JP2004055558A - Copper paste and wiring board using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a copper paste with excellent plating and soldering performances of a conductive layer in a wiring board using copper in the conductive layer and without bringing forth swelling and peeling of the conductive layer even if the wiring board is heated, and with a high reliability in connecting a heat dissipating component and various circuit components, and a wiring board using the same. <P>SOLUTION: A copper paste that contains copper powder, an organic vehicle, and Fe<SB>2</SB>O<SB>3</SB>particles is obtained. And a wiring board which has formed a conductive layer containing Fe element by coating and firing this copper paste on a ceramic green sheet is obtained. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a copper paste which is printed and co-fired to form a circuit on a ceramic substrate, and a wiring board using the same, and in particular, circuit components are connected by a joining method such as brazing. The present invention relates to a copper paste used for a wiring board and a wiring board using the same.

In recent years, wiring boards have been used in the high frequency region of the GHz band or higher with the increase in the speed of information communication, and there has been a demand for reduction of transmission loss. For this reason, in the wiring substrate, a conductor layer made of a low melting point metal such as silver or copper is formed on a ceramic substrate having a relatively low dielectric constant. In particular, as the circuit density increases, copper is used for the conductor layer to prevent migration.A ceramic substrate on which copper is printed as the conductor layer suppresses transmission of copper while suppressing oxidation of copper. Firing is performed in a wet nitrogen atmosphere (in a mixed atmosphere of water vapor and nitrogen gas) to obtain a low wiring substrate.

In general, a wiring board is formed by forming a ceramic green sheet from a slurry prepared using a ceramic raw material powder, an organic binder, a solvent, and the like by sheet forming such as a doctor blade method, and forming a wiring on the ceramic green sheet using a copper paste. After pattern printing and drying, the ceramic green sheet is debindered at a temperature of several hundred degrees Celsius in a mixed atmosphere of steam and nitrogen gas to remove the copper paste and organic components contained in the ceramic green sheet. The temperature is raised to about 1000 ° C. or more and firing is performed.

Wiring boards are mounted with various circuit components such as semiconductor elements such as transistors and diodes, heat-radiating components, terminals, etc. with the progress of high-density mounting and multifunctionalization of devices. Higher reliability is required for the adhesion strength of the layers.

In particular, a wiring board on which a semiconductor element such as a transistor or a diode is mounted, the semiconductor element generates heat due to an input signal and rises in temperature, thereby deteriorating the characteristics of the semiconductor element or the characteristics of other circuit components mounted on the circuit board. Therefore, it is important to take measures to dissipate heat. Therefore, a wiring board is often used with a radiator connected via a conductor layer, and the conductor layer formed on the wiring board is required to have an adhesion strength that does not cause blistering or peeling against a thermal load. Is done.

As a measure to prevent blistering and peeling of the conductor layer formed on the wiring board, we focused on that the organic vehicle contained in the copper paste generates gas in the firing process and causes blistering and peeling of the conductor layer, Copper oxide has a specific oxidation property such as devitrified glass frit selected from zinc-calcium aluminum silicate glass frit, zinc-magnesium-barium-aluminum silicate glass frit and mixtures thereof, bismuth oxide, cadmium oxide, etc. There is a method in which the generation of gas is suppressed by adding a substance to prevent peeling or swelling of the conductor layer (for example, see Patent Document 1).
JP-A-1-128488 (pages 4-7)

However, according to the technique of Patent Document 1, since glass frit is added to the copper paste, when used as a conductor layer on a wiring board, the glass emerges and remains on the surface of the conductor layer, and the solderability and plating property are reduced. In addition, there is a problem in that the conductor layer is bulged or peeled off when the wiring board is heated, so that measures for preventing bulging are insufficient.

The present invention solves the above problems, and in a wiring board using copper for the conductive layer, the plating property and the solderability of the conductive layer are good, and even if the wiring board is heated, the blistering of the conductive layer may occur. It is an object of the present invention to provide a copper paste having high reliability by connecting various circuit components such as semiconductor elements such as transistors and diodes, heat radiation components, terminals, and the like, without causing peeling, and a wiring board using the same. Is what you do.

The invention described in claim 1 for achieving the above object is a copper paste containing copper powder, an organic vehicle, and Fe ₂ O ₃ particles.
Since the copper paste according to claim 1 contains Fe ₂ O ₃ particles, the copper paste is fired in a non-oxidizing atmosphere to form a conductor layer having excellent adhesion strength to a wiring board, Various circuit components such as semiconductor elements such as transistors and diodes, heat dissipating components, terminals and the like are connected to this wiring board by heating and joining by a joining method such as soldering or joining materials such as various low melting point alloys. A wiring board having excellent adhesion strength of the conductor layer without swelling or peeling of the layer is obtained.

The reason why the adhesion strength of the conductor layer is improved by adding Fe ₂ O ₃ particles to the copper paste is presumed as follows.
In general, it is known that in a firing step for manufacturing a wiring board, the adhesion between the low-temperature fired porcelain material and the copper metal is poor because the wettability between the copper metal and the liquid phase component in the low-temperature fired porcelain material is poor. In general, a method of adding copper oxide to a copper paste to improve wettability with a liquid phase component of a low-temperature fired porcelain material and improve adhesion of copper metal is known. When the obtained wiring board is heated in a joining step such as brazing, the conductor layer bulges, and the adhesion between the conductor layer and the wiring board is insufficient.

That is, when the copper paste to which the copper oxide is added is used, the contact surface between the wiring substrate and the conductor layer is formed by mixing the interface where the metal oxide exists and the interface where the metal oxide does not exist, and is heated. It is considered that this caused blistering to occur from an interface where no metal oxide was present (an interface having poor adhesion).

Accordingly, the present invention provides a method in which Fe ₂ O ₃ particles are added to a copper paste to form an interface in which a metal oxide is uniformly present over the entire contact surface between the wiring substrate and the conductor layer, and that the adhesion between the conductor layer and the wiring substrate is improved. It is the one with improved characteristics.

When Fe ₂ O ₃ particles are added to the copper paste and the temperature is raised to a temperature higher than 700 ° C. in the firing step, a chemical reaction represented by the following (formula 1) occurs.
2Cu + 3Fe ₂ O ₃ → Cu ₂ O + 2Fe ₃ O ₄ ... (Equation 1)
That is, it is considered that Fe ₂ O ₃ acts as an oxidizing agent for Cu in the firing temperature range and slightly oxidizes Cu as a whole.

At this time, although the Cu is oxidized in a very small amount, the entire Cu is uniformly oxidized. Therefore, in the sintering, the wettability between the copper and the liquid phase component of the low-temperature sintering porcelain material is improved throughout, and the local It is considered that blistering is suppressed.

The Fe ₂ O ₃ is an iron oxide particle containing Fe ₂ O ₃ as a main component, and may contain iron oxide other than Fe ₂ O ₃ (for example, Fe ₃ O ₄ or FeO) or Fe metal. good.
The average particle diameter of the Fe ₂ O ₃ is preferably 1 μm or less. The reason is that if the average particle diameter of Fe ₂ O ₃ exceeds 1 μm, the dispersion of Fe in the conductor layer becomes uneven, and the effect of suppressing the blister of the conductor layer is reduced. The average particle size of Fe ₂ O ₃ is particularly preferably 500 nm or less, more preferably 100 nm or less. The reason is that even if a small amount of Fe ₂ O ₃ particles are added, the blister suppressing effect is exhibited. The lower limit of the average particle diameter of Fe ₂ O ₃ is preferably smaller as it has an effect of suppressing blistering of the conductor layer, but may be 5 nm in practical use.

Further, the addition amount of the Fe ₂ O ₃ is preferably in the range of 0.1 part by mass to 10.0 parts by mass with respect to 100 parts by mass of the copper powder. The reason is that if the added amount of Fe ₂ O ₃ is less than 0.1 parts by mass, the effect of suppressing the conductive layer swelling is reduced, and if the added amount of Fe ₂ O ₃ is more than 10.0 parts by mass, the conductor resistance is reduced. Is larger. The addition amount of Fe ₂ O ₃ is particularly preferably 0.1 to 5.0 parts by mass, more preferably 0.1 to 2.0 parts by mass. The reason is that the range is an optimum range for suppressing blistering without increasing the conductor resistance.

The copper powder preferably has an average particle size of 0.5 μm to 10 μm. The reason is that when the average particle size of the copper powder is smaller than 0.5 μm, the sintering start temperature of the copper becomes too low, and the wiring board may be warped or undulated. This is because if it is large, it becomes difficult to form a fine wiring pattern on the wiring board. The average particle size of the copper powder is more preferably 1 to 7 μm or 2 to 5 μm. The reason for this is that it is an optimal range for achieving both undulation suppression and fine wiring. At this time, the shape of the copper powder may be substantially spherical, dendritic, flake, or the like.

The organic vehicle is obtained by dissolving an organic polymer in an organic solvent, and the organic polymer is at least one of ethyl cellulose, acrylic resin, polymethylstyrene, butyral resin, PTFE, alkyd resin, and polyalkylene carbonate. Although one is used, an acrylic resin is particularly preferred since a decomposability is improved and a dense and low-resistance conductor layer can be obtained during firing, and further, poly-n-butyl methacrylate and poly-2-ethylhexyl methacrylate are preferred. .

As the organic solvent, a high-boiling solvent such as terpineol, butyl carbitol acetate, butyl carbitol, or dibutyl phthalate is preferably used.
The content of the organic vehicle is preferably in the range of 20 to 40 parts by mass, more preferably 20 to 30 parts by mass, based on 100 parts by mass of the copper powder. The reason is that when the content of the organic vehicle is less than 20 parts by mass, the fluidity of the copper paste is reduced, and when applying the copper paste to the wiring board, the workability is impaired, which is not preferable. If the content of the organic vehicle exceeds 40 parts by mass, the thickness of the conductor layer tends to vary when a copper paste is applied to the wiring substrate and dried, which is not preferable.

粘度 Further, the viscosity of the copper paste is preferably in the range of 5000 poise to 30 poise. The reason for this is that when the viscosity of the copper paste exceeds 5,000 poise, the fluidity of the copper paste decreases, and when the copper paste is applied to a wiring board, the workability is impaired, which is not preferable. This is because if the viscosity is less than 30 poise, the thickness of the conductor layer tends to vary when a copper paste is applied to the wiring substrate and dried, which is not preferable.

The copper paste may contain components such as a plasticizer, a thickener, a leveling agent, and an antifoaming agent.
Next, a second aspect of the present invention is a copper paste according to the first aspect, wherein the copper paste contains ceramic particles having an average particle diameter of 100 nm or less.

The copper paste according to claim 2 contains ceramic particles having an average particle diameter of 100 nm or less in order to improve the plating property and the sinterability of the copper powder. A wiring board with less undulation can be obtained.

セ ラ ミ ッ ク The ceramic particles preferably have an average particle size of 100 nm or less. The reason is that if the average particle size of the ceramic particles exceeds 100 nm, undulation is likely to occur on the wiring board, and the plating property of the conductor layer is impaired. The average particle size of the ceramic particles is particularly preferably 50 nm or less, and more preferably 30 nm or less. The reason is that it is an optimum range for suppressing the undulation and developing the plating property. The lower limit of the average particle size of the ceramic particles is preferably as small as possible because it has the effect of suppressing undulations and exhibiting plating properties, but is preferably 5 nm in practical use.

And it is preferable to add the ceramic particles in an amount of 0.1 to 5.0 parts by mass with respect to 100 parts by mass of the copper powder. The reason is that if the addition amount of the ceramic particles is less than 0.1 part by mass, the effect of suppressing the undulation does not appear, the plating property of the conductor layer is deteriorated, and the addition amount of the ceramic particles is 5.0 parts by mass. If the amount is larger, the sinterability of copper is impaired. The addition amount of the ceramic particles is more preferably in the range of 0.1 to 1.0 part by mass. The reason is that it is an optimum range for suppressing the undulation and developing the plating property.

In order to improve the sinterability of copper, the ceramic particles can be selected from glassy ceramic particles and materials that are sintered and vitrified. The glassy ceramic particles of the present invention include amorphous SiO ₂ and glass frit. In addition, the ceramic particles that are vitrified by sintering according to the present invention are those that melt into the glass contained in the ceramic green sheet by firing, and include, for example, glass-forming oxides such as crystalline SiO ₂ and B ₂ O _3. And alkali metals and alkaline earth metals such as MgO, CaO, Na ₂ O, and K ₂ O. In particular, SiO ₂ is preferable because undulation can be suppressed by adding a small amount thereof and floating of glass on the surface of the conductor layer can be reduced.

The surface of the ceramic particles is preferably hydrophilic. The reason for this is that, after the hydrophobic treatment, the decomposability of the organic component is deteriorated and the amount of residual carbon is increased.
In addition, in order to improve the plating property of the conductor layer, the ceramic fine particles are fired together with the ceramic green sheet without vitrification, and an additive contained in the composition and the copper paste constituting the ceramic green sheet. And a non-vitrified ceramic powder. The ceramic particles that are not vitrified by firing are crystalline ceramics that are not vitrified by reacting with additives contained in ceramic green sheets and copper paste.

The non-vitrified ceramic powder is selected from, for example, one containing at least one of Al ₂ O ₃ , TiO ₂ , CeO ₂ , and mullite, and specifically, is contained in a ceramic green sheet or a copper paste. Careful attention should be paid individually so as not to react with the additives, and the material should be appropriately selected. In particular, TiO ₂ is preferable because it can reduce the amount of undulation of the wiring board and further improve the adhesion strength of the conductor layer.

The ceramic particles for improving the sinterability of copper and the ceramic particles for improving the plating property of the conductor layer may be used separately, but in order to exert the advantages of both in a well-balanced ratio. May be used as a mixture.

Next, a third aspect of the present invention is a wiring substrate characterized in that the copper paste according to the first or second aspect is applied to a ceramic substrate and fired.
According to the wiring board of the third aspect, even if the wiring board is heated, the conductive layer does not bulge or peel off, and the effect of the plating property and the solderability of the conductive layer being good. can get.

Next, according to a fourth aspect of the present invention, at least one of a radiator, a connection terminal, a lid, and a circuit component is connected to the conductor layer of the wiring board according to the third aspect via a brazing material. A wiring board characterized by the following.

According to the wiring board of the fourth aspect, even if the brazing material is melted to connect the radiator, the connection terminal, the lid, and the circuit component, the conductor layer does not peel or bulge. High reliability can be obtained in connection terminals for mounting, lids for sealing electronic components (semiconductor elements and the like) that generate heat, and wiring boards for connecting circuit components and the like.

Examples of the heat radiator include a heat sink and a thermal via. Examples of the connection terminal include a pin terminal, a lead terminal, a flip chip terminal, a land terminal, a solder ball terminal, and the like. Examples of the lid include a plate-shaped metal lid and a ceramic lid. Examples of the circuit component include a semiconductor element and electronic components such as a capacitor, an inductor, and a resistor.

ろ う Various low-melting alloys such as solder (Sn-Pb alloy), Au brazing, Ag brazing, and Cu brazing can be used for the brazing material used for metal fitting connection. The melting point of this alloy is preferably from 270C to 800C. If the temperature is lower than 270 ° C., the alloy is melted by soldering at the time of mounting the PCB, and the position of the bracket is shifted. If the temperature is higher than 800 ° C., the softening point of the glass used for the wiring board is approached, and the wiring board is deformed. Particularly, an alloy having a melting point of 300 ° C to 600 ° C, more preferably 300 ° C to 500 ° C, is preferable. This is because alloys having these melting points are easy to handle.

Next, according to a fifth aspect of the present invention, a conductive layer is formed on a wiring board using Cu metal containing Fe, and at least one of a heat radiator, a connection terminal, a lid, and a circuit component is formed on the conductive layer. Are connected via a bonding material.

According to the wiring board of the fifth aspect, even if the brazing material is melted to connect the radiator, the connection terminal, the lid, and the circuit component, the conductor layer does not peel or bulge. High reliability can be obtained in connection terminals for mounting, lids for sealing electronic components (semiconductor elements and the like) that generate heat, and wiring boards for connecting circuit components and the like. The connection of the heat radiator, the connection terminals, the lid and the circuit components may be directly connected to the surface of the conductor layer which has been co-fired with the ceramic green sheet. A secondary conductor layer that is preferable for joining with a terminal, a lid, a circuit component, or the like may be formed and connected via the secondary conductor layer.

Examples of the heat radiator include a heat sink and a thermal via. Examples of the connection terminal include a pin terminal, a lead terminal, a flip chip terminal, a land terminal, a solder ball terminal, and the like. Examples of the lid include a plate-shaped metal lid and a ceramic lid. Examples of the circuit component include a semiconductor element and electronic components such as a capacitor, an inductor, and a resistor.

ろ う Various low-melting alloys such as solder (Sn-Pb alloy), Au brazing, Ag brazing, and Cu brazing can be used for the brazing material used for metal fitting connection. The melting point of this alloy is preferably from 270C to 800C. If the temperature is lower than 270 ° C., the alloy is melted by soldering at the time of mounting the PCB, and the position of the bracket is shifted. If the temperature is higher than 800 ° C., the softening point of the glass used for the wiring board is approached, and the wiring board is deformed. Particularly, an alloy having a melting point of 300 ° C to 600 ° C, more preferably 300 ° C to 500 ° C, is preferable. This is because alloys having these melting points are easy to handle.

Next, according to a sixth aspect of the present invention, in the wiring substrate according to the fifth aspect, a plating process is performed on a surface of the conductor layer.
According to the wiring substrate according to claim 6, a favorable plating treatment is obtained on the surface of the conductor layer, and even if the wiring substrate is heated, blistering or peeling of the conductor layer or plating does not occur, so that the transistor and the diode can be used. High reliability by connecting various circuit components such as semiconductor elements, heat dissipation components, terminals, etc.

Hereinafter, the present invention will be described using an example.
"Preparation of ceramic green sheets"
First, 50 parts by mass of a glass powder having a composition of 63.3 parts by mass of SiO ₂ , 24.1 parts by mass of B ₂ O ₃ , 5.7 parts by mass of Al ₂ O ₃ , and 6.9 parts by mass of CaO. By mixing with 50 parts by mass of alumina filler, a mixed powder having a particle size of 2.5 μm was prepared.

Next, a slurry was prepared by adding 20 parts by mass of an acrylic resin binder, 10 parts by mass of a plasticizer made of dibutyl phthalate, and an appropriate amount of a mixed solvent of toluene and MEK to 100 parts by mass of the mixed powder.

Next, a ceramic green sheet having a thickness of 250 μm was formed from the slurry by sheet forming such as a doctor blade method. The ceramic green sheet is a green sheet for low-temperature firing that can be fired at a relatively low temperature (here, 1000 ° C.).

"Preparation of copper paste"
Next, 25 parts by mass of the vehicle and the additives shown in (Table 1) were added to 100 parts by mass of copper powder having an average particle size of 2.8 μm, and mixed with a three-roll mill to prepare a copper paste. . The vehicle used was prepared by dissolving 30 parts by mass of polyisobutyl methacrylate in 70 parts by mass of terpineol.

　（表１）に示すように、本発明の実施例として実施例Ａ、Ｂの組成を有する銅ペーストを作製するとともに、本発明の効果と比較するために比較例Ａ〜Ｃの組成を有する銅ペーストを作製した。

As shown in (Table 1), copper pastes having compositions of Examples A and B were prepared as examples of the present invention, and copper pastes having compositions of Comparative Examples A to C were used for comparison with the effects of the present invention. A paste was made.

Example A is a copper paste obtained by adding 1.0 part by mass of Fe ₂ O ₃ having an average particle size of 21 nm and 1.0 part by mass of SiO ₂ having an average particle size of 12 nm to 100 parts by mass of copper powder. It is.
In Example B, based on 100 parts by mass of copper powder, 1.0 part by mass of Fe ₂ O ₃ having an average particle size of 21 nm, 1.0 part by mass of SiO ₂ having an average particle size of 12 nm, and an average particle size of 21 nm Is a copper paste to which 0.5 parts by mass of TiO ₂ is added.

Comparative Example A is a copper paste obtained by adding 1.0 part by mass of SiO ₂ having an average particle diameter of 12 nm and 0.5 parts by mass of TiO ₂ having an average particle diameter of 21 nm to 100 parts by mass of copper powder. .
In Comparative Example B, based on 100 parts by mass of copper powder, 1.0 part by mass of CuO having an average particle size of 20 nm, 1.0 part by mass of SiO ₂ having an average particle size of 12 nm, and TiO ₂ having an average particle size of 21 nm were used. Is added to the copper paste.

"Preparation of fired sample"
Next, the copper pastes of Examples A and B and Comparative Examples A, B and C shown in (Table 1) are printed on the ceramic green sheets to prepare respective fired samples.

First, a ceramic green sheet is cut into a size of 50 mm long × 60 mm wide to prepare a ceramic green sheet piece, and a copper paste having a size of 2 mm long × 2 mm wide × 20 μm thick is placed at a substantially central portion of the ceramic green sheet piece. A printed test piece A and a test piece B in which a copper paste was printed in a size of 15 mm long × 15 mm wide × 20 μm thick at substantially the center of the ceramic green sheet piece were prepared.

Next, one test piece A and three green sheets on which no copper paste was printed, a total of four sheets, were laminated and pressed to produce a laminate A in which the printed surface of the test piece A appeared on the upper surface. Then, one test piece B and three green sheets, on which no copper paste was printed, were laminated and pressurized to produce a laminate B in which the printed surface of the test piece B appeared on the upper surface. .

Next, the laminates A and B are exposed to a furnace in which a mixed atmosphere of steam and nitrogen gas (a mixed atmosphere in which the dew point of steam and nitrogen gas is 70 ° C.) is adjusted and left at a temperature of 850 ° C. , The organic components contained in the copper paste and the ceramic green sheet are degreased, then the temperature is raised to 1000 ° C., and the mixture is left for 2 hours and fired to produce fired samples A and B having a conductor layer on the upper surface. did.

The fired sample A was obtained by firing the laminate A, and was used for evaluation of the adhesion strength in the later operation. The fired sample B was obtained by firing the laminate B, and was used for the evaluation of blistering of the conductor layer described later.

"Evaluation of adhesion strength"
Next, a tin-plated wire having a diameter of 0.45 mm was soldered to the upper surface of the conductor layer of the fired sample A, the wire was pulled, and a vertical tensile load was applied to the upper surface of the fired sample A. The load from which was peeled off was taken as the adhesion strength and shown in Table 1.

"Evaluation of blistering of conductor layer"
Next, 4 μm thick Ni plating was performed on the upper surface of the conductor layer of the fired sample B by electrolytic plating, and further, 0.5 μm thick Au plating was performed on the upper surface of the Ni plating by electrolytic plating.

Next, the baked sample plated with Au was placed in a furnace heated to 390 ° C. for several minutes, and thereafter, the presence or absence of blisters on the conductor layer was visually checked, and the results are shown in (Table 1).
As shown in Table 1, in Examples A and B of the present invention, even when heated to 390 ° C., a good appearance was obtained without blistering of the conductor layer. On the other hand, in Comparative Examples A, B, and C, blistering of the conductor layer occurred by heating to 390 ° C.

Comparison of Comparative Example A with Example B of the present invention shows that Comparative Example B did not contain Fe ₂ O ₃ as an additive, and as a result, blisters were generated by heating.
Also, comparing Comparative Example B with Example B of the present invention, Comparative Example B added CuO as an oxide instead of Fe ₂ O ₃ , and as a result, the adhesion strength was higher than that of Example B of the present invention. Although almost the same, it can be seen that blisters were generated by heating.

Also, comparing Comparative Example C with Example B of the present invention, Comparative Example B added NiO instead of Fe ₂ O ₃ as an additive, and as a result, blisters were generated by heating, and the adhesion strength was also increased. It turns out that it is low.

Further, comparing Examples A and B of the present invention, it is found that the adhesion strength is further improved by further adding TiO ₂ as an additive.
"Production of wiring board"
Using the ceramic green sheet manufactured as described above and the copper paste having the composition shown in Example B, a wiring board was manufactured. FIG. 1 is a cross-sectional view illustrating a configuration of a wiring board according to one embodiment to which the present invention is applied.

In FIG. 1, reference numeral 1 denotes a wiring board. The wiring board 1 is bonded to a ceramic substrate 2 formed by laminating and firing a plurality of ceramic green sheets and a lower surface of the ceramic substrate 2 via a brazing material 12. The heat radiator 3, the semiconductor element 4 inserted in the hole of the ceramic substrate 2 and placed on the upper surface of the heat radiator 3, the hole of the ceramic substrate 2 is covered so as to cover the semiconductor 4, and the brazing material is formed on the conductor layer 10. A cover 7 is connected to the conductor layer 10 on the upper surface of the ceramic substrate 2 via a brazing material 14.

The ceramic substrate 2 was prepared by printing the copper paste of Example B on a ceramic green sheet, drying the green paste, and laminating a plurality of the pastes to form a laminate, in a 850 ° C. wet nitrogen atmosphere (dew point of water vapor and nitrogen gas was 70%). (A mixed atmosphere of 100 ° C.), followed by replacement with dry nitrogen and firing at 1000 ° C. for 2 hours. Further, every time the ceramic green sheets are stacked, the connection is made by the conductor layer 11 to connect the wiring circuits of the plurality of ceramic green sheets to each other.

The conductor layer 10 has a portion exposed on the surface of the ceramic substrate 2 plated with Ni having a thickness of 4 μm by an electroless plating method, and further, has an Au surface having a thickness of 0.5 μm deposited on the upper surface of the Ni plating by an electroless plating method. Plating has been performed.

The heat radiator 3 is formed of an alloy of copper and tungsten plated with Ni-Au, and is joined to the conductor layer plated with Ni-Au on the back surface of the ceramic substrate 2 by brazing. I have. At this time, the brazing is performed by using a brazing material 12 made of an alloy of gold and germanium and heating at approximately 390 ° C.

The semiconductor element 4 has a lower surface adhered to the upper surface of the heat radiator 3, and a terminal (not shown) formed on the upper surface of the semiconductor element 4 is a conductor in which the ceramic substrate 2 is subjected to Ni-Au plating by wire bonding 8, 9. It is connected to the layer 10.

The lid 7 is formed of an alloy of Ni, Co, and Fe and plated with Ni-Au, and is brazed to the Ni-Au-plated conductor layer 10 on the upper surface of the ceramic substrate 2 by brazing. Are joined. At this time, the brazing is performed by using a brazing material 13 made of an alloy of gold and germanium and heating at approximately 390 ° C.

The connection terminal 6 is formed of an alloy of copper and Fe plated with Ni-Au, and joined to the conductor layer 10 plated with Ni-Au on the upper surface of the ceramic substrate 2 by brazing. I have. At this time, the brazing is performed by using a brazing material 14 made of an alloy of gold and germanium and heating at approximately 390 ° C.

The operation and effect of the copper paste and the wiring board using the same in the embodiment of the present invention having the above configuration will be described below.
According to the copper paste of the embodiment of the present invention, the adhesive strength between the ceramic substrate 2 and the conductor layer 10 in the wiring board 1 is excellent, and the wiring board 1 has the semiconductor element 4 such as a power transistor and a diode and the radiator 3. Even if the connection terminals 6 and the like are connected by heating by brazing, a wiring board having excellent reliability can be obtained without swelling or peeling of the conductor layer 10.

Further, according to the copper paste of the embodiment of the present invention, a wiring board with further improved copper sinterability, good plating and soldering properties, and less warpage and undulation can be obtained.
Further, according to the wiring board 1 of the embodiment of the present invention, the plating property and the solderability of the conductor layer 10 are good, and the plating board does not bulge or peel even when the wiring board 1 is heated, so that the wiring board 1 has a high performance. A wiring board excellent in density mounting can be obtained.

According to the wiring board 1 of the embodiment of the present invention, even if the brazing materials 12 to 14 are melted and the radiator 3, the lid 7, the connection terminals 6, and the like are connected, peeling or swelling of the conductor layer 10 occurs. Therefore, high reliability can be obtained particularly in a wiring board on which a radiator, connection terminals between circuit components, a semiconductor element which generates heat, and the like are mounted.

In the embodiment of the present invention, Ni and Au are plated on the upper surface of the conductor layer 10, and the radiator 3, the connection terminal 6, the lid 7, and the like are provided on the Au plated surface via the brazing materials 12 to 14. Although connected, another metal having a low resistance may be plated instead of Ni and Au plating. Further, the present invention is not limited to performing the Au plating process, and the plating process may be omitted when the brazing can be surely performed without the plating process.

In the embodiment of the present invention, an alloy of gold and germanium is used as the brazing material, but solder or a copper alloy may be used.
When a wiring board is manufactured using the copper paste of the embodiment of the present invention, the ceramic green sheet coated with the copper paste is placed in wet nitrogen at 650 to 900 ° C. (dew point of water vapor and nitrogen gas is 70 ° C.). It is preferable to remove the organic component (debinding step) in a mixed atmosphere of (1) and then fire at 850 to 1050 ° C. Here, the debinding step is set within a range that does not exceed the subsequent firing temperature.

First, the organic components contained in the ceramic green sheet and the copper paste are removed in a wet nitrogen atmosphere at 650 to 900 ° C. (a binder removing step). Here, the binder removal step is set within a range not exceeding the subsequent firing temperature. Since the binder is removed in a state where the ceramic particles are dispersed around the copper powder in the copper paste, the start of sintering of the copper powder is suppressed during the binder removal, but in the subsequent firing process at a high temperature, Since the sintering of the copper powder is promoted by being exposed to the wet nitrogen at the time of debinding, a dense conductor layer can be obtained.

(4) In the firing step performed after the binder removal step, copper and the ceramic green sheet are simultaneously fired in nitrogen at 850 to 1050 ° C. or in wet nitrogen. Since the sintering start temperature and the firing shrinkage timing are controlled so as to be close to each other, it is possible to obtain a wiring board with less warpage and undulation, a dense and low resistance, and a low transmission loss of a high-frequency signal. .

FIG. 3 is a cross-sectional view illustrating a configuration of a wiring board according to an example to which the present invention is applied.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 ... Wiring board, 2 ... Board, 3 ... Heat radiator, 4 ... Semiconductor element, 5 ... Lid, 6 ... Connection terminal, 7 ... Lid, 8, 9 ... Wire bonding, 10, 11 ... Conductive layer, 12, 13, 14 ... brazing material.

Claims (6)

A copper paste containing copper powder, an organic vehicle, and Fe ₂ O ₃ particles. The copper paste according to claim 1, wherein the copper paste contains ceramic particles having an average particle diameter of 100 nm or less. (4) A wiring board, wherein the copper paste according to (1) or (2) is applied as a conductor layer to a ceramic green sheet and fired. The wiring board according to claim 3, wherein the wiring board has at least one of a heat radiator, a connection terminal, a lid, and a circuit component connected to a conductor layer via a bonding material. A conductor layer is formed on a wiring board using Cu metal containing Fe, and at least one of a heat radiator, a connection terminal, a lid, and a circuit component is connected to the conductor layer via a bonding material. Wiring board. 6. The wiring board according to claim 5, wherein the wiring board has been subjected to a plating process on a surface of the conductor layer.

Images