The subtractive route, step by step
Most boards start as copper-clad laminate. Inner layers are cleaned, coated with photoresist, exposed through a film, developed and then etched; the resist is stripped and the copper that remains is the circuit. Outer layers are imaged after lamination and drilling, and the pattern is built up by plating before the final etch.
Drilling and plating
Mechanical drilling covers through holes and, on thicker boards, buried and blind structures. Laser drilling produces the small vias used in HDI builds; our lines go down to 0.1 mm. After drilling, the holes are desmeared, sensitised and plated so that barrel and surface copper connect.
Solder mask, legend and finish
Liquid photoimageable mask is screened or sprayed, imaged and cured; legend is printed on top. The finish protects exposed copper: HASL for cost and rework tolerance, ENIG for fine pitch and long shelf life, and OSP where a flat, low-cost surface is enough. Each finish changes the minimum annular ring and the coplanarity you can expect.
Where method meets design rule
- 0.075 mm trace and spacing are routine on 1 oz copper; heavier copper needs wider features.
- 0.1 mm laser vias require a controlled dielectric build and a stackup that keeps the via depth shallow.
- Board size up to 580 × 1900 mm and thickness 0.1–6.0 mm are handled on our lines.
The practical lesson: choose the process before the layout is frozen. A stackup that suits 1 oz copper will not hold the same trace width at 4 oz, and a design that assumes laser vias needs a build-up structure that the fabricator can laminate repeatably.
