In electronic devices, printed circuit boards, or PCBs, are utilized to mechanically support electronic parts 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 component leads in thru-hole applications. A board style may have all thru-hole elements on the top or component side, a mix of thru-hole and surface install on the top side only, a mix of thru-hole and surface area install components on the top side and surface area install parts on the bottom or circuit side, or surface install elements on the leading and bottom sides of the board.
The boards are likewise utilized to electrically connect the required leads for each element using conductive copper traces. The component pads and connection traces are 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 only, 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 real copper pads and connection traces on the board surfaces as part of the board manufacturing procedure. A multilayer board includes a number 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 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 frequently utilized to provide power and ground connections, such as a +5 V airplane layer and a Ground plane layer as the 2 internal layers, with all other circuit and element connections made on the leading and bottom layers of the board. Extremely 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 lots of leads on ball grid variety devices and other large incorporated circuit bundle formats.
There are typically 2 kinds 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 form, normally about.002 inches thick. Core material is similar to an extremely thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, typically.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are 2 techniques used to build up the desired variety of layers. The core stack-up technique, which is an older innovation, uses a center layer of pre-preg material 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 film stack-up technique, a more recent innovation, would have core product as the center layer followed by layers of pre-preg and copper product built up above and listed below to form the last variety of layers required by the board style, sort of like Dagwood developing a sandwich. This technique enables the manufacturer versatility in how the board layer densities are combined to satisfy the completed product thickness requirements by differing the variety of sheets of pre-preg in each layer. Once the product layers are completed, the entire 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 producing printed circuit boards follows the actions listed below for many applications.
The process of determining products, processes, and requirements to meet the client's specifications for the board style based upon the Gerber file information supplied with the purchase order.
The procedure of moving the Gerber file information for a layer onto an etch withstand movie that is placed 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 eliminates the vulnerable copper, leaving the safeguarded copper pads and traces in place; newer processes use plasma/laser etching instead of chemicals to remove 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 of the holes for plated through applications; a second drilling process is utilized for holes that are not to be plated through. Information on hole place and size is contained in the drill drawing file.
The process 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 however the hole is not to be plated through. Prevent this procedure if possible because it adds 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 used; the solder mask secures against environmental damage, offers insulation, safeguards against solder shorts, and secures traces that run between pads.
The procedure of finish the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering process that will occur at a later date after the components have actually been placed.
The procedure of using the markings for part classifications and component lays out to the board. May be applied to simply the top or to both sides if components are mounted 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 needed.
A visual examination 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 approaches.
The procedure of looking for continuity or shorted connections on the boards by methods applying a voltage between different points on the board and determining if a present circulation takes place. Depending upon the board intricacy, this procedure may need a specially designed test component and test program to ISO 9001 consultants integrate with the electrical test system used by the board manufacturer.