Predictive Hydrodynamic Modeling of High-Viscosity Epoxy Flow in Ultra-Heavy Copper Cavities
Predictive non-Newtonian flow modeling prevents micro-voiding in ultra-heavy copper cavities by matching prepreg viscosity minimums to press force ramps.
Etch Factor Undercut
Etch Ratio
Subtractive copper processing metrics compare the lateral depth of conductor sidewall erosion against the vertical etch depth accomplished through the copper foil thickness. This geometric relationship, termed etch factor undercut, quantifies the deviation of printed circuit board trace cross-sections from ideal rectangular profiles. Chemical action by alkaline or cupric chloride etchants removes unwanted copper vertically while simultaneously attacking conductor sidewalls beneath photolithographic resist edges.
Fabricators evaluate this value by microsectioning finished trace geometry and calculating the ratio of total etch depth to lateral erosion distance. The metric ceases to apply in additive or semi-additive processing where conductor features grow through electroplating within photoresist channels rather than being carved from solid foil.
Profile Control
Chemical spray pressure and nozzle design govern the balance between vertical copper dissolution and lateral fluid undercut during conveyored etching operations. Higher spray impact forces speed vertical chemical replenishment along the board surface while reducing localized dwell time under resist margins. In high density interconnect circuit boards, uncorrected etch factor undercut creates trapezoidal trace profiles that deviate significantly from target conductor widths.
Compensation factors applied during computer-aided manufacturing adjustments widen nominal gerber artwork features to account for expected sidewall erosion. Inspection by automated optical imaging compares top and bottom trace dimensions against defined acceptance thresholds before solder mask application.
Impedance Impact
High speed signal transmission depends heavily on conductor geometry due to skin effect losses and edge-coupled electric fields. Trapezoidal trace shapes altered by excessive lateral erosion change line capacitance and characteristic differential impedance along critical transmission paths.