Solder alloy, solder paste, joining part, joining structure, and electronic control device

Abstract

This solder alloy, even when Bi is added, has heat cycle resistance and drop impact resistance, and can form a joining part that suppresses lift-off. The solder alloy comprises 35 mass% to 65 mass% of Bi, 0.1 mass% to 0.65 mass% of Sb, 0.05 mass% to 2 mass% of Ag, and 0.001 mass% to 0.1 mass% of at least one of Ni and Co, with the remainder consisting of Sn and inevitable impurities.

Description

Solder alloy, solder paste, joint, joint structure and electronic control device

[0001] The present invention relates to a solder alloy, a solder paste, a joint, a joint structure, and an electronic control device.

[0002] Solder alloys are one type of joining material used to join materials to be joined (e.g., printed wiring boards and electronic components). Bi is sometimes added to solder alloys to adjust their melting temperature. However, because Bi is hard and brittle, it reduces the ductility of the solder alloy.

[0003] Therefore, for example, the following solder alloys have been provided as Bi-containing solder alloys with improved ductility.

[0004] A solder alloy characterized by having an alloy composition consisting, in mass%, of 35 to 68% Bi, 0.1 to 2.0% Sb, 0.01 to 0.1% Ni, and the balance Sn (Patent Document 1).

[0005] A lead-free solder alloy containing 32% by mass or more and 40% by mass or less of Bi, 0.1% by mass or more and 1.0% by mass or less of Sb, 0.1% by mass or more and 1.0% by mass or less of Cu, 0.001% by mass or more and 0.1% by mass or less of Ni, and the remainder being Sn and unavoidable impurities (Patent Document 2).

[0006] A SnBiSb-based low-temperature lead-free solder is characterized in that the lead-free solder is composed, by mass percentage, of 32.8-56.5% Bi, 0.7-2.2% Sb, and the remainder Sn, and the mass percentages of Bi and Sb satisfy the relational expression b = 0.006a2 - 0.672a + 19.61 + c, where a represents the mass percentage of Bi and b represents the mass percentage of Sb, and the value range of c is -1.85≦c≦1.85, and further contains, by mass percentage, one or more metal elements of 0.01-2.5%, 0.05-2.0%, 0.5-0.8% Ag, and 0.05-1% In (Patent Document 3).

[0007] Patent No. 6477965 Patent No. 6804126 Patent No. 6951438

[0008] In an environment where heat cycles are repeated, fractures (cracks) due to thermal fatigue are likely to occur in the joints included in the joint structure (which in this specification refers to a structure in which multiple joined materials are joined via joints) in electronic devices. Furthermore, because joints formed with solder alloys containing Bi tend to be brittle, the cracks are likely to propagate rapidly within the joints.

[0009] Furthermore, when an electronic device is dropped or otherwise hits a floor, desk, wall, or the like, a strong, instantaneous, and concentrated external force, i.e., an impact force, acts on the joined materials and the joint. Joints that cannot fully absorb the impact energy generated by the impact force are damaged. Therefore, in order to prevent damage to joints due to impact force, it is necessary to improve the strength and ductility of the solder alloy in a balanced manner. However, since the ductility of joints formed with solder alloys containing Bi tends to be low, joints are easily damaged by impact force.

[0010] Furthermore, the through-hole mounting method is used to bond electronic components with terminals to printed wiring boards. This method involves inserting the terminals of the electronic components into through-holes in the printed wiring board and bonding the two together. In this bonding method, the molten solder hardens from the through-hole toward the printed wiring board upon cooling, forming a fillet that connects the terminal of the electronic component in the through-hole to the land (electrode) on the printed wiring board. Residual stress in the bond tends to concentrate on the land side. This residual stress, along with the thermal contraction of the printed wiring board in the vertical direction, can cause the bond to peel off from the land (this phenomenon is hereinafter referred to as "lift-off"). Lift-off is particularly likely to occur when bonding using solder alloys containing Bi.

[0011] Patent Documents 1 to 3 do not disclose or suggest a solder alloy that has resistance to the above-mentioned cracks (hereinafter referred to in this specification as "heat cycle resistance") and resistance to impact force (hereinafter referred to in this specification as "drop impact resistance") and that can suppress the occurrence of lift-off.

[0012] The object of the present invention is to solve the above-mentioned problems and to provide a solder alloy and solder paste containing Bi that have good heat cycle resistance and drop impact resistance and can form a joint that can suppress the occurrence of lift-off.

[0013] (1) The solder alloy of the present invention contains 35% by mass or more and 65% by mass or less of Bi, 0.1% by mass or more and 0.65% by mass or less of Sb, 0.05% by mass or more and 2% by mass or less of Ag, and 0.001% by mass or more and 0.1% by mass or less of Ni and / or Co, with the remainder being Sn and unavoidable impurities.

[0014] (2) The solder alloy of the present invention preferably further contains at least one element selected from the group consisting of P, Ga, and Ge in a total amount of 0.001% by mass to 0.05% by mass.

[0015] (3) The solder alloy of the present invention preferably further contains one or more elements selected from the group consisting of Mn, Ti, Al, Cr, V, Fe, Mg, Pd, Pb, and Mo in a total amount of 0.001% by mass or more and 0.05% by mass or less.

[0016] (4) A bonding material of the present invention includes the solder alloy according to any one of (1) to (3) above.

[0017] (5) The solder paste of the present invention comprises a powder of the solder alloy according to any one of (1) to (3) above, and a flux containing a base resin, a thixotropic agent, an activator, and a solvent.

[0018] (6) The joint of the present invention is formed from the solder alloy according to any one of (1) to (3) above.

[0019] (7) The joint of the present invention is formed from the joint material described in (4) above.

[0020] (8) The joint of the present invention is formed from the solder paste described in (5) above.

[0021] (9) The joined structure of the present invention has a first joined material, a joining portion, and a second joined material, and the joining portion is a joining portion described in any one of (6) to (8) above, and the first joined material and the second joined material are joined via the joining portion.

[0022] (10) An electronic control device of the present invention has the joint structure described in (9) above.

[0023] The solder alloy and solder paste of the present invention have good heat cycle resistance and drop impact resistance even when Bi is added, and can form a joint that can suppress the occurrence of lift-off.

[0024] (1) A plan view showing the shape of a test piece used in a tensile test.

[0025] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[0026] 1. Solder Alloy The solder alloy of this embodiment contains 35% by mass or more and 65% by mass or less of Bi, 0.1% by mass or more and 0.65% by mass or less of Sb, 0.05% by mass or more and 2% by mass or less of Ag, and 0.001% by mass or more and 0.1% by mass or less of at least one of Ni and Co, with the remainder being Sn and inevitable impurities.

[0027] The occurrence of the cracks described above is primarily due to shear stresses that repeatedly occur at the joint due to differences in the linear expansion coefficients between the joined materials and between the joined materials and the joint. Specifically, shear stresses cause dislocations to move in the slip direction at the joint surface. This dislocation movement causes plastic deformation (slip deformation) at the joint, resulting in cracks at the joint surface. Furthermore, shear stresses concentrate at the tip of the crack, causing dislocations to move along the grain boundaries (grain boundary sliding), propagating the crack. Furthermore, with the recent improvement in the performance and increased processing speed of electronic devices, the number of times electronic components within them operate is increasing. As a result, the joint is subjected to rapid and frequent temperature changes (heat cycles), which can lead to the occurrence of cracks within a short period of time.

[0028] On the other hand, the solder alloy of this embodiment contains a predetermined amount of Sn, Bi, Sb, Ag, Ni and / or Co, which can improve the strength of the joint without impairing the ductility of the joint formed, thereby suppressing the occurrence and propagation of the above-mentioned cracks.

[0029] That is, a portion of the joint formed with the solder alloy of this embodiment has a crystalline structure in which Bi and Sb atoms are embedded in Sn crystals. This crystalline structure suppresses dislocation movement due to the shear stress, improving the strength of the joint. As a result, plastic deformation of the joint is suppressed, thereby suppressing the occurrence of cracks. Furthermore, fine Sn—Sb, Sn—Ag, Sn—Ni, and / or Sn—Co intermetallic compounds precipitate in the joint during solidification. These fine intermetallic compounds improve the strength of the joint and suppress the occurrence of grain boundary sliding within the joint. As a result, even if cracks occur in the joint due to the shear stress, their propagation can be suppressed. Furthermore, because the joint formed with the solder alloy of this embodiment has the above-mentioned functions, the occurrence and propagation of cracks can be suppressed even when the joint is subjected to short-term and frequent temperature changes.

[0030] Furthermore, as described above, the solder alloy of this embodiment can improve the strength of the joint without impairing the ductility of the joint. Therefore, the joint can suppress damage to the joint caused by the impact force described above. That is, in order to suppress the occurrence of the cracks and the propagation of the cracks that have occurred, it is essential that dislocations are less likely to move within the joint. On the other hand, joints where dislocations are less likely to move are more likely to break because they absorb less impact energy generated by the impact force. Furthermore, the impact force acts on the joint from multiple directions (at least two of tension, compression, shear, bending, and torsion). Therefore, in order to prevent damage to the joint caused by the impact energy associated with the impact force, it is important that the joint have not only strength but also sufficient ductility. As described above, the solder alloy of this embodiment contains a predetermined amount of Sn, Bi, Sb, Ag, Ni, and / or Co, which allows the formation of the above-mentioned crystal structure in the joint without impairing the ductility of the joint, and also allows the precipitation of the above-mentioned intermetallic compounds, thereby achieving both strength and ductility of the joint. As a result, the solder alloy of this embodiment can provide a joint that has good resistance to the above-mentioned impact force, i.e., good drop impact resistance.

[0031] Furthermore, the solder alloy of this embodiment can alleviate the residual stress that occurs within the joint when the solder solidifies, and can suppress the occurrence of cracks within the joint caused by the residual stress and the occurrence of the above-mentioned lift-off.

[0032] (1) Bi The solder alloy of this embodiment contains 35% by mass or more and 65% by mass or less of Bi, which allows for solid-solution strengthening of the joint due to the solid solution of Bi in Sn without impairing the ductility of the joint, thereby providing a joint with a good balance of strength and ductility.

[0033] On the other hand, if the Bi content is outside the above range, the strength and ductility of the joint may decrease.

[0034] The Bi content is preferably 35% by mass or more and 60% by mass or less. Furthermore, the Bi content is more preferably 40% by mass or more and 59% by mass or less. The Bi content can be preferably 50% by mass or more, or 54% by mass or more, and can also be 58% by mass or less, 56.5% by mass or less, or 56% by mass or less. By setting the Bi content within this range, the heat cycle resistance and drop impact resistance of the joint can be further improved.

[0035] (2) Sb The solder alloy of this embodiment contains 0.1 mass % or more and 0.65 mass % or less of Sb. This allows for solid solution strengthening of the joint due to the dissolution of Sb into Sn without impairing the ductility of the joint. Furthermore, by precipitating and dispersing fine β-SnSb intermetallic compounds within the joint, the joint can be strengthened and its ductility improved. As a result, the joint can achieve both strength and ductility.

[0036] On the other hand, if the Sb content is less than 0.1 mass%, the joint may not be sufficiently strengthened, and if the Sb content exceeds 0.65 mass%, coarse β-SnSb intermetallic compounds are crystallized as primary crystals, which may impair the ductility of the joint.

[0037] The Sb content is preferably 0.2 mass% or more and 0.65 mass% or less. Furthermore, the Sb content is more preferably 0.3 mass% or more and 0.65 mass% or less, or 0.4 mass% or more and 0.65 mass% or less. The upper limit of Sb can also be set to 0.6 mass% or less. By setting the Sb content within this range, the ductility and strength of the joint can be further improved.

[0038] (3) Ag The solder alloy of this embodiment contains 0.05 mass % to 2 mass % of Ag. This allows fine Ag particles to be formed in the joint. ３ The precipitation and dispersion of Sn intermetallic compounds can strengthen the joint and improve the ductility of the joint, thereby achieving both strength and ductility at the joint.

[0039] On the other hand, if the Ag content is less than 0.05 mass %, there is a risk that precipitation strengthening of the joint will be insufficient. ３ The Sn intermetallic compounds become coarse, which may impair the ductility of the joint.

[0040] The Ag content is preferably 0.1% by mass or more and 1.5% by mass or less. The Ag content can be preferably 1% by mass or less, 0.8% by mass or less, or 0.5% by mass or less. Furthermore, the Ag content is more preferably 0.2% by mass or more and 0.4% by mass or less. By setting the Ag content within this range, the ductility and strength of the joint can be further improved.

[0041] (4) Ni / Co The solder alloy of this embodiment contains at least one of Ni and Co in an amount of 0.001% by mass or more and 0.1% by mass or less. This allows for the refinement of intermetallic compounds precipitated at the interface between the joint and the joined materials, thereby improving the strength near the interface, without impairing the ductility of the joint. Meanwhile, the crack propagation (grain boundary sliding) is likely to occur near the interface between the joint and the joined materials. Therefore, in order to suppress crack propagation near this interface, it is essential to improve the strength near the interface. On the other hand, the impact force also tends to concentrate at the interface, and in order to suppress damage near this interface, it is essential to have high ductility near the interface. Generally, there is a trade-off between the strength and ductility of a joint. However, as described above, the solder alloy of this embodiment contains at least one of Ni and Co and predetermined amounts of Sn, Bi, Sb, and Ag, thereby improving the strength near the interface without impairing ductility. As a result, the joint can simultaneously suppress crack propagation near the interface and damage due to the impact force.

[0042] When only Ni is added to the solder alloy of this embodiment, the preferred content is 0.001% by mass or more and 0.1% by mass or less. The Ni content can also be 0.07% by mass or less. A more preferred Ni content is 0.01% by mass or more and 0.06% by mass or less. The Ni content can also be 0.02% by mass or more, 0.03% by mass or more, or 0.04% by mass or more. By setting the Ni content within this range, the heat cycle resistance of the joint can be further improved without impairing ductility.

[0043] When only Co is added to the solder alloy of this embodiment, the Co content is preferably 0.001% by mass or more and 0.1% by mass or less. The Co content can also be 0.07% by mass or less. The Co content is more preferably 0.01% by mass or more and 0.06% by mass or less. The Co content can also be 0.02% by mass or more, 0.03% by mass or more, or 0.04% by mass or more.

[0044] When Ni and Co are added to the solder alloy of this embodiment, the total content is preferably 0.001% by mass or more and 0.1% by mass or less. The total content may also be 0.07% by mass or less. The more preferred total content is 0.01% by mass or more and 0.06% by mass or less. The total content may also be 0.02% by mass or more, 0.03% by mass or more, or 0.04% by mass or more.

[0045] If the content of at least one of Ni and Co exceeds 0.1 mass %, there is a risk that needle-like substances are likely to be generated in the solder alloy during the manufacturing process of the solder alloy. Here, when a solder alloy containing needle-like substances is powdered into spherical shapes, the presence of these needle-like substances may hinder the powdering, making it difficult to powder into spherical shapes.

[0046] The solder alloy of this embodiment may further contain one or more elements selected from the group consisting of P, Ga, and Ge in a total content of 0.001% by mass to 0.05% by mass. Adding one or more elements selected from the group consisting of P, Ga, and Ge to the solder alloy suppresses oxidation of the solder alloy and improves the wettability of the solder alloy, thereby providing a highly reliable joint. On the other hand, if the total content of one or more elements selected from the group consisting of P, Ga, and Ge exceeds 0.05% by mass, voids may occur in the joint, which may deteriorate the heat cycle resistance of the joint.

[0047] The solder alloy of this embodiment may further contain 0.001% by mass or more and 0.05% by mass or less of one or more elements selected from the group consisting of Mn, Ti, Al, Cr, V, Fe, Mg, Pd, Pb, and Mo. By adding one or more elements selected from the group consisting of Mn, Ti, Al, Cr, V, Fe, Mg, Pd, Pb, and Mo to the solder alloy, the intermetallic compounds in the joint are further refined, thereby suppressing crack propagation and achieving good heat cycle resistance. On the other hand, if the total content of one or more elements selected from Mn, Ti, Al, Cr, V, Fe, Mg, Pd, Pb, and Mo exceeds 0.05% by mass, voids may occur in the joint, which may deteriorate the heat cycle resistance. Furthermore, when Fe is added to the solder alloy of this embodiment, if the Fe content exceeds 0.05 mass %, there is a risk that needle-like substances will be easily generated in the solder alloy during the manufacturing process of the solder alloy. As described above, when a solder alloy containing needle-like substances is powdered into spherical shapes, the presence of these needle-like substances inhibits the powdering, making it difficult to powder into spherical shapes.

[0048] The balance of the solder alloy of this embodiment is Sn and unavoidable impurities, that is, the solder alloy of this embodiment may contain alloying elements other than the above-mentioned alloying elements as unavoidable impurities.

[0049] 2. Bonding Material The bonding material of this embodiment contains the solder alloy of this embodiment and can be used in the form of a solder paste, solder ball, wire, solder preform, flux-cored solder, etc., as described below. The form of the bonding material can be appropriately selected depending on the size, type, and application of the materials to be bonded, the solder bonding method, etc. Furthermore, by containing the solder alloy of this embodiment, the bonding material of this embodiment can form a bonded portion that has heat cycle resistance and drop impact resistance and suppresses the occurrence of lift-off.

[0050] 3. Solder Paste The solder paste of this embodiment contains the solder alloy of this embodiment in powder form (hereinafter referred to as "alloy powder"), and is produced, for example, by kneading the alloy powder with flux to form a paste.

[0051] <Flux> The flux may contain, for example, a base resin, a thixotropic agent, an activator, and a solvent.

[0052] Examples of the base resin include rosin resins, acrylic resins obtained by polymerizing at least one monomer such as acrylic acid, methacrylic acid, various esters of acrylic acid, various esters of methacrylic acid, crotonic acid, itaconic acid, maleic acid, maleic anhydride, esters of maleic acid, esters of maleic anhydride, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl chloride, and vinyl acetate, epoxy resins, and phenolic resins. These may be used alone or in combination.

[0053] Examples of the thixotropic agent include hydrogenated castor oil, hydrogenated castor oil, bisamide-based thixotropic agents (saturated fatty acid bisamide, unsaturated fatty acid bisamide, aromatic bisamide, etc.), oxyfatty acids, dimethyldibenzylidene sorbitol, etc. These can be used alone or in combination.

[0054] Examples of the activator include organic acids (monocarboxylic acids, dicarboxylic acids, and other organic acids), halogen-containing compounds, amine-based activators, etc. These can be used alone or in combination.

[0055] Examples of the solvent include alcohol-based, butyl cellosolve-based, glycol ether-based, and ester-based solvents, which can be used alone or in combination.

[0056] The flux may also contain an antioxidant, such as a hindered phenol antioxidant, a phenol antioxidant, a bisphenol antioxidant, or a polymer antioxidant. The flux may also contain additives such as a matting agent or an antifoaming agent.

[0057] When preparing the solder paste of this embodiment, the blending ratio (mass %) of the alloy powder to the flux can be set to 65:35 to 95:5 in terms of alloy powder:flux ratio. Alternatively, for example, the blending ratio can be set to 85:15 to 93:7 or 87:13 to 92:8.

[0058] The particle size of the alloy powder can be 1 μm or more and 40 μm or less, or 5 μm or more and 35 μm or less, or 10 μm or more and 30 μm or less, and the particle size of the alloy powder can be changed as appropriate.

[0059] Furthermore, the solder paste of this embodiment contains the alloy powder, and thus can form a joint that has heat cycle resistance and drop impact resistance and suppresses the occurrence of lift-off.

[0060] 4. Joint The joint of this embodiment is formed using the solder alloy or joining material of this embodiment (hereinafter, unless otherwise specified, this includes solder paste) and joins materials to be joined. The method for forming the joint of this embodiment may be any method that can be used to form the joint using the solder alloy or joining material of this embodiment, and any method such as a reflow method or a flow method may be used. The form of the joining material to be used may also be selected appropriately depending on the size, type, and application of the materials to be joined, the method for forming the joint, etc.

[0061] 5. Joined Structure The joined structure of this embodiment includes a first joined material, a joining portion, and a second joined material. The joining portion is the joining portion of this embodiment, and the first joined material and the second joined material are joined via the joining portion.

[0062] Examples of the first and second bonded materials that can be used include substrates (those whose surfaces are made of ceramic, metal, alloy, or resin and do not have electronic circuits formed thereon), printed wiring boards (substrates on which electronic circuits are formed but on which electronic components, etc. are not mounted), printed circuit boards (printed wiring boards on which electronic components, etc. are mounted), electronic components, silicon wafers, semiconductor packages, and semiconductor chips. Bonded materials of different types may be combined, or bonded materials of the same type may be combined. Specific combinations include, for example, a printed wiring board and an electronic component, a printed wiring board and a semiconductor chip, a semiconductor package and a printed circuit board, and a printed wiring board and a printed wiring board.

[0063] The bonded structure of this embodiment is fabricated, for example, by the following method. When a printed wiring board is used as the first material to be bonded and an electronic component is used as the second material to be bonded, the bonding material of this embodiment is first placed (or applied in the case of solder paste) at a predetermined position on the first material to be bonded, for example, on an electronic circuit, and the second material to be bonded is then placed on the bonding material. These are then reflowed at a predetermined heating temperature, for example, a peak temperature of 200°C, to form a bonded portion that bonds the first material to be bonded and the second material to be bonded. This completes the fabrication of the bonded structure (printed circuit board) of this embodiment.

[0064] When a solder preform is used as the joining material, the solder preform with flux applied to its surface is placed at a predetermined position on the first material to be joined, and the second material to be joined is placed on the solder preform and heated. When an electronic component with solder balls, such as a Ball Grid Array (BGA), is used as the second material to be joined, solder paste is applied to the surface of the BGA or at a predetermined position on the first material to be joined, and the second material to be joined is placed on the predetermined position on the first material to be joined and heated.

[0065] The bonded structure of this embodiment has the bonded portion of this embodiment, which allows the bonded structure of this embodiment to have heat cycle resistance and drop impact resistance, and is also less susceptible to lift-off, thereby maintaining high reliability.

[0066] 6. Electronic Control Device The electronic control device of this embodiment includes the joint structure of this embodiment, and for example, a printed circuit board, on which an electronic component and a printed wiring board are joined, is placed in a housing, and controls the operation of components that make up an electronic device. The electronic control device of this embodiment also includes the joint structure of this embodiment. As a result, the electronic control device of this embodiment has heat cycle resistance and drop impact resistance, is less likely to lift off, and can maintain high reliability.

[0067] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0068]

[0069]

[0070]

[0071] (1) Tensile Test For each of the solder alloys shown in Tables 1 to 3, a test piece 10 as shown in FIG. 1 was prepared. The test piece 10 was prepared so that the central parallel portion (between G1 and G2 in FIG. 1) had the following dimensions: Length of central parallel portion (L in FIG. 1): 12 mm Width of central parallel portion (W in FIG. 1): 2 mm Thickness of central parallel portion: 4 mm

[0072] Then, a tensile test was performed on the test piece 10 according to the following procedure. The test piece 10 was pulled in the X direction at room temperature with a stroke of 0.72 mm / min using a bench-top precision universal testing machine (product name: Autograph AG-50kNX plus, manufactured by Shimadzu Corporation) until it broke. The stroke distance at which the test piece 10 broke was designated GL1, and the length L of the central parallel part of the test piece before pulling was designated GL0. The elongation of the test piece 10 was calculated based on the following formula: Elongation (%) = (GL1 - GL0) / GL0 × 100 Five test pieces 10 were prepared for each type of solder alloy, and the elongation and the average elongation were calculated for each according to the above procedure, and evaluated based on the following criteria. The results are shown in Tables 4 to 6. ◎: The average elongation is 35% or more. ○: The average elongation is 30% or more and less than 35%. △: The average elongation is 25% or more and less than 30%. ×: The average elongation is less than 25%.

[0073] (2) Drop Impact Test Each solder paste was prepared by kneading a flux containing the following components with a solder alloy powder (powder particle size 20 μm to 38 μm) shown in Tables 1 to 3 at the following blending ratios (mass %). The solder alloy powder was prepared by atomization. Solder alloy powder: flux = 89:11 <Flux composition> Hydrogenated acid-modified rosin (product name: KE-604, manufactured by Arakawa Chemical Industries, Ltd.): 49% by mass; Activator (glutaric acid: 0.3% by mass, suberic acid: 2% by mass, malonic acid: 0.5% by mass, dodecanedioic acid: 2% by mass, dibromobutenediol: 2% by mass); Fatty acid amide (product name: Slipax ZHH, manufactured by Nippon Kasei Chemical Industries, Ltd.): 6% by mass; Diethylene glycol monohexyl ether: 35.2% by mass; Hindered phenol-based antioxidant (product name: Irganox 245, manufactured by BASF Japan Ltd.): 3% by mass.

[0074] The following tools were also prepared: LGA (Land Grid Array, pitch width: 0.5 mm, size: 12 mm long x 12 mm wide x 1 mm thick, number of terminals: 228 pins) Glass epoxy board (base material: FR-4, surface treatment: Cu-OSP, thickness: 1.0 mm, with a pattern on which the LGA can be mounted) Metal mask (thickness: 100 μm, corresponding to the pattern) For each solder paste, five of the glass epoxy boards and 20 LGAs were used. Then, using the above tools and each solder paste, test boards were fabricated according to the following procedure, and a drop impact test was performed.

[0075] First, solder paste was printed onto a glass epoxy substrate using a metal mask. Four LGAs were then placed on each glass epoxy substrate at predetermined positions on the printed solder paste. The thickness of the printed solder paste was adjusted using the metal mask. The glass epoxy substrate with the LGA placed on it was then reflowed using a reflow furnace (product name: TNV-M6110CR, manufactured by Tamura Corporation) to produce a test substrate comprising the LGA, glass epoxy substrate, and a joint for joining them. The reflow process consisted of a preheating period of 100°C to 120°C, a peak temperature of 200°C, a time of 60 seconds above 150°C, and a cooling rate of 1°C to 4°C / sec from the peak temperature to 100°C. The oxygen concentration was set to 200±100 ppm.

[0076] Next, the prepared test substrates were subjected to a drop impact test using a drop impact tester (product name: HDST-150J, Shinyei Technology Co., Ltd.) under the following conditions. Specifically, in accordance with JEDEC standard JESD22-B111, the test substrates were repeatedly free-dropped from a height at which an impact waveform with an acceleration of 1,500 G and a width of 0.5 ms was applied. During the drop impact test, the electrical resistance of each joint of the test substrate was constantly observed. Breakage was determined when the resistance value exceeded 1,000 Ω, and the number of drops until breakage was measured. Five test substrates were prepared for each type of solder paste, and the above measurement results were plotted as a Weibull plot for a total of 20 LGAs. The number of drops at which the cumulative failure rate reached 63.2% was estimated as the characteristic life, and the test substrates were evaluated according to the following criteria. The results are shown in Tables 4 to 6. ◎: Characteristic life is 110 times or more. ○: Characteristic life is 90 times or more but less than 110 times. △: Characteristic life is 70 times or more but less than 90 times. ×: Characteristic life is less than 70 times.

[0077] (3) Heat cycle test The following tools were prepared: Chip components (3.2 mm x 1.6 mm) Glass epoxy substrate (base material: FR-4, surface treatment: Cu-OSP, thickness: 1.2 mm, with a pattern on which the above chip components can be mounted) Metal mask (thickness: 120 μm, corresponding to the above pattern) For each solder paste, three of the above glass epoxy substrates and 30 chip components were used. Then, using the above tools and each solder paste, each test substrate was produced according to the following procedure, and a heat cycle test was performed.

[0078] First, solder paste was printed onto a glass epoxy substrate using a metal mask. Ten chip components were then placed on each glass epoxy substrate at predetermined positions on the printed solder paste. The thickness of the printed solder paste was adjusted using the metal mask. The glass epoxy substrates with the chip components were then reflowed using a reflow furnace (product name: TNV-M6110CR, manufactured by Tamura Corporation) to produce three mounting substrates each containing chip components, a glass epoxy substrate, and a joint for bonding them. The reflow process consisted of a preheating period of 100°C to 120°C, a peak temperature of 200°C, a time of 60 seconds above 150°C, and a cooling rate of 1°C to 4°C / sec from the peak temperature to 100°C. The oxygen concentration was set to 200±100 ppm.

[0079] Next, using a thermal shock testing device (product name: ES-76LMS, manufactured by Hitachi Appliances, Inc.), each mounting board was subjected to a thermal shock cycle as follows, with one cycle consisting of -40°C (30 minutes) to 125°C (30 minutes), to produce test boards a to c: a: Test board exposed to an environment in which the above thermal shock cycle was repeated 2,250 times b: Test board exposed to an environment in which the above thermal shock cycle was repeated 2,500 times c: Test board exposed to an environment in which the above thermal shock cycle was repeated 2,750 times

[0080] The target portion of each test substrate a to c was cut out and sealed using epoxy resin (product name: HERZOG Epo low viscosity resin (base and curing agent), manufactured by Herzog Japan Co., Ltd.). A wet polishing machine (product name: TegraPol-25, manufactured by Marumoto Struers Co., Ltd.) was then used to create a state where the central cross section of each chip component mounted on each test substrate could be seen. A scanning electron microscope (product name: TM-1000, manufactured by Hitachi High-Technologies Corporation) was then used to observe the condition of each joint on each test substrate a to c, confirming the presence or absence of cracks that completely crossed the joint, and evaluating the results according to the following criteria. The results are shown in Tables 4 to 6. ◎: In all test substrates a to c, no cracks occurred that completely crossed the joint. ○: In test substrates a and b, no cracks occurred that completely crossed the joint (in test substrate c, cracks occurred that completely crossed the joint). △: In test substrate a, no cracks occurred that completely crossed the joint (in test substrates b and c, cracks occurred that completely crossed the joint). ×: In all test substrates a to c, cracks occurred that completely crossed the joint.

[0081] (4) Lift-off Occurrence Confirmation Test The following tools were prepared: Connector part (product name: S15B-EH(LF)(SN), manufactured by JST Mfg. Co., Ltd.) Glass epoxy board (base material: FR-4, surface treatment: Cu-OSP, size: 50 mm x 50 mm, thickness: 1.6 mm, with 1.6 diameter lands and 1.0 mm diameter through holes at 2.5 mm pitch) 200 μm thick metal mask with 3 mm diameter opening pattern at 5 mm pitch Then, using the above tools and each solder paste, each test board was fabricated according to the following procedure, and a lift-off occurrence confirmation test was performed.

[0082] First, solder paste was printed on a glass epoxy substrate using a metal mask. Then, the terminals of the connector components were inserted into the designated through-holes provided in the glass epoxy substrate, and reflow was performed using a reflow oven (product name: TNP-538EM, manufactured by Tamura Corporation) to produce a test substrate having a solder joint (fillet) joining the connector components to the glass epoxy substrate. The reflow was performed under the same conditions as in (2) Drop Impact Test.

[0083] Next, the target portion of each test board was cut out and sealed with epoxy resin (product name: Epomount (main agent and curing agent), manufactured by Refine Tech Co., Ltd.). Furthermore, a wet polishing machine (product name: TegraPol-25, manufactured by Marumoto Struers Co., Ltd.) was used to make the central cross section of the terminal of each connector component mounted on each test board visible, and the test boards were observed with a scanning electron microscope (product name: TM-1000, manufactured by Hitachi High-Technologies Corporation) and evaluated according to the following criteria. The number of terminals evaluated was eight. The results are shown in Tables 4 to 6. ○: No lift-off occurred ×: Lift-off occurred

[0084] (5) Test for Confirmation of Needle-Shaped Material Generation Solder ingots were prepared from each solder alloy. Then, solder alloy powder was prepared for each solder ingot under the following conditions. First, 50 g of solder ingot, 890 g of castor oil, and 10 g of hydrogenated acid-modified rosin (product name: KE-604, manufactured by Arakawa Chemical Industries, Ltd.) were placed in a 2 L stainless steel beaker. This was then continuously heated using a mantle heater. When the temperature of the contents in the stainless steel beaker reached 100°C, a homogenizer (manufactured by SMT Corporation) was used, and the rotation speed was set to 2,000 rpm to begin stirring the contents in the stainless steel beaker. Heating using the mantle heater continued during stirring. When the temperature of the contents in the stainless steel beaker reached 200°C, heating was stopped, the homogenizer rotation speed was changed to 10,000 rpm, and the contents in the stainless steel beaker were then stirred for 5 minutes. After stirring, the contents of the stainless steel beaker were cooled to room temperature. The solder alloy powder that had settled in the castor oil was removed from the stainless steel beaker and washed with ethyl acetate to remove any deposits. The state of the solder alloy powder was then observed at 200x magnification using a digital microscope. The observation results were evaluated based on the following criteria. The results are shown in Tables 4 to 6. ○: No acicular matter was observed in the solder alloy powder. ×: Acicular matter was observed in the solder alloy powder.

[0085]

[0086]

[0087]

[0088] As described above, the solder alloy of this embodiment contains a predetermined amount of Bi, Ag, Sb, Ni, or Co and Sn, or Bi, Ag, Sb, Ni, Co and Sn, so that even when Bi is added, it is possible to form a joint that shows good results in any of the above (1) to (4). Furthermore, the solder alloy of this embodiment can suppress the generation of needle-like substances even when at least one of Ni and Co is added. Furthermore, the solder alloy of this embodiment can improve the strength near the interface between the joint and the joined material without impairing the ductility of the joint, so that it can suppress the progression of cracks even when subjected to high-frequency heat cycles, and can provide a joint with good drop impact resistance. Here, the strain rate when a car collides with an object is 10 －３ (s －１ ) to 10 ３ (s －１ ) In addition, (1) in the tensile test, a test piece with a GL0 of 12 mm is pulled at a stroke of 0.72 mm / min, which, when converted to a strain rate, is 10 ―３ (s －１ ) As described above, it is clear that the solder alloy of this example can form a joint having good resistance, i.e., good strength and ductility, even when a load equivalent to the strain rate when an automobile collides with an object is applied.

[0089] Thus, the solder alloy of this example, even with the addition of Bi, has heat cycle resistance and drop impact resistance, and can form a joint that can suppress the occurrence of lift-off. Furthermore, electronic control devices and electronic equipment having such a joint can exhibit high reliability.

[0090] 10 Test piece

Claims

1. A solder alloy containing 35% by mass or more and 65% by mass or less of Bi, 0.1% by mass or more and 0.65% by mass or less of Sb, 0.05% by mass or more and 2% by mass or less of Ag, and 0.001% by mass or more and 0.1% by mass or less of at least one of Ni and Co, with the remainder being Sn and unavoidable impurities.

2. The solder alloy according to claim 1, further comprising at least one element selected from the group consisting of P, Ga and Ge in a total amount of 0.001% by mass or more and 0.05% by mass or less.

3. The solder alloy according to claim 1 or 2, further comprising one or more elements selected from the group consisting of Mn, Ti, Al, Cr, V, Fe, Mg, Pd, Pb and Mo in a total amount of 0.001% by mass or more and 0.05% by mass or less.

4. A solder paste comprising: the solder alloy according to any one of claims 1 to 3 in powder form; and a flux containing a base resin, a thixotropic agent, an activator, and a solvent.

5. A joint formed from the solder alloy according to any one of claims 1 to 3.

6. A joint formed with the solder paste according to claim 4.

7. A joined structure comprising a first material to be joined, a joining portion, and a second material to be joined, the joining portion being the joining portion as defined in claim 5 or claim 6, and the first material to be joined and the second material to be joined being joined via the joining portion.

8. An electronic control device having the joint structure according to claim 7.

Images