Wafer double-side continuous vision inspection equipment

Abstract

The application discloses a kind of wafer double-face continuous visual inspection equipment, including first chain plate conveyor, second chain plate conveyor and two groups of visual imaging detection unit;The first chain plate conveyor is located above the second chain plate conveyor, and a plurality of wafer placement plates are equally spaced on the chain plate of the first chain plate conveyor and the second chain plate conveyor, and a wafer placement groove is provided on each wafer placement plate, and a vacuum chuck is provided in the wafer placement groove;Two visual imaging detection units are respectively installed on the first chain plate conveyor and the second chain plate conveyor;Two visual imaging detection units are respectively used to detect the front and back defects of a single wafer placement plate in continuous movement.The application can continuously and uninterruptedly detect the front and back of the wafer for visual defects, and can greatly improve the detection efficiency.

Description

Technical Field

[0001] This invention relates to the field of wafer defect detection technology, and in particular to a wafer double-sided continuous visual inspection device. Background Technology

[0002] A wafer is a silicon wafer used in the fabrication of silicon semiconductor integrated circuits. It is circular in shape, hence the name "wafer." Wafers are crucial for the production of integrated circuits (ICs). Various circuit element structures are fabricated on wafers to ultimately create IC products with specific electrical functions.

[0003] During wafer manufacturing, due to process conditions, a small number of wafers produced may have defects such as stains, bubbles, and pits on their surfaces. Therefore, surface defect inspection is necessary to remove defective products. Existing methods generally use visual imaging (using a visual imaging inspection head to visually image the wafer surface and comparing the image with images of qualified wafers to remove defective products) technology to inspect wafers on the transport line. To ensure imaging quality, the transport line stops moving when the wafer reaches the inspection point. During this time, the visual imaging device takes a picture of the wafer surface (for the visual imaging device to produce a clear image, it needs to remain relatively stationary with the wafer for a certain period of time, i.e., a certain reaction time is required). After the visual inspection is completed, the transport line starts moving again, resulting in low overall wafer inspection efficiency. Therefore, this application provides a wafer double-sided continuous visual inspection device to meet the requirements. Summary of the Invention

[0004] The purpose of this application is to provide a wafer double-sided continuous visual inspection device to solve the technical problem of low wafer defect detection effect in the prior art.

[0005] To achieve the above objectives, this application provides the following technical solution: a wafer double-sided continuous visual inspection device, comprising a first chain conveyor, a second chain conveyor, and two sets of visual imaging inspection units;

[0006] The first chain plate conveyor is located above the second chain plate conveyor. Multiple wafer placement plates are evenly spaced on the chain plates of the first chain plate conveyor and the second chain plate conveyor. Each wafer placement plate is provided with a wafer placement groove, and a vacuum suction cup is provided in each wafer placement groove.

[0007] The two visual imaging detection units are respectively installed on the first chain conveyor and the second chain conveyor;

[0008] The two vision imaging detection units are used to detect defects on the front and back sides of a single wafer placement board during continuous movement.

[0009] As a preferred embodiment of this example, the visual imaging detection unit includes a visual imaging detection head mounted on a U-shaped plate, a mounting plate with a limiting rod, a contact rod slidably mounted on the side of the wafer placement plate, and an arc-shaped plate that drives the contact rod to extend and retract relative to the wafer placement plate.

[0010] A sliding plate is fixed to the side wall of the U-shaped plate, and the sliding plate is slidably sleeved on the limiting rod;

[0011] The contact rod is connected to the wafer placement plate via a connecting spring located in the inner cavity of the wafer placement plate. The lower end of the contact rod is provided with two rotating rods that rotate relative to each other, and a limiting gap is formed between the two rotating rods. This limiting gap is consistent with the thickness of the arc plate. A first elastic magnetic pad is installed on the contact surface where the contact rod contacts the side end of the U-shaped plate.

[0012] The bottom of both lower ends of the U-shaped plate is equipped with ball bearings.

[0013] A return spring is installed on the end of the mounting plate away from the slide plate, which can form a pressing contact with the end face of the slide plate;

[0014] The side end of the skateboard and the mounting plate are respectively provided with a third elastic magnetic pad and a second elastic magnetic pad.

[0015] As a preferred embodiment of this invention, a deceleration unit is also included to decelerate the U-shaped plate that is performing the reset movement, so that it smoothly returns to its original position and stops moving.

[0016] In a preferred embodiment of this invention, the deceleration unit includes a deceleration magnet mounted on the mounting strip of the mounting plate and a permanent magnet mounted on the outer wall of the slide plate. The deceleration magnet and the permanent magnet are arranged opposite to each other and have the same magnetic poles at their opposite ends. Both the deceleration magnet and the permanent magnet are disposed inside a U-shaped magnetic shield, and the deceleration magnet is disposed away from the reset spring.

[0017] In a preferred embodiment of this invention, the deceleration magnet includes a plurality of deceleration permanent magnets arranged in a straight line. The magnetism of the plurality of deceleration permanent magnets gradually increases, and the magnetism of the deceleration magnet decreases as it approaches the reset spring.

[0018] As a preferred embodiment of this invention, a magnetic shielding unit is also included to shield the magnetic force between the deceleration magnet and the permanent magnet.

[0019] In a preferred embodiment of this invention, the magnetic shielding unit includes a magnetic shielding plate that extends laterally through the magnetic shielding cover containing the permanent magnet, and a first baffle and a second baffle respectively disposed on the mounting strip. The magnetic shielding plate is provided with a magnetic permeable hole adapted to the permanent magnet. Both ends of the magnetic shielding plate are provided with a semi-circular elastic positioning post. Both sides of the magnetic shielding cover are provided with positioning plates, and the positioning plates are provided with positioning grooves adapted to the elastic positioning posts.

[0020] In summary, the technical effects and advantages of this invention are as follows:

[0021] 1. The present invention has a reasonable structure and can continuously and uninterruptedly perform visual defect detection on both sides of the wafer, which can greatly improve the detection efficiency.

[0022] 2. In this invention, a deceleration unit is provided, which, together with the second and third elastic magnetic pads, enables the U-shaped plate to stop moving quickly and smoothly.

[0023] 3. The present invention also includes a magnetic shielding unit. When the U-shaped plate moves close to the return spring, it can shield the magnetic force of the deceleration section, reduce the movement resistance of the wafer placement plate, reduce the conveying energy consumption of the conveyor, and prevent the U-shaped plate from constantly changing its relative displacement to the wafer. This is beneficial for quickly forming a clear image and improving detection accuracy. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0026] Figure 2 for Figure 1 A magnified schematic diagram of the central part of the structure;

[0027] Figure 3 for Figure 2 Schematic diagram of the partial split structure in the middle;

[0028] Figure 4 for Figure 3 Exploded view of the wafer placement board;

[0029] Figure 5 for Figure 3 Schematic diagram of the mounting plate structure;

[0030] Figure 6 for Figure 3A magnified schematic diagram of a portion of the sliding plate structure;

[0031] Figure 7 This is a schematic diagram of the magnetic shielding unit structure;

[0032] Figure 8 Figure 7 A magnified schematic diagram of the central part of the structure.

[0033] In the diagram: 1. First chain conveyor; 2. Second chain conveyor; 3. Wafer placement plate; 4. Vacuum chuck; 5. Visual imaging inspection unit; 51. U-shaped plate; 52. Visual imaging inspection head; 53. Slide plate; 54. Mounting plate; 55. Limiting rod; 56. Return spring; 57. Contact rod; 58. First elastic magnetic pad; 59. Rotating rod; 510. Connecting spring; 511. Arc plate; 512. Second elastic magnetic pad; 513. Deceleration magnet; 514. Permanent magnet; 6. First baffle; 7. Second baffle; 8. Magnetic shielding plate; 9. Magnetic perforation hole; 10. Elastic positioning post; 11. Positioning plate. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Example: Reference Figures 1-2 The wafer double-sided continuous visual inspection equipment shown includes a first chain conveyor 1, a second chain conveyor 2, and two sets of visual imaging inspection units 5;

[0036] The first chain plate conveyor 1 is located above the second chain plate conveyor 2. Multiple wafer placement plates 3 are evenly spaced on the chain plates of the first chain plate conveyor 1 and the second chain plate conveyor 2, and each wafer placement plate 3 is provided with a wafer placement groove. A vacuum suction cup 4 is provided in each wafer placement groove.

[0037] The two visual imaging detection units 5 are respectively installed on the first chain conveyor 1 and the second chain conveyor 2;

[0038] The two visual imaging detection units 5 are respectively used to detect defects on the front and back sides of a single wafer placement plate 3 during continuous movement.

[0039] Before use, two bearing mounting seats are set on the first chain plate conveyor 1 and the second chain plate conveyor 2. Robotic arms are installed on the bearing mounting seats respectively. One of the two robotic arms on the first chain plate conveyor 1 is used for feeding and the other is used to remove the wafers that are not qualified on the front. One of the two robotic arms on the second chain plate conveyor 2 is used for unloading and the other is used to remove the wafers that are not qualified on the back.

[0040] In use, the first chain conveyor 1 and the second chain conveyor 2 are distributed along... Figure 1 The first chain conveyor 1 moves in the direction corresponding to the arrow in the diagram. The movement direction of the first chain conveyor 1 is opposite to that of the second chain conveyor 2 (their movement speeds are consistent, allowing the wafer placement groove on the lower part of the first chain conveyor 1 to align with the corresponding wafer placement groove on the upper part of the second chain conveyor 2). A robotic arm places the wafer into the wafer placement groove, and a vacuum suction cup holds the wafer in place. The first chain conveyor 1 and the second chain conveyor 2 operate continuously. The visual imaging detection unit 5 on the first chain conveyor 1 inspects the front side of the wafer. Wafers with a qualified front side are detected. The wafer will move to the bottom of the chain plate and align with the wafer placement groove above the second chain plate conveyor 2. At this point, the vacuum suction cup 4 releases its grip on the wafer, and the wafer falls into the wafer placement groove below due to gravity. The vacuum suction cup in the wafer placement groove is then controlled to fix the wafer, with one side facing up. The reverse side of the wafer is then detected by the visual imaging detection unit on the second chain plate conveyor 2. Both sides of the wafer can be detected. Throughout the entire detection process, the first chain plate conveyor 1 and the second chain plate conveyor 2 do not stop, thereby improving the efficiency of wafer front and back detection.

[0041] As a preferred embodiment of this example, Figures 1-5 As shown, the visual imaging detection unit 5 includes a visual imaging detection head 52 mounted on a U-shaped plate 51, a mounting plate 54 with a limiting rod 55 mounted on it, a contact rod 57 slidably mounted on the side of the wafer placement plate 3, and an arc plate 511 that drives the contact rod 57 to extend and retract relative to the wafer placement plate 3.

[0042] A sliding plate 53 is fixed on the side wall of the U-shaped plate 51, and the sliding plate 53 is slidably sleeved on the limiting rod 55;

[0043] The contact rod 57 is connected to the wafer placement plate 3 via a connecting spring 510 located in the inner cavity of the wafer placement plate 3. The lower end of the contact rod 57 is provided with two rotating rods 59 that rotate relative to each other, and a limiting gap is formed between the two rotating rods 59. The limiting gap is consistent with the thickness of the arc plate 511. A first elastic magnetic pad 58 is installed on the contact surface where the contact rod 57 contacts the side end of the U-shaped plate 51.

[0044] The bottom of both lower ends of the U-shaped plate 51 is provided with ball bearings;

[0045] A return spring 56 is installed on the end of the mounting plate 54 away from the slide plate 53, which can form a pressing contact with the end face of the slide plate 53;

[0046] The side end of the slide plate 53 and the mounting plate 54 are respectively provided with a third elastic magnetic pad and a second elastic magnetic pad 512.

[0047] Before testing, the U-shaped plate 51 is stably set on the frame of the first chain plate conveyor 1 (second chain plate conveyor 2) by the magnetic attraction between the third elastic magnetic pad and the second elastic magnetic pad 512.

[0048] When the wafer is transported directly below the visual imaging inspection unit 5, the contact rod 57 will contact the side end of the U-shaped plate 51. As the wafer placement plate 3 moves, it will cause the U-shaped plate 51 to move closer to the reset spring 56 (at this time, the wafer and the visual imaging inspection head move at the same speed, i.e., relatively stationary). As the U-shaped plate 51 gets closer and closer to the reset spring 56, the inspection is completed just before the slide plate 53 contacts the reset spring 56. When the slide plate 53 contacts the reset spring 56, the upper end of the arc-shaped plate 511 moves into the limiting gap. As the contact rod 57 moves along the path of the arc-shaped plate 511, it can cause the contact rod 57 to press against the connecting spring 510, i.e., the connection... The contact rod 57 moves toward the inner cavity of the wafer placement plate 3. After the contact rod 57 separates from the side end of the U-shaped plate 51, the U-shaped plate 51 is quickly moved in the opposite direction by the elastic force of the reset spring 56. The U-shaped plate 51 is buffered and fixed by the third elastic magnetic pad and the second elastic magnetic pad 512, so that the U-shaped plate 51 quickly changes from a moving state to a stable stationary state, which is conducive to the subsequent smooth contact with the contact rod 57 (correspondingly improving the detection efficiency). After the U-shaped plate 54 returns to its original position, the next contact rod 57 contacts the side end of the U-shaped plate 51 and pushes it to move. This process is repeated to form continuous detection, which can greatly improve the detection efficiency.

[0049] It is important to note the following: First, the lower end of the U-shaped plate 51 slides in contact with the upper end of the frame of the first chain conveyor 1 (second chain conveyor 2); the mounting plate 54 and the arc plate 511 are both mounted on the frame; Second, a first elastic magnetic pad 58 is provided, which can generate a magnetic attraction with the U-shaped plate 61, thereby preventing the U-shaped plate 51 from separating from the contact rod during the process of the contact rod pushing the U-shaped plate 51 to move. Such separation would cause a change in the relative displacement between the visual imaging detection head and the wafer, which is not conducive to clear imaging and improving detection accuracy; Third, shortly after the U-shaped plate 51 makes a reverse recovery movement, its arc plate 511 moves out of the limit gap. At this time, the contact rod 57 returns to its original position through the elastic force of the connecting spring 510; Fourth, all electrical equipment is electrically connected to the industrial control computer.

[0050] As a preferred embodiment of this invention, a deceleration unit is also included to decelerate the U-shaped plate 51 that is performing the reset movement, so that it smoothly returns to its original position and stops moving.

[0051] The U-shaped plate 51 is restored to its original position by the elastic force of the return spring 56. To ensure that the U-shaped plate 51 returns to its original position quickly, a return spring 56 with a large elastic coefficient can be used so that the U-shaped plate 51 can obtain a large reverse thrust, thereby increasing the movement speed of the U-shaped plate 51 (which is beneficial to improving detection efficiency). The second elastic magnetic pad 512 and the third elastic magnetic pad cannot make the U-shaped plate 51 stop quickly and smoothly. Therefore, a deceleration unit is set up. In conjunction with the second elastic magnetic pad 512 and the third elastic magnetic pad, the U-shaped plate 51 can stop moving quickly and smoothly.

[0052] As a preferred embodiment of this example, Figure 3 , Figure 5 and Figure 6 As shown, the deceleration unit includes a deceleration magnet 513 mounted on the mounting strip of the mounting plate 54 and a permanent magnet 514 mounted on the outer wall of the slide plate 53. The deceleration magnet 513 and the permanent magnet 514 are arranged opposite to each other, and the magnetic poles at the opposite ends are the same. Both the deceleration magnet 513 and the permanent magnet 514 are arranged inside the U-shaped magnetic shield. The deceleration magnet 513 is arranged away from the reset spring 56.

[0053] The repulsive force between the decelerating magnet 513 and the permanent magnet 514 rapidly decelerates the moving U-shaped plate 51. In conjunction with the second elastic magnetic pad 512 and the third elastic magnetic pad, the U-shaped plate 51 can be brought to a quick and smooth stop.

[0054] It should be noted that the deceleration magnet 513 is positioned away from the reset spring 56. This is to extend the distance the magnet travels before decelerating the U-shaped plate 51, which helps the U-shaped plate 51 return to its original position quickly after passing through this distance, reduces the interval time for the U-shaped plate 51 to return to its original position, and improves detection efficiency.

[0055] As a preferred embodiment of this invention (not shown in the figure), the deceleration magnet 513 includes several deceleration permanent magnets arranged in a straight line. The magnetism of the multiple deceleration permanent magnets gradually increases, and the magnetism of the deceleration magnet 513 decreases as it approaches the reset spring 56.

[0056] During the reset motion of the U-shaped plate 51, the magnetism of the deceleration permanent magnet gradually increases along its deceleration path, thereby achieving a continuous and gradually increasing deceleration effect on the U-shaped plate. This method is smoother than constant high-intensity magnetism and is more conducive to the stability of the electronic components inside the visual imaging detection head (sudden deceleration may cause components, connectors or cables on the circuit board to be subjected to excessive inertial forces, thus loosening or falling off; sudden deceleration may generate electromagnetic pulses or transient electromagnetic fields, and these electromagnetic interferences may enter the device through conduction or radiation, causing interference or damage to the signals in the circuit).

[0057] As a preferred embodiment of this invention, a magnetic shielding unit is also included to shield the magnetic interaction between the deceleration magnet 513 and the permanent magnet 514.

[0058] A magnetic shielding unit is set up so that when the U-shaped plate 51 moves to reset, there is a magnetic force between its deceleration magnet 513 and the permanent magnet 514. When the U-shaped plate 51 returns to its original position and moves closest to the reset spring 56, there is little or no magnetic resistance between the deceleration magnet 513 and the permanent magnet 514. The advantages are: first, it reduces the movement resistance of the wafer placement plate 3 and reduces the conveyor's energy consumption; second, when the U-shaped plate 51 moves close to the reset spring 56 and is subjected to magnetic force in this deceleration section, the squeezing force between the U-shaped plate 51 and the first elastic magnetic pad 58 on the surface of the contact rod 57 will change (the first elastic magnetic pad will deform to varying degrees), which will cause the displacement of the U-shaped plate 51 relative to the wafer to change continuously. This is not conducive to the visual imaging detection head quickly forming a clear image, and it is not conducive to improving detection efficiency and detection accuracy. Therefore, a magnetic shielding unit is set up to shield the magnetic force, which is conducive to quickly forming a clear image and improving detection accuracy.

[0059] As a preferred embodiment of this example, Figure 7 and Figure 8As shown, the magnetic shielding unit includes a magnetic shielding plate 8 that extends laterally through the magnetic shielding cover containing the permanent magnet 514, and a first baffle 6 and a second baffle 7 respectively disposed on the mounting strip. The magnetic shielding plate 8 is provided with a magnetic permeable hole 9 adapted to the permanent magnet 514. Both ends of the magnetic shielding plate 8 are provided with a semi-circular elastic positioning post 10. Both sides of the magnetic shielding cover are provided with positioning plates 11, and the positioning plates 11 are provided with positioning grooves adapted to the elastic positioning posts 10.

[0060] like Figure 7 and Figure 8 As shown, initially, the permanent magnet 514 is shielded by the magnetic shielding plate 8. At this time, the right end of the magnetic shielding plate 514 is in contact with the second baffle 7 and is fixed to the positioning plate 11 by the elastic positioning post 10 on the right side. After the permanent magnet 514 passes through the deceleration section, the left end of the magnetic shielding plate 8 is in contact with the first baffle 6, causing the magnetic shielding plate 8 to move relative to the permanent magnet 514. When the magnetic hole 9 is directly opposite the permanent magnet 514, the elastic positioning post 10 on the left side is fixed to the positioning plate 11 on the left side, and the contact rod 57 is separated from the U-shaped plate 51. The U-shaped plate 51 performs a reset movement. After passing through the deceleration section, it is decelerated to a stable stationary state by magnetic force. During this process, the second baffle 7 is in contact with the magnetic shielding plate 8 and causes it to move relative to the permanent magnet 51, shielding the permanent magnet 514 and thus isolating the magnetism of the permanent magnet 514.

[0061] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A wafer double-sided continuous visual inspection device, characterized in that: It includes a first chain plate conveyor (1), a second chain plate conveyor (2), and two sets of visual imaging detection units (5); The first chain plate conveyor (1) is located above the second chain plate conveyor (2). Multiple wafer placement plates (3) are evenly spaced on the chain plates of the first chain plate conveyor (1) and the second chain plate conveyor (2). Each wafer placement plate (3) is provided with a wafer placement groove, and a vacuum suction cup (4) is provided in each wafer placement groove. The two visual imaging detection units (5) are respectively installed on the first chain conveyor (1) and the second chain conveyor (2); The two visual imaging detection units (5) are used to detect defects on the front and back sides of a single wafer placement plate (3) during continuous movement, respectively; The visual imaging detection unit (5) includes a visual imaging detection head (52) mounted on a U-shaped plate (51), a mounting plate (54) with a limiting rod (55) mounted on it, a contact rod (57) slidably mounted on the side of the wafer placement plate (3), and an arc plate (511) that drives the contact rod (57) to extend and retract relative to the wafer placement plate (3). A sliding plate (53) is fixed on the side wall of the U-shaped plate (51), and the sliding plate (53) is slidably sleeved on the limiting rod (55); The contact rod (57) is connected to the wafer placement plate (3) via a connecting spring (510) located in the inner cavity of the wafer placement plate (3). The lower end of the contact rod (57) is provided with two rotating rods (59) that rotate relative to each other, and a limiting gap is formed between the two rotating rods (59). The limiting gap is consistent with the thickness of the arc plate (511). A first elastic magnetic pad (58) is installed on the contact surface where the contact rod (57) contacts the side end of the U-shaped plate (51). The bottom of both lower ends of the U-shaped plate (51) is provided with ball bearings; A return spring (56) that can form a pressing contact with the end face of the slide plate (53) is installed on the mounting plate (54) at one end away from the slide plate (53). The side end of the slide plate (53) and the mounting plate (54) are respectively provided with a third elastic magnetic pad and a second elastic magnetic pad (512).

2. The wafer double-sided continuous visual inspection equipment according to claim 1, characterized in that: It also includes a deceleration unit for decelerating the U-shaped plate (51) that is performing the reset movement, so that it can smoothly return to its original position and stop moving.

3. The wafer double-sided continuous visual inspection equipment according to claim 2, characterized in that: The deceleration unit includes a deceleration magnet (513) mounted on the mounting strip of the mounting plate (54) and a permanent magnet (514) mounted on the outer wall of the slide plate (53). The deceleration magnet (513) and the permanent magnet (514) are arranged opposite to each other and have the same magnetic poles at opposite ends. Both the deceleration magnet (513) and the permanent magnet (514) are arranged inside the U-shaped magnetic shield. The deceleration magnet (513) is arranged away from the reset spring (56).

4. The wafer double-sided continuous visual inspection equipment according to claim 3, characterized in that: The deceleration magnet (513) includes several deceleration permanent magnets arranged in a line. The magnetism of the multiple deceleration permanent magnets gradually increases, and the magnetism of the deceleration magnet (513) decreases as it approaches the reset spring (56).

5. The wafer double-sided continuous visual inspection equipment according to claim 4, characterized in that: It also includes a magnetic shielding unit for shielding the magnetic interaction between the decelerating magnet (513) and the permanent magnet (514).

6. The wafer double-sided continuous visual inspection equipment according to claim 5, characterized in that: The magnetic shielding unit includes a magnetic shielding plate (8) that runs horizontally through the magnetic shielding cover where the permanent magnet (514) is located, and a first baffle (6) and a second baffle (7) respectively set on the mounting strip. The magnetic shielding plate (8) is provided with a magnetic permeable hole (9) adapted to the permanent magnet (514). Both ends of the magnetic shielding plate (8) are provided with a semi-circular elastic positioning post (10). Both sides of the magnetic shielding cover are provided with positioning plates (11), and the positioning plates (11) are provided with positioning grooves adapted to the elastic positioning posts (10).

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