JP2005044677A - Conductive particle of detailed particle size - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide conductive particles of a fine grain diameter which is superior in a crimping resistance characteristic, and in which base material particles of particle size of 5 μm or less are used. <P>SOLUTION: This is the conductive particles of the fine grain diameter having a buffer plating layer composed of an Fe base or an Ni base corrosion resistance alloy of the average film thickness 0.01 to 0.1 μm on a surface of base material particles of particle size of 0.5 to 5 μm (for example silica particle or divinyl benzene resin series particle), and having a Pd plating layer or a Pd alloy plating layer of the average film thickness 0.01 to 0.1 μm on the buffer plating layer. For the buffer plating layer, (i) an Fe base corrosion resistance alloy containing Cr: 13 to 30 wt%, Ni: 3 to 20 wt%, (ii) a Ni base corrosion resistance alloy containing Mo: 20 to 35 wt%, Fe: 2 to 10 wt%, and (iii) a Ni base corrosion resistance alloy containing Cr: 10 to 25 wt%, Mo: 3 to 20 wt%, Fe: 2 to 25 wt%, can be suitably used. The respective plating layers can be formed by a sputtering method. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is a conductive particle whose surface is coated with metal, and in particular, a fine particle that can be suitably used as a conductive filler constituting an electrode part of a laminated electronic component having a small lamination interval or a liquid crystal having a short inter-electrode distance. Relates to conductive particles having a diameter.

  Many stacked electronic components are used in electronic devices that are becoming smaller. Typical examples of such multilayer electronic components include multilayer capacitors and inductors. These are produced by laminating a magnetic layer together with a conductive layer made of a conductive powder and integrally sintering. In addition, an anisotropic conductive filler is used for an electrode portion of liquid crystal or the like, in which conductive particles are deformed between electrodes by pressure bonding, and current is passed between specific electrodes or directions. In the case of conductive particles that undergo crimping deformation, it is necessary to form the base material with a material having good deformability and to form a conductive film on the outermost layer so that cracking and peeling do not occur during crimping.

  In the following Patent Document 1, as conductive particles having excellent pressure adhesion, Ni, Ag, Cu, Al having a thickness of 0.01 to 0.1 μm coated with base particles containing a resin, or Conductive particles are described having a buffer layer containing these alloys (except Ni-P) and an Au layer coated thereon. By interposing the buffer layer, it is possible to reduce the thickness of the expensive Au of the outermost layer, and to effectively prevent the Au layer from cracking and peeling at the time of pressure bonding. This coating structure was realized by the powder sputtering method disclosed in Patent Document 2 below. In the case of the conventional electroless plating method, it is necessary to interpose a Ni-P layer between the insulating resin layer and the outermost Au layer, and since this Ni-P layer is brittle, it is pressure resistant. However, there was a problem in the application to the use that is required. In this regard, the conductive particles of Patent Document 1 have solved the problem of pressure-resistant adhesion and contributed to improving the reliability of the multilayer electronic component.

JP-A-11-39937 JP-A-2-153068

  In recent years, due to the demand for miniaturization and higher density of electronic components, further reduction of the stacking interval or the electrode spacing is required. Along with this, the appearance of extremely fine conductive particles having a particle size of 5 μm, 4 μm, or 3 μm or less is awaited. The conductive particles described in Patent Document 1 have Au with very good conductivity and corrosion resistance on the outermost layer. Since Au has a high specific gravity, if the particle diameter of the base particles made of a resin having a low specific gravity is made small, a large amount of Au is required to perform uniform plating, which impairs economic efficiency. As a result of the inventors' investigation, it has been found that it is practically difficult to apply the technique of Patent Document 1 to resin particle powder having an average particle size of 5 μm or less.

  The present invention is a conductive particle having a fine particle size that can meet the needs for downsizing and increasing the density of electronic components as described above, and exhibits stable conductivity that is resistant to cracking and peeling even when used under pressure. The purpose is to provide.

  As a result of the inventor's study, when a conductive material is coated on the surface of a fine substrate particle having a particle size of 5 μm or less, or 4 μm or less, and further 3 μm or less, it is not a heavy metal such as Au, It was found that uniform coating is possible without increasing the coating thickness when using a metal with a light specific gravity. However, Au is inherently excellent in corrosion resistance, workability, and conductivity. By simply replacing Au in the outermost layer with other noble metals, fine conductivity with excellent corrosion resistance, conductivity, and pressure resistance is achieved. It was difficult to obtain particles stably. Therefore, when the inventor conducted detailed research and adopted a coating structure of “buffer plating layer made of Fe-based or Ni-based corrosion-resistant alloy + outermost layer made of Pd (palladium) or Pd alloy”, the above fine particles It has been found that excellent corrosion resistance, electrical conductivity, and pressure resistance can be imparted even when using as a base material. The present invention has been completed based on this finding.

That is, the object is to have a buffer plating layer made of an Fe-based or Ni-based corrosion-resistant alloy having an average film thickness of 0.01 to 0.1 μm on the surface of substrate particles having a particle size of 0.5 to 5 μm, and the buffer This is achieved by conductive particles having a fine particle diameter having a Pd plating layer or a Pd alloy plating layer having an average film thickness of 0.01 to 0.1 μm on the plating layer.
Here, the particle diameter in the case where the base particle is not spherical is represented by the maximum diameter. The Fe-based alloy and Ni-based alloy refer to alloys in which the elements having the highest content among the elements constituting the alloy are Fe and Ni, respectively. The corrosion resistant alloy refers to a plate-like test piece made of the alloy, which has a smaller mass change before and after the test than that of the Fe-13 mass% Cr alloy when a salt spray test based on JIS Z 2371 is performed. A Pd alloy refers to an alloy containing 50% or more of Pd by atomic ratio.

  In the conductive particles, the base particles are silica particles or divinylbenzene resin-based particles.

  Further, in the above conductive particles, the buffer plating layer is made of i) Cr: 13-30% by mass, Ni: Fe-based corrosion resistant alloy containing 3-30% by mass, ii) Mo: 20-35% by mass, Fe: made of Ni-based corrosion resistant alloy containing 2 to 10% by mass, iii) Cr: made of Ni-based corrosion resistant alloy containing 10 to 25% by mass, Mo: 3 to 20% by mass, Fe: 2 to 25% by mass Are provided respectively.

  Moreover, the said electroconductive particle WHEREIN: The thing in which the buffer plating layer and the Pd plating layer were formed by sputtering method is provided.

The conductive particles of the present invention are those in which a conductive material is stably coated on a substrate having a fine particle diameter of 5 μm or less, 4 μm or less, and further 3 μm or less. Conventionally, it has been difficult to obtain such fine conductive particles, but the conductive particles of the present invention can be industrially produced and have the following merits.
[1] Since the particle size is small, the powder composed of these particles can meet the needs of high-density electronic components in which the stacking interval and interelectrode distance are desired to be smaller than before.
[2] By adopting a coating structure with a specific thickness of “buffer plating layer made of Fe-base or Ni-base corrosion-resistant alloy + outermost layer made of Pd or Pd alloy”, even when the particle size is small, it is High resistance to cracking and peeling of coating layer. That is, it has excellent pressure resistance.
[3] By adopting the coating structure, it has excellent corrosion resistance and sufficient conductivity even though it does not have an Au plating layer.
[4] Since there is no need to form an Au plating layer, the material cost is low.
[5] Since it is not necessary to use the electroless plating method, environmental degradation due to waste liquid does not occur.

  The conductive particles of the present invention employ fine particles having a particle size of 5 μm or less as substrate particles. As a result, it is possible to provide a conductive filler suitable for constructing a high-density electronic component having a very small stacking interval or interelectrode distance. If the particle diameter of the substrate particles exceeds 5 μm, it is difficult to further reduce the stacking interval of the multilayer electronic component. In addition, in the case of such a large particle, in order to further reduce the distance between electrodes of liquid crystal parts and the like, it is necessary to apply a very large deformation to the particle at the time of pressure bonding. As a result, it becomes difficult to ensure stable conductivity. Therefore, in the present invention, fine substrate particles having a particle size of 5 μm or less are used, but it is more desirable to use extremely fine substrate particles having a particle size of less than 5 μm, 4 μm or less, and further 3 μm or less.

  However, when the particle diameter is less than 0.5 μm, the particles are very likely to aggregate, and it is difficult to uniformly plate the base particles one by one. Moreover, since the specific surface area increases as the particle size decreases, it is necessary to increase the amount of plating extremely, which is uneconomical. For this reason, in the present invention, the lower limit of the particle size of the substrate particles is specified to be 0.5 μm.

  The material of the base particles needs to be an inorganic substance or an organic substance having a regularity at least in a temperature range from room temperature to 100 ° C. Those capable of maintaining the formability in a temperature range of preferably up to 150 ° C, more preferably up to 250 ° C are desirable. Silica particles are optimal as the particles made of an inorganic substance. Glass particles and other various ceramic particles can also be used. As particles made of an organic substance, divinylbenzene resin-based particles can be suitably used. Resin particles such as benzoguanamine resin, acrylic resin, polystyrene resin, silicone resin, fluorine resin, and urethane resin can also be used.

  The shape of the substrate particles is not particularly limited. Various shapes of particles can be used depending on the application, such as spherical, granular, massive, crushed, porous, aggregated, flake, spike, filament, fiber, whisker. In general, in order to reduce the variation in electrical conductivity during use, it is considered preferable to use a true spherical powder having a uniform particle size as much as possible.

  Since it becomes expensive if the coating layer on the surface of the substrate particles is entirely composed of Pd or Pd alloy, a buffer plating layer is interposed under the outermost Pd or Pd alloy plating layer. Since Pd or Pd alloy is not as corrosion-resistant as Au, the buffer plating layer is made of an Fe-based or Ni-based corrosion-resistant alloy in order to ensure sufficient corrosion resistance in the entire coating layer.

  As the Fe-based corrosion resistant alloy, those containing Cr: 13 to 30% by mass and Ni: 3 to 30% by mass are suitable. These include SUS304, SUS310S, SUS316, SUS309S, SUS317, SUS321, and SUS347, which are austenitic stainless steels.

  Ni-based corrosion resistant alloys include Mo: 20 to 35 mass%, Fe: 2 to 10 mass%, or Cr: 10 to 25 mass%, Mo: 3 to 20 mass%, Fe: 2 to 25 mass% Those containing are preferred. Among these, a high corrosion resistance alloy called Hastelloy (registered trademark) is included. Examples include Hastelloy B, Hastelloy G, Hastelloy C, Hastelloy H, Hastelloy N, Hastelloy X, Hastelloy XR and the like.

  Such a complex alloy plating is impossible by the electroless plating method conventionally performed. Even in the vacuum deposition method, the melting point, boiling point, and vapor pressure under high vacuum of each metal constituting the alloy are different from each other, so that it is technically impossible to perform alloy plating with an arbitrary composition. A CVD method or the like in which the temperature during plating is 500 ° C. or higher cannot be applied to the present invention because the substrate particles themselves are affected by heat. In this respect, if the powder sputtering method is used, the above various alloys can be coated on the surface of the substrate particles.

The average thickness of the buffer plating layer is preferably 0.01 to 0.1 μm. When the average film thickness is less than 0.01 μm, it is difficult to uniformly coat the surface of the substrate particles, and it tends to be a scattered coating layer. In this case, sufficient adhesion of the outermost layer cannot be ensured, and the electrical conductivity as the conductive filler is lowered. On the other hand, when the average film thickness exceeds 0.1 μm, the unevenness on the surface of the plating layer becomes large. On the contrary, the electrical resistance between the particles increases, and the electrical conductivity as the conductive filler decreases.
Since the Fe-based or Ni-based corrosion resistant alloy has a lower specific gravity than Au, it can be controlled to a predetermined thickness by a relatively small amount of plating.

  On the buffer plating layer, a Pd plating layer or a Pd alloy plating layer is formed as the outermost layer. As described above, Au is very excellent in terms of corrosion resistance, workability, and conductivity. However, in the present invention, since a substrate having a fine particle diameter is used unlike the conventional one, the specific gravity is heavy and expensive. You can't use Au. Therefore, as a result of various studies, in combination with the buffer plating layer described above, Pd or Pd alloy is coated as the outermost layer, so that it has corrosion resistance, conductivity and pressure resistance that are practically comparable to those of Au plating. In addition, conductive particles having a fine particle size that cannot be obtained in the case of Au plating can be realized.

  The outermost layer can be a Pd plating layer made of high-purity Pd (for example, a purity of 99.99% by mass or more), and a Pd alloy plating layer according to required characteristics such as solder barrier resistance and wear resistance. You can also. Examples of the Pd alloy include a Pd—Au alloy, a Pd—Ag alloy, a Pd—Cu alloy, a Pd—Fe alloy, a Pd—Ni alloy, and a Pd—Pt alloy. Pd plating and Pd alloy plating can also be suitably performed by a powder sputtering method.

The average film thickness of the Pd or Pd alloy plating layer is preferably 0.01 to 0.1 μm. If the thickness is less than 0.01 μm, it is difficult to cover the entire surface of the buffer plating layer, and it tends to be scattered, so that the adhesion cannot be strengthened, and the electrical conductivity as the conductive filler becomes insufficient. On the other hand, even if the average film thickness exceeds 0.1 μm, the electrical conductivity as the conductive filler is not improved, and only the economy is impaired.
Since Pd or Pd alloy has a lower specific gravity than Au, it can be controlled to a predetermined film thickness by a relatively small amount of plating.

In order to form the buffer plating layer and the Pd or Pd alloy plating layer, the “powder sputtering method” disclosed in Patent Document 2 can be used. That is, if the powder of the base particle or the powder with the buffer plating layer is put in the rotating barrel and the powder is irradiated with sputtered particles of various metals excited to the plasma state while stirring, the individual particles are targeted. It is possible to coat the metal or alloy uniformly. As conditions, for example, the degree of vacuum: 1 × 10 ⁻³ Tor. Hereinafter, it is preferable that the argon gas flow rate is 5 ccm or less, the sputtering output is 10 W / cm ² or more, and the particle temperature is 100 ° C. or more.

  After finish plating of Pd or Pd alloy, surface treatment may be performed with various silane coupling agents or titanate coupling agents in order to improve dispersibility in the paint. Further, in order to suppress the change in conductivity of the coating film with time, the surface treatment may be performed with an antioxidant such as hydroquinone, triethanolamine, O-sulfobenzimide or N-octadecanoylbenzenesulfonylamide.

[Invention Example 1]
Using spherical silica particle powder with an average particle size of 2 μm as a base material, 58% Ni-22% Cr-13% Mo-4% Fe-3% W alloy (composition is mass%) is buffered on the surface of the particles. A plating layer was formed. This alloy is a Ni-based corrosion resistant alloy corresponding to Hastelloy C (trade name). Next, a Pd plating layer was formed on the buffer plating layer. The plating method used was a “powder sputtering method” in which a coating layer was formed by sputtering on the surface of the powder particles in the rotating barrel. The plating conditions are as follows: degree of vacuum: 1 × 10 ⁻³ Tor. Hereinafter, the argon gas flow rate: 5 ccm or less, the sputtering output: 10 W / cm ² or more, and the particle temperature: 100 ° C. or more. The buffer plating layer and the Pd plating layer were sequentially formed by changing the target in the middle. The obtained powder of plating particles was subjected to X-ray fluorescence analysis of Si, Ni and Pd, and the film thickness of each plating film was calculated based on the data. As a result, the average film thickness of the buffer plating layer was 0.05 μm, Pd The average film thickness of the plating layer was 0.05 μm.

The plating particle powder was mixed with 5% by mass of an epoxy resin to form a film having a thickness of 25 μm. Next, this film was sandwiched between glass substrates coated with thermoplastic polyethersulfone resin, and thermocompression bonded at a pressure of 20 kg / cm ² and a temperature of 150 ° C. for 15 seconds.

The cross section of the thermocompression-bonded film was observed with an optical microscope, and pressure resistance was evaluated according to the following criteria.
(Pressure resistant evaluation)
○: No cracking or peeling is observed in the plating film of particles.
(Triangle | delta): Although cracking is recognized by the plating film of particle | grains, peeling is not recognized.
X: Peeling is observed in the plating film of the particles.
Moreover, the electrical resistivity was measured by the 4 terminal method about the film after thermocompression bonding, and the electroconductivity was evaluated by the following references | standards.
(Conductivity evaluation)
○: Volume resistance is less than 5 × 10 ⁻³ Ω · cm (conductivity: good)
Δ: Volume resistance is 5 × 10 ⁻³ Ω · cm to less than 5 × 10 ⁻¹ Ω · cm (conductivity; somewhat inferior)
×: Volume resistance is 5 × 10 ⁻¹ Ω · cm or more (conductivity; inferior)
As shown in Table 1, both pressure resistance and conductivity were good.

[Invention Example 2]
Similar to Invention Example 1 except that spherical silica particle powder having an average particle diameter of 1 μm is used as the base material and the buffer plating layer is made of a 52% Ni-22% Cr-20% Fe-6% Mo alloy (composition is mass%). The experiment was carried out by the method. The alloy of the buffer plating layer is a Ni-based corrosion resistant alloy corresponding to Hastelloy G (trade name). The average film thickness of the buffer plating layer was 0.03 μm, and the average film thickness of the Pd plating layer was 0.03 μm. As shown in Table 1, both pressure resistance and conductivity were good.

[Invention Example 3]
The same method as Example 1 except that spherical silica particle powder having an average particle size of 0.5 μm is used as the base material, and the buffer plating layer is 55% Fe-25% Cr-20% Ni alloy (composition is mass%). The experiment was conducted. The alloy of the buffer plating layer is an Fe-based corrosion resistant alloy corresponding to SUS310S. The average film thickness of the buffer plating layer was 0.01 μm, and the average film thickness of the Pd plating layer was 0.01 μm. As shown in Table 1, both pressure resistance and conductivity were good.

[Invention Example 4]
The same as Example 1 except that spherical divinylbenzene resin particle powder having an average particle diameter of 5 μm is used as the base material, and the buffer plating layer is a 67% Ni-28% Mo-5% Fe alloy (composition is mass%). The experiment was conducted by the method. The alloy of the buffer plating layer is a Ni-based corrosion resistant alloy corresponding to Hastelloy B (trade name). The average film thickness of the buffer plating layer was 0.1 μm, and the average film thickness of the Pd plating layer was 0.1 μm. As shown in Table 1, both pressure resistance and conductivity were good.

[Invention Example 5]
The same as in Invention Example 1 except that spherical divinylbenzene resin particle powder having an average particle diameter of 4 μm is used as the base material and the buffer plating layer is made of 74% Fe-18% Cr-8% Ni alloy (composition is mass%). The experiment was conducted by the method. The alloy of the buffer plating layer is an Fe-based corrosion resistant alloy corresponding to SUS304. The average film thickness of the buffer plating layer was 0.08 μm, and the average film thickness of the Pd plating layer was 0.08 μm. As shown in Table 1, both pressure resistance and conductivity were good.

[Invention Example 6]
Example of invention, except that spherical divinylbenzene resin particle powder having an average particle diameter of 3 μm is used as the base material, and the buffer plating layer is made of 68% Fe-18% Cr-12% Ni-2% Mo alloy (composition is mass%). The experiment was conducted in the same manner as in 1. The alloy of the buffer plating layer is an Fe-based corrosion resistant alloy corresponding to SUS316. The average film thickness of the buffer plating layer was 0.06 μm, and the average film thickness of the Pd plating layer was 0.06 μm. As shown in Table 1, both pressure resistance and conductivity were good.

[Comparative Example 1]
An experiment was conducted in the same manner as in Invention Example 1 except that spherical silica particle powder having an average particle diameter of 2 μm was used as the base material, the formation of the buffer plating layer was omitted, and the Pd plating layer was directly formed on the base particle surface. . The average film thickness of the Pd plating layer was 0.05 μm. As shown in Table 1, when there was no buffer plating layer, the adhesiveness of the Pd plating layer was poor, and the pressure resistance was poor. In this case, the measured value of the electric resistance was good, but since the Pd film was peeled off, there was a risk of causing a localized current failure in actual use, resulting in lack of reliability.

[Comparative Example 2]
Experiments were performed in the same manner as in Invention Example 1 except that spherical silica particle powder having an average particle diameter of 2 μm was used as the substrate and the formation of the outermost Pd plating layer was omitted. The average film thickness of the film corresponding to Hastelloy C (trade name) was 0.05 μm. As shown in Table 1, the conductivity was inferior because there was no Pd plating layer.

[Comparative Example 3]
An experiment was performed in the same manner as in Invention Example 1 except that spherical silica particle powder having an average particle diameter of 2 μm was used as the substrate. However, the average film thickness of the buffer plating layer corresponding to Hastelloy C (trade name) was adjusted to 0.005 μm, and the average film thickness of the Pd plating layer was adjusted to 0.005 μm. As shown in Table 1, when the average film thickness of the buffer plating layer was thinner than the specified range of the present invention, the film adhesion decreased and the pressure-resistant adhesion was inferior. Further, since the average film thickness of the Pd plating layer was thinner than the range specified in the present invention, the conductivity was inferior.

[Comparative Example 4]
An experiment was performed in the same manner as in Invention Example 1 except that spherical silica particle powder having an average particle diameter of 2 μm was used as the substrate. However, the average film thickness of the buffer plating layer corresponding to Hastelloy C (trade name) was adjusted to 0.2 μm, and the average film thickness of the Pd plating layer was adjusted to 0.2 μm. In this case, when the average film thickness of the buffer plating layer and the Pd plating layer was thicker than the specified range of the present invention, the unevenness of the plating surface was increased. When stress is applied due to this, film cracking easily occurs, and the contact electrical resistance between particles also increases. For this reason, as shown in Table 1, the pressure resistance and conductivity were not very good.

Claims (6)

  A buffer plating layer made of an Fe-based or Ni-based corrosion-resistant alloy having an average film thickness of 0.01 to 0.1 μm is provided on the surface of the base particle having a particle size of 0.5 to 5 μm, and an average is formed on the buffer plating layer. Conductive particles having a fine particle diameter having a Pd plating layer or a Pd alloy plating layer having a thickness of 0.01 to 0.1 μm.   The conductive particles according to claim 1, wherein the base particles are silica particles or divinylbenzene resin-based particles.   3. The conductive particle according to claim 1, wherein the buffer plating layer is made of an Fe-based corrosion resistant alloy containing Cr: 13 to 30% by mass and Ni: 3 to 30% by mass.   The conductive particles according to claim 1 or 2, wherein the buffer plating layer is made of a Ni-based corrosion-resistant alloy containing Mo: 20 to 35 mass% and Fe: 2 to 10 mass%.   The conductive particles according to claim 1 or 2, wherein the buffer plating layer is made of a Ni-based corrosion resistant alloy containing Cr: 10 to 25% by mass, Mo: 3 to 20% by mass, and Fe: 2 to 25% by mass.   The conductive particles according to claim 1, wherein the buffer plating layer and the Pd plating layer are formed by a sputtering method.