JP6000730B2 - Core wire for fixed abrasive saw wire - Google Patents

Description

  The present invention relates to a core wire for a fixed abrasive saw wire. More specifically, the present invention relates to a core wire that is a core material of a saw wire that is used in a state in which abrasive grains are fixed to the surface, before the abrasive fixing process.

  As shown in FIG. 4, a saw wire 51 is used to slice a semiconductor ingot 52 such as silicon. One saw wire 51 is stretched over a plurality of rollers 53. The saw wire 51 is shifted a little at a predetermined pitch in the axial direction of the roller 53 and stretched over and over. The wire 51 travels by the rotation of the roller 53. The work (semiconductor ingot) 52 is cut by being pressed by the traveling wire 51. By this cutting, a large number of wafers are obtained.

  As the saw wire 51, conventionally, a loose abrasive saw wire and a fixed abrasive saw wire are used. The free abrasive grain type saw wire is a saw wire made of a steel wire, and cuts a workpiece while spraying a slurry containing abrasive grains. The fixed abrasive saw wire is obtained by fixing abrasive grains on the surface of a wire made of steel wire. A fixed abrasive saw wire cuts a workpiece directly without the need to spray abrasive grains. The fixed abrasive saw wire is superior to the free abrasive saw wire in terms of cutting speed, cutting accuracy and the like. Recently, fixed abrasive saw wires are becoming mainstream in place of loose abrasive saw wires.

  As the fixed abrasive saw wire, those disclosed in Japanese Patent Application Laid-Open Nos. 2004-261889 and 2007-152486 are known. As shown in FIG. 5, the fixed abrasive saw wire 54 disclosed in these publications is provided with a base plating (first plating) 56 on a metal wire 55 such as a piano wire, and then an abrasive fixed plating. (Second plating) 57 is applied. The metal wire in which the base plating 56 is applied and the abrasive grain fixed plating 57 is not yet applied is called a core wire. Examples of the metal for the base plating 56 include nickel, copper, lead, and brass. The abrasive grain fixed plating 57 is a metal plating containing the abrasive grains 58. As the abrasive fixed plating 57, nickel is generally used. As shown in the drawing, after the abrasive grain fixed plating 57 is applied, a third plating 59 for fixing the abrasive grains 58 may be further applied. As the third plating 59, nickel is generally used. In this case, in general, the first plating 57 is the temporary abrasive plating and the second plating 59 is the fixed abrasive plating.

  Generally, the ductility of a steel wire used for a core wire decreases as the tensile strength increases. The saw wire is stretched over the roller with high tension, and the workpiece is pressed while traveling at high speed. A strong twisting force is applied to the saw wire. As a result, the abrasive grains easily fall off due to peeling of the plating on the saw wire. If the plating is peeled off, the cross-sectional area of the portion of the saw wire is reduced, so that the torsional rigidity is lowered and there is a possibility of being cut off. Further, due to twisting, there is a risk that an axial vertical crack called delamination occurs in the saw wire, and it is easy to break.

JP 2004-261889 A JP 2007-152486 A

  The present invention has been made in view of the present situation, and an object of the present invention is to provide a core wire for a fixed abrasive saw wire that can prevent disconnection and plating peeling due to twisting of the saw wire during workpiece cutting. .

The core wire according to the present invention is a core wire for a fixed abrasive saw wire, in which a base plating layer is laminated on the surface of a steel wire,
The base plating layer is formed by plating containing brass,
In the base plating layer, the surface layer portion on the outer surface side is Zn-rich, the bottom layer portion on the steel wire side is Cu-rich, and the middle layer portion sandwiched between the surface layer portion and the bottom layer portion is α brass and β brass. It is comprised from at least any one of these.

  Preferably, Cu is less than 50% by weight in the surface layer part, Cu is 40% or more and 85% or less in the middle layer part, and Cu is 60% or more in weight ratio in the bottom layer part.

  Preferably, the composition of the base plating layer is such that Cu is 30% to 80% by weight and the balance is Zn.

  Preferably, the thickness of the base plating layer is 0.01 μm or more and 2.0 μm or less.

  Preferably, the thickness of the surface layer portion is 1% or more and 20% or less of the thickness of the base plating layer.

  Preferably, the twist value of the core wire is 30 / 100d or more.

  Preferably, the cross-sectional shape of the core wire is circular, and the deviation in diameter, which is the difference between the maximum value and the minimum value of the diameter, is 2.0 μm or less.

  Preferably, the steel wire has a weight ratio of C of 0.60% to 1.20%, Si of 0.02% to 2.0%, and Mn of 0.10% to 1.0%. , Cr is 0.5% or less, and the balance consists of Fe and impurities inevitably mixed.

  According to the present invention, plating peeling due to twisting of a fixed abrasive saw wire can be prevented, and the twist value of the saw wire can be improved.

FIG. 1A is a cross-sectional view of a fixed abrasive saw wire using a core wire according to an embodiment of the present invention, and FIG. 1B is a vertical cross-sectional view of the saw wire. FIG. 2A is a longitudinal sectional view showing a core wire constituting the saw wire of FIG. 1, and FIG. 2B is a first plating layer (underlayer) which is a II portion of the core wire of FIG. It is a graph which shows notionally an example of distribution of Cu composition ratio of a plating layer. Fig.3 (a) is a front view which shows the helical wrinkle of the core wire produced with the wire drawing, and FIG.3 (b) is the top view. FIG. 4 is a perspective view showing a saw wire stretched between a plurality of rollers together with a work to be cut. FIG. 5 is a cross-sectional view showing an example of a conventional saw wire.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  A saw wire 10 shown in FIG. 1 has a core wire 1 therein. The core wire 1 is obtained by applying a base plating (reference numeral 3 in the figure) as a first plating layer to a steel wire 2. The saw wire 10 has an abrasive grain temporary plating layer (second plating layer) 5 for temporarily attaching abrasive grains 4 to the outer peripheral surface of the core wire 1 and an abrasive fixed plating layer (third plating) for fixing the abrasive grains 4. Layer) 6. The base plating layer 3 contains brass. In general, both the abrasive temporary bonding plating layer 5 and the abrasive fixed plating layer 6 are made of nickel. The material of the abrasive grain temporary plating layer 5 and the abrasive grain fixed plating layer 6 is not particularly limited to nickel. The abrasive grains 4 protrude outward from the surface of the abrasive fixed plating layer 6. As the abrasive grains 4, silicon carbide abrasive grains, diamond abrasive grains and the like are generally used, but diamond abrasive grains are employed in this embodiment.

  The saw wire 10 is completed through the following manufacturing steps, for example. First, there is a dry wire drawing process for the steel material. Subsequently, the core wire 1 is completed through a heat treatment (patenting) process of the steel wire 2, each process of copper plating and galvanization (reference numeral 3 in the drawing), a diffusion heat treatment process, and a wet wire drawing process. The core wire 1 is subjected to a nickel plating process (reference numeral 5 in the figure) for temporarily attaching the abrasive grains 4 and a nickel plating process (reference numeral 6 in the figure) for fixing the abrasive grains 4. The saw wire 10 is completed. The manufacturing process described here is an example.

  As the steel wire 2, a high carbon steel wire, an austenitic stainless steel wire, a ferritic stainless steel wire, a martensitic stainless steel wire or the like is used. As the steel wire 2 in the present embodiment, a high carbon steel wire is used. This high carbon steel wire has a weight ratio of C from 0.60% to 1.20%, Si from 0.02% to 2.0%, Mn from 0.10% to 1.0%, Containing 0.5% or less of Cr, the balance is occupied by Fe and impurities inevitably mixed. With this composition, the steel wire 2 is high in strength and inexpensive, and is optimal as a core wire. Further, the depth of the surface flaw of the steel wire 2 is desirably suppressed to 5.0 μm or less, and preferably 1.0 μm or less.

  By limiting C to the above range, it is possible to increase the tensile strength of the steel wire 2 after heat treatment and to improve the hardening rate by wire drawing. As a result, an increase in the tensile strength of the steel wire 2 can be expected due to a small wire drawing strain.

  Si strengthens the ferrite in the pearlite to improve the tensile strength of the steel material and has a deoxidizing action. If the Si content is less than 0.02%, these effects may not be sufficiently obtained. On the other hand, if the Si content exceeds 2.0%, the steel wire 2 becomes too strong and the ductility decreases. As a result, there is a possibility that the wire drawing processability is lowered.

  Mn is effective for deoxidation, desulfurization and the like. Moreover, according to Mn, the hardenability of the steel wire 2 is improved, and the effect of improving the tensile strength after the patenting treatment is obtained. If the Mn content is less than 0.10%, these effects may not be sufficiently obtained. On the other hand, if the Mn content exceeds 1.0%, a supercooled structure accompanying center segregation is generated, and the drawability of the steel wire 2 may be reduced.

  Cr contributes to refinement of the lamellar spacing (cementite spacing in pearlite) after the patenting process. Thereby, while the tensile strength of the steel wire 2 after a patenting process improves, a wire drawing work hardening rate improves. If the Cr content exceeds 0.5%, the processing time for completing the pearlite transformation becomes longer in patenting, which may reduce productivity.

  An oxide film (not shown) is formed on the surface of the steel wire 2 by a heat treatment immediately before the base plating 3 treatment. The oxide film will be interposed between the steel wire 2 and the base plating layer 3 in the future. The amount of the oxide film is preferably smaller from the viewpoint of improving the adhesion of the base plating layer 3 to the surface of the steel wire 2. The thickness of the oxide film is preferably 0.5 μm or less from the surface of the steel wire 2.

  As shown in FIG. 2 (a), the steel wire 2 is subjected to the above-described base plating 3. As the metal of the base plating 3, a metal that is sufficiently softer than the steel wire 2 and excellent in ductility is selected so as to be compatible with the next wet drawing process. Furthermore, the metal excellent in the adhesiveness to the surface of the steel wire 2 and the adhesiveness to the metal of the abrasive grain temporary plating 5 in a later saw wire manufacturing process is selected. In this embodiment, Cu and Zn are employed as the base plating material. The constituent metal of the underlying plating layer 3 is preferably such that Cu is 30% to 80% by weight and the remainder is Zn in the entire layer. If Cu is less than 30%, it may be difficult to obtain a structure necessary for wire drawing of the core wire 1. On the other hand, when Cu exceeds 80%, Zn becomes relatively small. For this reason, the corrosion resistance of the underlying plating layer 3 is lowered, and it is difficult to form irregularities on the surface of the underlying plating layer 3, so that the adhesion strength of Ni plating in the subsequent process may be lowered.

  However, even if the Cu and Zn of the base plating layer 3 are configured as described above, they are not brass having a uniform composition. The base plating layer 3 has a composition ratio of Cu and Zn changed from the bottom layer portion 7 through the middle layer portion 8 to the surface layer portion 9. That is, Cu and Zn have a desired distribution over the entire underlying plating layer 3 by controlling the respective plating amounts and diffusion heat treatment.

  The bottom layer portion 7 is a Cu-rich layer. The Cu-rich layer has flexibility and good adhesion to the steel wire 2. The core wire 1 provided with such a base plating layer 3 has a high twist value (numerical value indicating twist resistance) described later. Even if the saw wire 10 formed from the core wire 1 is twisted while cutting the workpiece, Cu is difficult to separate from the steel wire 2. Further, since Cu is highly conductive, a Zn plating layer applied on the Cu plating tends to adhere uniformly. By controlling the diffusion heat treatment after Cu plating and Zn plating, Cu can also be present on the surface of the surface layer portion 9. Due to the Cu on the surface, the Ni plating layer in the subsequent process is likely to adhere uniformly.

  The middle layer portion 8 is made of at least one of α brass and β brass. Since α brass or β brass is soft, the drawability of the core wire 1 is improved. Since α brass is particularly soft, the wire drawing property is further improved.

  The surface layer portion 9 is a Zn rich layer. The Zn-rich surface layer portion 9 of the core wire 1 tends to have a rough surface and a large surface area in the wet wire drawing process. As a result, when Ni plating as the abrasive temporary plating 5 is performed in the subsequent process for manufacturing the saw wire 10 from the core wire 1 having a high twist value, adhesion of Ni to the underlying plating layer 3 due to the anchor effect. Strength increases. Thereby, the twist value of the saw wire 10 is further improved. Thus, when the twist value of the core wire to be used is high, it is known that the twist value of the fixed abrasive saw wire in which fixed abrasive plating or abrasive grains are attached thereto is also increased.

  It is preferable that each portion of the bottom layer portion 7, the middle layer portion 8 and the surface layer portion 9 of the base plating layer 3 described above has the following Cu composition ratio. The weight ratio of Cu in the bottom layer portion 7 is 60% or more (Cu rich), and the balance is Zn. The weight ratio of Cu in the middle layer portion 8 is not less than 40% and not more than 85%, and the balance is Zn. The weight ratio of Cu in the surface layer portion 9 is less than 50%, and the balance is Zn (Zn rich). The weight ratio of Cu may be 100% at the bottom surface of the bottom layer portion 7 and the vicinity thereof. The weight ratio of Cu may be 0% on the surface of the surface layer portion 9 and the vicinity thereof. However, it is preferable that Cu is also present on the surface of the surface layer portion 9. This is because, as described above, if Cu is also present on the surface, a Ni plating layer in a subsequent process is likely to adhere uniformly. FIG. 2B conceptually shows an example of the distribution of the composition ratio of Cu and Zn in the base plating layer 3. Each composition of the bottom layer part 7, the middle layer part 8, and the surface layer part 9 in the base plating layer 3 can be measured by, for example, an Auger electron spectroscopy analyzer.

  The thickness of the base plating layer 3 is preferably 0.01 μm or more and 2.0 μm or less. In this thickness range, appropriate adhesion, wire drawing and electrical conductivity can be secured with the steel wire 2. If it is less than 0.01 μm, the drawability may be lowered. If it exceeds 2.0 μm, the plating layer 3 becomes thicker than necessary, which may increase the cost. Of the thickness of the underlying plating layer 3, the proportion of the thickness of the surface layer portion 9 is preferably 1% or more and 20% or less. When this proportion is less than 1%, the anchor effect is hardly obtained, and when it exceeds 20%, the proportion of the middle layer portion rich in stretchability is relatively reduced. From this point of view, the ratio is more preferably 5% or more and 20% or less. The proportion of the thickness of the bottom layer portion 7 in the thickness of the base plating layer 3 is preferably 1% or more and 30% or less. Furthermore, the proportion of the thickness of the middle layer portion 8 in the thickness of the base plating layer 3 is preferably 50% or more and 98% or less.

  The cross-sectional shape of the core wire 1 on which the base plating layer 3 is formed is substantially circular. The diameter of this cross section is preferably 0.05 mm or more and 0.25 mm or less. This is a range of a wire diameter necessary for forming the saw wire 10. The difference in diameter of the circular cross section is preferably 2.0 μm or less. This is because deterioration of the properties of the cut surface of the workpiece by the saw wire 10 can be prevented. The difference in diameter is the difference between the maximum value and the minimum value of the cross-sectional diameter. The tensile strength of the core wire 1 is preferably set to 3500 MPa or more from the performance requirement as the saw wire 10.

  In the core wire 1 described above, the characteristic adhesion force of the underlying plating layer 3 to the steel wire 2 is high. By this base plating layer 3, the adhesion force of the Ni plating layer applied in the subsequent process is also enhanced. Thereby, peeling of the abrasive grain temporary plating layer 5 and the abrasive fixed plating layer 6 and dropping of the abrasive grains 4 during cutting of the workpiece are prevented. Furthermore, the twist value of the core wire 1 is improved. The twist value represents the strength of the core wire 1 against twisting. An example of the twist value is represented by the number of twists until a test piece having a length 100 times the wire diameter d of the core wire 1 is broken (twisted) by applying a tension and a twisting force. The twist value of the core wire 1 is 30 / 100d or more when a twisting force with a twisting speed of 50 to 100 rpm is applied in a state where a tension of 0.5 to 1.0 N is applied. Is preferred. This indicates that the test piece having a length 100 times the wire diameter d is broken by twisting 30 times or more.

  The steel wire 2 to which the base plating 3 has been applied is then subjected to wet wire drawing to become the core wire 1. Along with this wet wire drawing, the core wire 1 is wrinkled in a spiral shape (coil shape) due to plastic deformation. This coiled kite is a three-dimensional kite as follows.

  As shown in FIG. 3, when the sample 11 having a length of about 1 circle is cut from the coiled core wire 1, the sample 11 has a circular shape (FIG. 3B), It is also deformed in the direction of the central axis CL (FIG. 3A). In the drawing, the diameter (free coil diameter) of this circle is represented by D, and the displacement in the central axis CL direction is represented by H. The displacement H in the central axis CL direction is a distance between the one end 11a and the other end 11b of the sample 11 in the central axis CL direction. This displacement H is also called “bounce”. The starting points and ending points of the dimensions D and H are all the center lines of the core wire 1 itself. When the free coil diameter D of the core wire 1 is small and when the splash H is large, Ni plating in the next process may be difficult to adhere uniformly. Further, the saw wire 10 constituted by the core wire 1 having a small free coil diameter D and the saw wire 10 constituted by the core wire 1 having a large splash H may be swelled. That is, when the saw wire 10 is stretched over the roller 53 (FIG. 4), the saw wire 10 is wavy. There is a concern that the swell of the saw wire 10 may deteriorate the properties of the cut surface of the workpiece.

  From the above viewpoint, it is desirable that the free coil diameter D is large and the splash H is small. Specifically, the free coil diameter D of the completed core wire 1 is preferably 150 mm or more, and more preferably 300 mm or more. The splash H is preferably 25 mm or less. In order to obtain the core wire 1, a die having a large approach angle may be employed as the final die in the final wet drawing process. By this method, the processing depth in the central axis direction of the core wire 1 is reduced, and a core wire having a stable ridge in the longitudinal direction can be obtained. In the saw wire 10 manufactured from the core wire 1, the undulation at the time of workpiece cutting is sufficiently suppressed.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Example 1-4]
For each of Examples 1 to 4, 10 core wires shown in FIG. 2 were prepared. The diameters of these core wires are all 0.18 mm. The thickness of the base plating layer is 0.2 μm for all Examples 1 to 4. As the surface layer portion of the underlying plating layer, the Cu content was measured using an Auger electron spectroscopic analyzer in the range from the surface to a depth of 0.02 μm, and the content ratio was obtained. As the middle layer portion of the base plating layer, the Cu content was measured in the same manner as described above for the depth from the surface of 0.045 μm to 0.155 μm, and the content ratio was obtained. As the bottom layer portion of the base plating layer, the Cu content was measured in the same manner as described above for the depth from the surface of 0.16 μm to 0.20 μm, and the content ratio was obtained. The above measurement results are shown in Table 1. In addition, a structural analysis was performed on the middle layer. As a result, Examples 1 to 4 were α brass and β brass. Twist values were measured for each core wire of Examples 1 to 4 above. The method for measuring the twist value is as described above. That is, a twisting force with a twisting speed of 100 rpm is applied to a test piece 100 times as long as the wire diameter d while a 0.7 N tension is applied. Then, the number of twists until the test piece breaks is measured as a twist value and recorded. The twist values for each example are shown in Table 1.

[Comparative Example 1-3]
For each of the comparative examples 1 to 3, ten core wires each having a brass wire plated on the surface of the steel wire were prepared. The diameters of these core wires are all 0.18 mm. The thickness of the base plating layer is 0.2 μm for all Comparative Examples 1 to 3. As the surface layer portion of the base plating layer, the Cu content was measured in the range from the surface to a depth of 0.02 μm, and the content ratio was obtained. As the middle layer portion of the base plating layer, the Cu content was measured in the range from 0.045 μm to 0.155 μm in depth from the surface, and the content ratio was obtained. As the bottom layer portion of the base plating layer, the Cu content was measured in the range from 0.16 μm to 0.20 μm in depth from the surface, and the content ratio was obtained. This measurement method is the same as in Examples 1 to 4. The above measurement results are shown in Table 1. In addition, a structural analysis was performed on the middle layer. As a result, each of Comparative Examples 1 and 2 was α brass and β brass. Comparative Example 3 was a γ layer. Twist values were measured for each core wire of Comparative Examples 1 and 2 above. The method for measuring the twist value is the same as in Examples 1 to 4. Since the comparative example 3 includes many γ layers in the base plating layer, the hardness is high. In the core wire of Comparative Example 3, breakage occurred frequently during the wet drawing process, and the construction of the wet drawing itself became difficult. As a result, it was impossible to measure the twist value for Comparative Example 3.

[Evaluation]
As a characteristic evaluation of the core wire in each example, the measurement results of the twist value are shown in Table 1. In Examples 1 to 4, in which the surface layer portion of the base plating layer is Zn-rich, the bottom layer portion is Cu-rich, and the middle layer portion is α brass and β brass, the twist value is 31 or more. On the other hand, in Comparative Examples 1 and 2 where the surface layer portion is not Zn-rich, the twist value is 22 or less. In Comparative Example 2 where the surface layer portion was not Zn-rich and the bottom layer portion was not Cu-rich, many disconnections were observed. In Comparative Example 3 in which the middle layer portion is a γ layer, it was impossible to measure the twist value. From this evaluation result, the superiority of the present invention is clear.

  The core wire according to the present invention is suitable for a fixed abrasive saw wire for satisfactorily cutting silicon ingots, artificial crystals, cemented carbides, ceramics and the like.

DESCRIPTION OF SYMBOLS 1 ... Core wire 2 ... Steel wire 3 ... Undercoat (layer)
4 ... Abrasive grains 5 ... Abrasive grain temporary plating (layer)
6 ... Abrasive fixed plating (layer)
7 ... Bottom layer portion 8 ... Middle layer portion 9 ... Surface layer portion 10 ... Saw wire 11 ... Sample (of core wire) CL ... Center line (of sample)

Claims (6)

A core wire for a fixed-abrasive saw wire in which a base plating layer is laminated on the surface of a steel wire,
The base plating layer is formed by plating containing brass,
In the base plating layer, the surface layer portion on the outer surface side is Zn-rich, the bottom layer portion on the steel wire side is Cu-rich, and the middle layer portion sandwiched between the surface layer portion and the bottom layer portion is α brass and β brass. At least Do from either Ri,
In the surface layer part, Cu is less than 50% by weight, in the middle layer part, Cu is 40% or more and 85% or less, and in the bottom layer part, Cu is 60% or more by weight. The balance is Zn,
The thickness of the surface layer portion is 1% or more and 20% or less of the thickness of the base plating layer,
The thickness of the middle layer portion is 50% or more and 98% or less of the thickness of the base plating layer,
The thickness of the bottom layer portion, Ru 30% der less than 1% and not more than a thickness of the primary plating layer core wire. 2. The core wire according to claim 1 , wherein the composition of the base plating layer is such that Cu is 30% to 80% by weight and the balance is Zn. The core wire according to claim 1 or 2 , wherein a thickness of the base plating layer is 0.01 µm or more and 2.0 µm or less. The core wire according to any one of claims 1 to 3 , wherein a twist value is 30 / 100d or more. The core wire according to any one of claims 1 to 4 , wherein a cross-sectional shape is a circle, and a deviation in diameter that is a difference between a maximum value and a minimum value of the diameter is 2.0 µm or less. In the steel wire, by weight ratio, C is 0.60% or more and 1.20% or less, Si is 0.02% or more and 2.0% or less, Mn is 0.10% or more and 1.0% or less, Cr The core wire according to any one of claims 1 to 5 , wherein the core wire is 0.5% or less, and the balance is Fe and impurities inevitably mixed.

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