JPH10251069A - Silicon nitride circuit board and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a circuit board having both of high thermal conductivity and low dielectric property which enables fast and highly reliable signal processing by controlling the volume ratio and particle size of a particle phase in a silicon nitride sintered body to specified ranges and controlling the sum cross section of neck parts per one particle connected to other particles on the neck parts to a specified range of the surface area of the particle. SOLUTION: This silicon nitride circuit board consists of a silicon nitride sintered body having a silicon nitride particle phase and an intergranular phase of a material having a low dielectric const. The volume ratio of the particle phase in the silicon nitride sintered body is 50 to 65%, and the average primary particle size of the particles is >=1.0μm. The particles are connected to each other with a neck part in such a manner that the sum cross section of the neck parts per one particle is 30 to 70% in average of the surface area of the particle, that the diameter of the cross section of the neck is average >=0.5μm, and that the number of necks per one particle is 6 to 8 in average. The silicon nitride sintered body has <=2.10g/cm<2> apparent density, <=6.0 relative dielectric const., >=100MPa strength and >=0.20cm<2> /sec thermal diffusion ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board formed of a silicon nitride sintered body and a semiconductor device using the same, and more particularly, to a circuit board having high thermal conductivity and low dielectric property and using the same. Semiconductor device.

[0002]

2. Description of the Related Art An electronic circuit mainly includes an element such as an IC, a substrate, and wiring. In recent years, the speed, size, and output of electronic circuits have been increasing, and the amount of heat generated by elements has become so large that it cannot be ignored. In order to cope with this, circuit boards made of low dielectric constant glass ceramics or high thermal conductive aluminum nitride (AlN) have been developed. The characteristics required as a circuit board are various, but in particular, it has a low dielectric constant to reduce the signal delay time, and has a high thermal conductivity to efficiently dissipate the heat generated from the element, and It is important that the material be sintered at a low temperature in order to enable the use of a wiring material having a low electric resistance. A circuit board made of a sintered body such as AlN has high thermal conductivity, but has a high relative dielectric constant and a high sintering temperature as compared with those made of glass ceramic or conventional glass epoxy. .

[0003]

In order to obtain an AlN substrate having a low dielectric constant in order to obtain a substrate having a high thermal conductivity and a low dielectric constant, a low dielectric constant material such as resin or glass is used.
A method of dispersing and molding 1N particles has been proposed. However, the thermal conductivity of the substrate obtained by this method is greatly reduced, which impairs the inherent advantages of the AlN sintered body.

Japanese Patent Application Laid-Open Nos. 61-28088 and 3-30392 propose a circuit board made of a porous AlN sintered body and resin or glass. However, when manufacturing a circuit board in accordance with these proposals, using an AlN sintered body having a high porosity lowers the dielectric constant, but lowers the thermal conductivity and mechanical strength, and conversely, reduces the AlN sintered body having a low porosity. When the binder is used, the thermal conductivity and the mechanical strength are increased, but the dielectric constant is increased. Therefore, it is difficult to manufacture a circuit board that satisfies both high thermal conductivity and low dielectric property. The heavy use of an AlN sintered body as a carrier for heat conduction causes a practical problem due to low mechanical strength, and there is a limit to a decrease in dielectric constant.

In recent years, the thermal conductivity has become 100 W / mK.
The silicon nitride (Si ₃ N ₄ ) sintered body having high thermal conductivity as described above can be obtained, and is considered to be promising as a material for a heat radiation circuit board. For example, as disclosed in Japanese Patent Application Laid-Open No. 6-135771, Si ₃ having a thermal conductivity of 120 W / mK is used.
An N ₄ sintered body has been obtained. The Si ₃ N ₄ sintered body is made of Al
Although the dielectric constant is lower than that of N, it is considered to be suitable as a circuit board. However, at the present time, development in application is not sufficient and it has not been started yet.

As described above, a heat radiation circuit board formed of a material having both high thermal conductivity and low dielectric property has not been realized.

The present invention provides a circuit board which is improved from a silicon nitride sintered body and is made of a silicon nitride sintered body having both high thermal conductivity and low dielectric constant and capable of high-speed and highly reliable signal processing. The task is to

It is another object of the present invention to provide a semiconductor device using a circuit board having high thermal conductivity, low dielectric property and high mechanical strength.

[0009]

SUMMARY OF THE INVENTION A silicon nitride circuit board according to the present invention is formed by using a silicon nitride sintered body having a particle phase composed of silicon nitride particles and an interparticle phase composed of a low dielectric constant material. A silicon circuit substrate, wherein the volume ratio of the particle phase in the silicon nitride sintered body is 50 to 60%, and the average primary particle diameter of the silicon nitride particles in the particle phase is 1.0 μm or more; The silicon particles are connected to each other via a neck, and the total cross-sectional area of the neck per silicon nitride particle is 30 to 70% of the particle surface area on average.

The neck portion of the silicon nitride particles has an average cross-sectional diameter of 0.5 μm or more, and the number of neck portions per silicon nitride particle is 6 to 8 on average. Has an apparent density of 2.10 g · cm ⁻³ or less.

The silicon nitride sintered body has a relative dielectric constant of 6.0.
Below, the strength is 100 MPa or more, and the thermal diffusivity is 0.20 cm ² / sec or more.

A semiconductor device according to the present invention includes the above-described silicon nitride circuit board, and a semiconductor element mounted on the silicon nitride circuit board.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The dielectric constant of silicon nitride (Si ₃ N ₄ ) itself is about 7.9 in a frequency range of 12 GHz, which is lower than about 8.8 of aluminum nitride (AlN). It is expected that a lower dielectric constant than that of a system of AlN and a resin can be achieved by combining the resin with a resin or the like. Further, since silicon nitride has higher strength and lower density than AlN, it is considered that high strength and light weight can be achieved.

In order to produce a material having both high thermal conductivity and low dielectric property of a silicon nitride sintered body according to the above, silicon nitride particles are dispersed in a low dielectric material such as resin or glass and molded. There is a way to do it. However, in the silicon nitride sintered body obtained by this method, since the silicon nitride particles, which are carriers for heat conduction, only make point contact, the efficiency of heat conduction is low, and a desired material cannot be obtained. Therefore, in order to increase the heat conduction efficiency, it is necessary that the sintered body has silicon nitride particles in surface contact. As a method for obtaining such a sintered body, a method in which a porous silicon nitride sintered body is manufactured and impregnated with a low dielectric material is considered.

In the production of a normal sintered body, a porous sintered body can be obtained by changing the sintering conditions such as lowering the sintering temperature and cutting off the sintering in the middle. In such a method, the porosity increases as the sintering is suppressed. However, if sintering is suppressed in order to secure pores necessary for impregnation with a low dielectric material, bonding between silicon nitride particles becomes insufficient, and both thermal conductivity and mechanical strength become insufficient.

The silicon nitride circuit substrate according to the present invention is characterized in that the silicon nitride particles are grown while maintaining a high porosity without densifying the silicon nitride particles. A circuit board is formed using a silicon nitride sintered body obtained by forming a porous silicon nitride sintered body having a stronger bond between particles than a body and impregnating the porous silicon nitride sintered body with a low dielectric material. The obtained circuit board exhibits high thermal conductivity and mechanical strength due to the silicon nitride particle phase having strong interparticle bonds, and exhibits low dielectric properties due to the interparticle phase.
In other words, it has characteristics in the silicon nitride particle phase.

In the silicon nitride circuit board of the present invention, the volume ratio of the particle phase in the silicon nitride sintered body forming the circuit board is 50 to 6%.
5%, the average primary particle diameter of the silicon nitride particles in the silicon nitride particle phase is 1.0 μm or more, and the silicon nitride particles are connected to each other via a neck portion. Is characterized by an average of 30 to 70% of the particle surface area on average. When the volume ratio of the particle phase is 49% or less, the thermal conductivity and mechanical strength of the circuit board are low, and when it is 66% or more, the dielectric constant is high. When the particle size of the silicon nitride particles is less than 1.0 μm, the mechanical strength of the sintered body is reduced due to insufficient particle growth and sintering. 1
If the total cross-sectional area of the neck portion per silicon nitride particle is 29% or less of the particle surface area on average, the thermal conductivity is extremely reduced, and if it is 71% or more, the porosity of the sintered body, that is, The ratio of the phases cannot be secured, and the dielectric constant cannot be reduced.

Furthermore, it is preferable that the cross-sectional diameter of the neck portion of the silicon nitride particles is 0.5 μm or more on average, and the number of neck portions per silicon nitride particle is 6 to 8 on average. In other words, the thermal conductivity is improved by bonding the silicon nitride particles with a certain number or more of neck portions having a certain size or more.

The above-described silicon nitride sintered body has an apparent density of 2.10 g · cm ⁻³ or less. With this configuration, the relative permittivity of the silicon nitride sintered body is 6.0 or less,
Strength is 100MPa or more, thermal diffusivity is 0.20cm
^A silicon nitride circuit substrate having a speed of ² / sec or more is obtained.

A method for manufacturing the silicon nitride circuit board of the present invention will be described below.

One of the typical methods for producing silicon nitride is as follows:
There is a method of reducing and nitriding SiO ₂ by mixing SiO ₂ powder and carbon powder and firing in a nitrogen atmosphere. In this method, reductive nitridation proceeds by heating together with carbon in a nitrogen atmosphere. Even when a silicon nitride powder compact is heated and sintered in a nitrogen atmosphere, if a small amount of carbon is contained, silicon oxide contained as inevitable impurities in the silicon nitride powder or oxide added as a sintering aid Is similarly reduced-nitrided to produce silicon nitride and other nitrides. As silicon oxide and other oxides are reduced and nitrided and disappear, the silicon nitride does not substantially densify. Although the mechanism is not clear, liquid phase sintering does not proceed due to the absence of a liquid phase due to the reaction of the SiO ₂ -based liquid phase or SiO ₂ with the sintering aid during sintering. S into silicon nitride on the way
It is considered that the concentration of lattice defects in the silicon nitride crystal is reduced due to the disappearance of the solid solution of iO ₂ , and diffusion through holes is less likely to occur. As a result, densification does not proceed. As described above, under the above-described conditions, densification does not occur, but grain growth occurs in silicon nitride crystal grains, and a bond (neck) between the grains is formed. Therefore, sintering without densification proceeds. Although the resulting sintered body is a porous body, a network in which silicon nitride particles are bonded is formed. This network is sufficient to conduct heat efficiently.

In the present invention, the above-mentioned mechanism is used,
By forming a compact containing silicon nitride as a main component and containing carbon, and heating the compact in a nitrogen atmosphere, sintering is performed while minimizing densification and shrinkage as much as possible, and growing silicon nitride crystal grains. , The formation of the neck between the grains is advanced. During the sintering in a nitrogen atmosphere, the carbon contained in the compact is reduced and nitrided by silicon oxide impurities inevitably contained in the silicon nitride raw material powder and oxides added as sintering aids. Change to silicon and other nitrides. Furthermore, since oxygen impurities which have an adverse effect on thermal diffusivity disappear during sintering, no oxygen solid solution occurs in the silicon nitride lattice, and a sintered body made of high-purity silicon nitride can be obtained.

The silicon nitride powder used in the production method of the present invention is
Although virtually any available powder can be used, the amount of impurity oxygen is 0.2-1.8% by weight and the average primary particle size is 3.5 μm or less, more preferably 0.1-2.
5 μm is desirable. The carbon added to suppress the densification can be introduced by adding carbon powder itself and / or adding an organic substance and firing the carbon in a non-oxidizing atmosphere to carbonize. Examples of the carbon powder include carbon black, graphite, amorphous carbon, and the like, but the form of addition thereof is arbitrary.
As the organic substance, acrylic resin, paraffin, cellulose, sucrose, starch and the like are added in the form of powder and / or liquid or solution.

The amount of carbon suitable for reducing and nitriding silicon oxide impurities is 0.65 to 1.20 times the amount of carbon calculated from the reaction formula shown in the following equation (1).

[0025]

Embedded image

For SiO ₂ , the amount of oxygen contained in the silicon nitride powder is measured by, for example, a gas analysis method, and the obtained amount of oxygen is
Those converted to iO ₂ can be used. 0.65 of calculation amount
If the ratio is less than twice, reductive nitridation of the SiO ₂ impurity cannot sufficiently occur, and oxygen may be dissolved in silicon nitride or densification of silicon nitride may occur. On the other hand, when the ratio exceeds the above range, carbon remains in the sintered body, which may cause a decrease in mechanical strength and a case where sufficient electric insulation cannot be obtained.

In the present invention, silicon nitride and carbon are essential, and are basically composed of these two types. However, the compounds described below can be added as sintering aids. The sintering aid is used to control the degree of sintering of silicon nitride, promote grain growth, and eliminate sintering unevenness and color unevenness of the sintered body. Sintering aids are alkaline earth compounds, rare earth compounds,
It is selected from a phosphorus compound, a boron compound and an aluminum compound.

The alkaline earth and rare earth compounds are added as a powder or a liquid. For example, oxides, carbides,
Fluoride, oxyfluoride, carbonate, oxalate, nitrate,
Alkoxide and the like. Various combinations are possible, such as adding the alkaline earth compound and the rare earth compound powder, dissolving the rare earth nitrate in the alcohol, and then adding. When added as a powder, the average particle size is desirably 1.0 μm or less, more preferably 0.6 μm or less. The alkaline earth element is composed of Ca, Ba, Sr and Mg, and it is particularly desirable to use Ca. Rare earth element is S
consisting of c, Y and lanthanum series elements, especially Y, Ce,
It is desirable to use La or the like. The addition amount of the alkaline earth or rare earth is usually 0.2 to 10% by weight, more preferably 1.0 to 6.0% by weight in terms of oxide.

As phosphorus compounds, Ca (PO ₄ ) ₂ and phosphates of Ba and Sr having the same composition ratio, YPO ₄ and phosphates of La, Ce, Gd and Yb having the same composition ratio, Ca (H 4 ₂ PO ₄ ) ₂ , CaHPO _4, and phosphates of Ba and Sr having the same composition ratio as these, AlPO ₄ and A
l (PO ₃ ) _{3 and the} like. As boride,
Rare earth borides such as LaB ₆ , alkaline earth borides such as CaB _6, and transition metal borides such as WB are exemplified.

As the aluminum compound, Al ₂ O ₃
Or AlN, AlF or a compound that becomes Al ₂ O ₃ during firing
_{3 and the} like, and the addition of a small amount of these aluminum compounds is effective in improving sinterability.

The amount of the phosphorus compound, boride and aluminum compound as described above is usually 2% by weight or less, more preferably 0.8% by weight or less.

Further, as another additive, a transition metal compound can be added mainly for coloring or blackening. Examples of the transition metal compound include Ti, Nb, and Z.
r, Ta, W, MO, Cr, Fe, CO, and Ni oxides, nitrides, carbides, oxycarbides, oxynitrides, and the like can be added, and it is particularly desirable to have electrical conductivity for blackening. As such a transition metal compound having conductivity,
For example, a nitride or carbide of an element selected from metals of W and MO, Zr, Ti, Nb, and Ta can be given. The addition amount of these transition metals is 2.5% by weight or less, more preferably 1.0% by weight or less in terms of element.

As described above, the manufacture of the circuit board according to the present invention is generally performed according to the following procedure. For example, the amount of impurity oxygen is 0.3 to 2.0% by weight, the amount of cationic impurity is 0.4% by weight or less in terms of element, and the average particle diameter is 0.1 to 1 in which α phase is a main component. Carbon powder having an average particle size of 0.04 to 1.5 μm and other additives are added to the silicon nitride powder of 0.5 μm. An organic binder and an organic solvent are added to such powder, and the mixture is mixed and crushed while forming a paste by, for example, a ball mill. This paste is formed into a desired shape by forming it into a sheet by a doctor blade method or by press forming after removing the organic binder. Next, the binder is usually removed by heating in a non-oxidizing atmosphere such as nitrogen or argon. The maximum temperature required for debinding is 900 ° C. or less in the above non-oxidizing atmosphere, and 5 in an atmosphere containing oxygen.
50 ° C. or less is appropriate. The heating rate is usually 10 to 2
It is carried out at 00 ° C / h, more preferably at 30 to 100 ° C / h.
h.

As the binder, for example, acrylic type, methacrylic type, butyral type, PVB type, paraffin type and the like are used. As a solvent in which such a binder is dispersed, for example, 1-butanol, alcohol such as ethanol, methyl isobutyl, toluene, xylene and the like are used. The amount of the binder to be added varies depending on the particle size of the AlN powder to be used.
It is 45% by weight, preferably 4 to 20% by weight.

After the binder is removed, it is placed in a firing vessel made of a material which is unlikely to react with silicon nitride, such as silicon nitride ceramic, BN, carbon, etc. Sintered at 1600-2000 ° C in an oxidizing atmosphere. Sintering is usually 1
Although it is carried out under a pressurized atmosphere of 0 atm or less, it can be carried out under atmospheric pressure at about 1650 ° C. The sintering time is generally 0.5 to 12 hours, more preferably 2 to 8 hours, at the maximum temperature. Examples of the non-oxidizing atmosphere include nitrogen and / or argon and a mixed gas in which hydrogen, carbon dioxide, or the like is partially mixed. Examples of the sintering furnace for performing quenching include those provided with a heater selected from carbon, tungsten, molybdenum, and the like. The amount of oxygen in the atmosphere is acceptable if it is within 100 ppm.
The sintering schedule can be monotonically ramped to the maximum temperature, or it can be ramped to the maximum temperature as needed. The heating rate is 50 to 2000 ° C./hour,
More preferably, the temperature is set to 200 to 1000 ° C. per hour.
The rate of temperature decrease can be set to the same level. However, in order to crystallize the grain boundary phase in the sintered body and measure the increase in thermal conductivity, it is desirable to perform the heat treatment at 100 ° C. or less per hour.

The multilayer circuit board according to the present invention is manufactured, for example, by the following method. That is, first, referring to the above-mentioned manufacturing method, the mixed powder composed of silicon nitride and the additive, the binder and the solvent are thoroughly kneaded together to disintegrate and disperse the powder, and also have a predetermined viscosity. To prepare a slurry. After the obtained slurry is formed into a sheet by a doctor blade method, it is dried by heating to remove the solvent to obtain a green sheet. Next, using a conductive paste, a predetermined circuit pattern is formed on the surface of the green sheet by, for example, screen printing. At this time, when forming a multilayer circuit,
In order to obtain electrical connection between the layers, a hole is made in the green sheet in advance, and the hole is filled with a conductive paste by, for example, a press-fitting method. Next, the green sheet on which the conductive circuit is formed is heated in a non-oxidizing atmosphere to remove the binder in the conductive paste. If necessary, a circuit pattern is further formed on the surface, and hot pressing is performed to laminate the green sheets. After the binder in the green sheet is removed by heating in a non-oxidizing atmosphere, the green sheet is sintered with reference to the above-described conditions. After sintering, trimming, thin-film or thick-film circuit formation, and external electrodes can be performed as necessary. The silicon nitride sintered body according to the present invention can be used as a metallized substrate that does not include internal wiring, and can be used alone as a structural member.

For the above-mentioned conductor, a high melting point metal such as W or Mo is used. As the binder for the conductive paste, in addition to the above, a cellulose-based binder such as ethyl cellulose or nitrocellulose can be used. ) And carbenol are added as appropriate. The addition amount of the binder is desirably 2 to 7% by weight. Further, the conductive paste of the present invention contains silicon nitride or a nitride containing an additive in order to prevent the diffusion of the components and the bleeding of the components into the insulator layer, and to adjust the shrinkage ratio between the conductor layer and the insulator layer. Silicon can be added as a filler in an amount of 30 to 50% by volume.

FIG. 1 shows an example of the semiconductor device of the present invention.
The insulating layer 1 of the circuit board of this semiconductor device is a silicon nitride circuit board formed as described above. The conductor layer 2 is formed on the surface of the circuit board using a conductive paste, and the via holes 3 are provided with vias. The semiconductor element 5 is mounted on the circuit board, and is covered with a sealing cap to which cooling fins are attached. Lead pins 6 are attached to the lower surface of the circuit board. The semiconductor element 5 and the conductor layer 2 are connected by a bonding wire 7.

The porous silicon nitride sintered body itself has a high thermal diffusivity and can be used as a low dielectric constant, a low specific gravity, and a heat-resistant substance. However, by impregnating the pores with a resin, airtightness can be obtained. Application and strength can be increased. Although not particularly limited as the resin, epoxy-based, silicone-based, polyimide-based, polyamide-based,
Acrylic, methacrylic and the like are suitable. The silicon nitride-resin composite can be subjected to various post-processing such as mechanical, electrical, and chemical processing as needed. For example, it is also suitable for drilling with a drill or the like.

The semiconductor device according to the present invention is a semiconductor device using the silicon nitride sintered body formed as described above for a substrate and a heat sink. There are lead insertion type or surface mount type devices, and typical examples are leadless chip carriers (LCC), dual in-line packages (DIP), and quad flat packages (QF).
P), a pin grid array (PGA), a ball grid array (BG)
A), a semiconductor device called a power module equipped with a hybrid package, an IGBT, a GTR, and the like.

[0041]

Embodiments of the present invention will be described below in detail.

(Example 1) The amount of impurity oxygen was 1.3% by weight.
And the amount of cationic impurities is 0.15% by weight in terms of element and α
The proportion of silicon nitride powder having an average particle size of 0.55 μm containing 96% by weight of phase silicon nitride is 98.0% by weight, and the average particle size is 0.1%.
N-Butanol was added to a powder having a μm of 99.9% by weight of carbon black having a ratio of 2.0% by weight, and the mixture was crushed and mixed by a wet ball mill. Further, this is dispersed in an alcohol solvent together with an acrylic binder,
A slip having a viscosity of about 5000 CPS was prepared. Subsequently, using the slip, a green sheet having a uniform thickness of about 0.8 mm was produced by a doctor blade method. Subsequently, the green sheet was cut into a desired size. After performing external processing as needed, it was heated to a maximum temperature of 600 ° C. in a nitrogen atmosphere to remove the binder. The apparent density of the debinder is 1.75 g.
cm ^-3 . After removing the binder, it was placed in a silicon nitride ceramic container and sintered in a sintering furnace having a carbon heater in a nitrogen atmosphere at 1900 ° C. for 8 hours under a pressure of 9.8 atm.

The organic solvent was removed from the same slip as above, and this was passed through a 0.3 mm mesh to form granulated powder. Instead of forming into a sheet, it was press-molded by uniaxial pressing at 50 MPa. This was subjected to binder removal and sintering in the same manner as described above. In this case, the apparent density of the debinder was 1.70 g · cm ⁻³ .

Each of the sintered bodies obtained by the above two procedures has a white color, and the density of the sintered bodies is 2.01 g · cm ⁻³ and the density of silicon nitride is ³ when measured by the Archimedes method. It was hardly densified compared to .20 g · cm ^-3 . A disk having a diameter of 10 mm and a thickness of 3 mm was cut out from the sintered body obtained from the press-formed body, and was subjected to JIS at room temperature of 21 ± 2 ° C.
The thermal diffusivity measured by the laser flash method according to -R1611 was 0.22 cm ² sec ^-1 . After crushing one piece of the sintered body, the constituent phases were evaluated by X-ray diffraction. As a result, no diffraction peak other than silicon nitride was observed. Analysis of the microstructure by SEM and an image analyzer revealed that silicon nitride crystal grains had an average grain size of about 1.5 μm.
m, a neck was formed between the silicon nitride particles, and the diameter of the neck was estimated to be about 1.0 ± 0.2 μm on average. The number of necks per silicon nitride particle was 7 on average, and the total cross-sectional area of necks per silicon nitride particle was 48 on average. The porosity was about 42%.

Next, this sintered body was impregnated with a two-component epoxy resin under reduced pressure and cured at about 100 ° C. for 1 hour.
Thereafter, when the four-point bending strength was measured according to JIS-R1601, the average strength was 255 MPa. Further, according to JIS-C2141, the dielectric constant (room temperature, 10M
Hz), the dense silicon nitride sintered body was measured.
The dielectric constant was sufficiently lowered to 5.4 compared to 9. A sample rod was cut out from the obtained silicon nitride sintered body-epoxy composite,
Processed and 3 according to JIS R1601 as above
When evaluated by the point bending method, the bending strength was 257 MPa.

Comparative Example 1 A sintered body was obtained by repeating the same operation as in Example 1 except that only silicon nitride powder was used without adding carbon. The obtained sintered body had a white color and a density of 2.81 g · cm ⁻³ . From sintered body, diameter 10mm,
A disk having a thickness of 3 mm was cut out, and its thermal diffusivity was measured at room temperature of 21 ± 2 ° C. by a laser flash method.
It was 7 cm ² sec ^-1 . After crushing a piece of sintered body, X
When the constituent phases were evaluated by line diffraction, a diffraction peak of only silicon nitride was observed. When the microstructure was analyzed in the same manner as in Example 1, the silicon nitride crystal grains had an average grain size of about 2.3.
μm, a neck was formed between the silicon nitride particles, and the diameter of the neck was estimated to be about 1.9 ± 0.4 μm on average. The average number of the necks per silicon nitride particle was 6, and the total cross-sectional area of the neck per silicon nitride particle was 65% of the particle surface area on average. The porosity was about 17%.

Next, the sintered body was treated with 2 in the same manner as in Example 1.
After impregnating and curing the liquid epoxy resin, the three-point bending strength was measured, and the average strength was 580 MPa. The dielectric constant was 7.2.

(Example 2) The amount of impurity oxygen was 0.8% by weight.
And the amount of cationic impurities is 0.11% by weight in terms of element and α
The proportion of silicon nitride powder having an average particle diameter of 0.88 μm containing 97% by weight of phase silicon nitride is 98.5% by weight, and the average particle diameter is 0.1%.
A powder having a carbon content of 1 μm and a purity of 99.9% by weight of carbon black of 1.5% by weight was prepared in the same manner as in Example 1 except that the sintering temperature and time were set at 2000 ° C. for 10 minutes and the sintered body was subjected to Obtained. The density of the debinder is 1.74 g · cm ^−3.
Met. The obtained sintered body has a white color and a density of 1.8.
It was 8 g · cm ^-3 . Similarly, when the thermal diffusivity was measured by the laser flash method, it was 0.20 cm ² sec ^-1 . After crushing one piece of the sintered body, the constituent phases were evaluated by X-ray diffraction. As a result, no diffraction peak other than silicon nitride was observed. Analysis of the microstructure revealed that the silicon nitride crystal grains had an average grain size of about 1.2 μm, a neck was formed between the silicon nitride grains, and the neck diameter was about 0.6 ±
It was estimated to be 0.4 μm. The average number of the necks per silicon nitride particle is 8, and the total cross-sectional area of the necks per silicon nitride particle is 38 on the average of the particle surface area.
%Met. The porosity was about 43.

The sintered body was impregnated with a two-component epoxy resin under reduced pressure and cured at about 100 ° C. for 1 hour. When the three-point bending strength was measured, the average strength was 250 MPa. When the dielectric constant (room temperature, 10 MHz) was measured,
5.3.

Example 3 A mixture of silicon nitride powder and carbon powder having the same composition as in Example 1 was obtained in the same manner as in Example 1, except that the sintering temperature and time were set at 1900 ° C. for 12 hours to obtain a sintered body. Was. The obtained sintered body has a white color and a density of 2.05 g.
Cm- ³ . Similarly, when the thermal diffusivity was measured,
0.31 cm ² sec ^-1 . After crushing one piece of the sintered body, the constituent phases were evaluated by X-ray diffraction. As a result, no diffraction peak other than silicon nitride was observed. Analysis of the microstructure revealed that the silicon nitride crystal grains had an average grain size of about 1.8 μm.
The neck was formed between the silicon nitride particles, and the diameter of the neck was estimated to be about 1.0 ± 0.5 μm on average.
Further, the number of the necks per silicon nitride particle is 7 on average.
The total cross-sectional area of the neck portion per silicon nitride particle was about 63% of the particle surface area on average. The porosity is about 4
It was 0%.

The sintered body was impregnated with a two-part epoxy resin under reduced pressure and cured at about 100 ° C. for 1 hour. When the three-point bending strength was measured, the average strength was 261 MPa. When the dielectric constant (room temperature, 10 MHz) was measured,
5.5.

Example 4 The amount of impurity oxygen was 1.6% by weight.
And the amount of cationic impurities is 0.13% by weight in terms of element and α
95.3% by weight of silicon nitride powder having an average particle diameter of 0.38 μm containing phase silicon nitride of 97% by weight, the same average particle diameter as in Example 1 being 0.08 μm, and a purity of 99.99%
The purity of the proportion of carbon black powder is 1.7% by weight, an average particle size of 2 wt% ratio of 99.9% of Y ₂ O ₃ is at 0.1 [mu] m, and an average particle diameter in the 0.1 [mu] m 99.
A powder was prepared in which the proportion of 9% Nd ₂ O ₃ was 1% by weight. This was carried out in the same manner as in Example 1, except that the sintering conditions were 18
A sintered body was obtained at 50 ° C. for 8 hours. The obtained sintered body was white and had a density of 2.01 g · cm ⁻³ . When the thermal diffusivity was measured similarly, it was 0.23 cm ² sec ^-1 . After crushing one piece of the sintered body, the constituent phases were evaluated by X-ray diffraction, and diffraction peaks of yttrium nitride and an unknown phase other than silicon nitride were found. When the constituent phases were evaluated by X-ray diffraction, no diffraction peak other than silicon nitride was observed. Silicon nitride crystal grains are about 1.1 μm on average
The neck was formed between the silicon nitride particles, and the diameter of the neck was estimated to be about 0.8 ± 0.2 μm on average. The average number of the necks per silicon nitride particle was 6, and the total cross-sectional area of the necks per silicon nitride particle was 49% of the particle surface area on average. The porosity was about 41%.

The sintered body was impregnated with a two-component epoxy resin under reduced pressure and cured at about 100 ° C. for 1 hour. When the three-point bending strength was measured, the average strength was 248 MPa. When the dielectric constant (room temperature, 10 MHz) was measured,
It was 5.4.

Example 5 The content of impurity oxygen was 0.43% by weight, the average primary particle diameter was 0.8 μm, and the α phase was 98.4.
1.6 parts by weight of graphite powder having an average particle diameter of 0.1 μm and a purity of 99.9% by weight are added to 100 parts by weight of silicon nitride powder containing 100% by weight, and the mixture is crushed and mixed using a ball mill to obtain raw material powder. Was prepared. Subsequently, a binder-free product was obtained in the same manner as in Example 1. When the carbon content of the debinder was measured by a gas analyzer, it was found to have increased to 1.7% by weight, but it was considered that a part of the binder remained as carbon. As in Example 1, but at 1900 ° C. for 16 hours,
Heating was performed in a nitrogen atmosphere at 8.8 atm to obtain a sintered body. The obtained sintered body was white and had a density of 2.03 g · cm ⁻³ . Similarly, when the thermal diffusivity was measured by the laser flash method, it was 0.29 cm ² sec ^-1 . After crushing one piece of the sintered body, the constituent phases were evaluated by X-ray diffraction, and diffraction peaks of silicon nitride and graphite were observed.
The silicon nitride crystal grains grew to an average of about 1.9 μm, a neck was formed between the silicon nitride particles, and the diameter of the neck was estimated to be about 1.2 ± 0.4 μm on average. Also, 1
The average number of the necks per silicon nitride particle is 7 and 1
The total cross-sectional area of the neck per silicon nitride particle was 65% of the particle surface area on average. The porosity was about 40%.

The sintered body was impregnated with a two-part epoxy resin under reduced pressure and cured at about 100 ° C. for 1 hour. When the three-point bending strength was measured, the average strength was 258 MPa. When the dielectric constant (room temperature, 10 MHz) was measured,
It was 5.4.

(Example 6) The amount of impurity oxygen was 1.1% by weight.
And an average particle diameter of 0.1 with respect to 98.0 parts by weight of silicon nitride powder containing 98% by weight of an α phase having an average primary particle diameter of 0.6 μm.
2.0 parts by weight of a carbon powder having a purity of 99.9% by weight in μm was added, and the mixture was crushed and mixed using a ball mill to prepare a raw material powder. Subsequently, a debinder was obtained in the same manner as in Example 1, except that paraffin was added as a binder. The green density of the debinder was 1.78 g · cm ⁻³ . The carbon content of the debinder was measured with a gas analyzer and found to be 2.15% by weight. Example 1
Same as above, except that sintering was performed at 1800 ° C. for 16 hours. When the density of the sintered body was measured by the Archimedes method, it was 2.01
g · cm ⁻³ . Similarly, when the thermal diffusivity was measured,
0.31 cm ² sec ^-1 . After crushing one piece of the sintered body, the constituent phases were evaluated by X-ray diffraction. As a result, no diffraction peak other than that of silicon nitride was observed.

(Comparative Example 2) A sintered body was obtained in the same manner as in Example 1 except that only the same silicon nitride powder as in Example 1 was used without using carbon, except that the sintering temperature and time were set at 1650 ° C. for 16 hours. . The obtained sintered body has a white color and a density of 1.95 gcm.
^{Was -3} . When the thermal diffusivity was measured in the same manner, 0.2
It was 0 cm ² sec ^-1 . After crushing a piece of sintered body, X
When the constituent phases were evaluated by line diffraction, no diffraction peak other than silicon nitride was observed. When the microstructure was analyzed in the same manner as in Example 1, the silicon nitride crystal grains had an average grain size of about 0.8 μm, and no neck formation was observed between the silicon nitride grains.

Then, the sintered body was treated with 2 in the same manner as in Example 1.
After impregnating and curing the liquid epoxy resin, the three-point bending strength was measured, and the average strength was 120 MPa. The dielectric constant was 5.1.

Example 7 The average particle diameter was 98 parts by weight of silicon nitride powder containing 98.5% by weight of α phase having an impurity oxygen amount of 1.20% by weight and an average primary particle diameter of 0.6 μm. 0.
2.0 parts by weight of 1 μm graphite carbon powder having a purity of 99.9% by weight was added, and the mixture was crushed and mixed using a ball mill to prepare a raw material powder. Subsequently, a debindered body was obtained in the same manner as in Example 1, except that paraffin was used as the binder. The green density of the debinder is 1.78 g.
Cm- ³ . The carbon content of the debinder was measured by a gas analyzer and found to be 2.1 wt%. As in Example 1, except that sintering was performed at 1900 ° C. for 10 hours. The density of the sintered body was 2.03 g · cm ^{-3 as} measured by the Archimedes method. When the thermal diffusivity was measured similarly, it was 0.33 cm ² sec ^-1 . After crushing one piece of the sintered body, the constituent phases were evaluated by X-ray diffraction.
No diffraction peak other than that of silicon nitride was observed. Analysis of the microstructure revealed that the silicon nitride crystal grains had an average grain size of about 1.8 μm, a neck was formed between the silicon nitride grains, and the neck diameter was estimated to be about 1.1 ± 0.5 μm on average. I got it. The average number of the necks per silicon nitride particle was 7, and the total cross-sectional area of the necks per silicon nitride particle was 64% of the particle surface area on average. The porosity was about 40%.

Next, the sintered body was impregnated with a two-component epoxy resin under reduced pressure and cured at about 100 ° C. for 1 hour.
When the four-point bending strength was measured according to JIS-R1601, the average strength was 249 MPa. Further, according to JIS-C2141, the dielectric constant (room temperature, 10M
Hz) was 5.3.

Example 8 1 part by weight of YF ₃ having an average particle diameter of 0.1 μm and a purity of 99.9% by weight was added to 97.5 parts by weight of the silicon nitride powder used in Example 1, 0.2 diameter
1.5 μm carbon black having a purity of 99.9% by weight
1-Butanol was added to the powder by weight, and the mixture was crushed and mixed by a wet ball mill. Further, it is dispersed in an alcoholic solvent together with an acrylic binder and has a viscosity of about 500
A 0 cps slip was prepared. Subsequently, a green sheet having a uniform thickness of about 0.3 mm was prepared from the slip by a doctor blade method. Subsequently, the green sheets were cut into desired dimensions, and via holes for forming electrical connection between layers were formed in each green sheet. A conductive paste composed of 70 wt% of W particles having an average particle size of 0.8 μm and 30 wt% of the same silicon nitride powder as used for the insulator layer was filled into the via hole by press-fitting. A W paste was screen-printed on the green sheet in which the via hole was formed to form a desired pattern to be a conductor circuit.

A desired number of the green sheets obtained by such a method were laminated and integrated by hot pressing. afterwards,
The external processing was performed and the binder was removed by heating to a maximum temperature of 700 ° C. in a nitrogen atmosphere. The laminate after debinding is placed in a graphite container, and h-BN (hexagonal boron nitride) is interposed between the molded body and the graphite, in a sintering furnace having a carbon heater, in a nitrogen atmosphere.
Sintering was performed at 1900 ° C. for 8 hours under an atmospheric pressure of 9.8 atm.

Next, the pores of the circuit board including the internal wiring are impregnated with a two-component epoxy resin under reduced pressure to about 1 μm.
Cured at 00 ° C for 1 hour. The obtained package was swollen in appearance and inside, without disconnection, etc., and a good circuit pattern was formed. The specific resistance of the conductor was 3.2 Ωcm, which was sufficiently low.

[0064]

As described above, the circuit board made of the silicon nitride-resin composite of the present invention has a lower dielectric constant, higher thermal conductivity and higher strength than conventional circuit boards.
It is lightweight and has excellent characteristics as a recent high-speed, large-output electric circuit board. In addition, the composite according to the present invention is lightweight, high-strength, and high-thermal-conductivity, and thus can be widely used as a structural material.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an example of a semiconductor device using a multilayer circuit board of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating layer 2 Conductive layer 3 Via hole 4 Cooling fin 5 Semiconductor device 6 Lead pin 7 Bonding wire

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Fumio Ueno 1 Toshiba, Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Inside Toshiba R & D Center

Claims (4)

[Claims] 1. A silicon nitride circuit board formed by using a silicon nitride sintered body having a particle phase composed of silicon nitride particles and an interparticle phase composed of a low dielectric constant material, wherein The volume ratio of the particle phase is 50 to 65%, the average primary particle diameter of the silicon nitride particles in the particle phase is 1.0 μm or more, and the silicon nitride particles are connected to each other via a neck portion. 1. A silicon nitride circuit board, wherein the total cross-sectional area of the neck portion per silicon nitride particle is 30 to 70% of the particle surface area on average. 2. The neck portion of the silicon nitride particles has an average cross-sectional diameter of 0.5 μm or more, and the number of neck portions per silicon nitride particle is 6 to 8 on average. 2. The silicon nitride circuit board according to claim 1, wherein the apparent density of the aggregate is 2.10 g · cm ⁻³ or less. 3. The silicon nitride sintered body has a relative dielectric constant of 6.
The silicon nitride circuit board according to claim 1, wherein the strength is not more than 0, the strength is not less than 100 MPa, and the thermal diffusivity is not less than 0.20 cm ² / sec. 4. A semiconductor device comprising: the silicon nitride circuit board according to claim 1; and a semiconductor element mounted on the silicon nitride circuit board.