Optimal Use of PCB DFM Guidelines

March 10, 2020 , in Blog

In image processing, there is a concept known as the region of importance (ROI). The ability to identify and expand upon a specific location within an image frame is a fundamental capability for face recognition, which is the identification and categorization of defined features for the targeted area (2-D) or space (3-D) within an image, which contains a face. When applied to multiple image frames or a video, this capability must be extended to include continuous scanning and recognition of the targeted ROI, although its location may be changing.

Focusing on the important aspects

Scanning eye in focus

The ability to maintain focus on what is important is also required for PCBA development. And the degree to which this is done directly correlates with the quality and efficiency of the design⇒build⇒test (DBT) iteration cycle. An essential concept for circuit board development is design for manufacturing (DFM), and the manufacturability of your boards depends upon its application. Optimal development, however, requires that you know which PCB DFM guidelines are most important and how to ensure they are focused upon. Let’s identify these guidelines and see how to best implement them.

What are the Important PCB DFM Guidelines?

Undoubtedly, you have heard the word DFM used a lot, and you probably have a reasonable understanding of what DFM guidelines are. However, you may be surprised to learn that not all DFM guidelines are applicable to every design. For example, there are specific rules that should be included in your DFM for high-speed digital PCBs. In fact, there is no fixed number of guidelines that can be generically followed. This does not mean that a list of important PCB DFM guidelines that are relevant for most designs cannot be defined. They can, and are listed below.

Important PCB DFM Guidelines

  • Board
    • Improper plane copper balancing
    • Edge clearance violations

For more information on board edge clearance, refer to: Determining Board Edge Clearance Requirements Early in the PCB Design Process.

  • Components
    • Spacing and clearances violations
    • Pad misalignment

 For more information on pad layout, refer to: Best Footprint Pad Layout Guidelines for Your PCB.

  • Traces
    • Disconnected traces
    • Copper weight violations

   For more information on trace widths, refer to: Layout Restrictions on PCB Trace Width and Spacing.

  • Vias
    • No PTH to copper
    • Annular ring violations

 For more information on drill hole tolerances, refer to: PCB Drill Rules & Other DFM Considerations.

  • Solder mask
    • Missing solder dams
    • Missing solder mask clearances

For more information on the solder mask process and issues, refer to: Understanding How the Solder Mask Process Affects Your Manufactured PCB.

  • Silkscreen
    • Missing reference indicators
    • Unreadable

For more information on the importance of the silkscreen, refer to: Why You Should Care About the Silkscreen: PCB Identification and Labels.

Although the list above contains DFM guideline issues that should be included for any design, it is certainly not exhaustive, and your design may well include additional guidelines. Irrespective of the extent of DFM issues that are utilized, they must be used properly to optimize your PCBA development.

How to Use PCB DFM Guidelines

PCB DFM guidelines and rules are not mutually exclusive, and you may need to decide which ones to follow and which to discard. For example, spacing and clearance issues affect pad layouts, component placement, trace routing, drill holes, and the board edge. And the fact that equipment and some manufacturing processes may vary for different contract manufacturers (CMs) means many specifications and PCB tolerances are CM-dependent. Implementation of DFM is also dependent on the PCB layout software that you employ. Taking these requirements into consideration allows us to put forth the optimization method for PCB DFM guidelines utilization below.

Optimizing PCB DFM Guidelines

A. Acquiring PCB DFM guidelines

a. Do  use the DFM rules and guidelines supplied by the CM that is actually building your board.

b. Don’t  apply generic rules, as these may not be accurate for your CM’s equipment and processes.

B. Implementing PCB DFM guidelines

a. Do organize your DRC checks in order of importance and use them often during your layout design process, remembering to disregard those which are not important.

b. Don’t  simply input or upload DRC rules without prioritizing them for your rules checker and only check the final design.

C. Verifying PCB DFM guidelines

a. Do  have your CM perform a DFM validation prior to starting the manufacturing process, as it is much easier, less time-consuming, and more cost-effective to correct any errors at the outset as opposed to a later stage of manufacturing.

b. Don’t  have your boards made until they satisfy your manufacturer’s DFM specifications or are within all tolerances, as well as meet your design objectives. Otherwise, the process may be halted or you might wind up with boards you cannot use.

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By following the ABC paradigm of Do’s above, you can ensure that your boards are synchronized with your CM’s DFM requirements before manufacturing begins, which will aid in the efficiency of the process and the quality of the final product. At Tempo Automation, the industry leader for fast, high-quality manufacturing of prototype and low-volume PCBAs, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.

If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on PCB DFM guidelines or how to incorporate them into your design, contact us.

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