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AUGUST 2022 I DESIGN007 MAGAZINE 45 adds up. Dropping the size and the number of layers impacts the over- all cost. But you must iden- tify the tradeoffs. Reducing the PCB design's size impacts the manufacturing or electrical performance significantly when reducing layers has a critical impact on electrical performance. Almost every time I have reduced the num- ber of layers in a design, it hurt the design in a way that far outweighed the financial cost savings. For instance, taking a four-layer board and reducing it to two to save money resulted in problems. First, it involves physics, with a four-layer design producing 15 dB less radia- tion than a two-layer board. It allows you to route signals in a microstrip (or stripline) con- figuration. Finally, the ground plane signifi- cantly decreases the ground impedance (and, therefore, the ground noise). Am I saying we should never use a two-layer design? No. I am saying that you must consider the outcome of your decisions. With changes, mance, reliability, and manufacturability/yield. Each area has its require- ments and expectations. Furthermore, they all are inter- connected and impact one another. e "sweet spot" is that small area in the center where everything is balanced. It is a great designer who knows that spot. If you feel we don't have enough acronyms, such as design for manufacturing (DFM) or design for reliability (DFR), etc., let me give you another. Our current situation has brought about DFC—design for cost. As if there isn't enough for me to think about in your PCB, I know must keep in mind how much this costs? Designing for cost begins with the very first steps of your design. Know what contributes to the cost in both the fabrication and assem- bly process. For example, most of the cost of a PCB design is in the raw materials, specifically the bare PCB itself. It's found in the size of the PCB, the type of FR-4, and the number of layers. It all Figure 1: The best designs involve hitting the sweet spot where electrical and mechanical performance overlap reliability and manufacturability.