Solder flux and production method for electronic component–mounted board

Abstract

This solder flux is to be used to mount an electronic component on a board. The softening point of the solder flux is greater than 70ºC but less than 170ºC.

Description

Solder flux and method for manufacturing electronic component mounting board CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This disclosure claims the benefit of priority to Japanese Patent Application No. 2022-195026, filed on December 6, 2022 in the Japan Patent Office, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a solder flux and a method for manufacturing an electronic component mounting board.

[0003] 2. Description of the Related Art Electronic component mounting boards, on which a large number of electronic components are mounted, are currently used in a variety of electronic devices. Conventionally, methods for mounting electronic components on boards have been proposed.

[0004] Patent Document 1 (WO 2014 / 155535) discloses "an electronic circuit component mounting system including a component supplying device that supplies electronic circuit components, a target material holding device that holds a mounting target material on which the electronic circuit components are to be mounted, a component holder that holds the electronic circuit components, and a lifting device that raises and lowers the component holder, wherein the component holder receives the electronic circuit components from the component supplying device and mounts them on the mounting target material held by the target material holding device, and the electronic circuit component mounting system is characterized in that it also includes a damage detection device that detects damage to an electronic circuit component at least either when the component holder is brought into contact with an electronic circuit component as the component holder is lowered by the lifting device or when the electronic circuit component held by the component holder is brought into contact with the mounting target material."

[0005] International Publication No. 2014 / 155535

[0006] As electronic devices become smaller, mass production of boards with fine-pitch mounting of tiny electronic components is underway. As electronic components become smaller, their rigidity decreases, lowering the critical load during mounting. At the same time, there is a demand for faster mounting takt time and improved product quality.

[0007] To prevent damage to tiny electronic components, applying flux to the connection points of the board before placing the electronic components on the board is considered effective in preventing collisions between the electronic components and the connection points. However, when electronic components are placed on connection points on a board that have already been coated with flux, the joint quality between the electronic components and the board after reflow is strongly affected by the flux flow caused by heating. As a result, sufficient joint quality may not be ensured.

[0008] One aspect of the present disclosure relates to a solder flux used for mounting electronic components to connection portions of a substrate, the solder flux having a softening point higher than 70°C and lower than 170°C.

[0009] Another aspect of the present invention relates to a method for manufacturing an electronic component mounting board, the method including: step (i) of arranging the solder flux on a connection portion of a board; step (ii) of arranging electronic components on the solder flux; and step (iii) of soldering the electronic components to the connection portion by a reflow process.

[0010] According to the present disclosure, it is possible to suppress damage to electronic components when mounting the electronic components on a substrate, and to improve the bonding quality between the connection portion of the electronic components and the substrate after reflow.

[0011] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0012] 1 is a conceptual diagram showing an example of poor bonding between a connection portion of an electronic component and a substrate. 2 is a process diagram schematically showing an example of a manufacturing method of embodiment 1. 3 is a schematic diagram for explaining a test method in examples.

[0013] Hereinafter, embodiments of the present invention will be described using examples, but the present invention is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and other materials may be applied as long as the effects of the present invention are obtained. In this specification, the expression "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or more and numerical value B or less." In the following description, when lower and upper limits are exemplified for numerical values ​​of specific physical properties or conditions, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined as long as the lower limit is not equal to or greater than the upper limit.

[0014] The present disclosure also encompasses combinations of two or more features arbitrarily selected from the appended claims, i.e., two or more features arbitrarily selected from the appended claims can be combined unless a technical contradiction arises.

[0015] In the manufacture of component-mounted boards, the work of mounting electronic components (hereinafter simply referred to as "components") on the connection portions of the board is performed by a component mounting machine. To increase the productivity of the component mounting work, it is necessary to increase the processing speed of the component mounting machine. Meanwhile, the faster the processing speed of the component mounting machine, the greater the impact on the components during mounting. Such impact can be mitigated by applying solder flux (hereinafter simply referred to as "flux") to the connection portions of the board. However, as explained below, applying flux to the connection portions of the board and placing components on the connection portions via the flux can result in poor bonding after reflow soldering.

[0016] 1 conceptually illustrates the process of creating an example of a poor connection between a component and a connection portion when a component is placed on a connection portion of a substrate coated with flux. As shown in FIG. 1(a), the connection portion of the substrate 1 is composed of a land 2a formed on the substrate 1 and a solder precoat 2b formed in advance on the land 2a. When an electronic component 4 is mounted on the solder precoat 2b, flux 3 is applied to the solder precoat 2b to absorb impact on the electronic component 4 during mounting and to temporarily fix the electronic component 4.

[0017] As shown in Fig. 1(b), immediately after mounting, the electrodes 4a of the component 4 are attached to the flux 3 but are separated from the solder precoat 2b. When the board 1 is heated in a reflow furnace in this state (Fig. 1(c)), the flux 3 softens and flows, causing the component 4 to sink (Figs. 1(d1) and (d2)).

[0018] However, if the fluidity of the flux 3 is not controlled, the component 4 may not sink sufficiently, and the reflow process may end without the component electrodes 4a and the solder precoat 2b coming into contact. This results in a poor connection between the connection and the component 4 (FIG. 1(e1)). Furthermore, if only one side of the component electrodes 4a becomes wet with solder due to the mounting position of the component 4 or other factors, a defect occurs in which one side of the component 4 lifts up (FIG. 1(e2)). Furthermore, although not shown, if the flux 3 has too high a fluidity, the component 4 may be washed away from the land 2a along with the flux, or a bridge may form between the components.

[0019] Here, lowering the consistency of the solder flux can significantly reduce the impact applied to the electronic component 4. However, the lower the consistency of the solder flux, the greater the distance between the component 4 and the solder precoat 2b when the component 4 is placed on the solder precoat 2b with the flux 3 in between. In this case, poor bonding between the connection and the component 4 or poor lifting of the component 4 is more likely to occur.

[0020] Since the solder precoat is formed using cream solder, it is common for the solder precoat to be washed after formation to remove any residual flux. However, development of a method that omits the washing step is also underway. When washing is omitted, at least a portion of the solder precoat is covered with a resin film (i.e., flux residue). Because the resin film acts as a flux, the distance between the component 4 and the solder precoat 2b tends to increase.

[0021] On the other hand, according to the manufacturing method of an electronic component mounting board using the solder flux of the present disclosure, even when the consistency of the solder flux is low, it is possible to avoid poor bonding between the connection part and the component 4 and poor lifting of the component 4. In other words, even when small components are mounted using a mounting device, damage to the components can be prevented, and the bonding quality between the connection part of the electronic component and the board after reflow can be improved.

[0022] (Solder Flux) The solder flux according to the present disclosure is a solder flux used for mounting electronic components on a substrate (specifically, a connection portion of the substrate). Hereinafter, the solder flux according to the present embodiment may be referred to as "flux (F)."

[0023] The softening point of the flux (F) is higher than 70° C. and lower than 170° C. When the flux (F) is used, even when the flux (F) is applied to the connection portion of the substrate and the component is placed on the connection portion via the flux (F), the joining quality between the electronic component and the substrate after reflow can be improved.

[0024] Generally, solder flux begins to soften before the solder melts, and then its fluidity gradually increases. It is also desirable for the flux to sufficiently wet and spread over the solder before the solder melts. When placing a micro-component on a connection part of a flux-coated board, the micro-component is strongly affected by the flux flow and may sometimes flow off the connection part along with the flux. Conversely, even if the flux remains on the connection part, small and lightweight micro-components cannot sink into the flux under their own weight, resulting in poor connection or floating. The melting point of solder is usually 220°C or higher, and the flux softens before melting.

[0025] On the other hand, since the flux (F) has a softening point higher than 70°C, it does not soften excessively and flow before the solder melts, allowing most of it to remain on the connection. Furthermore, since the flux (F) has a softening point lower than 170°C and softens sufficiently before the solder melts, even small, lightweight components can sink into the flux, which has sufficient fluidity, under their own weight and come into contact with the solder precoat. Therefore, poor connection and lifting are significantly suppressed. From the viewpoint of ensuring higher connection reliability, the softening point of the flux (F) is preferably 80°C or higher, more preferably 100°C or higher. Furthermore, the softening point of the flux (F) is preferably 160°C or lower.

[0026] The softening point of the flux can be determined, for example, by differential scanning calorimetry (DSC) of the flux. In this case, the softening point is the inflection point of the endothermic curve obtained by DSC measurement. Alternatively, the softening point may be the temperature at the peak top of the differential DSC curve (DDSC). A measuring device such as a DSC600 manufactured by Hitachi High-Tech Science Corporation may be used. The softening point of the flux may also be measured using the ring and ball method in accordance with JIS K5902.

[0027] The softening point of the flux can be controlled by the constituent materials of the flux. The flux may contain a base resin and a thixotropic agent.

[0028] When the flux (F) contains a base resin, the softening point Td1 of the base resin is preferably higher than 70° C. and lower than 170° C. Td1 is preferably 80° C. or higher, more preferably 100° C. or higher. Furthermore, Td1 is preferably 160° C. or lower.

[0029] When the flux (F) contains a thixotropy-imparting agent, the softening point Td2 of the thixotropy-imparting agent is preferably higher than 50° C. and lower than 170° C. Td2 is preferably 60° C. or higher, more preferably 80° C. or higher. In addition, Td1 is preferably 160° C. or lower.

[0030] The consistency of the flux (F) is preferably 400 or less. When the consistency of the flux (F) is 400 or less, the impact applied to the components when the components are mounted on the connection portion of the board can be more significantly alleviated. The consistency of the flux (F) is more preferably in the range of 220 to 395.

[0031] The consistency of solder flux is a value (worked consistency) measured according to the procedure of the worked consistency test specified in JIS K2220:2013. The measurement is performed using a 1 / 2 cone, and the measured consistency may be converted to the consistency when using a standard cone according to the above JIS standard. The converted consistency may then be used as the consistency of the solder flux.

[0032] When the consistency of the flux (F) is 400 or less, or even in the range of 220 to 395, the distance between the mounted component and the solder precoat tends to become large, but by controlling the softening point of the flux (F), it is possible to effectively avoid poor bonding between the connection and the component and poor lifting of the component.

[0033] The consistency of the flux (F) may be 240 or more, 285 or more, or 320 or more. The consistency may be 375 or less, 320 or less, or 285 or less. The consistency may be in the range of 240 to 395, 285 to 395, or 320 to 395. Within these ranges, the upper limit may be 375, 320, or 285, as long as the lower limit is not greater than the upper limit. By setting the consistency to 400 or less, or even 395 or less, damage to electronic components during mounting can be effectively suppressed. On the other hand, the higher the consistency, the easier it is to apply the solder flux (F). Setting the consistency to 285 or more makes application of the solder flux (F) particularly easy. From these points of view, the consistency is preferably in the range of 240 to 395 (e.g., 285 to 395).

[0034] The viscosity of the flux (F) at 25°C is, for example, 70 Pa·s to 230 Pa·s, and may be 70 Pa·s to 170 Pa·s. Although there is no direct relationship between consistency and viscosity, increasing the viscosity tends to decrease the consistency. By setting the consistency to 400 or less and the viscosity within the above range, the handleability (particularly the applicability) of the flux (F) is improved.

[0035] The viscosity may be measured using a commercially available rheometer at a measurement temperature of 25°C. The measurement device may be, for example, an MCR series (MCR501, etc.) manufactured by Anton Paar. The cone used for the measurement may be a CP25-2 (diameter: 24.977 mm, angle: 1.993°).

[0036] The softening point of solder flux can be adjusted by the type and ratio of its constituent components. Generally, if the softening points of the base resin and thixotropy-imparting agent of the solder flux are high, the softening point of the solder flux tends to be high. Also, generally, if the solvent content is high, the softening point tends to be low. The softening point can be achieved by adjusting the type of base resin, the type and content of the thixotropy-imparting agent, and / or the solvent content.

[0037] The flux (F) contains, for example, a base resin and a thixotropic agent as essential components, and may contain an activator and a solvent as optional components. A rosin-based resin is preferably used as the base resin. The flux (F) may be prepared by mixing these components. A typical flux (F) contains a base resin, a thixotropic agent, an activator, and a solvent. An example of the base resin is a rosin-based resin.

[0038] The flux (F) may satisfy the following conditions (1) and / or (2). By satisfying the following conditions (1) and (2), it becomes easier to set the softening point within the above range. (1) The content of the thixotropy-imparting agent in the flux (F) is in the range of 1 to 20 mass% (e.g., in the range of 3 to 15 mass% or in the range of 3 to 14 mass%). (2) The content of the solvent in the flux (F) is in the range of 10 to 45 mass% (e.g., in the range of 15 to 40 mass% or in the range of 18 to 30 mass%).

[0039] The flux (F) may satisfy the following conditions (3) and / or (4). For example, the flux (F) may satisfy the above conditions (1) and (2) and also the following conditions (3) and / or (4): (3) The content of the base resin (e.g., rosin-based resin) in the flux (F) is in the range of 50 to 80 mass% (e.g., 55 to 80 mass% or 56 to 76 mass%). (4) The content of the activator in the flux (F) is in the range of 1 to 10 mass% (e.g., 1 to 5 mass%).

[0040] <Main Resin> As the main resin, for example, a rosin-based resin that itself has reducing properties is preferably used, but resins other than rosin-based resins can also be used. One main resin may be used alone, or two or more may be mixed or combined. Among the materials listed below, for example, rosin-based resins, acrylic resins, polyethylene glycol, etc. are desirable, but are not particularly limited.

[0041] Examples of rosin-based resins include natural rosins such as gum rosin and wood rosin, and derivatives thereof (polymerized rosin, hydrogenated rosin, disproportionated rosin, acid-modified rosin, rosin ester, etc.).

[0042] Examples of resins other than rosin-based resins that can be used include organic fatty acid esters, polyalkylene oxide-based resins, propylene glycol fatty acid esters, and acetylene glycols. Specific examples include organic fatty acid polyglycerol esters such as polyglycerol laurate, polyglycerol stearate, polyglycerol isostearate, polyglycerol sesquistearate, polyglycerol diisostearate, polyglycerol myristate, polyglycerol palmitate, polyglycerol oleate, polyglycerol behenate, and polyglycerol caprylate, polyethylene glycol, polyethylene glycol-polypropylene glycol copolymer, polyoxyethylene alkyl ester, polyoxyethylene tallow ester, polyglycerin, glycerin fatty acid ester, polyglycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid esters, and acetylene glycols such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol-ethylene oxide adduct.

[0043] Other resins that can be used besides rosin-based resins include terpene resins, terpene phenolic resins, styrene resins, xylene resins, acrylic resins, polyester resins, polyolefin resins, polyamides, polyamines, phenolic resins, phenoxy resins, and epoxy resins. Examples of terpene resins include aromatic-modified terpene resins, hydrogenated terpene resins, and hydrogenated aromatic-modified terpene resins. Examples of terpene phenolic resins include hydrogenated terpene phenolic resins. Examples of styrene resins include styrene-acrylic acid copolymers and styrene-maleic acid copolymers. Examples of xylene resins include phenol-modified xylene resins, alkylphenol-modified xylene resins, phenol-modified resol-type xylene resins, polyol-modified xylene resins, and polyoxyethylene-added xylene resins. Examples of acrylic resins include 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, and acrylic resins obtained by copolymerizing at least one monomer selected from vinyl chloride and vinyl acetate. Examples of polyolefin resins include polyethylene and polypropylene. Examples of epoxy resins include bisphenol A epoxy resin, bisphenol F epoxy resin, and bisphenol AD ​​epoxy resin.

[0044] <Thixotropy-imparting agent> Examples of the thixotropy-imparting agent (thixotropy-imparting agent) include wax-based thixotropy-imparting agents, amide-based thixotropy-imparting agents, sorbitol-based thixotropy-imparting agents, etc. Examples of the wax-based thixotropy-imparting agent include hydrogenated castor oil. Examples of the amide-based thixotropy-imparting agent include lauric amide, palmitic amide, stearic amide, behenic amide, hydroxystearic amide, saturated fatty acid amide, oleic amide, erucic amide, unsaturated fatty acid amide, p-toluenemethane amide, aromatic amide, methylene bisstearic amide, ethylene bislauric amide, ethylene bishydroxystearic amide, saturated fatty acid bisamide, methylene bisoleic amide, unsaturated fatty acid bisamide, m-xylylene bisstearic amide, aromatic bisamide, saturated fatty acid polyamide, unsaturated fatty acid polyamide, aromatic polyamide, substituted amide, methylolstearic amide, methylol amide, and fatty acid ester amide. Examples of sorbitol-based thixotropic agents include dibenzylidene-D-sorbitol, bis(4-methylbenzylidene)-D-sorbitol, etc. The thixotropic agents may be used alone or in combination of two or more.

[0045] <Activator> The activator is a compound that reduces the oxide film that covers the surface of solder used in soldering electronic components. Examples of such solder include, as mentioned above, solder precoats and solder applied to the terminals (component electrodes) of electronic components. Note that base resins such as rosin-based resins may also have a certain degree of activating effect. The activator described here refers to a compound other than base resins such as rosin-based resins.

[0046] The activator reduces the oxide film and helps form a good bond. Examples of activators with a reducing effect include organic acids, amines, and halides. One activator may be used alone, or two or more activators may be used in combination.

[0047] Examples of organic acids used as activators include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dimer acid, propionic acid, 2,2-bishydroxymethylpropionic acid, tartaric acid, malic acid, glycolic acid, diglycolic acid, thioglycolic acid, dithioglycolic acid, stearic acid, 12-hydroxystearic acid, palmitic acid, and oleic acid.

[0048] Examples of amines used as activators include ethylamine, triethylamine, ethylenediamine, triethylenetetramine, 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, and 1-benzyl-2-methylimidazole. Phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazolium trimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl-(1')] ]-ethyl-s-triazine, 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2-phenyl-4, 5-Dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, 2-methylimidazoline, 2-phenylimidazoline, 2,4-diamino-6-vinyl-s-triazine, 2,4-diamino-6-vinyl-s-triazine isocyanuric acid adduct, 2,4-Diamino-6-methacryloyloxyethyl-s-triazine, epoxy-imidazole adduct, 2-methylbenzimidazole, 2-octylbenzimidazole, 2-pentylbenzimidazole, 2-(1-ethylpentyl)benzimidazole, 2-nonylbenzimidazole, 2-(4-thiazolyl)benzimidazole, benzimidazole, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3',5'-di-tert-amylphenyl)benzotriazole, 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole, 2,2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-tert-octylphenol], 6 -(2-benzotriazolyl)-4-tert-octyl-6'-tert-butyl-4'-methyl-2,2'-methylenebisphenol, 1,2,3-benzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]benzotriazole, carboxybenzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]methylbenzotriazole, 2,2'-[[(methyl-1H-benzotriazol-1-yl)methyl]imino]bisethanol, 1-(1',2'-dicarboxyethyl)benzotriazole, 1-(2,3-dicarboxypropyl)benzotriazole, 1-[(2-ethylhexylamino)methyl]benzotriazole, 2,6-bis[(1H-benzotriazol-1-yl)methyl]-4-methylphenol, 5-methylbenzotriazole, 5-phenyltetrazole, and the like.

[0049] Examples of the halide used as an activator include amine hydrohalides, organic halogen compounds, etc. Examples of the amine constituting the amine hydrohalide include ethylamine, ethylenediamine, triethylamine, diphenylguanidine, ditolylguanidine, methylimidazole, 2-ethyl-4-methylimidazole, etc. Examples of the hydrogen halide include hydrogen chloride, hydrogen bromide, hydrogen iodide, etc. Examples of the organic halogen compound include trans-2,3-dibromo-2-butene-1,4-diol, triallyl isocyanurate hexabromide, 1-bromo-2-butanol, 1-bromo-2-propanol, 3-bromo-1-propanol, 3-bromo-1,2-propanediol, 1,4-dibromo-2-butanol, 1,3-dibromo-2-propanol, 2,3-dibromo-1-propanol, 2,3-dibromo-1,4-butanediol, and 2,3-dibromo-2-butene-1,4-diol.

[0050] <Solvent> Examples of the solvent include water, alcohol-based solvents, glycol-based solvents, ketone-based solvents, hydrocarbon-based solvents, ester-based solvents, glycol ether-based solvents, terpineols, etc. One type of solvent may be used alone, or two or more types may be used in combination.

[0051] Examples of alcohol-based solvents include isopropyl alcohol, 1,2-butanediol, isobornylcyclohexanol, 2,4-diethyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol, 2,5-dimethyl-2,5-hexanediol, 2,5-dimethyl-3-hexyne-2,5-diol, 2,3-dimethyl-2,3-butanediol, 1,1,1-tris(hydroxymethyl)ethane, 2-ethyl-2-hydroxymethyl-1,3-propanediol, 2,2'-oxybis(methylene)bis(2- ethyl-1,3-propanediol), 2,2-bis(hydroxymethyl)-1,3-propanediol, 1,2,6-trihydroxyhexane, bis[2,2,2-tris(hydroxymethyl)ethyl]ether, 1-ethynyl-1-cyclohexanol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, erythritol, threitol, guaiacol glycerol ether, 3,6-dimethyl-4-octyne-3,6-diol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, and the like.

[0052] Examples of glycol solvents include ethylene glycol monomethyl ether, triethylene glycol monomethyl ether, polyethylene glycol monomethyl ether, triethylene glycol monobutyl ether, diethylene glycol monohexyl ether (hexyl carbitol), diethylene glycol mono-2-ethylhexyl ether, ethylene glycol monophenyl ether, diethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, diethylene glycol monobenzyl ether, diethylene glycol dibutyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monobutyl ether, propylene glycol monophenyl ether, diethylene glycol dibutyl ether, tetraethylene glycol dimethyl ether, 2-methylpentane-2,4-diol, and triethylene glycol monobutyl ether.

[0053] Examples of ketone solvents include methyl ethyl ketone, methyl-n-propyl ketone, diethyl ketone, and cyclohexanone.

[0054] Examples of hydrocarbon solvents include normal hexane, isohexane, cyclohexane, methylcyclohexane, ethylcyclohexane, normal heptane, isoheptane, normal octane, isooctane, limonene, 2-methyl-2-butene, 2-methyl-1-pentene, 2-methyl-2-pentene, 3-ethyl-2-butene, 2,3-dimethyl-2-butene, 2,4,4-trimethyl-1-pentene, and 2,4,4-trimethyl-2-pentene.

[0055] Examples of ester-based solvents include butyl stearate, 2-ethylhexyl stearate, isotridecyl stearate, methyl oleate, isobutyl oleate, coconut fatty acid methyl ester, methyl laurate, isopropyl myristate, isopropyl palmitate, 2-ethylhexyl palmitate, and octyldodecyl myristate.

[0056] The flux (F) may contain other components in addition to the above-mentioned components, such as a surfactant, a silane coupling agent, an antioxidant, and a colorant.

[0057] (Electronic Components) The electronic components mounted on the connection portions may be of various sizes. For example, the electronic components may be electronic components of JIS (Japanese Industrial Standards) size 0402 or smaller (e.g., electronic components such as 0603, 0402, 0201, 03015, and 01005). The electronic components may be electronic components of JIS size 0201 or smaller. The smaller the electronic component, the lower the breaking strength and the lower the critical load. The 0402 size is 0.4 mm x 0.2 mm (length x width). The 0201 size is 0.25 mm x 0.125 mm (length x width).

[0058] The breaking strength of the electronic component is, for example, 170 MPa or less, and may be 100 MPa to 170 MPa. The breaking strength is the load at which the electronic component breaks when the load is gradually increased by pressing the electronic component with an indenter. The breaking strength of the electronic component can be measured using a commercially available micro-compression tester (for example, MCT-W500 manufactured by Shimadzu Corporation). For example, using a flat indenter with a tip diameter of 50 μm, the breaking strength of 10 electronic components is measured at a displacement rate of 5 μm / sec, and the average value is calculated.

[0059] (Method for manufacturing an electronic component mounting substrate) In the method for manufacturing an electronic component mounting substrate according to this embodiment, a flux (F) is used. Hereinafter, this manufacturing method may be referred to as the "manufacturing method (M)." The matters described regarding the flux (F) can be applied to the manufacturing method (M). Furthermore, the matters described regarding the manufacturing method (M) may also be applied to the flux (F). The manufacturing method (M) includes steps (i), (ii), and (iii) in this order. These steps will be described below.

[0060] Step (i) is a step of disposing flux (F) on the connection portions of the substrate. The method for disposing the flux (F) is not particularly limited, and a known application method may be used. For example, a screen printing method, a dispensing method, a spraying method, or the like may be used. The screen printing method is preferable in that it allows a layer of flux (F) with a uniform thickness to be formed on multiple connection portions at once.

[0061] The connection may include a land and a solder precoat formed on the land, in which case, in step (i), a flux (F) may be disposed on the solder precoat.

[0062] Since solder precoats are formed using cream solder, they are typically washed to remove flux residue after formation, but methods that eliminate the washing step are also being developed. In such cases, at least a portion of the solder precoat may be covered with a resin film (i.e., flux residue). The resin film softens when heated together with the flux applied to the solder precoat.

[0063] Step (ii) is a step of placing electronic components on the flux (F) placed in step (i). In step (ii), typically, multiple electronic components are placed on the flux (F) on multiple connection portions. In this case, the substrate includes connection portions corresponding to the multiple electronic components. There are no limitations on the electronic components, and electronic components of the above-mentioned sizes may be used. For example, as described above, the electronic components may include electronic components of JIS size 0402 or smaller. That is, at least one electronic component may be JIS size 0402 or smaller.

[0064] The method for placing electronic components is not particularly limited, and known mounting devices may be used. Typically, when placing components with a low critical load, the nozzle operating speed for placing the components is slower than when placing components with a relatively high critical load. However, in manufacturing method (M), the impact on the electronic components can be significantly reduced by the layer of flux (F), so the nozzle operating speed does not need to be significantly reduced. Alternatively, components may be placed by moving the nozzle at the same speed as when placing normal components.

[0065] Generally, in the process of placing electronic components, static electricity can cause the electronic components to not separate from the moving means (such as a mounting head) that carries them, resulting in mounting defects. The use of flux (F) can reduce such mounting defects.

[0066] The electronic component may include a terminal to which solder is applied. By performing soldering using solder that is already applied to the electronic component, it may be easier to solder a small electronic component accurately.

[0067] Step (iii) is a step of soldering the electronic components to the connection portions by a reflow process. There are no particular limitations on the reflow process, and any known reflow process may be used. Specifically, in step (ii), the substrate on which the electronic components are mounted is heated to a temperature equal to or higher than the solder melting temperature to melt the solder, and then the substrate is cooled to solidify the solder. The solder that melts and solidifies is solder contained in the connection portions of the substrate and / or solder applied to the terminals of the electronic components. Known solders used in reflow soldering can be used for this solder. Examples of solder contained in the connection portions of the substrate include solder precoat. For example, the solder contained in the connection portions of the substrate may be solder precoat formed on the lands of the substrate. In this case, the electronic components are soldered to the lands.

[0068] <Substrate> Examples of substrates include substrates such as laminated substrates, resin substrates, ceramic substrates, and silicon substrates, as well as semiconductor elements and semiconductor packages. The substrate may be a structure including various types of substrates and a semiconductor package mounted on the substrate. Examples of such structures include chip-on-board, chip-on-film, chip-on-glass, chip-on-chip, chip-on-package, and package-on-package.

[0069] The substrate is not particularly limited, and may be a laminate substrate, a resin substrate, a ceramic substrate, a silicon substrate, or the like. An example of a substrate on which a connection portion is formed (a substrate including a connection portion) is a printed circuit board. The electronic components mounted on the substrate are not particularly limited, and include surface-mounted components such as resistor elements, semiconductor elements, capacitors, coils, chip components, connectors, semiconductor packages, and module components.

[0070] The connection portion of the substrate is the portion to which the electronic component is soldered. Examples of the connection portion include wiring, such as printed wiring of a printed circuit board. When the connection portion includes a solder precoat, the method for forming the solder precoat is not particularly limited, and the solder precoat may be formed by a known method. Alternatively, a commercially available substrate on which a solder precoat is formed may be used.

[0071] An example of an embodiment according to the present disclosure will be specifically described below with reference to the drawings. The embodiment described below can be modified based on the above description. The matters described below may also be applied to the above embodiment. In the embodiment described below, matters that are not essential to the invention according to the present disclosure may be omitted. Note that the following figures are schematic diagrams, and hatching of some components may be omitted.

[0072] (Embodiment 1) In embodiment 1, an example of a manufacturing method (M) for an electronic component mounting board is described. First, as shown in the cross-sectional view of FIG. 2(a), a substrate 1 on which a connection portion 2 is formed is prepared. In the example described in embodiment 1, the connection portion 2 includes a land 2a and a solder precoat 2b formed on the land 2a. The substrate 1 on which the connection portion 2 is formed is referred to as a substrate 10.

[0073] 2(b), a mask pattern 101 is placed on the substrate 1. The mask pattern 101 has openings 101a in areas where solder flux is to be placed.

[0074] Next, as shown in the cross-sectional view of Fig. 2(c), solder flux 3 is disposed on the connection portion 2 by screen printing. The solder flux 3 is the solder flux (F) described above. In the example described in the first embodiment, the solder flux 3 is disposed on the solder precoat 2b.

[0075] Next, as shown in the cross-sectional view of FIG. 2(d), multiple electronic components 4 are placed on the solder flux 3. The illustrated example electronic component 4 includes two terminals (component electrodes) 4a and an element portion 4b disposed therebetween. The number of terminals of the electronic component varies depending on the type of electronic component. In the manufacturing method of embodiment 1, the use of flux (F) can prevent damage to the electronic components when they are placed.

[0076] Next, a reflow process is performed. As shown in FIG. 2( e), the electronic components 4 are soldered to the connection portions 2 (lands 2 a) with solder 5 during the reflow process. In the manufacturing method of embodiment 1, flux (F) is used, so the flux (F) does not soften excessively and flow before the solder melts, allowing most of the flux to remain on the connection portions of the board. Furthermore, the flux (F) has a softening point below 170°C and softens sufficiently before the solder melts, allowing even small, lightweight components to sink into the softened flux (F) and come into contact with the solder precoat. This significantly reduces connection failures and lifting. In this manner, an electronic component mounting board 1 x on which multiple electronic components 4 are mounted is obtained.

[0077] (Additional Notes) The above description discloses the following technologies. (Technology 1) A solder flux used for mounting electronic components on connection portions of a substrate, the solder flux having a softening point higher than 70°C and lower than 170°C. (Technology 2) The solder flux according to Technology 1, comprising a base resin and a thixotropy-imparting agent, the base resin having a softening point Td1 higher than 70°C and lower than 170°C. (Technology 3) The solder flux according to Technology 2, the thixotropy-imparting agent having a softening point Td2 higher than 50°C and lower than 170°C. (Technology 4) The solder flux according to any one of Technologies 1 to 3, the base resin including a rosin-based resin. (Technology 5) The solder flux according to any one of claims 2 to 4, wherein the thixotropy-imparting agent is at least one selected from the group consisting of wax-based thixotropy-imparting agents, amide-based thixotropy-imparting agents, and sorbitol-based thixotropy-imparting agents. (Technology 6) The solder flux according to any one of techniques 1 to 5, wherein the consistency of the solder flux at 25°C is 400 or less. (Technology 7) The solder flux according to any one of techniques 1 to 6, wherein the viscosity of the solder flux at 25°C is 70 Pa·s to 230 Pa·s. (Technology 8) The solder flux according to any one of techniques 1 to 7, wherein the breaking strength of the electronic component is 170 MPa or less. (Technology 9) The solder flux according to any one of techniques 1 to 8, wherein the electronic component is an electronic component of JIS size 0402 or less. (Technology 10) A method for manufacturing an electronic component mounting board, comprising: step (i) of arranging the solder flux according to claim 1 on a connection portion of the board; step (ii) of arranging an electronic component on the solder flux; and step (iii) of soldering the electronic component to the connection portion by a reflow process. (Technology 11) The connection portion includes a land and a solder precoat formed on the land, and in step (i), the solder flux is arranged on the solder precoat, and in step (iii), the electronic component is soldered to the land. The manufacturing method according to Technology 10.(Technology 12) The manufacturing method according to Technology 10 or 11, wherein the electronic component includes a terminal to which solder is applied. (Technology 13) The manufacturing method according to Technology 11 or 12, wherein at least a portion of the solder precoat is covered with a resin film.

[0078] While the present invention has been described with reference to presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all such changes and modifications that do not depart from the true spirit and scope of the invention.

[0079] EXAMPLES The present disclosure will now be described in more detail with reference to examples. In the following examples, a number of solder fluxes with different softening points were prepared and evaluated.

[0080] Example 1 First, the components constituting the solder flux were prepared. Specifically, a rosin-based resin, a thixotropic agent, a solvent, and additives as needed were prepared. Polymerized rosin (softening point 96°C) was used as the rosin-based resin. Hardened castor oil (softening point 83°C) was used as the thixotropic agent. Diethylene glycol monohexyl ether was used as the solvent.

[0081] Solder fluxes A1 to A6 and C1 were prepared by mixing the above components to obtain the content ratios shown in Table 1. The softening points, consistency and viscosity at 25°C of the obtained solder fluxes and solder flux C2 were measured by the methods described above.

[0082] Using the prepared solder flux, a test was conducted to reproduce the state of mounting an electronic component. Specifically, first, as shown in FIG. 3, solder flux 3 was applied to a glass plate 200. Then, an electronic component 4 was placed on the solder flux 3. Next, a predetermined load (the mounting load shown in Table 1) was applied to the electronic component 4 from above using a pressing member 210 for approximately two seconds. Ten electronic components 4 were tested for each solder flux 3. This test was conducted for each of the four types of electronic components with different sizes shown in Table 1.

[0083] The mounting load was varied depending on the size of the electronic component being tested. Specifically, the mounting loads shown in parentheses in Table 1 were applied for approximately 2 seconds. For example, in testing 0201-size electronic components, a load of 5 N was applied for approximately 2 seconds. The applied mounting load was the limit load (the load at which damage may occur) for each size of electronic component being tested.

[0084] The preparation conditions of the solder flux and the evaluation results are shown in Table 1. In Table 1, "good" indicates that no electronic components were damaged when 10 electronic components were tested, and "poor" indicates that one or more electronic components were damaged when 10 electronic components were tested.

[0085]

[0086] Example 2 Fluxes A101 to A315, A501 to A615, and C101 to C115 were prepared in the same manner as solder fluxes A1 to A3, A5 to A6, and C1, except that the softening point of the rosin-based resin in each composition was changed as shown in Table 2. The softening points of the fluxes were the same as that of the base resin (rosin-based resin).

[0087] The prepared solder flux was used to mount electronic components on a circuit board. Specifically, a solder precoat was formed on the land of a board designed to mount 100 0603 components with a 0.1 mm spacing between adjacent components. Flux was then applied to the solder precoat using a screen printing method, and 100 components were then mounted on the flux using a component mounting device. The mounting tact time of the component mounting device was controlled to minimize impact during component mounting. The component electrodes and lands were then bonded using a standard reflow profile (preheating conditions: 130°C to 180°C for 90 seconds, peak temperature: 230°C to 245°C), and the presence or absence of bonding defects was evaluated.

[0088] The evaluation results are shown in Table 2. In Table 2, "x" indicates that six or more electronic components experienced poor bonding, "△" indicates that five or fewer electronic components experienced poor bonding, and "◯" indicates that no electronic components experienced poor bonding.

[0089]

[0090] Example 3 Fluxes A116 to A330, A516 to A630, and C116 to C130 were prepared in the same manner as solder fluxes A1 to A3, A5 to A6, and C1, except that the softening point of the thixotropy-imparting agent in each composition was changed as shown in Table 3.

[0091] Using the prepared solder flux, a test was carried out to mount electronic components on a substrate in the same manner as in Example 2. The evaluation results are shown in Table 3.

[0092]

[0093] Solder fluxes A1 to A5, A101 to A315 (No. 3 to No. 11), A501 to A615 (No. 3 to No. 11), A116 to A330 (No. 18 to No. 26), and A516 to A630 (No. 18 to No. 26) are fluxes (F) according to the present disclosure.

[0094] Solder fluxes C1 to C2, A101 to A315 (Nos. 1, 2, 12 to 14), A501 to A615 (Nos. 1, 2, 12 to 14), A116 to A330 (Nos. 16, 17, 27 to 30), A516 to A630 (Nos. 16, 17, 27 to 30), and C101 to C130 are comparative example fluxes.

[0095] Solder flux C2 was a commercially available product, and the other components were prepared by mixing the components in the ratios shown in Tables 1 to 3. The consistency of solder flux C2 was 475 or more, and the exact value could not be measured.

[0096] As shown in Tables 1 to 3, joint defects could be significantly suppressed by controlling the softening point. When the softening point of the flux is low, joint defects occur due to components being washed away by the flux or bridging between components, while when the softening point of the flux is high, joint defects occur due to components being unable to contact the solder precoat.

[0097] In Example 3 (Table 3), the softening point of the flux was the same as that of the base resin (rosin-based resin) (96°C), but when the thixotropic agent had a softening point lower than 96°C, a small amount of flow occurred at that softening point. However, the sinking of the part was insufficient at that point, and the part began to sink sufficiently at the softening point of the base resin.

[0098] The present disclosure can be used for a method of manufacturing a solder flux and an electronic component mounting board.

[0099] 1, 10: Substrate 1x: Electronic component mounting substrate 2: Connection portion 2a: Land 2b: Solder precoat 3: Solder flux 4: Electronic component 4a: Terminal (component electrode) 5: Solder

Claims

1. A solder flux used for mounting electronic components to connection portions of a substrate, The softening point is higher than 70°C and lower than 170°C. A solder flux having a consistency of 400 or less at 25°C.

2. The composition includes a base resin and a thixotropic agent, The base resin has a softening point Td1, The solder flux according to claim 1 , wherein the softening point Td1 is higher than 70° C. and lower than 170° C.

3. The thixotropic agent has a softening point Td2, The solder flux according to claim 2 , wherein the softening point Td2 is higher than 50° C. and lower than 170° C.

4. The solder flux according to claim 2 or 3, wherein the base resin contains a rosin-based resin.

5. 4. The solder flux according to claim 2, wherein the thixotropy-imparting agent is at least one selected from the group consisting of wax-based thixotropy-imparting agents, amide-based thixotropy-imparting agents, and sorbitol-based thixotropy-imparting agents.

6. The solder flux according to any one of claims 1 to 3, wherein the viscosity of the solder flux at 25°C is 70 Pa·s to 230 Pa·s.

7. The solder flux according to any one of claims 1 to 3, wherein the electronic component has a breaking strength of 170 MPa or less.

8. The solder flux according to any one of claims 1 to 3, wherein the electronic component is an electronic component having a size of 0402 or less as defined by the JIS standard.

9. A method for manufacturing an electronic component mounting board, comprising: (i) placing the solder flux according to claim 1 on a connection portion of a substrate; (ii) placing an electronic component on the solder flux; and (iii) soldering the electronic components to the connection portions by a reflow process.

10. The connection portion includes a land and a solder precoat formed on the land, In the step (i), the solder flux is placed on the solder precoat; The manufacturing method according to claim 9 , wherein in the step (iii), the electronic component is soldered to the land.

11. The method according to claim 9 or 10, wherein the electronic component includes a terminal to which solder is applied.

12. The manufacturing method according to claim 10 , wherein at least a portion of the solder precoat is covered with a resin film.