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 area mount applications or through rilled holes in the board and copper pads for soldering the component leads in thru-hole applications. A board style might have all thru-hole elements on the top or element side, a mix of thru-hole and surface area mount on the top just, a mix of thru-hole and surface area mount components on the top and surface mount parts on the bottom or circuit side, or surface area install elements on the leading and bottom sides of the board.
The boards are likewise utilized to electrically connect the needed leads for each element utilizing conductive copper traces. The part 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 leading and bottom sides of the board, or multilayer designs with copper pads and traces on top and bottom of board with a variable variety 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 actual copper pads and connection traces on the board surface areas as part of the board production process. A multilayer board includes a number of layers of dielectric product that has been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All 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 technologies.
In a typical 4 layer board style, the internal layers are often used to provide power and ground connections, such as a +5 V airplane layer and a Ground plane layer as the 2 internal layers, with all other circuit and component connections made on the leading and bottom layers of the board. Extremely intricate board styles might have a a great deal of layers to make the numerous connections for various voltage levels, ground connections, or for linking the lots of leads on ball grid array devices and other big integrated circuit bundle formats.
There are typically 2 types of material used to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, usually about.002 inches thick. Core product resembles an extremely thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, normally.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two techniques used to build up the preferred variety of layers. The core stack-up technique, which is an older technology, uses a center layer of pre-preg material with a layer of core product above and another layer of core product below. This mix of one pre-preg layer and two core layers would make a 4 layer board.
The film stack-up technique, a newer technology, would have core product 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 required by the board style, sort of like Dagwood building a sandwich. This method allows the maker versatility in how the board layer thicknesses are integrated to fulfill the completed product density requirements by differing the number of sheets of pre-preg in each layer. Once the product layers are finished, the entire 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 making printed circuit boards follows the steps listed below for the majority of applications.
The process of figuring out products, processes, and requirements to meet the consumer's requirements for the board design based upon the Gerber file info provided 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 standard procedure of exposing the copper and other locations unprotected by the etch resist film to a chemical that gets rid of the unprotected copper, leaving the secured copper pads and traces in place; more recent procedures use plasma/laser etching rather of chemicals to eliminate the copper material, enabling finer line meanings.
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 product.
The process of drilling all the holes for plated through applications; a 2nd drilling process is utilized for holes that are not to be plated through. Info on hole place and size is consisted of 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 needed when holes are to be drilled through a copper area but the hole is not to be plated through. Avoid this process if possible due to the fact that it includes cost to the completed board.
The procedure of applying a protective masking material, a solder mask, over the bare copper traces or over the copper that has actually had a thin layer of solder used; the solder mask protects versus environmental damage, supplies insulation, secures versus solder shorts, and protects traces that run in between pads.
The process 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 happen at a later date after the parts have actually been put.
The process of using the markings for element designations and part lays out to the board. May be applied to simply the top 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 likewise permits cutting notches or slots into the board if required.
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 techniques.
The process of looking for connection or shorted connections on the boards by means using a voltage in between different points on the board and determining if an existing circulation happens. Relying on the board complexity, this process might need a specially developed test component and test program to incorporate with the electrical test system used by the board maker.