Destructive Micro-Sectioning Protocols for Detecting Hyper Corrosion Spikes in ENIG
Destructive micro-sectioning with nitric acid etching isolates ENIG hyper-corrosion spikes under SEM to reject defective PCB lots before assembly.
Coupon Sampling
Meaning
Destructive testing of production-line printed circuit boards is avoided by utilizing standardized test strips fabricated on the margin of each panel. Through coupon sampling, manufacturing facilities can evaluate the quality of copper plating and solderability without destroying the functional boards. This procedure is administered under GB/T 4677, which defines the geometric specifications and placement of the test coupons.
The applicability of this method is confined to the specific panel from which the test piece is removed.
Testing Practice
Cross-sectional evaluation of the extracted strip reveals the internal plating thickness of the through-holes. Technicians extract the coupon from the panel edge using a precision punch or saw. Once mounted in epoxy and polished, the specimen is subjected to microstructural inspection.
A single coupon provides a representative record of the manufacturing conditions across the entire panel.
Compliance Protocol
Quality assurance inspectors rely on these test specimens to issue conformity certificates for shipments destined for domestic and export markets. Under Chinese market supervision guidelines, these records must be archived for a minimum of three years for traceability purposes. Failing a coupon test triggers an automatic quarantine of the associated batch, requiring a full investigation.
The regulatory body retains the power to audit these archives during unscheduled factory inspections.
Statistical Yield
Using these test strips reduces scrap rates by eliminating the need to sacrifice finished functional assemblies. It allows factories to monitor copper deposition rates across different plating baths continuously.