JP7241795B2 - Residue-free flux composition and solder paste - Google Patents

Description

The present invention relates to residue-free flux compositions and solder pastes.

BACKGROUND ART Soldering using solder paste, which is a mixture of a flux composition and a solder alloy powder, is widely used as a method for joining electronic components onto electronic circuit boards such as printed wiring boards and module boards. In this method, solder paste is printed on a predetermined position on an electronic circuit board, an electronic component is placed on the predetermined position, and the electronic circuit board and the electronic component are soldered by heating.

On the other hand, in recent years, from the viewpoint of energy and environmental problems, power semiconductor devices for controlling and supplying power, so-called power semiconductors, have attracted attention. Normally, a power semiconductor is die-bonded on a DCB substrate using a bonding material such as solder, and then the electrodes formed on the power semiconductor and the electrodes formed on the DCB substrate are bonded (wire bonding).
Here, when solder paste is used for die bonding, if the residue of flux (flux residue) contained in the solder paste remains on the DCB substrate after die bonding, the flux residue will remain on the DCB substrate during subsequent wire bonding. There is a risk that it may spread to the upper electrode, which may cause a poor connection between the power semiconductor and the DCB substrate. Therefore, when bonding the power semiconductor to the DCB substrate, it is necessary to remove (clean) the flux residue after die bonding.

However, since a solvent is used for cleaning the flux residue, the environmental and cost burdens are large. Therefore, there is a demand for the development of a solder paste using a so-called residue-free flux composition that leaves very little (or almost no) flux residue after die bonding.

So far, as a flux composition (solder paste) that significantly reduces the flux residue remaining after soldering, for example, activators such as malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, One kind selected from maleic acid, citric acid, tartaric acid, and benzoic acid is mixed with 4.55 mmol/g to 45.5 mmol/g with respect to 100 g of flux, and the components other than the solder powder contained in the solder paste are A solder paste that evaporates below the melting temperature of solder powder (see Patent Document 1), a solid solvent that is solid at room temperature and evaporates at the reflow temperature, and a highly viscous fluid at room temperature that evaporates at the reflow temperature. A residue-free solder paste using a flux containing a highly viscous solvent and a liquid solvent that is liquid at room temperature and evaporates at the reflow temperature (see Patent Document 2) is disclosed.

A solder paste using a flux composition containing an organic acid with a small number of carbon atoms such as malonic acid and succinic acid can reduce residual flux remaining after soldering. However, an activator with a low carbon number reduces the wettability of the solder paste due to its low activation force, and thus such solder paste has poor bonding between the electronic component to be mounted and the board (electronic circuit board, DCB board, etc.). easily cause

In addition, although the use of a specific solvent in the flux composition can reduce the amount of flux residue remaining after soldering, the use of an activator with a low carbon number as described above can reduce the wettability of the solder paste. . On the other hand, if an activator with a large number of carbon atoms is used to improve the wettability of the solder paste, there is a problem that the residual flux remaining after soldering cannot be reduced.

JP 2017-209734 A Japanese Patent Application Laid-Open No. 2004-25305

An object of the present invention is to provide a residue-free flux composition and a solder paste that can reduce the residual flux remaining after soldering and exhibit good wettability of the solder paste. and

The residue-free flux composition of the present invention comprises an organic compound (A), a solvent (B), an activator (C), and a thixotropic agent (D), wherein the organic compound (A) is solid at room temperature. It is an aliphatic alcohol that becomes liquid at 50° C. or higher, and the activator (C) contains an organic acid (C-1) having 3 to 5 carbon atoms and a halogen compound (C-2). , the amount of the organic acid (C-1) having 3 to 5 carbon atoms is 0.1% by mass or more and 1.5% by mass or less with respect to the total amount of the residue-free flux composition, and the halogen compound (C -2) is 0.01% by mass or more and 0.1% by mass or less with respect to the total amount of the residue-free flux composition, and the organic acid (C-1) having 3 or more and 5 or less carbon atoms has a carbon number of is a dicarboxylic acid having 3 or more and 5 or less, and the halogen compound (C-2) is at least one of a bromine compound and an iodine compound.

In the residue-free flux composition of the present invention, the bromine compound is preferably at least one of 2-bromo-n-hexanoic acid and dibromobutenediol.
In the residue-free flux composition of the present invention, the iodine compound is preferably at least one of 2-iodobenzoic acid and 3,5-diiodosalicylic acid.

In the residue-free flux composition of the present invention, the thixotropic agent (D) is preferably a saturated fatty acid amide having 18 or less carbon atoms.

In the residue-free flux composition of the present invention, the saturated fatty acid amide having 18 or less carbon atoms is preferably at least one of palmitic acid amide and lauric acid amide.

Further, in the residue-free flux composition of the present invention, the thixotropic agent (D) content is preferably 1% by mass or more and 15% by mass based on the total amount of the residue-free flux composition.

The solder paste of the present invention is characterized by containing the residue-free flux composition and solder alloy powder.

The residue-free flux composition and solder paste of the present invention can reduce the residual flux remaining after soldering and exhibit good wettability of the solder paste.

A temperature profile showing the reflow conditions in the "chip component pillow failure confirmation test." A photograph showing a chip component in which a pillow defect has occurred in a "chip component pillow defect occurrence confirmation test." A photograph showing a chip component in which a bridge under the chip component is generated in the "test for confirming occurrence of bridge under the chip component". A photograph showing a test board with almost no flux residue on the outer peripheral portion of the solder and on the surface of the solder (can be evaluated as ◯) in the "Flux Residue Confirmation Test". Fig. 10 is a photograph showing a test substrate in which there is almost no flux residue on the solder surface, but there is some flux residue on the outer peripheral portion of the solder (which can be evaluated as △) in the "flux residue confirmation test". A photograph showing a test board in which flux residue exists on both the outer peripheral portion of the solder and the solder surface (which can be evaluated as x) in the "flux residue confirmation test".

One embodiment of the residue-free flux composition and solder paste of the present invention is described in detail below. It goes without saying that the present invention is not limited to these embodiments.

1. Residue-Free Flux Composition The flux of this embodiment includes an organic compound (A), a solvent (B), an activator (C), and a thixotropic agent (D).

Organic compound (A)
As the organic compound (A), an aliphatic alcohol that is solid at room temperature and becomes liquid at 50° C. or higher is preferably used. In addition, in this specification, "normal temperature" means about 15 degreeC to 30 degreeC.
As the organic compound (A), for example, trimethylolpropane is preferably used.
In addition, you may use the said organic compound individually by 1 type or in mixture of multiple types.

The blending amount of the organic compound (A) is preferably 20% by mass or more and 70% by mass or less with respect to the total amount of the residue-free flux composition. A more preferable blending amount thereof is 35% by mass or more and 65% by mass or less, and more preferably 45% by mass or more and 55% by mass or less.

Solvent (B)
Examples of the solvent (B) include triethylene glycol, deionized water, isopropyl alcohol, ethanol, acetone, toluene, xylene, ethyl acetate, ethyl cellosolve, butyl cellosolve, hexyl diglycol, (2-ethylhexyl) diglycol, diethylene glycol mono Hexyl ether, phenyl glycol, butyl carbitol, octanediol, α-terpineol, β-terpineol, tetraethylene glycol dimethyl ether and the like can be used. Among these, triethylene glycol is particularly preferably used.
In addition, these may be used individually by 1 type or in mixture of multiple types.

The blending amount of the solvent (B) is preferably 10% by mass or more and 65% by mass or less with respect to the total amount of the residue-free flux composition. A more preferable blending amount is 15% by mass or more and 40% by mass or less, and a particularly preferable blending amount is 20% by mass or more and 35% by mass or less.

Activator (C)
The residue-free flux composition of the present embodiment preferably contains an organic acid (C-1) having 3 to 5 carbon atoms and a halogen compound (C-2) as the activator (C).

As the organic acid (C-1) having 3 to 5 carbon atoms, a dicarboxylic acid (C-1) having 3 to 5 carbon atoms is preferably used.
Examples of the dicarboxylic acid (C-1) having 3 to 5 carbon atoms include malonic acid, succinic acid and glutaric acid. Among these, glutaric acid and succinic acid are particularly preferred.
In addition, these may be used individually by 1 type or in mixture of multiple types.

The content of the organic acid (C-1) having 3 or more and 5 or less carbon atoms is preferably 0.1 mass % or more and 1.5 mass % or less based on the total amount of the residue-free flux composition. More preferably, the blending amount is 0.5% by mass or more and 1.5% by mass or less. A more preferable blending amount thereof is 0.5% by mass or more and 1% by mass or less, and particularly preferably 0.5% by mass or more and 0.75% by mass or less.

Bromine compounds and iodine compounds are preferably used as the halogen compound (C-2).
Examples of the bromine compound include 2-bromo-n-hexanoic acid and dibromobutenediol.
Examples of the iodine compound include 2-iodobenzoic acid and 3,5-diiodosalicylic acid.
As the halogen compound (C-2), 2-bromo-n-hexanoic acid and dibromobutenediol are particularly preferably used.
In addition, these may be used individually by 1 type or in mixture of multiple types.

The content of the halogen compound (C-2) is preferably 0.01% by mass or more and 0.1% by mass or less relative to the total amount of the residue-free flux composition. A more preferable blending amount thereof is 0.01% by mass or more and 0.05% by mass or less.

In the residue-free flux composition of the present embodiment, as the activator (C), an organic acid (C-1) having 3 to 5 carbon atoms and a halogen compound (C-2) are used in combination, and By setting the blending amount within the above range, it is possible to reduce the flux residue remaining after soldering, and to exhibit good wettability of the solder paste using the residue-free flux composition.

That is, a solder paste using a residue-free flux composition containing an organic acid with a small number of carbon atoms such as malonic acid and succinic acid can reduce flux residue remaining after soldering. However, an activator with a small number of carbon atoms has a low activating force, and thus may reduce the wettability of the solder paste and cause poor bonding between the electronic component and the substrate (electronic circuit board, DCB substrate, etc.).
However, in the residue-free flux composition of the present embodiment, as the activator (C), an organic acid (C-1) having 3 to 5 carbon atoms and a halogen compound (C-2) are used in combination, and By adjusting the blending amount of, it is possible to reduce the flux residue remaining after soldering and to impart good activity to the residue-free flux composition, so that the solder paste using it exhibits good wettability. can do. Moreover, the residue-free flux composition of the present embodiment can also suppress the solvent (B) scattering phenomenon during heating.
Solder joints formed using such a solder paste can suppress the occurrence of defective joints, solder bridges, and the like, and can provide highly reliable electronic circuit mounting boards and power modules.

The amount of the activator (C) as a whole is preferably 0.11% by mass or more and 1.6% by mass or less with respect to the total amount of the residue-free flux composition. A more preferable blending amount is 0.51% by mass or more and 1.05% by mass or less, and a particularly preferable blending amount is 0.51% by mass or more and 0.8% by mass or less.

Thixotropic agent (D)
A saturated fatty acid amide is preferably used as the thixotropic agent (D).
Among the fatty acid amides, saturated fatty acid amides having 18 or less carbon atoms are particularly preferably used. Among these, fatty acid saturated amides having 14 or less carbon atoms are more preferable, and fatty acid saturated amides having 12 or less carbon atoms are particularly preferably used.
Such fatty acid saturated amides include, for example, palmitic acid amide and lauric acid amide.
In addition, these may be used individually by 1 type or in mixture of multiple types.

The content of the thixotropic agent (D) is preferably 1% by mass or more and 15% by mass or less with respect to the total amount of the residue-free flux composition. A more preferable blending amount is 3% by mass or more and 13% by mass or less, and a particularly preferable blending amount is 5% by mass or more and 8% by mass or less.

Antioxidant The residue-free flux composition of the present embodiment may contain an antioxidant for the purpose of suppressing oxidation of the solder alloy powder. Examples of such antioxidants include hindered phenolic antioxidants, phenolic antioxidants, bisphenolic antioxidants, polymer antioxidants, and the like, but are not limited to these. Among these, hindered phenol-based antioxidants are particularly preferably used. Examples of this hindered phenol antioxidant include Irganox 245 (manufactured by BASF Japan Ltd.).
In addition, these may be used individually by 1 type or in mixture of multiple types.

When the antioxidant is blended into the residue-free flux composition of the present embodiment, the blending amount is adjusted so as not to affect the effects of the residue-free flux composition of the present embodiment, that is, to leave no residue. be.

Additives such as antifoaming agents, antirust agents, surfactants, thermosetting agents, and matting agents can be added to the flux of the present embodiment. When the additive is blended into the residue-free flux composition of the present embodiment, the blending amount is adjusted so as not to affect the effect of the residue-free flux composition of the present embodiment, that is, to be residue-free. .

The residue-free flux composition of the present embodiment may be blended with a base resin such as a rosin-based resin or an acrylic resin within a range that does not affect the amount of residual flux residue. It is less than 1% by mass with respect to the total amount of the flux composition.

In this specification, "residue-free" means that the mass of flux residue is 1% or less of the mass of the residue-free flux composition before soldering (heating).

(2) Solder Paste The solder paste of the present embodiment is obtained by mixing the residue-free flux composition and solder alloy powder.
Examples of the solder alloy powder include alloys containing tin and lead, alloys containing tin and lead and at least one of silver, bismuth and indium, alloys containing tin and silver, alloys containing tin and copper, tin, silver and An alloy containing copper, an alloy containing tin and bismuth, or the like can be used. In addition to these, for example, solder alloy powder in which tin, lead, silver, bismuth, indium, copper, zinc, gallium, antimony, gold, palladium, germanium, nickel, chromium, aluminum, phosphorus, etc. are appropriately combined may be used. can be done. Elements other than those listed above can also be used in the combination.

The content of the solder alloy powder is preferably 65% by mass or more and 95% by mass or less with respect to the total amount of the solder paste. A more preferable blending amount is 85% by mass or more and 93% by mass or less, and a particularly preferable blending amount is 88% by mass or more and 92% by mass or less.

By using the residue-free flux composition, the solder paste of the present embodiment can reduce the flux residue remaining after soldering and impart good activity to the residue-free flux composition. can exhibit good wettability.
Moreover, the solder paste of the present embodiment can also suppress the phenomenon of scattering of the solvent (B) during heating by using the residue-free flux composition.
Solder joints formed using such a solder paste can suppress the occurrence of defective joints, solder bridges, and the like, and can provide highly reliable electronic circuit mounting boards and power modules.

Although the embodiment in which the residue-free flux composition is used in the solder paste has been described above, the use of the residue-free flux composition in this embodiment is not limited to this, and other fluxes such as solder balls can be used. Various applications are possible.

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

Each component shown in Tables 1 and 2 was kneaded to prepare each flux composition according to Examples 1 to 11 and Comparative Examples 1 to 6.
Further, 9.5% by mass of each of the above flux compositions and 90.5% by mass of Sn-3Ag-0.5Cu solder alloy powder (particle size 20 μm to 45 μm) were mixed, and from Examples 1 to 11 and Comparative Example 1, Each solder paste according to No. 6 was prepared.
Unless otherwise specified, the numerical values shown in Tables 1 and 2 mean % by mass.

※１ イソボルニルシクロヘキサノール 日本テルペン化学（株）製
※２ ラウリン酸アミド 東京化成工業（株）製

*1 Isobornylcyclohexanol manufactured by Nippon Terpene Chemical Co., Ltd.
*2 Lauric acid amide manufactured by Tokyo Chemical Industry Co., Ltd.

<Confirmation test for occurrence of pillow defects in chip parts>
I prepared the following tools.
・Chip parts (size: 1.6 mm x 0.8 mm, Sn plating)
・Printed wiring board with solder resist and electrodes (0.9 mm × 0.6 mm, Ni/Au plating) corresponding to the above chip parts ・Metal mask with the same pattern as the electrode pattern (thickness: 200 μm) )
Each solder paste according to Examples and Comparative Examples was printed on the printed wiring board using a printing machine (product name: SP60P-L, manufactured by Panasonic Corporation) and the metal mask.
The printing conditions were squeegee speed: 30 mm/sec, squeegee angle: 60 degrees, and plate separation speed: 2 mm/sec.
Then, 30 chip parts were mounted on each printed wiring board using a mounter (product name: YV100X, manufactured by Yamaha Motor Co., Ltd.), and these were placed in a reflow oven (product name: SMT Scope SK-5000). , manufactured by Sanyo Seiko Co., Ltd.), and the chip components were mounted on the printed wiring boards. In addition, the reflow condition at this time was performed according to the temperature profile shown in FIG. Also, the oxygen concentration was set to 100±50 ppm.
For each solder joint connecting the electrode on each printed wiring board and the electrode of each chip component, visually confirm whether or not a pillow defect as shown in FIG. 2 has occurred, according to the following evaluation criteria. evaluated. The results are shown in Tables 3 and 4.
〇: The number of chip components with bolster defects is 0 or more and 1 or less △: The number of chip components with bolster defects is 2 or more and 4 or less ×: The number of chip components with bolster defects is 5 or more

<Confirmation test for occurrence of bridging under chip parts>
The electrodes on each printed wiring board and the electrodes of each chip component are joined under the same conditions as the above test for confirming the occurrence of pillow defects in chip parts, except that the number of chip parts mounted on each printed wiring board is set to 10. Each solder joint was formed to
Then, for each solder joint connecting the electrode on each printed wiring board and the electrode on each chip component, visually confirm whether or not a bridge under the chip component as shown in FIG. 3 is generated. was evaluated according to the evaluation criteria of The results are shown in Tables 3 and 4.
○: The number of chip components with bridges under chip components is 0. △: The number of chip components with bridges under chip components is 1 to 3. ×: The number of chip components with bridges under chip components is 4 or more.

<Flux residue confirmation test>
I prepared the following tools.
・Cu plate ・Metal mask of 6 mm × 6 mm (thickness: 200 μm)
Each solder paste according to Examples and Comparative Examples was printed on the Cu plate using a printing machine (product name: SP60P-L, manufactured by Panasonic Corporation) and the metal mask.
The printing conditions were squeegee speed: 30 mm/sec, squeegee angle: 60 degrees, and plate separation speed: 2 mm/sec.
Next, each Cu plate was heated using a reflow furnace (product name: SMT Scope SK-5000, manufactured by Sanyo Seiko Co., Ltd.) to prepare each test substrate. The reflow conditions at this time were preheating from 170° C. to 190° C. for 110 seconds, a peak temperature of 240° C., a temperature increase rate of 0.6° C./second, and a time of 220° C. or higher for 100 seconds. Also, the oxygen concentration was set to 100±50 ppm.
Then, for each test substrate, it was visually confirmed whether or not any flux residue remained on each test substrate. And it evaluated according to the following evaluation criteria. The results are shown in Tables 3 and 4.
○: As shown in FIG. 4, there is almost no flux residue on the solder surface or on the solder surface. △: As shown in FIG. 5, there is almost no flux residue on the solder surface, but on the solder periphery There is some flux residue in the (see circled part)
×: As shown in FIG. 6, flux residue is present on both the outer peripheral portion of the solder and the solder surface (see circled portion).

<Comprehensive evaluation>
The evaluation results of each of the above tests were scored as 2 points for ◯, 1 point for Δ, and 0 points for ×.
Then, for the evaluation results (scores) of each of the above tests, a comprehensive evaluation score was calculated according to the following formula. In this embodiment, since the main problem is "reduction of flux residue after soldering", the evaluation result (score) of the "flux residue confirmation test" is squared in the following calculation formula.
(Evaluation result of chip component pillow defect occurrence confirmation test) x (Chip component bottom bridge occurrence confirmation test evaluation result) x (Flux residue confirmation test” evaluation result) ²
Comprehensive evaluation was performed on the calculated comprehensive evaluation points according to the following criteria. The results are shown in Tables 3 and 4.
◎: 8 points or more ○: 4 points or more and 7 points or less △: 1 point or more and 3 points or less ×: 0 points

As described above, the flux composition (residue-free flux composition) according to this embodiment includes an organic acid (C-1) having 3 to 5 carbon atoms and a halogen compound (C- 2) and by adjusting the blending amounts of these, it is possible to reduce the flux residue remaining after soldering, and to suppress the occurrence of pillow defects in chip parts and the occurrence of bridges under chip parts. , can provide reliable solder joints.

Claims (8)

A residue-free flux composition comprising trimethylolpropane , a solvent , an activator, and a thixotropic agent ,
The activator contains an organic acid having 3 to 5 carbon atoms and a halogen compound ,
The amount of the organic acid having 3 to 5 carbon atoms is 0.1% by mass or more and 1.5% by mass or less with respect to the total amount of the residue-free flux composition,
The amount of the halogen compound compounded is 0.01% by mass or more and 0.1% by mass or less with respect to the total amount of the residue-free flux composition,
The organic acid having 3 to 5 carbon atoms is a dicarboxylic acid having 3 to 5 carbon atoms,
A residue-free flux composition, wherein the halogen compound is at least one of a bromine compound and an iodine compound. 2. The residue-free flux composition according to claim 1, wherein the trimethylolpropane content is 20% by mass or more and 70% by mass or less based on the total amount of the residue-free flux composition. 3. The residue-free flux composition according to claim 1, wherein the bromine compound is at least one of 2-bromo-n-hexanoic acid and dibromobutenediol. 4. The residue-free flux composition according to claim 1, wherein the iodine compound is at least one of 2-iodobenzoic acid and 3,5-diiodosalicylic acid. 5. The residue-free flux composition according to any one of claims 1 to 4, wherein the thixotropic agent is a saturated fatty acid amide having 18 or less carbon atoms. 6. The residue-free flux composition according to claim 5 , wherein the saturated fatty acid amide having 18 or less carbon atoms is at least one of palmitic acid amide and lauric acid amide. 7. The residue-free flux composition according to any one of claims 1 to 6 , wherein the compounding amount of said thixotropic agent is 1% by mass or more and 15% by mass with respect to the total amount of the residue-free flux composition. . A solder paste comprising the residue-free flux composition according to claim 1 and a solder alloy powder.

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