Circuit boards are like blocks of cheese, filled with numerous holes. However, unlike the holes in cheese formed during fermentation, the holes on a PCB undergo a carefully designed and manufactured. These holes, integral to the PCB manufacturing process, serve various purposes, such as connecting circuits, providing mechanical support, or aiding in heat dissipation. Regardless of their intended use, particular attention is given to the location and quality of these holes. In this article, TechSparks will delve into the intricacies of PCB drilling, covering conceptual introductions, detailed procedures, and essential considerations to help you produce high-quality circuit boards.
What is PCB Drilling Process
Drilling process refers to the procedure of creating holes on a circuit board, typically conducted after lamination and before electroplating. The entire process is not overly complex, as the positions and purposes of the holes are usually marked during the design phase. In commercial operations, designers export drill files and provide them to manufacturers, who then import these files into equipment to guide the automated drilling process. For flexible PCB manufacturing, additional securing measures may be necessary due to their lightweight and thin characteristics, ensuring precision.
The drilling process employs CNC or laser equipment, enhancing drilling speed while maintaining the smoothness of the holes. However, for some enthusiasts, access to such equipment may be challenging. Nevertheless, this does not hinder DIY PCB. The principles of CNC drilling are not significantly different from using regular drill bits. If high-quality requirements are not a priority, and for small-scale projects, a hands-on approach can be taken.
PCB Drilling Techniques
CNC, or Computer Numerical Control, is an age-old mechanical processing method. In this entire process, the CNC system precisely controls the movement of the drill bit according to a predetermined program, completing the drilling of each hole. Although the technology is mature and cost-effective, its precision is constrained by the size of the drill bit, making it less suitable for high-demand or densely arranged holes. Additionally, the lifespan of the drill bit decreases in high-intensity continuous operations.
A more advanced technology widely used in modern processes for drilling is laser drilling, with UV and CO2 lasers being the most common. Although they have inherent differences, their principles are consistent. In comparison to mechanical processing, laser drilling allows for non-contact processing and the creation of smaller micro-holes. Furthermore, the hole walls produced after processing are cleaner without burrs or debris.
Further Reading: CO2, Fiber, and Ultraviolet Laser Drilling in PCB
Despite the numerous advantages of laser drilling, it presents two fatal issues. Firstly, it incurs extremely high costs, making CNC drilling a recommended alternative unless absolutely necessary. Additionally, laser drilling involves infrared and ultraviolet light, and substrate materials exhibit different optical characteristics, rendering some materials incompatible for use.
For simple boards or DIY projects, drilling your own holes is relatively straightforward. You just need to prepare a design drawing that includes hole positions and sizes, a drill bit, and necessary safety measures. Attach the appropriate-sized drill bit to the electric drill, align it with the positions on the design drawing, and start the drill. As mechanical processing generates debris, it’s important to promptly clean up after drilling, inspecting each hole for quality to ensure there are no cracks or deformations.
Formation of Holes in the Drilling Process
Some holes are utilized for component connections, achieved by electroplating the hole walls with a layer of copper after drilling. PCB vias include:
- Through-Holes: Holes that traverse the entire PCB, facilitating connections between different layers of the circuit.
- Blind Vias: Starting from one side of the PCB but not penetrating through the entire board, these are employed to connect circuits between external and internal layers.
- Buried Vias: Completely enclosed within the board and not visible from any side, these are used to connect circuits within different internal layers.
- Microvias: Extremely small holes, often formed through laser drilling processes, enabling smaller and denser layouts.
Mechanical holes are similar to through-holes in that they penetrate the entire board during drilling, but unlike through-holes, they do not require an electroplating process. Upon examining your PCBA board, you may notice that besides electronic components, there could be parts such as brackets used for support or fixation. These components, which do not require electrical connections, are mounted on mechanical holes. Additionally, mechanical holes serve extra functions:
- Thermal Conductivity: High-power components generate heat during operation, which can degrade PCB performance. To enhance PCB heat dissipation, mechanical holes can be drilled near high-power components.
- Tooling: In automated processes, boards are automatically positioned in equipment, and some holes are used to locate component positions, facilitating alignment with the equipment and simplifying production.
- Structural Support: Properly placed mechanical holes can reinforce the structural support of the PCB, preventing bending or deformation during the manufacturing process.
Considerations for Drilling PCB
While the positions for drilling holes are predetermined, issues such as equipment malfunctions, drill bit wear, or operational errors can still lead to inaccuracies in positioning, resulting in edge fractures or intersections between holes.
For manual drilling, ensuring precise positioning and stable operation is essential. In commercial operations, regular equipment maintenance is crucial, especially after continuous use. Maintenance tasks may include replacing worn drill bits, calibrating equipment, and cleaning the work area to ensure optimal performance. Additionally, when dealing with rigid substrates, laser drilling technology may present a more effective solution.
PCB are formed by stacking different layers together using adhesives. Improper handling during the drilling process can weaken the structure, leading to layer separation. This can occur when drilling deviates from the intended positions or when hole sizes do not align with design specifications.
Before commencing a project, ensure that the selected manufacturer has the appropriate capabilities to execute various steps of PCB manufacturing, including lamination and drilling. This involves scrutinizing the manufacturer’s equipment, technology, and quality management systems.
Burrs refer to small pieces or fine particles appearing in the processing area. Prolonged processing of hard or composite materials can severely damage drill bits, resulting in irregular edges and affecting the quality of the drilled holes. Additionally, excessively high drilling speeds can generate frictional heat in the drilling area, causing the processed material to soften and produce burrs.
Another often overlooked factor is the varying physical friction reactions of materials. As PCB consist of multiple layers of different materials, this can ultimately lead to the formation of burrs.
To address this, it is recommended to regularly replace drill bits to ensure sharpness. Furthermore, understanding the characteristics of the materials used in the project and selecting appropriate processes based on these characteristics is crucial. Lastly, the use of suitable coolant or cooling systems can also be employed.
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