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

Abstract

Provided are 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. The solder alloy has an alloy composition comprising 0.8-2.5% Ag, 0.10-1.00% Cu, 0.03-0.07% Ni, 0.006-0.014% Ge, and 0.001-0.030% 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 at an amount of 0.1% or less in total.

Description

Solder alloys, solder balls, solder pastes, and solder joints

[0001] The present invention relates to solder alloys, solder balls, solder pastes, and solder joints.

[0002] In recent years, there has been a demand for electronic devices with higher integration, larger capacity, and faster speeds. For example, semiconductor packages such as BGA (Ball Grid Array) are being used, and efforts are being made to achieve higher integration and higher functionality at the semiconductor chip level.

[0003] For microelectrodes such as BGA, solder bumps are formed using solder balls. When using solder balls, for example, adhesive flux is applied to the microelectrodes, and the solder balls are placed on the electrodes to which the flux has been applied. The solder balls are then heated in a reflow furnace to melt, and the molten solder wets the microelectrodes, forming solder bumps on the microelectrodes. In this way, when using solder balls, wettability with the electrodes is required.

[0004] Conventionally, Sn—Ag—Cu solder alloys have been widely used as solder alloys for forming solder bumps. This solder alloy is highly versatile and is used in various forms, such as solder balls and solder paste. However, although this solder alloy is highly versatile, there are properties that must be further improved depending on the application, such as solder balls and solder paste. Therefore, various studies have been conducted on the conventionally widely used Sn—Ag—Cu solder alloys in order to improve the properties depending on the application.

[0005] Patent Document 1 discloses a solder alloy for automotive electronic components that contains Ni as an essential element and may optionally contain Co and Ge in order to improve the vibration resistance of the Sn—Ag—Cu solder alloy. Patent Document 1 also discloses that when a repeated bending test is performed to evaluate vibration resistance, cracks occur in the intermetallic compound layer or in the solder alloy region, depending on the alloy composition.

[0006] Therefore, Patent Document 1 discloses that, in order to suppress the progression of fracture in the intermetallic compound layer, Ni or Co, which are atomic species having a smaller atomic radius than Cu, are substituted for Cu in the SnCu compound, thereby alleviating the strain in the intermetallic compound layer. It also discloses the addition of Fe, Ni, and Co to suppress the progression of fracture in the solder alloy region.

[0007] Patent Document 2 discloses a solder alloy containing Ni and Ge as essential elements and Co as an optional element in an Sn-Ag-Cu solder alloy to improve 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 responsible for suppressing non-fusion. Patent Document 2 further discloses that shear strength is improved by refining the Cu and Sn compounds and solid solution strengthening.

[0008] Patent Document 3 discloses a solder alloy in which the relational formula of each constituent element in a Sn-Ag-Cu-Ni-Co-Ge solder alloy is specified in order to suppress Ni erosion and the occurrence of voids. Patent Document 3 discloses that when each constituent element satisfies a predetermined relational formula, Ni diffusion is suppressed and voids occurring in the molten solder are easily expelled.

[0009] Japanese Patent Publication No. 2007-237252 Japanese Patent No. 6928284 Japanese Patent No. 6700568 Japanese Patent Publication No. 2001-58286

[0010] Patent Document 1 discloses Sn-Ag-Cu-Ni-Fe-Co solder alloy and Sn-Ag-Cu-Ni-Fe-Co-Ge-(P) solder alloy as solder alloys with the best results in repeated bending properties. Paragraphs 0036 to 0037 of Patent Document 1 state that by adding a small amount of Fe, a large amount of FeSn is formed as the nucleus of the primary crystal. ２It is said that intermetallic compounds are generated, the dendrite structure is refined, and excellent results are obtained in a repeated bending test to evaluate vibration resistance. Furthermore, 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 that can suppress non-fusion and improve shear strength, and specifies a relational expression for the content of constituent elements. Paragraph 0035 of Patent Document 2 describes that attention was paid to ΔT, which represents the temperature difference between the liquidus temperature and the solidus temperature, the viscosity of molten solder, and Ge oxide. Paragraph 0038 of Patent Document 2 also describes a (Cu, Ni) alloy in which part of Cu is replaced with Ni. ６ Sn ５ The document also discloses that the formation of the compound makes the compound formed at the bonding interface finer. Furthermore, the same paragraph also discloses that Ge dissolves in Ni to distort the crystalline structure of the compound, resulting in (Cu, Ni) ６ Sn ５ A Sn-Ag-Cu-Ni-Ge solder alloy is described in which the compounds are solid solution strengthened.

[0012] The invention described in Patent Document 3 is an excellent invention that suppresses Ni erosion and void generation. Paragraph 0044 of Patent Document 3 discloses that it is possible to minimize the dissolution of the Ni layer by utilizing the sudden change in melting temperature caused by Ni. Paragraph 0045 of Patent Document 3 also discloses that by forming a thin, brittle germanium oxide film instead of a strong tin oxide, the void discharge function due to convection of 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.

[0013] As described above, Patent Documents 1 to 3 discuss improving vibration resistance, suppressing discoloration, suppressing unfused solder, improving shear strength, and suppressing nickel erosion and void formation. However, none of the inventions described in these patent documents address chip standing. Rapid technological innovation in recent years has significantly reduced the size and weight of electronic components. For this reason, chip standing can occur when different amounts of solder alloy are supplied to the two electrodes on which electronic components are mounted. Chip standing occurs when the surface tension of the solder alloy supplied to the two electrodes that melted first pulls the chip. This can be caused, for example, by different amounts of solder alloy supplied. Another example is external factors, such as when the temperature rise of the solder alloy differs between peripheral components when the solder alloy is mixed and mounted on a board, even when the same amount of solder is supplied. Furthermore, considering the unique behavior of solder alloys, the solid phase changes to liquid immediately after the solder alloy begins to melt. However, the inventions described in Patent Documents 2 and 3 did not address chip standing due to these factors.

[0014] Paragraph 0032 of Patent Document 4 discloses that Ni, Cu, Co, Ge, etc. may be added to Sn—Ag solder alloys to suppress chipping. The same paragraph also discloses that solder alloys containing these elements exhibit two endothermic peaks in differential thermal analysis. However, this merely discloses the added elements, and the only solder alloys that have actually been investigated are Sn—Ag, Sn—Ag—Cu, Sn—Ag—Ni, and Sn—Ag—P. Therefore, there is no evidence at all that Co and Ge may be contained in the solder alloys described in Patent Documents 1 to 3.

[0015] In addition, when a solder alloy is used in a substrate that is used in a harsh environment, such as an in-vehicle device, excellent heat cycle resistance and drop impact resistance are required, but the above patent document does not consider heat cycle resistance.

[0016] Thus, even though the solder alloys described in Patent Documents 1 to 4 can solve the respective problems, it is desirable to have them better reflect the actual conditions when mounting electronic components. In other words, the inventions described in these documents do not consider simultaneously satisfying the various properties disclosed in Patent Documents 1 to 4. Furthermore, with the recent trend toward global warming, the usage environment is becoming more severe, and there is a demand for solder alloys that also have excellent heat cycle resistance.

[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 that have excellent mountability by suppressing non-fusion, chipping, and discoloration.

[0018] The present inventors have investigated the properties of the Sn—Ag—Cu—Ni—Ge(—Co) solder alloys disclosed in Patent Documents 1 to 3. First, they have found that the properties of the Sn—Ag—Cu—Ni—Ge solder alloy described in Patent Document 2 change depending on the content of each constituent element.

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

[0020] Even with a Sn—Ag—Cu—Ni—Ge—Co solder alloy (Example 29 of Patent Document 2), which contains Co to refine the alloy structure, the drop impact resistance was poor, and chipping and discoloration occurred. Thus, it was found that the relationship described in Patent Document 2 was insufficient to solve the above problems, and further investigation was necessary.

[0021] Patent Document 1 discloses a Sn—Ag—Cu—Ni—Ge—Co solder alloy in Example 89. However, it was found that the Ge content was as low as 0.005% and the Co content was as high as 0.040%, resulting in non-fusion and discoloration.

[0022] Patent Document 3 also discloses a Sn—Ag—Cu—Ni—Ge—Co solder alloy in Example 3. It has been discovered that discoloration occurs in this alloy composition because the Ge content is as low as 0.005%.

[0023] Thus, it became clear that even with a Sn—Ag—Cu—Ni—Ge(-Co) solder alloy, the required properties could not be obtained depending on the content of each constituent element. Here, in order to improve heat cycle resistance and drop impact resistance, it is necessary to alleviate the stress applied to the solder alloy, so it is desirable for the alloy structure to be fine. It is thought that in order for the alloy structure to become fine, a large amount of the liquid phase becomes a solid phase when the temperature drops slightly below the liquidus temperature, and each phase inhibits the growth of the other.

[0024] As mentioned above, chip standing occurs when the solder alloy introduced to the two electrodes melts at different times. It is thought that in electronic components with two electrodes, the upper end of the melted side of the chip component is pulled by the surface tension caused by the molten solder that melts first, resulting in chip standing.

[0025] More specifically, when the temperature of molten solder rises from the solidus temperature to the liquidus temperature, even a slight temperature rise above the solidus temperature causes the solid phase to become a large amount of liquid, increasing the effect of surface tension, which is thought to result in chipping. On the other hand, if the liquid phase does not form much even as the temperature rises above the solidus temperature, and only begins to form in large amounts just before reaching the liquidus temperature, the effect of surface tension is relatively suppressed, making chipping less likely to occur. Furthermore, it is thought that this behavior varies greatly depending on the alloy composition of the solder alloy, even if ΔT, which represents the temperature range between the solidus temperature and the liquidus temperature, is similar.

[0026] On the other hand, in terms of the heat resistance of the chip, it has been found that Sn-Ag-Cu-Ni-Ge-Co solder alloys tend to have a narrower ΔT temperature range and a lower liquidus temperature. For this reason, it is inferred that a narrower ΔT temperature range is better.

[0027] Furthermore, it is believed that the formation of a strong oxide film on the surface of the solder alloy leads to non-fusion. On the other hand, the formation of an appropriate oxide film can suppress discoloration. Therefore, it is believed that moderate oxidation is necessary to suppress non-fusion and discoloration.

[0028] From the above, considering the behavior from the solidus temperature to the liquidus temperature, it is inferred that heat cycle resistance, drop impact resistance, and chip standing each have opposing directions. Similarly, it is inferred that non-fusion and discoloration also have opposing directions. With conventional solder alloys, it has been difficult to simultaneously achieve the effects required by these opposing alloy structures. Furthermore, in order to simultaneously achieve excellent heat cycle resistance and drop impact resistance, it is thought that in addition to making the alloy structure fine, it is also necessary to refine the structure of the joining interface and strengthen the Sn crystal grains. Until now, in the pursuit of each characteristic, alloy compositions that exhibit more than necessary effects have been sought, but it is thought that alloy compositions that exhibit moderate effects evenly are more easily adapted to the actual mounting situation.

[0029] Therefore, the inventors of the present invention have once again thoroughly investigated the content of each constituent element so that all effects regarding alloy structure and oxidation can be simultaneously exerted. As a result, it has been discovered that, for the first time, when the content of each constituent element is within a specific range, the temperature range of ΔT is narrow, the alloy has excellent heat cycle resistance and drop impact resistance, and no non-fusion, chipping, or discoloration occurs, and this has led to the completion of the present invention. The present invention, which was obtained based on these findings, is as follows.

[0030] (0) A solder alloy characterized by having, by mass%, an alloy composition of 0.8 to 2.5% Ag, 0.10 to 1.00%, 0.03 to 0.07%, 0.006 to 0.014%, 0.001 to 0.030% Co, and the balance being Sn. (1) A solder alloy characterized by having, by mass%, an alloy composition of 0.8 to 2.5% Ag, 0.10 to 1.00%, 0.03 to 0.07%, 0.006 to 0.014%, 0.001 to 0.030% Co, and the balance being Sn.

[0031] (2) The solder alloy according to (0) or (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) A solder alloy according to any one of (0) to (2) above, wherein the alloy composition satisfies at least one of the following formulas (1) to (3): 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 formulas (1) to (3), Ag, Cu, Ni, Ge, and Co are each the content in mass % of the solder alloy.

[0033] (4) A solder ball comprising the solder alloy according to any one of (0) to (3) above.

[0034] (5) A solder paste comprising the solder alloy according to any one of (0) to (3) above.

[0035] (6) A soldered joint comprising the solder alloy according to any one of (0) to (3) above.

[0036] Fig. 1 shows cross-sectional SEM photographs of the solder alloy before and after a heat cycle test, with Fig. 1(a) being before the heat cycle test for Example 3, Fig. 1(b) being after the heat cycle test for Example 3, Fig. 1(c) being before the heat cycle test for Comparative Example 16, and Fig. 1(d) being after the heat cycle test for Comparative Example 16. Fig. 2 shows optical microscope photographs of solder balls before and after exposure to high temperatures, with Fig. 2(a) being before the high temperature exposure for Example 3, Fig. 2(b) being after the high temperature exposure for Example 3, Fig. 2(c) being before the high temperature exposure for Comparative Example 10, and Fig. 2(d) being after the high temperature exposure for Comparative Example 10. Fig. 3 shows cross-sectional SEM photographs showing the presence or absence of unfused portions, with Fig. 3(a) being for Example 3 and Fig. 3(b) being for Comparative Example 8.

[0037] 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.

[0038] 1. Solder alloy (1) Ag: 0.8 to 2.5% Ag is Ag ３ Since Sn is precipitated in a granular form, the precipitation strengthening of the solder alloy improves the heat cycle resistance and drop impact resistance. Furthermore, by lowering the melting point, the temperature range of ΔT is narrowed and chipping can be suppressed. If the Ag content is less than 0.8%, the amount of compound precipitated is small, resulting in poor heat cycle resistance. Furthermore, if the Ag, Cu, and Ni contents are too low, the Ge content becomes too high, resulting in a thick, hard and brittle Ge oxide film, which causes non-fusion. The lower limit of the Ag content is 0.8% or more, preferably 1.0% or more, and 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, and stress concentrates at the joint interface, resulting in poor drop impact resistance. The upper limit of the Ag content is 2.5% or less, preferably 2.3% or less, more preferably 2.0% or less, even more preferably 1.6% or less, and particularly preferably 1.4% or less. In the present invention, the Ag content range can be set by appropriately combining the above-mentioned lower and upper limits. The preferred range of Ag is 1.0 to 1.4%.

[0040] (2) Cu: 0.10 to 1.00% Cu suppresses the rise in melting point. It also prevents unfused and coarse Cu particles. ６ Sn ５ When the Cu content is less than 0.10%, the precipitation of Cu can be suppressed. ６ Sn ５ 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 other hand, when the Cu content exceeds 1.00%, coarse Cu particles appear at the bonding interface. ６ Sn ５ precipitates, resulting in poor drop impact resistance. Furthermore, if the Cu content significantly exceeds 1.00%, the temperature range of ΔT expands, and there is a concern that non-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, even more preferably 0.70% or less, and particularly preferably 0.60% or less. In the present invention, the range of the Cu content can be determined by appropriately combining the above-mentioned lower and upper limits. A preferred range of Cu is 0.40 to 0.60%.

[0042] (3) Ni: 0.03 to 0.07% Ni suppresses an increase in melting point, suppresses non-fusion, promotes refinement of Sn crystal grains, and improves heat cycle resistance and drop impact resistance. If the Ni content is less than 0.03%, the Sn crystal grains will not be refined, resulting in poor drop impact resistance. 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, if the Ni content exceeds 0.07%, coarse SnNi alloys precipitate on the surface of the solder alloy, resulting in non-fusion. Furthermore, the liquidus temperature rises, widening the temperature range of ΔT. Furthermore, if the Ni content is even higher, the drop impact resistance also deteriorates. The upper limit of the Ni content is 0.07% or less, preferably 0.06% or less. In the present invention, the Ni content range can be determined by appropriately combining the above-mentioned lower and upper limits. The preferred range of Ni is 0.04 to 0.06%.

[0044] (4) Ge: 0.006 to 0.014%. Ge can suppress non-fusion and discoloration of the solder alloy. Without Ge, tin oxide forms 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, brittle oxide film on the surface of the molten solder. Because this oxide film is brittle, it is easily destroyed by convection of the molten solder itself or by external forces applied by the chip when it is placed. This inhibits the formation of an oxide film of Sn and prevents the oxide film from being retained on the surface of the molten solder. Contrary to the oxide film of Sn, it actually promotes fusion between the solder balls and the solder powder in the paste.

[0045] Furthermore, Ge reacts with oxygen in the atmosphere to form a brittle oxide film, thereby suppressing discoloration of the solder alloy. Since Ge does not contribute to the suppression of supercooling, the time until solidification is delayed and Sn crystal grains become finer. Furthermore, Ge has a longer-lasting effect of inhibiting oxidation compared to P, which is used as an oxidation-suppressing element. Therefore, when Ge is used in solder balls in particular, it exhibits the effect of refining Sn crystal grains and the effect of sustaining oxidation suppression.

[0046] If 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, and more preferably 0.008% or more. On the other hand, if the Ge content exceeds 0.014%, a thick germanium oxide is formed on the surface of the solder alloy, covering it with a thick, hard and brittle Ge oxide film, resulting in non-fusion. Non-fusion may also occur when the total amount of Ag, Cu, and Ni is relatively low. The upper limit of the Ge content is 0.014% or less, preferably 0.012% or less, more preferably 0.011% or less, even more preferably 0.010% or less, and particularly preferably 0.009% or less. In the present invention, the Ge content range can be determined by appropriately combining the above-mentioned lower and upper limits. The preferred range of Ge is 0.006 to 0.012%.

[0047] (5) Co: 0.001 to 0.030% or less In the solder alloy according to the present invention, Co suppresses an increase in melting point, and through a synergistic effect with Ni, suppresses non-fusion, promotes the refinement of Sn crystal grains, and improves heat cycle resistance and drop impact resistance. In the solder alloy according to the present invention, the Co content is less than that of Ag or Cu, but the absence of Co results in inferior drop impact resistance, non-fusion, and chipping. For this reason, 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, resulting in poor heat cycle resistance. The lower limit of the Co content is 0.001% or more, preferably 0.004% or more, more preferably 0.006% or more, even more preferably 0.0070% or more, and particularly preferably 0.008% or more. On the other hand, if the Co content exceeds 0.030%, coarse SnCo compounds are formed on the surface of the solder alloy, resulting in the simultaneous presence of solid and liquid phases in the molten solder, increasing the liquidus temperature and deteriorating wettability, 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, even more preferably 0.012% or less, and particularly preferably 0.010% or less. In the present invention, the Co content range can be set by appropriately combining the above-mentioned lower and upper limits. The preferred range of Co is 0.006 to 0.012%.

[0049] (6) 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. The balance of the solder alloy according to the present invention may consist of Sn and unavoidable impurities. Even if unavoidable impurities are contained, the above-mentioned effects are not affected. Note that P acts as a solidification nucleus for Sn crystal grains to suppress supercooling, so it is better not to include it because it lengthens the time until solidification and causes the Sn crystal grains to become too large. Furthermore, in the present invention, there is a concern that Fe may form an SnFe intermetallic compound. As this increases the difficulty of processing, it is better not to include it.

[0050] (7) At least one of Ga, As, Pd, Mn, In, Zn, Zr, and Mg in a total content of 0.1% or less The solder alloy according to the present invention may contain at least one of Ga, As, Pd, Mn, In, Zn, Zr, and Mg in a total content of 0.1% or less as an optional element, to the extent that the effects of the present invention are not impaired. Preferably, the total content is 0.08% or less. There is no particular lower limit to the content, but it is sufficient as long as it is 0.001% or more.

[0051] (8) Formulas (1) to (3) 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 in mass % of the solder alloy.

[0052] The solder alloy according to the present invention can more fully exhibit all of the effects by satisfying formulas (1) to (3). Preferably, at least one of formulas (1) to (3) is satisfied, and most preferably all of formulas (1) to (3) are satisfied. With regard to formula (1), Ag is an element that contributes to chipping, and Cu, Ni, Ge, and Co are elements that contribute to effects other than chipping. With regard to heat cycle resistance, drop impact resistance, and chipping, their behavior from the liquidus temperature to the solidus temperature is contradictory, but it is better to ensure that one effect does not stand out more than necessary and that a balanced effect is exhibited overall.

[0053] To achieve this, it is necessary to control the behavior of the liquid and solid phases 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] Furthermore, by satisfying formula (2), the solder alloy of the present invention can further improve the synergistic effect of Ni and Co to a sufficient level, and can fully exert the effect of refining Sn crystal grains. Furthermore, ΔT is narrow, and the occurrence of non-fusion is suppressed, and other effects can be achieved at the same time.

[0055] By satisfying formula (3), the solder alloy according to the present invention has an extremely good balance of constituent elements that form compounds with Sn. Therefore, any of the AgSn compound, CuSn compound, NiSn compound, and SnCo compound does not precipitate in excessive amounts during solidification. As a result, the solder alloy that satisfies formula (3) has a high level of excellent heat cycle resistance.

[0056] The lower limit of formula (1) is preferably 400,000 or more, more preferably 428,571 or more, even 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, 714,286 or more, or even 750,000 or more. The upper limit of formula (1) is preferably 1,458,334 or less, more preferably 1,437,500 or less, even 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. In the present invention, the above-mentioned lower and upper limits can be appropriately combined to achieve the range of formula (1). The preferred range of formula (1) is 600,000 to 937,500.

[0057] The lower limit of formula (2) is preferably 2.50 or more, more preferably 3.75 or more, even 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 even more preferably 7.50 or less. In the present invention, the range of formula (2) can be achieved by appropriately combining the above-mentioned lower and upper limits. A preferred range of formula (2) is 5.00 to 7.50.

[0058] The lower limit of formula (3) is preferably 0.000168 or more, more preferably 0.000180 or more, even 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, even more preferably 0.000800 or less, even more preferably 0.000480 or less, particularly preferably 0.000460 or less, and most preferably 0.000400 or less, and may be 0.000336 or less, 0.000300 or less, 0.000280 or less, or 0.000252 or less. In the present invention, the above-mentioned lower and upper limits can be appropriately combined to achieve the range of formula (3). A preferred range of formula (3) is 0.000200 to 0.000400.

[0059] These formulas are obtained by the mutual dependence of each constituent element. This is because an alloy is a single entity formed by combining all of the constituent elements, and each constituent element influences the other. In this way, the solder alloy according to the present invention, which adjusts the content of each constituent element to the optimum content and further satisfies formulas (1) to (3), is set within a range that fully takes into account the mutual dependence of each constituent element. Therefore, when each constituent element is within the above-mentioned range and further satisfies formulas (1) to (3), various properties that were previously difficult to achieve simultaneously and at a high level can be achieved with a single composition.

[0060] The values ​​shown in Tables 1 and 2, which are the measured values ​​of the alloy compositions, were used in the calculations of formulas (1) to (3). For the values ​​calculated from formulas (1) to (3), formula (1) is calculated as an integer, formula (2) is calculated to two decimal places, and formula (3) is calculated to six decimal places. This calculation rule is used in this application, and is also intended to be used in calculations for additional solder alloys described in other documents, etc., since all solder alloys must be treated in the same way.

[0061] In the examples described below, a rating of "◎" indicates that the result is particularly preferable in practical use compared to "◯." "◯" indicates a more preferable result than the prior art, and is therefore within the scope of the present invention, and is treated as an example. "×" or "Δ" indicates an insufficient result in the present invention, and is therefore outside the scope of the present invention, and is treated as a comparative example.

[0062] 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 BGAs 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.

[0063] 3. Solder Paste The solder paste according to the present invention is a mixture of solder powder having the above-described alloy composition and flux. The flux used in the present invention is not particularly limited as long as it allows for soldering by conventional methods. Therefore, it is sufficient to use a flux containing a suitable blend of commonly used rosin, organic acid, activator, thixotropic material, and solvent. The blending ratio of the metal powder component and the flux component in the present invention is not particularly limited, but is preferably 70 to 90 mass% metal powder component and 10 to 30 mass% flux component.

[0064] 4. Solder Joint The solder joint according to the present invention is suitable for use in joining at least two or more members to be joined. The members to be joined are not particularly limited, as long as they are electrically connected using the solder alloy according to the present invention, and include, for example, elements, substrates, electronic components, printed circuit boards, insulating substrates, heat sinks, lead frames, semiconductors using electrode terminals, power modules, inverter products, etc.

[0065] 5. Manufacturing Method of Solder Alloy The solder alloy according to the present invention is preferably manufactured by adding a Sn—Ni mother alloy, a Sn—Co mother alloy, and a Sn—Ge mother alloy to an alloy containing predetermined amounts of Sn, Ag, and Cu, so that the contents of each constituent element are predetermined. Because Ni and Co have high melting points, adding them alone to Sn leaves them unmelted, resulting in coarse SnNi alloys and SnCo alloys. Furthermore, because Ge has a high melting point, it remains unmelted and cannot usually be added alone. For this reason, Ni, Co, and Ge are preferably added to the SnAgCu alloy in the form of a mother alloy with Sn.

[0066] 6. Others The solder alloy according to the present invention can be manufactured using low alpha radiation materials as its raw materials. When such low alpha radiation alloys are used to form solder bumps around memory, they can suppress soft errors.

[0067] The present invention will be described with reference to the following examples, but is not limited to these examples. To demonstrate the effects of the present invention, the solder alloys shown in Table 1 were used to (1) measure ΔT, (2) perform a thermal cycle test (TCT), and (3) perform a drop impact test (DROP), and confirm the presence or absence of (4) non-fusion, (5) standing chips, and (6) discoloration.

[0068] (1) ΔT For the solder alloys shown in Tables 1 and 2, each temperature was determined from the DSC curve. The DSC curve was obtained by raising the temperature at 5°C / min in the atmosphere using a Seiko Instruments DSC (Model: 6200). The liquidus temperature was determined from the obtained DSC curve. The solidus temperature was also evaluated from the DSC curve. The value obtained by subtracting the solidus temperature from the liquidus temperature was taken 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 "◯". When ΔT was more than 40°C, it was judged as "△".

[0069] (2) Heat Cycle Resistance Test (TCT) Each solder alloy listed in Tables 1 and 2 was atomized to prepare solder powder. A solder paste of each solder alloy was prepared by mixing it with a soldering flux ("GLV" manufactured by Senju Metal Industry Co., Ltd.) consisting of rosin, solvent, activator, thixotropic agent, organic acid, etc. The alloy powder in the solder paste was 88% by mass, and the flux was 12% by mass. 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 15 BGA components were mounted using a mounter. Test boards were then prepared by reflow soldering at a maximum temperature of 245°C and a holding time of 60 seconds.

[0070] The fabricated test board was placed in a heat cycle tester set to low temperature -40°C, high temperature +125°C, and a holding time of 10 minutes, and the number of cycles was determined at which the resistance value of at least one BGA component exceeded 15Ω from the initial resistance value of 3-5Ω. If the number of cycles was 700 or more, it was judged as "◎". If the number of cycles was 650-699, it was judged as "◯". If the number of cycles was less than 650, it was judged as "X".

[0071] (3) Drop Impact Test (DROP) A solder paste was prepared in the same manner as in (2). 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 BGA components were mounted on each board using a mounter. Two test boards were then produced by reflow soldering at a maximum temperature of 240°C and a holding time of 60 seconds. The BGA components were then individually separated.

[0072] Next, both ends of the test board were fixed to the base with bolts so that the BGA components faced the base. In this state, impact resistance was evaluated by applying an impact with an acceleration of 1500 G while measuring the electrical resistance in accordance with the JEDEC standard. The progress of cracks was evaluated by the number of drops required for the electrical resistance to increase by 50% from the initial value. If the number of drops was 100 or more, it was judged as "◎". If the number of drops was 90 or more but less than 100, it was judged as "◯". If the number of drops was less than 90, it was judged as "X".

[0073] (4) Unfused The solder alloys shown in Tables 1 and 2 were examined for the presence or absence of unfused portions. The examination method involved casting and rolling solder alloys prepared according to the compositions of the respective Examples and Comparative Examples, and then punching them to prepare small pieces (2 mm (length) × 2 mm (width) × 0.1 mm (thickness)). These small pieces were formed into plates of a predetermined size, placed on a copper plate that had been treated with a flux-coated OSP (organic solderability preservation) treatment, and subjected to reflow. After the surface was cleaned, the plate was left in an environment at a temperature of 125°C and a humidity of 100% RH for 24 hours.

[0074] Furthermore, solder balls (300 μm in diameter in this example) made using a solder alloy consisting of 3.0% Ag, 0.5% Cu, and the remainder Sn (Sn-3.0Ag-0.5Cu) were placed in an environment at 125°C and 100% RH for 24 hours, similar to the small piece members. Next, flux was applied to samples made of the solder alloy of the example or comparative example, and a predetermined number of solder balls were placed on them. In this example, five solder balls were prepared, with nine solder balls in each case. After reflow in air at a maximum temperature of 240°C and a holding time of 60 seconds, the number of unfused solder balls was counted. "Unfused" refers to a state in which the small piece and solder ball were not bonded. A case in which no unfused balls occurred was judged as "◎." A case in which even one unfused ball occurred was judged as "×."

[0075] (5) Chip Standing A solder paste was prepared in the same manner as in (2). This solder paste 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 12 3216 chip resistors were mounted using a mounter. The solder paste was then melted and reflowed under heating conditions of a maximum temperature of 245°C and a holding time of 40 seconds, and soldered to prepare a test board. The number of standing chips after mounting was counted. If there were zero standing chips, it was judged as "◎". If there was one standing chip, it was judged as "◯". If there were two or more standing chips, it was judged as "X".

[0076] (6) Discoloration The solder alloys shown in Tables 1 and 2 were placed in a crucible and heated at 245°C for 10 minutes to melt the solder alloy. The molten solder was dripped from an orifice at the bottom of the crucible, and the resulting droplets were rapidly cooled to room temperature (18°C) and formed into solder balls with a diameter of 600 μm. The formed solder balls were heated in a thermostatic chamber in an atmospheric environment at 300°C for 300 seconds, and the change in lightness was measured. The lightness was measured using a Konica Minolta CM-3500d spectrophotometer, using a D65 light source and a 10-degree field of view, to measure the spectral transmittance in accordance with JIS Z 8722 "Method for measuring color - reflected and transmitted object color," and the color value (L * , a * , b * ) was calculated. * , a* , b * ) is JIS Z 8729 "Color display method - L * a * b * Color system and L * u * v * It is specified in the "Color Space" * is the brightness, and a * is the redness, and b * is the yellowness index. When the brightness was 70 or more, it was judged as "◎". When the brightness was less than 70, it was judged as "×". The results of the evaluation as described above are shown in Tables 1 and 2.

[0077]

[0078]

[0079] As shown in Table 1, in Examples 1 to 30, the contents of each constituent element were all appropriate, and therefore all evaluations yielded results that were acceptable for practical use. Furthermore, it was found that Examples 2 to 5, 8, 9, 11, 12, 15 to 20, and 22 to 30, which satisfied the formulas (1) to (3), showed extremely excellent results in all evaluations.

[0080] On the other hand, as shown in Table 2, Comparative Example 1 had a low Ag content and therefore was inferior in TCT, and Comparative Example 2 had a high Ag content and therefore was inferior in DROP.

[0081] Comparative Example 3 had a low Cu content and therefore was inferior in TCT, and Comparative Example 4 had a high Cu content and therefore was inferior in DROP.

[0082] Comparative Examples 5 and 6 had poor DROP due to the low Ni content. Comparative Example 7 had a high Ni content, which caused non-fusion and widened ΔT. Comparative Example 8 had an even higher Ni content, which caused non-fusion, poor TCT and DROP, and widened ΔT.

[0083] In Comparative Examples 9 to 11, discoloration occurred due to the low Ge content, while in Comparative Examples 12 and 13, non-fusion occurred due to the even higher Ge content.

[0084] Comparative Example 14 had a low Co content and therefore had poor TCT. Comparative Example 15 had a high Co content and therefore did not fuse, and also had a wide ΔT, did not fuse, and caused discoloration due to the high Co content.

[0085] Comparative Example 16 contained no Co and had low Ag and Ni contents, resulting in poor TCT and non-fusion. Comparative Example 17 contained a low Ge content, resulting in discoloration. Comparative Examples 18 to 24 contained a low Ge content and a high Ag content, resulting in poor DROP and discoloration.

[0086] 1 shows cross-sectional SEM photographs of the solder alloy before and after the heat cycle test, in which Fig. 1(a) is before the heat cycle test of Example 3, Fig. 1(b) is after the heat cycle test of Example 3, Fig. 1(c) is before the heat cycle test of Comparative Example 16, and Fig. 1(d) is after the heat cycle test of Comparative Example 16. As shown in Fig. 1(a) and Fig. 1(b), in Example 3, after the heat cycle test, Sn and Ag around Sn were ３ Although Sn became slightly coarse, the coarsening was suppressed to the extent that the characteristics were not deteriorated. On the other hand, as shown in FIG. 1(c) and FIG. 1(d), after the heat cycle test of Comparative Example 16, Sn, Ag ３ Sn, and (Cu, Ni) ６ Sn ５ was found to be significantly coarser.

[0087] 2A and 2B show optical microscope photographs of solder balls before and after exposure to high temperatures, with FIG. 2A being Example 3 before exposure to high temperatures, FIG. 2B being Example 3 after exposure to high temperatures, FIG. 2C being Comparative Example 10 before exposure to high temperatures, and FIG. 2D being Comparative Example 10 after exposure to high temperatures. As shown in FIGS. 2A and 2B, no oxidation of the solder balls was observed in Example 3 after exposure to high temperatures. On the other hand, as shown in FIGS. 2C and 2D, Comparative Example 10 was entirely darkened after exposure to high temperatures.

[0088] 3A and 3B are cross-sectional SEM photographs showing the presence or absence of non-fusion, with FIG. 3A being Example 3 and FIG. 3B being Comparative Example 8. As shown in FIG. 3A, it was found that fusion with the solder balls occurred in Example 3. On the other hand, as shown in FIG. 3B, 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: 0.10 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.

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 at least one of the following formulas (1) to (3): 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 characterized by having the solder alloy according to claim 1 or 2.

5. A solder paste characterized by having the solder alloy according to claim 1 or 2.

6. A solder joint characterized by having the solder alloy according to claim 1 or 2.

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