CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the United States national phase of International Application No. PCT/JP2019/000891 filed Jan. 15, 2019, and claims priority to Japanese Patent Application No. 2018-005919 filed Jan. 17, 2018, the disclosures of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a flux for use in soldering and a solder paste using the flux.

BACKGROUND

In general, a flux used in soldering has effects of chemically removing metal oxides present on solder and the metal surface of a joint target to be soldered and allowing movement of metal elements at the boundary between the two. Therefore, by soldering using the flux, an intermetallic compound can be formed between the solder and the metal surface of the joint target, so that strong joint can be obtained.

In recent years, with the development of small information devices, rapid miniaturization of electronic components to be mounted has progressed. In order to meet the demand for the reduction of connection terminals and the reduction of the mounting area due to the demand for miniaturization, the electronic components employs a ball grid array (BGA) in which electrodes are arranged on their back surface.

Solder bumps are formed on the BGA electrodes. As a method for making a solder bump, a method of mounting a solder ball on an electrode coated with a flux followed by heating has been adopted. In recent years, with the miniaturization of electronic components, the narrowing of an electrode pitch, which is a soldering site of the electronic components, is progressing. Due to the narrowing of the electrode pitch, the diameter of the solder balls mounted on the electrodes is also becoming smaller.

In soldering using solder balls, there is a problem that, if the solder balls cannot be retained with flux at ordinary temperature before heating, the positions of the solder balls are displaced with respect to the electrodes, thereby giving rise to a state where the solder balls are detached from the electrode pad (ball missing). Such a problem becomes remarkable due to the narrowing of the electrode pitch.

The flux used for soldering contains an activator that removes metal oxides, rosin, a solvent, and the like. Rosin has heat resistance to heating up to a temperature range assumed for soldering, and has a function of protecting the activator. In addition, the addition of rosin increases the viscosity of the flux at ordinary temperature, and imparts solder ball retention to the flux. Furthermore, a flux having a viscosity increased by adding a high-viscosity solvent in addition to rosin has also been proposed (see, for example, Patent Document 1). A solder paste containing a flux having a viscosity increased by adding a high-viscosity solvent in addition to rosin has also been proposed (see, for example, Patent Document 2).

Also, in soldering using solder balls, there is a problem that, if solder wettability cannot be ensured, the solder does not spread evenly over the electrodes, and that the positions of the solder balls are displaced with respect to the electrodes, thereby giving rise to ball missing.

Patent Document 1: Japanese Patent Application Publication No. 2014-100737

Patent Document 2: Japanese Patent Application Publication No. 2015-142936

SUMMARY

When soldering is performed, it is required that molten solder should be sufficiently wet-spread, and thus the flux is required to have activity capable of removing a metal oxide film.

However, in the case of using a general organic acid to be added to the flux as the activator, if the amount to be added is small, the organic acid volatilizes by heating up to the temperature range assumed for soldering, resulting in insufficient activity and failure to ensure wettability. Moreover, when the amount to be added is increased to ensure wettability, the residue amount increases.

When the residue amount increases, the flux may become unsuitable for non-washing applications in which residues after soldering are not washed for use. Thus, a flux with low residue is required.

In addition, due to inclusion of rosin in the flux, it becomes possible to increase the viscosity of the flux at ordinary temperature and to retain the solder balls, and also to protect the organic acid with rosin against heating up to a temperature range assumed for soldering.

However, rosin does not volatilize by heating to a temperature range assumed for soldering, and the flux may become unsuitable for non-washing applications. Thus, a low residue flux is required.

Accordingly, in applications in which the residues after soldering are not washed for use, it is preferable that sufficient activity be obtained even with a small amount of a component that functions as an activator. In particular, the solder balls become smaller in diameter with narrowing of the electrode pitch. Furthermore, when the solder balls are miniaturized to a size called solder powder, activity is required by the flux. On the other hand, in order to retain the solder balls, a viscosity capable of retaining the solder balls at ordinary temperature is required.

The present invention has been made to solve such problems, and an object thereof is to provide a flux which can ensure the wettability of solder, can ensure solder ball retention, and can realize low residue that enables suppression of the residue amount after soldering and use in applications in which the residues after soldering are not washed for use, and a solder paste using this flux.

It has been found that an organic acid mixture including an organic acid with 10 or more carbon atoms or an organic acid with 12 or more carbon atoms can provide sufficient activity even when added in a small amount. Moreover, it has been found that the flux can have a predetermined viscosity by virtue of the inclusion of isobornyl cyclohexanol therein, even if it does not contain rosin.

Therefore, the present invention is a flux containing: 1 wt % or more and 15 wt % or less of an organic acid mixture including an organic acid with 10 or more carbon atoms; 50 wt % or more and 90 wt % or less of isobornyl cyclohexanol; and 5 wt % or more and 45 wt % or less of a different solvent, the flux being free of a thermosetting resin, wherein, when a total amount of the isobornyl cyclohexanol and the different solvent is 100 wt %, a ratio of the isobornyl cyclohexanol is 50 wt % or more and 95 wt % or less, and wherein the organic acid mixture including an organic acid with 10 or more carbon atoms includes 2-methylnonanedioic acid, 4-(methoxycarbonyl)-2,4-dimethylundecanedioic acid, 4,6-bis(methoxycarbonyl)-2,4,6-trimethyltridecanedioic acid, and 8,9-bis(methoxycarbonyl)-8,9-dimethylhexadecanedioic acid.

The organic acid mixture including an organic acid with 10 or more carbon atoms preferably includes 30 wt % or more and 60 wt % or less of 2-methylnonanedioic acid, 8 wt % or more and 20 wt % or less of 4-(methoxycarbonyl)-2,4-dimethylundecanedioic acid, 8 wt % or more and 20 wt % or less of 4,6-bis(methoxycarbonyl)-2,4,6-trimethyltridecanedioic acid, and 15 wt % or more and 30 wt % or less of 8,9-bis(methoxycarbonyl)-8,9-dimethylhexadecanedioic acid, when a total amount of the organic acid mixture is 100 wt %.

Further, the present invention is a flux containing: 1 wt % or more and 15 wt % or less of an organic acid with 12 or more carbon atoms; 50 wt % or more and 90 wt % or less of isobornyl cyclohexanol; and 5 wt % or more and 45 wt % or less of a different solvent, the flux being free of a thermosetting resin, wherein, when the total amount of the isobornyl cyclohexanol and the different solvent is 100 wt %, the ratio of the isobornyl cyclohexanol is 50 wt % or more and 95 wt % or less.

The organic acid with 12 or more carbon atoms is preferably any one of: a dimer acid which is a reaction product of oleic acid and linoleic acid, a trimer acid which is a reaction product of oleic acid and linoleic acid, a hydrogenated dimer acid obtained by adding hydrogen to (hydrogenating) the dimer acid which is a reaction product of oleic acid and linoleic acid, and a hydrogenated trimer acid obtained by adding hydrogen to (hydrogenating) the trimer acid which is a reaction product of oleic acid and linoleic acid; or two or more of: a dimer acid which is a reaction product of oleic acid and linoleic acid, a trimer acid which is a reaction product of oleic acid and linoleic acid, a hydrogenated dimer acid obtained by adding hydrogen to (hydrogenating) the dimer acid which is a reaction product of oleic acid and linoleic acid, and a hydrogenated trimer acid obtained by adding hydrogen to (hydrogenating) the trimer acid which is a reaction product of oleic acid and linoleic acid.

Preferably, the flux of the present invention further contains: 0 wt % or more and 15 wt % or less of an organic acid with less than 12 carbon atoms; 0 wt % or more and 5 wt % or less of an amine; 0 wt % or more and 1 wt % or less of an amine hydrohalide; and/or 0 wt % or more and 5 wt % or less of an organohalogen compound.

Moreover, the present invention is a solder paste including the flux described above and metal powder.

In the present invention, the flux contains: 1 wt % or more and 15 wt % or less of an organic acid mixture including an organic acid with 10 or more carbon atoms; 50 wt % or more and 90 wt % or less of isobornyl cyclohexanol; and 5 wt % or more and 45 wt % or less of a different solvent. When the total amount of the isobornyl cyclohexanol and the different solvent is 100 wt %, the ratio of the isobornyl cyclohexanol is 50 wt % or more and 95 wt % or less, and the organic acid mixture including an organic acid with 10 or more carbon atoms includes 2-methylnonanedioic acid, 4-(methoxycarbonyl)-2,4-dimethylundecanedioic acid, 4,6-bis(methoxycarbonyl)-2,4,6-trimethyltridecanedioic acid, and 8,9-bis(methoxycarbonyl)-8,9-dimethylhexadecanedioic acid. By virtue of this structure, the wettability of the solder can be obtained. Further, it is possible to suppress the residue amount to realize low residue. Furthermore, when placing a solder ball on an electrode coated with the flux of the present invention to form a solder bump, the solder ball can be retained with the flux at ordinary temperature before heating.

Further, in the present invention, the flux contains: 1 wt % or more and 15 wt % or less of an organic acid with 12 or more carbon atoms; 50 wt % or more and 90 wt % or less of isobornyl cyclohexanol; and 5 wt % or more and 45 wt % or less of a different solvent. When the total amount of the isobornyl cyclohexanol and the different solvent is 100 wt %, the ratio of the isobornyl cyclohexanol is 50 wt % or more and 95 wt % or less. By virtue of this, the wettability of the solder can be obtained. Further, it is possible to suppress the residue amount to realize low residue. Furthermore, when placing a solder ball on an electrode coated with the flux of the present invention to form a solder bump, the solder ball can be retained with the flux at ordinary temperature before heating.

<Example of Flux According to Present Embodiment>

The flux of the present embodiment contains an organic acid mixture including an organic acid with 10 or more carbon atoms, isobornyl cyclohexanol as a solvent, and a different solvent. It does not contain rosin. The organic acid mixture includes 2-methylnonanedioic acid with 10 carbon atoms, 4-(methoxycarbonyl)-2,4-dimethylundecanedioic acid with 15 carbon atoms, 4,6-bis(methoxycarbonyl)-2,4,6-trimethyltridecanedioic acid having 20 carbon atoms, and 8,9-bis(methoxycarbonyl)-8,9-dimethylhexadecanedioic acid having 20 carbon atoms.

The organic acid mixture including 2-methylnonanedioic acid, 4-(methoxycarbonyl)-2,4-dimethylundecanedioic acid, 4,6-bis(methoxycarbonyl)-2,4,6-trimethyltridecanedioic acid, and 8,9-bis(methoxycarbonyl)-8,9-dimethylhexadecanedioic acid has heat resistance to heating up to a temperature range assumed for soldering, is hardly volatile, and acts as an activator during soldering.

In order to realize a low residue flux, the flux contains neither rosin nor a resin such as a thermosetting resin. If all the components are configured to be easily volatilized, the organic acid would also be designed to volatilize during reflow, and the flux cannot be protected by a heat-resistant component such as a resin represented by rosin. Therefore, especially an organic acid having a small number of carbon atoms would volatilize and decompose.

In contrast, 2-methylnonanedioic acid, 4-(methoxycarbonyl)-2,4-dimethylundecanedioic acid, 4,6-bis(methoxycarbonyl)-2,4,6-trimethyltridecanedioic acid and 8,9-bis(methoxycarbonyl)-8,9-dimethylhexadecanedioic acid have a high molecular weight, heat resistance, and activity even in a relatively small amount, and thus improve solder wettability.

Hence, the organic acid mixture including 2-methylnonanedioic acid, 4-(methoxycarbonyl)-2,4-dimethylundecanedioic acid, 4,6-bis(methoxycarbonyl)-2,4,6-trimethyltridecanedioic acid, and 8,9-bis(methoxycarbonyl)-8,9-dimethylhexadecanedioic acid functions as an activator during soldering even if the amount thereof contained in the flux is small. Further, since the amount of the organic acid mixture in the flux is small, it is possible to suppress the residue amount after soldering to realize low residue, and also to use the flux in applications in which the residues after soldering are not washed for use.

When the added amount of the organic acid mixture including 2-methylnonanedioic acid, 4-(methoxycarbonyl)-2,4-dimethylundecanedioic acid, 4,6-bis(methoxycarbonyl)-2,4,6-trimethyltridecanedioic acid, and 8,9-bis(methoxycarbonyl)-8,9-dimethylhexadecanedioic acid is large, the residue amount after soldering increases.

Therefore, the organic acid mixture including 2-methylnonanedioic acid, 4-(methoxycarbonyl)-2,4-dimethylundecanedioic acid, 4,6-bis(methoxycarbonyl)-2,4,6-trimethyltridecanedioic acid, and 8,9-bis(methoxycarbonyl)-8,9-dimethylhexadecanedioic acid is contained in an amount of 1 wt % or more and 15 wt % or less.

In addition, the flux containing an organic acid mixture including an organic acid with 10 or more carbon atoms, according to the present embodiment, contains 50 wt % or more and 90 wt % or less of isobornyl cyclohexanol in consideration of the solder ball retention when used in applications for forming solder bumps. However, if the solvent is only isobornyl cyclohexanol, the viscosity of the flux will become too high. Therefore, a different solvent is contained in an amount of 5 wt % or more and 45 wt % or less, and the ratio of isobornyl cyclohexanol is 50 wt % or more and 95 wt % or less when the total amount of isobornyl cyclohexanol and the different solvent is 100 wt %.

The flux of the present embodiment contains an organic acid with 12 or more carbon atoms, isobornyl cyclohexanol as a solvent, and a different solvent. It does not contain rosin. An organic acid with 12 or more carbon atoms has a high molecular weight and heat resistance to heating up to a temperature range assumed for soldering, is hardly volatile, and has activity even in a relatively small amount, so that the solder wettability is improved.

As a result, the organic acid with 12 or more carbon atoms functions as an activator during soldering even if the amount thereof contained in the flux is small. Further, since the amount of the organic acid in the flux is small, it is possible to suppress the residue amount after soldering to realize low residue, and also to use the flux in applications in which the residues after soldering are not washed for use.

When the added amount of the organic acid with 12 or more carbon atoms is large, the residue amount after soldering increases. Therefore, the flux of the present embodiment contains 1 wt % or more and 15 wt % or less of an organic acid with 12 or more carbon atoms.

The organic acid with 12 or more carbon atoms is dodecanedioic acid with 12 carbon atoms. The organic acid with 12 or more carbon atoms is 12-hydroxystearic acid with 18 carbon atoms. Further, the organic acid with 12 or more carbon atoms is a dimer acid which is a reaction product of oleic acid and linoleic acid, a trimer acid which is a reaction product of oleic acid and linoleic acid, a hydrogenated dimer acid obtained by adding hydrogen to (hydrogenating) the dimer acid which is a reaction product of oleic acid and linoleic acid, or a hydrogenated trimer acid obtained by adding hydrogen to (hydrogenating) the trimer acid which is a reaction product of oleic acid and linoleic acid.

The dimer acid of the present embodiment is a reaction product of oleic acid and linoleic acid, which is a dimer with 36 carbon atoms. The trimer acid of the present embodiment is a reaction product of oleic acid and linoleic acid, which is a trimer with 54 carbon atoms.

Dodecanedioic acid, 12-hydroxystearic acid, a dimer acid which is a reaction product of oleic acid and linoleic acid, a trimer acid which is a reaction product of oleic acid and linoleic acid, a hydrogenated dimer acid obtained by adding hydrogen to (hydrogenating) the dimer acid which is a reaction product of oleic acid and linoleic acid, or a hydrogenated trimer acid obtained by adding hydrogen to (hydrogenating) the trimer acid which is a reaction product of oleic acid and linoleic acid has a high molecular weight, heat resistance to the temperature range assumed for soldering, and activity even in a relatively small amount. Therefore, solder wettability is improved.

Thus, dodecanedioic acid, 12-hydroxystearic acid, a dimer acid which is a reaction product of oleic acid and linoleic acid, a trimer acid which is a reaction product of oleic acid and linoleic acid, a hydrogenated dimer acid obtained by adding hydrogen to (hydrogenating) the dimer acid which is a reaction product of oleic acid and linoleic acid, or a hydrogenated trimer acid obtained by adding hydrogen to (hydrogenating) the trimer acid which is a reaction product of oleic acid and linoleic acid functions as an activator during soldering even if the amount contained in the flux is small. In addition, since the amount of the respective acids in the flux is small, the residue amount after soldering can be suppressed to realize low residue, which can be used in applications in which residues after soldering are not washed for use.

Even in the case where the organic acid with 12 or more carbon atoms is dodecanedioic acid, 12-hydroxystearic acid, a dimer acid which is a reaction product of oleic acid and linoleic acid, a trimer acid which is a reaction product of oleic acid and linoleic acid, a hydrogenated dimer acid obtained by adding hydrogen to (hydrogenating) the dimer acid which is a reaction product of oleic acid and linoleic acid, or a hydrogenated trimer acid obtained by adding hydrogen to (hydrogenating) the trimer acid which is a reaction product of oleic acid and linoleic acid, when the amount thereof to be added is large, the residue amount after soldering increases.

Therefore, any one of dodecanedioic acid, 12-hydroxystearic acid, a dimer acid which is a reaction product of oleic acid and linoleic acid, a trimer acid which is a reaction product of oleic acid and linoleic acid, a hydrogenated dimer acid obtained by adding hydrogen to (hydrogenating) the dimer acid which is a reaction product of oleic acid and linoleic acid, and a hydrogenated trimer acid obtained by adding hydrogen to (hydrogenating) the trimer acid which is a reaction product of oleic acid and linoleic acid, or two or more of dodecanedioic acid, 12-hydroxystearic acid, a dimer acid which is a reaction product of oleic acid and linoleic acid, a trimer acid which is a reaction product of oleic acid and linoleic acid, a hydrogenated dimer acid obtained by adding hydrogen to (hydrogenating) the dimer acid which is a reaction product of oleic acid and linoleic acid, and a hydrogenated trimer acid obtained by adding hydrogen to (hydrogenating) the trimer acid which is a reaction product of oleic acid and linoleic acid is/are contained in a total amount of 1 wt % or more and 15 wt % or less.

The flux of the present embodiment containing an organic acid with 12 or more carbon atoms contains 50 wt % or more and 90 wt % or less of isobornyl cyclohexanol in consideration of the solder ball retention when used in applications for forming solder bumps. However, if the solvent is only isobornyl cyclohexanol, the viscosity of the flux will become too high. Therefore, a different solvent is contained in an amount of 5 wt % or more and 45 wt % or less, and the ratio of isobornyl cyclohexanol is 50 wt % or more and 95 wt % or less when the total amount of isobornyl cyclohexanol and the different solvent is 100 wt %.

The flux of the present embodiment containing an organic acid mixture including an organic acid with 10 or more carbon atoms, containing isobornyl cyclohexanol in a solvent at a predetermined ratio, and free of rosin, or the flux of the present embodiment containing an organic acid with 12 or more carbon atoms, containing isobornyl cyclohexanol in a solvent at a predetermined ratio, and free of rosin contains 0 wt % or more and 15 wt % or less of a different volatile organic acid with less than 12 carbon atoms as an activator.

Further, the flux of the present embodiment containing an organic acid mixture including an organic acid with 10 or more carbon atoms, containing isobornyl cyclohexanol in a solvent at a predetermined ratio, and free of rosin, or the flux of the present embodiment containing an organic acid with 12 or more carbon atoms, containing isobornyl cyclohexanol in a solvent at a predetermined ratio, and free of rosin further contains 0 wt % or more and 5 wt % or less of an amine, 0 wt % or more and 1 wt % or less of an amine hydrohalide, and/or 0 wt % or more and 5 wt % or less of an organohalogen compound as activators.

In addition to the above, examples of the organic acid with 12 or more carbon atoms include lauric acid (12 carbon atoms), isocyanuric acid tris (2-carboxyethyl) (12 carbon atoms), dibutylaniline diglycolic acid (14 carbon atoms), palmitic acid (16 carbon atoms), stearic acid (18 carbon atoms), oleic acid (18 carbon atoms), linoleic acid (18 carbon atoms), linolenic acid (18 carbon atoms), and eicosane diacid (20 carbon atoms).

Further, examples of the organic acid with 12 or more carbon atoms include a dimer acid other than a reaction product of oleic acid and linoleic acid, a trimer acid other than a reaction product of oleic acid and linoleic acid, a hydrogenated dimer acid obtained by adding hydrogen to (hydrogenating) the dimer acid other than a reaction product of oleic acid and linoleic acid, or a hydrogenated trimer acid obtained by adding hydrogen to (hydrogenating) a trimer acid other than a reaction product of oleic acid and linoleic acid, including a dimer acid which is a reaction product of oleic acid, a trimer acid which is a reaction product of oleic acid, a dimer acid which is a reaction product of linoleic acid, a trimer acid which is a reaction product of linoleic acid, a dimer acid which is a reaction product of linolenic acid, a trimer acid which is a reaction product of linolenic acid, a dimer acid which is a reaction product of acrylic acid and oleic acid, a trimer acid which is a reaction product of acrylic acid and oleic acid, a dimer acid which is a reaction product of acrylic acid and linoleic acid, a trimer acid which is a reaction product of acrylic acid and linoleic acid, a dimer acid which is a reaction product of acrylic acid and linolenic acid, a trimer acid which is a reaction product of acrylic acid and linolenic acid, a dimer acid which is a reaction product of methacrylic acid and oleic acid, a trimer acid which is a reaction product of methacrylic acid and oleic acid, a dimer acid which is a reaction product of methacrylic acid and linoleic acid, a trimer acid which is a reaction product of methacrylic acid and linoleic acid, a dimer acid which is a reaction product of methacrylic acid and linolenic acid, a trimer acid which is a reaction product of methacrylic acid and linolenic acid, a dimer acid which is a reaction product of oleic acid and linolenic acid, a trimer acid which is a reaction product of oleic acid and linolenic acid, a dimer acid which is a reaction product of linoleic acid and linolenic acid, a trimer acid which is a reaction product of linoleic acid and linolenic acid, a hydrogenated dimer acid obtained by adding hydrogen to (hydrogenating) the dimer acid other than the reaction product of oleic acid and linoleic acid listed above, and a hydrogenated trimer acid obtained by adding hydrogen to (hydrogenating) a trimer acid other than the reaction product of oleic acid and linoleic acid listed above.

Examples of the organic acid with less than 12 carbon atoms include glycolic acid (2 carbon atoms), thioglycolic acid (2 carbon atoms), glycine (2 carbon atoms), malonic acid (3 carbon atoms), fumaric acid (4 carbon atoms), maleic acid (4 carbon atoms), succinic acid (4 carbon atoms), diglycolic acid (4 carbon atoms), tartaric acid (4 carbon atoms), malic acid (4 carbon atoms), glutaric acid (5 carbon atoms), 2,2-bis(hydroxymethyl) propionic acid (5 carbon atoms), adipic acid (6 carbon atoms), citric acid (6 carbon atoms), picolinic acid (6 carbon atoms), benzoic acid (6 carbon atoms), 2,2-bis(hydroxymethyl) butanoic acid (6 carbon atoms), salicylic acid (7 carbon atoms), dipicolinic acid (7 carbon atoms), 2,3-dihydroxybenzoic acid (7 carbon atoms), 3-hydroxybenzoic acid (7 carbon atoms), suberic acid (8 carbon atoms), phthalic acid (8 carbon atoms), isophthalic acid (8 carbon atoms), terephthalic acid (8 carbon atoms), parahydroxyphenylacetic acid (8 carbon atoms), 1,3-cyclohexanedicarboxylic acid (8 carbon atoms), p-anisic acid (8 carbon atoms), azelaic acid (9 carbon atoms), 2,4-diethylglutaric acid (9 carbon atoms), sebacic acid (10 carbon atoms), phenyl succinic acid (10 carbon atoms), 2-quinolinecarboxylic acid (10 carbon atoms), and 4-tert-butylbenzoic acid (11 carbon atoms).

The different solvent preferably has a viscosity lower than that of isobornyl cyclohexanol at ordinary temperature, and examples thereof include water, alcohol solvents, glycol ether solvents and terpineols. Examples of the alcohol solvents include industrial ethanol (mixed solvent obtained by adding methanol and/or isopropyl alcohol to ethanol), isopropyl alcohol, 1,2-butanediol, 2,2-dimethyl-1,3-propanediol, 2,5-dimethyl-2,5-hexanediol, 2,5-dimethyl-3-hexyne-2,5-diol, 2,3-dimethyl-2,3-butanediol, 1,1,1-tris(hydroxymethyl)ethane, 2-ethyl-2-hydroxymethyl-1,3-propanediol, 2,2′-oxybis(methylene)bis(2-ethyl-1,3-propanediol), 2,2-bis(hydroxymethyl)-1,3-propanediol, 1,2,6-trihydroxyhexane, bis[2,2,2-tris(hydroxymethyl)ethyl]ether, 1-ethynyl-1-cyclohexanol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, erythritol, threitol, guaiacol glycerol ether, 3,6-dimethyl-4-octin-3,6-diol, and 2,4,7,9-tetramethyl-5-decyne-4,7-diol. Examples of the glycol ether solvents include hexyl diglycol, diethylene glycol mono-2-ethyl hexyl ether, ethylene glycol monophenyl ether, 2-methylpentane-2,4-diol, diethylene glycol dibutyl ether, and triethylene glycol monobutyl ether.

Examples of the amine include monoethanolamine, diphenylguanidine, ethylamine, triethylamine, ethylenediamine, triethylenetetramine, 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazolium trimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2′-methylimidazolyl-(1′)]-ethyl-s-triazine, 2,4-diamino-6-[2′-undecylimidazolyl-(1′)]-ethyl-s-triazine, 2,4-diamino-6-[2′-ethyl-4′-methylimidazolyl-(1′)]-ethyl-s-triazine, 2,4-diamino-6-[2′-methylimidazolyl-(1′)]-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2,3-dihydro-1H-pyrrolo [1,2-a]benzimidazole, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, 2-methylimidazoline, 2-phenylimidazoline, 2,4-diamino-6-vinyl-s-triazine, 2,4-diamino-6-vinyl-s-triazine isocyanuric acid adduct, 2,4-diamino-6-methacryloyloxyethyl-s-triazine, epoxy-imidazole adduct, 2-methylbenzimidazole, 2-octylbenzimidazole, 2-pentylbenzimidazole, 2-(1-ethylpentyl)benzimidazole, 2-nonylbenzimidazole, 2-(4-thiazolyl)benzimidazole, benzimidazole, 2-(2′-hydroxy-5′-methylphenyl)benzotriazole, 2-(2′-hydroxy-3′-tert-butyl-5′-methylphenyl)-5-chlorobenzotriazole, 2-(2′-hydroxy-3′,5′-di-tert-amylphenyl)benzotriazole, 2-(2′-hydroxy-5′-tert-octylphenyl)benzotriazole, 2,2′-methylenebis[6-(2H-benzotriazol-2-yl)-4-tert-octylphenol], 6-(2-benzotriazolyl)-4-tert-octyl-6′-tert-butyl-4′-methyl-2,2′-methylene bisphenol, 1,2,3-benzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]benzotriazole, carboxybenzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]methyl benzotriazole, 2,2′-[[(methyl-1H-benzotriazol-1-yl)methyl]imino]bisethanol, 1-(1′,2′-dicarboxyethyl)benzotriazole, 1-(2,3-dicarboxypropyl)benzotriazole, 1-[(2-ethylhexylamino) methyl]benzotriazole, 2,6-bis [(1H-benzotriazol-1-yl)methyl]-4-methylphenol, 5-methyl benzotriazole, and 5-phenyltetrazole.

Examples of the organohalogen compound include organic bromo compounds such as trans-2,3-dibromo-1,4-butenediol, triallyl isocyanurate hexabromide, 1-bromo-2-butanol, 1-bromo-2-propanol, 3-bromo-1-propanol, 3-bromo-1,2-propanediol, 1,4-dibromo-2-butanol, 1,3-dibromo-2-propanol, 2,3-dibromo-1-propanol, 2,3-dibromo-1,4-butanediol, 2,3-dibromo-2-butene-1,4-diol, trans-2,3-dibromo-2-butene-1,4-diol, cis-2,3-dibromo-2-butene-1,4-diol, tetrabromophthalic acid, and bromosuccinic acid. Moreover, there are listed: organic chloro compounds including chloroalkane, chlorinated fatty acid ester, het acid, and het anhydride. Furthermore, there are listed: organic fluoro compounds including a fluorosurfactant, a surfactant having a perfluoroalkyl group, and polytetrafluoroethylene.

The amine hydrohalide is a compound obtained by causing an amine and hydrogen halide to react, and examples thereof include aniline hydrochloride and aniline hydrobromide. As the amine of the amine hydrohalide, the above-described amines can be used, and examples thereof include ethylamine, ethylenediamine, triethylamine, methylimidazole, and 2-ethyl-4-methylimidazole. Examples of the hydrogen halide include hydrides of chlorine, bromine, iodine, and fluorine (hydrogen chloride, hydrogen bromide, hydrogen iodide, and hydrogen fluoride). Moreover, a borofluoride may be contained in place of or in combination with the amine hydrohalide, and examples of the borofluoride include fluoroboric acid.

<Example of Solder Paste of Present Embodiment>

As described above, the solder paste of the present embodiment contains: a flux containing an organic acid mixture including an organic acid with 10 or more carbon atoms, containing isobornyl cyclohexanol in a solvent at a predetermined ratio, and free of rosin, or a flux containing an organic acid with 12 or more carbon atoms, containing isobornyl cyclohexanol in a solvent at a predetermined ratio, and free of rosin; and metal powder. The metal powder is preferably Pb-free solder, and contains solder powder containing: Sn metal; Sn—Ag, Sn—Cu, Sn—Ag—Cu, Sn—Bi, Sn—In, or the like; or a product obtained by adding Sb, Bi, In, Cu, Zn, As, Ag, Cd, Fe, Ni, Co, Au, Ge, P, or the like to any of these alloys.

<Action/Effect Example of Flux and Solder Paste of Present Embodiment>

The flux containing: 1 wt % or more and 15 wt % or less of an organic acid mixture including an organic acid with 10 or more carbon atoms; 50 wt % or more and 90 wt % or less of isobornyl cyclohexanol; and 5 wt % or more and 45 wt % or less of a different solvent, wherein, when the total amount of the isobornyl cyclohexanol and the different solvent is 100 wt %, the ratio of the isobornyl cyclohexanol is 50 wt % or more and 95 wt % or less, and wherein the organic acid mixture including an organic acid with 10 or more carbon atoms includes 2-methylnonanedioic acid, 4-(methoxycarbonyl)-2,4-dimethylundecanedioic acid, 4,6-bis(methoxycarbonyl)-2,4,6-trimethyltridecanedioic acid, and 8,9-bis(methoxycarbonyl)-8,9-dimethylhexadecanedioic acid, and the solder paste using the flux can provide wettability of the solder. Further, it is possible to suppress the residue amount to realize low residue.

Further, the flux containing: 1 wt % or more and 15 wt % or less of an organic acid with 12 or more carbon atoms; 50 wt % or more and 90 wt % or less of isobornyl cyclohexanol; and 5 wt % or more and 45 wt % or less of a different solvent, wherein, when the total amount of the isobornyl cyclohexanol and the different solvent is 100 wt %, the ratio of the isobornyl cyclohexanol is 50 wt % or more and 95 wt % or less, and the solder paste using the flux can provide wettability of the solder. Further, it is possible to suppress residue amount to realize low residue.

In the flux of each embodiment, isobornyl cyclohexanol is contained in an amount of 50 wt % or more and 90 wt % or less when the total amount of the flux is 100 wt %, and the ratio of isobornyl cyclohexanol is 50 wt % or more and 95 wt % or less when the total amount of isobornyl cyclohexanol and a different solvent is 100 wt %. Hence, the flux has a viscosity capable of retaining the solder ball at ordinary temperature. By virtue of this, in the case where the flux of each embodiment is applied to electrodes and solder balls are placed on the electrodes coated with the flux to form solder bumps, it is possible to retain the solder balls with the flux at ordinary temperature before heating, and to suppress the occurrence of ball missing.

