In electronics, printed circuit boards, or PCBs, are utilized to mechanically support electronic components which have their connection leads soldered onto copper pads in surface install applications or through rilled holes in the board and copper pads for soldering the element leads in thru-hole applications. A board design might have all thru-hole elements on the leading or element side, a mix of thru-hole and surface mount on the top only, a mix of thru-hole and surface install components on the top side and surface mount components on the bottom or circuit side, or surface area mount components on the top and bottom sides of the board.
The boards are also used to electrically connect the required leads for each component utilizing conductive copper traces. The component pads and connection traces are engraved from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are created as single agreed 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 designs 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 actual copper pads and connection traces on the board surfaces as part of the board production process. A multilayer board consists of a number of layers of dielectric product that has been impregnated with adhesives, and these layers are utilized 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 typically used to supply power and ground connections, such as a +5 V aircraft layer and a Ground plane layer as the 2 internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Extremely complicated board designs might have a large number of layers to make the different connections for various voltage levels, ground connections, or for connecting the many leads on ball grid variety gadgets and other large incorporated circuit bundle formats.
There are normally two kinds of product used to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, typically about.002 inches thick. Core product is similar to an extremely thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, normally.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are 2 techniques utilized to develop the wanted variety of layers. The core stack-up approach, which is an older innovation, utilizes a center layer of pre-preg product with a layer of core product 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 movie stack-up approach, a newer technology, would have core material as the center layer followed by layers of pre-preg and copper material developed above and below to form the last number of layers required by the board style, sort of like Dagwood developing a sandwich. This method permits the producer flexibility in how the board layer thicknesses are combined to satisfy the ended up item density requirements by varying the number of sheets of pre-preg in each layer. As soon as the material layers are completed, the entire stack undergoes 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 manufacturing printed circuit boards follows the steps below for many applications.
The procedure of figuring out products, processes, and requirements to satisfy the client's requirements for the board style based on the Gerber file information offered with the purchase order.
The procedure of transferring the Gerber file information for a layer onto an etch resist film that is put on the conductive copper layer.
The conventional process of exposing the copper and other locations unprotected by the etch withstand film to a chemical that removes the unprotected copper, leaving the protected copper pads and traces in location; more recent procedures use plasma/laser etching instead of chemicals to remove the copper product, allowing finer line definitions.
The procedure of lining up the conductive copper and insulating dielectric layers and pushing them under heat to trigger the adhesive in the ISO 9001 consultants dielectric layers to form a solid board material.
The procedure of drilling all of 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 included in the drill drawing file.
The process of applying 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. Avoid this procedure if possible because it includes cost to the ended up 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 safeguards against ecological damage, offers insulation, safeguards against solder shorts, and safeguards traces that run in between pads.
The procedure of finish the pad areas with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering process that will happen at a later date after the components have actually been placed.
The process of applying the markings for part designations and part describes to the board. Might be used to just the top or to both sides if components are installed on both leading and bottom sides.
The process of separating numerous boards from a panel of identical boards; this procedure likewise enables cutting notches or slots into the board if required.
A visual assessment of the boards; likewise can be the procedure of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The procedure of checking for continuity or shorted connections on the boards by methods using a voltage in between numerous points on the board and figuring out if an existing flow occurs. Depending upon the board intricacy, this process might need a specially developed test fixture and test program to integrate with the electrical test system utilized by the board maker.