JP2020192546A - Solder paste - Google Patents

Abstract

To provide a solder paste which can achieve soldering having reduced production of voids without impairing production efficiency and storage stability, has a thickening suppression effect and is excellent in wettability, has a small temperature difference between a liquidus line temperature and a solidus line temperature, and has high mechanical characteristics.SOLUTION: A solder paste contains: a flux for solder that contains a resin, a glycol-based solvent and an organic acid ester; and a solder alloy that has an alloy composition of 25-300 mass ppm As, 0 mass ppm or more and 25,000 mass ppm or less Bi, more than 0 mass ppm and 8,000 mass ppm or less Pb, and the balance Sn, and satisfies Expression (1): 275≤2As+Bi+Pb and Expression (2): 0<2.3×10-4×Bi+8.2×10-4×Pb≤7, in Expressions (1) and (2), As, Bi and Pb each satisfy a content (mass ppm) in the alloy composition.SELECTED DRAWING: None

Description

The present invention relates to a solder paste.

In recent years, in surface mounting of electronic components and the like, reflow soldering is performed in which solder that has been applied or adhered at room temperature in advance is later heated and melted and soldered.
In the case of reflow soldering using a solder paste, the solder paste mainly consists of solder powder and a flux containing a resin component, a solvent and various additives, which is applied and heated to the planned joining portion by screen printing or the like. Soldering is performed by doing so.
By the way, the additive added to the flux also contains a volatile component such as an organic acid, and the volatile component is gasified by heating during soldering. Further, when lead-free solder is used, the soldering temperature becomes high, so that the flux component other than the volatile component may be decomposed. Therefore, in reflow soldering, there is a problem that voids caused by such volatile gas and decomposition gas are generated in the 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 decomposition of the 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 also been narrowed, so that it takes a long time to use up the purchased solder paste. 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 2 includes Sn and one or more selected from the group consisting of Ag, Bi, Sb, Zn, In, and Cu in order to suppress the time-dependent change of the solder paste. And, 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% of the initial viscosity.

JP-A-2007-136491 JP-A-2015-98052

However, the flux containing the low-molecular-weight dibasic acid dialkyl ester compound used in Patent Document 1 is not yet sufficient from the viewpoint of suppressing thickening.

Patent Document 2 shows that the meltability is inferior when the As content is high, and the meltability is considered to correspond to the wettability of the molten solder. Generally, it is necessary to use a highly active flux in order to improve the wettability of the molten solder. 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, if a highly active flux is used, the viscosity increase rate of the flux increases. Further, 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 continuously increase the active force of the flux and the As content, which causes a vicious cycle.

Further, in order to join fine electrodes, it is necessary to improve the mechanical properties of the solder joint. Depending on the element, when the content increases, the liquidus temperature rises, the liquidus temperature and the solidus temperature spread, and segregation occurs during solidification to form a non-uniform alloy structure. If the solder alloy has such an alloy structure, the mechanical properties such as tensile strength are inferior and the solder alloy is easily broken due to external stress. This problem has become more prominent with the recent miniaturization of electrodes.

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

As a result of diligent studies to solve the above problems, the present inventors have diligently studied, and 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 promptly performed before the resin component solidifies. I noticed that I was able to get out of the part and did not remain as a void.
The melt viscosity of the flux during soldering is related to the amount of solvent present in the flux, and when the amount of solvent decreases due to volatilization due to heating during soldering (during joining), the melt viscosity However, it was found that the melt viscosity is low if a sufficient amount of solvent remains, and as a result, even if volatile gas or decomposition gas is generated during soldering, it can be removed from the soldered portion.

However, if a low volatility solvent is used so that a sufficient amount of solvent remains in the flux during soldering, the melt viscosity at the time of soldering can be lowered, but this time, heating is performed at the time of joining. However, it cannot be sufficiently dried, and another problem occurs that the surface of the soldered portion is sticky and dust or the like adheres to the soldered portion.
Therefore, as a result of further research while paying attention to the drying property after bonding, when a glycol solvent and an organic acid ester are used in combination as a solvent, the drying property and the low melt viscosity at the time of soldering conflict with each other. It was found that the flux can meet the requirements and the problem of void generation can be solved.
Moreover, since the organic acid ester has good compatibility with the main component of a general flux such as a glycol solvent or a rosin resin, even if it is added to the flux, its production efficiency and storage stability may be impaired. Absent.

In addition, the present inventors have obtained the finding that Bi and Pb exert the same thickening suppressing effect as As. The reason for this is not clear, but it can be inferred as follows.

Since the thickening suppressing effect is exerted by suppressing the reaction with the flux, an element having a low reactivity with the flux includes an element having a low ionization tendency. Generally, the ionization of an alloy is considered in terms of the ionization tendency as the alloy composition, that is, the standard electrode potential. For example, a SnAg alloy containing Ag, which is noble to Sn, is more difficult to ionize than Sn. Therefore, an alloy containing an element nobler than Sn is difficult to ionize, and it is presumed that the effect of suppressing thickening of the solder paste is high.

Here, in Patent Document 2, in addition to Sn, Ag, and Cu, Bi, Sb, Zn, and In are listed as equivalent elements, but in terms of ionization tendency, In and Zn are base to Sn. Element. That is, Patent Document 2 describes that the thickening suppressing effect can be obtained even if an element lower than Sn is added. Therefore, it is considered that the solder alloy containing the element selected according to the ionization tendency can obtain the same or higher thickening suppressing effect as compared with the solder alloy described in Patent Document 2. Further, as described above, as the As content increases, the wettability deteriorates.

The present inventors investigated in detail Bi and Pb found as an effect of suppressing thickening. Since Bi and Pb lower the liquidus temperature of the solder alloy, the wettability of the solder alloy is improved when the heating temperature of the solder alloy is constant. However, since the solidus temperature is significantly lowered depending on the content, ΔT, which is the temperature difference between the liquidus temperature and the solidus temperature, becomes too wide. If ΔT becomes too wide, segregation will occur during solidification, leading to deterioration of mechanical properties such as mechanical strength. Since the phenomenon that ΔT spreads remarkably appears when Bi and Pb are added at the same time, strict control is required.

In Sn, SnCu solder alloys, and SnAgCu solder alloys, in order to show excellent results in terms of thickening suppressing effect, excellent wettability, and narrowing of ΔT, the contents of As, Bi, and Pb should be adjusted. We thought that it was necessary to comprehensively control the contents of these elements, rather than controlling them individually. Therefore, as a result of various studies on the contents of these three elements, the present inventors happened to increase the content when the content of each element satisfies a predetermined relational expression within a predetermined amount range. We obtained findings that all of the anti-viscous effect, wettability, and stenosis of ΔT showed excellent results.

That is, the present invention is as follows.
[1]
Soldering flux containing resin, glycol solvent and organic acid ester; and As: 25-300 mass ppm, Bi: 0 mass ppm or more and 25,000 mass ppm or less, Pb: 0 mass ppm or more and 8000 mass ppm or less, and the balance Has an alloy composition consisting of Sn, and the following equations (1) and (2):
275 ≦ 2As + Bi + Pb (1)
0 <2.3 × 10 ^-4 × Bi + 8.2 × 10 ^-4 × Pb ≦ 7 (2)
[In the above equations (1) and (2), As, Bi, and Pb each represent the content (mass ppm) in the alloy composition].
Solder alloy that meets the requirements;
Including, solder paste.
[2]
The solder paste according to the above [1], further containing an organic acid.
[3]
The solder paste according to the above [1], further containing an activator.
[4]
The solder paste according to any one of [1] to [3] above, wherein the content of the organic acid ester is more than 0% by mass and 20% by mass or less.
[5]
The solder paste according to the above [4], wherein the content of the organic acid ester is in the range of 5 to 15% by mass.
[6]
The ratio of the content (mass%) of the organic acid ester to the content (mass%) of the glycol solvent (organic acid ester content / content of glycol solvent) is 0.01 to 1.25. The solder paste according to any one of the above [1] to [5].
[7]
The ratio of the content (mass%) of the organic acid ester to the content (mass%) of the glycol solvent (organic acid ester content / content of glycol solvent) is 0.15 to 0.72. The solder paste according to the above [6].
[8]
Solding containing rosin-based resin in the range of 30 to 60% by mass, glycol-based solvent in the range of 10 to 60% by mass, organic acid ester in the range of 0.5 to 30% by mass, and organic acid in the range of 1 to 15% by mass. Flux; and As: 25 to 300 mass ppm, Bi: 0 mass ppm or more and 25,000 mass ppm or less, Pb: 0 mass ppm or more and 8000 mass ppm or less, and the balance having an alloy composition of Sn, as described in (1) below. Equation and equation (2):
275 ≦ 2As + Bi + Pb (1)
0 <2.3 × 10 ^-4 × Bi + 8.2 × 10 ^-4 × Pb ≦ 7 (2)
[In the above equations (1) and (2), As, Bi, and Pb each represent the content (mass ppm) in the alloy composition].
Solder alloy that meets the requirements;
Including, solder paste.
[9]
The ratio of the content (mass%) of the organic acid ester to the content (mass%) of the glycol solvent (organic acid ester content / content of glycol solvent) is 0.01 to 1.25. The solder paste according to the above [8].
[10]
The solder paste according to any one of the above [1] to [9], further containing a thixotropic agent and / or an antioxidant.
[11]
One selected from the group consisting of dimethyl adipate, diisopropyl adipate, dibutyl maleate, dimethyl sebacate, diisobutyl adipate, diethyl sebacate, diisopropyl sebacate, dibutyl sebacate, and sioctyl sebacate. The solder paste according to any one of the above [1] to [10].
[12]
The alloy composition is based on 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 paste according to any one of the above [1] to [11], which satisfies the above conditions.
[13]
The alloy composition is 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]
The solder paste according to any one of the above [1] to [12], which satisfies the above conditions.
[14]
The alloy composition is the following formula (2a):
0.02 ≤ 2.3 x 10 ^-4 x Bi + 8.2 x 10 ^-4 x Pb ≤ 0.9 (2a)
[In the above formula (2a), Bi and Pb each represent the content (mass ppm) in the alloy composition]
The solder paste according to any one of the above [1] to [13], which satisfies the above conditions.
[15]
The solder paste according to any one of [1] to [14] above, 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] above, further comprising zirconium oxide powder.
[17]
The solder paste according to the above [16], which contains the zirconium oxide powder 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, Bi: 0 mass ppm or more and 25,000 mass ppm or less, Pb: 0 mass ppm or more and 8000 mass ppm or less, and the balance having an alloy composition of Sn, according to the following formula (1) and (2). )formula:
275 ≦ 2As + Bi + Pb (1)
0 <2.3 × 10 ^-4 × Bi + 8.2 × 10 ^-4 × Pb ≦ 7 (2)
[In the above equations (1) and (2), As, Bi, and Pb each represent the content (mass ppm) in the alloy composition].
For soldering a solder alloy that meets the requirements,
Flux containing resin, glycol solvent and organic acid ester.
[19]
As: 25 to 300 mass ppm, Bi: 0 mass ppm or more and 25,000 mass ppm or less, Pb: 0 mass ppm or more and 8000 mass ppm or less, and the balance having an alloy composition of Sn, according to the following formula (1) and (2). )formula:
275 ≦ 2As + Bi + Pb (1)
0 <2.3 × 10 ^-4 × Bi + 8.2 × 10 ^-4 × Pb ≦ 7 (2)
[In the above equations (1) and (2), As, Bi, and Pb each represent the content (mass ppm) in the alloy composition].
For soldering a solder alloy that meets the requirements,
A flux containing 30 to 60% by mass of a rosin-based resin, 10 to 60% by mass of a glycol-based solvent, 0.5 to 30% by mass of an organic acid ester, and 1 to 15% by mass of an organic acid.

According to the present invention, it is possible to realize soldering with less generation of voids without impairing manufacturing efficiency and storage stability, and 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 wire 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 to this, and various aspects are not deviated from the gist thereof. It can be transformed.

In this embodiment, a flux for soldering containing a resin, a glycol-based solvent and an organic acid ester; and As: 25 to 300 mass ppm, Bi: 0 mass ppm or more and 25,000 mass ppm or less, Pb: 0 mass ppm or more and 8000 mass by mass. It has an alloy composition of ppm or less and the balance is Sn, and the following equations (1) and (2):
275 ≦ 2As + Bi + Pb (1)
0 <2.3 × 10 ^-4 × Bi + 8.2 × 10 ^-4 × Pb ≦ 7 (2)
[In the above equations (1) and (2), As, Bi, and Pb each represent the content (mass ppm) in the alloy composition].
Solder alloy that meets the requirements;
Concerning solder paste, including.

<Flux>
The soldering flux contains a resin (base resin), a solvent, and various additives as required, and contains at least a glycol-based solvent and an organic acid ester as the solvent.

As the resin, various resins conventionally used for soldering flux can be used. Examples of such resins include rosin resins, acrylic resins, polyesters, polyethylenes, polypropylenes, polyamides, styrene-maleic acid copolymers, acrylic resins, epoxy resins, phenol resins, phenoxy resins, terpen resins, and terpenphenols. Examples thereof include resins and mixtures thereof, and among these, rosin-based resins are generally 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, etc.).
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, in the range of 20 to 70% by mass, or in the range of 30 to 60% by mass. May be good.

In the present embodiment, at least a glycol solvent and an organic acid ester are used as the solvent. Such organic acid esters have a boiling point in an appropriate range, and at the bonding temperature used in general soldering, they remain in the flux at the initial stage of bonding to keep the melt viscosity of the flux low, and decompose gas and the like. Volatilizes to some extent in the late bonding stage, while facilitating the release of the solder.
Here, the glycol-based solvent refers to a solvent composed of glycol (a compound having a structure in which one hydroxyl group is bonded to two different carbon atoms of an aliphatic or alicyclic hydrocarbon) or a derivative thereof. In the present embodiment, the type of glycol-based solvent is not limited, and for example, those generally used for soldering flux can be used. Specific examples thereof 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 Examples thereof include glycol ethers such as monophenyl ether. Of these, glycol ethers of alcohols having 2 to 24 carbon atoms (specifically, monoglycol ethers (carbon atoms: 4 to 26), diglycol ethers (carbon atoms: 6 to 28), oligoglycol ethers (carbon atoms: 6 to 28)). : 2 + 2 × n to 24 + 2 × n)) is preferable, alcohol glycol ethers having 4 to 16 carbon atoms are more preferable, and alcohol glycol ethers having 6 to 8 carbon atoms are particularly preferable.
As the glycol solvent, one kind may be used alone, or two or more kinds may be used in combination.

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

In the present embodiment, an organic acid ester is used in combination with the above glycol-based solvent as the solvent. As a result, a flux having a low melt viscosity can be realized at the time of soldering.

Since the flux containing the organic acid ester can suppress the reaction between the solder alloy powder and the activator during storage of the solder paste, the activity of the active agent remains even if the activity and the blending amount of the activator are not adjusted. Good wettability at the time of attachment can be ensured, and the generation of voids can be suppressed.

Examples of the organic acid ester include dimethyl adipate, diisopropyl adipate, dibutyl maleate, dimethyl sebacate, diisobutyl adipate, diethyl sebacate, diisopropyl sebacate, dibutyl sebacate, and sioctyl sebacate. These may be used alone or in admixture of a plurality of types.

The content of the organic acid ester in the flux (the total content when a plurality of types of organic acid esters are used) is not limited, but may be 0.5% by mass or more, or 1% by mass or more. It can also be 5% by mass or more. On the other hand, from the viewpoint of eliminating poor drying of the flux and solder paste and suppressing stickiness, it is preferable that the content is small, for example, 30% by mass or less, 20% by mass or less, or 15% by mass. It can also be as follows.

In addition, the ratio of the content (mass%) of the organic acid ester to the content (mass%) of the glycol solvent (the total amount when a plurality of types are used) (organic acid ester content / content of the glycol solvent) is also calculated. Although there is no limitation, it is preferably 0.01 to 1.25, more preferably 0.15 to 1.25, and 0.15 to 0.72 from the viewpoint of preventing the generation of voids. Is even more preferable.

In the present embodiment, in addition to the glycol-based solvent and the organic acid ester, other known solvents can be used in combination. Examples of such a solvent include alcohols such as benzyl alcohol, ethanol, isopropyl alcohol, butanol, 1,5-pentanediol, 2-ethyl-1,3-hexanediol, terpineol, ethyl cellosolve, and butyl cellosolve; toluene, Hydrocarbons such as xylene and n-hexane; esters such as isopropyl acetate and butyl benzoate can be mentioned, and one or more of these can be used.

The flux of the present embodiment is a flux of an activator, a thixotropic agent (thixotropic agent), an antioxidant, a rust preventive, a defoaming agent, a matting agent, a surfactant, a colorant, etc., in addition to a resin and a solvent. It can contain various additives that may be added to.

As the activator, for example, one or a combination of two or more of those generally used in fluxes such as organic acids, amines, organic halogen compounds, amine hydrohalates, phosphonic acids, and phosphoric acid esters. 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 these, 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, pimeric acid, diglycolic acid and the like. Dicarboxylic acid or its anhydride; oxyacids such as lactic acid, citric acid, tartaric acid; dimer acid, hydrogenated dimer acid, trimer acid, hydrogenated trimer acid, picolinic acid and the like, and one or more of these Can be used. Further, higher saturated or unsaturated fatty acids having 8 or more carbon atoms can also be used.
Many of these organic acids are volatile and their boiling points are lower than the soldering temperature, and such organic acids tend to generate void-causing gases during soldering. .. However, in the present embodiment, even if gas is generated, it does not remain in the soldered portion as voids, so that this embodiment is particularly effective when the flux contains an organic acid having a 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 the range of 1 to 15% by mass or in the range of 3 to 10% by mass.

Examples of amines include diphenylguanidine, ditrilguanidine, naphthylamine, triethanolamine, imidazole, 2-methylimidazole, 2-ethylimidazole, 2-phenylimidazole, 2-ethyl-4-methylimidazole, 2-phenyl-. Examples thereof include imidazole compounds such as 4-methylimidazole.
The content of 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 brominated organic compounds, and specifically, 1-bromo-2-butanol, 1-bromo-2-propanol, 3-bromo-1-propanol, and 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-1,4diol 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 hydrohalide salts include hydrohalic acids such as hydrobromic acid (HBr), hydrochloride (HCl), and hydrofluoric acid (HF), and aniline, diphenylguanidine, diethylamine, and isopropylamine. Examples thereof include salts in combination with amine compounds such as. Further, as an equivalent of amine hydrohalide, a salt in which tetrafluoroboric acid (HBF ₄ ) and an amine compound are combined can also be used.
The content of amine halide hydrohalates and the like 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-mentioned organic acids, amines, organic halogen compounds, amine hydrogen halides, phosphonic acids, phosphoric acid esters and the like can be added as activators, but other than that. It may play a role and may be added with such an intention.

The flux of the present embodiment may contain a thixotropic agent.
Examples of the thixotropy include wax-based thixotropy, amide-based thixotropy, and sorbitol-based thixotropy. Examples of the wax-based thixotropy include castor oil and the like. Examples of the amide-based thixo agent include monoamide-based thixo agent, bisamide-based thixo agent, and polyamide-based thixo agent. , Saturated fatty acid amide, oleic acid amide, erucic acid amide, unsaturated fatty acid amide, p-toluenemethane amide, aromatic amide, methylene bisstearic acid amide, ethylene bislauric acid amide, ethylene bishydroxystearic acid amide, saturated fatty acid bis amide , Methylenebisoleic acid amide, unsaturated fatty acid bisamide, m-xylylene bisstearic acid amide, aromatic bisamide, saturated fatty acid polyamide, unsaturated fatty acid polyamide, aromatic polyamide, substituted amide, methylolstearate amide, methylolamide, fatty acid Examples include ester amide. Examples of the sorbitol-based thixotropy include dibenzylidene-D-sorbitol and bis (4-methylbenzylidene) -D-sorbitol.

Further, the flux of the present embodiment may contain an ester compound as a thixotropic agent. Examples of the ester compound include castor oil and the like.

The total amount of the thixotropic agent contained in the flux is preferably 0% by mass or more and 15% by mass or less, and more preferably 0% by mass or more and 10% by mass or less. The content of the amido-based thixo agent is preferably 0% by mass or more and 12% by mass or less, and the content of the ester compound is preferably 0% by mass or more and 8.0% by mass or less, more preferably 0% by mass or more 4 It is 0.0% by mass or less.

As the antioxidant, for example, a hindered phenol-based antioxidant, a phenol-based antioxidant, a bisphenol-based antioxidant, a polymer-type antioxidant, etc. used in flux or various other fields may be used. Yes, 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 the range of 0 to 10% by mass or in the range of 0 to 5% by mass.

As an example of a preferable composition of the soldering flux of the present embodiment, rosin-based resin is 30 to 60% by mass, glycol-based solvent is 20 to 45% by mass, organic acid ester is 5 to 20% by mass, and organic acid is 1. Those containing within the range of ~ 15% by mass can be mentioned.

<Solder alloy>
As is an element capable of suppressing a change in the viscosity of the solder paste over time. Since As has low reactivity with flux and is a noble element with respect to Sn, it is presumed that it can exert an effect of suppressing thickening. If As is less than 25 mass ppm, the thickening suppressing effect cannot be sufficiently exhibited. The lower limit of the As content is 25 mass ppm or more, preferably 50 mass ppm or more, and more preferably 100 mass ppm or more. On the other hand, if the amount of As is too large, the wettability of the solder alloy deteriorates. The upper limit of the As content is 300 mass ppm or less, preferably 250 mass ppm or less, and more preferably 200 mass ppm or less.

Bi and Pb are elements that have low reactivity with flux and exhibit an effect of suppressing thickening. Further, these elements are elements that can suppress deterioration of wettability due to As because the liquidus temperature of the solder alloy is lowered and the viscosity of the molten solder is reduced.

If at least one element of Bi and Pb is present, deterioration of wettability due to As can be suppressed. When the solder alloy according to the present embodiment contains Bi, the lower limit of the Bi content is 0 mass ppm or more, preferably 25 mass ppm or more, more preferably 50 mass ppm or more, and further preferably 75 mass ppm or more. It is mass ppm or more, particularly preferably 100 mass ppm or more, and most preferably 250 mass ppm or more. When the solder alloy according to the present embodiment contains Pb, the lower limit of the Pb content is 0 mass ppm or more, preferably 25 mass ppm or more, more preferably 50 mass ppm or more, and further preferably 75 mass ppm or more. It is mass ppm or more, particularly preferably 100 mass ppm or more, and most preferably 250 mass 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, the liquid phase Bi and Pb will be concentrated because a high melting point crystal phase having a low content of Bi and Pb is precipitated in the solidification process of the molten solder. After that, when the temperature of the molten solder is further lowered, the low melting point crystal phase having a high concentration of Bi and Pb is segregated. Therefore, the mechanical strength of the solder alloy and the like are deteriorated. In particular, since the crystal phase having a high Bi concentration is hard and brittle, segregation in the solder alloy significantly reduces the mechanical strength and the like.

From this point of view, when the solder alloy according to the present embodiment contains Bi, the upper limit of the Bi content is 25,000 mass ppm or less, preferably 10,000 mass ppm or less, and more preferably 1000 mass ppm or less. Yes, more preferably 600 mass ppm or less, and particularly preferably 500 mass ppm or less. When the solder alloy according to the present embodiment contains Pb, the lower limit of the Pb content is 8000 mass ppm or less, preferably 5100 mass ppm or less, more preferably 5000 mass ppm or less, still more preferably. It is 1000 mass ppm or less, particularly preferably 850 mass ppm or less, and most preferably 500 mass ppm or less.

The solder alloy according to this embodiment needs to satisfy the following equation (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 have an effect of suppressing thickening. The total of these needs to be 230 mass ppm or more. In the formula (1), the As content is doubled because As has a higher effect of suppressing thickening than Bi and Pb.

If the formula (1) is less than 275, the thickening suppressing effect is not sufficiently exhibited. The lower limit of the equation (1) is 275 or more, preferably 300 or more, more preferably 700 or more, and further preferably 900 or more. On the other hand, the upper limit of (1) is not particularly limited from the viewpoint of the thickening suppressing effect, 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 10200 or less, particularly preferably 8200 or less, and most preferably 5300 or less.

The following equations (1a) and (1b) are obtained by appropriately selecting the upper limit and the lower limit 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.

The solder alloy according to this embodiment needs to satisfy the following equation (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, but if the content is too large, ΔT increases, so strict control is required. In particular, in an alloy composition containing Bi and Pb at the same time, ΔT tends to increase. In the present embodiment, the increase in ΔT can be suppressed by defining the total of the values obtained by multiplying the contents of Bi and Pb by a predetermined coefficient. In equation (2), the coefficient of Pb is larger than the coefficient of Bi. This is because Pb has a larger contribution to ΔT than Bi, and even if the content is slightly increased, ΔT is significantly increased.

The solder alloy having the formula (2) of 0 does not contain both Bi and Pb elements, and the deterioration of wettability due to the inclusion of As cannot be suppressed. The lower limit of the equation (2) is more than 0, preferably 0.02 or more, more preferably 0.03 or more, further preferably 0.05 or more, and particularly preferably 0.06 or more. , Most preferably 0.11 or more. On the other hand, if the equation (2) exceeds 7, the temperature range of ΔT becomes too wide, so that the crystal phase having a high concentration of Bi and Pb segregates 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, further preferably 5.75 or less, and even more preferably 4.18 or less. , Especially preferably 2.30 or less, and most preferably 0.90 or less.

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

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

Ag is an arbitrary element capable of forming Ag ₃ Sn at the crystal interface to improve the mechanical strength of the solder alloy and the like. In addition, Ag is an element whose ionization tendency is noble with respect to Sn, and when it coexists with As, Pb, and Bi, it promotes the effect of suppressing thickening. The Ag content is preferably 0 to 4%, more preferably 0.5 to 3.5%, and even more preferably 1.0 to 3.0%.

Cu is an optional element that can improve the joint strength of solder joints. Further, Cu is a noble element with respect to ionization tendency Sn, and when it coexists with As, Pb, and Bi, it promotes 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 even more preferably 0.2 to 0.7%.

The rest of the solder alloy according to this embodiment is Sn. In addition to the above-mentioned elements, unavoidable impurities may be contained. Even if it contains unavoidable impurities, it does not affect the above-mentioned effects. Further, as will be described later, even if an element not contained in the present embodiment is contained as an unavoidable impurity, the above-mentioned effect is not affected. If the content of In is too large, ΔT spreads, so if it is 1000 mass ppm or less, the above-mentioned effect is not affected.

<Solder paste>
The contents of the solder alloy and the flux in the solder paste are not limited, and 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 this embodiment preferably contains zirconium oxide powder. Zirconium oxide can suppress an increase in the viscosity of the paste due to aging. It is presumed that this is because the zirconium oxide is contained so that the oxide film thickness on the surface of the solder powder is maintained in the state before being put into the flux. Details are unknown, but it is inferred as follows. Normally, the active component of the flux has a slight activity even at room temperature, so that the surface oxide film of the solder powder becomes thin due to reduction, which causes the powders to aggregate with each other. Therefore, it is presumed that by adding the zirconium oxide powder to the solder paste, the active component of the flux reacts preferentially with the zirconium oxide powder, and the oxide film on the surface of the solder powder is maintained to such an extent that it does not aggregate.

In order to fully exert such effects, the content of the zirconium oxide powder in the solder paste is preferably 0.05 to 20.0% with respect to the total mass of the solder paste. When it is 0.05% or more, the above-mentioned action and effect can be exhibited, and when it is 20.0% or less, the content of the metal powder can be secured, and the thickening prevention effect can be exhibited. The content of zirconium oxide is preferably 0.05 to 10.0%, and the more preferable content is 0.1 to 3%.

The particle size 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. For the particle size, an SEM photograph of the zirconium oxide powder was taken, and the diameter equivalent to the projected circle was obtained by image analysis for each powder of 0.1 μm or more, and the average value was used.

The shape of zirconium oxide is not particularly limited, but if it has a different shape, the contact area with the flux is large and there is an effect of suppressing thickening. When it is spherical, good fluidity can be obtained, so that excellent printability as a paste can be obtained. The shape may be appropriately selected according to the desired characteristics.

The method for producing the soldering flux and the solder paste of the present embodiment is not limited, and the raw materials can be produced by mixing the raw materials simultaneously or sequentially by any method.
In the production of the flux, all the components of the flux may be finally mixed, and the glycol solvent and the organic acid ester may be mixed in advance to form a mixed solvent, or other components of the flux may be mixed at different timings. May be mixed with, or all the components of the flux including the glycol solvent and the organic acid ester may be mixed at the same time.
Further, in the production of the solder paste, it is not always necessary to prepare the flux in advance and mix it with the solder alloy, and finally it is added to all the 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 not be limited, and a part of the components of the flux and the solder alloy may be mixed, and then 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 were mixed in the formulations shown in the table to prepare fluxes of Examples A1 to A74 and Comparative Examples A1 and A2. The raw materials were compatible with each other and could be easily mixed.

For the fluxes of Examples and Comparative Examples, the void generation rate and solder wettability were evaluated by the following procedure.

(1) Void generation rate Flux of each example and comparative example and solder powder (average particle diameter φ: 21 μm) having a Sn-3.0Ag-0.5Cu (SAC305) composition are flux: solder powder = 11:89 mass. A solder paste mixed in a ratio was prepared.
The paste was then printed on an 8 mm × 8 mm Cu-OSP electrode (N = 15) at a height of 120 μm using a metal mask. After that, it reflowed in the air atmosphere. The reflow profile was held at 190 ° C. for 2 minutes and then warmed to 260 ° C. at 1.5 ° C./sec.
The transmission image of the soldered portion (solder bump) after the reflow was observed using Micro Focus X-ray System XVR-160 manufactured by UNi-HiTE SYSTEM, and the void generation rate was determined. Specifically, transmission observation is performed on the solder bumps from the upper part to the lower part, a circular solder bump transmission image is obtained, the metal filling portion and the void portion are identified based on the contrast of the color tone, and the void area ratio is automatically analyzed. Was calculated and used as the void occurrence rate. Using the void generation rate obtained in this way, the difficulty of void generation was evaluated according to the following criteria.
When the void generation rate is 15% or less in all 15 soldered parts: ○○
Among the 15 soldered parts, those with a void generation rate of more than 15% are included, but all of them are 20% or less: ○
When 15 soldered parts contain more than 20% void generation rate: ×

(2) Solder wettability The solder wettability of the flux was evaluated according to JIS Z 3198-4: 2003.
Specifically, the flux of each Example and Comparative Example is applied to the portion 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, which is fired at 150 ° C. for 1 hour, from the lower end to 3 mm in the length direction. And soaked in a solder bath under the following conditions, and the zero cross time was measured.
<Soaking conditions>
Solder composition: Sn-3.0Ag-0.5Cu
Solder tank temperature: 250 ° C JIS Z 3198-4: 2003
Immersion speed: 5 mm / sec JIS Z 3198-4: 2003
Immersion depth: 2 mm JIS Z 3198-4: 2003
Measurement time: 10 seconds JIS Z 3198-4: 2003

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: ×

(3) Comprehensive evaluation 〇: All the above evaluations are 〇 〇 or 〇 ×: There is × in each of the above evaluations

The results are shown in Tables 1-5. The fluxes of Examples A1 to A74 in which an organic acid ester and a glycol-based solvent were used in combination as a solvent had a good low void generation rate and also had good solder wettability.

<Solder alloy study>
The flux prepared in Example A1 and the solder alloy having the alloy composition shown in Tables 6 to 11 and having a size (particle size distribution) satisfying symbol 4 in the powder size classification (Table 2) in JIS Z 3284-1: 2004. Was mixed to prepare a solder paste. The mass ratio of the flux to the solder alloy is flux: solder powder = 11:89. For each solder paste, the change in viscosity with time 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 production. The details are as follows.

(4) Changes over time For each solder paste immediately after production, the viscosity was measured for 12 hours in the air at a rotation speed of 10 rpm and 25 ° C. using PCU-205 manufactured by Malcolm Co., Ltd. If the viscosity after 12 hours is 1.2 times or less of the viscosity when 30 minutes have passed since the solder paste was prepared, it was evaluated as "○" as having a sufficient effect of suppressing thickening. When it exceeded 1.2 times, it was evaluated as "x".

(5) ΔT
For the solder alloy before mixing with the flux, DSC measurement was performed using SII Nanotechnology Co., Ltd., model number: EXSTAR DSC7020, sample amount: about 30 mg, temperature rise rate: 15 ° C./min, and solid phase line. The temperature and the liquidus temperature were obtained. ΔT was obtained by subtracting the solidus temperature from the obtained liquidus temperature. When ΔT was 10 ° C. or lower, it was evaluated as “◯”, and when it exceeded 10 ° C., it was evaluated as “x”.

(6) Wetting property Each solder paste immediately after production was printed on a Cu plate, heated in an N ₂ atmosphere in a reflow furnace from 25 ° C. to 260 ° C. at a heating rate of 1 ° C./s, and then cooled to room temperature. .. Wetability was evaluated by observing the appearance of the solder bumps after cooling with an optical microscope. When the unmelted solder powder was not observed, it was evaluated as "◯", and when the unmelted solder powder was observed, it was evaluated as "x".

(7) Comprehensive evaluation 〇: All the above evaluations are 〇 ×: There is × in each of the above evaluations

As shown in Tables 6 to 11, it was found that all Examples B exhibited the thickening suppressing effect, the narrowing of ΔT, and the excellent wettability.

On the other hand, Comparative Examples B1, B10, B19, B28, B37, and B46 did not contain As, and therefore did not exhibit the thickening suppressing effect.

In Comparative Examples B2, B11, B20, B29, B38, and B47, since the formula (1) was less than the lower limit, the thickening suppressing effect was not exhibited.

Comparative Examples B3, B4, B12, B13, B21, B22, B30, B31, B39, B40, B48, and B49 showed inferior wettability because the As content exceeded the upper limit.

Comparative Examples B5, B7, B9, B14, B16, B18, B23, B25, B27, B32, B34, B36, B41, B43, B45, B50, B52, and B54 have an upper limit of Pb content and equation (2). Since the value was exceeded, the result was that ΔT exceeded 10 ° C.

In Comparative Examples B6, B15, B24, B33, B42, and B51, ΔT exceeded 10 ° C. because the equation (2) exceeded the upper limit.

Comparative Examples B8, B17, B26, B35, B44, and B53 showed the result that ΔT exceeded 10 ° C. because the Bi content and the equation (2) exceeded the upper limit.

<Combination of flux and solder alloy>
Even when various fluxes of Examples A2 to A74 are used in place of the flux of Example A1 and combined with various solder alloys of Example B, the void generation rate, the thickening suppressing effect, ΔT, and the wettability are also obtained. Good results were obtained in.

From this point of view, when the solder alloy according to the present embodiment contains Bi, the upper limit of the Bi content is 25,000 mass ppm or less, preferably 10,000 mass ppm or less, and more preferably 1000 mass ppm or less. Yes, more preferably 600 mass ppm or less, and particularly preferably 500 mass ppm or less. When the solder alloy according to the present embodiment contains Pb, the upper limit of the Pb content is 8000 mass ppm or less, preferably 5100 mass ppm or less, more preferably 5000 mass ppm or less, still more preferably. It is 1000 mass ppm or less, particularly preferably 850 mass ppm or less, and most preferably 500 mass ppm or less.

Claims (19)

Soldering flux containing resin, glycol solvent and organic acid ester; and As: 25-300 mass ppm, Bi: 0 mass ppm or more and 25,000 mass ppm or less, Pb: 0 mass ppm or more and 8000 mass ppm or less, and the balance Has an alloy composition consisting of Sn, and the following equations (1) and (2):
275 ≦ 2As + Bi + Pb (1)
0 <2.3 × 10 ^-4 × Bi + 8.2 × 10 ^-4 × Pb ≦ 7 (2)
[In the above equations (1) and (2), As, Bi, and Pb each represent the content (mass ppm) in the alloy composition].
Solder alloy that meets the requirements;
Including, solder paste. The solder paste according to claim 1, further comprising an organic acid. The solder paste according to claim 1, further comprising an activator. The solder paste according to any one of claims 1 to 3, wherein the content of the organic acid ester is more than 0% by mass and 20% by mass or less. The solder paste according to claim 4, wherein the content of the organic acid ester is in the range of 5 to 15% by mass. The ratio of the content (% by mass) of the organic acid ester to the content (% by mass) of the glycol solvent (organic acid ester content / content of glycol solvent) is 0.01 to 1.25. The solder paste according to any one of claims 1 to 5. The ratio of the content (mass%) of the organic acid ester to the content (mass%) of the glycol solvent (organic acid ester content / content of glycol solvent) is 0.15 to 0.72. The solder paste according to claim 6. Solding containing rosin-based resin in the range of 30 to 60% by mass, glycol-based solvent in the range of 10 to 60% by mass, organic acid ester in the range of 0.5 to 30% by mass, and organic acid in the range of 1 to 15% by mass. Flux; and As: 25 to 300 mass ppm, Bi: 0 mass ppm or more and 25,000 mass ppm or less, Pb: 0 mass ppm or more and 8000 mass ppm or less, and the balance having an alloy composition of Sn, as described in (1) below. Equation and equation (2):
275 ≦ 2As + Bi + Pb (1)
0 <2.3 × 10 ^-4 × Bi + 8.2 × 10 ^-4 × Pb ≦ 7 (2)
[In the above equations (1) and (2), As, Bi, and Pb each represent the content (mass ppm) in the alloy composition].
Solder alloy that meets the requirements;
Including, solder paste. The ratio of the content (mass%) of the organic acid ester to the content (mass%) of the glycol solvent (organic acid ester content / content of glycol solvent) is 0.01 to 1.25. The solder paste according to claim 8. The solder paste according to any one of claims 1 to 9, further comprising a thixotropic agent and / or an antioxidant. One selected from the group consisting of dimethyl adipate, diisopropyl adipate, dibutyl maleate, dimethyl sebacate, diisobutyl adipate, diethyl sebacate, diisopropyl sebacate, dibutyl sebacate, and sioctyl sebacate. The solder paste according to any one of claims 1 to 10, which is the above. The alloy composition is based on 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 paste according to any one of claims 1 to 11, which satisfies the above conditions. The alloy composition is 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]
The solder paste according to any one of claims 1 to 12, which satisfies the above conditions. The alloy composition is the following formula (2a):
0.02 ≤ 2.3 x 10 ^-4 x Bi + 8.2 x 10 ^-4 x Pb ≤ 0.9 (2a)
[In the above formula (2a), Bi and Pb each represent the content (mass ppm) in the alloy composition]
The solder paste according to any one of claims 1 to 13, which satisfies the above conditions. The solder paste according to any one of claims 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. The solder paste according to any one of claims 1 to 15, further comprising zirconium oxide powder. The solder paste according to claim 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. As: 25 to 300 mass ppm, Bi: 0 mass ppm or more and 25,000 mass ppm or less, Pb: 0 mass ppm or more and 8000 mass ppm or less, and the balance having an alloy composition of Sn, according to the following formula (1) and (2). )formula:
275 ≦ 2As + Bi + Pb (1)
0 <2.3 × 10 ^-4 × Bi + 8.2 × 10 ^-4 × Pb ≦ 7 (2)
[In the above equations (1) and (2), As, Bi, and Pb each represent the content (mass ppm) in the alloy composition].
For soldering a solder alloy that meets the requirements,
Flux containing resin, glycol solvent and organic acid ester. As: 25 to 300 mass ppm, Bi: 0 mass ppm or more and 25,000 mass ppm or less, Pb: 0 mass ppm or more and 8000 mass ppm or less, and the balance having an alloy composition of Sn, according to the following formula (1) and (2). )formula:
275 ≦ 2As + Bi + Pb (1)
0 <2.3 × 10 ^-4 × Bi + 8.2 × 10 ^-4 × Pb ≦ 7 (2)
[In the above equations (1) and (2), As, Bi, and Pb each represent the content (mass ppm) in the alloy composition].
For soldering a solder alloy that meets the requirements,
A flux containing 30 to 60% by mass of a rosin-based resin, 10 to 60% by mass of a glycol-based solvent, 0.5 to 30% by mass of an organic acid ester, and 1 to 15% by mass of an organic acid.