JPH10134636A - Conductive powder, conductive paste, and electric circuit using conductive paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide powder excellent in conductivity and migration resistance by covering the surface of copper powder with a specific quantity of silver, and setting the peak intensity ratio by an Auger spectral analysis to a specific value. SOLUTION: The silver quantity applied to the surface of copper powder, i.e., coating quantity, is set to 5-30wt.%, preferably to 10-25wt.% and more preferably to 15-25wt,%, against the copper powder. When the costing quantity is below 5wt.%, the exposure face of copper is increased, and the coating effect of silver rarely exists. When the coating quantity exceeds 30wt.%. the conductivity and printing property are deteriorated, and the cost is increased. The area where the copper powder is coated by silver is preferably set to 40% or above, more preferably to 50% or above, and most preferably to 60% or above, against the whole surface area. The peak intensity ratio between copper and silver in an Auger spectral analysis is set to 1:100-30:100, preferably to 5:100-25:100, more preferably to 10:100-20:100.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a conductive powder, a conductive paste, and an electric circuit using the conductive paste.

[0002]

2. Description of the Related Art Conventionally, as a method of forming an electric circuit (wiring conductor) such as a wiring board or an electronic component, a conductive metal powder such as gold, silver, palladium, copper, or aluminum is used as a conductive powder. It is generally known to form a paste by adding or printing a conductive paste formed by adding a binder such as resin or glass frit and a solvent. Of the various conductive metal powders, gold is extremely expensive, so silver is often used as a conductive powder in fields requiring high conductivity and copper is used in other fields.

[0003] However, silver is more expensive than gold and palladium, and when a DC voltage is applied in the presence of moisture, silver called electrode migration occurs in electrodes and electric circuits, and silver or silver is deposited between electrodes or wiring. Serious shortcomings arise.

[0004] In order to prevent migration of silver, a conductive material using a conductive powder of an alloy of silver and palladium is commercially available, but still has a problem that it is extremely expensive.

On the other hand, copper is inexpensive and migration is relatively unlikely, but when heating the conductive paste,
There is a problem that an oxide film is formed on the surface of the copper particles by air and oxygen in the binder to deteriorate the conductivity. For this reason, measures such as applying a moisture-proof paint to the surface of the conductor and adding corrosion and antioxidants to the conductive material have been studied, but have not been able to obtain a sufficient effect.

JP-A-56-8892 discloses a method of using silver-plated copper powder in order to improve both the oxidation resistance of copper and the migration resistance of silver with a conductive powder. Electroless plating is used as a plating method, particularly as a method of silver-plating fine powder, and the electroless plating method includes a displacement plating method involving elution into a metal plating solution serving as a base material to be plated, and a plating solution. The metal salt therein is roughly classified into a chemical reduction plating method in which electrons are received from a reducing agent in a plating solution to form a metal film.

In the displacement plating method, chemical reduction plating has been widely used because it is difficult to form a thick film and obtain a dense film quality. However, a soluble reducing agent, a pH adjuster, and a plating solution stabilizer are used. As the essential material, the adjustment and control of the plating solution was complicated, and the emphasis was on uniformly coating silver so that the copper was not exposed on the surface. Has not been practically used yet.

[0008]

SUMMARY OF THE INVENTION The first aspect of the present invention provides a conductive powder excellent in conductivity and migration resistance. The invention described in claim 2 provides a conductive paste having excellent conductivity and migration resistance. The third aspect of the present invention provides an electric circuit having excellent conductivity and resistance to migration.

[0009]

According to the present invention, a surface of a copper powder is coated with 5 to 30% by weight of silver based on the copper powder,
In addition, the intensity ratio between the copper peak and the silver peak determined by Auger spectroscopy indicates that the ratio of the copper peak to the silver peak is 1: 100 to 3
The present invention relates to a conductive powder containing silver-coated copper powder of 0: 100. The present invention also relates to a conductive paste comprising the above-mentioned conductive powder and a binder and a solvent. Further, the present invention relates to an electric circuit formed on the surface of the substrate using the above-mentioned conductive paste.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION With respect to the conductive powder of the present invention, there is no particular limitation on the average particle size of copper powder as a base material. The average particle size obtained by a general particle size distribution measurement method is 1
It is preferable to use a copper powder having a size of 30 μm or less. 1μ
It is extremely difficult to produce a powder of less than m inexpensively, and if it exceeds 30 μm, the resistance and printability tend to deteriorate. The shape of the copper powder is not particularly limited, but is preferably substantially spherical. Further, it is preferable to use copper powder whose surface is not oxidized and to which no fat or oil is attached.

The method of coating silver on the surface of the copper powder is not particularly limited, and examples thereof include a plating method, a vapor deposition method, and a mechanophase method of coating with mechanical energy. The plating method is preferable from the viewpoint of the migration property of silver and silver. Although there is no particular limitation on the plating method, it is preferable to perform plating by a displacement plating method. For this plating, while stirring and dispersing the copper powder in the plating bath, for example, a known method such as charging a plating solution in which silver cyanide and sodium cyanide are dissolved may be used, but in order to satisfy the requirements of the present invention. It is preferable to perform plating at a high plating rate by a method such as charging a predetermined amount of plating solution at a time.

The amount of silver coated on the surface of the copper powder (hereinafter referred to as
The amount is simply 5 to 30% by weight, preferably 10 to 25% by weight, more preferably 15% by weight based on the copper powder.
If the coating amount is less than 5% by weight, the exposed surface of copper is increased and there is almost no effect of coating silver. For example, a conductive paste is applied to a substrate or the like to perform heat treatment. Then, the underlying copper powder is oxidized and the conductivity is deteriorated. On the other hand, if the coating amount exceeds 30% by weight, the conductivity and printability deteriorate and the cost increases.

The area where the copper powder is covered with silver (hereinafter referred to as
Simply referred to as coating area) is 4 to the total surface area of the copper powder.
It is preferably at least 0%, more preferably at least 50%, even more preferably at least 60%. The coverage area is determined as follows. That is, 10 or more particles of silver-coated copper powder are randomly taken out, silver and copper powder are quantitatively analyzed with an Auger spectrometer, the ratio of silver is calculated, the average value is obtained, and this average value is coated. Area.

The Auger spectroscopic analyzer used in the present invention is:
It is a device that performs elemental analysis of the surface layer in a high vacuum atmosphere,
Copper peaks appearing at 910-930 eV and 330-3
The intensity ratio to the peak of silver appearing at 60 eV is 1: 100.
~ 30: 100, preferably 5: 100 ~ 25: 10
0, more preferably in the range of 10: 100 to 20: 100. If the strength ratio is less than 1: 100, there is no problem in terms of oxidation resistance, but the migration resistance is poor. Further, the adhesion of the silver layer is deteriorated, and the silver layer is likely to be partially peeled off during the paste process. On the other hand, when the intensity ratio is 3
If the ratio exceeds 0: 100, there is no problem in terms of migration resistance, but since the copper powder component on the surface is oxidized when the paste is heat-treated, the conductivity deteriorates. In addition,
The intensity ratio between the copper peak and the silver peak in the above is determined by randomly selecting 10 or more silver-coated copper powder particles, evaluating them with an Auger spectroscopic analyzer, and calculating the average value.

In order to prepare a conductive paste using the conductive powder according to the present invention, a binder such as epoxy resin, phenol resin, unsaturated polyester resin, hexamethylenetetramine, butyl cellosolve, ethylene carbitol, carbitol Solvents such as tall acetate, and if necessary, curing accelerators such as imidazole and amines, surfactants such as silane coupling agents and titanium coupling agents, and copper antioxidants such as imidazole compounds are added. Then, the mixture is uniformly mixed with a grinder, roll, kneader or the like.

The content of the binder and the solvent is 5 to 30% by weight based on the conductive paste and 3 to 50% by weight of the solvent.
%, More preferably 10 to 25% by weight of binder and 10 to 40% by weight of solvent. A curing accelerator, a surfactant, an antioxidant for copper, and the like are added as necessary. If added, the content is 0.5 to 3% by weight based on the conductive paste. Preferably, the surfactant is in the range of 0.05 to 0.5% by weight and the copper antioxidant is in the range of 0.01 to 0.1% by weight,
0.5 to 1.5% by weight of a curing accelerator and 0.1% of a surfactant.
1 to 0.3% by weight and an antioxidant of copper of 0.02 to 0.
More preferably, it is in the range of 06% by weight.

The conductive paste according to the present invention is most suitable as a material for forming an electric circuit by coating, printing and potting on various substrates and various films used as an insulating base material. It can be used for forming, for jumper wires, for EMI shielding, and the like. It can also be used as a conductive adhesive for connecting electronic components such as resistance elements, chip resistors, and chip capacitors to an insulating base material, and as a lead-free solder substitute.

Examples of the various substrates described above include a paper phenol substrate, a glass epoxy substrate, an enamel substrate, and a ceramic substrate. Examples of various films include polyethylene, polycarbonate, vinyl chloride, polystyrene, polyethylene terephthalate, polyphenylene sulfide, and the like. Flexible resin films such as polyetherketone, polyetherimide, and polyimide can be used. There is no particular limitation on the method for forming the electric circuit, and the electric circuit can be formed by a known method, for example, screen printing of a conductive paste or a drawing machine controlled by a computer. In the present invention, a part or all of a circuit or a resistor, or a jumper circuit can be formed in advance on a surface or a through hole of an insulating substrate by a method such as plating, printing, vapor deposition, or etching.

[0019]

Embodiments of the present invention will be described below. Example 1 Copper powder having an average particle size of 5 μm (Nippon Atomize Processing Co., Ltd.
After washing the product (SF-Cu) under stirring with water, the washed water was replaced with fresh water. Then, while stirring sufficiently so as not to precipitate the copper powder, a plating solution (20 g of AgCN and 40 g of NaCN dissolved in 1 liter of water) at a time is used in such a manner that 15% by weight of silver is plated when all the introduced silver is subjected to displacement plating. I put it in. Thirty minutes later, when no free silver ions were detected in the plating solution, the stirring was stopped, the waste liquid was removed by decanting, further washing with water and drying were performed to obtain silver-plated copper powder. The silver coverage (measured value) of the obtained silver-plated copper powder was 15% by weight.

Further, ten silver-plated copper powder particles were randomly taken out, and silver and copper were quantitatively analyzed by an Auger spectrometer to determine the silver covering area. The average was 55%. Further, as a result of randomly selecting ten silver-plated copper powder particles and analyzing the surface with an Auger spectroscopic analyzer, the average value of the intensity ratio of the copper peak and the silver peak is 1 for the copper peak: the silver peak.
4: 100.

A novolak type phenol resin (Gunei) was added to 70 parts by weight of the silver-plated copper powder and 30 parts by weight of flake silver powder having an average particle size of 8.5 μm (trade name: TCG-1 manufactured by Tokuri Chemical Laboratory). Chemical Industry Co., Ltd., trade name PS-26
07) 13 parts by weight and 13 parts by weight of butyl cellosolve were added and uniformly mixed to obtain a conductive paste. Next, the conductive paste was passed through a 200-mesh screen on the upper surface of a 1.6 mm thick paper phenol copper-clad laminate (manufactured by Hitachi Chemical Co., Ltd., trade name: MCL-437F) from which the copper foil had been removed. A test pattern having a width of 0.5 mm and a length of 100 mm was printed and heat-treated at 150 ° C. for 45 minutes in the atmosphere to obtain an electric circuit. The specific resistance of the cured conductive paste in the obtained electric circuit was 90 μΩcm.

On the other hand, separately from the above, an electrode having a width of 2 mm is printed on a slide glass by the same method as described above so as to be spaced apart from each other by 2 mm, and heat-treated under the same conditions as described above. I got Next, 0.05 cc of ion-exchanged water was dropped between the electrodes, a DC voltage of 20 V was applied between the electrodes, and the migration resistance was evaluated by measuring the elapsed time and the leakage current between the electrodes. As a result, 200 μ
The time required for the leakage current of A to flow was 40 minutes on average, and was excellent in migration resistance.

Example 2 A copper powder having an average particle diameter of 2 μm was obtained by classifying the copper powder used in Example 1, and silver plating was performed with a theoretical silver plating amount of 20% by weight. Through the same steps as in Step 1, silver-plated copper powder was obtained. The silver coating amount (actual value) of the obtained silver-plated copper powder was 19% by weight. The silver coating area was in the range of 60 to 75% of the total surface area, and the average was 65%. Furthermore, as a result of randomly selecting ten silver-plated copper powder particles and analyzing the surface with an Auger spectroscopic analyzer, the average value of the intensity ratio between the copper peak and the silver peak was as follows: copper peak: silver peak: 3: It was 100.

A novolak-type phenol resin (Gunei) was added to 70 parts by weight of the silver-plated copper powder and 30 parts by weight of a flaky silver powder having an average particle size of 8.5 μm (trade name: TCG-1 manufactured by Tokuri Chemical Laboratory). Chemical Industry Co., Ltd., trade name PS-26
07) 15 parts by weight and 15 parts by weight of butyl cellosolve were added and uniformly mixed to obtain a conductive paste. Then, the conductive paste was subjected to the same steps as in Example 1 to obtain an electric circuit and electrodes, and as a result of evaluating the characteristics, the specific resistance of the cured conductive paste in the obtained electric circuit was 80 μΩcm and the leakage current was 200 μA. The time required to flow was an average of 35 minutes, and was excellent in migration resistance.

Example 3 A silver-plated copper powder was obtained through the same process as in Example 1 except that silver plating was performed using the copper powder of Example 1 with a theoretical silver plating amount of 10% by weight. . The silver coating amount (actually measured value) of the obtained silver-plated copper powder was 10% by weight. The silver coating area was in the range of 35 to 50% of the total surface area, and the average was 40%. Further, as a result of randomly selecting ten silver-plated copper powder particles and analyzing the surface with an Auger spectrometer, the average value of the intensity ratio between the copper peak and the silver peak is 25: It was 100.

70 parts by weight of the silver-plated copper powder and 30 parts by weight of flaky silver powder having an average particle diameter of 8.5 μm (trade name: TCG-1 manufactured by Tokuri Chemical Laboratories) are mixed with a novolak-type phenol resin (Gunei). Chemical Industry Co., Ltd., trade name PS-26
07) 13 parts by weight and 13 parts by weight of butyl cellosolve were added and uniformly mixed to obtain a conductive paste. Next, the conductive paste was subjected to the same process as in Example 1 to obtain an electric circuit and electrodes, and as a result of evaluating the characteristics, the specific resistance of the cured conductive paste in the obtained electric circuit was 130 μΩcm and the leakage current was 200 μA. The time required to flow was an average of 60 minutes and was excellent in migration resistance.

Comparative Example 1 13 parts by weight of a novolak type phenol resin (trade name: PS-2607, manufactured by Gunei Chemical Industry Co., Ltd.) and 100 parts by weight of flake silver powder used in Example 1 and butyl cellosolve 13
A part by weight was added and mixed uniformly to obtain a conductive paste.
Next, an electric circuit and an electrode were obtained from the conductive paste through the same steps as in Example 1, and the characteristics were evaluated. As a result, the specific resistance of the cured conductive paste in the obtained electric circuit was 75.
Although it was μΩcm, the time required for a leakage current of 200 μA to flow was extremely short, averaging 30 seconds, and was poor in migration resistance.

[0028]

According to the present invention, the conductive powder has excellent conductivity and migration resistance. The conductive paste according to claim 2 has excellent conductivity and migration resistance. The electric circuit according to claim 3 is excellent in conductivity and migration resistance.

Claims (3)

[Claims] 1. The surface of the copper powder is 5 to 5 with respect to the copper powder.
The copper peak coated with 30% by weight of silver and having the intensity ratio of the copper peak to the silver peak determined by Auger spectroscopy:
A conductive powder containing silver-coated copper powder having a silver peak of 1: 100 to 30: 100. 2. A conductive paste comprising the conductive powder according to claim 1 and a binder and a solvent. 3. An electric circuit formed on the surface of a substrate using the conductive paste according to claim 2.