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

The present invention provides 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 that have a low melting point, have high shear strength, exhibit an appropriate fracture mode, and have excellent heat cycle resistance. The solder alloy has an alloy composition comprising, in mass%, 2.0-3.6% Ag, 0.6-0.9% Cu, 1.0-5.0% In, 3.0-5.0% Sb, 0.0010-0.0300% Fe, and 0.0010-0.0500% Co, with the remainder being Sn. Preferably, the alloy composition further contains, in mass%, at least one of Zr, Ge, Ga, P, As, Pb, Zn, Mg, Cr, Ti, Mo, Pt, Pd, Au, Al, and Si in a total amount of 0.100% or less.

Description

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

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

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

[0003] For example, automotive electronic circuits mounted in the engine compartment may be exposed to temperatures as high as 125°C or higher when the engine is running. On the other hand, when the engine is stopped, in cold regions, they may be exposed to temperatures as low as -40°C or lower. Highly reliable solder alloys are used for automotive electronic circuits that are used in such harsh environments.

[0004] Conventionally, Sn—Ag—Cu solder alloys have been used as versatile solder alloys. However, as mentioned above, in harsh environments not previously anticipated, Sn—Ag—Cu solder alloys have the risk of thickening the intermetallic compound layer formed at the joint interface, which can cause peeling at the joint interface between the electrode and the solder alloy due to shear stress. For this reason, there is a demand for solder alloys that can maintain joint strength even in harsh usage environments, and various studies have been conducted.

[0005] Patent Document 1 discloses a Sn—Ag—Cu—In—Sb—Co—Ge solder alloy, which contains In, Sb, and Co in a Sn—Ag—Cu solder alloy, as a solder alloy with high heat cycle resistance. The document explains that this solder alloy can suppress lift-off in addition to heat cycle resistance. To achieve this effect, the document also describes the addition of In instead of Bi, which has traditionally been added to suppress the melting point increase caused by Sb, in order to improve lift-off.

[0006] Patent Document 2 discloses a Sn-Ag-Cu-In-Sb-Ni-Co solder alloy as a solder alloy with high heat cycle resistance. The document explains that this solder alloy can suppress void generation and lift-off in addition to heat cycle resistance. The document also describes that by balancing the Sb and In contents, not only can heat cycle resistance be improved but also lift-off and void generation can be suppressed. The document also describes that the solder alloy may further contain Fe or the like from the viewpoint of heat cycle resistance and suppressing void generation.

[0007] Patent No. 6349615 Patent No. 6420936

[0008] As mentioned above, in both of the inventions described in Patent Documents 1 and 2, evaluations of heat cycle resistance and lift-off are carried out. Patent Document 2 further evaluates the occurrence of voids. Furthermore, evaluations of the melting point are carried out in order to suppress an increase in the reflow temperature.

[0009] However, these evaluations alone are not sufficient for solder alloys used in automotive electronic circuits. For example, when a vehicle equipped with an electronic circuit drives on rough roads, the electronic circuit is subjected to external stress. For this reason, high shear strength is extremely important for solder joints.

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

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

[0012] On the other hand, as mentioned above, heat cycle tests are used to evaluate solder joints in environments where stress is continuously applied. In this regard, the inventions described in Patent Documents 1 and 2 examine heat cycle resistance. However, Patent Document 1 evaluates the total length of cracks at 2000 cycles as the average value of four samples. Furthermore, Patent Document 2 appears to have observed the occurrence of cracks at 3000 cycles in 10 samples and evaluated the occurrence of cracks that crossed the solder joint.

[0013] As described in Patent Document 1, when evaluation is based solely on the average value, if there are samples with short crack lengths and samples with long crack lengths, and the sample with a smaller average value is treated as having a superior evaluation, the sample will be overlooked even though there is still a problem with heat cycle resistance in the solder joint if a sample with a long crack length is included.

[0014] The evaluation described in Patent Document 2 is thought to be able to generally grasp cracks that completely fracture the solder joint. However, even if there are samples that do not cross the solder joint but are close to crossing it, the sample is treated as having an excellent evaluation. If a large number of samples out of 10 have cracks that are close to crossing the solder joint, it is inevitable to conclude that there are some issues, but such a group of samples is also treated as having an excellent evaluation. Furthermore, the invention described in Patent Document 2 happens to evaluate cracks at 3,000 cycles, but if there is a concern that several more cycles would cause multiple cracks that cross the solder joint, it must be considered that there are still issues with heat cycle resistance.

[0015] In particular, for solder joints mounted on automotive electronic circuits, fracture of the solder joints must be minimized from a safety perspective. In the heat cycle resistance evaluations in Patent Documents 1 and 2, there is a possibility that some samples may fracture in an extremely short cycle. In other words, if there is a large variation in the evaluation results, even samples that are thought to be problem-free may include some that fracture immediately.

[0016] As described above, Patent Documents 1 and 2 do not consider shear strength and fracture mode, which are important characteristics of solder joints. Furthermore, as automobiles have become increasingly electrified in recent years, the number of circuit boards mounted on them is expected to continue to increase, so there is an urgent need to develop solder alloys that can ensure heat cycle resistance with a high probability. Furthermore, in consideration of the heat resistance of electronic components, it is also desirable for the solder alloys to exhibit a melting point comparable to that of conventional solder alloys.

[0017] Therefore, an object of the present invention is to provide a solder alloy, a solder paste, a solder ball, a solder preform, a solder joint, an on-vehicle electronic circuit, an ECU electronic circuit, an on-vehicle electronic circuit device, and an ECU electronic circuit device that have a low melting point, high shear strength, an appropriate fracture mode, and excellent heat cycle resistance.

[0018] The present inventors have reexamined the solder alloys disclosed in Patent Documents 1 and 2. Among the solder alloys disclosed in both documents, the Sn—Ag—Cu—In—Sb—Co—Ge solder alloy in Example 12 of Patent Document 1 and the Sn—Ag—Cu—In—Sb—Ni—Co—Fe solder alloy in Example 15 of Patent Document 2 both have shear strengths comparable to conventional solder alloys, and they have found that there is room for improvement.

[0019] These solder alloys do not have alloy compositions designed for the purpose of improving shear strength. For each solder alloy, if the content of even one of its constituent components differs, the overall properties will usually differ, and it should be understood that the entire combination of alloying elements with a specified content is technically evaluated as a single entity.

[0020] Therefore, the present inventors conducted detailed research into the improvement of shear strength and the fracture mode while suppressing an increase in melting point. As a result, they discovered that adding a predetermined amount of Fe to Example 12 of Patent Document 1 lowers the melting point by approximately 8 to 10°C. This is presumably because adding a predetermined amount of Fe to a Sn-Ag-Cu-In-Sb-Co-Ge solder alloy further refines the structure of the solder alloy due to a synergistic effect with Co, thereby suppressing the precipitation of coarse compounds.

[0021] Furthermore, it was found that adding Fe to a Sn-Ag-Cu-In-Sb-Co-Ge solder alloy results in equivalent melting points, shear strengths, and fracture modes regardless of the presence or absence of Ge. Accordingly, it was found that Ge can be treated as an optional element in a Sn-Ag-Cu-In-Sb-Co-Fe solder alloy.

[0022] It was found that Example 15 of Patent Document 2 had a slightly higher melting point. This is presumably because, when Ni is contained in a Sn—Ag—Cu—In—Sb—Co—Fe solder alloy, a solid phase due to Ni begins to precipitate at a higher temperature during the solidification process. It is also believed that the melting point increased due to a slight deviation from the Sn—Ag—Cu eutectic composition due to the low Cu content. Therefore, it was found that removing Ni from Example 15 of Patent Document 2 and increasing the Cu content by 0.1 to 0.4% lowered the melting point and significantly improved the shear strength.

[0023] Furthermore, it was found that in a composition containing Co and / or Fe to the extent that the alloy structure becomes fine, fracture occurs in the bulk, and therefore an appropriate fracture mode is exhibited. However, it was also found that even if the contents of Co and / or Fe are adjusted, if the contents of Ag and / or Sb are too high, fracture occurs at the bonding interface. This is presumably because the bulk strength is improved by the precipitation of compounds, and a similar result occurs when the contents of Co and / or Fe are too high. It was also found that if the Cu content is high, the shear strength deteriorates and the fracture mode becomes the bonding interface. This is because hypereutectic crystals form and coarse Cu particles appear at the bonding interface. ６ Sn ５ It is presumed that this is due to the precipitation of

[0024] In addition to the above findings, Patent Documents 1 and 2 indicate that heat cycle resistance can be exhibited. However, the present inventors have confirmed that even in the examples of each patent document, some solder alloys fracture after an extremely short cycle. This indicates a large variation in evaluation results. Therefore, even solder alloys that have been considered to have high heat cycle resistance using conventional evaluation methods include those with low heat cycle resistance, and more accurate evaluation is therefore necessary. Therefore, the present inventors have come to the conclusion that the most effective way to evaluate heat cycle resistance is to evaluate the number of cycles to fracture using the standard deviation. By evaluating using the standard deviation, solder alloys with low heat cycle resistance that have previously been overlooked can be identified, enabling the heat cycle resistance to be evaluated with greater accuracy.

[0025] The inventors then evaluated the heat cycle resistance by calculating the standard deviation of the number of cycles to fracture. As a result, they found that a solder alloy in which each constituent element falls within a predetermined range not only has a low melting point, high shear strength, and an appropriate fracture mode, as described above, but also has a standard deviation of the number of cycles to fracture that is equal to or less than a predetermined value, and thus the present invention was completed. The present invention, which was completed based on these findings, is as follows.

[0026] (0) A solder alloy characterized by having, by mass%, an alloy composition consisting of 2.0 to 3.6% Ag, 0.6 to 0.9% Cu, 1.0 to 5.0% In, 3.0 to 5.0% Sb, 0.0010 to 0.0300% Fe, 0.0010 to 0.0500% Co, and the balance being Sn. (1) A solder alloy characterized by having, by mass%, an alloy composition consisting of 2.0 to 3.6% Ag, 0.6 to 0.9% Cu, 1.0 to 5.0% In, 3.0 to 5.0% Sb, 0.0010 to 0.0300% Fe, 0.0010 to 0.0500% 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 %, 0.100% or less in total of at least one of Zr, Ge, Ga, P, As, Pb, Zn, Mg, Cr, Ti, Mo, Pt, Pd, Au, Al, and Si.

[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): 0.0020≦Ag×Cu×In×Sb×Fe×Co≦0.0090 (1) 445≦In / (Ag×Cu×Sb×Fe×Co)≦3560 (2) In the formulas (1) and (2), Ag, Cu, In, Sb, Fe, and Co are each the content in mass % of the solder alloy.

[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 comprising 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 according to (9) above.

[0037] FIG. 1 shows optical microscope photographs of the samples after measuring the shear strength, where FIG. 1(a) is Example 4, FIG. 1(b) is Comparative Example 19, and FIG. 1(c) is Comparative Example 3.

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

[0040] On the other hand, if the Ag content exceeds 3.6%, the Ag content becomes hypereutectic. ３Because a large amount of Sn precipitates, the bulk strength increases, and the fracture mode becomes the bonding interface. Also, the shear strength decreases, and the melting point may increase due to the large amount of compound precipitated. Furthermore, because the bulk strength increases, cracks occur during heat cycle testing, the standard deviation increases, and the heat cycle resistance decreases. The upper limit of the Ag content is 3.6% or less, preferably 3.4% or less, and more preferably 3.2% or less.

[0041] (2) Cu: 0.6 to 0.9% Cu contributes to improving shear strength, optimizing the fracture mode by controlling the amount of intermetallic compounds formed at the bonding interface, lowering the melting point, and improving heat cycle resistance. In addition, if the content is appropriate, coarse Cu ６ Sn ５ When the Cu content is less than 0.6%, the precipitation of Cu can be suppressed. ６ Sn ５ The lower limit of the Cu content is 0.6% or more, preferably 0.7% or more.

[0042] On the other hand, if the Cu content exceeds 0.9%, the alloy becomes hypereutectic, and coarse Cu particles appear at the bonding interface. ６ The shear strength deteriorates due to the precipitation of Sn5. Also, the fracture mode becomes the bonding interface. Furthermore, due to the deterioration of the shear strength, cracks occur during the heat cycle test, the standard deviation increases, and the heat cycle resistance deteriorates. The upper limit of the Cu content is 0.9% or less, preferably 0.8% or less.

[0043] (3) In: 1.0 to 5.0% In contributes to improving shear strength, optimizing fracture mode, and improving heat cycle resistance. If the In content is less than 1.0%, the shear strength will be poor, and the wettability will be reduced, resulting in insufficient wetting and spreading, and the effect of solid solution strengthening will be insufficient, resulting in an inappropriate fracture mode and poor heat cycle resistance. The lower limit of the In content is 1.0% or more, preferably 1.5% or more, more preferably 2.0% or more, even more preferably 2.5% or more, and particularly preferably 3.0% or more.

[0044] On the other hand, if the In content exceeds 5.0%, a large amount of compounds are precipitated, causing an increase in the melting point. Furthermore, the bulk strength is excessively increased, resulting in a decrease in shear strength. Furthermore, there is a concern of fracture at the joining interface or at the component. Furthermore, because the bulk strength increases, cracks occur during heat cycle testing, the standard deviation value increases, and heat cycle resistance deteriorates. The upper limit of the In content is 5.0% or less, preferably 4.5% or less, more preferably 4.0% or less, and even more preferably 3.5% or less.

[0045] (4) Sb: 3.0 to 5.0% Sb contributes to suppressing the rise in melting point, improving shear strength, optimizing the fracture mode, and improving heat cycle resistance. If the Sb content is less than 3.0%, the solid solution strengthening with respect to Sn and the precipitation strengthening of Sn-Sb compounds are insufficient, resulting in poor shear strength. The lower limit of the Sb content is 3.0% or more, preferably 3.5% or more, more preferably 3.6% or more, even more preferably 3.8% or more, particularly preferably 3.9% or more, and most preferably 4.0% or more.

[0046] On the other hand, if the Sb content exceeds 5.0%, coarse SnSb compounds are formed, resulting in poor shear strength. Furthermore, wettability deteriorates, and the failure mode becomes the joint interface or component failure, which is inappropriate. Furthermore, because the bulk strength increases, cracks occur during heat cycle testing, the standard deviation increases, and heat cycle resistance deteriorates. The upper limit of the Sb content is 5.0% or less, preferably 4.8% or less, more preferably 4.6% or less, even more preferably 4.5% or less, particularly preferably 4.3% or less, and most preferably 4.1% or less.

[0047] (5) Fe: 0.0010 to 0.0300% Fe contributes to improving shear strength, optimizing the fracture mode, and improving heat cycle resistance. If the Fe content is less than 0.0010%, the effect of strengthening the interface by modifying the intermetallic compound layer formed at the interface is insufficient, resulting in poor shear strength. The lower limit of the Fe content is 0.0010% or more, preferably 0.0050% or more, more preferably 0.0100% or more, even more preferably 0.0150% or more, and particularly preferably 0.0200% or more.

[0048] On the other hand, if the Fe content exceeds 0.0300%, a compound of Sn and Fe precipitates, which excessively improves the bulk strength, resulting in a deterioration in shear strength and a risk of fracture at the bonding interface. The upper limit of the Fe content is 0.0300% or less, preferably 0.0270% or less, and more preferably 0.0250% or less.

[0049] (6) Co: 0.0010 to 0.0500% Co contributes to suppressing the rise in melting point, improving shear strength, optimizing the fracture mode, and improving heat cycle resistance. If the Co content is less than 0.0010%, the bulk grain refinement effect is insufficient, resulting in a decrease in shear strength. The lower limit of the Co content is 0.0010% or more, preferably 0.0030% or more, more preferably 0.0060% or more, and even more preferably 0.0080% or more.

[0050] On the other hand, if the Co content exceeds 0.0500%, Sn and Co compounds precipitate, increasing the bulk strength, causing the fracture mode to occur at the bonding interface. Furthermore, the large amount of compound precipitation significantly increases the melting point, worsening wettability and reducing shear strength. Furthermore, the increased bulk strength leads to cracks during heat cycle testing, increasing the standard deviation and resulting in poor heat cycle resistance. The upper limit of the Co content is 0.0500%, preferably 0.0300%, and more preferably 0.0100%.

[0051] (7) Balance: Sn The balance of the solder alloy according to the present invention is Sn. In addition to the above elements, unavoidable impurities may be contained. Even if unavoidable impurities are contained, the above-mentioned effects are not affected. In the present invention, Ni is preferably not contained in a Sn-Ag-Cu-In-Sb-Fe-Co solder alloy, because the melting point rises sharply with the addition of a small amount when the respective contents are within the above-mentioned ranges. Furthermore, Mn is preferably not contained in the present invention because it increases the melting point, deteriorates wettability, prevents the formation of appropriate compounds, and reduces shear strength. Furthermore, Bi forms a Sn-In-Bi low-melting-point phase when coexisting with In. Considering creep deformation, the low-melting-point phase has a low melting point that makes a room temperature environment a high-temperature environment, making it prone to creep deformation and reducing strength. Therefore, it is preferable not to contain Bi in the present invention.

[0052] (8) At least one of Zr, Ge, Ga, P, As, Pb, Zn, Mg, Cr, Ti, Mo, Pt, Pd, Au, Al, and Si in a total content of 0.100% or less The solder alloy according to the present invention may contain at least one of Zr, Ge, Ga, P, As, Pb, Zn, Mg, Cr, Ti, Mo, Pt, Pd, Au, Al, and Si in a total content of 0.100% or less as an optional element, to the extent that the effects of the present invention are not impaired. Preferably, the total content is 0.080% or less. The lower limit of the content is not particularly limited, but may be 0.0001% or more, and may be 0.001% or more.

[0053] (9) Formulas (1) and (2): 0.0020≦Ag×Cu×In×Sb×Fe×Co≦0.0090 (1) 445≦In / (Ag×Cu×Sb×Fe×Co)≦3560 (2) In the formulas (1) and (2), Ag, Cu, In, Sb, Fe, and Co are each the content in mass % of the solder alloy.

[0054] Formula (1) takes into consideration the balance of the additive elements of the solder alloy of the present invention. The solder alloy of the present invention can exhibit a low melting point, high shear strength, an appropriate fracture mode, and high heat cycle resistance due to the synergistic effects of each constituent element. Therefore, if the balance of all constituent elements except Sn is further optimized, all of the effects of the present invention can be further improved. In formula (1), the contents of Ag, Cu, In, and Sb are approximately 10 to 100 times the contents of Fe and Co. However, their contribution to the solder alloy is considered to be approximately the same. Therefore, in order to further improve the low melting point, high shear strength, an appropriate fracture mode, and high heat cycle resistance simultaneously in a single composition, it is preferable to maintain a balanced content.

[0055] Formula (2) is a formula that takes into consideration the balance between In and other elements among the additive elements of the solder alloy of the present invention. Compared to other additive elements, if the In content is below the lower limit or above the upper limit of the content range, the shear strength is inferior and the fracture mode becomes inappropriate. This is a phenomenon unique to the Sn—Ag—Cu—In—Sb—Co—Fe solder alloy of the present invention. Although the reason for this is unclear, it is presumed that the decrease in wettability results in insufficient wetting and spreading, and the effect of solid solution strengthening is insufficient.

[0056] In calculating the formulas (1) and (2), the numerical values ​​themselves are used in the measured values ​​of the alloy compositions shown in Tables 1 and 2 below. That is, in calculating the formulas (1) and (2), all digits less than the number of significant figures in the measured values ​​shown in Tables 1 and 2 below are treated as zeros. For example, if the measured Co content is "0.008" mass%, the Co content used in calculating the formulas (1), (2), and (2) is treated as "0.008000..." rather than having a range of 0.0075 to 0.0084%. In formula (1), calculations are made to the fifth decimal place, and the fifth decimal place is rounded to the fourth decimal place. In formula (2), calculations are made to the first decimal place, and the first decimal place is rounded to the first decimal place to obtain the last decimal place. The same applies when formulas (1) and (2) are calculated from alloy compositions specifically disclosed in patent documents and other documents mentioned in this specification.

[0057] As mentioned above, alloys do not function individually, but rather all the constituent elements form a single entity as a whole. Therefore, it is rare for a single element to simultaneously exhibit all of the excellent effects. Therefore, as mentioned above, in order to achieve even better properties within the optimal content range of each constituent element, it is necessary to consider the constituent elements as a whole. In the solder alloy of the present invention, in order to achieve a low melting point, high shear strength, appropriate fracture mode, and high heat cycle resistance at an even higher level with a single composition, it is preferable that the formulas (1) and (2) be satisfied.

[0058] The lower limit of formula (1) is preferably 0.0020 or more, more preferably 0.0021 or more, even more preferably 0.0022 or more, still more preferably 0.0023 or more, particularly preferably 0.0024 or more, and most preferably 0.0028 or more, 0.0029 or more, 0.0033 or more, 0.0034 or more, 0.0035 or more, 0.0036 or more, 0.0038 or more, 0.0042 or more, 0.0043 or more, 0.0045 or more, 0.0046 or more, 0.0048 or more, 0.0049 or more, 0.0050 or more, or 0.0057 or more. The upper limit of formula (1) is preferably 0.0090 or less, more preferably 0.0086 or less, even more preferably 0.085 or less, still more preferably 0.0083 or less, particularly preferably 0.0076 or less, and most preferably 0.0073 or less, 0.0071 or less, 0.0069 or less, 0.0068 or less, 0.0067 or less, 0.0066 or less, 0.0065 or less, 0.0064 or less, 0.0061 or less, or 0.0060 or less.

[0059] The lower limit of formula (2) is preferably 445 or more, more preferably 525 or more, even more preferably 630 or more, still more preferably 700 or more, particularly preferably 787 or more, and most preferably 788 or more, 840 or more, 1050 or more, 1225 or more, 1260 or more, 1261 or more, 1313 or more, 1378 or more, 1379 or more, 1400 or more, 1401 or more, 1470 or more, 1471 or more, or 1488 or more. The upper limit of formula (2) is preferably 3560 or less, more preferably 3501 or less, even more preferably 3151 or less, still more preferably 2801 or less, particularly preferably 2679 or less, and most preferably 2678 or less, 2626 or less, 2450 or less, 2451 or less, 2363 or less, 2143 or less, 2142 or less, 2101 or less, 2100 or less, 1970 or less, 1969 or less, 1891 or less, 1890 or less, 1838 or less, 1786 or less, 1785 or less, 1751 or less, 1750 or less, 1681 or less, 1680 or less, 1576 or less, 1575 or less.

[0060] In the examples described below, a rating of "◎" indicates that the result is particularly preferable in practical use compared to "◯." Since "◯" indicates a more preferable result than the prior art, if other evaluation results are also excellent, it falls within the scope of the present invention and is treated as an example. Since "×" indicates an insufficient result in the present invention, it falls outside the scope of the present invention and is treated as a comparative example.

[0061] The heat cycle resistance in the present invention takes into consideration the variation among samples after the heat cycle test, and the smaller the deviation from the average value, the higher the evaluation. Therefore, the meaning is significantly different from the evaluation of heat cycle resistance that has been conventionally considered, which simply compares average values.

[0062] 2. Solder Paste The solder paste according to the present invention is a mixture of solder powder having the above-described alloy composition and flux. The flux used in the present invention is not particularly limited as long as it allows for soldering by conventional methods. Therefore, it is sufficient to use a flux containing a suitable blend of commonly used rosin, organic acid, activator, thixotropic agent, and solvent. The blending ratio of the metal powder component and the flux component in the present invention is not particularly limited, but is preferably 70 to 90 mass% of the metal powder component and 10 to 30 mass% of the flux component.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] The joining method using the solder alloy of the present invention may be carried out in a conventional manner, for example, using a reflow method. The melting temperature of the solder alloy when performing reflow soldering may be approximately 20°C higher than the liquidus temperature. Furthermore, when joining using the solder alloy of the present invention, taking into consideration the cooling rate during solidification can further refine the alloy structure. For example, the solder joint is cooled at a cooling rate of 2 to 3°C / s or more. Other joining conditions can be adjusted as appropriate depending on the alloy composition of the solder alloy.

[0067] 6. On-board electronic circuits, ECU electronic circuits, on-board electronic circuit devices, ECU electronic circuit devices As is clear from the above explanation, the solder alloy according to the present invention has a suppressed increase in melting point, excellent shear strength, an appropriate fracture mode, and excellent heat cycle resistance. Therefore, even when used in automobiles, which are exposed to harsh environments, i.e., when used on-board, fracture of soldered joints is suppressed with uniformity. Therefore, because it has such particularly outstanding properties, it can be seen that the solder alloy according to the present invention is particularly suitable for soldering electronic circuits mounted on automobiles.

[0068] As used herein, "excellent heat cycle resistance" means that, as shown in the examples described below, a heat cycle test is conducted in which the temperature is held at -40°C and +125°C for 10 minutes each, and the standard deviation of the number of cycles until the electrical resistance of the soldered joint increases by 20% from before the heat cycle test is 1000 or less. Such characteristics mean that even when used under extremely harsh conditions such as the heat cycle test, the possibility of breakage of the on-board electronic circuit is minimized, and no unusable or malfunction occurs.

[0069] Thus, the solder alloy according to the present invention is more particularly used for soldering on-board electronic circuits or ECU electronic circuits, and exhibits excellent heat cycle resistance.

[0070] An "electronic circuit" is a system that performs a desired function as a whole through the electronic engineering combination of multiple electronic components, each of which has its own function.

[0071] 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.

[0072] In the present invention, the substrate constituting such an electronic circuit device, for example, a printed wiring board, is not particularly limited. The material is also not particularly limited, but examples include heat-resistant plastic substrates (e.g., FR-4, which has a high Tg and low CTE). The printed wiring board is preferably a printed circuit board in which the Cu land surface is treated with an organic substance (OSP: Organic Surface Protection) such as amine or imidazole.

[0073] 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.

[0074] 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 1 and 2 were used to evaluate (1) melting point, (2) shear strength, (3) fracture mode, and (4) heat cycle resistance test (TCT). Regarding (4), Example 4 and Comparative Example 19 were selected from the following examples and comparative examples, and their evaluation results are shown.

[0075] (1) Melting Point For the solder alloys shown in Tables 1 and 2, each temperature was determined from the DSC curve. The DSC curve was obtained by raising the temperature at 5°C / min in the atmosphere using a Seiko Instruments DSC (Model: 6200). The liquidus temperature was determined from the obtained DSC curve and used as the melting point. If the melting point is 232°C or less, reflow soldering can be performed at temperatures similar to conventional ones. If the melting point is above 232°C, conventional reflow soldering cannot be performed due to the high melting point.

[0076] (2) Shear Strength (2-1) Sample Preparation The solder alloys shown in Tables 1 and 2 were cast to prepare solder sheets (diameter: 1 mm, thickness: 0.15 mm). A reflow furnace (SNR-615, manufactured by Senju Metal Industry Co., Ltd.) was used to solder chip resistors to Cu-OSP electrodes on an FR-4 substrate. The chip resistors used were 3216CR (CR32-114JV, manufactured by Hokuriku Electric Industry Co., Ltd.). The reflow profile consisted of holding at 220°C or higher for 40 seconds in a nitrogen atmosphere, with a peak temperature of 245°C. (2-2) Shear Strength Evaluation The shear strength of the samples prepared in this manner was measured using a shear tester (STR-1000, manufactured by RHESCA) at a shear rate of 6 mm / min. A shear strength of 84.0 N or higher was evaluated as "Excellent." When the shear strength was 70.0 N or more and less than 84.0 N, it was evaluated as "Good." When the shear strength was less than 70.0 N, it was evaluated as "Poor."

[0077] (3) Fracture mode The samples evaluated in "(2) Shear strength" above were observed for fracture mode using an optical microscope (VHX-5000: manufactured by KEYENCE Corporation). When the sample fractured in the bulk, it was evaluated as "◎". When the sample fractured in the bulk and in the intermetallic compound (IMC) at the bonding interface, it was evaluated as "◯". When the sample fractured in the intermetallic compound at the bonding interface, it was evaluated as "×".

[0078] (4) Heat Cycle Resistance Test (TCT) Example 4 from Table 1 and Comparative Example 19 from Table 2 were selected, and each solder alloy was atomized to prepare solder powder. A solder paste of each solder alloy was prepared by mixing with a soldering flux ("GLV" manufactured by Senju Metal Industry Co., Ltd.) consisting of rosin, solvent, activator, thixotropic agent, organic acid, etc. The alloy powder in the solder paste was 88% by mass, and the flux was 12% by mass. The solder paste was printed on a 0.8 mm thick printed circuit board (material: FR-4) using a 100 μm thick metal mask, and then a 12 mm × 12 mm LGA (Land Grid Array) component was mounted using a mounter. Reflow soldering was performed using the same reflow profile as in "(2) (2-1)" above to prepare samples. Fifteen samples were prepared for Example 4, and 14 samples were prepared for Comparative Example 18.

[0079] The prepared samples were placed in a heat cycle tester (TSA-101L-A, manufactured by Espec Corporation) set at a low temperature of -40°C, a high temperature of +125°C, and a holding time of 10 minutes, and the resistance value was measured during the test. A 20% increase in resistance from the initial resistance was considered to have caused breakage, and the average number of cycles at breakage and standard deviation were calculated. When the standard deviation was 1000 or less, the sample was evaluated as having a level of variation that was acceptable for practical use. On the other hand, when the standard deviation was more than 1000, samples were found that were far from the average value, and therefore the sample was evaluated as having a level of variation that was not practical. The evaluation results for (1) to (3) are shown in Tables 1 and 2. The evaluation results for (4) are also shown in Table 3.

[0080]

[0081]

[0082]

[0083] As shown in Tables 1 and 2, Examples 1 to 62 all had appropriate amounts of each constituent element, and therefore all evaluations yielded results that were acceptable for practical use. Furthermore, it was found that Examples 1 to 8, 10 to 17, 19 to 24, 27 to 31, 38, 39, 42, 43, and 46 to 62, which satisfied formulas (1) and (2), showed extremely excellent results in all evaluations. These were results that were significantly superior among the results that were acceptable for practical use.

[0084] On the other hand, as shown in Table 2, Comparative Example 1 did not contain In, Sb, Fe, and Co, and therefore had poor shear strength and an inappropriate fracture mode. Comparative Example 2 had poor shear strength due to a low Ag content. Comparative Examples 3 and 4 had poor shear strength and an inappropriate fracture mode due to a high Ag content.

[0085] Comparative Examples 5 and 6 had poor shear strength due to the low Cu content. In particular, Comparative Example 6 had an inappropriate fracture mode due to the inclusion of Ni. Comparative Example 7 had a poor shear strength and an inappropriate fracture mode due to the high Cu content.

[0086] In Comparative Examples 8 and 9, the shear strength was poor and the fracture mode was inappropriate due to the inappropriate In content. In Comparative Example 10, the shear strength was poor due to the low Sb content. In Comparative Example 11, the shear strength was poor and the fracture mode was inappropriate due to the high Sb content.

[0087] Comparative Examples 12 to 14 had poor shear strength due to the low Fe content, and Comparative Example 15 had poor shear strength and an inappropriate fracture mode due to the high Fe content.

[0088] Comparative Example 16 had poor shear strength due to the low Co content, and Comparative Example 17 had poor shear strength and an inappropriate fracture mode due to the high Co content.

[0089] In Comparative Examples 18 and 20, the melting point was significantly increased due to the inclusion of Ni or Mn, respectively, and the shear strength was poor and the fracture mode was inappropriate. In Comparative Example 19, the shear strength was poor due to the inclusion of Bi.

[0090] Furthermore, as is clear from Table 3, the difference in the average number of cycles between Example 4 and Comparative Example 19 was approximately 300. However, the standard deviation of the number of cycles in Example 4 was less than 1000, whereas the standard deviation of the number of cycles in Comparative Example 19 was significantly greater than 1000.

[0091] Therefore, in Example 4, only samples with small variations in the heat cycle test and small differences from the average were found. It was found that similar results were also obtained in other Examples. On the other hand, in Comparative Example 19, it was found that there were samples with large variations in the heat cycle test and extremely large differences from the average.

[0092] FIG. 1 shows optical microscope photographs of samples after shear strength measurement, with FIG. 1(a) being Example 4, FIG. 1(b) being Comparative Example 19, and FIG. 1(c) being Comparative Example 3. As is clear from FIG. 1, it was found that in Example 4, the solder joint broke due to bulk fracture. On the other hand, in Comparative Example 19, it was found that the solder joint broke due to both bulk fracture and fracture in the intermetallic compound at the joint interface. Furthermore, it was found that in Comparative Example 3, the solder joint broke at the intermetallic compound at the joint interface. Therefore, it was found that the fracture mode in Example 4 was appropriate. This result was similar in the other examples.

[0093] The solder according to the present invention can be used in on-board electronic circuits such as ECUs, which are electronic circuits that control automobiles using computers to improve fuel efficiency, but it can also be used in consumer electronic devices such as personal computers with excellent effects.

Claims

1. A solder alloy having an alloy composition, in mass%, of 2.0 to 3.6% Ag, 0.6 to 0.9% Cu, 1.0 to 5.0% In, 3.0 to 5.0% Sb, 0.0010 to 0.0300% Fe, 0.0010 to 0.0500% Co, and the balance being Sn, wherein the alloy composition satisfies the following formulas (1) and (2): 0.0020≦Ag×Cu×In×Sb×Fe×Co≦0.0090 (1) 445≦In / (Ag×Cu×Sb×Fe×Co)≦3560 (2) In the formulas (1) and (2), Ag, Cu, In, Sb, Fe, and Co are each the content in mass% of the solder alloy.

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

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

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

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

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

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

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

9. An on-vehicle electronic circuit device comprising the on-vehicle electronic circuit according to claim 7.

10. An ECU electronic circuit device comprising the ECU electronic circuit according to claim 8.

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