Standards for aspect ratios and drill tolerances.
At 5,000 meters, air is thinner; arc-over happens at 50% of the sea-level voltage. If your product is for a high-altitude city (e.g., Denver or Mexico City), the PDF requires you to multiply internal clearances by 1.5x. Ipc-2221 Pcb Design Pdf
Run the CAD’s DRC (Design Rule Check). It will highlight every violation of the IPC-2221 standard. Pay special attention to AC-to-DC isolation gaps near power supplies. Standards for aspect ratios and drill tolerances
Why is this interesting? Because that ratio comes from from 1972. The standard is a palimpsest—layers of military, telecom, and consumer rules stacked on top of each other. When you design to IPC-2221, you are unknowingly inheriting design wisdom from the Vietnam War, the Apollo program, and 1990s Nokia phones. air is thinner