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 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 components on the leading or element side, a mix of thru-hole and surface install on the top side just, a mix of thru-hole and surface install elements on the top and surface area install parts on the bottom or circuit side, or surface area mount parts on the leading and bottom sides of the board.
The boards are also utilized to electrically link the required leads for each part utilizing conductive copper traces. The element pads and connection traces are etched from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are designed 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 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 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 actual copper pads and connection traces on the board surfaces as part of the board manufacturing procedure. A multilayer board consists of a variety of layers of dielectric product that has been impregnated with adhesives, and these layers are utilized to separate the layers of copper plating. All of 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 frequently used to offer power and ground connections, such as a +5 V airplane layer and a Ground aircraft layer as the two internal layers, with all other circuit and element connections made on the leading and bottom layers of the board. Very complex board styles may have a large number of layers to make the numerous connections for various voltage levels, ground connections, or for connecting the many leads on ball grid variety devices and other big integrated circuit bundle formats.
There are generally two kinds of product utilized to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, typically about.002 inches thick. Core material is similar to 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 style, there are 2 approaches used to build up the preferred number of layers. The core stack-up approach, which is an older technology, utilizes a center layer of pre-preg material with a layer of core material above and another layer of core product listed below. This combination of one pre-preg layer and 2 core layers would make a 4 layer board.
The film stack-up technique, a newer Click here innovation, would have core material as the center layer followed by layers of pre-preg and copper material built up above and below to form the last number of layers needed by the board design, sort of like Dagwood developing a sandwich. This technique permits the producer versatility in how the board layer thicknesses are combined to fulfill the finished product density requirements by varying the variety of sheets of pre-preg in each layer. When the product 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 procedure of producing printed circuit boards follows the actions below for most applications.
The procedure of determining materials, processes, and requirements to meet the customer's requirements for the board style based on the Gerber file info supplied with the purchase order.
The procedure of moving the Gerber file information for a layer onto an etch resist film that is put on the conductive copper layer.
The conventional process of exposing the copper and other locations unprotected by the etch resist movie to a chemical that removes the vulnerable copper, leaving the safeguarded copper pads and traces in location; more recent procedures utilize plasma/laser etching rather of chemicals to remove the copper product, enabling finer line meanings.
The procedure of lining up 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. Information on hole place and size is included 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 positioned 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 process if possible due to the fact that it adds expense to the finished board.
The procedure of using a protective masking product, a solder mask, over the bare copper traces or over the copper that has actually had a thin layer of solder applied; the solder mask secures versus ecological damage, supplies insulation, protects versus solder shorts, and safeguards traces that run between pads.
The process of finishing the pad locations 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 parts have actually been positioned.
The process of applying the markings for component classifications and component outlines to the board. May be applied to simply the top or to both sides if components are mounted on both top and bottom sides.
The process of separating several boards from a panel of similar boards; this procedure likewise allows cutting notches or slots into the board if needed.
A visual evaluation 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 methods.
The procedure of checking for continuity or shorted connections on the boards by methods applying a voltage between various points on the board and determining if a present flow occurs. Relying on the board intricacy, this procedure might need a specially created test component and test program to incorporate with the electrical test system used by the board manufacturer.