PCB (Printed Circuit Board) circuit laser ablation method

Abstract

The invention discloses a PCB (printed circuit board) circuit laser ablation method. The PCB circuit laser ablation method comprises the following steps: drilling holes in a copper-clad plate; carrying out full-board electroplating on the drilled copper-clad plate, and forming an electroplating copper layer on the surface of the copper foil and the hole wall; forming a tin protection layer on the surface of the electroplating copper layer; ablating the tin protection layer by adopting laser to remove the tin protection layer in a non-circuit pattern area in the PCB design, and at least partially exposing the electroplating copper layer below the tin protection layer; etching the exposed copper layer to expose the dielectric layer; and removing the residual tin protection layer to form a PCB circuit pattern. The indispensable photosensitive dry film in the traditional negative film and positive film process and matched film pasting, exposure and development procedures are abandoned. Therefore, not only is the material cost generated by using the dry film directly eliminated, but also hidden quality dangers such as open circuit and short circuit of a circuit caused by damage of the dry film in the processing process are avoided, so that the product yield is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of PCB manufacturing technology, and in particular to a method for laser ablation of PCB circuits. Background Technology

[0002] Printed circuit boards (PCBs) are critical components in electronic devices, and their circuit forming process directly affects the product's performance and reliability. Currently, the circuit forming processes commonly used in the industry mainly include negative film processing and positive film processing.

[0003] In negative film processing, holes are first drilled on a copper-clad laminate, followed by full-board electroplating to achieve interlayer conductivity. Then, a series of processes including lamination, exposure, development, etching, and film removal are performed to form the desired circuit pattern. While this process can achieve relatively uniform copper plating thickness and is suitable for fabricating fine circuits, it is limited by the sealing capabilities of the photosensitive dry film, making it difficult to handle large-diameter or grooved metallized structures, resulting in insufficient process adaptability.

[0004] In positive film processing, the same steps are required: drilling, full-board electroplating, film lamination, exposure, and development. Then, copper and tin are sequentially plated on the exposed copper areas as protective layers. Finally, film removal, etching, and desoldering complete the circuit formation. While this process avoids the limitations of sealing the apertures in negative film processing, the dry film thickness limitation makes it prone to film trapping, affecting pattern integrity. Furthermore, uneven current distribution during electroplating leads to inconsistent plating thickness, affecting the uniformity of circuit etching and making it difficult to meet the requirements for high-precision circuit fabrication.

[0005] The aforementioned negative and positive film processes generate large amounts of wastewater due to the use of various chemical solutions for developing, stripping, and etching, which is detrimental to environmental protection. Furthermore, the processes are lengthy, have long production cycles, and are inefficient. Summary of the Invention

[0006] The purpose of this invention is to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a PCB laser ablation circuit method that can use tin to replace the protective function of dry film, eliminating a large number of materials and equipment that are compatible with dry film, and reducing labor and material costs.

[0007] The PCB laser ablation circuit method according to an embodiment of the present invention includes: Step 1: The copper clad laminate consists of a dielectric layer and a copper foil layer. Drilling is performed on the copper clad laminate. Step 2: Perform full-board electroplating on the drilled copper-clad laminate to form an electroplated copper layer on the copper foil surface and hole walls; Step 3: Form a tin protective layer on the surface of the electroplated copper layer; Step 4: Use laser ablation to remove the tin protective layer in non-circuit pattern areas of the PCB design, and at least partially expose the underlying electroplated copper layer. Step 5: Etch the exposed copper layer to expose the dielectric layer; Step 6: Remove the remaining solder protective layer to form the PCB circuit pattern.

[0008] The PCB laser ablation circuit method according to embodiments of the present invention has at least the following beneficial effects: First, it eliminates the indispensable photosensitive dry film in traditional negative and positive film processes, as well as the associated film lamination, exposure, and development processes. This not only directly eliminates the material costs incurred due to the use of dry film, but also avoids quality risks such as open circuits and short circuits caused by dry film damage during processing, thereby significantly improving product yield. Second, since dry film is no longer used, related chemical processes such as development and film removal are also eliminated, significantly reducing the discharge of organic wastewater and pollutants at the source, conforming to the development trend of green manufacturing and significantly improving environmental friendliness. Third, the simplification of the process flow directly leads to a shorter production cycle, improved production efficiency, and reduced labor and equipment maintenance costs. Finally, this method introduces laser ablation, a high-precision patterning technique, laying the foundation for the fabrication of fine circuits. By using a tin layer as a protective layer and combining it with selective laser ablation, this method can achieve superior circuit precision compared to traditional etching, providing a feasible process path for fabricating circuit patterns with high precision requirements such as line width spacing ≤50μm and line burr ≤10μm.

[0009] According to some embodiments of the present invention, in step 4, the laser parameters are adjusted so that the laser energy density reaches the ablation threshold of the tin protective layer but is lower than the ablation threshold of the electroplated copper layer, so as to ablate and remove the tin protective layer in the non-circuit pattern area, exposing the underlying electroplated copper layer.

[0010] According to some embodiments of the present invention, in step 4, the laser parameters are adjusted so that the energy density of the laser reaches the ablation critical value of the electroplated copper layer, so as to ablate the tin protective layer, the electroplated copper layer and the copper foil layer of a certain thickness in the non-circuit pattern area, leaving a residual copper layer attached to the dielectric layer.

[0011] According to some embodiments of the present invention, the thickness of the residual copper layer is controlled by controlling the energy density and feed rate of the laser.

[0012] According to some embodiments of the present invention, in step 5, the exposed copper layer is etched using a chemical solution.

[0013] According to some embodiments of the present invention, in step 6, the remaining tin protective layer is etched using a chemical solution.

[0014] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0015] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a schematic flowchart of the PCB laser ablation circuit method according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the copper-clad laminate structure in the PCB laser ablation circuit method of this invention. Figure 3 yes Figure 1 A schematic diagram of the structure of the borehole in step 1; Figure 4 yes Figure 1 A schematic diagram of the structure for full-plate electroplating in step 2; Figure 5 yes Figure 1 A schematic diagram of the tin plating structure in step 3; Figure 6 yes Figure 1 A schematic diagram of the laser tin burning process in step 4; Figure 7 yes Figure 1 A schematic diagram of the laser burning of tin and copper in step 4.

[0016] Figure 8 yes Figure 1 A schematic diagram of the structure of the copper layer etched in step 5 of the middle section; Figure 9 yes Figure 1 A schematic diagram of the structure of the tin protective layer etched in step 6.

[0017] Figure label: 1. Dielectric layer; 2. Copper foil layer; 3. Electroplated copper layer; 4. Tin protective layer; 5. Residual copper layer. Detailed Implementation

[0018] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0019] In the description of this invention, "several" means one or more, "more than" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0020] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0021] refer to Figures 1 to 9 A method for laser ablation of PCB circuits according to an embodiment of the present invention is described.

[0022] like Figures 1 to 9 As shown, the PCB laser ablation circuit method according to an embodiment of the present invention includes: Step 1: The copper clad laminate includes a dielectric layer 1 and a copper foil layer 2. Drilling is performed on the copper clad laminate. Step 2: Perform full-board electroplating on the drilled copper-clad laminate to form an electroplated copper layer 3 on the copper foil surface and hole walls; Step 3: Form a tin protective layer 4 on the surface of the electroplated copper layer 3; Step 4: Use laser to ablate the tin protective layer 4 to remove the tin protective layer 4 in the non-circuit pattern area of ​​the PCB design, and at least partially expose the underlying electroplated copper layer 3. Step 5: Etch the exposed copper layer to expose dielectric layer 1; Step 6: Remove the remaining tin protective layer 4 to form the PCB circuit pattern.

[0023] This method fundamentally transforms the process flow, comprehensively addressing multiple shortcomings of traditional methods in terms of environmental protection, efficiency, cost, and precision. First, it eliminates the photosensitive dry film, indispensable in traditional negative and positive film processes, along with its associated lamination, exposure, and development steps. This not only directly eliminates the material costs associated with using dry film but also avoids quality risks such as open circuits and short circuits caused by dry film damage during processing, thus significantly improving product yield. Second, by eliminating the use of dry film, related chemical processes such as developing and stripping are also eliminated, drastically reducing the discharge of organic wastewater and pollutants at the source, aligning with the trend of green manufacturing and significantly enhancing environmental friendliness. Third, the simplified process flow directly leads to a shorter production cycle, increased production efficiency, and reduced labor and equipment maintenance costs. Finally, this method introduces laser ablation, a high-precision patterning technique, laying the foundation for creating intricate circuits. By using a tin layer as a protective layer and combining it with selective laser ablation, this method can achieve superior line accuracy compared to traditional etching, providing a feasible process path for fabricating high-precision circuit patterns with line width spacing ≤50μm and line burrs ≤10μm.

[0024] like Figure 6 As shown, in step 4, the laser parameters are adjusted so that the laser energy density reaches the ablation threshold of the tin protective layer 4 but is lower than the ablation threshold of the electroplated copper layer 3, thereby ablating and removing the tin protective layer 4 in the non-circuit patterned areas, exposing the underlying electroplated copper layer 3. This achieves patterning while minimizing process costs and ensuring the integrity of the underlying copper foil. Because the laser energy is precisely controlled within the range that can only ablate the tin layer, it causes zero damage to the precious underlying electroplated copper layer 3 and the base copper, ensuring the electrical performance and mechanical strength of the circuit conductors. This "gentle" processing method reduces the stringent requirements on laser power and stability, allowing the use of relatively low-cost laser equipment. It is particularly suitable for the mass production of PCB products with conventional linewidth and spacing requirements, offering high economic efficiency and practicality. Simultaneously, this method fully preserves the copper layer thickness obtained from subsequent chemical etching, resulting in more precise and stable control of the final circuit impedance. Compared to the uneven copper thickness of circuits caused by uneven distribution of electroplating current in traditional positive film processes, this solution combines full-board electroplating with selective laser desoldering, which can ensure the uniformity of copper thickness before circuit etching while achieving patterning, thereby indirectly improving the uniformity of circuit etching and the consistency of the final product.

[0025] like Figure 7As shown, in step 4, the laser parameters are adjusted so that the laser energy density reaches the ablation critical value of the electroplated copper layer 3, thereby ablating the tin protective layer 4, the electroplated copper layer 3, and a portion of the copper foil layer 2 in the non-circuit pattern area, leaving a residual copper layer 5 attached to the dielectric layer 1. In the production of thick copper plates, traditional etching solutions require an extremely long time to completely etch through the thick copper layer, which leads to severe lateral etching, making it impossible to achieve the designed small linewidth and resulting in huge burrs on the lines. This solution pre-ablates away most of the unnecessary copper thickness with a laser, leaving only a thin residual copper layer 5, greatly reducing the burden on subsequent chemical etching. Because the residual copper layer 5 to be etched is very thin, the etching time is greatly shortened, and the chemical exchange rate is fast, thus achieving excellent pattern effects with minimal lateral etching, steep line walls, and burrs ≤10μm. This makes it possible to produce "thick copper lines with small linewidth spacing that exceed etching capabilities," solving a long-standing technical bottleneck in the industry and meeting the stringent requirements of high-end power modules, high-current boards, and other products that require both current carrying capacity and high wiring density. The thickness of the residual copper layer 5 is controlled by adjusting the laser's energy density and feed rate. The thickness of the residual copper layer 5 is a key process parameter in this solution, directly determining the difficulty of subsequent etching and the quality of the circuit formation. By precisely controlling the laser's energy density and scanning feed rate, operators can flexibly maintain the residual copper layer 5 at an ideal thinness. The thinner the residual copper, the shorter the time required for subsequent chemical etching, and the less the chemicals attack the sidewalls of the circuit, resulting in less side etching and smoother circuit edges, i.e., better circuit burrs and linewidth tolerances. This adjustability gives the process method extremely high flexibility and adaptability, enabling precise adjustments to the process window to meet different customer requirements for linewidth accuracy and different substrate copper thicknesses, achieving optimal product yield and performance. This demonstrates that the invention not only provides a new method but also provides the core control means to optimize that method.

[0026] like Figure 8 As shown, in step 5, chemical etching is used to etch the exposed copper layer. The final formation of accurate circuit patterns relies on chemical etching, a mature, controllable, and mass-producible process. Integrating chemical etching into this laser ablation scheme combines the advantages of high-precision laser patterning and the batch processing capabilities of wet etching. The laser precisely positions and transfers the pattern pairs, even pre-removing most of the copper layer, while chemical etching, with its isotropic properties, performs the final "finishing," stably removing the remaining thin copper layer. This utilizes the precision advantage of lasers while leveraging the economy and uniformity of chemical etching in large-area processing, ensuring the stability and reliability of the final circuit pattern quality and allowing the entire innovative process to be smoothly integrated into existing PCB production lines.

[0027] like Figure 9As shown, in step 6, the remaining tin protective layer 4 is etched using chemical solutions. This ensures the cleanliness and solderability of the circuit surface. After laser ablation and copper layer etching, the tin layer, acting as a protective layer, has completed its mission but still covers the circuit pattern. By using specific chemical solutions to thoroughly and cleanly remove this remaining tin layer, the complete circuit pattern made of pure copper, as required by the design, is finally revealed. This step not only directly determines the appearance and function of the circuit, but more importantly, it removes metal residue in non-circuit areas, preventing short circuits or decreased insulation performance that may be caused by tin residue. At the same time, the clean copper surface provides a good base for subsequent surface treatments, ensuring the final soldering reliability and long-term stability of the PCB product. It is an indispensable part of the entire process to ensure the quality of the final product.

[0028] Therefore, this PCB laser ablation method eliminates a large number of materials and equipment required for dry film production, reducing labor and material costs; it reduces the occurrence of open and short circuits during circuit forming, improving product yield; it reduces wastewater discharge, protecting the environment; it shortens the entire PCB production cycle; it breaks through the technical barriers to fine circuit fabrication in the industry, greatly improving the yield of fine circuit fabrication; it utilizes the high alignment accuracy of lasers to produce lines with a line width pitch tolerance ≤12.5um and a pad width ≤50um; it utilizes the small and adjustable laser path to produce lines with a line width pitch ≤50um; and it utilizes the high photon energy of lasers to directly break molecular bonds, forming smooth sidewalls. Combined with the principle of etching copper with specific chemical solutions, it can produce lines with burrs ≤10um and even lines with small line width pitch and thick copper exceeding etching capabilities.

[0029] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for laser ablation of circuits on a PCB, characterized in that, include: Step 1: The copper clad laminate consists of a dielectric layer and a copper foil layer. Drilling is performed on the copper clad laminate. Step 2: Perform full-board electroplating on the drilled copper-clad laminate to form an electroplated copper layer on the copper foil surface and hole walls; Step 3: Form a tin protective layer on the surface of the electroplated copper layer; Step 4: Use laser ablation to remove the tin protective layer in non-circuit pattern areas of the PCB design, and at least partially expose the underlying electroplated copper layer. Step 5: Etch the exposed copper layer to expose the dielectric layer; Step 6: Remove the remaining solder protective layer to form the PCB circuit pattern.

2. The PCB laser ablation circuit method according to claim 1, characterized in that, In step 4, the laser parameters are adjusted so that the laser energy density reaches the ablation threshold of the tin protective layer but is lower than the ablation threshold of the electroplated copper layer, so as to ablate and remove the tin protective layer in the non-circuit pattern area, exposing the underlying electroplated copper layer.

3. The PCB laser ablation method according to claim 1, characterized in that, In step 4, the laser parameters are adjusted so that the laser energy density reaches the ablation critical value of the electroplated copper layer, so as to ablate the tin protective layer, electroplated copper layer and part of the copper foil layer in the non-circuit pattern area, leaving a layer of residual copper layer attached to the dielectric layer.

4. The PCB laser ablation circuit method according to claim 3, characterized in that, The thickness of the residual copper layer can be controlled by adjusting the energy density and feed rate of the laser.

5. The PCB laser ablation method according to claim 1, characterized in that, In step 5, the exposed copper layer is etched using chemical solutions.

6. The PCB laser ablation circuit method according to claim 1, characterized in that, In step 6, the remaining tin protective layer is etched using a chemical solution.

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