In electronic devices, 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 part leads in thru-hole applications. A board style may have all thru-hole components on the leading or component side, a mix of thru-hole and surface area install on the top side only, a mix of thru-hole and surface mount parts on the top and surface mount components on the bottom or circuit side, or surface mount parts on the leading and bottom sides of the board.
The boards are likewise utilized to electrically connect the needed leads for each element 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 developed as single agreed copper pads and traces on one side of the board just, 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 actual copper pads and connection traces on the board surfaces as part of the board manufacturing procedure. A multilayer board includes a variety of layers of dielectric material that has been impregnated with adhesives, and these layers are utilized to separate the layers of copper plating. All of 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 innovations.
In a normal 4 layer board style, the internal layers are often used to offer 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 component connections made on the top and bottom layers of the board. Really complicated board designs might 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 selection devices and other large integrated circuit plan formats.
There are typically 2 kinds of product utilized to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, normally about.002 inches thick. Core product resembles a very 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 wanted variety of layers. The core stack-up technique, which is an older technology, utilizes a center layer of pre-preg product with a layer of core material above and another layer of core material listed below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The movie stack-up technique, 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 final variety of layers needed by the board style, sort of like Dagwood building a sandwich. This method permits the maker flexibility in how the board layer thicknesses are integrated to meet the completed item density requirements by differing the variety of sheets of pre-preg in each layer. As soon as the product layers are finished, the entire stack goes through heat and pressure that causes 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 steps below for a lot of applications.
The procedure of identifying products, processes, and requirements to meet the customer's requirements for the board style based on the Gerber file details offered with the order.
The procedure of transferring the Gerber file information for a layer onto an etch withstand film that is put on the conductive copper layer.
The conventional procedure of exposing the copper and other locations unprotected by the etch resist film to a chemical that gets rid of the unguarded copper, leaving the secured copper pads and traces in location; newer ISO 9001 Accreditation procedures use plasma/laser etching rather of chemicals to eliminate the copper material, allowing finer line meanings.
The procedure of aligning the conductive copper and insulating dielectric layers and pushing them under heat to activate the adhesive in the dielectric layers to form a solid board product.
The process of drilling all of the holes for plated through applications; a second drilling process is used for holes that are not to be plated through. Information 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 placed in an electrically charged bath of copper.
This is required when holes are to be drilled through a copper location however the hole is not to be plated through. Avoid this process if possible due to the fact that it includes expense to the ended up board.
The procedure of using a protective masking product, a solder mask, over the bare copper traces or over the copper that has had a thin layer of solder applied; the solder mask protects against ecological damage, supplies insulation, secures versus solder shorts, and secures traces that run between pads.
The process of finish the pad locations 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 using the markings for element designations and element describes to the board. Might be used to simply the top side or to both sides if components are mounted on both leading and bottom sides.
The process of separating numerous 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 process of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The process of checking for continuity or shorted connections on the boards by methods using a voltage between numerous points on the board and identifying if a present flow takes place. Depending upon the board intricacy, this process might require a specifically designed test fixture and test program to integrate with the electrical test system used by the board producer.