PCB Fabrication Process

The PCB fabrication process is an essential element of the electronics production lifecycle. PCB manufacturing employs many new areas of technology and this has enabled significant improvements to be made both in the reduction of sizes of components and tracks used, and in the reliability of the boards.

A PCB consists of a conducting layer that is made up of thin copper foil. The insulating layer di-electric is laminated together with epoxy resin prepreg. The most commonly used PCB type is the FR-4. Boards may be single sided or double sided. Double sided PCB can be used to connect electronic components on both sides through through-hole plating. This is done by copper plating the walls of each hole so as to connect the conductive layers of the PCB.

Typical Flow Chart For Single Sided Boards

PCB fabrication process

Basic PCB fabrication process

  • With the bare PCB boards chosen and available the next step is to create the required tracks on the board and remove the unwanted copper. The manufacture of the PCBs is normally achieved using a chemical etching process. The most common form of etch used with PCBs is ferric chloride.

  • In order to gain the correct pattern of tracks, a photographic process is used. Typically the copper on the bare printed circuit boards is covered with a thin layer of photo-resist. It is then exposed to light through a photographic film or photo-mask detailing the tracks required. In this way the image of the tracks is passed onto the photo-resist. With this complete, the photo-resist is placed in a developer so that only those areas of the board where tracks are needed are covered in the resist.

  • The next stage in the process is to place the printed circuit boards into the ferric chloride to etch the areas where no track or copper is required. Knowing the concentration of the ferric chloride and the thickness of the copper on the board, it is placed into the etch froth e required amount of time. If the printed circuit boards are placed in the etch for too long, then some definition is lost as the ferric chloride will tend to undercut the photo-resist.

  • Although most PCB boards are manufacturing using photographic processing, other methods are also available. One is to use a specialised highly accurate milling machine. The machine is then controlled to mill away the copper in those areas where the copper is not required. The control is obviously automated and driven from files generated by the PCB design software. This form of PCB manufacture is not suitable for large quantity but it is an ideal option in many instances where very small quantities of a PCB prototype quantities are needed.

  • Another method that is sometimes used for a PCB prototype is to print etch resistant inks onto the PCB using a silk screening process.

 

Drilling printed circuit boards

Electroless copper deposition

Image the outer layers

Plating

Etch outer layers

Apply soldermask

RoHS-compliant surface finishes – electroless gold over nickel

Plated gold edge connectors

Silk-screen and cure

Electrical test

Profiling -V-cut scoring

Final inspection


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