Solder alloys, solder pastes, solder spheres, preformed solders, and soldered joints

Abstract

The present invention provides a solder alloy, a solder paste, a solder ball, a preformed solder, and a soldered joint, which have excellent drop impact resistance and heat cycle resistance, can suppress the occurrence of chip standing and connected tin · tin tips, and can also suppress the occurrence of electromigration. The solder alloy has an alloy composition of Ag: 0.3 to 1.9%, Cu: 0.40 to 1.00%, Bi: 0.5 to 4.9%, P: 0.00100 to 0.02000% by mass, and the balance being Sn. The alloy composition can also contain at least one of Ge, Co, and Ga in an amount of 0.06% or less by mass, respectively. In addition, the alloy composition can also contain at least one of As, In, Zr, Mn, Ti, Zn, Fe, Al, Ni, Au, Mg, Cr, and Pt in an amount of 0.06% or less by mass, respectively.

Description

Technical Field

[0001] This invention relates to Sn-Ag-Cu-Bi-P solder alloy. Background Technology

[0002] In household appliances such as washing machines, refrigerators, and air conditioners, as well as electronic devices such as televisions, video recorders, radios, computers, copiers, and communication equipment, mounting substrates containing electronic components are used. In addition to single-layer substrates, mounting substrates are also made by stacking multiple substrates to achieve full functionality.

[0003] In the conduction between substrates and the mounting of electronic components onto substrates, methods such as surface mounting and mounting by inserting terminals into through-holes in the substrate can be listed. Examples of such mounting processes on printed circuit boards include wave soldering, reflow soldering, and manual soldering. Among these, wave soldering is typically used for mounting electronic components of a certain size.

[0004] For example, Patent Document 1 describes a study on forming brazed joints using wave soldering. The Sn-Ag-Cu-Bi-P solder alloy described in this document can suppress dross formation, improve bulk strength (tensile strength) by forming intermetallic compounds from Ag, and improve wettability through P. Patent Document 2 investigates the tensile strength, wettability during wave soldering, solidus temperature, liquidus temperature, and number of bridges in the Sn-Ag-Cu-Bi-P solder alloy.

[0005] In addition, Sn-Ag-Cu-Bi-P solder alloys, not limited to wave soldering, were investigated. Patent document 3 discloses a Sn-Ag-Cu-Bi-P solder alloy for use in paste-like or cored solders, achieving improvements in tensile strength, elongation, and thermal fatigue resistance. Patent document 4 discloses a Sn-Ag-Cu-Bi-P solder alloy for solder balls, and its impact resistance, yellowing, and thermal cycling resistance were investigated.

[0006] Patent Document 5 discloses a Sn-Ag-Cu-Bi solder alloy whose thermal cycling resistance was studied using a mounting substrate printed with solder paste. Patent Document 6 discloses a Sn-Ag-Cu-Bi-P solder alloy for piping connection and sealing, in which the liquidus temperature and solidus temperature were evaluated.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2007-7732

[0010] Patent Document 2: Japanese Patent Application Publication No. 2000-288772

[0011] Patent Document 3: Japanese Patent Application Publication No. 10-34376

[0012] Patent Document 4: Japanese Patent Application Publication No. 2004-261863

[0013] Patent Document 5: Japanese Patent Application Publication No. 2011-183430

[0014] Patent Document 6: Japanese Patent Application Publication No. 2-70033 Summary of the Invention

[0015] The problem the invention aims to solve

[0016] Sn-Ag-Cu-Bi-P solder alloys have long been recognized for their various advantages. Among them, the invention described in Patent Document 1 is an excellent invention exhibiting superior wettability and high tensile strength. However, in paragraph 0008 of Patent Document 1, as prior art, it is explained that when reducing the content of expensive Ag to achieve cost reduction, the tensile strength of the solder alloy is poor.

[0017] In fact, according to the research results in paragraph 0027 of Patent Document 1, the tensile strength of Example 7, with an Ag content of 2% by mass, increased by approximately two times compared to Example 4, with an Ag content of 0.3% by mass. This is believed to be because, as described in paragraph 0020 of Patent Document 1, Ag and Sn form an intermetallic compound. Therefore, it can be understood that, according to the invention described in Patent Document 1, increasing the Ag content is preferable to improve tensile strength.

[0018] Patent Document 2 also describes a study on tensile strength, disclosing an Ag content of 2.0 to 5.0% by mass. Paragraph 0008 of Patent Document 2 discloses that when the Ag content is less than 2.0% by mass, the elongation decreases significantly due to the addition of Bi, failing to meet the characteristics required for a solder material. In other words, the invention described in Patent Document 2 reflects the prior art described in Patent Document 1, and according to the invention described in Patent Document 2, the Ag content needs to be increased to 2.0% by mass or more. Furthermore, in the invention described in Patent Document 2, the contents of P and Ni were studied to suppress bridging.

[0019] In the invention described in Patent Document 3, in addition to tensile strength and elongation, thermal cycling resistance was also investigated. In Patent Document 3, to avoid a decrease in tensile strength, only solder alloys with an Ag content of 2.0% or more were disclosed in the embodiments. That is, the invention described in Patent Document 3 reflects the content explained and demonstrated in Patent Documents 1 and 2.

[0020] Patent Document 4 discloses a solder alloy in which Ni is added to Sn-Ag-Cu-Bi-P in the embodiments. The solder alloy described in Patent Document 4 differs from those in Patent Documents 1-3 in that it does not study tensile strength, but instead studies impact resistance. The Ag content of the solder alloy composed of Sn-Ag-Cu-Bi-P-Ni disclosed in the embodiments is suppressed to a low level.

[0021] In the invention described in Patent Document 4, drop impact resistance was studied as described above. According to Patent Document 4, to improve drop impact resistance, the Cu content needs to be suppressed to below 0.3% by mass. Specifically, paragraph 0018 of Patent Document 4 states that if the Cu content is below 0.3% by mass, the effect of suppressing intermetallic compounds is stronger than the increase in porosity, resulting in better drop impact resistance. Thus, in the invention described in Patent Document 4, the Cu content is suppressed to a low level to improve drop impact resistance.

[0022] In the invention described in Patent Document 5, the joint strength after a thermal shock test was studied as part of the research on thermal cycling resistance. Patent Document 5 discloses a Sn-Ag-Cu-Bi solder alloy as a specific alloy composition. Paragraph 0015 of Patent Document 5 states that, in order to improve thermal cycling resistance, instead of using a solder alloy that is as soft as possible, the tensile strength of the solder alloy, which is helpful in improving the joint strength of the brazed joint after the thermal shock test, is increased, thereby improving the thermal stress resistance of the brazed joint.

[0023] Furthermore, paragraph 0010 of Patent Document 5 describes the possibility of including P as an element equivalent to Ge, Ga, and In. However, Patent Document 5 does not specify the content of these elements. Paragraph 0012 of Patent Document 5 specifically discloses that the content of Ge, Ga, and In is in the range of 0.05 to 1.0% by mass. Therefore, even when P is added to the solder alloy of Patent Document 5, the content of P must still be in the range of 0.05 to 1.0% by mass.

[0024] Patent Document 6 discloses a Sn-Ag-Cu-Bi-P solder alloy for piping connections and sealing. Furthermore, it states that the Ag content is preferably 0.1 to 0.4% by mass for such applications. In the alloy compositions studied as examples in Patent Document 6, the Ag content is consistently 0.4% by mass or less. This is presumably because, especially for sealing applications, the elongation of the solder alloy needs to be considered, thus the tensile strength is intentionally reduced.

[0025] However, the inventions described in Patent Documents 1-6 need to be adapted to the actual conditions of electronic devices that have seen significant development in recent years. In particular, issues that should be addressed include chip lifting that may occur during the installation of electronic components and electromigration that may occur during operation.

[0026] Chip standing upright is a phenomenon where, when the solder alloy placed on the electrodes melts upon heating, if the solder alloy on one electrode begins to melt earlier than that on the other, the chip or other electronic components are pulled towards that electrode and tilted upwards. This phenomenon is increasingly common due to the trend towards thinner and smaller electronic devices in recent years, and the miniaturization and weight reduction of electronic components within these devices.

[0027] Regarding electromigration, the miniaturization of electronic components leads to increased current density during energization, resulting in an increase in the number of electrons moving within the brazed joint. Therefore, problems have become increasingly apparent in recent years. Electromigration can be explained as follows: Atoms constituting the brazed joint collide with electrons generating current, transferring momentum from the electrons to the atoms. Atoms gaining momentum from the electron flow move along the electron flow to the anode side of the brazed joint. At this point, in the Cu-containing solder alloy, Cu segregates towards the anode side, creating vacancies on the cathode side of the brazed joint. These vacancies gradually expand, forming voids. As voids grow, the resistance increases, causing the brazed joint to heat up due to Joule heating, or hindering the performance of the electronic components due to a decrease in current density. Ultimately, the brazed joint breaks.

[0028] Therefore, in recent years, there has been a search for Sn-Ag-Cu-Bi-P solder alloys that can suppress chip lift-up and electromigration while maintaining the existing properties. Thus, it is urgent to study the solder alloys described in Patent Documents 1-6 in light of the actual conditions of electronic components in recent years.

[0029] The objective of this invention is to provide solder alloys, solder pastes, solder balls, preformed solders, and brazing joints that have excellent resistance to drop impact and thermal cycling, can suppress chip stand-up and the formation of solder bridging and solder spikes, and can also suppress electromigration.

[0030] Solution for solving the problem

[0031] In the Sn-Ag-Cu-Bi-P solder alloys specifically studied in Patent Documents 1 to 6, the inventors extracted Sn-Ag-Cu-Bi-P solder alloys that were believed to be able to solve the above-mentioned problems and conducted detailed research. First, Sn-2Ag-0.5Cu-2Bi-0.005P from Example 7 of Patent Document 1, which utilizes Ag3Sn to achieve precipitation strengthening, Sn-2.8Ag-0.5Cu-1.0Bi-0.005P-0.005Ni from the examples in Table 2 of Patent Document 2, Sn-2.8Ag-0.5Cu-1.0Bi-0.01P from the comparative examples in Table 2 of Patent Document 2, Sn-2Ag-0.5Cu-5Bi-0.003P from Comparative Example 2 of Patent Document 3, and Sn-2Ag-0.5Cu-5Bi-0.001P-0.005Ni from Example 1 of Patent Document 3, etc. It should be noted that in the embodiments and comparative examples extracted from Patent Documents 1 to 6, when the element content is expressed as an integer, the first decimal place is considered as 0. The same applies below.

[0032] Next, in order to improve drop impact resistance, Sn-1Ag-0.05Cu-1Bi-0.005P-0.05Ni from Example 11 of Patent Document 4, where the Cu content was suppressed, was selected. Additionally, Sn-1.0Ag-0.5Cu-1.0Bi from Comparative Example 2 of Patent Document 5, which had a low Ag content and was presumed to improve drop impact resistance, and Sn-0.2Ag-0.2Cu-3.8Bi from Patent Document No. 3 were selected, both of which had low Ag content and were expected to improve drop impact resistance.

[0033] Firstly, it is observed that Example 7 of Patent Document 1, Comparative Example 2 of Patent Document 3, and Example 1, due to their high Ag content, exhibit poor drop impact resistance. In contrast, the examples and comparative examples of Patent Document 2, with even higher Ag content, demonstrate not only improved drop impact resistance but also increased chip stand-up.

[0034] Example 11 of Patent Document 4, due to its low Cu content, exhibits poor thermal cycling resistance. Comparative Example 2 of Patent Document 5, compared to Example 7 of Patent Document 1, shows slightly improved drop impact resistance, but due to the absence of P, it exhibits frequent bridging and / or solder spikes. Patent Document No. 3 of Patent Document 6 also exhibits poor thermal cycling resistance due to its low Ag content.

[0035] Furthermore, in addition to the aforementioned insights, the solder alloys disclosed in Patent Documents 2 and 6 also provide insights into chip erection. Moreover, they provide insights into electromigration occurring in the solder alloys disclosed in Patent Documents 4 and 6.

[0036] Based on the above insights, it is believed that simply increasing the Ag content to precipitate a large amount of Ag3Sn is insufficient; rather, it is necessary to prepare the solder with appropriate hardness to improve drop impact resistance and / or thermal cycling resistance. Furthermore, it is believed that the solder should be prepared such that, during heating of the solder alloy, two large endothermic alloy phases can be observed in the thermal history measured using DSC (Differential Scanning Calorimeter) at temperatures higher than the solidus temperature, thus suppressing chip stand-up. Moreover, it is believed that adjusting the viscosity of the molten solder is necessary to suppress bridging and / or solder spike formation. In addition, it is believed that moderate Ag3Sn precipitation and / or solid solution strengthening of the solder alloy by Bi are needed to improve electromigration resistance (hereinafter referred to as "EM resistance").

[0037] Here, the effect of a solder alloy is not achieved by the individual components exerting their effects separately, but rather by their synergistic interaction as a whole. Therefore, it is impossible for a single component to simultaneously exert all its effects by individually adjusting the composition to improve each property.

[0038] Therefore, based on the above-mentioned insights, the inventors conducted a detailed study on the composition of Sn-Ag-Cu-Bi-P solder alloy. As a result, a solder alloy was obtained that exhibits excellent resistance to drop impact and thermal cycling, suppresses chip stand-up and solder bridging / solder spikes, and also suppresses electromigration, provided that each constituent element is within a specified range. This invention thus completes the present invention.

[0039] The present invention derived from this insight is as follows.

[0040] (0) A soft solder alloy, characterized in that, by mass%, it comprises Ag: 0.3~1.9%, Cu: 0.40~1.00%, Bi: 0.5~4.9%, P: 0.00100~0.02000%, and the balance is Sn.

[0041] (1) A soft solder alloy, characterized in that it has the following alloy composition: Ag: 0.3~1.9%, Cu: 0.40~1.00%, Bi: 0.5~4.9%, P: 0.00100~0.02000%, and the balance is Sn.

[0042] (2) The solder alloy according to (0) or (1) above, wherein the alloy composition further contains at least one of Ge, Co and Ga in an amount of 0.06% or less by mass%.

[0043] (3) The solder alloy according to any one of (0) to (2) above, wherein the alloy composition further contains at least one of As, In, Zr, Mn, Ti, Zn, Fe, Al, Au, Mg, Cr and Pt in an amount of 0.06% or less by mass%.

[0044] (4) The solder alloy according to any one of (0) to (2) above, wherein the alloy composition further contains at least one of As, In, Zr, Mn, Ti, Zn, Fe, Al, Ni, Au, Mg, Cr and Pt in an amount of 0.06% or less by mass%.

[0045] (5~6) The solder alloy according to any one of (0) to (4) above, wherein the alloy composition satisfies all of the following formulas (1) to (3),

[0046] 0.0007≤Ag×Cu×Bi×P≤0.0110 (1)

[0047] 110≤Ag / (P×Cu)≤799 (2)

[0048] 0.67≤(Ag+Bi) / (Ag+Cu+Bi)≤0.91 (3) Formula

[0049] In equations (1) to (3) above, Ag, Cu, Bi and P represent the content of the alloy composition in terms of mass%.

[0050] (7~8) A solder paste having a solder powder composed of a solder alloy as described in any one of (0) to (6) above.

[0051] (9~10) A solder ball, which is composed of any one of the solder alloys described in (0) to (6) above.

[0052] (11~12) A preformed solder, which is composed of any one of the solder alloys described in (0) to (6) above.

[0053] (13~14) A brazing joint having any one of the soft solder alloys described in (0) to (6) above. Attached Figure Description

[0054] Figure 1 SEM images of the cross-section of the brazed joint. Figure 1 (a) is Comparative Example 1. Figure 1 (b) is Example 22. Detailed Implementation

[0055] The present invention will now be described in more detail. In this specification, unless otherwise specified, "%" in relation to the alloy composition of the solder alloy refers to "mass %".

[0056] 1. Soft solder alloy

[0057] (1) Ag: 0.3~1.9%

[0058] Ag (Ag) is an element that improves drop impact resistance, thermal cycling resistance, and EM resistance, and inhibits chip stand-up. Ag, through Ag3Sn precipitation strengthening, can suppress deformation of solder alloys, thus contributing to improved thermal cycling resistance and drop impact resistance. Furthermore, the precipitation of Ag3Sn hinders electron movement, improving EM resistance. Consequently, in the thermal history using DSC, two large endothermic peaks are observed between the solidus and liquidus temperatures during heating.

[0059] When the Ag content is below 0.3%, the precipitation of Ag3Sn is insufficient, leading to deterioration in thermal cycling resistance and EM resistance. Furthermore, chip stand-up is also more common. The lower limit for the Ag content is 0.3% or more, preferably 0.4% or more, more preferably 0.5% or more, and even more preferably 0.6% or more.

[0060] On the other hand, when the Ag content exceeds 1.9%, Ag3Sn forms a network, thus reducing its resistance to impact damage. Furthermore, when the Ag content reaches 2.5% or more, the endothermic peak becomes a single peak, leading to multiple chip impacts. The upper limit for Ag content is 1.9% or less, preferably 1.7% or less, more preferably 1.6% or less, further preferably 1.4% or less, even more preferably 1.3% or less, particularly preferably 1.2% or less, and most preferably 1.1% or less.

[0061] The preferred range for Ag content is 0.6% to 1.4%. The above upper and lower limits can specify a more preferred range for Ag content.

[0062] (2) Cu: 0.40~1.00%

[0063] Cu is an element that improves thermal cycling resistance and EM resistance, and suppresses the formation of tin bridging and / or tin spikes. Cu6Sn5, formed by Cu and Sn, precipitates finely at the interface, preventing fracture even under thermal stress caused by temperature differences. Furthermore, if the Cu content is 0.40–1.00%, it approximates the eutectic composition of Sn and Cu, suppressing the rise in liquidus temperature and thus inhibiting the formation of tin bridging and / or tin spikes. Moreover, the intermetallic compound formed by Cu and Sn hinders electron movement, thereby improving EM resistance.

[0064] When the Cu content is below 0.40%, the precipitation of fine Cu6Sn5 is insufficient, leading to deterioration in thermal cycling resistance and EM resistance. The lower limit of the Cu content is 0.40% or more, preferably 0.50% or more.

[0065] On the other hand, when the Cu content exceeds 1.00%, the liquidus temperature rises, and the viscosity of the molten solder increases during bonding at normal temperatures, resulting in more bridging and / or solder spikes. The upper limit of the Cu content is 1.0% or less, preferably 0.90% or less, more preferably 0.80% or less, further preferably 0.70% or less, and even more preferably 0.60% or less.

[0066] The preferred range for Cu content is 0.40% to 0.70%. The above upper and lower limits can specify a more preferred range for Cu content.

[0067] (3) Bi: 0.5~4.9%

[0068] Bi is an element that helps improve resistance to drop impact and EM. Because Bi is dissolved in Sn, it strengthens Sn through solid solution, causing Sn's lattice deformation and hindering the movement of Cu, thereby improving EM resistance.

[0069] When the Bi content is less than 0.5%, the solid solution strengthening of Sn becomes insufficient, and the EM resistance deteriorates. The lower limit of the Bi content is 0.5% or more, preferably 0.6% or more, more preferably 0.7% or more, further preferably 0.8% or more, particularly preferably 0.9% or more, and most preferably 1.0% or more.

[0070] On the other hand, when the Bi content exceeds 4.9%, the Bi content exceeds the solid solution limit of Bi, thus Bi segregates. Due to the hardening and / or embrittlement of the solder alloy, its drop impact resistance is poor. The upper limit of the Bi content is 4.9% or less, preferably 3.7% or less, more preferably 2.9% or less, even more preferably 2.0% or less, even more preferably 1.9% or less, particularly preferably 1.5% or less, and most preferably 1.1% or less.

[0071] The preferred range for Bi content is 0.5% to 3.7%. The above upper and lower limits can specify a more preferred range for Bi content.

[0072] (4) P: 0.00100~0.02000%

[0073] P is an element that inhibits the formation of bridging and / or solder spikes. P remains on the surface of the molten solder and hinders the formation of tin oxide, thus properly maintaining the fluidity of the molten solder. Therefore, it is possible to suppress the formation of bridging and / or solder spikes that may occur during solidification.

[0074] When the phosphorus (P) content is less than 0.00100%, the formation of tin oxide cannot be suppressed, resulting in frequent tin bridging and / or tin spikes. The lower limit of the P content is 0.00100% or more, preferably 0.00200% or more, and more preferably 0.00300% or more.

[0075] On the other hand, when the P content exceeds 0.0200%, intermetallic compounds of P will precipitate, resulting in frequent tin bridging and / or tin spikes. The upper limit of the P content is 0.0200% or less, preferably 0.0170% or less, more preferably 0.0160% or less, further preferably 0.0150% or less, even more preferably 0.0110% or less, particularly preferably 0.00900% or less, and most preferably 0.00600% or less or 0.00400% or less.

[0076] The preferred range for P is 0.00300 to 0.0200%. The above upper and lower limits can specify a more preferred range for the content of P.

[0077] (5) Ge, Co and Ga are each in amounts of less than 0.06%, and at least one of them is present.

[0078] To suppress oxidation of the solder alloy, the solder alloy of the present invention may contain Ge, Co, and Ga as arbitrary elements. If the content of each of these elements in the solder alloy is 0.06% or less, the rise in liquidus temperature can be suppressed, thereby further suppressing the formation of bridging and / or solder spikes. The content of each element is preferably 0.006% or less, more preferably 0.005% or less. The lower limit is not particularly limited, and 0.001% or more is acceptable. Furthermore, if at least one of these arbitrary elements is contained in a composition, the total content is acceptable to be 0.1% or less. The lower limit of the total content is acceptable to be 0.001% or more.

[0079] (6) As, In, Zr, Mn, Ti, Zn, Fe, Al, Ni, Au, Mg, Cr and Pt are each in amounts of less than 0.06%, and at least one of them is present.

[0080] The solder alloy of the present invention may contain at least one of the following elements as arbitrary elements, without impairing the above-mentioned effects: As, In, Zr, Mn, Ti, Zn, Fe, Al, Ni, Au, Mg, Cr, and Pt. The alloy composition may also contain As, In, Zr, Mn, Ti, Zn, Fe, Al, Ni, Au, Mg, Cr, and Pt in amounts of 0.06% or less by mass. Of these arbitrary elements, the group consisting of elements remaining after removing a small amount of Ni, which causes a sharp increase in melting point, from the aforementioned arbitrary elements is further preferred. More specifically, the alloy composition may also contain at least one of the following elements as arbitrary elements in amounts of 0.06% or less by mass: As, In, Zr, Mn, Ti, Zn, Fe, Al, Au, Mg, Cr, and Pt.

[0081] When the alloy composition contains at least one of As, In, Zr, Mn, Ti, Zn, Fe, Al, Ni, Au, Mg, Cr, and Pt, the upper limit of the content of each constituent element is preferably 0.06% or less. The lower limit is not particularly limited, and is 0.001% or more. Furthermore, when a composition contains at least one of multiple of these arbitrary elements, the total content is 0.1% or less. The lower limit of the total content is 0.001% or more.

[0082] (7) Equations (1)~(3)

[0083] 0.0007≤Ag×Cu×Bi×P≤0.0110 (1)

[0084] 110≤Ag / (P×Cu)≤799 (2)

[0085] 0.67≤(Ag+Bi) / (Ag+Cu+Bi)≤0.91 (3) Formula

[0086] In equations (1) to (3) above, Ag, Cu, Bi and P represent the content of the alloy composition in terms of mass%.

[0087] The constituent elements of the solder alloy of the present invention have excellent resistance to drop impact and thermal cycling, which can suppress chip stand-up and the formation of solder bridging and solder spikes, and can also suppress electromigration. In order to achieve these effects at a higher level with a single composition, in addition to the content of each constituent element being within the above-mentioned range, it is further preferred to satisfy equations (1) to (3). The technical significance of each equation is as follows.

[0088] Equation (1) is a relationship based on the balance of the contents of the essential elements. Equation (2) is a relationship regarding the contents of Ag, Cu, and P, which are elements capable of forming intermetallic compounds in the solder alloy of the present invention. The intermetallic compounds may affect the various properties of the present invention depending on the precipitation site, morphology, size, etc. Therefore, if the solder alloy satisfies equation (2), a particular composition can exert a particularly excellent effect. Equation (3) is an element that improves the strengthening of the solder alloy of the present invention. Ag and Bi are elements that contribute to resistance to drop impact. Ag, Cu, and Bi are elements that contribute to resistance to EM and / or thermal cycling. In order to improve each property to a high level in a balanced manner, it is preferable to satisfy equation (3).

[0089] The upper limit of formula (1) is preferably 0.0110 or less, more preferably 0.0094 or less, even more preferably 0.0088 or less, even more preferably 0.0083 or less, particularly preferably 0.0081 or less, and most preferably selected from 0.0061 or less, 0.0050 or less, 0.0048 or less, 0.0033 or less, and 0.0031 or less. The lower limit of formula (1) is preferably 0.0007 or more, more preferably 0.0009 or more, even more preferably 0.0010 or more, even more preferably 0.0011 or more, particularly preferably 0.0013 or more, and most preferably selected from 0.0014 or more, 0.0015 or more, 0.0017 or more, 0.0018 or more, 0.0020 or more, 0.0021 or more, 0.0022 or more, 0.0023 or more, 0.0025 or more, 0.0026 or more, and 0.0029 or more.

[0090] A further preferred range for equation (1) is 0.0017 to 0.0088. The above upper and lower limits can respectively define a more preferred range for equation (1).

[0091] (2) The upper limit of the formula is preferably 799 or less, more preferably 733 or less, further preferably 611 or less, even more preferably 600 or less, particularly preferably 550 or less, and most preferably 524 or less, 458 or less, or 400 or less. (2) The lower limit of the formula is preferably 110 or more, more preferably 129 or more, further preferably 138 or more, even more preferably 147 or more, particularly preferably 200 or more, and most preferably 244 or more, 267 or more, or 367 or more.

[0092] A further preferred range for equation (2) is 138 to 733. The above upper and lower limits can respectively define a more preferred range for equation (2).

[0093] The upper limit of formula (3) is preferably 0.91 or less, more preferably 0.89 or less, even more preferably 0.86 or less, even more preferably 0.85 or less, particularly preferably 0.84 or less, and most preferably 0.83 or less or 0.81 or less. The lower limit of formula (3) is preferably 0.67 or more, more preferably 0.68 or more, even more preferably 0.72 or more, even more preferably 0.74 or more, particularly preferably 0.75 or more, and most preferably 0.76 or more, 0.77 or more, 0.78 or more, 0.79 or more, and 0.80 or more.

[0094] A further preferred range for equation (3) is 0.76 to 0.89. The above upper and lower limits can respectively define a more preferred range for equation (1).

[0095] In the calculations of equations (1) to (3), 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) to (3), equation (1) is calculated to the fourth decimal place, equation (2) is calculated to the first integer place, and equation (3) is calculated to the second decimal place. This calculation rule is used in this application. In addition, all solder alloys must be treated in the same way, and therefore it is also intended to be used in calculations involving more solder alloys described in other documents, etc.

[0096] (8) Balance: Sn

[0097] The balance of the solder alloy of the present invention is Sn. In addition to the elements mentioned above, it may contain unavoidable impurities. Even in the presence of unavoidable impurities, the above-mentioned effects will not be affected. Furthermore, as will be described later, even if elements not contained in the present invention are included as unavoidable impurities, the above-mentioned effects will not be affected.

[0098] 2. Solder paste

[0099] The solder paste of the present invention is a mixture of solder powder composed of the above-mentioned 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, a substance appropriately mixed with commonly used rosin, organic acid, activator, 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.

[0100] 3. Solder ball

[0101] The solder alloy of the present invention can be used as solder balls. When used as solder balls, the solder alloy of the present invention can be manufactured by drop-addition using conventional methods in the art. Alternatively, brazed joints can be manufactured by processing conventional methods in the art, such as mounting solder balls on electrodes printed with flux and joining them. The particle size of the solder balls is preferably 1 μm or more, more preferably 10 μm or more, further preferably 20 μm or more, and 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, further preferably 800 μm or less, and particularly preferably 600 μm or less.

[0102] 4. Pre-formed soft solder

[0103] The solder alloy of the present invention can be used as a preform. Examples of preform shapes include washers, rings, granules, discs, strips, and wires. It can also be used as a solder rod.

[0104] 5. Brazed joints

[0105] 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 to be joined, as long as they are components such as semiconductors, power modules, inverter products, etc., that use the soft solder alloy of the present invention for electrical connection, including components such as elements, substrates, electronic components, printed circuit boards, insulating substrates, heat sinks, lead frames, electrode terminals, etc.

[0106] The joining method using the solder alloy of the present invention can be performed, for example, by conventional methods using reflow soldering. The melting temperature of the solder alloy during wave soldering can be approximately 20°C higher than the liquidus temperature. Furthermore, when joining using the solder alloy of the present invention, considering the cooling rate during solidification, the alloy microstructure can be further refined. For example, the brazed joint can be cooled at a cooling rate of 2~3°C / s or higher. Other joining conditions can be appropriately adjusted according to the alloy composition of the solder alloy.

[0107] 6. Uses

[0108] The solder alloy of the present invention is effective in various soldering methods, particularly in wave soldering. It is effective in wave soldering of multilayer substrates with multiple substrates stacked on top of each other. Since the composition of the jet solder used in wave soldering may change over time, it can also be used as a supplementary solder to adjust the composition of the jet solder to the desired level. In this case, the supplementary solder can be adjusted in composition within the scope of the present invention. The temperature of the jet solder during wave soldering is approximately 230~260°C. Furthermore, other bonding conditions can be appropriately adjusted according to the alloy composition, solid fraction, and liquid fraction of the solder alloy.

[0109] 7. Manufacturing method of soft solder alloy

[0110] The solder alloy of the present invention can be manufactured simply by pre-fabricating SnAg alloy and SnCu alloy, and then melting them together with Bi and P. As a manufacturing example, an alloy of Sn and Ag, and an alloy of Sn and Cu, are manufactured by weighing each alloy in a predetermined amount, and by weighing Bi and P. The reason for this manufacturing method is as follows: Melting Ag (with a melting point of approximately 860°C) and Cu (with a melting point of approximately 1100°C) into Sn takes a considerable amount of time. In particular, Cu exhibits significant surface oxidation, so a long melting time will result in oxidation. On the other hand, if a SnAg alloy in which Ag is pre-melted into Sn and a SnCu alloy in which Cu is pre-melted into Sn are prepared separately, the melting time into Sn can be significantly shortened. Regarding the intermetallic compounds formed during the preparation of each alloy, for example, Cu6Sn5 has a melting point of 415°C, and Ag3Sn has a melting point of 480°C, and these intermetallic compounds are mainly formed within the alloy, therefore the possibility of oxidation is considered low.

[0111] 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. When such a low-alpha-ray alloy is used to form solder bumps around a memory, it can suppress soft errors.

[0112] Example

[0113] Using solder alloys with the alloy compositions shown in Tables 1-2, the following evaluation methods were used: Evaluation 1: Drop Impact Test (DROP); Evaluation 2: Thermal Cycling Test (TCT); Evaluation 3: Chip Stand-Up Test; Evaluation 4: Solder Bridging and Solder Tip Test; Evaluation 5: Electromagnetic Impedance (EM) Resistance. The evaluation methods are explained below.

[0114] Evaluation 1: Drop Impact Test (DROP)

[0115] The solder alloys shown in Tables 1 and 2 were atomized to form solder powder. These powders were then mixed with a soldering flux (GLV, manufactured by Senju Metal Industries, Ltd.) containing rosin, solvent, activator, thixotropic agent, and organic acid to prepare solder pastes for each solder alloy. The solder pastes contained 88% alloy powder and 12% flux by mass.

[0116] Solder paste was printed onto a 0.8mm thick printed circuit board (material: FR-4) using a 100μm thick metal mask. Five BGA components were then mounted onto each board using a pick-and-place machine. Reflow soldering was performed at a maximum temperature of 240°C for 60 seconds to create two test boards. Then, the boards were individually divided into five pieces, each containing one BGA component, to create a total of ten evaluation samples.

[0117] Next, the evaluation sample was secured to the base with both ends bolted, with the BGA component facing the base. In this state, the resistance value was measured according to JEDEC standards, and an impact with an acceleration of 1500G was applied to evaluate drop impact resistance. The crack progression was evaluated by the number of drops taken up to a 50% increase in resistance value from its initial value. A score of 100 or more drops was marked with "◎". A score of 90 or more but less than 100 drops was marked with "〇". A score of less than 90 drops was marked with "×".

[0118] Evaluation 2: Thermal Cycling Test (TCT)

[0119] Prepare solder paste in the same manner as in Evaluation 1. Place the prepared test substrate in a thermal cycling test apparatus set to a low temperature of -40°C, a high temperature of +125°C, and a holding time of 10 minutes. Calculate the number of cycles at which the resistance value of at least one BGA component increases from an initial resistance of 3-5Ω to over 15Ω. A score of 700 cycles or more is marked with "◎". A score of 650-699 cycles is marked with "〇". A score of less than 650 cycles is marked with "×".

[0120] Evaluation 3: Chip Stands Up

[0121] Solder paste was prepared in the same manner as in Evaluation 1. The solder paste was printed onto the Cu pads of a 6-layer printed circuit board (FR-4, Cu-OSP) using a 150μm metal mask, and then 12 3216 chip resistors were mounted using a pick-and-place machine. The board was then melted and reflowed under a heating condition of 245°C for 40 seconds to create a test substrate. The number of chips that stood upright after mounting was counted. A count of 0 chips was marked with "◎". A count of 1 chip was marked with "〇". A count of 2 or more chips was marked with "×".

[0122] Rating 4: Lianxi·Xijian

[0123] First, prepare a 4-terminal Sn-plated resistor with 12 terminals, each 0.5 mm wide and 0.8 mm apart. Insert the terminals into a through-hole of the epoxy glass printed circuit board (CEM-3). Then, introduce the solder alloys shown in Tables 1 and 2 into the solder bath and perform wave soldering. Wave soldering was performed using a Malcom FS-1 reflow oven simulator under the following test conditions.

[0124] Test conditions

[0125] Solder bath: Malcom FS-1 reflow oven simulation demonstration device

[0126] solder weight: 15kg

[0127] Flux: Flux manufactured by Senju Metal Industries, Ltd. (trade name: ES-1061SP2)

[0128] Temperature of solder in the solder bath: 255℃

[0129] Visually evaluate whether solder bridging has occurred. Additionally, visually check for solder spikes at the rounded corners. If no solder bridging or solder spikes are found, rate it "◎"; if 1-2 resistors have solder bridging or solder spikes, rate it "〇"; if 3 or more resistors have solder bridging or solder spikes, rate it "×".

[0130] Evaluation 5: EM resistance

[0131] For the EM test samples, solder balls with a diameter of 0.24 mm, made of the solder alloys shown in Tables 1 and 2, were used to reflow solder on a 12 mm × 12 mm package substrate with a Cu electrode of 0.24 mm diameter to create a package. Then, solder paste composed of Sn-3.0Ag-0.5Cu was printed on an epoxy glass substrate (FR-4) with a size of 29 mm × 19 mm and a thickness of 0.8 mm. The package prepared above was mounted on the substrate, and a reflow soldering test substrate was created under conditions of a maximum temperature of 240 °C and a holding time of 90 seconds.

[0132] The fabricated test substrate was connected to a compact variable switching power supply (manufactured by Kikusui Electronics Industry Co., Ltd.: PAK-A), and tested in a silicone oil bath maintained at 125°C with a current density of 100 A / mm². 2 The test substrate was energized at 5.0V. The resistance of the sample was continuously measured during energization, and the time required for the resistance to increase by 150% from its initial value was recorded. Cases exceeding 350 hours were rated "◎", cases between 300 and 350 hours were rated "〇", and cases less than 300 hours were rated "×".

[0133] The results are shown in Tables 1 and 2.

[0134] [Table 1]

[0135]

[0136] [Table 2]

[0137]

[0138] As shown in Tables 1 and 2, all evaluations for Examples 1 to 51 are “0” or “◎”. In particular, the results show that Examples 2, 3, 10 to 22, 26 to 45, and 47 to 50, which do not contain Ni and satisfy equations (1) to (3), all have an evaluation of “◎”, and are superior in these examples.

[0139] On the other hand, Comparative Examples 1 and 2, due to their low Ag content, exhibited poor TCT, chip stand-up, and EM resistance. Comparative Example 3, due to its high Ag content, showed poor drop performance. Comparative Examples 4 through 10, due to their even higher Ag content, resulted in chip stand-up in addition to drop performance.

[0140] Comparative Examples 11 and 12 exhibited poor TCT and EM resistance due to their low Cu content. Comparative Example 13, with its high Cu content, resulted in frequent tin bridging and solder spikes. Comparative Example 14 suffered from poor EM resistance due to its low Bi content. Comparative Examples 15-19 exhibited poor drop performance due to their high Bi content. Comparative Examples 20-22 also showed frequent tin bridging and solder spikes due to their inappropriate P content.

[0141] For the specimens that underwent EM resistance evaluation, the results of observing the cross-section of the brazed joint are shown below. Figure 1 . Figure 1 SEM images of the cross-section of the brazed joint. Figure 1 (a) is Comparative Example 1. Figure 1 (b) is Example 22. From Figure 1 As is clearly seen in (a), in the quadrilateral-enclosed region of Comparative Example 1, the Cu of the upper electrode is cut, and Cu is deposited on the lower electrode. On the other hand, by Figure 1 As clearly shown in (b), no movement of Cu was observed in the quadrilateral-enclosed region of Example 22. The same result was obtained in other examples. It should be noted that typical Cu erosion is a phenomenon where both electrodes are eroded, and Cu does not deposit on the other electrode; therefore, Cu erosion and electromigration can be easily distinguished.

Claims

1. A soft solder alloy, characterized in that, It has the following alloy composition by mass%: Ag: 0.3~1.9%, Cu: 0.40~1.00%, Bi: 0.5~4.9%, P: 0.00100~0.02000%, with the balance being Sn.

2. The solder alloy according to claim 1, wherein, The alloy composition also contains Ga in an amount of less than 0.06% by mass.

3. The solder alloy according to claim 1 or 2, wherein, The alloy composition also contains at least one of As, In, Zr, Mn, Ti, Zn, Fe, Al, Au, Mg and Pt in amounts of less than 0.06% by mass.

4. The solder alloy according to claim 1 or 2, wherein, The alloy composition satisfies all of the following equations (1) to (3): 0.0007≤Ag×Cu×Bi×P≤0.0110 (1) 110≤Ag / (P×Cu)≤799 (2) 0.67≤(Ag+Bi) / (Ag+Cu+Bi)≤0.91 (3) Formula In equations (1) to (3), Ag, Cu, Bi and P represent the content of the alloy composition in terms of mass%.

5. The solder alloy according to claim 3, wherein, The alloy composition satisfies all of the following equations (1) to (3): 0.0007≤Ag×Cu×Bi×P≤0.0110 (1) 110≤Ag / (P×Cu)≤799 (2) 0.67≤(Ag+Bi) / (Ag+Cu+Bi)≤0.91 (3) Formula In equations (1) to (3), Ag, Cu, Bi and P represent the content of the alloy composition in terms of mass%.

6. A solder paste having a solder powder composed of a solder alloy as described in claim 1 or 2.

7. A solder paste having a solder powder composed of the solder alloy of claim 3.

8. A solder ball comprising the solder alloy of claim 1 or 2.

9. A solder ball comprising the solder alloy of claim 3.

10. A preformed solder, comprising the solder alloy of claim 1 or 2.

11. A preformed solder, comprising the solder alloy of claim 3.

12. A brazing joint having the soft solder alloy as described in claim 1 or 2.

13. A brazing joint having the soft solder alloy of claim 3.

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