Optimizing Modified Semi-Additive Process Parameters for Sub-30 Micron Feature Generation
Sub-30 micron mSAP feature generation requires controlling seed layer thickness, LDI resist profiles, plating additive dynamics, and flash etch undercut.
Trace Undercut Control
Etching Boundary
Copper removal during printed circuit board fabrication relies on chemical baths that dissolve exposed metal while protected areas remain under the photoresist mask. Chemical lateral attack beneath the protective film threatens fine conductor geometries by narrowing copper cross sections unexpectedly. Trace undercut control limits this lateral chemical dissolution by optimizing etchant chemistry, temperature, and spray pressure to preserve nominal conductor widths.
Automated optical inspection equipment measures the resulting trapezoidal conductor profile after etching to verify adherence to design tolerances.
Mask Adhesion
Photoresist integrity directly influences the lateral penetration of etchant solutions along copper sidewalls. Insufficient surface preparation or inadequate exposure energy reduces interfacial bonding between the dry film and the copper substrate. Compromised adhesion permits chemical undercutting to exceed allowable limits during conveyorized spray etching.
Electrolytic plating processes preceding etching demand clean copper surfaces to prevent localized delamination under aggressive chemical attack.
Conductor Tolerance
Conductor cross section geometry determines electrical resistance and current carrying capacity in finished assemblies. Excessive lateral etching reduces the copper base width below the minimum threshold required for reliable solder joint formation. Electrical testing identifies open circuits caused by over-etched traces, while metallographic cross sectioning verifies final sidewall angles.
Maintaining precise etching parameters ensures high yield during high density interconnect fabrication.