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In electronic devices, 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 components on the top or element side, a mix of thru-hole and surface install on the top just, a mix of thru-hole and surface area install parts on the top and surface area install elements on the bottom or circuit side, or surface area mount components on the top and bottom sides of the board.
The boards are likewise used to electrically connect the required leads for each part using conductive copper traces. The element pads and connection traces are etched from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are designed 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 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 material, 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 surface areas as part of the board manufacturing procedure. A multilayer board includes a variety of layers of dielectric material that has actually been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All of 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 technologies.
In a common four layer board design, the internal layers are typically utilized 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 element connections made on the top and bottom layers of the board. Extremely complicated board styles might have a large number of layers to make the numerous connections for different voltage levels, ground connections, or for linking the lots of leads on ball grid array devices and other big integrated circuit package formats.
There are typically 2 types of material utilized to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet form, typically about.002 inches thick. Core material resembles 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, typically.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are 2 methods used to develop the desired 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 material above and another layer of core product below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The movie stack-up approach, a newer innovation, would have core material as the center layer followed by layers of pre-preg and copper material developed above and below to form the final variety of layers required by the board design, sort of like Dagwood building a sandwich. This approach permits the producer flexibility in how the board layer thicknesses are integrated to satisfy the finished product density requirements by varying the variety of sheets of pre-preg in each layer. When the material layers are completed, the whole stack undergoes 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 listed below for many applications.
The procedure of identifying products, processes, and requirements to meet the customer's requirements for the board style based upon the Gerber file information supplied with the order.
The process of transferring the Gerber file data for a layer onto an etch resist movie that is placed on the conductive copper layer.
The traditional procedure of exposing the copper and other locations unprotected by the etch resist film to a chemical that removes the unprotected copper, leaving the secured copper pads and traces in location; newer procedures use plasma/laser etching rather of chemicals to get rid of the copper product, allowing finer line meanings.
The procedure of aligning the conductive copper and insulating dielectric layers and pressing them under heat to trigger the adhesive in the dielectric layers to form a strong board material.
The process of drilling all the holes for plated through applications; a 2nd drilling process is used for holes that are not to be plated through. Details on hole place and size is included 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 required when holes are to be drilled through a copper area but the hole is not to be plated through. Prevent this process if possible because it includes expense to the completed 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 protects versus environmental damage, offers insulation, secures versus solder shorts, and safeguards traces that run between pads.
The process of finishing the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering process that will take place at a later date after the components have actually been put.
The process of applying the markings for part designations and element lays out to the board. Might be used to simply the top or to both sides if elements are mounted on both leading and bottom sides.
The procedure of separating multiple boards from a panel of identical boards; this procedure also permits 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 techniques.
The process of looking for connection or shorted connections on the boards by methods applying a voltage in between various points on the board and figuring out if a current flow happens. Relying on the board intricacy, this process may require a specially developed test component and test program to integrate with the electrical test system used by the board producer.
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