In electronics, printed circuit boards, or PCBs, are utilized 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 element leads in thru-hole applications. A board style may have all thru-hole components on the leading or element side, a mix of thru-hole and surface area install on the top side only, a mix of thru-hole and surface area mount components on the top side and surface area install elements on the bottom or circuit side, or surface area mount components on the top and bottom sides of the board.
The boards are also utilized to electrically connect the needed leads for each element using conductive copper traces. The part 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 only, 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 etched away to form the real copper pads and connection traces on the board surfaces as part of the board production process. A multilayer board includes a number of layers of dielectric material that has actually been fertilized with adhesives, and these layers are utilized to separate the layers of copper plating. All of these layers are aligned then 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 utilized to supply 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 leading and bottom layers of the board. Very complicated board styles might have a a great deal of layers to make the numerous connections for various voltage levels, ground connections, or for linking the numerous leads on ball grid selection devices and other big integrated circuit plan formats.
There are normally 2 kinds of product used to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet form, normally about.002 inches thick. Core material is similar to a really thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, generally.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two approaches utilized to develop the wanted variety of layers. The core stack-up method, which is an older innovation, uses a center layer of pre-preg product with a layer of core product above and another layer of core product below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The film stack-up technique, a more recent innovation, 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 variety of layers needed by the board style, sort of like Dagwood constructing a sandwich. This approach permits the manufacturer flexibility in how the board layer densities are combined to fulfill the finished product density requirements by differing the number of ISO 9001 sheets of pre-preg in each layer. When the product 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 listed below for many applications.
The process of identifying materials, processes, and requirements to fulfill the customer's specifications for the board design based on the Gerber file details provided with the order.
The procedure of moving the Gerber file data for a layer onto an etch resist film that is placed on the conductive copper layer.
The conventional process of exposing the copper and other areas unprotected by the etch withstand movie to a chemical that eliminates the unguarded copper, leaving the secured copper pads and traces in place; newer procedures use plasma/laser etching rather of chemicals to get rid of the copper product, permitting finer line meanings.
The procedure of aligning the conductive copper and insulating dielectric layers and pressing them under heat to activate the adhesive in the dielectric layers to form a strong board product.
The process of drilling all of the holes for plated through applications; a second drilling process is utilized for holes that are not to be plated through. Information on hole area and size is included in the drill drawing file.
The process of applying 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 location but the hole is not to be plated through. Avoid this procedure if possible because it adds cost to the finished board.
The process 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 safeguards against ecological damage, supplies insulation, secures versus solder shorts, and secures traces that run between pads.
The procedure of finish the pad areas with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering procedure that will happen at a later date after the components have been positioned.
The procedure of using the markings for part classifications and part outlines to the board. May be used to simply the top or to both sides if elements are installed on both leading and bottom sides.
The procedure of separating several boards from a panel of identical boards; this procedure also enables cutting notches or slots into the board if required.
A visual examination of the boards; also can be the process of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The procedure of looking for continuity or shorted connections on the boards by ways applying a voltage between different points on the board and figuring out if an existing flow happens. Depending upon the board intricacy, this procedure might need a specially designed test fixture and test program to incorporate with the electrical test system utilized by the board manufacturer.