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.
Drill Smear
Resin Deposition
Thin coating of resin or polymer debris often covers the internal copper edges of a through-hole after mechanical penetration. This phenomenon, known as drill smear, results from the thermoplastic softening of the dielectric material under the intense heat of the drill bit. Removal typically involves a chemical etch or plasma treatment to expose the clean copper surface.
If left unaddressed, the residue acts as an insulator that blocks electrical continuity between the internal planes and the plated barrel.
Mechanical Influence
Tooling parameters and the physical condition of the drill bit dictate the volume of material transferred to the hole wall. High-speed rotation generates friction that melts the epoxy resin, which then adheres to the colder copper land as the bit retracts. While drill smear is common in FR-4 materials, it becomes more prevalent in high-temperature laminates with lower thermal conductivity.
Optimized cooling and chip removal during the drilling cycle help reduce the thickness of the deposited film.
Inspection Standard
Verification of a successful desmear process requires microsectional analysis of a test coupon under magnification. Quality standards define the maximum allowable amount of drill smear that can remain before a board is rejected. Visual confirmation shows a clear interface between the internal copper and the subsequent plating layer.