Destructive Coupon Microsection Preparation and Optical Feature Extraction
Precision destructive microsection preparation and calibrated optical extraction establish compliance for barrel plating, wrap copper, and internal layer interfaces.
Annular Ring Measurement
Registration Check
A dimensional assessment of the copper border remaining around a drilled hole defines the physical integrity of a printed circuit board connection. This inspection process, termed annular ring measurement, determines if the copper ring meets minimum thickness limits after drilling and plating.
Measurement Sequence
Non-destructive testing uses automatic optical inspection and X-ray systems to evaluate inner layers before lamination. After outer-layer plating, inspectors deploy cross-sectional analysis to verify the ring size directly under a calibrated microscope. The technique involves cutting the board, potting the specimen in resin, and polishing the surface to expose the hole diameter and copper borders.
This allows direct visual confirmation of registration accuracy across multiple board layers.
Acceptance Limit
Workmanship standards establish the threshold for minimum ring thickness to prevent circuit breaks and intermittent connections during thermal stress. For Class 3 electronics, the external ring must measure at least fifty micrometers, while internal rings require a minimum of twenty-five micrometers. Drilled holes that lie too close to the trace pad edge produce breakout, which severely compromises the reliability of the plated through-hole.
When drill wander occurs during fabrication, the resulting offset reduces the annular ring on one side of the hole. Corrective action requires modifying the drill coordinates or adjusting the scaling factors used for the photo-tooling films.