JP6428407B2 - Method for producing solder powder and method for producing solder paste using the powder - Google Patents

Description

The present invention relates to a method for producing a solder powder used for mounting electronic components and the like, and a method for producing a solder paste using this powder. More particularly, the present invention relates to a method for producing solder powder suitable for mounting electronic parts and the like that are unlikely to be remelted and reduced in bonding strength after reflow and exposed to a high temperature atmosphere, and a method for producing a solder paste using this powder. It is.

  Solder used for joining electronic parts and the like has been made lead-free from the viewpoint of the environment, and at present, solder powder mainly composed of tin is used. As a method for obtaining a fine metal powder such as a solder powder, in addition to an atomizing method such as a gas atomizing method or a rotating disk method, a melt spinning method, a rotating electrode method, a mechanical process, a chemical process, or the like is known. . As the gas atomizing method, a method is known in which after melting a metal in an induction furnace or a gas furnace, the molten metal is caused to flow down from a nozzle at the bottom of a tundish, and high pressure gas is sprayed from the surroundings to pulverize. The rotating disk method is also called a centrifugal atomizing method, and is a method in which a molten metal is dropped onto a rotating disk at high speed, and a shearing force is applied in a tangential direction to break and make a fine powder.

  In addition to the above-mentioned environmental characteristics, the solder is required to have various characteristics depending on the use of the electronic component to be mounted. For example, information electronic devices such as mobile phones and personal computers are required to be thinner and lighter with an emphasis on portability, and electronic components used in these manufactures are becoming smaller and finer pitches for joining components. Therefore, a solder powder having a finer particle size is required.

  On the other hand, in electronic parts used at high temperatures such as in-vehicle applications, it is necessary to prevent the solder after mounting from remelting by being exposed to a high temperature atmosphere and reducing the bonding strength. High heat resistance is required. In the case of the most common Sn—Pb type eutectic solder (composition ratio Sn: Pb = 63: 37% by mass), the melting point is about 187 ° C., and in the case of a general Sn—Ag—Cu type solder, It is about 217 ° C. In contrast, Au—Sn high temperature solder (composition ratio Sn: Au = 20: 80 mass%) known as heat resistant high temperature solder has a melting point of about 280 ° C., and Sn—Pb high temperature solder. (Composition ratio Sn: Pb = 5: 95% by mass) shows a high melting point of about 310 to 315 ° C.

  However, since the Au—Sn solder uses very expensive Au, there is a problem that the manufacturing cost increases. In addition, although Sn—Pb-based high-temperature solder exhibits very high heat resistance, it uses lead, and thus the above-mentioned environmental problems remain. In order to solve such problems, a technology is known that improves heat resistance, bonding strength, etc. by mixing low-melting and low-cost material powders that do not contain lead or gold with other material powders with high melting points. (For example, refer to 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 for contact between a ceramic member and a metal member. Further, Patent Document 2 does not contain lead, and Sn—Bi or the like, which has a melting point lower than that of a conventional tin-lead eutectic alloy, Sn—Ag or the like whose melting point is higher than that of a conventional tin-lead eutectic alloy. A solder paste containing a mixed powder obtained by mixing these alloy powders is disclosed. Patent Document 3 discloses cream solder in which metal particles such as Ag, Sn, and Cu having a higher melting point than eutectic solder are mixed in addition to eutectic solder. Patent Document 4 discloses a soldering composition in which a second metal component such as Ag or Cu having a melting point of 400 ° C. or higher is mixed with a first metal component such as Sn that does not contain lead. ing. Patent Document 5 includes a first metal component and a second metal component in powder form, and the first metal component is either a Sn—Cu based alloy or a Sn—Cu—Sb based alloy, or of these. One or more of Ag, In, Bi, Zn, or Ni is added to any of the above, and the second metal component is one or more metals of Cu, Sn, Sb, Ag, Zn, Ni, or these A composition for high-temperature cream solder, which is an alloy of two or more of these metals, is disclosed. Patent Document 6 includes a first metal powder that does not contain lead and contains tin as a main component, and a solder that contains a second metal powder that has a higher melting point than the first metal powder and mainly contains copper. A composition is disclosed.

  In the above-mentioned conventional Patent Documents 1 to 6, all use a solder powder obtained by mixing a low melting point metal powder not containing lead or gold and a high melting point metal powder, etc. As described above, in the solder powder obtained by mixing two or more powders having different melting points, compositions, etc., nonuniformity is likely to occur in the mixing of the powders. When non-uniformity occurs, partial melting unevenness and compositional deviation occur during reflow, which causes a problem that sufficient strength cannot be obtained at the joint portion.

  In order to solve this problem, the present applicant is composed of a central core and a coating layer that covers the central core, the central core is made of copper and an intermetallic compound of copper and tin, and the coating layer is made of tin. In the solder powder, the average particle size of the solder powder is 30 μm or less, and the copper content is more than 2.0 mass% and 40 mass% or less with respect to 100 mass% of the total amount of the solder powder. A patent application for the characteristic solder powder was made (see Patent Document 7). And the solder powder of this patent document 7 is manufactured by the following method. First, in a solvent such as water, alcohol, ether, ketone, ester, etc., a compound containing a central core, a metal element constituting the coating layer, that is, a compound containing copper such as copper (II) chloride and tin (II) chloride. A solution is prepared by adding and mixing such a tin-containing compound and a dispersant such as cellulose, vinyl, and polyhydric alcohol. The ratio of the compound containing tin and the compound containing copper in the solution is adjusted so that the content ratio of each metal element is within the above range after the solder powder is manufactured. Next, the pH of the prepared solution is adjusted to a range of 0 to 2.0 in consideration of re-dissolution of the generated solder powder. Next, a reducing agent aqueous solution is added to and mixed with the pH-adjusted solution, whereby each metal ion in the solution is reduced to obtain a dispersion in which metal powder is dispersed in the solution. In this reduction reaction, copper that is nobler than tin is first reduced, and finally tin is reduced. As a result, a metal powder having an average particle size of 30 μm or less, which is composed of a central core made of copper and a coating layer made of tin covering the central core, is formed. Subsequently, the dispersion is subjected to solid-liquid separation, and the collected solid is washed with water or a hydrochloric acid aqueous solution whose pH is 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 repeated 2 to 5 times. Further, 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, the central core made of copper of the metal powder formed by the above reduction reaction, a part of the coating layer made of tin covering the central core reacts, and a part thereof is made of copper and tin. A central nucleus composed of an intermetallic compound is formed. After heating, the steps from washing to solid-liquid separation are repeated 2 to 5 times, and then the collected solid content is vacuum-dried to obtain solder powder. In Patent Document 7, as Comparative Example 2, a reducing agent is added to a solution of copper chloride (II) and tin chloride (II) to reduce copper ions and tin ions, so that the total amount of solder powder becomes 100% by mass. On the other hand, the example which manufactures the solder powder whose content rate of copper is 60 mass% and whose content rate of tin is 40 mass% is disclosed.

JP-A-5-24943 (Claim 2, paragraph [0015]) JP-A-11-186712 (claim 2, paragraph [0018], paragraph [0023]) JP 2000-176678 A (Claims 1 and 3, paragraph [0010]) JP 2002-254195 A (Claims 1 to 5, paragraphs [0011] to [0013]) JP 2003-154485 A (Claim 1, paragraph [0009]) Japanese Patent No. 3782743 (Claims 1-4, paragraph [0005]) JP 2014-193473 A (Claim 1, paragraphs [0021], [0024] to [0034], [0051])

  As in Comparative Example 2 of Patent Document 7, a reducing agent is added to a solution of copper chloride (II) and tin chloride (II) to reduce copper ions to form a central core, and tin ions are reduced around it. When the copper content is increased to about 60% by the method of forming a coating layer (hereinafter referred to as a wet sequential deposition method of a central core and a tin coating layer), adjustment to a predetermined particle size, different production lots There is a problem that it is difficult to control the particle size such as the reproducibility of the particle size between them and the suppression of variation in the particle size distribution of the solder powder in the same production lot. Furthermore, accompanying the difficulty in controlling the particle size, there is a concern that the variation in the content ratio of tin and copper in each particle of the solder powder will increase, and the solder powder does not melt uniformly during reflow, resulting in However, there is a problem in that sufficient bonding strength cannot be obtained at the bonding site.

The first object of the present invention is to adjust the solder powder to a predetermined particle size, to achieve good reproducibility of the particle size between different production lots, and to reduce variation in the size distribution of the solder powder in the same production lot. An object of the present invention is to provide a solder powder manufacturing method capable of controlling the diameter. A second object of the present invention is to provide a method for producing a solder powder in which the solder powder is uniformly melted during reflow and sufficient bonding strength is obtained. A third object of the present invention is to provide a method for producing a solder powder which is less likely to be remelted and reduced in bonding strength when exposed to a high temperature atmosphere after reflow. Furthermore, the third object of the present invention is to provide a method for producing a solder paste using this powder, in which sufficient bonding strength can be obtained at the bonding site.

  As a result of repeated extensive research by the present inventors, instead of using a compound containing copper such as copper (II) chloride based on the wet sequential deposition method of the central core and the tin coating layer, it has a predetermined average particle size. Using copper powder with a small variation in particle size distribution, add this copper powder and dispersant to a solvent to prepare a copper powder dispersion, and then add and mix the tin-containing compound directly into this copper powder dispersion. When the solder powder is manufactured by a method of dissolving and reducing tin ions in the liquid in which the copper powder is dispersed (hereinafter referred to as a tin wet coating method on the copper powder), the copper content exceeds 40% by mass. The present inventors have found that it is possible to produce a solder powder that can be easily adjusted in particle size, that has good reproducibility of particle size between different production lots, and that has a small variation in particle size distribution. And by including at least 30% by mass of tin and changing the reflow conditions, the solder powder at the time of reflow can be uniformly and sufficiently melted and bonded to a substrate or the like, and even after being exposed to a high temperature atmosphere, The present inventors have found that the solder does not remelt, or a liquid phase does not occur in a part of the solder, and does not cause poor bonding with the substrate or the like, and has reached the present invention.

The first aspect of the present invention is a first step of preparing a first dispersion by dispersing copper powder having an average particle size in the range of 1 to 24 μm and a particle size distribution span value of less than 1.0 in a solvent. A second step of preparing a mixed solution in which the metal salt of tin is dissolved and the copper powder is dispersed by adding and mixing the metal salt of tin to the first dispersion of the copper powder, and the pH of the mixed solution A third step of adjusting to 0.1 to 2.0, and adding a reducing agent to the pH-adjusted liquid mixture and mixing them, tin ions are reduced, and precipitated tin covers the copper powder. a fourth step of preparing a 2 dispersion, the second dispersion liquid was subjected to solid-liquid separation, and a fifth step of obtaining a solder powder by drying the solid, wherein the solid-liquid separation, the in the first step With respect to the total amount of solder powder of 100% by mass, the copper powder has a copper content exceeding 40% by mass and 70 quality. % Was added to a less and with a metal salt of the tin in the second step was added pressure as the content of tin is less than 30 wt% to 60 wt%, as shown in FIG. 1, It is composed of a central core 11 and a coating layer 12 covering the central core 11, the central core 11 is made of copper and an intermetallic compound of copper and tin, and the coating layer 12 is made of tin, with an average particle diameter of 1 to 30 μm This is a method for producing a solder powder that is in the range and has a coefficient of variation of the average particle diameter of 0.15 or less. However, the span value of the particle size distribution of the copper powder is the particle diameter D ₁₀ , D ₅₀ when the accumulated amount occupies 10%, 50%, 90% in the accumulated particle amount curve of the particle size distribution measurement result, D ₉₀ is a value that serves as an index representing the dispersion of the particle size distribution obtained from the formula (D ₉₀ -D ₁₀ ) / D ₅₀ , and a series of steps from the first step to the fifth step using the same equipment. performed in and when to one lot to production lot of a group of solder powder produced, the variation coefficient of the average particle diameter, the manufacturing lot 5 lot said average particle standard deviation above the mean particle diameter in the case of The value divided by the diameter.

A second aspect of the present invention is an invention based on the first aspect, wherein the intermetallic compound of copper and tin further comprises Cu ₃ Sn, Cu ₆ Sn ₅ , Cu ₁₀ Sn ₃ and Cu ₄₁ Sn _11. It is one or two or more compounds selected from the group.

A third aspect of the present invention, the method of the first or second aspect to produce a solder powder, a method for producing a Ruha Sunda paste to a paste by mixing the solder powder and solder flux.

A fourth aspect of the present invention is a method for mounting an electronic component using the solder paste according to the third aspect .

The solder powder produced by the production how the solder powder of the first aspect of the present invention, in the cumulative particle weight curve of the average particle size is in the range of 1~24μm and span values of the particle size distribution (particle size distribution measurement result , An index representing the dispersion of the particle size distribution obtained from the formula (D ₉₀ -D ₁₀ ) / D ₅₀ from the particle diameters D ₁₀ , D ₅₀ , D ₉₀ when the integrated amount occupies 10%, 50%, 90% Copper value in the range of less than 1.0 is used as a constituent element of the core of the solder powder, and the coefficient of variation of the average particle size of the solder powder is 0.15 or less. Even if the ratio exceeds 40% by mass, the adjustment to a predetermined particle size, the reproducibility of the particle size between different production lots, and the same particle size distribution as the copper powder used in the same production lot Solder powder with a small variation in the size can be obtained. In the solder powder of the present invention, the powder surface is composed of tin having a low melting point. From these facts, even if the content ratio of tin is reduced as compared with the content ratio described in Patent Document 7, it is excellent in meltability and sinterability at the time of reflow. Unlike the solder powder described in Patent Document 7, the melting point of Cu ₆ Sn ₅ , Cu ₃ Sn or the like is high, because the content is higher than the content ratio of more than 2.0% by mass and 40% by mass or less. A bonding layer made of an intermetallic compound and copper can be formed.

In the solder powder produced by the method of the second aspect of the present invention, the intermetallic compound of copper and tin is selected from the group consisting of Cu ₃ Sn, Cu ₆ Sn ₅ , Cu ₁₀ Sn ₃ and Cu ₄₁ Sn _11. Or one or more compounds. To illustrate the melting point of this intermetallic compound, the melting point of the ε phase (Cu ₃ Sn) is 676 ° C., and the melting point of the η phase (Cu ₆ Sn ₅ ) is 415 ° C. Thus, when the solidification start temperature rises to about 640 to 760 ° C., remelting hardly occurs. For this reason, the solder powder produced by the method of the present invention has a feature that it does not remelt even when used for mounting electronic parts exposed to a high temperature atmosphere. In addition, in one metal particle constituting the powder, copper and tin are included, and since each variation in the content ratio and the particle size of the solder powder is small, the bonding strength due to melting unevenness or composition deviation at the time of reflow is reduced. Decrease can be prevented.

In a third aspect method for producing a solder paste of the present invention are prepared using a solder powder produced by the method of the present invention. Therefore, the manufactured solder paste, solder powder produced by the method of the present invention to have the above characteristics, uniformly and melted quickly during reflow, excellent meltability. Further, after reflowing, unlike the solder powder described in Patent Document 7, a bonding layer made of an intermetallic compound and silver is formed, and the melting solder powder forms an intermetallic compound having a higher melting point than that of Patent Document 7, and heat resistance Therefore, remelting due to heat hardly occurs. For this reason, the paste for solder manufactured by the method of the present invention can be suitably used for mounting electronic parts and the like exposed to a high temperature atmosphere.

In the method for mounting the 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 uniformly and quickly melted at the time of reflow. It can be mounted with high accuracy, and higher heat resistance can be imparted after mounting.

It is the figure which represented typically an example of the cross-sectional structure of the solder powder of embodiment of this invention.

  Next, an embodiment for carrying out the present invention will be described with reference to the drawings.

[Method for producing solder powder]
A method for producing the solder powder of the present invention will be described. First, a first dispersion is prepared by dispersing copper powder having an average particle diameter in the range of 1 to 24 μm in a solvent. A dispersant may be mixed in the solvent. Next, a metal salt of tin is added to and mixed with the first dispersion of copper powder to prepare a liquid mixture in which the metal salt of tin is dissolved and the copper powder is dispersed. Next, the pH of the mixed solution is adjusted to 0.1 to 2.0. By adding a reducing agent to the pH adjusted liquid mixture and mixing, tin ions are reduced, and after preparing a second liquid dispersion in which the deposited tin disperses the metal powder covering the copper powder, (2) The dispersion is subjected to solid-liquid separation, and the solid content thus separated is dried to obtain a solder powder. The ratio of the copper powder and the compound containing tin in the mixed liquid is adjusted so that the copper content exceeds 40% by mass and is equal to or less than 70% by mass after the solder powder is manufactured.

  The copper powder needs to have an average particle size of 1 μm or more and 24 μm or less, and the span value of the particle size distribution must be less than 1.0. If the lower limit is less than 1 μm, the average particle size of the solder powder produced by the method of the present invention does not reach the minimum value of 1 μm. When the average particle size of the solder powder is less than the minimum value of 1 μm, the specific surface area of the solder powder increases, and the meltability of the solder is lowered due to the influence of the surface oxide layer of the powder. Moreover, if it is less than 1 micrometer of the said lower limit, it will become difficult to exceed content of 40 mass% of copper which comprises solder powder. When the upper limit of 24 μm is exceeded, the average particle size of the solder powder exceeds the maximum value of 30 μm. When the average particle size of the solder powder exceeds the maximum value of 30 μm, the bump coplanarity is lowered when the bump is formed by the solder paste using the solder powder, and the uneven coating is applied when the pattern surface is coated with the solder. As a result, the entire surface of the pattern cannot be uniformly coated. The average particle size of the copper powder is preferably 2 to 10 μm. Also, when the span value of the particle size distribution is 1.0 or more, the coefficient of variation of the average particle size of the solder powder exceeds 0.15, so that the content ratio of tin and copper in each particle varies, and this solder powder is used. There is a problem that uneven melting and poor melting occur in solder bumps and solder coats obtained from the solder paste. This copper powder can be obtained not only by a chemical method using a reduction reaction but also by a physical method such as an atomizing method.

  Examples of the solvent of the first dispersion liquid in which the copper powder is dispersed include water, alcohol, ether, ketone, and ester. The prepared mixed solution is adjusted to a pH of 0.1 to 2.0 in consideration of re-dissolution of the generated solder powder. Note that a complexing agent may be added to the mixed solution to complex the tin element. By adding the complexing agent, tin ions do not precipitate even when the pH is alkaline, and synthesis in a wide range is possible. Examples of the complexing agent include succinic acid, tartaric acid, glycolic acid, lactic acid, phthalic acid, malic acid, citric acid, oxalic acid, ethylenediaminetetraacetic acid, iminodiacetic acid, nitrilotriacetic acid, and salts thereof. Examples of the dispersant include cellulose-based, vinyl-based, and polyhydric alcohols. In addition, gelatin, casein, and the like can be used. The dispersant may be added after adding the complexing agent.

  Examples of the tin compound used for preparing the mixed solution include tin metal salts such as tin (II) chloride, tin (II) sulfate, tin (II) acetate, and tin (II) oxalate. Among these, it is particularly preferable to use tin (II) chloride as a hydrochloride as the compound containing tin.

  Next, when adding a reducing agent to the pH-adjusted mixed solution, it is preferable to prepare an aqueous solution in which the reducing agent is dissolved in advance and adjust the pH of the aqueous solution to the same level as the mixed solution. Examples of the reducing agent include boron hydrides such as sodium tetrahydroborate and dimethylamine borane, nitrogen compounds such as hydrazine, metal ions such as trivalent titanium ions and divalent chromium ions, and the like.

  Next, a reducing agent aqueous solution is added to and mixed with the above mixed solution, whereby tin ions in the mixed solution are reduced, and a second dispersion in which the metal powder covering the copper powder with the deposited tin is dispersed is obtained. . By this reduction reaction, a metal powder composed of a central core made of copper and a coating layer made of tin covering the central core is formed. As a method of mixing the mixed solution and the reducing agent aqueous solution, the reducing agent aqueous solution is dropped into the mixed solution in the container at a predetermined addition rate and stirred with a stirrer or a reaction tube having a predetermined diameter. Examples include a method of pouring both solutions into a reaction tube at a predetermined flow rate and mixing them.

  Next, the second dispersion liquid in which the metal powder is dispersed is subjected to solid-liquid separation by decantation or the like, and the recovered solid content is water or a hydrochloric acid aqueous solution, a nitric acid aqueous solution, a sulfuric acid aqueous solution whose pH is adjusted to 0.5 to 2, or Wash with methanol, ethanol, acetone, etc. After washing, the solid content is recovered by solid-liquid separation again. The solder powder of the present invention can be obtained by repeating the steps from washing to solid-liquid separation, preferably 2 to 5 times, and then vacuum-drying the collected solid content.

  Further, the heat treatment described below may be performed. A high boiling point solvent having a boiling point of 100 ° C. or higher is added to and dispersed in the collected solid content before vacuum drying, and heated at a predetermined temperature in an inert gas atmosphere. By applying this heat treatment, the central core made of copper of the metal powder formed by the above reduction reaction reacts with a part of the coating layer made of tin covering the central core, and compared with the case where the heat treatment is not performed. Thus, a central core having a layer made of a thicker intermetallic compound of copper and tin is formed.

  Examples of the high boiling point solvent used include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, and castor oil.

  The heat treatment is preferably performed at a temperature of 100 to 130 ° C. for 20 minutes to 1 hour in an inert gas atmosphere such as nitrogen or argon. When the treatment temperature or holding time is less than the lower limit value, an intermetallic compound may not be formed in the central core. On the other hand, when the treatment temperature exceeds the upper limit value, tin in the coating layer is oxidized, resulting in a problem that the meltability is lowered. The effect does not change even if the holding time is set to the upper limit value or more. Among these, it is particularly preferable to carry out at a temperature of 115 to 125 ° C. for 30 to 40 minutes. The reason why the reaction is performed in an inert gas atmosphere is to prevent oxidation of tin.

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

[Solder powder]
As shown in FIG. 1, the solder powder produced by the method of the present invention is composed of a central core 11 and a coating layer 12 covering the central core 11, and the central core 11 is copper and an intermetallic compound of copper and tin. The coating layer 12 is a solder powder made of tin. Thus, the solder powder of the present invention basically has a structure in which the central core made of copper and an intermetallic compound of copper and tin is coated with a coating layer made of tin having a low melting point. Excellent meltability at the time. In addition to this, since the solder powder of the present invention is manufactured with copper powder as the central core, it is easy to adjust the particle size of the solder powder, the reproducibility of the particle size between different production lots, and the particle size distribution. Variation can also be reduced. Furthermore, the variation in the content ratio of tin and copper in the solder powder is reduced, and the meltability during reflow is excellent. Unlike the conventional solder powder, it is not a powder in which two or more kinds of metal powders having different melting points are mixed, but copper and tin are contained in one metal particle constituting the powder. And composition deviation hardly occur, and high bonding strength can be obtained. Furthermore, since a part of the central core has already formed an intermetallic compound of copper and tin before reflowing, for example, compared to a powder having a structure in which the central core made of copper is covered with tin, melting at the time of reflowing Good diffusibility, easy composition control during solder bump formation, and excellent wettability.

The solder powder 10 produced by the method of the present invention has an average particle diameter of 1 to 30 μm and a coefficient of variation of the average particle diameter of 0.15 or less. The reason why the average particle size of the solder powder is limited to 1 to 30 μm is that when it exceeds 30 μm, the bump coplanarity deteriorates when the bump is formed, and the coating unevenness occurs when the pattern surface is coated with solder. This is because a problem arises that the entire pattern surface cannot be uniformly coated. When the thickness is less than 1 μm, the specific surface area increases, and the meltability of the solder decreases due to the influence of the surface oxide layer of the powder. The average particle size of the solder powder is preferably in the range of 2 μm to 12 μm. In the present specification, the average particle size of the powder was measured with a particle size distribution measuring device (Horiba Seisakusho, laser diffraction / scattering particle size distribution measuring device LA-950) using a laser diffraction scattering method. Volume cumulative median diameter (Median diameter, D ₅₀ ). Also, if the coefficient of variation of the average particle size of the solder powder exceeds 0.15, the content ratio of tin and copper in each particle will vary, and it will melt in the solder bump and solder coat obtained by the solder paste using this solder powder. There are defects that cause unevenness and poor melting.

  Moreover, as for the solder powder 10 manufactured by the method of this invention, the content rate of copper exceeds 40 mass% and is 70 mass% or less with respect to 100 mass% of the whole quantity of powder. Since conventional solder powder is used as an alternative to Sn—Pb-based eutectic solder (composition ratio Sn: Pb = 63: 37 mass%), the melting point is close and the eutectic composition is required. The proportion is about 0.7% by mass and relatively small. On the other hand, in the solder powder of the present invention, an Sn—Cu alloy having a high solidification start temperature of about 640 to 760 ° C. is formed after reflowing by including a copper ratio in the above-mentioned range which is larger than that of Patent Document 7. To do. Even if the content ratio of copper is small, after reflowing, a Sn—Cu alloy having a higher solidification start temperature than tin is formed. However, if more copper is contained, the solidification start temperature is further increased. This is because the ratio of the intermetallic compound having a high melting point in the alloy is further increased. Thereby, in the solder bump formed by reflow of the solder paste containing this solder powder, the heat resistance is greatly improved, and remelting and reduction in bonding strength can be prevented. For this reason, it can be suitably used as a high-temperature solder used for mounting electronic parts and the like exposed to a high-temperature atmosphere. When the copper content is 40% by mass or less, the solidification start temperature is low, so that sufficient heat resistance cannot be obtained in the solder bump formed after reflow, remelting occurs when used in a high temperature atmosphere, and high temperature. It cannot be used as solder. On the other hand, if it exceeds 70% by mass, the solidification start temperature becomes too high, and the solder does not melt sufficiently, resulting in a problem that bonding failure occurs. Among these, it is preferable that the content rate of the copper which occupies for 100 mass% of the whole quantity of powder exceeds 40 mass%, and is 62 mass% or less.

  Further, the content ratio of tin in the solder powder produced by the method of the present invention is 30% by mass or more and less than 60% by mass with respect to the remainder other than the copper in the powder, that is, 100% by mass of the total amount of the solder powder. Preferably they are 38 mass% or more and less than 60 mass%. This is because if the tin content is less than 30% by mass, the low melting point required for the solder powder is not exhibited during reflow. Moreover, if it is 60 mass% or more, the content rate of copper will decrease as a result and the heat resistance of the solder bump formed after reflow will fall. That is, when the solder after mounting is exposed to a high temperature atmosphere, the solder after mounting may be remelted or a liquid phase may be generated in a part of the solder, which may reduce the bonding strength with the substrate or the like.

As an intermetallic compound of copper and tin constituting a part of the central core, one or more selected from the group consisting of Cu ₃ Sn, Cu ₆ Sn ₅ , Cu ₁₀ Sn ₃ and Cu ₄₁ Sn ₁₁ In practice, Cu ₃ Sn and Cu ₆ Sn ₅ mainly form a central nucleus depending on the composition ratio of copper and tin.

[Solder paste and its preparation method]
The solder powder of the present invention obtained by the above manufacturing process is suitably used as a material for a solder paste obtained by mixing with a solder flux to form a paste. The solder paste is prepared by mixing solder powder and solder flux at a predetermined ratio to form a paste. The solder flux used for the preparation of the solder paste is not particularly limited, but a flux prepared by mixing components such as a solvent, rosin, thixotropic agent and activator can be used.

  Solvents suitable for preparing the solder flux include diethylene glycol monohexyl ether, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, tetraethylene glycol, 2-ethyl-1,3-hexanediol, α-terpineol and the like having a boiling point of 180. An organic solvent having a temperature of not lower than ° C. can be mentioned. Examples of the rosin include gum rosin, hydrogenated rosin, polymerized rosin, and ester rosin.

  Further, as the thixotropic agent, hardened castor oil, fatty acid amide, natural fats and oils, synthetic fats and oils, N, N′-ethylenebis-12-hydroxystearylamide, 12-hydroxystearic acid, 1,2,3,4-dibenzylidene- Examples include D-sorbitol and its derivatives.

  The activator is preferably a hydrohalic acid amine salt, specifically, triethanolamine, diphenylguanidine, ethanolamine, butylamine, aminopropanol, polyoxyethyleneoleylamine, polyoxyethylenelaurylamine, polyoxyethylene. Stearylamine, diethylamine, triethylamine, methoxypropylamine, dimethylaminopropylamine, dibutylaminopropylamine, ethylhexylamine, ethoxypropylamine, ethylhexyloxypropylamine, bispropylamine, isopropylamine, diisopropylamine, piperidine, 2,6-dimethyl Piperidine, aniline, methylamine, ethylamine, butylamine, 3-amino-1-propene, isopropylamine , Dimethyl hexyl amines, hydrochloric acid salt or hydrobromide of an amine such as cyclohexylamine. In addition, organic acids, amines and salts thereof can be used.

  The soldering flux can be obtained by mixing the above components at a predetermined ratio. It is preferable that the ratio of the solvent in the total amount of flux of 100% by mass is 30 to 60% by mass, the ratio of the thixotropic agent is 1 to 10% by mass, and the ratio of the activator is 0.1 to 10% by mass. If the solvent ratio is less than the lower limit, the viscosity of the flux will be too high, so the viscosity of the solder paste using this will also increase accordingly, resulting in poor printability, such as poor solder filling and uneven coating. May cause malfunctions. On the other hand, when the upper limit is exceeded, the viscosity of the flux becomes too low, and the viscosity of the solder paste using the flux also decreases accordingly, which may cause a problem that the solder powder and the flux component settle and separate. In addition, when the ratio of the thixotropic agent is less than the lower limit, the viscosity of the solder paste becomes too low, which may cause a problem that the solder powder and the flux component are settled and separated. On the other hand, when the upper limit is exceeded, the viscosity of the solder paste becomes too high, which may cause problems such as poor solderability and poor printability such as coating unevenness. In addition, if the ratio of the activator is less than the lower limit value, the solder powder may not be melted and a sufficient bonding strength may not be obtained. On the other hand, if the upper limit value is exceeded, the activator may become solder powder during storage. This may cause a problem that the storage stability of the solder paste is lowered. In addition, a viscosity stabilizer may be added to the solder flux. Examples of the viscosity stabilizer include polyphenols that can be dissolved in a solvent, phosphoric acid compounds, sulfur compounds, tocophenols, tocophenol derivatives, ascorbic acid, ascorbic acid derivatives, and the like. If there are too many viscosity stabilizers, problems such as a decrease in the meltability of the solder powder may occur.

  The amount of solder flux mixed when preparing the solder paste is preferably such that the proportion of the flux in 100% by mass of the prepared paste is 5 to 30% by mass. If it is less than the lower limit, it becomes difficult to form a paste due to insufficient flux, while if it exceeds the upper limit, the content of the flux in the paste is too high and the content of metal is reduced, and solder bumps of the desired size when melting the solder This is because it becomes difficult to obtain.

  Since this solder paste is made of the above-described solder powder of the present invention, melting at the time of reflow is fast and excellent in meltability, and after reflow, the melting solder powder forms an intermetallic compound having a high melting point, Since heat resistance increases, remelting due to heat hardly occurs. For this reason, the solder paste of the present invention can be suitably used for mounting electronic components exposed to a high temperature atmosphere.

[Electronic component mounting method and joint using solder paste]
To mount electronic parts such as silicon chips and LED chips on various heat dissipation boards, FR4 (Flame Retardant Type 4) boards, and Kovar boards using the solder paste prepared by the above method, use the pin transfer method. The solder paste is transferred to a predetermined position of the substrate, or the solder paste is printed at a predetermined position by a printing method. Next, a chip element which is an electronic component is mounted on the transferred or printed paste. In this state, the solder powder is reflowed by holding in a reflow furnace in a nitrogen atmosphere at a temperature of 250 to 400 ° C. for 5 to 120 minutes. In some cases, the chip and the substrate may be joined while being pressed. Thus, the chip element and the substrate are bonded to obtain a bonded body, and the electronic component is mounted on the substrate.

  Next, examples of the present invention will be described in detail together with comparative examples.

<Example 1>
In Example 1, solder powder was manufactured by the tin wet coating method to copper powder. First, 2.20 g of copper powder having an average particle diameter of 1.0 μm and an average particle diameter span value of 0.9 was dispersed in 50 mL of water to prepare a first dispersion. To this dispersion, 2.56 × 10 ⁻² mol of tin (II) chloride was added and stirred for 5 minutes at a rotational speed of 300 rpm using a stirrer to prepare a mixed solution. After adjusting the pH of this mixed liquid to 0.5 with hydrochloric acid, 0.5 g of polyvinyl alcohol 500 (polyvinyl alcohol having an average molecular weight of 500) was added as a dispersant, and the mixture was further stirred for 10 minutes at a rotation speed of 300 rpm. Next, 50 mL of a 1.58 mol / L divalent chromium ion aqueous solution whose pH was adjusted to 0.5 was added to this mixed solution at an addition rate of 50 mL / sec. Reduced. A second dispersion was obtained in which the metal powder covering the copper powder with the tin deposited by this reduction was dispersed. The dispersion was allowed to stand for 60 minutes to settle the metal powder, and then the supernatant was discarded, 100 mL of water was added thereto, and the mixture was stirred for 10 minutes at a rotational speed of 300 rpm, and washed four times. It was. Finally, this was dried with a vacuum dryer to obtain a solder powder having Cu and intermetallic compounds Cu ₃ Sn and Cu ₆ Sn ₅ as the central core and Sn as the coating layer.

<Examples 2 to 25 and Comparative Examples 1 to 14>
Also in Examples 2 to 25 and Comparative Examples 1 to 14, solder powder was produced by a tin wet coating method on copper powder. As shown in Tables 1 and 2 below, copper powders having different average particle diameters and span values are used, or the amount of copper powder added is adjusted to be included in 100% by mass of solder powder. A solder powder was obtained in the same manner as in Example 1 except that the ratio of copper to be used was changed and the average particle size of the solder powder was controlled to a predetermined particle size.

<Comparative Example 15>
In Comparative Example 15, solder powder was produced by a wet sequential deposition method of a central core and a tin coating layer. First, 3.46 × 10 ⁻² mol of copper (II) chloride and 2.56 × 10 ⁻² mol of tin (II) chloride were added to 50 mL of water, and the mixture was stirred for 5 minutes at a rotation speed of 300 rpm using a stirrer. A lysis solution was prepared. After adjusting the pH of this solution to 0.5 with hydrochloric acid, 0.5 g of polyvinyl alcohol 500 (polyvinyl alcohol having an average molecular weight of 500) was added as a dispersant, and the mixture was further stirred for 10 minutes at a rotation speed of 300 rpm. Next, 50 mL of a 1.58 mol / L divalent chromium ion aqueous solution whose pH was adjusted to 0.5 was added to this solution at an addition rate of 50 mL / sec and stirred for 10 minutes at a rotational speed of 500 rpm. To obtain a dispersion in which the metal powder is dispersed in the liquid. The dispersion was allowed to stand for 60 minutes to settle the metal powder, and then the supernatant was discarded, 100 mL of water was added thereto, and the mixture was stirred for 10 minutes at a rotational speed of 300 rpm, and washed four times. It was. Thereafter, 100 mL of ethylene glycol was added and dispersed, and the mixture was heated at 120 ° C. for 30 minutes while stirring at a rotation speed of 300 rpm. After heating, the dispersion was allowed to stand again for 60 minutes to settle the heated metal powder, and then the supernatant was discarded, 100 mL of water was added thereto, and the operation of stirring at a rotational speed of 300 rpm for 10 minutes was repeated four times. Washing was performed. Finally, this was dried with a vacuum dryer to obtain a solder powder having Cu and intermetallic compounds Cu ₃ Sn and Cu ₆ Sn ₅ as the central core and Sn as the coating layer.

<Comparative Examples 16-19>
Also in Comparative Examples 16 to 19, solder powder was produced by the wet sequential deposition method of the central core and the tin coating layer. As shown in Table 3 below, the ratio of copper and tin contained in 100% by mass of solder powder was changed by adjusting the amount of copper (II) chloride or the amount of tin (II) chloride added. A solder powder was obtained in the same manner as in Comparative Example 15 except that the average particle size of the solder powder was controlled to a predetermined particle size.

<Comparison test and evaluation>
About the copper powder used in Examples 1-25 and Comparative Examples 1-19, and the solder powder obtained in the Examples and Comparative Examples, the structure of the solder powder, the average particle diameter of the copper powder and the solder powder, and each The particle size distribution variation (span value) was measured by the following method. Further, the coefficient of variation of the average particle diameter between solder powder production lots and the content ratio of tin and copper in the solder powder were measured by the following methods. These results are shown in Tables 1 to 3 below. In addition, solder pastes were prepared using these solder powders, and the bonding strength when the maximum holding temperature during reflow was changed was evaluated. These results are shown in Tables 4 to 10 below.

  (1) The structure of the solder powder was analyzed by a powder X-ray diffractometer (manufactured by Rigaku Corporation: RINT Ultimate + / PC).

(2) Regarding the dispersion of the average particle size and the particle size distribution (span value) of the copper powder, the particle size distribution measuring device using laser diffraction scattering method (manufactured by Horiba, Ltd., laser diffraction / scattering type particle size distribution measurement) The measurement was performed by measuring the particle size distribution of the copper powder with an apparatus LA-950). The average particle size _is determined by _{D 50,} span values _were determined from the equation _{(D 90 -D 10) / D} 50.

(3) For the average particle size of solder powder, variation in particle size distribution (span value), and coefficient of variation of average particle size between production lots, use the same particle size distribution measuring apparatus as described above using the laser diffraction scattering method. This was done by measuring the particle size distribution of the solder powder. The average particle size _is determined by _{D 50,} span values _were determined from the equation _{(D 90 -D 10) / D} 50. The coefficient of variation of the average particle diameter between production lots was determined from the formula D _{50 —dev} / D _{50 —ave} . D _{50 — ave} refers to the average value of the average particle diameter in the five manufactured lots, and D _{50 — dev} refers to the standard deviation of the average particle diameter in the five manufactured lots.

In the above (2) and (3), D ₁₀ , D ₅₀ and D ₉₀ are the particle size distribution measurement results (when the integrated amount occupies 10%, 50% and 90% in the integrated particle amount curve). Represents the particle size.

  (4) The content ratio of tin and copper in the solder powder was determined by inductively coupled plasma emission spectroscopic analysis (ICP emission analyzer: ICPS-7510 manufactured by Shimadzu Corporation).

  (5) The bonding strength was determined by the following method. First, 50% by mass of diethylene glycol monohexyl ether as a solvent, 46% by mass of polymerized rosin (softening point 95 ° C.) as rosin, 1.0% by mass of cyclohexylamine hydrobromide as an activator, and thixotropic agent A flux was prepared by mixing 3.0% by mass of hardened castor oil. Next, this flux and the solder powder obtained in Examples 1 to 20 and Comparative Examples 1 to 14 are mixed at a ratio of 88 mass% flux and 12 mass% solder powder, respectively, and solder paste is obtained. Prepared.

  The prepared paste was transferred to a predetermined position on a 0.5 mm thick Kovar (Fe—Ni—Co alloy) substrate using a pin having a diameter of 100 μm by a pin transfer method. The Kovar substrate was Ni-plated, and further Au flash-plated. Subsequently, a 0.9 mm □ LED chip was mounted on the transferred paste. Furthermore, while pressing the LED chip and the substrate at a pressure of 1.0 MPa using a pressurizing jig, a predetermined maximum holding temperature for 0.5 hours in a nitrogen atmosphere in a reflow furnace (SIKAMA Falcon 8500) The sample was obtained by reflowing and bonding the LED chip and the Kovar substrate. In addition, the maximum holding temperature at the time of the reflow was set to different temperatures of 250 ° C., 300 ° C., and 350 ° C., and three bonded samples were obtained for each of the examples or comparative examples.

  Regarding the bonding strength between the above-mentioned Kovar substrate and the LED chip, in accordance with “Lead-free solder test method described in JIS Z 3198-7—Part 7:“ Measurement method of shear strength of solder joint in chip parts ” The joint shear strength after holding at room temperature and 300 ° C. for 0 hour and 500 hours was measured, respectively. Further, the relative shear strength after holding at 300 ° C. for 0 hour and 500 hours when the shear strength at room temperature was 100 was determined. In the table, “excellent” indicates a case where the relative share strength is 90 or more, “good” indicates a case where it is less than 90 to 80 or more, and “good” indicates less than 80 to 70 or more. Indicates that there was a case, “impossible” indicates a case where it was less than 70

  From Tables 3 to 10, the following was found when Examples 1 to 25 and Comparative Examples 1 to 19 were compared.

(1) Structure of solder powder All the solder powders obtained in Examples 1 to 25 and Comparative Examples 1 to 19 have a central core formed of Cu, Cu ₃ Sn, and Cu ₆ Sn ₅ , and the central core is Sn. It was covered with.

(2) In Comparative Examples 5 to 9 where the average particle size of the copper powder and the solder powder was 0.5 μm when the solder powder was produced by the tin wet coating method on the copper powder. The average particle size of the solder powder was 0.52 to 0.60 μm, the specific surface area was increased, the ratio of the oxide film on the surface to the powder was increased, and the solder was not melted. As a result, the initial (0 hour, 300 ° C.) bonding was poor, and the bonding strength could not be determined. Further, in Comparative Examples 10 to 14 in which the average particle size of the copper powder was 30.0 μm when the solder powder was manufactured by the tin wet coating method on the copper powder, the average particle size of the solder powder was 31.3 to 36.0 μm. Thus, since the relative shear strength after holding at 300 ° C. for 500 hours was as low as 50 to 69, all the evaluation judgments of the bonding strength after holding for 500 hours were “impossible”. On the other hand, Example 1 in which the average particle diameter of the copper powder when the solder powder is produced by the wet tin coating method on the copper powder is 1 to 24 μm, and the average particle diameter of the solder powder is 1 to 30 μm. ˜25, the relative shear strength is improved, and all the judgments after holding for 0 hour and 500 hours of evaluation of the bonding strength in a high temperature atmosphere are “good”, “good” or “excellent”. It was. Particularly in Examples 1 to 5 in which the average particle diameter of the copper powder is 1.0 μm and Examples 21 to 24 in which the average particle diameter is 24.0 μm, the evaluation of the bonding strength in a high-temperature atmosphere is performed for 0 hour and 500 hours after holding. While all the judgments were “good”, in Examples 6 to 20 in which the average particle diameter was 2.0 to 10.0 μm, all of the above judgments were “good”, “good” or “excellent”. Results were obtained.

(3) Particle size distribution variation (span value) and bonding strength of copper powder In Comparative Examples 5 to 9 in which solder powder was manufactured by a tin wet coating method on copper powder, particle size distribution variation (span value) of copper powder This is because the content ratio of tin and copper in each particle varies, resulting in uneven melting and poor melting in solder bumps and solder coats obtained by solder paste using this solder powder. The solder did not melt. As a result, the initial (0 hour, 300 ° C.) bonding was poor, and the bonding strength could not be determined. In contrast, in Examples 1 to 25 in which the dispersion (span value) of the particle size distribution of the solder powder produced by the tin wet coating method on the copper powder is less than 1.0, the relative shear strength is improved. In addition, all the determinations after holding for 0 hour and 500 hours in the evaluation of the bonding strength in a high temperature atmosphere were all “good”, “good” or “excellent”.

(4) Coefficient of variation of average particle diameter between production lots and bonding strength In Comparative Examples 5 to 9 in which solder powder was produced by a tin wet coating method on copper powder, the span value of the copper powder was 1.0, Since the dispersion of the particle size distribution was large, the variation coefficient of the average particle size between production lots was 0.18. Further, in Comparative Examples 15 to 19 in which the solder powder was manufactured by the wet sequential deposition method of the central core and the tin coating layer, the generation speed or growth speed of the central core and the growth speed of the tin coating layer are the liquid temperature, the liquid stirring speed, etc. This greatly depends on the powder synthesis conditions, which makes it difficult to suppress variations in the powder synthesis conditions such as the liquid temperature and the liquid stirring speed among production lots, and the coefficient of variation of the average particle size is 0.30. . For this reason, in Comparative Examples 5 to 9 and Comparative Examples 15 to 19, variation occurs in the content ratios of tin and copper in each particle, and in the solder bumps and solder coats obtained by the solder paste using this solder powder, melting unevenness and melting The solder did not melt due to the failure. As a result, the initial (0 hour, 300 ° C.) bonding was poor, and the bonding strength could not be determined.

(5) Content ratio of tin and copper in solder powder In Comparative Example 1 and Comparative Example 3 in which the content ratio of copper in the solder powder produced by the wet coating method of tin on the copper powder is 40% by mass, the solidification start temperature is Since the solder was remelted because it became lower and the relative shear strength after holding at 300 ° C. for 500 hours decreased to 54 to 69, the evaluation judgment of the joint strength after holding for 500 hours was all “impossible” became. On the other hand, in Comparative Example 2 and Comparative Example 4 in which the copper content in the solder powder manufactured by the same method exceeds 70% by mass, the soldering powder does not melt at the time of reflow because the solidification start temperature is too high. Therefore, the joint shear strength could not be measured, and all the joint strength evaluation judgments after holding for 500 hours were “impossible”. On the other hand, in Examples 1 to 25 in which the copper content in the solder powder produced by the same method exceeds 40% by mass and is 70% by mass or less, the relative shear strength is improved, and the bonding strength in a high-temperature atmosphere is increased. A good result was obtained that all the judgments after the evaluation were held for 0 hour and 500 hours were “OK”, “Good” or “Excellent”.

  The solder powder produced by the method of the present invention can be suitably used for mounting electronic components exposed to a high temperature atmosphere.

10 Solder powder 11 Central core 12 Coating layer

Claims (4)

A first step of preparing a first dispersion by dispersing a copper powder having an average particle size in the range of 1 to 24 μm and a span value of the particle size distribution of less than 1.0 in a solvent;
A second step of adding a tin metal salt to the first dispersion of the copper powder to prepare a mixed solution in which the tin metal salt is dissolved and the copper powder is dispersed;
A third step of adjusting the pH of the mixed solution to 0.1 to 2.0;
A fourth step of preparing a second dispersion in which tin ions are reduced by adding a reducing agent to the pH-adjusted mixture and mixing, and the precipitated tin covers the copper powder;
And a fifth step of solid-liquid separating the second dispersion, and drying the solid-liquid separated solid to obtain a solder powder.
In the first step, the copper powder is added so that the copper content is more than 40% by mass and less than 70% by mass with respect to the total amount of the solder powder of 100% by mass, and in the second step, the tin powder is added. and a metal salt and added pressure, as the content of tin is less than 30 wt% to 60 wt%, is composed of a coating layer which covers the central core of the central core, the central core is copper and copper and tin A solder powder having an average particle diameter in the range of 1 to 30 μm and a coefficient of variation of the average particle diameter of 0.15 or less.
However, the span value of the particle size distribution of the copper powder is the particle diameter D ₁₀ , D ₅₀ when the accumulated amount occupies 10%, 50%, 90% in the accumulated particle amount curve of the particle size distribution measurement result, than D _90, it refers to a value as an index representing the variation in the particle size distribution obtained from the equation _{(D 90 -D 10) / D} 50, carried out in a series of steps in the same equipment up to the fifth step from the first step when the production lot of a group of solder powder and one lot to be manufactured Te, wherein the variation coefficient of the average particle diameter, the standard deviation of the average particle diameter when the production lot is 5 lots said average particle size The value divided by. The intermetallic compound of copper and tin is one or more compounds selected from the group consisting of Cu ₃ Sn, Cu ₆ Sn ₅ , Cu ₁₀ Sn ₃ and Cu ₄₁ Sn ₁₁ . A method for producing solder powder. The method according to manufacture the solder powder by the method of claim 1, Ruha Sunda paste to a paste by mixing the solder powder and solder flux. A method for mounting an electronic component using the solder paste according to claim 3 .