The boards are also used to electrically link the needed leads for each component 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 designed as single agreed copper pads and traces on one side of the board just, double agreed copper pads and traces on the leading and bottom sides of the board, or multilayer designs 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 fertilized with adhesives, and these layers are used to separate the layers of copper plating. All 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 normal four layer board style, the internal layers are typically used to offer 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. Extremely complex board styles might have a large number of layers to make the numerous connections for different voltage levels, ground connections, or for linking the lots of leads on ball grid selection devices and other big incorporated circuit package formats.
There are usually 2 types of material used to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, typically about.002 inches thick. Core product resembles an extremely thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, usually.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are two methods used to build up the wanted variety of layers. The core stack-up approach, which is an older technology, utilizes a center layer of pre-preg product with a layer of core material above and another layer of core product below. This mix of one pre-preg layer and two core layers would make a 4 layer board.
The movie stack-up technique, a newer innovation, 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 final number of layers needed by the board style, sort of like Dagwood constructing a sandwich. This method allows the producer flexibility in how the board layer thicknesses are integrated to fulfill the completed item density requirements by differing the variety of sheets of pre-preg in each layer. When the product layers are finished, the entire stack undergoes 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 procedure of producing printed circuit boards follows the steps listed below for many applications.
The process of identifying products, processes, and requirements to fulfill the client's requirements for the board style based upon the Gerber file info provided with the order.
The procedure of moving the Gerber file data for a layer onto an etch resist movie that is put on the conductive copper layer.
The standard procedure of exposing the copper and other areas unprotected by the etch resist movie to a chemical that eliminates Reference site the unguarded copper, leaving the safeguarded copper pads and traces in place; more recent processes use plasma/laser etching rather of chemicals to eliminate the copper material, permitting finer line meanings.
The procedure 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 second drilling process is used for holes that are not to be plated through. Info on hole area and size is included in the drill drawing file.
The procedure of applying 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 required when holes are to be drilled through a copper area but the hole is not to be plated through. Prevent this process if possible since it includes 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 actually had a thin layer of solder applied; the solder mask secures against environmental damage, offers insulation, secures against solder shorts, and secures traces that run in between pads.
The process of finish the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering process that will take place at a later date after the elements have actually been positioned.
The procedure of applying the markings for part designations and component details to the board. Might be applied to just the top side or to both sides if components are mounted on both top and bottom sides.
The process of separating multiple boards from a panel of identical boards; this process also enables cutting notches or slots into the board if needed.
A visual examination of the boards; likewise can be the process of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The process of looking for connection or shorted connections on the boards by means using a voltage between various points on the board and figuring out if a present circulation occurs. Relying on the board intricacy, this process may require a specially created test fixture and test program to integrate with the electrical test system utilized by the board producer.