Metallographic Preparation
Metallographic preparation of printed circuit board coupons allows destructive visual inspection of internal copper layers and plated through holes. Laboratory technicians execute microsection polishing to reveal structural anomalies hidden beneath epoxy laminates during board fabrication. Technicians grind through layered composite materials using progressively finer diamond abrasives until optical microscopy reveals grain structure and plating thickness.
The metallurgical analysis evaluates barrel cracking, resin recession, and copper foil thickness against acceptance criteria defined in procurement specifications. Board manufacturers rely on this destructive evaluation to verify plating uniformity before shipping production lots to assembly plants.
Abrasive Progression
Technicians mount cross section samples in thermosetting resin blocks before grinding the edge down to the target plane using silicon carbide papers. Automated rotary polishers apply diamond suspensions graded from nine microns down to one micron across polyurethane cloths to remove heavy scratches left by coarse papers. Operators introduce colloidal silica during the final step for mechanical chemical polishing to eliminate microscopic deformation zones created by earlier abrasive stages.
Fine particle suspensions relieve residual stresses at the metal surface so grain boundaries appear clearly under polarized light. Each polishing wheel rotates at controlled speeds while specimen holders apply downward force uniformly across the embedded coupon face.
Acceptance Boundary
Plating voids and barrel cracks discovered during microscopic examination dictate whether a production lot satisfies performance requirements for harsh service environments. Laboratory personnel measure annular ring thickness and copper wall integrity on multilayer circuit boards to confirm compliance with industrial standards before assembly begins. Thermal shock during soldering induces high mechanical stress within plated through holes if copper deposits contain structural inclusions or excessive grain boundary porosity.
Optical inspection stops at the detection of structural nonconformities because further reduction of the sample face destroys evidence needed for failure analysis reports. Correct execution of sample preparation prevents false rejections caused by polishing artifacts mimicking genuine manufacturing defects.
