In electronic devices, printed circuit boards, or PCBs, are used to mechanically support electronic parts 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 parts 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 install components on the top and surface area install parts on the bottom or circuit side, or surface area mount components on the leading and bottom sides of the board.
The boards are likewise utilized to electrically connect the needed leads for each part utilizing conductive copper traces. The component 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 just, 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 number of internal copper layers with traces and connections.
Single or double sided boards include a core dielectric product, 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 manufacturing process. A multilayer board includes a variety of layers of dielectric material that has been fertilized with adhesives, and these layers are utilized to separate the layers of copper plating. All 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 typical 4 layer board design, the internal layers are typically used to offer power and ground connections, such as a +5 V aircraft layer and a Ground aircraft layer as the two internal layers, with all other circuit and component connections made on the leading and bottom layers of the board. Really complex board designs may have a large number of layers to make the various connections for various voltage levels, ground connections, or for linking the many leads on ball grid array devices and other large incorporated circuit bundle formats.
There are normally two kinds of material utilized to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, usually about.002 inches thick. Core product is similar to a really thin double sided board because it has a dielectric material, 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 2 approaches used to develop the desired number of layers. The core stack-up approach, 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 combination of one pre-preg layer and 2 core layers would make a 4 layer board.
The film stack-up method, a more recent innovation, would have core material as the center layer followed by layers of pre-preg and copper product 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 method permits the maker versatility in how the board layer densities are integrated to fulfill the finished item density requirements by varying the variety of sheets of pre-preg in each layer. As soon as the material layers are finished, the entire stack undergoes 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 procedure of making printed circuit boards follows the actions below for a lot of applications.
The procedure of figuring out products, processes, and requirements to fulfill the customer's specifications for the board style based on the Gerber file information provided with the purchase order.
The process of transferring the Gerber file information for a layer onto an etch withstand film that is put on the conductive copper layer.
The standard procedure of exposing the copper and other areas unprotected by the etch resist film to a chemical that gets rid of the unprotected copper, leaving the safeguarded copper pads and traces in place; more recent processes use plasma/laser etching rather of chemicals to remove the copper material, allowing finer line definitions.
The process 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 material.
The procedure of drilling all of the holes for plated through applications; a second drilling process is used for holes that are not to be plated through. Details on hole location and size is included 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. Prevent this procedure if possible due to the fact that it adds cost to the finished 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 applied; the solder mask protects versus environmental damage, provides insulation, protects against solder shorts, and secures traces that run in between pads.
The procedure of coating the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will occur at a later date after the parts have been positioned.
The process of applying the markings for part designations and part details to the board. Might be applied to just the top side or to both sides if parts are mounted on both top and bottom sides.
The process of separating multiple boards from a panel of similar boards; this procedure likewise permits 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 techniques.
The process of looking for continuity or shorted connections on the boards by ways applying a voltage in between numerous points on the board and determining if a current circulation occurs. Depending upon the board intricacy, this procedure may need a specially developed test fixture and test program to integrate with the electrical More interesting details here test system used by the board producer.