Electronic Design Systems
Printed Circuitry Page

Welcome to the Electronic Design Systems Printed Circuitry Section. Printed circuitry can be as simple as "Printed Wiring" (which is the trade name for a Printed Circuit Board). - where copper traces are laid into a panel, or flexible plastic strip to just interconnect two or more devices. This takes the place of traditional point to pint wiring (a car dash board is an excellent example - instead of individual sets of wires to interconnect all the lamps, guages, and awrning lamps - they have flexible "printed circuit wiring".

Printed circuits can be a) Flexible, or b) Ridgid. They can be 1) single sides (copper traces on only one side), two sided (copper traces on top and bottom surfaces on the PCB), or "Multi-Level (where you can have three-four-five-six-seven, or many layers all bonded into a seemingly "single" board. A good example is the Computer Motherbaord in you Mac or PC.

Printed circuit boards are made by laminating copper sheets onto a phenolic ot fiberglass base. While this is "over simplification" it is intended to make a "basic point". A single sided PCB would have copper on one side, an double layer board would have copper on "both" sides. These boards are made into circuits by etching away the undersirable copper using an acid. Naturally, they areas desired need to be drawn using a resist paint/coating. The resist is an ink type coating that can be drawn directly onto the board blanks, or deposited using screen press printing (most common and economical), or using a Mask (a circuit pattern that is laid onto a clear sheet. The mask or "positive" is used in a photo resist system where a circuit board is coated with a chemical that reacts to light. When exposed to light it will change its properties and either bond to the copper (forming an acid resistant coating), or remain unboded. The photo mask is placed over the synthesized blank, and then exposed to UV Light. Then the exposed board is developed whre the photo magic takes place. The areas exposed to the light do not hold their acid resistant coatings (hence the name resist - resists acid). The PC Board blank can now be placed into an acid bath (called an etcher) where the undesired copper is eaten away. This leaves a circuit or series of copper traces that carry the voltages, signals, pulses, etc, and provides a graound or common point to make the intended circuits complete.

In small prototyping, some Printed Circuit Board are produced my milling away the undesired copper to form the required traces that are intended to provide interconnects for the circuit components. This is an expensive, but fast process. Fast is the key feature when prototyping. This allows you to see mistakes and correct them quickly before you make hundreds or millions of copies of un-useable boards.