Printed circuit boards (PCBs) are the boards that are used as the base in most electronics – both as a physical support piece and as the wiring area for the surface-mounted and socketed components.
fiberglass, composite epoxy, or another composite material are the material for making PCBs.
Most PCBs for simple electronics is simple and has only a single layer.
More sophisticated hardware such as computer graphics cards or motherboards can have multiple layers, sometimes up to twelve.
Electronic components are typically placed by machine onto a finished PCB that has solder dabs in place. The PCB bakes in an industrial oven to melt the solder, which joins the connections.
PCBs can be single-layer for simple electronic devices.
Printed circuit boards for complex hardware, such as computer graphics cards and motherboards, may have up to twelve layers.
PCBs are most often green but they can come in any color.
Other methods of PCB manufacturing include silk-screening and CNC-milling.
When the board has no embedded components it is more correctly called a printed wiring board (PWB) or etched wiring board.
However, the term printed wiring board has fallen into disuse. A PCB populated with electronic components is called a printed circuit assembly (PCA), printed circuit board assembly or PCB assembly (PCBA).
The IPC preferred term for assembled boards is the circuit card assembly (CCA), and for assembled backplanes, it is backplane assemblies.
The term PCB is used informally both for bare and assembled boards.
Initially, PCBs were designed manually by creating a photomask on a clear mylar sheet, usually at two or four times the true size. Starting from the schematic diagram the component pin pads were laid out on the mylar and then traces were routed to connect the pads.
Rub-on dry transfers of common component footprints increased efficiency. Traces were made with self-adhesive tape.
Pre-printed non-reproducing grids on the mylar assisted in the layout.
PCB – Printed Circuit Board solderless
To fabricate the board, the finished photomask was photolithographically reproduced onto a photoresist coating on the blank copper-clad boards.
Modern PCBs are designed with dedicated layout software, generally in the following steps:
Schematic capture through an electronic design automation (EDA) tool.
Card dimensions and template are decided based on required circuitry and case of the PCB.
The positions of the components and heat sinks are determined.
Layer stack of the PCB is decided, with one to tens of layers depending on complexity. Ground and power planes are decided. A power plane is the counterpart to a ground plane and behaves as an AC signal ground while providing DC power to the circuits mounted on the PCB. Signal interconnections are traced on signal planes. Signal planes can be on the outer as well as inner layers. For optimal EMI performance, high frequency signals are routed in internal layers between power or ground planes.
Line impedance is determined using dielectric layer thickness, routing copper thickness and trace-width. Trace separation is also considered in case of differential signals. Microstrip, stripline or dual stripline can be used to route signals.
With Components, Thermal considerations and geometry are taken into account.
It marks Vias and lands.
It routes single traces.
Electronic design automation tools usually create clearances and connections in power and ground planes automatically.