Geometric Compensation
Copper dissolution during subtractive printed circuit board fabrication proceeds isotropically, attacking exposed metal both downward into the laminate and laterally beneath the photoresist mask. Etch factor calculation determines the ratio between vertical depth removal and lateral undercut, providing the exact geometrical compensation required during photoplotting artwork generation. Phototool designers apply this ratio to pad diameters and conductor widths on exterior layers to counteract acid side-etching during conveyorized spray chamber processing.
Undercut Control
Chemical milling parameters dictate whether acidic cupric chloride or ammoniacal etchant chemistry maintains wall profile verticality within fine-line conductor arrays. Etch factor calculation relies on microscopic cross-section measurements taken after conveyor transport, quantifying copper thickness loss alongside horizontal base erosion beneath the dry film overhang. Etch rate monitors track bath temperature, cupric ion concentration, and dissolved metal loading to stabilize these sidewall angles before automated optical inspection flags bridging defects.
Impedance Tolerance
Controlled impedance traces depend on precise line width preservation because excessive lateral etching reduces copper cross-sectional area and shifts high-frequency signal propagation characteristics. Etch factor calculation ensures that differential pairs achieve target characteristic impedance values by predicting final conductor geometry from initial artwork dimensions. Dielectric thickness variations and copper foil weight fluctuations interact with this ratio, demanding rigorous pre-production etching compensation to prevent signal integrity failures during final electrical testing.
