What the number means
Liquid photoimageable mask is printed or sprayed, imaged and cured. Over a trace it builds to roughly 15–25 µm; over bare laminate it is thinner. A drawing that states a single thickness is therefore a simplification.
How it is measured
- Cross-section — the reference method: measure over traces, between pads and over laminate.
- Optical / eddy current — fast, non-destructive, used for process control after correlation.
- Tape and peel tests — adhesion and cure, not thickness.
Process levers
Screen mesh, ink viscosity, print speed and cure profile all move the result. When a design has a tight mask dam between fine-pitch pads, the print parameters are set for that geometry rather than for the panel average.
If mask thickness is a functional requirement — high-voltage isolation, for example — specify the minimum over copper and the measurement method, and we will report it with the lot. Mask print parameters are part of the pcb manufacturing package, so the functional minimum belongs on the drawing rather than in a later email.
