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 component leads in thru-hole applications. A board style may have all thru-hole components on the top or part side, a mix of thru-hole and surface area install on the top side just, a mix of thru-hole and surface install elements on the top and surface area mount components on the bottom or circuit side, or surface area install components on the top and bottom sides of the board.
The boards are likewise used to electrically link the required leads for each part using conductive copper traces. The part pads and connection traces are etched 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 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 surface areas as part of the board manufacturing procedure. A multilayer board includes a number of layers of dielectric material that has been fertilized with adhesives, and these layers are used to separate the layers of copper plating. All these layers are lined up 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 typically used to offer power and ground connections, such as a +5 V aircraft layer and a Ground plane layer as the 2 internal layers, with all other circuit and element connections made on the leading and bottom layers of the board. Extremely intricate board designs might have a a great deal of layers to make the different connections for various voltage levels, ground connections, or for connecting the numerous leads on ball grid array gadgets and other big integrated circuit package formats.
There are typically two types of product utilized to construct 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 product is similar to a really thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, generally.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are two techniques used to build up the desired variety of layers. The core stack-up method, which is an older innovation, uses a center layer of pre-preg material with a layer of core material 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 method, a more recent innovation, would have core material as the center layer followed by layers of pre-preg and copper product developed above and below to form the final number of layers required by the board design, sort of like Dagwood developing a sandwich. This approach allows the manufacturer versatility in how the board layer thicknesses are integrated to satisfy the ended up item thickness requirements by varying the variety 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 steps listed below for a lot of applications.
The procedure of figuring out products, procedures, and requirements to satisfy the customer's requirements for the board design based on the Gerber file details offered with the purchase order.
The process of moving the Gerber file data for a layer onto an etch withstand film that is placed on the conductive copper layer.
The standard process of exposing the copper and other locations unprotected by the etch withstand movie to a chemical that gets rid of the unprotected copper, leaving the protected copper pads and traces in location; newer procedures utilize plasma/laser etching instead of chemicals to get rid of the copper material, enabling 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 product.
The process of drilling all of the holes for plated through applications; a second drilling process is utilized for holes that are not to be plated through. Information on hole area and size is contained in the drill drawing file.
The process of using copper plating to ISO 9001 consultants 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 location but the hole is not to be plated through. Prevent this procedure if possible since it adds cost to the finished 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 safeguards against environmental damage, offers insulation, protects against solder shorts, and secures traces that run between pads.
The procedure of finishing the pad locations 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 been put.
The process of applying the markings for component designations and element describes to the board. Might be applied 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 procedure likewise enables cutting notches or slots into the board if required.
A visual assessment of the boards; likewise can be the procedure of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The procedure of checking for connection or shorted connections on the boards by methods using a voltage in between numerous points on the board and determining if a present flow happens. Relying on the board complexity, this procedure may need a specifically designed test fixture and test program to incorporate with the electrical test system utilized by the board maker.