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

Abstract

Provided are: a solder alloy which has a low melting point and excellent ductility, shear strength, and heat cycle resistance, and in which the occurrence of open circuit defects is suppressed, and residual voids are reduced even during large-area joining; a solder paste; a solder ball; and a solder joint. The solder alloy is composed of the following alloy components in percentage by mass: 35.0% to 68.0% of Bi, 0.1% to 2.0% of Sb, 0.010% to 0.050% of Ni, 0.007% to 0.090% of Ge and the balance of Sn. It is preferable that the alloy composition further contains at least one of Co, Ti, Al, Mn, As, Fe, Pd, Zn, Zr, Pb, In, Ce, P, and Ga in an amount of 0.1% by mass or less in total. In addition, this solder alloy can be suitably used in a solder paste, a solder ball, and a solder joint.

Description

(19) State Intellectual Property Office (12) Invention Patent Application (10) Application Publication Number (43) Application Publication Date (21) Application Number 202511583213.6 (22) Application Date 2025.10.31 (30) Priority Data 2024-224523 2024.12.19 JP (71) Applicant Senju Metal Industries, Ltd. Address Japan (72) Inventors Takashi Matsuto, Daisuke Asashi, Kaito Yoshikawa (74) Patent Agency Beijing Linda Liu Intellectual Property Agency (General Partnership) 11277 Patent Attorneys Li Maojia, Li Enhua (51) Int.Cl. B23K 35 / 26 (2006.01) (54) Invention Title: Solder Alloy, Solder Paste, Solder Ball, and Brazed Joint (57) Abstract: This invention provides a solder alloy, solder paste, solder ball, and brazed joint. The solder alloy has a low melting point and excellent ductility, shear strength, and thermal cycling resistance, thereby suppressing open circuit defects and reducing residual voids even in large-area joints. The solder alloy has the following alloy composition: Bi: 35.0~68.0% by mass, Sb: 0.1~2.0%, Ni: 0.010~0.050%, Ge: 0.007~0.090%, with the balance being Sn. Preferably, the alloy composition also contains at least one of Co, Ti, Al, Mn, As, Fe, Pd, Zn, Zr, Pb, In, Ce, P, and Ga, totaling less than 0.1% by mass. Furthermore, this solder alloy can be suitably used in solder paste, solder balls, and brazed joints. Claims 1 page, Description 13 pages, Drawings 2 pages, CN 122252857 A 2026.06.23 CN 1 22 25 28 57 A 1. A soft solder alloy, characterized in that it has the following alloy composition: Bi: 35.0~68.0% by mass, Sb: 0.1~2.0%, Ni: 0.010~0.050%, Ge: 0.007~0.090%, and the balance being Sn. 2. The soft solder alloy according to claim 1, wherein the alloy composition further contains at least one of Co, As, Fe, Pd, Zr, Pb, Ce and P, in a total of less than 0.1% by mass. 3. The solder alloy according to claim 1, wherein the alloy composition further comprises at least one of Co, Ti, Al, Mn, As, Fe, Pd, Zn, Zr, Pb, In, Ce, P and Ga in a total of less than 0.1% by mass.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 formulas (1) and (2), Bi, Sb, Ni and Ge respectively represent the content of the solder alloy in terms of mass%. 5. A solder paste having the solder alloy according to claim 1 or 3. 6. A solder ball having the solder alloy according to claim 1 or 3. 7. A brazed joint having the solder alloy according to 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 formulas (1) and (2), Bi, Sb, Ni and Ge respectively represent the content of the solder alloy in terms of mass%. Claims 1 / 1 page 2 CN 122252857 A Solder alloy, solder paste, solder ball and brazed joint Technical field

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

[0002] In recent years, there has been a demand for miniaturization of electronic devices such as CPU (Central Processing Unit). With the advancement of miniaturization of electronic devices, the heat load during soldering increases, which can cause defects such as substrate warping. Therefore, low temperature soldering is desired. If the soldering temperature is low, it is possible to manufacture circuit boards with high reliability. In order to perform soldering at low temperatures, low-melting-point solder alloys are required.

[0003] As low-melting-point solder alloys, Sn-58Bi and Sn-52In can be cited as examples. The melting temperatures of these alloys are 139°C and 119°C, respectively, and they are both alloy compositions that represent low-melting-point solders. In particular, Sn-58Bi is widely used as a low-cost solder alloy with excellent wettability.

[0004] However, the Bi phase is hard and brittle, which will degrade the mechanical properties of the solder alloy. If strain and stress are generated on the substrate due to thermal cycling or drop impact, there is a concern that the solder alloy may break. Therefore, in order to suppress the rise of the melting point and improve the reliability of the solder joint, various solder alloys have been studied.

[0005] For example, in Patent Document 1, a solder alloy that improves ductility and shear strength while maintaining a low melting point and exhibits excellent thermal cycling resistance was studied. 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] Furthermore, Patent Document 1 describes how the alloy microstructure is made finer through the synergistic effect of Sb and Ni, while simultaneously exhibiting ductility, shear strength, and thermal cycling resistance. Furthermore, Patent Document 1 discloses that Ge can be added as an element to inhibit Sn oxidation and improve wettability.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Patent No. 6477965 Summary of the Invention

[0010] Problems to be Solved by the Invention

[0011] As described above, the solder alloy described in Patent Document 1 is an excellent solder alloy that simultaneously exhibits ductility, shear strength, and thermal cycling resistance through a single alloy composition, and also improves oxidation inhibition and wettability. However, in recent years, with the advancement of thinner multilayer substrates and the enlargement of packages, defects caused by substrate warping due to heating during solder bonding have recurred.

[0012] Therefore, during the stage when the heating temperature rises from room temperature to reach the peak mounting temperature, or during the stage when the substrate cools from the peak temperature, the PKG (package) such as BGA (Ball Grid Array) and LGA (Land Grid Array) mounted on the substrate will bend due to the differences in the coefficients of thermal expansion and rigidity of the materials constituting the PKG, and will become misaligned from its mounting position. Accompanying this, the electrodes of the substrate and the electrodes of the PKG will solidify further apart than initially, resulting in a tearing phenomenon where the molten portion of the soft solder alloy constituting the brazing joint is torn, creating tiny voids. If only tearing occurs, the brazing joint will maintain the electrical connection as described on page 1 / 13 of the specification, 3 CN 122252857 A, thereby fulfilling its function as a brazing joint.

[0013] However, if tearing develops, an open circuit defect will occur, where the brazing joint remains in a separated state during molten phase and solidifies. Poor open circuitry can lead to the loss of electrical connection in brazed joints, becoming a fatal defect.

[0014] Furthermore, as mentioned above, in Patent Document 1, Ge is included to improve wettability. Here, the wettability of the substrate and the molten solder alloy is locally improved to suppress the generation of voids. However, when bonding large components such as heat sinks to the substrate, local void suppression based solely on improved wettability is insufficient to adequately suppress void generation.

[0015] In addition, Patent Document 1 states that as long as any element such as Ge is contained in no more than 0.1%, the flowability of the molten solder alloy will not be hindered. It is believed that when the molten solder alloy has good flowability, the voids generated will be released to the outside.Regarding the generation of voids, although there are cases where the deterioration of wettability affects the mounting of components on the substrate, voids can sometimes be generated due to the composition of solder paste. In such cases, even if the molten solder alloy has fluidity, the voids cannot always be completely released.

[0016] Even excellent solder alloys, such as the one described in Patent Document 1, which can achieve multiple effects with a single alloy composition, need to be appropriately improved according to changes in technological trends. Therefore, there is a need for an excellent solder alloy that can further address new challenges while maintaining the various effects that conventional solder alloys can achieve.

[0017] In particular, Ge has been extensively studied as an element that exerts an oxidation-inhibiting effect, starting with Patent Document 1. The liquid properties of molten Sn-Bi-based solder alloys can affect the solidification shape, making it more difficult to stably control them during installation in an atmospheric environment. In order to improve the installation quality of joints based on Sn-Bi-based low-temperature solder alloys, it is desirable that the solid properties of the solder alloy described in Patent Document 1 have the effect of improving reliability, and at the same time, it is suitable for installation processes and improves the joint quality even when it is a liquid. However, sufficient research has not been conducted on techniques and policies that take all these into account.

[0018] The object of the present invention is to provide: solder alloys, solder pastes, solder balls and brazed joints that have excellent low melting point, ductility, shear strength and thermal cycling resistance, thereby suppressing the occurrence of open circuit defects, and reducing residual voids even when joining large areas.

[0019] Solution to the problem

[0020] In the Sn-Bi-Sb-Ni-Ge solder alloy disclosed in Patent Document 1, the inventors focused on the fact that it is suitable for installation processes and improves the joint quality even when it is a liquid. Furthermore, the reasons for the existence of alloy compositions that cause open circuit defects when thin substrates warp were investigated, and it was found that if the oxidation state of the surface of the molten solder alloy becomes unstable, then when the alloy is entirely in liquid phase or exists as a mixture of solid and liquid phases, open circuit defects will occur due to tearing from the liquid phase portion.

[0021] In view of these circumstances, it is considered that increasing the Ge content is good in order to add a stable oxide film to the surface of the molten solder alloy. However, it was found that although open circuit defects are suppressed when the Ge content is high, there is an alloy composition that produces a large number of voids when using paste printed over a large area to form the solder joint. It is speculated that this is because if a thick oxide film of Ge is formed, the active components in the flux constituting the paste will be preferentially consumed by the reduction of the oxide film, and the reduction of the electrode will occur later, resulting in a large number of voids at the bonding interface.

[0022] Therefore, the inventors focused on the Ge content and realized that it was necessary to control the Ge content with high precision within a specified range. However, it was realized that even controlling only the Ge content in the Sn-Bi-Sb-Ni-Ge solder alloy could not achieve sufficient effect. Specification 2 / 13 pages 4 CN 122252857 A

[0023] It was also realized that in order to prevent open circuit defects from occurring even when the Ge content is reduced, by controlling the Bi and Ni contents in detail in addition to the Ge content, it is possible to suppress the occurrence of open circuit defects caused by the reduction of the Ge content.

[0024] Based on this realization, the inventors focused on the surface stability of the molten solder alloy and the ability to suppress the occurrence of open circuit defects caused by the progression of tearing. Therefore, it was envisioned that if the surface state is stable, the droplets of the molten solder alloy will also be stably maintained, and the droplet retention of the molten solder alloy was evaluated. As a result, the following insights were also obtained: In solder alloys with droplet retention properties, which are indicators of the stable retention of droplets, there is a tendency to suppress the occurrence of open circuit defects.

[0025] Furthermore, the following insights were also obtained: In order to sufficiently suppress voids that may be generated in brazed joints with a large area due to the presence of a certain amount of Ge, the generation of voids can be sufficiently suppressed when the content of Sb is also within a specified range based on the content of Bi, Ni, and Ge. In addition, the following insights were also obtained: The Sn-Bi-Sb-Ni-Ge solder alloy that achieves the above-mentioned effects has a low liquidus temperature, excellent ductility, shear strength, and thermal cycling resistance, similar to conventional solder alloys.

[0026] The present invention obtained based on the above insights is as follows.

[0027] (0) A solder alloy, characterized in that, by mass%, it comprises Bi: 35.0~68.0%, Sb: 0.1~2.0%, Ni: 0.010~0.050%, Ge: 0.007~0.090%, and the balance is Sn.

[0028] (1) A solder alloy, characterized in that it has the following alloy composition: by mass%, it comprises Bi: 35.0~68.0%, Sb: 0.1~2.0%, Ni: 0.010~0.050%, Ge: 0.007~0.090%, and the balance is Sn.

[0029] (2) The solder alloy according to (0) or (1) above, wherein the alloy composition (solder alloy) further comprises at least one of Co, As, Fe, Pd, Zr, Pb, Ce and P, in a total mass% of less than 0.1%.

[0030] (3) The solder alloy according to (0) or (1) above, wherein the alloy composition (solder alloy) further contains at least one of Co, Ti, Al, Mn, As, Fe, Pd, Zn, Zr, Pb, In, Ce, P and Ga in a total of 0.1% or less by mass.

[0031] (4, 8) The solder alloy according to any one of (0) to (3) above, wherein the alloy composition (solder alloy) satisfies the following formulas (1) and (2).

[0032] 0.0008≤Bi×Sb×Ni×Ge≤0.0347 (1)

[0033] 34.7≤(Bi×Ni) / Ge≤154.6 (2)

[0034] In formulas (1) and (2), Bi, Sb, Ni and Ge respectively represent the content in the solder alloy in mass%.

[0035] (5) A solder paste having any one of the soft solder alloys described in (0) to (3) above.

[0036] (6) A solder ball having any one of the soft solder alloys described in (0) to (3) above.

[0037] (7) A brazed joint having any one of the soft solder alloys described in (0) to (3) above. Brief Description of the Drawings

[0038] FIG1 is a schematic diagram showing a method for evaluating droplet retention. FIG1(a) is a schematic diagram showing the ejection state evaluated as “◎”. FIG1(b) is a schematic diagram showing the ejection state evaluated as “〇”. FIG1(c) is a schematic diagram showing the ejection state evaluated as “×”. FIG1(d) is a graph showing the ejection amount and time.

[0039] Figure 2 is a schematic diagram showing an evaluation method for avoiding open circuit defects at LGA joints. Figure 2(a) is a schematic diagram showing the state in which a PKG is placed on the substrate. Figure 2(b) is a schematic diagram showing the state in which the PKG is brought into contact with the solder paste printed on the substrate and heated. Figure 2(c) is a schematic diagram showing the state in which the PKG rises only 40 μm upward from the state in Figure 2(b) at 190°C. Figure 2(d) is a schematic diagram showing the state of the brazed joint before it rises only 40 μm upward in Figure 2(c). (See page 3 / 13 of the specification, CN 122252857 A) Figure 2(e) is a partial cross-sectional view of the area near the joint of the brazed joint in Figure 2(c). Figure 2(f) is a partial cross-sectional view of the state of the brazed joint without defects from the middle to the end of solidification. Figure 2(g) is a partial cross-sectional view of the state of the brazed joint with thermal tearing from the middle to the end of solidification. Figure 2(h) is a partial cross-sectional view of the state of the brazed joint with open circuit defects due to the progress of tearing from the middle to the end of solidification.

[0040] Figure 3 is an X-ray transmission plane photograph of the brazed joint after reflow soldering with the peak temperature set at 190°C. Figure 3(a) is an X-ray transmission plane photograph of Example 3, Figure 3(b) is an X-ray transmission plane photograph of Example 15, and Figure 3(c) is an X-ray transmission plane photograph of Comparative Example 11.

[0041] Explanation of reference numerals

[0042] 10, 20, 30 Droplets of molten solder alloy

[0043] 11, 21, 31 Syringe tip

[0044] 40 Heating stage

[0045] 41 Substrate

[0046] 42 Holding arm

[0047] 43 (Solder solder) paste

[0048] 44 LGA electrode

[0049] 45 PKG

[0050] 46~49 Solder alloy

[0051] 48a (Thermal) tearing

[0052] 49a Open circuit defect

[0053] 50~52 Void Detailed Description

[0054] The present invention will be described in more detail below. In this specification, the "%" referring to the composition of the solder alloy is "mass %" unless otherwise specified.

[0055] 1. Solder alloy

[0056] (1) Bi: 35.0~68.0%

[0057] Bi is an essential element for lowering the melting point of solder alloys. The melting point of Sn-Bi eutectic alloys is as low as 139 °C, so Bi can lower the liquidus temperature of solder alloys. In addition, solder alloys containing a specified amount of Bi exhibit superplasticity and excellent ductility. Therefore, solder alloys containing a specified amount of Bi have excellent ductility and shear strength.

[0058] If the Bi content is less than 35.0%, the liquidus temperature rises. The lower limit of the Bi content is 35.0% or more, preferably 41.0% or more, more preferably 48.0% or more, and even more preferably 56.0% or more.

[0059] On the other hand, if the Bi content exceeds 68.0%, a large amount of hard, brittle and coarse Bi phase precipitates, so the solder alloy itself becomes hard, and the ductility and shear strength deteriorate. Furthermore, with a significant increase in Bi content, the melting point rises. Consequently, when a large amount of Bi phase precipitates, the surface state of the molten solder alloy becomes unstable, droplet retention deteriorates, and open circuit defects occur due to the progression of tearing. The upper limit of Bi content is 68.0% or less, preferably 65.0% or less, more preferably 63.0% or less, further preferably 60.0% or less, and particularly preferably 58.0% or less.

[0060] In this invention, the aforementioned lower and upper limits can be appropriately combined to set the range of Bi content. The preferred range of Bi is 48.0% to 60.0%.Instruction manual 4 / 13 page 6 CN 122252857 A

[0061] (2) Sb: 0.1~2.0%

[0062] Sb is an element that helps improve ductility and thermal cycling resistance, and is necessary to suppress the formation of voids even when printed in paste form over a large area. Sb is about 10% solidly soluble in β-Sn at about 200°C, but as the temperature decreases, the solid solubility limit of Sb decreases, and β-SnSb is almost insoluble at room temperature. β-SnSb precipitates around the Sn phase and Bi phase when solidified, exerting a pinning effect, thereby suppressing the coarsening of each phase.

[0063] If the Sb content is less than 0.1%, ductility and thermal cycling resistance cannot be improved. The lower limit of 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.

[0064] On the other hand, if the Sb content exceeds 2.0%, β-SnSb will precipitate excessively, and the melting point will rise. In addition, since coarse β-SnSb will be formed, the ductility will decrease. Furthermore, when printed in paste form over a large 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, further preferably 1.2% or less, more preferably 1.0% or less, particularly preferably 0.8% or less, and most preferably 0.7% or less.

[0065] In the present invention, the range of Sb content can be set by appropriately combining the aforementioned lower and upper limits. The preferred range of Sb is 0.4 to 1.2%.

[0066] (3) Ni: 0.010 to 0.050%

[0067] Ni is an element required to improve the ductility and thermal cycling resistance of the solder alloy. Furthermore, for Ni, if an appropriate amount of Ge is added simultaneously, a thin and uniform Ge oxide film layer homogenizes the surface structure of the molten solder alloy. Therefore, droplet retention is excellent, and open circuit defects caused by tearing are suppressed. Consequently, even when printed in paste form over a large area, void formation can be suppressed.

[0068] If the Ni content is less than 0.010%, the ductility and thermal cycling resistance are poor. The lower limit of the Ni content is 0.010% or more, more preferably 0.012% or more, further preferably 0.013% or more, particularly preferably 0.014% or more, and most preferably 0.015% or more.

[0069] On the other hand, if the Ni content exceeds 0.050%, open circuit defects will occur due to the progression of tearing when the Ge content is within the range described later. If the Ni content is further increased, a large number of voids will be generated when printed in paste form over a large area.The upper limit of Ni content is 0.050% or less, preferably 0.039% or less, more preferably 0.029% or less, further preferably 0.019% or less, particularly preferably 0.018% or less, and most preferably 0.017% or less.

[0070] In this invention, the aforementioned lower and upper limits can be appropriately combined to set the Ni content range. The preferred range of Ni is 0.010~0.039%.

[0071] (4) Ge: 0.007~0.090%

[0072] Ge is an element necessary for improving the bonding quality of solder alloys as a liquid suitable for the mounting process. When the Ge content is appropriate, the amount of active ingredients in the flux consumed in the reduction of the oxides of the solder powder is small, so the reduction to the electrode surface is sufficient. Therefore, even when printed in paste form over a large area, the generation of voids can be suppressed. That is, in the solder alloy of the present invention, Ge is not mainly contained for the purpose of functioning as an oxidation inhibitor, but rather in an appropriate amount to suppress the meaningless consumption of active components in the flux.

[0073] In addition, besides trying to suppress the generation of voids that cannot be avoided when printing in paste form over a large area, the content of Ge needs to be precisely adjusted in order to stabilize the surface state of the molten solder alloy. When the content of Ge is appropriate and the surface state of the molten solder alloy is stable, open circuit defects caused by the progression of tearing can be suppressed. On the other hand, if a large amount of Ge is contained in order to stabilize the surface state, void generation will be promoted as mentioned above. Therefore, in the Sn-Bi-Sb-Ni-Ge solder alloy of the present invention, as mentioned above, the content of Ge also needs to be within the aforementioned range along with Bi, Sb and Ni.

[0074] If the Ge content is less than 0.007%, the surface state of the molten solder alloy becomes unstable, droplet retention deteriorates, and open circuit defects occur due to the progression of tearing. The lower limit of the Ge content is 0.007% or more, preferably 0.009% or more, more preferably 0.010% or more, further preferably 0.012% or more, further more preferably 0.013% or more, particularly preferably 0.014% or more, and most preferably 0.015% or more.

[0075] On the other hand, if the Ge content exceeds 0.090%, a thick oxide film will form, thereby generating a large number of voids when printed in paste form over a large area.The upper limit of the Ge content is 0.090% or less, preferably 0.075% or less, more preferably 0.050% or less, further preferably 0.030% or less, further more preferably 0.026% or less, particularly preferably 0.025% or less, and most preferably 0.024%, 0.022%, 0.020%, 0.018% or less, or 0.016% or less.

[0076] In this invention, the aforementioned lower and upper limits can be appropriately combined to set the Ge content range. The preferred range of Ge is 0.010~0.050%.

[0077] (5) The aforementioned alloy composition also contains at least one of Co, Ti, Al, Mn, As, Fe, Pd, Zn, Zr, Pb, In, Ce, P and Ga, with a total mass percentage of 0.1% or less.

[0078] The soft solder alloy of this invention may also contain any element within a range that does not impair the effects of this invention. The effects of this invention can be maintained as long as the total content of any of these elements is less than 0.1%. Specifically, the effects of this invention will not be particularly impaired even if at least one of Co, Ti, Al, Mn, As, Fe, Pd, Zn, Zr, Pb, In, Ce, P, and Ga is present in a total content of less than 0.1%. Specifically, the effects of this invention can be particularly maintained as long as the total content of at least one of Co, As, Fe, Pd, Zr, Pb, Ce, and P is less than 0.1%. The lower limit is not particularly limited, and is 0.001% or more.

[0079] (6) Equations (1) and (2)

[0080] 0.0008≤Bi×Sb×Ni×Ge≤0.0347 (1)

[0081] 34.7≤(Bi×Ni) / Ge≤154.6 (2)

[0082] In equations (1) and (2), Bi, Sb, Ni and Ge represent the content in the solder alloy by mass%.

[0083] For the solder alloy of the present invention, in order to maintain the solid properties of the Sn-Bi-Sb-Ni-Ge solder alloy while having better liquid properties, it is preferable to satisfy equations (1) and (2). The technical significance of each equation is as follows.

[0084] Equation (1) represents the relationship between the solid and liquid properties of the solder alloy at a higher level, and is a formula that takes into account the content of all necessary elements. Bi, Sb, and Ni are elements used to improve the solid properties of solder alloys, but to further improve the liquid properties, it is advisable to comprehensively consider the Ge content in addition to these. Since the constituent elements of a solder alloy are directly and indirectly related, the solder alloy as a whole exerts its effects as a unified substance. Moreover, in Sn-Bi-Sb-Ni-Ge solder alloys, in order to maintain solid properties while exhibiting better liquid properties, it is preferable to satisfy equation (1) which takes into account the content of each constituent element.

[0085] In detail, although Bi and Sn form a eutectic structure, which lowers the melting point, if the content of Sb is too high, the liquidus temperature will rise. In addition, Bi, Sb and Ni contribute to ductility, Bi and Sb contribute to shear strength, and Sb and Ni contribute to thermal cycling resistance. In addition, Bi, Ni and Ge contribute to droplet retention and suppress open circuit defects caused by the progression of tearing. Sb, Ni and Ge help suppress the generation of voids when printed in paste form over a large area. Thus, the constituent elements of the solder alloy of the present invention contribute to each other's effects, and therefore it is preferable to satisfy formula (1).

[0086] The lower limit of formula (1) is preferably 0.0008 or more, more preferably 0.0017 or more, further preferably 0.0028 or more, further more preferably 0.0030 or more, particularly preferably 0.0035 or more, and most preferably 0.0039 or more or 0.0044 or more.

[0087] The upper limit of formula (1) is preferably 0.0326 or less, more preferably 0.0317 or less, and even more preferably 0.0290 or less. (See page 6 / 13 of the specification, CN 122252857 A) The lower limit is more preferably 0.0261 or less, particularly preferably 0.0236 or less, and most preferably 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, or 0.0046 or less.

[0088] In this invention, the aforementioned lower limit and upper limit can be appropriately combined to form the range of formula (1).

[0089] Equation (2) represents the relationship between the content of Bi and Ni, which deteriorates droplet retention and causes open circuit defects when the content exceeds the upper limit, and the content of Ge, which deteriorates droplet retention and causes open circuit defects when the content is below the lower limit. When there is more Bi, the surface tension decreases, the surface oxidation rate increases, and the surface state of the molten solder alloy becomes unstable. For Ni, the large amount of Ni3Sn4 precipitation leads to the surface state of the molten solder alloy becoming unstable. On the other hand, since Ge can form a stable film on the surface of the molten solder alloy, it can fill these unstable elements. Therefore, when the Ge content is low, the surface state of the molten solder alloy becomes unstable.Furthermore, even within the aforementioned content ranges for Bi, Ni, and Ge, in order to further suppress open-circuit defects, it is preferable that the content of Bi and Ni and the content of Ge exhibit an appropriate relationship as shown in formula (2).

[0090] The lower limit of formula (2) is preferably 34.7 or more, more preferably 34.8 or more, further preferably 36.3 or more, more preferably 39.5 or more, particularly preferably 42.0 or more, and most preferably 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, or 87.0 or more.

[0091] The upper limit of formula (2) is preferably 154.6 or less, more preferably 145.0 or less, further preferably 124.3 or less, particularly preferably 113.1 or less, and most preferably 96.7 or less.

[0092] In this invention, the aforementioned lower limit and upper limit can be appropriately combined to form the range of equation (2).

[0093] In the calculations of equations (1) and (2), the values ​​shown in Tables 1 and 2, which are the measured values ​​of the alloy composition, are used. Regarding the values ​​calculated by equations (1) and (2), equation (1) is calculated to the fourth decimal place, and equation (2) is calculated to the first decimal place. This calculation rule is used in this application. In addition, since all solder alloys must be processed in the same way, it is intended to use the same rule in the calculation of other solder alloys described in other documents, etc.

[0094] (7) Balance: Sn

[0095] The balance of the solder alloy of this invention is Sn. In addition to the aforementioned elements, it may contain unavoidable impurities. The balance of the solder alloy of this invention may consist of Sn and unavoidable impurities. Even in the case of unavoidable impurities, the aforementioned effects will not be affected.

[0096] 2. Solder Paste

[0097] The solder paste of the present invention is a mixture of solder powder composed of the above-described alloy composition and flux. There are no particular limitations on the flux used in the present invention as long as it can be soldered by conventional methods. Therefore, any substance appropriately mixed with commonly used rosin, organic acid, activator, thixotropic material, and solvent can be used. In the present invention, there are no particular limitations on the mixing ratio of the metal powder component and the flux component; preferably, the metal powder component is 70-90% by mass, and the flux component is 10-30% by mass.

[0098] 3. Solder Ball

[0099] The solder alloy of the present invention can be used as a solder ball. When used as a solder ball, the solder ball can be manufactured from the solder alloy of the present invention using the drop-addition method, which is a conventional method in the art. Furthermore, a brazed joint can be manufactured by processing the solder ball using conventional methods in the art, such as mounting a solder ball on an electrode coated with flux and bonding it.The particle size of the solder balls is preferably 1 μm or more, more preferably 10 μm or more, and more preferably 20 μm or more, particularly preferably 30 μm or more. The upper limit of the particle size of the solder balls is preferably 3000 μm or less, more preferably 1000 μm or less, more preferably 800 μm or less, and particularly preferably 600 μm or less.

[0100] 4. Brazing Joint

[0101] The brazing joint of the present invention is suitable for joining at least two or more components. There are no particular limitations on the components that are electrically connected by the soft solder alloy of the present invention, such as components, substrates, electronic components, printed circuit boards, insulating substrates, heat sinks, lead frames, semiconductors using electrode terminals, power modules, inverter products, etc.

[0102] Regarding the joining method using the soft solder alloy of the present invention, it can be performed by conventional methods, for example, using reflow soldering. The melting temperature of the solder alloy used for flow soldering is approximately 20°C higher than the liquidus temperature. Furthermore, when using the solder alloy of the present invention for bonding, the cooling rate during solidification can be considered to further refine the alloy microstructure. For example, the brazed joint can be cooled at a cooling rate of 2-3°C / s or higher. Other bonding conditions can be appropriately adjusted according to the alloy composition of the solder alloy.

[0103] 5. Other

[0104] The solder alloy of the present invention can be used as a preform. Examples of preform shapes include washers, rings, particles, discs, strips, and wires.

[0105] In addition, the solder alloy of the present invention can be manufactured as a low-alpha-ray alloy by using low-alpha-ray materials as its raw materials. If such a low-alpha-ray alloy is used to form solder bumps around a memory chip, soft errors can be suppressed.

[0106] Examples

[0107] The present invention will be described through the following examples, but the present invention is not limited to the following examples.

[0108] To demonstrate the effectiveness of the present invention, the following were evaluated using the solder alloys listed in Tables 1 and 2: (Evaluation 1) liquidus temperature, (Evaluation 2) ductility, (Evaluation 3) shear strength, (Evaluation 4) TCT (thermal cycling resistance), (Evaluation 5) droplet retention, (Evaluation 6) avoidance of open circuit defects at LGA joints, and (Evaluation 7) voids in large-area printed areas.

[0109] (Evaluation 1) Liquidus Temperature

[0110] For each solder alloy having the composition listed in Tables 1 and 2, its temperature was determined by DSC curves. The DSC curves were obtained by heating the DSC (model: Q2000) at atmospheric temperature at a rate of 5°C / min using a DSC manufactured by TA Instruments. The liquidus temperature was determined from the obtained DSC curves and used as the melting temperature.Evaluation is “0” when the liquidus temperature is below 185°C. Evaluation is “×” when the liquidus temperature exceeds 185°C.

[0111] (Evaluation 2) Ductility

[0112] Ductility is measured according to JIS Z3198-2. For solder alloys with the alloy compositions listed in Tables 1 and 2, test pieces with a measurement length of 30 mm and a diameter of 8 mm are cast into molds. The test pieces are stretched at room temperature with a stroke of 0.6 mm / min using a Type 5966 manufactured by Instron, and the elongation (ductility) at the time of fracture is measured. In this embodiment, when the ductility is 80% or more, it is judged to be at a level that can cope with the miniaturization of future electronic devices and is evaluated as “○”, and when it is less than 80%, it is evaluated as “×”.

[0113] (Evaluation 3) Shear Strength

[0114] Solder alloys having the compositions described in Tables 1 and 2 were atomized to produce solder powder (particle size: 20~32μm). Solder pastes of each solder alloy were prepared by mixing with a soldering flux (manufactured by Senju Metal Industries, Ltd., product name: 155HF) containing rosin, solvent, activator, thixotropic agent, organic acid, etc. The solder powder in the solder paste accounted for 90% of the total mass of the solder paste. The solder paste was printed onto a Cu electrode on a 0.8mm thick printed circuit board (material: FR-4) using a 120μm thick metal mask. BGA components were then mounted using an mounting machine, and reflow soldering was performed at a maximum temperature of 190°C and a holding time of 60 seconds to prepare a test substrate.

[0115] For this test substrate, the shear strength (N) was measured using a shear strength measuring device (RHESCA STR-1000) at a speed of 6 mm / min. If the shear strength was 60.00 N or higher, it was judged to be a level that could be used without problems in practical applications and was rated as "0". If it was lower than 60.00 N, it was rated as "×".

[0116] (Evaluation 4) TCT (Thermal Cycling Resistance)

[0117] The solder paste prepared in Evaluation 3 was printed on Cu electrodes that had undergone OSP treatment with a 100 μm thick metal mask on a 0.8 mm thick printed substrate (material: FR-4). Fifteen BGA components were mounted using an mounting machine, and reflow soldering was performed at a maximum temperature of 190 °C and a holding time of 60 seconds to prepare the test substrate.

[0118] The test substrates that have been soft soldered with each soft solder alloy are placed in a thermal cycling test apparatus with conditions set at low temperature -40°C, high temperature +125°C, and holding time of 10 minutes, and the number of cycles is determined when the resistance value of at least one BGA component exceeds 15Ω starting from the initial resistance value of 3~5Ω.1700 cycles or more is marked as “○”, and less than 1700 cycles is marked as “×”.

[0119] The evaluation results are shown in Table 1.

[0120] (Evaluation 5) Droplet retention

[0121] • Evaluation of the separation of molten alloy droplets

[0122] Soft solder alloys with the alloy compositions described in Tables 1 and 2 were cast and processed into alloy sheets with a diameter of φ3 mm and a length of 4 cm by cutting and grinding. The alloy sheets were melted inside the syringe of a surface tension meter (manufactured by Kyowa Interface Science Co., Ltd.: Dmo-501), and the separation of droplets in the molten state was evaluated by using a pendant drop method in an atmospheric environment at 190°C, in which molten soft solder alloy was ejected from the tip of the syringe.

[0123] Starting from a state where there were no droplets of molten soft solder alloy at the tip of the syringe, as shown in Figure 1 (d), molten soft solder alloy was ejected at a rate of 1.0 μl / s. Since the molten solder alloy droplet, having lost the balance between surface tension and gravity, will fall from the syringe tip, the evaluation considers the time from when at least 5 μl is supplied until the droplet separates from the syringe tip.

[0124] If the molten solder alloy droplet 10 does not separate from the syringe tip 11 for more than 5 seconds, as shown in Figures 1(a) and 1(d), it is evaluated as "◎". If the molten solder alloy droplet 20 does not separate from the syringe tip 21 for more than 1 second but less than 5 seconds, as shown in Figures 1(b) and 1(d), it is evaluated as "〇". If the molten solder alloy droplet 30 separates from the syringe tip 31 in less than 1 second, as shown in Figures 1(c) and 1(d), it is evaluated as "×".

[0125] (Evaluation 6) Avoidance of open circuit defects at LGA joints

[0126] Using a metal mask with an opening diameter of 0.24 mm, a solder paste printout was formed on the test substrate using the same solder paste as in Evaluation 3. Then, as shown in FIG2(a), the substrate 41 was placed in a solder wettability tester (RHESCA, product name: 5200TN). The solder wettability tester is equipped with a heating stage 40 driven up and down and a PKG holding arm 42. A PKG 45 with an LGA electrode 44 is held at the front end of the holding arm 42. The LGA electrode 44 has an opening with the same pattern as the solder paste printout 43. Then, as shown in FIG2(b), the holding arm 42 is lowered to a position where the electrode spacing between the PKG 45 and the substrate 41 is 55 μm. After moving to a position where the solder paste printout 43 contacts the LGA electrode 44 of the PKG 45, the heating stage is heated to 190°C and held for 30 seconds.

[0127] After confirming that the paste printing section 43 is melted and the electrodes of the substrate and PKG are connected by molten solder, as shown in FIG2(c), the holding arm 42 holding the PKG45 is moved upward by 40 μm, and the distance between the substrate 41 and the PKG45 (distance: 95 μm) is separated, and then cooled to room temperature. The installed substrate 41 is cured with epoxy resin and ground in a vertical section, and the formation state of the brazed joint is observed under a microscope using the electronic manual page 9 / 13 11 CN 122252857 A. 18 LGA joints were observed from one ground plane.

[0128] In the case where there are no defects in the solder alloy 47 as shown in FIG2(f), the evaluation is "◎". As shown in FIG2(g), even in the case of thermal tear 48a belonging to shrinkage cavity from the side in the solder alloy 48, the electrical connection is not lost, and therefore the evaluation is "0". In cases where an open circuit defect 49a exists in the solder alloy 49 as shown in Figure 2(h), resulting in loss of electrical connection, the evaluation is "×".

[0129] (Evaluation 7) Voids in large-area printed portions

[0130] Solder paste was prepared in the same manner as in Evaluation 6 above. Using a metal mask with a 5mm square opening, a paste printed portion was formed on the test substrate with a thickness of 0.12mmt. A QFP component with a chip bonding area of ​​5mm square was mounted on a mounting machine, and a reflow soldering was performed with a peak temperature of 190°C and held for 90 seconds to form a solder joint.

[0131] For the mounted sample, a 25x X-ray transmission plane photograph was taken using a micro-focused X-ray system (model: XVR-160) from Uni-Hite System Corporation to observe the void residue status. In the X-ray transmission planar images of the 6 samples, the ratio of the area of ​​the void to the area of ​​the brazed joint was calculated (((area of ​​void) / (area of ​​brazed joint))×100(%)), and the average value of the 6 samples was taken as the average void area ratio. When the average void area ratio was less than 10%, it was rated as "◎", when it was more than 10% but less than 20%, it was rated as "〇", and when it was more than 20%, it was rated as "×".

[0132] The results are shown in Tables 1 and 2.

[0133] [Table 1] Specification 10 / 13 pages 12 CN 122252857 A

[0134]

[0135] [Table 2] Specification 11 / 13 pages 13 CN 122252857 A

[0136]

[0137] As shown in Tables 1 and 2, in Examples 1 to 56, the contents of Bi, Sb, Ni and Ge, which are essential elements, are all within the scope of the present invention, so all evaluations are judged as "0" or "◎".In particular, all evaluations of Examples 1-14, 22, 26-33, 35-41 that satisfy equations (1) and (2), Examples 42, 46-48, 50, 51, 53 and 54 that satisfy equations (1) and (2) and contain Co, As, Fe, Pd, Zr, Pb, Ce and P respectively, and Example 56 that contains all arbitrary elements contained in the solder alloys of Examples 42-55, are the highest results, and superior results are also shown in the examples.

[0138] In Examples 42-52, Ti of Example 43, Al of Example 44, Mn of Example 45, Zn of Example 49, In ​​of Example 52, and Ga of Example 55 form thicker oxide films, and some of the reducing components in the flux are consumed. As a result, the reduction of the solder powder and electrode surface becomes slightly less sufficient compared to the example with "◎", and it is speculated that the area ratio of the voids is slightly increased. Therefore, in these examples, the evaluation 6 is "0". However, these embodiments showed results far superior to the comparative examples.

[0139] On the other hand, in Comparative Example 1, the liquidus temperature increased due to the low Bi content. In Comparative Example 2, the ductility, shear strength, droplet retention, and open-circuit defect avoidance were poor due to the high Bi content.

[0140] In Comparative Example 3, the ductility and TCT were poor due to the low Sb content. In Comparative Example 4, the liquidus temperature increased due to the high Sb content, resulting in poor ductility and voids in the large-area printed area.

[0141] In Comparative Example 5, the ductility and TCT were poor due to the low Ni content.

[0142] In Comparative Examples 6 and 7, the droplet retention and open-circuit defect avoidance were poor due to the high Ni content. In particular, the Ni content in Comparative Example 7 was higher than that in Comparative Example 6, resulting in poor ductility and voids in the large-area printed area.

[0143] In Comparative Examples 8-10, due to the absence of Ge or a low Ge content, droplet retention and open-circuit defect avoidance were poor. In Comparative Examples 11 and 12, due to the high Ge content, there was a large void difference in the printed area.

[0144] The results of observing X-ray transmission planar images of Examples 3, 15, and Comparative Example 11 in Tables 1 and 2 are shown. Figure 3 is an X-ray transmission planar image of the brazed joint after reflow soldering with a peak temperature set to 190°C. Figure 3(a) is an X-ray transmission planar image of Example 3, Figure 3(b) is an X-ray transmission planar image of Example 15, and Figure 3(c) is an X-ray transmission planar image of Comparative Example 11. As shown in Figures 3(a) and 3(b), it can be seen that in Examples 3 and 15, the average void area ratio is less than 20%, reducing the generation of voids 50 and 51.In particular, in Example 3, the average void area ratio is less than 10%, which reduces the generation of voids 50 to a high standard. Instruction sheet 13 / 13 page 15 CN 122252857 A Figure 1 Instruction drawing 1 / 2 page 16 CN 122252857 A Figure 2 Figure 3 Instruction sheet drawing 2 / 2 page 17 CN 122252857 A Abstract: The present invention provides a solder alloy, a solder paste, a solder ball, and a solder joint, the solder alloy has a low melting point, are excellent in ductility, shear strength, and heat cycle resistance, further suppress the occurrence of open circuit defects, and have reduced residual voids even at the time of joining in a large area. balance being Sn. Preferably, the alloy composition further contains at least one of Co, Ti, Al, Mn, As, Fe, Pd, Zn, Zr, Pb, In, Ce, P, and Ga in 0.1% or less in total by mass%. Further, this solder alloy can be suitably used for solder pastes, solder balls, and solder joints..

Claims

1. A soft solder alloy, characterized in that, It has the following alloy composition by mass%: Bi: 35.0~68.0%, Sb: 0.1~2.0%, Ni: 0.010~0.050%, Ge: 0.007~0.090%, with the balance being Sn.

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

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

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

5. A solder paste having the solder alloy as described in claim 1 or 3.

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

7. A brazing joint having the soft solder alloy as described in claim 1 or 3.

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

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