In electronics, printed circuit boards, or PCBs, are used to mechanically support electronic elements which have their connection leads soldered onto copper pads in surface area 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 parts on the leading or part side, a mix of thru-hole and surface mount on the top side just, a mix of thru-hole and surface mount components on the top side and surface install components on the bottom or circuit side, or surface install elements on the top and bottom sides of the board.
The boards are likewise used to electrically connect 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 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 number of internal copper layers with traces and connections.
Single or double sided boards include 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 production procedure. A multilayer board includes a variety of layers of dielectric product that has been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All these layers are lined up 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 common four layer board design, the internal layers are frequently utilized to provide power and ground connections, such as a +5 V aircraft layer and a Ground plane layer as the two internal layers, with all other circuit and component connections made on the leading and bottom layers of the board. Extremely complicated board styles may have a a great deal of layers to make the various connections for different voltage levels, ground connections, or for connecting the many leads on ball grid variety devices and other big integrated circuit bundle formats.
There are typically two kinds of product used to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet kind, normally about.002 inches thick. Core material is similar to a very thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, usually.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are 2 techniques utilized to develop the preferred number of layers. The core stack-up technique, 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 combination 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 developed above and listed below to form the final variety of layers needed by the board style, sort of like Dagwood developing a sandwich. This approach permits the manufacturer flexibility in how the board layer densities are integrated to satisfy the finished item density requirements by differing the variety of sheets of pre-preg in each layer. As soon as 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 below for a lot of applications.
The process of identifying products, procedures, and requirements to satisfy the customer's specifications for the board design based on the Gerber file information supplied with the order.
The process of transferring the Gerber file data for a layer onto an etch withstand film 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 removes the vulnerable copper, leaving the protected copper pads and traces in location; newer processes utilize plasma/laser etching instead of chemicals to eliminate the copper product, permitting finer line definitions.
The procedure of lining up 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 2nd drilling procedure is utilized for holes that are not to be plated through. Information on hole location and size is consisted of 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 area but the hole is not to be plated through. Prevent this process if possible due to the fact that it includes expense to the completed board.
The process of using a protective masking product, a solder mask, over the bare copper traces or over the copper that has had Reference site a thin layer of solder used; the solder mask secures against environmental damage, offers insulation, safeguards against solder shorts, and secures traces that run in between pads.
The procedure of finish the pad locations with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will happen at a later date after the components have actually been placed.
The procedure of using the markings for part classifications and component outlines to the board. Might be used to just the top side or to both sides if elements are mounted on both leading and bottom sides.
The procedure of separating numerous boards from a panel of identical boards; this procedure also enables cutting notches or slots into the board if required.
A visual inspection of the boards; also can be the procedure of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The process of looking for connection or shorted connections on the boards by means using a voltage in between numerous points on the board and figuring out if a current flow takes place. Relying on the board complexity, this process might need a specifically created test component and test program to integrate with the electrical test system used by the board manufacturer.