JPH1065292A - Composite circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the toughness, strength and conductivity of the entire of a circuit board by arranging a high heat-conducting silicon nitride board having a specific heat conductivity and a board having a specific heat conductivity on the same plane, and jointing a metal circuit board at least to the high heat-conducting silicon nitride board having a specific heat conductivity. SOLUTION: A silicon nitride (Si3 N4 ) board 2, having a heat conductivity of 70W/m.K(60W/m.K or more) is formed, and on the other hand Al2 O3 boards 2a having heat conductivities less than 60W/m.K are formed, and they are combined on the same plane to form a composite board 10. In the circuit-layer forming regions of the surfaces of the silicon nitride board 2 and the alumina boards 2a, active metal soldering material layers 7a, 7b are formed, and they are heated in a vacuum with copper circuit boards 4 kept in touch with a metal board 5 at specified position to make a jointed substance. By arranging high heat-conducting silicon nitride boards, having sharply improved heat conductivities in addition to high strength toughness properties intrinsic in silicon nitride sintered compacts, at regions where signticntly improved strength and heat conduction are required, it becomes possible to improve the toughness, strength and conductivity for the entire of the circuit board.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board on which heat-generating electronic components such as semiconductor elements are mounted, and more particularly to a composite circuit board having improved heat radiation characteristics, mechanical strength and heat resistance cycle characteristics.

[0002]

2. Description of the Related Art Conventionally, an electrically conductive metal circuit board is integrally joined to a surface of a ceramic substrate or a resin substrate having excellent insulation properties, such as an alumina (Al ₂ O ₃ ) sintered body, with a brazing material. Further, ceramic circuit boards and resin circuit boards having electronic components such as semiconductor elements mounted at predetermined positions on a metal circuit board have become widespread.

[0003] On the other hand, a ceramic sintered body containing silicon nitride as a main component generally has excellent heat resistance even in a high temperature environment of 1000 ° C or higher and also has excellent thermal shock resistance. As a high-temperature structural material replacing the heat-resistant superalloy, application to various high-strength heat-resistant parts such as parts for gas turbines, parts for engines, and mechanical parts for steelmaking has been attempted.

[0004] Conventionally, as a composition of a silicon nitride ceramic sintered body, yttrium oxide (Y
It is known that an oxide of a rare earth element or an alkaline earth element such as ₂ O ₃ ), cerium oxide (CeO) and calcium oxide (CaO) is added as a sintering aid. Densification and high strength are achieved by improving sinterability.

A conventional silicon nitride sintered body is formed by adding the above-mentioned sintering aid to a silicon nitride raw material powder and molding the obtained molded body at a temperature of about 1600 to 2000 ° C. in a firing furnace. It is manufactured by a manufacturing method in which the sintered body obtained is calcined after sintering for an hour, and the obtained sintered body is ground and polished.

[0006]

However, although the silicon nitride sintered body manufactured by the above-mentioned conventional method has excellent mechanical strength such as toughness, it does not have the same thermal conductivity as other aluminum nitrides. AlN) sintered bodies, beryllium oxide (BeO) sintered bodies, silicon carbide (SiC) sintered bodies, and the like are significantly lower than sintered bodies. Has not been put into practical use, and has a drawback in that its application range is narrow.

On the other hand, aluminum nitride sintered bodies have characteristics of high thermal conductivity and low coefficient of thermal expansion as compared with other ceramic sintered bodies, so that high-speed, high-output, multifunctional, and large-sized products are developed. It is widely used as a circuit board component and a package material for mounting a semiconductor element (chip). However, there has been no problem that a sufficiently satisfactory mechanical strength has been obtained, so that the circuit board may be damaged in the mounting process, or the mounting process may be complicated and the manufacturing efficiency of the semiconductor device may be reduced. Was.

That is, when a circuit board mainly made of a ceramic substrate such as the above-mentioned aluminum nitride sintered body substrate is to be fixed to a mounting boat by screwing or the like in an assembly process, a slight deformation due to the pressing force of the screw occurs. Circuit board is damaged by
In some cases, the manufacturing yield of a semiconductor device may be significantly reduced.

On the other hand, in a ceramic substrate formed by integrally joining a heat generating component such as a metal circuit board and a semiconductor element to the surface of the aluminum nitride substrate as described above, the mechanical strength and toughness of the aluminum nitride substrate itself are insufficient. Therefore, the aluminum nitride substrate near the joint of the metal circuit board is liable to crack due to repeated thermal cycling accompanying the operation of the semiconductor element, and there has been a problem that heat cycle characteristics and reliability are low.

Further, even when a circuit board is manufactured using a ceramic substrate having a high thermal conductivity such as aluminum nitride, an aluminum nitride substrate having a large thickness is required to secure a certain strength value and insulation resistance. Had to be used. Therefore, despite the high thermal conductivity of the AlN substrate, the thermal resistance value of the entire circuit board increases, and a problem that high heat radiation in proportion to the thermal conductivity of the AlN substrate itself cannot be obtained. there were.

SUMMARY OF THE INVENTION The present invention has been made to address the above-mentioned problems, and utilizes the high strength and toughness characteristics inherent in a silicon nitride sintered body, and further has a high thermal conductivity and excellent heat dissipation. It is an object of the present invention to provide a composite circuit board for mounting electronic components with significantly improved heat cycle characteristics.

[0012]

Means for Solving the Problems To achieve the above object, the present inventor has set forth the heat radiation (thermal conductivity) of a ceramic substrate.
Research on substrate materials that satisfy both strength and toughness values without deteriorating the quality of the ceramic substrate, and conducted intensive research on measures to prevent tightening cracks that occur during the assembly process of ceramic substrates and cracks that occur when a thermal cycle is added. . As a result, it was found that a silicon nitride sintered body having a high thermal conductivity (60 W / m · K or more) can be obtained by appropriately controlling the composition and manufacturing conditions of the substrate material.

A part of such a highly thermally conductive silicon nitride sintered body having a thermal conductivity of 60 W / m · K or more has already been applied for a patent by the present inventor. And JP-A-7-48174
The application has been published by the official gazette. And the silicon nitride sintered body described in these patent applications,
It contains 2.0 to 7.5% by weight of a rare earth element in terms of oxide. However, as a result of further improvement research, the present inventor has found that when the content of the rare earth element exceeds 7.5% by weight in terms of oxide, the sintered body has higher thermal conductivity, and It has been found that it has good binding properties and is applied to the present invention. In particular, when the rare earth element is a lanthanoid element, the effect is remarkable. Incidentally, even when the ratio of the crystalline compound phase in the grain boundary phase to the whole grain boundary phase is 60 to 70%,
The silicon nitride sintered body can achieve a high thermal conductivity of 110 to 120 W / m · K or more.

However, this new silicon nitride sintered body uses a raw material powder with a strictly reduced amount of impurities, or a slow cooling rate after sintering, as is apparent from the manufacturing method described later. Therefore, there is a problem that the manufacturing time is lengthened, the process is complicated, and the manufacturing cost is significantly increased. That is, when the whole substrate is formed of the high thermal conductive silicon nitride sintered body, there is a problem that the production time, process and cost of the circuit substrate are significantly increased.

Therefore, in consideration of the required characteristics of each part of the circuit board, for example, a board made of the above-mentioned silicon nitride sintered body having a high thermal conductivity is disposed at a part of the circuit board where high strength characteristics and high thermal conductivity are required. On the other hand, a composite substrate was prepared by arranging a general-purpose, easy-to-manufacture and inexpensive substrate such as an alumina (Al ₂ O ₃ ) substrate or a resin substrate on the same plane at other portions. Further, a composite substrate was prepared by laminating a substrate made of a silicon nitride sintered body having high thermal conductivity and a general-purpose, easy-to-manufacture and inexpensive substrate in the thickness direction.

[0016] When a metal circuit board is integrally formed on the surface of the composite substrate and a semiconductor element is mounted on the composite circuit board to form a composite circuit board, the manufacturing cost can be greatly reduced. And found that the heat cycle characteristics can be significantly improved, and that the heat dissipation of the circuit board can be significantly improved, and the present invention has been completed.

Further, a substrate made of the high thermal conductive silicon nitride sintered body and a general-purpose, easy-to-manufacture and inexpensive alumina substrate or resin substrate are arranged on the same plane to form a composite substrate, or both are laminated. When a circuit board is manufactured by bonding a conductive metal circuit board to the surface of the composite board and mounting a semiconductor element on the metal circuit board, mechanical strength, toughness, heat resistance Experiments have confirmed that an inexpensive composite circuit board that satisfies all of the cycle characteristics and heat dissipation can be obtained.

Here, the development of the above-mentioned high thermal conductivity silicon nitride sintered body will be described below.

That is, a raw material mixture obtained by adding a predetermined amount of a rare earth element oxide or the like to fine and high-purity silicon nitride powder is molded and degreased, and the obtained molded body is heated and maintained at a predetermined temperature for a predetermined time. After performing the densification sintering, it is gradually cooled at a predetermined cooling rate or less, and when the obtained sintered body is manufactured by grinding and polishing, the thermal conductivity of the sintered body is equal to that of a conventional silicon nitride sintered body.
It has been found that a silicon nitride sintered body having a large improvement of at least 60 W / mK and a high strength and high toughness can be obtained. The present inventors have developed a silicon material.
It has been found that when this silicon nitride material is applied to a substrate material of a circuit board, excellent heat dissipation characteristics, durability and heat cycle characteristics can be simultaneously improved.

Further, a glass phase (amorphous phase) in a grain boundary phase is obtained by sintering a high-purity silicon nitride raw material powder having a reduced content of oxygen and impurity cation elements under the above conditions. Can be effectively suppressed, and the ratio of the crystalline compound phase in the grain boundary phase becomes 20% or more (based on the whole grain boundary phase), more preferably 50% or more, and only the rare earth element oxide is added to the raw material powder. 60W /
It has been found that a silicon nitride sintered body having a high thermal conductivity of at least m · K, more preferably at least 80 W / m · K can be obtained.

Conventionally, when the sintered body is cooled by turning off the heating power supply of the sintering furnace after the sintering operation is completed, the cooling rate was as fast as 400 to 800 ° C. per hour. According to the experiment of the inventor, the grain boundary phase of the silicon nitride sintered body structure is changed from an amorphous state to a crystalline state by controlling the cooling rate of the sintered body immediately after sintering slowly to 100 ° C./hour or less. It was found that the phase changed to a phase containing a phase, and high strength characteristics and high heat transfer characteristics were simultaneously achieved.

The silicon nitride sintered body satisfying both high strength characteristics and high heat transfer characteristics is used as a part of the substrate material.
By forming a circuit board by integrally bonding a metal circuit board to the surface of the board material, the toughness and thermal conductivity of the entire circuit board can be improved, especially when tightening cracks and thermal cycling during the circuit board assembly process It has been found that cracks can be effectively prevented from being generated by the addition of.

In particular, while the silicon nitride sintered body is arranged on a circuit board at a site where structural strength and high thermal conductivity are required, a general-purpose, easy-to-manufacture and inexpensive alumina or resin substrate is arranged at another site. By forming a composite substrate or laminating a substrate made of a silicon nitride sintered body and the above-mentioned alumina substrate or resin substrate to form a composite substrate, silicon nitride is formed only in a predetermined portion where heat dissipation is particularly required. It has been found that the use of the substrate made of the sintered body makes it possible to obtain a circuit board having improved heat radiation properties as a whole of the composite substrate and less occurrence of fastening cracks of the circuit board in the assembly process.

The present invention has been completed based on the above findings. That is, in the composite circuit board according to the first aspect of the present invention, the high thermal conductive silicon nitride substrate having a thermal conductivity of 60 W / m · K or more and the substrate having a thermal conductivity of less than 60 W / m · K are flush with each other. The metal circuit board is arranged on the high thermal conductive silicon nitride substrate having the thermal conductivity of at least 60 W / m · K.

The composite circuit board according to the second aspect of the present invention includes a high thermal conductive silicon nitride substrate having a thermal conductivity of 60 W / m · K or more and a substrate having a thermal conductivity of less than 60 W / m · K. And a metal circuit board is bonded to a high thermal conductive silicon nitride substrate having at least the thermal conductivity of 60 W / m · K or more.

Furthermore, the composite circuit board according to the third invention of the present application has a heat conductivity of less than 60 W / m · K on the surface of the board.
A plurality of high thermal conductivity silicon nitride substrates having a thermal conductivity of 60 W / m · K or more are arranged.

Here, as the substrate having a thermal conductivity of less than 60 W / m · K, an alumina (Al ₂ O ₃ ) substrate or a resin substrate can be used.

A metal plate may be joined via an oxide layer formed on the back surface of the high thermal conductivity silicon nitride substrate and a general-purpose, easy-to-manufacture and inexpensive substrate having a thermal conductivity of less than 60 W / m · K. Further, the metal plate may have a structure in which the metal plate is directly bonded to both a high thermal conductivity silicon nitride substrate and a general-purpose and inexpensive substrate via an oxide layer.

That is, the composite circuit board of the present invention maintains strength and heat dissipation by combining a silicon nitride board having excellent thermal conductivity, strength and toughness with a general-purpose, easy-to-manufacture and inexpensive board. Easy to manufacture and inexpensive circuit board,
That is, it is possible to obtain a composite circuit board. The above silicon nitride substrate and a thermal conductivity of 60 W / m
-The arrangement form of the substrate less than K is roughly divided into three types. That is, a configuration in which both substrates are arranged adjacently on the same plane, a configuration in which both substrates are stacked and arranged so as to have a sandwich structure, and a configuration in which a plurality of high thermal conductive silicon nitrides are formed on the surface of an alumina substrate or a resin substrate. Although there is a form in which the elementary substrate is arranged, the above-described forms may be used in combination depending on required characteristics.

For example, by arranging a high thermal conductive silicon nitride substrate at a portion where a semiconductor element which is a high thermal component is mounted, good heat radiation of the entire circuit board can be ensured. In addition, by constructing the surface part where mechanical pressure and mechanical stress act directly on a high-strength and high-toughness silicon nitride substrate, it suppresses the occurrence of cracks due to tightening cracks and the addition of thermal cycles during the assembly process. It is possible to do.

Further, in the composite circuit board according to the first aspect of the present invention, the high thermal conductive silicon nitride substrate and the Ti, Z formed on the surface of the general-purpose, easy-to-manufacture and inexpensive substrate are provided.
The metal circuit board may be bonded via a metal bonding layer containing at least one active metal selected from r, Hf and Nb.

Further, the metal plates may be bonded via a metal bonding layer formed on the back surface of a high thermal conductive silicon nitride substrate and a general-purpose, easily manufactured and inexpensive substrate. Further, the thickness of the metal circuit board is preferably set to be larger than the thickness of the metal board. Further, the metal plate is bonded to both the high thermal conductive silicon nitride substrate and the general-purpose and inexpensive substrate via the metal bonding layer. Furthermore, it is preferable that at least one metal circuit board is bonded to both the high thermal conductive silicon nitride substrate and the general-purpose and inexpensive substrate via the metal bonding layer.

Further, in the composite circuit board according to the second aspect of the present invention, a high thermal conductivity silicon nitride substrate having a thermal conductivity of 60 W / m · K or more and a general-purpose and inexpensive substrate are laminated, and the general-purpose substrate is used. The semiconductor device may be configured so as to be sandwiched by the silicon nitride substrate and bonded via a metal bonding layer containing at least one active metal selected from Ti, Zr, Hf and Nb. Here, the above-mentioned general-purpose and inexpensive substrate and the silicon nitride substrate are integrally joined by an active metal joining method, a glass joining method, or a direct joining method, similarly to the joining method of the metal plate. A general-purpose and inexpensive substrate may be formed thicker than a high-thermal-conductivity silicon nitride substrate.

The high thermal conductive silicon nitride substrate used in the present invention has a rare earth element converted to an oxide of 2.0 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 are configured to contain 0.3% by weight or less in total.

In another embodiment, the high thermal conductive silicon nitride substrate is formed by converting a rare earth element into an oxide in the range of 2.0 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.

It is particularly preferable to use a lanthanoid 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 for producing 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,
A rare earth element is added to a silicon nitride powder containing 0.3% by weight or less in total of Mg, Sr, Ba, Mn, and B and 90% by weight or more of α-phase silicon nitride and having an average particle size of 1.0 μm or less. A raw material mixture containing 2.0 to 17.5% by weight or less in terms of oxide and 1.0% by weight or less of at least one of alumina and aluminum nitride is added as needed to prepare a molded body. After degreasing the obtained molded body, the temperature was 1800
Atmospheric pressure sintering at ~ 2100 ° C. From the above sintering temperature,
The cooling rate of the sintered body to a temperature at which a liquid phase formed at the time of sintering by the rare earth element is solidified is set to 100 ° C./hour or less and gradually cooled.

In the above method, at least one of alumina and aluminum nitride may be added to the silicon nitride powder in an amount of 1.0% by weight or less.

Further, Ti, Z were 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 0.3% by weight or less, preferably 0.2% 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 size of 1.0 μm or less, a dense silicon nitride substrate having a porosity of 2.5% or less can be formed even with a small amount of a sintering aid. And the likelihood of the sintering aid interfering with the heat transfer properties 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. This can be achieved by making the total 0.3% by weight or less. Particularly for the same reason, the content of the impurity cation element is set to 0.2% by weight or less 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.

Furthermore, by using a 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 lanthanoid series elements such as Ho, Er and Yb as rare earth elements, sinterability or high thermal conductivity is improved, and sufficiently dense sintering can be achieved 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 2.0 to 17.5% by weight in terms of oxide based on the raw material powder.
When the addition amount is less than 2.0% 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-based 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 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 component plays a role of promoting 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, the total addition amount is desirably 1.0% by weight or less.

Aluminum nitride (AlN) as another additive component 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 a silicon nitride crystal and a grain boundary phase, and the ratio of the crystalline compound phase in the grain boundary phase greatly affects the thermal conductivity of the sintered body. However, in the silicon nitride substrate used in the present invention, the grain boundary phase 2
0% or more, more preferably 50% or more.
% Or more is desirably occupied by the crystal phase. Crystal phase 20
%, It is not possible to obtain a silicon nitride substrate having excellent heat radiation characteristics such that the thermal conductivity is 60 W / m · K or more and excellent in high-temperature strength.

Further, as described above, the porosity of the 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. Means that the silicon nitride compact is heated to a temperature of 1800 to 2100.
It is important to perform pressure sintering at about 2 ° C. for about 2 to 10 hours and gradually cool the sintered body immediately after completion of the sintering operation at a cooling rate of 100 ° C. or less per hour.

When 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 body immediately after the completion of the sintering operation is an important control factor for crystallizing the grain boundary phase, and when a 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 silicon nitride substrate used in the present invention is manufactured through, for example, 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 forming method of the raw material mixture, a general-purpose mold pressing method, a sheet forming method such as a doctor blade method, or the like can be applied. Subsequent to the molding operation, the molded body is heated in a non-oxidizing atmosphere at a temperature of 600 to 800 ° C. or in air at a temperature of 400 to 500 ° C. for 1 to 2 hours,
Organic binder components added in advance are sufficiently removed and degreased. Next, the molded body subjected to the degreasing treatment is subjected to 1800 in an inert gas atmosphere such as nitrogen gas, hydrogen gas or argon gas.
Atmospheric pressure sintering is performed at a temperature of ２2100 ° C. for a predetermined time.

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 the silicon nitride sintered body of which the thermal conductivity as a whole is 60 W / m · K or more by adding high thermal conductivity SiC or the like to silicon nitride having low thermal conductivity is the present invention. Not included in range. However, the thermal conductivity is 60W
/ M · K or higher silicon nitride sintered body with high thermal conductivity S
It goes without saying that a silicon nitride-based sintered body in which iC or the like is compounded is included in the scope of the present invention.

The thickness of the high thermal conductive silicon nitride substrate is set to various thicknesses according to the required characteristics when used as a circuit board, but is set to be twice or less the thickness of the circuit layer. Good to do. When the thickness of the silicon nitride substrate exceeds twice the thickness of the circuit layer, the thickness of the entire circuit substrate increases and the thermal resistance increases. The specific thickness of the silicon nitride substrate is 0.2
The range is 5 to 1.2 mm. In particular, by setting the thickness of the silicon nitride substrate to 0.8 mm or less, the thickness of the entire circuit board can be reduced, and the difference in thermal resistance between the upper and lower surfaces of the circuit board can be more effectively reduced. As a result, the heat radiation of the entire circuit board can be further improved.

On the other hand, the thermal conductivity used in the present invention is 60
The substrate having a value of less than W / m · K is not particularly limited. However, from the viewpoint of low manufacturing cost, a general-purpose and inexpensive substrate such as an alumina (Al ₂ O ₃ ) substrate or a resin substrate can be suitably used.

In the present invention, the thermal conductivity is 60 W / m · K
The above silicon nitride substrate having high thermal conductivity and a thermal conductivity of 60 W /
Two types of substrates, a general-purpose and inexpensive substrate of less than m · K, are selectively used according to the required characteristics of the circuit board, and are arranged on the same plane or laminated to form a composite substrate. That is, while the silicon nitride substrate having high thermal conductivity is arranged in a part where structural strength and heat dissipation are particularly required, a general-purpose, easy-to-manufacture and inexpensive substrate is arranged on the same plane in other parts, To form a composite substrate.

The composite circuit board according to the present invention is obtained by integrally bonding a metal circuit board having conductivity as necessary to the surface of the composite board manufactured as described above, and furthermore, connecting the semiconductor circuit via the metal circuit board. It is manufactured by mounting elements.

Further, as described above, the metal plate is provided on the back surface of the composite substrate obtained by combining the high thermal conductive silicon nitride substrate and the general-purpose and inexpensive substrate on the same plane, that is, the surface opposite to the metal circuit board bonding surface. It is good to join together. The metal plate is formed of the same material as the metal circuit board. By joining this metal plate integrally, it becomes easy to join the circuit board to a heat radiating component such as a heat sink, and the circuit board is warped or deformed due to the difference in thermal expansion between the composite board and the metal circuit board. It can be effectively prevented.

In particular, by setting the thickness of the relatively sparsely formed metal circuit board to be greater than the thickness of the densely formed metal board, the amount of metal disposed on the front and back of the composite board can be reduced. It is possible to make the same, the difference in thermal expansion between the front and back of the composite board is reduced, and the warpage and deformation of the composite circuit board can be more effectively prevented.

When at least one metal circuit board or at least one metal plate is integrally joined over both a high thermal conductive silicon nitride substrate and a general-purpose and inexpensive substrate, the same plane can be obtained. The silicon nitride substrate and the general-purpose and inexpensive substrate are connected to each other, and the integration of the composite circuit substrate can be improved.

The joining method of the metal circuit board and the metal plate is not particularly limited, and a direct joining method or an active metal method described below can be applied.

The direct bonding method has a thickness of 0.5 to 0.5 mm on the surface of a composite substrate composed of a silicon nitride substrate and a general-purpose and inexpensive substrate.
An oxide layer of about 10 μm is formed, and through this oxide layer,
This is a method of directly bonding a metal circuit board or a metal plate to be a circuit layer to the composite substrate. Here, the metal circuit board and the metal plate are directly bonded to the surface of the composite substrate without using a bonding agent such as a brazing material. That is, a eutectic compound of the component of the metal circuit board and the substrate component is generated by heating, and the two members are joined using the eutectic compound as a joining agent. This direct bonding method can be applied only to oxide-based ceramics such as Al ₂ O ₃ , and even if applied directly to non-oxide-based ceramics such as a silicon nitride substrate or an aluminum nitride substrate, the wettability to the substrate is low. Since it is low, sufficient bonding strength of the metal circuit board cannot be obtained.

Therefore, it is necessary to form an oxide layer on the surfaces of the silicon nitride substrate and the aluminum nitride substrate in advance to enhance the wettability to the substrate. This oxide layer is formed by subjecting the silicon nitride substrate and the aluminum nitride substrate to an oxidation atmosphere such as air at a temperature of about 1000 to 1400 ° C. for 0.1 to 4 hours.
It is formed by heating for 8 hours. The thickness of this oxide layer is 0.5
When the thickness is less than 10 μm, the effect of improving the wettability is small. On the other hand, when the thickness exceeds 10 μm, the improvement effect is saturated and the thermal conductivity tends to be lowered. In the range of 5 to 10 μm, more preferably 1
５5 μm.

The oxide layer of the Si ₃ N ₄ substrate is initially formed of Si
_Although it is composed only of SiO ₂ which is an oxide of the 3N ₄ substrate component, the rare earth element oxide added as a sintering aid to the Si ₃ N ₄ substrate during the joining operation of the metal circuit board by heating Is diffused and moved in the direction of the oxide layer, so that the rare earth oxide is concentrated in the oxide layer. For example oxide layer after heating the joining operation if as a sintering aid was used Y ₂ O ₃ is, SiO ₂ -Y ₂ O ₃ compound such yttria silicate containing Y ₂ O ₃ about 1 to 20 wt% Will be composed of On the other hand, when an AlN substrate is used as a general-purpose and inexpensive substrate, the oxide layer of the AlN substrate is composed of Al ₂ O ₃ .

The metal constituting the metal circuit board and the metal plate includes copper, aluminum, iron, nickel, chromium, and the like.
Simple substance of silver, molybdenum, cobalt or alloy thereof
The metal is not particularly limited as long as it is a metal that can form a eutectic compound with the substrate component and can be applied with the direct bonding method, but copper, aluminum or an alloy thereof is particularly preferable from the viewpoints of conductivity and cost.

The thickness of the metal circuit board (circuit layer) is determined in consideration of the current carrying capacity, etc., while the thickness of the silicon nitride substrate is in the range of 0.25 to 1.2 mm, If the thickness of the plate is set in the range of 0.1 to 0.5 mm and the two are combined, the plate is less susceptible to deformation or the like due to a difference in thermal expansion.

When the metal circuit board or the metal plate is a copper circuit board, the joining operation is performed as follows. That is, in a state where a copper circuit board is in contact with a predetermined position on the surface of a silicon nitride substrate on which an oxide layer is formed and a general-purpose and inexpensive substrate and pressed toward the substrate, the copper circuit board is pressed at a temperature lower than the melting point of copper (1083 ° C.). And eutectic temperature of copper-copper oxide (1065 ° C)
The copper circuit board and the like are directly bonded to the surface of the silicon nitride substrate and the general-purpose and inexpensive substrate by using the liquid phase of the Cu—O eutectic compound generated by heating as the bonding agent. This direct bonding method is a so-called copper direct bonding method (DBC: Direct Bonding C).
opper method). Further, a semiconductor element (Si chip) is soldered and mounted at a predetermined position on the copper circuit board directly bonded on the Si ₃ N ₄ substrate, whereby the composite circuit board according to the present invention is manufactured. In addition, as a general-purpose and cheap substrate, Al
_When an oxide ceramic substrate such as a ₂ O ₃ substrate is used, it is needless to say that it is not necessary to form an oxide layer as described above.

On the other hand, when the metal circuit board or the metal plate is an aluminum circuit board, the eutectic temperature of aluminum-silicon is obtained by pressing the Al circuit board against the surface of a Si ₃ N ₄ substrate or a general-purpose and inexpensive substrate. Al-S produced by heating above
The Al circuit board is directly bonded to the surface of the Si ₃ N ₄ substrate using the i-eutectic compound as a bonding agent. Then, the semiconductor element is soldered and mounted at a predetermined position on the Al circuit board directly bonded to the Si ₃ N ₄ substrate, whereby the composite circuit board of the present invention is manufactured.

As described above, according to the present invention, the metal circuit board is directly bonded to the composite substrate surface by using the direct bonding method, and a plurality of semiconductor elements are mounted on the metal circuit board on the Si ₃ N ₄ substrate. According to the composite circuit board according to
Since there is no inclusion such as an adhesive or a brazing material between the i ₃ N ₄ substrate and a general-purpose and inexpensive substrate, the thermal resistance between the two is small, and the semiconductor element provided on the metal circuit board is not provided. It is possible to quickly dissipate the heat generated outside the system.

Next, a method of joining metal circuit boards and the like by the active metal method will be described.

In the active metal method, a thickness of the Ag-Cu-Ti-based brazing material containing at least one active metal selected from Ti, Zr, Hf and Nb and having an appropriate composition ratio is applied to the surface of the composite substrate by using a thick metal. A metal bonding layer (active metal brazing material layer) having a thickness of about 20 μm is formed, and a metal circuit board such as a copper circuit board or a metal plate is bonded via the metal bonding layer. The active metal has an effect of improving the wettability of the brazing material to the substrate and increasing the bonding strength. As a specific example of the active metal brazing material, 1% to 10% of the active metal and 15% to
Preferred is a braze composition comprising 35%, with the balance substantially consisting of Ag. The metal bonding layer is formed by a method such as screen-printing a bonding composition paste prepared by dispersing the brazing material composition in an organic solvent on the surface of the composite substrate.

Then, in a state where a metal circuit board or a metal plate serving as a circuit layer is placed in contact with the screen-printed metal bonding layer in a vacuum or an inert gas atmosphere, for example, Ag is used.
By heating to a temperature not lower than the Cu eutectic temperature (780 ° C.) and not higher than the melting point of the metal circuit board (1083 ° C. for copper), the metal circuit board is bonded to the composite substrate via the metal bonding layer. You.

In the above-mentioned circuit board, a circuit layer is formed by integrally joining a metal circuit board or a metal plate on a composite board using a direct joining method or an active metal method. It is also possible to form a circuit layer. That is, in the metallization method, for example, molybdenum (Mo)
Method of baking a metallized composition mainly composed of a refractory metal such as tungsten or tungsten (W) and Ti or its compound on the surface of a composite substrate to form a refractory metal metallized layer as a circuit layer having a thickness of about 15 μm It is. When a circuit layer is formed by this metallization method, it is preferable to further form a metal plating layer of Ni or Au having a thickness of about 3 to 5 μm on the surface of the metallized layer. By forming the metal plating layer, the surface smoothness of the metallized layer is improved, the adhesion to the semiconductor element is further improved, and the solder wettability is improved. Therefore, the bonding strength of the semiconductor element using solder is improved. Can be further enhanced.

According to the composite circuit board having the above structure, in addition to the high strength and high toughness characteristics inherently possessed by the silicon nitride sintered body, a high thermal conductivity silicon nitride substrate having a significantly improved thermal conductivity is provided. In particular, while arranging the parts where structural strength and heat dissipation are required, general-purpose, easy-to-manufacture and inexpensive substrates such as alumina substrates and resin substrates are arranged in other parts, and both substrates are arranged on the same plane. The composite circuit board is formed by laminating, a metal circuit board is integrally joined to the surface of the composite board, and a semiconductor element is mounted on the metal circuit board joined to the silicon nitride substrate. Therefore, the manufacturing cost is low, and the heat generated from heat-generating components such as semiconductor elements is quickly transmitted to the outside of the system through the silicon nitride substrate having high thermal conductivity, so that heat dissipation is extremely good. In addition, a high thermal conductivity silicon nitride substrate with high strength and toughness,
In particular, by arranging the parts where structural strength is required,
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.

Since the silicon nitride substrate has a high toughness value,
It is possible to provide a semiconductor device in which cracks are less likely to occur in a joint portion between a substrate and a metal circuit board or a metal plate due to a heat cycle, heat resistance cycle characteristics are remarkably improved, and durability and reliability are excellent.

Since a silicon nitride substrate having a higher thermal conductivity is used, even when a semiconductor element for high output and high integration is mounted, deterioration of thermal resistance characteristics is small and excellent. Exhibits 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.

When only a conventional high thermal conductive aluminum nitride substrate is used as a constituent material of a circuit board, it is necessary to increase the thickness of the aluminum nitride substrate in order to secure a certain level of mechanical strength. However, in the circuit board of the present invention, high heat dissipation is ensured at the same time as high heat dissipation properties are secured by the silicon nitride substrate. In addition, the thickness of a general-purpose, easy-to-manufacture, inexpensive substrate such as an alumina substrate or a resin substrate can be reduced to the thickness of a silicon nitride substrate, so that the substrate can be formed in a small size. It is possible to further reduce the thermal resistance value synergistically. Therefore, according to the present invention, the heat radiation can be further improved as compared with a conventional circuit board using only a conventional general-purpose and inexpensive board having the same thermal conductivity.

[0090]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be specifically described with reference to the following examples. First, an embodiment of a composite circuit board in which a silicon nitride substrate and an alumina substrate as a general-purpose and inexpensive substrate are arranged on the same plane will be described.

Examples 1 to 3 1.3% by weight of oxygen, Li, as impurity cation element
Na, K, Fe, Ca, Mg, Sr, Ba, Mn, and B are contained in a total of 0.15% by weight, and α-phase silicon nitride is 97%.
Of silicon nitride raw material powder having an average particle size of 0.55 μm containing Y ₂ O having an average particle size of 0.7 μm as a sintering aid.
₃ (yttrium oxide) powder 5% by weight, average particle size 0.5
1.0 wt% of Al ₂ O ₃ (alumina) powder having a thickness of μm was added, and the mixture was wet-mixed in ethyl alcohol for 24 hours and then dried to prepare a raw material powder mixture. Next, a predetermined amount of an organic binder is added to the obtained raw material powder mixture, and the mixture is uniformly mixed, and then press-molded at a molding pressure of 1000 kg / cm ² ,
A number of molded bodies having a length of 80 mm, a width of 50 mm and a thickness of 1 to 5 mm were produced. Next, after the obtained molded body was degreased in an atmosphere gas at 700 ° C. for 2 hours, the degreased body was held in a nitrogen gas atmosphere at 7.5 atm at 1900 ° C. for 6 hours to carry out densification sintering. Then, the cooling rate of the sintered body until the temperature in the sintering furnace drops to 1500 ° C. is controlled by controlling the amount of electricity supplied to the heating device attached to the sintering furnace.
° C / hr, the sintered body was gradually cooled, and each of the obtained sintered bodies was polished to obtain a heat conductivity k of 7 or more.
0 W / m · K, and the thickness is 0.4 mm, 0.6 mm, 0.
Silicon nitride (Si ₃ N ₄ ) for Examples 1 to 3 which is 8 mm
A substrate was prepared.

On the other hand, a general-purpose and inexpensive substrate having a thermal conductivity of less than 60 W / m · K has a thermal conductivity of 20 W / m · K.
Example 1 which is K and has the same thickness as the Si ₃ N ₄ substrate
Alumina (Al ₂ O ₃ ) substrates for Nos. 1 to ₃ were manufactured.

Next, as shown in FIGS. 1 and 2, a composite substrate 10 was formed by combining an Si ₃ N ₄ substrate 2 and an Al ₂ O ₃ substrate 2a having the same thickness on the same plane. That is, the portion where the semiconductor element 6 is mounted is Si ₃ N
_{4 While the} substrate 2 is placed, Al ₂ O ₃
The substrate 2a was arranged to form the composite substrate 10.

Next, as shown in FIGS. 1 and 2, 30 wt% Ag is added to the portions where the circuit layers are formed on the surface of each silicon nitride substrate 2 and alumina substrate 2a and the portion where the metal plate (copper plate) on the back surface is joined. -65% Cu-5% Ti brazing material was screen-printed and dried to form active metal brazing layers 7a and 7b having a thickness of 20 μm. This active metal brazing material layer 7a,
7b, at a predetermined position, a thickness of 0.1 mm made of tough pitch electrolytic copper.
A temperature of 850 ° C. in vacuum with a 3 mm copper circuit board 4 and a metal plate (back copper plate) 5 having a thickness of 0.25 mm in contact with each other.
For 10 minutes to obtain a conjugate. Next, a predetermined circuit pattern (circuit layer) was formed by performing an etching process on each bonded body. Further, the semiconductor element 6 is disposed at the center of the copper circuit board 4 joined to the upper surface of the Si ₃ N ₄ substrate 2 via the solder layer 8.
To produce a large number of composite circuit boards 1 according to Examples 1 to 3.

Comparative Example 1 Si ₃ N ₄ substrate 2 used in Examples 1 to ₃ and Al ₂ O ₃
Instead of the composite substrate 10 comprising the substrate 2a, the thermal conductivity k
182 W / m · K, and a copper circuit was formed on the substrate surface by the active metal method in the same manner as in Examples 1 to 3 except that a ceramic substrate consisting of only an aluminum nitride (AlN) sintered body having a thickness of 0.8 mm was used. The ceramic circuit board according to Comparative Example 1 was manufactured by integrally joining the plate and the metal plate.

When the maximum deflection and flexural strength of the circuit boards according to Examples 1 to 3 and Comparative Example 1 thus prepared were measured, the composite circuit boards 1 according to Examples 1 to 3 It was found that the circuit board had a maximum deflection amount and bending strength twice or more as compared with the circuit board of Comparative Example 1 using only the aluminum nitride substrate. It was also confirmed that the amount of deflection and the bending strength were further improved as the thickness of the composite circuit board was reduced. Further, it was confirmed that the heat resistance was reduced by reducing the thickness of the substrate, so that the heat radiation characteristics of the entire circuit substrate could be further improved.

As shown in FIG. 2, when the composite circuit board of each of the above embodiments was mounted on a board in an assembly process after being joined to a heat sink 9, no tightening cracks occurred and the semiconductor device using the circuit board was expensive. Mass production was possible with a production yield.

Further, each circuit board is heated from -45 ° C. to room temperature (RT), and subsequently from room temperature to + 125 ° C.
A heat cycle test in which heating and cooling are repeated until the substrate is cooled down to −45 ° C. through room temperature, and the number of cycles until cracks or the like occur in the substrate is measured. In the composite circuit boards of Examples 1 to ₃ , cracking of the Si ₃ N ₄ substrate or Al ₂ O ₃ substrate and peeling of the metal circuit board (Cu circuit board) and the metal plate were observed even after 1000 cycles. It was found that there was none, and excellent heat cycle characteristics were exhibited.
On the other hand, in the circuit board of Comparative Example 1, cracks occurred in 100 cycles, and it was confirmed that the durability was low.

Example 4 The Si ₃ N ₄ substrates prepared in Examples 1 to 3 had a thermal conductivity k of 70 W / m · K and a thickness of 0.4 W each.
By heating each Si ₃ N ₄ substrate of mm, 0.6 mm and 0.8 mm in an oxidation furnace at a temperature of 1300 ° C. for 12 hours,
The entire surface of the substrate was oxidized to form an oxide layer having a thickness of 2 μm. The oxide layer is formed of a SiO ₂ film.

On the other hand, the Al prepared in Examples 1 to 3
₂ O ₃ is a substrate, the thermal conductivity k is 20W / m · K, thickness was 0.4mm, respectively, 0.6 mm, each the Al ₂ O ₃ substrate which is 0.8mm were prepared.

Next, as shown in FIG. 3, S having the same thickness
An i ₃ N ₄ substrate 2 and an Al ₂ O ₃ substrate 2 a were combined on the same plane to form composite substrates 10. That is, the Si ₃ N ₄ substrate 2 was disposed at the portion where the semiconductor element 6 was mounted, while the Al ₂ O ₃ substrate 2a was disposed at the other portions to form the composite substrate 10.

Next, the Si ₃ N ₄ substrate 2 on which the oxide layer 3 has been formed
A copper circuit board made of tough pitch electrolytic copper having a thickness of 0.3 mm is disposed in contact with the surface side of a composite substrate 10 obtained by compounding the substrate with each Al ₂ O ₃ substrate 2 a, while a 0.25 mm thick copper circuit board is provided on the back side. A metal plate made of tough pitch copper is contacted and arranged as a backing material to form a laminate, and the laminate is inserted into a heating furnace at a temperature of 1075 ° C. adjusted to a nitrogen gas atmosphere and heated for 1 minute, whereby each composite substrate 10 A copper circuit board or a metal plate was directly bonded to both surfaces of the substrate, and a semiconductor element was further soldered to prepare a composite circuit board 1a according to Example 4.

As shown in FIG. 3, each composite circuit board 1a has an oxide layer 3 made of SiO _{2 on} the entire surface of a Si ₃ N ₄ substrate 2.
Is formed. The copper circuit board 4 as a metal circuit board is directly joined to the front side of the composite board 10 composed of the Si ₃ N ₄ board 2 and the Al ₂ O ₃ board 2a, while the back copper board is provided on the back side. metal plate 5 as is bonded Similarly directly, further Si ₃
The semiconductor device 6 has a structure in which a semiconductor element 6 is integrally joined via a solder layer 8 at a predetermined position of the copper circuit board 4 joined to the front side of the N ₄ substrate 2. When the copper circuit board 4 or the metal plate 5 is joined to both surfaces of the composite substrate 10, the metal plate 5 as the back copper plate is effective because it contributes to promoting heat radiation and preventing warpage.

The maximum deflection of the composite circuit board according to Example 4 in which the circuit layer was formed by the direct bonding method as described above was in the range of 0.8 to 1.6 mm, and the flexural strength was 550.
９００900 MPa, and the same characteristic values as in the case where the circuit layer was formed by the active metal method as in Examples 1 to 3 were obtained. Also, even after 1000 cycles in the heat cycle test, there was no cracking of the Si ₃ N ₄ substrate and Al ₂ O ₃ substrate and no peeling of the metal circuit board and the metal plate,
Excellent heat cycle characteristics were exhibited.

Next, an embodiment of a composite circuit board formed by laminating a high thermal conductive silicon nitride substrate and an alumina substrate as a general-purpose and inexpensive substrate in the thickness direction will be described.

FIG. 4 is a sectional view showing one embodiment of the composite circuit board of the present invention. In the figure, reference numeral 2 denotes a silicon nitride (Si ₃ N ₄ ) substrate, and these two silicon nitride substrates 2 and 2 are laminated and integrated via an aluminum oxide (Al ₂ O ₃ ) substrate 2a. I have. That is, the aluminum oxide substrate 2a is sandwiched between the two silicon nitride substrates 2 and 2 arranged on the front surface side, and is composed of the silicon nitride substrate 2 / the aluminum oxide substrate 2a / the silicon nitride substrate 2. Composite substrate 10a by sandwich structure of layers
Is configured.

As the above-mentioned silicon nitride substrate 2 and aluminum oxide substrate 2a, conventional general ones can be used. In particular, the silicon nitride substrate 2 has a thermal conductivity of 60 W / It is preferable to use those having m · K or more.

The silicon nitride sintered body constituting the silicon nitride substrate 2 is well known as a high-strength, high-toughness ceramic sintered body. It is possible to obtain a silicon nitride sintered body having relatively high thermal conductivity, such as a thermal conductivity of 60 W / m · K or more, without impairing the mechanical properties of high strength and high toughness. In the present invention, it is preferable to use such a silicon nitride substrate 2 having relatively excellent thermal conductivity. The aluminum oxide substrate 2a has a thermal conductivity of 15 to 25 W / m, which is generally used conventionally.
It is preferable to use an inexpensive alumina (Al ₂ O ₃ ) substrate of about K.

The silicon nitride substrates 2 and 2 constituting the composite substrate 10a and the aluminum oxide substrate 2a are joined via an active metal joining layer 11, respectively. The active metal bonding method includes an active metal brazing method using an active metal brazing material containing an active metal such as a general Group 4A element or a Group 5A element, and an active metal brazing method using an active metal foil or powder. A phase joining method or the like can be applied. For example, as an active metal brazing material, a eutectic composition of Ag-Cu (72 wt% Ag-28
wt% Cu) or a brazing material having a composition in the vicinity of Ti,
A material obtained by adding at least one active metal selected from Zr, Hf and Nb, a material obtained by adding a similar active metal to Cu, and the like are used. It is also possible to use a low melting point active metal brazing material whose melting point is reduced by adding In, Sn, or the like to such an active metal brazing material.

The bonding between the silicon nitride substrates 2 and 2 and the aluminum oxide substrate 2a is not limited to the active metal bonding method described above, and a glass bonding method can be applied as shown in FIG. For the glass layers 12 serving as bonding layers, bonding glass such as borosilicate glass is used.

When the active metal bonding method is applied to the bonding between the silicon nitride substrates 2 and 2 and the aluminum oxide substrate 2a, there is an advantage that a copper plate (circuit) can be simultaneously formed by the active metal method. When the glass joining method is applied, there is an advantage that a copper plate (circuit) can be joined by a direct joining method (DBC method).

The thicknesses of the silicon nitride substrate 2 and the aluminum oxide substrate 2a constituting the composite substrate 10a vary depending on required characteristics, the thickness of the entire bonding substrate 10a, and the like. It is preferable that the silicon nitride substrate 2 having a sufficient mechanical strength has a thickness of 0.2 mm or more. If the thickness of the silicon nitride substrate 2 is less than 0.2 mm, the composite substrate 10a
May not be able to obtain sufficient mechanical strength. However, if the thickness of the silicon nitride substrate 2 is too large, the heat dissipation as the composite substrate 10a may be reduced. Therefore, the thickness of the silicon nitride substrate 2 is preferably 0.5 mm or less.

In the composite substrate 10a of the embodiment shown in FIG. 4, the surface on which mechanical pressure, mechanical stress, thermal stress and the like directly act is constituted by a high-strength and high-toughness silicon nitride substrate 2. Therefore, it is possible to suppress tightening cracks in the assembly process and cracks caused by the addition of a thermal cycle. That is, for example, since thermal stress and mechanical stress are basically applied only to the surface, generation of cracks and cracks is suppressed by forming the surface portion with the high-strength and high-toughness silicon nitride substrate 2. It is possible to do.

On both principal surfaces of the composite substrate 10a, that is, on the silicon nitride substrates 2 and 2, copper plates 4 and 4 are provided, respectively.
These copper plates 4 and 4 are connected to a circuit (wiring layer).
And a semiconductor element mounting portion, etc., thereby forming a composite circuit board 1b. Copper plate 4, 4
Can be bonded by, for example, the above-described active metal bonding method or copper direct bonding method, so-called DBC method. Further, the metal layer that becomes a circuit or the like is not limited to the above-described bonded copper plate 4, but may be formed by applying a thick film paste, firing, or the like. As the thick film paste, a paste containing a high melting point metal such as W or Mo, or an Ag-Cu alloy paste containing an active metal is used.

Next, another embodiment of the present invention will be described with reference to FIG.

FIG. 6 shows a case where the composite circuit board of the present invention is used for a heat sink, and the silicon nitride substrate 2 on the upper surface side is only the peripheral portion to which a mechanical pressure or the like is directly applied, that is, the aluminum oxide substrate 2a. Is bonded only to the upper peripheral portion. The silicon nitride substrate 2 on the lower surface side is joined to the entire surface of the aluminum oxide substrate 2a to form a composite substrate 10b. These silicon nitride substrates 2
Although not shown, the aluminum oxide substrate 2a is bonded to the aluminum oxide substrate 2a by an active metal bonding method, a glass bonding method, or the like, as in the above-described embodiment. A copper plate 4 is bonded to the lower surface of the silicon nitride substrate 2 in a similar manner.

As described above, in the composite ceramic substrate of this embodiment, the silicon nitride substrate 2 on the upper surface side is joined only to the peripheral portion to which a mechanical pressure or the like is directly applied. Electronic components such as 6 are mounted directly on the aluminum oxide substrate 2a. Thus, according to the composite circuit board for mounting electronic components of the present invention, while maintaining the characteristics as a heat sink, it is possible to suppress the occurrence of cracks due to tightening cracks and the addition of thermal cycles in the assembly process. Becomes

The composite substrate 10b having the structure shown in FIG. 6 can be used, for example, as a package base of a QFP. That is, by joining the lead frame to the silicon nitride substrate 2 joined to the upper surface side of the aluminum oxide substrate 2a, it is possible to prevent stress cracking and the like accompanying the joining of the lead frame.

In the composite circuit board of the present invention, the silicon nitride substrate 2 does not necessarily have to be joined to the entire surface of the aluminum oxide substrate 2a, as shown in FIG.
It is also possible to partially join a plurality of silicon nitride substrates 2 to the aluminum oxide substrate 2a.

The composite circuit board of the present invention can be used not only as a ceramic circuit board and a heat sink, but also as a base of a semiconductor package as described above. For example, when the composite circuit board of the present invention is used for a package base such as BGA or PGA, a thermal stress is particularly applied to a joint portion with a printed wiring board, so only the side to which such thermal stress is concentrated is applied. It is also possible to use a silicon nitride substrate bonded thereto. That is, in the present invention, a composite substrate in which a silicon nitride substrate is bonded and integrated only on one side of an aluminum oxide substrate can be used.

As described above, in the composite circuit board for mounting electronic parts of the present invention, the bonding position of the silicon nitride substrate to a general-purpose and inexpensive substrate such as an aluminum oxide substrate is not particularly limited, and the mechanical strength is not limited. The silicon nitride substrate can be bonded to various portions where the substrate is required, and it is possible to use composite substrates of various forms.

Next, an embodiment of a laminated composite circuit board will be further described with reference to Example 5 shown below.

Example 5 First, various silicon nitride substrates as components of a composite circuit board 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.

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

[0126]

[Table 1]

[0127]

[Table 2]

[0128]

[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 was appropriately controlled, and the silicon nitride sintered body immediately after the completion of the densification sintering was compared with the conventional example. Since the cooling rate of the sintered body 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 sintered body. was gotten.

On the other hand, 1.3 to 1.5% by weight of oxygen and 0.13 to 0.1 wt.
A silicon nitride raw material powder containing 6% by weight and containing 93% of α-phase silicon nitride and having an average particle diameter of 0.60 μm was used, and Y ₂ O ₃ (yttrium oxide) powder was added to the silicon nitride powder by 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, by polishing and polishing the surface of each of the obtained silicon nitride sintered bodies of Samples 1 to 51, two silicon nitride substrates each having a thickness of 0.2 mm were prepared from each of the sample sintered bodies. On the other hand, a large number of aluminum oxide substrates having the same planar shape as this silicon nitride substrate, a thermal conductivity of 20 W / m · K, and a thickness of 0.4 mm were prepared. Next, aluminum oxide substrate 2
By bonding the silicon nitride substrates 2 to both surfaces of the substrate a by the active metal method, composite substrates 10a having a sandwich structure as shown in FIG. 4 and having a thickness of 0.8 mm were prepared. Further, copper plates 4 and 4 are respectively bonded to both main surfaces of each composite substrate 10a by an active metal method, and thereafter, a predetermined wiring pattern is formed by etching.
A composite circuit board according to Example 5 was manufactured.

When the bending strength of each of the composite circuit boards 1b thus obtained was measured, the average value showed a favorable value of 500 MPa. In addition, each composite circuit board has 233K-R
When a heat cycle test of T to 398K was performed, 100
No crack was observed even after 0 cycles,
No decrease in withstand voltage occurred.

Example 6 An aluminum oxide substrate 2a having a thermal conductivity of 20 W / m · K and a thickness of 0.4 mm prepared in Example 5 and the same planar shape as the aluminum oxide substrate 2a,
The silicon nitride substrates 2, 2 each having a thickness of 0.2 mm cut out from each of the silicon nitride sintered bodies according to Nos. 1 to 51 were joined using borosilicate glass to have a sandwich structure as shown in FIG. A 0.8 mm composite substrate 10a was obtained. Further, the copper plates 4 and 4 were respectively bonded to both main surfaces of the composite substrate 10a by a direct bonding method (DBC method), and patterns were formed by etching. Thus, composite circuit substrates 1b according to Example 6 were manufactured.

When the bending strength of each of the composite circuit boards 1b thus obtained was measured, a good value of 500 MPa was obtained on average. When a thermal cycle test of 233K to RT to 398K was performed on each of the composite circuit boards 1b, no cracks were observed even after 1000 cycles, and no reduction in withstand voltage occurred.

Comparative Example 2 A copper plate was bonded to both principal surfaces of an aluminum nitride substrate having a thermal conductivity of 170 W / m · K and a thickness of 0.8 mm by a direct bonding method (DBC method), and a pattern was formed by etching. Formed. The bending strength of each of the ceramic circuit boards thus obtained was 300 MPa.
In addition, 233K-RT-3
When a 98K heat cycle test was performed, cracks occurred in 300 cycles, and the withstand voltage was reduced.

Comparative Example 3 Copper plates were joined to both principal surfaces of an aluminum nitride substrate having a thermal conductivity of 170 W / m · K and a thickness of 0.8 mm by an active metal joining method, and a pattern was formed by etching.
The bending strength of each of the ceramic circuit boards thus obtained was 300 MPa. When a thermal cycle test of 233K to RT to 398K was performed on the ceramic circuit board, cracks occurred in 500 cycles, and the withstand voltage was reduced.

As described above, according to the composite circuit board of the present embodiment, the heat dissipation and the mechanical strength of the entire circuit board can be improved, and the reliability can be greatly improved. Become.

[0138]

As described above, according to the composite circuit board of the present invention, in addition to the high strength and high toughness characteristics inherently possessed by the silicon nitride sintered body, in particular, the high thermal conductivity greatly improved thermal conductivity is obtained. The silicon nitride substrate is placed in a part where structural strength and heat dissipation are required, while a general-purpose, easy-to-manufacture and inexpensive substrate such as an alumina substrate or a resin substrate is placed in other parts. Since they are arranged on the same plane or formed by lamination, the manufacturing cost is low, and the heat generated from heat-generating components such as semiconductor elements is quickly generated through a silicon nitride substrate having high thermal conductivity. Since the heat is transmitted to the outside of the system, the heat radiation property is extremely good. In addition, by arranging a silicon nitride substrate having high strength and toughness in a portion where structural strength is required, 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 a configuration example of a composite circuit board according to the present invention.

FIG. 2 is a cross-sectional view showing one embodiment of the composite circuit board according to the present invention, and is a cross-sectional view taken along the line II-II in FIG.

FIG. 3 is a sectional view showing another embodiment of the composite circuit board according to the present invention, and is a sectional view taken along the line III-III in FIG. 1;

FIG. 4 is a sectional view showing another embodiment of the composite circuit board according to the present invention.

FIG. 5 is a sectional view showing a modification of the composite circuit board shown in FIG. 4;

FIG. 6 is a sectional view showing another embodiment of the composite circuit board according to the present invention.

[Explanation of symbols]

1,1a, 1b Composite circuit board 2 Silicon nitride (Si ₃ N ₄ ) board 2a Aluminum oxide (alumina) board (Al ₂ O ₃₎
Substrate) 3 Oxide layer (SiO ₂ film) 4 Metal circuit board (Cu circuit board), circuit layer, copper plate 5 Metal plate (back copper plate) 6 Semiconductor element (chip) 7a, 7b Metal bonding layer (active metal brazing material layer) Reference Signs List 8 solder layer 9 heat sink 10, 10a, 10b composite substrate 11 active metal bonding layer 12 glass bonding layer

Claims (8)

[Claims] 1. A high thermal conductivity silicon nitride substrate having a thermal conductivity of 60 W / m · K or more and a substrate having a thermal conductivity of less than 60 W / m · K are arranged on the same plane, A composite circuit board, wherein a metal circuit board is bonded to at least the high thermal conductivity silicon nitride substrate having a thermal conductivity of at least 60 W / m · K. 2. A high thermal conductivity silicon nitride substrate having a thermal conductivity of 60 W / m · K or more and a substrate having a thermal conductivity of less than 60 W / m · K are laminated, and at least the thermal conductivity is reduced. A composite circuit board, wherein a metal circuit board is bonded to a high thermal conductive silicon nitride substrate having a rate of 60 W / m · K or more. 3. A high thermal conductivity silicon nitride substrate having a thermal conductivity of 60 W / m · K or more is provided on a substrate surface having a thermal conductivity of less than 60 W / m · K. Composite circuit board. 4. A highly thermally conductive silicon nitride substrate having a thermal conductivity of 60 W / m · K or more is 2.0 to 17.5% by weight of a rare earth element converted into an oxide, and as an impurity cation element. Of Li, Na, K, Fe, Ca, Mg, Sr, Ba,
3. The composite circuit board according to claim 1, comprising a silicon nitride sintered body containing 0.3% by weight or less of Mn and B in total. 5. A highly thermally conductive silicon nitride substrate having a thermal conductivity of 60 W / m · K or more, containing 2.0 to 17.5% by weight of a rare earth element in terms of oxide, comprising silicon nitride. 3. The composite according to claim 1, comprising a silicon nitride sintered body comprising a 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. Circuit board. 6. A highly thermally conductive silicon nitride substrate having a thermal conductivity of 60 W / m · K or more, containing 2.0 to 17.5% by weight of a rare earth element in terms of oxide, and silicon nitride. 3. The composite according to claim 1, comprising a silicon nitride sintered body comprising a 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 50% or more. Circuit board. 7. The substrate according to claim 1, wherein the substrate having a thermal conductivity of less than 60 W / m · K is an alumina substrate.
The composite circuit board as described. 8. The composite circuit board according to claim 2, wherein the board having a thermal conductivity of less than 60 W / m · K is a resin board.