Reconciling Static Field Solvers with High-Frequency TDR Reflection Curves
Reconciling static field solvers with TDR curves requires transforming 2D RLGC parameters into causal, broadband S-parameters with instrument rise-time filtering.
Panel Etch Factor
Etching Ratio
Chemical subtractive processes remove unwanted copper from laminated substrates to establish conductive trace patterns. In printed circuit board fabrication, the panel etch factor represents the ratio of the downward etch depth to the lateral etch under the protective photoresist. When acid sprays onto the copper surface, it dissolves metal vertically while simultaneously eating sideways beneath the resist mask.
This lateral action creates a trapezoidal trace cross-section instead of a perfect rectangle. Managing this geometry is necessary for maintaining uniform current density and avoiding hot spots in high-power circuits.
Compensation Geometry
Photolithography phototools must be adjusted to account for the reduction in trace width caused by lateral etching. Fabrication engineers apply the panel etch factor during the computer-aided manufacturing stage to widen the trace dimensions on the production artwork. If the factor is known, the trace is designed wider on the mask so that the finished copper trace holds the target width after the chemical wash.
This adjustment ensures correct electrical impedance.
Line Control
Process variables such as temperature and conveyor speed affect the rate of sideways action during production. Process operators measure the finished conductor profiles on test coupons to calculate the panel etch factor. This testing prevents over-etching and keeps trace dimensions within specifications.