In electronics, printed circuit boards, or PCBs, are utilized to mechanically support electronic parts which have their connection leads soldered onto copper pads in surface mount applications or through rilled holes in the board and copper pads for soldering the part leads in thru-hole applications. A board style might have all thru-hole components on the top or part side, a mix of thru-hole and surface install on the top only, a mix of thru-hole and surface area mount elements on the top and surface area install elements on the bottom or circuit side, or surface install components on the leading and bottom sides of the board.
The boards are also utilized to electrically link the required leads for each component using 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 sided with copper pads and traces on one side of the board only, 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 number 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 real copper pads and connection traces on the board surfaces as part of the board production procedure. A multilayer board consists of a number of layers of dielectric product that has been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All these layers are lined up 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 frequently used to offer power and ground connections, such as a +5 V plane layer and a Ground aircraft layer as the two internal layers, with all other circuit and part connections made on the top and bottom layers of the board. Really intricate board styles might have a large number of layers to make the various connections for different voltage levels, ground connections, or for connecting the many leads on ball grid variety gadgets and other big incorporated circuit plan formats.
There are generally two kinds of product utilized to construct a multilayer board. Pre-preg product is thin Reference site layers of fiberglass pre-impregnated with an adhesive, and remains in sheet form, normally 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, usually.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are 2 approaches utilized to develop the desired number of layers. The core stack-up method, which is an older technology, uses a center layer of pre-preg material 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 method, a newer technology, would have core product as the center layer followed by layers of pre-preg and copper product built up above and below to form the final number of layers needed by the board design, sort of like Dagwood building a sandwich. This approach enables the manufacturer versatility in how the board layer thicknesses are integrated to fulfill the finished item density requirements by differing 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 causes 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 steps listed below for many applications.
The procedure of determining materials, processes, and requirements to fulfill the client's specifications for the board design based upon the Gerber file info provided with the purchase order.
The process of transferring the Gerber file data for a layer onto an etch withstand movie that is put on the conductive copper layer.
The conventional process of exposing the copper and other locations unprotected by the etch resist movie to a chemical that gets rid of the unprotected copper, leaving the safeguarded copper pads and traces in location; more recent procedures use plasma/laser etching rather of chemicals to remove the copper material, permitting finer line meanings.
The procedure 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 material.
The process of drilling all of the holes for plated through applications; a second drilling process is utilized for holes that are not to be plated through. Details on hole area 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 positioned in an electrically charged bath of copper.
This is required when holes are to be drilled through a copper area but the hole is not to be plated through. Avoid this procedure if possible because it adds cost to the finished board.
The process of using a protective masking material, a solder mask, over the bare copper traces or over the copper that has had a thin layer of solder applied; the solder mask protects against environmental damage, offers insulation, protects against solder shorts, and secures traces that run in between pads.
The process of covering the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering process that will happen at a later date after the parts have been put.
The process of applying the markings for element designations and component outlines to the board. Might be applied to just the top or to both sides if parts are installed on both top and bottom sides.
The procedure of separating several boards from a panel of identical boards; this procedure likewise enables cutting notches or slots into the board if required.
A visual assessment of the boards; likewise can be the process of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The process of checking for continuity or shorted connections on the boards by ways using a voltage between different points on the board and identifying if a current flow occurs. Relying on the board intricacy, this process might require a specifically designed test component and test program to incorporate with the electrical test system utilized by the board producer.