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

Abstract

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. 【Solution means】The solder alloy has 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 balance being Sn. The alloy composition may further contain each of Ge, Co, and Ga in an amount of 0.06% or less by mass% and at least one of them. Further, the alloy composition may further contain each 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% and at least one of them.

Description

Technical Field

[0001] The present invention relates to an 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, those in which a plurality of substrates are laminated to realize enhanced functions are used as 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 a mounting process on a printed circuit board include flow soldering, reflow soldering, and manual soldering. Among these, flow soldering is usually adopted as a 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 an intermetallic compound with Ag, and improve the wettability with P. In Patent Document 2, the tensile strength, wettability during flow soldering, solidus temperature, liquidus temperature, and number of bridge occurrences of the Sn-Ag-Cu-Bi-P solder alloy have been studied.

[0005] In addition, Sn-Ag-Cu-Bi-P solder alloys are being studied not only for flow soldering. Patent Document 3 discloses Sn-Ag-Cu-Bi-P solder alloys for cream solder or paste-in solder, aiming to improve tensile strength, elongation, and thermal fatigue characteristics. Patent Document 4 discloses Sn-Ag-Cu-Bi-P-based solder alloys for solder balls, and impact resistance, yellowing, and heat cycle resistance are being studied.

[0006] Patent Document 5 discloses Sn-Ag-Cu-Bi solder alloys whose heat cycle resistance was studied using a mounting substrate printed with solder paste. Patent Document 6 discloses Sn-Ag-Cu-Bi-P-based solder alloys whose liquidus temperature and solidus temperature were evaluated for pipe joining and sealing.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Summary of the Invention

Problems to be Solved by the Invention

[0008] Conventionally, various effects have been confirmed in 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 reduce costs results in inferior tensile strength of the solder alloy.

[0009] Actually, according to the examination results in Paragraph 0027 of Patent Document 1, Example 7 with an Ag content of 2% by mass has a tensile strength increased to about twice that of Example 4 with an Ag content of 0.3% by mass. This is considered to be because, as described in Paragraph 0020 of Patent Document 1, Ag and Sn form an intermetallic compound. Therefore, according to the invention described in Patent Document 1, it can be seen that increasing the Ag content is better in order to improve the tensile strength.

[0010] The invention described in Patent Document 2 has also examined the tensile strength, and it is disclosed that the Ag content is 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 significantly decreases due to the addition of Bi, and the characteristics as a solder material are not satisfied. That is, the conventional technique described in Patent Document 1 is reflected in the invention described in Patent Document 2, and according to the invention described in Patent Document 2, it is necessary to increase the Ag content to 2.0% by mass or more. Also, in the invention described in Patent Document 2, the contents of P and Ni have been examined to suppress the occurrence of bridges.

[0011] In the invention described in Patent Document 3, in addition to the tensile strength and elongation, the heat cycle resistance has also been examined. Patent Document 3 discloses that only solder alloys with an Ag content of 2.0% or more are used in the examples in order to avoid a decrease in tensile strength. That is, 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 in its examples a solder alloy in which Ni is added to Sn-Ag-Cu-Bi-P. Unlike Patent Documents 1 to 3, the solder alloy described in Patent Document 4 does not examine tensile strength but examines impact resistance instead. All of the solder alloys of the Sn-Ag-Cu-Bi-P-Ni composition disclosed in the examples have a low Ag content.

[0013] In the invention described in Patent Document 4, as described above, examination of drop impact resistance is carried out. According to Patent Document 4, it is necessary to suppress the Cu content to 0.3 mass% or less in order to improve the drop impact resistance. Specifically, in paragraph 0018 of Patent Document 4, it is described that if the Cu content is up to 0.3 mass%, the intermetallic compound suppression effect appears stronger than the increase in voids, and as a result, it becomes stronger against drop impact. Thus, in the invention described in Patent Document 4, the Cu content is suppressed low in order to improve the drop impact resistance.

[0014] In the invention described in Patent Document 5, as an examination of heat cycle resistance, the joint strength after a thermal shock test is examined. Patent Document 5 discloses a Sn-Ag-Cu-Bi solder alloy as a specific alloy composition. Paragraph 0015 of Patent Document 5 describes that in order to improve the heat cycle resistance, rather than using a solder alloy that is as soft as possible, improving the solder strength improves the thermal stress resistance of the solder joint.

[0015] Furthermore, paragraph 0010 of Patent Document 5 describes that P may be contained as an element equivalent 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 that the content of Ge, Ga, and In is in the range of 0.05 to 1.0 mass%. Therefore, even when 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 an Sn-Ag-Cu-Bi-P solder alloy for pipe joining and sealing. It is also described that for such applications, the Ag content is preferably 0.1 to 0.4% by mass. All the alloy compositions actually examined as examples in Patent Document 6 have an Ag content of 0.4% by mass or less. This is presumably because, especially for use in sealing, it is necessary to consider the elongation of the solder alloy, so the tensile strength is deliberately reduced.

[0017] However, in the inventions described in Patent Documents 1 to 6, it is necessary to take into account the actual situation of electronic devices that have made remarkable progress in recent years. In particular, as issues worthy of attention, chip standing that may occur during the mounting of electronic components and electromigration that may occur during driving can be cited.

[0018] Chip standing is a phenomenon in which when the solder alloy placed on an electrode melts due to heating, if the solder alloy on one electrode starts to melt earlier than the solder alloy on the other electrode, an electronic component such as a chip is attracted to one electrode and stands upside down. This has become frequent in recent years due to the miniaturization and weight reduction of electronic components mounted on electronic devices along with the trend of electronic devices becoming thinner, lighter, shorter, and smaller.

[0019] Electromigration is that as the miniaturization of electronic components progresses and the current density during energization increases, the number of electrons moving within the solder joint also increases. Therefore, in recent years, the problem has been becoming apparent. Electromigration can be explained as follows. The atoms constituting the solder joint collide with the electrons generating an electric current, and the momentum is transferred from the electrons to the atoms. The atoms that have obtained the momentum in the direction of the electron flow move to the anode side of the solder joint along the electron flow. At this time, in a solder alloy containing Cu, Cu segregates to the anode side, and vacant lattice sites are generated on the cathode side of the solder joint. Such vacant lattice sites gradually expand to form voids. When the voids grow, the resistance value increases, the solder joint generates heat due to Joule heat, or it becomes difficult to exhibit the performance of the electronic component due to the decrease in the current density. Eventually, the solder joint breaks.

[0020] Thus, in recent years, in Sn-Ag-Cu-Bi-P solder alloys, there has been a demand for a solder alloy 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 urgent 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 present inventors 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 examples 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 applies 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] In view of the above findings, it is not simply a matter of increasing the Ag content to precipitate a large amount of Ag3Sn, but it is considered necessary to adjust the hardness appropriately to improve the drop impact resistance and heat cycle resistance. Also, when heating the solder alloy, in the temperature range higher than the solidus temperature, when measuring the thermal history with a DSC (Differential Scanning Calorimeter), it is considered necessary to prepare an alloy composition in which a large endotherm is observed in two stages to suppress chip standing. Furthermore, it is also considered necessary to suppress the generation of bridges and whiskers by adjusting the viscosity of the molten solder. In addition, it is considered necessary to improve the electromigration resistance (hereinafter simply referred to as "EM resistance") by appropriate precipitation of Ag3Sn and solid solution strengthening of the solder alloy by Bi.

[0028] Here, the effects of the solder alloy are not separately exhibited by each constituent element, but are comprehensively exhibited as one substance while contributing to each other. For this reason, if each constituent element is individually prepared to improve each characteristic, various effects cannot be simultaneously exhibited in one composition.

[0029] Therefore, in view of the above findings and the like, the present inventors have conducted a detailed search for the composition of the Sn-Ag-Cu-Bi-P solder alloy. As a result, a solder alloy having excellent drop impact resistance and heat cycle resistance, suppressing the occurrence of chip standing and bridges / whiskers, and also suppressing the occurrence of electromigration can be obtained as long as each constituent element is within a predetermined range, and the present invention has been completed. The present invention obtained based on this finding is as follows.

[0030] (0) A solder alloy characterized in that, by mass%, it consists of Ag: 0.3 to 1.9%, Cu: 0.40 to 1.00%, Bi: 05 to 4.9%, P: 0.00100 to 0.02000%, and the balance being Sn. (1) A solder alloy characterized by having an alloy composition consisting of, in 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 balance 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 contains at least one kind.

[0032] (3) The solder alloy according to any one of (0) to (2) above, wherein the alloy composition further contains each of As, In, Zr, Mn, Ti, Zn, Fe, Al, Au, Mg, Cr, and Pt in an amount of 0.06% or less by mass% and contains at least one kind.

[0033] (4) The solder alloy according to any one of (0) to (2) above, wherein the alloy composition further contains each 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% and contains at least one kind.

[0034] (5 - 6) The solder alloy according to any one of (0) to (4) above, wherein the alloy composition satisfies all of the following (1) to (3) formulas. 0.0007 ≤ Ag × Cu × Bi × P ≤ 0.0110 (Formula (1)) 110 ≤ Ag / (P × Cu) ≤ 799 (Formula (2)) 0.67 ≤ (Ag + Bi) / (Ag + Cu + Bi) ≤ 0.91 (Formula (3)) In the above (1) to (3) formulas, Ag, Cu, Bi, and P each represent the content as mass% of the alloy composition.

[0035] (7 - 8) A solder paste having solder powder made of the solder alloy according to any one of (0) to (6) above.

[0036] (9 - 10) A solder ball made of the solder alloy according to any one of (0) to (6) above.

[0037] (11~12) A solder preform made of the solder alloy according to any one of (0) to (6) above.

[0038] (13~14) A solder joint having the solder alloy according to any one of (0) to (6) above.

Brief Description of the Drawings

[0039]

Figure 1

Embodiments for Carrying Out the Invention

[0040] The present invention will be described in more detail below. In this specification, “%” regarding the alloy composition of the solder alloy is “mass %” unless otherwise specified.

[0041] 1. Solder Alloy (1) Ag: 0.3 to 1.9% Ag is an element that improves drop impact resistance, heat cycle resistance, and EM resistance, and suppresses chip standing. Since Ag can suppress the deformation of the solder alloy by the precipitation strengthening of Ag3Sn, it contributes to the improvement of heat cycle resistance and drop impact resistance. In addition, the precipitation of Ag3Sn inhibits the movement of electrons and improves EM resistance. Furthermore, in the thermal history using DSC, two large endothermic peaks are shown between the solidus temperature and the liquidus temperature during heating.

[0042] When the content of Ag is less than 0.3%, the precipitation amount of Ag3Sn is insufficient, and the heat cycle resistance and EM resistance deteriorate. In addition, chip standing also occurs frequently. The lower limit of the content of Ag is 0.3% or more, preferably 0.4% or more, more preferably 0.5% or more, and still more preferably 0.6% or more.

[0043] On the one hand, when the Ag content exceeds 1.9%, Ag3Sn forms in a network pattern, resulting in deteriorated drop impact resistance. Also, when the Ag content is 2.5% or more, the endothermic peak becomes one, and chip standing 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, still 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 of Ag is 0.6 - 1.4%. The above upper and lower limits can define a further preferred range of the Ag content.

[0044] (2) Cu: 0.40 - 1.00% Cu is an element that improves heat cycle resistance and EM resistance, and suppresses the occurrence of bridges and whiskers. Since Cu6Sn5 formed by Cu and Sn precipitates finely at the bonding interface, the bonding interface does not break even under thermal stress due to temperature differences. Also, if the Cu content is 0.40 - 1.00%, it is close to the eutectic composition of Sn and Cu, and the increase in the liquidus temperature is suppressed, so the occurrence of bridges and whiskers can be suppressed. Furthermore, since the intermetallic compound formed by Cu and Sn inhibits the movement of electrons, the EM resistance is improved.

[0045] When the Cu content is less than 0.40%, the precipitation amount of fine Cu6Sn5 becomes insufficient, and the heat cycle resistance and EM resistance deteriorate. The lower limit of the Cu content is 0.40% or more, preferably 0.50% or more.

[0046] On the other hand, when the Cu content exceeds 1.00%, the liquidus temperature rises, and the viscosity of the molten solder increases when bonding at normal temperatures, so bridges and whiskers occur frequently. The upper limit of the Cu content is 1.0% or less, preferably 0.90% or less, more preferably 0.80% or less, still more preferably 0.70% or less, even more preferably 0.60% or less. The preferred range of Cu is 0.40 to 0.70%. The above upper and lower limits can define a further preferred range of the Cu content.

[0047] (3) Bi: 0.5 to 4.9% Bi is an element that contributes to the improvement of drop impact resistance and EM resistance. Since Bi is dissolved in Sn, the crystal lattice of Sn is distorted by solid solution strengthening of Sn, and the movement of Cu is hindered, thereby improving the EM resistance.

[0048] When the content of Bi 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, still more preferably 0.8% or more, particularly preferably 0.9% or more, and most preferably 1.0% or more.

[0049] On the other hand, when the content of Bi exceeds 4.9%, Bi segregates because it exceeds the solid solubility limit of Bi, and the drop impact resistance is poor due to the hardening and embrittlement of the solder alloy. The upper limit of the Bi content is 4.9% or less, preferably 3.7% or less, more preferably 2.9% or less, still 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 of Bi is 0.5 to 3.7%. The above upper and lower limits can define a further preferred range of the Bi content.

[0050] (4) P: 0.00100 to 0.02000% P is an element that suppresses the generation of bridges and whiskers. P stays on the surface of the molten solder and inhibits the formation of tin oxide, so that the fluidity of the molten solder is appropriately maintained. Therefore, the generation of bridges and whiskers that may occur during solidification can be suppressed.

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

[0052] On the other hand, if the content of P exceeds 0.0200%, intermetallic compounds of P precipitate, resulting in frequent occurrence of bridges and spines. The upper limit of the content of P is 0.0200% or less, preferably 0.0170% or less, more preferably 0.0160% or less, still 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 of P is 0.00300 to 0.0200%. The above upper and lower limits can define a further preferred range of the content of P.

[0053] (5) At least one of Ge, Co, and Ga in a total amount of 0.06% or less, and at least one The solder alloy according to the present invention may contain Ge, Co, and Ga as optional elements in order to suppress the oxidation of the solder alloy. If the content of each of these elements is 0.06% or less, the increase in the liquidus temperature can be suppressed, so that the occurrence of bridges and spines can be further suppressed. The content of each is preferably 0.006% or less, more preferably 0.005% or less. The lower limit value is not particularly limited, but may be 0.001% or more. When a plurality of at least one of these optional elements are contained in one composition, the total may be 0.1% or less. The lower limit of the total amount may be 0.001% or more.

[0054] (6) Each of As, In, Zr, Mn, Ti, Zn, Fe, Al, Ni, Au, Mg, Cr, and Pt in an amount of 0.06% or less, and at least one 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-described effects. Among these optional elements, more preferably, it is a group of elements excluding Ni, which is an element that rapidly raises the melting point with a small content, from among the above optional elements. Specifically, the alloy composition may further contain each of As, In, Zr, Mn, Ti, Zn, Fe, Al, Au, Mg, Cr, and Pt in an amount of 0.06% or less by mass% and contain at least one kind thereof.

[0055] When containing 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, but it may be 0.001% or more. Further, when containing a plurality of at least one of these optional elements in one composition, the total may be 0.1% or less. The lower limit of the total amount may be 0.001% or more.

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

[0057] The constituent elements of the solder alloy according to the present invention 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. In order to simultaneously exhibit these effects at a higher level in one composition, in addition to each constituent element being within the above-described range, it is more preferable to satisfy formulas (1) to (3). The technical significance of each formula is as follows.

[0058] (1) The formula is a relational expression considering the balance of the contents of essential elements. (2) The formula is a relational expression regarding the contents of Ag, Cu, and P, and these elements are a group of elements that can form intermetallic compounds in the solder alloy according to the present invention. Since the intermetallic compounds can affect various properties of the present invention depending on the precipitation location, form, size, etc., any solder alloy that satisfies (2) can exhibit particularly excellent effects in one composition. (3) The formula is for the elements that strengthen the solder alloy according to the present invention. Ag and Bi are elements that contribute to the drop impact resistance. Ag, Cu, and Bi are elements that contribute to the EM resistance and heat cycle resistance, and in order to balance and raise each property to a high level, it is preferable to satisfy (3).

[0059] (1) The upper limit of the formula is preferably 0.0110 or less, more preferably 0.0094 or less, still 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, 0.0031 or less. The lower limit of the formula is preferably 0.0007 or more, more preferably 0.0009 or more, still 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, 0.0029 or more. (1) A more preferable range of the formula is 0.0017 to 0.0088. The above upper and lower limits can respectively define a further preferable range of the formula.

[0060] (2) The upper limit of the formula is preferably 799 or less, more preferably 733 or less, still 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 the formula is preferably 110 or more, more preferably 129 or more, still 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 of the formula (2) is 138 to 733. The above upper and lower limits can each define a further preferred range of the formula (2).

[0061] (3) The upper limit of the formula is preferably 0.91 or less, more preferably 0.89 or less, still 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 the formula is preferably 0.67 or more, more preferably 0.68 or more, still 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 of the formula (3) is 0.76 to 0.89. The above upper and lower limits can each define a further preferred range of the formula (1).

[0062] For the calculations of formulas (1) to (3), the numerical values shown in Tables 1 and 2, which are the measured values of the alloy composition, were used. For the values calculated from formulas (1) to (3), formula (1) was calculated to the fourth decimal place, formula (2) was calculated to the first digit as an integer, and formula (3) was calculated to the second decimal place. This calculation rule is used in this application, and since all solder alloys must be treated in the same way, it is intended to be used in the same way for the calculations of other solder alloys described in other documents, etc.

[0063] (7) Balance: Sn The balance of the solder alloy according to the present invention is Sn. It may contain inevitable impurities in addition to the above-described elements. Even when it contains inevitable impurities, it does not affect the above-described effects. Further, as will be described later, even if an element not contained in the present invention is contained as an inevitable impurity, it does not affect the above-described effects.

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

[0065] 3. Solder ball The solder alloy according to the present invention can be used as a solder ball. When used as a solder ball, a solder ball can be manufactured by using the dropping method, which is a general method in the art, for the solder alloy according to the present invention. Further, a solder joint can be manufactured by processing in a general method in the art, such as mounting and joining a solder ball to an electrode printed with a flux. The particle size of the solder ball is preferably 1 μm or more, more preferably 10 μm or more, still more preferably 20 μm or more, and particularly preferably 30 μm or more. The upper limit of the particle size of the solder ball is preferably 3000 μm or less, more preferably 1000 μm or less, still 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 the shape of the preform include a washer, a ring, a pellet, a disk, a ribbon, a wire, etc. It can also be used as a bar solder.

[0067] 5. Solder Joint 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, for example, semiconductors using elements, substrates, electronic components, printed circuit boards, insulating substrates, heat sinks, lead frames, electrode terminals, etc., and power modules, inverter products, etc., using the solder alloy according to the present invention.

[0068] The joining method using the solder alloy according to the present invention may be carried out according to a conventional method using, for example, the reflow method. The melting temperature of the solder alloy when performing flow soldering may be approximately 20°C higher than the liquidus temperature. Also, when joining using the solder alloy according to the present invention, the alloy structure can be made finer by considering the cooling rate during solidification. For example, the solder joint is cooled at a cooling rate of 2 to 3°C / s or more. Other joining conditions can be appropriately adjusted according to the alloy composition of the solder alloy.

[0069] 6. Applications The solder alloy according to the present invention can exhibit its effects particularly when used for flow soldering among various soldering techniques. It is effective when performing flow soldering on a multilayer substrate in which a plurality of substrates are laminated. Since the composition of the jet solder in flow soldering may vary when used for a long time, it can also be used as a replenishing solder for making the jet solder have a desired composition. In this case, the replenishing solder can be replenished by adjusting the composition within the scope of the present invention. The temperature of the jet solder when performing flow soldering is generally 230 to 260°C. Also, other joining conditions can be appropriately adjusted according to the alloy composition, solid fraction, and liquid fraction of the solder alloy.

[0070] 7. Manufacturing Method of Solder Alloy The solder alloy according to the present invention may be manufactured by previously producing SnAg alloy and SnCu alloy and then melting them together with Bi and P. As a manufacturing example, alloys of Sn and Ag, and Sn and Cu may be produced, each alloy may be weighed to a predetermined amount, and Bi and P may be weighed and then produced. The reason for manufacturing in this way can be explained as follows. To dissolve Ag with a melting point of about 860°C and Cu with a melting point of about 1100°C in Sn, a lot of time would be spent. In particular, since Cu has significant surface oxidation, it will be affected by oxidation if the dissolution time is long. On the other hand, if an SnAg alloy with Ag previously dissolved in Sn and an SnCu alloy with Cu previously dissolved in Sn are each prepared in advance, the dissolution time in Sn can be significantly shortened. The intermetallic compounds formed when each alloy is produced, for example, the melting point of Cu6Sn5 is 415°C, the melting point of Ag3Sn is 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 produce a low-alpha-ray alloy by using a low-alpha-ray wire as its raw material. Such a low-alpha-ray alloy can suppress soft errors when used for forming solder bumps around the memory.

Examples

[0072] Using the solder alloys having the alloy compositions shown in Tables 1 to 2, as Evaluation 1, a drop impact test (DROP), as Evaluation 2, a thermal cycle test (TCT), as Evaluation 3, chip standing, as Evaluation 4, bridge whiskers, and as Evaluation 5, the electromagnetic resistance was evaluated. Each evaluation method will be described below.

[0073] Evaluation 1: Drop Impact Test (DROP) Each of the solder alloys shown in Tables 1 and 2 was atomized to obtain solder powder. It was mixed with a soldering flux (GLV manufactured by Senju Metal Industry Co., Ltd.) composed of rosin, a solvent, an activator, a thixotropic agent, an organic acid, etc. to prepare a solder paste of each solder alloy. The alloy powder of the solder paste was 88% by mass, and the flux was 12% by mass.

[0074] The solder paste was printed on a printed circuit board (material: FR-4) with a thickness of 0.8 mm using a metal mask with a thickness of 100 μm. Then, five BGA components were mounted on each board using a mounter, and reflow soldering was performed under the conditions of a maximum temperature of 240°C and a holding time of 60 seconds to produce two test boards. Subsequently, each board was separated into individual pieces (the board was divided into five pieces), resulting in a total of ten evaluation samples.

[0075] Next, both ends of the evaluation samples were fixed to the pedestal with bolts so that the BGA components faced the pedestal side. In this state, while measuring the electrical resistance value in accordance with the JEDEC standard, an impact of 1500 G was applied to evaluate the shock resistance. The progress of cracking 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 and less than 100, it was judged as "〇". If the number of drops was less than 90, it was judged as "×".

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

[0077] Evaluation 3: Chip Standing A solder paste was prepared in the same manner as in Evaluation 1. This solder paste was printed on the Cu lands of a 6-layer printed circuit board (FR-4, Cu-OSP) with a 150-μm metal mask, and then 12 3216 chip resistors were mounted with a mounter. Thereafter, melting was performed under heating conditions of a maximum temperature of 245°C and a holding time of 40 seconds to perform reflow, and soldering was performed to fabricate a test substrate. The number of standing chips after mounting was counted. When the number of standing chips was 0, it was judged as "◎". When the number of standing chips was 1, it was judged as "〇". When the number of standing chips was 2 or more, it was judged as "×".

[0078] Evaluation 4: Bridge and whisker First, 12 four-terminal Sn-plated resistors with a terminal width of 0.5 mm and a terminal pitch of 0.8 mm were prepared, and their terminals were inserted into the through-holes of a glass epoxy printed circuit board (CEM-3). The solder alloys shown in Tables 1 and 2 were introduced into a solder bath for flow soldering. For flow soldering, a flow simulator FS-1 manufactured by Malcolm Co., Ltd. was used, and flow soldering was performed under the following test conditions.

[0079] Test conditions Solder bath: Flow simulator FS-1 manufactured by Malcolm Co., Ltd. Solder amount: 15 kg Flux: Flux manufactured by Senju Metal Industry Co., Ltd. (product name: ES-1061SP2) Solder temperature in the solder bath: 255°C

[0080] Whether a bridge occurred was visually evaluated. Also, whether whiskers occurred on the fillets was visually confirmed. When no bridge or whisker could be confirmed, it was evaluated as "◎". When the number of resistors with a bridge or whisker was 1 to 2, it was evaluated as "〇". When the number of resistors with a bridge or whisker was 3 or more, it was evaluated as "×".

[0081] Evaluation 5: EMI 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. Reflow soldering was performed using a water-soluble flux on a 12 mm × 12 mm package substrate having a Cu electrode with a diameter of 0.24 mm to fabricate a package. Thereafter, a solder paste with a Sn-3.0Ag-0.5Cu composition was printed on a glass epoxy substrate (FR-4) with a size of 29 mm × 19 mm and a thickness of 0.8 mm, and the package fabricated above was mounted thereon to fabricate a reflow soldering test substrate under the conditions of a maximum temperature of 240°C and a holding time of 90 seconds.

[0082] The fabricated test substrate was connected to a compact variable switching power supply (manufactured by Kikusui Electronics Industry Co., Ltd.: PAK-A), and in a silicone oil bath maintained at 125°C, the current density was 100 A / mm 2 and the test substrate was energized under the condition that the voltage was 5.0 V. During the energization, the electrical resistance of the sample was continuously measured, and the time required for the resistance to increase by 150% from the initial resistance value was measured. If it exceeded 350 hours, it was evaluated as "◎", if it was between 300 and 350 hours, it was evaluated as "〇", and if it was less than 300 hours, it 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, in all of Examples 1 to 51, all evaluations were "〇" or "◎". In particular, Examples 2, 3, 10 to 22, 26 to 45, and 47 to 50, which do not contain Ni and satisfy formulas (1) to (3), all showed results with "◎" in all evaluation judgments, indicating superiority among the examples.

[0086] On the one hand, in Comparative Examples 1 and 2, since the Ag content was low, the TCT, chip standing, and EM resistance were inferior. In Comparative Example 3, since the Ag content was high, the DROP was inferior. In Comparative Examples 4 to 10, since the Ag content was even higher in all of them, chip standing occurred in addition to the DROP.

[0087] In Comparative Examples 11 and 12, since the Cu content was low, the TCT and EM resistance were inferior. In Comparative Example 13, since the Cu content was high, bridges and whiskers occurred frequently. In Comparative Example 14, since the Bi content was low, the EM resistance was inferior. In Comparative Examples 15 to 19, since the Bi content was high, the DROP was inferior. In Comparative Examples 20 to 22, since the P content was not appropriate, bridges and whiskers occurred frequently.

[0088] Regarding the samples for which the EM resistance was evaluated, the results of observing the cross-section of the solder joint are shown in FIG. 1. FIG. 1 is a cross-sectional SEM photograph of the solder joint. FIG. 1(a) is Comparative Example 1, and FIG. 1(b) is Example 22. As is clear from FIG. 1(a), in the region surrounded by the square in Comparative Example 1, it was found that the Cu of the upper electrode was scraped and Cu was deposited on the lower electrode. On the other hand, as is clear from FIG. 1(b), in the region surrounded by the square in Example 22, no movement of Cu was observed. Similar results were obtained in other examples. Note that general Cu erosion is a phenomenon in which both electrodes are eroded, and as shown in FIG. 1(a), since Cu does not deposit on the other electrode, Cu erosion and electromigration can be easily distinguished.

Claims

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

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

3. 3. The solder alloy according to claim 1, wherein the alloy composition further contains, in mass%, at least one of As, In, Zr, Mn, Ti, Zn, Fe, Al, Au, Mg, and Pt in an amount of 0.06% or less.

4. The solder alloy according to claim 1 or 2, wherein the alloy composition satisfies all of the following formulas (1) to (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 the above formulas (1) to (3), Ag, Cu, Bi, and P each represent the content in mass % of the alloy composition.

5. The solder alloy according to claim 3, wherein the alloy composition satisfies all of the following formulas (1) to (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 the above formulas (1) to (3), Ag, Cu, Bi, and P each represent the content in mass % of the alloy composition.

6. A solder paste comprising a solder powder made of the solder alloy according to claim 1 or 2.

7. A solder paste comprising a solder powder made of the solder alloy according to claim 3.

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

9. A solder ball made of the solder alloy according to claim 3.

10. A solder preform comprising the solder alloy according to claim 1 or 2.

11. A solder preform comprising the solder alloy according to claim 3.

12. A solder joint comprising the solder alloy according to claim 1 or 2.

13. A solder joint comprising the solder alloy of claim 3.

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