JP6794857B2 - Water-soluble flux for solder paste and solder paste - Google Patents

Description

The present invention relates to a water-soluble flux used for preparing a solder paste and a solder paste prepared using the flux. More specifically, the present invention relates to a water-soluble flux for a solder paste which is excellent in printability and meltability and can prepare a paste which can be washed only with water after reflowing, and a solder paste containing the flux.

Solder paste is widely used for mounting electronic components and joining other components in the manufacture of information electronic devices such as mobile phones and personal computers and in-vehicle devices. The characteristics required for solder paste vary depending on the application of the equipment to be manufactured, the usage environment, and the like. For example, information electronic devices such as mobile phones are required to be thinner and lighter with an emphasis on portability. Therefore, as well as downsizing the mounting parts, the solder paste used for mounting also has a fine pitch of the joint parts ( Characteristics suitable for narrow pitching and high-density mounting are required. On the other hand, in in-vehicle applications and the like, since the mounted components are exposed to a relatively high temperature, it is necessary to prevent the solder after mounting from being remelted in a high temperature atmosphere and the joint strength from being lowered. Therefore, the solder paste used is required to have a property of imparting high heat resistance to the solder after reflow (melting).

The solder paste used for mounting such electronic components and the like is prepared into a paste by mixing the solder powder and the flux. Flux generally contains a resin component, a solvent component, an activator and other components, and the resin component is generally rosin, which has excellent electrical insulation, moisture resistance, and soldering performance when melted. Widely used. In mounting using solder paste, cleaning is usually performed to remove active components and the like adhering to the solder surface after reflow, but in the case of solder paste prepared using a flux containing rosin as a main component, this is performed. Cleaning cannot be performed only with water, and cleaning with an organic solvent is required. However, if cleaning is performed using an organic solvent, the organic solvent volatilizes into the atmosphere and causes a fire or pollutes the air and wastewater. Therefore, in terms of safety and health during mounting and the environment, etc. There was a problem.

In order to solve such a problem, it is a flux used for soldering electronic components to a circuit board. It contains at least a resin component and a solvent component, and as a resin component, the residual film of the flux is washed with water. A flux for soldering a circuit board containing a water-cleanable resin that can be produced is disclosed (see, for example, Patent Document 1). In this flux, a nonionic resin is used instead of rosin as a resin component, and the nonionic resin is a polyglycerin ester compound, and polyethylene glycol and polypropylene glycol are alternately repeated at least once. At least one of acetylated EO / PO block polymers having an acetyl group at at least one end of the molecule is used. As a result, the residual film after reflow can be washed with water, and the long-term reliability of the circuit board with soldered electronic components is maintained without impairing the insulation between the conductors of the circuit pattern of the circuit board after the cleaning. It is said that it can be increased.

Japanese Unexamined Patent Publication No. 2004-158728 (claims 1-3, paragraph [0037], etc.)

However, the flux shown in the conventional Patent Document 1 is mainly used for solder paste in which electronic components are mounted on a circuit board or the like by so-called SMT (Surface mount technology). Therefore, when bump formation or narrow-pitch printing is performed with a solder paste using this flux, the bumps and printing patterns may sag after printing, causing problems such as so-called bridges in which adjacent bumps are connected to each other. .. Therefore, although the flux shown in Patent Document 1 is very excellent in terms of use in SMT applications and the environment, for example, bump formation and narrow pitch printing are required as in FC (Flip-Chip) bonding technology. It cannot be said that it is sufficiently suitable for solder paste used in mounting technology. Therefore, there has been a demand for the development of a flux for solder paste that can prepare a paste that can be washed only with water after reflow without deteriorating the printability or meltability suitable for bump formation and narrow pitch printing.

An object of the present invention is to provide a water-soluble flux for a solder paste which is excellent in printability and meltability and can prepare a paste which can be washed only with water after reflow, and a solder paste prepared by using the flux. ..

The first aspect of the present invention is that in a water-soluble flux for solder paste containing an organic acid polyglycerol ester which is a solid surfactant at room temperature, a thixo agent, and a solvent, the thixo agent is benzylidene sorbitol or a benzylidene sorbitol derivative. It is characterized by containing 0.1 to 20.0% by mass of a surfactant that is liquid at room temperature in 100% by mass of the water-soluble flux.

A second aspect of the present invention is an invention based on the first aspect, further characterized in that the HLB value of the organic acid polyglycerol ester is 10 to 19.

The third aspect of the present invention is an invention based on the first or second aspect, and further, the organic acid polyglycerol ester is laurate polyglycerol ester, stearate polyglycerol ester, isostearic acid polyglycerol ester, sesquistea. One selected from the group consisting of acid polyglycerol ester, diisostearic acid polyglycerol ester, myristic acid polyglycerol ester, palmitate polyglycerol ester, oleic acid polyglycerol ester and behenic acid polyglycerol ester, and caprylic acid polyglycerol ester. It is characterized by having two or more types.

The fourth aspect of the present invention is an invention based on the first to third aspects, and is further characterized in that the SP value of the solvent is 10 to 20.

A fifth aspect of the present invention is a solder paste containing the water-soluble flux for solder paste and the solder powder according to the first to fourth aspects.

The water-soluble flux for solder paste according to the first aspect of the present invention contains an organic acid polyglycerol ester which is a solid surfactant at room temperature, a thixo agent, and a solvent, and the thixo agent is benzylidene sorbitol or a benzylidene sorbitol derivative. is there. As a result, while maintaining excellent printability and meltability, after reflowing, it can be washed only with water (including hot water, the same applies hereinafter) without using organic solvents, etc., in terms of safety and health during mounting. It is possible to prepare a solder paste that is excellent in terms of the environment. Further, in 100% by mass of the water-soluble flux for solder paste, 0.1 to 20.0% by mass of a surfactant that is liquid at room temperature is contained in addition to the organic acid polyglycerol ester that is a solid surfactant at room temperature. When made into a paste, the fluidity of the paste can be appropriately increased, which can further improve the printability.

The water-soluble flux for solder paste according to the second aspect of the present invention has an HLB value of an organic acid polyglycerol ester of 10 to 19. As a result, the detergency with water after reflow can be further improved.

In the water-soluble flux for solder paste according to the third aspect of the present invention, the organic acid polyglycerol ester is laurate polyglycerol ester, stearate polyglycerol ester, isostearic acid polyglycerol ester, sesquistearate polyglycerol ester, diisostearate polyglycerol. One or more selected from the group consisting of esters, myristic acid polyglycerol esters, palmitic acid polyglycerol esters, oleic acid polyglycerol esters and behenic acid polyglycerol esters, and caprylic acid polyglycerol esters. As a result, the printability when forming bumps and the like, or the washability with water after reflow can be further improved.

The water-soluble flux for solder paste according to the fourth aspect of the present invention has a solvent SP value of 10 to 20. This makes it possible to further improve the stability of the viscosity over time when handling or storing the prepared flux or the panda paste prepared using the same.

Since the solder paste according to the fifth aspect of the present invention contains the water-soluble flux for the solder paste of the present invention, it is possible to perform cleaning after reflow only with water while maintaining excellent printability and meltability. It is excellent in terms of safety and health and environment during mounting.

Next, a mode for carrying out the present invention will be described.

The water-soluble flux for solder paste of the present invention is an improvement of the water-soluble flux for solder paste containing an organic acid polyglycerol ester which is a solid surfactant at room temperature, a thixo agent, and a solvent. The thyxo agent is benzylidene sorbitol or a benzylidene sorbitol derivative, and the surfactant which is liquid at room temperature in 100% by mass of the water-soluble flux (hereinafter, simply referred to as "surfactant") is 0.1 to 20.0% by mass. To include.

In the water-soluble flux for solder paste of the present invention, the organic acid polyglycerol ester is included as a substitute for rosins such as gum rosin, hydrogenated rosin, polymerized rosin, and ester rosin, which are generally used as the main component of the flux. That is, this flux does not contain rosin or other resin components. In addition, since organic acid polyglycerol ester is contained as a substitute for rosin (resin component) used in general solder paste, a very small amount is added to the flux of cream solder as an auxiliary component such as a viscosity modifier. is not.

The organic acid polyglycerol ester is obtained by subjecting polyglycerin obtained by dehydration condensation of glycerin to an organic acid in an esterification reaction. Specifically, laurate polyglycerol ester, stearic acid polyglycerol ester, isostearic acid polyglycerol ester, sesquistearic acid polyglycerol ester, diisostearic acid polyglycerol ester, myristic acid polyglycerol ester, palmitate polyglycerol ester, oleic acid. Examples thereof include polyglycerol ester, behenic acid polyglycerol ester, caprylic acid polyglycerol ester, and one or more of these may be used in combination. In addition, coconut oil fatty acids obtained from natural oils and fats can also be used as the organic acid polyglycerol ester.

Further, the organic acid polyglycerol ester used in the present invention preferably has an HLB (Hydrophile-Lipophile Balance) value of 10 to 19. The HLB value is an index indicating water solubility, and varies depending on the type of organic acid, the number of polymerizations of polyglycerin, and the like. The larger the value, the higher the water solubility. If the HLB value of the organic acid polyglycerol ester is less than the lower limit, sufficient water solubility is not imparted to the flux or paste, and a residue may be generated when washing after reflow is performed only with water. On the other hand, if the upper limit is exceeded, the affinity of the organic acid polyglycerol ester for water becomes too high, and there is no suitable organic solvent for sufficiently dissolving the organic acid polyglycerol ester, which makes it difficult to prepare a flux. Alternatively, even a soluble organic solvent is not suitable as a flux solvent because it becomes an organic solvent having extremely high polarity. Of these, the HLB value is more preferably in the range of 11 to 18, and particularly preferably in the range of 11 to 16.5.

Benzylidene sorbitol or a benzylidene sorbitol derivative is used as the thixotropy. There are many common thixo agents used in solder paste, such as hardened castor oil, fatty acid amide, natural fats and oils, synthetic fats and oils, and 12-hydroxystearic acid, but the present invention is limited to the above-mentioned benzylidene sorbitol or its derivatives. .. As a result of diligent research by the present inventor, this is because when an organic acid polyglycerol ester is used as a resin component in a solder paste used in a mounting method that requires bump formation, narrow pitch printing, etc. When limited to, it is based on the reason that good printability, shape retention after printing, and the like were obtained. Benzylidene sorbitol or its derivatives include 1,3: 2,4-bis-O- (benzylidene) sorbitol, 1,3: 2,4-bis-O- (4-methylbenzylidene) sorbitol, 1,3: 2. , 4-Bis-O- (3,4-dimethylbenzylidene) sorbitol and the like.

As the solvent, diethylene glycol monohexyl ether, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, triethylene glycol monomethyl ether, diethylene glycol, triethylene glycol, tetraethylene glycol, diglycerin, 2-ethyl-1,3-hexanediol, α- Examples thereof include organic solvents having a boiling point of 180 ° C. or higher, such as terpineol, and one or more of these may be used in combination.

Further, when an organic acid polyglycerol ester is used instead of rosin, if a solvent having low solubility of the organic acid polyglycerol ester is used, the organic acid polyglycerol ester once dissolved is gradually precipitated from the solvent after the flux is prepared. However, the viscosity of the flux tends to increase over time. Further, when the paste is prepared, if a flux using a solvent having low solubility of the organic acid polyglycerol ester is used, the organic acid polyglycerol ester gradually precipitated during kneading with the solder powder is redissolved in the solvent. Then, the redissolved organic acid polyglycerol ester may be precipitated again from the solvent, which may cause a problem that the paste viscosity increases with time. Therefore, in the present invention, the solvent used has excellent solubility in highly water-soluble organic acid polyglycerol ester, that is, SP value, in terms of the viscosity of the flux and the stability of the paste viscosity over time. It is desirable to use one that meets the desired range. The SP value is a solubility parameter (SP) proposed by Hildebrand as an index showing the solubility of a solvent and defined by regular solution theory. The SP value shown in the present specification is an SP value (unit: (cal / cm ³ ) ^1/2 ) calculated based on the Fedors formula. Specifically, it is preferable to use a solvent having an SP value in the range of 10 to 20. If the SP value of the solvent used is less than the lower limit, the organic acid polyglycerol ester may not be sufficiently dissolved, the viscosity of the flux and the viscosity of the paste may deteriorate over time, and the thickening over time may become significant. On the other hand, when the upper limit is exceeded, the reactivity of the activator contained as one component in the flux becomes high, and the reaction with the solder powder contained in the paste causes the paste to become significantly thickened over time. , The meltability of the paste may decrease. Of these, the SP value of the solvent used is particularly preferably in the range of 10 to 17.

The surfactant used in the present invention is a nonionic surfactant, a cationic surfactant, an anionic surfactant or an amphoteric surfactant.

Nonionic surfactants include polyoxyalkylene alkyl ethers such as polyoxyethylene lauryl ethers, ether-type nonionic surfactants such as polyalkylene glycols, polyoxyalkylene alkenyl ethers, and polyoxyalkylene derivatives; bis (2-hydroxy). (2-Hydroxyethyl) alkylamines such as ethyl) laurylamine, alcohol amines such as triethanol, polyoxyethylene alkylamines, N, N', N'-tris (2-hydroxyethyl) -N-alkyl-1, Alkylamine ether-type nonionic surfactants such as 3-diaminoalkane, N, N', N'-polyoxyethylene-N-alkyl-1,3-diaminoalcan, polyoxypropylene polyoxyethylene alkylamine; fatty acid ester , Glycol fatty acid ester, sorbitan fatty acid ester and other ester-type nonionic surfactants; polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene hydrogenated castor oil, alkyl Ether ester-type nonionic surfactants such as alkanolamide; amino acid derivative nonionic surfactants such as N-acylamino acid ester, N-acylglutamic acid ester, and pyroglutamic acid ester are exemplified. Other examples include phenol ethoxylate, silicone-based surfactant, and fluorine-based surfactant as nonionic surfactants.

Further, examples of the cationic surfactant include surfactants such as alkylamine salts such as quaternary ammonium salts such as lauryltrimethylammonium chloride.

Examples of anionic surfactants include polyoxyethylene alkyl ether sulfates such as polyoxyethylene lauryl ether sodium sulfate, aliphatic phosphoric acid esters such as aromatic phosphates, dioctyl sulfosuccinate Na salts, and alcohol sulfate Na. Surfactants such as salts, alkyl sulphate esters, alkylbenzene sulfonates, fatty acid salts, naphthalene sulfonic acid formarin condensates and the like are exemplified.

Further, examples of the amphoteric surfactant include alkyl betaines such as lauryl betaine, fatty acid amide alkyl acetate betaines, fatty acid amino acetate betaines, and alkyl amine oxides.

In addition to the above-mentioned organic acid polyglycerol ester, thixotropy, solvent, and surfactant, the flux may contain an activator, an antioxidant, and the like. As the activator, amines, organic acids, amine salts of hydrohalic acids, ammonium salts of organic acids, amine salts of organic acids, ammonium halides, organic halogen compounds and the like can be used.

Examples of amines include ethanolamine, diethanolamine, triethanolamine, 3,4-dihydroxybenzylamine, methyldiethanolamine, diphenylguanidine, aminopropanol, polyoxyethylene oleylamine, polyoxyethylene laurelamine, polyoxyethylene stearylamine, and methylamine. Dimethylamine, ethylamine, diethylamine, triethylamine, propylamine, dipropylamine, triisopropylamine, isopropylamine, diisopropylamine, tri-n-propylamine, n-butylamine, isobutylamine, tert-butylamine, di-n-butylamine, Tri-n-butylamine, n-hexylamine, tri-n-hexylamine, octylamine, dodecylamine, stearylamine, methoxypropylamine, dimethylhexylamine, allylamine, diallylamine, 2-bromoethylamine, 1,3-di- o-Triguanidine, dimethylaminopropylamine, dibutylaminopropylamine, ethylhexylamine, ethoxypropylamine, ethylhexyloxypropylamine, pyridine, 4-bromopyridine, piperidine, 2,6-dimethylpiperidin, pipecholine, aniline, dimethylamine, Ethylaniline, 2,4,6-trimethylaniline, morpholine, methylmorpholin, ethylmorpholine, ethylnaphthylamine, 3-amino-1-propene, cyclohexylamine, disirohexylamine, cyclohexyldimethylamine, cyclohexyldiethyleneamine, cyclohexylmethylethylamine , Cyclohexyldi-n-propylamine, cyclohexyldiisopropylamine, cyclohexyldi-n-butylamine, cyclohexyldiisobutylamine, cyclohexyldipentylamine, cyclohexyldihexylamine, dicyclohexylmethylamine and the like.

Examples of organic acids include formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, caproic acid, enanthic acid, capric acid, pelargonic acid, capric acid, lauric acid, myristic acid, pentadecylic acid, Palmitic acid, margaric acid, stearic acid, oleic acid, linoleic acid, linolenic acid, tubercrostearic acid, arachidic acid, arachidonic acid, eikosapentaenoic acid, bechenic acid, docosahexaenoic acid, lignoseric acid, azelaic acid, suberic acid, sebacic acid , Phthalic acid, cellotic acid, montanic acid, melisic acid, salicylic acid, gallic acid, benzoic acid, phthalic acid, caytic acid, meritic acid, oxalic acid, lactic acid, tartaric acid, maleic acid, fumaric acid, malonic acid, Examples thereof include succinic acid, malic acid, citric acid, aconitic acid, glutaric acid, adipic acid, terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid and the like.

Examples of the halogenated hydride amine salt include the above-mentioned amine hydride or hydrobromide, and examples of the organic acid ammonium salt include a salt of ammonia and the above-mentioned organic acid. Examples of the salt include a salt of the above amine and the above organic acid.

Examples of the organic halogen compound include alkyl halides, alcohol halides, halogenated esters, carboxylic acids halogenated, ketones halides, halogenated amides, and ether halides. Specific examples of alkyl halides include 1-bromo-3-methyl-1-butene, 1,4-dibromobutene, 1-bromo-1-propene, 2,3-dibromopropene, and 1,1-dibromotetrachloroethane. , 1,2-Dibromo-1-phenylethane, 1,2-dibromostyrene, 1,2,5,6,9,10-hexabromocyclododecane, 2,2-bis [4- (2,3-dibromo) Propyl) -3,5-dibromoferni] propane, α, β-dibromoethylbenzene and the like can be mentioned. Specific examples of the halogenated alcohol include 1-bromo-2-propanol, 3-bromo-1-propanol, 3-bromo-1,2-propanediol, 1,3-dibromo-2-propanol, and 1,4-. Dibromo-2,3-butanediol, 2,3-dibromo-1-propanol, 1-bromo-2-butanol, 1,4-dibromo-2-butanol, 2,3-dibromo-2-propanol, 1,4 -Dibromo-2-butanediol, 2,3-dibromo-2-butene-1,4-diol, 9,10,12,13,15,16-hexabromostearyl alcohol, 9,10,12,13- Examples thereof include tetrabromostearyl alcohol. Specific examples of the halogenated ester include ethyl bromoacetate, ethyl α-bromocaprylate, ethyl α-bromopropionate, ethyl β-bromopropionate, α-bromo-ethyl acetate, 9,10,12,13,15. , 16-Hexabromostearic acid methyl ester, the same ethyl ester, 9,10,12,13-tetrabromostearic acid, the same methyl ester, the same ethyl ester and the like. Specific examples of the halogenated carboxylic acid include 2,3-dibromosuccinic acid, 2-bromosuccinic acid, 2,2-dibromoadipic acid, 9,10,12,13,15,16-hexabromostearic acid and bis. (2,3-dibromopropyl) succinate, bis (2,3-dibromopropyl) o-phthalate, bis (2,3-dibromopropyl) p-phthalate, bis (2,3-dibromopropyl) p-phthalamide, tris Examples thereof include (2,3-dibromopropyl) trimellitate, 4-bromomethylbenzyl stearate, 2,4-bisbromomethylbenzyl stearate, tetra (2,3-dibromopropyl) pyromeritate and the like. Specific examples of the halogenated ketone include 2,4-dibromoacetophenone and the like. Specific examples of the halogenated amide include bis (2,3-dibromopropyl) o-phthalamide, tris (2,3-dibromopropyl) trimeritoamide, tetra (2,3-dibromopropyl) pyromeritoamide, and bis (2,3). Examples thereof include 3-dibromopropyl) tartamide, N, N'-bis (2,3-dibromopropyl) succiamide, N, N, N', N'-tetra (2,3-dibromopropyl) succiamide and the like. Further, specific examples of halogenated ethers include trimethylolpropane bis (2,3-dibromopropyl) ether, 4-palmitoyloxybenzyl bromide, 4-myristoyloxybenzyl bromide, 4-lauroyloxybenzyl bromide, and 4-undecanoyl. Examples thereof include oxybenzyl bromide.

Examples of the antioxidant include a phenol-based antioxidant, a phosphorus-based antioxidant, a sulfur-based antioxidant, an amine-based antioxidant, and the like.

The proportion of the organic acid polyglycerol ester in 100% by mass of the water-soluble flux is preferably 10% by mass or more and less than 50% by mass, and particularly preferably 15 to 45% by mass. The ratio of the solvent is 30 to 60% by mass, the ratio of the thixo agent is 1 to 10% by mass, the ratio of the activator is 0.1 to 10% by mass, and the ratio of the antioxidant is 1 to 10% by mass. Is preferable. Further, as described above, the ratio of the surfactant to 100% by mass of the water-soluble flux is 0.1 to 20.0% by mass, preferably 1.0 to 10.0% by mass.

If the proportion of the organic acid polyglycerol ester is less than the lower limit, the fluidity of the paste, the tackability to the substrate, and the like are lowered, so that the bumps after printing may have problems such as poor shape. On the other hand, if the upper limit is exceeded, the viscosity of the flux becomes too high, and the paste viscosity also becomes high accordingly, resulting in poor shape of the bumps after printing or bumps without the paste being ejected from the mask opening. Is not formed, so-called missing problems may occur. Further, when the ratio of the solvent is less than the lower limit value, the viscosity of the flux becomes high, and the paste viscosity becomes too high accordingly, which may cause the above-mentioned problems such as poor shape of bumps and missing. On the other hand, if the upper limit is exceeded, the viscosity of the flux becomes low, and the viscosity of the paste becomes too low accordingly, which may cause problems such as sedimentation and separation of the solder powder in the paste.

Further, if the ratio of the thixotropic agent is less than the lower limit value, the shape retention as a solder paste is lowered, and problems such as so-called bridges in which adjacent bumps are connected to each other may occur. On the other hand, if the upper limit is exceeded, the viscosity of the flux becomes high, and the paste viscosity becomes too high accordingly, which may cause problems such as poor shape of the bump and missing. If the ratio of the activator is less than the lower limit, the solder powder may not melt and sufficient bonding strength may not be obtained. On the other hand, if the ratio exceeds the upper limit, the activator reacts with the solder powder during storage. Since it becomes easy, the storage stability of the solder paste may decrease. Further, when the ratio of the antioxidant is less than the lower limit value, the solder powder and the flux component are likely to react with each other, so that the storage stability of the solder paste may be lowered. On the other hand, if the upper limit is exceeded, the meltability of the solder powder may decrease.

Further, when the ratio of the surfactant is less than the lower limit of 0.1% by mass, when a large number of solder bumps are formed on the substrate, the paste becomes difficult to flow when the solder paste is formed, and the missing bumps are not formed. Occurs. Further, when the ratio of the surfactant exceeds the upper limit value of 20.0% by mass, the paste tends to flow when it is made into a solder paste, and so-called bridges in which adjacent bumps are connected to each other occur.

To prepare a solder paste using the flux thus obtained, the flux and the solder powder are mixed in a desired ratio. The solder powder to be used is not particularly limited, and general tin-based solder powder or the like can be used. For example, Sn-Pb-based solder (composition Sn: Pb = 63: 37% by mass, etc.), Sn-Pb-Ag-based solder (composition Sn: Pb: Ag = 62: 36: 2% by mass, etc.), Sn-Pb- Bi-based solder (composition Sn: Pb: Bi = 57: 40: 3% by mass, etc.), Sn-Pb-Sb-based solder (composition Sn: Pb: Sb = 8: 86: 6% by mass, etc.), Sn-Ag-based solder Solder (composition Sn: Ag = 97.7: 2.3% by mass, etc.), Sn-Cu-based solder (composition Sn: Cu = 98.3: 0.7% by mass, etc.), Sn-Ag-Cu-based solder (composition Sn: Cu = 98.3: 0.7% by mass, etc.) Composition Sn: Ag: Cu = 96.5: 3: 0.5% by mass, etc.), Au-Sn-based high-temperature solder (composition Au: Sn = 75 to 85: 25 to 15% by mass, and composition Au: Sn = 5 to 15: 95 to 85% by mass, especially composition Au: Sn = 78 to 80: 22 to 20% by mass, composition Au: Sn = 10: 90% by mass, etc.), Au-Si based high temperature solder (composition Au) : Si = 81.4: 18.6% by mass, etc.), Au-Ge high-temperature solder (composition Au: Ge = 92.6: 7.4% by mass, etc.), Sn-Pb-based high-temperature solder (composition Sn) : Pb = 5: 95% by mass, etc.), Other Zn-Sn-based solder (composition Zn: Sn = 9: 91% by mass, etc.), In-Sn-based solder (composition In: Sn = 52: 48% by mass, etc.) , Bi-Sn-based solder (composition Bi: Sn = 58: 42% by mass, etc.), Sb-Sn-based solder (composition Sb: Sn = 5: 95% by mass, etc.), Al-Zn-based solder (composition Al: Zn =, etc.) 5:95 mass%, etc.) and the like. The average particle size of the solder powder is not particularly limited as long as it is within the range used for general solder pastes, but for example, those in the range of 0.1 μm to 1 mm can be preferably used. Considering narrow pitch printing and the like, the average particle size of the solder powder is preferably in the range of 0.1 μm to 50 μm, and further considering fine bump formation and the like, it is in the range of 1 μm to 20 μm. Is more preferable. In the present specification, the average particle size means a volume-based average particle size D ₅₀ measured using a laser diffraction / scattering type particle size distribution measuring device (manufactured by Horiba Seisakusho Co., Ltd., model name: Partica LA-950). ..

The mixing amount of the flux when preparing the solder paste is preferably adjusted to an amount such that the ratio of the flux to 100% by mass of the prepared paste is 3 to 60% by mass. If it is less than the lower limit, the amount of flux is small, which may make it difficult to make a paste or cause problems such as the solder powder not melting. On the other hand, if the upper limit is exceeded, the amount of solder powder contained in the paste may be reduced, and the required amount of solder may not be obtained after melting.

Since the solder paste prepared in this way uses the water-soluble flux for the solder paste of the present invention, it maintains good printability or meltability suitable for bump formation and narrow pitch printing, and after reflowing. Cleaning can be performed only with water, which is excellent in terms of safety and health during mounting and the environment. Therefore, this solder paste can be suitably used particularly in mounting technology such as FC bonding technology.

Next, examples of the present invention will be described in detail together with comparative examples.

<Examples 1 to 54, Comparative examples 2 to 25>
An organic acid polyglycerol ester, a thixo agent, a solvent, an activator, a phenolic antioxidant as an antioxidant, and a surfactant were prepared, respectively. These were blended in the ratios shown in Tables 2 to 7 below, and the flux was obtained by mixing and stirring. In Tables 2 to 7, organic acid polyglycerol esters represented by categories A to F, solvents represented by categories A to D, thixotropic agents represented by categories A and B, and activators represented by categories A and B. Is shown in Table 1 below. In Tables 5 to 7, the surfactants represented by categories A to E are polyoxyethylene lauryl ether (classification A), which is an ether-type nonionic surfactant, and bis (classification A), which is also an ether-type nonionic surfactant. 2-Hydroxyethyl) laurylamine (Category B), cationic surfactant lauryltrimethylammonium chloride (Category C), anionic surfactant sodium polyoxyethylene lauryl ether sulfate (Category D), amphoteric surfactant It is a lauryl betaine (classification E), which is an agent, and is also shown in Table 1. In Table 1, the number at the end of the name of the organic acid polyglycerol ester indicates the number of polyglycerol polymerized. In Comparative Example 2, Comparative Examples 11 to 14, Comparative Example 21, Comparative Example 23 and Comparative Example 24, no surfactant was blended.

<Comparative example 1>
Rosin (polymerized rosin) was used instead of organic acid polyglycerol esters, except that rosin, thixo agent, solvent, activator and antioxidant were blended in the proportions shown in Tables 4 and 7 below. A flux was obtained in the same manner as in Example 1. The flux obtained in Comparative Example 1 does not contain polyglycerol esters.

<Comparative tests and evaluations>
The following evaluations (i) to (iii) were carried out using the fluxes obtained in Examples 1 to 54 and Comparative Examples 1 to 25. These results are shown in Tables 8 to 10. Tables 8 to 10 also show the types of solder powder used.

(i) Bump printability (board): Two types of solder powder were prepared, and two types of solder paste were prepared. First, a Sn-Ag-Cu-based solder powder having an average particle size of 8 μm (composition: Sn96.5% by mass, Ag3.0% by mass, Cu0.5% by mass) was prepared, and 89.0 parts by mass of this solder powder was used. , 11.0 parts by mass of the fluxes obtained in Examples 1 to 49 and 52 and Comparative Examples 1 to 22, respectively, were stirred and mixed at room temperature to prepare a solder paste. In Tables 8 to 10, this solder powder is designated as "SAC305". Next, Au-Sn-based solder powder having an average particle size of 8 μm (composition: Au78.0% by mass, Sn22.0% by mass) was prepared, and 94.0 parts by mass of this solder powder and Examples 50 and 51, A solder paste was prepared by stirring and mixing 6.0 parts by mass of the fluxes obtained in 53 and 54 and Comparative Examples 23 to 25 at room temperature. In Tables 9 and 10, this solder powder is described as "Au22Sn". The average particle size of the solder powder is a volume-based average particle size D ₅₀ measured using a laser diffraction / scattering type particle size distribution measuring device (manufactured by Horiba Seisakusho, model name: Partica LA-950). A small semi-automatic screen printing machine equipped with a Ni-plated metal mask plate (external dimensions: length 300 mm x width 3000 mm x thickness 20 μm, opening diameter φ: 75 μm, opening pitch: 100 μm) provided with multiple openings is used. , The above-mentioned solder paste was printed on a substrate (dimensions: length 60 mm × width 60 mm × thickness 0.8 mm) to form solder bumps on the substrate. The substrate is a copper foil having a thickness of about 50 μm provided on one surface of the substrate, and a resist film (film) provided on the copper foil and having a plurality of openings penetrating to the copper foil. It has a thickness of 15 μm, an opening diameter of φ65 μm, and an opening pitch of 100 μm). Among the 20,000 solder bumps formed on the substrate, the number of missing bumps on which no bumps were formed and the number of bridges in which adjacent bumps were connected were measured. Those with the number of missing bumps and the number of bridges of 5 or less were regarded as acceptable.

(ii) Bump meltability (board): The board on which the solder bumps were formed in the above-mentioned bump printability test was melted under the following conditions using a reflow furnace (manufactured by Malcolm, model name: SRS-1C). For the solder bumps formed by the solder paste using the Sn-Ag-Cu-based solder powders of Examples 1 to 49 and Comparative Examples 1 to 22, the substrate was placed in a nitrogen atmosphere at 1.5 ° C./s from room temperature to 150 ° C. The temperature is raised at the temperature of 150 ° C., pre-dried at 150 ° C. for 2 minutes, then raised from 150 ° C. to 230 ° C. at a heating rate of 1.5 ° C./s, and heated at 230 ° C. for 5 seconds. By doing so, the solder bumps on the substrate were melted. Further, with respect to the solder bumps formed by the solder paste using the Au-Sn-based solder powders of Examples 50, 51, 53, 54 and Comparative Examples 23 to 25, the temperature was raised by 1.5 ° C./s from room temperature to 220 ° C. By raising the temperature at a rate, pre-drying at 220 ° C. for 2 minutes, then raising the temperature from 220 ° C. to 300 ° C. at a heating rate of 1.5 ° C./s, and heating at a temperature of 300 ° C. for 5 seconds. , The solder bumps on the substrate were melted. The appearance after reflow was visually observed, and the case where no unaggregated solder was confirmed around the bump was evaluated as "good", and the case where unaggregated solder was confirmed was evaluated as "bad".

(iii) Flux detergency (substrate): 50 ml of ion-exchanged water in a 100 ml glass beaker was heated to 60 ° C. using a hot plate. The substrate after the above-mentioned meltability test was put into the beaker containing the ion-exchanged water at 60 ° C., and the beaker was put into the ultrasonic cleaner and ultrasonically applied for 5 minutes. Then, the substrate was taken out from the beaker, water was removed by an air blow, and then dried at a temperature of 50 ° C. for 5 minutes using a dryer. The bump portion after reflow and cleaning was observed with a backscattered electron image of a scanning electron microscope (SEM; model name: JSM-6510LV manufactured by JEOL Ltd.) to confirm the presence or absence of residual organic components. From the presence or absence of the residue of the organic component at this time or the degree thereof, the case where there is almost no residue is "excellent", the case where a residue of less than 5% is confirmed with respect to the bump surface area of 100% is "good", and the bump surface area is 100. When a residue of 5% or more was confirmed with respect to%, it was regarded as “defective” and evaluated on a three-point scale.

As is clear from Tables 8 to 10, when Examples 1 to 54 and Comparative Examples 1 to 25 are compared, in Comparative Example 1 in which rosin was used as the flux component, the evaluation of bump printability was "good". Although there was, it was not possible to sufficiently wash with water alone, and the evaluation of flux cleanability was "poor". Further, in Comparative Examples 15 to 20, 22, and 25 using the cured castor oil, the organic acid polyglycerol ester was used as the resin component, so that the evaluation of the flux detergency was "good" or "excellent". Results were obtained, and the number of missing bumps in the bump printability met the acceptance criteria, but the number of bridges did not meet the acceptance criteria.

In addition, Comparative Examples 2, 11 to 14, 21, 23, 24 and the surfactant, which contained an organic acid polyglycerol ester and a specific solder as a component of the flux but did not contain a surfactant, were 0.05 mass by mass, respectively. In Comparative Examples 3 and 5 containing%, although the pass criteria were satisfied for the bump meltability and the flux cleanability, respectively, the paste did not flow easily when made into a solder paste, no bridge was generated, and the number of missing bumps was 8. It was ~ 57 and did not reach the acceptance criteria.

Further, in Comparative Examples 4 and 6 to 10 in which the organic acid polyglycerol ester and the specific soldering agent were contained in the flux component, while the surfactant was contained in an amount of 25.0% by mass, the bump meltability and the flux detergency were obtained, respectively. Although the acceptance criteria were met, the paste tended to flow when soldered, and the number of bridges between the bumps did not reach the acceptance criteria.

On the other hand, in Examples 1 to 54 in which an organic acid polyglycerol ester was used as a resin component, a specific thixotropic agent was used, and a specific amount of a surfactant was contained, the bump meltability and flux cleanability were high. Evaluation was obtained. In Example 1 in which the content of the nonionic surfactant was 0.1% by mass, the number of missing bumps was "2", and in Examples 9 and 22 in which the content of the anionic surfactant was 0.2% by mass, the missing bumps were missing bumps. In Examples 11 and 24 in which the numbers were "4" and "3" and the content of the surfactant including the nonionic and cationic surfactants was 0.2% by mass, the number of missing bumps was "2" and "1". On the other hand, in the other Examples 2-8, 10, 12-21, 23, 25-54, the number of missing bumps is "0", and all the examples 1 to 54 pass the number of missing bumps. It was.

Further, in Example 3 in which the content of the nonionic surfactant is 20.0% by mass, the number of bridges is "4", and in Example 7 where the content of another type of nonionic surfactant is 20.0% by mass. In Examples 10 and 23 in which the number of bridges was "2" and the content of the amphoteric surfactant was 15.0% by mass in 20, the number of bridges was "4" and "2", and the surface activity of the nonionic and anionic surfactants combined. In Examples 12 and 25 having an agent content of 15.0% by mass, the number of bridges was "2", and Examples 14 and 27 having a combined cationic and anionic surfactant content of 20.0% by mass. In the other Examples 1, 2, 4 to 6, 8, 9, 11, 13, 15 to 19, 21, 22, 24, 26, 28 to 54, the number of bridges is "4". The number was "0" and all Examples 1-54 passed with respect to the number of bridges.

The water-soluble flux for solder paste of the present invention can be widely used for mounting electronic components (particularly, mounting techniques that require bump formation, narrow pitch printing, etc., such as FC bonding technology), and for joining other components.

Claims (5)

In a water-soluble flux for solder paste containing an organic acid polyglycerol ester which is a solid surfactant at room temperature, a thixo agent, and a solvent.
The thixo agent is benzylidene sorbitol or a benzylidene sorbitol derivative, and is water-soluble for solder paste, which contains 0.1 to 20.0% by mass of a surfactant that is liquid at room temperature in 100% by mass of the water-soluble flux. flux. The water-soluble flux for a solder paste according to claim 1, wherein the organic acid polyglycerol ester has an HLB value of 10 to 19. The organic acid polyglycerol ester is lauric acid polyglycerol ester, stearic acid polyglycerol ester, isostearic acid polyglycerol ester, sesquistearic acid polyglycerol ester, diisostearic acid polyglycerol ester, myristic acid polyglycerol ester, palmitate polyglycerol ester, The water-soluble flux for solder paste according to claim 1 or 2, wherein it is one or more selected from the group consisting of an oleic acid polyglycerol ester, a behenic acid polyglycerol ester, and a caprylic acid polyglycerol ester. The water-soluble flux for solder paste according to any one of claims 1 to 3, wherein the SP value of the solvent is 10 to 20. A solder paste containing the water-soluble flux for solder paste according to claims 1 to 4 and a solder powder.