All You Should Know About CNC Milling in PCB Manufacturing

A crucial objective of circuit boards is to neatly accommodate components, avoiding tangled internal wiring within devices. To achieve this, a method for interconnecting these components is necessary, and the circuit patterns on circuit boards serve this purpose. Designers utilize software to create these connection patterns, which are then eventually manifested on the circuit board. Various techniques can be employed in the fabrication process of these circuit patterns, including milling, photolithography, etching, and printing. In this comprehensive guide, TechSparks will delve into the topic of PCB milling. While this technology is not frequently employed in modern manufacturing processes, it remains essential knowledge for DIY enthusiasts. Let’s dive in!

What Is PCB Milling

Milling is a process in PCB manufacturing that precisely removes unwanted copper from substrate using a Computer Numerical Control (CNC) machine. This technology assists engineers, manufacturers, and electronics enthusiasts in designing and fabricating circuit boards to their specific requirements.

CNC PCB milling creates the entire circuit through physical means without any chemicals, avoiding potential threats posed by factors like temperature and concentration that can affect the production of high-precision PCB. Moreover, the entire process is computer-program controlled, ensuring adherence to the required paths at all times, providing flexibility to projects.

For prototype manufacturing, this method is highly effective, offering manufacturers a one-time investment in CNC milling equipment, unlike other methods that may require multiple investments for repeated use, resulting in cost efficiency. Additionally, it eliminates the time constraints associated with chemical etching of copper, speeding up the prototype manufacturing process. However, milling has certain limitations for bulk projects and is challenging to implement for large-scale production.

The following YouTube video clearly shows the process of milling PCB, I hope it will help you understand it more clearly!

Milling Parameters

As mentioned earlier, the PCB milling process is computer-controlled, requiring you to input milling parameters into the control software or controller. For CNC equipment, the parameters needed include:

Spindle Speed: This represents the rotational speed of the milling tool and is typically expressed in rotations per minute (RPM). Different PCB substrate and tool types require different spindle speed settings.
Cutting Depth: This indicates how deep the tool penetrates into the substrate and is usually measured in millimeters or mils. Excessive cutting depth can lead to cutting issues or damage to the substrate.
Feed Rate: This represents the speed at which the milling machine moves during the machining process, typically measured in inches per minute (IPM) or millimeters per minute (MMPM).
Plunge Rate: The plunge rate defines the speed at which the tool vertically moves onto the substrate when starting a new cut.
Tool Offset: Specifies the distance between the centerline of the tool and the milling path, used for precise tool positioning.
Toolpath Strategy: Determines the sequence in which milling instructions move on the board. Different strategies are suitable for different milling tasks, such as contour rastering for cutting outer contours or pocketing for cutting internal spaces.

PCB Milling Tools

Name	Describe	Features	Usage
End Mills	Comprising a long rod and a milling cutter, one end of which is mounted on the spindle of the machine, it completes the machining through rotation and forward motion.	The replacement of the blade enables a wide range of applications.	It is used to create different widths of traces, mill grooves, drill holes, etc.
V-Bits:	Come with a V-shaped cutting edge.	Good for getting sharp, accurate cuts and making complicated designs on boards.	Mostly used for text engraving, making fine traces, and adding decorative features to boards.
Ball-End Mills	Ball-end mills come with a rounded, ball-like end.	Generate smooth contours and rounded features, making them best for complicated board designs.	Employed for milling curved traces, pockets, three-dimensional milling, and components with rounded edges.
Drill Bits	Specifically for making holes in the board’s substrate.	Select drill bit size based on design.	Create various component holes and mounting holes.
Routing Bits	Routing bits come with a flat bottom with cutting edges on the sides.	Cutting boards from larger panels	Used for board singulation, making board outlines, and cutting boards to their required size.
Chamfer Mills	With angled cutting edges.	Facilitates soldering and component placement.	Used in PCB designs that need precise chamfers on traces or component pads.
Depaneling Blades	Necessary equipment for batch projects.	Clean and burr-free cuts.	Used for separating individual boards from a panel.
Diamond-Cut Tools	Diamond-coated cutting edges.	Hard and sharp.	Employed for machining boards with hard or abrasive materials.

Milling VS Etching

Aspect	Milling	Etching
Definition	Subtractive manufacturing techniques using CNC milling machines.	A chemical process using an etchant solution.
Precision	Precision is controllable, and appropriate tools are chosen based on the complexity of the design to ensure accuracy.	It is influenced by the temperature and concentration of the solution, so after etching, remember to clean and remove any remaining solution.
Batch	Prototyping and small batches eliminate waiting times and expedite project progress.	It holds advantages in mass production and is the primary technology in the modern PCB industry.
Compatibility	It is suitable for rigid substrate materials and has limitations for flexible or special materials.	There are no restrictions on substrate materials, making it more versatile.
Cost	Paying a higher cost to purchase a CNC milling machine, which requires regular maintenance and tool replacement during subsequent use.	No need for specific equipment, but you need to purchase etching solution for each production run.
Pollution	Generates noise and dust during the production process, with minimal environmental impact.	Although there are no byproducts during the production process, proper disposal of waste is required afterward.