Here's a mistake that shows up constantly: designers defaulting to 4mil trace / 4mil space because that's what the last project used. Nobody questioned it. Nobody changed it. And it's quietly costing you money on every run.

When you go below 5mil/5mil, you cross into fine-line fabrication territory. Fewer shops can run it. Lead times get longer. Sometimes prices go up 20–40% more per panel for no electrical reason.

The fix is simple: Set your design rules to 5mil trace / 5mil space minimum. Use 6mil/6mil wherever your layout allows. Unless you're routing high-speed differential pairs, dense BGA fanout, or RF traces, you don't need to go tighter.

You'll open up your fab options, speed up your quotes, and drop your unit cost - without changing a single electrical characteristic of your design.

Tighter isn't smarter. It's just more expensive.