JP2006055925A - Saw wire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a saw wire having an excellent wire characteristic and allowing realizing of excellent slicing efficiency. <P>SOLUTION: This saw wire has surface layer part residual stress RS up to a depth of 10 μm from an external surface located on a compression side, an absolute value ≥10 kg/mm<SP>2</SP>of the residual stress RS, and circumference 10 points average roughness PRz ≥0.3 μm measured along the circumference of cross section. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a saw wire for a saw machine used for cutting hard materials such as solar cells and semiconductors, magnets, and crystals.

  Conventionally, when slicing hard materials such as solar cells, semiconductors, magnets, crystals, etc., a saw wire stretched in parallel is run in one or both directions, and a processing liquid containing an abrasive is applied to the saw wire. A saw machine is used that is thinly cut into pieces by pressing a cylindrical workpiece while spraying. Such a saw machine is described in Patent Document 1 as a wire-type cutting apparatus that cuts a wafer from a semiconductor single crystal ingot, for example.

  Workpieces to be sliced by a saw machine tend to have a large diameter. For example, it takes several to several tens of hours to slice a silicon single crystal ingot having a large diameter of 8 to 12 inches (200 to 300 mm). Therefore, improvement of slice efficiency is demanded.

In order to improve the slicing efficiency, it is conceivable to provide unevenness on the wire surface to promote the pulling of the abrasive.
Japanese Patent No. 3345018

  However, if grooves or irregularities are formed on the surface of the wire by machining or electric discharge machining using a wire drawing die, the mechanical strength of the wire decreases, and the wire may be broken during slicing. Since the saw machine is required to continuously operate from the start of slicing to the end of slicing, when the slicing process is interrupted due to wire breakage, the lot is discarded. For this reason, development of a saw wire that can improve the slice efficiency without disconnection until the end of the slice is desired.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a saw wire that has excellent wire characteristics and can realize excellent slicing efficiency.

In the saw wire according to the present invention, the surface layer residual stress RS from the outer surface to a depth of 10 μm is on the compression side, the absolute value of the residual stress RS is 10 kg / mm ² or more, and
The circumferential ten-point average roughness PRz measured along the circumference of the cross section is 0.3 μm or more.

According to the present invention, wire breakage can be prevented by applying a compressive residual stress RS of 10 kg / mm ² or more in absolute value to the surface layer, and the circumferential ten-point average roughness PRz is 0.3 μm or more. A saw wire capable of improving the slicing efficiency by providing the unevenness is provided.

  Hereinafter, an embodiment of a saw wire according to the present invention will be described.

1) Circumference 10-point average roughness PRz
The ten-point average roughness Rz is defined as follows, and the measurement follows the method specified in JIS-B7451 (issued in 1997).

  The “ten-point average roughness Rz” is the maximum to the fifth measured in the direction of the vertical magnification from the line that is parallel to the average line and does not cross the cross-section curve, in the portion extracted from the cross-section curve by the reference length. The difference between the average value of the altitude at the top of the mountain and the average value of the altitude at the bottom from the deepest to the fifth is expressed in micrometers (μm).

  In the present invention, the circumferential ten-point average roughness PRz measured along the circumference of the cross section perpendicular to the length of the saw wire is 0.3 μm or more.

  The circumferential ten-point average roughness PRz is defined as follows.

  About arbitrary different area | regions of n places on the same cross section of a saw wire, the 10-point average roughness Rz in the circumferential direction reference length W is each measured with the surface roughness measuring machine using a white light measuring method. The average value of the measured values of the obtained n (n is an integer of 2 or more) 10-point average roughness Rz is defined as the circumferential 10-point average roughness PRz.

Here, the "circumferential direction reference length W" as used herein, measured the width angle of the region measuring light beam diameter W _B due to the surface roughness tester illustrated in FIG. 1 is irradiated θ is 10 ° It shall be the length of the arc on the outer surface of the wire. The circumferential reference length W is given by the following equation (1).

W = (θ / 360 °) × πd (1)
However, the symbol θ indicates the measurement width angle, and the symbol d (μm) indicates the nominal diameter (designed diameter) of the wire. The width measured angle theta, as shown in Figure 1, corresponds to that shown the beam diameter W _B at an angle with respect to the center point O of the wire, as specified in 10 °. Here, the center point O corresponds to the center point of a circle whose diameter is the nominal diameter.

  Each measurement interval of the ten-point average roughness Rz can be defined as follows. Hereinafter, a case where the number of measured ten-point average roughness Rz for regions having different orientations is four times per cross section (n = 4) will be described, but the number of measured ten-point average roughness Rz is 1 It may be 2 or 3 times per cross section, or 5 times or more.

In the wire cross-section shown in FIG. 1, the optical axis of irradiation light in the measurement of ten-point average roughness Rz _e region E, the light of the irradiation light in the measurement of ten-point average roughness Rz _f region F The angle β formed with the axis is referred to as a measurement pitch angle β in this specification. The measurement pitch angle β is preferably an angle given by the following equation (2). The measurement pitch interval between the ten-point average roughness Rz _f of the region _F and the ten-point average roughness Rz _g of the region G, and the ten-point average roughness Rz _g of the region _G and the ten-point average roughness Rz _h of the region H It is preferable that the measurement pitch interval be the same.

β = 360 ° / n (2)
That is, in the example shown in FIG. 1, since the number of measurement points n is four, the measurement pitch angle β is 90 °. The number n of measurement points is preferably 4 or more.

  If the circumferential ten-point average roughness PRz is less than 0.3 μm, the size of the dent will be too small, or the absolute amount of the dent will be insufficient, so it will not be possible to draw a sufficient amount of abrasive, and the slicing time Can not be shortened. For this reason, the lower limit of the circumferential ten-point average roughness PRz is defined as 0.3 μm. A more preferable lower limit value of the circumferential ten-point average roughness PRz is 0.5 μm. On the other hand, in order to prevent a decrease in wire strength and a decrease in cut surface accuracy of the workpiece, the upper limit value of the circumferential ten-point average roughness PRz is set to 0.8 μm.

  The circumferential ten-point average roughness PRz can be controlled by forming a plurality of fine grooves on the wire surface using a leveling roll (also called a straightening roll, a straightening roll, a straightening roll). . The leveling roll generally has a finished state (smoothness) of the roll surface and is finished by polishing the surface. By variously changing the finished state, the desired circumferential ten-point average roughness PRz. Can be obtained.

2) Surface layer residual stress RS
The surface layer portion residual stress RS from the outer surface of the saw wire to a depth of 10 μm is the compression side, and the absolute value of the residual stress RS is 10 kg / mm ² or more.

  Here, in this specification, “to the depth of 10 μm from the outer surface of the saw wire” means that, in the case of a non-plated wire, the depth from the outer surface in the transverse section of the saw wire after drawing is up to 10 μm (10 μm In the case of a plated wire, it means a surface layer part having a depth including the plating thickness from the outer surface of the plating up to 10 μm (including 10 μm).

If there are irregularities on the surface of the wire, cracks are likely to occur with the concave portion as the starting point, which may develop and break the wire. Therefore, in the present invention, the surface layer residual stress RS is set to the compression side in order to suppress the occurrence and progress of cracks in the saw wire and prevent disconnection. As indicated by the characteristic line Q in FIG. 2, the compressive stress RS remaining on the surface layer of the saw wire increases from the wire surface toward the center, and if the absolute value is 10 kg / mm ² or more, cracks Generation and progress can be sufficiently reduced, and wire breakage in a short time can be prevented. More preferably, the surface layer residual stress RS from the outer surface of the saw wire to a depth of 5 μm is the compression side, and the absolute value of the stress is 40 kg / mm ² or more. In order to prevent the strain from becoming excessive, it is preferable that the surface layer residual stress RS from the outer surface to a depth of 10 μm is the compression side, and the absolute value of the stress is 100 kg / mm ² or less.

  Examples of the saw wire according to the present invention include a steel wire having the characteristics described below.

(I) Carbon content: 0.8 to 1.03 mass%
If the carbon content is less than 0.8% by mass, the tensile strength of the wire may be insufficient. On the other hand, if the amount of carbon exceeds 1.03% by mass, the wire becomes brittle and breaks easily. In addition, you may contain a trace amount chromium about 0.2 mass%.

(Ii) Nominal diameter (designed wire diameter); 0.06 to 0.3 mm
If the nominal diameter is less than 0.06 mm, the strength may be insufficient. On the other hand, if the nominal diameter exceeds 0.3 mm, the cutting loss of the workpiece becomes excessive.

(Iii) Deviation difference: 0.5 to 10 μm
It is the limit of manufacturing accuracy that the difference in diameter is 0.5 μm. On the other hand, if the deviation in diameter exceeds 10 μm, the accuracy of the cut surface may be lowered.

(Iv) Plating (Zinc plating)
Plating thickness: 0.1-10 μm
If the plating thickness is less than 0.1 μm, peeling of the plating is likely to occur. On the other hand, if the plating thickness exceeds 10 μm, the strand diameter (bare wire diameter) becomes small, so that the desired strength is obtained. There is a risk that it will not be obtained. The covering plating can be brass plating or nickel plating in addition to zinc plating.

(V) Tensile strength: 2800-4800 N / mm ²
In order to avoid disconnection, the tensile strength is preferably within the above range.

  The saw wire as described above can be manufactured, for example, as described below, but the lubricant, the die schedule, the type and shape of the die, and the surface treatment method are not limited to these, and may be changed as appropriate. Is possible.

  In an emulsion type wet lubricant, the final wire drawing material is obtained by passing it through about 20 dies having a surface area reduction per pass set to 12 to 18% in accordance with the initial diameter and finish diameter of the wire. At this time, the bearing length of the die is 20 to 50% of the diameter, and the reduction angle is 6 to 12 °.

  Subsequently, by subjecting the obtained final wire drawing material to surface treatment with a leveling roll, the circumferential ten-point average roughness PRz and the surface layer residual stress RS are controlled, and a saw wire in which these are within the above ranges is produced. Can do. For such surface treatment, for example, a leveling roll of 6 to 16 mmφ having a 10-point average roughness Rz in the range of 0.1 μm to 0.5 μm can be used. Can be arranged. As the material of the leveling roll, die steel, high speed steel, cemented carbide, cemented carbide, etc. are preferable because they have excellent hardness and can maintain a stable surface roughness of the saw wire.

  Next, the case where unevenness is provided on the outer surface of the wire by variously changing the arrangement of the leveling rolls will be described with reference to FIGS.

  As shown in FIG. 3, in the leveling roll unit 1, a plurality of leveling rolls 2 are alternately arranged at almost equal pitch intervals across the pass line, and the wires 3 are fed between these staggered rolls 2. By doing so, shallow groove-like irregularities are formed on the outer surface while the wire 3 meanders and passes in a zigzag manner.

  Further, as shown in FIG. 4, in the leveling roll unit 1A, a plurality of leveling rolls 2A are arranged so as to face each other at substantially equal pitch intervals across the pass line, and the roll gap intervals are made equal to each other. By feeding the wire 3 between the arrangement rolls 2A, a shallow groove-like unevenness different from the above case is formed on the outer surface of the wire 3 while it is pulled or compressed in the longitudinal direction. The

  Further, as shown in FIG. 5, in the leveling roll unit 1B, two pairs of inclined leveling rolls 2B are disposed on the upstream side across the pass line, and the other two pairs of leveling rolls 2B are disposed on the downstream side. It may be arranged. Two pairs of inclined leveling rolls 2B on the upstream side are each inclined 30 ° to 60 ° in a direction in which the roll axes are aligned with respect to the pass line, and two pairs of leveling rolls 2B on the downstream side are inclined with respect to the pass line. The roll axis is inclined 30 ° to 60 ° in opposite directions. By feeding the wire 3 between these inclined rolls 2B, while the wire 3 passes while slipping in a different direction with respect to the roll surface, a shallow groove-like unevenness different from the above case is formed on the outer surface thereof. It is formed.

  In addition, the surface layer portion residual stress RS and the circumferential ten-point average roughness PRz are set to desired ranges by variously changing the number of leveling rolls, the roll arrangement interval, the roll gap interval, and the surface treatment of the roll surface. Can do.

  In addition, a final wire drawing material can be obtained using a double die skin pass. The double die skin pass realizes the surface reduction rate per pass of the finished die as the total surface reduction rate of the two dies, and allows the wire to pass through the die without continuous winding. It is a method of line. Generally, by reducing the area reduction rate of the second die (final die), only the vicinity of the surface of the strand can be processed, and the residual tensile stress in the vicinity of the surface can be changed to the residual compressive stress. . The surface layer residual stress can be controlled by adjusting the area reduction ratio of the first die and the second die. Even when the double die skin pass is used, the final surface layer residual stress RS and the circumferential ten-point average roughness PRz are within the above ranges by performing the above-described surface treatment on the obtained final wire drawing material. It is possible to adjust.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

[Example]
Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings.

Example 1
A piano wire (JIS standard number: G3502, carbon content: 0.82% by mass) drawn to a predetermined wire diameter was prepared as a test material, and electrogalvanizing was performed on the test material under the following conditions. .

Composition of plating bath; Zinc sulfate Temperature of plating bath; 40 ° C
Plating adhesion amount: 3.0 g / kg (plating adhesion weight per kg of wire)
The obtained plated material having a predetermined wire diameter is drawn using a double die skin pass method, and surface treatment is performed using a roll unit for the final drawn wire obtained so that a large number of fine wires can be formed on the entire wire surface. A saw wire with a nominal diameter of 0.16 mm having a groove (groove width of 0.1 to 10 μm) was obtained. As the leveling roll, a roll having a roll surface with a 10-point average roughness of 0.3 μm and a diameter of 13 mm was used. Also, the leveling roll unit uses the above-described rolls arranged as described with reference to FIG. 3, and the number of leveling rolls is 19 in total, 9 on one side and on the other side. Ten pieces were arranged, and the roll arrangement interval was 18 mm.

The obtained saw wire had an average plating thickness of 0.2 μm and a deviation in diameter of 2 μm. The tensile strength was 3200 N / mm ² .

  The average plating thickness was measured as described below.

  Microscopic observation was performed on two arbitrary transverse sections of the obtained saw wire, and the plating thickness was measured at arbitrary four points in each field of view. The average value of these measurement results was taken as the average plating thickness.

  Moreover, the tensile strength was measured as described below using a tensile tester (manufacturer: Minebea Co., Ltd., model: TCM-1kNB).

  A sample cut to an appropriate length is subjected to a tensile test using a tensile tester, and the maximum observed force is divided by the original cross-sectional area (the cross-sectional area calculated by the diameter (or nominal diameter) of the sample before the test). Thus, the tensile strength was obtained. Measurement of tensile strength basically conformed to JIS-Z-2241. As measurement conditions, the measurement range was 20 kgf, and the test speed was 100 mm / min.

<Measurement of circumferential ten-point average roughness PRz>
The circumferential ten-point average roughness PRz of the obtained saw wire was measured as described below.

As a surface roughness measuring instrument using a white light measurement method, a NEW VIEW 100, a three-dimensional surface structure analyzer manufactured by ZYGO (Zygo), is used, and a measurement pitch angle β is set to 90 °, and four different locations (ie, and n = 4) of the region E, F, G, ten-point average roughness Rz _e for H, Rz _f, Rz _g, the Rz _h was measured. In each area E-H, by irradiating a laser beam of the beam on the wire surface diameter W _B, a circumferential reference length W in [(10/360) × πd] ( μm), i.e., measuring the width angle θ Was set to 10 °.

The resulting ten-point average roughness _{Rz e, Rz f, Rz g} , Table 1 shows the average value of Rz _h as the average roughness PRz circumferential ten-point.

<Measurement of surface layer residual stress RS>
Surface layer residual stress RS is a residual stress measuring machine (manufacturer: MacScience Corporation, model: (main body) M18XHF22-SRA, (X-ray generator) MXP18, (micro diffraction device) MDS-III / PSPC-IV) Was measured as described below.

A sample obtained by cutting the obtained saw wire into an appropriate length is attached to a sample stage, and in order to measure the axial stress of the wire, the sample is irradiated with X-rays focused by a collimator in parallel to the axial direction of the wire, The peak position θ of a specific diffraction surface was measured. At this time, the angle between the normal of the diffractive surface and the normal of the sample surface is ψ, and the peak position of the diffractive surface is measured at several ψ where sin ² ψ is in the range of 0.1 to 0.5. did. Using the obtained θ and ψ, a 2θ-sin ² ψ diagram was created, and the residual stress at a position of about 10 μm was determined in the range where the depth from the surface did not exceed 10 μm from the gradient. As measurement conditions, the diffractive surface was α-Fe (220), the target was Co, the tube voltage was 30 kV, the Young's modulus was 21000 kgf / mm ² , the Poisson's ratio was 0.28, and the parallel tilt method was used. The results are shown in Table 1.

  Note that the method described in Japanese Patent No. 2920439 can also be used to measure the residual stress of the wire surface layer.

  Using a multi-wire saw (model number: HWS-330) manufactured by Tosuna Machinery Co., Ltd. as a saw machine of the same type as that described in Japanese Patent No. 3345018 (Patent Document 1), one workpiece described below with the above saw wire Slicing was performed under the conditions described to obtain a desired silicon wafer.

<Work>
Material: Silicon single crystal ingot Size: Diameter 200mm x Length 150mm
<Slicing conditions>
Wire traveling speed: 900 m / min Wire reciprocating cycle; 1 cycle / min Processing fluid: Water-soluble slurry for CMP of particles # 1000 Wire tension: 25 N
(Examples 2 and 3)
A saw wire was obtained in the same manner as in Example 1 except that the area reduction rate of the die, the number of leveling rolls, the roll arrangement interval, the roll gap interval, and the surface smoothness of the roll surface were changed. Table 1 shows the nominal diameter, average plating thickness, tensile strength, circumferential ten-point average roughness PRz, and surface layer residual stress RS of the obtained saw wire. Using this saw wire, the workpiece was sliced in the same manner as in Example 1.

Example 4
Instead of electrogalvanizing, the test material is galvanized using conventional methods, and the number of leveling rolls, roll arrangement interval, roll gap interval, and surface smoothness of the roll surface are changed. A saw wire was obtained in the same manner as in Example 1. Table 1 shows the nominal diameter, average plating thickness, tensile strength, circumferential ten-point average roughness PRz, and surface layer residual stress RS of the obtained saw wire. Using this saw wire, the workpiece was sliced in the same manner as in Example 1.

(Comparative Examples 1 and 2)
A saw wire was obtained in the same manner as in Example 1 except that the area reduction rate of the die, the number of leveling rolls, the roll arrangement interval, the roll gap interval, and the surface smoothness of the roll surface were changed. Table 1 shows the nominal diameter, average plating thickness, tensile strength, circumferential ten-point average roughness PRz, and surface layer residual stress RS of the obtained saw wire. Using this saw wire, the workpiece was sliced in the same manner as in Example 1.

In the saw wire of Comparative Example 2, although the surface layer residual stress RS was on the compression side, the absolute value thereof was less than 10 kg / mm ² , and thus breakage occurred during slicing.

In contrast, the saw wires of Examples 1 to 4 and Comparative Example 1 were able to process the workpiece without disconnection during slicing. The slice time per workpiece obtained in Examples 1 to 4 and Comparative Example 1 is shown in Table 1 below.

  As apparent from Table 1, the saw wires of Examples 1 to 4 having the surface layer residual stress RS and the circumferential ten-point average roughness PRz within the scope of the present invention had a short slice time and excellent slice efficiency.

  On the other hand, the saw wire of Comparative Example 1 in which the circumferential ten-point average roughness PRz deviated from the scope of the present invention was longer in slice time and inferior in slice efficiency than the saw wires in Examples 1 to 4.

  In particular, compared to the saw wire of Example 2, the saw wire of Comparative Example 1 had a longer nominal time and a longer surface area than Example 2, despite having a larger nominal diameter and a larger surface area. From this, it has been confirmed that according to the present invention, excellent slice efficiency can be obtained without causing disconnection even when the wire diameter is reduced.

The cross-sectional schematic diagram of a saw wire for demonstrating the circumference 10-point average roughness PRz. The characteristic diagram for demonstrating the residual stress in the surface layer vicinity of a saw wire. The schematic block diagram which shows the leveling roll unit used for manufacture of the saw wire of this invention seeing from a roll axial direction. The schematic block diagram which shows the other leveling roll unit used for manufacture of the saw wire of this invention seeing from a roll axial direction. The schematic block diagram which shows the other leveling roll unit used for manufacture of the saw wire of this invention seeing from a roll axis orthogonal direction.

Explanation of symbols

  1, 1A, 1B ... leveling roll unit, 2, 2A, 2B ... leveling roll, 3 ... saw wire.

Claims (2)

The surface layer residual stress RS from the outer surface to a depth of 10 μm is on the compression side, the absolute value of the residual stress RS is 10 kg / mm ² or more, and
A saw wire characterized in that a circumferential ten-point average roughness PRz measured along the circumference of a transverse section is 0.3 μm or more.   The saw wire according to claim 1, wherein the circumferential ten-point average roughness PRz is 0.8 μm or less.

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