JP6638845B1 - Solder paste - Google Patents

Abstract

An object of the present invention is to achieve soldering with less voids without impairing manufacturing efficiency and storage stability, and also have an effect of suppressing viscosity increase, excellent wettability, and a liquidus temperature and a solidus temperature. To provide a solder paste having a small temperature difference and high mechanical properties. A flux for soldering containing a resin, a glycol-based solvent and a monohydric alcohol having 16 to 18 carbon atoms; and As: 25 to 300 mass ppm; Pb: more than 0 mass ppm to 5100 mass ppm or less; Sb: It has an alloy composition consisting of at least one of more than 0 mass ppm and not more than 3000 mass ppm and Bi: more than 0 mass ppm and not more than 10,000 mass ppm, and the balance: Sn, and the following formulas (1) and (2) : 275 ≦ 2As + Sb + Bi + Pb (1) 0.01 ≦ (2As + Sb) / (Bi + Pb) ≦ 10.00 (2) [In the above formulas (1) and (2), As, Sb, Bi, and Pb are each the alloys described above. Solder alloy paste that satisfies the content (mass ppm) in the composition]. [Selection diagram] None

Description

  The present invention relates to a solder paste.

2. Description of the Related Art In recent years, in surface mounting of electronic components, reflow soldering has been performed in which solder previously applied or bonded at room temperature is heated and melted and soldered later.
In the case of reflow soldering using a solder paste, the solder paste mainly consists of a solder powder and a flux containing a resin component, a solvent, and various additives, which is applied to a portion to be joined by screen printing or the like, and heated. By doing so, soldering is performed.
Incidentally, volatile components such as organic acids are also included in the additives added to the flux, and the volatile components are gasified by heating during soldering. In addition, when a lead-free solder is used, the soldering temperature is high, so that flux components other than volatile components may be decomposed. For this reason, in reflow soldering, there is a problem that voids due to such volatile gas and decomposition gas are generated in a soldered portion.
In this regard, Patent Document 1 discloses that the generation of voids is reduced by adding a low molecular weight dibasic acid dialkyl ester compound to prevent the decomposition of flux (Patent Document 1).

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

  Therefore, for example, Patent Document 2 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 temporal change 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 2007-136491 A JP-A-2005-98052

  The low molecular weight dibasic acid dialkyl ester compound used in Patent Literature 1 cannot be said to have high compatibility with rosin resins and glycol solvents generally used in flux. Therefore, when the low molecular weight dibasic acid dialkyl ester compound is added to the flux, the mixing efficiency in producing the flux and the solder paste is reduced. In addition, the flux may undergo phase separation during long-term storage.

  Patent Literature 2 discloses that if the As content is large, the meltability is poor, and the meltability is considered to correspond to the wettability of the molten solder. 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 2, 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 2, 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 2 to exhibit a lower viscosity increase rate and excellent wettability, it is necessary to keep increasing the flux activation power and As content, which results in a vicious cycle.

  Further, in order to join the 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.

  Therefore, the present invention can realize soldering with less generation of voids without impairing manufacturing efficiency and storage stability, and has an effect of suppressing viscosity increase, excellent wettability, liquidus temperature and solid phase. An object of the present invention is to provide a solder paste having a small temperature difference from a linear temperature and high mechanical properties.

The present inventors have conducted intensive studies to solve the above-described problems. As a result, if the melt viscosity of the flux at the time of soldering is low, even if volatile gas or decomposition gas is generated, soldering is quickly performed before the resin component is solidified. I noticed that I was able to get out of the section and not remain as a void.
The melt viscosity of the flux at the time of soldering is related to the amount of the solvent present in the flux. However, it was found that if a sufficient amount of the solvent remained, the melt viscosity was low, and as a result, even if volatile gas or decomposition gas was generated during soldering, it could be removed from the soldered portion.

However, if a low volatile solvent is used so that a sufficient amount of the solvent remains in the flux at the time of soldering, the melt viscosity at the time of soldering can be lowered. However, it cannot be dried sufficiently, and another problem arises in that the surface of the soldered portion is sticky and dust adheres.
Therefore, as a result of further study while paying attention to the drying property after joining, when the glycol solvent and the monohydric alcohol having 16 to 18 carbon atoms are used in combination, the drying property and the soldering It has been found that a flux that can satisfy conflicting requirements of low melt viscosity at the time can be achieved, and that the problem of void generation can be solved.
Moreover, since monohydric alcohols having 16 to 18 carbon atoms are alcohols, they have good compatibility with main components of general fluxes such as glycol solvents and rosin resins. The production efficiency and storage stability are not impaired.

  Further, the present inventors have found that Sb, Bi and Pb exert the same thickening suppressing effect as that of As. 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 2, 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 2 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 in accordance with the ionization tendency can obtain a thickening suppression effect equal to or greater than that of the solder alloy described in Patent Document 2. Further, as described above, when the As content increases, the wettability deteriorates.

  The present inventors have conducted a detailed investigation on 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 spreads becomes remarkable when Bi and Pb are added at the same time, it has also been found that strict control is required.

  Furthermore, the present inventors re-examined the Bi content and the Pb content in order to improve the wettability of the solder alloy, but ΔT became wider as the content of these elements increased. Therefore, the present inventors have selected Sb as an element whose ionization tendency is noble to Sn and also as an element for improving the wettability of the solder alloy, set the allowable range of the Sb content, and As a result of investigating the relationship between the contents of As, Bi, Pb, and Sb in detail, it was found that, by chance, when the contents of these elements satisfy a predetermined relational expression, an excellent thickening suppression effect, It was found that there is no practical problem in all of wettability and narrowing of ΔT.

That is, the present invention is as follows.
[1]
A soldering flux containing a resin, a glycol-based solvent and a monohydric alcohol having 16 to 18 carbon atoms; and As: 25 to 300 mass ppm, Pb: more than 0 mass ppm, 5100 mass ppm or less, and Sb: 0 It has an alloy composition consisting of at least one of not less than 3000 ppm by mass and not more than 3000 ppm by mass and not more than 10,000 ppm by mass of Bi and the balance: Sn, and the following formulas (1) and (2):
275 ≦ 2As + Sb + Bi + Pb (1)
0.01 ≦ (2As + Sb) / (Bi + Pb) ≦ 10.00 (2)
[In the above formulas (1) and (2), As, Sb, Bi, and Pb each represent the content (mass ppm) in the alloy composition]
Solder alloy that satisfies;
Including, solder paste.
[2]
The solder paste according to [1], further comprising an organic acid.
[3]
The solder paste according to [1], further including an activator.
[4]
The solder paste according to any one of [1] to [3], wherein the content of the monohydric alcohol having 16 to 18 carbon atoms is more than 0% by mass and 20% by mass or less.
[5]
The solder paste according to [4], wherein the content of the monohydric alcohol having 16 to 18 carbon atoms is within a range of 5 to 15% by mass.
[6]
The ratio of the content (% by mass) of the monohydric alcohol having 16 to 18 carbon atoms to the content (% by mass) of the glycol-based solvent (content of monohydric alcohol having 16 to 18 carbon atoms / glycol) The solder paste according to any one of [1] to [5], wherein the content of the solvent is 0.01 to 1.25.
[7]
The ratio of the content (% by mass) of the monohydric alcohol having 16 to 18 carbon atoms to the content (% by mass) of the glycol-based solvent (content of monohydric alcohol having 16 to 18 carbon atoms / glycol) The solder paste according to [6], wherein the content of the solvent is 0.15 to 0.72.
[8]
The rosin resin is 30 to 60% by mass, the glycol solvent is 20 to 45% by mass, the monohydric alcohol having 16 to 18 carbon atoms is 5 to 20% by mass, and the organic acid is 1 to 15% by mass. And As: 25 to 300 mass ppm, Pb: more than 0 mass ppm to 5100 mass ppm, Sb: more than 0 mass ppm to 3000 mass ppm, and Bi: more than 0 mass ppm to 10,000 mass ppm It has an alloy composition consisting of at least one of the following and the balance: Sn, and has the following formulas (1) and (2):
275 ≦ 2As + Sb + Bi + Pb (1)
0.01 ≦ (2As + Sb) / (Bi + Pb) ≦ 10.00 (2)
[In the above formulas (1) and (2), As, Sb, Bi, and Pb each represent the content (mass ppm) in the alloy composition]
Solder alloy that satisfies;
Including, solder paste.
[9]
The solder paste according to any one of [1] to [8], further comprising a thixotropic agent and / or an antioxidant.
[10]
The solder paste according to any one of [1] to [9], wherein the monohydric alcohol having 16 to 18 carbon atoms is a monohydric alcohol having 16 carbon atoms.
[11]
The solder paste according to [10], wherein the monohydric alcohol having 16 carbon atoms is 2-hexyldecanol.
[12]
The alloy composition has the following formula (1a):
275 ≦ 2As + Sb + Bi + Pb ≦ 25200 (1a)
[In the above formula (1a), As, Sb, Bi, and Pb each represent the content (mass ppm) in the alloy composition]
The solder paste according to any one of [1] to [11], which satisfies the following.
[13]
The alloy composition has the following formula (1b):
275 ≦ 2As + Sb + Bi + Pb ≦ 5300 (1b)
[In the above formula (1b), As, Sb, Bi, and Pb each represent the content (mass ppm) in the alloy composition]
The solder paste according to any one of [1] to [12], which satisfies the following.
[14]
The alloy composition has the following formula (2a):
0.31 ≦ (2As + Sb) / (Bi + Pb) ≦ 10.00 (2a)
[In the above formula (2a), As, Sb, Bi, and Pb each represent the content (mass ppm) in the alloy composition]
The solder paste according to any one of [1] to [13], which satisfies the following.
[15]
The solder paste according to any one of [1] to [14], wherein the alloy composition contains at least one of Ag: 0 to 4% by mass and Cu: 0 to 0.9% by mass.
[16]
The solder paste according to any one of [1] to [15], further comprising a zirconium oxide powder.
[17]
The solder paste according to [16], 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.
[18]
As: 25 to 300 mass ppm, Pb: more than 0 mass ppm to 5100 mass ppm or less, Sb: at least one of more than 0 mass ppm to 3000 mass ppm and Bi: more than 0 mass ppm to 10,000 mass ppm, and the balance: And an alloy composition comprising Sn and the following formulas (1) and (2):
275 ≦ 2As + Sb + Bi + Pb (1)
0.01 ≦ (2As + Sb) / (Bi + Pb) ≦ 10.00 (2)
[In the above formulas (1) and (2), As, Sb, Bi, and Pb each represent the content (mass ppm) in the alloy composition]
For soldering a solder alloy that satisfies
A flux containing a resin, a glycol-based solvent and a monohydric alcohol having 16 to 18 carbon atoms.
[19]
As: 25 to 300 mass ppm, Pb: more than 0 mass ppm to 5100 mass ppm or less, Sb: at least one of more than 0 mass ppm to 3000 mass ppm and Bi: more than 0 mass ppm to 10,000 mass ppm, and the balance: And an alloy composition comprising Sn and the following formulas (1) and (2):
275 ≦ 2As + Sb + Bi + Pb (1)
0.01 ≦ (2As + Sb) / (Bi + Pb) ≦ 10.00 (2)
[In the above formulas (1) and (2), As, Sb, Bi, and Pb each represent the content (mass ppm) in the alloy composition]
For soldering a solder alloy that satisfies
The rosin resin is 30 to 60% by mass, the glycol solvent is 20 to 45% by mass, the monohydric alcohol having 16 to 18 carbon atoms is 5 to 20% by mass, and the organic acid is 1 to 15% by mass. Included flux.

  According to the present invention, it is possible to realize soldering with less generation of voids, without impairing production efficiency and storage stability, and also has an effect of suppressing thickening, excellent wettability, liquidus temperature and solid phase It is possible to provide a solder paste having a small temperature difference from the linear temperature and high mechanical properties.

  Hereinafter, embodiments for carrying out the present invention (hereinafter, referred to as “the present embodiment”) will be described in more detail, but the present invention is not limited thereto, and various forms may be used without departing from the gist of the present invention. Deformation is possible.

In the present embodiment, a soldering flux containing a resin, a glycol-based solvent and a monohydric alcohol having 16 to 18 carbon atoms; and As: 25 to 300 mass ppm, and Pb: more than 0 mass ppm and 5100 mass ppm or less And at least one of Sb: more than 0 mass ppm to 3000 mass ppm and Bi: more than 0 mass ppm to 10,000 mass ppm, and the balance: Sn, and the following formula (1) and (2) )formula:
275 ≦ 2As + Sb + Bi + Pb (1)
0.01 ≦ (2As + Sb) / (Bi + Pb) ≦ 10.00 (2)
[In the above formulas (1) and (2), As, Sb, Bi, and Pb each represent the content (mass ppm) in the alloy composition]
Solder alloy that satisfies;
And a solder paste.

<Flux>
The soldering flux contains a resin (base resin) and a solvent, and various additives as necessary. The solvent contains at least a glycol solvent and a monohydric alcohol having 16 to 18 carbon atoms.

As the resin, various resins conventionally used for soldering flux can be used. Examples of such a resin include rosin resin, acrylic resin, polyester, polyethylene, polypropylene, polyamide, styrene-maleic acid copolymer, acrylic resin, epoxy resin, phenol resin, phenoxy resin, terpene resin, and terpene phenol. Resins and mixtures thereof are listed, and among them, rosin-based resins are generally and often used.
Examples of the rosin-based resin include natural rosins such as gum rosin and wood rosin, and derivatives thereof (polymerized rosin, hydrogenated rosin, disproportionated rosin, acid-modified rosin, rosin ester, and the like).
The content of the resin in the flux is not limited, and may be, for example, in the range of 10 to 80% by mass, may be in the range of 20 to 70% by mass, or may be in the range of 30 to 60% by mass. Is also good.

In the present embodiment, at least a glycol solvent and a monohydric alcohol having 16 to 18 carbon atoms are used as the solvent. Such a monohydric alcohol having a carbon number has a moderate boiling point, and at the joining temperature employed in general soldering, remains in the flux at the initial stage of joining to keep the melt viscosity of the flux low. In addition, it is easily volatilized in a later stage of bonding while facilitating release of decomposition gas and the like.
Here, the glycol solvent refers to a solvent composed of glycol (a compound having a structure in which a hydroxyl group is bonded to two different carbon atoms of an aliphatic or alicyclic hydrocarbon one by one) or a derivative thereof. In the present embodiment, the type of the glycol-based solvent is not limited, for example, those commonly used for soldering flux can be used, and specific examples include diethylene glycol, dipropylene glycol, and triethylene glycol. , Hexylene glycol, phenyl glycol, hexyl diglycol, 2-ethylhexyl diglycol, diethylene glycol monobutyl ether (butyl carbitol), diethylene glycol monomethyl ether (methyl carbitol), diethylene glycol monohexyl ether (hexyl carbitol), propylene glycol And glycol ethers such as monophenyl ether. Of these, glycol ethers of alcohols having 2 to 24 carbon atoms (specifically, monoglycol ether (carbon number: 4 to 26), diglycol ether (carbon number: 6 to 28), oligoglycol ether (carbon number : 2 + 2 × n to 24 + 2 × n)), more preferably a glycol ether of an alcohol having 4 to 16 carbon atoms, and particularly preferably a glycol ether of an alcohol having 6 to 8 carbon atoms.
The glycol solvents may be used alone or in combination of two or more.

  The content of the glycol-based solvent in the flux (when a plurality of types of glycol-based solvents are used, the total content thereof) is not limited, and may be, for example, in the range of 10 to 60% by mass or 15 to 50% by mass. % Or within a range of 20 to 45% by mass.

In the present embodiment, a monohydric alcohol having 16 to 18 carbon atoms is used as the solvent in addition to the glycol-based solvent. Thereby, a flux having a low melt viscosity at the time of soldering can be realized.
Examples of the monohydric alcohol having 16 to 18 carbon atoms include 1-hexadecanol (carbon number 16), 2-hexyldecanol (carbon number 16), isohexadecanol (carbon number 16), and 1-heptadecanol (carbon number). Formula 17), 1-octadecanol (carbon number 18), isostearyl alcohol (carbon number 18), etc., may be used alone or in combination of two or more.
Among them, those having 16 carbon atoms are preferable, and in particular, 2-hexyldecanol (CAS number: 2425-77-6) is preferable because it has less stickiness. As 2-hexyldecanol, for example, Fineoxocol 1600 (manufactured by Nissan Chemical Industries, Ltd., registered trademark) or the like can be used.

  The content of the monohydric alcohol having 16 to 18 carbon atoms in the flux is not limited, and it is sufficient that the flux contains a monohydric alcohol having 16 to 18 carbon atoms. From the viewpoint of reducing the melt viscosity of the flux or the solder paste at the time of soldering, the content is preferably high, for example, 0.5 mass% or more, 1 mass% or more, or 5 mass% or more. It can be set to not less than mass%. On the other hand, from the viewpoint of eliminating poor drying of the flux and the solder paste and suppressing stickiness, the content is preferably small, for example, 30% by mass or less, 20% by mass or less, or 15% by mass. It can also be as follows.

  Further, the ratio of the content (mass%) of the monohydric alcohol having 16 to 18 carbon atoms (mass%) to the content (mass%) of the glycol-based solvent (the total amount when a plurality of types are used) (the monovalent alcohol having 16 to 18 carbon atoms) (Alcohol content / glycol solvent content) is not limited, but is preferably 0.01 to 1.25, and more preferably 0.15 to 1 from the viewpoint of the balance between prevention of void generation and drying. .25, more preferably 0.15 to 0.72.

  In the present embodiment, in addition to the glycol-based solvent and the monohydric alcohol having 16 to 18 carbon atoms, another known solvent may be used in combination. Examples of such a solvent include alcohols such as benzyl alcohol, ethanol, isopropyl alcohol, butanol, 1,5-pentanediol, octanediol, terpineol, ethyl cellosolve, and butyl cellosolve; and carbonized solvents such as toluene, xylene, and n-hexane. Hydrogens; esters such as isopropyl acetate and butyl benzoate; and one or more of these can be used.

  The flux of the present embodiment includes fluxes such as an activator, a thixotropic agent (thixotropic agent), an antioxidant, a rust inhibitor, a defoaming agent, a matting agent, a surfactant, a coloring agent, in addition to the resin and the solvent. And various additives that may be added to the composition.

As the activator, for example, those commonly used in fluxes such as organic acids, amines, organic halogen compounds, amine hydrohalides, phosphonic acids, and phosphoric esters, or a combination of one or more kinds Can be used.
The content of the activator in the flux is not limited, and may be, for example, in the range of 0 to 30% by mass or in the range of 0 to 20% by mass.

Among them, organic acids include, for example, monocarboxylic acids such as formic acid, acetic acid, benzoic acid, and glycolic acid; oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, pimelic acid, diglycolic acid, and the like. Dicarboxylic acids or anhydrides thereof; oxyacids such as lactic acid, citric acid and tartaric acid; dimer acid, hydrogenated dimer acid, trimer acid, hydrogenated trimer acid, picolinic acid and the like. One or more of these may be used. Can be used. Also, higher saturated or unsaturated fatty acids having 8 or more carbon atoms can be used.
Many of these organic acids are volatile or those whose boiling point is lower than the soldering temperature, and such substances are liable to generate gases that cause voids during soldering . However, in this embodiment, even if gas is generated, the gas does not remain in the soldered portion as a void. Therefore, this embodiment is particularly effective when the flux contains an organic acid having low volatility or a low boiling point.
The content of the organic acid in the flux is not limited, and may be, for example, in a range of 1 to 15% by mass or in a range of 3 to 10% by mass.

As the amine, for example, diphenylguanidine, ditolylguanidine, naphthylamine, triethanolamine, imidazole, 2-methylimidazole, 2-ethylimidazole, 2-phenylimidazole, 2-ethyl-4-methylimidazole, 2-phenyl- Imidazole compounds such as 4-methylimidazole;
The content of the amine in the flux is not limited, and may be, for example, in the range of 0 to 10% by mass or in the range of 0 to 5% by mass.

Examples of the organic halogen compound include a brominated organic compound, and specifically, 1-bromo-2-butanol, 1-bromo-2-propanol, 3-bromo-1-propanol, 3-bromo -1,2-propanediol, 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, and one or more of these can be used.
The content of the organic halogen compound in the flux is not limited, and may be, for example, in the range of 0 to 10% by mass or in the range of 0 to 5% by mass.

Examples of amine hydrohalides include, for example, hydrohalic acids such as hydrobromic acid (HBr), hydrochloric acid (HCl), hydrofluoric acid (HF), aniline, diphenylguanidine, diethylamine, and isopropylamine. And the like in combination with an amine compound. In addition, a salt obtained by combining tetrafluoroboric acid (HBF ₄ ) with an amine compound can also be used as an amine hydrohalide equivalent.
The content of the amine hydrohalides in the flux is not limited, and may be, for example, in the range of 0 to 5% by mass or in the range of 0 to 2% by mass.

  In the present embodiment, the above-described organic acids, amines, organic halogen compounds, amine hydrohalides, phosphonic acids, phosphate esters, and the like can be added as an activator. It may play a role, and may be added with such an intention.

The thixotropic agent is an additive added for imparting thixotropic properties. Specific examples thereof include fatty acid amides such as stearic acid amide, methylenebisbehenic acid amide, and hydroxystearic acid ethylenebisamide, and aromatic compounds such as p-toluamide. Group amide, castor hardened oil, carnauba wax, beeswax, etc., and one or more of these can be used.
The content of the thixotropic agent in the flux is not limited, and may be, for example, in the range of 0 to 30% by mass or in the range of 0 to 10% by mass.

As the antioxidant, for example, a hindered phenolic antioxidant, a phenolic antioxidant, a bisphenol-based antioxidant, a polymer-type antioxidant, and the like used in flux or other various fields may be used. And one or more of these can be used.
The content of the antioxidant in the flux is not limited, and may be, for example, in a range of 0 to 10% by mass or in a range of 0 to 5% by mass.

  As an example of a preferred composition of the soldering flux of the present embodiment, a rosin-based resin is 30 to 60% by mass, a glycol-based solvent is 20 to 45% by mass, and a monohydric alcohol having 16 to 18 carbon atoms is 5 to 20%. And those containing an organic acid in the range of 1 to 15% by mass.

<Solder alloy>
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. When As is less than 25 ppm by mass, the effect of suppressing thickening cannot be sufficiently exhibited. The lower limit of the As content is 25 ppm by mass or more, preferably 50 ppm by mass or more, and more preferably 100 ppm by mass 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 by mass or less, preferably 250 ppm by mass or less, and more preferably 200 ppm by mass or less.

  Sb is an element having low reactivity with the flux and exhibiting a thickening suppressing effect. When the solder alloy according to the present invention contains Sb, the lower limit of the Sb content is more than 0 mass ppm, preferably 25 mass ppm or more, more preferably 50 mass ppm or more, and still more preferably 100 mass ppm. ppm or more, particularly preferably 300 ppm by mass or more. On the other hand, if the Sb content is too large, the wettability deteriorates, so it is necessary to make the Sb content appropriate. The upper limit of the Sb content is 3000 ppm by mass or less, preferably 1150 ppm by mass or less, more preferably 500 ppm by mass or less.

  Bi and Pb, like Sb, are elements having low reactivity with flux and exhibiting a thickening suppressing effect. Bi and Pb are elements that can lower the liquidus temperature of the solder alloy and reduce the viscosity of the molten solder, thereby suppressing the deterioration of wettability due to As.

  If at least one element of Sb, Bi and Pb is present, deterioration of wettability due to 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 mass ppm, preferably 25 mass ppm or more, more preferably 50 mass ppm or more, further more preferably 75 mass ppm. ppm or more, particularly preferably 100 ppm by mass or more, most preferably 250 ppm or more. When the solder alloy according to the present invention contains Pb, the lower limit of the Pb content is more than 0 mass ppm, preferably 25 mass ppm or more, more preferably 50 mass ppm or more, and still more preferably 75 mass ppm. ppm or more, particularly preferably 100 ppm or more, and most preferably 250 ppm 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 are deteriorated, and the reliability is deteriorated. In particular, since the crystal phase having a high Bi concentration is hard and brittle, the segregation in the solder alloy significantly lowers the reliability.

  From such a viewpoint, when the solder alloy according to the present invention contains Bi, the upper limit of the Bi content is 10,000 mass ppm or less, preferably 1,000 mass ppm or less, more preferably 600 mass ppm or less. , More preferably 500 ppm by mass or less. When the solder alloy according to the present invention contains Pb, the upper limit of the Pb content is 5100 mass ppm or less, preferably 5000 mass ppm or less, more preferably 1000 mass ppm or less, and still more preferably 850 mass ppm. ppm or less, and particularly preferably 500 ppm by mass or less.

  The solder alloy according to the present invention needs to satisfy the following expression (1).

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

  As, Sb, Bi and Pb are all elements that exhibit a thickening suppressing effect. These totals need to be 275 mass ppm or more. In the formula (1), the reason why the As content is doubled is that As has a higher effect of suppressing thickening than Sb, 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 350 or more, and more preferably 1200 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 10200 or less, from the viewpoint of setting ΔT in a suitable range. It is more preferably 5300 or less, particularly preferably 3800 or less.

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

  The solder alloy according to the present invention needs to satisfy the following expression (2).

0.01 ≦ (2As + Sb) / (Bi + Pb) ≦ 10.00 (2)
In the above formula (2), As, Sb, Bi, and Pb each represent the content (mass ppm) in the alloy composition.

  If the contents of As and Sb are large, the wettability of the solder alloy deteriorates. On the other hand, 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 management is required. In particular, in an alloy composition containing Bi and Pb simultaneously, ΔT tends to increase. In view of these, if the content of Bi and Pb is increased to excessively improve the wettability, ΔT will increase. On the other hand, when the content of As or Sb is increased to improve the effect of suppressing thickening, wettability deteriorates. Therefore, in the present invention, the group is divided into As and Sb groups and Bi and Pb groups, and when the total amount of both groups is within an appropriate predetermined range, the thickening suppression effect, the narrowing of ΔT, and the wettability Are all satisfied at the same time.

  If the expression (2) is less than 0.01, the total content of Bi and Pb becomes relatively larger than the total content of As and Pb, so that ΔT is widened. The lower limit of the formula (2) is 0.01 or more, preferably 0.02 or more, more preferably 0.41 or more, further preferably 0.90 or more, and particularly preferably 1.00 or more. And most preferably 1.40 or more. On the other hand, when the expression (2) exceeds 10.00, the total content of As and Sb becomes relatively larger than the total content of Bi and Pb, so that the wettability deteriorates. The upper limit of (2) is 10.00 or less, preferably 5.33 or less, more preferably 4.50 or less, further preferably 2.67 or less, and still more preferably 4.18 or less. And particularly preferably 2.30 or less.

Note that the denominator of the expression (2) is “Bi + Pb”, and the expression (2) is not satisfied unless these are included. That is, the solder alloy according to the present invention necessarily contains at least one of Bi and Pb. As described above, the alloy composition containing neither Bi nor Pb has poor wettability.
The following formula (2a) is obtained by appropriately selecting the upper and lower limits from the above preferred embodiments.

0.31 ≦ (2As + Sb) / (Bi + Pb) ≦ 10.00 (2a)
In the above formula (2a), As, Sb, Bi and Pb each represent the content (mass ppm) in the alloy composition.

Ag is an optional element that can form Ag ₃ Sn at the crystal interface to improve the reliability of the solder alloy. Ag is an element whose ionization coefficient is noble with respect to Sn, and promotes the effect of suppressing thickening of these elements by coexisting with As, Pb, and Bi. 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%.

  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.

<Solder paste>
There is no limitation on the contents of the solder alloy and the flux in the solder paste. For example, the solder alloy may be 5 to 95% by mass and the flux may be 5 to 95% by mass.

  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.

The method for producing the soldering flux and the solder paste according to the present embodiment is not limited, and it can be produced by mixing the raw materials simultaneously or sequentially by an arbitrary method.
In the production of the flux, all the components of the flux may be finally mixed, and the glycol solvent and the monohydric alcohol having 16 to 18 carbon atoms may be mixed in advance as a mixed solvent or may be separately mixed. May be mixed with other components of the flux at the timing described above, or all components of the flux containing the glycol-based solvent and the monohydric alcohol having 16 to 18 carbon atoms may be mixed at the same time.
Also, in manufacturing the solder paste, it is not always necessary to prepare the flux in advance and mix it with the solder alloy, and it is finally added to all components of the flux, the solder alloy and, if necessary, the solder paste. As long as the additives are mixed, the order of mixing may be performed irrespective of the order of mixing, and after a part of the components of the flux is mixed with the solder alloy, the remaining components of the flux may be added.

  Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

<Examination of flux>
The raw materials shown in Table 1 were mixed according to the formulations shown in Table 1, and the fluxes of Examples A1 to A28 and Comparative Examples A1 and A2 were prepared. In addition, each raw material was compatible and could be easily mixed.

With respect to the fluxes of Examples and Comparative Examples, the dryness, void generation rate, and solder wettability were evaluated by the following procedures.
(1) Dryness The dryness of the flux was evaluated according to JIS Z 3197: 2012, 8.5.1.
Specifically, the flux of each Example and Comparative Example and the solder powder (average particle diameter φ: 21 μm) of the composition of Sn-3.0Ag-0.5Cu (SAC305) were mixed with the mass ratio of flux: solder powder = 11: 89. To prepare a mixed solder paste. Next, a test piece is prepared and tested according to the above JIS test method, and the degree of drying of the flux (easiness of drying the flux, specifically, the tackiness of the flux residue) is sprinkled on the surface of the flux residue on the test piece. The evaluation was based on the degree of adhesion of powdered talc.
The evaluation was evaluated as を when powder talc could be removed by brushing, and as × when powder talc could not be removed.

(2) Void generation rate (1) A solder paste was prepared in the same manner as in the drying test.
Next, the paste was printed on a Cu-OSP electrode (N = 15) of 8 mm × 8 mm at a height of 120 μm using a metal mask. Thereafter, reflow was performed in an air atmosphere. The reflow profile was maintained at 190 ° C. for 2 minutes, and then heated to 260 ° C. at 1.5 ° C./sec.
The transmission image of the soldered portion (solder bump) after the reflow was observed using Microfocus X-ray System XVR-160 manufactured by UNi-HiTE SYSTEM, and the void generation rate was obtained. Specifically, transmission observation is performed from the top to the bottom of the solder bump, a circular solder bump transmission image is obtained, the metal filled part and the void part are identified based on the contrast of the color tone, and the void area ratio is automatically analyzed. Was calculated, and this was defined as a void generation rate. Using the void generation rate thus obtained, the following criteria were used to evaluate the difficulty of generating voids.
When the void generation rate is 15% or less in all 15 soldered portions: XX
When the void generation rate is more than 15% in 15 soldered portions, but all are 20% or less: ○
When the void generation rate exceeds 20% in 15 soldered portions: ×

(3) Solder wettability The solder wettability of the flux was evaluated according to JIS Z 3198-4.
Specifically, the flux of each Example and Comparative Example was applied to a portion of 3 mm from the lower end in the length direction of the surface of a copper plate having a width of 5 mm, a length of 25 mm and a thickness of 0.5 mm fired at 150 ° C. for 1 hour. And immersed in a solder bath under the following conditions, and measured the zero cross time.
<Immersion conditions>
Solder composition: Sn-3.0Ag-0.5Cu
Solder bath temperature: 250 ° C JIS Z 3198-4
Immersion speed: 5 mm / sec JIS Z 3198-4
Immersion depth: 2mm JIS Z 3198-4
Measurement time: 10 seconds JIS Z 3198-4

The solder wettability was evaluated according to the following criteria.
Zero cross time is 5.5 seconds or less: ○
Zero cross time exceeds 5.5 seconds: ×

Table 1 shows the results. The fluxes of Examples A1 to A28 in which 2-hexyldecanol (a monohydric alcohol having 16 carbon atoms) and a glycol-based solvent were used as the solvent, had both good drying properties and a low void generation rate, and also exhibited good solder wettability. It was good.

<Examination of solder alloy>
Fluxes prepared with 42 parts by mass of rosin, 35 parts by mass of glycol solvent, 8 parts by mass of thixotropic agent, 10 parts by mass of organic acid, 2 parts by mass of amine, and 3 parts by mass of halogen, and Tables 2 to 7 And a solder alloy having a size (particle size distribution) satisfying the symbol 4 in the powder size classification (Table 2) according to JIS Z 3284-1: 2014 according to JIS Z 3284-1: 2014. The mass ratio between the flux and the solder alloy is flux: solder alloy = 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 alloy were measured. Furthermore, the wettability was evaluated using the solder paste immediately after the preparation. Details are as follows.

(4) Temporal change The viscosity of each solder paste immediately after preparation was measured using PCU-205 manufactured by Malcom Corporation at a rotation speed of 10 rpm at 25 ° C. in the air for 12 hours. 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".

(5) ΔT
For the solder alloy before being mixed with the flux, DSC measurement was carried out 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. 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.

(6) Wettability Each solder paste immediately after preparation was printed on a Cu plate, heated from 25 ° C. to 260 ° C. at a rate of 1 ° C./s in a N ₂ atmosphere in a reflow furnace, and then 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".

  As shown in Tables 2 to 7, it was found that all Examples B exhibited a thickening suppressing effect, a narrowing of ΔT, and excellent wettability.

  On the other hand, Comparative Examples B1, B14, B27, B40, B53, and B66 did not contain As, and thus did not exhibit a thickening suppressing effect.

  In Comparative Examples B2, B15, B28, B41, B54, and B67, since the expression (1) was less than the lower limit, the thickening suppressing effect was not exhibited.

  Comparative Examples B3, B16, B29, B42, B55, and B68 were inferior in wettability because the expression (2) exceeded the upper limit.

  In Comparative Examples B4, B5, B17, B18, B30, B31, B43, B44, B56, B57, B69, and B70, the As content and the formula (2) exceeded the upper limits, and the results of poor wettability were obtained. Indicated.

  Comparative Examples B6 to B8, B19 to B21, B32 to B34, B45 to B47, B58 to B60, and B71 to B73 were inferior in wettability because the Sb content exceeded the upper limit.

  Comparative Examples B9, B10, B22, B23, B35, B36, B48, B49, B61, B62, B74, and B75 showed results in which ΔT exceeded 10 ° C. because the Bi content exceeded the upper limit.

  In Comparative Examples B11, B13, B24, B26, B37, B39, B50, B52, B63, B65, B76, and B78, since the Pb content exceeded the upper limit, ΔT exceeded 10 ° C.

  Comparative Examples B12, B25, B38, B51, B64, and B77 did not contain Bi and Pb and did not satisfy the expression (2), and thus had poor wettability.

<Combination of flux and solder alloy>
As a result of evaluating the solder paste containing the flux of Example A1 and the solder alloy of Example B1, good results were obtained in all of the drying degree, void generation rate, thickening suppression effect, ΔT, and wettability. Was.

  In the case of using each of the fluxes of Examples A2 to A28 instead of the flux of Example A1, good results were also obtained in terms of dryness, void generation rate, thickening suppression effect, ΔT, and wettability. .

  Similarly, when the various fluxes of Examples A1 to A28 are combined with the various solder alloys of the other Examples B, the degree of drying, the rate of occurrence of voids, the effect of suppressing thickening, ΔT, and the wettability are also increased. Good results were obtained.

Claims (13)

A flux for soldering containing a resin, a glycol-based solvent , a monohydric alcohol having 16 to 18 carbon atoms , and an organic acid ; and As: 25 to 300 mass ppm, and Pb: more than 0 mass ppm and 5100 mass ppm or less. , Sb: 0 mass ppm exceeds 3000 mass ppm or less, Bi: 0 mass ppm to 10,000 mass ppm hereinafter, the balance has a Sn, the alloy composition consisting of the following (1) and (2) below:
275 ≦ 2As + Sb + Bi + Pb (1)
0.01 ≦ (2As + Sb) / (Bi + Pb) ≦ 10.00 (2)
[In the above formulas (1) and (2), As, Sb, Bi, and Pb each represent the content (mass ppm) in the alloy composition]
Solder alloy that satisfies;
Consisting of
The content of the glycol-based solvent in the flux is 10 to 60% by mass,
The content of the monohydric alcohol having 16 to 18 carbon atoms in the flux is 0.5% by mass or more and 30% by mass or less,
The ratio of the content (% by mass) of the monohydric alcohol having 16 to 18 carbon atoms to the content (% by mass) of the glycol-based solvent (content of monohydric alcohol having 16 to 18 carbon atoms / glycol) Content of the system solvent) is 0.01 to 1.25,
The solder paste , wherein the content of the organic acid in the flux is 1 to 15% by mass . A flux for soldering containing a resin, a glycol-based solvent , a monohydric alcohol having 16 to 18 carbon atoms , and an activator ; and As: 25 to 300 mass ppm, and Pb: more than 0 mass ppm and 5100 mass ppm or less. , Sb: 0 mass ppm exceeds 3000 mass ppm or less, Bi: 0 mass ppm to 10,000 mass ppm hereinafter, the balance has a Sn, the alloy composition consisting of the following (1) and (2) below:
275 ≦ 2As + Sb + Bi + Pb (1)
0.01 ≦ (2As + Sb) / (Bi + Pb) ≦ 10.00 (2)
[In the above formulas (1) and (2), As, Sb, Bi, and Pb each represent the content (mass ppm) in the alloy composition]
Solder alloy that satisfies;
Consisting of
The content of the glycol-based solvent in the flux is 10 to 60% by mass,
The content of the monohydric alcohol having 16 to 18 carbon atoms in the flux is 0.5% by mass or more and 30% by mass or less,
The ratio of the content (% by mass) of the monohydric alcohol having 16 to 18 carbon atoms to the content (% by mass) of the glycol-based solvent (content of monohydric alcohol having 16 to 18 carbon atoms / glycol) Content of the system solvent) is 0.01 to 1.25,
The solder paste , wherein the content of the activator in the flux is more than 0% by mass and 30% by mass or less . 3. The solder paste according to claim 1, wherein the content of the monohydric alcohol having 16 to 18 carbon atoms is 0.5 % by mass or more and 20% by mass or less. The solder paste according to claim 3 , wherein the content of the monohydric alcohol having 16 to 18 carbon atoms is in a range of 5 to 15% by mass. The ratio of the content (% by mass) of the monohydric alcohol having 16 to 18 carbon atoms to the content (% by mass) of the glycol-based solvent (content of monohydric alcohol having 16 to 18 carbon atoms / glycol) The solder paste according to any one of claims 1 to 4 , wherein a content of the system solvent is 0.15 to 0.72. The rosin resin is 30 to 60% by mass, the glycol solvent is 20 to 45% by mass, the monohydric alcohol having 16 to 18 carbon atoms is 5 to 20% by mass, and the organic acid is 1 to 15% by mass. , soldering flux comprising at; and as: and 25 to 300 ppm by weight, Pb: 0 mass ppm exceeds 5100 mass ppm or less, Sb: 0 ppm by mass exceeds 3000 mass ppm or less and, Bi: 0 mass ppm to 10,000 mass and ppm hereinafter, the balance has a Sn, the alloy composition consisting of the following (1) and (2) below:
275 ≦ 2As + Sb + Bi + Pb (1)
0.01 ≦ (2As + Sb) / (Bi + Pb) ≦ 10.00 (2)
[In the above formulas (1) and (2), As, Sb, Bi, and Pb each represent the content (mass ppm) in the alloy composition]
Solder alloy that satisfies;
Consisting of
The ratio of the content (% by mass) of the monohydric alcohol having 16 to 18 carbon atoms to the content (% by mass) of the glycol-based solvent (content of monohydric alcohol having 16 to 18 carbon atoms / glycol) Solder paste whose content is 0.01 to 1.25 . Further comprising a thixotropic agent and / or an antioxidant, according to claim 1 to 6 any one of the description of the solder paste. The solder paste according to any one of claims 1 to 7 , wherein the monohydric alcohol having 16 to 18 carbon atoms is a monohydric alcohol having 16 carbon atoms. The solder paste according to claim 8 , wherein the monohydric alcohol having 16 carbon atoms is 2-hexyldecanol. The alloy composition has the following formula (1a):
275 ≦ 2As + Sb + Bi + Pb ≦ 25200 (1a)
[In the above formula (1a), As, Sb, Bi, and Pb each represent the content (mass ppm) in the alloy composition]
The solder paste according to any one of claims 1 to 9 , which satisfies the following. The alloy composition has the following formula (1b):
275 ≦ 2As + Sb + Bi + Pb ≦ 5300 (1b)
[In the above formula (1b), As, Sb, Bi, and Pb each represent the content (mass ppm) in the alloy composition]
The solder paste according to any one of claims 1 to 10 , which satisfies the following. The alloy composition has the following formula (2a):
0.31 ≦ (2As + Sb) / (Bi + Pb) ≦ 10.00 (2a)
[In the above formula (2a), As, Sb, Bi, and Pb each represent the content (mass ppm) in the alloy composition]
The solder paste according to any one of claims 1 to 11 , which satisfies the following. The solder paste according to any one of claims 1 to 12 , wherein the alloy composition contains at least one of Ag: 0 to 4% by mass and Cu: 0 to 0.9% by mass.