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 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 components on the top or element side, a mix of thru-hole and surface area mount on the top only, a mix of thru-hole and surface area mount components on the top side and surface install elements on the bottom or circuit side, or surface area mount elements on the top and bottom sides of the board.
The boards are also utilized to electrically connect the required leads for each element using 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 agreed 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 real copper pads and connection traces on the board surface areas as part of the board manufacturing procedure. A multilayer board consists of a number of layers of dielectric material that has been fertilized 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 technologies.
In a common four layer board design, the internal layers are typically utilized to provide power and ground connections, such as a +5 V plane layer and a Ground aircraft layer as the two internal layers, with all other circuit and component connections made on the top and bottom layers of the board. Really complex board designs might have a a great deal of layers to make the different connections for various voltage levels, ground connections, or for connecting the many leads on ball grid array gadgets and other big incorporated circuit plan formats.
There are usually 2 types of product used to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, normally about.002 inches thick. Core material resembles an extremely thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, generally.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are 2 methods used to develop the desired variety of layers. The core stack-up method, 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 product listed below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The film stack-up approach, a more recent technology, would have core material as the center layer followed by layers of pre-preg and copper product built up above and below to form the last variety of layers needed by the board design, sort of like Dagwood developing a sandwich. This technique allows the manufacturer flexibility in how the board layer densities are combined to fulfill the completed item thickness requirements by varying the number of sheets of pre-preg in each layer. Once the product layers are completed, the whole stack goes through 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 steps below for most applications.
The process of determining materials, procedures, and requirements to fulfill the client's specifications for the board design based on the Gerber file info provided with the order.
The procedure of moving the Gerber file data for a layer onto an etch withstand movie that is placed on the conductive copper layer.
The conventional process of exposing the copper and other areas unprotected by the etch resist film to a chemical that eliminates the vulnerable copper, leaving the protected copper pads and traces in place; more recent processes use plasma/laser etching rather of chemicals to get rid of the copper material, allowing finer line meanings.
The process of lining up the conductive copper and insulating dielectric layers and pushing them under heat to trigger the adhesive in the dielectric layers to form a strong board product.
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 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 positioned 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 process if possible due to the fact that it adds cost to the ended up board.
The process of using 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 secures versus environmental damage, provides insulation, safeguards versus solder shorts, and secures traces that run in between pads.
The procedure of finishing the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering procedure that will take place at a later date after the components have actually been put.
The process of applying the markings for part classifications and component details to the board. Might be applied to simply the top or to both sides if components are mounted on both top and bottom sides.
The process of separating multiple boards from a panel of identical boards; this process also allows cutting More interesting details here notches or slots into the board if required.
A visual inspection of the boards; also can be the procedure of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The procedure of checking for connection or shorted connections on the boards by means using a voltage between various points on the board and identifying if a present flow occurs. Depending upon the board intricacy, this process might need a specifically developed test fixture and test program to integrate with the electrical test system used by the board producer.