JP2017209690A - Soldering flux, manufacturing method of soldering flux, and solder paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide soldering flux capable of improving thixotropy of solder paste, and maintaining viscosity stability.SOLUTION: Soldering flux contains rosin, an organic solvent and a thixotropic agent. The organic solvent contains at least one kind selected from a group of 2-phenoxy ethanol, diethylene glycol mono-hexyl ether and alkyl cyclohexane, ethanol and isopropyl alcohol, and the thixotropic agent is hydrogenated castor oil.SELECTED DRAWING: None

Description

  The present invention relates to a soldering flux used for soldering, a method for producing the soldering flux, and a solder paste using the soldering flux.

  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.

  Resin-based fluxes mainly composed of rosin, modified rosin, synthetic resin, etc. are mainly used as soldering flux for board mounting. In order to control printability and shape after printing, thixotropic properties are used. Therefore, a thixotropic agent is added. As this thixotropic agent, hydrogenated castor oil is generally used because it is inexpensive (see, for example, Patent Document 1).

JP 2003-225795 A

  However, since hydrogenated castor oil is a powder at room temperature, if the activation at the time of use is insufficient, the expression of sufficient thixotropy may be impaired. Therefore, there is a problem that the application amount is not constant when the solder paste is used, and defects such as short-circuiting due to protrusion of the solder paste, scattering of the flux, and reduction in bonding strength occur. As a result, as an activation treatment of the thixotropic agent, it is important to swell powdered hydrogenated castor oil in an organic solvent for activation.

  Therefore, the present invention has been proposed in view of the above-mentioned problems of the prior art, and provides a solder flux, a solder flux manufacturing method, and a solder paste that improve thixotropy and is excellent in viscosity stability. The purpose is to do.

  That is, the solder flux according to one embodiment of the present invention includes a rosin, an organic solvent, and a thixotropic agent in order to solve the above-described problem, and the organic solvent includes 2-phenoxyethanol, diethylene glycol monohexyl ether, It contains at least one selected from the group of alkylcyclohexane, ethanol, and isopropyl alcohol, and the thixotropic agent is hydrogenated castor oil.

  In one embodiment of the present invention, the rosin is 45% by mass or more and less than 60% by mass, the organic solvent is 30% by mass or more and less than 40% by mass, and the thixotropic agent is 0.2% by mass or more and 5% by mass. It is preferable that it is less than%.

  In one embodiment of the present invention, the 2-phenoxyethanol is 80% by mass or more and less than 95% by mass, the ethanol is 0.2% by mass or more and less than 5% by mass, and the isopropyl alcohol is 0.005% by mass or more. It is preferable that it is less than 0.5 mass%.

  In addition, the method for producing a solder flux according to another aspect of the present invention includes a thixotropic organic solvent containing at least one selected from the group consisting of 2-phenoxyethanol, diethylene glycol monohexyl ether, and alkylcyclohexane, and ethanol and isopropyl alcohol. After the agent is added and the thixotropic agent is dispersed, the thixotropic agent is swelled by standing and heating under predetermined conditions to swell the thixotropic agent, and then the rosin and 2- A mixing step of obtaining a solder flux by further adding and mixing at least one selected from the group of phenoxyethanol, diethylene glycol monohexyl ether, and alkylcyclohexane, and the thixotropic agent is hydrogenated castor oil. It is characterized in.

  In another aspect of the present invention, it is preferable that the predetermined conditions are such that the liquid temperature is controlled to 20 ° C. or higher and lower than 50 ° C., and the stationary heating time is set to 12 hours or longer and shorter than 60 hours.

  Furthermore, the solder paste according to another aspect of the present invention includes 5% by mass or more and 20% by mass or less of the above-described solder flux and 80% by mass or more and 95% by mass or less of the solder alloy powder. To do.

  In another aspect of the present invention, it is preferable that a thixotropy index (TI value) obtained by a solder paste evaluation method based on JIS Z 3284 is 0.5 or more.

  By using the solder flux of the present invention, the thixotropy of the solder paste can be improved and the viscosity stability can be maintained.

It is a flow figure showing the outline of the manufacturing method of the flux for solder concerning the embodiment of the present invention.

  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 have repeated the selection of various organic solvents that are compatible with hydrogenated castor oil added to improve the viscosity characteristics in the solder paste. As a result, by adding hydrogenated castor oil to an organic solvent containing at least one selected from the group of 2-phenoxyethanol, diethylene glycol monohexyl ether, and alkylcyclohexane and ethanol and isopropyl alcohol, the network of hydrogenated castor oil can be effectively obtained. We gained the knowledge that the structure was built, the thixotropy was improved, and at the same time the viscosity stability was excellent. The present invention has been made based on such knowledge.

  Hereinafter, the present invention will be described separately for a solder flux, a manufacturing method thereof, and a solder paste. The solder paste according to the present embodiment contains a soldering flux and solder alloy powder. Furthermore, the solder flux according to the present embodiment includes a) a flux main component, b) a thixotropic agent, c) an organic solvent for thixotropic agent, d) an organic solvent, and e) other additives.

[1. Solder flux]
(1) Outline of soldering flux The soldering flux according to one embodiment of the present invention includes rosins, an organic solvent, and a thixotropic agent flux component. The organic solvent is 2-phenoxyethanol, diethylene glycol monohexyl ether, or alkylcyclohexane. It contains at least one selected from the group, ethanol and isopropyl alcohol, and the thixotropic agent is a solder flux containing hydrogenated castor oil. Furthermore, as 100% by mass of solder flux, rosin is 45% by mass or more and less than 60% by mass, organic solvent is 30% by mass or more and less than 40% by mass, and thixotropic agent is 0.2% by mass or more and 5% by mass. It is preferable that it is less than%. Hereinafter, each component of the solder flux will be described.

(2) Constituent Components of Solder Flux a) Flux Main Component 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 in the range of 45% by mass or more and less than 60% by mass with the solder flux being 100% by mass. When the content of the flux main component is less than 45% 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 60% by mass or more, the flux residue after joining increases, and the base material and the conductor may be corroded.

b) Thixotropic Agent Next, in the solder flux according to one embodiment of the present invention, it is necessary to add a thixotropic agent from the viewpoint of improving thixotropic properties. Here, hydrogenated castor oil is used as the thixotropic agent.

  In this embodiment, by using an organic solvent for thixotropic agent and hydrogenated castor oil, which will be described later, this hydrogenated castor oil is swollen to develop a network structure due to hydrogen bonding, and the structural viscosity increases, so that the thixotropic property is increased. Will be expressed. In addition, when an amide having a long chain structure rather than hydrogenated castor oil is used as a thixotropic agent, thixotropic properties are improved, but the viscosity is reduced due to the entanglement of long chain portions by amides and the hydrogen bonding force between amide groups. Too high. For this reason, solder flux using amide is not suitable as a raw material for solder paste.

  Therefore, this embodiment is characterized in that the thixotropic agent is hydrogenated castor oil. In addition, it is preferable that content of a thixotropic agent shall be 0.2 to 5 mass% as solder flux 100 mass%.

c) Organic solvent for thixotropic agent Next, in the solder flux according to one embodiment of the present invention, it is necessary to add an organic solvent from the viewpoint of dissolving the powdered thixotropic agent. This organic solvent for thixotropic agents is contained in the organic solvent described later.

d) Organic Solvent The solder flux according to one embodiment of the present invention includes an organic solvent in order to facilitate mixing of the solder alloy powder and the flux and making them into a paste. As this organic solvent, one having a boiling point of 200 ° C. to 300 ° C. is used 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 preferable to use those having a boiling point of 220 ° C to 300 ° C, and it is more preferable to use those having a boiling point of 230 ° C to 300 ° C.

  As a result of examining various organic solvents, in this embodiment, the organic solvent is selected from the group of 2-phenoxyethanol (boiling point: 244 to 246 ° C.), diethylene glycol monohexyl ether (boiling point: 261 ° C. to 265 ° C.), and alkylcyclohexane. It is essential to contain at least one selected from the group consisting of ethanol and isopropyl alcohol. Thereby, hydrogen bonding occurs between the hydroxyl group (OH) of hydrogenated castor oil and the hydroxyl group (OH) of ethanol and isopropyl alcohol by swelling the hydrogenated castor oil. As a result, it effectively builds a network structure of hydrogenated castor oil, improves thixotropy and at the same time has excellent viscosity stability.

  In addition, it is preferable that content of the organic solvent contained in the solder flux which concerns on this embodiment shall be 30 to 40 mass% as solder flux 100 mass%. When the content of the organic solvent is less than 30% by mass, the solder paste containing the solder flux does not have an appropriate flux viscosity. On the other hand, when the content of the organic solvent is 40% by mass or more, sagging or the like is likely to occur when the flux is applied.

  In addition, the blending amount of the organic solvent contained in the solder flux according to the present embodiment is 80% by mass of at least one selected from the group of 2-phenoxyethanol, diethylene glycol monohexyl ether, and alkylcyclohexane as 100% by mass of the organic solvent. It is preferably 95% by mass or less, ethanol is 0.2% by mass or more and less than 5% by mass, and isopropyl alcohol is preferably 0.005% by mass or more and less than 0.5% by mass. As a result, moderate hydrogen bonding occurs between the hydroxyl group (OH) of hydrogenated castor oil, which is a thixotropic agent, and the hydroxyl group (OH) of ethanol or isopropyl alcohol, thereby improving thixotropic properties more efficiently. At the same time, viscosity stability can be improved.

  Furthermore, the organic solvent contained in the solder flux according to this embodiment is at least one selected from the group consisting of 2-phenoxyethanol, diethylene glycol monohexyl ether, and alkylcyclohexane, 2-ethyl-1,3-hexanediol, and ethanol. Isopropyl alcohol is preferred. By including 2-ethyl-1,3-hexanediol in this organic solvent, the dispersibility of the solder flux can be improved. In addition, the compounding quantity of this organic solvent is 45 mass% or more and less than 60 mass% at least 1 sort (s) chosen from the group of 2-phenoxyethanol, diethylene glycol monohexyl ether, and alkylcyclohexane as 100 mass% of organic solvents, Ethyl-1,3-hexanediol is 35 mass% or more and less than 50 mass%, ethanol ethanol is 0.2 mass% or more and less than 5 mass%, and isopropyl alcohol is 0.005 mass% or more and 0.5 mass%. It is preferable that it is less than.

e) Other Additives In addition to the above-described components, the solder flux according to one embodiment of the present invention may contain a surface protective agent or a component that improves the temporary fixing adhesiveness, if necessary. Specifically, silane coupling agents and surfactants can be added as surface protecting agents, and phosphoric acid-based (meth) acrylic monomers and triazine dithiol-based monomers can be added as components for improving temporary adhesion. 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 total content of these additives is preferably 10% by mass or less, more preferably 1% by mass or more and 7% by mass or less, based on 100% by mass of solder flux. When the content of these additives is within the above range, characteristics such as temporary fixing adhesiveness and crack resistance can be improved while securing the characteristics of the solder flux.

  When the solder flux according to one embodiment of the present invention is used as a solder paste because hydrogen bonding occurs between the hydroxyl group (OH) of hydrogenated castor oil and the hydroxyl group (OH) of ethanol and isopropyl alcohol, The thixotropy of the solder paste can be improved and the viscosity stability can be maintained.

[2. Manufacturing method of solder flux]
FIG. 1 is a flowchart showing an outline of a method for producing a soldering flux according to one embodiment. As shown in FIG. 1, the solder flux manufacturing method according to the present embodiment includes a swelling step S1 for swelling the thixotropic agent and a mixing step S2 for mixing each component to obtain a solder flux. . Hereinafter, each of the swelling step S1 and the mixing step S2 will be described.

(1) Swelling step In the swelling step S1, the thixotropic agent is swollen by adding a thixotropic agent to an organic solvent and dispersing the thixotropic agent, followed by standing heating under predetermined conditions. Specifically, hydrogenated castor oil as a thixotropic agent is added to an organic solvent at room temperature (5 ° C. to 30 ° C.) and sufficiently dispersed. This stirring time is appropriately adjusted depending on the amount to be dispersed. Here, as the organic solvent for thixotropic agent, a thixotropic agent is used in a container containing at least one selected from the group of 2-phenoxyethanol, diethylene glycol monohexyl ether, and alkylcyclohexane and ethanol and isopropyl alcohol.

  As predetermined conditions, it is preferable to control the liquid temperature in the container to 20 ° C. or more and less than 50 ° C., and to set the stationary heating time to 12 hours or more and less than 60 hours. When the liquid temperature in the container is lower than 20 ° C. and the stationary heating time is shorter than 12 hours, the thixotropic agent cannot be swollen, and thus thixotropic properties may not be improved. On the other hand, when the liquid temperature in the container is 50 ° C. or higher and the stationary heating time is 60 hours or longer, the decomposition of the thixotropic agent proceeds and a solder paste having a desired thixotropic property may not be produced. There is.

  In order to swell the thixotropic agent, the organic solvent for thixotropic agent used in the swelling step S <b> 1 preferably adds 10 to 30 mass% of the thixotropic agent to the organic solvent, and adds 15 to 25 mass%. Is particularly preferred. This causes the thixotropic agent to swell and hydrogen bonding occurs between the thixotropic hydroxyl group (OH) and the hydroxyl group (OH) of ethanol and isopropyl alcohol, improving the thixotropic property of the solder paste and stabilizing the viscosity. Sexuality can also be enhanced.

  The amount of the organic solvent used in the swelling step S1 is such that at least one selected from the group of 2-phenoxyethanol, diethylene glycol monohexyl ether, and alkylcyclohexane is 70% by mass or more and less than 90% by mass, as 100% by mass of the organic solvent to be added. Yes, ethanol is preferably 5% by mass or more and less than 20% by mass, and isopropyl alcohol is preferably 0.02% by mass or more and less than 0.5% by mass, from the group of 2-phenoxyethanol, diethylene glycol monohexyl ether, and alkylcyclohexane. It is more preferable that at least one selected is 80% by mass or more and less than 85% by mass, ethanol is 10% by mass or more and less than 15% by mass, and isopropyl alcohol is 0.05% by mass or more and less than 0.2% by mass. preferable. Thereby, in order to swell, a hydrogen bond appears between the hydroxyl group (OH) of the thixotropic agent and the hydroxyl group (OH) of ethanol and isopropyl alcohol. As a result, the thixotropy of the solder paste can be improved.

(2) Mixing step In the mixing step S2, the thixotropic agent is swollen in an organic solvent in the swelling step S1, and then at least one selected from the group of rosins and 2-phenoxyethanol, diethylene glycol monohexyl ether, and alkylcyclohexane is further added. By adding and mixing, a soldering flux is obtained.

  The solder flux manufacturing method according to the present embodiment is obtained by weighing each constituent component (rosin, organic solvent, thixotropic agent, and other additives) so as to have the above-described content and mixing them uniformly. Can be obtained. The mixing means is not particularly limited, but is preferably mixed 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.

  The solder flux produced by the method for producing a solder flux according to the present embodiment has a hydrogen bond between the hydroxyl group (OH) of hydrogenated castor oil and the hydroxyl group (OH) of ethanol and isopropyl alcohol. When used as a solder paste, the thixotropy of the solder paste can be improved and the viscosity stability can be maintained.

[3. Solder paste]
(1) Solder alloy powder The solder alloy powder mixed with the solder flux according to one embodiment of the present invention is not particularly limited, but bismuth (Bi), zinc (Zn), silver (Ag), aluminum ( An alloy made of an alloy containing at least two selected from the group consisting of Al), lead (Pb), and tin (Sn) can be suitably used. For example, Pb-Sn alloy solder, Pb-free solder such as Bi-Zn alloy alloy solder, Sn-Ag alloy solder, etc., or those added with Cu, Bi, In, Al, etc. to these solder alloys are used. can do.

  The average particle size of the solder alloy powder is preferably in the range of 1 μm to 100 μm, more preferably less than 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, when the thickness exceeds 100 μm, a new conductive layer containing a resin is formed between the materials to be bonded at the time of bonding, so that the conductivity may be lowered. In the present invention, 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).

(2) Mixing ratio of solder flux and solder alloy powder The solder paste according to one embodiment of the present invention has a solder flux of 5 to 20% by mass, preferably 10 to 15% by mass, and 80% by mass. % To 95% by mass, preferably 85% to 90% by mass of solder alloy powder, and the solder flux according to this embodiment described above is used as the solder flux. Features. By controlling the mixing ratio of the soldering flux and the solder alloy powder in 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 adopted. For example, the mixing can be performed by a self-revolving mixer, a homogenizer, a Hayshell mixer, or the like.

(3) Characteristics Since the solder paste according to another embodiment of the present embodiment uses the solder flux described above, the viscosity characteristics are stable and the thixotropy is excellent.

a) Thixotropic Index The solder paste according to one embodiment exhibits stable thixotropy, and the thixotropic index (hereinafter also referred to as “TI value”) is preferably 0.5 or more, and more preferably 0.55 or more. . Here, the TI value can be determined by “solder paste part 3 printability viscosity characteristics and adhesion test (JISZ 3284-3)”. Specifically, by measuring the solder paste using a spiral viscometer (manufactured by Malcolm, PCU-205), the TI value can be obtained by the following formula 1.

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（３ｒｐｍ）
Ｄ_２＝１８Ｓ^−１（３ｒｐｍ）

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 (3 rpm)
D ₂ = 18S ⁻¹ (3 rpm)

b) Change in viscosity over time In the solder paste according to one embodiment of the present invention, 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 change rate α shown in the following formula 2 is 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４℃〜７℃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 storage at 4 ° C. to 7 ° C. after the solder paste is prepared

  Thus, the thixotropy of the solder paste can be improved and the viscosity stability can be maintained. 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 1-6 and Comparative Examples 1-2, in order to compare the thixotropic agent which is the organic solvent and activator which are described in Table 1 as a flux for solder, the composition ratio of each structural component was fixed. A solder flux was prepared with the composition shown in Table 2. The thixotropic agent d shown in Table 2 represents the active ingredient of amide obtained by subtracting the organic solvent from the thixotropic agent d shown in Table 1 as mass%. The subtracted organic solvent is shown in Table 2. It represents as an amide content of the organic solvent using thixotropic agent shown.

  First, in Examples 1 to 6 and Comparative Examples 1 and 2, the thixotropic agent and the organic solvent for thixotropic agent shown in Table 2 were added to the reaction vessel, respectively. Next, the powdered hydrogenated castor oil, which is a thixotropic agent in an organic solvent, was sufficiently dispersed by stirring, and then was heated by standing for a predetermined time according to the thixotropic agent swelling conditions shown in Table 2.

  Next, the main flux component, organic solvent, and other additives shown in Table 2 were added to the reaction vessel, and mixed for 10 minutes using a self-revolving mixer (AR-250, manufactured by Shinky Corporation). Each flux was produced.

  90% by mass of a solder alloy powder (Mitsui Metal Industry Co., Ltd.) made of Sn—Ag—Cu based alloy having an average particle size of 19 μm to 27 μm is added to 10% by mass of these solder fluxes. -250, manufactured by Shinky Corporation) for 10 minutes to produce a solder paste.

  The thixotropy index (TI value) and the viscosity change rate α of the solder paste thus prepared were evaluated as follows. The results are shown in Table 3.

The change over time of the solder paste was measured using a spiral viscometer (Malcom Co., Ltd., PCU-205) after measuring the viscosity η ₁ immediately after production of the solder paste and the viscosity η ₂ after storage for 2 weeks, The thixotropy index (TI value) shown in the following formula 1 was calculated.

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（３ｒｐｍ）
Ｄ_２＝１８Ｓ^−１（３ｒｐｍ）

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 (3 rpm)
D ₂ = 18S ⁻¹ (3 rpm)

The changes in the viscosity of the solder paste over time are: the viscosity η _{10 rpm-ini} at 25 ° C. and 10 rpm immediately after the preparation of the solder paste, and the viscosity η _{10 rpm-2w} at 25 ° C. and 10 rpm after refrigerated storage for 2 weeks. Measurement was performed using a meter (Malcom Co., Ltd., PCU-205), and the change rate α shown in Equation 2 below was evaluated.

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４℃〜７℃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 storage at 4 ° C. to 7 ° C. after preparation of solder paste

  From Table 3, it was confirmed that all of Examples 1-6 had good TI values of 0.5 or more. This is because by using a solvent having a hydroxyl group (OH) as the organic solvent used, there is a hydrogen bond between the hydroxyl group (OH) of this organic solvent and the hydroxyl group (OH) of hydrogenated castor oil which is a thixotropic agent. As a result, it is considered that the network structure is efficiently constructed and contributes to the expression of thixotropy. Moreover, since it was a stable network structure, the viscosity change rate of the obtained solder paste also became small, and it turned out that the stable viscosity is maintained.

  On the other hand, in Comparative Example 1, since the hydrogenated castor oil, which is a thixotropic agent, was tried to swell without using ethanol and isopropyl alcohol, the thixotropic index (TI value) of the solder paste was lower than 0.5. In Comparative Example 2, the viscosity change rate α of the solder paste was higher than 5.0% because amide having a longer alkyl group than hydrogenated castor oil was used instead of hydrogenated castor oil.

  Therefore, in the solder flux according to this embodiment, hydrogenated castor oil is used as the thixotropic agent, and at least one selected from the group of 2-phenoxyethanol, diethylene glycol monohexyl ether, and alkylcyclohexane as the organic solvent and ethanol. It was confirmed that it was essential to use isopropyl alcohol.

  From the above, it was confirmed that the solder paste using the solder flux according to the present embodiment can improve the thixotropy of the solder paste and maintain the viscosity stability.

Claims (7)

Including rosins, organic solvents and thixotropic agents;
The organic solvent includes at least one selected from the group of 2-phenoxyethanol, diethylene glycol monohexyl ether, and alkylcyclohexane, ethanol, and isopropyl alcohol.
The thixotropic agent is hydrogenated castor oil, a soldering flux.   The rosin is 45% by mass or more and less than 60% by mass, the organic solvent is 30% by mass or more and less than 40% by mass, and the thixotropic agent is 0.2% by mass or more and less than 5% by mass. 1. The soldering flux according to 1.   In the organic solvent, the 2-phenoxyethanol is 80% by mass or more and less than 95% by mass, the ethanol is 0.2% by mass or more and less than 5% by mass, and the isopropyl alcohol is 0.005% by mass or more and 0.0. The soldering flux according to claim 2, wherein the soldering flux is less than 5% by mass. A thixotropic agent is added to an organic solvent containing at least one selected from the group of 2-phenoxyethanol, diethylene glycol monohexyl ether, and alkylcyclohexane, and ethanol and isopropyl alcohol, and the thixotropic agent is dispersed under predetermined conditions. A swelling step to swell the thixotropic agent by stationary heating;
A mixing step of obtaining a soldering flux by further adding and mixing at least one selected from the group of rosins and 2-phenoxyethanol, diethylene glycol monohexyl ether, and alkylcyclohexane after swelling the thixotropic agent; Have
The said thixotropic agent is a hydrogenated castor oil, The manufacturing method of the flux for solders.   5. The method for producing a soldering flux according to claim 4, wherein the predetermined condition is that the liquid temperature is controlled to 20 ° C. or more and less than 50 ° C., and the stationary heating time is set to 12 hours or more and less than 60 hours. 5% by mass or more and 20% by mass or less of the solder flux according to any one of claims 1 to 3,
A solder paste comprising 80% by mass or more and 95% by mass or less of solder alloy powder.   The solder paste according to claim 6, wherein a thixotropy index (TI value) obtained by a solder paste evaluation method based on JIS Z 3284 is 0.5 or more.

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