A laser back drilling method and system

Abstract

This invention relates to the field of PCB manufacturing technology, specifically providing a laser back-drilling method and system. The method includes drilling, chemical deposition, laser back-drilling, copper electroplating, outer layer circuitry, solder masking, and surface finishing steps. The laser back-drilling step utilizes a carbon dioxide laser with a pulse width of 15 ps and a wavelength of 1000 nm. High-precision CCD alignment and surface scanning technology, combined with data on the board thickness, are used to independently generate a back-drilling depth control program for each hole, thereby precisely removing invalid copper segments from through-holes. The system includes a CCD vision positioning system, a control system, a motion platform, and a short-pulse laser generator. This invention can precisely control the stub length to within 0.1 mm, achieving a minimum processed hole diameter of 0.1 mm, and offers advantages such as high processing accuracy, no tool wear, no chemical pollution, and high processing efficiency.

Description

Technical Field

[0001] This invention belongs to the field of PCB manufacturing technology, specifically relating to a laser back drilling method and system. Background Technology

[0002] In the field of printed circuit board (PCB) or integrated circuit (IC) manufacturing technology, especially when high-frequency signal transmission is involved, the ineffective copper stubs in through-hole (PTH) vias can cause signal reflection, delay, and other phenomena, resulting in signal distortion and severely affecting the integrity of signal transmission. Therefore, minimizing stubs is crucial for improving signal transmission stability and reducing signal distortion.

[0003] Currently, back-drilling technology mainly includes the following methods: 1. Mechanical back drilling: This method uses a specialized micro drill bit on a CNC drilling machine to precisely drill to a certain depth, removing excess copper and substrate from the hole. This method has lower tooling costs and higher throughput, and can process back drills with hole diameters ≥0.2~0.3mm. However, the depth tolerance is relatively large (approximately ±0.05~0.1mm), and it generates significant mechanical stress on the substrate, which may produce burrs.

[0004] 2. Plasma back drilling: This method utilizes reactive plasma to generate active ions and free radicals, gradually etching away the stub layer through a combination of chemical and physical processes. It eliminates mechanical cutting stress, can process large areas or multiple boards simultaneously, and is well-suited for complex dielectric materials. However, the etching rate is relatively slow, and equipment and process calibration are more complex.

[0005] 3. Chemical Etching Back Drilling: This method uses selective chemical etching to dissolve the copper of the stub layer and the substrate, and then protects the layers that need to be retained with a masking film or photoresist. This method can process the entire board at the same time and is more suitable for small, densely packed holes, but the process is longer, requires multiple photomask alignments, and has high costs for chemical waste treatment, resulting in significant environmental pressure. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a laser back drilling method and system that can accurately remove stubs, has high processing precision, low cost and is environmentally friendly.

[0007] To achieve the above objectives, the present invention provides the following technical solution: On one hand, the present invention provides a laser back drilling method, comprising the following steps: S1. Drilling: Mechanical drilling is performed on the PCB board to form through holes; S2, Chemical deposition: A copper layer is chemically deposited on the wall of the through hole; S3. Laser back drilling: Short pulse laser is used to back drill the through hole to remove excess copper and substrate. S4. Electroplating copper: Electroplating is performed on the through holes after back drilling to fill the holes and thicken the copper layer on the hole walls. S5, Outer Layer Circuitry: Create the outer layer circuitry; S6. Solder resist: Solder resist ink is printed on the board surface; S7. Shape processing: Cut the PCB board into the finished shape.

[0008] As a further improvement of the present invention, the laser back drilling in step S3 further includes: Obtain the plate thickness data after drilling, and generate an independent back-drilling depth control program for each hole to be back-drilled; The PCB board image is captured by a CCD vision system, and the center coordinates of the hole to be drilled are identified and located by surface scanning technology. Based on the back-drilling depth control program and the center coordinates, a short-pulse laser is controlled to perform back-drilling on the through hole.

[0009] As a further improvement of the present invention, the short-pulse laser is a carbon dioxide laser with a pulse width of 15 ps, a wavelength of 1000 nm, and a laser energy of 15 W.

[0010] As a further improvement of the present invention, the laser back drilling in step S3 controls the length of the invalid hole copper segment to within 0.1 mm.

[0011] On the other hand, the present invention also provides a laser back-drilling system for implementing the above method, comprising: The CCD vision positioning system is used to capture images of PCB boards, perform high-precision alignment and coordinate transformation, and identify the locations of holes to be drilled. The control system receives data from the vision system and combines it with pre-stored data on the thickness of the drill plate to generate an independent back-drilling trajectory and laser triggering timing for each hole. A motion platform is used to move the laser head or workpiece to the target position according to the instructions of the control system. A short-pulse laser generator is used to generate a laser beam with specific parameters and project it into the hole to be processed.

[0012] As a further improvement of the present invention, the short-pulse laser generator is a carbon dioxide laser generator with a pulse width of 15 ps, a wavelength of 1000 nm, and a laser energy of 15 W.

[0013] As a further improvement of the present invention, a feedback detection unit is also included for post-processing inspection.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. Using laser back drilling eliminates the loss of raw materials such as drill bits, resulting in low cost and no chemical pollution, making it more environmentally friendly.

[0015] 2. Using a high-power laser generator, the processing speed is fast and the production efficiency is high.

[0016] 3. It adopts high-precision CCD alignment, combined with surface scanning technology, and generates an independent back-drilling depth program based on the plate thickness data to compensate for plate thickness differences. This allows the stub length to be precisely and stably controlled within 0.1mm, resulting in high processing accuracy.

[0017] 4. Using laser micro-hole technology, the minimum processed hole diameter can reach 0.1mm, which is suitable for micro-hole diameter and high-density interconnect structure. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the STUB structure in the background art of this invention; Figure 2 This is a schematic diagram of mechanical back drilling and STUB in the background art of this invention; Figure 3 This is a schematic diagram of the chemical deposition of copper layer, laser back drilling, and electroplating of copper according to the present invention; Figure 4 This is a schematic diagram of a laser back drilling method according to the present invention; Figure 5 This is a schematic diagram of the plate thickness data acquisition and back-drilling depth generation program of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0020] The following reference Figures 1-5 This application describes a laser back-drilling method and system according to an embodiment. It is particularly suitable for manufacturing PCBs used for high-frequency signal transmission, effectively removing invalid copper stubs from through-holes and improving signal integrity.

[0021] like Figures 2-5 As shown, the laser back drilling method of this invention includes the following specific steps: Drilling: Using a mechanical drilling machine to drill holes in the PCB board to form through holes that penetrate all layers, so as to facilitate electrical conduction between the layers.

[0022] Chemical copper: A very thin layer of copper is deposited on the hole wall using chemical methods, serving as a conductive substrate for subsequent copper electroplating.

[0023] Laser back drilling: This is the core step of the invention. A short-pulse laser is used to align with the drilling position according to a preset program, directly removing materials such as copper plating, resin, and fiberglass through light energy. In this embodiment, the laser type is a carbon dioxide laser with a pulse width of 15 ps, a wavelength of 1000 nm, and a laser energy of 15 W. A CCD captures an image of the workpiece, and a vision system performs high-precision positioning and coordinate transformation. The control system, based on the vision positioning result and the board thickness data measured after the first drill (i.e., the first mechanical drilling), independently calculates and generates a back-drilling depth control program for each back-drilling hole position. After the motion platform moves the workpiece into position according to the instructions, the laser outputs pulses according to the set parameters, precisely removing unnecessary stubs. This step effectively reduces insertion loss, signal reflection, and crosstalk, and supports extremely fine apertures and complex stacked structures.

[0024] Electroplating copper: Electroplating is used to fill holes and thicken the copper layer on the hole walls.

[0025] Outer layer circuitry: The circuit image on the photosensitive film (the exposed circuit image) is used to create the actual copper surface circuitry through etching and other processes.

[0026] Solder resist: On a mesh with an existing negative pattern, an appropriate amount of solder resist ink is scraped out with a squeegee, forming a positive pattern through the mesh and printed onto the flat copper surface of the substrate, forming a layer of masking solder resist to protect the circuit.

[0027] Shape processing: The finished circuit board is cut to shape, such as removing the outer frame or surrounding excess parts of the panel, or performing mechanical processing such as partial hollowing out inside the board, to obtain the final product.

[0028] like Figure 5 As shown, the method of this invention generates a laser program based on the plate thickness data, and independently controls the back-drilling depth for each back-drilling hole position, thereby effectively compensating for plate thickness differences and ensuring that the stub value is accurately and stably controlled within 0.1mm. Simultaneously, by employing laser micro-hole technology, the minimum processed hole diameter can reach 0.1mm, breaking through the hole diameter limitations of traditional mechanical back-drilling.

[0029] The overall workflow of the laser back drilling system that implements the above method is as follows: CCD captures image of the workpiece being processed → vision system positions and transforms coordinates → control system calculates back drill trajectory and laser triggering timing → motion platform moves or scanner is positioned → laser outputs pulses according to parameters → vision / sensor feedback checks and proceeds to the next hole.

[0030] The system mainly includes: CCD visual positioning system: used for high-precision image acquisition and hole location identification.

[0031] Control system: The core processing unit is responsible for data processing, trajectory calculation, and timing control.

[0032] Motion platform: Executes movement commands to achieve precise positioning.

[0033] Short-pulse laser generator: This embodiment uses a carbon dioxide laser to output a laser beam with a pulse width of 15 ps, a wavelength of 1000 nm, and an energy of 15 W.

[0034] Feedback detection unit: Used for quality inspection after processing to ensure processing results.

[0035] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0036] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A laser back drilling method, characterized in that: Includes the following steps: S1. Drilling: Mechanical drilling is performed on the PCB board to form through holes; S2, Chemical deposition: A copper layer is chemically deposited on the wall of the through hole; S3. Laser back drilling: Short pulse laser is used to back drill the through hole to remove excess copper and substrate. S4. Electroplating copper: Electroplating is performed on the through holes after back drilling to fill the holes and thicken the copper layer on the hole walls. S5, Outer Layer Circuitry: Create the outer layer circuitry; S6. Solder resist: Solder resist ink is printed on the board surface; S7. Shape processing: Cut the PCB board into the finished shape.

2. The laser back drilling method according to claim 1, characterized in that: Step S3, the laser back drilling, further includes: Obtain the plate thickness data after drilling, and generate an independent back-drilling depth control program for each hole to be back-drilled; The PCB board image is captured by a CCD vision system, and the center coordinates of the hole to be drilled are identified and located by surface scanning technology. Based on the back-drilling depth control program and the center coordinates, a short-pulse laser is controlled to perform back-drilling on the through hole.

3. The laser back drilling method according to claim 1, characterized in that: The short-pulse laser is a carbon dioxide laser with a pulse width of 15 ps, a wavelength of 1000 nm, and a laser energy of 15 W.

4. The laser back drilling method according to claim 1, characterized in that: In step S3, the laser back drilling controls the length of the invalid hole copper segment to within 0.1 mm.

5. A laser back-drilling system for implementing the laser back-drilling method according to any one of claims 1-4, characterized in that: include: The CCD vision positioning system is used to capture images of PCB boards, perform high-precision alignment and coordinate transformation, and identify the locations of holes to be drilled. The control system receives data from the vision system and combines it with pre-stored data on the thickness of the drill plate to generate an independent back-drilling trajectory and laser triggering timing for each hole. A motion platform is used to move the laser head or workpiece to the target position according to the instructions of the control system. A short-pulse laser generator is used to generate a laser beam with specific parameters and project it into the hole to be processed.

6. The laser back-drilling system according to claim 5, characterized in that: The short-pulse laser generator is a carbon dioxide laser generator with a pulse width of 15 ps, a wavelength of 1000 nm, and a laser energy of 15 W.

7. The laser back-drilling system according to claim 5, characterized in that: It also includes a feedback detection unit for post-processing inspection.

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