Writing Circuits with Light: LDI Technology
Traditional PCB imaging uses phototools - photographic films contact-printed onto resist-coated panels under UV flood exposure. This works above 4 mil trace/space. Below 4 mil, film hits three walls: dimensional instability (film expands with temperature/humidity), registration error accumulation (layer-to-layer alignment), and resolution limits (light scatters under film edges). LDI eliminates all three by replacing the phototool with a computer-controlled UV laser that writes the circuit pattern directly onto the photoresist, pixel by pixel.
Our workshop operates Synova LDI automatic exposure machines S100807 (2 units) alongside Orbotech and SCREEN LDI systems. These achieve 2/2 mil (50um/50um) trace/space resolution - the gold standard for HDI, IC substrate, and advanced multilayer designs.
How LDI Delivers Precision
A granite-base stage provides thermal and vibration stability. A high-resolution camera locates panel fiducials and inner-layer targets. The LDI reads Gerber/ODB++ data, calculates the exact laser path accounting for any panel distortion measured by the fiducial system, and scans the UV laser across the resist at megahertz modulation rates. Pixels as small as 2um are individually exposed. After exposure, the panel proceeds to developer where unexposed resist dissolves away - leaving the hardened pattern that protects copper during etching.
Applications Requiring LDI
Fine-pitch BGA breakouts (0.4mm pitch). HDI routing between micro-vias. Impedance-controlled differential pairs demanding near-zero line width variation. Solder mask imaging with micron-level alignment for dam formation between 0.3mm-pitch pads.
