JP5773330B2 - Ceramic sintered plate containing uniaxially oriented acicular Si3N4 particles - Google Patents

Description

  The present invention relates to a ceramic sintered plate, and more particularly to a ceramic sintered plate used as a high heat dissipation insulating substrate for controlling a large current and a large voltage that require excellent thermal conductivity and bonding strength.

Conventionally, a power module for supplying power among semiconductor elements has a relatively high calorific value. As a substrate on which the module is mounted, for example, on a ceramic substrate made of AlN, Al ₂ O ₃ , Si ₃ N ₄ , SiC, or the like. In addition, a power module substrate is used in which an aluminum layer is bonded via a brazing material such as an Al—Si system. This aluminum layer becomes a circuit layer by forming a circuit in etching in a later step. After etching, a power module is configured by mounting a power element (electronic component) such as a semiconductor chip on the surface of the circuit layer via a solder material. Among ceramic substrates, Si ₃ N ₄ is excellent in mechanical strength and can avoid problems such as cracking even under severe use conditions such as high temperature and impact, for example, in an automobile engine room. For example, see Patent Document 1 that has attracted attention.

  It is known that a metal plate such as Al is bonded to the lower surface of the ceramic substrate as a heat conductive layer for heat dissipation, and the entire power module substrate is bonded to a heat sink such as a heat sink via the metal plate. It has been.

  A ceramic sintered plate obtained by sintering a ceramic material can be used as the ceramic substrate of the power module substrate described above. For example, a ceramic sintered plate is formed of a matrix having ceramic particles as a base material, and ceramic spherical particles and ceramic plate-like particles dispersed in the matrix (see, for example, Patent Document 2).

  In addition, a process for producing a slurry by adding an organic solvent to a ceramic raw material powder composed of a raw material powder containing seed crystals, and a molding in which a slurry produced from the process is oriented with a specific raw material powder in a magnetic field of 1 Tesla or more There is known a method for producing a ceramic having orientation, comprising a step of producing a body and a step of firing the molded body to obtain a sintered body in which a main crystal phase is oriented in a specific direction (for example, Patent Literature 3)

JP 2009-76649 A Japanese Patent Laid-Open No. 7-82047 JP 2002-121076 A

However, Si ₃ N ₄ as disclosed in the aforementioned Patent Documents 1 and 2 has high strength, but its thermal conductivity is lower (about 70 W / m than that of AlN (about 170 W / m ° C.)). Therefore, in order to obtain high thermal conductivity, it is necessary to reduce the thickness of the substrate, and there is a problem that strength is weakened as a contradiction matter.

  Further, in the ceramic sintered body formed from the matrix using ceramic particles disclosed in Patent Document 2 as a base material and ceramic spherical particles and ceramic plate-like particles dispersed in the matrix, the mechanical properties are improved. However, since many particle interfaces exist in the sintered body, there is a problem that the thermal conductivity is lowered.

  Furthermore, according to the ceramic manufacturing method disclosed in Patent Document 3, the thermal conductivity of the ceramic sintered plate itself can be improved by increasing the orientation, but the ceramic sintered plate and the metal plate as the heat source Since the contact area between the main crystal phase and the metal plate at the contact surface with the metal plate decreases, there is a problem that a desired thermal conductivity cannot be obtained when applied to a power module.

  Therefore, a technical problem to be solved by the present invention, that is, an object of the present invention is to provide a ceramic sintered plate having improved thermal conductivity without reducing the thickness of the substrate.

  In order to achieve the above object, the present inventors have made intensive studies, and the present invention proposes the following means.

That is, the present invention is a ceramic sintered plate in which at least acicular Si ₃ N ₄ particles and granular amorphous Si ₃ N ₄ particles are sintered, and the acicular Si ₃ N ₄ particles are C-axis oriented. And the said subject is solved by the ceramic sintered board whose relative density is 94 to 98%.

Furthermore, the present invention is, in addition to the arrangement, the area ratio in the plane cross section of the needle-shaped Si ₃ N ₄ particles, by 85 to 95% is to further solve the problems.
The present invention provides a power obtained by bonding a metal plate serving as a circuit layer to the surface of a ceramic substrate formed of a ceramic sintered body obtained by sintering acicular Si ₃ N ₄ particles and granular amorphous Si ₃ N ₄ particles. In the module substrate, the needle-like Si ₃ N ₄ particles, which are constituent elements of the ceramic sintered body, are oriented along the C axis, and the ceramic sintered plate and the metal are arranged so that the C axis is perpendicular to the circuit surface of the metal plate. The board is joined.

The ceramic sintered plate according to the present invention pays attention to the fact that the thermal conductivity in the C-axis direction of the acicular Si ₃ N ₄ particles is larger than the vertical direction (C-axis direction: about 180 W / m ° C., vertical direction : About 70 W / m ° C.), and a substrate having high heat dissipation by placing a sintered body in which needle-like Si ₃ N ₄ particles are oriented in the C-axis direction in a direction perpendicular to the metal plate. It has gained.

Further, by mixing a particulate amorphous _Si 3 _{N 4} particles acicular _Si 3 _{N 4} particles, in particular, the surface of the sintered ceramic plate, i.e. the contact surface of the metal plate, granular amorphous _Si 3 N _{Since the four} particles block the space formed between the acicular Si ₃ N ₄ particles and the acicular Si ₃ N ₄ particles and increase the contact area with the metal plate, the thermal conductivity can be improved.

Here, in the present invention, if the relative density of the ceramic sintered plate is less than 94%, the bonding strength is lowered, which is not preferable. If it exceeds 98%, the existence ratio of the fine granular Si ₃ N ₄ particles is increased, and the heat conduction is increased. This is not preferable because it causes a decrease in rate. Therefore, the relative density was set to 94 to 98%.

Further, in the present invention, if the area ratio in the cross section in the plane direction of the acicular Si ₃ N ₄ particles is less than 85%, the proportion of the acicular Si ₃ N ₄ particles is decreased, which causes a decrease in thermal conductivity, which is not preferable. If it exceeds 95%, the relative density does not increase, and the bonding strength and the substrate strength decrease. Therefore, the area ratio in the plane cross section of the needle-shaped _Si 3 _{N 4} particles was determined to be 85% to 95%.

  According to the ceramic sintered plate according to the present invention, it is possible to obtain a ceramic sintered plate having high heat dissipation without reducing the thickness of the sintered plate, so that excellent mechanical strength and excellent thermal conductivity can be obtained. A power module substrate is also provided.

It is a schematic sectional drawing which shows one embodiment of the board | substrate for power modules using the ceramic sintered board of this invention. It is a schematic diagram which shows the orientation of the ceramic sintered plate of this invention, (a) The perspective view of a sintered plate, (b) The schematic diagram of the cross section of a sintered plate.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic perspective view showing an embodiment of a power module substrate constructed using the ceramic sintered plate of the present invention.

  As shown in FIG. 1, the power module substrate 10 according to the present embodiment is a rectangular plate-shaped ceramic substrate 11. In this configuration, the plate 13 is laminated, and the heat conduction layer metal plate 12 serving as a heat conduction layer for heat radiation is laminated on the back surface side. For example, the circuit layer metal plate 13 and the heat conductive layer metal plate 12 are made of pure Al.

The ceramic substrate 11 is constituted by a ceramic sintered plate in which acicular Si ₃ N ₄ and granular amorphous Si ₃ N ₄ particles described later are formed and sintered. Here, the thickness of the ceramic substrate 11 is, for example, 0.635 mm.

  The heat conductive layer metal plate 12 is formed of a metal having a high thermal conductivity such as Al (aluminum), and is bonded and fixed to the ceramic substrate 11 by a brazing material layer 16. Here, the thickness of the metal plate 12 for heat conductive layers is, for example, 0.6 mm. The brazing material layer 16 is formed of, for example, an Al—Si (silicon) -based brazing material (for example, Al: 93 wt%, Si: 7 wt%, a thickness of 10 μm to 15 μm) or an Al—Ge (germanium) brazing material. ing.

  The metal plate for circuit layer 13 is formed of a metal having a high thermal conductivity such as Al, for example, similarly to the metal plate for heat conduction layer 12, and constitutes a circuit by being arranged at an appropriate interval. To do. The circuit layer metal plate 13 is bonded and fixed to the ceramic substrate 11 by the brazing material layer 17. Here, the thickness of the circuit layer metal plate 13 is, for example, 0.6 mm. The brazing material layer 17 is made of, for example, an Al—Si or Al—Ge brazing material.

  Further, the electronic component 18 is fixed to the upper surface of the circuit layer metal plate 13 by a solder layer 19. Here, as the electronic component 18, for example, a semiconductor chip can be applied, and examples of the semiconductor chip include a power device such as an IGBT (Insulated Gate Bipolar Transistor).

In addition, the ceramic substrate 11 used for the power module substrate 10 of the present embodiment is manufactured by the following method, so that the needle-like Si ₃ N ₄ particles, which are constituent elements, are oriented in the C-axis direction. ing.
[Method for producing C-axis oriented ceramic sintered body]
First, silicon nitride powder is prepared. As the silicon nitride powder, acicular Si ₃ N ₄ particles and granular amorphous Si ₃ N ₄ particles can be used as the main ceramic powder. This granular amorphous Si ₃ N ₄ acicular Si ₃ N ₄ particles are easily oriented in a magnetic field than particulate, further based on a seed crystal composed of pre-oriented granular amorphous Si ₃ N ₄ particles As a result, the crystal grows, and a structure in which the needle-like crystal composed of needle-like Si ₃ N ₄ particles is oriented is formed. Therefore, in order to obtain a high degree of orientation, it is important to add 85 to 95 wt% of acicular Si ₃ N ₄ particles.

The average particle size of the acicular Si ₃ N ₄ particles is preferably at least a major axis of 0.4 to 2.5 μm, particularly 0.6 to 2.0 μm, and more preferably 0.8 to 1.5 μm. By controlling to this particle size range, the main particles themselves can easily move in the slurry and can be efficiently aligned in a magnetic field.

The needle-like Si ₃ N ₄ particles are coated with a magnetic metal such as Fe, Co, or Ni. As a coating method, for example, sputtering, vapor deposition, or wet chemical plating is used. Then, to the raw material powder obtained by mixing the coated needle-like Si ₃ N ₄ particles and the granular amorphous Si ₃ N ₄ particles, an organic solvent such as ethanol or isopropyl alcohol and a binder as required are added, A raw material powder is uniformly mixed and pulverized by a known kneading method, for example, a ball mill, a vibration mill, a rotary mill, a barrel mill or the like, to prepare a slurry.

Although these organic solvents and the binder itself have little influence on the orientation in the magnetic field, the combination of these addition ratios with low slurry viscosity and high solids content completes particle orientation in a short time. At the same time, it is preferable for improving the particle dispersibility during molding. For example, as the slurry viscosity, the viscosity at 100 sec ⁻¹ is 1.0 Pa · s or less, preferably 0.5 Pa · s or less, and the solid content is 30 to 60% by volume, preferably 40 to 50% by volume.

Next, the obtained slurry is formed in a magnetic field. In order to obtain a high degree of orientation, the magnetic field strength needs to be 1T or more, particularly 5T or more, and more preferably 9T or more. The slurry is formed in the superconducting magnet of the magnetic field generator. At this time, it is important that the magnetic field is applied in the direction parallel to the substrate, that is, the surface direction of the substrate (the lines of magnetic force are parallel to the surface direction of the substrate). . As a result, the a-axis of the acicular Si ₃ N ₄ particles is oriented in a direction parallel to the magnetic field application direction, and the c-axis is oriented in a direction perpendicular to the magnetic field application direction. That is, the magnetic field is applied in the direction of the surface of the substrate as indicated by the arrow in FIG.

  Since the orientation of the particles in the magnetic field is completed in a short time, an ultraviolet curable organic resin such as an acrylic resin, methacrylate, ammonium polycarboxylate, polydiolefin resin or the like is used in the slurry to solidify the molded body. It is important to solidify in a short time by irradiating ultraviolet rays and freeze the orientation in the compact. Moreover, a molded object can also be obtained by raising or lowering temperature using a thermosetting resin and a thermoplastic resin instead of an ultraviolet curable resin. For example, polydiolefin resins can be used as thermoplastic resins, and organic peroxides such as ketone peroxides, peroxyesters, peroxycarbonates and the like are added to the polydiolefin resins as curing catalysts. And can be used as a thermosetting resin.

  As a molding method, a known molding method such as a doctor blade method, a calender roll method, a rolling method, an extrusion molding method, a cast molding method, an injection molding method or the like may be used, but a doctor blade method or the like may be used to form a low-viscosity slurry. A so-called tape molding method, a casting molding method using a mold such as plaster, or an injection molding method is desirable.

  After that, the obtained molded body was debindered in a weakly oxidizing atmosphere, and then fired in a non-oxidizing atmosphere such as nitrogen at a temperature of 1500 to 2000 ° C. to produce an oriented ceramic sintered plate. can do.

Further, the particle size of the granular amorphous Si ₃ N ₄ particles is not limited, but the granular amorphous Si ₃ N ₄ particles also have an aspect ratio of 3 so that the acicular Si ₃ N ₄ particles are easily rotated when a magnetic field is applied. In the following, it is particularly preferable to use a small one of 2 or less. For example, the average particle diameter of the granular amorphous Si ₃ N ₄ particles is preferably 0.4 to 2.5 μm, particularly preferably 0.6 to 2.0 μm. When the average particle size exceeds 2.5 μm, the orientation of the acicular Si ₃ N ₄ particles, which are the main particles in a high magnetic field, is obstructed, and the particle orientation tends to be hindered.

The specific surface areas of the granular amorphous Si ₃ N ₄ particles and the acicular Si ₃ N ₄ particles are each preferably 10 m ² / g or less, particularly 7 m ² / g or less, and more preferably 5 m ² / g or less. If it exceeds 10 m ² / g, the viscosity of the slurry tends to be high and particle orientation tends to be hindered.

The ceramic sintered plate containing uniaxially oriented needle-like Si ₃ N ₄ particles of the present invention will be specifically described below based on examples.

Surfaces of acicular Si ₃ N ₄ particles (product name: silicon nitride powder, manufactured by Toshiba Ceramics) with an average diameter of 0.5 μm, an average length of 1.0 μm, and a specific surface area of 8 m ² / g by electroless plating A layered Fe plating having an average thickness of about 0.1 μm was applied thereon.

These coated needle-like Si ₃ N ₄ particles and granular amorphous Si ₃ N ₄ particles having an aspect ratio of 2, an average particle diameter of 10-20 nm, and a specific surface area of 115 m ² / g (manufactured by KFO, product name: The raw material powder mixed with the compounding ratio shown in Table 1 is mixed with isopropyl alcohol and a binder (in this example, a methacrylic acid acrylic acid copolymer which is an ultraviolet curable acrylic resin). After the addition, a raw material powder was uniformly mixed and pulverized by a known kneading method and a ball mill to prepare a slurry.

The viscosity and solid content at 100 sec ⁻¹ of the slurry were as shown in Table 1.

  Next, the obtained slurry was molded in a superconducting magnet (magnetic field strength: 10 T) of a magnetic field generator. As a forming method, a doctor blade method was used to form a plate shape (plate thickness 0.635 mm, a square having a side of 30 mm). The application direction of the magnetic field was a direction horizontal to the substrate, that is, the surface direction of the substrate (lines of magnetic force were parallel to the surface direction of the substrate). While the molded body was in a magnetic field, ultraviolet rays were irradiated to cure the ultraviolet curable organic resin contained in the slurry.

  The obtained molded body was debindered in a weakly oxidizing atmosphere, and then fired in a nitrogen atmosphere at a temperature of 1700 ° C. to obtain an oriented ceramic sintered plate.

  For the ceramic sintered bodies of the present invention thus obtained (Examples 1 to 3), relative density (%), bending strength (MPa), thermal conductivity (W / m · k), bonding strength ( The presence or absence of heat cycle peeling was measured.

The relative density was calculated as a ratio to the theoretical density of Si ₃ N ₄ .

  In addition, the bending strength test is performed by the fine ceramic bending strength test method specified by JIS R1601, and the thermal conductivity is measured by the laser flash method of the fine ceramics specified by JIS R1611. The test was performed.

  The bonding strength was evaluated for a power module prepared as follows.

A 28 mm square aluminum metal layer (circuit layer thickness: 0.6 mm, heat dissipation layer thickness: 1.5 mm) was disposed on both surfaces of the ceramic substrate of each example via a brazing foil of Al-Si alloy. Then, a carbon cushion sheet is laminated on both surfaces of each laminate, placed between the base plate and the pressing plate, and subjected to heat treatment (650 ° C., 2.5 × 10 ⁵ Pa) for each power module. A substrate was obtained.

  The power module substrate thus obtained was subjected to 1000 heat cycles of -40 ° C. × 30 minutes → room temperature × 10 minutes → 105 ° C. × 30 ° C. → room temperature × 10 minutes as one cycle. Thereafter, peeling of the sintered plate was observed by ultrasonic flaw detection.

For comparison, the amount of needle-like Si ₃ N ₄ particles was changed, and the one with a relative density deviated from 94 to 98% defined in the present invention was prepared. 2). Further, a ceramic sintered body with a relative density of 99% or more formed by acicular Si ₃ N ₄ particles and a sintering aid as raw materials and oriented with needle-like Si ₃ N ₄ particles (conventional example 1) ), And a conventional ceramic sintered body (conventional example 2) having a relative density of 99% or more formed without orientation of acicular Si ₃ N ₄ particles. Also for these, the same measurement as that of the ceramic sintered body of the present invention was performed, and the results are also shown in Table 1.

表１に示す結果から明らかなように、本発明によるセラミックス焼結板は、接合強度および曲げ強度が高く、しかも熱伝導率も高いため、パワーモジュール用のセラミックス基板にきわめて適していることがわかる。一方、本発明の条件から外れる比較例、従来例のセラミックス焼結板は、接合強度、曲げ強度、熱伝導率の少なくとも１つにおいて不十分な値を示すため、本発明によるセラミックス焼結板に比べて、パワーモジュール用のセラミックス基板に適していないことがわかる。

As is apparent from the results shown in Table 1, the ceramic sintered plate according to the present invention has a high bonding strength and bending strength, and also has a high thermal conductivity. Therefore, it can be seen that the ceramic sintered plate is very suitable for a ceramic substrate for a power module. . On the other hand, the comparative and conventional ceramic sintered plates that deviate from the conditions of the present invention show insufficient values in at least one of bonding strength, bending strength, and thermal conductivity. In comparison, it can be seen that it is not suitable for ceramic substrates for power modules.

  In addition, this invention is not limited to the said embodiment, A various change can be added in the range which does not deviate from the meaning of this invention. For example, in the present embodiment, an example in which a ceramic sintered plate is used for a power module substrate has been described. It is.

1 ... sintered ceramic plate 2 ... needle _Si 3 _{N 4} particles 3 ... particulate amorphous _Si 3 _{N 4} particles 10 ... power module substrate 11 ... ceramic substrate 12 ... Metal plate for heat conduction layer 13 ... Metal plates for circuit layer 16, 17 ... Brazing material layer 18 ... Electronic component 19 ... Solder layer

Claims (2)

A power module substrate in which a metal plate serving as a circuit layer is bonded to a surface of a ceramic substrate, wherein the ceramic substrate is a needle-like Si substrate. ₃ N ₄ Particles and granular amorphous Si ₃ N ₄ A sintered ceramic plate in which particles are sintered, the relative density of the sintered ceramic plate is 94 to 98%, and acicular Si that is a constituent element of the sintered ceramic plate ₃ N ₄ A power module substrate, wherein the ceramic sintered plate and the metal plate are joined so that the particles are oriented along the C axis and the C axis is perpendicular to a circuit surface of the metal plate. 2. The power module substrate according to claim 1, wherein an area ratio in a cross section in a plane direction of acicular Si ₃ N ₄ particles which are constituent elements of the ceramic sintered plate is 85 to 95% .

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