In electronics, 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 element 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 install on the top side only, a mix of thru-hole and surface area mount parts on the top side and surface mount elements on the bottom or circuit side, or surface area mount parts on the top and bottom sides of the board.
The boards are also used to electrically link the needed leads for each element utilizing conductive copper traces. The part pads and connection traces are engraved from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are created as single agreed 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 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 real copper pads and connection traces on the board surface areas as part of the board production procedure. A multilayer board includes a variety of layers of dielectric material that has been impregnated with adhesives, and these layers are used 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 normal four layer board design, the internal layers are often used to provide 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 element connections made on the leading and bottom layers of the board. Extremely complicated board styles might have a a great deal of layers to make the different connections for various voltage levels, ground connections, or for connecting the many leads on ball grid array devices and other big integrated circuit package formats.
There are generally 2 kinds of material used to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet kind, normally about.002 inches thick. Core product is similar to an extremely thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, normally.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are two approaches utilized to develop the wanted variety of layers. The core stack-up technique, which is an older technology, utilizes you can find out more a center layer of pre-preg product 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 movie stack-up approach, a newer technology, would have core product 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 required by the board design, sort of like Dagwood building a sandwich. This method allows the manufacturer versatility in how the board layer thicknesses are combined to fulfill the ended up product thickness requirements by varying the variety of sheets of pre-preg in each layer. Once the material 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 making printed circuit boards follows the actions listed below for many applications.
The process of determining products, procedures, and requirements to satisfy the customer's specifications for the board style based upon the Gerber file information supplied 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 conventional procedure of exposing the copper and other areas unprotected by the etch withstand movie to a chemical that gets rid of the unguarded copper, leaving the secured copper pads and traces in location; newer procedures utilize plasma/laser etching rather of chemicals to eliminate the copper product, enabling finer line definitions.
The process of lining up the conductive copper and insulating dielectric layers and pressing them under heat to trigger the adhesive in the dielectric layers to form a strong board material.
The procedure of drilling all the holes for plated through applications; a 2nd drilling process 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 procedure 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 location but the hole is not to be plated through. Avoid this process if possible because it includes cost 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 applied; the solder mask safeguards against environmental damage, offers insulation, safeguards versus solder shorts, and secures traces that run in between pads.
The process of finish the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will take place at a later date after the elements have been placed.
The procedure of applying the markings for element classifications and part details to the board. May be applied to just the top side or to both sides if parts are installed on both leading and bottom sides.
The procedure of separating several boards from a panel of similar boards; this process likewise permits cutting notches or slots into the board if required.
A visual inspection of the boards; also can be the process of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The procedure of checking for continuity or shorted connections on the boards by means using a voltage in between different points on the board and determining if a present flow happens. Depending upon the board complexity, this process might need a specially created test component and test program to incorporate with the electrical test system utilized by the board producer.