A TOP LED bracket substrate sealing method and welding device

Abstract

The invention discloses a TOP LED bracket substrate sealing welding method and a welding device, and relates to the technical field of LED bracket packaging. The sealing welding method comprises the following steps: first filling plastic between two metal plates; welding the plastic position by using a stir friction welding process; cutting off the middle part of the welding belt along the width direction of the welding belt to form a strip-shaped through groove; processing the metal plate into a lead frame, and filling the strip-shaped through groove with plastic to obtain a bracket substrate; the invention uses a stir friction welding process to weld the plastic filled between the metal plates, so as to ensure the sealing performance of the connection between the plastic and the metal plates, and refills the plastic, so that the connection between the plastic and the welding belt is actually the connection between the plastics, and no gap will be generated when the temperature changes due to different thermal expansion coefficients, thereby ensuring the airtightness of the TOP LED bracket after molding.

Description

Technical Field

[0001] The invention relates to the technical field of LED bracket packaging, and in particular to a TOP LED bracket substrate sealing welding method and a welding device. Background Art

[0002] Thermoplastic plastics bracket for LED devices, hereinafter referred to as TPP bracket, is a mature form of semiconductor device packaging bracket. After the 1990s, with the advancement of materials and process technology, this packaging bracket structure was introduced into the LED field, resulting in a new type of TOP LED device, with familiar models such as 2020, 3014, 3528, 5050, etc., which are widely used in graphic image display and various LED lighting projects. TPP bracket plastic packaging materials mainly use thermoplastic resins such as PPA, PA6T, PA9T, etc., and use injection molding process (Inject molding) to form the bracket on the copper lead frame. The bracket has high production efficiency and low cost, but the TPP bracket is a non-airtight packaging structure with poor performance. Moisture intrusion is still the primary factor leading to device failure. Therefore, improving the airtightness of the TPP bracket is one of the key ways to improve the reliability of TOP LED devices.

[0003] In the utility model patent with application number "201621055526.0" and name "A new type of TOP LED bracket and its TOP LED device", an I-shaped through groove is formed between the positive and negative electrodes on the substrate, and a thermoplastic plastic filler is filled in the through groove. The filler separates the positive and negative electrodes of the substrate. This shape is intended to increase the flow of water vapor entering the interior of the LED bracket along the positive and negative electrodes and the filler, accompanied by many flow channel mutations, thereby improving the overall airtightness of the LED bracket after packaging, reducing the entry of external gas or moisture into the LED package, and improving product reliability.

[0004] In the utility model patent with application number "201320498539.5" and name "A TOP-LED light bar with moisture-proof function", a transparent acrylic resin layer made of a special synthetic resin is used to coat the periphery of the TOP-LED chip used in the light bar. As a moisture-proof material, the acrylic resin layer has good moisture-proof performance, good moisture-proof effect and good high-temperature resistance. At the same time, it will not absorb light and cause color temperature drift. This not only avoids the absorption of light by the moisture-proof material, but also ensures the thermal stability at high temperature, and plays a good moisture-proof treatment. Similarly, a transparent acrylic resin layer of more than 2.5mm is applied manually or by equipment on the outer edge of the PPA bracket, the pins and the PCB board, and a protective layer is formed after curing at room temperature to prevent water vapor from invading the junction of the pins and PPA, thereby improving the moisture-proof performance of the TOP-LED chip.

[0005] However, the main factors affecting the poor air tightness of the TPP bracket are the quality of the blanking section of the lead frame and the matching relationship between the thermal expansion coefficients of the lead frame and the plastic packaging material. None of the above methods solves the problem of poor air tightness between metal and non-metal. Summary of the invention

[0006] The purpose of the present invention is to provide a TOP LED bracket substrate sealing method and welding device to solve the problems existing in the prior art, so that the material filled between the positive electrode and the negative electrode on the bracket substrate will not have different expansion coefficients and will not produce gaps when the temperature changes, thereby ensuring the airtightness of the formed TOP LED bracket.

[0007] To achieve the above object, the present invention provides the following solution: The present invention provides a TOP LED bracket substrate sealing method, comprising the following steps:

[0008] 1) Fill the gap between two coplanar metal plates with plastic;

[0009] 2) The plastic position is welded using a stir friction welding process. After the welding is completed, a welding band is formed between the two metal plates;

[0010] 3) Cut off the middle part of the welding strip along the width direction of the welding strip to form a strip-shaped through groove;

[0011] 4) Processing the metal plate into a lead frame, wherein the lead frame has a strip-shaped through groove between the positive electrode and the negative electrode;

[0012] 5) Filling the strip-shaped through grooves with plastic to obtain a bracket substrate.

[0013] Preferably, in step 2), the diameter of the stirring head is not less than the width of the plastic between the two metal plates.

[0014] Preferably, in step 3), the width of the cut-off portion of the welding strip accounts for 1 / 2 of the total width of the welding strip.

[0015] Preferably, the method of filling plastic in step 1) and step 5) is injection molding; the material filled in step 1) and step 5) is plastic PPA.

[0016] The present invention also provides a TOP LED bracket substrate welding device, which is used to implement the welding process of two metal plates in the above-mentioned TOP LED bracket substrate sealing method, including a stir friction welding mechanism for welding the two metal plates, a conveying mechanism for conveying the metal plates and a positioning mechanism for positioning the metal plates. The positioning mechanism includes a lifting rod, a pressure head and an elastic member. The pressure head is fixed at the bottom of the lifting rod and is located above the conveying mechanism. The elastic member is also sleeved on the lifting rod. The top end of the elastic member is fixed, and the bottom end abuts against the upper surface of the pressure head.

[0017] Preferably, along the conveying direction of the metal plate, the pressure head is in a gate-shaped structure, the stirring head on the stir friction welding mechanism passes through the gate-shaped structure and acts on the metal plate, the elastic member is connected to the front end of the gate-shaped structure, and the rear end of the gate-shaped structure is in an upturned shape.

[0018] Preferably, the conveying mechanism includes a load-bearing frame for placing metal plates, a sprocket group and a support rail arranged in parallel on both sides of the bottom of the load-bearing frame, the sprocket group includes front and rear sprockets and chains connecting the sprockets, the support rail is adapted to the shape of the chain and is fixed by a limiting portion; along the conveying direction of the metal plate, upper support wheels and lower support wheels of different heights are respectively arranged at the front and rear ends of the bottom of the load-bearing frame, the upper support wheel is hinged on the pin shaft of the chain, and the lower support wheel abuts against the support rail.

[0019] Preferably, the welding device also includes an annular mounting plate, which is arranged on the inner side of the sprocket and parallel to the sprocket, the support rail is fixed on one side surface of the mounting plate, and the other side surface has an annular groove, and the annular groove is concentrically arranged with the sprocket, the limiting part includes a limiting pin and a limiting plate, the limiting pin is arranged on the inner side surface of the sprocket and is stuck in the annular groove, a connecting shaft is also arranged between the two sprockets arranged opposite to each other, and the connecting shaft is also provided with the limiting plate which is smaller than the diameter of the support rail, and the limiting plate presses the mounting plate against the inner side surface of the sprocket.

[0020] Preferably, a limiting track is also provided on the side of the mounting plate, and the limiting track is adapted to the shape of the supporting track. In the radial direction of the mounting plate, the limiting track is located on the outside of the supporting track, and the lower supporting wheel is located between the supporting track and the limiting track.

[0021] Preferably, the load-bearing frame includes a load-bearing plate and a load-bearing bracket, the upper surface of the load-bearing plate is used to place the metal plate, and the load-bearing bracket is fixed to the bottom, the load-bearing plate is bent and forms a triangular structure with the load-bearing bracket, and the upper support wheel and the lower support wheel are respectively arranged at the bottom of the two corners of the triangular structure.

[0022] Compared with the prior art, the present invention has achieved the following technical effects:

[0023] 1. The present invention utilizes the process of friction stir welding to weld the plastic filled between the metal plates, which can ensure the sealing performance of the connection between the plastic and the metal plates, and the middle part of the welding band formed by the edge material of the metal plate and the plastic is cut off and refilled with plastic, so that the connection between the plastic and the welding band is actually the connection between plastics, and no gap will be generated when the temperature changes due to different thermal expansion coefficients, thereby ensuring the airtightness of the TOP LED bracket after molding;

[0024] 2. The present invention sets a conveying mechanism so that the stirring head remains in place while the metal plate moves, thereby replacing the welding method in which the stirring head moves along the weld in the traditional welding process. Since the stirring head does not need to move back and forth in the present invention, loading and unloading operations can be performed during the welding process, which makes the welding operation more continuous and the welding efficiency higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0026] Figure 1 It is a schematic diagram of the placement of two metal plates in the present invention;

[0027] Figure 2 This is a schematic diagram of the space between metal plates filled with plastic;

[0028] Figure 3 is a schematic diagram of the structure of the lead frame;

[0029] Figure 4 This is a schematic diagram of the structure of the TOP LED bracket;

[0030] Figure 5 It is a schematic diagram of the overall structure of the welding device;

[0031] Figure 6 It is a schematic structural diagram of the sprocket connecting shaft from an axial outward perspective;

[0032] Figure 7 It is a structural schematic diagram of the mounting plate;

[0033] Figure 8 is a schematic diagram of the three-dimensional structure of the mounting plate;

[0034] Fig. 9 It is a structural schematic diagram of the load-bearing frame;

[0035] Among them, 1. Metal plate; 2. Welding strip; 3. Plastic; 4. Strip groove; 5. Lead frame; 6. Bracket substrate; 7. Reflection shell; 8. Reflection cavity; 9. Stirring head; 10. Lifting rod; 11. Pressure head; 12. Elastic part; 13. Load-bearing frame; 14. Upper support wheel; 15. Lower support wheel; 16. Support track; 17. Sprocket; 18. Chain; 19. Mounting plate; 20. Annular groove; 21. Limit pin; 22. Limit track; 23. Limit plate; 24. Connecting shaft; 25. Load-bearing plate; 26. Load-bearing bracket. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] The purpose of the present invention is to provide a TOP LED bracket substrate sealing method and welding device to solve the problems existing in the prior art, so that the material filled between the positive electrode and the negative electrode on the bracket substrate will not have different expansion coefficients and will not produce gaps when the temperature changes, thereby ensuring the airtightness of the formed TOP LED bracket.

[0038] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0039] Embodiment 1:

[0040] like Figure 1 to Figure 4 As shown, this embodiment provides a TOP LED bracket substrate sealing method, comprising the following steps:

[0041] 1) Filling the gap between two coplanar metal plates 1 with a plastic 3 having the same thickness as the metal plates 1;

[0042] 2) The plastic 3 is welded by using a friction stir welding process. After the welding is completed, a welding band 2 is formed between the two metal plates 1;

[0043] 3) along the width direction of the welding strip 2, the middle part of the welding strip 2 is cut off to form a strip-shaped through groove 4, and a certain width of the welding strip 2 is left on both sides of the strip-shaped through groove 4. Preferably, the width of the welding strips 2 on both sides is the same;

[0044] 4) Processing the metal plate 1 into a lead frame 5, wherein the lead frame 5 has a strip-shaped through groove 4 between the positive electrode and the negative electrode, and the edges of the positive electrode and the negative electrode have a remaining welding strip 2;

[0045] 5) Fill the strip-shaped through groove 4 with plastic 3 to obtain a support substrate 6 .

[0046] It should be noted that, in the actual processing, the width of the plastic 3 is very small, and the diameter of the stirring head 9 is difficult to achieve the stir welding of only the joint of the plastic 3 and one metal plate 1. In this embodiment, the diameter of the stirring head 9 is not less than the width of the plastic 3 between the two metal plates 1. During welding, the joints of the plastic 3 and the two metal plates 1 are welded simultaneously, that is, the two metal plates 1 are directly welded; however, after the stir friction welding, a small amount of metal material will be melted into the welding strip 2, affecting the insulation of the welding strip 2. Therefore, in this embodiment, the middle part of the welding strip 2 is cut off to form After the strip-shaped through groove 4 is made into the lead frame 5 through processes such as bending and etching, the plastic 3 is then filled into the strip-shaped through groove 4, which can ensure the insulation between the positive electrode and the negative electrode of the lead frame 5; and when the plastic 3 is filled into the strip-shaped through groove 4, the main component of the residual welding strip 2 is still the plastic 3, so the filling process is still the combination between the plastic 3 and the plastic 3, and the thermal expansion coefficients of the two are basically the same, and no gap will be generated due to the different thermal expansion coefficients when heated; and the welding strip 2 formed by stir friction welding and the metal plate 1 are sealed and no gap will appear.

[0047] A reflective shell 7 is provided on the molded bracket, and a reflective cavity 8 for placing components is formed between the reflective shell 7 and the bracket substrate 6 .

[0048] Preferably, in step 3), the width of the cut-off portion of the welding tape 2 accounts for 1 / 2 of the total width of the welding tape 2.

[0049] The method of filling the plastic 3 in step 1) and step 5) is injection molding; the material filled in step 1) and step 5) is plastic 3PPA.

[0050] Embodiment 2:

[0051] like Figures 5 to 9 As shown, this embodiment provides a TOP LED bracket substrate 6 welding device, which is used to implement the welding process of the two metal plates 1 in the above-mentioned TOP LED bracket substrate 6 sealing method, including a stir friction welding mechanism for welding the two metal plates 1, a conveying mechanism for conveying the metal plate 1 and a positioning mechanism for positioning the metal plate 1, the positioning mechanism includes a lifting rod 10, a pressure head 11 and an elastic member 12, the pressure head 11 is fixed at the bottom of the lifting rod 10 and is located above the conveying mechanism, and the lifting rod 10 is also provided with an elastic member 12, the top end of the elastic member 12 is fixed, and the bottom end abuts against the upper surface of the pressure head 11.

[0052] When welding, two metal plates 1 are placed on the surface of the conveying mechanism. When they are about to enter under the stirring head 9 of the stir friction welding device, the lifting rod 10 is lifted, and then the metal plate 1 is pressed down under the action of the elastic member 12. The metal plate 1 continues to be conveyed, and the stirring head 9 is used to weld the plastic 3 filling area of ​​the two metal plates 1. After the welding is completed, the pressure head 11 and the stirring head 9 are lifted, waiting for the next metal plate 1 to be conveyed under the stirring head 9.

[0053] Therefore, in this embodiment, a conveying mechanism is set up so that the stirring head 9 remains in place and the metal plate 1 moves, thereby replacing the welding method in which the stirring head 9 moves along the weld in the traditional welding process. Since the stirring head 9 in this embodiment does not need to move back and forth, loading and unloading operations can be performed during the welding process, thereby improving the continuity of the welding operation and increasing the welding efficiency.

[0054] Furthermore, in the present embodiment, along the conveying direction of the metal plate 1, the pressure head 11 is in a gate-shaped structure, the stirring head 9 on the stir friction welding mechanism passes through the gate-shaped structure and acts on the metal plate 1, the elastic member 12 is connected to the front end of the gate-shaped structure, and the rear end of the gate-shaped structure is in an upturned shape. During the transmission process, the pressure head 11 does not need to move upward, and the next metal plate 1 directly enters the pressure head 11 and is lowered to wait for welding.

[0055] Furthermore, in this embodiment, the conveying mechanism includes a load-bearing frame 13 for placing the metal plate 1, a sprocket wheel 17 group and a support track 16 arranged in parallel on both sides of the bottom of the load-bearing frame 13, the sprocket wheel 17 group includes sprocket wheels 17 arranged in front and back and chains 18 connecting the sprocket wheels 17, and the support track 16 is adapted to the shape of the chain 18 and fixed by a limiting portion; along the conveying direction of the metal plate 1, the front and rear ends of the bottom of the load-bearing frame 13 are respectively provided with an upper support wheel 14 and a lower support wheel 15 of different heights, the upper support wheel 14 is hinged on the pin of the chain 18, and the lower support wheel 15 abuts on the support track 16. The support track 16 is made of rigid material, fixed under the limiting action of the limiting portion, and is used to bear the gravity of the load-bearing frame 13, the metal plate 1 and the pressure of the mixing head 9, which can ensure that the stability and load-bearing capacity of the conveying mechanism are stronger under the pressure of the mixing head 9.

[0056] In order to fix the support rail 16, the welding device in this embodiment also includes an annular mounting plate 19, which is arranged on the inner side of the sprocket 17 and parallel to the sprocket 17. The support rail 16 is fixed on one side surface of the mounting plate 19, and an annular groove 20 is provided on the other side surface. The annular groove 20 is concentrically arranged with the sprocket 17. The limiting part includes a limiting pin 21 and a limiting plate 23. The limiting pin 21 is arranged on the inner side surface of the sprocket 17 and is stuck in the annular groove 20. A connecting shaft 24 is also arranged between the two relatively arranged sprockets 17. A limiting plate 23 smaller than the diameter of the support rail 16 is also arranged on the connecting shaft 24. The limiting plate 23 presses the mounting plate 19 against the inner side surface of the sprocket 17. When the sprocket 17 rotates, the limit pin 21 moves along the circular track of the annular groove 20, and the limit pin 21 can limit the mounting plate 19 in the radial direction of the sprocket 17. In order to better limit the position, a plurality of limit pins 21 can be evenly arranged along the circumference of the sprocket 17; at the same time, the limit plate 23 on the connecting shaft 24 presses the mounting plate 19 against the side of the sprocket 17, and limits the mounting plate 19 in the axial direction of the rotation of the sprocket 17, thereby ensuring that the mounting plate 19 and the support track 16 on the mounting plate 19 are fixed during the rotation of the sprocket 17. Preferably, a sleeve that can be fixed on the connecting shaft 24 can be slidably mounted on the connecting shaft 24, and the end of the sleeve has the above-mentioned limit plate 23. By moving the sleeve, it is easy to disassemble and replace the connecting shaft 24, and it is also easy to replace the mounting plate 19.

[0057] The mounting plate 19 may be in the shape of a circular ring or a semicircular ring. In the figure, the embodiment is in the shape of a semicircular ring. The annular groove 20 may be formed by digging a groove on the surface of the mounting plate 19 or by providing two circular protrusions on the mounting plate 19. Figure 7 In this embodiment, the annular groove 20 is formed by two fixing rings concentrically arranged on the mounting plate 19.

[0058] Furthermore, in the present embodiment, a limiting track 22 is also provided on the side surface of the mounting plate 19, and the limiting track 22 is adapted to the shape of the supporting track 16. In the radial direction of the mounting plate 19, the limiting track 22 is located on the outside of the supporting track 16, and the lower supporting wheel is located between the supporting track 16 and the limiting track 22; when the load-bearing frame 13 rotates along the chain 18 to the bottom of the sprocket 17, the lower supporting wheel is pressed on the limiting track 22. If there is no limiting track 22, when the load-bearing frame 13 is located at the bottom of the sprocket 17, it may twist around the wheel axle of the upper wheel under the action of gravity, thereby affecting each other and even failing to work normally.

[0059] Furthermore, in this embodiment, the load-bearing frame 13 includes a load-bearing plate 25 and a load-bearing bracket 26. The upper surface of the load-bearing plate 25 is used to place the metal plate 1, and the load-bearing bracket 26 is fixed to the bottom. The load-bearing plate 25 is bent and forms a triangular structure with the load-bearing bracket 26, which has a stronger load-bearing capacity. The upper support wheel 14 and the lower support wheel 15 are respectively arranged at the bottom of the two corners of the triangular structure.

[0060] Adaptive changes made according to actual needs are all within the protection scope of the present invention.

[0061] It should be noted that it is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be regarded as exemplary and non-restrictive from any point of view, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any reference numerals in the claims should not be regarded as limiting the claims involved.

Claims

1. A TOP LED bracket substrate sealing method, characterized in that: The following steps are involved: 1) Fill the gap between two coplanar metal plates with plastic; 2) The plastic position is welded using a stir friction welding process. After the welding is completed, a welding band is formed between the two metal plates; 3) Cut off the middle part of the welding strip along the width direction of the welding strip to form a strip-shaped through groove; 4) Processing the metal plate into a lead frame, wherein the lead frame has a strip-shaped through groove between the positive electrode and the negative electrode; 5) Filling the strip-shaped through grooves with plastic to obtain a bracket substrate.

2. The TOP LED bracket substrate sealing method according to claim 1, characterized in that: In step 2), the diameter of the stirring head is not less than the width of the plastic between the two metal plates.

3. The TOP LED bracket substrate sealing method according to claim 2, characterized in that: In step 3), the width of the cut-off portion of the welding strip accounts for 1 / 2 of the total width of the welding strip.

4. The TOP LED bracket substrate sealing method according to claim 3, characterized in that: The method of filling plastic in step 1) and step 5) is injection molding; the material filled in step 1) and step 5) is plastic PPA.

5. A TOP LED bracket substrate welding device, used for implementing the welding process of two metal plates in the TOP LED bracket substrate sealing method according to any one of claims 1 to 4, characterized in that: It includes a stir friction welding mechanism for welding two metal plates, a conveying mechanism for conveying metal plates and a positioning mechanism for positioning the metal plates. The positioning mechanism includes a lifting rod, a pressure head and an elastic member. The pressure head is fixed at the bottom of the lifting rod and is located above the conveying mechanism. The lifting rod is also sleeved with the elastic member. The top end of the elastic member is fixed, and the bottom end abuts against the upper surface of the pressure head.

6. The TOP LED bracket substrate welding device according to claim 5, characterized in that: Along the conveying direction of the metal plate, the pressure head is in a gate-shaped structure, the stirring head on the stir friction welding mechanism passes through the gate-shaped structure and acts on the metal plate, the elastic member is connected to the front end of the gate-shaped structure, and the rear end of the gate-shaped structure is in an upturned shape.

7. The TOP LED bracket substrate welding device according to claim 5 or 6, characterized in that: The conveying mechanism includes a load-bearing frame for placing metal plates, a sprocket group and a support rail arranged in parallel on both sides of the bottom of the load-bearing frame, the sprocket group includes front and rear sprockets and chains connecting the sprockets, the support rail is adapted to the shape of the chain and is fixed by a limiting portion; along the conveying direction of the metal plate, upper support wheels and lower support wheels of different heights are respectively arranged at the front and rear ends of the bottom of the load-bearing frame, the upper support wheel is hinged on the pin shaft of the chain, and the lower support wheel abuts against the support rail.

8. The TOP LED bracket substrate welding device according to claim 7, characterized in that: The welding device also includes an annular mounting plate, which is arranged on the inner side of the sprocket and parallel to the sprocket. The support rail is fixed to one side surface of the mounting plate, and an annular groove is provided on the other side surface. The annular groove is concentrically arranged with the sprocket. The limiting part includes a limiting pin and a limiting plate. The limiting pin is arranged on the inner side surface of the sprocket and is stuck in the annular groove. A connecting shaft is also arranged between the two sprockets arranged opposite to each other. The connecting shaft is also provided with a limiting plate which is smaller than the diameter of the supporting rail. The limiting plate presses the mounting plate against the inner side surface of the sprocket.

9. The TOP LED bracket substrate welding device according to claim 8, characterized in that: A limiting track is also provided on the side of the mounting plate, and the limiting track is adapted to the shape of the supporting track. In the radial direction of the mounting plate, the limiting track is located outside the supporting track, and the lower supporting wheel is located between the supporting track and the limiting track.

10. The TOP LED bracket substrate welding device according to claim 7, characterized in that: The load-bearing frame includes a load-bearing plate and a load-bearing bracket. The upper surface of the load-bearing plate is used to place a metal plate, and the load-bearing bracket is fixed to the bottom. The load-bearing plate is bent and forms a triangular structure with the load-bearing bracket. The upper support wheel and the lower support wheel are respectively arranged at the bottom of the two corners of the triangular structure.

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