Solder alloy, solder ball, solder paste, and solder joint

Abstract

Provided are a solder alloy, a solder ball, a solder paste, and a solder joint, which have excellent thermal conductivity, fall impact resistance, and heat cycle resistance. This solder alloy has an alloy composition containing, in mass%, 1.0-4.0% of Ag, 0.10-1.00% of Cu, 1.0-7.0% of Sb, 0.001-0.030% of Co, and 0.005-0.050% of Fe, the remaining portion being Sn.

Description

Solder alloys, solder balls, solder paste and solder joints

[0001] The present invention relates to solder alloys, solder balls, solder pastes and solder joints for use in various electronic devices.

[0002] In recent years, electronic devices such as mobile terminals have become increasingly sophisticated, and the performance of electronic components mounted on circuit boards has improved dramatically. As electronic components become more sophisticated, larger currents are passed through them, and solder joints used on circuit boards of electronic devices are exposed to high temperatures due to Joule heat. On the other hand, when electronic devices are used in cold regions, solder joints are exposed to low-temperature environments.

[0003] Sn-3Ag-0.5Cu solder alloys are widely used as solder alloys for solder joints. In the past, this solder alloy did not pose any significant problems in environments with low power consumption and small temperature changes. However, in recent years, as the range of solder alloy applications has expanded, the environments in which they are used have become more severe, leading to reliability issues. As mentioned above, as the performance of electronic components increases, the temperature difference when exposed to the outside air in cold regions increases. Similarly, when electronic components are used indoors after being exposed to the outside air in cold regions, the temperature of the solder joints rises rapidly from low to high.

[0004] When electronic devices are exposed to temperature changes such as those mentioned above, stress concentrates on solder joints with small cross-sectional areas due to the difference in thermal expansion coefficients between the electronic components and the substrate that make up the electronic components. Furthermore, if the electronic device is subjected to external vibrations in such an environment, the solder joints are further subjected to stress. Electronic devices, such as mobile terminals, are used for at least several years. Therefore, the solder alloys that make up solder joints must be highly reliable so that problems do not occur in the solder joints even when used for long periods in harsh environments.

[0005] For example, Patent Document 1 discloses a solder alloy that aims to suppress crack growth in solder joints even under harsh environments such as temperature changes and vibration loads, and also suppress crack growth near the joint interface with an electrode that is not plated. Patent Document 2 discloses a solder alloy that aims to suppress crack growth under harsh environments such as temperature changes and vibration loads, and to suppress the occurrence of lift-off in through holes. To achieve these objectives, Patent Documents 1 and 2 disclose a Sn—Ag—Cu—Sb—Ni solder alloy in which Sb and Ni are added to a Sn—Ag—Cu solder alloy.

[0006] Patent Document 3, like Patent Document 1, discloses a solder alloy that aims to suppress crack growth in solder joints even under harsh environments such as temperature changes and vibration loads, and also suppress crack growth near the joint interface with electronic components that are not plated. Patent Document 4, like Patent Document 2, discloses a solder alloy that aims to suppress crack growth under harsh environments such as temperature changes and vibration loads, and to suppress the occurrence of through-hole lift-off. To achieve this purpose, Patent Documents 3 and 4 disclose a Sn—Ag—Cu—Sb—Bi—Ni solder alloy in which Sb, Bi, and Ni are added to a Sn—Ag—Cu solder alloy.

[0007] Patent Document 5 discloses a solder alloy that is excellent in reliability and prevents adverse effects on acoustic quality. To achieve this objective, Patent Document 5 discloses a Sn—Ag—Cu—Sb—Bi—Co—Fe solder alloy that contains Sb, Bi, Co, and Fe in a Sn—Ag—Cu solder alloy.

[0008] Japanese Patent Application Laid-Open No. 2017-170465 Japanese Patent Application Laid-Open No. 2019-058950 Japanese Patent No. 6719443 Japanese Patent No. 6795630 Japanese Patent No. 6889387

[0009] Paragraph 0008 of Patent Document 1 describes that solder alloys strengthened by the addition of Bi have the disadvantages of poor ductility and increased brittleness. Furthermore, paragraph 0010 of Patent Document 2 discloses that the Bi concentration is high near the interface with the land, which is difficult to solidify within the fillet when the solder alloy is cooled. The same paragraph also describes that near the interface where the Bi concentration is high, the fillet is even more difficult to solidify, and when a contraction force acting perpendicular to the substrate occurs, surface peeling of the fillet from the land becomes even more likely to occur. From these perspectives, it is preferable that the solder alloys described in Patent Documents 1 and 2 do not contain Bi.

[0010] The solder alloys described in these documents contain a predetermined amount of Ni as an essential element, and therefore, (Cu, Ni) ６ Sn ５ It is said that this forms a barrier to prevent cracks from progressing.

[0011] However, when a solder joint is exposed to an environment similar to that of aging treatment, a phenomenon called "spalling" occurs, in which the alloy layer is liberated from the interface. This "liberation" occurs when a solder joint is subjected to a suitable heat treatment (temperature and time), resulting in solid-state diffusion of the intermetallic compounds that make up the IMC layer formed at the joint interface into the solder bulk. When solder alloys such as those described in Patent Documents 1 to 4 contain Ni, which promotes the refinement of the IMC layer, "liberation" is more likely to occur.

[0012] Generally, the thermal conductivity of metals is a heat transfer phenomenon that is primarily due to the chain of atomic vibrations and the energy transfer based on conduction electrons, with the conduction electrons making a large contribution. Therefore, metals are good conductors of heat. However, when the amount of "free" intermetallic compounds increases, the movement of conduction electrons and the chain of atomic vibrations are locally impeded by the intermetallic compounds, which have relatively low thermal conductivity. This results in a deterioration of the thermal conductivity of the solder joint. It is speculated that the finer particle size of intermetallic compounds in Ni-containing solder alloys makes "free" more likely to occur, resulting in a decrease in the thermal conductivity of the solder joint.

[0013] It is also known that in solder alloys containing Bi, Bi segregates due to heat generated when electronic devices are operated, resulting in partial precipitation of a Bi phase in the eutectic. This phenomenon occurs even when the Bi content is less than 58 mass% at which the eutectic composition is formed. For this reason, the solder alloys containing Bi described in Patent Documents 3 to 5 become brittle, making the solder joints more susceptible to fracture due to drop impact.

[0014] It is stated that the solder alloys described in Patent Documents 1 to 5 all exhibit excellent effects even after heat cycle testing. According to this description, the solder alloys described in Patent Documents 1 to 5 are believed to be able to withstand external stresses caused by thermal expansion and contraction. However, the stress application rate in heat cycle testing is slower than the stress application rate in cases where stress is applied instantaneously, such as in drop impacts, because it is dependent on the expansion and contraction rates of the solder alloy and the substrate. Prior Art: Since electronic devices such as mobile terminals are inevitably dropped, solder joints that can withstand sudden external stresses are required.

[0015] An object of the present invention is to provide a solder alloy, a solder ball, a solder paste, and a solder joint that are excellent in thermal conductivity, drop impact resistance, and heat cycle resistance.

[0016] The present inventors have conducted a detailed investigation into the problems with the Sn—Ag—Cu—Sb—Ni solder alloys described in Patent Documents 1 and 2. Patent Documents 1 and 2 state that the reason for adding Ni is to prevent the formation of (Cu, Ni) in the molten solder alloy. ６ Sn ５ The document also describes that, during soldering, Ni migrates to the vicinity of the joint interface and forms fine (Cu, Ni) ６ Sn ５ In order to form Cu at the bonding interface ３ It is described that the growth of the Sn layer is suppressed.

[0017] Thus, it can be seen that Ni in the Sn—Ag—Cu—Sb—Ni solder alloy contributes to the refinement of the structure of the solder alloy.６ Sn ５ It is thought that the thermal conductivity of the solder joint will actually decrease because the ions are dispersed in the base material.

[0018] In Patent Documents 3 and 4, as in Patent Documents 1 and 2, the reason for adding Ni is that (Cu, Ni) is present in the molten solder alloy. ６ Sn ５ In addition to the formation and dispersion in the matrix, a synergistic effect with Co is also described. ６ Sn ５ It is also described that the alloy composition containing both Ni and Co has a further decrease in thermal conductivity because it is dispersed in the base material and suppresses the propagation of cracks. The Sn-Ag-Cu-Sb-Bi-Ni alloys disclosed in Patent Documents 3 and 4 contain Bi, and there is concern that Bi may decrease the drop impact resistance.

[0019] In view of these, the inventors investigated the elimination of Ni and Bi from Sn—Ag—Cu—Sb—Bi—Ni solder alloys. However, although the thermal conductivity of Sn—Ag—Cu—Sb solder alloys is improved because they do not contain Ni, the structure of the solder alloy does not become fine, and drop impact resistance and heat cycle resistance deteriorate. On the other hand, if the structure of the solder alloy becomes finer than necessary, the drop impact resistance and heat cycle resistance improve, but the thermal conductivity decreases due to the liberation of intermetallic compounds. Therefore, detailed investigation was conducted into elements that would make the alloy structure appropriately fine.

[0020] Adding Co to a Sn-Ag-Cu-Sb solder alloy is thought to decrease thermal conductivity, as mentioned above. However, it has been found that when Ni is not included, the thermal conductivity does not decrease significantly, but the drop impact resistance is poor due to insufficient fineness. Furthermore, it has been found that adding Fe to a Sn-Ag-Cu-Sb solder alloy suppresses liberation and makes the structure finer than Co, although not as fine as Ni, so the drop impact resistance does not decrease significantly, but the heat cycle resistance is insufficient. Here, the Sn-Ag-Cu-Sb-Bi-Co-Fe disclosed in Patent Document 5 contains Bi. These solder alloys are useful inventions with excellent acoustic quality. However, since audio products are not intended to be portable, there was no need to consider drop impact resistance.

[0021] The present inventors investigated elements and their contents that would moderately refine the alloy structure in Sn—Ag—Cu—Sb solder alloys, but would not unnecessarily refine the alloy structure as when Ni is added, and would suppress the liberation of intermetallic compounds. As a result, it was discovered that solder alloys containing Co and Fe simultaneously exist with alloy compositions that are relatively excellent in thermal conductivity, heat cycle resistance, and drop impact resistance. However, it was also discovered that there are alloy compositions in which the addition of Co and Fe alone does not simultaneously exhibit these effects to a practically acceptable extent. Generally, since all constituent elements of an alloy contribute to each other, it is rare for a single element to simultaneously exhibit all excellent effects. Therefore, in addition to the contents of Co and Fe, the contents of Ag, Cu, and Sb were also investigated in detail.

[0022] As mentioned above, in the past, considering the structure of a solder alloy, there was a contradictory relationship between the refinement of the alloy structure and the suppression of liberation. For this reason, it was thought difficult to provide a solder alloy that simultaneously satisfied the three effects of thermal conductivity, drop impact resistance, and heat cycle resistance. In particular, solder alloys containing many additive elements to Sn have low thermal conductivity due to the formation of various compounds, and therefore little research has been done on thermal conductivity. However, after detailed investigations, the inventors discovered that thermal conductivity, drop impact resistance, and heat cycle resistance are simultaneously improved only when the contents of Ag, Cu, Sb, Co, and Fe are each within a predetermined range, thereby completing the present invention. The present invention, which was developed based on these findings, is as follows.

[0023] (0) A solder alloy characterized by having, by mass%, an alloy composition of 1.0 to 4.0% Ag, 0.10 to 1.00% Cu, 1.0 to 7.0% Sb, 0.001 to 0.030% Co, 0.005 to 0.050% Fe, and the balance being Sn. (1) A solder alloy characterized by having, by mass%, an alloy composition of 1.0 to 4.0% Ag, 0.10 to 1.00% Cu, 1.0 to 7.0% Sb, 0.001 to 0.030% Co, 0.005 to 0.050% Fe, and the balance being Sn.

[0024] (2) The solder alloy according to (1) above, further containing, by mass %, 0.1% or less in total of at least one of P, Ge, Ga, and Mn.

[0025] (3) The solder alloy according to (1) or (2) above, further containing, by mass %, In: 6.0% or less.

[0026] (4) A solder alloy according to (1) or (2) above, wherein the alloy composition contains 0 to 4.0% In and satisfies the following formulas (1) and (2): 0.040≦Ag×Cu×Sb×Co≦0.075 (1) 1.6≦Ag×Cu×Sb×Co / Fe≦5.7 (2) In formulas (1) and (2), Ag, Cu, Sb, Co, and Fe represent the contents (mass %) of the alloy composition.

[0027] (5) A solder ball made of the solder alloy described in (1) or (2) above.

[0028] (6) A solder ball made of the solder alloy described in (3) above.

[0029] (7) A solder paste containing solder powder made of the solder alloy described in (1) or (2) above.

[0030] (8) A solder paste containing solder powder made of the solder alloy described in (3) above.

[0031] (9) A solder joint having the solder alloy described in (1) or (2) above.

[0032] (10) A solder joint comprising the solder alloy according to claim 3.

[0033] Fig. 1 shows cross-sectional SEM photographs of solder joints, Fig. 1(a) is a cross-sectional SEM photograph of a solder joint using the solder alloy of Comparative Example 18, and Fig. 1(b) is a cross-sectional SEM photograph of a solder joint using the solder alloy of Example 16. Fig. 2 shows cross-sectional SEM photographs of solder joints, Fig. 2(a) is a cross-sectional SEM photograph of a solder joint using the solder alloy of Comparative Example 18, Fig. 2(b) is a photograph showing the results of cross-sectional mapping analysis of the solder joint using the solder alloy of Comparative Example 18, and Fig. 2(c) is a cross-sectional SEM photograph of a solder joint using the solder alloy of Example 16.

[0034] The present invention will be described in more detail below. In this specification, "%" relating to the solder alloy composition is "% by mass" unless otherwise specified.

[0035] 1. Solder alloy (1) Ag: 1.0 to 4.0% Ag is Ag ３ Ag forms a Sn network, contributing to improved heat cycle resistance and drop impact resistance. Ag also contributes to improved wettability of molten solder. If the Ag content is less than 1.0%, Ag ３The lower limit of the Ag content is 1.0% or more, preferably 2.0% or more, more preferably 3.0% or more, and even more preferably 3.2% or more. On the other hand, if the Ag content exceeds 4.0%, coarse Ag particles will form. ３ The primary crystals of Sn are crystallized, which deteriorates the drop impact resistance. The thermal conductivity may also deteriorate. The upper limit of the Ag content is 4.0% or less, preferably 3.8% or less, and more preferably 3.5% or less.

[0036] (2) Cu: 0.10 to 1.00% Cu forms a compound with Sn in the solder bulk and near the joint interface. Therefore, the addition of Cu improves the thermal conductivity, heat cycle resistance, and drop impact resistance. It also improves the wettability of the molten solder. If the Cu content is less than 0.10%, the Cu ６ Sn ５ Since the amount of precipitation of Cu and the like is small, drop impact resistance is reduced. Heat cycle resistance may also be reduced. The lower limit of the Cu content is 0.10% or more, preferably 0.30% or more, and more preferably 0.50% or more. On the other hand, if the Cu content exceeds 1.00%, the intermetallic compounds formed at the bonding interface are liberated, resulting in a deterioration in thermal conductivity. Drop impact resistance may also be reduced. In addition, the liquidus temperature increases. The upper limit of the Cu content is 1.00% or less, preferably 0.80% or less, and more preferably 0.70% or less.

[0037] (3) Sb: 1.0 to 7.0% Sb dissolves in Sn and precipitates SnSb compounds, contributing to improved heat cycle resistance. If the Sb content is less than 1.0%, the amount of SnSb compounds precipitated is small, and heat cycle resistance is not improved. The lower limit of the Sb content is 1.0% or more, preferably 2.0% or more, and more preferably 3.0% or more. On the other hand, if the Sb content exceeds 7.0%, the amount of SnSb precipitated is too large, resulting in a decrease in thermal conductivity. The upper limit of the Sb content is 7.0% or less, preferably 6.0% or less, more preferably 5.0% or less, and even more preferably 4.0% or less.

[0038] (4) Co: 0.001 to 0.030% Co refines Sn crystal grains, contributing to improved drop impact resistance and heat cycle resistance. If the Co content is less than 0.001%, the Sn crystal grains are not refined, and heat cycle resistance is not improved. Furthermore, the liquidus temperature increases. The lower limit of the Co content is 0.001%, more preferably 0.003% by mass, and even more preferably 0.006% or more. On the other hand, if the Co content exceeds 0.030%, the amount of compounds becomes too large, further coarse compounds are generated, the structure deteriorates, and drop impact resistance deteriorates. The upper limit of the Co content is 0.030% or less, preferably 0.010% or less, and more preferably 0.008% or less.

[0039] (5) Fe: 0.005 to 0.050%. Fe refines the intermetallic compounds precipitated at the joint interface to a certain degree and inhibits their liberation into the solder bulk. Therefore, the addition of Fe improves thermal conductivity and drop impact resistance. If the Fe content is less than 0.005%, the intermetallic compounds precipitated at the joint interface cannot be refined, resulting in a deterioration in drop impact resistance. Furthermore, the liberation of intermetallic compounds is not inhibited, resulting in a failure to improve thermal conductivity. The lower limit of the Fe content is 0.005% or more, preferably 0.010% or more, and more preferably 0.020% or more. On the other hand, if the Fe content exceeds 0.050%, the intermetallic compounds are not refined, resulting in a decrease in drop impact resistance. Furthermore, the liquidus temperature increases. The upper limit of the Fe content is 0.050% or less, preferably 0.040% or less, and more preferably 0.025% or less.

[0040] (6) In: 6.0% or less In is an optional element that may be contained within a range that does not impair the above-described effects of the solder alloy according to the present invention. The upper limit of the In content is preferably 6.0% or less, more preferably 5.0% or less. The lower limit is not particularly limited, but is preferably more than 0%, more preferably 0.1% or more, and even more preferably 0.5% or more.

[0041] (7) At least one of P, Ge, Ga, and Mn, in total, 0.1% or less. P, Ge, Ga, and Mn are optional elements that may be contained to inhibit oxidation of the solder alloy. The total content of these elements is preferably 0.1% or less. There is no particular lower limit, but the total content should be 0.001% or more. The content of each of these elements is more preferably 0.001 to 0.1%, and even more preferably 0.001 to 0.050%.

[0042] (8) Balance: Sn The balance of the solder alloy according to the present invention is Sn. In addition to the above elements, unavoidable impurities may be contained. Even if unavoidable impurities are contained, the above-mentioned effects are not affected. It is preferable that the solder alloy according to the present invention does not contain Ni or Bi. Ni makes the alloy structure finer than necessary, which causes intermetallic compounds to be liberated from the joint interface into the solder bulk, resulting in a decrease in thermal conductivity. Bi forms a concentrated layer in the solder alloy, which reduces drop impact resistance and causes lift-off.

[0043] (9) Formulas (1) and (2): 0.040≦Ag×Cu×Sb×Co≦0.075 (1) 1.6≦Ag×Cu×Sb×Co / Fed≦5.7 (2) In the above formulas (1) and (2), Ag, Cu, Sb, Co, and Fe represent the content (mass%) of the alloy composition. Formula (1) is a formula related to elements that have the effect of improving heat cycle resistance. In formula (1), the contents of Ag, Cu, and Sb are higher than that of Co, but even a small content of Co contributes significantly to improving heat cycle resistance. Therefore, although the content of Co is about 10 to 100 times that of Ag, Cu, and Sb, it is considered that the degree of contribution to the properties of the solder alloy is similar. Therefore, in order to further improve the heat cycle resistance properties in the present invention, adding the constituent elements of (1) is meaningless, and it is preferable to maintain a balanced content. The formulas (1) and (2) are calculated using the numerical values ​​themselves shown in the measured values ​​of the alloy compositions shown in Tables 1 and 2 below. That is, in the calculation of 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 zero. For example, if the measured Co content is "0.008" mass%, the Co content used in the calculation of formulas (1) and (2) is treated as "0.008000..." rather than having a range of 0.0075 to 0.0084%. Formula (1) is calculated to three decimal places, and formula (2) is calculated to one decimal place. The same procedure is used when calculating formulas (1) and (2) from alloy compositions specifically disclosed in patent documents and other literature described in this specification.

[0044] Formula (2) relates to the ratio of elements contributing to improved impact resistance to elements contributing to improved thermal conductivity. Like formula (1), formula (2) contains relatively high amounts of Ag, Cu, and Sb, and relatively low amounts of Co and Fe. However, despite the relatively low Co content, it contributes to the refinement of the alloy structure, thereby significantly improving impact resistance. Although Fe has a content similar to that of Co, it contributes more to the refinement of the alloy structure than Co and also contributes to the suppression of liberation. Among the elements constituting the solder alloy according to the present invention, Fe is an element that can actively improve thermal conductivity. In order to achieve even higher levels of thermal conductivity, heat cycle resistance, and impact resistance, it is desirable to satisfy formula (2), which takes thermal conductivity and heat cycle resistance into consideration, in addition to formula (1).

[0045] Furthermore, when In is contained, it is desirable that the formulas (1) and (2) are 4.0% or less. In an alloy composition with 0% In, if formulas (1) and (2) are satisfied, the above-mentioned effects are exhibited. Since In can form compounds with Sn, if the In content is 4.0% or less, the decrease in thermal conductivity due to the formed compounds is suppressed, and the effects of satisfying formulas (1) and (2) are more likely to be exhibited.

[0046] 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 according to the present invention, in order to simultaneously achieve even higher levels of heat cycle resistance, thermal conductivity, and impact resistance, it is preferable that the In content be 4.0% or less and that formulas (1) and (2) be satisfied.

[0047] The lower limit of formula (1) is preferably 0.040 or more, more preferably 0.042 or more, even more preferably 0.043 or more, even more preferably 0.046 or more, particularly preferably 0.047 or more, and most preferably 0.050 or more, and may be 0.055 or more. The upper limit of formula (1) is preferably 0.075 or less, more preferably 0.070 or less, even more preferably 0.069 or less, even more preferably 0.058 or less, and particularly preferably 0.056 or less. Formula (1) is preferably 0.042 to 0.70, more preferably 0.043 to 0.069, even more preferably 0.046 to 0.058, and particularly preferably 0.047 to 0.056.

[0048] The lower limit of formula (2) is preferably 1.6 or more, more preferably 1.7 or more, even more preferably 1.8 or more, even more preferably 1.9 or more, particularly preferably 2.0 or more, most preferably 2.2 or more, and may be 2.3 or more. The upper limit of formula (2) is preferably 5.7 or less, more preferably 5.6 or less, even more preferably 5.2 or less, even more preferably 3.7 or less, particularly preferably 3.5 or less, and most preferably 2.7 or less. Formula (2) is preferably 1.7 to 5.6, more preferably 1.8 to 5.2, even more preferably 1.9 to 3.7, and particularly preferably 2.0 to 3.5. Most preferably 2.2 to 2.7, and may be 2.3 to 2.7.

[0049] The upper limit of In is preferably 4.0% or less, more preferably 3.0% or less, even more preferably 2.0% or less, and most preferably 1.0% or less. The lower limit of In is preferably 0% or more, more preferably 0.3% or more, even more preferably 0.5% or more, and most preferably 0.7% or more.

[0050] 2. Solder Balls The solder alloy according to the present invention can be used as solder balls. The solder balls according to the present invention are used to form electrodes of semiconductor packages such as BGA (ball grid array) and bumps on substrates. The diameter of the solder balls according to the present invention is preferably within the range of 1 to 1000 μm. The solder balls can be manufactured by a general solder ball manufacturing method.

[0051] 3. Solder Paste The solder alloy according to the present invention can be used as a solder paste. A solder paste is prepared by mixing a solder alloy powder with a small amount of flux to form a paste. The solder alloy according to the present invention may be used as a solder paste for mounting electronic components on a printed circuit board by reflow soldering. The flux used in the solder paste may be either a water-soluble flux or a water-insoluble flux. Typically, a rosin-based flux, which is a water-insoluble flux based on rosin, is used.

[0052] 4. Solder Joint The solder joint according to the present invention connects an electronic component to its substrate (interposer), or joins and connects an electronic component to a printed circuit board. In other words, the solder joint according to the present invention refers to the connection of electrodes, and can be formed using general soldering conditions.

[0053] 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 heating temperature may be adjusted appropriately depending on the heat resistance of the chip and the liquidus temperature of the solder alloy. Furthermore, when joining using the solder alloy of the present invention, taking into consideration the cooling rate during solidification can further refine the 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 appropriately depending on the alloy composition of the solder alloy.

[0054] The solder alloy according to the present invention can be manufactured by using a low-alpha ray material as its raw material, and when such a low-alpha ray alloy is used to form solder bumps around memory, it can suppress soft errors.

[0055] Solder alloys having the alloy compositions shown in Tables 1 and 2 were prepared, and the thermal conductivity was measured as Evaluation 1, the resistance value after a heat cycle test was measured as Evaluation 2, and the resistance value after a drop impact test was measured as Evaluation 3.

[0056] Evaluation 1: Measurement of thermal conductivity After casting each solder alloy in Tables 1 and 2, a test piece of approximately φ10 mm x 3 mm was prepared. ｔ The samples were processed to a size of 100 mm and their thermal conductivity was measured using a laser flash method in accordance with JIS R 1611. The measuring device used was an LF / TCM-8510B (trade name) manufactured by Rigaku Corporation. The measurement temperature was 23±1°C. A thermal conductivity of 52 W / m / K or more was evaluated as "◎", a thermal conductivity of 50 W / m / K or more but less than 52 W / m / K was evaluated as "◯", and a thermal conductivity of less than 50 W / m / K was evaluated as "×".

[0057] Evaluation 2: Measurement of resistance value after heat cycle test (TCT) Each solder alloy in Tables 1 and 2 was atomized to prepare solder powder. Solder paste for each solder alloy was prepared by mixing with a soldering flux consisting of rosin, solvent, activator, thixotropic agent, organic acid, etc. The solder paste was printed on a 0.8 mm thick printed circuit board (material: FR-4) using a 100 μm thick metal mask, after which 15 BGA components were mounted using a mounter and reflow soldered at a maximum temperature of 240°C for a holding time of 60 seconds to prepare a test board.

[0058] Test boards soldered with each solder alloy were placed in a heat cycle tester set to low temperature conditions of -40°C and high temperature conditions of +125°C, with a holding time of 10 minutes, and the number of cycles was determined at which the resistance of at least one BGA component exceeded 15Ω from the initial resistance value of 3-5Ω. 750 cycles or more were evaluated as "◎", 700-749 cycles as "◯", and less than 700 cycles as "×".

[0059] Evaluation 3: Measurement of resistance value after drop impact test Each solder alloy in Tables 1 and 2 was atomized to prepare solder powder. A solder paste of each solder alloy was prepared by mixing with a soldering flux consisting of rosin, solvent, activator, thixotropic agent, organic acid, etc. 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 five LGA components were then mounted using a mounter. Reflow soldering was performed at a maximum temperature of 240°C and a holding time of 60 seconds to prepare a test board. The LGA components were then cut into five individual pieces.

[0060] Next, both ends of each board were fixed to the base with bolts so that each individual LGA component faced the base. In this state, impact resistance was evaluated by applying an impact of 1500 g acceleration in accordance with the JEDEC standard. In this drop test, crack propagation in the solder joint was confirmed by determining whether the electrical resistance value increased by 50% from the initial value. Crack propagation was evaluated as follows: if the electrical resistance value did not increase by 50% from the initial value after 85 or more drops, it was evaluated as "◎"; if the number of drops when the electrical resistance value exceeded 50% from the initial value was 80 to 84, it was evaluated as "◯"; and if the number of drops when the electrical resistance value exceeded 50% from the initial value was 79 or fewer, it was evaluated as "X". The evaluation results are shown in Tables 1 and 2.

[0061]

[0062]

[0063] As is clear from Tables 1 and 2, Examples 1 to 41 all had appropriate contents of constituent elements, and therefore showed high thermal conductivity and a high number of TCT and drop impact tests. In particular, Examples 3 to 8, 11, 12, 16, 22, 23, 26, 27, 30, and 32 to 40, which satisfied formulas (1) and (2), were confirmed to show particularly excellent results in all evaluations. Note that Example 31, which had an In content of 5%, achieved a thermal conductivity of "Good."

[0064] On the other hand, Additional Comparative Example 1 did not contain Co and Fe, and therefore had poor TCT and drop impact resistance. Comparative Example 4 had poor heat cycle resistance due to a low Ag content. Comparative Example 5 had poor drop impact resistance due to a high Ag content. Comparative Example 6 had poor drop impact resistance due to a low Cu content. Comparative Example 7 had a high Cu content, which caused the intermetallic compounds at the bonding interface to become liberated in the solder bulk, resulting in a decrease in thermal conductivity.

[0065] Comparative Example 8 had poor heat cycle resistance due to a low Sb content. Comparative Example 9 had poor thermal conductivity due to a high Sb content. Comparative Example 10 had poor heat cycle resistance due to a low Co content. Comparative Example 11 had poor drop impact resistance due to a high Co content.

[0066] Comparative Examples 12 and 13 had poor drop impact resistance due to an inappropriate Fe content. Comparative Example 14 had poor drop impact resistance due to the inclusion of Bi. Comparative Examples 15 to 17 had poor thermal conductivity due to the inclusion of Ni. Comparative Example 18 also had poor drop impact resistance due to the inclusion of Bi.

[0067] The results of checking for the presence or absence of free particles are shown in Figure 1. Figure 1 shows cross-sectional SEM photographs of solder joints, with Figure 1(a) being a cross-sectional SEM photograph of a solder joint using the solder alloy of Comparative Example 18, and Figure 1(b) being a cross-sectional SEM photograph of a solder joint using the solder alloy of Example 16. Five samples were prepared for each of the examples and comparative examples, and observations were performed in the region 0 to 20 μm from the alloy layer and the surface treatment interface (the region shown as the "target region" in Figure 1). Powders of each solder alloy shown in Example 16 and Comparative Example 18 were produced by atomization. Solder pastes were prepared by mixing this alloy powder with a flux ("GLV" manufactured by Senju Metal Industry Co., Ltd.) containing rosin, solvent, thixotropic agent, organic acid, etc. The solder paste, which contained 88% by mass of alloy powder and 12% by mass of flux, was printed on the Cu lands of a six-layer printed circuit board (FR-4, Cu-OSP) using a 150 μm metal mask, and then 3216 chip resistors were mounted using a mounter. The solder paste was then melted and reflowed at a maximum temperature of 245°C for a holding time of 40 seconds to prepare a test board.

[0068] Thereafter, the test substrate was cut out and polished, and the vicinity of the bonding interface of the cross section was magnified 1000 times and observed. The total area and the area of ​​the CuSn-based compounds were calculated using image analysis software. Scandium was used as the image analysis software. The area ratio of the CuSn-based compounds was calculated using the results of each calculated area by (area ratio of CuSn-based compounds) (%) = (area of ​​CuSn-based compounds) × 100 / (area of ​​the target region).

[0069] As is clear from Figure 1(b), the CuSn compound ratio was 0% in the corresponding region of Example 16. Figure 1(a) is an image of Comparative Example 18, and the CuSnNi compound ratio in the corresponding region was 15 to 20%. As such, it was clear that no liberation of compounds occurred in the examples. The other examples also showed results similar to those of Example 16.

[0070] Figure 2 is a cross-sectional SEM photograph of a solder joint, where Figure 2(a) is a cross-sectional SEM photograph of a solder joint using the solder alloy of Comparative Example 18, Figure 2(b) is a photograph showing the results of cross-sectional mapping analysis of a solder joint using the solder alloy of Comparative Example 18, and Figure 2(c) is a cross-sectional SEM photograph of a solder joint using the solder alloy of Example 16.

[0071] A test substrate was prepared in the same manner as in Figure 1, and the cross-section near the bonding interface was photographed with an FE-SEM at 350x magnification. The cross-section was then subjected to qualitative analysis using an EDS attached to the SEM to identify Bi, and area analysis of Bi was measured using image analysis software (Scandium, manufactured by EMSIS GmbH). Figures 2(a) and 2(c) are cross-sectional SEM photographs, but it is difficult to confirm the presence or absence of a Bi-enriched layer from these. On the other hand, in Figure 2(b), a Bi-enriched layer was formed near the bonding interface, which was found to be the cause of poor drop impact resistance due to embrittlement.

[0072] The solder according to the present invention can be used in consumer electronic devices such as personal computers, but it can also be used with excellent effect in on-board electronic circuits such as ECUs (Engine Control Units), which are electronic circuits that control automobiles using computers to improve fuel efficiency.

Claims

1. A solder alloy having an alloy composition consisting of, in mass%, 1.0-4.0% Ag, 0.10-1.00% Cu, 1.0-7.0% Sb, 0.001-0.030% Co, 0.005-0.050% Fe, and the balance being Sn.

2. The solder alloy according to claim 1, further comprising, by mass%, 0.1% or less in total of at least one of P, Ge, Ga, and Mn.

3. The solder alloy according to claim 1 or 2, further comprising, by mass%, In: 6.0% or less.

4. The solder alloy according to claim 1 or 2, wherein the alloy composition contains 0 to 4.0% In and satisfies the following formulas (1) and (2): 0.040≦Ag×Cu×Sb×Co≦0.075 (1) 1.6≦Ag×Cu×Sb×Co / Fe≦5.7 (2) In the above formulas (1) and (2), Ag, Cu, Sb, Co, and Fe represent the contents (mass %) of the alloy composition.

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

6. A solder ball made of the solder alloy according to claim 3.

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

8. A solder paste comprising a solder powder made of the solder alloy according to claim 3.

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

10. A solder joint comprising the solder alloy of claim 3.

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