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 mount applications or through rilled holes in the board and copper pads for soldering the component leads in thru-hole applications. A board style may have all thru-hole parts on the top or component side, a mix of thru-hole and surface mount on the top only, a mix of thru-hole and surface mount parts on the top and surface install components on the bottom or circuit side, or surface area install components on the leading and bottom sides of the board.
The boards are likewise used to electrically link the required leads for each part 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 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 the top and bottom of board with a variable variety 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 etched away to form the real copper pads and connection traces on the board surfaces as part of the board manufacturing process. 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 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 innovations.
In a common 4 layer board design, the internal layers are often utilized to offer 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 part connections made on the top and bottom layers of the board. Very complicated board styles may 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 devices and other big integrated circuit plan formats.
There are generally 2 kinds of material utilized to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet form, typically about.002 inches thick. Core product resembles a very thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, typically.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are two methods utilized to build up the wanted variety of layers. The core stack-up technique, which is an older innovation, 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 2 core layers would make a 4 layer board.
The movie stack-up technique, a more recent technology, 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 last number of layers needed by the board design, sort of like Dagwood developing a sandwich. This method allows the maker flexibility in how the board layer densities are integrated to meet the finished item density requirements by varying the variety of sheets of pre-preg in each layer. As soon as the product layers are finished, the whole 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 producing printed circuit boards follows the actions listed below for most applications.
The process of determining products, procedures, and requirements to meet the consumer's requirements for the board design based on the Gerber file details offered with the 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 traditional process of exposing the copper and other areas unprotected by the etch withstand movie to a chemical that gets rid of the vulnerable copper, leaving the secured copper pads and traces in place; newer procedures utilize plasma/laser etching instead of chemicals to remove the copper material, allowing finer line definitions.
The process of aligning the conductive copper and insulating dielectric layers and pushing 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 2nd drilling procedure is utilized for holes that are not to be plated through. Info on hole area and size is contained in the drill drawing file.
The process of applying 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 location however the hole is not to be plated through. Prevent this procedure if possible due to the fact that it adds expense to the completed 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 used; the solder mask secures against environmental damage, provides insulation, safeguards against solder shorts, and safeguards traces that run in between pads.
The process of coating 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 components have actually been placed.
The process of applying the markings for element designations and component lays out to the board. Might be applied to simply the top or to both sides if elements are mounted on both top and bottom sides.
The process of separating numerous boards from a panel of similar boards; this process also enables cutting notches or slots into the board if required.
A visual evaluation of the boards; likewise 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 checking for continuity or shorted connections More interesting details here on the boards by methods applying a voltage between different points on the board and determining if an existing flow occurs. Relying on the board intricacy, this process might need a specially created test fixture and test program to incorporate with the electrical test system used by the board manufacturer.