A PCB tin spraying process for improving the flatness of the tin spraying surface

Abstract

The present invention discloses a PCB tin spraying process for improving the flatness of the tin spraying surface, which belongs to the technical field of printed circuit board process. The present invention adds an online detection method to the tin spraying process of the PCB, and then optimizes the process parameters such as the solder paste spraying pattern, the spraying area and the amount of tin spraying of common packaging components produced by the enterprise, and obtains the threshold range setting rules of the key parameters of the tin spraying point detection according to the shape characteristics of the solder paste spraying solder joints. Finally, the results of the spraying optimization are verified by repeatability tests, and it is proved in both theory and experiment that the optimization parameters improve the solder paste spraying quality and solder joint detection efficiency. The present invention solves the technical problems of poor flatness in the PCB tin spraying process in the prior art.

Description

Technical Field

[0001] The invention relates to the technical field of printed circuit board technology, and in particular to a PCB tin-spraying technology for improving the flatness of the tin-spraying surface. Background Art

[0002] At present, with the development of the electronics industry, PCB boards, as important electronic components, have been widely used. In the process of making PCB boards, tin spraying is an important process in making PCB boards. As a surface treatment process for PCB boards, tin spraying has many advantages such as reliable welding and good weldability. The traditional tin spraying method is to immerse the PCB board in molten solder, and then use hot air to blow off the excess solder on the surface of the PCB board and in the metallized holes, so as to obtain a smooth, uniform and bright solder coating layer.

[0003] When the PCB board is undergoing the tin spraying process, it is usually provided with a special tin spraying hanging hole, which is used to hang the PCB board through the tin spraying hanging hole and then perform the tin spraying operation. That is, the copper clad board that needs to be tin sprayed on the surface will be sent to the drilling process after cutting, and the tin spraying hanging hole will be punched by a pin machine at the process side, and then sent to the circuit workshop for circuit making. However, with the continuous development of technology, the functions of PCB boards are becoming more and more powerful. In order to meet more powerful functional requirements, some PCB boards must be made thicker to achieve this.

[0004] In the existing PCB board process, the board edge is designed with copper plating. The solder mask printing cannot completely cover the board edge, and the board edge will be tinned during tin spraying. Since the position of the tin spraying hanging hole on the board edge overlaps with the hook of the tin spraying machine, the hot air in this area is not evenly blown, and there will be unevenness and tin accumulation. This problem is more obvious for thick boards above 2mm. Due to the uneven tin surface and tin accumulation, the uniformity of the tin thickness of the whole board will be affected. If the forming method is die punching, it will affect the die punching times and the forming size. If the forming method is CNC, the stacking will be uneven, affecting the number of stacking sheets and the forming size accuracy. At the same time, the waste of tin bars and labor for soldering and polishing the tin spraying hanging holes greatly reduces the production efficiency. In the existing technology, the plate thickness production capacity of the vertical tin spraying machine is limited. For the tin spraying treatment of thick boards, it is generally necessary to change the surface treatment method, such as changing to immersion gold, immersion tin, immersion silver and other surface treatment methods. However, changing to immersion gold, immersion tin, and immersion silver will increase the production cost by 3-6 times on the original tin spraying surface treatment cost, and the performance will also decrease. Based on this, Chinese patent CN107683029B discloses a negative PCB board tin spraying process, which includes the following steps: A, water washing; B, micro-etching; C, hot water washing; D, applying flux; E, tin spraying hanging hole solder mask; F, tin spraying; G, brushing; H, water washing; I, drying. In the negative PCB board tin spraying process, the tin spraying hanging hole is subjected to solder mask countermeasures before the tin spraying operation. By applying solder mask printing ink to the tin spraying hanging hole position, and exposing, developing, and baking the printing ink, a layer of solder mask is formed to prevent the tin material from solidifying at the tin spraying hanging hole during the tin spraying operation, thereby causing the problem of tin accumulation at the tin spraying hanging hole position. Since the printing ink forms a solder mask layer at the tin spraying hanging hole, there is no tin material adhering to the tin spraying hanging hole during tin spraying, and the tin spraying hanging hole is flat. A smooth, uniform and bright solder coating layer is obtained around the tin spraying hanging hole position. The process method is simple and easy to operate, and the formation of tin accumulation at the tin spraying hanging hole position is effectively prevented, and the tin spraying hanging hole position is flat and uniform.

[0005] However, the above-disclosed PCB board tin-spraying process still has a technical problem of unstable product quality due to the lack of online detection technology. Specifically, with the rapid iterative development of production technology and the increasingly fierce competition in the electronic product market, product quality and cost savings have become the main research directions of electrical assembly technology, and optimization methods for production quality and cost control have also been applied to actual industrial production processes. However, whether it is the product quality control strategy or the direct arrangement of product production cycle and line change, the problem of online detection of solder joint quality during product production has always been difficult to solve. Restricted by many factors such as process, technology and production equipment, some important process parameters and testing standards are difficult to pass existing

[0006] There are devices that can achieve real-time detection and transmission, and data can only be detected and recorded by taking the method of timed quantitative offline analysis, that is, uniform quality inspection is carried out every period of time or when each batch of production reaches a certain number, and then production is improved based on the data obtained from the inspection. Obviously, such a detection method with a strong hysteresis can no longer meet the needs of current industrial production. Especially for the PCB manufacturing industry with a high degree of automation, due to the lack of an online detection system for the PCB tin spraying process, users have been unable to completely solve the problem of poor tin spraying and affecting the surface flatness of the PCB despite constantly changing improvement measures. The online detection technology is an emerging technology that has gradually developed to meet the real-time measurement and control needs of production. This technology provides a guarantee for further optimizing the production process, improving the production qualification rate, and reducing production costs through the control of the production process and the detection and analysis of product quality. Summary of the invention

[0007] Based on this, it is necessary to provide a PCB tin spraying process that improves the flatness of the tin spraying surface in order to address the technical problems such as poor flatness that may occur in the PCB tin spraying process in the prior art.

[0008] A PCB tin-spraying process for improving the flatness of the tin-spraying surface comprises the following steps:

[0009] S1: Use a fully automatic board loading machine to automatically transport the printed board, that is, put the printed board into the rack, and put the rack into the preset position, and then adjust the board loading machine to the automatic working mode, and the board loading machine automatically completes the board loading process;

[0010] S2: Use laser marking equipment to mark the QR code on the blank area on the surface of the printed board. The content of the QR code includes the product number, batch number, printed board number and production date of the printed board;

[0011] S3: Use the printed circuit board cleaning equipment to clean the printed circuit board with the QR code printed on it, and ensure that there is no obvious excess material on the surface of the printed circuit board, especially the area marked by laser, and the overall surface of the printed circuit board is clean and free of water marks;

[0012] S4: Compile the printing program of the solder paste printer in the offline computer according to the Gerber file of the surface pad of the printed circuit board, and add the QR code scanning area in the program to ensure that the device reads and recognizes the QR code of the printed circuit board; then, transfer the program to the printing device and complete the printing according to the correct operation;

[0013] S5: Use 3DSPI equipment to detect the tin spraying quality on the surface of the printed circuit board, and conduct manual re-judgment on the printed circuit board with tin spraying quality problems. The re-judgment results are retained on 3DSPI. At the same time, the re-judgment results will be uploaded to the MES system for storage;

[0014] S6: Use the fully automatic placement machine to place surface components according to the preset placement pressure, reference point, and packaging parameters;

[0015] S7: For the PCB that has been patched, use 2DAOI to check the patch quality; check whether the components are offset, reversed or wrong;

[0016] S8: welding using a vacuum vapor phase welding process according to a preset temperature curve;

[0017] S9: The soldered printed circuit board will be transmitted to the 3DAOI testing equipment for quality inspection. If the test parameters meet the set threshold, the product is qualified. The qualified product will be directly transmitted to the next process, while the unqualified product will be manually re-judged.

[0018] S10: The printed circuit boards that have passed the inspection are automatically stored in the rack by the unloader. When the rack is full, the unloader unloads the rack through the intelligent trolley and transports it to the preset location for storage.

[0019] Specifically, in step S5, the control condition between the solder joint area, the printing area, and the tin spraying amount is: solder joint area = (0.507*pad+0.329*vol±3.478)%.

[0020] Specifically, in step S5, the control condition between the solder joint height and the printing area and the tin spraying amount is: solder joint height = (0.433*pad+0.823*vol±2.589) μm.

[0021] Specifically, in step S5, the control condition between the solder joint volume and the printing area and the tin spraying amount is: solder joint volume = (0.484*pad+0.487vol±1.528)%.

[0022] Furthermore, in step S4, the ODB format file exported from the printed circuit board project or the CAD file converted from the pad surface Gerber file imported through the Mycenter offline software is used as the basic data and imported into the JPI module of the FactoryLogixExpress programming software; the JPI software generates a device program, defines data information including device movement, number of panels, single board size, coating medium, reference point, and QR code reading position, and at the same time, by reading the pad of the printed circuit board and its relative position to the Mark point, the position information where solder paste spraying is required is determined.

[0023] Furthermore, the JPI software automatically retrieves the information on the size, area, position and tin spraying amount of the printed graphics of the same or similar size from the MYDATA database, and sends it to the JPSys software. After the JPSys software generates the layout, it automatically plans the size and arrangement of the solder paste droplets that need to be evenly sprayed within the tin spraying range.

[0024] In summary, the PCB tin spraying process of the present invention improves the flatness of the tin spraying surface. An online detection method is added to the tin spraying process of the PCB. Then, the process parameters such as the solder paste spraying pattern, the spraying area and the amount of tin spraying of the common packaging components produced by the enterprise are optimized, and the threshold range setting rules of the key parameters of the tin spraying point detection are obtained according to the shape characteristics of the solder paste spraying solder joints. Finally, the results of the spraying optimization are verified by repeatability tests, and it is proved in both theory and experiment that the optimization parameters improve the quality of solder paste spraying and the efficiency of solder joint detection; thereby avoiding the problem that the existing technology has made multiple improvements on the defects of tin spraying and still cannot completely solve the problem that the surface flatness is insufficient after tin spraying in the PCB process. Therefore, the PCB tin spraying process of the present invention improves the flatness of the tin spraying surface to solve the technical problems of poor flatness in the PCB tin spraying process in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A process flow chart of a PCB tin-spraying process for improving the flatness of the tin-spraying surface according to the present invention;

[0026] Figure 2 A production line configuration diagram of a PCB tin-spraying process for improving the flatness of the tin-spraying surface according to the present invention;

[0027] Figure 3 This is a functional block diagram of an online detection system for a PCB tin-spraying process for improving the flatness of the tin-spraying surface of the present invention;

[0028] Figure 4 A schematic diagram of a tin-spraying process control flow of a PCB tin-spraying process for improving the flatness of a tin-spraying surface according to the present invention;

[0029] Figure 5 A schematic diagram of automatic planning of a tin spraying path for a PCB tin spraying process for improving the flatness of a tin spraying surface according to the present invention;

[0030] Figure 6 A schematic diagram of automatic planning of solder paste droplet size and arrangement mode in a PCB tin spraying process for improving the flatness of the tin spraying surface according to the present invention;

[0031] Figure 7 Schematic diagram of the laser triangulation algorithm principle in the prior art. DETAILED DESCRIPTION

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] Please also read Figure 1 and Figure 2 , Figure 1 A process flow chart of a PCB tin-spraying process for improving the flatness of the tin-spraying surface according to the present invention; Figure 2 This is a production line configuration diagram of a PCB tin spraying process for improving the flatness of the tin spraying surface of the present invention. Figure 1 As shown, a PCB tin-spraying process for improving the flatness of the tin-spraying surface of the present invention comprises the following steps:

[0039] S1: Use a fully automatic board loading machine to automatically transport the printed board, that is, put the printed board into the rack, and put the rack into the preset position, and then adjust the board loading machine to the automatic working mode, and the board loading machine automatically completes the board loading process;

[0040] S2: Use laser marking equipment to mark the QR code on the blank area on the surface of the printed board. The content of the QR code includes the product number, batch number, printed board number and production date of the printed board;

[0041] S3: Use the printed circuit board cleaning equipment to clean the printed circuit board with the QR code printed on it, and ensure that there is no obvious excess material on the surface of the printed circuit board, especially the area marked by laser, and the overall surface of the printed circuit board is clean and free of water marks;

[0042] S4: Compile the printing program of the solder paste printer in the offline computer according to the Gerber file of the surface pad of the printed circuit board, and add the QR code scanning area in the program to ensure that the device reads and recognizes the QR code of the printed circuit board; then, transfer the program to the printing device and complete the printing according to the correct operation;

[0043] S5: Use 3DSPI equipment to detect the tin spraying quality on the surface of the printed circuit board, and conduct manual re-judgment on the printed circuit board with tin spraying quality problems. The re-judgment results are retained on 3DSPI. At the same time, the re-judgment results will be uploaded to the MES system for storage;

[0044] S6: Use the fully automatic placement machine to place surface components according to the preset placement pressure, reference point, and packaging parameters;

[0045] S7: For the PCB that has been patched, use 2DAOI to check the patch quality; check whether the components are offset, reversed or wrong;

[0046] S8: welding using a vacuum vapor phase welding process according to a preset temperature curve;

[0047] S9: The soldered printed circuit board will be transferred to the 3DAOI testing equipment for quality inspection. The height, tin amount, wettability, and defects of solder joints, cold solder joints, or solder joint offset will be inspected. If the inspection parameters meet the set threshold, the product is qualified. The qualified product will be directly transferred to the next process, while the unqualified product will be manually reviewed.

[0048] S10: The printed circuit boards that have passed the inspection are automatically stored in the rack by the unloader. When the rack is full, the unloader unloads the rack through the intelligent trolley and transports it to the preset location for storage.

[0049] Specifically, the production equipment for online detection must have the ability to identify and read QR codes, and must also have the function of connecting to the network in order to upload and receive production, detection files and production status information. Among them, the online detection hardware equipment can be mainly divided into two parts: production equipment and detection equipment. The production equipment includes: automatic board loading machine, laser marking machine, PCB board cleaning equipment, solder paste spraying machine, automatic placement machine, vacuum vapor phase welding furnace, automatic board unloading machine. The detection equipment is: 3DSPI, 2DAOI before the furnace, and 3DAOI after the furnace. Each device is connected by an automatic docking station. For the specific connection sequence, please refer to Figure 2 Display.

[0050] Specifically, the 3DSPI solder paste detector is mainly used to detect the quality of solder paste coating and to warn of coating defects. The equipment itself has online detection capabilities, and can upload the test results to the MES system in real time and save the test records, which makes it possible to optimize the test parameters in time. In addition, when a printed circuit board needs to be inspected, the 2DAOI optical detector can use the built-in camera of the equipment to automatically scan the circuit board comprehensively, and use the corresponding algorithm to obtain the physical model of the test component from the collected image data. Then the detection system will compare the test data with the qualified parameter standards set in the database to determine whether the parameters exceed the detection standard threshold, so as to check whether the component has defects in the patch process, and mark the defects for the operator to repair in time. The detection methods include deep learning, OCR algorithm, TOC algorithm, WELD algorithm, etc. Furthermore, since the traditional 2DAOI can only be inspected by obtaining two-dimensional images, it lacks the important detection parameter of height, so that many defects caused by height cannot be successfully identified, and the 3DAOI detection technology can solve such defects. 3DAOI is used in the post-furnace printed circuit board assembly welding inspection. It can detect the offset, continuous welding, insufficient tin, wettability and other aspects of the component solder joints. It can also identify and judge the flatness of the tin-spraying surface of the PCB board. It effectively judges whether there are defects by establishing a three-dimensional model of the components and the three-dimensional morphology of the solder joints or the tin surface of the PCB pads, and uploads the specific inspection parameters for relevant personnel to carry out classification research on defects of different component types, so as to improve the consistency and stability of welding quality and tin-spraying quality.

[0051] For further information, please refer to Figure 3 ,like Figure 3As shown, the equipment used in the tin-spraying process is connected by a software system, and the software system includes five system modules: PDM, namely Product Data Management, ERP, namely Enterprise Resource Planning, MES, WMS, namely Warehouse Management System, and DCS, namely Distributed Control System. The main function of the PDM system is to send the product's bill of materials, process route and other data to the ERP system, and at the same time send the process route, process steps, working hours, equipment used, materials and auxiliary materials, production tooling, product production model parameters, equipment production procedures, process versions and other parameters to the MES system; the main function of the ERP system is to send the detailed information of the production order, the detailed parameters of the production products, the production quantity, batch, process, delivery information and other data to the MES system; the main function of the MES system is to feed back the processed order information, product information, the number of circulating products, the circulation time, the number of qualified products, the number of unqualified products and other information to the MES system. The ERP system sends product information, equipment information, coding information, production parameters, production procedures, production line status, track width and other information to the DCS system, and sends processed work order information, material information, production batches, production quantities, processes, production lines and other information to the WMS system; the main function of the DCS system is to feed back equipment information, equipment status, equipment parameters, operator information, equipment failure information, production line information, production procedures, production results, test procedures, and test results to the MES system; the main function of the WMS system is to upload work order information, material information, product quantity, production batches, warehouse locations and other information to the MES system.

[0052] Furthermore, in the automatic tin spraying process of PCB, if you want to realize the solder paste spraying of the printed circuit board, you need to convert the design data of the printed circuit board into machine language, and then drive the equipment hardware system to complete the coating of the pad. The system operation process is as follows Figure 4As shown. The device can be programmed in offline programming mode, and then the ODB format file exported from the printed circuit board project or the CAD file converted from the pad surface Gerber file imported through the Mycenter offline software is used as the basic data and imported into the JPI module of the FactoryLogixExpress programming software. The JPI software can generate equipment programs, define data information including equipment movement, number of panels, single board size, coating medium, reference point, QR code reading position, etc., and determine the location information where solder paste spraying is required by reading the pads of the printed circuit board and the relative position to the Mark point. During the programming process of the JPI software, the program will also automatically retrieve the size, area, position and tin spraying amount information of the same or similar size of the printed graphics in the MYDATA database. If it does not meet the standard requirements, it can also be re-edited and saved to the database. After the above program is compiled, the software is sent to JPSys and generates a layout. The layout automatically plans the tin spraying path according to the overall spraying requirements of the PCB. Because the software needs to spray solder paste droplets of different sizes according to the size of the pad, the nozzle needs to continuously adjust the nozzle to control the size of the solder paste droplets, which generally range from 330μm to 520μm. Therefore, the coating principle of the inkjet printer is to spray pads of the same size at the same time to reduce the frequency of adjusting the size of the nozzle, thereby reducing the printing time of the single board. After the program is compiled, the JPI software will automatically plan the size and arrangement of the solder paste droplets that need to be evenly sprayed within the tin spraying range based on the position, range, and amount of tin spraying in the tin spraying block diagram designed by the program. The interface of JPSys automatic planning of tin spraying paths is as follows Figure 5 As shown in the figure, JPI automatically plans the solder paste droplet size and arrangement interface. Figure 6 As shown. It can be seen that by using the online detection system to monitor and upload the defects of PCB in the tin spraying process in real time, the type of defects is determined after manual review, and then the design data is formed and imported into the offline computer. The JPI software program pre-installed in the offline computer compiles the design data and sends a copy to JPSys. Then, the JPSys software creates a layout for the program, and the layout is synchronously transmitted to the online equipment, that is, the solder paste printer. Finally, the solder paste printer sprays solder paste on the PCB according to the layout. After repeated learning and correction, the user's tin spraying production line can finally completely avoid the defects in the tin spraying process, including uneven tin spraying surface.

[0053] Furthermore, there are two key control variables in the solder paste printing process, namely the printing area, namely pad, and the amount of solder sprayed, namely vol. These two parameters directly affect the coating quality of the final solder joint. For the printed circuit board that has been printed and coated, the online inspection production line will automatically transmit it to the 3DSPI inspection equipment for quality inspection of the coated solder joints, and retain the parameters such as solder joint area, height, volume, etc. in the inspection results for subsequent analysis and processing.

[0054] Furthermore, 3DSPI equipment is mainly used to detect solder paste height and solder paste coating range. Its height detection is mainly based on phase measurement profile technology, which is evolved from the principle of laser triangulation algorithm. Laser triangulation algorithm, also known as light sectioning method, is the most basic measurement method in 3D measurement. Its principle is as follows Figure 7 As shown. It obtains measurement information by means of step-by-step linear scanning of the laser, and calculates the height of the current scanning pattern according to the principle of triangular relationship: H=L×tanθ, and generates the scanning result after the scanning is completed. The phase measurement profile technology adds a sinusoidal grating illumination model on the basis of the light section method. By establishing a transmission mathematical model, the grating illumination model can calculate the transmitted light intensity as shown in the formula, which is the following formula 1. The grayscale of the image can be calculated by the reflected illumination model as shown in the formula, which is the following formula 2. The following formula 3 can be derived from the above two formulas. Because the grating type is a sinusoidal function, four image grayscales I1 to I4 can be obtained according to the initial position of the grating, and the phase Φ can be calculated and obtained by the following formula 4. The detection height can be calculated by the phase value using the trigonometric relationship.

[0055] Formula 1: T=A+B*f(x)

[0056] Where A is the light source intensity; B is the light intensity amplitude; f(x) is the grating type, and f(x)=sin(Φ).

[0057] Formula 2: I=C*T

[0058] Where I is the image grayscale; C is the reflectivity; T is the transmitted light intensity.

[0059] Formula 3: I=I B +I R *sin(Φ)

[0060] Where I B - Object background light intensity; I R- The intensity of light reflected from the grating.

[0061] Formula 4: Φ = arctan (-(I4-I2) / (I3-I1)

[0062] Specifically, the area of ​​solder paste coating can be obtained by calculating the product of the number of pixels in the measurement range and the area of ​​each pixel, and this area is the measured area of ​​solder paste coating on the pad. The volume of solder paste is obtained by calculating the product of the height value of each pixel and its area value, and finally the average value of all pixel volumes is calculated by weighted calculation, and then divided by the product of the pad graphic size of the pad surface Gerber file compiled and collected by the program and the set screen thickness to obtain the volume percentage of solder paste coating on the pad.

[0063] Furthermore, the solder paste detection and judgment standards will directly affect the accuracy of the solder paste measurement of the printed circuit board. The pad database of the 3DSPI detection equipment will be classified according to the screen thickness and pad size used by different printed circuit boards, thereby forming detection standards for various pads. According to current requirements, the offset distance of solder paste deposition in the X / Y direction should be less than 25% of the total deposition length in the direction, the solder paste coating area should not be less than 75% of the template opening area, and the solder paste deposition height should reach 75% of the template opening height.

[0064] Furthermore, the height, area, and volume of solder joints formed by solder paste droplet stacking adopted by solder paste printing are quite different from those formed by traditional screen printing, and the area, height, and volume of solder joints are the key parameters of 3DSPI detection, and the setting of the threshold directly affects the reliability of detection. In order to reasonably set the detection threshold, it is necessary to have a reasonable estimate of the parameters for forming solder joints, and the core factors for controlling the size of solder joints are the area of ​​solder paste printing and the amount of tin spraying. Therefore, only by reasonably grasping the relationship between the area and amount of tin paste spraying and the area, height, and volume of solder joints can the size of the printed solder joints be accurately predicted. By using SPSS mathematical analysis software, the area, height, and volume detection results of solder paste coating on each solder joint on each control group printed board in the previous experiment were used as dependent variables, and the printing area and tin spraying amount parameters set in each group were used as independent variables. Regression analysis was performed to determine the mathematical relationship between the two, and the results are shown in Table 1 below.

[0065] Table 1: Regression analysis of tin spraying control process

[0066]

[0067] Specifically, it can be seen from Table 1 that in the 3DSPI detection threshold control, the control condition between the solder joint area and the printing area and the tin spraying amount is: area = (0.507*pad+0.329*vol±3.478)%. The control condition between the solder joint height and the printing area and the tin spraying amount is: height = (0.433*pad+0.823*vol±2.589)μm. The control condition between the solder joint volume and the printing area and the tin spraying amount is: volume = (0.484*pad+0.487vol±1.528)%. The following Table 2 is a partial embodiment of the detection threshold:

[0068] Table 2: Example of optimizing 3DSPI detection threshold

[0069]

[0070] Furthermore, in order to ensure that the actual effect of parameter optimization can meet expectations, repeatable tests can be conducted again based on the optimized printing parameters and 3DSPI detection threshold range. By using 20 identical printed boards for repeated production and testing, no variables are added except for the optimized parameters. After the production is completed, the detection parameters of the detection equipment during the production process are recorded, and the 3DSPI detection results are recorded in particular. The actual experimental results can determine that the qualified rate of each test result meets expectations, and then the x-ray detection equipment is used to manually detect all component solder joints, and the possibility of missed reports in the detection equipment has been ruled out. Finally, the manual inspection results of all component solder joints on the 20 test printed boards produced continuously meet the specified requirements, and the qualified rate of solder paste printing of conventional components and ultra-dense spacing components is greater than 99%, the pass rate of 3DSPI detection is greater than 99%, the false alarm rate is less than 1%, and there is no missed report. The test results are in line with expectations, which further proves that the technical problem of surface flatness of the tin spraying is improved by optimizing the detection parameters in the PCB tin spraying process, and then targeted optimization, and finally improving the surface flatness of the tin spraying.

[0071] In summary, the PCB tin spraying process of the present invention improves the flatness of the tin spraying surface. An online detection method is added to the tin spraying process of the PCB. Then, the process parameters such as the solder paste spraying pattern, the spraying area and the amount of tin spraying of the common packaging components produced by the enterprise are optimized, and the threshold range setting rules of the key parameters of the tin spraying point detection are obtained according to the shape characteristics of the solder paste spraying solder joints. Finally, the results of the spraying optimization are verified by repeatability tests, and it is proved in both theory and experiment that the optimization parameters improve the quality of solder paste spraying and the efficiency of solder joint detection; thereby avoiding the problem that the existing technology has made multiple improvements on the defects of tin spraying and still cannot completely solve the problem that the surface flatness is insufficient after tin spraying in the PCB process. Therefore, the PCB tin spraying process of the present invention improves the flatness of the tin spraying surface to solve the technical problems of poor flatness in the PCB tin spraying process in the prior art.

[0072] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0073] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A PCB tin-spraying process for improving the flatness of the tin-spraying surface, characterized in that: It includes the following steps: S1: Use a fully automatic board loading machine to automatically transport the printed board, that is, put the printed board into the rack, and put the rack into the preset position, and then adjust the board loading machine to the automatic working mode, and the board loading machine automatically completes the board loading process; S2: Use laser marking equipment to mark the QR code on the blank area on the surface of the printed board. The content of the QR code includes the product number, batch number, printed board number and production date of the printed board; S3: Use the printed circuit board cleaning equipment to clean the printed circuit board that has been marked with the QR code, and ensure that there is no obvious excess material on the surface of the printed circuit board where the laser is marked, and the overall surface of the printed circuit board is clean and free of water marks; S4: Compile the printing program of the solder paste printer in the offline computer according to the Gerber file of the surface pad of the printed circuit board, and add the QR code scanning area in the program to ensure that the device reads and recognizes the QR code of the printed circuit board; then, transfer the program to the printing device and complete the printing according to the correct operation; S5: Use 3DSPI equipment to detect the tin spraying quality on the surface of the printed circuit board, and conduct manual re-judgment on the printed circuit board with tin spraying quality problems. The re-judgment results are retained on 3DSPI. At the same time, the re-judgment results will be uploaded to the MES system for storage; S6: Use the fully automatic placement machine to place surface components according to the preset placement pressure, reference point, and packaging parameters; S7: For the PCB that has been patched, use 2DAOI to check the patch quality; check whether the components are offset, reversed or wrong; S8: welding using a vacuum vapor phase welding process according to a preset temperature curve; S9: The soldered printed circuit board will be transmitted to the 3DAOI testing equipment for quality inspection. If the test parameters meet the set threshold, the product is qualified. The qualified product will be directly transmitted to the next process, while the unqualified product will be manually re-judged. S10: The printed circuit boards that have passed the inspection are automatically stored in the rack by the unloader. When the rack is full, the unloader unloads the rack through the intelligent trolley and transports it to the preset location for storage.

2. A PCB tin-spraying process for improving the flatness of the tin-spraying surface according to claim 1, characterized in that: In step S5, the control condition between the solder joint area, the printing area and the tin spraying amount is: solder joint area = (0.507*pad+0.329*vol±3.478)%.

3. A PCB tin-spraying process for improving the flatness of the tin-spraying surface according to claim 1, characterized in that: In step S5, the control condition between the solder joint height and the printing area and the tin spraying amount is: solder joint height = (0.433*pad+0.823*vol±2.589) μm.

4. A PCB tin-spraying process for improving the flatness of the tin-spraying surface according to claim 1, characterized in that: In step S5, the control condition between the solder joint volume and the printing area and the tin spraying amount is: solder joint volume = (0.484*pad+0.487vol±1.528)%.

5. A PCB tin-spraying process for improving the flatness of the tin-spraying surface according to claim 3, characterized in that: In step S4, the ODB format file exported from the printed circuit board project or the CAD file converted from the pad surface Gerber file imported through the Mycenter offline software is used as the basic data and imported into the JPI module of the FactoryLogixExpress programming software; the JPI software generates a device program, defines data information including device movement, number of panels, single board size, coating medium, reference point, and QR code reading position, and at the same time, by reading the pad of the printed circuit board and its relative position to the Mark point, the position information where solder paste spraying is required is determined.

6. A PCB tin-spraying process for improving the flatness of the tin-spraying surface according to claim 5, characterized in that: The JPI software automatically retrieves the information of the size, area, position and tin spraying amount of the same or similar size of the printing graphics from the MYDATA database, and sends it to the JPSys software. After the JPSys software generates the layout, it automatically plans the size and arrangement of the solder paste droplets that need to be evenly sprayed within the tin spraying range.

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