JPH09209058A - High thermal conductivity composite material and manufacturing method thereof - Google Patents

Abstract

(57) [Abstract] [Problem] Having a high thermal conductivity and a small specific gravity,
Provided are a high thermal conductive composite material having excellent heat resistance and a method for producing the same. SOLUTION: A mixed powder consisting of 20 to 70% by weight of copper and the balance of silicon carbide powder having an oxygen content of 1.0% by weight or more is molded, and then an oxygen partial pressure is 1 × 10 5. ^-5 ~
1080-in a non-oxidizing atmosphere in the range of 1 × 10 ^-3 atmospheres
It is fired at a temperature of 1200 ° C., contains 20 to 70 wt% of copper, and the balance is silicon carbide. The coefficient of thermal expansion from room temperature to 800 ° C. is 10 ppm / ° C. or less, and the thermal conductivity is 80.
A composite material with high thermal conductivity of W / m · K or higher is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly heat-conductive composite material having a high heat conductivity and suitable as a heat radiator for a heat sink material of a semiconductor device such as an IC package or a multilayer wiring board, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Semiconductors, especially LSIs, tend to generate more heat due to higher integration and higher speed. When this heat generation is accumulated in the semiconductor chip, it causes malfunction of the circuit in the semiconductor and further damages the semiconductor circuit itself. Therefore, one of the important functions of a package containing a highly integrated semiconductor is to dissipate heat.

Generally, in an LSI package, an alumina ceramic material having a thermal conductivity of about 20 W / m · K is used as an insulating substrate, and a heat sink is provided to enhance heat dissipation. The package is being used.

As a material for a heat sink in a package using an alumina ceramic material as an insulating substrate as described above, about 10% by weight of copper is used from the viewpoint of matching the high thermal conductivity with the thermal expansion coefficient of the alumina ceramic material. Including, copper-tungsten alloy (heat conductivity about 180W
/ M · K and coefficient of thermal expansion of about 7 ppm / ° C) are widely used. Aluminum-silicon carbide composite materials have also been proposed as other materials for heat sinks.

[0005]

However, this copper-tungsten alloy has a great disadvantage that it has a large specific gravity.

While the specific gravity of alumina is 3.5 to 4.0, the specific gravity of, for example, 10 wt% copper-tungsten alloy is 17.1, and the weight of the package is extremely increased by joining the heat sink. Resulting in.

[0007] In recent years, particularly in the surface mount type packages and the like, the package and the wiring board are joined by solder. When such a surface mount type package is subjected to an external impact, the weight of the package itself is increased. When the value is large, stress tends to concentrate on the solder joint portion, and the reliability of the joint is significantly reduced.

In response to such requirements, aluminum-
Silicon carbide composite materials are attracting attention as heat sink materials with low specific gravity. However, since the heat resistance of aluminum in this material is low, the heat resistance of the composite material itself is also low.
The temperature cannot be raised above 00 ° C. Therefore, a widely used silver-copper eutectic wax (BAg8 melting point 7
Since a brazing material such as 78 ° C. cannot be used, there is a problem that the reliability and cost of the semiconductor package are significantly reduced.

Therefore, it is an object of the present invention to provide a high thermal conductivity composite material having high thermal conductivity, low specific gravity and excellent heat resistance, and a method for producing the same.

[0010]

The inventor of the present invention firstly found that the large specific gravity of the copper-tungsten alloy was due to the large specific gravity of tungsten. It is only necessary to combine copper with a material having a high coefficient of thermal expansion and a low coefficient of thermal expansion, and low specific gravity is expected if silicon carbide is selected as a material with a low specific gravity, a high thermal conductivity, and a low thermal expansion coefficient. I found that I could do it.

However, it was difficult to form a composite because silicon carbide has no wettability with copper. However, when a silicon oxide film is formed on the surface of silicon carbide to form a composite, it may be densified. It was possible to achieve the present invention, and it was found that low specific gravity and high thermal conductivity can be achieved thereby, and the present invention was accomplished.

That is, according to the present invention, the coefficient of thermal expansion is 10 pp, containing 20 to 70% by weight of copper and the balance being silicon carbide.
A high thermal conductivity composite material having a thermal conductivity of 80 W / m · K or more and m / ° C. or less, and as a manufacturing method thereof, copper is 20 to
After forming a mixed powder of 70% by weight and the balance of silicon carbide powder having an oxygen content of 1.0% by weight or more, the oxygen partial pressure is 1 × 10 ⁻⁵ to 1 × 10 ⁻³ atm. It is characterized by firing at a temperature of 1080 to 1200 ° C. in a non-oxidizing atmosphere in the range.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The high thermal conductive composite material of the present invention is
It is a material that is a composite of copper and silicon carbide, and contains 20 to 20% of copper.
70% by weight, with the balance being silicon carbide.

The thermal expansion coefficient of the heat sink needs to be substantially the same as those of the oxide ceramics such as alumina ceramics and mullite which are generally used when they are applied to a package having an insulating substrate. For that purpose, the thermal expansion coefficient from room temperature to 800 ° C. needs to be 10 ppm / ° C. or less.

In order to achieve this coefficient of thermal expansion in a copper-silicon carbide based composite material, 50% by volume or more of silicon carbide, in other words, 30% by weight, is produced even if a new compound is not formed between copper and silicon carbide. % Or more is required. Therefore, if the amount of silicon carbide is less than 30% by weight, the thermal expansion coefficient of 10 ppm / ° C. or less cannot be achieved.

From the viewpoint of thermal conductivity, it is desired that the copper content be large, and the heat sink characteristic is 80 W.
/ MK or more is desired. To achieve such thermal conductivity, copper needs to be 20% by weight or more. Therefore, if the copper content is less than 20% by weight, the thermal conductivity is 80 W / m.
It will be difficult to achieve K or above.

Therefore, the composite material of the present invention has a coefficient of thermal expansion of 1 at room temperature to 800 ° C. in the above composition range.
A thermal conductivity of 0 ppm / ° C. or lower and a thermal conductivity of 80 W / m · K or higher are achieved, and the specific gravity is 5.7 or lower. Among the above compositional ranges, 40 to 60% by weight of copper and the balance being silicon carbide make it possible to obtain a thermal expansion coefficient of 5.7 to 8.6 ppm / ° C and a thermal conductivity of 80 W / m · from room temperature to 800 ° C.
The composite material has a specific gravity of 5.2 or higher and a specific gravity of 5.2 or lower.

As a method for producing such a composite material of copper and silicon carbide, the melting method applied to the production of a metal-based composite material cannot be applied to a material system containing 50% by volume or more of silicon carbide. However, according to the impregnation method, a silicon carbide simple substance is first sintered to produce a porous body having a predetermined porosity, and then the pores are impregnated with copper at normal pressure or high pressure to produce a porous body. It is possible. However, in this impregnation method, the process is complicated and it is difficult to stably produce a porous silicon carbide sintered body having a predetermined porosity, and the cost is high as a whole and it is difficult to stabilize the thermal characteristics and quality. Tend.

Therefore, in the present invention, it is preferable to manufacture the composite material by the powder metallurgy method because the composite material can be obtained in a simple process and with stable characteristics. However, it is difficult to sinter copper powder and silicon carbide powder by mixing and molding a powder having a predetermined ratio and sintering at a high temperature.

Therefore, according to the present invention, a dense sintered body can be produced by forming a silicon oxide film on the surface of the silicon carbide powder in the raw material powder, mixing it with copper powder, and molding and firing. it can.

Specifically, as a method for forming a silicon oxide film on a silicon carbide powder as a raw material powder, 1) 80
Heat treatment in an oxidizing atmosphere at 0 to 1300 ° C. 2)
Acid treatment of silicon carbide powder, 3) chemically forming a silicon oxide film by a technique such as CVD, 4) coating a silicon compound such as polysilazane on the surface of silicon carbide, and heating it to form a silicon oxide film. It is possible to form a silicon oxide film having an arbitrary thickness on the surface of silicon carbide by a method such as synthesizing

The silicon oxide film on the surface of the silicon carbide powder has an average thickness of 50 nm or more, particularly 100 nm or more, in other words, the amount of oxygen in the powder is 1% by weight or more, particularly 2% by weight.
Oxidize until above. At this time, the particle size of the silicon carbide powder is appropriately 1 to 10 μm.

Next, the silicon carbide powder thus treated is mixed with copper powder having an average particle size of 0.5 to 3 μm so that the copper content is 20 to 70% by weight. Then, this mixed powder is molded into a desired shape by a desired molding means such as a die press, a cold isostatic press, an extrusion molding, and the like, and then fired.

When firing, the temperature is 1080-1200 ° C.
Is fired in a non-oxidizing atmosphere for about 0.5 to 2 hours,
The oxygen partial pressure in the atmosphere at this time is 1 × 10 ⁻⁵ to 1 × 10 ^−3.
It is necessary that the pressure is 1 × 10 ^{−4 to} 9 × 10 ⁻⁴ atm. This is because if the oxygen partial pressure is lower than 1 × 10 ⁻⁵ atm, the copper does not wet with silicon carbide and the sintering does not proceed.
This is because if the pressure is higher than 0 ^-3 atm, copper is oxidized and the thermal conductivity is lowered.

[0025]

In the copper-silicon carbide composite material according to the present invention, densification does not occur even when the copper powder and the silicon carbide powder are simply mixed and shaped and the temperature is raised to 1100 ° C. or higher without being oxidized. Absent. It is considered that this is because although silicon carbide decomposes in the copper melt, the wettability is insufficient.

On the other hand, considering the reaction between copper and silicon oxide, cupric oxide (Cu ₂ O) causes a eutectic reaction with silicon oxide, although metallic copper and silicon oxide do not wet. It is already known from the phase diagram and the like that metallic copper and cupric oxide also undergo a eutectic reaction. Therefore, the metallic copper (Cu), cupric oxide (Cu ₂ O), and silicon oxide can be coexisted and sintered by heating.

The conditions for coexisting Cu and Cu ₂ O can be calculated by, for example, thermodynamic calculation. First, when the equilibrium oxygen partial pressure in the reaction of (1) 2Cu (l) + 1 / 2O ₂ → Cu ₂ O (S) at 1200 ° C. is calculated, pO ₂ = 2.7.
× 10 ⁻⁵ atm.

Similarly, when the parallel oxygen partial pressure of the reaction of (2) Cu (l) + 1 / 2O ₂ → CuO (S) at 1200 ° C. is obtained, pO ₂ = 1 × 10 ^-3
It becomes atmospheric pressure.

Similarly, when the equilibrium oxygen partial pressure in the reaction (1) at 1100 ° C. is calculated, pO ₂
= 2.0 × 10 ⁻⁵ atm. Similarly, when the equilibrium oxygen partial pressure in the reaction (2) at 1100 ° C. is calculated,
pO ₂ = 1.0 × 10 ⁻³ atm.

Thus, copper becomes Cu, Cu ₂ O, or CuO depending on the heating temperature and the oxygen partial pressure.
In addition, it takes a predetermined time to reach the equilibrium in a certain state, and therefore, before reaching that time, the states of two or more kinds of substances are mixed depending on the starting state and the atmospheric conditions.

Therefore, according to the present invention, silicon oxide and
The oxygen partial pressure and the baking temperature at the time of baking are such that Cu and Cu ₂ O can coexist, that is, the oxygen partial pressure of 1100 to 1200 ° C. is 1 × 10 ⁻⁵ atm to 1 × 10 ⁻³ atm. By holding under the conditions of, the composite material of copper and silicon carbide can be sintered and densified by coexistence of silicon oxide, cupric oxide (Cu ₂ O), and copper, resulting in high thermal conductivity and low specific gravity. Thus, a copper-silicon carbide based composite material having a low coefficient of thermal expansion can be obtained.

[0032]

Example As a raw material powder, a copper powder having an average particle size of 1 μm and a silicon carbide powder having an oxygen content of 0.8% by weight and an average particle size of 5 μm were prepared. Then, the silicon carbide powder was heated at a temperature of 800 to 1000 ° C. for 30 minutes in an atmospheric air atmosphere to form a silicon oxide film on the surface. The oxygen content in the powder at this time is shown in Table 1. Then, the treated silicon carbide powder and copper powder were mixed in the ratio shown in Table 1, and 120 parts by weight of nylon balls were added to 100 parts by weight of the mixed powder, and the mixture was mixed in a ball mill for 8 hours in a dry system.

The mixed powder is filled in a predetermined mold and 3 t
Press molding was performed at a pressure of / cm ³ to obtain a molded body. Then, the molded body was held for 30 minutes under the firing conditions shown in Table 1 in a nitrogen stream whose oxygen partial pressure was adjusted as shown in Table 1 to sinter the material.

The obtained sintered body was cut into a predetermined size.
After that, polishing is performed and the specific gravity is determined by the Archimedes method.
Therefore, the coefficient of thermal expansion from room temperature to 800 ° C
Thickness Conduction by laser flash method as mm sample
The rate was measured, and the results are shown in Table 1. Also obtained
The sintered body was made of silver-copper eutectic wax (BAg8, melting point 778 ° C.).
Forming gas (N_Two
87.5%, H_Two12.5%), heat the surface, shape
The change in shape was observed.

[0035]

[Table 1]

As is clear from Table 1, sample No. 2
In the material composition within the scope of the present invention of 8 and 10 to 12, the material characteristics exhibiting a small specific gravity and a large thermal conductivity are exhibited, and the characteristics suitable for a heat sink for a semiconductor device are exhibited. Further, a material containing less copper than the range of the present invention, such as Sample No. 1, results in poor sintering, and as a result, sufficient thermal conductivity cannot be obtained. When the composition of copper is larger than the range of the present invention such as sample No. 9, the coefficient of thermal expansion becomes larger than 10 ppm / ° C., which is not suitable as a heat sink. When the amount of oxygen in the raw material silicon carbide is small as in sample No. 13, densification is not achieved. When the oxygen partial pressure in the firing atmosphere is small as in sample No. 14, copper is not wetted by the silicon carbide powder and is not densified. When the oxygen partial pressure in the firing atmosphere was high as in sample No. 15, metallic copper was almost oxidized to copper oxide and densified, but no large thermal conductivity was observed.

The Cu-silicon carbide composite material of the present invention was excellent in heat resistance without any change in surface or shape as a result of heat resistance test with a brazing material.

[0038]

As described in detail above, according to the present invention,
It is lightweight, has high thermal conductivity, has heat resistance, and has a thermal expansion coefficient close to that of oxide ceramics such as alumina. As a result, it is used for heat sinks such as packages that use oxide ceramics as an insulating substrate. It can be suitably used as a material.

Claims (2)

[Claims] 1. A high thermal conductivity composite having a thermal expansion coefficient of 10 ppm / ° C. or less at room temperature to 800 ° C. and a thermal conductivity of 80 W / m · K or more, comprising 20 to 70% by weight of copper and the balance being silicon carbide. material. 2. After molding a mixed powder comprising 20 to 70% by weight of copper and the balance of silicon carbide powder having an oxygen content of 1.0% by weight or more, the oxygen partial pressure is 1 ×. 10 ^-5 ~
1080-in a non-oxidizing atmosphere in the range of 1 × 10 ^-3 atmospheres
A method for producing a high thermal conductive composite material, which comprises firing at a temperature of 1200 ° C.