In electronics, printed circuit boards, or PCBs, are utilized to mechanically support electronic parts which have their connection leads soldered onto copper pads in surface 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 elements on the leading or part side, a mix of thru-hole and surface mount on the top only, a mix of thru-hole and surface area install parts on the top and surface mount elements on the bottom or circuit side, or surface area mount components on the leading and bottom sides of the board.
The boards are likewise used to electrically connect the needed leads for each element 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 developed as single sided with 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 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 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 includes a number of layers of dielectric material that has 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 typically utilized to supply 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 element connections made on the leading and bottom layers of the board. Really complex board styles might have a a great deal of layers to make the numerous connections for different voltage levels, ground connections, or for connecting the lots of leads on ball grid array gadgets and other big integrated circuit bundle formats.
There are generally 2 kinds of material utilized 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 product resembles a very thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, typically.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are 2 ISO 9001 Certification Consultants methods utilized to build up the desired number of layers. The core stack-up approach, which is an older innovation, uses a center layer of pre-preg product with a layer of core material above and another layer of core material below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The movie stack-up technique, a more recent innovation, would have core material as the center layer followed by layers of pre-preg and copper material developed above and listed below to form the final variety of layers needed by the board style, sort of like Dagwood constructing a sandwich. This technique permits the manufacturer flexibility in how the board layer densities are combined to satisfy the ended up product thickness requirements by differing the number of sheets of pre-preg in each layer. As soon as the product layers are completed, the entire 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 procedure of producing printed circuit boards follows the actions below for a lot of applications.
The process of determining materials, procedures, and requirements to satisfy the client's specs for the board style based upon the Gerber file info supplied with the purchase order.
The procedure of transferring the Gerber file data for a layer onto an etch resist film that is placed on the conductive copper layer.
The conventional process of exposing the copper and other locations unprotected by the etch resist film to a chemical that eliminates the unprotected copper, leaving the protected copper pads and traces in location; newer processes utilize plasma/laser etching rather of chemicals to remove the copper material, allowing finer line definitions.
The process of aligning the conductive copper and insulating dielectric layers and pressing them under heat to trigger the adhesive in the dielectric layers to form a strong board product.
The process of drilling all the holes for plated through applications; a second drilling process is used for holes that are not to be plated through. Details on hole area 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 required when holes are to be drilled through a copper location however the hole is not to be plated through. Avoid this procedure if possible since it adds expense to the finished board.
The process 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 secures against ecological damage, offers insulation, secures versus solder shorts, and secures traces that run between pads.
The procedure 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 occur at a later date after the elements have actually been placed.
The procedure of applying the markings for part classifications and part outlines to the board. May be used to just the top side or to both sides if elements are installed on both leading and bottom sides.
The process of separating numerous boards from a panel of similar boards; this procedure likewise allows cutting notches or slots into the board if needed.
A visual assessment of the boards; also can be the procedure of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The process of checking for connection or shorted connections on the boards by methods applying a voltage in between various points on the board and figuring out if an existing flow happens. Relying on the board complexity, this procedure might require a specially designed test component and test program to incorporate with the electrical test system utilized by the board maker.