JP6869531B2 - Conductive paste, aluminum nitride circuit board and its manufacturing method - Google Patents

Description

The present invention relates to a conductive paste, an aluminum nitride circuit board, and a method for producing the same.

A conductive paste in which metal particles are dispersed in a vehicle composed of an organic binder and a solvent is known. The conductive paste is used for forming a conductor pattern of a printed wiring board, forming an electrode of an electronic component, and the like. This type of conductive paste can be roughly classified into a resin curing type and a firing type. The resin-curable conductive paste is a conductive paste in which metal particles come into contact with each other by curing the resin to ensure conductivity. The firing type conductive paste is a conductive paste in which metal particles are sintered by firing to ensure conductivity.

In recent years, it has become desirable to use an aluminum nitride (AlN) substrate for a circuit board used in a high temperature environment, specifically for a high voltage application. The aluminum nitride substrate has a high thermal conductivity (130~200Wm ^-1 K ^-1), and a low coefficient of thermal expansion (CTE) (4~4.5ppmK ^-1), etc., because of their excellent properties, a promising candidate ing.

Various methods such as a sputtering method, a thin-film deposition method, a direct bonding method, and an active metal method are known for forming a circuit on an aluminum nitride substrate. These circuit forming methods require special manufacturing equipment and have problems in terms of process cost. Therefore, a simpler method capable of screen printing is preferred. As a simple method, a method is known in which a conductive paste is impregnated with glass frit, and after firing, the glass is physically bonded (glass bond) to an aluminum nitride substrate as an adhesive (Patent Document 1 and Patent). Document 2).

Japanese Unexamined Patent Publication No. 2014-239040 Japanese Unexamined Patent Publication No. 2014-154547

However, in order to glass bond the conductive paste to the aluminum nitride substrate, it is necessary to heat it to the melting temperature of the glass. In the process, nitrogen gas is generated from the aluminum nitride substrate, and a metal sintered film made of the conductive paste ( The present inventor has found that blisters occur in the conductive layer). As a result, there are problems that post-processes such as plating cannot be performed due to the generation of blisters, and sufficient adhesive strength cannot be obtained. Further, depending on the surface condition of the aluminum nitride substrate, the conventional conductive paste has a problem. It has been found that sufficient adhesive strength may not be obtained for an aluminum nitride substrate.

An object of the present invention is to provide a conductive paste which has high adhesive strength to an aluminum nitride substrate after firing and does not generate blisters in the obtained conductive layer. Another object of the present invention is to provide an aluminum nitride circuit board having high adhesive strength between the aluminum nitride substrate and the conductive layer and having no blisters on the conductive layer, and a method for manufacturing the same.

Specific means for solving the above problems are as follows.
The first embodiment of the present invention is
(A) Conductive particles and
(B1) and ZnO-based glass frit and (B2) _Bi 2 _{O 3} based glass frit,
(C) Organic binder and
(D) At least one oxide selected from the group consisting of _{TiO 2} , ZrO ₂ and Bi ₂ O _{3, and}
(E) A conductive paste containing a component containing at least one atom selected from the group consisting of copper atoms and manganese atoms.
A second embodiment of the present invention
The process of applying the above conductive paste to the aluminum nitride substrate and
This is a method for manufacturing an aluminum nitride circuit board, which comprises a step of firing the aluminum nitride substrate to form a conductive layer.
A third embodiment of the present invention
An aluminum nitride circuit board containing an aluminum nitride substrate, an adhesive layer, and a conductive layer in this order.
The conductive layer contains a conductive particle sintered body and a glass component, and contains
The adhesive layer is at least one atom selected from the group consisting of (D') Ti atom, Zr atom and Bi atom, and at least one kind selected from the group consisting of (E') copper atom and manganese atom. Including atoms
An aluminum nitride circuit board having a porosity of an adhesive layer of less than 5%.

According to the present invention, it is possible to provide a conductive paste which has high adhesive strength to an aluminum nitride substrate after firing and does not generate blisters in the obtained conductive layer. Further, according to the present invention, it is possible to provide an aluminum nitride circuit board having high adhesive strength between the aluminum nitride substrate and the conductive layer and having no blisters on the conductive layer, and a method for manufacturing the same.

It is a scanning electron microscope (SEM) photograph of the plane of the conductive layer obtained by firing the conductive paste of Example 1. It is an SEM photograph of the plane of the conductive layer obtained by firing the conductive paste of Comparative Example 1. 6 is an SEM photograph of a cross section of an aluminum nitride circuit board produced by using the conductive paste of Example 1. It is an SEM photograph of the cross section of the aluminum nitride circuit board produced by using the conductive paste of Comparative Example 1.

[Conductive paste]
The conductive paste of the present embodiment includes (A) conductive particles, (B1) ZnO-based glass frit, (B2) Bi ₂ O ₃ -based glass frit, (C) organic binder, and (D) TiO ₂ . It _{contains at least one oxide selected from the group consisting of ZrO 2} and Bi ₂ O ₃ and a component containing at least one atom selected from the group consisting of (E) copper atom and manganese atom. (B1) by a combination of ZnO-based glass frit and (B2) _Bi 2 _{O 3} based glass frit, can be made more robust glass bonding to aluminum nitride substrates. Further, it contains at least one oxide selected from the group consisting of (D) TiO ₂ , ZrO ₂ and Bi ₂ O ₃ and at least one atom selected from the group consisting of (E) copper atom and manganese atom. By using the components, it is possible to enable stronger adhesion to the aluminum nitride substrate.

(A) Conductive Particles The conductive paste of the present embodiment contains (A) conductive particles. The conductive particles (A) are not particularly limited, but are metal fine particles such as silver (Ag), gold (Au), copper (Cu), nickel (Ni), palladium (Pd), tin (Sn) and alloys thereof. , And an inorganic filler coated with gold, silver, or palladium, which is preferably silver (Ag) from the viewpoint of having high conductivity. The shape of the conductive particles (A) is not particularly limited, and examples thereof include spherical particles and flaky particles (phosphorus flakes), and spherical particles are preferable from the viewpoint of easily releasing nitrogen gas generated from the aluminum nitride substrate during firing. (A) Of 100 parts by mass of the conductive particles, 80 parts by mass or more is preferably spherical. As the conductive particles, one type may be used alone, or two or more types may be used in combination. The conductive particles have a particle size of preferably 0.1 to 10 μm, more preferably 1 to 5 μm, and a BET specific surface area of ^{preferably 0.1 to 5.0 m 2} / g, more preferably 0.1 to 1. It is .5 m ² / g, more preferably 0.1 to 0.7 m ² / g, and the tap density is preferably 0.5 to 8 g / cm ³ , more preferably 1 to 8 g / cm ³ , and further. ^{Preferably, 3 to} 8 g / cm 3 can be preferably used.

The content of the (A) conductive particles in the conductive paste is preferably 50 to 95% by mass, more preferably 60 to 90% by mass, still more preferably 70, based on 100% by mass of the total amount of the conductive paste. ~ 90% by mass. Here, "100% by mass of the total amount of the conductive paste" means 100% by mass of the total amount of the conductive paste containing no solvent when the conductive paste contains a solvent described later.

(B1) ZnO-based glass frit and (B2) Bi ₂ O _3- based glass frit The conductive paste of the present embodiment contains (B1) ZnO-based glass frit and (B2) Bi ₂ O _3- based glass frit in combination. .. By the conductive paste contains a combination of (B1) ZnO-based glass frit and (B2) Bi ₂ O ₃ based glass frit, it can be made more robust glass bonding to aluminum nitride substrates.
If glass frit is present in the conductive paste, a partial liquid phase is generated during sintering, which promotes sintering of conductive particles (liquid phase sintering). (B2) The Bi ₂ O ₃ glass frit has a low melting point and good wettability with a metal, so that the sintering of conductive particles can easily proceed. On the other hand, the (B1) ZnO-based glass frit crystallizes when the temperature becomes higher than the softening point, and the fluidity becomes smaller than that of other glass frit, so that the sintering of the conductive particles is delayed. Therefore, (B1) by a combination of ZnO-based glass frit and (B2) Bi ₂ O ₃ based glass frit, to promote sintering between the conductive particles can be appropriately suppressed, pores between conductive particles You can delay the closing of (voids). As a result, the nitrogen gas generated from the aluminum nitride substrate escapes from the pores (voids), and then when the pores (voids) are finally closed by sintering, the nitrogen gas has already escaped, so that the obtained metal sintered film ( No blistering occurs on the conductive layer).
Further, in the conventional technology, since the coefficient of thermal expansion (CTE) of the aluminum nitride substrate is low, the difference in the coefficient of thermal expansion between the conductive paste and the aluminum nitride substrate at the time of firing the conductive paste causes the aluminum nitride substrate and the metal sintered film. There was a problem that peeling occurred between the (conductive layer) and the (conductive layer). In the present invention, the low expansion coefficient of the (B1) ZnO-based glass frit allows the expansion coefficient of the conductive paste to be appropriately lowered, which is also effective in that peeling does not occur.

(B1) ZnO-based glass frit (B1) The ZnO-based glass frit is a glass frit containing 30% by mass or more and 80% by mass or less of ZnO with respect to 100 parts by mass of the glass frit, preferably 40% by mass or more and 70% by mass or less. Including. (B1) The ZnO-based glass frit may contain oxides such _{as SiO 2} , B ₂ O ₃ , Bi ₂ O ₃ , Li ₂ O, Al ₂ O ₃ , and ZrO _{2 as other components.}

The softening point of the (B1) ZnO-based glass frit is preferably 300 ° C. or higher, more preferably 400 ° C. or higher and 700 ° C. or lower. The crystallization temperature of the (B1) ZnO-based glass frit is preferably 600 ° C. or higher, more preferably 600 or higher and 1000 ° C. or lower, and further preferably 600 or higher and 800 ° C. or lower. The softening point and crystallization temperature of the glass frit can be measured using a thermogravimetric measuring device (for example, TG-DTA2000SA manufactured by BRUKER AXS).

The average particle size of the (B1) ZnO-based glass frit is preferably 0.1 to 20 μm, more preferably 0.2 to 10 μm, and most preferably 0.5 to 5 μm. The average particle size referred to here means a volume-based median diameter (d50) obtained by a laser diffraction / scattering type particle size distribution measurement method.

(B2) Bi ₂ O ₃ system glass frit (B2) Bi ₂ O ₃ system glass frit is a glass containing 40% by mass or more and 90% by mass or less of _{Bi 2} O ₃ with respect to 100 parts by mass of _{Bi 2} O _{3 system glass frit.} It is a frit and preferably contains 50% by mass or more and 90% by mass or less. (B2) The Bi ₂ O ₃ system glass frit may contain oxides such _{as SiO 2} , B ₂ O ₃ , ZnO, Li ₂ O, Al ₂ O ₃ , and ZrO _{2 as other components.}

(B2) _{The softening point of the Bi 2} O ₃ glass frit is preferably 300 ° C. or higher, more preferably 300 or higher and 1000 ° C. or lower, and further preferably 400 or higher and 700 ° C. or lower. (B2) As the Bi ₂ O ₃ system glass frit, it is preferable to use one that does not crystallize. The softening point and crystallization temperature of the glass frit can be measured using a thermogravimetric measuring device (for example, TG-DTA2000SA manufactured by BRUKER AXS).

The average particle size of the (B2) Bi ₂ O ₃ glass frit is preferably 0.1 to 20 μm, more preferably 0.2 to 10 μm, and most preferably 0.5 to 5 μm. The average particle size referred to here means a volume-based median diameter (d50) obtained by a laser diffraction / scattering type particle size distribution measurement method.

In the conductive paste of the present embodiment, (B1) the total content of ZnO-based glass frit and (B2) _Bi 2 _{O 3} based glass frit, preferably with respect to 100 parts by mass of the (A) conductive particles 0. It is 01 to 20 parts by mass, more preferably 0.1 to 10 parts by mass, and further preferably 1 to 7 parts by mass.

The ratio of the content of (B1) ZnO glass frit to the content of (B2) Bi ₂ O ₃ glass frit ((B1) / (B2)) is a mass ratio, preferably 0.3 to 5. Yes, more preferably 1-4, and even more preferably 1-3. When (B1) / (B2) is 5 or less, sintering can proceed appropriately, the density of the sintered film (conductive layer) is improved, and the adhesive strength is increased. When (B1) / (B2) is 0.3 or more, the promotion of sintering is appropriately suppressed, nitrogen gas is released from the pores (voids) between the metal particles, and the resulting sintered film (conductive layer) is blistered. Is less likely to occur.

The (B1) ZnO-based glass frit and the (B2) Bi ₂ O _3- based glass frit may be individual glass frit, respectively, and ZnO and Bi ₂ O ₃ may be contained in one glass frit. .. From the viewpoint of easy control of the content, it is preferable that each glass frit is used.

(C) Organic Binder The conductive paste of the present embodiment includes (C) an organic binder. The organic binder in the present invention connects conductive particles to each other in a conductive paste and is burnt out when the conductive paste is fired. The organic binder is not particularly limited, but for example, a thermoplastic resin or a thermosetting resin can be used.

As the thermoplastic resin, for example, cellulose-based resins such as ethyl cellulose and nitrocellulose, acrylic resins, alkyd resins, saturated polyester resins, butyral resins, polyvinyl alcohol, hydroxypropyl cellulose and the like can be used.
As the thermosetting resin, for example, epoxy resin, urethane resin, vinyl ester resin, silicone resin, phenol resin, urea resin, melamine resin, unsaturated polyester resin, diallyl phthalate resin, polyimide resin and the like can be used.
These resins may be used alone or in combination of two or more.

In the conductive paste of the present embodiment, the content of (C) organic binder is preferably 0.5 to 30 parts by mass, and more preferably 1.0 with respect to 100 parts by mass of (A) conductive particles. ~ 20 parts by mass. When the content of the (C) organic binder in the conductive paste is within the above range, the printability of the conductive paste on the substrate is improved, and a fine pattern can be formed with high accuracy.

(D) At _{least one oxide selected from the group consisting of TiO 2} , ZrO ₂ and Bi ₂ O ₃ The conductive paste of the present embodiment is composed of (D) TiO ₂ , ZrO ₂ and Bi ₂ O _3. Contains at least one oxide selected from the group. By containing the oxide (D), it is possible to enable stronger adhesion to the aluminum nitride substrate. The mechanism is not clear, but it is considered that the inclusion of the (D) oxide forms a strong adhesive layer between the aluminum nitride substrate and the conductive layer. It is considered that this adhesive layer is formed by diffusing the metal atoms in the (D) oxide into the aluminum nitride substrate and causing some kind of bond. As the oxide (D), TiO ₂ and ZrO _{2 are preferable, and TiO 2} is more preferable from the viewpoint of improving the adhesive strength. Incidentally, (D) if oxide containing _Bi 2 _{O 3,} from moderately suppressing the sintering promotion, (B2) _Bi 2 _{O 3} total _Bi 2 _{O 3} based glass frit and (D) oxide with respect to the content, (B1) the ratio of the ZnO content of ZnO-based glass frit (ZnO / _Bi 2 _{O 3)} is a mass ratio, preferably from 0.3 to 5, more preferably 1 to 4 , More preferably 2-3.

In the conductive paste of the present embodiment, the content of the (D) oxide is preferably 0.01 to 5 parts by mass, more preferably 0.1 parts by mass with respect to 100 parts by mass of the (A) conductive particles. ~ 2 parts by mass.

(E) A component containing at least one atom selected from the group consisting of copper atom and manganese atom The conductive paste of the present embodiment has at least one kind selected from the group consisting of (E) copper atom and manganese atom. Contains components containing the atom of. By including the component (E), it is possible to enable stronger adhesion to the aluminum nitride substrate. The mechanism is not clear, but it is considered that the inclusion of the component (E) forms a strong adhesive layer between the aluminum nitride substrate and the conductive layer. It is considered that this adhesive layer is formed by diffusing the metal atoms in the (E) oxide into the aluminum nitride substrate and causing some kind of bond.
The component (E) may be a carrier metal of copper or manganese, or may be an oxide, a hydroxide, or an organic resinate. For example, copper, may be the elemental metal (Cu), oxide (e.g., CuO, _Cu 2 O), hydroxides (e.g., Cu _{(OH) 2)} or copper organic resinate (e.g., carboxylate, carboxylic Acid esters, alkoxides, rosin esters, polycyclic organic compounds, siloxanes, boric acid compounds, etc.) may be used. Manganese may be a single metal (Mn), an oxide (eg, MnO, MnO ₂ ), a hydroxide (eg, Mn (OH) ₂ ) or an organic resinate (eg, carboxylate, carboxylic acid ester, alkoxide). , Rosin ester, polycyclic organic compound, siloxanes, boric acid compound, etc.).
The component (E) may be an alloy containing copper and manganese, and examples thereof include Cumn alloys and CumnSn alloys.
When the component (E) contains a carrier metal of copper, it is preferable that the conductive particles (A) are not copper (Cu).

Component (E) is _{preferably, CuO, Cu 2 O, MnO} , MnO 2, CuMn alloy or CuMnSn alloy.

The component (E) is preferably in the form of a powder from the viewpoint of ease of mixing.

In the conductive paste of the present embodiment, the content of the component containing at least one atom selected from the group consisting of (E) copper atom and manganese atom is the element conversion content of copper (Cu) and manganese (Mn). In terms of amount, (A) is preferably 0.1 to 5.0 parts by mass, more preferably 0.2 to 3.0 parts by mass, and even more preferably 0.3 with respect to 100 parts by mass of the conductive particles. ~ 2.0 parts by mass. When it is within 5.0 parts by mass, the adhesive strength is further improved without the oxides of copper and manganese hindering sintering. When the content of the component (E) in the conductive paste is within the above range, stronger adhesion can be made to the aluminum nitride substrate.

In the conductive paste of the present embodiment, from the viewpoint of enabling stronger adhesion to the aluminum nitride substrate, the amount of manganese of the component (E) is 100 parts by mass of the conductive particles (A) in terms of element equivalent content. On the other hand, it is preferably 0.0025 to 2.85 parts by mass, and more preferably 0.015 to 1 part by mass. The amount of copper of the component (E) is preferably 0.0025 to 2.85 parts by mass, and more preferably 0.015 to 1 part by mass with respect to 100 parts by mass of the conductive particles (A) in terms of element equivalent content. Is. For example, when (A) 1 part by mass of a CuMnSn alloy having a composition of 90.5: 7.0: 2.5 with a mass ratio of Cu: Mn: Sn to 100 parts by mass of conductive particles is added, copper is added. The elemental equivalent content of is 0.905 parts by mass, and the elemental equivalent content of manganese is 0.070 parts by mass.

(F) Other components The conductive paste of the present embodiment may contain a solvent for adjusting the viscosity and the like.
Examples of the solvent include alcohols such as methanol, ethanol and isopropyl alcohol (IPA), organic acids such as ethylene acetate, aromatic hydrocarbons such as toluene and xylene, and N-methyl-2-pyrrolidone (NMP). N-alkylpyrrolidones, amides such as N, N-dimethylformamide (DMF), ketones such as methylethylketone (MEK), terpineol (TEL), butylcarbitol (BC), butylcarbitol acetate (BCA), etc. Can be mentioned.
The content of the solvent is not particularly limited, but is preferably 1 to 100 parts by mass, and more preferably 5 to 60 parts by mass with respect to 100 parts by mass of the conductive particles (A).

The viscosity of the conductive paste of this embodiment is preferably 50 to 700 Pa · s, more preferably 100 to 300 Pa · s. By adjusting the viscosity of the conductive paste within this range, the printability and workability of the conductive paste on the substrate are improved, and the conductive paste can be printed on the substrate with a uniform thickness.

The conductive paste of the present embodiment may contain other additives such as a dispersant, a rheology regulator, a pigment and the like.

The conductive paste of the present embodiment may further contain a plasticizer, an antifoaming agent, and the like.

The conductive paste of the present embodiment can be produced by mixing each of the above components using, for example, a Raikai machine, a pot mill, a three-roll mill, a rotary mixer, a twin-screw mixer, or the like.

The conductive paste of the present embodiment can be used for forming circuits of electronic components, forming electrodes, joining electronic components to substrates, mounting through holes, filling vias, forming heat sinks, and the like. For example, it can be used to form a conductor circuit of a printed wiring board. Further, since the conductive paste of the present embodiment has excellent adhesiveness to the aluminum nitride substrate after sintering, it can be used for forming a conductive layer on the aluminum nitride substrate.

[Manufacturing method of aluminum nitride circuit board]
The method for manufacturing the aluminum nitride circuit board of the present embodiment is as follows.
The step of applying the conductive paste of the above embodiment to the aluminum nitride substrate, and
The step of firing the aluminum nitride substrate to form a conductive layer is included.

First, the conductive paste of the above embodiment is applied to the aluminum nitride substrate. The coating method is arbitrary, and for example, known methods such as dispense, jet dispense, stencil printing, screen printing, pin transfer, and stamping can be used for coating. From the viewpoint of convenience, screen printing is preferable as the coating method.

After applying the conductive paste on the aluminum nitride substrate, the substrate is put into an electric furnace or the like. Then, the conductive paste applied on the substrate is fired at 500 to 1000 ° C., more preferably 600 to 1000 ° C., and even more preferably 600 to 900 ° C. As a result, the conductive particles contained in the conductive paste are sintered with each other, and the components such as the organic binder contained in the conductive paste are burnt down to obtain a sintered film (conductive layer). The conductive layer thus obtained has excellent adhesiveness to the aluminum nitride substrate.

[Aluminum nitride circuit board]
The aluminum nitride circuit board manufactured by the conductive paste and the manufacturing method of the above embodiment has the following configuration.
The aluminum nitride circuit board of this embodiment is
An aluminum nitride circuit board containing an aluminum nitride substrate, an adhesive layer, and a conductive layer in this order.
The conductive layer contains a conductive particle sintered body and a glass component, and contains
The adhesive layer is at least one atom selected from the group consisting of (D') Ti atom, Zr atom and Bi atom, and at least one kind selected from the group consisting of (E') copper atom and manganese atom. Including atoms
The porosity of the adhesive layer is less than 5%.

The aluminum nitride circuit board includes the aluminum nitride substrate, the adhesive layer, and the conductive layer in this order. By the presence of the adhesive layer between the aluminum nitride substrate and the conductive layer, stronger adhesion between the aluminum nitride substrate and the conductive layer is achieved.

The conductive layer contains a conductive particle sintered body and a glass component. The conductive particle sintered body is a sintered body of (A) conductive particles contained in the conductive paste. The glass component is a glass component included is (B1) from ZnO-based glass frit and (B2) _Bi 2 _{O 3} based glass frit in the conductive paste.

The adhesive layer is at least one atom selected from the group consisting of (D') Ti atom, Zr atom and Bi atom, and at least one kind selected from the group consisting of (E') copper atom and manganese atom. Includes atoms. At least one atom selected from the group consisting of (D') Ti atom, Zr atom and Bi atom is from the group consisting of (D) TiO ₂ , ZrO ₂ and Bi 2 O _{3 contained in the conductive paste.} It is an atom derived from at least one oxide selected. The at least one atom selected from the group consisting of (E') copper atom and manganese atom is an atom derived from a component containing at least one atom selected from the group consisting of (E) copper atom and manganese atom. is there. The presence of these (D') and (E') atoms in the adhesive layer achieves stronger adhesion between the aluminum nitride substrate and the conductive layer. It is considered that this is because the (D') atom and the (E') atom are diffused in the aluminum nitride substrate to form some kind of bond. The components in the adhesive layer can be confirmed by elemental analysis of the cross section of the aluminum nitride circuit substrate by EDS (Energy Dispersive X-ray Spectrometry).

The adhesive layer has a porosity of less than 5%, more preferably less than 3%. When the porosity of the adhesive layer is less than 5%, stronger adhesion between the aluminum nitride substrate and the conductive layer is achieved. In the present embodiment, the porosity can be calculated by observing the cross section of the aluminum nitride circuit board with a scanning electron microscope (SEM) and performing image analysis.

The aluminum nitride circuit board of the present embodiment can be used as a thermal substrate, a substrate for an LED package, a substrate for a semiconductor, a thin film circuit board, and a substrate for a power resistor.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[Preparation of conductive paste]
The following components (A), (B1), (B2), (C), (D) and (E) are mixed in the proportions of Examples 1 to 15 and Comparative Examples 1 to 4 shown in Tables 1 and 2. It was mixed to prepare a conductive paste. In addition, the ratio of each component shown in Table 1 and Table 2 is shown by the mass part, and "-" means that it is not compounded.
(A) Spherical silver powder having an average particle size of 1.2 μm and a BET value of 0.3 m ^{2 / g.}
Spherical silver powder with an average particle size of 4.5 μm and a BET value of 0.2 m ^{2 / g.}
Flake silver powder with an average particle size of 3.5 μm and a BET value of 1.0 m ^{2 / g.}

(B1) ZnO-based glass frit A ZnO-based glass frit having an average particle size of 1.1 μm, a softening point of 635 ° C., and a crystallization temperature of 735 ° C. Ingredient composition: SiO _2- B ₂ O _3- Zn O. ZnO content: 50-60% by mass.
(B2) _Bi 2 _{O 3} based glass frit average particle diameter 2.3μm, _Bi 2 _{O 3} based glass frit having a softening point of 610 ° C.. Chemical _{composition: SiO 2 -B 2 O 3 -Al} 2 O 3 -ZrO 2 -Bi 2 O 3. Bi ₂ O ₃ content: 66-76% by mass.

(C) Organic binder Ethyl cellulose resin.

(D) Oxide TiO ₂ : Titanium oxide (IV) powder with an _{average particle size of 3 μm ZrO 2} : Zircon (IV) oxide powder with an _{average particle size of 3 μm Bi 2} O ₃ : Bismuth oxide (IV) powder with an average particle size of 3 μm

(E) Component CuMnSn alloy: Cu: Mn: Sn = 90.5: 7.0: 2.5, spherical alloy powder having an average particle size of 2.5 μm produced by the gas atomization method.
MnO ₂ : Manganese (IV) oxide powder with an average particle size of 2 μm Cu ₂ O: Copper (I) oxide powder with an average particle size of 3 μm CuO: Copper (II) oxide powder with an average particle size of 3 μm

[Manufacturing of conductor layer and aluminum nitride circuit board]
The conductive pastes of Examples 1 to 15 and Comparative Examples 1 to 4 were applied to the aluminum nitride substrate by screen printing. Next, the aluminum nitride substrate was put into an electric furnace and fired at 850 ° C. for 60 minutes. As a result, a conductive layer was formed on the aluminum nitride substrate to obtain an aluminum nitride circuit board. The obtained conductive layer and aluminum nitride circuit board were used for the following evaluation of various physical properties. The obtained results are shown in Tables 1 and 2.

[Measurement of adhesive strength]
The adhesive strength of the conductive layer prepared using the conductive pastes of Examples 1 to 15 and Comparative Examples 1 to 4 to the aluminum nitride substrate was measured by the following procedure.
First, the conductive paste was applied onto an aluminum nitride substrate in a size of 1.5 mm square by a screen printing method. This substrate was placed in an electric furnace and heated at 850 ° C. for 60 minutes. Then, after performing Ni plating and Au plating, preliminary soldering (M705, 260 ° C., 3s manufactured by Senju Metal Industry Co., Ltd.), and then soldering a tin-plated annealed copper wire (φ0.8) to the electrode, a desktop universal testing machine ( Using 1605HTP manufactured by Aiko Engineering Co., Ltd., pull the tin-plated annealed copper wire in the 90 ° direction with respect to the substrate at a tensile speed of 10 (mm / s), measure the tensile strength (N / mm ² ), and measure the adhesive strength. Evaluated as. The evaluation of "x" in the table means that the aluminum nitride substrate and the conductive layer were immediately peeled off, and the shear strength could not be measured.

[Observation of appearance (presence or absence of blisters)]
The conductive layers prepared as described above using the conductive pastes of Examples 1 to 15 and Comparative Examples 1 to 4 were visually observed and the presence or absence of blisters was evaluated.

[SEM observation]
The cross section of the aluminum nitride circuit board prepared as described above using the conductive pastes of Examples 1 to 13 and Comparative Examples 1 to 4 was observed with a scanning electron microscope (SEM). The porosity (%) was calculated from the image analysis. An SEM photograph of a flat surface of an aluminum nitride circuit board produced using the conductive paste of Example 1 is shown in FIG. 1, and an SEM photograph of a cross section is shown in FIG. 3, and aluminum nitride produced using the conductive paste of Comparative Example 1 is shown in FIG. An SEM photograph of the plane of the circuit board is shown in FIG. 2, and an SEM photograph of the cross section is shown in FIG.

[EDS analysis]
The cross section of the aluminum nitride circuit board prepared as described above using the conductive pastes of Examples 1 to 15 and Comparative Examples 1 to 4 was elementally analyzed by EDS (energy dispersive X-ray spectroscopy).

As can be seen from the results shown in Tables 1 and 2, the conductive layer obtained by firing the conductive paste of Examples 1 to 15 had high adhesive strength to the aluminum nitride substrate and did not generate blisters. On the other hand, the conductive layer obtained by firing the conductive pastes of Comparative Examples 1 to 4 was significantly inferior in adhesiveness to the aluminum nitride substrate, and blisters were generated.

The porosity of the conductive layer of the aluminum nitride circuit board produced using Examples 1 to 15 was less than 5%, whereas the porosity of the aluminum nitride circuit board produced using Comparative Examples 1 to 4 was conductive. The porosity of the layers exceeded 5% in each case. In the aluminum nitride circuit board produced using Examples 1 to 15, an adhesive layer exists between the aluminum nitride substrate and the conductive layer, and the adhesive layer contains atoms derived from the components (D) and (E). This was confirmed by SEM observation and EDS analysis.

1 Aluminum nitride substrate 2 Adhesive layer 3 Conductive layer 4 Voids

Claims (9)

(A) Conductive particles and
(B1) and ZnO-based glass frit and (B2) _Bi 2 _{O 3} based glass frit,
(C) Organic binder and
(D) At least one oxide selected from the group consisting of _{TiO 2} , ZrO ₂ and Bi ₂ O _{3, and}
(E) Containing a component containing at least one atom selected from the group consisting of copper atoms and manganese atoms.
(B2) for the content of _Bi 2 _{O 3} based glass frit, it is (B1) the ratio of the content of the ZnO-based glass frit ((B1) / (B2)), at a mass ratio, Ri 1-5 der,
Here, the (B1) ZnO-based glass frit is a glass frit containing 30% by mass or more and 80% by mass or less of ZnO with respect to 100 parts by mass of the glass frit, and the (B2) Bi ₂ O _3- based glass frit is a glass frit. A glass frit containing 40% by mass or more and 90% by mass or less of _{Bi 2} O ₃ with respect to 100 parts by mass.
Conductive paste. The ratio of the ZnO content in the (B1) ZnO-based glass frit to the total content _{of the Bi 2} O ₃ in the (B2) Bi ₂ O ₃ glass frit and (D) oxide _{(ZnO / Bi 2} O ₃ ) is The conductive paste according to claim 1, which has a mass ratio of 1 to 5. (D) The conductive paste according to claim 1 or 2, wherein the oxide is TiO _2. (A) Claims 1 to 3 containing 0.1 to 5.0 parts by mass of the component (E) in terms of elemental equivalent contents of copper (Cu) and manganese (Mn) with respect to 100 parts by mass of the conductive particles. The conductive paste according to any one of the above items. (A) The conductive paste according to any one of claims 1 to 4, wherein the conductive particles have a spherical shape. (A) The conductive paste according to any one of claims 1 to 5, wherein the conductive particles are silver. The conductive paste according to any one of claims 1 to 6, for forming a conductive layer on an aluminum nitride substrate. A step of applying the conductive paste according to any one of claims 1 to 7 to an aluminum nitride substrate, and
A method for manufacturing an aluminum nitride circuit board, which comprises a step of firing the aluminum nitride substrate to form a conductive layer. An aluminum nitride circuit board containing an aluminum nitride substrate, an adhesive layer, and a conductive layer in this order.
The conductive layer contains a conductive particle sintered body and a glass component, and the glass component is contained in the conductive paste according to any one of claims 1 to 7 (B1) ZnO-based glass frit and (B2). ) It is a glass component derived from _{Bi 2} O _{3 glass frit.}
The adhesive layer is at least one atom selected from the group consisting of (D') Ti atom, Zr atom and Bi atom, and at least one kind selected from the group consisting of (E') copper atom and manganese atom. Including atoms
An aluminum nitride circuit board in which the porosity of the adhesive layer is less than 5%.

Images