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.
Drill Table Repeatabilities
Data Fidelity
Coordinate mapping errors in printed circuit board fabrication stem directly from translation flaws between computer aided manufacturing software and CNC machinery. Drill table repeatabilities designate the positional constancy of spindle insertion points across successive panels processed under identical numerical control routines. Mechanical backlash within lead screws or optical encoder degradation alters these coordinates over extended operating hours.
Optical inspection systems measure residual offset by comparing finished copper layers against original Gerber coordinate files. Thermally induced expansion during high speed routing cycles further shifts hole centers beyond acceptable positional tolerances.
Spindle Variance
Positional drift degrades annular ring margins on multi layer circuit boards during subsequent mechanical drilling. Drill table repeatabilities dictate whether micro via destinations remain centered within internal power planes. Machine operators track axis calibration drift using standard coupon plates pierced at predetermined grid intersections.
Laser interferometry detects microscopic axis deviations before cumulative positioning errors violate final assembly specifications.
Tolerance Limits
Acceptable positional variation remains strictly bounded by pad diameters specified in IPC standards for high density interconnect fabrication. Drill table repeatabilities determine the maximum allowable displacement before component lead insertion fails during automated surface mount population. Structural integrity of plated through holes relies entirely on consistent spindle placement across production batches.
Final acceptance depends on cross sectional microscopic analysis verifying that barrel wall thickness meets minimum copper deposition requirements around every barrel.