Gap particles for solder paste, solder paste, and connection structure

Abstract

Provided are gap particles for solder paste with which it is possible, in an obtained connection structure, to enhance gap controllability when exposed to a high temperature environment, suppress the occurrence of voids in a connection portion, and enhance conduction reliability after thermal cycling.　The gap particles for solder paste according to the present invention are used in solder paste. The gap particles are resin particles or metal-coated particles. The metal-coated particles have a resin particle body and a metal portion disposed on the surface of the resin particle body. The gap particles have a particle diameter of 30 μm to 200 μm, inclusive. In a compression test, the compression deformation ratio of the gap particles at a loading value of 300mN is less than or equal to 55%. The compression recovery ratio of the gap particles at a loading value of 150mN during unloading is less than or equal to 20%.

Description

Gap particles for solder paste, solder paste, and connecting structures

[0001] This invention relates to gap particles used in solder paste. Furthermore, this invention relates to solder particles and a solder paste containing the gap particles. Finally, this invention relates to a connection structure using the solder paste described above.

[0002] Anisotropic conductive materials containing solder are known. The solder particle content in the above anisotropic conductive material is, for example, 40% by weight or less.

[0003] On the other hand, soldering materials containing a large amount of solder are known. Examples of soldering materials include solder paste. The solder particle content in soldering materials is, for example, more than 40% by weight.

[0004] The solder bonding materials described above are used to obtain various types of connection structures. Examples of connections in these structures include connections between flexible printed circuit boards and glass substrates (FOG (Film on Glass)), connections between semiconductor chips and flexible printed circuit boards (COF (Chip on Film)), connections between semiconductor chips and glass substrates (COG (Chip on Glass)), connections between flexible printed circuit boards and glass epoxy substrates (FOB (Film on Board)), and connections between electronic components, modules or their packages and rigid printed circuit boards (SMT (Surface Mount Technology)).

[0005] When electrically connecting electrodes, the soldering material is selectively applied to the electrodes, which are the soldering points on a circuit board, for example, by screen printing. Next, semiconductor chips are stacked, the solder is melted, and then solidified. The electrodes are electrically connected by the solidified solder.

[0006] Patent Document 1 below discloses a conductive paste containing tin-coated copper powder, resin, and solvent. In the tin-coated copper powder, the surface of the copper particles is coated with tin or a tin alloy. The amount of tin or tin alloy (coating amount) is 1% to 33% by mass of the total tin-coated copper powder.

[0007] Patent Document 2, described below, discloses a solder paste in which a plurality of solder particles are dispersed in a thermosetting resin composition. The solder paste may also contain high-melting-point metal particles that have a higher melting point than the solder particles.

[0008] Japanese Patent Publication No. 2018-131666 Japanese Patent Publication No. 2013-220466

[0009] When conventional solder paste containing particles is used to fabricate connection structures, voids (gaps) may occur in the connection area formed by the solder paste during the thermocompression bonding process. As a result, there is a problem of reduced conductivity reliability in the resulting connection structure. In particular, in connection structures for electronic components, the connection area connecting two members is repeatedly heated and cooled (exposed to thermal cycling conditions). If voids are present in the connection area, the conductivity reliability of the connection structure is more likely to decrease due to thermal cycling.

[0010] Furthermore, resin particles are sometimes used as gap particles (spacers) to control the gap between connected components in a connecting structure. However, when conventional resin particles are used as gap particles, they may deform excessively when exposed to high-temperature environments (e.g., 200°C). As a result, conventional resin particles have the problem of not being able to properly control the gap between substrates when exposed to high-temperature environments.

[0011] In other words, with conventional particles, it is difficult to effectively control the gap between substrates when exposed to high-temperature environments, suppress the generation of voids in the resulting connection structure, and improve the conductivity reliability of the connection structure after thermal cycling.

[0012] The object of the present invention is to provide gap particles for solder paste and solder paste that can improve gap control when exposed to high-temperature environments, suppress the generation of voids in the connection portion, and improve conductivity reliability after thermal cycling in the resulting connection structure. Another object of the present invention is to provide a connection structure using the above-mentioned gap particles for solder paste or solder paste.

[0013] This specification discloses the following gap particles for solder paste, the use of gap particles for solder paste, solder paste, and connection structures.

[0014] Item 1. Gap particles for use in solder paste, wherein the gap particles are resin particles or metal-coated particles, the metal-coated particles have a resin particle body and a metal portion disposed on the surface of the resin particle body, the particle diameter of the gap particles is 30 μm or more and 200 μm or less, and in the following compression test, the compression deformation rate of the gap particles at a load value of 300 mN is 55% or less, and the compression recovery rate of the gap particles at a load value of 150 mN when unloaded is 20% or less, wherein the gap particles for solder paste.

[0015] Compression test: The gap particles are subjected to a load of 300 mN over 30 seconds at 25°C, followed by a deloading test at 25°C over 30 seconds to a load of 0.40 mN.

[0016] Item 2. The gap particles for solder paste according to Item 1, wherein the particle diameter of the gap particles is 30 μm or more and 150 μm or less.

[0017] Item 3. Gap particles for solder paste according to item 1 or 2, wherein the CV value of the particle diameter of the gap particles is 10% or less.

[0018] Item 4. The gap particle for solder paste according to any one of items 1 to 3, wherein the metal portion includes a metal capable of forming an intermetallic compound with solder.

[0019] Item 5. The gap particles for solder paste according to any one of items 1 to 4, wherein the metal part comprises nickel or an alloy containing nickel.

[0020] Item 6. A gap particle for solder paste according to any one of items 1 to 5, wherein the thickness of the metal part is 5.0 μm or less.

[0021] Item 7. Gap particles for solder paste according to any one of items 1 to 6, wherein the thermal decomposition temperature of the resin particles or the resin particle body is 200°C or higher.

[0022] Item 8. The gap particles for solder paste according to any one of items 1 to 7, wherein the resin particles or the resin particle body contains a polymer of a polymerizable component, the polymerizable component contains a crosslinkable monomer, and the content of the crosslinkable monomer is 5% by weight or more of 100% by weight of the polymerizable component.

[0023] Item 9. Gap particles for solder paste according to any one of items 1 to 8, wherein the gap particles are the metal-coated particles.

[0024] Item 10. Use of the gap particles for solder paste described in Items 1-9 in solder paste.

[0025] Item 11. A solder paste comprising solder particles, gap particles for solder paste as described in any one of items 1 to 9, and flux or an organic solvent.

[0026] Item 12. The solder paste according to item 11, wherein the thermal decomposition temperature of the resin particles or the resin particle body is higher than the melting point of the solder particles.

[0027] Item 13. The solder paste according to item 11 or 12, wherein the weight loss rate of the components excluding the solder particles and gap particles in the solder paste is 80% by weight or more when heated at 200°C for 1 hour.

[0028] Item 14. The solder paste according to any one of items 11 to 13, wherein the total content of the solder particles and gap particles in 100% by weight of the solder paste is 50% by weight or more.

[0029] Item 15. A connection structure comprising a first connection target member having a first connection area on its surface, a second connection target member having a second connection area on its surface, and a connection portion connecting the first connection target member and the second connection target member, wherein the connection portion is formed of a solder paste containing solder particles and gap particles for solder paste as described in any one of items 1 to 9, and the first connection area and the second connection area are electrically or physically connected by a solder portion derived from the solder particles.

[0030] Item 16. The connection structure described in Item 15, which is an isotropic conductive connection structure.

[0031] The gap particles for solder paste according to the present invention are gap particles used in solder paste, and the gap particles are resin particles or metal-coated particles. In the gap particles for solder paste according to the present invention, the metal-coated particles have a resin particle body and a metal portion disposed on the surface of the resin particle body. The particle diameter of the gap particles for solder paste according to the present invention is 30 μm or more and 200 μm or less. In the compression test, the compression deformation rate of the gap particles at a load value of 300 mN is 55% or less, and the compression recovery rate of the gap particles at a load value of 150 mN when unloaded is 20% or less. Since the gap particles for solder paste according to the present invention are provided with the above configuration, the resulting connection structure can be made to improve gap controllability when exposed to high-temperature environments, suppress the generation of voids in the connection part, and improve conductivity reliability after the thermal cycle.

[0032] Figure 1 is a cross-sectional view showing gap particles for solder paste according to a first embodiment of the present invention. Figure 2 is a cross-sectional view showing gap particles for solder paste according to a second embodiment of the present invention. Figure 3 is a cross-sectional view showing gap particles for solder paste according to a third embodiment of the present invention. Figure 4 is a schematic cross-sectional view showing a connection structure using solder paste containing the gap particles for solder paste shown in Figure 1.

[0033] The details of the present invention will be described below.

[0034] (Gap particles for solder paste) The gap particles for solder paste according to the present invention (hereinafter sometimes referred to as "gap particles") are gap particles used in solder paste. The gap particles according to the present invention are resin particles or metal-coated particles. In the gap particles according to the present invention, the metal-coated particles have a resin particle body and a metal part disposed on the surface of the resin particle body. The particle diameter of the gap particles according to the present invention is 30 μm or more and 200 μm or less. In the following compression test, the gap particles according to the present invention have a compression deformation rate of 55% or less at a load value of 300 mN, and a compression recovery rate of 20% or less at a load value of 150 mN when unloaded.

[0035] Compression test: The above gap particles are subjected to a load of 300 mN over 30 seconds at 25°C, followed by a deloading test at 25°C over 30 seconds to a load of 0.40 mN.

[0036] When conventional solder paste containing particles is used to fabricate connection structures, voids may occur in the connection area formed by the solder paste during the thermocompression bonding process. Specifically, the particles deform due to the load and heating during the thermocompression bonding process, and then, upon unloading and cooling, the particles return to their original state before the solder paste (especially the molten solder) hardens, which can cause voids to form around the particles in the connection area formed by the solder paste. As a result, there is a problem of reduced conductivity reliability in the resulting connection structure. In particular, in connection structures for electronic components, the connection area connecting two members is repeatedly heated and cooled (exposed to thermal cycling conditions), and if voids exist in the connection area, the conductivity reliability of the connection structure is more likely to decrease due to the thermal cycling.

[0037] Furthermore, when conventional resin particles are used as gap particles, they may deform excessively when exposed to high-temperature environments (e.g., 200°C). As a result, conventional resin particles have the problem of not being able to properly control the gap between substrates when exposed to high-temperature environments.

[0038] In the gap particles according to the present invention, since the above configuration is provided, in the obtained connection structure, the gap controllability when exposed to a high-temperature environment can be enhanced. Also, in the gap particles according to the present invention, since the above configuration is provided, in the obtained connection structure, the generation of voids in the connection portion can be suppressed. Further, in the gap particles according to the present invention, since the above configuration is provided, in the obtained connection structure, the conduction reliability after thermal cycling can be enhanced.

[0039] In the gap particles according to the present invention, since the above configuration is provided, the gap particles can be suitably used in a solder paste.

[0040] The particle diameter of the above gap particles is 30 μm or more and 200 μm or less. In the above gap particles, since the above configuration is provided, in the obtained connection structure, the gap controllability when exposed to a high-temperature environment can be enhanced, the conduction reliability after thermal cycling can be enhanced, and the obtained connection structure can be miniaturized (low-profile).

[0041] The particle diameter of the above gap particles is preferably 35 μm or more, more preferably 40 μm or more, still more preferably 45 μm or more, and preferably 180 μm or less, more preferably 150 μm or less, still more preferably 120 μm or less. When the particle diameter of the above gap particles is at least the above lower limit, in the obtained connection structure, the gap controllability when exposed to a high-temperature environment can be further enhanced, and the conduction reliability after thermal cycling can be further enhanced. When the particle diameter of the above gap particles is at most the above upper limit, the obtained connection structure can be miniaturized (low-profile).

[0042] The particle diameter of the gap particles described above is preferably the average particle diameter, and more preferably the number-average particle diameter. The particle diameter of the gap particles can be determined, for example, by observing 50 arbitrary gap particles with an electron microscope or optical microscope and calculating the average particle diameter of each gap particle, or by using a particle size distribution analyzer. In observation with an electron microscope or optical microscope, the particle diameter of a single gap particle is determined as the particle diameter at the equivalent diameter of a circle. In observation with an electron microscope or optical microscope, the average particle diameter at the equivalent diameter of a circle of any 50 gap particles is approximately equal to the average particle diameter at the equivalent diameter of a sphere. In a particle size distribution analyzer, the particle diameter of a single gap particle is determined as the particle diameter at the equivalent diameter of a sphere. It is preferable to calculate the average particle diameter of the gap particles using a particle size distribution analyzer.

[0043] The coefficient of variation (CV value) of the particle size of the gap particles is preferably 10% or less, more preferably 5% or less. When the coefficient of variation of the particle size of the gap particles is below the upper limit, the gap particles disperse more uniformly in the solder paste. The lower limit of the coefficient of variation (CV value) of the particle size of the gap particles is not particularly limited. The coefficient of variation (CV value) of the particle size of the gap particles may be 0% or more, or 1% or more. The range of the coefficient of variation (CV value) of the particle size of the gap particles can be set by appropriately selecting the lower limit and upper limit.

[0044] The coefficient of variation (CV value) mentioned above can be measured as follows.

[0045] CV value (%) = (ρ / Dn) × 100 ρ: Standard deviation of the particle diameter of gap particles Dn: Mean value of the particle diameter of gap particles

[0046] From the viewpoint of further improving the gap controllability when exposed to high-temperature environments in the resulting connection structure, the aspect ratio of the gap particles is preferably 1.0 or higher, preferably 1.5 or lower, and more preferably 1.3 or lower. The lower limit of the aspect ratio of the gap particles is not particularly limited. The aspect ratio of the gap particles may be 1.0 or higher, or 1.1 or higher. The aspect ratio represents the major axis / minor axis. Preferably, the aspect ratio is determined by observing 10 arbitrary gap particles with an electron microscope or optical microscope, determining the major axis and minor axis as the maximum and minimum diameters, respectively, finding the major axis / minor axis of each spherical gap particle, and calculating the average value.

[0047] From the viewpoint of further improving the gap controllability when exposed to high-temperature environments in the resulting connection structure, it is preferable that the gap particles either do not contain gap particles having a particle diameter of 1.5 times or more the average particle diameter, or contain gap particles having a particle diameter of 1.5 times or more the average particle diameter in an amount of 1000 ppm or less. From the viewpoint of further improving the gap controllability when exposed to high-temperature environments in the resulting connection structure, it is preferable that the content of gap particles having a particle diameter of 1.5 times or more the average particle diameter is preferably 0 ppm (not contained) or more, preferably 1000 ppm or less, more preferably 10 ppm or less, even more preferably 0.1 ppm or less. From the viewpoint of further improving the gap controllability when exposed to high-temperature environments in the resulting connection structure, it is most preferable that the content of gap particles having a particle diameter of 1.5 times or more the average particle diameter is 0 ppm (not contained).

[0048] The content (ppm) of gap particles with a particle size 1.5 times or more the average particle size can be measured as follows: Filter the gap particles using a filter with a pore size 1.5 times the average particle size, observe the gap particles remaining on the filter with an optical microscope, and count the gap particles with a particle size 1.5 times or more the average particle size. Divide the number of counted gap particles by the total number of gap particles used for filtration to calculate the content (ppm) of gap particles with a particle size 1.5 times or more the average particle size.

[0049] The shape of the gap particles is not particularly limited. The gap particles may be spherical, non-spherical, or flattened.

[0050] In the above gap particles, in the following compression test, the compressive deformation rate of the gap particles at a load of 300 mN is 55% or less, and the compressive recovery rate of the gap particles at a load of 150 mN during unloading is 20% or less. Since the above gap particles are provided with the above configuration, the resulting connection structure can be made to improve gap controllability when exposed to high-temperature environments, suppress the generation of voids in the connection part, and improve conductivity reliability after the thermal cycle.

[0051] Compression test: The above gap particles are subjected to a load of 300 mN over 30 seconds at 25°C, followed by a deloading test at 25°C over 30 seconds to a load of 0.40 mN.

[0052] The compressive deformation rate of the gap particles at the above load value of 300 mN is the compressive deformation rate of the gap particles when the load value reverses after reaching 300 mN in the above compression test. In the above compression test, the compressive deformation rate of the gap particles at the above load value of 300 mN is preferably 10% or more, more preferably 15% or more, even more preferably 20% or more, preferably 53% or less, more preferably 50% or less, even more preferably 45% or less, particularly preferably 40% or less, and most preferably 38% or less. If the compressive deformation rate of the gap particles at the above load value of 300 mN is above the above lower limit, damage to the connected member during mounting can be suppressed, and the conductivity reliability after the thermal cycle in the resulting connection structure can be further improved. If the compressive deformation rate of the gap particles at the above load value of 300 mN is below the above upper limit, the gap controllability when exposed to a high-temperature environment in the resulting connection structure can be further improved. The range of compressive deformation of the gap particles at the above load value of 300 mN can be set by appropriately selecting the above lower limit and upper limit values.

[0053] The compression recovery rate of the gap particles at a load value of 150 mN during unloading is the compression recovery rate of the gap particles when the load value decreases from 300 mN to 150 mN in the compression test. In the compression test, the compression recovery rate of the gap particles at a load value of 150 mN during unloading is preferably 3% or more, more preferably 5% or more, even more preferably 8% or more, particularly preferably 10% or more, preferably 18% or less, more preferably 16% or less, even more preferably 14% or less, and particularly preferably 12% or less. If the compression recovery rate of the gap particles at a load value of 150 mN during unloading is above the lower limit, the gap controllability when exposed to a high-temperature environment in the resulting connection structure can be further improved. If the compression recovery rate of the gap particles at a load value of 150 mN during unloading is below the upper limit, the generation of voids in the connection part of the resulting connection structure can be further suppressed.

[0054] The above compression test can be carried out as follows.

[0055] Gap particles are scattered on a sample stage. For each scattered gap particle, a microcompression tester is used to apply a load (maximum test load) of 300 mN (reverse load) over 30 seconds at 25°C using the smooth end face of a cylindrical (100 μm diameter, diamond) indenter, directed towards the center of the gap particle (increasing the load). Then, the load is removed over 30 seconds at 25°C to 0.40 mN (origin load) (decreasing the load). The load (N) and compression displacement (mm) during this period are measured. The rate of increase in the load during loading and the rate of decrease in the load during unloading are constant. From the obtained measurements, the compression deformation rate of the gap particle at a load of 300 mN and the compression recovery rate of the gap particle at a load of 150 mN during unloading can be determined. Examples of the micro-compression testing machines used include the Fischerscope H-100 manufactured by Fischer GmbH and the ENT-5 manufactured by Elionix Corporation.

[0056] The compressive deformation ratio of the gap particle at the above load value of 300 mN can be calculated from the following formula.

[0057] Compression deformation rate (%) = (L1 / D) × 100 L1: Compression displacement from the origin load value of 0.40 mN to the reversal load value of 300 mN D: Particle diameter of the gap particles before compression

[0058] The compression recovery rate of the gap particles at the load value of 150 mN during unloading can be calculated using the following formula.

[0059] Compression recovery rate (%) = (L2 / L1) × 100 L1: Compression displacement from the origin load value of 0.40 mN to the reverse load value of 300 mN L2: Unloading displacement (compression recovery displacement or restoring displacement) from the reverse load value of 300 mN to the load value of 150 mN

[0060] As a method for adjusting the compressive deformation rate of the gap particles at the above load value of 300 mN and the compressive recovery rate of the gap particles at the above unloading load value of 150 mN to a preferred range, methods include selecting preferred materials and their proportions in the production of the resin particles or metal-coated particles. Specifically, the following methods can be used: A method using preferred polymerizable components described later. A method adjusting the molecular weight of the polymerizable components. A method adjusting the content of the polymerizable components. A method using preferred crosslinking agents described later. A method adjusting the polymerization temperature and polymerization time, etc. A method applying pressure during polymerization. A method washing away unreacted polymerizable components (monomers). A method using preferred metals described later for the metal portion of the metal-coated particles.

[0061] In the method of adjusting the content of polymerizable components described above, for example, by increasing the content of non-crosslinked monomers, the compressive deformation rate of the gap particles can be increased and the compressive recovery rate of the gap particles can be decreased. Furthermore, by decreasing the content of non-crosslinked monomers, the heat resistance of the gap particles can be increased. In the method of adjusting the polymerization temperature and polymerization time described above, for example, by increasing the polymerization temperature or increasing the polymerization time, the amount of unreacted monomers remaining can be reduced, so the content of non-crosslinked monomers can be increased, the compressive deformation rate of the gap particles can be increased and the compressive recovery rate of the gap particles can be decreased. In addition, by increasing the polymerization temperature or increasing the polymerization time, the heat resistance of the gap particles can be increased. In the method of applying pressure during polymerization described above, the amount of unreacted monomers remaining can be reduced by applying pressure, so the content of non-crosslinked monomers can be increased, the compressive deformation rate of the gap particles can be increased and the compressive recovery rate of the gap particles can be decreased. In addition, the heat resistance of the gap particles can be increased by applying pressure. In the method of washing the unreacted polymerizable components (monomers) described above, the amount of unreacted monomers remaining can be reduced by washing, thereby increasing the content of non-crosslinked monomers, increasing the compressive deformation rate of the gap particles, and decreasing the compressive recovery rate of the gap particles. Furthermore, washing can improve the heat resistance of the gap particles.

[0062] In the above compression test, the compressive modulus (10% K value) when the gap particle is compressed and deformed by 10% is preferably 1000 N / mm ２ Above all, a comfortable 2000 N / mm ２ More preferably, 3000 N / mm ２ The above is preferable, and preferably 10,000 N / mm ２ More preferably, 7000 N / mm ２ More preferably, 5000 N / mm ２The following is the case. When the 10% K value of the above gap particles is not less than the above lower limit, the gap controllability when exposed to a high temperature environment in the obtained connection structure can be further enhanced. When the 10% K value of the above gap particles is not more than the above upper limit, it is possible to suppress damage to the connection target member during mounting.

[0063] The 10% K value of the above gap particles can be obtained from the following formula.

[0064] 10% K value (N / mm ２ ) = (3 / 2 １／２ ) · F · S －３／２ · R －１／２ F: Load value (N) when the gap particles are compressed by 10% S: Compression displacement (mm) when the gap particles are compressed by 10% R: Radius (mm) of the gap particles

[0065] The above gap particles are resin particles or metal-coated particles. The above gap particles may be resin particles or metal-coated particles.

[0066] Hereinafter, the present invention will be specifically described with reference to the drawings. In FIG. 1 and the drawings described later, different parts can be replaced with each other.

[0067] FIG. 1 is a cross-sectional view showing gap particles for solder paste according to a first embodiment of the present invention.

[0068] The gap particles 1 for solder paste shown in FIG. 1 are resin particles.

[0069] In the gap particles 1 for solder paste, the particle diameter of the gap particles is 30 μm or more and 200 μm or less. In the gap particles 1 for solder paste, in the following compression test, the compression deformation rate of the gap particles at a load value of 300 mN is 55% or less, and the compression recovery rate of the gap particles at a load value of 150 mN during unloading is 20% or less.

[0070] Compression test: A test in which the above gap particles are loaded up to a load value of 300 mN over 30 seconds at 25°C and then unloaded up to a load value of 0.40 mN over 30 seconds at 25°C

[0071] Figure 2 is a cross-sectional view showing gap particles for solder paste according to a second embodiment of the present invention.

[0072] The solder paste gap particle 1A shown in Figure 2 is a metal-coated particle. The solder paste gap particle (metal-coated particle) 1A has a resin particle body 2A and a metal part 3A (metal layer). The metal part 3A is arranged on the surface of the resin particle body 2A. In the solder paste gap particle 1A, the metal part 3A is in contact with the surface of the resin particle body 2A, and the shape of the metal part 3A is layered. The solder paste gap particle 1A is a coated particle in which the surface of the resin particle body 2A is covered by the metal part 3A. The entire surface of the resin particle body 2A is covered by the metal part 3A.

[0073] In the gap particle 1A for solder paste, the metal portion 3A is a single layer of metal. In the metal-coated particle, the metal portion may cover the entire surface of the resin particle body, or it may cover a part of the surface of the resin particle body. The metal portion may or may not be in contact with the surface of the resin particle body. A layer other than the metal portion may be arranged between the resin particle body and the metal portion. From the viewpoint of exhibiting the effects of the present invention more effectively, it is preferable that the metal portion is in contact with the surface of the resin particle body.

[0074] Figure 3 is a cross-sectional view showing gap particles for solder paste according to a third embodiment of the present invention.

[0075] The gap particles 1B for solder paste shown in Figure 3 are metal-coated particles. The gap particles (metal-coated particles) 1B for solder paste have a resin particle body 2B and a metal part 3B (metal layer). The metal part 3B is arranged on the surface of the resin particle body 2B. In the third embodiment, the metal part 3B is in contact with the surface of the resin particle body 2B, and the shape of the metal part 3B is layered. The gap particles 1B for solder paste are coated particles in which the surface of the resin particle body 2B is coated with the metal part 3B. The entire surface of the resin particle body 2B is coated with the metal part 3B.

[0076] The metal part 3B has an inner layer, a first metal part 3BA (metal layer), and an outer layer, a second metal part 3BB (metal layer). The first metal part 3BA is arranged on the surface of the resin particle body 2B. The second metal part 3BB is arranged on the outer surface of the first metal part 3BA.

[0077] In the above-described metal-coated particles, the metal portion may be a single metal layer or a multilayer metal layer composed of two or more layers. The first metal portion and the second metal portion may be formed as metal portions of different compositions or as metal portions of the same composition.

[0078] In the above-described metal-coated particles, the metal portion may consist of one metal portion or of two or more metal portions. The first metal portion and the second metal portion may be formed as metal portions of different compositions or as metal portions of the same composition.

[0079] The above gap particles are used to obtain solder paste (use of the above gap particles to obtain solder paste / use of the above gap particles in solder paste). The above gap particles are preferably used to obtain solder paste containing 40% by weight or more solder particles in 100% by weight of solder paste (use of the above gap particles to obtain solder paste containing 40% by weight or more solder particles in 100% by weight of solder paste). The above gap particles are particularly preferably used to obtain solder paste containing 60% by weight or more solder particles in 100% by weight of solder paste (use of the above gap particles to obtain solder paste containing 60% by weight or more solder particles in 100% by weight of solder paste). From the viewpoint of exhibiting the effects of the present invention more effectively, it is preferable that the above gap particles are used to obtain isotropic conductive paste (use of the above gap particles to obtain isotropic conductive paste / use of the above gap particles in isotropic conductive paste). It is preferable that the above gap particles are used to obtain isotropic conductive connection structures (use of the above gap particles to obtain isotropic conductive connection structures / use of the above gap particles in isotropic conductive connection structures).

[0080] Further details regarding the resin particles and metal-coated particles are described below. In the following description, "(meth)acrylic" means either or both "acrylic" and "methacrylic," and "(meth)acrylate" means either or both "acrylate" and "methacrylate."

[0081] (Resin particles) The above resin particles are resin particles formed from resin.

[0082] Various organic materials are suitably used as the resin material for the above-mentioned resin particles. Examples of resins for the above-mentioned resin particles include polyolefin resins such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyisobutylene, and polybutadiene; acrylic resins such as polymethyl (meth)acrylate and polyisobornyl (meth)acrylate; polyalkylene terephthalate, polycarbonate, polyamide, phenol formaldehyde resin, melamine formaldehyde resin, benzoguanamine formaldehyde resin, urea formaldehyde resin, phenol resin, melamine resin, benzoguanamine resin, urea resin, epoxy resin, unsaturated polyester resin, saturated polyester resin, polysulfone, polyphenylene oxide, polyacetal, polyimide, polyamideimide, polyetheretherketone, polyethersulfone, and polymers obtained by polymerizing one or more polymerizable monomers having ethylenically unsaturated groups. Since the hardness of the resin particles can be easily controlled within a suitable range, the resin used to form the above-mentioned resin particles is preferably a polymer obtained by polymerizing one or more polymerizable monomers having multiple ethylenically unsaturated groups.

[0083] The above resin particles preferably contain a polymer of a polymerizable component. The above polymerizable component preferably contains a polymerizable monomer having an ethylenically unsaturated group. Examples of the polymerizable monomer having an ethylenically unsaturated group include non-crosslinked monomers and crosslinked monomers.

[0084] The above non-crosslinked monomers include styrene monomers such as styrene and α-methylstyrene; carboxyl group-containing monomers such as (meth)acrylic acid, maleic acid, and maleic anhydride; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate. Examples include alkyl (meth)acrylate compounds such as acrylate; oxygen atom-containing (meth)acrylate compounds such as 2-hydroxyethyl (meth)acrylate, glycerol (meth)acrylate, polyoxyethylene (meth)acrylate, and glycidyl (meth)acrylate; nitrile-containing monomers such as (meth)acrylonitrile; and halogen-containing monomers such as trifluoromethyl (meth)acrylate, pentafluoroethyl (meth)acrylate, vinyl chloride, vinyl fluoride, and chlorostyrene.

[0085] The above crosslinkable monomers include tetramethylolmethane tetra(meth)acrylate, tetramethylolmethane tri(meth)acrylate, tetramethylolmethane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate, glycerol tri(meth)acrylate, glycerol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly) Examples include polyfunctional (meth)acrylate compounds such as pyrene glycol di(meth)acrylate, (poly)tetramethylene glycol di(meth)acrylate, and 1,4-butanediol di(meth)acrylate; and silane-containing monomers such as triallyl(iso)cyanurate, triallyl trimellitate, divinylbenzene, diallyl phthalate, diallylacrylamide, diallyl ether, γ-(meth)acryloxypropyltrimethoxysilane, trimethoxysilylstyrene, and vinyltrimethoxysilane.

[0086] From the viewpoint of further improving the gap controllability when exposed to high-temperature environments in the resulting connection structure, it is preferable that the resin particles contain a polymer of a polymerizable component, and that the polymerizable component contains the crosslinkable monomer. From the viewpoint of improving the heat resistance of the gap particles (resin particles) and reducing the amount of unreacted polymerizable component (monomer) remaining, it is more preferable that the polymerizable component contains divinylbenzene or trimethylolpropane tri(meth)acrylate, and even more preferable that it contains divinylbenzene.

[0087] When obtaining resin particles using the above-mentioned crosslinkable monomer, a crosslinking agent can be used. Examples of the above-mentioned crosslinking agent include (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, (poly)tetramethylene glycol di(meth)acrylate, and 1,4-butanediol di(meth)acrylate. The above-mentioned crosslinking agent may be used alone or in combination of two or more types.

[0088] From the viewpoint of exhibiting the effects of the present invention more effectively, the crosslinking agent is preferably (poly)propylene glycol di(meth)acrylate, (poly)tetramethylene glycol di(meth)acrylate, or 1,4-butanediol di(meth)acrylate.

[0089] The above-mentioned polymerizable monomer having an ethylenically unsaturated group can be polymerized by known methods to obtain the resin particles. Examples of such methods include suspension polymerization in the presence of a radical polymerization initiator, and polymerization by swelling the monomer together with a radical polymerization initiator using non-crosslinked seed particles.

[0090] When the gap particles are the resin particles, the particle size of the resin particles is 30 μm or more and 200 μm or less. When the gap particles are the resin particles, the particle size of the resin particles is preferably 35 μm or more, more preferably 40 μm or more, even more preferably 45 μm or more, preferably 180 μm or less, more preferably 150 μm or less, and even more preferably 120 μm or less. If the particle size of the resin particles is above the lower limit, the gap controllability when exposed to high-temperature environments in the resulting connection structure can be further improved, and the conductivity reliability after the thermal cycle can be further improved. If the particle size of the resin particles is below the upper limit, the resulting connection structure can be miniaturized (reduced in height).

[0091] The particle size of the resin particles mentioned above refers to the diameter if the resin particles are spherical, and if the resin particles have a shape other than a perfect sphere, it refers to the diameter assuming they are spherical to the extent of their volume.

[0092] The particle diameter of the above-mentioned resin particles is preferably the average particle diameter, and more preferably the number-average particle diameter. The particle diameter of the resin particles can be determined, for example, by observing 50 arbitrary resin particles with an electron microscope or optical microscope and calculating the average value of the particle diameter of each resin particle, or by performing laser diffraction particle size distribution measurement. In observation with an electron microscope or optical microscope, the particle diameter of a single resin particle is determined as the particle diameter at the equivalent diameter of a circle. In observation with an electron microscope or optical microscope, the average particle diameter at the equivalent diameter of a circle of any 50 resin particles is approximately equal to the average particle diameter at the equivalent diameter of a sphere. In laser diffraction particle size distribution measurement, the particle diameter of a single resin particle is determined as the particle diameter at the equivalent diameter of a sphere. It is preferable to calculate the particle diameter of the above-mentioned resin particles by laser diffraction particle size distribution measurement.

[0093] When the gap particles are the resin particles, the coefficient of variation (CV value) of the particle size of the resin particles is preferably 0% or more, preferably 10% or less, and more preferably 5% or less. When the coefficient of variation of the particle size of the resin particles is below the upper limit, the resin particles disperse more uniformly in the solder paste.

[0094] The coefficient of variation (CV value) mentioned above can be measured as follows.

[0095] CV value (%) = (ρ / Dn) × 100 ρ: Standard deviation of the particle size of the resin particles Dn: Mean value of the particle size of the resin particles

[0096] The thermal decomposition temperature of the resin particles is preferably 200°C or higher, more preferably 230°C or higher, even more preferably 250°C or higher, preferably 350°C or lower, more preferably 320°C or lower, and even more preferably 300°C or lower. When the thermal decomposition temperature of the resin particles is above the lower limit and below the upper limit, the generation of gas derived from the resin particles during thermal bonding can be suppressed, and the generation of voids in the connection portion of the resulting connection structure can be further suppressed.

[0097] The thermal decomposition temperature of the above-mentioned resin particles can be measured using a differential thermogravimetric analyzer (for example, Hitachi High-Tech Science Corporation's "TG / DTA:STA7200"). The temperature at which the weight decreases by 10% from the initial weight is defined as the thermal decomposition temperature of the resin particles.

[0098] In 100% by weight of the above resin particles, the content of the polymerizable component polymer is preferably 80% by weight or more, more preferably 85% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more. When the content of the polymerizable component polymer is above the lower limit, the compressive deformation rate of the gap particles (resin particles) at a load value of 300 mN and the compressive recovery rate of the gap particles (resin particles) at a load value of 150 mN when unloaded can be easily adjusted to a preferred range. As a result, the gap controllability of the resulting connection structure when exposed to a high-temperature environment can be further improved. There is no particular upper limit to the content of the polymerizable component polymer in 100% by weight of the above resin particles. The content of the polymerizable component polymer in 100% by weight of the above resin particles may be 100% by weight (total amount) or less, or less than 100% by weight.

[0099] Of the polymerizable component at 100% by weight, the content of the crosslinkable monomer is preferably 5% by weight or more, more preferably 10% by weight or more, even more preferably 20% by weight or more, particularly preferably 40% by weight or more, preferably 100% by weight or less, more preferably 80% by weight or less, even more preferably 70% by weight or less, and particularly preferably 60% by weight or less. If the content of the crosslinkable monomer is above the lower limit, the heat resistance of the resin particles can be increased. If the content of the crosslinkable monomer is below the upper limit, the amount of unreacted polymerizable component (monomer) remaining can be reduced.

[0100] (Metal-coated particles) In the resulting connection structure, from the viewpoint of further suppressing the occurrence of voids in the connection portion, it is preferable that the gap particles are the metal-coated particles. The metal-coated particles have a resin particle body and a metal portion disposed on the surface of the resin particle body.

[0101] When the gap particles are the metal-coated particles, the particle size of the metal-coated particles is 30 μm or more and 200 μm or less. Preferably, the particle size of the metal-coated particles is 35 μm or more, more preferably 40 μm or more, even more preferably 45 μm or more, preferably 180 μm or less, more preferably 150 μm or less, and even more preferably 120 μm or less. If the particle size of the metal-coated particles is above the lower limit, the gap controllability when exposed to high-temperature environments in the resulting connection structure can be further improved, and the conductivity reliability after the thermal cycle can be further improved. If the particle size of the metal-coated particles is below the upper limit, the resulting connection structure can be miniaturized (reduced in height).

[0102] The particle size of the metal-coated particles mentioned above refers to the diameter if the metal-coated particles are spherical, and if the metal-coated particles have a shape other than a sphere, it refers to the diameter assuming they are spherical to the extent of their volume.

[0103] The particle diameter of the metal-coated particles is preferably the average particle diameter, and more preferably the number-average particle diameter. The particle diameter of the metal-coated particles can be determined, for example, by observing 50 arbitrary metal-coated particles with an electron microscope or optical microscope and calculating the average particle diameter of each metal-coated particle, or by using a particle size distribution analyzer. In observation with an electron microscope or optical microscope, the particle diameter of a single metal-coated particle is determined as the particle diameter at the equivalent diameter of a circle. In observation with an electron microscope or optical microscope, the average particle diameter at the equivalent diameter of a circle of any 50 metal-coated particles is approximately equal to the average particle diameter at the equivalent diameter of a sphere. In a particle size distribution analyzer, the particle diameter of a single metal-coated particle is determined as the particle diameter at the equivalent diameter of a sphere. It is preferable to calculate the average particle diameter of the metal-coated particles using a particle size distribution analyzer.

[0104] When the gap particles are the metal-coated particles, the coefficient of variation (CV value) of the particle size of the metal-coated particles is preferably 0% or more, preferably 10% or less, and more preferably 5% or less. When the coefficient of variation of the particle size of the metal-coated particles is below the above upper limit, the metal-coated particles disperse more uniformly in the solder paste.

[0105] The coefficient of variation (CV value) mentioned above can be measured as follows.

[0106] CV value (%) = (ρ / Dn) × 100 ρ: Standard deviation of particle size of metal-coated particles Dn: Mean value of particle size of metal-coated particles

[0107] Resin particle body: The resin particle body contains resin. The materials listed in the section on resin particles can be used as the material for the resin particle body. The resin particles themselves may be used as the resin particle body.

[0108] From the viewpoint of further improving gap controllability when exposed to high-temperature environments and further improving conductivity reliability after thermal cycling in the resulting connection structure, it is preferable that the resin particle body contains a polymer of a polymerizable component, and that the polymerizable component contains the crosslinkable monomer. From the viewpoint of improving the heat resistance of the resin particle body and reducing the amount of unreacted polymerizable component (monomer) remaining, it is more preferable that the polymerizable component contains divinylbenzene or trimethylolpropane tri(meth)acrylate, and even more preferable that it contains divinylbenzene.

[0109] In 100% by weight of the resin particle body, the content of the polymerizable component polymer is preferably 80% by weight or more, more preferably 85% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more. When the content of the polymerizable component polymer is above the lower limit, the compressive deformation rate of the gap particles (metal-coated particles) at a load of 300 mN and the compressive recovery rate of the gap particles (metal-coated particles) at a load of 150 mN during unloading can be easily adjusted to a preferred range. As a result, the gap controllability of the resulting connection structure when exposed to a high-temperature environment can be further improved. There is no particular upper limit to the content of the polymerizable component polymer in 100% by weight of the resin particle body. The content of the polymerizable component polymer in 100% by weight of the resin particle body may be 100% by weight (total amount) or less, or less than 100% by weight.

[0110] Of the polymerizable component at 100% by weight, the content of the crosslinkable monomer is preferably 5% by weight or more, more preferably 10% by weight or more, even more preferably 20% by weight or more, particularly preferably 40% by weight or more, preferably 100% by weight or less, more preferably 80% by weight or less, even more preferably 70% by weight or less, and particularly preferably 60% by weight or less. If the content of the crosslinkable monomer is above the lower limit, the heat resistance of the resin particle body can be increased. If the content of the crosslinkable monomer is below the upper limit, the amount of unreacted polymerizable component (monomer) remaining can be reduced.

[0111] It is particularly preferable that the above resin particles, or the resin particle body, contain a polymer of a polymerizable component, the polymerizable component contains the crosslinkable monomer, and the content of the crosslinkable monomer is 5% by weight or more of 100% by weight of the polymerizable component. In this case, the resulting connection structure can further improve gap control when exposed to a high-temperature environment and further improve conductivity reliability after a thermal cycle. That is, when the gap particles are the resin particles, it is preferable that the resin particles contain a polymer of a polymerizable component, the polymerizable component contains the crosslinkable monomer, and the content of the crosslinkable monomer is 5% by weight or more of 100% by weight of the polymerizable component. When the gap particles are the metal-coated particles, it is preferable that the resin particle body contains a polymerizable component, the polymerizable component contains the crosslinkable monomer, and the content of the crosslinkable monomer is 5% by weight or more of 100% by weight of the polymerizable component. In these cases, the resulting connection structure can further enhance gap controllability when exposed to high-temperature environments and improve conductivity reliability after thermal cycling.

[0112] The particle size of the resin particle body is preferably 25 μm or more, more preferably 40 μm or more, even more preferably 45 μm or more, preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 120 μm or less. If the particle size of the resin particle body is above the lower limit, aggregation becomes less likely when forming the metal part on the surface of the resin particle body by electroless plating, and aggregated metal-coated particles are less likely to form. If the particle size of the resin particle body is below the upper limit, the gap controllability of the resulting connection structure when exposed to a high-temperature environment can be further improved.

[0113] The particle size of the resin particle body mentioned above refers to the diameter if the resin particle body is spherical, and if the resin particle body has a shape other than a perfect sphere, it refers to the diameter assuming it is a perfect sphere of a volume equivalent to that shape.

[0114] The particle diameter of the resin particle body described above is preferably the average particle diameter, and more preferably the number-average particle diameter. The particle diameter of the resin particle body can be determined, for example, by observing 50 arbitrary resin particles with an electron microscope or optical microscope and calculating the average value of the particle diameter of each resin particle body, or by performing laser diffraction particle size distribution measurement. In observation with an electron microscope or optical microscope, the particle diameter of each resin particle body is determined as the particle diameter at the equivalent diameter of a circle. In observation with an electron microscope or optical microscope, the average particle diameter at the equivalent diameter of a circle of any 50 resin particles is approximately equal to the average particle diameter at the equivalent diameter of a sphere. In laser diffraction particle size distribution measurement, the particle diameter of each resin particle body is determined as the particle diameter at the equivalent diameter of a sphere. It is preferable to calculate the particle diameter of the resin particle body described above by laser diffraction particle size distribution measurement.

[0115] The coefficient of variation (CV value) of the particle size of the resin particle body is preferably 0% or more, preferably 10% or less, and more preferably 5% or less. When the coefficient of variation of the particle size of the resin particle body is below the above upper limit, the metal coating particles disperse more uniformly in the solder paste.

[0116] The coefficient of variation (CV value) mentioned above can be measured as follows.

[0117] CV value (%) = (ρ / Dn) × 100 ρ: Standard deviation of the particle size of the resin particles Dn: Average value of the particle size of the resin particles

[0118] The shape of the resin particle body described above is not particularly limited. The shape of the resin particle body may be spherical, or it may be a shape other than spherical, or it may be a flattened shape, etc.

[0119] The thermal decomposition temperature of the resin particle body is preferably 200°C or higher, more preferably 230°C or higher, even more preferably 250°C or higher, preferably 350°C or lower, more preferably 320°C or lower, and even more preferably 300°C or lower. When the thermal decomposition temperature of the resin particle body is above the lower limit and below the upper limit, the generation of gas originating from the resin particle body can be suppressed during thermocompression bonding, and the generation of voids at the connection portion in the resulting connection structure can be further suppressed.

[0120] The thermal decomposition temperature of the resin particle body can be measured using a differential thermogravimetric analyzer (for example, Hitachi High-Tech Science's "TG / DTA:STA7200"). The temperature at which the weight in the measurement result decreases by 10% from the initial weight is defined as the thermal decomposition temperature of the resin particle body. When measuring the thermal decomposition temperature of the resin particle body using the metal-coated particles, if the weight decrease when the weight in the measurement result decreases by 10% from the initial weight is due to the resin particles, the temperature at which the weight in the measurement result decreases by 10% from the initial weight can be defined as the thermal decomposition temperature of the resin particle body. Furthermore, when measuring the thermal decomposition temperature of the resin particle body using the metal-coated particles, if the weight of the metal part does not decrease at the temperature at which the weight in the measurement result decreases by 10% from the initial weight, the temperature at which the weight in the measurement result decreases by 10% from the initial weight can be defined as the thermal decomposition temperature of the resin particle body. Typically, the temperature at which the weight of the resin particle body decreases is lower than the temperature at which the weight of the metal part decreases (or the temperature at which the weight decrease of the metal part begins).

[0121] From the viewpoint of suppressing the generation of gas originating from the resin particle body during thermocompression bonding and further improving the gap controllability of the resulting connection structure when exposed to high-temperature environments, it is preferable that the thermal decomposition temperature of the resin particles or the resin particle body be 200°C or higher. That is, if the gap particles are the resin particles, it is preferable that the thermal decomposition temperature of the resin particles be 200°C or higher, and if the gap particles are the metal-coated particles, it is preferable that the thermal decomposition temperature of the resin particle body be 200°C or higher. In these cases, the generation of gas originating from the resin particle body during thermocompression bonding can be suppressed, and the gap controllability of the resulting connection structure when exposed to high-temperature environments can be further improved.

[0122] Metal portion: The metal portion in the metal-coated particles preferably contains a metal capable of forming an intermetallic compound with solder, a metal capable of melting and bonding with solder, or a metal capable of diffusing with solder. The metal portion may contain a metal capable of forming an intermetallic compound with solder, a metal capable of melting and bonding with solder, or a metal capable of diffusing with solder. The metal portion may further contain a metal that does not correspond to any of the following: a metal capable of forming an intermetallic compound with solder, a metal capable of melting and bonding with solder, or a metal capable of diffusing with solder.

[0123] Furthermore, a metal capable of forming intermetallic compounds with solder is a metal that can form intermetallic compounds with tin in the phase diagram of metals. A metal capable of melting and bonding with solder is a metal that melts upon heating and can bond with solder. A metal capable of diffusing with solder is a metal that does not melt upon heating but undergoes metallic diffusion into the solder when the solder melts.

[0124] In the resulting connection structure, from the viewpoint of further suppressing the generation of voids at the connection portion, it is preferable that the metal portion contains, on its outer surface, a metal capable of forming an intermetallic compound with the solder, a metal capable of melting and bonding with the solder, or a metal capable of diffusing with the solder.

[0125] In the resulting connection structure, from the viewpoint of further suppressing the generation of voids at the connection portion, it is preferable that the metal portion contains a metal capable of forming an intermetallic compound with solder, and it is more preferable that the outer surface portion of the metal portion contains a metal capable of forming an intermetallic compound with solder.

[0126] The metal capable of forming intermetallic compounds with the solder is preferably palladium, indium, silver, copper, tin, gold, nickel, or an alloy containing nickel, more preferably tin, gold, nickel, or an alloy containing nickel, and even more preferably nickel or an alloy containing nickel. The metal capable of fusion bonding with the solder is preferably indium, tin, or an alloy containing tin, more preferably tin or an alloy containing tin. The metal capable of diffusion with the solder is preferably nickel, gold, palladium, silver, or copper, more preferably nickel or gold. In these cases, the generation of voids at the connection portion can be further suppressed in the resulting connection structure.

[0127] The above-mentioned metal part preferably contains palladium, indium, silver, copper, tin, gold, nickel, or an alloy containing nickel; more preferably contains tin, gold, nickel, or an alloy containing nickel; and even more preferably contains nickel or an alloy containing nickel. In this case, the resulting connection structure can further suppress the generation of voids in the connection portion and improve connection reliability.

[0128] The metal part preferably contains palladium, indium, silver, copper, tin, gold, nickel, or an alloy containing nickel on its outer surface, and more preferably contains tin, gold, nickel, or an alloy containing nickel on its outer surface. The metal part is even more preferably contains nickel or an alloy containing nickel on its outer surface. In these cases, the generation of voids at the connection can be further suppressed in the resulting connection structure.

[0129] In the above metal portion, the nickel content is preferably 0.1% by weight or more, more preferably 1% by weight or more, preferably 100% by weight or less, and more preferably 90% by weight or less. The nickel content may be 80% by weight or less, 60% by weight or less, 40% by weight or less, 20% by weight or less, or 10% by weight or less. When the nickel content is above the lower limit and below the upper limit, the resulting connection structure can further suppress the occurrence of voids in the connection part and improve connection reliability.

[0130] When the above metal part is multilayered, the nickel content in 100% by weight of the nickel-containing layer is preferably 0.1% by weight or more, more preferably 1% by weight or more, preferably 100% by weight or less, and more preferably 90% by weight or less. The nickel content may be 80% by weight or less, 60% by weight or less, 40% by weight or less, 20% by weight or less, or 10% by weight or less. When the nickel content is above the lower limit and below the upper limit, the occurrence of voids in the connection part can be further suppressed in the resulting connection structure, and the reliability of the connection can be improved.

[0131] The content of various metals in the metal parts or metal-containing layers can be measured using a high-frequency inductively coupled plasma atomic emission spectrometer (Horiba, Ltd. "ICP-AES") or an X-ray fluorescence analyzer (Shimadzu Corporation "EDX-800HS"), etc.

[0132] The above metal part may be formed from a single layer. The above metal part may be formed from multiple layers. That is, the above metal part may have a laminated structure of two or more layers. From the viewpoint of more effectively improving conductivity reliability, it is preferable that the above metal part has a laminated structure of two or more layers.

[0133] In the above metal-coated particles, the resin particle body may or may not be completely covered by the metal part. The resin particle body may have portions that are not covered by the metal part. The inner layer metal part may or may not be completely covered by the outer metal part. The inner layer metal part may have portions that are not covered by the outer metal part.

[0134] In the above-mentioned metal-coated particles, the area of ​​the portion with the metal part (coverage rate by the metal part) out of 100% of the total surface area of ​​the resin particle body is preferably 5% or more, more preferably 10% or more, even more preferably 30% or more, still more preferably 50% or more, particularly preferably 70% or more, and most preferably 80% or more. The area of ​​the portion with the metal part out of 100% of the total surface area of ​​the resin particle body is preferably 100% or less. When the area of ​​the portion with the metal part is above the lower limit, the effects of the present invention are exhibited even more effectively.

[0135] The area of ​​the portion containing the metal part within the total surface area of ​​the resin particle body can be calculated by performing elemental mapping on the cross-section of the metal-coated particle using SEM-EDX analysis and then performing image analysis.

[0136] The thickness of the metal portion is preferably 0.005 μm or more, more preferably 0.01 μm or more, preferably 10 μm or less, more preferably 5.0 μm or less, even more preferably 1.0 μm or less, still more preferably 0.5 μm or less, and particularly preferably 0.3 μm or less. The thickness of the metal portion is the total thickness of the metal portion if the metal portion is multilayered. When the thickness of the metal portion is above the lower limit and below the upper limit, the metal coating particles do not become too hard, and the metal coating particles can be sufficiently deformed between the substrates (connected members).

[0137] When the above metal part is formed by multiple layers, the thickness of the outermost metal layer is preferably 0.001 μm or more, more preferably 0.01 μm or more, preferably 0.5 μm or less, and more preferably 0.1 μm or less. When the thickness of the outermost metal layer is above the lower limit and below the upper limit, the coating by the outermost metal layer becomes uniform, corrosion resistance is sufficiently high, and the reliability of the connection between connection areas can be further improved. Also, when the outermost layer is a gold layer, the thinner the gold layer, the lower the cost.

[0138] The thickness of the metal portion can be measured, for example, by observing the cross-section of the metal-coated particle using a transmission electron microscope (TEM). It is preferable to calculate the thickness of the metal portion of one metal-coated particle by taking the average of the thicknesses of five arbitrary metal portions, and more preferably by taking the average of the overall thickness of the metal portions. Alternatively, the thickness of the metal portion can be determined by calculating the average thickness of the metal portion of each of 50 arbitrary metal-coated particles. The thickness of the metal portion is preferably the average thickness.

[0139] The ratio of the average thickness of the metal part to the particle diameter of the resin particle body (average thickness of the metal part / particle diameter of the resin particle body) is preferably 0.0001 or more, more preferably 0.0005 or more, even more preferably 0.001 or more (0.0010 or more), still more preferably 0.00133 or more, particularly preferably 0.002 or more, and most preferably 0.003 or more. When the above ratio is above the above lower limit, the effects of the present invention can be exhibited even more effectively. The above ratio (average thickness of the metal part / particle diameter of the resin particle body) is preferably 0.5 or less, more preferably 0.1 or less, even more preferably 0.007 or less (0.0070 or less), still more preferably 0.006 or less (0.0060 or less), particularly preferably 0.005 or less (0.0050 or less), and most preferably 0.004 or less (0.0040 or less). If the above ratio is below the above upper limit, the metal coating particles will not become too hard, and the metal coating particles can deform sufficiently between the substrates (connected components).

[0140] The average thickness of the metal portion described above considers only the region on the resin particle body where the metal portion exists, and does not consider the region on the resin particle body where the metal portion does not exist. When the metal portion is partially placed on the surface of the resin particle body, the thickness of the region where the thickness of the metal portion is zero (i.e., zero) is not considered when calculating the average thickness of the metal portion.

[0141] The average thickness of the metal portion can be measured, for example, by observing the cross-section of the metal-coated particles using a transmission electron microscope (TEM). Preferably, the average thickness of the metal portion can be determined by calculating the average value of the thickness of the metal portion of each of 50 arbitrary metal-coated particles.

[0142] The method for forming the metal portion on the surface of the resin particle body is not particularly limited. Examples of methods for forming the metal portion include electroless plating, electroplating, physical impact, mechanochemical reaction, physical vapor deposition or physical adsorption, and coating the surface of the resin particle body with metal powder or a paste containing metal powder and a binder. The method for forming the metal portion is preferably electroless plating, electroplating, or physical impact. Examples of physical vapor deposition include vacuum deposition, ion plating, and ion sputtering. As for the physical impact method, a theta composer (manufactured by Tokuju Kogyo Co., Ltd.) can be used.

[0143] From the viewpoint of exhibiting the effects of the present invention more effectively, it is preferable that the metal coating particles contain a rust inhibitor or flux on the outer surface of the metal part. The metal coating particles may contain a rust inhibitor or flux on the outer surface of the metal part.

[0144] Rust inhibitor: The outer surface of the metal part may be treated with a rust inhibitor to prevent rust. The metal coating particles may have a rust-preventive film formed by the rust inhibitor on the outer surface of the metal part.

[0145] Examples of the above-mentioned rust inhibitors include compounds having an alkyl group with 6 to 22 carbon atoms (hereinafter sometimes referred to as Compound A). The above-mentioned rust inhibitors may also be compounds that do not contain phosphorus. Examples of the above-mentioned rust inhibitors include alkyl phosphate compounds or alkyl thiols. The above-mentioned rust inhibitors may be used individually or in combination of two or more.

[0146] If the alkyl group of compound A has 6 or more carbon atoms, rust will be even less likely to occur on the metal part. If the alkyl group of compound A has 22 or fewer carbon atoms, the conductivity will be higher. It is preferable that the alkyl group of compound A has 16 or fewer carbon atoms. The alkyl group may have a linear structure or a branched structure. It is preferable that the alkyl group has a linear structure.

[0147] Compound A is not particularly limited as long as it has an alkyl group having 6 to 22 carbon atoms. Preferably, Compound A is a phosphate ester or salt thereof having an alkyl group having 6 to 22 carbon atoms, a phosphite ester or salt thereof having an alkyl group having 6 to 22 carbon atoms, or an alkoxysilane having an alkyl group having 6 to 22 carbon atoms. Preferably, Compound A is an alkylthiol having an alkyl group having 6 to 22 carbon atoms, or a dialkyldisulfide having an alkyl group having 6 to 22 carbon atoms. Preferably, Compound A having an alkyl group having 6 to 22 carbon atoms is a phosphate ester or salt thereof, a phosphite ester or salt thereof, an alkoxysilane, an alkylthiol, or a dialkyldisulfide. By using these preferred Compound A, rust can be made even less likely to occur on the metal part. From the viewpoint of making rust even less likely to occur, Compound A is preferably a phosphate ester or salt thereof, a phosphite ester or salt thereof, or an alkylthiol, and more preferably a phosphate ester or salt thereof, or a phosphite ester or salt thereof. The above compound A may be used alone, or two or more may be used in combination.

[0148] The compound A described above preferably has reactive functional groups that can react with the outer surface of the metal part. The rust inhibitor is preferably chemically bonded to the metal part. The presence of the reactive functional groups and the chemical bond make it difficult for the rust inhibitor to peel off, and as a result, rust is even less likely to form on the metal part.

[0149] Examples of phosphate esters or salts thereof having an alkyl group with 6 to 22 carbon atoms include hexyl phosphate, heptyl phosphate, monooctyl phosphate, monononyl phosphate, monodecyl phosphate, monoundecyl phosphate, monododecyl phosphate, monotridecyl phosphate, monotetradecyl phosphate, monopentadecyl phosphate, monohexyl phosphate monosodium salt, monoheptyl phosphate monosodium salt, monooctyl phosphate monosodium salt, monononyl phosphate monosodium salt, monodecyl phosphate monosodium salt, monoundecyl phosphate monosodium salt, monododecyl phosphate monosodium salt, monotridecyl phosphate monosodium salt, monotetradecyl phosphate monosodium salt, and monopentadecyl phosphate monosodium salt. Potassium salts of the above phosphate esters may also be used.

[0150] Examples of phosphorous acid esters or salts thereof having an alkyl group with 6 to 22 carbon atoms include hexyl phosphorous acid, heptyl phosphorous acid, monooctyl phosphorous acid, monononyl phosphorous acid, monodecyl phosphorous acid, monoundecyl phosphorous acid, monododecyl phosphorous acid, monotridecyl phosphorous acid, monotetradecyl phosphorous acid, monopentadecyl phosphorous acid, monohexyl phosphorous acid monosodium salt, monoheptyl phosphorous acid monosodium salt, monooctyl phosphorous acid monosodium salt, monononyl phosphorous acid monosodium salt, monodecyl phosphorous acid monosodium salt, monoundecyl phosphorous acid monosodium salt, monododecyl phosphorous acid monosodium salt, monotridecyl phosphorous acid monosodium salt, monotetradecyl phosphorous acid monosodium salt, and monopentadecyl phosphorous acid monosodium salt. Potassium salts of the above phosphorous acid esters may also be used.

[0151] Examples of alkoxysilanes having an alkyl group with 6 to 22 carbon atoms include hexyltrimethoxysilane, hexyltriethoxysilane, heptyltrimethoxysilane, heptyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, nonyltrimethoxysilane, nonyltriethoxysilane, decyltrimethoxysilane, decyltriethoxysilane, undecyltrimethoxysilane, undecyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane, tridecyltrimethoxysilane, tridecyltriethoxysilane, tetradecyltrimethoxysilane, tetradecyltriethoxysilane, pentadecyltrimethoxysilane, and pentadecyltriethoxysilane.

[0152] Examples of alkylthiols having an alkyl group with 6 to 22 carbon atoms include hexylthiol, heptylthiol, octylthiol, nonylthiol, decylthiol, undecylthiol, dodecylthiol, tridecylthiol, tetradecylthiol, pentadecylthiol, and hexadecylthiol. It is preferable that the alkylthiol has a thiol group at the end of the alkyl chain.

[0153] Examples of dialkyl disulfides having an alkyl group with 6 to 22 carbon atoms include dihexyl disulfide, diheptyl disulfide, dioctyl disulfide, dinonyl disulfide, didecyl disulfide, diundecyl disulfide, didodecyl disulfide, ditridecyl disulfide, ditetradecyl disulfide, dipentadecyl disulfide, and dihexadecyl disulfide.

[0154] Flux: The outer surface of the metal part may be treated with flux. Using flux can prevent oxidation of the metal in the metal part and remove foreign matter and oxide films. The flux is not particularly limited. Flux commonly used in soldering and the like can be used.

[0155] Examples of the fluxes mentioned above include zinc chloride, mixtures of zinc chloride and inorganic halides, mixtures of zinc chloride and inorganic acids, molten salts, phosphoric acid, derivatives of phosphoric acid, organic halides, hydrazine, amine compounds, organic acids or their salts, and rosin. Only one of these fluxes may be used, or two or more may be used in combination.

[0156] Examples of the above molten salt include ammonium chloride. Examples of the above organic acid or its salt include lactic acid, citric acid, stearic acid, glutamic acid, and glutaric acid or their salts. Examples of the above rosin include activated rosin and inactivated rosin. The above flux is preferably an organic acid or its salt having two or more carboxyl groups, or rosin. The above flux may be an organic acid or its salt having two or more carboxyl groups, or rosin. The use of an organic acid or its salt having two or more carboxyl groups, or rosin, further improves connection strength and conductivity reliability.

[0157] Examples of organic acids or salts thereof having two or more carboxyl groups include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid or their salts.

[0158] Examples of the above-mentioned amine compounds include cyclohexylamine, dicyclohexylamine, benzylamine, benzhydrylamine, imidazole, benzimidazole, phenylimidazole, carboxybenzimidazole, benzotriazole, and carboxybenzotriazole.

[0159] The above-mentioned rosin is a rosin whose main component is abietic acid. Examples of such rosins include abietic acid and acrylic-modified rosin. The flux is preferably a rosin, and more preferably abietic acid. The use of this preferred flux further enhances the fluxing effect.

[0160] The activation temperature (melting point) of the flux is preferably 50°C or higher, more preferably 70°C or higher, even more preferably 80°C or higher, preferably 200°C or lower, more preferably 190°C or lower, even more preferably 160°C or lower, particularly preferably 150°C or lower, and most preferably 140°C or lower. When the activation temperature of the flux is above the lower limit and below the upper limit, the flux effect is further enhanced.

[0161] The melting point of the above flux can be determined by differential scanning calorimetry (DSC). Examples of differential scanning calorimetry (DSC) equipment include the EXSTAR DSC7020 manufactured by SII Corporation.

[0162] Furthermore, the boiling point of the flux is preferably 200°C or lower.

[0163] The flux described above is preferably a flux that releases cations upon heating. Using a flux that releases cations upon heating further improves connection strength and conductivity reliability.

[0164] Examples of fluxes that release cations upon heating include thermal cation initiators (thermal cation curing agents).

[0165] From the viewpoint of further enhancing the flux effect, the flux is preferably a salt of an acid compound and a base compound.

[0166] The above acid compound is preferably an organic compound having a carboxyl group. Examples of the above acid compound include aliphatic carboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, citric acid, and malic acid; cyclic aliphatic carboxylic acids such as cyclohexylcarboxylic acid and 1,4-cyclohexyldicarboxylic acid; and aromatic carboxylic acids such as isophthalic acid, terephthalic acid, trimellitic acid, and ethylenediaminetetraacetic acid. From the viewpoint of further effectively increasing connection strength and further effectively increasing conductivity reliability, the above acid compound is preferably glutaric acid, cyclohexylcarboxylic acid, or adipic acid.

[0167] The above base compound is preferably an organic compound having an amino group. Examples of the above base compound include diethanolamine, triethanolamine, methyldiethanolamine, ethyldiethanolamine, cyclohexylamine, dicyclohexylamine, benzylamine, benzhydrylamine, 2-methylbenzylamine, 3-methylbenzylamine, 4-tert-butylbenzylamine, N-methylbenzylamine, N-ethylbenzylamine, N-phenylbenzylamine, N-tert-butylbenzylamine, N-isopropylbenzylamine, N,N-dimethylbenzylamine, imidazole compounds, and triazole compounds. From the viewpoint of more effectively increasing connection strength and more effectively increasing conductivity reliability, the above base compound is preferably benzylamine.

[0168] (Solder paste) The solder paste according to the present invention comprises solder particles, the gap particles described above, and flux or an organic solvent. The solder paste according to the present invention is a gap particle-containing solder paste.

[0169] The solder paste according to the present invention has the above configuration, which improves gap control when exposed to high-temperature environments, suppresses the generation of voids in the connection portion, and enhances conductivity reliability after thermal cycling in the resulting connection structure.

[0170] In this specification, the term "solder paste" includes a soldering material that is in paste form, melts upon heating, and connects components to be connected.

[0171] From the viewpoint of more effectively exhibiting the effects of the present invention, it is preferable that the solder paste is different from an anisotropic conductive paste. From the viewpoint of more effectively exhibiting the effects of the present invention, it is preferable that the solder paste is an isotropic conductive paste. The solder paste is suitably used for electrical connection between connection areas (electrodes). The solder paste is suitably used to obtain a connection structure. The solder paste is suitably used to obtain an electronic component.

[0172] In the above solder paste, it is preferable that the thermal decomposition temperature of the resin particles or the resin particle body is higher than the melting point of the solder particles. That is, if the gap particles are the resin particles, it is preferable that the thermal decomposition temperature of the resin particles is higher than the melting point of the solder particles, and if the gap particles are the metal-coated particles, it is preferable that the thermal decomposition temperature of the resin particle body is higher than the melting point of the solder particles. In these cases, the generation of gas originating from the resin particles or the resin particle body can be suppressed during thermocompression bonding, the generation of voids in the connection portion of the resulting connection structure can be further suppressed, and the gap controllability when exposed to high-temperature environments can be further improved.

[0173] The thermal decomposition temperature of the resin particles or the resin particle body is preferably 5°C or more, more preferably 10°C or more, and even more preferably 20°C or more higher than the melting point of the solder particles. In this case, the generation of gas originating from the resin particles or the resin particle body is suppressed during thermocompression bonding, the generation of voids at the connection portion in the resulting connection structure is further suppressed, and the gap controllability when exposed to a high-temperature environment can be further improved. The thermal decomposition temperature of the resin particles or the resin particle body may be 200°C or less higher, 150°C or less higher, or 100°C or less higher than the melting point of the solder particles.

[0174] When the components of the solder paste, excluding the solder particles and gap particles, are heated at 200°C for 1 hour, the weight loss rate is preferably 30% by weight or more, more preferably 50% by weight or more, even more preferably 80% by weight or more, preferably 99% by weight or less, more preferably 95% by weight or less, and even more preferably 90% by weight or less. If the weight loss rate is above the lower limit, the flux or organic solvent acts effectively, and a stronger connection can be formed in the resulting connection structure. If the weight loss rate is below the upper limit, the occurrence of cracks due to residual stress in the connection can be effectively suppressed in the resulting connection structure.

[0175] The weight loss rate when the components of the solder paste described above, excluding the solder particles and gap particles, are heated at 200°C for 1 hour can be measured as follows.

[0176] A composition is obtained by blending components that exclude solder particles and gap particles from the solder paste. Alternatively, a composition may be obtained by removing the solder particles and gap particles from the solder paste. The obtained composition is heated at 200°C for 1 hour in a vacuum atmosphere using a vacuum drying apparatus (DP200, manufactured by Yamato Scientific Co., Ltd.), the weight of the composition is measured before and after heating, and the weight loss rate is calculated using the following formula.

[0177] Weight loss rate (weight %) = (Wa - Wb) × 100 / Wa Wa: Weight of the composition before heating at 200°C for 1 hour Wb: Weight of the composition after heating at 200°C for 1 hour

[0178] Solder particles: The particle size of the solder particles is preferably 0.1 μm or more, more preferably 1 μm or more, preferably 100 μm or less, and more preferably 50 μm or less. When the particle size of the solder particles is above the lower limit and below the upper limit, the effects of the present invention are exhibited even more effectively.

[0179] The particle diameter of the solder particles described above is preferably the average particle diameter, and more preferably the number-average particle diameter. The particle diameter of the solder particles described above can be determined, for example, by observing 50 arbitrary solder particles with an electron microscope or optical microscope and calculating the average value of the particle diameter of each solder particle, or by using a particle size distribution analyzer. In observation with an electron microscope or optical microscope, the particle diameter of a single solder particle is determined as the particle diameter at the equivalent diameter of a circle. In observation with an electron microscope or optical microscope, the average particle diameter at the equivalent diameter of a circle of any 50 solder particles is approximately equal to the average particle diameter at the equivalent diameter of a sphere. In a particle size distribution analyzer, the particle diameter of a single solder particle is determined as the particle diameter at the equivalent diameter of a sphere. It is preferable to calculate the average particle diameter of the solder particles described above using a particle size distribution analyzer.

[0180] The ratio of the particle diameter of the solder particles to the particle diameter of the gap particles (particle diameter of solder particles / particle diameter of gap particles) is preferably 0.1 or more, more preferably 0.5 or more, even more preferably 1 or more, and particularly preferably 1.5 or more. The ratio (particle diameter of solder particles / particle diameter of gap particles) is preferably 20 or less, more preferably 15 or less, even more preferably 10 or less, and particularly preferably 8 or less. When the ratio is above the lower limit and below the upper limit, the effects of the present invention are exhibited even more effectively. The range of the ratio (particle diameter of solder particles / particle diameter of gap particles) can be set by appropriately selecting the lower limit and upper limit values.

[0181] The coefficient of variation (CV value) of the particle size of the solder particles is preferably 0% or more, preferably 15% or less, and more preferably 10% or less. When the coefficient of variation of the particle size of the solder particles is below the above upper limit, the solder particles become even more uniformly dispersed in the solder paste.

[0182] The coefficient of variation (CV value) mentioned above can be measured as follows.

[0183] CV value (%) = (ρ / Dn) × 100 ρ: Standard deviation of solder particle size Dn: Mean value of solder particle size

[0184] The shape of the solder particles described above is not particularly limited. The shape of the solder particles may be spherical, or other shapes, such as flattened shapes.

[0185] The solder in the solder particles described above is preferably a metal with a melting point of 450°C or less (low melting point metal), based on JIS Z3001: Welding Terminology. A low melting point metal refers to a metal with a melting point of 450°C or less. The melting point of the low melting point metal is preferably 300°C or less, more preferably 250°C or less. The solder also contains tin. Of 100% by weight of the metal contained in the solder, the tin content is preferably 30% by weight or more, more preferably 40% by weight or more, even more preferably 70% by weight or more, particularly preferably 90% by weight or more, and preferably 100% by weight or less. When the tin content in the solder is above the lower limit described above, the effects of the present invention are exhibited even more effectively.

[0186] The content of various metals in solder particles can be measured using a high-frequency inductively coupled plasma atomic emission spectrometer (Horiba, Ltd. "ICP-AES") or an X-ray fluorescence analyzer (Shimadzu Corporation "EDX-800HS"), etc.

[0187] The low-melting-point metal constituting the solder described above is not particularly limited. The low-melting-point metal is preferably tin or an alloy containing tin. Examples of such alloys include tin-silver alloys, tin-copper alloys, tin-silver-copper alloys, tin-bismuth alloys, tin-zinc alloys, and tin-indium alloys. From the viewpoint of more effectively increasing connection strength and more effectively increasing conductivity reliability, the low-melting-point metal is preferably tin, tin-silver alloys, tin-silver-copper alloys, tin-gold alloys, tin-antimony alloys, tin-lead alloys, tin-bismuth alloys, and tin-indium alloys.

[0188] To further enhance connection strength, the solder may contain metals such as nickel, copper, antimony, aluminum, zinc, iron, gold, titanium, phosphorus, germanium, tellurium, cobalt, bismuth, manganese, chromium, molybdenum, and palladium. Furthermore, from the viewpoint of further enhancing connection strength, it is preferable that the solder contains nickel, copper, antimony, aluminum, or zinc. From the viewpoint of further enhancing connection strength, the content of these metals for enhancing connection strength is preferably 0.0001% by weight or more, and preferably 1% by weight or less, per 100% by weight of the solder.

[0189] From the viewpoint of exhibiting the effects of the present invention more effectively, the solder particles are preferably Sn-Ag-Cu particles (SAC particles), Sn-Bi particles, or Pb-Sn particles, more preferably Sn-Ag-Cu particles (SAC particles) or Sn-Bi particles, and more preferably Sn-Ag-Cu particles (SAC particles). The solder particles may be Sn-Ag-Cu particles (SAC particles), Sn-Bi particles, or Pb-Sn particles.

[0190] In 100% by weight of the above solder paste, the content of the above solder particles is preferably 20% by weight or more, more preferably 30% by weight or more, even more preferably 35% by weight or more, still more preferably 40% by weight or more, even more preferably 60% by weight or more, particularly preferably 70% by weight or more, and most preferably 80% by weight or more. In 100% by weight of the above solder paste, the content of the above solder particles is preferably 99% by weight or less, more preferably 98% by weight or less, even more preferably 95% by weight or less, and particularly preferably 90% by weight or less. When the content of the above solder particles is above the lower limit and below the upper limit, the effects of the present invention are exhibited even more effectively. In 100% by weight of the above solder paste, the range of the content of the above solder particles can be set by appropriately selecting the lower limit and the upper limit.

[0191] In 100% by weight of the above solder paste, the content of the gap particles is preferably 0.1% by weight or more, more preferably 1% by weight or more, even more preferably 5% by weight or more, particularly preferably 10% by weight or more, preferably 70% by weight or less, more preferably 60% by weight or less, even more preferably 50% by weight or less, and particularly preferably 40% by weight or less. When the content of the gap particles is above the lower limit and below the upper limit, the effects of the present invention are exhibited even more effectively.

[0192] In 100% by weight of the above solder paste, the total content of the above solder particles and gap particles is preferably 30% by weight or more, more preferably 40% by weight or more, even more preferably 50% by weight or more, still more preferably 60% by weight or more, still more preferably 70% by weight or more, particularly preferably 80% by weight or more, and most preferably 90% by weight or more. In 100% by weight of the above solder paste, the total content of the above solder particles and gap particles is preferably 99.9% by weight or less, more preferably 99.0% by weight or less, and even more preferably 98.0% by weight or less. When the total content of the above solder particles and gap particles is above the lower limit and below the upper limit, the effects of the present invention are exhibited more effectively. In 100% by weight of the above solder paste, the range of the total content of the above solder particles and gap particles can be set by appropriately selecting the lower limit and the upper limit.

[0193] The solder paste described above contains flux or an organic solvent. The solder paste may contain flux and may contain an organic solvent. Furthermore, the solder paste according to the present invention may optionally contain additives such as thixotropic agents and surfactants.

[0194] Flux: By using the above flux, oxidation of the metal in the solder particles, metal coating particles, and connection area (electrode) can be prevented, and foreign matter and oxide films can be removed. The flux used in the above solder paste is the flux described in the section describing the metal coating particles.

[0195] When the solder paste contains the flux, the flux content in 100% by weight of the solder paste is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, even more preferably 0.5% by weight or more, preferably 30% by weight or less, and more preferably 25% by weight or less. When the flux content is above the lower limit and below the upper limit, an oxide film is less likely to form on the surface of the solder and electrodes, and the oxide film formed on the surface of the solder and electrodes can be removed more effectively.

[0196] Organic solvents: By using the above-mentioned organic solvents, it is possible to improve the handling properties of the solder paste or adjust its viscosity. Examples of organic solvents in the above-mentioned solder paste include alcohol compounds such as ethanol, ketone compounds such as acetone, methyl ethyl ketone, and cyclohexanone, aromatic hydrocarbon compounds such as toluene, xylene, and tetramethylbenzene, glycol ether compounds such as cellosolve, methyl cellosolve, butyl cellosolve, carbitol, methyl carbitol, butyl carbitol, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol diethyl ether, and tripropylene glycol monomethyl ether, ester compounds such as ethyl acetate, butyl acetate, butyl lactate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, and propylene carbonate, aliphatic hydrocarbon compounds such as octane and decane, and petroleum-based solvents such as petroleum ether and naphtha.

[0197] When the solder paste contains the organic solvent, the content of the organic solvent in 100% by weight of the solder paste is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, even more preferably 0.5% by weight or more, preferably 30% by weight or less, and more preferably 25% by weight or less. When the content of the organic solvent is above the lower limit and below the upper limit, the handling properties of the solder paste can be improved, and gaps are less likely to occur in the connection after connection.

[0198] Other components: The solder paste described above may contain other components (hereinafter sometimes referred to as "other components") besides the solder particles, gap particles, organic solvent, and flux described above. Examples of these other components include vinyl resins, thermoplastic resins, curable resins, thermoplastic block copolymers, and elastomers. Only one of these other components may be used, or two or more may be used in combination.

[0199] Examples of vinyl resins include vinyl acetate resin, acrylic resin, and styrene resin. Examples of thermoplastic resins include polyolefin resin, ethylene-vinyl acetate copolymer, and polyamide resin. Examples of curable resins include epoxy resin, urethane resin, polyimide resin, and unsaturated polyester resin. The curable resin may be a room-temperature curing resin, a thermosetting resin, a photocuring resin, or a moisture-curing resin. The curable resin may be used in combination with a curing agent. Examples of thermoplastic block copolymers include styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, hydrogenated styrene-butadiene-styrene block copolymer, and hydrogenated styrene-isoprene-styrene block copolymer. Examples of elastomers include styrene-butadiene copolymer rubber and acrylonitrile-styrene block copolymer rubber.

[0200] (Connection Structure) The connection structure according to the present invention comprises a first connection target member having a first connection area on its surface, a second connection target member having a second connection area on its surface, and a connection portion connecting the first connection target member and the second connection target member. In the connection structure according to the present invention, the connection portion is formed of a solder paste containing solder particles and gap particles for solder paste. The connection portion includes a solder portion derived from the solder particles and the gap particles or particles derived from the gap particles. In the connection structure according to the present invention, the first connection area and the second connection area are electrically connected by the solder portion derived from the solder particles.

[0201] In the above-mentioned connection portion, it is preferable that the metal portion of the metal-coated particle forms an intermetallic compound with the solder, is bonded to the solder, or is diffused with the solder, and it is more preferable that it forms an intermetallic compound with the solder.

[0202] In the above-described connection structure, the gap particle or the particle derived from the gap particle does not need to be in contact with both the first connection region and the second connection region, and may be in contact with only one of the first connection region or the second connection region.

[0203] In connection structures, from the viewpoint of further improving gap controllability when exposed to high-temperature environments, the aspect ratio of the gap particles or particles derived from the gap particles is preferably 1.0 or higher, preferably 2.0 or lower, and more preferably 1.5 or lower. The lower limit of the aspect ratio of the gap particles or particles derived from the gap particles is not particularly limited. The aspect ratio of the gap particles or particles derived from the gap particles may be 1.0 or higher, or 1.1 or higher. The aspect ratio represents the major axis / minor axis. Preferably, the aspect ratio is determined by observing 10 arbitrary gap particles or particles derived from gap particles with an electron microscope or optical microscope, taking the maximum diameter and minimum diameter as the major axis and minor axis, respectively, and calculating the average value of the major axis / minor axis of each spherical gap particle or particle derived from the gap particles.

[0204] The average thickness of the above-mentioned connection portion is preferably greater than the particle diameter of the gap particles or particles derived from the gap particles.

[0205] In the resulting connection structure, it is preferable that the connection structure be an isotropic conductive connection structure, from the viewpoint of lowering the connection resistance between connection areas to be connected and further improving the conductivity reliability after the thermal cycle.

[0206] Figure 4 is a schematic cross-sectional view showing a connection structure using solder paste containing gap particles as shown in Figure 1.

[0207] The connection structure 21 shown in Figure 4 comprises a first connection target member 22, a second connection target member 23, and a connection portion 24 connecting the first connection target member 22 and the second connection target member 23. The connection portion 24 is formed of solder paste containing solder particles and gap particles 1 shown in Figure 1.

[0208] The connecting portion 24 includes a solder portion 24a derived from solder particles. The connecting portion 24 also includes particles 24b derived from gap particles 1.

[0209] The first connection target member 22 has multiple or a single first connection area 22a on its surface (upper surface). The second connection target member 23 has multiple or a single second connection area 23a on its surface (lower surface). The first connection area 22a and the second connection area 23a are electrically or physically connected by solder portions 24a derived from solder particles. Therefore, the first connection target member 22 and the second connection target member 23 are electrically or physically connected by solder portions 24a.

[0210] The method for manufacturing the above-mentioned connection structure is not particularly limited. An example of a method for manufacturing the connection structure is to place the solder paste between the first connection target member and the second connection target member to obtain a laminate, and then heat and pressurize the laminate. Heating and pressurizing causes the solder particles contained in the solder paste to melt, and the solder portion derived from the solder particles electrically or physically connects the connection areas. The pressure for the pressurization is, for example, 9.8 × 10⁻⁶. ４ Pa ~ 4.9 × 10 ６ The pressure is Pa. The heating temperature is, for example, 150°C to 250°C.

[0211] In the above-described connection structure, voids may or may not be present. Specifically, in the above-described connection structure, voids may be present around the gap particles or particles derived from the gap particles at the connection portion. In the above-described connection structure, voids may be present at the interface between the gap particles or particles derived from the gap particles and the solder portion formed by the solder particles at the connection portion. From the viewpoint of further improving the conductivity reliability of the connection structure after thermal cycling, it is preferable that voids are not present around the gap particles or particles derived from the gap particles at the connection portion of the above-described connection structure.

[0212] When a void exists in the above-mentioned connecting structure, the ratio of the length of the void to the particle diameter of the gap particle or particle derived from the gap particle (length of the void / particle diameter of the gap particle or particle derived from the gap particle) is preferably 0.2 or less, more preferably 0.1 or less, and even more preferably 0.05 or less. In this case, the conductivity reliability after the thermal cycle of the connecting structure can be further improved. The lower limit of the above ratio (length of the void / particle diameter of the gap particle or particle derived from the gap particle) is not particularly limited. The above ratio (length of the void / particle diameter of the gap particle or particle derived from the gap particle) may be 0.00001 or more, or 0.0001 or more. The range of the above ratio (length of the void / particle diameter of the gap particle or particle derived from the gap particle) can be set by appropriately selecting the above lower limit and upper limit.

[0213] The above ratio (void length / particle size of gap particles or particles derived from gap particles) can be measured, for example, as follows: After cutting out the connection part from the connecting structure, the cross-section of the connection part is polished using a low-load polishing device (IS-POLISHER ISPP-3000 manufactured by Ikegami Seiki Co., Ltd.) in the following order: waterproof sandpaper #220, waterproof sandpaper #2000, and diamond film (grain size 2 μm). Then, the cross-section of the connection part is observed using a microscope (VHX-5000 manufactured by Keyence Corporation), and the longest axis of the largest void is taken as the void length, and the above ratio (void length / particle size of gap particles or particles derived from gap particles) is calculated.

[0214] The first and second connection targets described above are not particularly limited. Examples of the first and second connection targets include electronic components such as semiconductor chips, semiconductor packages, LED chips, LED packages, capacitors, and diodes, as well as electronic components such as resin films, printed circuit boards, flexible printed circuit boards, flexible flat cables, rigid-flexible circuit boards, glass epoxy circuit boards, and glass circuit boards. Preferably, the first and second connection targets are electronic components.

[0215] The above-mentioned connection area may be an electrode.

[0216] Examples of electrodes provided on the above-mentioned connection target member include metal electrodes such as gold electrodes, nickel electrodes, tin electrodes, aluminum electrodes, copper electrodes, molybdenum electrodes, silver electrodes, SUS electrodes, and tungsten electrodes. When the above-mentioned connection target member is a flexible printed circuit board, the electrodes are preferably gold electrodes, nickel electrodes, tin electrodes, silver electrodes, or copper electrodes. When the above-mentioned connection target member is a glass substrate, the electrodes are preferably aluminum electrodes, copper electrodes, molybdenum electrodes, silver electrodes, or tungsten electrodes. In the case of aluminum electrodes, the electrodes may be made solely of aluminum, or they may be electrodes in which an aluminum layer is laminated on the surface of a metal oxide layer. Examples of materials for the metal oxide layer include indium oxide doped with a trivalent metal element and zinc oxide doped with a trivalent metal element. Examples of the trivalent metal element include Sn, Al, and Ga.

[0217] The present invention will be specifically described below with reference to examples and comparative examples. The present invention is not limited to the following examples.

[0218] The following materials were prepared as the resin particles and the resin particle bodies.

[0219] (Polymerizable components) Methyl methacrylate (Mitsubishi Chemical Corporation's "Acryester M") Isobornyl methacrylate (Kyoeisha Chemical Co., Ltd.'s "Light Ester IB-X") Divinylbenzene (NS Styrene Monomer Co., Ltd.'s "DVB960", a crosslinkable monomer) Trimethylolpropane trimethacrylate (Shin Nakamura Chemical Co., Ltd.'s "NK Ester TMPT", a crosslinkable monomer) Vinyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd.'s "KBM1003", a crosslinkable monomer) Cyclohexyl methacrylate (Fujifilm Wako Pure Chemical Industries, Ltd.'s "Cyclohexyl Methacrylate")

[0220] (Polymerization initiator) Benzoyl peroxide (BPO, manufactured by Tokyo Chemical Industry Co., Ltd.)

[0221] (Example 1) Preparation of resin particle body: 49 parts by weight of divinylbenzene was added to 50 parts by weight of trimethylolpropane trimethacrylate and stirred to obtain a monomer solution. Next, 1 part by weight of benzoyl peroxide (polymerization initiator) was added to the obtained monomer solution and stirred until homogeneous to obtain a monomer mixture. The obtained monomer mixture contained 49% by weight of divinylbenzene, 50% by weight of trimethylolpropane trimethacrylate, and 1% by weight of benzoyl peroxide (polymerization initiator). 200 parts by weight of a 1.0% aqueous solution of polyvinyl alcohol with a molecular weight of approximately 2000 dissolved in pure water was placed in a reaction vessel. 100 parts by weight of the obtained monomer mixture was added to this and stirred until the monomer droplets reached a predetermined particle size. Next, the mixture was heated at 90°C for 9 hours to carry out the polymerization reaction of the monomer droplets and obtain particles. The obtained particles were washed three times with hot water and acetone, respectively, and then classified to obtain the resin particle body.

[0222] Preparation of metal-coated particles (gap particles): 10 parts by weight of the resin particle body were dispersed in 100 parts by weight of an alkaline solution containing 5% by weight of palladium catalyst solution using an ultrasonic disperser. The resin particle body was then removed by filtering the solution. Next, the resin particle body was added to 100 parts by weight of a 1% by weight solution of dimethylamine borane to activate the surface of the resin particle body. After thoroughly washing the activated resin particle body with water, it was added to 500 parts by weight of distilled water and dispersed to obtain dispersion A.

[0223] In addition, a nickel plating solution (1) was prepared containing 0.14 mol / L nickel sulfate, 0.46 mol / L dimethylamine borane, and 0.2 mol / L sodium citrate (pH adjusted to 8.5 with sodium hydroxide).

[0224] 510g of the above dispersion A, containing 10 parts by weight of resin particles, was stirred at 70°C while nickel plating solution (1) was added dropwise at a dropping rate of 30 mL / min for 10 minutes. Subsequently, the solution was added dropwise at a dropping rate of 10 mL / min for 40 minutes, and then dropwise at a dropping rate of 4 mL / min for 80 minutes, thereby controlling the boron content incorporated into the plating film while performing electroless nickel-boron alloy plating. After that, the obtained dispersion was filtered to remove the particles, which were washed with water and dried to obtain metal-coated particles (gap particles) in which a metal part (nickel layer) was arranged on the surface of the resin particle body.

[0225] Preparation of solder paste: The following materials were blended: 10 parts by weight of the obtained metal-coated particles (gap particles). 90 parts by weight of SAC paste (paste containing SAC particles, "M705-RGS800" manufactured by Senju Metal Industry Co., Ltd., particle size of SAC particles 20 μm, melting point of SAC particles 210°C). The obtained composition was stirred using a planetary stirrer at 1200 rpm, 120 seconds, and 0.2 kPa to obtain solder paste. The content of SAC particles in the obtained solder paste was 70% by weight per 100% by weight.

[0226] Fabrication of the connection structure: An LGA substrate and semiconductor chips with pad sizes of 0.5 mm x 0.5 mm were prepared. The obtained solder paste was screen printed onto the LGA substrate to form a solder paste layer. Next, the semiconductor chips were stacked on the solder paste layer so that the electrodes faced each other. After that, heating was performed at 230°C, 1.0 x 10⁻⁶ ５ By performing thermocompression bonding with Pa and curing the solder paste layer, a connecting structure having a connecting portion formed by the solder paste was obtained.

[0227] (Examples 2-9 and Comparative Examples 1-5) Resin particle bodies and metal-coated particles (gap particles) were obtained in the same manner as in Example 1, except that the composition and particle size of the resin particle body, the thickness of the metal part, and the CV value of the particle size of the gap particles were set as shown in Tables 1-6 below. Solder paste and connecting structures were obtained in the same manner as in Example 1, except that the obtained metal-coated particles (gap particles) were used.

[0228] (Example 10) Preparation of resin particle body: A resin particle body was obtained in the same manner as in Example 1, except that the composition of the resin particle body was set as shown in Table 3 below.

[0229] Preparation of metal-coated particles (gap particles): In the same manner as in Example 1, particles were obtained in which a nickel layer (thickness 0.2 μm) was arranged on the surface of the resin particle body. Dispersion B was obtained by adding 10 parts by weight of the above particles to 500 parts by weight of distilled water and dispersing them.

[0230] A tin plating solution containing 15 g / L tin sulfate, 45 g / L ethylenediaminetetraacetic acid, and 1.5 g / L phosphinic acid (adjusted to pH 8.5 with sodium hydroxide) was prepared. A reducing solution containing 5 g / L sodium borohydride (adjusted to pH 10.0 with sodium hydroxide) was also prepared.

[0231] Electroless tin plating was performed by stirring 510 g of the above dispersion B at 50°C, dropping the above tin plating solution at a dropping rate of 15 mL / min for 10 minutes, and then reducing it with the above reducing solution, thereby obtaining metal-coated particles (gap particles) in which a tin layer (thickness 0.1 μm) was arranged on the surface of the nickel layer. The metal portion of the obtained metal-coated particles has a two-layer structure. Solder paste and connecting structures were obtained in the same manner as in Example 1, except that the obtained metal-coated particles (gap particles) were used.

[0232] (Example 11) Resin particles were obtained in the same manner as in Example 1, except that the composition of the resin particle body was set as shown in Table 3 below and no metal parts were formed. Solder paste and connecting structures were obtained in the same manner as in Example 1, except that the obtained resin particles were used as gap particles.

[0233] (Example 12) Preparation of solder paste: The following materials were blended: 10 parts by weight of metal-coated particles (gap particles) obtained in Example 1. 30 parts by weight of SAC particles (particle size 20 μm, melting point 210°C). 25 parts by weight of bisphenol A type phenoxy resin. 4 parts by weight of fluorene type epoxy resin. 30 parts by weight of phenol novolac type epoxy resin. 1 part by weight of SI-60L (manufactured by Sanshin Chemical Industry Co., Ltd.). The obtained composition was stirred using a planetary stirrer at 1200 rpm, 120 seconds, and 0.2 kPa to obtain solder paste. The content of SAC particles in the obtained solder paste was 30% by weight. A connecting structure was obtained in the same manner as in Example 1, except that the obtained solder paste was used.

[0234] (Evaluation) (1) Thermal decomposition temperature The thermal decomposition temperature of the resin particles obtained in Example 11 and the resin particle bodies of the metal-coated particles obtained in Examples 1 to 10, 12 and Comparative Examples 1 to 5 was measured using the method described above.

[0235] (2) Presence or absence of metals capable of forming intermetallic compounds with solder The metal-coated particles obtained in Examples 1 to 10, 12 and Comparative Examples 1 to 5 were subjected to compositional analysis of the metal portion using an ICP emission spectrometer (Horiba Ultima 2) to confirm whether the metal portion contained metals capable of forming intermetallic compounds with solder. The intermetallic compounds included palladium, indium, silver, copper, tin, gold, nickel, or nickel alloys. In the table, "○" indicates that the metal portion contains a metal capable of forming intermetallic compounds with solder, and "×" indicates that it does not.

[0236] (3) Compression Test The gap particles (resin particles or metal-coated particles) obtained were subjected to the following compression tests using the method described above, and the compression deformation rate at a load of 300 mN and the compression recovery rate at a load of 150 mN upon unloading were measured.

[0237] Compression test: The above gap particles are subjected to a load of 300 mN over 30 seconds at 25°C, followed by a deloading test at 25°C over 30 seconds to a load of 0.40 mN.

[0238] (4) Weight loss rate The weight loss rate of the components of the solder paste, excluding the solder particles and gap particles, was measured when heated at 200°C for 1 hour using the method described above.

[0239] (5) Gap controllability The connected structures obtained were heated in an oven to 250°C and left at that temperature for 1 hour. The minimum and maximum thicknesses of the connected parts formed by solder paste were measured by observation with a scanning electron microscope (SEM). Gap controllability was judged according to the following criteria.

[0240] [Criteria for determining gap controllability] ○○○: Maximum thickness is less than 1.1 times the minimum thickness ○○: Maximum thickness is 1.1 times or more but less than 1.3 times the minimum thickness ○: Maximum thickness is 1.3 times or more but less than 1.5 times the minimum thickness ×: Maximum thickness is 1.5 times or more the minimum thickness

[0241] (6) Suppression of void generation at connection points The obtained connection structures were observed using the method described above to determine whether or not voids were present at the connection points formed by solder paste. If voids were present, the ratio (length of void / particle size of gap particles or particles derived from gap particles) was calculated using the longest axis of the largest void in the cross-section of the connection point as the length of the void. The suppression of void generation at connection points was determined according to the following criteria.

[0242] [Criteria for determining the suppression of void generation at connection points] ○○○: No voids exist ○○: The above ratio is greater than 0 and 0.1 or less ○: The above ratio is greater than 0.1 and 0.2 or less ×: The above ratio is greater than 0.2

[0243] (7) Conductivity Reliability After Cold and Heat Cycles For the connection structures that were obtained, a cold and heat cycle test was conducted in which the process of heating from -20°C to 100°C and then cooling to -20°C was considered one cycle, and repeated for 1000 cycles. For the connection structures after the cold and heat cycles, the connection resistance per connection point between the upper and lower electrodes was measured using the four-terminal method. Note that the connection resistance can be determined by measuring the voltage when a constant current is flowing, based on the relationship voltage = current × resistance. The conductivity reliability after the cold and heat cycles was judged according to the following criteria.

[0244] [Criteria for determining continuity reliability after thermal cycling] ○○○: Connection resistance is 5 mΩ or less ○○: Connection resistance is greater than 5 mΩ and 7 mΩ or less ○: Connection resistance is greater than 7 mΩ and 10 mΩ or less ×: Connection resistance is greater than 10 mΩ, or a connection failure has occurred

[0245] The composition and results of the gap particles are shown in Tables 1 to 6 below.

[0246]

[0247]

[0248]

[0249]

[0250]

[0251]

[0252] 1... Gap particles for solder paste (resin particles) 1A, 1B... Gap particles for solder paste (metal coated particles) 2A, 2B... Resin particle body 3A, 3B... Metal part 3BA... First metal part 3BB... Second metal part 21... Connecting structure 22... First member to be connected 22a... First connection area 23... Second member to be connected 23a... Second connection area 24... Connecting part 24a... Solder part 24b... Particle

Claims

These are gap particles used in solder paste. The gap particles are resin particles or metal-coated particles. The metal-coated particle comprises a resin particle body and a metal portion disposed on the surface of the resin particle body. The particle diameter of the gap particle is 30 μm or more and 200 μm or less. Gap particles for solder paste, wherein, in the following compression test, the compression deformation rate of the gap particles at a load value of 300 mN is 55% or less, and the compression recovery rate of the gap particles at a load value of 150 mN upon unloading is 20% or less. 　 Compression test: The gap particles are subjected to a load of 300 mN over 30 seconds at 25°C, followed by a deloading test at 25°C over 30 seconds to a load of 0.40 mN. The gap particle for solder paste according to claim 1, wherein the particle diameter of the gap particle is 30 μm or more and 150 μm or less. 　 The gap particle for solder paste according to claim 1 or 2, wherein the CV value of the particle diameter of the gap particle is 10% or less. 　 The gap particle for solder paste according to any one of claims 1 to 3, wherein the metal portion includes a metal capable of forming an intermetallic compound with solder. 　 The gap particles for solder paste according to any one of claims 1 to 4, wherein the metal portion comprises nickel or an alloy containing nickel. 　 The gap particles for solder paste according to any one of claims 1 to 5, wherein the thickness of the metal portion is 5.0 μm or less. 　 The gap particles for solder paste according to any one of claims 1 to 6, wherein the thermal decomposition temperature of the resin particles or the resin particle body is 200°C or higher. 　 The resin particles, or the resin particle body, contain a polymer of a polymerizable component. The polymerizable component includes a crosslinkable monomer, Gap particles for solder paste according to any one of claims 1 to 7, wherein the content of the crosslinkable monomer is 5% by weight or more of the polymerizable component in 100% by weight. 　 The gap particle for solder paste according to any one of claims 1 to 8, wherein the gap particle is the metal-coated particle. 　 Use of gap particles for solder paste according to any one of claims 1 to 9 in a solder paste. 　 A solder paste comprising solder particles, gap particles for solder paste according to any one of claims 1 to 9, and flux or an organic solvent. 　 The solder paste according to claim 11, wherein the thermal decomposition temperature of the resin particles or the resin particle body is higher than the melting point of the solder particles. 　 The solder paste according to claim 11 or 12, wherein the weight loss rate of the components excluding the solder particles and gap particles in the solder paste when heated at 200°C for 1 hour is 80% by weight or more. 　 The solder paste according to any one of claims 11 to 13, wherein the total content of the solder particles and gap particles in 100% by weight of the solder paste is 50% by weight or more. 　 A first connection target member having a first connection area on its surface, A second connection target member having a second connection area on its surface, It comprises a connecting portion that connects the first member to be connected and the second member to be connected, The connecting portion is formed of a solder paste comprising solder particles and gap particles for solder paste according to any one of claims 1 to 9. A connection structure in which the first connection area and the second connection area are electrically or physically connected by a solder portion derived from the solder particles. 　 The connection structure according to claim 15, which is an isotropic conductive connection structure.

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