Precision Coating Method for Conformal Coating Based on Gradient Atomization Control

Abstract

The application discloses a three-proofing paint precision coating method based on gradient atomization control and relates to the field of intelligent control, which comprises the following steps: performing visual scanning on a PCB to be coated, obtaining the type, position and size information of each component on the PCB based on the scanning result, and establishing a mapping relationship between the components and coating requirements; and dividing the surface of the PCB into a plurality of independent coating areas according to the mapping relationship between the components and coating requirements, setting a threshold value of atomized airflow pressure and a threshold value of paint supply for each coating area to match the protection requirements of the coating area, wherein the component information of the PCB is obtained through visual scanning and the coating requirement mapping is established, different component protection and thickness requirements can be accurately matched, blind coating can be avoided, the independent coating areas are divided according to the protection level, size and gap characteristics, and the threshold values of the atomized airflow pressure and the paint supply are set to adapt, the coating requirements of each area can be more targetedly met, and paint waste and excessive coating can be reduced.

Description

Technical Field

[0001] This invention relates to the field of intelligent control technology, specifically to a method for precision coating of conformal coatings based on gradient atomization control. Background Technology

[0002] Conformal coating is a special coating used to protect electronic circuits. It is used to prevent moisture, dust, and corrosion of components. It can isolate moisture, dust, and chemicals, and prevent short circuits or aging. As the requirements for coating precision and efficiency continue to increase, conformal coating work is gradually being replaced by industrial intelligent equipment.

[0003] Patent application No. 202410888454.0 discloses an intelligent conformal coating method for products, including the following steps: S1. Thoroughly clean and dry the PCBA to remove moisture, water, and dust; S2. Make a dedicated spraying mold according to the PCBA size and component layout and position and install the PCBA; S3. Use a fully automatic conformal coating machine to spray, controlling the dry film thickness to 30-75µm; S4. After spraying, dry the coating layer in an oven; S5. Observe whether the conformal coating surface is clean and conduct reliability tests. This application aims to solve the problem that "in harsh environments such as pig farms, existing conformal coating technology often degrades rapidly due to its inability to adapt to high temperature, high humidity, and corrosive gas environments, losing long-term protection for PCBA boards. In addition, the low production efficiency and uneven coating quality caused by manual or semi-automatic spraying, coupled with the lack of comprehensive reliability testing, make PCBA boards prone to failure in special environments."

[0004] However, traditional conformal coating is still prone to problems such as uneven coating, material waste, and differences in protection requirements of complex PCB components.

[0005] To address this, we propose a precision coating method for conformal coatings based on gradient atomization control. Summary of the Invention

[0006] In view of the above-mentioned shortcomings of the existing technology, the present invention provides a precision coating method for conformal coating based on gradient atomization control, which can effectively solve the problems of the existing technology.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solutions;

[0008] This invention discloses a precision coating method for conformal coating based on gradient atomization control, comprising:

[0009] A visual scan is performed on the PCB board to be coated. Based on the scan results, the type, location, and size information of each component on the board are obtained to establish a mapping relationship between components and coating requirements. According to the mapping relationship, the surface of the PCB board is divided into several independent coating areas. For each coating area, an atomized airflow pressure threshold and a paint supply threshold matching its protection requirements are set. The prepared conformal coating system is activated, and the initial spraying operation is performed synchronously on each coating area of ​​the PCB board according to the atomized airflow pressure threshold and paint supply threshold of each coating area. During the initial spraying process, a non-contact coating thickness sensor is used to monitor the coating thickness in real time. The coating thickness at the center of each coating area is collected, and the actual thickness is compared with the target thickness value of the corresponding area in real time to obtain thickness deviation data. If the actual thickness of the coating area deviates from the target thickness, the atomizing airflow pressure and paint supply of the coating area are dynamically adjusted according to the deviation ratio until the actual thickness of all coating areas is consistent with the target thickness, and then the three-proof paint coating system operation ends. The surface of each component on the PCB board after coating is completed is tested again at multiple points using a non-contact coating thickness sensor, and the test results are compared with the target coating thickness of each component to confirm whether the coating of each component is qualified.

[0010] The coating requirements include the target coating thickness and protection level for each component on the PCB board.

[0011] The conformal coating system includes an array of atomizing nozzles, an airflow stabilizing unit, and a constant pressure paint supply unit.

[0012] Furthermore, when visually scanning the PCB board to be coated, a collaborative scanning method using a multispectral linear array camera and a laser contour sensor is employed.

[0013] The multispectral linear array camera collects the appearance features of components in the 380-780nm visible light band to distinguish the component types, and collects the pin arrangement of components in the 850-1050nm near-infrared band to locate the component positions.

[0014] The laser profile sensor scans line by line along the width of the PCB board to obtain the relative height difference between the component surface and the PCB board reference surface to determine the component size information;

[0015] The specific steps for establishing the mapping relationship between components and coating requirements are as follows:

[0016] Construct a four-dimensional mapping table of component type, protection level, target coating thickness, and paint viscosity compatibility;

[0017] The protection level includes high, medium and low. The protection level is manually set based on the severity of the working environment and the importance of the function of the components. The paint viscosity compatibility is preset according to the size of the gap between the components. That is, the smaller the gap, the lower the viscosity of the paint that is suitable. The four-dimensional mapping table is pre-stored in the control unit of the conformal coating system for use when dividing the coating area.

[0018] Furthermore, when dividing the PCB board surface into several independent coating areas, the division rules should conform to the same protection level, same size range, and same gap characteristics:

[0019] First, the PCB board is divided into three primary areas based on the protection level of the components: high protection zone, medium protection zone, and low protection zone.

[0020] Within each primary region, sub-regions are further divided according to the size of the components.

[0021] Finally, within each sub-region, local areas where the gap between components is less than the preset gap threshold are removed and these areas are separately classified as micro-gap independent coating areas.

[0022] The atomization airflow pressure threshold and paint supply threshold are set for each coating area. These are customized manually based on the atomization particle size requirements of the paint. Specifically, the atomization airflow pressure threshold is negatively correlated with the target atomization particle size, while the paint supply threshold is positively correlated with the coating area, the target coating thickness, and the paint solid content. Furthermore, the paint supply threshold for the micro-gap independent coating area is lower than that for other coating areas of the same protection level.

[0023] Furthermore, when dynamically adjusting the atomizing airflow pressure and paint supply in the coating area according to the deviation ratio, the following adjustment formula applies:

[0024] ;

[0025] In the formula: The adjusted pressure of the atomized airflow; The initial atomized gas flow pressure threshold for the coated area; This is the pressure regulation coefficient; This represents the deviation between the actual thickness and the target thickness. This represents the target thickness value for the coated area; The adjusted paint supply; The initial paint supply threshold for the coated area; This is the paint supply adjustment coefficient.

[0026] Furthermore, the non-contact coating thickness sensor is a laser confocal displacement sensor, and its acquisition frequency is linked to the nozzle movement speed of the conformal coating system.

[0027] The faster the nozzle moves, the higher the sensor's data acquisition frequency;

[0028] The coating thickness at the center of each coated area is acquired in real time, and the coordinates of the component center are obtained through visual scanning to calibrate the sensor's acquisition target point.

[0029] For rectangular and circular components, the center position is selected from their geometric center; for components other than rectangular and circular shapes, the center position is selected from the centroid of the component's pin distribution.

[0030] During the data acquisition process, when the sensor detects that the thickness data fluctuation exceeds the preset fluctuation threshold, the nozzle is triggered to pause its movement, recalibrate the acquisition target point, and then continue spraying.

[0031] Furthermore, the array of atomizing nozzles corresponds one-to-one with the independent coating area, and the number of nozzles is equal. Each nozzle is equipped with an independent pressure regulating valve and flow regulating valve. The airflow stabilizing unit provides a stable atomizing airflow for each nozzle, and its output pressure accuracy is controlled within ±0.1kPa.

[0032] The constant pressure paint supply unit distributes paint to each nozzle through a distributor valve, and the supply pressure is dynamically compensated according to the paint level.

[0033] Before starting the coating system, a preheating process is performed through the airflow stabilization unit and the paint constant pressure supply unit:

[0034] Maintain the atomizing airflow pressure at 80% of the initial pressure threshold, maintain the paint supply at 50% of the initial supply threshold, and preheat according to the paint flow characteristics.

[0035] Furthermore, a multi-point thickness measurement stage is performed on the surface of each component on the PCB board after coating, subject to the following:

[0036] The number of monitoring points is positively correlated with the surface area of ​​the component, and the points are evenly distributed, covering the center, edges, and pin roots of the component surface.

[0037] The center point is the center of the component surface;

[0038] Edge points are located at a preset distance inward from the edge of the component;

[0039] The pin root point is located no more than 1mm above the pin's solder joint with the PCB board.

[0040] At least three thickness data points are collected for each location, and the average value is taken as the final detected thickness for that location. If the detected thickness at any location of a component deviates from the target thickness by more than the preset acceptable deviation, the coating of that component is deemed unqualified, triggering a local recoating process.

[0041] For the coating area where the non-conforming points are located, according to , The calculation formula is recalculated to set the atomizing airflow pressure and paint supply. After single-point touch-up coating, the process is checked again. If the result of the second test is qualified, the process ends. If the result of the second test is still unqualified, the local touch-up coating process is executed again. If the result of three consecutive tests is unqualified, the PCB board containing the component is removed from the coating process.

[0042] Furthermore, the test results are compared with the target coating thickness of each component to confirm whether the coating is qualified. The following method is used to calculate the coating qualification index of the component:

[0043] ;

[0044] In the formula: The coating qualification index; This represents the total number of detection points for the component. Let be the thickness value at the i-th detection point; The target thickness value; The deviation distribution coefficient; The standard deviation of the thickness values ​​at all test points;

[0045] Among them, when ≥ It is deemed qualified at that time. Set a qualified threshold for the user terminal.

[0046] Furthermore, during the application phase of the adjustment formula, an interactive compensation mechanism is simultaneously implemented:

[0047] After adjusting the atomizing airflow pressure, check whether the atomized particle size of the paint deviates from the preset particle size range. If it does, compensate for the paint supply simultaneously.

[0048] When the particle size is too large, increase the paint supply:

[0049] Calculate the compensation coefficient ;

[0050] If the particle size is too small, reduce the amount of paint supplied. ;

[0051] In the formula These represent the actual atomized particle size and the target atomized particle size, respectively.

[0052] After obtaining the compensation coefficient, the paint supply quantity is adjusted accordingly using the compensation coefficient. The adjusted paint supply quantity is... ;

[0053] The atomized particle size of the paint is detected by a laser particle size sensor.

[0054] Furthermore, between the initial spraying operation and thickness inspection, a coating pre-leveling step can be added at the user's discretion:

[0055] The PCB board that has completed the initial spraying is transferred to a leveling chamber with constant temperature and humidity. The leveling temperature of the leveling chamber is set according to the physical properties of the paint, the leveling humidity is set to a preset humidity range and is not lower than the humidity of the coating operation environment, and the leveling time is set according to the coating thickness, that is, the thicker the coating, the longer the leveling time.

[0056] Compared with the known prior art, the technical solution provided by this invention has the following beneficial effects:

[0057] This invention provides a precision coating method for conformal coating based on gradient atomization control. During execution, the method acquires PCB component information through visual scanning and establishes a coating requirement mapping, which can accurately match the protection and thickness requirements of different components, avoiding blind coating. Independent coating areas are divided according to protection level, size, and gap characteristics, and appropriate atomization airflow pressure and paint supply threshold are set to better meet the coating needs of each area, reducing paint waste and over-coating. The coating thickness is collected in real time during the initial spraying and parameters are dynamically adjusted according to the deviation, which can quickly correct the thickness deviation and ensure coating accuracy. Preheating parameters are set according to the paint characteristics to stabilize paint flowability and atomization effect. Multi-point detection and recoating mechanism after coating can reduce the defect rate. Optional pre-leveling and dual-angle drip detection and parameter adjustment can reduce drip marks, improve the overall coating quality and efficiency, and adapt to the coating needs of different types of components. Attached Figure Description

[0058] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0059] Figure 1 This is a schematic diagram of the process for a precision coating method of conformal coating based on gradient atomization control. Detailed Implementation

[0060] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0061] The present invention will be further described below with reference to embodiments. Example

[0062] This embodiment presents a precision coating method for conformal coating based on gradient atomization control, such as... Figure 1 As shown, it includes:

[0063] Visual scanning is performed on the PCB board to be coated. Based on the scanning results, the type, location and size information of each component on the board are obtained to establish a mapping relationship between the components and the coating requirements.

[0064] When performing visual scanning on the PCB board to be coated, a collaborative scanning method using a multispectral linear array camera and a laser contour sensor is employed.

[0065] The multispectral linear array camera collects the appearance features of components in the 380-780nm visible light band to distinguish the component types, and collects the pin arrangement of components in the 850-1050nm near-infrared band to locate the component positions.

[0066] The laser profile sensor scans line by line along the width of the PCB board to obtain the relative height difference between the component surface and the PCB board reference surface to determine the component size information;

[0067] The specific steps to establish the mapping relationship between components and coating requirements are as follows:

[0068] Construct a four-dimensional mapping table of component type, protection level, target coating thickness, and paint viscosity compatibility;

[0069] The protection level includes high, medium, and low. The protection level is manually set based on the severity of the working environment and the importance of the function of the component (e.g., high protection level is required for dense pin components because moisture or dust can easily accumulate in the gaps; medium protection level can be used for surface mount components because of their compact structure and small exposed area; basic protection level can be used for passive components because of their single function and strong environmental tolerance). The paint viscosity compatibility is preset according to the size of the gap between the components, that is, the smaller the gap, the lower the viscosity of the paint that is suitable. The four-dimensional mapping table is pre-stored in the control unit of the conformal coating system for use when dividing the coating area.

[0070] Based on the mapping relationship between components and coating requirements, the PCB board surface is divided into several independent coating areas, and atomized airflow pressure threshold and paint supply threshold are set for each coating area to match its protection requirements.

[0071] When dividing the PCB board surface into several independent coating areas, the division rules should follow the same protection level, size range, and gap characteristics:

[0072] First, the PCB board is divided into three primary areas based on the protection level of the components: high protection zone, medium protection zone, and low protection zone.

[0073] Within each primary region, sub-regions are further divided according to the size of the components.

[0074] Finally, within each sub-region, local areas where the gap between components is less than the preset gap threshold are removed and these areas are separately classified as micro-gap independent coating areas.

[0075] Atomizing airflow pressure threshold and paint supply threshold are set for each coating area. These are customized manually based on the atomization particle size requirements of the paint. Specifically, the atomizing airflow pressure threshold is negatively correlated with the target atomization particle size, while the paint supply threshold is positively correlated with the coating area, target coating thickness, and paint solid content. Furthermore, the paint supply threshold for micro-gap independent coating areas is lower than that for other coating areas of the same protection level.

[0076] Among them, high protection areas include power module components, medium protection areas include signal processing components, and low protection areas include passive components.

[0077] Start the prepared conformal coating system and perform initial spraying operations on each coating area of ​​the PCB board simultaneously according to the atomized airflow pressure threshold and paint supply threshold of each coating area.

[0078] When dynamically adjusting the atomizing airflow pressure and paint supply in the coating area according to the deviation ratio, the following adjustment formula applies:

[0079] ;

[0080] In the formula: The adjusted pressure of the atomized airflow; The initial atomized gas flow pressure threshold for the coated area; This is the pressure regulation coefficient; This represents the deviation between the actual thickness and the target thickness. This represents the target thickness value for the coated area; The adjusted paint supply; The initial paint supply threshold for the coated area; This refers to the paint supply adjustment coefficient.

[0081] in, ∈ [0.3,0.8], and obeys the condition that the surface tension of the paint increases (such as high viscosity conformal coating). The larger the value, the lower the value. The smaller the value; ∈ [0.2, 0.6], and subject to the stronger ventilation conditions of the coated area (such as the area near the vent). The larger the value, the lower the value. The smaller the value;

[0082] In the above formula The formula ensures that the pressure adjustment directly corresponds to the degree of thickness deviation by using the thickness deviation ratio. It also avoids adjustment problems caused by the difference in atomization characteristics of different paints by using the adjustment coefficient linked to the surface tension of the paint. This makes the pressure adjustment more in line with the properties of the paint, effectively improving the accuracy of atomization pressure correction under different paints, and thus better correcting the coating thickness deviation.

[0083] The formula directly matches the supply adjustment with the thickness demand by using the thickness deviation ratio to make up for the thickness deviation; on the other hand, it incorporates ventilation environment factors into the adjustment coefficient, which can compensate for the consumption of paint that evaporates quickly in areas with strong ventilation, avoid ignoring the problem of environmental impact, make the supply adjustment more in line with the actual working conditions, and improve the effectiveness of thickness control.

[0084] During the application phase of the adjustment formula, an interactive compensation mechanism is simultaneously implemented.

[0085] After adjusting the atomizing airflow pressure, check whether the atomized particle size of the paint deviates from the preset particle size range. If it does, compensate for the paint supply simultaneously.

[0086] When the particle size is too large, increase the paint supply:

[0087] Calculate the compensation coefficient ;

[0088] When the atomized particle size of the paint is too large, the paint supply compensation coefficient is obtained by the ratio of the difference between the actual atomized particle size and the target atomized particle size to the target atomized particle size. This coefficient is then used to adjust the current paint supply to increase the supply. This design is because a large particle size means coarse atomized particles, which can easily lead to uneven coating coverage or insufficient thickness. Calculating the compensation coefficient based on the particle size deviation ratio and increasing the supply can specifically solve the quality problems caused by a large particle size, avoiding blindly increasing the supply and wasting paint. At the same time, through particle size feedback, a secondary supply compensation is formed after pressure adjustment, constructing a more complete atomization-supply adjustment closed loop to ensure that the coating thickness and uniformity are not affected by abnormal particle size.

[0089] If the particle size is too small, reduce the amount of paint supplied. ;

[0090] When the atomized particle size of the paint is too small, the paint supply compensation coefficient is obtained by the ratio of the difference between the actual atomized particle size and the target atomized particle size to the target atomized particle size. The current paint supply is then adjusted according to this coefficient to reduce the supply. This is because a small particle size indicates that the atomized particles are too fine, which can easily cause local accumulation of paint, resulting in an excessively thick coating or waste. By reducing the supply through a compensation coefficient that matches the degree of particle size deviation, the reduction can be precisely controlled, which avoids an excessively thick coating and ensures that the thickness meets the standard. At the same time, the compensation method based on the particle size deviation ratio makes the supply adjustment closely linked with the atomization effect, further optimizing the matching degree between atomization and supply parameters and improving coating stability.

[0091] In the formula These represent the actual atomized particle size and the target atomized particle size, respectively.

[0092] After obtaining the compensation coefficient, the paint supply quantity is adjusted accordingly using the compensation coefficient. The adjusted paint supply quantity is... ;

[0093] Among them, the atomized particle size of the paint is detected by a laser particle size sensor;

[0094] During the initial spraying process, the coating thickness at the center of each coating area is collected in real time using a non-contact coating thickness sensor. The collected actual thickness is then compared in real time with the target thickness value of the corresponding area to obtain thickness deviation data.

[0095] If the actual thickness of the coated area deviates from the target thickness, the atomized airflow pressure and paint supply of the coated area will be dynamically adjusted according to the deviation ratio until the actual thickness of all coated areas is consistent with the target thickness, and then the operation of the conformal coating system will be terminated.

[0096] The surface of each component on the PCB board after coating is completed is tested again at multiple points using a non-contact coating thickness sensor. The test results are compared with the target coating thickness of each component to confirm whether the coating of each component is qualified.

[0097] The process involves multi-point thickness measurement of the surfaces of various components on the PCB board after coating is completed, adhering to the following:

[0098] The number of monitoring points is positively correlated with the surface area of ​​the component, and the points are evenly distributed, covering the center, edges, and pin roots of the component surface.

[0099] The center point is the center of the component surface;

[0100] Edge points are located at a preset distance inward from the edge of the component;

[0101] The pin root point is located no more than 1mm above the pin's solder joint with the PCB board.

[0102] At least three thickness data points are collected for each location, and the average value is taken as the final detected thickness for that location. If the detected thickness at any location of a component deviates from the target thickness by more than the preset acceptable deviation, the coating of that component is deemed unqualified, triggering a local recoating process.

[0103] For the coating area where the non-conforming points are located, according to , The calculation formula is recalculated to set the atomizing airflow pressure and paint supply, and a single-point touch-up coating is performed and then tested again. If the test result is qualified, the process ends. If the test result is still unqualified, the local touch-up coating process is performed again. If the test results are unqualified three times in a row, the PCB board containing the component is removed from the coating process.

[0104] The test results are compared with the target coating thickness of each component to confirm whether the coating is qualified. The coating qualification index of the component is calculated as follows:

[0105] ;

[0106] In the formula: The coating qualification index; This represents the total number of detection points for the component. Let be the thickness value at the i-th detection point; The target thickness value; The deviation distribution coefficient; The standard deviation of the thickness values ​​at all test points;

[0107] Among them, when ≥ It is deemed qualified at that time. Preset a qualified threshold for the user terminal. The value range is a preset interval, initially set to (0.1, 0.3), and is subject to the higher the protection level of the component. The larger the value, the lower the value. The smaller the value;

[0108] The above formula uses a coefficient related to the protection level to make the uniformity requirements of high protection demand components higher, so that the qualification judgment is more in line with the actual working requirements of the components, and the scientificity and accuracy of the judgment are greatly improved.

[0109] The non-contact coating thickness sensor is a laser confocal displacement sensor, and its acquisition frequency is linked to the nozzle movement speed of the conformal coating system.

[0110] The faster the nozzle moves, the higher the sensor's data acquisition frequency;

[0111] The coating thickness at the center of each coated area is acquired in real time, and the coordinates of the component center are obtained through visual scanning to calibrate the sensor's acquisition target point.

[0112] For rectangular and circular components, the center position is selected from their geometric center; for components other than rectangular and circular shapes, the center position is selected from the centroid of the component's pin distribution.

[0113] During the data acquisition process, when the sensor detects that the thickness data fluctuation exceeds the preset fluctuation threshold, the nozzle is triggered to pause its movement, recalibrate the acquisition target point, and then continue spraying.

[0114] The coating requirements include the target coating thickness and protection level for each component on the PCB board.

[0115] The conformal coating system includes an array of atomizing nozzles, an airflow stabilizing unit, and a constant pressure paint supply unit.

[0116] The array of atomizing nozzles corresponds one-to-one with the independent coating area, and the number of nozzles is equal. Each nozzle is equipped with an independent pressure regulating valve and flow regulating valve. The airflow stabilizing unit provides a stable atomizing airflow for each nozzle, and its output pressure accuracy is controlled within ±0.1kPa.

[0117] The constant pressure paint supply unit distributes paint to each nozzle through a distributor valve, and the supply pressure is dynamically compensated according to the paint level.

[0118] Before starting the coating system, a preheating process is performed through the airflow stabilization unit and the paint constant pressure supply unit:

[0119] Maintain the atomized airflow pressure at 80% of the initial pressure threshold, maintain the paint supply at 50% of the initial supply threshold, and preheat according to the paint flow characteristics.

[0120] Among them, the flowability characteristics of the paint are measured by viscosity (dynamic viscosity at 25°C, in mPa·s) and thixotropic index (shear rate 10s). With 100s The viscosity index (viscosity ratio) is used to characterize the paint. A higher viscosity value indicates poorer initial flowability and a longer required preheating time. A higher thixotropic index (i.e., a more significant decrease in viscosity after shearing) indicates a longer preheating time is needed to stabilize the paint's flowability under low shear conditions. The conformal coating system control unit pre-stores a "viscosity-thixotropic index-preheating time" mapping table, which is constructed according to the following rules:

[0121] When the paint viscosity is within the first preset viscosity range (e.g., ≤500 mPa·s) and the thixotropic index is ≤ the preset thixotropic threshold (e.g., 2.0), the preheating time is set to the first preset duration (e.g., 30 s). When the viscosity is within the second preset viscosity range (e.g., 500-1500 mPa·s) or the thixotropic index is > the preset thixotropic threshold, the preheating time is set to the second preset duration (1.5-2 times the first preset duration). When the viscosity is > the upper limit of the second preset viscosity range, the preheating time is set to the third preset duration (1.2-1.5 times the second preset duration). Simultaneously, this mapping table supports dynamic correction based on the actual coating effect: if uneven paint atomization occurs during the first spray after preheating (determined by detecting the distribution of atomized particles using a visual sensor), the preheating time of the corresponding paint is automatically extended (by 10%-20% of the current preheating time), and updated in the mapping table to ensure real-time adaptation between the preheating time and the paint's flow characteristics.

[0122] Between the initial spraying operation and thickness inspection, the user can independently decide to add a coating pre-leveling step:

[0123] The PCB board that has completed the initial spraying is transferred to a leveling chamber with constant temperature and humidity. The leveling temperature of the leveling chamber is set according to the physical properties of the paint, the leveling humidity is set to a preset humidity range and is not lower than the humidity of the coating operation environment, and the leveling time is set according to the coating thickness, that is, the thicker the coating, the longer the leveling time.

[0124] After leveling, a preset visual sensor is used to perform drip detection:

[0125] The vision sensor uses dual-angle acquisition: vertical shooting to obtain an overall image of the PCB board surface, used to identify large-area drips; 45° tilt shooting to focus on areas prone to drips, such as component edges and pin gaps, to obtain local detail images.

[0126] The acquired images are processed to grayscale. By comparing the grayscale value difference between the coating area and the PCB substrate area, a preset grayscale difference threshold is set. When the grayscale difference between a certain position in the coating area and the substrate is lower than the threshold, it is determined to be a suspected sag mark. Then, the morphological features of the suspected area are extracted by combining the edge detection algorithm, including the length, width and continuity of the mark.

[0127] If the length of the trace in the suspected area exceeds the preset length threshold, the width exceeds the preset width threshold, and the number of consecutive segments is not less than two, then it is determined that there is a drip trace; otherwise, it is determined that there is no drip trace.

[0128] If there are no flow marks, the PCB board is directly transferred to the next inspection station for further inspection, such as the thickness inspection station; if flow marks are present, the leveling parameter adjustment mechanism is triggered.

[0129] First, read the relationship between the current leveling temperature and the optimal leveling temperature range of the paint. If the current leveling temperature is higher than the upper limit of the optimal leveling temperature range, then prioritize reducing the leveling temperature by the preset temperature step, and the adjusted temperature must still be within the optimal leveling temperature range.

[0130] If the current leveling temperature is within the optimal leveling temperature range, the leveling time should be shortened by the preset time step, and the adjusted time should not be less than the minimum effective leveling time (preset according to the minimum coating thickness). After parameter adjustment, the PCB board is sent back into the leveling chamber for pre-leveling. After re-leveling, the above-mentioned sagging mark detection process is repeated until no sagging marks are detected, and then subsequent detection is performed. If sagging marks still exist after adjusting the preset number of times, the system alarm is triggered, prompting to check the paint viscosity or initial spraying parameters.

[0131] In this embodiment, the above method can accurately identify the PCB board components to match coating requirements, set coating parameters according to protection and size zones, and dynamically adjust coating pressure and paint amount to ensure thickness compliance. It is combined with pre-leveling to prevent sagging and multi-point inspection to confirm qualification. This improves coating accuracy, adapts to different component protection needs, reduces coating defects, ensures three-proof performance, enhances PCB board environmental tolerance, optimizes the workflow, and improves overall coating efficiency and quality stability.

[0132] Referring to the method in the above embodiments, an application example of this method is shown:

[0133] For industrial control PCBs containing power module components (high protection requirements), signal processing components (medium protection requirements), and passive components such as resistors and capacitors (low protection requirements), precision coating is performed according to the following process:

[0134] First, a visual scan of the PCB board to be coated is performed, using a multispectral linear array camera and a laser contour sensor working together: the multispectral linear array camera distinguishes three types of components—power modules, signal processing, and passive components—through the 380-780nm visible light band, and locates the pin layout of each type of component through the 850-1050nm near-infrared band; the laser contour sensor scans line by line along the width of the PCB board to obtain the relative height difference between the component surface and the PCB reference surface, and determines the size information of the power module (12mm long, 8mm wide), signal processing components (6mm long, 4mm wide), and passive components (3mm long, 2mm wide).

[0135] Subsequently, a mapping relationship between components and coating requirements was established: the system's pre-stored four-dimensional mapping table of "component type - protection level - target coating thickness - paint viscosity compatibility" was called, and the power module was manually set to high protection level (target coating thickness 45μm), the signal processing components to medium protection level (target coating thickness 30μm), and the passive components to low protection level (target coating thickness 20μm). According to the gap size, the power module with dense pins (gap 0.12mm) is adapted to low viscosity paint (25℃ viscosity 280mPa·s), and the signal processing components (gap 0.25mm) and passive components (gap 0.4mm) are adapted to medium viscosity paint (25℃ viscosity 550mPa·s).

[0136] Next, the coating area is divided: First, the PCB board is divided into a high protection area (including all power modules), a medium protection area (including all signal processing components), and a low protection area (including all passive components) according to the protection level; then, each primary area is further subdivided according to size. For example, in the high protection area, power modules of different specifications are divided into two sub-areas; finally, local areas with gaps less than 0.15mm in each sub-area (such as areas with dense power module pins) are removed and separately divided into micro-gap independent coating areas.

[0137] Then, thresholds were set for each area: based on the requirements of paint atomization particle size, the initial atomization airflow pressure threshold for the high protection area was set to 0.38 MPa and the initial paint supply threshold was set to 1.1 mL / min, of which the paint supply threshold for the micro-gap area was set to 0.75 mL / min (lower than other areas of the same protection level); the initial atomization airflow pressure threshold for the medium protection area was 0.32 MPa and the paint supply threshold was 0.9 mL / min; and the initial atomization airflow pressure threshold for the low protection area was 0.28 MPa and the paint supply threshold was 0.7 mL / min.

[0138] Preheating is performed before starting the coating system: Based on the paint flowability (viscosity 550 mPa·s at 25℃, thixotropic index 2.0), the preheating time is set to 45s using the pre-stored mapping table; during preheating, the atomizing airflow pressure is maintained at 80% of the corresponding initial threshold (0.304 MPa in high protection zone, 0.256 MPa in medium protection zone, and 0.224 MPa in low protection zone), and the paint supply is maintained at 50% of the corresponding initial threshold (0.55 mL / min in high protection zone, 0.45 mL / min in medium protection zone, and 0.35 mL / min in low protection zone).

[0139] After preheating, the user adds a pre-leveling step: the PCB board is transferred to the leveling chamber, and the leveling temperature is set to 48℃ and the leveling humidity to 52% (not lower than the coating environment humidity of 45%) according to the paint characteristics. The leveling time is set to 8 minutes based on the coating thickness. After leveling, the visual sensor captures images by taking pictures vertically and at a 45° angle. After grayscale processing, the grayscale difference between the coating and the substrate is compared. No drip marks are detected, and the board is transferred to the thickness detection station.

[0140] Initial spraying was initiated, and the center thickness of each area was simultaneously collected in real time using a laser confocal displacement sensor (the acquisition frequency is linked to the nozzle speed): the actual thickness of the high protection zone was 38 μm (target 45 μm), the medium protection zone was 26 μm (target 30 μm), and the low protection zone was 18 μm (target 20 μm), indicating a deviation. Adjustments were made proportionally to the deviation: the pressure adjustment coefficient for the high protection zone was set to 0.45 (medium paint surface tension), resulting in an atomized airflow pressure of 0.34 MPa; the paint supply adjustment coefficient was set to 0.35 (moderate ventilation), resulting in a supply rate of 0.95 mL / min; a slightly large atomized particle size was detected, and the supply rate was adjusted to 1.02 mL / min after compensation. The medium protection zone was adjusted to 0.30 MPa and a supply rate of 0.83 mL / min; the low protection zone was adjusted to 0.26 MPa and a supply rate of 0.68 mL / min. Adjustments were continued until the actual thickness of each area matched the target, at which point the initial spraying was stopped.

[0141] Finally, multi-point testing was performed: Four testing points were set for the power module (surface area 96mm²) (center, two edges, and two pin roots). Three samples were taken at each point, and the average was calculated. The coating pass index was 0.82 (preset threshold 0.7), which is acceptable. One passive component's edge deviation exceeded the standard, triggering recoating: the pressure was reset to 0.27MPa and the supply rate to 0.69mL / min. After recoating, the pass index was 0.76, which is acceptable. All components passed the tests, and the coating process was completed.

[0142] In summary, the method acquires PCB component information through visual scanning and establishes a coating requirement mapping, which can accurately match the protection and thickness requirements of different components, avoiding blind coating. It divides independent coating areas according to protection level, size, and gap characteristics, and sets appropriate atomization airflow pressure and paint supply threshold, which can more specifically meet the coating needs of each area, reducing paint waste and over-coating. During the initial spraying, the coating thickness is collected in real time and the parameters are dynamically adjusted according to the deviation, which can quickly correct the thickness deviation and ensure coating accuracy. The preheating parameters are set according to the paint characteristics, which can stabilize the paint flow and atomization effect. The multi-point detection and recoating mechanism after coating can reduce the defect rate. Optional pre-leveling and dual-angle drip detection and parameter adjustment can reduce drip marks, improve the overall coating quality and efficiency, and can adapt to the coating needs of different types of components.

[0143] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A precision coating method of three-proofing paint based on gradient atomization control, characterized in that, The method comprises the following steps: visual scanning of the PCB to be coated to obtain the type, position and size information of each component on the PCB based on the scanning results to establish a mapping relationship between the components and the coating requirements; dividing the surface of the PCB into a plurality of independent coating areas according to the mapping relationship between the components and the coating requirements, and setting a threshold value of the atomized airflow pressure and a threshold value of the paint supply amount for each coating area to match the coating requirements of the coating area; starting the prepared three-proofing paint coating system to perform initial spraying on each coating area of the PCB according to the threshold value of the atomized airflow pressure and the threshold value of the paint supply amount of each coating area; in the initial spraying process, the thickness of the coating at the center position of each coating area is collected in real time by a non-contact coating thickness sensor, and the actual thickness collected is compared with the target thickness value of the corresponding area in real time to obtain thickness deviation data; if the actual thickness of a coating area deviates from the target thickness, the atomized airflow pressure and the paint supply amount of the coating area are dynamically adjusted according to the deviation ratio until the actual thickness of all coating areas is consistent with the target thickness, and the operation of the three-proofing paint coating system is ended; the surface of each component on the PCB after coating is detected again by a non-contact coating thickness sensor to determine whether the coating of each component is qualified by comparing the detection results with the target coating thickness of each component. The coating requirements include the target coating thickness and the protection level of each component on the PCB.

2. The precise coating method of the three-proofing paint based on the gradient atomization control according to claim 1, characterized in that, In the visual scanning of the PCB to be coated, a multi-spectral line array camera and a laser profile sensor are used in a cooperative scanning mode: the multi-spectral line array camera collects the appearance features of the components through the 380-780nm visible light band to distinguish the types of the components, and collects the pin arrangement of the components through the 850-1050nm near-infrared band to locate the positions of the components; the laser profile sensor scans along the width direction of the PCB to obtain the relative drop of the surface height of the components and the reference surface of the PCB to determine the size information of the components; The specific operation of establishing the mapping relationship between the components and the coating requirements is as follows: constructing a four-dimensional mapping table of component type, protection level, target coating thickness and paint viscosity adaptability; The protection level includes high, medium and low, and the protection level is manually set based on the harshness of the working environment and the importance of the function of the components. The paint viscosity adaptability is pre-set according to the gap size of the components, i.e. the smaller the gap, the lower the corresponding adaptive paint viscosity. The four-dimensional mapping table is pre-stored in the control unit of the three-proofing paint coating system for calling when dividing the coating areas.

3. The precise coating method of the three-proofing paint based on the gradient atomization control according to claim 1, characterized in that, When the surface of the PCB is divided into a plurality of independent coating areas, the division rules of the same protection level, the same size order and the same gap feature are followed: firstly, the PCB is divided into three first-level areas of high protection area, medium protection area and low protection area according to the protection level of the components; then, sub-areas are divided in each first-level area according to the size of the components; finally, in each sub-area, local areas with a gap smaller than a pre-set gap threshold value are removed and independently divided into micro-gap independent coating areas. The threshold values of atomizing airflow pressure and paint supply amount are set for each coating area to match the coating requirements, and are customized manually combined with the atomized particle size requirements of the paint, that is, the threshold value of atomizing airflow pressure is negatively correlated with the target atomized particle size, the threshold value of paint supply amount is positively correlated with the coating area, target coating thickness and paint solid content, and the threshold value of paint supply amount of the micro-gap independent coating area is lower than that of other coating areas of the same protection level.

4. The precise coating method of the three-proofing paint based on the gradient atomization control according to claim 1, characterized in that, When the atomizing airflow pressure and paint supply amount of the coating area are dynamically adjusted according to the deviation ratio, the following adjustment formula is followed: ； In the formula: is the adjusted atomizing gas flow pressure; is the initial atomizing gas flow pressure threshold value for the coating area; is the pressure adjustment coefficient; is the deviation value of the actual thickness from the target thickness; is the target thickness value for the coating area; is the adjusted paint supply amount; is the initial paint supply amount threshold value for the coating area; is the paint supply amount adjustment coefficient.

5. The precise coating method of the three-proofing paint based on the gradient atomization control according to claim 1, characterized in that, The non-contact coating thickness sensor is a laser confocal displacement sensor, and the acquisition frequency is linked with the moving speed of the spray head of the three-proofing paint coating system: The faster the moving speed of the spray head, the higher the acquisition frequency of the sensor; The coating thickness of the center position of each coating area is collected in real time, and the center coordinates of the components and parts are obtained through visual scanning to calibrate the acquisition target point of the sensor: For rectangular and circular components and parts, the geometric center is selected as the center position, and for components and parts with shapes other than rectangular and circular, the barycenter of the pin distribution is selected as the center position; During the acquisition process, when the sensor detects that the thickness data fluctuation amplitude exceeds the preset fluctuation threshold value, the movement of the spray head is paused, and the acquisition target point is recalibrated before the spraying is continued.

6. The precise coating method of the three-proofing paint based on the gradient atomization control according to claim 1, characterized in that, The three-proofing paint coating system comprises an array-type atomizing spray head group, an airflow pressure stabilizing unit and a paint constant pressure supply unit; The spray heads of the array-type atomizing spray head group correspond to the independent coating areas one by one, and the number is equal. Each spray head is equipped with an independent pressure adjusting valve and a flow adjusting valve. The airflow pressure stabilizing unit provides stable atomizing airflow for each spray head, and the output pressure accuracy is controlled within ±0.1 kPa; The paint constant pressure supply unit distributes paint to each spray head through a liquid distribution valve, and the supply pressure is dynamically compensated according to the liquid level height of the paint; Before starting the coating system, preheating operation is performed through the airflow pressure stabilizing unit and the paint constant pressure supply unit: The atomizing airflow pressure is maintained at 80% of the initial pressure threshold value, and the paint supply amount is maintained at 50% of the initial supply amount threshold value. The preheating time is set according to the flowability characteristics of the paint to perform preheating.

7. The precise coating method of the three-proofing paint based on the gradient atomization control according to claim 4, characterized in that, The surface of each component and part on the PCB board after coating is detected at multiple points, and the following formula is followed: The number of monitoring points is positively correlated with the surface area of the component and part, and the points are uniformly distributed to cover the center, edge and pin root of the component and part surface: The center point is the center of the component and part surface; The edge point is a preset distance inward from the edge of the component and part; The pin root point is not more than 1 mm above the welding position of the pin and the PCB board; Each point collects at least 3 thickness data, and the average value is taken as the final detection thickness of the point. If the detection thickness of any point of a component and part deviates from the target thickness by more than the preset qualified deviation, the coating of the component and part is determined to be unqualified, and the local re-coating process is triggered: For the coating area where the non-conforming points are located, according to , The calculation formula is recalculated to set the atomizing airflow pressure and paint supply. After single-point touch-up coating, the process is checked again. If the result of the second test is qualified, the process ends. If the result of the second test is still unqualified, the local touch-up coating process is executed again. If the result of three consecutive tests is unqualified, the PCB board containing the component is removed from the coating process.

8. The precise coating method of the three-proofing paint based on the gradient atomization control according to claim 7, characterized in that, The detection results are compared with the target coating thickness of each component and part to determine whether the coating is qualified, and the coating qualified index of the component and part is calculated as follows: ； In the formula: is a coating qualification index; is the total number of detection points of the component; is the thickness value of the i-th detection point; is the target thickness value; is the deviation distribution coefficient; is the standard deviation of the thickness values of all detection points; wherein, when ≥ is determined to be qualified, is a preset qualified threshold for the user end.

9. The precise coating method of the three-proofing paint based on the gradient atomization control according to claim 4, characterized in that, The adjustment formula is applied in the following stage, and an interactive compensation mechanism is provided simultaneously: When the pressure of the atomizing gas flow is adjusted, whether the paint atomization particle size deviates from the preset particle size range is detected, and if it deviates, the paint supply amount is compensated synchronously: When the particle size is too large, the paint supply amount is increased: Finding compensation coefficients ; The particle size is too small, and the paint supply amount is reduced: ; In the formula respectively represent the actual atomized particle size, the target atomized particle size; After the compensation coefficient is obtained, the compensation coefficient is applied to correct the paint supply amount synchronously, and the corrected paint supply amount ; The paint atomization particle size is detected by a laser particle size sensor.

10. The precise coating method of the three-proofing paint based on the gradient atomization control according to claim 1, characterized in that, Between the initial spraying operation and the thickness detection, a user terminal autonomously decides to add a coating pre-flow leveling link: The PCB board after completing the initial spraying is transferred to a constant temperature and humidity leveling room, the leveling temperature of the leveling room is set according to the physical properties of the paint, the leveling humidity is set to a preset humidity interval, and is not lower than the humidity of the coating operation environment, and the leveling time is set according to the coating thickness, that is, the thicker the coating, the longer the leveling time.

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