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 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 top or element side, a mix of thru-hole and surface mount on the top side only, a mix of thru-hole and surface mount parts on the top side and surface area mount elements on the bottom or circuit side, or surface mount parts on the leading and bottom sides of the board.
The boards are likewise used to electrically connect the needed leads for each element using conductive copper traces. The component pads and connection traces are etched from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are designed as single sided with copper pads and traces on one side of the board only, double agreed 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 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 includes a number of layers of dielectric product that has been fertilized with adhesives, and these layers are utilized 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 4 layer board design, the internal layers are frequently 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 leading and bottom layers of the board. Very intricate board designs may have a a great deal of layers to make the numerous connections for various voltage levels, ground connections, or for connecting the many leads on ball grid variety devices and other large incorporated circuit package formats.
There are generally two types of material used to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet kind, generally about.002 inches thick. Core material resembles an extremely thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, usually.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two approaches utilized to build up the wanted variety of layers. The core stack-up approach, which is an older technology, uses a center layer of pre-preg material with a layer of core material above and another layer of core material below. This combination of one pre-preg layer and 2 core layers would make a 4 layer board.
The movie stack-up method, a newer technology, would have core material as the center layer followed by layers of pre-preg and copper material developed above and listed below to form the last variety of layers needed by the board style, sort of like Dagwood building a sandwich. This approach permits the manufacturer flexibility in how the board layer densities are integrated to meet the completed product thickness requirements by differing the number of sheets of pre-preg in each layer. As soon as the product 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 procedure of producing printed circuit boards follows the steps below for the majority of applications.
The procedure of identifying products, processes, and requirements to meet the customer's specifications for the board design based on the Gerber file details supplied with the purchase order.
The procedure of transferring the Gerber file data for a layer onto an etch resist film that is put on the conductive copper layer.
The conventional process of exposing the copper and other locations unprotected by the etch resist film to a chemical that eliminates the vulnerable copper, leaving the safeguarded copper pads and traces in place; newer processes use plasma/laser etching instead of chemicals to get rid of the copper product, enabling finer line meanings.
The process of lining up 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 of the holes for plated through applications; a second drilling procedure is used for holes that are not to be plated through. Details on hole place and size is contained 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 positioned in an electrically charged bath of copper.
This is required when holes are to be drilled through a copper area however the hole is not to be plated through. Avoid this procedure if possible because it adds expense to the ended up board.
The process of using a protective masking product, a solder mask, over the bare copper traces or over the copper that has actually had a thin layer of solder applied; the solder mask protects against ecological damage, supplies insulation, safeguards versus solder shorts, and protects 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 procedure that will happen at a later date after the components have actually been put.
The procedure of applying the markings for element designations and component outlines to the board. Might be applied to just the top or to both sides if elements are installed on both leading and bottom sides.
The process of separating multiple boards from a panel of identical boards; this procedure likewise allows cutting notches or slots into the board if required.
A visual evaluation of the ISO 9001 Accreditation Consultants boards; also can be the procedure of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The procedure of checking for continuity or shorted connections on the boards by means applying a voltage between different points on the board and determining if a present flow occurs. Depending upon the board intricacy, this procedure might require a specifically developed test fixture and test program to incorporate with the electrical test system utilized by the board producer.