JP2017196663A - Solder Paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide solder paste having little dispersion of viscosity, since sedimentation of solder alloy powder in the solder paste is suppressed by coating the solder alloy powder with fatty acid.SOLUTION: In solder paste containing solder alloy powder as much as 80 mass% or more and 95 mass% or less, and a thixotropic agent as much as 0.2 mass% or more and 1.2 mass% or less, the solder alloy powder is coated with fatty acid, and the thixotropic agent contains at least hydrogenerated castor oil and amide, and a mass ratio between the hydrogenerated castor oil and the amide is in the range of 1:1 or higher and 4:1 or lower, and a viscosity ratio R is 0.95 or higher and 1.05 or lower.SELECTED DRAWING: None

Description

  The present invention relates to a solder paste used for solder joining.

  Circuit elements can be mounted on the printed circuit board by using a flow method in which the lower surface of the printed circuit board is immersed in a solder bath, or by adjusting the solder paste (solder flux to the solder alloy powder to an appropriate viscosity) on the printed circuit board. And a reflow method in which solder is heated and melted after the circuit element is placed on the printed circuit element. In either method, it is essential to use solder flux in order to remove the oxide film on the base material surface, prevent oxidation of the base material and solder, and ensure the wettability of the solder surface. Yes.

  As the solder paste used for board mounting, in addition to the solder alloy powder, resin-based fluxes using rosin, modified rosin, synthetic resin, etc. as the main component are mainly used. Because of its weak nature, a thixotropic agent is usually added to the solder paste. In addition, an activator, a solvent for the activator, a dispersion stabilizer, and the like may be added to the solder paste depending on the application.

  When the solder alloy powder settles and the flux is separated, the density of the flux is generated in the solder paste, and stable supply cannot be performed. In solder paste in which flux and solder alloy powder are mixed, the solder alloy powder settles in the flux. When the specific gravity of the flux is 1, the specific gravity of the solder alloy powder is about 7.4. This is because there is a big gap.

  In order to prevent the precipitation of solder alloy powder having a specific gravity difference from the flux, a network-structured precipitate is formed in the flux, and the thixotropic agent enables the precipitation of the network-structured material. It is. This network structure increases the elasticity of the solder paste. However, in reality, it is difficult to say that the effect of thixotropic agents is sufficiently exhibited.

In Patent Document 1, a higher fatty acid amide (sometimes referred to as a higher fatty acid amide) added to a solder paste flux as a thixotropic agent is excellent in fluidity improving properties as a viscosity modifier and decomposes upon heating. It is disclosed that there is an effect of no residue. Furthermore, Patent Document 2 discloses a technique in which a methacrylic acid polymer is added to a flux for the purpose of improving fluidity.

JP 2004-25305 A International Publication No. 2012-118076

  However, in Patent Document 1, a functional group containing nitrogen in the chemical structure of the higher fatty acid amide added to the solder paste flux as a thixotropic agent is adsorbed on the surface of the solder alloy powder. As a result, higher fatty acid amides cause a decrease in the viscosity stability with time of the solder paste flux.

  Further, in Patent Document 2, since the methacrylic acid polymer is added to the flux, the effect of improving the fluidity may not be sufficient depending on the mixing ratio with the solder alloy powder.

  Therefore, the present invention has been proposed in view of the above-mentioned problems of the prior art, and for the purpose of imparting anti-settling property of the solder alloy powder, the solder alloy powder is covered with a fatty acid coating, thereby wetting with the flux. An object of the present invention is to provide a solder paste in which the property is improved and the precipitation of the solder alloy powder in the solder paste is suppressed.

  The solder paste according to an aspect of the present invention contains 80% by mass or more and 95% by mass or less of a solder alloy powder and 0.2% by mass or more and 1.2% by mass or less of a thixotropic agent. The thixotropic agent coated with a fatty acid contains at least a hydrogenated castor oil represented by the following chemical formula (1) and an amide represented by the following chemical formula (2), and the mass ratio of the hydrogenated castor oil and the amide is: It is within the range of 1: 1 or more and 4: 1 or less, and the viscosity ratio R shown in the following formula 1 is 0.95 or more and 1.05 or less.

（ただし、式中のＲ_１およびＲ_２は、それぞれ独立に水素原子またはアルキル基を表す。）

(However, R ₁ and R ₂ in the formula each independently represent a hydrogen atom or an alkyl group.)

η_up ：測定温度２５℃における、５０ｍＬ試験管内のはんだペースト４０ｍＬのうち３５ｍＬ目盛りの粘度
η_under ：測定温度２５℃における、５０ｍＬ試験管内のはんだペースト４０ｍＬのうち５ｍＬ目盛りの粘度

η _up : Viscosity of 35 mL scale in 40 mL of solder paste in a 50 mL test tube at a measurement temperature of 25 ° C. η _under : Viscosity of 5 mL scale in 40 mL of solder paste in a 50 mL test tube at a measurement temperature of 25 ° C.

  In one aspect of the present invention, the fatty acid is caproic acid, enanthic acid, caprylic acid, pelargonic acid, lauric acid, myristic acid, pentadecylic acid, palmitic acid, palmitoleic acid, margaric acid, stearic acid, oleic acid, vaccenic acid , Linoleic acid, α-linolenic acid, γ-linolenic acid, eleostearic acid, arachidic acid, arachidonic acid, behenic acid, lignoceric acid, nervonic acid, serotic acid, montanic acid, melicic acid, N-lauroyl sarcosine, N- It is preferably at least one selected from the group of oleoyl sarcosine.

  In one aspect of the present invention, the amide is preferably any one selected from the group of amide lauric acid amide, palmitic acid amide, stearic acid amide, and hydroxystearic acid amide.

  In one aspect of the present invention, the solder alloy powder is at least two selected from the group of bismuth, zinc, silver, aluminum, lead and tin.

  According to the present invention, by coating the solder alloy powder with a fatty acid, sedimentation of the solder alloy powder in the solder paste is suppressed, so that it is possible to provide a solder paste with little variation in viscosity.

  Hereinafter, preferred embodiments of the present invention will be described in detail. The present embodiment described below does not unduly limit the contents of the present invention described in the claims, and all the configurations described in the present embodiment are essential as means for solving the present invention. Not necessarily.

  The inventors of the present invention repeatedly conducted a test study on variations in solder paste viscosity for optimization of thixotropic agents and further measures for improving fluidity described in Patent Documents 1 and 2. As a result, it was found that the dispersion of the viscosity of the solder paste is largely related to the precipitation of the solder alloy powder.

  As a result of further research on this point, the present inventors have controlled the upper / lower viscosity ratio of the solder paste to a specific range by coating the solder alloy powder with a fatty acid to solve the above-mentioned problems. I learned that I can do it. The present invention has been made based on such knowledge.

  Hereinafter, one embodiment of the present invention will be described separately for each component of the solder paste. The solder paste which concerns on one Embodiment of this invention contains the flux for solder and solder alloy powder. Further, the solder flux includes a) a flux main component, b) a thixotropic agent, c) a solvent for dissolving thixotropy, d) an organic solvent, and e) other additives.

[1. Solder flux]
First, the main component of the solder flux contained in the solder paste according to the embodiment will be described. As a flux main component, rosins having a softening point of 70 ° C. to 170 ° C. and an acid value of 150 mgKOH / g to 240 mgKOH / g can be used.

  When the softening point and acid value of the flux main component are in the above ranges, the amount of flux residue generated can be suppressed without sacrificing solderability such as wet spreadability of the solder paste. . Further, the generated minute amount of flux can be effectively used as an insulating film. On the other hand, when the softening point is less than 70 ° C. or the acid value is less than 150 mgKOH / g, the oxide film formed on the surface of the solder alloy powder at the time of joining may not be completely removed. On the other hand, when the softening point exceeds 170 ° C. or the acid value exceeds 240 mgKOH / g, characteristics including the viscosity of the solder paste deteriorate over time due to the reaction between the solder alloy powder and the main flux component. There is.

  As rosins, known materials can be widely applied. However, rosin, modified rosin, abietic acid, which is the main component of rosin, and modified abietic acid obtained by modifying rosin are used because of heat resistance and oxide film removal. It is preferable to use at least one selected from the group of

  As the flux main component, rosins having a softening point in the range of 70 ° C. to 170 ° C. and an acid value in the range of 150 mgKOH / g to 240 mgKOH / g are used for the solder joint temperature and the acid value of the entire flux. This is for adjustment. The softening point of the main flux component is preferably 70 ° C to 170 ° C, more preferably 80 ° C to 170 ° C. Moreover, it is preferable that the acid value of a flux main component is 150 mgKOH / g-240 mgKOH / g. As for the acid value of the flux main component, the mass (mg) of potassium hydroxide (KOH) required to neutralize the free fatty acid contained in 1 g of the flux main component is the same as the acid value of the solder flux as a whole. It is calculated | required based on the flux test method for soldering (JIS Z 3197 conformity).

  Specific examples of such a flux main component include natural rosin (softening point: 76 ° C. to 85 ° C., acid value: 167 mg KOH / g to 175 mg KOH / g), polymerized rosin (softening point: 96 ° C. to 99 ° C., acid Value: 159 mg KOH / g to 163 mg KOH / g), hydrogenated rosin (softening point: 74 ° C. to 75 ° C., acid value: 160 mg KOH / g to 170 mg KOH / g), abietic acid (softening point: 129 ° C. to 137 ° C., acid value 179 mg KOH / g to 182 mg KOH / g), dihydroabietic acid (softening point: 150 ° C. to 155 ° C., acid value: 154 mg KOH / g to 158 mg KOH / g), dehydroabietic acid (softening point: 160 ° C. to 168 ° C., acid value) : 174 mg KOH / g to 178 mg KOH / g) can be used.

  The content of the flux main component is preferably 35% by mass or more and less than 70% by mass, preferably 45% by mass or more and 60% by mass or less, with the flux being 100% by mass. If the content of the flux main component is less than 35% by mass, the activity of the obtained solder paste is insufficient, and the conductivity between the electronic component and the wiring board may not be sufficiently ensured. On the other hand, when the content of the flux main component is 70% by mass or more, the flux residue after joining increases and the base material and the conductor may be corroded.

  The thixotropic agent blended in the solder paste according to the embodiment includes at least hydrogenated castor oil represented by the following chemical formula (1) and amide represented by the following chemical formula (2). In this embodiment, by including such a thixotropic agent, the flux is gelled to prevent sedimentation of the solder alloy powder. Therefore, the mechanism of gelation is the hydrogen of the hydroxyl group added to the long-chain hydrogenated castor oil. Strengthened by bonding.

（ただし、式中のＲ_１およびＲ_２は、それぞれ独立に水素原子またはアルキル基を表す。）

(However, R ₁ and R ₂ in the formula each independently represent a hydrogen atom or an alkyl group.)

  Amide contained in the solder paste according to the embodiment is not particularly limited, and may be any one selected from the group of amide lauric acid amide, palmitic acid amide, stearic acid amide, and hydroxystearic acid amide. preferable. Thereby, sedimentation of the solder alloy powder in the solder paste is further suppressed, and wettability is improved.

  In addition to hydrogenated castor oil and amide, this thixotropic agent includes vegetable oil-based polymerized oil, oxidized polyethylene, surfactant, gum arabic, carpomer, sodium alginate, ethyl cellulose, cyclodextrin, xanthan gum, guar gum, pictin, Examples include sodium polyacrylate, carrageenan, propylene glycol alginate, sodium carboxymethylcellulose, urea-modified urethane, and the like.

  In the solder paste according to the present embodiment, the hydrogenated castor oil represented by the chemical formula (1) as the thixotropic agent and the amide represented by the chemical formula (2) are used in a mass ratio of the hydrogenated castor oil and the amide of 1: It mix | blends within the range of 1 or more and 4: 1 or less. Thereby, reaction of an amide and solder alloy powder is suppressed, and there exists an effect that the preservation stability as solder paste is maintained.

  It is important that the blending amount of the thixotropic agent with respect to the entire solder paste is 0.2% by mass or more and 1.2% by mass or less. If the amount of the thixotropic agent is less than 0.2% by mass, the thixotropic property as a solder paste will be insufficient. On the other hand, if the mixing amount of the thixotropic agent exceeds 1.2% by mass, the amide is excessive, the viscosity stability is lowered, and the fluidity is also lowered. Therefore, rubbing occurs when the solder paste is printed. However, this is not preferable because there is a risk of printing failure.

  Moreover, the mass ratio of hydrogenated castor oil and amide as a thixotropic agent blended in the solder paste according to the present embodiment is in the range of 1: 1 to 4: 1. When the mass ratio of hydrogenated castor oil and amide is lower than 1: 1, there is a tendency to exhibit a particularly high viscosity non-recovery rate. When the mass ratio of hydrogenated castor oil and amide is higher than 4: 1, thixotropy is present. The index (TI value) is lowered, which is not preferable.

  The solder paste according to the embodiment includes a solvent for thixotropic agent for the purpose of dissolving the thixotropic agent. Such a solvent is not particularly limited, and either an inorganic or organic solvent can be used, but an organic solvent is preferably used from the viewpoint of solubility. Specifically, 2-phenoxyethanol (boiling point: 244 ° C. to 246 ° C.) can be preferably used.

  The amount of the solvent for dissolving the thixotropic agent is preferably 10 to 20 times in terms of mass ratio to the thixotropic agent.

  The solder paste according to the embodiment includes an organic solvent. Such an organic solvent is not particularly limited, and a known one can be used. However, it is preferable to use one having a boiling point of 200 ° C. to 300 ° C. so that the viscosity of the solder paste obtained by mixing the solder flux and the solder alloy powder is in a suitable range at the time of soldering. It is more preferable to use what is 220 degreeC-300 degreeC, and it is still more preferable to use what is 230 degreeC-280 degreeC.

  Specific examples of such an organic solvent include 2-phenoxyethanol (boiling point: 244 ° C. to 246 ° C.), 2-ethyl-1,3-hexanediol (boiling point: 243 ° C. to 244 ° C.), diethylene glycol monohexyl ether ( Boiling point: 261 ° C. to 265 ° C.) and diethylene glycol monobutyl ether (boiling point: 230.4 ° C.) can be used.

  The blending amount of the organic solvent is preferably less than 50% by mass, more preferably 20% by mass or more and less than 50% by mass, and further preferably 25% by mass or more and 45% by mass or less, with the flux as 100% by mass. When the content of the organic solvent is 50% by mass or more, sagging or the like is likely to occur when the flux is applied.

  In addition to the above-described components, the flux for solder according to the present embodiment can be blended with a component that improves the surface protective agent and the temporary fixing adhesiveness as necessary. Specifically, a silane coupling agent or a surfactant is used as the surface protective agent, and a phosphoric acid (meth) acrylic monomer or a triazine dithiol monomer is added as a component for improving the temporary fixing adhesiveness. it can.

  Further, in the solder flux according to the present embodiment, a thermoplastic resin can be used as a material to be added to or partially substituted for the rosin component from the viewpoint of improving crack resistance in a heat cycle. Specifically, a polymer such as polyamide, butadiene, isoprene, styrene, acrylic acid or an ester thereof, methacrylic acid or an ester thereof, ethylene, or a copolymer composed of two or more of these may be used.

  The blending amount of these additives is preferably 1% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 7% by mass or less, with the flux as 100% by mass. When the blending amount of these additives is within the above range, it is possible to improve the properties such as temporary fixing adhesiveness and crack resistance while securing the properties of the solder flux. If the amount is less than 1% by mass, the above effect cannot be exhibited. On the other hand, if it exceeds 10% by mass, the content of the thixotropic agent in the entire soldering flux decreases, so that the viscosity of the solder paste varies and the viscosity non-recovery rate of the solder paste may increase. As a result, with such a solder paste, when printed on a printed circuit board, printing failure or wettability due to sagging occurs.

[1-1. Manufacturing method of solder flux]
Next, a method for manufacturing a solder flux according to one embodiment will be described. In the method for manufacturing a soldering flux according to one embodiment of the present invention, the soldering flux can be obtained by weighing each of the above-described components so as to have the above-described blending amount and mixing them uniformly. The mixing means is not particularly limited, but it is preferable to mix using a self-revolving mixer, a homogenizer, a Hayshell mixer or the like. In addition, from the viewpoint of uniformly mixing the constituent components, it is preferable to first mix only the solid components and then add an organic solvent and further mix them.

[2. Solder alloy powder]
The solder alloy powder mixed with the solder flux contained in the solder paste according to the present embodiment is bismuth (Bi), zinc (Zn), silver (Ag), aluminum (Al), lead (Pb), and tin. What consists of an alloy containing at least 2 sort (s) selected from the group of (Sn) can be used conveniently. For example, Pb-free solder such as Pb—Sn alloy solder, Bi—Zn alloy solder, Sn—Ag alloy solder, or a solder alloy obtained by adding Cu, Bi, In, Al, or the like is used. be able to.

  The solder alloy powder is characterized by being coated with a fatty acid. That is, a coating layer made of fatty acid is formed on the surface of the solder alloy powder. By coating the solder alloy powder with a fatty acid, the upper / lower viscosity ratio in the solder paste can be controlled within a predetermined range, so that the precipitation of the solder alloy powder in the solder paste is suppressed.

  The fatty acids include caproic acid, enanthic acid, caprylic acid, pelargonic acid, lauric acid, myristic acid, pentadecylic acid, palmitic acid, palmitoleic acid, margaric acid, stearic acid, oleic acid, vaccenic acid, linoleic acid, α-linolenic acid , Γ-linolenic acid, eleostearic acid, arachidic acid, arachidonic acid, behenic acid, lignoceric acid, nervonic acid, serotic acid, montanic acid, mellicic acid, N-lauroyl sarcosine, N-oleoyl sarcosine It is preferable to use at least one kind. When the coating layer of these fatty acids is directly present on the surface of the solder alloy powder, not only the precipitation of the solder alloy powder in the solder paste is suppressed, but also when the solder paste is stored for a long time under adverse conditions Even so, the wettability and the antioxidant effect can be maintained.

  Among these, from the viewpoint of productivity and workability, any of stearic acid, oleic acid, and N-oleoyl sarcosine is more preferable, and by covering the surface of the solder alloy powder with any of these fatty acids, Aggregated powdered solder alloy powder is obtained, and the precipitation of the solder alloy powder in the solder paste is more reliably suppressed. Furthermore, oleic acid is particularly preferred as the fatty acid. When the surface of the solder alloy powder is coated with oleic acid, the bond between the oleic acid and the solder alloy powder is obtained by having an unsaturated bond (cis type) in the carbon chain. The strength can be further increased. As a result, the precipitation of the solder alloy powder is suppressed, and the upper / lower viscosity ratio R in the solder paste can be further stabilized.

  The average particle diameter of the solder alloy powder is preferably in the range of 1 μm to 100 μm, and more preferably 1 μm to 50 μm.

  When the average particle size of the solder alloy powder is less than 1 μm, there is a possibility that the solder alloy powder aggregates in the solder paste. On the other hand, if the average particle size of the solder alloy powder exceeds 100 μm, a new conductive layer containing a resin is formed between the materials to be bonded at the time of bonding, which may lower the conductivity. In the present embodiment, the average particle size means a particle size having an integrated value of 50%, and can be measured by a particle size distribution measuring device such as SALD-7000 (Shimadzu Corporation).

[3. Solder paste]
Next, the solder paste according to the embodiment will be described. The solder paste according to an embodiment of the present invention has a solder flux of 5% by mass to 20% by mass, preferably 10% by mass to 15% by mass, and 80% by mass to 95% by mass, preferably 85% by mass. It is comprised from the above 90 mass% or less solder alloy powder. By controlling the mass ratio of the solder flux and the solder alloy powder within such a range, the wet spreadability at the time of joining of the obtained solder paste can be made excellent. Moreover, since a flux residue can be utilized as an insulating film, corrosion of the base material can be effectively prevented.

  In addition, the mixing method of the soldering flux and the solder alloy powder is not particularly limited, and a known method can be employed. For example, the mixing can be performed by a self-revolving mixer, a homogenizer, a Hayshell mixer, or the like.

  The solder paste according to an embodiment of the present invention is characterized in that the viscosity ratio R shown in the following formula 1 is 0.95 or more and 1.05 or less.

η_up ：測定温度２５℃における、５０ｍＬ試験管内のはんだペースト４０ｍＬのうち３５ｍＬ目盛りの粘度
η_under ：測定温度２５℃における、５０ｍＬ試験管内のはんだペースト４０ｍＬのうち５ｍＬ目盛りの粘度

η _up : Viscosity of 35 mL scale in 40 mL of solder paste in a 50 mL test tube at a measurement temperature of 25 ° C. η _under : Viscosity of 5 mL scale in 40 mL of solder paste in a 50 mL test tube at a measurement temperature of 25 ° C.

  First, 40 mL of solder paste is put into a 50 mL test tube and left at 25 ° C. for 48 hours. Next, using a viscometer, a predetermined amount of each of the upper 35 mL scale solder paste and the lower 5 mL scale solder paste is sampled with a syringe. The viscometer is not particularly limited, and examples thereof include a capillary viscometer, a rotational viscometer, a falling body viscometer, a vibration viscometer, a parallel plate viscometer, and the like, and a rotational viscometer is preferable. Among these, a spiral viscometer is particularly preferable.

Then, the viscosity of these samples is measured when the measurement temperature reaches 25 ° C., the rotation speed reaches 10 rpm, and the measurement time reaches 1 minute. Thereby, η _up shown in the above equation 1 is the viscosity of the 35 mL scale of 40 mL of solder paste in a 50 mL test tube at a measurement temperature of 25 ° C., and η _under is 5 mL of 40 mL of solder paste in a 50 mL test tube at a measurement temperature of 25 ° C. It is the viscosity of the scale. Then, the viscosity ratio R is calculated by dividing the value of η _under from the value of η _up . The viscosity ratio R calculated in this way is a parameter that can confirm the sedimentation property of the solder alloy powder in the solder paste.

  That is, in the solder paste according to the present embodiment, the viscosity ratio R is 0.95 or more and 1.05 or less, so that the precipitation of the solder alloy powder is suppressed and the viscosity variation as the solder paste is small and excellent. It can be confirmed.

  When the viscosity ratio R is less than 0.95, the solder alloy powder in the solder paste may be precipitated. On the other hand, when the viscosity ratio R exceeds 1.05, the viscosity of the solder paste may vary.

  The solder paste according to one embodiment has little change over time such as viscosity and reactivity, and is excellent in long-term storage stability. Moreover, since the oxide film on the surface of the solder alloy powder can be effectively removed at the time of soldering, it has excellent wet spreading properties. Furthermore, the generation of flux residue during solder bonding can be suppressed, and even when a flux residue is generated, it can be used as an insulating coating.

  The solder paste according to one embodiment of the present invention contains 80% by mass or more and 95% by mass or less of a solder alloy powder and 0.2% by mass or more and 1.2% by mass or less of a thixotropic agent. Coated with fatty acid, the thixotropic agent contains at least hydrogenated castor oil and amide, the mass ratio of hydrogenated castor oil and amide is in the range of 1: 1 to 4: 1, and the viscosity ratio R is It is 0.95 or more and 1.05 or less.

  As described above, the settling of the solder alloy powder is suppressed and higher thixotropy is maintained, so that there is little change with time in viscosity, reactivity, and the like. For example, since a solder paste that improves thixotropy and is excellent in viscosity stability can be used for board mounting, the industrial value is extremely high.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example and a comparative example, this invention is not limited to these Examples and a comparative example.

  In Examples 1 to 58 and Comparative Examples 1 to 5, as the solder flux, the flux main component, thixotropic agent, organic solvent for thixotropic agent, organic solvent, and other constituents described in Table 1 are used as carboxylic acid. Esters, organic solvents and activators were prepared. The composition ratio of each constituent component was adjusted as described in Tables 2 to 5, and a solder flux was prepared. In addition, the thixotropic agents a to e shown in Tables 2 to 5 represent the active ingredients of amides obtained by subtracting the organic solvent from the thixotropic agents a to e shown in Table 1 as mass%.

  First, in Examples 1-18, the stearic acid (made by Kanto Chemical Co., Inc.) adjusted to 10 mass% to the isopropyl alcohol solution was added to the solder alloy powders a to c having an average particle diameter of 19 μm to 27 μm shown in Table 1 Then, after impregnating for 1 hour, it was vacuum-dried at 60 ° C. for 6 hours to obtain a solder alloy powder coated with stearic acid.

  Next, in Examples 19 to 38, solder alloy powders a to c having an average particle diameter of 19 to 27 μm shown in Table 1 were treated with oleic acid (manufactured by Kanto Chemical Co., Ltd.) instead of stearic acid. That is, Example 19 was the same as Example 1 except that the solder alloy powder a was treated with oleic acid. Moreover, in Examples 20-24, it was respectively the same as Examples 2-6 except having processed the solder alloy powder a with oleic acid. Moreover, in Examples 25-34, 36, and 38, it was the same as that of Examples 7-18 except that the solder alloy powders a to c were treated with oleic acid. Furthermore, in Example 35, it was the same as Example 1 except that the solder alloy powder b was treated with oleic acid, and in Example 37, the solder alloy powder c was treated with oleic acid. Thus, in Examples 19 to 38, solder alloy powders coated with oleic acid were obtained.

  Next, in Examples 39 to 58, the solder alloy powders a to c having an average particle diameter of 19 μm to 27 μm shown in Table 1 were treated with N-oleoyl sarcosine (manufactured by Tokyo Chemical Industry Co., Ltd.) instead of stearic acid. That is, Example 39 was the same as Example 1 except that the solder alloy powder a was treated with N-oleoyl sarcosine. Moreover, in Examples 40-44, it was the same as that of Examples 2-6 except that the solder alloy powder a was treated with N-oleoyl sarcosine. Moreover, in Examples 45-54, 56, and 58, it was respectively the same as Examples 7-18 except having processed the solder alloy powders ac with N-oleoyl sarcosine. Furthermore, Example 55 was the same as Example 1 except that the solder alloy powder b was treated with N-oleoyl sarcosine, and in Example 57, the solder alloy powder c was treated with N-oleoyl sarcosine. Thereby, in Examples 19 to 38, solder alloy powders coated with N-oleoyl sarcosine were obtained.

  On the other hand, in Comparative Examples 1-5, the solder alloy powder a was used without performing the surface treatment with the fatty acid.

  Next, in Examples 1 to 58 and Comparative Examples 1 to 5, the solder alloy powder coated with these soldering flux and fatty acid was used for 10 minutes using an auto-revolving mixer (AR-250, manufactured by Shinky Corporation). Mixing was performed to prepare a solder paste.

  Thus, the upper / lower viscosity ratio R of the produced solder paste was evaluated as follows. Solder paste 40mL is put into a 50mL test tube, and left at a temperature of 25 ° C for 48 hours. Then, using a spiral viscometer (Malcom, PCU-02V), the upper 35mL scale solder paste and the lower 5mL The solder paste at the scale was sampled by 0.2 mL with a syringe, and the viscosity value was measured (measurement temperature: 25 ° C.). The viscosity value was read when the rotation speed was 10 rpm and the measurement time reached 1 minute.

  From the following mathematical formula 1, the upper / lower viscosity ratio R of the solder paste was calculated. The viscosity ratio R is shown in Tables 6 to 9, respectively.

η_up ：測定温度２５℃における、５０ｍＬ試験管内のはんだペースト４０ｍＬのうち３５ｍＬ目盛りの粘度
η_under ：測定温度２５℃における、５０ｍＬ試験管内のはんだペースト４０ｍＬのうち５ｍＬ目盛りの粘度

η _up : Viscosity of 35 mL scale in 40 mL of solder paste in a 50 mL test tube at a measurement temperature of 25 ° C. η _under : Viscosity of 5 mL scale in 40 mL of solder paste in a 50 mL test tube at a measurement temperature of 25 ° C.

  Specifically, those having a viscosity ratio R of 0.95 to 1.05 and an error of less than 5% were regarded as acceptable.

  As shown in Tables 6 to 8, the solder pastes of Examples 1 to 58 were confirmed to have an upper / lower viscosity ratio R in the range of 0.95 to 1.05. That is, it can be said that the solder pastes of Examples 1 to 58 are excellent in that the precipitation of the solder alloy powder is suppressed and there is little variation in viscosity as the solder paste.

  Also, when oleic acid is used as the fatty acid for coating the solder alloy powder, the upper / lower viscosity ratio R in the solder paste tends to be slightly more stable than when stearic acid or N-oleoyl sarcosine is used. there were. This is because the oleic acid is different from stearic acid and N-oleoyl sarcosine, and has an unsaturated bond (cis type) in the carbon chain, thereby further increasing the adhesive strength between the fatty acid and the solder alloy powder, so that the solder alloy The reason is considered that the sedimentation of the powder is suppressed.

  On the other hand, as shown in Table 9, the solder pastes of Comparative Examples 1 to 5 were mixed with the flux without coating the solder alloy powder with fatty acid, so that the viscosity of the lower portion was reduced due to the precipitation of the solder alloy powder in the solder paste. The value increased and the upper / lower viscosity ratio R was less than 0.95.

  From the above, it was confirmed that the solder pastes of Examples 1 to 58 had less viscosity variation because the solder alloy powder was coated with a fatty acid to suppress the precipitation of the solder alloy powder in the solder paste. .

Claims (4)

80% by mass or more and 95% by mass or less of solder alloy powder and 0.2% by mass or more and 1.2% by mass or less of thixotropic agent,
The solder alloy powder is coated with a fatty acid,
The thixotropic agent includes at least a hydrogenated castor oil represented by the following chemical formula (1) and an amide represented by the following chemical formula (2):
The mass ratio of the hydrogenated castor oil and the amide is in the range of 1: 1 to 4: 1,
The viscosity ratio R shown in the following mathematical formula 1 is a solder paste that is 0.95 or more and 1.05 or less.

(However, R ₁ and R ₂ in the formula each independently represent a hydrogen atom or an alkyl group.)

η _up : Viscosity of 35 mL scale in 40 mL of solder paste in a 50 mL test tube at a measurement temperature of 25 ° C. η _under : Viscosity of 5 mL scale in 40 mL of solder paste in a 50 mL test tube at a measurement temperature of 25 ° C.   The fatty acids are caproic acid, enanthic acid, caprylic acid, pelargonic acid, lauric acid, myristic acid, pentadecylic acid, palmitic acid, palmitoleic acid, margaric acid, stearic acid, oleic acid, vaccenic acid, linoleic acid, α-linolenic acid , Γ-linolenic acid, eleostearic acid, arachidic acid, arachidonic acid, behenic acid, lignoceric acid, nervonic acid, serotic acid, montanic acid, mellicic acid, N-lauroyl sarcosine, N-oleoyl sarcosine The solder paste according to claim 1, which is at least one kind.   The solder paste according to claim 1 or 2, wherein the amide is any one selected from the group consisting of amide lauric acid amide, palmitic acid amide, stearic acid amide, and hydroxystearic acid amide.   4. The solder paste according to claim 1, wherein the solder alloy powder is at least two selected from the group of bismuth, zinc, silver, aluminum, lead, and tin. 5.