Standard polarity markers like dots are often obscured once a component is placed. Using a square-shaped copper pad for pin 1, while other pads are round, provides a clear, permanent indicator that is visible during and after assembly, reducing inspection time and errors.
Standard 'pin 1' and 'pin 2' labels for LEDs are ambiguous, as the cathode isn't always pin 1. Labeling pads with 'A' for anode and 'C' for cathode on both the schematic and PCB footprint provides crystal clear orientation instructions for manufacturers, reducing significant verification time.
A specific 'cozy size' for silkscreen—1mm high by 1mm wide with a 0.18mm line width—balances on-board real estate with manufacturability. This size is large enough for easy human reading and compatible with faster, older screen printing methods, avoiding the slower inkjet-style processes required for finer text.
While aesthetically pleasing, black solder mask absorbs light, which can interfere with the optical sensors on automated assembly and inspection machines. It also requires larger clearances during fabrication (e.g., 4 mils vs. 2 mils for green) because it's harder for UV light to penetrate, making green the superior choice for manufacturability.
Designers should consider the human operators and machines that will assemble their product. By making choices that simplify manufacturing—providing clear instructions and avoiding known difficulties—the process becomes smoother and more efficient, akin to 'riding a bike downhill.'
Components that hang over a PCB's edge can collide with adjacent boards in a manufacturing panel. Adding a simple dimension on the silkscreen layer to indicate the overhang distance acts as a critical red flag for the manufacturer during the panelization setup, preventing costly rework.
Mixing very large and very small components requires complex and error-prone 'stepped' stencils to apply different amounts of solder paste. By keeping component sizes in a similar range, a simpler, flat stencil can be used, which dramatically improves the reliability and ease of the solder paste printing process.
Placing SMT components too close to through-hole pins obstructs automated selective soldering machines, forcing manufacturers to use slower, more expensive hand soldering or custom fixtures. Enforcing a 3mm keep-out zone around through-hole parts is a simple design rule that ensures compatibility with high-speed automation.
Pin-in-paste soldering requires precise calculations for pad and paste openings that depend on a manufacturer's specific process (paste type, stencil thickness, etc.). A designer cannot guess these values. You must proactively engage your manufacturer for these specs before finishing the layout to avoid being 'screwed'.