Solder alloy, solder paste, solder ball, solder preform, solder joint, vehicle-mounted electronic circuit, ECU electronic circuit, vehicle-mounted electronic circuit unit and ECU electronic circuit unit

Abstract

The present invention provides a solder alloy, solder paste, solder ball, solder preform, solder joint, vehicle-mounted electronic circuit, ECU electronic circuit, vehicle-mounted electronic circuit device, and ECU electronic circuit device having a low melting point, high shear strength, and an appropriate fracture mode. The solder alloy has an alloy composition consisting of, in mass%, Ag: 2.0 to 3.6%, In: 1.0 to 5.0%, Sb: 3.0 to 5.0%, Fe: 0.001 to 0.030%, Co: 0.0000% or more and 0.0500% or less, and 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 of 0.100% or less.

Description

Technology Field

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

[0002] Automobiles are equipped with electronic circuits (hereinafter referred to as "vehicle-mounted electronic circuits") formed by soldering electronic components onto printed circuit boards. Vehicle-mounted electronic circuits are used in devices that electrically control the engine, power steering, brakes, etc., and are critical safety components for driving. In particular, vehicle-mounted electronic circuits, such as the ECU (Engine Control Unit), which are electronic circuits that control the vehicle via a computer to improve fuel efficiency, must be able to operate in a stable state without failure over a long period of time. Due to the expansion of the mounting area, these vehicle-mounted electronic circuits have come to be installed in locations subjected to various external loads, such as shocks and vibrations.

[0003] Since the 1980s, Sn-Ag solder alloys have been discussed as an alternative to Sn-Pb solder alloys for use in engine bays. Sn-Ag solder alloys have long been known as highly versatile solder alloys, as evidenced by the JIS designation A35. However, Sn-Ag solder alloys have been considered as a basic alternative to Sn-Pb solder alloys as lead-free solder alloys, and further investigations have been conducted.

[0004] In addition, when Sn-Ag solder alloys are connected to a Cu electrode, Cu is hardly dissolved in Sn, so a coarse CuSn intermetallic compound layer is formed at the bonding interface by Cu diffused from the electrode and Sn in the solder alloy. Furthermore, there are various concerns as the solder alloy becomes brittle due to the precipitation of a large amount of Ag3Sn. For this reason, there is a demand for Sn-Ag solder alloys in which the solder joint does not fracture even in harsh operating environments, and various studies have been conducted in the past.

[0005] Patent Document 1 describes an alloy composition in which Sb, Bi, In, Ag, and Ga are added to a Sn-Co solder alloy to improve the tensile strength of the solder alloy. The solder alloy described in the document discloses that by containing Co, fine CoSn and CoSn2 are dispersed within the Sn matrix, thereby contributing to the improvement of tensile strength. Additionally, the addition of elements such as Sb to lower the melting point has been considered.

[0006] Patent Document 2 discloses a Sn-Ag-Sb-Ni-Bi-Co solder alloy that suppresses the occurrence of voids and also suppresses the occurrence of cracks even after a heat cycle test. The document explains that if Cu is not included, the melt viscosity can be lowered, thereby suppressing the occurrence of voids. Additionally, the document discloses that if Ni is included, the excessive diffusion of Cu is suppressed even without Cu, thus suppressing crack propagation. Prior art literature

[0007] Japanese Patent Publication No. Hei 6-344180 and Japanese Patent Publication No. 2018-1179 The problem to be solved

[0008] As described above, in the inventions described in Patent Documents 1 and 2, the tensile strength of the solder alloy is improved, and the occurrence of voids is suppressed to improve heat cycle resistance. In addition, in Patent Document 1, a study is conducted to lower the melting point.

[0009] However, for solder alloys used in vehicle-mounted electronic circuits, these evaluations alone are insufficient. For example, in vehicle-mounted electronic circuits, when a vehicle equipped with the circuit travels on rough terrain, stresses such as external shocks or vibrations are applied to the circuit. Therefore, exhibiting high shear strength to prevent the solder joint from fracturing is very important for solder joints.

[0010] Furthermore, even if a solder joint that is resistant to fracture is formed, it will eventually fracture if stress is continuously applied to the solder joint. Such continuous stress can be assumed to be applied by exposure to environments with extreme temperature differences. This is attributed to the difference in the coefficients of thermal expansion between the electrode, the intermetallic compound formed at the bonding interface, and the bulk. In this case, the fracture mode indicating the fracture site must not be at the bonding interface. Since the bonding interface is bonded to the electrode, it is not easy to relieve stress at the bonding interface. However, physical and electrical loads are mainly applied to the bonding interface of the solder joint. For this reason, it is thought that relieving stress in the bulk, which is relatively easy to deform, can suppress fracture.

[0011] However, since patent documents 1 and 2 do not examine shear strength and failure modes at all, it is difficult to say that they reflect the actual situation regarding the use of solder joints. Since solder joints electrically connect substrates and electronic components, fracture at the bonding interface must be avoided as much as possible.

[0012] As such, Patent Documents 1 and 2 do not examine shear strength and failure mode, which are important characteristics for solder joints. There is a demand for solder alloys that exhibit these characteristics even if they are solder alloys that do not contain Cu. However, as automobiles have become increasingly electrified in recent years and the number of installed substrates is expected to continue increasing, the development of solder alloys exhibiting these characteristics is an urgent priority. Furthermore, considering the heat resistance of electronic components, it is also desired to exhibit a melting point similar to that of conventional alloys.

[0013] Therefore, the objective of the present invention is to provide a solder alloy, solder paste, solder ball, solder preform, solder joint, vehicle-mounted electronic circuit, ECU electronic circuit, vehicle-mounted electronic circuit device, and ECU electronic circuit device having a low melting point, high shear strength, and an appropriate fracture mode. means of solving the problem

[0014] The inventors reviewed the solder alloys disclosed in Patent Documents 1 and 2. Among the solder alloys disclosed in both documents, the shear strength of the Sn-Ag-In-Sb-Co-Ga solder alloy of Example 5 of Patent Document 1, the Sn-Ag-In-Sb-Co-Ni-Bi solder alloy of Example 19 of Patent Document 2, and the Sn-Ag-Sb-Co-Fe-Ni-Bi solder alloy of Example 24 of the same document were all of the same as conventional ones, and it was found that there is room for improvement.

[0015] These solder alloys do not have alloy compositions designed for the purpose of improving shear strength. It is common for the overall properties of each solder alloy to differ if the content of even one of its compositional components differs, and it should be understood that the entire combination of alloy elements having a specified content is technically evaluated as a whole.

[0016] Therefore, the inventors conducted a detailed investigation into the improvement of shear strength and fracture modes while suppressing the rise in melting point. Here, Patent Document 1 explains that the melting point can be lowered by adding Ag, In, Sb, and Ga to a Sn-Co solder alloy. However, since the melting point varies significantly depending on the content of these elements, the composition described in Example 5 of Patent Document 1 cannot be considered valid.

[0017] In addition, Patent Document 1 discloses the addition of Co for the purpose of improving tensile strength. However, the improvement of shear strength has not been considered at all. Furthermore, if the tensile strength of the solder alloy is improved beyond what is necessary, the failure mode becomes the bond interface. For this reason, it is presumed that the addition of Co is undesirable in Sn-Ag-In-Sb-Co-Ga solder alloys.

[0018] Patent Document 2 states that the occurrence of voids can be suppressed if Ni and Co are within a predetermined range. As such, considering the description in Patent Document 2, Co can exert an effect by coexisting with Ni. Therefore, based on the finding that the alloy composition of Patent Document 1 had low shear strength and an inappropriate fracture mode, it is presumed that the addition of Ni in Patent Document 2 is also undesirable.

[0019] In addition, Patent Document 2 explains that thermal shock resistance can be maintained if the Bi content is below a predetermined amount. However, in Patent Document 2, since Bi is dissolved in Sn up to about 3%, the tensile strength of the solder alloy increases due to the solid solution strengthening of Sn, and the failure mode becomes the bond interface.

[0020] Therefore, taking into account the above-mentioned findings, the inventors focused on Sn-Ag-In-Sb solder alloys in which Ni, Co, and Bi were excluded from the additive elements for Sn in Patent Documents 1 and 2. Furthermore, in order to improve the shear strength of this solder alloy and to make the fracture mode bulk, the inventors conducted a detailed examination of the selection of additional additive elements and the content of Ag, In, and Sb.

[0021] First, in order to properly control the failure mode, it is necessary to suppress the growth of intermetallic compounds at the bonding interface in solder alloys that do not contain Cu or Ni. Intermetallic compounds grow as Cu diffuses from the electrode into the solder alloy. Here, the intermetallic compounds are mainly composed of compounds of Sn and Cu. Furthermore, if the intermetallic compound layer present at the interface between the solder alloy and the electrode becomes coarse, the failure mode is prone to becoming inappropriate.

[0022] Therefore, focusing on the fact that the interface is modified by the inclusion of Fe, the content of additive elements in Sn-Ag-In-Sb-Fe solder alloys was investigated in detail. As a result, it was found that shear strength improvement and the optimization of the fracture mode can be achieved only when the content of additive elements is within a predetermined range.

[0023] The present invention, completed based on these findings, is as follows.

[0024] (0) A solder alloy characterized by being composed of, in mass%, Ag: 2.0 to 3.6%, In: 1.0 to 5.0%, Sb: 3.0 to 5.0%, Fe: 0.0010 to 0.0300%, Co: 0.0000% or more and 0.0500% or less, and the remainder being Sn.

[0025] (1) A solder alloy characterized by having an alloy composition in mass% of Ag: 2.0 to 3.6%, In: 1.0 to 5.0%, Sb: 3.0 to 5.0%, Fe: 0.0010 to 0.0300%, Co: 0% or more and 0.050% or less, and the remainder being Sn.

[0026] (2) The alloy composition (solder alloy) further contains at least one of Zr, Ge, Ga, P, As, Pb, Zn, Mg, Cr, Ti, Mo, Pt, Pd, Au, Al, and Si in a total of 0.100% or less in mass%, as described in (0) or (1).

[0027] (3) The alloy composition (solder alloy) is a solder alloy described in any one of (0) to (2) above, satisfying the following formulas (1) and (2).

[0028] 0.36≤Ag×In×Sb×Fe≤1.19 (1)

[0029] 47≤(In×Sb) / (Ag×Fe)≤319 (2)

[0030] In the above formulas (1) and (2), Ag, In, Sb, and Fe are each the content as mass% of the solder alloy.

[0031] (4) A solder paste having solder powder made of a solder alloy described in any one of claims (0) to (2).

[0032] (5) A solder ball made of a solder alloy described in any one of (0) to (2) above.

[0033] (6) A solder preform made of a solder alloy described in any one of (0) to (2) above.

[0034] (7) A solder joint having a solder alloy described in any one of (0) to (2) above.

[0035] (8) A vehicle-mounted electronic circuit characterized by having a solder alloy described in any one of (0) to (2) above.

[0036] (9) An ECU electronic circuit characterized by having a solder alloy described in any one of (0) to (2) above.

[0037] (10) A vehicle-mounted electronic circuit device characterized by having the vehicle-mounted electronic circuit described in (8) above.

[0038] (11) An ECU electronic circuit device characterized by having the ECU electronic circuit described in (9) above. Brief explanation of the drawing

[0039] FIG. 1 shows optical microscope images of samples after measuring shear strength, FIG. 1 (a) is Example 14, FIG. 1 (b) is Example 2, and FIG. 1 (c) is Comparative Example 3. Specific details for implementing the invention

[0040] The present invention will be described in more detail below. In this specification, “%” regarding the solder alloy composition is “mass%” unless specifically designated.

[0041] 1. Solder alloy

[0042] (1) Ag: 2.0 to 3.6%

[0043] Ag contributes to the improvement of shear strength, the optimization of the failure mode by the precipitation of Ag3Sn, and the lowering of the melting point. If the Ag content is less than 2.0%, the amount of compound precipitation is small, and the shear strength is reduced. 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.

[0044] Meanwhile, if the Ag content exceeds 3.6%, it becomes hypereutectic, so a large amount of Ag3Sn precipitates, causing the strength of the bulk to increase excessively, and thus the failure mode becomes the bond interface. In addition, since the failure mode is the bond interface, the shear strength decreases. The upper limit of the Ag content is 3.6% or less, preferably 3.5% or less, and more preferably 3.4% or less.

[0045] (2) In: 1.0 to 5.0%

[0046] In contributes to the improvement of shear strength and the appropriateness of the failure mode. If the In content is less than 1.0%, the shear strength decreases and the failure mode becomes inappropriate because the effect of solid solution strengthening is insufficient along with insufficient wetting spread due to reduced wettability. 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.

[0047] Meanwhile, if the In content exceeds 5.0%, the melting point increases due to the precipitation of a large amount of compounds. In addition, the bulk strength increases, raising concerns about failure at the bonding interface or in the parts. 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.

[0048] (3) Sb: 3.0 to 5.0%

[0049] Sb contributes to the improvement of shear strength and the optimization of failure modes. If the Sb content is less than 3.0%, the shear strength decreases because solid solution strengthening for Sn and precipitation strengthening of Sn-Sb compounds are insufficient. 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.

[0050] Meanwhile, if the Sb content exceeds 5.0%, the shear strength decreases because coarse SnSb compounds are formed. In addition, wettability deteriorates, and the failure mode becomes unsuitable as it becomes failure at the bonding interface or part. 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.

[0051] (4) Fe: 0.0010 to 0.0300%

[0052] Fe contributes to the improvement of shear strength and the optimization of the failure mode. If the Fe content is less than 0.0010%, the effect of interfacial strengthening by the modification of the intermetallic compound layer formed at the interface is insufficient, so the shear strength decreases and the failure mode becomes the bonding interface, which is not optimized. 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.

[0053] Meanwhile, if the Fe content exceeds 0.0300%, a compound of Sn and Fe precipitates, and the bulk strength is excessively enhanced, so there is a risk of failure 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.

[0054] (5) Co: 0.0000% or more, 0.0500% or less

[0055] Co is an optional element that contributes to suppressing the rise in melting point, improving shear strength, and optimizing the fracture mode. In conventional solder alloys, it was considered better not to include it from the perspective of improving shear strength and optimizing the fracture mode. However, as a result of adding Co, high shear strength is maintained, and the fracture mode remains the same as in the bulk. In Sn-Ag-In-Sb solder alloys, it is thought that Co causes fine dispersion of CoSn, etc. However, it does not go so far as to refine the alloy structure of Sn. In this alloy system, since the alloy structure of Sn is refined by Fe, it is presumed that if the microstructure of CoSn, etc. is dispersed, the overall alloy structure becomes even finer. Therefore, in the solder alloy according to the present invention, Co can exert a synergistic effect in the presence of Fe.

[0056] In addition, in the solder alloy according to the present invention, since Co is an optional element, high shear strength and optimization of the fracture mode can be maintained even when Co is not contained. The lower limit of the Co content is 0.0000% or more, preferably greater than 0.0000%, more preferably 0.0010% or more, even more preferably 0.0030% or more, particularly preferably 0.0060% or more, and most preferably 0.0080% or more.

[0057] On the other hand, if the Co content exceeds 0.0500%, Sn and Co compounds precipitate, causing the bulk strength to increase excessively, and thus the failure mode becomes the bond interface. In addition, the shear strength decreases because the melting point rises significantly and wettability deteriorates due to the precipitation of a large amount of compounds. The upper limit of the Co content is 0.0500% or less, preferably 0.0300% or less, and more preferably 0.0100% or less.

[0058] (6) Remaining parts: Sn

[0059] The remainder of the solder alloy according to the present invention is Sn. In addition to the elements described above, unavoidable impurities may be contained. Even if unavoidable impurities are contained, they do not affect the effects described above. Furthermore, in the present invention, if the Sn-Ag-In-Sb-Fe solder alloy contains Ni, SnNi compounds are precipitated. Since SnNi compounds precipitate using intermetallic compounds formed at the interface as nuclei, the intermetallic compound layer formed at the interface becomes thicker. As a result, a decrease in shear strength occurs. Therefore, in the present invention, it is preferable not to contain Ni. Additionally, when Bi coexists with In, it forms a Sn-In-Bi low-melting point phase. Considering creep deformation, the low-melting point phase has a low melting point equivalent to a room temperature environment becoming a high-temperature environment; thus, it is susceptible to creep deformation, and shear strength decreases. For this reason, in the present invention, it is preferable not to contain Bi.

[0060] (7) At least one of Zr, Ge, Ga, P, As, Pb, Zn, Mg, Cr, Ti, Mo, Pt, Pd, Au, Al, and Si in total of 0.100% or less

[0061] 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 as an optional element in a total amount of 0.100% or less, to the extent that the effects of the present invention are not impaired. Preferably, the total amount is 0.080% or less. The lower limit of the content is not particularly limited, but it may be 0.0001% or more, and may be 0.001% or more.

[0062] (8) (1) and (2) formulas

[0063] 0.36≤Ag×In×Sb×Fe≤1.19 (1)

[0064] 47≤(In×Sb) / (Ag×Fe)≤319 (2)

[0065] In the above formulas (1) and (2), Ag, In, Sb, and Fe are each the content as mass% of the solder alloy.

[0066] (1) is a formula that takes into account the balance of additive elements in the solder alloy according to the present invention. The solder alloy according to the present invention can exhibit a low melting point, high shear strength, and appropriate fracture mode through the synergistic effect of each constituent element. For this reason, if the balance of all constituent elements except Sn is further optimized, all effects of the present invention can be further enhanced. In (1), the content of Ag, In, and Sb is about 10 to 100 times that of Fe. However, their contribution to the solder alloy is considered to be of the same degree. Therefore, in order to further enhance the low melting point, high shear strength, and appropriate fracture mode in the present invention simultaneously, it is desirable to have a balanced content.

[0067] (2) is an equation that takes into account the balance within the group of In and Sb, where the shear strength increases until the part is fractured if the upper limit is exceeded among the additive elements, and the balance within the group of Ag and Fe, where the fracture ends at the interface, and also takes into account the balance between the two groups. If equation (2) is satisfied, the fracture mode may become more appropriate depending on the alloy composition.

[0068] (1) The lower limit of the formula is preferably 0.36 or higher, more preferably 0.39 or higher, even more preferably 0.42 or higher, even more preferably 0.43 or higher, particularly preferably 0.44 or higher, most preferably 0.52 or higher, 0.53 or higher, 0.60 or higher, 0.656 or higher, 0.66 or higher, 0.70 or higher, 0.75 or higher, 0.78 or higher, 0.79 or higher, 0.84 or higher, 0.87 or higher, 0.88 or higher. The upper limit of the formula is preferably 1.19 or lower, more preferably 1.18 or lower, even more preferably 1.09 or lower, even more preferably 1.08 or lower, particularly preferably 1.05 or lower, most preferably 1.02 or lower, 0.91 or lower, 0.92 or lower, 0.90 or lower.

[0069] (2) The lower limit of the formula is preferably 47 or higher, more preferably 51 or higher, even more preferably 57 or higher, even more preferably 68 or higher, particularly preferably 69 or higher, most preferably 85 or higher, 86 or higher, 91 or higher, 102 or higher, 103 or higher, 114 or higher, 120 or higher, 133 or higher, 137 or higher, 141 or higher, 142 or higher, 143 or higher, 154 or higher, 160 or higher. (2) The upper limit of the formula is preferably 319 or less, more preferably 286 or less, even more preferably 285 or less, even more preferably 267 or less, particularly preferably 266 or less, most preferably 257 or less, 240 or less, 229 or less, 228 or less, 213 or less, 206 or less, 205 or less, 200 or less, 192 or less, 183 or less, 182 or less, 171 or less.

[0070] In the calculation of Equation (1) and Equation (2), the numerical values ​​themselves indicated in the measured values ​​of the alloy composition shown in Tables 1 and 2 below are used. That is, in the calculation of Equation (1) and Equation (2), all digits smaller than the number of significant figures in the measured values ​​shown in Tables 1 to 3 below are treated as 0. For example, if the Fe content is "0.0250" mass% as a measured value, the Fe content used in the calculation of Equation (1) and Equation (2) is not in the range of 0.02505 to 0.02514%, but is treated as "0.025000...". In Equation (1), the calculation is performed to the third decimal place and the third decimal place is rounded to the second decimal place, and in Equation (2), the calculation is performed to the first decimal place and the first decimal place is rounded to the ones place.

[0071] In addition, when calculating formulas (1) and (2) from alloy compositions specifically disclosed in the patent documents or other documents described in this specification, they are treated in the same manner.

[0072] As described above, in alloys, since all constituent elements do not function individually but rather form a single whole, it is rare for all excellent effects to be simultaneously exhibited by only one type of element. For this reason, as described above, in order to exhibit superior characteristics within the optimal content range of each constituent element, it is necessary to examine the constituent elements as a whole. In the solder alloy according to the present invention, in order to satisfy all of the low melting point, high shear strength, and appropriate fracture mode to a higher level with a single composition, it is desirable to satisfy equations (1) and (2).

[0073] Furthermore, in the embodiments described below, if the judgment result is “◎”, it indicates that it is particularly advantageous in practical terms compared to “○”. Since “○” represents a result that is more advantageous than conventional results, if other evaluation results are also excellent, it falls within the scope of the present invention and is treated as an example. Since “×” represents an insufficient result for the present invention, it falls outside the scope of the present invention and is treated as a comparative example.

[0074] 2. Solder paste

[0075] The solder paste according to the present invention is a mixture of solder powder and flux comprising the alloy composition described above. The flux used in the present invention is not particularly limited as long as soldering is possible by commercial methods. Accordingly, a mixture of commonly used rosin, organic acid, activator, thixotropic agent, and solvent in appropriate proportions may be used. In the present invention, the mixing ratio of the metal powder component and the flux component is not particularly limited, but preferably, the metal powder component is 70 to 90 mass% and the flux component is 10 to 30 mass%.

[0076] 3. Solder ball

[0077] 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 as a solder ball using the dropping method, which is a common method in the industry. Additionally, a solder joint can be manufactured by processing the solder ball using a common method in the industry, such as by mounting a solder ball onto a single electrode coated with flux and joining them. 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.

[0078] 4. Solder Preform

[0079] The solder alloy according to the present invention can be used as a preform. Examples of preform shapes include washers, rings, pellets, discs, ribbons, wires, etc.

[0080] 5. Solder joint

[0081] The solder joint according to the present invention is suitable for joining at least two or more members to be joined. The members to be joined are not particularly limited, provided they are electrically connected using the solder alloy according to the present invention, such as semiconductor and power modules, inverter products, etc., using, for example, devices, substrates, electronic components, printed circuit boards, insulating substrates, heat sinks, lead frames, electrode terminals, etc.

[0082] The joining method using the solder alloy according to the present invention may be carried out according to the standard method, for example, using the reflow method. When performing reflow soldering, the melting temperature of the solder alloy should be approximately 20°C higher than the liquidus temperature. In addition, when joining using the solder alloy according to the present invention, the alloy structure can be made finer by considering the cooling rate during solidification. For example, the solder joint is cooled at a cooling rate of 2 to 3°C / s or higher. Other joining conditions can be appropriately adjusted according to the alloy composition of the solder alloy.

[0083] 6. Vehicle-mounted electronic circuit, ECU electronic circuit, vehicle-mounted electronic circuit device, ECU electronic circuit device

[0084] As is evident from the description above, the solder alloy according to the present invention suppresses the rise in the melting point and has an appropriate fracture mode. For this reason, even when used for automobiles exposed to harsh environments, that is, for vehicle mounting, the fracture of the solder joint is suppressed without variation. Therefore, because it possesses such particularly remarkable characteristics, it can be seen that the solder alloy according to the present invention is particularly suitable for soldering electronic circuits mounted in automobiles.

[0085] As such, the solder alloy according to the present invention exhibits excellent effects when used, more specifically, for soldering electronic circuits mounted on vehicles or for soldering electronic circuits of ECUs.

[0086] An "electronic circuit" is a system that achieves a intended function as a whole through the electronic combination of multiple electronic components, each having a specific function.

[0087] Examples of electronic components constituting such electronic circuits include chip resistors, multi-layer resistors, QFPs, QFNs, power transistors, diodes, and capacitors. Electronic circuits incorporating these components are mounted on a circuit board to form an electronic circuit device.

[0088] In the present invention, the substrate constituting such an electronic circuit device, for example, a printed circuit board, is not particularly limited. In addition, the material is not particularly limited, but a heat-resistant plastic substrate (e.g., FR-4 with high Tg and low CTE) may be exemplified. The printed circuit board is preferably a printed circuit board in which the surface of the Cu lands is treated with an organic material (OSP: Organic Surface Protection) such as amine or imidazole.

[0089] 7. Others

[0090] The solder alloy according to the present invention can be manufactured as a low-α dose alloy by using a low-α dose material as its raw material. When such a low-α dose alloy is used to form solder bumps around memory, it becomes possible to suppress soft errors.

[0091] Examples

[0092] The present invention will be explained by the following examples, but the present invention is not limited to the following examples.

[0093] To demonstrate the effects of the present invention, solder alloys listed in Tables 1 to 3 were used to evaluate (1) melting point, (2) shear strength, and (3) fracture mode.

[0094] (1) Melting point

[0095] For the solder alloys shown in Tables 1 to 3, the respective temperatures were determined from the DSC curves. The DSC curves were obtained by heating in air at a rate of 5°C / min using a DSC (model number: 6200) manufactured by Seiko Instruments. The liquidus temperature was determined from the obtained DSC curves and set as the melting point. If the melting point is 232°C or lower, reflow soldering can be performed at a temperature similar to that of conventional methods. If the melting point exceeds 232°C, conventional reflow soldering cannot be performed because the melting point is too high.

[0096] (2) Shear strength

[0097] (2-1) Production of samples

[0098] Solder sheets were fabricated by casting the solder alloys shown in Tables 1 to 3 (diameter: 1 mm, thickness: 0.15 mm). Chip resistors were soldered to the Cu-OSP electrodes on the FR-4 substrate using a reflow furnace (SNR-615: manufactured by Senju Kinzoku High School Co., Ltd.). 3216CR (CR32-114JV: manufactured by Hokuriku Electric High School) chip resistors were used. The reflow profile maintained a temperature of 220°C or higher for 40 seconds, and the peak temperature was set to 245°C in a nitrogen atmosphere.

[0099] (2-2) Evaluation of Shear Strength

[0100] The shear strength of the sample prepared in this manner was measured using a shear tester (STR-1000: manufactured by RHESCA) at a shear rate of 6 mm / min. If the shear strength was 84.0 N or higher, it was evaluated as “◎”. If the shear strength was 70.0 N or higher and less than 84.0 N, it was evaluated as “○”. If the shear strength was less than 70.0 N, it was evaluated as “×”.

[0101] (3) Destruction mode

[0102] The failure mode of the sample evaluated in the above “(2) Shear Strength” was observed using an optical microscope (VHX-5000: manufactured by KEYENCE). If the sample was fractured in the bulk, it was evaluated as “◎”. If the sample was fractured in the intermetallic compound (IMC) at the interface between the bulk and the bond, it was evaluated as “○”. If the sample was fractured in the intermetallic compound at the interface between the bond, it was evaluated as “×”.

[0103] The evaluation results are shown in Tables 1 to 3.

[0104]

[0105]

[0106]

[0107] As shown in Tables 1 and 2, since the content of each constituent element in Examples 1 to 110 was appropriate, all evaluations yielded results that were practically acceptable. In addition, Examples 3 to 14, 16, 19, 22, 28 to 31, 37 to 48, 50, 54, 57, 66, 68 to 73, and 77 to 110, which satisfy Equation (1) and Equation (2), showed excellent results in all evaluations. These were excellent results, to the extent that there was a significant difference among the results that were practically acceptable.

[0108] Meanwhile, as shown in Table 3, Comparative Example 1 did not contain In, Sb, and Fe, so the shear strength was reduced and the failure mode was inappropriate. Comparative Example 2 had a low Ag content, so the shear strength was reduced. Comparative Example 3 had a high Ag content, so the shear strength was reduced and the failure mode was inappropriate.

[0109] Comparative Example 4 did not contain In, and Comparative Example 5 had a low In content, so the shear strength was reduced and the failure mode was inappropriate. Comparative Example 6 had a high In content, so the failure mode was inappropriate.

[0110] Comparative Example 7 had a low Sb content and did not contain Fe, so the shear strength was reduced and the failure mode was inappropriate. Comparative Example 8 had a low Sb content, so the shear strength was reduced. Comparative Example 9 had a high Sb content, so the shear strength was reduced and the failure mode was inappropriate.

[0111] Comparative Examples 10 to 12 had an inappropriate Fe content, so the shear strength decreased and the failure mode was inappropriate. Comparative Example 13 had a high Co content, so the melting point increased significantly, the shear strength decreased, and the failure mode was inappropriate. Comparative Examples 14 and 15 each contained Ni or Bi, so the shear strength decreased.

[0112] Figure 1 shows optical microscope images of samples after measuring shear strength, where Figure 1(a) is Example 14, Figure 1(b) is Example 2, and Figure 1(c) is Comparative Example 3. As is evident from Figure 1, in Example 14, it was found that the solder joint fractured due to bulk failure. In addition, in Example 2, it was found that failure occurred in the intermetallic compound at the bulk and bonding interface. Meanwhile, in Comparative Example 3, it was found that the solder joint fractured due to failure in the intermetallic compound at the bonding interface. For this reason, it was found that the failure mode in Example 14 was appropriate. This result was the same for the other examples. Industrial applicability

[0113] The solder according to the present invention can be used as an electronic circuit mounted on a vehicle, such as an ECU, which is an electronic circuit that controls a vehicle with a computer to improve fuel efficiency, but it can also be used in consumer electronic devices, such as personal computers, to produce excellent effects.

Claims

Claim 1 A solder alloy characterized by having an alloy composition in mass% consisting of Ag: 2.0 to 3.6%, In: 1.0 to 5.0%, Sb: 3.0 to 5.0%, Fe: 0.0010 to 0.0300%, Co: 0.0000% or more and 0.0500% or less, and the remainder being Sn. Claim 2 A solder alloy according to claim 1, wherein the alloy composition further contains, in mass%, a total of 0.100% or less of at least one of Zr, Ge, Ga, P, As, Pb, Zn, Mg, Cr, Ti, Mo, Pt, Pd, Au, Al, and Si. Claim 3 In claim 1 or 2, the alloy composition is a solder alloy satisfying the following formulas (1) and (2). 0.36 ≤ Ag × In × Sb × Fe ≤ 1.19 (1) 47 ≤ (In × Sb) / (Ag × Fe) ≤ 319 (2) In formulas (1) and (2), Ag, In, Sb, and Fe are each content as mass% of the solder alloy. Claim 4 A solder paste having solder powder made of the solder alloy described in claim 1 or 2. Claim 5 A solder ball made of the solder alloy described in paragraph 1 or 2. Claim 6 A solder preform made of the solder alloy described in paragraph 1 or 2. Claim 7 A solder joint having the solder alloy described in paragraph 1 or 2. Claim 8 A vehicle-mounted electronic circuit characterized by having the solder alloy described in claim 1 or 2. Claim 9 An ECU electronic circuit characterized by having the solder alloy described in claim 1 or 2. Claim 10 A vehicle-mounted electronic circuit device characterized by having a vehicle-mounted electronic circuit as described in claim 8. Claim 11 An ECU electronic circuit device characterized by having the ECU electronic circuit described in claim 9.

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