Flux composition, solder paste, and electronic circuit mounting substrate

Abstract

To provide a flux composition and a solder paste which prevent air bubbles from existing in the solder paste and the flux composition after printing, and an electronic circuit mounting board having a solder joint part formed using the same.SOLUTION: A flux composition contains a base resin (A), a thixotropic agent (B), an activator (C), and a solvent (D), wherein the thixotropic agent (B) contains 1.5 mass% or more and 9.5 mass% or less of a thixotropic agent (B-1) having a hydroxyl group with respect to the total amount of the flux composition, and 0.2 mass% or more and 5.5 mass% or less of a thixotropic agent (B-2) having no hydroxyl group with respect to the total amount of the flux composition.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a flux composition, a solder paste, and an electronic circuit mounting substrate.

Background Art

[0002] As a bonding material for bonding an electronic circuit formed on a substrate (such as a printed wiring board or a silicon wafer) and an electronic component, a solder alloy is widely used. As a bonding method using this solder alloy, for example, there are a method using a solder paste in which a flux composition and solder alloy powder are mixed, and a method using solder balls made of a solder alloy (so-called Ball Grid Array (BGA) bonding).

[0003] Whether using a solder paste or using solder balls, generally, solder bonding is performed through a printing process, a heating process, and a cleaning process if necessary.

[0004] That is, when using a solder paste, the solder paste is printed on the substrate in a predetermined pattern (printing process), an electronic component is placed at a predetermined position on the substrate, and this is heated at a predetermined temperature (heating process), and if necessary, the flux residue formed on the substrate is cleaned (cleaning process), thereby performing solder bonding. Or when using solder balls, a BGA substrate (having solder balls at each electrode) is prepared, a flux is printed on a substrate (bonding substrate) on which the BGA substrate is mounted in accordance with the electrode pattern of the BGA substrate (printing process), the BGA substrate is placed at a predetermined position on the bonding substrate, and this is heated at a predetermined temperature (heating process), and if necessary, the flux residue formed on the bonding substrate is cleaned (cleaning process), thereby performing solder bonding.

[0005] By the way, voids generated and remaining in solder during soldering cause poor bonding and cracks in the solder joint, affecting the reliability of the solder joint. Therefore, in particular, voids generated during the heating process, that is, the generation of bubbles caused by the flux composition (solvent and activator) volatilized by heating, are a problem, and there are many solder pastes that attempt to solve this problem (see Patent Document 1). Also, even outside the heating process, for example, bubbles may exist in the solder paste or the flux composition on the substrate immediately after the printing process, particularly immediately after the printing process. These bubbles are presumed to be air taken into the solder paste or the flux composition during the production or printing of the solder paste. On the other hand, when applying flux to the solder bumps (solder balls) formed on electronic components or BGA substrates, there is a flux application device that can suppress the generation of bubbles inside the flux during the printing process by using a special structure and printing method (see Patent Documents 2 and 3).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] The above-mentioned bubbles are a factor in deforming the printed shape of the solder paste or the flux composition. Therefore, a substrate with bubbles in the printed solder paste or flux composition may be rejected in the appearance inspection, which may cause a reduction in the yield rate. Even when the inspection of the appearance is passed, if the solder paste or the flux composition (including solder balls) is heated while containing air bubbles, solder balls or solder bridges caused by defective printing shapes are likely to occur. However, regarding the air bubbles present in the solder paste or the flux composition after the printing process and the means for solving the problem, there is no mention or suggestion in Patent Document 1.

[0008] In addition, the coating devices disclosed in Patent Document 2 and Patent Document 3 have special methods and structures, and therefore can solve the problem.

[0009] The present invention solves the above problems, and an object thereof is to provide a flux composition and a solder paste in which air bubbles are hardly present in the solder paste and the flux composition after printing, and an electronic circuit mounting substrate having a solder joint formed using the same.

Means for Solving the Problems

[0010] The flux composition of the present invention contains a base resin (A), a thixotropic agent (B), an activator (C), and a solvent (D), and the thixotropic agent (B) contains a thixotropic agent (B-1) having a hydroxyl group in an amount of 1.5% by mass or more and 9.5% by mass or less based on the total amount of the flux composition, and a thixotropic agent (B-2) having no hydroxyl group in an amount of 0.2% by mass or more and 5.5% by mass or less based on the total amount of the flux composition.

[0011] The flux composition of the present invention preferably contains a bisamide having a hydroxyl group as the thixotropic agent (B-1).

[0012] The flux composition of the present invention preferably contains a bisamide having no hydroxyl group as the thixotropic agent (B-2).

[0013] The base resin (A) preferably contains a rosin-based resin and an acrylic resin.

[0014] The blending ratio (mass %) of the rosin-based resin and the acrylic resin is preferably 1:1.5 to 1:3 in terms of the rosin-based resin:the acrylic resin.

[0015] The solder paste of the present invention contains a flux composition having the above configuration and a powder (E) made of a solder alloy.

[0016] The electronic circuit mounting substrate of the present invention preferably has a solder joint formed using the solder paste having the above configuration.

Advantages of the Invention

[0017] In the flux composition and the solder paste of the present invention, it is difficult for air bubbles to exist in the solder paste and the flux composition after printing.

Brief Description of the Drawings

[0018]

Figure 1

Embodiments for Carrying Out the Invention

[0019] Hereinafter, an embodiment of the flux composition, the solder paste, and the electronic circuit mounting substrate of the present invention will be described in detail. Note that the present invention is not limited to these embodiments.

[0020] 1. Flux Composition The flux composition of the present embodiment contains a base resin (A), a thixotropic agent (B), an activator (C), and a solvent (D). The thixotropic agent (B) contains a thixotropic agent (B-1) having a hydroxyl group in an amount of 1.5% by mass or more and 9.5% by mass or less based on the total amount of the flux composition, and a thixotropic agent (B-2) not having a hydroxyl group in an amount of 0.2% by mass or more and 5.5% by mass or less based on the total amount of the flux composition.

[0021] The flux composition of this embodiment with such a configuration is less likely to have bubbles in the flux composition and the solder paste even after printing, for example, immediately after printing, without using an antifoaming agent or the like in combination. That is, the flux composition can suppress the generation of bubbles in the flux composition and the solder paste during the production or printing of the flux composition and the solder paste, and even when bubbles are generated in the flux composition and the solder paste during printing, the bubbles are easily discharged to the outside, so it is less likely that bubbles exist in the solder paste and the flux composition after printing. Therefore, the flux composition of this embodiment can suppress deformation of the printed shape of the flux composition or the solder paste, and can suppress the generation of solder balls and solder bridges caused by such defective printed shapes.

[0022] In addition, the flux composition of this embodiment can achieve both easy escape of the above bubbles and good printability. Therefore, the flux composition and the solder paste containing the flux composition are excellent in printing transferability and can suppress the occurrence of abnormal printed shapes (printing horn formation) caused by transfer defects.

[0023] Base resin (A) Examples of the base resin (A) include rosin resins, acrylic resins, styrene-maleic acid resins, epoxy resins, urethane resins, polyester resins, phenoxy resins, terpene resins, polyalkylene carbonates, and the like. These can be used alone or in combination. As the base resin (A), rosin resins and acrylic resins are preferably used.

[0024] Examples of the rosin resin include rosins such as tall oil rosin, gum rosin, and wood rosin; rosin-based modified resins such as hydrogenated rosin, polymerized rosin, disproportionated rosin, acrylic acid-modified rosin, maleic acid-modified rosin, and formylated rosin; and derivatives thereof. These can be used alone or in combination.

[0025] Examples of the acrylic resin include acrylic resins obtained by polymerizing at least one monomer such as acrylic acid, methacrylic acid, various esters of acrylic acid, various esters of methacrylic acid, crotonic acid, itaconic acid, maleic acid, maleic anhydride, esters of maleic acid, esters of maleic anhydride, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl chloride, and vinyl acetate. These can be used alone or in combination.

[0026] The blending amount of the base resin (A) is preferably 10% by mass or more and 90% by mass or less based on the total amount of the flux composition. More preferably, the blending amount is 30% by mass or more and 70% by mass or less, and particularly preferably 40% by mass or more and 60% by mass or less.

[0027] Moreover, it is preferable to use a rosin-based resin and an acrylic resin in combination as the base resin (A). When a rosin-based resin and an acrylic resin are used in combination, it becomes difficult for further bubbles to exist in the solder paste and the flux composition after printing.

[0028] When the rosin-based resin and the acrylic resin are used in combination as the base resin (A), the blending ratio (mass%) is preferably 1:1.5 to 1:3 of the rosin-based resin:the acrylic resin.

[0029] Thixotropic agent (B) The flux composition of the present embodiment contains a thixotropic agent (B-1) having a hydroxyl group in an amount of 1.5% by mass or more and 9.5% by mass or less based on the total amount of the flux composition, and a thixotropic agent (B-2) not having a hydroxyl group in an amount of 0.2% by mass or more and 5.5% by mass or less based on the total amount of the flux composition.

[0030] The thixotropic agent (B-1) may be any thixotropic agent having a hydroxyl group, and the position and number of the hydroxyl groups are not limited. Examples of the thixotropic agent (B-1) include bisamide-based thixotropic agents and the like having a hydroxyl group. These can be used alone or in combination of two or more.

[0031] Moreover, it is preferable that the flux composition of the present embodiment contains, as the thixotropic agent (B-1), a thixotropic agent having a hydroxyl group with a saturated fatty acid structure.

[0032] Moreover, it is preferable that the flux composition of the present embodiment contains, as the thixotropic agent (B-1), a bisamide having a hydroxyl group. As the bisamide having a hydroxyl group, bis(hydroxystearic acid)amide is preferable, and ethylene bis(hydroxystearic acid)amide is particularly preferable. The flux composition containing ethylene bis(hydroxystearic acid)amide as the thixotropic agent (B-1) has better printability, is more excellent in printing transferability, and can further suppress the occurrence of printing shape abnormalities caused by transfer defects.

[0033] The thixotropic agent (B-2) may be any thixotropic agent having no hydroxyl group. Examples of the thixotropic agent (B-2) include bisamide-based thixotropic agents and the like having no hydroxyl group. These can be used alone or in combination of two or more.

[0034] Moreover, it is preferable that the flux composition of the present embodiment contains, as the thixotropic agent (B-2), a thixotropic agent having no hydroxyl group with a saturated fatty acid structure.

[0035] Moreover, it is preferable that the flux composition of the present embodiment contains, as the thixotropic agent (B-2), a bisamide having no hydroxyl group. As the bisamide having no hydroxyl group, bis(stearic acid)amide is preferable, and ethylene bis(stearic acid)amide is particularly preferable. Since the flux composition containing ethylene bisstearamide as the thixotropic agent (B-2) has even better printability, it is excellent in printing transferability and can further suppress the occurrence of abnormal printing shapes caused by transfer defects.

[0036] In addition, a flux composition containing ethylene bis(hydroxystearic acid) amide as the thixotropic agent (B-1) having a hydroxyl group and ethylene bisstearamide as the thixotropic agent (B-2) not having a hydroxyl group has particularly good printability, so it is excellent in printing transferability and can further suppress the occurrence of abnormal printing shapes caused by transfer defects.

[0037] The total blending amount of the thixotropic agent (B) is preferably 1.7% by mass or more and 15% by mass or less based on the total amount of the flux composition. A more preferable blending amount thereof is 2.5% by mass or more and 10.5% by mass or less, and particularly preferably 3.5% by mass or more and 8% by mass or less.

[0038] The blending amount of the thixotropic agent (B-1) is preferably 2% by mass or more and 7% by mass or less based on the total amount of the flux composition. A more preferable blending amount thereof is 3% by mass or more and 6% by mass or less. By setting the blending amount of the thixotropic agent (B-1) within the above range, better printing transferability can be imparted to the flux composition, and the occurrence of abnormal printing shapes caused by transfer defects can be further suppressed.

[0039] The blending amount of the thixotropic agent (B-2) is preferably 0.5% by mass or more and 5% by mass or less based on the total amount of the flux composition. A more preferable blending amount thereof is 0.5% by mass or more and 2% by mass or less. By setting the blending amount of the thixotropic agent (B-2) within the above range, better printing transferability can be imparted to the flux composition, and the occurrence of abnormal printing shapes caused by transfer defects can be further suppressed.

[0040] Activator (C) Examples of the activator (C) include organic acids, halogen-based activators, and amine-based activators. These can be used alone or in combination.

[0041] Examples of organic acids include monocarboxylic acids, dicarboxylic acids, and other organic acids.

[0042] Examples of monocarboxylic acids include propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, capric acid, lauric acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, tuberculostearic acid, arachidic acid, behenic acid, lignoceric acid, glycolic acid, etc.

[0043] Examples of dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, eicosanedioic acid, fumaric acid, maleic acid, tartaric acid, diglycolic acid, 1,4-cyclohexanedicarboxylic acid, etc.

[0044] Examples of other organic acids include dimer acid, levulinic acid, lactic acid, acrylic acid, benzoic acid, salicylic acid, anisic acid, citric acid, picolinic acid, anthranilic acid, etc.

[0045] Examples of halogen-based activators include bromine-based activators, iodine-based activators, etc. These activators may be compounds formed by covalent bonds of each single element of chlorine, bromine, or fluorine such as chlorides, bromides, or fluorides, or compounds in which two or more different halogen atoms are covalently bonded.

[0046] Examples of amine-based activators include organic amines, amine salts such as hydrogen halide salts of organic amines (inorganic acid salts or organic acid salts), organic acid salts, organic amine salts, etc.

[0047] The blending amount of the activator (C) is preferably 1% by mass or more and 20% by mass or less with respect to the total amount of the flux composition. A more preferable blending amount thereof is 1% by mass or more and 15% by mass or less, and particularly preferably 5% by mass or more and 15% by mass or less.

[0048] Solvent (D) Examples of the solvent (D) include solvents such as alcohol-based, ethanol-based, acetone-based, toluene-based, xylene-based, ethyl acetate-based, ethyl cellosolve-based, butyl cellosolve-based, glycol ether-based, and ester-based solvents. These can be used alone or in combination of two or more.

[0049] The blending amount of the solvent (D) is preferably 20% by mass or more and 70% by mass or less with respect to the total amount of the flux composition. A more preferable blending amount thereof is 25% by mass or more and 65% by mass or less, and particularly preferably 30% by mass or more and 60% by mass or less.

[0050] An antioxidant can be further blended in the flux composition of the present embodiment. Examples of the antioxidant include hindered phenol-based antioxidants, phenol-based antioxidants, bisphenol-based antioxidants, polymer-type antioxidants, and the like. The antioxidant is not limited to these, and its blending amount is not particularly limited. A general blending amount thereof is about 0.5% by mass to 5% by mass with respect to the total amount of the flux composition.

[0051] Additives such as a matting agent may be further added to the flux composition of the present embodiment. The blending amount of the additive is preferably 10% by mass or less with respect to the total amount of the flux composition, and a more preferable blending amount is 5% by mass or less.

[0052] 2. Solder paste The solder paste of the present embodiment can be produced by mixing the above flux composition and an alloy powder (E) made of a solder alloy by a known method.

[0053] Examples of the solder alloy used for the alloy powder (E) made of the solder alloy include those obtained by combining a plurality of Sn, Ag, Cu, Bi, Zn, In, Ga, Sb, Au, Pd, Ge, Ni, Cr, Al, P, In, etc.

[0054] The blending amount of the alloy powder made of the solder alloy is preferably 80% by mass or more and 94% by mass or less with respect to the total amount of the solder paste. A more preferable blending amount thereof is 84% by mass or more and 92% by mass or less, and a particularly preferable blending amount thereof is 88% by mass or more and 90% by mass or less.

[0055] Since the solder paste of the present embodiment uses the above flux composition, even without using an antifoaming agent or the like in combination, bubbles are unlikely to be present in the solder paste after printing, for example, immediately after printing. Therefore, the solder paste of the present embodiment can suppress deformation of the printed shape of the solder paste, and can suppress the generation of solder balls and solder bridges caused by such defective printed shapes. In addition, the solder paste of the present embodiment using the above flux composition is excellent in printing transferability and can suppress the occurrence of abnormal printed shapes caused by transfer defects. Therefore, the solder paste of the present embodiment can form a highly reliable solder joint.

[0056] 3. Electronic circuit mounting substrate The electronic circuit mounting substrate of the present embodiment has a solder joint formed using the above solder paste, the above flux composition, and solder balls. In the present specification, the solder joint means a joint that joins the materials to be joined, such as a joint that electrically joins an electrode on a substrate and an electronic component.

[0057] When forming a solder joint using the above solder paste, for example, the solder paste is printed on an electrode formed on a substrate so as to form a predetermined pattern, an electronic component is placed at a predetermined position on the substrate, and this is heated at a predetermined temperature. Thereby, an electronic circuit mounting substrate having a solder joint formed using the above solder paste is produced. Optionally, after heating, the flux residue formed on the substrate is washed.

[0058] When forming a solder joint using the above flux composition and solder balls, for example, a BGA substrate (one having solder balls on each electrode) is prepared, and the flux composition is printed on a substrate (joint substrate) on which the BGA substrate is mounted in accordance with the electrode pattern of the BGA substrate, the BGA substrate is placed at a predetermined position on the joint substrate, and this is heated at a predetermined temperature. Thereby, an electronic circuit mounting substrate having a solder joint formed using the above flux composition and solder balls is produced. Optionally, after heating, the flux residue formed on the substrate is washed. Also, solder balls may be formed using the above solder paste, and furthermore, the above solder paste can be used for joining the BGA substrate and the joint substrate.

[0059] Such a solder joint is formed using the above solder paste. Therefore, even without using an antifoaming agent or the like in combination, bubbles are unlikely to exist in the solder paste after printing, for example, immediately after printing. Therefore, in the formation of the solder joint, the generation of solder balls and solder bridges due to deformation of the printed shape of the solder paste can be suppressed. This is the same for solder joints formed using solder balls and the above flux composition. Also, in the solder joint of this embodiment formed using the solder paste, abnormal printing shapes due to poor transfer of the solder paste are unlikely to occur. Thus, the solder joint of this embodiment has high reliability.

Examples

[0060] The present invention will be described in detail below with reference to Examples and Comparative Examples. Note that the present invention is not limited to these Examples.

[0061] Synthesis of Acrylic Resin 200 g of diethylhexyl glycol was charged into a 500 ml four-necked flask equipped with a stirrer, a reflux tube, and a nitrogen inlet tube, and this was heated to 110°C. Also, 0.2 mass% to 5 mass% of dimethyl 2,2'-azobis(2-methylpropionate) (product name: V-601, manufactured by Wako Pure Chemical Industries, Ltd.) as an azo radical initiator was added to 300 g of a mixture of 10 mass% methacrylic acid, 51 mass% 2-ethylhexyl methacrylate, and 39 mass% lauryl acrylate, and this was dissolved to prepare a solution. Next, the solution was dropped into the four-necked flask over 1.5 hours, and the components in the four-necked flask were stirred at 110°C for 1 hour, and then the reaction was terminated to obtain an acrylic resin. The weight average molecular weight of the acrylic resin was 7,800 Mw, the acid value was 40 mgKOH / g, and the glass transition temperature was -47°C.

[0062] Preparation of Flux Composition Each component was kneaded with the composition and blending shown in Tables 1 and 2 to prepare each flux composition according to Examples and Comparative Examples. In Tables 1 and 2, the unit of the numerical value representing the composition is parts by mass unless otherwise specified.

[0063] Preparation of Solder Paste Examples 1, Comparative Examples 1 and 2: 11.0 mass% of each flux composition and 89.0 mass% of Sn-3Ag-0.5Cu solder alloy powder (powder particle size 20 μm to 38 μm) were mixed to obtain each solder paste. Examples 2 to 16, Comparative Examples 3 to 9: 11.0 mass% of each flux composition and 89.0 mass% of Sn-3Ag-0.5Cu-5Sb-5In-0.02Ni solder alloy powder (powder particle size 20 μm to 38 μm) were mixed to obtain each solder paste.

[0064]

Table 1

[0065]

Table 2

[0066] ※1 Hydrogenated acid-modified rosin, manufactured by Arakawa Chemical Industries, Ltd. ※2 Ethylene bis-hydroxystearic acid amide, manufactured by Mitsubishi Chemical Corporation ※3 Bisamide-based thixotropic agent with hydroxyl groups, manufactured by Elementis ※4 Hexamethylene bis-hydroxystearic acid amide, manufactured by Mitsubishi Chemical Corporation ※5 Methylene bis-stearic acid amide, manufactured by Mitsubishi Chemical Corporation ※6 Ethylene bis-stearic acid amide, manufactured by Mitsubishi Chemical Corporation ※7 Pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], manufactured by Shiraishi Calcium Co., Ltd.

[0067] (1) Bubble confirmation test For each of the examples and comparative examples, a bubble confirmation test was conducted according to the following procedure. The following tools were prepared. · Printed wiring board (FR-4 substrate, having Cu lands (3.0 mm × 0.45 mm) corresponding to the pins on the Cu land portion of 145 mm × 105 mm (0.8 mm pitch, 80 pins)) · Metal mask having a pattern corresponding to the above Cu land portion (thickness: 150 μm) · Metal squeegee Using the above metal mask and metal squeegee, solder paste was printed on the printed wiring board. For printing, a printing machine (product name: SP60P-L, manufactured by Panasonic Corporation) was used. The printing conditions were set as follows: squeegee speed: 80 mm / second, and plate separation speed: 5.0 mm / second. The surface of the printed wiring board immediately after printing was observed using a microscope (product name: Digital Microscope VHX-900, manufactured by KEYENCE). Then, it was confirmed whether or not there were bubbles as shown in Fig. 1 (the circled area) in the solder paste printed on each electrode (pin) on the printed wiring board, and evaluation was performed based on the following criteria. The number of pins for evaluation was 80. The results are shown in Tables 3 and 4. ○: No bubbles are present △: The number of pins with bubbles is 1 or more and 10 or less ×: The number of pins with bubbles is 11 or more

[0068] (2) Printing Shape Confirmation Test For each of the examples and comparative examples, a printing shape confirmation test was conducted according to the following procedure. When observing the surface of the printed wiring board immediately after printing in the above (1) bubble confirmation test, the shape of the printed solder paste was also confirmed and evaluated based on the following criteria. The number of pins for evaluation was 80. The results are shown in Tables 3 and 4. ○: No collapse in shape △: There is collapse in shape, but mounting is possible ×: Considerable collapse in shape

[0069] (3) Solder Ball Generation Confirmation Test For each of the examples and comparative examples, a solder ball generation confirmation test was conducted according to the following procedure. The following tools were prepared. · Chip components (size: 1.6 mm × 0.8 mm, 20 pieces) · Printed wiring board (FR-4 substrate, with a solder resist and electrodes (0.6 mm × 0.9 mm) corresponding to the above chip components formed thereon) · Metal mask (corresponding to the pattern on the above printed wiring board. Thickness: 150 μm) · Metal squeegee Using the metal mask and the metal squeegee, solder paste was printed on the printed wiring board. For printing, a printing machine (product name: SP60P-L, manufactured by Panasonic Corporation) was used. The printing conditions were set as follows: squeegee speed: 80 mm / second, and plate separation speed: 5.0 mm / second. The chip components were placed on the printed wiring board after printing. Next, the printed wiring board was heated in a reflow oven (product name: TNP-538EM, manufactured by Tamura Corporation) to fabricate a test substrate. The reflow conditions were as follows: preheat from 170°C to 190°C for 110 seconds, peak temperature of 260°C, time at 200°C or higher was 70 seconds, time at 220°C or higher was 60 seconds, and the cooling rate from the peak temperature to 200°C was 3°C to 8°C / second. The oxygen concentration in the reflow oven was set to 1,500 ± 500 ppm. The surface of the test substrate was observed using a microscope (product name: Digital Microscope VHX-900, manufactured by KEYENCE), the number of chip components with solder balls generated around them was counted, and the evaluation was performed based on the following criteria. The results are shown in Tables 3 and 4. ◎: 0 pieces ○: 1 or more and 6 or less △: 7 or more and 12 or less ×: 13 or more

[0070] (4) Printing transfer volume ratio confirmation test For each of the examples and comparative examples, a printing transfer volume ratio confirmation test was conducted according to the following procedure. The following tools were prepared. · Printed wiring board (FR-4 substrate, having 120 Cu lands of 0.6 mm × 0.5 mm) · Metal mask having a pattern corresponding to the above Cu lands (thickness: 150 μm) Using the metal mask and the metal squeegee, solder paste was continuously printed on six of the printed wiring boards. For printing, a printing machine (product name: SP60P-L, manufactured by Panasonic Corporation) was used. The printing conditions were set as follows: squeegee speed: 80 mm / second, and plate separation speed: 3.0 mm / second. The surface of the printed wiring board immediately after printing was observed using a solder printing inspection device (product name: aSPIre2, manufactured by KOHYOUNG TECHNOLOGY). Then, the total value (X) of the volume of the solder paste after printing at all Cu lands (6 sheets × 120 locations = 720 locations) and the total value (Y) of the volume of the openings of the metal mask were calculated, and the average of the printing transfer volume ratios was obtained based on the following formula. Printing transfer volume ratio (average) (%) = (X / Y × 100) / 720 ※Y = 0.6 mm × 0.5 mm (size of the Cu land) × 0.15 mm (thickness of the metal mask) × 720 = 16.2 mm 3 Regarding each calculated printing transfer volume ratio (average), evaluation was performed based on the following criteria. The results are shown in Tables 3 and 4. ◎: Printing transfer volume ratio (average) is 90% or more ○: Printing transfer volume ratio (average) is 70% or more and less than 90% △: Printing transfer volume ratio (average) is 60% or more and less than 70% ×: Printing transfer volume ratio (average) is less than 60%

[0071] (5) Solder bump standing confirmation test For each of the examples and comparative examples, a solder bump standing confirmation test was conducted according to the following procedure. The surface of the printed wiring board used in the above (4) printing transfer volume ratio confirmation test was observed using a solder printing inspection device (product name: aSPIre2, manufactured by KOHYOUNG TECHNOLOGY). For each Cu land, the average height and the maximum height of the printed solder paste were calculated. Then, among the 720 Cu lands, the value of the difference between the average height and the maximum height of the solder paste (maximum height - average height) with the largest value was taken as the evaluation value (μm), and evaluation was performed based on the following criteria. The results are shown in Tables 3 and 4. ◎: Evaluation value is less than 100 μm ○: Evaluation value is 100 μm or more and less than 120 μm △: Evaluation value is 120 μm or more and less than 200 μm ×: Evaluation value is 200 μm or more

[0072] (6) Comprehensive Evaluation For each of the examples and comparative examples, the test results of (1) to (5) above were scored according to the following criteria, and the total value was taken as the comprehensive evaluation. The results are shown in Tables 3 and 4. ◎: 5 points ○: 3 points △: 1 point ×: 0 point

[0073]

Table 3

[0074]

Table 4

[0075] As shown above, since the solder paste of each example uses a flux composition containing a predetermined amount of a thixotropic agent (B-1) having a hydroxyl group and a thixotropic agent (B-2) not having a hydroxyl group as the thixotropic agent (B), it can be seen that bubbles are hardly present in the solder paste even immediately after printing, and deformation of the printed shape can be suppressed. In addition, since the solder paste of each example can achieve both the difficulty of the presence of the above bubbles and good printability, it is excellent in printing transferability even for lands with small area and volume, and it can be seen that the occurrence of printing shape abnormalities (printing horn formation) caused by transfer defects can be suppressed. Thus, the solder paste of each example can suppress the occurrence of solder balls and solder bridges caused by deformation of its printed shape, and can provide a highly reliable solder joint. It can also be seen that the solder paste of each example can suppress the generation of solder balls even when using a solder alloy powder composed of a solder alloy containing Sb or In that is easily oxidized.

Claims

1. A flux composition comprising a base resin (A), a thixotropic agent (B), an activator (C), and a solvent (D), wherein the base resin (A) comprises a rosin resin and an acrylic resin, and the blending ratio (mass %) of the rosin resin to the acrylic resin is 1:1.5 to 1:3, i.e., the rosin resin: the acrylic resin, and the thixotropic agent (B) comprises a thixotropic agent (B-1) having a hydroxyl group in an amount of 1.5 mass % or more and 9.5 mass % or less based on the total amount of the flux composition, and a thixotropic agent (B-2) having no hydroxyl group in an amount of 0.2 mass % or more and 5.5 mass % or less based on the total amount of the flux composition, and the thixotropic agent (B-1) contains a bisamide having a hydroxyl group, the flux composition.

2. A flux composition comprising a base resin (A), a thixotropic agent (B), an activator (C), and a solvent (D), wherein the base resin (A) comprises a rosin resin and an acrylic resin, and the blending ratio (mass %) of the rosin resin to the acrylic resin is 1:1.5 to 1:3, i.e., the rosin resin: the acrylic resin, and the thixotropic agent (B) comprises a thixotropic agent (B-1) having a hydroxyl group in an amount of 1.5 mass % or more and 9.5 mass % or less based on the total amount of the flux composition, and a thixotropic agent (B-2) having no hydroxyl group in an amount of 0.2 mass % or more and 5.5 mass % or less based on the total amount of the flux composition, and the thixotropic agent (B-2) contains a bisamide having no hydroxyl group, the flux composition.

3. The flux composition according to claim 1, wherein the thixotropic agent (B-1) contains ethylene bis-hydroxy stearic acid amide.

4. The flux composition according to claim 2, wherein the thixotropic agent (B-2) contains ethylene bis-stearic acid amide.

5. A solder paste comprising the flux composition according to any one of Claims 1 to 4 and a powder (E) made of a solder alloy.

6. An electronic circuit mounting substrate having a solder joint formed using the solder paste according to Claim 5.

Images