In electronics, printed circuit boards, or PCBs, are used to mechanically support electronic elements which have their connection leads soldered onto copper ISO 9001 Accreditation pads in surface mount applications or through rilled holes in the board and copper pads for soldering the element leads in thru-hole applications. A board style might have all thru-hole parts on the leading or part side, a mix of thru-hole and surface install on the top side only, a mix of thru-hole and surface mount components on the top side and surface area mount components on the bottom or circuit side, or surface mount parts on the top and bottom sides of the board.
The boards are also used to electrically link the required leads for each component 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 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 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 surface areas as part of the board manufacturing process. A multilayer board includes a variety of layers of dielectric material that has been fertilized with adhesives, and these layers are utilized to separate the layers of copper plating. All these layers are aligned 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 often utilized to provide power and ground connections, such as a +5 V airplane layer and a Ground aircraft layer as the 2 internal layers, with all other circuit and element connections made on the leading and bottom layers of the board. Very complicated board designs may have a large number of layers to make the numerous connections for different voltage levels, ground connections, or for connecting the numerous leads on ball grid variety gadgets and other large incorporated circuit plan formats.
There are generally two kinds of material utilized to build a multilayer board. Pre-preg material 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 very thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, usually.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are two approaches used to develop the desired number of layers. The core stack-up technique, which is an older innovation, utilizes a center layer of pre-preg product with a layer of core material above and another layer of core product below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The movie stack-up technique, a newer technology, would have core product as the center layer followed by layers of pre-preg and copper material built up above and below to form the final number of layers required by the board style, sort of like Dagwood building a sandwich. This method enables the maker versatility in how the board layer thicknesses are integrated to fulfill the finished product density requirements by differing the number of sheets of pre-preg in each layer. As soon as the product layers are completed, the whole stack is subjected to 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 procedure of making printed circuit boards follows the steps listed below for most applications.
The procedure of determining materials, procedures, and requirements to meet the customer's specs for the board style based on the Gerber file details supplied with the order.
The process of transferring the Gerber file information for a layer onto an etch withstand film that is put on the conductive copper layer.
The traditional process of exposing the copper and other locations unprotected by the etch resist movie to a chemical that eliminates the vulnerable copper, leaving the safeguarded copper pads and traces in place; newer processes utilize plasma/laser etching instead of chemicals to remove the copper material, permitting finer line meanings.
The process of lining up the conductive copper and insulating dielectric layers and pressing them under heat to activate the adhesive in the dielectric layers to form a strong board material.
The procedure of drilling all the holes for plated through applications; a second drilling process is used for holes that are not to be plated through. Details on hole location 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 placed 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 expense to the ended up board.
The process of applying 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 safeguards against environmental damage, supplies insulation, safeguards versus solder shorts, and safeguards traces that run between pads.
The procedure of covering the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering process that will occur at a later date after the elements have actually been placed.
The procedure of applying the markings for component classifications and component describes to the board. Might be applied to just the top or to both sides if elements are mounted on both leading and bottom sides.
The procedure of separating numerous boards from a panel of similar boards; this process likewise enables cutting notches or slots into the board if required.
A visual inspection of the boards; also can be the process of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The process of looking for connection or shorted connections on the boards by methods using a voltage between numerous points on the board and determining if a present circulation happens. Depending upon the board complexity, this process might need a specially developed test fixture and test program to integrate with the electrical test system used by the board maker.