JPH0964235A - Silicon nitride circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon nitride circuit board with good thermal conductivity, heat radiation, and heat-resistant cyclic characteristics, by utilizing the good strength and toughness in silicon nitride sintered body. SOLUTION: In a silicon nitride circuit board 1, a W- or Mo-based refractory metal circuit layer 3 is formed on a highly heat-conductive silicon nitride substrate 2 with heat conductivity of 60W/m.K or above. The strength of adhesion between a refractory metal circuit layer 4 and the heat-conductive silicon nitride substrate 2 is made 3kg/mm<2> or above. The heat-conductive silicon nitride substrate 2 and the circuit layer 3 may be formed in a simultaneous baking method.

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 used for a semiconductor device or the like, and particularly, the adhesion strength between the circuit layer and the board is large, and the mechanical strength and heat cycle characteristics can be improved and the heat dissipation characteristics can be improved. To a silicon nitride circuit board excellent in

[0002]

2. Description of the Related Art Conventionally, a conductive metal circuit layer is integrally joined with a brazing material to the surface of a ceramic substrate having excellent insulating properties such as an alumina (Al ₂ O ₃ ) sintered body, A circuit board in which a semiconductor element is mounted at a predetermined position on a circuit layer is widely used.

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 that replaces the heat-resistant superalloy described above, it has been tried to be applied to various high-strength heat-resistant parts such as gas turbine parts, engine parts, and steel-making machine parts. In addition, since it has excellent corrosion resistance to metals, it has been tried to apply it as a melt-resistant material of molten metal, and because it has excellent wear resistance, it can be put to practical use in sliding members such as bearings and cutting tools. ing.

Conventionally, as a composition of a silicon nitride ceramics sintered body, yttrium oxide (Y
₂ O ₃ ), cerium oxide (CeO), calcium oxide (CaO) and other rare earth elements or alkaline earth element oxides are known to be added as sintering aids. The sinterability is enhanced to achieve higher density and higher strength.

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 sintered body at a temperature of about 1600 to 1850 ° C. in a firing furnace. It is manufactured by a manufacturing method in which after firing for a time, the furnace is cooled, and the resulting 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 is different from other aluminum nitrides in terms of thermal conductivity. AlN) sintered body, beryllium oxide (BeO) sintered body, silicon carbide (SiC) sintered body, etc. are significantly lower than those in electronic materials such as semiconductor circuit boards that require heat dissipation. Has not been put to practical use, and has a drawback that its application range is narrow.

On the other hand, the above-mentioned aluminum nitride sintered body has the characteristics of high thermal conductivity and low thermal expansion coefficient as compared with other ceramics sintered bodies, so that it is possible to achieve high speed, high output, and multi-functionality.
Although it is the mainstream as a circuit board component or a package material for mounting a semiconductor element (chip), which is becoming larger in size, a material that is sufficiently satisfactory in mechanical strength has not been obtained. Therefore, there has been a demand for the development of a ceramics sintered body having high mechanical strength and high thermal conductivity.

That is, when the circuit board mainly composed of the aluminum nitride sintered body substrate is to be fixed to the mounting boat by screwing or the like in the assembly process, slight deformation due to the pressing force of the screw or handling at the time of handling may occur. The impact may damage the circuit board, which may significantly reduce the manufacturing yield of semiconductor devices. Accordingly, there is a demand for a circuit board that has both high strength characteristics to withstand external force, high toughness characteristics, and excellent heat dissipation characteristics capable of coping with high output and high heat generation.

Further, in the circuit board formed by integrally bonding the metal circuit layer and the semiconductor element on the surface of the aluminum nitride substrate as described above, excellent heat dissipation characteristics due to the high heat conductivity inherent to aluminum nitride are exhibited, Since the mechanical strength and toughness of the aluminum nitride substrate itself were insufficient, the aluminum nitride substrate in the vicinity of the joint portion of the metal circuit layer was likely to be cracked due to repeated thermal cycles associated with the operation of the semiconductor element, and There is a problem that the circuit layer is easily peeled off, and the heat resistance cycle characteristic and reliability are low.

The present invention has been made in order to meet the above-mentioned demands, and utilizes the high strength and high toughness characteristic originally possessed by a silicon nitride sintered body, and further has a high thermal conductivity and an excellent heat dissipation property. Another object of the present invention is to provide a silicon nitride circuit board having significantly improved heat resistance cycle characteristics.

[0011]

In order to achieve the above object, the present inventor has researched a substrate material which does not deteriorate the heat dissipation (thermal conductivity) of a circuit board and satisfies both strength and toughness values. At the same time, we have conducted intensive studies on measures to prevent tightening cracks that occur in the circuit board assembly process, cracks that occur when heat cycles are applied, and circuit layer peeling. As a result, it was found that by appropriately controlling the composition and manufacturing conditions of the substrate material, a silicon nitride sintered body having a high thermal conductivity which has never been obtained can be obtained. In addition, by adding the substrate component and the Ti compound to the high melting point metal paste for forming the circuit layer, the adhesion strength between the circuit layer and the silicon nitride substrate is significantly improved and the durability is excellent. It was found that a circuit board having Further, after forming a raw material mixture in which a resin binder and a solvent are mixed with silicon nitride powder into a sheet, a circuit pattern is printed on the sheet molded body with a paste containing a refractory metal as a main component, and the circuit pattern and the sheet are formed. By simultaneously degreasing and sintering the compact and forming a circuit layer on the surface of the board to form a circuit board, it is possible to greatly increase the deflection amount and bending strength of the circuit board. The inventors have completed the present invention by finding that it is possible to effectively reduce the tightening cracks and the like of the circuit board in the process, and significantly improve the heat resistance cycle characteristics.

That is, the present inventor has made a study on the type of silicon nitride powder, the type and amount of sintering aids and additives, and the sintering conditions that have been conventionally used, and the conventional silicon nitride sintered body has been investigated. Has developed a silicon nitride sintered body having a high thermal conductivity which is more than twice as high as that of. Further, after using this silicon nitride composition as a substrate material to form a green sheet using a sheet forming method such as a doctor blade method, a high melting point metal such as tungsten (W) is a main component on the surface of the green sheet. After forming a circuit pattern by printing a conductor paste with a predetermined shape on the circuit board, co-firing and then forming a plating layer such as nickel on the circuit layer to produce a circuit board, the circuit layer and silicon nitride As the adhesion strength with the substrate increases, mechanical strength, toughness value,
It was confirmed by an experiment that a silicon nitride circuit board satisfying all the heat cycle characteristics and heat dissipation was obtained.

Specifically, a raw material mixture obtained by adding a predetermined amount of a rare earth element oxide or the like to fine, high-purity silicon nitride powder is molded and degreased, and the obtained molded body is heated and maintained at a predetermined temperature for a certain period of time. After performing densification and sintering, the resulting sintered body is annealed at a cooling rate not higher than a predetermined value, and the resulting sintered body is ground and polished to have a thermal conductivity of 2 times that of a conventional silicon nitride sintered body. It has been found that a silicon nitride sintered body having a high strength and a high toughness, which is greatly improved by more than double, specifically 60 W / m · K or more, can be obtained, and a new nitriding that satisfies both heat dissipation characteristics and strength characteristics. Developed silicon material. It has been found that when this silicon nitride material is applied to a substrate material for a co-fired metallized substrate, excellent heat dissipation characteristics, durability and heat cycle characteristics can be achieved at the same time.

Further, a high-purity silicon nitride raw material powder having a reduced content of oxygen and impurity cation elements is used, and after sintering under the above conditions, the silicon nitride sintered body is cooled at a slow speed. It is possible to effectively suppress the formation of the glass phase (amorphous phase) in the grain boundary phase, and to reduce the amount of the crystalline compound in the grain boundary phase to 20
Volume% or more (based on the entire grain boundary phase), more preferably 50
By adjusting the content to be at least volume%, a silicon nitride sintered body substrate having a high thermal conductivity of 60 W / m · K or more, and more preferably 80 W / m · K or more, even when only the rare earth element oxide is added to the raw material powder. We obtained the knowledge that

Further, conventionally, when the heating power source of the firing furnace was turned off after the sintering operation was finished and the sintered body was cooled in the furnace, the cooling rate was as rapid as 400 to 800 ° C./hour. According to the experiments by the inventor, the cooling rate is 10
By controlling the temperature slowly to 0 ° C or lower, the grain boundary phase of the silicon nitride sintered body structure changes from an amorphous state to a phase containing a crystalline phase, and high strength characteristics and high heat transfer characteristics are simultaneously achieved. It turned out that

As described above, a silicon nitride sintered body satisfying both high strength characteristics and high heat transfer characteristics is used as a substrate material, and a metal circuit layer is integrally formed on the surface of the substrate material by the simultaneous firing method to obtain a circuit board. As a result, it has been found that the toughness and thermal conductivity of the entire circuit board can be improved, and in particular, tightening cracks in the assembly process of the circuit board and generation of cracks due to the addition of heat cycles can be effectively prevented.

It has also been found that the bonding strength between the circuit layer and the silicon nitride substrate can be increased by adding silicon nitride powder or adding a titanium compound to the circuit layer made of a refractory metal.

The present invention has been completed based on the above findings. That is, the silicon nitride circuit board according to the present invention has a circuit layer made of a refractory metal containing W or Mo as a main component on a high thermal conductivity silicon nitride board having a thermal conductivity of 60 W / m · K or more. In the formed silicon nitride circuit board, the adhesion strength between the circuit layer made of the refractory metal and the high thermal conductivity silicon nitride board is 3 kgf / mm ² or more. Further, the high thermal conductivity silicon nitride substrate and the circuit layer may be formed by a co-firing method.

Further, silicon nitride powder is added to the circuit layer made of a high melting point metal containing W or Mo as a main component. Here, the silicon nitride powder is preferably added at a ratio of 1 to 10% by weight with respect to the circuit layer made of a high melting point metal. The average particle size of the silicon nitride powder is 0.5 to 10
It may be set in the range of μm.

Further, the circuit layer made of a high melting point metal containing W or Mo as a main component contains a Ti compound. Here, the Ti compound may be added in a proportion of 0.5 to 5% by weight with respect to the circuit layer made of a refractory metal. Also, the high thermal conductivity silicon nitride substrate is 80 W / m.
It is more desirable to have a thermal conductivity of K or higher. Various components such as a semiconductor element, a resistance element, and a lead frame are generally mounted on the uppermost surface of the circuit board, and are integrally joined to the circuit layer by brazing such as soldering. Therefore, the joint portion between the circuit layer and the substrate needs to have an adhesion strength of at least 3 kgf / mm ² so as not to separate from each other even at the above brazing temperature.

The silicon nitride powder added to the circuit layer as a co-material reduces the difference in thermal expansion between the circuit layer and the high-thermal-conductivity silicon nitride substrate, and reacts with the substrate components to form the circuit layer and silicon nitride. In order to increase the bonding strength with the base substrate, it is added in the range of 1 to 10% by weight with respect to the circuit layer. When the amount added is less than 1% by weight, the effect of relaxing the difference in thermal expansion and the effect of improving the bonding strength are insufficient, while the amount added is 1
If it exceeds 0% by weight, the electric resistance of the circuit layer increases,
It becomes difficult to deal with high-speed signal processing.

The average particle size of the silicon nitride powder is 0.5.
If the average particle size is less than μm, the effect of improving the bonding strength of the circuit layer is small, while if the average particle size is too large to exceed 10 μm, the electrical resistance of the circuit layer is adversely affected. It is desirable to use silicon nitride.

Ti compounds such as TiO ₂ are decomposed during the firing process, and the generated Ti atoms are diffused and adsorbed on the Si ₃ N ₄ substrate side to form reaction products such as TiN. This reaction product is continuously formed at the bonding interface while maintaining an epitaxy relationship with the Si ₃ N ₄ crystal lattice, and the anchor effect enhances the adhesion strength between the circuit layer and the Si ₃ N ₄ substrate. When the content of the above Ti compound is less than 0.5% by weight with respect to the circuit layer, the effect of improving the adhesion strength is small, while when the content exceeds 5% by weight, it is similar to silicon nitride powder. In order to increase the electric resistance of the circuit layer, the content of the Ti compound is set in the range of 0.5 to 5% by weight with respect to the circuit layer.

The silicon nitride circuit board according to the present invention is manufactured, for example, by the following method. That is, 1.7% by weight or less of oxygen, Li, Na as impurity cation elements,
K, Fe, Ca, Mg, Sr, Ba, Mn, B 0.3
1.0% to 12.5% by weight in terms of oxide of a rare earth element in a silicon nitride powder having an average particle size of 0.8 μm or less and containing 90% by weight or less of α-phase type silicon nitride. The raw material mixture added with is molded by a sheet molding method such as a doctor blade method to form a sheet-shaped green sheet. On the other hand, W powder or Mo powder is mixed with a predetermined amount of silicon nitride powder or Ti compound powder, if necessary, and further uniformly mixed with an organic binder to prepare a paste-like circuit layer material. Then, using a screen printing machine, the paste-like circuit layer material is printed on a green sheet to obtain a printed body on which a circuit pattern of a predetermined shape having a film thickness of about 15 μm is formed, and dried. Further, after degreasing the dried printed body at a temperature of 600 to 800 ° C. in a non-oxidizing gas atmosphere, the degreased body is kept at 1800 to 2000 ° C. in a non-oxidizing gas atmosphere of about 2 to 10 atm for 2 to 10 hours. Holding the same, the Si ₃ N ₄ green sheet and the material for the circuit layer are co-fired, and the sintered body is cooled from the sintering temperature to a temperature at which the liquid phase formed during sintering by the rare earth element solidifies. It is manufactured by setting the speed to 100 ° C. or less per hour and cooling at a slow speed. The amount of carbon derived from the binder remaining in the degreased body is 0.3% by weight in the substrate material.
The following is preferred. If the amount of carbon is 0.3% by weight or less, it acts as an oxygen scavenger in the sintering process and contributes to the development of high thermal conductivity, but if the amount exceeds 0.3% by weight, it inhibits sintering and increases the compactness. This is because it causes a decrease in

In the above manufacturing method, the raw material mixture for forming the silicon nitride substrate portion having high thermal conductivity is further provided with oxides and carbides of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W. 0.2 to 3.0% by weight of at least one selected from the group consisting of, nitride, silicide, and boride.
And, if necessary, 0.1 to 2.0% by weight of at least one of alumina and aluminum nitride may be added.

According to the above manufacturing method, a grain boundary phase containing a rare earth element or the like is formed in the crystal structure of silicon nitride, the porosity is 1.5% or less, the thermal conductivity is 60 W / mK or more, and A silicon nitride circuit board having a point bending strength of 80 kg / mm ² or more at room temperature and having excellent mechanical properties and heat conduction properties can be obtained.

The silicon nitride powder, which is the main raw material of the high thermal conductivity silicon nitride substrate constituting the circuit board of the present invention, is as follows:
Considering sinterability, strength and thermal conductivity, the oxygen content is 1.7 wt% or less, preferably 0.5 to 1.5 wt%,
Li, Na, K, Fe, Mg, Ca, Sr, Ba, M
The content of impurity cation elements such as n and B is 0.3% by weight or less, preferably 0.2% by weight or less, and α phase silicon nitride excellent in sinterability is 90% by weight or more, preferably 93
Fine silicon nitride powder is used, which is contained by weight% or more and has an average particle size of 0.8 μm or less, preferably about 0.4 to 0.6 μm.

By using a fine raw material powder having an average particle size of 0.8 μm or less, it is possible to form a dense sintered body having a porosity of 1.5% or less even with a small amount of a sintering aid. It is also possible to reduce the risk of the sintering aid impairing the heat conduction characteristics.

Fe, Mg, Ca, Sr, Ba, M
Since n, B, Li, Na and K act as substances that impede thermal conductivity as impurity cation elements, 60 W / m
In order to secure the thermal conductivity of K or more, the total content of the impurity cation elements is set to 0.3% by weight or less. Furthermore, 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 high-thermal-conductivity silicon nitride substrate is manufactured. can do.

The rare earth elements added to the silicon nitride raw material powder as a sintering aid include Y, La, Sc, Pr and C.
The oxides of e, Nd, Dy, Ho, Gd, etc., or the substances which become these oxides by the sintering operation may include a single substance or a combination of two or more types of oxides, but in particular yttrium oxide. (Y ₂ O ₃ ) is preferred. These sintering aids react with the silicon nitride raw material powder to generate a liquid phase, and function as a sintering accelerator.

The addition amount of the sintering aid is set in the range of 1.0 to 12.5% by weight based on the raw material powder in terms of oxide. If the addition amount is too small, less than 1.0% by weight,
The sintered body (high thermal conductivity silicon nitride substrate) is not densified,
On the other hand, if the added amount exceeds 12.5% by weight,
An excessive amount of grain boundary phase is generated, and the thermal conductivity and the strength start to decrease, so the above range is set. Particularly preferably 3.
It is desirable to set 0 to 6.0% by weight.

Further, alumina (Al ₂ O ₃ ) as another additive component plays a role of promoting the function of the above-mentioned sintering promoter for rare earth elements, and is particularly remarkable when performing pressure sintering. It is effective. Al ₂ O ₃
If the addition amount is less than 0.1% by weight, the densification is insufficient, while if it exceeds 2.0% by weight, an excessive amount of grain boundary phase is generated, or silicon nitride is added. The amount of addition is 2.
It is set to 0% by weight or less, preferably 0.1 to 2.0% by weight. In particular, in order to secure good performances in both strength and thermal conductivity, it is desirable to set the addition amount within the range of 0.2 to 1.5% by weight.

When used in combination with AlN, which will be described later, the total addition amount is preferably set to 2.0% by weight or less.

Further, aluminum nitride (AlN) as another additive component suppresses the evaporation of silicon nitride in the sintering process, and further promotes the function of the above rare earth element as a sintering accelerator. Is.

When the amount of AlN added is less than 0.3% by weight (less than 0.1% by weight when used in combination with alumina), the densification is insufficient, while an excess amount of more than 2.0% by weight. In such a case, an excessive amount of grain boundary phase is generated, or solid solution begins to form a solid solution in silicon nitride, and thermal conductivity decreases, so the addition amount is 2.0% by weight or less, preferably 0.3 to
It is set in the range of 2.0% by weight. In particular, in order to secure good performance in both strength and thermal conductivity, the addition amount is 0.5 to
It is desirable to set in the range of 1.5% by weight. When used in combination with Al ₂ O ₃ , the addition amount of AlN is preferably in the range of 0.1 to 2.0% by weight.

Ti and Z used as other additive components
oxides of r, Hf, V, Nb, Ta, Cr, Mo, W,
Carbides, nitrides, suicides, and borides promote the function of the above-mentioned rare earth element sintering promoter, and also have the function of dispersion strengthening in the crystal structure to improve the mechanical strength of the Si ₃ N ₄ substrate. Is. The addition amount of these compounds is 0.
When it is less than 2% by weight, the densification of the structural member is insufficient, while when it exceeds 3.0% by weight, the thermal conductivity, mechanical strength and electric breakdown strength decrease. The addition amount is set in the range of 0.2 to 3.0% by weight. Particularly preferably, it is desirable to set it to 0.3 to 2.0% by weight.

The compounds such as Ti, Zr and Hf also function as a light-shielding agent that colors the silicon nitride substrate and imparts opacity. Therefore, especially when applied to a circuit board on which an integrated circuit or the like that easily causes a malfunction due to light is applied,
It is desirable to add the above compound appropriately to form a silicon nitride substrate having excellent light-shielding properties.

While aluminum nitride (AlN) suppresses evaporation of silicon nitride in the sintering process, it further promotes the function of the above-mentioned sintering promoter, and, like alumina, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W
It serves to relatively reduce the amount of oxides added such as.
The amount of aluminum compound such as alumina or aluminum nitride added is Ti, Zr, Hf, V, Nb, Ta,
There is a close relationship with the amounts of Cr, Mo and W oxides added. That is, the addition amount of the above Ti compound is 0.2% by weight.
And an aluminum compound such as Al ₂ O ₃ and AlN is added alone or in combination, and the addition amount is less than 0.1% by weight, the densification is insufficient, while 2.0% by weight
If the amount exceeds an excessive amount, an excessive amount of grain boundary phase is generated, or solid solution starts to form a solid solution in silicon nitride, and thermal conductivity decreases, so the addition amount is in the range of 0.1 to 2.0% by weight. Is set to. In particular, in order to secure good performances in both strength and thermal conductivity, it is desirable to set the addition amount within the range of 0.2 to 1.5% by weight.

The porosity of the silicon nitride substrate has a great effect on the thermal conductivity and strength, and is therefore set to 1.5% or less, preferably 0.5% or less. If the porosity exceeds 1.5%, the heat conduction is hindered, the thermal conductivity of the silicon nitride substrate lowers, and the strength of the silicon nitride substrate lowers.

Further, since the grain boundary phase formed in the silicon nitride crystal structure has a great influence on the thermal conductivity of the silicon nitride substrate, the high thermal conductivity silicon nitride substrate used in the present invention has a volume ratio of It is important that 20% or more of the grain boundary phase is occupied by the crystal phase. This is because if the crystal phase is less than 20%, it is not possible to obtain a silicon nitride substrate having excellent heat dissipation properties such as a thermal conductivity of 60 W / m · K or more and excellent high temperature strength.

Further, as described above, the porosity of the silicon nitride substrate is set to 1.5% or less, and 20% by volume or more of the grain boundary phase formed in the silicon nitride crystal structure is occupied by the crystal phase. A silicon nitride compact at a temperature of 1800-20
Pressure sintering is performed at 00 ° C for about 0.5 to 10 hours, and the cooling rate of the sintered body immediately after the completion of the sintering operation is 100 ° C / hour.
It is necessary to adjust and control the following.

When the sintering temperature is set to less than 1800 ° C., the densification of the sintered body is insufficient, the porosity becomes 1.5 vol% or more, and both mechanical strength and thermal conductivity decrease. . On the other hand, when the sintering temperature exceeds 2000 ° C., the silicon nitride component itself tends to evaporate and decompose. Not especially pressure sintering,
When pressureless sintering is carried out, decomposition vaporization of silicon nitride begins at around 1800 ° C.

The cooling rate of the sintered body immediately after the completion of the above-mentioned sintering operation is an important control factor for crystallizing the grain boundary phase, and when the cooling rate is 100 ° C./hour, rapid cooling is performed. Indicates that the grain boundary phase of the sintered body structure becomes amorphous (glass phase), and the liquid phase generated in the sintered body occupies less than 20% by volume as a crystal phase in the grain boundary phase, resulting in strength and thermal conductivity. Will decrease together.

The temperature range in which the cooling rate is to be strictly adjusted is a temperature range from a predetermined sintering temperature (1800 to 2000 ° C.) to the solidification of the liquid phase produced by the reaction of the sintering aid. Is enough. By the way, the liquidus freezing point when the above-mentioned sintering aid is used is about 1500 to 16
It is about 00 ° C. The cooling rate of the sintered body from at least the sintering temperature to the liquidus solidification temperature is set to 10 per hour.
By controlling the temperature to 0 ° C. or lower, preferably 50 ° C. or lower, 20% or more, preferably 50% or more of the grain boundary phase becomes a crystal phase, and high thermal conductivity silicon nitride excellent in both thermal conductivity and mechanical strength. The substrate is finally obtained.

The high thermal conductivity silicon nitride substrate used in the present invention is manufactured, for example, through the following process. That is, a predetermined amount of sintering aid, necessary additives such as an organic binder, and Al ₂ O are added to a fine silicon nitride powder having the above-mentioned predetermined fine particle size and a low impurity content.
_The raw material mixture is adjusted by adding ₃ , AlN or a compound such as Ti, Zr, Hf and the like, and then the obtained raw material mixture is molded to obtain a molded product having a predetermined shape. As a forming method of the raw material mixture, a general-purpose die pressing method, a sheet forming method such as a doctor blade method, or the like can be applied. Following the above molding operation, the molded body is heated to a temperature of 600 in a non-oxidizing atmosphere.
By heating at ˜800 ° C. for 1 to 2 hours, the previously added organic binder component is sufficiently removed and degreased. Next, the degreased molded body is subjected to atmospheric pressure sintering at a temperature of 1800 to 2000 ° C. for a predetermined time in an inert gas atmosphere such as nitrogen gas, hydrogen gas or argon gas, and the obtained sintered body is obtained. A high thermal conductivity silicon nitride substrate having a predetermined shape is obtained by grinding and polishing.

The high thermal conductivity silicon nitride substrate manufactured by the above manufacturing method has a porosity of 1.5% or less, 60 W / m · K.
It has a high thermal conductivity of (25 ° C) or higher and a three-point bending strength of 60 kgf / mm ² or more at room temperature, further 80 kgf / mm ² or more, which is excellent in mechanical properties.

The thickness of the high thermal conductivity silicon nitride substrate is set to various thicknesses according to the required characteristics when used as a circuit board, but it is usually in the range of 0.25 to 1.2 mm. Is. Especially, the thickness of this silicon nitride substrate is 0.8
By setting the thickness to be less than or equal to mm, the thickness of the entire circuit board can be reduced, and the thermal resistance difference between the upper and lower surfaces of the circuit board can be reduced.
It is possible to more effectively reduce the heat dissipation of the entire circuit board.

The silicon nitride circuit board according to the present invention has a high thermal conductivity silicon nitride substrate manufactured as described above,
It is manufactured by integrally joining conductive circuit layers.

The method of forming the above-mentioned circuit layer is not particularly limited, but it is desirable to form it by the high melting point metallizing method described below. That is, in the metallization method, a paste-like metallized composition containing a refractory metal such as molybdenum (Mo) or tungsten (W) and Ti or a compound thereof as main components is baked on the surface of the silicon nitride substrate to have a thickness of 1
This is a method of forming a refractory metallized layer as a circuit layer having a thickness of about 5 μm. Note that the silicon nitride substrate and the circuit layer can be formed by the simultaneous firing method. When the circuit layer is formed by this metallizing 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 metallizing layer. By forming this metal plating layer, the surface smoothness of the metallized layer is improved, the adhesion with the semiconductor element is further improved, and the solder wettability is improved, so the bonding strength of the semiconductor element using solder is improved. Can be increased.

The maximum amount of deflection of the silicon nitride circuit board manufactured as described above is a factor that greatly affects the rate of occurrence of tightening cracks in the assembly process of the circuit board. In the present invention, the maximum amount of deflection is 0. A circuit board of 0.6 mm or more, and further 0.8 mm or more can be obtained. If the maximum amount of deflection is less than 0.6 mm, tightening cracks on the circuit board in the assembly process will increase rapidly, and the manufacturing yield of semiconductor devices using the circuit board will decrease sharply.

Further, the bending strength of the circuit board is a factor which influences the occurrence rate of the above-mentioned tightening cracks and also controls whether or not the silicon nitride board can be thinned. In the present invention, the bending strength of the circuit is 500 MPa or more. A substrate is obtained. When the bending strength is less than 500 MPa, tightening cracks of the circuit board increase, but it becomes difficult to make the thickness thinner than other conventional ceramics boards. It becomes difficult to reduce synergistically.

According to the silicon nitride circuit board of the present invention, in addition to the high strength and toughness characteristics inherent in the silicon nitride sintered body, the surface of the highly heat conductive silicon nitride board having greatly improved thermal conductivity is obtained. Since it is formed by integrally joining the circuit layers to each other, the maximum deflection amount is large and the bending strength is high.
It is possible to mass-produce a semiconductor device using a circuit board with a high manufacturing yield without causing a tightening crack of the circuit board in the assembly process.

Further, since the toughness value of the silicon nitride substrate is high,
It is possible to provide a semiconductor device in which cracks are less likely to occur in a substrate due to heat cycle, heat cycle characteristics are remarkably improved, and durability and reliability are excellent.

Furthermore, since a silicon nitride substrate having a high thermal conductivity, which has not been achieved in the past, is used, the thermal resistance characteristics of the semiconductor device can be improved even when a semiconductor element for high output and high integration is mounted. Shows excellent heat dissipation characteristics with little deterioration.

Particularly, since the silicon nitride substrate itself has excellent mechanical strength, it is possible to further reduce the substrate thickness as compared with other ceramic substrates when the required mechanical strength characteristics are kept constant. It will be possible. Since the substrate thickness can be reduced, the thermal resistance value can be further reduced, and the heat radiation characteristics can be further improved. Further, since it is possible to sufficiently meet the required mechanical characteristics even with a substrate thinner than before, it is possible to mount the circuit board at a high density and further downsize the semiconductor device.

[0056]

EXAMPLES The present invention will now be specifically described with reference to the following examples.

Examples 1 to 3 A silicon nitride raw material containing 1.3% by weight of oxygen, 0.15% by weight of an impurity cation element, and 97% of α-phase type silicon nitride and having an average particle diameter of 0.55 μm. 5% by weight of Y ₂ O ₃ (yttrium oxide) powder having an average particle size of 0.7 μm as a sintering aid and Al ₂ O having an average particle size of 0.5 μm with respect to the powder
1.5% by weight of ₃ (alumina) powder was added, 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 was added to the obtained raw material powder mixture and uniformly mixed to prepare a raw material slurry. Next, the prepared raw material slurry was molded by the doctor blade method to have a thickness of 0.49 mm,
Sheet-like molded bodies for Examples 1 to 3 having 0.73 mm and 0.98 mm were prepared.

On the other hand, 5% by weight of powder obtained by degreasing the above silicon nitride raw material powder mixture was added to tungsten powder having an average particle size of 1.0 μm, and mixed with an organic binder to prepare a paste-like circuit material. Next, the paste-like circuit material is applied to the sheet-like molded body with a film thickness of 15 by a screen printer.
After printing so as to have a thickness of μm, it was dried to form a printed material.

Next, the obtained printed body was degreased in a nitrogen atmosphere at 650 ° C. for 2 hours, and then the degreased body was held in a nitrogen gas atmosphere at 7.5 atm and 1900 ° C. for 6 hours.
After carrying out the simultaneous densification and sintering, the cooling rate of the sintered body is 100% until the temperature inside the sintering furnace drops to 1500 ° C. by controlling the amount of electricity supplied to the heating device attached to the sintering furnace. The sintered body was cooled by adjusting the temperature to be ° C / hr and the thermal conductivity k of the substrate portion was 70 W / mK.
Examples 1 to 1 having thicknesses of 0.4 mm, 0.6 mm and 0.8 mm
A co-fired substrate for 3 was prepared.

Further, the co-fired substrate thus prepared was held in a nitrogen gas atmosphere of 7.5 atm at 1800 ° C. for 2 hours for re-curling. Then, the thickness of 4 μm is applied to the circuit part of the co-fired substrate by electroless nickel plating.
Nickel plating layers are formed to form Examples 1 to 3, respectively.
A large number of silicon nitride circuit boards according to the present invention were manufactured.

Examples 4 to 6 Titanium oxide (TiO ₂ ) powder was used in place of the paste-like circuit material containing 5% by weight of the degreased powder of the silicon nitride raw material powder mixture used in Examples 1 to 3. Molding, circuit printing, degreasing, cofiring, warping treatment, and plating treatment were carried out under the same conditions as in Examples 1 to 3 except that a paste-like circuit material containing 5% by weight was used. A large number of silicon nitride circuit boards according to Examples 4 to 6 having the same dimensions as those of Nos.

As shown in FIG. 1, the Si ₃ N ₄ circuit boards 1 according to Examples 1 to 6 have a thermal conductivity of 70 W / m · K.
The circuit layer 3 made of a refractory metal (W) metallized layer is integrally formed on the surface of the high thermal conductive Si ₃ N ₄ substrate 2 by the simultaneous firing method. A nickel plating layer 4 having a thickness of 4 μm is formed on the surface of the circuit layer 3, and the semiconductor element 5 is joined to the upper surface of the nickel plating layer 4 by soldering.

Comparative Example Instead of the silicon nitride substrate formed in Examples 1 to 6, an aluminum nitride (AlN) substrate having a thermal conductivity k of 70 W / mK and a thickness of 0.8 mm was used. Is Example 1
In the same manner as in No. 6, a circuit layer having the same shape as in Examples 1 to 6 was integrally formed on the surface of the AlN substrate by the W metallizing method to manufacture a circuit substrate according to a comparative example.

In order to measure the adhesion strength of the metallized parts (circuit layers) of the circuit boards according to Examples 1 to 6 and Comparative Example thus prepared, a Kovar alloy pin having a Neel head with a diameter of 0.8 mm. Was soldered to the surface of the circuit layer and the pulling force when the pin was pulled upward to separate the circuit layer was divided by the joint cross-sectional area of the pin to measure the adhesion strength. As a result, in each of the examples, breakage occurred at the pins, and in the circuit boards according to Examples 1 to 3, the adhesion strength was 4 kgf / mm ² or more, and in the circuit boards according to Examples 4 to 6, It was 3.5 kgf / mm ² or more, and high adhesion strength was obtained in all cases. On the other hand, in the comparative example, 1.8 to
It was confirmed that only an adhesion strength of about 2.1 kgf / mm ² was obtained, and the peeling of the circuit layer was likely to occur.

Further, the maximum deflection amount and the bending strength of the circuit boards according to each of the examples and the comparative example were measured. Here, the maximum deflection amount was measured as the maximum deflection height until the Si ₃ N ₄ substrate or the AlN substrate was broken by applying a load to the central portion while supporting each circuit substrate with a supporting span of 50 mm. The bending strength was calculated from the load at break and the substrate cross-sectional area.

As a result, the maximum amount of deflection of the silicon nitride circuit board 1 according to Examples 1 to 6 is in the range of 1.0 to 1.8 mm, and the flexural strength is in the range of 650 to 950 MPa, which is the conventional value. It was found that the circuit board of the comparative example using the aluminum nitride substrate had a maximum deflection amount and a bending strength more than double. It was also confirmed that as the thickness of the silicon nitride substrate was reduced, the amount of deflection and the bending strength were further improved. Further, it was confirmed that the thermal resistance is reduced due to the reduction of the board thickness, so that the heat dissipation characteristics of the entire circuit board can be further improved.

When the circuit boards according to the above-mentioned respective examples were mounted on the boards in the assembly process, tightening cracks did not occur, and semiconductor devices using the circuit boards could be mass-produced with a high manufacturing yield.

Each circuit board is heated from −45 ° C. to room temperature (RT), then heated from room temperature to + 125 ° C., and then cooled to −45 ° C. through room temperature, which is one cycle. A cycle was repeatedly added, and a heat resistance cycle test was carried out to measure the number of cycles until a crack or the like was generated in the substrate part. With the circuit boards of Examples 1 to 6, even after 1000 cycles, Si ₃ N ₄ It was found that there was no cracking of the substrate or peeling of the circuit layer, and that it exhibited excellent heat cycle characteristics. On the other hand, in the circuit board of the comparative example, cracking occurred after 100 cycles, and it was confirmed that the durability was low.

[0069]

As described above, according to the silicon nitride circuit board of the present invention, in addition to the high strength and high toughness characteristics inherent in the silicon nitride sintered body, the high thermal conductivity in which the thermal conductivity is greatly improved is achieved. The circuit board is formed by integrally bonding the circuit layer to the surface of the conductive silicon nitride board, and since the maximum amount of deflection is large and the bending strength is high, the circuit board does not suffer from tightening cracks during the assembly process. It becomes possible to mass-produce semiconductor devices using the above with a high manufacturing yield.

Since the toughness value of the silicon nitride substrate is high,
It is possible to provide a semiconductor device in which cracks are less likely to occur in a substrate due to heat cycle, heat cycle characteristics are remarkably improved, and durability and reliability are excellent.

Furthermore, since a silicon nitride substrate having a high thermal conductivity, which has not been achieved in the past, is used, the thermal resistance characteristics of the semiconductor device can be improved even when a semiconductor device for high output and high integration is mounted. Shows excellent heat dissipation characteristics with little deterioration.

In particular, since the silicon nitride substrate itself has excellent mechanical strength, it is possible to further reduce the substrate thickness as compared with other ceramic substrates when the required mechanical strength characteristics are kept constant. It will be possible. Since the substrate thickness can be reduced, the thermal resistance value can be further reduced, and the heat radiation characteristics can be further improved. Further, since it is possible to sufficiently meet the required mechanical characteristics even with a substrate thinner than before, it is possible to mount the circuit board at a high density and further downsize the semiconductor device.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration example of a silicon nitride circuit board according to the present invention.

[Explanation of symbols]

1 Silicon Nitride Circuit Board (Si ₃ N ₄ Circuit Board) 2 High Thermal Conductivity Silicon Nitride (Si ₃ N ₄ ) Board 3 Circuit Layer (Refractory Metallization Layer) 4 Nickel Plating Layer 5 Semiconductor Device (Chip)

Front Page Continuation (72) Inventor Mitsuyasu Komatsu 4 2-4 Suehiro-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Toshiba Corporation Keihin Office

Claims (8)

[Claims] 1. A silicon nitride circuit substrate in which a circuit layer made of a refractory metal containing W or Mo as a main component is formed on a high thermal conductivity silicon nitride substrate having a thermal conductivity of 60 W / m · K or more. ^{2. The} silicon nitride circuit board as set forth in claim 1, wherein the adhesion strength between the circuit layer made of the refractory metal and the high thermal conductivity silicon nitride board is 3 kgf / mm ² or more. 2. The silicon nitride circuit board according to claim 1, wherein the high thermal conductivity silicon nitride board and the circuit layer are formed by a co-firing method. 3. The silicon nitride circuit board according to claim 1, wherein silicon nitride powder is added to the circuit layer made of a high melting point metal containing W or Mo as a main component. 4. The silicon nitride circuit board according to claim 3, wherein the silicon nitride powder is added in a ratio of 1 to 10% by weight with respect to the circuit layer made of a refractory metal. 5. The silicon nitride powder has an average particle size of 0.5 to 10.
The silicon nitride circuit board according to claim 3, wherein the silicon nitride circuit board has a thickness of μm. 6. The silicon nitride circuit board according to claim 1, wherein the circuit layer made of a refractory metal containing W or Mo as a main component contains a Ti compound. 7. The silicon nitride circuit board according to claim 6, wherein the Ti compound is contained in a ratio of 0.5 to 5% by weight with respect to the circuit layer made of a refractory metal. 8. The high thermal conductivity silicon nitride substrate is 80 W / m.
· It has a thermal conductivity of K or more.
The described silicon nitride circuit board.