JPH1093211A - Silicon nitride circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon nitride circuit board having superior radiation property and structural strength, enabling effective prevention of generation of cracks and deterioration in strength of a ceramic board, even when a temperature cycle and the like is added, and has superior reliability and productivity. SOLUTION: A silicon nitride circuit board 4B includes a high thermal conductivity silicon nitride board 1, which contains a rare earth element at 1.0-17.5wt.% on reduction to the oxide, and Li, Na, K, Fe, Ca, Mg, Sr, Ba, Mn, and B as impurity cationic elements at 1.0wt.% or less in total (including 0wt.% as the detection limit), and which has a thermal conductivity of 60w/m.k or higher, and metal plates 2, 3 jointed with the high thermal conductivity silicon nitride board 1. In this silicon nitride circuit board 4B, a thin portion such as an inclined portion 2a or a step portion is formed on the outer peripheral end of the metal plate 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride circuit board, and more particularly to a silicon nitride circuit board having improved reliability against the addition of a thermal cycle and improved heat dissipation and structural strength.

[0002]

2. Description of the Related Art In recent years, a ceramic circuit board in which a metal plate such as a copper plate is bonded on a ceramic substrate has been used as a substrate for mounting semiconductor components handling relatively high power such as a power transistor module and a switching power supply module. I have.

[0003] As a method of joining a ceramic substrate and a metal plate in the above-described process of manufacturing a ceramic circuit substrate, an active metal such as Ti, Zr, Hf, or Nb is formed of Ag.
A method using an active metal brazing material containing 1 to 10% in a Cu brazing material or the like (active metal method);
1 tough pitch electrolytic copper containing 0 to 1000 ppm
A so-called direct bonding method (DBC method: direct bonding copper method) in which a ceramic substrate and a copper plate are directly bonded using copper oxidized to a thickness of 10 to 10 μm.
Etc. are known.

For example, in the direct joining method, first, a copper circuit board having a thickness of 0.3 to 0.5 mm stamped into a predetermined shape is formed.
0.6 to 1.0 mm thick made of aluminum oxide (Al ₂ O ₃ ) sintered body or aluminum nitride (AlN) sintered body
Heated is disposed in contact with the ceramic substrate, the bonding interface to produce a eutectic liquid phase of Cu-Cu ₂ O, after wetting the surface of the ceramic substrate in the liquid phase by cooling and solidifying the liquid phase Then, the ceramic substrate and the copper circuit board are joined. A ceramic circuit board to which such a direct bonding method is applied has a strong bonding strength between the ceramic substrate and the copper circuit board, and can be miniaturized and mounted with a simple structure that does not require a metallization layer or a brazing material layer. And the manufacturing process can be shortened.

In a ceramic circuit board in which a metal plate is bonded to a ceramic substrate by the above-described direct bonding method or active metal method, the thickness of the metal plate is set to 0.3 to 0.5 mm so that a large current can flow. There is a problem that the reliability of the heat history is poor because the thickness is often large. That is, when a ceramic substrate and a metal plate having significantly different coefficients of thermal expansion are joined, a thermal stress due to the difference in thermal expansion is generated due to a cooling process after the joining or the addition of a cooling / heating cycle. This stress exists as a compressive and tensile residual stress distribution on the ceramic substrate side near the joint, and the main residual stress mainly acts on the ceramic portion adjacent to the outer peripheral end of the metal plate. This residual stress causes cracks in the ceramic substrate or causes peeling of the metal plate. Further, even if cracks do not occur in the ceramic substrate, the ceramic substrate has an adverse effect of reducing its strength.

[0006] Of the above-mentioned residual stresses, those based on thermal stress generated in the cooling process after joining the metal plates can be reduced to some extent by adjusting the cooling rate or the like, but generate heat from the mounted components during actual use. It is difficult to reduce the residual stress due to the external conditions and the like depending on external conditions. For this reason, the above-mentioned ceramic circuit board is usually joined to a metal plate which is the same as the front surface, that is, the mounting portion of the semiconductor component, or is 5 to 30% thinner on the back surface of the ceramic substrate to reduce the warpage of the ceramic circuit board. However, the problem of residual stress has not been fundamentally solved.

To cope with the above-mentioned problems due to thermal stress and residual stress, that is, measures against the decrease in bonding strength and the occurrence of cracks, for example, Japanese Patent Publication No. 5-25397 discloses
The outer peripheral edge of the copper plate as a metal plate has a thin shape (thin portion),
Specifically, it is described that the outer peripheral end has a stepped shape or a tapered shape. Also, Japanese Patent Application Laid-Open No. 3-145748
The publication describes that a groove is formed inside along the outer peripheral edge of a metal plate. Thus, the stress concentrated on the outer peripheral end of the metal plate is dispersed by the groove, thereby preventing a decrease in bonding strength and the occurrence of cracks.

[0008]

However, of the above-mentioned conventional methods for improving the reliability of the thermal history in the ceramic circuit board, the method described in Japanese Patent Publication No. 5-25397 discloses an outer peripheral end portion of a metal plate. Since the thin portion is formed by etching or the like at the same time as the formation of the circuit pattern, the manufacturing process becomes complicated, resulting in an increase in the number of manufacturing steps.

Japanese Patent Application Laid-Open No. 3-145748 also mainly describes that a groove is formed along the outer peripheral edge of a metal plate by an etching method. According to the etching method, a groove can be formed simultaneously with the formation of a circuit pattern. However, as described above, the etching method has a disadvantage that the steps are complicated and the number of manufacturing steps is increased. Further, it is also shown that the groove is formed by machining using a mold or the like.However, when the groove is formed over the entire inner periphery of the outer peripheral edge of the metal plate by this method of machining, the groove is formed by pressing or the like. When forming the metal sheet, plastic deformation occurs in the metal plate around the pressing portion, and accompanying this, deformation such as distortion occurs particularly in the central portion of the metal plate. The deformation of the metal plate causes poor bonding of the metal plate or a decrease in bonding strength.

[0010] From the above, by adding a cooling process or a cooling / heating cycle after joining the metal plates, thermal stress and residual stress generated in the metal plate are dispersed and relaxed, thereby effectively preventing cracks and strength reduction of the ceramic substrate. There is a strong demand for a technique capable of preventing deformation of a metal plate even by machining that can prevent the deformation and simplify the manufacturing process.

On the other hand, higher integration and higher output of the semiconductor element,
With an increase in size, there is an increasing technical demand for a circuit board structure capable of efficiently dissipating heat generated from an element to the outside and a high-strength circuit board structure capable of withstanding thermal stress. Therefore, an attempt was made to use a silicon nitride (Si ₃ N ₄ ) substrate having higher strength than a conventional alumina (Al ₂ O ₃ ) substrate as a ceramic substrate. However, Si ₃ N ₄
Substrates have excellent mechanical strength such as toughness, but their thermal conductivity is significantly lower than that of aluminum nitride substrates.Therefore, they are practically used as components of circuit boards for semiconductors that require heat dissipation. Not.

On the other hand, an aluminum nitride substrate has high thermal conductivity and low thermal expansion characteristics as compared with other ceramic substrates, but it does not provide satisfactory mechanical strength. The circuit board is easily damaged by the slight pressing force and impact force added in the process,
In some cases, the manufacturing yield of a semiconductor device is significantly reduced.

The present invention has been made in order to solve such problems, and has excellent heat dissipation and structural strength, and can reduce the thermal stress and residual stress generated in a metal plate even when a cooling / heating cycle is added. It is an object of the present invention to provide a silicon nitride circuit board that can be dispersed.

[0014]

According to a first aspect of the present invention, there is provided a silicon nitride circuit board, comprising: a rare earth element in an amount of 1.0 to 17.5% by weight in terms of oxide; Li, Na, K, Fe, Ca, Mg, S as elements
r, Ba, Mn, B in total of 1.0% by weight or less, preferably 0.3% by weight or less (including 0% by weight as a detection limit) and a thermal conductivity of 60 w / mk or more. In a silicon nitride circuit board including a high thermal conductive silicon nitride substrate and a metal plate bonded to the high thermal conductive silicon nitride substrate, a thin portion is formed at an outer peripheral end of the metal plate. It is characterized by:

The content range of the rare earth element oxide, 1.0 to 17.5% by weight, is naturally understood as a mathematical expression, but the lower limit of the content is 1.0% by weight.
And an upper limit of 17.5% by weight.
Hereinafter, the same applies to other component ranges.

According to another aspect of the present invention, there is provided a silicon nitride circuit board containing 1.0 to 17.5% by weight of a rare earth element in terms of oxide. A highly thermally conductive silicon nitride substrate comprising a crystal phase and a grain boundary phase, wherein the ratio of the crystalline compound phase to the entire grain boundary phase in the grain boundary phase is 20% or more, preferably 50% or more; A metal plate bonded to a silicon nitride substrate, wherein a thin portion is formed at an outer peripheral end of the metal plate.

Here, the outer peripheral end of the metal plate may be an end with respect to the center, but as shown in FIGS. 4 and 6, the outer peripheral end of the metal plate 2 is directed toward the center. The portion L within 1 mm is preferable.

Further, in the silicon nitride circuit board according to the present invention, the thin portion may have an inclined portion, a step portion or the like.

Further, in the silicon nitride circuit board of the present invention, the thin portion such as the inclined portion or the step portion is formed on all the metal plates bonded to the high thermal conductive silicon nitride substrate. It is preferable that at least one metal plate bonded to the high thermal conductive silicon nitride substrate is formed with a thin portion such as the above-mentioned inclined portion or step portion. Also, it is included even if it is not the entire circumference of the metal plate.

A more preferred embodiment of the above-described silicon nitride circuit board of the present invention is as follows.
7. The method according to claim 6, wherein the metal plate is bonded to the high thermal conductive silicon nitride substrate by a direct bonding method, and the metal plate is bonded to the high thermal conductive silicon nitride substrate by an active metal method. Are joined.

The high thermal conductive silicon nitride substrate used in the present invention has a rare earth element content of 1.0 to 1 in terms of oxide.
7.5% by weight, Li, N as impurity cation element
a, K, Fe, Ca, Mg, Sr, Ba, Mn, and B in a total content of 1.0% by weight or less, preferably 0.3% by weight or less (including 0% by weight as a detection limit). It is composed of

In another embodiment, the high thermal conductive silicon nitride substrate is formed by converting a rare earth element into an oxide in an amount of from 1.0 to 17.
5% by weight, comprising a silicon nitride crystal phase and a grain boundary phase, wherein the ratio of the crystalline compound phase in the grain boundary phase to the entire grain boundary phase is 20% or more, preferably 50% or more. May be formed.

Further, it is particularly preferable to use a lanthanoid series element as the rare earth element in order to improve the thermal conductivity.

Further, the high thermal conductive silicon nitride substrate may be constituted so as to contain 1.0% by weight or less of aluminum nitride or alumina. Further, 1.0% by weight or less of alumina and 1.0% by weight or less of aluminum nitride may be used in combination.

The high thermal conductive silicon nitride substrate used in the present invention is made of Ti, Zr, Hf, V, Nb, Ta,
At least one selected from the group consisting of Cr, Mo, W
It is preferable to contain the seed in an amount of 0.1 to 3.0% by weight in terms of oxide. This Ti, Zr, Hf, V, Nb, T
At least one selected from the group consisting of a, Cr, Mo, and W can be contained as an oxide, carbide, nitride, silicide, or boride by being added to the silicon nitride powder.

Further, the method of manufacturing a silicon nitride substrate having high thermal conductivity used in the present invention is characterized in that oxygen is not more than 1.7% by weight and Li, Na, K, Fe, Ca,
Mg, Sr, Ba, Mn, B in total of 1.0% by weight or less, preferably 0.3% by weight or less, containing 90% by weight or more of α-phase silicon nitride and having an average particle size of 1.0 μm or less. Rare earth elements are converted to oxides in silicon nitride powder in an amount of 1.0 to
A raw material mixture containing 17.5% by weight or less and, if necessary, at least one of alumina and aluminum nitride added at 1.0% by weight or less is molded to prepare a molded body. After the obtained molded body is degreased, Atmospheric pressure sintering at a temperature of 1800 to 2100 ° C, and a cooling rate of the sintered body from the sintering temperature to a temperature at which a liquid phase formed at the time of sintering by the rare earth element solidifies is set to 100 ° C or less per hour. And gradually cooled.

In the above production method, it is preferable to add at least one of alumina and aluminum nitride to the silicon nitride powder in an amount of 1.0% by weight or less.

Further, Ti, Z are added to the silicon nitride powder.
oxides of r, Hf, V, Nb, Ta, Cr, Mo, W;
At least one selected from the group consisting of carbides, nitrides, silicides, and borides may be added in an amount of 0.1 to 3.0% by weight.

According to the above manufacturing method, a grain boundary phase containing a rare earth element or the like is formed in the silicon nitride crystal structure, the porosity is 2.5% or less, the thermal conductivity is 60 W / m · K or more, and A silicon nitride substrate having a point bending strength of 650 MPa or more at room temperature and excellent in both mechanical properties and heat conduction properties is obtained.

The silicon nitride powder used as the main component of the sintered body used in the above manufacturing method has an oxygen content of 1.7% by weight or less in consideration of sinterability, strength, and thermal conductivity. Preferably 0.5-1.5% by weight, Li, Na,
Α-phase silicon nitride in which the total content of impurity cation elements such as K, Fe, Mg, Ca, Sr, Ba, Mn, and B is suppressed to 1.0% by weight or less, preferably 0.3% by weight or less. Containing 90% by weight or more, preferably 93% by weight or more, and having an average particle size of 1.0 μm or less, preferably 0.4 to
A fine silicon nitride powder of about 0.8 μm can be used.

By using a fine raw material powder having an average particle diameter of 1.0 μm or less, a dense high thermal conductive silicon nitride substrate having a porosity of 2.5% or less even with a small amount of a sintering aid. Can be formed, and the possibility that the sintering aid impairs the heat conduction characteristics is reduced.

Further, Li, Na, K, Fe, Ca, Mg,
Since the impurity cation elements of Sr, Ba, Mn, and B are substances that hinder thermal conductivity, the content of the impurity cation element must be as follows in order to secure a thermal conductivity of 60 W / m · K or more. It can be achieved by setting the total to 1.0% by weight or less. In particular, for the same reason, the content of the impurity cation element is preferably not more than 0.3% by weight in total.
More preferred. Here, the silicon nitride powder used for obtaining a normal silicon nitride sintered body includes, in particular, Fe, C
a, Mg are contained in a relatively large amount, so that Fe, C
The total amount of a and Mg is a measure of the total content of the impurity cation element.

In the high thermal conductive silicon nitride substrate used in the present invention, the content of the impurity cation element cannot be completely 0% by weight in a mathematical sense. Therefore, the content of the impurity cation element specified in the present invention substantially includes 0% by weight as a detection limit.

Further, by using silicon nitride raw material powder containing 90% by weight or more of α-phase type silicon nitride which is superior in sinterability as compared with β-phase type, a high-density silicon nitride substrate can be formed. Can be manufactured.

The rare earth elements to be added to the silicon nitride raw material powder as a sintering aid include Ho, Er, Yb, Y,
Oxides such as La, Sc, Pr, Ce, Nd, Dy, Sm, and Gd, or substances that become these oxides by sintering operation alone or in combination of two or more oxides are included. Good, but especially holmium oxide (Ho ₂ O
₃ ) Erbium oxide (Er ₂ O ₃ ) is preferred.

In particular, by using Ho, Er, and Yb, which are lanthanoid series elements, as a rare earth element, sinterability or high thermal conductivity is improved, and sufficiently dense sintering can be performed even in a low temperature range of about 1850 ° C. Solidification is obtained. Therefore, the effect of reducing the equipment cost and running cost of the firing apparatus can be obtained. These sintering aids are
It reacts with the silicon nitride raw material powder to form a liquid phase and functions as a sintering accelerator.

The amount of the sintering aid to be added is in the range of 1.0 to 17.5% by weight relative to the raw material powder in terms of oxide.
When the addition amount is less than 1.0% by weight, the sintered body is insufficiently densified. In particular, when the rare earth element is an element having a large atomic weight such as a lanthanoid element, a relatively low strength is obtained. A sintered body having a relatively low thermal conductivity is formed. on the other hand,
If the added amount exceeds 17.5% by weight, an excessive amount of grain boundary phase is generated, and the thermal conductivity and strength start to decrease. It is particularly desirable to set the content to 4 to 15% by weight for the same reason.

In addition, Ti, Zr, Hf, V, Nb, T
The oxides, carbides, nitrides, silicides, and borides of a, Cr, Mo, and W promote the function of the sintering accelerator of the rare earth element, and also have the function of strengthening the dispersion of Si _{3 in the} crystal structure. It is intended to improve the mechanical strength of the N ₄ sintered body, and particularly, compounds of Hf and Ti are preferable. When the added amount of these compounds is less than 0.1% by weight, the effect of the addition is insufficient, while when the added amount exceeds 3.0% by weight, the thermal conductivity and mechanical strength and electric breakdown are caused. Since the strength is reduced, the amount of addition is in the range of 0.1 to 3.0% by weight. In particular, it is desirable that the content be 0.2 to 2% by weight.

The above compounds such as Ti, Zr, and Hf also function as a light-shielding agent that imparts opacity by coloring the silicon nitride sintered body to a black color. Therefore, in particular, when manufacturing a circuit board on which an integrated circuit or the like which easily malfunctions due to light is mounted, it is desirable to appropriately add the compound such as Ti and the like to obtain a silicon nitride substrate excellent in light shielding properties.

Further, in the above-mentioned production method, alumina (Al ₂ O ₃ ) as another optional additive serves to promote the function of the sintering accelerator for the rare earth element, This has a remarkable effect when sintering. When the addition amount of Al ₂ O ₃ is less than 0.1% by weight, sintering at a higher temperature is required. On the other hand, when the addition amount exceeds 1.0% by weight, an excessive amount of grain boundaries is required. Since a phase is formed or a solid solution starts to be formed in silicon nitride to cause a decrease in heat conduction, the amount of addition is set to 1% by weight or less, preferably 0.1 to 0.75% by weight.
In particular, in order to ensure good performance in both strength and thermal conductivity, it is desirable that the amount of addition be in the range of 0.1 to 0.5% by weight.

When used in combination with AlN, which will be described later, it is desirable that the total addition amount be 1.0% by weight or less.

Further, aluminum nitride (AlN) as another additive serves to suppress the evaporation of silicon nitride during the sintering process and to further promote the function of the rare earth element as a sintering accelerator. It is.

When the addition amount of AlN is less than 0.1% by weight (less than 0.05% by weight when used in combination with alumina), sintering at a higher temperature is required, while
If the amount exceeds 0% by weight, an excessive amount of the grain boundary phase is generated, or the solid solution starts to be dissolved in silicon nitride to cause a decrease in thermal conductivity. % By weight. In particular, in order to ensure good performance in sinterability, strength, and thermal conductivity, it is desirable that the addition amount be in the range of 0.1 to 0.5% by weight. When used in combination with Al ₂ O ₃ , the addition amount of AlN is 0.05 to 0.5% by weight.
Is preferable.

Since the porosity of the sintered body greatly affects the thermal conductivity and strength, the sintered body is manufactured to be 2.5% or less. If the porosity exceeds 2.5%, it hinders heat conduction,
As the thermal conductivity of the sintered body decreases, the strength of the sintered body decreases.

The silicon nitride sintered body is systematically composed of silicon nitride crystals and a grain boundary phase, and the proportion of the crystalline compound phase in the grain boundary phase greatly affects the thermal conductivity of the sintered body. However, in the high thermal conductive silicon nitride substrate used in the present invention,
It is necessary that the content be 20% or more of the grain boundary phase, and more preferably 50% or more is occupied by the crystal phase. If the crystal phase is less than 20%, it is not possible to obtain a silicon nitride substrate having high heat conductivity of 60 W / m · K or more and having excellent heat radiation characteristics and high temperature strength.

Further, as described above, the porosity of the high thermal conductive silicon nitride substrate is set to 2.5% or less, and the crystal phase accounts for 20% or more of the grain boundary phase formed in the silicon nitride crystal structure. To achieve this, the silicon nitride compact is heated to a temperature of 1800
Pressure sintering is performed at a temperature of ℃ 2100 ° C. for about 2 to 10 hours, and the cooling rate of the sintered body immediately after the completion of the sintering operation is 100
It is important that the temperature is lowered to below ℃.

If the sintering temperature is lower than 1800 ° C., the densification of the sintered body is insufficient, the porosity becomes 2.5 vol% or more, and both the mechanical strength and the thermal conductivity decrease. On the other hand, when the sintering temperature exceeds 2100 ° C., the silicon nitride component itself tends to be vaporized and decomposed. Especially not pressure sintering,
When normal-pressure sintering is performed, decomposition and evaporation of silicon nitride starts at about 1800 ° C.

The cooling rate of the sintered compact immediately after the completion of the sintering operation is an important control factor for crystallizing the grain boundary phase, and when rapid cooling is performed such that the cooling rate exceeds 100 ° C./hour. Is that the grain boundary phase of the sintered body structure becomes non-crystalline (glass phase), the ratio of the liquid phase generated in the sintered body as a crystalline phase to the grain boundary phase is less than 20%, and the strength and thermal conductivity are reduced. Both will fall.

The temperature range in which the cooling rate should be strictly adjusted is a temperature range from a predetermined sintering temperature (1800 to 2100 ° C.) to a temperature at which a liquid phase produced by the reaction of the sintering aid solidifies. Is enough. Incidentally, the liquidus freezing point when using the sintering aid as described above is approximately 1600 to 15
It is about 00 ° C. The cooling rate of the sintered body at least from the sintering temperature to the above-mentioned liquid phase solidification temperature is set to 10
0 ° C. or lower, preferably 50 ° C. or lower, more preferably 2 ° C.
By controlling the temperature to 5 ° C. or less, 20% or more of the grain boundary phase can be obtained.
Particularly preferably, 50% or more becomes a crystalline phase, and a sintered body excellent in both thermal conductivity and mechanical strength can be obtained.

The high thermal conductive silicon nitride substrate used in the present invention is manufactured, for example, through the following process. That is, a predetermined amount of a sintering aid, a necessary additive such as an organic binder, and optionally Al ₂ O are added to the fine silicon nitride powder having the predetermined fine particle size and a small impurity content. _A raw material mixture is prepared by adding ₃ or an AlN or Ti compound, and then the obtained raw material mixture is molded to obtain a molded body having a predetermined shape. As a molding method of the raw material mixture,
A general-purpose mold pressing method, a sheet forming method such as a doctor blade method, and the like can be applied. Subsequent to the above molding operation, the molded body is heated at a temperature of 600 to 800 in a non-oxidizing atmosphere.
C. or in air at a temperature of 400 to 500.degree. C. for 1 to 2 hours to sufficiently remove the organic binder component added in advance and degrease. Next, the degreased molded body is subjected to atmospheric pressure sintering at a temperature of 1800 to 2100 ° C. for a predetermined time in an inert gas atmosphere such as nitrogen gas, hydrogen gas or argon gas.

The silicon nitride substrate manufactured by the above method has a porosity of 2.5% or less and 60 W / m · K (25 ° C.).
It has the above thermal conductivity and a three-point bending strength of 65 at room temperature.
It has excellent mechanical properties of 0 MPa or more.

It should be noted that a silicon nitride substrate having a high thermal conductivity of 60 W / m · K or more by adding high thermal conductivity SiC or the like to low thermal conductivity silicon nitride is within the scope of the present invention. Is not included. However, the thermal conductivity is 60 W /
m.K or higher silicon nitride sintered body with high thermal conductivity Si
Needless to say, a silicon nitride-based substrate in which C is compounded is included in the scope of the present invention.

The silicon nitride circuit board according to the present invention is provided on the surface of the high thermal conductive silicon nitride substrate manufactured as described above.
It is manufactured by integrally joining metal plates having conductivity using the direct joining method or the active metal method.

In the silicon nitride circuit board of the present invention,
A thin portion such as an inclined portion or a step portion is formed at an outer peripheral end portion of the metal plate. Here, the thermal stress generated in the cooling process after the joining of the metal plate, the thermal stress due to the addition of a cooling / heating cycle, and the residual stress based thereon are caused by the inclined portion or the step portion provided on the outer peripheral end of the metal plate. And the like, are absorbed and dispersed by plastic deformation of the thin part, so that stress concentration on the outer peripheral end of the metal plate is reduced. As a result, the stress value itself at the outer peripheral end of the metal plate can be reduced, so that it is possible to effectively prevent the occurrence of cracks and a decrease in strength of the ceramic substrate, which have conventionally been problems.

In particular, a high thermal conductive silicon nitride substrate having a significantly improved thermal conductivity in addition to the inherently high strength and toughness characteristics of a silicon nitride sintered body is used as a ceramic substrate. Heat generated from a heat-generating component such as a semiconductor element mounted on the substrate is quickly transmitted to the outside of the system via the high thermal conductivity silicon nitride substrate, so that heat dissipation is extremely good. In addition, since a silicon nitride substrate having high strength and toughness is used, a large amount of maximum deflection of the circuit board can be secured. For this reason, the circuit board does not suffer from tightening cracks in the assembly process, and it is possible to mass-produce semiconductor devices using the circuit board at a high production yield and at low cost.

[0056]

Next, an embodiment of the present invention will be described.
A specific description will be given with reference to the following embodiments and the accompanying drawings. First, a high thermal conductive silicon nitride substrate used in the present invention will be described, and thereafter, a silicon nitride circuit board using this high thermal conductive silicon nitride substrate as a ceramic substrate will be described.

First, various silicon nitride substrates having high thermal conductivity to be used as components of the silicon nitride circuit board of the present invention were manufactured by the following procedure.

That is, a silicon nitride raw material containing 1.3% by weight of oxygen and 0.15% by weight of the impurity cation element in total and containing 97% of α-phase silicon nitride and having an average particle size of 0.55 μm. As shown in Tables 1 to 3, as shown in Tables 1 to ₃ , rare earth oxides such as Y ₂ O ₃ and Ho ₂ O ₃ as sintering aids, and Ti, Hf compounds, and Al ₂ O ₃ powders as needed. ,
AlN powder was added, and the mixture was wet-mixed in ethyl alcohol using a silicon nitride ball for 72 hours, and then dried to prepare raw material powder mixtures. Next, a predetermined amount of an organic binder was added to each of the obtained raw material powder mixtures, mixed uniformly, and then press-molded at a molding pressure of 1000 kg / cm ² to produce a large number of molded bodies having various compositions. Next, each of the obtained compacts was degreased in an atmosphere gas at 700 ° C. for 2 hours, and then the degreased bodies were subjected to densification sintering under the sintering conditions shown in Tables 1 to 3, and then attached to a sintering furnace. The cooling rate of the sintered body until the temperature in the sintering furnace falls to 1500 ° C. is controlled by controlling the amount of electricity supplied to the heating device, and the sintering is performed by adjusting the cooling rate to the values shown in Tables 1 to 3, respectively. Cool the body,
Silicon nitride sintered bodies according to Samples 1 to 51 were prepared. Further, the obtained sintered body was processed and polished to obtain a high thermal conductive silicon nitride substrate having a predetermined shape.

The average values of the porosity, the thermal conductivity (25 ° C.), and the three-point bending strength at room temperature were measured for the silicon nitride substrates according to Samples 1 to 51 thus obtained. Furthermore, the ratio of the crystal phase to the grain boundary phase was measured by X-ray diffraction for each silicon nitride substrate, and the results shown in Tables 1 to 3 below were obtained.

[0060]

[Table 1]

[0061]

[Table 2]

[0062]

[Table 3]

As is clear from the results shown in Tables 1 to 3, in the silicon nitride sintered bodies according to Samples 1 to 51, the raw material composition and the impurity amount were appropriately controlled, and the densified sintering was performed as compared with the conventional example. Since the cooling rate of the sintered compact immediately after completion is set lower than before, the crystal phase is included in the grain boundary phase, and the higher the proportion of the crystal phase, the higher the heat conductivity and the higher the strength of the silicon nitride. An elementary substrate was obtained.

On the other hand, 1.3 to 1.5% by weight of oxygen and 0.13 to 1.5%
A raw material powder having an average particle size of 0.60 μm containing 0% by weight and containing 93% of α-phase type silicon nitride was used, and Y ₂ O ₃ (yttrium oxide) powder was added to the silicon nitride powder in an amount of 3%. To 6% by weight and 1.3 to 1.6% by weight of alumina powder
The added raw material powder is molded, degreased, sintered at 1900 ° C. for 6 hours, and cooled in a furnace (cooling rate: 400 ° C./hour) to obtain a sintered body having a low thermal conductivity of 25 to 28 W / m · K. The value was close to the thermal conductivity of a silicon nitride sintered body manufactured by a conventional general manufacturing method.

Next, a metal plate is integrally bonded to both surfaces of each of the obtained high thermal conductive silicon nitride substrates according to Samples 1 to 51 by using a direct bonding method or an active metal method, thereby obtaining silicon nitride. A circuit board was manufactured.

FIGS. 1 to 4 are a plan view, a back view, and a plan view, respectively, showing the structure of a silicon nitride circuit board according to one embodiment of the present invention.
It is sectional drawing and the principal part enlarged sectional view. 1 to 4, a copper plate 2 is bonded to a surface 1a of a high thermal conductive silicon nitride substrate 1 as a metal plate. Also, a copper plate 3 is similarly bonded to the back surface 1b of the high thermal conductive silicon nitride substrate 1, and these constitute a silicon nitride circuit substrate 4A.

The copper plates 2 and 3 in the silicon nitride circuit board 4A shown in FIGS. 1 to 4 are bonded to the high thermal conductive silicon nitride substrate 1 by a direct bonding method, so-called DBC method. As the copper plates 2 and 3 when such a DBC method is used, oxygen such as tough pitch copper is used for 100 to 100%.
It is preferable to use copper containing 3,000 ppm, but it is also possible to use oxygen-free copper depending on the joining conditions. Instead of a single plate of copper or a copper alloy, a clad plate or the like with another metal member having at least a joining surface with the high thermal conductive silicon nitride substrate 1 made of copper can be used.

The copper plate 2 joined to the surface 1a of the high thermal conductive silicon nitride substrate 1 is to be a mounting portion for semiconductor components and the like, and is patterned into a desired circuit shape.
The copper plate 3 bonded to the back surface 1b side of the high thermal conductive silicon nitride substrate 1 prevents warpage of the high thermal conductive silicon nitride substrate 1 at the time of bonding.
In a divided state, it is bonded and formed on almost the entire back surface 1b of the silicon nitride substrate 1 having high thermal conductivity. As the copper plate 3 on the back surface 1b side, a copper plate having the same thickness as the copper plate 2 serving as a mounting portion for semiconductor components or the like may be used.
% Of the copper plate is preferably used.

Here, the silicon nitride circuit board 4A shown in FIGS.
5 and 6, for example, as shown in FIGS. 5 and 6, a silicon nitride circuit board 5A in which copper plates 2 and 3 are bonded to a high thermal conductive silicon nitride substrate 1 by an active metal method. You may. The active metal method includes, for example, Ti,
Brazing material containing at least one active metal selected from Zr, Hf, Nb, etc. (hereinafter referred to as active metal-containing brazing material)
Via a layer 6, a high thermal conductive silicon nitride substrate 1 and a copper plate 2,
3 is joined. As the composition of the active metal-containing brazing material to be used, for example, a eutectic composition of Ag-Cu (72 wt.
% Ag-28wt% Cu) or its composition near Ag-
Cu-based brazing filler metal or Cu-based brazing filler metal
A composition in which at least one active metal selected from Ti, Zr, Hf, Nb and the like is added at 0% by weight is exemplified.
In addition, a low melting point metal such as In may be added to the active metal-containing brazing material.

The silicon nitride circuit board 4A shown in FIGS.
As described above, those obtained by bonding the copper plates 2 and 3 to the high thermal conductive silicon nitride substrate 1 by the DBC method have advantages such as a simple structure, high bonding strength, and simplification of the manufacturing process.
In addition, when the copper plates 2 and 3 are joined to the high thermal conductive silicon nitride substrate 1 by the active metal method like the silicon nitride circuit board 5A shown in FIGS.
Since the active metal-containing brazing material layer 6 also functions as a stress relaxation layer, the reliability can be further improved. For this reason, it is preferable to select a joining method according to required characteristics, applications, and the like.

When a metal plate is joined to the high thermal conductive silicon nitride substrate 1 by the active metal method, not only a copper plate but also various metal plates, such as a nickel plate, a tungsten plate, a molybdenum plate, depending on the application. It is also possible to use these alloy plates, clad plates (including clad plates with copper plates), and the like.

Then, the above-described silicon nitride circuit board 4
In FIGS. 1A and 5A, as shown in FIGS. 1 and 5, a thin inclined portion 2a is provided along the outer peripheral edge of the copper plate 2 serving as a mounting portion for a semiconductor component or the like, that is, the copper plate 2 is provided.
Are formed along the outer peripheral edge of each circuit pattern portion.

In place of the inclined portion 2a, a step may be formed as a thin portion. FIG. 7 shows a silicon nitride circuit board 4B in which the copper plate 2 on which the step portion 2b is formed is integrally joined to the surface 1a of the high thermal conductive silicon nitride substrate 1 by a direct joining method. This silicon nitride circuit board 4B has the same configuration as that of the silicon nitride circuit board 4A shown in FIG. 1 except that a step 2b is formed.

FIG. 7 shows a copper plate 2 on which a step 2b is formed.
Is also a plan view showing a silicon nitride circuit board 5B integrally joined to the surface 1a of the high thermal conductive silicon nitride substrate 1 via an active metal-containing brazing material layer (not shown). This silicon nitride circuit board 5B has the same configuration as that of the silicon nitride circuit board 5A shown in FIGS.

Then, the above-described silicon nitride circuit board 4
7A and 7B, as shown in FIG. 7, a stepped portion 2b is provided along the outer peripheral end of the copper plate 2 to be a mounting portion for a semiconductor component or the like, that is, the outer peripheral end of each circuit pattern of the copper plate 2. It is formed along the part.

The thin portions such as the continuous inclined portion 2a and the stepped portion 2b are formed by machining such as pressing using a die in order to avoid complication of the manufacturing process and reduce the number of manufacturing steps. It is desirable to do. However, application of another formation method is not necessarily excluded.

Here, as shown in FIGS. 4, 6 and 9, the outer peripheral end of the above-described copper plate 2 (metallic plate) has a portion L within 1.0 mm from the outer peripheral end of the copper plate 2 toward the center. Is preferred. When the formation region of the thin portion such as the inclined portion 2a and the step portion 2b reaches the central portion beyond the outer peripheral end L, the stress concentration at the outer peripheral end of the copper plate 2 cannot be sufficiently alleviated, and at the same time, it becomes difficult for semiconductor components. This leads to a reduction in the mounting area.

As shown in FIGS. 4 and 6, the shape of the inclined portion 2a as a thin portion formed at the outer peripheral end of the copper plate 2 is such that the angle θ formed between the plane direction of the metal plate 2 and the inclined portion 2a is as follows. 3
It is good to form so that it may become 0-60 degrees. Also the inclined part 2
It is preferable that the thickness t of the leading end of a is not more than 1/2 of the thickness T of the mounting portion, preferably 0.1 mm or less.

On the other hand, when the step 2b is formed as a thin portion at the outer peripheral end of the copper plate 2, as shown in FIG.
Is less than or equal to 1/2 of the thickness T of the mounting portion, preferably 0.1 mm.
It is preferable that the thickness be 1 mm or less.

If the thickness t of the tip portion of the inclined portion 2a or the thickness t of the step portion 2b exceeds １ ／ of the thickness T of the portion to be the mounting surface, the plasticity of the inclined portion 2a or the step portion 2b is increased. The effect of reducing residual stress due to deformation cannot be obtained sufficiently. The residual stress can be reduced by reducing the thickness t. However, in the case where the step 2b is formed, if the thickness t is too small, there is a risk of breakage due to thermal stress. It is preferable that the thickness is up to about 0.05 mm.

It is preferable that the thin portions such as the above-described inclined portion 2a and step portion 2b be formed continuously along the outer peripheral edge of each circuit pattern portion of the copper plate 2. As described above, by continuously forming the thin portions such as the inclined portion 2a or the step portion 2b, the concentration of stress on the outer peripheral end portion of the copper plate 2 can be efficiently reduced, in other words, the stress is efficiently dispersed. be able to.

The copper plate 2 to be bonded to the front surface 1a of the high thermal conductive silicon nitride substrate 1 serving as a mounting portion for semiconductor components and the like has been described in detail.
As for the copper plate 3 to be joined to the surface b, it is preferable to form a thin portion such as the inclined portion 3a or the step portion 3b at the outer peripheral end, similarly to the copper plate 2 on the front surface 1a side. In particular, when a relatively thick copper plate (metal plate) is used from the viewpoint of heat dissipation and the like, it is desirable to form the inclined portion 3a or the step portion 3b also on the copper plate 3 on the back surface 1b side.

Each of the above-described silicon nitride circuit boards 4 is manufactured, for example, as follows. That is, for example, an oxygen-containing copper plate such as tough pitch copper is processed into a predetermined shape (a circuit pattern shape with respect to the copper plate 2), and a continuous inclined portion 2a, 3a or a stepped portion 2 is formed on an outer peripheral end thereof.
Thin portions such as b and 3b are formed by machining such as press working. Such inclined portions 2a, 3a or step portions 2b,
The copper plates 2 and 3 having 3b are placed in contact with each other on a silicon nitride substrate having high thermal conductivity and heated at a temperature not higher than the melting point of copper (1356K) and higher than the eutectic temperature of copper and copper oxide (1338K). The copper plates 2 and 3 are joined to produce a silicon nitride circuit board 4. When an oxygen-containing copper plate is used as the copper plate, the atmosphere for this heating is preferably an inert gas atmosphere.

The silicon nitride circuit board 5 to which the metal plates are joined by the active metal method is manufactured, for example, as follows. First, copper plates 2 and 3 having thin portions such as continuous inclined portions 2a and 3a or step portions 2b and 3b are prepared in the same manner as the silicon nitride circuit board 4. On the other hand, a paste of the active metal-containing brazing material as described above is applied to, for example, the high thermal conductive silicon nitride substrate 1 side. The coating thickness of the brazing material layer is preferably such that the thickness of the brazing material layer 6 after the heat bonding is not too large in order to improve the thermal cycle characteristics. Next, the copper plates 2 and 3 are respectively laminated on the high thermal conductive silicon nitride substrate 1 to which the brazing material paste is applied, and heat-treated at a temperature corresponding to the brazing material used. Is prepared.

In the silicon nitride circuit boards 4 and 5 having the above-described structure, the thermal stress generated in the cooling process after the joining of the copper plates 2 and 3 and the thermal stress due to the addition of a cooling cycle and the residual stress based on the thermal stress. The stress is absorbed and dispersed by plastic deformation of the thin portions such as the inclined portions 2a, 3a or the step portions 2b, 3b provided at the outer peripheral end portions of the copper plates 2, 3, and is dispersed.
The stress concentration on each outer peripheral end of 3 is alleviated. As a result, the stress value itself at the outer peripheral end portions of the copper plates 2 and 3 is reduced, so that it is possible to effectively prevent the occurrence of cracks and a decrease in strength of the ceramic substrate portion, which have conventionally been problems. Since the above-described dispersion of the stress is achieved by the thin portions such as the inclined portions 2a and 3a or the step portions 2b and 3b, the forming of the inclined portions 2a and 3a or the step portions 2b and 3b is performed by machining such as press working. Is applied, the deformation of the copper plates 2 and 3, particularly the central portion thereof, can be prevented. Therefore, the copper plate 2,
The manufacturing process can be simplified and the number of manufacturing steps can be reduced without lowering the bonding strength due to the deformation of No. 3.

Next, a specific example of an embodiment in which the above-mentioned inclined portion is formed as a thin portion, and evaluation results thereof will be described.

Example 1 First, a sample 1 was prepared as a high thermal conductive silicon nitride substrate 1.
The silicon nitride substrate according to any one of (1) to (51) is oxidized in the air to form a 4 μm thick oxide layer (SiO 2) on the surface.
A high thermal conductive silicon nitride substrate having a thickness of 0.7 mm having _two layers) is prepared, and a slope 2a,
Copper plates 2 and 3 each having a predetermined shape and made of tough pitch copper (oxygen content: 300 ppm) and having a thickness of 0.3 mm were prepared by pressing the 3a along the outer peripheral edge.

The shapes of the inclined portions 2a and 3a are such that the inclination angle θ shown in FIG. 4 is 30 degrees, the thickness t of the thin portion at the tip is 0.05 mm, and the formation positions are the copper plates 2 and 3 The distance L from the outer peripheral edge was set to 0.05 mm.

Then, as shown in FIGS. 1 to 3, two copper plates 2 and 3 are respectively disposed in direct contact with both surfaces of the high thermal conductive silicon nitride substrate 1 and are placed in a nitrogen gas atmosphere at 1348.
By heating under the condition of K and joining, a target silicon nitride circuit board 4A was obtained.

On the other hand, as a comparative example, the inclined portions 2a, 3
A silicon nitride circuit board according to a comparative example was manufactured in the same manner as in Example 1 except that the copper plates 2 and 3 not forming a were used.

The silicon nitride circuit boards according to Example 1 and Comparative Example thus obtained were subjected to a thermal cycle test (T
CT: 233K x 30 minutes + RT x 10 minutes + 398K x 3
0 minutes is defined as one cycle), and the rate of occurrence of cracks in the silicon nitride substrate was measured. As a result, no crack occurred in the silicon nitride circuit board of Example 1 even after 100 cycles of TCT, whereas the silicon nitride circuit board of the comparative example had a crack of 100 cycles. Cracks occurred in 12 to 18%.

Example 2 A high thermal conductive silicon nitride substrate having a thickness of 0.6 mm according to samples 1 to 51 was prepared as the high thermal conductive silicon nitride substrate 1, and the same shape as in Example 1 was formed at the outer peripheral end. Inclined portion 2a,
3a is formed into a predetermined shape having a thickness of 0.3 by pressing.
mm copper plates 2 and 3 were prepared.

Then, as shown in FIG. 5, In: Ag: Cu: Ti = 1 on both surfaces of the high thermal conductive silicon nitride substrate.
An active metal-containing brazing material having a composition of 4.0: 59.0: 23.0: 4.0 is applied as a paste, and the copper plates 2 and 3 are stacked and arranged via this coating layer. The inside was heated and joined to obtain a target silicon nitride circuit board 5A.

The silicon nitride circuit board 5 thus obtained
When a heat cycle test was performed on A under the same conditions as in Example 1, the same good results as in Example 1 were obtained.
It has been confirmed that it has excellent reliability for cooling and heating cycles.

Next, an embodiment of the present invention in which a step portion as a thin portion is formed on a metal plate (copper plate) will be described.

FIG. 7 shows a silicon nitride circuit board 4B in which the copper plate 2 on which the step 2b is formed is integrally joined to the surface 1a of the high thermal conductive silicon nitride substrate 1 by a direct joining method. This silicon nitride circuit board 4B has a stepped portion 2b instead of the inclined portion 2a.
The silicon nitride circuit board 4A shown in FIG.
This is the same configuration as.

FIG. 7 shows a copper plate 2 on which a step 2b is formed.
Is also a plan view showing a silicon nitride circuit board 5B integrally joined to the surface 1a of the high thermal conductive silicon nitride substrate 1 via an active metal-containing brazing material layer (not shown). This silicon nitride circuit board 5B has the same configuration as the silicon nitride circuit board 5A shown in FIG. 5 except that a stepped portion 2b is formed instead of the inclined portion 2a.

Then, the above-described silicon nitride circuit board 4
8B and FIG. 9B, as shown in FIG. 8 and FIG. Are formed. The cross section of the step 2b may be formed in a rectangular shape as shown in FIG. The step 2b is preferably formed by press working using a mold in order to avoid complication of the manufacturing process and reduce the number of manufacturing steps. However, application of another formation method is not necessarily excluded.

It is preferable that the step 2b be formed continuously along the outer peripheral edge of each circuit pattern of the copper plate 2. As described above, by continuously forming the step portion 2b, the concentration of stress on the outer peripheral end portion of the copper plate 2 can be efficiently reduced, in other words, the stress can be efficiently dispersed.

Here, as shown in FIG. 9, the step portion 2b has a thickness t of the step portion 2b of not more than １ ／ of the thickness T of the mounting portion.
Preferably, it is formed to have a thickness of 0.1 mm or less.
The thickness t of the stepped portion 2b is 1 of the thickness T of the portion to be the mounting surface.
If the ratio exceeds / 2, the effect of reducing the residual stress due to the plastic deformation of the step 2b cannot be sufficiently obtained. Further, as the thickness t is reduced, the residual stress can be reduced.
Practically, up to about 0.05 mm is preferable.

As shown in FIG. 9, the formation position of the step 2b, that is, the formation region L of the step 2b formed on the outer peripheral end of the copper plate 2 varies depending on the thickness and size of the copper plate 2, etc. It is preferable that the thickness be within 1.0 mm.

In the above, the copper plate 2 to be bonded to the front surface 1a of the high thermal conductive silicon nitride substrate 1 serving as a mounting portion for semiconductor components and the like has been described in detail. However, the copper plate 2 is bonded to the rear surface 1b of the high thermal conductive silicon nitride substrate 1. As with the copper plate 2 on the front side, it is preferable to form a step 3b at the outer peripheral end of the copper plate 3 as well. Especially, a relatively thick copper plate (metal plate) from the viewpoint of heat dissipation
In the case where is used, it is preferable to form the step 3b also on the copper plate 3 on the back side. Step 3 formed on copper plate 3 on the back side
The shape and the like of b shall conform to the steps 2b formed on the copper plate 2 on the front side.

As described above, the silicon nitride circuit board 4B,
5B, as in the first and second embodiments, a metal plate such as a copper plate 2 or 3 having step portions 2b and 3b formed on a high thermal conductive silicon nitride substrate 1 using a direct bonding method or an active metal method. Manufactured by joining together.

In the silicon nitride circuit boards 4B and 5B having the above-described configuration, the thermal stress generated in the cooling process after the joining of the copper plates 2 and 3, the thermal stress due to the addition of the thermal cycle, and the residual stress based on the thermal stress. The stress is absorbed by the plastic deformation of the steps 2b and 3b provided on the outer peripheral ends of the copper plates 2 and 3, and the concentration of stress on the outer peripheral ends of the copper plates 2 and 3 is reduced. As a result, the stress value itself at the outer peripheral edges of the copper plates 2 and 3 is reduced, so that it is possible to effectively prevent the occurrence of cracks and a decrease in strength of the ceramic substrate portion, which have conventionally been problems.

Next, a specific example of an embodiment in which a step is formed and its evaluation result will be described.

Example 3 First, the silicon nitride substrate used in Example 1 was employed as the high thermal conductive silicon nitride substrate 1. That is, a high thermal conductive silicon nitride substrate having a thickness of 0.7 mm having an oxide layer having a thickness of 4 μm on the surface, and tough pitch copper (oxygen) formed by pressing steps 2b and 3b along the outer peripheral edge. Content: 300 ppm) and copper plates 2 and 3 having a predetermined shape were prepared. The shape of the steps 2b and 3b is the rectangular shape shown in FIGS. 8 and 9, and the thickness t of the thin portion is 0.15 mm (= 1.
/ 2T) and the formation position is the distance L from the copper plates 2 and 3.
Was 1.0 mm.

Then, as shown in FIG. 8, two copper plates 2 and 3 are placed in direct contact with each other on both surfaces of the silicon nitride substrate 1 having a high thermal conductivity, and are heated at 1348 K in a nitrogen gas atmosphere. To obtain the desired silicon nitride circuit board 4B.

On the other hand, as a comparative example, the steps 2b, 3b
Example 3 except that the copper plates 2 and 3 not forming the
Then, a silicon nitride circuit board according to a comparative example was manufactured.

A thermal cycle test was carried out on the silicon nitride circuit boards 4B according to Example 3 and Comparative Example obtained in this manner under the same conditions as in Example 1. Results were obtained. By the way, Example 3
The silicon nitride circuit board according to the comparative example hardly cracked even after 200 cycles of TCT (cracking occurred at 1%), whereas the silicon nitride circuit board according to the comparative example had high thermal conductivity after 200 cycles. Silicon nitride substrate 1-2
Cracks occurred in 1 to 29%.

Example 4 The silicon nitride substrate used in Example 2 was employed as the high thermal conductive silicon nitride substrate 1. That is, a high-heat-conductivity silicon nitride substrate having a thickness of 0.6 mm, a stepped portion 2b, 3b similar to that of the third embodiment, and a copper plate having a thickness of 0.3 mm having a predetermined shape formed by pressing at the outer peripheral end. And 3 were prepared.

The weight ratio of In: Ag: Cu: Ti = 14.0: 5 on both surfaces of the high thermal conductive silicon nitride substrate 1.
An active metal-containing brazing material having a composition of 9.0: 23.0: 4.0 is applied in the form of a paste, and the copper plates 2 and 3 are stacked and arranged via this coating layer. Heating and bonding were performed to obtain a target silicon nitride circuit board 5B.

The silicon nitride circuit board 5 thus obtained
When a heat cycle test was performed on B under the same conditions as in Example 3, the same good results as in Example 3 were obtained.
It has been confirmed that it has excellent reliability for cooling and heating cycles.

According to the silicon nitride circuit boards 4 and 5 according to the above embodiments, in addition to the high strength and high toughness characteristics inherently possessed by the silicon nitride sintered body, a high heat A conductive silicon nitride substrate 1 is used. Therefore, heat generated from a heat-generating component such as a semiconductor element mounted on the substrate is quickly transmitted to the outside of the system through the silicon nitride substrate 1 having high thermal conductivity, so that heat dissipation is extremely good.

Further, since the high thermal conductivity silicon nitride substrate 1 having high strength and high toughness is used, a large amount of maximum deflection of the circuit board can be secured. For this reason, the circuit board does not suffer from tightening cracks in the assembly process, and it is possible to mass-produce semiconductor devices using the circuit board at a high production yield and at low cost.

Further, since the high thermal conductivity silicon nitride substrate 1 has a high toughness, cracks are less likely to occur at the junction between the substrate 1 and the metal circuit board or the metal plates 2 and 3 due to thermal cycling. Is significantly improved, and a semiconductor device excellent in durability and reliability can be provided.

Since the silicon nitride substrate 1 having a higher thermal conductivity is used, even when a semiconductor element for high output and high integration is mounted, deterioration of the thermal resistance characteristic is small and excellent. Demonstrate heat dissipation.

In particular, since the mechanical strength of the silicon nitride substrate itself is excellent, when the required mechanical strength characteristics are fixed, the thickness of the substrate is more reduced than when other ceramic substrates are used. It becomes possible to reduce. Since the substrate thickness can be reduced, the thermal resistance value can be further reduced,
The heat radiation characteristics can be further improved. In addition, since the required mechanical characteristics can be sufficiently coped with even a thinner substrate than before, the substrate manufacturing cost can be further reduced.

[0118]

As described above, according to the silicon nitride circuit board of the present invention, even when a thermal cycle is applied, the thermal stress or residual stress generated in the metal plate is reduced by the inclined portion or the step portion. Absorption by plastic deformation of thin parts such as can reduce stress concentration on the outer peripheral edge of the metal plate, and prevent deformation of the metal plate even by machining that is advantageous in the manufacturing process. it can. Therefore, after simplifying the manufacturing process and reducing the number of manufacturing steps, it is possible to effectively prevent the occurrence of cracks and a decrease in the strength of the ceramic substrate portion due to the addition of a cooling / heating cycle and the like. It is possible to provide a silicon nitride circuit board.

In particular, according to the silicon nitride circuit board according to the present invention, in addition to the high strength and toughness characteristics inherently possessed by the silicon nitride sintered body, in particular, the high thermal conductive silicon nitride having significantly improved thermal conductivity. Since the elementary substrate is used, heat generated from a heat-generating component such as a semiconductor element mounted on the substrate is quickly transmitted to the outside of the system via the high thermal conductivity silicon nitride substrate, so that heat dissipation is extremely good. In addition, since a silicon nitride substrate having high strength and toughness is used, a large amount of maximum deflection of the circuit board can be secured. For this reason, the circuit board does not suffer from tightening cracks in the assembly process, and it is possible to mass-produce semiconductor devices using the circuit board at a high production yield and at low cost.

[Brief description of the drawings]

FIG. 1 is a plan view showing the structure of a silicon nitride circuit board according to one embodiment of the present invention.

FIG. 2 is a back view of the silicon nitride circuit board shown in FIG. 1;

FIG. 3 is a cross-sectional view showing the structure of the silicon nitride circuit board shown in FIG.

FIG. 4 is an enlarged sectional view of a portion IV in FIG. 3;

FIG. 5 is a sectional view showing a structure of a silicon nitride circuit board according to another embodiment of the present invention.

FIG. 6 is an enlarged sectional view of a portion VI in FIG. 5;

FIG. 7 is a plan view showing the structure of a silicon nitride circuit board according to another embodiment of the present invention.

FIG. 8 is a side view showing the silicon nitride circuit board shown in FIG.

FIG. 9 is an enlarged sectional view of a portion IX shown in FIG. 8;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 High thermal conductive silicon nitride substrate 1a Surface of high thermal conductive silicon nitride substrate 1b Back surface of high thermal conductive silicon nitride substrate 2,3 Copper plate (metal plate) 2a, 3a Inclined portion (thin portion) 2b, 3b Step portion (Thin portion) 4,5,4A, 5A, 4B, 5B Silicon nitride circuit board 6 Active metal-containing brazing material layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takayuki Nami 2-4 Suehirocho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Inside the Keihin Plant of Toshiba Corporation (72) Inventor Kotoshi Sato 8-8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Toshiba Yokohama Office

Claims (9)

[Claims] 1. The method according to claim 1, wherein the conversion of the rare earth element to oxide is 1.0 to 1.0.
17.5% by weight, Li, N as impurity cation element
Contains a, K, Fe, Ca, Mg, Sr, Ba, Mn, and B in total of 1.0% by weight or less (including 0% by weight as a detection limit), and has a thermal conductivity of 60 w / mk or more. A high thermal conductive silicon nitride substrate, and a metal plate bonded to the high thermal conductive silicon nitride substrate, wherein a thin portion is formed at an outer peripheral end of the metal plate. A silicon nitride circuit board. 2. The high thermal conductive silicon nitride substrate is composed of Li, Na, K, Fe, Ca, M as impurity cation elements.
2. The silicon nitride circuit board according to claim 1, wherein g, Sr, Ba, Mn, and B are contained in a total of 0.3% by weight or less (including 0% as a detection limit). 3. The method according to claim 1, wherein the conversion of the rare earth element to oxide is 1.0 to 1.0.
A high thermal conductive silicon nitride substrate containing 17.5% by weight, comprising a silicon nitride crystal phase and a grain boundary phase, wherein a ratio of a crystal compound phase in the grain boundary phase to the whole grain boundary phase is 20% or more. And a metal plate joined to the high thermal conductivity silicon nitride substrate, wherein a thin portion is formed at an outer peripheral end of the metal plate. Circuit board. 4. The high thermal conductive silicon nitride substrate is composed of a silicon nitride crystal phase and a grain boundary phase, and the ratio of the crystalline compound phase in the grain boundary phase to the entire grain boundary phase is 50.
5% or more. 5. The silicon nitride circuit board according to claim 1, wherein the metal plate is bonded to the high thermal conductive silicon nitride substrate by a direct bonding method. 6. The silicon nitride circuit board according to claim 1, wherein said metal plate is bonded to said high thermal conductive silicon nitride substrate by an active metal method. 7. The thin part is 1.m from the outer peripheral end of the metal plate.
4. The silicon nitride circuit board according to claim 1, wherein said silicon nitride circuit board is formed within 0 mm. 8. The silicon nitride circuit board according to claim 1, wherein said thin portion is an inclined portion. 9. The silicon nitride circuit board according to claim 1, wherein the thin portion is a step.