JP2008110369A - Cream solder flux and cream solder - Google Patents

Abstract

The present invention provides a flux composition and a cream solder that are capable of forming a flux residue film that is excellent in insulation without causing cracks in a flux residue film after soldering even in an environment with a large temperature difference. thing.
A cream solder flux containing a flux base, a solvent, a thixotropic agent and an activator, wherein the flux base contains an acrylic resin (A) having a glass transition temperature of -100 to -50 ° C. A cream solder flux containing solder powder and the cream solder flux.
[Selection figure] None

Description

  The present invention relates to a flux for cream solder and cream solder.

  As the flux used for mounting electronic parts, etc., a liquid flux that is applied by spraying or the like, and a paste-like flux for use as a so-called cream solder composition in which a flux composition and solder powder are kneaded are known. Yes.

  The liquid flux is generally composed of a rosin, an activator, a solvent, and the like, and the paste flux is generally composed of a rosin, a solvent, an activator, a thixotropic agent, a solder powder, and the like.

  As described above, rosins (rosin or derivatives thereof) are generally used as the base resin used for liquid flux and paste-like flux. This is probably because rosins are excellent in corrosion resistance due to the rosin skeleton, and are excellent in electrical properties such as electrical insulation resistance and dielectric properties. However, since rosins are hard and brittle, a flux residue film obtained after soldering a rosin-containing flux is used in an environment with a large temperature difference, for example, in a low temperature atmosphere of about −40 ° C. and a high temperature atmosphere of about 125 ° C. In the case of repeated exposure to each other, there is a problem that cracks are easily generated. When cracks occur in the flux residue film, moisture in the atmosphere adheres to and penetrates into the cracks, causing serious problems such as a decrease in insulation resistance and the occurrence of migration.

  In order to prevent the occurrence of the above problems, measures such as cleaning and removing the flux residue film after soldering with an organic solvent-based cleaning liquid such as chlorofluorocarbon, alternative chlorofluorocarbon, and organic solvents, and a moisture-proof coating treatment have been taken. It was. However, the use of the cleaning solution is not desirable from the viewpoint of protecting the global environment, and also from the viewpoint of reducing production costs, the role of the flux residual film that does not require a cleaning process or a moisture-proof coating process, that is, the role of the moisture-proof coating. There is also a need for a flux residue film that also combines. More specifically, a flux residue film that has excellent electrical reliability, does not crack even in an environment with a large temperature difference, and covers the solder surface and circuit surface after soldering to provide a moisture-proof effect is provided. The appearance of excellent flux compositions and cream solder compositions that can be made is desired.

  The present applicants have previously proposed a flux composition for cream soldering comprising a polyether ester amide resin, a solvent, an activator and a thixotropic agent (see Patent Document 1), but further printing stability, There has been a demand for improved storage stability.

JP 2004-230426 A

  The present invention provides a flux composition and cream solder capable of forming a flux residue film having excellent insulation without cracking in the flux residue film after soldering even in an environment with a large temperature difference. The purpose is to do.

In order to solve the above problems, the present inventor pays attention to the base resin in the soldering flux composition, and lowers the glass transition temperature (Tg) of the flux residue in order to control the occurrence of cracks in the flux residue. In addition, the flexibility of the residue is maintained even at low temperatures, the stress caused by the thermal cycle is efficiently relieved, and the composition is not changed by exposure to high temperature during reflow so that the Tg is not increased. As a result of intensive studies on heat-resistant base resins so that deterioration does not occur on the high temperature side during the assumed cooling cycle, acrylic resins obtained using specific monomers have both low Tg and heat resistance It has been found that the above problems can be solved by using the resin, and the present invention has been completed.

  That is, the present invention is characterized in that in a flux for cream solder containing a flux base, a solvent, a thixotropic agent and an activator, the flux base contains an acrylic resin having a glass transition temperature of −100 to −50 ° C. The present invention relates to a cream solder containing a solder powder and the cream solder flux.

According to the present invention, a flux composition and a cream that are capable of forming a flux residue film that is excellent in insulation without cracking in the flux residue film after soldering even in an environment with a large temperature difference. Solder can be provided.

  The acrylic resin (A) having a glass transition temperature of −100 to −50 ° C. (hereinafter referred to as “component (A)”) used in the present invention is obtained by polymerizing a (meth) acrylic monomer. When the glass transition temperature is lower than −100 ° C., the heat resistance cannot be maintained, which is not preferable. When the glass transition temperature exceeds −50 ° C., the flexibility of the residue at low temperatures is insufficient, which is not preferable. In the present invention, the glass transition temperature is a value measured according to a JIS K7121 plastic transition temperature measurement method.

The acrylic monomer used when the component (A) is produced is not particularly limited as long as the glass transition temperature of the component (A) to be obtained is -100 to -50 ° C. However, it is preferable to use alkyl (meth) acrylates (a) (hereinafter referred to as component (a)) having 13 or more carbon atoms in the alkyl group from the viewpoint of flexibility and heat resistance of the residue at low temperatures. The alkyl group may be linear or have a branched structure. Moreover, it may have an alicyclic structure such as an aromatic functional group such as a phenyl group or a cyclohexyl group (however, in this case, when counting the number of carbon atoms, an aromatic group or an alicyclic carbon Numbers shall not be counted.) Specific examples of the component (a) include tridecyl (meth) acrylate, tetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate, ( Examples thereof include octadecyl (meth) acrylate and nonadecyl (meth) acrylate. These may be used alone or in combination of two or more. In addition, it is preferable that the carbon number of the alkyl group is 13 to 18 because the raw material is easily available.

In addition to the component (a), alkyl (meth) acrylates (b) (hereinafter referred to as the component (b)) having 12 or less carbon atoms in the alkyl group may be used. It is preferable to use the component (b) because it is easy to adjust physical properties such as viscosity when used in the flux. Specific examples of the component (b) include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, and t-butyl (meth) acrylate. , Octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, (meth) acrylic acid And isobornyl. These may be used alone or in combination of two or more.

Furthermore, in addition to the component (a) and the component (b), an anionic monomer (c) (hereinafter referred to as the component (c)) may be used. The component (c) is not particularly limited as long as it has at least one anionic functional group and one vinyl group, and known components can be used. Specifically, for example, monocarboxylic acids such as (meth) acrylic acid and crotonic acid; dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, muconic acid and citraconic acid; vinyl sulfonic acid, styrene sulfonic acid, 2- Examples thereof include organic sulfonic acids such as acrylamido-2-methylpropanesulfonic acid; and sodium salts and potassium salts of these various organic acids. These may be used alone or in combination of two or more.

(A) Although the usage-amount of each component used in order to obtain a component is not specifically limited, Usually, polymerizing the monomer component which contains about 5 to 100 weight% of (a) component is flexible of the residue at the time of low temperature This is preferable because the heat resistance and heat resistance are improved. In addition, the amount of component (b) used / the amount of component (a) used (weight ratio) is set to 0.01 to 0.5, so that the flexibility and heat resistance of component (a) are not impaired. Since it becomes easy to adjust physical properties, such as a viscosity at the time of using, it is preferable.

The method for polymerizing these monomer components is not particularly limited, and a known method can be employed. Specifically, for example, the monomer component may be polymerized in the presence of a polymerization initiator, a solvent, a chain transfer agent or the like, if necessary.

The physical properties of the component (A) thus obtained are not particularly limited as long as the glass transition temperature is −100 to −50 ° C. Usually, the weight average molecular weight is about 1,000 to 1,000,000. , Preferably it is 2,000-200,000.

Moreover, well-known flux bases other than (A) component can also be used together for a flux base. Specifically, for example, rosin resins such as gum rosin, polymerized rosin, hydrogenated rosin, disproportionated rosin, modified rosin (for example, acrylic acid-modified rosin), rosin esters, and other various rosin derivatives, and polyester resins And synthetic resins such as polyetheresteramide resin, polyamide resin, polyimide resin, phenoxy resin, and terpene resin. These may be used alone or in combination of two or more. When these known flux bases are used, it is usually preferable that the amount of the component (A) used is about 20% by weight or more in the flux base.

The solvent is not particularly limited, and known solvents can be used. Specifically, alcohols such as ethanol, n-propanol, isopropanol, isobutanol, glycol ethers such as butyl carbitol, hexyl carbitol, phenyl glycol, hexyl diglycol, isopropyl acetate, ethyl propionate, butyl benzoate And esters such as diethyl adipate and hydrocarbons such as n-hexane, dodecane and tetradecene. These may be used alone or in combination of two or more.

The thixotropic agent is not particularly limited as long as it is a thixotropic agent used in the production of a flux, and known ones can be used. Specifically, for example, hardened castor oil, beeswax, carnauba wax, stearic acid amide, hydroxystearic acid ethylene bisamide, hydroxystearic acid hexamethylene bisamide, and the like can be used. These may be used alone or in combination of two or more.

The amount of each of these components may be appropriately adjusted according to the application, but is usually about 30 to 75 parts by weight of flux base, about 20 to 60 parts by weight of solvent, about 1 to 10 parts by weight of thixotropic agent, and 0. About 1 to 20 parts. In addition, in the flux for cream solder of this invention, additives, such as antioxidant, an antifungal agent, a rust preventive agent, and a matting agent, can be contained as needed.

  The cream solder of the present invention contains solder powder and the cream solder flux.

  The alloy composition of the solder powder of the present invention is not particularly limited, and various known ones can be used. For example, as a solder alloy, a conventionally known tin-lead alloy, a solder alloy composition such as a tin-silver alloy and a tin-zinc-based alloy that have been developed as a lead-free solder; , Indium, antimony and the like can be used.

Further, the shape of the solder powder is not particularly limited, and any shape such as a true sphere, an indefinite shape, or a mixture of both can be used.

Although the usage-amount of each component should just be determined suitably according to a use etc., a solder powder is about 80-95 weight part normally, and the flux for cream solder is about 5-20 weight part. Moreover, you may add various well-known additives as needed.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in more detail, this invention is not limited to the following Example. The glass transition temperature conforms to “JIS K7121 Plastic Dislocation Temperature Measurement Method”, and a differential scanning calorimeter (Seiko Denshi Kogyo Co., Ltd., DSC220C) is used to prepare a 10 mg sample at a heating rate of 10 ° C./second. The measurement was performed under the conditions, and the intersection point was determined by the tangent method.

Production Example 1
A glass reaction vessel equipped with a thermometer, a stirrer, a dropping funnel, and a nitrogen introduction tube was charged with 100 parts by weight of butyl glycol, and this was stirred at 115 ° C. under a nitrogen stream, and then 250 parts by weight of butyl glycol, A mixed solution of 125 parts by weight of dodecyl methacrylate, 125 parts by weight of octadecyl methacrylate and 15 parts by weight of azoisobutyronitrile (AIBN) was added dropwise. The reaction was further continued for 4 hours while maintaining the temperature at 100 ° C., and then unreacted substances were distilled off under reduced pressure to obtain an acrylic resin 1 having a glass transition temperature of −56 ° C.

Production Example 2
A glass reaction vessel equipped with a thermometer, a stirrer, a dropping funnel and a nitrogen introduction tube was charged with 100 parts by weight of methyl isobutyl ketone, and after stirring at 100 ° C. under a nitrogen stream, 250 parts by weight of methyl isobutyl ketone A mixed solution of 200 parts by weight of dodecyl acrylate, 50 parts by weight of 2-ethylhexyl acrylate, and 20 parts by weight of AIBN was added dropwise. The reaction was further continued for 4 hours while maintaining the temperature at 100 ° C., and then unreacted substances were distilled off under reduced pressure to obtain an acrylic resin 2 having a glass transition temperature of −72 ° C.

Production Example 3
A glass reaction vessel equipped with a thermometer, a stirrer, a dropping funnel, and a nitrogen introducing tube was charged with 100 parts by weight of hexyl glycol, and the mixture was stirred at 110 ° C. in a nitrogen stream, and then 100 parts by weight of dodecyl methacrylate. A mixed solution of 80 parts by weight of octadecyl methacrylate, 50 parts by weight of 2-ethylhexyl acrylate, 20 parts by weight of butyl acrylate and 20 parts by weight of AIBN was added dropwise. The reaction was further continued for 4 hours while maintaining the temperature at 100 ° C., and then unreacted substances were distilled off under reduced pressure to obtain an acrylic resin 3 having a glass transition temperature of −68 ° C.

Examples 1-3 and Comparative Examples 1-2
(Preparation of flux composition)
Each component of the flux shown in Table 1 (the amount used of each component in the table is parts by weight) was charged into a container, heated and dissolved at about 200 ° C., and then cooled to obtain a cream solder flux.

(Preparation of cream solder composition)
89 parts by weight of solder powder (Sn—Ag—Cu alloy having a particle size of 20 to 40 μm, Sn / Ag / Cu content is 96.5 wt% / 3 wt% / 0.5 wt%) 11 parts by weight of each flux composition prepared by the method was placed in a container and stirred to prepare a cream solder composition.

(Evaluation)
(Cooling cycle test)
After the cream solder composition obtained above is printed on the QFP pattern provided on the glass epoxy substrate and reflowed, -40 ° C., 30 minutes, 125 ° C., 30 minutes as one cycle, 1000-2500 cycles The presence or absence of cracks in the flux residue film after the cooling cycle was observed. Judgment criteria are as follows. The results are shown in Table 1.
○: Good (no crack), △: Usable (crack is observed, but does not penetrate to the substrate surface or solder surface), ×: Bad (crack penetrates to the substrate surface or solder surface)

(Insulation resistance test)
A cream solder composition is printed on a comb-shaped electrode substrate JISII type (no resist), reflowed, put into a constant temperature and humidity chamber at a temperature of 85 ° C and a relative humidity of 85%, and the insulation resistance value after 1000 hours is measured by an insulation resistance meter. It measured using.
○: 1 × 10 ⁹ Ω or more ×: Less than 1 × 10 ⁹ Ω

(Solderability)
Conforms to “JIS Z 3284 Annex 10 Wetting Efficacy and Dewetting Test”. Judgment criteria followed the extent of spread. The results are shown in Table 1.
○: Spread degree category 2 or more ×: Spread degree category 3 or less

In the table, hydrogenated rosin is manufactured by Arakawa Chemical Industries, Ltd., trade name “KR-614”, and polymerized rosin is manufactured by Arakawa Chemical Industries, Ltd., trade name “China Polymerized Rosin 140”, polyether ester amide resin. Is a reaction product of linear diamine, polymerized fatty acid and polyethylene glycol having a glass transition temperature of −60 ° C. and a number average molecular weight of 30,000 (polystyrene conversion value by gel permeation chromatography), and hydrogenated dimer acid is The product name “Pripol 1010” manufactured by Unikema Co., Ltd., and the castor wax produced by Toyokuni Oil Co., Ltd. were used as the hardened castor oil.

Claims (6)

A cream solder flux containing a flux base, a solvent, a thixotropic agent and an activator, wherein the flux base contains an acrylic resin (A) having a glass transition temperature of −100 to −50 ° C. flux. The cream resin for cream solder according to claim 1, wherein the acrylic resin (A) is an acrylic resin obtained by polymerizing a monomer mixture containing at least an alkyl (meth) acrylate having an alkyl group having 13 or more carbon atoms (a). flux. The flux for cream solder according to claim 2, wherein the monomer mixture further contains alkyl (meth) acrylates (b) having 12 or less carbon atoms in the alkyl group. The flux for cream solder according to claim 2 or 3, wherein the monomer mixture further contains an anionic monomer (c). The acrylic resin (A) is an acrylic resin obtained by polymerizing a monomer mixture containing 5 to 100% by weight of an alkyl (meth) acrylate (a) having at least 13 carbon atoms in the alkyl group. The flux for cream solder in any one of -4. The cream solder containing the solder powder and the flux for cream solder according to any one of claims 1 to 5.