Vacuum coating process and coating device suitable for ultra-thin film layer circuit board

Abstract

The application discloses a vacuum coating process and a coating device suitable for an ultra-thin film layer circuit board in the technical field of vacuum coating, and relates to the technical field of vacuum coating. The process comprises the following steps: transferring a circuit board base material to a vacuum chamber, inputting argon into the vacuum chamber, ionizing the argon into positively charged argon ions, and accelerating the positively charged argon ions to move to the surface of a target material with negative charges under the action of an electric field, and knocking out the evaporation material atoms or molecules on the surface of the target material. The positively charged argon ions are accelerated by the electric field to bombard the surface of the target material, the molecules of the evaporation material on the target material release a high-energy particle stream with high kinetic energy, the particles move along irregular paths in a plasma environment, the complex structure of the circuit board, the fine gap, the edge and the three-dimensional surface are effectively covered, the particles quickly and uniformly form an ultra-thin film layer on the surface of the circuit board, the probability of uneven film thickness distribution caused by natural deposition of the vapor is reduced, and therefore the coating effect of the device is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of vacuum coating, in particular to a vacuum coating process and a coating device suitable for ultra-thin film layer circuit board. BACKGROUND

[0002] The vacuum coating process can be divided into physical vapor deposition and chemical vapor deposition according to different deposition technologies, wherein the physical vapor deposition includes vacuum evaporation, that is, the coating material is heated into vapor particles in a vacuum environment, and then the vapor particles are deposited on the surface of the circuit board to form an ultra-thin film on the surface of the circuit board. In the technical field of vacuum coating, the "ultra-thin film" mainly refers to a metal coating layer with a thickness of 0.1 microns to 1 micron (100 nanometers to 1000 nanometers).

[0003] With the development of lightweight and miniaturization of electronic equipment, the ultra-thin film layer circuit board is widely used due to its excellent conductivity and space utilization. The vacuum coating technology is a key process for preparing such thin films. However, the existing vacuum coating process and device rely on natural deposition to form a thin film on the surface of the circuit board substrate. The movement trajectory of the vapor particles is single (affected by gravity to deposit along a straight trajectory downward), and the electronic components on the surface of the circuit board substrate have a large number of edges and gaps and other structures, which will cause the deposited vapor particles to not reach the non-direct-viewing area of the circuit board substrate, resulting in uneven distribution of the circuit board substrate, and further affecting the coating effect of the circuit board substrate. SUMMARY

[0004] In order to overcome the shortcomings proposed in the background art, the present application provides a vacuum coating process and a coating device suitable for ultra-thin film layer circuit board.

[0005] The technical scheme is as follows: a vacuum coating process suitable for ultra-thin film layer circuit board, which is based on its coating device, and the coating process includes the following steps:

[0006] Step 1: Place the circuit board substrate into ultra-pure water with a flow rate of 0.4 m / s and rinse for 12 minutes, and then dry;

[0007] Step 2: Use anion airflow with a flow rate of 1.6 m / s to blow dust on the surface of the circuit board substrate for 2 minutes;

[0008] Step 3: Remove the static electricity from the cleaned circuit board substrate, and use an ion air gun to remove the surface charge of the circuit board;

[0009] Step 4: Transfer the circuit board substrate to the vacuum chamber, and pre-evacuate the vacuum chamber after transfer until the vacuum degree reaches 6x10 -3 pa;

[0010] Step 5: vacuum evaporation coating process is carried out, the heating temperature is controlled at 250-300℃, so that the vacuum chamber generates the evaporation material required for film formation;

[0011] Step 6: input argon into the vacuum chamber, control the vacuum degree at 3x10 -1 pa-4x10 -1 pa, turn on the magnetron sputtering power supply, and control the voltage at 300-600V, ionize the argon into positively charged argon ions and free charges;

[0012] Step 7: the positively charged argon ions accelerate to the surface of the target material with negative charge under the action of the electric field, knock out the evaporation material atoms or molecules on the surface of the target material, assist the movement and deposition of the particles knocked out on the surface of the circuit board substrate, and gradually form a uniform ultra-thin film layer on the surface of the circuit board substrate;

[0013] Step 8: after the vacuum coating is completed, restore the atmospheric pressure in the vacuum chamber and turn off the power supply.

[0014] A coating device suitable for ultra-thin film layer circuit board is also provided, which is applied to the vacuum coating process suitable for ultra-thin film layer circuit board. The coating device comprises a shell, the shell is rotatably connected with an electric control door, the shell is rotatably connected with an electric control rotating frame in the shell, the electric control rotating frame is fixedly connected with a plurality of connecting frames, all the connecting frames are commonly fixedly connected with a plurality of upper fixed frames which are distributed in an upper and lower interval, the lower side of the upper fixed frame is provided with a plurality of upper fixed hooks which are distributed in a rectangular array, all the connecting frames are commonly slidably connected with a plurality of lower sliding frames which are distributed in an upper and lower interval, the upper side of the lower sliding frame is provided with a plurality of lower fixed hooks which are distributed in a rectangular array, all the upper fixed frames and all the lower sliding frames are alternately and interval distributed, the number of the lower fixed hooks on the lower sliding frame is the same as the number of the upper fixed hooks on the upper fixed frame, the lower sliding frame and one of the connecting frames are fixedly connected with an elastic piece, the shell is fixedly connected with guide blocks which are distributed in an upper and lower interval and have the same number as the lower sliding frames, and the guide blocks are used for guiding the adjacent lower sliding frames.

[0015] Further, the guide blocks distributed in an upper and lower interval are distributed in a staggered manner, so that different guide blocks guide the adjacent lower sliding frames in sequence.

[0016] Further, the moving distance of the lower fixed hook is less than the distance between the adjacent two upper fixed hooks above it.

[0017] Further, the upper fixed hook is rotatably connected between the adjacent upper fixed frames, and the lower fixed hook is fixedly connected with a tension spring between the adjacent lower sliding frames.

[0018] Further, the upper fixed hook is provided with a cylindrical guide portion.

[0019] Further, the guiding part is fixed with a flexible block.

[0020] Further, the diameter of the flexible block gradually increases from the position close to the adjacent upper fixed hook to the position far away from the adjacent upper fixed hook.

[0021] Further, the upper fixed frame is provided with the same number of flow-through parts as the number of the upper fixed hooks.

[0022] Further, the flow-through part is aligned with the corresponding guiding part.

[0023] Compared with the prior art, the present application has at least the following beneficial effects: 1. The present application uses positively charged argon ions to bombard the target surface after acceleration by an electric field, so that the molecules of the evaporated material on the target release a high-energy particle stream with high kinetic energy. These particles move along irregular paths in a plasma environment, effectively covering the fine gaps, edges, and three-dimensional surfaces of the complex structure of the circuit board, allowing the particles to quickly and uniformly form an ultra-thin film layer on the surface of the circuit board, reducing the probability of uneven film thickness distribution caused by natural deposition of the vapor, thereby improving the film plating effect of the device;

[0024] 2. The lower part of the circuit board substrate is moved by the lower fixed hook, causing the circuit board substrate to tilt, with its surface facing the direction of the falling vapor deposition, improving the efficiency of vapor deposition on the surface of the circuit board substrate, and allowing each layer of the circuit board to tilt in turn, reducing the shielding phenomenon of the upper layer of the circuit board substrate on the lower layer, thereby improving the uniformity of the film plating on the surface of each layer of the circuit board, reducing the probability of cracks in the plating layer of the upper layer of the circuit board substrate due to excessive thickness of the plating layer, and further improving the film plating efficiency of the device while ensuring the film plating effect of the device;

[0025] 3. The guiding part provides a horizontal movement space for the tilted circuit board substrate, allowing the circuit board substrate to move away from the position directly below the upper fixed hook, reducing the shielding area of the upper fixed hook on the circuit board substrate, and the flexible block provides resistance for the sliding of the circuit board substrate, reducing the probability of the circuit board substrate itself shaking, thereby improving the stability of the circuit board substrate during the film plating process, ensuring that the vapor material can be stably deposited everywhere on the circuit board substrate, and improving the uniformity of the film plating of the circuit board substrate. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a schematic diagram of the three-dimensional structure of the present application;

[0027] Figure 2 is a schematic diagram of the three-dimensional structure of the shell of the present application;

[0028] Figure 3 is a schematic diagram of the three-dimensional structure of the electric control rotating frame of the present application;

[0029] Figure 4 Fig. 1 is a perspective view of the upper fixed frame and the lower sliding frame of the present application;

[0030] Figure 5 Fig. 2 is a perspective view of the guide block of the present application;

[0031] Figure 6 Fig. 3 is a perspective view of the upper fixed hook and the lower fixed hook of the present application;

[0032] Figure 7 Fig. 4 is a perspective view of the flow-through part of the present application;

[0033] Figure 8 Fig. 5 is a perspective view of the flexible block of the present application.

[0034] Wherein: 1 - housing, 101 - electric control door, 2 - electric control rotating frame, 3 - connecting frame, 4 - upper fixed frame, 401 - upper fixed hook, 5 - lower sliding frame, 501 - lower fixed hook, 6 - elastic member, 7 - guide block, 8 - tension spring, 9 - flexible block, 10 - guide part, 11 - flow-through part. DETAILED DESCRIPTION

[0035] The present application will be described in detail below with reference to the accompanying drawings and examples.

[0036] Example 1

[0037] A vacuum coating process suitable for ultra-thin film layer circuit board, the vacuum coating process suitable for ultra-thin film layer circuit board is based on its coating device, and the coating process comprises the following steps:

[0038] Step 1: Place the circuit board substrate into ultra-pure water with a flow rate of 0.4 m / s for 12 min, and then dry;

[0039] Step 2: Use anion airflow with a flow rate of 1.6 m / s to clean the surface of the circuit board substrate for 2 min;

[0040] Step 3: Perform static removal on the cleaned circuit board substrate, and use an ion air gun to remove the surface charge of the circuit board;

[0041] Step 4: Transfer the circuit board substrate to the vacuum chamber, and perform pre-evacuation on the vacuum chamber until the vacuum degree reaches 6 x 10 -3 Pa;

[0042] Step 5: Perform vacuum evaporation coating treatment, and control the heating temperature at 250-300℃ to generate the evaporation material required for forming the thin film in the vacuum chamber;

[0043] Step 6: input argon into the vacuum chamber, control the vacuum degree at 3x10 -1 pa-4x10 -1 pa, turn on the magnetron sputtering power supply, and control the voltage at 300V-600V, ionize argon into positively charged argon ions and free charges;

[0044] Step 7: the positively charged argon ions accelerate to the surface of the target material with negative charge under the action of the electric field, knock out the evaporated material atoms or molecules on the surface of the target material, and assist the movement and deposition of the particles knocked out on the surface of the circuit board substrate, gradually forming a uniform ultra-thin film layer on the surface of the circuit board substrate;

[0045] Step 8: after the vacuum coating is completed, restore the atmospheric pressure in the vacuum chamber, and turn off the power supply.

[0046] Example 2

[0047] The existing circuit board substrate is mostly used in the static clamping method of multiple layers from top to bottom when coating, which will cause the vapor particles to be blocked by various protruding elements on the surface of the circuit board during vertical deposition, resulting in uneven distribution of the film thickness on the surface of the substrate, and the upper circuit board substrate will block the vapor deposition path of the lower circuit board substrate, resulting in poor coating effect of the lower circuit board substrate and over-thick coating of the upper circuit board, especially for ultra-thin film layers (thickness ≤100nm), slight thickness deviation may cause abnormal circuit impedance or stress cracking, thereby affecting the performance of the circuit board substrate after coating.

[0048] On the basis of example 1, a coating device suitable for ultra-thin film layer circuit board is applied to the vacuum coating process suitable for ultra-thin film layer circuit board, such as Figures 1-6As shown, the coating device comprises a shell 1, the shell 1 is provided with a control terminal not shown in the figure, the shell 1 is rotatably connected with an electric control door 101 electrically connected with the control terminal, the shell 1 is rotatably connected with an electric control rotating frame 2 electrically connected with the control terminal in the shell 1, the electric control rotating frame 2 is fixedly connected with a plurality of groups of connecting frames 3 distributed in a straight line from front to back, each group of connecting frames 3 has two left-right symmetrical distribution, the electric control rotating frame 2 is used to drive all the connecting frames 3 to rotate, all the connecting frames 3 are commonly fixedly connected with a plurality of upper fixed frames 4 distributed in an upper and lower interval, the number of upper fixed frames 4 in the figure is taken as an example, the lower side of the upper fixed frame 4 is provided with a plurality of upper fixed hooks 401 distributed in a rectangular array, all the connecting frames 3 are commonly connected with a plurality of lower sliding frames 5 distributed in an upper and lower interval, the number of lower sliding frames 5 in the figure is taken as an example, when the electric control rotating frame 2 drives all the connecting frames 3 to rotate, all the connecting frames 3 commonly drive all the upper fixed frames 4 and all the lower sliding frames 5 to rotate, the upper side of the lower sliding frame 5 is provided with a plurality of lower fixed hooks 501 distributed in a rectangular array, the upper fixed hook 401 is used to fix the upper part of the circuit board substrate, the lower fixed hook 501 is used to fix the lower part of the circuit board substrate, in this embodiment, the upper fixed hook 401 is fixedly connected with the adjacent upper fixed frame 4, the lower fixed hook 501 is fixedly connected with the adjacent lower sliding frame 5, all the upper fixed frames 4 and all the lower sliding frames 5 are alternately and interval distributed, the number of upper fixed hooks 401 on the upper fixed frame 4 is the same as the number of lower fixed hooks 501 on the lower sliding frame 5, the lower sliding frame 5 and one of the connecting frames 3 are fixedly connected with an elastic element 6, wherein the elastic element 6 can be a compression spring or an elastic block, when the lower sliding frame 5 moves to the left due to the right side being pressed, the elastic element 6 is deformed under pressure, when the right side of the lower sliding frame 5 is no longer blocked, the elastic element 6 rebounds and drives the adjacent lower fixed hook 501 to reset, the shell 1 is fixedly connected with guide blocks 7 distributed in an upper and lower direction and the number of which is the same as that of the lower sliding frames 5, for example, the right side guide block 7, the thickness of the right side guide block 7 gradually thickens from the front and back sides to the middle, when the lower sliding frame 5 rotates to contact the adjacent guide block 7, the lower sliding frame 5 continues to rotate and moves along the surface of the adjacent guide block 7, the guide block 7 guides the adjacent lower sliding frame 5, so that the lower fixed hook 501 moves horizontally in the rotating process, the guide blocks 7 distributed in an upper and lower direction are distributed in a staggered manner, all the guide blocks 7 are sequentially arranged in a counterclockwise direction from top to bottom, wherein the counterclockwise direction is taken as the reference for the plan view, so that different guide blocks 7 sequentially guide the adjacent lower sliding frame 5, respectively, Figure 1 the plan view is taken as the reference, so that different guide blocks 7 sequentially guide the adjacent lower sliding frame 5, respectively, Figure 1The top view is the reference of the rotating direction, and taking the example of the counterclockwise rotation of all the upper fixed frames 4 and all the lower sliding frames 5 driven by the electric control rotating frame 2 through the connecting frames 3, the upper first lower sliding frame 5 first contacts the adjacent guide block 7 in the counterclockwise rotating process, so that the upper first lower sliding frame 5 moves horizontally in the rotating process, then the upper second lower sliding frame 5 contacts the adjacent guide block 7 in the counterclockwise rotating process, the upper second lower sliding frame 5 moves horizontally in the rotating process, and so on, all the lower sliding frames 5 move horizontally from top to bottom in the rotating process, and the moving distance of the lower fixed hook 501 is less than the distance between the two adjacent upper fixed hooks 401 above it, in the process of the vapor depositing on the surface of the circuit board substrate, when the lower fixed hook 501 drives the lower part of the circuit board substrate to move left, the circuit board substrate tilts, reducing the shielding of the upper fixed hook 401 to the circuit board substrate.

[0049] The specific working principle is as follows:

[0050] When the operator needs to use the device to perform film plating on a plurality of circuit board substrates at the same time, the operator opens the electric control door 101 through the control terminal, rotates and opens the electric control door 101, inserts the lower part of the pretreated circuit board substrate into the fixed hook of the lower fixed hook 501, and hangs the upper part of the circuit board substrate on the fixed hook of the upper fixed hook 401, so that all the circuit board substrates are fixed between the corresponding upper fixed hooks 401 and lower fixed hooks 501, and then the electric control door 101 is rotated and reset through the control terminal, and the electric control door 101 is closed.

[0051] After the electric control door 101 is closed, the operator opens the electric control rotating frame 2 through the control terminal, the electric control rotating frame 2 drives all the connecting frames 3 to rotate, all the connecting frames 3 jointly drive all the upper fixed frames 4 and all the lower sliding frames 5 to rotate, and the upper and lower distributed lower sliding frames 5 are in contact with the adjacent guide blocks 7 in turn in the rotating process of all the lower sliding frames 5, taking the example of the contact of the upper lower sliding frame 5 with the guide block 7, the upper lower sliding frame 5 gradually contacts and is extruded by the guide block 7 with the rotation of the lower sliding frame 5, so that the upper lower sliding frame 5 moves left, the upper elastic member 6 is deformed under pressure, and the upper lower sliding frame 5 drives all the lower fixed hooks 501 above it to move left, with the rotation of all the lower sliding frames 5, all the lower sliding frames 5 move horizontally from top to bottom in the rotating process.

[0052] When the upper side lower sliding frame 5 drives all the lower fixed hooks 501 on it to move left, the lower fixed hooks 501 drive the lower part of the circuit board substrate to move left, so that the lower part of the circuit board substrate is inclined to the left, the circuit board is inclined and actively contacts the deposited vapor, improves the efficiency of the vapor deposited on the surface of the circuit board substrate, and by making each layer of circuit board distributed in turn to produce inclination, the upper layer of circuit board substrate reduces the shielding of the lower layer of circuit board, thereby improving the uniformity of the surface plating film of each layer of circuit board, so as to reduce the probability of the upper layer of circuit board substrate cracking due to the excessive thickness of the plating film, which causes the internal stress of the plating layer to be too large, thereby improving the plating efficiency of the device while ensuring the plating effect of the device.

[0053] When the circuit board plating is completed, the operator closes the electric control rotating frame 2 and opens the electric control door 101 through the control terminal, so that the electric control door 101 is turned on and the circuit board substrate with completed plating is taken out, then the inside of the shell 1 is cleaned for the next use, and finally the electric control door 101 is closed.

[0054] Example 3

[0055] The existing circuit board substrate is shielded by the fixed structure above the circuit board substrate during the plating process, so that the vapor particles cannot be deposited on the shielded part of the circuit board substrate, thereby affecting the plating effect of the circuit board substrate.

[0056] Based on example 2, such as Figure 4 and Figures 6-8As shown in the above embodiment, the upper fixing hook 401 is fixedly connected with the adjacent upper fixing frame 4 and the lower fixing hook 501 is fixedly connected with the adjacent lower sliding frame 5, in the embodiment, the upper fixing hook 401 is rotatably connected with the adjacent upper fixing frame 4, and the lower fixing hook 501 is fixedly connected with the adjacent lower sliding frame 5 and provided with a tension spring 8, when the lower sliding frame 5 moves horizontally, the lower sliding frame 5 drives all the lower fixing hooks 501 to move, the lower fixing hook 501 and the upper fixing hook 401 move relatively, the circuit board substrate is inclined, the upper fixing hook 401 rotates, the tension spring 8 is stretched, the probability of the circuit board substrate moving by itself is reduced, the stability of the circuit board substrate in the plating process is improved, the vapor material can be stably deposited on the circuit board substrate, the uniformity of the plating of the circuit board substrate is improved, the upper fixing hook 401 is provided with a cylindrical guide part 10, when the upper fixing hook 401 rotates, the axis of the guide part 10 is parallel to the horizontal plane, when the lower fixing hook 501 moves to the left to drive the lower part of the circuit board substrate to move, the upper part of the circuit board substrate can move horizontally along the transversely arranged guide part 10, the shielding area of the upper fixing hook 401 to the circuit board substrate is reduced, the guide part 10 is fixedly connected with a flexible block 9, the flexible block 9 is circular table-shaped, the diameter of the flexible block 9 gradually increases from right to left, when the circuit board moves to the flexible block 9, the flexible block 9 is deformed under pressure, the flexible block 9 provides resistance for the sliding of the circuit board substrate, the shaking amplitude of the circuit board in the moving process is reduced, and the stability of the circuit board substrate is improved.

[0057] As Figure 5 With Figure 7 As shown in the above embodiment, the upper fixing hook 401 is fixedly connected with the adjacent upper fixing frame 4 and the lower fixing hook 501 is fixedly connected with the adjacent lower sliding frame 5, in the embodiment, the upper fixing hook 401 is rotatably connected with the adjacent upper fixing frame 4, and the lower fixing hook 501 is fixedly connected with the adjacent lower sliding frame 5 and provided with a tension spring 8, when the lower sliding frame 5 moves horizontally, the lower sliding frame 5 drives all the lower fixing hooks 501 to move, the lower fixing hook 501 and the upper fixing hook 401 move relatively, the circuit board substrate is inclined, the upper fixing hook 401 rotates, the tension spring 8 is stretched, the probability of the circuit board substrate moving by itself is reduced, the stability of the circuit board substrate in the plating process is improved, the vapor material can be stably deposited on the circuit board substrate, the uniformity of the plating of the circuit board substrate is improved, the upper fixing hook 401 is provided with a cylindrical guide part 10, when the upper fixing hook 401 rotates, the axis of the guide part 10 is parallel to the horizontal plane, when the lower fixing hook 501 moves to the left to drive the lower part of the circuit board substrate to move, the upper part of the circuit board substrate can move horizontally along the transversely arranged guide part 10, the shielding area of the upper fixing hook 401 to the circuit board substrate is reduced, the guide part 10 is fixedly connected with a flexible block 9, the flexible block 9 is circular table-shaped, the diameter of the flexible block 9 gradually increases from right to left, when the circuit board moves to the flexible block 9, the flexible block 9 is deformed under pressure, the flexible block 9 provides resistance for the sliding of the circuit board substrate, the shaking amplitude of the circuit board in the moving process is reduced, and the stability of the circuit board substrate is improved.

[0058] Finally, it should be noted that: the above is only the preferred embodiment of the present application, and is not used to limit the present application, although the present application is described in detail by referring to the foregoing embodiments, for those skilled in the art, the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced, any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application, should be included in the protection scope of the present application.

Claims

1. A coating apparatus suitable for ultra-thin film circuit boards, the coating apparatus comprising a housing (1), wherein an electrically controlled door (101) is rotatably connected to the housing (1), and an electrically controlled rotating frame (2) is rotatably connected inside the housing (1), characterized in that, The electrically controlled rotating frame (2) is fixedly connected to several connecting frames (3). All the connecting frames (3) are fixedly connected to several upper fixed frames (4) that are spaced apart vertically. Several upper fixed hooks (401) are arranged in a rectangular array on the lower side of the upper fixed frame (4). All the connecting frames (3) are slidably connected to several lower sliding frames (5) that are spaced apart vertically. Several lower fixed hooks (501) are arranged in a rectangular array on the upper side of the lower sliding frame (5). All the upper fixed frames (4) and all the lower sliding frames (5) are alternately spaced apart. The number of lower fixed hooks (501) on the lower sliding frame (5) is the same as the number of upper fixed hooks (401) on the upper fixed frame (4). An elastic element (6) is fixedly connected between the lower sliding frame (5) and one of the connecting frames (3). A guide block (7) is fixedly connected inside the outer shell (1) and is arranged vertically and in the same number as the number of lower sliding frames (5). The guide block (7) is used to guide the adjacent lower sliding frames (5). The guide blocks (7) distributed vertically are staggered so that different guide blocks (7) guide the adjacent lower sliding frames (5) in turn. The upper fixed hook (401) is rotatably connected to the adjacent upper fixed frame (4), and the lower fixed hook (501) is fixedly connected to the adjacent lower sliding frame (5) by a tension spring (8). The upper fixing frame (4) is provided with a number of flow sections (11) that are the same as the number of the upper fixing hooks (401) mentioned above. The upper fixing hook (401) is provided with a cylindrical guide part (10). The flow section (11) is aligned with the corresponding guide section (10); The moving distance of the lower fixed hook (501) is less than the distance between the two adjacent upper fixed hooks (401) above it.

2. The coating apparatus for ultra-thin film circuit boards according to claim 1, characterized in that, The guide part (10) is fixedly connected to a flexible block (9).

3. The coating apparatus for ultra-thin film circuit boards according to claim 2, characterized in that, The diameter of the flexible block (9) gradually increases from the point near the adjacent upper fixing hook (401) to the point far away.

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