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

Abstract

To provide a solder alloy, a solder paste, a solder ball, and a soldered joint, having excellent heat cycle resistance and drop impact resistance, and excelling in mounting properties by suppressing non-fusion, tombstoning, and discoloration.SOLUTION: A solder alloy according to the present invention has an alloy composition comprising 0.8-2.5% of Ag, 0.1-1.0% of Cu, 0.03-0.07% of Ni, 0.006-0.014% of Ge, and 0.001-0.030% of Co, with the remainder being Sn. Preferably, the alloy composition further contains, in terms of mass%, at least one of Ga, As, Pd, Mn, In, Zn, Zr, and Mg in a total amount of 0.1% or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a solder alloy, a solder ball, a solder paste, and a solder joint.

Background Art

[0002] In recent years, electronic devices have been required to be highly integrated, have a large capacity, and operate at high speed. For example, semiconductor packages such as BGA (Ball Grid Array) are used, and high integration and high functionality are achieved at the semiconductor chip level.

[0003] In the case of microelectrodes such as BGA, solder bumps are formed using solder balls. When using a solder ball, for example, an adhesive flux is applied to the microelectrode, and the solder ball is placed on the electrode coated with the flux. Then, it is heated in a reflow furnace to melt the solder ball, and the molten solder wets the microelectrode, thereby forming a solder bump on the microelectrode. Thus, when using a solder ball, wettability with the electrode is required.

[0004] As a solder alloy for forming solder bumps, Sn-Ag-Cu solder alloy has been widely used conventionally. This solder alloy has high versatility and is used in various forms such as solder balls and solder pastes. However, although this solder alloy has high versatility, there are characteristics that need to be further improved depending on the applications such as solder balls and solder pastes. Therefore, various studies have been made to improve the characteristics of the Sn-Ag-Cu solder alloy that has been widely used conventionally according to the applications.

[0005] Patent Document 1 discloses a solder alloy for automotive-mounted electronic components in which Ni is an essential element and Co and Ge may be contained as optional elements in order to improve the vibration resistance of the Sn-Ag-Cu solder alloy. Patent Document 1 discloses that when a repeated bending test for evaluating vibration resistance is performed, cracks occur in the intermetallic compound layer or in the region of the solder alloy depending on the alloy composition.

[0006] Therefore, Patent Document 1 discloses that, in order to suppress the progress of fracture in the intermetallic compound layer, Ni or Co, which is an atomic species with a smaller atomic radius than Cu, replaces Cu in the SnCu compound, thereby relaxing the strain in the intermetallic compound layer. In addition, in order to suppress the progress of fracture within the solder alloy region, it is disclosed that Fe, Ni, and Co are added.

[0007] Patent Document 2 discloses a solder alloy containing Ni and Ge as essential elements and Co as an optional element in a Sn-Ag-Cu solder alloy in order to improve the shear strength and suppress non-fusion. Patent Document 2 also discloses that the balance between the Ag, Cu, and Ni contents and the Ge content is attributable to the suppression of non-fusion. Furthermore, Patent Document 2 discloses that the shear strength is improved by the refinement and solid solution strengthening of the Cu-Sn compound.

[0008] Patent Document 3 discloses a solder alloy in which the relational expressions of the respective constituent elements are defined in a Sn-Ag-Cu-Ni-Co-Ge solder alloy in order to suppress Ni consumption and the generation of voids. Patent Document 3 discloses that by satisfying the relational expressions of the respective constituent elements, the diffusion of Ni is suppressed and the voids generated in the molten solder are easily discharged.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0010] Patent Document 1 discloses an Sn-Ag-Cu-Ni-Fe-Co solder alloy and an Sn-Ag-Cu-Ni-Fe-Co-Ge-(P) solder alloy as solder alloys having the most excellent results in terms of repeated bending characteristics. Paragraphs 0036 to 0037 of Patent Document 1 state that by containing a small amount of Fe, a large amount of FeSn2 intermetallic compound is generated as nuclei of primary crystals, the dendrite structure is refined, and excellent results are shown in the repeated bending test for evaluating vibration resistance. Further, paragraphs 0038 to 0039 of Patent Document 1 disclose that when Ni, Co, and Fe are contained, the thickness of the SnCu intermetallic compound layer becomes thin and grows uniformly. Furthermore, paragraph 0056 of Patent Document 1 discloses that Ge may be added to suppress discoloration of the solder surface.

[0011] The invention described in Patent Document 2 is an excellent invention capable of suppressing non-fusion and improving shear strength, and a relational expression of the contents of constituent elements is defined. Paragraph 0035 of Patent Document 2 describes that attention is paid to ΔT representing the temperature difference between the liquidus temperature and the solidus temperature, the viscosity of the molten solder, and Ge oxide. Further, paragraph 0038 of Patent Document 2 discloses that by forming a (Cu,Ni)6Sn5 compound in which a part of Cu is replaced by Ni, the compound formed at the bonding interface becomes fine. Furthermore, in the same paragraph, an Sn-Ag-Cu-Ni-Ge solder alloy is described in which Ge is dissolved in Ni, the crystal structure of the compound is distorted, and the (Cu,Ni)6Sn5 compound is solid-solution strengthened.

[0012] The invention described in Patent Document 3 is an excellent invention in which Ni corrosion and void generation are suppressed. Paragraph 0044 of Patent Document 3 discloses that it is possible to minimize the elution of the Ni layer by utilizing the rapid change in melting temperature due to Ni. Further, Paragraph 0045 of Patent Document 3 discloses that by forming a thin and brittle germanium oxide film instead of a strong tin oxide, the void discharge function due to the convection of the molten solder is maintained. Furthermore, Paragraph 0054 of Patent Document 3 discloses that it is better to narrow ΔT in order to suppress segregation of the alloy structure during solidification and the like.

[0013] As described above, Patent Documents 1 to 3 have considered improvements in vibration resistance, suppression of discoloration, suppression of non-fusion, improvement of shear strength, and suppression of Ni corrosion and void generation. However, for any of the inventions described in the patent documents, chip standing has not been considered. Due to recent rapid technological innovation, the miniaturization and weight reduction of electronic components have progressed significantly. For this reason, when different amounts of solder alloy are supplied to two electrodes on which electronic components are mounted, chip standing may occur. Chip standing occurs when the chip is pulled by the surface tension on the side that melts earlier among the solder alloys supplied to the two electrodes. Examples of the causes include cases where the supply amounts of the solder alloy are different. Also, in the case of external factors, that is, even if the same solder supply amount is used, a difference in the temperature rise of the solder alloy may occur in peripheral components and the like in the mixed mounting on the substrate. Furthermore, considering the behavior peculiar to the solder alloy, it can be mentioned that the solid phase immediately changes to the liquid phase after the solder alloy starts to melt. However, the inventions described in Patent Documents 2 and 3 have not considered chip standing caused by these causes.

[0014] Here, in paragraph 0032 of Patent Document 4, it is disclosed that in order to suppress chip standing, Ni, Cu, Co, Ge, etc. may be added to the Sn-Ag solder alloy. And in the same paragraph, it is disclosed that the solder alloy added with these shows two endothermic peaks in differential thermal analysis. However, only the additive elements are disclosed, and the actually studied solder alloys are only Sn-Ag, Sn-Ag-Cu, Sn-Ag-Ni, and Sn-Ag-P. Therefore, regarding Co and Ge that can be contained in the solder alloys described in Patent Documents 1 to 3, nothing has been proven at all.

[0015] In addition, when the solder alloy is used for a substrate used in a harsh environment such as in-vehicle applications, excellent heat cycle resistance and drop impact resistance are required. However, in the above patent documents, heat cycle resistance has not been studied.

[0016] Thus, even if the solder alloys described in Patent Documents 1 to 4 can solve their respective problems, it is desired to better reflect the actual situation during the mounting of electronic components. That is, in the inventions described in these documents, no study has been conducted to simultaneously satisfy the various characteristics disclosed in Patent Documents 1 to 4. Furthermore, due to recent global warming, the use environment is becoming harsher, and a solder alloy that simultaneously satisfies excellent heat cycle resistance is desired.

[0017] Therefore, an object of the present invention is to provide a solder alloy, a solder paste, a solder ball, and a solder joint that have excellent heat cycle resistance and drop impact resistance, and are excellent in mountability by suppressing non-fusion, chip standing, and discoloration.

Means for Solving the Problems

[0018] The inventors of the present invention studied each characteristic in the Sn-Ag-Cu-Ni-Ge(-Co) solder alloy disclosed in Patent Documents 1 to 3. First, in the Sn-Ag-Cu-Ni-Ge solder alloy described in Patent Document 2, a finding was obtained that the characteristics change according to the content of each constituent element.

[0019] In the solder alloy with 0.5% Ag content (Example 1 of Patent Document 2), the heat cycle resistance is poor, but in the solder alloys with a high Ag content (Examples 2 to 4, 9 to 11, 14, 16 to 22 of Patent Document 2), the finding that the heat cycle resistance is improved was obtained. Even in these solder alloys with improved heat cycle resistance, depending on the alloy composition, the drop impact resistance was poor, and non-fusion, chip standing, and discoloration occurred.

[0020] Even in the Sn-Ag-Cu-Ni-Ge-Co solder alloy containing Co to refine the alloy structure (Example 29 of Patent Document 2), the drop impact resistance was poor, and chip standing and discoloration occurred. Thus, it was found that the relational expressions described in Patent Document 2 were insufficient to solve the above problems, and further investigation was required.

[0021] Example 89 of Patent Document 1 discloses a Sn-Ag-Cu-Ni-Ge-Co solder alloy. However, since the Ge content is as low as 0.005% and the Co content is as high as 0.040%, the findings that non-fusion and discoloration occur were obtained.

[0022] Example 3 of Patent Document 3 also discloses a Sn-Ag-Cu-Ni-Ge-Co solder alloy. Since the Ge content of this alloy composition is as low as 0.005%, the finding that discoloration occurs was obtained.

[0023] Thus, it became clear that even in the Sn-Ag-Cu-Ni-Ge(-Co) solder alloy, the necessary characteristics cannot be obtained depending on the content of each constituent element. Here, in order to improve the heat cycle resistance and drop impact resistance, it is necessary to relax the stress applied to the solder alloy, so it is desirable that the alloy structure is fine. In order for the alloy structure to become fine, it is considered that when the temperature drops slightly from the liquidus temperature, a large amount of the liquid phase becomes the solid phase, and they inhibit each other's growth.

[0024] As described above, chip standing occurs when the timing of melting of the solder alloy introduced into the two electrodes is different. It is presumed that in the electronic component equipped with the two electrodes, the upper end of the melting side of the chip component is pulled due to the influence of the surface tension caused by the melting of the solder that melted earlier, resulting in chip standing.

[0025] More specifically, when the temperature of the molten solder rises from the solidus temperature to the liquidus temperature, it is presumed that chip standing occurs because just a slight temperature rise from the solidus temperature causes a large amount of solid phase to become liquid phase and the influence of surface tension becomes large. On the other hand, when even if the temperature rises from the solidus temperature, little liquid phase is formed and finally a large amount of liquid phase starts to be formed at the temperature just before the liquidus temperature, it is presumed that chip standing is less likely to occur because the influence of surface tension is relatively suppressed. And it is presumed that this behavior varies greatly depending on the alloy composition of the solder alloy even if the temperature range ΔT representing the temperature range between the solidus temperature and the liquidus temperature is about the same.

[0026] On the other hand, considering the heat resistance of the chip, it was found that in the Sn-Ag-Cu-Ni-Ge-Co based solder alloy, the temperature range of ΔT tends to be narrow and the liquidus temperature tends to be low. For this reason, it is presumed that it is better for the temperature range of ΔT to be narrow.

[0027] Furthermore, it is presumed that non-fusion occurs when a strong oxide film is formed on the surface of the solder alloy. On the other hand, when an appropriate oxide film is formed, discoloration can be suppressed. Therefore, it is considered that appropriate oxidation is necessary in order to suppress both non-fusion and discoloration.

[0028] From the above, considering the behavior from the solidus temperature to the liquidus temperature, it is inferred that the heat cycle resistance, drop impact resistance, and chip standing have opposite directions. Similarly, it is inferred that non-fusion and discoloration also have opposite directions. In conventional solder alloys, it has been difficult to simultaneously exhibit the effects required by these opposing alloy structures. In addition, in order to simultaneously satisfy excellent heat cycle resistance and drop impact resistance, it is considered necessary to refine the alloy structure, refine the structure of the bonding interface, and strengthen the Sn crystal grains. So far, in the pursuit of each characteristic, an alloy composition that exhibits more effects than necessary has been explored, but it is considered that an alloy composition that exhibits appropriate effects evenly is more likely to conform to the actual situation of mounting.

[0029] Therefore, the inventors of the present invention re-examined in detail the content of each constituent element so that all effects of the alloy structure and oxidation are simultaneously exhibited. As a result, when the content of each constituent element is within a specific range, for the first time, the temperature range of ΔT is narrow, having excellent heat cycle resistance and drop impact resistance, and the findings that non-fusion, chip standing, and discoloration do not occur were obtained, and the present invention was completed. The present invention obtained from these findings is as follows.

[0030] (1) A solder alloy characterized by having an alloy composition consisting of, by mass%, Ag: 0.8 to 2.5%, Cu: 0.10 to 1.00%, Ni: 0.03 to 0.07%, Ge: 0.006 to 0.014%, Co: 0.001 to 0.030%, and the balance being Sn.

[0031] (2) The solder alloy according to (1) above, wherein the alloy composition further contains, by mass%, at least one of Ga, As, Pd, Mn, In, Zn, Zr, and Mg in a total amount of 0.1% or less.

[0032] (3) The solder alloy according to (1) or (2) above, wherein the alloy composition satisfies the following formula (1). 400000 ≦ Ag / (Cu × Ni × Ge × Co) ≦ 1458334 (1) 2.50 ≦ Ni / Co ≦ 8.40 (2) 0.000168 ≦ Ag × Cu × Ni × Co ≦ 0.004900 (3) In the above formulas (1) to (3), Ag, Cu, Ni, Ge, and Co are each the content as mass % of the solder alloy.

[0033] (4) A solder ball characterized by having the solder alloy described in the above (1) or (2).

[0034] (5) A solder paste characterized by having the solder alloy described in the above (1) or (2).

[0035] (6) A solder joint characterized by having the solder alloy described in the above (1) or (2).

Brief Description of the Drawings

[0036]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0037] The present invention will be described in more detail below. In this specification, “%” regarding the solder alloy composition is “mass %” unless otherwise specified.

[0038] 1. Solder alloy (1) Ag: 0.8 - 2.5% Ag precipitates in the form of granular Ag3Sn, improving the heat cycle resistance and drop impact resistance of the solder alloy through precipitation strengthening. Also, by lowering the melting point, the temperature range of ΔT can be narrowed, and chip standing can be suppressed. If the Ag content is less than 0.8%, the amount of compound precipitation is small and the heat cycle resistance is poor. Also, if the contents of Ag, Cu, and Ni are too low, the Ge content becomes relatively too high, so the hard and brittle Ge oxide film thickly covers the surface, resulting in non-fusion. The lower limit of the Ag content is 0.8% or more, preferably 1.0% or more, more preferably 1.2% or more.

[0039] On the other hand, if the Ag content exceeds 2.5%, the hardness of the solder alloy increases, stress concentrates at the bonding interface, and the drop impact resistance is poor. The upper limit of the Ag content is 2.5% or less, preferably 2.3% or less, more preferably 2.0% or less, still more preferably 1.6% or less, and particularly preferably 1.4% or less.

[0040] (2) Cu: 0.10 - 1.00% Cu suppresses the increase in melting point. Also, it can suppress non-fusion and the precipitation of coarse Cu6Sn5. If the Cu content is less than 0.10%, Cu6Sn5 does not precipitate sufficiently and the heat cycle resistance is poor. The lower limit of the Cu content is 0.10% or more, preferably 0.20% or more, more preferably 0.30% or more, still more preferably 0.40% or more, and particularly preferably 0.50% or more.

[0041] On the one hand, when the Cu content exceeds 1.00%, coarse Cu6Sn5 precipitates at the bonding interface, resulting in poor drop impact resistance. Further, when the Cu content significantly exceeds 1.00%, the temperature range of ΔT expands, and there is a concern that lack of fusion may occur. The upper limit of the Cu content is 1.00% or less, preferably 0.90% or less, more preferably 0.80% or less, still more preferably 0.70% or less, and particularly preferably 0.6% or less.

[0042] (3) Ni: 0.03 - 0.07% Ni suppresses the increase in melting point, suppresses lack of fusion, promotes the refinement of Sn crystal grains, and improves heat cycle resistance and drop impact resistance. When the Ni content is less than 0.03%, the Sn crystal grains do not become fine, and the drop impact resistance is poor. The lower limit of the Ni content is 0.03% or more, preferably 0.04% or more, and more preferably 0.05% or more.

[0043] On the other hand, when the Ni content exceeds 0.07%, coarse SnNi alloy precipitates on the surface of the solder alloy, and lack of fusion occurs. Also, since the liquidus temperature rises, the temperature range of ΔT widens. Furthermore, when the Ni content is even higher, the drop impact resistance is also poor. The upper limit of the Ni content is 0.07% or less, preferably 0.06% or less.

[0044] (4) Ge: 0.006 - 0.014% Ge can suppress lack of fusion and discoloration of the solder alloy. When Ge is not contained, tin oxide is formed on the surface of the molten solder. Tin oxide is strong and difficult to break. On the other hand, Ge added to the solder alloy reacts with oxygen in the atmosphere to form a hard and brittle oxide film on the surface of the molten solder. Since this oxide film is brittle, it is easily broken by the convection of the molten solder itself or the external force applied from the chip when the chip is placed. Therefore, the formation of the Sn oxide film is inhibited, and no oxide film is retained on the surface of the molten solder. On the contrary to the Sn oxide film, rather, the fusion of the solder ball and the solder powder in the paste is promoted.

[0045] In addition, Ge reacts with oxygen in the atmosphere to form a brittle oxide film, thus suppressing discoloration of the solder alloy. Since Ge does not contribute to the suppression of supercooling, the time until solidification becomes slower and the Sn crystal grains become finer. Also, Ge has a lasting oxidation prevention and suppression effect compared to P used as an oxidation suppression element. Therefore, especially when used for solder balls, it exhibits the effect of making Sn crystal grains finer and the effect of lasting oxidation suppression.

[0046] When the Ge content is less than 0.006%, discoloration occurs due to the formation of tin oxide. The lower limit of the Ge content is 0.006% or more, preferably 0.007% or more, more preferably 0.008% or more. On the other hand, when the Ge content exceeds 0.014%, thick germanium oxide is generated on the surface of the solder alloy, and the hard and brittle Ge oxide film thickly covers it, resulting in non-fusion. Also, non-fusion may similarly occur when the total amount of Ag, Cu, and Ni is relatively small. The upper limit of the Ge content is 0.014% or less, preferably 0.012% or less, more preferably 0.011% or less, still more preferably 0.010% or less, and particularly preferably 0.009% or less.

[0047] (5) Co: 0.001 to 0.030% or less In the solder alloy according to the present invention, Co suppresses an increase in the melting point, and due to a synergistic effect with Ni, suppresses non-fusion, promotes refinement of Sn crystal grains, and improves heat cycle resistance and drop impact resistance. In the solder alloy according to the present invention, although the Co content is less than that of Ag and Cu, if Co is not contained, the drop impact resistance is inferior and non-fusion and chip standing occur. Therefore, although Co is a trace additive element, it is treated as an essential element in the present invention.

[0048] If the Co content is less than 0.001%, the refinement of Sn crystal grains is impaired and the heat cycle resistance is poor. The lower limit of the Co content is 0.001% or more, preferably 0.004% or more, more preferably 0.006% or more, still more preferably 0.0070% or more, and particularly preferably 0.008% or more. On the other hand, when the Co content exceeds 0.030%, coarse SnCo compounds are formed on the surface of the solder alloy, so that a solid phase and a liquid phase coexist in the molten solder, the liquidus temperature rises, and the wettability deteriorates, resulting in non-fusion. The upper limit of the Co content is 0.030% or less, preferably 0.020% or less, more preferably 0.015% or less, still more preferably 0.012% or less, and particularly preferably 0.010% or less.

[0049] (6) Balance: Sn The balance of the solder alloy according to the present invention is Sn. It may contain inevitable impurities in addition to the aforementioned elements. Even when inevitable impurities are contained, it does not affect the aforementioned effects. Note that P should not be contained because it serves as a solidification nucleus of Sn crystal grains for suppressing supercooling, the time until solidification becomes long, and the Sn crystal grains become too large. Also, in the present invention, there is a concern that Fe forms an intermetallic compound of SnFe. Along with this, the processing difficulty increases, so it is better not to contain it.

[0050] (7) At least one of Ga, As, Pd, Mn, In, Zn, Zr, and Mg in total of 0.1% or less The solder alloy according to the present invention can contain at least one of Ga, As, Pd, Mn, In, Zn, Zr, and Mg as optional elements in a total range of 0.1% or less without impairing the effects of the present invention. Preferably, the total amount is 0.08% or less. The lower limit of the content is not particularly limited, but it may be 0.001% or more.

[0051] (8) Formula (1) 400000 ≦ Ag / (Cu × Ni × Ge × Co) ≦ 1458334 (1) 2.50 ≦ Ni / Co ≦ 8.40 (2) 0.000168 ≦ Ag × Cu × Ni × Co ≦ 0.004900 (3) In the above formulas (1) to (3), Ag, Cu, Ni, Ge, and Co are each the content as mass % of the solder alloy.

[0052] By satisfying formulas (1) to (3), the solder alloy according to the present invention can further sufficiently exhibit all the effects. Regarding formula (1), Ag is an element contributing to chip standing, and Cu, Ni, Ge, and Co are elements contributing to effects other than chip standing. Regarding heat cycle resistance, drop impact resistance, and chip standing, the behavior from the liquidus temperature to the solidus temperature is contradictory, but it is better that not only one effect protrudes more than necessary and an overall balanced effect is exhibited.

[0053] For this purpose, it is required to control the behavior of the liquid phase and the solid phase in the temperature range from the liquidus temperature to the solidus temperature. In order to meet the requirements in view of such circumstances, it is preferable that the solder alloy according to the present invention satisfies formula (1).

[0054] Also, by satisfying formula (2), the solder alloy according to the present invention can further improve the synergistic effect of Ni and Co to a more sufficient level and sufficiently exhibit the effect of refining the Sn crystal grains. Furthermore, ΔT is narrow, the occurrence of non-fusion is suppressed, and other effects can be achieved simultaneously.

[0055] By satisfying formula (3), the balance of the constituent elements forming a compound with Sn in the solder alloy according to the present invention becomes extremely good. For this reason, none of the AgSn compound, CuSn compound, NiSn compound, and SnCo compound precipitates prominently during solidification. As a result, the solder alloy satisfying formula (3) is excellent in heat cycle resistance at a high level.

[0056] The lower limit of formula (1) is preferably 400,000 or more, more preferably 428,571 or more, still more preferably 500,000 or more, even more preferably 535,714 or more, particularly preferably 600,000 or more, most preferably 625,000 or more, and may be 714,286 or more, 750,000 or more. The upper limit of formula (1) is preferably 1,458,334 or less, more preferably 1,437,500 or less, still more preferably 1,250,000 or less, even more preferably 1,000,000 or less, particularly preferably 937,500 or less, and most preferably 875,000 or less.

[0057] The lower limit of formula (2) is preferably 2.50 or more, more preferably 3.75 or more, still more preferably 5.00 or more, and even more preferably 6.25 or more. The upper limit of formula (2) is preferably 8.40 or less, more preferably 8.33 or less, and still more preferably 7.50 or less.

[0058] The lower limit of formula (3) is preferably 0.000168 or more, more preferably 0.000180 or more, still more preferably 0.000192 or more, even more preferably 0.000200 or more, and particularly preferably 0.000240 or more. The upper limit of formula (3) is preferably 0.004900 or less, more preferably 0.000900 or less, still more preferably 0.000800 or less, even more preferably 0.000480 or less, particularly preferably 0.000460 or less, most preferably 0.000400 or less, and may be 0.000336 or less, 0.000300 or less, 0.000280 or less, 0.000252 or less.

[0059] These formulas are obtained because each constituent element depends on each other. An alloy is an integrated entity formed by combining all constituent elements, because each constituent element affects each other. Thus, on the basis of adjusting the optimal content of each constituent element, the solder alloy according to the present invention that further satisfies formulas (1) to (3) is set within a range that fully considers the mutual dependence of each constituent element. For this reason, when each constituent element is within the above range and further satisfies formulas (1) to (3), various properties that were conventionally difficult to achieve simultaneously can be achieved at a high level with a single composition.

[0060] In addition, in the examples described later, when the determination result is "◎", it indicates that it is particularly preferable in practical use compared to "〇". Since "〇" is a more preferable result than the conventional one, it is within the scope of the present invention and is treated as an example. "×" or "△" is an insufficient result in the present invention, so it is outside the scope of the present invention and is treated as a comparative example.

[0061] 2. Solder ball The solder alloy according to the present invention can be used as a solder ball. The solder ball according to the present invention is used for forming electrodes of semiconductor packages such as BGA and bumps on substrates. The diameter of the solder ball according to the present invention is preferably in the range of 1 to 1000 μm. The solder ball can be manufactured by a general method for manufacturing solder balls.

[0062] 3. Solder paste The solder paste according to the present invention is a mixture of solder powder having the above alloy composition and a flux. The flux used in the present invention is not particularly limited as long as soldering can be performed by a conventional method. Therefore, a commonly used rosin, organic acid, activator, thixotropic agent, and solvent appropriately blended may be used. The blending ratio of the metal powder component and the flux component in the present invention is not particularly limited, but preferably, the metal powder component: 70 to 90% by mass, and the flux component: 10 to 30% by mass.

[0063] 4. Solder joint The solder joint according to the present invention is preferably used for 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, such as, for example, semiconductors using elements, substrates, electronic components, printed circuit boards, insulating substrates, heat sinks, lead frames, electrode terminals, etc., and power modules, inverter products, etc.

[0064] 5. Method for manufacturing solder alloy The solder alloy according to the present invention is preferably manufactured by adding an Sn-Ni master alloy, an Sn-Co master alloy, and an Sn-Ge master alloy to an alloy containing a predetermined amount of Ag and Cu in Sn so that the content of each constituent element becomes a predetermined amount. Since Ni and Co have high melting points, when added to Sn alone, they remain undissolved and the SnNi alloy and SnCo alloy become coarse. Also, since Ge has a high melting point, it remains undissolved and usually cannot be added alone. Therefore, for Ni, Co, and Ge, it is preferable to add them to the SnAgCu alloy in the form of a master alloy with Sn.

[0065] 6. Others The solder alloy according to the present invention can be manufactured into a low α-dose alloy by using a low α-dose material as its raw material. Such a low α-dose alloy can suppress soft errors when used for forming solder bumps around the memory.

Examples

[0066] The present invention will be described by the following examples, but the present invention is not limited to the following examples. To prove the effects of the present invention, using the solder alloys listed in Table 1, (1) ΔT was measured, (2) a heat cycle test (TCT), and (3) a drop impact test (DROP) were performed, and (4) non-fusion, (5) chip standing, and (6) the presence or absence of discoloration were confirmed.

[0067] (1) ΔT For the solder alloys shown in Tables 1 and 2, the respective temperatures were determined from the DSC curves. The DSC curves were obtained by heating at a rate of 5 °C / min in air using a DSC (model number: 6200) manufactured by Seiko Instruments Inc. The liquidus temperature was determined from the obtained DSC curves. Also, the solidus temperature was evaluated from the DSC curves. The value obtained by subtracting the solidus temperature from the liquidus temperature was defined as ΔT. When ΔT was less than 11 °C, it was judged as "◎". When ΔT was 11 °C or more and 40 °C or less, it was judged as "〇". When ΔT exceeded 40 °C, it was judged as "△".

[0068] (2) Thermal Cycle Test (TCT) Each of the solder alloys shown in Tables 1 and 2 was atomized to obtain solder powder. It was mixed with a soldering flux (manufactured by Senju Metal Industry Co., Ltd., "GLV") composed of rosin, solvent, activator, thixotropic agent, organic acid, etc. to prepare a solder paste for each solder alloy. The alloy powder of the solder paste was 88% by mass, and the flux was 12% by mass. The solder paste was printed on a printed circuit board with a thickness of 0.8 mm (material: FR-4) using a metal mask with a thickness of 100 μm, and then 15 BGA components were mounted with a mounter and reflow soldered under the conditions of a maximum temperature of 245 °C and a holding time of 60 seconds to prepare a test substrate.

[0069] The prepared test substrate was placed in a thermal cycle test apparatus set to the conditions of a low temperature of -40 °C, a high temperature of +125 °C, and a holding time of 10 minutes. The number of cycles was determined when the resistance value exceeded 15 Ω at at least one BGA component starting from the initial resistance value of 3 to 5 Ω. When the number of cycles was 700 or more, it was judged as "◎". When the number of cycles was 650 to 699, it was judged as "〇". When the number of cycles was less than 650, it was judged as "×".

[0070] (3) Drop Impact Test (DROP) A solder paste was prepared in the same manner as in (2). The solder paste was printed on a printed circuit board (material: FR-4) with a thickness of 0.8 mm using a metal mask with a thickness of 100 μm. Then, five BGA components were mounted on each board using a mounter, and reflow soldering was performed under the conditions of a maximum temperature of 240°C and a holding time of 60 seconds to fabricate two test boards. After that, the BGA components were separated one by one.

[0071] Next, both ends of the test board were fixed to the pedestal with bolts so that the BGA components faced the pedestal side. In this state, an impact of 1500 G was applied while measuring the electrical resistance value in accordance with the JEDEC standard to evaluate the shock resistance. The situation where cracks were progressing was evaluated by the number of drops until the electrical resistance value increased by 50% from the initial value. When the number of drops was 100 or more, it was determined as "◎". When the number of drops was 90 or more and less than 100, it was determined as "〇". When the number of drops was less than 90, it was determined as "×".

[0072] (4) Incomplete fusion Regarding the solder alloys shown in Table 1 and Table 2, the presence or absence of incomplete fusion was verified. The verification method was to punch out a small piece-shaped member (2 mm (length) × 2 mm (width) × 0.1 mm (thickness)) from the solder alloy prepared according to the compositions of each example and comparative example after casting and rolling. This small piece was formed into a plate shape of a predetermined size, placed on a Cu plate treated with OSP (Organic Solderability Presevation) with a water-soluble preflux applied, reflowed, the surface was washed, and then placed in an environment of a temperature of 125°C and a humidity of 100% RH for 24 hours.

[0073] Furthermore, a solder ball (in this example, with a diameter of 300 μm) made of a solder alloy (Sn-3.0Ag-0.5Cu) consisting of 3.0% Ag, 0.5% Cu, and the balance being Sn was placed in an environment of a temperature of 125°C and a humidity of 100% RH for 24 hours in the same manner as the small piece member. Next, flux was applied onto a sample made of the solder alloy of the example or the comparative example, and a predetermined number of solder balls were placed. In this example, the number of solder balls was 9, and 5 pieces of each were prepared. Then, after performing reflow under the conditions of a maximum temperature of 240°C and a holding time of 60 seconds in the atmosphere, the number of unfused solder balls was counted. Unfused means a state where the small piece and the solder ball are not joined. When no unfused solder ball occurred, it was judged as "◎". When even one unfused solder ball occurred, it was judged as "×".

[0074] (5) Chip Standing (2) A solder paste was prepared in the same manner. This solder paste was printed on the Cu land of a 6-layer printed circuit board (FR-4, Cu-OSP) with a 150-μm metal mask, and then 12 3216 chip resistors were mounted with a mounter. Then, melting was performed under heating conditions of a maximum temperature of 245°C and a holding time of 40 seconds to perform reflow and soldering to produce a test substrate. The number of standing chips after mounting was counted. When the number of standing chips was 0, it was judged as "◎". When the number of standing chips was 1, it was judged as "〇". When the number of standing chips was 2 or more, it was judged as "×".

[0075] (6) Discoloration The solder alloys shown in Table 1 and Table 2 were put into a crucible, heated at 245°C for 10 minutes to melt the solder alloy, the molten solder was dropped from an orifice provided at the bottom of the crucible, and the generated droplets were rapidly cooled to room temperature (18°C) to form spheres into solder balls with a diameter of 600 μm. The sphered solder balls were heated at a set temperature of 300°C for 300 seconds using a thermostatic bath in an air atmosphere, and the change in lightness was measured. The lightness was measured by measuring the spectral transmittance in accordance with JIS Z 8722 "Method of Measuring Color - Reflecting and Transmitting Object Colors" with a D65 light source and a 10-degree field of view using a CM-3500d type spectral colorimeter manufactured by Konica Minolta, and the color values (L * ,a * ,b* ) was obtained from. Note that (L * , a * , b * ) is defined in JIS Z 8729 "Color Display Method - L * a * b * Color System and L * u * v * Color System". L * is lightness, a * is red chroma, b * is yellow chroma. When the lightness is 70 or more, it was judged as "◎". When the lightness is less than 70, it was judged as "×". The results of the evaluation as described above are shown in Table 1 and Table 2.

[0076]

Table 1

[0077]

Table 2

[0078] As shown in Table 1, in Examples 1 to 30, since the content of each constituent element was an appropriate amount, all evaluations resulted in practically acceptable results. Also, Examples 2 to 5, 8, 9, 11, 12, 15 to 20, and 22 to 30 that satisfy formulas (1) to (3) were found to show extremely excellent results in all evaluations.

[0079] On the other hand, as shown in Table 2, in Comparative Example 1, since the content of Ag was low, the TCT was inferior. In Comparative Example 2, since the content of Ag was high, the DROP was inferior.

[0080] In Comparative Example 3, since the content of Cu was low, the TCT was inferior. In Comparative Example 4, since the content of Cu was high, the DROP was inferior.

[0081] In Comparative Examples 5 and 6, since the Ni content was low, the DROP was inferior. In Comparative Example 7, since the Ni content was high, lack of fusion occurred and ΔT widened. In Comparative Example 8, since the Ni content was even higher, lack of fusion occurred, the TCT and DROP were inferior, and ΔT widened.

[0082] In Comparative Examples 9 to 11, since the Ge content was low, discoloration occurred. In Comparative Examples 12 and 13, since the Ge content was even higher, lack of fusion occurred.

[0083] In Comparative Example 14, since the Co content was low, the TCT was inferior. In Comparative Example 15, since the Co content was high, lack of fusion occurred. Also, since the Co content was high, ΔT widened, lack of fusion occurred, and discoloration occurred.

[0084] Comparative Example 16 contained no Co, and had low Ag and Ni contents, so the TCT was inferior and lack of fusion occurred. In Comparative Example 17, since the Ge content was low, discoloration occurred. In Comparative Examples 18 to 24, since the Ge content was low and the Ag content was high, the DROP was inferior and discoloration occurred.

[0085] Figure 1 shows cross-sectional SEM photographs of the solder alloy before and after the heat cycle test. Figure 1(a) is before the heat cycle test of Example 3, Figure 1(b) is after the heat cycle test of Example 3, Figure 1(c) is before the heat cycle test of Comparative Example 16, and Figure 1(d) is after the heat cycle test of Comparative Example 16. As shown in Figures 1(a) and 1(b), in Example 3 after the heat cycle test, although Sn and Ag3Sn around Sn became slightly coarser, the coarsening was suppressed to the extent that the characteristics did not deteriorate. On the other hand, as shown in Figures 1(c) and 1(d), after the heat cycle test of Comparative Example 16, it was found that Sn, Ag3Sn, and (Cu,Ni)6Sn5 became significantly coarser.

[0086] Figure 2 is an optical microscope photograph of solder balls before and after high-temperature storage. Figure 2(a) shows before high-temperature storage of Example 3, Figure 2(b) shows after high-temperature storage of Example 3, Figure 2(c) shows before high-temperature storage of Comparative Example 10, and Figure 2(d) shows after high-temperature storage of Comparative Example 10. As shown in Figures 2(a) and 2(b), no oxidation of the solder balls was observed after high-temperature storage in Example 3. On the other hand, as shown in Figures 2(c) and 2(d), Comparative Example 10 was entirely blackened after high-temperature storage.

[0087] Figure 3 is a cross-sectional SEM photograph showing the presence or absence of non-fusion. Figure 3(a) is Example 3, and Figure 3(b) is Comparative Example 8. As shown in Figure 3(a), it was found that the solder balls were fused in Example 3. On the other hand, as shown in Figure 3(b), it was found that non-fusion occurred in Comparative Example 8.

Claims

1. A solder alloy having an alloy composition consisting of, by mass%, Ag: 0.8 to 2.5%, Cu: 0.1 to 1.0%, Ni: 0.03 to 0.07%, Ge: 0.006 to 0.014%, Co: 0.001 to 0.030%, and the balance being Sn.

2. The solder alloy according to Claim 1, wherein the alloy composition further contains, by mass%, at least one of Ga, As, Pd, Mn, In, Zn, Zr, and Mg in a total amount of 0.1% or less.

3. The solder alloy according to Claim 1 or 2, wherein the alloy composition satisfies the following formula (1). 400000 ≦ Ag / (Cu × Ni × Ge × Co) ≦ 1458334 (1) 2.50 ≦ Ni / Co ≦ 8.40 (2) 0.000168 ≦ Ag × Cu × Ni × Co ≦ 0.004900 (3) In the above formulas (1) to (3), Ag, Cu, Ni, Ge, and Co are the contents as mass% of the solder alloy, respectively.

4. A solder ball comprising the solder alloy according to Claim 1 or 2.

5. A solder paste comprising the solder alloy according to Claim 1 or 2.

6. A solder joint comprising the solder alloy according to Claim 1 or 2.

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