KR100494238B1 - Process for Manufacturing Copper Matrix Composite Sheets Reinforced with High Volume Fraction of Tungsten - Google Patents

Abstract

Powder metallurgy methods, such as liquid sintering and impregnation, cannot raise the temperature at which tungsten particles can be melted, so that more pores exist in the product than when tungsten particles are slightly melted by a hot plasma flame. In addition, the conventional powder metallurgy has a disadvantage in that not only the manufacturing cost is increased due to the complicated manufacturing process requiring molding and sintering but also the productivity is low. In particular, when the portion to be utilized is a thin plate shape having a thickness of 1 mm or less and a large area, these methods are limited in size. Therefore, in the present invention, a copper base composite material thin plate using atmospheric plasma spraying is produced by preparing a W-Cu composite material which is mixed or spheroidized with copper powder and tungsten powder which can make a complicated shape with a simple manufacturing process. It provides a method of manufacturing.

Description

Process for Manufacturing Copper Matrix Composite Sheets Reinforced with High Volume Fraction of Tungsten}

The present invention relates to the manufacture of metal-based composites, and more particularly, to a method of manufacturing a tungsten-reinforced copper matrix composite sheet using plasma spraying.

Tungsten-reinforced Cu-based composite materials can easily control ductility and strength, thermal expansion coefficient and heat transfer coefficient according to the type and fraction of reinforcing material, and have a high melting temperature of tungsten. In this regard, W-Cu composites are not only heat dissipating materials such as heat sink for electronic package materials, but also high load electrical contact materials and motor drivers due to the arc resistance of tungsten and the thermal and electrical properties of copper. It is widely used in electrode materials, warhead materials, and the like.

Such W-Cu composites are usually manufactured by powder metallurgy such as liquid sintering and impregnation. The liquid sintering method is a method of mixing and molding tungsten powder and copper powder, and then sintering at a temperature above the melting point of copper. The ball milling, mechanical alloying method, and trace elements (Co, Ni) are applied according to powder processing to increase the sinter density. It is divided into active sintering method using). According to the liquid sintering method, the liquid copper melted in the tungsten sintered body in which the pores exist can enter all the pores by capillary force, thereby obtaining a high density composite material. However, this method has a difficulty in producing a porous tungsten preform composed only of continuous and open pores. In particular, in the liquid phase sintering method, it is difficult to uniformly mix the powder due to the density difference between tungsten (19.3 g / cm 3) and copper (8.96 g / cm 3), resulting in uneven distribution of tungsten particles after sintering.

For this reason, package heat sink suppliers such as AMETEK, SPECTRA MAT, POLSE, BRUSHWELLMANN in the United States and PLANSEE in Austria employ impregnation instead of liquid sintering. Most of these manufacturers produce products with a copper composition of 10 to 30% by weight through impregnation and then produce them through precision machining.

However, when manufacturing a copper base composite material having a high tungsten content, copper and tungsten have small solid solubility, and thus many pores are contained. Particularly, when the powder metallurgy method such as liquid sintering or impregnation is applied, the melting temperature of tungsten particles is increased. It cannot be raised to (3410 ° C.) and there are more pores in the composite because the tungsten particles are slightly melted. In addition, powder metallurgy methods such as Osram Sylvania (US Pat. No. 6,103,992) and Korea Institute of Science and Technology (US Pat. No. 5,963,773) in the United States go through complex manufacturing processes such as molding and sintering, resulting in increased manufacturing costs. But there is a downside in productivity. Moreover, when the product to be manufactured has a thickness of 1 mm or less and varies in shape or a large area, the above methods are limited in dimensions.

The present invention has been proposed to improve the above-mentioned problems of the prior art, and its purpose is to eliminate the complicated process and minimize the pores in the material by using plasma spraying, so that the thin plate-shaped W-Cu composite material suitable for the thermal management device of the electronic device. It is to provide a method for producing a.

W-Cu composite material manufacturing method according to the present invention for achieving the above object, in the manufacturing method of a metal-based composite material, after mixing the copper powder and W powder to obtain a thermal spray powder, the thermal spray powder And forming a thin plate by plasma spraying on the substrate.

Hereinafter, the present invention will be described in detail.

The method for producing a composite material according to the present invention is suitable for producing a copper matrix composite material reinforced with W powder. Preferably the thickness is suitable for the production of a thin W-Cu composite sheet of various shapes having a thickness of 0.2 ~ 2mm size. In particular, the production method of the present invention is more suitable for the production of a copper matrix composite material containing a high volume fraction of W powder, more preferably a thin sheet composite material containing 50 to 95% by volume of W in a copper matrix. . Such a composite material is very useful as a thermal management device for electronic packages.

In order to manufacture the composite material according to the present invention, first, Cu powder and W powder are mixed to obtain a thermal spray powder. It is preferable to mix the said thermal spraying powder in the said range. Mixing the powder may be a method of simply mixing the two kinds of powder, but it is preferable to prepare a powder spheroidized by a spray-drying process after mixing in a ball mill (ball mill). This spheroidized thermal spray fine powder melts copper and tungsten in a high temperature plasma flame to reduce pores.

Such thermal spray powder is dried into a thin sheet through atmospheric plasma spraying.

Figure 1 shows a schematic diagram for explaining the manufacturing process of the thin plate using a plasma spray. As shown in FIG. 1, the composite thin plate 1 of the present invention is supplied with the thermal spraying powder through the powder inlet 4 toward the tip of the thermal spray gun 3, and the thermal spray 3 It is produced by spraying the thermal spraying powder with a flame on a substrate 2 facing away from the predetermined distance.

As the substrate 2 used for the thermal spraying, Cu or Cu-Zn, Cu-Al, Cu-Sn copper alloys or graphite substrates are preferable. This is because peeling after spraying is easy. More preferably, boron nitride (BN) is sprayed onto the substrate 2 to coat the surface of the substrate to facilitate peeling of the composite material and the substrate after the thermal spraying. The substrate 2 may increase its size to control the size of the thin plate.

The substrate 2 is located on a fixed stand (not shown), and the plasma sprayed gun 3 may be installed on a moving table (not shown) to move at a constant speed through a program.

When plasma spraying in the present invention, the plasma arc is suitable about 15 ~ 40kW. If the plasma arc is 15 kW or less, the powder is not heated to a sufficient temperature, making it difficult to stack on the substrate, and the recovery rate is reduced. On the other hand, if the plasma arc is 40 kW or more, the defects such as oxides are increased due to the thermal spraying at high temperatures. not.

Moreover, as for the distance from the front end nozzle of the thermal spraying 3 to a board | substrate, 50-110 mm is suitable. If the distance is 50 mm or less, the temperature of the substrate is too high due to the plasma arc, so the stability of the process is lowered. On the other hand, if the distance is 110 mm or more, the recovery rate due to the solidification of the molten powder is not preferable.

The moving speed (injection amount) of the thermal spray powder is set in the range of 10 to 100 g / min, and the flow rate of the primary gas (Ar, N _2, etc.) is in the range of 23 to 94 l / min, and the secondary gas. It is preferable to adjust the flow rate of (H ₂ , He, etc.) in the range of 1.5-50 l / min. This is because if the feed rate of the powder is 10g / min or less, the amount of powder to be sprayed is too small and economically undesirable. If the feed rate is 100g / min or more, the powder flow is not smooth and it is difficult to obtain an even spray surface. . In addition, if the primary and secondary gas flow rate is out of the above range, it is not preferable because the powder is transferred outside the center of the plasma arc under insufficient operating conditions and uniform spraying is impossible.

When plasma spraying is used under such conditions, it is possible to produce a composite thin plate having a high reinforcing material fraction, which is difficult to manufacture by conventional techniques. In addition, the composite sheet thus produced has a high coefficient of heat transfer and a low coefficient of thermal expansion, which is very suitable for thermal management materials of electronic devices. In particular, in the present invention, when manufacturing the composite sheet, the desired physical properties can be designed according to the type and volume fraction of the reinforcing material powder to be selected.

Hereinafter, the present invention will be described in detail by way of examples, but the following examples are only for explaining the present invention, and according to the gist of the present invention, the scope of the present invention is not limited to the following examples. Will be evident to those of ordinary knowledge.

Example 1

Copper powder of 325 mesh or less and tungsten powder of 400 mesh or less were mixed at a volume fraction of 28:72 in a stirrer to prepare a thermal spray powder. The thermal sprayed powder was dried at 110 ° C. for 1 hour to remove moisture. The thermal sprayed powder was injected into a plasma arc of about 30 kW and laminated to a preheated graphite substrate having a size of 100 × 100 × 10 mm 3. Plasma spray operation conditions were as Table 1 below.

Arc current 500 A Arc voltage 60 V Input power 30 kW Primary gas flow rate (Ar) 75psi, 70ℓ / min Secondary gas flow rate (H ₂ ) 50 psi, 1.98 L / min Distance from nozzle to substrate 100 mm Movement Speed of the Champion Event 30 mm / sec Powder dosage 40 g / min

The shape of the thin W-Cu composite sheet produced by the above method is shown in FIG. 2 and the microstructure of the thin plate is shown in FIG. 3.

As can be seen in Figure 2, according to the present invention it can be produced a thin plate-shaped W-Cu composite material having a length of 100mm, width 100mm, thickness of about 1mm or less, as shown in Figure 3 the volume fraction of the W particles is about Evenly distributed around 70%.

Table 2 also shows the actual measured coefficient of thermal expansion and thermal conductivity of the W-Cu composites prepared by the present invention. In the case of the composite material, the coefficient of thermal expansion and thermal conductivity can be calculated theoretically according to the fraction of the reinforcing phase and the base metal, and compared with the theoretical coefficient of thermal expansion and the thermal conductivity of the composite material of the present invention.

division Example 1 Theory 1 Theory 2 Coefficient of thermal expansion (ppm / ℃) 7.2 6.4 (Kengery & Turner's model) 8.1 (Rule of Mixture) Thermal Conductivity (W / mK) 210 220 (Landauer's model) 225 (Maxwell model)

As can be seen from Table 2, it can be seen that the coefficient of thermal expansion and thermal conductivity actually measured for the composite material of the present invention are similar to the theoretical values.

Example 2

Tungsten powder with an average particle diameter of 2 mu m and copper powder with an average particle diameter of 26 mu m were charged into a stainless steel ball mill with a volume fraction of 90:10, and then cemented tungsten carbide balls were added. At this time, the weight ratio of the powder and the ball was 1: 1, and after mixing for about 24 hours at a speed of 100 rpm by a simple rotation method, the mixed powder was dispersed in water, and then polyvinyl alcohol as a binder. 0.5% was added, and spheroidized thermal spray powder was prepared by making the rotating disk speed into 20,000 rpm in 100 degreeC nitrogen gas. The spheroidized thermal spray powder was dried and then coarse powder was removed with a 200mesh sieve.

Plasma spraying was performed on an oxygen-free copper substrate having a size of 120 × 100 × 10 μs in a 25 kW plasma arc using the thermal spray powder prepared by the above method, and then a 120 × 100 × 1 μ size W-Cu composite plate was prepared. . The microstructure of the thin W-Cu composite sheet produced by the above method is shown in FIG. 4.

As shown in FIG. 4, the composite thin plate of the present invention had an even distribution in which the volume fraction of W was about 90%.

In addition, as a result of measuring the thermal expansion coefficient of the composite material, it showed a slightly lower than the theoretical value (Kengery & Turner's model; 6ppm / ℃), 6.3ppm / ℃, the thermal conductivity is 195W lower than the theoretical value (Maxwell Model; 205W / mK) / mK was shown. The difference with the theoretical value is because the reinforcement in the theory is oriented as an independent particle. In actual specimens, it is almost isotropic, there is no solid solution between copper and tungsten, and the increase of tungsten volume fraction increases the contact between particles, resulting in low ratio of independent particles.

As described above, according to the manufacturing method of the present invention, since the manufacturing process is simple, without undergoing an essential process in the conventional powder metallurgy, that is, a molding and a sintering process, the production cost of the product can be reduced. In addition, in the present invention, since a high temperature plasma is used, tungsten and copper can be simultaneously melted to obtain a high density thin plate, and the composite thin plate thus manufactured has a high heat transfer coefficient and a low coefficient of thermal expansion. Very useful for thermal management materials. In addition, in the present invention, the desired physical properties can be designed according to the type and volume fraction of the reinforcing material powder to be selected. Particularly, the powder metallurgy method has limitations for gradually adjusting the volume fraction of dimensional and reinforcing materials in the manufacture of composite materials having a large area (100 × 100 mm 2 or more) and thin plates (thickness: 1 mm or less). In the present invention, since plasma spraying is used, the volume fraction of the reinforcing material can be selectively adjusted even in thin thin plates without being restricted by these dimensions.

Figure 1 is a schematic diagram for explaining the W-Cu composite sheet manufacturing process of the present invention.

2 is a shape of the W-Cu composite thin plate prepared according to the first embodiment of the present invention.

3 is a microstructure photograph of a composite material prepared according to the first embodiment of the present invention.

Figure 4 is a microstructure photograph of the composite material prepared according to the second embodiment of the present invention.

Explanation of symbols on main parts of the drawing

1 ..... lamination 2 ..... Substrate

3 ..... Spraying 4 ..... Powder inlet

Claims (6)

In the manufacturing method of a metal base composite material, After the copper powder and tungsten powder are mixed to obtain a thermal spray powder, the thermal spray powder is plasma-sprayed on a graphite substrate to form a thin plate, and the thin plate is peeled off from the substrate using a difference in thermal expansion coefficient from the graphite substrate. W-Cu composite material thin plate manufacturing method comprising a. The method of claim 1, The thermal spraying powder is a volume%, the method for producing a thin sheet of W-Cu composite material, characterized in that 50 to 95% tungsten powder is mixed with the copper powder. The method of claim 1, The thermal spraying powder is mixed with a ball mill, and then a powder spheroidized by spray drying characterized in that the manufacturing method of the thin plate composite. The method of claim 1, The plasma spraying has a distance from the thermal spray nozzle to the substrate in the range of 50 to 110 mm, the moving speed of the thermal spraying powder is set in the range of 10 to 100 g / min, and the flow rate of the primary gas is 23 to 94 l / min. It is adjusted to the range of, the flow rate of the secondary gas 1.5 to 50 l / min, and then the method of producing a thin sheet of W-Cu composite material, characterized in that carried out in the plasma arc range of 15 to 40kW. delete The method of claim 1, The surface of the substrate is coated with boron nitride (BN) to increase the ease of peeling, characterized in that the manufacturing method of W-Cu composite sheet.