Rosin-based base resin for lead-free solder flux, lead-free solder flux, lead-free solder paste

Abstract

To provide a novel rosin-based base resin for lead-free solder flux which is easily soluble in a solvent, and further, has excellent wettability and storage stability even when being made into a solder paste, and in which flux residue after mounting exhibits high transparency.SOLUTION: A rosin-based base resin for lead-free solder flux contains dehydroabietic acid, dihydroabietic acid and tetrahydroabietic acid. In this rosin-based base resin for lead-free solder flux, the content of tetrahydroabietic acid in the base resin is 45 to 80% by weight.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a rosin-based resin for lead-free solder flux, a lead-free solder flux, and a lead-free solder paste.

Background Art

[0002] For surface mounting of a circuit board, a solder paste, which is a mixture of a lead-free solder flux (hereinafter also referred to as "solder flux" or "flux") and lead-free solder powder, is supplied to electrodes on the circuit board by a method such as screen printing or dispenser discharge. After mounting an electronic component such as a capacitor thereon, the circuit board is heated in a reflow furnace to melt the lead-free solder powder and join the electronic component and the electrode.

[0003] Conventionally, natural rosin has been widely used as the base resin of solder flux. However, natural rosin is very easily oxidized and has poor thermal stability such as easily discoloring when heated. Therefore, when used as a rosin-based resin for solder flux, the wettability during soldering is likely to be significantly deteriorated. In addition, since natural rosin itself contains a large amount of abietic acid, it has high crystallinity and is also insoluble in solvents (for example, hexyldiglycol, etc.) used when preparing flux.

[0004] As a method for solving these problems, it is known to use hydrogenated rosin and / or disproportionated rosin of special pine-derived rosins as a rosin-based resin for solder flux (Patent Document 1). However, the base resin is still insoluble in solvents, and there is also a problem of thickening over time when it is made into a lead-free solder paste (hereinafter also referred to as "solder paste").

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The main object of the present invention is to provide a novel lead-free solder flux rosin-based resin that is easily soluble in solvents, has excellent wettability and storage stability even when made into a solder paste, and exhibits high transparency of flux residues after mounting.

Means for Solving the Problems

[0007] The inventor of the present invention has conducted intensive studies focusing on the resin acid composition in the rosin-based resin, and as a result, has found that the above problems can be solved by using a rosin-based resin containing a certain amount of tetrahydroabietic acid. That is, the present invention relates to the following rosin-based resins for lead-free solder fluxes, lead-free solder fluxes, and lead-free solder pastes.

[0008] 1. A rosin-based resin for lead-free solder flux containing dehydroabietic acid, dihydroabietic acid, and tetrahydroabietic acid, wherein the content of tetrahydroabietic acid in the base resin is 45 to 80% by weight.

[0009] 2. The rosin-based resin for lead-free solder flux according to item 1 above, having a color tone of Hazen 250 or less.

[0010] 3. The rosin-based resin for lead-free solder flux according to item 1 or 2 above, wherein the content of dehydroabietic acid in the base resin is 10% by weight or less.

[0011] 4. A lead-free solder flux containing the rosin-based resin for lead-free solder flux according to any one of items 1 to 3 above, an activator, a thixotropic agent, and a solvent.

[0012] 5. A lead-free solder paste containing the lead-free solder flux and solder powder according to item 4 above.

Advantages of the Invention

[0013] According to the rosin-based resin for lead-free solder flux of the present invention, it exhibits excellent solubility in solvents. Further, the paste has excellent wettability and excellent viscosity stability during long-term storage. Furthermore, the flux residue after mounting exhibits high transparency.

Embodiments for Carrying Out the Invention

[0014] The rosin-based resin for lead-free solder flux of the present invention (hereinafter referred to as "base resin") contains dehydroabietic acid (hereinafter abbreviated as DAA), dihydroabietic acid (hereinafter abbreviated as DHAA), and tetrahydroabietic acid (hereinafter abbreviated as THAA), and the content of tetrahydroabietic acid in the base resin is 45 to 80% by weight.

[0015] The base resin of the present invention has a THAA content of 45% by weight or more. When the content is less than 45% by weight, the crystallinity of the rosin-based resin increases, and as a result, it becomes difficult to dissolve in solvents and cannot be used as the base resin of the solder flux. Also, from the viewpoint of the excellent solubility of the base resin in solvents, the THAA content is usually 80% by weight or less, preferably 70% by weight or less, and more preferably 60% by weight or less.

[0016] Note that the THAA content in the base resin of the present invention is a value obtained by determining the area ratio derived from THAA with the total peak area of each resin acid obtained by gas chromatograph analysis (GC) as 100%.

[0017] Specifically, the rosin-based resin is dissolved in an on-column methylating agent (a methanol solution of phenyltrimethylammonium hydroxide (PTAH)) for methyl esterification. Then, 1 μL of the solution is injected into a commercially available gas chromatograph-mass spectrometer (GC / MS), and the peak area derived from tetrahydroabietic acid ester (molecular weight: 320) is read from the detected peaks. By determining the area ratio with respect to the peak area of all resin acids, the content of THAA can be known.

[0018] Also, regarding the content of DAA described later, it can be measured by the same method, and the peak area derived from dehydroabietic acid ester (molecular weight: 314) can be determined by reading it respectively.

[0019] The base resin of the present invention contains DAA and DHAA in addition to THAA.

[0020] The content of DAA is not particularly limited, but from the viewpoint that the base resin dissolves well in the solvent, it is preferably 10% by weight or less, more preferably 7% by weight or less. Also, the content of DHAA is not particularly limited, but from the same viewpoint, it is preferably 40% by weight or less, more preferably 35% by weight or less.

[0021] The base resin of the present invention may contain resin acids other than DAA, DHAA, and THAA (for example, abietic acid, pimaric acid, isopimaric acid, levopimaric acid, etc.), and low molecular weight components having a molecular weight of usually 280 or less such as impurities derived from rosin-based resins. Also, their content is usually 5% by weight or less.

[0022] The base resin of the present invention can be obtained from rosin-based raw materials by various known methods (vacuum distillation method, hydrogenation, disproportionation). Among them, in order to efficiently obtain a base resin containing the specific amounts of DAA, DHAA, and THAA and showing the color tone described later, it is preferably carried out by the vacuum distillation method.

[0023] Examples of rosin-based raw materials include natural rosins such as gum rosin, wood rosin, tall oil rosin, Merkus pine rosin, slash pine rosin, and king pine rosin. Examples of rosin-based materials also include purified rosins obtained by purifying the above natural rosins.

[0024] Purified rosin can be obtained, for example, by purifying the unmodified rosin by various known purification methods such as vacuum distillation, extraction, and recrystallization. The conditions of the purification method are not particularly limited. For example, in the case of vacuum distillation, the temperature is about 200 to 300 °C, and the distillation is carried out at a reduced pressure of about 60 to 3000 Pa. In the case of the extraction method, the unmodified rosin is made into an alkaline aqueous solution, and the unsaponifiable matter that is not dissolved in the aqueous solution is extracted with various organic solvents, and then the remaining aqueous layer is neutralized. In the case of the recrystallization method, it can be obtained by dissolving the unmodified rosin in an organic solvent as a good solvent, then distilling off the organic solvent to obtain a concentrated solution, and further adding an organic solvent as a poor solvent.

[0025] Examples of organic solvents include aromatic hydrocarbons such as benzene, toluene, and xylene; ketones such as acetone and methyl ethyl ketone; aliphatic hydrocarbons such as n-heptane, n-hexane, n-heptane, and isooctane; and alicyclic hydrocarbons such as cyclohexane and decalin.

[0026] The procedure for subjecting the rosin-based raw material to vacuum distillation is not particularly limited, but it is preferable to heat and melt the rosin-based raw material at a temperature of 250 °C or higher for 0.5 to 1 hour and then carry out distillation under reduced pressure. The conditions for vacuum distillation are usually a pressure of about 1 to 5 kPa (preferably about 1 to 3 kPa), a temperature of about 250 to 270 °C (preferably about 250 to 260 °C), and a time of about 0.5 to 2 hours (more preferably about 0.5 to 1 hour).

[0027] The physical properties of the base resin of the present invention are not particularly limited, but its color tone is usually Hazen 250 or less, preferably Hazen 200 or less. The Hazen color tone refers to the value measured in accordance with JIS K 0071-1. When the base resin exhibits the above color tone, when the solder paste prepared from the base is mounted, the flux residue exhibits high transparency, so that the solder inspection after mounting becomes easier.

[0028] The softening point of the base resin is usually about 70 to 90 °C, preferably 75 to 85 °C. The softening point is the value measured by the ring and ball method (in accordance with JIS K 5601-2-2).

[0029] The acid value of the base resin is usually about 150 to 190 mgKOH / g, preferably about 160 to 180 mgKOH / g. The acid value is the value calculated by titrating a solution in which a rosin-based resin is dissolved in a mixed solvent of acetone / potassium hydroxide with hydrochloric acid after adding a small amount of a phenolphthalein solution (in accordance with JIS K 0070).

[0030] The lead-free solder flux of the present invention (hereinafter referred to as "solder flux") contains the above base resin, activator, thixotropic agent, and solvent.

[0031] Examples of the activator include amines, acids, halogens, etc. These may be used alone or in combination of two or more.

[0032] Examples of the amine include monoalkylamines such as n-butylamine, n-pentylamine, n-hexylamine, n-heptylamine, n-octylamine and the like; dialkylamines such as di-n-butylamine, di-n-pentylamine, di-n-hexylamine, di-n-heptylamine, di-n-octylamine, di-n-nonylamine, di-n-decylamine, di(1-ethylhexyl)amine, di(2-ethylhexyl)amine and the like; trialkylamines such as tri-n-butylamine, tri-n-pentylamine, tri-n-hexylamine, tri-n-heptylamine, tri-n-octylamine, N,N-diethylmethylamine and the like; alkanolamines such as monoethanolamine, diethanolamine, triethanolamine and the like; alicyclic amines such as cyclohexylamine, dicyclohexylamine and the like; aromatic amines such as diphenylamine, triphenylamine and the like; N,N'-bis(4-aminobutyl)-1,2-ethanediamine, triethylenetetramine, N,N'-bis(3-aminopropyl)ethylenediamine, N,N'-bis(3-aminopropyl)piperazine and the like. These may be used alone or in combination of two or more.

[0033] Examples of the acid include non-halogenated aliphatic monobasic acids such as capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, picolinic acid and the like; non-halogenated dibasic acids such as succinic acid, malonic acid, adipic acid, glutaric acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid and the like; non-halogenated alicyclic dibasic acids such as cyclohexanecarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid and the like; dimer acid (dimer of unsaturated fatty acids such as linolenic acid, tall oil fatty acid, oleic acid, linoleic acid and the like). These may be used alone or in combination of two or more.

[0034] Examples of the halogen include bromates such as methylamine hydrobromide, ethylamine hydrobromide, diethylamine hydrobromide, cyclohexylamine hydrobromide, and diphenylguanidine hydrobromide; bromocarboxylic acids such as 3-bromopropionic acid, 2-bromopentanoic acid, 3-bromopentanoic acid, 5-bromopentanoic acid, 2-bromoisopentanoic acid, 2,3-dibromosuccinic acid, 2-bromosuccinic acid, and 2,2-dibromoadipic acid; bromoalcohols such as 1-bromo-2-butanol, 1-bromo-2-propanol, 3-bromo-1-propanol, 3-bromo-1,2-propanediol, 1,4-dibromo-2-butanol, 1,3-dibromo-2-propanol, 2,3-dibromo-1-propanol, 1,4-dibromo-2,3-butanediol, 2,3-dibromo-1,4-butenediol, and 2,3-dibromo-2-butene-1,4-diol; bromoalkanes such as 1,2,3,4-tetrabromobutane and 1,2-dibromo-1-phenylethane; and bromoalkenes such as 1-bromo-3-methyl-1-butene, 1,4-dibromobutene, 1-bromo-1-propene, 2,3-dibromopropene, 1,2-dibromostyrene, and trans-2,3-dibromo-2-butene-1,4-diol. These may be used alone or in combination of two or more.

[0035] Examples of the thixotropic agent include animal and plant-based thixotropic agents such as hydrogenated castor oil, beeswax, and carnauba wax; and amide-based thixotropic agents such as stearic acid amide and ethylene bisamide of 12-hydroxystearic acid. These may be used alone or in combination of two or more.

[0036] Examples of the solvent include monoalkyl ethers such as ethylene glycol mono-n-butyl ether, ethylene glycol mono-n-hexyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-n-butyl ether, ethylene glycol monophenyl ether, propylene glycol monophenyl ether, ethylene glycol monobenzyl ether, diethylene glycol monobenzyl ether, tripropylene glycol monomethyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol monohexyl ether, diethylene glycol 2-ethylhexyl ether, and tripropylene glycol monomethyl ether; alcohols such as benzyl alcohol, 1,3-butanediol, 1,4-butanediol, and octanediol; esters such as butyl benzoate, diethyl adipate, and 2-(2-n-butoxyethoxy)ethyl acetate; terpene solvents such as α-terpinene, myrcene, allo-ocimene, limonene, dipentene, α-pinene, β-pinene, carvone, ocimene, and felandrene; terpineols such as α-terpineol and terpineol; hydrocarbons such as dodecane and tetradecene; and pyrrolidones such as N-methyl-2-pyrrolidone.

[0037] The contents of the base resin, activator, thixotropic agent, and solvent in the solder flux of the present invention are not particularly limited. Considering the wettability of the solder paste and the viscosity stability during long-term storage, they are as follows. Base resin: Usually about 25 to 50% by weight, preferably 30 to 50% by weight Activator: Usually about 5 to 20% by weight, preferably 5 to 15% by weight Thixotropic agent: Usually about 3 to 10% by weight, preferably 5 to 10% by weight Solvent: Usually about 30 to 50% by weight, preferably 35 to 50% by weight

[0038] The solder flux of the present invention may contain, for example, acrylic acid-modified rosin, hydrogenated acrylic acid-modified rosin, itaconic acid-modified rosin, hydrogenated itaconic acid-modified rosin, maleic acid-modified rosin, hydrogenated maleic acid-modified rosin, fumaric acid-modified rosin, hydrogenated fumaric acid-modified rosin, formylated rosin, hydrogenated formylated rosin, polymerized rosin, hydrogenated polymerized rosin, etc., as long as the resin acid composition of the base resin is satisfied (hereinafter referred to as "rosin-based derivatives").

[0039] The solder flux of the present invention may contain a non-rosin-based base resin and additives.

[0040] Examples of the non-rosin-based base resin include synthetic resins such as epoxy resin, acrylic resin, polyimide resin, polyamide resin (nylon resin), polyester resin, polyacrylonitrile resin, vinyl chloride resin, vinyl acetate resin, polyolefin resin, fluororesin, and ABS resin. These may be used alone or in combination of two or more.

[0041] Examples of the additives include antioxidants, fungicides, and matting agents.

[0042] Note that the contents of the rosin-based derivatives, non-rosin-based base resin, and additives in the solder flux of the present invention are not particularly limited and are as follows. Rosin-based derivatives: Usually less than 30% by weight, preferably less than 25% by weight Non-rosin-based base resin: Usually less than 5% by weight, preferably less than 1% by weight Additives: Usually less than 5% by weight, preferably less than 1% by weight

[0043] The production method of the solder flux of the present invention is not particularly limited. For example, it can be obtained by sufficiently mixing the base resin, activator, thixotropic agent, and solvent, and, if necessary, rosin-based derivatives, non-rosin-based base resin, and additives until they are melted under heating.

[0044] The lead-free solder paste of the present invention contains the solder flux of the present invention and lead-free solder powder.

[0045] Examples of the lead-free solder powder include Sn solder powder, Sn-Ag system, Sn-Cu system, Sn-Zn system, Sn-Sb system, Sn-Ag-Cu system, Sn-Ag-Bi system, Sn-Ag-Cu-Bi system, Sn-Ag-Cu-In system, Sn-Ag-Cu-S system, Sn-Ag-Cu-Ni-Ge system, and the like.

[0046] The blending ratio of each component in the solder paste of the present invention is not particularly limited, and in terms of weight conversion, solder flux / lead-free solder powder = about 5 / 95 to 30 / 70, preferably about 8 / 92 to 20 / 80.

Examples

[0047] Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. In each example, % is based on weight unless otherwise specified.

[0048] <Content of rosin-based resin> The content of the rosin-based resin was measured by dissolving 0.005 g of the sample (rosin-based resin) in 0.5 g of an on-column methylating agent (a methanol solution of phenyltrimethylammonium hydroxide (PTAH) (0.2 mol / L, manufactured by GL Sciences Inc.)), and injecting 1 μL into a commercially available gas chromatograph-mass spectrometry (GC / MS). Each content was determined from the methyl ester form of the resin acid. The analyzer and column are shown below. <Analyzer and column> · Gas chromatograph-mass spectrometer: "Agilent6890", "Agilent5973N"; manufactured by Agilent technologies · Column: "Advance-DS"; manufactured by Shinwa Chemical Industry Co., Ltd.

[0049] <Softening point> Measured in accordance with JIS K 5601-2-2.

[0050] <Hue> For the rosin-based resin immediately after synthesis, the Hazen color tone was measured in accordance with JIS K 0071-1, and the Gardner color tone was measured in accordance with JIS K 0071-2. Also, after storing the rosin-based resin in a circulating air dryer at 180 °C for 24 hours, the Gardner color tone was measured in the same manner.

[0051] Example 1 Hydrogenated rosin (DAA 5.2 wt%, THAA 55.0 wt%) was charged into a vacuum distillation vessel, heated to 250 °C and held for 1 hour, and then distilled under a reduced pressure of 1 kPa under a nitrogen seal to obtain a rosin-based resin (1). The physical properties of the rosin-based resin (1) are shown in Table 1 (the same applies hereinafter).

[0052] Example 2 In Example 1, the hydrogenated rosin (DAA 7.5 wt%, THAA 65.3 wt%) was changed and distilled in the same manner to obtain a rosin-based resin (2).

[0053] Example 3 In Example 1, the hydrogenated rosin (DAA 6.4 wt%, THAA 45.8 wt%) was changed and distilled in the same manner to obtain a rosin-based resin (3).

[0054] Example 4 In Example 1, the hydrogenated rosin (DAA 13.2 wt%, THAA 46.4 wt%) was changed and distilled in the same manner to obtain a rosin-based resin (4).

[0055] Comparative Example 1 In Example 1, the hydrogenated rosin (DAA 7.5 wt%, THAA 41.0 wt%) was changed and distilled in the same manner to obtain a rosin-based resin (5).

[0056] Comparative Example 2 In Example 1, the hydrogenated rosin (DAA 0.0 wt%, THAA 96.0 wt%) was changed and distilled in the same manner to obtain a rosin-based resin (6).

[0057] Comparative Example 3 In Example 1, disproportionated rosin (DAA 55.1 wt%, THAA 32.0 wt%) was used instead, and distilled in the same manner to obtain a rosin-based resin (7).

[0058] Comparative Example 4 In Example 1, hydrogenated rosin (DAA 20.1 wt%, THAA 42.1 wt%) was used instead, and distilled in the same manner to obtain a rosin-based resin (8).

[0059] Comparative Example 5 In Example 1, hydrogenated rosin (DAA 10.0 wt%, THAA 18.0 wt%) was used instead, and distilled in the same manner to obtain a rosin-based resin (9).

[0060] Comparative Example 6 In Example 1, hydrogenated rosin (DAA 12.3 wt%, THAA 34.5 wt%) was used instead, and distilled in the same manner to obtain a rosin-based resin (10).

[0061] <Solubility in solvent> Each rosin-based resin was added to diethylene glycol monohexyl ether (HeDG) to a concentration of 70%, heated to dissolve, and then cooled to room temperature and left for 5 days. The appearance of the solution (crystallization of the base resin) was visually observed. (Evaluation criteria) ○: The base resin is not crystallized △: The base resin is slightly crystallized ×: The base resin is crystallized

[0062]

Table 1

[0063] <Preparation of solder flux (1)> Evaluation Example 1 Into a beaker, 24 g of a rosin-based resin (1), 24 g of KE-604 (a hydride of acrylic acid-modified rosin, trade name: "KE-604", manufactured by Arakawa Chemical Industries, Ltd.), 5 g of glutaric acid, 1 g of picolinic acid, 1 g of dibromosuccinic acid, 3 g of tri-n-butylamine as an activator, 6 g of ethylene bisamide of 12-hydroxystearic acid (trade name: "MAWAXO", manufactured by KF Trading Co., Ltd.) as a thixotropic agent, and 36 g of diethylene glycol monohexyl ether (HeDG) as a solvent were added and heated to dissolve to prepare a solder flux.

[0064] Evaluation Examples 2 to 5, Comparative Evaluation Examples 1 to 7 Solder fluxes were prepared in the same manner as in Evaluation Example 1 with the compositions shown in Table 2.

[0065] <Preparation of Solder Paste> 11 g of the solder flux of Evaluation Example 1 and 89 g of lead-free solder powder (Sn-Ag-Cu alloy; 96.5% / 3% / 0.5%, average particle diameter 25 to 38 μm) were stirred for 10 minutes with a solder paste kneader (trade name: "SPS-2", manufactured by Malcolm Co., Ltd.) to prepare a solder paste. The solder fluxes of Evaluation Examples 2 to 5 and Comparative Evaluation Examples 1 to 7 were prepared in the same manner.

[0066] <Wettability> In accordance with JIS Z 3284-4, the wettability of each solder paste with respect to a copper plate during heating and reflow in an air atmosphere was evaluated by a dewetting test. The evaluation criteria are as follows. The evaluation results are shown in Table 2 (the same applies hereinafter). (Evaluation Criteria) ○: All the portions applied to the copper electrode are wetted and spread. △: Slight non-wetting occurs. ×: It does not wet at all with respect to the copper electrode substrate.

[0067] <Appearance (Transparency of Flux Residue)> After performing the wettability test of each solder paste as described above, the appearance of the flux residue was visually confirmed and evaluated according to the following criteria. (Evaluation Criteria) ○: The flux residue is transparent. △: The flux residue is slightly colored. ×: The flux residue is colored.

[0068] <Viscosity stability> The viscosity of each solder paste immediately after preparation and the viscosity of the paste after being kept in a thermostat at 40°C for 24 hours were measured respectively using a spiral viscometer (trade name: "PCU-205", coaxial double cylindrical rotation type, manufactured by Malcolm Co., Ltd.), and based on the following calculation formula, the thickening rate of the solder paste was calculated.

[0069] Thickening rate (%) = [({viscosity at 10 rpm after keeping the solder paste at 40°C for 24 hours} - {viscosity at 10 rpm immediately after preparing the solder paste}) ÷ {viscosity at 10 rpm immediately after preparing the solder paste}] × 100

[0070] Note that the heat preservation condition is intended for a temperature acceleration test, and the thickening rate in this test generally reproduces the thickening rate after storage at 0 to 10°C for 6 months or more. And when the thickening rate is less than 10%, considering the measurement error, it was regarded that the viscosity stability was good. The results are shown in Table 2.

[0071]

Table 2

Claims

1. A rosin-based resin for lead-free solder flux containing dehydroabietic acid, dihydroabietic acid, and tetrahydroabietic acid, wherein the content of tetrahydroabietic acid in the base resin is 45 to 80% by weight, the content of dehydroabietic acid is 10% by weight or less, and the content of dihydroabietic acid is 40% by weight or less, a rosin-based resin for lead-free solder flux.

2. The rosin-based resin for lead-free solder flux according to Claim 1, having a color tone of Hazen 250 or less.

3. A lead-free solder flux comprising the rosin-based resin for lead-free solder flux according to Claim 1 or 2, an activator, a thixotropic agent, a solvent, and a rosin derivative, wherein the contents in the solder flux are 25 to 50% by weight of the base resin, 5 to 20% by weight of the activator, 3 to 10% by weight of the thixotropic agent, 30 to 50% by weight of the solvent, and 36% by weight or less of the rosin derivative, a lead-free solder flux.

4. A lead-free solder paste comprising the lead-free solder flux according to Claim 3 and solder powder.

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