Solder alloy, solder paste, solder ball, solder preform, solder joint, on-vehicle electronic circuit, ECU electronic circuit, on-vehicle electronic circuit device, and ECU electronic circuit device

Abstract

Provided are: a solder alloy having a low melting point, a high shear strength, and a suitable fracture mode; a solder paste; a solder ball; a solder preform; a solder joint; an on-vehicle electronic circuit; an ECU electronic circuit; an on-vehicle electronic circuit device; and an ECU electronic circuit device. This solder alloy has an alloy composition comprising, in terms of mass%, 2.0-3.6% Ag, 1.0-5.0% In, 3.0-5.0% Sb, 0.001-0.030% Fe, and 0.0000-0.0500% Co, inclusive, with the remainder being Sn. Preferably, this alloy composition also contains at least one element from among Zr, Ge, Ga, P, As, Pb, Zn, Mg, Cr, Ti, Mo, Pt, Pd, Au, Al, and Si at a total amount of 0.100% or less in terms of mass%.

Description

Solder alloy, solder paste, solder ball, solder preform, solder joint, on-vehicle electronic circuit, ECU electronic circuit, on-vehicle electronic circuit device, and ECU electronic circuit device

[0001] The present invention relates to a solder alloy, a solder paste, a solder ball, a solder preform, a solder joint, an on-vehicle electronic circuit, an ECU electronic circuit, an on-vehicle electronic circuit device, and an ECU electronic circuit device.

[0002] Automobiles are equipped with electronic circuits (hereinafter referred to as "on-board electronic circuits"), which are made up of electronic components soldered to a printed circuit board. On-board electronic circuits are used in devices that electrically control the engine, power steering, brakes, etc., and are extremely important safety components for the operation of the automobile. In particular, on-board electronic circuits called ECUs (Engine Control Units), which are electronic circuits that control the vehicle via a computer to improve fuel efficiency, must be able to operate stably and without failure for long periods of time. As the mounting area of ​​such on-board electronic circuits has expanded, they are now installed in locations that are subject to various external loads such as shocks and vibrations.

[0003] Since the 1980s, Sn-Ag solder alloys, which are an alternative to Sn-Pb solder alloys, have been considered for use in engine compartments. Sn-Ag solder alloys have long been known as highly versatile solder alloys, as evidenced by the JIS symbol A35 assigned to them. However, Sn-Ag solder alloys are considered to be a basic lead-free solder alloy to replace Sn-Pb solder alloys, and further investigation has been carried out.

[0004] Furthermore, when an Sn-Ag solder alloy is connected to a Cu electrode, Cu hardly dissolves in Sn, so a coarse CuSn intermetallic compound layer is formed at the joint interface by Cu diffused from the electrode and Sn in the solder alloy. ３ The large amount of Sn precipitated in the solder alloy makes the solder alloy brittle, which raises various concerns. Therefore, there is a demand for Sn-Ag solder alloys that do not break solder joints even in harsh operating environments, and various studies have been conducted to address this issue.

[0005] In Patent Document 1, an alloy composition in which Sb, Bi, In, Ag, and Ga are added to a Sn—Co solder alloy is investigated in order to improve the tensile strength of the solder alloy. The solder alloy described in the document contains Co, which allows the formation of fine CoSn or CoSn ２ It has been disclosed that Sn disperses in the Sn matrix and contributes to improving the tensile strength. In addition, the addition of an element such as Sb has been investigated to lower the melting point.

[0006] Patent Document 2 discloses a Sn—Ag—Sb—Ni—Bi—Co solder alloy that suppresses the generation of voids and also suppresses the generation of cracks even after a heat cycle test. This document explains that the absence of Cu reduces the melt viscosity, thereby suppressing the generation of voids. Furthermore, this document also discloses that the inclusion of Ni suppresses excessive diffusion of Cu, even without the inclusion of Cu, thereby suppressing the propagation of cracks.

[0007] JP 6-344180 A JP 2018-1179 A

[0008] As described above, the inventions described in Patent Documents 1 and 2 aim to improve the tensile strength of the solder alloy, suppress the generation of voids, and improve the heat cycle resistance. Patent Document 1 also studies lowering the melting point.

[0009] However, these evaluations alone are insufficient for solder alloys used in automotive electronic circuits. For example, when a vehicle equipped with an electronic circuit drives on rough roads, the electronic circuit is subjected to stress from external impacts and vibrations. For this reason, it is extremely important for solder joints to exhibit high shear strength to prevent fracture.

[0010] Furthermore, even if a solder joint is formed that is resistant to fracture, it will eventually fracture if stress is continuously applied to the solder joint. Such continuous stress is thought to be caused by exposure to environments with extreme temperature differences. This is due to the difference in the thermal expansion coefficients of the electrodes, the intermetallic compounds formed at the joint interface, and the bulk. In this case, the fracture mode, which indicates the location of fracture, should not be at the joint interface. Because the joint interface is connected to the electrode, it is not easy to relieve stress at the joint interface. However, physical and electrical loads are mainly applied to the joint interface of the solder joint. For this reason, it is thought that stress relief in the bulk, which is relatively easily deformed, can prevent fracture.

[0011] However, Patent Documents 1 and 2 do not consider shear strength and fracture modes at all, and it is difficult to say that they reflect the actual situation when using solder joints. Because solder joints electrically connect substrates and electronic components, fracture at the joint interface should be avoided as much as possible.

[0012] As described above, Patent Documents 1 and 2 do not consider shear strength and fracture mode, which are important properties for solder joints. Even if the solder alloy does not contain Cu, a solder alloy that exhibits these properties is desired. However, with the increasing electrification of automobiles in recent years, the number of circuit boards mounted on automobiles is expected to continue to increase, so the development of a solder alloy that exhibits these properties is urgently needed. Furthermore, in consideration of the heat resistance of electronic components, it is also desired that the solder alloy exhibit a melting point comparable to that of conventional solder alloys.

[0013] Therefore, an object of the present invention is to provide a solder alloy, a solder paste, a solder ball, a solder preform, a solder joint, an on-vehicle electronic circuit, an ECU electronic circuit, an on-vehicle electronic circuit device, and an ECU electronic circuit device, which have a low melting point, high shear strength, and an appropriate fracture mode.

[0014] The present inventors have reexamined the solder alloys disclosed in Patent Documents 1 and 2. Among the solder alloys disclosed in both documents, the shear strength of the Sn—Ag—In—Sb—Co—Ga solder alloy in Example 5 of Patent Document 1, the Sn—Ag—In—Sb—Co—Ni—Bi solder alloy in Example 19 of Patent Document 2, and the Sn—Ag—Sb—Co—Fe—Ni—Bi solder alloy in Example 24 of the same document are all comparable to conventional solder alloys, and it has been discovered that there is room for improvement.

[0015] These solder alloys do not have alloy compositions designed for the purpose of improving shear strength. For each solder alloy, if the content of even one of its constituent components differs, the overall properties will usually differ, and it should be understood that the entire combination of alloying elements with a specified content is technically evaluated as a single entity.

[0016] Therefore, the inventors conducted detailed research into the improvement of shear strength and the fracture mode while suppressing the increase in melting point. Patent Document 1 explains that the melting point can be lowered by adding Ag, In, Sb, and Ga to a Sn—Co solder alloy. However, since the melting point varies greatly depending on the content of these elements, the composition described in Example 5 of Patent Document 1 is not necessarily appropriate.

[0017] Furthermore, Patent Document 1 discloses the addition of Co to improve tensile strength. However, no study has been conducted on improving shear strength. Furthermore, if the tensile strength of a solder alloy is increased more than necessary, the fracture mode will be at the joint interface. For this reason, it is presumed that the addition of Co is not desirable in Sn—Ag—In—Sb—Co—Ga solder alloys.

[0018] Patent Document 2 describes that the occurrence of voids can be suppressed if the contents of Ni and Co are within a predetermined range. In light of the description in Patent Document 2, Co can be effective when it coexists with Ni. Therefore, based on the knowledge that the alloy composition in Patent Document 1 had low shear strength and an inappropriate fracture mode, it is presumed that the addition of Ni is also undesirable in Patent Document 2.

[0019] Furthermore, Patent Document 2 explains that thermal shock resistance can be maintained when the Bi content is equal to or less than a predetermined amount. However, Patent Document 2 also explains that Bi dissolves in Sn up to about 3%, so that the tensile strength of the solder alloy increases due to the solid solution strengthening of Sn, and the fracture mode becomes the joint interface.

[0020] Therefore, in view of the above findings, the present inventors focused on the Sn—Ag—In—Sb solder alloy in which Ni, Co, and Bi were excluded from the additive elements to Sn in Patent Documents 1 and 2. Then, in order to improve the shear strength of this solder alloy and ensure that the fracture mode is bulk, the present inventors conducted detailed studies on the selection of additional additive elements and the contents of Ag, In, and Sb.

[0021] First, in order to optimize the fracture mode, it is necessary to suppress the growth of intermetallic compounds at the joint interface in solder alloys that do not contain Cu or Ni. Intermetallic compounds grow due to the diffusion of Cu from the electrode into the solder alloy. Here, the intermetallic compounds are mainly composed of Sn and Cu compounds. Furthermore, if the intermetallic compound layer present at the interface between the solder alloy and the electrode is coarse, the fracture mode is likely to be inappropriate.

[0022] Therefore, focusing on the fact that the interface is modified by the inclusion of Fe, the content of the additive elements in Sn-Ag-In-Sb-Fe solder alloys was investigated in detail. As a result, it was found that only when the content of the additive elements is within a predetermined range, it is possible to improve the shear strength and optimize the fracture mode. The present invention, which was completed based on these findings, is as follows.

[0023] (0) A solder alloy characterized by having, in mass %, an alloy composition consisting of 2.0 to 3.6% Ag, 1.0 to 5.0% In, 3.0 to 5.0% Sb, 0.0010 to 0.0300% Fe, 0.0000% to 0.0500% Co, and the balance being Sn. (1) A solder alloy characterized by having, in mass %, an alloy composition consisting of 2.0 to 3.6% Ag, 1.0 to 5.0% In, 3.0 to 5.0% Sb, 0.0010 to 0.0300% Fe, 0% to 0.050% Co, and the balance being Sn.

[0024] (2) The solder alloy according to (0) or (1) above, wherein the alloy composition (solder alloy) further contains, by mass %, 0.100% or less in total of at least one of Zr, Ge, Ga, P, As, Pb, Zn, Mg, Cr, Ti, Mo, Pt, Pd, Au, Al, and Si.

[0025] (3) A solder alloy according to any one of (0) to (2) above, wherein the alloy composition (solder alloy) satisfies the following formulas (1) and (2): 0.36≦Ag×In×Sb×Fe≦1.19 (1) 47≦(In×Sb) / (Ag×Fe)≦319 (2) In the formulas (1) and (2), Ag, In, Sb, and Fe are each the content in mass % of the solder alloy.

[0026] (4) A solder paste containing solder powder made of the solder alloy according to any one of (0) to (2) above.

[0027] (5) A solder ball made of the solder alloy according to any one of (0) to (2) above.

[0028] (6) A solder preform made of the solder alloy according to any one of (0) to (2) above.

[0029] (7) A soldered joint having the solder alloy according to any one of (0) to (2) above.

[0030] (8) An in-vehicle electronic circuit comprising the solder alloy according to any one of (0) to (2) above.

[0031] (9) An ECU electronic circuit comprising the solder alloy according to any one of (0) to (2) above.

[0032] (10) An on-vehicle electronic circuit device comprising the on-vehicle electronic circuit according to (8) above.

[0033] (11) An ECU electronic circuit device comprising the ECU electronic circuit described in (9) above.

[0034] FIG. 1 shows optical microscope photographs of the samples after measuring the shear strength, where FIG. 1( a) is Example 14, FIG. 1( b) is Example 2, and FIG. 1( c) is Comparative Example 3.

[0035] The present invention will be described in more detail below. In this specification, "%" relating to the solder alloy composition is "% by mass" unless otherwise specified.

[0036] 1. Solder alloy (1) Ag: 2.0-3.6% Ag improves shear strength, ３ The precipitation of Sn contributes to optimizing the fracture mode and lowering the melting point. If the Ag content is less than 2.0%, the amount of compound precipitated is small, resulting in a decrease in shear strength. The lower limit of the Ag content is 2.0% or more, preferably 2.5% or more, more preferably 2.7% or more, and even more preferably 3.0% or more.

[0037] On the other hand, if the Ag content exceeds 3.6%, the Ag content becomes hypereutectic. ３ The large amount of Sn precipitated causes the bulk strength to increase excessively, resulting in the fracture mode occurring at the bonded interface. Furthermore, the fracture mode occurring at the bonded interface results in a decrease in shear strength. The upper limit of the Ag content is 3.6% or less, preferably 3.5% or less, and more preferably 3.4% or less.

[0038] (2) In: 1.0 to 5.0% In contributes to improving shear strength and optimizing the fracture mode. If the In content is less than 1.0%, the wettability is reduced, resulting in insufficient wetting and spreading, and the effect of solid solution strengthening is insufficient, resulting in poor shear strength and an inappropriate fracture mode. The lower limit of the In content is 1.0% or more, preferably 1.5% or more, more preferably 2.0% or more, even more preferably 2.5% or more, and particularly preferably 3.0% or more.

[0039] On the other hand, if the In content exceeds 5.0%, a large amount of compounds are precipitated, raising the melting point. Furthermore, the bulk strength increases, raising the risk of fracture at the bonding interface or at the component. The upper limit of the In content is 5.0% or less, preferably 4.5% or less, more preferably 4.0% or less, and even more preferably 3.5% or less.

[0040] (3) Sb: 3.0 to 5.0% Sb contributes to improving shear strength and optimizing the fracture mode. If the Sb content is less than 3.0%, the solid solution strengthening with Sn and the precipitation strengthening of Sn-Sb compounds are insufficient, resulting in poor shear strength. The lower limit of the Sb content is 3.0% or more, preferably 3.5% or more, more preferably 3.6% or more, even more preferably 3.8% or more, particularly preferably 3.9% or more, and most preferably 4.0% or more.

[0041] On the other hand, if the Sb content exceeds 5.0%, coarse SnSb compounds are formed, resulting in poor shear strength. Furthermore, wettability deteriorates, and the failure mode becomes failure at the bonding interface or at the component, making this unsuitable. The upper limit of the Sb content is 5.0% or less, preferably 4.8% or less, more preferably 4.6% or less, even more preferably 4.5% or less, particularly preferably 4.3% or less, and most preferably 4.1% or less.

[0042] (4) Fe: 0.0010 to 0.0300% Fe contributes to improving shear strength and optimizing the fracture mode. If the Fe content is less than 0.0010%, the effect of strengthening the interface by modifying the intermetallic compound layer formed at the interface is insufficient, resulting in poor shear strength and the fracture mode occurring at the bonded interface, which is not appropriate. The lower limit of the Fe content is 0.0010% or more, preferably 0.0050% or more, more preferably 0.0100% or more, even more preferably 0.0150% or more, and particularly preferably 0.0200% or more.

[0043] On the other hand, if the Fe content exceeds 0.0300%, a compound of Sn and Fe precipitates, which excessively improves the bulk strength, raising concerns about fracture at the bonding interface. The upper limit of the Fe content is 0.0300% or less, preferably 0.0270% or less, and more preferably 0.0250% or less.

[0044] (5) Co: 0.0000% or more and 0.0500% or less. Co is an optional element that contributes to suppressing the rise in melting point, improving shear strength, and optimizing the fracture mode. In conventional solder alloys, it was considered preferable to not include Co in order to improve shear strength and optimize the fracture mode. However, when Co was added, high shear strength was maintained while the fracture mode remained bulk. In Sn-Ag-In-Sb solder alloys, Co is thought to finely disperse CoSn and other elements. However, this does not result in a refinement of the Sn alloy structure. In this alloy system, Fe refines the Sn alloy structure, so it is presumed that the dispersion of fine structures such as CoSn further refines the overall alloy structure. Therefore, in the solder alloy of the present invention, Co can exert a synergistic effect in the presence of Fe.

[0045] Furthermore, since Co is an optional element in the solder alloy according to the present invention, high shear strength and an optimized fracture mode can be maintained even when Co is not contained. The lower limit of the Co content is 0.0000% or more, preferably more than 0.0000%, more preferably 0.0010% or more, even more preferably 0.0030% or more, particularly preferably 0.0060% or more, and most preferably 0.0080% or more.

[0046] On the other hand, if the Co content exceeds 0.0500%, Sn and Co compounds precipitate, causing the bulk strength to increase excessively, resulting in the fracture mode occurring at the bonding interface. Furthermore, the large amount of compound precipitation significantly increases the melting point, worsening wettability and reducing shear strength. The upper limit of the Co content is 0.0500%, preferably 0.0300%, and more preferably 0.0100%.

[0047] (6) Balance: Sn The balance of the solder alloy according to the present invention is Sn. In addition to the above elements, unavoidable impurities may be contained. Even if unavoidable impurities are contained, the above-mentioned effects are not affected. In the present invention, when the Sn—Ag—In—Sb—Fe solder alloy contains Ni, SnNi compounds precipitate. The SnNi compounds precipitate using the intermetallic compounds formed at the interface as nuclei, resulting in a thick intermetallic compound layer formed at the interface. As a result, shear strength decreases. Therefore, in the present invention, it is preferable not to contain Ni. Furthermore, when Bi coexists with In, it forms a Sn—In—Bi low-melting-point phase. Considering creep deformation, the low-melting-point phase has a low melting point that makes a room temperature environment a high-temperature environment, making it prone to creep deformation and resulting in reduced shear strength. For this reason, it is preferable not to contain Bi in the present invention.

[0048] (7) At least one of Zr, Ge, Ga, P, As, Pb, Zn, Mg, Cr, Ti, Mo, Pt, Pd, Au, Al, and Si in a total content of 0.100% or less The solder alloy according to the present invention can contain at least one of Zr, Ge, Ga, P, As, Pb, Zn, Mg, Cr, Ti, Mo, Pt, Pd, Au, Al, and Si in a total content of 0.100% or less as an optional element, to the extent that the effects of the present invention are not impaired. Preferably, the total content is 0.080% or less. The lower limit of the content is not particularly limited, but may be 0.0001% or more, and may be 0.001% or more.

[0049] (8) Formulas (1) and (2): 0.36≦Ag×In×Sb×Fe≦1.19 (1) 47≦(In×Sb) / (Ag×Fe)≦319 (2) In the above formulas (1) and (2), Ag, In, Sb, and Fe are each the content in mass % of the solder alloy.

[0050] Formula (1) takes into consideration the balance of the additive elements of the solder alloy of the present invention. The solder alloy of the present invention can exhibit a low melting point, high shear strength, and appropriate fracture mode due to the synergistic effects of each constituent element. Therefore, if the balance of all constituent elements except Sn is further optimized, all of the effects of the present invention can be further improved. In formula (1), the contents of Ag, In, and Sb are approximately 10 to 100 times the content of Fe. However, their contribution to the solder alloy is considered to be approximately the same. Therefore, in order to further improve the low melting point, high shear strength, and appropriate fracture mode simultaneously in a single composition in the present invention, it is preferable to maintain a balanced content.

[0051] Formula (2) takes into consideration the balance within the group of additive elements In and Sb, which, if exceeded, increase shear strength to the point of component failure, and the balance within the group of Ag and Fe, which are limited to interfacial failure, and further takes into consideration the balance between both groups. When formula (2) is satisfied, the failure mode may become more appropriate depending on the alloy composition.

[0052] The lower limit of formula (1) is preferably 0.36 or more, more preferably 0.39 or more, even more preferably 0.42 or more, still more preferably 0.43 or more, particularly preferably 0.44 or more, and most preferably 0.52 or more, 0.53 or more, 0.60 or more, 0.656 or more, 0.66 or more, 0.70 or more, 0.75 or more, 0.78 or more, 0.79 or more, 0.84 or more, 0.87 or more, 0.88 or more. The upper limit of formula (1) is preferably 1.19 or less, more preferably 1.18 or less, even more preferably 1.09 or less, still more preferably 1.08 or less, particularly preferably 1.05 or less, and most preferably 1.02 or less, 0.91 or less, 0.92 or less, 0.90 or less.

[0053] The lower limit of formula (2) is preferably 47 or more, more preferably 51 or more, even more preferably 57 or more, still more preferably 68 or more, particularly preferably 69 or more, and most preferably 85 or more, 86 or more, 91 or more, 102 or more, 103 or more, 114 or more, 120 or more, 133 or more, 137 or more, 141 or more, 142 or more, 143 or more, 154 or more, or 160 or more. The upper limit of formula (2) is preferably 319 or less, more preferably 286 or less, even more preferably 285 or less, still more preferably 267 or less, particularly preferably 266 or less, and most preferably 257 or less, 240 or less, 229 or less, 228 or less, 213 or less, 206 or less, 205 or less, 200 or less, 192 or less, 183 or less, 182 or less, or 171 or less.

[0054] The calculations for formulas (1) and (2) use the numerical values ​​themselves shown in the measured values ​​of the alloy compositions shown in Tables 1 and 2 below. That is, in the calculations for formulas (1) and (2), all digits less than the number of significant figures in the measured values ​​shown in Tables 1 to 3 below are treated as zeros. For example, if the measured Fe content is "0.0250" by mass, the Fe content used in the calculations for formulas (1) and (2) is treated as "0.025000..." rather than having a range of 0.02505 to 0.02514%. Formula (1) calculates to the third decimal place and rounds off to the second decimal place, while formula (2) calculates to the first decimal place and rounds off to the first decimal place. The same procedure is used when calculating formulas (1) and (2) from alloy compositions specifically disclosed in patent documents and other literature mentioned herein.

[0055] As mentioned above, alloys do not function individually, but rather all the constituent elements form a single entity as a whole. Therefore, it is rare for a single element to simultaneously exhibit all of the excellent effects. Therefore, as mentioned above, in order to achieve even better properties within the optimal content range of each constituent element, it is necessary to consider the constituent elements as a whole. In the solder alloy of the present invention, in order to achieve a high level of low melting point, high shear strength, and appropriate fracture mode all in one composition, it is preferable that formulas (1) and (2) be satisfied.

[0056] In the examples described below, a rating of "◎" indicates that the result is particularly preferable in practical use compared to "◯." Since "◯" indicates a more preferable result than the prior art, if other evaluation results are also excellent, it falls within the scope of the present invention and is treated as an example. Since "×" indicates an insufficient result in the present invention, it falls outside the scope of the present invention and is treated as a comparative example.

[0057] 2. Solder Paste The solder paste according to the present invention is a mixture of solder powder having the above-described alloy composition and flux. The flux used in the present invention is not particularly limited as long as it allows for soldering by conventional methods. Therefore, it is sufficient to use a flux containing a suitable blend of commonly used rosin, organic acid, activator, thixotropic agent, and solvent. The blending ratio of the metal powder component and the flux component in the present invention is not particularly limited, but is preferably 70 to 90 mass% of the metal powder component and 10 to 30 mass% of the flux component.

[0058] 3. Solder Balls The solder alloy according to the present invention can be used as solder balls. When used as solder balls, the solder alloy according to the present invention can be manufactured using a dropping method, which is a common method in the industry. Alternatively, a solder joint can be manufactured by processing the solder balls using a common method in the industry, such as by mounting one solder ball on an electrode coated with flux and joining the solder balls. The particle size of the solder balls is preferably 1 μm or more, more preferably 10 μm or more, even more preferably 20 μm or more, and particularly preferably 30 μm or more. The upper limit of the particle size of the solder balls is preferably 3000 μm or less, more preferably 1000 μm or less, even more preferably 800 μm or less, and particularly preferably 600 μm or less.

[0059] 4. Solder Preform The solder alloy according to the present invention can be used as a preform, which may be in the form of a washer, ring, pellet, disk, ribbon, wire, or the like.

[0060] 5. Solder Joint The solder joint according to the present invention is suitable for use in joining at least two or more members to be joined. The members to be joined are not particularly limited, as long as they are electrically connected using the solder alloy according to the present invention, and include, for example, elements, substrates, electronic components, printed circuit boards, insulating substrates, heat sinks, lead frames, semiconductors using electrode terminals, power modules, inverter products, etc.

[0061] The joining method using the solder alloy of the present invention may be carried out in a conventional manner, for example, using a reflow method. The melting temperature of the solder alloy when performing reflow soldering may be approximately 20°C higher than the liquidus temperature. Furthermore, when joining using the solder alloy of the present invention, taking into consideration the cooling rate during solidification can further refine the alloy structure. For example, the solder joint is cooled at a cooling rate of 2 to 3°C / s or more. Other joining conditions can be adjusted as appropriate depending on the alloy composition of the solder alloy.

[0062] 6. On-board electronic circuits, ECU electronic circuits, on-board electronic circuit devices, ECU electronic circuit devices As is clear from the above explanation, the solder alloy according to the present invention has a suppressed increase in melting point and an appropriate fracture mode. Therefore, even when used in automobiles, i.e., for on-board use, which are exposed to harsh environments, fracture of soldered joints is suppressed with uniformity. Therefore, because it has such particularly outstanding properties, it can be seen that the solder alloy according to the present invention is particularly suitable for soldering electronic circuits mounted on automobiles.

[0063] Thus, the solder alloy according to the present invention is particularly effective when used for soldering on-board electronic circuits or ECU electronic circuits.

[0064] An "electronic circuit" is a system that performs a desired function as a whole through the electronic engineering combination of multiple electronic components, each of which has its own function.

[0065] Examples of electronic components that make up such electronic circuits include chip resistor components, multi-resistor components, QFP, QFN, power transistors, diodes, capacitors, etc. Electronic circuits incorporating these electronic components are mounted on a substrate to form electronic circuit devices.

[0066] In the present invention, the substrate constituting such an electronic circuit device, for example, a printed wiring board, is not particularly limited. The material is also not particularly limited, but examples include heat-resistant plastic substrates (e.g., FR-4, which has a high Tg and low CTE). The printed wiring board is preferably a printed circuit board in which the Cu land surface is treated with an organic substance (OSP: Organic Surface Protection) such as amine or imidazole.

[0067] 7. Others The solder alloy according to the present invention can be manufactured using low alpha dose materials as its raw materials. When such low alpha dose alloys are used to form solder bumps around memory, they can suppress soft errors.

[0068] The present invention will be described with reference to the following examples, but the present invention is not limited to these examples. To demonstrate the effects of the present invention, the solder alloys shown in Tables 1 to 3 were used to evaluate (1) melting point, (2) shear strength, and (3) fracture mode.

[0069] (1) Melting Point For the solder alloys shown in Tables 1 to 3, each temperature was determined from the DSC curve. The DSC curves were obtained by raising the temperature at 5°C / min in the atmosphere using a Seiko Instruments DSC (Model: 6200). The liquidus temperature was determined from the obtained DSC curve and used as the melting point. If the melting point is 232°C or less, reflow soldering can be performed at temperatures similar to conventional ones. If the melting point is above 232°C, conventional reflow soldering cannot be performed due to the high melting point.

[0070] (2) Shear Strength (2-1) Sample Preparation The solder alloys shown in Tables 1 to 3 were cast to prepare solder sheets (diameter: 1 mm, thickness: 0.15 mm). A reflow furnace (SNR-615, manufactured by Senju Metal Industry Co., Ltd.) was used to solder chip resistors to Cu-OSP electrodes on an FR-4 substrate. The chip resistors used were 3216CR (CR32-114JV, manufactured by Hokuriku Electric Industry Co., Ltd.). The reflow profile consisted of holding at 220°C or higher for 40 seconds in a nitrogen atmosphere, with a peak temperature of 245°C. (2-2) Shear Strength Evaluation The shear strength of the samples prepared in this manner was measured using a shear tester (STR-1000, manufactured by RHESCA) at a shear rate of 6 mm / min. A shear strength of 84.0 N or higher was evaluated as "Excellent." When the shear strength was 70.0 N or more and less than 84.0 N, it was evaluated as "Good." When the shear strength was less than 70.0 N, it was evaluated as "Poor."

[0071] (3) Fracture mode The samples evaluated in "(2) Shear strength" above were observed for fracture mode using an optical microscope (VHX-5000: manufactured by KEYENCE Corporation). If the sample fractured in the bulk, it was evaluated as "◎". If the sample fractured in the bulk and in the intermetallic compound (IMC) at the bonding interface, it was evaluated as "◯". If the sample fractured in the intermetallic compound at the bonding interface, it was evaluated as "×". The evaluation results are shown in Tables 1 to 3.

[0072]

[0073]

[0074]

[0075] As shown in Tables 1 and 2, Examples 1 to 110 all had appropriate amounts of each constituent element, and therefore all evaluations yielded results that were acceptable for practical use. Furthermore, Examples 3 to 14, 16, 19, 22, 28 to 31, 37 to 48, 50, 54, 57, 66, 68 to 73, and 77 to 110, which satisfied formulas (1) and (2), were found to exhibit extremely excellent results in all evaluations. These were results that were significantly superior among the results that were acceptable for practical use.

[0076] On the other hand, as shown in Table 3, Comparative Example 1 did not contain In, Sb, or Fe, so the shear strength was poor and the fracture mode was inappropriate. Comparative Example 2 had a low Ag content, so the shear strength was poor. Comparative Example 3 had a high Ag content, so the shear strength was poor and the fracture mode was inappropriate.

[0077] Comparative Example 4 did not contain In, and Comparative Example 5 had a low In content, resulting in poor shear strength and an inappropriate fracture mode. Comparative Example 6 had a high In content, resulting in an inappropriate fracture mode.

[0078] Comparative Example 7 had a low Sb content and no Fe, resulting in poor shear strength and an inappropriate fracture mode. Comparative Example 8 had a low Sb content and therefore poor shear strength. Comparative Example 9 had a high Sb content and therefore poor shear strength and an inappropriate fracture mode.

[0079] In Comparative Examples 10 to 12, the Fe content was inappropriate, resulting in poor shear strength and an inappropriate fracture mode. In Comparative Example 13, the Co content was high, resulting in a significant increase in melting point, poor shear strength, and an inappropriate fracture mode. In Comparative Examples 14 and 15, the Ni or Bi content was included, resulting in poor shear strength.

[0080] FIG. 1 shows optical microscope photographs of samples after shear strength measurement, with FIG. 1(a) being Example 14, FIG. 1(b) being Example 2, and FIG. 1(c) being Comparative Example 3. As is clear from FIG. 1, it was found that in Example 14, the solder joint broke due to bulk fracture. In Example 2, it was found that fracture occurred in the bulk and in the intermetallic compound at the joint interface. On the other hand, it was found that in Comparative Example 3, the solder joint broke due to fracture in the intermetallic compound at the joint interface. Therefore, it was found that the fracture mode in Example 14 was appropriate. This result was similar in the other examples.

[0081] The solder according to the present invention can be used in on-board electronic circuits such as ECUs, which are electronic circuits that control automobiles using computers to improve fuel efficiency, but it can also be used in consumer electronic devices such as personal computers with excellent effects.

Claims

1. A solder alloy characterized by having an alloy composition consisting of, in mass%, 2.0 to 3.6% Ag, 1.0 to 5.0% In, 3.0 to 5.0% Sb, 0.0010 to 0.0300% Fe, 0.0000% to 0.0500% Co, and the balance being Sn.

2. The solder alloy according to claim 1, wherein the alloy composition further contains, by mass%, 0.100% or less in total of at least one of Zr, Ge, Ga, P, As, Pb, Zn, Mg, Cr, Ti, Mo, Pt, Pd, Au, Al, and Si.

3. The solder alloy according to claim 1 or 2, wherein the alloy composition satisfies the following formulas (1) and (2): 0.36≦Ag×In×Sb×Fe≦1.19 (1) 47≦(In×Sb) / (Ag×Fe)≦319 (2) In the formulas (1) and (2), Ag, In, Sb, and Fe are each the content in mass % of the solder alloy.

4. A solder paste comprising a solder powder made of the solder alloy according to claim 1 or 2.

5. A solder ball made of the solder alloy according to claim 1 or 2.

6. A solder preform made of the solder alloy according to claim 1 or 2.

7. A solder joint comprising the solder alloy of claim 1 or 2.

8. An on-vehicle electronic circuit comprising the solder alloy according to claim 1 or 2.

9. An ECU electronic circuit comprising the solder alloy according to claim 1 or 2.

10. An on-vehicle electronic circuit device comprising the on-vehicle electronic circuit according to claim 8.

11. An ECU electronic circuit device comprising the ECU electronic circuit according to claim 9.

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