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In electronics, printed circuit boards, or PCBs, are utilized to mechanically support electronic components 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 part leads in thru-hole applications. A board design may have all thru-hole parts on the top or part side, a mix of thru-hole and surface mount on the top just, a mix of thru-hole and surface area mount components on the top and surface area install parts on the bottom or circuit side, or surface area install components on the leading and bottom sides of the board.
The boards are also used to electrically link the needed leads for each part utilizing conductive copper traces. The component pads and connection traces are engraved 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 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 engraved away to form the real copper pads and connection traces on the board surfaces as part of the board production process. A multilayer board consists of a variety of layers of dielectric material that has actually been fertilized with adhesives, and these layers are utilized to separate the layers of copper plating. All of ISO 9001 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 typical 4 layer board style, the internal layers are frequently used to supply 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 component connections made on the top and bottom layers of the board. Extremely intricate board styles might have a large number of layers to make the numerous connections for various voltage levels, ground connections, or for connecting the many leads on ball grid array devices and other big incorporated circuit plan formats.
There are typically 2 types of material utilized to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, typically about.002 inches thick. Core product is similar to an extremely thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, generally.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are 2 methods utilized to build up 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 listed below. This mix of one pre-preg layer and 2 core layers would make a 4 layer board.
The film stack-up technique, a newer innovation, would have core product as the center layer followed by layers of pre-preg and copper material developed above and listed below to form the last number of layers needed by the board design, sort of like Dagwood developing a sandwich. This technique enables the manufacturer flexibility in how the board layer densities are integrated to satisfy the completed item density requirements by varying the number of sheets of pre-preg in each layer. As soon as the product layers are completed, the entire stack is subjected to 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 determining materials, procedures, and requirements to fulfill the customer's specs for the board style based upon the Gerber file information offered 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 conventional procedure of exposing the copper and other areas unprotected by the etch withstand film to a chemical that eliminates the unguarded copper, leaving the secured copper pads and traces in place; newer processes use plasma/laser etching rather of chemicals to remove the copper material, permitting finer line definitions.
The process of aligning the conductive copper and insulating dielectric layers and pushing them under heat to trigger the adhesive in the dielectric layers to form a strong board material.
The process of drilling all of the holes for plated through applications; a 2nd drilling process is utilized for holes that are not to be plated through. Information on hole place and size is consisted of in the drill drawing file.
The process of using 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 however the hole is not to be plated through. Avoid this procedure if possible since it adds expense to the ended up 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 used; the solder mask safeguards against ecological damage, provides insulation, safeguards against solder shorts, and protects traces that run between pads.
The process of covering the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will occur at a later date after the parts have been positioned.
The procedure of applying the markings for part designations and component details to the board. Might be used to just the top side or to both sides if components are installed on both leading and bottom sides.
The process of separating numerous boards from a panel of identical boards; this process likewise permits cutting notches or slots into the board if required.
A visual evaluation 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 procedure of checking for continuity or shorted connections on the boards by methods using a voltage between different points on the board and identifying if a current flow takes place. Depending upon the board intricacy, this process may require a specially designed test fixture and test program to integrate with the electrical test system utilized by the board maker.