Lithographic Resolution
Modified semi-additive processes enable the production of extremely fine conductive patterns that exceed the limits of traditional subtractive etching. Evaluating msap trace capability involves measuring the minimum width and spacing that a fabrication line can reliably produce without shorts or opens. A hybrid approach combines laser imaging with electrolytic deposition.
Process Sequence
Manufacturing starts with a thin seed layer of copper on a core material followed by the application of a high resolution photoresist. The msap trace capability is defined by the precision of the lithography and the electrolytic plating step that builds the circuit features upwards. After plating, the resist is stripped and the thin seed layer is removed using a quick flash etch.
Because the bulk of the trace is grown rather than etched, the sidewalls remain nearly vertical with very little undercut. Vertical profiles allow for much tighter spacing between adjacent lines. Sophisticated chemical controls maintain the balance of the plating bath.
Design Density
Dense routing requirements in mobile devices and high performance computing drive the adoption of this advanced manufacturing method. Improvements in msap trace capability allow for trace widths below twenty five micrometres. Smaller geometries reduce the overall footprint of the circuit and allow for higher pin counts on ball grid array packages.
Consistent thickness across the panel remains a challenge that requires sophisticated plating current control.
