JP2006348387A - Production method of nickel composite particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production method of a nickel composite particle suitable for forming a conductive layer on an electronic component, in which sintering is suppressed at a low temperature, proceeding rate of sintering is moderately suppressed at elevated temperature and shrinkage behavior due to sintering is similar to that of an unfired ceramic. <P>SOLUTION: In the production method, the nickel composite particle is produced by forming a fine liquid droplet from a solution containing (a) at least one thermally decomposable nickel compound and (b) at least one thermally decomposable metal compound capable of forming a spinel together with nickel, heating the liquid droplet at a temperature higher than the decomposition temperatures of compounds (a) and (b) to produce a nickel particle and deposit a nickel-containing spinel layer, either alone or together with a metal oxide layer, near the surface of the nickel particles. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a novel method for producing nickel composite particles suitable for thick film conductor pastes.

  In the field of electronics, thick film pastes such as conductor pastes and resistor pastes are used to manufacture components such as electronic circuits, resistors, capacitors, and IC packages. This is a paste in which conductive particles such as metals, alloys and metal oxides are mixed and dispersed uniformly in an organic vehicle together with a glassy binder and other additives as necessary. A conductor film or a resistor film is formed by baking at a high temperature after being applied to.

  Ceramic multilayer electronic components such as multilayer capacitors and multilayer inductors, and ceramic multilayer substrates are generally laminated with multiple layers of unfired ceramic green sheets such as dielectrics and magnetic materials and internal conductor paste layers, which are fired simultaneously at high temperatures. It is manufactured by. As the inner conductor, it has been the mainstream to use noble metals such as palladium, silver-palladium, and platinum. However, in recent years, resource saving and delamination caused by oxidative expansion at the time of firing palladium or silver-palladium, Base metal materials such as nickel are attracting attention because of demands for improvement of cracks and the like.

  These laminated parts and multilayer boards tend to increase the number of laminated layers. For example, multilayer capacitors having a number of laminated layers of several hundreds have been manufactured. For this reason, it is required to reduce the thickness of the ceramic layer and to further reduce the thickness of the inner conductor layer. For example, when the thickness of the ceramic layer is about 3 μm, the inner conductor film thickness is 1 μm or less, and preferably about 0.5 μm, the central portion of the laminate becomes thick, leading to structural defects and reduced reliability.

  However, when normal nickel particles are used for the internal conductor paste, oversintering of the nickel particles during firing causes the internal conductor to become a discontinuous film, leading to an increase in resistance and disconnection. There is a problem that the conductor thickness is increased, and there is a limit to the reduction in the thickness. That is, when nickel particles are fired in a non-oxidizing atmosphere such as an inert atmosphere or a reducing atmosphere in order to prevent oxidation, even if they are single crystal particles having a relatively low activity even if they are single crystal particles having a relatively low activity, Start sintering and shrinking at low temperature. On the other hand, the temperature at which the ceramic layer begins to sinter is generally much higher than this, for example, about 1200 ° C. for barium titanate and does not shrink together with the nickel film even when co-fired. It becomes a shape to be pulled by. For this reason, the small voids generated in the nickel film due to sintering at a relatively low temperature tend to expand into large holes as the sintering progresses in the high temperature region, and the film easily grows in the thickness direction along with it. It is considered to be. Therefore, in order to reduce the thickness of the nickel inner conductor layer, the nickel particles must be made finer and more dispersible, making it difficult to create voids as much as possible during firing, and matching the sintering shrinkage behavior with the ceramic layer. It is considered necessary to

  In addition, even when the film thickness is increased, the mismatch in the sintering shrinkage behavior between the conductor layer and the ceramic layer as described above can cause structural defects such as delamination and cracks, which reduces yield and reliability. So it was a problem.

  Conventionally, various studies have been made to suppress the sintering of the conductor up to the sintering start temperature of the ceramic layer. For example, by adding various metal oxides or ceramic particles having the same composition as that used in the ceramic layer, the shrinkage start of the conductor film can be delayed to about 800 ° C. apparently. However, since the sinterability of the metal particles themselves is not suppressed, when baked at a high temperature of about 1300 ° C., the continuity and conductivity of the conductor film are also impaired. Moreover, since these additives are not effective unless they are added in a large amount, there is a problem that the resistance value is increased.

  US Pat. No. 5,126,915 describes a method for suppressing sintering by coating metal particles with titanium oxide, aluminum oxide, chromium oxide or other metal oxide by a wet method. However, in this case, although there is an effect of increasing the sintering start temperature, there is a tendency for the sintering shrinkage to occur suddenly after the sintering starts, and there is no discrepancy between the sintering shrinkage behavior of the conductor layer and the ceramic layer at high temperatures. It will not be resolved. This is presumably because these oxide layers rapidly decompose or separate from nickel particles at a high temperature, for example, a temperature of 1200 ° C. or higher in a non-oxidizing atmosphere.

  The present inventors previously described a method of controlling the sintering by allowing a glassy thin film to be present on the surface of the metal particles, and further forming a specific composite oxide layer on the surface of the nickel particles to overfire the nickel particles. Although a method for preventing stagnation has been developed, further studies have been made based on these studies, and the present invention has been achieved.

US Pat. No. 5,126,915

  The nickel particles according to the present invention can suppress the sintering effectively and can obtain a highly conductive conductor film even when the film thickness is thin. In addition, when used in a conductor paste that is simultaneously fired with an unfired ceramic layer, such as a laminated electronic component, the sintering start of nickel particles is delayed, and the sintering shrinkage behavior is approximated to the ceramic layer as much as possible. It prevents wire breakage and structural defects of the conductor film and enables thinning.

  An object of the present invention is to provide a simple and excellent method for producing such nickel particles.

  As a result of further research based on the previous research, the present inventors have obtained the knowledge that the above object can be achieved by providing a spinel layer containing nickel on the surface of nickel particles, thereby completing the present invention. .

  That is, the present invention provides nickel composite particles having a spinel layer containing one or more selected from aluminum oxide, chromium oxide and manganese oxide and nickel oxide on at least a part of the surface of the nickel particles. A method comprising: (a) one or more of thermally decomposable nickel compounds; and (b) one or more of thermally decomposable compounds of metals selected from aluminum, chromium and manganese. The solution containing the particles is made into fine droplets, and the droplets are heated at a temperature higher than the decomposition temperature of (a) and higher than the decomposition temperature of (b), thereby generating nickel particles and at the same time the surface of the nickel particles A spinel layer containing nickel oxide and one or more selected from aluminum oxide, chromium oxide and manganese oxide is deposited in the vicinity. Method for producing nickel composite particle in which the gist of the.

  The present invention also includes an oxide layer of a metal other than nickel on at least a part of the surface of the nickel particles, and aluminum oxide, chromium oxide and manganese oxide at the interface between the nickel particles and the metal oxide layer. A method for producing nickel composite particles in which a spinel layer containing one or two or more selected from a product and nickel oxide is present, wherein (a) one or more of thermally decomposable nickel compounds, and (B) A solution containing one or more metal decomposable compounds selected from aluminum, chromium and manganese is made into fine droplets, and the droplets are higher than the decomposition temperature of (a) and ( By heating at a temperature higher than the decomposition temperature of b), nickel particles are generated, and at the same time, a metal oxide layer, aluminum oxide, chromium oxide and manganese are formed in the vicinity of the surface of the nickel particles. It is intended to be one or gist a method of manufacturing the nickel composite particles, characterized in that to deposit a layer of spinel containing two or more and nickel oxide selected from halides.

  Further, according to the present invention, the solution further comprises (c) one or more of an alkaline earth metal thermally decomposable compound, and the heating of the droplets is (a), (b), (c) The gist of the present invention is a method for producing nickel composite particles, which is performed at a temperature higher than any decomposition temperature.

  The nickel composite particle according to the present invention suppresses sintering at a low temperature, delays the start of shrinkage when firing the nickel paste, and moderately suppresses the rate of progress of sintering even at a high temperature. And oversintering does not occur. Therefore, in electronic parts such as multilayer capacitors, the sintering shrinkage behavior of the nickel conductor layer can be approximated to that of a ceramic layer, and there is no disconnection or structural defect in the conductor film, yielding highly reliable and high-performance products. It is possible to manufacture well. In addition, the inner conductor layer can be made thinner, and the multilayer electronic component can be further reduced in size and heightened.

  According to the present invention, the above-mentioned nickel composite particles having good crystallinity, high density and high dispersibility can be obtained, the particle size can be easily controlled, and a metal compound such as an aluminum compound is added to the raw material nickel compound solution. By adding the nickel composite particles, the nickel composite particles can be obtained by a single operation, so that there is an advantage that a new coating step is not required.

  Further, since the composition of the generated particles basically matches the composition of the starting metal compound in the solution, the composition can be easily controlled.

  The spinel containing nickel (hereinafter referred to as “nickel spinel”) according to the present invention is a composite metal oxide having a spinel structure or a spinel-like structure containing nickel as a constituent element.

Examples of the metal oxide other than nickel constituting the nickel spinel include aluminum oxide, chromium oxide, manganese oxide, and oxides of alkaline earth metals such as magnesium, calcium, barium, and strontium. Aluminum oxide, chromium oxide, manganese oxide, etc. form a complex metal oxide having a spinel structure that is stable with nickel oxide at high temperatures, that is, NiAl ₂ O ₄ , NiCr ₂ O ₄ , NiMn ₂ O _4, etc. To do. Alkaline earth metal oxides are present in a form that substitutes a part of nickel in these spinels, and are considered to produce a composite metal oxide having a spinel structure or a spinel-like structure. Nickel spinels such as NiAl ₂ O ₄ may react with barium titanate and the like when decomposed at a high temperature in a reducing atmosphere, which may deteriorate capacitor characteristics. However, alkaline earth metal oxides are spinel. Has the effect of stabilizing.

  The nickel spinel layer may be in the form of covering the surface of the nickel particles or segregating at a high concentration on and / or in the vicinity of the surface of the nickel particles, and is effective in inhibiting nickel sintering. It only needs to exist in the vicinity. When an oxide layer of a metal other than nickel is present on the particle surface, it is necessary that a nickel spinel layer be present at the interface with the nickel particles. The metal oxide layer preferably contains a metal oxide other than nickel constituting the nickel spinel or a composite oxide thereof.

  Hereinafter, composite particles having an oxide layer of metal other than nickel (hereinafter referred to as “metal oxide layer”) and a nickel spinel layer (hereinafter referred to as “spinel layer”) will be described. It is the same.

  In the nickel composite particles according to the present invention, since the spinel layer is present at the interface between the metal oxide layer and the nickel particles from the beginning, the adhesion between the metal oxide layer and the nickel layer is improved, and in a non-oxidizing atmosphere. No rapid phase separation occurs even when calcined at. Rather, since the metal oxide and spinel are gradually separated or decomposed, the nickel particle surface will stably exist as a solid phase up to a high temperature state, not only increase the sintering start temperature of the nickel particles, Sintering is controlled to a considerably high temperature even after the start of sintering, and therefore, the sintering proceeds at a moderate rate until the end of sintering. For this reason, the increase in conductor resistance, disconnection, increase in film thickness, delamination, etc., caused by oversintering of nickel particles and inconsistent contraction behavior when the conductor layer and the ceramic layer are simultaneously fired are prevented, and thinned. In addition, a nickel conductor having good conductivity and adhesion is formed.

  The amount of the metal oxide other than nickel contained in the nickel composite particles according to the present invention is the total of the amount present in the metal oxide layer and the amount present in the spinel layer, and is 0.01% by weight relative to nickel. Although a small amount is effective, it is desirable that the amount be 0.05% by weight or more. If the amount is too large, it may not sinter at all, and the conductivity decreases due to a decrease in the nickel fraction, and when used in a capacitor, etc., it affects the electrical properties of the dielectric, Up to about 20% by weight is practical. Note that a small amount of nickel oxide may be present on the surface of the composite particle as long as the effect of the present invention is not hindered.

  In the present invention, the metal oxide layer and the spinel layer are produced by a spray pyrolysis method. The spray pyrolysis method is performed by spraying a solution containing one or more metal compounds as described in Japanese Patent Publication No. Sho 63-31522, Japanese Patent Laid-Open No. Hei 6-279816, etc. A method in which the droplet is heated at a temperature higher than the decomposition temperature of the metal compound, desirably near the melting point of the metal or higher, and the metal compound is thermally decomposed to precipitate metal or alloy particles. is there.

  According to this method, nickel particles having good crystallinity, high density, and high dispersibility can be obtained, and the particle size can be easily controlled, and a metal compound such as an aluminum compound is added to the raw material nickel compound solution. By doing so, the nickel composite particles according to the present invention can be obtained by one operation, and therefore there is an advantage that a new coating step is not required. Metal oxides such as aluminum deposited by pyrolysis are ejected to the surface because the crystallinity of the generated nickel particles is good, precipitates near the surface, reacts with nickel at the interface, and turns the spinel layer into both layers. It is presumed to be generated in a biting form. For this reason, a metal oxide layer and a nickel layer are joined firmly. The joint interface between nickel and metal oxide is presumed to have a metal-ceramic gradient structure, and in addition to the presence of the spinel layer, a strong joint layer is obtained, and thermal expansion during firing is also achieved. In order to prevent the destruction of the particle structure due to the mismatch of the coefficients, it is considered that the stable metal-ceramic bonding body structure is maintained even at a high temperature of about 1000 ° C. and effectively works to prevent sintering. In addition, since the metal oxide is deposited relatively uniformly on the surface, the desired effect can be achieved even with a small amount. Further, in the spray pyrolysis method, the composition of the generated particles basically matches the composition of the starting metal compound in the solution, so that the composition can be easily controlled and suitable for the production of the nickel composite particles according to the present invention. .

  In the method of the present invention, the nickel compound and the raw material compound of the metal oxide include nitrate, sulfate, oxynitrate, oxysulfate, chloride, ammonium complex, phosphate, carboxylate, metal alcoholate, resinate 1 type (s) or 2 or more types of thermally decomposable compounds, such as, are used. A double salt, a complex salt, or a metal oxide colloid solution may be used.

  A solution in which these compounds are dissolved in water, organic solvents such as alcohol, acetone, ether, or mixed solvents thereof are formed into fine droplets by an atomizer such as an ultrasonic type or a two-fluid nozzle type, and then a metal compound. The thermal decomposition is carried out by heating at a temperature higher than the decomposition temperature of and producing a spinel composed mainly of nickel and the metal oxide. The generation temperature of spinel is approximately 800 ° C. or higher although it depends on the type and conditions of the oxide. The heat treatment is desirably performed at a high temperature equal to or higher than the melting point of nickel, but may be performed at a temperature lower than the melting point when high density and shape uniformity are not required. Heating is performed in a reducing or inert atmosphere, preferably in a weakly reducing atmosphere containing hydrogen, carbon monoxide and the like.

  The conductor paste containing the nickel composite particles according to the present invention as a conductive component is produced by uniformly mixing and dispersing in an organic vehicle according to a conventional method. If necessary, other conductive particles, inorganic binders such as glass particles, and other additives may be contained.

  The nickel composite particles according to the present invention are particularly suitable for ceramic multilayer electronic parts such as multilayer capacitors and multilayer PTC elements, composite parts incorporating these, and internal conductor pastes such as composite substrates. It can also be used for a film conductor paste.

Next, the present invention will be specifically described with reference to Examples and Comparative Examples.
Examples 1-5
Nickel nitrate hexahydrate was dissolved in water so that the nickel concentration was 50 g / l. In this solution, aluminum nitrate nonahydrate was dissolved so that the nickel element would be 0.05, 0.1, 0.5, 1.0, and 2.0% by weight in terms of Al ₂ O ₃ , respectively. Thus, a raw material solution was prepared.

  This raw material solution was made into fine droplets using an ultrasonic atomizer, and a gas adjusted to be weakly reducing was used as a carrier and supplied into a ceramic tube heated to 1500 ° C. in an electric furnace. The droplets were pyrolyzed through a heating zone to produce nickel particles containing aluminum oxide.

The specific surface area of the obtained particles was about 1.2 m ² / g. When nickel particles containing 1.0% by weight of Al ₂ O ₃ were analyzed by an X-ray diffractometer, nickel and a trace amount of nickel aluminum spinel (NiAl ₂ O ₄ ) were detected. For those containing 2.0% by weight of Al ₂ O ₃ , nickel, trace amounts of NiAl ₂ O ₄ and Al ₂ O ₃ were detected by X-ray diffraction, and the vicinity of the particle surface was observed by TEM. As a result, Al ₂ O ₃ It was observed that the fine particles considered to be firmly adhered to the nickel particles by NiAl ₂ O ₄ .

Further, these composite particles were subjected to thermomechanical analysis (TMA) in a reducing atmosphere of N ₂ —H ₂ to evaluate the sintering behavior of the particles, and the sintering shrinkage start temperature and sintering shrinkage end temperature were expressed. It was shown in 1.

Next, the obtained nickel composite particles were pasted using a dihydroterpineol solution of ethyl cellulose as a vehicle. This paste was printed on a 99.6% alumina substrate and baked at 1300 ° C. in a reducing atmosphere of N ₂ —H ₂ to form a conductive film having a film thickness of about 1 μm. It was shown together.
Examples 6 and 7
Nickel particles having a chromium oxide layer on the surface were obtained in the same manner as in Examples 1 to 5 except that chromium nitrate nonahydrate was added instead of aluminum nitrate nonahydrate. X-ray diffraction and TEM revealed that NiCr ₂ O ₄ having a spinel structure was present on the surface of the nickel particles.

The particle sintering shrinkage start temperature and sintering shrinkage end temperature were measured by TMA, and are shown in Table 1 together. Further, a nickel conductive film having a film thickness of about 1 μm was formed in the same manner as in Example 1, and the sheet resistance values are shown in Table 1.
Example 8
A composite oxidation containing aluminum and magnesium was carried out in the same manner as in Example 4 except that aluminum nitrate nonahydrate and magnesium nitrate hexahydrate were mixed and added so that aluminum oxide and magnesium oxide were equimolar. Nickel particles having a physical layer on the surface were obtained.

X-ray diffraction and TEM revealed that an oxide layer having a spinel structure was present on the surface of the nickel particles. The diffraction position of the spinel phase is slightly shifted to a lower angle side than the diffraction position of NiAl ₂ O ₄ , and a part of Ni is substituted with Mg, and exists as (Mg, Ni) Al ₂ O _4. It was shown that In addition to the spinel phase diffraction line, a weak diffraction line considered to be MgO was also detected.

The particle sintering shrinkage start temperature and sintering shrinkage end temperature were measured by TMA and shown in Table 1. Table 1 also shows the sheet resistance value of the nickel conductive film formed in the same manner as in Example 1.
Example 9
Nickel particles having a composite oxide layer containing chromium and magnesium on the surface were obtained in the same manner as in Example 8 except that chromium nitrate nonahydrate was used instead of aluminum nitrate nonahydrate.

X-ray diffraction and TEM revealed that an oxide layer with a spinel structure was present. A shift was also observed in the diffraction position of the spinel phase, indicating that a part of Ni was present as (Mg, Ni) Cr ₂ O ₄ substituted with Mg.

The particle sintering shrinkage start temperature and sintering shrinkage end temperature were measured by TMA and shown in Table 1. Table 1 also shows the sheet resistance value of the nickel conductive film formed in the same manner as in Example 1.
Comparative Example 1
Pure nickel particles were obtained in the same manner as in Example 1 except that aluminum nitrate nonahydrate was not added. Table 1 shows the sintering shrinkage start temperature and the sintering shrinkage end temperature, and the sheet resistance value of the nickel conductive film formed in the same manner as in the example.

Comparative Example 2
0.5% by weight of Al ₂ O ₃ fine particles were added to the pure nickel particles of Comparative Example 1, and a nickel conductive film was formed in the same manner as in the example. When the sheet resistance value was measured, it was 314 mΩ / □.

  As is clear from the examples and comparative examples, pure nickel particles start sintering shrinkage at about 300 ° C. and end at about 600 ° C., whereas the nickel composite particles of the present invention exhibit sintering shrinkage. As the end temperature increases, sintering shrinkage occurs more slowly than pure nickel particles. Further, as the added amount of the metal oxide increases, sintering at a low temperature can be suppressed, and the effect is particularly great when the amount is 0.5% by weight or more.

When the conductive film was produced, in Comparative Example 1, oversintering of the film progressed with an increase in the firing temperature, and the resistance value increased greatly due to a disconnection. This phenomenon was not improved only by adding Al ₂ O ₃ to the paste as in Comparative Example 2, but the resistance value was increased. However, by using the nickel composite particles according to the present invention, oversintering of the film is suppressed and the conductivity is improved.

Claims (3)

A method for producing nickel composite particles having a spinel layer containing one or more selected from aluminum oxide, chromium oxide and manganese oxide and nickel oxide on at least a part of the surface of the nickel particles,
(A) one or more of thermally decomposable nickel compounds;
(B) one or more kinds of thermally decomposable compounds of metals selected from aluminum, chromium and manganese;
The solution containing is made into fine droplets, and the droplets are heated at a temperature higher than the decomposition temperature of (a) and higher than the decomposition temperature of (b), thereby generating nickel particles, and at the same time, A method for producing nickel composite particles, comprising depositing a spinel layer containing one or more selected from aluminum oxide, chromium oxide and manganese oxide and nickel oxide in the vicinity of the surface. One kind selected from aluminum oxide, chromium oxide and manganese oxide at the interface between the nickel particles and the metal oxide layer, having an oxide layer of a metal other than nickel on at least a part of the surface of the nickel particles Or a method for producing nickel composite particles in which a spinel layer containing two or more types and nickel oxide exists,
(A) one or more of thermally decomposable nickel compounds;
(B) one or more kinds of thermally decomposable compounds of metals selected from aluminum, chromium and manganese;
The solution containing is made into fine droplets, and the droplets are heated at a temperature higher than the decomposition temperature of (a) and higher than the decomposition temperature of (b), thereby generating nickel particles, and at the same time, Nickel composite particles characterized by depositing a metal oxide layer in the vicinity of a surface, and a spinel layer containing one or more selected from aluminum oxide, chromium oxide and manganese oxide and nickel oxide Manufacturing method.   The solution further contains one or more of (c) an alkaline earth metal thermally decomposable compound, and the heating of the droplets is higher than any of the decomposition temperatures of (a), (b), and (c). The method for producing nickel composite particles according to claim 1, wherein the method is performed at a temperature.