JP7208619B2 - Electronic component manufacturing method - Google Patents

Description

The present invention relates to a method of manufacturing an electronic component.

Oxide substrates (glass, crystal, aluminum oxide, gallium oxide, barium titanate, lead zirconate titanate, ferrite oxide, etc.), nitride substrates (aluminum nitride , silicon nitride, gallium nitride, etc.), and ceramic substrates such as carbide substrates (silicon carbide, etc.). Such ceramic substrates are used in electronic components for a wide range of applications, such as wireless communication devices and power conversion devices.

A via electrode, which is one of the electronic components, has a structure in which a metal electrode is embedded in a through hole of a ceramic substrate. Through this metal electrode, a conductive path of a chip provided by sandwiching the ceramic substrate is secured. It is something to do.

On the other hand, in recent years, instead of silver electrodes and nickel electrodes, which are conventionally used as metal electrodes, less expensive copper electrodes have attracted attention.

However, copper has poor adhesion to ceramics. In addition, in order to manufacture a via electrode, generally, a conductive paste is buried inside the through hole and then sintered in a nitrogen atmosphere. Shrinks with sintering. Therefore, when copper paste is used to form the via electrodes, the electrodes tend to come off from the through holes. Therefore, various studies have been made to suppress such desorption.

For example, Patent Literature 1 discloses a method for manufacturing a via electrode, in which aluminum powder, which shrinks little during sintering, is added to a through hole provided in an alumina substrate together with copper powder, and sintered in a nitrogen gas atmosphere. It is It is disclosed that the via electrode thus obtained can reduce the shrinkage of the metal sintered body as compared with the case where only copper powder is used as the conductive metal.

JP 2016-139488 A

However, the method of Patent Document 1 merely suppresses the shrinkage of the sintered body, that is, shrinkage occurs at a certain rate, which inevitably leads to a decrease in adhesion strength. Therefore, there is still room for improvement in order to increase the adhesion between the copper electrode and the ceramic substrate in the through hole of the via electrode.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of manufacturing an electronic component in which a copper electrode embedded in a through-hole provided in an inorganic substrate and a ceramic substrate have strong adhesion. and

The present inventors have found a embedding step of embedding a paste containing copper particles and inorganic oxide particles having a softening point in a through hole provided in an inorganic substrate, an oxygen-containing gas atmosphere, and A sintering step of heating at a temperature equal to or higher than the sintering temperature of the copper particles to form a sintered body containing at least copper, and a softening step of heating at a temperature equal to or higher than the softening point of the inorganic oxide particles in an inert gas atmosphere. and a reduction step of heating at a temperature below the softening point of the inorganic oxide particles in a reducing gas atmosphere. The inventors have found that the copper electrode embedded in the ceramic substrate and the ceramic substrate have strong adhesion and that the resistance of the metal electrode is low, thereby completing the present invention. Specifically, the present invention provides the following.

(1) a embedding step of embedding a paste containing copper particles and inorganic oxide particles having a softening point in a through hole provided in an inorganic substrate; A sintering step of heating at a temperature equal to or higher than the sintering temperature of the particles to form a sintered body, a softening step of heating at a temperature equal to or higher than the softening point of the inorganic oxide particles in an inert gas atmosphere, and a reducing gas. and a reduction step of heating in an atmosphere at a temperature lower than the softening point of the inorganic oxide particles.

(2) The method for manufacturing an electronic component according to (1), wherein the heating temperature in the sintering step is 250°C or higher and lower than 750°C.

(3) The method for manufacturing an electronic component according to (1) or (2), wherein the oxygen concentration in the oxygen-containing gas atmosphere in the sintering step is 1000 ppm or more.

(4) The method for producing an electronic component according to any one of (1) to (3), wherein in the softening step, the component derived from the inorganic oxide particles and the inorganic substrate are integrated.

According to the present invention, it is possible to obtain an electronic component having strong adhesion between the copper electrodes embedded in the through-holes of the inorganic substrate and the ceramic substrate.

Specific embodiments of the present invention will be described in detail below. The present invention is by no means limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the object of the present invention.

<Method for manufacturing electronic components>
The method for manufacturing an electronic component according to the present embodiment includes a embedding step of embedding a paste containing copper particles and inorganic oxide particles having a softening point in a through hole provided in an inorganic substrate, and an inorganic oxide under an oxygen-containing gas atmosphere. A sintering step of forming a sintered body by heating at a temperature lower than the softening point of the particles and higher than the sintering temperature of the copper particles, and a softening of heating at a temperature higher than the softening point of the inorganic oxide particles in an inert gas atmosphere. and a reduction step of heating at a temperature below the softening point of the inorganic oxide particles in a reducing gas atmosphere.

In this specification, the term "copper electrode" refers to an electrode containing copper as a main component (60% by mass or more), and when it functions as an electrode, it does not exclude the inclusion of other metals and the like. Absent.

A "through hole" means a hole penetrating both surfaces of an inorganic substrate, and is also called a "via hole". Furthermore, the "softening point" can be obtained by using DTA to determine its presence or absence and temperature.

An electronic component obtained by such a method has a porous copper sintered body inside a through hole provided in an inorganic substrate. The pores of this copper sintered body are filled with an inorganic oxide. In a preferred embodiment, the inorganic oxide filling the pores of the copper sintered body is integrated with the inner walls of the through holes of the inorganic substrate.

A paste containing copper particles and inorganic oxide particles having a softening point is embedded in the through-holes of the inorganic substrate. The copper particles contained in the paste are sintered in an oxidizing atmosphere in the sintering process to form a porous structure of copper oxide (which may partially contain metallic copper), which causes volume expansion, and the inorganic substrate be physically attached to. Next, in the softening step, when the inorganic oxide particles are heated to a softening point or higher, the inorganic oxide particles are softened, pass through the pores of the porous structure formed in the sintering step, come into contact with the inorganic substrate, and undergo inorganic oxidation. An integrated structure is formed between the component derived from the material particles (inorganic oxide particles are softened and filled in the pores of the porous copper sintered body) and the inorganic substrate. be. Then, in the reduction step, the copper oxide is reduced to metallic copper to ensure sufficient electrical conductivity as an electrode.

Thus, in the sintering process, copper oxide is once formed and expanded in volume. Thereby, the volume of the copper electrode can be positively increased, and the adhesion between the copper electrode and the substrate can be enhanced. The reduction step involves volumetric shrinkage due to the desorption reaction of oxygen, which is smaller than the volumetric expansion in the sintering step. Moreover, since the porous structure has already been formed as a sintered body, the shrinkage is not large in the first place.

Moreover, in addition to the improvement in adhesion due to the volume expansion of the sintered body, the component derived from the inorganic oxide particles forms a structure in which the inorganic substrate is integrated. Since the component derived from the inorganic oxide particles is filled in the pores of the porous structure of the copper electrode having a complicated shape, it is also in close contact with the copper electrode. The adhesiveness between the copper electrode and the inorganic substrate can also be enhanced by the component derived from.

[Embedding process]
The embedding step is a step of embedding a paste containing copper particles and inorganic oxide particles having a softening point in a through hole provided in the inorganic substrate.

[Inorganic substrate]
The inorganic substrate has at least through holes. The inorganic substrate is, for example, a semiconductor substrate and may have an oxide on its surface. In the softening step described later, the inorganic oxide particles are softened and the components derived from the inorganic substrate and the inorganic oxide particles react with each other. The component derived from the inorganic oxide particles is contained in the pores of the porous body (electrode) formed by sintering the copper particles and the copper oxide particles and/or nickel oxide particles. By reacting with the inorganic substrate, the adhesion between the electrode, which is a porous body, and the inorganic substrate can be enhanced.

[paste]
The paste contains copper particles and inorganic oxide particles having a softening point. The copper particles are sintered in an oxygen-containing gas atmosphere to form a copper oxide porous body that expands in volume. .

An example of such a paste includes copper particles, inorganic oxide particles having a softening point, a binder resin, and a solvent. In addition, hereinafter, an organic component mainly composed of a binder resin, a solvent, and the like is referred to as an "organic vehicle".

(copper particles)
Although the copper particles are not particularly limited, they are particles produced by a method such as a gas atomization method, a water atomization method, or a liquid phase reduction precipitation method, and preferably have a 50% particle size of 70 nm or more and 10 μm or less. .

Although the particle size of the copper particles is not particularly limited, it is preferably 0.3 μm or more, and more preferably 0.5 μm or more. When the average particle size of the copper particles is 0.3 μm or more, gaps can be formed between the sintered copper particles. If it is less than 0.3 μm, the gaps between the densely sintered copper particles in the sintering process become small, and the inorganic oxide does not reach the interface in the subsequent softening process, resulting in poor adhesion. When the thickness is 0.5 μm or more, the adhesion strength is further increased. The average particle shape of the copper particles is a value measured by a laser diffraction particle size distribution analyzer such as Microtrac.

(Inorganic oxide particles)
Inorganic oxide particles have a softening point. In this way, since the inorganic oxide has a softening point, it can be softened in the softening step to be described later, and the inside of the porous sintered body can be moved to the vicinity of the inorganic substrate via the pores.

The inorganic oxide particles contain three or more metal elements selected from the group consisting of B, Al, Si, Zn, Ba, Bi, Ca, Mg, Sr, Hf, K, Zr, Ti and Na. is preferred. A softening point tends to occur due to the inclusion of oxides of a plurality of metal elements in this way.

The softening point of the inorganic oxide particles is not particularly limited, but for example, it is preferably 550° C. or higher, more preferably 570° C. or higher, further preferably 590° C. or higher, and 600° C. or higher. is particularly preferred. When the temperature is 550° C. or higher, a difference from the sintering temperature of the copper particles can be provided, and softening can be suppressed in the sintering process. On the other hand, the softening point is preferably 750° C. or lower, more preferably 740° C. or lower, even more preferably 720° C. or lower, and even more preferably 700° C. or lower. When the temperature is 750° C. or less, it is possible to prevent the components derived from the inorganic oxide particles from reacting with the inorganic substrate to release gas and form bubble-like voids at the interface, thereby preventing the copper particles from forming. It is possible to further increase the adhesion strength between the copper porous body produced by sintering and the inorganic substrate.

The content of the inorganic oxide particles in the paste is not particularly limited, but is preferably 0.4% by mass or more, more preferably 1.0% by mass or more, relative to the mass of the copper particles. . When the content of the inorganic oxide particles is 0.4% by mass or more, the amount of inorganic oxide that migrates to the interface with the inorganic substrate in the softening process can be increased, and the adhesion strength with the inorganic substrate can be ensured. Further, by setting the content of the inorganic oxide particles to 1.0% by mass or more, the adhesion strength can be further increased. On the other hand, the content of the inorganic oxide particles is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 4.8% by mass or less, and 4% by mass. The following are particularly preferred. When the content of inorganic oxide particles is 20% by mass or less, adhesion strength can be ensured. In addition, especially when the content of the inorganic oxide particles is 4.8% by mass or less, the electrical resistance can be reduced while maintaining the adhesion strength.

The average particle size of the inorganic oxide particles is not particularly limited, but for example, the 50% particle size (D ₅₀ ) in the laser diffraction particle size distribution is preferably 0.5 μm or more, more preferably 0.7 μm or more. It is more preferably 1 μm or more, and particularly preferably 1.5 μm or more. When the average particle size of the inorganic oxide particles is 0.5 μm or more, it is possible to prevent aggregation of the particles, improve the printability of the paste, and prevent the formation of spherical voids inside the sintered body. This can be prevented and the mechanical strength of the electronic component can be enhanced. On the other hand, the average particle size of the inorganic oxide particles is preferably 10 μm or less, more preferably 8 μm or less, even more preferably 7 μm or less, and particularly preferably 5 μm or less. When the average particle size of the inorganic oxide particles is 7 μm or less, it is possible to uniformly and sufficiently apply heat to the glass, and to suppress the inorganic oxide particles that are not softened in the softening step described below. As a result, the adhesion strength between the porous body produced by sintering copper and the inorganic substrate can be increased.

(binder resin)
The content % of the binder resin in the organic vehicle is preferably 0.05% by mass or more and 17% by mass or less. The binder resin is not particularly limited as long as it is decomposed by heating. Examples thereof include cellulose resins such as methyl cellulose, ethyl cellulose and carboxymethyl cellulose, acrylic resins, butyral resins, alkyd resins, epoxy resins and phenol resins. Among them, it is preferable to use a cellulose-based resin that tends to easily disappear from the paste by reacting with oxygen or carbon monoxide. Among the cellulose-based resins, it is more preferable to use ethyl cellulose.

In the sintering process described later, by heating in an oxygen-containing gas atmosphere, the binder resin reacts with oxygen, the amount of resin remaining in the wiring after sintering is reduced as much as possible, and the wiring resistance is increased due to the residual resin. is suppressed. However, the binder resin component still remains in the wiring, and there is a risk that the sinterability will deteriorate and the wiring resistance will increase. Also, the influence of the binder resin component remaining in the wiring after sintering on the wiring resistance can be neglected. On the other hand, if the content of the binder resin in the organic vehicle is less than 0.05% by mass, the viscosity of the paste will be low, possibly deteriorating the printability.

(solvent)
The solvent contained in the conductive paste is not particularly limited as long as it has an appropriate boiling point, vapor pressure and viscosity. For example, hydrocarbon solvents, chlorinated hydrocarbon solvents, cyclic ether solvents Solvents, amide solvents, sulfoxide solvents, ketone solvents, alcohol compounds, polyhydric alcohol ester solvents, polyhydric alcohol ether solvents, terpene solvents and mixtures thereof. Among these, it is preferable to use texanol, butyl carbitol, butyl carbitol acetate, and terpineol, which have boiling points in the vicinity of 200°C.

(ingredients in other organic vehicles)
An organic vehicle is a liquid in which a binder resin, a solvent, and other organic substances added as necessary are all mixed. When sintering in the atmosphere described in the present invention, it is sufficient to use an organic vehicle prepared by mixing a binder resin and a solvent, but if necessary, a metal salt and a polyol may be mixed and used. can. Examples of metal salts include copper (II) acetate, copper (II) benzoate, copper (II) bis(acetylacetonate), and the like when Cu is used as the first metal element. Examples of polyols include ethylene glycol, diethylene glycol, trimethylene glycol, propylene glycol and tetraethylene glycol. By adding these, the polyol reduces the metal salt during sintering, and the reduced metal is deposited in the gaps between the particles, so that the electrical conductivity between the particles is enhanced.

Although the content of the organic vehicle contained in the paste is not particularly limited, it is preferably 3% by mass or more and 19% by mass or less, more preferably 8% by mass or more and 15% by mass or less.

By setting the content of the organic vehicle contained in the paste to 3% by mass or more and 19% by mass or less, it is possible to maintain a good wiring shape. If the content of the organic vehicle is more than 19% by mass, the viscosity of the paste becomes low, and there is a risk that the printed wiring shape will sag. On the other hand, if the content of the organic vehicle is less than 3% by mass, the viscosity of the paste becomes too high, which may make it impossible to form electrodes of uniform shape.

[Paste manufacturing method]
The paste can be prepared by mixing the above binder resin and solvent, adding copper particles, and kneading the mixture using a device such as a planetary mixer. Also, a three-roll mill can be used to enhance the dispersibility of the particles, if desired.

Moreover, the method of applying the paste is not particularly limited, and for example, an inkjet method, a dispensing method, a screen printing method, or the like can be used.

Moreover, it is preferable to dry the inorganic substrate after applying the paste at room temperature or at a high temperature to remove a predetermined amount of the solvent.

[Sintering process]
In the sintering step, the embedded substrate obtained in the above-described embedding step is heated in an oxygen gas-containing atmosphere at a temperature lower than the softening point of the inorganic oxide particles and higher than or equal to the sintering temperature of the copper particles to form a sintered body. It is a process to do.

Although the oxygen concentration in the oxygen-containing atmosphere is not particularly limited, it is preferably 1000 ppm or more, more preferably 2000 ppm or more, and even more preferably 5000 ppm or more. The gas atmosphere may be, for example, air (oxygen concentration of about 20%=about 20,000 ppm) or pure oxygen atmosphere (oxygen concentration of 100%). When the oxygen concentration is within the above range, the copper particles are oxidized and volumetrically expanded, so that a dense sintered body can be formed and can be strongly adhered to the sidewall of the via. Gases contained in the atmosphere other than oxygen include inert gases such as nitrogen, helium, and argon.

The heating temperature in the sintering step is not particularly limited as long as it is lower than the softening point of the inorganic oxide particles. For example, it is preferably 250°C or higher, more preferably 350°C or higher, and 400°C or higher. is more preferred. When the heating temperature is within the above range, the copper particles are oxidized to cause volume expansion, so that a dense sintered body can be formed and can be strongly adhered to the sidewall of the via. On the other hand, the heating temperature is preferably less than 750°C, more preferably 700°C or less, even more preferably 650°C or less, and particularly preferably 620°C or less.

In addition, the heating temperature in the sintering step is not particularly limited, but it is preferably 30 ° C. or more lower than the softening point of the inorganic oxide particles, more preferably 50 ° C. or more lower, and 70 ° C. or more lower than the softening point. A temperature lower than 100° C. is particularly preferred. When the heating temperature is 30° C. or more lower than the softening point of the inorganic oxide particles, softening of the inorganic oxide particles in the sintering step can be more reliably prevented.

The heating time in the copper particle sintering step is not particularly limited, but is preferably 5 minutes or longer, more preferably 15 minutes or longer. By setting the heating time within the above range, the copper particles can be sufficiently sintered without clogging the flow path of the softened glass.

[Softening process]
The softening step is a step of heating at a temperature equal to or higher than the softening point of the inorganic oxide particles in an inert atmosphere.

The inert atmosphere may be any atmosphere that does not substantially contain an oxidizing gas or a reducing gas. For example, a nitrogen atmosphere, a helium atmosphere, an argon atmosphere, or the like can be used. Among them, a nitrogen atmosphere is preferable from the viewpoint of cost. Even though it is an inert atmosphere, there is a limit to the equipment used to perform the operation to exclude oxidizing gases and reducing gases. It is not excluded until

The heating temperature in the softening step is not particularly limited as long as it is a temperature equal to or higher than the softening point of the inorganic oxide particles. It is even more preferable to have When the heating temperature is within the above range, the inorganic substrate and the component derived from the inorganic oxide particles can be integrated, and the adhesion between the inorganic substrate and the copper sintered body can be further enhanced. The heating temperature is preferably 900° C. or lower, more preferably 870° C. or lower, and even more preferably 850° C. or lower. When the heating temperature is within the above range, it is possible to suppress the deterioration of the adhesion between the inorganic substrate and the copper sintered body due to the generation of bubbles due to evaporation of the metal component.

The heating temperature in the softening step is preferably 30° C. or higher, more preferably 50° C. or higher, and even more preferably 70° C. or higher than the softening point of the inorganic oxide particles. When the heating temperature is 30° C. or more higher than the softening point of the inorganic oxide particles, the inorganic oxide particles can be easily softened.

The heating time in the softening step is not particularly limited, but is preferably 5 minutes or longer, more preferably 15 minutes or longer. Also, the heating time is preferably 60 minutes or less, more preferably 45 minutes or less. By setting the heating time within the above range, the softened inorganic oxide particles can be sufficiently moved to the vicinity of the inorganic substrate.

As for the inorganic oxide particles, inorganic oxide particles having one composition can be used alone, or inorganic oxide particles having a plurality of compositions can be used in combination. In the case of using multiple types of inorganic oxides, "at least the softening point of the inorganic oxide particles" is based on the one having the lowest softening point among the multiple types of inorganic oxides.

[Reduction step]
The reduction step is a step of heating at a temperature below the softening point of the inorganic oxide particles in a reducing gas atmosphere.

In this reduction step, the copper oxide produced in the copper particle sintering step described above is reduced to metallic copper, thereby imparting sufficient electrical conductivity as a copper electrode.

The reducing gas in the reducing atmosphere is not particularly limited, and hydrogen, formic acid vapor, alcohol vapor, CO gas, etc. can be used, for example. Gases contained in the atmosphere other than the reducing gas include inert gases such as nitrogen, helium, and argon.

The concentration of the reducing gas is not particularly limited. For example, when hydrogen gas is used as the reducing gas, the hydrogen gas concentration is preferably 0.5% by volume or more, and more preferably 1% by volume or more. On the other hand, the hydrogen gas concentration is preferably 10% by volume or less, more preferably 5% by volume or less. Reduction efficiency can be improved by setting the hydrogen gas concentration to 0.5% by volume or more.

The heating temperature in the reduction step is not particularly limited as long as it is lower than the softening point of the inorganic oxide particles. For example, it is preferably 250°C or higher, more preferably 350°C or higher, and 400°C or higher is more preferred. By setting the heating temperature within the above range, the copper oxide contained in the copper sintered body can be efficiently reduced. On the other hand, the heating temperature is preferably less than 750°C, more preferably 700°C or less, even more preferably 650°C or less, and particularly preferably 620°C or less. By setting the heating temperature within the above range, it is possible to further prevent reduction of the components derived from the inorganic substrate and the inorganic oxide particles.

Further, the heating temperature in the reduction step is not particularly limited, but for example, it is preferably 30° C. or more lower than the softening point of the inorganic oxide particles, more preferably 50° C. or more lower, and further preferably 70° C. or more lower. A temperature lower than 100° C. is particularly preferred. When the heating temperature is 30° C. or more lower than the softening point of the inorganic oxide particles, it is possible to prevent detachment from the inorganic substrate caused by softening and reduction of the components derived from the inorganic oxide particles.

The heating time in the reduction step is not particularly limited, but is preferably 5 minutes or longer, more preferably 15 minutes or longer.

The electronic component (via electrode) obtained by the manufacturing method described above can be used, for example, as a large-current board for power modules, an insulating heat-dissipating board for LEDs, and the like.

The present invention will be described in more detail with reference to examples below. The invention is not limited by these examples.

66.6% by mass of approximately spherical copper particles with a _D50 of 4.0 μm, 33.3% by mass of approximately spherical copper particles with a _D50 of 1.0 μm (a total of 100% by mass as copper particles), and softening with a _D50 of 3 μm A predetermined amount of inorganic oxide particles having dots was kneaded with a vehicle to prepare a copper paste.

On the other hand, a through hole (via) with a diameter of 300 μm was formed in an alumina substrate using a laser beam. The substrate was placed on a pedestal with a vacuum chuck, and copper paste was applied to the surface of the substrate. At this time, the vacuum chuck moved the copper paste on the via into the via, filling the entire via with the copper paste.

The alumina substrate coated with the copper paste was fired in an air atmosphere for 60 minutes. After that, softening firing was performed at 750° C. for 15 minutes in a nitrogen atmosphere, and reduction treatment was performed at 550° C. for 30 minutes in an Ar+5%H ₂ atmosphere. A tungsten needle with a diameter of 150 μm was attached to the obtained sample on a universal mechanical testing machine, and the needle was pushed through the upper surface of the copper electrode formed in the via to obtain the indentation load value that changes as the indentation displacement increases. rice field. When the load value exceeds the adhesion strength between the via electrode and the side wall of the alumina substrate via, the load decreases abruptly. Also, the central portion of the via electrode was cut and polished to expose the cross section of the via electrode, and four probes were placed on the polished flat surface to measure electrical resistivity. Table 1 shows the elements contained in the inorganic oxide particles (excluding oxygen), the amount of inorganic oxide particles added (% by mass), the softening point of the inorganic oxide particles (° C.), and the heating in the sintering process. The temperature (° C.), heating temperature (° C.) in the softening step, heating temperature (° C.) in the reduction step, extrusion strength (N) and electrical resistivity (μΩ·cm) of the obtained electrode are shown in Table 1 below.

Claims (4)

An embedding step of embedding a paste containing copper particles and inorganic oxide particles having a softening point in a through hole provided in an inorganic substrate;
a sintering step of forming a sintered body by heating in an oxygen-containing gas atmosphere at a temperature lower than the softening point of the inorganic oxide particles and higher than or equal to the sintering temperature of the copper particles;
A softening step of heating at a temperature equal to or higher than the softening point of the inorganic oxide particles in an inert gas atmosphere;
a reduction step of heating at a temperature below the softening point of the inorganic oxide particles in a reducing gas atmosphere;
A method of manufacturing an electronic component. The heating temperature in the sintering step is 250° C. or more and less than 750° C.
A method for manufacturing an electronic component according to claim 1 . The oxygen concentration in the oxygen-containing gas atmosphere in the sintering step is 1000 ppm or more,
3. The method of manufacturing an electronic component according to claim 1 or 2. In the softening step, the component derived from the inorganic oxide particles and the inorganic substrate are integrated,
A method for manufacturing an electronic component according to any one of claims 1 to 3.