JP2020131257A - Flux and solder paste - Google Patents

Abstract

To provide a flux in which reflowability of solder particles is excellent and no residue is generated at a reflow temperature of a high temperature range, and a solder paste.SOLUTION: A flux contains: at least one kind of solid solvent which is a solid at normal temperature, and is evaporated at a reflow temperature; at least one kind of liquid solvent which is a liquid at normal temperature, and is evaporated at a reflow temperature; and polyethylene glycol which has a molecular weight of 1000 or less, and is 1 to 10 mass% to flux total mass.SELECTED DRAWING: None

Description

The present invention relates to flux and solder paste.

Flux is used to bond electronic components such as printed circuit boards, and in particular, solder paste in which solder particles and paste-like flux are mixed is widely used. For joining electronic components using solder paste, for example, an appropriate amount of solder paste is applied to the solder joint, and then the solder particles are melted by heating at the reflow temperature and joined to the solder joint (hereinafter, reflow). Also called a process). However, solid components are generated as flux residues at the solder joints after the reflow process, which causes problems such as deterioration of electronic circuit performance and corrosion.

Therefore, in recent years, a flux that suppresses a flux residue generated at a solder joint after a reflow step has been proposed (Patent Documents 1 and 2). These fluxes are characterized in that the flux is vaporized by heating at the reflow temperature, so that no flux residue is generated around the solder joint. The fact that no flux residue is generated is also referred to as no residue.

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

According to the RoHS Directive, the lead-containing solder composition is subject to regulation, and lead-free solder (lead-free solder) that does not contain lead is used for joining electronic components. However, the use of high temperature lead solder is still permitted for some parts. When reflow is performed using a solder paste that is a mixture of high-temperature lead solder and conventional residue-free flux, the flux volatilizes before the solder melts, and no flux remains when the solder melts, resulting in sufficient meltability and reflow. There is a problem that sex cannot be secured.

Therefore, an object of the present invention is to provide a flux and a solder paste which are excellent in reflowability of solder particles and do not generate residue at a reflow temperature in a high temperature range.

In order to achieve the above object, the flux of the present invention is used.
At least one solid solvent that is solid at room temperature and evaporates at reflow temperature,
At least one liquid solvent that is liquid at room temperature and evaporates at reflow temperature,
It has a molecular weight of 1000 or less, and is characterized by containing polyethylene glycol containing 1 to 10% by mass with respect to the total mass of the flux.

The solder paste of the present invention contains the flux of the present invention and solder particles.

According to the present invention, it is possible to provide a flux and a solder paste which are excellent in reflowability of solder particles and do not generate a residue at a reflow temperature in a high temperature range.

In the present invention, "residual-free" means that the amount of flux residue is 5% or less in the flux.

The flux of the present invention further comprises, for example, at least one additive component selected from the group consisting of thixotropic agents and activators, wherein the additive component evaporates together with other components at the reflow temperature.

In the flux of the present invention, for example, the solid solvent is 2,2-dimethyl-1,3-propanediol, 2,5-dimethylhexane-2,5-diol, trimethylolpropane, and 2-butyl-2-. Includes at least one selected from the group consisting of ethyl-1,3-propanediol.

In the flux of the present invention, for example, the liquid solvent is 1,2,6-hexanetriol, isobornylcyclohexanol, isooctadecanol, pentaerythritol, behenyl behenate, liquid paraffin, diethylene glycol monohexyl ether, diethylene glycol mono. Selected from the group consisting of -2-ethylhexyl ether, ethylene glycol monophenyl ether, diethylene glycol dibutyl ether, triethylene glycol monobutyl ether, methylpropylene triglycol, butylpropylene triglycol, triethylene glycol butylmethyl ether, and tetraethylene glycol dimethyl ether. Includes at least one.

In the flux of the present invention, for example, the thixotropic material is selected from fatty acid amides.

In the flux of the present invention, for example, the fatty acid amide is selected from the group consisting of stearic acid amide, lauric acid amide, palmitate amide, oleic acid amide, erucic acid amide, bechenic acid amide, hydroxystearic acid amide, and toluamide. At least one.

The flux of the present invention is, for example, at least one in which the activator is selected from the group consisting of monooctyl maleate, trimellitic acid, and isooctadecanoic acid.

The flux of the present invention contains, for example, 3% by mass or less of components that do not evaporate at the reflow temperature.

In the solder paste of the present invention, for example, the melting temperature of the solder particles is 280 ° C. to 330 ° C.

Hereinafter, embodiments of the present invention will be described in more detail with reference to examples. The present invention is not limited to the following embodiments. Each solvent is evaporable at the reflow temperature, that is, its boiling point or decomposition temperature is equal to or lower than the reflow temperature.

<Flux>
The flux of the present embodiment contains a solid solvent, a liquid solvent, and polyethylene glycol (hereinafter, PEG). The solid solvent is at least one solvent that is solid at room temperature and evaporates at the reflow temperature. The solid solvent is not particularly limited, and examples of the flux solvent include commonly used solid solvents. Specifically, 2,2-dimethyl-1,3-propanediol, 2,5-dimethylhexane-2,5-diol, trimethylolpropane, and 2-butyl-2-ethyl-1,3-propanediol. And so on. These may be used alone or in combination of two or more. The blending amount of the solid solvent is not particularly limited, and is, for example, 25 to 60% by mass, preferably 40 to 60% by mass, and more preferably 45 to 55% by mass with respect to the total mass of the flux. Is.

The reflow temperature is not particularly limited, and is, for example, 300 to 380 ° C, preferably 330 to 360 ° C.

The liquid solvent is at least one kind of solvent that is liquid at room temperature and evaporates at the reflow temperature. The liquid solvent is not particularly limited, and examples of the flux solvent include commonly used liquid solvents. Specifically, 1,2,6-hexanetriol, isobornylcyclohexanol, isooctadecanol, pentaerythritol, behenyl behenate, liquid paraffin, diethylene glycol monohexyl ether, diethylene glycol mono-2-ethylhexyl ether, ethylene glycol. Examples thereof include monophenyl ether, diethylene glycol dibutyl ether, triethylene glycol monobutyl ether, methylpropylene triglycol, butylpropylene triglycol, triethylene glycol butylmethyl ether, tetraethylene glycol dimethyl ether and the like. These may be used alone or in combination of two or more. The blending amount of the liquid solvent is not particularly limited, and is, for example, 20 to 60% by mass, preferably 25 to 50% by mass, and more preferably 25 to 35% by mass with respect to the total mass of the flux. Is.

The PEG has a molecular weight of less than 1500. The molecular weight of the PEG may be less than 1500, for example, 200, 300, 400, 600, 800, 1000, etc., specifically 1000 or less, more preferably 400 to 600. When the molecular weight of the PEG reaches 1500, it may not evaporate completely and a part of it may remain as a flux residue. The blending amount of the PEG is 1 to 10% by mass with respect to the total mass of the flux. The shape of the PEG is not particularly limited, and examples thereof include a liquid, a paste, and a solid, and a liquid is preferable.

The flux of the present embodiment may further contain additive components such as a thixotropic agent and an activator. In this case, the additive component that evaporates together with other components at the reflow temperature is used. These may be used alone or in combination of two or more. This makes it possible to enhance thixotropy and wettability. In the conventional solder paste, in order to make it residue-free, the activator and thixotropy are difficult to evaporate, so they are not contained at all, or even if they are contained, they are limited to those that vaporize at the reflow temperature, which is sufficient. Those having good activity or fluidity improving properties could not be used.

The thixotropy has a function of preventing separation of the flux from other components, improving storage stability, and improving flow characteristics so as to improve transferability during printing and ejection. Examples of the thixo agent include fatty acid amides, and specific examples thereof include stearic acid amides, lauric acid amides, palmitic acid amides, oleic acid amides, erucic acid amides, bechenic acid amides, hydroxystearic acid amides, and toluamides. And so on. The blending amount of the thixotropy is not particularly limited, and is, for example, 5 to 25% by mass, preferably 15 to 25% by mass, based on the total mass of the flux.

The activator has the effect of reducing and removing oxides on the surface of the soldered portion and powdered solder to purify the solder, increasing the wettability of the molten solder, and metallically adhering to the solder joint portion. Examples of the activator include monooctyl maleate, trimellitic acid, isooctadecaneic acid and the like. The blending amount of the activator is not particularly limited, and is, for example, 5 to 20% by mass, preferably 5 to 10% by mass, based on the total mass of the flux.

The flux of the present invention may further contain rosin. The rosin is a natural resin containing abietic acid and an isomer thereof as a main component, and the addition of the rosin has effects such as viscosity adjustment, adhesion retention of electronic parts, and reduction and removal of oxides by abietic acid. Examples of the rosin include hydrogenated rosin, acid-modified rosin, polymerized rosin, and rosin ester. The blending amount of the rosin is preferably 0.1 to 1% by mass with respect to the total mass of the flux.

In the flux of the present invention, the flux may contain a component that does not evaporate at the reflow temperature in an amount of 5% by mass or less. Since the flux of the present invention contains a large amount of solid solvent, at least a part of such a non-evaporable component can be evaporated during the reflow, so that the actual flux residue may be further reduced. Preferably, the content of the non-evaporable component in the flux is 0.5% by mass or less. It is preferable that this non-evaporable component does not adversely affect the reflowability and meltability even if a trace amount remains as a flux residue.

It is preferable that the flux of the present invention can be used in either a reducing atmosphere or a nitrogen atmosphere. The reducing atmosphere may be, for example, an atmosphere containing hydrogen radicals described in JP-A-2001-58259, in addition to a general reducing atmosphere containing formic acid or hydrogen gas.

The reflow soldering in an atmosphere containing hydrogen radicals can be performed using a reflow furnace provided with a hydrogen gas supply device and a plasma generator and capable of evacuating the inside to a vacuum.

When reflow soldering is performed in a reducing atmosphere using the flux of the present invention, the flux does not need to contain an activator at all because the atmospheric gas exhibits an oxide removing action.

<Solder paste>
The solder paste of the present embodiment contains the flux of the present invention and solder particles. The description of the flux of the present invention can be incorporated into the solder paste of the present embodiment. The solder particles are not particularly limited, and examples thereof include solder particles having a melting point of 280 ° C. to 330 ° C.

In the solder paste of the present embodiment, the flux of the present invention preferably contains a fatty acid amide as a thixotropy material, as described above. The fatty acid amide is the same as described above. By having the thixotropic agent, it is possible to prevent separation of powder solder and flux having significantly different specific densities in the solder paste of the present invention, improve storage stability, and improve flow characteristics so as to improve transferability during printing and ejection. ..

The particle size of the solder particles is not particularly limited and may be, for example, in the range of 10 to 60 μm, but may be a larger diameter or a smaller diameter. The blending amount of the solder particles and the flux of the present invention varies depending on the particle size of the solder particles, but generally, the flux of the present invention may be 8 to 15% by mass and the solder particles may be 85 to 92% by mass.

By containing the flux of the present invention, the solder paste of the present embodiment has excellent reflowability even at a reflow temperature in a high temperature range, and can be soldered without generating a residue at a solder joint.

Hereinafter, examples of the present invention will be described. However, the present invention is not limited to the following examples.

<Making flux>
Table 1 below shows Examples 1 to 23, and Table 2 below shows Comparative Examples 1 to 3. By mixing each of the materials shown in Table 1 and Table 2 below and heating and melting them, Example 1 to Example 23 and Comparative Example 1 to Comparative Example 3 were uniformly dispersed.

Details of the liquid paraffin and isooctadecanol in Tables 1 and 2 are shown below.
Liquid paraffin: Product name HYCOAL K-350, manufactured by Kaneda Co., Ltd. Isooctadecanol: Product name Fine Oxocol 180T, manufactured by Nissan Chemical Industries, Ltd.

<Making solder paste>
A solder paste was prepared using each flux having the composition shown in each of the Examples (Table 1) and Comparative Example (Table 2). Specifically, each solder paste is prepared by mixing 10% by mass of each of the above fluxes with 90% by mass of 90Pb-10Sn solder powder (particle size: 20 to 38 μm) with respect to the entire solder paste. Made. The solder particles are high-temperature lead (Pbrich) solder containing 90% by mass of lead (Pb) and 10% by mass of tin (Sn), and the melting point of the solder particles is 301 ° C.

<Residual amount evaluation test>
The amount of residue of each flux was evaluated using each of the fluxes prepared based on each of the Examples and Comparative Examples. The evaluation method of the residue amount will be described. 10 mg of each of the above fluxes was placed in an aluminum pan and heated at a peak temperature of 350 ° C. and a heating rate of 1 ° C./sec using a ULVAC TGD9600. The heated sample was used as an evaluation sample, and the weight of each flux after heating was calculated and evaluated according to the following evaluation criteria.

Residual amount evaluation test Evaluation criteria ◎: Weight was 3% or less before heating 〇: Weight was more than 3% before heating and 5% or less ×: Weight was more than 5% before heating

<Reflowability evaluation test>
A solder paste was prepared using the fluxes of each of the Examples and Comparative Examples, and the reflowability was evaluated by performing a solder spreading test. The solder spread test conformed to JIS Z3197. The reflow conditions will be described. Preheating was performed at 170 ° C. for 90 seconds and held at a peak temperature of 330 ° C. for 60 seconds to melt the solder. The reflow was performed in a nitrogen atmosphere. The melted product was used as an evaluation sample, and the wett spread ratio of each of the solder pastes after reflow was calculated and evaluated according to the following evaluation criteria.

Reflowability evaluation test Evaluation criteria ◎: Wetting spread rate is 90% or more 〇: Wetting spread rate is 85% or more and less than 90% ×: Wetting spread rate is less than 85%, or the solder did not melt

Table 3 below shows the results of each evaluation of the residual amount and reflowability of each of the Examples and Comparative Examples.

As is clear from Table 3, each of the solder pastes used in the comparative example has good properties on one side, but it can be confirmed that all of them have an adverse effect in the test on the other side. On the other hand, according to the present invention, good results are obtained in both the residue amount evaluation test and the reflowability evaluation test.

Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above-described embodiments. Various changes that can be understood by those skilled in the art can be made to the structure and details of the present invention within the scope of the present invention.

As described above, according to the present invention, for example, in a high temperature region, the reflowability of the solder particles is excellent and no residue can be generated. Therefore, the present invention is useful, for example, in the field of using solder particles having a high melting temperature.

Claims (10)

At least one solid solvent that is solid at room temperature and evaporates at reflow temperature,
At least one liquid solvent that is liquid at room temperature and evaporates at reflow temperature,
A flux having a molecular weight of 1000 or less and containing 1 to 10% by mass of polyethylene glycol with respect to the total mass of the flux. The flux according to claim 1, further comprising at least one additive component selected from the group consisting of thixotropy and activator, wherein the additive component evaporates together with other components at the reflow temperature. The solid solvent is 2,2-dimethyl-1,3-propanediol, 2,5-dimethylhexane-2,5-diol, trimethylolpropane, and 2-butyl-2-ethyl-1,3-propanediol. The flux according to claim 1 or 2, comprising at least one selected from the group consisting of. The liquid solvent is 1,2,6-hexanetriol, isobornylcyclohexanol, isooctadecanol, pentaerythritol, behenyl behenate, liquid paraffin, diethylene glycol monohexyl ether, diethylene glycol mono-2-ethylhexyl ether, ethylene glycol. Claimed to include at least one selected from the group consisting of monophenyl ether, diethylene glycol dibutyl ether, triethylene glycol monobutyl ether, methylpropylene triglycol, butylpropylene triglycol, triethylene glycol butyl methyl ether, and tetraethylene glycol dimethyl ether. The flux according to any one of Items 1 to 3. The flux according to any one of claims 2 to 4, wherein the thixotropy material is selected from fatty acid amides. The fatty acid amide is at least one selected from the group consisting of stearic acid amides, lauric acid amides, palmitic acid amides, oleic acid amides, erucic acid amides, bechenic acid amides, hydroxystearic acid amides, and toluamides. The flux according to claim 5. The flux according to any one of claims 2 to 6, wherein the activator is at least one selected from the group consisting of monooctyl maleate, trimellitic acid, and isooctadecanoic acid. The flux according to any one of claims 1 to 7, wherein the component that does not evaporate at the reflow temperature is 3% by mass or less. A solder paste containing the flux according to any one of claims 1 to 8 and solder particles. The solder paste according to claim 9, wherein the melting temperature of the solder particles is 280 ° C to 330 ° C.