JPH10209357A - Heat sink and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cast a heat sink having many columnar cooling fins, by converting a salt core having circuit small holes with ceramic fibers, injecting a molten A, and applying a high pressure to it. SOLUTION: The top face of a salt core 3 is covered with a nonwoven cloth 5 of ceramic fibers formed like a mat as a melt leak blocking layer and Al melt is injected onto it. The melt never leaks because of a high surface tension. The ceramic fiber 5 is formed like a mat serving as a heat insulator to prevent the core from depriving the Al melt of its heat until application of a high pressure after the injection of the melt. When the high pressure is applied, the melt 6 breaks the ceramic fiber mat 5 to penetrate in circular small holes of the core 3 to form a cooling fin 1, and if continuing the pressuring, a base 2 is formed to be integrated with a heat sink by casting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a heat sink used for cooling semiconductor devices.

[0002]

2. Description of the Related Art Conventionally, a heat sink made of an extruded aluminum material has been widely used. However, as the power of the semiconductor element has been increased, the cooling efficiency of the conventional extrusion-type material has been limited, and a higher-performance heat sink has been required. In addition, in order to increase the cooling efficiency, plate-shaped fins made of extruded molds are cut into rods to increase the surface area of the fins.However, this method requires a lot of work and increases cost. Further, the fins were also square and it was difficult to produce a cylindrical fin.

[0003]

SUMMARY OF THE INVENTION According to the present invention, a radiating fin is formed in a cylindrical shape to enhance the cooling efficiency of a heat sink, and the cooling air is made non-directional. The challenge was how to make the fins integrally by casting.

[0004]

SUMMARY OF THE INVENTION The inventor of the present invention has a fear that even if the fins stand on the base plate like a heat sink, the fins may be broken if they are cast by a high pressure casting method. I thought it could be cast without it. This is because the base plate is strongly pressed from above, so that the thickness decreases as the aluminum hardens, but does not shrink in the plane direction. Conventionally, the spacing between the fins contained in the core does not change even when the aluminum hardens, but the base plate with the fins shrinks in the direction of the surface, so it breaks at the base of the fins and casts. It has not been possible. Also, I thought that if a salt core was used as the core, the salt core could be removed with water after casting, which would make production easier. That is, in the case where a heat sink provided with a large number of columnar radiation fins on a base plate is manufactured by casting, a salt core having a plurality of small holes having a circular cross section is used for a core in a mold. After the molten aluminum is poured, the high pressure is applied to the molten aluminum to destroy the molten metal leakage prevention layer, and the molten metal is pressed into the small hole of the salt core at once, This is a method of manufacturing a heat sink by continuously applying high pressure until the portion solidifies. A bulk or mat-like ceramic fiber was used as the hot water leakage prevention layer, and was placed over the salt core to prevent the molten metal from entering the hole.

[0005] The bulk or mat-like material may be a ceramic and porous molded body and has a thickness of 0.2 to 0.2 mm.
About 5 mm is good. The salt used for the core is obtained by molding powder of sodium chloride or potassium chloride as a main component under high pressure. The small hole may be formed by using a mold when forming the salt core, or may be formed later by a drill or the like. The shape of the small hole is circular and the diameter is 0.
Those having a size of 5 mm or more and 5 mm or less are preferred. If it is less than 0.5 mm, the strength of the fin is weak, and if it exceeds 5 mm, the cooling efficiency decreases, which is not preferable. Further, the shape of the fin may be a conical core shape whose diameter increases toward the base plate. The molten aluminum used may be an alloy or JIS-A1000. Note that high-pressure casting refers to applying a pressure of 1 kg / cm ² or more in a hot water state. By using this hot water leak prevention layer,
The injected aluminum melt is hindered by the ceramic fibers and stays in the casting mold at a high temperature without contacting the salt core, staying above the salt core. If high pressure is applied to the molten aluminum in this state, the molten metal will break the ceramic fibers and be pressed into the pin-shaped portion of the salt core at once,
Cooling fins are formed, but high pressure continues to be applied while the temperature of aluminum decreases and the volume shrinks. It can be cast side by side.

As described above, a salt core provided with a plurality of small holes having a circular cross section is covered with ceramic fibers, and an aluminum melt is poured thereon. Breaks the ceramic fibers at a stretch and press-fits into a plurality of small holes having a circular cross section provided in the salt core to form cooling fins. Further, by continuing the pressurization, the shrinkage of the base body in the planar direction was prevented, and the problem of casting a heat sink having a large number of cooling fins was solved.

[0007]

The gist of the present invention is that a large number of cylindrical cooling fins are cast as if they were grown from a base plate so that the heat of the base plate is efficiently transmitted to the fins. With this structure, a method has been developed in which a heat sink without uniform cooling can be uniformly manufactured at low cost. Generally, a sand mold or a metal mold is used for casting. However, as in the present invention, it has been difficult to produce a casting in which a large number of thin cylindrical pins are erected. If this is a sand mold,
The interval between the cylindrical pins was narrow, and it was difficult to pour the molten metal into the pins having a length of 10 times or more the diameter of the pins. In the case of die casting or die casting, it has been difficult to remove the casting from the die. A further problem is that the base shrinks at the surface due to cooling, but the cooling fin cannot be shrunk together with the base because it is fixed by the core, and is broken at the base of the cooling fin.

The present invention has taken the following three measures in order to solve these problems. 1. First, a high-pressure casting method was employed as a method for preventing damage to the fin base due to shrinkage of the base. After injecting the aluminum melt and applying high pressure to the melt until it solidifies, the molten metal is replenished by the high pressure from the thickness direction and solidified by the amount of cooling and shrinkage, and the gap is filled until the volume shrinks. The fin base is not affected by the shrinkage of the base because the surface portion does not shrink because of the continuation. 2. Next, a method using a salt as a material that is neither a sand mold nor a mold is used for a core forming a cylindrical cooling fin. If a plurality of small holes having a circular cross section are made in the salt core, and a molten aluminum is poured into the small holes for casting, the cast core can be easily taken out by dissolving the salt core with water after casting. In addition, since the salt core can be manufactured densely, it can be used as a high-pressure casting core.
3. The remaining problem is that the injected molten metal contacts the core and is cooled and partially solidified due to the time difference between the molten metal injection and pressurization. As a countermeasure, a hot water leak prevention layer made of ceramic fibers is provided on the upper surface of the core having a large number of holes, so that even if the molten aluminum is injected, the molten metal does not enter the holes of the salt core. When a high pressure is applied to the molten metal in this state, the molten metal destroys the leak prevention layer made of ceramic fibers at a stretch, and the cross section provided in the core is pressed into a small circular hole,
The heat sink in which the base plate and the cooling fin were integrated was manufactured.

[0009]

FIG. 1 is a perspective view of a heat sink to be manufactured according to the present invention. The cooling fin (1) is cylindrical and has a large surface area, and has no directivity to heat radiation, so that uniform cooling can be performed. Base (2) is fin (1)
Since it is made in one piece, it has good heat conduction efficiency and great cooling effect. FIG. 2 is an explanatory view showing a casting method according to the present invention. On the upper surface of the salt core (3), a ceramic fiber is matted as a hot water leakage preventing layer, and a nonwoven fabric (5) having a thickness of about 0.5 mm is put thereon. Then, a state in which the molten aluminum (6) is poured thereon is shown. Since the molten aluminum has a large surface tension, the molten aluminum cannot pass through a mat-shaped gap and does not leak. In addition, the ceramic fiber (5) also serves as a heat insulating material because of its mat shape, and prevents the heat of the aluminum melt from being taken away by the salt core until the high pressure is applied after the injection of the melt. In. If high pressure is applied to the aluminum melt from above,
The molten metal (6) destroys the ceramic fiber mat (5), and a small hole (4) having a circular cross section provided in the salt core (3).
To form cooling fins, and the base is formed without shrinkage by continued pressurization, so that the heat sink can be integrally manufactured.

[0010] As a prototype, a fin having a diameter of 3 mm and a length of 30 mm is placed on a disk-shaped base plate at intervals of 10 mm.
What was crossed and arranged in a cross shape to the length of the millimeter,
Cast according to the method of the present invention. As a result, none of the radiation fins was broken. Also, if you play the heat radiation fins with your fingertips, you will hear a clear sound of metal, so the base plate (2)
And the fins (1) were found to be completely integrated and cast.

As another method, a mat is floated on a molten aluminum and a salt core is placed on the mat. The salt core sinks to some extent, but the molten metal does not enter the small holes. In this method, the thickness of the mat can be reduced because the salt core receives the pressure of the molten aluminum more uniformly than when the molten metal is poured onto the mat. Alternatively, there is a method in which the salt core is floated in the air slightly above the molten aluminum and held, and the mold is used to push the salt core into the molten aluminum and cast at a high pressure. In this case, the mold side wall may be used as a foothold to float above the aluminum melt, or may be attached to the upper mold. Also, even if the feet are attached to the salt core so that it stays on the aluminum melt, and if pressure is applied from above, the feet of the salt core break, and the salt core enters the aluminum melt. Good. In this case, no mat is required.

[0012]

As described above, according to the present invention, a heat sink having high cooling efficiency in which a base plate and a large number of columnar radiating fins are integrally formed under high pressure can be easily and inexpensively manufactured by casting. In addition, a large base plate, for example, 200
Even large cooling fins of mm square or more can be made by casting without breaking or cracking the cooling fins at the base of the base plate. Further, as the material of aluminum, even a material having a large shrinkage and a poor flow of hot water can be used freely, and therefore, a material having the best heat conduction can be used. Further, the number, size and length of the fins can be easily manufactured only by changing the shape of the salt core.

[Brief description of the drawings]

FIG. 1 is a perspective view of a heat sink.

FIG. 2 is an explanatory view showing a casting method.

[Explanation of symbols]

1 Cooling fins 2 Heat sink base 3 Salt core 4 Small hole with a circular cross section provided on salt core 5 Water leak prevention layer made of ceramic fiber mat 6 Aluminum 7 ‥‥ metal mold

Claims (2)

[Claims] In a case where a heat sink provided with a large number of columnar radiation fins on a base plate is manufactured by casting, a salt core having a plurality of small holes having a circular cross section is used as a core in a mold, A molten metal leakage prevention layer is provided on the salt core, and after pouring the molten aluminum, high pressure is applied to the molten aluminum to destroy the molten metal leakage preventing layer, and the molten metal is pressed into the small hole of the salt core at a stretch, and the base is formed. A method of manufacturing a heat sink by continuously applying high pressure until a portion of a plate solidifies. 2. A heat sink manufactured by casting using the method of claim 1.