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

Abstract

Provided are a solder alloy, a solder paste, a solder ball, a solder preform, a solder joint, an in-vehicle electronic circuit, an ECU electronic circuit, an in-vehicle electronic circuit device, and an ECU electronic circuit device, which have excellent reliability because the liquidus temperature is not too high, the tensile strength is high, the surface tension of the molten solder is low, and the tensile strength after aging is also high.SOLUTION: The solder alloy has an alloy composition consisting of, by mass%, Ag: 3.0 to 4.0%, Cu: 0.1 to 1.0%, Sb: 3.1 to 6.0%, Bi: 0.1 to 1.5%, In: 0.2 to 6.0%, Ni: 0.02 to 0.07%, Co: 0.0010 to 0.0200%, and the balance of Sn. Preferably, the alloy composition further contains, by mass%, at least one of Ge, Ga, As, Pd, Mn, Zn, Zr, and Mg in a total amount of 0.1% or less.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, Patent Document 1 discloses a solder alloy having heat cycle resistance properties, which is Sn-Ag-Cu-Sb-Ni and optionally contains In and Co. Patent Document 2 also discloses a solder alloy having heat cycle resistance properties, which is Sn-Ag-Cu-Bi-Ni-Co and optionally contains Sb and In. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6275178 [Patent Document 2] Patent No. 5349703 Summary of the Invention [Problem to be solved by the invention]

[0008] Paragraph 0008 of Patent Document 1 states that lead-free solder alloys strengthened by the addition of Bi have the disadvantages of poor ductility and increased brittleness. The same paragraph also discloses that when soldered using a conventional lead-free solder alloy containing Bi and placed in an environment with large temperature differences, cracks occur in the fillet portion on the chip resistor component side in the longitudinal direction of the chip resistor component.

[0009] Paragraphs 0026 and 0027 of Patent Document 1 state that a part of the Sn crystal lattice is substituted with Sb, and SnSb is finely dispersed in the Sn grain boundaries even when exposed to an environment with large temperature differences, thereby suppressing coarsening of Sn crystals. Meanwhile, paragraph 0042 of Patent Document 1 states that Bi and the like can be contained within a range that does not impair the effects of the invention described in Patent Document 1.

[0010] However, as mentioned above, Patent Document 1 discloses a Sn-Ag-Cu-Sb-In-Ni-Co solder alloy, but does not disclose a solder alloy containing Bi. The range of Bi content is also not specified. Furthermore, paragraph 0038 of the same document discloses formula (B) which assumes an alloy composition containing Bi.

[0011] According to formula (B), when Bi is contained, the maximum Ag content is 2.55 mass%. Therefore, in the invention described in Patent Document 1, when a solder alloy containing Bi is assumed, the Ag content is limited. Furthermore, in this document, solder alloys with an Ag content of 2.55 mass% or less are disclosed only in reference examples and comparative examples. This proves that the invention described in Patent Document 1 does not provide sufficient heat cycle resistance even when Bi is contained.

[0012] As described in paragraph 0010 of Patent Document 2, the invention described therein is said to have a low melting point, excellent mechanical properties such as durability, crack resistance, and erosion resistance, and to be able to suppress the occurrence of voids. Furthermore, paragraphs 0036, 0039, and 0054 of the same document state that the inclusion of predetermined amounts of Ni, Co, and In can make the solder structure finer.

[0013] However, the melting point is not evaluated in the invention described in Patent Document 2. Furthermore, according to paragraphs 0105, 0106, Table 4 of paragraph 0123, and Table 5 of paragraph 0124 of the same document, it is evaluated that the solder structure can be made fine if the maximum structure is less than 50 μm and 50 to 100 μm.

[0014] However, in recent years, with the progress of global warming and rising maximum temperatures, the operating environment has become even more severe. On the other hand, even in cold regions, although the effects of global warming are present, 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 2.

[0015] 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.

[0016] In order to prevent a solder joint from breaking even when continuously exposed to the above-mentioned harsh environment, the solder joint must have properties that prevent breakage at least before the cycle test. Furthermore, it is preferable that such properties are specific to the solder alloy and do not depend on, for example, the electrodes that make up the solder joint.

[0017] In order to suppress deformation of the solder alloy, for example, the tensile strength of the solder alloy can be improved. High tensile strength is thought to suppress deformation of the solder alloy constituting the solder joint, thereby suppressing fracture of the solder joint.

[0018] 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.

[0019] Furthermore, since the reflow temperature of the conventionally used Sn-3Ag-0.5Cu solder alloy is 235 to 240°C, when components with large heat capacity are used, it may be necessary to perform reflow soldering at the higher end of the temperature range. Furthermore, as electronic devices become more powerful, the amount of current flowing through them increases, raising concerns about heat generation in electronic components. Even if electronic devices generate heat, the solder joint must not break. Therefore, solder alloys are also required to have a structure that does not coarsen under high-temperature conditions.

[0020] Therefore, an object of the present invention is to provide a solder alloy, solder paste, solder balls, solder preforms, solder joints, on-vehicle electronic circuits, ECU electronic circuits, on-vehicle electronic circuit devices, and ECU electronic circuit devices that have excellent reliability due to having a liquidus temperature that is not too high, high tensile strength, low surface tension of molten solder, and high tensile strength after aging. [Means for solving the problem]

[0021] The present inventors have reexamined the solder alloys specifically disclosed in Patent Document 1 and Patent Document 2. As the solder alloys disclosed in Patent Document 1, the inventors have examined the Sn-3.0Ag-0.5Cu-4.0Sb-3.0In-0.03Ni-0.008Co solder alloy (numerical values ​​represent mass %) disclosed in Example 16 of Patent Document 1 and the Sn-3.0Ag-0.5Cu-4.0Sb-6.0In-0.03Ni-0.008Co solder alloy (numerical values ​​represent mass %) disclosed in Example 17 of Patent Document 1.

[0022] These solder alloys do not contain Bi, so there is no concern about embrittlement, but they cannot achieve significant solid solution strengthening of Sn. In and Sb are also solid solution strengthening elements, but they also have precipitation strengthening properties, so they do not achieve solid solution strengthening to the same extent as Bi. As a result, it has been found that tensile strength decreases when exposed to high-temperature environments. It has also been found that the surface tension of molten solder is high because they do not contain Bi. It has also been found that similar results are obtained when a small amount of Bi is added.

[0023] This is thought to be because the invention described in Patent Document 1 states that Bi may be contained to an extent that does not impair the effects of the invention described in Patent Document 1. It is also thought that this is because the effect of improving wettability was not desired. Furthermore, in the invention described in Patent Document 1, when Bi is contained, the Ag content is limited, so there is a concern that the effects of the invention described in Patent Document 1 will not be achieved. In view of these, the present inventors have focused on the need to add Bi to the solder alloy disclosed in Patent Document 1.

[0024] Patent Document 2 specifically discloses a Sn-Ag-Cu-Bi-Sb-In-Ni-Co solder alloy containing Bi. In this alloy system, the authors focused on the solder alloy's properties of suppressing the rise in melting point and contributing to heat cycle resistance. They then investigated alloy compositions that exhibit high tensile strength and tensile strength in high-temperature environments. In such solder alloys, Bi improves wettability but does not form compounds. Therefore, a high Bi content can easily form a low-melting-point phase, potentially impairing reliability, so the Bi content must be reduced.

[0025] However, as mentioned above, solder alloys with a low Bi content or solder alloys that do not contain Bi, such as those disclosed in Patent Document 1, tend to have a decrease in tensile strength after exposure to high-temperature environments. Therefore, it is necessary to increase the Sb content to compensate for this. An example of such a solder alloy is the Sn-3.0Ag-0.5Cu-1.0Bi-3.0Sb-4.3In-0.05Ni-0.005Co solder alloy (values ​​represent mass %) disclosed in Example 37 of Patent Document 2.

[0026] This solder alloy has a reduced Bi content and a relatively high Sb content among the solder alloys disclosed in Patent Document 2. However, even in this solder alloy, the reduced Bi content means that the solid solution strengthening of Sb and the precipitation strengthening of SnSb are insufficient, and it has been found that the tensile strength deteriorates when exposed to a high-temperature environment.

[0027] Thus, in the Sn-Ag-Cu-Bi-Sb-In-Ni-Co solder alloy, it is necessary to reduce the Bi content as in the past and to include more Sb than in the past. On the other hand, if the Sb content is too high, the above-mentioned problems will occur. Therefore, the Sb content must be kept within an appropriate range.

[0028] Furthermore, Ag, Cu, Ni, and Co also form compounds with Sn, which contribute to improving wettability by precipitating these compounds in fine particles. It is believed that the fine precipitation of these compounds can improve tensile strength and tensile strength after exposure to high temperatures.

[0029] The present inventors did not focus solely on Bi and Sb, but instead investigated with high precision the contents of the constituent elements that form the compound. As a result, they discovered that the tensile strength of the solder alloy is improved, the surface tension of the molten solder itself is reduced, and the tensile strength after exposure to a high-temperature environment (hereinafter referred to as "aging") is also improved, leading to the completion of the present invention. Note that 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.

[0030] (0) A solder alloy comprising, by mass%, 3.0 to 4.0% Ag, 0.1 to 1.0% Cu, 3.1 to 6.0% Sb, 0.1 to 1.5% Bi, 0.2 to 6.0% In, 0.02 to 0.07% Ni, 0.0010 to 0.0200% Co, and the remainder being Sn. (1) A solder alloy characterized by having an alloy composition, in mass%, of 3.0 to 4.0% Ag, 0.1 to 1.0% Cu, 3.1 to 6.0% Sb, 0.1 to 1.5% Bi, 0.2 to 6.0% In, 0.02 to 0.07% Ni, 0.0010 to 0.0200% Co, and the remainder being Sn.

[0031] (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.

[0032] (3) The solder alloy according to any one of (0) to (2) above, wherein the alloy composition (solder alloy) satisfies the following formulae (1) to (4): 0.00029≦Sb×Ni×Co / (Cu×Bi×In)≦0.00151 (1) 0.0039≦Ag×Cu×Sb×In×Ni×Co / Bi≦0.0332 (2) 4.0≦Cu×Sb×In≦20.0 (3) 265≦Ag×Sb / Ni≦499 (4) In the above formulas (1) to (4), Ag, Cu, Bi, Sb, In, Ni, and Co each represent the content (mass %) of the alloy composition.

[0033] (4) A solder paste containing a solder powder made of the solder alloy according to any one of (0) to (3) above.

[0034] (5) A solder ball made of the solder alloy according to any one of (0) to (3) above.

[0035] (6) A solder preform made of the solder alloy according to any one of (0) to (3) above.

[0036] (7) A soldered joint comprising the solder alloy according to any one of (0) to (3) above.

[0037] (8) An on-vehicle electronic circuit comprising the solder alloy according to any one of (0) to (3) above.

[0038] (9) An ECU electronic circuit comprising the solder alloy according to any one of (0) to (3) above.

[0039] (10) An on-vehicle electronic circuit device comprising the on-vehicle electronic circuit according to (8) above.

[0040] (11) An ECU electronic circuit device comprising the ECU electronic circuit described in (9) above. [Brief explanation of the drawings]

[0041] [Figure 1] FIG. 1 is a SEM photograph of a cross section after a tensile strength test, enlarged 1000 times, where FIG. 1(a) is Comparative Example 12, FIG. 1(b) is Example 3, and FIG. 1(c) is Example 25. [Figure 2]2A and 2B are SEM photographs of FIG. 1 enlarged 3000 times, where FIG. 2A shows Comparative Example 12, FIG. 2B shows Example 3, and FIG. 2C shows Example 25. DETAILED DESCRIPTION OF THE INVENTION

[0042] 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.

[0043] 1. Solder alloy (1) Ag: 3.0-4.0% Ag forms a network structure of Ag3Sn, which contributes to improving the tensile strength after aging. If the Ag content exceeds 4.0%, coarse Ag3Sn particles are formed, which reduces the toughness of the solder alloy and therefore reduces the tensile strength after aging. The upper limit of the Ag content is 4.0% or less, preferably 3.8% or less, more preferably 3.7% or less, and even more preferably 3.6% or less.

[0044] On the other hand, if the Ag content is less than 3.0%, the Ag3Sn network structure is not formed, and the tensile strength after aging decreases. 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%.

[0045] (2) Cu: 0.1 to 1.0% Cu reduces surface tension and improves tensile strength and tensile strength after aging through precipitation strengthening. If the Cu content exceeds 1.0%, coarse Cu6Sn5 is formed, resulting in a decrease in tensile strength after aging. 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.

[0046] 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 tensile strength after aging. 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%.

[0047] (3) Sb: 3.1 to 6.0% Sb reduces surface tension by forming fine SnSb particles. It also improves tensile strength and tensile strength after aging. If the Sb content exceeds 6.0%, coarse SnSb compounds precipitate, inhibiting the fluidity of the molten solder, increasing the surface tension and preventing it from decreasing. Furthermore, the tensile strength after aging is poor. The upper limit of the Sb content is 6.0%, preferably 5.5%, more preferably 5.0%, and even more preferably 4.5%.

[0048] On the other hand, if the Sb content is less than 3.1%, precipitation strengthening is not achieved and solid solution strengthening is insufficient, resulting in a deterioration in tensile strength and tensile strength after aging. The lower limit of the Sb content is 3.1% or more, preferably 3.5% or more, more preferably 4.0% or more, and even more preferably 4.1% or more. The preferred range of Sb is 4.1 to 6.0%.

[0049] (4) Bi: 0.1 to 1.5% Bi improves wettability by reducing surface tension, and can improve tensile strength and tensile strength after aging through solid solution strengthening. If the Bi content exceeds 1.5%, Bi beyond the solid solubility limit segregates, promoting hardening and embrittlement of the solder alloy, resulting in poor tensile strength after aging. 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, particularly preferably 0.8% or less, and most preferably 0.7% or less.

[0050] On the other hand, if the Bi content is less than 0.1%, the amount of Bi dissolved in the alloy will be insufficient, resulting in poor tensile strength after aging. Furthermore, the low Bi content makes it impossible to reduce the surface tension. The lower limit of the Bi content is 0.1% or more, preferably 0.3% or more, more preferably 0.4% or more, and even more preferably 0.5% or more. The preferred range of Bi is 0.5 to 1.5%.

[0051] (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. In contributes to the precipitation of various compounds, and the precipitated compounds exhibit fine precipitation behavior, so high wettability is maintained. Furthermore, In contributes to improving tensile strength after aging by controlling the phase transformation of Sn.

[0052] 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 tensile strength after aging. 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.

[0053] 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 tensile strength after aging. Also, because the In content is low, fine InSb does not precipitate, and the effect of improving wettability is not achieved. The lower limit of In is 0.2% or more, preferably 0.6% or more, 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%.

[0054] (6) Ni: 0.02-0.07% Ni functions as a solidification nucleus during solidification of molten solder, suppressing supercooling and resulting in fine Sn crystal grains, improving tensile strength after aging. Furthermore, the precipitation of fine SnNi compounds reduces surface tension, and at a certain content, it can suppress an increase in liquidus temperature. If the Ni content exceeds 0.07%, the precipitation of coarse SnNi compounds inhibits the fluidity of the molten solder, increasing surface tension and reducing wettability. This, in turn, reduces tensile strength after aging. Furthermore, the liquidus temperature increases. The upper limit of the Ni content is 0.07% or less, preferably 0.06% or less, and more preferably 0.05% or less.

[0055] On the other hand, if the Ni content is less than 0.02%, the alloy structure will not be refined and the tensile strength after aging will decrease. The lower limit of the Ni content is 0.02% or more, preferably 0.03% or more, and more preferably 0.04% or more. The preferred range of Ni is 0.04 to 0.05%.

[0056] (7) Co: 0.0010 to 0.0200% Co disperses and precipitates SnCo compounds in the solder alloy, resulting in a finer alloy structure and improving tensile strength after aging. If the Co content exceeds 0.0200%, the liquidus temperature rises and the surface tension deteriorates due to the precipitation of coarse SnCo compounds. The upper limit of the Co content is 0.0200% or less, preferably 0.0150% or less, more preferably 0.0120% or less, even more preferably 0.0100% or less, and particularly preferably 0.0090% or less.

[0057] On the other hand, if the Co content is less than 0.0010%, the alloy structure will not be refined and the tensile strength after aging will decrease. The lower limit of the Co content is 0.0010% or more, preferably 0.0030% or more, more preferably 0.0050% or more, even more preferably 0.0060% or more, and particularly preferably 0.0080% or more. The preferred range of Co is 0.0060 to 0.0100%.

[0058] (8) Equations (1) to (4) 0.00029≦Sb×Ni×Co / (Cu×Bi×In)≦0.00151 (1) 0.0039≦Ag×Cu×Sb×In×Ni×Co / Bi≦0.0332 (2) 4.0≦Cu×Sb×In≦20.0 (3) 265≦Ag×Sb / Ni≦499 (4) In the above formulas (1) to (4), Ag, Cu, Bi, Sb, In, Ni, and Co each represent the content (mass %) of the alloy composition.

[0059] 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 tensile strength after aging. To achieve these effects simultaneously at a high level with a single composition, it is more preferable that the constituent elements are within the aforementioned ranges and that the following formulas (1) to (4) are satisfied. The technical significance of each formula is as follows:

[0060] Formula (1) is a relational expression that takes into account the content of elements that deteriorate wettability when their content exceeds the upper limit and the content of elements that deteriorate wettability when their content falls below the lower limit. Formula (2) is a relational expression that takes into account the content of elements that form compounds and the content of elements that do not form compounds. Formula (3) is a relational expression that takes into account the content of elements that contribute to tensile strength. Formula (4) is a relational expression that takes into account the content of three elements: Ag, which contributes to improving tensile strength after aging; Ni, which suppresses the rise in liquidus temperature and contributes to improving tensile strength after aging; and Sb, which is contained in a higher amount than conventional materials and contributes to reducing surface tension and improving tensile strength and tensile strength after aging.

[0061] Formulas (1) to (4) are formulas that encompass all the essential elements that constitute the solder alloy of the present invention. As described above, a solder alloy that satisfies each formula can exert the effects of the present invention at an even higher level with just one composition.

[0062] The upper limit of formula (1) is preferably 0.00151 or less, more preferably 0.00114 or less, even more preferably 0.00109 or less, still more preferably 0.00091 or less, particularly preferably 0.00080 or less, most preferably 0.00076 or less, and may further be 0.00069 or less, 0.00065 or less, or 0.00063 or less. The lower limit of formula (1) is preferably 0.00029 or more, more preferably 0.00030 or more, even more preferably 0.00032 or more, still more preferably 0.00034 or more, particularly preferably 0.00037 or more, most preferably 0.00038 or more, or may further be 0.00040 or more, 0.00046 or more, 0.00048 or more, 0.00053 or more, 0.00055 or more, or 0.00057 or more. A more preferable range of the formula (1) is 0.00037 to 0.00109. The above upper and lower limits can each define a more preferable range of the formula (1).

[0063] The upper limit of formula (2) is preferably 0.0332 or less, more preferably 0.0286 or less, even more preferably 0.0272 or less, even more preferably 0.0238 or less, particularly preferably 0.0228 or less, particularly more preferably 0.0224 or less, and most preferably 0.0218, and may even be 0.0202 or less or 0.0190 or less. The lower limit of formula (2) is preferably 0.0039 or more, more preferably 0.0076 or more, even more preferably 0.0095 or more, even more preferably 0.0114 or more, particularly preferably 0.0118 or more, particularly more preferably 0.0127 or more, and most preferably 0.0143 or more, or even 0.0152 or more, 0.0156 or more, 0.0159 or more, 0.0163 or more, 0.0168 or more, or 0.0179 or more. A more preferable range of the formula (2) is 0.0152 to 0.0272. The above upper and lower limits can each define a more preferable range of the formula (2).

[0064] The upper limit of formula (3) is preferably 20.0 or less, more preferably 17.5 or less, even more preferably 15.0 or less, and even more preferably 14.4 or less. The lower limit of formula (3) is preferably 4.0 or more, more preferably 7.0 or more, even more preferably 10.5 or more, even more preferably 10.9 or more, and particularly preferably 14.0 or more. A more preferable range of the formula (3) is 10.5 to 17.5. The above upper and lower limits can each define a more preferable range of the formula (3).

[0065] The upper limit of formula (4) is preferably 499 or less, more preferably 450 or less, even more preferably 425 or less, even more preferably 400 or less, and particularly preferably 375 or less. The lower limit of formula (4) is preferably 265 or more, more preferably 283 or more, even more preferably 340 or more, and even more preferably 348 or more. A more preferable range of the formula (4) is 340 to 425. The above upper and lower limits can each define a more preferable range of the formula (4).

[0066] The values ​​shown in Tables 1 and 2, which are the measured values ​​of the alloy composition, were used in the calculations of equations (1) to (4). Regarding the values ​​calculated from equations (1) to (4), equation (1) is calculated to five decimal places, equation (2) is calculated to four decimal places, equation (3) is calculated to one decimal place, and equation (4) is calculated as an integer. This calculation rule is used in this application, and is intended to be used in the same way for calculations regarding additional solder alloys described in other documents, etc., since all solder alloys must be treated in the same way.

[0067] (9) 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.

[0068] (10) Remainder: Sn The balance of the solder alloy according to the present invention is Sn. In addition to the above elements, the solder alloy may contain unavoidable impurities. The balance of the solder alloy according to the present invention may consist of Sn and unavoidable impurities. Even if the solder alloy contains unavoidable impurities, the above-mentioned effects are not affected.

[0069] 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 and less than 0.535 N / m, the solder alloy can wet electrodes without any problems. If it exceeds 0.535 N / m, the solder alloy has poor wettability.

[0070] 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 %.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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]

[0079] 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 1 and 2 were evaluated for (1) solidus temperature and liquidus temperature, (2) surface tension, (3) tensile strength, and (4) tensile strength after aging.

[0080] (1) Solidus and liquidus temperatures For solder alloys having each alloy composition listed in Tables 1 and 2, the respective temperatures were determined from the DSC curves. The DSC curves were obtained by raising the temperature at 5°C / min in the atmosphere using a Seiko Instruments Inc. DSC (model number: 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 205°C or higher and less than 230°C, it was judged as "◎". When the liquidus temperature was 230°C or higher but less than 246°C, it was judged as "◯". When the liquidus temperature was 246°C or higher, it was judged as "X".

[0081] (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 "×".

[0082] (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 of 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 90 MPa or greater were evaluated as "◎", those of 85 MPa or greater but less than 90 MPa were evaluated as "〇", and those less than 85 MPa were evaluated as "×".

[0083] (4) Tensile strength after aging Test pieces similar to those in "(3) Tensile strength" were prepared and subjected to aging treatment in a thermostatic chamber in the atmosphere at 105°C for 200 hours. The test pieces after the aging treatment were subjected to a tensile test in a 105°C environment, similar to "(3) Tensile strength". Tensile strengths of 43 MPa or more were judged as "◎", those of 42 MPa or more but less than 43 MPa were judged as "◯", and those of less than 42 MPa were judged as "×".

[0084] [Table 1]

[0085] [Table 2]

[0086] As is clear from Tables 1 and 2, in Examples 1 to 48, the contents of the essential elements Ag, Cu, Sb, Bi, In, Ni, and Co were all within the ranges of the present invention, and therefore all were evaluated as "good" or "double circle." In particular, in Examples 1 to 4, 7, 8, 11, 12, 17 to 19, 24 to 29, 33, 34, 37, 38, and 40 to 48, which satisfied the formulas (1) to (4), all were evaluated as "good," demonstrating superior results among the Examples.

[0087] On the other hand, Comparative Examples 1 and 2 had poor tensile strength after aging due to an inappropriate Ag content. Comparative Example 3 had poor surface tension, tensile strength, and tensile strength after aging due to a low Cu content. Comparative Example 4 had poor tensile strength after aging due to a high Cu content.

[0088] Comparative Example 5 had a low Sb content, which resulted in poor tensile strength and tensile strength after aging. Comparative Example 6 had a high Sb content, which resulted in poor surface tension and tensile strength after aging. Comparative Examples 7 to 9 did not contain Bi or had a low Bi content, which resulted in poor surface tension and tensile strength after aging. Comparative Example 10 had a high Bi content, which resulted in poor tensile strength after aging.

[0089] Comparative Example 11 had a low In content, resulting in poor surface tension, tensile strength, and tensile strength after aging. Comparative Example 12 had a high In content, resulting in poor tensile strength after aging. Comparative Example 13 had a low Ni content, resulting in poor tensile strength after aging. Comparative Example 14 had a high Ni content, resulting in a high liquidus temperature and poor surface tension and tensile strength after aging.

[0090] Comparative Example 15 had poor tensile strength after aging due to the low Co content, while Comparative Example 16 had a high Co content, which increased the liquidus temperature and resulted in poor surface tension.

[0091] 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, with Figure 1(a) being Comparative Example 12, Figure 1(b) being Example 3, and Figure 1(c) being Example 25. Figure 2 is an SEM photograph of Figure 1, enlarged 3000 times, with Figure 2(a) being Comparative Example 12, Figure 2(b) being Example 3, and Figure 2(c) being Example 25. As is clear from Figures 1 and 2, it was found that InSb and Ag3(Sn,In) precipitated in Example 3 and Example 25. On the other hand, it was found that InSb and Ag3(Sn,In) coarsened in Comparative Example 12 due to the high In content.

[0092] 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.

[0093] 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.

[0094] (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:

[0095] 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.

[0096] (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".

[0097] [Table 3]

[0098] 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, 3.1 to 6.0% Sb, 0.1 to 1.5% Bi, 0.2 to 6.0% In, 0.02 to 0.07% Ni, 0.0010 to 0.0200% 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. 3. The solder alloy according to claim 1, wherein the alloy composition satisfies the following formulas (1) to (4): 0.00029≦Sb×Ni×Co / (Cu×Bi×In)≦0.00151 (1) 0.0039≦Ag×Cu×Sb×In×Ni×Co / Bi≦0.0332 (2) 4.0≦Cu×Sb×In≦20.0 (3) 265≦Ag×Sb / Ni≦499 (4) In the above formulas (1) to (4), Ag, Cu, Bi, Sb, In, Ni, 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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