In electronic devices, printed circuit boards, or PCBs, are utilized to mechanically support electronic elements 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 part leads in thru-hole applications. A board design may have all thru-hole components on the top or element side, a mix of thru-hole and surface area mount on the top just, a mix of thru-hole and surface area install elements on the top and surface area mount components on the bottom or circuit side, or surface area mount elements on the top and bottom sides of the board.
The boards are likewise utilized to electrically link the required leads for each component utilizing 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 sided with copper pads and traces on the leading and bottom sides of the board, or multilayer designs with copper pads and traces on the top and bottom of board with a variable variety of internal copper layers with traces and connections.
Single or double sided boards consist of a core dielectric product, 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 production process. A multilayer board consists of a number of layers of dielectric product 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 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 4 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 styles may have a a great deal of layers to make the numerous connections for different voltage levels, ground connections, or for connecting the many leads on ball grid array gadgets and other big integrated circuit bundle formats.
There are usually two types of material utilized to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet form, generally about.002 inches thick. Core product is similar to a really thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, usually.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are 2 approaches utilized to develop the preferred 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 material below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The movie stack-up technique, a more recent technology, would have core product as the center layer followed by layers of pre-preg and copper product developed above and listed below to form the last variety of layers needed by the board design, sort of like Dagwood constructing a sandwich. This method permits the manufacturer flexibility in how the board layer densities are integrated to satisfy the ended up item thickness requirements by differing the number of sheets of pre-preg in each layer. As soon as the material layers are completed, 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 process of making printed circuit boards follows the steps listed below for most 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 procedure of transferring the Gerber file data ISO 9001 Certification Consultants for a layer onto an etch withstand movie that is put on the conductive copper layer.
The traditional procedure of exposing the copper and other areas unprotected by the etch resist film to a chemical that eliminates the unprotected copper, leaving the protected copper pads and traces in place; more recent processes utilize plasma/laser etching instead of chemicals to eliminate the copper material, allowing finer line meanings.
The procedure of aligning the conductive copper and insulating dielectric layers and pressing them under heat to trigger the adhesive in the dielectric layers to form a solid board material.
The process of drilling all the holes for plated through applications; a second drilling procedure is used for holes that are not to be plated through. Info on hole area and size is contained in the drill drawing file.
The procedure of using 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 area however the hole is not to be plated through. Prevent this procedure if possible due to the fact that it includes expense to the ended up board.
The procedure of applying 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 versus environmental damage, offers insulation, safeguards against solder shorts, and safeguards traces that run in between pads.
The procedure of finish the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering process that will occur at a later date after the components have been put.
The procedure of using the markings for element designations and component details to the board. Might be applied to simply the top side or to both sides if parts are installed on both leading and bottom sides.
The process of separating multiple boards from a panel of identical boards; this process also permits cutting notches or slots into the board if needed.
A visual examination of the boards; likewise can be the process of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The process of checking 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 current circulation takes place. Depending upon the board complexity, this procedure may require a specifically designed test fixture and test program to integrate with the electrical test system utilized by the board producer.