In electronic devices, printed circuit boards, or PCBs, are utilized to mechanically support electronic parts 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 design might have all thru-hole components on the top or element side, a mix of thru-hole and surface install on the top only, a mix of thru-hole and surface mount elements on the top side and surface mount parts on the bottom or circuit side, or surface mount components on the top and bottom sides of the board.
The boards are also utilized to electrically link the required leads for each element utilizing conductive copper traces. The part pads and connection traces are etched from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are designed as single agreed 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 styles with copper pads and traces on 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 manufacturing procedure. A multilayer board includes a number of layers of dielectric material that has been impregnated with adhesives, and these layers are used 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 technologies.
In a typical 4 layer board style, the internal layers are frequently used to provide power and ground connections, such as a +5 V plane 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. Really complicated board designs may have a a great deal of layers to make the numerous connections for different voltage levels, ground connections, or for connecting the numerous leads on ball grid variety devices and other large integrated circuit bundle formats.
There are typically 2 types of material used to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet kind, generally about.002 inches thick. Core product resembles a really thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, generally.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are 2 approaches utilized to develop the wanted number of layers. The core stack-up method, which is an older innovation, uses a center layer of pre-preg material with a layer of core material above and another layer of core material listed below. This combination of one pre-preg layer and 2 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 final variety of layers needed by the board style, sort of like Dagwood constructing a sandwich. This method permits the producer flexibility in how the board layer densities are combined to fulfill the completed item thickness requirements by differing the number of sheets of pre-preg in each layer. When the product layers are completed, 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 procedure of manufacturing printed circuit boards follows the actions below for the majority of applications.
The process of determining products, procedures, and requirements to meet the client's specs for the board design based on the Gerber file details supplied with the purchase order.
The procedure of moving the Gerber file information 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 locations unprotected by the etch resist movie to a chemical that removes the unguarded copper, leaving the secured copper pads and traces in place; newer procedures utilize plasma/laser etching rather of chemicals to get rid of the copper product, permitting finer line meanings.
The process of lining up the conductive copper and insulating dielectric layers and pressing them under heat to trigger the adhesive in the dielectric layers to form a strong board product.
The procedure of drilling all of the holes for plated through applications; a 2nd drilling process is used for holes that are not to be plated through. Details on hole area and size is contained in the drill drawing file.
The process of using copper plating to the pads, traces, ISO 9001 Accreditation and drilled through holes that are to be plated through; boards are placed in an electrically charged bath of copper.
This is required when holes are to be drilled through a copper area but the hole is not to be plated through. Avoid this procedure if possible due to the fact that it includes expense to the completed board.
The procedure of using a protective masking product, a solder mask, over the bare copper traces or over the copper that has had a thin layer of solder used; the solder mask protects versus environmental damage, offers insulation, secures against solder shorts, and secures traces that run in between pads.
The process of finish the pad areas with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering process that will happen at a later date after the components have actually been placed.
The process of using the markings for part classifications and component outlines to the board. Might be used to simply the top side or to both sides if parts are installed on both leading and bottom sides.
The process of separating several boards from a panel of similar boards; this procedure also permits cutting notches or slots into the board if needed.
A visual evaluation of the boards; likewise can be the process of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The process of looking for connection or shorted connections on the boards by ways using a voltage in between various points on the board and identifying if an existing circulation happens. Depending upon the board intricacy, this procedure may require a specifically developed test component and test program to integrate with the electrical test system used by the board producer.