Modified Semi Additive Process Yield Loss Recovery Contract Mechanics
Modified semi additive process contracts require clear yield baselines, defect attribution formulas, and flash-etch metrology to recover scrap costs cleanly.
Trace Trapezoid Ratio
Etch Geometry
Geometric proportions describe the width difference between the top and the bottom of a copper conductor. The trace trapezoid ratio quantifies how much wider the base of the line is than its upper surface. Because chemicals eat the top of the metal longer than the bottom during spray cycles, perfectly square traces are impossible to manufacture.
Profile Precision
Design integrity depends on knowing how much the signal carrying mass varies from the intended rectangular model. In a trace trapezoid ratio, a value near one point zero indicates an almost straight wall, which is only possible with specialized thin copper foils. Typical subtractive processes result in values around zero point six to zero point eight.
Excessive etching leads to an undercut where the top is wider than the base, making the trace unstable. Plating engineers monitor nozzle pressures to keep the etch factor consistent across the whole panel frame. If the solution is too aggressive, it will thin the top of the line so far that it increases the electrical resistance of the circuit.
Density Constraint
High speed signals suffer from unpredictable changes when the conductor shape varies wildly across the board. Monitoring the trace trapezoid ratio allows for better control of controlled impedance requirements. Acceptance focuses on maintaining a shape that matches the simulated electrical models used in the design.