JP2024019041A - Rosin base resin for lead-free solder flux, manufacturing method of rosin base resin for lead-free solder flux, lead-free solder flux and lead-free solder paste - Google Patents

Abstract

[Problem] The object of the present invention is to provide a rosin-based base for lead-free solder flux that exhibits excellent color tone without requiring a hydrogenation reaction and also has excellent wettability, storage stability, and insulation resistance when made into a solder paste. An object of the present invention is to provide a resin and a method for producing the base resin. [Solution] A rosin base resin for lead-free solder flux that contains fumaric acid-modified rosin (A), has an acid value of 200 to 300 mgKOH/g, and has a color tone of Gardner 3 or less, a method for producing the base resin, and lead Related to free solder flux and lead-free solder paste. [Selection diagram] None

Description

The present invention relates to a rosin base resin for lead-free solder flux, a method for producing a rosin base resin for lead-free solder flux, a lead-free solder flux, and a lead-free solder paste.

For surface mounting of circuit boards, solder paste, which is a mixture of lead-free solder flux (hereinafter also referred to as "solder flux" or "flux") and lead-free solder powder, is applied to the electrodes on the circuit board using screen printing or a dispenser. After supplying it by a method such as dispensing and mounting electronic components such as a capacitor on it, the circuit board is heated in a reflow oven to melt the lead-free solder powder and join the electronic components and electrodes.

Conventionally, natural rosin has been widely used as the base resin for solder flux. However, natural rosin is highly susceptible to oxidation, easily discolors when heated, and has poor thermal stability. Therefore, when used as a rosin-based base resin for solder flux, wettability during soldering becomes significantly poor. Cheap.

Furthermore, as other base resins, those using hydrogenated acid-modified rosins and fumarized rosins are also known (Patent Documents 1 and 2). However, acrylated hydrogenated rosin requires a hydrogenation reaction during production, resulting in high production costs, and fumarated rosin has a problem of poor color tone. Furthermore, when lead-free solder pastes (hereinafter also referred to as "solder pastes") are made using these base resins, they tend to increase in viscosity over time and have poor insulation resistance.

Japanese Patent Application Publication No. 2015-131336 Japanese Patent Application Publication No. 2015-142936

The object of the present invention is to provide a rosin-based resin for lead-free solder flux that exhibits excellent color tone without requiring a hydrogenation reaction, and has excellent wettability, storage stability, and insulation resistance when made into a solder paste. An object of the present invention is to provide a method for producing a base resin.

The inventors of the present invention have conducted extensive studies on the composition and physical properties of rosin base resins, and have found that the above-mentioned problems can be solved. That is, the present invention relates to a rosin base resin for lead-free solder flux, a method for producing a rosin base resin for lead-free solder flux, a lead-free solder flux, and a lead-free solder paste as described below.

1. A rosin base resin for lead-free solder flux that contains fumaric acid-modified rosin (A), has an acid value of 200 to 300 mgKOH/g, and has a color tone of Gardner 3 or less.

2. The rosin base resin for lead-free solder flux according to item 1 above, wherein the modification rate of the rosin with fumaric acid is 15 to 60%.

3. In the presence of one or more antioxidants selected from hindered phenolic antioxidants and sulfur-based antioxidants, rosins and fumaric acid are reacted to produce an acid value of 200 to 300 mgKOH/g and a color tone. A method for producing a rosin base resin for lead-free solder flux, comprising the step of obtaining a fumaric acid-modified rosin (A) having a Gardner value of 3 or less.

4. 3. The method for producing a rosin base resin for lead-free solder flux according to item 3, wherein the content of the antioxidant is 0.01 to 3 parts by weight based on 100 parts by weight of the rosin.

5. A lead-free solder flux containing a rosin base resin for lead-free solder flux as described in 1 or 2 above, an activator, a thixotropic agent, and a solvent.

6. A lead-free solder paste containing the lead-free solder flux and lead-free solder powder described in 5 above.

The rosin base resin for lead-free solder flux of the present invention exhibits excellent color tone, and when made into a solder paste, has excellent wettability, storage stability, and insulation resistance. Moreover, the production method of the present invention can obtain a resin exhibiting excellent color tone without requiring a hydrogenation reaction.

The rosin base resin for lead-free solder flux of the present invention (hereinafter referred to as "base resin") contains fumaric acid-modified rosin (A) (hereinafter also referred to as component (A)).

Fumaric acid-modified rosin (A) is a reaction product of rosins and fumaric acid.

Rosins are divided into natural rosins and modified rosins.

Natural rosin is a mixture of resin acids collected from plants of the Pinaceae family, and is classified into gum rosin, tall oil rosin, and wood rosin depending on the production method. The resin acid is mainly abietic acid, and others include neoabietic acid, parastric acid, dehydroabietic acid, levopimaric acid, pimaric acid, isopimaric acid, sandaracopimaric acid, and the like. Furthermore, natural rosins containing dihydroagatic acid, combic acid, etc. can also be used. These may be used alone or in combination of two or more.

Further, as the natural rosin, a purified rosin (hereinafter also referred to as purified rosin) can also be used.

Purified rosin can be obtained by purifying natural rosin using a purification method such as vacuum distillation, extraction, recrystallization, or the like. Further, the purification conditions are not particularly limited.

In the case of vacuum distillation, the temperature is about 200 to 300°C and the degree of vacuum is 60 to 3000 Pa. Purified rosin obtained by this method is also called distilled rosin.

In the case of the extraction method, natural rosin is made into an alkaline aqueous solution, unsaponifiable substances not dissolved in the aqueous solution are extracted with various organic solvents, and then the remaining aqueous layer is neutralized.

In the case of the recrystallization method, the rosin is dissolved in an organic solvent as a good solvent, then the organic solvent is distilled off to obtain a concentrated solution, and an organic solvent as a poor solvent is further added.

Examples of good solvents include aromatic hydrocarbons such as benzene, toluene, and xylene; organic halogens such as chloroform; ketones such as acetone and methyl ethyl ketone; alcohols such as methanol, ethanol, and isopropyl alcohol; and esters such as methyl acetate and ethyl acetate. etc. These may be used alone or in combination of two or more.

Examples of the poor solvent include aliphatic hydrocarbons such as n-hexane, n-heptane, and isooctane; and alicyclic hydrocarbons such as cyclohexane and decalin. These may be used alone or in combination of two or more.

The modified rosin is not particularly limited as long as it reacts with fumaric acid, and examples thereof include esterified products (rosin esters), hydrides (hydrogenated rosins), and disproportionated products (disproportioned rosins) of the natural rosin or purified rosin. (hydrogenated rosin ester), an esterified product of the hydrogenated rosin (hydrogenated rosin ester), an esterified product of the disproportionated rosin (disproportionated rosin ester), and the like. These may be used alone or in combination of two or more. Note that the modified rosin may contain unreacted natural rosin.

The modified rosin that has been purified after modification can also be used.

Among these, natural rosin and purified rosin are preferred, and purified rosin is more preferred, since the base resin exhibits excellent color tone.

The amount of fumaric acid used is usually 5 to 20 parts by weight, preferably 5 to 15 parts by weight, per 100 parts by weight of rosin based on the solid weight, since the solder paste exhibits excellent storage stability. Parts by weight.

The method for producing the base resin of the present invention involves reacting rosins with fumaric acid in the presence of one or more antioxidants selected from hindered phenolic antioxidants and sulfur-based antioxidants. The method includes a step of obtaining a fumaric acid-modified rosin (A) having a value of 200 to 300 mgKOH/g and a color tone of Gardner 3 or less.

In the above manufacturing method, when one or more antioxidants selected from hindered phenolic antioxidants and sulfur-based antioxidants are used, a base resin exhibiting excellent color tone can be obtained, and when made into a solder paste, It tends to have excellent wettability, storage stability, and insulation resistance.

Among the antioxidants, examples of hindered phenolic antioxidants include 2,5-di-tert-butylhydroquinone, anthraquinone, triethylene glycol bis{3-(3-t-butyl-5-methyl- 4-hydroxyphenyl)propionate}, 1,6-hexanediol bis{3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate}, pentaerythritol tetrakis{3-(3,5-di- t-butyl-4-hydroxyphenyl)propionate}, octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 3,9-bis[2-{3-(3-t- Butyl-4-hydroxy-5-methylphenyl)propionyloxy}-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane, N,N'-hexamethylenebis( 3,5-di-t-butyl-4-hydroxy-hydrocinnamide), 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl) Examples include benzene, Irganox (registered trademark) 565, and the like. These may be used alone or in combination of two or more.

Among the antioxidants, examples of sulfur-based antioxidants include 4,4'-thiobis(6-t-butyl-3-methylphenol) and 2,4-bis(dodecylthiomethyl)-6-methyl. Phenol, 4,4'-bis(phenol) sulfide, 4,4'-bis(phenol) sulfoxide, 4,4'-bis(phenol) sulfone, 4,4'-bis(phenol)thiol sulfinate, 4 , 4'-bis(phenol)thiol sulfonate, 2,2'-bis(p-cresol) sulfide, 2,2'-bis(p-cresol) sulfoxide, 2,2'-bis(p-cresol) sulfone , 2,2'-bis(pt-butylphenol) sulfide, 2,2'-bis(pt-butylphenol) sulfoxide, 2,2'-bis(pt-butylphenol) sulfone, 4,4' -Bis(6-t-butyl-m-cresol) sulfoxide, 4,4'-bis(6-t-butyl-m-cresol) sulfide, 4,4'-bis(6-t-butyl-o-cresol) ) sulfoxide, 4,4'-bis(6-t-butyl-o-cresol) sulfone, 4,4'-bis(6-t-butyl-o-cresol) sulfide, 4,4'-bis(resorcinol) Sulfide, 4,4'-bis(resorcinol) sulfoxide, 4,4'-bis(resorcinol) sulfone, 1,1'-bis(β-naphthol) sulfide, 1,1'-bis(β-naphthol) sulfoxide, 1,1'-bis(β-naphthol) sulfone, 4,4'-bis(α-naphthol) sulfide, 4,4'-bis(α-naphthol) sulfoxide, 4,4'-bis(α-naphthol) Examples include sulfone, t-amylphenol disulfide oligomer, nonylphenol disulfide oligomer, and t-butylphenol disulfide oligomer. These may be used alone or in combination of two or more.

Among the antioxidants, sulfur-based antioxidants are preferred because they quickly extract hydrogen atoms from rosins, giving the base resin excellent color tone.

The amount of the antioxidant used is usually 0.01 to 3 parts by weight, and 0.05 parts by weight, based on solid content, per 100 parts by weight of rosin, since the base resin exhibits excellent color tone. -3 parts by weight is preferred, and 0.05-0.5 parts by weight is more preferred.

In addition, regarding the rosin, fumaric acid, and antioxidant, the order and method of preparation (for example, batch preparation, divided preparation, etc.) can be freely selected.

In the above production method, the reaction temperature is preferably 180 to 250°C, more preferably 180 to 220°C. Further, the reaction time is preferably 1 to 5 hours, more preferably 1 to 3 hours.

The above manufacturing method may be carried out while blowing an inert gas such as nitrogen or argon into the closed reaction system in order to enhance the color tone of the obtained base resin.

In the above production method, various known catalysts may be further added. Examples of the catalyst include Lewis acids such as zinc chloride, iron chloride, and tin chloride; organic sulfonic acids such as para-toluenesulfonic acid and methanesulfonic acid. These may be used alone or in combination of two or more. The amount of catalyst used is usually about 0.01 to 10% by weight based on 100% by weight of the rosin.

Further, after the above steps are completed, a hindered phenol antioxidant or a sulfur antioxidant may be added.

The modification rate of rosins with fumaric acid is 15 to 60%. Note that the denaturation rate is a value of area ratio measured by GPC (gel permeation chromatography). When the modification rate is 15 to 60%, the solder paste tends to maintain good solderability and storage stability. Further, from the same point of view, the modification rate of rosins with fumaric acid is preferably 20 to 55%, more preferably 20 to 50%.

The acid value of the base resin obtained by the above production method is 200 to 300 mgKOH/g. The acid value here is calculated by dissolving the rosin base resin in a mixed solvent of ethanol/toluene, adding a small amount of phenolphthalein solution, and adding a small amount of phenolphthalein solution to ethanol containing potassium hydroxide at a concentration of 0.5 mol/L. This is a value calculated by titration with a solution (based on JIS K 0070). If the acid value of the base resin is less than 200 mgKOH/g, the wettability of the solder paste tends to be poor, and if it exceeds 300 mgKOH/g, the solder paste tends to increase in viscosity over time and the insulation resistance tends to deteriorate.

Further, the color tone of the base resin is Gardner 3 or less. Here, the Gardner color tone refers to a value measured in accordance with JIS K 0071-2, and the Hazen color tone refers to a value measured in accordance with JIS K 0071-1. When the base resin exhibits a Gardner color tone of 3 or less, the flux residue exhibits high transparency when a solder paste prepared from the base resin is mounted, making it easier to inspect the solder after mounting. Moreover, when the color tone becomes darker than Gardner 3, the wettability of the solder paste decreases and the insulation resistance tends to deteriorate. Further, from the same point of view, the color tone of the base resin is preferably Gardner 2 or less.

As for other physical properties of the base resin, the softening point is preferably 80 to 150°C, and 80 to 140°C, since it is easy to obtain a solder paste with an appropriate viscosity when using a solder flux containing the base resin. is more preferable. Note that the softening point is a value measured by the ring and ball method (based on JIS K 5601-2-2).

The lead-free solder flux (hereinafter referred to as "solder flux") of the present invention includes the base resin, an activator, a thixotropic agent, and a solvent.

Examples of the activator include amines, acids, halogen compounds, and the like. These may be used alone or in combination of two or more.

Examples of amines include monoalkylamines such as n-butylamine, n-pentylamine, n-hexylamine, n-heptylamine, and n-octylamine;
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 - dialkylamines such as ethylhexyl)amine;
Trialkylamines such as tri-n-butylamine, tri-n-pentylamine, tri-n-hexylamine, tri-n-heptylamine, tri-n-octylamine, N,N-diethylmethylamine;
Alkanolamines such as monoethanolamine, diethanolamine, triethanolamine;
Alicyclic amines such as cyclohexylamine and dicyclohexylamine;
Aromatic amines such as diphenylamine and triphenylamine;
N,N'-bis(4-aminobutyl)-1,2-ethanediamine, triethylenetetramine, N,N'-bis(3-aminopropyl)ethylenediamine, N,N'-bis(3-aminopropyl) Examples include piperazine. These may be used alone or in combination of two or more.

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

Examples of halogen compounds include hydrobromic acids such as methylamine hydrobromide, ethylamine hydrobromide, diethylamine hydrobromide, cyclohexylamine hydrobromide, and diphenylguanidine hydrobromide. salt;
3-bromopropionic acid, 2-bromopentanoic acid, 3-bromopentanoic acid, 5-bromopentanoic acid, 2-bromoisopentanoic acid, 2,3-dibromosuccinic acid, 2-bromosuccinic acid, 2,2-dibromoadipic acid Bromocarboxylic acids 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, 2,3-dibromo-2-butene Bromo alcohols such as -1,4-diol;
Bromo alkanes such as 1,2,3,4-tetrabromobutane and 1,2-dibromo-1-phenylethane;
1-bromo-3-methyl-1-butene, 1,4-dibromobutene, 1-bromo-1-propene, 2,3-dibromopropene, 1,2-dibromostyrene, trans-2,3-dibromo-2 Bromo alkenes such as -butene-1,4-diol and the like can be mentioned. These may be used alone or in combination of two or more.

Examples of thixotropic agents include animal and vegetable thixotropic agents such as hydrogenated castor oil, beeswax and carnauba wax; and amide thixotropic agents such as stearic acid amide and ethylene bisamide 12-hydroxystearate. These may be used alone or in combination of two or more.

Examples of the solvent include 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, and propylene glycol monophenyl ether. , monoalkyl ethers such as ethylene glycol monobenzyl ether, diethylene glycol monobenzyl ether, tripropylene glycol monomethyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol mono-n-hexyl ether, diethylene glycol 2-ethylhexyl ether, tripropylene glycol monomethyl ether;
Alcohols such as benzyl alcohol, 1,3-butanediol, 1,4-butanediol, octanediol;
Esters such as butyl benzoate, diethyl adipate, 2-(2-n-butoxyethoxy)ethyl acetate;
Terpene solvents such as α-terpinene, myrcene, alloocimene, limonene, dipentene, α-pinene, β-pinene, carvone, ocimene, phellandrene;
Terpineols such as α-terpineol and terpineol;
Examples include hydrocarbons such as dodecane and tetradecene; and pyrrolidones such as N-methyl-2-pyrrolidone. These may be used alone or in combination of two or more.

The contents of the base resin, activator, thixotropic agent, and solvent in the solder flux of the present invention are not particularly limited, and are as follows in consideration of the wettability of the solder paste and the storage stability during long-term storage. .
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

As long as the solder flux of the present invention satisfies the resin acid composition of the base resin, for example, the natural rosin, the purified rosin, the hydride of the natural rosin or purified rosin, the disproportionated product of the natural rosin or purified rosin, etc. , acrylic acid modified rosin, acrylic acid modified rosin hydride, itaconic acid modified rosin, itaconic acid modified rosin hydride, maleic acid modified rosin, maleic acid modified rosin hydride, fumaric acid modified rosin hydride, formylation Rosin, a hydride of formylated rosin, a polymerized rosin, a hydride of a polymerized rosin, an esterified product of these rosins, etc. may be included (hereinafter referred to as "rosin resin other than component (A)"). These may be used alone or in combination of two or more.

The solder flux of the present invention may also contain a non-rosin base resin and additives.

Non-rosin base resins include, for example, epoxy resins, acrylic resins, polyimide resins, polyamide resins (nylon resins), polyester resins, polyacrylonitrile resins, vinyl chloride resins, vinyl acetate resins, polyolefin resins, fluorine resins, and ABS resins. Synthetic resins such as These may be used alone or in combination of two or more.

Examples of additives include antioxidants, antifungal agents, matting agents, and the like.

Note that the contents of the rosin resin, non-rosin base resin, and additives other than the component (A) in the solder flux of the present invention are not particularly limited, and are as follows.
Rosin resin other than component (A): Usually less than 30% by weight, preferably less than 25% by weight Non-rosin base resin: Usually less than 5% by weight, preferably less than 1% by weight Additive: Usually less than 5% by weight, preferably is less than 1% by weight

The method for producing the solder flux of the present invention is not particularly limited, and includes, for example, the base resin, an activator, a thixotropic agent and a solvent, a rosin resin other than the component (A), and a non-rosin base, if necessary. It is obtained by melting the resin and additives under heating while mixing them.

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

Examples of lead-free solder powder include Sn solder powder, Sn-Ag series, Sn-Cu series, Sn-Zn series, Sn-Sb series, Sn-Ag-Cu series, Sn-Ag-Bi series, and Sn-Ag-Cu. -Bi system, Sn-Ag-Cu-In system, Sn-Ag-Cu-S system, Sn-Ag-Cu-Ni-Ge system, etc.

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

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In addition, in each example, all percentages are based on weight unless otherwise specified.

<Color tone>
Hazen color tone was measured in accordance with JIS K 0071-1, and Gardner color tone was measured in accordance with JIS K 0071-2.

<Acid value>
Measured in accordance with JIS K 0070.

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

<Denaturation rate>
A commercially available gel permeation chromatography device (manufactured by Tosoh Corporation, HLC-8320GPC), a commercially available column (manufactured by Tosoh Corporation, TSK-GEL column), polystyrene as a standard substance, and tetrahydrofuran (THF) as a developing solvent. Using a differential refractometer as a detector, 40 μL of a THF solution of base resin with a concentration of 0.30% was injected and measured at a flow rate of 1.0 μL/min. A value calculated using the sum of all peak areas detected in the polystyrene equivalent molecular weight range of 150 to 2000 as the denominator, and the sum of the peak areas derived from the reaction products of rosins and fumaric acid as the numerator. The denaturation rate was determined by multiplying by 100.

Example 1
In a four-necked flask equipped with a stirrer, a thermometer, a nitrogen inlet tube, and a condenser, add 150 g of distilled rosin (color tone: 100H) and a hindered phenolic antioxidant (product name: "IRGANOX1010", manufactured by BASF Japan Co., Ltd.). ) and 0.15 g of a sulfur-based antioxidant (trade name: "Rosinox", manufactured by Arkema) were added, and the temperature was raised to 200° C. to melt them. After keeping the temperature as it was for 3 hours, 30.0 g of fumaric acid was added and reacted for 2 hours to obtain a rosin base resin for flux (A-1). The physical properties of the base resin (A-1) are shown in Table 1 (the same applies below).

Example 2
The same procedure as in Example 1 was carried out except that the amount of fumaric acid charged was changed to 22.5 g to obtain a rosin base resin for flux (A-2).

Example 3
The same procedure as in Example 1 was carried out except that the amount of fumaric acid charged was changed to 10.5 g to obtain a rosin base resin for flux (A-3).

Example 4
The same procedure as in Example 1 was carried out except that the amount of fumaric acid charged was changed to 7.5 g to obtain a rosin base resin for flux (A-4).

Example 5
The same procedure as in Example 1 was carried out using distilled rosin (color tone: 2G) as the raw material to obtain a rosin-based base resin for flux (A-5).

Example 6
The same procedure as in Example 1 was carried out by changing Rosinox to a sulfur-based antioxidant (trade name: "Sumilizer WX-R", manufactured by Sumitomo Chemical Co., Ltd.) to obtain a base resin for flux (A-6). .

Example 7
In Example 1, the same procedure was carried out except that the hindered phenolic antioxidant (IRGANOX1010) was changed to 0.08g and the sulfur-based antioxidant (Rosinox) was changed to 0.08g. ) was obtained.

Example 8
In Example 1, the same procedure was carried out except that the hindered phenol antioxidant (IRGANOX1010) was changed to 0.03 g, and the sulfur-based antioxidant (Rosinox) was changed to 0.03 g. ) was obtained.

Commercially available rosin-based resins such as fumaric acid-modified rosin (product name: "Marquid No. 33", manufactured by Arakawa Chemical Industry Co., Ltd.), hydride of acrylic acid-modified rosin (product name: "Pine Crystal KE-604", Arakawa Chemical Industries, Ltd.) was used as the rosin base resin for flux (B-1) to (B-2).

Comparative example 1
The same procedure as in Example 1 was carried out except that the amount of fumaric acid charged was changed to 40.5 g to obtain a rosin base resin for flux (B-3).

Comparative example 2
The same procedure as in Example 1 was carried out except that the amount of fumaric acid charged was changed to 1.5 g to obtain a rosin base resin for flux (B-4).

Comparative example 3
The same procedure as in Example 3 was carried out except that the distilled rosin was replaced with gum rosin (trade name: "CG-WW", manufactured by Arakawa Chemical Industries, Ltd.) to obtain a rosin base resin for flux (B-5).

<Preparation of solder flux>
Evaluation example 1
In a beaker, 40 g of rosin base resin (A-1), 8.5 g of dimer acid, 1 g of glutaric acid, 5 g of sebacic acid, 1 g of dibromosuccinic acid, 3 g of tri-n-butylamine, and thixotropic agent as activators. As an antioxidant, 6 g of 12-hydroxystearic acid ethylene bisamide (trade name: "MAWAXO", manufactured by KF Trading Co., Ltd.), and as an antioxidant, a hindered phenolic antioxidant (trade name: "Irganox 1010", manufactured by BASF Japan (trade name: "Irganox 1010") Co., Ltd.) and 35 g of diethylene glycol mono-n-hexyl ether (HeDG) as a solvent were added and heated and dissolved while mixing to prepare a solder flux.

Evaluation examples 2 to 9, comparative evaluation examples 1 to 5
Solder fluxes were prepared in the same manner as in Evaluation Example 1 with the compositions shown in Table 2.

<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 size 25 to 38 μm) were mixed in a solder paste kneader (product name: A solder paste was prepared by stirring for 10 minutes using "SPS-2" (manufactured by Malcolm Co., Ltd.). The solder fluxes of Evaluation Examples 2 to 9 and Comparative Evaluation Examples 1 to 5 were prepared in the same manner. Note that in the solder paste of Comparative Evaluation Example 4, the base resin (B-4) was crystallized, so the following evaluation was not performed.

<Wettability>
In accordance with JIS Z 3284-4, the wettability of each solder paste to a copper plate during heating and reflow was visually evaluated by a dewetting test. The evaluation criteria are as follows. The evaluation results are shown in Table 2 (the same applies below).
(Evaluation criteria)
○: The entire area applied to the copper electrode gets wet and spread. ×: The copper electrode substrate does not get wet at all.

<Storage stability>
The viscosity of each solder paste immediately after preparation and the viscosity after keeping the paste in a constant temperature bath at a temperature of 40°C for 24 hours were measured using a spiral viscometer (product name: "PCU-205", coaxial double cylindrical rotating type). The thickening rate of the solder paste was calculated based on the formula shown below.

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)} ÷ (Immediately after preparing the solder paste) viscosity at 10 rpm)]×100

Note that the heat retention conditions are intended for temperature accelerated testing, and the thickening rate in this test roughly reproduces the thickening rate after storage at 0 to 10°C for 6 months or more. When the viscosity increase rate was less than 10%, the storage stability was considered to be good, taking measurement errors into account. The evaluation criteria are shown below.

(Evaluation criteria)
○: Viscosity increase rate is less than 10% ×: Viscosity increase rate is 10% or more

<Insulation resistance>
In accordance with JIS Z3284, each solder paste was reflowed and the insulation resistance value of the flux residue was measured after being exposed for 7 days in an environment of 85°C and 85% humidity, and the insulation resistance value was 1 x 10 ⁸ Ω or more. was rated as good (“○”).

The English notations in Table 2 represent the following compounds.
・CRW-300: Hydrogenated rosin (product name: “CRW-300”, acid value: 170 mgKOH/g, softening point: 84°C, manufactured by Arakawa Chemical Industry Co., Ltd.)
・MAWAXO: 12-hydroxystearic acid ethylene bisamide (product name: "MAWAXO", manufactured by KF Trading Co., Ltd.)
・Irganox1010: Hindered phenol antioxidant (product name: "Irganox1010", manufactured by BASF Japan Ltd.)
・HeDG: diethylene glycol mono-n-hexyl ether

Claims (6)

A rosin base resin for lead-free solder flux that contains fumaric acid-modified rosin (A), has an acid value of 200 to 300 mgKOH/g, and has a color tone of Gardner 3 or less. The rosin base resin for lead-free solder flux according to claim 1, wherein the modification rate of the rosin with fumaric acid is 15 to 60%. In the presence of one or more antioxidants selected from hindered phenolic antioxidants and sulfur-based antioxidants, rosins and fumaric acid are reacted to produce an acid value of 200 to 300 mgKOH/g and a color tone. A method for producing a rosin base resin for lead-free solder flux, comprising the step of obtaining a fumaric acid-modified rosin (A) having a Gardner value of 3 or less. The method for producing a rosin base resin for lead-free solder flux according to claim 3, wherein the content of the antioxidant is 0.01 to 3 parts by weight based on 100 parts by weight of the rosin. A lead-free solder flux comprising the rosin base resin for lead-free solder flux according to claim 1 or 2, an activator, a thixotropic agent, and a solvent. A lead-free solder paste comprising the lead-free solder flux and lead-free solder powder according to claim 5.