Many PCB designs fail not because of obvious mistakes, but because of tolerances that are too tight to be realistic.
On paper, everything looks correct. In production, yield quietly collapses. At Comtec Labs, tolerance-related issues are among the most common root causes of scrap,
rework, delayed deliveries, and unstable production.
This article explains why tolerances must be treated as manufacturing decisions,
not just geometric constraints, and which tolerances most often destroy yield.
Why Tolerances Matter More in Production Than in Prototypes
Prototypes often hide tolerance problems.
Low volumes, manual handling, and extra inspection mask issues that become unavoidable in series production.
Once volumes increase:
Process variation becomes visible
Margins disappear
Small deviations turn into defects
Yield loss rarely comes from one big error. It comes from many small tolerances stacked together.
Annular Rings Below Process Capability
One of the most common issues is annular rings specified tighter than fabrication capability. Even minor drill wander can turn a passing design into scrap.
If annular rings have no functional requirement, designing margin is the fastest way to improve yield.
Hole-to-Copper and Registration Margins
Hole-to-copper clearances often look generous on screen, but when combined with layer registration tolerances, they quickly become critical.
Designing for worst-case stack-up, not nominal values, is essential for stable production..
Impedance and Trace Width Tolerances
Electrical tolerances are often copied directly from simulation tools.
Manufacturing processes, however, have natural variation. Overly tight impedance or trace width tolerances increase inspection effort and scrap without improving performance.
DFM: Designing With the Process, Not Against It
Good DFM aligns design intent with real process capability.
Tolerances should reflect what is required—not what is possible in CAD.
Yield improves when margin is intentional.
Ready to Reduce PCB Surprises?
If you’re navigating complex requirements, tight schedules, or production risk, Comtec Labs offers a full suite of services to streamline your workflow:
PCB design service
PCB prototyping service
PCB component sourcing
PCB component assembly
PCB testing service
PCB repair and modifications
Printed circuit board production
PCB mass production