Solder alloys, solder pastes, solder balls, solder preforms, and solder fittings

Abstract

The present invention provides solder alloys, solder pastes, solder balls, solder preforms, and solder joints that have excellent resistance to drop impact and heat cycling, suppress the occurrence of chipping, bridging, and icicle formation, and also suppress the occurrence of electromigration. [Solution] The solder alloy has an alloy composition consisting of, by mass%, Ag: 0.3~1.9%, Cu: 0.40~1.00%, Bi: 0.5~4.9%, P: 0.00100~0.02000%, and the remainder being Sn. The alloy composition may further contain Ge, Co, and Ga in amounts of 0.06% or less by mass, and at least one of each. The alloy composition may also further contain As, In, Zr, Mn, Ti, Zn, Fe, Al, Ni, Au, Mg, Cr, and Pt in amounts of 0.06% or less by mass, and at least one of each.

Description

Technical Field

[0001] The present invention relates to Sn-Ag-Cu-Bi-P solder alloy.

Background Art

[0002] In home appliances such as washing machines, refrigerators, and coolers, and electronic devices such as televisions, videos, radios, computers, copiers, and communication devices, a mounting substrate on which electronic components are mounted is used. In addition to single-layer substrates, substrates formed by laminating a plurality of substrates to realize enhanced functions are also used for mounting substrates.

[0003] For electrical connection between substrates and mounting of electronic components on substrates, methods such as connection by surface mounting and mounting by inserting terminals into through-holes of the substrate can be mentioned. Examples of such mounting processes on printed circuit boards include flow soldering, reflow soldering, and manual soldering. Among these, flow soldering is usually adopted as the mounting process for electronic components having a certain size.

[0004] For example, in Patent Document 1, studies have been conducted on forming solder joints using flow soldering. The Sn-Ag-Cu-Bi-P solder alloy described in the same document can suppress the generation of dross, improve the bulk strength (tensile strength) by forming intermetallic compounds with Ag, and improve the wettability with P. In Patent Document​​​Furthermore, Sn-Ag-Cu-Bi-P solder alloys are being investigated not only for flow soldering. Patent Document 3 discloses a Sn-Ag-Cu-Bi-P solder alloy for paste solder or rosin-core solder, with improvements in tensile strength, elongation, and thermal fatigue resistance. Patent Document 4 discloses a Sn-Ag-Cu-Bi-P solder alloy for solder balls, with studies on impact resistance, yellowing resistance, and heat cycle resistance.

[0006] Patent Document 5 discloses a Sn-Ag-Cu-Bi solder alloy whose heat cycle resistance was investigated using a mounting substrate on which solder paste was printed. Patent Document 6 discloses a Sn-Ag-Cu-Bi-P solder alloy whose liquidus temperature and solidus temperature were evaluated for use in pipe joining and sealing. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2007-7732 [Patent Document 2] Japanese Patent Publication No. 2000-288772 [Patent Document 3] Japanese Patent Application Publication No. 10-34376 [Patent Document 4] Japanese Patent Publication No. 2004-261863 [Patent Document 5] Japanese Patent Publication No. 2011-183430 [Patent Document 6] Japanese Patent Application Publication No. 2-70033 [Overview of the project] [Problems that the invention aims to solve]

[0008] Various effects have been confirmed with Sn-Ag-Cu-Bi-P solder alloys. Among them, the invention described in Patent Document 1 is an excellent invention that exhibits excellent wettability and high tensile strength. Paragraph 0008 of Patent Document 1 explains that, as a conventional technique, reducing the content of expensive Ag to lower costs results in a decrease in the tensile strength of the solder alloy.

[0009] In fact, according to the results of the study in paragraph 0027 of Patent Document 1, Example 7, which has an Ag content of 2 mass%, has a tensile strength that is approximately twice that of Example 4, which has an Ag content of 0.3 mass%. This is thought to be because Ag and Sn form an intermetallic compound, as described in paragraph 0020 of Patent Document 1. Therefore, according to the invention described in Patent Document 1, it is clear that increasing the Ag content is beneficial in order to improve tensile strength.

[0010] The invention described in Patent Document 2 also includes studies on tensile strength, disclosing that the Ag content is 2.0 to 5.0 mass%. Paragraph 0008 of Patent Document 2 discloses that when the Ag content is less than 2.0 mass%, the elongation decreases significantly upon addition of Bi, and the material fails to satisfy the properties required for soldering. 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 mass% or more. Furthermore, the invention described in Patent Document 2 also examines the content of P and Ni in order to suppress the formation of bridges.

[0011] In the invention described in Patent Document 3, in addition to tensile strength and elongation, heat cycle resistance is also considered. In Patent Document 3, in order to avoid a decrease in tensile strength, only solder alloys with an Ag content of 2.0% or more are disclosed in the examples. In other words, the invention described in Patent Document 3 reflects what has been explained and proven in Patent Documents 1 and 2.

[0012] Patent Document 4 discloses a solder alloy in which Ni is added to Sn-Ag-Cu-Bi-P in an example. Unlike Patent Documents 1 to 3, the solder alloy described in Patent Document 4 does not have its tensile strength considered, but rather its impact resistance is considered, and all of the Sn-Ag-Cu-Bi-P-Ni solder alloys disclosed in the example have a low Ag content.

[0013] In the invention described in Patent Document 4, as mentioned above, resistance to drop impact has been investigated. According to Patent Document 4, in order to improve resistance to drop impact, it is necessary to keep the Cu content to 0.3 mass% or less. Specifically, paragraph 0018 of Patent Document 4 states that if the Cu content is up to 0.3 mass%, the intermetallic compound suppression effect will be stronger than the increase in voids, and as a result, the material will be stronger against drop impact. Thus, in the invention described in Patent Document 4, the Cu content is kept low in order to improve resistance to drop impact.

[0014] In the invention described in Patent Document 5, the joint strength after a thermal shock test is examined as part of the study of heat cycle 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 heat cycle resistance, rather than using the softest possible solder alloy, the thermal stress resistance of the solder joint is improved by improving the solder strength.

[0015] Furthermore, paragraph 0010 of Patent Document 5 states that P may be included as an equivalent element to Ge, Ga, and In. However, Patent Document 5 does not mention the content of these elements. Paragraph 0012 of Patent Document 5 specifically discloses the content of Ge, Ga, and In in the range of 0.05 to 1.0 mass%. Therefore, even if P is added to the solder alloy of Patent Document 5, the content of P must be in the range of 0.05 to 1.0 mass%.

[0016] Patent document 6 discloses Sn-Ag-Cu-Bi-P as a solder alloy for pipe joining and sealing. It also states that for such applications, the Ag content is preferably 0.1 to 0.4 mass%. The alloy compositions actually examined as examples in Patent document 6 all have an Ag content of 0.4 mass% or less. This is presumably because, especially for use in sealing, the elongation of the solder alloy needs to be considered, and therefore the tensile strength was deliberately reduced.

[0017] However, the inventions described in Patent Documents 1 to 6 need to take into account the current state of electronic devices, which have made remarkable progress in recent years. In particular, the issues that should be considered are chip detachment, which can occur when mounting electronic components, and electromigration, which can occur during operation.

[0018] Chip uprighting is a phenomenon that occurs when solder alloy placed on electrodes melts due to heating. If the solder alloy on one electrode begins to melt faster than the solder alloy on the other electrode, electronic components such as chips are attracted to the electrode and stand upright. This has become more frequent in recent years due to the miniaturization and reduction of electronic components mounted on electronic devices, which have led to the miniaturization and reduction of electronic components.

[0019] Electromigration is a problem that has become increasingly apparent in recent years as electronic components become smaller and the current density increases, leading to an increase in the movement of electrons within solder joints. Electromigration can be explained as follows: Atoms constituting the solder joint collide with electrons that generate the current, and momentum is transferred from the electrons to the atoms. The atoms, having gained momentum in the direction of the electron flow, move towards the anode side of the solder joint along the electron flow. In the case of copper-containing solder alloys, copper segregates towards the anode side, and vacancies are created on the cathode side of the solder joint. These vacancies gradually expand, creating voids. As voids grow, the resistance increases, causing the solder joint to heat up due to Joule heating, and reducing the current density, making it difficult for electronic components to perform optimally. Ultimately, the solder joint fractures.

[0020] Thus, in recent years, in Sn-Ag-Cu-Bi-P solder alloys, there has been a demand for solder alloys that can suppress chip standing and electromigration while maintaining conventional characteristics. Therefore, in the solder alloys described in Patent Documents 1 to 6, it is an urgent task to conduct studies in view of the actual situation of recent electronic components.

[0021] An object of the present invention is to provide a solder alloy, a solder paste, a solder ball, a solder preform, and a solder joint that have excellent drop impact resistance and heat cycle resistance, suppress the occurrence of chip standing and bridge whiskers, and can also suppress the occurrence of electromigration.

Means for Solving the Problems

[0022] The inventors of the present invention extracted those that seemed to be able to solve the above problems from the Sn-Ag-Cu-Bi-P solder alloys specifically studied in Patent Documents 1 to 6 and conducted detailed studies. First, Sn-2Ag-0.5Cu-2Bi-0.005P of Example 7 of Patent Document 1 in which precipitation strengthening by Ag3Sn is achieved, Sn-2.8Ag-0.5Cu-1.0Bi-0.005P-0.005Ni of the examples in Table 2 of Patent Document 2, Sn-2.8Ag-0.5Cu-1.0Bi-0.01P of the comparative example in Table 2 of Patent Document 2, Sn-2Ag-0.5Cu-5Bi-0.003P of Comparative Example 2 of Patent Document 3, and Sn-2Ag-0.5Cu-5Bi-0.001P-0.005Ni of Example 1 of Patent Document 3 were selected. In addition, in the examples and comparative examples extracted from Patent Documents 1 to 6, when the element content was expressed as an integer, the first decimal place was regarded as 0. The same shall apply hereinafter.

[0023] Next, in order to improve the drop impact resistance, Sn-1Ag-0.05Cu-1Bi-0.005P-0.05Ni of Example 11 of Patent Document 4 with a low Cu content was selected. Also, Sn-1.0Ag-0.5Cu-1.0Bi of Comparative Example 2 of Patent Document 5 and Sn-0.2Ag-0.2Cu-3.8Bi of No. 3 of Patent Document 6, where the Ag content is low and an improvement in drop impact resistance is presumed, were selected.

[0024] First, in Example 7 of Patent Document 1, Comparative Example 2 and Example 1 of Patent Document 3, etc., since the Ag content is high, it was found that the drop impact resistance is poor. In the examples and comparative examples of Patent Document 2, since the Ag content is even higher in all cases, in addition to the drop impact resistance, it was found that chip standing occurs frequently.

[0025] In Example 11 of Patent Document 4, since the Cu content is low, it was found that the heat cycle resistance is poor. In Comparative Example 2 of Patent Document 5, although the drop impact resistance was somewhat improved compared to Example 7 of Patent Document 1, etc., it was found that bridges and whiskers occur frequently because it does not contain P. In No. 3 of Patent Document 6, since the Ag content is low, it was found that the heat cycle resistance is poor.

[0026] Also, in the above-mentioned solder alloys disclosed in Patent Document 2 and Patent Document 6, in addition to the above findings, it was also found that chip standing occurs frequently. Furthermore, in the above-mentioned solder alloys disclosed in Patent Document 4 and Patent Document 6, it was also found that electromigration occurs.

[0027] Considering the above findings, it is not simply a matter of increasing the Ag content to precipitate a large amount of Ag3Sn; it is necessary to adjust the hardness to an appropriate level to improve resistance to drop impacts and heat cycling. Furthermore, when heating the solder alloy, in the temperature range above the solidus temperature, it is considered necessary to adjust the alloy composition so that a large amount of endothermic activity is observed in two stages when measuring the thermal history with a DSC (Differential Scanning Calorimeter) to suppress chipping. Moreover, it is considered necessary to suppress the formation of bridges and icicles by adjusting the viscosity of the molten solder. In addition, it is considered necessary to improve electromigration resistance (hereinafter simply referred to as "EM resistance") by precipitation of an appropriate amount of Ag3Sn and solid solution strengthening of the solder alloy with Bi.

[0028] Here, the effect of a solder alloy is not due to the effects of each constituent element being exerted separately, but rather to their mutual contributions and the overall effect being exerted as a single substance. Therefore, if each constituent element is prepared individually to improve each property, it will not be possible to simultaneously exhibit various effects in a single composition.

[0029] Therefore, in consideration of the above findings, the inventors conducted a detailed search for the composition of Sn-Ag-Cu-Bi-P solder alloy. As a result, a solder alloy was obtained that, only when each constituent element is within a predetermined range, has excellent resistance to drop impact and heat cycling, suppresses the occurrence of chipping, bridging, and icicle formation, and also suppresses the occurrence of electromigration. Thus, the present invention was completed. The present invention, derived from this finding, is as follows:

[0030] (0) A solder alloy characterized by having, by mass%, Ag: 0.3~1.9%, Cu: 0.40~1.00%, Bi: 0.5~4.9%, P: 0.00100~0.02000%, and the remainder being Sn. (1) A solder alloy characterized by having an alloy composition in mass%, consisting of Ag: 0.3-1.9%, Cu: 0.40-1.00%, Bi: 0.5-4.9%, P: 0.00100-0.02000%, and the remainder being Sn.

[0031] (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 a total amount of 0.06% or less by mass%, and at least one of these.

[0032] (3) The solder alloy according to any one of the above items (0) to (2), wherein the alloy composition further contains, by mass%, 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.

[0033] (4) The solder alloy according to any one of the above (0) to (2), wherein the alloy composition further contains, by mass%, 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.

[0034] (5-6) The alloy composition is a solder alloy described in any one of the above items (0) to (4), satisfying all of the following equations (1) to (3). 0.0007≦Ag×Cu×Bi×P≦0.0110 Formula (1) 110≦Ag / (P×Cu)≦799 (2) formula 0.67≦(Ag+Bi) / (Ag+Cu+Bi)≦0.91(3) formula In equations (1) to (3) above, Ag, Cu, Bi, and P each represent the content as mass percent of the alloy composition.

[0035] (7-8) A solder paste having solder powder made from any one of the solder alloys described in item (0) to (6) above.

[0036] (9~10) A solder ball made of any one of the solder alloys described in item (0) to (6) above.

[0037] (11-12) A solder preform made of any one of the solder alloys described in item (0) to (6) above.

[0038] (13-14) A solder joint having the solder alloy described in any one of the above items (0) to (6). [Brief explanation of the drawing]

[0039] [Figure 1] Figure 1 shows cross-sectional SEM images of solder joints, where Figure 1(a) is Comparative Example 1 and Figure 1(b) is Example 22. [Modes for carrying out the invention]

[0040] The present invention will be described in more detail below. In this specification, "%" in relation to the alloy composition of solder alloys refers to "mass%" unless otherwise specified.

[0041] 1. Solder alloy (1) Ag: 0.3~1.9% Ag is an element that improves resistance to drop impact, heat cycles, and electrochemical reactions (EM), and suppresses chipping. Ag contributes to improved heat cycle and drop impact resistance because it can suppress deformation of the solder alloy through Ag3Sn deposition strengthening. Furthermore, the deposition of Ag3Sn inhibits electron transfer, improving EM resistance. In addition, thermal history using DSC shows two large endothermic peaks between the solidus temperature and liquidus temperature during heating.

[0042] If the Ag content is less than 0.3%, the amount of Ag3Sn precipitated will be insufficient, resulting in a deterioration of heat cycle resistance and EM resistance. Furthermore, chipping will occur frequently. The lower limit of 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.

[0043] On the other hand, if the Ag content exceeds 1.9%, Ag3Sn forms a network structure, which deteriorates the drop impact resistance. Also, if the Ag content exceeds 2.5%, there is only one endothermic peak, and chipping occurs frequently. The upper limit of the Ag content is 1.9% or less, preferably 1.7% or less, more preferably 1.6% or less, even more 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. The preferred range for Ag is 0.6–1.4%. The above upper and lower limits can define a further preferred range for the Ag content.

[0044] (2) Cu: 0.40~1.00% Cu is an element that improves heat cycle resistance and EM resistance, as well as suppressing the formation of bridges and icicles. Because Cu6Sn5, formed from Cu and Sn, precipitates finely at the bonding interface, fracture does not occur at the bonding interface even when subjected to thermal stress due to temperature differences. Furthermore, if the Cu content is 0.40 to 1.00%, it is close to the eutectic composition of Sn and Cu, and the rise in liquidus temperature is suppressed, thereby suppressing the formation of bridges and icicles. In addition, the intermetallic compound formed from Cu and Sn inhibits electron transfer, thus improving EM resistance.

[0045] If the Cu content is less than 0.40%, the amount of fine Cu6Sn5 precipitate will be insufficient, resulting in a deterioration of heat cycle resistance and EM resistance. The lower limit of the Cu content is 0.40% or more, preferably 0.50% or more.

[0046] On the other hand, if the Cu content exceeds 1.00%, the liquidus temperature rises, and the viscosity of the molten solder increases when joining at normal temperatures, resulting in frequent bridging and icicle formation. The upper limit of the Cu content is 1.0% or less, preferably 0.90% or less, more preferably 0.80% or less, even more preferably 0.70% or less, and even more preferably 0.60% or less. The preferred range for Cu is 0.40–0.70%. The above upper and lower limits can define a further preferred range for the Cu content.

[0047] (3) Bi: 0.5~4.9% Bi is an element that contributes to improved resistance to drop impacts and electromagnetism (EM). Because Bi is a solid solution in Sn, the solid solution strengthening of Sn distorts the crystal lattice of Sn, hindering the movement of Cu and thus improving EM resistance.

[0048] If the Bi content is less than 0.5%, the solid solution strengthening of Sn will be insufficient, and the EM resistance will deteriorate. The lower limit of the Bi content is 0.5% or more, preferably 0.6% or more, more preferably 0.7% or more, even more preferably 0.8% or more, particularly preferably 0.9% or more, and most preferably 1.0% or more.

[0049] On the other hand, if the Bi content exceeds 4.9%, the Bi segregates because it exceeds the solid solubility limit, resulting in hardening and embrittlement of the solder alloy and poor resistance to drop impact. 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. The preferred range for Bi is 0.5–3.7%. The above upper and lower limits can specify a further preferred range for the Bi content.

[0050] (4) P: 0.00100~0.02000% P is an element that suppresses the formation of bridges and icicles. P remains on the surface of molten solder and inhibits the formation of tin oxide, thus maintaining the proper fluidity of the molten solder. This suppresses the formation of bridges and icicles that may occur during solidification.

[0051] If the P content is less than 0.00100%, the formation of tin oxide cannot be suppressed, and bridging and icicle formation occur frequently. The lower limit of the P content is 0.00100% or more, preferably 0.00200% or more, and more preferably 0.00300% or more.

[0052] On the other hand, if the P content exceeds 0.0200%, intermetallic compounds of P precipitate, leading to frequent bridging and icicle formation. The upper limit of the P content is 0.0200% or less, preferably 0.0170% or less, more preferably 0.0160% or less, even more 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. The preferred range for P is 0.00300 to 0.0200%. The above upper and lower limits can define a further preferred range for the P content.

[0053] (5) Ge, Co, and Ga, in an amount of 0.06% or less in total, and at least one of them The solder alloy according to the present invention may contain Ge, Co, and Ga as optional elements to suppress oxidation of the solder alloy. Solder alloys containing these elements can suppress the rise in liquidus temperature if the content of each element is 0.06% or less, thereby further suppressing the formation of bridges and icicles. The content of each element is preferably 0.006% or less, and more preferably 0.005% or less. The lower limit is not particularly limited, but it should be 0.001% or more. Furthermore, if at least one of these optional elements is contained in multiple compositions, the total amount should be 0.1% or less. The lower limit of the total amount should be 0.001% or more.

[0054] (6) At least one of each of As, In, Zr, Mn, Ti, Zn, Fe, Al, Ni, Au, Mg, Cr, and Pt in an amount of 0.06% or less. The solder alloy according to the present invention may contain at least one of As, In, Zr, Mn, Ti, Zn, Fe, Al, Ni, Au, Mg, Cr, and Pt as an optional element, within a range that does not impair the above-mentioned effects. Among these optional elements, it is more preferable to exclude Ni, which is an element that causes a rapid increase in melting point when present in small amounts from the above optional elements. More specifically, the alloy composition may further contain 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%.

[0055] When As, In, Zr, Mn, Ti, Zn, Fe, Al, Ni, Au, Mg, Cr, and Pt are included, the upper limit of the content of each constituent element is preferably 0.06% or less. The lower limit is not particularly limited, but it should be 0.001% or more. Furthermore, when at least one of these optional elements is included in multiple quantities in one composition, the total amount should be 0.1% or less. The lower limit of the total amount should be 0.001% or more.

[0056] (6) Equations (1)~(3) 0.0007≦Ag×Cu×Bi×P≦0.0110 Formula (1) 110≦Ag / (P×Cu)≦799 (2) formula 0.67≦(Ag+Bi) / (Ag+Cu+Bi)≦0.91(3) formula In equations (1) to (3) above, Ag, Cu, Bi, and P each represent the content as mass percent of the alloy composition.

[0057] The constituent elements of the solder alloy according to the present invention have excellent resistance to drop impact and heat cycles, suppressing chipping, bridging, and icicle formation, as well as suppressing electromigration. In order to achieve these effects simultaneously and at a higher level with a single composition, it is even more preferable that, in addition to each constituent element being within the aforementioned range, equations (1) to (3) are satisfied. The technical significance of each equation is as follows.

[0058] Equation (1) is a relational expression that takes into account the balance of the content of essential elements. Equation (2) is a relational expression relating to the content of Ag, Cu, and P, and these elements are a group of elements that can form intermetallic compounds in the solder alloy of the present invention. Since the intermetallic compounds can affect the various properties of the present invention depending on the location, form, and size of precipitation, a solder alloy that satisfies equation (2) can exhibit particularly excellent effects with a single composition. Equation (3) is an element that strengthens the solder alloy of the present invention. Ag and Bi are elements that contribute to drop impact resistance. Ag, Cu, and Bi are elements that contribute to EM resistance and heat cycle resistance, and it is preferable to satisfy equation (3) in order to raise each property to a high level in a well-balanced manner.

[0059] The upper limit of equation (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. (1) The lower limit of formula is preferably 0.0007 or higher, more preferably 0.0009 or higher, even more preferably 0.0010 or higher, even more preferably 0.0011 or higher, particularly preferably 0.0013 or higher, most preferably 0.0014 or higher, 0.0015 or higher, 0.0017 or higher, 0.0018 or higher, 0.0020 or higher, 0.0021 or higher, 0.0022 or higher, 0.0023 or higher, 0.0025 or higher, 0.0026 or higher, and 0.0029 or higher. A more preferred range for equation (1) is 0.0017 to 0.0088. The above upper and lower limits can each define a more preferred range for equation (1).

[0060] The upper limit of formula (2) is preferably 799 or less, more preferably 733 or less, even more preferably 611 or less, even more preferably 600 or less, particularly preferably 550 or less, and most preferably selected from 524 or less, 458 or less, and 400 or less. The lower limit of formula (2) is preferably 110 or more, more preferably 129 or more, even more preferably 138 or more, even more preferably 147 or more, particularly preferably 200 or more, and most preferably selected from 244 or more, 267 or more, and 367 or more. A more preferred range for equation (2) is 138 to 733. The above upper and lower limits can each define a more preferred range for equation (2).

[0061] 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 selected from 0.83 or less and 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 selected from 0.76 or more, 0.77 or more, 0.78 or more, 0.79 or more and 0.80 or more. A more preferred range for equation (3) is 0.76 to 0.89. The above upper and lower limits can each define a more preferred range for equation (1).

[0062] The calculations in equations (1) to (3) used the measured values ​​of the alloy composition shown in Tables 1 and 2. For the values ​​calculated from equations (1) to (3), equation (1) is calculated to four decimal places, equation (2) is calculated to one integer digit, and equation (3) is calculated to two decimal places. This calculation rule is used in this application and is intended to be used similarly in calculations concerning further solder alloys described in other literature, as all solder alloys must be treated in the same way.

[0063] (7) Remainder: Sn The remainder of the solder alloy according to the present invention is Sn. In addition to the elements mentioned above, it may contain unavoidable impurities. Even if it contains unavoidable impurities, it will not affect the effects described above. Furthermore, as will be described later, even if elements not included in the present invention are included as unavoidable impurities, it will not affect the effects described above.

[0064] 2. Solder paste The solder paste according to the present invention is a mixture of solder powder having the alloy composition described above and flux. The flux used in the present invention is not particularly limited as long as it can be soldered by conventional methods. Therefore, a mixture of commonly used rosin, organic acid, activator, and solvent may be used as appropriate. In the present invention, the mixing ratio of the metal powder component and the flux component is not particularly limited, but preferably, the metal powder component is 70-90% by mass and the flux component is 10-30% by mass.

[0065] 3. Solder ball The solder alloy according to the present invention can be used as solder balls. When used as solder balls, the solder alloy according to the present invention can be manufactured using the dropping method, which is a common method in the industry. Alternatively, solder joints can be manufactured by processing using methods common in the industry, 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, even more 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, even more preferably 800 μm or less, and particularly preferably 600 μm or less.

[0066] 4. Solder preform The solder alloy according to the present invention can be used as a preform. Examples of preform shapes include washers, rings, pellets, discs, ribbons, and wires. It can also be used as solder bars.

[0067] 5. Solder joints The solder joint according to the present invention is suitably used for joining at least two or more members to be joined. The members to be joined are not particularly limited as long as they are electrically connected using the solder alloy according to the present invention, such as semiconductors using elements, substrates, electronic components, printed circuit boards, insulating substrates, heat sinks, lead frames, electrode terminals, etc., and power modules, inverter products, etc.

[0068] The joining method using the solder alloy according to the present invention can be carried out according to a conventional method, for example, using the reflow method. When performing flow soldering, the melting temperature of the solder alloy may be approximately 20°C higher than the liquidus temperature. Furthermore, when joining using the solder alloy according to the present invention, considering the cooling rate during solidification can further refine the alloy structure. For example, the solder joint should 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.

[0069] 6. Application The solder alloy according to the present invention is particularly effective when used in flow soldering among various soldering methods. It is effective when performing flow soldering on laminated substrates in which multiple substrates are stacked. Since the composition of the solder jet used in flow soldering may change when used for a long time, it can also be used as a replenishment solder to bring the solder jet to a desired composition. In this case, the replenishment solder can be replenished by adjusting its composition within the scope of the present invention. The temperature of the solder jet when performing flow soldering is generally 230 to 260°C. In addition, other joining conditions can be appropriately adjusted according to the alloy composition, solid phase ratio, and liquid phase ratio of the solder alloy.

[0070] 7. Method for manufacturing solder alloys The solder alloy according to the present invention can be manufactured by pre-fabricating SnAg alloy and SnCu alloy and melting them together with Bi and P. For example, alloys of Sn and Ag, and Sn and Cu can be manufactured by weighing each alloy to a predetermined amount, and then weighing Bi and P. The reason for manufacturing in this way can be explained as follows. Melting Ag, which has a melting point of about 860°C, and Cu, which has a melting point of about 1100°C, into Sn takes a lot of time. In particular, Cu is prone to surface oxidation, so if the melting time is long, it will be affected by oxidation. On the other hand, if SnAg alloy, which is made by pre-melting Ag into Sn, and SnCu alloy, which is made by pre-melting Cu into Sn, are prepared in advance, the melting time into Sn can be significantly reduced. The intermetallic compounds formed during the fabrication of each alloy, for example, Cu6Sn5 has a melting point of 415°C and Ag3Sn has a melting point of 480°C, and since these intermetallic compounds are mainly formed inside the alloy, there is considered to be little concern about oxidation.

[0071] The solder alloy according to the present invention can be manufactured by using low-alpha wire material as a raw material. When such a low-alpha wire alloy is used to form solder bumps around memory, it is possible to suppress soft errors. [Examples]

[0072] Using solder alloys with the alloy compositions shown in Tables 1 and 2, we evaluated the following: drop impact test (DROP) as Evaluation 1, heat cycle resistance test (TCT) as Evaluation 2, chip formation as Evaluation 3, bridging / icicle formation as Evaluation 4, and EM resistance as Evaluation 5. Each evaluation method is described below.

[0073] Evaluation 1: Drop Impact Test (DROP) Each solder alloy shown in Tables 1 and 2 was atomized to produce solder powder. Solder pastes were prepared for each solder alloy by mixing them with soldering flux (GLV, manufactured by Senju Metal Industry Co., Ltd.) consisting of rosin, solvent, activator, thixotropic agent, organic acid, etc. The solder paste consisted of 88% alloy powder by mass and 12% flux by mass.

[0074] 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 mounter, and reflow soldering was performed at a maximum temperature of 240°C with a holding time of 60 seconds to produce two test boards. Subsequently, each BGA component was separated from the board (divided into five sections), resulting in a total of 10 evaluation samples.

[0075] Next, the evaluation sample was fixed to the base with bolts at both ends so that the BGA component faced the base. In this state, the impact resistance was evaluated by applying an acceleration of 1500G while measuring the electrical resistance value in accordance with JEDEC standards. The progression of cracks was evaluated by the number of drops until the electrical resistance value increased by 50% from the initial value. If the number of drops was 100 or more, it was judged as "◎". If the number of drops was 90 or more but less than 100, it was judged as "〇". If the number of drops was less than 90, it was judged as "×".

[0076] Evaluation 2: Heat Cycle Resistance Test (TCT) A solder paste was prepared in the same manner as in Evaluation 1. The prepared test board was placed in a heat cycle test apparatus set to low temperature -40°C, high temperature +125°C, and holding time 10 minutes. The number of cycles was determined from the initial resistance value of 3-5Ω until the resistance value of at least one BGA component exceeded 15Ω. A cycle count of 700 or more was judged as "◎". A cycle count of 650-699 was judged as "〇". A cycle count of less than 650 was judged as "×".

[0077] Rating 3: Tip Stand A solder paste was prepared in the same manner as in Evaluation 1. This solder paste was paste-printed onto the Cu lands of a 6-layer printed circuit board (FR-4, Cu-OSP) using a 150 μm metal mask, and then 12 3216 chip resistors were mounted using a mounter. After that, the board was reflowed by melting it under heating conditions of a maximum temperature of 245°C and a holding time of 40 seconds, and soldering was performed to create a test board. The number of chips standing upright after mounting was counted. If the number of chips standing upright was 0, it was judged as "◎". If the number of chips standing upright was 1, it was judged as "〇". If the number of chips standing upright was 2 or more, it was judged as "×".

[0078] Rating 4: Bridge Icicle First, twelve 4-terminal Sn-plated resistors with a terminal width of 0.5 mm and a terminal spacing of 0.8 mm were prepared. These resistors were inserted into through-holes of a glass epoxy printed circuit board (CEM-3), and flow soldering was performed by introducing the solder alloys shown in Tables 1 and 2 into the solder bath. A Malcolm Corporation FS-1 flow simulator was used for the flow soldering, and the process was carried out under the following test conditions.

[0079] Test conditions Soldering bath: Malcolm Corporation Flow Simulator FS-1 Solder quantity: 15kg Flux: Flux manufactured by Senju Metal Industry Co., Ltd. (Product name: ES-1061SP2) Solder temperature in the solder bath: 255℃

[0080] We visually inspected whether a bridge had formed. We also visually checked whether icicles had formed on the fillets. If no bridge or icicle was found, we evaluated it as "◎" (excellent). If 1-2 resistors had bridges or icicles, we evaluated it as "〇" (good). If 3 or more resistors had bridges or icicles, we evaluated it as "×" (bad).

[0081] Rating 5: EM resistance For the EM test samples, solder balls made of the solder alloys shown in Tables 1 and 2, with a diameter of 0.24 mm, were used and reflow soldered onto a 12 mm × 12 mm package substrate with a 0.24 mm diameter Cu electrode using water-soluble flux to fabricate a package. Subsequently, a solder paste with a Sn-3.0Ag-0.5Cu composition was printed onto a 29 mm × 19 mm, 0.8 mm thick glass epoxy substrate (FR-4), and the package fabricated above was mounted on it. A reflow soldering test substrate was then prepared under conditions of a maximum temperature of 240°C and a holding time of 90 seconds.

[0082] The fabricated test board was connected to a compact variable switching power supply (Kikusui Electronics Co., Ltd.: PAK-A) and subjected to a current density of 100 A / mm² in a silicon oil bath maintained at 125°C. 2 The test board was energized under the condition that the voltage was 5.0V. The electrical resistance of the sample was continuously measured while energized, and the time required for the resistance to increase by 150% from the initial value was measured. A result exceeding 350 hours was evaluated as "◎", a result between 300 and 350 hours was evaluated as "〇", and a result less than 300 hours was evaluated as "×". The results are shown in Tables 1 and 2.

[0083] [Table 1]

[0084] [Table 2]

[0085] As is clear from Tables 1 and 2, all of Examples 1 to 51 received either a "○" or "◎" rating in all evaluations. In particular, Examples 2, 3, 10-22, 26-45, and 47-50, which do not contain Ni and satisfy equations (1) to (3), all received an "◎" rating in all evaluations, demonstrating superior results among the examples.

[0086] On the other hand, Comparative Examples 1 and 2 had poor TCT, tipping, and EM resistance due to their low Ag content. Comparative Example 3 had poor DROP due to its high Ag content. Comparative Examples 4-10 all had even higher Ag content, resulting in tipping in addition to DROP.

[0087] Comparative Examples 11 and 12 had poor TCT and EM resistance due to their low Cu content. Comparative Example 13 had a high Cu content, resulting in frequent bridging and icicle formation. Comparative Example 14 had a low Bi content, resulting in poor EM resistance. Comparative Examples 15-19 had a high Bi content, resulting in poor DROP. Comparative Examples 20-22 had an inappropriate P content, resulting in frequent bridging and icicle formation.

[0088] Figure 1 shows the results of observing the cross-section of the solder joints of the samples whose EM resistance was evaluated. Figure 1 is a cross-sectional SEM image of the solder joint, with Figure 1(a) being Comparative Example 1 and Figure 1(b) being Example 22. As is clear from Figure 1(a), in the area enclosed by the square in Comparative Example 1, the Cu on the upper electrode was eroded, and Cu was deposited on the lower electrode. On the other hand, as is clear from Figure 1(b), no Cu migration was observed in the area enclosed by the square in Example 22. Similar results were obtained in the other examples. It should be noted that general Cu erosion is a phenomenon in which both electrodes are eroded, and as shown in Figure 1(a), Cu does not deposit on the other electrode, so Cu erosion and electromigration can be easily distinguished.

Claims

1. A solder alloy characterized by having an alloy composition consisting of, by mass%, Ag: 0.3 to 1.9%, Cu: 0.40 to 1.00%, Bi: 0.5 to 4.9%, P: 0.00100 to 0.02000%, and the remainder being Sn.

2. The solder alloy according to claim 1, wherein the alloy composition further contains at least one of Ge, Co, and Ga in an amount of 0.06% or less by mass%.

3. The solder alloy according to claim 1 or 2, wherein the alloy composition further contains, by mass%, 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.

4. The solder alloy according to claim 1 or 2, wherein the alloy composition further contains, by mass%, 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.

5. The aforementioned alloy composition satisfies all of the following formulas (1) to (3), the solder alloy according to claim 1 or 2. 0.0007≦Ag×Cu×Bi×P≦0.0110 (1) Formula 110≦Ag / (P×Cu)≦799 (2) formula 0.67≦(Ag+Bi) / (Ag+Cu+Bi)≦0.91 Formula (3) In formulas (1) to (3) above, Ag, Cu, Bi, and P each represent the content as mass percent of the alloy composition.

6. The aforementioned alloy composition satisfies all of the following formulas (1) to (3), the solder alloy according to claim 3. 0.0007≦Ag×Cu×Bi×P≦0.0110 (1) Formula 110≦Ag / (P×Cu)≦799 (2) formula 0.67≦(Ag+Bi) / (Ag+Cu+Bi)≦0.91 Formula (3) In formulas (1) to (3) above, Ag, Cu, Bi, and P each represent the content as mass percent of the alloy composition.

7. A solder paste having solder powder made of the solder alloy according to claim 1 or 2.

8. A solder paste having solder powder made of the solder alloy described in claim 4.

9. A solder ball made of the solder alloy according to claim 1 or 2.

10. A solder ball made of the solder alloy described in claim 4.

11. A solder preform made of the solder alloy according to claim 1 or 2.

12. A solder preform made of the solder alloy described in claim 4.

13. A solder joint having the solder alloy according to claim 1 or 2.

14. A solder joint having the solder alloy described in claim 4.

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