In electronic devices, printed circuit boards, or PCBs, are used 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 part leads in thru-hole applications. A board design may have all thru-hole elements on the top or element side, a mix of thru-hole and surface mount on the top only, a mix of thru-hole and surface area install elements on the top side and surface install elements on the bottom or circuit side, or surface area mount components on the leading and bottom sides of the board.
The boards are likewise utilized to electrically link the required leads for each part using conductive copper traces. The element pads and connection traces are etched from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are designed as single agreed 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 styles with copper pads and traces on the top and bottom of board with a variable number of internal copper layers with traces and connections.
Single or double sided boards include 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 surfaces as part of the board production procedure. A multilayer board includes 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 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 innovations.
In a normal four layer board design, the internal layers are typically utilized to offer 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 component connections made on the top and bottom layers of the board. Really complicated board designs may have a a great deal of layers to make the various connections for different voltage levels, ground connections, or for linking the numerous leads on ball grid array gadgets and other large integrated circuit plan formats.
There are usually two 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, usually about.002 inches thick. Core product resembles an extremely 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 product with 1 ounce copper layer on each side. In a multilayer board style, there are 2 techniques used to build up the wanted number of layers. The core stack-up method, which is an older technology, utilizes a center layer of pre-preg material with a layer of core product above and another layer of core material below. This mix of one pre-preg layer and two core layers would make a 4 layer board.
The movie stack-up technique, a more recent innovation, would have core product as the center layer followed by layers of pre-preg and copper material developed above and below to form the final variety of layers needed by the board style, sort of like Dagwood developing a sandwich. This technique allows the maker versatility in how the board layer densities are integrated to satisfy the ended up product thickness requirements by differing the variety of sheets of pre-preg in each layer. When the product layers are completed, the whole stack undergoes heat and pressure that causes 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 most applications.
The procedure of identifying materials, processes, and requirements to satisfy the customer's specs for the board design based upon the Gerber file details offered with the purchase order.
The process of transferring the Gerber file data for a layer ISO 9001 Accreditation onto an etch resist film that is put on the conductive copper layer.
The traditional process of exposing the copper and other areas unprotected by the etch resist movie to a chemical that eliminates the unguarded copper, leaving the safeguarded copper pads and traces in location; more recent processes utilize plasma/laser etching rather of chemicals to get rid of the copper product, permitting 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 solid board material.
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. 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 but the hole is not to be plated through. Avoid this procedure if possible due to the fact that it includes expense 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, supplies insulation, safeguards versus solder shorts, and protects traces that run between pads.
The procedure of finishing the pad locations with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will occur at a later date after the parts have actually been put.
The procedure of using the markings for component classifications and element describes to the board. Might be applied to simply the top side or to both sides if parts are mounted on both leading and bottom sides.
The procedure of separating several boards from a panel of similar boards; this procedure likewise allows cutting notches or slots into the board if required.
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 approaches.
The procedure of looking for continuity or shorted connections on the boards by methods using a voltage between different points on the board and identifying if an existing flow takes place. Depending upon the board complexity, this procedure may require a specially created test component and test program to integrate with the electrical test system utilized by the board producer.