In electronic devices, printed circuit boards, or PCBs, are utilized to mechanically support electronic elements 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 element leads in thru-hole applications. A board style might have all thru-hole components on the top or element side, a mix of thru-hole and surface area install on the top side only, a mix of thru-hole and surface area mount components on the top and surface install components on the bottom or circuit side, or surface area install elements on the leading and bottom sides of the board.
The boards are also utilized to electrically link the required 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 developed 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 number of internal copper layers with traces and connections.
Single or double sided boards consist of a core dielectric material, 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 See more as part of the board production procedure. A multilayer board consists of 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 these layers are aligned and 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 four layer board design, the internal layers are frequently utilized to offer power and ground connections, such as a +5 V airplane layer and a Ground plane layer as the 2 internal layers, with all other circuit and component connections made on the leading and bottom layers of the board. Extremely complicated board designs might have a a great deal of layers to make the numerous connections for different voltage levels, ground connections, or for linking the many leads on ball grid range gadgets and other large incorporated circuit package formats.
There are typically 2 kinds of product utilized to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet form, usually about.002 inches thick. Core material is similar to a really thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, normally.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are 2 techniques used to develop the wanted variety of layers. The core stack-up approach, 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 product below. This combination 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 product as the center layer followed by layers of pre-preg and copper product developed above and below to form the last variety of layers required by the board design, sort of like Dagwood developing a sandwich. This approach enables the maker flexibility in how the board layer thicknesses are integrated to meet the completed item density requirements by differing the number of sheets of pre-preg in each layer. As soon as the product layers are finished, the entire stack goes through 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 procedure of producing printed circuit boards follows the steps below for most applications.
The process of identifying materials, procedures, and requirements to meet the consumer's specs for the board design based on the Gerber file details supplied with the order.
The procedure of moving 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 areas unprotected by the etch resist movie to a chemical that gets rid of the unguarded copper, leaving the secured copper pads and traces in place; newer procedures utilize plasma/laser etching instead of chemicals to eliminate the copper material, enabling finer line meanings.
The process of aligning the conductive copper and insulating dielectric layers and pressing them under heat to trigger the adhesive in the dielectric layers to form a solid board material.
The process of drilling all of the holes for plated through applications; a 2nd drilling process is used for holes that are not to be plated through. Info on hole area and size is consisted of 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 put 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. Prevent this process if possible since it adds cost to the completed board.
The procedure 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 used; the solder mask secures against ecological damage, supplies insulation, secures versus solder shorts, and secures traces that run between pads.
The procedure of covering the pad locations with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will take place at a later date after the parts have been put.
The procedure of applying the markings for part classifications and component details to the board. May be used to just the top or to both sides if components are mounted on both top and bottom sides.
The procedure of separating several boards from a panel of similar boards; this process also permits cutting notches or slots into the board if required.
A visual inspection 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 methods.
The procedure of checking for continuity or shorted connections on the boards by ways using a voltage in between various points on the board and determining if a current circulation takes place. Relying on the board complexity, this process may need a specifically developed test component and test program to incorporate with the electrical test system used by the board maker.