TWI668065B - Solder powder, method for producing same, and method for preparing solder paste using the same - Google Patents

Abstract

The subject of the present invention is to produce a solder powder in which copper does not diffuse into tin during storage, and the powders do not adhere to each other, and the thickness of the diffusion preventing layer and the tin layer composed of nickel are small.

The solution is to add a metal salt of nickel mixed to the dispersion of the copper powder to obtain a first solution in which the metal salt is dissolved and copper powder is dispersed. After the pH of the solution was adjusted, a first reducing agent was added and the nickel ions were reduced to obtain a dispersion in which the precipitated nickel-coated copper powder was dispersed. This liquid was subjected to solid-liquid separation, and the solid component was dried to obtain a metal powder obtained by coating a copper core with a diffusion preventing layer made of nickel. A metal salt containing tin is added to the dispersion of the metal powder to obtain a second solution in which the metal salt is dissolved and the metal powder is dispersed. After the pH of the solution is adjusted, a second reducing agent is added and the tin ions are reduced to obtain a dispersion in which the precipitated tin is coated with the metal powder and dispersed. This liquid was subjected to solid-liquid separation, and the solid component was dried to obtain a solder powder in which the metal powder was coated with a tin layer.

Description

Solder powder, method for producing same, and method for preparing solder paste using the same

The present invention relates to a solder powder comprising a center core for mounting an electronic component or the like, a solder layer comprising a tin layer, a method for producing the same, and a method for preparing a solder paste using the powder.

In the past, a solder powder having a center core of copper and a coating layer made of tin and having an average particle diameter of 5 μm or less has been disclosed (for example, see Patent Document 1). This solder powder is lead-free and environmentally friendly, and is fine, so that it is excellent in printability. Further, since the metal element constituting the central core is made of copper, not only the coating layer but also the central core is melted to form a Cu-Sn alloy during reflow, and therefore the mechanical strength of the solder is enhanced by the formed Cu-Sn alloy.

However, in the case where the center core described in Patent Document 1 is made of copper and the coating layer is made of tin, the diffusion coefficient of copper to tin is larger than the diffusion coefficient of tin to copper when the solder powder is produced for a long period of time. The copper having the central core diffuses into the coating layer, and an intermetallic compound layer having a high melting point such as Cu ₃ Sn or Cu ₆ Sn ₅ or a copper-coated layer of the central core is formed between the central core and the coating layer. In the middle, the entire coating layer forms an intermetallic compound of copper and tin.

In order to solve this problem, there has been disclosed a solder layer having a core layer made of Cu balls and a tin-based solder layer covering the core layer, and a diffusion preventing layer made of Ni is formed between the Cu balls and the solder layer. Cu nucleus (see, for example, Patent Document 2). This diffusion preventing layer is for preventing diffusion of Cu constituting the Cu ball to the solder layer. In Patent Document 2, as a method of forming a solder layer on a Cu ball, a plating method such as a known barrel plating or a pump connected to a plating bath causes a high-speed turbulent flow of a plating solution in a plating tank. A method of forming a plating film on a Cu ball by a turbulent flow of a plating solution, and providing a vibration plate at a plating tank to vibrate at a predetermined frequency, thereby causing the plating solution to be stirred at a high speed by a high-speed turbulent flow, by a plating solution A method of forming a plating film on a Cu ball by turbulent flow, etc., in which it is disclosed that a Cu layer is coated with a Ni plating layer to form a solder layer.

Further, Patent Document 2 discloses that the solder layer contains 40% or more of Sn and contains 20 ppm or more of 220 ppm or less of Ge, and a Cu plating layer having a diameter of 100 μm is coated with a film thickness of 1 μm (one side) of Ni plating layer to form a film thickness. (Single side) 18 μm Sn-Ag-Cu-Ge solder plating film, showing Cu nuclear spheres having a diameter of about 140 μm.

[Previous Technical Literature] [Patent Document]

[Patent Document 1] Japanese Laid-Open Patent Publication No. 2008-138266 (Request Item 1, Paragraph [0005], Paragraph [0014])

[Patent Document 2] Japanese Patent No. 5652560 (Request Item 1, Paragraph [0033], Paragraph [0035], Paragraph [0067], Paragraph [0068]

However, as described in Patent Document 2, in the method of coating a Cu ball by a diffusion preventing layer made of Ni by nickel plating by a barrel plating method or the like, the balls are easily adhered to each other due to the close contact of the balls, and plating is performed. The film thickness of the applied film is liable to cause unevenness. In addition, when the radius of the Cu ball (copper core) is set to 1, the thickness of the diffusion preventing layer made of Ni of the Cu core ball shown in Patent Document 2 is 0.02, so that it is difficult to prevent the diffusion of Cu into tin. .

A first object of the present invention is to provide a solder powder which is produced by dispersing copper which does not penetrate into the tin layer during the storage of the powder, does not adhere to each other, and has a small thickness unevenness of the diffusion preventing layer made of nickel. The method and the welding paste using the powder. Further, a second object of the present invention is to provide a reflow process in which solder powder which has been stored for a long period of time is reflowed at a temperature at which solder powder which is short before storage or during storage is melted, and which does not cause insufficient bonding due to insufficient solder melting. A solder powder, a method for producing the same, and a method for preparing a solder paste using the powder. Further, a third object of the present invention is to provide a solder powder which is less likely to cause remelting and a decrease in joint strength after reflow, and is particularly suitable for mounting an electronic component or the like which is required to be exposed to a high temperature environment, a method for producing the same, and a method for producing the same. A method of preparing a paste for soldering of powder.

According to a first aspect of the invention, there is provided a method for producing a solder powder comprising: a step S1 of preparing a first dispersion liquid in which copper powder is dispersed; and a metal salt of nickel added to the copper powder. a first dispersion liquid to prepare a first dissolving solution in which a metal salt of nickel is dissolved and in which copper powder is dispersed; a step S2 of adjusting the pH of the first dissolving liquid; and a step S3 of adjusting the pH of the first dissolving liquid; and adding and mixing the pH-adjusted first dissolving liquid In the first reducing agent, the nickel ion is reduced to prepare a second dispersion liquid in which the precipitated nickel is coated with the copper powder, and the second dispersion liquid is subjected to solid-liquid separation, and the solid component separated by solid-liquid separation is dried. Step S5 of preparing a metal powder obtained by coating a copper core with a diffusion preventing layer made of nickel; preparing a third dispersion liquid in which the metal powder is dispersed; and adding a metal salt of tin to the third dispersion of the metal powder a step S7 of preparing a second metal solution in which a metal salt of tin is dispersed and dispersing a metal powder; a step S8 of adjusting the pH of the second solution; and a second addition of the pH-adjusted second solution; Reducing agent to reduce tin ions and prepare for precipitation Step S9 of dispersing the fourth dispersion liquid in which tin is coated with the metal powder; and solid-liquid separation of the fourth dispersion liquid, and drying the solid component separated by solid-liquid separation to prepare a solder powder in which the metal powder is coated with a tin layer Step S10.

According to the second aspect of the present invention, as shown in FIG. 2, the metal powder 13 in which the diffusion preventing layer 12 made of nickel is coated with the copper core 11 is coated with the solder powder 10 of the tin layer 14. It is characterized in that the solder powder has an average particle diameter of 1 μm or more and 30 μm or less, relative to the front. The total amount of the solder powder is 100% by mass, and the content ratio of copper is 2% by mass or more and 70% by mass or less. When the radius of the copper core is 1, the thickness of the diffusion preventing layer made of nickel is 0.04 or more and 0.51 or less. The ratio.

According to a third aspect of the present invention, there is provided a method of preparing a solder paste by mixing a solder powder prepared by the method according to the first aspect or a solder powder of the second aspect with a soldering flux.

A fourth aspect of the present invention is a method of mounting an electronic component using a solder paste prepared by the method of the third aspect.

In the method for producing a solder powder according to the first aspect of the present invention, the diffusion preventing layer made of nickel is formed on the surface of the copper core by reducing nickel ions in the first solution in which the copper powder is dispersed, and the tin layer is formed. A solder powder is produced by forming a surface of a metal powder formed by coating a copper core with a diffusion preventing layer made of nickel. As a result, unlike the method such as the barrel plating method described in Patent Document 2, the layer structure of the solder powder is such that the unevenness of each powder is small, the powders do not adhere to each other, and the diffusion preventing layer made of nickel is used. The thickness is not uniform.

As shown in Fig. 2, in the solder powder 10 according to the second aspect of the present invention, the metal powder 13 obtained by coating the copper core 11 with the diffusion preventing layer 12 made of nickel is covered with the tin layer 14, and the radius of the copper core is set to 1 The thickness of the diffusion preventing layer 12 made of nickel is a ratio of 0.04 or more and 0.51 or less. That is, in the solder powder 10 of the present invention, since the diffusion preventing layer 12 made of nickel having a predetermined thickness is interposed between the copper core 11 and the tin layer 14, the conventional copper core and the coating are not greatly changed. The soldering property of the solder powder formed of the tin layer not only prevents the diffusion of tin from the central core to the tin layer, but also prevents the tin of the tin layer from diffusing to the central core. As a result, it is possible to perform reflow soldering at a temperature at which the solder powder which has been stored for a long period of time is melted before the storage or the storage period is short, and it is excellent in the joint failure caused by insufficient solder melting. Further, after reflow, Cu ₃ Sn, Cu ₆ Sn ₅ , Ni ₃ Sn, Ni ₃ Sn ₂ , Ni ₃ Sn ₄ , NiSn ₃ , (Ni, Cu) ₃ Sn ₄ , (Ni, Cu) are formed. ₆ Intermetallic compound such as Sn ₅ and a bonding layer made of copper. Therefore, after reflow, remelting and reduction of joint strength are less likely to occur, and it is particularly suitable for mounting on electronic parts that are exposed to a high temperature environment.

The solder paste prepared by the method of the third aspect of the present invention is obtained by using the above-described solder powder of the present invention. Therefore, this solder paste is rapidly melted at the time of reflow, and is excellent in meltability.

In the method of mounting an electronic component according to the fourth aspect of the present invention, since the solder paste of the present invention is used, the solder paste is rapidly melted during reflow, and the meltability is excellent, so that the electronic component can be easily mounted with high precision. The joint body on which the electronic component is mounted is not only coated but also the central core is melted to form a Cu-Sn alloy or a Sn-Ni-Cu alloy during reflow, and therefore, a Cu-Sn alloy or Sn- formed by the Cu-Sn alloy or Sn- The Ni-Cu alloy is less likely to cause remelting and a decrease in joint strength even after exposure to a high temperature environment after solder bonding.

10‧‧‧ solder powder

11‧‧‧ copper core

12‧‧‧Diffusion prevention layer composed of nickel

13‧‧‧Metal powder

14‧‧‧ tin layer

Fig. 1 is a view showing a manufacturing procedure of the solder powder of the embodiment.

Fig. 2 is a cross-sectional structural view of a solder powder in which a metal powder obtained by coating a copper core with a diffusion preventing layer made of nickel is coated with a tin layer.

[Formation of the Invention]

The form in which the present invention is carried out will be described below based on the drawings.

[Method of Manufacturing Solder Powder]

Copper powder is used to form the central core. First, as shown in steps S1 and S2 of Fig. 1, a copper powder and a dispersing agent are added to a solvent to prepare a first dispersion liquid in which copper powder is dispersed, and a nickel-containing compound is added and mixed to disperse the copper powder. The first solution in which the nickel-containing compound is dissolved is prepared. The copper powder preferably has an average particle diameter of 0.1 μm or more and 27 μm or less. If the lower limit is not reached, the average particle diameter of the solder powder tends to be less than 1 μm, and the specific surface area is increased, and the meltability of the solder is lowered by the influence of the surface oxide layer of the powder. Moreover, if it exceeds the upper limit, the average particle diameter of the solder powder easily exceeds 30 μm. When the thickness exceeds 30 μm, the coplanarity of the bumps is lowered when the bumps are formed, and coating unevenness occurs when the surface of the pattern is coated with solder, and the entire surface of the pattern cannot be uniformly coated. Shortcomings. The average particle diameter of the copper powder is more preferably 2 to 20 μm. This copper powder can be borrowed It is obtained by a chemical method of a reduction reaction, and can also be obtained by a physical method such as an atomization method. In addition, in the present specification, the average particle diameter of the powder refers to a particle size distribution measuring apparatus (Radio Diffraction/Scattering Particle Size Distribution Measuring Apparatus LA-950, manufactured by Horiba, Ltd.) using a laser diffraction scattering method. The measured volume cumulative median diameter (Median diameter, D50).

The ratio of the copper powder and the nickel compound in the first dissolution liquid is adjusted so that the content ratio of each metal element is a range described later after the production of the solder powder. Examples of the nickel compound include nickel (II) chloride, nickel (II) sulfate, and nickel (II) nitrate. Examples of the solvent include water, alcohol, ether, ketone, ester, and the like. Further, examples of the dispersing agent include cellulose, vinyl, and polyhydric alcohol, and gelatin, casein, and the like can be used.

The pH adjustment of the prepared first solution is performed as shown in step S3 of Fig. 1 . The pH is preferably measured in the range of 0.1 to 2.0 by re-dissolving the generated solder powder. Further, after dissolving the above nickel compound in a solvent and dissolving the nickel, a dislocation agent may be added to the mixture, and then a dispersing agent may be added. By adding a miscending agent, even if the pH is on the alkali side, nickel ions are not precipitated, and synthesis can be carried out over a wide range. Examples of the blocking agent include succinic acid, tartaric acid, glycolic acid, lactic acid, phthalic acid, malic acid, citric acid, oxalic acid, ethylenediaminetetraacetic acid, iminodiacetic acid, nitrogen triacetic acid or a salt thereof. .

Next, an aqueous solution in which a reducing agent is dissolved is prepared, and the pH of the aqueous solution is adjusted to the same level as that of the first solution. Examples of the reducing agent include a phosphoric acid compound such as sodium phosphinate, a borohydride such as sodium tetrahydroborate or dimethylamine borane, a nitrogen compound such as hydrazine, a trivalent titanium ion or a divalent compound. Metal ions such as chromium ions.

Next, as shown in step S4 of Fig. 1, by adding a reducing agent aqueous solution to the first solution containing nickel ions, the nickel ions in the first solution are reduced to prepare nickel precipitated copper. The second dispersion liquid dispersed in powder. As a method of mixing the first solution and the reducing agent aqueous solution, a method of dropping a reducing agent aqueous solution into a solution in a container at a predetermined addition rate and stirring it with a stirrer or the like; and using a reaction tube having a predetermined diameter, A method of injecting two liquids at a predetermined flow rate in the reaction tube, and mixing them.

Next, as shown in step S5 of Fig. 1, the second dispersion is subjected to solid-liquid separation by decantation or the like, and adjusted to 0.5 to 2 aqueous hydrochloric acid, nitric acid aqueous solution, sulfuric acid aqueous solution, or methanol by water or pH. The solid components recovered by washing, ethanol, acetone, etc. After washing, the solid-liquid separation was again performed and the solid content was recovered. It is preferred to repeat the washing to the solid-liquid separation step 2 to 5 times. By vacuum drying the recovered solid component, a Cu core composed of a central nucleus (copper core) made of copper and a nickel layer (a diffusion preventing layer made of nickel) covering the central nucleus is formed with a Ni layer. Metal powder.

Next, as shown in steps S6 and S7 of Fig. 1, the metal powder and the dispersing agent are added to the solvent to prepare a third dispersion in which the metal powder having the Cu core and the Ni layer is dispersed, and the mixed tin is added thereto. The compound disperses the metal powder in which the Cu core is attached with the Ni layer, and prepares the second solution in which the tin-containing compound is dissolved. Examples of the tin compound include tin (II) chloride, tin (II) sulfate, tin (II) acetate, and tin (II) oxalate. The addition ratio of the tin-containing compound is adjusted so that the content ratio of each metal element after the production of the solder powder is a range described later. As the dispersion medium and the solvent, the same dispersion medium and solvent as described above can be used.

The pH adjustment of the prepared second solution is performed as shown in step S8 of Fig. 1 . The pH is preferably measured in the range of 0.1 to 2.0 by re-dissolving the generated solder powder. Further, after adding the above tin compound to a solvent to dissolve it, a dislocation agent may be added to align the tin, and then a dispersant may be added. By adding a miscending agent, even if the pH is on the alkali side, tin ions are not precipitated, and synthesis can be carried out over a wide range. As the blocking agent, the same complexing agent as described above can be used.

Next, as shown in step S9 of Fig. 1, a reducing agent aqueous solution in which the same reducing agent as the above reducing agent is dissolved is added to the second solution containing the tin ions in the same manner as the above-described method. The tin ion in the second solution is reduced, and the precipitated tin is coated with a fourth dispersion in which the Cu core is coated with the metal powder of the Ni layer and dispersed.

Finally, as shown in step S10 of Fig. 1, the fourth dispersion liquid is washed in the same manner as the above-described method, and subjected to solid-liquid separation to recover a solid component. It is preferred to repeat the washing to the solid-liquid separation step 2 to 5 times. A solder powder in which a metal powder having a Cu layer and a Ni layer is coated with a tin layer is formed by vacuum drying the recovered solid component.

[solder powder]

As shown in Fig. 2, the solder powder 10 produced by the above method is coated with a tin layer 14 by a metal powder 13 in which a diffusion preventing layer 12 made of nickel is coated with a copper core 11 of a center core. Since the solder powder is formed such that the center core made of copper is coated with a coating layer of a tin layer having a low melting point, the meltability at the time of reflow is excellent. Further, since copper and tin are contained in one metal particle constituting the powder, melting unevenness or composition variation at the time of reflow is less likely to occur, and high joint strength can be obtained. Further, since the solder powder has a diffusion preventing layer made of nickel between the center core and the coating layer, diffusion of copper into tin and diffusion of tin into copper can be prevented. Further, after reflow, Cu ₃ Sn, Cu ₆ Sn ₅ , Ni ₃ Sn, Ni ₃ Sn ₂ , Ni ₃ Sn ₄ , NiSn ₃ , (Ni, Cu) ₃ Sn ₄ , (Ni, Cu) are formed. ) ₆ Intermetallic compound with a high melting point such as Sn ₅ and a bonding layer made of copper. Therefore, remelting and reduction of joint strength are less likely to occur after reflow, and it is particularly suitable for mounting on electronic parts that are exposed to a high temperature environment.

When the radius of the copper core is set to 1, the diffusion preventing layer 12 made of nickel has a thickness of 0.04 or more and 0.51 or less. It is preferably a ratio of 0.05 or more and 0.20 or less. If it is less than 0.04, the diffusion of copper or tin cannot be prevented, and if it exceeds 0.51, the meltability of the solder powder is lowered.

thus

The solder powder 10 produced by the above method has an average particle diameter of 1 μm or more and 30 μm or less. The reason why the average particle diameter of the solder powder is limited to 1 μm or more and 30 μm or less is based on the above reasons.

In addition, the solder powder 10 produced by the above method has a copper content of 2% by mass or more and 70% by mass or less based on 100% by mass of the total amount of the powder. The conventional solder powder is used as a substitute for Sn-Pb eutectic solder (composition ratio Sn: Pb = 63: 37% by mass). Therefore, the ratio of copper is contained in a ratio of 0.5 to 1.5% by mass based on the reason that the melting point is close and the eutectic composition is required. On the other hand, the solder powder produced by the above method is more than 2% by mass, whereby after reflowing, Sn having a higher solidification initiation temperature of about 880 to 600 ° C is formed. A Cu alloy or a Sn-Ni-Cu alloy having a higher solidification initiation temperature of about 800 to 400 °C. In addition, even if the content ratio of copper is small, after reflow, a Sn-Cu alloy or a Sn-Ni-Cu alloy having a higher solidification initiation temperature than tin is formed, and solidified by containing more copper. The initial temperature is further increased because the ratio of the intermetallic compound having a high melting point in the alloy is further increased. Thereby, the solder bump formed by the reflow of the solder paste containing the solder powder is greatly improved in heat resistance, and remelting and reduction in bonding strength can be prevented. Therefore, it is particularly applicable to high-temperature solder which is used for mounting of electronic parts or the like which are required to be exposed to a high-temperature environment. If the content ratio of copper is less than 2% by mass, since the solidification initiation temperature becomes low, the solder bump formed after reflowing cannot obtain sufficient heat resistance, and remelting occurs in a high-temperature environment, and cannot be used as a high temperature. Solder is used. On the other hand, if it exceeds 70% by mass, the solidification initiation temperature is too high, and the solder cannot be sufficiently melted, which causes a disadvantage of occurrence of joint failure. Among them, the content of copper in 100% by mass of the total amount of the powder is preferably from 10 to 60% by mass.

In addition, the content ratio of nickel in the solder powder is 1% by mass or more and less than 15% by mass, and preferably 2 to 10% by mass, based on 100% by mass of the total amount of the solder powder. Based on this content ratio, the thickness of the diffusion preventing layer made of nickel described above is determined. If the content of nickel is less than 1 When the mass is %, it is difficult to prevent the diffusion of copper or tin; if it exceeds 15% by mass, the meltability of the solder powder is lowered.

In addition, the content of the tin in the solder powder is preferably 29% by mass or more and less than 97% by mass based on 100% by mass of the total amount of the solder powder in the powder, and the remainder other than the copper and nickel in the powder. 40 to 90% by mass. This is because if the content ratio of tin is less than 29% by mass, the low melting point required for the solder powder is not exhibited at the time of reflow. In addition, when it is 97% by mass or more, the content ratio of copper is decreased, and the heat resistance of the solder bump formed after the reflow is lowered. In other words, when the solder after the mounting is exposed to a high temperature environment, the solder after the mounting is remelted or a liquid phase is formed in a part of the solder, and the bonding strength with the substrate or the like is lowered.

[Welding paste and its preparation method]

The solder powder produced by the above method is suitable for use as a material for a solder paste obtained by paste-mixing with a soldering flux. The preparation of the solder paste is carried out by paste-mixing the solder powder and the soldering flux in a predetermined ratio. The soldering flux used for the preparation of the solder paste is not particularly limited, and a flux prepared by mixing various components such as a solvent, a rosin, a thixotropic agent, and an active agent can be used.

Examples of the solvent to be used in the preparation of the flux for soldering include diethylene glycol monohexyl ether, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, tetraethylene glycol, and 2- An organic solvent having a boiling point of 180 ° C or higher, such as ethyl-1,3-hexanediol or α-terpineol. Further, examples of the rosin include rosin gum, hydrogenated rosin, polymerized rosin, and ester rosin.

Further, examples of the thixotropic agent include hardened castor oil, fatty acid decylamine, natural fats and oils, synthetic fats and oils, N,N'-extended ethyl bis-12-hydroxystearic acid decylamine, and 12-hydroxystearic acid. 1,2,3,4-dibenzylidene-D-sorbitol and its derivatives.

Further, as the active agent, a hydrohalic acid amine salt is preferred, and specific examples thereof include triethanolamine, diphenylguanidine, ethanolamine, butylamine, aminopropanol, polyoxyethylene oleylamine, and polyoxyethylene laurel. Amine, polyoxyethylene stearylamine, diethylamine, triethylamine, methoxypropylamine, dimethylaminopropylamine, dibutylaminopropylamine, ethylhexylamine, B Oxypropylpropylamine, ethylhexyloxypropylamine, dipropylamine, isopropylamine, diisopropylamine, piperidine, 2,6-dimethylpiperidine, aniline, methylamine, ethylamine, butylamine, 3 a hydrochloride or hydrobromide salt of an amine such as amino-1-propene, isopropylamine, dimethylhexylamine or cyclohexylamine.

The flux for soldering can be obtained by mixing the above components in a predetermined ratio. The proportion of the solvent in the total amount of the flux 100% by mass is preferably from 30 to 60% by mass, the proportion of the thixotropic agent is preferably from 1 to 10% by mass, and the proportion of the active agent is preferably from 0.1 to 10% by mass. If the ratio of the solvent is less than the lower limit, the viscosity of the flux may be too high, and the viscosity of the solder paste used therewith may be increased, and the solder filling property of the solder may be lowered frequently or the printing property may be uneven. A situation in which the disadvantages are reduced. On the other hand, when the upper limit is exceeded, the viscosity of the flux is too low, so that the viscosity of the solder paste used therewith is also lowered, and there is a disadvantage that the solder powder and the flux component are precipitated and separated. Moreover, if the ratio of the thixotropic agent does not reach the lower limit value, the viscosity of the solder paste is too low, and the solder is generated. The disadvantage of the sedimentation separation of the powder and the flux component. On the other hand, when it exceeds the upper limit, the viscosity of the solder paste may be too high, and there is a case in which the printability of solder filling property or coating unevenness is lowered. Further, when the ratio of the active agent is less than the lower limit, the solder powder is not melted, and there is a disadvantage that sufficient joint strength cannot be obtained. On the other hand, if the ratio exceeds the upper limit, the active agent is easily stored during storage. The solder powder reacts, and there is a case where the storage stability of the solder paste is lowered. In addition, a viscosity stabilizer may be added to the flux for soldering. Examples of the viscosity stabilizer include polyphenols, phosphate compounds, sulfur compounds, tocopherols, tocopherol derivatives, ascorbic acid, and ascorbic acid derivatives which are soluble in a solvent. When the viscosity stabilizer is too large, there is a disadvantage that the meltability of the solder powder is lowered. Therefore, it is preferably 10% by mass or less.

The amount of the flux for soldering in the case of preparing the solder paste is preferably such that the flux accounts for 5 to 30% by mass of the solder paste after preparation. This is because if the lower limit is not reached, the flux is not easily formed due to insufficient flux. On the other hand, if the upper limit is exceeded, the flux content in the solder paste is too large, and the metal content is reduced. It is not easy to obtain a solder bump of a desired size when the solder is melted.

Since the solder paste of the present invention is made of the above-described solder powder of the present invention, it is rapidly melted during reflow and has excellent meltability; on the other hand, after reflow, the molten solder powder forms a high melting point intermetallic compound, and is resistant to heat. The sex rises, so that it is less likely to cause remelting caused by heat. Therefore, the solder paste of the present invention is particularly suitable for mounting electronic parts and the like which are required to be exposed to a high temperature environment.

[Installation method and joint body of electronic parts using solder paste]

The soldering paste prepared by the above method is used to mount electronic components such as a germanium wafer or an LED chip on various heat radiating substrates, FR4 (Flame Retardant Type 4) substrates, and Kovar alloy substrates by a needle transfer method. The paste for soldering at a predetermined position of the substrate or the paste for printing is printed at a predetermined position by a printing method. Next, a wafer component as an electronic component is loaded on the transferred or printed solder paste. In this state, the solder powder is reflowed in a reflow furnace or a nitrogen atmosphere at a temperature of 250 to 400 ° C for 5 to 120 minutes. Depending on the case, the wafer and the substrate may be pressed while being joined. Thereby, the wafer element and the substrate are bonded to each other to obtain a bonded body, and the electronic component is mounted on the substrate.

[Examples]

Next, an embodiment of the present invention will be described in detail in conjunction with a comparative example.

<Example 1>

First, add 4.35 × 10 ^-3 mol of nickel (II) sulfate, 9.66 × 10 ^-4 mol of sodium phosphinate, 3.29 × 10 ^-4 mol of sodium citrate to 50 mL of water, and stir at a rotation speed of 300 rpm using a stirrer. 5 minutes, prepared into a solution. After the pH of the solution was adjusted to 5.0 with sulfuric acid, 0.2 g of polyvinyl alcohol 500 (polyvinyl alcohol having an average molecular weight of 500) as a dispersing agent was added, and the mixture was further stirred at a rotation speed of 300 rpm for 10 minutes. Next, to this solution, 0.2 g of polyvinyl alcohol 500 (polyvinyl alcohol having an average molecular weight of 500) as a dispersing agent was dissolved in 50 mL of water, and a dispersion of 3.40 g of copper powder having an average particle diameter of 0.18 μm was dispersed. The mixture was stirred at a rotation speed of 500 rpm for 10 minutes to obtain a dispersion liquid of nickel-coated copper powder in which nickel was precipitated on the surface of the copper powder. The following operation was repeated four times to carry out washing: After the dispersion was allowed to stand for 60 minutes to precipitate the formed powder, the supernatant liquid was discarded, 100 mL of water was added thereto, and the mixture was stirred at a rotation speed of 300 rpm for 10 minutes. Finally, this was dried by a vacuum dryer to obtain a powder having copper as a center core and nickel as a first coating layer (diffusion preventing layer).

Next, 0.37 g of the above powder was dispersed in 50 mL of water to prepare a dispersion. To the dispersion, 2.56 × 10 ^-2 mol of tin (II) sulfate was added, and the mixture was stirred at a rotation speed of 300 rpm for 5 minutes using a stirrer to prepare a mixed solution. After the pH of the mixture was adjusted to 0.5 with sulfuric acid, 0.5 g of polyvinyl alcohol 500 (polyvinyl alcohol having an average molecular weight of 500) as a dispersing agent was added, and the mixture was further stirred at a rotation speed of 300 rpm for 10 minutes. Next, 50 mL of a divalent chromium ion aqueous solution having a pH adjusted to 0.5 to 1.58 mol/L was added to the mixed solution at a rate of 50 mL/min, and tin ions were reduced by stirring at a rotation speed of 500 rpm for 10 minutes to thereby obtain a dispersed tin. A dispersion of nickel-coated copper powder on the outermost layer of the nickel-coated copper powder is tin. The following operation was repeated four times to carry out washing: After the dispersion was allowed to stand for 60 minutes to precipitate the formed powder, the supernatant liquid was discarded, 100 mL of water was added thereto, and the mixture was stirred at a rotation speed of 300 rpm for 10 minutes. Finally, the film was dried in a vacuum dryer to obtain an average particle diameter of 1.1 μm, and each of them was formed to have copper as a center core, nickel as a first coating layer (diffusion preventing layer), and tin as a second coating. The layer (outermost layer) of solder powder.

<Examples 2 to 28, Comparative Examples 1 to 55>

In addition, in Examples 2 to 28 and Comparative Examples 1 to 55, the particle diameter of the copper powder to be used, the amount of copper powder added, the amount of nickel (II) sulfate and tin (II) sulfate added, and the like were adjusted. The solder powder was obtained in the same manner as in Example 1 except that the ratio of the components was controlled to a predetermined copper center core radius, a thickness of the nickel diffusion preventing layer and the tin outermost layer, and even a solder powder having a predetermined particle diameter.

<Comparative Example 56>

First, add 4.35 × 10 ^-3 mol of nickel (II) sulfate, 9.66 × 10 ^-4 mol of sodium phosphinate, 3.29 × 10 ^-4 mol of sodium citrate to 50 mL of water, and stir at a rotation speed of 300 rpm using a stirrer. 5 minutes, prepared into a solution. After the pH of the solution was adjusted to 5.0 with sulfuric acid, 0.2 g of polyvinyl alcohol 500 (polyvinyl alcohol having an average molecular weight of 500) as a dispersing agent was added, and the mixture was further stirred at a rotation speed of 300 rpm for 10 minutes. Next, to this solution, 0.2 g of polyvinyl alcohol 500 (polyvinyl alcohol having an average molecular weight of 500) as a dispersing agent was dissolved in 50 mL of water, and a dispersion of 3.40 g of copper powder having an average particle diameter of 0.18 μm was dispersed. The mixture was stirred at a rotation speed of 500 rpm for 10 minutes to obtain a dispersion liquid of nickel-coated copper powder in which nickel was precipitated on the surface of the copper powder. The following operation was repeated four times to carry out washing: After the dispersion was allowed to stand for 60 minutes to precipitate the formed powder, the supernatant liquid was discarded, 100 mL of water was added thereto, and the mixture was stirred at a rotation speed of 300 rpm for 10 minutes. Finally, this was dried by a vacuum dryer to obtain a powder having copper as a center core and nickel as a first coating layer (diffusion preventing layer).

Next, the powder of the above-mentioned copper-centered core and nickel as a diffusion preventing layer was tin-plated using a small-sized roller apparatus manufactured by Yamamoto gold-plated tester (strand). The composition of the plating solution to be used was a solution in which 5.0 g of a powder was dispersed in 150 mL of a plating solution of sodium stannate 100 g/L, sodium hydroxide 10 g/L, and sodium acetate 15 g/L. Further, in the plating treatment conditions, tin was used for the anode, the bath temperature was set to 50 ° C, the drum rotation speed was set to 19 rpm, and the voltage was set to 0.8 V. The thickness of the tin-plated film was adjusted by the treatment time. In this comparative example, by coating for 0.3 hours, the coated nickel having the outermost layer of tin precipitated on the surface of the nickel-coated copper powder was dispersed. A dispersion of copper powder. The following operation was repeated four times to carry out washing: After the dispersion was allowed to stand for 60 minutes to precipitate the formed powder, the supernatant liquid was discarded, 100 mL of water was added thereto, and the mixture was stirred at a rotation speed of 300 rpm for 10 minutes. Finally, the film was dried in a vacuum dryer to obtain an average particle diameter of 3.3 μm, and each of them was formed with copper as a center core, nickel as a first coating layer (diffusion preventing layer), and tin as a second coating. The layer (outermost layer) of solder powder.

<Comparative Examples 57 to 65>

In addition to Comparative Examples 57 to 65, the particle diameter of the copper powder used and the amount of copper powder added, nickel (II) sulfate, and tin (II) sulfate were adjusted. The addition amount, the ratio of the other components, and the treatment conditions were the same as those of Comparative Example 56 except that the predetermined copper center core radius, the thickness of the nickel diffusion preventing layer and the tin outermost layer, and even the solder powder having a predetermined particle diameter were controlled. The way to get the solder powder.

<Comparative test and evaluation>

With respect to the solder powders obtained in Examples 1 to 28 and Comparative Examples 1 to 65, the content ratio [% by mass] of copper of the solder powder, the average particle diameter [μm], and the central core composed of copper were measured by the following method. The average radius [μm], the average thickness [μm] of the diffusion preventing layer made of nickel, and the average thickness [μm] of the coating layer made of tin. These results are shown in Tables 1 to 5 below. Further, the solder paste was prepared by using these solder powders, and the joint strength at the time of changing the maximum holding temperature at the time of reflow was evaluated. These results are shown in Tables 6 to 10 below. Further, the sum of the average radius of the center core made of copper, the average thickness of the diffusion preventing layer made of nickel, and the average thickness of the coating layer made of tin is taken as the average radius of the solder powder.

(1) Analysis of the content ratio of copper in the solder powder: The ratio of the copper content of the solder powder was analyzed by inductively coupled plasma atomic emission spectrometry (ICP emission spectrometer manufactured by Shimadzu Corporation: ICPS-7510).

(2) Average particle diameter of the solder powder: The particle size distribution is measured by a particle size distribution measuring apparatus (Radio Diffraction/scattering type particle size distribution measuring apparatus LA-950, manufactured by Horiba, Ltd.) using a laser diffraction scattering method. The volume cumulative median diameter (Median diameter, D ₅₀ ) was taken as the average particle diameter of the solder powder.

(3) The radius of the center core made of copper, the thickness of the diffusion preventing layer made of nickel, and the thickness of the coating layer made of tin: the solder powder is embedded in the thermosetting epoxy resin, and the solder powder is placed. After dry grinding of the section, use an electron microscope (Scanning Electron) Microscope, SEM), measured the radius of the center core made of copper, the thickness of the diffusion preventing layer made of nickel, and the thickness of the coating layer made of tin for 30 solder particles, and obtained the average value of each. . Further, the ratio of the average value of the thickness (the thickness of the diffusion preventing layer/the radius of the center core) is calculated from the average value of the thickness of the diffusion preventing layer made of nickel and the radius of the central core made of copper.

(4) Cohesiveness of the solder powder: It is judged by the following method: a particle size distribution measuring apparatus using a laser diffraction scattering method (Rapid diffraction/scattering particle size distribution measuring apparatus LA-950, manufactured by Horiba, Ltd.) The particle size distribution is measured, and in the obtained particle size distribution curve, in addition to the distribution peak of the desired particle diameter, the case where there are two or more particle diameter curves of the distribution peak on the larger particle diameter side is rated as " There is "cohesion"; the case where no such peak is observed is rated as "no" condensation.

(5) Bonding strength: 50% by mass of diethylene glycol monohexyl ether as a solvent, 46% by mass of a rosin as a polymerized rosin (softening point: 95 ° C), and an active agent of cyclohexylamine hydrobromide 1.0 The mass % was mixed with 3.0% by mass of the hardened castor oil as a thixotropic agent to prepare a flux. Then, the flux and the solder powder obtained in Examples 1 to 28 and Comparative Examples 1 to 65 were mixed at a ratio of 88% by mass of the flux and 12% by mass of the solder powder to prepare a solder paste.

The solder paste prepared as described above was transferred to a predetermined position of a 0.5 mm thick Kovar alloy (Fe-Ni-Co alloy) substrate by a needle transfer method using a needle having a tip end diameter of 100 μm. Further, nickel plating is performed on the Kovar substrate, and then rapid gold plating is performed thereon. Next, after transfer The solder paste is loaded with a 0.9 mm square LED chip. Furthermore, while the LED wafer and the substrate were pressurized at a pressure of 1.0 MPa using a pressurizing jig, the reflow was performed in an infrared heating furnace in a nitrogen atmosphere at a predetermined maximum holding temperature for 0.17 hours to cause the LED wafer and the section. The alloyed substrate was joined to obtain a bonded sample. Further, the maximum holding temperature at the time of the above reflowing was set to a temperature different from 250 ° C, 300 ° C, and 350 ° C, and each of the examples or the comparative examples was carried out three times to obtain a joined sample.

The bonding strength of the bonded Kovar substrate and the LED wafer is in accordance with the lead-free solder test method described in JIS Z 3198-7 - "Parts "Measurement method for shear strength of wafer parts by solder bonding") The joint shear strength was measured under the conditions of 300 ° C and 0 days and 30 days after storage, and the relative shear strength after storage at 300 ° C for 0 days and 30 days was obtained when the shear strength at room temperature was 100. . In the table, "excellent" means that the relative shear strength is above 90; "good" means less than 90 to 80; "can" means less than 80 to 70; "poor" means The situation has not reached 70.

Comparing Examples 1 to 28 with Comparative Examples 1 to 65 from Tables 6 to 10, the following results were obtained.

In the comparative example in which the average particle diameter of the solder powder was 0.5 μm, since the particle diameter was too small, the solder powder was not melted before the solder powder was preserved due to the influence of the oxide film on the surface of the powder. When the radius of the copper core is set to 1, the thickness of the diffusion preventing layer made of nickel is 0.03. Since the thickness of the diffusion preventing layer is too thin, diffusion of copper or tin cannot be prevented, and the bonding strength is insufficient. Good situation. Further, in the comparative example in which the content of copper was about 75% by mass, the content of copper was too large, and the solidification initiation temperature was too high, and the solder was not melted during reflow. In the comparative example in which the content of copper is about 1.5% by mass, the content of copper is too small, the solidification initiation temperature is lowered, and sufficient heat resistance cannot be obtained, and the joint strength is not good.

In the comparative example in which the average particle diameter of the solder powder was about 40 μm, the particle diameter was too large, and a bonding layer having a large void (void) was formed after the reflow, and a dense bonding layer could not be obtained. Therefore, the bonding strength was poor. The situation. Further, in the comparative example in which the ratio of the thickness of the diffusion preventing layer to the radius of the center core is less than 0.04, since the diffusion preventing effect is small, copper is diffused to the coating layer made of tin, and the meltability of the solder powder is lowered, and there is a deficiency. Good situation. On the other hand, in the comparative example in which the ratio of the thickness of the diffusion preventing layer to the radius of the central core exceeds 0.51, since the ratio of nickel is too high, the meltability of the solder powder is lowered, and the joint strength is unsatisfactory. In the comparative example in which the coating layer made of tin was formed by barrel plating, the average particle diameter of the solder powder obtained by the laser diffraction scattering method and the measurement by SEM observation were obtained because a large amount of strongly agglomerated powder was formed. The value of the average particle diameter of the solder powder was greatly different, and a good printed film could not be obtained, and the joint strength could not be measured for any of the samples.

On the other hand, the average particle diameter of the solder powder is in the range of 1 μm or more and 30 μm or less, and the content ratio of copper is in the range of 2% by mass or more and 70% by mass or less based on 100% by mass of the total amount of the solder powder. When the radius of the copper core is set to 1, the thickness of the diffusion preventing layer made of nickel is in the range of 0.04 or more and 0.51 or less, and the powder is not aggregated, and a good printed film can be obtained, and the solder powder can be obtained. The joint strength was acceptable, good or excellent at all reflow temperatures of 250 ° C, 300 ° C, and 350 ° C before storage and after 30 days of storage.

[Industrial Applicability]

The present invention can be suitably utilized for a solder powder which is sometimes stored for a long time. Moreover, it can be suitably used for the mounting of electronic parts, especially the mounting of electronic parts exposed to a high temperature environment.

Claims (4)

A method for producing a solder powder, comprising: a step of preparing a first dispersion liquid of copper powder; and adding a metal salt of nickel to the first dispersion liquid of the copper powder to prepare a metal salt of the nickel to be dissolved and the copper a step of dispersing the first solution in the powder; a step of adjusting the pH of the first solution; and adding the first reducing agent to the pH-adjusted first solution to reduce nickel ions to prepare precipitated nickel a step of coating the copper powder to disperse the second dispersion; and performing solid-liquid separation on the second dispersion; and drying the solid component separated by solid-liquid separation to form a diffusion preventing layer made of nickel to coat the copper core a step of preparing a metal powder; a step of preparing a third dispersion of the metal powder; and adding a metal salt of tin to the third dispersion of the metal powder to prepare a solution in which the metal salt of tin is dissolved and the metal powder is dispersed a step of dissolving the solution; a step of adjusting the pH of the second solution; and adding a second reducing agent to the pH-adjusted second solution to reduce tin ions to prepare precipitated tin a step of coating the metal powder to disperse the fourth dispersion; and solid-liquid separating the fourth dispersion, and drying the solid-liquid separated solid component to prepare a solder powder in which the metal powder is coated with a tin layer A step of. A solder powder in which a metal powder obtained by coating a copper core with a diffusion preventing layer made of nickel is coated with a tin layer, wherein the solder powder has an average particle diameter of 1 μm or more and 30 μm or less with respect to the solder. The total amount of the powder is 100% by mass, and the content ratio of copper is 2% by mass or more and 70% by mass or less. When the radius of the copper core is 1, the thickness of the diffusion preventing layer made of nickel is 0.05 or more and 0.20 or less. . A method for producing a solder paste, which is obtained by using the solder powder produced by the method of claim 1 or the solder powder of claim 2 and the soldering flux for 100% by mass of the solder paste after preparation The ratio of the flux is 5 to 30% by mass, and the mixture is paste-formed. A method of mounting an electronic component using the solder paste prepared by the method of claim 3.