In electronics, printed circuit boards, or PCBs, are utilized to mechanically support electronic elements 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 part leads in thru-hole applications. A board style may have all thru-hole elements on the top or element side, a mix of thru-hole and surface area install on the top only, a mix of thru-hole and surface mount components on the top and surface mount parts on the bottom or circuit side, or surface area install parts on the leading and bottom sides of the board.
The boards are also utilized to electrically link the needed leads for each element utilizing conductive copper traces. The part pads and connection traces are engraved from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are created as single agreed copper pads and traces on one side of the board only, double sided with copper pads and traces on the leading and bottom sides of the board, or multilayer styles with copper pads and traces on top and bottom of board with a variable variety of internal copper layers with traces and connections.
Single or double sided boards consist of a core dielectric product, 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 surfaces as part of the board manufacturing process. A multilayer board consists of a number of layers of dielectric material that has been impregnated with adhesives, and these layers are utilized to separate the layers of copper plating. All these layers are aligned 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 technologies.
In a typical 4 layer board style, the internal layers are typically utilized to provide power and ground connections, such as a +5 V airplane layer and a Ground aircraft layer as the two internal layers, with all other circuit and part connections made on the top and bottom layers of the board. Extremely complicated board styles might have a large number of layers to make the numerous connections for various voltage levels, ground connections, or for linking the lots of leads on ball grid variety devices and other large incorporated circuit bundle formats.
There are usually two kinds of product utilized to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, normally about.002 inches thick. Core material resembles a really thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, typically.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are 2 approaches used to build up the desired number of layers. The core stack-up method, which is an older technology, uses a center layer of pre-preg product with a layer of core product above and another layer of core product listed below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The movie stack-up technique, a newer technology, would have core material as the center layer followed by layers of pre-preg and copper material built up above and listed below to form the final variety of layers needed by the board design, sort of like Dagwood constructing a sandwich. This method permits the maker flexibility in how the board layer thicknesses are combined to fulfill the ended up item density requirements by varying the number of sheets of pre-preg in each layer. As soon as the material layers are completed, the whole 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 procedure of producing printed circuit boards follows the steps listed below for most applications.
The procedure of identifying products, procedures, and requirements to satisfy the client's specifications for the board style based upon the Gerber file information provided 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 standard procedure of exposing the copper and other areas unprotected by the etch withstand movie to a chemical that removes the vulnerable copper, leaving the secured copper pads and traces in location; more recent processes utilize plasma/laser etching rather of chemicals to eliminate the copper material, allowing finer line meanings.
The procedure of aligning the conductive copper and insulating dielectric layers and pushing them under heat to activate the adhesive in the dielectric layers to form a solid board material.
The procedure of drilling all the holes for plated through applications; a 2nd drilling process is utilized for holes that are not to be plated through. Details on hole place 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 placed in an electrically charged bath of copper.
This is needed when holes are to be drilled through a copper location however the hole is not to be plated through. Avoid this procedure if possible because it adds cost to the completed board.
The process 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 against ecological damage, provides insulation, safeguards versus solder shorts, and safeguards traces that run in between pads.
The procedure of coating the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering process that will take place at a later date after the components have actually been put.
The procedure of applying the markings for component classifications and part outlines to the board. May be applied to simply the top side or to both sides if components are installed on both leading and bottom sides.
The procedure of separating several boards from a panel of identical boards; this procedure likewise allows cutting notches or slots into the board if required.
A visual evaluation of the boards; also can be the procedure of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The procedure of looking for connection or shorted connections on the boards by methods applying a voltage between different points on the board and figuring out if a present circulation happens. Depending upon the board complexity, this process might need a specifically designed test component and test program to incorporate with the electrical test system utilized by the board manufacturer.