Printed Circuit Board

Printed Circuit Board

Printed Circuit Board

A printed circuit board (PCB) serves as a foundation and mechanical support for electronic components. Non-conductive surfaces, printed circuit boards are also referred to as etched wiring boards and printed wiring boards. After it is populated with conductive pathways, signal traces and electronic components, it is referred to either as a printed circuit board assembly (PCBA) or a printed circuit assembly (PCA).

Printed circuit board assembly is one of several methods of creating circuits, along with wire-wrapped circuits and point-to-point circuits. PCB assemblies tend to require greater effort for layout and a higher initial cost than the other available options, but they are more cost-effective over time and offer greater reliability. After initial costs associated with the circuit board design, printed circuit board manufacturing is cheaper and also offers quicker high-volume production.

The materials used in manufacturing printed circuit board (PCB) assemblies can vary depending on how they will be used. Typically, the conducting layers in the printed circuit board assembly are made of a thin copper foil, and the dielectric insulating layers are laminated together using epoxy resin. Often, what is known as a blank PCB is created when the substrate is completely covered on one or both sides by a copper-bonding layer. A temporary mask is applied, allowing any unwanted copper to be removed by way of pattern etching.

In some printed circuit board construction, traces are added to rather than removed from the substrate. This typically is done through electroplating. The chosen manufacturing method for a printed circuit board will vary depending on whether the PCB is a one-off or must be reproduced in large quantities.

Photographic printing and silk-screen printing are the most common methods of etching printed circuit board assemblies for commercial purposes. Photoengraving relies on a photo mask and a chemical process to remove unwanted copper. Etching processes typically use ammonium persulfate, ferric chloride or hydrochloric acid to eat away unwanted layers of copper. Silk-screen printing relies on inks that are etch resistant, protecting the underlying copper foil so that only the unwanted copper is etched away. Another option is PCB milling, which requires a special machine to remove the copper.

There are different types of dielectrics available, including composite epoxy material (CEM) and flame-retardant (FR) material, and each provides a different insulating value depending on the circuitry requirements. Teflon, FR-1, FR-4, CEM-1 and CEM-3 are some examples of dielectrics. Materials commonly used in PCB construction include phenolic cotton paper (FR-2), cotton paper with epoxy (FR-3 and CEM-1), woven glass with epoxy (FR-4) and matte glass with polyester (FR-6).

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