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 mount applications or through rilled holes in the board and copper pads for soldering the component leads in thru-hole applications. A board design might have all thru-hole parts on the top or component side, a mix of thru-hole and surface install on the top side only, a mix of thru-hole and surface area mount parts on the top side and surface area install elements on the bottom or circuit side, or surface area install parts on the top and bottom sides of the board.
The boards are likewise utilized to electrically link the required leads for each component 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 designed as single agreed 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 designs 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 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 actual copper pads and connection traces on the board surfaces as part of the board manufacturing process. A multilayer board includes a variety of layers of dielectric material that has actually been fertilized with adhesives, and these layers are utilized to separate the layers of copper plating. All of these layers are lined up 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 normal 4 layer board design, the internal layers are frequently used to offer power and ground connections, such as a +5 V aircraft layer and a Ground airplane layer as the two internal layers, with all other circuit and part connections made on the top and bottom layers of the board. Very complex board designs might have a a great deal of layers to make the various connections for various voltage levels, ground connections, or for linking the lots of leads on ball grid selection gadgets and other large integrated circuit plan formats.
There are typically two 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, generally about.002 inches thick. Core material resembles a very thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, generally.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are 2 approaches utilized to develop the desired variety of layers. The core stack-up approach, which is an older technology, uses a center layer of pre-preg product with a layer of core product above and another layer of core product 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 material built up above and listed below to form the last number of layers needed by the board style, sort of like Dagwood constructing a sandwich. This approach enables the producer flexibility in how the board layer densities are combined 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 undergoes heat and pressure that causes the ISO 9001 Accreditation adhesive in the pre-preg to bond the core and pre-preg layers together into a single entity.
The process of producing printed circuit boards follows the steps listed below for many applications.
The procedure of determining products, procedures, and requirements to fulfill the consumer's specs for the board design based upon the Gerber file information supplied with the purchase order.
The process of moving the Gerber file information for a layer onto an etch resist movie that is put on the conductive copper layer.
The standard process of exposing the copper and other areas unprotected by the etch resist movie to a chemical that gets rid of the unguarded copper, leaving the protected copper pads and traces in location; more recent procedures utilize plasma/laser etching rather of chemicals to remove the copper product, permitting finer line definitions.
The process of lining up the conductive copper and insulating dielectric layers and pressing them under heat to trigger the adhesive in the dielectric layers to form a solid board material.
The process of drilling all the holes for plated through applications; a second drilling procedure is utilized for holes that are not to be plated through. Information on hole location and size is contained 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 put in an electrically charged bath of copper.
This is needed when holes are to be drilled through a copper location but the hole is not to be plated through. Prevent this process if possible due to the fact that it includes expense to the finished board.
The process of applying a protective masking product, a solder mask, over the bare copper traces or over the copper that has had a thin layer of solder applied; the solder mask protects versus ecological damage, provides insulation, protects versus solder shorts, and secures traces that run in between pads.
The process of covering the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering procedure that will occur at a later date after the components have actually been positioned.
The process of using the markings for component classifications and component details to the board. Might be applied to simply the top side or to both sides if parts are installed on both leading and bottom sides.
The procedure of separating multiple boards from a panel of identical boards; this procedure also permits cutting notches or slots into the board if needed.
A visual evaluation of the boards; also can be the procedure of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The process of checking for continuity or shorted connections on the boards by methods applying a voltage in between numerous points on the board and determining if a present circulation occurs. Depending upon the board intricacy, this procedure might need a specially developed test component and test program to incorporate with the electrical test system used by the board manufacturer.