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 install applications or through rilled holes in the board and copper pads for soldering the element leads in thru-hole applications. A board design might have all thru-hole parts 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 install components on the top and surface mount components on the bottom or circuit side, or surface install components on the leading and bottom sides of the board.
The boards are likewise used to electrically connect the needed leads for each part using conductive copper traces. The element pads and connection traces are engraved 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 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 include 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 surface areas as part of the board production procedure. A multilayer board includes a variety of layers of dielectric product that has been fertilized with adhesives, and these layers are utilized to separate the ISO 9001 layers of copper plating. All 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 innovations.
In a common 4 layer board design, the internal layers are often utilized to supply power and ground connections, such as a +5 V airplane layer and a Ground plane layer as the two internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Extremely complex board styles may have a large number of layers to make the various connections for different voltage levels, ground connections, or for connecting the numerous leads on ball grid array devices and other large incorporated circuit package formats.
There are usually two types of material used to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, typically 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 deposited on each side, typically.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are 2 approaches used to develop the wanted variety of layers. The core stack-up approach, which is an older technology, uses 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 material built up above and listed below to form the last number of layers needed by the board design, sort of like Dagwood building a sandwich. This approach permits the maker flexibility in how the board layer thicknesses are integrated to satisfy the completed item density requirements by differing the number of sheets of pre-preg in each layer. When the product layers are completed, 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 procedure of producing printed circuit boards follows the actions below for a lot of applications.
The process of figuring out materials, procedures, and requirements to satisfy the customer's requirements for the board style based on the Gerber file info offered with the purchase order.
The process of moving the Gerber file information for a layer onto an etch resist film that is put on the conductive copper layer.
The conventional process of exposing the copper and other areas unprotected by the etch withstand movie to a chemical that removes the unprotected copper, leaving the safeguarded copper pads and traces in place; more recent procedures utilize plasma/laser etching instead of chemicals to eliminate the copper material, permitting finer line definitions.
The procedure 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 second drilling process is used for holes that are not to be plated through. Info on hole area and size is included in the drill drawing file.
The procedure of applying copper plating to 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 required when holes are to be drilled through a copper location however the hole is not to be plated through. Prevent this process if possible since it adds cost to the ended up board.
The process of using a protective masking material, a solder mask, over the bare copper traces or over the copper that has actually had a thin layer of solder applied; the solder mask safeguards versus environmental damage, supplies insulation, safeguards versus solder shorts, and secures traces that run between pads.
The process of finish the pad locations with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering process that will occur at a later date after the components have been put.
The procedure of applying the markings for part classifications and element outlines to the board. Might be used to simply the top side or to both sides if elements are installed on both top and bottom sides.
The process of separating numerous boards from a panel of similar boards; this process likewise permits cutting notches or slots into the board if required.
A visual examination of the boards; likewise can be the process of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The procedure of checking for continuity or shorted connections on the boards by ways applying a voltage between different points on the board and identifying if a current flow occurs. Depending upon the board complexity, this procedure may need a specially developed test component and test program to integrate with the electrical test system used by the board producer.