In electronics, printed circuit boards, or PCBs, are used 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 element leads in thru-hole applications. A board style may have all thru-hole elements on the leading or part side, a mix of thru-hole and surface install on the top only, a mix of thru-hole and surface area mount components on the top and surface mount components on the bottom or circuit side, or surface install elements on the top and bottom sides of the board.
The boards are likewise utilized to electrically connect the required leads for each element utilizing conductive copper traces. The part pads and connection traces are engraved from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are developed as single sided with copper pads and traces on one side of the board just, double agreed copper pads and traces on the top and bottom sides of the board, or multilayer designs 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 product, such as FR-4 epoxy fiberglass, with copper plating on one or both sides. This copper plating is etched away to form the real copper pads and connection traces on the board surface ISO 9001 Accreditation areas as part of the board manufacturing process. A multilayer board includes a variety of layers of dielectric product that has actually been fertilized with adhesives, and these layers are utilized 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 innovations.
In a common 4 layer board design, the internal layers are frequently used to provide 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 part connections made on the top and bottom layers of the board. Really complex board styles may have a large number of layers to make the different connections for different voltage levels, ground connections, or for linking the many leads on ball grid selection devices and other big integrated circuit package formats.
There are generally two kinds of material utilized to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet form, normally about.002 inches thick. Core product is similar to a very thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, normally.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are 2 methods utilized to develop the wanted number 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 combination of one pre-preg layer and 2 core layers would make a 4 layer board.
The movie stack-up method, a newer technology, would have core product as the center layer followed by layers of pre-preg and copper product developed above and listed below to form the final number of layers needed by the board design, sort of like Dagwood constructing a sandwich. This approach enables the manufacturer versatility in how the board layer thicknesses are combined to meet the completed item density requirements by varying the number of sheets of pre-preg in each layer. Once the material layers are finished, the entire stack goes through 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 producing printed circuit boards follows the steps listed below for many applications.
The procedure of figuring out products, procedures, and requirements to fulfill the consumer's requirements for the board design based upon the Gerber file info offered with the purchase order.
The procedure of transferring the Gerber file data for a layer onto an etch resist movie that is placed on the conductive copper layer.
The conventional process of exposing the copper and other areas unprotected by the etch resist movie to a chemical that gets rid of the vulnerable copper, leaving the secured copper pads and traces in place; more recent processes use plasma/laser etching rather of chemicals to eliminate the copper product, allowing finer line definitions.
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 process of drilling all the holes for plated through applications; a second drilling procedure is used for holes that are not to be plated through. Info on hole area 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 put 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 because it adds expense to the ended up board.
The procedure 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 applied; the solder mask secures against environmental damage, supplies insulation, secures against solder shorts, and safeguards traces that run between pads.
The process of coating the pad areas 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 elements have been placed.
The process of applying the markings for component designations and element outlines to the board. May be applied to simply the top or to both sides if parts are installed on both top and bottom sides.
The procedure of separating numerous boards from a panel of identical boards; this procedure likewise permits cutting notches or slots into the board if needed.
A visual assessment of the boards; likewise can be the procedure of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The process of looking for connection or shorted connections on the boards by ways applying a voltage in between different points on the board and figuring out if an existing circulation happens. Relying on the board complexity, this process might require a specially designed test fixture and test program to incorporate with the electrical test system used by the board maker.