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

To provide a solder alloy which suppresses surface tension and has high tensile strength and shear strength, and thereby has excellent reliability, 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.SOLUTION: A solder alloy has an alloy composition comprises, 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, by mass%, 0.1% or less of at least one of Ge, Ga, As, Pd, Mn, Zn, Zr and Mg.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[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. [Background technology]

[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 is an electronic circuit that 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 that they are used in a fairly harsh environment.

[0003] The area near 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 as the engine is repeatedly turned on and off.

[0004] Automotive 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 automotive electronic circuits are exposed to a heat cycle environment, the electronic components and printed circuit boards each undergo repeated thermal expansion and contraction. 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, which eventually lead to their fracture.

[0005] Even if the solder joint does not break completely, partial breakage can increase the resistance of the electronic circuit and cause malfunctions. Malfunctions of ECUs installed in automobiles can lead to serious accidents. Therefore, improving heat cycle resistance is particularly important to prevent ECU malfunctions.

[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. The same document also discloses that In may be contained as an optional element. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 7323855 Summary of the Invention [Problem to be solved by the invention]

[0008] The solder alloy described in Patent Document 1 is an excellent invention that achieves both heat cycle resistance and thermal conductivity. However, with the progress of global warming in recent years and rising maximum temperatures, the usage environment is becoming even more severe. Meanwhile, even in cold regions, despite the effects of 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 other than the solder alloy described in Patent Document 1 that are specialized for improved heat cycle resistance.

[0009] Here, it is believed that heat cycle resistance is improved by suppressing fracture of the solder joint. Here, in regions with large temperature differences, it is believed that tensile stress and compressive stress are repeatedly applied to the solder joint due to the difference in the thermal expansion coefficient between the solder alloy and the electrode 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 was explored that would satisfy both heat cycle resistance and thermal conductivity in one composition.

[0011] However, in order to prevent the solder joint from breaking even when continuously exposed to such a severe environment, the solder joint must have a property that prevents the solder joint from breaking at least before the cycle test. Furthermore, it is preferable that such a property is a property specific to the solder alloy, and does not depend on, for example, the electrodes that make up 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 is thought to suppress deformation of the solder alloy constituting the solder joint, thereby suppressing 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, because meniscograph tests typically use copper plates, wettability evaluation depends on the surface properties of the copper plate, and wettability indicators have been measured by measuring the time and stress required for wettability to fully develop. 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 of 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 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 fracture even in environments where internal and external stresses are constantly applied. When studying how to prevent solder joint fracture, it is necessary to pay attention to how the properties of the solder alloy itself can be improved to prevent fracture even when internal stress is applied, in addition to external stress.

[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 excellent reliability due to high tensile strength, low surface tension of molten solder, and high shear strength. [Means for solving the problem]

[0017] The present inventors have focused 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, and have investigated an alloy composition that exhibits high tensile strength and low surface tension. In the above solder alloy, if the Bi content is too high, there is a concern that the solder alloy will become embrittled due to segregation of Bi, so it is necessary to reduce the Bi content.

[0018] However, a low Bi content tends to reduce tensile strength, so the Sb content must be increased to compensate. In the above solder alloy, the Bi content is reduced while 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 these elements 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. Therefore, the present inventors noticed that it is necessary to add an element that contributes to solid solution strengthening and precipitation strengthening in addition to Bi and Sb to the solder alloy described in Patent Document 1. As such an element, the present inventors focused on In, which is exemplified as an additive element in Patent Document 1.

[0020] In Sn-Ag-Cu-Bi-Sb-Fe-Co solder alloys, In dissolves in Sn at approximately 0.5% by mass. However, if the In content exceeds this limit, InSb precipitates because it is more active than Sn. This reduces the amount of SnSb precipitated. When Sb is consumed by the precipitation of InSb, Ag3In, Ag2In, AgIn2, and other elements precipitate. However, as mentioned above, Patent Document 1 discloses that the In content that can be contained in Sn-Ag-Cu-Bi-Sb-Fe-Co solder alloys is 0.1% by 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, the Sn-Ag-Cu-Bi-Sb-Fe-Co-In solder alloy described in Patent Document 1 cannot be expected to achieve further improvement in tensile strength.

[0021] Bi improves wettability, but does not form compounds, so it is prone to forming low-melting-point phases, which can 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 amount of Sb + Ag, it is consumed as a compound, and the amount of In that dissolves in Sn is optimized, making it less likely to form a low-melting-point phase. If the Ag content (Ag3In (Ag and In 3:1), Ag2In (Ag and In 2:1)) or the Sb content (InSb:In and Sb 1:1) is less than the In content, there is a concern that the amount of In that dissolves in Sn will exceed the amount that can form a low-melting-point phase.

[0022] Here, Bi improves wettability but does not form compounds, so a high Bi content can easily form a low-melting-point phase, which can impair reliability. In also easily forms a low-melting-point phase, so like Bi, it can also impair reliability.

[0023] However, unlike Bi, In preferentially forms compounds with Sb and Ag. If the In content is less than the sum of the Sb and Ag contents, In is consumed as a compound, and the amount of In dissolved in Sn is optimized, making it less likely to form a low-melting-point phase. If the Ag content (Ag3In (Ag and In 3:1), Ag2In (Ag and In 2:1), or Sb content (InSb:In and Sb 1:1)) is less than the In content, the In content exceeds the amount that dissolves in Sn, raising concerns about the formation of a low-melting-point phase. Furthermore, the addition of a large amount of In transforms the βSn phase into InSn4, raising concerns about fracture of the solder joint due to deformation of the solder alloy.

[0024] Thus, in Sn-Ag-Cu-Bi-Sb-Fe-Co solder alloys, 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 will occur. Therefore, the In content must be kept within an appropriate range.

[0025] Furthermore, since Ag, Cu, Fe, and Co also form compounds with Sn, 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 wettability improves. Thus, the solder alloy according to the present invention has been found to improve the tensile strength of the solder alloy, reduce the surface tension of the molten solder itself, and further improve the shear strength, leading to the completion of the present invention. While 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 made based on these findings, is as follows.

[0026] (0) A solder alloy comprising, 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 remainder being Sn. (1) A solder alloy characterized by having an alloy composition consisting of, in 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 remainder 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 the above items (0) to (2), 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 above 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 a 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 comprising the solder alloy according to any one of (0) to (2) above.

[0033] (8) An on-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. [Brief explanation of the drawings]

[0037] [Figure 1] FIG. 1 is a SEM photograph of a cross section after a tensile strength test, magnified 1000 times, where FIG. 1(a) is Comparative Example 9, FIG. 1(b) is Example 12, and FIG. 1(c) is Example 14. [Figure 2] 2A and 2B are SEM photographs of FIG. 1 enlarged 3000 times, where FIG. 2A shows Comparative Example 9, FIG. 2B shows Example 12, and FIG. 2C shows Example 14. DETAILED DESCRIPTION OF THE INVENTION

[0038] The present invention will be described in more detail below. In this specification, "%" relating to the solder alloy composition means "% by mass" unless otherwise specified.

[0039] 1. Solder alloy (1) Ag: 3.0-4.0% Ag contributes to improving wettability and also contributes to improving shear strength by forming a network structure of Ag3Sn, which improves the toughness of the solder alloy. If the Ag content exceeds 4.0%, coarse Ag3Sn particles are formed, which reduces the toughness of the solder alloy and therefore the shear strength. 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, if the Ag content is less than 3.0%, the Ag3Sn network structure 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 also improves shear strength by forming a thin intermetallic compound at the bonding interface. If the Cu content exceeds 1.0%, a thick intermetallic compound is 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 and improves wettability by lowering the melting point, and can improve tensile strength by 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 reduces 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 the shear strength. If the Sb content exceeds 6.0%, coarse SnSb compounds precipitate, inhibiting the fluidity of the molten solder, increasing the surface tension and degrading wettability. Furthermore, the segregation of Sb embrittles the solder alloy, degrading the shear strength. The upper limit of the Sb content is 6.0%, preferably 5.5%, more preferably 5.0%, and even more preferably 4.5%.

[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. Accordingly, shear strength also deteriorates. 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 contributes to improving tensile strength through solid solution strengthening by dissolving in Sn and precipitation strengthening through the precipitation of InSb and Ag3In. Furthermore, the inclusion of In in a 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%. At 0.5% or more, In is activated to form InSb. Sb exceeding the solubility limit is consumed by InSb, and if In is contained in excess of the solubility limit, it forms Ag3In, Ag2In, etc. In this way, In can achieve solid solution strengthening and precipitation strengthening, contributing to improved tensile strength.

[0049] If the In content exceeds 6.0%, the Sn phase undergoes a phase transformation 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. Also, the In content is too low, and the effect of improving wettability is not exerted. 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: 0.020-0.040% 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) Equations (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 above 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, satisfying formula (1) can further enhance these effects with a single composition. Formula (2) is composed of elements that contribute to solid solution strengthening and precipitation strengthening, and also improve wettability by forming compounds that reduce surface tension. 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, and may be 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, most preferably 0.0069 or more, and may be 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 preferable range of the formula (1) is 0.0050 to 0.0119. The above upper and lower limits can each define a more preferable range of the 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 preferable range for formula (2) is 51.0 to 85.0. The above upper and lower limits can each define a more preferable range for formula (1).

[0059] The calculations for formulas (1) and (2) used the values ​​shown in Tables 1 and 2, which are the measured values ​​of the alloy compositions. 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 regarding 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 total, not more than 0.1% 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 can be maintained as long as the total amount of these optional elements is 0.1% or less.

[0061] (9) Remainder: 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. The balance of the solder alloy according to the present invention may consist of Sn and unavoidable impurities. Even if unavoidable impurities are contained, the above-mentioned effects are not affected. Note that Ni promotes the release 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 this invention is static surface tension, and is evaluated using the pendant drop method. In the pendant drop method employed in this 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 this 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 this 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 to 0.535 N / m or greater, the solder alloy can wet electrodes without any problems. If it exceeds 0.535 N / m, the solder alloy has poor wettability.

[0063] 2. Solder paste The solder paste of the present invention is a mixture of solder powder having the above-mentioned 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. In the present invention, the blending ratio of the metal powder component and the flux component 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 a solder ball. When used as a solder ball, 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 ball 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 ball 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 ball 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 joints 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 solder alloy of the present invention can be used in a conventional joining method, such as a reflow method. The melting temperature of the solder alloy when performing flow soldering is generally about 20°C higher than the liquidus temperature. Furthermore, when joining using the solder alloy of the present invention, the alloy structure can be further refined by taking into consideration the cooling rate during solidification. 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. In-vehicle electronic circuit, ECU electronic circuit, in-vehicle electronic circuit device, ECU electronic circuit device 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. Other The solder alloy of the present invention can be manufactured by using a low alpha dose material as its raw material, and when such a low alpha dose alloy is used to form solder bumps around memory, it can suppress soft errors. [Example]

[0072] The present invention will be described by the following examples, but the present invention is not limited to the following examples. To demonstrate the effectiveness of the present invention, the solder alloys listed 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 and liquidus temperatures For solder alloys having each alloy composition listed in Tables 1 and 2, the respective temperatures were determined from 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. A solidus temperature of 206°C or higher and less than 230°C was evaluated as "◎". A solidus temperature of less than 206°C and less than 230°C, or a solidus temperature of 206°C or higher and a liquidus temperature of 230°C or higher but less than 240°C, was evaluated as "◯". A liquidus temperature of 240°C or higher was evaluated as "X".

[0074] (2) Surface tension For solder alloys having each alloy composition listed in Tables 1 and 2, a contact angle meter (Model DM-700, manufactured by Kyowa Interface Science Co., Ltd.) was used to measure 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 but less than 0.535 N / m was judged as "◯", and a surface tension of more than 0.535 N / m was judged as "×".

[0075] (3) Tensile strength 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 test specimens with a gauge length of 30 mm and a diameter of 8 mm. The prepared test specimens were pulled at room temperature with an Instron Type 5966 at a stroke of 6 mm / min, and the strength at which the test specimen broke was measured. The reduction in area was also measured from the ratio of the cross-sectional area S1 of the broken portion of the test specimen to the cross-sectional area S0 before the test. Tensile strengths of 40 MPa or greater were evaluated as "◎", those between 35 MPa and 40 MPa were evaluated as "〇", and those less than 35 MPa were evaluated as "×".

[0076] (4) Share strength (4-1) Preparation of paste Powders of each solder alloy listed 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 and flux were 88% by mass and 12% by mass, respectively. This solder paste was printed onto the Cu lands of a six-layer printed circuit board (FR-4, Cu-OSP) using a 150 μm metal mask, after which 3216 chip resistors were mounted using a mounter. The solder paste was then melted and reflowed at a maximum temperature of 245°C for 40 seconds in a reflow atmosphere of N2 (oxygen concentration 2000 ppm or less), and soldered to prepare test boards.

[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 at 25°C, a test speed of 6 mm / min, and a test height of 100 μm. A shear strength of 90 MPa or more was judged as "◎", a shear strength of 85 MPa or more but less than 90 MPa was judged as "◯", and a shear strength of less than 85 MPa was judged as "×".

[0078] [Table 1]

[0079] [Table 2]

[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 "Excellent." 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 "Excellent," 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. 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 shows SEM photographs of the cross section after the tensile strength test, enlarged 1000 times. Figure 1(a) shows Comparative Example 9, Figure 1(b) shows Example 12, and Figure 1(c) shows Example 14. Figure 2 shows SEM photographs of Figure 1, enlarged 3000 times. Figure 2(a) shows Comparative Example 9, Figure 2(b) shows Example 12, and Figure 2(c) shows Example 14. As is clear from Figures 1 and 2, it was found that InSb, Ag2In, and Ag3In precipitated in Example 12 and Example 14. It was also found that Cu6Sn5 precipitated in Example 14 in addition to InSb, Ag2In, and Ag3In.

[0085] Table 3 below shows the wettability results evaluated in this example and the evaluation results using the conventional meniscograph method for examples and comparative examples arbitrarily selected from Tables 1 and 2.

[0086] The meniscograph method was evaluated as follows: (1) Preparation of test plates Flux ("ES-1100" manufactured by Senju Metal Industry Co., Ltd.) was applied to a copper plate (10 mm wide x 30 mm long x 0.3 mm thick). 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 immersed in a solder bath containing molten solder having the alloy composition shown in Table 3, and the zero cross time (sec) was measured. 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 time (sec) of the five test plates for each example and comparative example. The test conditions were set as follows:

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

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

[0090] [Table 3]

[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 of, in 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.

2. 2. The solder alloy according to claim 1, wherein the alloy composition further contains, in 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 above 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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