Flux and solder paste

Abstract

Invention details;

Description

Flux and solder paste

[0001] The present invention relates to a flux and a solder paste.

[0002] In recent years, the miniaturization of information devices has led to rapid progress in miniaturization and thinning of electronic components mounted on information devices. To meet the demand for thinner electronic components, ball grid arrays (BGA) with electrodes provided on the back surface are used to accommodate narrower connection terminals and smaller mounting areas (see, for example, Patent Document 1).

[0003] An example of an electronic component that uses a BGA is a semiconductor package. In a semiconductor package, a semiconductor chip having electrodes is sealed with resin, and solder bumps are formed on the electrodes of the semiconductor package. These solder bumps are formed by joining solder balls to the electrodes of the semiconductor package.

[0004] In a semiconductor package using BGA, each solder bump is aligned and placed on an electrode of a substrate to which solder paste has been applied, and the solder bump and electrode are joined by heating the solder paste to melt the solder paste, and the package is then mounted on the substrate.

[0005] The solder paste used here is a composition containing solder powder and flux. When the solder paste applied to the electrodes of the substrate is heated in a reflow furnace, the solder particles melt above their melting point, and the oxide film on the surface of the solder particles is removed by the action of the flux. This unifies the solder particles, completing the bonding between the solder bump and the electrode.

[0006] JP 2008-71779 A

[0007] In recent years, semiconductor packages using BGA have been required to be thinner, and semiconductor packages are becoming thinner. As semiconductor chips become thinner, warping of semiconductor packages caused by heating during reflow soldering increases at temperatures lower than the main activation temperature range of the flux, which was previously negligible, and this has become a new problem in soldering.

[0008] In the soldering process, as shown in FIG. 1 , solder bumps 2 are formed on electrodes (not shown) of a semiconductor package 1. Furthermore, solder paste 5A is applied to board electrodes 4 provided on a substrate 3. The solder bumps 2 of the semiconductor package 1 are placed on the board electrodes 4 to which the solder paste 5A has been applied. In the process prior to reflow, shown in FIG. 1( a), the solder bumps 2 and the solder paste 5A applied to the board electrodes 4 are in contact with each other. In the subsequent reflow process, the semiconductor package 1 is first heated at a low temperature, which causes warping throughout the semiconductor package 1. The warping is particularly severe at the component edges. As a result, while most of the solder paste 5A remains on the board electrodes 4, the solder bumps 2, with only a portion of the solder paste 5A still attached, peel off from the board electrodes 4 ( FIG. 1( b)). This creates a clearance (gap) between the solder bumps 2 and the solder paste 5A applied to the board electrodes 4.

[0009] Because the solder bumps 2 have peeled off from the substrate electrodes 4 in this way, the melting solder paste 5A and the substrate electrodes 4 do not have a sufficient contact area or time for solder bonding during the main heating process, or they cannot come into contact at all. As a result, the metal oxide film on the surface of the substrate electrodes 4 does not react sufficiently with the activator components in the flux, and the metal oxide film on the surface of the substrate electrodes 4 cannot be removed. As a result, the solder bumps and the electrodes are not sufficiently bonded, resulting in poor bonding. Alternatively, if the soldering process ends with the solder bumps 2 and the substrate electrodes 4 still separated, the solder bumps 2 and the substrate electrodes 4 are not sufficiently bonded, resulting in poor bonding.

[0010] The present invention has been made in consideration of these problems, and has an object to provide a flux for solder paste and a solder paste that can suppress peeling of solder bumps from board electrodes due to warping of components that occurs in a temperature range lower than the main activation temperature range of the flux, in particular.

[0011] The present inventors have discovered that by using a solder joint failure inhibitor having a specific structure, it is possible to obtain a solder paste that can be prevented from peeling off from the object to be joined, even when stress is applied due to warping of the substrate, etc., and have completed the present invention.

[0012] According to the present invention, there is provided a flux comprising a base resin, an activator, a thixotropic agent, a solvent, and an agent for suppressing solder joint failure, wherein the agent for suppressing solder joint failure is a copolymer comprising a structural unit represented by formula (1) and a structural unit represented by formula (2), the weight average molecular weight of the copolymer is 1,000 or more and 100,000 or less, and the agent for suppressing solder joint failure is contained in an amount of 1 mass % or more and 25 mass % or less relative to the total amount of the flux. In formula (1), R １ is a saturated or unsaturated, linear, branched or cyclic alkyl group having 1 to 24 carbon atoms, or a substituted or unsubstituted aryl group, In formula (2), R ２ is a group represented by formula (2-1), In formula (2-1), n ​​is an integer of 1 to 20, and R ２１ is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and R ２２ is a straight-chain, branched-chain, or cyclic alkylene group having 1 to 6 carbon atoms.

[0013] According to the present invention, there is provided a flux comprising a base resin, an activator, a thixotropic agent, a solvent, a polyoxyalkylene monoalkyl ether, and an inhibitor for suppressing solder joint failure, wherein the inhibitor for suppressing solder joint failure is a copolymer comprising a structural unit represented by formula (1) and a structural unit represented by formula (2), the weight average molecular weight of the copolymer is 1,000 or more and 100,000 or less, and the inhibitor for suppressing solder joint failure is contained in an amount of 1 mass % or more and 25 mass % or less with respect to the total amount of the flux. In formula (1), R １ is a saturated or unsaturated, linear, branched or cyclic alkyl group having 1 to 24 carbon atoms, or a substituted or unsubstituted aryl group, In formula (2), R ２ is a group represented by formula (2-1), In formula (2-1), n ​​is an integer of 1 to 20, and R ２１ is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and R２２ is a straight-chain, branched-chain, or cyclic alkylene group having 1 to 6 carbon atoms.

[0014] The present invention also provides a solder paste containing solder powder and the above-mentioned flux.

[0015] According to the present invention, there are provided a solder paste that can be prevented from peeling off from an object to be joined even when stress due to warping of a substrate or the like is applied, thereby preventing poor joining, and a flux for use in such a solder paste.

[0016] 1A and 1B are explanatory diagrams showing a soldering process using a conventional flux, and FIG. 1C are explanatory diagrams showing an example of the effects of the flux of the present embodiment.

[0017] Hereinafter, embodiments of the present invention will be described in detail. In this specification, the notation "X to Y" in the description of a numerical range means at least X and at most Y, unless otherwise specified. For example, "1 to 5 mass %" means at least 1 mass % and at most 5 mass %. In the description of groups (atomic groups) in this specification, notations that do not specify whether they are substituted or unsubstituted include both those that do not have a substituent and those that have a substituent. For example, the term "alkyl group" includes not only alkyl groups that do not have a substituent (unsubstituted alkyl groups) but also alkyl groups that have a substituent (substituted alkyl groups).

[0018] [Flux] (First embodiment) The flux in the first embodiment includes a base resin, an activator, a thixotropic agent, a solvent, and an agent for suppressing solder joint failure. In the flux of the first embodiment, the agent for suppressing solder joint failure is a copolymer including a structural unit represented by formula (1) and a structural unit represented by formula (2).

[0019]

[0020] In formula (1), R １ is a saturated or unsaturated, linear, branched or cyclic alkyl group having 1 to 24 carbon atoms, or a substituted or unsubstituted aryl group.

[0021]

[0022] In formula (2), R ２ is a group represented by formula (2-1).

[0023]

[0024] In formula (2-1), n ​​is an integer of 1 to 20, and R ２１ is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and R ２２ is a straight-chain, branched-chain, or cyclic alkylene group having 1 to 6 carbon atoms.

[0025] The flux of this embodiment contains a copolymer containing a structural unit represented by formula (1) and a structural unit represented by formula (2), thereby suppressing solder joint failure. Here, in the present invention, "joint failure" means, for example, the failure to form a joint between the solder and the object to be soldered (non-wet open: NWO). "Joint failure" can be measured, for example, by electrical resistance measurement. In the present invention, "suppression of joint failure" means, for example, a significant reduction in the frequency of joint failure when joining using a control solder or solder paste having the same composition but without the inhibitor of the present invention. The frequency of joint failure can be measured based on the NWO evaluation test described below. By containing the copolymer, the flux of this embodiment has excellent adhesion to solder bumps, thereby achieving a robust connection between the semiconductor package electrodes and the substrate electrodes. Therefore, a solder paste containing the flux of this embodiment does not peel off from the object to be joined even when stress due to warpage of the substrate is applied, resulting in suppression of joint failure between the solder bumps of the semiconductor package and the electrodes of the substrate. More specifically, when the solder paste containing the flux of this embodiment is used, even if the semiconductor package 1 warps due to heating in the reflow process, the solder bumps 2 do not peel off from the board electrodes 4, as shown in Fig. 1(b). By using the solder paste containing the flux of this embodiment, even if the semiconductor package 1 warps, the solder paste 5A does not peel off from both the board electrodes 4 and the solder bumps 2, as shown in Fig. 2, and therefore no clearance occurs between the solder bumps 2 and the board electrodes 4. This ensures bonding between the solder bumps 2 and the board electrodes 4.

[0026] Second Embodiment The flux of the second embodiment includes a base resin, an activator, a thixotropic agent, a solvent, a polyoxyalkylene monoalkyl ether, and an agent for suppressing solder joint defects. The flux of the second embodiment differs from the flux of the first embodiment in that it includes a polyoxyalkylene monoalkyl ether.

[0027] The components used in the fluxes of the first and second embodiments will be described in detail below.

[0028] (Solder joint failure inhibitor) The flux of the present embodiment contains, as a solder joint failure inhibitor, a copolymer (referred to as "copolymer P" in this specification) containing a structural unit represented by formula (1) and a structural unit represented by formula (2).

[0029]

[0030] In formula (1), R １ is a saturated or unsaturated, linear, branched or cyclic alkyl group having 1 to 24 carbon atoms, or a substituted or unsubstituted aryl group.

[0031]

[0032] In formula (2), R ２ is a group represented by formula (2-1).

[0033]

[0034] In formula (2-1), n ​​is an integer of 1 to 20, and R ２１ is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and R ２２ is a straight-chain, branched-chain, or cyclic alkylene group having 1 to 6 carbon atoms.

[0035] The flux of this embodiment contains the copolymer P, which suppresses solder joint failure. More specifically, the flux of this embodiment contains the copolymer P, which provides excellent adhesion to both the substrate electrodes and the solder bumps. This allows for a robust connection between the semiconductor package and the substrate electrodes. Therefore, a solder paste containing the flux of this embodiment does not peel off from the object to be joined even when stress is applied due to warpage of the substrate, thereby suppressing joint failure between the solder bumps of the semiconductor package and the electrodes of the substrate. The reasons for the above-mentioned effects achieved by using the copolymer P are not entirely clear. However, it is believed that, first, the copolymer P has high heat resistance and can maintain adhesion to the substrate electrodes and solder bumps even when exposed to high-temperature environments during the soldering process. Second, the copolymer P's high heat resistance is believed to have the effect of uniformly dispersing the solder powder in the solder paste, even in high-temperature environments.

[0036] In the structural unit represented by the above formula (1) in the copolymer P used in this embodiment, R １ is a saturated or unsaturated, linear, branched or cyclic alkyl group having 1 to 24 carbon atoms, or a substituted or unsubstituted aryl group. １ is a saturated linear alkyl group having 1 to 24 carbon atoms or an unsubstituted aryl group, and more preferably, R １ is a saturated linear alkyl group having 6 to 18 carbon atoms, a phenyl group, or an alkylphenyl group. １ By having the above structure, the copolymer P can have an excellent effect of suppressing solder joint defects.

[0037] Here, R １Examples of the saturated or unsaturated, linear, branched or cyclic alkyl group having 1 to 24 carbon atoms that can constitute the above include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a sec-pentyl group, a tert-pentyl group, a neopentyl group, a (n-)hexyl group, a (n-)heptyl group, a (n- ) octyl group, (n-) nonyl group, (n-) decyl group, (n-) udecyl group, (n-) dodecyl group, (n-) tridecyl group, (n-) tetradecyl group, (n-) pentadecyl group, (n-) hexadecyl group, (n-) heptadecyl group, (n-) octadecyl group, (n-) nanodecyl group, (n-) henicosyl group, (n-) docosyl group, (n-) tricosyl group, (n-) tetracosyl group, and the like. １ is a hexyl group, an octadecyl group, an (n-)octyl group (-C ８ H １７ ) is preferable in that copolymer P has an excellent effect of suppressing solder joint defects.

[0038] R １ Examples of the substituted or unsubstituted aryl group that can constitute the above group include a phenyl group, an alkylphenyl group, etc., and preferably a phenyl group or a methylphenyl group. The alkyl group in the alkylphenyl group is, for example, a saturated or unsaturated linear, branched, or cyclic alkyl group having 1 to 5 carbon atoms, and preferably a saturated linear alkyl group having 1 to 5 carbon atoms. Examples of the alkyl group in the alkylphenyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, etc. In the aryl group, the hydrogen atom of the aromatic ring such as a benzene ring may be substituted with, for example, another substituent, and examples of the other substituent include a hydroxy group, a halogen group, an amino group, an alkyl group, etc. Here, examples of the halogen group include a chlorine atom, a bromine atom, etc.

[0039] The proportion of the structural unit represented by formula (1) in all structural units of copolymer P is, for example, 20 to 80 mol %, preferably 30 to 70 mol %, and more preferably 40 to 60 mol %.

[0040] In the structural unit represented by the above formula (2) in the copolymer P used in this embodiment, R ２ is a group represented by the above formula (2-1). In the above formula (2-1), n ​​is an integer of 1 to 30, and R ２１ is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and R ２２ is a linear, branched, or cyclic alkylene group having 1 to 6 carbon atoms. In formula (2-1), n ​​is preferably an integer of 1 to 20, more preferably an integer of 4 to 15, and even more preferably an integer of 8 to 13. In formula (2-1), R ２１ is preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and more preferably an alkyl group having 1 or 2 carbon atoms (methyl group or ethyl group). ２２ is preferably a linear alkylene group having 1 to 6 carbon atoms, and more preferably an alkylene group having 2 or 3 carbon atoms. ２１ The O-group is preferably an oxyethylene group or an oxypropylene group. When copolymer P has the structural unit represented by formula (2), the dispersibility of the solder powder in the solder paste can be improved.

[0041] The proportion of the structural unit represented by formula (2) in all structural units of copolymer P is, for example, 20 to 80 mol %, preferably 30 to 70 mol %, and more preferably 40 to 60 mol %.

[0042] In a preferred embodiment, the copolymer P is a copolymer (p1) having a repeating structure represented by formula (p1).

[0043]

[0044] In formula (p1), l and m represent the molar contents in the copolymer (p1), l is greater than 0 and less than 1, and m is greater than 0 and less than 1; R １ is a saturated or unsaturated linear, branched or cyclic alkyl group having 1 to 24 carbon atoms; R ２ has the same definition as in the above formula (2).

[0045] The copolymer (p1) represented by formula (p1) may be an alternating copolymer in which the structural units are alternately bonded, a random copolymer in which the structural units are randomly layered, or a block copolymer in which the structural units are bonded in block units.

[0046] In another preferred embodiment, the copolymer P is a copolymer (p2) having a repeating structure represented by formula (p2).

[0047]

[0048] In formula (p2), l and m represent the molar contents in the copolymer (p2), l is greater than 0 and less than 1, and m is greater than 0 and less than 1; R ２ is defined as in the above formula (2). The copolymer (p2) represented by formula (p2) may also be an alternating copolymer in which the structural units are alternately bonded, a random copolymer in which the structural units are randomly layered, or a block copolymer in which the structural units are bonded in block units.

[0049] The copolymer (p2) corresponds to the case where the above formula (1) is a structural unit represented by formula (6). The structural unit represented by formula (6) is chemically robust. Therefore, the copolymer (p2) containing this structural unit has the effect of suppressing solder joint defects and can have high heat resistance.

[0050]

[0051] In one embodiment, the weight average molecular weight (Mw) of the copolymer P is, for example, 1,000 to 100,000. The lower limit of the weight average molecular weight (Mw) of the copolymer P is preferably 2,000 or more, more preferably 4,000 or more, even more preferably 6,000 or more, and particularly preferably 7,000 or more. The lower limit of the weight average molecular weight (Mw) of the copolymer P is preferably 50,000 or less, more preferably 40,000 or less, even more preferably 30,000 or less, and particularly preferably 20,000 or less.

[0052] In one embodiment, the number average molecular weight (Mn) of the copolymer P is, for example, 1000 to 4000, preferably 2000 to 3000. In one embodiment, the dispersity (Mw / Mn) of the copolymer P is, for example, 1.0 to 5.0, preferably 2.0 to 4.0, and more preferably 3.0 to 4.0. By using a copolymer P having a molecular weight and distribution within the above ranges, the dispersibility of the solder powder in the resulting solder paste is improved, and the solder joints can have high strength and high toughness. These values ​​can be determined by gel permeation chromatography (GPC) measurement using polystyrene as a standard substance.

[0053] (Method for producing agent for suppressing solder joint failure) A method for producing copolymer P used as an agent for suppressing solder joint failure will be described below. Copolymer P used in this embodiment can be obtained, for example, by introducing a group represented by formula (2-1) above into a copolymer of an olefin and / or vinyl aromatic compound and maleic anhydride represented by formula (p3) (hereinafter referred to as a "precursor polymer").

[0054]

[0055] In formula (p3), R １ has the same definition as in the above formula (1), l and m represent the molar contents in the precursor polymer (p3), l is greater than 0 and less than 1, and m is greater than 0 and less than 1.

[0056] More specifically, the copolymer P can be produced by reacting a precursor polymer (p3), which is a copolymer of an olefin and / or a vinyl aromatic compound with maleic anhydride, with an alcohol represented by the following formula (7) in the presence of a basic catalyst. The reaction of this precursor polymer (p3) with the compound of formula (7) esterifies the maleic anhydride moiety in the precursor polymer (p3), thereby obtaining the target copolymer P represented by formula (p). Here, the precursor polymer (p3) may be any of a random copolymer, an alternating copolymer, and a block copolymer. Since maleic anhydride is generally known as a monomer with strong alternating copolymerizability, the precursor polymer (p3) is typically an alternating copolymer.

[0057]

[0058] In formula (p), l and m represent the molar contents in copolymer P, l is greater than 0 and less than 1, m is greater than 0 and less than 1, and R １ is the same as defined in the above formula (1), and R ２ has the same definition as in the above formula (2).

[0059] The precursor polymer (p3) represented by formula (p3) may be produced by a polymerization reaction between an olefin or a vinyl aromatic compound and maleic anhydride, or a commercially available product may be used. The polymerization reaction between an olefin or a vinyl aromatic compound and maleic anhydride can be carried out using a known method of reacting an olefin or a vinyl aromatic compound with maleic anhydride in the presence of a polymerization initiator. Preferred olefins used to produce the precursor polymer (p3) are α-olefins such as ethylene, propylene, 1-butene, isobutene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-nonene, 1-decene, and 1-dodecene. Preferred vinyl aromatic compounds used to produce the precursor polymer (p3) include styrene, α-methylstyrene, p-methylstyrene, divinylbenzene, 1,1-diphenylethylene, N,N-dimethyl-p-aminoethylstyrene, and N,N-diethyl-p-aminoethylstyrene. From the viewpoint of production costs, styrene is preferably used. The olefin or vinyl aromatic compound may be used alone or in combination of two or more. Examples of the styrene-maleic anhydride copolymer used as the precursor polymer (p3) include the Xiran series (manufactured by Polyscope).

[0060] The step of introducing the group represented by formula (2-1) into the precursor polymer (p3) is carried out by reacting the precursor polymer (p3) with a compound represented by the following formula (7) in the presence of a basic catalyst:

[0061]

[0062] Here, in formula (7), n, R ２１ and R ２２ has the same definition as in formula (2-1).

[0063] The compound represented by formula (7) used in the above step includes polyoxyalkylene monoalkyl ethers, preferably polyethylene glycol monomethyl ethers or polyethylene glycol monoethyl ethers in which n is 1 to 30, or polypropylene glycol monomethyl ethers or polypropylene glycol monoethyl ethers in which n is 1 to 30. In the compound represented by formula (7), n is more preferably an integer of 1 to 20, even more preferably an integer of 4 to 15, and still more preferably an integer of 8 to 13.

[0064] In one embodiment, copolymer P may include a structural unit represented by formula (8), a structural unit represented by formula (9), or a structural unit represented by formula (10).

[0065]

[0066]

[0067]

[0068] In formula (9), R ２ has the same meaning as in the above formula (2). When copolymer P contains a structural unit represented by formula (8), a structural unit represented by formula (9), or a structural unit represented by formula (10), the content thereof is 1 to 10 mol % based on the total structural units of copolymer P.

[0069] The content of copolymer P in the flux is 1% by mass or more and 25% by mass or less, based on the total flux. In one embodiment, the lower limit of the content of copolymer P in the flux is preferably 1.5% by mass or more, more preferably 2% by mass or more, even more preferably 5% by mass or more, even more preferably 8% by mass or more, and particularly preferably 10% by mass or more, based on the total flux. In one embodiment, the upper limit of the content of copolymer P in the flux is preferably 24% by mass or less, more preferably 22% by mass or less, even more preferably 20% by mass or less, and particularly preferably 18% by mass or less, based on the total flux.

[0070] (Base Resin) Examples of base resins used in the flux of this embodiment include rosin-based resins, (meth)acrylic resins, urethane-based resins, polyester-based resins, phenoxy resins, vinyl ether-based resins, terpene resins, modified terpene resins (e.g., aromatic-modified terpene resins, hydrogenated terpene resins, hydrogenated aromatic-modified terpene resins, etc.), terpene-phenolic resins, modified terpene-phenolic resins (e.g., hydrogenated terpene-phenolic resins, etc.), styrene resins, modified styrene resins (e.g., styrene-acrylic resins, styrene-maleic resins, etc.), xylene resins, modified xylene resins (e.g., phenol-modified xylene resins, alkylphenol-modified xylene resins, phenol-modified resol-type xylene resins, polyol-modified xylene resins, polyoxyethylene-added xylene resins, etc.). These resins may be used alone or in combination of two or more. In this specification, the term "(meth)acrylic resin" refers to a concept that includes methacrylic resins and acrylic resins.

[0071] Among these, the base resin preferably contains a rosin-based resin. Examples of rosin-based resins include raw rosins such as gum rosin, wood rosin, and tall oil rosin, as well as derivatives obtained from raw rosins. Examples of derivatives include purified rosin, hydrogenated rosin, disproportionated rosin, polymerized rosin, and α,β-unsaturated carboxylic acid modified products (acrylated rosin, maleated rosin, fumarated rosin, etc.), as well as purified products, hydrogenated products, and disproportionated products of polymerized rosin, and purified products, hydrogenated products, and disproportionated products of α,β-unsaturated carboxylic acid modified products. These rosin-based resins may be used alone or in combination of two or more.

[0072] The content of the base resin in the flux is, for example, 10 to 60 mass % and preferably 20 to 50 mass % with respect to the total mass of the flux.

[0073] (Activator) The flux of this embodiment contains an activator that has a fluxing effect. Here, the fluxing effect means a reducing effect of removing an oxide film formed on the metal surface to which the solder paste is applied, and an effect of reducing the surface tension of the molten solder to promote the wettability of the solder to the joining metal surface. Examples of the activator include organic acids, organic halogen compounds, and amine hydrohalides.

[0074] Examples of organic acids include monocarboxylic acids, dicarboxylic acids, dicarboxylic anhydrides, and oxyacids. These may be used alone or in combination of two or more. Among these, polyvalent organic acids having two or more hydroxy groups and / or two or more carboxy groups in the molecule may be used.

[0075] Specific examples of organic acids include glutaric acid, adipic acid, azelaic acid, eicosane diacid, citric acid, glycolic acid, succinic acid, salicylic acid, diglycolic acid, dipicolinic acid, dibutylaniline diglycolic acid, suberic acid, sebacic acid, thioglycolic acid, terephthalic acid, dodecanedioic acid, parahydroxyphenylacetic acid, picolinic acid, phenylsuccinic acid, phthalic acid, fumaric acid, maleic acid, malonic acid, lauric acid, benzoic acid, tartaric acid, isopropyl alcohol, and the like. Examples of such an acid include tris(2-carboxyethyl) cyanurate, glycine, 1,3-cyclohexanedicarboxylic acid, 2,2-bis(hydroxymethyl)propionic acid, 2,2-bis(hydroxymethyl)butanoic acid, 2,3-dihydroxybenzoic acid, 2,4-diethylglutaric acid, 2-quinolinecarboxylic acid, 3-hydroxybenzoic acid, malic acid, p-anisic acid, stearic acid, 12-hydroxystearic acid, oleic acid, linoleic acid, and linolenic acid.

[0076] As the organic acid, dimer acid, trimer acid, hydrogenated dimer acid which is a hydrogenated product of dimer acid with hydrogen added, hydrogenated trimer acid which is a hydrogenated product of trimer acid with hydrogen added, etc. can also be used. Examples include dimer acids which are the reaction products of oleic acid and linoleic acid, trimer acids which are the reaction products of oleic acid and linoleic acid, dimer acids which are the reaction products of acrylic acid, trimer acids which are the reaction products of acrylic acid, dimer acids which are the reaction products of methacrylic acid, trimer acids which are the reaction products of methacrylic acid, dimer acids which are the reaction products of acrylic acid and methacrylic acid, trimer acids which are the reaction products of acrylic acid and methacrylic acid, dimer acids which are the reaction products of oleic acid, trimer acids which are the reaction products of oleic acid, dimer acids which are the reaction products of linoleic acid, trimer acids which are the reaction products of linolenic acid, trimer acids which are the reaction products of linolenic acid, dimer acids which are the reaction products of acrylic acid and oleic acid, trimer acids which are the reaction products of acrylic acid and oleic acid, dimer acids which are the reaction products of acrylic acid and linoleic acid, acrylic acid and linoleic acid. Examples of the dimer acid include a trimer acid which is a reaction product of acrylic acid and linolenic acid, a dimer acid which is a reaction product of acrylic acid and linolenic acid, a dimer acid which is a reaction product of methacrylic acid and oleic acid, a trimer acid which is a reaction product of methacrylic acid and oleic acid, a dimer acid which is a reaction product of methacrylic acid and linoleic acid, a trimer acid which is a reaction product of methacrylic acid and linoleic acid, a dimer acid which is a reaction product of methacrylic acid and linolenic acid, a trimer acid which is a reaction product of methacrylic acid and linolenic acid, a dimer acid which is a reaction product of oleic acid and linolenic acid, a trimer acid which is a reaction product of oleic acid and linolenic acid, a dimer acid which is a reaction product of linoleic acid and linolenic acid, a trimer acid which is a reaction product of linoleic acid and linolenic acid, hydrogenated dimer acids which are hydrogenated products of the above-mentioned dimer acids, and hydrogenated trimer acids which are hydrogenated products of the above-mentioned trimer acids.

[0077] The organic halide preferably has a polar group such as a hydroxyl group or a carboxyl group, such as a halogenated alcohol or a halogenated carboxyl compound, in order to improve solubility in aqueous solvents. Examples of halogenated alcohols include brominated alcohols such as 2,3-dibromopropanol, 2,3-dibromobutanediol, trans-2,3-dibromo-2-butene-1,4-diol, 1,4-dibromo-2-butanol, and tribromoneopentyl alcohol, chlorinated alcohols such as 1,3-dichloro-2-propanol and 1,4-dichloro-2-butanol, fluorinated alcohols such as 3-fluorocatechol, and other compounds similar thereto. Examples of halogenated carboxyl compounds include iodinated carboxyl compounds such as 2-iodobenzoic acid, 3-iodobenzoic acid, 2-iodopropionic acid, 5-iodosalicylic acid, and 5-iodoanthranilic acid; chlorinated carboxyl compounds such as 2-chlorobenzoic acid and 3-chloropropionic acid; and brominated carboxyl compounds such as 2,3-dibromopropionic acid, 2,3-dibromosuccinic acid, and 2-bromobenzoic acid.

[0078] Examples of amine hydrohalides include reaction products of amines and hydrogen halides, such as ethylamine, diethylamine, triethylamine, ethylenediamine, cyclohexylamine, 1,3-diphenylguanidine, 1,3-di-o-tolylguanidine, and 1-o-tolylbiguanide, and examples of hydrogen halides include chlorine, bromine, and iodine hydrides.

[0079] The content of the activator in the flux is, for example, 1 to 20 mass % and preferably 5 to 15 mass % with respect to the total mass of the flux.

[0080] (Thixotropic Agent) The flux of this embodiment contains a thixotropic agent. The thixotropic agent has the effect of improving the flow characteristics of the flux and the solder paste obtained using the same. Examples of thixotropic agents include wax-based thixotropic agents and amide-based thixotropic agents. Examples of wax-based thixotropic agents include castor oil. Examples of amide-based thixotropic agents include lauric amide, palmitic amide, stearic amide, behenic amide, hydroxystearic amide, saturated fatty acid amide, oleic amide, erucic amide, unsaturated fatty acid amide, p-toluenemethane amide, aromatic amide, substituted amide, methylol stearic amide, methylol amide, fatty acid ester amide, etc. The amide-based thixotropic agent may be a bisamide-based thixotropic agent and / or a polyamide-based thixotropic agent. Examples of bisamide-based thixotropic agents include methylene bisstearic acid amide, ethylene bislauric acid amide, ethylene bishydroxystearic acid amide, saturated fatty acid bisamide, methylene bisoleic acid amide, unsaturated fatty acid bisamide, m-xylylene bisstearic acid amide, and aromatic bisamides. Examples of polyamide-based thixotropic agents include saturated fatty acid polyamides, unsaturated fatty acid polyamides, and aromatic polyamides.

[0081] The content of the thixotropic agent in the flux is, for example, 1 to 15 mass % and preferably 5 to 10 mass % with respect to the total mass of the flux.

[0082] (Solvent) The flux of this embodiment contains a solvent. The solvent is used to adjust the viscosity of the flux to a level appropriate for application. Examples of solvents that can be used include alcohol-based solvents, glycol ether-based solvents, terpineols, hydrocarbons, esters, water, and the like. These may be used alone or in combination of two or more. Among these, at least one of alcohol-based solvents and glycol ether-based solvents may be used.

[0083] Examples of alcohol-based solvents include isopropyl alcohol, 1,2-butanediol, isobornylcyclohexanol, 2,4-diethyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol, 2,5-dimethyl-2,5-hexanediol, 2,5-dimethyl-3-hexyne-2,5-diol, 2,3-dimethyl-2,3-butanediol, 1,1,1-tris(hydroxymethyl)ethane, 2-ethyl-2-hydroxymethyl-1,3-propanediol, 2,2'-oxybis(methylene)bis(2- ethyl-1,3-propanediol), 2,2-bis(hydroxymethyl)-1,3-propanediol, 1,2,6-trihydroxyhexane, bis[2,2,2-tris(hydroxymethyl)ethyl]ether, 1-ethynyl-1-cyclohexanol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, erythritol, threitol, guaiacol glycerol ether, 3,6-dimethyl-4-octyne-3,6-diol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, and the like.

[0084] Examples of glycol ether solvents include hexyl diglycol, diethylene glycol mono-2-ethylhexyl ether, ethylene glycol monophenyl ether, 2-methylpentane-2,4-diol, diethylene glycol monohexyl ether, diethylene glycol dibutyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol monomethyl ether.

[0085] Examples of ester solvents include diisobutyl succinate, dibutyl succinate, dimethyl adipate, diethyl adipate, dibutyl adipate, diisopropyl adipate, diisobutyl adipate, diisodecyl adipate, dibutyl maleate, dimethyl sebacate, diethyl sebacate, dibutyl sebacate, dioctyl sebacate, and diisopropyl decanedioate.

[0086] The content of the solvent in the flux can be selected in an amount that allows smooth application, taking into consideration the properties and amounts of the base resin and organic acid added, and is, for example, 10 to 60 mass %, and preferably 25 to 50 mass %, of the total flux.

[0087] (Polyoxyalkylene Monoalkyl Ether) The flux in the second embodiment contains a polyoxyalkylene monoalkyl ether. Examples of polyoxyalkylene monoalkyl ethers include polyethylene glycol monomethyl ether having a weight-average molecular weight of 76 to 5,000, polyethylene glycol monoethyl ether having a weight-average molecular weight of 90 to 5,000, polypropylene glycol monomethyl ether having a weight-average molecular weight of 90 to 5,000, and polypropylene glycol monoethyl ether having a weight-average molecular weight of 104 to 5,000. The lower limit of the weight-average molecular weight of the polyoxyalkylene monoalkyl ether used is preferably 200 or more, more preferably 300 or more, and even more preferably 400 or more. The upper limit of the weight-average molecular weight of the polyoxyalkylene monoalkyl ether used is preferably 3,000 or less, more preferably 2,000 or less, and even more preferably 1,500 or less. By using polyoxyalkylene monoalkyl ether, the application properties and handling properties of the resulting solder paste are improved, and therefore electronic circuit mounting boards produced using this paste have excellent connection reliability.

[0088] The content of the polyoxyalkylene monoalkyl ether in the flux of the second embodiment is, for example, 0.1 mass % to 10 mass %, or preferably 2 mass % to 8 mass %, based on the total mass of the flux.

[0089] (Other Components) The flux of the present embodiment may further contain an amine. The amine may function as a flux activator. Examples of amines include ethylamine, diethylamine, triethylamine, ethylenediamine, cyclohexylamine, 1,3-diphenylguanidine, 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, imidazole, 2-ethylimidazole, 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 4-methyl-2-phenylimidazole, 1-benzyl-2-methylimidazole, and 1-benzyl-2-phenylimidazole.

[0090] When the flux of the present embodiment contains an amine, the content of the amine is 0.1 mass % or more and 5 mass % or less, and preferably 1 mass % or more and 5 mass % or less, based on the total amount of the flux.

[0091] The flux of the present invention may further contain an antioxidant. The antioxidant can suppress oxidation of the solder powder. Examples of antioxidants include hindered phenol-based antioxidants, phenol-based antioxidants, bisphenol-based antioxidants, and polymer-type antioxidants. One type of antioxidant may be used alone, or two or more types may be used in combination.

[0092] The amount of the antioxidant in the flux is not particularly limited, and is, for example, 1 mass % or more and 10 mass % or less, and preferably 1 mass % or more and 5 mass % or less, based on the total amount of the flux.

[0093] The flux of this embodiment may further contain additives other than those described above, provided that the effects of the present invention are not impaired. Examples of additives include colorants, antifoaming agents, surfactants, and matting agents. The amount of the additives is not particularly limited and may be, for example, 0% by mass or more and 5% by mass or less based on the total amount of the flux.

[0094] [Solder Paste] The solder paste of this embodiment contains the above-mentioned flux and solder powder.

[0095] The type of solder powder (such as alloy composition) is not particularly limited, and specific examples include Sn—Ag alloy, Sn—Cu alloy, Sn—Ag—Cu alloy, Sn—In alloy, Sn—Pb alloy, Sn—Bi alloy, Sn—Ag—Cu—Bi alloy, and alloys in which Ag, Cu, In, Ni, Co, Sb, Ge, P, Fe, Zn, Ga, or the like is further added to the above alloy compositions.

[0096] The solder paste of this embodiment can usually be produced by mixing the above-mentioned flux with solder powder (metal powder). The mixing ratio of the flux and solder powder is not particularly limited, as long as the final solder paste has a viscosity that does not cause any practical problems. The mixing ratio of the flux and solder powder, in mass ratio, is typically flux:solder powder = 1:99 to 30:70, preferably flux:solder powder = 3:97 to 20:80, and more preferably flux:solder powder = 5:95 to 15:85.

[0097] The solder paste of this embodiment uses the above-mentioned flux, which can suppress solder joint defects, and therefore, by using the solder paste of this embodiment, it is possible to provide a highly reliable electronic circuit mounting board.

[0098] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations may be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention.

[0099] EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these.

[0100] <Preparation of Flux> The compositions of Examples 1 to 11 and Comparative Example 1 are shown in Table 1 below. The materials in the amounts shown in Table 1 below were mixed together and melted by heating to obtain uniformly dispersed fluxes of Examples 1 to 11 and Comparative Example 1.

[0101] The components listed in Table 1 are as follows: (Base resins) Base resin 1: acrylic acid modified hydrogenated rosin Base resin 2: maleic acid modified hydrogenated rosin (Activators) Activator 1: glutaric acid Activator 2: suberic acid Activator 3: azelaic acid Activator 4: succinic acid Activator 5: sebacic acid Activator 6: trans-2,3-dibromo-2-butene-1,4-diol Activator 7: 2-phenyl-4-methylimidazole (Thixotropic agents) Thixotropic agent 1: polyamide Thixotropic agent 2: hydrogenated castor oil (Solvents) Solvent 1: diethylene glycol monohexyl ether (Antioxidants) Antioxidant 1: hindered phenol antioxidant (Additives) Additive 1: mixture of polyethylene glycol monomethyl ethers with a weight average molecular weight of 400 to 800

[0102] (Bonding failure inhibitor) Inhibitor 1: A copolymer having a structural unit of the following formula (p1) (weight average molecular weight (Mw): 7855, number average molecular weight (Mn): 2058, Mw / Mn: 3.8).

[0103]

[0104] (In formula (p1), R １ is a decyl group, and R ２ is -(CH ２ -CH ２ -O-) ｎ -C ２ H ５ (Mixture of n = 8 to 13)

[0105] Inhibitor 2: A copolymer having a structural unit of the following formula (p2) (weight average molecular weight (Mw): 8495, number average molecular weight (Mn): 2397, Mw / Mn: 3.5)

[0106]

[0107] (In formula (p2), R ２ is -(CH ２ -CH ２ -O-) ｎ -C ２ H ５ (Mixture of n = 8 to 13)

[0108] <Preparation of Solder Paste> Solder pastes were prepared using the fluxes having the compositions shown in the above-mentioned examples and comparative examples. Specifically, the solder pastes of Examples 1 to 11 and Comparative Example 1 were prepared by mixing 12 mass % of each flux with 88 mass % of Sn-3Ag-0.5Cu (melting point 217°C) solder powder (particle size: 20 to 38 μm) based on the total solder paste.

[0109] <Solder Paste Performance Evaluation> The solder pastes of each Example and Comparative Example obtained by the above-described method were evaluated for the following performance. (NWO Evaluation) Each of the above-described solder pastes was evaluated for the occurrence of bonding failure (Non Wet Open: NWO). Specifically, each of the solder pastes was printed on a substrate (Cu-OSP-treated glass epoxy substrate) using a metal mask with an opening diameter of 0.30 mm, a mask thickness of 0.12 mm (120 μm), and 132 openings. A 0.5 mm pitch BGA was then mounted on the printed circuit board. This was heated in a reflow furnace at a heating rate of 3°C / sec from 25°C to 130°C, a heating rate of 1.0°C / sec from 130°C to 190°C, and a peak temperature of 200°C, and then cooled. After cooling, the substrate and BGA were peeled off. After peeling, the locations where the printed solder paste adhered to the solder bumps and where no solder paste adhered to the substrate side were considered to be locations where NWO occurred. The number of locations where NWO occurred was counted and recorded as "Number of NWO occurrences" in Table 1. Furthermore, a sample with 20 or fewer NWO occurrences was evaluated as having good bonding, and recorded as "◯" in Table 1. A sample with more than 20 NWO occurrences was evaluated as having poor bonding, and recorded as "X" in Table 1.

[0110] As described above with reference to Figure 1, BGAs can warp due to heating during the reflow process, causing the solder bumps to peel off from the board electrodes. If the soldering process is completed with the solder bumps and board electrodes separated, the solder bumps and board electrodes will not be sufficiently bonded together, resulting in poor bonding. In other words, this evaluation method makes it possible to estimate potential locations where NWO may occur.

[0111] (Reflowability (Fusibility)) The meltability of each of the above-mentioned solder pastes was evaluated by the following method. First, each of the solder pastes was printed on a substrate (Cu-OSP-treated glass epoxy substrate) using a metal mask with an opening diameter of 0.28 mm, a mask thickness of 0.1 mm, and 64 openings. This substrate was subjected to air reflow to melt the solder alloy using a reflow profile that included a heating rate of 4°C / sec from 50°C to 170°C, a heating rate of approximately 0.2°C / sec from 170°C to 195°C, a peak temperature of 236.5°C, and a melting time of 43 seconds at 220°C or higher. For the evaluation of meltability, a case in which all 64 printed points were melted was evaluated as "Good," and a case in which even one point was not melted was evaluated as "Poor." The results are shown in Table 1.

[0112] (Stability over time) For each of the above solder pastes, the viscosity was measured for 10 hours in the atmosphere at 25°C and a rotation speed of 10 rpm using a PCU-205 manufactured by Malcom Co., Ltd., in accordance with the JIS Z3284-3 spiral method. If the viscosity after 10 hours was 1.3 times or less compared to the initial viscosity of the solder paste, it was evaluated as having sufficient stability over time and was given a rating of "Good." If the viscosity exceeded 1.3 times, it was evaluated as "Poor." The initial viscosity refers to the viscosity at the start of continuous stirring. The results are shown in Table 1.

[0113] (Sagging behavior during heating) For each of the above solder pastes, the sagging behavior during heating in the reflow process was measured in accordance with JIS Z3284-3. Note that the metal mask used was one with a smaller hole diameter than that shown in Figure 6 of JIS Z3284-3. The minimum spacing within each pattern at which the printed solder paste did not all become one was measured visually. The smaller the minimum spacing, the better the shape retention during heating. Measurement results for minimum spacing of 0.4 mm or less were evaluated as "Good", and results of 0.5 mm or more were evaluated as "Poor".

[0114] (Adhesion (Tacking Property)) Measurements were carried out for each of the above solder pastes in accordance with JIS 3284-3. The measurement was carried out four times, and an average value of the force required to peel off the probe of 1.1 N or more was evaluated as "Good", and an average value of less than 1.1 N was evaluated as "Poor". A higher force required to peel off the probe indicates higher adhesion and better chip retention.

[0115]

[0116] As is clear from Table 1, when the solder paste of Comparative Example 1 was used, the NWO evaluation value of the joint was 35, whereas when each of the solder pastes of Examples 1 to 11 was used, the NWO evaluation value of the joint was 20 or less, thereby suppressing the occurrence of poor joints. Furthermore, the NWO evaluation value of the solder pastes of Examples 3 to 11 was 7 or less, thereby more effectively suppressing the occurrence of poor joints. Furthermore, the NWO evaluation value of the solder pastes of Examples 5 to 11 was 0, thereby completely suppressing the occurrence of poor joints. From these results, it was found that the occurrence of poor joints can be more effectively suppressed by adding 1.6 to 20% by weight of copolymer (p1) of formula (p1) relative to the total mass of the flux. Furthermore, it was found that the occurrence of poor joints can be more effectively suppressed by adding copolymer (p1) of 3.2% by weight or more or 5.6% by weight or more relative to the total mass of the flux, and that the occurrence of poor joints can be completely suppressed by adding copolymer (p1) of 12.8% by weight or more relative to the total mass of the flux. Furthermore, the solder pastes of Examples 1 to 10 had superior melting properties (reflow properties) compared to the solder paste of Example 11. From these results, it was found that by adding 1.6 to 16 mass % of copolymer (p1) to the total mass of the flux, the occurrence of poor bonding can be more effectively suppressed and superior melting properties can be obtained.

[0117] This application claims priority based on Japanese Patent Application No. 2021-059865, filed on March 31, 2021, the disclosure of which is incorporated herein in its entirety.

Claims

DEPCT671. Flux composed of: base resin; activator; thixotropic agent; solvent; and solder joint defect stopper, where the solder joint defect stopper is a copolymer in which the structural unit represented by formula(1) and the structural unit represented by formula(2), the average molecular weight of the copolymer is equal to or greater than 1,000 and equal to or less than 100,000, and the amount of the solder joint defect stopper in the total portion of the flux is equal to or greater than 1% by mass. and equal to or less than 25% by mass,[Chemical Formula 1](Chemical Formula)(1) in formula(1)R1 is a saturated or unsaturated alkyl group, straight, branched or cyclic with 1 to 24 carbon atoms or a substituted or unsubstituted aryl group,[Chemical Formula 2](Chemical Formula)(2) in formula(2)R2 is the group represented by formula(2-1),[Chemical Formula 3](Chemical Formula)(2-1) in formula(2-1)n is an integer 1 to 20,R21 is a hydrogen atom or an alkyl group with 1 to 6 carbon atoms andR22 is a straight, branched or cyclic alkyl group with 1 to 6 carbon atoms.2.Fluxes are composed of: a base resin; an activator; a thixotropic agent; a solvent; a polyoxyalkylene monoalkyl ether; and a solder joint defect stopper, where the solder joint defect stopper is a copolymer containing the structural unit represented by formula(1) and the structural unit represented by formula(2), the copolymer's mean molecular weight is 1,000 or greater and 100,000 or less, and the amount of the solder joint defect stopper in the total portion of the flux is 1% or greater by mass and 25% or less by mass. [Chemical Formula 4](Chemical Formula)(1) In Formula (1) R1 is a saturated or unsaturated alkyl group, straight-chain, branched or cyclic with 1 to 24 carbon atoms or a substituted or unsubstituted aryl group, [Chemical Formula 5](Chemical Formula)(2) In Formula (2) R2 is the group represented by Formula (2-1), [Chemical Formula 6](Chemical Formula)(2-1) In Formula (2-1) n is an integer 1 to 30, R21 is a hydrogen atom or an alkyl group with 1 to 6 carbon atoms and R22 is a straight-chain, branched or cyclic alkyl group with 1 to 6 carbon atoms.

3. Flux according to claim 1 or 2 where in Formula (1) R1 is a substituted or unsubstituted aryl group. 4.Flux according to any of the claims 1 to 3 in which formula (1) has a structure represented by formula (6) [chemical formula 7](chemical formula)(6)5. Flux according to any of the claims 1 to 4 in which in formula (2-1) R22 is an alkylene group with 2 or 3 carbon atoms6. Solder paste consisting of: solder powder; and any of the fluxes according to claims 1 to 5;.