In electronic devices, printed circuit boards, or PCBs, are utilized to mechanically support electronic elements which have their connection leads soldered onto copper pads in surface install 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 elements on the leading or element side, a mix of thru-hole and surface install on the top side only, a mix of thru-hole and surface area mount elements on the top side and surface install components on the bottom or circuit side, or surface install components on the leading and bottom sides of the board.
The boards are likewise used to electrically link the required leads for each component 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 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 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 number of internal copper layers with traces and connections.
Single or double sided boards consist of 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 surfaces as part of the board production procedure. A multilayer board includes a variety of layers of dielectric product that has actually been fertilized with adhesives, and these layers are utilized to separate the layers of copper plating. All these layers are aligned 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 innovations.
In a common four layer board style, the internal layers are often utilized 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 part connections made on the leading and bottom layers of the board. Very complicated board styles may have a a great deal of layers to make the various connections for various voltage levels, ground connections, or for linking the numerous leads on ball grid array gadgets and other large integrated circuit bundle formats.
There are normally 2 types of material utilized to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, usually about.002 inches thick. Core product resembles a very thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, generally.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are 2 approaches used to develop the wanted number of layers. The core stack-up method, 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 method, a more recent innovation, would have core material as the center layer followed by layers of pre-preg and copper material built up above and listed below to form the final number of layers needed by the board style, sort of like Dagwood constructing a sandwich. This technique allows the producer versatility in how the board layer thicknesses are integrated to meet the ended up item density requirements by differing the number of sheets of pre-preg in each layer. As soon as the product layers are completed, the entire stack is subjected to heat and pressure that triggers the adhesive in the pre-preg to bond the core and pre-preg layers together into a single entity.
The process of making printed circuit boards follows the actions listed below for a lot of applications.
The process of identifying materials, procedures, and requirements to satisfy the customer's specifications for the board style based on the Gerber file details offered with the purchase order.
The procedure of transferring the Gerber file information for a layer onto an etch withstand film that is put on the conductive copper layer.
The traditional procedure of exposing the copper and other locations unprotected by the etch resist movie to a chemical that removes the unprotected copper, leaving the safeguarded copper pads and traces in location; newer processes utilize plasma/laser etching instead of chemicals to get rid of the copper material, permitting finer line meanings.
The process of lining up the conductive copper and insulating dielectric layers and pushing them under heat to trigger the adhesive in the dielectric layers to form a strong board material.
The process of drilling all the holes for plated through applications; a second drilling procedure is used for holes that are not to be plated through. Info on hole place and size is included in the drill drawing file.
The procedure 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 area however the hole is not to be plated through. Prevent this process if possible due to the fact that it adds expense to the finished board.
The procedure of using 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 ISO 9001 Certification Consultants ecological damage, offers insulation, secures versus solder shorts, and protects traces that run in between pads.
The procedure 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 happen at a later date after the parts have actually been positioned.
The procedure of using the markings for component designations and element details to the board. May be applied to simply the top side 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 process also enables cutting notches or slots into the board if required.
A visual evaluation of the boards; likewise can be the process of inspecting 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 means applying a voltage in between various points on the board and determining if a current circulation occurs. Depending upon the board complexity, this process may need a specially designed test component and test program to incorporate with the electrical test system used by the board maker.