Manufacturing Process Flowchart

Pre-Clean and Imaging Resist Coat

  • Copper laminate surface is mechanically and chemically pre-cleaned
  • Resist or dry film is a photo-imageable polymer which is hot-rolled onto the top and bottom of the copper core
  • Protective sheet attached to the resist is called mylar

CCL (Copper-Clad Laminate) “core”

Inner Layer Image Print

  • Negative polarity artwork film is placed on both sides of the resist-coated cores
  • Core is then exposed to UV light on both sides
  • Resist in the exposed areas is hardened (polymerized)
  • Newer Laser Direct Imaging (LDI) technology uses CAM files projected on the panel with UV light instead of artwork film

Develop Etch Strip (DES)


  • Protective mylar sheet is removed
  • Boards processed through a three-part conveyorized flood-chamber chemical line
  • Develop - Unexposed resist is removed exposing bare copper
  • Etch - Unwanted copper is etched away (subtractive process)
  • Strip – Protective (exposed) resist is stripped away from copper image

Post Etch Punch (PEP)

  • PEP is a crucial manufacturing step in inner layer to drill registration
  • Etched targets in the border files are lined up in an optical machine
  • Machine finds “best fit” of target values
  • Punches holes or slots are used to align layers with hard tooling pins in future process steps

Automated Optical Inspection (AOI)

  • AOI is the inner layer inspection process
  • Boards are inspected against an optical machine against the known CAM files and reports discrepancies
  • Technicians validate defects and rework if possible
  • Non-conforming cores can be scrapped and restarted with minimal added build cost

Oxide

  • The copper surfaces are micro-roughened in preparation for multilayer lamination
  • Copper roughening is needed to enhance the bond between the oxidized copper and the prepreg (B stage) layers
  • Most PCB factories use black oxide but there are other formulations

Lamination (Press)

  • Foil, etched cores, and prepregs (B-stage) are layered on pins using the PEP slots according to the stackup to form one manufacturing panel
  • Multiple panels are stacked together (separated by aluminum release sheets) into a “book”
  • Multiple books are heated above the Tg of the material under vacuum and pressure
  • When the prepreg is heated above the Tg, it “gels”, flows & fills between the Cu features, then glues the layers together as it cools
  • Books are “broken down” into mfg panels and excess prepreg squeeze out is cleaned up from around panel edges

Drilling

  • After lamination, holes are drilled or lasered in the panel
  • Drill must align to pads already formed at inner layer etching process
  • X-ray or smart drill machines do a registration pre-check to help align the drill
  • Average drill count is 25,000 per mfg panel
  • Boards are passed through an air knife deburr process to clear most of the residual drill debris from the holes
Mechanical Drill

Laser


Electroless Copper

  • All the holes and surfaces are first chemically cleaned to ensure the layer interconnects are clean from any remaining drill debris
  • Hole are also chemically conditioned to activate the exposed glass and resin
  • Hole walls and board surface are then deposited with a thin layer of palladium followed by ~ .07 mil (.00007”) of Electroless Cu
  • Standard processing creates negative etchback at the interconnect post
  • Special glass-etching processing is needed to create positive etchback