In electronic devices, printed circuit boards, or PCBs, are used 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 may have all thru-hole parts 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 area install components on the top and surface area install parts on the bottom or circuit side, or surface mount elements on the top and bottom sides of the board.
The boards are also used to electrically connect the required leads for each component using conductive copper traces. The part pads and connection traces are etched from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are developed as single sided with copper pads and traces on one side of the board just, double agreed 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 product, 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 process. A multilayer board includes a variety 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 common four layer board design, the internal layers are typically utilized to supply power and ground connections, such as a +5 V plane layer and a Ground plane layer as the 2 internal layers, with all other circuit and element connections made on the leading and bottom layers of the board. Very complex board styles may have a large number of layers to make the numerous connections for different voltage levels, ground connections, or for connecting the lots of leads on ball grid range gadgets and other large integrated circuit plan formats.
There are generally two kinds of product used to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, generally about.002 inches thick. Core product resembles a really thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, generally.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are 2 approaches used to develop the wanted variety 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 material listed below. This combination of one pre-preg layer and 2 core layers would make a 4 layer board.
The film stack-up approach, a newer innovation, would have core product as the center layer followed by layers of pre-preg and copper product developed above and below to form the final number of layers required by the board design, sort of like Dagwood developing a sandwich. This method allows the maker versatility in how the board layer densities are integrated to satisfy the completed item density requirements by differing the variety of sheets of pre-preg in each layer. When the product layers are finished, the whole stack goes through 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 making printed circuit boards follows the steps below for the majority of applications.
The process of identifying products, processes, and requirements to satisfy the customer's requirements for the board style based on the Gerber file info provided with the purchase order.
The process of transferring the Gerber file information for a layer onto an etch resist movie that is put on the conductive copper layer.
The traditional procedure of exposing the copper and other areas unprotected by the etch resist movie to a chemical that removes the vulnerable copper, leaving the safeguarded copper pads and traces in place; more recent processes use plasma/laser etching instead of chemicals to eliminate the copper product, enabling finer line meanings.
The process of aligning 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 product.
The procedure of drilling all the holes for plated through applications; a 2nd drilling process is utilized for holes that are not to be plated through. Details on hole location 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 positioned in an electrically charged bath of copper.
This is required when holes are to be drilled through a copper location but the hole is not to be plated through. Prevent this procedure if possible due to the fact that it adds cost to the finished board.
The procedure of applying 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 used; the solder mask secures versus ecological damage, supplies insulation, secures against solder shorts, and protects traces that run in between pads.
The process of covering the pad areas with a thin layer of solder ISO 9001 consultants to prepare the board for the eventual wave soldering or reflow soldering process that will take place at a later date after the elements have been positioned.
The process of using the markings for component designations and part lays out to the board. May be applied to just the top or to both sides if parts are mounted on both leading and bottom sides.
The procedure of separating numerous boards from a panel of identical boards; this process also allows cutting notches or slots into the board if needed.
A visual assessment of the boards; also can be the process of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The procedure of checking for connection or shorted connections on the boards by methods applying a voltage between different points on the board and determining if a present circulation happens. Relying on the board intricacy, this procedure may require a specifically created test fixture and test program to incorporate with the electrical test system utilized by the board producer.