KR102324999B1 - Soldering flux and solder paste - Google Patents

Abstract

An object of the present invention is to provide a soldering flux capable of suppressing heat sagging during a reflow step and good immersion cleaning properties, and having good printability and an effect of suppressing release bumps, and a solder paste using the same.
A solution for the present invention is a brazing flux comprising a rosin-based resin, a solvent, an activator, and a thixotropic agent, wherein the thixotropic agent comprises hydrogenated castor oil and a dibenzylidene sorbitol compound. am.

Description

Soldering flux and solder paste

The present invention provides a soldering flux capable of both preventing heat sagging during a reflow process and good immersion cleaning properties during a cleaning process, and having good printability and an effect of suppressing mold release bumps, and a solder paste using the same is about

The solder paste used when mounting an electronic component on a board|substrate is produced by mixing the flux for soldering and solder alloy powder. In general, the soldering flux contains a base resin, an activator and a solvent. As this base resin, rosin-type resin is used conventionally.

The pattern and electrode formed on a board|substrate are also becoming high-definition with high performance, high density, etc. of recent electronic products. Therefore, the solder paste printed on the electrode also needs to respond to this high precision.

However, in the case of a solder paste using a conventional soldering flux, there is a problem that heat sagging occurs during the reflow process after being printed on the electrode, and this flux flows out around the electrode. In particular, in the case of a substrate having a high-definition pattern as described above, flux residues are formed in unnecessary locations due to heat sagging of the flux, which tends to cause poor insulation.

As a method for solving such a problem, for example, a soldering flux containing dibenzylidene sorbitols as a thixotropic agent is disclosed (refer to Patent Document 1).

Japanese Patent Laid-Open No. 2006-75875

The flux for soldering containing the said dibenzylidene sorbitol as a thixotropic agent can suppress the heating sagging of the flux at the time of reflow reliably. On the other hand, however, such a flux has a problem of impairing its immersion cleaning properties when cleaning the flux residue after the reflow step.

Moreover, the soldering flux containing the said dibenzylidene sorbitol as a thixotropic agent also has the problem that the printability of the solder paste using this is impaired.

It is an object of the present invention to provide a soldering flux capable of suppressing heat sagging during a reflow process and good immersion cleaning properties, and having good printability and an effect of suppressing release bumps, and a solder paste using the same. have.

The present invention is characterized in that it includes the following structures in order to achieve the above object.

(1) The brazing flux of the present invention includes a rosin-based resin, a solvent, an activator, and a thixotropic agent, and the thixotropic agent is characterized in that it includes hydrogenated castor oil and a dibenzylidene sorbitol compound.

(2) In the configuration of (1) above, the blending amount of the hydrogenated castor oil is 1 wt% to 10 wt% based on the total amount of the brazing flux, and the blending amount of the dibenzylidene sorbitol compound is 0.5 wt% with respect to the total amount of the brazing flux. % to 4.5% by weight.

(3) The composition of (1) or (2) above, wherein the dibenzylidene sorbitol compound is dibenzylidene sorbitol.

(4) In any one of (1) to (3) above, the thixotropic agent is characterized in that it further comprises a bisamide-based thixotropic agent.

(5) The solder paste of the present invention is characterized in that it contains a soldering flux having the structure in any one of (1) to (4), and solder alloy powder.

The flux for soldering of the present invention and the solder paste using the same can achieve both suppression of heating sagging during reflow and good immersion cleaning properties, and exhibit the effect of suppressing release bumps with good printability.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the thermal profile when each solder paste printed on FR board|substrate is heat-melted in the release bump generation|occurrence|production evaluation of the solder paste which concerns on an Example and a comparative example.

EMBODIMENT OF THE INVENTION Hereinafter, one Embodiment of the flux for soldering of this invention and a solder paste is demonstrated in detail. In addition, it goes without saying that this invention is not limited to the said embodiment.

1. Soldering flux

The flux for brazing of the present embodiment contains a rosin-based resin, a solvent, an activator, and a thixotropic agent.

<Rosin-based resin>

Examples of the rosin-based resin include rosin such as tall oil rosin, gum rosin, and wood rosin; and rosin derivatives such as hydrogenated rosin, polymerized rosin, heterogeneous rosin, acrylic acid-modified rosin, and maleic acid-modified rosin.

These rosins can be used individually or in combination of a plurality.

It is preferable that the compounding quantity of the said rosin-type resin is 35 weight% - 50 weight% with respect to the whole quantity of flux for brazing.

<solvent>

Examples of the solvent include isopropyl alcohol-based, ethanol-based, acetone-based, toluene-based, xylene-based, ethyl acetate-based, ethyl cellosolve-based, butyl cellosolve-based and glycol ether-based solvents. These can be used individually or in combination of plurality.

It is preferable that the compounding quantity of the said solvent is 20 weight% - 50 weight% with respect to the whole quantity of the flux for brazing.

<Activator>

Examples of the activator include amine salts (inorganic acid salts and organic acid salts) such as hydrogen halide salts of organic amines, organic acids, organic acid salts, organic amine salts, and the like. Specific examples thereof include diphenylguanidine hydrobromide, cyclohexylamine hydrobromide, diethylamine salt, acid salt, succinic acid, adipic acid, and sebacic acid. These can be used individually or in combination of plurality.

It is preferable that the compounding quantity of the said activator is 5 weight% - 15 weight% with respect to the whole amount of flux for brazing.

<Thixo agent>

The flux for brazing of this embodiment uses hydrogenated castor oil and a dibenzylidene sorbitol compound together as said thixo agent.

As said dibenzylidene sorbitol compound, dibenzylidene sorbitol, monomethyl dibenzylidene sorbitol, dimethyl dibenzylidene sorbitol, etc. are mentioned, for example. Among these, dibenzylidene sorbitol and dimethyl dibenzylidene sorbitol are particularly preferably used. Moreover, these can be used individually or in combination of plurality.

In addition, when dimethyldibenzylidenesorbitol is used as the dibenzylidenesorbitol compound and tris(2,3-dibromopropyl)isocyanurate is used together as an activator, mold release is performed when soldering using a solder paste. The occurrence of bumps can be suppressed.

It is preferable that the compounding quantity of the said dibenzylidene sorbitol compound is 0.5 weight% - 4.5 weight% with respect to the whole amount of flux for brazing. When the blending amount is less than 0.5% by weight, the flux for brazing hardly exerts the effect of suppressing sagging by heating, and when the blending amount is more than 4.5% by weight, the printability of the solder paste may be impaired, which is not preferable.

Moreover, it is preferable that the compounding quantity of the said hardened castor oil is 1 weight% - 10 weight% with respect to the whole amount of flux for brazing. When the blending amount is less than 1% by weight, it is difficult for the solder paste to exhibit good immersion cleaning properties, and when the blending amount is more than 10% by weight, the heating sagging inhibitory effect of the soldering flux may be impaired, which is not preferable. .

A bisamide-based thixotropic agent may be blended with the thixotropic agent in order to further improve the printability of the solder paste. Examples of the bisamide thixotropic agent include saturated fatty acid bisamides such as methylenebisstearic acid amide, ethylenebislauric acid amide, and ethylenebishydroxystearic acid amide; unsaturated fatty acid bisamides such as methylenebisoleic acid amide; and aromatic bisamides such as m-xylylenebisstearic acid amide. Among these, saturated fatty acid bisamide is particularly preferably used. Moreover, these can be used individually or in combination of plurality.

It is preferable that the compounding quantity of the said bisamide-type thixo agent is 0.1 weight% - 5 weight% with respect to the whole amount of flux for brazing. When the said compounding quantity is more than 5 weight%, since it will become difficult for a solder paste to exhibit favorable immersion cleaning property, it is unpreferable.

Substrates soldered using solder paste require cleaning of flux residues formed on the substrate after the reflow process, depending on the nature and type of the final product on which it is embedded. At the time of this washing|cleaning, the immersion washing|cleaning method of immersing in the washing|cleaning liquid at room temperature, dissolving the flux residue, and washing|cleaning is generally used. Therefore, in the case of the substrate on which the above-described flux residues are cleaned, good immersion cleaning properties are required.

The flux for brazing in which the said dibenzylidene sorbitol compound is mix|blended as a thixo agent can exhibit the heating sagging inhibitory effect at the time of a reflow process. On the other hand, however, such a flux for brazing produces a problem that the immersion cleaning property at the time of subsequent cleaning is impaired. That is, heat sagging suppression and immersion cleaning property have a conflicting relationship.

However, as mentioned above, the flux for brazing of this embodiment enabled coexistence of heat-sagging suppression and favorable immersion cleaning property by using together hydrogenated castor oil and a dibenzylidene sorbitol compound as said thixotropic agent.

In addition, other thixotropic agents can also be mix|blended with the flux for brazing of this embodiment in the range which does not impair the said heating sagging suppression and favorable immersion cleaning property.

<Others>

In the brazing flux of the present embodiment, as a resin other than the rosin-based resin, for example, other resins such as acrylic resin, styrene-maleic acid resin, epoxy resin, urethane resin, polyester resin, phenoxy resin, terpene resin, etc. can be combined. These can be used individually or in combination of plurality.

It is preferable that the compounding quantity of the said other resin is 35 weight% - 50 weight% with respect to the whole amount of flux for brazing.

An antioxidant can be blended with the soldering flux of the present embodiment for the purpose of suppressing oxidation of the solder alloy powder.

As said antioxidant, a hindered phenol type antioxidant, a phenol type antioxidant, a bisphenol type antioxidant, a polymer type antioxidant etc. are mentioned, for example. Among these, a hindered phenol-type antioxidant is used especially preferably.

The compounding quantity of the said antioxidant is not specifically limited. Its general blending amount is about 0.5 wt% to 5 wt% with respect to the total amount of the brazing flux.

Additives, such as a halogen, a matting agent, and an antifoamer, can also be further added to the flux for brazing of this embodiment. It is preferable that the compounding quantity of the said additive is 10 weight% or less with respect to the whole quantity of flux for brazing, and a more preferable compounding quantity is 5 weight% or less.

2. Solder paste

The solder paste of the present embodiment is produced by mixing the soldering flux and the solder alloy powder by a known method.

Examples of the solder alloy powder include a combination of a plurality of Sn, Ag, Cu, Bi, Zn, In, Ga, Sb, Au, Pd, Ge, Ni, Cr, Al, P, In, Pb and the like. have. As a typical solder alloy powder, a lead-free solder alloy powder such as Sn-Ag-Cu or Sn-Ag-Cu-In is used, but a solder alloy powder containing lead can also be used.

It is preferable that the compounding quantity of the said solder alloy powder is 65 weight% - 95 weight% with respect to the solder paste whole quantity. A more preferable blending amount thereof is 85 wt% to 93 wt%, and a particularly preferable blending amount thereof is 89 wt% to 92 wt%.

In the solder paste in which the blending amount of the solder alloy powder is less than 65% by weight, it tends to be difficult to form a sufficient solder joint at the time of soldering. On the other hand, in a solder paste in which the blending amount of the solder alloy powder exceeds 95% by weight, the flux for soldering as a binder is insufficient, so that it tends to be difficult to mix the flux for soldering with the solder alloy powder.

[Example]

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. In addition, this invention is not limited to these Examples.

Preparation of flux for soldering

Each component was kneaded with the composition and mixing|blending shown in Table 1 and Table 2, and each flux for brazing was produced. In addition, in Table 1 and Table 2, the unit of the numerical value regarding which shows a composition is weight% unless otherwise indicated.

In addition, the physical properties (viscosity and Ti) of each soldering flux are shown in Tables 1 and 2.

Then, 12 wt% of each of the above soldering fluxes and 88 wt% of Sn-3Ag-0.5Cu solder alloy powder were mixed to obtain solder pastes according to Examples 1 to 9 and Comparative Examples 1 to 9.

※1 Saturated fatty acid bisamide manufactured by Nippon Kasei Co., Ltd.

※2 Dibenzylidene sorbitol manufactured by New Nippon Rica Co., Ltd.

※3 Dimethyldibenzylidenesorbitol manufactured by New Nippon Rica Co., Ltd.

※4 Tris (2,3-dibromopropyl) isocyanurate manufactured by Nippon Kasei Co., Ltd.

※5 Acid anhydride: manufactured by Okamura Seiyu Co., Ltd.

※6 Hindered phenolic antioxidant BASF Japan Co., Ltd. product

※7 Polyethylene glycol-polypropylene glycol block copolymer manufactured by Nichiyu Co., Ltd.

<Pre-hit stretchability>

The FR4 board|substrate (a soldering resist opening diameter 200 micrometers) was used. Each solder paste was manually printed using a metal mask (thickness of 50 µm, metal mask opening diameter of 250 µm, pitch size of 400 µm) having a pattern corresponding to the FR4 substrate.

Then, each said board|substrate was preheated under the conditions of 190 degreeC and 90 second in nitrogen atmosphere (oxygen concentration 100 ppm) using a reflow oven (product name: TNP25-538EM, Tamura Seisakusho Co., Ltd. product).

The diameter (D1) of the solder paste on each substrate before preheating and the diameter (D2) of the solder paste on each substrate after preheating were measured using a metallographic microscope, and the difference was calculated by subtracting the value of D1 from the value of D2. . The results are shown in Table 3.

<Occurrence of abnormal bumps>

FR substrate (Cu-OSP treatment, 50 mm × 50 mm × 1.6 mm, solder resist opening diameter 200 μm) and additive processing stencil mask (manufactured by Process Lab Micron, 205 mm × 245 mm frame, thickness 50) μm, a metal mask opening diameter of 250 μm, and a pitch size of 400 μm) were prepared. Using the mask, each solder paste was manually printed onto each of the substrates with a stencil squeegee.

Subsequently, each substrate after printing was placed in a reflow oven (product name: TNP25-538EM, manufactured by Tamura Seisakusho Co., Ltd.), under a nitrogen atmosphere (oxygen concentration of 100 ppm), under the thermal profile conditions shown in Fig. 1, on each substrate. The solder paste was heated and melted. Then, each heated board|substrate was cooled to room temperature, the molten state was observed using the microscope, and the following criteria evaluated whether needle-like or plate-shaped protrusion came out from the formed bump. The results are shown in Table 3.

(double-circle): Needle-like or plate-shaped protrusion does not generate|occur|produce

○: Although needle-like or plate-like protrusions are generated, they do not grow beyond the circle of the bump outline.

Δ: While needle-like or plate-like projections are occurring, they are growing beyond the circle of the bump contour when observed from the upper surface

x: While needle-like or plate-like protrusions are occurring, they are growing to a size that bridges adjacent bumps

<Immersion cleaning property>

Cleanthrough 750K (manufactured by Kao Co., Ltd.) was prepared as a cleaning liquid. 250 cc to 300 cc of the washing liquid was placed in a 300 cc beaker, and this was stirred and heated on a hot plate equipped with a stirring device. In addition, a crosshead stirrer with a diameter of 30 mm was used for stirring.

Each of the substrates after the release bump test was hung so as to be immersed in a beaker containing the cleaning solution, and this was cleaned for a predetermined time and rotation speed. Each substrate after cleaning is rinsed with pure water, and the presence or absence of flux residues around bumps formed on each substrate is observed using a metallographic microscope (magnification: 100 to 200) for each of the substrates, according to the following criteria. evaluated as The results are shown in Table 3.

◎: Can be washed at a cleaning solution temperature of 60°C/revolutions 400rpm/cleaning time 120 seconds

○: Can be washed at a cleaning liquid temperature of 60°C/revolutions 400rpm/cleaning time 300 seconds

△: washing solution temperature 70°C/rotation speed 400rpm/washing time 120 seconds

×: Cannot be washed at a cleaning liquid temperature of 70° C./revolutions 400 rpm/cleaning time 120 seconds

<Printability>

An FR4 substrate (a solder resist opening diameter of 75 µm) and a metal mask (thickness of 30 µm, a metal mask opening diameter of 95 µm, a pitch size of 130 µm) having a pattern corresponding to the FR4 substrate were used. Each solder paste was printed on each said board|substrate with a metal squeegee with the printing apparatus (product name: SP-060, Panasonic Factory Solutions Co., Ltd. product).

Each board|substrate after printing was observed using the metallurgical microscope, and the following reference|standard evaluated the ratio in which the solder paste was transcribe|transferred on Cu land (9,800 places). The results are shown in Table 3.

◎: 100% transferred

○: non-transfer ratio less than 0.1%

(triangle|delta): non-transfer rate 0.1% or more and less than 0.5%

x: non-transfer ratio is 0.5% or more

As shown above, it can be seen that the solder paste of the present Example can achieve both preheat sagging properties and good immersion cleaning properties, and has an effect of suppressing release bumps with good printability.

Claims (13)

A soldering flux comprising a rosin-based resin, a solvent, an activator, and a thixotropic agent,
The thixotropic agent includes hydrogenated castor oil and a dibenzylidene sorbitol compound,
The blending amount of the hydrogenated castor oil is 1 wt% to 10 wt% based on the total amount of the brazing flux, and the blending amount of the dibenzylidene sorbitol compound is 1.5 wt% to 4.5 wt% based on the total amount of the brazing flux. flux. A soldering flux comprising a rosin-based resin, a solvent, an activator, and a thixotropic agent,
The thixotropic agent includes hydrogenated castor oil and a dibenzylidene sorbitol compound,
The blending amount of the hydrogenated castor oil is 1 wt% to 10 wt% based on the total amount of the brazing flux, and the blending amount of the dibenzylidene sorbitol compound is 0.5 wt% to 4.5 wt% based on the total amount of the brazing flux,
A flux for soldering characterized in that it contains tris(2,3-dibromopropyl)isocyanurate as the activator. The soldering flux according to claim 1 or 2, wherein the dibenzylidene sorbitol compound is dibenzylidene sorbitol. The soldering flux according to claim 1 or 2, wherein the thixotropic agent contains a bisamide-based thixotropic agent. The soldering flux according to claim 3, wherein the thixotropic agent contains a bisamide-based thixotropic agent. The flux for brazing according to claim 4, wherein the blending amount of the bisamide-based thixoagent is 0.1 wt% to 5 wt% based on the total amount of the flux for brazing. 6. The flux for brazing according to claim 5, wherein the blending amount of the bisamide-based thixoagent is 0.1 wt% to 5 wt% based on the total amount of the flux for brazing. A solder paste comprising the soldering flux according to claim 1 or 2 and solder alloy powder. A solder paste comprising the soldering flux according to claim 3 and solder alloy powder. A solder paste comprising the soldering flux according to claim 4 and solder alloy powder. A solder paste comprising the soldering flux according to claim 5 and solder alloy powder. A solder paste comprising the soldering flux according to claim 6 and solder alloy powder. A solder paste comprising the soldering flux according to claim 7 and solder alloy powder.

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