JP2020011294A - Solder alloy, solder powder, solder paste, and solder joint with use thereof - Google Patents

Abstract

To provide a solder alloy which suppresses paste change over time and is excellent in wettability, in which a temperature difference between a liquidus line temperature and a solidus line temperature is small, and which has high and excellent mechanical property, a solder powder, a solder paste, and a solder joint with use thereof.SOLUTION: A solder alloy has an alloy composition comprising As: 25 to 300 ppm by mass, Bi: 0 ppm by mass or more and 25000 ppm or less and Pb: more than 0 ppm by mass and 8000 ppm by mass or less and the remainder of Sn in order to suppress viscosity change over time and become a homogeneous structure, and satisfies the following formulae (1) and (2): 275≤2As+Bi+Pb (1), 0<2.3×10×Bi+8.2×10×Pb≤7 (2). In the formulae (1) and (2), As, Bi, and Pb respectively represent a content (ppm by mass) in the alloy composition.SELECTED DRAWING: None

Description

  The present invention relates to a solder alloy, a solder powder, a solder paste, which suppresses a change over time of a paste, has excellent wettability, and has a small temperature difference between a liquidus temperature and a solidus temperature, and a solder joint using the same.

  In recent years, electronic devices having solder joints such as CPUs (Central Processing Units) have been required to be smaller and have higher performance. Accordingly, it is necessary to reduce the size of the printed circuit board and the electrodes of the electronic device. Since an electronic device is connected to a printed circuit board via an electrode, the size of the electrode is reduced, and the size of the solder joint connecting the two is also reduced.

  In order to connect an electronic device and a printed board via such fine electrodes, a solder paste is generally used. The solder paste is supplied on the electrodes of the printed circuit board by printing or the like. Solder paste printing consists of placing a metal mask with an opening on a printed circuit board, moving the squeegee while pressing it against the metal mask, and applying the solder paste to the electrodes on the printed circuit board from the metal mask opening. It is performed by Thereafter, the electronic component is placed on the solder paste printed on the printed circuit board and held by the solder paste until the soldering is completed.

  And, for example, when it takes several hours from when the electronic component is mounted on the printed circuit board to when it is introduced into the reflow furnace, the solder paste cannot maintain its shape at the time of printing due to the aging of the solder paste. is there. In this case, it may cause the inclination of the electronic component or the bonding failure. In addition, when the solder paste is purchased, it is not usually used up in one printing, so that the solder paste must maintain an appropriate viscosity at the beginning of manufacturing so as not to deteriorate the printing performance.

  However, in recent years, as the size of the electrode has been reduced, the printed area of the solder paste has also been reduced, so that the time until the purchased solder paste has been used has been prolonged. Solder paste is a mixture of solder powder and flux, and if the storage period is long, the viscosity of the solder paste will increase depending on the storage conditions, and the printing performance at the time of purchase cannot be exhibited. Sometimes.

  Therefore, for example, Patent Document 1 includes Sn and one or more kinds selected from the group consisting of Ag, Bi, Sb, Zn, In, and Cu in order to suppress the change with time of the solder paste. Also, a solder alloy containing a predetermined amount of As is disclosed. The document shows that the viscosity after 2 weeks at 25 ° C. is less than 140% as compared with the viscosity at the beginning of production.

JP-A-2005-98052

  As described above, the invention described in Patent Document 1 is a solder alloy that can selectively contain six types of elements in addition to Sn and As. In addition, the document shows that a high As content results in inferior meltability.

  Here, the meltability evaluated in Patent Document 1 is considered to correspond to the wettability of the molten solder. The meltability disclosed in this document is evaluated by observing the appearance of the melt with a microscope and by the presence or absence of solder powder that cannot be melted completely. This is because if the wettability of the molten solder is high, the solder powder that cannot be completely melted hardly remains.

  Generally, in order to improve the wettability of molten solder, it is necessary to use a highly active flux. In the flux described in Patent Document 1, it is considered that a highly active flux may be used in order to suppress the deterioration of wettability due to As. However, when a highly active flux is used, the rate of increase in the viscosity of the flux increases. Also, in view of the description of Patent Document 1, it is necessary to increase the As content in order to suppress the increase in the viscosity increase rate. In order for the solder paste described in Patent Document 1 to exhibit a further lower viscosity increase rate and excellent wettability, it is necessary to continuously increase the flux activation power and As content, which causes a vicious cycle.

  Recently, solder pastes are required to maintain stable performance for a long period of time irrespective of use environment or storage environment, and further higher wettability is required due to miniaturization of solder joints. When trying to respond to recent demands using the solder paste described in Patent Document 1, a vicious cycle is inevitable as described above.

  Furthermore, in order to join fine electrodes, it is necessary to improve the mechanical properties and the like of the solder joint. For some elements, when the content increases, the liquidus temperature rises, the liquidus temperature and the solidus temperature broaden, and segregates during solidification to form a non-uniform alloy structure. When the solder alloy has such an alloy structure, mechanical properties such as tensile strength are inferior and the solder alloy is easily broken by an external stress. This problem has become remarkable with the recent miniaturization of electrodes.

  The object of the present invention is to suppress the change over time of the paste, to have excellent wettability, a solder alloy having high mechanical properties with a small temperature difference between the liquidus temperature and the solidus temperature, solder powder, solder paste, and It is to provide a solder joint using these.

  When the suppression of the aging of the paste and the improvement of the excellent wettability are simultaneously improved, it is necessary to use a flux having a high activity and avoid a vicious cycle due to an increase in the As content. The present inventors have focused on the alloy composition of the solder powder, and have conducted intensive studies in order to achieve both suppression of temporal change of the paste and excellent wettability regardless of the type of flux.

  First, the present inventors studied a solder powder containing As as a basic composition based on Sn, SnCu, and SnAgCu solder alloys conventionally used as solder alloys. Then, the As content was investigated by paying attention to the cause of suppressing the temporal change of the solder paste when this solder powder was used.

  It is considered that the reason why the viscosity of the solder paste increases with time is that the solder powder reacts with the flux. When the results of Example 4 of Table 1 of Patent Document 1 and Comparative Example 2 are compared, it is found that the viscosity increase rate is lower when the As content exceeds 100 mass ppm. In view of these, it was considered that the As content may be further increased when attention is paid to the effect of suppressing the temporal change of the paste (hereinafter, appropriately referred to as “thickening suppressing effect”). It was confirmed that when the As content was increased, the thickening suppressing effect was slightly increased with the As content, but when the As content was too large, the wettability of the solder alloy was deteriorated.

  Therefore, the present inventors came to the conclusion that it was necessary to add an element exhibiting a thickening suppressing effect in addition to As. When the various elements were investigated, Bi and Pb were found to be the same as As. The knowledge which exerts the effect of was obtained. The reason for this is not clear, but is presumed as follows.

  Since the effect of suppressing thickening is exhibited by suppressing the reaction with the flux, an element having low reactivity with the flux includes an element having a low ionization tendency. Generally, the ionization of an alloy is considered based on the ionization tendency as an alloy composition, that is, the standard electrode potential. For example, a SnAg alloy containing Ag which is noble to Sn is less likely to be ionized than Sn. For this reason, an alloy containing an element nobler than Sn is less likely to be ionized, and it is presumed that the effect of suppressing thickening of the solder paste is high.

  Here, in Patent Document 1, Bi, Sb, Zn, and In are listed as equivalent elements in addition to Sn, Ag, and Cu. However, in terms of ionization tendency, In and Zn are lower than Sn. Element. In other words, Patent Literature 1 describes that the effect of suppressing thickening can be obtained even when an element lower than Sn is added. For this reason, it is considered that a solder alloy containing an element selected according to the ionization tendency can obtain a thickening suppression effect equal to or greater than that of the solder alloy described in Patent Document 1. Further, as described above, when the As content increases, the wettability deteriorates.

  The present inventors investigated in detail Bi and Pb found as a thickening suppressing effect. Since Bi and Pb lower the liquidus temperature of the solder alloy, when the heating temperature of the solder alloy is constant, the wettability of the solder alloy is improved. However, since the solidus temperature remarkably decreases depending on the content, ΔT, which is the temperature difference between the liquidus temperature and the solidus temperature, becomes too wide. If ΔT is too wide, segregation occurs at the time of solidification, leading to a decrease in mechanical properties such as mechanical strength. Since the phenomenon that ΔT is widespread becomes remarkable when Bi and Pb are added simultaneously, strict control is required.

  In the Sn, SnCu solder alloy, and SnAgCu solder alloy, the content of As, Bi, and Pb must be set so that the thickening suppression effect, excellent wettability, and narrowing of ΔT all show excellent results. We thought that it was necessary to manage the contents of these elements comprehensively instead of managing them individually. Therefore, the present inventors have conducted various studies on the contents of these three elements, and as a result, when the contents of the respective elements satisfy a predetermined relational expression within the range of the predetermined amounts, the present inventors have found that the increase has occurred. The present invention was completed based on the finding that all of the viscosity suppressing effect, the wettability, and the narrowing of ΔT show excellent results.

The present invention obtained based on these findings is as follows.
(1) As: 25 to 300 mass ppm, Bi: 0 mass ppm to 25,000 mass ppm, Pb: more than 0 mass ppm to 8000 mass ppm, and the balance has an alloy composition consisting of Sn, and the following formula (1) And a solder alloy satisfying the formula (2).

275 ≦ 2As + Bi + Pb (1)
0 <2.3 × 10 ⁻⁴ × Bi + 8.2 × 10 ⁻⁴ × Pb ≦ 7 (2)
In the above formulas (1) and (2), As, Bi, and Pb each represent the content (ppm by mass) in the alloy composition.

(2) The solder alloy according to (1), wherein the alloy composition further satisfies the following formula (1a).
275 ≦ 2As + Bi + Pb ≦ 25200 (1a)
In the above formula (1a), As, Bi, and Pb each represent the content (mass ppm) in the alloy composition.

(3) The solder alloy according to (1), wherein the alloy composition satisfies the following formula (1b).
275 ≦ 2As + Bi + Pb ≦ 5300 (1b)
In the above formula (1b), As, Bi, and Pb each represent the content (mass ppm) in the alloy composition.

  (4) The solder alloy according to any one of (1) to (3), wherein the alloy composition satisfies the following expression (2a).

0.02 ≦ 2.3 × 10 ⁻⁴ × Bi + 8.2 × 10 ⁻⁴ × Pb ≦ 0.9 (2a)
In the above formula (2a), Bi and Pb each represent the content (mass ppm) in the alloy composition.

  (5) The alloy composition according to any one of (1) to (4), wherein the alloy composition contains at least one of Ag: 0 to 4% by mass and Cu: 0 to 0.9% by mass. Solder alloy.

  (6) A solder powder comprising the solder alloy according to any one of (1) to (5).

(7) A solder paste having the solder powder according to (6).
(8) The solder paste according to the above (7), further comprising a zirconium oxide powder.

  (9) The solder paste according to the above (8), wherein the solder paste contains 0.05 to 20.0% by mass of zirconium oxide powder based on the total mass of the solder paste.

  (10) A solder joint having the solder alloy according to any one of (1) to (5).

  The present invention is described in more detail below. In this specification, “ppm” regarding the solder alloy composition is “mass ppm” unless otherwise specified. “%” Is “% by mass” unless otherwise specified.

1. Alloy composition (1) As: 25 to 300 ppm
As is an element capable of suppressing a change with time in the viscosity of the solder paste. It is presumed that As has low reactivity with flux and is an element noble to Sn, so that it can exhibit a thickening suppressing effect. If the content of As is less than 25 ppm, the effect of suppressing thickening cannot be sufficiently exerted. The lower limit of the As content is 25 ppm or more, preferably 50 ppm or more, and more preferably 100 ppm or more. On the other hand, if the content of As is too large, the wettability of the solder alloy deteriorates. The upper limit of the As content is 300 ppm or less, preferably 250 ppm or less, and more preferably 200 ppm or less.

(2) Bi: 0 ppm or more and 25,000 ppm or less, Pb: more than 0 ppm and 8000 ppm or less Bi and Pb are elements having low reactivity with flux and exhibiting a thickening suppressing effect. Further, these elements are elements that can suppress the deterioration of wettability due to As in order to lower the liquidus temperature of the solder alloy and reduce the viscosity of the molten solder.

  If Pb or Bi in some cases exists, deterioration of wettability by As can be suppressed. When the solder alloy according to the present invention contains Bi, the lower limit of the Bi content is more than 0 ppm, preferably 25 ppm or more, more preferably 50 ppm or more, even more preferably 75 ppm or more, and particularly preferably. It is at least 100 ppm, most preferably at least 250 pp. The lower limit of the Pb content is more than 0 ppm, preferably 25 ppm or more, more preferably 50 ppm or more, further preferably 75 ppm or more, particularly preferably 100 ppm or more, and most preferably 250 pp or more.

  On the other hand, if the content of these elements is too large, the solidus temperature is remarkably lowered, so that ΔT, which is the temperature difference between the liquidus temperature and the solidus temperature, becomes too wide. If ΔT is too wide, a liquid phase Bi or Pb is concentrated in the solidification process of the molten solder because a high melting point crystalline phase having a low content of Bi or Pb is deposited. Thereafter, when the temperature of the molten solder further decreases, a low melting point crystalline phase having a high concentration of Bi or Pb segregates. For this reason, the mechanical strength and the like of the solder alloy deteriorate. In particular, since the crystal phase having a high Bi concentration is hard and brittle, segregation in the solder alloy significantly lowers the mechanical strength and the like.

  From such a viewpoint, when the solder alloy according to the present invention contains Bi, the upper limit of the Bi content is 25,000 ppm or less, preferably 10000 ppm or less, more preferably 1000 ppm or less, further more preferably 600 ppm or less. And particularly preferably 500 ppm or less. The upper limit of the Pb content is 8000 ppm or less, preferably 5100 ppm or less, more preferably 5000 ppm or less, further preferably 1000 ppm or less, particularly preferably 850 ppm or less, and most preferably 500 ppm or less.

(3) Formula (1) The solder alloy according to the present invention needs to satisfy the following formula (1).

275 ≦ 2As + Bi + Pb (1)
In the above formula (1), As, Bi, and Pb each represent the content (mass ppm) in the alloy composition.

  As, Bi and Pb are all elements that exhibit a thickening suppressing effect. Thickening inhibition The sum of these needs to be 230 ppm or more. In the formula (1), the reason why the As content is doubled is that As has a higher viscosity-suppressing effect than Bi or Pb.

  If the value of the expression (1) is less than 275, the effect of suppressing thickening is not sufficiently exhibited. The lower limit of the formula (1) is 275 or more, preferably 300 or more, more preferably 700 or more, and even more preferably 900 or more. On the other hand, the upper limit of (1) is not particularly limited from the viewpoint of the effect of suppressing thickening, but is preferably 25200 or less, more preferably 15200 or less, from the viewpoint of setting ΔT in a suitable range. It is more preferably at most 10,200, particularly preferably at most 8,200, most preferably at most 5,300.

  The following formulas (1a) and (1b) are those in which the upper and lower limits are appropriately selected from the above preferred embodiments.

275 ≦ 2As + Bi + Pb ≦ 25200 (1a)
275 ≦ 2As + Bi + Pb ≦ 5300 (1b)
In the above formulas (1a) and (1b), As, Bi, and Pb each represent the content (mass ppm) in the alloy composition.

(4) Formula (2) The solder alloy according to the present invention needs to satisfy the following formula (2).

0 <2.3 × 10 ⁻⁴ × Bi + 8.2 × 10 ⁻⁴ × Pb ≦ 7 (2)
In the above formula (2), Bi and Pb each represent the content (mass ppm) in the alloy composition.

  Bi and Pb suppress the deterioration of wettability due to the inclusion of As. However, if the content is too large, ΔT increases, so strict control is required. Particularly, in an alloy composition containing Bi and Pb simultaneously, ΔT tends to increase. In the present invention, an increase in ΔT can be suppressed by defining the sum of values obtained by multiplying the Bi and Pb contents by a predetermined coefficient. In the equation (2), the coefficient of Pb is larger than the coefficient of Bi. This is because Pb has a large contribution to ΔT as compared with Bi, and ΔT greatly increases even if the content is slightly increased.

  (2) The solder alloy in which the formula is 0 does not contain both elements of Bi and Pb, so that the deterioration of wettability due to the inclusion of As cannot be suppressed. The lower limit of the formula (2) is more than 0, preferably 0.02 or more, more preferably 0.03 or more, further more preferably 0.05 or more, and particularly preferably 0.06 or more. , Most preferably 0.11 or more. On the other hand, if the expression (2) exceeds 7, the temperature range of ΔT becomes too wide, so that a crystal phase having a high concentration of Bi or Pb is segregated during solidification of the molten solder, and the mechanical strength and the like deteriorate. The upper limit of (2) is 7 or less, preferably 6.56 or less, more preferably 6.40 or less, still more preferably 5.75 or less, and even more preferably 4.18 or less. , Particularly preferably 2.30 or less, and most preferably 0.90 or less.

  The following formula (2a) is obtained by appropriately selecting the upper and lower limits from the above preferred embodiments.

0.02 ≦ 2.3 × 10 ⁻⁴ × Bi + 8.2 × 10 ⁻⁴ × Pb ≦ 0.9 (2a)
In the above formula (2a), Bi and Pb each represent the content (mass ppm) in the alloy composition.

(4) At least one of Ag: 0 to 4% and Cu: 0 to 0.9% Ag is an optional element that can form Ag ₃ Sn at the crystal interface to improve the mechanical strength and the like of the solder alloy. It is. Ag is an element whose ionization coefficient is noble to Sn, and promotes the effect of suppressing thickening of these elements by coexisting with As, Pb, and Bi. The Ag content is preferably 0 to 4%, more preferably 0.5 to 3.5%, and still more preferably 1.0 to 3.0%.

  Cu is an optional element that can improve the bonding strength of the solder joint. Further, Cu is an element whose ionization coefficient is noble with respect to Sn and coexists with As, Pb, and Bi to promote the effect of suppressing thickening of these elements. The Cu content is preferably 0 to 0.9%, more preferably 0.1 to 0.8%, and still more preferably 0.2 to 0.7%.

(5) Remainder: Sn
The balance of the solder alloy according to the present invention is Sn. Inevitable impurities may be contained in addition to the aforementioned elements. Even if unavoidable impurities are contained, the effects described above are not affected. Further, as described later, even if an element which is not contained in the present invention is contained as an unavoidable impurity, the above-mentioned effect is not affected. If the content of In is too large, ΔT is widened. Therefore, if the content is 1000 ppm or less, the above-mentioned effect is not affected.

2. Solder Powder The solder powder according to the present invention is used for a solder paste described later. The solder powder according to the present invention preferably satisfies the size (particle size distribution) satisfying the symbols 1 to 8 in the powder size classification (Table 2) in JIS Z 3284-1: 2004. More preferably, it is a size (particle size distribution) that satisfies the symbols 4 to 8, and still more preferably a size (particle size distribution) that satisfies the symbols 5 to 8. When the particle size satisfies this condition, the surface area of the powder is not so large that the increase in viscosity is suppressed, and the aggregation of the fine powder is suppressed, so that the increase in viscosity may be suppressed. For this reason, soldering to finer components becomes possible.

3. Solder Paste The solder paste according to the present invention contains the above-mentioned solder powder and flux.

(1) Components of flux The flux used for the solder paste is an organic acid, an amine, an amine hydrohalide, an organic halogen compound, a thixo agent, a rosin, a solvent, a surfactant, a base agent, a polymer compound, a silane. A coupling agent, a coloring agent, or a combination of two or more.

  As organic acids, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dimer acid, propionic acid, 2,2-bishydroxymethylpropionic acid, tartaric acid, malic acid, glycolic acid, Examples include diglycolic acid, thioglycolic acid, dithioglycolic acid, stearic acid, 12-hydroxystearic acid, palmitic acid, oleic acid and the like.

  As the amine, ethylamine, triethylamine, ethylenediamine, triethylenetetramine, 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenyl Imidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1- Cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazolium trimellitate, 1-cyanoethyl-2-phenylimidazo Um trimellitate, 2,4-diamino-6- [2'-methylimidazolyl- (1 ')]-ethyl-s-triazine, 2,4-diamino-6- [2'-undecylimidazolyl- (1 ')]-Ethyl-s-triazine, 2,4-diamino-6- [2'-ethyl-4'-methylimidazolyl- (1')]-ethyl-s-triazine, 2,4-diamino-6 [2'-Methylimidazolyl- (1 ')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4- Methyl-5-hydroxymethylimidazole, 2,3-dihydro-1H-pyrrolo [1,2-a] benzimidazole, 1-dodecyl-2-methyl-3-benzyl Midazolium chloride, 2-methylimidazoline, 2-phenylimidazoline, 2,4-diamino-6-vinyl-s-triazine, 2,4-diamino-6-vinyl-s-triazine isocyanuric acid adduct, 2,4 -Diamino-6-methacryloyloxyethyl-s-triazine, epoxy-imidazole adduct, 2-methylbenzimidazole, 2-octylbenzimidazole, 2-pentylbenzimidazole, 2- (1-ethylpentyl) benzimidazole, 2-nonyl Benzimidazole, 2- (4-thiazolyl) benzimidazole, benzimidazole, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3'-tert-butyl-5 ' -Methylphenyl) -5-chlorobe Benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-amylphenyl) benzotriazole, 2- (2'-hydroxy-5'-tert-octylphenyl) benzotriazole, 2,2 '-Methylenebis [6- (2H-benzotriazol-2-yl) -4-tert-octylphenol], 6- (2-benzotriazolyl) -4-tert-octyl-6'-tert-butyl-4' -Methyl-2,2'-methylenebisphenol, 1,2,3-benzotriazole, 1- [N, N-bis (2-ethylhexyl) aminomethyl] benzotriazole, carboxybenzotriazole, 1- [N, N- Bis (2-ethylhexyl) aminomethyl] methylbenzotriazole, 2,2 '-[[(methyl-1H-benzo Liazol-1-yl) methyl] imino] bisethanol, 1- (1 ′, 2′-dicarboxyethyl) benzotriazole, 1- (2,3-dicarboxypropyl) benzotriazole, 1-[(2-ethylhexyl) Amino) methyl] benzotriazole, 2,6-bis [(1H-benzotriazol-1-yl) methyl] -4-methylphenol, 5-methylbenzotriazole, 5-phenyltetrazole and the like.

  Amine hydrohalide is a compound obtained by reacting an amine with a hydrogen halide. Examples of the amine include ethylamine, ethylenediamine, triethylamine, methylimidazole, 2-ethyl-4-methylimidazole, and the like. Examples include hydrides of chlorine, bromine and iodine.

  Examples of the organic halogen compound include 1-bromo-2-butanol, 1-bromo-2-propanol, 3-bromo-1-propanol, 3-bromo-1,2-propanediol, and 1,4-dibromo-2-butanol. , 1,3-dibromo-2-propanol, 2,3-dibromo-1-propanol, 2,3-dibromo-1,4-butanediol, 2,3-dibromo-2-butene-1,4-diol and the like Is mentioned.

  Examples of the thixo agent include a wax thixo agent and an amide thixo agent. Examples of the wax-based thixotropic agent include castor hardened oil. Amide-based thixotropic agents include lauric acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, hydroxystearic acid amide, saturated fatty acid amide, oleic acid amide, erucic acid amide, unsaturated fatty acid amide, p-toluene methane amide, Aromatic amide, methylenebisstearic acid amide, ethylenebislauric acid amide, ethylenebishydroxystearic acid amide, saturated fatty acid bisamide, methylenebisoleic acid amide, unsaturated fatty acid bisamide, m-xylylenebisstearic acid amide, aromatic bisamide , Saturated fatty acid amide, unsaturated fatty acid amide, aromatic polyamide, substituted amide, methylol stearic amide, methylol amide, fatty acid ester Amide, and the like.

  Examples of the base agent include polyethylene glycol and rosin. Examples of the rosin include raw rosins such as gum rosin, wood rosin and tall oil rosin, and derivatives obtained from the raw rosin. Examples of the derivative include purified rosin, hydrogenated rosin, disproportionated rosin, polymerized rosin and α, β unsaturated carboxylic acid modified products (acrylated rosin, maleated rosin, fumarated rosin, etc.), and the polymerized rosin And hydrogenated and disproportionated products of the above, and purified, hydrogenated and disproportionated products of the α, β unsaturated carboxylic acid-modified product, and two or more of them can be used. Further, in addition to the rosin resin, at least one resin selected from a terpene resin, a modified terpene resin, a terpene phenol resin, a modified terpene phenol resin, a styrene resin, a modified styrene resin, a xylene resin, and a modified xylene resin is further added. Can be included. As the modified terpene resin, an aromatic modified terpene resin, a hydrogenated terpene resin, a hydrogenated aromatic modified terpene resin, or the like can be used. As the modified terpene phenol resin, a hydrogenated terpene phenol resin or the like can be used. As the modified styrene resin, a styrene acrylic resin, a styrene maleic acid resin, or the like can be used. Examples of the modified xylene resin include a phenol-modified xylene resin, an alkylphenol-modified xylene resin, a phenol-modified resole-type xylene resin, a polyol-modified xylene resin, and a polyoxyethylene-added xylene resin.

Examples of the solvent include water, alcohol solvents, glycol ether solvents, terpineols, and the like. Examples of alcohol solvents include isopropyl alcohol, 1,2-butanediol, isobornylcyclohexanol, 2,4-diethyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol, 2,5 -Dimethyl-2,5-hexanediol, 2,5-dimethyl-3-hexyne-2,5-diol, 2,3-dimethyl-2,3-butanediol, 1,1,1-tris (hydroxymethyl) Ethane, 2-ethyl-2-hydroxymethyl-1,3-propanediol, 2,2'-oxybis (methylene) bis (2-ethyl-1,3-propanediol), 2,2-bis (hydroxymethyl)
-1,3-propanediol, 1,2,6-trihydroxyhexane, bis [2,2,2-tris (hydroxymethyl) ethyl] ether, 1-ethynyl-1-cyclohexanol, 1,4-cyclohexanediol 1,4-cyclohexanedimethanol, erythritol, threitol, guaiacol glycerol ether, 3,6-dimethyl-4-octyne-3,6-diol, 2,4,7,9-tetramethyl-5-decyne-4 , 7-diol and the like. Examples of glycol ether solvents include diethylene glycol mono-2-ethylhexyl ether, ethylene glycol monophenyl ether, 2-methylpentane-2,4-diol, diethylene glycol monohexyl ether, diethylene glycol dibutyl ether, and triethylene glycol monobutyl ether. .

  Examples of the surfactant include polyoxyalkylene acetylene glycols, polyoxyalkylene glyceryl ether, polyoxyalkylene alkyl ether, polyoxyalkylene ester, polyoxyalkylene alkylamine, and polyoxyalkylene alkylamide.

(2) Flux Content The flux content is preferably 5 to 95%, more preferably 5 to 15%, based on the total mass of the solder paste. Within this range, the effect of suppressing thickening caused by the solder powder is sufficiently exhibited.

The solder paste according to the present invention preferably contains zirconium oxide powder.
(3) Zirconium oxide powder The solder paste according to the present invention preferably contains zirconium oxide powder. Zirconium oxide can suppress an increase in viscosity of the paste due to a change with time. This is presumed to be due to the inclusion of zirconium oxide to maintain the oxide film thickness on the surface of the solder powder before it was introduced into the flux. Details are unknown, but are presumed as follows. Normally, since the active component of the flux has a slight activity even at room temperature, the surface oxide film of the solder powder is thinned by reduction, which causes the powder to agglomerate. Therefore, it is presumed that by adding zirconium oxide powder to the solder paste, the active component of the flux reacts preferentially with the zirconium oxide powder, and is maintained to such an extent that the oxide film on the surface of the solder powder does not aggregate.

  In order to sufficiently exhibit such effects, the content of the zirconium oxide powder in the solder paste is preferably 0.05 to 20.0% based on the total mass of the solder paste. When the content is 0.05% or more, the above-described effects can be exhibited, and when the content is 20.0% or less, the content of the metal powder can be secured, and the effect of preventing thickening can be exhibited. The content of zirconium oxide is preferably 0.05 to 10.0%, and more preferably 0.1 to 3%.

  The particle diameter of the zirconium oxide powder in the solder paste is preferably 5 μm or less. When the particle size is 5 μm or less, the printability of the paste can be maintained. The lower limit is not particularly limited, but may be 0.5 μm or more. The particle diameter was determined by taking an SEM photograph of the zirconium oxide powder, obtaining the equivalent diameter of the projected circle by image analysis for each powder of 0.1 μm or more, and taking the average value thereof.

  The shape of the zirconium oxide is not particularly limited. However, if the shape is zirconium oxide, the contact area with the flux is large, and there is an effect of suppressing thickening. Spherical shape provides good fluidity, and therefore excellent printability as a paste. What is necessary is just to select a shape suitably according to a desired characteristic.

(4) Manufacturing Method of Solder Paste The solder paste according to the present invention is manufactured by a general method in the art. First, in the production of the solder powder, a known method such as a dropping method of dropping a molten solder material to obtain particles, a spraying method of centrifugal spraying, and a method of pulverizing bulk solder material can be adopted. In the dropping method or the spraying method, the dropping or spraying is preferably performed in an inert atmosphere or a solvent in order to form particles. Then, the above components are heated and mixed to prepare a flux, and the above-mentioned solder powder and, in some cases, zirconium oxide powder are introduced into the flux, followed by stirring and mixing.

4. Solder Joint The solder joint according to the present invention is suitable for use in connection between an IC chip in a semiconductor package and its substrate (interposer) or connection between the semiconductor package and a printed wiring board. Here, the “solder joint” refers to a connection portion of an electrode.

5. Others The solder alloy according to the present invention may be in the form of a wire in addition to being used as a solder powder as described above.

The method for forming a solder joint according to the present invention may be performed according to a conventional method.
The joining method using the solder paste according to the present invention may be performed according to an ordinary method using, for example, a reflow method. The melting temperature of the solder alloy in the case of performing the flow soldering may be approximately 20 ° C. higher than the liquidus temperature. In the case of joining using the solder alloy according to the present invention, it is preferable to consider the cooling rate at the time of solidification from the viewpoint of making the structure finer. 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.

  The solder alloy according to the present invention can produce a low α dose alloy by using a low α dose material as a raw material. When such a low α-dose alloy is used for forming solder bumps around a memory, it is possible to suppress soft errors.

  The present invention will be described with reference to the following examples, but the present invention is not limited to the following examples.

  Rosin was 42 parts by mass, glycol solvent was 35 parts by mass, thixotropic agent was 8 parts by mass, organic acid was 10 parts by mass, amine was 2 parts by mass, and halogen was 3 parts by mass. And a solder powder having a size (particle size distribution) satisfying the symbol 4 in the powder size classification (Table 2) in JIS Z 3284-1: 2004 according to JIS Z 3284-1: 2004. The mass ratio of the flux to the solder powder is flux: solder powder = 11: 89. For each solder paste, the change over time in viscosity was measured. In addition, the liquidus temperature and the solidus temperature of the solder powder were measured. Furthermore, the wettability was evaluated using the solder paste immediately after the preparation. Details are as follows.

-Time-dependent change The viscosity of each solder paste immediately after the preparation was measured using PCU-205 manufactured by Malcom Corporation at a rotation speed of 10 rpm at 25 ° C for 12 hours in the air. If the viscosity after 12 hours is 1.2 times or less as compared to the viscosity when 30 minutes have passed since the preparation of the solder paste, it was evaluated as "O" as a sufficient thickening suppression effect was obtained, When it exceeded 1.2 times, it was evaluated as "x".

・ ΔT
For the solder powder before mixing with the flux, DSC measurement was performed using SII Nanotechnology Co., Ltd., model number: EXSTAR DSC7020, at a sample amount of about 30 mg, at a heating rate of 15 ° C./min, and the solid phase was measured. Temperature and liquidus temperature were obtained. ΔT was determined by subtracting the solidus temperature from the obtained liquidus temperature. When ΔT was 10 ° C. or less, “○” was evaluated, and when ΔT exceeded 10 ° C., “X” was evaluated.

· Wettability producing the solder paste immediately after printed on a Cu plate, a N ₂ atmosphere in a reflow furnace, after heating from 25 ° C. to 260 ° C. at a heating rate of 1 ° C. / s, and cooled to room temperature. The wettability was evaluated by observing the appearance of the cooled solder bumps with an optical microscope. When no unmelted solder powder was observed, it was evaluated as "O", and when unmelted solder powder was observed, it was evaluated as "x".

  Table 1 shows the results of the evaluation.

  As shown in Tables 1 to 6, it was found that, in each example, all the alloy compositions satisfy the requirements of the present invention, and thus exhibit an effect of suppressing thickening, narrowing of ΔT, and excellent wettability.

  In contrast, Comparative Examples 1, 10, 19, 28, 37, and 46 did not contain As, and thus did not exhibit the effect of suppressing thickening.

  In Comparative Examples 2, 11, 20, 29, 38, and 47, since the expression (1) was less than the lower limit, the thickening suppressing effect was not exhibited.

  Comparative Examples 3, 4, 12, 13, 21, 22, 30, 31, 39, 40, 48, and 49 showed poor wettability because the As content exceeded the upper limit.

  In Comparative Examples 5, 7, 9, 14, 16, 18, 23, 25, 27, 32, 34, 36, 41, 43, 45, 50, 52, and 54, the upper limit is the Pb content and the formula (2). Since the value exceeded the value, the result showed that ΔT exceeded 10 ° C.

  Comparative Examples 6, 15, 24, 33, 42, and 51 showed that ΔT exceeded 10 ° C. because Equation (2) exceeded the upper limit.

  Comparative Examples 8, 17, 26, 35, 44, and 53 showed results in which ΔT exceeded 10 ° C. because the Bi content and the expression (2) exceeded the upper limit.

Claims (10)

As: 25-300 mass ppm, Bi: 0 mass ppm or more and 25,000 mass ppm or less, Pb: more than 0 mass ppm and 8000 mass ppm or less, and the balance is an alloy composition consisting of Sn; A solder alloy characterized by satisfying the formula:
275 ≦ 2As + Bi + Pb (1)
0 <2.3 × 10 ⁻⁴ × Bi + 8.2 × 10 ⁻⁴ × Pb ≦ 7 (2)
In the formulas (1) and (2), As, Bi, and Pb each represent the content (mass ppm) in the alloy composition. The solder alloy according to claim 1, wherein the alloy composition satisfies the following formula (1a).
275 ≦ 2As + Bi + Pb ≦ 25200 (1a)
In the above formula (1a), As, Bi, and Pb each represent the content (mass ppm) in the alloy composition. The solder alloy according to claim 1, wherein the alloy composition satisfies the following expression (1b).
275 ≦ 2As + Bi + Pb ≦ 5300 (1b)
In the above formula (1b), As, Bi, and Pb each represent the content (mass ppm) in the alloy composition. The solder alloy according to any one of claims 1 to 3, wherein the alloy composition satisfies the following expression (2a).
0.02 ≦ 2.3 × 10 ⁻⁴ × Bi + 8.2 × 10 ⁻⁴ × Pb ≦ 0.9 (2a)
In the above formula (2a), Bi and Pb each represent the content (mass ppm) in the alloy composition.   The solder alloy according to any one of claims 1 to 4, wherein the alloy composition contains at least one of Ag: 0 to 4% by mass and Cu: 0 to 0.9% by mass.   A solder powder comprising the solder alloy according to claim 1.   A solder paste comprising the solder powder according to claim 6.   The solder paste according to claim 7, further comprising a zirconium oxide powder.   9. The solder paste according to claim 8, wherein the zirconium oxide powder is contained in an amount of 0.05 to 20.0% by mass based on the total mass of the solder paste. A solder joint having the solder alloy according to claim 1.