A double-row horizontally inserted graphite boat

Abstract

The present invention discloses a graphite boat with a double-row horizontally inserted layout structure, which relates to the field of semiconductor equipment technology. The graphite boat sheets include double-row inner sheets, double-row outer sheets, and an expansion portion. The double-row horizontally inserted graphite boat also includes a stabilizing portion for improving the stability of the graphite boat after loading silicon wafers, and an adjustment portion for adjusting the position of the silicon wafers loaded between the double-row outer sheets and the double-row inner sheets. By providing a positioning portion, the spacing between the graphite boat sheets can still be kept consistent under manual installation conditions, thereby avoiding inconsistent spacing between the graphite boat sheets caused by human installation factors. By ensuring consistent spacing between the graphite boat sheets, the silicon wafers can be heated evenly during subsequent high-temperature processing, thereby improving the qualified rate of silicon wafer processing to a certain extent.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor equipment, and in particular to a graphite boat with a double-row horizontal insertion layout structure. Background Art

[0002] In the semiconductor and photovoltaic industries, high-temperature processing of silicon wafers is a key link in determining product performance and quality. Graphite boats are the core equipment for carrying silicon wafers for high-temperature diffusion, oxidation, annealing and other processes. Their structural design and assembly accuracy have a direct impact on the silicon wafer processing effect. A stable and precise graphite boat structure can ensure that the silicon wafers are evenly heated in a high-temperature environment, thereby ensuring the performance consistency and product qualification rate of the processed silicon wafers. However, the graphite boats currently on the market have significant defects in the assembly process. Most existing graphite boats are assembled manually. After assembly, it is difficult to ensure that the spacing between the graphite boat slices is completely consistent. Since manual operation is affected by subjective factors such as the operator's proficiency and working status, it is impossible to accurately control the spacing between the graphite boat slices during the assembly process. Even if the individual spacing is measured and adjusted during assembly, it is difficult to avoid overall spacing deviation due to cumulative errors.

[0003] During high-temperature processing of silicon wafers, inconsistent spacing between graphite boats can have serious consequences. In areas with smaller spacing, heat conduction and convection between the wafers are affected, leading to localized overheating. Meanwhile, in areas with larger spacing, the wafers receive less heat. This uneven heating can lead to variations in key parameters such as doping concentration and oxide thickness on the wafer surface, resulting in inconsistent electrical performance and a consequent impact on wafer yield. Therefore, improvements are urgently needed. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a graphite boat with a double-row horizontal insertion layout structure, aiming to solve the above technical problems.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A graphite boat with a double-row horizontal insertion layout structure includes a graphite boat sheet, wherein the graphite boat sheet includes:

[0007] There are multiple double-row inner sheets, and the spacing between the multiple double-row inner sheets is consistent;

[0008] There are two double-row outer sheets, and the two double-row outer sheets are respectively distributed on one side of the outer double-row inner sheet, and the distance between the double-row outer sheets and the outer double-row inner sheets is consistent with the distance between the double-row inner sheets;

[0009] There are two groups of expansion parts, and the two groups of expansion parts are respectively distributed on one side of the two double-row outer slices. The expansion parts are used to increase the carrying capacity of the graphite boat for the silicon wafers;

[0010] The double-row horizontal layout graphite boat also includes:

[0011] A plurality of stabilizing parts are provided on the graphite boat, and the stabilizing parts are used to improve the stability of the graphite boat after loading the silicon wafers;

[0012] The adjusting part has two groups, and the adjusting part is used to adjust the position of the silicon wafers loaded between the double rows of outer wafers and the double rows of inner wafers.

[0013] Preferably, the expansion unit includes:

[0014] A single-row inner sheet is located on a side of the double-row outer sheet away from the double-row inner sheet;

[0015] The single-row outer sheet is located on a side of the single-row inner sheet away from the double-row outer sheet.

[0016] Preferably, first boat ears are fixedly provided at both ends of the double-row inner sheets and the double-row outer sheets, second boat ears are fixedly provided at both ends of the double-row inner sheets and the double-row outer sheets, and the second boat ears are located below the first boat ears.

[0017] Preferably, the two ends of the single-row inner sheet are fixedly provided with second boat ears, and the two ends of the single-row outer sheet are fixedly provided with first boat ears.

[0018] Preferably, a graphite pad is provided between each of the first boat ears, and a graphite pad is also provided between each of the second boat ears.

[0019] Preferably, the double-row inner plates, double-row outer plates, single-row inner plates and single-row outer plates are all provided with a plurality of regularly distributed card holes, and the double-row inner plates, double-row outer plates, single-row inner plates and single-row outer plates are also provided with positioning grooves, and the positioning grooves are provided with positioning parts for facilitating the installation and positioning of the graphite boat plates.

[0020] Preferably, the stabilizing portion comprises:

[0021] There are multiple ceramic sleeves, and the multiple ceramic sleeves are respectively arranged between the double-row inner sheets, between the double-row outer sheets and the double-row inner sheets, between the single-row inner sheet and the double-row outer sheets, and between the single-row outer sheet and the single-row inner sheet;

[0022] There are multiple ceramic rods, each of which is equidistantly inserted through the graphite boat sheet and the ceramic sleeve. The ceramic rods are also inserted through the first boat ear, the second boat ear, and the graphite pad. The ceramic rods are provided with multiple equidistantly distributed ball grooves.

[0023] There are two groups of fasteners, and the two groups of fasteners are respectively arranged at both ends of the ceramic rod, and the fasteners are used to fix the ceramic rod on the graphite boat.

[0024] Preferably, the fastener comprises:

[0025] A carbon-carbon flat washer is sleeved on the portion of the ceramic rod located outside the graphite boat;

[0026] The graphite nut is arranged on the portion of the ceramic rod located outside the graphite boat, and the graphite nut is threadedly connected to the ceramic rod.

[0027] Preferably, the positioning portion includes:

[0028] A positioning spring is arranged in the positioning groove, and the positioning spring is always in a compressed state;

[0029] The positioning ball is slidably arranged in the positioning groove, and the positioning ball is engaged with the ball groove.

[0030] Preferably, the adjustment unit includes:

[0031] An adjusting screw is provided through the double-row outer plates and the double-row inner plates, the adjusting screw is rotatably connected to the double-row outer plates and the double-row inner plates, and a knob is fixedly provided at either end of the adjusting screw;

[0032] There are multiple adjustment plate groups, and the multiple adjustment plate groups are respectively located between the double-row outer plates and the double-row inner plates and between each double-row inner plate. The adjustment plate group includes two adjustment plates, and the two adjustment plates are both threadedly connected to the adjustment screw, and the thread rotation directions of the two adjustment plates in the same adjustment plate group are opposite.

[0033] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0034] By providing a positioning portion, after the ceramic rod is completely passed through the graphite boat, the staff manually moves the ceramic rod until the staff hears a "click" sound, which indicates that the positioning ball has a tendency to move toward the axis of the ceramic rod under the force of the positioning spring. When the ball groove on the ceramic rod slides to correspond to the positioning ball, the positioning ball slides into the ball groove, thereby completing the assembly and positioning of the graphite boat and the ceramic rod; such a setting makes it possible to keep the spacing between the graphite boats consistent even under manual installation conditions, thereby avoiding inconsistent spacing between the graphite boats caused by human installation factors, and by ensuring the consistent spacing between the graphite boats, it ensures that the silicon wafers can be heated evenly during subsequent high-temperature processing, thereby improving the qualified rate of silicon wafer processing to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0036] Figure 1 A schematic diagram of the three-dimensional structure of a graphite boat with a double-row horizontal insertion layout is shown.

[0037] Figure 2 A front view of a graphite boat with a double-row horizontal insertion layout is shown.

[0038] Figure 3 Shown Figure 2 Cross-sectional view of AA in the figure.

[0039] Figure 4 Shown Figure 3 A magnified schematic diagram of the local structure at point A in the middle.

[0040] Figure 5 Shown Figure 3 A magnified schematic diagram of the local structure at point B in the middle.

[0041] Figure 6 A side view of a graphite boat with a double-row horizontal insertion layout is shown.

[0042] Figure 7 A top view of a graphite boat with a double-row horizontal insertion layout is shown.

[0043] Legend:

[0044] 1. Double-row inner plate; 2. Double-row outer plate; 3. Single-row inner plate; 4. Single-row outer plate; 5. First boat ear; 6. Second boat ear; 7. Graphite gasket; 8. Clamping hole; 9. Positioning groove; 10. Ceramic sleeve; 11. Ceramic rod; 12. Ball groove; 13. Carbon-carbon flat washer; 14. Graphite nut; 15. Positioning spring; 16. Positioning ball; 17. Adjusting screw; 18. Adjusting plate; 19. Knob. DETAILED DESCRIPTION

[0045] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0046] In the description of the present invention, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0047] It should be noted that when a component is referred to as being "fixed to" another component, it may be directly on the other component or there may also be a central component. When a component is considered to be "connected to" another component, it may be directly connected to the other component or there may also be a central component. When a component is considered to be "set on" another component, it may be directly set on the other component or there may also be a central component. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only.

[0048] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0049] Reference Figures 1 to 7 An embodiment of a graphite boat with a double-row horizontal insertion structure according to the present invention is further described.

[0050] A graphite boat with a double-row horizontal insertion layout structure includes a graphite boat sheet, wherein the graphite boat sheet includes:

[0051] There are multiple double-row inner sheets 1, and the spacing between the multiple double-row inner sheets 1 is consistent;

[0052] There are two double-row outer sheets 2, and the two double-row outer sheets 2 are respectively distributed on one side of the outer double-row inner sheet 1, and the distance between the double-row outer sheets 2 and the outer double-row inner sheet 1 is consistent with the distance between the double-row inner sheets 1;

[0053] The expansion part has two groups, and the two groups of expansion parts are respectively distributed on one side of the two double-row outer sheets 2. The expansion part is used to increase the carrying capacity of the graphite boat for the silicon wafer. The expansion part includes:

[0054] The single-row inner sheet 3 is located on the side of the double-row outer sheet 2 away from the double-row inner sheet 1;

[0055] The single-row outer sheet 4 is located on a side of the single-row inner sheet 3 away from the double-row outer sheet 2 .

[0056] By arranging the expansion parts on the outside of the double-row outer sheets 2 on both sides, the loading capacity of the graphite boat for silicon wafers is effectively increased. At the same time, arranging the expansion parts on the outside of the double-row outer sheets 2 on both sides does not affect the entry of the graphite boat into the furnace tube, thereby improving the space utilization of the furnace tube to a certain extent.

[0057] The double-row horizontal layout graphite boat also includes:

[0058] The stabilizing part has multiple groups, and the multiple groups of stabilizing parts are arranged on the graphite boat. The stabilizing part is used to improve the stability of the graphite boat after loading the silicon wafer. The stabilizing part includes:

[0059] There are multiple ceramic sleeves 10, and the multiple ceramic sleeves 10 are respectively arranged between the double-row inner sheet 1, between the double-row outer sheet 2 and the double-row inner sheet 1, between the single-row inner sheet 3 and the double-row outer sheet 2, and between the single-row outer sheet 4 and the single-row inner sheet 3. By arranging the ceramic sleeves 10 between the graphite boat sheets, the graphite boat sheets are isolated from direct contact, thereby avoiding short circuit caused by current passing through the graphite boat sheets.

[0060] There are multiple ceramic rods 11, each of which is equidistantly disposed on the graphite boat sheet and the ceramic sleeve 10. The ceramic rods 11 are also disposed on the first boat ear 5, the second boat ear 6, and the graphite pad 7. The ceramic rods 11 are provided with multiple equidistantly distributed ball grooves 12.

[0061] By passing the ceramic rods 11 through the graphite boat sheets, a gridded fixed structure is formed, thereby improving the torsional rigidity of the entire graphite boat (especially for the problem that long graphite boats are prone to bending).

[0062] There are two sets of fasteners, and the two sets of fasteners are respectively provided at both ends of the ceramic rod 11, and the fasteners are used to fix the ceramic rod 11 on the graphite boat sheet, and the fasteners include:

[0063] A carbon-carbon flat washer 13 is sleeved on the portion of the ceramic rod 11 located outside the graphite boat sheet. The carbon-carbon flat washer 13 disperses the surface pressure when the graphite nut 14 is tightened, thereby preventing the end of the ceramic rod 11 from breaking due to point load.

[0064] The graphite nut 14 is arranged on the portion of the ceramic rod 11 located outside the graphite boat, and the graphite nut 14 is threadedly connected to the ceramic rod 11. The arrangement of the graphite nut 14 allows the self-lubricating property of the graphite to reduce the risk of biting when the graphite nut 14 and the ceramic rod 11 are threaded together, and there is no oxidation bonding problem at high temperatures (compared to metal nuts that are prone to getting stuck).

[0065] The adjustment part has two groups, and is used to adjust the position of the silicon wafers loaded between the double-row outer wafers 2 and the double-row inner wafers 1. The adjustment part includes:

[0066] An adjusting screw 17 is provided through the double-row outer sheet 2 and the double-row inner sheet 1. The adjusting screw 17 is rotatably connected to the double-row outer sheet 2 and the double-row inner sheet 1, and a knob 19 is fixedly provided at either end of the adjusting screw 17.

[0067] There are multiple groups of adjustment plates 18, and the multiple groups of adjustment plates 18 are respectively located between the double-row outer plates 2 and the double-row inner plates 1 and between each double-row inner plate 1. The adjustment plate 18 group includes two adjustment plates 18, and the two adjustment plates 18 are both threadedly connected to the adjustment screw 17, and the thread rotation directions of the two adjustment plates 18 in the same adjustment plate 18 group are opposite.

[0068] After the silicon wafer is placed in the two adjustment plates 18 of the same adjustment plate 18 group between the graphite boats, the staff manually rotates the knob 19, thereby rotating the adjustment screw 17 fixedly connected to the knob 19, and through the threaded transmission cooperation between the adjustment screw 17 and the two adjustment plates 18 in the adjustment plate 18 group, the two adjustment plates 18 in the same adjustment plate 18 group are synchronously moved toward the surface of the silicon wafer until the adjustment plates 18 on both sides of the silicon wafer are attached to the surface of the silicon wafer, thereby firmly fixing the silicon wafer in the middle between each graphite boat, so that the silicon wafer can be heated evenly during the subsequent high-temperature processing, thereby further improving the qualified rate of silicon wafer processing.

[0069] The double-row inner sheet 1 and the double-row outer sheet 2 are fixedly provided with first boat ears 5 at both ends, the double-row inner sheet 1 and the double-row outer sheet 2 are fixedly provided with second boat ears 6 at both ends, and the second boat ears 6 are located below the first boat ears 5, the second boat ears 6 are fixedly provided at both ends of the single-row inner sheet 3, and the first boat ears 5 are fixedly provided at both ends of the single-row outer sheet 4.

[0070] By providing the first boat ear 5 and the second boat ear 6, a four-point support structure is formed, which effectively improves the bending strength of the graphite boat sheet. The second boat ear 6 is located below the first boat ear 5. By dispersing the shear stress of the graphite boat sheet when it is suspended (such as gravity sagging under high temperature in the furnace), the deformation amount is made ≤0.1mm (the deformation amount of the conventional single-row boat ear structure is ≥0.3mm), thereby avoiding deformation of the graphite boat sheet. By providing the first boat ear 5 and the second boat ear 6, the distance between the graphite boat sheet and the furnace hanger is compensated to avoid the risk of jamming.

[0071] A graphite pad 7 is provided between each of the first boat ears 5 , and a graphite pad 7 is also provided between each of the second boat ears 6 .

[0072] By providing a graphite pad 7, the gap between the first boat ears 5 and the gap between the second boat ears 6 can be filled, thereby avoiding the deviation of the graphite boat sheet. At the same time, it can also absorb the vibration energy of the graphite boat, effectively reducing the position deviation of the silicon wafer. The setting of the graphite pad 7 isolates the current path between the adjacent first boat ears 5 and the second boat ears 6, thereby avoiding uneven film layer caused by abnormal distribution of the electric field in the coating process.

[0073] The double-row inner sheet 1, the double-row outer sheet 2, the single-row inner sheet 3 and the single-row outer sheet 4 are all provided with a plurality of regularly distributed card point holes 8. It should be noted that the card point holes 8 are provided to facilitate interference fit of graphite card points in the card point holes 8. The double-row inner sheet 1, the double-row outer sheet 2, the single-row inner sheet 3 and the single-row outer sheet 4 are also provided with positioning grooves 9. The positioning grooves 9 are provided with positioning parts that facilitate the installation and positioning of the graphite boat sheet. The positioning parts include:

[0074] A positioning spring 15 is disposed in the positioning groove 9, and the positioning spring 15 is always in a compressed state;

[0075] The positioning ball 16 is slidably disposed in the positioning groove 9 , and the positioning ball 16 is engaged with the ball groove 12 .

[0076] By providing a positioning portion, after the ceramic rod 11 is completely passed through the graphite boat, the staff manually moves the ceramic rod 11 until the staff hears a "click" sound, which indicates that the positioning ball 16 has a tendency to move toward the axis of the ceramic rod 11 under the force of the positioning spring 15. When the ball groove 12 on the ceramic rod 11 slides to correspond to the positioning ball 16, the positioning ball 16 slides into the ball groove 12, thereby completing the assembly and positioning of the graphite boat and the ceramic rod 11; such a setting makes it possible to keep the spacing between the graphite boats consistent even in the case of manual installation, thereby avoiding the inconsistent spacing between the graphite boats caused by human installation factors, and by ensuring the consistent spacing between the graphite boats, thereby ensuring that the silicon wafers can be heated evenly during the subsequent high-temperature processing, thereby improving the qualified rate of silicon wafer processing to a certain extent.

[0077] The above description of the embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A double-row horizontally inserted graphite boat, characterized in that: A graphite boat is provided, wherein the graphite boat comprises: There are multiple double-row inner sheets (1), and the spacing between the multiple double-row inner sheets (1) is consistent; There are two double-row outer sheets (2), and the two double-row outer sheets (2) are respectively distributed on one side of the outer double-row inner sheet (1), and the spacing between the double-row outer sheets (2) and the outer double-row inner sheet (1) is consistent with the spacing between the double-row inner sheets (1); The expansion part has two groups, and the two groups of expansion parts are respectively distributed on one side of the two double-row outer sheets (2), and the expansion part is used to increase the carrying capacity of the graphite boat for the silicon sheet; The double-row horizontal layout graphite boat also includes: A plurality of stabilizing parts are provided on the graphite boat, and the stabilizing parts are used to improve the stability of the graphite boat after loading the silicon wafers; An adjustment part having two groups, wherein the adjustment part is used to adjust the position of silicon wafers loaded between the double-row outer wafers (2) and the double-row inner wafers (1); The double-row inner sheet (1), the double-row outer sheet (2), the single-row inner sheet (3) and the single-row outer sheet (4) are all provided with a plurality of regularly distributed card point holes (8), and the double-row inner sheet (1) and the double-row outer sheet (2) are also provided with positioning grooves (9), and the positioning grooves (9) are provided with positioning parts for facilitating the installation and positioning of the graphite boat sheet; The stabilizing portion includes: There are multiple ceramic sleeves (10), and the multiple ceramic sleeves (10) are respectively arranged between the double-row inner sheets (1), the double-row outer sheets (2) and the double-row inner sheets (1); There are multiple ceramic rods (11), the ceramic rods (11) are equidistantly penetrated on the graphite boat sheet and the ceramic sleeve (10), and the ceramic rods (11) are provided with multiple equidistantly distributed ball grooves (12); The positioning portion includes: A positioning spring (15) is disposed in the positioning groove (9), and the positioning spring (15) is always in a compressed state; A positioning ball (16) is slidably disposed in the positioning groove (9), and the positioning ball (16) is engaged with the ball groove (12).

2. The double-row horizontally inserted graphite boat according to claim 1, characterized in that: The expansion unit includes: A single-row inner sheet (3) is located on a side of the double-row outer sheet (2) away from the double-row inner sheet (1); The single-row outer sheet (4) is located on a side of the single-row inner sheet (3) away from the double-row outer sheet (2).

3. The double-row horizontally inserted graphite boat according to claim 2, characterized in that: First boat ears (5) are fixedly provided at both ends of the double-row inner sheet (1) and the double-row outer sheet (2), and second boat ears (6) are fixedly provided at both ends of the double-row inner sheet (1) and the double-row outer sheet (2), and the second boat ears (6) are located below the first boat ears (5).

4. The double-row horizontally inserted graphite boat according to claim 3, characterized in that: The two ends of the single-row inner sheet (3) are fixedly provided with second boat ears (6), and the two ends of the single-row outer sheet (4) are fixedly provided with first boat ears (5).

5. The double-row horizontally inserted graphite boat according to claim 4, characterized in that: A graphite pad (7) is provided between each of the first boat ears (5), and a graphite pad (7) is also provided between each of the second boat ears (6).

6. The double-row horizontally inserted graphite boat according to claim 5, characterized in that: Positioning grooves (9) are also provided in the single-row inner sheet (3) and the single-row outer sheet (4), and positioning portions are provided in the positioning grooves (9) for facilitating the installation and positioning of the graphite boat sheet.

7. The double-row horizontally inserted graphite boat according to claim 6, characterized in that: A ceramic sleeve (10) is also provided between the single-row inner sheet (3) and the double-row outer sheet (2), and between the single-row outer sheet (4) and the single-row inner sheet (3); the ceramic rod (11) is also passed through the first boat ear (5), the second boat ear (6) and the graphite pad (7); two sets of fasteners are provided at both ends of the ceramic rod (11), and the fasteners are used to fix the ceramic rod (11) on the graphite boat sheet.

8. The double-row horizontally inserted graphite boat according to claim 7, characterized in that: The fastener comprises: A carbon-carbon flat washer (13) is sleeved on a portion of the ceramic rod (11) located outside the graphite boat sheet; A graphite nut (14) is arranged on a portion of the ceramic rod (11) located outside the graphite boat sheet, and the graphite nut (14) is threadedly connected to the ceramic rod (11).

9. The double-row horizontally inserted graphite boat according to claim 8, characterized in that: The adjustment unit includes: An adjusting screw (17) is provided through the double-row outer plates (2) and the double-row inner plates (1), the adjusting screw (17) is rotatably connected to the double-row outer plates (2) and the double-row inner plates (1), and a knob (19) is fixedly provided at either end of the adjusting screw (17); The adjusting plate (18) group comprises a plurality of groups, and the plurality of adjusting plate (18) groups are respectively located between the double-row outer plates (2) and the double-row inner plates (1) and between each double-row inner plate (1). The adjusting plate (18) group comprises two adjusting plates (18), and the two adjusting plates (18) are both threadedly connected to the adjusting screw (17), and the thread rotation directions of the two adjusting plates (18) in the same adjusting plate (18) group are opposite.

Images