PCB Design and DFM: A Path to Reliable Manufacturing 

What is Design for Manufacturability (DFM)?

Design for Manufacturability (DFM) is a set of guidelines aimed at simplifying the manufacturing process of electronic components, specifically Printed Circuit Boards (PCBs). DFM ensures that features like traces, vias, and pads are designed in a way that makes the manufacturing process efficient and error-free. 

Why is DFM Important?

DFM is crucial for preventing common manufacturing issues such as via damage, electrical shorts, and other defects that could compromise the performance and reliability of the PCB. Adhering to IPC standards like IPC-2221 (Generic Standard on Printed Board Design) ensures that the design meets industry-accepted reliability criteria.

Common DFM Check list for PCBs

When designing a PCB, there are several critical factors to consider for manufacturability. Below is a checklist that can serve as a guide: 

Copper Spacing

• Importance: Proper copper spacing is essential for avoiding shorts and ensuring impedance control. 

• Best Practices: follow the rules provided by the PCB manufactures.

  • Trace to Trace Spacing

  • Via to Via Spacing

  • Pad to Pad Spacing

  • Trace to Via, Trace to Pad, Pad to Via Spacing, etc.

Drill Checks

• Size: Ensure the drill sizes match the requirements for the vias and holes.

• Power and Ground Shorts: Double check that there are no unintended connections between power and ground planes before gerbering out. Sometimes shorts can happen if DRCs (Design rule checks) are waived due to time pressure. This happened to my past projects.

Annular Ring

• Definition: The annular ring is the area of copper pad that surrounds a drilled and plated hole.

• Consideration: Make sure the annular ring meets the minimum size requirements to prevent via damage.

Thermal Relief

• Ensure that pads connected to large copper planes have proper thermal relief patterns to aid in soldering.

Soldermask

• Definition: Soldermask is the protective layer on top of the copper traces and pads.

• Consideration:  Ensure that Non-Solder Mask Defined (NSMD) pads are properly exposed for effective soldering.

Follow Manufacturer DFM Guidelines

While general DFM guidelines provide a solid foundation for designing manufacturable PCBs, it's crucial to also adhere to the specific rules provided by your chosen manufacturer. Each manufacturing facility may have unique capabilities and constraints, including but not limited to:

• Materials: Types of laminates, copper weights, and soldermask materials they can handle.

• Tolerances: Minimum trace widths, via diameters, and annular rings they can accurately produce.

• Finishes: Availability of specific surface finishes like HASL, ENIG, or OSP.

• Special Processes: Capabilities like blind/buried vias, impedance control, or HDI design.

Failure to comply with these specifics can lead to increased costs, delays, or even outright rejection of your design files. Therefore, it's a good practice to download or request the manufacturer's DFM guidelines and cross-verify your design against these before proceeding to the next steps.

DFM Review Before Generating Gerber Files

Before finalizing your PCB design, it's crucial to undergo a DFM review with your chosen manufacturer. The process is straightforward:

• Send Preliminary Files: Share an initial version of your design files with the manufacturer for a pre-review.

• Receive and Implement Feedback: Make adjustments to your design based on the manufacturer's feedback.

• Final Review: Submit the revised design for a final check to ensure it meets all manufacturing criteria.

• Generate Gerber Files: Once alignment is reached between you and the manufacture, proceed to generate the Gerber files required for fabrication.

Remember, DFM is a two-way conversation. A manufacturer might have the capability for tighter tolerances but may not opt for them by default. Be proactive and push for optimal manufacturing conditions; don't just accept things as they are presented. 

IPC Standards for PCB Design and Manufacturability

It very important to refere to the IPC standards for PCB design, essentitally these are the backbones for PCB manufacturing.

Here's the table summarizing the standards: