In electronics, printed circuit boards, or PCBs, are used to mechanically support electronic components 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 element leads in thru-hole applications. A board style might have all thru-hole parts 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 elements on the bottom or circuit side, or surface area install components on the top and bottom sides of the board.
The boards are also used to electrically connect the needed leads for each element utilizing conductive copper traces. The component pads and connection traces are etched from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are developed as single agreed copper pads and traces on one side of the board only, double agreed 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 product, such as FR-4 epoxy fiberglass, with copper plating on one or both sides. This copper plating is engraved 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 consists of a number of layers of dielectric product that has actually 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 innovations.
In a typical four layer board design, the internal layers are often 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 top and bottom layers of the board. Extremely intricate board designs might have a a great deal of layers to make the different connections for different voltage levels, ground connections, or for linking the many leads on ball grid variety gadgets and other large integrated circuit package formats.
There are usually 2 types of product utilized to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet form, generally about.002 inches thick. Core product is similar to an extremely thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, typically.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are 2 techniques utilized to build up the desired number of layers. The core stack-up technique, which is an older innovation, utilizes a center layer of pre-preg material 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 innovation, would have core product as the center layer followed by layers of pre-preg and copper material built up above and listed below to form the final number of layers needed by the board style, sort of like Dagwood developing a sandwich. This approach permits the maker flexibility in how the board layer thicknesses are combined to fulfill the finished product density requirements by differing the variety of sheets of pre-preg in each layer. When the product layers are completed, the whole 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 producing printed circuit boards follows the steps below for the majority of applications.
The process of identifying products, processes, and requirements to fulfill the customer's requirements for the board design based on the Gerber file info provided with the purchase order.
The process of transferring the Gerber file information for more about the author a layer onto an etch withstand movie that is put on the conductive copper layer.
The conventional procedure of exposing the copper and other locations unprotected by the etch withstand film to a chemical that eliminates the unguarded copper, leaving the safeguarded copper pads and traces in place; more recent procedures utilize plasma/laser etching instead of chemicals to get rid of the copper material, enabling finer line meanings.
The process of lining up the conductive copper and insulating dielectric layers and pushing them under heat to trigger the adhesive in the dielectric layers to form a solid board product.
The process 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 location 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 put in an electrically charged bath of copper.
This is required when holes are to be drilled through a copper location but the hole is not to be plated through. Avoid this process if possible due to the fact that it adds expense to the completed board.
The procedure of using a protective masking material, 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 versus ecological damage, provides insulation, safeguards versus 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 elements have been put.
The procedure of using the markings for element classifications and element details to the board. May be used to simply the top or to both sides if parts are installed on both top and bottom sides.
The process of separating several boards from a panel of identical boards; this procedure also enables cutting notches or slots into the board if needed.
A visual inspection 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 checking for continuity or shorted connections on the boards by ways using a voltage in between numerous points on the board and figuring out if a current 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 used by the board producer.