JP6399759B2 - Acrylic resin-containing soldering flux and solder paste composition - Google Patents

Description

  The present invention relates to a flux used when soldering electronic components or the like to a printed circuit board and a solder paste composition using the same, even in a harsh environment that is exposed to an intense cooling cycle over a long period of time. The present invention relates to a soldering flux capable of preventing cracks in the flux residue and suppressing stickiness of the flux residue, and a solder paste composition using the flux.

  Conventionally, a solder paste composition used for mounting electronic components on a substrate improves the wettability by removing the metal oxide on the substrate and reducing the surface tension of the solder alloy powder together with the solder alloy powder. For this purpose, a flux is blended.

  Of the substrates on which electronic components are mounted, for example, a vehicle-mounted substrate disposed in an engine room of an automobile is placed in a thermal cycle environment where there is a very high temperature difference between −40 ° C. and 125 ° C. during use. For this reason, the flux residue remaining on the in-vehicle board when mounting electronic components is prone to cracking due to this long-term difference in temperature, and moisture penetrates into the circuit part of the board through this crack and causes the circuit to break. Problems arise, such as shorting or corroding the metal of the circuit.

As a flux composition which solves such a problem, for example, (meth) acrylic acid ester having an alkyl group having _{6 to 15} carbon atoms and (meth) acrylic acid ester other than (meth) acrylic acid ester and Polymerization of a flux composition containing an acrylic resin obtained by radical copolymerization (see Patent Document 1) and a monomer component containing a long-chain alkyl (meth) acrylate in which the long-chain alkyl moiety has a branched structure having 12 to 23 carbon atoms A flux composition (Patent Document 2) containing a thermoplastic alkyl resin obtained by heating is disclosed.

JP 2011-121059 A JP 2012-200785 A

  The flux composition disclosed in Patent Document 1 and Patent Document 2 reduces the glass transition temperature (Tg) of the acrylic resin used for the base resin, thereby reducing the flux residue when the substrate is placed under a long-term cooling cycle. This is intended to suppress cracking.

  In order to prevent an increase in Tg of the acrylic resin due to the influence of the carboxylic acid derived from (meth) acrylic acid, the flux composition used for the in-vehicle substrate is similar to the acrylic resin disclosed in Patent Document 1 and Patent Document 2. An acrylic resin copolymerized with a monomer that does not contain (meth) acrylic acid is often used.

The number of carbon atoms is disclosed in Patent Document 1 has a C ₆ or C ₁₅ an alkyl group (meth) acrylic acid ester, a branched structure of a long-chain alkyl moieties disclosed in Patent Document 2 is 12 to 23 carbon atoms If an acrylic resin using a long-chain alkyl (meth) acrylate having a high temperature is used, the Tg of the flux composition can be greatly reduced, and it is assumed that it has a certain resistance to cooling in a long-term cooling cycle. Is done.

However, in the case of such a flux composition containing an acrylic resin having a low Tg, a flux residue formed using the same is easily sticky and its transparency is also lowered.
If the flux residue becomes sticky, for example, dust and dust drifting in the engine room are easily adsorbed and the transparency is deteriorated, which causes a problem that it is difficult to inspect the solder after reflow.

  In particular, an acrylic resin composed of a monomer that does not contain (meth) acrylic acid as described above has poor compatibility with an activator and an organic acid, so that each composition of the flux composition is easily separated. Therefore, a solder paste composition using such a flux composition has poor printability, and the flux residue formed thereby tends to be sticky or have a reduced transparency.

  SUMMARY OF THE INVENTION The present invention solves the above-described problems, and can achieve both the suppression of cracking of the flux residue and the suppression of stickiness of the flux residue under a long-term cooling cycle, or a soldering flux excellent in solderability, and a solder paste It is an object to provide a composition.

  The soldering flux and solder paste composition of the present invention are characterized by having the following constitution.

(1) The soldering flux of the present invention is characterized by containing an acrylic resin having an aromatic ring and an ethylene glycol structure.

(2) In the configuration described in (1) above, the acrylic resin is obtained by polymerizing a monomer containing at least one of phenoxyethylene glycol (meth) acrylate and phenoxydiethylene glycol (meth) acrylate, and is included in the monomer The blending amount of at least one of the phenoxyethylene glycol (meth) acrylate and the phenoxydiethylene glycol (meth) acrylate is 10% by weight or more based on the total amount of the monomers.

(3) In the constitution described in (1) or (2) above, the acrylic resin has a weight average molecular weight of 6,000 to 25,000.

(4) In the configuration described in any one of (1) to (3) above, the solid content acid value of the acrylic resin is 120 mgKOH / g or less.

(5) In the configuration described in any one of (1) to (4) above, the blending amount of the acrylic resin is 10 wt% to 40 wt% in terms of solid content with respect to the total amount of soldering flux It is characterized by being.

(6) The solder paste composition of the present invention is characterized by containing the soldering flux according to any one of (1) to (5) above and a solder alloy powder.

  Since the soldering flux of the present invention contains an acrylic resin having an aromatic ring and an ethylene glycol structure, it is possible to achieve both suppression of cracking of the flux residue and suppression of stickiness of the flux residue under a long-term cooling cycle.

  In particular, when the acrylic resin is obtained by polymerizing a monomer containing at least one of phenoxyethylene glycol (meth) acrylate and phenoxydiethylene glycol (meth) acrylate, it affects the flexibility of the acrylic resin obtained by the phenoxyethylene glycol group. Therefore, the stickiness can be suppressed, and it is easy to balance the cracking suppression of the flux residue and the stickiness suppression of the flux residue.

  Further, when the weight average molecular weight of the acrylic resin is 6,000 to 25,000, good solder wettability can be obtained, and when the solid content acid value of the acrylic resin is 120 mgKOH / g or less, solder is obtained. The activity of the attaching flux can be improved.

  Furthermore, when the blending amount of the acrylic resin is 10% by weight to 40% by weight in terms of solid content with respect to the total amount of soldering flux, the effect of both suppressing cracking of the flux residue and suppressing stickiness of the flux residue is more exhibited. be able to.

  And since the solder paste composition of the present invention contains such a soldering flux and a solder alloy powder, the board on which the electronic component or the like is soldered using this is placed under a long-term cooling cycle. Even if it exists, it can aim at coexistence with the crack generation suppression of the flux residue formed on the board | substrate, and the suppression of stickiness of a flux residue.

  As described above, the soldering flux and the solder paste composition of the present invention are excellent in solderability, and the flux residue formed by using the soldering flux composition for a long time under a harsh cooling / heating cycle such as −40 ° C. to 125 ° C. Even if it is a case where it exposes, suppression of a crack generation and suppression of the stickiness can be made compatible. Therefore, the soldering flux and the solder paste composition of the present invention can be suitably used for a vehicle-mounted substrate that is exposed to a severe thermal cycle for a long time.

  Hereinafter, an embodiment of the soldering flux and solder paste composition of the present invention will be described in detail.

<Acrylic resin having aromatic ring and ethylene glycol structure>
The acrylic resin having an aromatic ring and an ethylene glycol structure according to this embodiment includes, for example, a monomer containing a (meth) acrylate having an aromatic ring, a monomer containing a (meth) acrylate having an ethylene glycol structure, and an aromatic ring and an ethylene glycol structure. It is obtained by polymerizing (meth) acrylates having these or (meth) acrylic acid, alone or in combination, so that the acrylic resin produced has an aromatic ring and an ethylene glycol structure. In this polymerization, a publicly known method can be used.
As such an acrylic resin, those in which an aromatic ring and an ethylene glycol structure are directly bonded are preferably used.

  Examples of the (meth) acrylate having an aromatic ring include benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, and phenyl (meth) acrylate.

  Examples of the (meth) acrylate having an ethylene glycol structure include ethylene glycol (meth) acrylate and diethylene glycol (meth) acrylate.

  Examples of the (meth) acrylate having an aromatic ring and an ethylene glycol structure include phenoxyethylene glycol (meth) acrylate, phenoxydiethylene glycol (meth) acrylate, phenoxypolyethylene glycol (meth) acrylate, and nonylphenoxypolyethylene glycol (meth) acrylate. Can be mentioned.

In the polymerization of the acrylic resin, among these, phenoxyethylene glycol (meth) acrylate and phenoxydiethylene glycol (meth) acrylate are particularly preferably used. The acrylic resin obtained by polymerizing a monomer containing at least one of phenoxyethylene glycol (meth) acrylate and phenoxydiethylene glycol (meth) acrylate is easy to balance the suppression of cracking of the flux residue and the stickiness of the flux residue. This is because the phenoxy group contained in such an acrylic resin raises the Tg of the acrylic resin to suppress the occurrence of stickiness, and the ethylene glycol structure directly bonded to this increases the flexibility of the acrylic resin due to the rise in the Tg. It is presumed that it can be exhibited by suppressing the influence of.
When the acrylic resin is obtained by polymerizing a monomer containing at least one of phenoxyethylene glycol (meth) acrylate and phenoxydiethylene glycol (meth) acrylate, the phenoxyethylene glycol (meth) acrylate and the phenoxydiethylene glycol (meth) contained in the monomer It is preferable that the blending amount of at least one of acrylates is 10% by weight or more based on the total amount of the monomers.

  The monomer for producing the acrylic resin may contain other monomer components such as (meth) acrylic acid and (meth) acrylic acid esters such as methyl methacrylate.

（式中、Ｒ１は水素原子又はメチル基を示し、Ｒ２およびＲ３はそれぞれ炭素数２から２０の飽和アルキル基を示す。Ｒ２およびＲ３の炭素鎖は直鎖構造であり、分岐構造を含まない。） Of the monomer components, a monomer containing a compound represented by the following general formula (1) is preferably used.

(In the formula, R1 represents a hydrogen atom or a methyl group, and R2 and R3 each represent a saturated alkyl group having 2 to 20 carbon atoms. The carbon chains of R2 and R3 have a linear structure and do not include a branched structure. )

  Examples of the compound include compounds represented by the following general formulas (2) to (5).

Among the compounds represented by the general formula (1), when a compound having a saturated alkyl group having 6 to 12 carbon atoms is blended with the monomer component, the flexibility of soldering flux and flux residue is further improved. can do.
The compound represented by the general formula (1) can be obtained, for example, by subjecting a saturated alcohol having 2 to 20 carbon chains to branch at the 2-position and (meth) acrylic acid to a dehydration esterification reaction. . A known method can be used as the dehydration esterification method.

  The acrylic resin obtained by containing (meth) acrylic acid as the monomer component has good compatibility with the activator and the organic solvent contained in the soldering flux. Therefore, the soldering flux containing such an acrylic resin can suppress separation of its constituent components, improve the transparency of the flux residue formed using this, and further suppress the occurrence of stickiness. Can do.

The weight average molecular weight of the acrylic resin in this embodiment is preferably 6,000 to 25,000. The solid content acid value is preferably 120 mgKOH / g or less, and the Tg is preferably −60 ° C. or more and −20 ° C. or less.
The weight average molecular weight, acid value, and Tg of the acrylic resin can be adjusted by a known method according to the blending ratio, blending amount, and polymerization conditions of each monomer component.

  The blending amount of the acrylic resin in the present embodiment is preferably 10% by weight to 40% by weight in terms of solid content with respect to the total amount of soldering flux.

  In the present specification, (meth) acrylate means acrylate and / or methacrylate, and (meth) acryl means acryl and / or methacryl.

<Other acrylic resins>
For the soldering flux of this embodiment, an acrylic resin other than an acrylic resin having an aromatic ring and an ethylene glycol structure can be used.
Examples of such acrylic resins include monomers having a carboxyl group such as (meth) acrylic acid, itaconic acid, maleic acid, and crotonic acid; octyl (meth) acrylate, nonyl (meth) acrylate, and (meth) acrylic acid Decyl, undecyl (meth) acrylate, dodecyl (meth) acrylate, tridecyl (meth) acrylate, tetradecyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, and isoforms thereof , By polymerizing monomers such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, propyl (meth) acrylate, alone or in combination can get.

The total amount of the acrylic resin containing the aromatic resin having an aromatic ring and an ethylene glycol structure is preferably 10% by weight to 40 % by weight in terms of solid content with respect to the total amount of the soldering flux.

<Activator>
An activator can be blended in the soldering flux of this embodiment. Examples of the activator include amine salts (inorganic acid salts and organic acid salts) such as organic amine hydrogen halide salts, organic acids, organic acid salts, organic amine salts, and the like. Specifically, diphenylguanidine hydrobromide, cyclohexylamine hydrobromide, diethylamine salt, acid salt, succinic acid, adipic acid, sebacic acid and the like can be mentioned as the activator. These can be used alone or in combination.
The blending amount of the activator is preferably 5% by weight to 15% by weight with respect to the total amount of soldering flux.

<Organic solvent>
An organic solvent can be further blended in the soldering flux of this embodiment. As such an organic solvent, for example, isopropyl alcohol, ethanol, acetone, toluene, xylene, ethyl acetate, ethyl cellosolve, butyl cellosolve, glycol ether and the like can be used. These can be used alone or in combination.
The amount of the organic solvent is preferably 20% by weight to 50% by weight with respect to the total amount of soldering flux.

<Other resins>
The soldering flux of this embodiment includes gum rosin, polymerized rosin, hydrogenated rosin, heterogeneous rosin, acrylic acid modified rosin, maleic acid modified rosin and other rosin resins; styrene-maleic acid resin; Polyester resin; phenoxy resin; terpene resin, hydrogenated rosin-dimer diol condensate, and the like. These can be used alone or in combination.
When blending these resins, it is preferable to adjust the blending amount of the acrylic resin having an aromatic ring and an ethylene glycol structure to 40% by weight or more with respect to the total blending amount of the resin including the acrylic resin.

In the soldering flux of this embodiment, an antioxidant can be blended for the purpose of suppressing the oxidation of the solder alloy powder. Examples of such antioxidants include hindered phenolic antioxidants, phenolic antioxidants, bisphenolic antioxidants, and polymer-type antioxidants. Of these, hindered phenol-based oxidizing agents are particularly preferably used, but usable antioxidants are not limited to these. These can be used alone or in combination.
The blending amount of the antioxidant is not particularly limited, but is generally about 0.5 to 5% by weight with respect to the total amount of soldering flux.

In the soldering flux of this embodiment, a thixotropic agent can be blended for the purpose of adjusting the solder paste composition to a viscosity suitable for printing. Examples of such thixotropic agents include, but are not limited to, hydrogenated castor oil, fatty acid amides, and oxy fatty acids.
The blending amount of the thixotropic agent is preferably 3% by weight to 15% by weight with respect to the total amount of soldering flux.

  Furthermore, you may add additives, such as a halogen, a delustering agent, and an antifoamer, to the flux for soldering of this embodiment. The blending amount of the additive is preferably 10% by weight or less with respect to the total amount of soldering flux. A more preferable blending amount is 5% by weight or less with respect to the total amount of soldering flux.

<Solder alloy powder>
Examples of the solder alloy powder used in the solder paste composition of the present embodiment include Sn, Ag, Cu, Bi, Zn, In, Ga, Sb, Au, Pd, Ge, Ni, Cr, Al, P, and In. A combination of a plurality of As typical solder alloy powders, lead-free solder alloy powders such as Sn-Ag-Cu and Sn-Ag-Cu-In are used. Of course, solder alloy powders containing lead can also be used.

The amount of the solder alloy powder is preferably 65% by weight or more and 95% by weight or less based on the total amount of the solder paste composition. A more preferable blending amount is 85 wt% or more and 93 wt% or less, and a particularly preferable blending amount is 89 wt% or more and 92 wt% or less.
When the blending amount of the solder alloy powder is less than 65% by weight, there is a tendency that sufficient solder joints are hardly formed when the obtained solder paste composition is used. On the other hand, when the content of the solder alloy powder exceeds 95% by weight, the flux composition as a binder is insufficient, and therefore, it tends to be difficult to mix the flux composition and the solder alloy powder.

  The solder paste composition of the present embodiment is prepared by mixing the soldering flux and the solder alloy powder by a known method.

  Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. The present invention is not limited to these examples.

<Preparation of acrylic resin>
200 g of diethylhexyl glycol was charged into a 500 ml four-necked flask equipped with a stirrer, a reflux tube and a nitrogen introduction tube, and heated to 110 ° C. Thereafter, an azo radical initiator (dimethyl 2,2-azobis (2-methylpropionate: trade name) was added to a solution (total 300 g) in which monomers prepared with the compositions and blends shown in Tables 1 and 2 were mixed. : V-601, manufactured by Wako Pure Chemical Industries, Ltd.) was added in an amount of 0.2 to 5% by weight, and this solution was added dropwise to the above four-necked flask over 1.5 hours. After stirring this at 1 ° C. for 1 hour, the reaction was terminated to obtain acrylic resins A to I and acrylic resins J to N. The weight average molecular weight and acid value of acrylic resins A to I are shown in Table 3. The weight average molecular weights and acid values of the resins J to N are as shown in Table 4.

＊２ ２−エチルヘキシルメタクリレート

＊３ ラウリルメタクリレート

＊４ ２−デシルテトラデシルメタクリレート

＊５ フェノキシエチレングリコールメタクリレート
＊６ フェノキシエチレングリコールアクリレート
＊７ フェノキシジエチレングリコールメタクリレート
＊８ フェノキシジエチレングリコールアクリレート
＊９ ブトキシジエチレングリコールメタクリレート

＊１０ メトキシポリエチレングリコールモノメタクリレート

＊１１ ポリプロピレングリコールモノメタクリレート

* 1 2-Ethylhexyl acrylate

* 2 2-Ethylhexyl methacrylate

* 3 Lauryl methacrylate

* 4 2-decyltetradecyl methacrylate

* 5 Phenoxyethylene glycol methacrylate * 6 Phenoxyethylene glycol acrylate * 7 Phenoxydiethylene glycol methacrylate * 8 Phenoxydiethylene glycol acrylate * 9 Butoxydiethylene glycol methacrylate

* 10 Methoxypolyethylene glycol monomethacrylate

* 11 Polypropylene glycol monomethacrylate

<Preparation of hydrogenated rosin-dimer diol condensate>
138.6 g of acrylated rosin (trade name: KE-604, COOH: 0.6 mol, manufactured by Arakawa Chemical Industries, Ltd.) in a 500 ml four-necked flask equipped with a stirrer, a reflux pipe and a nitrogen introduction pipe, 85.5 g of dimer diol (trade name: PRIPOL 2033, OH: 0.3 mol, manufactured by CRODA) was added and stirred at 150 ° C. for 1 hour in a nitrogen atmosphere to dissolve the acrylated rosin. Next, after raising the temperature to 180 ° C., 2.3 g of a metal catalyst (trade name: ZA-45, manufactured by Matsumoto Fine Chemical Co., Ltd.) was added, and this was heated and stirred for 15 hours, and the completion of the reaction was confirmed by IR. Then, after cooling this solution to 60 degreeC, 38.6g of diethylhexyl glycol was added, and it was set as the homogeneous solution, and obtained 257g of the solution of the hydrogenated rosin-dimer diol condensate. The hydrogenated rosin-dimer diol condensate had a weight average molecular weight (Mw) of 2400 and a solid acid value of 60 mgKOH / g.

<Preparation of flux for soldering>
The soldering fluxes according to Examples 1 to 12 and Comparative Examples 1 to 5 were prepared with the formulations shown in Tables 5 and 6.

＊１２ 荒川化学工業（株）製 アクリル化ロジン
＊１３ 日本化成（株）製 チキソ剤
＊１４ ＢＡＳＦジャパン（株）製 酸化防止剤

* 12 Arakawa Chemical Industries, Ltd. Acrylic rosin * 13 Nippon Kasei Co., Ltd. thixotrope * 14 BASF Japan, Ltd. Antioxidant

  11.0 wt% of each soldering flux of Examples 1 to 12 and Comparative Examples 1 to 5 and 89.0 wt% of Sn-3Ag-0.5Cu solder alloy powder were mixed. Each solder paste composition was produced.

  The solder paste compositions of Examples 1 to 12 and Comparative Examples 1 to 5 were measured and evaluated as follows. The results are shown in Table 7 and Table 8, respectively.

<Flux residue crack resistance>
Each solder paste composition was printed on a substrate having a PQFP (Plastic Quad Flat Package) pattern with a pitch of 0.65 mm using a metal mask having the same pattern and a thickness of 150 μm. Using a reflow furnace (product name: TNP40-577PH, manufactured by Tamura Corporation), reflow was performed at a maximum temperature of 240 ° C. under an oxygen concentration of 4,000 ppm for each substrate within 10 minutes after printing. After leaving this at 150 ° C. for 120 hours, each substrate was subjected to a thermal cycle load under the condition of −40 ° C. × 30 minutes → 125 ° C. × 30 minutes for 150 cycles, and then the PQFP pattern of each substrate was The crack generation state in the soldered portion was visually observed and evaluated according to the following criteria.
○ The number of cracks connecting PQFP leads (96 locations in total) is 0.
△ Number of cracks connecting PQFP leads (96 locations in total) is less than 10 × Number of cracks connecting PQFP leads (total 96 locations) is 10 or more

<Flux residue adhesiveness>
A solder ball having a diameter of 300 μm was sprinkled on the flux residue after reflowing each substrate at 240 ° C. under the same conditions as described for the flux residue crack resistance, and the number of balls adhering to the flux residue was counted and evaluated according to the following criteria: .
〇 The number of attached balls is 0 △ The number of attached balls is 1 to 30 × The number of attached balls exceeds 30

<Flux residue appearance>
The flux residue after reflowing each substrate at 240 ° C. under the same conditions as those described for the flux residue crack resistance was visually observed and evaluated according to the following criteria.
〇 Residue after reflow at 240 ° C is clear and free of deposits △ Residue after reflow at 240 ° C is turbid but has no precipitates × Residue after 240 ° C reflow has oily content

As described above, as shown in the examples, the solder paste composition using the acrylic resin of the present invention has excellent resistance to flux residue cracking, flux residue adhesiveness and flux residue appearance, and cracks in flux residue under a long-term cooling cycle. It is possible to achieve both suppression of occurrence and stickiness of flux residue. Such a solder paste composition is particularly suitable for an on-vehicle substrate that is required to have high reliability and is exposed to a harsh cooling cycle of -40 ° C to 125 ° C for a long time.

Claims (4)

An acrylic resin having an aromatic ring and an ethylene glycol structure,
The acrylic resin includes at least one of phenoxyethylene glycol (meth) acrylate and phenoxydiethylene glycol (meth) acrylate, at least one of a compound represented by the following general formula (1) and a compound represented by the following general formula (8). Obtained by polymerizing a monomer containing
The solid content acid value of the acrylic resin is 120 mgKOH / g or less,
A soldering flux, wherein a blending amount of at least one of the phenoxyethylene glycol (meth) acrylate and the phenoxydiethylene glycol (meth) acrylate contained in the monomer is 10% by weight or more based on the total amount of the monomer.

(In the formula, R1 represents a hydrogen atom or a methyl group, and R2 and R3 each represent a saturated alkyl group having 2 to 20 carbon atoms. The carbon chains of R2 and R3 have a linear structure and do not include a branched structure. )

The soldering flux according to claim 1, wherein the acrylic resin has a weight average molecular weight of 6,000 to 25,000. The amount of the acrylic resin soldering flux according to any one of claims 1 or claim 2, characterized in that a 40% to 10% by weight in terms of solid content relative to the soldering flux total amount . A solder paste composition comprising the soldering flux according to any one of claims 1 to 3 and a solder alloy powder.