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 area install applications or through rilled holes in the board and copper pads for soldering the component leads in thru-hole applications. A board design might have all thru-hole elements on the top or element side, a mix of thru-hole and surface mount on the top side only, a mix of thru-hole and surface mount components on the top side and surface area mount components on the bottom or circuit side, or surface install parts on the top and bottom sides of the board.
The boards are also utilized to electrically link the needed leads for each component 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 designed as single agreed 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 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 actual copper pads and connection traces on the board surface areas as part of the board production process. A multilayer board includes a variety of layers of dielectric product that has been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All these layers are aligned and 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 style, the internal layers are typically utilized to supply power and ground connections, such as a +5 V airplane layer and a Ground plane layer as the two internal layers, with all other circuit and component connections made on the leading and bottom layers of the board. Really complicated board designs might have a a great deal of layers to make the various connections for different voltage levels, ground connections, or for connecting the many leads on ball grid variety devices and other large incorporated circuit plan formats.
There are typically 2 kinds of material utilized to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, generally about.002 inches thick. Core material resembles an extremely 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 style, there are two methods utilized to develop the desired variety of layers. The core stack-up technique, which is an older technology, uses a center layer of pre-preg material with a layer of core product 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 movie stack-up approach, a more recent technology, would have core material 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 method enables the producer versatility in how the board layer densities are integrated to fulfill the finished item thickness requirements by differing the number of sheets of pre-preg in each layer. Once the material layers are finished, 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 procedure of making printed circuit boards follows the actions listed below for most applications.
The procedure of identifying materials, processes, and requirements to fulfill the customer's specs for the board design based upon the Gerber file details supplied with the purchase order.
The process of transferring the Gerber file data for a layer onto an etch withstand film that is put on the conductive copper layer.
The traditional process of exposing the copper and other locations unprotected by the etch withstand film to a chemical that eliminates the unprotected copper, leaving the secured copper pads and traces in place; newer procedures use plasma/laser etching rather of chemicals to remove the copper material, permitting finer line meanings.
The process of lining up the conductive copper and insulating dielectric layers and pressing 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 2nd drilling process is used for holes that are not to be plated through. Details on hole location 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 area but the hole is not to be plated through. Avoid this procedure if possible since it includes cost to the completed board.
The procedure of applying a protective masking product, 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 versus ecological damage, supplies insulation, safeguards against solder shorts, and protects traces that run in between pads.
The procedure of coating the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering procedure that will occur at a later date after the components have actually been positioned.
The process of using the markings for component designations and part details to the board. Might be used to simply the top or to both sides if components are mounted on both top and bottom sides.
The procedure of separating multiple boards from a panel of identical boards; this procedure also enables cutting notches or slots into the board if required.
A visual examination of the boards; also can be the process of examining wall More interesting details here quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The procedure of looking for connection or shorted connections on the boards by means applying a voltage in between various points on the board and determining if a present flow occurs. Relying on the board intricacy, this procedure may need a specifically designed test fixture and test program to incorporate with the electrical test system utilized by the board maker.