1. Design and Output (Pre-Production Engineering)

Why It Affects Lead Time

  • Engineers create the schematic and PCB layout using software like Altium Designer, KiCad, or Eagle.
  • They generate manufacturing files: Gerber files (for layers, solder mask, silkscreen), drill files (NC Drill), netlists, and BOM if needed.
  • The manufacturer performs a Design for Manufacturability (DFM) check to catch issues like trace widths, clearances, or via sizes.
  • It moves directly into fabrication flow

2. Film Generation / Imaging Preparation

  • A plotter creates photo films (or uses direct laser imaging in modern processes) from the Gerber files.
  • These films act as masks: black areas block UV light, clear areas allow it (patterns reverse for outer vs. inner layers).

3. Inner Layer Printing (for Multilayer PCBs)

  • Start with copper-clad laminate (core: fiberglass + epoxy with copper foil on both sides).
  • Apply photoresist (light-sensitive film) to the copper.
  • Align the photo film and expose to UV light: light hardens the photoresist where copper traces should remain.
  • Develop: wash away unhardened photoresist with alkaline solution, exposing unwanted copper.

4. Etching Inner Layers

  • Chemical etching (e.g., using alkaline or acidic solutions) removes exposed copper.
  • Strip remaining photoresist, leaving only the desired copper traces on inner layers.

5. Layer Alignment, Optical Inspection (AOI), and Oxide Treatment

  • Inspect inner layers automatically (AOI) against the original design for defects.
  • Apply oxide or black oxide treatment to inner layers for better bonding in lamination.

6. Lamination (Layer Bonding)

  • Stack inner layers with prepreg (pre-impregnated fiberglass sheets) and outer copper foils.
  • Use heat and high pressure in a hydraulic press to bond everything into a solid multilayer panel.

7. Drilling

  • Drill holes for through-hole components, vias (connections between layers), and mounting.
  • Use CNC machines with precise drill bits. X-ray may locate inner features for accuracy.
  • Distinguishes plated through-holes (PTH) from non-plated.

Engineering Control

  • Ask what cores/prepreg are stocked
  • Choose common dielectric thicknesses
  • Stay with standard 1 oz outer copper
  • Material availability can add days before fabrication even begins.

8. Electroless Copper Plating / Through-Hole Plating

  • Deposit a thin layer of copper chemically inside drilled holes to make them conductive (connecting layers).
  • Follow with electroplating to thicken the copper.

9. Outer Layer Imaging and Plating

  • Similar to inner layers: apply photoresist, image with UV through outer layer films, develop.
  • Electroplate additional copper (and often tin) on exposed areas for protection.

10. Outer Layer Etching and Stripping

  • Etch away unwanted outer copper.
  • Strip the photoresist and tin (if used as etch resist).

11. Solder Mask Application

  • Clean the board and apply epoxy solder mask ink (green, usually).
  • Expose with UV through a solder mask film to cure the mask over non-solder areas.
  • Develop and cure in an oven. This prevents shorts and protects traces.

12. Silkscreen (Legend Printing)

  • Print component labels, polarity marks, logos, etc., using ink-jet or screen printing.
  • Cure the ink.

13. Surface Finish

Apply a protective coating on exposed copper pads for solderability and corrosion resistance. Common options:
  • HASL (Hot Air Solder Leveling)
  • ENIG (Electroless Nickel Immersion Gold)
  • OSP, Immersion Silver, etc.

14. Electrical Testing

  • Use flying probe or bed-of-nails testers to verify continuity and isolation on every net.
  • Ensures no shorts or opens.

15. Profiling / Routing and V-Scoring

  • Cut individual boards from the panel using CNC routers or V-grooves.
  • Add any edge bevels or slots.

16. Final Inspection, Cleaning, and Packaging

  • Visual and automated optical inspection.
  • Clean, pack (often with desiccant), and ship.

Key Notes:

  • Single/Double-sided boards skip many multilayer steps (no inner layer lamination).
  • Modern factories use automation, laser direct imaging (LDI) instead of films for higher precision, and cleanroom environments.
  • The entire process for a standard multilayer board can take days, depending on complexity and queue.
  • Tolerances are tight (e.g., trace widths down to microns in advanced boards), so DFM is critical.
  • This process turns your digital design into reliable hardware. For prototypes, quick-turn services like JLCPCB or PCBWay handle small runs efficiently. If you're designing one, always run a DFM check before ordering!