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 element leads in thru-hole applications. A board style may have all thru-hole parts on the top or part side, a mix of thru-hole and surface area install on the top side only, a mix of thru-hole and surface install components on the top and surface install parts on the bottom or circuit side, or surface area mount elements on the top and bottom sides of the board.
The boards are likewise used to electrically link the needed leads for each component utilizing conductive copper traces. The component 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 agreed copper pads and traces on the leading 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 material, 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 manufacturing process. A multilayer board consists of a variety of layers of dielectric material that has been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All of 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 technologies.
In a common four layer board design, the internal layers are frequently used to supply power and ground connections, such as a +5 V plane layer and a Ground airplane layer as the 2 internal layers, with all other circuit and component connections made on the leading and bottom layers of the board. Extremely complex board designs may have a large number of layers to make the various connections for various voltage levels, ground connections, or for linking the many leads on ball grid array gadgets and other large incorporated circuit bundle formats.
There are usually two kinds of material used to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet kind, usually 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 deposited on each side, generally.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are 2 methods used to develop the wanted variety of layers. The core stack-up technique, which is an older technology, utilizes a center layer of pre-preg material with a layer of core product 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 technology, would have core material as the center layer followed by layers of pre-preg and copper material developed above and listed below to form the last variety of layers required by the board style, sort of like Dagwood building a sandwich. This approach allows the producer flexibility in how the board layer thicknesses are integrated to meet the completed product density requirements by differing the number of sheets of pre-preg in each layer. When the material layers are finished, the whole stack goes through heat and pressure that causes the adhesive in the pre-preg to bond the core and pre-preg layers together into a single entity.
The procedure of making printed circuit boards follows the actions listed below for many applications.
The process of identifying products, procedures, and requirements to meet the client's specs for the board style based on the Gerber file info supplied with the purchase order.
The procedure of transferring the Gerber file data for a layer onto an etch resist movie that is placed 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 unguarded copper, leaving the protected copper pads and traces in location; more recent procedures use plasma/laser etching instead of chemicals to remove the copper product, allowing 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 strong 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. Details on hole area and size is consisted of in the drill ISO 9001 Certification Consultants drawing file.
The process 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 required when holes are to be drilled through a copper location however the hole is not to be plated through. Avoid this process if possible due to the fact that 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 safeguards versus environmental damage, offers insulation, secures against solder shorts, and safeguards traces that run in between pads.
The process of finishing the pad areas 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 components have been placed.
The procedure of using the markings for part designations and component describes to the board. Might be used to simply the top or to both sides if parts are installed on both leading and bottom sides.
The process of separating numerous boards from a panel of similar boards; this process likewise allows cutting notches or slots into the board if needed.
A visual evaluation 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 methods.
The procedure of looking for connection or shorted connections on the boards by methods using a voltage between numerous points on the board and identifying if an existing circulation takes place. Depending upon the board intricacy, this procedure might require a specifically designed test fixture and test program to incorporate with the electrical test system used by the board maker.