Techie Talk: Common Methods of PCB Fabrication

Most electronic devices need a PCB (printed circuit board) to support and connect its surface-mounted and socketed components to sophisticated computer systems. This device holds a conductive system of circuits etched or printed onto non-conductive substrates. Creating such a piece involves the process of assembling a substrate, drilling and plating holes, crafting the circuit pattern to be printed on the substrate, mounting the parts, and packaging.

There are a number of methods for PCB fabrication, each with its own pros and cons. The four most commonly known ones are etching, send out, direct plating and copper removal.

Etching

This is the most utilized method of PCB fabrication because, aside from the simplicity of its design, it is also cost-effective. It involves the process of manually removing excess copper from the board with the use of a chemical (either ferric chloride or sodium persulphate etchant). The remaining portion is used to conduct electrical current through the board.

Placing a pattern on the board could be done through any of the following methods:

Manually

It is a simple process of drawing the pattern by hand with the use of waterproof resist pens. Specialty tapes could be used as a guide.

Photographic

Pcb fabricationThe circuit board is initially coated with a thin layer of resist material. An Ultra Violet translucent artwork film is positioned on top of the board and, after being exposed to UV light (with the use of a UV exposure box), is placed into a developer bath. This acts to get rid of the sensitized photoresist; the remainder embodies the circuit. It is capable of producing consistently high quality outputs.

Direct Etch

This makes use of special transfer paper. The laser printer-generated image etched on the transfer paper is ironed onto the circuit board for approximately 2 minutes. Afterwards, the board is submerged in water to dissolve the special coating, leaving the ironed pattern behind.

Silkscreen

A screen, which has been covered by a photo-sensitive material, is developed and exposed before it is positioned beneath a frame. Afterwards, special ink is loaded on top of the setup and is raked through the frame.

The major disadvantage of etching is that it requires a lot of time and effort in creating each PCB.

Send Out

As the name suggests, send out involves the process of sending premade PCB templates to a Board House where it will me professionally manufactured. The template must include assembly sketches, a layout file, and an NC drill file of hole positions.

This method of PCB fabrication is rather slow and very expensive, but it produces high quality outputs. It is therefore recommended for bulk purchases and not for small scale production.

Direct Plating

This is a fully automated method that uses an industrial machine to “directly plate” the board on the track. It is fast and produces the highest quality outputs out of the lot, but is quite costly. It is not recommended for neophyte manufacturers.

Copper Removal

This process requires the use of a cutter plotter – a printer that generates a hard copy of computer-aided designs. To use this, simply install PCB layout software, select the desired outline, and print it out.

The downside to this PCB fabrication method is the speed of production: it is rather sluggish. This should only be used to build prototypes and not the final products.
In selecting the right method to use, consider the budget, number of items to manufacture, and availability of materials or equipment. Do keep in mind that aseptic technique must be used when creating and assembling the board – the environment must be clean and uncontaminated by harmful microorganisms. Dirt only decreases the functionality and reliability of the PCB.