In electronic devices, printed circuit boards, or PCBs, are utilized web site to mechanically support electronic components 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 component leads in thru-hole applications. A board design may have all thru-hole components on the top or component side, a mix of thru-hole and surface area mount on the top side just, a mix of thru-hole and surface install parts on the top and surface area mount components on the bottom or circuit side, or surface install parts on the leading and bottom sides of the board.
The boards are also used to electrically connect the needed leads for each part utilizing conductive copper traces. The component pads and connection traces are engraved 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 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 top and bottom of board with a variable number 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 actual copper pads and connection traces on the board surfaces as part of the board production procedure. A multilayer board includes a number of layers of dielectric product that has been impregnated 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 typical 4 layer board design, the internal layers are typically used 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. Very intricate board designs may have a large number of layers to make the numerous connections for different voltage levels, ground connections, or for linking the numerous leads on ball grid variety devices and other large integrated circuit bundle formats.
There are generally 2 types of material utilized to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, usually 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, typically.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are 2 approaches utilized to build up the desired number of layers. The core stack-up approach, which is an older technology, uses 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 two core layers would make a 4 layer board.
The film stack-up technique, a newer innovation, would have core material as the center layer followed by layers of pre-preg and copper material built up above and listed below to form the final number of layers needed by the board style, sort of like Dagwood developing a sandwich. This approach allows the manufacturer flexibility in how the board layer thicknesses are integrated to satisfy the finished item density requirements by varying the number of sheets of pre-preg in each layer. When the material layers are finished, the whole stack is subjected to 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 procedure of figuring out products, processes, and requirements to fulfill the customer's specs for the board style based on the Gerber file info offered with the order.
The procedure of moving 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 areas unprotected by the etch withstand movie to a chemical that gets rid of the vulnerable copper, leaving the secured copper pads and traces in place; newer procedures utilize plasma/laser etching instead of chemicals to remove the copper product, allowing finer line meanings.
The procedure of lining up the conductive copper and insulating dielectric layers and pressing them under heat to activate the adhesive in the dielectric layers to form a strong board material.
The procedure of drilling all of the holes for plated through applications; a 2nd drilling process is utilized 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 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 since it includes cost to the finished board.
The process 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 applied; the solder mask safeguards against environmental damage, supplies insulation, safeguards against solder shorts, and secures traces that run in between pads.
The procedure of finish the pad areas with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering process that will take place at a later date after the parts have been placed.
The process of applying the markings for part classifications and part lays out to the board. May be used to simply the top or to both sides if elements are mounted on both top and bottom sides.
The procedure of separating numerous boards from a panel of similar 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 checking for connection or shorted connections on the boards by means applying a voltage between different points on the board and identifying if an existing circulation happens. Depending upon the board complexity, this procedure may need a specifically created test component and test program to incorporate with the electrical test system utilized by the board manufacturer.