Printed Circuit Board (PCB) Etching

The process of manufacturing the Printed Circuit Board laminate is handled by subcontractors. It is messy, time consuming, needs hundreds of square meters of space and few companies integrate it into their manufacturing process. It is a very interesting process to watch (well, if you enjoy visiting factories...) - we have some photos of an older PCB manufacturing plant. We outline the steps in the process below.

Offshore vs. Made in Australia

We buy some PCBs in Australia, and have some PCBs made offshore. An Australian company offers you dependable quality and delivery, and they value your business. To an offshore manufacturer your order will seem small, but the work will be cheap. Unfortunately, going offshore is the trend. If you make a list of PCB manufacturers in Australia, there are only a couple that don't send at least some of their work offshore. Out of that list, only a handful are real manufacturers and even have the capability to manufacture in Australia - the rest are sales agents sending the work to China.
It does surprise me a little. It costs $60 an hour to employ the technician that installs, configures or services specialist electronics - and $120 an hour if you want him subcontract, without sick pay etc. Yet for the board inside the product that this guy installs, we send it offshore to gain a difference in price of $1.80 vs $6 a PCB (in volume). It is strategically irrepsonsible, But that is the way things are.

The PTH Printed Circuit board manufacturing process.

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

The future - 3D printing?

An idea put forward recently is that PCB manufacture will be replaced by 3D printing. My opinion is that the scale of the task is wrong for this to happen in the near future. Right now the price of PCB manufacture for double sided work (offshore) is trending towards about $80 per square metre even in moderately small volumes. That is for a circuit board that has geometries of 8mil x 8 mil or less, thousands of holes, thru-hole vias, routing, soldermask, overlay.

We saw the advent of robotic assembly for surface mount (pick and place), but it is my opinion that traditional plate and etch lines will stay the standard production method for PCBs for some time to come - with the exposure and screen print steps becoming more automated - and so, more flexible. As a side note I would add that existing PCB milling is an alternative way to produce prototypes, although without PTH holes, and it is on the same individual scale as 3D printing - giving it a certain adventurous appeal.

©2013 AirBorn - Last updated 27 April 2013