In electronics, printed circuit boards, or PCBs, are utilized 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 part leads in thru-hole applications. A board design might have all thru-hole elements on the top or component side, a mix of thru-hole and surface mount on the top side just, a mix of thru-hole and surface install elements on the top side and surface area install components on the bottom or circuit side, or surface install components 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 etched 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 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 include 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 manufacturing 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 lined up 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 4 layer board design, the internal layers are often used to provide 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 top and bottom layers of the board. Extremely complicated board designs may have a large number of layers to make the numerous connections for various voltage levels, ground connections, or for connecting the lots of leads on ball grid array gadgets and other big integrated circuit package formats.
There are usually two kinds of product used to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet kind, generally about.002 inches thick. Core product resembles a really thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, generally.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two methods used to develop the wanted number of layers. The core stack-up technique, which is an older innovation, utilizes a center layer of pre-preg product with a layer of core product above and another layer of core material below. This mix of one pre-preg layer and 2 core layers would make a 4 layer board.
The movie stack-up technique, a more recent technology, would have core product as the center layer followed by layers of pre-preg and copper product built up above and listed below to form the last number of layers required by the board design, sort of like Dagwood developing a sandwich. This approach enables the manufacturer flexibility in how the board layer densities are combined to meet the completed product thickness requirements by varying the number of sheets of pre-preg in each layer. When the material layers are finished, the entire stack goes through 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 manufacturing printed circuit boards follows the actions below for most applications.
The process of figuring out products, procedures, and requirements to satisfy the client's specifications for the board style based on the Gerber file info supplied with the 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 locations unprotected by the etch withstand film to a chemical that eliminates the unprotected copper, leaving the safeguarded copper pads and traces in place; newer procedures use plasma/laser etching instead of chemicals to get rid of the copper material, allowing finer line meanings.
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 solid board product.
The procedure of drilling all of the holes for plated through applications; a 2nd drilling process is used for holes that are not to be plated through. Information on hole location and size is consisted of 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 placed 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. Prevent this procedure if possible due to the fact that it includes expense to the completed board.
The procedure of applying a protective masking product, a solder mask, over the bare copper traces or over the copper that has had a thin layer of solder used; the solder mask safeguards against ecological damage, offers insulation, secures against solder shorts, and safeguards traces that run in between pads.
The process of finishing the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will happen at a later date after the components have actually been placed.
The procedure of applying the markings for component designations and component outlines to the board. May be used to simply the top or to both sides if components are mounted on both top and bottom sides.
The process of separating numerous boards from a panel of identical boards; this process likewise allows cutting notches or slots into the board if required.
A visual evaluation of the boards; also 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 flow takes place. Relying on the board complexity, this process might ISO 9001 consultants require a specially developed test component and test program to integrate with the electrical test system used by the board producer.