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,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 arelarger 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.
- 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 or plated – solder, silver or gold is applied to exposed pads
- The PCB is levelled – bumps in the solder are made flat by using hot air
- 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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