JP2016043397A - Water-soluble flux for solder paste, and solder paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide water-soluble flux for solder paste capable of performing cleaning after reflow only by water, while maintaining excellent printability and fusibility; and to provide solder paste prepared by using the flux.SOLUTION: In water-soluble flux for solder paste containing organic acid polyglycerol ester, a thixotropic agent and a solvent, the thixotropic agent is benzylidene sorbitol or a benzylidene sorbitol derivative. The HLB value of the organic acid polyglycerol ester is preferably 10-19.SELECTED DRAWING: None

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 solder paste capable of preparing a paste that is excellent in printability and meltability and can be washed only with water after reflow, and a solder paste prepared using the flux.

  Solder paste is widely used for mounting electronic components, joining other components, and the like when manufacturing information electronic devices such as mobile phones and personal computers, and in-vehicle devices. The properties required for solder paste vary depending on the application of the equipment to be manufactured, the usage environment, and the like. For example, since information electronic devices such as mobile phones are required to be thinner and lighter with emphasis on portability, as well as miniaturization of mounting components, solder paste used for mounting also has a fine pitch ( Narrow pitch) and characteristics suitable for high-density mounting are required. On the other hand, in a vehicle-mounted application or the like, since the mounted component is exposed to a relatively high temperature, it is necessary to prevent the solder after mounting from remelting in a high-temperature atmosphere and reducing the bonding strength. Therefore, the solder paste to be used is required to have a characteristic of imparting high heat resistance to the solder after reflow (melting).

  A solder paste used for mounting such electronic components is prepared in a paste form by mixing solder powder and flux. The flux generally includes an activator and other components in addition to the resin component and the solvent component, and the resin component is generally a rosin that is excellent in electrical insulation, moisture resistance, soldering performance when melted, etc. Widely used. In mounting using a solder paste, cleaning is usually performed to remove active components adhering to the solder surface after reflow, but in the case of a solder paste prepared using a flux containing rosin as a main component, Cleaning cannot be performed with water alone, and cleaning with an organic solvent is required. However, cleaning with an organic solvent may cause a fire due to volatilization of the organic solvent in the atmosphere or contaminate the air or wastewater. There was a problem.

  In order to solve such a problem, it is a flux used for soldering electronic components to a circuit board, which contains at least a resin component and a solvent component, and the residual film of the flux is washed with water as a resin component A circuit board soldering flux containing a water-washable resin that can be produced is disclosed (for example, see Patent Document 1). In this flux, a nonionic resin is used as a resin component instead of rosin, and the polyionic ester compound and at least one of polyethylene glycol and polypropylene glycol are alternately repeated as the nonionic resin. As the block polymer, 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 remaining film after reflow can be washed with water, and after the washing, the insulation between the conductors of the circuit pattern of the circuit board is not impaired, and the long-term reliability of the circuit board with soldered electronic components is improved. It can be increased.

JP 2004-158728 A (Claims 1-3, paragraph [0037], etc.)

  However, the flux shown in the above-mentioned conventional patent document 1 is mainly used for a 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, narrow pitch printing, etc. are performed with solder paste using this flux, adjacent bumps and print patterns may sag after printing, causing problems such as so-called bridges that contact each other. . For this reason, the flux shown in Patent Document 1 is very excellent in terms of use in SMT applications, environmental aspects, and the like, but requires bump formation, narrow pitch printing, etc. as in the FC (Flip-Chip) bonding technology, for example. It cannot be said that it is sufficiently suitable for solder paste used in packaging technology. Therefore, there has been a demand for the development of a solder paste flux that can prepare a paste that can be washed only with water after reflow without deteriorating the printability or meltability suitable for bump formation or narrow pitch printing.

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

  A first aspect of the present invention is characterized in that in a water-soluble flux for solder paste containing an organic acid polyglycerol ester, a thixotropic agent, and a solvent, the thixotropic agent is benzylidene sorbitol or a benzylidene sorbitol derivative.

  A second aspect of the present invention is an invention based on the first aspect, wherein the organic acid polyglycerol ester has an HLB value of 10 to 19.

  A third aspect of the present invention is the invention based on the first or second aspect, wherein the organic acid polyglycerol ester is lauric acid polyglycerol ester, stearic acid polyglycerol ester, isostearic acid polyglycerol ester, sesquistearin. One or more selected from the group consisting of acid polyglycerol ester, diisostearic acid polyglycerol ester, myristic acid polyglycerol ester, palmitic acid polyglycerol ester, oleic acid polyglycerol ester and behenic acid polyglycerol ester It is characterized by.

  A fourth aspect of the present invention is an invention based on the first to third aspects, wherein the SP value of the solvent is 10-20.

  A fifth aspect of the present invention is a solder paste obtained by stirring and mixing the water-soluble flux for solder paste and the solder powder of the first to fourth aspects.

  The water-soluble flux for solder paste according to the first aspect of the present invention includes an organic acid polyglycerol ester, a thixotropic agent, and a solvent, and the thixotropic agent is benzylidene sorbitol or a benzylidene sorbitol derivative. As a result, while maintaining excellent printability and meltability, after reflow, it can be cleaned only with water (including hot water, the same shall apply hereinafter) without using an organic solvent, etc. Solder paste with excellent environmental aspects can be prepared.

  The water soluble flux for solder paste according to the second aspect of the present invention has an organic acid polyglycerol ester having an HLB value of 10 to 19. Thereby, the washability by the water after reflow can be improved more.

  In the water-soluble flux for solder paste according to the third aspect of the present invention, 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. One or more selected from the group consisting of ester, myristic acid polyglycerol ester, palmitic acid polyglycerol ester, oleic acid polyglycerol ester and behenic acid polyglycerol ester. Thereby, the printability when forming bumps or the like, or the washability with water after reflow can be further enhanced.

  In the water-soluble flux for solder paste according to the fourth aspect of the present invention, the SP value of the solvent is 10-20. Thereby, when dealing with the flux after preparation or the panda paste prepared using this, or when storing it, the temporal stability of a viscosity can be improved more.

  Since the solder paste of the fifth aspect of the present invention uses the water-soluble flux for solder paste of the present invention, the post-reflow cleaning is performed only with water while maintaining excellent printability and meltability. It is excellent in terms of safety and health during mounting and environmental aspects.

  Next, the form for implementing this invention is demonstrated.

  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, a thixotropic agent, and a solvent, and the thixotropic agent is benzylidene sorbitol or a benzylidene sorbitol derivative. It is to be.

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

  The organic acid polyglycerol ester can be obtained by esterifying a polyglycerol obtained by dehydration condensation of glycerol and an organic acid. Specifically, lauric acid polyglycerol ester, stearic acid polyglycerol ester, isostearic acid polyglycerol ester, sesquistearic acid polyglycerol ester, diisostearic acid polyglycerol ester, myristic acid polyglycerol ester, palmitic acid polyglycerol ester, oleic acid Examples thereof include polyglycerol esters and behenic acid polyglycerol esters, 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.

  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. When the HLB value of the organic acid polyglycerol ester is less than the lower limit value, sufficient water solubility is not imparted to the flux or paste, and a residue may be produced when washing after reflow is performed only with water. On the other hand, when the upper limit is exceeded, the affinity of the organic acid polyglycerol ester to water becomes too high, and there is no suitable organic solvent that can sufficiently dissolve it, making it difficult to produce a flux. Alternatively, even an organic solvent that can be dissolved is not suitable as a flux solvent because it becomes an organic solvent having a very high polarity. Of these, the HLB value is particularly preferably in the range of 11-18.

  As the thixotropic agent, benzylidene sorbitol or a benzylidene sorbitol derivative is used. There are many common thixotropic agents used for solder paste, such as hydrogenated castor oil, fatty acid amide, natural fats and oils, synthetic fats and oils, and 12-hydroxystearic acid. . As a result of intensive studies by the inventor, the thixotropic agent is used when using an organic acid polyglycerol ester as a resin component in a solder paste used in a mounting method that requires bump formation or narrow pitch printing. The reason is based on the reason that good printability, shape retention after printing, and the like were obtained. As benzylidene sorbitol or derivatives thereof, 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.

  Examples of the solvent include diethylene glycol monohexyl ether, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, triethylene glycol monomethyl ether, diethylene glycol, triethylene glycol, tetraethylene glycol, 2-ethyl-1,3-hexanediol, α-terpineol, etc. The organic solvent whose boiling point is 180 degreeC or more is mentioned, You may use these 1 type (s) or 2 or more types together.

In addition, when using organic acid polyglycerol ester instead of rosin, if a solvent with low solubility of organic acid polyglycerol ester is used, once dissolved, the organic acid polyglycerol ester that has been dissolved will gradually precipitate from the solvent. However, there is a tendency that the viscosity of the flux tends to increase with time. Furthermore, when preparing a paste, if a flux using a solvent having low solubility of the organic acid polyglycerol ester is used, the organic acid polyglycerol ester that gradually precipitates is redissolved in the solvent when kneaded with the solder powder. Then, the redissolved organic acid polyglycerol ester is precipitated again from the solvent, which may cause a problem that the paste viscosity increases with time. Therefore, in the present invention, the solvent to be used is one that exhibits excellent solubility in a highly water-soluble organic acid polyglycerol ester from the viewpoint of temporal stability of flux viscosity and paste viscosity, that is, SP value. It is desirable to use those that satisfy the desired range. The SP value is a solubility parameter (SP) proposed by Hildebrand as an index representing the solubility of a solvent and defined by regular solution theory. Note that the SP value shown in this specification is an SP value (unit: (cal / cm ³ ) ^1/2 ) calculated based on the Fedors equation. Specifically, it is preferable to use a solvent having an SP value in the range of 10-20. When the SP value of the solvent to be used is less than the lower limit, the organic acid polyglycerol ester is not sufficiently dissolved, the stability of the flux viscosity and paste viscosity with time may deteriorate, and the viscosity increase with 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 increases, and the viscosity of the paste with time increases significantly by reacting with the solder powder contained in the paste. The meltability of the paste may be reduced. Of these, the SP value of the solvent used is particularly preferably in the range of 10-17.

  In addition to the organic acid polyglycerol ester, thixotropic agent, and solvent described above, the flux may contain an activator, an antioxidant, and the like. As the activator, amine, organic acid, hydrohalic acid amine salt, organic acid ammonium salt, organic acid amine salt, ammonium halide, organic halogen compound and the like can be used.

  Examples of amines include ethanolamine, diethanolamine, triethanolamine, 3,4-dihydroxybenzylamine, methyldiethanolamine, diphenylguanidine, aminopropanol, polyoxyethylene oleylamine, polyoxyethylene laurylamine, polyoxyethylene stearylamine, 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-dimethylpiperidine, pipecoline, aniline, dimethylamine, ethylaniline, 2,4,6-trimethylaniline, morpholine, methylmorpholine, ethylmorpholine, ethylnaphthylamine 3-amino-1-propene, cyclohexylamine, disohexylamine, cyclohexyldimethylamine, cyclohexyldiethyleneamine, cyclohexyl Sill methylethylamine, cyclohexyl di -n- propylamine, cyclohexylamine diisopropylamine, cyclohexyl di -n- butylamine, cyclohexylamine diisobutylamine, cyclohexylamine dipentylamine, cyclohexyl dihexylamine or dicyclohexylamine methyl amine.

  Examples of organic acids include formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, pentadecylic acid, Palmitic acid, margaric acid, stearic acid, oleic acid, linoleic acid, linolenic acid, tuberculostearic acid, arachidic acid, arachidonic acid, eicosapentaenoic acid, behenic acid, docosahexaenoic acid, lignoceric acid, azelaic acid, suberic acid, sebacic acid , Phthalic acid, serotic acid, montanic acid, mellic acid, salicylic acid, gallic acid, benzoic acid, phthalic acid, cinnamic acid, melittic acid, oxalic acid, lactic acid, tartaric acid, maleic acid, fumaric acid, malonic acid, Succinic acid, malic acid, citric acid, aconitic acid, glutaric acid, adipic acid, terf Le acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, and the like.

  Examples of the hydrohalic acid amine salt include a hydrochloride or hydrobromide of the above amine, and examples of the organic acid ammonium salt include a salt of ammonia and the above organic acid. Examples of the salt include a salt of the amine and the organic acid.

  Examples of the organic halogen compound include alkyl halides, halogenated alcohols, halogenated esters, halogenated carboxylic acids, halogenated ketones, halogenated amides, and halogenated ethers. Specific examples of the alkyl halide include 1-bromo-3-methyl-1-butene, 1,4-dibromobutene, 1-bromo-1-propene, 2,3-dibromopropene, 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. 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, 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, bis (2,3-dibromopropyl) succinate, bis (2,3-dibromopropyl) o-phthalate, bis (2,3-dibromopropyl) p-phthalate, bis (2,3-dibromopropyl) p-phthalamide, tris (2,3-dibromopropyl) trimellitate, 4-bromomethylbenzyl stearate, 2,4-bisbromomethylbenzyl stearate, tetra (2,3-dibromopropyl) pyromellitate and the like. Specific examples of the halogenated ketone include 2,4-dibromoacetophenone. Specific examples of the halogenated amide include bis (2,3-dibromopropyl) o-phthalamide, tris (2,3-dibromopropyl) trimellitic amide, tetra (2,3-dibromopropyl) pyromellitamide, bis (2, 3-dibromopropyl) tertamide, N, N′-bis (2,3-dibromopropyl) succinamide, N, N, N ′, N′-tetra (2,3-dibromopropyl) succinamide and the like. Specific examples of the halogenated ether include trimethylolpropane bis (2,3-dibromopropyl) ether, 4-palmitoyloxybenzyl bromide, 4-myristoyloxybenzyl bromide, 4-lauroyloxybenzyl bromide, 4-undecanoyl. And oxybenzyl bromide.

  Examples of the antioxidant include phenolic antioxidants, phosphorus antioxidants, sulfur antioxidants, and amine antioxidants.

  The proportion of the organic acid polyglycerol ester in 100% by mass of the total flux is preferably 10% by mass or more and less than 50% by mass, and particularly preferably 15 to 45% by mass. Further, the proportion of the solvent is 30 to 60% by mass, the proportion of the thixotropic agent is 1 to 10% by mass, the proportion of the activator is 0.1 to 10% by mass, and the proportion of the antioxidant is 1 to 10% by mass. Is preferred. If the ratio of the organic acid polyglycerol ester is less than the lower limit, the fluidity of the paste, the tackiness to the substrate, and the like are deteriorated, so that defects such as shape defects may occur in the bumps after printing. On the other hand, if the upper limit is exceeded, the viscosity of the flux becomes too high, and the paste viscosity increases accordingly, resulting in a defective shape in the bump after printing, or the paste is not ejected from the mask opening. In some cases, a defect such as so-called missing may occur. Moreover, 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 defects such as the above-described bump shape failure and missing. On the other hand, when 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 settling and separation of solder powder in the paste.

  Further, when the ratio of the thixotropic agent is less than the lower limit value, the shape retention as a solder paste is lowered, and there may be a problem such as a so-called bridge in which adjacent bumps are connected. On the other hand, when 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 the above-mentioned bump shape defect and missing. If the ratio of the activator is less than the lower limit value, the solder powder may not melt and sufficient bonding strength may not be obtained. On the other hand, if the upper limit value is exceeded, the activator reacts with the solder powder during storage. Since it becomes easy, the storage stability of a solder paste may fall. Further, when the proportion 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 be reduced.

In order 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 solder powder mainly composed of tin can be used. For example, Sn—Pb solder (eutectic composition Sn: Pb = 63: 37% by mass, etc.), Sn—Pb—Ag solder, Sn—Pb—Bi solder, Sn—Pb—Sb solder, Sn—Ag Solder, Sn—Cu solder, Sn—Ag—Cu solder, Au—Sn high temperature solder (eutectic composition Sn: Au = 20: 80% by mass, etc.), Au—Si high temperature solder, Au— Ge-based high-temperature solder, Sn-Pb-based high-temperature solder (composition Sn: Pb = 5: 95% by mass, etc.), Zn-Sn solder, In-Sn solder, Bi-Sn solder, Sb-Sn Type solder, Al-Zn type solder and the like. Further, the average particle size of the solder powder is not particularly limited as long as it is within the range used for general solder paste, but, for example, one having a range of 0.1 μm to 1 mm can be suitably used. In consideration of narrow pitch printing, the average particle size of the solder powder is preferably in the range of 0.1 μm to 50 μm, and in consideration of the formation of fine bumps, it is in the range of 1 μm to 20 μm. Is more preferable. In the present specification, the average particle diameter means a volume-based average particle diameter D ₅₀ measured using a laser diffraction / scattering particle diameter distribution measuring apparatus (manufactured by Horiba, Ltd., model name: Partica LA-950). .

  The amount of flux mixed when preparing the solder paste is preferably adjusted so that the proportion of the flux in 100% by mass of the prepared paste becomes 3 to 60% by mass. If the amount is less than the lower limit, the amount of flux is small, so that it may be difficult to form a paste or the solder powder may not be melted. On the other hand, if the upper limit is exceeded, the amount of solder powder contained in the paste decreases, and the necessary amount of solder may not be obtained after melting.

  Since the solder paste prepared in this way uses the water-soluble flux for solder paste of the present invention, it maintains the good printability or meltability suitable for bump formation and narrow pitch printing, and after reflow. Cleaning can be performed only with water, which is excellent in terms of safety and health during mounting and environmental aspects. 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.

<Example 1>
An organic acid polyglycerol ester, a thixotropic agent, a solvent, an activator, and a phenolic antioxidant (trade name: Irganox 1010, manufactured by BASF) were prepared as an antioxidant. These were blended in the proportions shown in Table 2 below, mixed and stirred to obtain a flux. In Table 2, the specific substance names of the organic acid polyglycerol esters represented by the classifications A to E, the solvents represented by the classifications A to C, the thixotropic agents and the active agents represented by the classifications A and B are as follows. Table 1 shows. In Table 1, the number written at the end of the name of the organic acid polyglycerol ester indicates the polymerization number of polyglycerol.

<Examples 2 to 22 and Comparative Examples 2 to 7>
A flux was obtained in the same manner as in Example 1 except that the organic acid polyglycerol ester, thixotropic agent, solvent, activator and antioxidant were blended in the proportions shown in Table 2 below.

<Comparative Example 1>
Example 1 except that rosin (polymerized rosin) was used instead of organic acid polyglycerol esters, and rosin, thixotropic agent, solvent, activator and antioxidant were blended in the proportions shown in Table 2 below. In the same manner, a flux was obtained. The flux obtained in Comparative Example 1 does not contain polyglycerol esters.

<Comparison test and evaluation>
Using the fluxes obtained in Examples 1 to 22 and Comparative Examples 1 to 7, the following (i) to (v) were evaluated. These results are shown in Table 3 below.

(i) Solder meltability (copper foil): First, an Sn—Ag—Cu solder powder (composition: Sn 96.5 mass%, Ag 3.0 mass%, Cu 0.5 mass%) having an average particle diameter of 8 μm is prepared. Then, 89.0 parts by mass of this solder powder and 11.0 parts by mass of the flux obtained in Example 1 were stirred and mixed at room temperature to prepare a solder paste. The average particle size of the solder powder is a volume-based average particle size D ₅₀ measured using a laser diffraction / scattering particle size distribution analyzer (manufactured by Horiba, Ltd., model name: Partica LA-950).

  Further, a phosphorous deoxidized copper foil (dimensions: length 40 mm × width 20 mm × thickness 0.3 mm) having a purity of 99.9% or more (3N) whose surface was polished with water-resistant abrasive paper (# 400) was prepared. Next, the prepared solder paste was printed on the copper foil using a SUS metal mask (opening diameter φ6.5 mm, thickness 0.2 mm) provided with two openings. Then, the copper foil on which the paste was printed was elevated at a temperature increase rate of 1.5 ° C./s from room temperature to 150 ° C. in a nitrogen atmosphere using a reflow furnace (Malcom Co., Ltd., model name: SRS-1C). After heating at 150 ° C. for 2 minutes, the temperature is raised from 150 ° C. to 240 ° C. at a rate of 1.5 ° C./s, and heated at 240 ° C. for 20 seconds, so Solder was melted. The appearance after reflow was visually observed, and the case where no undissolved solder powder was confirmed was evaluated as “good”, and the case where undissolved residue was confirmed was evaluated as “bad”.

  (ii) Flux detergency (copper foil): 50 ml of ion exchange water in a 100 ml glass beaker was heated to 60 ° C. using a hot plate. The copper foil after performing the above-mentioned meltability test was put into this beaker containing 60 ° C. ion-exchanged water, and the whole beaker was put into an ultrasonic cleaner, and ultrasonic waves were applied for 5 minutes. Then, after taking out copper foil from a beaker and removing water with an air blow, it was made to dry for 5 minutes at the temperature of 50 degreeC using the dryer. About the copper foil after drying, the solder fusion | melting part was observed visually and in the reflection electron image of the scanning electron microscope (SEM; JEOL Co., Ltd. model name: JSM-6510LV), and the presence or absence of the residue of the organic component was confirmed. At this time, the case where the residue of the organic component was not confirmed was evaluated as “good”, and the case where the residue of the organic component was confirmed was evaluated as “bad”.

  (iii) Bump printability (substrate): Ni-plated metal mask plate provided with a plurality of openings (external dimensions: length 300 mm × width 300 mm × thickness 20 μm, opening diameter φ: 120 μm, opening pitch: 150 μm The solder paste prepared by the above-described meltability test is printed on a substrate (dimensions: 60 mm long × 60 mm wide × 0.8 mm thick) to form solder bumps on the substrate. Formed. The substrate is a resist film (film) having a copper foil having a thickness of about 50 μm provided on one surface of the substrate and a plurality of openings provided on the copper foil and penetrating to the copper foil. A thickness of 15 μm, an opening diameter of 70 μm, and an opening pitch of 150 μm). The printability was evaluated from the shape of solder bumps formed on the substrate. Specifically, the evaluation was made in four stages based on the presence or absence of printing defects such as a bridge in which adjacent bumps are connected to each other and a missing in which no paste is ejected from the mask opening and bumps are not formed. In addition, the numerical value shown in Table 3 has shown that the evaluation of printing property was so high that the numerical value was high, and made 3 or more into the pass.

  (iv) Bump meltability (substrate): The substrate on which the solder bumps were formed in the above-described printability test was used in a nitrogen atmosphere from room temperature to 150 ° C. using a reflow oven (Malcom Corp., model name: SRS-1C). The temperature was raised at a rate of 1.5 ° C./s, pre-dried at 150 ° C. for 2 minutes, and then heated from 150 ° C. to 230 ° C. at a rate of 1.5 ° C./s. The solder bumps on the substrate were melted by heating at a temperature of 5 seconds. The appearance after reflow was visually observed, and the case where unaggregated solder was not confirmed around the bump was evaluated as “good”, and the case where unaggregated solder was confirmed was evaluated as “bad”.

  (v) Flux cleaning property (substrate): The substrate after the above-described bump meltability test was subjected to ultrasonic blow for 5 minutes in ion-exchanged water at 60 ° C., as in the above-described cleaning property test, and then air blown. The water was removed by heating at 50 ° C. for 5 minutes. The bump part after reflow and washing was observed with the reflected electron image of the SEM, and the presence and extent of organic component residues were confirmed. Based on the presence or absence of organic component residues at this time or the extent thereof, “excellent” indicates that there is almost no residue, “good” indicates that a residue of less than 5% with respect to 100% bump surface area is identified, and bump surface area 100 A case where a residue of 5% or more with respect to% was confirmed as “bad” and evaluated in three stages.

  As is apparent from Table 3, when Examples 1-22 and Comparative Examples 1-7 were compared, Comparative Example 1 using rosin as a flux component was highly evaluated in the evaluation of bump printability. In addition, sufficient cleaning was not possible with water alone, and flux cleaning performance was evaluated as “bad” in both the copper foil and the substrate. Further, in Comparative Examples 2 to 7 using hardened castor oil, the organic acid polyglycerol ester was used as the resin component. Therefore, in the evaluation of the flux cleaning property, “good” or “ Although the result of “excellent” was obtained, the evaluation of the bump printability did not satisfy the acceptance criteria. On the other hand, in Examples 1-22 using organic acid polyglycerol ester as a resin component and using a specific thixotropic agent, high evaluation was obtained in all evaluations including evaluation of bump printability.

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

Claims (5)

In a water-soluble flux for solder paste containing an organic acid polyglycerol ester, a thixotropic agent, and a solvent,
A water-soluble flux for solder paste, wherein the thixotropic agent is benzylidene sorbitol or a benzylidene sorbitol derivative.   The water-soluble flux for 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, palmitic acid polyglycerol ester, The water-soluble flux for solder paste according to claim 1 or 2, wherein the flux is one or more selected from the group consisting of oleic acid polyglycerol ester and behenic acid polyglycerol ester.   The water-soluble flux for solder paste according to any one of claims 1 to 3, wherein the solvent has an SP value of 10 to 19.   Solder paste obtained by stirring and mixing the water-soluble flux for solder paste according to claim 1 and solder powder.