JP2000057843A - Conductive particle excellent in migration resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent migration resulting from the use of silver and to impart excellent conductivity and corrosion resistance to copper particles to provide conductive particles that inhibit oxidation and reactivity with resin during soldering and that change little in conductivity over aging by coating the surfaces of the copper particles with a copper-nickel alloy. SOLUTION: 1 to 20 wt.% copper-nickel alloy coated layers are formed by physical deposition method on the surfaces of copper particles having average particle diameters of 1 to 100 μm. The copper-nickel coated layers are either nickel silver, Constantan, or Monel metal and formed on the surfaces of the copper particles by e.g. a sputtering method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to highly conductive particles for paste used for forming internal electrodes and internal conductors of various laminated electronic components, and paints for antistatic and EMI shielding. The present invention relates to highly conductive particles used for plastic molded articles, plastic films, synthetic fibers, and the like.

[0002]

2. Description of the Related Art Among multilayer electronic components, multilayer capacitors, inductors and the like are manufactured by laminating a magnetic layer on a conductive layer made of highly conductive particles and sintering them integrally. I have. Among them, a conductive paper for forming a conductive layer
The performance of the strike is the most important factor that determines the performance of the multilayer electronic component. The highly conductive particles, which are the main components of the conductive paste, are required to have not only conductivity but also excellent migration resistance, which is a problem when used in a high-temperature and humid environment. Silver has been conventionally used as such highly conductive particles. In addition, silver is used in many cases in coatings for antistatic and EMI shielding, plastic molded products, plastic films, synthetic fibers, and the like, particularly when high conductivity is required. However, while silver has excellent conductivity and corrosion resistance, it has a problem in migration resistance.

In a migration, when a DC voltage is applied between two insulated circuits in a state where moisture is present between the two circuits, silver ions elute from silver used as an anode and are discharged to a cathode. This is a phenomenon in which silver that has migrated and grown in the cathode portion eventually short-circuits both circuits. In particular, migration becomes a serious problem in electronic equipment used in a wet environment, and the reliability of electronic parts is impaired. The migration by silver is carried out by using silver-palladium alloy powder or silver-palladium.
The use of copper alloy powder can be controlled to some extent. However, in a silver-palladium alloy, for example, when a pattern is formed on a substrate as a conductive paste, palladium exhibits catalytic activity at a soldering temperature at the time of connecting the substrates,
The resin added as a solidifying agent in the conductive paste is decomposed. As a result, the conductive paste may not be sufficiently solidified. On the other hand, a silver-copper alloy has poor migration resistance in a region containing a large amount of silver, and conversely oxidizes during soldering in a region containing a large amount of copper, thereby impairing the life stability of electronic components.

For this reason, new highly conductive particles have been developed. For example, the migration resistance is improved by coating two or more layers of different noble metals on the surface of powder particles such as copper and iron. Conductive electrode material (Japanese Unexamined Patent Publication No.
No. 66,101) and a silver-plated composite powder for conductive paint in which silver is electrolessly plated on the surface of spherical particles of a polystyrene resin or a phenol resin (JP-A-2-118,079). . However, JP-A-2-66,
The conductive electrode material disclosed in Japanese Patent Application Publication No.
It is extremely expensive because it uses platinum, silver and the like. In addition, if the coating has pinholes or unplated portions, the silver elution phenomenon is promoted electrochemically, and the migration resistance is rather poor. On the other hand, Japanese Patent Laid-Open No. 2-11
The silver-plated composite powder disclosed in Japanese Patent No. 8,079 has excellent conductivity, but low adhesion between the silver-plated layer and the resin.
In addition, migration cannot be completely prevented because the plating layer is silver.

[0005]

SUMMARY OF THE INVENTION The present invention has been devised to solve such a problem, and the use of silver by coating a copper-nickel alloy on the surface of copper particles. At the same time as preventing the occurrence of migration caused by the above, imparting excellent conductivity and corrosion resistance to the copper particles, suppressing oxidation and reactivity with the resin at the time of soldering, and little change in conductivity with time. An object is to provide conductive particles.

[0006]

Means for Solving the Problems The conductive particles of the present invention are:
In order to achieve the object, a copper / nickel alloy coating layer of 1 to 20% by weight is formed on the surface of copper powder particles having an average particle diameter of 1 to 100 μm by a physical vapor deposition method and contains no silver. The biggest feature is that it is not. Electroless copper plating or electroless nickel plating is generally used as a method of coating metal on the surface of particles, but it is extremely difficult to coat copper / nickel alloy by electroless plating. Met. On the other hand, it is basically possible to coat a copper / nickel alloy on the surface of particles by physical vapor deposition. For example, the present inventors disclosed in Japanese Patent Laid-Open No.
According to the sputtering method introduced in Japanese Patent Publication No. 68, it can be easily carried out. In this method, copper powder is put into a rotating barrel, and the sputtered copper and nickel particles collide with the copper powder while stirring, so that the surface of the copper powder particles is coated with a copper / nickel alloy having a predetermined composition. Can be Although a vacuum evaporation method can be used, it is difficult to keep the alloy composition of copper and nickel constant because the melting points and vapor pressures of copper and nickel are significantly different.

The copper / nickel alloy according to the present invention has the following features. (1) Copper having good solid solubility with nickel contained in the coating metal is used as powder particles. Therefore, an alloy layer is formed at the interface between the coating layer and the powder particles due to the temperature rise during sputtering, and the adhesion becomes extremely strong. (2) When pure nickel is coated on the surface of copper powder particles, if there is a pinhole or unplated portion of the coating, an internal battery is formed due to the difference in ionization tendency, and nickel is selectively eluted. A phenomenon occurs. However, in the present invention, since the coating layer is an alloy of copper and nickel, even if there is a pinhole or an unplated portion of the coating, the electrochemical elution phenomenon of nickel hardly occurs. (3) In the case of using only copper powder particles, when an oxide film is formed due to deterioration over time, a high specific resistance of the order of 10 ⁶ Ω · cm is exhibited. However, a coating layer of a copper / nickel alloy has a low specific resistance of the order of 10 ⁻⁴ Ω · cm because of its excellent corrosion resistance, and its change with time is small. (4) If the conductivity is significantly reduced due to storage or corrosion for an extremely long period of time, about 20
By performing the reduction treatment at a low temperature of 0 ° C. for 1 hour,
It can return to a low specific resistance of the order of 0 ^-4 Ω · cm.

As the composition of the coating film, use other than the copper / nickel alloy was considered. However, other than the copper / nickel alloy, a copper / cobalt alloy, a copper / chromium alloy, a copper / iron alloy, a copper / tin alloy was used. We examined various combinations of copper, zinc alloys, etc.
All of the conductivity and the migration resistance could not be satisfied.

The copper / nickel alloy may be composed of two components, but may further contain tin, zinc, iron or manganese. However, if the nickel content is too small, less than 8% by weight, the corrosion resistance is reduced, and if the nickel content is more than 70% by weight, the conductivity is reduced. Therefore, the range of 8 to 70% by weight is most preferable. More specifically, nickel white containing 8% to 70% by weight of nickel, constantan containing 40% to 45% by weight, and Monel metal containing 60% to 70% by weight have the most balanced corrosion resistance, conductivity and anti-migrain resistance. -Has an optional property.

It is necessary that the copper powder particles have an average particle size of 1 to 100 μm. If the average particle size is less than 1 μm, the particles will agglomerate significantly, making it difficult to coat the copper / nickel alloy uniformly. In addition, the smaller the particle size, the larger the specific surface area of the powder. Therefore, it is necessary to increase the coating amount, which causes an increase in manufacturing cost. Conversely, if the average particle size exceeds 100 μm, a large amount of copper powder particles need to be added, which increases the cost. In addition, since conduction failure is likely to occur, the reliability of the conductive particles decreases. The shape of the copper powder particles is not particularly limited. However, in order to exhibit excellent conductivity by adding as little as possible, whisker-like and fluffy particles are more preferable than spherical, resinous and crushed particles. -A fiber or a short fiber is preferred.

The amount of coating of the copper / nickel alloy with respect to the copper powder particles is regulated in the range of 1 to 20% by weight from the viewpoint of ensuring excellent migration resistance. When the coating amount is less than 1% by weight, the coating thickness becomes extremely thin, so that the corrosion resistance decreases. On the other hand, when the content is 20% by weight or more, the thickness of the coating becomes extremely large, so that the unevenness of the coating surface becomes remarkable. For this reason, the contact state between the particles is deteriorated, so that the conductivity is rather lowered. Incidentally, in order to improve the dispersibility in the paint, a surface treatment may be performed with various silane coupling agents or titanate coupling agents after coating the copper / nickel alloy. However, in this case, care must be taken because conductivity is reduced when the coating is too thick.

The conductive particles of the present invention have excellent oxidation resistance at a soldering temperature, do not react with a resin, and have an improved migration resistance effectively with a small coating amount.
Further, since expensive silver is not used and the manufacturing method is simple, the cost can be reduced. Hereinafter, the present invention will be described with reference to examples.

[Examples 1 and 2] JP-A-2-1
Using a powder sputtering apparatus introduced in Japanese Patent No. 53068, 1% by weight and 3% by weight of nickel white (JIS 1 type, 73% by weight) were respectively applied to the surface of flake copper powder having an average particle diameter of 1 μm and 5 μm. % Copper, 18% by weight nickel,
9% by weight zinc) was coated. The migration resistance of each of the obtained conductive particles was examined according to the test method described below. The conductive particles were pasted, printed on a glass epoxy substrate at intervals of 1 mm, and the solvent was evaporated and solidified to prepare a migration measuring electrode having a thickness of 30 μm. The ratio of the conductive particles in the electrode was 40% by volume (constant). After dropping deionized water between the electrodes, a DC voltage of 5 V is applied,
The time when current began to flow between the electrodes was measured and evaluated as the migration start time. The longer the migration start time, the better the migration resistance. Table 1 shows the measurement results. Table 1 also shows the specific resistivity of the conductive particles measured by a four-terminal method for reference.

[Examples 3 and 4] Following the same procedure as in Example 1, 5% by weight and 10% by weight of flake copper powder having an average particle size of 10 μm and 20 μm
% By weight of constantan (55% by weight copper, 45% by weight nickel) was coated. Table 1 shows the migration resistance and the specific resistivity of the obtained conductive particles.

[Examples 5 and 6] According to the same procedure as in Example 1, the average particle diameters were 50 μm and 100 μm.
15% by weight and 20% by weight of monel metal (70% by weight nickel, 24% by weight)
Wt% copper, 2.5 wt% iron, 2.0 wt% manganese, and others). Table 1 shows the migration resistance and the specific resistivity of the obtained conductive particles.

[0016]

[Table 1]

[Comparative Example 1 and Comparative Example 2] According to the same procedure as in Example 1, 10% by weight of pure nickel and pure silver were coated on the surface of flake copper powder having an average particle diameter of 20 μm by a sputtering method. -I did it. Table 1 shows the migration resistance and the specific resistivity of the obtained conductive particles.

Comparative Example 3 Electroless nickel plating of 10% by weight was performed on the surface of a flaky copper powder having an average particle diameter of 20 μm according to the following procedure. First, distilled water 1
100 g of flake-form copper powder was put into a dilute hydrochloric acid aqueous solution in which 40 ml of concentrated hydrochloric acid was added to L, and stirred at room temperature for 30 minutes to dissolve and remove an oxide film on the surface of the powder. next,
100 g of this pickled flaked copper powder was put into a beaker containing 0.8 L of an electroless plating solution mixed with 30 g of nickel sulfate and 15 g of sodium acetate, followed by stirring. While maintaining the temperature at 90 ° C., while adjusting the pH to a range of 5 to 6 by adding diluted ammonia water, a reducing solution 0.8 g in which 5 g of sodium hypophosphite was dissolved was added.
L was added in small portions over 1 hour. With this work,
The surface of a flaky copper powder having an average particle size of 20 μm
The electroless nickel plating of weight% was performed. Thereafter, the produced electroless nickel-plated copper powder was thoroughly washed with water, filtered and dried. Table 1 shows the migration resistance and the specific resistivity of the obtained conductive particles.

Comparative Example 4 A 10% by weight electroless silver plating was performed on the surface of a flaky copper powder having an average particle diameter of 20 μm according to the following procedure. First, 100 g of flaky copper powder was put into a diluted hydrochloric acid aqueous solution obtained by adding 40 ml of concentrated hydrochloric acid to 1 L of distilled water, and then stirred at room temperature for 30 minutes to dissolve and remove an oxide film on the surface of the powder. Next, 40 ml of concentrated ammonia water, 14 g of potassium hydroxide, 20 g of silver nitrate
bead containing 1 L of electroless silver plating solution mixed at a ratio of 1 g
In the car, the pickled flake copper powder 1
After charging 100 g, 12 g of glucose was placed in 1 L of 0.2 N formalin while maintaining the temperature at 60 ° C. with stirring.
Was dissolved and 20 ml of diluted ammonia water was added over 1 hour. Thereafter, the produced electroless silver-plated copper powder was thoroughly washed with water, filtered and dried. By this operation, on the surface of the flake-like copper powder having an average particle diameter of 20 μm,
Electroless silver plating of 10% by weight was performed. Table 1 shows the migration resistance and the specific resistivity of the obtained conductive particles.

As can be seen from the survey results in Table 1, 1-2
In the examples in which the copper / nickel alloy was coated at 0% by weight, the specific resistance was as low as 9.3 × 10 ⁻⁴ Ω · cm or less in each case, and the migration resistance was excellent. However, the sputtering method and the electroless plating method
In the case of a comparative example in which nickel was coated by weight%,
Although the migration resistance was excellent, the specific resistance was as high as 5.0 × 10 ⁻³ Ω · cm or more. On the other hand, in the case of the comparative example in which 10% by weight of silver was coated by a sputtering method or an electroless plating method, the specific resistance was 1.3 × 10 ⁻⁴ Ω.
Cm, but low, but the migration resistance was markedly inferior.

[Effects of the Invention] As described above, the conductive particles of the present invention are formed by coating a copper / nickel alloy on the surface of a flake-like copper powder by physical vapor deposition.
Relatively low electric resistance, excellent in corrosion resistance and migration resistance. In addition, since no expensive silver is used, it is inexpensive and excellent in terms of resource saving. Therefore, high conductive particles which are a main component of high quality conductive paste suitable for forming internal electrodes and internal conductors of various laminated electronic components for which miniaturization is strongly required, as well as antistatic and EMI shielding. It is widely used as general-purpose highly conductive particles used in paints for plastics, plastic molded products, plastic films and synthetic fibers.

Claims (3)

[Claims] 1. A copper-nickel alloy coating layer of 1 to 20% by weight is formed on a surface of copper powder particles having an average particle diameter of 1 to 100 μm by physical vapor deposition, and has excellent migration resistance. Conductive particles. 2. The conductive particles according to claim 1, wherein the copper / nickel alloy is one of nickel silver, constantan, and monel metal. 3. The conductive particles according to claim 1, wherein the physical vapor deposition method is a sputtering method.