In electronic devices, printed circuit boards, or PCBs, are utilized to mechanically support electronic components 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 component leads in thru-hole applications. A board design might have all thru-hole components on the top or element side, a mix of thru-hole and surface install on the top only, a mix of thru-hole and surface mount parts on the top side and surface area install elements on the bottom or circuit side, or surface mount elements on the top and bottom sides of the board.
The boards are likewise used to electrically connect 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 created as single agreed copper pads and traces on one side of the board only, double sided with copper pads and traces on the top 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 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 manufacturing procedure. A multilayer board consists of a number of layers of dielectric material that has been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All of these layers are lined up 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 technologies.
In a typical 4 layer board style, the internal layers are typically utilized to offer 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 component connections made on the leading and bottom layers of the board. Extremely complex board designs may 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 devices and other big integrated circuit bundle formats.
There are typically 2 types of material used to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet form, typically about.002 inches thick. Core product resembles a very thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, generally.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are two techniques utilized to build up the desired number of layers. The core stack-up technique, 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 listed below. This mix of one pre-preg layer and two core layers would make a 4 layer board.
The film stack-up method, a more recent innovation, would have core product as the center layer followed by layers of pre-preg and copper material developed above and below to form the last variety of layers needed by the board design, sort of like Dagwood building a sandwich. This technique enables the maker versatility in how the board layer densities are combined to satisfy the completed item density requirements by differing the number of sheets of pre-preg in each layer. Once the material layers are completed, the whole stack undergoes 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 process of producing printed circuit boards follows the actions below for most applications.
The procedure of determining materials, processes, and requirements to fulfill the client's specifications for the board style based on the Gerber file details provided with the order.
The procedure of moving the Gerber file information for a layer onto an etch withstand film that is placed on the conductive copper layer.
The conventional procedure of exposing the copper and other areas unprotected by the etch resist film to a chemical that eliminates the unguarded copper, leaving the protected copper pads and traces in location; more recent processes use plasma/laser etching rather of chemicals to remove the copper product, enabling finer line meanings.
The procedure 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 strong board product.
The process of drilling ISO 9001 all of the holes for plated through applications; a 2nd drilling procedure is utilized 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 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 since it adds 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 applied; the solder mask protects against environmental damage, supplies insulation, protects versus solder shorts, and safeguards traces that run between pads.
The procedure of coating the pad locations with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering process that will occur at a later date after the elements have actually been put.
The procedure of using the markings for part classifications and part details to the board. Might be used to just the top or to both sides if components are installed on both leading and bottom sides.
The process of separating multiple boards from a panel of identical boards; this process also enables cutting notches or slots into the board if needed.
A visual inspection of the boards; also can be the process of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The process of looking for continuity or shorted connections on the boards by means applying a voltage in between different points on the board and figuring out if an existing flow happens. Relying on the board intricacy, this process may need a specially created test fixture and test program to incorporate with the electrical test system used by the board manufacturer.