The Basics Of Printed Circuit Boards
Computer electronic boards are the foundation of every computer and digital device. They contain a matrix of copper wires and other conductive materials that connect electrical components to each other. Printed circuit boards were developed as the electronics industry moved away from vacuum tubes and relays to silicon and integrated circuits. These were smaller, lighter and cheaper to produce than their predecessors. Previously, electronic devices were wired point-to-point on chassis and assembled by hand with jumper wires or soldered to the leads of small electronics chips or metal parts using crimp connector lugs or screw terminals.
The first PCBs were single-layer, with a layer of copper mounted on a substrate like phenolic cotton paper or epoxy glass. Subsequent developments allowed double-layer and multi-layer boards that could support a much higher density of components, making the computers we use today far more powerful than their predecessors.
PCBs can be fabricated with a wide variety of dielectrics or insulators. Polytetrafluoroethylene (Teflon) is used in high-density and microwave boards, while FR-4 and FR-5 are common insulators for standard electronics. Aluminum is also a good insulator, but can be difficult to work with due to its weight and cost. Boards that need to dissipate heat may be made with a heavy copper layer of more than three ounces per square foot, which allows for more efficient heat transfer.
A PCB can be designed with a graphic program and realized as an empty, green solder resist-coated board or as a fully populated circuit with all the component connections made and etched into the copper layers. The traces are usually labeled with their part numbers and designations, switch settings, test points and other indications necessary for assembling, testing and servicing the unit. The legend is often printed with silkscreen or liquid photo imaging and can vary from a simple schematic diagram to text, bar codes and serial numbers.
After a design is captured on the computer, the manufacturer laminates a layer of copper foil to the base material and draws a wiring pattern with acid-resistant ink. The copper not covered by the ink is etched away, leaving an almost bare circuit board. Drill holes are then placed with a laser for placement of the components.
How do circuit boards work is complete it’s plated with copper to ensure that all conductive paths have the proper conductivity. A final step involves using chemicals to remove the etch resist and the remaining copper. Depending on the type of copper used and the insulating properties of the dielectric, the finished board can be a high-reliability product such as those produced for aerospace or military uses. Alternatively, the boards can be recycled through electrochemical processing or bioleaching. These methods recycle the majority of the metals in the circuit board and can be more environmentally friendly than traditional disposal techniques. For example, electrochemical processing can recover up to ninety percent of the copper, while bioleaching can recycle up to seventy-two percent.