A method of slotting a printed circuit board

Abstract

The application relates to the field of circuit board processing, and particularly provides a slotting method for a printed circuit board, which comprises the following steps: step 1, fixing the printed circuit board in a slotting station and determining a slotting area; step 2, scanning the slotting area by using a laser beam to remove the upper layer material layer by layer by ablation; and step 3, removing residues after the laser ablation is completed; in step 2, spraying atomized medium to the slotting area before scanning by the laser beam, and the spraying at least lasts until the scanning by the laser beam is completed. The atomized medium reduces the temperature peak, promotes the outward escape of resin cracking products, and makes the resin not easy to be in a high-temperature and high-viscosity state for a long time; for the formed composite group, the atomized medium can reduce the fluidity of the surface layer resin, adjust the interface state of the slot inner wall, weaken the wet spreading and solidification of the composite group on the slot wall, and then reduce the residues on the slot wall and improve the flatness of the slot wall.

Description

Technical Field

[0001] This application relates to the field of circuit board processing, and more specifically, to a method for slotting printed circuit boards. Background Technology

[0002] In terms of manufacturing processes, slotting in printed circuit boards (PCBs) is commonly used for structural slots for device recessed or embedded mounting, heat dissipation slots to enhance heat dissipation and shorten thermal paths, assembly slots to allow connectors or structural components to pass through, and electrical isolation slots to improve creepage distances and insulation. After slotting, the board must also support device mounting, thermally conductive material filling, encapsulation fixation, and electrical insulation. Therefore, the slotting process requires a high degree of flatness in the slot walls. Especially in scenarios such as device embedding and encapsulation, thermal interface bonding, localized adhesive application, and high-density structural assembly, rough slot walls, slag buildup, or localized protrusions can lead to poor device bonding, discontinuous thermal paths, uneven adhesive spread, and even stress concentration and assembly failure. Therefore, slot wall flatness is a critical indicator in the slotting process.

[0003] Laser etching utilizes a high-energy laser beam focused on a predetermined grooving area, causing the local material to absorb energy and undergo melting, vaporization, thermal decomposition, or ablation within a very short time, thus gradually removing the material and ultimately forming the desired groove. For multilayer printed circuit boards, the laser typically acts sequentially on the upper copper layer, solder mask layer, dielectric layer, and deeper functional layers during the grooving process. The upper copper layer mainly consists of copper foil pads and circuit patterns, the solder mask layer is usually a photosensitive resin protective film, and the dielectric layer is generally FR-4, PP, or other resin-fiber insulating materials. During the laser etching process, the products formed after the removal of these layers either escape as smoke, vapor, or fine coking powder, or the particles are relatively light and can be easily removed from the groove under the laser recoil pressure, thermal buoyancy airflow, or accompanying vacuum action, and are not likely to remain inside the groove.

[0004] However, the conductive adhesive layer is composed of a resin matrix and conductive metal particles, such as silver powder, copper powder, or silver-copper composite powder dispersed in the resin. Under laser irradiation, the resin softens, melts, cracks, and cokes, entering a high-temperature, high-viscosity transitional state. Simultaneously, the metal particles originally dispersed in the resin are gradually exposed, and these particles are easily retained in the tank for a short time under the influence of localized heat flow and backflow. The resin cracking products in a viscous state entrain the metal particles, forming composite agglomerates. These agglomerates are heavier than smoke and stickier than ordinary dust, making them highly susceptible to impact and adhesion to the tank wall under the influence of backflow, low-velocity areas at the tank opening, and weak-flow areas at the tank corners. The outer layer of the composite agglomerates is semi-molten or coked resin, exhibiting strong adhesion and rapid formation. Furthermore, the tank walls and corners themselves contain localized low-velocity areas, making it difficult for residues to be removed by vacuuming once they adhere to the resin. Conventional plasma descaling utilizes the active free radicals and ion bombardment in low-pressure plasma to decompose, oxidize, and peel off organic resin residues. However, for composite residues that have already incorporated metal particles and are firmly adhered to the tank wall, the metal particles prevent the active particles from further contacting the internal resin, and the outer resin layer is partially carbonized and agglomerated, making it difficult for plasma to fully penetrate and completely remove them. Acid pickling mainly relies on chemical solutions to swell, decompose, or assist in the peeling of resin residues. For composite clusters containing internal metal particles that have formed stable attachments on the tank wall, acid solutions have difficulty effectively penetrating their internal interfaces. Furthermore, to avoid corrosion of the copper layer and the board surface structure, acid pickling conditions cannot be infinitely increased, limiting its removal capacity.

[0005] In summary, existing grooving methods often result in groove walls with a lot of residue, making it difficult to meet the high flatness requirements of device embedding, thermal interface bonding, and high-precision packaging. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of the prior art by providing a slotting method for printed circuit boards, thereby solving the problem that the slot walls obtained by existing slotting methods often have a lot of residue attached, making it difficult to meet the requirements for high flatness of the slot walls for device embedding, thermal interface bonding, and high-precision packaging.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This application provides a method for slotting a printed circuit board, the method comprising the following steps: Step 1: Fix the printed circuit board at the slotting station and determine the slotting area; Step 2: Use a laser beam to scan the grooved area and ablate and remove the upper material layer by layer; Step 3: After laser ablation is completed, remove the residue; In step 2, a spray medium is applied to the slotted area before the laser beam scan, and this continues at least until the laser beam scan is completed.

[0008] In step 2 of this application, a sprayed medium is applied to the grooving area during laser scanning. This atomized medium reduces the probability of resin-laden particles forming and weakens the adhesion of the resulting aggregates to the grooving wall, thereby improving the smoothness of the grooving wall. Specifically, on the one hand, the atomized medium can continuously absorb heat from the surrounding area of ​​the laser processing zone, making it less likely for the resin phase in the conductive adhesive to maintain a high-temperature, high-viscosity state in a localized area for a long time during the softening, melting, and thermal decomposition process. Instead, it transitions more quickly from a flowable, adhesive transitional state to a decomposition and dispersion or loose coking state. During the evaporation of the atomized medium, the local gas volume expansion and boundary layer renewal exert an outward traction effect on the small molecules, low-molecular-weight fragments, and light coking products generated after resin decomposition, promoting their transformation from a localized stagnant state to a decomposition and dispersion state. This prevents them from remaining near the grooving opening and re-aggregating into highly adhesive intermediate residues. On the other hand, for already formed aggregates, the atomized medium can act on the surface resin, rapidly reducing the surface temperature and causing the resin viscosity to rise rapidly and its fluidity to decrease rapidly, thus preventing it from fully wetting and spreading on the wall surface. Simultaneously, the atomized medium forms an extremely thin, moist gas-liquid boundary layer on the inner wall surface of the tank, reducing the interfacial driving force and making it difficult for the spreading process to continue, thereby reducing the adhesion of aggregates to the inner wall. In other words, the atomized medium reduces the formation of aggregates and the adhesion of the formed aggregates to the inner wall, ultimately improving the smoothness of the inner wall.

[0009] Furthermore, the atomizing medium is deionized water or an alcohol-water mixture with a mass fraction of 3wt%-10wt%. Deionized water has a high specific heat and latent heat of vaporization, which can effectively absorb heat and cool the laser processing area, while avoiding the introduction of new contamination due to ionic impurities remaining in the tank. Using an alcohol-water mixture with a mass fraction of 3wt%-10wt% utilizes the low surface tension and high volatility of alcohols, resulting in more uniform droplet distribution, faster evaporation response, and stronger interfacial regulation of resin pyrolysis products. Excessive alcohol content leads to rapid evaporation, insufficient liquid phase retention, and increased flammability. A small amount of alcohol can also weaken the tendency of high-temperature resin pyrolysis products to continuously aggregate in local areas, making it less likely for the resin phase to form a persistent, high-viscosity continuous phase. This reduces the coating and bridging ability of conductive particles, decreases the formation of aggregates, and improves the smoothness of the tank walls.

[0010] Furthermore, the atomizing medium is sprayed onto the slotted area using a pulsed spray method. Compared to continuous spraying, pulsed spraying has a short pause between adjacent sprays. This allows the tiny droplets that have entered the slotted area to fully evaporate under the influence of residual heat from laser processing and the high-temperature atmosphere near the slot opening. Droplets from the previous spray are evaporated and removed, the local high-humidity boundary layer is renewed, and resin pyrolysis products and fine particles are less likely to continuously accumulate in the near-field of the slot opening, thereby reducing resin coating, bridging, and agglomeration of particles. At the same time, the pause phase also allows the high-humidity boundary layer at the slot opening to be gradually replaced by a new gas phase environment, reducing the local water vapor and droplet concentration. If continuous spraying is used, droplets tend to accumulate continuously at the edge of the slot opening, the slot wall, and low-flow-rate areas, forming an over-humid state, which in turn leads to the formation of a local liquid film, disturbing laser energy transfer, increasing local thermal field fluctuations, and pressing or retaining the formed residue on the slot wall.

[0011] Furthermore, the temperature of the atomizing medium is 5-15℃. A temperature slightly below room temperature better suppresses excessively high local temperature peaks, allowing the atomizing medium to rapidly absorb heat upon contact with the high-temperature pyrolysis zone. This shortens the time the resin remains in a high-temperature, high-viscosity state, enabling the resin to transition more quickly from a flowable, adhesive state to a pyrolysis / dispersion or loose, charred state. It also avoids excessively low temperatures that could lead to localized condensation, excessive droplet aggregation, or excessive thermal shock, affecting the stability of laser etching. For already formed composite clusters, the lower-temperature atomizing medium can also more quickly remove heat from the surface resin, causing its viscosity to rise rapidly and its flowability to decrease, making it less likely to spread continuously on the tank wall. Simultaneously, the lower temperature also helps maintain a low-temperature boundary layer near the tank wall, reducing the thermal coupling between the inner wall and the high-temperature resin, thereby reducing the probability of adhesion and fixation, and improving the smoothness of the tank wall.

[0012] Furthermore, the particle size of the atomizing medium is 5μm-30μm. If the droplet size is too large, the inertia increases, making it difficult to follow the streamline and enter the near field of the tank opening under the action of thermal buoyancy flow. It is more likely to directly impact the edge of the tank opening or the tank wall, causing liquid stagnation, blocking the laser, disturbing the local thermal field, and even pressing the formed residue onto the tank wall surface. Conversely, if the droplet size is too small, the heat capacity per unit droplet is insufficient, and the specific surface area is too large, resulting in an excessively fast evaporation rate. It often vaporizes before approaching the resin cracking zone and the tank wall. Moreover, smaller droplets have a strong ability to escape with the airflow, making it difficult to form an effective temperature regulation, interface conditioning, and boundary layer effect on the resin surface and near the tank wall. Thus, it cannot fully exert the effect of inhibiting the formation of complex clusters and weakening adhesion.

[0013] Furthermore, the atomizing medium is also sprayed into the annular area surrounding the slotted area. Simultaneous spraying in the annular area lowers the temperature of the outer edge and surrounding area of ​​the slot. The resin pyrolysis products, light coking products, and microparticles escaping to the outer edge and surrounding area experience a rapid temperature reduction, weakening their fluidity and adhesion. This makes it less likely for them to maintain a high-temperature, high-viscosity state and accumulate as continuous residues on the surface. Residues falling onto the outer edge and surrounding surface of the slot are more likely to exist in a loose state and be carried away by subsequent airflow or suction, making them less likely to remain in the outer edge area of ​​the slot for extended periods. The spraying in the annular area also continuously removes heat from the edge of the slot and adjacent areas of the slot wall through heat transfer, lowering the slot wall temperature. This causes the outer layer of resin in the composite to transition more quickly from a flowable state to a high-viscosity or near-cured state upon contact with the slot wall, weakening its leading edge propulsion ability and making the spreading process more likely to be interrupted in the initial stage. Simultaneously, the lower-temperature slot wall surface is not conducive to the continuous wetting of the high-temperature resin, slowing the growth rate of the effective contact area between the resin and the slot wall, and consequently weakening the interfacial spreading driving force. Synchronous spraying in the annular area not only reduces the residue at the outer edge and surrounding area of ​​the tank opening, but also further reduces the adhesion probability of composite clusters on the tank wall by lowering the tank wall temperature and weakening the interfacial spreading driving force, thereby helping to improve the smoothness of the tank wall.

[0014] Furthermore, a biased airflow is positioned above the grooved area, sweeping from one side to the other. This biased airflow causes products such as resin degradation products, coking debris, and conductive particles released during laser etching to migrate to one side, rather than lingering disorderly above the groove opening or repeatedly falling back down. Local backflow, weak flow zones, and particle retention zones easily form near the groove opening; relying solely on natural thermal buoyancy is insufficient to ensure rapid particle detachment from the groove area. For already formed small aggregates, the biased airflow also reduces their residence time near the groove opening and the probability of them falling back to the inner wall, preventing further wetting, spreading, and adhesion after impacting the groove wall, thus contributing to improved groove wall smoothness.

[0015] Furthermore, a bias electric field is set above the slotted area, parallel to the bias airflow. In the high-temperature laser etching environment, particles, coking particles, and pyrolysis fumes undergo processes such as thermal decomposition, frictional collision, interface separation, and airflow propulsion. Local particles carry trace amounts of charge or undergo induced polarization in the external electric field, thus exhibiting a certain responsiveness to the electric field. Light particles, coking debris, and micro-complexes escaping from above and near the slot opening enter the bias electric field region. Under the influence of the electric field, charged particles can deflect to one side more quickly, thereby reducing the probability of residue re-aggregating near the slot opening and falling back onto the inner wall. The parallel setting of the bias electric field and the bias airflow ensures that they act in the same direction on the particle migration direction, preventing their effects from canceling each other out or causing trajectory disruption. With the bias electric field parallel to the bias airflow, the airflow is responsible for overall transport, while the electric field is responsible for slight deflection and directional enhancement, further improving the efficiency of particle detachment from key slot wall areas and reducing the probability of slag formation.

[0016] Furthermore, step 2 uses a laser wavelength of 10.6 μm and an average power of 5-80 W. The 10.6 μm wavelength laser has a good absorption matching relationship with the resin phase in the solder mask layer, dielectric layer, and resin matrix in the conductive adhesive layer of the printed circuit board, enabling these organic materials to more effectively convert laser energy into heat energy, resulting in softening, pyrolysis, and ablation removal. Controlling the average power to 5-80 W helps ensure sufficient removal capacity while avoiding excessive resin coking, severe particle exposure, and increased residue entrainment caused by excessive power; simultaneously, it avoids insufficient material removal, excessively long processing time, and unstable local heat accumulation due to insufficient power. This facilitates effective etching of resin layers in multilayer structures and reduces slag buildup and thermal damage on the tank walls, thereby improving flatness.

[0017] Furthermore, step 3 includes plasma desizing and / or acid washing. Building upon the reduced probability of aggregate formation and adhesion due to the atomized medium, step 3 further employs plasma desizing and / or acid washing to post-process and remove the slight resin film, charring, and some adhering residue remaining after laser etching. Plasma desizing primarily utilizes active particles to decompose, oxidize, and peel off organic resin residues, removing a thin layer of charred resin and light residues; acid washing can swell, assist in peeling, or clean surface residues. Because the atomized medium has already reduced the large-scale formation and firm adhesion of aggregates, the residues required for subsequent plasma desizing and / or acid washing are less and looser, thus making it easier to achieve better cleaning results. Both, as end-of-pipe cleaning methods, further reduce tank wall residue, improve surface cleanliness and geometric integrity, ultimately contributing to a smoother tank wall.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: This application involves spraying an atomizing medium into the grouted area during laser scanning. This atomizing medium regulates the local thermal environment and interface state of the grouted area, reducing the formation of resin-encapsulated particles and their adhesion to the grouted wall. Specifically, the atomizing medium reduces local temperature peaks through endothermic evaporation and promotes the outward dispersion of resin decomposition products, preventing the resin from remaining in a high-temperature, high-viscosity state for extended periods, thereby reducing its coating and agglomeration of conductive particles. For already formed aggregates, the atomizing medium reduces the fluidity of the surface resin and regulates the interface state of the grouted wall, weakening the wetting, spreading, and adhesion of the aggregates to the grouted wall, thus reducing residue on the grouted wall and improving its smoothness. Attached Figure Description

[0019] Figure 1 A schematic diagram of a slotting method for a printed circuit board provided by the present invention; Figure 2 A schematic diagram of the spray medium nozzle arrangement in a grooving method for a printed circuit board provided by the present invention; Figure 3 This is a schematic diagram of the implementation device corresponding to the slotting method for a printed circuit board provided by the present invention; Figure 4 This is a schematic diagram of the control system used in a slotting method for a printed circuit board provided by the present invention. Detailed Implementation

[0020] To make the implementation process of this invention clearer, a detailed description will be provided below in conjunction with the accompanying drawings.

[0021] Example 1:

[0022] This invention provides a method for slotting a printed circuit board. The printed circuit board, from top to bottom, includes at least an upper copper layer, a solder mask layer, a dielectric layer, a conductive adhesive layer, an inner copper layer, and a bottom copper layer. The conductive adhesive layer includes a resin matrix and conductive particles dispersed within the resin matrix. The conductive particles are silver powder, copper powder, or a silver-copper composite powder, with a particle size of 2-10 μm. Due to the stickiness of the intermediate products, the conductive adhesive layer is difficult to remove completely. Figure 1 As shown, the slotting method of this application includes the following steps: Step 1: Fix the printed circuit board at the slotting station and determine the slotting area.

[0023] The printed circuit board (PCB) to be processed is placed on the processing platform of the laser grooving equipment, with the side to be grooved facing upwards. The laser beam is then incident on the PCB surface from this side. Typically, the side to be grooved is the side of the PCB with the upper copper layer and solder mask layer. The laser beam ablates and removes the upper layers sequentially from top to bottom. The grooving station includes a conventional support platform, positioning mechanism, clamping mechanism, and position calibration mechanism. The support platform supports the PCB, the positioning mechanism defines the PCB's position in the plane, the clamping mechanism prevents vibration, warping, or displacement of the PCB during processing, and the position calibration mechanism ensures accurate alignment between the preset grooving area and the laser scanning path. Specifically, after the PCB is placed on the support platform, it can be fixed using clamping plates, mechanical blocks, edge limiting components, vacuum adsorption, or a combination thereof. Preferably, the carrier platform is provided with vacuum adsorption holes. After the printed circuit board is placed on the carrier platform, the lower surface of the printed circuit board is made to fit with the carrier platform by vacuum adsorption to reduce board warping. At the same time, clamps or pressure blocks are used to assist in limiting the position of the printed circuit board at the edge to prevent the board from moving in the plane during laser scanning.

[0024] After fixing, the position and range of the slotted area are determined according to the processing data of the preset slotted pattern. The slotted area is initially determined by reading the coordinate information in the processing program. Subsequently, the printed circuit board is positionally calibrated to correct its actual placement deviation on the support platform. Reference marks, pad features, positioning holes, or edge features on the printed circuit board can be obtained through visual alignment. The actual identified position is then compared with the theoretical position in the processing program to obtain the positional deviation, and the laser scanning path is compensated and corrected accordingly. Alternatively, mechanical reference alignment can be used to achieve board position correction using positioning pins, limit blocks, or edge reference surfaces. Generally, the printed circuit board remains stationary while the laser beam moves and scans. The laser beam is driven to move within the preset slotted area by a galvanometer system, scanning head, or optical deflection mechanism to achieve laser trajectory scanning. Alternatively, it can be performed in a mode that combines galvanometer scanning with platform micro-motion, where the laser beam completes a local rapid scan while the support platform performs small-range displacement compensation or large-range repositioning. After fixing, positioning and calibration are completed, the center position, outer contour dimensions, groove depth parameters and relative positional relationship with the surrounding graphics of the grooving area can be further determined, and the above information is transmitted to the laser control system for subsequent laser scanning grooving.

[0025] Step 2: Use a laser beam to scan the grooved area and ablate and remove the upper material layer by layer.

[0026] In this embodiment, the laser beam is incident on the slotted area in a direction perpendicular to the surface of the printed circuit board. The laser is a carbon dioxide laser with a wavelength of 10.6 μm, an average power of 5-80 W, a pulse width of 5 μs-100 μs, a pulse frequency of 5 kHz-100 kHz, a spot size of 20 μm-300 μm, a scanning speed of 100 mm / s-1200 mm / s, and a defocusing amount of -1 mm to +1 mm. Specifically, the slotted area is processed by multiple scans and layer-by-layer ablation removal. The laser beam does not ablate the entire slotted area to the target depth in one go. Instead, it first scans and removes the surface material of the slotted area, and then performs subsequent scans based on the depth already removed and the state of the remaining material, thereby gradually removing the upper layer material along the thickness direction. This is beneficial for controlling the slotting depth and slot shape boundaries, and also reduces the problems of heat accumulation, coking, and slagging caused by excessive heat input in a single operation.

[0027] Specifically, the laser beam first acts on the copper layer and solder mask layer on the surface of the slotted area. For the copper layer, due to the high reflectivity and rapid thermal conductivity of copper, the laser mainly performs localized thermal action and removal. For the solder mask layer, since it is usually a photosensitive resin material, it has good absorption capacity for 10.6μm wavelength laser, thus it can soften, crack, and ablate relatively quickly. After the solder mask layer and the localized copper layer on the upper surface are removed, the laser beam continues to act downwards on the dielectric layer. The dielectric layer is usually FR-4, PP, or other resin-insulated fiberglass materials. Resin has good absorption capacity for the relative wavelength laser, and under the action of the laser, it further softens, cracks, cokes, and is removed. Compared with the copper layer, solder mask layer, and dielectric layer, the conductive adhesive layer, because it includes a resin matrix and dispersed metal particles, is more likely to form resin composite residues containing particles under the action of the laser. For the upper copper foil and solder mask layer, a higher scanning speed and fewer scans are used to complete the surface opening, with a scanning speed of 500 mm / s-1200 mm / s and 1-2 scans. For the dielectric layer and conductive adhesive layer, a smaller single removal amount and more scans are used for gradual cutting, with a scanning speed of 100 mm / s-400 mm / s and 3-5 scans. After multiple scans, the upper material in the grooved area is removed sequentially along the thickness direction, ultimately forming a groove that reaches the preset depth and contour dimensions.

[0028] Atomizing medium is sprayed into the slotted area before laser beam scanning and continues at least until the laser beam scanning ends. The atomizing medium is deionized water or a mixture of alcohol and water with a mass fraction of 3wt%-10wt%. Deionized water has a high specific heat and latent heat of vaporization, which can stably absorb heat in the slotted area; at the same time, it avoids the residue of impurity ions. The mixture of alcohol and water with a mass fraction of 3wt%-10wt% can reduce the surface tension of the liquid, improve the atomization uniformity and evaporation response rate, and prevent resin decomposition products from forming a continuous high-viscosity phase in local areas. The alcohol can be at least one of ethanol and isopropanol. The temperature of the atomizing medium is preferably 5-15℃, and the particle size is preferably 5μm-30μm. The temperature can provide a cooling effect without causing significant condensation and droplet coalescence; the particle size range can ensure that the droplets have a certain heat capacity and enter the near field and wall area of ​​the slot, while avoiding the formation of large droplets that impact the slot wall or vaporize too quickly before contacting the resin. During use, the atomizing medium has a small particle size, and the area above the slotted region is simultaneously exposed to the high-temperature environment created by laser processing and the bias airflow. After entering the working area, the atomizing medium mainly functions through heat absorption, evaporation, and boundary layer regulation, making it less likely to form large-area drips and liquid accumulation on the circuit board surface. Even if a small number of droplets come into contact with the circuit board surface, they will quickly evaporate or be carried away by the local high temperature and airflow, thus avoiding long-term liquid retention at the slot opening, slot wall, or circuit board surface, and reducing the impact on the stability of laser etching and the electric field distribution. Because the medium evaporates quickly, the impact of the sprayed medium on the bias electric field electrodes is also relatively small.

[0029] Preferably, the atomizing medium is sprayed onto the slotted area using a pulse spray method. The pulse spray period can be 0.05s-2s, the spray on-time can be 0.02s-0.3s, and the spray off-time can be 0.03s-1.7s. The conductive adhesive layer includes a resin matrix and metal conductive particles, which easily form resin composite clusters containing particles under laser irradiation. Pulse spray can reduce local temperature peaks during the spraying phase, inhibit the resin from maintaining a high-viscosity intermediate state for a long time, and allow droplets that have entered the processing area to fully evaporate, be extracted, and have their boundary layer renewed during the spray pause phase, thereby reducing the accumulation of droplets at the slot opening and the slot wall, and reducing the probability of composite cluster formation and adhesion.

[0030] For the solder mask and dielectric layers, the atomizing medium primarily functions to suppress localized overheating, reduce charring, and minimize edge thermal damage. This allows fumes, vapors, and light charred powder to escape more easily, reducing edge scorching and residue. For the top copper layer, the atomizing medium mainly controls surface heat accumulation and reduces thermal damage to adjacent resin layers, preventing premature carbonization of subsequent lower resin layers due to excessive localized heat. For the upper structure of the conductive adhesive layer, the atomizing medium can be sprayed continuously or with reduced intervals, for example, half the interval of the conductive adhesive layer, to improve heat absorption. In other words, the upper layer material focuses more on heat accumulation control and edge quality improvement, while the conductive adhesive layer focuses more on suppressing aggregate formation and adhesion. Fine-tuning the parameters of the same pulse spray device can meet the different needs of each layer, ensuring the quality of multi-layer grooving.

[0031] Furthermore, the atomizing medium is sprayed not only towards the center of the slotted area but also towards the annular area surrounding it. The annular area is a spray band encircling the outer contour of the slotted area, with a width extending 0.5mm-3mm outward from the outer edge of the slotted area. The spray parameters for the central slotted area and the annular area can differ. Preferably, the spray in the central slotted area suppresses the high-viscosity intermediate state of the resin, reduces the formation of aggregates, and weakens the flowability of already formed aggregates; therefore, a relatively high pulse frequency can be used for the central area spray. The spray in the annular area cools the periphery, constrains the escape path of pyrolysis products, suppresses residue accumulation at the outer edge of the slot, and reduces the temperature of the adjacent area of ​​the slot wall through heat transfer; therefore, a relatively low spray volume and a lower spray frequency are used for the annular area. Specifically, the spray volume in the central slotted area is 1.5-3 times that in the annular area; the duty cycle of the central area spray is 30%-60%; and the duty cycle of the annular area spray is 15%-35%. The spray temperature in the central area can be 5-15℃, while the spray temperature in the annular area can be the same as the central area or 1-5℃ lower to enhance the cooling effect on the periphery. The spray particle size in the annular area is smaller than that in the central area, ranging from 5μm to 20μm, to form a more stable peripheral humid gas-liquid boundary layer and temperature buffer zone. Simultaneous spraying in the annular area not only lowers the temperature of the outer edge and surrounding areas of the tank opening, making it less likely for resin pyrolysis products and light coking products escaping to this area to form high-viscosity continuous residues, but also surrounds and confines the spray in the central area, preventing the atomized medium in the central area from being carried away too quickly by the external large-scale airflow, thus allowing it to function more fully within the tank area.

[0032] The atomizing medium is sprayed through a spray assembly. The spray assembly includes a liquid storage unit, a liquid delivery line, an air supply unit, an atomizing nozzle, a nozzle mounting bracket, and a spray control module. The liquid storage unit stores the atomizing medium, the liquid delivery line delivers the atomizing medium to the atomizing nozzle, and the flow control unit controls the spray volume, spray cycle, and spray pressure. It is linked to the laser scanning system, initiating spraying before the laser beam begins scanning and maintaining the preset spray state during the laser scanning process. The air supply unit provides the airflow required for atomization, and the temperature of the atomizing medium is maintained between 5-15℃. Two sets of nozzles can be installed in the aforementioned annular area and the central slotted area to allow for separate control of the corresponding spray parameters. The specific control method and the structure of the spray device are existing technologies.

[0033] Preferably, the spraying device is a fixed spraying structure, stationary relative to the circuit board. Laser scanning is performed by a scanning head located above, with the laser beam rapidly deflecting and scanning within the slotted area, while the circuit board is fixed to the support platform. If the spraying device moves synchronously at high speed with the laser beam, the mechanism becomes highly complex and easily interferes with the stability of the optical path. Specifically, the atomizing nozzle assembly can be positioned around the laser scanning head, avoiding the central laser beam path. For example, at least two nozzles are positioned around the laser beam incident axis, distributed in a ring or symmetrical manner. Preferably, 6-8 nozzles are distributed around the laser incident center, with some nozzles facing the center of the slotted area and some facing the ring area, such as... Figure 2 As shown, both the vertically oriented nozzles and the angled nozzles are evenly distributed along the circumference. The angled nozzle axis forms a 5-10° angle with the laser incident axis, causing the spray to be directed at an angle towards the slotted area and the surrounding annular area. This avoids directly obstructing the laser beam path and facilitates droplet entry into the near-field of the slot opening and the adjacent area of ​​the wall. The nozzle outlet orifice diameter can be selected according to the target particle size and spray volume, for example, 0.1mm-1.0mm, and the atomization pressure can be 0.05MPa-0.5MPa. The liquid and gas supply lines can be fixed to the nozzle mounting bracket, which is then fixed to an independent support arm. The distance from the nozzle to the upper surface of the circuit board is 30mm-80mm. Too small a distance makes it susceptible to laser heat radiation and splash contamination, while too large a distance results in spray dispersion and reduced accuracy. Furthermore, the central nozzle employs a larger flow rate and a higher duty cycle, while the annular nozzle uses a lower flow rate and a lower duty cycle; the temperature of the central nozzle is 5-15℃, and the temperature of the annular nozzle is 1-10℃. This ensures that the laser main beam path is unobstructed and that the spray acts stably on the slotted area and its surrounding near field. Combined with the subsequent bias airflow and optional bias electric field, this suppresses the formation and adhesion of composite clusters, thereby improving the smoothness of the slot wall.

[0034] Step 3: After laser ablation is completed, remove the residue.

[0035] This embodiment includes plasma desmearing and / or acid washing. Plasma desmearing involves introducing a reactive gas under low pressure and exciting it to form plasma. The active free radicals, ions, and electrons in the plasma act on the residual organic resin, oxidizing, decomposing, and stripping it, thereby converting the residual organic phase into volatile small molecule products that are then discharged from the processing chamber. Specifically, the laser-grooved printed circuit board is placed in the plasma processing chamber with the grooved area facing upwards. The processing chamber is evacuated, and a plasma processing gas is introduced. The processing gas can be oxygen, argon, nitrogen, carbon tetrafluoride, or a combination thereof. Oxygen is used to remove organic resin residue, argon can be used to enhance the physical bombardment effect, and fluorine-containing gases can assist in treating some more difficult-to-decompose residues. Preferably, the plasma processing gas is mainly oxygen, and a small amount of inert gas can be used for synergistic treatment. The plasma processing pressure is 30Pa-200Pa, the radio frequency power is 50W-300W, and the processing time is 30s-10min. During plasma treatment, active particles primarily act on the thin layers of coke and organic resin residue on the tank walls, bottom, and corners, reducing their thickness, loosening their structure, and partially removing them. For composite residues with encapsulated particles formed by laser etching, the focus of plasma debinding is to remove the outer and surface resin phases, making the residue structure loose and creating conditions for acid washing or cleaning.

[0036] Pickling involves swelling, softening, and weakening the interface of residual resin phase, and penetrating the loosened residue into the interface between the residue and the tank wall through liquid phase penetration, thereby making the residue easier to detach from the tank wall surface. Specifically, the printed circuit board that has undergone plasma adhesive removal is immersed in the pickling solution, or the pickling solution is sprayed onto the tank area. The pickling solution is at least one of hydrochloric acid, sulfuric acid, phosphoric acid, citric acid, and acetic acid, or a composite pickling system thereof. The pickling time is 30 seconds to 10 minutes. During the pickling process, gentle stirring, circulating rinsing, ultrasonic assistance, or spray agitation can be combined to enhance the liquid's penetration into the tank wall and corner interfaces and the residue removal ability.

[0037] After plasma descaling and / or acid pickling, the printed circuit board (PCB) undergoes cleaning and drying. The grooved areas are rinsed with deionized water via spraying, immersion, or circulating rinsing to remove loose organic debris from the plasma treatment, particulate residue from acid pickling, and residual treatment solution. Then, moisture is removed from the groove using air knife blowing, compressed air drying, hot air drying, or vacuum drying. The drying temperature is 40℃-60℃, and the drying time is 1min-30min. After drying, the grooved areas should be free of obvious droplets and residual liquid accumulation, and the groove wall surface should remain dry and clean.

[0038] Example 2:

[0039] Based on Example 1, a bias airflow is provided above the slotted area, sweeping from one side of the slotted area to the other. Specifically, the bias airflow passes through a bias airflow assembly. The bias airflow assembly includes: an outlet unit, an air supply pipeline, a flow regulation unit, and a bias airflow control module. The outlet unit is used to output directional airflow above the slotted area, the air supply pipeline is used to deliver the air source to the outlet unit, the flow regulation unit is used to regulate the airflow velocity, pressure, and start / stop sequence, the mounting bracket is used to fix the outlet unit, and the bias airflow control module is used to link the bias airflow with the laser scanning process. The outlet unit is a slit nozzle, which forms a relatively uniform sheet-like sweeping flow above the slotted area. The length of the slit nozzle covers the width of the slotted area; preferably, the length of the slit nozzle is 1.5 to 2 times the width of the slotted area. The nozzle is positioned above one side of the slotted area, with the airflow direction spanning the slotted area and facing the other side, so that the bias airflow sweeps across the area above the slot in a direction substantially parallel to the circuit board surface. Optionally, a flow guide and collection port is provided on the other side of the slotted area. The flow guide and collection port is connected to the air extraction system to ensure that resin pyrolysis products, coking debris, conductive particles, and micro-complexes carried away from the slotted area by the biased airflow are collected in a timely manner. While an air outlet is provided on one side, a suction structure is provided on the other side to prevent the airflow from spreading disorderly and rewinding back into the slotted area, thereby reducing the formation of local backflow, weak flow zones, and particle retention zones.

[0040] The air supply line is connected to the air source device. The air source device can be a compressed air source, an inert gas source, or an air pump. The bias airflow uses clean compressed air or nitrogen to reduce the entry of additional impurities into the grooving area. The air supply pressure is 0.02MPa-0.2MPa; the flow velocity of the bias airflow above the grooving area is 0.5m / s-2m / s; the distance between the air outlet unit and the circuit board surface is 1cm-3cm. When the flow velocity is too low, the guiding effect on the migration of resin pyrolysis products and small particles is insufficient; when the flow velocity is too high, it will disturb the laser transmission and increase the local flow field disturbance at the grooving opening. The bias airflow assembly is preferably fixedly installed above the grooving station and stationary relative to the printed circuit board, rather than moving synchronously with the laser beam.

[0041] The start and stop timing of the bias airflow can be linked to the laser scanning process. Preferably, the bias airflow is started 0.05s-2s before the laser beam begins scanning, so that a stable directional near-field transport channel is first formed above the slot opening. After the laser scanning ends, the bias airflow can continue to be maintained for 0.1s-5s to remove the pyrolysis products and fine particles that remain in the near field of the slot opening after processing. Furthermore, the bias airflow and pulse spray are alternately activated. The bias airflow is also a pulse airflow and is alternately activated with the spray medium. The bias airflow is used to maintain the overall migration direction, while the pulse spray is sprayed into the slotted area according to a preset cycle. During each spray activation phase, the bias airflow can maintain a low flow rate or be turned off, so that the atomized medium preferentially enters the slot opening and slot wall area. During the spray deactivation phase, the bias airflow can be restored to a higher flow rate or turned on to accelerate the removal of cooled and loosened pyrolysis products and light particles. With the biased airflow setting, the resin pyrolysis products, coking debris, conductive particles, and small aggregates released by laser etching preferentially migrate to one side, rather than lingering disorderly above the groove or repeatedly falling back. This reduces the residence time of particles and pyrolysis products in the near field of the groove, weakening their chances of re-aggregating, abruptly stopping, and wetting and solidifying near the groove edge and inner wall, thus helping to further reduce slag buildup and improve the smoothness of the groove wall.

[0042] Example 3:

[0043] Based on Example 1, a bias electric field is set above the slotted area, parallel to the bias airflow. The bias electric field is generated by a bias electric field assembly, which includes opposing electrode units, insulating mounting components, an electric field control module, and an external power supply. The electrode units form a directional electric field above the slotted area; the insulating mounting components fix the electrodes to the frame and electrically isolate the electrode units from the metal body, circuit board platform, and spray assembly; the electric field control module adjusts the electric field strength, start / stop sequence, and polarity; and the external power supply provides a bias voltage to the electrode units. The electrode units include a first electrode and a second electrode, respectively positioned on opposite sides above the slotted area. The distance between the first and second electrodes along the bias electric field direction is 1.5-3 times the dimension of the slotted area along that direction, preferably avoiding the main area of ​​spray action to prevent the electrodes from contacting a large amount of spray medium for a short time. A transverse bias electric field is formed above the slotted area.

[0044] The first and second electrodes are sheet-like electrodes, slightly offset in height from the slit nozzle, and positioned closer to the circuit board to avoid obstructing the airflow channel and the laser main beam path. The electrodes are positioned on both sides of the biased airflow path and parallel to the biased airflow direction, ensuring the electric field direction is consistent with or has the same directional component as the overall transport direction of the biased airflow, thereby enhancing the unidirectionality of particle migration. Insulating mounting components are ceramic supports, insulating resin supports, or insulating sleeves, which are used to mount the electrodes to the frame or independent support arm via screws, snap-fit ​​connections, or bracket fixation. The external power supply is an adjustable DC bias power supply, creating a stable potential difference between the first and second electrodes. The bias voltage is 20V-200V. Insufficient electric field strength will not adequately deflect small particles, coking debris, and pyrolysis particles; excessive electric field strength may cause partial discharge, air breakdown, abnormal response of the atomizing medium, or place excessive demands on the equipment's insulation design.

[0045] Furthermore, the electrodes can be arc-shaped, with the arc surfaces of the two electrodes facing each other and both concave, wherein the radius of curvature can be 15-20 mm. The arc-shaped electrodes can reduce the local field concentration at the electrode edges, making the bias electric field distribution between the two electrodes more uniform and continuous. This is beneficial for applying a stable deflection effect to small particles, coking debris, and micro-agglomerates in the near field of the slot opening. Simultaneously, the arc-shaped electrodes can also reduce flow separation and local backflow when the bias airflow passes over the electrode surface, resulting in a smoother directional purge flow from above. The residue is first pre-guided between the two electrodes and then carried away by the bias airflow, thereby reducing the probability of residue falling back and adhering.

[0046] The bias electric field is set before laser scanning begins and remains continuously during the scanning process. Under the high-temperature laser etching environment, resin pyrolysis products, coking particles, and small particles undergo processes such as thermal decomposition, frictional collision, interface separation, and airflow. Local particles carry trace charges or undergo induced polarization in the external electric field, thus responding to the bias electric field. After entering the vicinity of the slot, small particles and micro-complexes are deflected under the influence of the bias electric field, making them less likely to remain above the slot for extended periods. With electrodes positioned on both sides of the slotted area, a confined near-field channel is formed above the slot, allowing small particles, coking debris, and micro-complexes generated by laser etching to first enter the localized area between the two electrodes before entering the main bias airflow channel above. This confines particle migration within the space between the two electrodes, reducing disordered diffusion and lateral scattering of residue above the slot, and allowing particles to enter the bias airflow zone more concentratedly. Simultaneously, the localized electric field between the electrodes also applies a pre-deflection effect to particles with trace charges or polarizable properties, making them more easily carried away along the bias airflow direction.

[0047] Example 4:

[0048] Based on the DC bias voltage of Example 3, an AC perturbation voltage is further superimposed. The AC voltage is used to induce periodic micro-oscillations in the small particles and micro-complexes, disrupting their initial adhesion points and continuous spreading conditions on the tank wall, while maintaining a stable migration trend. Specifically, the amplitude is 10V-50V, and the AC frequency is 100Hz-500Hz. This frequency range is sufficient to repeatedly perturb the newly formed initial adhesion points, weakening the transition from instantaneous contact to stable adhesion. It also continuously interrupts the interfacial spreading on the tank wall while the outer resin layer of the complexes is still in a flowable stage. This is more conducive to disrupting the initial adhesion points and inhibiting spreading and fixation, making it difficult for residues to further stabilize and adhere, thereby improving the smoothness of the tank wall.

[0049] A schematic diagram of an implementation device for the method of this application is shown below. Figure 3 As shown. In this embodiment, the control system is used to coordinate the control of laser scanning, spraying, bias airflow, and bias electric field. The laser scanning head is positioned above the grooving station and includes a galvanometer system and a focusing optical system. During processing, the laser scanning head is fixedly mounted on a bracket, and the galvanometer system drives the laser beam to deflect and move within the grooving area, achieving high-speed trajectory scanning within the grooving area. The laser scanning head achieves localized high-speed scanning through the galvanometer system; when the area to be processed exceeds the field of view of a single scan, the carrying platform moves or the laser scanning head moves along a straight module, allowing different grooving areas to sequentially enter the effective laser scanning range. For example... Figure 4 As shown, the control system includes a main control unit, a laser control module, a timing and synchronization module, a spray control module, a bias airflow control module, and an electric field control module. The laser control module is connected to the main control unit and provides it with laser scanning start / stop signals, power signals, and corresponding processing status signals. The timing and synchronization module is also connected to the main control unit and provides it with timing synchronization signals and process parameter setting signals. The main control unit is connected to the spray control module, bias airflow control module, and electric field control module, and outputs corresponding control commands to each module. The main control unit outputs pulsed spray signals to the spray control module to control the spray frequency, duty cycle, spray duration, and spray intensity; it outputs airflow control signals to the bias airflow control module to control the opening, closing, and wind speed of the bias airflow; and it outputs electric field control signals to the electric field control module to control the DC voltage, AC amplitude, and AC frequency. Through these connections, the main control unit can perform time-linked control of the spray, bias airflow, and bias electric field according to the laser scanning status and preset process parameters, enabling each execution unit to work collaboratively during the laser grooving process.

[0050] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for slotting a printed circuit board, the slotting method comprising the following steps: Step 1: Fix the printed circuit board at the slotting station and determine the slotting area; Step 2: Use a laser beam to scan the grooved area and ablate and remove the upper material layer by layer; Step 3: After laser ablation is completed, remove the residue; Its features are, In step 2, a spray medium is applied to the slotted area before the laser beam scan, and this process continues at least until the laser beam scan is completed.

2. The slotting method for a printed circuit board according to claim 1, characterized in that, The atomizing medium is deionized water or an alcohol-water mixture with a mass fraction of 3wt%-10wt%.

3. The slotting method for a printed circuit board according to claim 2, characterized in that, The atomizing medium is sprayed onto the slotted area using a pulse spray method.

4. The slotting method for a printed circuit board according to claim 3, characterized in that, The temperature of the atomizing medium is 5-15℃.

5. The slotting method for a printed circuit board according to claim 4, characterized in that, The particle size of the atomizing medium is 5μm-30μm.

6. The slotting method for a printed circuit board according to claim 5, characterized in that, The atomizing medium is also sprayed onto the annular area surrounding the slotted area.

7. The slotting method for a printed circuit board according to claim 6, characterized in that, A biased airflow is provided above the slotted area, and the biased airflow is blown from one side of the slotted area to the other side.

8. The slotting method for a printed circuit board according to claim 7, characterized in that, A bias electric field is set above the slotted area, and the bias electric field is set parallel to the bias airflow.

9. The slotting method for a printed circuit board according to claim 1, characterized in that, The laser wavelength used in step 2 is 10.6 μm, and the average power is 5-80 W.

10. The slotting method for a printed circuit board according to claim 1, characterized in that, Step 3 includes plasma degumming and / or acid washing.

Images