Manufacturing method for electronic component mounting boards

Abstract

An adhesive for provisional fixing an electronic component to a solder precoat, at least a part of which is covered by an organic film, wherein: the adhesive contains a base resin and a solvent that dissolves the base resin; the content of the solvent is 25% to 40% by mass; and the organic film dissolves into the solvent when the solder precoat is melted. Consequently, the present invention suppresses the formation of an oxide coating film on the surface of a solder precoat, while being capable of suppressing connection failure between an electronic component and an electrode which has the solder precoat.

Description

Technical Field

[0001] The present invention relates to an adhesive for temporarily fixing electronic components to a solder precoat and a method for manufacturing an electronic component mounting substrate.

Background Art

[0002] Patent Document 1 discloses a printed circuit board (1) having a fine pitch pad portion (5) with a pad array pitch of less than 0.5 mm and a rough pitch pad portion (4) with a pad array pitch of 0.5 mm or more. For the printed circuit board (1), solder paste (8) is printed on the pads (3) of the rough pitch pad portion (4), and then a solder deposition composition (12) mainly composed of an organic acid lead salt and tin powder is applied thickly to the fine pitch pad portion (5). Then, the printed circuit board (1) is heated to melt the solder paste (8) and form a solder layer (13) on the pads (3) of the rough pitch pad portion (4), and at the same time, solder is deposited from the solder deposition composition (12) on the pads (3) of the fine pitch pad portion (5) to form a solder layer (13). Next, flux (15) is applied to the printed circuit board (1), and an electronic component (1) is mounted thereon. The leads (17) are temporarily fixed to the solder layer (13) on the pads (3) by the adhesive force of the flux (15). Then, the printed circuit board (1) on which the electronic component (16) is mounted is heated to melt the solder layer (13), and the leads (17) of the electronic component (16) are soldered to the pads (3). A method for mounting an electronic component on a printed circuit board is proposed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As electronic components become smaller, solder precoats are also becoming smaller. Because tiny solder precoats have a large surface area relative to the solder volume, they are susceptible to the effects of oxide films formed on the surface, which can easily lead to poor connections between electrodes and electronic components. While it is possible to suppress oxide film formation by applying organic substances such as antioxidants to the surface of the solder precoat, these organic substances can conversely cause poor connections between electrodes and electronic components. [Means for solving the problem]

[0005] One aspect of the present invention relates to an adhesive for temporarily fixing electronic components to a solder precoat that is at least partially covered with an organic film, wherein the adhesive comprises a main resin and a solvent for dissolving the main resin, the content of the solvent being 25% by mass or more and 40% by mass or less, and the organic film dissolves in the solvent when the solder precoat is melted.

[0006] Another aspect of the present invention relates to a method for manufacturing an electronic component mounting substrate, comprising the steps of: preparing a circuit member having a solder precoat that is at least partially covered with an organic film; applying an adhesive to the solder precoat for temporarily fixing electronic components such that at least a portion of the organic film is covered; mounting the electronic components on the solder precoat via the adhesive; and reflowing the solder precoat to mount the electronic components on the circuit member, wherein the adhesive comprises a main resin and a solvent for dissolving the main resin, the solvent content being 25% by mass or more and 40% by mass or less, and the organic film dissolves in the solvent when the solder precoat is reflowed. [Effects of the Invention]

[0007] According to the present invention, the formation of an oxide film on the surface of the solder precoat is suppressed, and connection failures between the electrode having the solder precoat and the electronic component can be suppressed.

[0008] Novel features of the present invention are described in the appended claims, but the present invention, both in terms of structure and content, will be better understood by the following detailed description in conjunction with the drawings, together with other objects and features of the present application. [Brief explanation of the drawing]

[0009] [Figure 1] This diagram schematically illustrates the process of forming a solder precoat on circuit components. [Figure 2] This diagram schematically illustrates a part of the process of mounting electronic components onto circuit members that have a solder precoat. [Figure 3] This diagram schematically shows the remaining steps in the process of mounting electronic components onto a circuit member that has a solder precoat. [Figure 4] This diagram schematically illustrates part of the process of mounting electronic components onto a circuit member that has a separate solder precoat. [Figure 5] This diagram schematically shows the remaining steps in the process of mounting electronic components onto a circuit member that has a separate solder precoat. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described below with reference to examples. However, the present invention is not limited to the examples described below.

[0011] The adhesive according to this embodiment is an adhesive for temporarily fixing electronic components to a solder precoat that is at least partially covered with an organic film. The solder precoat does not have the tackiness of solder paste or solder cream. Therefore, the adhesive is applied to the solder precoat to impart tackiness. The electronic components are mounted on the solder precoat via the adhesive.

[0012] Next, the method for manufacturing an electronic component mounting substrate according to this embodiment comprises the steps of: preparing a circuit member having a solder precoat that is covered in at least a portion with an organic film; applying the adhesive for temporarily fixing electronic components onto the solder precoat so that at least a portion of the organic film is covered; mounting the electronic components onto the solder precoat via the adhesive; and reflowing the solder precoat to mount the electronic components onto the circuit member.

[0013] Circuit components may include, for example, substrates such as multilayer substrates, resin substrates, ceramic substrates, and silicon substrates, as well as semiconductor elements and semiconductor packages. For example, a structure in which a semiconductor package is mounted on various substrates may also be used. Examples of such structures include chip-on-board, chip-on-film, chip-on-glass, chip-on-chip, chip-on-package, and package-on-package.

[0014] The organic film covering at least a portion of the solder precoat can be any film containing organic matter. The term "film" in "organic film" is not necessarily limited to a homogeneous and dense film, but is a broad concept that includes coatings, layers, precipitates, etc., that cover at least a portion of the surface of the solder precoat in various states. The organic film can be rephrased as organic matter adhering to the surface of the solder precoat, or organic matter covering at least a portion of the surface of the solder precoat. The organic film may be composed substantially (for example, 99% or more by mass) of organic matter.

[0015] Organic materials have the function of inhibiting contact between the solder precoat and oxygen. By shielding against oxygen, the formation of an oxide film on the surface of the solder precoat is suppressed.

[0016] The organic film may be a residue generated when forming the solder precoat. The solder precoat is formed by supplying a solder paste containing solder particles and flux to an electrode (such as a pad or land) provided on a circuit member, and then heating the solder paste. By heating, the solder particles in the solder paste melt and adhere to the electrode surface in a film form. When the solder solidifies, the solder precoat is formed, and the surface of the solder precoat is covered with the residue of the flux. That is, the residue generated when forming the solder precoat is the residue of the flux.

[0017] The residue contains an organic substance derived from the flux and has a function of inhibiting the contact between the solder precoat and oxygen. The residue may contain, for example, a resin described later as the main resin of the adhesive or a thermally modified product thereof as the main component. The main component refers to a component that can occupy 30% by mass or more, and further 50% by mass or more of the residue.

[0018] The residue generated when forming the solder precoat is usually removed by cleaning. However, when it is used as an organic film covering at least a part of the solder precoat without removing the residue, the cleaning process can be omitted.

[0019] (Adhesive) The adhesive contains a main resin and a solvent that dissolves the main resin. The content of the solvent in the adhesive is 25% by mass or more and 40% by mass or less. The organic film dissolves in the solvent when melting the solder precoat. In other words, the solvent is selected so that it can dissolve the organic film when melting the solder precoat.

[0020] A part of the solvent volatilizes due to the heat when reflowing the solder precoat. On the other hand, the organic film softens or melts due to the heat when reflowing the solder precoat. When the adhesive contains 25% by mass or more of the solvent, even when the solder precoat is reflowed, an amount of solvent sufficient to dissolve the softened or melted organic film exists in the adhesive.

[0021] When the softened or melted organic film dissolves in the solvent, the main resin dissolved in the solvent and the organic film are compatible. Before most of the solvent volatilizes, the compatibility between the organic film and the main resin makes the organic substances constituting the organic film easily separate from the molten solder generated by reflow together with the main resin. That is, it becomes difficult for the organic film to remain on the surface of the solder precoat. On the other hand, the molten solder spreads over the electrodes covered by the solder precoat and the electrodes of the electronic components to form a joint. As a result, connection failures caused by the organic film are suppressed.

[0022] On the other hand, when the adhesive contains a solvent of 40% by mass or less, sufficient adhesiveness or tackiness is ensured to temporarily fix the electronic component on the solder precoat. To ensure the adhesiveness or tackiness of the adhesive, it is necessary to suppress the solvent content in the adhesive to 40% by mass or less.

[0023] When the electronic component is, for example, below the size of 0402 of the JIS standard (Japanese Industrial Standard) (0402, 0201, 03015, 01005, etc.), if the adhesiveness or tackiness of the adhesive is insufficient, due to static electricity or the like, the electronic component does not separate from the moving means (mounting head, etc.) that picks up the electronic component and transports it onto the solder precoat of the circuit member, and mounting failures may occur. Also, if the adhesiveness or tackiness of the adhesive is insufficient, even for extremely small electronic components, displacement of the electronic component may occur due to vibration until the circuit member on which the electronic component is mounted is transported to a reflow apparatus that reflows the solder precoat. When the solvent content in the adhesive is controlled to 40% by mass or less, such mounting failures and displacements of the micro-components can be significantly suppressed. In other words, the adhesive according to the present embodiment is particularly suitable for temporarily fixing electronic components of a size of 0402 or less defined by the JIS standard to the solder precoat.

[0024] The tackiness of an adhesive can be evaluated by measuring its adhesive strength according to the solder paste tackiness test method described in JIS Z 3284-3. This adhesive strength can be measured using a commercially available tack strength tester. When the obtained value (gf) is converted to N, an adhesive strength of 0.5 N or higher is desirable, and an adhesive strength of 1.0 N or higher is more desirable. The higher the solvent content in the adhesive, the lower the adhesive strength. However, if the size of the electronic component is 0402 or smaller, an adhesive strength achieved with a solvent content of 25% by mass or more and 40% by mass or less is sufficient.

[0025] As the main resin, for example, a rosin-based resin that has reducing properties itself is preferably used, but resins other than rosin-based resins may also be used. The main resin may be used alone, or two or more types may be mixed or combined. Among the materials listed below, for example, rosin-based resins, acrylic resins, polyethylene glycol, etc. are desirable, but the material is not particularly limited.

[0026] Examples of rosin-based resins include natural rosins such as gum rosin and wood rosin, and their derivatives (polymerized rosin, hydrogenated rosin, disproportionated rosin, acid-modified rosin, rosin esters, etc.).

[0027] Resins other than rosin-based resins include, for example, organic fatty acid esters, polyalkylene oxide resins, propylene glycol fatty acid esters, and acetylene glycols. Specifically, 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, and 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-decine-4,7-diol-ethylene oxide adducts.

[0028] Other resins besides rosin-based resins include terpene resins, terpene phenol resins, styrene resins, xylene resins, acrylic resins, polyester resins, polyolefin resins, polyamides, polyamines, phenol resins, phenoxy resins, epoxy resins, etc. Examples of terpene resins include aromatically modified terpene resins, hydrogenated terpene resins, and hydrogenated aromatically modified terpene resins. Examples of terpene phenol resins include hydrogenated terpene phenol 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, vinyl chloride, and acrylic resins obtained by copolymerizing at least one monomer of vinyl acetate. Examples of polyolefin resins include polyethylene and polypropylene. Examples of epoxy resins include bisphenol A type epoxy resin, bisphenol F type epoxy resin, and bisphenol AD ​​type epoxy resin.

[0029] Examples of solvents include water, alcohol-based solvents, glycol-based solvents, ketone-based solvents, hydrocarbon-based solvents, ester-based solvents, glycol ether-based solvents, and terpineols. A single solvent may be used, or two or more solvents may be used in combination.

[0030] 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, and 2,2'-oxybis(methylene)bis(2- Examples include 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, treitol, guaiacolglycerol ether, 3,6-dimethyl-4-octin-3,6-diol, and 2,4,7,9-tetramethyl-5-decine-4,7-diol.

[0031] Examples of glycol-based solvents include ethylene glycol monomethyl ether, triethylene glycol monomethyl ether, polyethylene glycol monomethyl ether (295°C), 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.

[0032] Examples of ketone-based solvents include methyl ethyl ketone, methyl-n-propyl ketone, diethyl ketone, and cyclohexanone.

[0033] Examples of hydrocarbon solvents include n-hexane, isohexane, cyclohexane, methylcyclohexane, ethylcyclohexane, n-heptane, isoheptane, n-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.

[0034] Examples of ester-based solvents include butyl stearate, 2-ethylhexyl stearate, isotridecyl stearate, methyl oleate, isobutyl oleate, methyl coconut fatty acid, methyl laurate, isopropyl myristate, isopropyl palmitate, 2-ethylhexyl palmitate, and octyldodecyl myristate.

[0035] The adhesive may contain, in addition to the main resin and solvent, an activator that reduces the oxide film covering the surface of the solder precoat. Although at least part or all of the surface of the solder precoat is covered with an organic film, it is impossible to completely suppress the formation of an oxide film. An oxide film is inevitably present on the surface of the solder precoat. The activator reduces the oxide film and helps to form a good joint. Examples of activators with reducing properties include organic acids, amines, and halides. The activator may be used alone or in combination of two or more types.

[0036] Examples of organic acids 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.

[0037] Examples of amines 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-phenylimidazole. 1-Cyanoethyl-2-methylimidazole, 1-Cyanoethyl-2-undecylimidazole, 1-Cyanoethyl-2-ethyl-4-methylimidazole, 1-Cyanoethyl-2-phenylimidazole, 1-Cyanoethyl-2-undecylimidazolium trimellitate, 1-Cyanoethyl-2-phenylimidazolium trimellitate, 2,4-Diamino-6-[2'-methylimidazolyl-(1')]-ethyl- s-triazine, 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanurate adduct, 2-phenylimidazole isocyanurate adduct, 2-phenyl-4,5-di Hydroxymethylimidazole, 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 isocyanurate 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-benzotriazole-2-yl)-4-tert-octylphenol], 6 Examples include -(2-benzotriazol)-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-benzotriazole-1-yl)methyl]imino]bisethanol, 1-(1',2'-dicarboxyethyl)benzotriazole, 1-(2,3-dicarboxypropyl)benzotriazole, 1-[(2-ethylhexylamino)methyl]benzotriazole, 2,6-bis[(1H-benzotriazole-1-yl)methyl]-4-methylphenol, 5-methylbenzotriazole, 5-phenyltetrazole, etc.

[0038] Examples of halides include amine hydrohalides and organic halogen compounds. Examples of amines that make up amine hydrohalides include ethylamine, ethylenediamine, triethylamine, diphenylguanidine, ditylguanidine, methylimidazole, and 2-ethyl-4-methylimidazole, and examples of hydrogen halides include hydrogen chloride, hydrogen bromide, and hydrogen iodide. Examples of organic halogen compounds 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.

[0039] The adhesive may contain a thixotropic agent. Examples of thixotropic agents include wax-based thixotropic agents, amide-based thixotropic agents, and sorbitol-based thixotropic agents. Examples of wax-based thixotropic agents include hydrogenated castor oil. Examples of amide-based thixotropic agents include laurate amide, palmitate amide, stearate amide, behenate amide, hydroxystearate amide, saturated fatty acid amide, oleate amide, erucate amide, unsaturated fatty acid amide, p-toluenemethane amide, aromatic amide, methylenebisstearate amide, ethylenebislaurate amide, ethylenebishydroxystearate amide, saturated fatty acid bisamide, methylenebisoleate amide, unsaturated fatty acid bisamide, m-xylylenebisstearate amide, aromatic bisamide, saturated fatty acid polyamide, unsaturated fatty acid polyamide, aromatic polyamide, substituted amide, methylolstearate amide, methylolamide, and fatty acid ester amide. Examples of sorbitol-based thixotropic agents include dibenzylidene-D-sorbitol and bis(4-methylbenzylidene)-D-sorbitol. Thixotropic agents may be used individually or in combination of two or more.

[0040] The adhesive may further include, for example, a surfactant, a silane coupling agent, an antioxidant (for example, an antioxidant that may be contained in an organic film), a colorant, and the like.

[0041] (organic film) When an organic film contains organic matter such as residue generated during the formation of a solder precoat (i.e., flux residue), such residue may mainly consist of, for example, a main resin that can be contained in an adhesive or a heat-modified product thereof.

[0042] When the organic film contains organic residue generated during the formation of the solder precoat, it is desirable from the viewpoint of compatibility between the organic film and the main resin to use at least one solvent selected from the group consisting of alcohol-based solvents, ester-based solvents, glycol-based solvents, ketone-based solvents, and hydrocarbon-based solvents.

[0043] The organic substance may be, for example, an antioxidant, an organic acid, or an organic fatty acid ester. The antioxidant may be a phenolic antioxidant, an amine antioxidant, a phosphorus antioxidant, a sulfur antioxidant, etc. These organic substances may be used individually or in combination of two or more.

[0044] When the organic film contains a phenolic antioxidant and / or a phosphorus-based antioxidant as organic matter, it is desirable from the viewpoint of compatibility between the organic film and the main resin to use at least one solvent selected from the group consisting of alcohol-based solvents, glycol-based solvents, and ketone-based solvents.

[0045] When the organic film contains amine-based antioxidants and / or sulfur-based antioxidants as organic substances, it is desirable from the viewpoint of compatibility between the organic film and the main resin to use at least one solvent selected from the group consisting of alcohol-based solvents, glycol-based solvents, and hydrocarbon-based solvents.

[0046] When the organic film contains organic fatty acids as organic matter, it is desirable from the viewpoint of compatibility between the organic film and the main resin to use at least one solvent selected from the group consisting of alcohol-based solvents, glycol-based solvents, ketone-based solvents, and hydrocarbon-based solvents.

[0047] Examples of phenolic antioxidants include hindered phenolic compounds having a bulky substituent (e.g., a branched or cyclic alkyl group such as a t-butyl group) at least one of the ortho positions of the phenol. Examples include bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionic acid][ethylenebis(oxyethylene)], N,N'-hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanamide], 1,6-hexanediolbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 2,2'-methylenebis[6-(1-methylcyclo [Hexyl)-p-cresol], 2,2'-methylenebis(6-tert-butyl-p-cresol), 2,2'-methylenebis(6-tert-butyl-4-ethylphenol), triethylene glycol-bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate], 1,6-hexanediol-bis-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2, 4-Bis-(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazine, pentaerythrityl-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2,2-thio-diethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) (Ciphenyl)propionate, N,N'-hexamethylenebis(3,5-di-t-butyl-4-hydroxyhydrocinnamamide), 3,5-di-tert-butyl-4-hydroxybenzylphosphonate-diethyl ester, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, N,N'-bis[2-[2-(3,5-di-tert-butyl-4-hydroxyphenyl Examples include [nyl]ethylcarbonyloxyethyl]oxamide.

[0048] Examples of amine-based antioxidants include alkylated diphenylamine, tris-(3,5-di-t-butyl-4-hydroxybenzyl)-isocyanurate, N,N-di-sec-butyl-p-phenylenediamine, p-phenylenediamine derivatives, and 1,3,5-tris(4-t-butyl-3-hydroxy-2,6-dimethyl)isocyanurate.

[0049] Examples of phosphorus-based antioxidants include tris-nonylphenyl phosphite, triphenyl phosphite, tris(2,4-di-t-butylphenyl) phosphite, and tris(isodecyl) phosphite.

[0050] Examples of sulfur-based antioxidants include 2,4-bis[(octylthio)methyl]-o-cresol, dilauryl-3,3-thiodipropionate, dimyristyl-3,3-thiodipropionate, distearyl-3,3-thiodipropionate, pentaerythrityltetrakis(3-laurylthiopropionate), ditridecyl-3,3-thiodipropionate, 2-mercaptobenzimidazole, and bis[2-methyl-4-(3-n-alkylthiopropionyloxy)-5-t-butylphenyl]sulfide.

[0051] Examples of organic acids include the organic acids mentioned earlier as reducing agents that can be contained in adhesives.

[0052] Examples of organic fatty acid esters include organic fatty acid esters that can be included as the main resin component in adhesives.

[0053] Next, the method for manufacturing an electronic component mounting substrate according to this embodiment will be described with reference to the drawings. In each drawing, the dimensions of each component are shown relatively to clarify their shape or characteristics, but they are not necessarily the dimensions of the actual objects. Also, the same reference numeral is used for the same component in each drawing.

[0054] (1st step) First, a circuit component is prepared that has a solder precoat that is covered with an organic film, at least in part. Figure 1 is a schematic diagram showing the process of forming the organic film together with the solder precoat on the circuit component.

[0055] Figure 1(a) shows a cross-sectional view of the main part of the circuit component 10. The circuit component 10 is a circuit board having minute electrodes 11 (lands or pads).

[0056] Figures 1(b) to 1(d) show the solder paste application process. The solder paste 20 is applied to predetermined locations on the circuit component 10, for example, by a printing method.

[0057] Figure 1(b) shows a state in which a mask 12 having an opening 12a corresponding to an electrode 11 is superimposed on the circuit member 10. For example, a screen mask can be used as the mask 12.

[0058] Next, as shown in Figure 1(c), solder paste 20 is applied to the circuit member 10 via the mask 12. The solder paste 20 contains solder particles 21 and flux 22. The particle size of the solder particles is not particularly limited, as long as it is smaller than the opening 12a of the mask 12, but may be, for example, 20 μm or less.

[0059] As shown in Figure 1(d), when the mask 12 is retracted from the circuit member 10, the circuit member 10 with solder paste 20 applied to the electrodes 11 is obtained. At this point, the solder paste 20 may be bridging the nearest electrodes 11. In this state, the circuit member 10 is heated to the melting temperature of the solder particles 21.

[0060] When the solder particles 21 melt, the molten solder forms a film and adheres to the electrode surface, wetting it. At this time, the solder present between the electrodes 11 is attracted to the surface of the electrodes 11 by the surface tension of the molten solder. When the solder solidifies due to cooling, a circuit member 10X having a solder precoat 23 is obtained, as shown in Figure 1(e). The surface of the solder precoat 23 is covered with an organic film 24 containing flux residue. Due to the influence of the surface tension of the molten solder, the solder precoat 23 takes on a shape with a curved surface that is convex toward the organic film 24 (i.e., convex upwards in the plane of the paper). The smaller the area of ​​each electrode 11, the greater the curvature of the curved surface of the solder precoat 23.

[0061] (2nd process) Next, an adhesive 25 for temporarily fixing electronic components is applied to the solder precoat 23 so that at least a portion of the organic film 24 is covered, and the electronic components 30 are mounted on the solder precoat 23 via the adhesive 25. Figure 2 is a schematic diagram showing the process of mounting the electronic components 30 on the circuit member 10X after applying the adhesive 25 to the solder precoat 23.

[0062] Figure 2(a) shows the process of pressing a solder precoat 23, which has an upwardly convex curved surface and is covered with an organic film 24, against a circuit member 10X using a jig 40 having a flat pressing surface. Due to the pressing, the upwardly convex curved surface is flattened, so that the solder precoat 23 becomes a shape suitable for stable mounting of electronic components 30. At the same time, although not shown, cracks may form in the organic film 24, or the organic film 24 may partially peel off from the solder precoat 23, partially exposing the surface of the solder precoat 23. As a result, contact between the adhesive 25 and the solder precoat 23 is promoted, and if the adhesive has reducing properties, the reducing effect is more likely to occur.

[0063] Figure 2(b) shows a state in which an adhesive 25 has been applied to a solder precoat 23 that has been flattened and covered with an organic film 24. The adhesive 25 is applied to the solder precoat 23 of the circuit member 10X via the organic film 24, for example, by a printing method. That is, although not shown, a mask having an opening corresponding to the solder precoat 23 is placed on the circuit member 10X, the adhesive 25 is applied to the circuit member 10X via the mask, and then the mask is removed from the circuit member 10X, resulting in a circuit member 10X in which the adhesive 25 has been applied to the solder precoat 23 via the organic film 24. The adhesive 25 may bridge the nearest electrodes 11, as shown in Figure 2(b).

[0064] Figure 2(c) shows a circuit member 10X in which an electronic component 30 is mounted on a solder precoat 23 via an organic film 24 and an adhesive 25. The adhesive 25 serves to temporarily fix the electronic component 30 on the solder precoat 23 until it is mounted on the circuit member 10X by reflow soldering. In the illustrated example, the electronic component 30 is a chip component having a pair of lead terminals 30L on the left and right sides of the paper. The pair of lead terminals 30L are aligned so that each is joined to an adjacent pair of electrodes 11.

[0065] (3rd step) Next, the electronic component 30 is mounted onto the circuit member 10X by reflow soldering. Figure 3 schematically shows the changes in the state of the solder precoat 23, organic film 24, and adhesive 25 during reflow soldering.

[0066] Figure 3(a) shows a circuit member 10X in which an electronic component 30 is mounted on a solder precoat 23 via an organic film 24 and an adhesive 25, which is introduced into a reflow apparatus and heated, causing the organic film 24 and adhesive 25 to liquefy and become miscible, forming a single liquid phase 245. Upon heating, the organic film 24 and adhesive 25 soften and then liquefy. The adhesive 25 contains a sufficient amount of solvent. Until the miscible between the softened or liquefied adhesive 25 and the organic film 24 has sufficiently progressed, at least a portion of the solvent remains in the liquid phase 245 without volatilizing.

[0067] Figure 3(b) shows the state in which the solder precoat 23 has melted, generating molten solder 23m, and the molten solder 23m has wetted and spread over the lead terminals 30L of the electronic component 30. That is, the electrode 11 of the circuit member 10 and the lead terminals 30L of the electronic component 30 are connected by the molten solder 23m. Note that if the electronic component is smaller than or equal to the 0402 size specified in the JIS standard and has multiple terminals (e.g., lead terminals 30L) connected to the solder precoat, the weight of the electronic component per terminal is, for example, 0.05 mg or less. In this case, the amount of terminal sinking becomes small, so the hurdle for ensuring a secure connection with the molten solder 23m is generally higher. Allowing sufficient compatibility between the adhesive 25 and the organic film 24 is important for ensuring the amount of terminal sinking and achieving a good connection between the electrode 11 and the lead terminals 30L.

[0068] Figure 3(c) shows the circuit member 10Y after it has cooled and the solder has solidified to form a solder joint 23s. The surface of the solder joint 23s is covered with residue 27 of the organic film 24 and adhesive 25. The residue 27 is cleaned as needed.

[0069] Next, a modified example of the manufacturing method for the electronic component mounting substrate described above will be explained.

[0070] Figure 4(a) shows a circuit member 10X having another solder precoat 23. The solder precoat 23 is also formed between a pair of electrodes 11, forming a bridge 231 between the pair of electrodes 11. Because the electrodes 11 of the circuit member 10 are minute, such bridges 231 can occur when forming the solder precoat 23.

[0071] The bridge 231 can generally be resolved when the solder precoat 23 melts and molten solder 23m is generated, and the molten solder 23m is attracted to the electrode 11 and lead terminal by the surface adhesion of the molten solder 23m. However, if the electrode 11 is a microelectrode for joining electronic components 30 smaller than the size of 0402 (e.g., 0402, 0201, 03015, 01005), the bridge 231 may be difficult to resolve due to the influence of the organic film 24. The adhesive 25 used in this embodiment contains a sufficient amount of solvent, so the organic film 24 is converted to the liquid phase 245 relatively easily, but it is beneficial to construct a process that can more reliably resolve the bridge 231.

[0072] In this modified example, after the process of flattening the solder precoat 23 shown in Figure 4(b), a notch 232 is formed in the center of the bridge 231 with the tip of a blade member 50 having a sharp tip, as shown in Figure 4(c). Then, an adhesive 25 is applied onto the solder precoat 23 via the organic film 24 (Figure 4(d)), and the electronic component 30 is mounted onto the solder precoat 23 via the organic film 24 and the adhesive 25 (Figure 5(a)).

[0073] Next, when the circuit component 10X is introduced into the reflow apparatus, the organic film 24 and adhesive 25 liquefy to form a liquid phase 245 (Figure 5(b)). Subsequently, the solder precoat 23 melts and molten solder 23m is formed. The molten solder 23m wets and spreads over the lead terminals 30L of the electronic component 30, and is easily separated starting from the notch 232, as shown in Figure 5(c). Thus, when the solder solidifies and a solder joint 23s is formed, a circuit component similar to the circuit component Y shown in Figure 3(c) is obtained (Figure 5(d)).

[0074] The adhesives relating to this disclosure will be further described below based on examples, but the following examples are not intended to limit the present invention.

[0075] Example 1 (1) Preparation of circuit components A circuit component 10 was prepared by forming a solder precoat 23 on a substrate having electrodes 11 for mounting electronic components (0402 size chip capacitors). The solder paste, which is the raw material for the solder precoat 23, is a mixture of solder particles (average particle size 20 μm, melting point 217°C) and flux, with a solder particle content of 90% by mass. The main component of the flux is a rosin-based resin. The surface of the solder precoat 23 is covered with flux residue (organic film 24).

[0076] (2) Preparation of adhesive To 60 parts by mass of a rosin-based resin, which is the main resin, 20 parts by mass of adipic acid, which is an activator, and 10 parts by mass of hydrogenated castor oil, which is a thixotropic agent, were added. Then, hexyl carbitol, which is a solvent, was added so that its content relative to the adhesive was 10% to 50% by mass, as shown in Table 1, to obtain several adhesives 25.

[0077] (3) Evaluation (3-1) Tack test As previously described, the adhesive strength of the adhesive was evaluated in accordance with JIS Z 3284-3. Here, a predetermined amount of adhesive was printed onto a test ceramic plate using a mask, and the force required to peel it off by pressing a probe against it was measured. A "TK-1" tack force tester manufactured by Malcolm Corporation was used. The following indicators are shown in Table 1. Less than 0.5N: × 0.5N or higher, less than 1.0N: △ 1.0N or higher: ○

[0078] (3-2) Compatibility An adhesive 25 was screen printed onto a solder precoat 23 via an organic film 24, and an electronic component 30 was mounted on the adhesive 25. Subsequently, the electronic component 30 was mounted by reflow soldering, and the shear strength of the solder joint was evaluated. When the compatibility is low, the molten solder and the lead terminals of the electronic component (chip capacitor) cannot make sufficient contact, or the lead terminals do not sink in sufficiently, resulting in low shear strength. A universal bond tester "4000plus" manufactured by Nordson Advanced Technologies, Inc. was used as the measurement device, and the value when shearing from the long side of the chip capacitor was evaluated using the following index. Less than 0.3N: × 0.3N or higher, less than 0.7N: △ 0.7N or higher: ○

[0079] [Table 1]

[0080] Table 1 shows that when the solvent content in the adhesive is between 25% by mass and 40% by mass, an adhesive with an excellent balance of compatibility with organic films and tack strength can be obtained.

[0081] Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention. [Industrial applicability]

[0082] This disclosure is useful in the field of manufacturing electronic component mounting boards by mounting electronic components on circuit members having a solder precoat. This disclosure is particularly useful in the manufacturing of electronic component mounting boards using extremely small components of 0402 size or smaller, or electronic components with a self-weight (weight) of 0.05 mg or less per terminal. [Explanation of Symbols]

[0083] 10, 10X, 10Y: Circuit components 11: Electrode 12: Mask 12a:Aperture 20: Solder paste 21: Solder particles 22: Flux 23: Handa Precoat 23m: Molten solder 23s: Solder joint 231: Bridge 232: Notch 24:Organic film 245:Liquid phase 25: Adhesive 27: Residue 30: Electronic components 30L: Lead terminal 40: Jig with a flat pressing surface 50: Blade component

Claims

1. A step of preparing a circuit component comprising a solder precoat in which at least a portion is covered with an organic film containing 99% or more by mass of flux residue as an organic material, A step of applying an adhesive for temporarily fixing electronic components onto the solder precoat such that at least a portion of the organic film is covered, A step of mounting the electronic component onto the solder precoat via the adhesive, The process of reflowing the solder precoat to mount the electronic components onto the circuit member, It is equipped with, The adhesive comprises a main resin containing a rosin-based resin or an acrylic resin, and a solvent for dissolving the main resin. The solvent content is 25% by mass or more and 40% by mass or less. A method for manufacturing an electronic component mounting substrate, wherein the solvent comprises at least one selected from the group consisting of alcohol-based solvents, ester-based solvents, glycol-based solvents, ketone-based solvents, and hydrocarbon-based solvents, and dissolves the organic film covering the solder precoat when the solder precoat is reflowed, and the flux residue mainly consists of the resin contained in the adhesive or a heat-modified product thereof.

2. The method for manufacturing an electronic component mounting substrate according to claim 1, wherein the organic film contains an antioxidant.

3. The method for manufacturing an electronic component mounting substrate according to claim 1, wherein the flux residue contained in the organic film is a residue generated when forming the solder precoat.

4. The method for manufacturing an electronic component mounting substrate according to any one of claims 1 to 3, wherein the adhesive further comprises an activator that reduces the oxide film covering the surface of the solder precoat.

5. A method for manufacturing an electronic component mounting substrate according to any one of claims 1 to 4, wherein the electronic component is no larger than or equal to the 0402 size specified in the JIS standard.

6. A method for manufacturing an electronic component mounting substrate according to any one of claims 1 to 5, wherein the electronic component has a plurality of terminals connected to the solder precoat, and the self-weight of the electronic component per terminal is 0.05 mg or less.

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