High-temperature solder joint material and solder joint

Abstract

An object of the present invention is to provide a high-temperature lead-free solder alloy that has high bonding reliability even in an environment with a large temperature difference or the like and can be supplied at low cost.SOLUTION: The present invention provides a lead-free solder alloy composition including, by mass%, 3.0% to 5.0% of Sb, 3.0% to 4.5% of Ag, 0.1% to 2.0% of Cu, more than 0% and 0.1% or less of Au, inevitable impurities, and the balance of Sn. When one or more elements selected from Fe, Co, Ni, Pd, As, P, Ge, Si, Al, Ga, Mn, Zn, Ti, and Ca are contained in a total amount of 0.0001% by mass to 1% by mass in the lead-free solder alloy having high bonding reliability and having a basic composition of Sn-Sb-Ag-Cu-Au described above, effects such as suppression of oxidation and further refinement of crystal grains can be expected.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a lead-free solder alloy, and in particular to a lead-free solder alloy having high bonding reliability, and to a soldered joint, an electronic circuit board, and an electronic device using this lead-free solder alloy. [Background technology]

[0002] In recent years, in the mounting of electronic components, Sn-Ag-Cu based lead-free solder alloys and Sn-Cu-Ni based lead-free solder alloys have been used for soldering at temperatures below approximately 250°C in order to avoid environmental impact. However, when exposed to environments with large temperature differences, such as when an in-vehicle electronic circuit is directly connected to the engine or when it is located adjacent to another circuit, it is susceptible to the effects of the outside air, and when used in an environment with large temperature differences, defects such as cracks can occur in the solder joints, reducing the reliability of the joint.

[0003] Research and development has been carried out into lead-free solder alloys that have high bonding reliability even in these environments, and Patent Document 1 discloses technology related to a quinary solder alloy in which Sb and Ni are added to an Sn-Ag-Cu composition.

[0004] Furthermore, Patent Document 2 discloses a technology relating to a lead-free solder alloy having a basic composition of Sn-Sb-Cu suitable for high-brightness LED applications, containing 3 to 10 mass % of Sb, and further containing one or more elements selected from Ag, Ni, and Co.

[0005] Furthermore, Patent Document 3 discloses a technology relating to a lead-free solder alloy having a composition in which a binary alloy having a basic composition of Sn-Ag contains 1 to 5 wt% Al and 0.1 to 3 wt% Cu, and further contains 0.1 to 5 wt% of one or more elements selected from In, Bi, Ni, Au, Sb, Zn, Mg, La, and Ce, in order to improve mechanical properties. However, among the lead-free solder alloys disclosed in the aforementioned patent documents, no solder composition has been found that satisfies the bonding reliability required in environments where large temperature differences occur or in situations where high bonding reliability is required. Therefore, there is a demand for a solder bonding material that can withstand use in environments with large temperature differences and has high bonding reliability. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-58950 A [Patent Document 2] Japanese Patent Application Publication No. 2018-134685 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-211283 Summary of the Invention [Problem to be solved by the invention]

[0007] In view of the above circumstances, the present invention provides a high-temperature lead-free solder alloy that has high bonding reliability even in environments with large temperature differences and that can be supplied at low cost. [Means for solving the problem]

[0008] The present invention provides a lead-free solder alloy with high joint reliability, characterized by a composition of 3.0 to 5.0 mass% Sb, 3.0 to 4.5 mass% Ag, 0.1 to 2.0 mass% Cu, more than 0 to 0.1 mass% Au, unavoidable impurities, and the remainder being Sn.

[0009] Furthermore, by adding 0.0001% by mass to 1% by mass of one or more elements selected from Fe, Co, Ni, Pd, As, P, Ge, Si, Al, Ca, Mn, Zn, Ti, and Ca to a lead-free solder alloy having the aforementioned Sn-Sb-Ag-Cu-Au basic composition, it is possible to expect effects such as inhibition of oxidation and further refinement of crystal particles. [Effects of the Invention]

[0010] When electronic components are joined using the lead-free solder alloy of the present invention, which has a basic composition of Sn-Sb-Ag-Cu-Au, highly reliable solder joints can be achieved even when the components are directly connected to the engine in a vehicle, when circuits are arranged adjacent to each other, or in environments where large temperature differences occur, such as on an aircraft.Therefore, the alloy can be widely applied to the mounting of electronic components that require high reliability. [Brief explanation of the drawings]

[0011] [Figure 1] A diagram showing the crystal shape and grain size of a solder alloy without Au addition. [Figure 2] A diagram showing the crystal shape and grain size of a solder alloy containing 10 ppm of Au. [Figure 3] A diagram showing the crystal shape and grain size of a solder alloy containing 30 ppm of Au. [Figure 4] A diagram showing the crystal shape and grain size of a solder alloy containing 50 ppm of Au. [Figure 5] A diagram showing the crystal shape and grain size of a solder alloy containing 100 ppm of Au. [Figure 6] A diagram showing the crystal shape and grain size of a solder alloy containing 300 ppm of Au. [Figure 7] A diagram showing the crystal shape and grain size of a solder alloy containing 500 ppm of Au. [Figure 8] A diagram showing the crystal shape and grain size of a solder alloy containing 1000 ppm of Au. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described below in terms of embodiments. The lead-free solder alloy of the present invention, having a basic composition of Sn-Sb-Ag-Cu-Au, is characterized by containing 3.0 to 5.0 mass% Sb, 3.0 to 4.5 mass% Ag, 0.1 to 2.0 mass% Cu, more than 0 to 0.1 mass% Au, unavoidable impurities, and the remainder being Sn. Depending on the purpose of use, the composition can contain one or more elements selected from Fe, Co, Ni, Pd, As, P, Ge, Si, Al, Ga, Mn, Zn, Ti, and Ca in a total amount of 0.0001 to 1 mass%.

[0013] The lead-free solder alloy of the present invention having the basic composition of Sn-Sb-Ag-Cu-Au as described above can be used for dip soldering to form solder joints. Furthermore, the solder alloy can be powdered and mixed with flux to form a solder paste that can be used for reflow soldering. In addition to the dip soldering and solder paste, the solder can be processed into balls, preforms, flux-cored solder, and other shapes depending on the purpose of soldering. [Example]

[0014] The present invention will be described in detail below with reference to examples. (Observation of crystal grain size)

[0015] 200 g of an alloy having the composition shown in Table 1 is prepared, placed in a graphite crucible, and left to stand in an electric furnace at 650°C for 5 minutes to completely melt the alloy. After the alloy is melted, the crucible is removed from the electric furnace, and when the temperature of the molten alloy reaches the liquidus temperature + 50°C, it is poured into a mold and allowed to cool naturally at room temperature. After the alloy reached room temperature, it was removed from the mold and used as a sample for observation. Next, the observation sample obtained above is cut and then polished to give a mirror finish to the observation surface. Thereafter, the observation sample was mirror-finished using a digital microscope manufactured by Keyence Corporation, and the alloy surface was observed. The grain boundaries obtained from the observed images were analyzed using image software (Image J), ​​and the results shown in Figs. 1 to 8 were obtained.

[0016] [Table 1]

[0017] (hardness measurement) The samples used for observing the crystal grain size were used to measure the Vickers hardness using a microhardness tester manufactured by Akashi Seisakusho Co., Ltd. The results are shown in Table 1.

[0018] As shown in FIGS. 1 to 8, it is clear that the crystal grain size of the alloys to which 10 ppm to 1000 ppm of Au has been added is all finer than that of the alloys to which no Au has been added.

[0019] Furthermore, the results of the Vickers hardness measurements show that the hardness of the alloys to which Au was added at 10 ppm, 30 ppm, 100 ppm, 300 ppm, 500 ppm and 1000 ppm was increased compared to the alloy without Au addition, except for the alloy with 50 ppm Au addition.

[0020] The lead-free solder alloy of the present invention, which has a basic composition of Sn-Sb-Ag-Cu-Au, has a finer crystal grain size than alloys without Au, and is therefore expected to have high bonding reliability even in environments with large temperature differences. Furthermore, the lead-free solder alloy of the present invention undergoes refinement of the crystal grain size even when allowed to cool naturally, and this effect is more pronounced when the amount of Au added is within the specific range of 30 ppm to 50 ppm.

[0021] The effects of the present invention can also be expected in solder joints and solder joints made using the lead-free solder alloy of the present invention having a basic composition of Sn-Sb-Ag-Cu-Au, as well as in electric circuits and electronic devices in which electronic components are joined to a substrate. Furthermore, even when the composition of the solder joints in electrical circuits and electronic devices is based on the Sn-Sb-Ag-Cu-Au composition of the present invention, the same effects can be expected as with joints using this solder alloy. [Industrial Applicability]

[0022] The lead-free solder alloy of the present invention, which has a basic composition of Sn-Sb-Ag-Cu-Au, enables highly reliable solder joints even in environments where large temperature differences occur, and is therefore expected to be used in applications such as automotive and aircraft, where high reliability is required.

Claims

1. A lead-free solder alloy comprising 3.0% by mass or more and 5.0% by mass or less of Sb, 3.0% by mass or more and 4.5% by mass or less of Ag, 0.1% by mass or more and 2.0% by mass or less of Cu, more than 0% by mass or more and 0.1% by mass or less of Au, unavoidable impurities, and the remainder being Sn.

2. Soldered joints and soldered joints made using the lead-free solder alloy, as well as electric circuits and electronic devices in which electronic components are joined to a substrate.

3. A solder joint and a solder joint composition of an electric circuit and an electronic device in which an electronic component is joined to a substrate using lead-free solder, characterized in that the composition is the lead-free solder composition described in claim 1.

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