JP2007030075A - Electric discharge machining wire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the purity of a body to be machined and to simplify a grinding process and cleaning process. <P>SOLUTION: This electric discharge machining wire is characterized in that it is formed of carbon fiber, and preferably the diameter of the section of the carbon fiber is equal to or less than 0.02 mm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electric discharge machining wire. More specifically, the present invention relates to an electric discharge machining wire whose workpiece is a silicon carbide sintered body.

As one of the types of electrical discharge machining equipment, a hole is drilled in a workpiece, a wire electrode is passed through the drilled hole, and the workpiece is cut by moving the wire electrode and the workpiece relative to each other. There is an electrical discharge machining device. According to this electric discharge machining apparatus, a final molded product having a ring-shaped portion can be obtained. Since the wire used in such an apparatus is made of a metal such as brass, galvanized piano wire, tungsten wire, or the like, metal impurities in the wire tend to stick to the surface of the workpiece. For this reason, when processing a semiconductor manufacturing part that requires high purity, it is necessary to grind the seizure part or remove the impurity part by chemical cleaning before shipping the product (see, for example, Patent Document 1). ). In particular, when grinding a narrow line width groove on the workpiece, great care and skill are required.
JP 2001-9394 A

  Therefore, improvement in the purity of the workpiece and simplification of the grinding process and cleaning process have been demanded.

That is, the present invention relates to the following items:
(1) A wire for electric discharge machining formed of carbon fiber.
(2) The wire for electric discharge machining according to (1), wherein the carbon fiber has a cross-sectional diameter of 0.02 mm or less.
(3) The wire for electric discharge machining according to (1) or (2), wherein the carbon fiber has a tensile strength of 3500 MPa or more.
(4) The wire for electric discharge machining according to any one of (1) to (3), wherein the carbon fiber includes a bundle of a plurality of filaments and is twisted at 15 times / m or more.
(5) The wire for electric discharge machining according to (4), wherein the number of filaments is 1000 or more.
(6) The wire for electric discharge machining according to any one of (1) to (5), wherein the carbon fiber is a polyacrylonitrile-based carbon resin.
(7) The electric discharge machining wire according to any one of (1) to (6), wherein the workpiece of the electric discharge machining wire is a silicon carbide sintered body.
(8) The wire for electric discharge machining according to any one of (1) to (7), wherein a surface of the carbon fiber is plated.

  The grinding process and the cleaning process can be simplified.

Hereinafter, the present invention will be described with reference to embodiments, but it goes without saying that the present invention is not limited to the following embodiments.
FIG. 1 is a schematic conceptual diagram of an electric discharge machining apparatus in which a workpiece 1 is arranged. Such an electric discharge machine is
A wire supply roller 11;
A wire 3 that is supplied from the wire supply roller 11 and passes through the through hole 1a of the workpiece 1 via the wire guide 13 and the upper wire guide 15;
Stage 4 on which workpiece 1 is arranged;
A processing tank 35 indicated by an imaginary line surrounding the work 1,
A processing liquid tank 31 connected to the processing tank 35 via a pump 33;
A wire take-up roller 19 for winding the wire 3 via a lower wire guide 17 disposed at the lower part of the stage 4;
Controls the operation of the stage 4 and the upper wire guide 15 connected to the X axis drive unit 21 and the Y axis drive unit 23 of the stage 4 and connected to the X axis drive unit 25 and the Y axis drive unit 27 of the upper wire guide 15. CPU50 to do,
An electrical energy supply unit 42 connected between the wire guide 13 and the upper wire guide 15 and a machining power supply 40 for supplying power to the wire 3 having the electrical energy supply unit 44 connected to the stage 4 are provided.

  The wire 3 is preferably made of carbon fiber. This is because carbon fibers are electrically conductive, have mechanical properties such as a density lower than that of metal, high tensile strength and tensile elastic modulus, and excellent fatigue properties, wear properties, and lubricity. Furthermore, the thermal characteristics such as the linear expansion coefficient are small, the dimensional stability is excellent, the mechanical properties are lowered at high temperatures, and the thermal conductivity in the cryogenic temperature range is also small. Further, the carbon fiber wire 3 has a very low impurity concentration compared to the metal wire, and therefore, when the workpiece 1 is subjected to electric discharge machining, the possibility that the impurities of the wire 3 are seized on the surface of the workpiece 1 is extremely low. .

  From the viewpoint of performing microfabrication on the workpiece 1, the diameter of the cross section of the carbon fiber is preferably 0.02 mm or less. The lower limit of the diameter of the cross section of the wire 3 is not particularly limited, but is about 0.005 mm. The tensile strength of the carbon fiber is preferably 3500 MPa or more. This is because if the strength is lower than the above strength, the wire 3 may be broken during electric discharge machining. The carbon fiber is preferably composed of a plurality of filaments, preferably 1000 or more filament bundles. This is because the strength of the wire 3 is increased to prevent the wire 3 from being cut. The wire 3 may be twisted at 15 turns / m or more. This is because it becomes easy to insert the wire 3 into the through hole 1a of the workpiece 1. In addition, the wire diameter is constant and the dimensional accuracy is improved. From the viewpoint of increasing the purity of the workpiece 1, the total concentration of all impurities such as iron (Fe), copper (Cu), zinc (Zn), tungsten (W), etc. in the carbon fiber is preferably 100 ppm or less.

  Examples of the carbon fiber include polyacrylonitrile-based carbon resin and pitch-based carbon fiber. As the polyacrylonitrile-based carbon resin, for example, “BETHFITE” manufactured by Toho Tenax Co., Ltd. can be used. From the viewpoint of increasing the electric discharge machining speed, the surface of the carbon fiber may be plated. However, from the viewpoint of improving the purity of the workpiece 1, it is preferable that the plating process is not performed.

  The relative movement between the workpiece 1 and the wire 3 is performed by the movement of the stage 4. The stage 4 is moved by controlling the X-axis drive unit 21 and the Y-axis drive unit 23, respectively. In addition, as an electric discharge machine, if it is an apparatus provided with the said structure, a commercially available electric discharge machine can be used without a restriction | limiting in particular. For example, the product name “ADOMAQ” manufactured by Mitsubishi Electric Corporation can be used.

(Electrical discharge machining method)
First, work 1 is prepared. Here, as an example, a disk-shaped workpiece 1 having a trade name “Pure Beta” manufactured by Bridgestone Corporation and made of a high-purity silicon carbide sintered body having conductivity is used. It is assumed that the final shape of the work 1 after being cut out is a ring-shaped product.

  Next, the through-hole 1a is provided in the predetermined position of the workpiece | work 1 using the electrical discharge machining method. As shown in FIG. 2, the through-hole 1 a presses the discharge electrode 61 including the hollow portion 61 a on the surface of the work 1. Then, a current is passed through the discharge electrode 61 while supplying the machining solution, and the workpiece 1 is pulverized by a spark generated between the discharge electrode 61 and the workpiece 1. This step is performed while gradually moving the discharge electrode 61 in the direction of arrow A. At that time, it is preferable to carry out electric discharge machining while pouring pure water or a machining solution from the hollow portion 61 a of the discharge electrode 61 into the machining groove of the workpiece 1 and pushing the pulverized powder in the machining groove to the surface of the workpiece 1. In this way, a workpiece 1 having a through hole 1a indicated by a virtual line shown in FIG. 3 is obtained.

  Subsequently, as shown in FIGS. 4A and 4B, the work 1 provided with the through hole 1 a is arranged at the center of the stage 4. Then, as shown in FIG. 5, the wire 3 supplied from the wire supply roller 11 is passed through the through hole 1a of the work 1 through the wire 3 guide and the upper wire guide 15, and is arranged at the lower part of the stage 4 as shown in FIG. The wire 3 is wound up by the wire winding roller 19 through the lower wire guide 17 and the wire 3 is stretched.

  Thereafter, a voltage is applied between the workpiece 1 and the wire 3 from the machining power source 40, and a part of the workpiece 1 is melted and scattered by electric discharge. At that time, the machining liquid sent from the machining liquid tank 31 via the pump 33 is directly supplied to the workpiece 1 from a nozzle (not shown) provided in the machining tank 35 indicated by a virtual line. A processing liquid or pure water may be immersed in the processing tank 35. Usually, ion-exchanged water (water close to pure water) is used as the processing liquid. Then, the position of the stage 4 is moved little by little to form a groove having a desired pattern on the work 1.

Finally, the surface of the workpiece 1 is cleaned. Examples of the cleaning liquid include pure water, distilled water, ion exchange water, and acid solution. Pure water is preferable from the viewpoint of preventing back contamination of the workpiece. The pure water preferably has a purity level of 100 ppt or less and a specific resistance of 16 to 18 MΩ · cm, more preferably a purity of less than 10 ppt. In the case of using an acid solution as the washing liquid, it is preferable to use a boiling nitric acid solution {HF / HNO ₃ / water (0.5 / 0.5 / 3) (volume ratio)}. The time for immersing the silicon carbide sintered body in the cleaning liquid is preferably 2 minutes to 60 minutes, more preferably 5 minutes to 30 minutes, and even more preferably 10 minutes to 20 minutes. When immersing in the cleaning liquid, the overflow method may be performed so that the cleaning liquid is always cleaned with a new cleaning liquid, and this method may be combined with the cascade method. As a cleaning device used in the method for cleaning a silicon carbide sintered body, a conventionally known device or a device obtained by improving a conventionally known device can be used. Note that the cleaning method is not limited to the solution cleaning described above, and ultrasonic cleaning and the solution cleaning may be combined.

  According to the electric discharge machining method according to the above embodiment, since the wire 3 made of carbon fiber is used, impurities are difficult to adhere to the workpiece 1. Therefore, it is possible to simplify the grinding process and the cleaning process that have been conventionally required. Furthermore, since the wire 3 made of carbon fiber has a shorter diameter than a conventional wire, a groove having a narrow line width can be processed.

  The silicon carbide sintered body obtained according to the present embodiment can be suitably used for various semiconductor members and electronic components. Examples of various semiconductor members include members that require high purity, such as dummy wafers, heaters, plasma etching electrodes, ion implantation apparatus targets, and the like.

  Examples of the present invention will be shown below, but the present invention is not limited to these examples.

(Example) (Comparative Examples 1 and 2)
The workpiece 1 was subjected to electric discharge machining according to the method of the above embodiment.
As the work 1, a disk-shaped test piece having a diameter of 40 mm and a thickness of 30 mm made of a high-purity silicon carbide sintered body manufactured by Bridgestone Corporation and trade name “Pure Beta” was used.
As the electric discharge machine, an improved electric discharge machine manufactured by Mitsubishi Electric Corporation and having a trade name “ADOMAQ” was used.
As the carbon fiber wire 3, a wire 3 made by Toho Lanax Co., Ltd., having a trade name of “Besfite” having 12,000 filaments, 15 twists / m, and a diameter of 0.007 mm was used. As the brass wire 3, a wire 3 having a diameter of 0.15 mm manufactured by KHS Corporation and having a trade name “KH wire 3” was used. As the brass-coated piano wire 3, a wire 3 having a diameter of 0.05 mm made by KHS Co., Ltd. and trade name “AP wire 3” was used.
As cleaning conditions, pure water cleaning for 40 minutes while applying ultrasonic waves, FMN solution (hydrofluoric acid, nitric acid, pure water) cleaning for 40 minutes, pure water cleaning for 30 minutes while applying ultrasonic waves, 50% nitric acid cleaning for 60 minutes The workpiece 1 was cleaned in the order of 5 minutes of pure water cleaning while applying ultrasonic waves and 5 minutes of pure water cleaning.
Immediately after electric discharge machining was performed on the workpiece 1, the impurity element concentration was measured. Further, after cleaning, the impurity element concentrations in the plane and groove of the workpiece 1 were measured. As a reference example, the impurity element concentration on the surface of the workpiece 1 before electric discharge machining was measured. The obtained analysis results are shown in Tables 1, 2, and 3, respectively. As the impurity element concentration, the concentrations of iron (Fe), copper (Cu), and zinc (Zn) were measured. A total reflection X-ray fluorescence analyzer was used as the analyzer.

FIG. 1 is a schematic conceptual diagram of an electric discharge machining apparatus in which a workpiece is arranged. FIG. 2 is a process diagram in which a through hole is provided in a workpiece using an electric discharge machining method. FIG. 3 shows a side view of a workpiece having a through hole. 4A shows a side view of the stage, and FIG. 4B shows a top view of the stage. FIG. 5 shows a process diagram for passing the wire through the through hole of the workpiece. FIG. 6 is a process diagram for winding the wire passed through the through hole of the workpiece.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Work 1a ... Through-hole 3 ... Wire 4 ... Stage 11 ... Wire supply roller 13, 18 ... Wire guide 15 ... Upper wire guide 17 ... Lower wire guide 19 ... Wire winding roller 21, 25 ... X-axis drive part 23, 27 ... Y-axis drive unit 31 ... working fluid tank 33 ... pump 35 ... processing tank 40 ... processing power supply 42, 44 ... electric energy supply unit 50 ... CPU

Claims (8)

  A wire for electric discharge machining formed of carbon fiber.   The wire for electric discharge machining according to claim 1, wherein a diameter of a cross section of the carbon fiber is 0.02 mm or less.   The wire for electric discharge machining according to claim 1 or 2, wherein the carbon fiber has a tensile strength of 3500 MPa or more.   The wire for electric discharge machining according to any one of claims 1 to 3, wherein the carbon fiber comprises a bundle of a plurality of filaments and is twisted at 15 times / m or more.   The wire for electric discharge machining according to claim 4, wherein the number of filaments is 1000 or more.   The wire for electric discharge machining according to any one of claims 1 to 5, wherein the carbon fiber is a polyacrylonitrile-based carbon resin.   The electric discharge machining wire according to any one of claims 1 to 6, wherein a workpiece of the electric discharge machining wire is a silicon carbide sintered body.   The wire for electric discharge machining according to claim 1, wherein a surface of the carbon fiber is plated.

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