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

Abstract

To provide a solder alloy which has a low melting point, high shear strength, and an appropriate destruction mode, and excellent heat cycle resistance, a solder paste, a solder ball, a solder preform, a solder joint, an on-vehicle electronic circuit, an ECU electronic circuit, an on-vehicle electronic circuit device, and an ECU electronic circuit device.SOLUTION: A solder alloy has an alloy composition comprising, by mass%, 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 Sn. Preferably, the alloy composition further contains, by mass%, 0.1% or less of the total of at least one of Zr, Ge, Ga, P, As, Pb, Zn, Mg, Cr, Ti, Mo, Pt, Pd, Au, Al and Si.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 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 a vehicle. In particular, on-board electronic circuits called ECUs (Engine Control Units), which are electronic circuits that control the vehicle via 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 can 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, they can be exposed to temperatures as low as -40°C or lower in cold regions. Highly reliable solder alloys are used for automotive electronic circuits that are used in such harsh environments.

[0004] Sn-Ag-Cu solder alloys have traditionally been used as versatile solder alloys. However, as mentioned above, in harsh environments not previously anticipated, the intermetallic compound layer formed at the joint interface of Sn-Ag-Cu solder alloys can thicken, raising concerns that shear stress could cause delamination at the joint interface between the electrode and the solder alloy. For this reason, there is a demand for solder alloys that can maintain their joint strength even in harsh operating environments, and various studies have been conducted.

[0005] Patent Document 1 discloses a Sn-Ag-Cu-In-Sb-Co-Ge solder alloy that contains In, Sb, and Co in a Sn-Ag-Cu solder alloy as a solder alloy with high heat cycle resistance. It is said 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 rise in melting point caused by Sb.

[0006] Patent Document 2 discloses a Sn-Ag-Cu-In-Sb-Ni-Co solder alloy as a solder alloy with high heat cycle resistance. It is said that this solder alloy can suppress void generation and lift-off in addition to heat cycle resistance. The same 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 same 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. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6349615 [Patent Document 2] Patent No. 6420936 Summary of the Invention [Problem to be solved by the invention]

[0008] As mentioned above, the inventions described in Patent Documents 1 and 2 are evaluated for heat cycle resistance and lift-off. Patent Document 2 also evaluates void generation. Furthermore, the melting point is evaluated to prevent an increase in 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 or 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, in Patent Document 1, the total length of cracks at 2000 cycles is evaluated as the average value of four samples. In addition, in Patent Document 2, it appears that the occurrence of cracks at 3000 cycles was observed in 10 samples, and the presence or absence of cracks crossing the solder joint was evaluated.

[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, the sample with the smaller average value will be treated as having a superior rating. In reality, if a sample with long crack lengths is included, the problem of heat cycle resistance as a solder joint will remain, but this problem will be overlooked.

[0014] The evaluation described in Patent Document 2 is likely to provide a general understanding of cracks that completely fracture the solder joint. However, even if there are samples that do not cross the solder joint but nearly do, the sample is still treated as having an excellent rating. If a large number of samples out of 10 have cracks that nearly cross the solder joint, it is inevitable to conclude that there are some issues, but such samples are also treated as having an excellent rating. Furthermore, the invention described in Patent Document 2 happens to evaluate cracks at 3,000 cycles, but if there is a concern that multiple cracks that cross the solder joint would occur if the test cycle were a few more cycles, 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 prevented as much as possible 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 such, Patent Documents 1 and 2 do not consider shear strength and fracture mode, which are important properties for solder joints. Furthermore, with the increasing electrification of automobiles in recent years, the number of circuit boards installed is expected to continue to increase, so there is an urgent need to develop solder alloys that can guarantee high heat cycle resistance. Furthermore, in consideration of the heat resistance of electronic components, it is also desirable for the solder alloys to have a melting point comparable to conventional solder alloys.

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

[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 inventors have found that the shear strength of 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 is comparable to that of conventional solder alloys, and 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 elements 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 the increase in melting point. As a result, it was discovered that adding a predetermined amount of Fe to Example 12 of Patent Document 1 lowers the melting point by approximately 8 to 10 degrees. 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 Sn-Ag-Cu-In-Sb-Co-Ge solder alloys results in the same melting point, shear strength, and fracture mode regardless of whether Ge is present or not. As a result, it was found that Ge can be treated as an optional element in Sn-Ag-Cu-In-Sb-Co-Fe solder alloys.

[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 originating from Ni begins to precipitate at a higher temperature during the solidification process. It is also believed that the low Cu content caused a slight deviation from the Sn-Ag-Cu eutectic composition, resulting in a higher melting point. 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 compositions containing enough Co and Fe to refine the alloy structure exhibited the appropriate fracture mode, since fracture occurred in the bulk. However, even if the Co and Fe contents were adjusted, excessive Ag and Sb contents caused fracture at the bonding interface. This is thought to be because the bulk strength increased due to the precipitation of compounds, and a similar result would occur if the Co or Fe content was too high. It was also found that a high Cu content resulted in a decrease in shear strength and the fracture mode shifted to the bonding interface. This is thought to be due to the formation of a hypereutectic structure, which causes the precipitation of coarse Cu6Sn5 at the bonding interface.

[0024] In addition to the above findings, Patent Documents 1 and 2 indicate that solder alloys can exhibit heat cycle resistance. 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 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] Therefore, the inventors 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 having each constituent element within a predetermined range has a low melting point, high shear strength, and an appropriate fracture mode, as described above, and also found that the standard deviation of the number of cycles to fracture is equal to or less than a predetermined value, thereby completing the present invention. The present invention, which was made based on these findings, is as follows.

[0026] (0) A solder alloy characterized by comprising, in mass%, 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 remainder being Sn. (1) A solder alloy characterized by having an alloy composition consisting of, in mass%, 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 remainder being Sn.

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

[0028] (3) The 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 above formulas (1) and (2), Ag, Cu, In, Sb, Fe, and Co each represent the content in mass % of the solder alloy.

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

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

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

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

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

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

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

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

[0037] [Figure 1] FIG. 1 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. DETAILED DESCRIPTION OF THE INVENTION

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

[0039] 1. Solder alloy (1) Ag: 2.0-3.6% Ag contributes to improving shear strength, optimizing the fracture mode due to Ag3Sn precipitation, 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%, a hypereutectic structure is formed, causing a large amount of Ag3Sn to precipitate, increasing the bulk strength, and the fracture mode becomes the bonded interface. Also, shear strength decreases, and the melting point may increase due to the large amount of compound precipitation. Furthermore, because the bulk strength increases, cracks may occur during heat cycle testing, the standard deviation increases, and heat cycle resistance deteriorates. 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: 0.6-0.9% Cu contributes to improving shear strength, optimizing fracture modes by controlling the amount of intermetallic compounds formed at the bonding interface, lowering the melting point, and improving heat cycle resistance. Furthermore, an appropriate content can suppress the precipitation of coarse Cu6Sn5. If the Cu content is less than 0.6%, Cu6Sn5 does not precipitate sufficiently, resulting in poor shear strength and an increase in the melting point. 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%, a hypereutectic structure occurs, and coarse Cu6Sn5 precipitates at the bonded interface, deteriorating the shear strength. Furthermore, the fracture mode shifts to the bonded interface. Furthermore, because the shear strength deteriorates, cracks occur during heat cycle testing, the standard deviation increases, and the heat cycle resistance deteriorates. The upper limit of the Cu content is 0.9%, preferably 0.8%.

[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 risk of fracture at the joining interface or at the component. Furthermore, because the bulk strength increases, cracks may 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: 3.0-5.0% 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 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 bonded interface or component failure, making it unsuitable. Furthermore, the bulk strength increases, leading to cracks during heat cycle testing, increasing the standard deviation and poor heat cycle resistance. 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 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%, compounds of Sn and Fe are precipitated, which excessively increases the bulk strength, resulting in a decrease in shear strength and the risk of fracture at the bonding interface. The upper limit of the Fe content is 0.0300%, preferably 0.0270%, and more preferably 0.0250%.

[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 bond interface. Furthermore, the large amount of compound precipitation significantly increases the melting point, worsening wettability and reducing shear strength. Furthermore, the increased bulk strength can lead 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) Remainder: Sn The balance of the solder alloy according to the present invention is Sn. In addition to the aforementioned elements, unavoidable impurities may be contained. Even if unavoidable impurities are contained, the aforementioned effects are not affected. In the present invention, Ni is preferably not contained in the 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 is prone to creep deformation and reduces strength because room temperature is a very high temperature environment compared to the melting point. 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, total content of 0.1% 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 amount of 0.1% or less as an optional element, provided that the effect of the present invention is not impaired. Preferably, the total amount is 0.08% or less. There is no particular lower limit to the content, but it should be 0.0001% or more, and may be 0.001% or more.

[0053] (9) Equations (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 above formulas (1) and (2), Ag, Cu, In, Sb, Fe, and Co are each contained in the solder alloy in mass %.

[0054] Formula (1) takes into consideration the balance of the additive elements in 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, a balance of all constituent elements except Sn can further improve all of the effects of the present invention. 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 a 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) 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] The calculations for formulas (1) and (2) use the numerical values shown in the measured values of the alloy composition shown in Tables 1 and 2 below. That is, in the calculations for formulas (1) and (2), all digits less than the number of significant figures in the measured values shown in Tables 1 and 2 below are treated as zeros. For example, if the measured Co content is "0.008" mass%, the Co content used in the calculations for formulas (1) and (2) is treated as "0.008000..." rather than having a range of 0.0075 to 0.0084%. Formula (1) calculates to five decimal places and then rounds the fifth decimal place to four decimal places, while formula (2) calculates to one decimal place and then rounds the first decimal place to one decimal place to find 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, and may be 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, and may be 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, and may be 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, even more preferably 2801 or less, particularly preferably 2679 or less, and most preferably 2678 or less, and may be 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, or 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 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, thixotropic agent, and solvent may be used. The blending ratio of the metal powder component and the flux component in the present invention is not particularly limited, but 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 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.

[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 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.

[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, consideration of the cooling rate during solidification can further refine the alloy structure. For example, the solder joint is cooled at a cooling rate of 2 to 3°C / s or more. Other joining conditions can be adjusted as appropriate depending on the alloy composition of the solder alloy.

[0067] 6. In-vehicle electronic circuit, ECU electronic circuit, in-vehicle electronic circuit device, ECU electronic circuit device As is clear from the above explanation, the solder alloy of 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, i.e., as an in-vehicle component exposed to harsh environments, fracture of solder joints is consistently suppressed. Therefore, because it has such particularly outstanding properties, it can be seen that the solder alloy of 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 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. These characteristics mean that even when used under extremely harsh conditions such as those in the heat cycle test, the possibility of breakage of the on-board electronic circuit is minimized, and no unusable or malfunctioning 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. 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]

[0074] The present invention will be described by the following examples, but the present invention is not limited to the following examples. To demonstrate the effects of the present invention, (1) melting point, (2) shear strength, (3) fracture mode, and (4) heat cycle resistance test (TCT) were evaluated using the solder alloys listed in Table 1. Note that for (4), Example 4 and Comparative Example 19 were selected from the following Examples and Comparative Examples, and the evaluation results are shown here.

[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 air using a Seiko Instruments DSC (Model No. 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 lower, reflow soldering can be performed at temperatures similar to conventional ones. If the melting point is higher than 232°C, conventional reflow soldering cannot be performed due to the high melting point.

[0076] (2) Share 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 the temperature at 220°C or higher for 40 seconds in a nitrogen atmosphere, with a peak temperature of 245°C. (2-2) Evaluation of share strength The shear strength of the samples prepared in this manner was measured using a shear tester (STR-1000, manufactured by RHESCA) at a shear speed of 6 mm / min. Shear strength of 84.0 N or more was evaluated as "◎". Shear strength of 70.0 N or more but less than 84.0 N was evaluated as "◯". Shear strength of less than 70.0 N was evaluated as "×".

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

[0078] (4) Thermal Cycle 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. Each solder alloy was mixed with a soldering flux ("GLV" manufactured by Senju Metal Industry Co., Ltd.) consisting of rosin, solvent, activator, thixotropic agent, organic acid, etc. to prepare a solder paste of each solder alloy. The solder paste contained 88 mass% alloy powder and 12 mass% flux. 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 to 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 value was considered to be a break, and the average number of cycles to break and the standard deviation were calculated. A standard deviation of 1000 or less was evaluated as a level of variation that was acceptable for practical use. On the other hand, a standard deviation of more than 1000 was evaluated as a level of variation that was not practical, since there were samples that were far from the average value. The evaluation results of (1) to (3) are shown in Tables 1 and 2. The evaluation results of (4) are shown in Table 3.

[0080] [Table 1]

[0081] [Table 2]

[0082] [Table 3]

[0083] As shown in Tables 1 and 2, Examples 1 to 62 all had appropriate contents of each constituent element, and therefore all evaluations yielded results 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), yielded extremely excellent results in all evaluations. These results were significantly superior among the results 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 Ni content. 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 In content was inappropriate, resulting in poor shear strength and an inappropriate fracture mode. In Comparative Example 10, the Sb content was low, resulting in poor shear strength. In Comparative Example 11, the Sb content was high, resulting in poor shear strength and an inappropriate fracture mode.

[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] Comparative Examples 18 and 20 contained Ni or Mn, respectively, which resulted in a significant increase in melting point, poor shear strength, and an inappropriate fracture mode. Comparative Example 19 contained Bi, which resulted in poor shear strength.

[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, in Example 4, it was found that 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, in Comparative Example 3, it was found that 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. [Industrial Applicability]

[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 characterized by having an alloy composition consisting of, in mass%, 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.

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 Zr, Ge, Ga, P, As, Pb, Zn, Mg, Cr, Ti, Mo, Pt, Pd, Au, Al, and Si.

3. The solder alloy according to claim 1 or 2, wherein the alloy composition satisfies the following formulas (1) and (2): 0.0020≦Ag×Cu×In×Sb×Fe×Co≦0.0090 (1) 445≦In / (Ag×Cu×Sb×Fe×Co)≦3560 (2) In the above formulas (1) and (2), Ag, Cu, In, Sb, Fe, and Co each represent the content in mass % of the solder alloy.

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

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

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

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

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

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

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

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

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