In electronic devices, printed circuit boards, or PCBs, are used to mechanically support electronic components which have their connection leads soldered onto copper pads in surface area mount applications or through rilled holes in the board and copper pads for soldering the component leads in thru-hole applications. A board design might have all thru-hole components on the leading or part side, a mix of thru-hole and surface install on the top only, a mix of thru-hole and surface mount parts on the top side and surface install parts on the bottom or circuit side, or surface area install elements on the leading and bottom sides of the board.
The boards are likewise used to electrically link the needed leads for each part using conductive copper traces. The part pads and connection traces are engraved from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are developed as single sided with 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 top and bottom of board with a variable variety of internal copper layers with traces and connections.
Single or double sided boards consist of a core dielectric product, such as FR-4 epoxy fiberglass, with copper plating on one or both sides. This copper plating is etched away to form the actual copper pads and connection traces on the board surfaces as part of the board manufacturing process. A multilayer board consists of a number of layers of dielectric material 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 then 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 common 4 layer board design, the internal layers are typically used to offer power and ground connections, such as a +5 V plane layer and a Ground aircraft layer as the 2 internal layers, with all other circuit and element connections made on the top and bottom layers of the board. Extremely complicated board styles may have a large number of layers to make the different connections for various voltage levels, ground connections, or for linking the numerous leads on ball grid range gadgets and other big integrated circuit plan formats.
There are generally 2 types of product used to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, normally 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, usually.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are 2 approaches utilized to develop the preferred number of layers. The core stack-up technique, which is an older technology, utilizes a center layer of ISO 9001 Accreditation pre-preg product with a layer of core material above and another layer of core product listed below. This mix 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 product as the center layer followed by layers of pre-preg and copper product developed above and below to form the final variety of layers needed by the board design, sort of like Dagwood developing a sandwich. This method allows the manufacturer flexibility in how the board layer thicknesses are integrated to fulfill the finished product thickness requirements by differing the number of sheets of pre-preg in each layer. As soon as the product layers are finished, the whole 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 process of manufacturing printed circuit boards follows the steps below for a lot of applications.
The procedure of identifying products, processes, and requirements to fulfill the customer's specs for the board design based on the Gerber file info offered with the order.
The process of moving the Gerber file information for a layer onto an etch withstand movie that is put on the conductive copper layer.
The conventional process of exposing the copper and other locations unprotected by the etch withstand film to a chemical that gets rid of the unprotected copper, leaving the secured copper pads and traces in location; newer procedures use plasma/laser etching instead of chemicals to get rid of the copper product, permitting 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 solid board product.
The process of drilling all the holes for plated through applications; a 2nd drilling process is used for holes that are not to be plated through. Information on hole place and size is included 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 put 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 process if possible due to the fact that it includes expense to the finished board.
The process 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 secures versus ecological damage, supplies insulation, secures versus solder shorts, and protects traces that run between pads.
The process of covering 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 parts have been put.
The procedure of using the markings for component classifications and component outlines to the board. Might be applied to simply the top or to both sides if components are mounted on both leading and bottom sides.
The process of separating multiple boards from a panel of similar boards; this procedure also enables cutting notches or slots into the board if required.
A visual assessment of the boards; likewise 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 between different points on the board and identifying if a present circulation occurs. Relying on the board complexity, this procedure may need a specifically created test component and test program to integrate with the electrical test system used by the board maker.