In electronic devices, printed circuit boards, or PCBs, are used to mechanically support electronic components 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 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 mount on the top side only, a mix of thru-hole and surface install elements on the top and surface install components on the bottom or circuit side, or surface area install elements on the top and bottom sides of the board.
The boards are likewise used to electrically connect 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 designed as single agreed 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 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 real copper pads and connection traces on the board surfaces as part of the board production process. A multilayer board includes a variety of layers of dielectric product that has been fertilized 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 normal four layer board design, the internal layers are typically utilized to provide power and ground connections, such as a +5 V airplane layer and a Ground aircraft layer as the two internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Very complex board styles may have a a great deal of layers to make the various connections for different voltage levels, ground connections, or for linking the numerous leads on ball grid array gadgets and other large integrated circuit bundle formats.
There are typically two kinds of product utilized to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet kind, usually about.002 inches thick. Core product resembles a very thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, usually.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two methods used to develop the wanted number of layers. The core stack-up method, 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 ISO 9001 material below. This combination of one pre-preg layer and 2 core layers would make a 4 layer board.
The movie stack-up approach, a newer technology, 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 last variety of layers required by the board style, sort of like Dagwood building a sandwich. This method allows the producer flexibility in how the board layer thicknesses are combined to fulfill the finished product thickness requirements by differing the variety of sheets of pre-preg in each layer. As soon as the material layers are finished, the entire 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 procedure of manufacturing printed circuit boards follows the actions listed below for a lot of applications.
The process of identifying materials, procedures, and requirements to meet the customer's specs for the board style based on the Gerber file details provided with the 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 traditional process of exposing the copper and other locations unprotected by the etch withstand movie to a chemical that eliminates the unguarded copper, leaving the secured copper pads and traces in location; newer processes utilize plasma/laser etching instead of chemicals to eliminate the copper material, allowing finer line meanings.
The procedure 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 product.
The procedure of drilling all the holes for plated through applications; a 2nd drilling procedure is utilized for holes that are not to be plated through. Information on hole area 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 positioned in an electrically charged bath of copper.
This is required when holes are to be drilled through a copper area however the hole is not to be plated through. Avoid this procedure if possible because it adds expense to the ended up 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 protects versus environmental damage, offers insulation, safeguards versus solder shorts, and protects 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 ultimate wave soldering or reflow soldering process that will occur at a later date after the parts have been positioned.
The process of applying the markings for part classifications and element outlines to the board. Might be applied to simply the top or to both sides if elements are mounted on both leading and bottom sides.
The procedure of separating several boards from a panel of similar boards; this procedure likewise enables cutting notches or slots into the board if required.
A visual examination of the boards; also can be the procedure of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The process of looking for continuity or shorted connections on the boards by means using a voltage between numerous points on the board and determining if a current circulation takes place. Depending upon the board complexity, this process might require a specifically developed test component and test program to incorporate with the electrical test system used by the board manufacturer.