Flux and solder paste

Abstract

To provide a flux which can improve printability of a solder paste, and a solder paste which can improve printability.SOLUTION: A flux is used for soldering, contains a resin, an unsaturated aliphatic compound having 18 to 22 carbon atoms and having one unsaturated bond, a thixotropic agent, and a solvent, wherein the resin contains a rosin-based resin and a liquid resin having viscosity measured under conditions of a measurement temperature of 30°C and the number of rotation of 50 rpm by an E type viscometer of 300 mPa s or more and 55,000 mPa s or less, and the content of the unsaturated aliphatic compound is 3.0 mass% or more and 25.0 mass% or less with respect to the whole flux.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a flux used for soldering and a solder paste containing the flux.

Background Art

[0002] In the mounting technology of mounting electronic components such as chip components and package substrates on an electronic circuit board such as a printed wiring board, a solder paste in which a solder alloy and a flux are mixed is used. Specifically, after screen-printing the solder paste using a metal mask on pads on the surface of the electronic circuit board, the electronic components are mounted and heated (reflowed), whereby the electronic components are joined to the electronic circuit board.

[0003] Conventionally, as the flux contained in the solder paste, a resin-based flux containing a synthetic resin, a rosin-based resin, or the like as a resin component has been widely used. And when soldering is performed using a solder paste containing a resin-based flux, it is widely known that a film portion called flux residue caused by the resin component remains on the electronic circuit board after soldering.

[0004] Such flux residues may crack due to temperature changes such as thermal cycles. Therefore, when moisture penetrates into the flux residue from the crack, there is a risk of causing defects such as a decrease in insulation between leads. Therefore, in order to suppress the occurrence of cracks, it has been proposed to use a liquid resin having a relatively high viscosity as the resin component in the flux. For example, Patent Document 1 discloses a flux containing a polybutadiene (meth) acrylate compound and a hydrogenated dimer acid.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] However, if a relatively high-viscosity liquid resin is used as the resin component in the flux, as described in Patent Document 1, the solder paste is more likely to adhere to the sides of the openings in the metal mask, which may reduce the amount of solder supplied. In particular, when a metal mask with a low aspect ratio (ratio of the opening area to the opening side area) is used, the solder paste is more likely to adhere to the sides of the openings in the metal mask, which may result in insufficient solder supply. Therefore, even when a relatively high-viscosity liquid resin is used as the resin component in the flux, it is desirable to suppress the reduction in the amount of solder supplied to the openings in the metal mask and improve the printability of the solder paste.

[0007] This invention has been made in view of the above circumstances, and aims to provide a flux capable of improving the printability of solder paste. It also aims to provide a solder paste capable of improving printability. [Means for solving the problem]

[0008] The flux according to the present invention is a flux used for soldering, and contains a resin, an unsaturated aliphatic compound having 18 to 22 carbon atoms and one unsaturated bond, a thixotropic agent, and a solvent, wherein the resin includes a rosin-based resin and a liquid resin whose viscosity, as measured by an E-type viscometer at a temperature of 30°C and a rotation speed of 50 rpm, is 300 mPa·s to 55000 mPa·s, and the content of the unsaturated aliphatic compound is 3.0% by mass to 25.0% by mass of the total flux.

[0009] The solder paste according to the present invention contains the flux described above and solder alloy powder. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a flux that can improve the printability of solder paste. Furthermore, it is possible to provide a solder paste that can improve printability. [Modes for carrying out the invention]

[0011] The flux and solder paste according to embodiments of the present invention will be described below.

[0012] <Flux> The flux according to this embodiment contains a resin, an unsaturated aliphatic compound, a thixotropic agent, and a solvent.

[0013] (resin) The resin contains a rosin-based resin and a liquid resin whose viscosity, as measured by an E-type viscometer at a temperature of 30°C and a rotation speed of 50 rpm, is between 300 mPa·s and 55,000 mPa·s.

[0014] The rosin-based resin is not particularly limited, and for example, one or more rosin-based resins selected from rosin and rosin derivatives (e.g., hydrogenated rosin, polymerized rosin, disproportionated rosin, acrylic acid-modified rosin, etc.) can be used.

[0015] The content of the rosin-based resin is preferably 10.0% by mass or more, and more preferably 20.0% by mass or more, relative to the total flux, from the viewpoint of improving printability by enhancing the dispersibility of the thixotropic agent and stabilizing the viscosity of the solder paste. Furthermore, from the viewpoint of maintaining the form of the solder paste, the content of the rosin-based resin is preferably 60.0% by mass or less, and more preferably 35.0% by mass or less, relative to the total flux. If two or more types of rosin-based resins are included, the above content refers to the total content of the rosin-based resins.

[0016] The liquid resin has a viscosity measured in accordance with JIS K 7117-2 using an E-type viscometer at a temperature of 30°C and a rotation speed of 50 rpm, preferably between 300 mPa·s and 55,000 mPa·s, and more preferably between 5,000 mPa·s and 50,000 mPa·s. Examples of such liquid resins include GI-1000, GI-2000, and GI-3000 (all manufactured by Nippon Soda Co., Ltd.), which are hydrogenated polybutadienes with hydroxyl groups at both ends (hydroxyl-terminated hydrogenated polybutadienes); G-1000, G-2000, and G-3000 (all manufactured by Nippon Soda Co., Ltd.), which are liquid polybutadienes with hydroxyl groups at both ends (hydroxyl-terminated liquid polybutadienes); Poly-bd R-15HT, Poly-bd R-45HT (manufactured by Idemitsu Kosan Co., Ltd.), Poly-ip (manufactured by Idemitsu Kosan Co., Ltd.), a liquid polyisoprene with hydroxyl groups at both ends (hydroxyl-terminated liquid polyisoprene), EPOL (manufactured by Idemitsu Kosan Co., Ltd.), a liquid polyolefin with hydroxyl groups at both ends (hydroxyl-terminated liquid polyolefin), NOF Polybutene O-15N, NOF Polybutene 3N, NOF Polybutene 10N, NOF Polybutene 30N (all manufactured by NOF Corporation), Nippon Oil Polybutene Grade LV-7, Grade LV-50, Grade LV-100, Grade HV-15, Grade 35, Grade HV-50, Grade HV-100, Grade HV-300 (all manufactured by ENEOS Corporation), and acrylic resin. Examples include Acrylic O (manufactured by Arakawa Chemical Industries, Ltd.), Outflow UMM-1001, UT-1001, CB-3060, CBB-3098 (manufactured by Soken Chemical Co., Ltd.), Bisphenol A type epoxy resins such as YD-8125, YD-825GS (manufactured by Nippon Steel Chemical & Material Co., Ltd.), EPICLON840, 840-S, 850, 850-S, EXA-850CRP, 850-LC (manufactured by DIC Corporation), and Bisphenol F type epoxy resins such as YDF-YDF-8170, YDF-870GS (manufactured by Nippon Steel Chemical & Material Co., Ltd.), EPICLON830, 830-S, 835, EXA-830CRP, EXA-830LVP, EXA-835LV (manufactured by DIC Corporation). Among these, from the viewpoint of reducing cracks in flux residue and ease of handling the resin, it is preferable that the liquid resin contains at least one selected from hydrogenated polybutadiene with hydroxyl groups at both ends and acrylic resin.Furthermore, the liquid resin may be used alone or in combination of two or more types.

[0017] From the viewpoint of suppressing the occurrence of cracks in the flux residue, the content of the liquid resin is preferably 10.0% by mass or more, and more preferably 20.0% by mass or more, relative to the total flux. Furthermore, from the viewpoint of maintaining the form of the solder paste, the content of the liquid resin is preferably 60.0% by mass or less, and more preferably 35.0% by mass or less, relative to the total flux. If two or more types of liquid resin are included, the above content refers to the total content of the liquid resins.

[0018] The resin may include other resins besides the rosin-based resin and the liquid resin. Examples of other resins include terpene phenol resins, phenol resins, polyvinyl acetate resins, ethylene-vinyl acetate copolymers, polylactic acid, and polystyrene. The other resins may be used individually or in combination of two or more.

[0019] From the viewpoint of its effect on the wettability of the solder, the content of the other resins is preferably 5.0% by mass or more, and more preferably 10.0% by mass or more, relative to the total flux. Furthermore, from the viewpoint of its effect on the wettability of the solder, the content of the other resins is preferably 30.0% by mass or less, and more preferably 20.0% by mass or less, relative to the total flux. If two or more types of other resins are included, the above content refers to the total content of the other resins.

[0020] The total resin content is preferably 30.0% by mass or more, and more preferably 40.0% by mass or more, relative to the total flux. Furthermore, the total resin content is preferably 70.0% by mass or less, and more preferably 60.0% by mass or less, relative to the total flux.

[0021] (unsaturated aliphatic compounds) The flux according to this embodiment contains an unsaturated aliphatic compound having 18 to 22 carbon atoms and one unsaturated bond. It is preferable that the unsaturated aliphatic compound contains at least one selected from unsaturated aliphatic alcohols, unsaturated fatty acids, and unsaturated fatty acid esters, and it is more preferable that it contains an unsaturated aliphatic alcohol.

[0022] From the viewpoint of improving the slipperiness of the solder paste, the content of the unsaturated aliphatic compound is 3.0% by mass or more, preferably 5.0% by mass or more, based on the entire flux. Also, from the viewpoint of maintaining the form as a solder paste, the content of the unsaturated aliphatic compound is 25.0% by mass or less, preferably 15.0% by mass or less, based on the entire flux. When two or more kinds of the unsaturated aliphatic compounds are contained, the content is the total content of the unsaturated aliphatic compounds.

[0023] The unsaturated aliphatic alcohol has 18 to 22 carbon atoms and one unsaturated bond. Examples of the unsaturated aliphatic alcohol include oleyl alcohol, elaidyl alcohol, ricinoleyl alcohol, erucyl alcohol, etc. Among these, from the viewpoint of improving the slipperiness of the solder paste, it is preferable that the unsaturated aliphatic alcohol contains oleyl alcohol, and it is more preferable that it consists of oleyl alcohol. The unsaturated aliphatic alcohol may be used alone or in combination of two or more kinds.

[0024] From the perspective of improving the slipperiness of the solder paste, the content of the unsaturated aliphatic alcohol is preferably 3.0% by mass or more, more preferably 5.0% by mass or more, based on the total amount of the flux. Also, from the perspective of maintaining the form of the solder paste, the content of the unsaturated aliphatic alcohol is preferably 25.0% by mass or less, more preferably 15.0% by mass or less, based on the total amount of the flux. When two or more kinds of the unsaturated aliphatic alcohols are contained, the content is the total content of the unsaturated aliphatic alcohols.

[0025] The unsaturated fatty acid has 18 to 22 carbon atoms and one unsaturated bond. Examples of the unsaturated fatty acid include oleic acid, elaidic acid, vaccenic acid, gadoleic acid, eicosenoic acid, erucic acid, etc. Among these, from the perspective of improving the slipperiness of the solder paste, the unsaturated fatty acid preferably contains oleic acid. The unsaturated fatty acid may be used alone or in combination of two or more kinds.

[0026] From the perspective of improving the slipperiness of the solder paste, the content of the unsaturated fatty acid is preferably 3.0% by mass or more, more preferably 5.0% by mass or more, based on the total amount of the flux. Also, from the perspective of maintaining the form of the solder paste, the content of the unsaturated fatty acid is preferably 25.0% by mass or less, more preferably 15.0% by mass or less, based on the total amount of the flux. When two or more kinds of the unsaturated fatty acids are contained, the content is the total content of the unsaturated fatty acids.

[0027] The aforementioned unsaturated fatty acid ester has 18 to 22 carbon atoms and possesses one unsaturated bond. Examples of the aforementioned unsaturated fatty acid ester include methyl oleate, ethyl oleate, butyl oleate, pentyl oleate, hexyl oleate, heptyl oleate, octyl oleate, nonyl oleate, dosyl oleate, undecyl oleate, dodecyl oleate, isopropyl oleate, isobutyl oleate, 2-ethylhexyl oleate, octyldodecyl oleate, methyl erucate, ethyl erucate, butyl erucate, hexyl erucate, heptyl erucate, octyl erucate, nonyl erucate, dosyl erucate, undecyl erucate, dodecyl erucate, isopropyl erucate, isobutyl erucate, 2-ethylhexyl erucate, and octyldodecyl erucate. Among these, from the viewpoint of improving the lubricity of the solder paste, it is preferable that the unsaturated fatty acid ester contains methyl oleate. Note that the unsaturated fatty acid ester may be used alone or in combination of two or more types.

[0028] From the viewpoint of improving the slipperiness of the solder paste, the content of the unsaturated fatty acid ester is preferably 3.0% by mass or more, and more preferably 5.0% by mass or more, relative to the total flux. Furthermore, from the viewpoint of maintaining the form of the solder paste, the content of the unsaturated fatty acid ester is preferably 25.0% by mass or less, and more preferably 15.0% by mass or less, relative to the total flux. If two or more types of unsaturated fatty acid esters are included, the above content refers to the total content of the unsaturated fatty acid esters.

[0029] (Tixotropic agent) The flux according to this embodiment contains a thixotropic agent. Examples of thixotropic agents include hydrogenated castor oil, fatty acid amides, fatty acid bisamides, polyamide compounds, kaolin, colloidal silica, organic bentonite, and glass frit. Among these, from the viewpoint of heat resistance, the thixotropic agent is preferably a fatty acid bisamide (fatty acid bisamide) or a polyamide compound. Examples of fatty acid bisamides include methylene bisstearate, ethylene biscaprate, ethylene bislaurate, ethylene bisstearate, ethylene bishydroxystearate, ethylene bisbehenamide, hexamethylene bisstearate, hexamethylene bisbehenamide, hexamethylene bis-12-hydroxystearate, N,N'-distearyl adipic acid amide, and N,N'-xylylene bis-12-hydroxystearylamide. Examples of polyamide compounds include aliphatic polyamide compounds such as Talen VA-79, AMX-6096A, WH-215, WH-255 (all manufactured by Kyoeisha Chemical Co., Ltd.), SP-10, SP-500 (both manufactured by Toray Industries, Inc.), Grilamid L20G, Grilamid TR55 (both manufactured by M-Chemistry Japan Co., Ltd.), and aromatic polyamide compounds (semi-aromatic polyamide compounds or fully aromatic polyamide compounds) containing cyclic compounds such as benzene rings and naphthalene rings in the main chain, such as JH-180 (manufactured by Ito Oil Co., Ltd.). The thixotropin may be used alone or in combination of two or more types.

[0030] The content of the thixotropin is preferably 1.0% by mass or more, and more preferably 3.0% by mass or more, relative to the total flux. Furthermore, the content of the thixotropin is preferably 7.0% by mass or less, and more preferably 5.0% by mass or less, relative to the total flux. If two or more types of thixotropin are included, the above content refers to the total content of the thixotropin.

[0031] (solvent) The flux according to this embodiment contains a solvent. As the solvent, for example, known solvents such as glycol ethers such as diethylene glycol monohexyl ether (hexyl diglycol), diethylene glycol dibutyl ether (dibutyl diglycol), diethylene glycol mono-2-ethylhexyl ether (2-ethylhexyl diglycol), diethylene glycol monobutyl ether (butyl diglycol), triethylene glycol monobutyl ether (butyl triglycol), polyethylene glycol dimethyl ether, and tripropylene glycol n-butyl ether can be used; aliphatic compounds such as n-hexane, isohexane, and n-heptane; esters such as isopropyl acetate, methyl propionate, and ethyl propionate; ketones such as methyl ethyl ketone, methyl-n-propyl ketone, and diethyl ketone; and alcohols such as ethanol, n-propanol, isopropanol, and isobutanol can be used. Note that one solvent may be used alone, or two or more may be used in combination.

[0032] The solvent content is preferably 15.0% by mass or more, and more preferably 23.0% by mass or more, relative to the total flux. Furthermore, the solvent content is preferably 40.0% by mass or less, and more preferably 30.0% by mass or less, relative to the total flux. If two or more solvents are included, the content refers to the total content of the solvents.

[0033] (Saturated aliphatic alcohols) The flux according to this embodiment may contain saturated aliphatic alcohols. The saturated aliphatic alcohols are not particularly limited and include, for example, 1-tridecanol, cetanol, 1-heptadecanol, stearyl alcohol, isostearyl alcohol, etc. From the viewpoint of improving the slipperiness of the solder paste against the opening side surface of the metal mask, the content of the saturated aliphatic alcohols is preferably 8.0% by mass or less, more preferably 5.0% by mass or less, and even more preferably no saturated aliphatic alcohols at all, relative to the total flux. Note that one type of saturated aliphatic alcohol may be used alone, or two or more types may be used in combination.

[0034] (Activating agent) The flux according to this embodiment may contain an activator. The activator is not particularly limited and examples include organic acid-based activators, amine compounds, amino acid compounds, halogen-based activators such as amine halogen salts and halogen compounds. The activator may be used alone or in combination of two or more.

[0035] The aforementioned organic acid-based surfactants are not particularly limited and include, for example, monocarboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, capric acid, lauric acid, myristic acid, pentadecyl acid, palmitic acid, margaric acid, stearic acid, tubercurostearic acid, arachidic acid, behenic acid, lignoceric acid, and glycolic acid; dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, methylsuccinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, tartaric acid, and diglycolic acid; and other organic acids such as dimer acid, levulinic acid, lactic acid, acrylic acid, benzoic acid, salicylic acid, anisic acid, citric acid, picolinic acid, tris(2-carboxyethyl)isocyanuric acid, and tris(2-carboxypropyl)isocyanuric acid.

[0036] Examples of the halogen compounds include tris(2,3-dibromopropyl)isocyanuric acid, 2,3-dibromo-2-butene-1,4-diol, 2-bromo-3-iodo-2-butene-1,4-diol, and TBA-bis(2,3-dibromopropyl ether).

[0037] The content of the activator is preferably 0.5% by mass or more, and more preferably 3.0% by mass or more, relative to the total flux. Furthermore, the content of the activator is preferably 20.0% by mass or less, and more preferably 10.0% by mass or less, relative to the total flux. If two or more types of activators are included, the content refers to the total content of the activators.

[0038] The flux according to this embodiment may also contain, as other additives, at least one selected from, for example, stabilizers, surfactants, defoamers, and antioxidants. The total content of the other additives is not particularly limited and can be, for example, 5.0% by mass or less of the total flux.

[0039] The flux according to this embodiment is a flux used for soldering and contains a resin, an unsaturated aliphatic compound having 18 to 22 carbon atoms and one unsaturated bond, a thixotropic agent, and a solvent. The resin includes a rosin-based resin and a liquid resin whose viscosity, as measured by an E-type viscometer at a temperature of 30°C and a rotation speed of 50 rpm, is 300 mPa·s to 55000 mPa·s. The content of the unsaturated aliphatic compound is 3.0% by mass to 25.0% by mass of the total flux, which improves the slipperiness of the solder paste against the side surface of the opening of the metal mask and makes it less likely for the solder paste to adhere to the side surface of the opening of the metal mask. As a result, the flux can improve the printability of the solder paste.

[0040] In this embodiment, the flux contains at least one unsaturated aliphatic compound selected from unsaturated aliphatic alcohols, unsaturated fatty acids, and unsaturated fatty acid esters, thereby improving the slipperiness of the solder paste against the opening side surface of the metal mask and making it less likely for the solder paste to adhere to the opening side surface of the metal mask. As a result, the flux can improve the printability of the solder paste.

[0041] In this embodiment, the flux contains 5.0% to 15.0% by mass of the unsaturated aliphatic compound relative to the total flux, which improves the slipperiness of the solder paste against the side surface of the opening of the metal mask, making it less likely for the solder paste to adhere to the side surface of the opening of the metal mask. As a result, the printability of the solder paste can be improved.

[0042] <Solda paste> The solder paste according to this embodiment contains the flux described above and solder alloy powder. The solder paste is obtained by mixing the flux and the solder alloy powder. The flux content is preferably 5.0% by mass or more and 20.0% by mass or less of the total solder paste. The solder alloy powder content is preferably 80.0% by mass or more and 95.0% by mass or less of the total solder paste.

[0043] Examples of alloys for the solder alloy powder include lead-free solder alloys and lead-containing eutectic solder alloys, but from the viewpoint of reducing environmental impact, lead-free solder alloys are preferred. Examples of lead-free solder alloys include alloys containing tin, silver, copper, indium, zinc, bismuth, antimony, etc. More specifically, examples of alloys include Sn / Ag, Sn / Ag / Cu, Sn / Cu, Sn / Ag / Bi, Sn / Bi, Sn / Ag / Cu / Bi, Sn / Sb, Sn / Zn / Bi, Sn / Zn, Sn / Zn / Al, Sn / Ag / Bi / In, Sn / Ag / Cu / Bi / In / Sb, and In / Ag. Among these, the alloy for the solder alloy powder is preferably a Sn / Ag / Cu alloy. Furthermore, it is more preferable that the Sn / Ag / Cu alloy contains at least one selected from In, Bi, Sb, and Ni. Furthermore, the alloy contains unavoidable impurities. Unavoidable impurities refer to components that are inevitably mixed in during the manufacturing process and are acceptable to the extent that they do not affect the effects of the present invention.

[0044] The particle size of the solder alloy powder is preferably 5 μm or more and 45 μm or less, and more preferably 15 μm or more and 39 μm or less.

[0045] The solder paste according to this embodiment contains the flux described above and solder alloy powder. The flux improves the slipperiness of the solder paste against the side surface of the opening of the metal mask, making it less likely for the solder paste to adhere to the side surface of the opening of the metal mask. As a result, the solder paste can improve printability.

[0046] In this embodiment, the solder paste may also be made of a Sn / Ag / Cu alloy. The solder paste can improve printability even for Sn / Ag / Cu alloys that are widely used.

[0047] The solder paste according to this embodiment may further contain at least one element selected from In, Bi, Sb, and Ni in addition to the Sn / Ag / Cu alloy. The solder paste can be improved in printability even if these metal elements are added for the purpose of improving the thermal durability of the solder alloy. [Examples]

[0048] The following describes embodiments of the present invention, but the present invention is not limited to the following embodiments.

[0049] <Preparation of Solder Paste> The raw materials in the amounts shown in Tables 1 to 4 were placed in a heating container and heated to dissolve all the raw materials. Afterward, the mixture was cooled to room temperature to obtain a uniformly dispersed flux. Note that the amounts shown in Tables 1 to 4 are equal to the content of each component in the flux. Next, each flux was mixed with the solder alloy powders shown in Tables 1 to 4 to a concentration of 88.2% by mass to obtain the solder pastes for each example and comparative example.

[0050] [Table 1]

[0051] [Table 2]

[0052] [Table 3]

[0053] [Table 4]

[0054] Table 5 shows the details of each raw material contained in the flux shown in Tables 1 to 4. Table 6 shows the details of the solder alloys shown in Tables 1 to 4. Table 7 shows the details of the unsaturated aliphatic alcohols shown in Tables 1 to 4. In Table 7, "components other than oleyl alcohol" includes stearyl alcohol, palmitrail alcohol, and cetanol. The effective proportion of oleyl alcohol in Tables 1 to 4 was calculated from the oleyl alcohol content in each unsaturated aliphatic alcohol shown in Table 7. The effective proportion of oleyl alcohol shown in Tables 1 to 4 is equal to the oleyl alcohol content in the specification.

[0055] [Table 5]

[0056] [Table 6]

[0057] [Table 7]

[0058] <Measurement of viscosity of liquid resin> The viscosity (Pa·s) of the liquid resin was measured using an E-type viscometer (RE-100U, manufactured by Toki Sangyo Co., Ltd.) according to the measurement method in accordance with JIS K 7117-2, under the following measurement conditions. Note that the liquid resin "TEAI-1000" used in Comparative Example 4 could not be measured because it exceeded the upper limit of the range measurable by the above E-type viscometer (60,000 mPa·s). The measurement results are shown in Table 5.

[0059] (Measurement conditions) Rotation speed during measurement: 50 rpm Measurement temperature: 30℃ Viscosity value: Read the value 2 minutes after the start of measurement.

[0060] <Evaluation of printability> 300g of the solder paste from each example and comparative example was placed on a metal mask set up in a printing press (YVP-Xg, manufactured by Yamaha Motor Co., Ltd.), and the solder paste was rolled four times to adhere to the metal mask. After dry cleaning the back of the metal mask, printing was performed twice under the following printing conditions.

[0061] (Printing conditions) Printing environment: Temperature 24-26°C, humidity 50-60%RH Printing squeegee: Metal squeegee Squeegee angle: 60° Metal mask thickness: 150 μm Printing speed: 40mm / sec Pad shape and size: Square shape, 0.30mm x 0.30mm Number of pads: 100 (50 pads x n=2) Pad material: OSP treated copper Aspect ratio of the metal mask (Aperture area of ​​the metal mask (0.09 mm) 2 ) / Opening area of ​​metal mask (0.18mm²) 2 )):0.50

[0062] The solder transfer rate was calculated by detecting the solder on the copper pads of each printed circuit board using a KOHYOUNG aSPIer (manufactured by KOH YOUNG TECHNOROGY) and determining its volume percentage. Tables 1 to 4 show the percentage of pads with a volume percentage of 105% or more (filling rate of 105% or more), the percentage of pads with a volume percentage of 75% or more but less than 105% (filling rate of 75% or more but less than 105%), and the percentage of pads with a volume percentage of less than 75% (filling rate of less than 75%) relative to the total number of pads (100 pads).

[0063] The transfer rate was evaluated as follows: a rating of "1 (Excellent)" was given if 90% or more of the products had a filling rate of 75% or more but less than 105%; a rating of "2 (Good)" was given if 10% or more of the products had a filling rate of 105% or more; and a rating of "3 (Poor)" was given in all other cases. The evaluation results are shown in Tables 1 to 4.

[0064] As can be seen from the results in Tables 1 to 4, the solder pastes of each embodiment that satisfy all the requirements of the present invention exhibit excellent printability, as 90% or more have a filling rate of 75% or more and less than 105%.

Claims

1. A flux used for soldering, It contains a resin, an unsaturated aliphatic compound having 18 to 22 carbon atoms and one unsaturated bond, a thixotropic agent, and a solvent. The aforementioned resin comprises a rosin-based resin and a liquid resin whose viscosity, as measured by an E-type viscometer at a temperature of 30°C and a rotation speed of 50 rpm, is between 300 mPa·s and 55,000 mPa·s. The content of the unsaturated aliphatic compound is 3.0% by mass or more and 25.0% by mass or less relative to the total flux. The content of the rosin-based resin is 11.4% by mass or more and 35.0% by mass or less relative to the total flux. The liquid resin content is 24.6% by mass or more and 45.5% by mass or less relative to the total flux. A flux comprising at least one unsaturated aliphatic compound selected from unsaturated aliphatic alcohols, unsaturated fatty acids, and unsaturated fatty acid esters.

2. The flux according to claim 1, wherein the content of the unsaturated aliphatic compound is 5.0% by mass or more and 15.0% by mass or less of the total flux.

3. A solder paste comprising the flux described in claim 1 or 2 and solder alloy powder.

4. The solder paste according to claim 3, wherein the alloy of the solder alloy powder is a Sn / Ag / Cu alloy.

5. The solder paste according to claim 4, wherein the Sn / Ag / Cu alloy further contains at least one selected from In, Bi, Sb, and Ni.

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