JP2016011218A - Silicon nitride substrate, circuit board including the same, and electronic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a silicon nitride substrate with improved strength of connection with metal while having excellent mechanical strength; a circuit board including the silicon nitride substrate; and an electronic device.SOLUTION: A silicon nitride substrate is made of a sintered body that is composed mainly of silicon nitride and has a surface serving as a surface connected with metal. Rhombohedral boron nitride exists in the surface. A content of the rhombohedral boron nitride is not less than 5 mass% and not more than 20 mass% with respect to 100 mass% of all ingredients in the surface. The silicon nitride substrate makes it possible to improve strength of connection with metal while having excellent mechanical strength.

Description

  The present invention relates to a silicon nitride substrate, a circuit substrate including the same, and an electronic device.

  In recent years, insulated gate bipolar transistor (IGBT) elements, metal oxide field effect transistor (MOSFET) elements, light emitting diode (LED) elements, freewheeling diode (FWD) elements, giant transistor (GTR) elements, etc. 2. Description of the Related Art An electronic device in which various electronic components such as a semiconductor element, a sublimation thermal printer head element, a thermal ink jet printer head element, and a Peltier element are mounted on a circuit member of a circuit board is used.

  Such a circuit board is used, for example, by bonding a circuit member mainly composed of copper to the surface of a silicon nitride substrate having high insulation and excellent mechanical strength. And in order to improve the reliability of a circuit board and by extension, an electronic device, examination for improving the joint strength of a silicon nitride board | substrate and a circuit member is made.

  For example, in Patent Document 1, a silicon nitride circuit board is obtained by brazing and bonding a metal circuit board to a silicon nitride substrate, and the bonding surface of the silicon nitride substrate has an arithmetic average roughness Ra of Ra <1 μm and a maximum height Ry. , Ry <10 μm, a skewness Rsk obtained from a roughness curve is 1> Rsk> 0, and a silicon nitride circuit board having a void area ratio of 3% or less at a brazed joint interface has been proposed.

JP 2010-76948 A

  In recent years, a silicon nitride substrate on which electronic components are mounted via a circuit member has excellent mechanical strength and further increases the reliability of the circuit substrate and the electronic device. There is a need for further improvement in bonding strength.

  The present invention has been devised to satisfy the above-described requirements, and provides a silicon nitride substrate having excellent mechanical strength and improved bonding strength with a metal, a circuit substrate including the same, and an electronic device It is intended to do.

The silicon nitride substrate of the present invention is composed of a sintered body having silicon nitride as a main component and having a surface serving as a joint surface with a metal, rhombohedral boron nitride is present on the surface, and all components on the surface are present. 100
Of the mass%, the rhombohedral boron nitride content is 5 mass% or more and 20 mass% or less.

  The circuit board of the present invention is characterized in that a circuit member is provided on the surface of the silicon nitride substrate having the above structure.

The electronic device according to the present invention is characterized in that an electronic component is mounted on the circuit member in the circuit board having the above-described configuration.

  The silicon nitride substrate of the present invention can improve bonding strength with a metal while having excellent mechanical strength.

  In addition, the circuit board and the electronic device of the present invention have excellent durability that can withstand use for a long period of time because the metal circuit member and the silicon nitride substrate are firmly bonded. High reliability.

An example of the circuit board of this embodiment is shown, (a) is a plan view, and (b) is a sectional view taken along line A-A ′ of (a). The other example of the circuit board of this embodiment is shown, (a) is a top view, (b) is sectional drawing in the B-B 'line | wire of (a). Still another example of the circuit board of the present embodiment is shown, (a) is a plan view, and (b) is a sectional view taken along line C-C ′ of (a). An example of the electronic device of this embodiment is shown, (a) is a plan view, and (b) is a cross-sectional view taken along line D-D 'in (a).

  First, the silicon nitride substrate of this embodiment will be described.

The silicon nitride substrate of the present embodiment is composed of a sintered body having silicon nitride as a main component and a surface serving as a bonding surface with a metal, rhombohedral boron nitride is present on the surface, and all components 100 on the surface are present. Of the mass%, the rhombohedral boron nitride content is 5 mass% or more and 20 mass% or less. By satisfying such a configuration, the silicon nitride substrate of the present embodiment can improve the bonding strength with the metal while having excellent mechanical strength.

  Here, boron nitride has a hexagonal crystal and a rhombohedral crystal as the crystal structure at normal pressure, and rhombohedral boron nitride has a c-axis lattice constant (1.0000 nm) in the unit cell of boron nitride. It is larger than the lattice constant (0.66813 nm) on the c-axis of the unit cell.

  Since such rhombohedral boron nitride exists, a part of the unit cell constituting the silicon nitride columnar crystal grains penetrates into the rhombohedral boron nitride unit cell during sintering. Thus, it is considered that the rhombohedral boron nitride and silicon nitride are firmly bonded, and the bonding strength can be improved because the bonded crystal has a complicated shape.

If the content of rhombohedral boron nitride is less than 5% out of 100% by mass of the total component on the surface of the silicon nitride substrate, the effect of improving the bonding strength described above tends to decrease, and 20% by mass. When it exceeds, there exists a tendency for mechanical strength to fall.

  Further, in boron nitride, it is preferable that the boron nitride having a hexagonal crystal structure is small, and the content of hexagonal boron nitride is preferably 10% or less of the content of rhombohedral boron nitride. It is.

  In the present embodiment, the surface of the silicon nitride substrate refers to the outer surface of the silicon nitride substrate to which the metal is bonded, but when collecting samples for component identification and content measurement, a sampling region is used. The depth from the surface to the depth of 50 μm is regarded as the surface.

Here, the content of each component on the surface that becomes the bonding surface with the metal is determined using a fluorescent X-ray analyzer (XRF) after identifying the component on the surface using an X-ray diffractometer (XRD), What is necessary is just to obtain | require element content and to convert into content of the identified component. Or, using a polishing powder obtained by polishing from the surface of the silicon nitride substrate to a depth of about 30 μm to 50 μm in the depth direction as a sample, using an ICP emission spectrometer (ICP), the element content is obtained, You may convert into content of the identified component. Specifically, if the identified components are silicon nitride, boron nitride, and zirconium nitride, the silicon, boron, and zirconium contents obtained by measuring with XRF or ICP, respectively, are the nitride contents. Convert to.

When the rhombohedral only boron nitride is identified when measured using XRD, the boron nitride content obtained by the above-described method is the rhombohedral boron nitride content. When hexagonal boron nitride is identified, it is 30 μm to 50 μm in the depth direction from the surface of the silicon nitride substrate.
Using a polishing powder obtained by polishing to a depth of about μm as a sample, calculate the mass percentage for each crystal structure by the Rietveld method using XRD, and multiply the boron nitride content by the mass percentage of rhombohedral crystals. do it.

And the silicon nitride substrate of this embodiment has silicon nitride as a main component. The main component means that 63% by mass or more of silicon nitride is contained in 100% by mass of all components constituting the sintered body, and in particular, when 70% by mass or more is contained, the mechanical strength tends to be higher. This is preferable. Moreover, a metal is a metal plate, a metal layer, a metal foil, or the like, and is a concept including a metal plate joined by a brazing material or the like. The mechanical strength of the silicon nitride substrate of the present embodiment can be evaluated by a four-point bending strength at room temperature in accordance with JIS R 1601-2008 (ISO 14704: 2000 (MOD)). The silicon nitride substrate of the form has a 4-point bending strength of 900 MPa or more. Moreover, the joint strength with the metal in the silicon nitride substrate of the present embodiment can be measured according to JIS C 6481-1996.

In the silicon nitride substrate of this embodiment, zirconium nitride exists in the grain boundary phase between silicon nitride crystals, and zirconium is converted to nitride out of 100% by mass of all components constituting the sintered body. It is preferable that the content is 0.2 mass% or more and 1.0 mass% or less.

  When the above configuration is satisfied, the zirconium nitride is a high melting point crystal having oxidation resistance while having a dielectric breakdown characteristic capable of withstanding a high voltage, so that it has excellent mechanical strength even at high temperatures. Have.

Here, regarding the dielectric breakdown characteristics, JIS C 2141-1992 (IEC 672-2 (1980))
) In accordance with the strength of dielectric breakdown (MV / m). Note that the strength of dielectric breakdown in the silicon nitride substrate of the present embodiment is preferably 20 MV / m or more.

  In addition, the silicon nitride substrate of the present embodiment preferably includes magnesium and aluminum oxynitride (MgAlON) in the grain boundary phase between the silicon nitride crystals. When such a configuration is satisfied, the number of crystals in the grain boundary phase increases, so that it has excellent mechanical strength even at high temperatures. In addition, the linear expansion coefficient of oxynitride of magnesium and aluminum is closer to that of silicon nitride than that of magnesium oxide and aluminum oxide. Therefore, when heating and cooling are repeated, Cracks are less likely to occur. Furthermore, since oxynitride of magnesium and aluminum is excellent in corrosion resistance, it can be suitably used for a member disposed in an environment of highly corrosive gas such as halogen-based gas.

Here, magnesium and aluminum oxynitrides may be identified using XRD. The composition formula of oxynitride of magnesium and aluminum is, for example, Mg _0.2 Al _{1.45
Expressed} as O _2.15 N _0.15 . As another method, the grain boundary phase is confirmed using a scanning electron microscope (SEM), and X-rays are applied to crystals confirmed in the grain boundary phase using an energy dispersive X-ray analyzer (EDS). The presence of magnesium and aluminum oxynitrides can also be confirmed by irradiation and confirmation of Mg, Al, O and N.

  In addition, the silicon nitride substrate of the present embodiment preferably includes a rare earth metal and magnesium in the grain boundary phase, and the total content converted to an oxide is 3% by mass or more and 6% by mass or less. . Since the rare earth metal has a high affinity with oxygen, a large amount of oxygen is incorporated between the raw material powders of silicon nitride at the time of sintering, and the grain growth of silicon nitride is promoted. Magnesium promotes densification by the sintering promoting action of the oxide.

  Therefore, when the total content of rare earth metals and magnesium converted into oxides is 3% by mass or more and 6% by mass or less among all the components constituting the silicon nitride substrate, the occupied area of the grain boundary phase is increased. Thus, the mechanical strength of the silicon nitride substrate can be increased while suppressing the deterioration of the heat dissipation characteristics. The content of magnesium in terms of oxide is preferably 1% by mass or more and 2% by mass or less, and the content of rare earth metal in terms of oxide is 2% by mass or more and 4% by mass or less. Is preferred.

Further, whether or not rare earth metal (RE) and magnesium (Mg) are contained in the grain boundary phase may be confirmed by irradiating the grain boundary phase with X-rays using EDS. Alternatively, the contents of RE and Mg can be obtained by ICP, and these contents can be obtained by converting them into RE ₂ O ₃ and MgO.

The electrical characteristics of the silicon nitride substrate of this embodiment are preferably such that the volume resistivity at room temperature is 10 ¹⁴ Ω · cm or more and the volume resistivity at 300 ° C. is 10 ¹² Ω · cm or more. is there. This volume resistivity may be measured according to JIS C 2141-1992. However, when the size of the silicon nitride substrate is small and a test piece having a size specified in JIS C 2141-1992 cannot be obtained from the silicon nitride substrate, the two-terminal method is used for evaluation. It is preferable that the result satisfies the above numerical value.

  Next, the circuit board of this embodiment will be described with reference to the drawings.

  1A and 1B show an example of a circuit board according to the present embodiment. FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along line A-A ′ in FIG.

  A circuit board 10 of this embodiment shown in FIG. 1 is an example in which a circuit member 2 is directly bonded to the surface of a silicon nitride substrate 1 of this embodiment. In the following description, the circuit member 2 is first described, and then the silicon nitride substrate 1 is described.

First, the circuit member 2 has a metal component as a main component, and the main component in the circuit member 2 is a component that occupies 50% by mass or more out of 100% by mass of all components constituting the circuit member 2. .

More specifically, it is preferable to use copper, and the content of copper is 90% by mass or more, and the content of copper is any of oxygen-free copper, tough pitch copper, and phosphorus deoxidized copper. Is preferred. In particular, it is preferable that the oxygen-free copper is made of any of linear crystalline oxygen-free copper having a copper content of 99.995% by mass or more, single-crystal high-purity oxygen-free copper, and vacuum-melted copper. Thus, when the copper content in the circuit member 2 is large, the heat dissipation characteristics are improved due to the high thermal conductivity, and the circuit characteristics (characteristics for suppressing the heat generation of the electronic components and reducing the power loss) due to the low electrical resistance. Will improve. Further, when the copper content is large, the yield stress is low, and plastic deformation is easily caused by heating, so that the bonding strength of the circuit member 2 is increased and the reliability is further increased. The thickness of the circuit member 2 is preferably 0.5 mm or more and 5 mm or less.

  Next, FIG. 2 shows another example of the circuit board of the present embodiment, in which (a) is a plan view and (b) is a sectional view taken along line B-B ′ of (a).

  The circuit board 20 in the example shown in FIG. 2 is different from the circuit board 10 shown in FIG. 1 in that the silicon nitride substrate 1 and the circuit member 2 are bonded via the bonding layer 3. By joining the circuit member 2 via the brazing material to be the joining layer 3, the thick circuit member 2 can be easily joined to the silicon nitride substrate 1.

  As the brazing material to be the bonding layer 3, it is preferable that the main component is at least one of silver and copper, and contains at least one selected from titanium, zirconium, hafnium and niobium, The thickness is preferably 5 μm or more and 20 μm or less, for example.

  Next, FIG. 3 shows still another example of the circuit board of the present embodiment, where (a) is a plan view and (b) is a sectional view taken along line C-C ′ of (a).

  In the circuit board 30 of the example shown in FIG. 3, the circuit member 2 is bonded to the surface of the silicon nitride substrate 1 of this embodiment from the silicon nitride substrate 1 side through the bonding layer 3 and the copper material 4 sequentially. An example is shown.

  In the circuit board 20 shown in FIG. 2, the temperature when the circuit member 2 is joined to the silicon nitride substrate 1 is 800 to 900 ° C., whereas the copper material 4 is made as in the circuit board 30 shown in FIG. By interposing, since the joining between the circuit member 2 and the copper material 4 can be joined at a relatively low temperature of about 300 to 500 ° C. by the diffusion of copper, the warpage generated in the silicon nitride substrate 1 is suppressed. can do. As a result, since the stress generated in the silicon nitride substrate 1 is small, cracks are hardly generated even when heat is repeatedly applied. Moreover, since the circuit member 2 can be thickened, the heat dissipation characteristics of the circuit board 30 can be enhanced.

  The copper material 4 is preferably made of any one of oxygen-free copper, tough pitch copper and phosphorous deoxidized copper having a large copper content. In particular, among oxygen-free copper, it is preferably composed of any one of linear crystalline oxygen-free copper having a copper content of 99.995% by mass or more, single-crystal high-purity oxygen-free copper, and vacuum-melted copper. For example, 0.1 mm or more and 0.6 mm or less are preferable.

  As described above, the circuit boards 10 to 30 of FIGS. 1 to 3 have excellent durability that can be used for a long time since the circuit member 2 is bonded to the surface of the silicon nitride substrate 1 of the present embodiment. It has high reliability.

  4A and 4B show an example of the electronic apparatus according to the present embodiment. FIG. 4A is a plan view, and FIG. 4B is a cross-sectional view taken along line D-D ′ in FIG. The electronic device S of the example shown in FIG. 4 is one in which an electronic component 5 such as a semiconductor element is mounted on the circuit member 2 of the circuit board 10 of the present embodiment.

  According to the electronic device S of the example shown in FIG. 4, the circuit member 2 and the silicon nitride substrate 1 are firmly bonded while the silicon nitride substrate 1 has excellent mechanical strength. It has high reliability because it has excellent durability that can withstand use during a period. Further, since the electronic component 5 is placed on the circuit board 10 having high mechanical strength and high dielectric breakdown strength, the electronic device S with high reliability can be obtained.

  Next, a method for manufacturing the silicon nitride substrate of this embodiment will be described.

First, a silicon nitride powder having a β conversion rate of 20% or less and a purity of 98% or more, a first additive component (hereinafter referred to as a silicon nitride powder having a purity of 98% or more, Together with the additive components, it is referred to as a primary raw material.) Magnesium oxide (MgO) and rare earth metal oxides (for example, Sc ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ , Ce ₂ O ₃ , Pr _{6) O 11, Nd 2 O 3,} Pm 2 O 3, Sm 2 O 3, Eu 2 O 3, Gd 2 O 3, Tb 2 O 3, Dy 2 O 3, Ho 2 O 3, Er 2 O 3, Tm 2 Each powder of O ₃ , Yb ₂ O ₃ and Lu ₂ O ₃ ) is wet with water using a mixing device such as a barrel mill, a rotating mill, a vibration mill, a bead mill, a sand mill, an agitator mill, etc. Mix and grind to make slurry To.

  Here, the addition amount of each powder of magnesium oxide and rare earth metal oxide is, for example, 1% by mass or more and 2% by mass or less, 2% by mass or more and 4% by mass or less, and the balance is powder of silicon nitride. .

The ball used for pulverization of the powder of silicon nitride and the first additive component is preferably a ball made of a material in which impurities are hardly mixed or a silicon nitride sintered body having the same material composition. The primary raw material is pulverized with a cumulative volume of 90% when the total cumulative volume of the particle size distribution curve is 100%.
It is preferable to grind until the particle size (D ₉₀ ) of% becomes 3 μm or less from the viewpoint of improving the sinterability. The particle size distribution obtained by pulverization can be adjusted by the outer diameter of the ball, the amount of the ball, the viscosity of the slurry, the pulverization time, and the like.

Next, the obtained slurry was passed through a mesh having a particle size number of 200 described in ASTM E 11-61 or a sieve having a finer mesh than this mesh, and then dried to obtain granules containing silicon nitride as a main component (hereinafter referred to as “silicone nitride”). , Referred to as silicon nitride granules). Drying may be performed by a spray dryer, and there is no problem even if other methods are used. Then, a silicon nitride granule is formed into a sheet by using a powder rolling method to form a ceramic green sheet, and the ceramic green sheet is cut into a predetermined length to form a molded body containing silicon nitride as a main component (hereinafter referred to as nitriding). This is referred to as a silicon-like molded body). Alternatively, instead of the powder rolling method, a silicon nitride-based molded body may be obtained by using a pressure molding method or a cold isostatic pressure method and filling the mold with the silicon nitride granules and then pressing.

Then, a paste obtained by adding each powder of silicon nitride, first additive component and rhombohedral boron nitride to a solvent such as ethanol together with a binder is applied to the surface of the obtained silicon nitride-like molded body by a screen printing method. And when the temperature is dried at, for example, 60 ° C. or more and 100 ° C. or less,
A silicon nitride-based molded body having rhombohedral boron nitride on the surface is obtained. Note that the amount of rhombohedral boron nitride powder added may be 5% by mass or less and 20% by mass or less, out of a total of 100% by mass of the above powders.

Alternatively, instead of the above method, a silicon nitride-based molded body is arranged at a predetermined position in the reaction vessel, and boron source gas is BCl ₃ , BF ₃ , BBr ₃ , B ₂ H ₆ , B ₃ N ₃ H ₃ , B _{At least one of 3} N ₃ H ₃ C ₁₃ and B (C ₂ H ₅ ) ₃ , and HN ₃ , NH ₃ , N ₂ H ₂ , NH ₄ Cl, NH ₄ Br, NH as a nitrogen source gas _At least one of ₄ F, NH ₄ Hf _2, and NH ₄ I and at least one of Ar, He, and H ₂ are introduced into the reaction vessel as a diluted carrier gas (carrier gas). The vapor phase synthesis may be performed at a temperature of 600 to 800 ° C. and for a time of 1 to 3 hours. By this vapor phase synthesis, it is possible to obtain a silicon nitride-based molded body in which silicon nitride particles and boron nitride particles are mixed on the surface.

And, in a state where a plurality of silicon nitride-based molded bodies having rhombohedral boron nitride on the surface are stacked inside a mortar made of a silicon nitride-based sintered body having a relative density of 55% or more and 95% or less, It is fired in a firing furnace in which a graphite resistance heating element is installed. At this time, in order to suppress volatilization of the components contained in the silicon nitride-based molded body, a common material having a composition similar to that of the silicon nitride-based molded body is disposed around the silicon nitride-based molded body. The amount of the co-material is preferably 2 parts by mass or more and less than 10 parts by mass with respect to 100 parts by mass of the silicon nitride-based molded body.

Moreover, about baking conditions, it heats up in a vacuum atmosphere from room temperature to 300-1000 degreeC, Then, nitrogen gas is introduce | transduced and nitrogen partial pressure is maintained at 15-900 kPa. Further, by further increasing the temperature, the additive component forms a liquid phase component in the vicinity of 1000 to 1400 ° C through a solid phase reaction, and the phase transition of silicon nitride from α-type to β-type in the temperature range of 1400 ° C or higher Happens irreversibly.

Then, the temperature in the firing furnace is raised and held at 1640 ° C. or higher and lower than 1700 ° C. for 4 hours or longer and 10 hours or shorter, and then cooled at a temperature lowering rate of 170 ° C./hour or higher and 230 ° C./lower, thereby joining the metal. A rhombohedral boron nitride is present on the surface, and all components on the surface are 100
The silicon nitride substrate of the present embodiment having a rhombohedral boron nitride content of 5% by mass or more and 20% by mass or less can be obtained. Note that at 1700 ° C. or higher, rhombohedral boron nitride is easily changed to hexagonal boron nitride.

Next, zirconium nitride is present in the grain boundary phase between the silicon nitride crystals, and out of 100 mass% of all components constituting the sintered body, the content of zirconium converted to nitride is 0.2 mass% or more and 1.0.
In order to obtain a silicon nitride substrate having a mass% or less, zirconium oxide or zirconium nitride powder may be added to the above-mentioned primary raw material as the second additive component. At this time, when the second additive component is a powder of zirconium oxide, it is added so that it is 0.2% by mass or more and 1.2% by mass or less in the total 100% by mass of the raw material to be added. In the case of zirconium powder, it may be added so as to be 0.2% by mass or more and 1.0% by mass or less. It goes without saying that zirconium oxide powder or zirconium nitride powder may be added to the paste applied to the surface of the silicon nitride-based molded body.

  In addition, in order to obtain a silicon nitride substrate containing magnesium and aluminum oxynitride (MgAlON) in the grain boundary phase, aluminum nitride powder is added to the above-mentioned primary raw material, magnesium oxide powder, aluminum nitride powder, The molar ratio may be, for example, 1: 0.8 to 1: 1.2.

Furthermore, in order to obtain a silicon nitride substrate that contains rare earth metal and magnesium in the grain boundary phase, and the total content converted to oxides is 3% by mass or more and 6% by mass or less, a total of 100 raw materials are added. What is necessary is just to weigh so that the sum total of each powder of the rare earth metal and the first additive component of magnesium is 3% by mass to 6% by mass and the remainder is silicon nitride.

The silicon nitride substrate obtained by the above-described method has a relative density of 98% or more, particularly 99.95%.
The above is preferable, and inevitable impurities may be included.

  Next, the manufacturing method of the circuit board of this embodiment is demonstrated.

  In order to obtain the circuit board 10 of the example shown in FIG. 1, first, the silicon nitride substrate 1 is prepared by the manufacturing method described above. Next, the circuit member 2 containing copper as a main component is disposed on the surface of the silicon nitride substrate 1 (the surface shown in FIG. 1A). Thereafter, the circuit board 10 in which the circuit member 2 is bonded to the surface of the silicon nitride substrate 1 by direct bonding by heating at 1065 ° C. to 1085 ° C. in a nitrogen atmosphere and simultaneously applying a pressure of 30 MPa or more. Can be obtained.

In order to obtain the circuit substrate 20 of the example shown in FIG. 2, first, after preparing the silicon nitride substrate 1 described above, the surface of the silicon nitride substrate 1 (surface shown in FIG. 2A) is made of titanium, A silver (Ag) -copper (Cu) alloy paste-like brazing material containing at least one selected from zirconium, hafnium and niobium is applied to any method such as screen printing, roll coater, and brush coating. The circuit member 2 containing copper as a main component is disposed thereon. The pasty brazing material may contain one or more selected from molybdenum, tantalum, osmium, rhenium and tungsten. Thereafter, the circuit is formed by heating the circuit member 2 to the surface of the silicon nitride substrate 1 through the bonding layer 3 by heating at 800 ° C. to 900 ° C. in a vacuum atmosphere and simultaneously applying a pressure of 30 MPa or more. The substrate 20 can be obtained.

  In order to obtain the circuit board 30 of the example shown in FIG. 3, first, the silicon nitride substrate 1 described above is prepared. Next, a silver (Ag) -copper (Cu) -based alloy containing one or more selected from titanium, zirconium, hafnium and niobium is formed on the surface of the silicon nitride substrate 1 (the surface shown in FIG. 3A). The paste-like brazing material is applied by any method such as a screen printing method, a roll coater method, and a brush coating method. This pasty brazing material may also contain one or more selected from molybdenum, tantalum, osmium, rhenium and tungsten. Then, a thin copper material 4 is disposed on the brazing material. Thereafter, the copper material 4 is bonded to the surface of the silicon nitride substrate 1 via the bonding layer 3 by heating at 800 ° C. or more and 900 ° C. or less.

  Then, after polishing the surface of the copper material 4 facing the circuit member 2, the circuit member 2 is disposed on the copper material 4. Subsequently, the bonding layer is formed on the surface of the silicon nitride substrate 1 by heating at 300 ° C. or more and 500 ° C. or less in an atmosphere selected from hydrogen, nitrogen, neon, and argon, and simultaneously applying a pressure of 30 MPa or more. 3. A circuit board 30 formed by joining the circuit members 2 sequentially through the copper material 4 can be obtained.

  In addition, the electronic device S of the present embodiment can be obtained by mounting electronic components on the circuit member 2 in the circuit boards 10 to 30 obtained by the above-described manufacturing method. Needless to say, a heat radiating member may be provided on the surface opposite to the surface on which the circuit member 2 of the silicon nitride substrate 1 is provided.

  Examples of the present embodiment will be specifically described below, but the present embodiment is not limited to these examples.

First, silicon nitride powder having a β conversion rate of 10% (that is, an α conversion rate of 90%) and a purity of 98%, and magnesium oxide (MgO) and yttrium oxide (Y Each powder of ₂ O ₃ ) was wet-mixed using a rotary mill, and pulverized until the particle size (D ₉₀ ) became 1 μm or less to obtain a slurry.

  Here, each of the powders was weighed so that the contents of magnesium and yttrium in the silicon nitride substrate were 1.5% by mass and 2.5% by mass, respectively, in terms of oxide.

Next, after adding an organic binder to the obtained slurry, it is passed through a sieve having a mesh size of 250 described in ASTM E 11-61, and then dried using a spray dryer, thereby obtaining silicon nitride. Granules were obtained. Then, using a powder rolling method, the silicon nitride granule was formed into a sheet shape to form a ceramic green sheet, and the ceramic green sheet was cut into a predetermined length to obtain a flat silicon nitride molded body. Moreover, using a cold isostatic pressure method, the pressure was set to 150 MPa, and a thick silicon nitride-based molded body having an outer dimension of the silicon nitride substrate of 60 mm × 60 mm × 20 mm was obtained.

  The flat silicon nitride molded body obtained here is for evaluating the bonding strength between the circuit member and the silicon nitride substrate, and the thick silicon nitride molded body is formed of the silicon nitride substrate. It is for evaluating mechanical strength.

  Next, each of the primary raw material and each boron nitride powder having a rhombohedral or hexagonal crystal structure is prepared, and the addition amount of the boron nitride powder is as shown in Table 1, with the remainder being the primary raw material. A paste added to a solvent such as ethanol together with a binder was applied by screen printing and dried at a temperature of 80 ° C.

Then, a graphite resistance heating element is installed in a state in which a plurality of pastes and dried silicon nitride-based molded bodies are stacked inside a mortar made of a silicon nitride-based sintered body having a relative density of 75%. It was fired in a baking furnace. At this time, a common material having the same composition as that of the silicon nitride-based molded body of 6 parts by mass was disposed around the silicon nitride-based molded body with respect to 100 parts by mass of the silicon nitride-based molded body.

Regarding the firing conditions, the temperature was raised in a vacuum atmosphere from room temperature to 500 ° C., and then nitrogen gas was introduced to maintain the nitrogen partial pressure at 100 kPa. And the temperature in the firing furnace is raised and Table 1
Was held for 5 hours. Then, by cooling at a temperature drop rate of 200 ° C./hour, the sample No. 1 which is a silicon nitride substrate is used. 1-9 were obtained.

  Then, the content of each component on the surface that becomes the joint surface with the metal is determined by using XRD, then determining the content of the element using XRF, and the content of the identified component. Table 1 shows only the boron nitride content.

  Here, the sample No. 1 in which only rhombohedral or hexagonal boron nitride was identified using XRD. Except for 8, the boron nitride content determined by the above-described method was used as the rhombohedral or hexagonal boron nitride content. On the other hand, sample No. With respect to the crystal No. 8, since rhombohedral and hexagonal boron nitride were identified, the surface was polished by 50 μm in the depth direction from the above surface. The mass percentages of the rhombohedral and hexagonal crystals were determined and calculated by multiplying the boron nitride content by the mass percentage. Table 1 shows the contents of the rhombohedral and hexagonal crystals.

Next, the silicon nitride substrate was heat-treated at 850 ° C. to remove organic substances and residual carbon adhering to the surface of the silicon nitride substrate. A paste-like brazing material was applied by screen printing to a portion corresponding to the arrangement of the circuit members on the surface of the heat-treated silicon nitride substrate, and then dried at 135 ° C.

Thereafter, a circuit member made of oxygen-free copper is placed in the dry brazing material existing area, and heated in a vacuum atmosphere at 840 ° C., so that the circuit member is attached to the surface of the silicon nitride substrate via the bonding layer. A bonded circuit board was obtained.

  Then, the bonding strength between the circuit member and the silicon nitride substrate was evaluated by measuring the peel strength between the silicon nitride substrate and the circuit member in accordance with JIS C 6481-1996.

Further, a test piece having a thickness, width and length of 3 mm, 4 mm and 50 mm, respectively, was cut out from a silicon nitride substrate having an outer dimension of 60 mm × 60 mm × 20 mm, and JIS 1601-2008 (ISO 14704: 2000 (MOD)). ), The four-point bending strength at room temperature was determined. Table 1 shows the results.
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As shown in Table 1, Sample No. No. 1 has a peeling strength of 29 KN / m. 7 to 9 had a 4-point bending strength value of less than 900 MPa. In contrast, sample no. In Nos. 2 to 6, large values were obtained in the four-point bending strength and the peel strength, and rhombohedral boron nitride was present on the surface, and out of 100% by mass of all components on the surface, rhombohedral nitridation. It has been found that when the boron content is 5% by mass or more and 20% by mass or less, the bonding strength with the metal can be improved while having excellent mechanical strength.

Sample No. 1 of Example 1 In the same manner as the method shown in Example 1, the zirconium oxide powder as the second additive component was added to the powder used in No. 4 in the addition amount shown in Table 2 out of a total of 100% by mass of these powders. Silicon nitride granules were obtained.

  Then, using a powder rolling method, the silicon nitride granule was formed into a sheet shape to form a ceramic green sheet, and the ceramic green sheet was cut into a predetermined length to obtain a flat silicon nitride molded body.

Further, in order to evaluate the mechanical strength of the silicon nitride substrate, a cold isostatic pressure method is used, the pressure is set to 150 MPa, and the silicon nitride substrate has a thickness of 60 mm × 60 mm × 20 mm. A silicon nitride-like molded body was obtained.

  Thereafter, the same method as shown in Example 1 was used, and the sample No. 10 to 16 silicon nitride substrates were obtained. The firing temperature was 1670 ° C. for all samples.

  As a result of identifying the components using XRD, it was confirmed that silicon nitride and rhombohedral boron nitride were present on the surface of each sample, and zirconium nitride was present in the XRD confirmation in the cross section. .

Moreover, the content of zirconium in the cross section of each sample was determined using XRF, and converted to the content of zirconium nitride.

Further, a test piece having a thickness, width and length of 3 mm, 4 mm and 50 mm, respectively, was cut out from a silicon nitride substrate having an outer dimension of 60 mm × 60 mm × 20 mm, and JIS R 1601-2008 (ISO 14704: 2000 (MOD )), 4 point bending strength S ₀ at room temperature and JIS
In accordance with R 1604-2008 (ISO 17565: 2003 (MOD)), the four-point bending strength S ₁ at 800 ° C. was measured. And the reduction | decrease rate (DELTA) S of 4-point bending strength was calculated | required by the following formula. ΔS = (S ₀ −S ₁ ) / S ₀ × 100 (1)

Moreover, in order to evaluate the strength of dielectric breakdown of each sample, the strength of dielectric breakdown (MV / m) of each sample was determined in accordance with JIS C 2110-1-2010 (IEC 60243-1 (1998)). It was measured.
The external dimensions of each sample, the voltage applied to each sample, the pressure increase rate and the frequency were 25 mm × 25 mm × 0.32 mm, 3.5 kV, 0.5 kV / second, and 60 Hz, respectively. Moreover, the material of the electrode arranged in the thickness direction of each sample was brass, and silicone oil was used as the surrounding medium of each sample. The results are shown in Table 2.

As shown in Table 2, Sample No. In Nos. 11 to 15, the 4-point bending strength at 800 ° C. was 820 MPa or more, the decrease in the 4-point bending strength was small, and the dielectric breakdown strength was 24 MV / m or more. From this result, zirconium nitride is present in the grain boundary phase, and out of 100 mass% of all components constituting the sintered body, the content of zirconium converted to nitride is 0.2 mass% or more and 1.0 mass% or less. As a result, it was found that the film had excellent mechanical strength even at high temperatures while having dielectric breakdown characteristics capable of withstanding high voltages.

  Sample No. 1 of Example 1 was adjusted so that the molar ratio of the magnesium oxide powder and the aluminum nitride powder was 1: 1. Aluminum nitride powder was added to the powder used in Step 4, and silicon nitride granules were obtained by the same method as shown in Example 1.

Then, using the cold isostatic pressure method, the pressure is 150 MPa, and the outer dimension of the silicon nitride substrate is 60.
A silicon nitride-based molded body having a size of mm × 60 mm × 20 mm was obtained.

Thereafter, the sample No. 1 which is the silicon nitride substrate by the same method as shown in Example 1 was used. 17 was obtained. The firing temperature was 1670 ° C. As a comparative example, the sample No. 4 was prepared as Sample No.18.

  And when the presence or absence of the oxynitride of magnesium and aluminum was confirmed using XRD about the cross section of each sample, sample no. Sample No. 18 was not confirmed but confirmed. The composition formula of 17 is shown in Table 3.

Then, test pieces having a thickness, width and length of 3 mm, 4 mm and 50 mm, respectively, were cut out from the silicon nitride substrate, and JIS R 1604-2008 (ISO 17565: 2003 (MOD)).
In conformity with the intensity S ₂ 4-point bending at 1200 ° C. were measured. The values in Table 3.

  As shown in Table 3, Sample No. Sample No. 17 Larger value is obtained in 4-point bending strength at 1200 ° C than 18 and the presence of oxynitride of magnesium and aluminum in the grain boundary phase makes it excellent in mechanical strength even at high temperatures. all right.

1: Silicon nitride substrate 2: Circuit member 3: Bonding layer 4: Copper material 5: Electronic component
10, 20, 30: Circuit base

Claims (5)

  The rhombohedral is composed of a sintered body having silicon nitride as a main component and having a surface serving as a bonding surface with a metal, and rhombohedral boron nitride is present on the surface, and out of 100% by mass of all components on the surface. A silicon nitride substrate, wherein the content of crystalline boron nitride is 5% by mass or more and 20% by mass or less.   Zirconium nitride is present in the grain boundary phase between the silicon nitride crystals, and out of 100 mass% of all components constituting the sintered body, the content of zirconium converted to nitride is 0.2 mass% or more. It is 1.0 mass% or less, The silicon nitride substrate of Claim 1 characterized by the above-mentioned.   3. The silicon nitride based substrate according to claim 1, wherein magnesium and aluminum oxynitrides are present in the grain boundary phase. 4.   A circuit board comprising a circuit member bonded to the surface of the silicon nitride substrate according to any one of claims 1 to 3.   An electronic device comprising an electronic component mounted on the circuit member in the circuit board according to claim 4.

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