In electronics, printed circuit boards, or PCBs, are utilized to mechanically support electronic parts which have their connection leads soldered onto copper pads in surface area mount applications or through rilled holes in the board and copper pads for soldering the element leads in thru-hole applications. A board design might have all thru-hole parts on the top or component side, a mix of thru-hole and surface area mount on the top only, a mix of thru-hole and surface install parts on the top side and surface install elements on the bottom or circuit side, or surface mount elements on the leading and bottom sides of the board.
The boards are likewise used to electrically connect the needed leads for each element using conductive copper traces. The part pads and connection traces are etched from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are created as single sided with copper pads and traces on one side of the board just, double sided with copper pads and traces on the leading and bottom sides of the board, or multilayer designs with copper pads and traces on the top and bottom of board with a variable number of internal copper layers with traces and connections.
Single or double sided boards include a core dielectric material, such as FR-4 epoxy fiberglass, with copper plating on one or both sides. This copper plating is etched away to form the actual copper pads and connection traces on the board surface areas as part of the board manufacturing procedure. A multilayer board consists of a variety of layers of dielectric product that has been fertilized with adhesives, and these layers are used to separate the layers of copper plating. All these layers are lined up and after that bonded into a single board structure under heat and pressure. Multilayer boards with 48 or more layers can be produced with today's innovations.
In a normal 4 layer board style, the internal layers are frequently used to provide power and ground connections, such as a +5 V aircraft layer and a Ground aircraft layer as the 2 internal layers, with all other circuit and component connections made on the top and bottom layers of the board. Extremely intricate board designs might have a large number of layers to make the various connections for different voltage levels, ground connections, or for linking the numerous leads on ball grid variety devices and other big integrated circuit package formats.
There are usually 2 kinds of product utilized to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, normally about.002 inches thick. Core product is similar to a very thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, usually.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are two methods utilized to build up the wanted number of layers. The core stack-up technique, which is an older innovation, utilizes a center layer of pre-preg product with a layer of core material above and another layer of core material below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The film stack-up method, a more recent technology, would have core material as the center layer followed by layers of pre-preg and copper material built up above and below to form the last number of layers required by the board design, sort of like Dagwood building a sandwich. This approach permits the manufacturer versatility in how the board layer thicknesses are combined to fulfill the completed item thickness requirements by differing the number of sheets of pre-preg in each layer. Once the material layers are finished, the whole stack is subjected to heat and pressure that triggers the adhesive in the pre-preg to bond the core and pre-preg layers together into a single entity.
The process of manufacturing printed circuit boards follows the actions listed below for the majority of applications.
The procedure of identifying products, processes, and requirements to meet the consumer's requirements for the board style based upon the Gerber file info supplied with the purchase order.
The process of transferring the Gerber file data for a layer onto an etch resist film that is placed on the conductive copper layer.
The traditional procedure of ISO 9001 exposing the copper and other areas unprotected by the etch resist film to a chemical that gets rid of the unprotected copper, leaving the secured copper pads and traces in place; newer procedures use plasma/laser etching instead of chemicals to get rid of the copper product, enabling finer line definitions.
The procedure of lining up the conductive copper and insulating dielectric layers and pushing them under heat to activate the adhesive in the dielectric layers to form a strong board material.
The procedure of drilling all the holes for plated through applications; a second drilling procedure is utilized for holes that are not to be plated through. Details on hole area and size is consisted of in the drill drawing file.
The process of using copper plating to the pads, traces, and drilled through holes that are to be plated through; boards are placed in an electrically charged bath of copper.
This is needed when holes are to be drilled through a copper location but the hole is not to be plated through. Prevent this process if possible due to the fact that it adds expense to the finished board.
The procedure of applying a protective masking product, a solder mask, over the bare copper traces or over the copper that has had a thin layer of solder applied; the solder mask protects against ecological damage, offers insulation, protects against solder shorts, and safeguards traces that run between pads.
The procedure of covering the pad locations with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will happen at a later date after the components have actually been positioned.
The procedure of using the markings for component classifications and part outlines to the board. Might be applied to simply the top side or to both sides if parts are installed on both leading and bottom sides.
The procedure of separating several boards from a panel of identical boards; this process also enables cutting notches or slots into the board if required.
A visual inspection of the boards; likewise can be the procedure of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The procedure of checking for continuity or shorted connections on the boards by methods applying a voltage between numerous points on the board and identifying if an existing circulation takes place. Relying on the board intricacy, this process might need a specially developed test fixture and test program to incorporate with the electrical test system used by the board maker.