Film expanding and cutting knife device used after wafer cutting

Abstract

A film expanding and cutting knife device after wafer cutting belongs to the technical field of wafer production auxiliary equipment, and comprises a PLC (Programmable Logic Controller), a limiting ring, a rack, an inner ring table tray mechanism, an outer ring table tray mechanism and a cutting knife mechanism, the limiting ring, the inner ring table tray mechanism, the outer ring table tray mechanism, the cutter mechanism and the rack are installed together, the inner ring table tray mechanism comprises multiple sets of air cylinders, a fixing plate, an outer limiting ring, a top plate, a lead screw driving motor and linear bearings, and the linear bearings and the air cylinders are arranged; the outer ring table plate mechanism comprises an air cylinder A, a linear bearing A, a servo motor, a driving belt wheel, a driven belt wheel, a lower fixing plate, a lower ring and a supporting plate. According to the utility model, a worker only needs to place an outer ring, an inner ring and a film-pasted wafer with a film pasting frame on corresponding stations, and then the equipment can automatically complete the processes of stretching and film expanding, edge cutting and film pasting frame separation, so that convenience is brought to the worker, the working efficiency is improved, and the stretching and film expanding quality is ensured. In conclusion, the device has a good application prospect.

Description

TECHNICAL FIELD

[0001] The utility model relates to wafer production auxiliary equipment technical field, especially a kind of film expansion and cutter device after wafer cutting. BACKGROUND

[0002] Wafer refers to the silicon wafer used for making silicon semiconductor circuit, and its raw material is silicon, in specific production, high-purity polycrystalline silicon is dissolved and then added into silicon crystal seed, and then slowly pulled out to form single silicon crystal rod, after grinding, polishing and slicing, silicon wafer is formed, which is wafer. After wafer production, the upper end surface needs to be pasted with film, and the film and wafer are located at the lower end of the hollow film frame, in actual situation,

[0003] Although wafer looks like a whole circle by naked eye after cutting, it is actually composed of a plurality of dies, so after pasting film, the film does not have strength and is not tight, and the arrangement between a plurality of dies is not stable, so that the interval between a plurality of dies (chips) is too small, which will cause adverse effects on subsequent sorting and picking processes (small interval is not convenient for sorting, which may cause die adhesion and chip damage, etc.).

[0004] In order to prevent the above problems, in the prior art, inner ring and outer ring are needed to stretch and fix the pasted film and separate it from the film frame, specifically, the staff first removes the film frame, then puts the inner ring on the outer side of the wafer from top to bottom, and the inner ring flattens the film along the outer side of the wafer and the edge of the film is distributed to the lower end, then the staff puts the outer ring on the outer side of the inner ring from bottom to top, so that the edge of the film is clamped between the inner side of the outer ring and the outer side of the inner ring, finally, the staff cuts the excess part of the film edge at the lower end of the inner ring and the outer ring with a tool for subsequent sorting and picking processes. The above-mentioned manual operation is not only inconvenient for the staff and relatively low in work efficiency, but also uneven in the force applied to the inner ring, which will cause some areas of the film to be uneven after expansion, and cannot achieve good expansion effect, which will adversely affect the subsequent process. UTILITY MODEL CONTENTS

[0005] To overcome the drawbacks of existing wafer manufacturing processes, which require manual stretching and fixing of the film using inner and outer rings, and manual trimming of excess film at the bottom, resulting in inconvenience, low efficiency, and compromised stretching and fixing quality, this invention provides a wafer stretching and cutting device. Through the combined action of related structures, the device automatically completes the stretching, cutting, and separation of the film-mounted wafer after wafer dicing by simply placing the outer ring, inner ring, and film-mounted wafer holder at the appropriate workstation. This provides convenience for workers, improves work efficiency, and ensures the quality of stretching and film expansion.

[0006] The technical solution adopted by this utility model to solve its technical problem is:

[0007] A wafer dicing and wafer expansion and dicing device includes a PLC, a limiting ring, a frame, and also has an inner ring platform mechanism, an outer ring platform mechanism, and a dicing mechanism. The inner ring platform mechanism includes cylinders, a fixed plate, an outer limiting ring, a top plate, a lead screw drive motor, and linear bearings. Multiple sets of linear bearings and cylinders are provided. The lower ends of the cylinder bodies and bearing seats of the multiple sets of linear bearings are fixedly mounted around the upper edge of the fixed plate. The lower end of the fixed bracket of the lead screw drive motor is fixedly mounted in the middle of the upper edge of the fixed plate. The upper end of the outer limiting ring and the lower ends of the piston rods of the multiple sets of cylinders and the bearing rods of the multiple sets of linear bearings are fixedly mounted together. The upper edge of the top plate and the lower end of the movable column of the lead screw drive motor are fixedly mounted together. The rear end of the fixed plate is fixedly mounted on the upper edge of the frame, and a fixing ring is fixedly mounted on the outer side of the lower end of the top plate. The rear side of the limiting ring is fixedly mounted in the middle of the frame. The outer ring platform mechanism includes cylinder A, linear bearing A, and a servo motor. The system includes a motor, a drive pulley, a driven pulley, a lower fixed plate, a lower ring, a support plate, and multiple sets of linear bearings A. The cylinder body of cylinder A is fixedly installed in the middle of the lower end of the lower fixed plate. The bearing seats of the multiple sets of linear bearings A are respectively fixedly installed around the lower end of the lower fixed plate. The upper ends of the bearing rods of the multiple sets of linear bearings A are respectively fixedly installed around the lower part of one side of the support plate. The servo motor is fixedly installed in the lower part of the other side of the support plate. The drive pulley is fixedly installed on the shaft of the servo motor. A bearing is fixedly installed on the outer side of the middle of the piston rod of cylinder A. A fixed ring is fixedly installed on the outer side of the outer ring of the bearing. The fixed ring rotates and is located on the outer side of the middle of the support plate. The inner side of the driven pulley is fixedly installed on the outer side of the fixed ring. A synchronous transmission belt is installed between the driven pulley and the drive pulley. The lower end of the lower ring is fixedly installed on the upper end of the piston rod of cylinder A. The rear end of the lower fixed plate is fixedly installed on the lower side of the frame. The cutting mechanism is installed between the other side of the support plate and the outer side of the fixed ring.

[0008] Furthermore, the cutting mechanism includes a cylinder B, an electromagnet, a magnet, a sliding block, a guide rod, a connecting plate, and a blade. One side of the connecting plate is fixedly installed on one side of the fixing ring, one side of the guide rod is fixedly installed on the other side of the connecting plate, the lower part of the sliding block is slidably sleeved on the other side of the guide rod, the blade is fixedly installed on one side of the upper end of the sliding block, the cylinder B is fixedly installed on the other end of the support plate, the electromagnet is fixedly installed on the piston rod side of the cylinder B, and the magnet is fixedly installed on one side of the sliding block.

[0009] Furthermore, the outer diameter of the top plate is smaller than the inner diameter of the outer limiting ring, the height of the fixing ring is lower than the height of the inner ring of the fixing wafer, the outer side of the fixing ring and the upper part of the inner side of the inner ring are in a movable tight-fitting structure, the outer diameter of the inner ring is smaller than the inner diameter of the outer limiting ring, and the outer diameter of the inner ring is the same as the outer diameter of the top plate.

[0010] Furthermore, the inner diameter of the limiting ring is larger than the outer diameter of the top plate, the fixing ring, and the inner ring, and the inner diameter of the outer limiting ring is larger than the inner diameter of the limiting ring.

[0011] Furthermore, a retaining ring is fixedly installed on the outer side of the upper end of the lower ring, and the inner side of the retaining ring and the lower part of the outer side of the outer ring that fixes the wafer are in a movable tight-fitting structure.

[0012] Furthermore, the outer diameter of the outer ring is smaller than the inner diameter of the limiting ring, and the inner diameter of the outer ring is larger than the outer diameter of the inner ring.

[0013] Furthermore, the outer limiting ring, top plate, limiting ring, and lower ring are all on the same vertical plane from top to bottom.

[0014] The beneficial effects of this utility model are as follows: Under the combined action of related structures, the operator only needs to place the outer ring, inner ring, and the wafer with film-applied support onto the lower ring, the lower part of the fixing ring, and the limiting ring. The PLC then controls the cylinder and lead screw drive motor to press the film-applied support onto the outer side of the upper end of the limiting ring, and press the inner ring down from the outer side of the wafer under the film-applied support. During this pressing process, the film on the wafer surface is stretched and extended, pushing the inner ring down into the inner side of the outer ring. Thus, after stretching and extending, the edge of the film is tightly fitted between the inner side of the outer ring and the outer side of the inner ring. Then, cylinder B, via an electromagnet, pushes the sliding block and blade inward to their designated positions (then the electromagnet is de-energized, and cylinder B drives the electromagnet to move outward to its designated positions). Subsequently, the servo motor drives the blade to rotate via the driving pulley and driven pulley, cutting the excess film located between the inner ring and the top plate. This new model brings convenience to the operator, improves work efficiency, and ensures the quality of the stretched and expanded film. In summary, this new model has good application prospects. Attached Figure Description

[0015] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0016] Figure 1This is a schematic diagram of the overall structure of this utility model.

[0017] Figure 2 This is a schematic diagram of the structure between the outer ring platform mechanism and the cutting mechanism of this utility model.

[0018] Figure 3 This is a schematic diagram of the structure between the film-applying frame, wafer, film, inner ring, and outer ring processed by this utility model.

[0019] Figure 4 This is a schematic diagram of the structure between the inner ring and the top plate of this utility model.

[0020] Figure 5 This is a structural diagram of the inner ring, outer ring, film, top plate, and lower ring of this utility model. Detailed Implementation

[0021] Figure 1 , 2As shown in Figures 3, 4, and 5, a wafer dicing and expansion device includes a PLC (not shown), a limiting ring 1, and a frame 2. It also includes an inner ring platform mechanism 3, an outer ring platform mechanism, and a cutting mechanism. The inner ring platform mechanism includes cylinders 31, a fixed plate 32, an outer limiting ring 33, a top plate 34, a lead screw drive motor 35, and linear bearings 36. The linear bearings 36 (which guide the outer limiting ring 33 upwards and downwards) and cylinders 31 are in four sets. The lower ends of the cylinders of the four sets of cylinders 31 are vertically distributed and fixedly installed on the upper periphery of the fixed plate 32, and the piston rods of the four sets of cylinders 31 are movably located at the lower end of the fixed plate 32. The bearing seats of the four sets of linear bearings 36 are vertically distributed and fixedly installed on the middle periphery of the upper periphery of the fixed plate 32, and the shafts of the four sets of linear bearings 36 are... The support rod is located at the lower end of the fixed plate 32; there is a shaft hole in the middle of the fixed plate 32, the lower end of the fixed frame of the screw drive motor 35 is fixedly installed in the middle of the upper end of the fixed plate 32 and the middle of its movable column is located in the shaft hole; the upper end of the outer limiting ring 33 and the lower ends of the piston rods of the four sets of cylinders 31 and the bearing rods of the four sets of linear bearings 36 are respectively fixedly installed together, the middle of the upper end of the top plate 34 and the lower end of the movable column of the screw drive motor 35 are installed together, the rear end of the fixed plate 32 is fixedly installed in the front of the upper end of the frame 2, the upper and lower ends of the cylinder barrels of the four sets of cylinders 31 and the exhaust pipe of the air compressor (not shown in the figure) are connected in parallel through pipelines, and a fixing ring 341 is welded to the outer side of the lower end of the top plate 34; the rear outer side of the limiting ring 1 is fixedly installed in the outer side of the front middle of the frame 2;The outer ring platform mechanism includes a cylinder A41, linear bearings A42 (for guiding the upward and downward movement of the lower ring, etc.), a servo motor 43, a drive pulley 44, a driven pulley 45, a lower fixed plate 46, a lower ring 47, and a support plate 48. The cylinder body of cylinder A41 is vertically distributed and fixedly installed at the lower middle of the lower fixed plate 46, and the piston rod of cylinder A41 is movably located at the upper end of the lower fixed plate 46. The bearing seats of four sets of linear bearings A42 are vertically distributed and fixedly installed at the lower middle of the lower perimeter of the lower fixed plate 46, and the bearing rods of the four sets of linear bearings A42 are movably located at the upper end of the lower fixed plate 46. The upper ends of the bearing rods of the four sets of linear bearings A42 are fixedly installed at the lower perimeter of the right side of the support plate 48. The support plate 48 has an opening in the middle and at the right side. The servo motor 43 is fixedly installed below the opening in the middle of the support plate 48. The drive pulley 44 is fixedly installed on the shaft of the servo motor 42. The piston rod of cylinder A41 rotates in the middle within the opening at the right end. A bearing 49 is fixedly installed on the outer side of the middle of the piston rod. A fixed ring 491 is fixedly installed on the outer side of the outer ring of the bearing (the fixed ring rotates on the outer side of the middle of the support plate). The driven pulley 45 is fixedly installed on the outer side of the fixed ring 491 (the outer diameter of the fixed ring is larger than the inner diameter of the opening at the right end of the support plate). A synchronous transmission belt (not shown in the figure) is installed between the driven pulley 45 and the driving pulley 44. The lower end of the lower ring 47 is fixedly installed on the upper end of the piston rod of cylinder A41 and is located on the upper side of the fixed ring 491 (the distance between the upper end of the fixed ring 491 and the lower ring 47 is [missing information]). The rear end of the lower fixed plate 46 is fixedly installed on the lower front side of the frame 2. The cutting mechanism 5 is installed between the left end of the support plate 48 and the left side of the fixed ring 491. The upper and lower end intake and exhaust solenoid valves of cylinder A41 and the exhaust pipe of the air compressor's air tank are connected in parallel via pipelines.

[0022] Figure 1 , 2As shown in Figures 3, 4, and 5, the cutting mechanism 5 includes a cylinder B51, an electromagnet 52, a permanent magnet 53, a sliding block 54, a guide rod 55, a "┌"-shaped connecting plate 56, and a blade 57. The right side of the connecting plate 56 is welded to the left side of the upper end of the fixed ring 491 and is located on the upper end of the driven pulley 45. There are two guide rods 55, which are horizontally distributed and fixedly installed on the lower left side of the connecting plate 56 with a front-to-back gap on the right side. The sliding block 54 has a guide hole at the lower part of each of its front and rear ends. The sliding block 54 slides through the two guide holes and is respectively fitted on the outside of the two guide rods 55 (the left end of the guide rod 55 has a limiting plate with an outer diameter larger than the inner diameter of the guide hole). The left side of the blade 57 is fixedly installed on the upper right end of the sliding block 54. The cylinder B51 is horizontally installed on the left end of the support plate 48. The electromagnet 52 is fixedly installed on the right side end of the piston rod of the cylinder B51 and is on the same plane as the sliding block. The left side of the permanent magnet 53 is fixedly installed in the middle of the lower right side end of the sliding block 54. The outer diameter of the top plate 34 is smaller than the inner diameter of the outer limiting ring 33. The height of the fixing ring 341 is lower than the height of the inner ring 6 that fixes the wafer. The outer side of the fixing ring 341 and the upper inner side of the inner ring 6 are in a movable clamping structure. The outer diameter of the inner ring 6 is smaller than the inner diameter of the outer limiting ring 33, and the outer diameter of the inner ring 6 is the same as the outer diameter of the top plate 34. The inner diameter of the limiting ring 1 is larger than the outer diameter of the circular top plate 34, the fixing ring 341, and the inner ring 6. The inner diameter of the outer limiting ring 33 is larger than the inner diameter of the limiting ring 1. A retaining ring 471 with a height lower than the outer ring that fixes the wafer is welded to the outer side of the upper end of the lower ring 47. The inner side of the retaining ring 471 and the lower outer side of the outer ring 7 are in a movable clamping structure. The outer diameter of the outer ring 7 is smaller than the inner diameter of the limiting ring 1, and the inner diameter of the outer ring 7 is slightly larger than the outer diameter of the inner ring 6. The outer limiting ring 33, the top plate 34, the limiting ring 1, and the lower ring 47 are on the same vertical plane from top to bottom. The power input terminals of electromagnet 52, lead screw drive motor 35, and servo motor 43, as well as the power input terminals of the upper and lower cylinder inlet and outlet solenoid valves of cylinders 31, A41, and B51, and the multi-channel power output terminals of the PLC are connected by wires.

[0023] Figure 1 , 2As shown in 3, 4, and 5, the working process of this new type is as follows: (1) The worker places the outer ring 7 inside the retaining ring 471 of the lower ring 47, puts the upper end of the inner ring 6 on the outside of the fixing ring 341, and then puts the wafer 9 with the film-applying frame 8 on the limiting ring 1; (2) The PLC controls the cylinder A41 to work, and the cylinder A41 drives the lower ring, the retaining ring, and the outer ring 7 to move up to a certain height and stop. At this time, the PLC controls the electromagnet 52 to be energized and attracts the left outer side of the sliding block 54. The piston rod of the PLC controls the cylinder B to move to the left outer side and then stops. The right side of the blade 57 and the left outer side of the lower ring 47 are spaced apart. The distance does not obstruct the operation of the stretch film 10; (3) The PLC controls the cylinder 31 and the screw drive motor 35 to work respectively. The cylinder 31 drives the outer limit ring 33 to move down and press the film frame 8 on the outer side of the upper end of the limit ring 1. Then the cylinder 31 stops moving. The screw drive motor 35 drives the top plate 34 to move down and press the inner ring 6 down from the outer side of the wafer 9 under the film frame 8. During the pressing process, the film 10 on the surface of the wafer 9 will be stretched and extended. Then the screw drive motor 35 stops moving. In this way, the inner ring 6 will be pushed into the inner side of the outer ring 7. After stretching and extending, the edge of the film is tightly wrapped between the inner side of the outer ring 7 and the outer side of the inner ring 6. (4) When the PLC controls the electromagnet 52 to lose power, it will no longer attract the sliding block 54 to the left outer side. The PLC controls the piston rod of cylinder B to move to the right inner side and then stop moving. The right side of permanent magnet 53 and the left side of connecting plate 56 will be attracted together. The right side of blade 57 will contact the lower outer side of fixing ring 341. Then the PLC controls the piston rod of cylinder B to move to the left outer side and then stop moving (the distance between the right side of electromagnet and the left outer side of guide rod 55). (5) The PLC drives the servo motor 43 to work and drive the blade 57 to rotate one revolution through the driving pulley 44, synchronous belt, driven pulley 45, and connecting rod 56 to cut off the excess film between the inner ring and the top plate fixing ring (located at the lower outer end of the fixing ring as the cutting point).(6) The PLC controls the cylinder A41 to work. The cylinder A41 drives the lower ring, the retaining ring, and the outer ring 7 to move down to a certain height and stop. At this moment, the PLC controls the electromagnet 52 to be energized and attract the sliding block 54 to the left outer side (the PLC first controls the piston rod of the cylinder B to move to the right inner side and then stops to attract the guide rod 55). The PLC controls the piston rod of the cylinder B to move to the left outer side and then stops. The distance between the right side of the blade 57 and the left outer side of the lower ring 47, and the distance between the blade and the outer side of the lower ring, facilitates the subsequent removal of the stretched wafer (wafer and film, outer ring, inner ring). (3) The PLC controls the cylinder 31 and the screw drive motor 35 to work respectively. The cylinder 31 drives the outer limit ring 33 to move upward and no longer presses the film frame 8 on the upper end of the limit ring 1. After the cylinder 31 stops moving (the staff can remove the film frame), the screw drive motor 35 drives the top plate 34 to move upward. After the lower end of the top plate and the upper limit ring are separated by a certain distance, the screw drive motor 35 stops moving. In this way, the staff can take out the wafer (the outer side of the wafer 9 has an inner ring and an outer ring) that has been stretched and extended in the lower ring to complete all the work. This new invention brings convenience to the staff, improves work efficiency, and ensures the quality of stretching and expanding film. It should be noted that the PLC, cylinder, screw drive motor and other technologies are all mature technologies (including the working mode of PLC controlling cylinder, screw drive motor and other technologies). This application does not elaborate on the above technical solutions, nor does it protect the above technical solutions. This application protects the wafer stretching and expanding film technology points realized by the above components and application solutions.

[0024] Those skilled in the art should understand that although this specification describes embodiments, the embodiments do not necessarily contain only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in the embodiments can also be appropriately combined to form other embodiments that can be understood by those skilled in the art. Therefore, the scope of protection of this invention is defined by the claims.

Claims

1. A wafer dicing and wafer expansion and dicing device, comprising a PLC, a limiting ring, and a frame, characterized in that, It also features an inner ring platform mechanism, an outer ring platform mechanism, and a cutting mechanism. The inner ring platform mechanism includes cylinders, a fixed plate, an outer limit ring, a top plate, a lead screw drive motor, and linear bearings. Multiple sets of linear bearings and cylinders are used, with the cylinder bodies and bearing seats of the multiple sets of linear bearings fixedly mounted around the upper edge of the fixed plate. The lower end of the fixed bracket of the lead screw drive motor is fixedly mounted in the middle of the upper edge of the fixed plate. The upper end of the outer limit ring and the lower ends of the piston rods of the multiple sets of cylinders and the bearing rods of the multiple sets of linear bearings are fixedly mounted together. The upper edge of the top plate and the lower end of the movable column of the lead screw drive motor are fixedly mounted together. The rear end of the fixed plate is fixedly mounted on the upper edge of the frame, and a fixed ring is fixedly mounted on the outer side of the lower end of the top plate. The rear side of the limit ring is fixedly mounted in the middle of the frame. The outer ring platform mechanism includes cylinder A, linear bearing A, a servo motor, a driving pulley, a driven pulley, and a lower... The system comprises a fixed plate, a lower ring, a support plate, and multiple sets of linear bearings A. The cylinder body of cylinder A is fixedly installed in the middle of the lower end of the fixed plate. The bearing seats of the multiple sets of linear bearings A are respectively fixedly installed around the lower end of the fixed plate. The upper ends of the bearing rods of the multiple sets of linear bearings A are respectively fixedly installed around the lower part of one side of the support plate. A servo motor is fixedly installed in the lower part of the other side of the support plate. A drive pulley is fixedly installed on the shaft of the servo motor. A bearing is fixedly installed on the outer side of the middle of the piston rod of cylinder A. A fixed ring is fixedly installed on the outer side of the outer ring of the bearing. The fixed ring rotates and is located on the outer side of the middle of the support plate. The inner side of the driven pulley is fixedly installed on the outer side of the fixed ring. A synchronous transmission belt is installed between the driven pulley and the drive pulley. The lower end of the lower ring is fixedly installed on the upper end of the piston rod of cylinder A. The rear end of the lower fixed plate is fixedly installed on the lower side of the frame. The cutting mechanism is installed between the other side of the support plate and the outer side of the fixed ring.

2. The wafer dicing and dicing apparatus according to claim 1, characterized in that, The cutting mechanism includes cylinder B, electromagnet, magnet, sliding block, guide rod, connecting plate, and blade. One side of the connecting plate is fixedly installed on one side of the fixing ring, and one side of the guide rod is fixedly installed on the other side of the connecting plate. The lower part of the sliding block is slidably sleeved on the other side of the guide rod. The blade is fixedly installed on one side of the upper end of the sliding block. Cylinder B is fixedly installed on the other end of the support plate. Electromagnet is fixedly installed on the piston rod side of cylinder B, and magnet is fixedly installed on one side of the sliding block.

3. The wafer dicing and dicing apparatus according to claim 1, characterized in that, The outer diameter of the top plate is smaller than the inner diameter of the outer limiting ring, the height of the fixing ring is lower than the height of the inner ring fixing the wafer, the outer side of the fixing ring and the upper part of the inner side of the inner ring are in a movable clamping structure, the outer diameter of the inner ring is smaller than the inner diameter of the outer limiting ring, and the outer diameter of the inner ring is the same as the outer diameter of the top plate.

4. The wafer dicing and dicing apparatus according to claim 1, characterized in that, The inner diameter of the limiting ring is larger than the outer diameter of the top plate, the fixing ring, and the inner ring, and the inner diameter of the outer limiting ring is larger than the inner diameter of the limiting ring.

5. The wafer dicing and dicing apparatus according to claim 1, characterized in that, A retaining ring is fixedly installed on the outer side of the upper end of the lower ring, and the inner side of the retaining ring and the lower part of the outer side of the outer ring that fixes the wafer are in a movable tight-fitting structure.

6. The wafer dicing and dicing apparatus according to claim 1, characterized in that, The outer diameter of the outer ring is smaller than the inner diameter of the limiting ring, and the inner diameter of the outer ring is larger than the outer diameter of the inner ring.

7. The wafer dicing and dicing apparatus according to claim 1, characterized in that, The outer limiting ring, top plate, limiting ring, and lower ring are all on the same vertical plane from top to bottom.

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