Air knife structure, printed circuit board tin spraying method and printed circuit board

Abstract

The invention discloses an air knife structure, a printed circuit board tin spraying method and a printed circuit board, the air knife structure comprises an air knife body, the air knife body is provided with a spraying pipe, a spraying cavity is formed by the spraying pipe and the air knife body, the spraying cavity is communicated with an air outlet of the spraying pipe and an air outlet of the air knife, and air entering from the spraying pipe enters the spraying cavity through the air outlet of the spraying pipe and then enters the spraying cavity. And then the air enters the air outlet of the air knife. Through the designed air knife structure, the circuit board engineering design and process technical parameters are optimized, so that the bad problems of high tin content, continuous tin and the like in areas of large copper surfaces, dense PADs, PTH welding rings and the like of existing tin spraying products are effectively solved, the yield of the products is improved, and the production cost is saved.

Description

Technical Field

[0001] The invention relates to the technical field of circuit board manufacturing, and in particular to an air knife structure, a printed circuit board tin spraying method and a printed circuit board. Background Art

[0002] Tin spraying is also known as hot air leveling. The PCB board (circuit board) coated with flux is immersed in molten tin liquid through the guide rail of the tin spraying machine, so that the PCB surface is coated with tin liquid, and then the excess tin on the board surface is leveled by heated compressed air through the wind knife. The molten tin liquid is evenly attached to the copper skin, completing the entire tin spraying process. The tin layer after tin spraying can effectively protect the copper skin and circuit from corrosion and oxidation, and increase the mechanical properties and service life of the copper skin and circuit. However, at present, PCB boards with tin spraying surface treatment in areas such as large copper surfaces, dense PADs and PTH solder rings often have tin short circuits, tin high pressure flatness (tin cakes), and the cursor point cannot be properly identified and aligned due to the influence of tin high, which causes quality problems. Summary of the invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide an air knife structure, a printed circuit board tin spraying method and a printed circuit board.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] In the first aspect, the present invention provides a wind knife structure, including a wind knife body, the wind knife body is provided with a nozzle, the nozzle and the wind knife body form a spray chamber, the spray chamber is connected with the air outlet of the nozzle and the air outlet of the wind knife, the gas entering from the nozzle enters the spray chamber through the air outlet of the nozzle, and then enters the air outlet of the wind knife.

[0006] Furthermore, the air knife body is provided with a slot hole, the nozzle is arranged in the slot hole, and the spacing area between the inner side wall of the slot hole and the outer wall of the nozzle forms the spray cavity.

[0007] Furthermore, the spray chamber is an annular structure.

[0008] Furthermore, the air outlet of the air knife and the air outlet of the nozzle are arranged opposite to each other along the spray chamber.

[0009] In a second aspect, the present invention further provides a tin spraying method for a printed circuit board, wherein the tin spraying operation is performed based on a tin spraying device, wherein the tin spraying device comprises a tin spraying machine track, a fixture, a tin cylinder and the above-mentioned air knife structure, wherein the air knife structure is provided with two, namely a front air knife and a rear air knife, wherein the front air knife and the rear air knife are installed on the tin spraying machine track and can be moved relative to the tin spraying machine track and the angle can be adjusted, wherein the tin spraying machine track is connected to the circuit board to be processed through the fixture, and tin liquid is contained in the tin cylinder, and the circuit board to be processed can be immersed in the tin liquid through the tin spraying machine track; the method comprises:

[0010] Perform micro-etching on the circuit board to be processed;

[0011] Use tin bars and cooperate with front and rear air knives to spray tin on the circuit board after micro-etching;

[0012] Brush the circuit board after tin spraying treatment;

[0013] Perform ultrasonic water washing on the circuit board after the brushing treatment;

[0014] Drying the circuit board after ultrasonic washing;

[0015] Perform hole inspection on the baked circuit board.

[0016] Furthermore, the method of using a tin bar in combination with a front air knife and a rear air knife to spray tin on the circuit board after micro-etching includes:

[0017] Place the lead-free tin bar as the tin spraying material in the tin tank, and control the temperature of the tin tank at 260℃-280℃;

[0018] Adjust the front air knife to a first angle, and adjust the rear air knife to a second angle, wherein the first angle is less than or equal to the second angle;

[0019] First turn on the front air knife to work, then turn on the rear air knife to work, and the air pressure of the front air knife is lower than the air pressure of the rear air knife.

[0020] Furthermore, when the thickness of the circuit board is less than 0.8mm, the time to descend into the tin tank is 1.9s; when the thickness of the circuit board is less than the thickness of 0.8mm-2.0mm, the time to descend into the tin tank is 1s; when the thickness of the circuit board is greater than 2mm, the time to descend into the tin tank is 1.8S; the time for the circuit board to be immersed in the tin tank is 4.5s.

[0021] Furthermore, it also includes:

[0022] When the distance between two adjacent pads of the circuit board is 0.2mm-0.15mm, the pads are designed with green oil solder bridge; if the distance from the line to the edge of the pad is less than 5mil, the two adjacent pads are designed as H-type connection.

[0023] Furthermore, it also includes:

[0024] If the distance between the annular rings or between the annular rings and the pad is less than 0.4 mm, the annular rings and copper foil shall be cut.

[0025] In a third aspect, the present invention further provides a printed circuit board, wherein the printed circuit board is prepared by the above-mentioned printed circuit board tin spraying method.

[0026] Compared with the prior art, the present invention has the following beneficial effects: an air knife structure, including an air knife body, the air knife body is provided with a nozzle, the nozzle and the air knife body form a spray chamber, the spray chamber is connected with the air outlet of the nozzle and the air outlet of the air knife, and the gas entering from the nozzle enters the spray chamber through the air outlet of the nozzle and then enters the air outlet of the air knife. The present invention has a designed air knife structure and optimizes the circuit board engineering design and process technology parameters, thereby effectively solving the existing tin spraying products in the large copper surface, dense PAD and PTH solder ring area. The defective problems such as high tin and tin connection are improved, thereby improving the product yield and saving production costs.

[0027] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the following preferred embodiments are specifically cited and described in detail as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying any creative work.

[0029] Figure 1 A schematic structural diagram of an air knife structure provided for a specific embodiment of the present invention;

[0030] Figure 2 A schematic diagram of the structure of a tin spraying device provided in a specific embodiment of the present invention;

[0031] Figure 3 A comparison diagram of the solder bridge design provided by a specific embodiment of the present invention and the existing design;

[0032] Figure 4A comparison diagram of the H-type connection method provided by a specific embodiment of the present invention and the existing design;

[0033] Figure 5 A comparison diagram of the use of a punched hole ring and copper skin treatment provided in a specific embodiment of the present invention and the existing design;

[0034] Figure 6 A schematic diagram of designing multiple lines for a process edge provided by a specific embodiment of the present invention;

[0035] Figure 7 The present invention is a flowchart of a method for spraying tin on a printed circuit board provided in a specific embodiment of the present invention.

[0036] Reference numerals

[0037] 1. Air knife body; 11. Nozzle; 111. Air outlet of the nozzle; 12. Spray chamber; 13. Air outlet of the air knife; 2. Tin spraying machine track; 3. Fixture; 4. Tin cylinder; 100. Circuit board to be processed; 1A. Front air knife; 1B. Rear air knife. DETAILED DESCRIPTION

[0038] The technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention. Obviously, the described embodiments are 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.

[0039] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0040] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0041] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0042] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0043] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used herein are for illustrative purposes only and are not intended to be the only implementation method.

[0044] like Figure 1 As shown, an embodiment of the present invention provides a wind knife structure, including a wind knife body 1, the wind knife body 1 is provided with a nozzle 11, the nozzle 11 and the wind knife body 1 form a spray chamber 12, the spray chamber 12 is connected with the air outlet 111 of the nozzle 11 and the air outlet 13 of the wind knife, the gas entering from the nozzle 11 enters the spray chamber 12 through the air outlet 111 of the nozzle 11, and then enters the air outlet 13 of the wind knife.

[0045] The air knife body 1 is the main part of the entire air knife structure and is made of metal materials, such as stainless steel, to ensure that it has good strength and corrosion resistance in a high temperature and high pressure working environment. The air knife body 1 has a certain shape and size, and its shape and size design needs to be based on the actual application scenario.

[0046] The nozzle 11 is installed on the air knife body 1, and the material of the nozzle 11 is a high temperature resistant and corrosion resistant metal material. The diameter of the nozzle 11 will affect the flow rate and flow of the gas, and thus affect the working effect of the air knife. In practical applications, the nozzle 11 of a suitable diameter can be selected according to the required gas pressure and flow. For example, in the case where a larger airflow impact force is required to remove excess tin liquid on the PCB board, a nozzle 11 with a slightly larger diameter can be selected. The nozzle 11 can be installed on the air knife body 1 by welding or threaded connection to ensure a firm connection and prevent gas leakage.

[0047] A spray chamber 12 is formed between the nozzle 11 and the air knife body 1. In one embodiment, the air knife body 1 is provided with a slot, and the nozzle 11 is provided in the slot. The interval area between the inner wall of the slot and the outer wall of the nozzle 11 forms the spray chamber 12. This structural design is simple and easy to manufacture. The shape of the slot can be circular, rectangular, etc., and the shape of the nozzle 11 needs to be compatible with the slot to ensure the sealing of the spray chamber 12 and the smoothness of the gas flow.

[0048] The gas entering from the nozzle 11 first enters the spray chamber 12 through the air outlet 111 of the nozzle 11. The air outlet 111 of the nozzle 11 can be designed into a variety of shapes, such as circular, elliptical or slit-shaped. Air outlets of different shapes will affect the initial distribution of the gas entering the spray chamber 12. After the gas enters the spray chamber 12, due to the special structural design of the spray chamber 12, it will be mixed and diffused to a certain extent in the spray chamber 12, and then blown out from the air outlet 13 of the wind knife. The air outlet 13 of the wind knife is arranged relative to the air outlet 111 of the nozzle 11 along the spray chamber 12. This relative arrangement enables the gas to form a relatively stable flow path in the spray chamber 12, ensuring that the gas blown out from the air outlet of the wind knife has a uniform pressure and flow rate distribution.

[0049] Through the coordinated design of the nozzle 11, the spray chamber 12 and the air knife outlet, the gas entering from the nozzle 11 can be blown back from the air knife outlet after passing through the spray chamber 12, so that the wind pressure is more uniform, thereby improving the uniformity of the tin thickness on the tin surface and avoiding the problem of high tin.

[0050] In one embodiment, the spray chamber 12 is an annular structure. The annular spray chamber 12 can make the gas more evenly distributed in the chamber. When the gas enters the annular spray chamber 12 from the nozzle 11, due to the symmetry of the annular structure, the gas can be evenly diffused in the annular space, avoiding the situation where the gas gathers in a local area or the flow rate is uneven. In the PCB board tin spraying process, the air flow blown out from the air knife outlet is more evenly distributed on the surface of the PCB board, which can more effectively blow the tin liquid flat and reduce the occurrence of problems such as high tin and tin bridging.

[0051] The embodiment of the present invention also provides a tin spraying method for a printed circuit board, wherein the tin spraying operation is performed based on a tin spraying device, such as Figure 2 As shown, the tin spraying device includes a tin spraying machine track 2, a clamp 3, a tin cylinder 4 and the above-mentioned air knife structure. The air knife structure is provided with two, namely a front air knife 1A and a rear air knife 1B. The front air knife 1A and the rear air knife 1B are installed on the tin spraying machine track 2, and can be moved relative to the tin spraying machine track 2 and the angle can be adjusted. The tin spraying machine track 2 is connected to the circuit board 100 to be processed by the clamp 3. The tin cylinder 4 contains tin liquid, and the circuit board 100 to be processed can be immersed in the tin liquid through the tin spraying machine track 2.

[0052] The tin spraying machine track 2 is made of high-strength metal materials, such as aluminum alloy or stainless steel. The track is linear in shape, and its length is determined according to the space of the production site and actual production requirements. The cross-sectional shape of the track can be rectangular or I-shaped.

[0053] The main function of the tin spraying machine track 2 is to provide a moving path for the fixture 3 and the circuit board 100 to be processed. It is fixed to the workbench of the tin spraying equipment through a support structure installed at the bottom, and the support structure can be an adjustable height anchor bolt to adjust the horizontality of the track according to actual production needs.

[0054] The design of the clamp 3 needs to be customized according to the size, shape and material of the circuit board. For common rectangular PCB boards, a clamp-type clamp 3 can be used, and the material of the clamp is usually high-temperature resistant plastic or metal, such as polytetrafluoroethylene or aluminum alloy. The inner side of the clamp can be designed with anti-skid patterns or rubber pads to increase the friction with the circuit board to prevent the circuit board from slipping during movement. The opening and closing method of the clamp 3 can be manual, and the opening and closing of the clamp is achieved by rotating the screw or pulling the handle. This method is suitable for small-scale production or experimental stages; it can also be pneumatic or electric, and the movement of the clamp is controlled by compressed air or motor drive, which is suitable for large-scale production and can improve production efficiency and consistency of operation.

[0055] The fixture 3 is connected to the tin spraying machine track 2 through a slider or a roller, and the slider or the roller is generally made of wear-resistant engineering plastic or metal, such as nylon or carbon steel. Such a connection method enables the fixture 3 to move smoothly on the track, and the moving speed can be adjusted according to the production process requirements.

[0056] The tin cylinder 4 is used to hold the tin liquid and is made of stainless steel to ensure its corrosion resistance and strength in a high temperature environment. The tin cylinder 4 is in the shape of a cuboid or a cylinder, and its size is determined according to the production scale and the number of circuit boards processed at one time. A heating device, such as an electric heating wire or a gas heating furnace, is provided at the bottom of the tin cylinder 4 to melt the tin bar and keep the temperature of the tin liquid within a suitable range.

[0057] The front air knife 1A and the rear air knife 1B are installed on the tin spraying machine track 2, and the installation method can be fixed by an adjustable bracket. The bracket is made of metal material, such as aluminum alloy or carbon steel, and has sufficient strength and stability. An adjustment mechanism is provided on the bracket to realize the movement and angle adjustment of the air knife relative to the tin spraying machine track 2. For example, the adjustment mechanism can be a translation adjustment device composed of a screw and a nut, and the air knife can be moved back and forth in the direction of the track by rotating the nut; the angle adjustment device can be composed of a hinge and an angle dial, and the angle of the air knife can be adjusted by loosening the hinge bolt, and then tightening the bolt to fix it.

[0058] The front air knife 1A and the rear air knife 1B work together when working. The front air knife 1A is turned on first to perform preliminary blowing and leveling of the tin liquid on the surface of the circuit board rising from the tin cylinder 4 at a lower air pressure and a smaller angle to preliminarily remove excess tin liquid. The rear air knife 1B is then turned on to perform further fine blowing and leveling of the circuit board surface at a higher air pressure and a slightly larger angle to make the tin liquid adhere to the circuit board surface more evenly.

[0059] Through the movable and angle-adjustable wind knife structure, the position and angle of the wind knife can be accurately adjusted according to the shape, size and tin-spraying process requirements of different circuit boards, so that the airflow blown by the wind knife can act more effectively on the surface of the circuit board, evenly remove excess tin liquid, avoid problems such as high tin and tin bridging, and thus improve the quality of tin-spraying. For example, for PCB boards with complex shapes and dense circuits, by accurately adjusting the wind knife angle, it can be ensured that the airflow can reach every area that needs to be processed, so that the tin layer is evenly covered.

[0060] The combined design of the tin spraying machine track 2, the fixture 3 and the adjustable air knife enables the tin spraying device to meet the tin spraying requirements of circuit boards of different sizes, shapes and materials.

[0061] like Figure 7 As shown, a method for tin spraying on a printed circuit board includes the following steps: S10-S60.

[0062] S10, performing micro-etching on the circuit board 100 to be processed.

[0063] The main components of the micro-etching solution are H2SO4 (concentration 3%) and Na2S208 (concentration 120±20g / L). The micro-etching amount is controlled at 0.8±0.1μm, the conveying speed is 3000±100mm / min, and the solution spraying pressure is 1.3±0.3kgf / cm2.

[0064] S20, using a tin bar in conjunction with the front air knife 1A and the rear air knife 1B to perform tin spraying on the circuit board after the micro-etching treatment.

[0065] In one embodiment, step S20 specifically includes the following steps: S201 - S203 .

[0066] S201, placing a lead-free tin bar as a tin spraying material in a tin tank 4, and controlling the temperature of the tin tank 4 at 260°C-280°C.

[0067] S202, adjusting the front air knife 1A to a first angle, and adjusting the rear air knife 1B to a second angle, wherein the first angle is less than or equal to the second angle.

[0068] S203, first turn on the front air knife 1A to work, then turn on the rear air knife 1B to work, and the air pressure of the front air knife 1A is lower than the air pressure of the rear air knife 1B.

[0069] For steps S201-S203, the angle of the front air knife 1A is set to 2-4°, the angle of the rear air knife 1B is set to 4-6, the temperature of the air outlet 13 of the air knife is 360°C, and the distance between the front air knife 1A and the rear air knife 1B on the tin spraying machine track 2 is 2-4mm. The air pressure of the front air knife 1A is set to 3.8kg / c㎡, and the air pressure of the rear air knife 1B is set to 4.3kg / c㎡. The front air knife 1A is turned on first and then the rear air knife 1B. Since the air pressure of the front air knife 1A is lower than that of the rear air knife 1B, the front air knife 1A is turned on first, and the hot air will flatten the solder of the front PCB board pad, and the solder in the hole ring will be blown to the back, causing the hole ring solder to accumulate. At this time, the rear air knife 1B is turned on again, and the air pressure is increased, so that the excess solder on the back hole ring can be removed and flattened.

[0070] Specifically, when the thickness of the circuit board is less than 0.8mm, the time for it to descend to the tin tank 4 is 1.9s; when the thickness of the circuit board is less than the thickness of 0.8mm-2.0mm, the time for it to descend to the tin tank 4 is 1s; when the thickness of the circuit board is greater than 2mm, the time for it to descend to the tin tank 4 is 1.8S; the time for the circuit board to be immersed in the tin tank 4 is 4.5s, and the time for the circuit board to rise after tin spraying is 2.5S.

[0071] In addition, when the 3rd tin spraying stops production for more than or equal to 3 minutes, when reproducing, it is necessary to spray twice without spraying / soak for 10 seconds to prevent tin from sticking and causing tin high and tin connection. In addition, after spraying 60 circuit boards, the front air knife 1A and the rear air knife 1B need to be cleaned to avoid tin slag causing air knife blockage and board surface residue.

[0072] S30, performing a grinding and brushing process on the circuit board after the tin-spraying process.

[0073] The PCB boards after tin spraying are transported at a speed of 4000 mm per minute to ensure that the PCB boards maintain an appropriate rhythm during the subsequent processing, neither inadequate processing due to too fast speed nor affecting production efficiency due to too slow speed. The air floating bed is a device that uses airflow to suspend and transport PCB boards. In this process, it is necessary to prevent the boards from overlapping each other, because once the boards are stacked together, friction may occur during the transportation process, which will scratch the tin-sprayed surface and affect the appearance and performance of the PCB board.

[0074] When the PCB board after tin spraying is transported to the designated location, the PCB board is processed with a brush to effectively remove burrs, debris or uneven tin layer that may exist on the surface of the PCB board, making the board surface smoother and flatter.

[0075] S40, performing ultrasonic water washing treatment on the circuit board after the grinding and brushing treatment.

[0076] After grinding and brushing, ultrasonic water washing is used to further clean the PCB board. Ultrasonic water washing uses the cavitation effect produced by ultrasound in liquid to rapidly generate, grow and rupture tiny bubbles in the liquid under the action of ultrasound, generating strong impact force and micro jets, which can penetrate into the tiny holes and gaps of the PCB board, and thoroughly clean the debris, residual abrasive and other impurities generated during the grinding and brushing process, ensuring the cleanliness of the PCB board.

[0077] S50, drying the circuit board after the ultrasonic washing process.

[0078] After grinding and ultrasonic washing, moisture will remain on the surface of the PCB board and needs to be dried. The drying process can remove moisture from the surface and holes of the PCB board to prevent moisture residue from causing short circuits, corrosion and other problems during subsequent use of the PCB board. It also provides dry surface conditions for inspection, facilitating clearer observation and detection.

[0079] S60, performing hole detection on the dried circuit board.

[0080] After drying, the PCB board should be fully inspected, with the focus on checking whether there is any hole blockage. Blockage will affect the electrical connection performance of the PCB board, leading to problems such as poor signal transmission or short circuit. Therefore, each hole needs to be carefully inspected to ensure that there is no debris blocking the hole to ensure that the quality and performance of the PCB board meet the requirements.

[0081] It should be noted that if Figure 3 As shown in the figure, when the distance between two adjacent pads of the circuit board is 0.2mm-0.15mm, the pads are designed with a green oil solder bridge. This design can prevent the problem of poor tin connection and short circuit during tin spraying due to the small distance between the pads.

[0082] It should also be noted that if Figure 4 As shown in the figure, for the same network pad, if the distance from the line to the edge of the pad is less than 5 mil, the two adjacent pads should be designed as an H-type connection, or an anti-tombstone design should be adopted to avoid the risk of tin connection of the pad after SMT.

[0083] It should also be noted that if Figure 5 As shown, if the spacing between the annular rings or between the annular rings and the pad is less than 0.4 mm, the annular rings and the copper foil are cut. This design can increase the spacing between the annular rings and prevent the problem of short circuit during tin spraying.

[0084] It should also be noted that if Figure 6 As shown, multiple circuits are designed on the process side to improve the connection ability between the fixture 3 and the PCB board during tin spraying, so as to prevent the PCB board from falling into the tin tank 4 during the tin spraying process, causing problems such as tin high, tin connection and board damage.

[0085] The embodiment of the present invention further provides a printed circuit board, which is prepared by the printed circuit board tin spraying method as described above.

[0086] The present invention adopts a designed wind knife structure and optimizes the circuit board engineering design and process technical parameters, thereby effectively solving the problems of high tin and bridging tin in existing tin-spraying products in areas such as large copper surfaces, dense PADs and PTH solder rings, thereby improving the product yield and saving production costs.

[0087] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A wind knife structure, characterized in that: It includes an air knife body, which is provided with a nozzle. The nozzle and the air knife body form a spray chamber, and the spray chamber is connected with the air outlet of the nozzle and the air outlet of the air knife. The gas entering from the nozzle enters the spray chamber through the air outlet of the nozzle and then enters the air outlet of the air knife.

2. The wind knife structure according to claim 1, characterized in that: The air knife body is provided with a slot hole, the nozzle is arranged in the slot hole, and the interval area between the inner side wall of the slot hole and the outer wall of the nozzle forms the spray cavity.

3. The wind knife structure according to claim 1, characterized in that: The spray chamber is an annular structure.

4. The wind knife structure according to claim 1, characterized in that: The air outlet of the wind knife and the air outlet of the nozzle are arranged opposite to each other along the spray cavity.

5. A method for spraying tin on a printed circuit board, characterized in that: The tin spraying operation is performed based on a tin spraying device, the tin spraying device comprises a tin spraying machine track, a fixture, a tin cylinder and the air knife structure according to any one of claims 1 to 4, the air knife structure is provided with two, namely a front air knife and a rear air knife, the front air knife and the rear air knife are installed on the tin spraying machine track, and can be moved relative to the tin spraying machine track and the angle is adjusted, the tin spraying machine track is connected to the circuit board to be processed through the fixture, the tin cylinder contains tin liquid, and the circuit board to be processed can be immersed in the tin liquid through the tin spraying machine track; the method comprises: Perform micro-etching on the circuit board to be processed; Use tin bars and cooperate with front and rear air knives to spray tin on the circuit board after micro-etching; Brush the circuit board after tin spraying treatment; Perform ultrasonic water washing on the circuit board after the brushing treatment; Drying the circuit board after ultrasonic washing; Perform hole inspection on the baked circuit board.

6. A method for spraying tin on a printed circuit board according to claim 5, characterized in that: The method of using a tin bar in combination with a front air knife and a rear air knife to spray tin on a circuit board after micro-etching treatment includes: Place the lead-free tin bar as the tin spraying material in the tin tank, and control the temperature of the tin tank at 260℃-280℃; Adjust the front air knife to a first angle, and adjust the rear air knife to a second angle, wherein the first angle is less than or equal to the second angle; First turn on the front air knife to work, then turn on the rear air knife to work, and the air pressure of the front air knife is lower than the air pressure of the rear air knife.

7. A method for spraying tin on a printed circuit board according to claim 6, characterized in that: When the thickness of the circuit board is less than 0.8mm, the time to descend to the tin tank is 1.9s; when the thickness of the circuit board is less than 0.8mm-2.0mm, the time to descend to the tin tank is 1s; when the thickness of the circuit board is greater than 2mm, the time to descend to the tin tank is 1.8S; the time for the circuit board to be immersed in the tin tank is 4.5s.

8. A method for spraying tin on a printed circuit board according to claim 5, characterized in that: Also includes: When the distance between two adjacent pads of the circuit board is 0.2mm-0.15mm, the pads are designed with green oil solder bridge; if the distance from the line to the edge of the pad is less than 5mil, the two adjacent pads are designed as H-type connection.

9. A method for spraying tin on a printed circuit board according to claim 5, characterized in that: Also includes: If the distance between the annular rings or between the annular rings and the pad is less than 0.4 mm, the annular rings and copper foil shall be cut.

10. A printed circuit board, characterized in that: The printed circuit board is prepared by the printed circuit board tin spraying method according to any one of claims 5 to 9.

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