Solder composition and electronic substrate

Abstract

To provide a solder composition which can sufficiently suppress voids, and is excellent in solder melting property in a fine land.SOLUTION: A solder composition comprises a flux composition comprising (A) a rosin-based resin, (B) an activator, (C) a solvent, (D) a thixotropic agent and (E) an antioxidant, and (F) solder powder comprising 90% or more of powder having a melting point of 200°C or higher and 250°C or lower and a particle diameter of 10 μm or more and 25 μm or less by mass ratio, wherein the component (C) comprises (C1) any one dialkyl ether of dialkylene glycol, trialkylene glycol and tetraalkylene glycol, and a blending amount of the component (C1) is 40 mass% or more with respect to 100 mass% of the component (C).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a solder composition and an electronic substrate. [Background technology]

[0002] The solder composition is a paste-like mixture made by kneading solder powder with a flux composition (rosin-based resin, activator, solvent, etc.) (see, for example, Patent Document 1). This solder composition is required to have solderability, such as solder meltability and solder wetting and spreading properties (solder wetting and spreading), as well as void suppression and printability. Meanwhile, as the functionality of electronic devices becomes more diverse, large electronic components such as LGA (Land Grid Array) are increasingly being mounted on electronic circuit boards. Mounting LGA requires minute lands, which require solder compositions to have solder melting properties on the minute lands. Furthermore, some large electronic components have large electrode terminals (e.g., QFN (Quad Flatpack No Lead) and power transistors). These electronic components tend to have large solder composition printing areas, making them prone to voids. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5756067 Summary of the Invention [Problem to be solved by the invention]

[0004] Furthermore, in order to accommodate narrow-pitch components such as LGAs, solder powder particle sizes need to be reduced. However, when solder powder with such small particle sizes is used, voids tend to occur more easily and solder melting properties tend to be reduced. As described above, it has been difficult to achieve both solder melting properties on micro-lands and void suppression effects in a solder composition.

[0005] An object of the present invention is to provide a solder composition that can sufficiently suppress voids and has excellent solder melting properties on minute lands, and an electronic substrate using the same. [Means for solving the problem]

[0006] According to the present invention, there are provided the following solder compositions and electronic substrates. [1] A flux composition containing (A) a rosin-based resin, (B) an activator, (C) a solvent, (D) a thixotropic agent, and (E) an antioxidant, and (F) a solder powder having a melting point of 200°C or higher and 250°C or lower, and in which powder having a particle size of 10 μm or higher and 25 μm or lower accounts for 90% or more of the total by mass, the component (C) contains (C1) a dialkyl ether of any one of a dialkylene glycol, a trialkylene glycol, and a tetraalkylene glycol, The blending amount of the (C1) component is 40% by mass or more relative to 100% by mass of the (C) component. Solder composition. [2] The solder composition according to [1], The component (C1) is at least one selected from the group consisting of diethylene glycol dibutyl ether and tetraethylene glycol dimethyl ether. Solder composition. [3] The solder composition according to [1] or [2], The component (E) contains pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. Solder composition. [4] The solder composition according to any one of [1] to [3], The flux composition further contains an imidazole compound. Solder composition. [5] The solder composition according to any one of [1] to [4], Used when reflow soldering QFN. Solder composition. [6] A soldered portion using the solder composition according to any one of [1] to [5]. Electronic board. [Effects of the Invention]

[0007] According to one aspect of the present invention, it is possible to provide a solder composition that can sufficiently suppress voids and has excellent solder melting properties on minute lands, and an electronic substrate using the same. DETAILED DESCRIPTION OF THE INVENTION

[0008] The solder composition according to this embodiment contains a flux composition containing (A) a rosin resin, (B) an activator, (C) a solvent, (D) a thixotropic agent, and (E) an antioxidant, and (F) a solder powder having a melting point of 200°C to 250°C and a particle size of 10 μm to 25 μm, the powder accounting for 90% or more by mass of the total. The (C) solvent contains (C1) a dialkyl ether of any one of dialkylene glycol, trialkylene glycol, and tetraalkylene glycol. The blending amount of this component (C1) is 40% or more by mass relative to 100% by mass of component (C).

[0009] According to this embodiment, a solder composition can be obtained that can sufficiently suppress voids and has excellent solder melting properties on minute lands. The reason for this is not entirely clear, but the inventors speculate as follows. Specifically, the solder composition according to this embodiment uses (C1) a dialkyl ether of a dialkylene glycol, trialkylene glycol, or tetraalkylene glycol as the solvent (C). This component (C1) has a high void suppression effect and can improve solder meltability in fine lands. Furthermore, in this embodiment, to accommodate narrow-pitch components, the particle size of the solder powder is reduced, with powder having a particle size of 10 μm to 25 μm accounting for 90% or more by mass. When using solder powder with such a small particle size, voids tend to occur more easily and solder meltability tends to decrease. In response to this, this embodiment uses (E) an antioxidant. Typically, solder meltability is addressed by using an activator composition such as an organic acid, but depending on the type of organic acid, voids can occur. Therefore, in this embodiment, solder meltability is maintained by using component (E), which does not cause voids. The inventors believe that the above-mentioned effects of the present invention are achieved in this manner.

[0010] [Flux composition] First, the flux composition used in this embodiment will be described. The flux composition used in this embodiment is the components of the solder composition other than the solder powder, and contains (A) a rosin resin, (B) an activator, (C) a solvent, (D) a thixotropic agent, and (E) an antioxidant, which will be described below.

[0011] [Component (A)] The rosin-based resin (A) used in this embodiment includes rosins and rosin-modified resins. Examples of rosins include gum rosin, wood rosin, and tall oil rosin. Examples of rosin-modified resins include disproportionated rosin, polymerized rosin, hydrogenated rosin, and derivatives thereof. Examples of hydrogenated rosins include fully hydrogenated rosin, partially hydrogenated rosin, and hydrogenated products of unsaturated organic acid-modified rosins (also referred to as "hydrogenated acid-modified rosin"), which are rosins modified with unsaturated organic acids (e.g., aliphatic unsaturated monobasic acids such as (meth)acrylic acid, aliphatic unsaturated dibasic acids such as α,β-unsaturated carboxylic acids such as fumaric acid and maleic acid, and unsaturated carboxylic acids having an aromatic ring such as cinnamic acid). These rosin-based resins may be used alone or in combination of two or more.

[0012] The blending amount of component (A) is preferably 20% by mass to 60% by mass, and more preferably 30% by mass to 50% by mass, based on 100% by mass of the flux composition. When the blending amount of component (A) is above the lower limit, oxidation of the copper foil surface of the soldering land is prevented, making the surface more easily wetted by molten solder, improving so-called solderability and sufficiently suppressing solder balls. Furthermore, when the blending amount of component (A) is below the upper limit, the amount of flux residue can be sufficiently suppressed.

[0013] [(B) Component] The activator (B) used in this embodiment preferably contains an organic acid (B1) having 10 or more carbon atoms. This component (B1) is resistant to deactivation and can improve melting properties over a small area. Furthermore, this component (B1) tends not to be a cause of copper corrosion.

[0014] Examples of the component (B1) include dodecanedioic acid, eicosanedioic acid, dimer acid, trimer acid, 1-hydroxy-2-naphthoic acid, 3-hydroxy-2-naphthoic acid, and 1,4-dihydroxy-2-naphthoic acid. These may be used alone or in combination of two or more.

[0015] The blending amount of component (B1) is preferably 2% by mass to 15% by mass, and more preferably 4% by mass to 10% by mass, based on 100% by mass of the flux composition. If the blending amount of component (B1) is equal to or greater than the lower limit, the melting property in a small area tends to be improved, while if it is equal to or less than the upper limit, the insulating properties of the flux composition tend to be maintained.

[0016] The component (B) may contain (B2) an organic acid having less than 10 carbon atoms, as long as the effects of the present invention can be achieved. Examples of the component (B2) include monocarboxylic acids, dicarboxylic acids, and other organic acids having less than 10 carbon atoms. Monocarboxylic acids having less than 10 carbon atoms include formic acid, acetic acid, propionic acid, and butyric acid. Examples of dicarboxylic acids having less than 10 carbon atoms include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, and azelaic acid. Other organic acids having less than 10 carbon atoms include lactic acid, benzoic acid, salicylic acid, and citric acid.

[0017] In addition to components (B1) and (B2), component (B) may further contain other activators (such as (B3) a halogen-based activator and (B4) an amine-based activator) within the range that does not impair the effects of the present invention. The total amount of components (B1) and (B2) blended is preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 95% by mass or more, based on 100% by mass of component (B).

[0018] The blending amount of component (B) is preferably 4% by mass or more and 20% by mass or less, more preferably 7% by mass or more and 18% by mass or less, and particularly preferably 10% by mass or more and 16% by mass or less, based on 100% by mass of the flux composition. If the blending amount of component (B) is equal to or more than the lower limit, the activation effect tends to be improved, while if it is equal to or less than the upper limit, the insulating properties of the flux composition tend to be maintained.

[0019] [(C) component] The solvent (C) used in this embodiment must contain (C1) a dialkyl ether of any one of dialkylene glycol, trialkylene glycol, and tetraalkylene glycol. The component (C1) can suppress the generation of voids and improve solder melting properties on minute lands. Taking into account the melting point of component (F), the boiling point of component (C1) is preferably 230°C or higher and 290°C or lower. Examples of the component (C1) include diethylene glycol dibutyl ether (boiling point: 256° C.) and tetraethylene glycol dimethyl ether (boiling point: 275° C.). Among these, diethylene glycol dibutyl ether is preferred from the viewpoint of suppressing voids. In this specification, the boiling point refers to the boiling point at 1013 hPa.

[0020] The blending amount of component (C1) is 40% by mass or more relative to 100% by mass of component (C). If the blending amount of component (C1) is less than 40% by mass, the blending amount of glycol-based solvents having hydroxyl groups in the molecules may be too high, resulting in insufficient solder melting properties at micro-lands. From the same viewpoint, the blending amount of component (C1) is preferably 50% by mass or more relative to 100% by mass of component (C), more preferably 60% by mass or more, and particularly preferably 70% by mass or more. It is particularly preferable that the flux composition used in this embodiment does not contain glycol-based solvents having hydroxyl groups in the molecules.

[0021] The component (C) may contain a solvent (component (C2)) other than the component (C1) as long as the object of the present invention can be achieved. Examples of component (C2) include diethylene glycol monohexyl ether (HeDG), diethylene glycol monobutyl ether, α,β,γ-terpineol, benzyl glycol, diethylene glycol mono-2-ethylhexyl ether (EHDG), tripropylene glycol, diethylene glycol monobenzyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monobutyl ether, dipropylene glycol monobutyl ether, diethylene glycol monoethyl ether acetate, and 2,2-dimethyl-1,3-propanediol. These may be used alone or in combination of two or more.

[0022] The blending amount of component (C) is preferably 20% by mass to 60% by mass, more preferably 24% by mass to 50% by mass, and particularly preferably 28% by mass to 40% by mass, based on 100% by mass of the flux composition. If the blending amount of the solvent is within the above range, the viscosity of the resulting solder composition can be appropriately adjusted to an appropriate range.

[0023] [(D) component] The (D) thixotropic agent used in this embodiment can be any known thixotropic agent. Examples of the (D) component include hydrogenated castor oil, amides, kaolin, colloidal silica, organic bentonite, and glass frit. These may be used alone or in combination of two or more.

[0024] The blending amount of component (D) is preferably 1% by mass or more and 12% by mass or less, more preferably 2% by mass or more and 10% by mass or less, and particularly preferably 3% by mass or more and 8% by mass or less, based on 100% by mass of the flux composition. When the blending amount of component (D) is equal to or greater than the lower limit, thixotropy is obtained and sagging during printing can be suppressed. When the blending amount of component (D) is equal to or less than the upper limit, thixotropy is not too high and printing defects can be suppressed.

[0025] [(E) component] The antioxidant (E) used in this embodiment can be any known antioxidant. Examples of the antioxidant (E) include sulfur compounds, hindered phenol compounds, and phosphite compounds. Among these, hindered phenol compounds are preferred. This component (E) allows solder melting to be maintained even when using solder powder with a small particle size.

[0026] Examples of hindered phenol compounds include pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionic acid][ethylenebis(oxyethylene)], N,N'-bis[2-[2-(3,5-di-tert-butyl-4-hydroxyphenyl)ethylcarbonyloxy]ethyl]oxamide, and N,N'-bis{3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl}hydrazine. Among these, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is particularly preferred from the viewpoint of solder melting property. These may be used alone or in combination of two or more, but it is preferable to use a combination of two or more, specifically, it is preferable to use a combination of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and another hindered phenol compound.

[0027] The blending amount of component (E) is preferably 1% by mass or more and 12% by mass or less, more preferably 2% by mass or more and 8% by mass or less, and particularly preferably 3% by mass or more and 6% by mass or less, based on 100% by mass of the flux composition. The blending amount of component (E) is preferably within the above range from the viewpoint of the balance between solder melting properties and other physical properties.

[0028] [Imidazole compounds] The flux composition used in this embodiment may further contain an imidazole compound to further improve solder melting properties. Known solvents can be used as the imidazole compound. Examples of such imidazole compounds include 2-ethylimidazole and 2-ethyl-4-methylimidazole. When an imidazole compound is used, the blending amount thereof is preferably 0.01% by mass to 14% by mass, more preferably 1% by mass to 12% by mass, and particularly preferably 3% by mass to 10% by mass, based on 100% by mass of the flux composition. When the blending amount of the imidazole compound is within the above range, the solder melting property can be improved while maintaining viscosity stability during storage.

[0029] [Other ingredients] In addition to the components (A), (B), (C), (D), and (E), and the imidazole compound, the flux composition used in this embodiment may contain other additives and even other resins, as needed. Examples of other additives include antifoaming agents, modifiers, matting agents, and foaming agents. The amount of these additives added is preferably 0.01% by mass or more and 5% by mass or less, based on 100% by mass of the flux composition. Examples of other resins include acrylic resins.

[0030] [Solder composition] Next, the solder composition according to this embodiment will be described. The solder composition according to this embodiment contains the flux composition used in this embodiment described above and the solder powder (F) described below. The amount of the flux composition is preferably 5% by mass or more and 35% by mass or less, more preferably 7% by mass or more and 18% by mass or less, and particularly preferably 8% by mass or more and 15% by mass or less, relative to 100% by mass of the solder composition. If the amount of the flux composition is less than 5% by mass (if the amount of the solder powder exceeds 95% by mass), there will be an insufficient amount of flux composition as a binder, making it difficult to mix the flux composition and the solder powder. On the other hand, if the amount of the flux composition is more than 35% by mass (if the amount of the solder powder is less than 65% by mass), it will be difficult to form a satisfactory solder joint when using the resulting solder composition.

[0031] [Component (F)] The solder powder (F) used in this embodiment has a melting point of 200° C. or higher and 250° C. or lower. In this embodiment, component (C) with an appropriate boiling point is used, assuming that solder powder with a melting point of 200° C. or higher and 250° C. or lower is used. The solder alloy in this solder powder is preferably an alloy primarily composed of tin (Sn). Examples of secondary elements in this alloy include silver (Ag), copper (Cu), zinc (Zn), bismuth (Bi), indium (In), and antimony (Sb). Other elements (third and subsequent elements) may be added to this alloy as needed. Examples of other elements include copper, silver, bismuth, indium, antimony, and aluminum (Al). Here, lead-free solder powder refers to a powder of solder metal or alloy to which no lead is added. Although the presence of lead as an unavoidable impurity in lead-free solder powder is permitted, in this case, the amount of lead is preferably 300 ppm by mass or less.

[0032] Specific examples of solder alloys in lead-free solder powder include Sn-Ag and Sn-Ag-Cu alloys. Among these, Sn-Ag-Cu solder alloys are preferred from the viewpoint of solder joint strength. The melting point of Sn-Ag-Cu solder is usually 200°C or higher and 250°C or lower (preferably 200°C or higher and 240°C or lower). Among Sn-Ag-Cu solders, solders with low silver content have a melting point of 210°C or higher and 250°C or lower (preferably 220°C or higher and 240°C or lower).

[0033] Component (F) must be a powder with a particle size of 10 μm to 25 μm inclusive, which must account for 90% or more by mass. If the powder has a particle size of 10 μm or less or 25 μm or more inclusive, which accounts for 10% or more by mass, it will not be compatible with electronic circuit boards with narrow solder pad pitches. From the viewpoint of compatibility with electronic substrates having narrow solder pad pitches, the average particle size of component (F) is preferably from 1 μm to 25 μm, even more preferably from 2 μm to 22 μm, and particularly preferably from 3 μm to 20 μm. The average particle size can be measured using a dynamic light scattering particle size analyzer.

[0034] [Method for manufacturing solder composition] The solder composition according to this embodiment can be produced by blending the above-described flux composition and the above-described (E) solder powder in the predetermined ratio, and stirring and mixing them.

[0035] [Electronic board] Next, the electronic substrate according to this embodiment will be described. The electronic substrate according to this embodiment is characterized by having a soldered portion using the solder composition described above. The electronic substrate according to this embodiment can be manufactured by mounting electronic components on an electronic substrate (such as a printed wiring board) using the solder composition. The solder composition according to the present embodiment can sufficiently suppress large voids even when the solder composition is printed over a large area, and is therefore particularly suitable for use in QFN electronic components. Examples of the coating device used here include a screen printer, a metal mask printer, a dispenser, and a jet dispenser. Furthermore, an electronic component can be mounted on an electronic board by a reflow process in which an electronic component is placed on the solder composition applied by the application device, and heated under predetermined conditions in a reflow furnace to mount the electronic component on a printed wiring board.

[0036] In the reflow process, the electronic component is placed on the solder composition and heated in a reflow furnace under predetermined conditions. This reflow process allows for sufficient solder bonding between the electronic component and the printed wiring board. As a result, the electronic component can be mounted on the printed wiring board. The reflow conditions may be set appropriately depending on the melting point of the solder. For example, the preheat temperature is preferably 140°C or higher and 200°C or lower, and more preferably 150°C or higher and 160°C or lower. The preheat time is preferably 60 seconds or higher and 120 seconds or lower. The peak temperature is preferably 230°C or higher and 270°C or lower, and more preferably 240°C or higher and 255°C or lower. Furthermore, the holding time at a temperature of 220°C or higher is preferably 20 seconds or higher and 60 seconds or lower.

[0037] Furthermore, the solder composition and electronic substrate according to this embodiment are not limited to the above-described embodiment, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention. For example, in the electronic substrate, the printed wiring board and electronic components are bonded by a reflow process, but this is not limiting. For example, instead of the reflow process, the printed wiring board and electronic components may be bonded by a process of heating the solder composition using laser light (laser heating process). In this case, the laser light source is not particularly limited and can be appropriately selected depending on the wavelength that matches the absorption band of the metal. Examples of laser light sources include solid-state lasers (ruby, glass, YAG, etc.), semiconductor lasers (GaAs, InGaAsP, etc.), liquid lasers (dye, etc.), and gas lasers (He-Ne, Ar, CO2, excimer, etc.). [Example]

[0038] The present invention will now be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples. The materials used in the examples and comparative examples are listed below. (Component (A)) Rosin-based resin A: hydrogenated acid-modified rosin, product name "Pine Crystal KE-604", manufactured by Arakawa Chemical Industries, Ltd. Rosin-based resin B: Special modified rosin, product name "Haritack F-85", manufactured by Harima Chemicals Co., Ltd. ((B1) component) Organic acid A: 3-hydroxy-2-naphthoic acid, manufactured by Tokyo Chemical Industry Co., Ltd. Organic acid B: Dimer acid, product name "UNIDYME14", manufactured by Maruzen Yuka Shoji Co., Ltd. ((B2) component) Organic acid C: Malonic acid Organic Acid D: Adipic Acid ((C1) component) Solvent A: Diethylene glycol dibutyl ether (boiling point: 256°C), trade name "Hisolv BDB", manufactured by Toho Chemical Industry Co., Ltd. Solvent B: Tetraethylene glycol dimethyl ether (boiling point: 275°C), trade name "Hisorb MTEM", manufactured by Toho Chemical Industry Co., Ltd. ((C2) component) Solvent C: Diethylene glycol monohexyl ether (hexyl diglycol, HeDG, boiling point: 258°C), manufactured by Nippon Nyukazai Co., Ltd. Solvent D: Diethylene glycol mono-2-ethylhexyl ether (2-ethylhexyl diglycol (EHDG), boiling point: 272°C), manufactured by Nippon Nyukazai Co., Ltd. Solvent E: Tripropylene glycol monobutyl ether (BFTG, boiling point: 276°C) ((D) component) Thixotropic agent: High-grade fatty acid polyamide, trade name "Talen VA-79", manufactured by Kyoeisha Chemical Co., Ltd. ((E) component) Antioxidant A: Pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], trade name "ANOX20", manufactured by Shiraishi Calcium Co., Ltd. Antioxidant B: N,N'-bis{3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl}hydrazine, trade name "Irganox MD1024", manufactured by BASF (Other ingredients) Imidazole compound: 2-ethyl-4-methylimidazole (Component (F)) Solder powder: alloy composition Sn-3.0Ag-0.5Cu, particle size distribution 15-25μm (equivalent to Type 5 of IPC-J-STD-005A), solder melting point 217-220℃

[0039] [Example 1] 35 mass% of rosin-based resin A, 5 mass% of rosin-based resin B, 2 mass% of organic acid A, 5 mass% of organic acid B, 2 mass% of organic acid C, 5 mass% of organic acid D, 30.5 mass% of solvent A, 4 mass% of antioxidant A, 1 mass% of antioxidant B, 5 mass% of imidazole compound, and 5.5 mass% of thixotropic agent were charged into a container and mixed using a planetary mixer to obtain a flux composition. Thereafter, 12% by mass of the obtained flux composition and 88% by mass of solder powder (total of 100% by mass) were placed in a container and mixed with a planetary mixer to prepare a solder composition.

[0040] [Example 2] A solder composition was obtained in the same manner as in Example 1, except that the materials were mixed according to the composition shown in Table 1. [Comparative Examples 1 to 3] A solder composition was obtained in the same manner as in Example 1, except that the materials were mixed according to the composition shown in Table 1.

[0041] <Evaluation of solder composition> The solder composition was evaluated (microland melting, QFN voids, LGA voids) by the following methods. The results are shown in Table 1. (1) Micro-land melting The solder composition was printed onto the substrate using a 0.1 mm thick metal mask. Test patterns of 100 copper foil pads with diameters of 0.28 mm, 0.26 mm, 0.24 mm, 0.22 mm, and 0.20 mm were printed. The test substrates were then subjected to a reflow treatment under the following conditions: a preheat temperature of 140 to 200°C for 120 seconds, a holding time of 220°C or higher for 40 seconds, and a peak temperature of 250°C. The test substrates were observed under a microscope to measure the diameter (unit: mmφ) of the smallest melting pad. The microland melting property was then evaluated according to the following criteria. ◯: The diameter of the smallest melt pad is 0.20 mm. ×: The diameter of the smallest melt pad is 0.22 mm or more. (2) QFN voids A solder composition was printed onto the substrate using a 0.1 mm thick metal mask, and a 0.5 mm pitch QFN (Quad Flat Non-leaded Package) was mounted. The reflow process was then performed under the same conditions as for the evaluation of micro-land melting properties to prepare an evaluation board. Then, voids were measured using an X-ray inspection system, "MUX-3400" manufactured by Mars Tohken Solutions, and the void area ratio [(total void area / total land area) x 100] in the QFN pad area was calculated using the system's standard application. Voids were evaluated according to the following criteria. ◯: The void area ratio is 20% or less. △: The void area ratio is more than 20% and 25% or less. ×: The void area ratio is more than 25%. (3) LGA void A solder composition was printed onto the board using a 0.1 mm thick metal mask, and a 0.5 mm pitch LGA (Land Grid Array) was mounted. The reflow process was then performed under the same conditions as for the evaluation of micro-land melting properties to create an evaluation board. Then, voids were measured using an X-ray inspection system, the "MUX-3400" manufactured by Mars Tohken Solutions, and the void area ratio in the LGA pad area [(total void area / total land area) x 100] was calculated using the system's standard application. Voids were then evaluated according to the following criteria: ◯: The void area ratio is 20% or less. △: The void area ratio is more than 20% and 25% or less. ×: The void area ratio is more than 25%.

[0042] [Table 1]

[0043] As is clear from the results shown in Table 1, it was confirmed that the solder compositions of the present invention (Examples 1 and 2) were good in all of the results for microland melting, QFN voids, and LGA voids. Therefore, it was confirmed that the solder composition of the present invention can sufficiently suppress voids and has excellent solder melting properties on minute lands. [Industrial Applicability]

[0044] The solder composition of the present invention can be suitably used in a technique for mounting electronic components on electronic substrates such as printed wiring boards of electronic devices.

Claims

1. A flux composition comprising (A) a rosin-based resin, (B) an activator, (C) a solvent, (D) a thixotropic agent, and (E) an antioxidant; and (F) a solder powder having a melting point of 200°C or higher and 250°C or lower, the powder having a particle size of 10 μm or higher and 25 μm or lower accounting for 90% or more by mass of the total solder powder, the component (C) contains (C1) a dialkyl ether of any one of a dialkylene glycol, a trialkylene glycol, and a tetraalkylene glycol, The blending amount of the (C1) component is 40% by mass or more relative to 100% by mass of the (C) component. Solder composition.

2. The solder composition according to claim 1, The component (C1) is at least one selected from the group consisting of diethylene glycol dibutyl ether and tetraethylene glycol dimethyl ether. Solder composition.

3. The solder composition according to claim 1 or 2, The component (E) contains pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. Solder composition.

4. The solder composition according to claim 1 or 2, The flux composition further contains an imidazole compound. Solder composition.

5. The solder composition according to claim 1 or 2, Used when reflow soldering QFN. Solder composition.

6. A soldered portion using the solder composition according to claim 1 or 2. Electronic board.

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