A printed circuit board, or PCB, is the support that electrically connects and mechanically holds the components of an electronic board. It consists of an insulating substrate, most often a glass-fibre cloth impregnated with epoxy resin (FR-4), on which copper tracks are etched. A solder mask, often green, protects the tracks and leaves free only the areas to be soldered, and a silkscreen prints the markings. Once the components are soldered, we speak of an assembled board (PCBA): see SMT assembly.
A distinction is made between single-sided, double-sided and multilayer boards, the latter stacking several copper layers connected by plated holes, the vias, which may be through, blind or buried. The usual final thickness is 1.6 mm and the copper is 35 µm (1 oz) as standard. The surface finish of the pads, such as HASL (tin-lead or lead-free), ENIG (electroless nickel immersion gold) or OSP (organic protection), influences solderability, flatness and price. There are also flexible circuits, aluminium-based boards to dissipate the heat of LEDs and substrates for high frequencies.
Manufacture starts from the files produced by electronic CAD: Gerber files, one layer per file, a drill file (Excellon) and a fabrication drawing specifying the stack-up, thickness and finish. The quality level is often expressed in IPC classes (1, 2 or 3, class 3 corresponding to high-reliability applications), defined notably by IPC-6012 for rigid boards. An electrical test, with flying probe or bed of nails, checks for the absence of open and short circuits.
In a quote request
Supply the complete Gerber and drill files, the number of layers, the thickness of the board and the copper, the finish, the solder mask colour, the format and quantity, the IPC class expected and the type of test. Say whether panelisation is up to you and whether the same workshop is to assemble the components. See the guide making an electronic prototype and the electronics workshops.