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.
