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.
Class 3 Acceptance
Standard Hierarchy
High-reliability quality classifications define manufacturing and inspection thresholds for electronic assemblies where continuous performance or performance-on-demand is critical. Meeting class 3 acceptance requires strict adherence to minimum solder fillet heights and zero tolerance for internal voids in barrel plating. Industrial sectors producing aerospace and medical life-support systems mandate this standard.
Defect Tolerance
Structural criteria for high-performance electronics eliminate process variations that commercial assemblies tolerate without functional failure. Under class 3 acceptance rules, barrel copper plating thickness inside plated through-holes must maintain an average minimum of 25 micrometers without dropping below 20 micrometers at any localized thin spot. Solder wetting on surface mount components must exceed 75 percent of vertical height on end terminations, whereas lower classifications permit reduced vertical coverage.
Microsection analysis reveals inner-layer interconnect separation and copper foil delamination that breach performance limits. Assemblies failing these microsection standards undergo immediate quarantine, halting lot movement until engineering review completes root-cause analysis.
Verification Method
Non-destructive inspection procedures combined with microsectioning establish objective compliance with high-reliability manufacturing specifications. Evaluating class 3 acceptance relies on automated optical inspection and cross-sectioning witness coupons to detect hidden defects. Visual inspection under controlled magnification verifies surface cleanliness and absence of metallic solder spatter across adjacent traces.