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 mount 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 area install on the top side just, a mix of thru-hole and surface area install elements on the top side and surface mount elements on the bottom or circuit side, or surface area mount components on the leading and bottom sides of the board.
The boards are likewise used to electrically link the required leads for each part 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 sided with 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 top and bottom of board with a variable number 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 consists of a variety of layers of dielectric material that has been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All of these layers are lined up 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 style, the internal layers are typically used to provide power and ground connections, such as a +5 V plane layer and a Ground aircraft layer as the 2 internal layers, with all other circuit and component connections made on the top and bottom layers of the board. Really complicated board styles 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 package formats.
There are usually 2 types of material used to construct a multilayer board. Pre-preg ISO 9001 product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, normally about.002 inches thick. Core product is similar to a really thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, typically.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are two methods used to develop the wanted number 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 material above and another layer of core material listed below. This mix of one pre-preg layer and two 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 product developed above and listed below to form the final variety of layers required by the board design, sort of like Dagwood developing a sandwich. This method allows the manufacturer flexibility in how the board layer thicknesses are integrated to fulfill the ended up product density requirements by differing the variety of sheets of pre-preg in each layer. As soon as the product layers are finished, the whole 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 manufacturing printed circuit boards follows the actions listed below for a lot of applications.
The procedure of identifying products, procedures, and requirements to meet the client's specifications for the board style based upon the Gerber file info supplied with the purchase order.
The process of transferring the Gerber file information for a layer onto an etch resist movie that is put on the conductive copper layer.
The standard procedure of exposing the copper and other locations unprotected by the etch withstand film to a chemical that eliminates the vulnerable copper, leaving the protected copper pads and traces in place; more recent procedures utilize plasma/laser etching instead of chemicals to remove the copper material, enabling finer line meanings.
The process of lining up 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 2nd drilling procedure is used for holes that are not to be plated through. Info on hole area and size is included 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 positioned in an electrically charged bath of copper.
This is required when holes are to be drilled through a copper area but the hole is not to be plated through. Prevent this procedure if possible due to the fact that 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 applied; the solder mask protects versus environmental damage, provides insulation, secures versus solder shorts, and secures traces that run in between pads.
The procedure 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 parts have actually been put.
The process of applying the markings for element classifications and element lays out to the board. May be used to simply the top side or to both sides if parts are mounted on both top and bottom sides.
The process 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 evaluation of the boards; also can be the process of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The process of looking for connection or shorted connections on the boards by methods using a voltage in between numerous points on the board and figuring out if a present flow happens. Depending upon the board intricacy, this procedure may need a specially developed test component and test program to integrate with the electrical test system utilized by the board manufacturer.