In electronics, printed circuit boards, or PCBs, are used to mechanically support electronic components which have their connection leads soldered onto copper pads in surface area install applications or through rilled holes in the board and copper pads for soldering the part leads in thru-hole applications. A board style may have all thru-hole parts on the top or element side, a mix of thru-hole and surface area install on the top just, a mix of thru-hole and surface area mount parts on the top and surface install elements on the bottom or circuit side, or surface install parts on the leading and bottom sides of the board.
The boards are also utilized to electrically connect the needed leads for each element utilizing conductive copper traces. The part pads and connection traces are etched from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are developed as single agreed copper pads and traces on one side of the board only, double sided with copper pads and traces on the leading and bottom sides of the board, or multilayer styles with copper pads and traces on the 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 engraved away to form the actual copper pads and connection traces on the board surfaces as part of the board manufacturing process. A multilayer board includes a number 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 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 style, the internal layers are typically used to offer power and ground connections, such as a +5 V plane layer and a Ground airplane layer as the two internal layers, with all other circuit and component connections made on the leading and bottom layers of the board. Really intricate board designs might have a large number of layers to make the various connections for different voltage levels, ground connections, or for linking the lots of leads on ball grid array gadgets and other big integrated circuit bundle formats.
There are typically two kinds of product used to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet kind, generally about.002 inches thick. Core product is similar to a very thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, normally.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are 2 methods utilized to develop the desired number of layers. The core stack-up method, which is an older innovation, utilizes a center layer of pre-preg product with a layer of core material 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 film stack-up technique, a newer technology, would have core product as the center layer followed by layers of pre-preg and copper material developed above and listed below to form the last number of layers required by the board design, sort of like Dagwood building a sandwich. This approach enables the maker flexibility in how the board layer thicknesses are integrated to meet 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 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 making printed circuit boards follows the actions below for most applications.
The procedure of identifying materials, procedures, and requirements to meet the consumer's requirements for the board design based upon the Gerber file information supplied with the purchase order.
The Reference site procedure of transferring the Gerber file data for a layer onto an etch resist movie that is placed on the conductive copper layer.
The standard procedure of exposing the copper and other locations unprotected by the etch resist movie to a chemical that eliminates the unguarded copper, leaving the secured copper pads and traces in place; more recent processes use plasma/laser etching rather of chemicals to get rid of the copper product, permitting finer line meanings.
The process of aligning the conductive copper and insulating dielectric layers and pushing them under heat to activate the adhesive in the dielectric layers to form a strong board material.
The procedure 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 location 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 procedure if possible because it adds expense to the finished board.
The procedure of using a protective masking product, a solder mask, over the bare copper traces or over the copper that has actually had a thin layer of solder used; the solder mask protects against environmental damage, supplies insulation, protects versus solder shorts, and safeguards traces that run in between pads.
The process of coating 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 parts have actually been positioned.
The process of using the markings for part classifications and element details to the board. May be used to just the top or to both sides if elements are installed on both leading and bottom sides.
The process of separating several boards from a panel of similar boards; this process also permits cutting notches or slots into the board if needed.
A visual assessment of the boards; also 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 looking for connection or shorted connections on the boards by methods using a voltage between different points on the board and figuring out if a present circulation happens. Relying on the board complexity, this process might need a specially developed test fixture and test program to incorporate with the electrical test system used by the board manufacturer.