In electronic devices, printed circuit boards, or PCBs, are utilized to mechanically support electronic elements 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 part leads in thru-hole applications. A board style may have all thru-hole components on the top or part side, a mix of thru-hole and surface install on the top side just, a mix of thru-hole and surface area install elements on the top and surface area install parts on the bottom or circuit side, or surface area mount parts on the leading and bottom sides of the board.
The boards are likewise 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 agreed copper pads and traces on the top 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 surfaces as part of the board manufacturing procedure. A multilayer board includes a variety of layers of dielectric material that has actually been fertilized with adhesives, and these layers are used to separate the layers of copper plating. All these layers are aligned 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 typical four layer board design, the internal layers are typically utilized to supply power and ground connections, such as a +5 V plane layer and a Ground aircraft 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 designs may have a a great deal of layers to make the various connections for various voltage levels, ground connections, or for connecting the many leads on ball grid array gadgets and other large integrated circuit package formats.
There are typically two kinds of product used to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, usually about.002 inches thick. Core material is similar to an extremely thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, typically.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are 2 techniques used to build up the wanted number of layers. The core stack-up technique, which is an older technology, utilizes a center layer of pre-preg material with a layer of core material 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 approach, a more recent innovation, would have core product as the center layer followed by layers of pre-preg and copper material developed above and below to form the last number of layers needed by the board design, sort of like Dagwood developing a sandwich. This technique allows the manufacturer versatility in how the board layer thicknesses are integrated to satisfy the ended up item density requirements by varying the variety of sheets of pre-preg in each layer. Once the material layers are finished, 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 process of producing printed circuit boards follows the steps below for many applications.
The process of figuring out materials, procedures, and requirements to meet the consumer's specifications for the board design based on the Gerber file info supplied with the purchase order.
The process of transferring the Gerber file information for a layer onto an etch withstand film that is placed on the conductive copper layer.
The traditional procedure of exposing the copper and other locations unprotected by the etch withstand film to a chemical that eliminates the unprotected copper, leaving the protected copper pads and traces in place; newer processes use plasma/laser etching instead of chemicals to remove the copper material, 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 solid board product.
The procedure of drilling all the holes for plated through applications; a second drilling procedure is used for holes that are not to be plated through. Info on hole place 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 location but the hole is not to be plated through. Prevent this procedure if possible due to the fact that it includes cost 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 a thin layer of solder used; the solder mask protects against ecological damage, offers insulation, secures versus solder shorts, and secures traces that run between pads.
The process of finishing the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering process that will occur at a later date after the components have been put.
The process of using the markings for part classifications and component outlines to the board. May be applied to just the top or to both sides if parts are mounted on both leading and bottom sides.
The process of separating numerous boards from a panel of identical boards; this process likewise enables cutting notches or slots into the board if required.
A visual examination of the boards; likewise can be the procedure of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The process of checking for connection or shorted connections on the boards by methods using a voltage in between different points on the board and figuring out if a current flow takes place. Depending upon the board intricacy, this process may require a specially created test fixture and test program to incorporate with the electrical test system used by the board producer.