JPH0465013A - Copper conductive paste compound - Google Patents

Abstract

PURPOSE:To improve conductive and soldering wet characteristics and close contactness to a substrate by containing a fixed amount of specified copper powder hydroxide on the basis of the total amount of copper powder and copper power hydroxide. CONSTITUTION:A copper powder hydroxide having an average particle diameter of 5mum or less is contained by 2-7wt.% on the basis of the total amount of copper powder and copper hydroxide powder. As the copper hydroxide any one of Cu(OH)2, CuOH or Cu(OH)2+CuOH can be used. If it is not more than 2wt.% based on the total amount, unevenness is generated and the bonding effect is decreased, while if it exceeds 7wt.% conductive and soldering wet properties are decreased. With the preparation, a copper conductive paste compound with high bonding property, soldering property and conductive property is obtained.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a copper conductor paste composition used for forming electrodes and wiring patterns on insulating substrates such as ceramics. The present invention also relates to a copper conductor paste composition (hereinafter sometimes simply referred to as copper conductor paste) that has excellent solder wettability and good adhesion to a substrate.

(Prior art) Conductor paste is a paste that is applied to an insulating substrate such as glass or ceramics in a predetermined pattern using a screen printing method, direct writing method, etc., and then baked to form a thick conductor film. . Conventionally, powders of gold, silver, silver/Pd, copper, nickel, etc. have been used for such conductor pastes, but it is well known that in recent years there has been a trend to use copper conductor pastes.

That is, gold conductor paste can be fired in the atmosphere but is expensive, silver conductor paste is prone to electromigration, silver/Pd conductor paste is also expensive, and nickel conductor paste has drawbacks such as high wiring resistance. However, copper conductor paste is low in cost, has low wiring resistance, and is less prone to migration, making it an ideal conductor material.

Conventional copper conductor paste has an average particle size of 0.5 to 11, for example.
0A1 copper powder is dispersed in an organic vehicle together with an inorganic binder to form a paste. When fired, the copper powder forms a mesh fired film which is a conductive film.

The organic vehicle has the role of providing thixotropic rheology as a liquid binder for pasting, enables coating and printing on a substrate, and decomposes and scatters during firing. Usually, the organic vehicle used is a resin dissolved in a volatile solvent.

The inorganic binder has the effect of making this net-fired film adhere to the substrate, and glass frit, metal oxide, etc. are used.

In particular, the adhesion effect caused by glass frit is called glass bond, and the glass frit melts when the conductor paste is fired.
This flows from between the copper powders to the substrate due to the wetting phenomenon, thereby bringing the net-fired film and the substrate into close contact. Conventionally used glass lifts have a softening point of 300 to 7.
Glasses containing metal oxides such as CdO, ZnO1AQzOi, CaO, etc. in the Pb0-BzOz-5iOz system, and borosilicate glasses are used.

On the other hand, the adhesion effect by the metal oxide is called a chemical bond, and the net-fired film and the substrate are brought into close contact by the reaction between the substrate and the metal oxide. Since the portion formed by this reaction is less susceptible to solder erosion, chemical bonding is characterized by less loss of adhesion due to high-temperature aging after soldering. Traditionally used metal oxides are mainly Cu, O and CuO, but
Others: Biz03, Cd01PbOz, 5b203,
V205, ZnO, etc. may also be used.

Also, in recent years, a method has been provided in which a chemical bond is more effectively developed by using a powder in which an oxide layer is formed on the surface of copper powder. See JP-A-1196192 and JP-A-60-35405.

Note that mixed bond is a combination of glass bond and chemical bond, and it is a bonding method that is currently widely used.

(Problem to be solved by the invention) Conventionally, in chemical bonds and mixed bonds,
Methods for adding metal oxide include a method of adding metal oxide powder and a method of using copper powder with an oxide layer formed on the surface in advance.

The problem when adding metal oxide powder is that high temperatures are required for the entire metal oxide particles to react (e.g. 1026°C for CuO, 900-100°C for CdO).
0°C), and under normal firing conditions where the firing temperature is 900°C or less, incomplete reactants tend to remain.

For this reason, not only is it not possible to obtain the desired adhesion, but as a side effect, the conductivity and solder wettability are rather reduced.

On the other hand, when copper powder with a surface oxidation layer is used, although a certain degree of adhesion can be obtained, the surface oxidation layer significantly inhibits the sintering of the copper powder, resulting in low conductivity and poor solder wettability. There's a problem.

The present invention was made to solve the above-mentioned drawbacks, and an object of the present invention is to provide a copper conductor paste composition that has excellent adhesion to a substrate, and also has excellent solder wettability and conductivity.

(Means for Solving the Problems) In order to achieve the above object, the present inventor investigated various copper compounds and found that when copper hydroxide is used in place of conventional copper oxide, the copper hydroxide is activated by low-temperature heating. They discovered that copper oxide was produced and that this reacted sufficiently even at low temperatures, leading to the completion of the present invention.

That is, in the copper conductor paste composition of the present invention, in a conductor paste containing copper powder as conductive particles, the amount of copper hydroxide powder with a particle size of 5 or less is 2 to 7, based on the total amount of copper powder and copper hydroxide powder. % by weight of a copper conductor paste composition.

More specifically, the present invention is a copper conductor paste composition comprising copper powder, copper hydroxide powder, glass frit, and an organic vehicle.

The reason why the copper conductor paste of the present invention was able to satisfy all of the properties required for a conductor, such as conductivity, solder wettability, and adhesion to the board, is because metal oxide powder is added as a compound to the paste. The point is that copper hydroxide powder is added without using copper powder, and preferably without using copper powder with advanced surface oxidation.

In other words, copper hydroxide undergoes a dehydration reaction at a temperature of 150°C to 200"C. During this reaction process, copper oxide is produced as a byproduct, but the copper oxide produced at that time is highly reactive. It is ideal because it reacts more actively with the substrate than the conventional oxide state (addition of copper oxide powder, surface oxidation layer of copper powder), and there is no unreacted copper oxide after firing. It is thought that chemical ponding occurs.

(effect) The structure and operation of the present invention will be explained.

The average particle size of the copper powder used in the present invention is 0.1 to 10/Al
+, preferably 0.5 to 5p. method for producing copper powder,
There are no particular restrictions on the shape of the particles, but from the perspective of screen printing, particles that are close to spherical are preferred.

Copper powder is generally easily oxidized, so surface oxidation is observed, and as mentioned above, this oxidized layer deteriorates the sinterability of copper powder, but in the case of the present invention, the oxidation layer is oxidized to a level that is normally seen, for example, 0.6%.
It is permissible until Preferably it is limited to 0.5% or less.

The copper hydroxide powder used in the present invention mainly refers to hydroxide M [Cu (OH) zl ], but it also contains a small amount of metallic copper and cuprous hydroxide (Cu(Of()I). It can be used even if it is

As the copper hydroxide, any of Cu(OH)z, Cu0H, and Cu(OH)z+cuOH can be used. For uniform dispersion, the particle size must be 5p or less; if it is larger than this, the reaction will be uneven. Furthermore, if the amount added is less than 2% by weight based on the total amount of copper powder + copper hydroxide powder, the adhesion effect will be poor;
If it exceeds this value, the conductivity and solder wettability will deteriorate. Preferably it is 3 to 4%.

The copper conductor paste of the present invention is made into a paste by cross-dispersing the above-described copper powder and copper hydroxide powder in an organic vehicle together with glass frit in an amount of 2% by weight or less of the total amount thereof, if necessary.

As the glass frit used in the present invention, any known glass frit can be used. For example, PbO-8
, 0, -510□ Glass-based materials to which various metals are added can be used. The average particle size of the glass flint is 0.1 to 10 m, preferably 0.3 to 5 p.

The organic vehicle used in the present invention is not limited to any particular one, as long as it is generally used for thick film conductor pastes. Examples include those obtained by dissolving resins such as ethyl cellulose and polybutyl methacrylate in solvents such as terpineol, dibutyl calpitol, dibutyl phthalate, dibutyl calpitol, and 22.4-trimethyl-1,3-bentanediol monoisobutyrate. .

As the pasting method, various known methods can be used. For example, a common method is to pre-knead using a universal stirring mixer and then knead with three rolls.

The copper conductor paste thus obtained is then applied by printing or drawing onto a ceramic substrate, the solvent is dried and volatilized, and the paste is then fired to obtain a conductive film.

Known printing methods can be used to print the copper conductor paste of the present invention. Examples of such printing methods include a screen printing method, a printing method using a metal mask, a direct drawing method, and the like.

Further, as a method for firing the conductor paste of the present invention, any known firing method can be used, but a belt furnace is more preferable than a hatch furnace from the viewpoint of productivity and safety.

(Example) The present invention will be explained below using specific examples.

Purity 9 of each copper conductor paste adjusted according to the composition ratio in Table 1
A suitable pattern was printed on a 11% alumina substrate using a screen printer, dried at 120°C for 10 minutes to remove the solvent, and then heated in a belt furnace in a nitrogen atmosphere at a peak temperature of 750°C. Firing was performed with a profile of 40 minutes per cycle including a holding time of 10 minutes, and the film thickness was 2.
A copper conductor thick film of 0/Jl was obtained.

Each of the fired films obtained in this way was evaluated for conductor properties based on conductivity, solder wettability, and adhesive strength.

The evaluation procedure was as follows.

(Conductivity) Evaluated by measuring conductor resistance value. Specifically, the specific resistance value was determined from the four-terminal resistance measurement and the line width and film thickness of the thick copper film.

(Solder wettability) 63%5N with fired parts maintained at a temperature of 230±3°C
- Immerse in 37% pb solder bath for 3±0.5 seconds,
The adhesion rate of the solder deposited on the 4 m copper film was visually measured.

(Adhesion strength) 3±0.5 to 211!11 square copper conductor coating in a 63%5N-37%PB solder bath maintained at a temperature of 230±3°C
After dipping for seconds, a 0.6 mmφ tin plated copper wire was soldered thereon using a soldering iron. Bend the tinted copper wire 90 degrees at position 11 from the end of the coating so that it is perpendicular to the board,
[by tensile testing machine with the board fixed]Ocm/m
The tin-plated copper wire was pulled at a speed of 1.5 in, and the adhesive strength was measured when the tin-plated copper wire was peeled off from the substrate.

The adhesive strength is the value immediately after soldering (initial adhesive strength), and 1
Values were measured after aging at 50°C for 100 hours.

These results are also summarized in Table 1.

In Comparative Example 1.2, which did not contain copper hydroxide powder, the average particle size of the copper powder was 1.4p, but the conductivity and solder wettability were insufficient. Further, in Comparative Example 3.4, copper oxide powder was used as in the prior art, but the conductivity, adhesive strength, and solder wettability were all insufficient.

On the other hand, those using the copper conductor paste according to the present invention were able to exhibit satisfactory characteristics in all of these respects.

In this example, Cu (OH) z was used as the copper hydroxide, but similar results can be obtained by using Cu (Of() or a mixture of both).

(Effects of the Invention) The present invention is constructed as described above, and as is clear from the above-mentioned examples, the copper conductor paste of the present invention has good conductivity and solderability by containing copper hydroxide powder. The wettability and adhesion to the substrate (both initially and after aging) have been improved to a level that is practically satisfactory, making it an innovative conductive paste and extremely useful industrially.

Claims (2)

[Claims] (1) A conductive paste containing copper powder as conductive particles, containing 2 to 7% by weight of copper hydroxide powder with a particle size of 5 μm or less based on the total amount of copper powder + copper hydroxide powder. Conductor paste composition. (2) The copper conductor paste composition according to claim 1, wherein 2% by weight or less of glass frit is added to the total amount of copper powder + copper hydroxide powder.