JP2022022508A - Flux, solder paste, electronic circuit mounting substrate, and electronic control device - Google Patents

Abstract

To provide a flux which can suppress occurrence of a whisker in a solder joint part and can exhibit good solderability and storage stability, a solder paste, an electronic circuit mounting substrate and an electronic control device.SOLUTION: A flux contains a base resin, an organic acid, a heterocyclic compound and a solvent, and contains 0.05 mass% or more and less than 15 mass% of a cyclohexanedicarboxylic acid as the organic acid with respect to the total amount of the flux, and contains 0.05 mass% or more and less than 15 mass% of the heterocyclic compound with respect to the total amount of the flux.SELECTED DRAWING: None

Description

The present invention relates to flux, solder paste, electronic circuit mounting boards and electronic control devices.

As a method of joining electronic components to an electronic circuit formed on an electronic circuit board (printed wiring board, silicon wafer, etc.), a solder joining method using a solder joining material such as a solder alloy is generally used. .. Examples of this solder joining method include flow soldering (a method in which an electronic circuit board and an electronic component are brought into contact with molten solder to perform soldering) and reflow soldering (a method in which an alloy powder made of a solder alloy and a flux are mixed). A method of remelting solder paste, solder preform, etc. in a reflow oven and soldering) and the like.
Then, by this solder bonding, a solder bonding portion is formed on the electronic circuit mounting board, and the electrodes on the electronic circuit mounting board and the electrodes of the electronic components are electrically bonded.

Conventionally, lead has been used for this solder alloy. However, since the use of lead is restricted by the RoHS Directive from the viewpoint of environmental load, in recent years, a solder joining method using a so-called lead-free solder alloy that does not contain lead is becoming common.

As the lead-free solder alloy, for example, Sn—Cu type, Sn—Ag—Cu type, Sn—Bi type, Sn—Zn type solder alloy and the like are well known. Among them, Sn-Ag-Cu-based solder alloys, which are relatively well-balanced in terms of solder alloy strength, melting point, cost, etc., are widely used for electronic circuit mounting boards of consumer electronic devices and in-vehicle electronic devices. ing.

However, when solder bonding is performed using a lead-free solder alloy, the generation of whiskers, which could hardly occur in a lead-containing solder alloy, has become a problem.
Here, the whisker is a crystal that grows mainly like a whiskers from the surface of the metal crystal toward the outside. When soldering using a lead-free solder alloy, many whiskers containing Sn as a main component have been confirmed, especially in electrodes on electronic circuit mounting boards and electrodes of electronic components.

It is considered that the cause of this whisker is that Sn contained in the plating is recrystallized by the residual stress generated inside the plating applied to the electrodes on the electronic circuit mounting substrate and the electrodes of the electronic components. Therefore, such growth of whiskers can be prevented by reflowing the plating and resolidifying it to remove internal stress.

However, in recent years, it has been reported that whiskers also occur in solder joints formed on electronic circuit mounting boards. Since the whiskers generated in the solder joints have conductivity, they may cause a short circuit in the electric circuit and significantly reduce the electrical reliability.
In particular, the environment in which in-vehicle electronic devices are used is a high-temperature and high-humidity environment in which corrosion is more likely to be promoted than consumer electronic devices, and since they may be used for a long period of time, whiskers are likely to occur and grow. If easy.

In the future, further electrification and autonomous driving of automobiles will progress, and it is expected that the number of sensors and communication devices installed in automobiles will further increase accordingly. However, since there is a limit to the mounting space for electronic devices in automobiles, further downsizing is required for electronic devices.
Space saving of electronic devices naturally leads to space saving of electronic circuit mounting boards and electronic components mounted on them. Therefore, the electronic components mounted on the electronic circuit mounting board are required to be further miniaturized and densified.

Due to the miniaturization and high density of electronic components, the pitch between electronic components and conductor patterns becomes even narrower, so that short circuits in electric circuits caused by whiskers generated at solder joints are more likely to occur. As described above, suppressing the generation of whiskers at the solder joints is becoming one of the important issues, especially in in-vehicle electronic devices.

Here, the lead-free solder alloy is inferior in solderability as compared with the lead-containing solder alloy. Therefore, a method of adding a halogen compound containing a halogen element such as bromine or iodine is widely used for the purpose of supplementing the solderability to the flux used as an auxiliary material at the time of solder bonding.

However, the halogen compound (halogen element) contained in the flux is considered to be one of the causes of whiskers generated in the solder joint described above.
That is, Sn contained in the lead-free solder alloy forming the solder joint is oxidized and corroded by moisture and oxygen in the surrounding environment and a halogen component contained in the flux residue remaining around the solder joint. It changes to SnO ₂ . Since the volume of the portion of the solder joint where Sn becomes SnO ₂ expands, when corrosion (change to SnO ₂ ) progresses, compressive stress is generated in the uncorroded portion of the solder joint, and this compressive stress is generated. It is thought that it will lead to the outbreak of whiskers.
As described above, the halogen compound (halogen element) contained in the flux acts as a catalyst to promote the corrosion reaction of Sn contained in the solder joint, and is deeply involved in the generation of whiskers in the solder joint. it is conceivable that.

Applicants prepared a flux A to which a halogen compound containing bromine or iodine was added and a flux B to which a halogen compound was not added, and the flux A and the flux B were each an alloy powder made of a lead-free solder alloy. Using the solder pastes A and B kneaded with the above, it was confirmed whether or not whiskers were generated at the solder joint in a high temperature and high humidity environment.
As a result, whiskers were confirmed to be generated in the formed solder joints in the solder paste A using the flux A, whereas the solder paste B using the flux B was 2,000 in a high temperature and high humidity environment. No whiskers were found at the solder joints even after being left for a long time.

As described above, it can be seen that it is effective to use a flux that does not contain a halogen compound in order to suppress the generation of whiskers in the solder joint. However, as described above, the lead-free solder alloy is inferior in solderability in terms of wettability and generation of voids as compared with the lead-containing solder alloy. Therefore, it is naturally expected that the solderability will be deteriorated when soldering is performed using a lead-free solder alloy and a flux not containing a halogen compound as compared with a flux containing a halogen compound.
Therefore, it is a flux that can suppress the generation of whiskers even if it contains a halogen compound, or does not contain a halogen compound, or has a reduced amount of the flux, and its solderability even when a lead-free solder alloy is used. Providing a flux that does not impair the problem has been an issue.

Patent No. 4325746 Patent No. 6370324 Japanese Unexamined Patent Publication No. 2011-143445 International Publication No. 2012/118074 Pamphlet Patent No. 446109 Patent No. 5667101

Patent Document 1 discloses a non-cleaning resin-based flux for lead-free solder containing 0.2 to 4% by mass of at least one compound selected from an acidic phosphoric acid ester and a derivative thereof. By containing a small amount of acidic phosphoric acid ester in the flux, the flux can suppress the generation of whiskers in the solder joint even when a halogen compound is used as an activator.

Patent Document 2 contains a hydrotalcite compound having a chlorine concentration of 900 mass ppm or less, a bromine concentration of 900 mass ppm or less, and a halogen concentration of 1,500 mass ppm or less in the flux composition. Disclosed is a solder composition comprising a flux composition. By setting the chlorine concentration and the halogen concentration to a predetermined value or less, the flux composition can suppress the generation of Sn whiskers in the solder joint portion.

The flux containing the acidic phosphoric acid ester disclosed in Patent Document 1 and the flux composition containing the hydrotalcite compound disclosed in Patent Document 2 are the flux and air taken into the molten solder at the time of solder bonding. May be difficult to discharge. Therefore, there is a possibility that voids are likely to occur inside the solder joint portion formed by using the solder paste using these fluxes. When the voids generated in the solder joints are placed in an environment with a large temperature difference such as in-vehicle electronic devices, they cause cracks in the solder joints, which may lead to a decrease in reliability. be.

Further, Patent Document 3 discloses a flux containing no halogen compound. The flux does not contain a halogen compound, and by using at least one of an organic acid and an amine compound as an activator, it is possible to suppress the generation of whiskers at the solder joint and improve the wettability at the same time. ..
However, it is not disclosed that the flux disclosed in Patent Document 3 can exhibit high reliability even in the mounting of miniaturized and high-density electronic components, that is, in the mounting of electronic components having a narrow pitch. ..

Patent Document 4 discloses a flux containing no halogen compound. By combining an organic acid with an imidazole derivative or an organic amine as an activator, the flux can improve the wettability of the flux even when a halogen compound is not added.

Patent Document 5 discloses a solder flux composition that does not positively contain a halogen compound. The solder flux composition can exhibit appropriate viscosity, fluidity, adhesiveness and slipperiness by containing an activating component composed of methylsuccinic acid and an imidazole compound or an imidazole derivative.

Patent Document 6 discloses a solder composition having a vehicle containing no halogen compound. The solder composition exhibits excellent solderability and storage stability by containing an unsaturated fatty acid having 8 or more carbon atoms, an organic acid other than the unsaturated fatty acid, and a vehicle containing a predetermined imidazole compound. It is possible.

However, a flux containing an imidazole derivative or an imidazole compound may deteriorate the storage stability of the flux and the solder paste using the flux.
Here, as described above, in the mounting of miniaturized and high-density electronic components, the average particle size of the alloy powder made of a lead-free solder alloy is about 10 μm from the conventionally used one of about 30 μm. It is being considered to change to the one. Such an alloy powder having a small average particle size can increase the amount of the oxide film as the surface area per unit volume increases.
Therefore, a more active flux may be required to remove the oxide film.
However, although it is disclosed that the flux of Patent Document 6 can exhibit excellent storage stability, it also provides good storage stability even in a solder paste using an alloy powder having a large surface area per unit volume. It is not disclosed that it can be exerted.

An object of the present invention is to provide a flux, a solder paste, an electronic circuit mounting board, and an electronic control device capable of suppressing the generation of whiskers in a solder joint and exhibiting good solderability and storage stability.

The flux of the present invention contains a base resin, an organic acid, a heterocyclic compound, and a solvent, and the compound represented by the following general formula (1) is added as the organic acid by 0.05 mass with respect to the total amount of the flux. % Or more and less than 15% by mass, and the heterocyclic compound is contained in an amount of 0.05% by mass or more and less than 15% by mass with respect to the total amount of the flux.

（前記一般式（１）中、Ｘは１つ以上のカルボキシル基、アルキル基及び水素原子の群から選ばれる少なくともいずれかであって、これらの各置換基及び水素原子の位置並びにその数は限定されず、単一及び複数の組合せのいずれであってもよい。）

(In the above general formula (1), X is at least one selected from the group of one or more carboxyl groups, alkyl groups and hydrogen atoms, and the positions and numbers of each of these substituents and hydrogen atoms are limited. It may be either a single or a combination of two or more.)

The flux of the present invention preferably contains cyclohexanedicarboxylic acid as the compound represented by the general formula (1).

The flux of the present invention preferably contains at least one of 1,3-cyclohexanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid as the cyclohexanedicarboxylic acid.

The heterocyclic compound preferably contains at least one of an imidazole skeleton, an imidazoline skeleton and a benzimidazole skeleton.

The heterocyclic compound containing the imidazole skeleton preferably has an alkyl group.

The flux of the present invention preferably further contains a thixotropic agent in an amount of more than 0% by mass and 15% by mass or less based on the total amount of the flux.

The solder paste of the present invention contains the flux and an alloy powder made of a lead-free solder alloy.

The average particle size of the alloy powder made of the lead-free solder alloy is preferably 10 μm or more and 30 μm or less.

The electronic circuit mounting board of the present invention has a solder joint formed by using the solder paste.

The electronic control device of the present invention has the electronic circuit mounting board.

The flux, solder paste, electronic circuit mounting board, and electronic control device of the present invention can exhibit whisker generation suppression, good solderability, and storage stability at the solder joint.

Hereinafter, one embodiment of the flux, solder paste, electronic circuit mounting board, and electronic control device of the present invention will be described in detail. It goes without saying that the present invention is not limited to the following embodiments.

(1) Flux The flux of the present embodiment contains a base resin, an organic acid, a heterocyclic compound, and a solvent.
Further, the flux of the present embodiment does not contain a halogen compound, whereby the generation of whiskers at the solder joint can be suppressed. In addition, in this embodiment, the fact that the halogen compound is not contained means that the halogen compound is not intentionally added.

<Base resin>
Examples of the base resin include rosins such as tall oil rosin, gum rosin and wood rosin, hydrogenated rosins, polymerized rosins, heterogeneous rosins, acrylic acid-modified rosins and maleic acid-modified rosins and other rosin-based resins; acrylics. Acids, methacrylic acid, acrylic acid various esters, methacrylic acid various esters, crotonic acid, itaconic acid, maleic acid, maleic anhydride, maleic acid ester, maleic anhydride ester, acrylonitrile, methacrylonitrile, acrylamide, methacryl Acrylic resin obtained by polymerizing at least one monomer such as amide, vinyl chloride, vinyl acetate, etc .; styrene-maleic acid resin; epoxy resin; urethane resin; polyester resin; phenoxy resin; terpene resin; polyalkylene carbonate and the like. Be done. These can be used alone or in combination of two or more.

As the base resin, it is preferable to use a rosin-based resin and other resins in combination, and it is more preferable to use a rosin-based resin and an acrylic resin in combination.
As the rosin-based resin, hydrogenated acid-modified rosin obtained by hydrogenating an acid-modified rosin is particularly preferably used.

The acid value of the base resin is preferably 10 mgKOH / g or more and 250 mgKOH / g or less. The acid value thereof is more preferably 100 mgKOH / g or more and 250 mgKOH / g or less, and particularly preferably 140 mgKOH / g or more and 250 mgKOH / g or less.
The blending amount of the base resin is preferably 10% by mass or more and 90% by mass or less with respect to the total amount of the flux. The blending amount thereof is more preferably 20% by mass or more and 50% by mass or less, and particularly preferably 30% by mass or more and 50% by mass or less.

When the flux of the present embodiment contains a rosin-based resin as the base resin, the blending amount thereof is preferably 5% by mass or more and 70% by mass or less with respect to the total amount of the flux. The blending amount thereof is more preferably 10% by mass or more and 60% by mass or less, and particularly preferably 20% by mass or more and 50% by mass or less.

When the rosin resin and the acrylic resin are used in combination as the base resin, the blending amount of the acrylic resin is preferably 5% by mass or more and 90% by mass or less with respect to the total amount of the flux. The blending amount thereof is more preferably 10% by mass or more and 60% by mass or less, and particularly preferably 20% by mass or more and 50% by mass or less.

<Organic acid>
The flux of the present embodiment preferably contains the compound represented by the following general formula (1) as the organic acid. Even if the flux of the present embodiment contains a heterocyclic compound described later, good storage stability can be exhibited by using the compound represented by the following general formula (1) in combination as the organic acid.

（前記一般式（１）中、Ｘは１つ以上のカルボキシル基、アルキル基及び水素原子の群から選ばれる少なくともいずれかであって、これらの各置換基及び水素原子の位置並びにその数は限定されず、単一及び複数の組合せのいずれであってもよい。）

(In the above general formula (1), X is at least one selected from the group of one or more carboxyl groups, alkyl groups and hydrogen atoms, and the positions and numbers of each of these substituents and hydrogen atoms are limited. It may be either a single or a combination of two or more.)

The flux of the present embodiment preferably contains cyclohexanedicarboxylic acid as the compound represented by the general formula (1).
When the flux of the present embodiment contains cyclohexanedicarboxylic acid as the compound represented by the general formula (1), the storage stability of the flux can be further improved while ensuring wettability and solderability.
Further, it is particularly preferable that the flux of the present embodiment contains at least one of 1,3-cyclohexanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid as the cyclohexanedicarboxylic acid. Further, as the isomer of the cyclohexanedicarboxylic acid, either a cis type or a trans type can be used, but the cis type is more preferable.
These can be used alone or in combination of two or more.

The blending amount of the compound represented by the general formula (1) is preferably 0.05% by mass or more and less than 15% by mass with respect to the total amount of the flux. The blending amount thereof is more preferably 2% by mass or more and 10% by mass or less, and particularly preferably 4% by mass or more and 10% by mass or less.
By setting the blending amount of the compound represented by the general formula (1) within this range, the storage stability of the flux can be further improved.

The flux of the present embodiment may contain other organic acids (hereinafter referred to as "other organic acids") in addition to the compound represented by the general formula (1).
Examples of the other organic acid include monocarboxylic acid, dicarboxylic acid, and other organic acids.
Examples of the monocarboxylic acid include formic acid, acetic acid, propionic acid, butanoic acid, pentanoic acid, caproic acid, enanthic acid, capric acid, lauric acid, myristic acid, pentadecic acid, palmitic acid, margaric acid, stearic acid and tubercrostearic. Examples thereof include acid, arachidic acid, behenic acid, lignoseric acid, glycolic acid and the like.
Examples of the dicarboxylic acid include oxalic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, tartaric acid, and diglycolic acid.
Further, examples of other organic acids include dimer acid, levulinic acid, lactic acid, acrylic acid, benzoic acid, salicylic acid, anis acid, citric acid, picolin acid and the like.
These can be used alone or in combination of two or more.

When the compound represented by the general formula (1) and the other organic acid are used in combination as the organic acid, the total blending amount thereof is preferably 0.5% by mass or more and 20% by mass or less. The blending amount thereof is more preferably 0.5% by mass or more and 10% by mass or less, and particularly preferably 0.5% by mass or more and 5% by mass or less.

<Heterocyclic compound>
The flux of the present embodiment preferably contains a heterocyclic compound. By containing the heterocyclic compound, the flux of the present embodiment can exhibit good solderability even if it does not contain a halogen compound. Further, as described above, the flux of the present embodiment can exhibit good storage stability by using the compound represented by the general formula (1) in combination.

The flux of the present embodiment preferably contains at least one of an imidazole skeleton, an imidazoline skeleton, and a benzimidazole skeleton as the heterocyclic compound.

As such a heterocyclic compound, alkylimidazole is preferably used.
Examples of the alkylimidazole include 2-ethyl-4-methylimidazole and undecylimidazole.
These can be used alone or in combination of two or more.

The blending amount of the heterocyclic compound is preferably 0.05% by mass or more and less than 15% by mass with respect to the total amount of the flux. The blending amount thereof is more preferably 1% by mass or more and 10% by mass or less, and particularly preferably 2% by mass or more and 8% by mass or less.
By setting the blending amount of the heterocyclic compound in this range, the solderability of the flux can be further improved.

<Solvent>
As the 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 of two or more.
The blending amount of the solvent is preferably 5% by mass or more and 50% by mass or less with respect to the total amount of the flux. The blending amount thereof is more preferably 10% by mass or more and 40% by mass or less, and particularly preferably 20% by mass or more and 40% by mass or less.

<Thixotropic agent>
The thixotropic agent can be further contained in the flux of the present embodiment. Examples of the thixotropic agent include hydrogenated castor oil, fatty acid amides, and oxyfatty acids. These can be used alone or in combination of two or more.
The blending amount of the thixotropic agent is preferably more than 0% by mass and 15% by mass or less with respect to the total amount of the flux. The blending amount thereof is more preferably 1% by mass or more and 10% by mass or less, and particularly preferably 3% by mass or more and 8% by mass or less.

<Antioxidant>
The flux of the present embodiment may further contain an antioxidant for the purpose of suppressing oxidation of the lead-free solder alloy. Examples of the antioxidant include hindered phenolic antioxidants, phenolic antioxidants, bisphenolic antioxidants, polymer-type antioxidants and the like. Among them, hindered phenolic antioxidants are particularly preferably used. These can be used alone or in combination of two or more.
The blending amount of the antioxidant is not particularly limited, but is generally preferably 0.5% by mass or more and 5% by mass or less with respect to the total amount of the flux.

<Additives>
The flux of the present embodiment may further contain additives such as a matting agent, a defoaming agent and an inorganic filler.
The blending amount of the additive is preferably 10% by mass or less with respect to the total amount of the flux. Further, a more preferable blending amount thereof is 5% by mass or less with respect to the total amount of the flux.

(2) Solder paste The flux of the present embodiment can be, for example, mixed with an alloy powder made of a lead-free solder alloy to form a solder paste.
However, the flux of this embodiment can be used for solder joining methods other than using solder paste, for example, mounting with solder balls (solder joining), solder joining with a lead-free solder alloy and a solder joining material containing the flux of this embodiment, and the like. Can also be used.
The flux of this embodiment is particularly preferably used for solder paste.

<Alloy powder made of lead-free solder alloy>
Examples of the alloy powder made of the lead-free solder alloy include Sn, Ag, Cu, Bi, Sb, Ni, Co, P, Ga, Ge, Fe, Mn, Cr, Mo, In, Cd, Tl, Se, Au. , Ti, Si, Al, Mg, Zn and the like can be used.
It should be noted that elements other than the above-mentioned elements can be used in the combination thereof, and of course, unavoidable impurities are also included.

When the solder paste is produced, the blending ratio of the alloy powder made of the lead-free solder alloy and the flux is preferably 65:35 to 95: 5 in the ratio of the alloy powder made of the lead-free solder alloy: flux. .. A more preferred blending ratio is 85:15 to 93: 7, and a particularly preferred blending ratio is 87:13 to 92: 8.

The average particle size of the alloy powder made of the lead-free solder alloy is preferably 1 μm or more and 40 μm or less, more preferably 10 μm or more and 30 μm or less, and particularly preferably 5 μm or more and 15 μm or less.

Here, as described above, especially in in-vehicle electronic devices, the miniaturization and high density of electronic components mounted on electronic circuit mounting boards are progressing, and along with this, fine lead (small average particle size) is being used. Solder bonding using alloy powder made of free solder alloy has been performed.
However, the smaller the average particle size of the alloy powder made of lead-free solder alloy, the larger the surface area per unit volume. As the surface area increases, the amount (area) of the oxide film on the surface of the alloy powder increases, and the reaction between the flux and the alloy powder is more likely to proceed, so that the solderability and storage stability of the flux are impaired. There is a risk of

However, since the solder paste of the present embodiment contains the flux, it has good solderability and storage stability even when an alloy powder made of a lead-free solder alloy having an average particle size of about 10 μm is used. Can exert sex.
As described above, the solder paste of the present embodiment can be suitably used in an in-vehicle electronic device (vehicle-mounted electronic circuit mounting board) that requires miniaturization and high density of electronic components and high reliability. ..

(3) Electronic circuit mounting board The electronic circuit mounting board of the present embodiment is formed by, for example, the following method. The substrate on which the solder joint portion of the present embodiment is formed is not limited to a printed wiring board, a silicon wafer, a ceramic package substrate, or any other substrate used for mounting or mounting electronic components.

That is, for example, the solder paste is printed in accordance with this pattern on an electronic circuit board having a predetermined pattern of electrodes and an insulating layer at a predetermined position. An electronic circuit having a solder joint formed by using the solder paste by mounting an electronic component at a predetermined position on the electronic circuit board and reflowing the electronic component at a temperature of, for example, 220 ° C to 245 ° C. A mounting board is manufactured.

Since the solder paste contains the flux, it can exhibit good storage stability and solderability, so that a highly reliable solder joint can be formed. Further, since the flux does not contain a halogen compound, it is possible to suppress the generation of whiskers at the solder joint and improve its reliability.

As described above, the electronic circuit mounting board having the solder joint portion of the present embodiment can be particularly preferably used as an in-vehicle electronic circuit mounting board that requires high reliability.

(4) Electronic control device By incorporating such an electronic circuit mounting board, a highly reliable electronic control device can be manufactured. And such an electronic control device can be suitably used as an in-vehicle electronic control device that requires particularly high reliability.

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.

Each component shown in Tables 1 and 2 was kneaded to prepare fluxes according to Examples 1 to 8 and Comparative Examples 1 to 7. The units of the numerical values in the table are all mass%.
Then, 11% by mass of each of these fluxes and 89% by mass of Sn-3Ag-0.5Cu solder alloy powder (average particle diameter: 10 μm) were mixed to prepare each solder paste.

※１ 水添酸変性ロジン 荒川化学工業（株）製
※２ 脂肪酸アマイド 三菱ケミカル（株）

* 1 Hydrogenated acid-modified rosin manufactured by Arakawa Chemical Industry Co., Ltd. * 2 Fatty acid amide Mitsubishi Chemical Corporation

※１ 水添酸変性ロジン 荒川化学工業（株）製
※２ 脂肪酸アマイド 三菱ケミカル（株）

* 1 Hydrogenated acid-modified rosin manufactured by Arakawa Chemical Industry Co., Ltd. * 2 Fatty acid amide Mitsubishi Chemical Corporation

1. 1. Whisker occurrence confirmation test The following tools were prepared.
・ QFP parts (pitch width: 0.5 mm, length 20 mm x width 20 mm x thickness 1.7 mm, number of terminals: 144 pins, Sn plating)
-Printed wiring board provided with a solder resist having a pattern on which the QFP component can be mounted and an electrode for connecting the QFP component-Metal mask having the above pattern and having a thickness of 150 μm Each using the metal mask on the printed wiring board. Each solder paste according to the examples and each comparative example was printed, and the QFP component was mounted.
After that, each printed wiring board is heated using a reflow furnace (product name: TNV30-508EM2-X, manufactured by Tamura Seisakusho Co., Ltd.), and solder that electrically connects each printed wiring board and each QFP component. Each electronic circuit mounting board having a joint was manufactured. The reflow conditions at this time were a preheat of 170 ° C. to 190 ° C., a peak temperature of 245 ° C., a time of 220 ° C. or higher for 45 seconds, and a cooling rate from the peak temperature to 200 ° C. of 1 ° C. to 8 ° C./sec. The oxygen concentration was set to 1,500 ± 500 ppm.
Then, each of the above electronic circuit mounting boards is left in a constant temperature and humidity chamber for 200 hours under the condition of 85 ° C. and 85%, and then left for 24 hours under the condition of 25 ° C. and 50%, and this step is defined as one cycle. Five cycles were performed to prepare each test substrate.
Then, the state of the solder joint of each test substrate was observed using a scanning electron microscope (product name: TM-1000, manufactured by Hitachi High-Technologies Corporation) and evaluated according to the following criteria. The results are shown in Tables 3 and 4.
〇: Whiskers are not generated at the solder joints ×: Whiskers are generated at the solder joints

2. 2. Storage stability test Each solder paste according to each example and each comparative example (hereinafter collectively referred to as "solda paste for storage stability test") is placed in a container, and these are placed at room temperature (25 ° C.). It was left for 2 to 3 hours. Then, the lid of each container was opened, and each of the contained solder pastes was stirred with a spatula for 1 to 2 minutes so as to avoid air contamination.
Next, the solder paste for storage stability test was set in a spiral viscometer (product name: PCU-II type, manufactured by Malcolm Co., Ltd.), and the rotor was rotated for 6 minutes under the conditions of a rotation speed of 10 rpm and a temperature of 25 ° C. I let you. After that, the rotation of the rotor was stopped once, the temperature was adjusted, the rotation speed was adjusted to 10 rpm, and the rotor was further rotated for 3 minutes, and then the respective viscosity values (viscosity a) of the solder paste for the storage stability test. ) Was measured.

Further, each of the solder pastes for storage stability test was housed in a container, placed in a constant temperature bath set in a temperature environment of 30 ° C., and left for 7 days. Then, each viscosity value (viscosity b) of the solder paste for storage stability test was measured under the same conditions as above.
Then, the viscosity increase rate of each of the solder pastes for storage stability test based on the viscosity a and the viscosity b was calculated and evaluated according to the following criteria. The results are shown in Tables 3 and 4.
⊚: Viscosity increase rate less than 5% 〇: Viscosity increase rate 5% or more and less than 10% Δ: Viscosity increase rate 10% or more and 20% or less ×: Viscosity increase rate 21% or more

3. 3. Wetting property test The test was carried out in accordance with the provisions of JIS standard Z3284-4: 2014 (4.1: Wetting efficacy and dewetting test).
A clean copper plate and a metal mask (thickness: 0.2 mm) with a hole having a diameter of 6.5 mm were prepared.
The solder paste according to each Example and each Comparative Example was printed on the copper plate using the metal mask to prepare each substrate.
Next, each of the substrates was heated with the printed surface of the solder paste facing up on a solder bath set at a temperature 35 ° C. higher (error: within 3 ° C.) than that of the Sn-3Ag-0.5Cu solder alloy. After heating was continued for 5 seconds from the time when a part of the solder paste printed on each of the substrates was melted, each of the substrates was taken out in a horizontal state. Then, each substrate was cooled to room temperature to prepare each test plate. The spread of the solder (melted alloy powder made of lead-free solder alloy contained in the solder paste) on each of the test plates was visually confirmed and evaluated according to the following criteria. The results are shown in Tables 3 and 4.
⊚: The molten solder spreads beyond the area where the solder paste is applied and the test plate is wet. 〇: The part where the solder paste is applied is all wet with the solder. △: The solder paste is applied. Most of the parts are wet with solder (including dewetting). ×: The test plate does not appear to be wet with solder, and the molten solder is in one or more solder balls. (Non-wetting)

4. Solder ball generation confirmation test Performed in accordance with JIS standard Z3284-4: 2014 (4.2: Solder ball test).
2. Except for preparing a ceramic plate and a metal mask (thickness: 0.2 mm) having a hole with a diameter of 6.5 mm, and printing solder paste on the ceramic plate using the metal mask. Each test plate was prepared under the same conditions as the wettability test.
Then, the particle size and the number of solder balls generated on each test plate were evaluated according to the following criteria. The results are shown in Tables 3 and 4.
⊚: Solder becomes one large sphere and the number of solder balls with a diameter of 75 μm or less generated around it is 3 or less. 〇: Solder becomes one large sphere and the number of solder balls with a diameter of 75 μm or less generated around it is 4. There are two or more, and these are not arranged in a semi-continuous ring. Δ: Solder is one large sphere, and many fine spheres are arranged in a semi-continuous ring around it. ×: Solder is one large sphere. Many small spheres are scattered

表４のうち、「－」は未評価を示す。

In Table 4, "-" indicates unevaluated.

As shown above, it can be seen that the solder paste according to the embodiment can suppress the generation of whiskers at the solder joint, and also exhibit good storage stability and wettability (suppression of the generation of solder balls).
Further, the solder paste according to the embodiment has good storage stability and wettability (suppression of solder ball generation) even when an alloy powder made of a fine lead-free solder alloy having an average particle diameter of about 10 μm is used. It can be effective.

As described above, the solder paste according to the embodiment can be suitably used for mounting miniaturized and high-density electronic components, and is also suitable for an in-vehicle electronic circuit mounting board that requires high reliability. Can be used.

Claims (10)

Contains a base resin, an organic acid, a heterocyclic compound, and a solvent.
The organic acid contains a compound represented by the following general formula (1) in an amount of 0.05% by mass or more and less than 15% by mass with respect to the total amount of the flux.
A flux containing the heterocyclic compound in an amount of 0.05% by mass or more and less than 15% by mass with respect to the total amount of the flux.

(In the above general formula (1), X is at least one selected from the group of one or more carboxyl groups, alkyl groups and hydrogen atoms, and the positions and numbers of each of these substituents and hydrogen atoms are limited. It may be either a single or a combination of two or more.) The flux according to claim 1, which comprises cyclohexanedicarboxylic acid as the compound represented by the general formula (1). The flux according to claim 2, wherein the cyclohexanedicarboxylic acid contains at least one of 1,3-cyclohexanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid. The flux according to any one of claims 1 to 3, wherein the heterocyclic compound contains at least one of an imidazole skeleton, an imidazoline skeleton, and a benzimidazole skeleton. The flux according to claim 4, wherein the heterocyclic compound containing an imidazole skeleton has an alkyl group. The flux according to any one of claims 1 to 5, further comprising a thixotropic agent in an amount of more than 0% by mass and 15% by mass or less based on the total amount of the flux. A solder paste containing the flux according to claim 1 to claim 6 and an alloy powder made of a lead-free solder alloy. The solder paste according to claim 7, wherein the alloy powder made of the lead-free solder alloy has an average particle size of 10 μm or more and 30 μm or less. An electronic circuit mounting board having a solder joint formed by using the solder paste according to claim 7. An electronic control device having the electronic circuit mounting board according to claim 9.