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 is 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 having excellent reliability as a result of suppressing surface tension low and having high tensile strength and shear strength. The solder alloy has an alloy composition comprising, by mass %, 3.0-4.0% Ag, 0.1-1.0% Cu, 0.1-1.5% Bi, 3.0-6.0% Sb, 0.2-6.0% In, 0.020-0.040% Fe, 0.001-0.020% Co, and the balance Sn. Preferably, the alloy composition further contains, in terms of mass%, at least one of Ge, Ga, As, Pd, Mn, Zn, Zr, and Mg at an amount of 0.1% or less in total.

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 on-board electronic circuits used in devices that electrically control the engine, power steering, brakes, etc. On-board electronic circuits are extremely important safety components for the operation of a vehicle. In particular, the on-board electronic circuit known as the ECU (Engine Control Unit), which controls the vehicle via computer to improve fuel efficiency, must be able to operate stably and without failure for long periods of time. These ECUs are generally installed near the engine, which means they are used in fairly harsh environments.

[0003] The area around the engine where such on-board electronic circuits are installed reaches extremely high temperatures of over 125°C when the engine is running. On the other hand, when the engine is stopped, the outside air temperature drops to low temperatures of -40°C or below in winter in cold regions such as North America or Siberia. Therefore, the on-board electronic circuits are exposed to a heat cycle environment of at least -40°C to +125°C due to repeated engine operation and shutdown.

[0004] In-vehicle electronic circuits are electronic circuits in which electronic components are soldered to a printed circuit board. The linear thermal expansion coefficients of electronic components and printed circuit boards are significantly different. When in-vehicle electronic circuits are exposed to a heat cycle environment, the electronic components and printed circuit boards repeatedly expand and contract. This repetition causes a certain amount of thermal displacement to repeatedly occur at the soldered joints (hereinafter referred to as "solder joints") that join the electronic components and printed circuit boards. As a result, in a heat cycle environment, stress is continuously applied to the solder joints, eventually causing the solder joints to fracture.

[0005] Even if the solder joint does not completely break, partial breakage can increase the resistance of the electronic circuit, causing malfunction. Malfunction of the ECU installed in an automobile can lead to serious accidents. Therefore, improving heat cycle resistance is particularly important to prevent ECU malfunction.

[0006] Therefore, for example, Patent Document 1 discloses a Sn-Ag-Cu-Bi-Sb-Fe-Co solder alloy as a solder alloy with heat cycle resistance. In addition to heat cycle resistance, this solder alloy has excellent thermal conductivity and suppresses the generation of liberation. This document also discloses that the solder alloy may contain In as an optional element.

[0007] Patent No. 7323855

[0008] The solder alloy described in Patent Document 1 is an excellent invention that can achieve both heat cycle resistance and thermal conductivity. However, in recent years, global warming has progressed and maximum temperatures have risen, making the usage environment even more severe. On the other hand, even in cold regions, although affected by global warming, temperatures can still fall below -40°C, just as they have in the past. For this reason, there is a demand for solder alloys that are specialized for improving heat cycle resistance, in addition to the solder alloy described in Patent Document 1.

[0009] Here, heat cycle resistance is thought to be improved by suppressing fracture of solder joints. In regions with large temperature differences, it is thought that tensile stress and compressive stress are repeatedly applied to solder joints due to the difference in thermal expansion coefficient between the solder alloy and the electrodes that make up the solder joint. For this reason, if the solder joint is continuously exposed to a harsh usage environment, it will fracture.

[0010] From this perspective, various compositions have been explored to improve heat cycle resistance. For example, in Patent Document 1, in order to meet the demand for a solder alloy with high versatility, an alloy composition that satisfies both heat cycle resistance and thermal conductivity with a single composition was explored.

[0011] However, it is desirable that the fracture of the solder joint be suppressed even when continuously exposed to the above-mentioned harsh environment. To achieve this, the solder joint must have properties that suppress fracture at least before the cycle test. Furthermore, it is preferable that such properties are specific to the solder alloy and do not depend on the electrodes that constitute the solder joint.

[0012] For example, the tensile strength of the solder alloy can be used to suppress deformation of the solder alloy. High tensile strength suppresses deformation of the solder alloy that constitutes the solder joint, which is thought to prevent fracture of the solder joint.

[0013] In addition, tests using the meniscograph method, for example, have traditionally been used to evaluate the wettability of molten solder. However, in meniscograph tests, a copper plate is typically used. As a result, the evaluation of wettability depends on the surface properties of the copper plate, and the time and stress required for wettability have been used as indicators of wettability. This method is significantly affected by the surface properties of the base material, making it difficult to accurately evaluate wettability. Therefore, a method for evaluating the wettability specific to solder alloys can be used to measure the surface tension using a droplet of molten solder. This makes it possible to evaluate the wettability specific to solder alloys without relying on the surface properties of the copper plate or other materials.

[0014] Furthermore, a solder joint must not break over a long period of time even in an environment where external stress is applied to the solder joint, apart from internal stresses that depend on the material that constitutes the solder joint, such as heat cycle resistance.

[0015] Thus, solder joints must be prevented from breaking even in environments where internal and external stresses are constantly applied. When studying ways to prevent solder joints from breaking, it is important to pay attention not only to external stresses but also to improving the properties of the solder alloy itself to prevent breakage even when internal stresses are applied.

[0016] Therefore, an object of the present invention is to provide a solder alloy, solder paste, solder ball, solder preform, solder joint, on-board electronic circuit, ECU electronic circuit, on-board electronic circuit device, and ECU electronic circuit device that have high tensile strength, low surface tension of molten solder, and high shear strength, and therefore have excellent reliability.

[0017] The present inventors have investigated an alloy composition that exhibits high tensile strength and low surface tension, focusing on the properties of the solder alloy that contribute to heat cycle resistance in the Sn-Ag-Cu-Bi-Sb-Fe-Co solder alloy disclosed in Patent Document 1. In the above solder alloy, if the Bi content is too high, there is a concern that the solder alloy may become embrittled due to segregation of Bi, so it is necessary to reduce the Bi content.

[0018] However, since a low Bi content tends to reduce tensile strength, it is necessary to increase the Sb content to compensate for this. In the above solder alloy, the Bi content is reduced and the Sb content is increased, so further improvement in tensile strength cannot be expected from both Bi and Sb. Furthermore, although Co and Fe contribute to the refinement of the alloy structure, adding large amounts of them causes the precipitation of coarse compounds, which actually reduces tensile strength.

[0019] Here, the tensile strength needs to be improved synergistically by solid solution strengthening and precipitation strengthening of the solder alloy. The present inventors have noticed that, in addition to Bi and Sb, an element that contributes to solid solution strengthening and precipitation strengthening needs to be added to the solder alloy described in Patent Document 1. As such an element, the present inventors have focused on In, which is exemplified as an additive element in Patent Document 1.

[0020] In a Sn-Ag-Cu-Bi-Sb-Fe-Co solder alloy, In dissolves in Sn up to about 0.5 mass %, but if the content exceeds this, InSb precipitates because In is more active than Sn. As a result, the amount of SnSb precipitated decreases. When Sb is consumed by the precipitation of InSb, Ag ３ In, Ag ２ In, AgIn ２However, as mentioned above, Patent Document 1 discloses that the In content that can be contained in a Sn—Ag—Cu—Bi—Sb—Fe—Co solder alloy is 0.1 mass % or less. Therefore, the solder alloy described in Patent Document 1 has a low In content, and solid solution strengthening by In is insufficient. Therefore, further improvement in tensile strength cannot be expected from the Sn—Ag—Cu—Bi—Sb—Fe—Co—In solder alloy described in Patent Document 1.

[0021] Bi improves wettability but does not form compounds, so it is prone to forming a low melting point phase, which may impair reliability. The same is true for In. However, In preferentially forms compounds with Sb and Ag. If the amount of In is less than the total amount of Sb and Ag, it is consumed as a compound, and the amount of In dissolved in Sn is optimized, so In is less likely to form a low melting point phase. The Ag content ((Ag ３ In (Ag and In 3:1), Ag ２ If the contents of In (Ag and In are 2:1)) and Sb (InSb (In and Sb are 1:1)) are less than the content of In, the content of In exceeds the amount that dissolves in Sn, and there is a concern that In will form a low-melting-point phase.

[0022] Here, Bi improves wettability but does not form compounds, so if the Bi content is high, it is likely to form a low-melting-point phase, which may impair reliability. In also easily forms a low-melting-point phase, so it may impair reliability in the same way as Bi.

[0023] However, unlike Bi, In preferentially forms compounds with Sb and Ag, as described above. In detail, as described above, if the content of In is less than the total content of Sb and Ag, In is consumed as a compound, and the amount of In dissolved in Sn is optimized, so In is less likely to form a low melting point phase. ３ In (Ag and In 3:1), Ag ２ When the content of In (Ag and In are 2:1) and Sb (InSb (In and Sb are 1:1)) is less than the amount of In, the content of In exceeds the amount of solid solution in Sn, and there is a concern that In will form a low melting point phase. Furthermore, the addition of a large amount of In will cause the βSn phase to turn into InSn ４This promotes a phase transformation, which raises concerns about the possibility of fracture of the solder joint due to deformation of the solder alloy.

[0024] As described above, in the Sn—Ag—Cu—Bi—Sb—Fe—Co solder alloy, it is necessary to reduce the Bi content as in the past and to include more In than in the past. On the other hand, if the In content is too high, the above-mentioned problems occur. Therefore, the In content must be within an appropriate range.

[0025] Furthermore, Ag, Cu, Fe, and Co also form compounds with Sn. Therefore, it is presumed that when various compounds are formed in the molten solder together with Sb and In, the surface tension of the molten solder decreases and the wettability improves. Thus, by carefully examining the content of each constituent element in the solder alloy according to the present invention, it was discovered that the tensile strength of the solder alloy is improved, the surface tension of the molten solder itself is reduced, and the shear strength is also improved, leading to the completion of the present invention. Note that, although the present invention has been exemplified with respect to electronic circuits, the present invention is not limited to such applications as long as these effects must be simultaneously exerted. The present invention, which was achieved based on these findings, is as follows.

[0026] (0) A solder alloy characterized by having, by mass%, 3.0 to 4.0% Ag, 0.1 to 1.0% Cu, 0.1 to 1.5% Bi, 3.0 to 6.0% Sb, 0.2 to 6.0% In, 0.020 to 0.040% Fe, 0.001 to 0.020% Co, and the balance being Sn. (1) A solder alloy characterized by having, by mass%, an alloy composition of 3.0 to 4.0% Ag, 0.1 to 1.0% Cu, 0.1 to 1.5% Bi, 3.0 to 6.0% Sb, 0.2 to 6.0% In, 0.020 to 0.040% Fe, 0.001 to 0.020% Co, and the balance being Sn.

[0027] (2) The solder alloy according to (0) or (1) above, wherein the alloy composition (solder alloy) further contains, by mass%, 0.1% or less in total of at least one of Ge, Ga, As, Pd, Mn, Zn, Zr, and Mg.

[0028] (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): 0.0049≦Ag×Cu×Bi×Sb×In×Fe×Co≦0.0148 (1) 49.4≦Ag×Sb×In≦88.3 (2) In the formulas (1) and (2), Ag, Cu, Bi, Sb, In, Fe, and Co each represent the content (mass %) of the alloy composition.

[0029] (4) A solder paste containing solder powder made of the solder alloy according to any one of (0) to (2) above.

[0030] (5) A solder ball made of the solder alloy according to any one of (0) to (2) above.

[0031] (6) A solder preform made of the solder alloy according to any one of (0) to (2) above.

[0032] (7) A soldered joint having the solder alloy according to any one of (0) to (2) above.

[0033] (8) An in-vehicle electronic circuit comprising the solder alloy according to any one of (0) to (2) above.

[0034] (9) An ECU electronic circuit comprising the solder alloy according to any one of (0) to (2) above.

[0035] (10) An on-vehicle electronic circuit device comprising the on-vehicle electronic circuit according to (8) above.

[0036] (11) An ECU electronic circuit device comprising the ECU electronic circuit described in (9) above.

[0037] Fig. 1 shows SEM photographs of cross sections after a tensile strength test, enlarged 1000 times, with Fig. 1(a) showing Comparative Example 9, Fig. 1(b) showing Example 12, and Fig. 1(c) showing Example 14. Fig. 2 shows SEM photographs of Fig. 1, enlarged 3000 times, with Fig. 2(a) showing Comparative Example 9, Fig. 2(b) showing Example 12, and Fig. 2(c) showing Example 14.

[0038] 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.

[0039] 1. Solder alloy (1) Ag: 3.0 to 4.0% Ag contributes to improving wettability and ３ The formation of a Sn network structure improves the toughness of the solder alloy, thereby contributing to an improvement in shear strength. ３ The upper limit of the Ag content is 4.0% or less, preferably 3.8% or less, and more preferably 3.6% or less.

[0040] On the other hand, when the Ag content is less than 3.0%, Ag ３ The network structure of Sn is not formed, and the toughness is reduced, resulting in a deterioration in shear strength. The lower limit of the Ag content is 3.0% or more, preferably 3.1% or more, more preferably 3.2% or more, even more preferably 3.3% or more, and particularly preferably 3.4% or more. The preferred range of Ag is 3.2 to 3.6%.

[0041] (2) Cu: 0.1 to 1.0% Cu reduces surface tension, improves tensile strength through precipitation strengthening, and can also improve shear strength by forming thin intermetallic compounds at the bonding interface. If the Cu content exceeds 1.0%, thick intermetallic compounds are formed at the bonding interface, resulting in a decrease in shear strength. The upper limit of the Cu content is 1.0% or less, preferably 0.9% or less, more preferably 0.8% or less, and even more preferably 0.7% or less.

[0042] On the other hand, if the Cu content is less than 0.1%, the compound with Sn does not precipitate sufficiently, resulting in poor surface tension, and therefore poor tensile strength and shear strength. The lower limit of the Cu content is 0.1% or more, preferably 0.3% or more, more preferably 0.5% or more, and even more preferably 0.6% or more. The preferred range of Cu is 0.5 to 0.9%.

[0043] (3) Bi: 0.1 to 1.5% Bi reduces surface tension by lowering the melting point, improving wettability, and can improve tensile strength through solid solution strengthening. Bi can also improve shear strength as well as tensile strength. If the Bi content exceeds 1.5%, Bi segregates and the solder alloy becomes embrittled, resulting in poor shear strength. The upper limit of the Bi content is 1.5% or less, preferably 1.2% or less, more preferably 1.0% or less, even more preferably 0.9% or less, and particularly preferably 0.8% or less.

[0044] On the other hand, if the Bi content is less than 0.1%, the amount of Bi dissolved in the alloy is insufficient, resulting in poor tensile strength. Furthermore, the low Bi content does not provide the effect of improving wettability. Furthermore, although a low Bi content suppresses embrittlement, it also deteriorates the tensile strength and shear strength. The lower limit of the Bi content is 0.1% or more, preferably 0.3% or more, more preferably 0.4% or more, even more preferably 0.5% or more, particularly preferably 0.6% or more, and most preferably 0.7% or more. The preferred range of Bi is 0.5 to 1.5%.

[0045] (4) Sb: 3.0 to 6.0% Sb contributes to precipitation strengthening of the solder alloy by forming SnSb. This also improves shear strength. If the Sb content exceeds 6.0%, coarse SnSb compounds precipitate, inhibiting the fluidity of the molten solder, increasing surface tension and degrading wettability. Furthermore, Sb segregation causes embrittlement of the solder alloy, resulting in a deterioration in shear strength. The upper limit of the Sb content is 6.0% or less, preferably 5.5% or less, more preferably 5.0% or less, and even more preferably 4.5% or less.

[0046] On the other hand, if the Sb content is less than 3.0%, precipitation strengthening is not achieved and solid solution strengthening is insufficient, resulting in a deterioration in tensile strength. This also leads to a deterioration in shear strength. The lower limit of the Sb content is 3.0% or more, preferably 3.1% or more, more preferably 3.5% or more, and even more preferably 4.0% or more. The preferred range of Sb is 3.1 to 6.0%.

[0047] (5) In: 0.2 to 6.0% In is dissolved in Sn to strengthen the solid solution, and InSb and Ag ３ Precipitation strengthening due to the precipitation of In and other elements contributes to improving tensile strength. Furthermore, the inclusion of In in the solder alloy lowers the melting point, thereby reducing surface tension and contributing to improved wettability. As mentioned above, In contributes to the precipitation of various compounds, but the precipitated compounds exhibit fine precipitation behavior, so high wettability is maintained. Furthermore, In contributes to improving shear strength by controlling the phase transformation of Sn.

[0048] In Sn-Ag-Cu-Bi-Sb-Fe-Co solder alloys, In dissolves in Sn up to 0.5%, but when the content is 0.5% or more, InSb is formed due to the activity of In. Sb that exceeds the solubility limit is consumed by InSb, and if In is contained in excess of the solubility limit, Ag ３ In and Ag ２ In, etc. In this way, In can achieve solid solution strengthening and precipitation strengthening, and therefore contributes to improving tensile strength.

[0049] If the In content exceeds 6.0%, the Sn phase will transform from βSn to γSn, causing deformation of the solder alloy and a deterioration in shear strength. The upper limit of In is 6.0% or less, preferably 5.5% or less, more preferably 5.0% or less, and even more preferably 4.0% or less.

[0050] On the other hand, if the In content is less than 0.2%, solid solution strengthening becomes insufficient, resulting in deterioration of tensile strength and shear strength. Furthermore, the low In content does not provide the effect of improving wettability. The lower limit of In is 0.2% or more, preferably 1.0% or more, more preferably 2.0% or more, and even more preferably 3.0% or more. The preferred range of In is 3.0 to 6.0%.

[0051] (6) Fe: 0.020 to 0.040%. Fe functions as a solidification nucleus during solidification of molten solder, resulting in a finer alloy structure and improved toughness of the solder alloy, thereby improving shear strength. If the Fe content exceeds 0.040%, coarse SnFe compounds precipitate, inhibiting the fluidity of the molten solder, increasing surface tension and reducing wettability. The upper limit of the Fe content is 0.040% or less, preferably 0.035% or less, and more preferably 0.030% or less.

[0052] On the other hand, if the Fe content is less than 0.020%, the alloy structure will not be refined, and the toughness of the solder alloy will decrease, resulting in a deterioration in shear strength. The lower limit of the Fe content is 0.020% or more, preferably 0.025% or more. The preferred range of Fe is 0.020 to 0.030%.

[0053] (6) Co: 0.001 to 0.020%. Like Fe, Co functions as a solidification nucleus during solidification of molten solder, resulting in a finer alloy structure and improved toughness of the solder alloy, thereby improving shear strength. If the Co content exceeds 0.020%, the liquidus temperature rises and coarse SnCo compounds precipitate, resulting in a deterioration in surface tension. The upper limit of the Co content is 0.020% or less, preferably 0.015% or less, more preferably 0.012% or less, even more preferably 0.010% or less, and particularly preferably 0.009% or less.

[0054] On the other hand, if the Co content is less than 0.001%, the alloy structure will not be refined, and the toughness of the solder alloy will decrease, resulting in a deterioration in shear strength. The lower limit of the Co content is 0.001% or more, preferably 0.003% or more, more preferably 0.005% or more, even more preferably 0.006% or more, and particularly preferably 0.008% or more. The preferred range of Co is 0.006 to 0.010%.

[0055] (7) Formulas (1) and (2): 0.0049≦Ag×Cu×Bi×Sb×In×Fe×Co≦0.0148 (1) 49.4≦Ag×Sb×In≦88.3 (2) In the formulas (1) and (2), Ag, Cu, Bi, Sb, In, Fe, and Co each represent the content (mass%) of the alloy composition.

[0056] The elements constituting the solder alloy of the present invention have liquidus and solidus temperatures comparable to those of conventional solder alloys, reducing surface tension and contributing to improved tensile strength and shear strength. Therefore, when formula (1) is satisfied, these effects can be further enhanced with a single composition. Furthermore, formula (2) is composed of elements that contribute to solid solution strengthening and precipitation strengthening, and also improve wettability by reducing surface tension through the formation of compounds. Formulas (1) and (2) are preferred embodiments of the present invention, and even alloy compositions that do not satisfy these formulas can still achieve practically acceptable effects as long as the contents of each constituent element are appropriate, as described above. Alloy compositions that simultaneously satisfy these formulas achieve the highest level of evaluation in the present invention.

[0057] The upper limit of formula (1) is preferably 0.0148 or less, more preferably 0.0145 or less, even more preferably 0.0143 or less, particularly preferably 0.0140 or less, and most preferably 0.0136 or less, 0.0129 or less, 0.0124 or less, 0.0119 or less, 0.0114 or less, 0.0113 or less, or 0.0112 or less. The lower limit of formula (1) is preferably 0.0049 or more, more preferably 0.0050 or more, even more preferably 0.0059 or more, particularly preferably 0.0065 or more, and most preferably 0.0069 or more, 0.0071 or more, 0.0083 or more, 0.0085 or more, 0.0086 or more, 0.0095 or more, or 0.0105 or more. A more preferred range of formula (1) is 0.0050 to 0.0119. The above upper and lower limits can each define a further preferred range of formula (1).

[0058] The upper limit of formula (2) is preferably 88.3 or less, more preferably 85.0 or less, even more preferably 81.0 or less, and even more preferably 80.0 or less. The lower limit of formula (2) is preferably 49.4 or more, more preferably 51.0 or more, even more preferably 68.0 or more, and particularly preferably 75.0 or more. A more preferred range of formula (2) is 51.0 to 85.0. The above upper and lower limits can each define a further preferred range of formula (1).

[0059] The values ​​shown in Tables 1 and 2, which are the measured values ​​of the alloy compositions, were used in the calculations of formulas (1) and (2). The values ​​calculated from formulas (1) and (2) are rounded to four decimal places for formula (1) and one decimal place for formula (2). This calculation rule is used in this application and is intended to be used in the same way for calculations of additional compositions described in other documents, etc., since all compositions must be treated in the same way.

[0060] (8) At least one of Ge, Ga, As, Pd, Mn, Zn, Zr, and Mg in a total amount of 0.1% or less by mass. The solder alloy according to the present invention may contain optional elements as long as the effects of the present invention are not impaired. The effects of the present invention are maintained as long as the total amount of these optional elements is 0.1% or less.

[0061] (9) Balance: Sn The balance of the solder alloy according to the present invention is Sn. In addition to the above elements, inevitable impurities may be contained. The balance of the solder alloy according to the present invention may consist of Sn and inevitable impurities. Even if inevitable impurities are contained, the above-mentioned effects are not affected. Note that Ni promotes the liberation of compounds that precipitate at the joint interface of the solder joint, so it is preferable not to include Ni.

[0062] The surface tension value evaluated in the present invention is static surface tension and is evaluated using the pendant drop method. In the pendant drop method employed in the present invention, a liquid is extruded from the tip of a tube (needle), and the surface tension is calculated from the shape of the droplet formed at the tip of the needle. Conventional methods for determining the contact angle with Cu vary the measured value depending on the surface properties of the Cu or other materials, so the surface tension of the solder alloy itself is not measured. However, in the present invention, the wettability of the solder alloy itself can be evaluated by measuring the surface tension of the solder alloy itself, which is independent of the electrode material or surface properties. For the solder alloy of the present invention, if the surface tension is 0.515 N / m or less, the solder alloy can sufficiently wet electrodes, and if it is greater than 0.515 and less than 0.535 N / m, the solder alloy can wet electrodes without any problems. If it exceeds 0.535 N / m, the wettability is poor.

[0063] 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 soldering by conventional methods. Therefore, a suitable blend of commonly used rosin, organic acid, activator, and solvent may be used. The blending ratio of the metal powder component and the flux component in the present invention is not particularly limited, but preferably the metal powder component: 70 to 90 mass % and the flux component: 10 to 30 mass %.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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 flow soldering may be approximately 20°C higher than the liquidus temperature. Furthermore, when joining using the solder alloy of the present invention, consideration of 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.

[0068] 6. On-board Electronic Circuits, ECU Electronic Circuits, On-board Electronic Circuit Devices, ECU Electronic Circuit Devices The solder alloy according to the present invention may be used for soldering electronic circuits mounted on automobiles.

[0069] 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.

[0070] 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). A preferred printed wiring board is one in which the Cu land surface is treated with an organic substance (OSP: Organic Surface Protection) such as amine or imidazole.

[0071] 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.

[0072] The present invention will be described with reference to the following examples, but is not limited to these examples. To demonstrate the effects of the present invention, the solder alloys shown in Tables 2 and 3 were evaluated for (1) solidus temperature and liquidus temperature, (2) surface tension, (3) tensile strength, and (4) shear strength.

[0073] (1) Solidus Temperature and Liquidus Temperature For the solder alloys having the alloy compositions listed in Tables 1 and 2, the respective temperatures were determined from the DSC curves. The DSC curves were obtained by heating at a rate of 5°C / min in air using a Seiko Instruments Inc. DSC (Model: Q2000). The liquidus temperature was determined from the obtained DSC curve and used as the melting temperature. The solidus temperature was also evaluated from the DSC curve. When the solidus temperature was 206°C or higher and less than 230°C, it was judged as "◎". When the solidus temperature was less than 206°C and less than 230°C, or when the solidus temperature was 206°C or higher and the liquidus temperature was 230°C or higher but less than 240°C, it was judged as "◯". When the liquidus temperature was 240°C or higher, it was judged as "X".

[0074] (2) Surface tension For the solder alloys having each alloy composition listed in Tables 1 and 2, a contact angle meter (manufactured by Kyowa Interface Science Co., Ltd., model number DM-700) was used to measure the surface tension by the pendant drop method in a nitrogen atmosphere (oxygen concentration 2000 ppm or less) at 250°C. The surface tension formed was determined using an image processing type solid-liquid interface analysis system, DropMaster 500, manufactured by Kyowa Interface Science Co., Ltd. A surface tension of 0.515 N / m or less was judged as "◎", a surface tension of more than 0.515 N / m and less than 0.535 N / m was judged as "◯", and a surface tension of more than 0.535 N / m was judged as "X".

[0075] (3) Tensile Strength The tensile strength was measured in accordance with JIS Z3198-2. Each solder alloy listed in Tables 1 and 2 was cast into a mold to prepare a test piece with a gauge length of 30 mm and a diameter of 8 mm. The prepared test piece was pulled at room temperature with a stroke of 6 mm / min using an Instron Type 5966, and the strength at the time of breakage of the test piece was measured. In addition, the cross-sectional area S ０ Cross-sectional area S of the fractured part of the test piece １ When the tensile strength was 40 MPa or more, it was evaluated as "◎", when it was 35 MPa or more and less than 40 MPa, it was evaluated as "◯", and when it was less than 35 MPa, it was evaluated as "×".

[0076] (4) Shear Strength (4-1) Paste Preparation Powders of each solder alloy shown in Tables 1 and 2 were prepared by atomization. Solder pastes were prepared by mixing these alloy powders with a flux ("GLV" manufactured by Senju Metal Industry Co., Ltd.) containing rosin, solvent, thixotropic agent, organic acid, etc. The alloy powder in the solder paste was 88% by mass, and the flux was 12% by mass. This solder paste was paste-printed onto the Cu lands of a six-layer printed circuit board (FR-4, Cu-OSP) using a 150 μm metal mask, and then 3216 chip resistors were mounted using a mounter. The solder paste was then heated at a maximum temperature of 245°C for a holding time of 40 seconds in a reflow atmosphere of N. ２ The solder was melted in an atmosphere of 2000 ppm or less (oxygen concentration), reflowed, and soldered to prepare a test substrate.

[0077] (4-2) Measurement of Shear Strength The shear strength test was performed on the above test substrates using a joint strength tester STR-5100 under the conditions of 25° C., a test speed of 6 mm / min, and a test height of 100 μm. When the shear strength was 90 MPa or more, it was judged as "◎", when it was 85 MPa or more but less than 90 MPa, it was judged as "◯", and when it was less than 85 MPa, it was judged as "×".

[0078]

[0079]

[0080] As is clear from Tables 1 and 2, in Examples 1 to 40, the contents of the essential elements Ag, Cu, Bi, Sb, In, Fe, and Co were all within the ranges of the present invention, and therefore all were evaluated as "good" or "good." In particular, Examples 2, 3, 6, 7, 12 to 17, 20, 25, 26, 28, and 32 to 40, which satisfied formulas (1) and (2), were all evaluated as "good," demonstrating superior results among the Examples.

[0081] On the other hand, Comparative Examples 1 and 2 had poor shear strength due to an inappropriate Ag content, Comparative Example 3 had poor surface tension, tensile strength, and shear strength due to a low Cu content, and Comparative Example 4 had poor shear strength due to a high Cu content.

[0082] Comparative Example 5 had poor surface tension, tensile strength, and shear strength due to a low Bi content. Comparative Example 6 had poor shear strength due to a high Bi content. Comparative Example 7 had poor tensile strength and shear strength due to a low Sb content. Comparative Example 8 had poor surface tension and shear strength due to a high Sb content.

[0083] Comparative Example 9 had poor surface tension, tensile strength, and shear strength due to a low In content. Comparative Example 10 had poor shear strength due to a high In content. Comparative Example 11 had poor surface tension due to a low Fe content. Comparative Example 13 had poor shear strength due to a low Co content. Comparative Example 14 had a high Co content, which increased the liquidus temperature and showed high surface tension.

[0084] The results of observing the cross section after the tensile strength test are shown in Figures 1 and 2. Figure 1 is an SEM photograph of the cross section after the tensile strength test, enlarged 1000 times, where Figure 1(a) is Comparative Example 9, Figure 1(b) is Example 12, and Figure 1(c) is Example 14. Figure 2 is an SEM photograph of Figure 1, enlarged 3000 times, where Figure 2(a) is Comparative Example 9, Figure 2(b) is Example 12, and Figure 2(c) is Example 14. As is clear from Figures 1 and 2, in Examples 12 and 14, InSb, Ag ２ In, and Ag ３ In Example 14, InSb, Ag ２ In, and Ag ３ In addition to In, Cu ６ Sn ５ was found to be precipitated.

[0085] Table 3 below shows the wettability evaluation results for Examples and Comparative Examples arbitrarily selected from Tables 1 and 2, as well as the evaluation results using the conventional meniscograph method.

[0086] The meniscograph method was evaluated as follows. (1) Preparation of test plate A flux ("ES-1100" manufactured by Senju Metal Industry Co., Ltd.) was applied to a copper plate (width 10 mm x length 30 mm x thickness 0.3 mm). The flux-coated copper plate was heat-treated at 120°C for 15 minutes in an air atmosphere to obtain a test plate. Five such test plates were prepared for each of the Examples and Comparative Examples shown in Table 3.

[0087] (2) Evaluation Method The obtained test plates were each immersed in a solder bath containing molten solder having the alloy composition shown in Table 3, and the zero cross time (sec) was measured. Here, a Solder Checker SAT-5100 (manufactured by RHESCA) was used as the test device, and the evaluation was carried out as follows. The solder wettability was evaluated based on the average value of the zero cross times (sec) of the five test plates for each example and each comparative example. The test conditions were set as follows:

[0088] Immersion speed in solder bath: 10 mm / sec Immersion depth in solder bath: 4 mm Immersion time in solder bath: 10 sec Solder bath temperature: 255°C The shorter the average zero cross time (sec), the faster the wetting speed, which means better solder wettability.

[0089] (3) Judgment criteria When the average value of the zero cross time (sec) was 1.2 seconds or less, it was judged as "◎", when it was more than 1.2 seconds but less than 1.3 seconds, it was judged as "◯", and when it was more than 1.3 seconds, it was judged as "X".

[0090]

[0091] As is clear from Table 3, it was found that the meniscograph method and the pendant drop method used in this example sometimes produce different evaluation results. Furthermore, even for alloy compositions that were evaluated as "◎" by the meniscograph method, the pendant drop method evaluated them as "◯." Therefore, it was found that the pendant drop method used in this example can directly evaluate the wettability of the molten solder itself, allowing for a more rigorous evaluation of wettability.

Claims

1. A solder alloy characterized by having an alloy composition consisting, in mass%, of 3.0 to 4.0% Ag, 0.1 to 1.0% Cu, 0.1 to 1.5% Bi, 3.0 to 6.0% Sb, 0.2 to 6.0% In, 0.020 to 0.040% Fe, 0.001 to 0.020% Co, and the balance being Sn.

2. The solder alloy according to claim 1, wherein the alloy composition further contains, by mass %, 0.1% or less in total of at least one of Ge, Ga, As, Pd, Mn, Zn, Zr, and Mg.

3. The solder alloy according to claim 1 or 2, wherein the alloy composition satisfies the following formulas (1) and (2): 0.0049≦Ag×Cu×Bi×Sb×In×Fe×Co≦0.0148 (1) 49.4≦Ag×Sb×In≦88.3 (2) In the formulas (1) and (2), Ag, Cu, Bi, Sb, In, Fe, and Co each represent the content (mass %) of the alloy composition.

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 of 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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