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In electronic devices, printed circuit boards, or PCBs, are utilized to mechanically support electronic parts 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 component leads in thru-hole applications. A board style might have all thru-hole elements on the leading or component side, a mix of thru-hole and surface install on the top only, a mix of thru-hole and surface area install components on the top side and surface area install components on the bottom or circuit side, or surface area install parts on the leading and bottom sides of the board.
The boards are also used to electrically link 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 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 styles 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 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 procedure. A multilayer board includes a variety of layers of dielectric material that has been impregnated with adhesives, and these layers are utilized to separate the layers of copper plating. All of 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 innovations.
In a common 4 layer board design, the internal layers are typically utilized to offer 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 part connections made on the top and bottom layers of the board. Extremely complicated board designs might have a large number of layers to make the various connections for various voltage levels, ground connections, or for linking the many leads on ball grid selection devices and other large integrated circuit bundle formats.
There are typically two kinds of material used 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 material is similar to a really thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, generally.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are 2 techniques utilized to develop the wanted variety of layers. The core stack-up technique, which is an older technology, utilizes a center layer of pre-preg product with a layer of core material 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 movie 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 listed below to form the last number of layers needed by the board design, sort of like Dagwood developing a sandwich. This method permits the producer versatility in how the board layer densities are integrated to meet the completed item thickness requirements by differing the variety of sheets of pre-preg in each layer. When the material layers are finished, the whole 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 process of producing printed circuit boards follows the actions below for many applications.
The process of identifying materials, 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 withstand movie that is placed on the conductive copper layer.
The traditional process of exposing the copper and other areas unprotected by the etch resist film to a chemical that gets rid of the unprotected copper, leaving the protected copper pads and traces in place; newer procedures use plasma/laser etching rather of chemicals to get rid of the copper material, enabling finer line meanings.
The procedure 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 solid board material.
The process of drilling all of the holes for plated through applications; a second drilling procedure is used 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 placed 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. Avoid this procedure if possible since it includes expense to the completed board.
The process of using a protective masking material, a solder mask, over the bare copper traces or over the copper that has had a thin layer of solder used; the solder mask secures versus environmental damage, provides insulation, secures versus solder shorts, and protects traces that run 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 process that will happen at a later date after the components have been positioned.
The procedure of applying the markings for element designations and component outlines to the board. May be applied to simply the top side or to both sides if elements are installed on both leading and bottom sides.
The procedure 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 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 methods using a voltage between various points on the board and determining if a current circulation takes place. Relying on the board intricacy, this procedure may need a specifically designed test component and test program to integrate with the electrical test system utilized by the board maker.