Soldering flux and method for producing a bonded body

Abstract

Provided is a flux that can be used for mounting of indium sheet, has high wettability even in relatively low-temperature joining, and has improved void generation suppression ability. The flux contains rosin, an organic acid, and a solvent (S). The organic acid contains a monocarboxylic acid (A1) having a melting point of 35°C or higher and 90°C or lower, and the solvent (S) contains a solvent (S1) having a boiling point of 100°C or lower.

Description

Technical Field

[0001] This invention relates to flux and a method for preparing a solder joint. This application claims priority based on Japanese Patent Application No. 2022-135185, filed on August 26, 2022, the contents of which are incorporated herein by reference. Background Technology

[0002] In recent years, there has been a growing demand for higher capacity and higher speed in electronic devices. The highly integrated bare chips mounted on these devices generate a significant amount of heat during operation. Therefore, it is necessary to effectively dissipate this heat by installing heat sinks or similar devices on the bare chips.

[0003] In contrast, for example, Patent Document 1 proposes a scheme to sandwich a polymer-containing thermal interface material (TIM) between the bare chip and the heat sink cover in order to transfer the heat generated by the operation of the bare chip to the heat sink more efficiently.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Publication No. 2010-539706 Summary of the Invention

[0007] The problem to be solved by the present invention

[0008] As a TIM (Technical Insulation Model), a sheet material composed solely of indium (hereinafter referred to as indium sheet) is proposed. Indium has low hardness compared to other metallic elements, and the indium sheet exhibits high conformability and adhesion to the surfaces of the bare die and the heatsink. Therefore, the indium sheet provides high heat transfer efficiency from the bare die to the heatsink-equipped heatsink. Consequently, by using the indium sheet, the heat dissipation efficiency of the bare die operation can be improved.

[0009] In indium sheet assembly, an indium sheet coated with flux is used to bond a heatsink-equipped cover to a bare die. Because indium has a relatively low melting point of 156°C, the indium sheet bonding is performed using reflow soldering at lower temperatures compared to typical bonding methods.

[0010] When mounting indium sheets using conventional soldering flux at conditions such as 170°C, the flux does not wet and spread on the surface of the indium sheet but accumulates on the bonding surface, potentially creating numerous voids. These voids reduce the efficiency of heat transfer from the bare die through the indium sheet to the heatsink cover, resulting in reduced efficiency of heat dissipation from the operation of the bare die.

[0011] Therefore, the object of the present invention is to provide a flux that is suitable for mounting indium sheets, exhibits high wettability even in bonding at relatively low temperature conditions, and improves the ability to suppress void formation.

[0012] Problem-solving methods

[0013] The present invention includes the following methods.

[0014] [1] A flux containing rosin, an organic acid and a solvent (S), wherein the organic acid contains a monocarboxylic acid (A1) with a melting point above 35°C and below 90°C, and the solvent (S) contains a solvent (S1) with a boiling point below 100°C.

[0015] [2] According to the flux described in [1], wherein the molecular weight of the monocarboxylic acid (Al) is 180 or more and 350 or less.

[0016] [3] According to the flux described in [1] or [2], wherein the content of the solvent (S1) is 50% by mass or more relative to the total mass of the solvent (S).

[0017] [4] The flux according to any one of [1] to [3], wherein the flux further contains an alkanolamine.

[0018] [5] The flux according to any one of [1] to [4], wherein the content of the monocarboxylic acid (Al) is 0.5% by mass or more and 20% by mass or less relative to the total mass of the flux.

[0019] [6] The flux according to any one of [1] to [5], wherein the monocarboxylic acid (A1) contains palmitic acid, and the content of palmitic acid is 60% by mass or more relative to the total mass of the monocarboxylic acid (A1).

[0020] [7] The flux according to any one of [1] to [6], wherein the rosin content is 10% by mass or more and 50% by mass or less relative to the total mass of the flux.

[0021] [8] A method for preparing a bonding body, wherein the bonding body is formed by bonding a bare chip and a cover via a thermal interface material (TIM), wherein the TIM is an indium sheet, and the flux described in any one of [1] to [7] is between the TIM and the bare chip or between the TIM and the cover, and the bonding is performed by reflow soldering.

[0022] [9] According to the method for preparing the joint as described in [8], the reflow soldering method is performed at a temperature below 200°C.

[0023] Effects of the present invention

[0024] According to the present invention, a flux can be provided that is suitable for mounting indium sheets, exhibits high wettability even in joints at relatively low temperatures, and improves the ability to suppress void formation. Attached Figure Description

[0025] Fig. 1 This is an embodiment of a method for preparing a bonding assembly, showing a cross-sectional view of the cap, TIM, and bare die.

[0026] Fig. 2 This is a cross-sectional view of one embodiment of a method for preparing a bonding assembly, showing the process of applying flux to a TIM and a bare die.

[0027] Fig. 3 This is an embodiment of a method for preparing a bonding assembly, showing a cross-sectional view of the bonding assembly obtained by fixing a cap to a substrate using a TIM after applying flux. Detailed Implementation

[0028] (Fluoride)

[0029] The flux of this embodiment contains rosin, an organic acid, and a solvent (S). The organic acid contains a monocarboxylic acid (Al) with a melting point of 35°C or higher and 90°C or lower. The solvent (S) contains a solvent (S1) with a boiling point of 100°C or lower.

[0030] In indium sheet mounting, a heatsink-equipped cover is bonded to a bare die by reflow soldering at low temperatures (e.g., 170°C). In conventional fluxes, the flux does not wet and spread on the surface of the indium sheet, but instead accumulates on the bonding surface, potentially creating numerous voids.

[0031] The flux according to this embodiment contains monocarboxylic acid (Al) with a melting point of 35°C or higher and 90°C or lower. The monocarboxylic acid (Al) can melt to a degree that easily releases gas even under low-temperature reflow soldering, and it can have sufficient wettability on indium sheets.

[0032] The flux in this embodiment contains monocarboxylic acid (Al), which has lower reactivity than dicarboxylic acid, thus making it easier to suppress the formation of voids.

[0033] Furthermore, the flux in this embodiment contains a solvent (S1) with a boiling point below 100°C, which will evaporate before the indium sheet melts, even during low-temperature reflow soldering. As a result, no voids from the solvent (S1) are generated when the indium melts.

[0034] Through these synergistic effects, the flux of this embodiment can suppress the formation of voids even during the mounting of indium sheets.

[0035] <Rosin>

[0036] In this invention, "rosin" includes natural resins containing a mixture of arosin acid and its isomers, with arosin acid as the main component, as well as substances obtained by chemically modifying natural resins (sometimes referred to as rosin derivatives).

[0037] For example, the total content of rosin acid and its isomers in natural resin is 40% by mass or more and 80% by mass or less relative to natural resin.

[0038] In this specification, "main component" refers to a component that constitutes a compound and is present in a concentration of 40% or more by mass.

[0039] Representative examples of isomers of abietic acid include neorosinic acid, longleaf abietic acid, and L-piperidine. The structure of abietic acid is shown below.

[0040] [Chemical Formula 1]

[0041]

[0042] Examples of "natural resins" include, for example, rosin, wood rosin, and oil rosin.

[0043] In this invention, "substances obtained by chemically modifying natural resins (rosin derivatives)" include substances obtained by subjecting the "natural resins" to one or more treatments selected from hydrogenation, dehydrogenation, neutralization, alkyl epoxide addition, amidation, dimerization and polymerization, esterification and Diels-Alder cyclization addition.

[0044] Examples of rosin derivatives include purified rosin and modified rosin.

[0045] Examples of modified rosin include, for example, hydrogenated rosin, polymerized rosin, polymerized hydrogenated rosin, disproportionated rosin, acid-modified rosin, rosin esters, acid-modified hydrogenated rosin, acid anhydride-modified hydrogenated rosin, acid-modified disproportionated rosin, acid anhydride-modified disproportionated rosin, phenol-modified rosin and α,β-unsaturated carboxylic acid modified products (acrylic acid modified rosin, maleic acid modified rosin, fumaric acid modified rosin, etc.), as well as purified products, hydrides and disproportions of the polymerized rosin, as well as purified products, hydrides and disproportions of the α,β-unsaturated carboxylic acid modified products, rosin alcohol, rosin amine, hydrogenated rosin alcohol, rosin esters, hydrogenated rosin esters, rosin soap, hydrogenated rosin soap, acid-modified rosin soap, etc.

[0046] As a rosin amine, such as a mixture of dehydrorosin amine, dihydrorosin amine, and tetrahydrorosin amine, it refers to the so-called disproportionated rosin amine. The structures of dehydrorosin amine, dihydrorosin amine, and tetrahydrorosin amine are shown below.

[0047] [Chemical Formula 2]

[0048]

[0049] Rosin can be used alone or in combination with two or more types.

[0050] The rosin preferably contains rosin derivatives, and more preferably contains one or more selected from acid-modified hydrogenated rosin and hydrogenated rosin.

[0051] The rosin content in the flux is preferably 5% by mass or more and 70% by mass or less relative to the total mass of the flux (100% by mass), more preferably 10% by mass or more and 50% by mass or less, and even more preferably 15% by mass or more and 45% by mass or less.

[0052] When the rosin content is above the lower limit of the range, the wettability of the flux is easily improved, and the formation of voids is easily suppressed. When the rosin content is below the upper limit of the range, the formation of voids is easily suppressed.

[0053] <Organic acids>

[0054] The flux of this embodiment contains organic acids, including monocarboxylic acids (Al) with a melting point of 35°C or higher and 90°C or lower. In addition to monocarboxylic acids (Al), the flux of this embodiment may also contain other organic acids.

[0055] Monocarboxylic acid (A1)

[0056] Monocarboxylic acids (Al) have melting points above 35°C and below 90°C. A monocarboxylic acid is a carboxylic acid with one carboxyl group within its molecule.

[0057] The melting point of the monocarboxylic acid (A1) is preferably 40°C or higher and 85°C or lower, more preferably 45°C or higher and 80°C or lower, even more preferably 50°C or higher and 72°C or lower, particularly preferably 55°C or higher and 66°C or lower, and most preferably 60°C or higher and 66°C or lower.

[0058] Because indium has a low melting point of 156°C, indium sheets are mounted using low-temperature reflow soldering (e.g., 170°C).

[0059] Since the melting point of monocarboxylic acid (Al) is above the lower limit of the range, the reaction between indium sheet and monocarboxylic acid (Al) during reflow soldering is easily suppressed, thus easily suppressing the generation of voids during reflow soldering.

[0060] Because the melting point of monocarboxylic acid (Al) is below the upper limit of the aforementioned range, the monocarboxylic acid (Al) in the flux melts easily during reflow soldering, thus making it easier for voids generated during reflow soldering to detach from the flux. Additionally, it easily improves the wettability of the flux.

[0061] The molecular weight of the monocarboxylic acid (A1) is preferably 180 or more and 350 or less, more preferably 190 or more and 310 or less, even more preferably 220 or more and 275 or less, particularly preferably 240 or more and 265 or less, and most preferably 250 or more and 260 or less.

[0062] By having the molecular weight of monocarboxylic acid (Al) above the lower limit of the range, the molar amount of monocarboxylic acid (Al) contained in the flux at the same content (mass%) becomes less, thus making it easier to suppress the formation of voids during reflow soldering.

[0063] By having the molecular weight of monocarboxylic acid (A1) below the upper limit of the range, the molar amount of monocarboxylic acid (A1) contained in the flux at the same content (mass%) increases, thus making it easier to improve the wettability of the flux.

[0064] Examples of monocarboxylic acids (A1) include aliphatic monocarboxylic acids or aromatic monocarboxylic acids, with aliphatic monocarboxylic acids being preferred.

[0065] Aliphatic monocarboxylic acids may or may not contain hydroxyl groups.

[0066] The hydrocarbon group of an aliphatic monocarboxylic acid can be any of straight-chain, branched, or cyclic. The hydrocarbon group is preferably straight-chain or branched, and more preferably straight-chain.

[0067] The hydrocarbon group can be a saturated hydrocarbon group or an unsaturated hydrocarbon group. The hydrocarbon group is preferably a saturated hydrocarbon group.

[0068] The number of carbon atoms in the aliphatic monocarboxylic acid is preferably 12 to 24, more preferably 12 to 18, even more preferably 14 to 17, particularly preferably 15 to 17, and most preferably 16.

[0069] When the monocarboxylic acid (A1) is a linear aliphatic monocarboxylic acid, examples of monocarboxylic acids (A1) include lauric acid (C12, 45°C, 200), tridecanoic acid (C13, 41°C, 214), myristic acid (C14, 54°C, 228), pentadecanoic acid (C15, 52°C, 242), palmitic acid (C16, 63°C, 256), heptadecanoic acid (C17, 61°C, 270), stearic acid (C18, 70°C, 284), nonadecanoic acid (C19, 69°C, 299), arachidic acid (C20, 76°C, 313), dodecanoic acid (C21, 75°C, 327), dodecanoic acid (C22, 76°C, 341), tridecanoic acid (C23, 80°C, 355), and tetradecanoic acid (C24, 84°C, 369). The information in parentheses refers to the number of carbon atoms, melting point, and molecular weight.

[0070] When the monocarboxylic acid (A1) is a linear aliphatic monocarboxylic acid, the monocarboxylic acid (A1) described above is preferably selected from one or more of lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid and stearic acid, more preferably selected from one or more of myristic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid and stearic acid, even more preferably selected from one or more of palmitic acid and stearic acid, and particularly preferably palmitic acid.

[0071] When the monocarboxylic acid (A1) is an aliphatic monocarboxylic acid containing a hydroxyl group, 12-hydroxystearic acid is preferred as the monocarboxylic acid (A1). 12-hydroxystearic acid has a melting point of 76.5°C, a molecular weight of 300, and 18 carbon atoms.

[0072] Monocarboxylic acids (A1) can be used alone or in combination with two or more.

[0073] The content of monocarboxylic acid (Al) relative to the total amount of the flux (100% by mass) is preferably 0.1% by mass or more and 30% by mass or less, more preferably 0.5% by mass or more and 20% by mass or less, further preferably 1% by mass or more and 20% by mass or less, particularly preferably 1% by mass or more and 15% by mass or less, and most preferably 3% by mass or more and 15% by mass or less.

[0074] By keeping the content of monocarboxylic acid (Al) above the lower limit of the range, the wettability of the flux is easily improved, and the formation of voids is easily suppressed. By keeping the content of monocarboxylic acid (Al) below the upper limit of the range, the formation of voids is easily suppressed.

[0075] The content of palmitic acid is preferably 60% by mass or more and 100% by mass or less relative to the total mass of monocarboxylic acid (A1).

[0076] By ensuring that the palmitic acid content is above the lower limit of the aforementioned range, it is easier to improve the ability to suppress void formation.

[0077] Other Organic Acids

[0078] Other organic acids include, for example, carboxylic acids and organic sulfonic acids. Carboxylic acids include, for example, aliphatic carboxylic acids and aromatic carboxylic acids. Aliphatic carboxylic acids include aliphatic monocarboxylic acids other than monocarboxylic acids (A1) and aliphatic dicarboxylic acids.

[0079] Examples of aliphatic monocarboxylic acids include hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, isononanoic acid, decanoic acid, decenoic acid, undecanoic acid, lindeic acid, myristoneuric acid, isopalmitic acid, palmitoleic acid, hexadecanetrienoic acid, cyclopentene undecanoic acid, isostearic acid, transoleic acid, parsleyic acid, stearatetraenoic acid, tung acid, tarric acid, isoleic acid, ricinoleic acid, piperidinic acid, stearic acid, linoleic acid, and linolenic acid.

[0080] Examples of aliphatic dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, dodecanoic acid, eicosanoic acid, tartaric acid, 2,4-diethylglutaric acid, diethylene glycol acid, 2-methylnonanediic acid, 4-(methoxycarbonyl)-2,4-dimethylundecanoic acid, 4,6-di(methoxycarbonyl)-2,4,6-trimethyltetrazoic acid, and 8,9-di(methoxycarbonyl)-8,9-dimethylhexadecanoic acid.

[0081] Examples of aromatic carboxylic acids include salicylic acid, dibutylaniline diethanolic acid, terephthalic acid, p-hydroxyphenylacetic acid, phenylsuccinic acid, phthalic acid, benzoic acid, 2,3-dihydroxybenzoic acid, 2-quinoline carboxylic acid, 3-hydroxybenzoic acid, p-anestic acid, pyridinecarboxylic acid, pyridinedicarboxylic acid, and 3-hydroxypyridinecarboxylic acid.

[0082] In addition, examples of carboxylic acids include tris(2-carboxyethyl) isocyanurate and 1,3-cyclohexanedicarboxylic acid.

[0083] In addition, hydroxycarboxylic acids can be cited as other organic acids.

[0084] Examples of hydroxycarboxylic acids include, for example, 2,2-bis(hydroxymethyl)propionic acid, 2,2-bis(hydroxymethyl)butyric acid, citric acid, isocitric acid, malic acid, tartaric acid, etc.

[0085] In addition, other organic acids include dimer acids, trimer acids, hydrogenated dimer acids as hydrides of hydrogenated dimer acids, and hydrogenated trimer acids as hydrides of hydrogenated trimer acids.

[0086] Examples of organic sulfonic acids include, for example, aliphatic sulfonic acids and aromatic sulfonic acids. Examples of aliphatic sulfonic acids include, for example, alkyl sulfonic acids and alkylol sulfonic acids.

[0087] The flux in this embodiment may or may not contain other organic acids.

[0088] Other organic acids can be used alone or in combination of two or more.

[0089] In the case where the flux of this embodiment contains other organic acids, the content of other organic acids relative to the total amount of the flux (100% by mass) can be more than 0% by mass and less than 10% by mass, more than 0% by mass and less than 7% by mass, more than 0% by mass and less than 5% by mass, more than 0% by mass and less than 3% by mass, more than 0% by mass and less than 2% by mass, more than 0% by mass and less than 1% by mass, more than 0% by mass and less than 0.5% by mass, more than 0% by mass and less than 0.3% by mass, or more than 0% by mass and less than 0.1% by mass.

[0090] Solvent (S)

[0091] The solvent (S) contains a solvent (S1) with a boiling point below 100°C. Examples of solvents (S1) include 2-propanol and ethanol.

[0092] Solvent (S1) can be used alone or in combination with two or more solvents.

[0093] The boiling point of the solvent (S1) is preferably 50°C or higher and 100°C or lower, more preferably 60°C or higher and 90°C or lower, and even more preferably 70°C or higher and 85°C or lower.

[0094] In this specification, boiling point refers to the temperature of a liquid at which its saturated vapor pressure equals one atmosphere (i.e., 10¹³ hPa).

[0095] In addition to solvent (S1), solvent (S) may also contain other solvents (S2).

[0096] Other solvents (S2) can be used alone or in combination of two or more.

[0097] The boiling point of the other solvent (S2) is above 100°C. Preferably, the boiling point of the other solvent (S2) is above 100°C and below 350°C, more preferably above 150°C and below 300°C, and even more preferably above 200°C and below 280°C.

[0098] Other solvents (S2) include, for example, alcohol solvents, glycol ether solvents, terpineols, etc.

[0099] Examples of alcohol-based solvents include 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, isobornylcyclohexanol, 2,4-diethyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol, 2,5-dimethyl-2,5-hexanediol, 2,5-dimethyl-3-hexyn-2,5-diol, 2,3-dimethyl-2,3-butanediol, 2-methylpentane-2,4-diol, 1,1,1-tris(hydroxymethyl)propane, 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, 1-ethynyl-1-cyclohexanol, 1,4-cyclohexanediol, 1,4-cyclohexanediol, 2,4,7,9-tetramethyl-5-decyn-4,7-diol, 2-hexyl-1-decanol, 2-methyl-2,4-pentanediol (hexanediol), octanediol, etc.

[0100] Examples of glycol ether solvents include diethylene glycol mono-2-ethylhexyl ether, ethylene glycol monophenyl ether, ethylene glycol monobutyl ether (ethylene glycol butyl ether), ethylene glycol monohexyl ether (ethylene glycol hexyl ether), diethylene glycol monohexyl ether (hexyl diethylene glycol), diethylene glycol dibutyl ether, triethylene glycol monobutyl ether, methyl glycerol, triethylene glycol butyl methyl ether, tetraethylene glycol, tetraethylene glycol dimethyl ether, and tripropylene glycol n-butyl ether.

[0101] Examples of terpineols include α-terpineol, β-terpineol, γ-terpineol, and mixtures of terpineols (i.e., mixtures whose main component is α-terpineol and which contain β-terpineol or γ-terpineol).

[0102] Other solvents include, for example, dioctyl sebacate (DOS) and liquid paraffin.

[0103] Other solvents can be used alone or in combination of two or more.

[0104] Relative to the total amount of the flux (100% by mass), the content of solvent (S) in the flux is preferably 10% by mass or more and 95% by mass or less, more preferably 25% by mass or more and 90% by mass or less.

[0105] Relative to the total amount of the flux (100% by mass), the content of the solvent (S1) in the flux is preferably 10% by mass or more and 95% by mass or less, more preferably 25% by mass or more and 90% by mass or less, and even more preferably 29.5% by mass or more and 88.5% by mass or less.

[0106] The content of solvent (S1) relative to the total mass of the solvent (S) is preferably 50% by mass or more and 100% by mass or less, more preferably 55% by mass or more and 100% by mass or less, further preferably 60% by mass or more and 100% by mass or less, particularly preferably 65% ​​by mass or more and 100% by mass or less, and may be 70% by mass or more and 100% by mass or less, or 80% by mass or more and 100% by mass or less, or 90% by mass or more and 100% by mass or less, or 95% by mass or more and 100% by mass or less, or 100% by mass or less.

[0107] By ensuring that the solvent (S1) content is above the lower limit of the aforementioned range, the ability to suppress void formation can be further improved. Additionally, the flux can be easily applied.

[0108] <Other Ingredients>

[0109] In addition to rosin, organic acids, and solvents (S), the flux in this embodiment may contain other components as needed.

[0110] Other components include resins other than rosin, surfactants other than organic acids, thixotropic agents, metal passivators, surfactants, silane coupling agents, antioxidants, colorants, etc.

[0111] Resin components other than rosin

[0112] Other resins besides rosin include, for example, terpene resins, modified terpene resins, terpene phenol resins, modified terpene phenol resins, styrene resins, modified styrene resins, xylene resins, modified xylene resins, acrylic resins, polyethylene resins, acrylic-polyethylene copolymer resins, ethylene-vinyl acetate copolymer resins, and other thermosetting resins.

[0113] Examples of modified terpene resins include aromatic modified terpene resins, hydrogenated terpene resins, and hydrogenated aromatic modified terpene resins. Examples of modified terpene phenol resins include hydrogenated terpene phenol resins. Examples of modified styrene resins include styrene acrylic resins and styrene maleic acid resins. Examples of modified xylene resins include phenol modified xylene resins, alkylphenol modified xylene resins, phenol-modified methylphenolic resin-type xylene resins, polyol modified xylene resins, and polyoxyethylene addition xylene resins.

[0114] Other thermosetting resins, for example, include epoxy resins.

[0115] Examples of epoxy resins include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, glycidylamine type resin, alicyclic epoxy resin, aminopropane type epoxy resin, biphenyl type epoxy resin, naphthalene type epoxy resin, anthracene type epoxy resin, triazine type epoxy resin, dicyclopentadiene type epoxy resin, triphenylmethane type epoxy resin, fluorene type epoxy resin, phenol aralkyl type epoxy resin, and phenolic varnish type epoxy resin.

[0116] The flux in this embodiment may not contain resin components other than rosin.

[0117] When the flux in this embodiment contains resin components other than rosin, the content of resin components other than rosin relative to the total amount of the flux (100% by mass) may exceed 0% by mass and be less than 10% by mass, or exceed 0% by mass and be less than 7% by mass, or exceed 0% by mass and be less than 5% by mass, or exceed 0% by mass and be less than 3% by mass, or exceed 0% by mass and be less than 2% by mass, or exceed 0% by mass and be less than 1% by mass, or exceed 0% by mass and be less than 0.5% by mass, or exceed 0% by mass and be less than 0.3% by mass, or exceed 0% by mass and be less than 0.1% by mass.

[0118] Surfactants other than organic acids

[0119] Examples of active agents other than organic acids include amines, halogenated compounds, and organophosphorus compounds.

[0120] [amine]

[0121] Examples of amines include azoles, guanidines, alkanolamines, alkylamine compounds, and amine polyoxyethylene adducts.

[0122] Examples of azoles include, for instance, 2-methylimidazole, 2-ethylimidazole, 2-undecylimidazole, 2-heptadecanylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 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-undecylimidazole trimellitate, 1-cyanoethyl-2-phenylimidazole trimellitate, and 2,4-diamino-6-[2'-methylimidazole-(1')]-ethyltrimethylimidazole. Azine, 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyltriazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyltriazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyltriazine isocyanuric acid adduct, 2-phenylimidazolyl isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazolium, 2-phenyl-4-methyl-5-hydroxymethylimidazolium, 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, 2-methylimidazoline, 2-phenylimidazoline, 2,4-diamino-6-vinyltriazine, 2,4-Diamino-6-vinyltriazine isocyanuric acid adduct, 2,4-diamino-6-methacryloyloxyethyltriazine, epoxy-imidazolium adduct, 2-methylbenzimidazole, 2-octylbenzimidazole, 2-pentylbenzimidazole, 2-(1-ethylpentyl)benzimidazole, 2-nonylbenzimidazole, 2-(4-thiazolyl)benzimidazole, benzimidazole, 1,2,4-triazole, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3',5'-di-tert-pentylphenyl)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]diethanol, 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, etc.

[0123] Examples of guanidines include, for example, 1,3-diphenylguanidine, 1,3-di-o-tolylguanidine, 1-o-tolylguanidine, 1,3-di-o-isopropylphenylguanidine, and 1,3-di-o-isopropylphenyl-2-propionylguanidine.

[0124] Examples of alkanolamines include, for example, N,N,N',N'-tetra(2-hydroxypropyl)ethylenediamine, N,N,N',N'-tetra(2-hydroxyethyl)ethylenediamine, monoethanolamine, diethanolamine, triethanolamine, 1-amino-2-propanol, bis(2-hydroxypropyl)amine, tri(2-hydroxypropyl)amine, etc.

[0125] Examples of alkylamine compounds include, for example, ethylamine, triethylamine, ethylenediamine, triethylenetetramine, cyclohexylamine, hexadecylamine, stearylamine, etc.

[0126] Examples of amine polyoxyethylene adducts include terminal diamine polyalkylene glycols, aliphatic amine polyoxyethylene adducts, aromatic amine polyoxyethylene adducts, and polyamine polyoxyethylene adducts.

[0127] Examples of epoxides that are added to amine polyoxyethylene adducts include ethylene oxide, propylene oxide, and butane oxide.

[0128] Terminal diamine polyalkylene glycols are compounds formed by amylating both ends of polyalkylene glycols.

[0129] Examples of terminal diamine polyalkylene glycols include, for example, terminal diamine polyethylene glycol, terminal diamine polypropylene glycol, and terminal diamine polyethylene glycol-polypropylene glycol copolymer.

[0130] Examples of terminal diamine polyethylene glycol-polypropylene glycol copolymers include polyethylene glycol-polypropylene glycol copolymer bis(2-aminopropyl) ether and polyethylene glycol-polypropylene glycol copolymer bis(2-aminoethyl) ether.

[0131] Aliphatic amine polyoxyalkylene adducts, aromatic amine polyoxyalkylene adducts, and polyamine polyoxyalkylene adducts are adducts in which a polyoxyalkylene group is bonded to the nitrogen atom of an amine. Examples of such amines include ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, hexamethylenediamine, diethylenetriamine, laurylamine, stearylamine, oleylamine, tallow amine, cured tallow amine, tallow propyl diamine, m-xylenediamine, toluenediamine, p-xyleneamine, phenylenediamine, isophoronediamine, 1,10-decanediamine, 1,12-dodecanediamine, 4,4-diaminodicyclohexylmethane, 4,4-diaminodiphenylmethane, butane-1,1,4,4-tetramine, and pyrimidine-2,4,5,6-tetramine.

[0132] Amines can be used alone or in combination with two or more.

[0133] As an amine, an alkanolamine is preferred, more preferably one or more selected from monoethanolamine, diethanolamine, triethanolamine and 1-amino-2-propanol, and even more preferably diethanolamine.

[0134] The content of the amine relative to the total mass of the flux is preferably 0.1% by mass or more and 5% by mass or less, more preferably 0.2% by mass or more and 3% by mass or less, and even more preferably 0.2% by mass or more and 1% by mass or less.

[0135] The flux of this embodiment, by containing amines, preferably alkanolamines, easily improves wettability and further enhances the ability to suppress void formation.

[0136] [Halogen compounds]

[0137] Examples of halogen compounds include, for example, hydrohalates and other organic halogen compounds.

[0138] Amino halides are compounds formed by reacting amines with hydrogen halides.

[0139] As an amine here, one can cite the amines mentioned above in "Amines".

[0140] Alternatively, halogen compounds other than amine hydrohalides can be used, for example, salts formed by reacting an amine with tetrafluoroboric acid (HBF4) or complexes formed by reacting an amine with boron trifluoride (BF3). Examples of such complexes include boron trifluoride piperidine.

[0141] Other halogenated compounds besides amine hydrohalates include, for example, halogenated aliphatic compounds. A halogenated aliphatic hydrocarbon group is a group in which some or all of the hydrogen atoms constituting the aliphatic hydrocarbon group are replaced by halogen atoms.

[0142] Halogenated aliphatic compounds include halogenated aliphatic alcohols and halogenated heterocyclic compounds.

[0143] Examples of halogenated aliphatic alcohols include, for example, 1-bromo-2-propanol, 3-bromo-1-propanol, 3-bromo-1,2-propanediol, 1-bromo-2-butanol, 1,3-dibromo-2-propanol, 2,3-dibromo-1-propanol, 1,4-dibromo-2-butanol, and trans-2,3-dibromo-2-buten-1,4-diol.

[0144] Examples of halocyclic heterocyclic compounds include those represented by the following general formula (h1).

[0145] R h11 -(R h12 ) n (h1)

[0146] [In the formula, R] h11 Represents an n-valent heterocyclic group. R h12 This indicates a halogenated aliphatic hydrocarbon group.

[0147] As R h11 The heterocycle with an n-valent heterocyclic group can be exemplified by a ring structure in which a portion of the carbon atom constituting an aliphatic or aromatic hydrocarbon ring is replaced by a heteroatom. Examples of heteroatoms in this heterocycle include oxygen, sulfur, and nitrogen atoms. This heterocycle is preferably a 3- to 10-membered ring, more preferably a 5- to 7-membered ring. Examples of such heterocycles include isocyanurate rings.

[0148] R h12 The halogenated aliphatic hydrocarbon group in the compound preferably has 1 to 10 carbon atoms, more preferably 2 to 6 carbon atoms, and even more preferably 3 to 5 carbon atoms. Additionally, R... h12 Preferably, it is a brominated aliphatic hydrocarbon group or a chlorinated aliphatic hydrocarbon group, more preferably a brominated aliphatic hydrocarbon group, and even more preferably a brominated saturated aliphatic hydrocarbon group.

[0149] Examples of halogenated heterocyclic compounds include, for example, tri-(2,3-dibromopropyl)isocyanurate.

[0150] In addition, examples of halogenated compounds other than aminohydrohalides include, for example, iodinated carboxyl compounds such as 2-iodobenzoic acid, 3-iodobenzoic acid, 2-iodopropionic acid, 5-iodosalicylic acid, and 5-iodoaminoanisic acid; chlorinated carboxyl compounds such as 2-chlorobenzoic acid and 3-chloropropionic acid; and halogenated carboxyl compounds such as brominated carboxyl compounds such as 2,3-dibromopropionic acid, 2,3-dibromosuccinic acid, and 2-bromobenzoic acid.

[0151] In addition, halogen compounds other than aminohydrohalides can be cited as examples of organochlorine compounds. Examples of organochlorine compounds include chlorinated alkanes, chlorinated fatty acid esters, chlorinated bactericidal acid, and chlorinated bactericidal anhydride.

[0152] Halogen compounds can be used alone or in combination of two or more.

[0153] Organophosphorus compounds

[0154] Examples of organophosphorus compounds include, for example, acidic phosphate esters, acidic phosphonates, and acidic hypophosphonates.

[0155] Organophosphorus compounds can be used alone or in combination of two or more.

[0156] Thixotropic agents

[0157] Examples of thixotropic agents include ester-based thixotropic agents, amide-based thixotropic agents, and sorbitol-based thixotropic agents.

[0158] Examples of ester-based thixotropic agents include, for example, ester compounds, specifically hydrogenated castor oil and ethyl myristate.

[0159] Examples of amide-based thixotropic agents include monoamides, diamides, and polyamides.

[0160] Examples of monoamides include laurylamide, palmitamide, stearamide, behenamide, hydroxystearamide, saturated fatty acid amide, oleamide, erucamide, unsaturated fatty acid amide, 4-methylbenzamide (p-toluamide), p-toluenemethaneamide, aromatic amide, hexamethylene hydroxystearamide, substituted amide, hydroxymethylstearamide, hydroxymethylamide, fatty acid ester amide, etc.

[0161] Examples of diamides include ethylenedicarboxylic acid (C6-24 carbon atoms in fatty acids) amides, ethylenedihydroxycarboxylic acid (C6-24 carbon atoms in fatty acids) amides, hexamethylenedicarboxylic acid (C6-24 carbon atoms in fatty acids) amides, hexamethylenedihydroxycarboxylic acid (C6-24 carbon atoms in fatty acids) amides, and aromatic diamides. Examples of fatty acids used as raw materials for these diamides include stearic acid (C18 carbon atoms), oleic acid (C18 carbon atoms), and lauric acid (C12 carbon atoms).

[0162] Examples of polyamides include saturated fatty acid polyamides, unsaturated fatty acid polyamides, aromatic polyamides, 1,2,3-propanetricarboxylic acid tris(2-methylcyclohexylamide), cyclic amide oligomers, and non-cyclic amide oligomers.

[0163] Examples of cyclic amide oligomers include amide oligomers obtained by condensing dicarboxylic acids and diamines into a cyclic form, amide oligomers obtained by condensing tricarboxylic acids and diamines into a cyclic form, amide oligomers obtained by condensing dicarboxylic acids and triamines into a cyclic form, amide oligomers obtained by condensing tricarboxylic acids and triamines into a cyclic form, amide oligomers obtained by condensing dicarboxylic acids and tricarboxylic acids and diamines into a cyclic form, amide oligomers obtained by condensing dicarboxylic acids and tricarboxylic acids and triamines into a cyclic form, amide oligomers obtained by condensing dicarboxylic acids and diamines and triamines into a cyclic form, and amide oligomers obtained by condensing dicarboxylic acids and tricarboxylic acids and diamines and triamines into a cyclic form.

[0164] Furthermore, examples of acyclic amide oligomers include those obtained by the condensation polymerization of monocarboxylic acids with diamines and / or triamines to form acyclic amide oligomers, and those obtained by the condensation polymerization of dicarboxylic acids and / or tricarboxylic acids with monoamines to form acyclic amide oligomers. When the amide oligomer contains a monocarboxylic acid or a monoamine, the monocarboxylic acid or monoamine functions as terminal molecules, resulting in acyclic amide oligomers with reduced molecular weight. Additionally, in the case of amide compounds obtained by the condensation polymerization of dicarboxylic acids and / or tricarboxylic acids with diamines and / or triamines to form acyclic amide compounds, the acyclic amide oligomer becomes an acyclic polymeric amide polymer. Furthermore, acyclic amide oligomers also include those obtained by the condensation polymerization of monocarboxylic acids and monoamines to form acyclic amide oligomers.

[0165] Examples of sorbitol-based thixotropic agents include, for example, dibenzylidene-D-sorbitol, di(4-methylbenzylidene)-D-sorbitol, (D-)sorbitol, monobenzylidene(-D-)sorbitol, and mono(4-methylbenzylidene)-(D-)sorbitol.

[0166] The flux of this embodiment may or may not contain a thixotropic agent. When the flux of this embodiment contains a thixotropic agent, a single thixotropic agent may be used, or two or more thixotropic agents may be used in combination.

[0167] Metal passivating agents

[0168] Examples of metal passivating agents include hindered phenolic compounds and nitrogen compounds.

[0169] The "metal passivating agent" mentioned here refers to a compound that has the property of preventing metals from deteriorating due to contact with a certain compound.

[0170] Hindered phenolic compounds are phenolic compounds that have a large substituent (such as a branched chain or cyclic alkyl group such as tert-butyl) at at least one ortho position of phenol.

[0171] Hindered phenolic compounds are not particularly limited; examples include bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionic acid][ethylene bis(oxyethylene)], N,N'-hexamethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionamide], 1,6-hexanediol bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 2,2'-dihydroxy-3,3 '-Bis(α-methylcyclohexyl)-5,5'-dimethyldiphenylmethane, 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-tert-butylimino)-1,3,5-triazine, pentaerythritol tetratetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2,2-thiodiethylidene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, N,N'-hexamethylene Compounds such as bis(3,5-di-tert-butyl-4-hydroxy-hydrogenated cinnamamide), 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)ethylcarbonyloxy]ethyl]oxalamide, and compounds represented by the following chemical formulas.

[0172] [Chemical Formula 3]

[0173]

[0174] (where Z represents a substituted alkylene group. R) 81 and R 82 Each can be independently a substituted alkyl, aralkyl, aryl, heteroaryl, cycloalkyl, or heterocycloalkyl group. 83 and R 84 Each is an alkyl group that can be substituted independently.

[0175] Nitrogen compounds used as metal passivating agents include, for example, hydrazide nitrogen compounds, amide nitrogen compounds, triazole nitrogen compounds, and melamine nitrogen compounds.

[0176] As nitrogen compounds of the acylhydrazine class, any nitrogen compound with an acylhydrazine skeleton is acceptable. Examples include dodecanoic acid bis[N2-(2-hydroxybenzoyl)hydrazine], N,N'-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine, decanedicarboxylic acid disalicylic acid hydrazine, N-salicyl-N'-salicylic acid hydrazine, m-nitrobenzoyl hydrazine, 3-aminophthalic acid hydrazine, phthalic acid dihydrazine, adipic acid hydrazine, oxaloyl di(2-hydroxy-5-octylphenylmethylene hydrazine), N'-benzoylpyrrolidone carboxylic acid hydrazine, and N,N'-bis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hydrazine.

[0177] As an amide-based nitrogen compound, any nitrogen compound with an amide skeleton is acceptable, such as N,N'-bis{2-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxy]ethyl}oxalamide.

[0178] As a triazole nitrogen compound, any nitrogen compound with a triazole skeleton is acceptable, such as N-(2H-1,2,4-triazol-5-yl)salicylic acid amide, 3-amino-1,2,4-triazole, 3-(N-salicylic acid)amino-1,2,4-triazole, etc.

[0179] As a melamine-based nitrogen compound, any nitrogen compound with a melamine skeleton is acceptable, including melamine and melamine derivatives. More specifically, examples include triaminotriazine, alkylated triaminotriazine, alkoxyalkylated triaminotriazine, melamine, alkylated melamine, alkoxyalkylated melamine, N2-butylmelamine, N2,N2-diethylmelamine, and N,N,N',N',N",N"-hexa(methoxymethyl)melamine.

[0180] Metal passivating agents can be used alone or in combination of two or more.

[0181] Surfactants

[0182] Examples of surfactants include, for instance, nonionic surfactants.

[0183] Examples of nonionic surfactants include, for instance, polyoxyethylene adducts.

[0184] Examples of epoxides derived from polyoxyethylene adducts include ethylene oxide, propylene oxide, and butane oxide.

[0185] Examples of polyoxyethylene adducts include, for example, polyethylene glycol, polypropylene glycol, polyethylene glycol-polypropylene glycol copolymer, ethylene oxide-resorcinol copolymer, polyoxyethylene acetylene glycol, polyoxyethylene glycerol ether, polyoxyethylene alkyl ether, polyoxyethylene ester, polyoxyethylene alkylamide, etc.

[0186] Alternatively, polyoxyethylene adducts of alcohols can be cited as nonionic surfactants. Examples of alcohols include, for instance, aliphatic alcohols, aromatic alcohols, and polyols.

[0187] Surfactants can be used alone or in combination of two or more.

[0188] Antioxidants

[0189] As antioxidants, examples include hindered phenolic antioxidants such as 2,2'-dihydroxy-3,3'-bis(α-methylcyclohexyl)-5,5'-dimethyldiphenylmethane.

[0190] The term "antioxidant" as used here refers to compounds that have the property of inhibiting the oxidation of solder alloys.

[0191] Antioxidants can be used alone or in combination of two or more.

[0192] During the installation of indium sheets, reflow soldering is performed at low temperatures because the melting point of indium, which makes up the sheets, is as low as 156°C.

[0193] The flux of this embodiment exhibits high wettability even in relatively low-temperature bonding and can improve the ability to suppress void formation. Although the reason for this effect is not yet certain, it is speculated as follows.

[0194] Monocarboxylic acids (Al) such as palmitic acid have lower melting points than dicarboxylic acids such as adipic acid. The flux of this embodiment, by containing monocarboxylic acids (Al) with relatively low melting points, can exert sufficient wetting properties even in reflow soldering at relatively low temperatures.

[0195] Compared to dicarboxylic acids, monocarboxylic acids (Al) have lower reactivity due to the carboxyl group, thus reducing the amount of voids resulting from the reaction between carboxylic acids and metal oxides.

[0196] Solvents (S1) with a boiling point below 100°C will evaporate even during low-temperature reflow soldering before the indium sheet melts. As a result, no voids from the solvent (S1) are generated when the indium melts.

[0197] Through these synergistic effects, the flux of this embodiment can suppress the formation of voids even during the mounting of indium sheets.

[0198] The flux of this embodiment, because it achieves the above-mentioned effects, is suitable for mounting indium sheets.

[0199] (Preparation method of the conjugate)

[0200] The method for preparing the bonding body in this embodiment is to use the flux described above to bond the bare die and the cover via a thermal interface material (TIM) to obtain the bonding body.

[0201] The preparation method of the joint in this manner will be illustrated by an example method that includes a flux application step, a cap installation step, and a reflow soldering step.

[0202] use Figs. 1-3 A preferred embodiment of the method for preparing the joint according to this method will be described. In the method for preparing the joint of this embodiment, as follows... Fig. 1 As shown, a substrate 40 is prepared to be equipped with a cover 10, a TIM 20, and a bare chip 41.

[0203] A metallization layer 42 is provided on the surface of the bare chip 41. The metallization layer 42 can be, for example, a Ni-plated layer, a Ni / Au-plated layer, etc. The metallization layer 42 can also have multiple layers with different compositions. The metallization layer 42 can be formed, for example, by sputtering or other methods.

[0204] The cover 10 has a metallization layer 11 on the surface opposite to the TIM 20. The metallization layer 11 can be the same as the metallization layer 42 of the bare chip 41. The cover 10 has a heat sink 12 on the surface opposite to the surface opposite to the TIM 20. The heat sink 12 can be made of, for example, metals such as aluminum, iron, or copper.

[0205] TIM20 is an indium sheet made entirely of indium. TIM20 is plate-shaped. The dimensions of TIM20 are equal to or smaller than the dimensions of the metallization layer 11 of the cover 10 and the metallization layer 42 of the bare chip 41.

[0206] <Fluorescence Application Process>

[0207] As flux 50, the flux 50 described in the above embodiment is preferably used. (See also...) Fig. 2 The flux application process is explained. Fig. 2 This is a cross-sectional view showing the TIM20 and the bare die 41 coated with flux 50. In the flux coating process, flux 50 is placed between the TIM20 and the bare die 41, and between the TIM20 and the cap 10.

[0208] In the flux application process, flux 50 is applied to the bonding surfaces (42a, 20b) of the bare chip 41 and TIM20 and the bonding surfaces (11a, 20a) of the cover 10 and TIM20.

[0209] Flux 50 is applied to the bonding surface as described below. Flux 50 is applied to the surface 42a of the metallization layer 42 of the bare die 41. Next, a TIM 20 is placed on the metallization layer 42 of the bare die 41 with flux 50 applied. Flux 50 is applied to the surface 20a of the TIM 20 stacked on the bare die 41, opposite to the surface 20b that contacts the bare die 41.

[0210] Examples of flux 50 application devices include spray flux applicators and foam flux applicators. Among these, spray flux applicators are preferred from the viewpoint of coating amount stability.

[0211] <Cover Installation Procedure>

[0212] In the cover mounting process, after applying flux 50 to the bonding surface, the cover 10 is fixed to the substrate 40 on which the TIM 20 and bare chip 41 are stacked. (Refer to...) Fig. 3 The installation process for the cover is explained. Fig. 3 This diagram shows a laminate 60 in which the cover 10 and the substrate 40 are bonded together by adhesive resin 43 after the flux 50 is applied.

[0213] In the cover mounting process, after applying flux 50, adhesive resin 43 is applied to one side of the substrate 40. Next, the cover 10 is heat-pressed onto the substrate 40, on which the TIM 20 and bare chip 41 are stacked, and the adhesive resin 43 is cured. Thus, the cover 10 is fixed relative to the substrate 40. Through the cover mounting process, a laminate 60 is obtained in which the cover 10 and the substrate 40 are bonded together by the adhesive resin 43.

[0214] <Reflow Soldering Process>

[0215] In the reflow soldering process, the laminate 60 is reflow soldered. Through reflow soldering, the cover 10 and the bare die 41 are bonded via TIM20.

[0216] The reflow soldering temperature is preferably below 200°C. Since indium, which constitutes the indium sheet used as the TIM, has a melting point of 156°C, the indium sheet can be bonded even at temperatures lower than normal reflow soldering temperatures. The reflow soldering temperature is preferably 160–200°C, more preferably 170–190°C.

[0217] According to the bonding method of the embodiment described above, the flux of the above embodiment exhibits excellent wettability even at low temperatures, thus easily improving the adhesion of the TIM to the cap and the bare die. As a result, the bare die and the cap can be bonded well by the TIM (i.e., indium sheet). Furthermore, since the amount of voids on the bonding surface of the indium sheet is reduced, the bonding body bonded in the above manner can efficiently dissipate the heat generated from the bare die.

[0218] (Other implementation methods)

[0219] As described above, the method for preparing the bonding body in this manner is to place flux 50 between TIM20 and bare chip 41, or between TIM20 and cap 10, at least one of these.

[0220] In the above embodiment, flux 50 is applied to the bonding surface 42a of the bare chip 41 with the TIM20 and the bonding surface 11a of the TIM20 with the cover 10, but the surfaces on which flux 50 is applied are not limited to these.

[0221] For example, in order to place the flux 50 between the TIM20 and the bare chip 41, the flux 50 can be applied to the bonding surface 20b of the TIM20 and the bare chip 41, or the flux 50 can be applied to the bonding surface 11a of the cover 10 and the TIM20.

[0222] Example

[0223] The present invention will be described below through embodiments, but the present invention is not limited to the following embodiments.

[0224] <Preparation of Flux>

[0225] (Examples 1-45, Comparative Examples 1-4)

[0226] The fluxes of the formulation examples and comparative examples are shown in Tables 1-6. The composition of the raw materials used is shown below. The composition percentages in Tables 1-6 are based on the total mass of the flux as 100% by mass, with blank columns indicating 0% by mass.

[0227] Rosin: Acrylic acid modified hydrogenated rosin, hydrogenated rosin

[0228] As organic acids, monocarboxylic acids (A1) and dicarboxylic acids are used.

[0229] Monocarboxylic acids (A1): Lauric acid (melting point 45℃, molecular weight 200), palmitic acid (melting point 63℃, molecular weight 256), stearic acid (melting point 70℃, molecular weight 284), 12-hydroxystearic acid (melting point 76.5℃, molecular weight 300).

[0230] Dicarboxylic acids: eicosanedioic acid, adipic acid, sebacic acid

[0231] Amine: Diethanolamine

[0232] As solvent (S), solvent (S1) and solvent (S2) are used.

[0233] Solvent (S1): 2-Propanol (boiling point 82℃)

[0234] Solvent (S2): Diethylene glycol monohexyl ether (boiling point 259℃)

[0235] The conjugate was prepared according to the evaluation method described in <Evaluation 1> below, and the evaluation of void generation inhibition ability and wettability were carried out. The evaluation results are shown in Tables 1 to 5.

[0236] <Evaluation 1>

[0237] Evaluation of the ability to suppress void generation

[0238] Method for preparing the conjugate:

[0239] Prepare a cover with an Au / Ni plating portion (8mm×8mm) on its surface, and a substrate with an Au / Ni plating portion (8mm×8mm) on its surface.

[0240] As solder sheet material, prepare an indium sheet consisting only of indium (size: 7mm × 7mm × 400μm). Spray 2mg of flux for each example onto the front and back sides of the indium sheet.

[0241] A 300μm thick copper plate is placed around the Au / Ni plating area of ​​the substrate as a spacer. Then, an indium sheet coated with flux is clamped between the cover and the Au / Ni plating area of ​​the substrate and fixed with a jig.

[0242] Next, the cover holding the solder sheet and the substrate are reflow soldered to obtain a joint. The reflow soldering is carried out in the atmosphere at a heating rate of 10°C / minute until it reaches 170°C.

[0243] Verification method:

[0244] The resulting bond was irradiated with X-rays perpendicular to the substrate, and the void area was determined by analyzing the transmitted X-rays. The measurement was performed using an XD7600NT (manufactured by Nordson). In the void area measurement, the presence of a void was considered confirmed when X-rays passed through at least one void. Voids with a diameter of 0.1 μm or larger were detected. The ratio of the total void area to the total area of ​​the indium sheet was then calculated as the void area percentage (%).

[0245] Judgment criteria:

[0246] A: The porosity is less than 10%.

[0247] B: The void area ratio is 10% or more but less than 15%.

[0248] C: The void area ratio is 15% or more.

[0249] Fluxes with an evaluation result of A or B are considered qualified, while fluxes with an evaluation result of C are considered unqualified.

[0250] Evaluation of wettability

[0251] Verification method:

[0252] As solder sheet material, prepare indium sheet material composed only of indium (size: 2mm×2mm×100μm).

[0253] 0.5 mg of flux was applied to both the front and back sides of the indium sheet. The flux-coated solder sheet was then placed on the Au / Ni electrode.

[0254] Next, the electrodes with indium sheets were reflow soldered under the following conditions: The reflow soldering temperature was increased to 180°C at a rate of 6°C / min, and held at 180°C for 3 minutes.

[0255] Next, after removing the flux, the area of ​​wetting spread is measured.

[0256] Judgment criteria:

[0257] A: The area of ​​the wetting extension is 2.5 mm. 2 above.

[0258] B: The area of ​​the infiltration extension is 2.0 mm. 2 Above and below 2.5mm 2 .

[0259] Fluxes with an evaluation result of A or B are considered qualified.

[0260] The evaluation methods described in <Evaluation 2> below were used to evaluate the ability to suppress void formation and the wettability. The results of these evaluations are shown in Table 6.

[0261] <Evaluation 2>

[0262] Evaluation of the ability to suppress void generation

[0263] As solder sheet material, a SAC alloy sheet (size: 7mm × 7mm × 400μm) is prepared, which is composed of a solder alloy with Ag of 3% by mass, Cu of 0.5% by mass and Sn as the balance.

[0264] Using SAC alloy sheets and the fluxes of Example 5 and Comparative Example 3, the verification was conducted using the same method as in Evaluation 1, "Evaluation of Void Generation Suppression Ability". The reflow soldering was performed in atmospheric conditions at a heating rate of 30°C / min until reaching 250°C.

[0265] Evaluation of wettability

[0266] As solder sheet material, a SAC alloy sheet (size: 2mm × 2mm × 100μm) is prepared, which is composed of a solder alloy with Ag of 3% by mass, Cu of 0.5% by mass and Sn as the balance.

[0267] Using SAC alloy sheets and the fluxes of Example 5 and Comparative Example 3, the wettability was verified using the same method as in Evaluation 1, "Evaluation of Wetting". The reflow soldering was performed by heating to 250°C at a rate of 6°C / min and holding at 250°C for 3 minutes.

[0268] [Table 1]

[0269]

[0270] The fluxes of Examples 1 to 9, which contain monocarboxylic acid (Al) with a melting point of 35°C or higher and 90°C or lower, are evaluated as having an A or B ability to suppress void formation.

[0271] The fluxes of Comparative Examples 1-4, which do not contain monocarboxylic acid (Al), were rated as C in terms of their ability to suppress void formation.

[0272] The flux of Example 5, which contains palmitic acid, was rated A for its ability to suppress void formation. The fluxes of Examples 7-9, which contain lauric acid, stearic acid, or 12-hydroxystearic acid, were rated B for their ability to suppress void formation.

[0273] The flux containing alkanolamine in Example 5 was rated A for its ability to suppress void formation and its wettability.

[0274] The flux of Example 6, which does not contain alkanolamines, was rated B in terms of void formation suppression ability and wettability.

[0275] [Table 2]

[0276]

[0277] The flux of Example 10, whose palmitic acid content is 60% or more by mass relative to the total mass of monocarboxylic acid (Al), was rated as A for its ability to suppress void formation.

[0278] The flux of Example 11, whose palmitic acid content is less than 60% by mass relative to the total mass of monocarboxylic acid (A1), was rated as having a void generation inhibition ability of B.

[0279] The flux of Example 12, in which the content of solvent (S1) is 65% by mass or more relative to the total mass of solvent (S), is rated as A for its ability to suppress void formation.

[0280] The flux of Example 13, in which the content of solvent (S1) is less than 65% by mass relative to the total mass of solvent (S), has an evaluation of B for its ability to suppress void formation.

[0281] [Table 3]

[0282]

[0283] [Table 4]

[0284]

[0285] [Table 5]

[0286]

[0287] The fluxes of Examples 15, 17-19, 22-25, 27, and 29-31, in which the total rosin content relative to the total mass of the flux is 15% to 45% by mass and the palmitic acid content relative to the total mass of the flux is 3% to 15% by mass, are rated as A in terms of void generation inhibition ability and wettability.

[0288] The fluxes of Examples 34 and 38, with a total rosin content of 10% by mass relative to the total mass of flux, were rated as B for void formation inhibition and wettability.

[0289] The fluxes of Examples 37, 41, and 45, with a total rosin content of 50% by mass relative to the total mass of flux, were rated as having a void generation inhibition ability of B.

[0290] The fluxes of Examples 26 and 38, with a palmitic acid content of 1% by mass relative to the total mass of the flux, were rated as B in terms of void formation inhibition ability and wettability.

[0291] The fluxes in Examples 20-21, 32-33, and 44-45, with a palmitic acid content of 20% by mass relative to the total mass of the flux, were rated as having a void generation inhibition ability of B.

[0292] [Table 6]

[0293]

[0294] In Evaluation 2, the void formation suppression ability and wettability were rated A when using SAC alloy sheet and the flux of Example 5. Furthermore, the void formation suppression ability and wettability were also rated A when using SAC alloy sheet and the flux of Comparative Example 3.

[0295] For the flux of Comparative Example 3, which does not contain monocarboxylic acid (Al), the void suppression capability is A when using SAC alloy sheet and C when using indium sheet. That is, indium sheet is more prone to void formation compared to SAC alloy sheet.

[0296] The flux of Example 5, which contains monocarboxylic acid (A1), is able to adequately suppress voids even when using indium sheets.

[0297] Industrial applicability

[0298] The flux of the present invention is suitable for preparing a high-efficiency heat dissipation bond where a heat sink cover and a bare chip are bonded together by an indium sheet.

[0299] Explanation of symbols

[0300] 10. Cover, 11. Metallization layer, 11a. Bonding surface, 12. Heat sink, 20. Thermal interface material (TIM), 20a and 20b. Bonding surfaces, 40. Substrate, 41. Bare die, 42. Metallization layer, 42a. Bonding surface, 43. Adhesive resin, 50. Flux, 60. Laminate

Claims

1. A flux comprising rosin, organic acid, solvent (S), and alkanolamine, The organic acid contains a monocarboxylic acid (Al) with a melting point above 35°C and below 90°C, and a molecular weight above 180 and below 350. The solvent (S) contains a solvent (S1) with a boiling point below 100°C. The rosin content, relative to the total mass of the flux, is 5% by mass or more and 70% by mass or less. The content of the monocarboxylic acid (Al) relative to the total mass of the flux is 0.1% by mass or more and 30% by mass or less. The solvent (S) content is 10% by mass or more and 90% by mass or less relative to the total mass of the flux. The content of solvent (S1) relative to the total mass of solvent (S) is 50% by mass or more and 100% by mass or less. The content of the alkanolamine relative to the total mass of the flux is 0.1% by mass or more and 5% by mass or less.

2. The flux according to claim 1, wherein The content of solvent (S1) is 65% by mass or more relative to the total mass of solvent (S).

3. The flux according to claim 1 or 2, wherein The content of the monocarboxylic acid (Al) relative to the total mass of the flux is 0.5% by mass or more and 20% by mass or less.

4. The flux according to claim 1 or 2, wherein, The monocarboxylic acid (A1) contains palmitic acid. The content of palmitic acid is 60% by mass or more relative to the total mass of the monocarboxylic acid (A1).

5. The flux according to claim 1 or 2, wherein The rosin content is 10% by mass or more and 50% by mass or less relative to the total mass of flux.

6. A flux comprising rosin, an organic acid, and a solvent (S), The organic acid contains a monocarboxylic acid (Al) with a melting point above 35°C and below 90°C, and a molecular weight above 180 and below 350. The solvent (S) contains a solvent (S1) with a boiling point below 100°C. The flux does not contain ethylene-vinyl acetate copolymer resin. The rosin content, relative to the total mass of the flux, is 10% by mass or more and 70% by mass or less. The content of the monocarboxylic acid (Al) relative to the total mass of the flux is 0.1% by mass or more and 30% by mass or less. The solvent (S) content is 10% by mass or more and 90% by mass or less relative to the total mass of the flux. The content of solvent (S1) relative to the total mass of solvent (S) is 50% by mass or more and 100% by mass or less.

7. The flux according to claim 6, wherein, The content of solvent (S1) is 65% by mass or more relative to the total mass of solvent (S).

8. The flux according to claim 6 or 7, wherein, The flux also contains alkanolamines.

9. The flux according to claim 6 or 7, wherein, The content of the monocarboxylic acid (Al) relative to the total mass of the flux is 0.5% by mass or more and 20% by mass or less.

10. The flux according to claim 6 or 7, wherein, The monocarboxylic acid (A1) contains palmitic acid. The content of palmitic acid is 60% by mass or more relative to the total mass of the monocarboxylic acid (A1).

11. The flux according to claim 6 or 7, wherein The rosin content is 10% by mass or more and 50% by mass or less relative to the total mass of flux.

12. A method for preparing a bonding assembly, wherein the bonding assembly is formed by bonding a bare die to a cover via a thermal interface material (TIM). wherein The TIM is indium sheet. The method includes a process of interposing a flux between at least one of the TIM and the bare chip or the TIM and the cap, and performing reflow joining, The flux contains rosin, an organic acid, and a solvent (S), The organic acid contains a monocarboxylic acid (A1) having a melting point of 35°C or higher and 90°C or lower and a molecular weight of 180 or higher and 350 or lower, The solvent (S) contains a solvent (S1) having a boiling point of 100°C or lower, The content of the rosin is 5% by mass or more and 70% by mass or less with respect to the total mass of the flux, The content of the monocarboxylic acid (A1) is 0.1% by mass or more and 30% by mass or less with respect to the total mass of the flux, The content of the solvent (S) is 10% by mass or more and 88.5% by mass or less with respect to the total mass of the flux, The content of the solvent (S1) is 50% by mass or more and 100% by mass or less with respect to the total mass of the solvent (S).

13. The method for producing a junction body according to claim 12, wherein The reflow joining is performed at lower than 200°C.

14. The method for producing a junction body according to claim 12 or 13, wherein The content of the solvent (S1) is 65% by mass or more with respect to the total mass of the solvent (S).

15. The method for producing a junction body according to claim 12 or 13, wherein The flux further contains an alkanolamine.

16. The method for producing a junction body according to claim 12 or 13, wherein The content of the monocarboxylic acid (A1) is 0.5% by mass or more and 20% by mass or less with respect to the total mass of the flux.

17. The method for producing a junction body according to claim 12 or 13, wherein The monocarboxylic acid (A1) contains palmitic acid, The content of palmitic acid is 60% by mass or more with respect to the total mass of the monocarboxylic acid (A1).

18. The method for producing a junction body according to claim 12 or 13, wherein The content of the rosin is 10% by mass or more and 50% by mass or less with respect to the total mass of the flux.

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