In electronic devices, printed circuit boards, or PCBs, are used to mechanically support electronic elements 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 element leads in thru-hole applications. A board design may have all thru-hole parts on the top or part side, a mix of thru-hole and surface mount on the top side only, a mix of thru-hole and surface install elements on the top and surface area install elements on the bottom or circuit side, or surface install elements on the top and bottom sides of the board.
The boards are likewise utilized to electrically link the required leads for each part 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 sided with copper pads and traces on one side of the board just, 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 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 engraved away to form the real copper pads and connection traces on the board surfaces as part of the board manufacturing process. A multilayer board consists of a variety of layers See more 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 aligned 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 design, the internal layers are often used to supply power and ground connections, such as a +5 V airplane layer and a Ground aircraft layer as the 2 internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Extremely complex board designs may have a a great deal of layers to make the numerous connections for different voltage levels, ground connections, or for connecting the lots of leads on ball grid selection gadgets and other large integrated circuit package formats.
There are typically two types of material used to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet form, usually about.002 inches thick. Core material is similar to an extremely 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 density dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are 2 approaches used to develop the wanted number of layers. The core stack-up technique, which is an older innovation, uses a center layer of pre-preg material with a layer of core product above and another layer of core product listed below. This combination of one pre-preg layer and 2 core layers would make a 4 layer board.
The film 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 listed below to form the last variety of layers required by the board style, sort of like Dagwood constructing a sandwich. This technique allows the producer flexibility in how the board layer thicknesses are integrated to satisfy the ended up product thickness requirements by varying the number of sheets of pre-preg in each layer. As soon as the material layers are completed, 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 producing printed circuit boards follows the actions listed below for many applications.
The procedure of identifying materials, processes, and requirements to fulfill the customer's specs for the board style based upon the Gerber file information supplied with the order.
The process of transferring 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 areas unprotected by the etch resist movie to a chemical that eliminates the unprotected copper, leaving the safeguarded copper pads and traces in location; newer procedures utilize plasma/laser etching instead of chemicals to get rid of the copper material, allowing 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 2nd drilling process is used for holes that are not to be plated through. Info on hole place and size is contained 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. Avoid this process if possible because it adds expense to the ended up board.
The process of using 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, safeguards against solder shorts, and safeguards traces that run between pads.
The procedure of covering the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering process that will occur at a later date after the parts have actually been placed.
The process of using the markings for part classifications and component outlines to the board. Might be used to simply the top side or to both sides if elements are installed on both leading and bottom sides.
The process of separating multiple boards from a panel of similar boards; this process likewise permits cutting notches or slots into the board if required.
A visual evaluation of the boards; also 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 looking for continuity or shorted connections on the boards by methods using a voltage in between numerous points on the board and identifying if a current circulation occurs. Depending upon the board complexity, this procedure may need a specially developed test fixture and test program to incorporate with the electrical test system used by the board maker.