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 components on the top or part side, a mix of thru-hole and surface area mount on the top side just, a mix of thru-hole and surface area mount parts on the top and surface mount components on the bottom or circuit side, or surface install parts on the leading and bottom sides of the board.
The boards are likewise used to electrically link the needed leads for each element utilizing 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 just, double sided with copper pads and traces on the leading 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 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 real copper pads and connection traces on the board surface areas as part of the board manufacturing process. A multilayer board includes a number of layers of dielectric material that has been impregnated with adhesives, and these layers are utilized to separate the layers of copper plating. All these layers are aligned 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 typical four layer board style, the internal layers are typically utilized to provide power and ground connections, such as a +5 V aircraft 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. Really intricate board styles may have a large number of layers to make the numerous connections for different voltage levels, ground connections, or for linking the lots of leads on ball grid range devices and other large integrated circuit bundle formats.
There are generally two types of product utilized to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, typically about.002 inches thick. Core product resembles an extremely thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, normally.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 wanted variety of layers. The core stack-up approach, which is an older technology, utilizes a center layer of pre-preg material with a layer of core material above and another layer of core material listed below. This mix of one pre-preg layer and two core layers would make a 4 layer board.
The film stack-up method, a newer innovation, would have core product as the center layer followed by layers of pre-preg and copper product built up above and listed below to form the final variety of layers required by the board design, sort of like Dagwood building a sandwich. This approach permits the manufacturer versatility in how the board layer densities are combined to meet the finished product thickness requirements by differing the variety of sheets of pre-preg in each layer. As soon as the material layers are completed, the entire 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 actions below for most applications.
The process of figuring out materials, procedures, and requirements to fulfill the consumer's specs for the board design based upon the Gerber file details supplied with the purchase order.
The procedure of transferring the Gerber file data for a layer onto an etch withstand movie that is put on the conductive copper layer.
The standard procedure of exposing the copper and other areas unprotected by the etch resist movie to a chemical that gets rid of the unprotected copper, leaving the secured copper pads and traces in location; newer processes utilize plasma/laser etching instead of chemicals to get rid of the copper material, allowing finer line definitions.
The process of aligning the conductive copper and insulating dielectric layers and pushing them under heat to trigger the adhesive in the dielectric layers to form a strong board material.
The process of drilling all the holes for plated through applications; a second drilling process is used for holes ISO 9001 consultants that are not to be plated through. Info on hole location and size is consisted of 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 location but the hole is not to be plated through. Avoid this process if possible because it includes expense to the completed 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 applied; the solder mask safeguards against environmental damage, offers insulation, safeguards against solder shorts, and safeguards traces that run between pads.
The process 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 take place at a later date after the elements have been placed.
The procedure of applying the markings for component designations and component outlines to the board. Might be used to just the top side or to both sides if elements are installed on both top and bottom sides.
The procedure of separating several boards from a panel of identical boards; this process also permits cutting notches or slots into the board if required.
A visual examination 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 looking for continuity or shorted connections on the boards by ways using a voltage in between numerous points on the board and figuring out if a present flow happens. Depending upon the board complexity, this procedure might require a specially developed test component and test program to incorporate with the electrical test system used by the board producer.