Destructive Cross-Sectioning
The procedure known as microsection analysis reveals internal board architecture through deliberate physical reduction. Technicians mount printed circuit board coupons in thermosetting resin, grind toward target planes using progressively finer abrasives, and polish the exposed metal until scratches disappear. Chemical etching then highlights grain boundaries, plating thickness, and layer boundaries.
This destructive inspection protocol governs structural acceptance across multilayer fabrication and rigid flex production, defining compliance for barrel wall thickness, copper wrap reduction, and dielectric spacing. Verification stops at the physical boundary of the sample coupon, leaving the remaining manufactured hardware untouched by the cutting wheel.
Resin Mounting
Sample preparation begins by positioning the circuit coupon inside a cylindrical mold before pouring liquid epoxy or acrylic resin over the piece. Polymerization hardens the matrix, locking internal features in place so that grinding belts do not smear copper across dielectric layers. Technicians rotate the cured puck across rotating wheels charged with silicon carbide grit, moving from coarse removal down to submicron diamond suspensions.
Ultrasonic baths remove polishing debris from drilled holes before etchants such as ammonium persulfate reveal copper crystal structures. Microscope illumination then allows inspectors to measure barrel cracking, resin recession, and inner layer misregistration against internal workmanship limits.
Etching Protocol
Chemical enhancement selectively colors specific metals and laminates to differentiate electrodeposited copper from foil layers. Acidic ferric chloride reveals structural anomalies in plated through holes, exposing voids, thin walls, and anomalous nodule formations that survive electrical continuity tests. Metallurgical microscopes record magnification images for permanent quality archives, proving compliance with IPC standards for barrel integrity and intermetallic compound thickness.
Thermal stress blistering and lamination delamination appear clearly after exposure to high temperature solder floats, distinguishing manufacturing process failures from raw material defects. Destructive cross-sectioning remains the definitive laboratory test for qualifying electroplated copper reliability prior to high reliability electronic assembly delivery.
