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 install applications or through rilled holes in the board and copper pads for soldering the component leads in thru-hole applications. A board style may have all thru-hole components on the top or part side, a mix of thru-hole and surface area mount on the top side just, a mix of thru-hole and surface mount components on the top side and surface area install parts on the bottom or circuit side, or surface install elements on the leading and bottom sides of the board.
The boards are also used to electrically link the required leads for each element utilizing conductive copper traces. The element pads and connection traces are engraved 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 sided with copper pads and traces on the leading 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 material, such as FR-4 epoxy fiberglass, with copper plating on one or both sides. This copper plating is engraved 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 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 lined up 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 typical four layer board style, the internal layers are typically used to offer 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 leading and bottom layers of the board. Really complicated board styles may have a a great deal ISO 9001 Accreditation of layers to make the different connections for different voltage levels, ground connections, or for linking the numerous leads on ball grid array gadgets and other big incorporated circuit bundle formats.
There are usually 2 kinds of product utilized to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, generally about.002 inches thick. Core material is similar to a really thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, typically.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two techniques used to develop the wanted number of layers. The core stack-up method, which is an older technology, uses a center layer of pre-preg product 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 method, a more recent innovation, would have core material as the center layer followed by layers of pre-preg and copper product built up above and below to form the final number of layers needed by the board design, sort of like Dagwood developing a sandwich. This method enables the producer flexibility in how the board layer densities are integrated to meet the completed item density requirements by differing the number of sheets of pre-preg in each layer. When 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 process of producing printed circuit boards follows the steps listed below for the majority of applications.
The process of identifying products, procedures, and requirements to meet the client's specifications for the board style based upon the Gerber file info supplied with the purchase order.
The procedure of transferring the Gerber file data for a layer onto an etch withstand movie that is placed on the conductive copper layer.
The conventional process of exposing the copper and other areas unprotected by the etch resist movie to a chemical that eliminates the unprotected copper, leaving the secured copper pads and traces in location; more recent processes use plasma/laser etching instead of chemicals to eliminate the copper material, 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 strong board material.
The procedure of drilling all the holes for plated through applications; a 2nd drilling procedure is used for holes that are not to be plated through. Info on hole area and size is included in the drill drawing file.
The procedure of using 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 due to the fact that it includes cost to the completed board.
The process 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 applied; the solder mask protects versus ecological damage, supplies insulation, safeguards versus solder shorts, and safeguards traces that run in between pads.
The process of coating the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering process that will happen at a later date after the elements have been put.
The process of using the markings for component designations and component outlines to the board. May be applied to simply the top or to both sides if elements are installed on both leading and bottom sides.
The process of separating several boards from a panel of similar boards; this procedure likewise permits 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 methods.
The procedure of looking for connection or shorted connections on the boards by means applying a voltage between different points on the board and identifying if a present flow takes place. Depending upon the board intricacy, this procedure might need a specially developed test component and test program to incorporate with the electrical test system utilized by the board maker.