Solder paste and connection structures

Abstract

The present invention provides a solder paste that, when used to electrically connect substrates, can improve the dispersibility of the gap material at the connection portion of the resulting connection structure, suppress delamination between substrate particles and the coating portion in the gap material, and suppress the occurrence of cracks at the connection portion. The solder paste according to the present invention is a solder paste comprising solder particles and a gap material, wherein the gap material comprises base material particles and a coating portion disposed on the surface of the base material particles, the specific gravity of the gap material is 1.50 or less, a predetermined solder paste layer is formed, and the ratio of the thickness T of the portion of the solder paste layer without the gap material after heating to the particle diameter of the gap material is 0.60 or more and 1.20 or less.

Description

[Technical Field]

[0001] This invention relates to a solder paste containing solder particles. Furthermore, this invention relates to a connection structure using the above-mentioned solder paste. [Background technology]

[0002] Anisotropic conductive materials containing solder are known. The solder particle content in the above anisotropic conductive material is, for example, 80% 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 80% 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] In the soldering materials described above, gap fillers are sometimes used to control the gap between the members (base materials) being connected in the connection structure.

[0007] Patent Document 1 below discloses a solder paste comprising a plurality of solder particles and a plurality of metal-coated particles. In the solder paste, the metal-coated particles have a specific gravity of 6.0 or less. Furthermore, in the solder paste, the metal-coated particles have a base material particle and a metal portion disposed on the surface of the base material particle, and the metal portion contains 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.

[0008] Patent Document 2 below discloses a surface-mount connector for electronic components, which is interposed between an electronic component and a motherboard when mounting the electronic component, such as a semiconductor chip or semiconductor package, onto a motherboard, to electrically connect the electronic component and the motherboard. The surface-mount connector mainly comprises a mixture containing flux, solder powder, and heat-resistant resin powder having a melting point higher than the solder melting temperature, and the surface of the heat-resistant resin powder is coated with a conductive thin film. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] WO2021 / 177283A1 [Patent Document 2] Japanese Patent Application Publication No. 11-245082 [Overview of the project] [Problems that the invention aims to solve]

[0010] In a conventional solder paste, the dispersibility of the gap filler in the solder paste may not be sufficient. In this case, when electrically connecting between base materials using the solder paste, the gap filler may aggregate at the connection part of the obtained connection structure, and it may not be possible to sufficiently control the gap between the base materials. Further, when the dispersibility of the gap filler in the solder paste is not sufficient, when electrically connecting between base materials using the solder paste, due to the stress between the base materials, voids (peeling) may occur at the interface between the base material particles and the coating part in the gap filler, or cracks may occur in part or all of the connection part in the obtained connection structure. When the base material particles and the coating part are peeled off, there is a problem that poor conduction occurs in the connection structure. Also, when cracks occur in the connection part, there is a problem that the conduction reliability of the connection structure deteriorates.

[0011] An object of the present invention is to provide a solder paste that can enhance the dispersibility of the gap filler in the connection part of the obtained connection structure, suppress the peeling between the base material particles and the coating part in the gap filler, and suppress the occurrence of cracks in the connection part when electrically connecting between base materials using the solder paste. Another object of the present invention is to provide a connection structure using the above solder paste.

Means for Solving the Problems

[0012] In this specification, the following solder paste and connection structure are disclosed.

[0013] Item 1. A solder paste containing solder particles and a gap filler, wherein the gap filler includes base material particles and a coating part disposed on the surface of the base material particles, the specific gravity of the gap filler is 1.50 or less, and the ratio of the following thickness T to the particle diameter of the gap filler is 0.60 or more and 1.20 or less: a solder paste.

[0014] Thickness T: Apply the solder paste to form a solder paste layer with the same thickness as the particle diameter of the gap material in the solder paste, when the solder paste layer is heated at 240°C for 45 seconds, the thickness of the part where the gap material does not exist in the heated solder paste layer

[0015] Item 2. The solder paste according to Item 1, wherein the coefficient of variation of the particle diameter of the gap material is 6.0% or less.

[0016] Item 3. The solder paste according to Item 1 or 2, wherein the coated portion of the gap material has a metal layer.

[0017] Item 4. The solder paste according to Item 3, wherein the metal layer does not contain tin, indium, silver, lead, bismuth, and copper.

[0018] Item 5. The solder paste according to Item 3 or 4, wherein the metal layer contains nickel.

[0019] Item 6. The solder paste according to any one of Items 1 to 5, wherein the thickness of the coated portion of the gap material is 0.01 μm or more and 1.0 μm or less.

[0020] Item 7. The solder paste according to any one of Items 1 to 6, wherein the base material particles in the gap material are resin particles or organic-inorganic hybrid particles.

[0021] Item 8. The solder paste according to any one of Items 1 to 7, wherein the surface of the gap material is not rust-proof treated.

[0022] Item 9. The solder paste according to any one of Items 1 to 8, wherein the particle diameter of the gap material is 3.0 μm or more and 150 μm or less.

[0023] Item 10. The solder paste according to any one of Items 1 to 9, wherein the amount of outgas generated when the gap material is heated at 250°C for 10 minutes is 1000 ppm or less.

[0024] Item 11. Solder paste according to any one of items 1 to 10, comprising an organic solvent or binder resin.

[0025] Item 12. 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 connecting portion connecting the first connection target member and the second connection target member, wherein the material of the connecting portion is the solder paste described in any one of items 1 to 11, and the first connection area and the second connection area are electrically connected by the solder portion in the connecting portion. [Effects of the Invention]

[0026] The solder paste according to the present invention is a solder paste comprising solder particles and a gap material. In the solder paste according to the present invention, the gap material comprises base material particles and a coating portion disposed on the surface of the base material particles. In the solder paste according to the present invention, the specific gravity of the gap material is 1.50 or less. In the solder paste according to the present invention, the ratio of the thickness T to the particle diameter of the gap material is 0.60 or more and 1.20 or less. Because the solder paste according to the present invention has the above configuration, when base materials are electrically connected using the solder paste, the dispersibility of the gap material at the connection portion of the resulting connection structure can be improved, peeling between the base material particles and the coating portion of the gap material can be suppressed, and the occurrence of cracks at the connection portion can be suppressed. [Brief explanation of the drawing]

[0027] [Figure 1] Figure 1 is a schematic cross-sectional view showing the gap material in solder paste according to the first embodiment of the present invention. [Figure 2] Figure 2 is a schematic cross-sectional view showing the gap material in solder paste according to a second embodiment of the present invention. [Figure 3] Figure 3 is a cross-sectional view showing an example of a connection structure obtained using solder paste according to the first embodiment of the present invention. [Figure 4]Figure 4 is a diagram illustrating the portion of the solder paste layer after heating in which no gap material is present (the portion where thickness T is measured). [Modes for carrying out the invention]

[0028] The details of the present invention will be described below.

[0029] (Solder paste) The solder paste according to the present invention is a solder paste comprising solder particles and a gap material. In the solder paste according to the present invention, the gap material comprises base material particles and a coating portion disposed on the surface of the base material particles. In the solder paste according to the present invention, the specific gravity of the gap material is 1.50 or less. In the solder paste according to the present invention, the ratio of the thickness T to the particle diameter of the gap material is 0.60 or more and 1.20 or less.

[0030] Thickness T: When the above solder paste is applied to form a solder paste layer with the same thickness as the particle size of the gap material in the solder paste, and the solder paste layer is heated at 240°C for 45 seconds, this is the thickness of the portion of the solder paste layer where the gap material is not present after heating.

[0031] Figure 4 is a diagram illustrating the portion of the solder paste layer after heating in which no gap material is present (the portion where thickness T is measured).

[0032] Figure 4 shows a view of the solder paste layer 101 after heating, viewed from the thickness direction. The solder paste layer 101 after heating shown in Figure 4 includes a gap material 101A. The portion of the solder paste layer 101 after heating where the gap material 101A is absent (the portion for which thickness T is measured) is the shaded area in Figure 4 when the solder paste layer 101 after heating is viewed from the thickness direction. Thickness T is the average thickness of the portion of the solder paste layer 101 after heating where the gap material 101A is absent (the shaded area in Figure 4).

[0033] Conventional solder pastes may not adequately disperse gap fillers. In this case, when solder paste is used to electrically connect substrates, the dispersibility of the gap filler at the connection point of the resulting connection structure cannot be improved, and the gap filler may aggregate, making it difficult to adequately control the gap between substrates. Furthermore, when solder paste is used to electrically connect substrates when the dispersibility of the gap filler in the solder paste is insufficient, stress between the substrates may cause voids (delamination) at the interface between the substrate particles and the coating in the gap filler, or cracks may occur in part or all of the connection point of the resulting connection structure. Delamination between the substrate particles and the coating point leads to poor conductivity in the connection structure. Additionally, cracks at the connection point lead to a deterioration in the conductivity reliability of the connection structure.

[0034] Furthermore, with conventional solder pastes, when a substrate is electrically connected using the solder paste, the solder particles in the solder paste melt against the metal part (coating) of the gap material, which can cause a gap (delamination) at the interface between the substrate particles and the metal part (coating) of the gap material. As a result, poor conductivity may occur in the connection structure.

[0035] The solder paste according to the present invention has the above configuration, which improves the dispersibility of the gap material in the solder paste. As a result, when substrates are electrically connected using the solder paste, the dispersibility of the gap material at the connection portion of the resulting connection structure can be improved, preventing aggregation of the gap material and allowing for sufficient control of the gap between substrates. Therefore, stress at the connection portion can be uniformly distributed, and the occurrence of cracks at the connection portion can be suppressed. As a result, the conductivity reliability of the resulting connection structure can be improved. Furthermore, the solder paste according to the present invention has the above configuration, which improves the adhesion between the substrate particles and the coating portion of the gap material, which suppresses delamination between the substrate particles and the coating portion of the gap material when substrates are electrically connected using the solder paste. As a result, the occurrence of conductivity failures in the resulting connection structure can be suppressed.

[0036] The solder paste described above is suitably used for electrical connections of electrodes (connection areas). Preferably, the solder paste is a circuit connection material.

[0037] The solder paste described above is preferably used for electrical connection between a first connection target member having a first electrode on its surface and a second connection target member having a second electrode on its surface. Since the solder particles can be efficiently moved between the upper and lower electrodes, the solder paste can be applied to the first electrode so as to extend laterally beyond the first electrode, or applied to multiple first electrodes so as to span multiple first electrodes. However, the solder paste may also be applied so as not to span multiple first electrodes, or it may be selectively applied to a single first electrode.

[0038] To more efficiently arrange the solder on the electrode, the solder paste is preferably liquid at 25°C. The viscosity (η25) of the solder paste at 25°C is preferably 50 Pa·s or more, more preferably 100 Pa·s or more, even more preferably 150 Pa·s or more, particularly preferably 200 Pa·s or more, preferably 800 Pa·s or less, more preferably 600 Pa·s or less, even more preferably 500 Pa·s or less, even more preferably 400 Pa·s or less, even more preferably 300 Pa·s or less, particularly preferably 280 Pa·s or less, and most preferably 250 Pa·s or less. When the viscosity (η25) is above the lower limit and below the upper limit, the solder can be arranged more efficiently on the electrode. The viscosity (η25) can be appropriately adjusted depending on the type and amount of the compounding components.

[0039] The viscosity (η25) mentioned above is measured, for example, using an E-type viscometer under conditions of 25°C and 5 rpm. Examples of such E-type viscometers include the "VISCOMETER TV-22" manufactured by Toki Sangyo Co., Ltd.

[0040] The following explains each component contained in the solder paste mentioned above.

[0041] <Gap material> The gap material described above comprises base material particles and a coating portion disposed on the surface of the base material particles.

[0042] The specific gravity of the gap material is 1.50 or less. Preferably, the specific gravity of the gap material is less than 1.50, more preferably 1.47 or less, even more preferably 1.45 or less, particularly preferably 1.43 or less, and most preferably 1.40 or less. When the specific gravity of the gap material is below or below the upper limit, the dispersibility of the gap material at the connection portion of the resulting connection structure can be further improved when the substrates are electrically connected using solder paste, and the gap between the substrates can be controlled more effectively. The lower limit of the specific gravity of the gap material is not particularly limited. The specific gravity of the gap material may be 1.10 or more, 1.15 or more, 1.20 or more, or 1.30 or more. The range of the specific gravity of the gap material can be set by appropriately selecting the lower limit and upper limit values.

[0043] The specific gravity of the gap material can be measured, for example, using a hydrometer. Examples of hydrometers include the Shimadzu Corporation's "AccuPic 1330".

[0044] When the above gap material is heated at 250°C for 10 minutes, the amount of outgassing is preferably 2000 ppm or less, more preferably 1000 ppm or less, even more preferably 800 ppm or less, still more preferably 500 ppm or less, particularly preferably 400 ppm or less, and most preferably 300 ppm or less. This range includes 0 ppm (no outgassing). It is most preferable that the amount of outgassing when the above gap material is heated at 250°C for 10 minutes is 0 ppm (no outgassing). When the amount of outgassing when the above gap material is heated at 250°C for 10 minutes is below the above upper limit, it is possible to suppress the formation of voids in the connection portion of the resulting connection structure, suppress the peeling between the base material particles and the coating portion in the gap material, and suppress the formation of cracks in the connection portion. As a result, the conductivity reliability of the connection structure can be improved. The lower limit of the amount of outgassing when the above gap material is heated at 250°C for 10 minutes is not particularly limited. The amount of outgassing generated when the above gap material is heated at 250°C for 10 minutes may be 0 ppm or more, greater than 0 ppm, 5 ppm or more, or 10 ppm or more. The range of the amount of outgassing generated when the above gap material is heated at 250°C for 10 minutes can be set by appropriately selecting the above lower limit and upper limit.

[0045] The amount of outgassing generated when the above gap material is heated at 250°C for 10 minutes can be measured, for example, as follows.

[0046] Two samples are prepared: 5 mg of the gap material and toluene of a known concentration. Using a thermal desorption apparatus, 5 mg of the gap material is heated at 250°C for 10 minutes while passing helium gas through it at a flow rate of 20 mL / min, and the generated component (A) is adsorbed and collected on a glass tube filled with adsorbent. While passing helium gas through the glass tube in which component (A) is collected, the glass tube in which component (A) is collected is heated at 350°C for 40 minutes, and the component desorbed from the adsorbent is directly introduced into a gas chromatograph-mass spectrometer and analyzed. Using a thermal desorption apparatus, toluene of a known concentration is heated at 250°C for 10 minutes while passing helium gas through it at a flow rate of 20 mL / min, and the generated component (B) is adsorbed and collected on a glass tube filled with adsorbent. While passing helium gas through the glass tube in which the above component (B) is collected, the glass tube in which the above component (B) is collected is heated at 350°C for 40 minutes, and the component desorbed from the adsorbent is directly introduced into a gas chromatograph-mass spectrometer and analyzed. The peak area values ​​of each component detected when the above gap material is used are compared with the peak area values ​​detected when the above known concentration of toluene is used, and the amount of outgassing when the gap material is heated at 250°C for 10 minutes is calculated.

[0047] The known concentration of toluene mentioned above may be 5 mg of toluene.

[0048] The amount of outgassing generated when the above gap material is heated at 250°C for 10 minutes is measured in more detail as follows.

[0049] Enclose the sample (5 mg of the gap material or toluene of a known concentration) in a sample tube, and heat it under heating conditions of 250°C and for 10 minutes while passing helium gas through the sample tube at a flow rate of 20 mL / min. Adsorb and collect the components volatilized by heating in a glass tube filled with a trapping agent (for example, TENAX-TA). While passing helium gas through the glass tube in which the volatilized components have been collected, heat the glass tube under heating conditions of 350°C and for 40 minutes. Introduce the components desorbed from the adsorbent by heating directly into a gas chromatograph mass spectrometer (hereinafter referred to as GC / MS) for analysis (ATD-GC / MS). Examples of the apparatus used for the above measurement and the analysis conditions are as follows.

[0050] [ATD-GC / MS] Thermal desorption apparatus: "TurboMatrix350" manufactured by PerkinElmer GC: "7890A" manufactured by Agilent Technologies MS: "JMS-Q1000GCQ" manufactured by JEOL Ltd. Column: "EQUITY-1 60m × 0.25mm I.D. × 0.25μm" manufactured by SUPELCO

[0051] <Conditions of the thermal desorption apparatus> Heating temperature of the sample tube: 250°C Heating time: 10 minutes Flow rate of helium gas: 20 mL / min Cold trap temperature: 4°C Desorption temperature and time from the collection tube (glass tube): 350°C and 40 minutes Split: Inlet; 25 mL / min, Outlet; 25 mL / min

[0052] <GC / MS conditions> Carrier gas: Helium, contact flow Column flow rate: 1.5 mL Split ratio: 1:30 Initial oven temperature: 40°C Hold time: 4 minutes Temperature rising rate: 10°C / min Final temperature: 300°C Hold time: 10 minutes MS:EI mode, 70eV, transfer line; 250℃, ion source; 230℃

[0053] The sum of the peak area values ​​of each component detected when using the above gap material is compared with the peak area values ​​detected when using a toluene solution of known concentration (for example, "VOCs Mixed Standard Stock Solution III" manufactured by Kanto Chemical Co., Ltd.). This allows the concentration of volatile components (outgassing) from the gap material to be calculated in toluene equivalent. In this invention, the amount of outgassing (ppm) when the gap material is heated at 250°C for 10 minutes is calculated using the following formula.

[0054] Outgassing rate (ppm) = [(Sum of peak area values ​​of volatile components from gap material) / (Peak area value of toluene) × Concentration of toluene in toluene solution (μg / g) × Amount of toluene solution measured (g)] / Weight of gap material

[0055] The following are some methods for adjusting the amount of outgassing generated when the above gap material is heated at 250°C for 10 minutes to a desirable range: Adjusting the type and molecular weight of polymerizable components and crosslinking agent in the base particle material; Adjusting the polymerization temperature and polymerization time when the base particle is made; Pressurizing during polymerization of polymerizable components in the base particle material; Washing unreacted polymerizable components (monomers); Adjusting the plating conditions during the formation of the metal layer, as described later, to make the metal layer denser.

[0056] The compressive modulus (20% K value of the gap material at 25°C) when the above gap material is compressed by 20% at 25°C is preferably 1500 N / mm 2 More preferably, 2000 N / mm 2 More preferably 2500 N / mm 2 The above is preferable, preferably 20,000 N / mm 2 More preferably, 15,000 N / mm 2 More preferably, 8000 N / mm 2The following holds. When the 20% K value of the above gap material at 25°C is not less than the above lower limit, when electrically connecting between base materials using a solder paste, in the obtained connection structure, the gap between the base materials can be more effectively controlled. When the 20% K value of the above gap material at 25°C is not more than the above upper limit, when electrically connecting between base materials using a solder paste, the above gap material can more favorably follow the connection target member, and in the obtained connection structure, the gap between the base materials can be more favorably controlled.

[0057] The compression elastic modulus (20% K value of the gap material at 100°C) when the above gap material is compressed by 20% at 100°C is preferably 1000 N / mm 2 or more, more preferably 1500 N / mm 2 or more, still more preferably 2000 N / mm 2 or more, and preferably 20000 N / mm 2 or less, more preferably 10000 N / mm 2 or less, still more preferably 6000 N / mm 2 or less. When the 20% K value of the above gap material at 100°C is not less than the above lower limit, when electrically connecting between base materials using a solder paste, in the obtained connection structure, the gap between the base materials can be more favorably controlled. When the 20% K value of the above gap material at 100°C is not more than the above upper limit, it is possible to prevent the gap material from being destroyed.

[0058] The 20% K values of the above gap material at 25°C and 100°C can be measured as follows.

[0059] Using a micro compression tester, compress the gap material under the conditions of applying a load of 90 mN for 30 seconds at 25°C or 100°C with the smooth end face of a cylindrical (diameter 50 μm, made of diamond) indenter. Measure the load value (N) and the compression displacement (mm) at this time. From the obtained measurement values, the above compression elastic modulus can be obtained by the following formula. As the above micro compression tester, for example, "Fischer Scope H-100" manufactured by Fischer and "ENT-5" manufactured by Erionix are used.

[0060] 20%K value (N / mm 2 )=(3 / 2 1 / 2 )·F·S -3 / 2 ·R -1 / 2 F: Load value (N) when the gap material is compressed by 20% S: Compressive displacement (mm) when the gap material is compressed by 20% R: Radius of the gap material (mm)

[0061] Methods for controlling the 20%K values ​​of the above gap material at 25°C and 100°C to a preferred range include the following: adjusting the type of monomer, molecular weight of the monomer, type of crosslinking agent, polymerization temperature, and polymerization time of the base particle material; adjusting the type and thickness of the coating; and adjusting the arrangement of the metal layer in the coating, as described later.

[0062] From the viewpoint of further improving the effects of the present invention, the compression recovery rate of the gap material at 25°C is preferably 20% or more, more preferably 25% or more, even more preferably 30% or more, preferably 95% or less, more preferably 90% or less, and even more preferably 85% or less.

[0063] The above compression recovery rate can be measured as follows.

[0064] The gap material is scattered on the sample stage. For each scattered gap material, a microcompression tester is used to apply a load (reverse load value) towards the center of the gap material at 25°C using the smooth end face of a cylindrical (100 μm diameter, diamond) indenter until the gap material is compressed by 40%. Then, the load is removed to the origin load value (0.40 mN). The load-compression displacement during this time is measured, and the compression recovery rate can be calculated from the following formula. The loading speed is set to 0.33 mN / sec. As the microcompression tester, for example, the Fischerscope H-100 manufactured by Fischer GmbH can be used.

[0065] Compression recovery rate (%) = [L2 / L1] × 100 L1: Compressive displacement from the origin load value to the reverse load value when a load is applied. L2: Unloading displacement from the reversal load value when the load is released to the origin load value.

[0066] The particle size of the gap material described above is preferably 1.0 μm or more, more preferably 2.0 μm or more, even more preferably 3.0 μm or more, particularly preferably 5.0 μm or more, most preferably 10 μm or more, preferably 300 μm or less, more preferably 200 μm or less, even more preferably 150 μm or less, even more preferably 100 μm or less, and particularly preferably 80 μm or less. When the particle size of the gap material is above the lower limit and below the upper limit, the dispersibility of the gap material at the connection portion of the resulting connection structure can be further improved when the substrates are electrically connected using solder paste, and the gap between the substrates can be controlled even better. Note that the particle size of the gap material described above refers to the particle size of the gap material in the solder paste before heating.

[0067] The particle diameter of the gap material described above is preferably the average particle diameter, and more preferably the number-average particle diameter. The particle diameter of the gap material can be determined, for example, by observing 50 arbitrary gap material samples with an electron microscope or optical microscope and calculating the average particle diameter of each gap material, or by performing laser diffraction particle size distribution measurement. In observation with an electron microscope or optical microscope, the particle diameter of each gap material sample 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 for any 50 gap material samples 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 gap material sample is determined as the particle diameter at the equivalent diameter of a sphere. It is preferable to calculate the particle diameter of the gap material described above using laser diffraction particle size distribution measurement.

[0068] From the viewpoint of further controlling the gap between substrates in the resulting connection structure, it is preferable that the particle diameter of the gap material is larger than the particle diameter of the solder particles. The ratio of the particle diameter of the gap material to the particle diameter of the solder particles is denoted as the ratio (particle diameter of gap material / particle diameter of solder particles). The ratio (particle diameter of gap material / particle diameter of solder particles) is preferably 1.5 or more, more preferably 2.0 or more, even more preferably 2.5 or more, particularly preferably 3.0 or more, most preferably 7.0 or more, preferably 30 or less, and more preferably 20 or less. When the ratio (particle diameter of gap material / particle diameter of solder particles) is above the lower limit and below the upper limit, the gap between substrates can be controlled even more effectively in the resulting connection structure.

[0069] In the above solder paste, the ratio of the thickness T to the particle diameter of the gap material (thickness T / particle diameter of the gap material) is between 0.60 and 1.20.

[0070] Thickness T: When the above solder paste is applied to form a solder paste layer with the same thickness as the particle size of the gap material in the solder paste, and the solder paste layer is heated at 240°C for 45 seconds, this is the thickness of the portion of the solder paste layer after heating in which the gap material is not present.

[0071] The above ratio (thickness T / particle diameter of gap material) is preferably 0.65 or more, more preferably 0.70 or more, even more preferably 0.80 or more, preferably 1.15 or less, more preferably 1.10 or less, and even more preferably 1.00 or less. When the above ratio (thickness T / particle diameter of gap material) is above the lower limit and below the upper limit, the gap material deforms uniformly during mounting, which allows for better control of the gap between substrates in the resulting connection structure and uniform distribution of stress at the connection. Furthermore, when the above ratio (thickness T / particle diameter of gap material) is above the lower limit, the occurrence of cracks at the connection can be further suppressed. Note that the particle diameter of the gap material in the above ratio (thickness T / particle diameter of gap material) refers to the particle diameter of the gap material in the solder paste before heating.

[0072] The above ratio (thickness T / particle size of gap material) can be measured, for example, as follows: The above solder paste is screen printed (screen printing method) on a 1 cm square area on the surface of a substrate (made of glass) at 25°C. 2 The solder paste is applied to the substrate to form a solder paste layer with the same thickness as the particle diameter of the gap material in the solder paste. For example, if the particle diameter of the gap material in the solder paste is 50 μm, a solder paste layer with a thickness of 50 μm is formed. The solder paste layer is heated at 240°C for 45 seconds. The thickness of the portion of the solder paste layer where the gap material is not present after heating is measured using a metal laser microscope (Keyence Corporation "VX-X3000"), and the ratio (thickness T / particle diameter of gap material) is calculated by dividing it by the particle diameter of the gap material. The method of applying the solder paste is not particularly limited. The solder paste may be applied by screen printing, by inkjet printing, or by dispensing. It is preferable that the solder paste be applied by screen printing. Alternatively, chips or the like may be laminated on the surface of the solder paste layer opposite to the substrate (made of glass), and the resulting laminate may be heated.

[0073] Methods for controlling the above ratio (thickness T / particle diameter of gap material) to a preferred range include the following: adjusting the type of monomer, molecular weight of the monomer, type of crosslinking agent, polymerization temperature, and polymerization time of the base material particles; adjusting the type and thickness of the coating; adjusting the viscosity (η25) of the solder paste at 25°C; and adjusting the content of the gap material.

[0074] The coefficient of variation (CV value) of the particle size of the gap material is preferably 15.0% or less, more preferably 10.0% or less, even more preferably 6.0% or less, particularly preferably 5.0% or less, and most preferably 3.0% or less. When the coefficient of variation of the particle size of the gap material is below the upper limit, the gap material deforms uniformly during mounting, allowing for better control of the gap between substrates in the resulting connection structure and uniform distribution of stress at the connection. The lower limit of the coefficient of variation of the particle size of the gap material is not particularly limited. The coefficient of variation of the particle size of the gap material may be 0% or more, 0.1% or more, 0.5% or more, or 1.0% or more. The range of the coefficient of variation of the particle size of the gap material can be set by appropriately selecting the lower and upper limits.

[0075] The coefficient of variation (CV value) of the particle size of the above gap material can be measured as follows.

[0076] CV value (%) of particle size of gap material = (ρ / Dn) × 100 ρ: Standard deviation of particle size of gap material Dn: Average particle size of the gap material

[0077] The shape of the gap material described above is not particularly limited. The shape of the gap material may be spherical, or it may be a shape other than spherical, or it may be flattened, etc. From the viewpoint of further improving the dispersibility of the gap material at the connection part of the connection structure obtained when the substrates are electrically connected using solder paste, the shape of the gap material is preferably spherical.

[0078] The surface of the gap material (outer surface of the covering portion) may or may not be treated with rust prevention. From the viewpoint of good diffusion of the gap material and solder particles when the substrates are electrically connected using solder paste, and further improving the dispersibility of the gap material at the connection portion of the resulting connection structure, it is preferable that the surface of the gap material (outer surface of the covering portion) is not treated with rust prevention.

[0079] The present invention will be described in detail below with reference to the drawings.

[0080] Figure 1 is a schematic cross-sectional view showing the gap material in solder paste according to the first embodiment of the present invention.

[0081] The gap material 1 shown in Figure 1 has base particles 2 and a coating portion 3 disposed on the surface of the base particles 2. The coating portion 3 covers the surface of the base particles 2. The gap material 1 is a coated particle in which the surface of the base particles 2 is covered by the coating portion 3.

[0082] Figure 2 is a schematic cross-sectional view showing the gap material in solder paste according to a second embodiment of the present invention.

[0083] The gap material 1A shown in Figure 2 has base material particles 2 and a coating portion 3A disposed on the surface of the base material particles 2. The coating portion 3A covers the surface of the base material particles 2. The gap material 1A is a coated particle in which the surface of the base material particles 2 is covered by the coating portion 3A.

[0084] In the gap material 1A, the coating portion 3A has two layers of coating (metal layers). The coating portion 3A is a coating portion having a two-layer structure. The coating portion 3A has a first metal layer 3AA and a second metal layer 3AB. Specifically, the coating portion 3A has the first metal layer 3AA and the second metal layer 3AB in this order, from the inner surface to the outer surface of the coating portion 3A. The first metal layer 3AA is located on the surface of the base material particles 2. The first metal layer 3AA is in contact with the base material particles 2. The first metal layer 3AA is the innermost layer of the coating portion 3A. The first metal layer 3AA is located between the base material particles 2 and the second metal layer 3AB. The second metal layer 3AB is located on the surface of the first metal layer 3AA. The second metal layer 3AB is in contact with the first metal layer 3AA. The second metal layer 3AB is the outermost layer of the coating portion 3A. The second metal layer 3AB is the outermost coating portion (metal layer) of the gap material 1A.

[0085] Further details about the gap material 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."

[0086] [Base material particles] Examples of the above-mentioned base material particles include resin particles, inorganic particles excluding metal particles, organic-inorganic hybrid particles, and metal particles. The above-mentioned base material particles may also be core-shell particles comprising a core and a shell disposed on the surface of the core. The core may be an organic core. The shell may be an inorganic shell. From the viewpoint of exhibiting the effects of the present invention more effectively, the above-mentioned base material particles in the gap material are preferably resin particles or organic-inorganic hybrid particles, and more preferably resin particles.

[0087] Various organic materials are suitably used as the resin material for the above-mentioned resin particles. Examples of resins that can be used as the material 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 base particles can be easily controlled within a suitable range, the resin used to form the resin particles is preferably a polymer of polymerizable monomers having multiple ethylenically unsaturated groups. A polymer can be obtained by polymerizing one or more of the polymerizable monomers having multiple ethylenically unsaturated groups.

[0088] When the above resin particles are obtained by polymerizing a polymerizable monomer having an ethylenically unsaturated group, the polymerizable monomer having an ethylenically unsaturated group can be a non-crosslinked monomer or a crosslinked monomer.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] The above-mentioned polymerizable monomer having an ethylenically unsaturated group can be polymerized by known methods to obtain the above-mentioned 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.

[0094] When the above-mentioned base material particles are inorganic particles excluding metal particles or organic-inorganic hybrid particles, examples of inorganic materials for the base material particles include silica and carbon black. Preferably, the above-mentioned inorganic material is not a metal. Examples of particles formed from silica include particles obtained by hydrolyzing a silicon compound having two or more hydrolyzable alkoxysilyl groups to form crosslinked polymer particles, and then firing them as necessary. Examples of organic-inorganic hybrid particles include organic-inorganic hybrid particles formed from a crosslinked alkoxysilyl polymer and an acrylic resin.

[0095] When the above-mentioned base material particles are metal particles, examples of metals that make up the metal particles include silver, copper, nickel, silicon, gold, and titanium. However, it is preferable that the above-mentioned base material particles are not metal particles, and it is preferable that they are not copper particles.

[0096] The compressive modulus (20% K value of the base particles at 25°C) when the above base particles are compressed by 20% at 25°C is preferably 550 N / mm². 2 More preferably, 850 N / mm 2 More preferably, 1100 N / mm 2 In particular, 2200 N / mm 2 The above is preferable, preferably 14000 N / mm 2 More preferably, 9500 N / mm 2 More preferably, 7300 N / mm 2 The following is particularly preferred: 5600 N / mm 2 The following applies: When the 20%K value of the above substrate particles at 25°C is above the lower limit and below the upper limit, the hardness of the resulting gap material can be improved, and when the substrates are electrically connected using solder paste, the gap between the substrates in the resulting connection structure can be sufficiently controlled.

[0097] The 20% K value of the above substrate particles at 25°C can be measured as follows.

[0098] Using a microcompression testing machine, the substrate particles are compressed under the conditions of 25°C and a maximum test load of 90 mN applied for 30 seconds using the smooth end face of a cylindrical diamond indenter (50 μm in diameter). The load value (N) and compression displacement (mm) are measured at this time. From the obtained measurements, the compressive modulus can be calculated using the following formula. Examples of microcompression testing machines used include the Fischerscope H-100 from Fischer GmbH and the ENT-5 from Elionix Corporation.

[0099] 20%K value (N / mm 2 )=(3 / 2 1 / 2 )·F·S -3 / 2 ·R -1 / 2 F: Load value (N) when the base material particles are compressed and deformed by 20%. S: Compression displacement (mm) when the substrate particles are compressed by 20%. R: Radius of the base particle (mm)

[0100] Methods for controlling the 20%K value of the above-mentioned base particles at 25°C to a preferred range include the following: adjusting the type of monomer, molecular weight of the monomer, type of crosslinking agent, polymerization temperature, and polymerization time of the base particle material.

[0101] The particle size of the above-mentioned base material particles is preferably 0.5 μm or more, more preferably 1.0 μm or more, even more preferably 2.0 μm or more, particularly preferably 3.0 μm or more, most preferably 10 μm or more, preferably 300 μm or less, more preferably 200 μm or less, even more preferably 100 μm or less, and particularly preferably 80 μm or less. When the particle size of the above-mentioned base material particles is above the lower limit and below the upper limit, the dispersibility of the gap material at the connection portion of the resulting connection structure can be further improved when the base materials are electrically connected using solder paste, and the gap between the base materials can be controlled more effectively.

[0102] The particle diameter of the above-mentioned base material particles represents the number-average particle diameter. The particle diameter of the above-mentioned base material particles can be determined using a particle size distribution analyzer or the like. Preferably, the particle diameter of the base material particles can be determined by observing 50 arbitrary base material particles with an electron microscope or optical microscope and calculating the average value. In observation with an electron microscope or optical microscope, the particle diameter of each base material particle can be 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 base material particles is approximately equal to the average particle diameter at the equivalent diameter of a sphere. With a particle size distribution analyzer, the particle diameter of each base material particle can be determined as the particle diameter at the equivalent diameter of a sphere. Preferably, the particle diameter of the above-mentioned base material particles can be calculated using a particle size distribution analyzer. When measuring the particle diameter of the above-mentioned base material particles in a gap material, for example, it can be measured as follows.

[0103] A gap material is added to Kulzer's "Technovit 4000" so that the gap material content is 30% by weight, and dispersed to create an embedded resin body for gap material inspection. An ion milling device (Hitachi High-Technologies Corporation's "IM4000") is used to cut a cross-section of the gap material, passing through the vicinity of the center of the substrate particles in the gap material dispersed in the embedded resin body. Then, using a field emission scanning electron microscope (FE-SEM) with the image magnification set to 25,000x, 50 gap materials are randomly selected, and the substrate particles of each gap material are observed. The particle size of the substrate particles in each gap material is measured, and these are arithmetic mean to obtain the particle size of the substrate particles.

[0104] The coefficient of variation (CV value) of the particle size of the above-mentioned base material particles is preferably 15.0% or less, more preferably 10.0% or less, even more preferably 6.0% or less, particularly preferably 5.0% or less, and most preferably 3.0% or less. When the coefficient of variation of the particle size of the above-mentioned base material particles is below the above upper limit, the gap between the base materials can be controlled more effectively in the resulting connecting structure, and the stress at the connection can be uniformly distributed. The lower limit of the coefficient of variation of the particle size of the above-mentioned base material particles is not particularly limited. The coefficient of variation of the particle size of the above-mentioned base material particles may be 0% or more, 0.1% or more, 0.5% or more, or 1.0% or more. The range of the coefficient of variation of the particle size of the above-mentioned base material particles can be set by appropriately selecting the above lower limit and upper limit.

[0105] The coefficient of variation (CV value) of the particle size of the above-mentioned substrate particles can be measured as follows.

[0106] CV value (%) of the particle size of the base material particles = (ρ / Dn) × 100 ρ: Standard deviation of the particle size of the substrate particles Dn: Average particle size of the substrate particles

[0107] [Covered part] The material used to form the above-mentioned coating is not particularly limited. The material used to form the above-mentioned coating may be an organic material or an inorganic material. Examples of the organic material include the resins mentioned above. The above-mentioned coating is preferably formed from an inorganic material, and more preferably from a metal.

[0108] The above-mentioned covering portion may be formed by a single layer. The above-mentioned covering portion may be formed by multiple layers. That is, the above-mentioned covering portion may have a laminated structure of two or more layers.

[0109] From the viewpoint of exhibiting the effects of the present invention even more effectively, it is preferable that the coating portion of the gap material has a metal layer. From the viewpoint of exhibiting the effects of the present invention even more effectively, if the coating portion is formed by a plurality of layers, it is preferable that the innermost layer of the coating portion (the layer laminated on the surface of the base material particles) is a metal layer.

[0110] The above metal layer may be formed by a single layer. The above metal layer may be formed by multiple layers. That is, the above metal layer may have a laminated structure of two or more layers.

[0111] Examples of metals in the above-mentioned metal layer include gold, silver, palladium, copper, platinum, zinc, iron, tin, lead, aluminum, cobalt, indium, nickel, chromium, titanium, antimony, bismuth, thallium, germanium, cadmium, silicon, tungsten, molybdenum, and alloys thereof. Alternatively, the above-mentioned metal may be tin-doped indium oxide (ITO) or solder.

[0112] From the viewpoint of exhibiting the effects of the present invention even more effectively, it is preferable that the melting point of the layer laminated on the surface of the base material particles (or, if the coating portion is formed by multiple layers, the innermost layer of the coating portion) is higher than the melting point of the solder particles. The melting point of the layer laminated on the surface of the base material particles is preferably 300°C or higher, more preferably 400°C or higher, even more preferably 450°C or higher, preferably 2000°C or lower, more preferably 1800°C or lower, and even more preferably 1600°C or lower. When the melting point of the layer laminated on the surface of the base material particles is above the lower limit and below the upper limit, when the base materials are electrically connected using solder paste, it is possible to suppress the melting of the solder particles in the solder paste and the coating portion in the gap material, and to prevent the formation of voids at the interface between the base material particles and the coating portion in the gap material. As a result, the conductivity reliability of the connection structure can be further improved.

[0113] The above metal layer (coating) preferably contains nickel, palladium, or copper, more preferably nickel or palladium, and even more preferably nickel. When the above metal layer (coating) contains nickel, it may contain pure nickel or a nickel-containing alloy. When the above metal layer (coating) contains these preferred metals, when the substrates are electrically connected using solder paste, it is possible to suppress the melting of the solder particles in the solder paste and the metal layer (coating) in the gap material, and to prevent the formation of voids at the interface between the substrate particles and the coating in the gap material. In addition, it is possible to diffuse the solder particles in the solder paste and the metal on the outer surface of the metal layer (coating). As a result, the conductivity reliability of the connection structure can be further improved.

[0114] The above metal layer (coating) may or may not contain tin, indium, silver, lead, bismuth, or copper. Preferably, the above metal layer does not contain tin, indium, silver, lead, bismuth, and copper, or contains tin, indium, silver, lead, bismuth, and copper in total at 5.0% by weight or less per 100% by weight of the above metal layer. Preferably, the total content of tin, indium, silver, lead, bismuth, and copper in 100% by weight of the above metal layer is 5.0% by weight or less, more preferably 3.0% by weight or less, even more preferably 1.0% by weight or less, and most preferably 0% by weight (not contained). In other words, it is preferable that the above metal layer (coating) does not contain tin, indium, silver, lead, bismuth, and copper. Preferably, the above metal layer (coating) does not contain any of tin, indium, silver, lead, bismuth, and copper. The above metal layer (coating) preferably does not contain tin, preferably does not contain indium, preferably does not contain silver, preferably does not contain lead, preferably does not contain bismuth, and preferably does not contain copper. When the above metal layer (coating) satisfies the above preferred embodiments, when the substrates are electrically connected using solder paste, it is possible to suppress the melting of the solder particles in the solder paste and the coating in the gap material, and to prevent the formation of voids at the interface between the substrate particles and the coating in the gap material. As a result, the conductivity reliability of the connection structure can be further improved.

[0115] Various known analytical methods can be used to measure the metal content contained in the above-mentioned metal layer (coating). Examples of methods for measuring the metal content contained in the above-mentioned metal layer (coating) include absorption spectroscopy and spectral analysis. For absorption spectroscopy, flame spectrophotometers and electric furnace spectrophotometers can be used. Examples of spectral analysis include plasma emission spectrometry and plasma ion source mass spectrometry.

[0116] The metal content in the above-mentioned metal layer (coating) can be measured, for example, using an ICP emission spectrometer. Examples of commercially available ICP emission spectrometers include the "ICP Emission Spectrometer" manufactured by HORIBA Corporation.

[0117] The layer laminated on the surface of the base material particles (or, if the coating is formed by multiple layers, the innermost layer of the coating) preferably contains nickel or palladium, and more preferably contains nickel. The layer laminated on the surface of the base material particles is more preferably a layer containing nickel or palladium, and even more preferably a layer containing nickel. The layer laminated on the surface of the base material particles is preferably free from tin, indium, silver, lead, bismuth, and copper. The layer laminated on the surface of the base material particles is preferably not a layer containing tin, indium, silver, lead, bismuth, or copper. When the layer laminated on the surface of the base material particles satisfies the above preferred embodiments, when the base materials are electrically connected using solder paste, melting of the solder particles in the solder paste and the coating in the gap material can be suppressed, and voids can be prevented from forming at the interface between the base material particles and the coating in the gap material. As a result, the conductivity reliability of the connection structure can be further improved.

[0118] If the coating portion is formed by multiple layers, the outermost layer of the coating portion preferably contains nickel or palladium, and more preferably contains nickel. The layer laminated on the surface of the base material particles is more preferably a layer containing nickel or palladium, and even more preferably a layer containing nickel. The layer laminated on the surface of the base material particles preferably does not contain tin, indium, silver, lead, bismuth, and copper. The layer laminated on the surface of the base material particles preferably does not contain tin, indium, silver, lead, bismuth, or copper. When the outermost layer of the coating portion satisfies the above preferred embodiments, when the base materials are electrically connected using solder paste, melting of the solder particles in the solder paste and the coating portion in the gap material can be suppressed, and voids can be prevented from forming at the interface between the base material particles and the coating portion in the gap material. As a result, the conductivity reliability of the connection structure can be further improved.

[0119] Preferably, the coating portion contains a metal that is diffusible with solder on its outer surface. A metal that is diffusible with solder is a metal that does not melt when heated, but diffuses with the solder when the solder melts.

[0120] From the viewpoint of exhibiting the effects of the present invention more effectively, the nickel content in 100% by weight of the nickel-containing layer is preferably 90.0% by weight or more, more preferably 95.0% by weight or more, even more preferably 98.0% by weight or more, still more preferably 99.0% by weight or more, particularly preferably 99.9% by weight or more, and most preferably 100% by weight. The nickel content in 100% by weight of the nickel-containing layer may be 100% by weight or less, or 99.9% by weight or less.

[0121] The method for forming the coating on the surface of the substrate particles is not particularly limited. Examples of methods for forming the coating include electroless plating, electroplating, physical vapor deposition, and coating the surface of the resin particles with metal powder or a paste containing metal powder and a binder. From the viewpoint of making the coating easier to form, electroless plating is preferred. Examples of physical vapor deposition include vacuum deposition, ion plating, and ion sputtering.

[0122] The thickness of the coating portion in the gap material described above is preferably 0.005 μm or more, more preferably 0.01 μm or more, preferably 5.0 μm or less, more preferably 1.0 μm or less, and even more preferably 0.5 μm or less. When the thickness of the coating portion in the gap material described above is above the lower limit and below the upper limit, the gap material does not become too rigid and can be sufficiently deformed between the substrates. Note that the thickness of the coating portion in the gap material described above is the total thickness of the coating portion if the coating portion is multilayered.

[0123] The thickness of the above metal layer is preferably 0.005 μm or more, more preferably 0.01 μm or more, preferably 5.0 μm or less, more preferably 1.0 μm or less, and even more preferably 0.5 μm or less. When the thickness of the above metal layer is above the lower limit and below the upper limit, the gap material does not become too hard, and the gap material can be sufficiently deformed between the substrates. Note that the thickness of the above metal layer refers to the total thickness of the metal layer when the metal layer is multilayered.

[0124] The thickness of the nickel-containing layer is preferably 0.005 μm or more, more preferably 0.01 μm or more, preferably 5.0 μm or less, more preferably 1.0 μm or less, and even more preferably 0.5 μm or less. When the thickness of the nickel-containing layer is above the lower limit and below the upper limit, when the substrates are electrically connected using solder paste, it is possible to prevent the solder particles in the solder paste from melting with the coating portion of the gap material, and to prevent the formation of voids at the interface between the substrate particles and the coating portion of the gap material. As a result, the conductivity reliability of the connection structure can be further improved.

[0125] The thickness of the coating portion and the metal layer can be measured, for example, by observing the cross-section of the gap material using a transmission electron microscope (TEM). It is preferable to calculate the thickness of the coating portion and the metal layer by taking the average of the thicknesses of five arbitrary locations within the coating portion and metal layer as the thickness of the coating portion and metal layer of one gap material, and more preferably by taking the average of the total thickness of the coating portion and metal layer as the thickness of the coating portion and metal layer of one gap material. It is preferable to determine the thickness of the coating portion and the metal layer by calculating the average thickness of the coating portion and metal layer for 50 arbitrary gap materials. The thickness of the coating portion and the metal layer is preferably the average thickness.

[0126] The outer surface of the coated portion may be treated with flux. Using flux can prevent oxidation of the metal in the coated portion (metal layer) and remove foreign matter and oxide films.

[0127] The flux described above is not particularly limited. Any flux commonly used in soldering and the like can be used. Examples of such fluxes 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, and rosin. Only one type of flux may be used, or two or more types may be used in combination.

[0128] Examples of the above molten salt include ammonium chloride. Examples of the above organic acid include lactic acid, citric acid, stearic acid, glutamic acid, and glutaric acid. Examples of the above rosin include activated rosin and inactivated rosin. The above flux is preferably an organic acid having two or more carboxyl groups, or rosin. The above flux may be an organic acid having two or more carboxyl groups, or rosin. The use of an organic acid having two or more carboxyl groups, or rosin, further improves connection strength and conductivity reliability.

[0129] Examples of organic acids having two or more carboxyl groups include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid.

[0130] Examples of the above-mentioned amine compounds include cyclohexylamine, dicyclohexylamine, benzylamine, benzhydrylamine, imidazole, benzimidazole, phenylimidazole, carboxybenzimidazole, benzotriazole, and carboxybenzotriazole.

[0131] 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.

[0132] 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, even more preferably 150°C or lower, and even more 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.

[0133] 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.

[0134] Furthermore, it is preferable that the boiling point of the flux is 200°C or lower.

[0135] 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.

[0136] Examples of fluxes that release cations upon heating include the thermal cation initiator (thermal cation curing agent) mentioned above.

[0137] From the viewpoint of further enhancing the flux effect, the flux is preferably a salt of an acid compound and a base compound.

[0138] 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 cyclohexyl carboxylic 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 more effectively increasing connection strength and more effectively increasing conductivity reliability, the above acid compound is preferably glutaric acid, cyclohexyl carboxylic acid, or adipic acid.

[0139] 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.

[0140] In 100% by weight of the solder paste, the content of the gap material is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, preferably 80% by weight or less, more preferably 60% by weight or less, even more preferably 40% by weight or less, particularly preferably 20% by weight or less, and most preferably 10% by weight or less. When the content of the gap material is above the lower limit and below the upper limit, the gap between substrates can be controlled even better in the connection structure obtained when the substrates are electrically connected using the solder paste.

[0141] In 100% by volume of the above solder paste, the content of the gap material is preferably 0.01% by volume or more, more preferably 0.1% by volume or more, preferably 80% by volume or less, more preferably 60% by volume or less, even more preferably 40% by volume or less, particularly preferably 20% by volume or less, and most preferably 10% by volume or less. When the content of the gap material is above the lower limit and below the upper limit, the gap between substrates can be controlled even more effectively in the connection structure obtained when the substrates are electrically connected using the solder paste.

[0142] With respect to 100 parts by weight of the solder particles, the content of the gap material is preferably 1 part by weight or more, more preferably 2.5 parts by weight or more, even more preferably 4 parts by weight or more, preferably 20 parts by weight or less, more preferably 15 parts by weight or less, and even more preferably 10 parts by weight or less. When the content of the gap material is above the lower limit and below the upper limit, the gap between substrates can be controlled even better in the connection structure obtained when the substrates are electrically connected using solder paste.

[0143] <Solder particles> The solder particles electrically connect the electrodes (connection areas) of the components to be connected. The solder particles are formed of solder. Both the central portion and the outer surface portion of the solder particles are formed of solder. The solder particles are particles in which both the central portion and the outer surface are solder. The solder particles do not have a base material particle as a core particle. The solder particles are different from conductive particles that have a base material particle and a solder portion disposed on the surface of the base material particle. The solder particles preferably contain 90% by weight or more, more preferably 95% by weight or more, of solder.

[0144] The solder described above is preferably a metal with a melting point of 450°C or less (low melting point metal). The solder particles described above are preferably metal particles with a melting point of 450°C or less (low melting point metal particles). The low melting point metal particles described above are particles containing a low melting point metal. The 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 220°C or less, and even more preferably 190°C or less.

[0145] The melting point of the solder particles is preferably 100°C or higher, more preferably 105°C or higher, preferably 250°C or lower, and more preferably 245°C or lower. When the melting point of the solder particles is above the lower limit and below the upper limit, when electrodes are electrically connected using solder paste, the cohesiveness of the solder can be increased, the conductivity reliability can be improved, and the insulation reliability can be improved.

[0146] The melting point of the solder particles mentioned above can be determined, for example, by differential scanning calorimetry (DSC). Examples of differential scanning calorimetry (DSC) equipment include the "EXSTAR DSC7020" manufactured by SII Corporation.

[0147] The specific gravity of the solder particles is preferably 7.0 or higher, more preferably 7.2 or higher, even more preferably 7.4 or higher, preferably 9.5 or lower, more preferably 9.0 or lower, and even more preferably 8.5 or lower. When the specific gravity of the solder particles is above the lower limit or below the upper limit, the dispersibility of the gap material at the connection portion of the resulting connection structure can be further improved, and the conductivity reliability can be further enhanced.

[0148] The specific gravity of the solder particles mentioned above can be measured, for example, using a hydrometer. Examples of such hydrometers include the Shimadzu Corporation's "AccuPic 1330".

[0149] The solder particles described above preferably contain tin. The tin content in the solder particles is preferably 30% by weight or more, more preferably 40% by weight or more, even more preferably 70% by weight or more, and particularly preferably 90% by weight or more, based on 100% by weight of the metal. When the tin content in the solder particles is above the lower limit, the reliability of the connection between the solder and the electrode can be more effectively improved. The tin content in the solder particles may be 100% by weight or less, or less than 100% by weight, based on 100% by weight of the metal.

[0150] The tin content can be measured using a high-frequency inductively coupled plasma emission spectrometer (Horiba, Ltd. "ICP-AES") or an X-ray fluorescence analyzer (Shimadzu Corporation "EDX-800HS"), etc.

[0151] By using the above-mentioned solder particles, the solder melts and joins to the electrodes, and the soldered portion creates electrical conductivity between the electrodes. For example, because the soldered portion and the electrodes are more likely to make surface contact rather than point contact, the connection resistance is reduced. Furthermore, by using the above-mentioned solder particles, the bonding strength between the soldered portion and the electrodes is increased, resulting in a further reduction in the likelihood of delamination between the soldered portion and the electrodes, thereby more effectively improving conductivity reliability and connection reliability.

[0152] The low-melting-point metal constituting the solder particles described above is not particularly limited. The low-melting-point metal is preferably tin or a tin-containing alloy. 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. Because of their excellent wettability to electrodes, the low-melting-point metal is preferably tin, a tin-silver alloy, a tin-silver-copper alloy, a tin-bismuth alloy, or a tin-indium alloy. More preferably, the low-melting-point metal is a tin-bismuth alloy or a tin-indium alloy.

[0153] The solder particles described above are preferably filler materials with a liquidus temperature of 450°C or lower, based on JIS Z3001: Welding Terminology. Examples of the composition of the solder particles include metal compositions containing zinc, gold, silver, lead, copper, tin, bismuth, indium, etc. The solder particles are preferably lead-free and contain either tin and indium, or tin and bismuth.

[0154] To further effectively enhance the bonding strength between the solder and the electrode, the solder particles 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 the bonding strength between the solder and the electrode, it is preferable that the solder particles contain nickel, copper, antimony, aluminum, or zinc. From the viewpoint of further effectively enhancing the bonding strength between the solder and the electrode, the content of these metals for enhancing bonding strength is preferably 0.0001% by weight or more, and preferably 1% by weight or less, out of 100% by weight of the metal contained in the solder particles.

[0155] The average particle size of the solder particles is preferably 0.01 μm or more, more preferably 0.03 μm or more. When the average particle size of the solder particles is above the lower limit, the solder can be arranged on the electrode more efficiently. The average particle size of the solder particles may be 10 μm or less, 5 μm or less, or 3 μm or less.

[0156] The average particle diameter of the solder particles mentioned above is the number-average particle diameter. The average particle diameter of the solder particles can be determined, for example, by observing 50 arbitrary solder particles with an electron microscope or optical microscope and calculating the average particle diameter of each solder 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 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 laser diffraction particle size distribution measurement, 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 using laser diffraction particle size distribution measurement.

[0157] The coefficient of variation (CV value) of the particle size of the solder particles is preferably 20% or less, more preferably 10% or less, and even more preferably 5.0% or less. When the coefficient of variation of the particle size of the solder particles is below the upper limit, the solder can be arranged on the electrode more efficiently. The coefficient of variation of the particle size of the solder particles may be 0% or more, 1.0% or more, 5.0% or more, or 10.0% or more. The range of the coefficient of variation of the particle size of the solder particles can be set by appropriately selecting the lower limit and upper limit values.

[0158] The coefficient of variation (CV value) of the particle size of the solder particles described above can be measured as follows.

[0159] CV value (%) of solder particle size = (ρ / Dn) × 100 ρ: Standard deviation of the particle size of solder particles Dn: Average particle size of solder particles

[0160] The shape of the solder particles is not particularly limited. The shape of the solder particles may be spherical, or other shapes, such as flattened. From the viewpoint of improving the dispersibility of the solder particles in the binder resin, the shape of the solder particles is preferably spherical.

[0161] 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 50% by weight or more, particularly preferably 70% by weight or more, 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 content of the above solder particles is above the lower limit and below the upper limit, solder can be arranged on the electrodes more efficiently, it is easy to arrange a large amount of solder between the electrodes, and the conductivity reliability of the resulting connection structure can be more effectively improved. From the viewpoint of more effectively improving conductivity reliability, a higher content of the above solder particles is preferable.

[0162] In 100% by volume of the above solder paste, the content of the above solder particles is preferably 1% by volume or more, more preferably 2% by volume or more, even more preferably 10% by volume or more, particularly preferably 20% by volume or more, most preferably 30% by volume or more, preferably 80% by volume or less, more preferably 60% by volume or less, and even more preferably 50% by volume or less. When the content of the above solder particles is above the lower limit and below the upper limit, solder can be arranged on the electrodes more efficiently, it is easy to arrange a large amount of solder between the electrodes, and the conductivity reliability of the resulting connection structure can be more effectively improved. From the viewpoint of more effectively improving conductivity reliability, a higher content of the above solder particles is preferable.

[0163] In 100% by weight of the above solder paste, the total content of the above solder particles and the above gap material is preferably 21% by weight or more, more preferably 31% by weight or more, even more preferably 51% by weight or more, particularly preferably 71% by weight or more, preferably 100% by weight or less, more preferably 99.9% by weight or less, even more preferably 99.0% by weight or less, and particularly preferably 98.0% by weight or less. When the total content of the above solder particles and the above gap material is above the lower limit and below the upper limit, the effects of the present invention are exhibited even more effectively.

[0164] The solder paste described above may contain an organic solvent or a binder resin.

[0165] <Organic solvents> By using the above-mentioned organic solvents, the handling properties of the solder paste can be improved, or the viscosity of the solder paste can be adjusted. Examples of the above-mentioned organic solvents 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.

[0166] 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 of the solder paste can be improved, and gaps are less likely to occur in the connection part of the resulting connection structure.

[0167] <Binder resin> By using the above-mentioned binder resin, the handling properties of the solder paste can be improved, and the viscosity of the solder paste can be adjusted. The above-mentioned binder resin is not particularly limited. Known insulating resins can be used as the above-mentioned binder resin. Examples of the above-mentioned binder resins include vinyl resins, thermoplastic resins, curable resins, thermoplastic block copolymers, and elastomers. Only one type of the above-mentioned binder resin may be used, or two or more types may be used in combination.

[0168] 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.

[0169] A conventionally known dispersion method can be used to disperse the gap material and solder particles in the binder resin. Examples of methods for dispersing the gap material and solder particles in the binder resin include the following: A method in which the gap material and solder particles are added to the binder resin and then mixed and dispersed using a planetary mixer or the like. A method in which the gap material and solder particles are uniformly dispersed in water or an organic solvent using a homogenizer or the like, then added to the binder resin and mixed and dispersed using a planetary mixer or the like. A method in which the binder resin is diluted with water or an organic solvent, then the gap material and solder particles are added and mixed and dispersed using a planetary mixer or the like.

[0170] When the above solder paste contains the above binder resin, the content of the binder resin in 100% by weight of the solder paste is preferably 40% by weight or more, more preferably 50% by weight or more, even more preferably 55% by weight or more, particularly preferably 60% by weight or more, preferably 99% by weight or less, and more preferably 95% by weight or less. When the content of the binder resin is above the lower limit and below the upper limit, the handling of the solder paste can be improved, and when the substrates are electrically connected using the solder paste, gaps are less likely to occur at the connection point.

[0171] When the solder paste contains the binder resin, the binder resin content in 100% by volume of the solder paste is preferably 25% by volume or more, more preferably 40% by volume or more, even more preferably 45% by volume or more, particularly preferably 50% by volume or more, preferably 95% by volume or less, and more preferably 90% by volume or less. When the binder resin content is above the lower limit and below the upper limit, the handling properties of the solder paste can be improved, and when the solder paste is used to electrically connect substrates, gaps are less likely to occur at the connection point.

[0172] When the above solder paste contains the above binder resin, the amount of the binder resin per 100 parts by weight of the solder particles is preferably 40 parts by weight or more, more preferably 50 parts by weight or more, even more preferably 55 parts by weight or more, preferably 99 parts by weight or less, more preferably 95 parts by weight or less, and even more preferably 90 parts by weight or less. When the amount of the binder resin is above the lower limit and below the upper limit, the handling properties of the solder paste can be improved, and when the solder paste is used to electrically connect substrates, gaps are less likely to occur at the connection point.

[0173] <Other ingredients> The solder paste described above may contain various additives as needed, such as flux, fillers, bulking agents, softeners, plasticizers, polymerization catalysts, curing catalysts, colorants, antioxidants, heat stabilizers, light stabilizers, UV absorbers, lubricants, antistatic agents, and flame retardants.

[0174] The solder paste described above preferably contains flux. By using the flux, oxidation of the metal in the solder particles, gap material, and electrodes can be prevented, and foreign matter and oxide films can be removed. Examples of the flux include those described in the section on gap material.

[0175] 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.

[0176] (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 material of the connection portion is the solder paste described above. 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 in the connection portion.

[0177] The connection structure according to the present invention, having the above configuration, can improve the dispersibility of the gap material at the connection portion of the connection structure. Furthermore, the connection structure according to the present invention, having the above configuration, can suppress the peeling of the base material particles and the coating portion in the gap material, thereby improving conductivity reliability. Furthermore, the connection structure according to the present invention, having the above configuration, can suppress the occurrence of cracks at the connection portion, thereby suppressing the occurrence of conductivity failures. Furthermore, the connection structure according to the present invention, having the above configuration, can adequately control the gap between base materials.

[0178] In the above-mentioned connection, it is preferable that the metal on the outer surface of the covering portion (especially the metal layer) of the gap material is diffused with the solder.

[0179] Figure 3 is a cross-sectional view showing an example of a connection structure obtained using the solder paste according to the first embodiment of the present invention. In Figure 3, the gap material 1 is shown schematically for convenience of illustration. Other gap materials such as gap material 1A may be used instead of gap material 1.

[0180] The connection structure 11 shown in Figure 3 comprises a first connection target member 42, a second connection target member 43, and a connection portion 44 connecting the first connection target member 42 and the second connection target member 43. The material of the connection portion 44 is the solder paste described above. The connection portion 44 is formed from the solder paste described above. The solder paste includes a gap material 1 and solder particles. In this embodiment, the gap material 1 has an average particle diameter larger than that of the solder particles. The gap material 1 is used as a spacer. The gap material 1 controls the distance between the first connection target member 42 and the second connection target member 43.

[0181] In the connecting structure 11, the connecting portion 44 has a solder portion 5 formed by the aggregation and joining of multiple solder particles, and a gap material 1. In the above connecting structure, the gap material may be particles derived from the gap material. In the case of particles derived from the gap material, it is preferable that the metal on the outer surface of the coating portion (particularly the metal layer) of the gap material is diffused with the solder in the solder portion.

[0182] In the above-described connection structure, it is preferable that the gap material or particles derived from the gap material are in contact with both the first connection area and the second connection area.

[0183] The first connection target member 42 has a plurality of first connection areas 42a on its surface (upper surface). The second connection target member 43 has a plurality of second connection areas 43a on its surface (lower surface). The first connection areas 42a and the second connection areas 43a are electrically connected by solder joints 5. Therefore, the first connection target member 42 and the second connection target member 43 are electrically connected by solder joints 5.

[0184] As shown in Figure 3, in the connection structure 11, multiple solder particles accumulate between the first connection area 42a and the second connection area 43a. After the multiple solder particles melt, the molten solder particles wet and spread across the surface of the connection area before solidifying, forming the solder portion 5. As a result, the contact area between the solder portion 5 and the first connection area 42a, and between the solder portion 5 and the second connection area 43a, becomes larger. In other words, by using solder particles, the contact area between the solder portion 5 and the first connection area 42a, and between the solder portion 5 and the second connection area 43a, becomes larger compared to the case where conductive particles with a conductive outer surface portion made of metal such as nickel, gold, or copper are used. As a result, the conductivity reliability and connection reliability of the resulting connection structure 11 are improved.

[0185] The method for manufacturing the above-described connection structure is not particularly limited. One example of a method for manufacturing the above-described 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. By heating and pressurizing, the solder particles contained in the solder paste melt, and the connection areas are electrically connected by the solder.

[0186] The pressure for the above pressurization is preferably 9.8 × 10⁻⁶. 4 Pa or higher, preferably 4.9 × 10 6 The pressure is less than or equal to Pa. The heating temperature is preferably 80°C or higher, more preferably 100°C or higher, preferably 300°C or lower, and more preferably 250°C or lower.

[0187] From the viewpoint of more effectively exhibiting the effects of the present invention, the thickness of the connecting portion in the above-mentioned connecting structure is preferably 10 μm or more, more preferably 20 μm or more, preferably 100 μm or less, and more preferably 80 μm or less.

[0188] 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.

[0189] The above-mentioned connection area may be an electrode.

[0190] Examples of electrodes 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 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 connection target member is a glass substrate, the electrodes are preferably aluminum electrodes, copper electrodes, molybdenum electrodes, silver electrodes, or tungsten electrodes. When the electrode is an aluminum electrode, it may be an electrode made of aluminum only, or an electrode 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.

[0191] 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.

[0192] The following materials were prepared.

[0193] (base material particles) Base particle A (indicated as "A" in the table's type column, divinylbenzene copolymer resin particles, manufactured by Sekisui Chemical Co., Ltd. as "Micropearl SP-250", average particle size 50 μm) Base particle B (indicated as "B" in the table's type column; an organic-inorganic hybrid particle having an organic core formed from acrylic resin and an inorganic shell formed from a crosslinked alkoxysilyl polymer; average particle diameter 50 μm; prepared according to Synthesis Example 1 below) Base particle C (indicated as "C" in the table's type column, acrylic copolymer resin particles, manufactured by Sekisui Chemical Co., Ltd. as "Micropearl EZ3P-050", average particle size 50 μm) Base particle D (indicated as "D" in the table's type column, divinylbenzene copolymer resin particles, manufactured by Sekisui Chemical Co., Ltd. as "Micropearl SP-230", average particle size 30 μm) Base particle E (indicated as "E" in the table's type column, divinylbenzene copolymer resin particles, manufactured by Sekisui Chemical Co., Ltd. as "Micropearl SP-240", average particle size 40 μm) Base particle F (indicated as "F" in the table's type column, divinylbenzene copolymer resin particles, manufactured by Sekisui Chemical Co., Ltd. as "Micropearl SP-275", average particle size 75 μm) Base particle G (indicated as "G" in the table's type column; divinylbenzene copolymer resin particles, manufactured by Sekisui Chemical Co., Ltd. as "Micropearl SP-L100"; average particle size 100 μm)

[0194] <Synthesis Example 1> 300 g of 0.13 wt% aqueous ammonia solution was placed in a 500 mL reaction vessel equipped with a stirrer and thermometer. Next, a mixture of 4.1 g of methyltrimethoxysilane, 19.2 g of vinyltrimethoxysilane, and 0.7 g of silicone alkoxy oligomer (Shin-Etsu Chemical Co., Ltd. "X-41-1053") was slowly added to the aqueous ammonia solution in the reaction vessel. After allowing the hydrolysis and condensation reactions to proceed while stirring, 2.4 mL of 25 wt% aqueous ammonia solution was added. Particles were isolated from the aqueous ammonia solution, and the obtained particles were subjected to an oxygen partial pressure of 10. -17 Organic-inorganic hybrid particles were obtained by firing at 350°C for 2 hours.

[0195] (Solder particle-containing paste) Solder particle-containing paste A (indicated as "A" in the table's type column, paste containing SAC particles, manufactured by Senju Metal Industry Co., Ltd., "M705-RGS800", specific gravity 7.4, SAC particle size 20 μm, SAC particle melting point 210°C) Solder particle-containing paste B (indicated as "B" in the table's type column, paste containing Sn-Bi particles, manufactured by Nippon Superior Co., Ltd., "TempSave B58 P610 D4", specific gravity 8.7, Sn-Bi particle size 20 μm, Sn-Bi particle melting point 139°C)

[0196] (Example 1) (1) Fabrication of gap material 10 parts by weight of the above-mentioned base material particles A were dispersed in 100 parts by weight of an alkaline solution containing 5% by weight of palladium catalyst solution using an ultrasonic disperser, and then the base material particles A were extracted by filtering the solution. Next, base material particles A were added to 100 parts by weight of a 1% by weight solution of dimethylamine borane to activate the surface of base material particles A. After thoroughly washing the activated base material particles A with water, they were added to 500 parts by weight of distilled water and dispersed to obtain suspension A.

[0197] In addition, a nickel plating solution (pH 9.0) containing 0.25 mol / L nickel sulfate, 0.25 mol / L sodium hypophosphite, and 0.15 mol / L sodium citrate was prepared.

[0198] The obtained suspension A was stirred at 70°C, and the nickel plating solution was gradually added dropwise to suspension A to perform electroless nickel plating. The dropping rate of the nickel plating solution was 30 mL / min, and the dropping time was 30 minutes. After that, the suspension was filtered to remove the particles, which were washed with water and dried to obtain a gap material in which a nickel layer (200 nm thick) was placed on the surface of the substrate particles A.

[0199] (2) Preparation of solder paste 2.0 parts by weight of the obtained gap material and 98.0 parts by weight of solder particle-containing paste A (paste containing SAC particles, "M705-RGS800" manufactured by Senju Metal Industry Co., Ltd., specific gravity 7.4, particle size of SAC particles 20 μm, melting point of SAC particles 210°C) were mixed and stirred using a planetary stirrer at 1200 rpm, 120 seconds, and 0.2 kPa to obtain solder paste.

[0200] (3) Fabrication of connecting structures A copper plate (approximately square with sides of 10.0 mm and a height of 0.1 mm) was prepared as the first component to be connected. A silicon chip (approximately square with sides of 2.0 mm and a height of 0.1 mm) was prepared as the second component to be connected. Using a metal mask with dimensions of 2.5 mm (length), 2.5 mm (width), and 60 μm (height), the obtained solder paste was screen printed onto the first component to be connected. After printing, the second component to be connected was laminated to obtain a laminate. The obtained laminate was reflow-treated at an average heating temperature of 1.2 °C / sec and a peak temperature of 240 °C to obtain a connected structure.

[0201] (Examples 2-12 and Comparative Example 2) A gap material, solder paste, and connecting structure were obtained in the same manner as in Example 1, except that the configuration of the gap material was set as shown in the table below.

[0202] (Example 13) (1) Fabrication of gap material Fabrication of the first metal layer: Coated particles were obtained in which a first metal layer (nickel layer, 180 nm thick) was placed on the surface of a base particle A.

[0203] Formation of the second metal layer: Ten parts by weight of the obtained coated particles were dispersed in 500 parts by weight of deionized water using an ultrasonic device to obtain suspension B. A tin plating solution (1) (adjusted to pH 8.5 with sodium hydroxide) containing 15 g / L of tin sulfate, 70 g / L of ethylenediaminetetraacetic acid, 30 g / L of sodium gluconate, and 1.5 g / L of phosphinic acid was prepared. A reducing solution A (adjusted to pH 10.0 with sodium hydroxide) containing 5 g / L of sodium borohydride was also prepared.

[0204] The obtained suspension B was stirred at 55°C, and the tin plating solution (1) was gradually added to the suspension B. Electroless tin plating was then performed by reducing the suspension with reducing solution A, forming a second metal layer. A gap material was obtained in which the second metal layer (tin layer, 140 nm thick) was positioned on the surface of the first metal layer.

[0205] (2) Preparation of solder paste and (3) Preparation of connecting structures The solder paste and connecting structure were prepared in the same manner as in Example 1, except that the obtained gap material was used.

[0206] (Example 14) As an electroless copper plating solution, a mixture containing 100 g / L of copper sulfate, 75 g / L of disodium ethylenediaminetetraacetate, 50 g / L of sodium gluconate, and 50 g / L of formaldehyde was prepared by adjusting the pH to 10.5 with ammonia.

[0207] The suspension A obtained in Example 1 was heated to 50°C, and the copper plating solution was gradually added dropwise to perform electroless copper plating. The copper plating solution was added at a rate of 30 mL / min for 30 minutes. After that, the suspension was filtered to remove the particles, which were then washed with water and dried to obtain a gap material in which a copper layer (260 nm thick) was placed on the surface of the substrate particles A. Solder paste and connecting structures were prepared in the same manner as in Example 1, except that the obtained gap material was used.

[0208] (Comparative Example 1) (1) Fabrication of gap material Fabrication of the first metal layer: Coated particles were obtained in which a first metal layer (nickel layer, thickness 220 nm) was placed on the surface of a base particle A.

[0209] Formation of the second metal layer: Ten parts by weight of the obtained coated particles were dispersed in 500 parts by weight of deionized water using an ultrasonic device to obtain suspension C. A tin plating solution (1) (adjusted to pH 8.5 with sodium hydroxide) containing 15 g / L of tin sulfate, 70 g / L of ethylenediaminetetraacetic acid, 30 g / L of sodium gluconate, and 1.5 g / L of phosphinic acid was prepared. In addition, a reducing solution A (adjusted to pH 10.0 with sodium hydroxide) containing 5 g / L of sodium borohydride was prepared.

[0210] The obtained suspension C was stirred at 55°C, and the tin plating solution (1) was gradually added to the suspension C. Electroless tin plating was then performed by reducing the suspension with reducing solution A, forming a second metal layer. A gap material was obtained in which the second metal layer (tin layer, 220 nm thick) was positioned on the surface of the first metal layer.

[0211] (2) Preparation of solder paste and (3) Preparation of connecting structures The solder paste and connecting structure were prepared in the same manner as in Example 1, except that the obtained gap material was used.

[0212] (Comparative Example 3) (1) Fabrication of gap material Fabrication of the first metal layer: Coated particles were obtained in which a first metal layer (nickel layer, 500 nm thick) was placed on the surface of a base particle C.

[0213] Formation of the second metal layer: Ten parts by weight of the obtained coated particles were dispersed in 500 parts by weight of deionized water using an ultrasonic device to obtain suspension D. A tin plating solution (1) (adjusted to pH 8.5 with sodium hydroxide) containing 15 g / L of tin sulfate, 70 g / L of ethylenediaminetetraacetic acid, 30 g / L of sodium gluconate, and 1.5 g / L of phosphinic acid was prepared. A reducing solution A (adjusted to pH 10.0 with sodium hydroxide) containing 5 g / L of sodium borohydride was also prepared.

[0214] The obtained suspension D was stirred at 55°C, and the tin plating solution (1) was gradually added to the suspension D. Electroless tin plating was then performed by reducing the suspension D with reducing solution A, forming a second metal layer. A gap material was obtained in which the second metal layer (tin layer, 15 nm thick) was positioned on the surface of the first metal layer.

[0215] (2) Preparation of solder paste and (3) Preparation of connecting structures The solder paste and connecting structure were prepared in the same manner as in Example 1, except that the obtained gap material was used.

[0216] (Examples 15-17 and Comparative Example 4) Examples 15-17 and Comparative Example 4 were modified only from Examples 2, 4, 12, or Comparative Example 1 as follows.

[0217] Example 15: The process was the same as in Example 2, except that solder particle-containing paste A was changed to solder particle-containing paste B in the preparation of the solder paste.

[0218] Example 16: The process for preparing the solder paste was the same as in Example 4, except that solder particle-containing paste A was changed to solder particle-containing paste B.

[0219] Example 17: The process for preparing the solder paste was the same as in Example 12, except that solder particle-containing paste A was changed to solder particle-containing paste B.

[0220] Comparative Example 4: The same as Comparative Example 1, except that the gap material configuration was set as shown in the table below, and solder particle-containing paste A was changed to solder particle-containing paste B in the preparation of the solder paste.

[0221] (evaluation) (1) Particle size (average particle size) and CV value of particle size of gap material For the obtained gap material, the particle size of approximately 100,000 gap material particles was measured using a particle size distribution analyzer (Beckman Coulter's "Multisizer 4"), and the average value was calculated. In addition, the coefficient of variation (CV value) of the particle size of the gap material was determined using the method described above.

[0222] (2) Specific gravity of gap material The specific gravity of the obtained gap material was measured using a hydrometer (Shimadzu Corporation's "AccuPic 1330").

[0223] (3) Amount of outgassing when heated at 250°C for 10 minutes The amount of outgassing generated in the obtained gap material was measured when it was heated at 250°C for 10 minutes using the method described above.

[0224] (4) Viscosity at 25°C The viscosity (η25) of the obtained solder paste at 25°C was measured using an E-type viscometer (manufactured by Toki Sangyo Co., Ltd.) under the conditions of 25°C and 5 rpm.

[0225] (5) Thickness T and ratio (thickness T / particle size of gap material) The resulting solder paste is screen printed at 25°C over a 1cm square area on the surface of a substrate (made of glass). 2A solder paste layer was formed by applying the gap material to the above solder paste to a thickness equal to the particle size of the gap material particles. The above solder paste layer was heated in a reflow oven at a rate of 3°C / second to 160°C and preheated for 60 seconds, then heated at a rate of 3°C / second to 240°C and heated for 45 seconds. After heating, the temperature was lowered at a rate of 4°C / second to 100°C, removed from the reflow oven, and left to cool at room temperature until it reached 25°C. The thickness (thickness T) of the portion of the solder paste layer where the above gap material was not present after cooling was measured using a metal laser microscope (Keyence "VX-X3000"). The ratio (thickness T / particle size of gap material) was calculated by dividing the thickness by the particle size (average particle size) of the above gap material.

[0226] (6) Dispersibility of gap material The obtained connection structure was placed in a Kulzer "Technobit 4000" and cured to create an embedded resin body for gap material inspection. An ion milling device (Hitachi High-Technologies Corporation "IM4000") was used to cut out a cross-section of the connection structure, passing through the vicinity of the center of the connected structure within the inspection embedded resin body.

[0227] Then, using a field emission scanning electron microscope (FE-SEM), the cross-section of the obtained connection structure was observed, and the dispersion state of the gap material was confirmed by measuring the number of locations where the gap material was aggregated in the vertical direction (between the connected members) of the connection structure. The dispersion of the gap material at the connection part of the connection structure was determined according to the following criteria.

[0228] [Criteria for determining the dispersibility of gap fillers] ○○○: There are 0 locations where gap material is aggregated in the vertical direction of the connecting structure. ○○: There are 1 to 4 locations where gap material is aggregated in the vertical direction of the connecting structure. ○: There are 5 to 19 locations where gap material is aggregated in the vertical direction of the connecting structure. ×: There are 20 or more locations where the gap material is aggregated in the vertical direction of the connecting structure.

[0229] (7) Suppression of peeling between the base material particles and the coating in the gap material. (6) In the same manner as the dispersibility of the gap material, cross-sections of the connecting structures were cut out, and using a field emission transmission electron microscope (FE-TEM) (JEM-ARM200F, manufactured by JEOL Ltd.), the image magnification was set to 10,000x, and 100 gap materials were randomly selected to observe the interface between the substrate particles and the coating in the gap material. The number of particles (detached particles) with fractures or voids having a length of 1 / 2 or more of the circumference of the substrate particle when the substrate particle is considered to be a circle was measured at the interface between the substrate particles and the coating. The ability of the gap material to suppress delamination between the substrate particles and the coating was judged according to the following criteria.

[0230] [Criteria for determining the effectiveness of suppressing delamination between base material particles and coating in gap fillers] ○○: 9 or fewer detached particles ○: 10 to 39 detached particles ×: More than 40 detached particles

[0231] (8) Suppression of crack occurrence at connection points (6) In the same manner as the dispersibility of the gap material, a cross-section of the connecting structure was cut out, and the cross-section of the connecting portion of the connecting structure was observed using a field emission scanning electron microscope (FE-SEM) (Hitachi High-Tech Corporation "S-8200") with the image magnification set to 10,000x. The presence or absence of cracks (small cracks) that exceeded the average particle diameter of the gap material and had a length of less than 1 / 2 the thickness of the connecting portion, and cracks (large cracks) that exceeded the average particle diameter of the gap material and had a length of 1 / 2 or more the thickness of the connecting portion was checked in the cross-section of the connecting portion. The ability to suppress crack occurrence at the connecting portion was judged according to the following criteria.

[0232] [Criteria for determining the effectiveness of crack prevention at connection points] ○○: No small or large cracks have occurred. ○: Small cracks have occurred, but no large cracks have occurred. ×: Large cracks have occurred.

[0233] The configurations and results of the gap materials are shown in Tables 1 to 5 below.

[0234]

Table 1

[0235]

Table 2

[0236]

Table 3

[0237]

Table 4

[0238]

Table 5

Explanation of Signs

[0239] 1, 1A… Gap material 2… Substrate particles 3, 3A… Coated part 3AA… First metal layer 3AB… Second metal layer 5… Solder part 11… Connection structure 42… First connection target member 42a… First connection area part 43… Second connection target member 43a… Second connection area part 44… Connection part 101… Solder paste layer after heating 101A… Gap material

Claims

1. This is a solder paste containing solder particles and a gap material. The gap material comprises base material particles and a coating portion disposed on the surface of the base material particles, The specific gravity of the gap material is 1.50 or less. A solder paste in which the ratio of the thickness T to the particle size of the gap material is 0.60 or more and 1.20 or less. Thickness T: The thickness of the portion of the solder paste layer where the gap material is not present after heating, when the solder paste is applied to form a solder paste layer with the same thickness as the particle size of the gap material in the solder paste, and the solder paste layer is heated at 240°C for 45 seconds.

2. The solder paste according to claim 1, wherein the coefficient of variation of the particle size of the gap material is 6.0% or less.

3. The solder paste according to claim 1, wherein the covering portion of the gap material has a metal layer.

4. The solder paste according to claim 3, wherein the metal layer does not contain tin, indium, silver, lead, bismuth, and copper.

5. The solder paste according to claim 3, wherein the metal layer contains nickel.

6. The solder paste according to any one of claims 1 to 5, wherein the thickness of the covering portion in the gap material is 0.01 μm or more and 1.0 μm or less.

7. The solder paste according to any one of claims 1 to 5, wherein the base material particles in the gap material are resin particles or organic-inorganic hybrid particles.

8. The solder paste according to any one of claims 1 to 5, wherein the surface of the gap material is not treated for rust prevention.

9. The solder paste according to any one of claims 1 to 5, wherein the particle size of the gap material is 3.0 μm or more and 150 μm or less.

10. The solder paste according to any one of claims 1 to 5, wherein the amount of outgassing when the gap material is heated at 250°C for 10 minutes is 1000 ppm or less.

11. A solder paste according to any one of claims 1 to 5, comprising an organic solvent or a binder resin.

12. 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, The device comprises a connecting portion that connects the first member to be connected and the second member to be connected, The material of the connecting portion is the solder paste according to any one of claims 1 to 5. A connection structure in which the first connection area and the second connection area are electrically connected by a solder portion in the connection area.

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