What is PCB machining?

PCB machining refers to the process of creating physical features in a printed circuit board using mechanical means such as drilling, routing, or milling. These features can serve a variety of purposes, such as:

• Providing mounting points for components or the board itself
• Creating openings for connectors or other through-hole components
• Removing excess material to create custom board shapes or cutouts
• Enhancing Thermal dissipation or reducing weight

Some common examples of machined features in PCBs include:

Feature	Description
Slots	Elongated openings that can be used for mounting or as strain reliefs
Milled areas	Recessed areas on the surface of the board, often used for component placement or heat dissipation
Contours	Custom shapes or outlines of the board, created by routing or milling away excess material
Rout-outs	Openings or cutouts within the board, used for mounting or to provide access to components

Indicating Slots in Your PCB Design

Slots are elongated openings in a PCB that can serve various purposes, such as providing mounting points, acting as strain reliefs for cables, or allowing access to components on the opposite side of the board. When designing a PCB with slots, it’s important to clearly communicate their dimensions, locations, and tolerances to your manufacturer.

In your PCB design files, slots should be indicated using a separate mechanical layer. This layer should be clearly labeled and distinguished from the electrical layers of your design. When creating the slot outlines, consider the following:

• Slot dimensions: Specify the length, width, and corner radius of each slot. If the slot has a non-rectangular shape, provide a detailed drawing or use a vector format to define its contours.
• Location and orientation: Clearly indicate the position of each slot relative to the board edges and other features. Use dimensioned drawings or coordinate systems to avoid ambiguity.
• Tolerances: Specify the acceptable range of variation for the slot dimensions and position. This is especially important if the slots need to align with other mechanical components or mounting hardware.

Here’s an example of how slot specifications might be communicated in a PCB Fabrication drawing:

Slot ID	Length (mm)	Width (mm)	Corner Radius (mm)	Location (X, Y)	Tolerance
S1	10.0	2.0	0.5	(25.0, 15.0)	±0.1 mm
S2	8.0	3.0	0.0	(40.0, 30.0)	±0.2 mm

Milled Areas in PCB Design

Milled areas are recessed regions on the surface of a PCB, created by selectively removing material using a milling machine. These areas can serve several purposes, such as providing a flat surface for mounting components, creating cavities for embedded components, or enhancing thermal dissipation by exposing the underlying copper layers.

To indicate milled areas in your PCB design, follow these guidelines:

• Use a dedicated mechanical layer: Create a separate layer in your design files to outline the milled areas. This layer should be clearly labeled and distinguished from the electrical layers.
• Define the milling depth: Specify the desired depth of the milled area, either as a fixed value or a range. This information is crucial for the manufacturer to set up the milling equipment correctly.
• Provide dimensions and tolerances: Clearly indicate the size and shape of each milled area, along with any required tolerances. Use dimensioned drawings or coordinate systems to avoid confusion.
• Consider the milling tool: Keep in mind the limitations of the milling equipment when designing milled areas. The size and shape of the milling tool will affect the minimum size and maximum depth of the areas that can be created.

Here’s an example of how milled area specifications might be communicated in a PCB fabrication drawing:

Milled Area ID	Size (mm)	Depth (mm)	Location (X, Y)	Tolerance
M1	10.0 x 5.0	0.5	(15.0, 20.0)	±0.1 mm
M2	Ø 6.0	1.0	(35.0, 40.0)	±0.2 mm

Contour Routing in PCB Design

Contour routing involves creating custom shapes or outlines for a PCB by routing or milling away excess material. This technique is often used to create non-rectangular board shapes, cutouts for mounting or ventilation, or to accommodate mechanical constraints in the final assembly.

When designing a PCB with contour routing, consider the following:

• Define the contour path: Use a dedicated mechanical layer to outline the desired contour of the board. This path should be a continuous, closed shape that defines the final outline of the PCB.
• Specify routing parameters: Provide information about the routing tool diameter, depth, and any required tolerances. This helps the manufacturer select the appropriate tools and set up the routing equipment correctly.
• Consider the minimum feature size: Keep in mind the limitations of the routing equipment when designing contours. The diameter of the routing tool will determine the minimum radius of corners and the smallest features that can be created.
• Provide reference dimensions: Include dimensioned drawings or coordinate information to clearly communicate the size and position of the contour relative to other board features.

Example contour routing specifications in a PCB fabrication drawing:

Contour ID	Path Width (mm)	Routing Depth (mm)	Tolerance
C1	2.0	1.6	±0.1 mm
C2	1.5	1.6	±0.1 mm

Rout-Outs in PCB Design

Rout-outs are openings or cutouts within the PCB, created by routing or milling away material. These features can be used to provide mounting points, create openings for connectors or components, or improve thermal dissipation by exposing internal layers.

When indicating rout-outs in your PCB design, follow these guidelines:

• Use a dedicated mechanical layer: Create a separate layer in your design files to outline the rout-outs. This layer should be clearly labeled and distinguished from the electrical layers.
• Define the rout-out dimensions: Specify the size, shape, and location of each rout-out using dimensioned drawings or coordinate systems. Include any required tolerances to ensure proper fit and functionality.
• Consider the routing tool: Keep in mind the limitations of the routing equipment when designing rout-outs. The diameter of the routing tool will affect the minimum size and maximum depth of the features that can be created.
• Specify the routing depth: Clearly indicate the desired depth of the rout-outs, either as a fixed value or a range. This information is essential for the manufacturer to set up the routing equipment correctly.

Example rout-out specifications in a PCB fabrication drawing:

Rout-Out ID	Size (mm)	Depth (mm)	Location (X, Y)	Tolerance
R1	5.0 x 5.0	1.6	(10.0, 30.0)	±0.1 mm
R2	Ø 3.0	1.6	(50.0, 25.0)	±0.1 mm

Communicating with Your PCB Manufacturer

Effective communication with your PCB manufacturer is essential for ensuring that your machined features are fabricated according to your specifications. When preparing your design files for production, consider the following:

• Use industry-standard file formats: Export your PCB design files in formats that are widely supported by PCB Manufacturers, such as Gerber files (RS-274X) or ODB++. These formats allow you to include all necessary information, including mechanical layers and fabrication notes.
• Provide a clear fabrication drawing: Create a detailed drawing that showcases all the machined features, dimensions, and tolerances. This drawing should be easily understandable by the manufacturer and serve as a reference for the fabrication process.
• Communicate special requirements: If your design has any unique or non-standard machining requirements, make sure to discuss them with your manufacturer in advance. They may need to use specialized equipment or processes to accommodate your needs.
• Request a design review: Before finalizing your design, ask your manufacturer to review your files and provide feedback. They can help identify any potential issues or suggest improvements based on their experience and capabilities.

FAQ

1. What is the minimum slot width that can be machined in a PCB?

The minimum slot width depends on the capabilities of the PCB manufacturer and the equipment they use. Typically, slot widths as small as 0.5mm can be achieved with standard milling tools. However, for smaller slots, specialized equipment like laser cutters may be necessary. Always consult with your manufacturer to determine their minimum feature size for slots.

2. Can milled areas have different depths within the same PCB?

Yes, it is possible to have milled areas with different depths on the same PCB. However, this requires additional setup and machining time, which can increase the cost of fabrication. When designing milled areas with different depths, make sure to clearly specify the depth requirements for each area in your fabrication drawing.

3. What is the minimum radius for contour routed corners?

The minimum radius for contour routed corners depends on the size of the routing tool used by the manufacturer. Typically, the minimum radius is equal to half the diameter of the routing tool. For example, if a 2mm diameter routing tool is used, the minimum corner radius would be 1mm. Consult with your manufacturer to determine their capabilities and limitations for contour routing.

4. Can rout-outs be placed anywhere on the PCB?

Rout-outs can be placed anywhere on the PCB, as long as they do not interfere with the electrical functionality or mechanical integrity of the board. However, it’s essential to consider the proximity of rout-outs to other features, such as components, traces, or mounting holes. Ensure that there is sufficient clearance around the rout-outs to avoid any potential issues during fabrication or assembly.

5. What should I do if my PCB design requires non-standard machining features?

If your PCB design requires non-standard machining features, it’s crucial to communicate your requirements clearly with your manufacturer. Provide detailed drawings, specifications, and tolerances for the features you need. Discuss the feasibility of your design with the manufacturer and be open to their suggestions for alternative solutions if necessary. In some cases, custom machining or specialized equipment may be required, which can impact the cost and lead time of your project.

Conclusion

Incorporating machined features like slots, milled areas, contours, and rout-outs in your PCB design can enhance the functionality, mechanical stability, and thermal performance of your board. However, it’s crucial to communicate these features effectively to your PCB manufacturer to ensure a smooth fabrication process and a final product that meets your specifications.

By following the guidelines outlined in this article, you can create clear and comprehensive design files that accurately convey your machining requirements. Use dedicated mechanical layers, provide detailed dimensions and tolerances, and consider the capabilities and limitations of the manufacturing equipment when designing your features.

Remember to work closely with your PCB manufacturer throughout the design and fabrication process. Their expertise and guidance can help you optimize your design, avoid potential issues, and achieve the best possible results for your PCB project.