JP6396817B2 - Silicon nitride substrate, circuit board including the same, and electronic device - Google Patents

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.

  As a circuit board including a circuit member on which electronic components are mounted, for example, a circuit board mainly composed of copper is bonded to the main surface of an insulating silicon nitride substrate.

As such a silicon nitride substrate, for example, in Patent Document 1, a rare earth metal is converted to oxide in an amount of 2.0 to 17.5% by weight, Mg is converted into an oxide in an amount of 0.3 to 3.0% by weight, and an impurity cation element is used. Al, Li, Na, K, Fe, Ba, Mn, B in a total of 0.3 wt% or less,
A silicon nitride substrate (high thermal conductivity silicon nitride sintered body) composed of a silicon nitride crystal and a grain boundary phase and having a ratio of the crystalline compound phase in the grain boundary phase to the whole grain boundary phase of 20% or more has been proposed. .

JP 2000-34172 A

However, when the ratio of the crystalline compound phase in the grain boundary phase to the entire grain boundary phase is as high as 20% or more as in the silicon nitride substrate proposed in Patent Document 1, a crystalline compound phase is generated in the sintering process. Due to volume shrinkage in the process, many voids are likely to be generated at the grain boundaries. Since the voids generated at the grain boundaries appear as white spots when the main surface of the silicon nitride substrate is magnified 100 times, the voids may be described as white spots in the following.

  For example, when a circuit member is joined using a silicon nitride substrate in which many white spots are confirmed, the amount of the metal component that constitutes the circuit member invades into the white spot, and the silicon nitride substrate is insulated. There was a problem that the yield strength decreased. Conversely, when the white spot is small or the number is small, the amount of the metal component that penetrates into the white spot is small and the resulting anchor effect is small, so that there is a problem that the bonding strength is lowered.

  The present invention has been devised in view of the above-mentioned problems, and can provide a silicon nitride substrate having high dielectric strength and a circuit substrate and an electronic device having the same, which can increase the bonding strength with a circuit member. It is intended to provide.

The silicon nitride substrate of the present invention is a silicon nitride substrate in which circuit members are provided on the main surface, and 50 white spots having a circle equivalent diameter of 2 μm or more and 30 μm or less per 1 mm ^{2 of the} main surface. More than 20
It is characterized by zero or less.

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

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

  According to the silicon nitride substrate of the present invention, the bonding strength with the circuit member can be increased and a silicon nitride substrate having a high dielectric strength can be obtained.

  Further, according to the circuit board of the present invention, it is possible to obtain a highly reliable circuit board that can be used for a long period of time due to high bonding strength and high dielectric strength.

  Further, according to the electronic device of the present invention, it is possible to provide a highly reliable electronic device that can be used for a long period of time.

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 ′ in (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 in (a). Another example of the circuit board of this embodiment is shown, (a) is a plan view, and (b) is a cross-sectional view taken along line C-C ′ in (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, a silicon nitride substrate of this embodiment, a circuit board including the same, and an electronic device will be described with reference to the drawings. Note that the thickness of each component in the cross-sectional view is partially exaggerated.

  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 the present embodiment shown in FIG. 1 is provided with a circuit member 2 on the main surface side of the silicon nitride substrate 1 of the present embodiment. In addition, in the circuit board 10 shown in FIG. 1, the silicon nitride board | substrate 1 and the circuit member 2 have shown the example joined directly. In the following description, the circuit member 2 is first described, and then the silicon nitride substrate 1 is described.

In the circuit board 10 of this embodiment, the circuit member 2 contains a metal component as a main component. The main component in the circuit member 2 is 50% by mass out of 100% by mass of all components constituting the circuit member 2.
The component which occupies the above.

More specifically, it is preferable that the metal component is copper, and it is preferable that the content of copper is as high as 90% by mass or more, and is made of any one of oxygen-free copper, tough pitch copper, and phosphorus deoxidized copper, 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. Therefore, the bonding strength between the silicon nitride substrate 1 and 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, the silicon nitride substrate 1 of this embodiment will be described. In the silicon nitride substrate 1 of this embodiment, 50 or more and 200 or less white spots having an equivalent circle diameter of 2 μm or more and 30 μm or less exist per 1 mm ^{2 of the} main surface.

  By satisfying such a configuration, when the circuit member 2 is joined to the main surface of the silicon nitride substrate 1, the metal component constituting the circuit member 2 penetrates into the white spots, and a strong anchor effect is obtained. Therefore, the bonding strength can be increased, and the amount of the metal component that penetrates into the white spot is not too large, so that it has a high dielectric strength.

On the other hand, when the circle equivalent diameter of the white spot is less than 2 μm or the number of white spots per 1 mm ^{2 of} the main surface is less than 50, the amount of the metal component constituting the circuit member 2 entering the white spot is small. Since the obtained anchor effect is small, the bonding strength is lowered. In addition, since the crystal grains of silicon nitride are columnar and needle-shaped, and the crystal grains are three-dimensionally entangled, when the circle equivalent diameter of the white spot exceeds 30 μm, the white spot As a result, the depth of the void that is visible as is likely to be deep, and a large amount of metal components are likely to enter, so that the dielectric strength decreases. Further, even when the number of white spots per 1 mm ^{2 of} the main surface exceeds 200, a large amount of metal components are likely to enter, so that the dielectric strength is reduced and dielectric breakdown is likely to occur.

  Moreover, according to the silicon nitride substrate 1 of the present embodiment, it is preferable that the average value of the distances between adjacent white spots is 4 μm or more.

  Thus, when the average value of the distances between adjacent white spots is 4 μm or more, the discharge due to the metal component that has invaded each white spot is suppressed, so that a reduction in dielectric strength can be suppressed. The average value of the distance between adjacent white spots is the average value of the distance between the centroids of each white spot and the average value of the circle equivalent diameters of the white spots within the measurement range. It is the value obtained by subtracting the average value of the equivalent circle diameter from the average value.

  Further, according to the silicon nitride substrate 1 of the present embodiment, it is preferable that the degree of unevenness at the white point is 1.1 or more and 2.9 or less.

  Here, the degree of unevenness indicates the degree of unevenness of the outline of the white point, and the larger the numerical value, the more unevenness exists in the outline. And, when the unevenness degree of the white spot is 1.1 or more and 2.9 or less, in the application of the brazing material to join the circuit member 2 or the like, a defect is generated from the unevenness of the outline of the white spot, and the member to be applied is damaged, The bonding strength with the circuit member 2 can be improved without remaining in the circuit member 2.

  Further, according to the silicon nitride substrate 1 of the present embodiment, it is preferable that the circularity at the white point is 0.7 or more and 0.9 or less.

  Here, as the circularity is larger, the outline of the white spot is closer to a perfect circle, and the perfect circle has a circularity of 1. And when the circularity at the white spot is 0.7 or more and 0.9 or less, in the application of the brazing material for joining the circuit member 2 or the like, the white spot outline is uneven, thereby damaging the member to be applied, The bonding strength with the circuit member 2 can be improved without remaining in the circuit member 2.

Next, how to obtain the number per 1 mm ² of white spots having an equivalent circle diameter of 2 μm or more and 30 μm or less, the degree of unevenness of the white spots, and the circularity will be described. First, the main surface of the silicon nitride substrate 1 is polished and processed into a mirror surface. Then, the mirror-polished surface is used as a measurement surface, and is observed with an optical microscope at a magnification of 100 times. For example, the area is 1.2 mm ² (the horizontal length is 1.2 mm, and the vertical length is 1 mm). ) Is taken with a CCD camera. Next, using the photographed image, image analysis software “A Image-kun” (registered trademark, manufactured by Asahi Kasei Engineering Co., Ltd.) and image analysis software “A Image-kun” will be referred to as Asahi Kasei Engineering Co., Ltd. ) The image analysis software made by the above method is used to analyze the number of white spots with an equivalent circle diameter of 2 μm or more and 30 μm or less per 1 mm ² , the degree of unevenness and circularity of the white spots. Can be requested. In calculating the number per 1 mm ² of white spots having an equivalent circle diameter of 2 μm or more and 30 μm or less, it is necessary to convert the number per 1 mm ² .

  In addition, the average value of the distance between adjacent white spots is first analyzed by a technique called particle analysis using the image analysis software “A image kun” using the same image as described above, thereby obtaining a circle of white spots. The average value of the equivalent diameters is obtained, and then the average value of the distances between the centroids of the white spots is obtained by analyzing by a technique called the distance between centroids of dispersion measurement. Then, by subtracting the average value of the circle equivalent diameters of the white points from the average value of the distances between the centroids of the white points, the average value of the distances between the adjacent white points can be obtained.

As setting conditions in these methods of the center-of-gravity distance method for particle analysis and dispersion measurement, for example, the brightness is bright, the binarization method is manual, the small figure removal area is 0 μm ² , and the brightness of the image The threshold value, which is an index indicating the brightness, may be 0.8 to 2 times the peak value of the histogram indicating the brightness of each point (each pixel) in the image.

In addition, according to the silicon nitride substrate 1 of the present embodiment, rhombohedral boron nitride is present on the main surface, and the rhombohedral boron nitride out of the total 100 mass% of all components constituting the main surface. Content is 5% by mass
The content is preferably 20% by mass or less.

  By satisfying such a configuration, the silicon nitride substrate 1 of the present embodiment can improve the bonding strength with the metal component constituting the circuit member 2 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. In addition, the rhombohedral boron nitride and silicon nitride are firmly bonded, and the bonded crystal has a complicated shape, so that the bonding strength can be improved.

  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.

Next, how to determine the content of rhombohedral boron nitride out of a total of 100 mass% of all the components constituting the main surface of the silicon nitride substrate 1 will be described. The sampling for determining the content of rhombohedral boron nitride is for a powder cut to a depth of 30 μm from the main surface. Then, using the obtained powder as a sample, the quantitative value obtained by the Rietveld method using an X-ray diffractometer (XRD) is 100% by mass in total of all the components constituting the main surface of the silicon nitride substrate 1. The content of rhombohedral boron nitride is used.

The silicon nitride substrate 1 of the present embodiment is mainly composed of silicon nitride. Here, the main component is 63% of silicon nitride out of 100% by mass of all components constituting the sintered body. % Or more. In particular, when silicon nitride is contained in an amount of 70% by mass or more, the mechanical strength tends to be higher, which is preferable.

The mechanical strength of the silicon nitride substrate 1 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 1 of the embodiment has a four-point bending strength of 900 MPa or more. Further, the bonding strength with the metal component in the silicon nitride substrate 1 of the present embodiment can be measured according to JIS C 6481-1996.

  Further, the silicon nitride substrate 1 of the present embodiment is mainly composed of silicon nitride, and, for example, magnesium, rare earth metal (RE), and aluminum are 2% by mass to 6% by mass and 12% by mass in terms of oxides, respectively. It is preferably contained in an amount of 16% by mass or less and 0.1% by mass or more and 0.5% by mass or less.

The contents of magnesium, rare earth metal (RE) and aluminum in terms of oxides are determined using Mg, RE using an X-ray fluorescence analyzer (XRF) or an inductively coupled plasma (ICP) emission spectrometer (ICP). And Al content can be obtained and converted to MgO, RE ₂ O ₃ and Al ₂ O ₃ , respectively. The content can also be determined by an energy dispersive X-ray analyzer (EDX). Furthermore, for silicon nitride, the Si content is obtained by XRF or ICP and converted to Si ₃ N ₄ , or the N content is obtained and converted to Si ₃ N ₄ using a nitrogen analyzer. However, it can also be obtained by subtracting the content other than Si and N from 100% by mass.

  When the content of magnesium oxide in terms of oxide is 2% by mass or more and 6% by mass or less, densification can be achieved even at a low firing temperature by the sintering promoting action of the magnesium oxide, which is excellent. The silicon nitride substrate 1 having mechanical characteristics can be obtained. In addition, it is preferable that content in conversion of the oxide of magnesium is 3 mass% or more and 5 mass% or less.

  In addition, when the content of the rare earth metal in terms of oxide is 12% by mass or more and 16% by mass or less, due to the high affinity with oxygen, a large amount of oxygen is taken into the liquid phase between the silicon nitride powders, and nitriding Since silicon grain growth is promoted, the silicon nitride substrate 1 having excellent heat dissipation characteristics can be obtained. In addition, the content of the rare earth metal in terms of oxide is preferably 13% by mass or more and 15% by mass or less.

  Moreover, when the content of aluminum in terms of oxide is 0.1% by mass or more and 0.5% by mass or less, the mechanical strength of silicon nitride substrate 1 can be improved while suppressing a decrease in thermal conductivity. The content of aluminum in terms of oxide is more preferably 0.2% by mass or more and 0.4% by mass or less.

The dielectric strength of the silicon nitride substrate 1 can be evaluated by the strength of dielectric breakdown (MV / m) measured according to JIS C 2141-1992 (IEC 672-2 (1980)). The silicon nitride substrate 1 of this embodiment has a dielectric breakdown strength of 20 MV / m or more.

The electrical properties of the silicon nitride substrate 1, a volume resistivity, a is at normal temperature 10 ¹⁴ Ω · cm or more and 300 ° C. at 10 ¹² Ω · cm or more. This volume resistivity is JIS

What is necessary is just to measure based on C2141-1992. However, when the silicon nitride substrate 1 is small and cannot be made the size specified by JIS C 2141-1992 from the silicon nitride substrate 1, the evaluation is made using the two-terminal method, and the result is the above numerical value. Is preferably satisfied.

  Since the circuit board 10 of the present embodiment includes the silicon nitride substrate 1 of the present embodiment having high dielectric strength and bonding strength, it can be used for a long period of time and has high reliability.

  Next, FIG. 2 shows another example of the circuit board of the present embodiment, where (a) is a plan view and (b) is a cross-sectional view taken along line B-B ′ in (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 4. By joining the circuit member 2 via the brazing material to be the joining layer 4, the thick circuit member 2 can be easily joined to the silicon nitride substrate 1 via the joining layer 4.

  As the brazing material to be the bonding layer 4, 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, (a) is a plan view, and (b) is a sectional view taken along line C-C ′ in (a).

  The circuit board 30 of the example shown in FIG. 3 is provided with the circuit member 2 on the main surface side of the silicon nitride substrate 1 of the present embodiment, and sequentially through the bonding layer 4 and the copper material 5 from the silicon nitride substrate 1 side. Are joined.

  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 5 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 5 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 5 is preferably composed of any one of oxygen-free copper, tough pitch copper and phosphorous deoxidized copper having a large copper content, and in particular, the oxygen content of oxygen-free copper. Is preferably composed of any one of linear crystalline oxygen-free copper, monocrystalline high-purity oxygen-free copper, and vacuum-melted copper having a thickness of 99.995% by mass or more, and the thickness is preferably 0.1 mm or more and 0.6 mm or less, for example.

  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 6 such as a semiconductor element is mounted on the circuit member 2 of the circuit board 10 of this embodiment.

  According to the electronic apparatus S of the example shown in FIG. 4, since the electronic component 6 is mounted on the circuit board 10 having high dielectric strength and high bonding strength with the circuit member 2, the electronic apparatus having high reliability. S. In addition, although the circuit member 2 was illustrated in the case of using one, a plurality of circuit members 2 may be used.

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

First, silicon nitride powder having a β conversion rate of 20% or less and a purity of 98% or more, and magnesium oxide (MgO) and rare earth metal oxides (for example, Sc ₂ O ₃ , Y ₂ ) as additive components. _{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 Each powder of O ₃ , Ho ₂ O ₃ , Er ₂ O ₃ , Tm ₂ O ₃ , Yb ₂ O ₃ and Lu ₂ O ₃ ), a barrel mill, a rotating mill, a vibration mill, a bead mill, Using a mixing device such as a sand mill and an agitator mill, the mixture is wet-mixed with water and pulverized to produce a slurry.

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

In addition, the circle equivalent diameter of the white spot existing in the silicon nitride substrate 1 and the number per unit area can be adjusted by the calcium content. Specifically, in order to obtain a silicon nitride substrate 1 having 50 or more and 200 or less per 1 mm ² of a white spot having a circle equivalent diameter of 2 μm or more and 30 μm or less, it is included in the silicon nitride substrate 1. What is necessary is just to add a calcium powder so that content of calcium to become 2 mass ppm or more and 100 mass ppm or less.

  Further, in order to obtain the silicon nitride substrate 1 having an average distance between adjacent white spots of 4 μm or more, 2.5 parts of dispersant is added to 100 parts by mass of the silicon nitride powder and the additive component powders in total. The slurry may be prepared by adding parts by mass, wet-mixing with water, and pulverizing.

  In addition, in order to obtain the silicon nitride substrate 1 having the unevenness of white spots of 1.1 or more and 2.9 or less, the mixing / pulverization time by the mixing device may be set to 24 hours or more and 72 hours or less, for example.

  Furthermore, in order to obtain the silicon nitride substrate 1 having a white dot circularity of 0.7 or more and 0.9 or less, the mixing / pulverization time by the mixing device may be set to 36 hours or more and 60 hours or less, for example.

Further, as another composition example, nitriding containing magnesium, rare earth metal and aluminum in terms of oxides of 2% by mass to 6% by mass, 12% by mass to 16% by mass and 0.1% by mass to 0.5% by mass, respectively. To make the silicon substrate 1, when the total of the silicon nitride powder and the total of these additive component powders is 100 mass%, the additive component magnesium oxide (Mg
O) powder is 2 to 6% by mass, rare earth metal oxide powder is 12 to 16% by mass, aluminum oxide (Al ₂ O ₃ ) powder is 0.1 to 0.5% by mass, and the balance is silicon nitride. What is necessary is just to weigh.

The ball used for mixing and pulverizing the powder of silicon nitride and additive components 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 silicon nitride and additive component powders are pulverized until the particle size (D ₉₀ ) is ₉₀ μm or less when the total volume of the particle size distribution curve is 100%. Is preferable from the viewpoint of improving the sinterability. The particle size distribution obtained by mixing and grinding can be adjusted by the outer diameter of the ball, the amount of the ball, the viscosity of the slurry, the grinding time, and the like.

Next, after adding an organic binder to the resulting slurry and mixing, the slurry was passed through a sieve having a particle size number of 200 described in ASTM E 11-61 or a mesh finer than this mesh, and then dried. Granules mainly composed of silicon nitride (hereinafter referred to as silicon nitride granules) are obtained. 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 is obtained by using a pressure molding method and filling the mold with silicon nitride granules and then pressurizing.

Next, the obtained silicon nitride-based molded body is placed in a mortar made of a silicon nitride-based sintered body having a relative density of 55% to 95%, and a firing furnace in which a graphite resistance heating element is installed Is fired. In addition, at this time, a silicon nitride-based molded body having an amount of not less than 2 parts by mass and less than 10 parts by mass and a material similar in composition to 100 parts by mass of the silicon nitride-based molded body are disposed around the silicon nitride-based molded body. By disposing and firing, volatilization of the components contained in the silicon nitride-based molded body can be suppressed.

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 1750 ° C. or lower 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./hour or lower. The silicon nitride substrate 1 can be obtained.

Further, rhombohedral boron nitride is present on the main surface, and the content of rhombohedral boron nitride is 5% by mass or more and 20% by mass or less among the total of 100% by mass of all components constituting the main surface. In order to obtain a silicon nitride substrate, first, silicon nitride, additive components, and rhombohedral boron nitride powder were added to a solvent such as ethanol together with a binder on the main surface of the obtained silicon nitride molded body. The paste is applied by screen printing and dried at a temperature of 60 ° C to 100 ° C. Note that the amount of rhombohedral boron nitride powder added may be 5% by mass or more and 20% by mass or less, out of a total of 100% by mass of the above powders.

Then, after maintaining the temperature of the firing furnace at 1640 ° C. or more and less than 1700 ° C. for 4 hours or more and 10 hours or less, the main surface of the silicon nitride substrate is cooled by a temperature decreasing rate of 170 ° C./hour or more and 230 ° C./hour or less. In which rhombohedral boron nitride is present, and the content of rhombohedral boron nitride is 5% by mass or more and 20% by mass or less, out of 100% by mass of all components in the main surface. it can. Note that at 1700 ° C. or higher, rhombohedral boron nitride is easily changed to hexagonal boron nitride.

  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, a circuit member 2 mainly composed of copper is disposed on the main surface side of the silicon nitride substrate 1. Thereafter, heating is performed at 1065 ° C. or higher and 1085 ° C. or lower in a nitrogen atmosphere, and at the same time, a pressure of 30 MPa or higher is applied to obtain a circuit substrate 10 in which the circuit member 2 is directly bonded to the main surface side of the silicon nitride substrate 1. be able to.

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, titanium, zirconium, which becomes the bonding layer 4 on the main surface of the silicon nitride substrate 1, A silver (Ag) -copper (Cu) alloy paste-like brazing material containing at least one selected from hafnium and niobium is applied by any one of a screen printing method, a roll coater method, a brush coating method, and the like. On this, the circuit member 2 which has copper as a main component is arrange | positioned. The pasty brazing material may contain one or more selected from molybdenum, tantalum, osmium, rhenium and tungsten. Then, heat in a vacuum atmosphere at 800 ° C or higher and 900 ° C or lower, and simultaneously 30
By applying a pressure equal to or higher than MPa, a circuit board 20 in which the circuit member 2 is joined to the main surface side of the silicon nitride substrate 1 via the brazing material 4 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 paste of silver (Ag) -copper (Cu) alloy containing at least one selected from titanium, zirconium, hafnium and niobium, which becomes the bonding layer 4, is formed on the main surface of the silicon nitride substrate 1. The brazing material is applied by any one of a screen printing method, a roll coater method and a brush coating method. The pasty brazing material may also contain one or more selected from molybdenum, tantalum, osmium, rhenium and tungsten. And the thin copper material 5 is each arrange | positioned on a brazing material. Thereafter, the copper material 5 is bonded to the main surface side of the silicon nitride substrate 1 through the bonding layer 4 by heating at 800 ° C. or more and 900 ° C. or less.

  Then, after polishing the surface of the copper material 5 facing the circuit member 2, the circuit member 2 is disposed on the copper material 5. Subsequently, a circuit is formed on the main surface side 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. A circuit board 30 in which the member 2 is bonded through the bonding layer 4 and the copper material 5 in this order can be obtained.

  In the description of the present embodiment, the circuit boards 10 to 30 and the electronic device S provided with the circuit member 2 on the main surface side of the silicon nitride substrate 1 have been described. However, the circuit member 2 is provided on the silicon nitride substrate 1. A heat radiating member may be provided on the main surface opposite to the main surface.

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

First, a silicon nitride powder having a β conversion rate of 10% (that is, an α conversion rate of 90%) and a purity of 98%, magnesium oxide (MgO), erbium oxide (Er ₂ O ₃ ), oxidation as additive components Each powder of aluminum (Al ₂ O ₃ ) and molybdenum oxide (MoO ₃ ) was wet-mixed using a rotary mill, and mixed and pulverized until the particle size (D ₉₀ ) became 1 μm or less to obtain a slurry. At this time, calcium powder having the contents shown in Table 1 was also added.

Here, the content of each of the above powders is 2.5% by mass and 14% by mass, respectively, in terms of oxides for each content of magnesium, erbium, aluminum, and molybdenum in the silicon nitride substrate.
, 0.3% by mass and 0.5% by mass, respectively.

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.

Next, the obtained silicon nitride-based molded body was placed in a mortar made of a silicon nitride-based sintered body having a relative density of 75%. At this time, the common material containing components such as silicon nitride, magnesium oxide and rare earth metal oxide is added in an amount of 6 parts by mass with respect to 100 parts by mass of the silicon nitride based molded body. In a state of being arranged around, it was fired in a firing furnace provided with a graphite resistance heating element.

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. Then raise the temperature in the firing furnace to 1690
Hold at 5 ° C. for 5 hours. Then, by cooling at a cooling rate of 200 ° C./hour, the sample No. 1 to 7 silicon nitride substrates were obtained.

Then, in order to measure the number per 1 mm ² of white spots having an equivalent circle diameter of 2 μm or more and 30 μm or less existing on the main surface of each sample, first, the surface obtained by polishing the main surface into a mirror surface is measured. And observed with an optical microscope at a magnification of 100 times, the area is 1.2 mm ² (the lateral length is 1.2 mm
This is obtained by analyzing the range of 1 mm in the vertical direction with a CCD camera and analyzing it with a method called particle analysis using image analysis software “A Image-kun”. Converted to the number per 1 mm ² did.

Here, as setting conditions of this method, the brightness is bright, the binarization method is manual, the small figure removal area is 0 μm ² , and a threshold value that is an index indicating the brightness of the image is set to each point ( It was set to 1.2 times the peak value of the histogram indicating the brightness of each pixel).

Next, in order to evaluate the dielectric strength of each sample, the dielectric breakdown strength (MV / m) of each sample was measured in accordance with JIS C 2141-1992 (IEC 672-2 (1980)). The values are shown in Table 1. In addition, the material of the electrode formed in each sample was brass, and silicone oil was used as the surrounding medium of each sample.

Next, the silicon nitride substrate was heat-treated at 850 ° C. to remove organic substances and residual carbon adhering to the main 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 main surface of the heat-treated silicon nitride substrate, and then dried at 135 ° C. to form a bonding layer.

Then, a circuit member made of oxygen-free copper is disposed on the main surface of the silicon nitride substrate so as to be in contact with the bonding layer, and is heated at 840 ° C. in a vacuum atmosphere so that the circuit member is nitrided through the bonding layer. A circuit board bonded to the silicon substrate was obtained.

  Moreover, the bonding strength between the circuit member and the silicon nitride substrate was evaluated by measuring the peel strength (kN / m) between the silicon nitride substrate and the circuit member in accordance with JIS C 6481-1996. The results are shown in Table 1.

As shown in Table 1, Sample No. Nos. 2 to 6 have 50 or more and 200 or less white spots with a circle equivalent diameter of 2 μm or more and 30 μm or less per 1 mm ^{2 of the} main surface, so that the bonding strength with the circuit member is high and high insulation. It was found to be a silicon nitride substrate having proof stress.

As in Example 1, silicon nitride powder and magnesium oxide powder, erbium oxide powder, aluminum oxide powder, and molybdenum oxide powder were used as additive components, and weighed in the same amount as in Example 1. In addition, calcium powder having a content of 5 ppm out of 100% by mass of all components of the silicon nitride substrate is added, wet-mixed using a rotary mill, and pulverized until the particle size (D ₉₀ ) is 1 μm or less. To make a slurry. In this pulverization, the amount of dispersant (carboxyl group-containing water-soluble polymer) shown in Table 2 was added to 100 parts by mass of the silicon nitride powder and each of the additive component powders. For the subsequent steps, the same method as shown in Example 1 was used. 8-12 silicon nitride substrates were obtained.

  In order to obtain an average value of the distance between adjacent white spots, first, using an image photographed by the same method as in the first embodiment, analysis is performed by a method called particle analysis by image analysis software “A image kun”. Then, the average value of the circle equivalent diameters of the white spots was obtained, and then the average value of the distances between the center of gravity of the white spots was obtained by analyzing by a method called the center-of-center distance method of dispersion measurement. And the average value of the distance between adjacent white spots was calculated | required by subtracting the average value of the circle equivalent diameter of a white spot from the average value of the distance between the gravity centers of a white spot. The setting conditions were the same as in Example 1.

  Moreover, the dielectric strength of each sample measured the strength of dielectric breakdown (MV / m) using the same method as the method shown in Example 1. The results are shown in Table 2.

  As shown in Table 2, Sample No. Nos. 9 to 12 have large dielectric breakdown strength values, and the average value of the distance between adjacent white spots is 4 μm or more, indicating that the dielectric breakdown strength is high. It was.

As in Example 1, silicon nitride powder and magnesium oxide powder, erbium oxide powder, aluminum oxide powder, and molybdenum oxide powder were used as additive components, and weighed in the same amount as in Example 1. In addition, calcium powder having a content of 5 ppm out of 100% by mass of all components of the silicon nitride substrate is added, wet-mixed using a rotary mill, and pulverized until the particle size (D ₉₀ ) is 1 μm or less. To make a slurry. The mixing / pulverizing time by the rotary mill was as shown in Table 2. For the subsequent steps, the same method as shown in Example 1 was used. 13 to 19 silicon nitride substrates were obtained.

  And using the image image | photographed by the method similar to Example 1, it analyzed by the method of particle | grain analysis by image analysis software "A image kun", and calculated | required the unevenness | corrugation degree of a white spot. The setting conditions were the same as in Example 1.

  Further, a circuit board was produced by the same method as shown in Example 1, and the peel strength (kN / m) of the circuit member was determined. The results are shown in Table 3.

  As shown in Table 3, Sample No. 14 to 18, a large value was obtained as the peel strength value, and the unevenness degree of the white spots was 1.1 or more and 2.9 or less, which increases the bonding strength between the silicon nitride substrate and the circuit member. all right.

  Sample No. 4 was prepared in the same manner as in Example 3 except that yttrium oxide powder was used instead of erbium oxide powder, and the mixing and grinding time using a rotary mill was changed to the time shown in Table 4. 20 to 26 silicon nitride substrates were prepared.

  Then, by using an image photographed by the same method as in Example 1 and analyzing by a method of particle analysis using image analysis software “A image kun”, the circularity of the white spot was obtained. The setting conditions were the same as in Example 1.

  Further, a circuit board was produced by the same method as shown in Example 1, and the peel strength (kN / m) of the circuit member was determined. The results are shown in Table 4.

  As shown in Table 4, Sample No. For 21 to 25, a large value is obtained as the peel strength, and the circularity of the white point is 0.7 or more and 0.9 or less, which increases the bonding strength between the silicon nitride substrate and the circuit member. all right.

As in Example 1, silicon nitride powder and magnesium oxide powder, erbium oxide powder, aluminum oxide powder, and molybdenum oxide powder were used as additive components, and weighed in the same amount as in Example 1. In addition, calcium powder having a content of 5 ppm out of 100% by mass of all components of the silicon nitride substrate is added, wet-mixed using a rotary mill, and pulverized until the particle size (D ₉₀ ) is 1 μm or less. To make a slurry.

Next, silicon nitride granules were obtained by the same method as shown in Example 1. Then, using a powder rolling method, a silicon nitride granule was formed into a sheet shape and cut into a predetermined length to obtain a flat silicon nitride molded body. In addition, using the same granule, the outer size of the silicon nitride substrate was 60 mm by the cold isostatic pressing method using a cold isostatic pressure method and the pressure being 150 MPa.
A thick silicon nitride molded body having a size of 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, silicon nitride, additive components, and boron nitride powders each having a rhombohedral or hexagonal crystal structure are prepared, and the content of 100% by mass of all components on the main surface has the values shown in Table 5. like,
Boron nitride powder was weighed, and a paste was prepared in which the balance was added to a solvent such as ethanol together with a binder as the silicon nitride having the above composition ratio and an additional component. And it apply | coated by the screen-printing method and it was made to dry at temperature 80 degreeC.

Next, each molded body was put into a mortar made of a silicon nitride sintered body having a relative density of 75%, and fired at a temperature shown in Table 5 in a firing furnace provided with a graphite resistance heating element. At this time, a common material having the same composition as that of the silicon nitride-based molded body, which is 6 parts by mass with respect to 100 parts by mass of the silicon nitride-based molded body, was disposed around 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. Then, the temperature in the firing furnace was raised and Table 5
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. 27-35 were obtained.

Then, the content of rhombohedral or hexagonal boron nitride out of a total of 100% by mass of all components constituting the main surface of the silicon nitride substrate was determined. As a method of determination, a powder cut to a depth of 30 μm from the main surface is used as a sample, and the quantitative value obtained by the Rietveld method using XRD is 100 masses in total for all components constituting the main surface of the silicon nitride substrate. % Of rhombohedral or hexagonal boron nitride.

  Next, a circuit board was produced by the same method as shown in Example 1, and the peel strength (kN / m) of the circuit member was determined.

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. The results are shown in Table 5.

As shown in Table 5, sample no. In 28 to 32, excellent values were obtained in the four-point bending strength and the peel strength, rhombohedral boron nitride was present on the main surface, and the total amount of all the components constituting the main surface was 100% by mass. Among these, it was found that when the rhombohedral boron nitride content is 5% by mass or more and 20% by mass or less, the bonding strength with the circuit member can be improved while having excellent mechanical strength.

1: Silicon nitride substrate 2: Circuit member 4: Bonding layer 5: Copper material 6: Electronic component
10, 20, 30: Circuit board

Claims (7)

A silicon nitride substrate on which a circuit member is provided on a main surface, wherein there are 50 or more white spots having a circle equivalent diameter of 2 μm or more and 30 μm or less per 1 mm ^{2 of the} main surface. A silicon nitride substrate.   2. The silicon nitride substrate according to claim 1, wherein an average value of distances between adjacent white spots is 4 [mu] m or more.   3. The silicon nitride based substrate according to claim 1, wherein the white spot has an unevenness degree of 1.1 or more and 2.9 or less.   The silicon nitride substrate according to any one of claims 1 to 3, wherein the white point has a circularity of 0.7 to 0.9.   There is rhombohedral boron nitride on the principal surface, and the content of rhombohedral boron nitride is 5% by mass or more and 20% by mass or less, out of a total of 100% by mass of all components constituting the principal surface. The silicon nitride substrate according to claim 1, wherein the silicon nitride substrate is provided.   A circuit board comprising the circuit member on the main surface of the silicon nitride substrate according to any one of claims 1 to 5.   An electronic device comprising an electronic component mounted on the circuit member in the circuit board according to claim 6.

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