Background Theory > From Concept to Creation: Mastering PCB Design > Design for Manufacturability (DFM) and Design for Testability (DFT) > Best practices to ensure efficient manufacturing and testing

Ensuring efficient PCB (Printed Circuit Board) manufacturing and testing requires adherence to a set of best practices throughout the design phase. These practices aim to improve the manufacturability and testability of the boards, thereby reducing costs and lead times while maintaining high quality. Below are key best practices:

Design for Manufacturing (DFM)

Component Placement

•Respect the manufacturer's guidelines for component spacing to avoid soldering issues.

•Use standard components when possible to reduce lead times and costs.

•Verify component orientations, especially for polarized elements.

Routing

•Adhere to recommended trace width, clearance, and copper thickness.

•Consider the manufacturer's capabilities for via sizes and types.

•Use teardrops where traces join pads to strengthen the connection.

Materials and Layer Stackup

•Select board materials that meet the project’s mechanical, thermal, and electrical requirements.

•Define the layer stackup, considering signal integrity and manufacturing capabilities.

Panelization

•Utilize panelization to optimize the manufacturing process, especially for small PCBs.

•Include breakaway tabs or V-grooves for easy separation.

Documentation

•Provide comprehensive documentation, including Gerber files, drill files, assembly drawings, and a detailed Bill of Materials (BOM).

•Clearly indicate any special instructions or requirements.

Design for Testability (DFT)

Test Points and Probes

•Incorporate test points for critical signals and power rails, ensuring they are easily accessible.

•Design for automated testing tools like In-Circuit Test (ICT) or Flying Probe, considering probe sizes and clearances.

Testing Pads

•Use uniform test pads sizes and shapes throughout the PCB for consistency.

•Avoid placing test pads near the edge of the board to prevent contact issues.

Functional Test Planning

•Develop a strategy for functional testing that verifies the operation of the board in a state that closely resembles its final application.

•Plan the test sequence to systematically check for various types of potential failures.

Boundary Scan

•Implement boundary scan techniques, particularly for digital circuits, to test the functionality of pins and interconnected devices.

•Ensure components are JTAG (Joint Test Action Group) compatible if boundary scan testing is planned.

Design for Assembly (DFA)

Component Orientation

•Standardize component orientation, with all polarized components facing the same direction, to streamline the assembly process.

•Avoid mixed-technology (through-hole and surface-mount) components on one side of the board, if possible.

Solderability

•Choose components with easily solderable terminations.

•Provide solder mask defined (SMD) pads to improve the precision of component placement and soldering.

Thermal Balance

•Design boards with a uniform copper distribution to avoid areas of differing thermal mass, which can lead to soldering issues.

•Use thermal reliefs on through-hole pads connected to large copper areas to improve soldering.

Fiducial Marks

•Include fiducial marks to help automated assembly equipment accurately place components.

•Place fiducials in a manner that they are not obstructed by components or board fixtures.

Feedback and Collaboration

Communication

•Maintain open communication with manufacturers from early design stages through production.

•Seek feedback on your design and be prepared to adapt based on their capabilities and expertise.

Pilot Run

•Consider a small-scale production run initially to identify and rectify any issues before mass production.

•Review assembled boards from pilot runs closely for any potential improvements or optimizations.

Conclusion

Efficiency in PCB manufacturing and testing is achieved through careful design choices and ongoing collaboration with manufacturing partners. By considering manufacturability, testability, and assembly during the design phase, designers can avoid common pitfalls, reduce revisions, and ensure a smooth transition from prototype to production. This approach saves time, reduces costs, and ensures the quality and reliability of the final product.