In electronic devices, printed circuit boards, or PCBs, are utilized to mechanically support electronic parts which have their connection leads soldered onto copper pads in surface area install applications or through rilled holes in the board and copper pads for soldering the element leads in thru-hole applications. A board style might have all thru-hole parts on the top or element side, a mix of thru-hole and surface mount on the top side just, a mix of thru-hole and surface install components on the top side and surface install elements on the bottom or circuit side, or surface area mount components on the top and bottom sides of the board.
The boards are also used to electrically connect the needed leads for each part using conductive copper traces. The part pads and connection traces are engraved 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 only, double agreed copper pads and traces on the top 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 engraved away to form the real copper pads and connection traces on the board surfaces as part of the board manufacturing process. A multilayer board includes a number of layers of dielectric product that has actually been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All of these layers are lined up 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 style, the internal layers are typically used to supply 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 element connections made on the leading and bottom layers of the board. Really complex board designs might have a large number of layers to make the numerous connections for different voltage levels, ground connections, or for connecting the lots of leads on ball grid variety gadgets and other big integrated circuit plan formats.
There are typically two kinds of product used to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet kind, typically about.002 inches thick. Core product is similar to a really thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, generally.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two techniques utilized to build up the desired number 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 product below. This mix of one pre-preg layer and 2 core layers would make a 4 layer board.
The movie stack-up technique, a newer technology, would have core material as the center layer followed by layers of pre-preg and copper product developed above and below to form the final number of layers needed by the board style, sort of like Dagwood building a sandwich. This approach enables ISO 9001 consultants the producer flexibility in how the board layer densities are combined to satisfy the ended up item density requirements by differing the variety of sheets of pre-preg in each layer. As soon as the material layers are completed, the whole stack goes through 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 manufacturing printed circuit boards follows the steps listed below for a lot of applications.
The process of identifying materials, procedures, and requirements to meet the client's specs for the board design based upon the Gerber file info supplied with the purchase order.
The process of moving the Gerber file information for a layer onto an etch resist film that is put on the conductive copper layer.
The standard procedure 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 place; more recent procedures utilize plasma/laser etching instead of chemicals to get rid of the copper material, permitting finer line definitions.
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 material.
The process of drilling all of the holes for plated through applications; a 2nd drilling procedure is used for holes that are not to be plated through. Info on hole location and size is contained 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 placed in an electrically charged bath of copper.
This is required when holes are to be drilled through a copper area however the hole is not to be plated through. Avoid this procedure if possible since it adds cost to the finished board.
The process of using 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 safeguards against environmental damage, offers insulation, safeguards versus solder shorts, and safeguards traces that run between pads.
The procedure of finish the pad areas with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering process that will occur at a later date after the elements have actually been put.
The process of using the markings for component classifications and part details to the board. Might be applied to just the top or to both sides if elements are mounted on both top and bottom sides.
The process of separating several boards from a panel of identical boards; this process likewise permits cutting notches or slots into the board if needed.
A visual examination of the boards; likewise can be the process of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The process of checking for continuity or shorted connections on the boards by ways applying a voltage in between numerous points on the board and figuring out if an existing circulation occurs. Depending upon the board intricacy, this procedure might need a specifically created test component and test program to integrate with the electrical test system utilized by the board producer.