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 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 part side, a mix of thru-hole and surface area install on the top side only, a mix of thru-hole and surface install elements on the top and surface install parts on the bottom or circuit side, or surface install components on the top and bottom sides of the board.
The boards are likewise used to electrically link the required leads for each part 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 created as single agreed copper pads and traces on one side of the board only, double sided with 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 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 surfaces as part of the board production process. A multilayer board consists of a number of layers of dielectric product that has actually been impregnated with adhesives, and these layers are utilized to separate the layers of copper plating. All of these layers are lined up 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 typical four layer board design, the internal layers are typically used to provide power and ground connections, such as a +5 V airplane 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 complex board designs might have a large number of layers to make the numerous connections for various voltage levels, ground connections, or for connecting the numerous leads on ball grid range gadgets and other big integrated circuit package formats.
There are usually 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 type, typically about.002 inches thick. Core material is similar to a very thin double sided board in that 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 two techniques utilized to develop the preferred variety 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 below. This mix of one pre-preg layer and 2 core layers would make a 4 layer board.
The film stack-up technique, a newer technology, would have core product as the center layer followed by layers of pre-preg and copper product developed above and below to form the last number of layers required by the board style, sort of like Dagwood constructing a sandwich. This approach allows the manufacturer flexibility in how the board layer densities are combined to satisfy the finished product density requirements by varying the variety of sheets of pre-preg in each layer. As soon as the product layers are finished, the whole stack is subjected to heat and pressure that triggers ISO 9001 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, processes, and requirements to satisfy the customer's requirements for the board style based on the Gerber file details supplied with the order.
The process of moving the Gerber file information for a layer onto an etch withstand film that is put on the conductive copper layer.
The standard process of exposing the copper and other areas unprotected by the etch withstand film to a chemical that eliminates the vulnerable copper, leaving the safeguarded copper pads and traces in location; more recent procedures use plasma/laser etching instead of chemicals to get rid of the copper product, enabling finer line definitions.
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 solid board material.
The process of drilling all 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 procedure 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 needed when holes are to be drilled through a copper area but the hole is not to be plated through. Avoid this process if possible since it includes cost to the finished board.
The procedure 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 used; the solder mask protects versus environmental damage, provides insulation, protects versus solder shorts, and safeguards traces that run between pads.
The process of coating the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering procedure that will take place at a later date after the elements have been placed.
The process of applying the markings for part designations and element lays out to the board. May be used to simply the top side or to both sides if elements are mounted on both top and bottom sides.
The process of separating numerous boards from a panel of similar boards; this procedure likewise permits cutting notches or slots into the board if needed.
A visual assessment of the boards; likewise can be the process of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The procedure of looking for continuity or shorted connections on the boards by means using a voltage in between different points on the board and determining if a present circulation happens. Depending upon the board intricacy, this procedure might require a specially created test component and test program to integrate with the electrical test system used by the board maker.