Cutting Degradation
Machining metrics quantify cutting tip volumetric loss per drilled hole in solid carbide tools during printed circuit board primary drilling operations. The drill bit wear rate tracks the progressive rounding of the primary cutting edge and margin wear across thousands of hole hits. Excessive wear increases entry burrs and internal hole wall roughness while elevating mechanical stress on inner layer copper foils.
Acceptable thresholds depend on drill diameter and substrate glass content, stopping before tip fracture or severe resin smear occurs. Higher wear rates force shortened hit counts on abrasive high-glass substrates to preserve hole wall integrity.
Hole Quality
Mechanical deformation during spindle rotation creates distinct physical defects inside drilled vias as tool geometry degrades. Outer corner loss alters chip clearance, driving drill debris into hole walls and generating friction heat. Localized heat melts resin systems, smearing non-conductive epoxy over internal copper land rings.
Secondary contact along the hole wall creates nail-heading where inner copper layers deflect outward under heavy axial force.
Inspection Threshold
Verification procedures evaluate tool health through direct optical measurement of cutting margins alongside post-drill hole wall microsectioning. Fabricators measure corner radius loss under optical inspection stations after predefined hit counts. Exceeding maximum radial reduction triggers immediate tool retirement before smear exceeds class limits.
