In electronics, printed circuit boards, or PCBs, are utilized to mechanically support electronic parts which have their connection leads soldered onto copper pads in surface 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 leading or component side, a mix of thru-hole and surface mount on the top side just, a mix of thru-hole and surface mount elements on the top and surface area mount elements on the bottom or circuit side, or surface mount components on the leading and bottom sides of the board.
The boards are likewise utilized to electrically link the required leads for each component 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 agreed copper pads and traces on one side of the board just, double sided with copper pads and traces on the top 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 consist of a core dielectric material, 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 process. A multilayer board includes a number 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 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 typical 4 layer board design, the internal layers are frequently 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 element connections made on the leading and bottom layers of the board. Very complicated board styles may have a large number of layers to make the numerous connections for different voltage levels, ground connections, or for connecting the many leads on ball grid range gadgets and other big integrated circuit package formats.
There are normally two types of product used to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, typically about.002 inches thick. Core product resembles a very thin double sided board because 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 style, there are two approaches utilized to build up the desired variety of layers. The core stack-up approach, 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 material listed below. This mix of one pre-preg layer and 2 core layers would make a 4 layer board.
The movie stack-up technique, a more recent technology, would have core product as the center layer followed by layers of pre-preg and copper material developed ISO 9001 consultants above and listed below to form the last number of layers required by the board style, sort of like Dagwood constructing a sandwich. This technique allows the manufacturer versatility in how the board layer densities are combined to fulfill the finished product thickness requirements by varying the number of sheets of pre-preg in each layer. When the product layers are completed, the entire stack is subjected to 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 manufacturing printed circuit boards follows the actions below for many applications.
The process of identifying products, processes, and requirements to meet the customer's specs for the board style based upon the Gerber file information provided with the purchase order.
The procedure of transferring the Gerber file data for a layer onto an etch withstand film that is put on the conductive copper layer.
The conventional procedure of exposing the copper and other locations unprotected by the etch resist film to a chemical that removes the unprotected copper, leaving the safeguarded copper pads and traces in location; newer processes utilize plasma/laser etching rather of chemicals to eliminate the copper product, permitting finer line meanings.
The procedure of lining up 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 the holes for plated through applications; a 2nd drilling procedure is utilized for holes that are not to be plated through. Info on hole place and size is included in the drill drawing file.
The procedure 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 however the hole is not to be plated through. Prevent this process if possible because it adds cost to the ended up board.
The process of applying a protective masking material, a solder mask, over the bare copper traces or over the copper that has had a thin layer of solder applied; the solder mask protects against ecological damage, supplies insulation, safeguards against solder shorts, and secures traces that run between pads.
The procedure of covering the pad areas with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering process that will occur at a later date after the elements have actually been placed.
The process of using the markings for component classifications and part outlines to the board. Might be used to simply the top side or to both sides if elements are installed on both top 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; likewise can be the process of inspecting 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 applying a voltage in between various points on the board and figuring out if a present flow occurs. Relying on the board intricacy, this procedure may need a specially designed test fixture and test program to integrate with the electrical test system utilized by the board manufacturer.