JPH10188671A - Copper conductive paste and board printed therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper conductive paste, whose electric resistance is lowered, and a board printed with the copper conductive paste by making it easy to print the paste on the board to enable its shaped to be maintained thereafter, making it easy to pack the paste into a through hole provided in the board, so as to enable the paste to be fixed into place, and preventing cohesion of particles to form dense burned film. SOLUTION: A copper conductive paste comprises particles made of copper, copper oxide, or their mixture with an average particle diameter in the range of 1 to 500nm, to which mixed copper powders to which at least one kind or more of auxiliary copper powders composed mainly of base copper powders with an average powder diameter in the range of 0.5 to 10μm and having a smaller range of average powder diameters than the auxiliary copper powder, a binder resin, and an organic solvent are added.

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 and a substrate on which the copper conductor paste is printed, and more particularly, to a copper conductor paste which can be easily printed on a substrate, retains its shape after printing, and is filled in a through hole provided in a ceramic substrate. The present invention relates to a copper conductor paste which is easy to form, forms a dense fired film, and has a reduced electric resistance value, and a substrate on which the copper conductor paste is printed.

[0002]

2. Description of the Related Art Today, a conductor paste is used for printing a circuit on a ceramic substrate or filling a conductor in a through hole provided in the substrate. Examples of the conductor paste include an Ag-Pd paste containing silver and palladium as main components, a silver paste,
There are a gold-based paste, an Ag-Pt-based paste containing silver and platinum as main components, and a copper-based paste.

[0003] Among them, the Ag-Pd-based paste is typical for use in wiring, but has some disadvantages. For example, when the paste is used for wiring on a substrate, silver is ionized through moisture in the air and the like, and a phenomenon called migration occurs in which the ionized silver moves to an adjacent conductor path to short circuit. I was For this reason, the distance between the conductor paths could not be reduced. Further, in a soldered portion for mounting or connecting other components on the conductor path, silver was easily eroded by the solder, and solder resistance was poor.

When the paste is adhered to a substrate, metal particles having a micron size cannot be reacted and adhered to a ceramic substrate. Therefore, about 4 to 10% by weight of glass powder is mixed into the paste. However, the glass powder on the substrate after printing has given a role of bonding the substrate and the metal film after firing. However, on the other hand, a large amount of glass powder remains in the metal film after firing, so that the electrical resistance value of the metal film increases, and since the metal film and the substrate are bonded by the glass layer, the difference in thermal expansion is increased. As a result, there was a problem that the heat shock was weakened.

[0005] A copper-based paste is known as a paste partially resolving such disadvantages. This paste has a composition in which copper, glass powder, and a non-copper-based material such as tungsten, molybdenum, and rhenium are dispersed in an organic solvent, as described in, for example, JP-A-60-70746. Also, Japanese Patent Publication 3-50365
As described in Japanese Patent Application Laid-Open Publication No. H10-209, the composition is composed of a metal oxide particle coated with a copper oxide, a copper oxide particle, and a glass powder such as glass dispersed in an organic solvent.

As another method of manufacturing a substrate in which through-holes are filled, a method of simultaneously firing alumina having through-holes buried in through-holes has been proposed.

[0007]

The above-mentioned copper-based paste also plays a role of adhesion between the substrate and the conductor by adding a large amount of glass powder, preferably 4 to 10% by weight, as glass powder. However, the paste has a low dynamic viscosity to improve printability, but also has a low static viscosity.
When this is screen-printed on a substrate, the edge of the conductor after the paste is dripped and printed hardly appears sharply, and accurate printing cannot be performed. This leads to the problem that the conductor cross-sectional area is difficult to grasp in circuit design,
On the other hand, when the viscosity is increased, the printability deteriorates, so that irregularities are generated in the conductor path, and the irregularities may cause noise in the electric signal.

[0008] Further, in the case of firing and filling the through hole after filling in the through hole, a large amount of glass powder remains in the conductor in the through hole after firing, so that the electric resistance value of the conductor is reduced. In addition, there is a problem that the glass layer existing at the interface between the conductor and the substrate is easily distorted due to the difference in thermal expansion, the heat resistance and the thermal shock resistance are weak, and the filled conductor does not adhere to the through hole. This thermal shock resistance is evaluated based on the adhesive force between the conductor and the substrate after repeatedly moving the substrate having the conductor from a low-temperature atmosphere to a high-temperature atmosphere and in the opposite direction. In addition, since lead glass borosilicate having a low softening point is also used for the glass powder, lead in the glass hinders plating in a plating step performed for oxidation prevention and Au wire bonding.

The present invention has been made to solve such a problem, and it is easy to print on a substrate so that the shape can be maintained thereafter, and it is easy to fill a through hole provided in the substrate and fix it. It is an object of the present invention to provide a copper conductor paste in which a dense fired film is formed by preventing aggregation of fine particles and its electric resistance value is reduced, and a substrate on which the copper conductor paste is printed.

[0010]

That is, according to the first aspect of the present invention, fine particles made of copper, copper oxide, or a mixture thereof having an average particle size of 1 to 500 nm are added to a fine particle having an average particle size of 0 to 500 nm. Copper mixed with at least one kind of auxiliary copper powder containing at least one auxiliary copper powder having a smaller average particle diameter in the range of 0.5 to 10 μm, a binder resin, and an organic solvent. In the conductive paste, the static viscosity is high, the edge of the film after printing appears sharply, the shape retention is good, and the printability is also good because the dynamic viscosity is not high. In addition, the auxiliary copper powder fills the gaps and voids generated by the arrangement of the base copper powder, so that a fired film having no internal defects and good compaction can be obtained. Further, by adjusting the viscosity of the copper conductor paste, the filling into the through-holes is facilitated, and the volume filling of the paste filled in the through-holes after firing is small, so that the fillability is good.

According to the second aspect of the present invention, there is provided a copper conductor paste having an average particle diameter of fine particles made of copper, copper oxide or a mixture thereof in the range of 100 to 200 nm, and particularly having a large average particle diameter. Even if the fine particles are mixed with the mixed copper powder, they do not agglomerate. As a result, a dense fired film is formed, and the electric resistance value is reduced.

According to the third aspect of the present invention, at least two resins having different thermal decomposition temperatures are used as the binder resin.
It is a copper conductor paste containing more than one kind. Even when the copper conductor paste is fired, the binder resin does not thermally decompose at once but decomposes in accordance with the environmental temperature, and therefore does not remain in the fired film.

In the invention according to claim 4 of the present application, the mixed copper powder has a base copper powder having the largest average particle diameter in the range of 2 to 5 μm and a first copper powder having the average particle diameter of 1 to 2 μm. Since the auxiliary copper powder is composed of the auxiliary copper powder and the second auxiliary copper powder having an average particle diameter of 0.5 to 1 μm, the auxiliary copper powder fills gaps and voids generated by the arrangement of the base copper powder, and It is possible to obtain a fired film having no defects and good shrinkage.

In the invention according to claim 5 of the present application, the mixed copper powder has a base copper powder having the largest average particle diameter in the range of 0.5 to 1 μm and a base copper powder having an average particle diameter of 0.1 to 0.5 μm. In the same manner as in the fourth aspect of the present invention, it is possible to obtain a fired film which is composed of the auxiliary copper powder in the range and has good compaction.

In the invention according to claim 6 of the present application, the glass powder is mixed with the mixed copper powder and copper, copper oxide having an average particle diameter in the range of 1 to 500 nm, or a total of 100 parts by weight of fine particles comprising a mixture thereof. 0.1 to 2.0 parts by weight to improve cracking and baking of the fired film.

In the invention according to claim 7 of the present application, the organic content of the binder resin and the organic solvent is in the range of 2 to 16% by weight, and the copper conductor paste whose viscosity has been adjusted is easily filled in the through-hole. The shrinkage of the copper conductor paste filled in the holes is moderate to improve fillability.

According to the invention of claim 8 of the present application, fine particles made of copper, copper oxide, or a mixture thereof having an average particle diameter of 1 to 500 nm are added to an average particle diameter of 0.5 to 500 nm.
A copper conductor paste obtained by adding a mixed copper powder, a binder resin, and an organic solvent to which at least one kind of auxiliary copper powder, which is mainly a base copper powder in a range of 10 μm and has a smaller average particle diameter than the above, is added. This is a substrate on which a copper conductor paste printed and fired on a substrate is printed, a dense fired film is formed, and the electric resistance value is small.

According to the invention of claim 9 of the present application, the fine particles made of copper, copper oxide or a mixture thereof have an average particle diameter in the range of 100 to 200 nm, and a more dense fired film is formed. The electric resistance value also decreases.

[0019]

DETAILED DESCRIPTION OF THE INVENTION Fine particles composed of copper, copper oxide, or a mixture thereof, which are the first component of the copper conductor paste of the present invention and the copper conductor paste to be printed on the substrate of the present invention, are prepared, for example, by a precipitation method. This is a method called precipitation of metal fine particles directly from a metal salt solution using a reducing agent. Fine metal particles can be obtained by adding a reducing agent such as formalin, hydrazine, sodium hypophosphite, or borohydride salt to an aqueous solution containing metal ions under appropriate conditions. The fine particles are subjected to a surface treatment with an organic fatty acid or a coupling agent to improve oxidation resistance, dispersibility, and the like. The average particle diameter of the fine particles is in the range of 1 to 500 nm. Preferably, 100-
It is in the range of 200 nm, and within this range, the aggregation of the fine particles is eliminated, a dense fired film is formed, and the electric resistance value is reduced.

The mixed copper powder, which is the second component of the copper conductor paste of the present invention, is based on copper powder having an average particle diameter in the range of 0.5 to 5 μm, and auxiliary copper having an average particle diameter smaller than this. It is a powder to which at least 1 to 3 kinds of powder are added. Specific mixed copper powder is a base copper powder having the largest average particle diameter in the range of average particle diameter of 2 to 5 μm, and a first auxiliary copper having the next largest average particle diameter in the range of average particle diameter of 1 to 2 μm. Powder and the second auxiliary copper powder having the smallest average particle diameter in the range of 0.5 to 1 μm in the three-stage particle diameter range, or the average particle diameter of 0.5 to 1 μm.
base copper powder in the range of μm and an average particle diameter of 0.1 to
The auxiliary copper powder has a two-stage particle size range of 0.5 μm. In the case where the mixed copper powder is composed of three ranges of particle diameters, the base copper powder in the mixed copper powder has a particle size of 8%.
The first auxiliary copper powder is 1 to 19% by weight and the second auxiliary copper powder is 1 to 19% by weight based on 0 to 98% by weight. In particular, for auxiliary copper powder, without being limited to this,
You may use the 3rd auxiliary copper powder below the range of these average particle diameters.

It is desirable that each copper powder of the auxiliary copper powder be relatively spherical. This is because the copper powders are arranged with a reduced number of voids. When copper powders having different average particle diameters are used, auxiliary copper powder having a small average particle diameter fills gaps and voids generated when the base copper powder having the largest average particle diameter is arranged. There is an effect that the number of internal defects is small and the compaction becomes good.

If the average particle diameter of the base copper powder exceeds 5 μm, the influence of oxidation is less likely to be exerted, and the setting of firing conditions is wide. Of the adhesive decreases. Further, the copper powder may be crushed in the ink roll process to form a copper foil, which may cause mesh displacement during screen printing.
On the other hand, when the average particle diameter of the base copper powder is less than 0.5 μm,
Since the total particle area of the mixed copper powder becomes too large, the influence of oxidation increases, and the electric resistance value increases. In addition, since the bulk density is high, the compaction property deteriorates.

If the amount of the base copper powder exceeds 98% by weight, sintering will not be sufficient at a low temperature, resulting in insufficient tightening, resulting in a decrease in the adhesive strength between the fired film and the substrate or through hole. If it is less than 80% by weight, the total particle area of the mixed copper powder becomes too large, and the same problem as described above occurs. The auxiliary copper powder is added to fill gaps and voids generated when the base copper powder is arranged, and the average particle size and the amount added are greatly affected by those of the base copper powder.

The binder resin as the third component of the copper conductor paste of the present invention includes, for example, celluloses such as nitrocellulose, ethylcellulose, cellulose acetate and butylcellulose; polyethers such as polyoxymethylene;
Polyvinyls such as polybutadiene and polyisoprene; acrylics such as polybutyl methacrylate and polymethyl methacrylate; and polyamides such as nylon 6, nylon 6.6, and nylon 11, but are not particularly limited, but need to be decomposed during firing. .

It is preferable that the binder resin contains at least two kinds of resins having different thermal decomposition temperatures. This is because even when fired, the binder resin does not thermally decompose at once but decomposes according to the environmental temperature, so that it does not remain in the fired film.

Examples of the organic solvent for dissolving the binder resin include carbitol, carbitol acetate, terpinol, metacresol, dimethylimidazolidinone,
It is a high boiling organic solvent such as dimethylformamide, terpinol, diacetone alcohol, triethylene glycol, paraxylene, ethyl lactate, and isophorone, and may be used in combination of two or more.

The glass powder, which is the fourth component added to the present invention, may be added to improve the cracks in the fired film or to carry an auxiliary role to improve the hardening. This glass powder does not contain lead, has a softening point of 200 to 700 ° C. in an average particle diameter of 1 to 10 μm, and is added in the amount of all copper powder and ultrafine copper oxide. 0.1 to 2.0 parts by weight with respect to 100 parts by weight of the total amount of the substance, copper, or a mixture thereof. 2.0
If the amount is more than 10 parts by weight, the glass powder remains in the fired film after firing, so that the electrical resistance of the fired film tends to increase, and a glass layer is formed at the interface between the fired film and the substrate, resulting in thermal expansion. Easily cause distortion and weak thermal shock.
On the other hand, if it is less than 0.1, improvement of cracking and baking of the fired film cannot be expected.

The copper conductor paste of the present invention has an organic content of 2 to 16% by weight comprising a binder resin and an organic solvent.
And the viscosity is adjusted. When the organic content is less than 2% by weight, the viscosity of the copper conductor paste becomes high, making it difficult to fill the through-hole. When the organic content exceeds 16% by weight, the paste filled in the through-hole is fired. Due to shrinkage, fillability is poor.

Further, fine particles composed of all the contained copper powder and copper oxide, copper, or a mixture thereof are 84%.
９８98% by weight. If the content exceeds 98% by weight, the paste becomes too viscous to cause insufficient tightening, and the adhesive strength between the fired film and the substrate or through hole is reduced.
When the content is less than the percentage by weight, the paste filled in the through-holes shrinks by firing, so that the same problem as described above occurs.

The copper conductor paste thus obtained is applied to a ceramic substrate such as alumina, aluminum nitride, silicon carbide, silicon nitride, sialon, barium titanate, PBZT or the like by screen printing or the like. The screen printing procedure involves a screen placed horizontally (eg,
The printed circuit boards are placed under a stainless steel plain fabric (300 mesh) at intervals of several millimeters. After the copper conductor paste is placed on the screen, it is spread over the entire screen using a squeegee. At this time, the screen and the printed circuit board have an interval. Subsequently, printing is performed by pressing and moving the screen with a squeegee to such an extent that the screen contacts the print substrate. Thereafter, this is repeated.

The substrate is directly placed in a belt furnace without pre-baking as in the prior art, and is placed in a nitrogen furnace at 600 to 100
The powder is fired at a temperature of 0 ° C. for 5 to 20 minutes (peak retention time) to sinter the copper powder and make it react with the substrate.
At this time, a predetermined amount of oxygen is fed into the furnace, and the adhesion between the fired film and the substrate is increased to decrease the electric resistance value of the fired film.

[0032]

Next, the present invention will be described in more detail with reference to specific examples. Examples 1 to 8 and Comparative Examples 1 and 2 (Preparation of Copper Conductor Paste) Cu or Cu _{20 having a} particle size of 40 nm, mixed copper powder, and glass powder were mixed as shown in Table 1. Three kinds of base copper powder and two kinds of auxiliary copper powder were used as the mixed copper powder. In addition, a resin prepared by dissolving an acrylic resin with terpinol and carbitol acetate was prepared. These were mixed and further uniformly mixed with an ink roll to produce a brown copper conductor paste.

(Preparation of fired film) A copper conductor paste was printed at 2 × 2 mm on an alumina substrate for adhesion evaluation using a polyester 200 screen, and an alumina substrate for electric resistance evaluation was a copper conductor paste. To polyester 2
Using a 00 screen, printing was performed to a diameter of 15 mm. Further, as the through-hole evaluation substrate, a copper conductor paste was screen-printed on an alumina substrate having a plurality of through-holes having a diameter of 0.3 mm using a polyester 200 screen, and the copper conductor paste was simultaneously pushed into the through-holes. These were placed directly in a belt furnace and fired in nitrogen at a firing temperature of 900 ppm and an oxygen concentration of 150 ppm for a peak holding time of 10 minutes to produce a substrate.

(Evaluation Method) The adhesion of the fired film, the electric resistance of the fired film, the adhesiveness of the through-hole filling portion, the fillability, and the printing edge were measured by the following methods.

1. Adhesion strength of fired film (L-peel strength) Tin-plated copper wire with a diameter of 0.8 mm bent into L-shape is 2 mm
The adhesive strength of the copper wire which was fixed to the surface of the fired film fired to a size of × 2 mm by soldering and was bent vertically was measured with a spring meter to determine the adhesive force between the substrate and the fired film.

2. Electric Resistance Value of Fired Film Using a fired film having a thickness of 10 μm and a diameter of 15 mm on an aluminum nitride substrate, the electric resistance value was measured by a four-point probe method.

3. Adhesiveness of the through-hole filling part The through-hole filling part is 100 with Taber abrasion tester
The state after abrasion 0 times was visually observed. The evaluation was made in three stages, ◎ is excellent, ○ is good, and Δ is bad.

4. Filling ability The filling part of the through hole was observed with a microscope. The evaluation was made in three stages, ◎ is excellent, ○ is good, and Δ is bad.

5. Printing edge Horizontally laid screen (polyester plain fabric, 20
0 mesh), a printed circuit board is placed at a distance of several millimeters, a copper conductor paste is placed on this screen, and then spread over the entire screen using a squeegee. Then, the screen contacts the printed circuit board. Press the screen with a squeegee to move it, and print. The substrate after baking was magnified with a microscope and the edge of the film was observed. If the edge is sharp and angular,
When the edge was round and the central part was flat, it was evaluated as ○, and when the edge was round and the central part was depressed, it was evaluated as Δ.

6. Viscosity Using a viscometer (DVO-E type, manufactured by Tokyo Keiki Co., Ltd.), place No. in a container containing a copper conductor paste. No. 9 rotor was inserted and rotated, and the static viscosity (rotor rotation 1 rpm) and dynamic viscosity (rotor rotation 5 rpm) were measured. Measurement temperature is 25 °
C. Table 1 shows the results obtained by the above evaluation methods.
Shown in

[0041]

[Table 1]

According to the results, in the examples, the through holes are easily filled, the filling properties of the paste filled therein are good after firing, the printing is easy on the substrate, and the shape after printing is good. It turns out that it can hold. However, in some of the comparative examples, the printing edge is poor.

Examples 9 to 15 Copper having a predetermined particle size, mixed copper powder, and glass powder were mixed as shown in Table 2. Three kinds of base copper powder and two kinds of auxiliary copper powder were used as the mixed copper powder. Further, a resin prepared by dissolving an acrylic resin and a phenol resin in a weight ratio of 9: 1 with terpinol and carbitol acetate was prepared. These were mixed in the same manner as in Example 1 to produce a brown copper conductor paste, and a fired film was similarly produced. Table 2 shows the adhesion of the obtained fired film and the electric resistance value of the fired film.

[0044]

[Table 2]

According to the result, as in the embodiment, 100
To use fine copper particles having a particle size of
It can also be seen that the use of two types of resins having different thermal decomposition temperatures improves the adhesion of the fired film and further reduces the electric resistance.

[0046]

As described above, according to the present invention, the average particle size of 1
Fine particles made of copper, copper oxide or a mixture thereof having a mean particle size of 0.5 to 10
Copper conductor paste containing a base copper powder in the range of μm and at least one kind of auxiliary copper powder having a smaller average particle size in the range above, a binder resin, and a copper conductor paste containing an organic solvent and the paste (1) The static viscosity is high, the edge of the film after printing appears sharply and the shape retention is good, and the printability is good because the dynamic viscosity does not increase. (2)
The fine particles react and adhere to the substrate, bake the mixed copper powder,
(3) The auxiliary copper powder fills the gaps and voids generated by the arrangement of the base copper powder, resulting in a fired film having no internal defects and good compaction. (4) By adjusting the viscosity of the copper conductor paste, This has the effect of facilitating filling of the through-holes, and of having good fillability since the volume of the paste filled in the through-holes after firing is small.

In addition, when fine particles composed of copper, copper oxide, or a mixture thereof having an average particle diameter of 100 to 200 nm are mixed with the mixed copper powder in the copper conductor paste, (5) the fine particles are agglomerated. This results in the formation of a dense fired film and a decrease in the electric resistance value. When at least two kinds of resins having different thermal decomposition temperatures are used as the binder resin, (6) the binder resin is heated at a time. Decomposes according to environmental temperature without decomposing,
There is an excellent effect that a dense fired film is formed without remaining in the fired film, and the electric resistance value is reduced.

Claims (9)

[Claims] 1. Fine particles comprising copper, copper oxide or a mixture thereof having an average particle diameter of 1 to 500 nm, and a base copper powder having an average particle diameter of 0.5 to 10 μm. A copper conductor paste comprising a mixed copper powder to which at least one kind of auxiliary copper powder having a small average particle diameter is added, a binder resin, and an organic solvent. 2. The copper conductor paste according to claim 1, wherein the average particle diameter of the fine particles made of copper, copper oxide, or a mixture thereof is in the range of 100 to 200 nm. 3. A binder resin containing at least two kinds of resins having different thermal decomposition temperatures.
Or the copper conductor paste according to 2. 4. The base copper powder having the largest average particle diameter in the range of 2 to 5 μm in the mixed copper powder, and the base copper powder having an average particle diameter of 1 to 5 μm.
3. The copper conductor paste according to claim 1, comprising a first auxiliary copper powder having a size in a range of from 2 μm to 2 μm, and a second auxiliary copper powder having an average particle size in a range of from 0.5 to 1 μm. 5. The mixed copper powder comprises a base copper powder having the largest average particle diameter in the range of 0.5 to 1 μm in average particle diameter and an auxiliary copper powder in the range of 0.1 to 0.5 μm in average particle diameter. The copper conductor paste according to claim 1, wherein 6. The glass powder is mixed copper powder with an average particle size of 1 to 6.
3. The composition according to claim 1, wherein 0.1 to 2.0 parts by weight is added to 100 parts by weight of the total amount of fine particles comprising copper, copper oxide, or a mixture thereof in the range of 500 nm.
The copper conductor paste as described in the above. 7. The copper conductor paste according to claim 1, wherein the organic content of the binder resin and the organic solvent is in the range of 2 to 16% by weight. 8. Fine particles comprising copper, copper oxide or a mixture thereof having an average particle diameter in the range of 1 to 500 nm, and a base copper powder having an average particle diameter in the range of 0.5 to 10 μm. Copper characterized in that a copper conductor paste obtained by adding at least one kind of auxiliary copper powder having a small range of the average particle diameter, a binder resin, and an organic solvent to a substrate is printed and fired, Substrate printed with conductive paste. 9. The printed circuit board according to claim 8, wherein the fine particles made of copper, copper oxide or a mixture thereof have an average particle diameter in the range of 100 to 200 nm.