) has a plurality of protrusions 11. The plurality of protrusions 11 may be regularly arranged in a predetermined pattern. In this case, the solder particles formed on the protrusions 11 can be transferred to a resin material or the like, thereby allowing the solder particles to be regularly arranged.

[0029] The base 10 may have a first surface 10a that includes a plurality of protrusions 11 and bottoms 12 formed between the protrusions 11. The first surface 10a may be composed of tops 11a of the protrusions 11 and a bottom surface 12a that is composed of the bottoms 12.

[0030] If the protrusions 11 are too close to each other, the solder particles on the protrusions 11 may come into contact with each other and fuse together in the fusing step described below, resulting in large-sized solder particles. From the viewpoint of suppressing the formation of such large-sized particles, the ratio of the projected area of ​​the bottom 12 to the projected area of ​​the first surface 10a (i.e., the ratio of the area of ​​the bottom surface 12a to the projected area of ​​the first surface 10a) is preferably 8% or more, more preferably 10% or more, and may even be 15% or more. There is no particular upper limit to this ratio. From the viewpoint of further improving the manufacturing efficiency of the solder particles, it may be, for example, 95% or less, preferably 90% or less, and more preferably 80% or less.

[0031] 1(a) and 1(b), the protrusions 11 are formed in a cylindrical shape, but the shape of the protrusions 11 is not limited to this. The protrusions 11 may be in a cylindrical shape such as a cylindrical, elliptical, triangular, square, or polygonal prism, or in a truncated cone shape such as a truncated circular cone, an elliptical, triangular, square, or polygonal prism.

[0032] 1(a) and 1(b), the top 11a of the protrusion 11 is depicted as a flat surface, but the top 11a does not necessarily have to be a flat surface. For example, the top 11a may have a depression or a protrusion. From the viewpoint of improving the retention of solder particles formed on the top 11a, it is preferable that the top 11a have a depression in the center.

[0033] Fig. 2(a) is a cross-sectional view showing an example of a protrusion, and Fig. 2(b) is a cross-sectional view showing an example of a protrusion. Protrusion 11 shown in Fig. 2(a) is a columnar protrusion, and protrusion 21 shown in Fig. 2(b) is a frustum-shaped protrusion.

[0034] The protrusion 11 has a width D at the top 11a. 11 and width D at the contact surface with the bottom 12 12 The width D may be approximately the same as the width D. 11 and width D 12 is not particularly limited, and may be, for example, 200 nm or more, and is preferably 400 nm or more, more preferably 1.0 μm or more, from the viewpoint of avoiding contact between solder particles on adjacent protrusions. 11 and width D 12 For example, it may be 10 μm or less, and from the viewpoint of producing extremely fine solder particles with a particle size of 800 nm or less, it is preferably 4.0 μm or less, and more preferably 2.0 μm or less.

[0035] The height H1 of the protrusion 11 is not particularly limited, and for example, 11 From the viewpoint of avoiding contact with the solder on the bottom 12 and making it easier to obtain solder particles with higher precision, the width D 11 25% or more of width D 11 It is more preferable that the height H1 of the protrusion 11 is equal to or greater than 50% of the width D11 From the viewpoint of avoiding damage to the protrusions 11 and further increasing the recovery rate of the solder particles, the width D 11 500% or less of width D 11 It is more preferable that the value is 300% or less of the above.

[0036] The protrusions 11 can be disposed at any positions on the base 10 .

[0037] The distance L1 between adjacent protrusions 11 is not particularly limited, but from the viewpoint of suppressing the formation of large-sized particles due to contact and fusion of solder particles on the protrusions 11, the distance L1 may be set to, for example, a width D 11 and preferably the width D 11 8% or more of width D 11 The distance L1 between adjacent protrusions 11 is, for example, 15% or more of the width D 11 From the viewpoint of further improving the manufacturing efficiency of the solder particles, it is preferable that the width is equal to or less than the width D 11 500% or less of width D 11 is less than 200% of the

[0038] The protrusion 21 has a width D at the top 21a. 21 The width D at the contact surface with the bottom 22 22 It is smaller than width D 21 is not particularly limited, and may be, for example, 200 nm or more, and is preferably 400 nm or more, more preferably 1.0 μm or more, from the viewpoint of avoiding contact between solder particles on adjacent protrusions. 21 The width D may be, for example, 10 μm or less, and from the viewpoint of producing extremely fine solder particles with a particle size of 800 nm or less, the width D is preferably 4.0 μm or less, and more preferably 2.0 μm or less. 22 is not particularly limited, and may be, for example, 200 nm or more, and is preferably 400 nm or more, more preferably 1.0 μm or more, from the viewpoint of avoiding contact between solder particles on adjacent protrusions. 22 For example, it may be 10 μm or less, and from the viewpoint of producing extremely fine solder particles with a particle size of 800 nm or less, it is preferably 4.0 μm or less, and more preferably 2.0 μm or less.

[0039] Width D 21 and width D 22 Ratio to (D 22 / D 21 ) is not particularly limited and may be, for example, 1.1 or more, and from the viewpoint of avoiding contact between solder particles on adjacent protrusions, it is preferably 1.3 or more, and more preferably 1.5 or more. 22 / D 21 ) may be, for example, 3.0 or less, and preferably 2.0 or less.

[0040] Width D 21 and width D 22 The difference between (D 22 -D 21 ) is not particularly limited and may be, for example, 2.0 μm or less, and from the viewpoint of reducing the amount of solder supplied to the side surface and bottom 22 of the protrusion 21 and making it easier to obtain solder particles with higher precision, it is preferably 1.0 μm or less, and more preferably 500 nm or less.

[0041] The height H2 of the protrusion 21 is not particularly limited, and may be, for example, 22 From the viewpoint of avoiding contact with the solder on the bottom 12 and making it easier to obtain solder particles with higher precision, the width D 22 25% or more of width D 22 It is more preferable that the height H2 of the protrusion 21 is equal to or greater than 50% of the width D 22 From the viewpoint of avoiding damage to the protrusions 11 and further increasing the recovery rate of the solder particles, the width D 22 500% or less of width D 22 It is more preferable that the value is 300% or less of the above.

[0042] The distance L2 between adjacent protrusions 21 is not particularly limited, but from the viewpoint of suppressing the formation of large-diameter particles due to contact and fusion of solder particles on the protrusions 21, the distance L2 may be set to, for example, a width D 22 and preferably the width D 22 8% or more of width D 22 The distance L2 between adjacent protrusions 21 is, for example, 15% or more of the width D 22From the viewpoint of further improving the manufacturing efficiency of the solder particles, it is preferable that the width is equal to or less than the width D 22 500% or less of width D 22 is less than 200% of the

[0043] The cross-sectional shapes of the protrusions 11 and 21 perpendicular to the height direction are not particularly limited, and may be, for example, shapes as shown in Fig. 3. Figs. 3(a) to 3(e) are diagrams schematically showing examples of the cross-sectional shapes of the protrusions perpendicular to the height direction.

[0044] The material constituting the base 10 is not particularly limited, and is preferably a heat-resistant material that does not change in quality at the melting temperature of the solder layer. The material constituting the base 10 may be, for example, an inorganic material such as silicon, various ceramics, glass, or stainless steel, or an organic material such as various resins.

[0045] The method for manufacturing the base 10 is not particularly limited, and it can be manufactured appropriately by a known method capable of forming the convex portions 11 (for example, photolithography, etc.).

[0046] Next, a solder layer is formed on at least some of the protrusions of the base (solder layer forming step). As the solder material for forming the solder layer, any commercially available solder material can be used without particular limitation, and can be appropriately selected depending on the desired characteristics of the solder particles, the method for forming the solder layer, etc. For example, when the solder layer is formed by sputtering, a solder plate that can be used as a sputtering target is selected.

[0047] The solder material may contain, for example, tin or a tin alloy. Examples of tin alloys that can be used 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 include the following: In-Sn (In 52% by mass, Bi 48% by mass, melting point 118°C) ·In-Sn-Ag (In20% by mass, Sn77.2% by mass, Ag2.8% by mass, melting point 175℃) Sn-Bi (Sn 43% by mass, Bi 57% by mass, melting point 138°C) Sn-Bi-Ag (Sn 42% by mass, Bi 57% by mass, Ag 1% by mass, melting point 139°C) Sn-Ag-Cu (Sn 96.5% by mass, Ag 3% by mass, Cu 0.5% by mass, melting point 217°C) Sn-Cu (Sn 99.3% by mass, Cu 0.7% by mass, melting point 227°C) ·Sn-Au (Sn21.0% by mass, Au79.0% by mass, melting point 278℃)

[0048] The solder material may contain, for example, indium or an indium alloy. Examples of indium alloys that can be used include In-Bi alloys and In-Ag alloys. Specific examples of these indium alloys include the following: In-Bi (In 66.3 mass%, Bi 33.7 mass%, melting point 72°C) In-Bi (In 33.0 mass%, Bi 67.0 mass%, melting point 109°C) In-Ag (In 97.0 mass%, Ag 3.0 mass%, melting point 145°C)

[0049] The above-mentioned tin alloy or indium alloy can be selected as the solder material depending on the application (temperature during use) of the solder particles. For example, if solder particles for low-temperature fusion are desired, an In-Sn alloy or an Sn-Bi alloy can be used, which will result in solder particles that can be fused at 150°C or less. If a solder material with a high melting point, such as an Sn-Ag-Cu alloy or an Sn-Cu alloy, is used, solder particles that maintain high reliability even after being left at high temperatures can be obtained.

[0050] The solder material may further contain one or more elements selected from Ag, Cu, Ni, Bi, Zn, Pd, Pb, Au, P, and B. Of these elements, Ag or Cu may be contained for the following reasons: By containing Ag or Cu in the solder material, the melting point of the resulting solder particles can be lowered to about 220°C, and solder particles with excellent bonding strength to the electrodes can be obtained, thereby achieving better electrical conductivity reliability.

[0051] The Cu content of the solder material is, for example, 0.05 to 10 mass%, or may be 0.1 to 5 mass%, or 0.2 to 3 mass%. When the Cu content is 0.05 mass% or more, solder particles that can achieve good solder connection reliability are easily obtained. When the Cu content is 10 mass% or less, solder particles with a low melting point and excellent wettability are easily obtained, which results in better connection reliability of the joints formed by the solder particles.

[0052] The Ag content of the solder material is, for example, 0.05 to 10 mass%, and may be 0.1 to 5 mass%, or 0.2 to 3 mass%. If the Ag content is 0.05 mass% or more, solder particles that can achieve good solder connection reliability are easily obtained. Furthermore, if the Ag content is 10 mass% or less, solder particles with a low melting point and excellent wettability are easily obtained, which results in better connection reliability of the joints made by the solder particles.

[0053] In the solder layer forming step, a solder layer is formed on each of the protruding portions of the base. The solder layer forming step may be a step of forming a solder layer on all of the protruding portions of the base prepared in the preparation step, or a step of forming a solder layer on some of the protruding portions of the base prepared in the preparation step.

[0054] In the solder layer forming step, the method for forming the solder layer is not particularly limited. Examples of methods for forming the solder layer include plating, vapor deposition, sputtering, spray coating, etc. Among these, sputtering is preferred from the viewpoints that the thickness of the solder layer can be strictly controlled and solder particles with a narrower particle size distribution can be easily obtained.

[0055] In the solder layer forming step, the amount of the solder layer to be formed is not particularly limited and may be appropriately changed depending on the desired size of the solder particles. By appropriately changing the amount of the solder layer to be formed on the protrusions, the size of the solder particles formed on the protrusions can be easily adjusted.

[0056] In the solder layer forming step, the solder layer may be formed only on the convex portions of the base, or may be formed in locations other than the convex portions of the base. For example, in the solder layer forming step, the solder layer may be formed on the convex portions and the bottom portion of the base.

[0057] 4 is a cross-sectional view schematically showing an example of a state in which a solder layer 50 is formed on the protrusions 11 of the base 10. In the embodiment shown in FIG. 4, the solder layer is formed only on the protrusions 11 of the base 10. The solder layer is formed using the above-mentioned solder material and may contain at least one selected from the group consisting of tin, a tin alloy, indium, and an indium alloy. The solder layer may also contain at least one selected from the group consisting of an In-Bi alloy, an In-Sn alloy, an In-Sn-Ag alloy, an Sn-Au alloy, an Sn-Bi alloy, an Sn-Bi-Ag alloy, an Sn-Ag-Cu alloy, and an Sn-Cu alloy.

[0058] Fig. 6 is a cross-sectional view schematically showing another example of a state in which a solder layer 50 is formed on the protrusions 11 of the base 10. In the embodiment shown in Fig. 6, the solder layer 50 is formed on the protrusions 11 of the base 10, and a solder layer 51 is also formed on the bottom 12 of the base 10. In this embodiment, the amount of the solder layer 50 formed on the protrusions 11 is, for example, preferably 20% or more, more preferably 30% or more, even more preferably 50% or more, and even more preferably 60% or more of the total volume of the solder layers formed on the base (total volume of the solder layers 50 and 51).

[0059] Next, the solder layer formed on the convex portion is fused to form solder particles on the convex portion (fusion process). In the fusion process, the solder layer formed on the convex portion is melted and coalesced, and is sphericalized by surface tension to form solder particles.

[0060] A method for melting the solder layer includes heating the solder layer to a temperature equal to or higher than the melting point of the solder material constituting the solder layer. Due to the influence of an oxide film, the solder layer may not melt even when heated to a temperature equal to or higher than the melting point, or may not wet, spread, or coalesce even after melting. Therefore, it is preferable to expose the solder layer to a reducing atmosphere, remove the oxide film on the surface of the solder layer, and then heat the solder layer to a temperature equal to or higher than the melting point of the solder material. Furthermore, it is preferable to melt the solder layer in a reducing atmosphere. Melting the solder layer in a reducing atmosphere facilitates more efficient melting, wetting, spreading, and coalescence of the solder layer.

[0061] The method for creating a reducing atmosphere is not particularly limited as long as it can achieve the above-mentioned effects, and examples include methods using hydrogen gas, hydrogen radicals, formic acid gas, etc. For example, a hydrogen reduction furnace, a hydrogen radical reduction furnace, a formic acid reduction furnace, or a conveyor furnace or continuous furnace thereof can be used to melt the solder layer in a reducing atmosphere. These devices may be equipped with a heating device, a chamber filled with an inert gas (nitrogen, argon, etc.), a mechanism for creating a vacuum in the chamber, etc., within the furnace, which makes it easier to control the reducing gas. Furthermore, if the chamber can be evacuated, voids can be removed by reducing the pressure after the solder layer has melted and coalesced, resulting in solder particles with even better connection stability.

[0062] The profile of the reduction of the solder layer, the melting conditions, the temperature, the adjustment of the atmosphere in the furnace, etc. may be set as appropriate taking into consideration the melting point of the solder layer, the particle size, the size of the recesses, the material of the base, etc. For example, a base with a solder layer formed on the protrusions is inserted into a furnace, and after evacuation, a reducing gas is introduced to fill the furnace with the reducing gas, the surface oxide film of the solder layer is removed, and then the reducing gas is removed by evacuation, and then the furnace is heated to a temperature above the melting point of the solder layer to melt and coalesce the solder layer and form solder particles on the protrusions, and then nitrogen gas is filled in and the furnace temperature is returned to room temperature to obtain the solder particles. Furthermore, for example, a substrate having a solder layer formed on the protrusions is inserted into a furnace, and after evacuation, a reducing gas is introduced to fill the furnace, the solder layer is heated with an in-furnace heater to remove the surface oxide film of the solder layer, and then the reducing gas is removed by evacuation, and the solder layer is heated above its melting point to melt and coalesce, forming solder particles on the protrusions. After that, nitrogen gas is filled in and the furnace temperature is returned to room temperature to obtain the solder particles. Heating the solder layer in a reducing atmosphere has the advantage of increasing the reducing power and making it easier to remove the surface oxide film of the solder layer.

[0063] Furthermore, for example, a substrate with a solder layer formed on the protrusions is inserted into a furnace, and after evacuation, reducing gas is introduced to fill the furnace, and the substrate is heated by a furnace heater to above the melting point of the solder layer, the surface oxide film of the solder layer is removed by reduction and at the same time the solder layer is melted and coalesced to form solder particles on the protrusions, and after evacuation, the reducing gas is removed and further voids in the solder particles are reduced, and then nitrogen gas is filled in and the furnace temperature is returned to room temperature to obtain the solder particles. In this case, the furnace temperature only needs to be adjusted up and down once each, which has the advantage of allowing for a short processing time.

[0064] After forming the solder particles on the protrusions, a further step may be added in which the furnace is again placed in a reducing atmosphere to remove any remaining surface oxide film, thereby reducing the amount of solder layer that remains unfused and the remaining oxide film.

[0065] When an atmospheric pressure conveyor furnace is used, a substrate having a solder layer formed on its protrusions can be placed on a conveyor and passed through multiple zones in succession to obtain solder particles. For example, a substrate having a solder layer formed on its protrusions can be placed on a conveyor set at a constant speed, passed through a zone filled with an inert gas such as nitrogen or argon at a temperature lower than the melting point of the solder layer, then passed through a zone containing a reducing gas such as formic acid gas at a temperature lower than the melting point of the solder layer to remove the surface oxide film of the solder layer, then passed through a zone filled with an inert gas such as nitrogen or argon at a temperature higher than the melting point of the solder layer to melt and coalesce the solder layer, and then passed through a cooling zone filled with an inert gas such as nitrogen or argon to obtain solder particles. For example, a substrate with a solder layer formed on its protruding portions can be placed on a conveyor set at a constant speed and passed through a zone filled with an inert gas such as nitrogen or argon at a temperature above the melting point of the solder layer, then through a zone containing a reducing gas such as formic acid gas at a temperature above the melting point of the solder layer to remove the surface oxide film of the solder layer, melt it, and coalesce it. The substrate can then be passed through a cooling zone filled with an inert gas such as nitrogen or argon to obtain solder particles. Because the conveyor furnace can operate at atmospheric pressure, it can also process film-like materials continuously in a roll-to-roll process. For example, a continuous roll of a substrate with a solder layer formed on its protruding portions can be produced, and a roll unwinder is installed at the entrance of the conveyor furnace and a roll winder is installed at the exit of the conveyor furnace. The substrate can be transported at a constant speed through each zone in the conveyor furnace to fuse the solder layer formed on the protruding portions.

[0066] The formed solder particles may be transported, stored, etc., in the state where they are formed on the convex portions of the substrate. The substrate with the solder particles formed on the convex portions can be conveniently handled as a substrate with solder particles. The substrate with solder particles comprises a substrate having a plurality of convex portions and a plurality of solder particles arranged on the convex portions of the substrate. The average particle diameter of the solder particles may be 100 nm or more and less than 1 μm, and the CV value of the solder particles may be 20% or less. The formed solder particles may be collected from the convex portions. Alternatively, a resin material may be arranged opposite the convex portions of the substrate, and the solder particles on the convex portions may be transferred to the resin material. In this case, if the convex portions are arranged regularly, the solder particles can be arranged regularly on the resin material.

[0067] Fig. 5 is a cross-sectional view showing a schematic example of a state in which solder particles are formed on protrusions of a substrate. The substrate 100 with solder particles shown in Fig. 5 is obtained by subjecting the substrate 10 having the solder layer 50 shown in Fig. 4 formed thereon to a fusing process. In the substrate 100 with solder particles, the substrate 10 has a plurality of protrusions 11, and solder particles 1 are formed on the protrusions 11.

[0068] FIG. 7 is a cross-sectional view schematically illustrating another example of a state in which solder particles are formed on protrusions of a substrate. The substrate 110 with solder particles shown in FIG. 7 is obtained by subjecting the substrate 10, on which the solder layer 50 and solder layer 51 shown in FIG. 6 are formed, to a fusing process. In the substrate 110 with solder particles, the substrate 10 has a plurality of protrusions 11, and solder particles 1 are formed on the protrusions 11. In the substrate 110 with solder particles, solder particles 2 derived from the solder layer 51 are formed on the bottoms 12 between the protrusions 11. Since the solder particles 2 do not necessarily have a small particle size distribution, in this embodiment, it is preferable to collect or transfer only the solder particles 1. The solder particles 2 are fixed to the bottoms 12 of the substrate 10 and are located at a lower position than the solder particles 1 on the protrusions 11. Therefore, for example, by arranging a resin material so as to face the protrusions 11 of the base 10 and transferring the solder particles 1 on the protrusions 11 to the resin material, it is possible to collect only the solder particles 1.

[0069] The manufacturing method of this embodiment can form solder particles of uniform size regardless of the material and shape of the solder material. For example, indium-based solder can be deposited by plating, but it is difficult to deposit in particulate form and is soft and difficult to handle. However, the manufacturing method of this embodiment uses an indium-based solder plate as a raw material, making it easy to produce indium-based solder particles with uniform particle size. Furthermore, the formed solder particles can be handled in the state where they are formed on the convex portions of the base, allowing for transportation and storage without deformation of the solder particles. Furthermore, since the formed solder particles are simply formed on the convex portions of the base, they are easily removed, and can be recovered and surface-treated without deformation of the solder particles.

[0070] Furthermore, the solder material may have a large variation in size or particle size distribution, or may have an irregular shape, and as long as a solder layer can be formed on the convex portion by techniques such as sputtering, plating, or spray painting, it can be used as a raw material in the manufacturing method of this embodiment.

[0071] Furthermore, in the manufacturing method of this embodiment, the shape of the convex portions of the base can be freely designed by photolithography, imprinting, mechanical processing, electron beam processing, radiation processing, etc. Since the size of the solder particles depends on the amount of the solder layer formed on the convex portions, in the manufacturing method of this embodiment, the size of the solder particles can be freely designed by the design of the convex portions.

[0072] (solder particles) The solder particles according to this embodiment have an average particle diameter of 100 nm or more and 30 μm or less, and a CV value of 20% or less, and preferably an average particle diameter of 100 nm or more and less than 1 μm, and a CV value of 20% or less. Such solder particles have both a small average particle diameter and a narrow particle size distribution, and can be suitably used as conductive particles for anisotropic conductive materials with high conductive reliability and insulating reliability. The solder particles according to this embodiment are manufactured by the above-described manufacturing method.

[0073] The average particle size of the solder particles is not particularly limited as long as it is within the above range, and may be, for example, 30 μm or less, 15 μm or less, 10 μm or less, 5 μm or less, 3 μm or less, or 2 μm or less, and preferably less than 1 μm. The average particle size of the solder particles may be, for example, 100 nm or more, 200 nm or more, 300 nm or more, 400 nm or more, or 500 nm or more.

[0074] The average particle diameter of solder particles can be measured using various methods suited to the size. For example, dynamic light scattering, laser diffraction, centrifugal sedimentation, electrical sensing zone analysis, and resonance mass measurement can be used. Furthermore, particle size can be measured from images obtained using an optical microscope, electron microscope, or the like. Specific devices include a flow particle image analyzer, Microtrac, and Coulter counter.

[0075] From the viewpoint of realizing better conductive reliability and insulating reliability, the CV value of the solder particles is preferably 20% or less, more preferably 10% or less, even more preferably 7% or less, and particularly preferably 5% or less. The lower limit of the CV value of the solder particles is not particularly limited. For example, the CV value of the solder particles may be 1% or more, or may be 2% or more.

[0076] The CV value of the solder particles is calculated by dividing the standard deviation of the particle diameter measured by the above-mentioned method by the average particle diameter and multiplying the result by 100.

[0077] The solder particles may have a flat portion formed on a part of the surface, and at this time, the surface other than the flat portion is preferably spherical-crown-shaped. That is, the solder particles may have a flat portion and a spherical-crown-shaped curved surface portion. The ratio (A / B) of the diameter A of the flat portion to the diameter B of the solder particles may be, for example, more than 0.01 and less than 1.0 (0.01 < A / B < 1.0), or may be 0.1 to 0.9. When the solder particles have a flat portion, the sitting of the solder particles becomes better and the handling property is improved. Specifically, when arranging the solder particles on an object to be connected by the solder particles such as an electrode, the presence of the flat portion makes it easy to arrange them at a predetermined position, and there is an effect of suppressing the solder particles from moving from the predetermined position due to vibration, wind, external force, static electricity, etc. Also, when the member on which the solder particles are arranged is tilted, there is an effect that the solder particles are less likely to move due to gravity as compared with, for example, spherical solder particles without a flat portion.

[0078] In the above manufacturing method, solder particles are formed on the convex portion of the substrate. At this time, the flat portion may be formed at the contact surface between the solder particles and the top of the convex portion.

[0079] When a quadrilateral circumscribing the projection image of the solder particles is created by two pairs of parallel lines, when the distances between the opposing sides are X and Y (where Y < X), the ratio (Y / X) of Y to X may be more than 0.8 and less than 1.0 (0.8 < Y / X < 1.0), or may be 0.9 or more and less than 1.0. Such solder particles can be said to be particles closer to a true sphere. According to the manufacturing method of the present embodiment described above, such solder particles can be easily obtained. Since the solder particles are close to a spherical shape, for example, when electrically connecting a plurality of opposing electrodes through the solder particles, unevenness in contact between the solder particles and the electrodes is less likely to occur, and a stable connection tends to be obtained. Further, when producing a conductive film or resin in which the solder particles are dispersed in a resin material, high dispersibility tends to be obtained, and dispersion stability during production tends to be obtained. Additionally, when using a film or paste in which the solder particles are dispersed in a resin material for connection between electrodes, 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 viewed in a projection image. Therefore, when connecting the electrodes to each other, a stable electrical connection with little variation is likely to be obtained.

[0080] FIG. 8 is a diagram showing distances X and Y (where Y < X) between opposing sides when a quadrilateral circumscribing the projection image of the solder particles is created by two pairs of parallel lines. For example, an arbitrary particle is observed with a scanning electron microscope to obtain a projection image. For the obtained projection image, two pairs of parallel lines are drawn. One pair of parallel lines is arranged at a position where the distance between the parallel lines is minimized, and the other pair of parallel lines is arranged at a position where the distance between the parallel lines is maximized, and Y / X of the particle is determined. This operation is performed on 300 solder particles, and an average value is calculated, which is defined as Y / X of the solder particles.

[0081] The solder particles may contain tin or a tin alloy. As the tin alloy, for example, In-Sn alloy, In-Sn-Ag alloy, Sn-Au alloy, Sn-Bi alloy, Sn-Bi-Ag alloy, Sn-Ag-Cu alloy, Sn-Cu alloy, etc. can be used. Specific examples of these tin alloys are as follows. ·In-Sn (In 52 mass%, Bi 48 mass%, melting point 118°C) ·In-Sn-Ag (In 20 mass%, Sn 77.2 mass%, Ag 2.8 mass%, melting point 175°C) ·Sn-Bi (Sn 43 mass%, Bi 57 mass%, melting point 138°C) ·Sn-Bi-Ag (Sn 42 mass%, Bi 57 mass%, Ag 1 mass%, melting point 139°C) ·Sn-Ag-Cu (Sn 96.5 mass%, Ag 3 mass%, Cu 0.5 mass%, melting point 217°C) Sn-Cu (Sn 99.3% by mass, Cu 0.7% by mass, melting point 227°C) ·Sn-Au (Sn21.0% by mass, Au79.0% by mass, melting point 278℃)

[0082] The solder particles may contain indium or an indium alloy. Examples of indium alloys that can be used include In-Bi alloys and In-Ag alloys. Specific examples of these indium alloys include the following: In-Bi (In 66.3 mass%, Bi 33.7 mass%, melting point 72°C) In-Bi (In 33.0 mass%, Bi 67.0 mass%, melting point 109°C) In-Ag (In 97.0 mass%, Ag 3.0 mass%, melting point 145°C)

[0083] The above-mentioned tin alloy or indium alloy can be selected depending on the application of the solder particles (temperature during use), etc. For example, when using solder particles for low-temperature fusion, an In-Sn alloy or an Sn-Bi alloy can be used, and in this case, fusion can be performed at 150°C or less. When a material with a high melting point, such as an Sn-Ag-Cu alloy or an Sn-Cu alloy, is used, high reliability can be maintained even after exposure to high temperatures.

[0084] The solder particles may contain one or more elements selected from Ag, Cu, Ni, Bi, Zn, Pd, Pb, Au, P, and B. Of these elements, Ag or Cu may be contained for the following reasons: When the solder particles contain Ag or Cu, the melting point of the solder particles can be lowered to about 220°C, and the bonding strength with the electrode is further improved, making it easier to obtain better electrical conductivity reliability.

[0085] The Cu content of the solder particles is, for example, 0.05 to 10 mass%, and may be 0.1 to 5 mass%, or 0.2 to 3 mass%. When the Cu content is 0.05 mass% or more, better solder connection reliability is more likely to be achieved. Furthermore, when the Cu content is 10 mass% or less, the solder particles tend to have a low melting point and excellent wettability, which results in better connection reliability at the joints formed by the solder particles.

[0086] The Ag content of the solder particles is, for example, 0.05 to 10 mass%, and may be 0.1 to 5 mass%, or 0.2 to 3 mass%. When the Ag content is 0.05 mass% or more, better solder connection reliability is more likely to be achieved. Furthermore, when the Ag content is 10 mass% or less, the solder particles tend to have a low melting point and excellent wettability, which results in better connection reliability at the joints formed by the solder particles.

[0087] The solder particles are not particularly limited in their applications, and can be suitably used, for example, as conductive particles for anisotropic conductive materials. They can also be suitably used for applications such as electrically connecting electrodes together in ball grid array connection methods (BGA connections), which are widely used in the implementation of semiconductor integrated circuits, as well as for sealing and sealing components such as MEMS, brazing, and spacers for controlling height and gaps. In other words, the solder particles can be used in general applications where solder has traditionally been used.

[0088] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. [Example]

[0089] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0090] Example 1 (Step a1) Preparation of the substrate A substrate (polyimide film, 50 μm thick) was prepared, which had multiple protrusions with a top diameter of 0.15 μm, a bottom diameter of 0.15 μm, and a height of 0.13 μm. The multiple protrusions were regularly arranged at intervals of 0.15 μm.

[0091] (Step b1) Formation of solder layer The substrate having multiple protrusions obtained in step a1 was placed in a sputtering device (manufactured by Arios Co., Ltd.), and after evacuation, argon gas was introduced to create an argon atmosphere inside the device at 1 Pa. Thereafter, sputtering was carried out under the following conditions for the time shown in Table 1 to form a solder layer. (equipment conditions) Target: Sn-Bi solder plate (melting point 139°C) Input power...60W

[0092] (Step c1) Formation of solder particles The substrate with the solder layer obtained in step b1 was placed in a formic acid radical reduction furnace (a reflow device manufactured by Shinko Seiki Co., Ltd.). After evacuation, formic acid mixed nitrogen gas (formic acid content 4%) was introduced into the furnace to fill it. The furnace was then adjusted to 120°C and reduction treatment was carried out for 5 minutes. After heating to 180°C, the gas in the furnace was removed by evacuation, nitrogen was introduced into the furnace to return it to atmospheric pressure, and the temperature in the furnace was then lowered to room temperature to form solder particles.

[0093] (Evaluation of solder particles) The substrate with the solder particles obtained in step c1 was fixed onto conductive tape attached to the surface of a SEM observation stage. Platinum sputtering was then performed at 20 mA for 60 seconds. The diameters of 200 core-shell solder particles were measured using an SEM, and the average particle diameter and CV value were calculated. The results are shown in Table 1.

[0094] <Examples 2 to 12> Solder particles were produced and evaluated in the same manner as in Example 1, using the top diameter, bottom diameter, height, interval, sputtering time, and material shown in Table 1. The results are shown in Table 1. Also, an SEM image of the solder particles obtained in Example 2 is shown in FIG.

[0095] <Examples 13 to 17> Except for performing the following step c2 instead of step c1, solder particles were produced and evaluated in the same manner as in Example 1 using the top diameter, bottom diameter, height, interval, sputtering time, and material shown in Table 1. The results are shown in Table 1. Figure 9 shows an SEM image of the substrate prepared in Example 13, Figure 10 shows an SEM image of the solder layer formed on the substrate, and Figure 11 shows an SEM image of the solder particles formed.

[0096] (Step c2) Formation of solder particles The substrate with the solder layer obtained in step b1 was placed in a hydrogen radical reduction furnace (a plasma reflow device manufactured by Shinko Seiki Co., Ltd.). After evacuating, hydrogen gas was introduced into the furnace, filling it with hydrogen gas. The temperature inside the furnace was then adjusted to 130°C, and hydrogen radicals were irradiated for 5 minutes. The hydrogen gas inside the furnace was then removed by evacuating, and the furnace was heated to 165°C. Nitrogen was then introduced into the furnace to return it to atmospheric pressure, and the temperature inside the furnace was then lowered to room temperature to form solder particles.

[0097] <Comparative Example 1> Sn-Bi solder particles (5N Plus, melting point 139°C, Type 8, D 50 500g of the sample was divided into five 100g portions, each of which was immersed in distilled water and ultrasonically dispersed, then allowed to stand and the solder particles floating in the supernatant were collected. This process was repeated until a total of 1g of solder particles was collected. The average particle size and CV value of the resulting solder particles are shown in Table 1.

[0098] <Comparative Example 2> Except for preparing a smooth substrate (polyimide film, thickness 50 μm) without protrusions, solder particles were produced and evaluated in the same manner as in Example 2. The results are shown in Table 1. An SEM image of the obtained solder particles is shown in FIG.

[0099] [Table 1] [Explanation of symbols]

[0100] 1...solder particles, 10...base, 11, 21...projections, 12, 22...bottom, 50...solder layer, 100, 110...base with solder particles.

Claims

1. a preparation step of preparing a base body having a plurality of protrusions; a solder layer forming step of forming a solder layer on at least a part of the protrusions of the base; a melting step of melting the solder layer formed on the protrusions, and causing the molten solder layer to become spherical due to surface tension, thereby forming solder particles on the protrusions; A method for producing solder particles, comprising:

2. The method for producing solder particles according to claim 1 , wherein the protrusions are columnar or frustum-shaped.

3. the base has a first surface including a plurality of protrusions and bottoms formed between the protrusions; The method for producing solder particles according to claim 1 or 2, wherein a ratio of the projected area of ​​the bottom to the projected area of ​​the first surface is 8% or more.

4. 4. The method for manufacturing solder particles according to claim 1, wherein in the solder layer forming step, the solder layer is formed on the convex portion by at least one method selected from the group consisting of plating, vapor deposition, sputtering, and spray coating.

5. 5. The method for manufacturing solder particles according to claim 1, further comprising a reduction step of exposing the solder layer formed on the protrusion to a reducing atmosphere before the melting step.

6. 6. The method for manufacturing solder particles according to claim 1, wherein in the melting step, the solder layer formed on the convex portion is melted in a reducing atmosphere.

7. 7. The method for producing solder particles according to claim 1, wherein the solder layer contains at least one selected from the group consisting of tin, a tin alloy, indium, and an indium alloy.

8. 8. The method for producing solder particles according to claim 7, wherein the solder layer contains at least one selected from the group consisting of an In—Bi alloy, an In—Sn alloy, an In—Sn—Ag alloy, a Sn—Au alloy, a Sn—Bi alloy, a Sn—Bi—Ag alloy, a Sn—Ag—Cu alloy, and a Sn—Cu alloy.

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