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 mount applications or through rilled holes in the board and copper pads for soldering the component leads in thru-hole applications. A board design may have all thru-hole parts on the leading or element side, a mix of thru-hole and surface mount on the top side only, a mix of thru-hole and surface area mount elements on the top side and surface mount components on the bottom or circuit side, or surface mount elements on the leading and bottom sides of the board.
The boards are likewise utilized to electrically connect the needed leads for each part utilizing conductive copper traces. The part pads and connection traces are etched 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 agreed copper pads and traces on the top and bottom sides of the board, or multilayer designs 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 etched away to form the real copper pads and connection traces on the board surfaces as part of the board production procedure. A multilayer board consists of a number of layers of dielectric material that has been impregnated with adhesives, and these layers are utilized 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 common four layer board style, the internal layers are often utilized to provide power and ground connections, such as a +5 V aircraft layer and a Ground airplane layer as the two internal layers, with all other circuit and component connections made on the top and bottom layers of the board. Really intricate board styles may have a large number of layers to make the numerous connections for different voltage levels, ground connections, or for connecting the many leads on ball grid range devices and other big incorporated circuit bundle formats.
There are typically two kinds of product used to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet kind, typically 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 deposited See more here on each side, typically.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 preferred number 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 product below. This mix 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 material as the center layer followed by layers of pre-preg and copper material developed above and below to form the last variety of layers required by the board style, sort of like Dagwood constructing a sandwich. This technique enables the manufacturer versatility in how the board layer thicknesses are integrated to fulfill the ended up product thickness requirements by varying the variety of sheets of pre-preg in each layer. Once the product layers are finished, the entire 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 procedure of making printed circuit boards follows the actions below for most applications.
The process of figuring out materials, processes, and requirements to meet the consumer's specifications for the board design based upon the Gerber file info offered with the order.
The procedure of moving the Gerber file data for a layer onto an etch resist movie that is placed on the conductive copper layer.
The conventional procedure of exposing the copper and other locations unprotected by the etch resist movie to a chemical that gets rid of the unguarded copper, leaving the protected copper pads and traces in location; newer processes utilize plasma/laser etching instead of chemicals to remove the copper product, enabling finer line definitions.
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 solid board product.
The process of drilling all of the holes for plated through applications; a 2nd drilling process is utilized for holes that are not to be plated through. Details 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 put in an electrically charged bath of copper.
This is needed when holes are to be drilled through a copper location but the hole is not to be plated through. Avoid this procedure if possible since it adds cost to the finished board.
The process of using 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 protects against ecological damage, supplies insulation, protects versus solder shorts, and secures traces that run between pads.
The process of coating the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering process that will happen at a later date after the parts have been positioned.
The procedure of applying the markings for component designations and component outlines to the board. May be used to just the top 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 permits cutting notches or slots into the board if required.
A visual examination of the boards; also 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 means using a voltage between numerous points on the board and determining if a present circulation occurs. Relying on the board complexity, this process might need a specifically designed test component and test program to integrate with the electrical test system used by the board producer.