JP2015086090A - Conductor paste and heat-dissipating substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductor paste excellent in adhesion with a substrate having a small thermal expansion coefficient.SOLUTION: The conductor paste (copper paste) contains a copper powder, a glass frit, a resin as a binder, and a solvent. Then, the glass frit fulfils the conditions (1)-(3):(1) having a glass softening point of 300°C or higher and 400°C or lower;(2) having a thermal expansion coefficient of 6 ppm/°C or more and 7.5 ppm/°C or less; and (3) containing Sn and P as indispensable constituting elements. In one preferred aspect, in the glass frit, molar contents of components thereof are, when the whole of the components in terms of the following oxides are assumed to be 100 mol%, SnO: 40-50 mol%, PO: 10-20 mol%, SiO: 15-25 mol%, AlO: 5-15 mol%, and at least one of MgO, CaO, and SrO: 10-15 mol%, and the total content of these components in the glass frit is 95 mol% or more.

Description

  The present invention relates to a heat dissipating substrate used for a ceramic electronic material such as a power semiconductor. Specifically, the present invention relates to a conductor paste for directly forming a heat dissipation layer on a substrate.

  In recent years, next-generation semiconductor devices (typically power devices) used for power control of converters and inverters have been actively researched and developed. In such semiconductor devices, the amount of heat release increases with the progress of high performance such as downsizing, high density, and high speed, and it is an important issue to release the heat.

As an example of the heat dissipation mechanism, a heat dissipation substrate provided with a metal layer (heat dissipation layer) made of a metal having high thermal conductivity on the surface of a ceramic substrate having electrical insulation properties can be given.
Conventionally, an active metal method has been used to manufacture such a heat-dissipating substrate. In the active metal method, a bonding agent (such as a brazing material) is applied to the surface of the ceramic substrate, and a metal plate (for example, a copper foil) is superimposed thereon and fired at a high temperature (for example, 900 ° C. to 1200 ° C.), Metallization (metallization) treatment. However, since the above method requires firing at a high temperature, there is a problem that thermal stress accumulates and the heat dissipation substrate is distorted or warped. Further, in order to form a complicated wiring pattern on the metal layer, a complicated process such as etching after bonding the metal plate to the surface of the substrate has to be performed. Furthermore, it has been difficult to easily produce heat dissipation layers having different thicknesses by the above method.

  Therefore, in recent years, a method of directly applying a conductor paste (for example, copper paste) on a ceramic substrate and firing at a lower temperature (typically 500 ° C. or lower, for example, 400 ° C. to 500 ° C.) has been studied. Patent documents 1 and 2 are mentioned as a technique relevant to this.

Japanese Patent Laid-Open No. 03-093683 JP 2007-201346 A JP 2012-227183 A JP 2007-001817 A Japanese Unexamined Patent Publication No. 07-066972 JP 2001-048579 A

However, in the above technique, when a substrate made of a material having a small thermal expansion coefficient is used, sufficient adhesion at the interface between the substrate and the metal layer (heat dissipation layer) is obtained due to the difference in the thermal expansion coefficient with the metal material. There was a problem that it was difficult to be. For example, the thermal expansion coefficient (25 ° C. to 500 ° C.) of copper (Cu) generally used as the main component of the heat dissipation layer is 16 ppm / ° C., whereas the thermal expansion coefficient of nitride ceramics (25 ° C. to 500 ° C.). ) Is in the range of 2.6 ppm / ° C. (Si ₃ N ₄ ) to 4.6 ppm / ° C. (AlN), 3 times to 5 times or more. Accordingly, there is a demand for a conductive paste that can realize excellent adhesion even to a substrate having a small thermal expansion coefficient such as nitride ceramics.
This invention is made | formed in view of this point, The objective is to provide the conductor paste (typically copper paste) which is excellent in adhesiveness with a board | substrate with a small thermal expansion coefficient. Another object is to provide a heat dissipating substrate provided with a heat dissipating layer formed using such a conductive paste.

  In order to achieve the above object, the present invention provides a conductive paste containing copper powder, glass frit, a resin as a binder, and a solvent. The glass frit has the following conditions: (1) The glass softening point is 300 ° C. or higher and 400 ° C. or lower; (2) The thermal expansion coefficient is 6 ppm / ° C. or higher and 7.5 ppm / ° C. or lower; (3) Both of Sn and P are included as essential constituent elements.

The conductor paste disclosed herein (hereinafter sometimes simply referred to as “copper paste”) is excellent in adhesive strength with a substrate having a small coefficient of thermal expansion because the glass frit satisfying the above properties functions as a binder. . Moreover, since this conductor paste is equipped with the glass frit which satisfy | fills the above-mentioned property, it can be sintered (metallized) at low temperature (typically 500 degrees C or less, for example, 400 degreeC-500 degreeC) compared with the past. For this reason, a thermal stress can be suppressed small and it can prevent that a crack, a distortion, etc. arise in a thermal radiation layer. Therefore, according to the present invention, it is possible to realize a heat dissipating substrate having high adhesion to a substrate having a small coefficient of thermal expansion and in which the substrate and the heat dissipating layer are firmly integrated.
In addition, the cited documents 3-6 are mentioned as a prior art relevant to a glass composition. However, none of the documents describes a conductive paste provided with a glass frit having properties as in the present invention.

In the present specification, the “glass frit” is a term including a crystallized glass having a crystal phase in addition to a normal amorphous glass.
Further, in the present specification, the “glass softening point” means a temperature at which almost any glass frit molding operation is impossible at a temperature lower than this, and the viscosity is approximately 10 ^7.6 dPa · S. Refers to the corresponding temperature. Such a glass softening point can be measured in accordance with JIS R 3103-1 (2001). Specifically, using a glass fiber with a circular cross section having a diameter of 0.65 mm and a length of 235 mm, the upper 100 mm portion is heated in a specified furnace at a temperature increase rate of (5 ± 1) ° C./min. The temperature at which the glass fiber elongates by its own weight at a speed of 1 mm / min is defined as the softening point.
In the present specification, unless otherwise specified, the “thermal expansion coefficient” refers to a temperature below the glass softening point (for example, 300 ° C.) from room temperature (25 ° C.) using a thermomechanical analyzer (TMA). Means the average linear expansion coefficient measured in the temperature range up to, and is a value obtained by dividing the change in the length of the sample by the temperature difference. Such a linear expansion coefficient can be measured according to JIS R 3102 (1995).

In a preferred embodiment of the conductor paste disclosed herein, the glass frit has a molar content of each component when the following oxide conversion components as a whole are 100 mol%,
SnO 40-50 mol%,
P ₂ O ₅ 10~20mol%,
SiO ₂ 15~25mol%,
Al ₂ O ₃ 5~15mol%,
10-15 mol% of at least one of MgO, CaO and SrO,
And the total of these components is 95 mol% or more of the entire glass frit.
By using the conductor paste provided with the glass frit having such a composition, the adhesive strength of the heat dissipation layer formed using the conductor paste can be further improved.

In the suitable one aspect | mode of the conductor paste disclosed here, when the conductor paste whole is 100 mass%, the content rate of the said glass frit is 5 mass% or more and 30 mass% or less.
According to such a configuration, even when the heat dissipation layer is formed relatively thick (for example, about 100 μm to 400 μm) for the purpose of improving heat dissipation, problems such as peeling are unlikely to occur in the heat dissipation layer. Further, by suppressing the content of the glass component as a binder to a relatively low level, a heat dissipation layer having further excellent heat dissipation and electrical conductivity can be realized.

In a preferred embodiment of the conductor paste disclosed herein, the glass frit does not contain an alkali metal element as a glass constituent element.
By not containing an alkali metal component (typically an alkali metal oxide) in the conductor paste, the thermal expansion coefficient can be further reduced. In addition, a heat dissipation layer having excellent thermal stability and physical stability can be realized.

The conductive paste as described above can be suitably used for forming a heat dissipation layer on the surface of an insulating substrate made of, for example, nitride ceramics (particularly silicon nitride).
As described above, nitride ceramics have a relatively small thermal expansion coefficient among ceramics. In particular, silicon nitride (Si ₃ N ₄ ) has a remarkably small thermal expansion coefficient of about 3 ppm / ° C. For this reason, application of the technique disclosed here is particularly effective.

As another aspect of the present invention, there is provided a heat dissipating substrate comprising an insulating substrate made of ceramics and a heat dissipating layer provided on the surface of the insulating substrate. The heat dissipation layer is formed using the conductor paste disclosed herein.
As described above, according to the conductor paste disclosed herein, the substrate and the heat dissipation layer can be firmly integrated. Thereby, for example, even when a heat cycle of room temperature to high temperature is repeated, the heat dissipation layer is hardly peeled off from the ceramic substrate, and a heat dissipation substrate excellent in reliability and durability can be realized.

In a preferred aspect of the heat dissipation substrate disclosed herein, the insulating substrate contains silicon nitride as a main component.
Since silicon nitride has a remarkably small thermal expansion coefficient of about 3 ppm / ° C., the application of the technique disclosed herein is particularly effective. In addition, since silicon nitride is particularly excellent in mechanical strength among ceramics, it is possible to realize a heat dissipation substrate having high durability (for example, toughness and impact resistance in a high temperature environment).

In a preferred embodiment of the heat dissipation substrate disclosed herein, the heat dissipation layer has a thickness of 100 μm or more and 400 μm or less.
According to the above configuration, higher heat dissipation can be realized.

It is sectional drawing which shows typically the heat dissipation board | substrate which concerns on one Embodiment. It is the cross-sectional SEM image which observed the interface of a silicon nitride board | substrate and a glass layer, (A) has shown the image which concerns on Example 1, (B) has each shown the image which concerns on Example 3.

  Hereinafter, preferred embodiments of the technology disclosed herein will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

The conductor paste (copper paste) disclosed here contains copper powder, glass frit (glass powder), a resin as a binder, and a solvent. The glass frit has the following conditions: (1) the glass softening point is 300 ° C. to 400 ° C .; (2) the thermal expansion coefficient is 6 ppm / ° C. to 7.5 ppm / ° C .; (3) Sn Including P as an essential constituent element. Therefore, the other components are not particularly limited, and can be arbitrarily determined according to various uses.
Hereinafter, each component will be described in order.

[Copper powder]
Copper powder is a component for imparting electrical conductivity and heat dissipation to the heat dissipation layer.
In the present specification, “copper powder” refers to an aggregate of particles mainly composed of copper (Cu), and is typically an aggregate of particles composed of simple copper, for example, mainly composed of copper. Even if it contains a trace amount of impurities other than alloys and copper, it can be included in the “copper powder” as long as it is an aggregate of particles mainly composed of copper.
As the particles constituting the copper powder, particles having a size (particle size) suitable for sintering at a low temperature (500 ° C. or less) can be suitably used. Specifically, those having an average particle diameter of 10 μm or less (for example, 0.1 μm to 10 μm) based on the laser diffraction / light scattering method are suitable, and 5 μm or less (typically 1 μm to 5 μm, for example, 1 μm to 2 μm). Can be preferably used. The particles constituting the copper powder are preferably those having a sharp (narrow) particle size distribution. For example, it is preferable that the particle diameter does not substantially contain particles exceeding 10 μm. In a preferred aspect, in a volume-based particle size distribution measured based on a laser diffraction / light scattering method, a particle size having a cumulative frequency of 10% (D ₁₀ ) and a particle size having a cumulative frequency of 90% (D ₉₀ ) A relatively sharp copper powder having a particle size distribution such that the ratio (D ₁₀ / D ₉₀ ) is 0.2 or more (for example, 0.2 to 0.5) is used. Moreover, the shape of the particles constituting the copper powder can be, for example, spherical, scaly, conical, fibrous or the like. Among these, spherical or scaly particles can be preferably used for reasons such as easy filling and a good heat dissipation layer. According to the copper paste using copper powder having such a particle size distribution and / or particle shape, a heat dissipation layer excellent in heat dissipation, electrical conductivity, and mechanical strength can be realized.

  The copper content in the conductor paste is not particularly limited, but is typically 50% by mass or more (for example, 60% by mass or more, preferably 65% by mass or more, more preferably 70% by mass or more) of the entire conductor paste. And 98 mass% or less (typically 90 mass% or less, for example, 85 mass% or less). Thereby, it is possible to suitably realize a heat dissipation layer having excellent adhesion to the substrate and having high heat dissipation and electrical conductivity.

[Glass frit]
The glass frit is, for example, an adhesive (inorganic binder) that improves the adhesive strength between copper components or between a copper component and a substrate.
In the technique disclosed herein, the glass softening point of the glass frit is 300 ° C. or higher (typically 320 ° C. or higher, such as 330 ° C. or higher), and 400 ° C. or lower (typically 390 ° C. or lower, such as 380 ° C.). ° C or lower). As described above, by using a glass frit having a softening point lower than that of the conventional one as a binder, the thermal stress can be suppressed to be small, and defects such as distortion are hardly generated at the interface with the substrate. For this reason, it can adhere firmly on a board | substrate.
In the technique disclosed herein, the thermal expansion coefficient of the glass frit from 25 ° C. to 300 ° C. is 6 ppm / ° C. or more (typically larger than 6 ppm / ° C., for example, 6.2 ppm / ° C. or more). 7.5 ppm / ° C. or less (typically less than 7.5 ppm / ° C., for example, 7.2 ppm / ° C. or less). As described above, by using a glass frit having a smaller thermal expansion coefficient than the conventional one as a binder, it is possible to match the thermal expansion coefficient with the substrate. For this reason, it can adhere firmly on a board | substrate.

  Moreover, the glass frit disclosed here contains a tin (Sn) component and a phosphorus (P) component as essential components in order to realize the above properties. Such components are typically included in the glass frit in the form of an oxide (ie, tin oxide, phosphorus oxide).

  The tin component (typically SnO) is a component that lowers the glass softening point or adjusts the thermal expansion coefficient as a network modifier (network modifier oxide). The ratio of the tin component in the entire glass frit is not particularly limited as long as the glass softening point and the coefficient of thermal expansion are realized, but typically it is the main component (the component that occupies the largest proportion) and is converted to oxide. Is preferably about 40 mol% or more (typically 42 mol% or more, for example 43 mol% or more), and preferably 50 mol% or less (typically 49 mol% or less, for example 48 mol% or less). . Thereby, the said characteristic can be implement | achieved suitably. Furthermore, the stability of the glass can be improved, and at least one of water resistance, chemical resistance, and durability can be improved.

The phosphorus component (typically P ₂ O ₅ ) is a component that functions as a glass network former (network-forming oxide). The proportion of the phosphorus component in the entire glass frit is not particularly limited as long as the glass softening point and the coefficient of thermal expansion are realized, but it is approximately 10 mol% or more (typically 10 mol%) in terms of the molar content of oxide. It is preferably set to 20 mol% or less (typically 15 mol% or less, for example, 12 mol% or less). Thereby, high adhesiveness can be suitably realized. Furthermore, the stability of the glass can be improved, and at least one of water resistance, chemical resistance, and thermal shock resistance can be improved.

In a preferred embodiment, the molar ratio of the tin component and phosphorus component in terms of the oxide is SnO: P ₂ O ₅ = 1: 4 to 1: 5. Thereby, even if it is a case where it bakes at low temperature, the thermal radiation layer excellent in environmental resistance (for example, tolerance with respect to the change of environmental temperature) is realizable.
Moreover, in another suitable one aspect | mode, the sum total of a tin component and a phosphorus component occupies 50 mol% or more (for example, 55 mol% or more) of the whole glass frit. Thereby, the heat dissipation layer having the above-described properties can be stably realized.

In a preferred embodiment, the glass frit has a molar content of each component of 100% by mole as a whole of the following oxide equivalent components:
SnO 40-50 mol% (for example, 42-49 mol%),
P ₂ O ₅ 10~20mol% (e.g. 10~15mol%),
SiO ₂ 15 to 25% (e.g. 16~24mol%),
Al ₂ O ₃ 5~15mol% (e.g. 7~13mol%),
10-15 mol% of at least one of MgO, CaO and SrO,
And the total of these components is 95 mol% or more of the entire glass frit.
By setting it as such a composition, since glass frit is comprised by a multi-component system, physical stability can be improved. Therefore, the effect of the present invention can be exhibited at a higher level.

A silicon component (typically, silicon oxide (SiO ₂ )) is a component that functions as a glass network former (network-forming oxide), and is also a component that adjusts the glass softening point. Moreover, by containing silicon (Si) as a constituent element, for example, the affinity with a ceramic substrate such as silicon nitride or silicon carbide can be improved, and the resistance (contact resistance) at the interface between the substrate and the heat dissipation layer Can be reduced. Therefore, it is possible to realize a heat dissipating substrate excellent in water resistance, chemical resistance and thermal shock resistance.
An aluminum component (typically, aluminum oxide (Al ₂ O ₃ )) is a component that contributes to adhesion stability by controlling fluidity during melting of the glass frit. By containing this component, a heat radiation layer can be stably (homogeneously) formed on the surface of the substrate. Furthermore, the chemical resistance of the heat dissipation layer can be improved by containing this component.
An alkaline earth metal component (typically, at least one of magnesium oxide (MgO), calcium oxide (CaO), and strontium oxide (SrO)) improves the thermal stability of the glass frit (thermal expansion). A component that adjusts a coefficient), and a component that also functions as a network modifier oxide (network modifier). Moreover, the physical stability and thermal stability of a thermal radiation layer can be improved by containing this component. In addition to this, the magnesium component (MgO) is also a component capable of adjusting the viscosity at the time of melting the glass frit. The calcium component (CaO) is also a component that increases the hardness of the glass frit and improves the wear resistance of the heat dissipation layer. For this reason, it is good to contain a magnesium component and / or a calcium component in a glass frit according to the objective and a use.

The glass frit contained in the conductor paste disclosed herein may be composed of only the above-described two or five main components, or any other than the above as long as the effects of the present invention are not significantly impaired. These components may be included. Such additional components, in the form of _{oxides, TiO 2, V 2 O 5} , FeO, Fe 2 O 3, Fe 3 O 4, CuO, Cu 2 O, ZnO, ZrO 2, Nb 2 _{O 5, La 2 O 3,} CeO 2, Bi 2 O 3 and the like. Moreover, the additive generally used for this kind of glass frit conventionally can also be included as needed. Furthermore, it goes without saying that trace amounts of elements due to unavoidable impurities are allowed to enter. The proportion of these secondary components is preferably about 5% by mass or less (typically less than 5% by mass, for example, less than 1% by mass) of the entire glass frit.

Further, the glass frit contained in the conductor paste disclosed herein has an alkali metal component (typically Li ₂ O, Na ₂ O, K ₂ O, Rb ₂ O, Cs ₂ O, Fr ₂ O, particularly Li ₂ O, Na ₂ O, K ₂ O) are preferably not contained (inevitable impurities and the like can be allowed). Alkali metal components are known as components that lower the glass softening point. On the other hand, the alkali metal component can cause a decrease in stability and electrical characteristics (for example, electrical conductivity) of the heat dissipation layer. According to the technology disclosed herein, it is possible to realize a conductor paste having a low glass softening point and excellent adhesion to a substrate without containing an alkali metal component.

  The content of the glass frit in the conductor paste is not particularly limited because it varies depending on the thickness of the heat radiation layer to be formed and the like, but typically 1% by mass or more (typically 5% by mass or more, typically, for example, 6 mass% or more) and 30 mass% or less (typically 20 mass% or less, for example, less than 20 mass%). Thereby, it is possible to suitably realize a heat dissipation layer having excellent adhesion to the substrate and having high heat dissipation and electrical conductivity.

In addition, the manufacturing method of such a glass frit should just follow a conventionally well-known thing. Specifically, for example, first, industrial products, reagents, or various mineral raw materials including oxides, carbonates, nitrates, composite oxides, and the like containing each of the above-described components are prepared, and these are desired. Mix so that the composition becomes. In one preferred embodiment, such a glass raw material powder, in a molar ratio of oxide _{equivalent, SnO 40~50mol%, P 2 O} 5 10~20mol%, SiO 2 15~25mol%, Al 2 O 3 5~15mol% At least one of MgO, CaO and SrO is prepared to have a composition of 10 to 15 mol%. Next, after drying the glass raw material powder thus obtained, the glass raw material powder is heated and melted under a high temperature (typically 1000 to 1500 ° C.) condition, and then cooled or quenched. A glass frit can be prepared by adjusting the obtained glass to an appropriate size (particle size) by pulverization or sieving (classification). The average particle size of the glass frit is typically approximately the same as that of the copper powder, and is generally preferably about 0.5 μm to 50 μm (for example, 1 μm to 10 μm).

〔resin〕
The resin is, for example, an adhesive (organic binder) for temporarily fixing the copper components or the copper component and the substrate when the conductor paste is dried. As the resin, those conventionally used generally for this type of conductor paste can be used without particular limitation. Among them, those that are thermally decomposed during firing at a low temperature (500 ° C. or lower) and do not leave a residue are preferable. Preferable examples include acrylic resins, epoxy resins, phenolic resins, alkyd resins, cellulosic polymers (for example, ethyl cellulose), polyvinyl alcohol (for example, polyvinyl butyral), and rosin resins.
The content of the resin (organic binder) in the conductor paste is not particularly limited, but is typically 0.01% by mass or more (typically 0.1% by mass or more, for example, 1% by mass or more) of the entire conductor paste. And it is good to set it as 10 mass% or less (typically 5 mass% or less, for example, 3 mass% or less). Thereby, it is possible to suitably realize a heat dissipation layer having excellent adhesion to the substrate and having high heat dissipation and electrical conductivity.

〔solvent〕
The solvent disperses the constituent components of the conductor paste disclosed herein (that is, copper powder, glass frit, and resin as solid contents). The conductor paste disclosed herein is typically used for applying to the surface of a substrate to form a heat dissipation layer. By preparing it in a paste form (including an ink form and a slurry form), it is possible to stably form a uniform heat dissipation layer with excellent moldability.
The solvent is not particularly limited as long as the above components can be uniformly dispersed (or dissolved), and those conventionally used generally for this type of conductor paste can be used without particular limitation. Preferable examples include alcohol solvents (for example, terpineol), ether solvents (for example, diethylene glycol monobutyl ether), ester solvents (for example, ethylene glycol monobutyl ether acetate), ketone solvents, amide solvents, aromatic hydrocarbon solvents ( Examples thereof include organic solvents such as toluene and xylene.
The solvent to be used may be an amount that can uniformly disperse (or dissolve) the above components. Although not particularly limited, it is typically 0.1% by mass or more (typically 1% by mass or more, for example, 5% by mass or more) and 20% by mass or less (typically 10% by mass) of the entire conductor paste. % Or less, for example, less than 10% by mass). Further, when forming the heat dissipation layer, for example, it can be appropriately adjusted so as to have a viscosity suitable for coating. Thereby, a homogeneous heat dissipation layer can be formed stably.

  The conductor paste disclosed herein contains various additives in addition to the above main components for the purpose of adjusting the conductor paste to suitable properties (for example, viscosity, pH, adhesive strength, etc.). It may be. Examples of such additives include surfactants, antifoaming agents, plasticizers, thickeners, antioxidants, dispersants, pH adjusters, preservatives, colorants and the like.

  The conductor paste (copper paste) can be prepared by blending the above-described constituent components to a predetermined ratio and kneading them with a conventionally known dispersion / kneading technique (for example, a roll mill, a mixer, etc.). The conductor paste thus prepared can be sintered at a lower temperature (typically 500 ° C. or less, for example, 400 ° C. to 500 ° C.) compared to the prior art, and has heat dissipation, conductivity, and adhesion to ceramics. It is characterized by being excellent. Therefore, it can be preferably used for the purpose of forming a heat dissipation layer or a wiring (circuit) pattern on an insulating substrate made of ceramics.

[Heat dissipation substrate]
Hereinafter, a heat dissipating substrate according to a preferred embodiment will be described with reference to FIG. In addition, in the following drawings, the same code | symbol is attached | subjected and demonstrated to the member and site | part which show | plays the same effect | action, and the overlapping description may be abbreviate | omitted or simplified. The embodiments shown in the drawings are modeled as necessary to clearly explain the present invention, and do not necessarily accurately reflect the dimensional relationship (length, width, thickness, etc.) of the actual heat-dissipating substrate. It was n’t.

  As shown in FIG. 1, the heat dissipating substrate 1 disclosed here is a so-called DBC (Direct Bonded Copper) substrate that directly includes a heat dissipating layer 4 on the surface of an insulating substrate (circuit substrate) 2. That is, the heat dissipation layer 4 disclosed here is provided directly on the surface of the insulating substrate 2 without using a bonding agent such as a brazing material, unlike the conventional active metal method. In the example shown in FIG. 1, a plurality of (seven in this case) heat dissipation layers 4 a having different sizes (length, etc.) and thicknesses are provided separately on one surface of the insulating substrate 2. The other surface of the insulating substrate 2 is provided with a heat radiation layer 4b over almost the entire surface. Thus, the heat dissipation layer 4 may be provided on a part of the insulating substrate 2 or may be provided over almost the entire surface of the insulating substrate 2. Moreover, the heat-radiation layer 4 should just be provided in the at least one surface of the insulated substrate 2, for example, may be provided only in the single side | surface.

The insulating substrate 2 is made of ceramics. Examples of such ceramics include carbide ceramics made of metal carbide; nitride ceramics made of metal nitride; oxide ceramics made of metal oxide; metal boride, fluoride, hydroxide, carbonate, And ceramics made of phosphate or the like. Among these, ceramics having a relatively small thermal expansion coefficient can be suitably used in the technology disclosed herein. Preferred examples include nitride ceramics such as silicon nitride (silicon nitride: Si ₃ N ₄ ), aluminum nitride (aluminum nitride: AlN), and boron nitride (BN); carbides such as silicon carbide (silicon carbide: SiC). Composite oxide ceramics such as cordierite (2MgO · 2Al ₂ O ₃ · 5SiO ₂ ) and mullite (3Al ₂ O ₃ · 2SiO ₂ ). Particularly, those having a small thermal expansion coefficient (and the thermal expansion coefficient (25 ° C. to 500 ° C.) of the ceramic) are exemplified by cordierite (<0.1 ppm / ° C.), boron nitride (1.4 ppm / ° C.), nitriding Examples include silicon (2.6 ppm / ° C.), silicon carbide (3.7 ppm / ° C.), aluminum nitride (4.6 ppm / ° C.), and mullite (5.0 ppm / ° C.). When a substrate made of such a material is used, the application of the technique disclosed herein is particularly effective. Among these, silicon nitride is particularly excellent in mechanical strength such as a bending strength of about 600 MPa to 800 MPa. For this reason, it can be preferably used in applications requiring durability.

The heat dissipation layer 4 is characterized by using the above-described conductor paste. That is, it contains at least a copper component, a glass component (inorganic binder component), and a resin component (organic binder component). In addition, about the composition and property of these components, since it is equivalent to what comprises the said conductor paste, detailed description is abbreviate | omitted.
The ratio of the copper component and the glass component in the heat dissipation layer 4 is not particularly limited. For example, when the total of the copper component and the glass component is 100% by mass, the glass component is 5% by mass or more (typically 10%). It is preferably contained in a proportion of 30% by mass or less (typically 25% by mass or less, eg 20% by mass or less). By making a glass component into the said ratio, the heat dissipation layer 4 excellent in adhesiveness with the insulating substrate 2 and having high heat dissipation and electrical conductivity can be realized.
The size and thickness of the heat dissipation layer 4 may be determined in consideration of, for example, the dimensions, height, and spacing (arrangement) of the semiconductor elements to be mounted (connected), and is not particularly limited. From the viewpoint of heat dissipation, it is preferable to form the heat dissipation layer as thick as possible in as wide a region as possible. For this reason, in a preferred embodiment, the thickness of the heat dissipation layer 4 can be 100 μm or more (typically 120 μm or more, for example, 200 μm or more) and 400 μm or less (for example, 350 μm or less).

[Method of manufacturing heat-radiating substrate]
Such a heat dissipating substrate has the following steps:
Preparing the above-mentioned conductor paste and an insulating substrate made of ceramic;
Applying the conductive paste onto the insulating substrate; and firing the insulating substrate provided with the conductive paste at 500 ° C. or lower to form a heat dissipation layer;
It can produce by the manufacturing method including this. Hereinafter, each process is demonstrated in order.

First, a conductor paste and an insulating substrate made of ceramics are prepared. As these materials, those already described above can be used.
Next, a conductor paste is applied to the surface of the insulating substrate. Conventionally known methods (for example, screen printing method, metal mask printing method, gravure printing method, doctor blade method, dispenser coating method, dip coating method, ink jet method, etc.) are used for applying the conductor paste (typically coating). Can be used. Of these, various printing methods can be preferably employed. By using the printing method, for example, application corresponding to a wiring pattern having a complicated shape (for example, different thickness or size) can be performed easily and accurately.
Next, the applied conductor paste is typically pre-dried at a suitable temperature (typically 30 ° C. to 100 ° C., for example 80 ° C. to 100 ° C.).
After the drying, firing is performed for a predetermined time at a temperature at which the conductor paste can be sufficiently sintered. The firing temperature is 500 ° C. or lower, and typically 350 ° C. to 500 ° C., for example, 400 ° C. to 500 ° C.). The firing time can be usually about 0.1 to 5 hours (typically 0.5 to 3 hours). Moreover, it is preferable to perform baking in an inert gas atmosphere. Here, the inert gas atmosphere can be defined as an atmosphere substantially free of oxygen and hydrocarbon gas. Typical atmospheric gases include nitrogen gas and rare gases such as argon and helium. By making the inert gas atmosphere at the time of firing, oxidation of copper can be prevented, and problems such as a decrease in electrical conductivity and volume expansion can be suppressed.

  The heat dissipating substrate thus manufactured is excellent in heat dissipating property and electric conductivity, and the substrate and the heat dissipating layer are firmly integrated. Therefore, it can be suitably used as a member constituting a ceramic electronic material such as a power semiconductor.

  EXAMPLES Examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the following examples.

[Evaluation of adhesiveness (1)]
Here, the “wetability” between the substrate and the glass frit (inorganic binder component in the conductor paste) was examined.
Specifically, first, a commercially available silicon nitride substrate (manufactured by Mitsubishi Materials) was prepared as a ceramic insulating substrate. Moreover, the glass frit (Example 1- Example 7) of the property shown in Table 1 was prepared. Next, a glass frit was placed on the silicon nitride substrate and baked at 500 ° C. for 1 hour to form glass layers (Examples 1 to 7) on the silicon nitride substrate. The obtained composite was subjected to CP (Cross section polisher) processing to obtain a cross section, and then the “silicon nitride substrate-glass layer” interface was observed with a scanning electron microscope (SEM). An example is shown in FIG. 2A is an image obtained by SEM observation of the interface between the silicon nitride substrate and the glass layer in Example 1, and FIG. 2B is an image obtained by SEM observation of the interface between the silicon nitride substrate and the glass layer in Example 3. is there.
As can be seen from this image, in Example 1 (FIG. 2A), the silicon nitride substrate 12 and the heat dissipation layer 14 were bonded over the entire interface. On the other hand, in Example 3 (FIG. 2B), a crack of several μm occurred between the substrate 12 and the heat dissipation layer 14. Based on such images, the adhesion between the silicon nitride substrate and glass in Examples 1 to 7 was quantitatively evaluated. Here, “wetting area ratio” was adopted as an index of adhesion. That is, the total length of the interface in an arbitrary region and the length in which the silicon nitride substrate and the glass layer are in close contact with each other are measured, and the following formula:
The “wet area ratio” was determined. The evaluation results are shown in the column of “Wet area ratio” in Table 1. Table 1 shows the arithmetic average value of the wetted area ratio calculated at any 10 locations.

  As shown in Table 1, in Examples 5 to 7, the wet area ratio was 0%, and the silicon nitride substrate and the glass layer were not bonded. Further, in Examples 3 and 4, the wet area ratio was 70%, and a peeled portion (crack) was observed at a partial interface between the silicon nitride substrate and the glass layer. On the other hand, in Examples 1 and 2, the wet area ratio was 90% or more, and it was found that the wettability between the silicon nitride substrate and the glass was high.

[Evaluation of adhesiveness (2)]
Here, a conductor paste was prepared using the glass shown in Table 1, a heat dissipation layer was formed on the substrate using the conductor paste, and the adhesion between the substrate and the heat dissipation layer was evaluated.
First, a conductor paste was prepared. Specifically, copper powder (average particle diameter: 1 μm), glass frit (Examples 1 to 7), and acrylic resin as a binder were mixed at a mass ratio of 70: 20: 0.1. Next, the mixture and diethylene glycol monobutyl ether as a solvent were kneaded to make 100% by mass as a whole to prepare conductor pastes (Examples 1 to 7) for forming a heat dissipation layer.

  Next, a heat dissipation substrate was produced. Specifically, the above prepared conductor paste (Examples 1 to 7) was stencil-printed on the surface of a commercially available silicon nitride substrate by a doctor blade method. The printing pattern was a 30 mm × 30 mm square, and the coating thickness was 0.3 mm. This was fired in an inert gas atmosphere (500 ° C., 1 hour) to produce a heat dissipating substrate (Examples 1 to 7) having a heat dissipating layer on the surface of an insulating substrate made of silicon nitride.

  The obtained heat-radiating substrate was observed, and it was confirmed from the appearance (visually) whether there were any defects such as distortion and cracking. Next, it was confirmed whether the heat dissipation layer could be peeled from the substrate using tweezers, and it was evaluated whether the silicon nitride substrate and the heat dissipation layer were mechanically bonded. The evaluation results are shown in the column “Adhesion with silicon nitride substrate” in Table 1. In Table 1, “◯” indicates that no defects in appearance such as distortion or cracking were confirmed and both were well bonded, “×” indicates that defects in appearance were confirmed, and / or Or it represents that both were not adhere | attached.

  As shown in Table 1, in the heat dissipating substrates of Examples 3 to 7, the silicon nitride substrate and the heat dissipating layer were not bonded. On the other hand, in the heat dissipating substrates of Examples 1 and 2, the silicon nitride substrate and the heat dissipating layer were securely bonded. Such a result supports the technical significance of the invention disclosed herein.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

1 Heat-dissipating substrate 2, 12 Insulating substrate (silicon nitride substrate)
4, 4a, 4b, 14 Heat dissipation layer

Claims (8)

A conductor paste,
Including copper powder, glass frit, resin as binder, and solvent,
The glass frit has the following conditions:
(1) The glass softening point is 300 ° C. or higher and 400 ° C. or lower;
(2) The coefficient of thermal expansion is 6 ppm / ° C. or more and 7.5 ppm / ° C. or less;
(3) containing Sn and P as essential constituent elements;
A conductor paste comprising: The glass frit has a molar content of each component when the following oxide conversion components as a whole are 100 mol%.
SnO 40-50 mol%,
P ₂ O ₅ 10~20mol%,
SiO ₂ 15~25mol%,
Al ₂ O ₃ 5~15mol%,
10-15 mol% of at least one of MgO, CaO and SrO,
The conductor paste according to claim 1, wherein the total of these components is 95 mol% or more of the entire glass frit.   The conductor paste according to claim 1 or 2, wherein the content of the glass frit is 5% by mass or more and 30% by mass or less when the entire conductor paste is 100% by mass.   The conductor paste according to any one of claims 1 to 3, wherein the glass frit does not contain an alkali metal element as a glass constituent element.   The conductor paste according to any one of claims 1 to 4, which is used for forming a heat dissipation layer on a surface of an insulating substrate made of a nitride-based ceramic.   A heat dissipating substrate comprising: an insulating substrate made of ceramics; and a heat dissipating layer provided on the surface of the insulating substrate, the heat dissipating layer using the conductor paste according to claim 1.   The heat dissipating substrate according to claim 6, wherein the insulating substrate is mainly composed of silicon nitride.   The heat dissipation board according to claim 6 or 7, wherein the heat dissipation layer has a thickness of 100 µm or more and 400 µm or less.