Lateral Undercut Definition
Chemical milling depth and horizontal feature width define the etch factor mechanics during copper removal from printed circuit board substrates. This ratio calculates the horizontal loss of conductor sidewalls relative to the total vertical depth achieved by the etchant. Precise control over this phenomenon prevents narrow tracks from suffering excessive narrowing or total loss during prolonged exposure in the spray chamber.
High precision processes demand a geometry where the vertical bite far exceeds the lateral chemical creep.
Subtractive Geometry Constraints
Manufacturers maintain target trace profiles by balancing spray pressure and conveyor speed against the specific chemistry chemistry activity levels. Smaller features encounter proportional increases in copper loss because the etchant penetrates the sidewalls while moving toward the board base. Excessively long residence times convert rectangular cross sections into trapezoidal shapes or rounded pedestals.
Standard production tolerances require the calibration of nozzle angles to minimize stagnant pockets that promote erratic lateral consumption.
Process Inspection Standards
Automated optical equipment validates the copper cross section after the completion of the stripping cycle. Discrepancies between the design file and the realized trace geometry identify faults in chemical replenishment or flow dynamics. Final acceptance relies upon the ratio remaining within established limits to ensure signal integrity and proper solder mask registration for subsequent assembly steps.
Thin traces require tighter control of this variable to prevent impedance mismatches.
