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 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 elements on the leading or element side, a mix of thru-hole and surface area install on the top only, a mix of thru-hole and surface area mount components on the top side and surface area mount elements on the bottom or circuit side, or surface install elements on the leading and bottom sides of the board.
The boards are also utilized to electrically connect the needed leads for each component using conductive copper traces. The component pads and connection traces are etched 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 just, double sided with copper pads and traces on the leading and bottom sides of the board, or multilayer designs 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 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 utilized to separate the layers of copper plating. All of these layers are aligned and after that 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 frequently utilized to provide power and ground connections, such as a +5 V airplane layer and a Ground airplane layer as the 2 internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Really complex board designs may have a large number of layers to make the various connections for various voltage levels, ground connections, or for linking the numerous leads on ball grid selection gadgets and other large integrated circuit package formats.
There are typically two types of material used to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet form, generally about.002 inches thick. Core product resembles an extremely thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, typically.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are 2 techniques used to build up the desired variety of layers. The core stack-up approach, which is an older technology, utilizes a center layer of pre-preg product with a layer of core material above and another layer of core material below. This mix of one pre-preg layer and 2 core layers would make a 4 layer board.
The movie stack-up method, a more recent technology, would have core material as the center layer followed by layers of pre-preg and copper product developed above and listed below to form the last number of layers needed by the board style, sort of like Dagwood constructing a sandwich. This technique permits the manufacturer versatility in how the board layer densities are combined to fulfill the ended up product density requirements by varying the variety of sheets of pre-preg in each layer. Once the product layers are finished, 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 manufacturing printed circuit boards follows the steps below for most applications.
The procedure of identifying products, processes, and requirements to meet the customer's specifications for the board style based on the Gerber file information offered with the order.
The procedure of moving the Gerber file data for a layer onto an etch withstand film that is placed on the conductive copper layer.
The conventional process See more of exposing the copper and other areas unprotected by the etch resist film to a chemical that removes the unguarded copper, leaving the protected copper pads and traces in location; newer processes utilize plasma/laser etching instead of chemicals to get rid of the copper product, permitting finer line definitions.
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 the holes for plated through applications; a 2nd drilling procedure 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 process of applying copper plating to the pads, traces, and drilled through holes that are to be plated through; boards are put 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 process if possible since it includes cost to the ended up board.
The procedure 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 used; the solder mask safeguards versus environmental damage, supplies insulation, protects against solder shorts, and safeguards traces that run in between pads.
The procedure of finishing the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will occur at a later date after the components have been positioned.
The process of using the markings for element designations and component describes to the board. Might be used to just the top or to both sides if parts are installed on both top and bottom sides.
The procedure of separating several boards from a panel of similar boards; this process also enables cutting notches or slots into the board if required.
A visual examination of the boards; also can be the procedure of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The procedure of checking for connection or shorted connections on the boards by means applying a voltage between various points on the board and identifying if a current flow takes place. Depending upon the board intricacy, this procedure may require a specifically developed test fixture and test program to incorporate with the electrical test system utilized by the board producer.