Standard Microsection Inspection Procedures for Class Two and Class Three Annular Rings
Class 3 microsections require zero inner layer breakout and 0.050 mm minimum ring width, whereas Class 2 permits 90-degree breakout if conductor spacing holds.
Diamond Micro-Polishing
Surface Finish
Metallographic preparation techniques utilize industrial grade synthetic diamond suspensions to achieve a mirror finish on cross sectioned PCB samples. During diamond micro-polishing, technician labor focuses on removing the smear layer and fine scratches left by coarser silicon carbide grinding steps. This step is necessary to reveal the true grain structure of copper plating and the integrity of intermetallic compounds at the solder joint interface.
Abrasive Application
The process involves applying diamond paste or liquid suspension to a rotating lint free cloth wheel. Consistent pressure and lubricant flow prevent frictional heat from distorting the relatively soft copper or plastic substrate. Gradually reducing the grit size from six microns down to a quarter micron produces the clarity required for high magnification microscopy.
Each successive stage clears the debris of the previous one while maintaining the flatness of the specimen across the entire mount surface and preventing the rounding of the edges.
Inspection Integrity
Quality of the final image depends entirely on the elimination of surface artifacts that could be mistaken for voids or cracks. Smearing of the metal across the boundary of a glass reinforced epoxy layer often hides small delamination defects if the polishing is incomplete. High quality microsections provide the evidence needed to accept or reject a production lot based on plating thickness and hole wall quality.