JP2014195830A - Flux for lead-free solder for clearance resist, and lead-free solder paste for clearance resist - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide flux that increases wettability of lead-free solder metal on a clearance resist in the atmosphere.SOLUTION: Flux for lead-free solder paste for a clearance resist comprises a rosin-based base resin (A), a solvent (B) and an activator (C). The (A) component comprises α,β unsaturated carboxylic acid-modified rosin (a1). The (B) component is a propylene glycol-based ether (b1) with a boiling point of 275°C or less. The (C) component is a dibasic acid (c1) represented by the general formula (1) defined by HOOC-R-COOH, where R is a C2-C4 hydrocarbon group.

Description

  The present invention relates to a flux for lead-free solder for clearance resist and a lead-free solder paste for clearance resist.

  The soldering flux is a material used for surface mounting electronic parts such as ICs, capacitors, and resistors on a printed board or the like. In surface mounting, for example, electronic components are mounted by supplying solder paste onto a printed circuit board by screen printing or a dispenser, placing an electronic component on the printed circuit board, and then reflowing the substrate above the melting point of the solder metal. Bonded onto the electrode of the substrate.

  By the way, the current mainstream lead-free solder (Sn—Ag—Cu system, Sn—Cu system, etc.) has a higher melting point than the mainstream lead eutectic solder (Sn—Pb system, etc.) and is oxidized. For this reason, when a solder paste using this is melted on a substrate electrode such as copper, gold, or tin, many solder balls may be generated around the electrode. Therefore, in this field, the preheating temperature is adjusted or soldering is performed in a nitrogen atmosphere, and the latter method is particularly useful. However, in recent years, there has been a tendency to perform reflow in an air atmosphere in consideration of manufacturing costs, and solder balls have been more likely to occur than before.

  In recent years, as electrical appliances are further reduced in size, solder paste is strongly required to have mounting performance corresponding to a minute electrode pattern on a mounting board. Furthermore, as the electrode pattern becomes smaller, in recent years, from the conventional overresist structure in which a solder resist is formed on the outer periphery of the conductor land (FIG. 2), from the viewpoint of suppressing the chip standing of components and improving the bonding strength, the outer periphery of the land There is a tendency to use a clearance resist structure (FIG. 3) in which no solder resist is formed on the part. Regarding the clearance resist system, for example, Patent Document 1 is detailed to some extent.

  Unlike the over-resist structure, the clearance resist structure tends to cause liquid flux to easily flow out of the conductor land from the solder paste that has been heated during reflow to reduce its viscosity. At this time, the oxide film formed on the surface of the solder particles Is not reduced, and there is a problem that a solder melting defect (wetting defect) occurs (see Patent Document 2). Furthermore, this defect becomes more prominent when the reflow atmosphere is air.

JP2003-249747 JP 2010-212318 A

  The main object of the present invention is to provide a flux capable of enhancing the wettability of lead-free solder metal in an electrode on a clearance resist even in an air atmosphere.

  As a result of intensive studies, the present inventors have found that a compound containing a predetermined base resin, a solvent and an activator is effective as a flux for a lead-free solder paste for a clearance resist.

  That is, the present invention relates to rosin-based base resin (A) (hereinafter referred to as component (A)), solvent (B) (hereinafter referred to as component (B)), activator (C) (hereinafter referred to as component (C). ), Thixotropic agent (D) (hereinafter referred to as component (D)) and antioxidant (E) (hereinafter referred to as component (E)), A propylene glycol ether (b1) (hereinafter referred to as component (b1)) having a saturated carboxylic acid-modified rosin (a1) (hereinafter referred to as component (a1)) and a component (B) having a boiling point of 275 ° C. or lower. And a dibasic acid (c1) represented by the general formula (1): HOOC-R-COOH (wherein R represents a hydrocarbon group having 2 to 4 carbon atoms) , (C1) component)) for clearance resists Flux for lead-free solder paste (hereinafter sometimes referred to simply as flux), and lead-free solder paste for clearance resist containing the flux and lead-free solder powder (hereinafter sometimes simply referred to as lead-free solder paste) , Regarding.

  According to the flux of the present invention, sufficient wettability of the lead-free solder metal on the electrode on the clearance resist can be ensured even in an air atmosphere. Further, since this flux does not require any residue to be removed, it is particularly suitable for a non-cleaning type mounting substrate. Moreover, the lead-free solder paste obtained by using the flux of the present invention is excellent in screen printing suitability.

It is the graph which showed the reflow temperature profile in an Example and a comparative example. FIG. 2 is a schematic diagram (cross section) of an overresist structure, a top view (photograph) of a soldered land, and a state diagram (photograph) when the lead-free solder paste according to Comparative Example 1 is melted on the land. FIG. 2 is a schematic diagram (cross section) of a clearance resist structure, a top view (photograph) of a soldered land, and a state diagram (photograph) when the lead-free solder paste according to Comparative Example 1 is melted on the land. It is a state figure (photograph) when the lead-free solder paste which concerns on Example 1 is fuse | melted on the soldering land of an over resist structure. FIG. 6 is a state diagram (photograph) when the lead-free solder paste according to Example 1 is melted on a soldering land having a clearance resist structure.

  In order to obtain the effect of the present invention, the component (A) has the component (a1) as an essential requirement. Examples of the α, β unsaturated carboxylic acid constituting the component (a1) include α, β unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid, and α, β unsaturated acids such as maleic acid, maleic anhydride and fumaric acid. Saturated sidicarboxylic acid is mentioned. The rosins constituting the component (a1) include, for example, raw rosins such as gum rosin and wood rosin, purified rosins (purified rosins), hydrides thereof (hydrogenated rosins), and their disproportionates. In particular, purified rosins are preferred. As the component (a1), α, β unsaturated monocarboxylic acid-modified rosin is preferable, and hydrogenated acrylic acid-modified rosin is particularly preferable.

  In addition to the component (a1), the raw material rosins, purified rosins, hydrogenated rosins (excluding the component (a1)), disproportionated rosins, polymerized rosins, and a combination of these rosins and polyols Esters (rosin esters) can be used in combination. Examples of the polyol include glycerin and pentaerythritol. Among these, hydrogenated rosins (except for those corresponding to α, β unsaturated carboxylic acid-modified rosins) and / or disproportionated rosins are excellent in removing oxide film of lead-free solder metal. This is preferable for improving wettability.

  The component (B) has the component (b1) as an essential requirement for obtaining the effects of the present invention. The component (b1) is a high boiling point solvent having a boiling point of 275 ° C. or lower, specifically about 200 to 275 ° C., preferably about 200 to 250 ° C., for example, butyl propylene triglycol (boiling point 274 ° C.) methylpropylene tri Examples include glycol (boiling point 242 ° C.), phenylpropylene glycol (boiling point 243 ° C.), butyl propylene diglycol (boiling point 231 ° C.), propyl propylene diglycol (boiling point 212 ° C.), and the like. Among these, at least one selected from the group consisting of methylpropylene triglycol, butylpropylene diglycol, phenylpropylene glycol and butylpropylene triglycol from the viewpoint of wettability on the clearance resist, particularly methylpropylene triglycol and butylpropylene At least one selected from the group consisting of diglycol and phenylpropylene glycol is preferred. If a solvent other than the propylene glycol ether is used, or a propylene glycol ether having a higher boiling point is used, unmelting of the solder is likely to occur on the clearance resist when the component is mounted.

  The component (C) has the component (c1) as an essential requirement for obtaining the effects of the present invention. The component (c1) is a compound represented by the general formula (1): HOOC-R-COOH (wherein R represents a hydrocarbon group having 2 to 4 carbon atoms). Alkylene aliphatic dibasic acids such as succinic acid, glutaric acid and adipic acid, and / or alkenylene aliphatics such as fumaric acid, maleic acid, maleic anhydride, pentenedicarboxylic acid, hexenedicarboxylic acid and acetylenedicarboxylic acid Among these, dibasic acids are mentioned, and among these, at least one selected from the group consisting of succinic acid, glutaric acid and adipic acid, fumaric acid and maleic acid is preferable from the viewpoint of wettability on the clearance resist. Note that it is difficult to obtain the effect of the present invention even when a dibasic acid having R of 1 or more than 5 is used.

  In addition, (C) component can contain activators other than (c1) component as needed. Examples thereof include saturated or unsaturated aliphatic dibasic acids such as oxalic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, dimer acid and itaconic acid; trans-2,3-dibromo -1,4-butenediol, cis-2,3-dibromo-1,4-butenediol, 1-bromo-2-butanol, 1-bromo-2-propanol, 3-bromo-1-propanol, 3-bromo Bromo alcohols such as -1,2-propanediol, 1,4-dibromo-2-butanol, 1,3-dibromo-2-propanol, 2,3-dibromo-1-propanol; 3-bromopropionic acid, 2 -Bromovaleric acid, 5-bromo-n-valeric acid, 2-bromoisovaleric acid, 2,3-dibromosuccinic acid, 2-bromosuccinic acid, 2,2-dibromoazi Brominated dicarboxylic acids such as acids; saturated or unsaturated aliphatic monobasic acids such as capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, stearic acid, oleic acid, linoleic acid; benzoylbenzoic acid, benzoic acid Monobasic acids having aromatic or heterocyclic rings such as hydroxybenzoic acid, picolinic acid, furancarboxylic acid; bromohydroxycarboxylic acids such as dibromosalicylic acid; ethylamine bromate, diethylamine bromate, diethylamine hydrochloride, methyl Amine-based bromo compounds such as amine bromate; 1-bromo-3-methyl-1-butene, 1,4-dibromobutene, 1-bromo-1-propene, 2,3-dibromopropene, 1,2-dibromo -1-phenylethane, 1,2-dibromostyrene, 4-stearoyloxybenzene Bromide, 4-stearyloxybenzyl bromide, 4-stearylbenzyl bromide, 4-bromomethylbenzyl stearate, 4-stearoylaminobenzyl bromide, 2,4-bisbromomethylbenzyl stearate, 4-palmitoyloxybenzyl bromide, Active hydrogen-free bromo compounds such as 4-myristoyloxybenzyl bromide, 4-lauroyloxybenzyl bromide, 4-undecanoyloxybenzyl bromide; Halogen atom-free amines such as stearylamine, distearylamine, and dibutylamine Etc., and these can be used alone or in combination of two or more.

  As the component (D), various known ones can be used without particular limitation, but polyamide thixotropic agents and / or animal and plant thixotropic agents are particularly preferable from the viewpoint of printability of the lead-free solder paste. Examples of the polyamide thixotropic agent include stearic acid amide and 12-hydroxystearic acid ethylene bisamide, and examples of the animal and plant type thixotropic agent component include hardened castor oil, beeswax, carnauba wax, and the like. Or in combination of two or more.

  Specific examples of the component (E) include pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- ( 3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 2 , 4-Bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino) -1,3,5-triazine, 2,2-thio-diethylenebis [3- (3 , 5-di-t-butyl-4-hydroxyphenyl) propionate], octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, N, N ′ Hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinamide), 3,5-di-t-butyl-4-hydroxybenzylphosphonate-diethyl ester, 1,3,5- Hindered phenolic antioxidants of trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene; 2,6-di-t-butyl-p-cresol, 2 , 4-Dimethyl-6-t-butyl-phenol, styrenatephenol, 2,4-bis [(octylthio) methyl] -o-cresol, and other phenolic antioxidants; triphenyl phosphite, triethyl phosphite , Trilauryl trithiophosphato, tris (tridecyl) phosphite and other phosphorus antioxidants; Sulfur antioxidants such as luthiodipropionate, dilauryl sulfide, 2-mercaptobenzimidazole, lauryl stearyl thiodipropionate can be exemplified, and these can be used alone or in combination of two or more. . Among these, a hindered phenol antioxidant is preferable from the viewpoint of wettability and color tone of the flux residue. When the color tone of the flux residue is good, visual inspection (confirmation of wetting spread, etc.) of the solder joint becomes easy, and cleaning is not necessary.

Although content of (A) component-(F) component in the flux of this invention is not specifically limited, Usually, it is as follows.
Component (A): Usually about 25 to 50% by weight, preferably 35 to 45% by weight
Component (B): Usually about 20 to 70% by weight, preferably 25 to 55% by weight
Component (C): Usually about 3 to 15% by weight, preferably 5 to 7% by weight
Component (D): Usually about 0 to 20% by weight, preferably 2.5 to 10% by weight
Component (E): Usually about 0 to 10% by weight, preferably 2 to 8% by weight

  The lead-free solder paste of the present invention is a composition containing the flux of the present invention and lead-free solder powder. Moreover, although the usage-amount of each is not specifically limited, Usually, the former is about 5 to 30 weight% and the latter is about 70 to 95 weight%.

  As the lead-free solder powder, various known ones can be used without particular limitation as long as they do not contain lead, but Sn-based lead-free solder powders such as Sn-Ag series, Sn-Cu series, Sn-- Sb-based, Sn-Zn-based, and Sn-Bi-based lead-free solder powders are preferred. The lead-free solder powder is doped with one or more elements of Ag, Al, Au, Bi, Co, Cu, Fe, Ga, Ge, In, Ni, P, Pt, Sb, and Zn. It may be a thing. Specific examples of the lead-free solder powder include Sn95Sb5, Sn99.3Cu0.7, Sn97Cu3, Sn92Cu6Ag2, Sn99Cu0.7Ag0.3, Sn95Cu4Ag1, Sn97Ag3, Sn96.3Ag3.7, Sn42-Bi58 and the like. Moreover, although the average particle diameter of lead-free solder powder is not specifically limited, Usually, about 1-50 micrometers, Preferably it is 15-40 micrometers. Further, the shape of the powder is not particularly limited, and may be spherical or irregular. The spherical shape preferably means that the aspect ratio of the powder is within 1.2.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the technical scope of the present invention is not limited to these examples. In the examples, “%” and “part” mean “% by weight” and “part by weight” unless otherwise specified.

<Preparation of flux>
Example 1
44.5 parts of commercially available hydrogenated acrylic acid-modified rosin (trade name “KE-604”, manufactured by Arakawa Chemical Industries, Ltd.), 44 parts of commercially available methylpropylene triglycol (manufactured by Nippon Emulsifier Co., Ltd.), 5 parts of succinic acid (SA), 6 parts of polyamide thixotropic agent (trade name “MA-WAX-O”, manufactured by Kawaken Fine Chemical Co., Ltd.), and antioxidant (trade name “Irganox 1010”), Ciba -Japan Co., Ltd.) was mixed well under heating to prepare a flux.

Examples 2-12, Comparative Examples 1-7
The raw materials of Example 1 were mixed well under heating in the parts shown in Tables 1 and 2 to prepare a flux.

<Confirmation of wettability: Aspect of solder paste>
89 g of commercially available lead-free solder powder (96.5Sn / 3Ag / 0.5Cu, manufactured by Mitsui Kinzoku Co., Ltd., particle size 20-38 μm, normal product), and the flux of Example 1 in order of 89 wt% and 11 wt% A solder paste was prepared by kneading with a softener. Next, this solder paste is printed on a pattern having a clearance resist structure using a stencil mask having a thickness of 100 μm, and then a 0603 capacitor is mounted on a mounter, and reflow is performed in an air atmosphere with a temperature profile shown in FIG. It was. After reflow, the wettability of the solder on the part was visually judged according to the following criteria. Moreover, the wettability of the solder was similarly judged visually about the flux of Examples 2-12 and Comparative Examples 1-7.

(Degree of wettability)
A: There is no unmelted solder in the solder bonded to the part.
○: Partially unmelted solder can be confirmed.
X: All the solders are not melted.

  FIG. 2 is a photograph of the solder paste using the flux of Comparative Example 1 when reflowed on a pattern having an over resist structure, and it can be seen that the solder powder is melted.

  On the other hand, FIG. 3 is a photograph when the solder paste using the flux of Comparative Example 1 is reflowed on the pattern having the clearance resist structure, and it can be confirmed that the solder powder remains almost unmelted.

  On the other hand, FIG. 4 is a photograph when the solder paste using the flux of Example 1 is reflowed on a pattern having an over resist structure, and it can be confirmed that there is no unmelted solder.

  Moreover, FIG. 5 is a photograph when the solder paste using the flux of Example 1 is reflowed on the pattern having the clearance resist structure, and it can be confirmed that there is no unmelted solder.

* 1 ... Commercial hydrogenated rosin (trade name “CRW-300”, manufactured by Arakawa Chemical Industries, Ltd.)
* 2 ... Methyl propylene triglycol (trade name “MFTG”, manufactured by Nippon Emulsifier Co., Ltd., boiling point 242 ° C.)
* 3 ... Butyl propylene diglycol (trade name “BFDG”, manufactured by Nippon Emulsifier Co., Ltd., boiling point 231 ° C.)
* 4 ・ ・ ・ Phenylpropylene glycol (trade name “PhFG”, Nippon Emulsifier Co., Ltd., boiling point 243 ° C.)
* 5 ... Butylpropylene triglycol (Brand name "BFTG", Nippon Emulsifier Co., Ltd., boiling point 274 ° C)
* 6 Succinic acid (manufactured by Tokyo Chemical Industry Co., Ltd.)
* 7 ... Glutaric acid (manufactured by Tokyo Chemical Industry Co., Ltd.)
* 8 ... Adipic acid (manufactured by Tokyo Chemical Industry Co., Ltd.)
* 9 ... Fumaric acid (manufactured by Tokyo Chemical Industry Co., Ltd.)

* 10: Hexyl diglycol (trade name “HeDG”, Nippon Emulsifier Co., Ltd., boiling point 259 ° C.)
* 11 ... 2-ethylhexyl diglycol (trade name “EHDG”, manufactured by Nippon Emulsifier Co., Ltd., boiling point 272 ° C.)
* 12 ... 2-hexyldecanol (trade name “Engecol 160BR”, manufactured by Shin Nippon Rika Co., Ltd., boiling point 195-215 ° C.)
* 13 ... Oxalic acid (manufactured by Tokyo Chemical Industry Co., Ltd.)
* 14 ... Suberic acid (manufactured by Tokyo Chemical Industry Co., Ltd.)
* 15 ... Dodecanedioic acid (manufactured by Tokyo Chemical Industry Co., Ltd.)
* 16: In the flux of Comparative Example 2, precipitation of CRW-300 was remarkable, and it was difficult to prepare a homogeneous solder paste, so wettability was not evaluated.

Claims (11)

The rosin base resin (A), the solvent (B) and the activator (C) are included, the component (A) includes the α, β unsaturated carboxylic acid-modified rosin (a1), and the component (B) has a boiling point of 275. The propylene glycol ether (b1) at a temperature not higher than ° C. and the component (C) is represented by the general formula (1): HOOC-R—COOH (wherein R represents a hydrocarbon group having 2 to 4 carbon atoms). A flux for a lead-free solder paste for a clearance resist, which is a dibasic acid (c1) represented. The flux according to claim 1, wherein the component (a1) is a hydrogenated acrylic acid-modified rosin. The flux according to claim 1 or 2, wherein the component (A) further contains a hydrogenated rosin and / or a disproportionated rosin. The flux according to any one of claims 1 to 3, wherein the component (b1) is at least one selected from the group consisting of methylpropylene triglycol, butylpropylene diglycol, phenylpropylene glycol, and butylpropylene triglycol. The flux according to any one of claims 1 to 4, wherein the component (c1) is at least one selected from the group consisting of succinic acid, glutaric acid, adipic acid, fumaric acid and maleic acid. Furthermore, the flux in any one of Claims 1-5 containing a thixotropic agent (D). The flux according to claim 6, wherein the component (D) is a polyamide thixotropic agent and / or an animal or plant type thixotropic agent. Furthermore, the flux in any one of Claims 1-7 containing antioxidant (E). (E) The flux in any one of Claims 1-8 whose component is a hindered phenolic antioxidant. The flux in any one of Claims 1-9 whose content of (A) component, (B) component and (C) component, and (D) component and (E) component is as follows.
(A) component: 25-50 weight%
(B) component: 20 to 70% by weight
Component (C): 3 to 15% by weight
(D) component: 0 to 20% by weight
(E) component: 0 to 10% by weight
A lead-free solder paste for a clearance resist containing the flux according to any one of claims 1 to 10 and a lead-free solder powder.