Destructive Coupon Microsection Preparation and Optical Feature Extraction
Precision destructive microsection preparation and calibrated optical extraction establish compliance for barrel plating, wrap copper, and internal layer interfaces.
Copper Smearing
Material Transfer
Redistribution of ductile metal across the dielectric layers of a multilayer circuit board occurs when mechanical drilling forces exceed the material’s structural limits. High temperatures generated at the drill tip soften the wall surfaces, allowing copper smearing to bridge the gap between internal planes. This thin layer of conductive material creates a low-resistance path that can lead to intermittent short circuits or signal degradation.
Chemical desmear processes must be employed to remove these deposits before plating begins.
Thermal Cause
Friction between the rotating drill bit and the copper foil generates localized heating that reaches the glass transition temperature of the resin. When copper smearing forms, it typically indicates that the drill feed rate was too high or the spindle speed was improperly synchronized with the descent. Dull cutting edges contribute to the problem by tearing the metal during the drilling cycle.
Modern fabrication houses monitor drill bit life cycles and use backup boards to dissipate heat and minimize the occurrence of this defect.
Electrical Consequence
Presence of conductive debris on the insulation prevents the formation of a clean hole wall for subsequent electroplating. If copper smearing remains undetected, the internal layers may fail to connect correctly to the plated through-hole barrel. Reliability is compromised as the thin film of smeared metal might crack during thermal cycling in the field.