1. Field of the Invention
The present invention relates to a method for fabricating a Alxe2x80x94Si alloy packaging material for semiconductor device, and in more particular to a method for fabricating an Alxe2x80x94Si alloy packaging material which is capable of increasing Si content by mixing Si powders with Alxe2x80x94Si powders and pressurizing-forming the mixture or by pressurizing-filling Si powders or a preforming body of Si powders with Alxe2x80x94Si alloy melt.
2. Description of the Prior Art
A packaging material for semiconductor device means a material fabricated as a box-shaped body in order to protect a semiconductor device disposed therein. In general, a package is largely divided into a homogeneous package and a heterogeneous package.
FIG. 1a illustrates a homogeneous package consisting of a base 1, a side-wall 2 and a lid 3. Herein, a feedthrough 4 is arranged between the base and the side-wall 2, and semiconductor substance 5 is disposed in the package. FIG. 1b illustrates a heterogeneous package fabricated by joining the base 1, the side-walls 2 and the lid 3, herein, feedthrough 4 is formed on the sidewalls 2.
There are required characteristics for a packaging material for semiconductor device.
First, a packaging material has to have a thermal expansive coefficient similar to that of a semiconductor device. In more detail, when the semiconductor device is operated, heat is generated, and accordingly a temperature of the semiconductor and the package rises, herein, if they have different thermal expansive coefficients, the semiconductor device may be dissected from the package.
In addition, it is preferable for the packaging material to have a high heat transfer modulus. When the packaging material has a high heat conductivity, heat generated in the operation of the semiconductor device can be quickly emitted to the outside, and accordingly it is advantageous in maintaining performance of the semiconductor device.
The lighter the packaging material, the more it is advantageous. By using the packaging material having a low density, a weight of electronic appliance can be reduced, and accordingly mobility of electronic appliance can be improved.
The packaging material is required to have a good processability. In more detail, in order to fabricate an intricate package or a package required to have a precise measure tolerance, the packaging material having a good processability has to be used.
In addition, the packaging material is required to have a good plating characteristic. If a surface of the packaging material is plated with nickel, copper, silver and gold, etc. by an electroplating method and the joining between the packaging and the plating layer is strong, a life-span of the packaging can be improved.
Besides the above-mentioned characteristics, it is preferable to use a packaging material having a good bonding characteristic. In joining of the base, the side-walls and the lid, by using a material having a good bonding characteristic, a life-span and bonding characteristics of the packaging can be improved. Herein, the base, the side-walls and the lid are fabricated with the same material or different materials, and welding or soldering or adhesion agent can be used to join the construction parts.
Lastly, it is required for the packaging material to have a simple fabrication process and low production cost.
Various packaging materials having all those characteristics have been developed, among them typical packaging materials will be described with reference to following table 1.
The above-mentioned packaging materials respectively have merits and demerits. For example, kovar has an appropriate thermal expansive coefficient, however, its heat conductivity is low and a density is high. Titanium has a good thermal expansive coefficient and a low density, however, it has low heat conductivity and is expensive. Aluminum has an appropriate heat conductivity and a low density for a packaging material, however, because it has a high thermal expansive coefficient, its usage for a packaging material is restricted. Beryillia and diamond respectively have a low thermal expansive coefficient, a high high heat conductivity and a low density, however, they are excessively expensive.
In the meantime, a metal matrix composite fabricated by adding a stiffening agent such as SiC, B4N3 and Al2O3, etc. to a metal material such as aluminum, etc. shows good characteristics as a packaging material in several aspects such as a thermal expansive coefficient, a heat conductivity, a density and a price, etc.
FIG. 2 illustrates a pressureless infiltration method as one of typical methods for fabricating Alxe2x80x94SiC one of metal matrix composites. In the pressureless infiltration method, in order to make metal melt 8 easily penetrate into a preforming SiC body 7, a certain processes are required. In more detail, in order to improve a wetability of ceramic to the metal melt, a coating layer such as oxide, etc. is formed onto the ceramic surface or a chemical reaction between the melt and the ceramic surface is induced by using a special bonding agent. Afterward, the melt can easily penetrate into the preforming ceramic body. However, the above-described method is intricate. In addition, ceramic has bad processing characteristics.
In the meantime, in consideration of a thermal expansive coefficient, a heat conductivity and a density, etc., Si-30 wt % Al alloy is appropriate for a packaging material. In addition, its material cost, processability and bondingability are good, its application range will be gradually expanded.
Recently, a method for fabricating Alxe2x80x94Si alloy having the content of Si in the range of 50xcx9c70% by total weight of Alxe2x80x94Si alloy with a low cost has been developed in the U.K. FIG. 3 illustrates the conventional method for fabricating an Alxe2x80x94Si alloy packaging material. In the method, by fabricating preforming alloy Alxe2x80x94Si melt 9, spraying it as liquid 10 having a 50 micronxcx9c200 micron size by using high pressure gas such as high pressure nitrogen and argon, etc., the alloy having a billet shape, etc. is formed onto a substrate moving rotatively and horizontally. After cuffing the formed Alxe2x80x94Si alloy body 11 so as to have a certain width, a hydrostatic press process (HIP, process for eliminating internal air holes), a mechanical process, a plating process, a semiconductor device adhesion process, and a packaging sealing process, etc. are sequentially performed. FIG. 4 is an enlarged photograph of the Al-70Si alloy fabricated by a spray forming method of OSPREY company in the U.K. taken with an electronic microscope ZEISS Axioskip (Germany).
However, the conventional method has following demerits. In the conventional method, a temperature of the melt has to be not less than 1000xc2x0 C., in cutting of the formed body and fabricating it as a certain package box, material loss occurs, and accordingly a fabrication cost is increased. In more detail, in fabricating of Alxe2x80x94Si packaging material by the conventional spray forming method, because the more the Si content, the higher a temperature of Alxe2x80x94Si melt has to be risen, there is lots of energy loss. In addition, because the spray-fabricated Alxe2x80x94Si alloy body has to be cut again to have a request size, lots of material and time loss occur.
In order to solve the above-mentioned problems, it is an object of the present invention to provide a method for fabricating an Alxe2x80x94Si packaging material which is capable of simplifying fabrication processes and lowering a production cost in comparison with the conventional Alxe2x80x94Si fabrication method by mixing Si powders with Alxe2x80x94Si alloy powders and filling the mixture as a request size from beginning.
It is another object of the present invention to provide a method for fabricating an Alxe2x80x94Si packaging material which is capable of fabricating an Alxe2x80x94Si alloy material having lots of Si content by easily adjusting the Si content in fabrication.
In addition, it is yet another object of the present invention to provide a method for fabricating an Alxe2x80x94Si packaging material which is capable of reducing internal air holes and performing full filling without using outer big stress by mixing-filling Alxe2x80x94Si alloy powders having a high temperature flowability with Si powders not having plastic deformation characteristic.
In addition, it is still another object of the present invention to provide a method for fabricating an Alxe2x80x94Si packaging material having different Si content in the thickness direction by differentiating a mixing proportion of Si of each or both Si powders and Alxe2x80x94Si alloy powders.