JP2017185541A - Solder Paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solder paste exhibiting little change in viscosity, reactivity and the like since high thixotropy is maintained and further the reaction of solder alloy powders and an amide as a thixotropic agent is suppressed.SOLUTION: A solder paste contains a solder alloy powder of 80 mass% or more and 95 mass% or less and a thixotropic agent of 0.2 mass% or more and 1.2 mass% or less. The thixotropic agent contains at least hydrogenated castor oil and an amide and a mass ratio of the hydrogenated castor oil and the amide is in the range of 1:1 or more and 4:1 or less.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.

  In addition to solder alloy powder, a resin-based flux using rosin, modified rosin, synthetic resin, etc. as the main component is used as the solder paste used for board mounting, but the main component alone is the thixotropy required for printing. 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.

  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 is not decomposed during heating. It is disclosed that there is an effect of becoming a residue.

JP 2004-25305 A

  However, in patent document 1, the 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.

  Then, this invention is proposed in view of the problem of the said prior art, and it aims at providing the solder paste which improves thixotropy property and is excellent in viscosity stability.

  The solder paste according to one 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. At least a hydrogenated castor oil represented by the following chemical formula (1) and an amide represented by the following chemical formula (2), wherein the mass ratio of the hydrogenated castor oil and the amide is in the range of 1: 1 to 4: 1. It is characterized by being.

（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.)

  In one aspect of the present invention, the amide is preferably amide lauric acid amide, palmitic acid amide, stearic acid amide, or hydroxystearic acid amide.

  In one embodiment of the present invention, the thixotropy index determined by a solder paste evaluation method according to JIS Z 3284 is 0.4 to 0.8 and the viscosity non-recovery rate is 0% to 5%. preferable.

  In one embodiment of the present invention, the change rate α is preferably 0% or more and 10% or less according to the following Equation 1.

η_10rpm-ini：はんだペーストの作製直後の２５℃、１０ｒｐｍにおける粘度
η_10rpm-2W：はんだペーストの作製から冷蔵保管２週間経過後の２５℃、１０ｒｐｍにおける粘度

η _{10 rpm-ini} : Viscosity at 25 ° C. and 10 rpm immediately after preparation of solder paste η _{10 rpm-2 W} : Viscosity at 25 ° C. and 10 rpm after 2 weeks of refrigerated storage from preparation of solder paste

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

  In one aspect of the present invention, the solder alloy powder is preferably coated with a fatty acid.

  In one aspect of the present invention, the fatty acid is preferably stearic acid, oleic acid, linoleic acid, N-lauroyl sarcosine, or N-oleoyl sarcosine.

  According to the present invention, since the reaction between the amide as the thixotropic agent and the solder alloy powder is suppressed while maintaining high thixotropic properties, a solder paste with less change over time in viscosity, reactivity, etc. is provided. can do.

  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 present inventors mainly conducted a study on thixotropy index (TI value), viscosity non-recovery rate, and storage stability of solder paste, focusing on solder paste using amide as a thixotropic agent described in Patent Document 1. Was repeated. As a result, it has been found that the blending ratio of amide, which is a thixotropic agent, is largely related to the change in viscosity of solder paste with time.

  As a result of further research on this point, the present inventors have mixed and blended hydrogenated castor oil and amide at a specific blending ratio as a thixotropic agent, so that the thixotropic index (TI value) of the solder paste and viscosity The knowledge that the above-mentioned problem can be solved by controlling the recovery rate within a specific range was obtained. The present invention has been made based on such knowledge.

  Hereinafter, the present invention will be described separately for each component of the solder paste. The solder paste of the present invention contains a solder flux and a solder alloy powder. The solder flux includes a) a flux main component, b) a thixotropic agent, c) a solvent for dissolving thixotropy, d) an organic solvent, e) including 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 range, it is possible to suppress the amount of flux residue generated without sacrificing the solderability such as the wet spreadability of the solder paste. Become. 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).

（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.)

  The amide used in the present embodiment is not particularly limited, and examples thereof include lauric acid amide, palmitic acid amide, stearic acid amide, and hydroxystearic acid amide.

  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 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 mixed at a mass ratio of the hydrogenated castor oil and the amide of 1: 1. It is important to mix within the range of 4: 1 or less, and the effect of suppressing the reaction between amide and solder alloy powder, which was a problem of the conventional method, and maintaining the storage stability as a solder paste. Play.

  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 amount of the thixotropic agent exceeds 1.2% by mass, the amide becomes excessive, the viscosity stability is lowered, and the fluidity is also lowered. 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 to 246 ° C.) can be preferably used.

  The amount of the solvent for dissolving the thixotropic agent is preferably 10 to 20 times the mass ratio of 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 solder flux according to one embodiment of the present invention can be blended with a component that improves the surface protective agent and the temporary fixing adhesiveness as necessary. Specifically, a silane coupling agent and a surfactant may be used as the surface protective agent, and a phosphoric acid (meth) acrylic monomer and a triazine dithiol monomer may be added as components 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.

  In addition, the compounding 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.

[1-1. Manufacturing method of solder flux]
Next, a method for manufacturing a solder flux according to one embodiment will be described. The solder flux according to one embodiment of the present invention can be obtained by weighing each of the above-described constituent 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 soldering flux contained in the soldering 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 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).

  Furthermore, it is preferable that the solder alloy powder is coated with a fatty acid. That is, a coating layer made of fatty acid is formed on the surface of the solder alloy powder. 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 At least one or more types can be used. By allowing these fatty acid thin films to be directly present on the surface of the solder alloy powder, even when the solder paste is stored for a long time under adverse conditions, wettability and antioxidant effects can be maintained.

  Among these, stearic acid is particularly preferable from the viewpoints of productivity and workability, and by appropriately coating the surface of the solder alloy powder with stearic acid, it is possible to obtain a solder alloy powder in an appropriately agglomerated powder form.

[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.

[3-1. Characteristics of solder paste]
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.

[3-2. Change in viscosity over time]
In the solder paste according to the present embodiment, when the viscosity at 25 ° C. and 10 rpm immediately after the preparation of the solder paste is η _{10 rpm-ini} and the viscosity after two weeks is η _{10 rpm-2w} , The rate of change α is not less than 0% and not more than 10%, preferably less than 5%. Note that the viscosity of the solder paste can be measured by, for example, a spiral viscometer.

η_10rpm-ini：はんだペーストの作製直後の２５℃、１０ｒｐｍにおける粘度
η_10rpm-2W：はんだペーストの作製から冷蔵保管２週間経過後の２５℃、１０ｒｐｍにおける粘度

η _{10 rpm-ini} : Viscosity at 25 ° C. and 10 rpm immediately after preparation of solder paste η _{10 rpm-2 W} : Viscosity at 25 ° C. and 10 rpm after 2 weeks of refrigerated storage from preparation of solder paste

  The solder paste according to the embodiment includes 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. It contains at least hydrogenated castor oil and amide, and the mass ratio of hydrogenated castor oil and amide is in the range of 1: 1 to 4: 1 by mass ratio.

  As described above, since the reaction between the amide as the thixotropic agent and the solder alloy powder is suppressed while maintaining high thixotropy, there is little change with time in viscosity and reactivity. 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 43 and Comparative Examples 1 to 5, as the solder flux, the flux main components described in Table 1, thixotropic agents, organic solvents for thixotropic agents, organic solvents, and carboxylic acid as other constituents Esters, organic solvents and activators were prepared.

  In Examples 1-43 and Comparative Examples 1-5, the mass ratio of each structural component was adjusted as described in Tables 2 to 4 to produce solder flux. The thixotropic agents a to e shown in Tables 2 to 4 represent the active ingredient of amide obtained by subtracting the organic solvent from the thixotropic agents a to e shown in Table 1 as mass%.

  First, in Examples 1 to 18, the solder alloy powders a to c having an average particle diameter of 19 μm to 27 μm shown in Table 1 were added to stearic acid adjusted to 10% by mass in an isopropyl alcohol solution and impregnated for 1 hour. Solder alloy powders a to c coated with fatty acid (stearic acid) were obtained by vacuum drying at 60 ° C. for 6 hours. Further, in Examples 19 to 24, the solder alloy powders a to c having an average particle diameter of 19 to 27 μm shown in Table 1 were used as fatty acids (oleic acid) in the same manner as in Example 1 except that they were treated with oleic acid instead of stearic acid. Thus, solder alloy powders a to c coated with (1) were obtained. Further, in Examples 25 to 30, the solder alloy powders a to c having an average particle diameter of 19 μm to 27 μm shown in Table 1 were used as fatty acids (linoleic acid) in the same manner as in Example 1 except that they were treated with linoleic acid instead of stearic acid. Thus, solder alloy powders a to c coated with (1) were obtained. Further, in Examples 31 to 36, the solder alloy powders a to c having an average particle diameter of 19 μm to 27 μm shown in Table 1 were converted into fatty acids (N) as in Example 1 except that they were treated with N-lauroyl sarcosine instead of stearic acid. Solder alloy powders a to c coated with (lauroyl sarcosine) were obtained. Further, in Examples 37 to 42, the solder alloy powders a to c having an average particle diameter of 19 μm to 27 μm shown in Table 1 were converted into fatty acids (as in Example 1 except that they were treated with N-oleoyl sarcosine instead of stearic acid. Solder alloy powders a to c coated with (N-oleoyl sarcosine) were obtained. In Example 43, the solder alloy powder a having an average particle size of 19 μm to 27 μm shown in Table 1 was not treated with stearic acid. Further, in Comparative Examples 1 to 5, similar to Example 1, solder alloy powder a obtained by coating solder alloy powder a having an average particle diameter of 19 μm to 27 μm shown in Table 1 with fatty acid (stearic acid) was obtained.

  In Examples 1-42 and Comparative Examples 1-5, as described above, 88 mass% of the solder alloy powders a to c coated with fatty acid are added to 12 mass% of the flux for solder, and the revolving mixer (AR-250, manufactured by Shinky Corporation) was mixed for 10 minutes to prepare a solder paste. Moreover, in Example 43, the solder paste was produced similarly to Example 1 except having added 88 mass% of solder alloy powder a which is not coat | covered with the fatty acid.

  The thixotropy index (TI value), the viscosity non-recovery rate R, and the viscosity change rate α of the solder paste thus produced were evaluated as follows. The result of the characteristic evaluation of the solder paste obtained in Examples 1 to 43 and Comparative Examples 1 to 5 is shown in Tables 5 to 7, respectively.

  The thixotropy index (TI value) of the solder paste was measured based on a solder paste (based on JIS Z 3284).

  After leaving the solder paste at a temperature of 25 ° C. for 3 hours, the viscosity value was measured using a spiral viscometer (manufactured by Malcolm, PCU-205) (measurement temperature 25 ° C.). The rotational speed and the measurement time at each rotation were as shown in Table 8. The viscosity value at the time when each measurement time was reached was read, and the thixotropy index (TI value) was calculated from the following formula 2.

η_１：ずり速度１．８Ｓ^−１時の粘度
η_２：ずり速度１８Ｓ^−１時の粘度
Ｄ_１＝１．８Ｓ^−１
Ｄ_２＝１８Ｓ^−１

η ₁ : viscosity at a shear rate of 1.8S ⁻¹ η ₂ : viscosity at a shear rate of 18S ⁻¹ D ₁ = 1.8S ⁻¹
D ₂ = 18S ⁻¹

  Furthermore, the viscosity non-recovery rate R was calculated from the following formula 3.

η_ａ：ずり速度６Ｓ^−１時の初期粘度
η_ｂ：ずり速度６Ｓ^−１時の回復後の粘度

η _a : initial viscosity at a shear rate of 6S ⁻¹ η _b : viscosity after recovery at a shear rate of 6S ⁻¹

The changes in the viscosity of the solder paste over time were determined by using a spiral viscometer of a viscosity η _{10 rpm-ini} at 25 ° C. and 10 rpm immediately after the solder paste was prepared, and a viscosity η _{10 rpm-2w} at 25 ° C. and 10 rpm after storage for 2 weeks. Measurement was performed using (Malcom Co., Ltd., PCU-205), and the change rate α shown in the following formula 1 was obtained and evaluated. Specifically, “Excellent (◎)” indicates that the change rate α is less than 5%, “Good” indicates that the change rate α is 5% or more and 10% or less, and “Poor” indicates that the change rate α exceeds 10%. (×) ”.

η_10rpm-ini：はんだペーストの作製直後の２５℃、１０ｒｐｍにおける粘度
η_10rpm-2W：はんだペーストの作製から冷蔵保管２週間経過後の２５℃、１０ｒｐｍにおける粘度

η _{10 rpm-ini} : Viscosity at 25 ° C. and 10 rpm immediately after preparation of solder paste η _{10 rpm-2W} : Viscosity at 25 ° C. and 10 rpm after 2 weeks of refrigerated storage from preparation of solder paste

  From Tables 2-3 and Tables 5-6, the solder pastes of Examples 1 to 43 all have a thixotropic index TI in the range of 0.4 to 0.8, and the viscosity non-recovery rate R is less than 5%. Furthermore, it was confirmed that the viscosity change rate α was also less than 5%. That is, it can be said that the solder pastes obtained in Examples 1 to 43 are excellent in thixotropy and little change with time.

  On the other hand, the solder paste of Comparative Example 1 has a thixotropic index TI of 0.4 due to the fact that less than 0.2 mass% of two types of thixotropic agents were added from Tables 4 and 7. Never exceeded.

  In addition, the solder pastes of Comparative Examples 2 to 4 have a thixotropic index TI in the range of 0.4 to 0.8 due to the addition of only thixotropic agents c to e from Tables 4 and 7. The viscosity non-recovery rate R could be less than 5%, but the viscosity change rate α exceeded 5%, and it was not possible to suppress the change in the viscosity of the solder paste over time.

  Moreover, the solder paste of Comparative Example 5 has a thixotropic index TI exceeding 0.8 due to the addition of the thixotropic agent exceeding 1.2% by mass from Tables 4 and 7, and addition of amide The rate was excessive, and the viscosity change rate α exceeded 5%.

  From the above, it was confirmed that the solder paste according to one embodiment of the present invention has little change with time such as viscosity and reactivity because the reaction between the amide as the thixotropic agent and the solder alloy powder is suppressed. .

Claims (7)

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 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 solder paste whose mass ratio of the said hydrogenated castor oil and the said amide is in the range of 1: 1 or more and 4: 1 or less.

(However, R ₁ and R ₂ in the formula each independently represent a hydrogen atom or an alkyl group.)   The solder paste according to claim 1, wherein the amide is any one of amide lauric acid amide, palmitic acid amide, stearic acid amide, and hydroxystearic acid amide.   The thixotropic index calculated | required by the solder paste evaluation method based on JISZ3284 is 0.4 or more and 0.8 or less, and a viscosity non-recovery rate is 0% or more and 5% or less, The claim 1 or 2 Solder paste. 4. The solder paste according to claim 1, wherein a change rate α shown in the following formula 1 is 0% or more and 10% or less.

η _{10 rpm-ini} : Viscosity at 25 ° C. and 10 rpm immediately after production of solder paste η _{10 rpm-2 W} : Viscosity at 25 ° C. and 10 rpm after 2 weeks from preparation of solder paste to refrigerated storage   5. The solder paste according to claim 1, wherein the solder alloy powder is at least two selected from the group consisting of bismuth, zinc, silver, aluminum, lead, and tin.   The solder paste according to any one of claims 1 to 5, wherein the solder alloy powder is coated with a fatty acid.   The solder paste according to claim 6, wherein the fatty acid is any one of stearic acid, oleic acid, linoleic acid, N-lauroyl sarcosine, and N-oleoyl sarcosine.