JPH05225823A - Copper conductor paste and its manufacture - Google Patents

Abstract

PURPOSE:To improve the adhesive strength with a base. CONSTITUTION:While the carbon content of a copper powder used as conductive particles in a copper conductor paste is limited less than 0.10%, a copper powder manufactured by reducing a copper oxide powder in a water solution including an interface activate agent is used. By regulating the adding amount of the interface active agent in such a way, the diameter of particle and the carbon content can be controlled, and the copper particles are made into spherical and its carbon content is made less than 0.10 %. Consequently, the adhesive strength with a base can be improved extensively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copper conductor paste for forming a copper thick film electrode and a wiring pattern on an insulating substrate such as ceramics, and a method for producing the same, and more specifically, to an adhesive strength to the substrate. The present invention relates to a copper conductor paste for forming electrodes and wirings having a high copper thick film and a manufacturing method thereof.

[0002]

2. Description of the Related Art Techniques for forming electrodes and wirings by applying a conductive paste in a predetermined pattern on an insulating substrate such as glass or ceramics by a screen printing method or a direct drawing method and baking the same are already known as thick film technology. It has been put to practical use. It is well known that in such a thick film technology, a copper conductor paste, which has a low resistivity and is excellent in anti-maglation, can be used for forming fine circuit wiring, instead of the conventional Ag / Pd-based conductor paste. It is a fact.

Copper conductor pastes generally consist of copper powder dispersed in a vehicle together with glass frit and metal oxide powder. The copper powder forms a conductor thick film by sintering during firing, and the glass frit and the metal oxide powder have an action of adhering the copper thick film to the substrate. The vehicle is an organic liquid medium for making these powders printable.

Copper powder having a particle size of 0.5 μm to 10 μm is used as the copper powder for the copper conductor paste. Powders with a particle size of less than about 0.5 μm are not preferable because they have a large bulk density and require a large amount of vehicle to be pasted.On the other hand, when powders with a particle size of more than about 10 μm are used, normal firing conditions are sufficient. It is not preferable because it is difficult to form a thick film that is sintered, and it is difficult to print fine wiring in terms of printability. The particle shape of the copper powder is preferably spherical particles having excellent screen printability and filling properties.

The specific particle size of the powder used for the conductor paste is determined by the firing temperature within the above range. Usually, a powder having a smaller particle size is used as the firing temperature is lower. In particular, in order to improve the productivity and reliability of a copper thick film circuit board, it is essential to form a copper thick film in which the sintering state is controlled with high accuracy at a firing temperature as low as possible. The particle size distribution must be strictly controllable.

The glass frit is melted at the time of firing and flows from between the copper powder to the interface of the substrate to bond the copper thick film to the substrate. That is, since the glass frit is fixed to the substrate in a protruding shape, the anchor connection is realized between the thick copper film and the substrate by mechanical engagement. The metal oxide powder has a function of adhering the copper thick film to the substrate similarly to the glass frit, and has a function of chemically bonding the copper thick film to the glass frit and the substrate.

The vehicle is a resin in which a resin is dissolved, and is mixed in order to ensure printability. However, the vehicle volatilizes and burns during firing and disappears. Normally, firing of the copper conductor paste is performed in a nitrogen atmosphere. In the firing process, first about 120
Volatile solvents evaporate near ℃. Then from 200 ℃ to 400
The resin burns and scatters over the temperature range of ℃. This reaction is called binder removal. When the temperature rises further, the glass frit melts and flows to the substrate. Thereafter, the copper powder sinters to form a thick conductor film and the metal oxide reacts to bond the thick film to the substrate.

[0008]

The conventional copper conductor paste has the following problems. (1) Adhesive strength between the copper thick film and the substrate is not sufficient, and especially when placed in a high temperature environment for a long time, that is, aging strength is not sufficient. Especially, as recently, the integration density is improved and the amount of heat generated is large.
There is a strong demand for improvement of such aging strength in a copper thick film substrate on which C is mounted. (2) As the circuit becomes finer, the electrode area becomes smaller and effective soldering is required in a short time, but for that purpose, further improvement of wettability to solder is required. However, current copper conductor pastes do not always meet such requirements.

In view of the above points, the present invention provides a copper conductor paste capable of forming a copper conductor thick film having high adhesion strength to a substrate, particularly high aging strength, and improved wettability with solder, and manufacturing thereof. The purpose is to provide a method. Another object of the present invention is to provide a copper conductor paste that is easy to manufacture and inexpensive, and a method for manufacturing the same, while improving the adhesive strength with a substrate and the wettability to solder.

[0010]

The present inventor has found the following points. (1) In order to increase the adhesion strength of the copper conductor thick film to the substrate, it is necessary to use copper powder having excellent sinterability and high purity. In order to satisfy the above properties, it is desirable that the copper powder has a spherical particle shape and has a small amount of impurities, especially carbon content.
Until now, no attention has been paid to the carbon content of the copper particles, and it has been usual that the carbon derived from the protective colloid is contained at about 0.15 wt%.

The mechanism is not yet fully understood, but it is considered as follows. That is, the spherical powder has a high filling property and thus a high sinterability, and since the specific surface area is small, it can be made into a paste with a minimum amount of vehicle, so that the binder can be easily removed. On the other hand, a copper powder with a high carbon content has a low adhesive strength because the copper powder containing a large amount of carbon among impurities such as oxygen, sodium and iron has low sinterability and is unlikely to cause a chemical bond with the substrate. Conceivable.

A usual method for producing a copper powder for a paste is a wet reduction method in which a reducing agent is added to an aqueous copper salt solution or a copper oxide slurry to precipitate the copper powder, but a spherical copper powder is obtained as it is. Therefore, protective colloids, silane coupling agents, etc. are added to copper oxide, and surfactants, etc. are added to copper sulfate aqueous solution (Japanese Patent Publication No. 61-55562).
(See JP-A-2-34708 and JP-A-62-27508).

However, it is difficult to produce a copper powder suitable for a copper conductor paste even by these conventional methods. That is, spheroidizing with protective colloid is ineffective unless the protective colloid covers the surface of the copper particles thickly, and thus a large amount of protective colloid is required, so the amount of carbon mixed from them cannot be ignored. As a result, the amount of carbon in the copper powder itself is as high as 1.5%, which is not preferable. Also,
The protective colloid deteriorates during storage and thus lacks stability.
When a silane coupling agent is used, it is difficult to treat the waste liquid, and the operation requires a considerable cost.

According to the method disclosed in Japanese Patent Laid-Open No. 62-27508, copper particles are instantly precipitated because the hydrazine and the aqueous solution of copper sulfate are directly reacted with each other in the presence of a surfactant. Since the particle size of is strongly affected by the mixing operation of both, it is not reproducible.Because of the active reaction, the nitrogen gas is strongly released due to the decomposition of hydrazine, so that the surfactant is hard to act and the obtained particles are indefinite. And
In addition, impurities such as sulfate ions are mixed, which is not preferable.

(2) The conductor characteristics of the copper thick film are greatly influenced by the particle size of the copper powder which is the raw material of the conductor paste. For this reason,
In order to improve the reliability of the conductor characteristics of the copper thick film, it is necessary to use copper powder whose particle size is precisely controlled. As mentioned above, the particle size of the copper powder used in the conductor paste is approximately 0.5 μm.
Since it is 10 μm, the variation is ± 10% within this particle size range.
A controlled powder of any controlled particle size should be used below.

In this respect, the conventional particle size control method is as follows:
(1) Change the type of starting copper salt, (2) Control copper ion concentration in aqueous solution, (3) Change the particle size of starting copper oxide powder, (4)
Control of reaction temperature, (5) addition of various protective colloids, (6) addition of various silane coupling agents, etc.

However, the above particle size control methods are
(1) Dangerous or expensive copper salt, or copper salt that may be mixed with impurities must be used. (2) The yield of copper powder is low depending on the particle size. (3) It is necessary to procure copper oxide powder with an arbitrary particle size. (4) When the temperature is high, a large amount of heat is required and it is difficult to control, so that the particle size of the copper powder easily varies. (5) Since the protective colloid is a natural polymer, the copper powder to which the protective colloid adheres has a high carbon content,
Furthermore, protective colloids are unreliable because they deteriorate during storage. (6) The copper oxide powder needs to be surface-treated with a silane coupling agent in advance, and the silane coupling agent has drawbacks such as weak dispersion ability of solid particles.

In this respect, by reducing the copper oxide powder in an aqueous medium containing a surfactant, spherical copper powder having a uniform particle size is produced, and by adjusting the content of the surfactant, the copper powder is adjusted. It is possible to control the particle size of. Here, the present invention is a copper conductor paste containing a copper powder, a glass frit, a metal oxide powder, and a vehicle, wherein the copper powder has a carbon content of 0.10% by weight or less and is spherical. And a copper conductor paste. Also, from another aspect, the present invention comprises reducing the copper oxide powder in an aqueous medium containing a surfactant and mixing the resulting copper powder with glass frits, metal oxide particles, and a vehicle. It is a characteristic method for producing a copper conductor paste.

[0019]

As described above, according to the present invention, since the copper powder has a spherical particle shape and the carbon content is 0.10% by weight or less and the purity is high, a highly adhesive thick conductor film can be obtained. If the carbon content exceeds 0.10% by weight, the adhesive strength, particularly the aging strength, is significantly reduced. The particle shape is spherical, but this is for improving printability. The glass frit used in the present invention may be a known glass frit. For example, PbO-Bc ₂ O ₃ -SiO ₂ based glass can be used. The particle size of the glass frit is preferably 1 μm to 10 μm. The amount of glass frit added is preferably 2 to 5% by weight with respect to 100 parts by weight of copper powder.

The metal oxide powder added to the conductor paste of the present invention is not particularly limited, but copper oxide and cadmium oxide powders are preferable. It should be noted that an excessive addition of the metal oxide hinders the sintering of the copper powder and remarkably lowers the wettability of the copper thick film to the solder, and therefore an appropriate amount must be added. The amount is preferably 1 part by weight or more and 2 parts by weight or less with respect to 100 parts by weight of the copper powder. As the vehicle used in the present invention, a known vehicle can be used. For example, an acrylic resin or a cellulose resin dissolved in a solvent such as terpineol can be used.

The copper conductor paste of the present invention can be applied to all ceramic substrates such as alumina. The firing atmosphere of the copper conductor paste of the present invention can be performed under a generally used nitrogen atmosphere. The copper powder for such a copper conductor paste is obtained by reducing copper oxide powder in an aqueous medium containing a surfactant. Since the surfactant has a high adsorption efficiency on the surface of the solid particles, it has a spheroidizing action even when added in a small amount, and a high-purity powder having a carbon content of 0.1% or less can be obtained.

That is, since the copper oxide powder is dispersed in the aqueous medium containing the surfactant in the initial stage, the surfactant adheres to the surface of the copper oxide powder and the surplus surfactant floats in the water. ing. Next, when the reducing agent is added, the copper oxide powder is decomposed and the copper particles are deposited while being coated with the surfactant. Eventually all the surfactant will coat the copper powder. Therefore, spherical copper powder with less variation in particle size can be obtained, and the larger the amount of the surfactant, the smaller the particle size of the copper powder. Therefore, by adjusting the amount of the surfactant, the particle size of the copper powder can be reduced. The diameter can be controlled. The relation between the particle size d of the copper powder and the additive amount X of the surfactant is d = c by a simple calculation.
/ X (c: constant) is derived.

In the present invention, the copper oxide powder required for producing the copper powder may be either cuprous oxide powder or cupric oxide powder. Surfactant effective in spheroidizing the copper powder is preferably an anionic surfactant, specifically, a naphthalene sulfonic acid formalin condensate having a strong dispersive power,
It is a special polycarboxylic acid type polymer surfactant.

In the present invention, as the reducing agent used for the reduction of copper oxide to metallic copper, hydrazine and hydrazine compounds, alkali hypophosphite, alkali borohydride, formalin and the like can be used. Hydrazine and a hydrazine compound are preferable in terms of properties and cost. The optimum addition amount of hydrazine depends on the reaction temperature and the reaction time, but 0.1 mol of hydrazine is added to 1 mol of copper oxide.
More than a mole is good. The reaction temperature in the production of copper powder can be set in the range of room temperature to 80 ° C, but is preferably set in the range of room temperature to 60 ° C from the viewpoint of controllability.

The particle size of the copper powder can be controlled by adjusting the reaction temperature, the solution temperature and the amount of the surfactant added, but it is preferably adjusted in the range of 0.5 μm to 10 μm. If the particle size of the copper powder is less than 0.5 μm, the specific surface area is large and bulky, so a large amount of vehicle is required to form a paste, which is not preferable.If it exceeds 10 μm, the sinterability is reduced and it is difficult to print fine lines. is there. The finally obtained copper powder may be rust-proofed with benzotriazole or the like.

[0026]

EXAMPLES The present invention will be described below with reference to specific examples. Example 1 An aqueous solution in which 11.26 g of cuprous oxide powder having a particle size of 2 μm was dissolved in a special polycarboxylic acid type polymer surfactant in an amount of 0.1 to 0.4%.
Disperse in 160 ml and adjust the temperature to 60 ° C with stirring. Then inject 20 ml of hydrazine hydrate (80%)
React for 20 minutes to produce copper powder. The obtained copper powder was washed with water, dried and weighed, and 10 g of the copper powder was recovered. The particle size and particle shape were examined with a scanning electron microscope.
The results are summarized in Table 1.

11.26 g of the same cuprous oxide powder for comparison
Was dispersed in 160 ml of an aqueous solution containing 1% of gum arabic and adjusted to 60 ° C. Then, with stirring, 20 ml of hydrazine hydrate (80%) was injected and reacted for 20 minutes to produce a copper powder. The obtained copper powder was filtered and dried, and then weighed, and 10 g was recovered. The particle size and shape were examined with a scanning electron microscope. The results are also shown in Table 1. FIG. 1 is a graph showing the results in Table 1, and it can be seen that the particle size obtained can be adjusted by adjusting the addition amount of the surfactant. In the comparative example, since no surfactant is used, the variation in particle size is large, the carbon content is as high as 0.4%, and the shape of the produced particles is indefinite, which is not stable.

[0028]

[Table 1]

(Note) * Irregular shape: not spherical shape but irregular shape or surface irregularity Example 2 11.26 g of cuprous oxide powder having a particle size of 2 μm is dispersed in 160 g of water to form a naphthalenesulfonic acid formalin condensation product. 0.48 to 0.15 g of the physical polymer surfactant is added, and the temperature is adjusted to 50 ° C. while stirring. Next, add 20 ml of hydrazine hydrate (80
%) And react for 30 minutes to produce copper powder. The obtained copper powder was washed with water and then dried to obtain copper powders A to F shown in Table 2.

As comparative examples, copper powders G to I produced without adding a surfactant were used. Copper powder G was obtained by the same operation by adding 0.2 g of protective colloid gum arabic instead of the surfactant, and copper powder H was obtained by adding 0.1 g of protective colloid gelatin instead of the surfactant. The obtained copper powder I is a commercially available copper powder, and Mitsui Mining & Smelting
It was Cu Fine Powder 1110 lot No. S-900603PN manufactured by Co., Ltd. The average particle size and particle shape of the copper powder were determined by a scanning electron microscope. The judgment of "spherical" and "granular"
By a scanning electron microscope.

[0031]

[Table 2]

(Note) * 1: Protective colloid gum arabic, *
2: Protective colloidal gelatin * 3: Using commercially available copper powder Next, a copper conductor paste was prepared using the copper powder thus produced. Each conductor paste prepared by the composition ratio in Table 3 was printed on a 96% pure alumina substrate in an appropriate pattern with a screen printer, dried at 120 ° C for 10 minutes, and then peaked in a belt furnace in a nitrogen atmosphere.
A copper conductor thick film with a film thickness of 20 μm was obtained by firing in a profile of 70 minutes for 1 cycle including 900 ° C. × 10 minutes. Each property of the obtained copper conductor thick film was evaluated in the following manner.

(Adhesive strength) A 2 mm square copper thick film was maintained at a temperature of 230 ± 3 ° C and immersed in a 63% Sn-37% Pb solder bath for 3 ± 0.5 seconds, and then tin-plated with a diameter of 0.6 mm. The copper wire was soldered with a soldering iron. Bend the tin-plated copper wire at a position of 1 mm from the end of the coating at 90 ° C to make it perpendicular to the substrate. With the substrate fixed, pull the tin-plated copper wire at a speed of 10 cm / min with a tensile tester to remove the tin-plated copper wire. The adhesive strength when peeled from the substrate was measured. The adhesive strength is the value immediately after soldering
(Initial strength) and the value after aging at 150 ° C. for 1000 hours (aging strength) were measured.

(Solder wettability) The fired parts were immersed in a 63% Sn-37% Pb solder bath maintained at a temperature of 230 ± 3 ° C for 3 ± 0.5 seconds, and a solder layer deposited on a 10 mm square copper thick film. The number of pinholes generated in the above was measured.

[0035]

[Table 3]

[0036]

As described above, the copper conductor paste according to the present invention has an effect of forming a thick conductor film having high adhesive strength with a substrate and good solder wetting. Moreover, they can be manufactured in a spherical shape while controlling the particle size with high accuracy, and can be supplied at a considerably low cost comprehensively, which is of great practical value.

[Brief description of drawings]

FIG. 1 is a graph showing the results of Examples.

Claims (2)

[Claims] 1. A copper conductor paste containing copper powder, glass frit, metal oxide powder, and vehicle, wherein the copper powder has a carbon content of 0.10% by weight or less and is spherical. Copper conductor paste. 2. A copper conductor paste, comprising reducing a copper oxide powder in an aqueous medium containing a surfactant, and mixing the obtained copper powder with glass frit, metal oxide particles, and a vehicle. Production method.