JPH10283840A - Copper conductor paste for aluminum nitride board, and aluminum nitride board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper conductor paste which adheres satisfactorily even to an aluminum nitride board and provide such an aluminum nitride board using the copper conductor paste. SOLUTION: Particulates are formed from copper, copper oxide, or mixture thereof whose mean particle size ranges between 1-500 nm, and a mixture copper powder is prepared by adding to the particulates the base copper powder as chief component with the mean perticle size ranging between 0.5-10 μm and one sort or more of aux. copper powder having a smaller mean particle size, and therefrom a copper conductor paste is formed together with a binder resin, glass powder, and organic solvent, wherein the binder resin should consist of a resin having at least a pyrolytic temp. of 250-350 deg.C, and the glass powder has a softening point lower than the sintering point of the particulates or mixture copper powder and higher than the decomposing temp. of the binder resin.

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 an aluminum nitride substrate and an aluminum nitride substrate, and more particularly to a copper conductor paste and a nitride for an aluminum nitride substrate having improved adhesion between the aluminum nitride substrate and a fired film. Related to aluminum substrate.

[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 bonded to a substrate, micron-sized metal fine particles cannot be bonded to a ceramic substrate by reaction. Therefore, about 4 to 10% by weight of glass frit is added to the paste. However, the glass frit 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 frit remains in the fired metal film,
Since the electrical resistance of the metal film is increased, and the metal film and the substrate are adhered to each other with the glass layer, distortion due to a difference in thermal expansion is likely to occur, and the thermal shock resistance is weakened.

[0005] A copper-based paste is known as a paste partially resolving such disadvantages. This paste is obtained by dispersing a non-copper-based material such as copper, glass fill, and tungsten, molybdenum, and rhenium in an organic solvent, as described in, for example, JP-A-60-70746. Also, as described in Japanese Patent Publication No. 3-50365, a copper oxide-coated metal copper particle, a copper oxide particle, and a glass powder such as glass dispersed in an organic solvent are known. ing.

[0006]

In the above-mentioned copper-based paste, the glass frit of 4 to 10% by weight contained therein plays a role of adhesion between the substrate and the conductor. At present, the sintered film of the paste and the substrate containing oxygen such as alumina have good adhesion but do not adhere to a substrate containing no oxygen such as aluminum nitride at all.

An object of the present invention is to improve such a problem, and an object of the present invention is to provide a copper conductor paste which sufficiently adheres to an aluminum nitride substrate and an aluminum nitride substrate using the same.

[0008]

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. A mixed copper powder obtained by adding at least one kind of auxiliary copper powder having a small average particle diameter to a base copper powder mainly in a range of 0.5 to 10 μm, and a copper conductor to which a binder resin, glass powder and an organic solvent are added. A paste containing at least a resin having a thermal decomposition temperature of 250 to 350 ° C. as the binder resin, wherein the glass powder is lower than the sintering temperature of the fine particles or the mixed copper powder and lower than the decomposition temperature of the binder resin. It is a copper conductor paste for aluminum nitride substrates having a high softening point.

That is, in the present invention, the reaction layer (CuAlO ₂ or C ₂ O) formed by the reaction between copper powder and aluminum nitride by the resin component decomposing at a relatively low temperature below the softening point of the glass powder.
By supplying oxygen necessary for producing uAl ₂ O ₄ ) to the interface between the copper powder and the aluminum nitride, the adhesive strength between the aluminum nitride substrate and the fired film is improved.

In the invention of claim 2 of the present application, a resin having a thermal decomposition temperature of 250 to 350 ° C. and a resin having a thermal decomposition temperature of 450 to 550 ° C. are used as the binder resin, and a resin having a low thermal decomposition temperature is used. It is a copper conductor paste for aluminum nitride substrates that has been frequently used. In addition to the effects of the invention described in claim 1, by adding a small amount of a high-temperature decomposition binder resin, the leveling property at the time of raising the firing temperature is improved, and the fired film is smoothed. Performance can be improved.

According to the invention of claim 3 of the present application, there is provided a copper conductor paste for an aluminum nitride substrate using an acrylic resin and a phenol resin having a higher thermal decomposition temperature as a binder resin, and these resins are used at respective temperatures. Moreover, it is decomposed in a nitrogen atmosphere furnace for firing.

In the present invention, the weight ratio of the acrylic resin and the phenol resin in the binder resin is 9
In the copper conductor paste for aluminum nitride substrate in the range of 0:10 to 99: 1, when the amount of the high-temperature decomposition binder resin is large, the supply of oxygen is small and the reaction layer cannot be sufficiently formed.

In the invention according to claim 5 of the present application, the glass powder is in a copper conductor paste for an aluminum nitride substrate using at least two kinds of powders having different softening points. The powder is softened and leveled, so that the smoothness of the fired film can be improved and the denseness of the film can be improved.

In the invention according to claim 6 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 if it is less than 2% by weight, the print is blurred and the circuit cannot be written. If the content exceeds 16% by weight, the paste will drip after printing or will be connected to the next one.

In the invention according to claim 7 of the present invention, copper, copper oxide or a mixture thereof having an average particle diameter of 1 to 100 nm is added to a base copper powder having an average particle diameter of 0.5 to 10 μm. A mixed copper powder obtained by adding at least one kind of auxiliary copper powder having a small average particle diameter to the above, a binder resin containing a resin having a thermal decomposition temperature of at least 250 to 350 ° C., and baking of the fine particles and the mixed copper powder. A glass powder having a softening point lower than the sintering temperature and higher than the decomposition temperature of the binder resin, and a copper conductor paste obtained by adding an organic solvent is printed on an aluminum nitride substrate and fired. It is a substrate that can form circuits by printing and etching.

In the invention according to claim 8 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.

According to the ninth aspect of the present invention, the weight ratio of the acrylic resin and the phenol resin in the binder resin is 9
It is on an aluminum nitride substrate in the range of 0:10 to 99: 1.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Fine particles composed of copper, copper oxide, or a mixture thereof, which are the first component of the conductive paste of the present invention and the conductive paste to be printed on the substrate of the present invention, are obtained, for example, by a method called precipitation method. That is, this is a method of directly precipitating and depositing metal fine particles from a metal salt solution using a reducing agent. Formalin, hydrazine, sodium hypophosphite,
Fine metal particles can be obtained by adding a reducing agent such as a borohydride salt to an aqueous solution containing metal ions under appropriate conditions. The fine particles are resistant to oxidation,
In order to improve dispersibility and the like, a surface treatment is performed with an organic fatty acid or a coupling agent. The average particle diameter of the fine particles is 1
１００100 nm, preferably 40-60 nm.
It is.

The mixed copper powder as the second component of the 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 powder having an average particle diameter smaller than this. At least 1 to 3 or more 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.

When the mixed copper powder is composed of three stages of particle size ranges, the base copper powder in the mixed copper powder is 80 to 98%.
1 to 19% by weight of the first auxiliary copper powder with respect to
Is 1 to 19% by weight. In particular, the auxiliary copper powder is not limited to this, and a third auxiliary copper powder having a range of the average particle diameter or less may be used.

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 using copper powder with different average particle diameter, auxiliary copper powder with small average particle diameter fills gaps and voids generated when base copper powder with the largest average particle diameter is arranged, so the conductor after firing is There is an effect that the number of internal defects is small and the compaction becomes good.

When the average particle size 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 widened. Adhesive strength 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, the total particle area of the mixed copper powder becomes too large, and 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, it does not sinter sufficiently at a low temperature, resulting in insufficient compaction, resulting in a decrease in the adhesive strength between the conductor and the substrate or through hole. When the content is less than the weight percentage, 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 conductor paste of the present invention has a thermal decomposition temperature of at least 250 to 35.
It is a resin containing a resin at 0 ° C., specifically, a resin having a thermal decomposition temperature of 250 to 350 ° C. and a thermal decomposition temperature of 450 to 550.
A combination of resins at a temperature of ° C. is preferable in that the oxidation of the copper powder is suppressed for a long time and the electrical resistance of the fired conductor is reduced by thermal decomposition without leaving any binder resin.

Examples of the resin having a thermal decomposition temperature of 250 to 350 ° C. include acrylic resins such as isobutyl methacrylate, n-butyl methacrylate, methyl methacrylate, ethyl methacrylate, n-butyl / isobutyl methacrylate copolymer, nitrocellulose, and polyoxymethylene. There is.

Examples of the resin having a thermal decomposition temperature of 450 to 550 ° C. include phenol resins such as terpene phenol copolymer and polyamides such as cellulose acetate, nylon 6, nylon 6.6 and nylon 11.

The weight ratio of the resin having a thermal decomposition temperature of 250 to 350 ° C. to the resin having a thermal decomposition temperature of 450 to 550 ° C. is 90: 1.
When the ratio is 0 to 99: 1 and less than 90:10, the proportion of the resin having a high thermal decomposition temperature occupies a large portion, which remains without being thermally decomposed at the time of calcination, a reaction layer is not formed, and the electric conductivity of the conductor is not increased. The result is to increase the resistance. On the other hand, if the ratio exceeds 99: 1, the proportion of the resin having a low thermal decomposition temperature occupies a large amount, the binder resin is thermally decomposed in a short time, and the amount of the resin surrounding the copper powder is reduced. Oxygen in excess of the oxygen amount is supplied to the film, and the copper film is oxidized to increase the electrical resistance of the conductor.

The most preferable combination of the binder resin is an acrylic resin and a phenol resin.

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 in order to improve the crack of the conductor or to carry an auxiliary role of improving 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 exceeds the weight part, since the glass powder remains in the conductor after firing, the electric resistance value of the conductor tends to increase, and a glass layer is formed at the interface between the conductor and the substrate, and distortion due to thermal expansion is reduced. It is easy to cause and the thermal shock resistance is weak. on the other hand,
If it is less than 0.1, improvement in cracking and baking of the conductor cannot be expected.

The conductive paste of the present invention has an organic content of 2 to 16% by weight consisting of a binder resin and an organic solvent. When the organic content is less than 2% by weight, the viscosity of the conductive paste becomes high and it becomes difficult to fill the through-hole. When the organic content exceeds 14% by weight, the paste filled in the through-hole shrinks by firing. To do
Poor fillability.

The content of all the copper powder and fine copper oxide, copper, or a mixture thereof is in the range of 84 to 98% by weight. If the content exceeds 98% by weight, the paste becomes highly viscous and insufficient tightening occurs, resulting in a decrease in the adhesive force between the conductor and the substrate or the through-hole. On the other hand, when the content is less than 84% by weight, the paste filled in the through-hole shrinks by firing. Therefore, the same problem as described above occurs.

The conductor paste thus obtained is
It is applied to a ceramic substrate such as alumina, aluminum nitride, silicon carbide, silicon nitride, sialon, barium titanate, and PBZT by a method such as screen printing. In the screen printing procedure, a printed circuit board is placed under a horizontally placed screen (for example, stainless steel plain fabric, 300 mesh) at an interval of several millimeters. After the conductive 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
It is baked at a temperature of 0 ° C. for 5 to 20 minutes (peak holding time) to sinter the copper powder and make it adhere to the substrate by reaction.

[0035]

Next, the present invention will be described in more detail with reference to specific examples. Examples 1-3, Comparative Examples 1-2 (Preparation of Conductive Paste) Cu or C having a particle size of 40 nm
u ₂ O, mixed copper powder, and glass powder were mixed as shown in Table 1. Three kinds consisting of base copper powder and two kinds of auxiliary copper powder as mixed copper powder, and one in which acrylic resin was dissolved in terpinol and carbitol acetate as binder resin, and one in which phenol resin was dissolved in terpinol and carbitol acetate, respectively Prepared. The binder resin was 30% by weight of the resin, 35% by weight of terpinol,
Consists of 35% by weight carbitol acetate. A predetermined amount of the above was mixed and further uniformly mixed with an ink roll to produce a brown conductive paste.

(Preparation of Conductor) Conductor paste was applied to an aluminum nitride substrate with a film thickness of 1 using a stainless steel 300 screen.
Printing was performed at 5 μm to 2 × 2 mm. Place the above substrate directly in a belt furnace, oxygen concentration 0 to 10 ppm in nitrogen, 900 °
The substrate was baked at a calcination temperature of C for a peak holding time of 10 minutes to produce a substrate.

(Evaluation Method) The method of measuring the adhesive strength and electric resistance of the conductor after firing is as follows. Table 1 shows the results obtained by this evaluation method.

1. Adhesive strength of conductor film after firing (L-type peel strength) Tin-plated copper wire with a diameter of 0.8 mm bent into an L-type is 2 mm
The adhesive strength between the substrate and the conductor was determined by measuring the adhesion of the copper wire, which was fixed to the surface of the conductor baked to a size of × 2 mm by soldering, and bent vertically using a spring meter.

2. Electrical Resistance of Conductor Using a conductor having a thickness of 10 μm and a diameter of 15 mm on an aluminum nitride substrate, the electrical resistance was measured by a four-point probe method.

[0040]

[Table 1]

According to the results, it can be seen that in the example, the adhesive strength between the aluminum nitride substrate and the conductor is high, and the resistance value of the conductor is small. However, in the comparative example, there is substantially no adhesive force between the aluminum nitride substrate and the conductor.

[0042]

As described above, according to the copper conductor paste for aluminum nitride substrate and the aluminum nitride substrate described in the claims of the present application, the adhesive strength between the aluminum nitride substrate and the fired film is improved, and the resistance value of the fired film is further improved. Also has a small effect.

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 mixed copper powder to which at least one kind of auxiliary copper powder having a small average particle diameter is added, and a copper conductor paste to which a binder resin, a glass powder and an organic solvent are added, wherein the binder resin has a thermal decomposition temperature of at least 250 to 350 ° C. A copper conductor for an aluminum nitride substrate, wherein the glass powder has a softening point lower than the sintering temperature of the fine particles or mixed copper powder and higher than the decomposition temperature of the binder resin. paste. 2. A binder resin having a thermal decomposition temperature of 25.
0-350 ° C resin and pyrolysis temperature 450-550 ° C
2. The copper conductor paste for an aluminum nitride substrate according to claim 1, wherein said resin is used and said resin has a low thermal decomposition temperature. 3. The copper conductor paste for an aluminum nitride substrate according to claim 2, wherein an acrylic resin and a phenol resin having a higher thermal decomposition temperature are used as the binder resin. 4. The copper conductor paste for an aluminum nitride substrate according to claim 3, wherein the weight ratio of the acrylic resin and the phenol resin in the binder resin is in the range of 90:10 to 99: 1. 5. The copper conductor paste for an aluminum nitride substrate according to claim 1, wherein at least two kinds of glass powders having different softening points are used. 6. The method 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.
Or the copper conductor paste for an aluminum nitride substrate according to 5. 7. Copper or copper oxide having an average particle diameter in the range of 1 to 100 nm or a mixture thereof and a base copper powder having an average particle diameter in the range of 0.5 to 10 μm. A mixed copper powder to which at least one kind of auxiliary copper powder having a small diameter is added;
Binder resin containing a resin at a temperature of up to 350 ° C., glass powder having a softening point lower than the sintering temperature of the fine particles and mixed copper powder and higher than the decomposition temperature of the binder resin, and a copper conductor paste obtained by adding an organic solvent Printed on an aluminum nitride substrate and fired. 8. The aluminum nitride substrate according to claim 7, wherein the organic content of the binder resin and the organic solvent is in the range of 2 to 16% by weight. 9. The aluminum nitride substrate according to claim 7, wherein the weight ratio of the acrylic resin and the phenol resin in the binder resin is in the range of 90:10 to 99: 1.