Component test fixture with strong compatibility

Abstract

The invention discloses a component test fixture with strong compatibility, and relates to the technical field of electronic equipment manufacturing, the component test fixture comprises a lower cover, a lower guide rail bracket, a lower guide rail bracket, an upper guide rail bracket and an upper cover, the lower guide rail bracket is fixedly arranged in the lower cover, the upper guide rail bracket is buckled on the lower guide rail bracket, the upper cover is buckled on the lower cover, and the upper cover is fixedly arranged on the lower cover. A wire seat is arranged on the right end face of the upper cover, a probe opening is formed between the left end face of the upper cover and the lower cover, a cavity is formed between the upper guide rail frame and the lower guide rail frame, and a first push plate, a second push plate and a third push plate are horizontally arranged in the cavity at a time. Through the design of three gears, different numbers of jig chucks are pushed out, so that components with different packaging sizes are tested, the applicability of the test jig is improved, adjustment is convenient and rapid, and the test efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of electronic equipment manufacturing technology, specifically to a component testing fixture with strong compatibility. Background Technology

[0002] In the field of modern electronic equipment manufacturing and testing, components exist in various packaging forms, such as QFP, QFN, BGA, and SOP. Currently, the industry generally uses the following two methods to test components with these different packaging forms: Dedicated test fixture method: A custom-made test fixture is manufactured to perfectly match the package type and dimensions of a specific component. The fixture is then connected to the corresponding testing equipment for testing. While this method offers reliable connections, a single fixture is typically only suitable for components with a single package size. With the increasing variety of component package types, testing departments need to prepare and manage a large number of fixtures of different specifications, leading to a sharp increase in production costs, heavy warehousing and management burdens, and a lack of flexibility.

[0003] Solder lead method: Electrical leads are directly soldered from the pins of the component under test (DUT) and then the ends of the leads are connected to the test equipment. While this method seems flexible and not limited by package shape, manual soldering is inefficient and difficult to adapt to the needs of batch testing. Secondly, the high temperature and stress during the soldering process can easily cause thermal or mechanical damage to the delicate pins of the component, introducing potential defects and seriously affecting the inherent reliability of the component. After testing, removing the solder joints may also cause secondary damage to the pins.

[0004] Therefore, both of the existing mainstream testing methods have certain shortcomings, and there is an urgent need for a universal testing fixture that can adapt to various package sizes, is easy to operate, and will not damage the components themselves. Summary of the Invention

[0005] To address the aforementioned shortcomings of existing technologies, this invention provides a highly compatible component testing fixture. Through a three-position design, it allows for the deployment of different numbers of fixture chucks, thereby testing components of different package sizes. This enhances the applicability of the testing fixture, makes adjustment convenient and quick, and improves testing efficiency.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a highly compatible component testing fixture, comprising a lower cover, a lower guide rail frame, an upper guide rail frame, and an upper cover. The lower guide rail frame is fixedly disposed within the lower cover, the upper guide rail frame is fastened onto the lower guide rail frame, and the upper cover is fastened onto the lower cover. A wire seat is provided on the right end face of the upper cover, and a probe is provided between the left end face of the upper cover and the lower cover. A cavity is formed between the upper guide rail frame and the lower guide rail frame. A first push plate, a second push plate, and a third push plate are horizontally disposed in the cavity. The first push plate... The system is equipped with three slots. The second push plate has two slots, and the first push plate has one slot. Each of the first, second, and third push plates is electrically connected to a pair of clamping plates on one side corresponding to the probe opening. These clamping plates are elastic and extend through the space between the upper and lower guide rails. A clamping head is provided on the side of each clamping plate corresponding to the probe opening. All three pairs of clamping heads can extend out of the probe opening. The lower guide rail has a third sliding opening corresponding to each slot, and the upper guide rail has a second sliding opening corresponding to the third sliding opening. A clamping head is provided on the side corresponding to each slot. A guide post is provided, which slides vertically through the second and third sliding openings. A push rod is fixedly connected to the upper end of the guide post in the leftmost slot of the first push plate. A push rod is also connected to the upper ends of the guide posts in the middle slot of the first and leftmost slots of the second push plate. A push rod is also connected to the upper ends of the guide posts in the rightmost slot of the first, rightmost, and thirdmost slots of the second and third push plates. Each of the three push rods has a fixed fastening post, and a sliding key is fixedly installed at the upper end of each fastening post. The top cover corresponds to each… Each sliding key has a first sliding opening, through which the sliding key can slide. The upper guide rail has a wire opening on the side near the wire seat. Wires are connected to the first push plate, second push plate, and third push plate near the wire opening. The wires pass through the wire opening and the wire seat and are connected to an external detection system. A first elastic component is provided on the upper surface of the upper guide rail. A second elastic component is provided on the right end of the first push rod, second push rod, and third push rod. The first and second elastic components can respectively apply a rightward force to each push rod.

[0007] Preferably, the first elastic component includes a pair of guide rods, three pairs of compression springs, and four pairs of fixing brackets. The four pairs of fixing brackets are fixedly installed on the upper surface of the upper guide rail frame near the front and rear edges. The four pairs of fixing brackets are distributed near the end of the second sliding opening. The pair of guide rods are arranged in parallel and fixedly installed on the fixing brackets. The push rod is slidably installed on the pair of guide rods. The compression spring is sleeved on the guide rod and is located between the left side wall of the push rod and the fixing bracket.

[0008] Preferably, the second elastic component includes a tension spring and a pull ring. The right ends of the first push rod, the second push rod, and the third push rod are respectively provided with protruding locking blocks. A fixing plate is provided on the right side of the upper surface of the upper guide rail frame. One end of the tension spring is connected to the fixing plate, and the other end is connected to the pull ring. The pull ring is engaged with the locking block.

[0009] Preferably, the upper cover and the lower cover are provided with pins at positions close to the probe opening. The pins are located between each pair of clamps, and the clamps and clips can separate the pairs of clips when they extend out of the probe.

[0010] Preferably, a limit plate is provided on the lower guide rail frame at the position corresponding to the edge of the first push plate, the second push plate and the third push plate.

[0011] Preferably, a limiting seat is provided inside the lower cover, and the lower guide rail frame is snapped into the limiting seat.

[0012] Preferably, the upper guide rail frame and the lower guide rail frame are connected by a snap-fit ​​connection.

[0013] Preferably, the upper cover and the lower cover are connected by a snap-fit ​​connection.

[0014] This invention provides a highly compatible component testing fixture, which has the following advantages: 1. This invention, through its three-position design, introduces different numbers of fixture chucks, thereby testing components of different package sizes, improving the applicability of the test fixture, making adjustment convenient and quick, and improving testing efficiency; 2. This invention eliminates the need to develop dedicated fixtures for each new package, fundamentally saving on fixture design, manufacturing, procurement, and warehousing management costs; 3. This invention eliminates the cumbersome process of soldering leads and uses elastic clips to achieve a non-destructive electrical connection with the pins, completely avoiding damage to components caused by soldering thermal and mechanical stress, and ensuring test accuracy and product reliability. Attached Figure Description

[0015] Figure 1 This is a schematic diagram showing the overall structure of the invention. Figure 2 This is a schematic diagram of the overall invention; Figure 3 This is a schematic diagram of the upper guide rail frame of the present invention; Figure 4 This is a schematic diagram of the lower guide rail frame of the present invention; Figure 5 This is a schematic diagram of the first push plate of the present invention; Figure 6 This is a schematic diagram of the second pusher plate of the present invention; Figure 7This is a schematic diagram of the third pusher plate of the present invention; Figure 8 This is a schematic diagram of the clip of the present invention; Figure 9 This is a schematic diagram of the invention with the top cover open.

[0016] In the diagram: 1. Lower cover; 2. Limiting seat; 3. Lower guide rail frame; 4. Upper guide rail frame; 5. First push plate; 6. Second push plate; 7. Third push plate; 8. Clamping piece; 9. Pin; 10. Pull ring; 11. Tension spring; 12. Guide rod; 13. Compression spring; 14. Push rod; 15. Fastening post; 16. Sliding key; 17. Guide post; 18. Upper cover; 19. Probe; 20. Wire seat; 21. First sliding opening; 22. Wire opening; 23. Second sliding opening; 24. Fixing frame; 25. Fixing plate; 26. Third sliding opening; 27. Limiting plate; 28. Slot; 29. ​​Clamp; 30. Clamping block. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] like Figure 1-9As shown, a highly compatible component testing fixture includes a lower cover 1, a lower guide rail frame 3, an upper guide rail frame 4, and an upper cover 18. The lower guide rail frame 3 is fixedly installed inside the lower cover 1, the upper guide rail frame 4 is fastened to the lower guide rail frame 3, and the upper cover 18 is fastened to the lower cover 1. A wire seat 20 is provided on the right end face of the upper cover 18, and a probe 19 is provided between the left end face of the upper cover 18 and the lower cover 1. A cavity is formed between the upper guide rail frame 4 and the lower guide rail frame 3. A first push plate 5, a second push plate 6, and a third push plate 7 are horizontally arranged in the cavity. The first push plate 5 is provided with three slots 28, and the second push plate 6 is provided with two slots 29. 8. A slot 28 is provided on the first push plate 5. A pair of clamping pieces 8 are electrically connected to one side of the first push plate 5, the second push plate 6, and the third push plate 7 corresponding to the probe 19, and the clamping pieces 8 have a certain elasticity. The clamping pieces 8 move through the upper guide rail frame 4 and the lower guide rail frame 3. A clamping head 29 is provided on the side of the clamping piece 8 corresponding to the probe 19. The three pairs of clamping heads 29 can extend out of the probe 19. The lower guide rail frame 3 has a third sliding opening 26 at the position corresponding to each slot 28. The upper guide rail frame 4 has a second sliding opening 23 at the position corresponding to the third sliding opening 26. A guide post 17 is provided through the slot 28. The guide post 17 passes through the second sliding opening 23 vertically. The upper end of the guide post 17 in the leftmost slot 28 of the first push plate 5 is fixedly connected to a push rod 14. The upper end of the guide post 17 in the middle slot 28 of the first push plate 5 and the upper end of the guide post 17 in the left slot 28 of the second push plate 6 are jointly connected to a push rod 14. The upper ends of the guide post 17 in the rightmost slot 28 of the first push plate 5, the upper ends of the guide post 17 in the right slot 28 of the second push plate 6, and the upper ends of the guide post 17 in the slot 28 of the third push plate 7 are jointly connected to a push rod 14. Each of the three push rods 14 is fixedly provided with a fastening post 15. The upper end of the fastening post 15 is fixedly provided with a sliding key 16. The upper cover 18 corresponds to each Each sliding key 16 is provided with a first sliding opening 21, through which the sliding key 16 passes and can slide. The upper guide rail frame 4 has a wire opening 22 on the side near the wire seat 20. The first push plate 5, the second push plate 6 and the third push plate 7 are respectively connected to wires near the wire opening 22. The wires pass through the wire opening 22 and the wire seat 20 and are connected to the external detection system. The upper surface of the upper guide rail frame 4 is provided with a first elastic component. The right end of the first push rod 14, the second push rod 14 and the third push rod 14 is provided with a second elastic component. The first elastic component and the second elastic component can respectively apply a rightward force to each push rod 14.The first elastic component includes a pair of guide rods 12, three pairs of compression springs 13, and four pairs of fixing brackets 24. The four pairs of fixing brackets 24 are fixedly mounted on the upper surface of the upper guide rail frame 4 near the front and rear edges. The four pairs of fixing brackets 24 are distributed near the end of the second sliding opening 23. The pair of guide rods 12 are arranged in parallel and fixedly mounted on the fixing brackets 24. The push rod 14 is slidably mounted on the pair of guide rods 12. The compression springs 13 are sleeved on the guide rods 12 and are located between the left side wall of the push rod 14 and the fixing brackets 24. The second elastic component includes a tension spring 11 and a pull ring 10. The right ends of the first push rod 14, the second push rod 14, and the third push rod 14 are respectively provided with protruding locking blocks 30. The right side of the upper surface of the upper guide rail frame 4 A fixing plate 25 is provided at the position of the probe. One end of the tension spring 11 is connected to the fixing plate 25, and the other end is connected to the pull ring 10. The pull ring 10 is engaged with the locking block 30. A pin 9 is provided on the upper cover 18 and the lower cover 1 near the probe opening 19. The pin 9 is located between each pair of clamps 29. When the clamps 29 and the clamping pieces 8 extend out of the probe, the pairs of clamping pieces 8 can be separated. A limit plate 27 is provided on the lower guide rail frame 3 at the position corresponding to the edge of the first push plate 5, the second push plate 6, and the third push plate 7. A limit seat 2 is provided inside the lower cover 1, and the lower guide rail frame 3 is engaged in the limit seat 2. The upper guide rail frame 4 and the lower guide rail frame 3 are connected by a snap-fit. The upper cover 18 and the lower cover 1 are connected by a snap-fit.

[0019] Its detailed connection methods are well-known technologies in this field. The following mainly introduces the working principle and process, as follows: According to the instruction manual Figure 1-9It can be seen that, when the present invention is used, since a push rod 14 is fixedly connected to the upper end of the guide post 17 in the leftmost slot 28 on the first push plate 5, the upper end of the guide post 17 in the middle slot 28 on the first push plate 5 and the upper end of the guide post 17 in the left slot 28 on the second push plate 6 are jointly connected to a push rod 14, and the upper ends of the guide post 17 in the rightmost slot 28 on the first push plate 5, the rightmost slot 28 on the second push plate 6, and the upper ends of the guide post 17 in the slot 28 on the third push plate 7 are jointly connected to a push rod 14, therefore, personnel... Sliding the leftmost slide key 16 to the left causes the fastening post 15, push rod 14, and the leftmost guide post 17 to move to the left. The guide post 17 in the slot 28 causes the first push plate 5 to move to the left, thereby causing the clamping piece 8 and the chuck 29 to extend out of the probe 19. The chuck 29 is used to hold the component's measuring point. The clamping piece 8 and the first push plate 5 (including the second push plate 6 and the third push plate 7) are connected to an external testing system via wires to test the components. Extending a pair of chucks 29 can test components with dimensions ≤0.4mm. When the center slide key 16 is slid to the left, the center guide post 17 connected to the push rod 14 moves simultaneously with the first push plate 5 and the second push plate 6. Then, two pairs of chucks 29 and clamping pieces 8 extend out of the probe 19, increasing the width and enabling the testing of components with dimensions from 0.6mm to 1.0mm. When the right-side slide key 16 is slid to the left, the central guide post 17 connected to the push rod 14 moves simultaneously, corresponding to the first push plate 5, the second push plate 6, and the third push plate 7. This causes three pairs of chucks 29 and clamping plates 8 to extend out of the probe opening 19, further increasing the width and enabling the testing of components ranging from 1.2mm to 2mm in size. This invention, through its three-position design, allows for the deployment of different numbers of fixture chucks 29, thereby testing components of different package sizes. This improves the applicability of the test fixture, makes adjustment convenient and quick, and increases testing efficiency. Furthermore, it eliminates the need to develop dedicated fixtures for each new package, fundamentally saving on fixture design, manufacturing, procurement, and warehousing management costs.

[0020] In this invention, the clamping pieces 8 exist in pairs and possess a certain degree of elasticity. They cover the clamp 29 and extend out of the probe 19, splitting to clamp the component. Although the first and second elastic components can apply a rightward force to each push rod 14, causing the clamping pieces 8 and the clamp 29 to tend to retract, the component is in a split state when the clamp 29 is holding it. Friction occurs between the clamping pieces 8 and the probe 19, and there is also friction between the clamp 29 and the component. Therefore, the clamping pieces 8, the clamp 29, and the component are in a balanced state, and this actually makes the clamping by the clamp 29 more stable. This invention eliminates the cumbersome process of soldering leads, achieving a non-destructive electrical connection with the pins using the elastic clamping pieces 8. It completely avoids damage to the component caused by soldering thermal and mechanical stress, ensuring testing accuracy and product reliability.

[0021] The first elastic component includes a pair of guide rods 12, three pairs of compression springs 13, and four pairs of fixing brackets 24. The four pairs of fixing brackets 24 are fixedly installed on the upper surface of the upper guide rail frame 4 near the front and rear edges, avoiding the second sliding opening 23. The four pairs of fixing brackets 24 are distributed near the end of the second sliding opening 23. The pair of guide rods 12 are arranged in parallel and fixedly installed on the fixing brackets 24. The push rod 14 is slidably installed on the pair of guide rods 12. It can be installed on the guide rods 12 by means of limiting holes. The compression springs 13 are installed on the guide rods 12 and are located between the left side wall of the push rod 14 and the fixing brackets 24. The purpose is to make the push rod 14 tend to the right by the force, so that the chuck 29 and the clamping plate 8 can retract when not clamping.

[0022] During operation, the operator slides the slide key 16 to the left, causing the fastening column 15 and push rod 14 to move to the left, compressing the compression spring 13 and storing force. This increases the retraction force of the clamping plate and chuck 29 when holding components, thereby increasing the friction between the split clamping piece 8 and the probe 19, as well as the friction between the chuck 29 and the component, ensuring the stability of component clamping. Furthermore, after testing, sliding the slide key 16 to the left extends the clamping piece 8 further, leaving sufficient clearance. The component is then removed, and the slide key 16 is released. The force of the compression spring 13 causes the clamping piece 8 and chuck 29 to retract between the lower cover 1 and the upper cover 18.

[0023] The second elastic component includes a tension spring 11 and a pull ring 10. The right ends of the first push rod 14, the second push rod 14, and the third push rod 14 are each equipped with a protruding locking block 30. A fixing plate 25 is located on the right side of the upper surface of the upper guide rail frame 4. One end of the tension spring 11 is connected to the fixing plate 25, and the other end is connected to the pull ring 10. The pull ring 10 is engaged with the locking block 30. This engagement allows the locking block 30 to move the pull ring 10 when the chuck 29 is pushed out, causing the tension spring 11 to extend. However, the pull ring 10 cannot move the locking block 30, ensuring that the movement of the first push plate 5 does not affect the second push plate 6 and the third push plate 7, and vice versa. The tension spring 11 extends to store force, and the reaction force causes the working push plate to move to the right, similar to the function of the first elastic component.

[0024] Among them, the upper cover 18 and the lower cover 1 are provided with pins 9 near the probe opening 19. The pins 9 are located between each pair of clamps 29. When the clamps 29 and the clamping pieces 8 extend out of the probe, they can separate the pairs of clamping pieces 8 without the need for subsequent personnel to split them apart. At the same time, it also increases the friction experienced by the clamping pieces 8 when clamping.

[0025] Among them, limit plates 27 are provided on the lower guide rail frame 3 at the positions corresponding to the edges of the first push plate 5, the second push plate 6 and the third push plate 7, so that its movement is more stable.

[0026] The lower cover 1 is provided with a limiting seat 2, and the lower guide rail 3 is snapped into the limiting seat 2 to ensure the stability of the lower guide rail 3.

[0027] The upper guide rail frame 4 and the lower guide rail frame 3 are connected by a snap-fit ​​mechanism, and the upper cover 18 and the lower cover 1 are also connected by a snap-fit ​​mechanism, which allows for disassembly and facilitates maintenance.

[0028] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A component testing fixture with strong compatibility, characterized in that, The system includes a lower cover (1), a lower guide rail frame (3), an upper guide rail frame (4), and an upper cover (18). The lower guide rail frame (3) is fixedly installed inside the lower cover (1). The upper guide rail frame (4) is fastened to the lower guide rail frame (3). The upper cover (18) is fastened to the lower cover (1). A wire seat (20) is provided on the right end face of the upper cover (18). A probe (19) is provided between the left end face of the upper cover (18) and the lower cover (1). A cavity is formed between the upper guide rail frame (4) and the lower guide rail frame (3). A first push plate (5), a second push plate (6), and a third push plate (7) are horizontally arranged in the cavity. The first push plate (5) is provided with three slots (28). The second push plate (6) is provided with... There are two slots (28). The first push plate (5) is provided with one slot (28). The first push plate (5), the second push plate (6) and the third push plate (7) are electrically connected to a pair of clamps (8) on the side corresponding to the probe (19) and the clamps (8) have a certain elasticity. The clamps (8) move through the upper guide rail frame (4) and the lower guide rail frame (3). The side of the clamps (8) corresponding to the probe (19) is provided with a clamp (29). The three pairs of clamps (29) can extend out of the probe (19). The lower guide rail frame (3) is provided with a third sliding opening (26) at the position corresponding to each slot (28). The upper guide rail frame (4) is provided with a second sliding opening (23) at the position corresponding to the third sliding opening (26). A guide post (17) is provided through the slot (28). The guide post (17) passes through the second sliding opening (23) and the third sliding opening (26) and can slide. A push rod (14) is fixedly connected to the upper end of the guide post (17) in the leftmost slot (28) on the first push plate (5). The upper end of the guide post (17) in the middle slot (28) on the first push plate (5) and the upper end of the guide post (17) in the left slot (28) on the second push plate (6) are connected to a push rod (14). The upper ends of the guide post (17) in the rightmost slot (28) on the first push plate (5), the upper ends of the guide post (17) in the right slot (28) on the second push plate (6), and the upper ends of the guide post (17) in the slot (28) on the third push plate (7) are connected to a push rod (14). There is a push rod (14), and fastening posts (15) are fixedly installed on the three push rods (14). A sliding key (16) is fixedly installed at the upper end of the fastening post (15). The upper cover (18) is provided with a first sliding opening (21) corresponding to each sliding key (16). The sliding key (16) passes through the first sliding opening (21) and can slide. The upper guide rail frame (4) has a wire opening (22) on the side near the wire seat (20). The first push plate (5), the second push plate (6) and the third push plate (7) are respectively connected to wires near the wire opening (22). The wires pass through the wire opening (22) and the wire seat (20) and are connected to the external detection system. The upper surface of the upper guide rail frame (4) is provided with a first elastic component.The right ends of the first push rod (14), the second push rod (14), and the third push rod (14) are provided with second elastic components. The first elastic component and the second elastic component are respectively capable of applying a rightward force to each push rod (14).

2. The component testing fixture with strong compatibility according to claim 1, characterized in that, The first elastic component includes a pair of guide rods (12), three pairs of compression springs (13) and four pairs of fixing brackets (24). The four pairs of fixing brackets (24) are fixedly installed on the upper surface of the upper guide rail frame (4) near the front and rear edges. The four pairs of fixing brackets (24) are distributed near the end of the second sliding opening (23). The pair of guide rods (12) are arranged in parallel and fixedly installed on the fixing brackets (24). The push rod (14) is slidably installed on the pair of guide rods (12). The compression springs (13) are sleeved on the guide rods (12) and are located between the left side wall of the push rod (14) and the fixing brackets (24).

3. The component testing fixture with strong compatibility according to claim 1, characterized in that, The second elastic component includes a tension spring (11) and a pull ring (10). The right ends of the first push rod (14), the second push rod (14), and the third push rod (14) are respectively provided with protruding locking blocks (30). A fixing plate (25) is provided on the right side of the upper surface of the upper guide rail frame (4). One end of the tension spring (11) is connected to the fixing plate (25), and the other end is connected to the pull ring (10). The pull ring (10) is attached to the locking block (30).

4. The component testing fixture with strong compatibility according to claim 1, characterized in that, The upper cover (18) and the lower cover (1) are provided with pins (9) at positions close to the probe opening (19). The pins (9) are located between each pair of clamps (29). When the clamps (29) and the clips (8) extend out of the probe, the pairs of clips (8) can be separated.

5. The component testing fixture with strong compatibility according to claim 1, characterized in that, Limiting plates (27) are provided on the lower guide rail frame (3) at positions corresponding to the edges of the first push plate (5), the second push plate (6) and the third push plate (7).

6. The component testing fixture with strong compatibility according to claim 1, characterized in that, The lower cover (1) is provided with a limiting seat (2), and the lower guide rail frame (3) is snapped into the limiting seat (2).

7. The component testing fixture with strong compatibility according to claim 1, characterized in that, The upper guide rail frame (4) and the lower guide rail frame (3) are connected by a snap-fit ​​connection.

8. The component testing fixture with strong compatibility according to claim 1, characterized in that, The upper cover (18) and the lower cover (1) are connected by a snap fastener.

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