Why You Need DFM Check for PCBs


For anything manufactured, Design For Manufacturability (DFM) is an important process. For Printed Circuit Boards (PCBs), DFM is the process of composing the layout topology for mitigating problems that the PCB manufacturing and assembly process could encounter, when manufacturing an electronic system. Although these are two separate issues and addressing fabrication issues is the realm of Design for Fabrication (DFF), with Design for Assembly (DFA) addressing assembly issues, the two together mostly make up the DFM analysis.

Designers use the term Design Rule Checking (DRC) during the design process, but this is not to be confused with DFM. Of course, DRC issues noticed in manufacturing do indeed affect the PCB manufacturability directly. The role of DRC is diverse, and starts from ensuring the connectivity of a PCB layout properly reflects the connectivity defined in the associated schematic diagram of the board. The rules part of DRC also defines the minimum spacing allowed between PCB objects on the entire PCB. That makes DRC a subset of DFM. However, that is true only when the rules relate to the manufacturer’s requirement for spacing. Most often, DRC verifies electrical requirements only.

In general terms, DFM identifies issues in the PCB topology that could create manufacturing problems. Additionally, whereas a DRC defect will crop up in every PCB made, DFM issues may manifest in some PCBs, while others perform as expected. For instance, a PCB layout with extremely thin copper tracks created in a design tool by rule, and spaced properly, would pass DRC. However, very thin tracks have the potential of detaching on the physical PCB and shorting to other tracks during assembly—creating shorts on some PCBs, but not on others. Without DFM, such a problem would remain undetected and result in rework or scrap.

For these reasons, it is advisable to include the DFM process with the PCB design flow. Doing so reduces the cost of finished PCBs, maintains the design intent, and reduces the potential for future design failures.

Although theoretically, designs submitted without DFM defects being addressed are less expensive to manufacture, it creates other issues not so desirable. These include issues with electromagnetic interference, signal integrity, cross talk, etc., which are commonplace in today’s complicated electronic technology. For a CAM engineer to take a design with DFM issues and make it comply with their manufacturing processes, may inadvertently introduce the above issues. Therefore, even if the PCB is fully manufacturable, it may remain non-functional. These considerations mandate that the DFM process and PCB design go together.

Mainstream DFM tools are now readily affordable in the market. Everyday design engineers can easily use the tools and deploy them during the PCB layout process. Some manufacturing rules may be manufacturer dependent, and DFM tools allow users to model the rules to the requirements suitable to a specific intended manufacturer. Users can switch the rules to model for a different manufacturer as the design moves on from, say, prototype to production.

DFM tools can be free from the constraints of the PCB CAD, and allow detection of problems in a design that the standard PCB CAD tools do not support. Good DFM will ensure a design not only performs functionally as expected, but also can be manufactured in high volumes without increasing the risk or cost, or adding unnecessarily to the design time.

Royal Circuits performs a free DFM check on all orders. Click here to learn more about our specific service.