JP2010162573A - Method for producing porous metal and method for producing heat sink - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a porous metal which can efficiently and uniformly take bubbles in a cross-section vertical to a casting direction. <P>SOLUTION: In the method where a crucible 2 is arranged at the inside of a chamber 1 in a prescribed gas atmosphere, a metal raw material stored in the crucible 2 is heated and melted, the temperature of the molten metal M melted in the crucible 2 and the gas pressure in the chamber 1 are controlled so as to control the concentration of dissolved gas in the molten metal M, and the molten metal M in which the dissolved gas concentration is controlled is cooled and solidified so as to produce a porous metal, the lower edge side of a cylindrical mold 6 is immersed into the molten metal M in the crucible 2, and the ingot 15 of the porous metal is continuously pulled out through the mold 6. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a porous metal and a method for manufacturing a heat sink, and more particularly to a method for manufacturing a porous metal using a mold and a method for manufacturing a heat sink using a porous metal.

In the production of a porous metal, a porous metal is produced by utilizing the property that supersaturated gas is precipitated in a solid phase in the process of melting and solidifying a gas in a molten metal melt. That is, the solubility of the gas in the molten metal is higher as the temperature is higher and lower as the temperature is lower, and the solubility of the gas in the solidified metal decreases more rapidly, so the dissolved gas element that is supersaturated when the temperature of the molten metal is lowered and solidified. Becomes gas molecules, bubbles are deposited in the solid phase metal, and a porous metal (porous metal) is formed.
Conventionally, a method of casting a porous metal using a mold (see Patent Documents 1 to 3) and a method of manufacturing a porous metal using a floating zone melting method (see Patent Document 4) have been proposed.

On the other hand, heat sink materials such as semiconductor chips and heat spreader materials are required to have good thermal conductivity, and copper and copper alloys have been conventionally used for these materials. However, the linear expansion coefficient of copper is about 17 ppm, whereas the linear expansion coefficient of Si serving as a base material of a normal semiconductor chip is about 4.5 ppm. Due to this mismatch in the linear expansion coefficient, stress is generated at the interface between the semiconductor chip and the heat sink (or heat spreader) at the time of heating, and there are many problems that peeling or cracking occurs. As means for solving these problems, materials having high thermal conductivity and a small mismatch of linear expansion coefficient (high thermal conductivity, low thermal expansion material) have been developed. Examples of the high thermal conductivity low thermal expansion material include Cu—Mo, Cu—W, Al—SiC, and Cu—Cu ₂ O. Also, there is a semiconductor device in which a semiconductor chip is mounted on a porous metal layer (heat sink) in which a porous resin layer is formed in pores of the porous metal using a porous metal obtained by mixing a binder and a foaming agent in a metal powder and sintering. It is known (see Patent Document 5).

JP 2004-322143 A JP 2000-104130 A JP 2000-239760 A Republished patent WO2003 / 070401 JP 2006-128222 A

  The conventional method for producing a porous metal utilizes only the solubility curve of a metal gas, that is, the higher the dissolution temperature, the higher the solubility of the gas, and the greater the decrease in solubility during solidification. The dissolved gas element which becomes supersaturated when the molten metal temperature is lowered and solidified becomes gas molecules and becomes bubbles. Therefore, in order to increase the dissolved amount of gas in the molten metal, it is necessary to increase the gas partial pressure, and it is necessary to adjust the pressure of the melting chamber. Further, part of the dissolved gas that becomes supersaturated when the molten metal temperature is lowered in the mold rises as bubbles. In the conventional manufacturing method, since the casting direction is downward or sideways, the rising gas is released from the surface of the molten metal into the atmosphere, and bubbles cannot be taken into the solidified metal efficiently.

Further, the above-described conventional high heat conduction low thermal expansion material used for the heat sink material has the following problems. Cu-Mo and Cu-W have good characteristics (high thermal conductivity and low thermal expansion characteristics), but expensive metals such as Mo and W are added to Cu at least 5 wt%, usually about 30-50 wt%. The material cost is very high. Furthermore, in recent years, the material costs of rare metals such as Mo and W have continued to rise, and there is a problem that supply risk is very high. Moreover, although Al-SiC has a lower material cost than Cu-Mo and Cu-W, it is inferior in characteristics. Furthermore, the manufacturing cost is higher than the copper plate, and the total cost is higher than that of the copper plate. Further, Cu-Cu 2 _O is cost cheaper than the high thermal conductivity a low thermal expansion material, is inferior in characteristic. Therefore, a material that can sufficiently achieve both characteristics and low cost has not been developed.
In addition, the porous metal sintered by mixing a binder and a foaming agent with the above-mentioned metal powder has no anisotropy in the pores, so when used as a heat sink material, the thermal conductivity in the plate thickness direction and the mounting of the semiconductor element The mitigation of the mismatch of the linear expansion coefficient of the semiconductor element and the heat sink in the surface direction of the heat sink surface is not compatible.

An object of the present invention is to provide a method for producing a porous metal capable of efficiently incorporating bubbles in a cross section perpendicular to the casting direction.
Another object of the present invention is to provide a method for manufacturing a heat sink that can achieve both thermal conductivity in the thickness direction and relaxation of mismatch in linear expansion coefficient in the surface direction with a heating element such as a semiconductor element. .

  In order to solve the above problems, the present invention is configured as follows.

  According to a first aspect of the present invention, a crucible is disposed in a chamber of a predetermined gas atmosphere, the metal raw material stored in the crucible is heated and melted, and the temperature of the molten metal melted in the crucible and the above In the method of controlling the dissolved gas concentration in the molten metal by controlling the gas pressure in the chamber, and cooling and solidifying the molten metal in which the dissolved gas concentration is controlled, This is a method for producing a porous metal in which the lower end side of a cylindrical mold is immersed in a molten metal, and a porous metal ingot is continuously drawn upward through the mold.

  According to a second aspect of the present invention, in the method for producing a porous metal according to the first aspect, a porous plug is provided at a lower portion of the crucible, and the molten metal in the crucible is inserted from the porous plug into the molten metal in the crucible. It is a manufacturing method of porous metal which supplies the bubble containing gas.

  According to a third aspect of the present invention, in the method for producing a porous metal according to the first aspect or the second aspect, a cooling rate and a heat extraction direction when a porous metal ingot is cast with the mold are controlled. Thus, the density, growth direction, size, and distribution state of the bubbles precipitated in the ingot by the gas supersaturated when the molten metal is solidified are controlled to produce a porous metal.

  According to a fourth aspect of the present invention, in the method for producing a porous metal according to any one of the first to third aspects, a dummy bar provided movably in the cylindrical mold is inserted into the mold. A porous metal manufacturing method in which growth of a porous metal ingot is started by pulling up the dummy bar after making contact with the molten metal surface in the crucible.

  According to a fifth aspect of the present invention, there is provided the porous metal manufacturing method according to any one of the first to fourth aspects, wherein a water cooling jacket for cooling the mold is provided on an outer periphery of the cylindrical mold. It is a manufacturing method.

A sixth aspect of the present invention is a method for producing a porous metal according to any one of the first to fifth aspects, wherein the cylindrical mold has a circular or rectangular cross section.

  According to a seventh aspect of the present invention, there is provided a porous metal ingot produced by the method for producing a porous metal according to any one of the first to sixth aspects, in which bubbles extend in a casting direction, perpendicular to the casting direction. This is a heat sink manufacturing method in which a heat sink is produced by cutting and using the cut porous metal member.

According to the method for producing a porous metal of the present invention, the porous metal ingot is continuously drawn upward through the mold, so that the porous metal in which bubbles are efficiently taken in a cross section perpendicular to the casting direction efficiently. An ingot is obtained.
Further, according to the heat sink manufacturing method of the present invention, by using a porous metal ingot having anisotropy in which bubbles extend in the casting direction, the heat conductivity in the thickness direction, and a heating element such as a semiconductor element Thus, it is possible to provide a heat sink that can simultaneously reduce the mismatch of the linear expansion coefficient in the surface direction.

It is a figure which shows 1 process of the manufacturing method of the porous metal which concerns on one Embodiment of this invention. It is a figure which shows 1 process of the manufacturing method of the porous metal which concerns on one Embodiment of this invention.

Below, embodiment of the manufacturing method of the porous metal which concerns on this invention is described.
The method for producing a porous metal according to the present embodiment includes a crucible placed in a chamber in a predetermined gas atmosphere, the metal raw material stored in the crucible is heated and melted, and the temperature of the molten metal melted in the crucible And a gas pressure in the chamber to control a dissolved gas concentration in the molten metal, and to cool and solidify the molten metal in which the dissolved gas concentration is controlled, to manufacture a porous metal, the crucible The lower end side of the cylindrical mold is immersed in the molten metal, and the porous metal ingot is continuously drawn upward through the mold.

The inventor has sought for an efficient method of taking bubbles into the porous metal, and variously changed the casting method, gas pressure, molten metal temperature, cooling rate (drawing speed), heat removal direction (heat release direction), etc. We have intensively investigated and studied the density, growth direction, size, and distribution of pores in the resulting porous metal.
As a result, by setting the casting direction upward (drawing the ingot upward), it is possible to efficiently trap gas bubbles (pores) at the solidification interface while suppressing the floating separation of gas bubbles, It has been found that the pore distribution in the cross section perpendicular to the casting direction can be made uniform.
It was also found that the pore density in the porous metal can be controlled by controlling the molten metal temperature and the gas pressure (in the case of a mixed gas, the gas partial pressure of each gas). Furthermore, it has been found that the growth direction and size of the pores in the porous metal can be controlled by controlling the cooling rate and heat release direction during casting.

The gas to be used is not particularly limited, but a gas having a large change in melt temperature and solubility before and after solidification is effective. For example, hydrogen, nitrogen, etc., or a gas in which an inert gas is mixed therewith can be used.
The metal to be cast is not particularly limited, but when used as a heat sink material, copper, copper alloy, aluminum, or aluminum alloy is effective. It should be noted that heating of the porous metal after casting is undesirable because it causes expansion and deformation due to gas expansion.

  A more specific embodiment of the method for producing a porous metal according to the present invention will be described below. FIG. 1 shows a schematic longitudinal sectional view of an apparatus used in the method for producing a porous metal ingot according to this embodiment.

  As shown in FIG. 1, the porous metal ingot manufacturing apparatus includes a chamber 1 that is sealed in a predetermined gas atmosphere, a carbon crucible 2 that is installed in the chamber 1, and a support that supports the crucible 2. The lower end of the member 3 and the induction heating coil 5 provided on the outer periphery of the crucible 2 and heating means for heating and melting the metal raw material in the crucible 2 and the molten metal M in the crucible 2 are inserted during continuous casting. And a cylindrical mold 6 to be used.

  The mold 6 is made of carbon, and a water cooling jacket 7 made of copper is integrally provided on the outer periphery of the mold 6. Cooling water is supplied to the water cooling jacket 7, and the mold 6 is cooled by the water cooling jacket 7. The mold 6 and the water cooling jacket 7 are vertically provided through the ceiling wall 1a of the chamber 1, and the mold 6 and the water cooling jacket 7 can be moved up and down by driving means (not shown). A metal dummy bar 8 is slidably provided in the mold 6. The dummy bar 8 is provided so as to be movable up and down in the mold 6 by a pinch roll 9 provided above the mold 6. A ring-shaped heat-resistant seal 10 made of silicon rubber is provided on the upper part of the mold 6 in order to hermetically seal a gap between the mold 6 and the dummy bar 8 (ingot pulled up during continuous casting). A structure in which carbon or the like is fitted to the tip of the dummy bar 8 may be used.

  A gas supply pipe 11 that supplies gas into the chamber 1 and a gas discharge pipe 12 that exhausts the gas in the chamber 1 are provided on the side wall of the chamber 1. A gas supply system (not shown) for introducing gas to the gas supply pipe 11 is connected to the gas supply pipe 11, and a controller and a flow path for controlling and adjusting the gas flow rate and the like are connected to the gas supply system. A gas supply amount control means (not shown) including a valve for controlling opening and closing is provided. The gas exhaust pipe 12 is connected to a gas exhaust system (not shown) including a pump that sucks and exhausts the gas in the chamber 1 and a valve that controls opening and closing of the flow path. The pressure in the chamber 1 is detected by a pressure sensor (not shown), and the chamber 1 is controlled by controlling the gas supply amount of the gas supply system and the gas exhaust amount of the gas exhaust system based on the detection value of the pressure sensor. The gas pressure inside is controlled to a predetermined pressure.

  Further, the temperature of the molten metal M in the crucible 2 is controlled by detecting the temperature of the molten metal M in the crucible 2 with a temperature sensor (not shown) and controlling the amount of current supplied to the induction heating coil 5. . The induction heating coil 5 is divided into a plurality of zones in the vertical direction, and the temperature of each zone can be controlled individually.

  A cylindrical support shaft 4 is provided on the bottom wall of the chamber 1 so as to penetrate the chamber 1. The support shaft 4 is connected to the support member 3 that supports the crucible 2 and supports the support member 3. A porous plug 13 made of porous ceramic is embedded in the bottom of the crucible 2. The porous plug 13 is connected to a gas introduction pipe 14 disposed in the cylindrical support shaft 4, and gas is introduced from the gas introduction pipe 14 to the porous plug 13. The gas introduced from the gas introduction pipe 14 is the same gas as the gas supplied into the chamber 1 from the gas supply pipe 11 or a gas containing the same gas. The gas introduced into the porous plug 13 is blown into the molten metal M in the crucible 2 to adjust and make the dissolved gas concentration in the molten metal M uniform and to make the temperature of the molten metal M in the crucible 2 uniform. It is done.

Next, a method for manufacturing a porous metal using the manufacturing apparatus shown in FIG. 1 will be described.
A predetermined metal raw material is put into the crucible 2, and the metal raw material in the crucible 2 is melted by the induction heating coil 5 to form the molten metal M, and the temperature of the molten metal M is controlled.
Further, a predetermined gas is supplied from the gas supply pipe 11 into the chamber 1 and, if necessary, a gas is blown from the porous plug 13 into the molten metal M in the crucible 2 so that a predetermined gas pressure ( In the case of a mixed gas, it is controlled to a predetermined gas partial pressure). The gas concentration in the molten metal M is proportional to the square root of the gas pressure of the atmospheric gas in the chamber 1 (gas partial pressure in the case of a mixed gas) according to Sievertz's law in an equilibrium bear.
By controlling the gas pressure in the chamber 1 and the temperature of the molten metal M, the dissolved gas concentration in the molten metal M can be controlled.

After the dissolved gas concentration in the molten metal M becomes saturated, the mold 6 and the water cooling jacket 7 are lowered, and the lower end of the mold 6 is immersed in the molten metal M in the crucible 2 by a predetermined length. .
Next, by driving the pinch roll 9, the dummy bar 8 is lowered and brought into contact with the surface of the molten metal M in the mold 6, and then the dummy bar 8 is pulled up at a predetermined pulling speed. As a result, as shown in FIG. 2, the porous metal ingot 15 in which the molten metal M is cooled and solidified by the mold 6 and the dummy bar 8 cooled by the water-cooling jacket 7 continuously passes upward in the mold 6. To be raised. During this continuous casting, the mold 6 and the water cooling jacket 7 are lowered at a predetermined speed so that the lower end portion of the mold 6 is always kept immersed in the molten metal M by a certain length.
The porous metal ingot 15 that has passed through the mold 6 and further pulled up by the pinch roll 9 is cut into predetermined lengths during continuous casting (or after continuous casting) by a flying saw or the like (not shown).

By controlling the gas pressure (gas partial pressure) in the chamber 1 and the temperature of the molten metal M, the dissolved gas concentration in the molten metal M can be controlled, and the pore density of the porous metal ingot 15 can be controlled. It becomes.
Further, by controlling the drawing speed of the porous metal ingot 15 during continuous casting and the amount of heat removed from the mold 6, the cast structure of the ingot 15 and the pore shape in the ingot 15 can be controlled. For example, when the amount of heat removed upward is increased at a slow drawing speed, the cast structure becomes a structure that is long and elongated in the casting direction, and those having large pores are elongated in the casting direction. In addition, when the amount of heat extracted from the mold is increased at a high drawing speed, the cast structure has a relatively thin structure extending in the cross-sectional direction perpendicular to the casting direction, and the pores are also relatively narrow in the cross-sectional direction perpendicular to the casting direction. extend. Thus, by changing the drawing speed of the ingot 15 and the amount of heat removed from the mold 6, it is possible to control the growth direction and thickness of the pores.
In this way, by controlling the gas pressure (gas partial pressure), molten metal temperature, drawing speed, cooling amount, heat removal from the mold, pore density, growth direction, size, distribution state of the resulting porous metal ingot Can be controlled.

Next, a method of manufacturing a heat sink or the like using the porous metal ingot 15 manufactured according to the above embodiment will be described.
By the porous metal manufacturing method of the above embodiment, the porous metal ingot 15 in which bubbles extend in the casting direction (axial center direction of the cylindrical mold 6) is cut perpendicularly to the casting direction with a flying saw or the like. A heat sink is produced using the cut porous metal member having anisotropy. That is, the heat sink is manufactured with the casting direction perpendicular to the cut surface of the porous metal member as the thickness direction of the heat sink and the cut surface as the mounting surface on which the semiconductor element is mounted. As a result, a heat sink having anisotropy that has good thermal conductivity in the thickness direction and can alleviate the mismatch of the linear expansion coefficient with the semiconductor element within the mounting surface can be obtained.

Further, in the porous metal manufacturing method of the above embodiment, a porous metal ingot 15 having a circular cross section perpendicular to the casting direction is manufactured using a cylindrical mold 6, and the resulting porous metal having a circular cross section is obtained. By extruding or drawing the ingot 15 in the casting direction, a work-hardened porous metal rod or porous metal wire is obtained.
Furthermore, in the porous metal manufacturing method of the above embodiment, a rectangular cylindrical shape is used as the mold 6 to manufacture a porous metal ingot 15 having a rectangular cross section perpendicular to the casting direction, and the resulting porous porous cross section is obtained. By rolling the metal ingot 15 in the casting direction, a work-hardened porous metal plate or porous metal strip is obtained.

  In the manufacturing method of the above embodiment, the mold 6 is lowered in accordance with the lowering speed of the surface of the molten metal M at the time of continuous casting. However, by fixing the mold 6 at the time of continuous casting, the support shaft 4 is raised. The crucible 2 may be raised at a predetermined speed to keep the surface of the molten metal M in the crucible 2 at a certain position. Alternatively, a partition plate that can be moved up and down and can be liquid-tightly partitioned in the crucible 2 is provided at the bottom of the crucible 2, and the molten metal in the crucible 2 is raised at a predetermined speed during continuous casting. Continuous casting may be performed by keeping the position of the M surface constant or by pouring the molten metal M into the mold 6.

Next, examples of the present invention will be described.
In this example, a porous metal ingot was manufactured using the manufacturing apparatus shown in FIG. 1 used in the above embodiment.

Hydrogen gas was supplied to the chamber 1 from the gas supply pipe 11, and the inside of the chamber 1 was set to a 100% H ₂ atmosphere at atmospheric pressure. Further, before continuous casting, hydrogen gas was blown into the molten metal M in the crucible 2 from the porous plug 13 made of alumina. The crucible 2 (melting furnace) was made of carbon and had a circular cross section with an inner diameter of 200 mm. The mold 6 is made of carbon and has a cylindrical shape with an inner diameter of 30 mm. As the dummy bar 8, a round bar made of pure copper was used.

Heating was started by energizing the induction heating coil 5, and 10 kg of pure copper in the crucible 2 was dissolved. The surface of the molten metal M was not covered, and was in contact with the H ₂ atmosphere. The position in the height direction was adjusted so that the tip of the mold 6 was immersed about 10 mm from the surface of the molten metal M, and the mold 6 was lowered so that this state was maintained even during continuous casting. After bringing the dummy bar 8 into contact with the molten metal M in the mold 6, casting was started by pulling the dummy bar 8 upward by the pinch roll 9. The pulling speed (casting speed) was 50 mm / min, and the cooling water flow rate of the water cooling jacket 7 of the mold 6 was adjusted to control the heat removal direction in the mold 6 to be obliquely upward. As a result, the H ₂ gas phase precipitated at the solidification interface extended obliquely upward like the cast structure.

After the completion of casting, the structure and porosity of the cross section perpendicular to the casting direction of the obtained porous metal ingot 15 were confirmed. The average crystal grain size was about 2 mm and the porosity was about 20%.
After removing the oxide on the surface of the obtained cast rod by chamfering, it was made into a porous copper rod having a diameter of 10 mm by cold drawing. This was sliced at a thickness of 2 mm to obtain a disk-shaped heat sink. In order to compare with the heat sink of this example, a heat sink having a diameter of 10 mm and a thickness of 2 mm was prepared from a pure copper ingot produced by ordinary casting and extrusion as a heat sink of a comparative material.
A Si chip having a cross-sectional size of 5 mm × 5 mm was bonded to the heat sink of this example and a comparative material with solder, and 3000 heat cycles were applied between 125 ° C. and room temperature. As a result, cracks occurred at the interface with the solder near the corner of the Si chip in the heat sink of the comparative example, whereas no cracks occurred at all in the heat sink of the example. Further, when the thermal conductivity in the thickness direction (casting direction in the example) of the heat sink of the example and the comparative material, the thermal expansion coefficient in the direction of the Si chip joint surface, and the Young's modulus were measured, the results shown in Table 1 were obtained. It was. As shown in Table 1, in the heat sink of this example, despite the thermal conductivity equivalent to that of the heat sink of the comparative example, both the thermal expansion coefficient and Young's modulus are lower than the heat sink material of the comparative example, and the thermal expansion with Si It turns out that rate mismatch can be mitigated.

  In the above embodiment, the manufactured porous metal ingot was applied to the heat sink, but as other uses, in addition to the vibration isolating material, the shock absorbing material, the sound insulating material, the electrode of the fuel cell, the water-cooled heat sink, and the like can be considered.

DESCRIPTION OF SYMBOLS 1 Chamber 2 Crucible 3 Support member 4 Support shaft 5 Induction heating coil 6 Mold 7 Water cooling jacket 8 Dummy bar 9 Pinch roll 10 Heat resistant seal 11 Gas supply pipe 12 Gas discharge pipe 13 Porous plug 14 Gas introduction pipe 15 Ingot M Molten metal

Claims (7)

A crucible is arranged in a chamber having a predetermined gas atmosphere, the metal raw material stored in the crucible is heated and melted, and the temperature of the molten metal in the crucible and the gas pressure in the chamber are controlled. In the method for producing a porous metal by controlling the dissolved gas concentration in the molten metal and cooling and solidifying the molten metal in which the dissolved gas concentration is controlled,
A method for producing a porous metal, wherein a lower end side of a cylindrical mold is immersed in a molten metal in the crucible, and a porous metal ingot is continuously drawn upward through the mold.   2. The porous metal according to claim 1, wherein a porous plug is provided at a lower portion of the crucible, and bubbles containing the same gas as in the chamber are supplied from the porous plug into the molten metal in the crucible. Production method.   By controlling the cooling rate and heat removal direction when the porous metal ingot is cast with the mold, the density and growth of bubbles precipitated in the ingot by the gas supersaturated when the molten metal solidifies 3. The method for producing a porous metal according to claim 1, wherein the direction, size, and distribution state are controlled.   A dummy bar movably provided in the cylindrical mold is inserted into the mold and brought into contact with the molten metal surface in the crucible, and then the dummy bar is pulled up to grow a porous metal ingot. The method for producing a porous metal according to any one of claims 1 to 3, wherein the method is started.   The method for producing a porous metal according to any one of claims 1 to 4, wherein a water-cooling jacket for cooling the mold is provided on an outer periphery of the cylindrical mold.   The method for producing a porous metal according to any one of claims 1 to 5, wherein a cross section of the cylindrical mold is circular or rectangular.   The porous metal member produced by the method for producing a porous metal according to any one of claims 1 to 6, wherein the ingot of the porous metal with bubbles extending in the casting direction is cut perpendicularly to the casting direction, and the cut porous metal member A method of manufacturing a heat sink, characterized by producing a heat sink using

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