JP2018122323A - Flux composition, solder paste and electronic circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flux composition which can exhibit excellent printability while suppressing occurrence of a void, occurrence of a solder ball and a solder joint failure in a solder joint even when a solder alloy containing an alloy element having strong oxidation property is used; a solder paste; and an electronic circuit board.SOLUTION: A flux composition contains (A) a base resin, (B) an activator, (C) a thixotropic agent and (D) a solvent, where a blended amount of the activator (B) is 4.5 mass% or more and 35 mass% or less with respect to the total amount of the flux composition, and the activator (B) contains predetermined amounts of (B-1) straight-chain saturated dicarboxylic acid having 3 to 4 carbon atoms, (B-2) dicarboxylic acid having 5 to 13 carbon atoms, and (B-3) dicarboxylic acid having 20 to 22 carbon atoms.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a flux composition, a solder paste, and an electronic circuit board.

  In order to join an electronic component to an electronic circuit formed on a substrate such as a printed wiring board or a silicon wafer, a solder joining method using a solder alloy is employed. Conventionally, lead has been generally used for the solder alloy. However, since the use of lead is restricted by the RoHS directive or the like from the viewpoint of environmental load, solder joining using a so-called lead-free solder alloy that does not contain lead is becoming common in recent years.

  As this lead-free solder alloy, for example, Sn—Cu, Sn—Ag—Cu, Sn—Bi, and Sn—Zn solder alloys are often used. Among them, Sn-3Ag-0.5Cu solder alloy is often used in consumer electronic devices used for televisions, mobile phones, etc. and in-vehicle electronic devices mounted on automobiles.

  Further, in recent years, for example, an electronic circuit board used in an electronic control device has a particularly severe temperature difference such as engine compartment, engine direct mounting, or mechanical / electrical integration with a motor (for example, −30 ° C. to 110 ° C., −40 ° C. In addition, the arrangement and implementation of electronic circuit boards have been studied in a severe environment in which a vibration load such as a temperature difference of from 125 to 125 ° C. and from −40 ° C. to 150 ° C. is applied.

  In Patent Document 1 to Patent Document 7, in a solder alloy used for an on-vehicle electronic circuit board placed in such an environment with a severe temperature difference, In, Bi, and Sb are highly oxidizable for the purpose of improving the mechanical characteristics thereof. A method of adding such an element is disclosed.

  Further, in Patent Document 8, in order to suppress the time-dependent change of the solder paste using the solder alloy containing the highly oxidizable element, the solder paste flux has 3 to 5 carbon dicarboxylic acid and 15 carbon as an activator. A method of using -20 dicarboxylic acids in combination is disclosed.

Japanese Patent Laid-Open No. 5-228685 Japanese Patent Laid-Open No. 9-326554 Japanese Patent Laid-Open No. 2000-190090 JP 2000-349433 A JP 2008-28413 A International Publication Pamphlet WO2009 / 011341 JP 2012-81521 A JP 2003-260589 A

However, the Sn-3Ag-0.5Cu solder alloy has a higher solidus temperature / liquidus temperature of about 40 ° C. or higher than that of conventional Sn—Pb eutectic solder, and also contains highly viscous Cu. ing. Therefore, if the activator contained in the flux composition cannot sufficiently remove the Sn-3Ag-0.5Cu-based solder alloy oxide film, voids are generated during the soldering especially when this is used for solder paste. There is a risk that voids are likely to remain in the formed solder joints.
In particular, when a highly oxidizable element such as Bi, In and Sb is added to the Sn-Ag-Cu solder alloy, the surface oxide film tends to be more difficult to remove than the Sn-3Ag-0.5Cu solder alloy. . Therefore, when the active force of the flux composition to be used is insufficient, particularly when this is used for solder paste and soldered, the viscosity of the molten alloy powder made of the solder alloy is less likely to decrease, and voids are formed in the solder joint. There is a problem that the alloy powder tends to remain, and the alloy powders are difficult to agglomerate and fuse together, and solder balls are easily generated. Solder balls cause open defects such as an unfused phenomenon between the electrodes of the electronic components mounted on the board and the solder paste, and short-circuits. Therefore, solder balls are particularly useful for automotive electronic circuit boards that require high reliability. Suppression of occurrence is one of the important issues.
Also, in solder balls used for solder joints such as Ball Grid Array (BGA) parts, if the removal of the oxide film of the solder alloy is insufficient, poor joints between the electrodes on the substrate and the electrodes on the electronic parts are likely to occur. Become. In particular, when using a solder ball in which a highly oxidizable element such as Bi, In and Sb is added to a Sn—Ag—Cu based solder alloy, the above-described bonding failure is more likely to occur.

  Even when a strong active agent and a weak active agent are used in combination in order to suppress the generation of solder balls and poor bonding due to insufficient removal of the surface oxide film of the solder alloy described above, these If only the combination is used, the oxidizing action on the solder alloy containing Bi, In, Sb and the like becomes insufficient, and it may be difficult to sufficiently exert the effect of suppressing the generation of solder balls and voids and poor bonding.

  The present invention solves the above-mentioned problems, and even when a solder alloy containing a highly oxidizable alloy element is used, it is favorable while suppressing the generation of voids in solder joints, the generation of solder balls, and poor solder joints. It is an object of the present invention to provide an electronic circuit board having a flux composition, a solder paste, and a solder joint formed using the same, which can exhibit excellent printability.

(1) The flux composition according to the present invention is a flux composition comprising (A) a base resin, (B) an activator, (C) a thixotropic agent, and (D) a solvent, wherein the activator The blending amount of (B) is 4.5% by mass or more and 35% by mass or less with respect to the total amount of the flux composition, and (B-1) linear saturation having 3 to 4 carbon atoms as the activator (B). The dicarboxylic acid is 0.5% by mass to 3% by mass with respect to the total amount of the flux composition, and (B-2) the dicarboxylic acid having 5 to 13 carbon atoms is 2% by mass to 15% by mass with respect to the total amount of the flux composition. And (B-3) containing 2 to 15% by mass of a dicarboxylic acid having 20 to 22 carbon atoms based on the total amount of the flux composition.

(2) In the configuration described in (1) above, the linear saturated dicarboxylic acid (B-1) having 3 to 4 carbon atoms is at least one of malonic acid and succinic acid, and the carbon number is Dicarboxylic acids 5 to 13 (B-2) are glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, 2-methyl azelaic acid, sebacic acid, undecanedioic acid, 2,4-dimethyl-4-methoxycarbonyl. It is at least one selected from undecanedioic acid, dodecanedioic acid, tridecanedioic acid, and 2,4,6-trimethyl-4,6-dimethoxycarbonyltridecanedioic acid, and the dicarboxylic acid having 20 to 22 carbon atoms ( B-3) is eicosadioic acid, 8-ethyloctadecanedioic acid, 8,13-dimethyl-8,12-eicosadienedioic acid and 11-vinyl-8-octadecenedioic acid. And its features is at least one selected et.

(3) In the configuration described in (1) or (2) above, the dicarboxylic acid (B-3) having 20 to 22 carbon atoms is liquid or semi-solid at normal temperature. .

(4) The flux composition according to the present invention has the structure described in any one of (1) to (3) above, and further includes an antioxidant.

(5) In the configuration described in any one of (1) to (4) above, the base resin (A) includes (A-1) a rosin resin.

(6) In the configuration described in (5) above, the base resin (A) further includes (A-2) a synthetic resin.

(7) The solder paste according to the present invention includes the flux composition according to any one of (1) to (6) above and a solder alloy powder.

(8) In the configuration described in (7) above, the solder alloy powder is characterized by being made of an alloy containing Sn and at least one selected from Pb, Ag, Bi, In, and Sb.

(9) The electronic circuit board according to the present invention is characterized by having a solder joint formed by using the solder paste according to (7) or (8).

  The electronic circuit board having the flux composition of the present invention, the solder paste, and the solder joint formed by using the solder paste generates voids in the solder joint even when a solder alloy containing a highly oxidizable alloy element is used. It is possible to exhibit good printability while suppressing the generation of solder balls and poor solder joints.

The photograph taken from the chip component side using the X-ray transmissive apparatus showing the area | region under the electrode of a chip component, and the area | region in which the fillet is formed in the test board which concerns on the Example and comparative example of this invention.

  Hereinafter, one embodiment of the flux composition, solder paste, and electronic circuit board of the present invention is described in detail. Of course, the present invention is not limited to the following embodiments.

(1) Flux composition It is preferable that the flux composition of this embodiment contains (A) base resin, (B) activator, (C) thixotropic agent, and (D) solvent.

(A) Base resin As said base resin (A), it is preferable to use at least one of (A-1) rosin resin and (A-2) synthetic resin, for example.
Examples of the rosin resin (A-1) include rosins such as tall oil rosin, gum rosin, and wood rosin; polymerization, hydrogenation, heterogeneity, acrylation, maleation, esterification, or phenol addition reaction of rosin. And a modified rosin resin obtained by subjecting these rosin or rosin derivative and an unsaturated carboxylic acid (acrylic acid, methacrylic acid, maleic anhydride, fumaric acid, etc.) to a Diels-Alder reaction. Among these, a modified rosin resin is particularly preferably used, and a hydrogenated acrylic acid-modified rosin resin hydrogenated by reacting acrylic acid is particularly preferably used. In addition, you may use these individually by 1 type or in mixture of multiple types.

  The acid value of the rosin resin (A-1) is preferably 140 mgKOH / g to 350 mgKOH / g, and its mass average molecular weight is preferably 200 Mw to 1,000 Mw.

  Examples of the synthetic resin (A-2) include acrylic resin, styrene-maleic acid resin, epoxy resin, urethane resin, polyester resin, phenoxy resin, terpene resin, polyalkylene carbonate, rosin resin having a carboxyl group, and dimer acid. Derivative compounds formed by dehydration condensation with a derivative flexible alcohol compound are exemplified. In addition, you may use these individually by 1 type or in mixture of multiple types. Among these, an acrylic resin is particularly preferably used.

  The acrylic resin can be obtained by, for example, homopolymerizing (meth) acrylate having an alkyl group having 1 to 20 carbon atoms or copolymerizing a monomer having the acrylate as a main component. Among such acrylic resins, acrylic resins obtained by polymerizing methacrylic acid and monomers containing two saturated alkyl groups having 2 to 20 carbon atoms in which the carbon chain is linear are preferably used. It is done. In addition, you may use the said acrylic resin individually by 1 type or in mixture of multiple types.

Regarding a derivative compound obtained by dehydrating and condensing the rosin resin having a carboxyl group and a dimer acid derivative flexible alcohol compound (hereinafter referred to as “rosin derivative compound”), as the rosin resin having a carboxyl group, for example, Rosin such as tall oil rosin, gum rosin, wood rosin; hydrogenated rosin, polymerized rosin, heterogeneous rosin, rosin derivatives such as acrylic acid modified rosin, maleic acid modified rosin, etc. Can be used. These may be used alone or in combination of two or more.
Next, examples of the dimer acid derivative flexible alcohol compound include compounds derived from dimer acid such as dimer diol, polyester polyol, and polyester dimer diol, and those having an alcohol group at the terminal thereof. For example, PRIPOL 2033, PRIPLAST 3197, PRIPLAST 1838 (manufactured by Croda Japan Co., Ltd.) and the like can be used.
The rosin derivative compound is obtained by dehydrating and condensing the rosin resin having a carboxyl group and the dimer acid derivative flexible alcohol compound. As the dehydration condensation method, a generally used method can be used. In addition, a preferable mass ratio when dehydrating and condensing the rosin resin having a carboxyl group and the dimer acid derivative flexible alcohol compound is 25:75 to 75:25, respectively.

  The acid value of the synthetic resin (A-2) is preferably 0 mgKOH / g to 150 mgKOH / g, and its mass average molecular weight is preferably 1,000 Mw to 30,000 Mw.

  Further, the blending amount of the base resin (A) is preferably 10% by mass or more and 60% by mass or less, and more preferably 30% by mass or more and 55% by mass or less with respect to the total amount of the flux composition.

  When the rosin resin (A-1) is used alone, the blending amount is preferably 20% by mass or more and 60% by mass or less, and 30% by mass or more and 55% by mass or less with respect to the total amount of the flux composition. More preferably. By setting the blending amount of the rosin resin (A-1) within this range, good solderability can be realized.

  Moreover, when using the said synthetic resin (A-2) independently, it is preferable that the compounding quantity is 10 to 60 mass% with respect to the flux composition whole quantity, and is 15 to 50 mass%. It is more preferable.

  Further, when the rosin resin (A-1) and the synthetic resin (A-2) are used in combination, the blending ratio is preferably rosin resin: synthetic resin = 20: 80 to 50:50, 25 : 75 to 40:60 is more preferable.

  The base resin (A) is preferably a rosin resin (A-1) alone or an acrylic resin in combination as the rosin resin (A-1) and the synthetic resin (A-2).

(B) Activator As the activator (B), (B-1) a linear saturated dicarboxylic acid having 3 to 4 carbon atoms is 0.5% by mass or more and 3% by mass or less, based on the total amount of the flux composition. (B-2) The dicarboxylic acid having 5 to 13 carbon atoms is 2% by mass to 15% by mass with respect to the total amount of the flux composition, and (B-3) the dicarboxylic acid having 20 to 22 carbon atoms is the flux composition. It is preferable to contain 2 mass% or more and 15 mass% or less with respect to the whole quantity.
It is preferable that the compounding quantity of the said activator (B) is 4.5 to 35 mass%, and it is more preferable that it is 4.5 to 20 mass%.

The linear saturated dicarboxylic acid (B-1) having 3 to 4 carbon atoms is preferably at least one of malonic acid and succinic acid.
Moreover, the more preferable compounding quantity of the said C3-C4 linear saturated dicarboxylic acid (B-1) is 0.5 mass% to 2 mass% with respect to the flux composition whole quantity.

The carbon chain in the dicarboxylic acid (B-2) having 5 to 13 carbon atoms may be either linear or branched, but glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid 2-methyl azelaic acid, sebacic acid, undecanedioic acid, 2,4-dimethyl-4-methoxycarbonylundecanedioic acid, dodecanedioic acid, tridecanedioic acid, and 2,4,6-trimethyl-4,6-dimethoxy It is preferably at least one selected from carbonyl tridecanedioic acid. Of these, adipic acid, suberic acid, sebacic acid and dodecanedioic acid are particularly preferably used.
Moreover, the more preferable compounding quantity of the said C5-C13 dicarboxylic acid (B-2) is 3 mass% to 12 mass% with respect to the flux composition whole quantity.

  The carbon chain in the dicarboxylic acid (B-3) having 20 to 22 carbon atoms may be either a straight chain or a branched chain, but eicosadioic acid, 8-ethyloctadecanedioic acid, 8,13 It is preferably at least one selected from dimethyl-8,12-eicosadiene diacid and 11-vinyl-8-octadecenedioic acid.

  Further, as the dicarboxylic acid (B-3) having 20 to 22 carbon atoms, those that are liquid or semi-solid at room temperature are more preferably used. In this specification, normal temperature refers to a range of 5 ° C to 35 ° C. The semi-solid state refers to a state corresponding to a liquid state and a solid state, a part of which has fluidity and a state of non-fluidity but deformed when external force is applied. As the dicarboxylic acid (B-3) having 20 to 22 carbon atoms, 8-ethyloctadecanedioic acid is particularly preferably used.

  Moreover, the more preferable compounding quantity of the said C20-C22 dicarboxylic acid (B-3) is 3 mass% to 12 mass% with respect to the flux composition whole quantity.

  As the activator (B), a dicarboxylic acid corresponding to each carbon number range of the activators (B-1), (B-2) and (B-3) is blended according to the blending amount. The flux composition of the embodiment can sufficiently remove the oxide film even when a solder alloy to which an element having high oxidizing properties such as Bi, In, and Sb is added is used. Therefore, when this is used as a solder paste, it is possible to improve the cohesive force between the alloy powders made of the solder alloy and to reduce the viscosity at the time of melting the solder, and this occurs in the solder balls and solder joints generated beside the electronic components. Voids can be reduced. Further, even when solder bonding is performed using solder balls, surface oxidation of the solder balls can be sufficiently suppressed, so that bonding failure between the electrodes on the substrate and the electrodes of the electronic component can be suppressed.

Particularly when used in solder paste, the linear saturated dicarboxylic acid (B-1) having 3 to 4 carbon atoms is partially mixed with the alloy powder when the flux composition and the alloy powder are kneaded. The surface can be coated to suppress its surface oxidation. Further, the dicarboxylic acid (B-3) having 20 to 22 carbon atoms is slow in reactivity, so that it is stable in a solder paste printing process on a substrate for a long time and hardly volatilizes even during reflow heating. Therefore, it is possible to cover the surface of the molten alloy powder and suppress oxidation by a reducing action.
However, the dicarboxylic acid (B-3) having 20 to 22 carbon atoms has low activity, and the combination with the linear saturated dicarboxylic acid (B-1) having 3 to 4 carbon atoms oxidizes the surface of the alloy powder. There is a possibility that the film cannot be sufficiently removed. Therefore, particularly when a solder alloy powder containing Bi, In, Sb or the like is used, the oxidizing action on the alloy powder becomes insufficient, and it is difficult to sufficiently exhibit the effect of suppressing solder balls and voids.

  However, the flux composition of the present embodiment is a dicarboxylic acid having 5 to 13 carbon atoms (B-2) that exerts a strong activity from the preheating agent (B-1) and (B-3). ) Is contained in a predetermined amount, the oxide film can be sufficiently removed even when such an alloy powder is used while ensuring the reliability of the flux residue. Therefore, the flux composition of the present embodiment improves the cohesive force between the alloy powders and reduces the viscosity at the time of melting the solder, thereby causing voids generated in the solder balls and solder joints generated beside the electronic component. Can be reduced. In addition, due to such an action, even when the flux composition is used for a solder ball, it is possible to suppress a bonding failure between the electrode on the substrate and the electrode on the electronic component.

  That is, the flux composition of this embodiment is a combination of dicarboxylic acids corresponding to a specific carbon number range of the activators (B-1), (B-2), and (B-3) in a predetermined blending amount. By blending with each other, it is possible to exhibit a better redox effect on the solder alloy than a combination of a so-called short-chain dicarboxylic acid and a long-chain dicarboxylic acid. Moreover, the flux composition combined with such an activator can also exhibit good printability.

The flux composition of the present embodiment can be blended with other active agents as long as the above effects are not impaired.
Examples of such other activators include amine salts (inorganic acid salts and organic acid salts) such as organic acid hydrogen halide salts, organic acids, organic acid salts, and organic amine salts. Specifically, diphenylguanidine hydrobromide, cyclohexylamine hydrobromide, diethylamine salt, dimer acid, levulinic acid, lactic acid, acrylic acid, benzoic acid, salicylic acid, anisic acid, citric acid, 1,4- Examples include cyclohexanedicarboxylic acid, anthranilic acid, picolinic acid, and 3-hydroxy-2-naphthoic acid. You may use these individually by 1 type or in mixture of multiple types.
It is preferable that the compounding quantity of the said other active agent is more than 0 mass% and 20 mass% or less with respect to the flux composition whole quantity.

(C) Thixotropic agent Examples of the thixotropic agent (C) include hydrogenated castor oil, fatty acid amides, saturated fatty acid bisamides, oxy fatty acids, and dibenzylidene sorbitols. You may use these individually by 1 type or in mixture of multiple types.
The blending amount of the thixotropic agent (C) is preferably 2% by mass or more and 15% by mass or less, and more preferably 2% by mass or more and 10% by mass or less with respect to the total amount of the flux composition.

(D) Solvent Examples of the solvent (D) include isopropyl alcohol, ethanol, acetone, toluene, xylene, ethyl acetate, ethyl cellosolve, butyl cellosolve, hexyl diglycol, (2-ethylhexyl) diglycol, phenyl glycol, and butyl carbitol. , Octanediol, α-terpineol, β-terpineol, tetraethylene glycol dimethyl ether, trimellitic acid tris (2-ethylhexyl), bisisopropyl sebacate and the like. You may use these individually by 1 type or in mixture of multiple types.
The blending amount of the solvent (D) is preferably 20% by mass or more and 50% by mass or less, and more preferably 25% by mass or more and 40% by mass or less with respect to the total amount of the flux composition.

The flux composition of this embodiment can be blended with an antioxidant for the purpose of suppressing oxidation of the solder alloy. Examples of the antioxidant include hindered phenolic antioxidants, phenolic antioxidants, bisphenolic antioxidants, and polymer-type antioxidants. Of these, hindered phenol-based oxidizing agents are particularly preferably used. You may use these individually by 1 type or in mixture of multiple types.
The blending amount of the antioxidant is not particularly limited, but generally it is preferably about 0.5% by mass or more and about 5% by mass or less based on the total amount of the flux composition.

An additive can be mix | blended with the flux composition of this embodiment as needed. Examples of the additive include an antifoaming agent, a surfactant, a matting agent, and an inorganic filler. You may use these individually by 1 type or in mixture of multiple types.
The blending amount of the additive is preferably 0.5% by mass or more and 20% by mass or less, and more preferably 1% by mass or more and 15% by mass or less with respect to the total amount of the flux composition.

(2) Solder paste It is preferable that the solder paste of this embodiment contains the said flux composition and the solder alloy powder which consists of a solder alloy.

<Solder alloy powder>
As the solder alloy powder, a lead-free solder alloy powder is preferably used. The solder paste of the present embodiment is free from the occurrence of voids in the solder joints, regardless of the components of the solder alloy used, and even when highly oxidizable components such as Bi, In, and Sb are used. Good printability can be exhibited while suppressing generation and solder joint failure.

  Examples of alloys that can be used for the solder alloy powder include, for example, Sn and Ag, Bi, In, Sb, Cu, Zn, Ga, Ge, Au, Pa, Ni, Cr, Al, P, Cd, Tl, An alloy containing at least one selected from Se, Ti, Si, Mg, and the like can be given. Even elements other than those listed above can be used in combination.

The solder paste of this embodiment can be obtained, for example, by kneading the flux composition and the solder alloy powder.
The mixing ratio of the solder alloy powder and the flux composition is preferably 65:35 to 95: 5 in the ratio of solder alloy powder: flux composition. The more preferred blending ratio is 85:15 to 93: 7, and the particularly preferred blending ratio is 87:13 to 92: 8.

  The average particle size of the alloy powder is preferably 1 μm or more and 40 μm or less, more preferably 5 μm or more and 35 μm or less, and particularly preferably 10 μm or more and 30 μm or less.

(3) Electronic Circuit Board The electronic circuit board according to the present embodiment includes a solder joint formed using the solder paste and a flux residue (in this specification, the solder joint and the flux residue are combined to form a “solder joint”). It is preferable to have a body. The electronic circuit board includes, for example, an electrode and a solder resist film formed at a predetermined position on the substrate, the solder paste of this embodiment is printed using a mask having a predetermined pattern, and an electronic component conforming to the pattern is obtained. It is manufactured by mounting it at a predetermined position and reflowing it.
In the electronic circuit board thus manufactured, a solder joint is formed on the electrode, and the solder joint electrically joins the electrode and the electronic component. And on the said board | substrate, the flux residue has adhered so that it may adhere | attach to a solder joint part at least.

In the electronic circuit board of this embodiment, the solder joint is formed using the solder paste. Therefore, even when a solder alloy containing a highly oxidizable alloy element is used, voids are generated in the solder joint and solder is formed. Good printability can be exhibited while suppressing the generation of balls.
An electronic circuit board having such a solder joint can be suitably used for an electronic circuit board that is required to have high reliability, such as a vehicle-mounted electronic circuit board.

  Further, an electronic control device is manufactured by incorporating such an electronic circuit board.

  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.

<Synthesis of acrylic resin>
A solution in which 10% by mass of methacrylic acid, 51% by mass of 2-ethylhexyl methacrylate, and 39% by mass of lauryl acrylate were mixed was prepared.
Thereafter, 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. Next, dimethyl 2,2′-azobis (2-methylpropionate) (product name: V-601, manufactured by Wako Pure Chemical Industries, Ltd.) as an azo radical initiator was added to 300 g of the solution from 0.2% by mass to 5%. Mass% was added to dissolve it.
This solution was added dropwise to the four-necked flask over 1.5 hours, and the components in the four-necked flask were stirred at 110 ° C. for 1 hour, and then the reaction was terminated to obtain a synthetic resin. The weight average molecular weight of the synthetic resin was 7,800 Mw, the acid value was 40 mgKOH / g, and the glass transition temperature was −47 ° C.

  Each component described in Table 1 to Table 4 was kneaded to obtain each flux composition according to Examples 1 to 16 and Comparative Examples 1 to 18. In addition, unless otherwise indicated, the unit of blending amounts in Tables 1 to 4 is mass%.

* 1 Hydrogenated acid-modified rosin manufactured by Arakawa Chemical Co., Ltd. * 2 Hexamethylenebishydroxystearic acid amide manufactured by Nippon Kasei Co., Ltd. * 3 Hindered phenolic antioxidant manufactured by BASF Japan

<Preparation of solder paste>
The solder composition according to Examples 1 to 16 and Comparative Examples 1 to 18 was prepared by mixing 11.2% by mass of the flux composition and 88.8% by mass of the following solder alloy powder.
Example 1, Comparative Example 4: Sn-3Ag-0.5Cu Solder Alloy Example 2, Comparative Example 5: Sn-3Ag-59Bi Solder Alloy Example 3, Comparative Example 6: Sn-2Ag-58Bi-0.5Cu- 0.1Ni solder alloy Example 4 and Comparative Example 7: Sn-3Ag-0.5Cu-3.5Bi-3Sb-0.04Ni-0.01Co solder alloy Examples 5 to 16, Comparative Examples 1 to 3 and 8 18: Sn-3Ag-0.5Cu-0.5Bi-2.5Sb-4In-0.15Ni solder alloy * The particle size of the solder alloy powder is 20 μm to 36 μm.

(1) Void test A chip component having a size of 2.0 mm × 1.2 mm, a solder resist having a pattern on which the chip component of the size can be mounted, and an electrode (1.25 mm × 1.0 mm) for connecting the chip component And a 150 μm thick metal mask having the same pattern were prepared.
Each solder paste was printed on the glass epoxy substrate using the metal mask, and the chip component was mounted on each glass paste substrate.
Thereafter, using a reflow furnace (product name: TNP-538EM, manufactured by Tamura Seisakusho Co., Ltd.), each of the glass epoxy substrates is heated to electrically bond the glass epoxy substrate and the chip component to each other. A part was formed, and the chip component was mounted. The reflow conditions at this time are: preheating from 170 ° C. to 190 ° C. for 110 seconds, peak temperature of 245 ° C., time of 200 ° C. or higher for 65 seconds, time of 220 ° C. or higher for 45 seconds, peak temperature to 200 ° C. The cooling rate was 3 ° C. to 8 ° C./second, and the oxygen concentration was set to 1500 ± 500 ppm.
Next, the surface state of each test substrate was observed with an X-ray transmission device (product name: SMX-160E, manufactured by Shimadzu Corporation), and the area under the electrode of the chip component (see FIG. The area ratio of voids (ratio of the total area of voids; the same applies hereinafter) and the area where fillets are formed (area (b) surrounded by broken lines in FIG. 1) The average value of the area ratio of voids in the area was determined and evaluated as follows. The results are shown in Tables 5 to 8, respectively.
A: The average value of the void area ratio is 3% or less and the effect of suppressing the generation of voids is very good. ○: The average value of the void area ratio is more than 3% and 5% or less, and the effect of suppressing the generation of voids. △: The average value of the void area ratio is more than 5% and 8% or less, and the effect of suppressing the generation of voids is sufficient. ×: The average value of the void area ratio exceeds 8%, and the effect of suppressing the generation of voids insufficient

(2) Solder ball test Each test substrate under the same conditions as in the above (1) void test except that the peak temperature of the reflow condition is 260 ° C., the time of 200 ° C. or higher is 70 seconds, and the time of 220 ° C. or higher is 60 seconds. The surface state of each test substrate was observed with an X-ray transmission device (product name: SMX-160E, manufactured by Shimadzu Corporation), and the number of solder balls generated on the periphery and lower surface of the chip component was counted. And evaluated as follows. The results are shown in Tables 5 to 8, respectively.
A: No. of balls generated around 10 chip resistors of 2.0 mm × 1.2 mm. O: No. of balls generated around 10 chip resistors of 2.0 mm × 1.2 mm exceeds 0 and less than 5. : The number of balls generated around 10 chip resistors of 2.0 mm × 1.2 mm exceeds 5 and less than 10 ×: The number of balls generated around 10 chip resistors of 2.0 mm × 1.2 mm exceeds 10

(3) Copper plate corrosion test A test was conducted in accordance with the conditions specified in JIS standard Z 3284 (1994) and evaluated as follows. The results are shown in Tables 5 to 8, respectively.
○: No discoloration of Cu plate ×: Discoloration of Cu plate (4) Printability test Glass epoxy substrate having solder resist and electrode (diameter 0.25 mm) having a pattern capable of mounting 100-pin 0.5 mm pitch BGA A 120 μm thick metal mask having the same pattern was prepared.
6 pieces of each solder paste are printed continuously on the glass epoxy substrate using the metal mask, and the transfer volume ratio at a diameter of 0.25 mm is measured by an image inspection machine (product name: aspire2, manufactured by Koyon Technology Co., Ltd.) Was evaluated according to the following criteria. The results are shown in Tables 5 to 8, respectively.
A: Number of transfer volume ratio of 35% or less is 0; O: Transfer volume ratio of 35% or less is more than 0 and 10 or less Δ: Number of transfer volume ratio of 35% or less is more than 10 and 50 or less × : Number of transfer volume ratio 35% or less exceeds 50

As shown above, the solder paste according to the example includes the linear saturated dicarboxylic acid (B-1) having 3 to 4 carbon atoms and the dicarboxylic acid having 5 to 13 carbon atoms as the activator (B). If only an alloy powder of Sn-3Ag-0.5Cu solder alloy is used by using a flux composition containing a predetermined amount of acid (B-2) and dicarboxylic acid (B-3) having 20 to 22 carbon atoms, In addition, even when a solder alloy powder containing a large amount of highly oxidizable Bi and a solder alloy powder containing highly oxidizable Sb, In, Bi, Ni, and Co are used, It can be seen that generation of solder balls can be sufficiently suppressed, corrosion of the copper plate can be suppressed, and good printability can be exhibited.
In addition, for example, even when the flux composition containing the dicarboxylic acid (B-2) having 5 to 13 carbon atoms is used as in Comparative Examples 5 to 10, if the blending amount is small, the solder joint is used. It can be seen that the effect of suppressing the generation of voids and solder balls is insufficient.

As mentioned above, the flux composition of this invention can be used suitably also for the electronic circuit board by which high reliability is calculated | required, such as a vehicle-mounted electronic circuit board. Furthermore, such an electronic circuit board can be suitably used for an electronic control device that requires higher reliability.

Claims (9)

A flux composition comprising (A) a base resin, (B) an activator, (C) a thixotropic agent, and (D) a solvent,
The blending amount of the activator (B) is 4.5% by mass or more and 35% by mass or less based on the total amount of the flux composition.
As the activator (B), (B-1) linear saturated dicarboxylic acid having 3 to 4 carbon atoms is 0.5% by mass or more and 3% by mass or less, and (B-2) carbon based on the total amount of the flux composition. 2 to 15% by mass of the dicarboxylic acid having 5 to 13 with respect to the total amount of the flux composition, and (B-3) 2% of the dicarboxylic acid having 20 to 22 carbon atoms with respect to the total amount of the flux composition. % Or more and 15% by mass or less. The linear saturated dicarboxylic acid (B-1) having 3 to 4 carbon atoms is at least one of malonic acid and succinic acid,
The dicarboxylic acid (B-2) having 5 to 13 carbon atoms is glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, 2-methyl azelaic acid, sebacic acid, undecanedioic acid, 2,4-dimethyl- And at least one selected from 4-methoxycarbonylundecanedioic acid, dodecanedioic acid, tridecanedioic acid and 2,4,6-trimethyl-4,6-dimethoxycarbonyltridecanedioic acid,
The dicarboxylic acid (B-3) having 20 to 22 carbon atoms is eicosadioic acid, 8-ethyloctadecanedioic acid, 8,13-dimethyl-8,12-eicosadienedioic acid and 11-vinyl-8-octadecenedioic acid. It is at least 1 sort (s) chosen from these, The flux composition of Claim 1 characterized by the above-mentioned.   The flux composition according to claim 1 or 2, wherein the dicarboxylic acid (B-3) having 20 to 22 carbon atoms is liquid or semi-solid at normal temperature.   The flux composition according to any one of claims 1 to 3, further comprising an antioxidant.   The flux composition according to any one of claims 1 to 4, wherein the base resin (A) includes (A-1) a rosin resin.   The flux composition according to claim 5, wherein the base resin (A) further comprises (A-2) a synthetic resin.   A solder paste comprising the flux composition according to any one of claims 1 to 6 and a solder alloy powder.   The solder paste according to claim 7, wherein the solder alloy powder is made of Sn and an alloy containing at least one selected from Ag, Bi, In, Sb, Cu, Ni, and Co.   An electronic circuit board having a solder joint formed by using the solder paste according to claim 7 or 8.