Designing Circuit Board Landing Pads for Standard Fabrication Capabilities
Designing component landing pads to standard fabrication tolerances ensures high panel yield, eliminates engineering queries, and stabilizes bare board unit costs.
Chemical Etch Undercut
Lateral Reduction
Subtractive printed circuit board manufacturing removes unwanted copper through liquid chemical reactions that attack exposed metal beneath photoresist edges. This lateral erosion process produces chemical etch undercut when acid or alkaline spray penetrates sideways beneath the polymer mask during conductor formation. Processing etch factor defines the ratio of downward etch depth to lateral erosion distance along conductor sidewalls.
Fabricators calculate artwork compensation based on copper foil weight, conveyor speed and chemical concentration. Conductor width design rules incorporate tolerance margins to offset this reduction across inner and outer circuit layers.
Etch Factor
Chemical etch undercut increases in direct proportion to copper foil thickness, requiring wider artwork compensation on heavy copper layers. Fine line geometries demand tight control of spray nozzle pressure, specific gravity and temperature inside the etching chamber. Excessive dwell time accelerates sidewall attack, leaving thin trapezoidal conductor profiles that fail cross-sectional microsection inspection under IPC-A-600 standards.
Defect Boundary
Severe lateral removal causes photoresist overhang to collapse. Trapped chemical residues create latent short circuits during thermal lamination. Solder mask coverage becomes unreliable when trace crests narrow beyond physical limits.
Dimensional inspection verifies copper line width at the narrowest point to ensure compliance with trace width allowances.