In electronic devices, printed circuit boards, or PCBs, are used to mechanically support electronic parts which have their connection leads soldered onto copper pads in surface area mount applications or through rilled holes in the board and copper pads for soldering the part leads in thru-hole applications. A board style might have all thru-hole parts on the top or component side, a mix of thru-hole and surface area mount on the top side only, a mix of thru-hole and surface area mount elements on the top side and surface mount elements on the bottom or circuit side, or surface area mount elements on the top and bottom sides of the board.
The boards are likewise utilized to electrically connect 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 only, double agreed 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 engraved away to form the real copper pads and connection traces on the board surface areas as part of the board manufacturing process. A multilayer board includes a number of layers of dielectric material that has been impregnated with adhesives, and these layers are utilized to separate the layers of copper plating. All 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 normal four layer board design, the internal layers are often used to offer power and ground connections, such as a +5 V aircraft layer and a Ground aircraft layer as the two 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 various connections for various voltage levels, ground connections, or for connecting the many leads on ball grid range devices and other big integrated circuit package formats.
There are normally 2 types of product utilized to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, normally about.002 inches thick. Core material resembles an extremely ISO 9001 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 material with 1 ounce copper layer on each side. In a multilayer board style, there are 2 approaches utilized to develop the preferred variety of layers. The core stack-up approach, which is an older innovation, uses a center layer of pre-preg product with a layer of core material 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 method, 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 final variety of layers required by the board style, sort of like Dagwood building a sandwich. This technique enables the manufacturer versatility in how the board layer densities are integrated to fulfill the completed item thickness requirements by varying the number of sheets of pre-preg in each layer. When the product layers are completed, the entire stack goes through 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 manufacturing printed circuit boards follows the actions below for the majority of applications.
The process of determining products, procedures, and requirements to meet the customer's specs for the board style based upon the Gerber file details supplied with the order.
The process of transferring the Gerber file information for a layer onto an etch withstand movie that is put on the conductive copper layer.
The standard process of exposing the copper and other areas unprotected by the etch resist film to a chemical that gets rid of the unguarded copper, leaving the safeguarded copper pads and traces in location; more recent processes utilize plasma/laser etching rather of chemicals to remove the copper material, enabling finer line meanings.
The process 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 procedure of drilling all of the holes for plated through applications; a second drilling procedure is utilized for holes that are not to be plated through. Details on hole place and size is contained 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 placed in an electrically charged bath of copper.
This is required when holes are to be drilled through a copper location but the hole is not to be plated through. Avoid this procedure if possible due to the fact that it includes cost to the completed board.
The procedure of applying a protective masking material, a solder mask, over the bare copper traces or over the copper that has actually had a thin layer of solder applied; the solder mask safeguards against environmental damage, offers insulation, safeguards against solder shorts, and secures traces that run between pads.
The procedure of finishing the pad areas 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 actually been put.
The process of using the markings for element designations and component describes to the board. Might be applied to just the top side or to both sides if elements are mounted on both leading and bottom sides.
The procedure of separating several boards from a panel of similar boards; this procedure likewise enables cutting notches or slots into the board if needed.
A visual assessment of the boards; also can be the process of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The process of checking for continuity or shorted connections on the boards by means using a voltage between numerous points on the board and figuring out if a current flow happens. Relying on the board intricacy, this process might need a specifically created test fixture and test program to incorporate with the electrical test system utilized by the board maker.