JP2018131666A - Tin coat copper powder, manufacturing method thereof and conductive paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide tin coat copper powder that can be favorably used as a material for a conductive paste, etc. through covering a surface of copper powder with tin (Sn) or a tin alloy, the tin coat copper alloy simultaneously having sinterability and oxidation resistance while being minute, high crystal and high filling, and also to provide a manufacturing method thereof and a conductive paste.SOLUTION: Tin coat copper powder has copper particles having an octahedral particle and a granular particle other than octahedron mixed together, a surface of the copper particle is covered with tin or a tin alloy. In the tin coat copper powder, an average particle diameter is 0.1-3.0 μm, a crystallite diameter of the copper particle/the average particle diameter of the tin coat copper powder is 0.10 or more, and a tap density is 3.0-5.0 g/cm. A coating amount of the tin or the tin alloy is 1-33 mass% with regard to the tin coat copper powder in total.SELECTED DRAWING: None

Description

  The present invention relates to a tin-coated copper powder and a method for producing the same, and a conductive paste. More specifically, the surface of the copper powder is coated with tin (Sn) or a tin alloy so that a material such as a conductive paste can be highly filled. The present invention relates to a fine and highly crystalline tin-coated copper powder having both sinterability and oxidation resistance, a method for producing the same, and a conductive paste.

  In order to form wiring layers, electrodes, and the like in electronic devices, conductive pastes using metal fillers such as silver powder and copper powder, such as resin pastes and fired pastes, are frequently used. A paste using a metal filler such as silver powder or copper powder is applied or printed on various substrates, and is subjected to heat curing or heat baking treatment to form a conductive film to be a wiring layer, an electrode, or the like.

  Also, as integration and density increase in the electronic material field, as a multilayering method, a through hole (through hole) is provided to obtain conduction between the front and back surfaces of the printed wiring board, and the wall surface portion There is a method in which through-hole plating is applied to the through hole and a conductive paste is filled in the through hole.

  The type of paste is a resin-type conductive paste, which consists of a metal filler, resin, curing agent, solvent, etc., printed on a conductor circuit pattern or terminal, and heated and cured at 100 ° C to 200 ° C. A conductive film is formed, and wiring and electrodes are formed. In the resin-type conductive paste, since the thermosetting resin is cured and contracted by heat, the metal fillers are pressed and brought into contact with each other, so that the metal fillers overlap each other, and as a result, an electrically connected current path is formed. . Furthermore, since the metal powder generally has a higher sinterability as the particle size becomes finer, the use of a metal filler having a smaller particle size also increases the sintering effect and lowers the resistance. Since this resin-type conductive paste is processed at a curing temperature of 200 ° C. or lower, it is used for a substrate using a heat-sensitive material such as a printed wiring board. As the metal filler used in this resin-type conductive paste, silver powder, copper powder, silver-coated copper powder, or the like is used.

  Another type of paste is a baked conductive paste, which consists of a metal filler, glass, solvent, etc., printed on a conductor circuit pattern or terminal, and baked at a high temperature of 600 ° C to 800 ° C. Thus, a conductive film is formed, and wirings and electrodes are formed. In the firing type conductive paste, it is processed at a high temperature, and the metal filler is sintered to ensure conductivity. Since the fired conductive paste is treated at such a high firing temperature, the metal particles are diffused and alloyed to conduct, and high connection reliability can be expected. Examples of the metal filler used in the fired conductive paste include eutectic solder (Sn—Pb alloy), Pb-free solder powder (for example, Sn—Ag—Cu alloy), copper powder with tin (Sn) plating, and silver powder. And those plated with Sn.

However, in the case of lead-containing solder, when a wiring board or the like using it is discarded, lead is eluted and there is a risk of environmental pollution. .
As a Pb-free solder powder that is an alternative to the Sn—Pb alloy, a binary or multi-element Sn alloy containing silver, bismuth, copper, indium, antimony, zinc or the like can be cited as a candidate. With this Pb-free solder powder, via holes are formed in order to obtain electrical continuity between layers as a multilayer substrate from the viewpoint of producing a higher performance wiring substrate, and the via holes are filled with a conductive paste or plating. . When the conductive paste is filled, it is required that the conductive paste composition in the via is highly metal diffusion bonded to reduce the resistance value of the via. However, there is a problem that the Sn alloy having a melting point lower than the stacking temperature is melted by the temperature at the time of stacking, and the filled shape is deformed due to deformation / shrinkage behavior, thereby reducing the connection reliability in the via hole.

  In order to solve these problems, it is necessary to minimize shape deformation due to melting, and it is necessary to reduce as much as possible the region of the Sn alloy that is melted by the lamination temperature. For this purpose, it is conceivable that the metal filler particles used are not Pb-free solder powder, but metal filler particles in which Sn alloy is coated on a powder having copper or silver as a core.

  Here, the metal powder used for both the resin-type paste and the fired-type paste, and as a method for producing the core copper powder, the electrolytic solution containing copper ions is electrolyzed and the copper powder is deposited on the cathode. Electrolytic method for precipitation, atomizing method for melting copper raw material and making the molten liquid into droplets, quenching and solidifying to produce copper powder, wet method for producing copper powder by adding reducing agent in solution, etc. It has been known. These production methods are employed as industrial production methods because of their high productivity and low production costs.

Although the copper powder obtained by the electrolytic method has a feature that it becomes highly pure, most of the electrolytic copper powder is precipitated in a dendritic shape, and moreover, the particle size tends to be as coarse as 10 μm or more. Furthermore, it is not suitable for wiring applications requiring a low resistance with a conductive paste having a wide particle size distribution.
In addition, the atomizing method is a method in which a jet fluid is blown into a flow of molten metal obtained by melting a metal at a high temperature as shown in, for example, Patent Document 1, but it contains impurities when the metal is melted. There is a problem that it is easy to oxidize and is easily oxidized when sprayed, and copper fine particles of 1 μm or less cannot be produced. As described above, the copper powder obtained by the atomizing method and the electrolytic method has a particle size of 2 μm or more and poor sinterability, so it is difficult to be low resistance, and it is polycrystalline and has grain boundaries, so it has poor oxidation resistance. The field of use is limited as a conductive paste that requires electrical conductivity.

  On the other hand, the wet method is a method of reducing and precipitating copper ions or the like in a solution with a reducing agent. Specifically, for example, as shown in Patent Document 2, an alkaline agent is added to a solution containing a copper salt to cause reaction to precipitate copper hydroxide, and then a reducing agent such as glucose is added to suboxidize. It reduces to copper, Furthermore, a secondary reducing agent like hydrazine is added and it reduces to metal copper, and obtains copper powder. Such a wet method has the advantage that a very fine spherical copper fine powder of submicron can be produced. However, as in Patent Document 1, since it is polycrystalline and has grain boundaries, its oxidation resistance is inferior. As a field of use is limited.

On the other hand, Patent Documents 3 and 4 propose a method for obtaining single crystal copper powder having a fixed crystal orientation, but the main particle size is about 2 to 5 μm and the resin mold has a curing temperature of 100 to 200 ° C. The conductive paste does not satisfy the low resistance. Further, if the curing temperature is 200 ° C. or higher in order to reduce the resistance, the oxidation resistance becomes insufficient.
In Patent Document 3, in order to produce copper powder that is a regular octagonal pyramidal single crystal, it is reduced to a solution containing tartaric acid and alkali hydroxide in a molar ratio of 1 to 5 times the copper salt and copper. It is described that formaldehyde is added within 1 minute as an agent.
Moreover, since the manufacturing method of patent document 4 requires a chelating agent such as tartrate at a molar ratio of 1 to 5 times with respect to copper, the cost of the chemical solution increases, and at the same time the cost of waste liquid treatment also increases. There is also a problem that the manufacturing cost becomes high. Furthermore, there is a condition that formaldehyde as a reducing agent is added within 1 minute for reduction, which is unsuitable for industrial mass production. Furthermore, although the copper powder obtained by patent document 4 is a high crystal | crystallization, it is plate shape, a specific surface area becomes high and it is easy to oxidize, and since a wiring edge becomes uneven, it is unsuitable for the use of an electrically conductive film. .

  In general, when a conductive paste is used for an IC substrate, a printed circuit board, or the like, in order to form a fine pattern, for example, an acid resistance of 1% by mass or less at an oxidation increase of 200 ° C. in the atmosphere by thermogravimetric (TG) analysis. There is a demand for metal fillers that are excellent in chemical properties, fine, and have good dispersibility. In addition, due to the substrate heat resistance, etc., the contact resistance when the resin is cured and contracted at a low temperature is lowered, and when the filler is fired in the air, for example, the powder resistivity may be as low as 500 μΩ · cm or less. Desired. However, in the case of metal powders, particularly copper powders, there is a tendency to oxidize more easily as the particle size becomes finer. Therefore, there is a demand for a method of obtaining copper powders that are fine and excellent in oxidation resistance. ing.

  Therefore, Patent Document 5 proposes a method for obtaining single-crystal copper fine powder by gas phase reaction. However, when the obtained copper powder is observed using a scanning electron microscope (SEM), it is a chamfered polyhedron. Since it is a single crystal and the powder particles are a single crystal, it has a smooth surface, no defects, and excellent oxidation resistance. However, in the production of copper powder by gas phase reaction, cuprous chloride is reacted with a reducing gas at a high temperature of 700 ° C. or higher to obtain single crystal copper powder, which complicates the mechanism of the apparatus and increases production costs. Further, there is a problem that the yield is poor, for example, the obtained copper powder is remelted and connected.

  As described above, as a metal filler used in the baked conductive paste, a copper powder obtained by tin (Sn) plating is known. However, as a core copper powder, those described in Patent Documents 3 to 5 are used. However, even if the surface is coated with tin, it does not have both sinterability and oxidation resistance, and weatherability and filling properties are insufficient. There is also a need for a method suitable for industrially producing tin-coated copper powder having these characteristics at low cost.

Japanese Patent No. 4342746 Japanese Patent No. 4406738 Japanese Patent Publication No.7-111592 JP 2014-58713 A Japanese Patent Publication No. 6-76609

  In view of the above-mentioned problems of the prior art, the object of the present invention is a fine material that can be suitably used as a material such as a conductive paste, has high filling, has both sinterability and oxidation resistance, and has high weather resistance. The object is to provide a highly crystalline tin-coated copper powder, a method for producing the same, and a conductive paste.

  In order to solve the above-mentioned object, the inventors of the present invention have made extensive studies focusing on a wet reduction method that is excellent in mass production, and tin or tin on the surface of copper particles in which octahedral particles and non-octahedral granular particles are mixed. An alloy-coated tin-coated copper powder having an average particle size of 0.1 μm to 3.0 μm, and a crystallite diameter of copper particles / an average particle size of tin-coated copper powder and a tap density within a specific range. The tap density and weather resistance can be increased, and such a tin-coated copper powder can be reduced by adding and mixing two types of reducing agents having different oxidation-reduction potentials to the copper salt solution. After synthesizing copper powder, it is obtained by coating the surface of the obtained copper powder with tin or a tin alloy, and has high crystallinity, small particle size, tap density and acid resistance, which were not obtained by conventional manufacturing methods. And found that the tin-coated copper powder with improved weatherability and weather resistance, It came to be completed.

That is, according to the first invention of the present invention, tin-coated copper powder in which tin or a tin alloy is coated on the surface of copper particles in which octahedral particles and granular particles other than octahedral particles are mixed,
The average particle diameter is 0.1 μm to 3.0 μm, the crystallite diameter of the copper particles / the average particle diameter of the tin-coated copper powder is 0.10 or more, and the tap density is 3.0 g / cm ^{3 to} 5.0 g / cm ^3. And
A tin-coated copper powder is provided, wherein the coating amount of tin or a tin alloy is 1% by mass to 33% by mass of the entire tin-coated copper powder.

  According to a second aspect of the present invention, there is provided the tin-coated copper powder according to the first aspect, wherein the tin alloy contains one or more elements selected from silver, bismuth and zinc. Provided.

  According to a third aspect of the present invention, in the second aspect of the present invention, the element content of the tin alloy is 0.1% by mass to 50% by mass with respect to the tin alloy. A tin-coated copper powder is provided.

According to the fourth aspect of the present invention, a strong reducing agent and a weak reducing agent having different oxidation-reduction potentials are added to a copper salt solution obtained by mixing a copper compound aqueous solution, an alkali metal hydroxide aqueous solution, and a dispersant aqueous solution. A method for producing a tin-coated copper powder in which two kinds of reducing agents are added to form a reaction solution, and copper particles are produced in the reaction solution, followed by tin plating.
In the step of generating copper particles, first, a strong reducing agent of 0.07 equivalents or more and 0.5 equivalents or less is added to the copper salt solution with respect to the amount of copper in the copper compound, and reacted to form octahedral particles. While generating nuclei, the reaction solution is held and octahedral particles are grown, and then a weak reducing agent is added to the reaction solution and reacted to increase the crystallinity of the octahedral particles. It is characterized by forming a copper or tin alloy film on the copper particle surface by adding an aqueous solution containing a tin salt to a copper particle slurry in which the copper particles are dispersed, and copper particles mixed with granular particles other than the faceted particles. A method for producing a tin-coated copper powder is provided.

  According to a fifth aspect of the present invention, in the fourth aspect of the present invention, the amount of the weak reducing agent added is 1 equivalent or more and 7 equivalents or less with respect to the amount of copper in the copper compound. A method for producing a tin-coated copper powder is provided.

  According to a sixth aspect of the present invention, in the fifth aspect of the present invention, the reaction solution has a difference in oxidation-reduction potential between the addition of the strong reducing agent and the addition of the weak reducing agent of 1.0 V. The manufacturing method of the tin coat copper powder characterized by the above is provided.

  According to a seventh invention of the present invention, in the fourth to sixth inventions of the present invention, the reaction solution is retained for 10 minutes or more after the addition of a strong reducing agent. A manufacturing method is provided.

  According to an eighth aspect of the present invention, there is provided the tin-coated copper powder according to any one of the fourth to seventh aspects of the present invention, wherein the copper compound is copper sulfate pentahydrate. A manufacturing method is provided.

  According to a ninth aspect of the present invention, there is provided the tin-coated copper powder according to any one of the fourth to eighth aspects of the present invention, wherein the alkali metal hydroxide is sodium hydroxide. A manufacturing method is provided.

  According to a tenth aspect of the present invention, there is provided the tin-coated copper powder according to any one of the fourth to ninth aspects of the present invention, wherein the strong reducing agent is hydrazine monohydrate. A manufacturing method is provided.

  According to an eleventh aspect of the present invention, there is provided the method for producing tin-coated copper powder according to any one of the fourth to tenth aspects of the present invention, wherein the weak reducing agent is ascorbic acid. Provided.

  According to a twelfth aspect of the present invention, in any one of the fourth to eleventh aspects of the present invention, the dispersant is polyvinyl alcohol, polyethyleneimine, polyvinylpyrrolidone, a modified silicone oil surfactant, or There is provided a method for producing tin-coated copper powder, which is at least one selected from polyether surfactants.

  According to the thirteenth aspect of the present invention, in any one of the fourth to twelfth aspects of the present invention, the amount of the dispersant added is 0.1% by mass relative to the amount of copper in the copper compound. The manufacturing method of the tin coat copper powder characterized by being -10 mass% is provided.

Furthermore, according to the fourteenth aspect of the present invention, in any one of the fourth to thirteenth aspects of the present invention, the obtained tin-coated copper powder has an average particle size of 0.1 to 3.0 μm and a copper particle an average particle size of the crystallite diameter / tin coating copper powder is 0.10 or more, a manufacturing method of tin-coated copper powder, wherein tap density of 3.0g ^/ cm ³ ~5.0g ^/ cm 3 Provided.

  According to the fifteenth aspect of the present invention, in any one of the fourth to fourteenth aspects of the present invention, the coating amount of tin or a tin alloy is 1% by mass to 33% by mass or less of the entire tin-coated copper powder. A method for producing a tin-coated copper powder is provided.

  According to a sixteenth aspect of the present invention, in the fifteenth aspect of the present invention, the element added as the tin alloy is at least one selected from silver, bismuth and zinc. A method for producing a tin-coated copper powder according to claim 15 is provided.

  Further, according to a seventeenth aspect of the present invention, in the sixteenth aspect of the present invention, the element added as the tin alloy is 0.1% by mass to 20% by mass with respect to the tin alloy. A method for producing a tin-coated copper powder is provided.

  On the other hand, according to the eighteenth aspect of the present invention, there is provided a conductive paste containing the tin-coated copper powder of any one of the first to third aspects of the present invention, a resin, and a solvent.

  The tin-coated copper powder of the present invention has a high crystallinity and a small particle size, and since octahedral particles and non-octahedral particles are mixed, the tap density can be increased. This tin-coated copper powder uses inexpensive raw materials such as copper sulfate and is easy to handle, and after carrying out a reduction reaction in an aqueous solution system suitable for industrial mass production to obtain copper particles, it is said that a tin coat is applied by plating. It can be manufactured by a relatively simple method. Furthermore, according to the production method of the present invention, a tin-coated copper powder in which particles having different shapes and particle sizes are mixed can be obtained by a single reduction reaction using two kinds of reducing agents. Productivity and cost can be reduced.

  Therefore, if such tin-coated copper powder having high crystallinity, a small particle size, and a high tap density is used, a conductive paste suitable for forming an electronic material wiring can be obtained. Moreover, since it is excellent in oxidation resistance and weather resistance, this conductive paste is suitable for forming a conductive film by low-temperature firing, and can also cope with thinning of the conductive film.

  Hereinafter, specific embodiments of the tin-coated copper powder according to the present invention, a manufacturing method thereof, and a conductive paste using the same will be described in detail. It should be noted that the present invention is not limited only to the following embodiments without departing from the object of the present invention.

1. (Tin coated copper powder)
The tin-coated copper powder of the present invention is a tin-coated copper powder in which tin or a tin alloy is coated on the surface of a copper particle in which octahedral particles and granular particles other than octahedral particles are mixed, and the average particle size is 0.1 μm. ～3.0Myuemu, an average particle diameter of the crystallite diameter / tin-coated copper powder of the copper particles 0.10 or more, the tap density is characterized by a 3.0g ^/ cm ³ ~5.0g ^/ cm 3 .

  That is, the tin-coated copper powder according to the present invention is a mixture of octahedral particles and non-octahedral granular particles, has high crystallinity, high tap density, and an average particle size controlled within a specific range. Yes.

  Tin-coated copper powder is a mixture of octahedral particles and non-octahedron particles, and the octahedral particles before coating with tin or tin alloy are single crystals, twin crystals, or the grains contained in the particles are Since it is composed of several tens of particles or less, it has the effect of increasing the crystallinity of the mixture. The octahedral particles include particles having a shape of a truncated octahedron in which a part of the apex is cut out in addition to particles exhibiting an octahedron. The octahedral particles are preferably separated by specific crystal planes to form smooth surfaces.

However, the tap density of the tin-coated copper powder is not improved only by the octahedral particles. In the tin-coated copper powder of the present invention, not only octahedral particles but also granular particles other than octahedrons are present, so that the tap density can be increased.
The granular particles are large particles that are aggregated so that the number of crystal grains exceeds several tens, and are not limited by the shape, but there are no corners or protrusions, or a polyhedron with few corners, for example, a substantially spherical shape. The thing which exhibits is preferable.

  The number ratio of octahedral particles in the tin-coated copper powder according to the present invention is preferably 20% to 80% of the total number of tin-coated copper powders. This ratio is obtained by, for example, observing tin-coated copper powder with a scanning electron microscope (SEM), and discriminating octahedral particles and other particles from this image by a method such as image processing, and measuring the number ratio. be able to.

  The number ratio of octahedral particles in the tin-coated copper powder is 20% or more, and as described later, a copper powder containing highly crystalline particles having a relatively large crystallite diameter compared to the average particle diameter may be used. preferable. When the number ratio of octahedral particles in the tin-coated copper powder exceeds 80%, the tap density decreases, and when the conductive film is formed using the paste containing the tin-coated copper powder, the electric resistance value of the conductive film is It may become high and may not satisfy a desired value (standard value). Therefore, the number ratio of octahedral particles in the tin-coated copper powder is more preferably 30% to 70% of the total number of tin-coated copper powders.

  The average particle diameter of the tin-coated copper powder according to the present invention is 0.1 μm to 3.0 μm, and more preferably 0.3 μm to 2.5 μm. By setting the average particle size within this range, a thinned wiring can be formed when pasted. The average particle diameter is an average value of the particle diameters of primary particles obtained by observing and measuring a certain number of tin-coated copper powders with a scanning electron microscope (SEM). The primary particles refer to those considered as unit particles from the SEM observation image, and do not mean particles (secondary particles) formed by aggregation and bonding of the unit particles. When the average particle size is less than 0.1 μm, not only the particles are likely to aggregate, but also the tap density may not satisfy the above range. When the average particle diameter exceeds 3.0 μm, it is difficult to reduce the line width when the wiring is formed, which is not suitable for thinning the wiring.

  In the tin-coated copper powder according to the present invention, the crystallite diameter of the copper particles / the average particle diameter of the tin-coated copper powder is 0.10 or more. Here, the copper particle crystallite diameter can be calculated from the X-ray diffraction result using the Scherrer method. The higher the index, the higher the crystallinity because the number of crystal grains constituting each powder is smaller. The upper limit of the crystallite diameter of the copper particles / the average particle diameter of the tin-coated copper powder is not particularly limited, but it has been confirmed that the mixed tin-coated copper powder of octahedral particles and granular particles shows a value within 0.40. Yes. The range of the preferable crystallite diameter of the copper particles / average particle diameter of the tin-coated copper powder is 0.10 to 0.38, and more preferably 0.12 to 0.35.

Tin-coated copper powder according to the present invention is a tap density of ^{3.0g / cm 3 ~5.0g / cm 3} , 3.3g / cm 3 ~5.0g / cm 3 is preferable, 3.5 g / cm ^{3 to} 5.0 g / cm ³ is more preferable. Within this range, when the conductive film of the wiring forming material is formed using the tin-coated copper powder as the conductive paste, the filling density of the tin-coated copper powder in the conductive film increases, and the electric resistance value of the conductive film is reduced. Can be reduced. When the tap density is less than 3.0 g / cm ³ , the filling density of the tin-coated copper powder in the conductive film is lowered, and the electrical resistance value may not satisfy a desired value (standard value) as a wiring forming material. . Moreover, what has a tap density exceeding 5.0 g / cm < ³ > is difficult to manufacture at present.

  In the tin-coated copper powder according to the present invention, the coating amount of tin or tin alloy is preferably 1% by mass or more and 33% by mass or less of the entire tin-coated copper powder. If it is less than 1% by mass, the coating with tin may be insufficient, and in some cases, the surface may be oxidized to increase the resistance. On the other hand, if it exceeds 33% by mass, the film strength is lowered, the oxidation resistance is inferior, and the cost is increased, which is not preferable. Note that, with the coating amount of tin or tin alloy, the average thickness of tin or tin alloy coated on the surface is about 0.1 μm at the maximum, and the average particle diameter, tap density, and eight before and after the tin or tin alloy coating. The face structure does not change substantially. The coating amount of tin or tin alloy is preferably 5% by mass or more and 30% by mass or less, and more preferably 5% by mass or more and 25% by mass or less of the copper powder.

  Further, as will be described later, in the tin-coated copper powder, the tin coated with the copper particles may be a tin alloy. As an element added as a tin alloy, 1 or more types chosen from silver, bismuth, and zinc are preferable.

  As a content ratio of metal elements other than tin constituting these tin alloys, from the viewpoint of melting point and wettability, 0.1% by mass to the entire coating film of the tin alloy coated with the tin-coated copper powder. The content is preferably 50% by mass. If the content is too large, it causes an increase in melting point and a decrease in mechanical strength, and therefore it is preferably 50% by mass or less. On the other hand, if the content is less than 0.1% by mass, the effect of lowering the melting point or improving wettability may not be obtained sufficiently. Accordingly, the content of 1% by mass to 20% by mass is more preferable, and the content of 2% by mass to 10% by mass is more preferable with respect to the entire tin alloy coating film.

  In addition, content of the metal which comprises a tin alloy can be measured by converting content of each element which comprises tin coat copper powder, for example by a high frequency inductively coupled plasma (ICP) emission-spectral-analysis method. In addition, each element in the tin alloy film can be quantitatively analyzed from the cross section of the tin-coated copper powder by an energy dispersive X-ray spectroscopy (EDX) method or an Auger electron spectroscopy (AES) method.

2. (Method for producing tin-coated copper powder)
The method for producing tin-coated copper powder according to the present invention comprises a copper salt solution in which a copper compound aqueous solution, an alkali metal hydroxide aqueous solution and a dispersant aqueous solution are mixed, a strong reducing agent having a different redox potential, and a weak reducing agent 2. A method for producing a tin-coated copper powder comprising adding a reducing agent of a kind to form a reaction solution, producing copper particles in the reaction solution, and then performing tin plating,
In the step of generating copper particles, first, a strong reducing agent of 0.07 equivalents or more and 0.5 equivalents or less is added to the copper salt solution with respect to the amount of copper in the copper compound, and reacted to form octahedral particles. While generating nuclei, the reaction solution is held and octahedral particles are grown, and then a weak reducing agent is added to the reaction solution and reacted to increase the crystallinity of the octahedral particles. It is characterized by forming a copper or tin alloy film on the copper particle surface by adding an aqueous solution containing a tin salt to a copper particle slurry in which the copper particles are dispersed, and copper particles mixed with granular particles other than the faceted particles. To do.

  That is, the present invention prepares a copper salt solution by mixing a copper compound aqueous solution, an alkali metal hydroxide aqueous solution and a dispersant aqueous solution, and after adding a strong reducing agent to the copper salt solution and holding it for a predetermined time, A method for producing a tin-coated copper powder by plating by adding a tin salt aqueous solution to a copper particle slurry in which copper particles are dispersed by adding a reducing agent and dispersing the obtained copper particles. The copper particles are obtained by using two kinds of reducing agents having different oxidation-reduction potentials.

  In conventional manufacturing methods, tin-coated copper powders with different shapes and particle sizes are blended to produce tin-coated copper powders with high crystallinity, high tap density, and small average particle size within a specific range. In the past, tin-coated copper powder could not be produced by a series of operations using a wet method. On the other hand, the present invention uses two types of reducing agents having different oxidation-reduction potentials, and appropriately controls the amount of strong reducing agent added so that the tin-coated copper powder can be used in a series of operations by a wet method. Manufacturing was possible.

  Specifically, an aqueous copper compound solution, an alkali metal hydroxide aqueous solution, and an aqueous dispersant solution are mixed to prepare a copper salt solution, and a strong reducing agent is added to the copper salt solution to obtain a reaction solution, for a predetermined time. After holding, a weak reducing agent is further added to produce copper fine particles, a tin salt aqueous solution is added to the copper particle slurry in which the copper fine particles are dispersed, and plating is performed to produce tin-coated copper powder.

Here, the strong reducing agent means a reducing agent having a strong reducing power among the two types of reducing agents used in the present embodiment, and the weak reducing agent means that the standard electrode potential is higher than that of the strong reducing agent. It means that the reducing agent is high, that is, the reducing power is weak. Tin coating with high crystallinity, high tap density, and small average particle size within a specific range by adding a strong reducing agent to 0.07 equivalents or more and 0.5 equivalents or less with respect to the amount of copper in the copper compound Copper powder can be obtained.
Hereinafter, the manufacturing method of the tin coat copper powder which concerns on this invention is demonstrated in detail.

(1) Preparation of copper salt solution First, a copper salt solution containing a copper compound is prepared. As a copper compound which is a starting material, any salt may be used as long as it dissolves as an aqueous solution, such as known copper sulfate, copper chloride, copper carbonate, copper acetate, copper phosphate, and one kind alone or a plurality of various copper compounds may be used. Although it can be used, it is preferable to use copper chloride, copper carbonate, or copper sulfate pentahydrate. In particular, copper sulfate pentahydrate is easier to obtain than other copper compounds because anionic elements are not mixed in the copper powder, and there are few impurities and it is easy to obtain inexpensive ones including wastewater treatment costs.

  The copper sulfate pentahydrate concentration in the copper salt solution is not particularly limited, but is preferably 100 to 2000 g / L. Even if the copper concentration is low, the growth of particles can occur and copper particles can be obtained. However, if the concentration is less than 100 g / L, the amount of drainage increases and the cost increases, and the productivity cannot be increased. On the other hand, if the concentration of copper sulfate pentahydrate exceeds 2000 g / L, it is close to the solubility of copper sulfate pentahydrate in water and may not be sufficiently dissolved, which is not preferable.

Various known hydroxides can be used as the alkali metal hydroxide, but sodium hydroxide and potassium hydroxide are preferably used, and sodium hydroxide is more preferable. These alkali metal hydroxides are readily available and are less expensive than other alkali metal hydroxides.
It is preferable to adjust the amount of the alkali metal hydroxide aqueous solution so as to have a pH at which the reduction reaction of the weak reducing agent proceeds sufficiently after adding the weak reducing agent described later. Specifically, when ascorbic acid is used as the weak reducing agent, the addition amount is preferably set so that the pH of the reaction solution is 3.0 or more. When the pH of the reaction solution is less than 3.0, the reduction reaction with ascorbic acid, which is a weak reducing agent, hardly proceeds.

  In the present invention, an aqueous solution of a dispersant is used so that the copper particles produced by the reduction reaction do not aggregate. The dispersant is preferably at least one selected from polyvinyl alcohol, polyethyleneimine, polyvinyl pyrrolidone, a modified silicone oil surfactant, or a polyether surfactant. The addition amount of the dispersant is preferably 0.01% by mass to 10% by mass and more preferably 0.05% by mass to 3% by mass with respect to the amount of copper in the copper compound. When the addition amount is less than 0.01% by mass, the aggregation suppressing effect may not be sufficiently obtained. On the other hand, when the addition amount exceeds 10% by mass, a load such as wastewater treatment is exerted on the aggregation suppressing effect. Will increase.

(2) Reaction of copper salt solution and strong reducing agent Next, a strong reducing agent is added to the copper salt solution and reacted. The copper salt solution to which the reducing agent is added is hereinafter referred to as a reaction solution. The strong reducing agent is a reducing agent having a low standard electrode potential and a strong reducing power. Specifically, the standard electrode potential is −1.15 V hydrazine, −1.24 V sodium borohydride, 0.056 V. Formalin, dimethylamine borane, or the like can be preferably used. Among them, it is more preferable to use hydrazine having a particularly strong reducing power and hydrazine monohydrate, which is a hydrate thereof, because a large amount of nuclei can be generated and the average particle size tends to be small.

The addition amount of the strong reducing agent needs to be 0.07 equivalent or more and 0.5 equivalent or less with respect to the copper amount in the copper compound, and if the addition amount of the strong reducing agent is out of this range, It is not possible to obtain a mixture of highly octahedral particles and granular particles. The addition amount of the strong reducing agent is preferably 0.08 equivalents or more and 0.4 equivalents or less, and more preferably 0.1 equivalents or more and 0.3 equivalents or less.
When the addition amount of the strong reducing agent is less than 0.07 equivalent to the copper amount in the copper compound, the effect of adding the strong reducing agent is small, and only granular particles are obtained. On the other hand, when the amount exceeds 0.5 equivalents, nucleation and grain growth by the strong reducing agent occur rapidly, so that the crystal grains constituting the octahedral grains become fine and the crystallinity becomes low.

  The reaction temperature is preferably 30 to 80 ° C. When the reaction temperature is less than 30 ° C., only granular particles may be obtained. When the reaction temperature exceeds 80 ° C., the crystal grains constituting the octahedral particles become fine and the crystallinity may be lowered. The preferred reaction temperature is 40-70 ° C. Further, when hydrazine or hydrazine monohydrate is used as a strong reducing agent, foaming may occur during the reduction reaction, so an antifoaming agent may be added to the reaction solution.

  It is preferable that the retention time of the reaction liquid after addition of the strong reducing agent is 10 minutes or longer. When the retention time is less than 10 minutes, the reaction with the strong reducing agent and the reduction reaction with the next weakly reducing agent occur simultaneously, and the reduction rate is increased, so that the crystallinity of the octahedral particles is lowered. The upper limit of the holding time of the reaction liquid after addition of the strong reducing agent is not particularly limited, but may be held, for example, for about 120 minutes until the reduction reaction with the strong reducing agent is completed. Preferred is 10 to 100 minutes, and more preferred is 20 to 60 minutes.

  By this reaction, octahedral particles mainly having high crystallinity are precipitated in the reaction solution. As described above, the number ratio of octahedral particles in the tin-coated copper powder according to the present invention is preferably 20% to 80% of the total number of tin-coated copper powders. It is controlled by the amount of strong reducing agent added during production.

(3) Production of copper fine particles by addition of weak reducing agent Thereafter, a copper reducing fine particle is produced by adding a weak reducing agent having a standard electrode potential different from that of the strong reducing agent to the reaction solution. The weak reducing agent used is a reducing agent having a higher standard electrode potential than that of the strong reducing agent and having a weak reducing power. As the weak reducing agent, it is preferable to use ascorbic acid having a standard electrode potential of 0.058 V or an organic compound having a similar lactone structure. Ascorbic acid has a mild reducing action, and if an organic compound having such a lactone structure is used, copper powder with high crystallinity can be easily obtained.

  The higher the difference in reducing power between the strong reducing agent and the weak reducing agent in the reaction solution, the more easily the highly crystalline octahedral particles are produced. The difference in reducing power can be expressed as a difference in redox potential. In the reaction solution, the difference between the redox potential when a strong reducing agent is added and the redox potential when a weak reducing agent is added is 1.0 V or more. Is preferable, and 1.2 V or more is more preferable. When the potential difference is less than 1.0 V, the crystallinity of the produced copper powder is lowered.

  Although the addition amount of a weak reducing agent is not specifically limited, It is preferable to set it as 1 equivalent-7 equivalent with respect to the amount of copper in a copper compound. When the addition amount is less than 1 equivalent with respect to the amount of copper in the copper salt solution, unreduced copper salt may remain, and when it exceeds 7 equivalents, the cost increases. As will be described later, tin, tin alloy coating treatment is performed using a reduction type electroless plating method, and a tin salt aqueous solution is added without filtering the copper particle slurry containing the produced copper particles, When the tin coating treatment is continuously performed using the reducing agent used for generation, the reducing agent is preferably 1.5 equivalents or more, more preferably 2 equivalents or more with respect to the amount of copper.

The reaction temperature is preferably 30 to 80 ° C. If the reaction temperature is less than 30 ° C., unreduced copper salt may remain, and if it exceeds 80 ° C., crystal grains other than octahedral particles may increase and the tap density may be lowered. The preferred reaction temperature is 40-70 ° C. The holding time of the reaction solution after addition of the weak reducing agent is not particularly limited, but is preferably 1 hour or longer. When the retention time of the reaction solution is less than 1 hour, the reduction reaction is not completed and an unreduced copper salt remains, which is not preferable. The upper limit of the holding time of the reaction liquid after addition of the weak reducing agent is not particularly limited, but may be held within, for example, 5 hours until the reduction reaction with the weak reducing agent is completed. Preferred is 1 to 4 hours, more preferred is 2 to 3 hours.
A pH adjuster, a complexing agent, an antifoaming agent, and the like can be appropriately added to the reaction solution as necessary. What is necessary is just to adjust these addition amounts suitably according to the objective.

(4) Tin coating treatment The copper particle slurry produced as described above is subjected to tin coating treatment on the surface of the copper particles using, for example, a reduction type electroless plating method to obtain tin coated copper particles.

  However, the tin coating treatment is not limited to the electroless plating method, and the tin coating treatment may be performed on the surface of the copper powder by other known methods. However, if the surface of the copper particles is coated with tin by an electroless plating method, oxidation of the powder surface can be suppressed with high productivity at a relatively low cost, and the conductivity is increased when a conductive film is formed using this powder. be able to.

Specifically, a copper particle slurry in which the generated copper particles are dispersed is used, and a tin salt aqueous solution is added to the copper particle slurry to perform a tin coating treatment.
As a method of making this copper particle slurry, the copper particles are filtered from the reaction solution, the reaction solution is washed with water and dried, the copper particles are taken out, and the copper particles are dispersed in the solution to obtain the copper particles. A method of making a slurry, a method of removing a reaction solution by decantation, etc., adding water or the like to make a copper particle slurry, and using the reaction solution as it is to disperse copper particles in the reaction solution to make a copper particle slurry There is a way.

  In order to coat tin or tin alloy with a uniform thickness on the surface of the copper powder, it is preferable to wash before tin plating, and the copper particles can be dispersed in the washing solution and washed with stirring. . This washing treatment is preferably carried out in an acidic solution. After washing, filtration and separation of copper particles and washing with water are repeated as appropriate to obtain a water slurry in which copper particles are dispersed in water. In addition, what is necessary is just to use a well-known method about filtration, isolation | separation, and water washing.

  Specifically, when tin coating is performed by an electroless plating method, an electroless tin plating solution is added to the copper particle slurry obtained after washing the copper particles, or a copper particle slurry is added to the electroless tin plating solution. By stirring uniformly, the surface of the copper powder can be coated more uniformly with tin or a tin alloy.

  A method for coating tin or a tin alloy by an electroless plating method is not particularly limited. Electroless tin plating includes substitutional tin plating in which tin ions in the plating solution are reduced and precipitated as the underlying copper particles are eluted, and tin coating is performed by reducing the tin ions in the plating solution with a reducing agent. Examples include reduction-type tin plating and disproportionation-type tin plating in which tin coating is performed using the fact that tin ion is disproportionated to form metal tin, and any method may be used.

  Specifically, as a substitutional tin plating solution, a tin compound and a complexing agent for keeping the tin compound stable in an aqueous solution are essential components, and a surfactant, a pH adjuster, etc. are added as necessary. Can be used. Further, as the reduced tin plating solution, a composition obtained by adding a reducing agent to the above-described substitutional tin plating solution can be used.

In the disproportionation reaction type tin plating, tin ions exist as HSnO ²⁻ ions in an alkaline aqueous solution, and the HSnO ²⁻ ions become metal tin by a disproportionation reaction represented by the following formula. In the disproportionation reaction type tin plating, tin plating is performed with metallic tin generated by the reaction, and a plating solution having the same composition as the substitutional tin plating solution in the strong alkaline bath can be used.
2HSnO ² + + 2H ₂ O ⇔ Sn (OH) ₆ ² + + Sn

As the tin compound, there are a divalent tin compound and a tetravalent tin compound, and the divalent tin compound and the tetravalent tin compound may be used alone or in combination, respectively.
Specifically, as the tin compound, for example, stannous borofluoride, stannous sulfosuccinate, stannous chloride, stannic chloride, stannous sulfate, stannic sulfate, stannous oxide, stannous oxide Distinous, stannous methanesulfonate, stannous ethanesulfonate, stannous 2-hydroxypropane-1-sulfonate, stannous p-phenolsulfonate, tin borofluoride, tin silicofluoride, tin sulfamate Tin oxalate, tin tartrate, tin gluconate, tin sulfosuccinate, tin pyrophosphate, 1-hydroxyethane-1,1-bisphosphonic acid tin, tripolyphosphate, and the like.

As the complexing agent, a thiourea derivative, a carboxylic acid or an amine compound, titanium chloride, or the like can be used.
Specifically, thiourea derivatives include thiourea, 1,3-dimethylthiourea, trimethylthiourea, diethylthiourea (eg, 1,3-diethyl-2-thiourea), N, N′-diisopropylthiourea, Examples include allyl thiourea, acetyl thiourea, ethylene thiourea, 1,3-diphenyl thiourea, thiourea dioxide, and thiosemicarbazide.
In addition, as carboxylic acid or amine compound, citric acid, tartaric acid, malic acid, gluconic acid, golcoheptonic acid, glycolic acid, lactic acid, trioxybutyric acid, ascorbic acid, isocitric acid, tartronic acid, glyceric acid, hydroxybutyric acid, leucine acid , Citramalic acid, succinic acid, mercaptosuccinic acid, sulfosuccinic acid, glutaric acid, malonic acid, adipic acid, oxalic acid, maleic acid, citraconic acid, itaconic acid, mesaconic acid, glycolic acid, sodium citrate, glycine, hydroxyethylethylenediamine Triacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraminehexaacetic acid, ethylenediaminetetraacetic acid, ethylenediaminetetraacetic acid disodium salt, ethylenediaminetetrapropionic acid, nitrilotriacetic acid, iminodiacetic acid, hydroxyethylimino Acetic acid, iminodipropionic acid, aminotrimethylene phosphate, aminotrimethylene phosphate pentasodium salt, benzylamine, 2-naphthylamine, isobutylamine, isoamylamine, 1,3-propanediaminetetraacetic acid, 1,3-diamino- 2-hydroxypropanetetraacetic acid, glycol etherdiaminetetraacetic acid, metaphenylenediaminetetraacetic acid, 1,2-diaminocyclohexane-N, N, N ′, N′-tetraacetic acid, diaminopropionic acid, ethylenediaminetetramethylene phosphate, diethylenetriamine Pentamethylene phosphoric acid, glutamic acid, dicarboxymethyl glutamic acid, ornithine, cysteine, N, N-bis (2-hydroxyethyl) glycine, (S, S) -ethylenediamine succinic acid, methylenediamine, ethylenediamine, ethyl Diaminetetraacetic acid, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, diethylenetriamine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, cinnamylamine, p-methoxycinnamylamine and the like.

Examples of the reducing agent include phosphoric acid compounds, borohydride compounds, hydrazine derivatives, and the like, and these can be used alone or in combination of two or more.
Specifically, examples of the phosphoric acid compound include hypophosphorous acid, phosphorous acid, pyrophosphoric acid, polyphosphoric acid, and the like. Examples of the borohydride compound include methylhexaborane, dimethylamineborane, diethylamineborane, morpholineborane, pyridineamineborane, piperidineborane, ethylenediamineborane, ethylenediaminebisborane, t-butylamineborane, imidazoleborane, methoxyethylamineborane, hydrogen Examples thereof include sodium borohydride.
As the hydrazine derivative, hydrazine salts such as hydrazine sulfate and hydrazine hydrochloride, hydrazine derivatives such as pyrazoles, triazoles and hydrazides, and the like can be used. Among these, as pyrazoles, pyrazole derivatives such as 3,5-dimethylpyrazole and 3-methyl-5-pyrazolone can be used in addition to pyrazole. As triazoles, 4-amino-1,2,4-triazole, 1,2,3-triazole, and the like can be used. As hydrazides, adipic hydrazide, maleic hydrazide, carbohydrazide, and the like can be used.

In addition, additives such as a pH buffer, a pH adjuster, and a surfactant can be contained as necessary. Furthermore, you may use an antifoamer and a dispersing agent as needed.
A known complexing agent can be used as the pH buffering agent. For example, ammonium chloride, ammonium sulfate, boric acid, sodium acetate and the like can be mentioned.
A known complexing agent can be used as the pH adjuster. For example, an acid or alkali compound can be used, and examples thereof include alkali metal hydroxides such as ammonia and sodium hydroxide, carbonic acid, sulfuric acid, and hydrochloric acid. In addition, when using ammonia, it can supply as ammonia water.

  Surfactants can be used to improve the permeability of the plating solution. Specifically, any of nonionic, cationic, anionic, amphoteric, etc. surfactants should be used as the surfactant. It can be used alone or in combination of two or more.

  Furthermore, the properties such as melting point and wettability can be changed by containing other elements than tin in the formed tin film, that is, by forming a film of tin alloy on the surface of the copper powder. . For example, as a specification of Pb-free solder, use temperature, wettability, and mechanical strength become problems depending on the use and material used. In this respect, by forming a tin alloy film, the properties can be changed to suit the intended use and material.

  Specifically, elements contained in the tin coating, that is, elements other than tin constituting the tin alloy include silver, bismuth, copper, indium, antimony, and zinc. The tin alloy can be a binary or multi-element alloy containing these elements. Among them, elements that can be alloyed when tin is coated by the electroless plating method include silver, bismuth, and zinc. One or more compounds containing these elements should be added to the above-described electroless tin plating solution. Thus, the tin alloy coating can be easily coated.

  Specifically, when a tin alloy containing silver is used, examples of the silver compound added to the electroless tin plating solution include silver oxide, silver nitrate, silver sulfate, silver chloride, silver bromide, silver iodide, and benzoic acid. Silver, silver sulfamate, silver citrate, silver lactate, silver mercaptosuccinate, silver phosphate, silver trifluoroacetate, silver pyrophosphate, silver 1-hydroxyethane-1,1-bisphosphonate, silver borofluoride, silver tartrate Silver gluconate, silver oxalate, silver methanesulfonate, silver p-phenolsulfonate, silver benzoate and the like.

  When a bismuth-containing tin alloy is used, examples of the bismuth compound added to the electroless tin plating solution include bismuth nitrate, bismuth chloride, bismuth methanesulfonate, bismuth ethanesulfonate, and bismuth p-phenolsulfonate. Is mentioned.

  Moreover, when setting it as the tin alloy containing zinc, as a zinc compound added in an electroless tin plating solution, zinc oxide, zinc chloride, zinc sulfate etc. are mentioned, for example.

  As a content ratio of metal elements other than tin constituting these tin alloys, from the viewpoint of melting point and wettability, 0.1% by mass to the entire coating film of the tin alloy coated with the tin-coated copper powder. The content is preferably 50% by mass. The content of 1% by mass to 20% by mass is more preferable, and the content of 2% by mass to 10% by mass is more preferable with respect to the entire tin alloy film.

  Furthermore, the method for forming the tin alloy film is not limited to the above-described electroless plating method. For example, an element other than tin constituting the tin alloy is contained in the copper particles before coating with tin, and after forming a film made only of tin (tin film), the copper particles are previously included in the copper particles. The tin alloy film can also be formed by diffusing the elements contained in the tin film.

(5) Filtration, washing and drying After producing the tin-coated copper particle slurry as described above, the tin-coated copper particle slurry is filtered, and the tin-coated copper powder is separated, washed and dried.

  The cleaning method is not particularly limited, but for example, tin-coated copper particles are put into water, stirred using a stirrer or ultrasonic cleaner, and then filtered with a suction filter or a filter press. A method of recovery can be used. In this washing method, it is preferable to repeat the operations consisting of charging into water, stirring washing and filtration several times. Further, as cleaning water, it is preferable to use water that does not contain an impurity element harmful to tin-coated copper powder, particularly pure water.

  Further, in order to prevent aggregation of the tin-coated copper powder, a surface treatment agent may be added to the cleaning liquid or the like to surface-treat the tin-coated copper powder during cleaning. For example, a treatment with an aqueous carboxylic acid solution can be added during cleaning. When surface treatment is performed, it is preferable that washing and filtration are performed thereafter to sufficiently remove excess surface treatment agent.

  Next, the washed tin-coated copper powder is dried to evaporate water. The drying method is not particularly limited. For example, the cleaned tin-coated copper particles are placed on a stainless steel vat, and a commercially available drying apparatus such as an atmospheric oven or a vacuum dryer is used, and the temperature is about 40 ° C to 80 ° C. It can carry out by heating at the temperature of.

(6) Conductive paste In the present invention, a conductive paste can be obtained by mixing at least the tin-coated copper powder, a resin (binder resin), and a solvent, and kneading them.

  In addition to the tin-coated copper powder, resin, and solvent according to the present invention as a constituent component, the conductive paste further includes an antioxidant, a coupling agent, etc., if necessary, in order to improve the conductivity after curing. Additives can be blended.

Although the kind of resin is not specifically limited, An epoxy resin, a phenol resin, an ethyl cellulose resin, etc. can be used.
Moreover, as a solvent, organic solvents, such as ethylene glycol, diethylene glycol, triethylene glycol, glycerol, and terpineol, can be used. Further, the amount of the organic solvent is not particularly limited, but the addition amount can be adjusted in consideration of the average particle size of the copper powder so as to have a viscosity suitable for a conductive film forming method such as screen printing or a dispenser. it can.

  Moreover, the kind of antioxidant is not specifically limited, For example, hydroxycarboxylic acid etc. can be mentioned. More specifically, hydroxycarboxylic acids such as citric acid, malic acid, tartaric acid, and lactic acid are preferable, and citric acid or malic acid having a high adsorptive power to copper is particularly preferable. In addition, a coupling agent, a viscosity modifier, a dispersant, a flame retardant, an anti-settling agent, and the like can be used.

This conductive paste can be manufactured by a method similar to the conventional technique as long as the above-described constituent components can be uniformly dispersed. For example, the above-described constituent components can be uniformly kneaded by a three roll mill or the like.
The timing of adding the above-mentioned additives is not particularly limited, and the tin-coated copper powder and the binder resin may be added to the solvent and kneaded at the same time, or the tin-coated copper powder and the binder resin may be mixed with the solvent. And kneaded, and may be added using a self-revolving mixer or the like.

  Since the tin-coated copper powder of the present invention has high crystallinity, a small particle size, and a high tap density, a conductive paste suitable for forming an electronic material wiring can be obtained. This conductive paste is suitable for forming a conductive film by low-temperature firing, and can also cope with thinning of the conductive film.

  EXAMPLES The present invention will be described in further detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

(Average particle size)
The obtained particles were observed using a scanning electron microscope (SEM, JEOL, JSM-7100F), the particle size of primary particles of 300 or more tin-coated copper powders was measured, and the average value was determined as the average particle size. It was. Moreover, among the same number of tin-coated copper powders, octahedral ones were counted to calculate the ratio.

(Tap density)
The tap density was measured by putting 20 g of tin-coated copper powder in a 20 mL graduated cylinder and tapping 500 times using a shaking specific gravity measuring instrument (Kurachi Chemical Instruments Co., Ltd., KRS-409). A value obtained by weight of copper powder / volume after tapping was defined as a tap density.

(Crystallite diameter)
The crystallite diameter of the copper particles in the obtained tin-coated copper powder was measured using an X-ray diffractometer (PANallylic, X'pert PRO), and calculated from the X-ray diffraction results using the Scherrer method.

(Oxidation resistance)
Oxidation resistance was obtained by drying the tin-coated copper powder obtained by drying into cylindrical pellets having a diameter of about 3 mm and a thickness of 2 mm by a tableting press, and by thermogravimetry (TG; manufactured by Rigaku) in the atmosphere at 200 ° C. The temperature was raised to 0 and the weight gain due to oxidation was measured. 1 mass% or less is preferable.

(Sintering resistance)
Sintering resistance measured the resistance value of the pellet after oxidation-resistant TG evaluation with a 4-terminal resistance measuring instrument (manufactured by Mitsubishi Chemical Analytical), and calculated the resistivity (μΩ · cm) from the pellet shape.

(Weatherability)
For weather resistance, the pellets after measuring the firing resistance are allowed to stand under constant temperature and humidity, and the resistivity is calculated by measuring the resistance value for each fixed time using the above four-terminal method resistance measuring instrument. The rate of change in resistivity (%) was calculated based on the pre-measurement. Specifically, as a typical example of constant temperature and humidity conditions, a temperature of 85 ° C. and a humidity of 85% R.D. H. Thus, the rate of change in resistivity after 500 hours is calculated, and is required to be 20% or less.

[Example 1]
25.0 g of copper sulfate pentahydrate (manufactured by Sumitomo Metal Mining Co., Ltd.) is dissolved in 150 mL of pure water, and 30 mL of 25% sodium hydroxide aqueous solution (manufactured by Kanto Chemical Co., Ltd.) and a dispersant are added to this aqueous solution. A dispersant aqueous solution in which 0.06 g of a certain polyvinyl alcohol (manufactured by Kuraray Co., Ltd., PVA205) was dissolved in 50 mL of pure water was added. Further, an antifoaming agent (manufactured by Adeka Co., Ltd., Adecanol LG-126) was diluted 100 times by volume, and 5 mL of this antifoaming agent dilution was added to obtain a copper salt solution. The copper salt solution was kept at 40 ° C. with stirring.
Subsequently, 0.25 mL of hydrazine monohydrate (manufactured by Wako Pure Chemical Industries, Ltd.) (when the reduction reaction of hydrazine is a 4-electron reaction) was added to this aqueous solution with respect to copper in copper sulfate pentahydrate. 0.1 equivalent) was added to a strong reducing agent solution dissolved in 10 mL of pure water and held at 40 ° C. for 30 minutes with stirring.
Next, a weak reducing agent solution in which 44 g of ascorbic acid (manufactured by Wako Pure Chemical Industries, Ltd.) (5 equivalents with respect to copper in copper sulfate pentahydrate) was dissolved in 100 mL of pure water was added, and 40 ° C. For 3 hours with stirring. The obtained copper powder was once filtered, filtered again after surface treatment by washing with water and addition of a stearic acid emulsion for preventing aggregation, and dried in a vacuum oven at 30 ° C. for 6 hours.
Next, using the copper particles produced by the method described above, the surface of the copper particles was coated with tin by electroless tin plating to produce a tin-coated copper powder. Specifically, a tin film was formed on the surface of the copper particles using 100 g by an electroless plating method. As an electroless tin plating solution, a plating solution in which stannous borofluoride 20 g / L, borofluoric acid 200 g / L, thiourea 50 g / L, sodium borohydride 40 g / L, and sodium borate 10 g / L are added at various concentrations. Prepared. In this electroless tin plating solution, 100 g of the copper particles produced by the above-described method was added and stirred at 25 ° C. for 10 minutes, and then the bath temperature was heated to 60 ° C. and stirred for 60 minutes. After the reaction was completed, the powder was filtered, washed with water and dried through ethanol.
The shape of the tin-coated copper powder thus obtained was observed by the method using the SEM described above. In the tin-coated copper powder, 63% of highly crystalline octahedral particles and 37% of granular particles were mixed. The average particle size was measured to be 0.95 μm. Moreover, the tap density of this tin coat copper powder was 3.8 g / cm ³ . The crystallite diameter of the copper particles was 0.15 μm, and the average particle diameter of the crystallite diameter of the copper particles / tin-coated copper powder was 0.16. Since the crystallite diameter of the copper particles / the average particle diameter of the tin-coated copper powder is 0.1 or more, it is sufficiently high in crystallinity, and particles of different shapes and particle diameters are mixed, so that the high tap density Tin-coated copper powder was obtained.
Moreover, when the coating amount of tin was measured, the coating amount of tin was 11.6% by mass relative to the entire tin-coated copper powder, and the 200 ° C. oxidation increase (TG measurement) was as small as 0.7% by mass. The resistivity was as low as 200 μΩ · cm. The weather resistance was as good as 12.7%. The above results are summarized in Table 1.

[Example 2]
In Example 1 above, the amount of addition of hydrazine monohydrate, which is a strong reducing agent, was 0.74 mL (when the reduction reaction of hydrazine was a four-electron reaction, the amount was 0. 0 with respect to copper in copper sulfate pentahydrate. A tin-coated copper powder was produced in the same manner as in Example 1 except that the amount was 3 equivalents).
In this tin-coated copper powder, 51% of highly crystalline octahedral particles and 49% of granular particles were mixed. The average particle size was measured to be 0.46 μm. Moreover, the tap density of the tin-coated copper powder was 3.4 g / cm ³ . The crystallite diameter of the copper particles was 0.13 μm, and the crystallite diameter of the copper particles / the average particle diameter of the tin-coated copper powder was 0.28. Copper particle crystallite diameter / tin coat Since the average particle diameter of the copper powder is 0.1 or more, it has high crystallinity, and particles of different shapes and particle diameters are mixed, so a high tap density tin coat. Copper powder was obtained.
Moreover, when the coating amount of tin was measured, it was 15.0% by mass with respect to the entire tin-coated copper powder, the 200 ° C. oxidation increase (TG measurement) was as small as 0.7% by mass, and the resistivity was 220 μΩ · cm. Low resistance. The weather resistance was as good as 14.2%.

[Example 3]
In Example 1 above, instead of hydrazine monohydrate, which is a strong reducing agent, the amount of formalin (60% by volume liquid) added was 4.9 mL (when the reduction reaction of formalin was a one-electron reaction, copper sulfate pentahydrate) A tin-coated copper powder was produced in the same manner as in Example 1 except that the amount was 0.5 equivalent to the copper in the Japanese product.
In this tin-coated copper powder, 68% of highly crystalline octahedral particles and 32% of granular particles were mixed. The average particle size was measured to be 0.24 μm. Moreover, the tap density of this tin-coated copper powder was 3.1 g / cm ³ . The crystallite diameter of the copper particles was 0.11 μm, and the crystallite diameter of the copper particles / the average particle diameter of the tin-coated copper powder was 0.46. Copper particle crystallite diameter / tin coat Since the average particle diameter of the copper powder is 0.1 or more, it has high crystallinity, and particles of different shapes and particle diameters are mixed, so a high tap density tin coat. Copper powder was obtained.
Moreover, when the coating amount of tin was measured, it was 18.1% by mass with respect to the entire tin-coated copper powder, the 200 ° C. oxidation increase (TG measurement) was as small as 0.9% by mass, and the resistivity was 369 μΩ · cm. Low resistance. The weather resistance was as good as 14.0%.

[Example 4]
In Example 1, a tin-coated copper powder was produced under the same conditions except that stannous borofluoride was changed to 45 g / L.
In this tin-coated copper powder, the mixing ratio of octahedral particles and granular particles having high crystallinity, the average particle diameter, the tap density, and the crystallite diameter of the copper particles were the same as in Example 1.
Moreover, when the coating amount of tin was measured, it was 28.6% by mass with respect to the entire tin-coated copper powder, the 200 ° C. oxidation increase (TG measurement) was as small as 0.5% by mass, and the resistivity was 378 μΩ · cm. Low resistance. The weather resistance was as good as 9.4%.

[Example 5]
In Example 1, as an electroless tin plating solution, a plating solution in which stannous chloride 10 g / L, sodium citrate 40 g / L, ethylenediaminetetraacetic acid 20 g / L, and titanium chloride 50 g / L were added at respective concentrations was prepared. . To this electroless tin plating solution, 100 g of the copper powder prepared by the above-described method was added and stirred at 25 ° C. for 10 minutes, and then the bath temperature was heated to 65 ° C. and stirred for 60 minutes. After the reaction was completed, the powder was filtered, washed with water and dried through ethanol.
In this tin-coated copper powder, the mixing ratio of octahedral particles and granular particles having high crystallinity, the average particle diameter, the tap density, and the crystallite diameter of the copper particles were the same as in Example 1.
Moreover, when the coating amount of tin was measured, it was 15.5% by mass with respect to the entire tin-coated copper powder, the 200 ° C. oxidation increase (TG measurement) was as small as 0.6% by mass, and the resistivity was 280 μΩ · cm. Low resistance. The weather resistance was as good as 13.8%.

[Example 6]
In Example 1, as an electroless tin plating solution, a plating solution to which 10 g / L of stannous chloride, 100 g / L of sodium hydroxide, and 40 g / L of sodium citrate were added at respective concentrations was prepared. To this electroless tin plating solution, 100 g of the copper powder prepared by the above-described method was added and stirred at 25 ° C. for 10 minutes, and then the bath temperature was heated to 80 ° C. and stirred for 60 minutes. After the reaction was completed, the powder was filtered, washed with water and dried through ethanol.
In this tin-coated copper powder, the mixing ratio of octahedral particles and granular particles having high crystallinity, the average particle diameter, the tap density, and the crystallite diameter of the copper particles were the same as in Example 1.
Moreover, when the coating amount of tin was measured, it was 6.6% by mass with respect to the entire tin-coated copper powder, the 200 ° C. oxidation increase (TG measurement) was as small as 0.8% by mass, and the resistivity was 415 μΩ · cm. Low resistance. The weather resistance was as good as 15.8%.

[Example 7]
In Example 1, 50 g / L of stannous methanesulfonate, 20 g / L of silver citrate, 100 g / L of thiourea, and 30 g / L of sodium hypophosphite at various concentrations were added as electroless tin plating solutions for alloys. A prepared plating solution was prepared. To this electroless tin plating solution, 100 g of the copper powder produced by the above-described method was added and stirred at 25 ° C. for 10 minutes, and then the bath temperature was heated to 70 ° C. and stirred for 60 minutes. After the reaction was completed, the powder was filtered, washed with water and dried through ethanol.
In this tin-coated copper powder, the mixing ratio of octahedral particles and granular particles having high crystallinity, the average particle diameter, the tap density, and the crystallite diameter of the copper particles were the same as in Example 1.
When the coating amount of the tin alloy was measured, it was 8.4% by mass with respect to the entire tin-coated copper powder, and the content of silver contained in the tin alloy was 5.0% by mass with respect to the tin alloy. .
The 200 ° C. oxidation increase (TG measurement) was as small as 0.6 mass%, and the resistivity was as low as 150 μΩ · cm. The weather resistance was as good as 9.1%.

[Example 8]
In Example 1, as an electroless tin plating solution for an alloy, stannous methanesulfonate 40 g / L, bismuth methanesulfonate 40 g / L, thiourea 100 g / L, ethylenediaminetetraacetic acid 20 g / L, sodium hypophosphite A plating solution to which 80 g / L was added at each concentration was prepared. To this electroless tin plating solution, 100 g of the copper powder prepared by the above-described method was added and stirred at 25 ° C. for 10 minutes, and then the bath temperature was heated to 70 ° C. and stirred for 60 minutes. After the reaction was completed, the powder was filtered, washed with water and dried through ethanol.
In this tin-coated copper powder, the mixing ratio of octahedral particles and granular particles having high crystallinity, the average particle diameter, the tap density, and the crystallite diameter of the copper particles were the same as in Example 1.
When the coating amount of tin was measured, it was 8.0% by mass with respect to the entire tin-coated copper powder, and the content of bismuth contained in the tin alloy was 10.1% by mass with respect to the tin alloy.
The 200 ° C. oxidation increase (TG measurement) was as small as 0.7% by mass, and the resistivity was as low as 305 μΩ · cm. The weather resistance was as good as 16.1%.

[Example 9]
In Example 1, as an electroless tin plating solution for an alloy, stannous chloride 10 g / L, zinc sulfate 5 g / L, thiourea 100 g / L, sodium citrate 40 g / L, sodium hypophosphite 70 g / L. A plating solution added at each concentration was prepared. To this electroless tin plating solution, 100 g of the copper powder prepared by the above-described method was added and stirred at 25 ° C. for 10 minutes, and then the bath temperature was heated to 70 ° C. and stirred for 60 minutes. After the reaction was completed, the powder was filtered, washed with water and dried through ethanol.
In this tin-coated copper powder, the mixing ratio of octahedral particles and granular particles having high crystallinity, the average particle diameter, the tap density, and the crystallite diameter of the copper particles were the same as in Example 1.
When the coating amount of tin was measured, it was 7.9% by mass with respect to the entire tin-coated copper powder, and the content of zinc contained in the tin alloy was 10.2% by mass with respect to the tin alloy.
The 200 ° C. oxidation increase (TG measurement) was as small as 0.7% by mass, and the resistivity was as low as 268 μΩ · cm. The weather resistance was as good as 14.7%.

[Example 10]
In Example 1, as an electroless tin plating solution for an alloy, 50 g / L of stannous methanesulfonate, 5 g / L of bismuth methanesulfonate, 20 g / L of silver citrate, 100 g / L of thiourea, hypophosphorous acid A plating solution to which 30 g / L of sodium was added at each concentration was prepared. To this electroless tin plating solution, 100 g of the copper powder prepared by the above-described method was added and stirred at 25 ° C. for 10 minutes, and then the bath temperature was heated to 70 ° C. and stirred for 60 minutes. After the reaction was completed, the powder was filtered, washed with water and dried through ethanol.
In this tin-coated copper powder, the mixing ratio of octahedral particles and granular particles having high crystallinity, the average particle diameter, the tap density, and the crystallite diameter of the copper particles were the same as in Example 1.
As a result of measuring the coating amount of tin, it was 13.4% by mass with respect to the entire tin-coated copper powder, and the content of silver and bismuth contained in the tin alloy was 4.3% by mass with respect to the tin alloy, respectively. It was 6.0 mass%.
The 200 ° C. oxidation increase (TG measurement) was as small as 0.5% by mass, and the resistivity was as low as 170 μΩ · cm. The weather resistance was as good as 8.6%.

[Comparative Example 1]
In Example 1 above, the addition amount of hydrazine monohydrate, which is a strong reducing agent, was 0.12 mL (when the reduction reaction of hydrazine was a four-electron reaction, the amount was 0. A tin-coated copper powder was produced in the same manner as in Example 1 except that the amount was changed to 05 equivalent).
This tin-coated copper powder was only granular particles. When the average particle size was measured, it was 1.91 μm, and the tap density was 2.5 g / cm ³ . The crystallite diameter of the copper powder of the copper particles was 0.12 μm, and the average particle diameter of the crystallite diameter of the copper particles / tin-coated copper powder was 0.06. Since the crystallite diameter of the copper particles / the average particle diameter of the tin-coated copper powder is less than 0.1, the tap density is low because it is not highly crystalline and is only a single shape and particle diameter. .
Further, when the tin coating amount was measured, the tin coating amount was 8.5% by mass with respect to the entire tin-coated copper powder, but the 200 ° C. oxidation increase (TG measurement) was 1.1% by mass. The resistivity deteriorated with 510 μΩ · cm, and the weather resistance with 33.6%.

[Comparative Example 2]
In Example 1 above, the addition amount of hydrazine monohydrate, which is a strong reducing agent, was 2.5 mL (when the reduction reaction of hydrazine was a 4-electron reaction, 1. A tin-coated copper powder was produced in the same manner as in Example 1 except that the amount was 0 equivalent).
This tin-coated copper powder was only granular particles. The average particle size was measured and found to be 0.13 μm. Moreover, the tap density of this tin-coated copper powder was 0.6 g / cm ³ . The crystallite diameter of the copper particles was 0.03 μm, and the crystallite diameter of the copper particles / the average particle diameter of the tin-coated copper powder was 0.23. The crystallite size of the copper particles / the average particle size of the tin-coated copper powder is 0.1 or more, so that the crystallinity is high. It is not preferable as a copper powder for adhesive paste.
Moreover, when the tin coating amount was measured, the tin coating amount was 8.1% by mass with respect to the entire tin-coated copper powder, but the 200 ° C. oxidation increase (TG measurement) was 4.5% by mass. The resistivity deteriorated with 800 μΩ · cm and the weather resistance with 38.9%.

[Comparative Example 3]
In Example 1 above, tin-coated copper powder was prepared in the same manner as in Example 1 except that hydrazine monohydrate, which is a strong reducing agent, was not used.
This tin-coated copper powder was only granular particles. When the average particle diameter was measured, it was 1.68 μm, and the tap density of this silver-coated copper powder was 2.5 g / cm ³ . The crystallite diameter of the copper particles is 0.08 μm, and the crystallite diameter of the copper particles / the average particle diameter of the Suko coat copper powder is 0.05. Since the crystallite diameter of the copper particles / the average particle diameter of the tin-coated copper powder is less than 0.1, the tap density is not high crystallinity and only particles having a single shape and a relatively uniform particle diameter. Became lower.
Further, when the tin coating amount was measured, the tin coating amount was 7.6% by mass with respect to the entire tin-coated copper powder, but the oxidation increase at 200 ° C. (TG measurement) was 1.6% by mass. The resistivity deteriorated with 630 μΩ · cm and the weather resistance with 15.8%.

[Comparative Example 4]
In Example 1, tin-coated copper powder was prepared under the same conditions except that stannous borofluoride was changed to 4 g / L.
In this tin-coated copper powder, the mixing ratio of octahedral particles and granular particles having high crystallinity, the average particle diameter, the tap density, and the crystallite diameter of the copper particles were the same as in Example 1.
When the tin coating amount was measured, the tin coating amount was reduced to 0.9% by mass with respect to the entire tin-coated copper powder, and the 200 ° C. oxidation increase (TG measurement) was found to be 2.6% by mass. The resistivity deteriorated with 1000 μΩ · cm or more, and the weather resistance deteriorated with 22.7%.

[Comparative Example 5]
A tin-coated copper powder was produced under the same conditions as in Example 1 except that stannous borofluoride was changed to 100 g / L.
In this tin-coated copper powder, the mixing ratio of octahedral particles and granular particles having high crystallinity, the average particle diameter, the tap density, and the crystallite diameter of the copper particles were the same as in Example 1.
Moreover, when the tin coating amount was measured, the tin coating amount was reduced to 40.4% by mass with respect to the entire tin-coated copper powder, and the 200 ° C. oxidation increase (TG measurement) was found to be 2.2% by mass. The resistivity was 1000 μΩ · cm or more, and the weather resistance was deteriorated with 10.7%.

"Evaluation"
From Table 1 that summarizes the results of Examples 1 to 10 and Comparative Examples 1 to 5, the following can be said. In Examples 1 to 10, the copper powder obtained by the wet method is mixed with octahedral particles and granular particles other than octahedral particles, the average particle size is 0.1 μm to 3.0 μm, and the crystallites of the copper particles The average particle diameter of the diameter / tin-coated copper powder is 0.10 or more, the tap density is 3.0 g / cm ^{3 to} 5.0 g / cm ³ , and the coating amount of tin or tin alloy is the entire tin-coated copper powder Therefore, it was highly crystalline. Further, the surface of the copper powder is coated with tin or a tin alloy, so that the 200 ° C. oxidation increase (TG measurement) is as small as 0.5 to 0.9 mass%, and the resistivity is as low as 150 to 415 μΩ · cm. Resistance was obtained, and the rate of change in resistance (weather resistance) was as good as 16.1% or less. Thus, if a tin coat copper powder with high crystallinity, a small particle size, and a high tap density is used, a conductive paste suitable for forming a wiring of an electronic material can be obtained. This conductive paste is suitable for forming a conductive film by low-temperature firing, and can also cope with thinning of the conductive film.

  On the other hand, although Comparative Examples 1-3 were wet processes, since the conditions did not satisfy the conditions of the present invention, the obtained copper powder did not contain octahedral particles, and the tap density was small. In Comparative Examples 4 and 5, the obtained tin-coated copper powder did not have the desired tin coating amount, so the 200 ° C. oxidation increase (TG measurement) was 2.2% by mass or more, and the resistivity was as large as 1000 μΩ · cm or more. became. Such tin-coated copper powder is difficult to use as a raw material filler for conductive paste for wiring formation.

  The tin-coated copper powder of the present invention can be used as a wiring forming material for an electronic component such as a conductive paste, for printed wiring, semiconductor internal wiring, connection between a printed wiring board and an electronic component, and the like. In recent years, especially in the field of solar cell electrodes and the like, demand for low-temperature firing and thinning of wiring has been increased. However, low-temperature firing has low resistance and is useful as a conductive paste that can cope with thinning.

Claims (18)

The copper particle surface in which octahedral particles and granular particles other than octahedral particles are mixed, tin-coated copper powder coated with tin or a tin alloy,
The average particle diameter is 0.1 μm to 3.0 μm, the crystallite diameter of the copper particles / the average particle diameter of the tin-coated copper powder is 0.10 or more, and the tap density is 3.0 g / cm ^{3 to} 5.0 g / cm ^3. And
The tin-coated copper powder is characterized in that the coating amount of tin or tin alloy is 1% by mass to 33% by mass of the entire tin-coated copper powder.   The tin-coated copper powder according to claim 1, wherein the tin alloy contains one or more elements selected from silver, bismuth, and zinc.   The tin-coated copper powder according to claim 2, wherein an element content of the tin alloy is 0.1 mass% to 50 mass% with respect to the tin alloy. To a copper salt solution obtained by mixing a copper compound aqueous solution, an alkali metal hydroxide aqueous solution and a dispersing agent aqueous solution, two kinds of reducing agents having different oxidation-reduction potentials, a strong reducing agent and a weak reducing agent, are added to form a reaction solution, After producing copper particles in the reaction solution, a method for producing tin-coated copper powder for tin plating,
In the step of generating copper particles, first, a strong reducing agent of 0.07 equivalents or more and 0.5 equivalents or less is added to the copper salt solution with respect to the amount of copper in the copper compound, and reacted to form octahedral particles. While generating nuclei, the reaction solution is held and octahedral particles are grown, and then a weak reducing agent is added to the reaction solution and reacted to increase the crystallinity of the octahedral particles. It is characterized by forming a copper or tin alloy film on the copper particle surface by adding an aqueous solution containing a tin salt to a copper particle slurry in which the copper particles are dispersed, and copper particles mixed with granular particles other than the faceted particles. A method for producing tin-coated copper powder.   5. The method for producing a tin-coated copper powder according to claim 4, wherein the addition amount of the weak reducing agent is 1 equivalent or more and 7 equivalents or less with respect to the amount of copper in the copper compound.   6. The tin-coated copper powder according to claim 4, wherein the reaction liquid has a difference in oxidation-reduction potential of 1.0 V or more when the strong reducing agent is added and when the weak reducing agent is added. Method.   The method for producing a tin-coated copper powder according to any one of claims 4 to 6, wherein the reaction solution is held for 10 minutes or more after the addition of a strong reducing agent.   The said copper compound is copper sulfate pentahydrate, The manufacturing method of the tin coat copper powder of any one of Claims 4-7 characterized by the above-mentioned.   The method for producing tin-coated copper powder according to any one of claims 4 to 8, wherein the alkali metal hydroxide is sodium hydroxide.   The method for producing a tin-coated copper powder according to any one of claims 4 to 9, wherein the strong reducing agent is hydrazine monohydrate.   The said weak reducing agent is ascorbic acid, The manufacturing method of the tin coat copper powder of any one of Claims 4-10 characterized by the above-mentioned.   The dispersant according to any one of claims 4 to 11, wherein the dispersant is at least one selected from polyvinyl alcohol, polyethyleneimine, polyvinylpyrrolidone, a modified silicone oil surfactant, or a polyether surfactant. The manufacturing method of the tin coat copper powder of any one.   The tin-coated copper according to any one of claims 4 to 12, wherein an addition amount of the dispersant is 0.1% by mass to 10% by mass with respect to an amount of copper in the copper compound. Powder manufacturing method. The obtained tin-coated copper powder has an average particle diameter of 0.1 to 3.0 μm, a crystallite diameter of copper particles / an average particle diameter of tin-coated copper powder of 0.10 or more, and a tap density of 3.0 g / cm. ³ to 5.0 g / cm ³ a method of manufacturing a tin-coated copper powder according to any one of claims 4-13, characterized in that.   The method for producing a tin-coated copper powder according to any one of claims 4 to 14, wherein the coating amount of tin or a tin alloy is 1% by mass to 33% by mass of the entire tin-coated copper powder.   The element added as said tin alloy is 1 or more types chosen from silver, bismuth, and zinc, The manufacturing method of the tin coat copper powder of Claim 15 characterized by the above-mentioned.   The element added as said tin alloy is 0.1 mass%-50 mass% with respect to a tin alloy, The manufacturing method of the tin coat copper powder of Claim 16 characterized by the above-mentioned. The electrically conductive paste containing the tin coat copper powder of any one of Claims 1-3, resin, and a solvent.