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 mount applications or through rilled holes in the board and copper pads for soldering the element leads in thru-hole applications. A board design may have all thru-hole components on the top or element side, a mix of thru-hole and surface area mount on the top side only, a mix of thru-hole and surface area mount components on the top side and surface install elements on the bottom or circuit side, or surface mount elements on the top and bottom sides of the board.
The boards are also utilized to electrically connect the needed leads for each component 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 created as single sided with copper pads and traces on one side of the board just, double sided with copper pads and traces on the leading and bottom sides of the board, or multilayer designs with copper pads and traces on the 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 surface areas as part of the board manufacturing process. A multilayer board includes a variety of layers of dielectric product 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 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 common 4 layer board style, the internal layers are frequently used to offer power and ground connections, such as a +5 V aircraft layer and a Ground plane layer as the 2 internal layers, with all other circuit and element connections made on the top and bottom layers of the board. Extremely complex board styles might have a a great deal of layers to make the numerous connections for different voltage levels, ground connections, or for linking the many leads on ball grid selection devices and other large incorporated circuit plan formats.
There are generally 2 types of ISO 9001 product utilized to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet form, generally 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, normally.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are 2 techniques utilized to build up the desired number of layers. The core stack-up approach, which is an older innovation, uses a center layer of pre-preg material with a layer of core product above and another layer of core product below. This mix of one pre-preg layer and 2 core layers would make a 4 layer board.
The film stack-up method, a more recent technology, 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 design, sort of like Dagwood constructing a sandwich. This method allows the manufacturer versatility in how the board layer densities are combined to fulfill the completed product thickness requirements by varying the variety of sheets of pre-preg in each layer. When the material layers are completed, the entire stack goes through 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 steps listed below for the majority of applications.
The procedure of identifying products, processes, and requirements to fulfill the customer's requirements for the board style based upon the Gerber file information provided with the order.
The procedure of transferring the Gerber file data for a layer onto an etch resist movie that is placed on the conductive copper layer.
The traditional process of exposing the copper and other locations unprotected by the etch resist film to a chemical that gets rid of the unprotected copper, leaving the secured copper pads and traces in place; newer processes utilize plasma/laser etching rather of chemicals to eliminate the copper product, allowing finer line definitions.
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 solid board product.
The procedure 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. Info on hole location and size is contained 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. Prevent this process if possible due to the fact that it includes cost to the finished board.
The procedure 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 versus environmental damage, supplies insulation, safeguards against solder shorts, and protects traces that run between pads.
The process 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 components have actually been put.
The procedure of using the markings for element designations and element outlines to the board. May be applied to simply the top or to both sides if parts are mounted on both top and bottom sides.
The procedure of separating several boards from a panel of similar boards; this process also enables cutting notches or slots into the board if required.
A visual inspection of the boards; also can be the process of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The procedure of looking for connection or shorted connections on the boards by means applying a voltage between numerous points on the board and figuring out if an existing flow occurs. Relying on the board intricacy, this process may require a specifically developed test component and test program to incorporate with the electrical test system used by the board manufacturer.