JP3490225B2 - Flux composition - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soldering flux composition. More particularly, the present invention relates to a composition for a non-cleaning flux for soldering, which is used when an electronic component is soldered to a printed wiring board. 2. Description of the Related Art When an electronic component is soldered to a printed wiring board, a flux is used to improve the adhesion of the solder. As flux, for example,
Resins such as rosin, phenol-modified rosin, and maleic acid-modified rosin, and a solution in which a halogen salt of ammonium, an organic acid, or the like is dissolved in a lower alcohol-based organic solvent such as isopropyl alcohol (iPA) are used. [0003] When soldering is performed using such a flux, resin residues of flux components and halogen ions generated by thermal decomposition remain on the printed wiring board. Such resin residues and halogen ions not only impair the appearance of the printed wiring board, but also cause insulation failure and corrosion,
Further, when a thermal cycle test is performed under severe conditions, cracks are generated in the flux residue, and as a result, the electrical and mechanical reliability of the printed wiring board is reduced. Furthermore, if the resin residue has a tack, there is a problem that the transfer roll of the printed circuit board is contaminated, the appearance is dirty, and dust is easily attached.Therefore, the flux is usually washed and removed after soldering. For cleaning, a CFC-based solvent is generally used. However, there is a problem that adding a washing step leads to an increase in product cost. In addition, there is a problem that it is difficult to use a chlorofluorocarbon solvent in the future due to environmental conservation problems. [0004] Therefore, a non-cleaning type low solid content flux having good solder adhesion has been proposed. For example, Japanese Unexamined Patent Publication (Kokai) No. 4-262893 discloses a low solids flux comprising a mixture of a partially esterified product of an organic acid such as adipic acid and a polyhydric alcohol or a higher alcohol. Such low solids fluxes have the characteristic that substantially no residues or only minimal residues remain after soldering. However, such a flux tends to be inferior in moisture resistance, for example, under severe environmental conditions (for example, 65 ° C., 95% RH, DC 100 V).
When a voltage application moisture resistance test is performed under the conditions described above, there is a problem that copper migration occurs although electrical insulation is maintained. An object of the present invention is to provide a non-cleaning type flux which has improved the conventional drawbacks and has excellent moisture resistance, cold-heat crack resistance and the like. The inventors of the present invention have studied the above problems, and as a result, have found that by using a specific acrylic copolymer as a flux composition, moisture resistance,
The present inventors have found a non-cleaning type flux having good resistance to cold and heat cracks, and have completed the present invention. That is, the flux composition of the present invention comprises:
(Meth) acrylic acid ester having an alkyl group having 8 to 15 carbon atoms (provided that methacrylic acid-n-octyl
( Excluding stell) (a) 40 to 80% by weight, carboxyl group-containing vinyl monomer (b) 3 to 60% by weight, another vinyl monomer copolymerizable with components (a) and (b) (c ) 0
It is characterized by containing an acrylic copolymer comprising up to 62% by weight. DETAILED DESCRIPTION OF THE INVENTION The (meth) acrylate (a) having an alkyl group having 8 to 15 carbon atoms, which constitutes the acrylic copolymer used in the flux composition of the present invention, is A component that imparts moisture resistance and cold / hot crack resistance to the flux, such as 2-ethylhexyl (meth) acrylate, nonyl (meth) acrylate, isononyl (meth) acrylate, lauryl (meth) acrylate, and tridecyl (meth) acrylate. Is mentioned. These components (a) can be used alone or in combination of two or more. Among them, 2-ethylhexyl (meth) acrylate is particularly preferred, and 30% by weight is preferred.
It is preferably used in an amount of at least 40% by weight. [0010] In the acrylic copolymer of the present invention,
The (meth) acrylate (a) having an alkyl group having 8 to 15 carbon atoms is used in a range of 40 to 80% by weight. If the amount of the component (a) is less than 40 % by weight, the resulting flux will have insufficient moisture resistance and cold / hot crack resistance, and if it exceeds 80% by weight, the resulting flux will have poor drying properties. This causes a tack to be applied to the applied flux, thereby contaminating the transport roll of the printed circuit board, making the appearance dirty, and tending to make dust easily adhere. Preferably, it is in the range of 50 to 75% by weight. The carboxyl group-containing vinyl monomer (b) constituting the acrylic copolymer used in the flux composition of the present invention is a component for imparting moisture resistance and drying property to the flux, and (meth) acrylic Examples include acid, itaconic acid, fumaric acid, crotonic acid, maleic acid, monomethyl itaconate, monobutyl itaconate, monomethyl maleate, monobutyl maleate and the like. These components (b) can be used alone or in combination of two or more. Among them, (meth) acrylic acid is particularly preferred. In the acrylic copolymer of the present invention,
The carboxyl group-containing vinyl monomer (b) is used in the range of 3 to 60% by weight. If the amount of the component (b) is less than 3% by weight, the resulting flux tends to have reduced moisture resistance, and also has a reduced drying property. If the content is more than 10% by weight, the acrylic copolymer tends to gel during polymerization and storage. Preferably, 5-4
0% by weight, more preferably 10 to 30% by weight. In the acrylic copolymer of the present invention, if necessary, another vinyl monomer (c) copolymerizable with the above components (a) and (b) can be used. Other vinyl monomers (c) include, for example, ethylene, propylene, chloroethylene, 1,1-dichloroethylene,
1-butene, isobutene, 1-pentene, 3-methyl-
1-butene, 4-methyl-1-pentene, 1-hexene, vinylcyclohexane, cyclobutene, cyclopentene, cyclohexene, norbornene, styrene, α-
Hydrocarbon monomers such as methylstyrene, dimethylstyrene, monochlorostyrene, dichlorostyrene, α-pinene, β-pinene, and indene; conjugated dienes such as butadiene, isoprene, chloroprene, and phenylpropadiene; 1,5-hexadiene; Non-conjugated dienes such as 1,9-decadiene; cyclopentadiene, 1,5-norbornadiene, 1,3-cyclohexadiene, 1,4-cyclohexadiene, 1,5-cyclooctadiene, 1,
Cyclic dienes such as 3-cyclooctadiene; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and isobutyl vinyl ether; methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) Acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, t-butyl (meth) acrylate, Sec-butyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, tetrahydrofurfuryl ( Meth) acrylates,
2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 2-butoxyethyl (meth) acrylate, 2-phenoxyethyl (meth)
(Meth) acrylate monomers such as acrylate, ethylcarbinol (meth) acrylate and allyl (meth) acrylate; 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl ( (Meth) acrylate, 2-hydroxyethyl vinyl ether, 4-hydroxystyrene, Alonix 5700 (2-hydroxy-
3-phenoxypropyl acrylate, Toagosei Co., Ltd.
HE-10, HE-20, HP-10 and HE
-20 (Acrylic ester oligomer having a hydroxyl group at each end, Nippon Shokubai Chemical Industry Co., Ltd.
), Blemmer PE (polyethylene glycol monomethacrylate, manufactured by NOF Corporation) and Blemmer P
P (polypropylene glycol methacrylate, manufactured by NOF Corporation), hydroxyl group-containing vinyl compound and ε
Hydroxyl-containing vinyl monomers such as ε-caprolactone-modified hydroxyalkylvinyl monomers obtained by reaction with caprolactone; other acrylamide, acrylonitrile, vinyl acetate, maleic anhydride, methyl vinyl ketone, N- Examples include radically polymerizable monomers such as vinyl carbazole. These components (c) can be used alone or in combination of two or more. In the acrylic copolymer of the present invention,
The other vinyl monomer (c) copolymerizable with the components (a) and (b) is used in the range of 0 to 62% by weight. If the amount of the component (c) exceeds 62% by weight, there is a problem that the obtained flux has insufficient moisture resistance and cooling / heat cracking resistance, and the flux composition of the present invention has the original characteristics. This is because they can no longer do it. The molecular weight of the acrylic copolymer of the present invention can be appropriately selected as required. However, in consideration of the required fluidity of the flux at the time of heating, the weight average molecular weight is 4,000 to 4,000. It is preferably in the range of 30,000. This is because, when the weight average molecular weight is less than 4,000, the melt viscosity of the flux at the time of soldering becomes too low, and as a result, soldering defects such as icicles and bridges are likely to occur, and the weight average molecular weight decreases. 30,0
If it exceeds 00, the melt viscosity of the flux at the time of soldering becomes too high, and solder balls tend to be easily formed at the time of soldering. More preferred weight average molecular weight is in the range of 5,000 to 20,000,
More preferably, it is in the range of 6,000 to 15,000. The glass transition temperature of the acrylic copolymer of the present invention is preferably 10 ° C. or less. This is because if the glass transition temperature exceeds 10 ° C., the resulting flux tends to have insufficient cold-heat crack resistance. More preferably, it is in the range of -40 to 0 ° C. Further, the acid value of the acrylic copolymer of the present invention is preferably in the range of 30 to 200 mgKOH / g. This is because when the acid value is less than 30 mgKOH / g, the moisture resistance and drying property of the obtained flux tend to decrease, and when the acid value exceeds 200 mgKOH / g,
This is because the resulting copolymer tends to gel during polymerization and storage. A more preferred acid value is 50
-180 mgKOH / g, more preferably 70-170 mgKOH / g. In order to use the acrylic copolymer of the present invention as a flux composition, it is necessary to dissolve it in a solvent. The solvent to be used can be appropriately selected as needed, but isopropyl alcohol is preferred in consideration of polarity, solubility, volatility, and the like. Thus, the acrylic copolymer of the present invention
The above-mentioned copolymer components (a) to (c) can be produced by a known polymerization method such as a solution polymerization method, a bulk polymerization method, and an emulsion polymerization method. When a flux composition is produced by a solution polymerization method using, a flux composition can be efficiently obtained. In this case, solution polymerization is preferably carried out using an azo radical initiator such as azobisisobutyronitrile or a peroxide initiator from the viewpoint of ease of production. Solvents other than isopropyl alcohol used in the solution polymerization include, for example, hydrocarbons such as toluene, xylene, n-hexane, cyclohexane, octane; methanol, ethanol, n-butanol, i-butanol, sec-
Alkyl alcohols such as butanol; ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono n-butyl ether, ethylene glycol monoethyl ether acetate, diethylene glycol dibutyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether Acetates such as ethyl acetate and butyl acetate; and ketones such as methyl ethyl ketone, ethyl acetoacetate, acetylacetone, methyl isobutyl ketone, acetone and cyclohexanone. These can be used alone or in combination of two or more. Among them, lower alcohols such as ethanol and ethers such as ethylene glycol monomethyl ether and propylene glycol monomethyl ether are compatible with isopropyl alcohol. Preferred from the point. In the polymerization, if necessary, n-
Dodecyl mercaptan, t-dodecyl mercaptan, n
Chain transfer agents such as -butyl mercaptan, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, γ-mercaptopropylmethyldimethoxysilane, and γ-mercaptopropylmethyldiethoxysilane can be used. The flux composition of the present invention in which the acrylic copolymer is dissolved in the above-mentioned solvent can be used as a flux as it is, but if necessary, an activator or the like can be added to the flux composition. The flux composition of the present invention may contain a small amount of a fungicide, a matting agent, a film-forming auxiliary, etc., if necessary. As a method of applying the flux to the printed wiring board, a generally known brush coating method, dipping method, spraying method, foaming method, wave method and the like are applied. Drying of the coated film after application may be drying at normal temperature or drying by heating. Further, by applying an acrylic resin or the like after applying the flux, the moisture-proof property and reliability of the printed wiring board can be further improved. The present invention will be specifically described below with reference to examples. All parts and percentages in the examples are by weight. The evaluation of physical properties in Examples and Comparative Examples was performed using the following methods. (1) Viscosity Value measured by Gardner-Holt foam viscometer (25 ° C.) (2) 1 g of solid acrylic copolymer was sampled in an aluminum dish,
Residue ratio after drying at 150 ° C. for 1 hour (%) (3) Number of mg of potassium hydroxide required to neutralize 1 g of acid value acrylic copolymer (4) Glass transition temperature DSC (differential calorimeter) (5) Weight average molecular weight Measured value by gel permeation chromatography (6) Insulation resistance In conformity with JIS Z 3197 (1986) ○: 10 ¹² Ω or more ×: 10 ¹² Ω or less (7) Spreading test According to JIS Z 3197 (1986) (8) Tack Printed wiring board is coated with flux and then electronic components are mounted, and the presence or absence of tack of flux residue on printed wiring board after soldering is evaluated. Yes (9) Moisture resistance 65 ° C in accordance with JIS Z 3197 (1986)
A voltage application humidity resistance test was performed under the conditions of 95% RH and DC 100 V, and the results were evaluated according to the following criteria. ：: No copper migration occurred even after 360 hours elapse: Copper migration occurred after 240 hours x: Copper migration occurred after 96 hours (10) Cold-heat crack resistant print The film thickness after drying the flux on the wiring board is 30μ
m, and dried at 250 ° C. for 30 seconds. Then, the cycle of −40 ° C. × 30 minutes → 120 ° C. × 30 minutes was set as one cycle, and after repeating 1000 cycles, the appearance of the coating film was visually judged. ：: No change in appearance ×: Cracked [Example 1] Isopropyl alcohol 9 was used as a solvent in a reaction vessel equipped with a stirrer, a temperature controller, and a condenser.
After heating to 80 ° C. while stirring, 8 parts of methyl methacrylate, 8 parts of n-butyl acrylate,
A mixture of a vinyl-based monomer composed of 45 parts of ethylhexyl acrylate, 10 parts of lauryl methacrylate, 7 parts of 2-hydroxyethyl methacrylate, 22 parts of methacrylic acid, and 3 parts of azobisisobutyronitrile and a polymerization initiator for 4 hours. Then, 0.2 parts of azobisisobutyronitrile was added three times every hour,
After hours, the reaction was terminated. Further, 10 parts of isopropyl alcohol was added to obtain a flux composition (P-1) containing an acrylic copolymer. Tables 1 and 2 show the physical property values and the evaluation results of the flux characteristics of the flux composition (P-1). Example 2 90 parts of propylene glycol monomethyl ether was added as a solvent to a reaction vessel equipped with a stirrer, a temperature controller and a condenser, heated to 100 ° C. with stirring, and then 40 parts of 2-ethylhexyl acrylate was added. A mixture of 25 parts of lauryl methacrylate, 10 parts of stearyl methacrylate, 25 parts of methacrylic acid, 5 parts of azobisisobutyronitrile and a vinyl monomer and a polymerization initiator was dropped into the reaction vessel over 4 hours. 0.2 parts of azobisisobutyronitrile was added three times every hour, and the reaction was terminated after 9 hours. Further, 10 parts of propylene glycol monomethyl ether was added to obtain a flux composition (P-2) containing an acrylic copolymer. Tables 1 and 2 show the physical property values and the evaluation results of the flux characteristics of the flux composition (P-2). Example 3 and Comparative Examples 1-4 The flux compositions (P-3) to (P-6) were prepared in the same manner as in Example 2 except that the vinyl monomers shown in Table 1 were used. ) Got. Tables 1 and 2 show the evaluation results of the physical properties and flux characteristics of these compositions. [Table 1] · IPA: isopropyl alcohol · PGM: propylene glycol monomethyl ether The composition is% by weight. IPA: isopropyl alcohol The printed wiring boards coated with the flux composed of the flux compositions (P-1) to (P-3) of the present invention are shown in Examples 1 to 3. As described above, it had excellent characteristics. On the other hand, the printed wiring boards coated with the flux compositions (P-4) to (P-6) and the flux composed of natural rosin, which do not satisfy the conditions defined by the present invention, were prepared in Comparative Examples 1 to 4. As shown in the above, it was inferior in moisture resistance, cold-heat crack resistance and the like. As is clear from the above examples, when the flux composition containing the acrylic copolymer of the present invention is used, printed wiring excellent in moisture resistance, resistance to thermal cracking, etc. Substrates can be provided, which is very useful industrially.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-9-186442 (JP, A) JP-A-5-228689 (JP, A) JP-A-4-143309 (JP, A) JP-A-3- 47694 (JP, A) JP 3-72394 (JP, B2) (58) Fields surveyed (Int. Cl. ⁷ , DB name) B23K 35/363

Claims (1)

(57) Claims 1. A (meth) acrylic ester having an alkyl group having 8 to 15 carbon atoms (provided that methacrylic acid
( excluding n-octyl ester) (a) 40 to 80% by weight, carboxyl group-containing vinyl monomer (b) 3 to 60% by weight, other vinyl monomer copolymerizable with components (a) and (b) A flux composition comprising an acrylic copolymer consisting of 0 to 62% by weight of the body (c).