In electronics, printed circuit boards, or PCBs, are utilized to mechanically support electronic elements 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 element leads in thru-hole applications. A board style may have all thru-hole components 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 area mount components on the top and surface area install elements on the bottom or circuit side, or surface area install components on the leading and bottom sides of the board.
The boards are also used to electrically link the needed leads for each component using conductive copper traces. The part pads and connection traces are engraved from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are created as single sided with copper pads and traces on one side of the board just, double sided with copper pads and traces on the top and bottom sides of the board, or multilayer styles 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 consist of a core dielectric product, such as FR-4 epoxy fiberglass, with copper plating on one or both sides. This copper plating is engraved away to form the real 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 product that has been fertilized with adhesives, and these layers are used to separate the layers of copper plating. All these layers are aligned 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 design, the internal layers are often utilized to supply 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 element connections made on the top and bottom layers of the board. Extremely complex board styles may have a large number of layers to make the various connections for various voltage levels, ground connections, or for connecting the many leads on ball grid range gadgets and other big incorporated circuit plan formats.
There are normally 2 types of product used 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 resembles an extremely thin double sided board because it has a dielectric product, 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 design, there are 2 techniques utilized to build up the preferred number of layers. The core stack-up approach, which is an older innovation, utilizes a center layer of pre-preg material with a layer of core material above and another layer of core product listed below. This combination of one pre-preg layer and 2 core layers would make a 4 layer board.
The film stack-up technique, a newer innovation, would have core product as the center layer followed by layers of pre-preg and copper ISO 9001 material developed above and below to form the final number of layers needed by the board design, sort of like Dagwood building a sandwich. This approach permits the manufacturer flexibility in how the board layer densities are integrated to satisfy the completed product density requirements by varying the number of sheets of pre-preg in each layer. As soon as the material layers are finished, the entire stack is subjected to 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 producing printed circuit boards follows the steps listed below for a lot of applications.
The procedure of figuring out products, procedures, and requirements to fulfill the client's specifications for the board style based upon the Gerber file info offered with the purchase order.
The process of moving the Gerber file data for a layer onto an etch withstand movie that is placed on the conductive copper layer.
The conventional procedure of exposing the copper and other areas unprotected by the etch withstand movie to a chemical that eliminates the vulnerable copper, leaving the safeguarded copper pads and traces in place; more recent procedures utilize plasma/laser etching instead of chemicals to remove the copper material, allowing finer line meanings.
The procedure of aligning the conductive copper and insulating dielectric layers and pushing 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. Information on hole place and size is consisted of in the drill drawing file.
The procedure of applying 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 location however the hole is not to be plated through. Prevent this process if possible since it adds cost to the ended up board.
The procedure of applying a protective masking material, a solder mask, over the bare copper traces or over the copper that has actually had a thin layer of solder used; the solder mask protects versus environmental damage, offers insulation, protects versus solder shorts, and safeguards traces that run in between pads.
The process of covering the pad areas with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering process that will take place at a later date after the components have been positioned.
The process of applying the markings for part designations and element describes to the board. May 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 numerous boards from a panel of identical boards; this procedure also allows cutting notches or slots into the board if needed.
A visual examination of the boards; also can be the process of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The process of checking for connection or shorted connections on the boards by methods using a voltage between different points on the board and determining if a present circulation takes place. Relying on the board complexity, this process may need a specially created test component and test program to incorporate with the electrical test system utilized by the board manufacturer.