Solder paste

Abstract

To provide a solder paste capable of sufficiently preventing void formation and ensuring sufficient bonding strength in a high-temperature operation region.SOLUTION: A solder paste is prepared by mixing a metal particle and a flux, wherein the metal particle comprises a mother phase containing Sn, an Sn-Cu alloy, and Sb, Bi, or Ga; in the mother phase, intermetallic compound crystals containing Sn, Cu, Ni, Sb, Ge, Si, and Ti are present; and the composition of the metal particle is 0.7 to 25 mass% of Cu, 0.1 to 5 mass% of Ni, 0 to 14 mass% of Sb, Bi, or Ga, 0.001 to 0.2 mass% of Ge, 0.001 to 0.1 mass% of Si, 0.001 to 0.2 mass% of Ti, and the balance being Sn.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to solder paste.

Background Art

[0002] Solder paste is a material obtained by mixing solder alloy powder and flux. Generally, the flux has the performance of removing metal oxides present on the metal surface of the object to be joined and improving the wetting spreadability of the solder, thereby forming an intermetallic compound at the interface between the solder and the object to be joined, and enabling good joining strength to be imparted between the two.

[0003] As conventional technologies of solder paste, for example, Patent Documents 1 and 2 below can be cited.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, conventional solder paste has a problem in that, for example, voids of 10% or more are generated in the obtained joint layer, and sufficient joint strength cannot be obtained in the high-temperature operating region. Therefore, an object of the present invention is to provide a solder paste that can sufficiently suppress the generation of voids and obtain sufficient joint strength in the high-temperature operating region.

Means for Solving the Problems

[0006] As a result of intensive studies, the present inventors have found that a solder paste using specific metal particles and a flux having a specific composition can solve the above problems, and have completed the present invention.

[0007] That is, the present invention provides a solder paste containing the following metal particles and the following flux. Metal particles: having a matrix phase containing at least Sn and a Sn-Cu alloy, and having an intermetallic compound crystal containing at least Sn and Cu, wherein the proportion of the intermetallic compound crystal accounts for 1 to 40% by mass in the metal particles. Flux: a flux containing rosin-based resin at 50% by mass or less, solvent at 30 to 70% by mass, activator at 15% by mass or less, antioxidant at 1% by mass or less, and thixotropic agent at 10% by mass or less. Further, the present invention provides a solder paste containing the following metal particles and the following flux. Metal particles: having an intermetallic compound crystal containing Sn, Cu, Ni, Sb, Ge, Si, and Ti in a matrix phase containing Sn, a Sn-Cu alloy, and Sb, Bi, or Ga, wherein the composition of the metal particles is Cu 0.7 to 25% by mass, Ni 0.1 to 5% by mass, Sb, Bi, or Ga 0.0 to 14% by mass, Ge 0.001 to 0.2% by mass, Si 0.001 to 0.1% by mass, Ti 0.001 to 0.2% by mass, and the balance being Sn. Flux: a flux containing rosin-based resin at 50% by mass or less, solvent at 30 to 70% by mass, activator at 15% by mass or less, antioxidant at 1% by mass or less, and thixotropic agent at 10% by mass or less.

Effects of the Invention

[0008] According to the present invention, it is possible to provide a solder paste that sufficiently suppresses the generation of voids and obtains sufficient bonding strength in a high-temperature operating region.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0010] Hereinafter, the present invention will be described in more detail. First, the terminology in this specification is as follows, even if not particularly explained. (1) When referring to a metal, it may include not only a single metal element but also an alloy containing a plurality of metal elements and an intermetallic compound. (2) When referring to a single metal element, it does not mean only a substance composed entirely and purely of that metal element, but also includes cases where a trace amount of other substances is included. That is, it is of course not meant to exclude those containing trace amounts of impurities that hardly affect the properties of the metal element. For example, in the case of a matrix phase, it is not meant to exclude those in which some of the atoms in the crystal of Sn are replaced by other elements (for example, Cu). For example, the other substance or other element may be contained in the metal particles in an amount of 0 to 0.1% by mass. (3) Endotaxial bonding means that an intermetallic compound precipitates in a substance that becomes a metal or alloy (matrix phase in the present invention), and during this precipitation, the Sn-Cu alloy and the intermetallic compound are joined at the crystal lattice level to form crystal grains. The term endotaxial is well known and is described, for example, in the last paragraph of the left column on page 160 of Nature Chemisry 3(2): 160-6, 2011.

[0011] First, the metal particles used in the present invention (hereinafter sometimes referred to as the metal particles of the present invention) will be described.

[0012] The metal particles of the present invention have a matrix phase containing at least Sn and Sn-Cu alloy, and an intermetallic compound crystal containing at least Sn and Cu, and the proportion of the intermetallic compound crystal occupies 1 to 40% by mass in the metal particles. In a preferred embodiment of the present invention, the metal particles have an intermetallic compound crystal containing Sn, Cu, Ni, Sb, Ge, Si and Ti in a matrix phase containing Sn, Sn-Cu alloy, and Sb, Bi or Ga, and the proportion of the intermetallic compound crystal occupies 1 to 40% by mass in the metal particles, and the composition of the metal particles is Cu 0.7 to 25% by mass, Ni 0.1 to 5% by mass, Sb, Bi or Ga 0.0 to 14% by mass (preferably 0.1 to 14% by mass), Ge 0.001 to 0.2% by mass, Si 0.001 to 0.1% by mass, Ti 0.001 to 0.2% by mass, and the balance is Sn.

[0013] The metal particles of the present invention can be produced from a raw material having a composition such as Cu 8 to 15% by mass, Sb, Bi or Ga 1 to 5% by mass, Ni 0.1 to 0.5% by mass, Ge 0.001% by mass, Si 0.001% by mass, Ti 0.001% by mass, and the balance being Sn. For example, the raw material is melted, supplied onto a dish-shaped disk rotating at high speed in a nitrogen gas atmosphere, the molten metal is scattered as droplets by centrifugal force, and cooled and solidified under reduced pressure.

[0014] An example of a manufacturing apparatus suitable for manufacturing the metal particles of the present invention will be described with reference to FIG. 1. The granulation chamber 1 has a cylindrical upper part and a conical lower part, and has a lid 2 at the upper part. A nozzle 3 is vertically inserted into the center of the lid 2, and a dish-shaped rotating disk 4 is provided directly below the nozzle 3. Reference numeral 5 is a mechanism for supporting the dish-shaped rotating disk 4 so as to be movable up and down. A discharge pipe 6 for the generated particles is connected to the lower end of the conical portion of the granulation chamber 1. The upper part of the nozzle 3 is connected to an electric furnace (high-frequency furnace: conventionally, a ceramic crucible was used, but in the present invention, a carbon crucible is used) 7 for melting the metal to be granulated. The atmosphere gas adjusted to a predetermined component in the mixed gas tank 8 is supplied to the inside of the granulation chamber 1 and the upper part of the electric furnace 7 through pipes 9 and 10, respectively. The pressure in the granulation chamber 1 is controlled by a valve 11 and an exhaust device 12, and the pressure in the electric furnace 7 is controlled by a valve 13 and an exhaust device 14, respectively. The molten metal supplied from the nozzle 3 onto the dish-shaped rotating disk 4 is scattered in the form of fine droplets by the centrifugal force of the dish-shaped rotating disk 4 and is cooled under reduced pressure to become solid particles. The generated solid particles are supplied from the discharge pipe 6 to an automatic filter 15 and separated. Reference numeral 16 is a fine particle recovery device.

[0015] The process of cooling and solidifying the molten metal from high-temperature melting is important for forming the metal particles of the present invention. For example, the following conditions can be mentioned. Set the melting temperature of the metal in the melting furnace 7 to 600°C to 900°C, and while maintaining that temperature, supply the molten metal from the nozzle 3 onto the dish-shaped rotating disk 4. As the dish-shaped rotating disk 4, use a dish-shaped disk with an inner diameter of 35 mm and a rotating body thickness of 5 mm, and rotate it at 80,000 to 100,000 revolutions per minute. As the granulation chamber 1, after depressurizing using a vacuum chamber having a performance of depressurizing to about 9×10 -2 Pa, while supplying nitrogen gas at 15 to 50°C, exhaust is simultaneously performed to make the atmospheric pressure in the granulation chamber 1 1×10 -1 Pa or less.

[0016] In addition, the composition of the matrix phase in the metal particles of the present invention is preferably Sn 85 to 99.9% by mass, Cu 5% by mass or less (for example, 0.1 to 4% by mass), Sb, Bi or Ga 0.1 to 14% by mass, and unavoidable impurities 0.1% by mass or less.

[0017] In addition, the composition of the intermetallic compound crystal in the metal particles of the present invention is Sn 50 to 90% by mass, Cu 0.1 to 45% by mass, Ni 0.1 to 6.5% by mass, Sb 0.00 to 2.00% by mass (preferably Sb 1.00 to 2.00% by mass) Ge 0.001 to 0.1% by mass, Si 0.001 to 0.1% by mass, Ti 0.001 to 0.1% by mass, and is preferably as follows. In addition, the proportion of the intermetallic compound in the metal particles of the present invention is, for example, 20 to 60% by mass with respect to the entire metal particles, and preferably 30 to 60% by mass. The intermetallic compound exists included in the matrix phase.

[0018] The composition and proportion of the matrix phase and the intermetallic compound can be satisfied by following the manufacturing conditions of the metal particles.

[0019] It is preferable that at least a part of the matrix phase and the intermetallic compound of the metal particles of the present invention is endoaxially joined. As described above, endoaxial joining means that an intermetallic compound precipitates in a substance that becomes a metal / alloy (the matrix phase in the present invention), and during this precipitation, the Sn-Cu alloy and the intermetallic compound are joined at the crystal lattice level to form crystal grains. By forming endoaxial joining, the problem of the brittleness of the intermetallic compound can be solved, the decrease in mechanical strength due to the change in the crystal structure of Sn can be suppressed, and a joint portion having higher heat resistance, joint strength, and mechanical strength can be provided. The inventors have confirmed that the endoaxial joining of the metal particles is maintained in the joint portion formed using the metal particles of the present invention. The endo-taxial joining of the metal particles of the present invention can be achieved by following the manufacturing conditions of the metal particles.

[0020] In the metal particles of the present invention, when the entire joining surface of the matrix phase and the intermetallic compound crystal is taken as 100%, the endo-taxial joining is preferably 30% or more, and more preferably 60% or more. The ratio of the endo-taxial joining can be calculated, for example, as follows. Take an electron micrograph of the cross-section of the metal particles and randomly sample 50 locations of the joining surface between the Sn-Cu alloy and the intermetallic compound crystal. Subsequently, perform image analysis on the joining surface to examine the extent to which endo-taxial joining as shown in the following examples exists on the sampled joining surface.

[0021] The crystal structure of Sn is tetragonal in the temperature range of about 13°C to about 160°C (note that Sn having a tetragonal crystal structure is called β-Sn). When the temperature is lower than this range, the crystal structure changes to cubic (note that Sn having a cubic crystal structure is called α-Sn). Also, the crystal structure of β-Sn changes to orthorhombic, the high-temperature phase crystal, in the temperature range exceeding about 160°C (note that Sn having an orthorhombic crystal structure is called γ-Sn). And it is generally known that a large volume change occurs particularly during the phase transition between tetragonal β-Sn and cubic α-Sn. The metal particles of the present invention contain high-temperature phase crystals even at about 160°C or lower (for example, even at room temperature). For example, when heating a bonding material containing such metal particles in a bonding process, if the bonding material is brought into a semi-molten state where it is not completely melted and into a state including endothermal bonding between an intermetallic compound and a matrix phase, a state containing high-temperature phase crystals is maintained even in a temperature range of 160°C or lower after cooling. And such high-temperature phase crystals are less likely to undergo a phase transition to tetragonal low-temperature phase crystals β-Sn even when the temperature is lowered to a certain extent. For Sn that does not undergo a phase transition to β-Sn of the tetragonal crystal and remains as Sn, no phase transition to α-Sn occurs, and no large volume change associated with the phase transition to α-Sn due to a decrease in temperature occurs. Therefore, a bonding material containing Sn having high-temperature phase crystals even in a temperature range of 160°C or lower (for example, even at room temperature) has a reduced volume change due to temperature changes compared to other bonding materials containing Sn in their composition (that is, those that do not intentionally contain high-temperature crystal phases even in a temperature range of 160°C or lower). In addition, various metals such as Cu, Ag, Au, and Ni are used for electronic components, and Sn bonds well with these various metals. Therefore, the metal particles of the present invention contain a high-temperature phase crystal phase in a wide temperature range (for example, even at room temperature), and by avoiding the occurrence of tetragonal low-temperature phase β-Sn as much as possible, they have the property of being less likely to cause a large volume change associated with the phase transition from tetragonal β-Sn to cubic α-Sn due to temperature changes, and also bond well with various metals used for electronic components. Thus, they are particularly useful as a bonding material for very fine bonding sites.

[0022] The effect of suppressing the change in the crystal structure of Sn as described above is achieved well by endothermal bonding in the metal particles.

[0023] In addition, in the solder paste of the present invention, Cu or a Cu alloy may be added at a ratio of 40 parts by mass or less with respect to 100 parts by mass of the metal particles of the present invention. Further, other particles such as SnAgCu-based alloy particles, Ni, Ni alloy particles, or a mixture thereof may be added to form a mixture with the metal particles of the present invention. These other particles may be coated with a metal such as Si as needed. For example, when Cu or Ni alloy particles with higher conductivity than Sn are combined with metal particles, a metal bonding layer with good conductivity and suppressed volume change in a relatively wide temperature range can be obtained.

[0024] Next, the flux used in the present invention (hereinafter sometimes referred to as the flux of the present invention) will be described.

[0025] The flux of the present invention contains rosin-based resin at 50% by mass or less, solvent at 30 - 70% by mass, activator at 15% by mass or less, antioxidant at 1% by mass or less, and thixotropic agent at 10% by mass or less, when the total is taken as 100% by mass.

[0026] Examples of the rosin-based resin include unmodified rosins such as gum rosin, wood rosin, and tall oil rosin, and derivatives obtained from the rosin. Examples of the derivatives include purified rosin, hydrogenated rosin, disproportionated rosin, polymerized rosin, acid-modified rosin, phenol-modified rosin, and α,β-unsaturated carboxylic acid-modified products (acrylated rosin, maleated rosin, fumarated rosin, etc.), and purified products, hydrides, and disproportionated products of the polymerized rosin, and purified products, hydrides, and disproportionated products of the α,β-unsaturated carboxylic acid-modified products, etc.

[0027] Among them, from the viewpoint of improving the effects of the present invention, in the flux, as the rosin-based resin, it is preferable that the acid-modified rosin occupies 20 - 30% by mass and the unmodified rosin occupies 15 - 25% by mass.

[0028] Examples of the solvent include alcohol solvents, glycol ether solvents, terpineols, etc. Examples of the alcohol solvents include isopropyl alcohol, 1,2-butanediol, octanediol, trimethylolpropane, isobornyl cyclohexanol, 2-ethyl-1,3-hexanediol, 2,4-diethyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol, 2,5-dimethyl-2,5-hexanediol, 2,5-dimethyl-3-hexyne-2,5-diol, 2,3-dimethyl-2,3-butanediol, 2-methylpentane-2,4-diol, 1,1,1-tris(hydroxymethyl)propane, 2-ethyl-2-hydroxymethyl-1,3-propanediol, 2,2'-oxybis(methylene)bis(2-ethyl-1,3-propanediol), 2,2-bis(hydroxymethyl)-1,3-propanediol, 1,2,6-trihydroxyhexane, 1-ethynyl-1-cyclohexanol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2-amino-2-ethyl-1,3-propanediol, etc. Examples of the glycol ether solvents include tetraethylene glycol, diethylene glycol mono-2-ethylhexyl ether, ethylene glycol monophenyl ether, diethylene glycol monohexyl ether, diethylene glycol dibutyl ether, triethylene glycol monobutyl ether, methylpropylene triglycol, butylpropylene triglycol, triethylene glycol butyl methyl ether, tetraethylene glycol dimethyl ether, etc.

[0029] Among these, from the viewpoint of improving the effects of the present invention, in the solvent, when the total amount of the solvent is 100% by mass, tetraethylene glycol preferably accounts for 25 to 35% by mass, 2-amino-2-ethyl-1,3-propanediol preferably accounts for 30 to 35% by mass, trimethylolpropane preferably accounts for 15 to 25% by mass, and octanediol preferably accounts for 10 to 15% by mass. In the case of this form, as the thixotropic agent, for example, a compound represented by the following formula 1 preferably accounts for 0.5 to 2.5% by mass, and a higher fatty acid amide preferably accounts for 0.1 to 2.5% by mass. Separately from this, from the viewpoint of improving the effects of the present invention, in the solvent, when the total amount of the solvent is 100% by mass, diethylene glycol monohexyl ether preferably accounts for 20 to 40% by mass, and 2-ethyl-1,3-hexanediol preferably accounts for 5 to 10% by mass. In the case of this form, as the thixotropic agent, hydrogenated castor oil preferably accounts for 1% by mass or less, and a higher fatty acid amide preferably accounts for 5 to 9% by mass.

[0030] Examples of the activator include organic acids, organic halogen compounds, organic acid salts, organic amine salts, and the like. These can be used alone or in combination of a plurality.

[0031] Examples of the organic acid include monocarboxylic acids, dicarboxylic acids, and other organic acids. Examples of the monocarboxylic acid include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, capric acid, lauric acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, tuberculostearic acid, arachidic acid, behenic acid, lignoceric acid, glycolic acid, and the like. Examples of the dicarboxylic acid include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, tartaric acid, diglycolic acid, and the like. Examples of the other organic acids include dimer acid, levulinic acid, lactic acid, acrylic acid, benzoic acid, salicylic acid, anisic acid, citric acid, picolinic acid, and the like. Among these, picolinic acid is preferably used for the purpose of obtaining good wettability and heat sag resistance of the solder paste in particular.

[0032] Examples of the organic halogen compound include dibromobutenediol, dibromosuccinic acid, 5-bromobenzoic acid, 5-bromonicotinic acid, 5-bromophthalic acid, 1,3-diphenylguanidine hydrobromide, 2,3-dibromo-2-butene-1,4-diol, and the like.

[0033] Among them, from the viewpoint of improving the effects of the present invention, it is preferable that sebacic acid accounts for 0.5 to 1% by mass, 1,3-diphenylguanidine hydrobromide accounts for 0.1 to 0.5% by mass, and 2,3-dibromo-2-butene-1,4-diol accounts for 0.5 to 1% by mass in the flux.

[0034] Examples of the antioxidant include hindered phenol-based antioxidants and the like.

[0035] As the thixotropic agent, higher fatty acid amide is suitable. The higher fatty acid amide is preferably a higher fatty acid amide having an acid value of 4.0 to 6.0 mg / KOH and an amine value of 4.0 to 6.0 mg / KOH. Specific examples of the higher fatty acid amide include capric acid amide, lauric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, arachidic acid amide, behenic acid amide, lignoceric acid amide, 12-hydroxystearic acid amide, oleic acid amide, erucic acid amide, ricinoleic acid amide, and the like. The higher fatty acid amide in the present invention can be a commercially available product, and examples thereof include VA-750B manufactured by Kyoeisha Chemical Co., Ltd. In addition, thixotropic agents other than higher fatty acid amides can also be used as necessary, and examples thereof include wax-based thixotropic agents. Examples of the wax-based thixotropic agent include hydrogenated castor oil and the like. In addition, the compound represented by the following formula 1 (Gelol MD manufactured by Shin Nippon Rika Co., Ltd.) can also be used.

[0036] [Chemical formula]

[0037] Among them, from the viewpoint of improving the effects of the present invention, it is preferable that the compound represented by the following formula (1) occupies 0.5 to 2.5% by mass and the higher fatty acid amide occupies 0.1 to 2.5% by mass in the flux.

[0038] Further, it is preferable that the flux of the present invention contains bromine and chlorine at 900 ppm or less respectively and the total is 1000 ppm or less.

[0039] When the total of the solder paste of the present invention is 100% by mass, it preferably contains 70 to 92% by mass of the metal particles of the present invention and 30 to 8% by mass of the flux of the present invention.

[0040] A mounting substrate on which an electronic component is mounted using the solder paste of the present invention is produced, for example, by forming electrodes and a solder resist film at predetermined positions on the substrate, printing the solder paste using a mask having a predetermined pattern, mounting an electronic component conforming to the pattern at a predetermined position, and reflowing this. The mounting substrate produced in this way has a solder joint formed on the electrode, and the solder joint electrically joins the electrode and the electronic component. Further, flux residues are attached to the substrate. The flux residues have good insulation resistance. For example, when the insulation resistance between the electrodes is measured in accordance with JIS Z 3197 under the conditions of 85°C and 85% R.H. (relative humidity) for the flux residues, the insulation resistance value after 30 hours of voltage application is 1.0×10 10 Ω or more.

Examples

[0041] Hereinafter, the present invention will be further described with reference to examples, but the present invention is not limited to the following examples.

[0042] Example 1 A raw material with a composition consisting of 15% by mass of Cu, 5% by mass of Sb, 0.1% by mass of Ni, 0.001% by mass of Ge, 0.001% by mass of Si, 0.001% by mass of Ti, and the balance being Sn was used, and the metal particles 1 of the present invention with a diameter of about 3 to 13 μm were produced by the production apparatus shown in FIG. 1. The SEM image of the cross section of the metal particles 1 is shown in FIG. 2. At that time, the following conditions were adopted. A melting crucible was installed in the melting furnace 7, the above raw material was put into it, melted at 850 ° C., and while maintaining the temperature, the molten metal was supplied from the nozzle 3 onto the dish-shaped rotating disk 4. As the dish-shaped rotating disk 4, a dish-shaped disk with a diameter of 35 mm and a rotating disk thickness of 5 to 3 mm was used, and the rotation speed was 80,000 to 100,000 revolutions per minute. As the granulation chamber 1, after depressurizing using a vacuum chamber having a performance of depressurizing to about 9 × 10 -2 Pa, while supplying nitrogen gas at 15 to 50 ° C. and exhausting simultaneously, the atmospheric pressure in the granulation chamber 1 was set to 1 × 10 -1 Pa or less.

[0043] When the obtained metal particles 1 were subjected to elemental mapping analysis by EDS of the cross section as shown in FIG. 3, Cu 20.5% by mass, Sb 3.96% by mass, Ni 0.22% by mass, Ge 0.17% by mass, Si 0.001% by mass, Ti 0.12% by mass, It was found that the balance was Sn.

[0044] Also, the composition of the intermetallic compound crystal is Sn 55.97% by mass, Cu 40.73% by mass, Ni 0.52% by mass, Sb 1.31% by mass, Ge 0.002% by mass, Si 0.001% by mass, Ti 0.001% by mass, and the intermetallic compound in the metal particles 1 accounted for 30 to 35% by mass in the metal particles.

[0045] Flux A was prepared with the following composition. Rosin resin: Acid-modified rosin (Pink Crystal KE-604 manufactured by Arakawa Chemical Industries, Ltd.) 27.00 parts by mass Unmodified rosin (Pink Crystal KR-612 manufactured by Arakawa Chemical Industries, Ltd.) 20.00 parts by mass Solvent: HeDG (diethylene glycol monohexyl ether) 25.30 parts by mass 2-Ethyl-1,3-hexanediol 6.70 parts by mass Hexyl diglycol 11.00 parts by mass Activator: Sebacic acid 1.00 part by mass 1,3-Diphenylguanidine hydrobromide 0.30 part by mass 2,3-Dibromo-2-butene-1,4-diol 0.70 part by mass Antioxidant: Hindered phenol-based antioxidant (IRGANOX245) 1.00 part by mass Thixotropic agent: Compound represented by the above formula 1 (Gelol MD manufactured by Shin Nippon Rika Co., Ltd.) 1.00 part by mass Higher fatty acid amide (Talen VA-750B manufactured by Kyoeisha Chemical Co., Ltd.) 6.00 parts by mass

[0046] The metal particles 1 of the present invention and the above Flux A were mixed at 85:15 (mass ratio) to prepare the solder paste 1 of the present invention.

[0047] (Confirmation of void generation situation) 1: Using the solder paste 1, a copper substrate and an Si chip were mounted and joined, and the joint was observed by X-ray to confirm the void ratio. The results are shown in FIG. 4. 2: Using a solder paste obtained by blending the conventional lead solder metal particles (diameter 3 μm to 13 μm) and the above Flux A in the above ratio, the void ratio was confirmed in the same manner as in item 1 above. The results are shown in FIG. 5. 3: Using the solder paste obtained by blending the conventional SAC metal particles (diameter 3 μm to 13 μm) and the flux A in the above ratio, the void ratio was confirmed in the same manner as in Item 1 above. The results are shown in Fig. 6.

[0048] Example 2 In Example 1, the composition of the flux A was changed as shown below, the flux B was prepared, and Example 1 was repeated except that the solder paste 2 was prepared using this flux B. In the solder paste 2 as well, the metal particles 1 and the flux B were mixed at 85:15 (mass ratio).

[0049] The flux B was prepared with the following composition. Rosin resin: Acid-modified rosin (Pink Crystal KE-604 manufactured by Arakawa Chemical Industries, Ltd.) 27.00 parts by mass Unmodified rosin (Pink Crystal KR-612 manufactured by Arakawa Chemical Industries, Ltd.) 20.00 parts by mass Solvent: Tetraethylene glycol 30.00 parts by mass 2-Amino-2-ethyl-1,3-propanediol 34.00 parts by mass Trimethylolpropane 20.00 parts by mass Octanediol 15.00 parts by mass Activator: Sebacic acid 1.00 part by mass 1,3-Diphenylguanidine hydrobromide 0.30 part by mass 2,3-Dibromo-2-butene-1,4-diol 0.70 part by mass Antioxidant: Hindered phenol-based antioxidant (IRGANOX245) 1.00 part by mass Thixotropic agent: Gelol MD 0.50 part by mass Higher fatty acid amide (Talen VA-750B manufactured by Kyoeisha Chemical Co., Ltd.) 0.50 part by mass

[0050] 4: Using solder paste 2, the copper substrate and the Si chip were mounted and joined, the joint was observed by X-ray, and the void ratio was confirmed. The void ratio was 1.53%. 5: Using the solder paste obtained by blending the conventional lead solder metal particles (diameter 3 μm to 13 μm) and the flux B in the above ratio, the void ratio was confirmed in the same manner as in item 4 above. The void ratio was 5.09%. 6: Using the solder paste obtained by blending the conventional SAC metal particles (diameter 3 μm to 13 μm) and the flux B in the above ratio, the void ratio was confirmed in the same manner as in item 4 above. The void ratio was 5.21%.

Explanation of symbols

[0051] 1 Granulation chamber 2 Lid 3 Nozzle 4 Dish-shaped rotating disk 5 Rotating disk support mechanism 6 Particle discharge pipe 7 Electric furnace 8 Mixed gas tank 9 Pipe 10 Pipe 11 Valve 12 Exhaust device 13 Valve 14 Exhaust device 15 Automatic filter 16 Fine particle recovery device

Claims

1. A solder paste containing the following metal particles and the following flux. Metal particles: having a matrix phase containing at least Sn and a Sn-Cu alloy, and intermetallic compound crystals containing at least Sn and Cu, and the proportion of the intermetallic compound crystals accounts for 1 to 40% by mass in the metal particles. Flux: A flux containing rosin-based resin at 50% by mass or less, solvent at 30 to 70% by mass, activator at 15% by mass or less, antioxidant at 1% by mass or less, and thixotropic agent at 10% by mass or less.

2. The solder paste according to claim 1, wherein the thixotropic agent is a higher fatty acid amide.

3. A solder paste containing the following metal particles and the following flux. Metal particles: having intermetallic compound crystals containing Sn, Cu, Ni, Sb, Ge, Si, and Ti in a matrix phase containing Sn, a Sn-Cu alloy, and Sb, Bi, or Ga, and the proportion of the intermetallic compound crystals accounts for 1 to 40% by mass in the metal particles, and the composition of the metal particles is Cu 0.7 to 25% by mass, Ni 0.1 to 5% by mass, Sb, Bi, or Ga 0.0 to 14% by mass, Ge 0.001 to 0.2% by mass, Si 0.001 to 0.1% by mass, Ti 0.001 to 0.2% by mass, and the balance is Sn. Flux: A flux containing rosin-based resin at 50% by mass or less, solvent at 30 to 70% by mass, activator at 15% by mass or less, antioxidant at 1% by mass or less, and thixotropic agent at 10% by mass or less.

4. The solder paste according to claim 3, wherein the thixotropic agent is a higher fatty acid amide.

5. The solder paste according to claim 1 or 3, wherein Cu or a Cu alloy is added in a proportion of 40 parts by mass or less per 100 parts by mass of the metal particles.

6. In the solvent, tetraethylene glycol accounts for 25 to 35% by mass, 2-amino-2-ethyl-1,3-propanediol accounts for 30 to 35% by mass, trimethylolpropane accounts for 15 to 25% by mass, and octanediol accounts for 10 to 15% by mass. In the flux, as the thixotropic agent, the compound represented by the following formula 1 accounts for 0.5 to 2.5% by mass, and the higher fatty acid amide accounts for 0.1 to 2.5% by mass. The solder paste according to claim 1 or 3. 【Chemical 1】

7. In the flux, as the rosin-based resin, acid-modified rosin accounts for 20 to 30% by mass, and unmodified rosin accounts for 15 to 25% by mass. In the solvent, diethylene glycol monohexyl ether accounts for 20 to 40% by mass, and 2-ethyl-1,3-hexanediol accounts for 5 to 10% by mass. In the flux, as the activator, suberic acid accounts for 0.5 to 1% by mass, 1,3-diphenylguanidine hydrobromide accounts for 0.1 to 0.5% by mass, and 2,3-dibromo-2-butene-1,4-diol accounts for 0.5 to 1% by mass. In the flux, as the antioxidant, the hindered phenol-based antioxidant accounts for 1% by mass or less. In the flux, as the thixotropic agent, hydrogenated castor oil accounts for 1% by mass or less, and higher fatty acid amide accounts for 5 to 9% by mass. Bromine and chlorine contained in the flux are each 700 ppm or less and the total is 1000 ppm or less. The solder paste according to claim 1 or 3.

8. The composition of the intermetallic compound crystal is Sn 50 to 90% by mass, Cu 0.1 to 45% by mass, Ni 0.1 to 6.5% by mass, Sb 0.00 to 2.00% by mass Ge 0.001 to 0.1% by mass, Si 0.001 to 0.1% by mass, Ti 0.001 to 0.1% by mass, The solder paste according to claim 3, characterized in that it is as described above.

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