JP7517669B2 - Flux and solder paste - Google Patents

Description

The present invention relates to a flux used in soldering and a solder paste containing the flux.

When mounting a joining component on an electronic circuit board such as a printed wiring board, a solder paste made of a mixture of a solder alloy and flux is used. The solder paste is applied to the electrode parts on the surface of the electronic circuit board, and is heated (reflowed) with the electrode parts of the joining component in contact with the electrode parts. This melts the solder alloy to form a solder joint, and the board and the joining component are joined via the solder joint.

The flux contained in solder paste generally consists of rosin, activators, solvents, thixotropic agents, etc. Among these, rosin is the main component, accounting for approximately half of the total flux, and improves the wettability of the solder due to its high activity. However, because rosin is non-volatile, it remains as a residue around the solder joint after reflow. Residues in rosin-containing flux may reduce the adhesion between the resin and the board during resin sealing in post-mounting processes, or may hinder the bonding between the electrode and the board during wire bonding.

Conventionally, residues were removed by performing a cleaning process using a cleaning agent, followed by post-processing such as resin sealing and wire bonding. However, due to problems of air pollution caused by cleaning agents and increased costs in the cleaning process, there is a demand for non-cleaning. In order to perform post-processing without cleaning, it is desirable to reduce residues after reflow as much as possible. For this reason, in recent years, efforts have been made to develop fluxes that can achieve low residues without containing rosin. For example, Patent Document 1 discloses a flux that reduces residues after reflow without cleaning by using an organic acid mixture consisting of organic acids with 10 or more carbon atoms as an activator.

Patent No. 6399242 specification

However, for example, in the case of a flux that does not contain rosin, such as that in Patent Document 1, it is necessary to include a non-volatile activator (e.g., an organic acid having 10 or more carbon atoms) as part of the activator in order to improve the wettability of the solder in place of rosin. This makes it difficult to sufficiently volatilize the flux components at the reflow temperature, and as a result, it is not possible to sufficiently reduce the residue after reflow.

The present invention was made in consideration of the above circumstances, and aims to provide a flux that can improve the wettability of solder and reduce residue after reflow, and a solder paste containing the flux.

The flux according to the present invention contains a fatty acid and an imidazole compound.

Since both fatty acids and imidazole compounds have high activity, the flux improves the wettability of the solder without using a non-volatile activator. Furthermore, since both fatty acids and imidazole compounds are volatile components, they can reduce residues after reflow.

In the flux according to the present invention, the total content of the fatty acid and the imidazole compound is preferably 40% by weight or more and 95% by weight or less with respect to the entire flux.

With this configuration, the flux can further improve the wettability of the solder.

In the flux according to the present invention, the fatty acid is preferably at least one of a saturated fatty acid having a main chain carbon number of 10 or less and an unsaturated fatty acid having a main chain carbon number of 18 or less.

This configuration allows the flux to have a high viscosity and the viscosity can be adjusted to an appropriate range.

In the flux according to the present invention, the unsaturated fatty acid is preferably at least one selected from the group consisting of oleic acid, linoleic acid, and linolenic acid.

This configuration allows the viscosity of the flux to be adjusted to a more appropriate range.

In the flux according to the present invention, the imidazole compound is preferably at least one selected from the group consisting of 2-phenylimidazole, 2-ethyl-4-methylimidazole, and 2-phenyl-4-methylimidazole.

These imidazole compounds volatilize at 260°C or less. Generally, reflow temperatures are set at 260°C or less to prevent damage to components. Therefore, by volatilizing the imidazole compounds at 260°C or less, the flux can further reduce residues after reflow.

In the flux according to the present invention, it is preferable that the ratio of the content of the imidazole compound to the content of the fatty acid is 0.2 or more and 4.9 or less.

This configuration allows the flux to have a high viscosity and the viscosity can be adjusted to an appropriate range.

The solder paste according to the present invention contains the above-mentioned flux and a solder alloy powder having a melting point of 260°C or less.

By including the above-mentioned flux, the solder paste can improve the wettability of the solder and reduce the residue after reflow.

The solder paste according to the present invention preferably contains the flux in an amount of 8% by weight or more and 12% by weight or less based on the total weight of the solder paste.

With this configuration, the solder paste can further improve the wettability of the solder and further reduce the residue after reflow.

The present invention provides a flux that has excellent solder wettability and can reduce residue after reflow, and a solder paste containing the flux.

The following describes the flux according to an embodiment of the present invention and the solder paste containing the flux.

<Flux>
(fatty acid)
The flux according to the present embodiment contains a fatty acid. The fatty acid is preferably at least one of a saturated fatty acid having 10 or less carbon atoms in the main chain and an unsaturated fatty acid having 18 or less carbon atoms. Examples of the saturated fatty acid include nonanoic acid, octanoic acid, decanoic acid, heptanoic acid, 2-ethylhexanoic acid, 2-hexyldecanoic acid, and 4-methylnonanoic acid. Among these, the saturated fatty acid is preferably a saturated fatty acid having 9 or less carbon atoms in the main chain. The unsaturated fatty acid having 18 or less carbon atoms is preferably at least one selected from the group consisting of oleic acid, linoleic acid, and linolenic acid. The fatty acids may be used alone or in combination of two or more.

The fatty acid content is preferably 11% by weight or more, and more preferably 15% by weight or more, based on the total weight of the flux. The fatty acid content is preferably 60% by weight or less, and more preferably 51% by weight or less, based on the total weight of the flux. When two or more fatty acids are included, the above content is the total content of the fatty acids.

(Imidazole Compounds)
The flux according to the present embodiment includes an imidazole compound. Here, the imidazole compound means a compound having an imidazole group. The imidazole compound is preferably an imidazole compound that volatilizes at 260°C or less. Examples of such imidazole compounds include 2-phenylimidazole, 2-phenyl-4-methylimidazole, and 2-ethyl-4-methylimidazole. The imidazole compounds may be used alone or in combination of two or more kinds.

The content of the imidazole compound is preferably 11% by weight or more, and more preferably 15% by weight or more, based on the total weight of the flux. The content of the imidazole compound is preferably 54% by weight or less, and more preferably 50% by weight or less, based on the total weight of the flux. When two or more types of imidazole compounds are included, the above content is the total content of the imidazole compounds.

In the flux according to this embodiment, the total content of the fatty acid and the imidazole compound is preferably 40% by weight or more, more preferably 60% by weight or more, based on the total flux. Moreover, the total content is preferably 95% by weight or less, more preferably 90% by weight or less, based on the total flux.

In the flux according to this embodiment, the ratio of the imidazole compound content to the fatty acid content is preferably 0.2 or more, more preferably 0.5 or more, and particularly preferably 0.8 or more. Moreover, the ratio is preferably 4.9 or less, more preferably 2.1 or less, and particularly preferably 1.0 or less.

The flux according to this embodiment contains a fatty acid and an imidazole compound. Both fatty acids and imidazole compounds have high activity, improving the wettability of the solder. Furthermore, both fatty acids and imidazole compounds are volatile components, so they can reduce residues after reflow.

The flux according to this embodiment has a total content of fatty acid and imidazole compound of 40% by weight or more and 95% by weight or less of the entire flux, which can further improve the wettability of the solder.

The flux according to this embodiment has high viscosity and can be adjusted to an appropriate range because the fatty acid is at least one of a saturated fatty acid with a main chain carbon number of 10 or less and an unsaturated fatty acid with a main chain carbon number of 18 or less.

The flux according to this embodiment has an unsaturated fatty acid of at least one selected from the group consisting of oleic acid, linoleic acid, and linolenic acid, so that the viscosity can be adjusted to a more appropriate range.

In the flux according to this embodiment, the imidazole compound is at least one selected from the group consisting of 2-phenylimidazole, 2-ethyl-4-methylimidazole, and 2-phenyl-4-methylimidazole. These imidazole compounds volatilize at 260°C or less. In general, reflow is performed at a temperature of 260°C or less in order to prevent damage to components. Therefore, by volatilizing the imidazole compound at 260°C or less, the flux can further reduce residue after reflow.

The flux according to this embodiment has a ratio of the imidazole compound content to the fatty acid content of 0.2 or more and 4.9 or less, so that the viscosity is high and can be adjusted to an appropriate range.

(Activator)
The flux according to the present embodiment may further contain an activator from the viewpoint of further improving the wettability of the solder. The activator is preferably a volatile activator from the viewpoint of reducing residue after reflow. Examples of the volatile activator include organic acid activators, amine compound activators, and halogen compound activators. Among these, the activator is preferably an organic acid activator from the viewpoint of reducing the environmental load. The activators may be used alone or in combination of two or more kinds.

The organic acid activator is not particularly limited, and examples thereof include monocarboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, capric acid, lauric acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, tuberculostearic acid, arachidic acid, behenic acid, lignoceric acid, and glycolic acid; dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, tartaric acid, diglycolic acid, methylsuccinic acid, and phenylsuccinic acid; and other organic acids such as dimer acid, levulinic acid, lactic acid, acrylic acid, benzoic acid, salicylic acid, anisic acid, citric acid, and tris(2-carboxyethyl)isocyanurate.

Amine compound-based activators are not particularly limited, but examples include trimethylamine, triethylamine, tetramethylethylenediamine, ethylenediamine, triethylenediamine, triethanolamine, aniline, pyridine, piperidine, etc.

Halogen compound activators are not particularly limited, but examples include trans-2,3-dibromo-2-butene-1,4-diol, dibromosalicylic acid, and tris(2,3-dibromopropyl)isocyanurate.

The content of the activator is preferably 1% by weight or more, and more preferably 5% by weight or more, based on the total weight of the flux. The content of the activator is preferably 10% by weight or less, and more preferably 8% by weight or less, based on the total weight of the flux. When two or more types of activators are included, the above content is the total content of the activators.

The activator may contain a non-volatile activator. The content of the non-volatile activator is preferably 20% by weight or less based on the total weight of the flux. Even if the content of the non-volatile activator is 20% by weight or less, good wettability is exhibited due to the high activity of the fatty acid and the imidazole compound.

(thixotropic agent)
The flux according to the present embodiment may further contain a thixotropic agent in order to further enhance the thixotropic properties of the flux. Examples of the thixotropic agent include castor hardened oil, fatty acid amide, kaolin, colloidal silica, organic bentonite, and glass frit. Among these, the thixotropic agent is preferably a fatty acid amide in order to enhance volatility. Examples of the fatty acid amide that enhances volatility include stearic acid amide, lauric acid amide, palmitic acid amide, oleic acid amide, erucic acid amide, behenic acid amide, and myristic acid amide. The thixotropic agent may be used alone or in combination of two or more kinds.

The content of the thixotropic agent is preferably 1% by weight or more, and more preferably 8% by weight or more, based on the total flux. The content of the thixotropic agent is preferably 20% by weight or less, and more preferably 12% by weight or less, based on the total flux. When two or more types of thixotropic agents are included, the above content is the total content of the thixotropic agents.

(solvent)
The flux according to the present embodiment may contain a solvent in order to adjust the viscosity of the flux to an appropriate range. Examples of the solvent include 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), and diethylene glycol monobutyl ether (butyl diglycol); aliphatic compounds such as n-hexane, isohexane, and n-heptane; esters such as isopropyl acetate, methyl propionate, ethyl propionate, and Cosmol 43N (trade name); ketones such as methyl ethyl ketone, methyl-n-propyl ketone, and diethyl ketone; and alcohols such as ethanol, n-propanol, isopropanol, isobutanol, octanediol, trimethylolpropane, neopentyl glycol, 2,5-dimethyl-2,5-hexanediol, 3-methyl-1,5-pentanediol, and Fine Oxocol (trade name, registered trademark). The solvents may be used alone or in combination of two or more.

The solvent content is preferably 1% by weight or more, and more preferably 8% by weight or more, based on the total flux. The solvent content is preferably 38% by weight or less, and more preferably 20% by weight or less, based on the total flux. When two or more types of solvents are included, the above content is the total solvent content.

The flux according to this embodiment may contain at least one of the following other additives: a stabilizer, a surfactant, an antifoaming agent, and a corrosion inhibitor. The total content of the other additives is not particularly limited, and may be, for example, 5% by weight or less of the entire flux.

The flux according to this embodiment desirably does not contain resin, from the viewpoint of reducing residue after reflow. If the flux contains resin, the content is preferably 5% by weight or less of the entire flux, from the viewpoint of reducing residue after reflow.

Examples of resins include rosin-based resins such as gum rosin, tall oil rosin, wood rosin, polymerized rosin, hydrogenated rosin, disproportionated rosin, acrylated rosin, rosin ester, acid-modified rosin, and very light-colored rosin; known synthetic resins, etc.

The method for producing the flux according to this embodiment is not particularly limited. For example, a fatty acid, an imidazole compound, and optionally an activator, a thixotropic agent, a solvent, and other additives are placed in a heating vessel, and then all the raw materials are dissolved by heating to 100 to 120°C. The flux according to this embodiment can be obtained by cooling to room temperature.

The flux according to this embodiment includes a fatty acid, an imidazole compound, an activator, a thixotropic agent, a solvent, and other additives, but is not limited to this configuration. Fluxes according to other embodiments are composed of a fatty acid, an imidazole compound, an activator, a thixotropic agent, a solvent, and other additives, and are preferably composed of a fatty acid, an imidazole compound, and an activator.

<Solder paste>
The solder paste according to the present embodiment contains the above-mentioned flux and a solder alloy powder having a melting point of not more than 260° C. The solder paste according to the present embodiment preferably contains the flux in an amount of 8% by weight or more and 12% by weight or less with respect to the entire solder paste.

In general, the reflow temperature is 260°C or less in order to prevent damage to components. Therefore, solder alloy powders with a melting point of 260°C or less are usually used. Examples of such solder alloy powders include Sn-Pb eutectic solder alloys and lead-free solder alloys. 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.

The solder paste according to this embodiment contains the above-mentioned flux and a solder alloy powder having a melting point of 260°C or less. By containing the above-mentioned flux, the solder paste can improve the wettability of the solder and reduce the residue after reflow.

The solder paste according to this embodiment contains flux in an amount of 8% by weight or more and 12% by weight or less relative to the total solder paste, which improves the wettability of the solder and reduces the residue after reflow.

The method for producing the solder paste according to this embodiment is not particularly limited. For example, the solder paste according to this embodiment can be obtained by mixing flux and solder alloy powder.

The following describes examples of the present invention, but the present invention is not limited to the following examples.

[Preparation of solder paste]
Each raw material was placed in a heating vessel in the amounts shown in Tables 1 to 3 and heated to 120°C to dissolve all the raw materials. The mixture was then cooled to room temperature to obtain uniformly dispersed fluxes for each Example and Comparative Example. The amounts shown in Table 1 are equal to the contents of each component contained in the flux. Next, 10% by mass of each flux and 90% by mass of solder powder (Sn-3.0 wt% Ag-0.5 wt% Cu) were mixed to obtain solder pastes for each Example and Comparative Example.

Details of each raw material shown in Tables 1 to 3 are shown below.
(fatty acid)
Nonanoic acid: Product name "Nonanoic acid" manufactured by Tokyo Chemical Industry Co., Ltd.
Octanoic acid: Product name "n-octanoic acid" manufactured by Tokyo Chemical Industry Co., Ltd.
Heptanoic acid: Product name "Heptanoic acid" manufactured by Tokyo Chemical Industry Co., Ltd.
2-Ethylhexanoic acid: Product name "2-ethylhexanoic acid" manufactured by Tokyo Chemical Industry Co., Ltd.
2-Hexyldecanoic acid: manufactured by Tokyo Chemical Industry Co., Ltd., product name "2-hexyldecanoic acid"
Linolenic acid: Product name "Linolenic acid" manufactured by Tokyo Chemical Industry Co., Ltd.
Oleic acid: Product name "Oleic acid" manufactured by Tokyo Chemical Industry Co., Ltd.
(Imidazole Compounds)
2PZ-PW: 2-phenylimidazole, manufactured by Shikoku Kasei Co., Ltd., product name "2PZ-PW"
2P4MZ: 2-phenyl-4-methylimidazole, manufactured by Shikoku Kasei Co., Ltd., product name "2P4MZ"
2E4MZ: 2-ethyl-4-methylimidazole, manufactured by Shikoku Kasei Co., Ltd., product name "2E4MZ"
(resin)
KE-604: Acid-modified rosin, manufactured by Arakawa Chemical Industries, Ltd., product name "KE-604"
KR-612: Ultra-light-colored rosin, manufactured by Arakawa Chemical Industries, Ltd., product name "KR-612"
LONDISU R: Disproportionated rosin, manufactured by Arakawa Chemical Industries, Ltd., product name "LONDISU R"
(solvent)
ODA: Manufactured by KH Neochem Co., Ltd., product name "Octanediol"
Trimethylolpropane: Mitsubishi Gas Chemical Company, Inc., product name "Trimethylolpropane"
NPG: Mitsubishi Gas Chemical Company, Inc., product name "Neopentyl glycol"
DMHD: LUZHOU FUBANG CHEMICAL CO., LTD., product name "2,5-dimethyl-2,5-hexanediol"
C-43N: Product name "Cosmol 43N" manufactured by Nisshin Oillio Group, Ltd.
Fine Oxocol 180A: Nissan Chemical Co., Ltd., product name "Fine Oxocol 180A"
MPD: 3-methyl-1,5-pentanediol, manufactured by Kuraray Co., Ltd., product name "MPD"
HeDG: Hexyl diglycol, manufactured by Nippon Nyukazai Co., Ltd., product name "HeDG"
(Activator)
MeSA: Product name "Methyl succinic acid" manufactured by Komatsugawa Chemical Co., Ltd.
PhSA: Beijing Hercules chemicals Co., Ltd., product name "Phenylsuccinic Acid"
Adipic acid: Sumitomo Chemical Co., Ltd., product name "Adipic acid"
Glutaric acid: Product name "Glutaric acid" manufactured by Tokyo Chemical Industry Co., Ltd.
AZA: Emery Oleochemicals Japan Co., Ltd., product name "Emerox 1144"
Maleic acid: Fuso Chemical Co., Ltd., product name: "Hydrated maleic acid"
Diglycolic acid: Midori Chemical Co., Ltd., product name "Diglycolic acid"
DBBD: trans-2,3-dibromo-2-butene-1,4-diol, manufactured by Tokyo Chemical Industry Co., Ltd., product name "DBBD"
(thixotropic agent)
Lauramide: Product name "Diamid Y" manufactured by Nippon Kasei Co., Ltd.
Stearamide: Kao Corporation, product name "Fatty Acid Amide S"
J-630: N,N'-hexamethylene-bis-12-hydroxystearylamide, manufactured by Ito Oil Mills, product name "J-630"
Castor oil: Product name: "Castor oil" manufactured by Ito Oil Mills, Ltd.
(Other additives)
2,2'-methylenebis(6-tert-butyl-4-methylphenol): stabilizer, manufactured by Tokyo Chemical Industry Co., Ltd.

[Evaluation of Residue]
Using a TG/TDA device (TG 8120, manufactured by Rigaku Corporation), 5 mg of each flux was weighed into an aluminum pan and heated to 573 K at a temperature increase rate of 10 K/min under a nitrogen stream. The weight change rate by TG at 533 K was measured. The results are shown in Tables 1 to 3. A weight change rate of 95% or more was judged to be good.

[Wettability evaluation]
Each solder paste was printed on an FR-4 resin board (OSP-treated) so that the mask aperture ratio was 100% at a thickness of 120 μm. Then, a solder reflow device (NIS-20-82-C, manufactured by Atec) was used to perform heat treatment under a nitrogen atmosphere with an oxygen concentration of 1000 ppm. The heat treatment was first performed by increasing the temperature from the start of the heat treatment (room temperature) to 180° C. at a rate of 1.5° C./sec, and then maintaining the temperature at 180° C. for 100 seconds. Then, the temperature was increased from 180° C. to 250° C. at a rate of 2.0° C./sec, and maintained at 250° C. for 15 seconds, after which the temperature was cooled from 250° C. to room temperature at a rate of 3.0° C./sec. The wettability evaluation was performed visually based on the following criteria.
⊚: Solder has spread over the entire land.
◯: There is no unmelted solder.

As can be seen from the results in Table 1, the solder pastes of the examples that met all the requirements of the present invention had a weight change rate due to TG of 95% or more, and were able to reduce residue after reflow. In addition, the solder pastes of the examples also had good solder wettability.

On the other hand, the solder paste of Comparative Example 1, which did not contain fatty acids or imidazole compounds, had good solder wettability, but the weight change rate due to TG was 68%, and the residue after reflow could not be sufficiently reduced.

Claims (6)

Contains a fatty acid and an imidazole compound,
The flux does not contain resin or contains 5 mass % or less of resin based on the entire flux,
A flux, the total content of the fatty acid and the imidazole compound being 40% by mass or more and 95% by mass or less with respect to the entire flux;
and a solder alloy powder having a melting point of 260° C. or less. The solder paste according to claim 1, wherein the fatty acid is at least one of a saturated fatty acid having a main chain carbon number of 10 or less and an unsaturated fatty acid having a main chain carbon number of 18 or less. 3. The solder paste according to claim 2 , wherein the unsaturated fatty acid is at least one selected from the group consisting of oleic acid, linoleic acid, and linolenic acid. The solder paste according to any one of claims 1 to 3, wherein the imidazole compound is at least one selected from the group consisting of 2-phenylimidazole, 2-ethyl-4-methylimidazole, and 2-phenyl-4-methylimidazole. The solder paste according to any one of claims 1 to 4, wherein the ratio of the content of the imidazole compound to the content of the fatty acid is 0.2 or more and 4.9 or less. 6. The solder paste according to claim 1, wherein the content of the flux is 8 mass % or more and 12 mass % or less with respect to the entire solder paste.