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Printed Circuit Board (PCB) Etching

The process of manufacturing the Printed Circuit Board laminate is handled by a subcontractor. It is a very interesting process to watch (well, if you enjoy seeing factories...) - we have some photos of a PCB manufacturing plant. We outline the steps in the process below.

The PTH Printed Circuit board manufacturing process.

CAD File processing
• The PCB CAD files (or Gerber files) are sent to the manufacturer by email
• The PCB manufacturer has their own pre-production inspection of the files at which they add a drill list and identification
• The CAD files are rasterised and photoplotted to make film artwork

Laminate drilling and electroplating
• The process starts with bare laminate material - usually FR-4
• The laminates, (with copper on both sides, but no pattern yet) are drilled with holes. For reasons of economy, the laminates are larger panels that often contain several PCBs
• The drilled laminates are coated in a chemical to enhance electroplating of holes. This is usually done using a multistep process called electroless copper.
• The laminates are put in a copper plating bath, all the holes are electroplated. This connects pads on opposite sides of the PCB, electrically, through copper in each hole.

Laminate etching
• The laminates are coated with a UV-sensitive photo-resist
• The track pattern is imaged onto each side of each PCB, using the photoplots and UV light
• The photo-resist is developed, leaving photo-resist only where copper is required
• The laminates are put in acid, to etch away unrequired copper, forming the track pattern
• The bare copper PCB, with tracks and pads now finished, is cleaned

Laminate solder masking and tinning
• The bare copper PCB is silkscreened with a solder mask (usually green)
  (Sometimes the solder mask is applied by photoimaging or dry film)
• The solder mask is dried or cured
• The PCB is tinned - solder is applied to exposed pads
• The PCB is levelled - bumps in the solder are made flat by using hot air

Final stages
• The PCB is silkscreened with component Identification lettering (usually white)
• The silkscreen legend is dried or cured
• Any final drilling is done of holes that are not to be plated through, any routing is done, and the laminate is cut into individual printed circuit boards

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PCB Layout Flame Retardant FR-4 PCB Prototyping