In electronics, 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 ISO 9001 Certification Consultants copper pads for soldering the component leads in thru-hole applications. A board style might have all thru-hole parts on the leading or component side, a mix of thru-hole and surface mount on the top side just, a mix of thru-hole and surface area mount parts on the top and surface area install components on the bottom or circuit side, or surface mount parts on the leading and bottom sides of the board.
The boards are also utilized to electrically link the required leads for each element using conductive copper traces. The element pads and connection traces are engraved from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are developed as single agreed copper pads and traces on one side of the board just, 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 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 real copper pads and connection traces on the board surfaces as part of the board production process. A multilayer board consists of a number of layers of dielectric product that has been impregnated with adhesives, and these layers are utilized to separate the layers of copper plating. All of 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 common 4 layer board design, the internal layers are often utilized to supply power and ground connections, such as a +5 V aircraft layer and a Ground plane layer as the two internal layers, with all other circuit and element connections made on the leading and bottom layers of the board. Extremely complex board designs may have a large number of layers to make the numerous connections for different voltage levels, ground connections, or for linking the numerous leads on ball grid selection devices and other large incorporated circuit package formats.
There are usually two kinds of product utilized to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet form, normally 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 transferred on each side, generally.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are 2 approaches used to develop the desired 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 product listed below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The film stack-up approach, a newer technology, would have core product as the center layer followed by layers of pre-preg and copper product built up above and listed below to form the final variety of layers needed by the board design, sort of like Dagwood constructing a sandwich. This method permits the producer flexibility in how the board layer thicknesses are integrated to fulfill the completed product thickness requirements by differing the number of sheets of pre-preg in each layer. Once the material 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 process of figuring out products, procedures, and requirements to meet the customer's specs for the board design based on the Gerber file details provided with the 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 traditional process of exposing the copper and other areas unprotected by the etch withstand film to a chemical that eliminates the vulnerable copper, leaving the secured copper pads and traces in location; more recent procedures utilize plasma/laser etching instead of chemicals to remove the copper product, allowing finer line definitions.
The procedure 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 product.
The procedure of drilling all of the holes for plated through applications; a 2nd drilling procedure is used for holes that are not to be plated through. Information on hole place and size is included in the drill drawing file.
The process 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 needed when holes are to be drilled through a copper area but the hole is not to be plated through. Prevent this procedure if possible since it adds cost to the finished board.
The procedure 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 used; the solder mask protects against environmental damage, supplies insulation, protects versus solder shorts, and safeguards traces that run in between pads.
The process of finishing 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 parts have been positioned.
The procedure of using the markings for part classifications and component details to the board. May be used to simply the top side or to both sides if components are installed on both leading and bottom sides.
The process of separating several boards from a panel of identical boards; this procedure likewise permits cutting notches or slots into the board if needed.
A visual evaluation of the boards; likewise can be the procedure of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The procedure of looking for connection or shorted connections on the boards by ways applying a voltage between various points on the board and determining if a current circulation takes place. Relying on the board complexity, this procedure may require a specially created test fixture and test program to incorporate with the electrical test system used by the board producer.