KR20140118747A - Solder powder and solder paste using the powder - Google Patents

Abstract

The present invention provides solder powder and solder paste using the same. The solder powder is rarely molten again and bonding strength is also rarely decreased after a reflow process. Especially, the solder powder is proper to be used for installing electrical parts, exposed to an environment at high temperatures. The soldering powder (10) is composed of a core (11) and a cover layer (12), which covers the core (11). The core (11) is made of silver and a compound of silver and tin. The cover layer (12) is made of tin. An average diameter of a solder powder particle is 30 μm or smaller. The solder powder (10) includes more than 10 wt% and 70 wt% or less of silver with respect to 100 wt% of the total weight of the solder powder (10).

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to solder powder and solder paste using the solder powder,

The present invention relates to a solder powder used for mounting electronic components and the like and a solder paste using the powder. More particularly, the present invention relates to a solder powder suitable for mounting electronic parts or the like which does not cause a reduction in re-melting and bonding strength after reflow, and which is particularly exposed to a high-temperature atmosphere, and a solder paste using the powder.

BACKGROUND ART [0002] Solder used for joining electronic components and the like is lead-free in terms of the environment, and currently solder powder mainly comprising tin is employed. As a method for obtaining a fine metal powder such as a solder powder, a melt spinning method, a rotating electrode method, a mechanical process, a chemical process, and the like are known in addition to the atomization method such as the gas atomization method and the rotary disk method. In the gas atomization method, a method is known in which a metal is melted in an induction furnace or a gas furnace, a molten metal is flowed from a nozzle at the bottom of the tundish, and a high-pressure gas is sprayed therefrom to pulverize the molten metal. The rotary disk method is also referred to as a centrifugal atomization method. The molten metal is dropped onto a disk rotating at a high speed, and a shear force is applied in a tangential direction to break it to form a fine powder.

The solder is required to have various characteristics in addition to the above-described characteristics in the environmental surface, depending on the use of the electronic component to be mounted. For example, information electronic appliances such as cellular phones and PCs are required to be thinner and lighter in weight, which is important in portability. Further, miniaturization of electronic parts used in the manufacture of these electronic parts and fine pitches of joint parts are progressing, A solder powder having a particle diameter is required.

On the other hand, in an electronic component used under high temperature in a vehicle application or the like, since the solder after mounting is remelted by being exposed to a high-temperature atmosphere, it is necessary to prevent the bonding strength from lowering, and high heat resistance after reflow is required. The melting point is about 187 ° C in the case of the most common Sn-Pb type eutectic solder (composition ratio Sn: Pb = 63: 37 mass%), and about 217 ° C in general Sn-Ag- . On the other hand, in a high temperature solder of Au-Sn type (composition ratio Sn: Au = 20: 80 mass%) known as heat-resistant high-temperature solder, a melting point after reflow is about 280 ° C and a high temperature solder of Sn- : Pb = 5: 95 mass%) exhibits a high melting point of about 310 to 315 ° C.

However, in the Au-Sn-based solder, there is a problem that the manufacturing cost is increased because a very expensive Au is used. Although the Sn-Pb-based high-temperature solder exhibits high heat resistance, since the lead is used, the above-described environmental problem remains. In order to solve such a problem, there is known a technique for improving heat resistance, bonding strength, and the like by mixing another material powder having a high melting point with a low melting point and low cost material powder not containing lead or gold (for example, , And Patent Documents 1 to 6).

Patent Document 1 discloses a joining method using a metal material in which a metal Cu powder, a metal Sn powder, and an Ag-Cu-Ti alloy powder are mixed to bond the ceramics member and the metal member. Patent Document 2 discloses an alloy powder of Sn-Ag or the like having a melting point higher than that of a conventional tin lead-based alloy in an alloy powder containing no lead and having a melting point lower than that of a conventional tin lead- A solder paste containing a mixed powder mixed is disclosed. Patent Document 3 discloses a cream solder in which metal particles such as Ag, Sn, Cu and the like having a melting point higher than that of the process solder are mixed in addition to the process solder. Patent Document 4 discloses a composition for soldering which contains no lead and a first metal component such as Sn and a second metal component such as Ag or Cu having a melting point of 400 캜 or higher. Patent Document 5 discloses a method of manufacturing a semiconductor device that includes a first metal component and a second metal component that form a powder phase and the first metal component is any one of Sn-Cu alloy and Sn-Cu-Sb alloy, Ag, In, Bi, Zn or Ni, and the second metal component is at least one of Cu, Sn, Sb, Ag, Zn and Ni, A composition for a solder is disclosed. Patent Document 6 discloses a solder composition containing no lead and containing a first metal powder containing tin as a main component and a second metal powder having a melting point higher than that of the first metal powder and mainly containing copper .

Japanese Patent Application Laid-Open No. 5-24943 (Claim 2, paragraph [0015]) Japanese Patent Application Laid-Open No. 11-186712 (Claim 2, paragraph [0018], paragraph [0023]) Japanese Patent Application Laid-Open No. 2000-176678 (claims 1 and 3, paragraph [0010]) Japanese Patent Application Laid-Open No. 2002-254195 (claims 1 to 5, paragraph [0011] to paragraph [0013]) Japanese Laid-Open Patent Publication No. 2003-154485 (Claim 1, Paragraph [0009]) Japanese Patent Publication No. 3782743 (Claims 1 to 4, paragraph [0005])

In the above-mentioned conventional Patent Documents 1 to 6, all of the solder powder obtained by mixing the metal powder having a low melting point and the metal powder having a high melting point, which do not contain lead or gold, is used. In the solder powder obtained by mixing two or more different powders, the degree of mixing of the powders tends to be uneven. If unevenness occurs, a partial melting deviation or a compositional deviation occurs at the time of reflow, and there arises a problem that sufficient strength can not be obtained at the joint portion.

It is an object of the present invention to provide a solder powder which is suitable for mounting electronic parts or the like which does not cause a reduction in re-melting and bonding strength after reflow and is particularly exposed to a high-temperature atmosphere, and a solder paste using the powder.

A first aspect of the present invention is to provide a core layer 11 made of a core layer 11 and a coating layer 12 covering the core core 11 and having a core 11 made of silver and an intermetallic compound of silver and tin And the cover layer 12 is made of tin, the average particle diameter of the solder powder 10 is 30 占 퐉 or less and the content ratio of silver to the total amount of the solder powder 10 is 100 mass% Is 10% by mass or more and 70% by mass or less.

A second aspect of the present invention is the invention based on the first aspect, further characterized in that the intermetallic compound of silver and tin is Ag ₃ Sn and / or Ag ₄ Sn.

A third aspect of the present invention is a solder paste obtained by mixing a solder powder of the first or second aspect with a flux for solder to make a paste.

The fourth aspect of the present invention is further characterized in that the electronic component is mounted by using the solder paste of the third aspect.

The solder powder of the first and second aspects of the present invention is a solder powder composed of a coating layer covering the core and the core, the core being made of silver and an intermetallic compound of silver and tin, and the covering layer being made of tin, The average particle size of the powder is 30 占 퐉 or less and the content of silver is 10% by mass or more and 70% by mass or less based on 100% by mass of the total amount of the solder powder. As described above, in the solder powder of the present invention, since the surface of the powder is composed of tin having a low melting point, the melting property at the time of reflowing is excellent. On the other hand, after reflow, due to the presence of silver contained in the above- Due to the presence of the intermetallic compound, an intermetallic compound having a high melting point is formed. For example, since the melting point of the ε phase (Ag ₃ Sn) is 480 ° C. and the melting point of the ζ phase (Ag ₄ Sn) is as high as 724 ° C., the coagulation starting temperature rises to about 300 to 640 ° C. it's difficult. For this reason, the solder powder of the present invention can be preferably used as a high-temperature solder used for mounting electronic components and the like exposed to a high-temperature atmosphere. In addition, since silver and tin are contained in one metal particle constituting the powder, it is possible to prevent a decrease in the joining strength due to a melting deviation and a composition shift at the time of reflow.

The solder paste of the third aspect of the present invention is obtained by using the solder powder of the present invention. For this reason, the solder paste has a high melting property at the time of reflow and is excellent in melting property. On the other hand, after reflow, the solder powder to be melted forms an intermetallic compound having a high melting point, Melting is difficult to occur. For this reason, the solder paste of the present invention can be suitably used for mounting electronic parts or the like which are particularly exposed to a high-temperature atmosphere.

In the method of mounting the electronic component according to the fourth aspect of the present invention, since the above-described solder paste of the present invention is used, the solder paste can be easily and highly precisely mounted And it is possible to impart high heat resistance after mounting.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram schematically showing an example of a cross-sectional structure of a solder powder according to an embodiment of the present invention. FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments for carrying out the present invention will be described with reference to the drawings.

As shown in Fig. 1, the solder powder of the present invention is composed of a core 12 and a coating layer 12 covering the core 11. The core 11 is made of silver and an intermetallic compound of silver and tin And the coating layer 12 is made of tin. The solder powder of the present invention is excellent in the melting property at the time of reflow since the core composed of silver and an intermetallic compound of silver and tin is covered with a coating layer composed of tin having a low melting point. Further, since silver and tin are contained in one metal particle constituting the powder instead of a powder obtained by mixing two or more metal powders different in melting point or the like as the conventional solder powder described above, The displacement does not occur well and a high bonding strength is obtained. In addition, since a part of the core nucleus forms an intermetallic compound of silver and tin before reflow, compared with a powder having a structure in which the core made of silver is coated with tin, the melting diffusion property upon reflow is good The composition control at the time of forming the solder bumps is easy, and the wettability is excellent.

The solder powder 10 of the present invention has an average particle diameter of 30 mu m or less. The reason why the mean particle size of the solder powder is limited to 30 mu m or less is that when the thickness exceeds 30 mu m, the coplanarity of the bump is lowered when the bump is formed, and when the pattern surface is coated with solder, This is because unevenness occurs and a problem arises that the entire surface of the pattern can not be uniformly coated. When the average particle size is less than 1 mu m, the specific surface area increases and the melting property of the solder decreases due to the influence of the surface oxide layer of the powder. Therefore, the average particle diameter of the solder powder is preferably in the range of 1 to 30 mu m, And particularly preferably in the range of 3 to 20 mu m. In the present specification, the average particle diameter of the powder refers to the volume cumulative median diameter (measured by a laser diffraction / scattering type particle size distribution measuring apparatus LA-950 manufactured by Horiba Ltd.) using a laser diffraction scattering method Median diameter, D ₅₀ ).

The solder powder (10) of the present invention has a silver content of more than 10 mass% and not more than 70 mass% with respect to the total amount of 100 mass% of the powder. Since the conventional solder powder is used as a substitute for a Sn-Pb process solder (composition ratio Sn: Pb = 63: 37 mass%), the ratio of silver is 1.0 to 3.5 mass% Less. On the other hand, in the solder powder of the present invention, Sn-Ag alloy having a high solidification starting temperature of about 300 to 640 ° C after reflow is formed by containing silver in the above-mentioned range in a relatively large proportion. Further, even when the content of silver is small, an Sn-Ag alloy having a higher coagulation starting temperature than tin is formed after reflow, and the coagulation starting temperature is further increased by containing silver in a larger amount. The ratio of the compound is increased. As a result, in the solder bumps formed by reflowing the solder paste containing the solder powder, the heat resistance is greatly improved, and the reduction of the re-melting and the bonding strength can be prevented. Therefore, it can be preferably used as a high-temperature solder used for mounting electronic components or the like exposed to a high temperature atmosphere. When the content of silver is less than the lower limit, the coagulation starting temperature is lowered, so that sufficient heat resistance can not be obtained in the solder bumps formed after reflow, and re-melting occurs during use in a high temperature atmosphere and can not be used as high temperature solder. On the other hand, if the upper limit is exceeded, the solidification starting temperature becomes too high, and the solder does not sufficiently melt, resulting in a problem that bonding failure occurs. Among them, the content of silver in the total amount of 100 mass% of the powder is preferably 10 to 70 mass%.

The content of tin in the solder powder, that is, the remaining amount of the silver in the powder is 30 to 90% by mass, preferably 50 to 90% by mass based on 100% by mass of the total amount of the solder powder. If the content of tin is less than the lower limit, the low melting point required for the solder powder at reflow is not exhibited. On the other hand, if the upper limit is exceeded, the content ratio of silver is reduced, and the heat resistance of the solder bumps formed after reflow is lowered.

The intermetallic compounds of silver and tin that form part of the core include Ag ₃ Sn and / or Ag ₄ Sn.

Next, a method for producing the solder powder of the present invention will be described. First, a solution containing a compound containing a metal element constituting the core and a coating layer, that is, a compound containing silver and a compound containing tin, and a dispersant are added to the solvent and mixed to prepare a dissolution liquid. The proportion of the tin-containing compound and silver-containing compound in the solution is adjusted such that the content ratio of each metal element is in the above range after the solder powder is produced.

In addition, for the above-mentioned dissolution solution, the silver powder and the dispersant are added to and mixed with a solvent by using silver powder instead of the silver-containing compound to prepare a silver powder dispersion, and the above tin- And a dissolving solution in which silver powder is dispersed may be used. The proportion of the silver powder and the tin-containing compound used in this case is adjusted so that the content ratio of each metal element is in the above range after the solder powder is produced.

Examples of the silver compounds used for preparing the dissolving solution include silver (I) sulfate, silver chloride (I) and silver nitrate (I), and the tin compounds include tin chloride (II), tin sulfate Tin acetate (II), tin oxalate (II), and the like. On the other hand, as the silver powder to be used in place of the silver compound, a silver powder obtained by a physical method such as an atomization method can be used in addition to the silver powder obtained by a chemical method by an average particle diameter of 0.1 to 2.0 탆. Among them, when a solution containing a silver or a solution containing a tin-containing compound is used, it is particularly preferable to use silver (I) nitrate nitrate or tin (II) nitrate.

Examples of the solvent include water, alcohol, ether, ketone, ester and the like. Examples of the dispersing agent include cellulose-based, vinyl-based, polyhydric alcohol, and gelatin and casein. The pH of the prepared solution is adjusted. The pH is preferably adjusted in the range of 0 to 2.0 in consideration of redissolution of the resulting solder powder. Alternatively, a dispersant may be added after complexing each metal element by adding a complexing agent after adding and dissolving the metal compound in a solvent, respectively. The addition of the complexing agent makes it possible to synthesize the metal ion in a wide range without precipitating the metal ion even on the alkali side. Examples of the complexing agent include succinic acid, tartaric acid, glycolic acid, lactic acid, phthalic acid, malic acid, citric acid, oxalic acid, ethylenediamine acetic acid, iminoacetic acid and nitrilo triacetic acid or salts 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 the solution prepared above. Examples of the reducing agent include boron hydrides such as sodium tetrahydroborate and dimethylamine borane, nitrogen compounds such as hydrazine, and metal ions such as trivalent titanium ions and divalent chromium ions.

Next, by adding a reducing agent aqueous solution to the solution and mixing the solutions, each metal ion in the solution is reduced to obtain a dispersion in which the metal powder is dispersed in the solution. In this reduction reaction, when a solution containing a silver-containing compound or a solution containing a tin-containing compound is used, noble silver is first reduced to tin, and finally tin is reduced. Thereby, a metal powder having an average particle diameter of 30 mu m or less and consisting of a core composed of silver and a coating layer composed of tin covering the core is formed. As a method of mixing the dissolving solution and the aqueous solution of the reducing agent, there may be mentioned a method in which a reducing agent aqueous solution is added dropwise to the solution in the vessel at a predetermined addition rate and stirred with a stirrer or the like, And a method in which both liquids are poured at a predetermined flow rate and mixed.

Then, the dispersion is subjected to solid-liquid separation by decantation or the like, and the recovered solid component is washed with an aqueous hydrochloric acid solution, an aqueous nitric acid solution, an aqueous sulfuric acid solution, or a methanol, ethanol, acetone or the like with water or a pH adjusted to 0.5 to 2. After washing, the solid content is recovered by solid-liquid separation again. The process from washing to solid-liquid separation is preferably repeated 2 to 5 times.

Then, a high boiling point solvent having a boiling point of 100 ° C or higher is added to the recovered solid content and dispersed, and heated at a predetermined temperature in an inert gas atmosphere. By performing this heat treatment, a part of the coating layer made of silver and the coating of tin covering the core of the metal powder formed by the reduction reaction reacts to form a core part composed of an intermetallic compound of silver and tin do.

Examples of the high-boiling solvent to be used include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, castor oil and the like.

The heat treatment is preferably performed at a temperature of 100 to 130 DEG C for 20 minutes to 1 hour. When the treatment temperature or the holding time is less than the lower limit, an intermetallic compound may not be formed in the core. When the treatment temperature exceeds the upper limit value, tin in the coating layer is oxidized to lower the melting property. Even if the holding time exceeds the upper limit value, the effect does not change. It is particularly preferable to carry out the reaction at a temperature of 115 to 125 ° C for 30 to 40 minutes.

After the heating, the step from washing to solid-liquid separation is repeated preferably 2 to 5 times, and the recovered solid content is vacuum-dried to obtain the solder powder of the present invention.

The solder powder of the present invention can be obtained by the above process. The solder powder is preferably used as a material for a solder paste obtained by mixing with a solder flux to make a paste. The preparation of the solder paste is carried out by mixing the solder powder and the solder flux at a predetermined ratio to form a paste. The flux for solder used for preparing the solder paste is not particularly limited, but a flux prepared by mixing each component such as solvent, rosin, thixotropic agent and activator can be used.

Preferred solvents for preparing the flux for solder include diethylene glycol monohexyl ether, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, tetraethylene glycol, 2-ethyl-1,3-hexanediol, - terpineol, etc., having a boiling point of 180 ° C or higher. Examples of the rosin include gum rosin, hydrogenated rosin, polymerized rosin, and ester rosin.

Examples of thixotropic agents include hardened castor oil, fatty acid amide, natural fat, synthetic fat, N, N'-ethylene bis-12-hydroxystearyl amide, 12-hydroxystearic acid, -Dibenzylidene-D-sorbitol and derivatives thereof.

As the activator, a hydrohalogenated amine salt is preferable, and specific examples thereof include triethanolamine, diphenylguanidine, ethanolamine, butylamine, aminopropanol, polyoxyethylene oleylamine, polyoxyethylene laurylamine, polyoxyethylene stearate Examples of the amines include allyl amine, diethylamine, triethylamine, methoxypropylamine, dimethylaminopropylamine, dibutylaminopropylamine, ethylhexylamine, ethoxypropylamine, ethylhexyloxypropylamine, bispropylamine, isopropylamine, There may be mentioned a hydrochloride or bromide of an amine such as diisopropylamine, piperidine, 2,6-dimethylpiperidine, aniline, methylamine, ethylamine, 3-amino-1-propene, dimethylhexylamine, cyclohexylamine, Hydrobromide.

The flux for solder is obtained by mixing the respective components at a predetermined ratio. It is preferable that the ratio of the solvent to the total flux of 100 mass% is 30 to 60 mass%, the ratio of the thixotropic agent is 1 to 10 mass%, and the ratio of the activator is 0.1 to 10 mass%. If the ratio of the solvent is less than the lower limit, the viscosity of the flux becomes excessively high. Therefore, the viscosity of the solder paste using the solder becomes too high, and the problem of lowering the filling property of the solder, have. On the other hand, if the upper limit value is exceeded, the viscosity of the flux becomes too low, and the viscosity of the solder paste using the solder paste is also lowered, so that the solder powder and the flux component may be separated by sedimentation. If the ratio of the thixotropic agent is less than the lower limit, the viscosity of the solder paste becomes excessively low, which may cause a problem that the solder powder and the flux component are separated by sedimentation. On the other hand, if the upper limit is exceeded, the viscosity of the solder paste becomes excessively high, which may cause problems such as poor solderability and non-uniformity in printing properties. If the proportion of the activator is less than the lower limit value, the solder powder is not melted and a sufficient bonding strength can not be obtained. On the other hand, if the ratio exceeds the upper limit, the activator tends to react with the solder powder during storage. There arises a problem that the storage stability of the paste for use is lowered. In addition, a viscosity stabilizer may be added to the solder flux. Examples of the viscosity stabilizer include polyphenols, phosphoric acid compounds, sulfur compounds, tocophenol, derivatives of tocopherol, arconvic acid and derivatives of arconvic acid, which are soluble in solvents. If the amount of the viscosity stabilizer is too large, there is a case that the meltability of the solder powder is lowered, and the like. Therefore, the viscosity stabilizer is preferably 10 mass% or less.

The mixing amount of the solder flux when preparing the solder paste is preferably such that the ratio of the flux occupying in 100 mass% of the paste after preparation is 5 to 30 mass%. When the content is less than the lower limit, it becomes difficult to form a paste due to the lack of flux. On the other hand, if the content exceeds the upper limit, the content of the flux in the paste becomes too large to contain a small proportion of the metal and it becomes difficult to obtain a solder bump of a desired size at the time of melting the solder Because.

Since the solder paste of the present invention is made of the solder powder of the present invention as described above, the solder paste is excellent in fast melting property and excellent in melting property on reflowing. On the other hand, after reflowing, the solder powder to be melted forms an intermetallic compound having a high melting point So that the re-melting due to heat is unlikely to occur. For this reason, the solder paste of the present invention can be suitably used for mounting electronic parts or the like which are particularly exposed to a high-temperature atmosphere.

Example

EXAMPLES Next, examples of the present invention will be described in detail with reference to comparative examples.

≪ Example 1 >

First, 1.74 × 10 ^-3 mol of sulfuric acid was added to 50 mL of water, and 2.56 × 10 ^-2 mol of tin (II) sulfate was added. The mixture was stirred for 5 minutes at a rotation speed of 300 rpm using a stirrer to obtain a solution Was prepared. After the pH of the solution 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 dispersant was added, and the mixture was further stirred at a rotation speed of 300 rpm for 10 minutes. Subsequently, 50 ml of a 1.58 mol / l aqueous solution of divalent chromium ion adjusted to pH 0.5 was added to this solution at an addition rate of 50 ml / sec and stirred at a rotation speed of 500 rpm for 10 minutes to reduce each metal ion To obtain a dispersion liquid in which the metal powder was dispersed in the liquid. The dispersion was allowed to stand for 60 minutes to precipitate the resulting metal powder. The supernatant was discarded, 100 ml of water was added thereto, and the operation of stirring at a rotation speed of 300 rpm for 10 minutes was repeated four times to perform cleaning . Thereafter, 100 ml of ethylene glycol was added and dispersed, and the mixture was heated at 120 DEG C for 30 minutes while stirring at a rotation speed of 300 rpm. After heating, the dispersion was again allowed to stand for 60 minutes to precipitate the heated metal powder. The supernatant was discarded, and 100 ml of water was added thereto. The operation of stirring for 10 minutes at a rotation speed of 300 rpm was repeated four times to perform cleaning. Finally, this was dried with a vacuum drier to obtain a solder powder containing Ag and intermetallic compounds Ag ₃ Sn, Ag ₄ Sn as a core and Sn as a coating layer.

≪ Examples 2 to 7, Comparative Examples 1 and 2 >

As shown in the following Table 1, except that the ratio of silver contained in 100 mass% of the solder powder was changed by adjusting the addition amount of the sulfuric acid (I) and that the average particle diameter of the solder powder was controlled to a predetermined particle diameter, A solder powder was obtained in the same manner as in Example 1.

<Comparative Test and Evaluation>

For the solder powder obtained in Examples 1 to 7 and Comparative Examples 1 and 2, the structure of the metal particles constituting the powder, the average particle diameter of the powder and the composition thereof were analyzed or measured by the method described below. These solder powders were used to prepare solder pastes, respectively, and the bonding strength was evaluated. The results are shown in Table 1 below.

(1) Structural analysis: Structural analysis was performed with a powder X-ray diffractometer (Rigaku Corporation: RINT Ultima + / PC).

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

(3) Composition: The metal element content was measured by inductively coupled plasma emission spectrochemical analysis (ICP emission spectrometer: ICPS-7510 manufactured by Shimadzu Corporation).

(4) Bond strength: 50% by mass of diethylene glycol monohexyl ether as a solvent, 46% by mass of a polymerization rosin (softening point: 95 占 폚) as a rosin, 1.0% by mass of cyclohexylamine hydrobromide as an activator, 3.0% by mass of hardened castor oil was mixed to prepare a flux. Next, the flux and solder powder obtained in Examples 1 to 7 and Comparative Examples 1 and 2 were mixed at a ratio of flux of 88 mass% and solder powder of 12 mass%, respectively, to prepare solder paste.

The prepared paste was transferred to a predetermined position of a 0.5 mm thick Kovar (Fe-Ni-Co-based alloy) substrate using a pin having a diameter of the front end of 100 mu m by a pin transfer method. On the Kobar substrate, Ni plating and Au flash plating were further performed thereon. Subsequently, 0.9 mm 0.9 mm LED chips were mounted on the transferred paste. In addition, a bonded sample was obtained by reflowing at a predetermined maximum holding temperature in a nitrogen atmosphere in reflow furnace (Falcon 8500 manufactured by SIKAMA), and joining the LED chip and the COBAR substrate. The maximum holding temperature at the time of reflow was set at a different temperature of 250 ° C, 300 ° C and 350 ° C, respectively, and three bonded samples were obtained for each of Examples and Comparative Examples except for Comparative Example 1.

The bonding strength between the bonded Kovar substrate and the LED chip was measured according to the method of measuring the shear strength of the solder joint in the chip component of the lead-free solder test method described in JIS Z 3198-7 Shear strength at room temperature and 250 ° C were measured respectively and the relative shear strength at 250 ° C when the shear strength at room temperature was 100 was determined. In the table, &quot; Excellent &quot; indicates a case where the relative shear strength was 95 or more, &quot; Good &quot; indicates a case where the value was less than 95 or more than 80, 60 &lt; / RTI &gt;

As is apparent from Table 1, in Examples 1 to 7 and Comparative Examples 1 and 2, in Comparative Example 1 in which the content of silver was less than 10 mass%, the solidification starting temperature was too low, so that the solder remelted , And the evaluation of the evaluation of the bonding strength was all "impossible" in that the relative shear strength was lowered. On the other hand, in Comparative Example 2 in which the content of silver was more than 70% by mass, since the coagulation start temperature was too high, the solder powder did not melt at the time of reflow and sufficient bonding could not be obtained, All of the evaluations of the evaluation of the bonding strength became &quot; impossible &quot;. On the other hand, in Examples 1 to 7, the relative shear strength was improved with the increase of the content of silver, and all the evaluations of the evaluation of bond strength in a high-temperature atmosphere were both "possible" .

INDUSTRIAL APPLICABILITY The present invention can be suitably used for the mounting of electronic parts, particularly for mounting electronic parts exposed to a high temperature atmosphere.

10: solder powder
11: Core
12:

Claims (4)

A solder powder comprising a core and a coating layer covering the core, wherein the core is made of silver and an intermetallic compound of silver and tin, and the coating layer is tin,
Wherein the solder powder has an average particle diameter of 30 mu m or less,
Wherein a content of silver is more than 10 mass% and not more than 70 mass% with respect to 100 mass% of the total amount of the solder powder. The method according to claim 1,
Wherein the intermetallic compound of silver and tin is Ag ₃ Sn and / or Ag ₄ Sn. A solder paste obtained by mixing the solder powder according to claim 1 or 2 with a flux for solder to obtain a paste. A method for mounting an electronic component using the solder paste according to claim 3.

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