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.
Flash Etch Undercut
Removal Error
Side wall erosion happens during the rapid removal of thin sacrificial copper layers. Any flash etch undercut results in the trace base being narrower than the initial design intended. Excessive loss of metal structure threatens the physical bond between the copper and the substrate.
Geometric Accuracy
Over etching occurs when the chemical solution bites sideways while clearing the surface between isolated pads. Within the context of flash etch undercut, the amount of lateral removal depends directly on the immersion time and the spray pressure inside the machine. Proper setup ensures the base of the trace remains wide enough to support its vertical load.
Technicians measure the foot of the conductor using cross section views to ensure it meets standard specs. If the copper foil starts too thick, the flash etch takes too long, which increases the likelihood of thinning the main lines. These defects often remain hidden under solder mask until thermal stress causes them to lift from the board.
Profile Retention
Narrowing at the interface reduces the surface area available for adhesion. High levels of flash etch undercut cause entire circuit paths to peel away during rework or heating. Quality controls reject panels where the loss of width exceeds a specific percentage of the nominal trace width.