Annular Ring Tolerances a Volume Shop Actually Holds
Volume PCB shops hold a real-world minimum annular ring of 0.002 inches for Class 2 designs when artwork grants 0.005 inches of nominal land margin over tool size.
Class 3
Maximum Allowance
Maximum allowance for plated through-hole barrel voids defines the strictest quality tier in printed circuit board fabrication. Class 3 designates high reliability electronic equipment where uninterrupted continuous service is required and equipment downtime cannot be tolerated under any circumstance. Manufacturing limits for internal layer copper plating thickness require a minimum average of twenty-five micrometres within the barrel walls.
Acceptance criteria prohibit any measurable reduction in annular ring copper thickness below specific percentage thresholds during subsequent reflow soldering operations.
Thermal Resistance
Thermal resistance limits dictate how rigid laminate materials must behave during extreme assembly conditions such as multiple lead-free soldering excursions. Class 3 substrates demand high glass transition temperature dielectrics that withstand localized mechanical stresses without delaminating from internal copper planes. Board shops verify these baseline laminate parameters through thermomechanical analysis prior to releasing bare panels into automated surface mount placement lines.
Component placement pressure must remain strictly controlled to prevent excessive micro-cracking in newly formed solder joints during final board population.
Inspection Protocol
Inspection protocol mandates rigorous microscopic cross-sectioning to verify barrel wall integrity after thermal stress testing. Quality engineers examine polished cross-sections at high magnification to detect micro-voids or resin recession within plated through-holes. Any detected anomaly exceeding specified percentage limits triggers immediate lot rejection before functional electrical testing takes place on the finished assembly.