In electronics, printed circuit boards, or PCBs, are used to mechanically support electronic components which have their connection leads soldered onto copper pads in surface install applications or through rilled holes in the board and copper pads for soldering the part leads in thru-hole applications. A board style may have all thru-hole components on the leading or component side, a mix of thru-hole and surface mount on the top side only, a mix of thru-hole and surface install components on the top and surface area install elements on the bottom or circuit side, or surface mount elements on the leading and bottom sides of the board.
The boards are also used to electrically link the required leads for each element using conductive copper traces. The component pads and connection traces are engraved from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are designed as single sided with copper pads and traces on one side of the board just, double sided with copper pads and traces on the top 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 consist of a core dielectric material, such as FR-4 epoxy fiberglass, with copper plating on one or both sides. This copper plating is engraved away to form the real copper pads and connection traces on the board surface areas as part of the board production procedure. A multilayer board includes a number of layers of dielectric material 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 then bonded into a single board structure under heat and pressure. Multilayer boards with 48 or more layers can be produced with today's technologies.
In a common 4 layer board design, the internal layers are frequently used to provide power and ground connections, such as a +5 V airplane layer and a Ground airplane layer as the two internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Very complex board designs might have a a great deal of layers to make the different connections for different voltage levels, ground connections, or for linking the numerous leads on ball grid array devices and other big integrated circuit package formats.
There are generally 2 types of material utilized to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet kind, usually about.002 inches thick. Core product is similar to an extremely thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, generally.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are two methods utilized to build up the preferred variety of layers. The core stack-up method, which is an older innovation, utilizes a center layer of pre-preg product with a layer of core product above and another layer of core material below. This combination of one pre-preg layer and 2 core layers would make a 4 layer board.
The film stack-up technique, a newer technology, would have core product as the center layer followed by layers of pre-preg and copper product built up above and listed below to form the last variety of layers required by the board style, sort of like Dagwood building a sandwich. This technique permits the manufacturer flexibility in how the board layer densities are combined to meet the finished item density requirements by differing the variety of sheets of pre-preg in each layer. Once the material layers are finished, the entire stack undergoes heat and pressure that causes the adhesive in the pre-preg to bond the core and pre-preg layers together into a single entity.
The process of making printed circuit boards follows the actions below for the majority of applications.
The procedure of figuring out materials, processes, and requirements to satisfy the customer's requirements for the board style based upon the Gerber file info supplied with the purchase order.
The procedure of moving the Gerber file information for a layer onto an etch resist movie that is put on the conductive copper layer.
The traditional procedure of exposing the copper and other areas unprotected by the etch withstand movie to a chemical that eliminates the unprotected copper, leaving the protected copper pads and traces in location; more recent processes utilize plasma/laser etching rather of chemicals to get rid of the copper product, permitting finer line definitions.
The process of aligning the conductive copper and insulating dielectric layers and pressing them under heat to trigger the adhesive in the dielectric layers to form a solid board product.
The procedure of drilling all the holes for plated through applications; a 2nd drilling process is used for holes that are not to be plated through. Info on hole location and size is contained 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 positioned in an electrically charged bath of copper.
This is needed when holes are to be drilled through a copper area however the hole is not to be plated through. Avoid this process if possible since it includes expense to the ended up board.
The procedure of applying a protective masking material, 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 versus environmental damage, provides insulation, safeguards against solder shorts, and protects traces that run in 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 take place at a later date after the parts have been placed.
The procedure of using the markings for component classifications and element details to the board. Might be used to simply the top or to both sides if components are installed on both top and bottom sides.
The procedure of separating multiple boards from a panel of identical boards; this procedure likewise allows cutting notches or slots into the board if needed.
A visual assessment of the boards; likewise can be the process of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The process of checking for connection or shorted connections on the boards by means using a voltage in between numerous points on the board and figuring out if a current flow occurs. Depending upon the board intricacy, this procedure might need a specially created test component and test program to incorporate with the electrical test system used by the board manufacturer.