In electronic devices, printed circuit boards, or PCBs, are used 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 element leads in thru-hole applications. A board design might have all thru-hole components on the top or component side, a mix of thru-hole and surface mount on the top just, a mix of thru-hole and surface area install components on the top and surface mount elements on the bottom or circuit side, or surface area install elements on the leading and bottom sides of the board.
The boards are also utilized to electrically connect the required leads for each part using conductive copper traces. The component pads and connection traces are See more engraved 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 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 actual 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 product that has actually been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All of these layers are aligned 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 often used to provide power and ground connections, such as a +5 V plane layer and a Ground aircraft layer as the 2 internal layers, with all other circuit and component connections made on the top and bottom layers of the board. Really complex board designs may have a large number of layers to make the different connections for different voltage levels, ground connections, or for connecting the numerous leads on ball grid array gadgets and other big incorporated circuit bundle formats.
There are normally 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 form, typically about.002 inches thick. Core material is similar to a really thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, usually.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two approaches utilized to develop the desired number of layers. The core stack-up method, which is an older technology, utilizes a center layer of pre-preg product with a layer of core product 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 technique, a newer innovation, would have core material as the center layer followed by layers of pre-preg and copper product developed above and listed below to form the final variety of layers required by the board design, sort of like Dagwood constructing a sandwich. This method allows the maker flexibility in how the board layer thicknesses are combined to satisfy the ended up product density requirements by varying the number of sheets of pre-preg in each layer. Once the product layers are finished, the whole 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 process of making printed circuit boards follows the actions listed below for many applications.
The procedure of identifying materials, processes, and requirements to fulfill the consumer's specifications for the board style based on the Gerber file information provided with the order.
The process of moving the Gerber file data for a layer onto an etch withstand movie that is put on the conductive copper layer.
The conventional process of exposing the copper and other locations unprotected by the etch resist movie to a chemical that removes the unprotected copper, leaving the safeguarded copper pads and traces in location; more recent procedures utilize plasma/laser etching instead of chemicals to eliminate the copper material, permitting finer line definitions.
The process of lining up the conductive copper and insulating dielectric layers and pushing them under heat to activate the adhesive in the dielectric layers to form a strong board product.
The procedure of drilling all the holes for plated through applications; a 2nd drilling process is used for holes that are not to be plated through. Information on hole place and size is included 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 placed 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 due to the fact that it includes cost 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 protects against environmental damage, provides insulation, safeguards against solder shorts, and secures traces that run between pads.
The process of covering the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering procedure that will happen at a later date after the components have been put.
The process of using the markings for component designations and component outlines to the board. Might be applied to simply the top or to both sides if components are mounted on both leading and bottom sides.
The process of separating several boards from a panel of similar boards; this procedure also enables cutting notches or slots into the board if needed.
A visual inspection of the boards; likewise can be the process of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The procedure of looking for connection or shorted connections on the boards by methods applying a voltage in between various points on the board and determining if an existing circulation takes place. Depending upon the board complexity, this process may need a specially created test fixture and test program to incorporate with the electrical test system utilized by the board producer.