In electronics, printed circuit boards, or ISO 9001 Accreditation Consultants PCBs, are utilized to mechanically support electronic components which have their connection leads soldered onto copper pads in surface area mount applications or through rilled holes in the board and copper pads for soldering the part leads in thru-hole applications. A board style may have all thru-hole parts on the top or part side, a mix of thru-hole and surface area install on the top only, a mix of thru-hole and surface install parts on the top side and surface area mount parts on the bottom or circuit side, or surface area install elements on the leading and bottom sides of the board.
The boards are likewise utilized 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 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 include a core dielectric material, 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 process. A multilayer board includes 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 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 innovations.
In a typical 4 layer board design, the internal layers are typically used to supply 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 component connections made on the top and bottom layers of the board. Extremely complicated board designs may have a large number of layers to make the numerous connections for different voltage levels, ground connections, or for linking the many leads on ball grid array devices and other large integrated circuit bundle formats.
There are usually 2 types of product used to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet form, normally about.002 inches thick. Core material resembles an extremely thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, normally.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are two methods utilized to build up the desired variety of layers. The core stack-up method, which is an older technology, utilizes a center layer of pre-preg material with a layer of core material above and another layer of core product below. This mix of one pre-preg layer and two core layers would make a 4 layer board.
The film stack-up technique, a newer innovation, would have core product 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 required by the board design, sort of like Dagwood developing a sandwich. This technique permits the maker flexibility in how the board layer thicknesses are integrated to meet the ended up item thickness requirements by varying the variety of sheets of pre-preg in each layer. As soon as the material layers are finished, the whole 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 manufacturing printed circuit boards follows the actions below for many applications.
The process of figuring out products, processes, and requirements to meet the customer's specs for the board design based on the Gerber file info provided with the order.
The process of moving the Gerber file data for a layer onto an etch resist movie that is put on the conductive copper layer.
The conventional procedure of exposing the copper and other areas unprotected by the etch resist movie to a chemical that gets rid of the vulnerable copper, leaving the protected copper pads and traces in place; more recent processes use plasma/laser etching instead of chemicals to remove the copper product, permitting finer line meanings.
The process of aligning the conductive copper and insulating dielectric layers and pressing them under heat to activate 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 process is used for holes that are not to be plated through. Details 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 required when holes are to be drilled through a copper area but the hole is not to be plated through. Prevent this procedure if possible because it includes expense to the completed board.
The process 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 applied; the solder mask safeguards against environmental damage, offers insulation, secures against solder shorts, and protects 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 ultimate wave soldering or reflow soldering procedure that will happen at a later date after the parts have been put.
The procedure of using the markings for part designations and part lays out to the board. May be applied to just the top side or to both sides if elements are mounted on both top and bottom sides.
The procedure of separating numerous boards from a panel of similar boards; this process also permits cutting notches or slots into the board if needed.
A visual examination 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 procedure of checking for continuity or shorted connections on the boards by ways applying a voltage in between different points on the board and identifying if a present flow occurs. Depending upon 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 maker.