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 component leads in thru-hole applications. A board design might have all thru-hole parts on the leading or part side, a mix of thru-hole and surface area install on the top side only, a mix of thru-hole and surface mount parts on the top and surface area mount parts on the bottom or circuit side, or surface mount elements on the leading and bottom sides of the board.
The boards are likewise utilized to electrically connect the needed leads for each element 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 created 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 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 etched away to form the real copper pads and connection traces on the board surface areas as part of the board manufacturing procedure. 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 of 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 normal four layer board style, the internal layers are typically utilized to supply power and ground connections, such as a +5 V aircraft layer and a Ground airplane layer as the 2 internal layers, with all other circuit and element connections made on the top and bottom layers of the board. Very complex board designs might have a large number of layers to make the different connections for various voltage levels, ground connections, or for connecting the numerous leads on ball grid variety gadgets and other big incorporated circuit plan formats.
There are usually two kinds of product used to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet kind, normally about.002 inches thick. Core product resembles a very thin double sided board because it has a dielectric product, 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 two approaches used to develop the preferred number of layers. The core stack-up technique, which is an older innovation, utilizes a center layer of pre-preg material with a layer of core product above and another layer of core material below. This combination of one pre-preg layer and 2 core layers would make a 4 layer board.
The film stack-up technique, a newer innovation, would have core product as the center layer followed by layers of pre-preg and copper material built up above and listed below to form the last number of layers needed by the board design, sort of like Dagwood developing a sandwich. This technique permits the manufacturer flexibility in how the board layer densities are integrated to fulfill the finished item density requirements by varying the number of sheets of pre-preg in each layer. As soon as the material layers are finished, the whole stack undergoes 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 determining products, procedures, and requirements to satisfy the client's requirements for the board style based on the Gerber file information provided with the order.
The process of moving the Gerber file data for a layer onto an etch withstand movie that is placed on the conductive copper layer.
The conventional procedure of exposing the copper and other locations unprotected by the etch resist film to a chemical that gets rid of the vulnerable copper, leaving the safeguarded copper pads and traces in location; more recent processes utilize plasma/laser etching rather of chemicals to eliminate the copper product, permitting finer line meanings.
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 solid board product.
The procedure of drilling all the holes for plated through applications; a 2nd drilling procedure is used for holes that good are not to be plated through. Info on hole location and size is contained in the drill drawing file.
The procedure 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 area but the hole is not to be plated through. Prevent this procedure if possible because it includes cost to the finished board.
The procedure of applying a protective masking material, 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 protects against environmental damage, supplies insulation, safeguards against solder shorts, and safeguards traces that run in between pads.
The process of covering the pad locations with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering process that will take place at a later date after the parts have actually been put.
The process of applying the markings for part classifications and element outlines to the board. Might be used to just the top or to both sides if elements are installed on both leading and bottom sides.
The process of separating several boards from a panel of identical boards; this process also allows cutting notches or slots into the board if needed.
A visual inspection of the boards; likewise can be the procedure of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The procedure of checking for continuity or shorted connections on the boards by ways applying a voltage between different points on the board and identifying if an existing circulation occurs. Depending upon the board complexity, this procedure may require a specifically designed test fixture and test program to incorporate with the electrical test system used by the board maker.