In electronic devices, printed circuit boards, or PCBs, are utilized to mechanically support electronic components 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 style may have all thru-hole parts on the leading or part side, a mix of thru-hole and surface area install on the top only, a mix of thru-hole and surface mount elements on the top side and surface mount parts on the bottom or circuit side, or surface install parts on the top and bottom sides of the board.
The boards are also used to electrically connect the needed leads for each component using conductive copper traces. The component pads and connection traces are etched 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 only, 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 include 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 consists of a variety of layers of dielectric material that has actually been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All of these layers are lined up and after that 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 normal four layer board style, the internal layers are frequently used to offer power and ground connections, such as a +5 V plane layer and a Ground airplane layer as the 2 internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Really complicated board styles may have a a great deal ISO 9001 Accreditation of layers to make the numerous connections for different voltage levels, ground connections, or for linking the many leads on ball grid array devices and other large integrated circuit plan formats.
There are usually 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 kind, normally about.002 inches thick. Core material resembles an extremely thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, generally.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are two methods utilized to build up the preferred variety of layers. The core stack-up method, 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 product below. This mix of one pre-preg layer and two core layers would make a 4 layer board.
The movie stack-up method, a newer innovation, would have core product as the center layer followed by layers of pre-preg and copper product built up above and below to form the final number of layers required by the board design, sort of like Dagwood developing a sandwich. This technique enables the producer flexibility in how the board layer thicknesses are combined to fulfill the finished item thickness requirements by differing the number of sheets of pre-preg in each layer. As soon as the material 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 steps listed below for the majority of applications.
The process of identifying materials, processes, and requirements to fulfill the customer's specs for the board style based on the Gerber file info supplied with the order.
The process of moving the Gerber file information for a layer onto an etch resist film that is placed on the conductive copper layer.
The traditional process of exposing the copper and other areas unprotected by the etch resist film to a chemical that eliminates the unguarded copper, leaving the safeguarded copper pads and traces in place; newer processes utilize plasma/laser etching instead of chemicals to get rid of the copper product, enabling finer line meanings.
The process of aligning 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 process of drilling all the holes for plated through applications; a second drilling process is utilized for holes that are not to be plated through. Details on hole place and size is consisted of 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 placed in an electrically charged bath of copper.
This is needed when holes are to be drilled through a copper area however the hole is not to be plated through. Avoid this process if possible since it includes expense to the completed board.
The process of applying 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 versus ecological damage, offers 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 components have actually been positioned.
The process of using the markings for element classifications and component lays out to the board. Might be used to just the top side or to both sides if parts are mounted on both top and bottom sides.
The procedure of separating multiple boards from a panel of similar boards; this process likewise enables cutting notches or slots into the board if required.
A visual evaluation of the boards; likewise can be the procedure of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The procedure of checking for connection or shorted connections on the boards by ways using a voltage between different points on the board and figuring out if an existing circulation happens. Depending upon the board complexity, this procedure might need a specially developed test fixture and test program to integrate with the electrical test system used by the board manufacturer.