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

Abstract

The present invention provides a solder alloy, a solder paste, a solder ball, and a solder joint that have a low melting point, excellent ductility, shear strength, and heat cycle resistance, and further suppress the occurrence of open defects and further reduce residual voids even when bonding large areas. [Solution] The solder alloy has an alloy composition consisting of, by mass%, 35.0-68.0% Bi, 0.1-2.0% Sb, 0.010-0.050% Ni, 0.007-0.090% Ge, and the remainder being Sn. Preferably, the alloy composition further contains, by mass%, at least one of Co, Ti, Al, Mn, As, Fe, Pd, Zn, Zr, Pb, In, Ce, P, and Ga in a total amount of 0.1% or less. This solder alloy can be suitably used for solder paste, solder balls, and solder joints.

Description

[Technical field]

[0001] The present invention relates to a low melting point solder alloy, a solder paste, a solder ball, and a solder joint. [Background technology]

[0002] In recent years, there has been a demand for miniaturization of electronic devices such as CPUs (Central Processing Units). As electronic devices become smaller, the thermal load during soldering increases, causing defects such as board warping, so soldering at low temperatures is desired. Lower soldering temperatures would enable the manufacture of highly reliable circuit boards. To perform soldering at low temperatures, it is necessary to use a solder alloy with a low melting point.

[0003] As disclosed in JIS Z 3282 (2017), examples of low-melting-point solder alloys include Sn-58Bi and Sn-52In. The melting temperatures of these alloys are 139°C and 119°C, respectively, and both are representative alloy compositions of low-melting-point solders. In particular, Sn-58Bi is widely used as a solder alloy that is low cost and has excellent wettability.

[0004] However, the Bi phase is hard and brittle, which deteriorates the mechanical properties of the solder alloy. When distortion or stress occurs in the board due to thermal cycling or drop impact, there is a risk of fracture in the solder alloy. Therefore, various solder alloys are being investigated to suppress the rise in melting point and improve the reliability of the solder joint.

[0005] For example, Patent Document 1 discusses a solder alloy that has a low melting point, improved ductility and shear strength, and excellent heat cycle resistance. The solder alloy described in this document is a Sn-Bi-Sb-Ni solder alloy in which Sb and Ni are added to a Sn-Bi solder alloy.

[0006] Patent Document 1 also describes that the alloy structure becomes fine due to the synergistic effect of Sb and Ni, and that ductility, shear strength, and heat cycle resistance are simultaneously exhibited. Furthermore, Patent Document 1 discloses that Ge may be added as an element that suppresses oxidation of Sn and improves wettability. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6477965 Summary of the Invention [Problem to be solved by the invention]

[0008] As mentioned above, the solder alloy described in Patent Document 1 is a very excellent solder alloy that can simultaneously exhibit ductility, shear strength, and heat cycle resistance with a single alloy composition, and can also suppress oxidation and improve wettability. However, in the past few years, boards have become thinner due to multilayering, and packages have become larger, which has led to a recurrence of defects caused by board warping due to heating during soldering.

[0009] As a result, when the heating temperature rises from room temperature to reach the peak mounting temperature, or when it cools down from the peak temperature, the PKG (Package) such as BGA (Ball Grid Array) or LGA (Land Grid Array) mounted on the board bends due to the differences in the thermal expansion coefficient and rigidity of the materials that make up the inside, and becomes misaligned from the position when it was mounted. As a result, the electrodes of the board and the electrodes of the PKG solidify at a greater distance than the initial distance, and a tear phenomenon occurs in which the molten part of the solder alloy that makes up the solder joint is torn apart, creating a tiny gap. If the tear phenomenon occurs, the solder joint will maintain its electrical connection and will function as a solder joint.

[0010] However, as the tear phenomenon progresses, open defects occur in which the solder joints separate when melted and solidify, which can lead to the loss of electrical connection in the solder joints and become fatal defects.

[0011] As mentioned above, Patent Document 1 contains Ge to improve wettability. Here, the wettability between the substrate and the molten solder alloy is improved locally to suppress the generation of voids. However, when a large component such as a heat sink is bonded to the substrate, the generation of voids cannot be sufficiently suppressed by only suppressing local voids based on the improvement of wettability.

[0012] In addition, Patent Document 1 describes that the fluidity of the molten solder alloy is not hindered unless the content of any element such as Ge exceeds 0.1%. When the molten solder alloy has good fluidity, it is believed that the generated voids are released to the outside. The generation of voids is caused by deterioration of wettability, and may be caused by being caught when mounting components on a board, but when a solder paste is used, voids may be generated due to its components. In this case, even if the molten solder alloy has fluidity, the voids may not be completely released.

[0013] Even if there is a very excellent solder alloy that can exhibit multiple effects with one alloy composition, such as the solder alloy described in Patent Document 1, it is necessary to appropriately improve it in accordance with changes in technical trends. Furthermore, there is a demand for an excellent solder alloy that can solve new problems while maintaining the various effects that can be exhibited by conventional solder alloys.

[0014] In particular, Ge has been studied extensively as an element that exhibits an oxidation suppression effect, including in Patent Document 1. The liquid properties of a Sn-Bi based solder alloy in a molten state are affected by the solidification shape, etc., and it is even more difficult to stably control them in mounting in an air environment. In order to improve the mounting quality of joints using Sn-Bi based low-temperature solder alloys, it is desirable for the solid properties to have the effect of increasing reliability, as in the solder alloy described in Patent Document 1, and at the same time, for the alloy to be compatible with the mounting process as a liquid and have the effect of improving the joint quality, but sufficient studies have not been conducted on the technology and guidelines for achieving both of these.

[0015] An object of the present invention is to provide a solder alloy, a solder paste, a solder ball, and a solder joint which have a low melting point, excellent ductility, shear strength, and heat cycle resistance, and further suppress the occurrence of open defects, and further reduce residual voids even when bonding over a large area. [Means for solving the problem]

[0016] The present inventors have focused on the fact that the Sn-Bi-Sb-Ni-Ge solder alloy disclosed in Patent Document 1 is compatible with the mounting process even in a liquid state and exhibits the effect of improving joint quality. As a result of examining the cause of the existence of an alloy composition that causes open defects when a thin substrate is warped, it has been found that when the oxidation state of the surface of the molten solder alloy becomes unstable, in cases where the alloy is entirely in the liquid phase or is a mixture of solid and liquid phases, open defects occur due to the progression of the tear phenomenon from the liquid phase portion.

[0017] Considering these, it seems that it would be better to increase the Ge content in order to increase the stable oxide film on the surface of the molten solder alloy. However, it was found that there are alloy compositions that, although a high Ge content suppresses open defects, cause a large number of voids when a solder joint is formed using a paste printed over a large area. It is presumed that when a thick Ge oxide film is generated, the active components in the flux that makes up the paste are consumed preferentially in the reduction of the oxide film, and the reduction of the electrode occurs later, resulting in the generation of a large number of voids at the joint interface.

[0018] Therefore, the present inventors have focused on the Ge content and have found that it is necessary to precisely control the Ge content within a predetermined range. However, they have found that in a Sn-Bi-Sb-Ni-Ge solder alloy, controlling only the Ge content does not provide sufficient effects.

[0019] In order to prevent open defects from occurring even when the Ge content is reduced, it has been discovered that the occurrence of open defects due to a reduction in the Ge content can be suppressed by precisely controlling the contents of Bi and Ni in addition to Ge.

[0020] In obtaining this knowledge, the inventors focused on the fact that if the surface state of the molten solder alloy is stable, the occurrence of open defects due to the progression of the tear phenomenon can be suppressed. Then, assuming that if the surface state is stable, the droplets of the molten solder alloy will also be stably held, they evaluated the droplet retention of the molten solder alloy. As a result, they also found that solder alloys having droplet retention, which is an index of the droplets being stably held, tend to be able to suppress the occurrence of open defects.

[0021] Furthermore, it was found that the inclusion of a certain amount of Ge sufficiently suppresses the generation of voids in a solder joint having a large area, and that when the Sb content is within a predetermined range in addition to the Bi, Ni, and Ge contents, the generation of voids can be sufficiently suppressed. It was also found that the Sn-Bi-Sb-Ni-Ge solder alloy that exhibits these effects has a low liquidus temperature and is excellent in ductility, shear strength, and heat cycle resistance, similar to conventional solder alloys. The present invention, which has been made based on these findings, is as follows.

[0022] (0) A solder alloy comprising, by mass%, 35.0-68.0% Bi, 0.1-2.0% Sb, 0.010-0.050% Ni, 0.007-0.090% Ge, and the remainder being Sn. (1) A solder alloy having an alloy composition consisting essentially of, in mass%, 35.0-68.0% Bi, 0.1-2.0% Sb, 0.010-0.050% Ni, 0.007-0.090% Ge, and the remainder being Sn.

[0023] (2) The solder alloy according to (0) or (1) above, wherein the alloy composition (solder alloy) further contains, by mass%, at least one of Co, As, Fe, Pd, Zr, Pb, Ce, and P in a total amount of 0.1% or less.

[0024] (3) The solder alloy according to (0) or (1) above, wherein the alloy composition (solder alloy) further contains, by mass%, 0.1% or less in total of at least one of Co, Ti, Al, Mn, As, Fe, Pd, Zn, Zr, Pb, In, Ce, P, and Ga.

[0025] (4, 8) A solder alloy according to any one of (0) to (3) above, the alloy composition (solder alloy) satisfying the following formulae (1) and (2): 0.0008≦Bi×Sb×Ni×Ge≦0.0347 (1) 34.7≦(Bi×Ni) / Ge≦154.6 (2) In formulas (1) and (2), Bi, Sb, Ni, and Ge each represent the content in mass % of the solder alloy.

[0026] (5) A solder paste comprising the solder alloy according to any one of (0) to (3) above.

[0027] (6) A solder ball comprising the solder alloy according to any one of (0) to (3) above.

[0028] (7) A solder joint comprising the solder alloy according to any one of (0) to (3) above. [Brief description of the drawings]

[0029] [Figure 1] FIG. 1 is a schematic diagram showing a method for evaluating droplet retention, in which FIG. 1(a) is a schematic diagram showing an ejection state rated as "◎", FIG. 1(b) is a schematic diagram showing an ejection state rated as "◯", FIG. 1(c) is a schematic diagram showing an ejection state rated as "×", and FIG. 1(d) is a diagram showing the ejection amount and time. [Diagram 2] FIG. 2 is a schematic diagram showing an evaluation method for avoiding open defects in an LGA joint, in which FIG. 2(a) is a schematic diagram showing a state in which a PKG is placed on a substrate, FIG. 2(b) is a schematic diagram showing a state in which the PKG is brought into contact with solder paste printed on the substrate and the temperature is increased, FIG. 2(c) is a schematic diagram showing a state in which the PKG is raised 40 μm upward from the state of FIG. 2(b) in a 190° C. environment, and FIG. 2(d) shows the area near the joint of the solder joint before being raised 40 μm upward in FIG. 2(c). FIG. 2(e) is a partial cross-sectional schematic diagram showing the area near the joint of the solder joint in FIG. 2(c). FIG. 2(f) is a partial cross-sectional schematic diagram showing the state of a solder joint without defects from mid-way through solidification to after solidification is completed. FIG. 2(g) is a partial cross-sectional schematic diagram showing the state of a solder joint in which a hot tear phenomenon has occurred from mid-way through solidification to after solidification is completed. FIG. 2(h) is a partial cross-sectional schematic diagram showing the state of a solder joint in which an open defect has occurred due to the progression of the tear phenomenon from mid-way through solidification to after solidification is completed. [Diagram 3] FIG. 3 is a planar X-ray photograph of a solder joint after reflow at a peak temperature of 190° C., where FIG. 3(a) is a planar X-ray photograph of Example 3, FIG. 3(b) is a planar X-ray photograph of Example 15, and FIG. 3(c) is a planar X-ray photograph of Comparative Example 11. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] The present invention will be described in more detail below. In this specification, "%" relating to the solder alloy composition is "mass %" unless otherwise specified.

[0031] 1. Composition of solder alloy (1) Bi: 35.0-68.0% Bi is an element necessary to lower the melting point of solder alloys. Since the melting point of Sn-Bi eutectic alloy is low at 139°C, Bi can lower the liquidus temperature of solder alloys. In addition, solder alloys containing a certain amount of Bi are known to exhibit superplasticity and excellent ductility. Therefore, solder alloys containing a certain amount of Bi have excellent ductility and shear strength.

[0032] If the Bi content is less than 35.0%, the liquidus temperature increases. The lower limit of the Bi content is 35.0% or more, preferably 41.0% or more, more preferably 48.0% or more, and further preferably 56.0% or more.

[0033] On the other hand, when the Bi content exceeds 68.0%, a large amount of hard, brittle, and coarse Bi phase precipitates, hardening the solder alloy itself, and deteriorating ductility and shear strength. In addition, when the Bi content is significantly high, the melting point rises. Furthermore, when a large amount of Bi phase precipitates, the surface state of the molten solder alloy becomes unstable, and open defects occur due to the progression of droplet retention and tear phenomenon. The upper limit of the Bi content is 68.0% or less, preferably 65.0% or less, more preferably 63.0% or less, even more preferably 60.0% or less, and particularly preferably 58.0% or less.

[0034] In the present invention, the range of the Bi content can be determined by appropriately combining the above-mentioned lower and upper limits. The preferred range of Bi is 48.0 to 60.0%.

[0035] (2) Sb: 0.1-2.0% Sb contributes to improving ductility and heat cycle resistance, and is an element necessary for suppressing the occurrence of voids even when printed as a paste over a wide area. At about 200°C, Sb dissolves in β-Sn at about 10%. However, as the temperature decreases, the solubility limit of Sb decreases, and at room temperature, it hardly dissolves and β-SnSb precipitates. β-SnSb precipitates around the Sn phase and Bi phase during solidification, exerting a pinning effect and suppressing the coarsening of each phase.

[0036] If the Sb content is less than 0.1%, it is not possible to improve ductility or heat cycle resistance. The lower limit of the Sb content is 0.1% or more, preferably 0.2% or more, more preferably 0.3% or more, further preferably 0.4% or more, and particularly preferably 0.5% or more.

[0037] On the other hand, if the Sb content exceeds 2.0%, β-SnSb will precipitate excessively, raising the melting point. In addition, coarse β-SnSb will be formed, lowering the ductility. Furthermore, when printed as a paste over a wide area, a large number of voids will be generated. The upper limit of the Sb content is 2.0% or less, preferably 1.5% or less, more preferably 1.3% or less, even more preferably 1.2% or less, even more preferably 1.0% or less, particularly preferably 0.8% or less, and most preferably 0.7% or less.

[0038] In the present invention, the range of the Sb content can be determined by appropriately combining the above-mentioned lower and upper limits. The preferred range of Sb is 0.4 to 1.2%.

[0039] (3) Ni: 0.010~0.050% Ni is an element necessary for improving the ductility and heat cycle resistance of solder alloys. In addition, when an appropriate amount of Ge is added at the same time, Ni forms a thin and uniform Ge oxide film layer that homogenizes the surface structure of the molten solder alloy, which provides excellent droplet retention and suppresses open defects caused by the progression of the tear phenomenon, and further suppresses the occurrence of voids even when the solder alloy is printed as a paste over a wide area.

[0040] If the Ni content is less than 0.010%, the ductility and heat cycle resistance are poor. The lower limit of the Ni content is 0.010% or more, more preferably 0.012% or more, even more preferably 0.013% or more, particularly preferably 0.014% or more, and most preferably 0.015% or more.

[0041] On the other hand, if the Ni content exceeds 0.050%, within the Ge content range described below, open defects will occur due to the progression of the tear phenomenon, and if it is contained in a larger amount, a large number of voids will occur when printed as a paste over a wide area. The upper limit of the Ni content is 0.050% or less, preferably 0.039% or less, more preferably 0.029% or less, even more preferably 0.019% or less, particularly preferably 0.018% or less, and most preferably 0.017% or less.

[0042] In the present invention, the range of the Ni content can be determined by appropriately combining the above-mentioned lower and upper limits. The preferred range of Ni is 0.010 to 0.039%.

[0043] (4) Ge: 0.007 to 0.090% Among the various physical properties of the solder alloy, Ge is an element necessary for adapting to the mounting process as a liquid and for exhibiting the effect of improving the joining quality. When the content of Ge is appropriate, only a small amount of the active components in the flux is consumed for the reduction of the oxides of the solder powder, so that the reduction to the electrode surface is sufficiently performed. Therefore, even when printed as a paste over a wide area, the occurrence of voids can be suppressed. That is, the solder alloy according to the present invention does not contain Ge mainly to function as an oxidation inhibitor, but needs to contain an appropriate amount of Ge to suppress the wasteful consumption of the active components in the flux.

[0044] In addition to suppressing the occurrence of voids that are inevitable when printed as a paste on a wide area, the Ge content must be precisely adjusted to stabilize the surface state of the molten solder alloy. If the Ge content is appropriate and the surface state of the molten solder alloy is stable, open defects due to the progression of the tear phenomenon can be suppressed. On the other hand, if a large amount of Ge is contained to stabilize the surface state, the occurrence of voids will be promoted as described above. Therefore, in the Sn-Bi-Sb-Ni-Ge solder alloy according to the present invention, the Ge content must be within the above-mentioned range, along with Bi, Sb, and Ni, as described above.

[0045] If the Ge content is less than 0.007%, the surface state of the molten solder alloy becomes unstable, the droplet retention property deteriorates, and the tear phenomenon progresses, causing open defects. The lower limit of the Ge content is 0.007% or more, preferably 0.009% or more, more preferably 0.010% or more, even more preferably 0.012% or more, even more preferably 0.013% or more, particularly preferably 0.014% or more, and most preferably 0.015% or more.

[0046] On the other hand, if the Ge content exceeds 0.090%, a thick oxide film is formed, and a large number of voids are generated when the paste is printed over a wide area. The upper limit of the Ge content is 0.090% or less, preferably 0.075% or less, more preferably 0.050% or less, even more preferably 0.030% or less, even more preferably 0.026% or less, particularly preferably 0.025% or less, and most preferably 0.024% or less, 0.022% or less, 0.020% or less, 0.018% or less, or 0.016% or less.

[0047] In the present invention, the Ge content can be set within a range by appropriately combining the above-mentioned lower and upper limits. The preferred range of Ge is 0.010 to 0.050%.

[0048] (5) The alloy composition further contains, by mass%, 0.1% or less in total of at least one of Co, Ti, Al, Mn, As, Fe, Pd, Zn, Zr, Pb, In, Ce, P, and Ga.

[0049] The solder alloy according to the present invention may contain optional elements within a range that does not impair the effects of the present invention. The effects of the present invention are maintained as long as the total content of these optional elements is 0.1% or less. Among these, the effects of the present invention are not particularly impaired even if at least one of Co, Ti, Al, Mn, As, Fe, Pd, Zn, Zr, Pb, In, Ce, P, and Ga is contained in a total of 0.1% or less. Among these, the effects of the present invention are particularly maintained as long as the total content of at least one of Co, As, Fe, Pd, Zr, Pb, Ce, and P is 0.1% or less. The lower limit is not particularly limited, but may be 0.001% or more.

[0050] (6) Equations (1) and (2) 0.0008≦Bi×Sb×Ni×Ge≦0.0347 (1) 34.7≦(Bi×Ni) / Ge≦154.6 (2) In formulas (1) and (2), Bi, Sb, Ni, and Ge each represent the content in mass % of the solder alloy. The solder alloy according to the present invention preferably satisfies the formulae (1) and (2) in order to have better liquid properties while maintaining the solid properties of the Sn-Bi-Sb-Ni-Ge solder alloy. The technical meanings of each formula are as follows:

[0051] Formula (1) represents the relationship for satisfying the solid and liquid properties of the solder alloy at a higher level, and is a formula that takes into account the contents of all essential elements. Bi, Sb, and Ni are elements for improving the solid properties of the solder alloy, but in order to further improve the liquid properties, it is better to comprehensively consider the Ge content in addition to these. Since the respective constituent elements of the solder alloy are directly and indirectly related to each other, the entire solder alloy exerts each effect as an integrated substance. In addition, in order to exhibit even better liquid properties while maintaining the solid properties of the Sn-Bi-Sb-Ni-Ge solder alloy, it is preferable to satisfy formula (1) that takes into account the contents of each constituent element.

[0052] In detail, Bi forms a eutectic structure with Sn to lower the melting point, but if the Sb content is too high, the liquidus temperature will rise. Bi, Sb, and Ni contribute to ductility, Bi and Sb contribute to shear strength, and Sb and Ni contribute to heat cycle resistance. Bi, Ni, and Ge contribute to droplet retention and suppression of open defects caused by the progression of the tear phenomenon. Sb, Ni, and Ge contribute to the generation of voids when printed as a paste over a wide area. In this way, the constituent elements of the solder alloy according to the present invention contribute to each other's effects, so it is preferable to satisfy formula (1).

[0053] The lower limit of formula (1) is preferably 0.0008 or more, more preferably 0.0017 or more, even more preferably 0.0028 or more, even more preferably 0.0030 or more, particularly preferably 0.0035 or more, and most preferably 0.0039 or more, or 0.0044 or more.

[0054] The upper limits of formula (1) are, in order of preference, 0.0326 or less, 0.0317 or less, 0.0290 or less, 0.0261 or less, 0.0236 or less, 0.0218 or less, 0.0209 or less, 0.0174 or less, 0.0168 or less, 0.0157 or less, 0.0153 or less, 0.0122 or less, 0.0117 or less, 0.0109 or less, 0.0104 or less, 0.0096 or less, 0.0088 or less, 0.0087 or less, 0.0084 or less, 0.0070 or less, 0.0067 or less, 0.0065 or less, 0.0062 or less, 0.0061 or less, 0.0059 or less, 0.0057 or less, 0.0053 or less, 0.0052 or less, and 0.0046 or less.

[0055] In the present invention, the above-mentioned lower and upper limits can be appropriately combined to obtain the range defined by formula (1).

[0056] Formula (2) expresses the relationship between the contents of Bi and Ni, which deteriorate the droplet retention and cause open defects when the content exceeds the upper limit, and the content of Ge, which deteriorates the droplet retention and cause open defects when the content falls below the lower limit. When the Bi content is high, the surface tension decreases, the surface oxidation rate increases, and the surface state of the molten solder alloy becomes unstable. Ni makes the surface state of the molten solder alloy unstable due to the precipitation of a large amount of Ni3Sn4. On the other hand, Ge can compensate for these unstable elements to form a stable film on the surface of the molten solder alloy. Therefore, when the Ge content is low, the surface state of the molten solder alloy becomes unstable. And, even if the Bi, Ni, and Ge are within the above-mentioned content range, in order to further suppress open defects, it is preferable that the contents of Bi and Ni and the content of Ge show the appropriate relationship shown in formula (2).

[0057] The lower limits of formula (2) are, in order of preference, 34.7 or more, 34.8 or more, 36.3 or more, 39.5 or more, 42.0 or more, 43.5 or more, 48.3 or more, 49.3 or more, 54.4 or more, 55.1 or more, 58.0 or more, 62.1 or more, 66.9 or more, 72.5 or more, 84.1 or more, and 87.0 or more.

[0058] The upper limit of the formula (2) is preferably 154.6 or less, more preferably 145.0 or less, even more preferably 124.3 or less, particularly preferably 113.1 or less, and most preferably 96.7 or less.

[0059] In the present invention, the range defined by formula (2) can be achieved by appropriately combining the above-mentioned lower and upper limits.

[0060] The values ​​shown in Tables 1 and 2, which are the measured values ​​of the alloy composition, were used to calculate the formulas (1) and (2). The values ​​calculated from the formulas (1) and (2) are calculated to four decimal places for the formula (1) and one decimal place for the formula (2). This calculation rule is used in this application and is intended to be used for calculations for additional solder alloys described in other documents, etc., as all solder alloys must be treated in the same manner.

[0061] (7) Remainder: Sn The balance of the solder alloy according to the present invention is Sn. In addition to the above elements, inevitable impurities may be contained. The balance of the solder alloy according to the present invention may consist of Sn and inevitable impurities. Even if inevitable impurities are contained, the above-mentioned effects are not affected.

[0062] 2. Solder paste The solder paste according to the present invention is a mixture of solder powder having the above-mentioned alloy composition and flux. The flux used in the present invention is not particularly limited as long as it allows soldering by a normal method. Therefore, a suitable mixture of commonly used rosin, organic acid, activator, thixotropic material, and solvent may be used. 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 % of the metal powder component and 10 to 30 mass % of the flux component.

[0063] 3. Solder balls The solder alloy according to the present invention can be used as a solder ball. When used as a solder ball, the solder alloy according to the present invention can be manufactured into a solder ball by a dropping method, which is a common method in the industry. Also, a solder joint can be manufactured by processing the solder ball by a common method in the industry, such as mounting one solder ball on one electrode coated with flux and joining the solder ball. The particle size of the solder ball is preferably 1 μm or more, more preferably 10 μm or more, even more preferably 20 μm or more, and particularly preferably 30 μm or more. The upper limit of the particle size of the solder ball is preferably 3000 μm or less, more preferably 1000 μm or less, even more preferably 800 μm or less, and particularly preferably 600 μm or less.

[0064] 4. Solder joints 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, and the like.

[0065] The solder alloy according to the present invention may be used for bonding in a conventional manner, for example, by using a reflow method. The melting temperature of the solder alloy when performing flow soldering may be about 20°C higher than the liquidus temperature. Furthermore, when using the solder alloy according to the present invention for bonding, the alloy structure can be made finer by taking into consideration the cooling rate during solidification. For example, the solder joint is cooled at a cooling rate of 2 to 3°C / s or more. Other bonding conditions can be appropriately adjusted depending on the alloy composition of the solder alloy.

[0066] 5.Other The solder alloy according to the present invention can be used as a preform, which may be in the form of a washer, ring, pellet, disk, ribbon, wire, or the like.

[0067] In addition, the solder alloy according to the present invention can be manufactured using a low alpha radiation material as its raw material, and when such a low alpha radiation alloy is used to form solder bumps around a memory, it becomes possible to suppress soft errors. EXAMPLES

[0068] The present invention will be described with reference to the following examples, but the present invention is not limited to the following examples. In order to demonstrate the effects of the present invention, the solder alloys shown in Tables 1 and 2 were used to evaluate (Evaluation 1) liquidus temperature, (Evaluation 2) ductility, (Evaluation 3) shear strength, (Evaluation 4) TCT (heat cycle resistance), (Evaluation 5) droplet retention, (Evaluation 6) avoidance of open defects in LGA joints, and (Evaluation 7) voids in large area printed parts.

[0069] (Evaluation 1) Liquidus temperature For the solder alloys having each alloy composition shown in Tables 1 and 2, the respective temperatures were obtained from the DSC curves. The DSC curves were obtained by raising the temperature at 5°C / min in air using a TA Instruments DSC (model number: Q2000). The liquidus temperature was obtained from the obtained DSC curve and was taken as the melting temperature. When the liquidus temperature was 185°C or lower, it was evaluated as "Good". When the liquidus temperature was higher than 185°C, it was evaluated as "Poor".

[0070] (Rating 2) Ductility The ductility was measured according to JIS Z3198-2. The solder alloys having the alloy compositions shown in Tables 1 and 2 were cast into a mold to prepare test pieces with a gauge length of 30 mm and a diameter of 8 mm. The prepared test pieces were stretched at room temperature with a stroke of 0.6 mm / min using an Instron Type 5966, and the elongation (ductility) at the time the test pieces broke was measured. In this example, when the ductility was 80% or more, it was determined that the level was compatible with the miniaturization of future electronic devices and was evaluated as "○", and when it was less than 80%, it was evaluated as "×".

[0071] (Rating 3) Share Strength Solder alloys having the alloy compositions shown in Tables 1 and 2 were atomized to produce solder powder (particle size: 20-32 μm). Solder pastes of each solder alloy were prepared by mixing with soldering flux (Senju Metal Industry Co., Ltd., product name: 155HF) consisting of rosin, solvent, activator, thixotropic agent, organic acid, etc. In this solder paste, the solder powder accounted for 90% of the total mass of the solder paste. The solder paste was printed on Cu electrodes on a 0.8 mm thick printed circuit board (material: FR-4) with a 120 μm thick metal mask, after which BGA components were mounted with a mounter and reflow soldered at a maximum temperature of 190°C and a holding time of 60 seconds to produce test boards.

[0072] The shear strength (N) of this test substrate was measured at 6 mm / min using a shear strength measuring device (RHESCA STR-1000). If the shear strength was 60.00 N or more, it was determined that the test substrate could be used without any problems in practice and was rated as "good", and if it was less than 60.00 N, it was rated as "poor".

[0073] (Rating 4) TCT (heat cycle resistance) The solder paste prepared in Evaluation 3 was printed on a Cu electrode that had been OSP-treated using a 100 μm-thick metal mask on a 0.8 mm-thick printed circuit board (material: FR-4), and then 15 BGA components were mounted using a mounter and reflow soldered at a maximum temperature of 190°C and a holding time of 60 seconds to create a test board.

[0074] Test boards soldered with each solder alloy were placed in a heat cycle test device set to low temperature of -40℃, high temperature of +125℃, and a holding time of 10 minutes, and the number of cycles at which the resistance value of at least one BGA component exceeded 15Ω from the initial resistance value of 3-5Ω was calculated. 1700 cycles or more were marked as "○", and less than 1700 cycles were marked as "×". The evaluation results are shown in Table 1.

[0075] (Rating 5) Droplet retention -Evaluation of droplet separation of molten alloy Solder alloys having the alloy compositions shown in Tables 1 and 2 were cast, and alloy pieces measuring φ3 mm and length 4 cm were prepared by cutting and polishing. The prepared alloy pieces were melted inside the syringe of a surface tensiometer (Kyowa Interface Science Co., Ltd.: Dmo-501), and the separation property of the droplets in the molten state was evaluated using the hanging drop method in which the molten solder alloy was discharged from the tip of the syringe in an air environment at 190°C.

[0076] Starting from a state where there were no droplets of molten solder alloy at the tip of the syringe, molten solder alloy was discharged at 1.0 μl / s, as shown in Fig. 1(d). Because the balance between the surface tension of the droplets and gravity is lost and the droplets of molten solder alloy fall from the tip of the syringe, the time from when a total amount of 5 μl or more was supplied until the droplets separated from the syringe tip was evaluated.

[0077] As shown in Figures 1(a) and 1(d), when a droplet 10 of molten solder alloy does not separate from the syringe tip 11 for 5 seconds or more, it was evaluated as "◎". As shown in Figures 1(b) and 1(d), when a droplet 20 of molten solder alloy does not separate from the syringe tip 21 for 1 second or more but less than 5 seconds, it was evaluated as "◯". As shown in Figures 1(c) and 1(d), when a droplet 30 of molten solder alloy separates from the syringe tip 31 in less than 1 second, it was evaluated as "X".

[0078] (Evaluation 6) Avoidance of open defects in LGA joints A paste-printed portion was formed on the test board using a metal mask with an opening diameter of 0.24 mm and the solder paste prepared in the same manner as in Evaluation 3. Then, as shown in FIG. 2(a), the board 41 was placed on a solder wettability tester (manufactured by RHESCA, product name: 5200TN). The solder wettability tester is equipped with a heating stage 40 that moves up and down and a PKG holding arm 42. A PKG 45 having an LGA electrode 44 with an opening of the same pattern as the paste-printed portion 43 was held at the tip of the holding arm 42. Then, as shown in FIG. 2(b), the holding arm 42 was lowered to a position where the electrode distance between the PKG 45 and the board 41 was 55 μm, and the paste-printed portion 43 was moved to a position where it contacted the LGA electrode 44 of the PKG 45, and the heating stage was heated to 190° C. and held for 30 seconds.

[0079] After confirming that the paste printing section 43 had melted and that the electrodes of the board and PKG had been connected by the molten solder, the holding arm 42 holding the PKG 45 was moved 40 μm upward as shown in FIG. 2(c), increasing the distance between the board 41 and the PKG 45 (distance: 95 μm), and then cooled to room temperature. After mounting, the board 41 was cured with epoxy resin and polished vertically, and the state of the solder joint formation was observed with an electron microscope. 18 LGA joints were observed from one polished plane.

[0080] As shown in Figure 2(f), when solder alloy 47 had no defects, it was rated as "◎". As shown in Figure 2(g), even when solder alloy 48 had hot tears 48a, which were shrinkage cavities from the side, it was rated as "◯" because electrical connection was not lost. As shown in Figure 2(h), when solder alloy 49 had open defects 49a and lost electrical connection, it was rated as "×".

[0081] (Rating 7) Voids in large printed areas A solder paste was prepared in the same manner as in Evaluation 6 above. A metal mask with a 5 mm square opening was used to create a 0.12 mm thick solder paste. t After forming a paste-printed area on the test board so that the solder joint was as shown in Fig. 1, a QFP component having a die bond area of ​​5 mm square was mounted on the board using a mounter, and reflow was performed by holding the peak temperature at 190°C for 90 seconds to form a solder joint.

[0082] After mounting, the samples were photographed at 25x magnification using a microfocus X-ray system (model number: XVR-160) from Unihite System Co., Ltd., to observe the state of remaining voids. In the X-ray planar photographs of six samples, the ratio of the void area to the solder joint area ((void area) / (solder joint area)) x 100(%)) was calculated, and the average of the six samples was taken as the average void area ratio. Average void area ratios of 10% or less were evaluated as "◎", those between 10% and less than 20% were evaluated as "〇", and those of 20% or more were evaluated as "×". The results are shown in Tables 1 and 2.

[0083] [Table 1]

[0084] [Table 2]

[0085] As shown in Tables 1 and 2, in Examples 1 to 56, the contents of the essential elements Bi, Sb, Ni, and Ge are all within the range of the present invention, so all the evaluations were judged to be "◯" or "◎". In particular, Examples 1 to 14, 22, 26 to 33, and 35 to 41, which satisfy the formulas (1) and (2), Examples 42, 46 to 48, 50, 51, 53, and 54, which satisfy the formulas (1) and (2) and contain Co, As, Fe, Pd, Zr, Pb, Ce, and P, respectively, and Example 56, which contains all the optional elements contained in the solder alloys of Examples 42 to 55, were all evaluated as "◎", showing superior results among the Examples.

[0086] Among Examples 42 to 52, Ti in Example 43, Al in Example 44, Mn in Example 45, Zn in Example 49, In ​​in Example 52, and Ga in Example 55 formed a relatively thick oxide film, and it is presumed that the reduction of the solder powder and the electrode surface was slightly insufficient compared to the examples marked with "◎" due to some consumption of the reducing components in the flux, and the area ratio of the voids increased slightly accordingly. For this reason, in these Examples, the evaluation 6 was "◯". However, these Examples showed results far superior to the Comparative Examples.

[0087] On the other hand, in Comparative Example 1, the liquidus temperature increased due to the low Bi content, while in Comparative Example 2, the ductility, shear strength, droplet retention, and avoidance of open defects were poor due to the high Bi content.

[0088] In Comparative Example 3, the Sb content was low, and therefore the ductility and TCT were poor. In Comparative Example 4, the Sb content was high, and therefore the liquidus temperature rose, and the ductility and voids in the large-area printed portion were poor.

[0089] Comparative Example 5 was inferior in ductility and TCT due to the low Ni content.

[0090] In Comparative Examples 6 and 7, the Ni content was high, and therefore the droplet retention and open defect avoidance were poor. In particular, Comparative Example 7, which contained more Ni than Comparative Example 6, was also poor in ductility and voids in large-area printed parts.

[0091] Comparative Examples 8 to 10 did not contain Ge or contained a small amount of Ge, and therefore were inferior in droplet retention and in avoiding open defects. Comparative Examples 11 and 12 contained a large amount of Ge, and therefore were inferior in voids in large-area printed portions.

[0092] The results of observing the X-ray transmission planar photographs of Example 3, Example 15, and Comparative Example 11 in Tables 1 and 2 are shown. FIG. 3 shows X-ray transmission planar photographs of solder joints after reflow at a peak temperature of 190° C., where FIG. 3(a) is an X-ray transmission planar photograph of Example 3, FIG. 3(b) is an X-ray transmission planar photograph of Example 15, and FIG. 3(c) is an X-ray transmission planar photograph of Comparative Example 11. As shown in FIG. 3(a) and FIG. 3(b), it was found that in Example 2 and Example 15, the average void area ratio was less than 20%, and the occurrence of voids 50 and 51 was reduced. In particular, in Example 3, the average void area ratio was 10% or less, and the occurrence of voids 50 was reduced to a high level. [Explanation of symbols]

[0093] 10, 20, 30 Droplets of molten solder alloy 11,21,31 Syringe tip 40 Heating Stage 41 Substrate 42 Holding Arm 43 (Solder) Paste 44 LGA electrode 45 PKG 46~49 Solder alloy 48a (Hot) Tear Phenomenon 49a Open failure 50~52 Void

Claims

1. A solder alloy having an alloy composition consisting of, in mass%, 35.0 to 68.0% Bi, 0.1 to 2.0% Sb, 0.010 to 0.050% Ni, 0.007 to 0.090% Ge, and the balance Sn.

2. 2. The solder alloy according to claim 1, wherein the alloy composition further contains, by mass%, at least one of Co, As, Fe, Pd, Zr, Pb, Ce, and P in a total amount of 0.1% or less.

3. 2. The solder alloy according to claim 1, wherein the alloy composition further contains, in mass%, 0.1% or less in total of at least one of Co, Ti, Al, Mn, As, Fe, Pd, Zn, Zr, Pb, In, Ce, P, and Ga.

4. The solder alloy according to claim 1 or 2, wherein the alloy composition satisfies the following formulas (1) and (2): 0.0008≦Bi×Sb×Ni×Ge≦0.0347 (1) 34.7≦(Bi×Ni) / Ge≦154.6 (2) In the formulas (1) and (2), Bi, Sb, Ni, and Ge each represent the content in mass % of the solder alloy.

5. A solder paste comprising the solder alloy of claim 1 or 3.

6. A solder ball comprising the solder alloy of claim 1 or 3.

7. A solder joint comprising the solder alloy of claim 1 or 3.

8. The solder alloy according to claim 3 , wherein the alloy composition satisfies the following formulas (1) and (2): 0.0008≦Bi×Sb×Ni×Ge≦0.0347 (1) 34.7≦(Bi×Ni) / Ge≦154.6 (2) In the formulas (1) and (2), Bi, Sb, Ni, and Ge each represent the content in mass % of the solder alloy.

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