Issue link: https://iconnect007.uberflip.com/i/1500943
JUNE 2023 I DESIGN007 MAGAZINE 17 designer should fix it, and then document it. On the next design, go through your list before you release it for any other types of review. • Vias need to be dropped in an organized fashion, on a grid system, during the place- ment stage for designs with a lot of connec- tions. Vias placed in a random fashion cause headaches during the routing stage and can choke off the power planes. If you ask a manufacturer, you may hear: • Manufacturability matters, and it matters much more than just meeting minimum requirements. Optimization for manufactur- ing process tolerances is critical for accept- able yields in a high-volume environment. Understanding manufacturing processes that allow the designer to consider tradeoffs to create this optimization is important. For example, some rules are for initial manu- facturing, and some are for rework. Initial manufacturing takes priority. • By being aware of manufacturing capabili- ties, tolerances, and constraints during the design process, designers can create PCBs that are more efficient and cost-effective to produce. A focus on DFM helps to reduce the number of manufacturing errors and rework, shorten production times, and lower overall production costs. Design- ers must consider various aspects, such as appropriate trace widths, via sizes, and com- ponent clearances, along with the selection of suitable materials and surface finishes. • Clean, correct, complete data is important. Relying on fab shops to make edits to meet requirements creates a disconnect between the design database and the actual product. If these updates aren't captured in the design database, future respins will require edits to be made again, and it is unlikely those edits will be the same. With a respin, it is a com- mon misconception that, "We built it this way before so it's good." What was built is what the fab shop edited. • ere is a difference between drill size and finished size and how that impacts the use of press fit connectors. ere are risks associ- ated with allowing the PCB manufacturer to determine drill size. ese should be deter- mined on the design drawings. • Know the design requirements such as export restrictions, ITAR, EAR, ESD/SMI, safety, environmental, Class 2, Class 3, and space specifications. All these need to be identified and their implications understood up front to ensure they can be met during the design process. If you ask a signal integrity engineer, these will probably be at the top of the list: • Signal integrity needs to be a priority, par- ticularly in high-speed designs. It is one of the most critical factors that PCB design- ers should be aware of. Maintaining signal integrity ensures the reliable performance of a PCB, and designers need to be aware of aspects such as impedance control, cross- talk, and reflections, which can impact the quality of the signal. • ey must employ proper routing tech- niques and carefully consider component placement to minimize the negative effects of these factors. Additionally, the use of termination resistors can help maintain signal integrity and prevent signal degrada- tion. • Selection of a stackup, appropriate materials, routing plans, and the use of power planes as a reference can all impact the performance of high-speed signals. • Be sure to recognize the importance of ground return vias for transitioning between layers. Insufficient vias will impact the performance. So, it's important to understand that the answer you get will depend upon who you ask and their place in the design and manufactur- ing cycle. Whoever you ask will be sure to have a unique perspective. DESIGN007