Solder particles, methods for manufacturing solder particles, and substrates containing solder particles

Abstract

The present invention provides a method for manufacturing solder particles, comprising: a preparation step of preparing a substrate having a plurality of protrusions; a solder layer forming step of forming a solder layer on at least a portion of the protrusions of the substrate; and a fusion step of fusing the solder layer formed on the protrusions to form solder particles on the protrusions.

Description

Technical Field

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

[0002] Previously, the use of solder particles as conductive particles in conjunction with anisotropic conductive materials such as anisotropic conductive films and anisotropic conductive pastes has been studied. For example, Patent Document 1 describes a conductive paste that contains thermosetting components and multiple solder particles that have undergone specific surface treatment.

[0003] Previous technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2016-76494 Summary of the Invention

[0006] The technical problem to be solved by the invention

[0007] In recent years, with the increasing precision of circuit components and the miniaturization of connection parts, the requirements for the conductivity and insulation reliability of anisotropic conductive materials have become more stringent. To ensure conductivity and insulation reliability, it is necessary to miniaturize and homogenize the conductive particles that are compatible with anisotropic conductive materials. However, in the previous methods of manufacturing solder particles, it was difficult to manufacture solder particles that have both a small average particle size and a narrow particle size distribution.

[0008] The present invention was made in view of the above-mentioned problems, and its object is to provide a method for manufacturing solder particles that can produce solder particles with small average particle size and narrow particle size distribution. Furthermore, the object of the present invention is to provide solder particles with both small average particle size and narrow particle size distribution through the above-described manufacturing method.

[0009] means for solving technical problems

[0010] 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 protrusions; a solder layer forming step of forming a solder layer on at least a portion of the protrusions of the substrate; and a fusion step of fusing the solder layer formed on the protrusions to form solder particles on the protrusions.

[0011] According to the manufacturing method described above, by appropriately adjusting the shape of the protrusion and the thickness of the solder layer, solder particles with the desired particle size can be obtained with a narrow particle size distribution. That is, according to the manufacturing method described above, solder particles with both small average particle size and narrow particle size distribution, which were previously difficult to manufacture, can be easily manufactured.

[0012] In one embodiment, the aforementioned protrusion may be columnar or frustum-shaped.

[0013] In one embodiment, the substrate may have a first surface having a plurality of protrusions and a bottom formed between the protrusions, wherein the proportion of the projected area of ​​the bottom in the projected area of ​​the first surface may be 8% or more.

[0014] One manufacturing method, in the solder layer forming step, involves forming the solder layer on the protrusion by selecting at least one method selected from the group consisting of plating, vapor deposition, sputtering, and spraying.

[0015] One manufacturing method may further include a reduction step prior to the fusion step, in which the solder layer formed on the protrusion is exposed to a reducing atmosphere.

[0016] In one manufacturing method, during the fusion step, the solder layer formed on the protrusion is fused in a reducing atmosphere.

[0017] In one embodiment, the solder layer may comprise at least one selected from the group consisting of tin, tin alloys, indium, and indium alloys.

[0018] In one embodiment, the solder layer may 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.

[0019] Another aspect of the present invention relates to solder particles having an average particle size of 100 nm or more and less than 1 μm, and a CV value of 20% or less.

[0020] In one method, solder particles can be formed by creating a quadrilateral circumscribed by the projected image of the solder particles using two pairs of parallel lines. When the distances between opposite sides are set as X and Y, and Y < X, X and Y satisfy the following equation:

[0021] 0.8 < Y / X < 1.0.

[0022] A solder particle composition that may contain at least one selected from the group consisting of tin, tin alloys, indium, and indium alloys.

[0023] A solder particle comprising 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.

[0024] Another aspect of the present invention relates to a substrate with solder particles, comprising: a substrate having a plurality of protrusions; and a plurality of solder particles disposed on the protrusions of the substrate. This substrate with solder particles can be easily manufactured by the fusion step in the above-described manufacturing method. With this substrate with solder particles, the solder particles are easy to transport, store, and manage.

[0025] In one embodiment, the average particle size of the solder particles can be greater than 100 nm and less than 1 μm, and the CV value of the solder particles can be less than 20%.

[0026] Invention Effects

[0027] According to the present invention, a method for manufacturing solder particles that can produce solder particles with both small average particle size and narrow particle size distribution is provided. Furthermore, according to the present invention, solder particles with both small average particle size and narrow particle size distribution are provided. Attached Figure Description

[0028] Figure 1 (a) is a top view schematically representing an example of a substrate. Figure 1 (b) is Figure 1 (a) is a cross-sectional view along line Ib-Ib shown.

[0029] Figure 2 (a) is a cross-sectional view schematically showing an example of a convex portion. Figure 2 (b) is a cross-sectional view schematically representing another example of a convex portion.

[0030] Figure 3 (a) to (e) are schematic diagrams illustrating examples of the shape of a cross section perpendicular to the height direction of the convex part.

[0031] Figure 4 This is a cross-sectional view schematically showing an example of a state in which a solder layer is formed on a protrusion of a substrate.

[0032] Figure 5 This is a cross-sectional view schematically showing an example of a state in which solder particles are formed on a protrusion of a substrate.

[0033] Figure 6 This is a cross-sectional view schematically showing another example of a solder layer formed on a protrusion of a substrate.

[0034] Figure 7 This is a cross-sectional view schematically illustrating another example of a state in which solder particles are formed on a protrusion of a substrate.

[0035] Figure 8It is a graph representing the distances X and Y (where Y < X) between opposite sides when a quadrilateral circumscribed by the projected image of solder particles is created from two pairs of parallel lines.

[0036] Figure 9 SEM images of the substrate prepared in Example 13 were captured.

[0037] Figure 10 It is a SEM image of the state in which a solder layer is formed on the protrusion of the substrate in Example 13.

[0038] Figure 11 It is a SEM image of the state in which solder particles are formed on the protrusion of the substrate in Example 13.

[0039] Figure 12 SEM images of the solder particles obtained in Example 2 were captured.

[0040] Figure 13 SEM images of solder particles obtained in Comparative Example 2 were captured. Detailed Implementation

[0041] The embodiments of the present invention will be described below. The present invention is not limited to the following embodiments. Furthermore, unless otherwise stated, the materials exemplified below may be used alone or in combination of two or more. In the case where multiple substances equivalent to each component exist in the composition, unless otherwise stated, the content of each component in the composition refers to the total amount of the multiple substances present in the composition. Numerical ranges indicated by “~” represent the ranges including the minimum and maximum values, respectively, of the values ​​recorded before and after “~”. In the numerical ranges described in stages in this specification, the upper or lower limit of the numerical range for one stage may be replaced by the upper or lower limit of the numerical range for another stage. In the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced by the values ​​shown in the embodiments.

[0042] <Method for Manufacturing Solder Particles>

[0043] The method for manufacturing solder particles according to this embodiment includes: a preparation step of preparing a substrate having a plurality of protrusions; a solder layer forming step of forming a solder layer on at least a portion of the protrusions of the substrate; and a fusion step of fusing the solder layer formed on the protrusions to form solder particles on the protrusions.

[0044] According to the manufacturing method described above, by appropriately adjusting the shape of the protrusion and the thickness of the solder layer, solder particles with the desired particle size can be obtained with a narrow particle size distribution. That is, according to the manufacturing method described above, solder particles with both small average particle size and narrow particle size distribution (e.g., solder particles with an average particle size of 100 nm to 30 μm and a CV value of less than 20%) that were previously difficult to manufacture can be easily manufactured.

[0045] Furthermore, according to the above manufacturing method, solder particles that are difficult to manufacture by conventional methods can be obtained. For example, according to the above manufacturing method, extremely small solder particles with an average particle size of 100 nm or more and less than 1 μm can be obtained with a narrow particle size distribution (e.g., CV value of 20% or less).

[0046] The following is for reference. Figures 1-7 The manufacturing method of solder particles is explained.

[0047] First, prepare the substrate for forming the solder layer (preparation step). Figure 1 (a) is a diagram schematically representing an example of a matrix. Figure 1 (b) is Figure 1 (a) is a cross-sectional view along line Ib-Ib shown. Figure 1 (a) The substrate 10 shown has a plurality of protrusions 11. The plurality of protrusions 11 can be regularly arranged in a prescribed pattern. In this case, by transferring solder particles formed on the protrusions 11 onto a resin material or the like, the solder particles can be regularly arranged.

[0048] The substrate 10 may have a first surface 10a, which has a plurality of protrusions 11 and a bottom 12 formed between the protrusions 11. The first surface 10a may be composed of a top surface 11a of the protrusions 11 and a bottom surface 12a formed by the bottom surface 12.

[0049] If the protrusions 11 are too close to each other, during the fusion step described later, solder particles on the protrusions 11 may come into contact with and fuse together, resulting in large-diameter solder particles. From the viewpoint of suppressing the formation of such large-diameter particles, the proportion of the projected area of ​​the bottom 12 in the projected area of ​​the first surface 10a (i.e., the proportion of the area of ​​the bottom surface 12a in the projected area of ​​the first surface 10a) is preferably 8% or more, more preferably 10% or more, and may also be 15% or more. The upper limit of this proportion is not particularly limited. From the viewpoint of further improving the manufacturing efficiency of solder particles, it can be, for example, 95% or less, preferably 90% or less, and more preferably 80% or less.

[0050] exist Figure 1 (a) and Figure 1In (b), the protrusion 11 is formed in a cylindrical shape, but the shape of the protrusion 11 is not limited to this. For example, the protrusion 11 can be a cylindrical, elliptical cylindrical, triangular prism, square prism, polygonal prism, or other columnar shape, or a frustum-shaped, elliptical frustum-shaped, triangular frustum-shaped, square frustum-shaped, polygonal frustum-shaped, or other conical shape.

[0051] exist Figure 1 (a) and Figure 1 In (b), the top 11a of the protrusion 11 is described as a flat surface, but the top 11a does not necessarily have to be flat. 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, the top 11a preferably has a depression in the center.

[0052] Figure 2 (a) is a cross-sectional view schematically showing an example of a convex portion. Figure 2 (b) is a cross-sectional view schematically representing an example of a convex portion. Figure 2 (a) The protrusion 11 shown is a columnar protrusion. Figure 2 (b) The protrusion 21 shown is a frustoconical protrusion.

[0053] In the protrusion 11, the width D in the top 11a 11 and the width D in the contact surface with the bottom 12 12 They can be roughly the same. Width D 11 and width D 12 It is not particularly limited; for example, it can be 200 nm or more. From the viewpoint of avoiding contact between solder particles on adjacent protrusions, it is preferably 400 nm or more, and more preferably 1.0 μm or more. Furthermore, the width D... 11 and width D 12 For example, it can be 10 μm or less. From the viewpoint of producing solder particles with an extremely small particle size of 800 nm or less, it is preferably 4.0 μm or less, and more preferably 2.0 μm or less.

[0054] The height H1 of the protrusion 11 is not particularly limited; for example, it can be the width D. 11 The width D is preferably 10% or more, based on the viewpoint of avoiding contact with the solder on the bottom 12 and easily obtaining solder particles with higher precision. 11 More than 25%, preferably width D 11 More than 50%. Furthermore, the height H1 of the protrusion 11 can, for example, be the width D. 11 From the viewpoint of avoiding damage to the protrusion 11 and further improving the recovery rate of solder particles, the width D is preferably below 1000%. 11 Below 500%, more preferably width D 11 Less than 300%.

[0055] The protrusion 11 can be positioned at any location on the base 10.

[0056] The distance L1 between adjacent protrusions 11 is not particularly limited, but from the viewpoint of suppressing the formation of large-diameter particles due to the contact and fusion of solder particles on the protrusions 11, it can be, for example, the width D. 11 More than 3%, preferably width D 11 More than 8%, preferably width D 11 More than 15%. Furthermore, the distance L1 between adjacent protrusions 11 can, for example, be the width D. 11 From the viewpoint of further improving the manufacturing efficiency of solder particles, a width D of less than 1000% is preferred. 11 Below 500%, more preferably width D 11 Less than 200%.

[0057] The width D of the protrusion 21 on the top 21a 21 The width D of the contact surface with the bottom 22 is less than the width of the bottom 22. 22 Width D 21 It is not particularly limited; for example, it can be 200 nm or more. From the viewpoint of avoiding contact between solder particles on adjacent protrusions, it is preferably 400 nm or more, and more preferably 1.0 μm or more. Furthermore, the width D... 21 For example, it can be 10 μm or less; from the viewpoint of producing solder particles with an extremely small particle size of 800 nm or less, it is preferably 4.0 μm or less, and more preferably 2.0 μm or less. Width D 22 It is not particularly limited; for example, it can be 200 nm or more. From the viewpoint of avoiding contact between solder particles on adjacent protrusions, it is preferably 400 nm or more, and more preferably 1.0 μm or more. Furthermore, the width D... 22 For example, it can be 10 μm or less. From the viewpoint of producing solder particles with an extremely small particle size of 800 nm or less, it is preferably 4.0 μm or less, and more preferably 2.0 μm or less.

[0058] Width D 21 With width D 22 The ratio (D) 22 / D 21 The ratio (D) is not particularly limited, and can be, for example, 1.1 or higher. From the viewpoint of avoiding contact between solder particles on adjacent protrusions, a ratio of 1.3 or higher is preferred, and 1.5 or higher is more preferred. Furthermore, the above ratio (D) 22 / D 21 For example, it can be 3.0 or less, preferably 2.0 or less.

[0059] Width D 21 With width D 22 The difference (D)22 -D 21 The solder particle size is not particularly limited, for example, it can be 2.0 μm or less. From the viewpoint of reducing the amount of solder supplied to the side and bottom 22 of the protrusion 21 and easily obtaining solder particles with higher precision, it is preferably 1.0 μm or less, and more preferably 500 nm or less.

[0060] The height H2 of the protrusion 21 is not particularly limited; for example, it can be the width D. 22 The width D is preferably 10% or more, based on the viewpoint of avoiding contact with the solder on the bottom 12 and easily obtaining solder particles with higher precision. 22 More than 25%, preferably width D 22 More than 50%. Furthermore, the height H2 of the protrusion 21 can, for example, be the width D. 22 From the viewpoint of avoiding damage to the protrusion 11 and further improving the recovery rate of solder particles, the width D is preferably below 1000%. 22 Below 500%, more preferably width D 22 Less than 300%.

[0061] 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 the contact and fusion of solder particles on the protrusions 21, it can be, for example, the width D. 22 More than 3%, preferably width D 22 More than 8%, preferably width D 22 More than 15%. Furthermore, the distance L2 between adjacent protrusions 21 can, for example, be the width D. 22 From the viewpoint of further improving the manufacturing efficiency of solder particles, a width D of less than 1000% is preferred. 22 Below 500%, more preferably width D 22 Less than 200%.

[0062] The shape of the cross section perpendicular to the height direction of protrusions 11 and 21 is not particularly limited; for example, it can be as follows: Figure 3 The shape shown. Figure 3 (a) to (e) are schematic diagrams illustrating examples of the shape of a cross section perpendicular to the height direction of the convex part.

[0063] The material constituting the substrate 10 is not particularly limited, but is preferably a heat-resistant material that does not deteriorate at the melting temperature of the solder layer. The material constituting the substrate 10 can be inorganic materials such as silicon, various ceramics, glass, and stainless steel, or organic materials such as various resins.

[0064] The manufacturing method of the substrate 10 is not particularly limited, and it can be appropriately manufactured by known methods (such as photolithography) that can form the protrusion 11.

[0065] Next, a solder layer is formed on at least a portion of the protrusions of the substrate (solder layer formation step). As the solder material used to form the solder layer, commercially available solder materials can be used without particular restriction, and can be appropriately selected based on the desired characteristics of the solder particles, the solder layer formation method, etc. For example, in the case of forming the solder layer by sputtering, a solder plate that can be used as a sputtering target is selected.

[0066] Solder materials may include, for example, tin or tin alloys. 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 are given below.

[0067] •In-Sn (In 52% by mass, Bi 48% by mass, melting point 118℃)

[0068] • In-Sn-Ag (In 20% by mass, Sn 77.2% by mass, Ag 2.8% by mass, melting point 175℃)

[0069] • Sn-Bi (Sn 43% by mass, Bi 57% by mass, melting point 138℃)

[0070] • 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℃)

[0071] • Sn-Cu (Sn 99.3% by mass, Cu 0.7% by mass, melting point 227℃)

[0072] • Sn-Au (Sn 21.0 wt%, Au 79.0 wt%, melting point 278℃)

[0073] Solder materials may contain indium or indium alloys, for example. Indium alloys, such as In-Bi alloys and In-Ag alloys, can be used. Specific examples of these indium alloys are given below.

[0074] •In-Bi (In 66.3% by mass, Bi 33.7% by mass, melting point 72℃)

[0075] •In-Bi (In 33.0 wt%, Bi 67.0 wt%, melting point 109℃)

[0076] •In-Ag (In 97.0% by mass, Ag 3.0% by mass, melting point 145℃)

[0077] Depending on the intended use of the solder particles (temperature at which they are used), the aforementioned tin alloys or indium alloys can be selected as solder materials. For example, if solder particles intended for low-temperature welding are desired, In-Sn alloys or Sn-Bi alloys can be used, resulting in solder particles that can weld at temperatures below 150°C. When using solder materials with high melting points, such as Sn-Ag-Cu alloys or Sn-Cu alloys, solder particles that maintain high reliability can be obtained even after being placed at high temperatures.

[0078] The solder material may also contain one or more elements selected from Ag, Cu, Ni, Bi, Zn, Pd, Pb, Au, P, and B. Ag or Cu may be included among these elements. Specifically, by including Ag or Cu in the solder material, solder particles with excellent bonding strength to the electrode are obtained, resulting in a lower melting point to approximately 220°C, thus achieving good conductivity reliability.

[0079] The Cu content of the solder material is, 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 more, solder particles that can achieve good solder joint reliability are easily obtained. Furthermore, if the Cu content is 10% by mass or less, solder particles with low melting point and excellent wettability are easily obtained, resulting in better joint reliability of the solder particle-based joints.

[0080] The Ag content of the solder material is, 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 more, solder particles that can achieve good solder joint reliability are easily obtained. Furthermore, if the Ag content is 10% by mass or less, solder particles with low melting point and excellent wettability are easily obtained, resulting in better joint reliability of the solder particle-based joints.

[0081] In the solder layer formation step, a solder layer is formed on each protrusion of the substrate. The solder layer formation step can be a step of forming the solder layer entirely on the protrusion of the substrate prepared in the preparation step, or it can be a step of forming the solder layer on a portion of the protrusion of the substrate prepared in the preparation step.

[0082] In the solder layer formation 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, and spraying. Among these, sputtering is preferred from the viewpoint that it allows for strict control of the solder layer thickness and facilitates obtaining solder particles with a smaller particle size distribution.

[0083] In the solder layer formation step, the amount of solder layer formed is not particularly limited and can be appropriately varied according to the desired solder particle size. By appropriately varying the amount of solder layer formed on the protrusion, the size of the solder particles formed on the protrusion can be easily adjusted.

[0084] In the solder layer formation step, the solder layer may be formed only on the protrusions of the substrate, or it may be formed on other parts of the substrate. For example, in the solder layer formation step, the solder layer may be formed on both the protrusions and the bottom of the substrate.

[0085] Figure 4 This is a cross-sectional view schematically showing an example of a solder layer 50 formed on the protrusion 11 of the substrate 10. Figure 4 In the manner shown, a solder layer is formed only on the protrusion 11 of the substrate 10.

[0086] The solder layer is formed using the solder material and may contain at least one selected from the group consisting of tin, tin alloys, indium, and indium alloys. Furthermore, the solder layer may contain at least one selected from the group consisting of In-Bi alloys, 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.

[0087] Figure 6 This is a cross-sectional view schematically illustrating another example of a solder layer 50 formed on the protrusion 11 of the substrate 10. Figure 6 In the illustrated configuration, a solder layer 50 is formed on the protrusion 11 of the substrate 10, and a solder layer 51 is also formed on the bottom 12 of the substrate 10. In this configuration, the amount of solder layer 50 formed on the protrusion 11 is preferably 20% or more, more preferably 30% or more, further preferably 50% or more, and even more preferably 60% or more, relative to the total volume of the solder layers formed on the substrate (the total volume of solder layer 50 and solder layer 51).

[0088] Next, the solder layer formed on the protrusion is fused together to form solder particles on the protrusion (fusion step). In the fusion step, the solder layer formed on the protrusion melts and coalesces, and becomes spherical due to surface tension, thereby forming solder particles.

[0089] One method for melting the solder layer is to heat it to a temperature above the melting point of the solder material constituting the solder layer. However, even when heated above the melting point due to the oxide film, the solder layer may not melt; even if it does melt, it may not wet and diffuse, or it may not coalesce. Therefore, it is preferable to expose the solder layer to a reducing atmosphere to remove the oxide film on the surface of the solder layer, and then heat the solder layer to a temperature above the melting point of the solder material. Furthermore, it is preferable to melt the solder layer in a reducing atmosphere. By melting the solder layer in a reducing atmosphere, melting, wetting, diffusion, and coalescing of the solder layer are easier and more effective.

[0090] The method of using a reducing atmosphere is not particularly limited if it achieves the aforementioned effects; for example, methods using hydrogen, hydrogen radicals, or formic acid gas are possible. For instance, by using a hydrogen reduction furnace, a hydrogen radical reduction furnace, a formic acid reduction furnace, or these conveyor-type or continuous furnaces, the solder layer can be melted in a reducing atmosphere. These apparatuses can include heating devices, chambers filled with inert gases (nitrogen, argon, etc.), and mechanisms for maintaining a vacuum inside the chamber, thus making it easier to control the reducing gas. Furthermore, if the chamber can be maintained under vacuum, after the solder layer melts and coalesces, depressurization can remove porosity, resulting in solder particles with superior bonding stability.

[0091] The range (profile) of solder layer reduction and dissolution conditions, temperature, and furnace atmosphere adjustment can be appropriately set considering factors such as the solder layer's melting point, particle size, recess size, and substrate material. For example, a substrate with a solder layer formed on a protrusion is inserted into the furnace. After evacuation, a reducing gas is introduced to fill the furnace. After removing the surface oxide film of the solder layer, the reducing gas is removed by evacuation. Then, the furnace is heated above the solder layer's melting point to dissolve and coalesce the solder layer, thereby forming solder particles on the protrusion. Nitrogen gas is then added, and the furnace temperature is restored to room temperature, thus obtaining solder particles. Furthermore, for example, a substrate with a solder layer formed on the protrusion is inserted into a furnace. After evacuation, a reducing gas is introduced to fill the furnace. The solder layer is then heated by a furnace heater to remove the surface oxide film. The reducing gas is then removed by evacuation, and the solder layer is heated above its melting point to dissolve and coalesce, forming solder particles on the protrusion. Nitrogen gas is then added, and the furnace temperature is allowed to return to room temperature, thus obtaining solder particles. Heating the solder layer in a reducing atmosphere increases the reducing power, which has the advantage of easily removing the surface oxide film of the solder layer.

[0092] Alternatively, for example, a substrate with a solder layer formed on the recess is inserted into the furnace. After evacuation, a reducing gas is introduced to fill the furnace. The substrate is then heated above the melting point of the solder layer by a furnace heater. This reduction process removes the surface oxide film of the solder layer, causing it to dissolve and coalesce, forming solder particles on the protrusion. The reducing gas is then removed by evacuation. After reducing the porosity of the solder particles, nitrogen is added, and the furnace temperature is restored to room temperature, thus obtaining solder particles. In this case, since the furnace temperature adjustment is performed only once, it has the advantage of being able to process the material in a short time.

[0093] After solder particles are formed on the aforementioned protrusions, an additional step can be performed to set the furnace interior to a reducing atmosphere to remove any remaining surface oxide film. Therefore, it is possible to reduce residues such as unfused solder layers and portions of unfused oxide films.

[0094] In the case of using an atmospheric pressure conveyor belt furnace, a substrate with a solder layer formed on a protrusion is placed on a conveyor belt and continuously passed through multiple zones to obtain solder particles. For example, the substrate with the solder layer formed on the protrusion is placed on a conveyor belt set to a constant speed and passed through a zone filled with inert gases such as nitrogen and argon at temperatures lower than the melting point of the solder layer. Then, it is passed through a zone containing reducing gases such as formic acid at temperatures lower than the melting point of the solder layer to remove the surface oxide film of the solder layer. Next, it is passed through a zone filled with inert gases such as nitrogen and argon at temperatures above the melting point of the solder layer to melt and coalesce the solder layer. Finally, it is passed through a cooling zone filled with inert gases such as nitrogen and argon to obtain solder particles. For example, a substrate with a solder layer formed on a protrusion is mounted on a conveyor belt set to a constant speed and passed through an area filled with inert gases such as nitrogen and argon at temperatures above the melting point of the solder layer. Next, it passes through an area containing reducing gases such as formic acid at temperatures above the melting point of the solder layer to remove the surface oxide film of the solder layer, causing it to melt and coalesce. Then, it passes through a cooling zone filled with inert gases such as nitrogen and argon, thereby obtaining solder particles. Since the conveyor belt furnace can process at atmospheric pressure, it can also continuously process film materials in a roll-to-roll manner. For example, in producing continuous roll products with a solder layer formed on a protrusion, an unwinding machine is installed at the inlet side of the conveyor belt furnace, and a winding machine is installed at the outlet side. The substrate is transported at a constant speed and passed through various areas within the conveyor belt furnace, thus enabling the solder layer formed on the protrusion to fuse.

[0095] The formed solder particles can be transported / stored in a state where they are formed on the protrusions of a substrate. The substrate with solder particles formed on the protrusions can be appropriately processed as a substrate containing solder particles. The substrate containing solder particles comprises a substrate having multiple protrusions and multiple solder particles disposed on the protrusions of the substrate. The average particle size of the solder particles is 100 nm or more and less than 1 μm, and the CV value of the solder particles can be 20% or less. The formed solder particles can be recovered from the protrusions. Furthermore, a resin material can be disposed opposite to the protrusions of the substrate to transfer the solder particles on the protrusions onto the resin material. In this case, if the protrusions are regularly arranged, the solder particles can be regularly disposed on the resin material.

[0096] Figure 5 This is a cross-sectional view schematically showing an example of a state in which solder particles are formed on a protrusion of a substrate. Figure 5 The substrate 100 shown will contain solder particles Figure 4 The substrate 10 with solder layer 50 is provided in the fusion step. In the substrate 100 with solder particles, solder particles 1 are formed on the protrusions 11 of the substrate 10 having a plurality of protrusions 11.

[0097] Figure 7 This is a cross-sectional view schematically illustrating another example of a state in which solder particles are formed on a protrusion of a substrate. Figure 7 The substrate 110 with solder particles shown can... Figure 6 The substrate 10, in which solder layers 50 and 51 are formed, is provided for the fusion step. In the substrate 110 with solder particles, solder particles 1 are formed on the protrusions 11 of the substrate 10, which have a plurality of protrusions 11. Furthermore, in the substrate 110 with solder particles, solder particles 2 originating from the solder layer 51 are formed on the bottom 12 between the protrusions 11. The solder particles 2 are not necessarily limited to exhibiting a small particle size distribution; therefore, it is preferable to only recover or transfer solder particles 1 in this manner. The solder particles 2 are fixed to the bottom 12 of the substrate 10 and exist at a position lower than the solder particles 1 on the protrusions 11. Therefore, by, for example, arranging the resin material in a manner opposite to the protrusions 11 of the substrate 10, the solder particles 1 on the protrusions 11 are transferred to the resin material, thus enabling only the solder particles 1 to be recovered.

[0098] According to the manufacturing method of this embodiment, solder particles of uniform size can be formed, regardless of the material and shape of the solder. For example, indium-based solder can be deposited through plating, but it is difficult to deposit into particles because it is soft and difficult to handle. However, in the manufacturing method of this embodiment, by using an indium-based solder plate as raw material, indium-based solder particles with uniform particle size can be easily manufactured. Furthermore, since the formed solder particles can be processed in a state where they are formed on the protrusions of the substrate, they can be handled / stored without deformation. In addition, since the formed solder particles are formed only on the protrusions of the substrate, they are easy to remove, and can be recycled or surface-treated without deformation.

[0099] Furthermore, even if the solder material has large deviations in size and particle size distribution, or is deformed in shape, if a solder layer can be formed on the protrusion by methods such as sputtering, plating, and spraying, it can be used as a raw material for the manufacturing method of this embodiment.

[0100] Furthermore, in the manufacturing method of this embodiment, the shape of the protrusion can be freely designed on the substrate using photolithography, imprinting, machining, electron beam processing, or radiation processing. Since the size of the solder particles depends on the amount of solder layer formed on the protrusion, the size of the solder particles can also be freely designed according to the design of the protrusion in the manufacturing method of this embodiment.

[0101] (Solder particles)

[0102] The solder particles of this embodiment have an average particle size of 100 nm or more and 30 μm or less, and a CV value of 20% or less. Preferably, the average particle size is 100 nm or more and less than 1 μm, and the CV value is 20% or less. These solder particles possess both a small average particle size and a narrow particle size distribution, making them suitable for use as conductive particles in anisotropic conductive materials with high conductivity and insulation reliability. The solder particles of this embodiment are manufactured using the manufacturing method described above.

[0103] The average particle size of the solder particles is not particularly limited if it is within the above-mentioned range. For example, it can be less than 30 μm, less than 15 μm, less than 10 μm, less than 5 μm, less than 3 μm, or less than 2 μm, and preferably less than 1 μm. Furthermore, the average particle size of the solder particles can be, for example, more than 100 nm, more than 200 nm, more than 300 nm, more than 400 nm, or more than 500 nm.

[0104] The average particle size of solder particles can be determined using various methods that match the size. For example, methods such as dynamic light scattering, laser diffraction, centrifugal sedimentation, electrical detection banding, and resonant mass determination can be used. Additionally, particle size can be determined from images obtained using optical microscopes, electron microscopes, etc. Specific devices include flow cytometry particle image analyzers, Microtrac particle size analyzers, and Coulter counters.

[0105] 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, even more preferably 7% or less, and particularly preferably 5% or less. Furthermore, the lower limit of the CV value of the solder particles is not particularly limited. For example, the CV value of the solder particles can be 1% or more, or 2% or more.

[0106] The CV value of solder particles is calculated by dividing the standard deviation of the particle size determined by the method by the average particle size and multiplying by 100.

[0107] 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 portion. The ratio (A / B) of the diameter A of the planar portion to the diameter B of the solder particle can be, for example, greater than 0.01 and less than 1.0 (0.01 < A / B < 1.0), or it can be 0.1 to 0.9. Since the solder particles have a planar portion, the placement of the solder particles is improved and the operability is enhanced. Specifically, when solder particles are placed on an object to be connected by solder particles such as electrodes, the planar portion makes it easy to place them in a predetermined position, and has the effect of suppressing the movement of solder particles from the predetermined position due to vibration, wind, external force, static electricity, etc. Furthermore, when the component on which the solder particles are placed is tilted, compared with spherical solder particles that do not have a planar portion, the solder particles are less likely to move due to gravity.

[0108] In the above manufacturing method, solder particles are formed on the protrusions of the substrate. At this time, sometimes the aforementioned planar portion is formed on the contact surface between the solder particles and the top of the protrusion.

[0109] When a quadrilateral circumscribed by the projected image of the solder particles is created using two pairs of parallel lines, and the distance between opposite sides is set as X and Y (where Y < X), the ratio of Y to X (Y / X) can be greater than 0.8 and less than 1.0 (0.8 < Y / X < 1.0), or it can be greater than 0.9 and less than 1.0. Such solder particles can be described as particles that are closer to spheres. According to the manufacturing method of this embodiment described above, such solder particles can be easily obtained.

[0110] Because solder particles are nearly spherical, when multiple opposing electrodes are electrically connected via solder particles, non-uniformity is less likely to occur in the contact between the solder particles and the electrodes, resulting in a tendency to obtain a stable connection. Furthermore, when a conductive film or resin in which solder particles are dispersed in a resin material is fabricated, high dispersibility and dispersion stability during manufacturing are achieved. Additionally, when a film or paste in which solder particles are dispersed in a resin material is used to connect electrodes, even if the solder particles rotate in the resin, if the solder particles are spherical, their projected areas are close when observed in a projection image. Therefore, when connecting electrodes, it is easier to obtain a stable electrical connection with minimal deviation.

[0111] Figure 8 This is a graph representing the distances X and Y (where Y < X) between opposite sides when a quadrilateral circumscribed by a projection image of a solder particle is constructed from two pairs of parallel lines. For example, a projection image is obtained by observing an arbitrary particle using a scanning electron microscope. Two pairs of parallel lines are plotted on the obtained projection image, one pair positioned at the point of minimum distance between parallel lines and the other pair positioned at the point of maximum distance between parallel lines, and the Y / X of that particle is calculated. This operation is performed on 300 solder particles, and the average value is calculated and set as the Y / X of the solder particle.

[0112] 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.

[0113] •In-Sn (In 52% by mass, Bi 48% by mass, melting point 118℃)

[0114] • In-Sn-Ag (In 20% by mass, Sn 77.2% by mass, Ag 2.8% by mass, melting point 175℃)

[0115] • Sn-Bi (Sn 43% by mass, Bi 57% by mass, melting point 138℃)

[0116] • 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℃)

[0117] • Sn-Cu (Sn 99.3% by mass, Cu 0.7% by mass, melting point 227℃)

[0118] • Sn-Au (Sn 21.0 wt%, Au 79.0 wt%, melting point 278℃)

[0119] 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 given below.

[0120] •In-Bi (In 66.3% by mass, Bi 33.7% by mass, melting point 72℃)

[0121] •In-Bi (In 33.0 wt%, Bi 67.0 wt%, melting point 109℃)

[0122] •In-Ag (In 97.0% by mass, Ag 3.0% by mass, melting point 145℃)

[0123] Depending on the intended use of the solder particles (temperature at which they are used), the aforementioned tin alloys or indium alloys can be selected. For example, when using solder particles for low-temperature welding, In-Sn alloys or Sn-Bi alloys can be used, in which case 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 placement at high temperatures.

[0124] Solder particles may contain one or more elements selected from Ag, Cu, Ni, Bi, Zn, Pd, Pb, Au, P, and B. Ag or Cu may be included among these elements. Specifically, because the solder particles contain Ag or Cu, the melting point of the solder particles can be lowered to around 220°C, and the bonding strength with the electrode is further improved, thus making it easier to obtain better conductivity reliability.

[0125] The Cu content of the solder particles is, for example, 0.05–10% by mass, or 0.1–5% by mass or 0.2–3% by mass. If the Cu content is 0.05% by mass or more, it is easier to achieve better solder joint reliability. Furthermore, if the Cu content is 10% by mass or less, it is easier to produce solder particles with low melting point and excellent wettability, resulting in better joint reliability based on solder particles.

[0126] The Ag content of the solder particles is, for example, 0.05–10% by mass, or 0.1–5% by mass or 0.2–3% by mass. If the Ag content is 0.05% by mass or higher, better solder joint reliability is easily achieved. Furthermore, if the Ag content is 10% by mass or lower, it easily results in solder particles with low melting points and excellent wettability, thus making the joint reliability of solder particle-based connections easier to achieve.

[0127] The applications of solder particles are not particularly limited; for example, they can be appropriately used as conductive particles for anisotropic conductive materials. Furthermore, they can also be appropriately used for applications such as electrically connecting electrodes to each other in ball grid array (BGA) connections, which are widely used in the mounting of semiconductor integrated circuits; and for sealing and encapsulating components such as MEMS, soldering, and spacers for height and gap control. In other words, the aforementioned solder particles can be used in conventional applications where solder has been previously used.

[0128] The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments.

[0129] Example

[0130] The present invention will be described in more detail below through embodiments, but the present invention is not limited to these embodiments.

[0131] <Example 1>

[0132] (Step a1) Preparation of the substrate

[0133] A substrate (polyimide film, 50 μm thick) with multiple protrusions having a top diameter of 0.15 μm φ, a bottom diameter of 0.15 μm φ, and a height of 0.13 μm was prepared. The multiple protrusions were regularly arranged at 0.15 μm intervals.

[0134] (Step b1) Formation of solder layer

[0135] The substrate with multiple protrusions obtained in step a1 is placed in a sputtering apparatus (manufactured by ARIOS INC.). After evacuation, argon gas is introduced, and the interior of the apparatus is set to an argon atmosphere of 1 Pa. Then, sputtering is performed for only the durations shown in Table 1 under the following conditions to form a solder layer.

[0136] (Apparatus conditions)

[0137] Target... Sn-Bi solder plate (melting point 139℃)

[0138] Input power... 60W

[0139] (Step c1) Formation of solder particles

[0140] The substrate with the solder layer obtained in step b1 was placed in a formic acid radical reduction furnace (a reflow apparatus manufactured by SHINKO SEIKICO.,LTD.). After evacuation, a mixture of formic acid and nitrogen (4% formic acid content) was introduced into the furnace to fill it. The furnace was then set to 120°C and reduced for 5 minutes. After heating to 180°C, the gases inside the furnace were removed by evacuation, and nitrogen was introduced to restore atmospheric pressure. The furnace temperature was then lowered to room temperature, thereby forming solder particles.

[0141] <Evaluation of solder particles>

[0142] A substrate containing solder particles obtained in step c1 was fixed onto a conductive strip attached to the surface of a SEM observation base. Platinum sputtering was then performed at 20 mA for 60 seconds. The diameters of 200 core-shell solder particles were measured by SEM, and the average particle size and CV value were calculated. The results are shown in Table 1.

[0143] <Examples 2-12>

[0144] Solder particles were fabricated and evaluated in the same manner as in Example 1, using the top diameter, bottom diameter, height, spacing, sputtering time, and material as shown in Table 1. The results are shown in Table 1. Furthermore, SEM images of the solder particles obtained in Example 2 are shown. Figure 12 middle.

[0145] <Examples 13-17>

[0146] Step c2 was performed instead of step c1, except that solder particles were fabricated and evaluated using the same method as in Example 1, with the top diameter, bottom diameter, height, spacing, sputtering time, and material as described in Table 1. The results are shown in Table 1. SEM images of the substrate prepared in Example 13 are shown in... Figure 9 The image shown is a SEM image of the shape of the solder layer formed on the substrate. Figure 10 The SEM image showing the shape of solder particles is shown in the image. Figure 11 middle.

[0147] (Step c2) Formation of solder particles

[0148] The substrate with the solder layer obtained in step b1 was placed in a hydrogen radical reduction furnace (manufactured by SHINKO SEIKICO.,LTD., a plasma reflow apparatus). After evacuation, hydrogen gas was introduced into the furnace to fill it with hydrogen. The furnace was then set to 130°C and irradiated with hydrogen radicals for 5 minutes. The hydrogen gas in the furnace was then removed by evacuation, and after heating to 165°C, nitrogen gas was introduced into the furnace to restore atmospheric pressure. The furnace temperature was then lowered to room temperature, thereby forming solder particles.

[0149] <Comparative Example 1>

[0150] Sn-Bi solder particles (manufactured by 5N Plus Inc., melting point 139℃, type 8, D) 50＝ 500g of solder particles (3.0μm, CV value 42%) were divided into 5 portions of 100g each and immersed in distilled water. After ultrasonic dispersion, the particles were allowed to stand, and the solder particles floating in the supernatant were recovered. This operation was repeated to recover a total of 1g of solder particles. The average particle size and CV value of the obtained solder particles are shown in Table 1.

[0151] <Comparative Example 2>

[0152] A smooth substrate (polyimide film, 50 μm thick) without protrusions was prepared. Solder particles were fabricated and evaluated using the same method as in Example 2. The results are shown in Table 1. SEM images of the obtained solder particles are shown in Table 1. Figure 13 middle.

[0153] [Table 1]

[0154]

[0155] Symbol Explanation

[0156] 1-Solder particles, 10-Base, 11, 21-Raised parts, 12, 22-Bottom, 50-Solder layer, 100, 110-Base with solder particles.

Claims

1. A method for manufacturing solder particles, comprising: Preparation steps: Prepare a substrate with multiple protrusions, wherein the width of the top of the protrusions is more than 0.15 μm and less than 10 μm; The solder layer forming step involves forming a solder layer on at least a portion of the protrusion of the substrate; The fusion step fuses the solder layer formed on the protrusion to form solder particles on the protrusion. as well as The process of recovering solder particles from the protrusion or transferring them onto the resin material. The solder particles recovered from the protrusion or transferred to the resin material have an average particle size of 100 nm or more and less than 1 μm, and a CV value of less than 20%.

2. The method for manufacturing solder particles according to claim 1, wherein, The protrusion is columnar or frustum-shaped.

3. The method for manufacturing solder particles according to claim 1 or 2, wherein, The substrate has a first surface, which has a plurality of protrusions and a bottom formed between the protrusions. The proportion of the projected area of ​​the first surface to the projected area of ​​the bottom surface is more than 8%.

4. The method for manufacturing solder particles according to claim 1 or 2, wherein, In the solder layer formation step, the solder layer is formed on the protrusion by at least one method selected from the group consisting of plating, vapor deposition, sputtering and spraying.

5. The method for manufacturing solder particles according to claim 1 or 2, wherein, Prior to the fusion step, a reduction step is included, in which the solder layer formed on the protrusion is exposed to a reducing atmosphere.

6. The method for manufacturing solder particles according to claim 1 or 2, wherein, In the fusion step, the solder layer formed on the protrusion is fused in a reducing atmosphere.

7. The method for manufacturing solder particles according to claim 1 or 2, wherein, The solder layer comprises at least one selected from the group consisting of tin, tin alloys, indium, and indium alloys.

8. The method for manufacturing solder particles according to claim 7, wherein, The solder layer comprises 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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