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 area install applications or through rilled holes in the board and copper pads for soldering the part leads in thru-hole applications. A board design might have all thru-hole components on the leading or component side, a mix of thru-hole and surface install on the top side only, a mix of thru-hole and surface area mount parts on the top side and surface mount parts on the bottom or circuit side, or surface area mount elements on the top and bottom sides of the board.
The boards are also ISO 9001 Accreditation used to electrically connect the needed leads for each element 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 created as single agreed 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 actual copper pads and connection traces on the board surface areas as part of the board production procedure. A multilayer board consists of a number of layers of dielectric product that has actually been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All of these layers are aligned and 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 normal four layer board style, the internal layers are typically used to offer power and ground connections, such as a +5 V airplane layer and a Ground airplane layer as the two internal layers, with all other circuit and part connections made on the top and bottom layers of the board. Extremely intricate board styles may have a a great deal of layers to make the various connections for different voltage levels, ground connections, or for connecting the numerous leads on ball grid array gadgets and other large integrated circuit package formats.
There are generally 2 kinds 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, normally about.002 inches thick. Core product resembles a very thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, generally.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are 2 approaches utilized to build up the preferred number of layers. The core stack-up approach, 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 approach, a newer technology, would have core product as the center layer followed by layers of pre-preg and copper material developed above and below to form the last variety of layers needed by the board style, sort of like Dagwood constructing a sandwich. This approach enables the producer versatility in how the board layer densities are combined to satisfy the ended up product thickness requirements by differing the variety of sheets of pre-preg in each layer. When 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 many applications.
The procedure of determining products, processes, and requirements to satisfy the client's specs for the board style based upon the Gerber file info provided with the order.
The procedure of moving the Gerber file information for a layer onto an etch resist movie that is placed on the conductive copper layer.
The standard process of exposing the copper and other locations unprotected by the etch resist film to a chemical that eliminates the unguarded copper, leaving the safeguarded copper pads and traces in place; newer procedures use plasma/laser etching instead of chemicals to get rid of the copper product, allowing finer line meanings.
The process 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 strong 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. Info on hole area and size is contained 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 area but the hole is not to be plated through. Prevent this process if possible due to the fact that it includes cost to the ended up board.
The procedure 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 used; the solder mask protects against ecological damage, provides insulation, protects against solder shorts, and safeguards traces that run in between pads.
The procedure of finishing the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering process that will occur at a later date after the parts have actually been put.
The procedure of applying the markings for part classifications and element lays out to the board. May be used to simply the top or to both sides if parts are installed on both leading and bottom sides.
The procedure of separating several boards from a panel of similar boards; this process also allows cutting notches or slots into the board if needed.
A visual inspection of the boards; likewise can be the procedure of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The process of looking 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 takes place. Depending upon the board complexity, this process may require a specially developed test component and test program to incorporate with the electrical test system utilized by the board manufacturer.