In electronics, printed circuit boards, or PCBs, are utilized to mechanically support electronic components which have their connection leads soldered onto copper pads in surface install 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 components on the leading or component side, a mix of thru-hole and surface mount on the top only, a mix of thru-hole and surface area install components on the top side and surface mount components on the bottom or circuit side, or surface mount parts on the top and bottom sides of the board.
The boards are likewise used to electrically link the required leads for each element using 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 agreed copper pads and traces on one side of the board only, 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 the top and bottom of board with a variable number of internal copper layers with traces and connections.
Single or double sided boards include 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 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 actually been fertilized 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 typical 4 layer board design, the internal layers are frequently utilized to offer power and ground connections, such as a +5 V airplane layer and a Ground airplane layer as the two internal layers, with all other circuit and component connections made on the leading and bottom layers of the board. Really complex board styles might have a a great deal of layers to make the various connections for various voltage levels, ground connections, or for connecting the lots of leads on ball grid array gadgets and other big incorporated circuit package formats.
There are usually 2 types of product utilized to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet kind, typically about.002 inches thick. Core product is similar to a very thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, generally.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are two techniques used to build up the wanted variety of layers. The core stack-up method, which is an older technology, uses a center layer of pre-preg product with a layer of core product 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 film stack-up approach, a newer innovation, would have core product as the center layer followed by layers of pre-preg and copper material developed above and below to form the last number of layers required by the board style, sort of like Dagwood building a sandwich. This approach permits the manufacturer flexibility in how the board layer densities are combined to meet the completed product thickness requirements by varying the variety of sheets of pre-preg in each layer. As soon as the product layers are completed, the whole 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 procedure of manufacturing printed circuit boards follows the actions listed below for a lot of applications.
The procedure of figuring out materials, processes, and requirements to satisfy the customer's requirements for the board style based upon the Gerber file information supplied with the order.
The procedure of moving the Gerber file data for a layer onto an etch withstand film that is placed on the conductive copper layer.
The standard process of exposing the copper and other areas unprotected by the etch resist movie to a chemical that eliminates the unprotected copper, leaving the safeguarded copper pads and traces in place; more recent processes use plasma/laser etching rather of chemicals to remove the copper material, allowing 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 material.
The procedure of drilling all the holes for plated through applications; a second drilling procedure is utilized for holes that are not to be plated through. Details on hole location 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 procedure if possible since it includes cost to the finished board.
The procedure of applying a protective ISO 9001 Accreditation 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 secures versus environmental damage, provides insulation, safeguards versus solder shorts, and safeguards traces that run between pads.
The process of finishing the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will happen at a later date after the elements have been positioned.
The process of using the markings for part classifications and element describes to the board. May be applied to simply the top or to both sides if elements are installed on both leading and bottom sides.
The procedure of separating multiple boards from a panel of identical boards; this process likewise allows cutting notches or slots into the board if required.
A visual evaluation 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 procedure of looking for continuity or shorted connections on the boards by means applying a voltage between different points on the board and identifying if an existing circulation happens. Relying on the board intricacy, this process may require a specifically developed test fixture and test program to incorporate with the electrical test system used by the board manufacturer.