JP2022022506A - Flux composition for solder paste - Google Patents

Abstract

To provide a flux composition for solder paste that can naturally suppress fluxes from remaining, does not require washing and can solve conventional problems such as occurrence of voids and anti-scattering, as well as solder paste using the flux composition.SOLUTION: The flux composition for solder paste, in which rosin is not contained in a flux component, has an excellent effect of suppressing the fluxes from remaining and has an excellent effect of preventing occurrence of voids and scattering caused during soldering. The composition is made to contain a liquid solvent having high viscosity at a normal temperature, a solvent liquid at a normal temperature, fatty acid whose molecular weight is less than 300, and amide composed of amine. Further dicarboxylic acid whose boiling point is 250°C or less is added to the flux composition for solder paste and soldering is performed under a formic acid atmosphere, which can synergistically improve a printing property and improve an effect of suppressing occurrence of voids and scattering caused during soldering.SELECTED DRAWING: None

Description

The present invention relates to a flux composition for solder paste used for joining electronic parts and the like, and a solder paste using the flux composition.

Generally, the flux of a solder paste is composed of rosin, a thixo agent, an activator and a solvent, and after dissolving the rosin or the like with the solvent to make it uniform, it is mixed with the solder powder to form a solder paste. The conventional solder paste contains a resin component and a solid component, and a large amount of the solid component and the resin remain in the soldered portion as a flux residue after reflow.
Such residual flux residue absorbs moisture over time to lower the insulation resistance value of the circuit of the electronic component, and corrosive substances may be generated to interrupt the circuit. Therefore, after reflow. Work was done to clean the soldered part and remove the flux residue.

Further, in a power module or the like, in order to ensure its reliability, the soldered portion is coated with a moisture-proof protective agent such as resin, or the entire component is molded.
Since the flux residue hinders the resin coating and the adhesion between the molding agent and the work, it is necessary to clean the entire part.
Therefore, there has been a demand for a solder paste that does not generate a flux residue that remains after reflow.

Several proposals have been made for solder pastes that do not generate flux residues. In 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 evaporate at the reflow temperature. A technique for 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 is described.

Further, Patent Document 2 describes a solder paste technique using a flux containing polyalkyl methacrylate as a methacrylic acid polymer and stearic acid amide as a viscosity modifier in an amount that decomposes or evaporates in the heating process during soldering. ing.

Further, Patent Document 3 contains a thickener, a solvent and a soldering agent, has an acid value of 100 mgKOH / g or less, has a reduction rate of 80% by mass or more at 300 ° C. in thermal weight measurement, and has a viscosity of 0.5 Pa. Described is a solder paste technique capable of suppressing the generation of a residue using a flux for solder paste having a tacking force of 1.0 N or more and s or more.

However, although the above-mentioned solder paste technology that does not generate flux residue has solved the problem of flux residue to some extent, it has not overcome other problems such as suppression of voids and no cleaning, and voids are generated. There is a demand for a solder paste that has less residue, is free of residue, and can be washed.

Japanese Unexamined Patent Publication No. 2004-25305 Japanese Unexamined Patent Publication No. 2013-132654 Japanese Unexamined Patent Publication No. 2019-25546

In view of such a situation, the present invention has a flux composition for solder paste that overcomes conventional problems such as suppression of flux residue, non-cleaning, prevention of scattering during soldering, and prevention of void generation. It is an object of the present invention to provide a product, a solder paste using the flux, and a solder joint portion joined with the solder paste.

INDUSTRIAL APPLICABILITY The present invention provides a flux composition for solder paste, which has an excellent effect of suppressing a flux residue without containing rosin and an excellent effect of preventing voids and scattering generated during soldering in order to solve the above-mentioned problems. We have found that the above problems can be overcome by preparing a flux composition containing a liquid solvent having high viscosity at room temperature, a solvent liquid at room temperature, and an amide composed of a fatty acid having a molecular weight of less than 300 and an amine. The invention was completed.

Further, by adding a dicarboxylic acid having a boiling point of 250 ° C. or lower to the above-mentioned flux composition for solder paste of the present invention and further soldering in a formic acid gas atmosphere, the effect of suppressing scattering generated during soldering is achieved. It was found that the effect of suppressing soldering and voids is synergistically improved.

By soldering using the solder paste composed of the flux composition for solder paste and the solder powder of the present invention, the generation of flux residue is extremely small or eliminated, and the generation of scattering and the generation of voids during soldering are suppressed. Therefore, cleaning after soldering becomes unnecessary, and defects at the time of soldering are extremely suppressed, so that it can be widely applied to soldering of electronic parts and the like.

The flux composition for solder paste of the present invention is characterized by containing a liquid solvent having high viscosity at room temperature, a solvent liquid at room temperature, and an amide composed of a fatty acid having a molecular weight of less than 300 and an amine.

The liquid solvent having a high viscosity at room temperature that can be used for the flux for solder paste of the present invention is not particularly limited as long as it has the effect of the present invention, but the viscosity is 10,000 mPa · s or more at 30 ° C. Preferably, isobornylcyclohexanol can be exemplified.

The solvent liquid at room temperature that can be used for the flux for solder paste of the present invention is not particularly limited as long as it has the effect of the present invention, but has a viscosity of 500 mPa · s or less at 20 ° C. and terpylene. A system solvent and a derivative thereof are preferable, and glycols such as dipropylene glycol, hexylene glycol, octanediol and pentandiol, alcohols such as decanol and phenoxyethanol, and aromatic alcohols may be used in combination.

Further, the amide composed of a fatty acid having a molecular weight of less than 300 and an amine that can be used in the flux composition for solder paste of the present invention is not particularly limited as long as it has the effect of the present invention, but is composed of saturated fatty acids and amines. The amide is preferable, and examples of the fatty acid include stearate amide and palmitic acid amide which are composed of amines with saturated fatty acids such as stearic acid and palmitic acid.

Then, in addition to the above-mentioned essential components, an organic acid having a boiling point lower than the melting point of the solder powder used for the solder paste is added to the flux composition for solder paste of the present invention, so that the scattering generated at the time of soldering is scattered. And the occurrence of voids are suppressed.

The organic acid that can be used in the flux composition for solder paste of the present invention is not particularly limited as long as it has the effect of the present invention, but a dicarboxylic acid is preferable, and when the melting point of the solder powder is 250 ° C. or lower, it is preferable. , Malonic acid (boiling point: 135 ° C.), maleic acid (decomposition temperature: 135 ° C.), succinic acid (boiling point: 235 ° C.), glutaric acid (boiling point: 200 ° C.) can be exemplified. The organic acid having is more preferable.

On the other hand, the additive component that can be used in the flux composition for solder paste of the present invention is not particularly limited as long as it has the effect of the present invention, and an antioxidant or a tincture agent can be arbitrarily added. Is.

Regarding the solder paste using the flux composition for solder paste of the present invention, the solder powder that can be used for the solder paste is not particularly limited as long as the effect of the present invention is obtained, but lead-free solder is preferable. , Sn single unit, Sn-Cu-based solder, Sn-Cu-Ni-based solder, Sn-Ag-Cu-based solder, Sn-Bi-based solder, Sn-Zn-based solder, etc. can be exemplified, and these solder alloys include Sb, Solder powder having a composition to which elements such as Bi, Cu, Ag, In, Ni, Zn, Co, Fe, Ge, Ga, Ti, Si, Zr, and P are added may be used.
The particle size of these solder powders is not particularly limited as long as the effect of the present invention is obtained, and is preferably 0.1 to 100 μm.
Further, to the solder paste using the flux composition for solder paste, it is possible to add metal particles in addition to the solder alloy powder within the range having the effect of the present invention, and it is possible to add Cu, Ni, and Cu. Metallic compounds such as Ni alloys and Cu ₆ Sn ₅ can be exemplified, and the average particle size is preferably 5 μm or more, more preferably 50 μm or more.

Next, the present invention will be described in detail.
A flux composition for solder paste was prepared with the composition shown in Table 1.
Further, as the solder paste, a flux composition for solder paste and a solder powder having the next solder alloy composition of Sn-0.7Cu-0.05Ni-0.005Ge and a particle size of 45 to 75 μm are applied to the solder paste 100 with a flux. It was prepared by mixing at a ratio of 9% by mass of the composition and 91% by mass of the solder powder.

Table 2 shows the evaluation results of the solder paste prepared by using the flux composition for solder paste shown in Table 1.
Table 3 shows the evaluation criteria for the solder paste.

When evaluating the solder paste, two types of oxygen-free copper plates were used, and the sizes were (1) size: 50 mm x 50 mm, thickness: 0.5 mm, (2) size: 35 mm x 35 mm, thickness: Using 0.5 mm each, the solder paste to be evaluated on the copper plate of (1) was printed in a size of about 35 mm × 35 mm with a thickness of 50 μm, and the copper plate of (2) was placed on the printed solder paste. Soldering was performed using a vacuum reflow device VADU100 manufactured by PINK, and the bonding state was evaluated.
The reflow conditions are as follows.
・ Temperature rise speed to preheat temperature: 5.7 ° C / sec ・ Preheat temperature: 190-200 ° C (8 minutes)
・ Peak temperature: 255 ° C (holding for 6 minutes)
・ Formic acid gas atmosphere: 100 mbar
-Raising rate from preheat temperature to peak temperature: 0.87 ° C / sec-Peak decompression 30 seconds, nitrogen purge 60 seconds-Cooling rate :: -2.2 ° C / sec

As shown in Table 2, in Examples 1 to 7 of the present invention, the flux residue is suppressed, the printability is excellent, and the scattering and voids generated during soldering are also evaluated as Δ or higher, and soldering is performed. It can be seen that it can be used for soldering and has the effect of the present invention.
In particular, Examples 1 to 3 to which malonic acid, which is an organic acid having a boiling point of 150 ° C. or lower, is added show excellent evaluation.
On the other hand, in Comparative Example 1, Comparative Example 4 and Comparative Example 5, almost no flux residue was observed, but the printability was remarkably inferior, and in Comparative Example 2 and Comparative Example 3, the flux residue was large and the problem of the present invention could not be overcome.

Further, when soldering was performed using the solder paste of Example 1 only in a nitrogen gas atmosphere without injecting formic acid gas, it can be used for solder bonding, but soldering is performed in an fornic acid gas atmosphere. It was confirmed that not only the flux residue but also the scattering and the generation of voids during soldering were more frequent than in Example 1 in which the above was performed.
As a result, the solder paste using the flux composition for solder paste of the present invention is soldered in a formic acid gas atmosphere, so that the flux residue is further reduced and the scattering and voids during soldering are synergistically reduced. It was found to have a suppressive effect.
The solder joint portion soldered with the solder paste using the flux composition for solder paste of the present invention has high bonding reliability because the flux residue and scattering and voids during soldering are suppressed. A joint can be provided.

The solder paste using the flux composition for solder paste of the present invention produces almost no flux residue and suppresses scattering and voids during soldering, so that highly reliable solder bonding can be realized and soldering can be achieved. Since cleaning after soldering is not required, it can be expected to be widely applied to semiconductor bonding in addition to conventional electronic component bonding.

Claims (4)

A flux composition for a solder paste, which comprises a liquid solvent having high viscosity at room temperature, a solvent liquid at room temperature, and an amide formed of a fatty acid having a molecular weight of less than 300 and an amine. A solder paste comprising a mixture of the flux composition for solder paste according to claim 1 and solder powder. The solder joining method using the solder paste according to claim 2, wherein the solder joining method is characterized by heating by heating in a formic acid gas atmosphere. A solder joint portion characterized by being soldered by the solder joint method of claim 3.