A plane non-continuous shear thickening SiC polishing device

Abstract

The present application belongs to the technical field of hard and brittle material grinding and polishing, and particularly relates to a plane non-continuous shear thickening SiC grinding and polishing integrated polishing device, which comprises a workbench, a polishing disc assembly and a polishing head assembly. The polishing disc assembly comprises a polishing disc main body, a polishing disc driving mechanism, a constant pressure liquid supply mechanism and a polishing pad. A central liquid distribution cavity is arranged in the center of the polishing disc main body. A plurality of annular polishing liquid storage grooves are arranged on the upper surface of the polishing disc main body in a plurality of circles with the central liquid distribution cavity as the center. The present application solves the problems of long SiC substrate plane grinding and polishing process, high cost and rough surface. When the relative shear rate is high, shear thickening of the polishing liquid occurs, and the grinding process of the SiC substrate is realized. When the relative shear rate is low, the polishing process of the SiC substrate is realized, so that the SiC substrate with low damage is obtained, and a better substrate is provided for the subsequent CMP process.

Description

Technical Field

[0001] This invention belongs to the field of grinding and polishing technology for hard and brittle materials, and specifically relates to a planar discontinuous shear thickening SiC grinding and polishing integrated device. Background Technology

[0002] Silicon carbide (SiC) ceramics, as a representative of hard and brittle materials, possess unique physicochemical properties and have enormous application prospects in aerospace, optics, semiconductors, and biomedicine, attracting significant attention from scholars worldwide. However, the high hardness, high brittleness, and low fracture toughness of SiC ceramics make them prone to processing damage during machining, primarily in the form of cracks, breakage, and residual stress, thus reducing the reliability and service life of parts made from this material.

[0003] Shear-thickening polishing slurry is a non-Newtonian fluid containing a certain proportion of abrasive particles. A non-Newtonian fluid is a fluid that does not obey Newton's law of viscosity, meaning the relationship between its shear strain rate and viscosity is not linear. Typically, a non-Newtonian fluid is a heterogeneous suspension of nano- or micro-sized particles dispersed within a Newtonian fluid. The phenomenon that viscosity increases with increasing shear rate at high volume fractions is called the shear thickening effect. The continuous shear thickening effect is characterized by a slow increase in viscosity with increasing shear rate, while the discontinuous shear thickening effect is characterized by a sharp increase in viscosity with increasing shear rate. Under the discontinuous shear thickening effect, a non-Newtonian fluid reaching a certain shear rate can undergo a liquid-solid transition.

[0004] Due to the unique characteristics of discontinuous shear-thickened polishing slurries—namely, their extremely high initial viscosity—traditional drip-feeding methods are unsuitable. Currently, the mainstream polishing method for planar polishing using discontinuous shear-thickened slurries involves creating holes in the polishing pad, treating the slurry, and filling the holes to create a semi-solidified abrasive grinding disc. However, this mainstream polishing method suffers from problems such as a long process, high cost, and rough surface finish on SiC substrates. Summary of the Invention

[0005] To address the issues of long, costly, and rough surface finishes in the planar grinding and polishing process of SiC substrates, this invention provides a technical solution for an integrated planar discontinuous shear-thickening SiC grinding and polishing device. This solution involves designing and constructing a planar shear-thickening polishing experimental platform. At higher relative shear rates, the shear-thickening polishing slurry undergoes shear thickening, generating strong holding forces in the polymer particles within the polishing base slurry. This holds the micro-abrasive particles in the slurry, forming polymer particle-abrasive clusters, thus completing the grinding process on the SiC substrate. At lower relative shear rates, the abrasive particles and polymer particles in the polishing slurry revert to a free state, completing the polishing process on the SiC substrate. This results in a low-damage SiC substrate, providing a better substrate for subsequent CMP processes.

[0006] The technical solution provided by this invention is as follows:

[0007] A planar discontinuous shear thickening SiC polishing device includes a worktable and a polishing disc assembly and a polishing head assembly mounted on the worktable. The polishing disc assembly includes a polishing disc body, a polishing disc drive mechanism, a constant pressure liquid supply mechanism, and a polishing pad. The central part of the polishing disc body has a built-in central liquid distribution chamber. The upper surface of the polishing disc body has several annular polishing liquid storage tanks arranged around the central liquid distribution chamber. Adjacent polishing liquid storage tanks are connected by a first liquid distribution hole, and the central liquid distribution chamber is connected to adjacent polishing liquid storage tanks by a second liquid distribution hole. The polishing disc drive mechanism is used to drive the polishing disc body to rotate, the constant pressure liquid supply mechanism is used to supply liquid to the central liquid distribution chamber, and the polishing pad covers all polishing liquid storage tanks.

[0008] Furthermore, in the polishing disc body, multiple first dispensing holes are arranged in a ring between adjacent polishing liquid storage tanks, and multiple second dispensing holes are arranged in a ring between the central dispensing chamber and adjacent polishing liquid storage tanks; the bottom position of all polishing liquid storage tanks gradually decreases from the inside to the outside.

[0009] Furthermore, a waste liquid collection tank is provided at the bottom of the polishing disc body, and an annular waste liquid collection trough centered on the central liquid distribution chamber is provided on the upper surface of the polishing disc body. The waste liquid collection trough is connected to the waste liquid collection tank through a waste liquid collection channel. The waste liquid collection trough is located on the outer layer of the outermost polishing liquid storage tank, and the two are connected through an overflow port.

[0010] Furthermore, the constant pressure liquid supply mechanism is a cylindrical structure, which is located at the upper center of the polishing disc body, and its inner cavity is connected to the central liquid distribution cavity.

[0011] Furthermore, a support is provided on the worktable, which extends to the upper end of the polishing disc body. The constant pressure liquid supply mechanism and the polishing head assembly are both mounted on the support, and the lower end of the constant pressure liquid supply mechanism is rotatably connected to the polishing disc body.

[0012] Furthermore, the polishing disc assembly also includes a slewing bearing located at the lower end of the polishing disc body. The slewing bearing includes a rotating inner ring and an outer ring. The inner ring is fixedly connected to the worktable, and the outer ring is a gear structure that is fixedly connected to the polishing disc body. The polishing disc drive mechanism includes a drive gear and a polishing disc drive motor. The drive gear meshes with the outer ring of the slewing bearing, and the polishing disc drive motor is used to drive the drive gear to rotate.

[0013] Furthermore, the polishing head assembly includes a polishing shaft, a polishing head body disposed at the lower end of the polishing shaft, a polishing head lifting drive mechanism, and a polishing head rotation drive mechanism. The polishing head lifting drive mechanism is used to drive the polishing shaft to lift and lower, and the polishing head rotation drive mechanism is used to drive the polishing shaft to rotate.

[0014] Furthermore, a support is provided on the worktable, extending to the upper end of the polishing disc body, and the polishing head assembly is mounted on the support; a mounting base is provided at the output end of the polishing head lifting drive mechanism, and the polishing head rotation drive mechanism includes a polishing head drive motor and an intermediate transmission mechanism. The upper end of the polishing shaft is rotatably engaged with the mounting base, and a spline sleeve is slidably fitted onto the lower outer wall. The spline sleeve is rotatably mounted on the support, and the polishing head drive motor drives the spline sleeve to rotate through the intermediate transmission mechanism, thereby driving the polishing shaft to rotate.

[0015] Furthermore, a connector is provided on the mounting base, the connector is connected to an air pump, and a cavity communicating with the connector is provided inside the polishing shaft along its axial direction. The lower end of the cavity leads to the polishing head body and is sealed by the polishing head body.

[0016] Furthermore, a polishing pad support plate is sandwiched between the polishing pad and the polishing disc body, and the polishing pad and the polishing pad support plate are evenly distributed with corresponding through holes; a splash guard is provided around the upper edge of the polishing disc body.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] 1) This invention solves the problems of long process, high cost and rough surface of SiC substrate planar grinding and polishing by designing and building a planar shear thickening polishing experimental platform. When the relative shear rate is high, the shear thickening polishing liquid undergoes shear thickening phenomenon to realize the grinding process of SiC substrate. When the relative shear rate is low, the polishing process of SiC substrate is realized, thereby obtaining a low-damage SiC substrate and providing a better substrate for subsequent CMP process.

[0019] 2) This invention designs a polishing disk for a discontinuous shear-thickened SiC substrate with a unique liquid supply method. By designing the polishing disk and liquid supply device, the shortcomings of semi-solidified abrasive grinding disks with no abrasive supply and excessively high polishing costs are solved. The motor drives the slewing bearing through gears, and a connecting bearing is added to the center of the polishing disk to ensure that the constant pressure liquid supply device installed on the support box remains stationary relative to the rotating polishing disk. The waste liquid collection tank is installed at the bearing inside the slewing bearing, which can also ensure that it remains stationary relative to the slewing bearing.

[0020] 3) The present invention designs an annular boss as a polishing pad support for the polishing pad body, which provides support for the polishing pad support plate that supports the polishing pad.

[0021] 4) The present invention is designed with a method of supplying liquid from the center to the surrounding area, and the pressure provided by the constant pressure liquid supply device ensures the fluidity of the polishing liquid.

[0022] 5) The present invention designs a waste liquid collection channel, which uses the centrifugal force when the polishing disc body rotates to collect the waste liquid into the waste liquid collection bucket.

[0023] 6) This invention utilizes the liquid-solid conversion characteristics of discontinuous shear thickening fluid to achieve integrated polishing and grinding of SiC substrates. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of the present invention;

[0025] Figure 2 This is a schematic diagram of the cross-sectional structure of the polishing disk assembly in this invention;

[0026] Figure 3 This is a schematic diagram of the polishing disc assembly in this invention.

[0027] Figure 4 This is a schematic diagram of the cross-sectional structure of the polishing head assembly in this invention.

[0028] In the figure: Polishing head assembly 100; Polishing head lifting drive mechanism 110; Support frame 120; Mounting base 130; Polishing shaft 140; Support box 150; Polishing head body 160; Polishing head rotation drive mechanism 170; Polishing head drive motor 171; First gear 172; Belt 173; Second gear 174; Connector 180; Spline sleeve 190; Polishing disc assembly 200; Constant pressure liquid supply mechanism 210; Polishing disc body 220 Polishing pad 221a; polishing pad support plate 221b; central dispensing chamber 222; annular boss 223; polishing fluid storage tank 224; first dispensing hole 225; waste liquid collection tank 226; second dispensing hole 227; waste liquid collection channel 228; drive gear 230; polishing disc drive motor 240; slewing bearing 250; waste liquid collection bucket 260; air pump 300; worktable 400; bracket 410; splash guard 500. Detailed Implementation

[0029] In the description of this invention, it should be understood that the terms "one end", "the other end", "outer side", "upper side", "inner side", "horizontal", "coaxial", "center", "end", "length", "outer end", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0030] The invention will now be further described with reference to the accompanying drawings.

[0031] Please see Figures 1-4 A planar discontinuous shear thickening SiC grinding and polishing integrated polishing device includes a worktable 400, on which a support 410, a polishing disc assembly 200 and an air pump 300 are arranged. The support 410 extends above the polishing disc assembly 200 and is provided with a support box 150. A support frame 120 is provided on the support box 150. A polishing head assembly 100 is jointly arranged on the support box 150 and the support frame 120.

[0032] Continue reading Figure 2 and Figure 3The polishing disc assembly 200 includes a polishing disc body 220, a polishing disc drive mechanism, a constant pressure liquid supply mechanism 210, a polishing pad 221a, and a polishing pad support plate 221b. The polishing disc body 220 has a central liquid distribution chamber 222 built into its center. The upper surface of the polishing disc body 220 is provided with several annular polishing liquid storage tanks 224 around the central liquid distribution chamber 222. The bottom position of all polishing liquid storage tanks 224 gradually decreases from the inside to the outside, and the top position is flush. Annular bosses 223 are formed between adjacent polishing liquid storage tanks 224. Adjacent polishing liquid storage tanks 224 are also connected by several first liquid distribution holes 225 evenly distributed on the corresponding annular bosses. The central liquid distribution chamber 222 and adjacent polishing liquid storage tanks 224 are connected by several second liquid distribution holes 227 evenly distributed. The polishing slurry storage tank 224 has an open top, a central dispensing chamber 222 as its inner cavity, and is connected to adjacent polishing slurry storage tanks 224 via second dispensing holes 227. Its top has an opening connected to the constant pressure supply mechanism 210. The polishing disc drive mechanism drives the polishing disc body 220 to rotate. The constant pressure supply mechanism 210 is a cylindrical structure, rotatably mounted on the upper center of the polishing disc body 220 via bearings. Its inner cavity is connected to the opening of the central dispensing chamber 222, and it supplies slurry to the central dispensing chamber 222. The polishing pad 221a and polishing pad support plate 221b are annular structures with numerous through holes, sequentially covering the upper end of the polishing disc body 220 and all polishing slurry storage tanks 224. The polishing pad 221a is a flexible structure, supported by annular bosses 223 and polishing pad support plate 221b.

[0033] The constant pressure liquid supply mechanism 210 is mounted on the side of the support box 150, so that the constant pressure liquid supply mechanism 210 will not rotate with the polishing disc body 220. Specifically, the outer wall of the constant pressure liquid supply mechanism 210 is provided with a buckle 211, which is engaged with the support box 150 through the buckle 211.

[0034] See further 2 and Figure 3 The bottom of the polishing disc body 220 is provided with a waste liquid collection tank 260. The inner ring of the bearing mentioned above is fixed below the waste liquid collection tank 260. The upper surface of the polishing disc body 220 is provided with an annular waste liquid collection trough 226 centered on the central liquid distribution chamber 222. The waste liquid collection trough 226 is connected to the waste liquid collection tank 260 through the waste liquid collection flow channel 228. The waste liquid collection trough 226 is located outside the outermost polishing liquid storage tank 224, and the two are connected through the overflow port 229.

[0035] See further 2 and Figure 3The polishing disc assembly 200 also includes a slewing bearing 250 located at the lower end of the polishing disc body 220. The slewing bearing 250 includes a rotating inner ring and an outer ring. The inner ring is fixedly connected to the worktable 400, and the outer ring is a gear structure fixed to the lower end of the polishing disc body 220. The polishing disc drive mechanism includes a drive gear 230 and a polishing disc drive motor 240. The drive gear 230 meshes with the outer ring of the slewing bearing 250. The polishing disc drive motor 240 is mounted on the underside of the worktable 400, and its output shaft drives the drive gear 230 to rotate.

[0036] Continue reading Figure 4 The polishing head assembly 100 includes a polishing shaft 140, a polishing head body 160 disposed at the lower end of the polishing shaft 140, a polishing head lifting drive mechanism 110, and a polishing head rotation drive mechanism 170. The polishing head lifting drive mechanism is used to drive the polishing shaft 140 to lift and lower, and the polishing head rotation drive mechanism 170 is used to drive the polishing shaft 140 to rotate.

[0037] Further reading Figure 4 The polishing head lifting drive mechanism 110 is preferably a pneumatic cylinder, but an electric cylinder, hydraulic cylinder, etc. can also be used. It is mounted on the support frame 120, and the output end is provided with a mounting base 130. The polishing head rotation drive mechanism 170 includes a polishing head drive motor 171 and an intermediate transmission mechanism. The polishing head drive motor 171 is mounted on the support box 150. The upper end of the polishing shaft 140 is inserted into the mounting base 130 and rotates with the mounting base 130 through a bearing. The lower end of the outer wall is slidably fitted with a spline sleeve 190, and the two are connected by a spline. The spline sleeve 190 is rotated and mounted on the support box 150 through a bearing. The polishing head drive motor 170 drives the spline sleeve 190 to rotate through the intermediate transmission mechanism. The spline sleeve 190 can drive the polishing shaft 140 to rotate.

[0038] The intermediate transmission mechanism of this invention is a pulley mechanism, including a first gear 172 that cooperates with the polishing head drive motor 171, a second gear 174 that is sleeved on the spline sleeve 190, and a belt 173 that connects the first gear 172 and the second gear 174. Alternatively, the intermediate transmission mechanism may also be a gear transmission mechanism or a sprocket transmission mechanism.

[0039] For further information Figure 4 A connector 180 is provided on the mounting base 130. The connector 180 is connected to the air pump 300 through a pipeline. The polishing shaft 140 has a cavity that communicates with the connector 180 along its axial direction. The lower end of the cavity is connected to the polishing head body 160 and is sealed by the polishing head body 160.

[0040] During a polishing process, the polishing head lifting drive mechanism 110 drives the polishing head body 160 to rise and fall, driving the polishing head body 160 to a designated position. Meanwhile, the polishing head rotation drive mechanism 170 drives the spline sleeve 190 to rotate, and the spline sleeve 190 drives the polishing shaft 140 to rotate. The polishing shaft 140 is connected to the polishing head body 160. At this time, the polishing head body 160 can generate a relative shearing speed with the polishing disc body 220.

[0041] This invention differs from traditional drip-type and semi-solidified grinding disc polishing and liquid supply methods. The polishing liquid is stored at the bottom of the polishing disc body 220. Through the combined action of the polishing head body 160 squeezing the polishing pad 221a and the constant pressure liquid supply device, the polishing liquid in the polishing disc body 220 overflows, realizing semi-immersion polishing of the workpiece.

[0042] Before the polishing process begins, the constant pressure liquid supply device 210 supplies polishing liquid to the central distribution chamber 222 at a constant pressure. The polishing liquid flows through the first distribution hole 227 to the adjacent polishing liquid storage tank 224, and then through the second distribution hole 225 to the remaining polishing liquid storage tanks 224. The constant pressure liquid supply device 210 continuously supplies polishing liquid until each polishing liquid storage chamber 224 is filled. At the same time, the polishing head body 160 moves to the designated position on the polishing pad 221a, and the air pump 300 starts to inflate the inner cavity of the polishing shaft 140 with air, pneumatically pressurizing the polishing head onto the polishing pad 221a supported by the polishing pad support plate 221b. At this point, the polishing process begins. The constant pressure liquid supply device 210 continues to supply polishing liquid to the central liquid distribution chamber 222 at a constant pressure. The polishing disc drive motor 240 drives the polishing disc body 220, which is fixed to the outer ring gear of the slewing bearing 250, to rotate through the drive gear 230. The polishing head body 160 is driven by the polishing head rotation drive mechanism 170 to generate a relative shear rate with the rotating polishing disc body 220. When the shear rate is higher than the critical shear rate at which the shear thickening phenomenon occurs, the SiC substrate grinding process is performed. When the shear rate is lower than the critical shear rate, the SiC substrate polishing process is performed.

[0043] As the polishing slurry fills and overflows from the polishing slurry storage tank 224 onto the surface of the polishing pad 221a, the rotation of the polishing disk body 220 causes the polishing slurry to gradually move away from the center due to centrifugal force. At this time, the waste polishing slurry mixes with SiC substrate debris and flows through the overflow port 228 into the waste liquid collection channel 226, and then into the waste liquid collection tank 260. The waste liquid collection tank 260 is installed in the bearing of the slewing bearing 250 and remains relatively stationary when the polishing disk body 220 rotates.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A planar discontinuous shear thickening SiC grinding and polishing integrated device, comprising a worktable (400) and a polishing disk assembly (200) and a polishing head assembly (100) disposed on the worktable (400), characterized in that, The polishing disc assembly (200) includes a polishing disc body (220), a polishing disc drive mechanism, a constant pressure liquid supply mechanism (210), and a polishing pad (221a). The polishing disc body (220) has a central liquid distribution chamber (222) built into its center. The upper surface of the polishing disc body (220) is provided with several annular polishing liquid storage tanks (224) around the central liquid distribution chamber (222). Adjacent polishing liquid storage tanks (224) are connected through a first liquid distribution hole (225). The central liquid distribution chamber (222) and adjacent polishing liquid storage tanks (224) are connected through a second liquid distribution hole (227). The polishing disc drive mechanism is used to drive the polishing disc body (220) to rotate. The constant pressure liquid supply mechanism is used to supply liquid to the central liquid distribution chamber (222). The polishing pad (221a) covers all polishing liquid storage tanks (224). In the polishing disc body (220), a plurality of first dispensing holes (225) are arranged in a ring between adjacent polishing liquid storage tanks (224), and a plurality of second dispensing holes (227) are arranged in a ring between the central dispensing chamber (222) and adjacent polishing liquid storage tanks (224); the bottom position of all polishing liquid storage tanks (224) gradually decreases from the inside to the outside; Waste liquid collection tank (260) is provided at the bottom of the polishing disc body (220), and a ring-shaped waste liquid collection trough (226) centered on the central liquid distribution chamber (222) is provided on the upper surface of the polishing disc body (220). The waste liquid collection trough (226) is connected to the waste liquid collection tank (260) through the waste liquid collection channel (228). The waste liquid collection trough (226) is located on the outer layer of the outermost polishing liquid storage tank (224), and the two are connected through the overflow port (229).

2. The planar discontinuous shear thickening SiC grinding and polishing integrated polishing device according to claim 1, characterized in that, The constant pressure liquid supply mechanism (210) is a cylindrical structure, which is located at the upper center of the polishing disc body (220), and its inner cavity is connected to the central liquid distribution cavity (222).

3. The planar discontinuous shear thickening SiC grinding and polishing integrated polishing device according to claim 2, characterized in that, A bracket (410) is provided on the worktable (400), which extends to the upper end of the polishing disc body (220). The constant pressure liquid supply mechanism (210) and the polishing head assembly (100) are both provided on the bracket (410), and the lower end of the constant pressure liquid supply mechanism (210) is rotatably connected to the polishing disc body (220).

4. The planar discontinuous shear thickening SiC grinding and polishing integrated polishing device according to claim 1, characterized in that, The polishing disc assembly (200) also includes a slewing bearing (250) located at the lower end of the polishing disc body (220). The slewing bearing (250) includes a rotating inner ring and an outer ring. The inner ring is fixedly connected to the worktable (400), and the outer ring is a gear structure that is fixedly connected to the polishing disc body (220). The polishing disc drive mechanism includes a drive gear (230) and a polishing disc drive motor (240). The drive gear (230) meshes with the outer ring of the slewing bearing (250), and the polishing disc drive motor (240) is used to drive the drive gear (230) to rotate.

5. The planar discontinuous shear thickening SiC grinding and polishing integrated polishing device according to claim 1, characterized in that, The polishing head assembly (100) includes a polishing shaft (140), a polishing head body (160) disposed at the lower end of the polishing shaft (140), a polishing head lifting drive mechanism (110), and a polishing head rotation drive mechanism (170). The polishing head lifting drive mechanism (110) is used to drive the polishing shaft (140) to lift and lower, and the polishing head rotation drive mechanism (170) is used to drive the polishing shaft (140) to rotate.

6. The planar discontinuous shear thickening SiC grinding and polishing integrated polishing device according to claim 5, characterized in that, A bracket (410) is provided on the worktable (400), which extends to the upper end of the polishing disc body (220). The polishing head assembly (100) is provided on the bracket (410). A mounting base (130) is provided at the output end of the polishing head lifting drive mechanism (110). The polishing head rotation drive mechanism (170) includes a polishing head drive motor (171) and an intermediate transmission mechanism. The upper end of the polishing shaft (140) is rotatably engaged with the mounting base (130), and a spline sleeve (190) is slidably fitted on the lower outer wall. The spline sleeve (190) is rotatably mounted on the bracket (410). The polishing head drive motor (171) drives the spline sleeve (190) to rotate through the intermediate transmission mechanism. The spline sleeve (190) can drive the polishing shaft (140) to rotate.

7. The planar discontinuous shear thickening SiC grinding and polishing integrated polishing device according to claim 6, characterized in that, The mounting base (130) is provided with a connector (180), the connector (180) is connected to an air pump (300), and the polishing shaft (140) has a cavity that communicates with the connector (180) along its axial direction. The lower end of the cavity is connected to the polishing head body (160) and is blocked by the polishing head body (160).

8. The planar discontinuous shear thickening SiC grinding and polishing integrated polishing device according to claim 1, characterized in that, A polishing pad support plate (221b) is sandwiched between the polishing pad (221a) and the polishing disc body (220). The polishing pad (221a) and the polishing pad support plate (221b) are evenly covered with corresponding through holes. A splash guard (500) is provided around the upper edge of the polishing disc body (220).

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