In electronics, printed circuit boards, or PCBs, are used to mechanically support electronic components 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 part leads in thru-hole applications. A board style may have all thru-hole elements on the top or element side, a mix of thru-hole and surface mount on the top side only, a mix of thru-hole and surface area mount components on the top side and surface mount components on the bottom or circuit side, or surface area mount elements on the top and bottom sides of the board.
The boards are also utilized to electrically connect the needed leads for each element 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 styles 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 include a core dielectric material, 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 procedure. A multilayer board consists of a variety of layers of dielectric product that has actually been fertilized with adhesives, and these layers are used to separate the layers of copper plating. All of these layers are aligned 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 normal 4 layer board style, the internal layers are frequently used to supply power and ground connections, such as a +5 V airplane layer and a Ground plane layer as the two internal layers, with all other circuit and element connections made on the top and bottom layers of the board. Very intricate board styles may have a large number of layers to make the different connections for various voltage levels, ground connections, or for linking the many leads on ball grid range gadgets and other big integrated circuit bundle formats.
There are typically 2 kinds of product utilized to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet kind, typically about.002 inches thick. Core material resembles a very thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, typically.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are 2 techniques used to develop the preferred variety of layers. The core stack-up method, 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 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 last variety of layers required by the board design, sort of like Dagwood constructing a sandwich. This method allows the producer versatility in how the board layer densities are combined to meet the completed item density requirements ISO 9001 consultants by varying the number of sheets of pre-preg in each layer. When the product layers are finished, 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 manufacturing printed circuit boards follows the actions below for the majority of applications.
The procedure of figuring out materials, processes, and requirements to meet the customer's specs for the board style based on the Gerber file details provided 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 locations unprotected by the etch resist movie to a chemical that removes the unprotected copper, leaving the protected copper pads and traces in location; more recent procedures utilize plasma/laser etching rather of chemicals to eliminate the copper material, allowing finer line meanings.
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 solid board product.
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. Details on hole location 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 positioned in an electrically charged bath of copper.
This is needed when holes are to be drilled through a copper area however the hole is not to be plated through. Avoid this process if possible since it includes expense to the completed board.
The process of using 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 protects versus environmental damage, provides insulation, secures versus solder shorts, and safeguards traces that run between pads.
The procedure of finish 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 elements have actually been put.
The procedure of applying the markings for part designations and element outlines to the board. May be applied to simply the top side or to both sides if elements are mounted on both top and bottom sides.
The process of separating several boards from a panel of similar boards; this process also allows cutting notches or slots into the board if required.
A visual inspection of the boards; likewise can be the procedure of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The procedure of checking for connection or shorted connections on the boards by methods using a voltage between numerous points on the board and identifying if a present flow occurs. Depending upon the board complexity, this procedure may require a specifically developed test fixture and test program to incorporate with the electrical test system used by the board manufacturer.