In electronic devices, printed circuit boards, or PCBs, are used 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 component leads in thru-hole applications. A board design may have all thru-hole components on the leading or component side, a mix of thru-hole and surface install on the top only, a mix of thru-hole and surface mount components on the top and surface mount parts on the bottom or circuit side, or surface install parts on the leading and bottom sides of the board.
The boards are likewise used to electrically connect the required leads for each part using 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 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 as part of the board production process. A multilayer board consists of a number of layers of dielectric material that has been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All of 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 innovations.
In a common four layer board style, the internal layers are frequently utilized to supply power and ground connections, such as a +5 V plane layer and a Ground plane layer as the 2 internal layers, with all other circuit and element connections made on the top and bottom layers of the board. Extremely intricate board styles might have a large number of layers to make the different connections for various voltage levels, ground connections, or for linking the numerous leads on ball grid selection gadgets and other large integrated circuit bundle formats.
There are typically two types of material used to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, generally about.002 inches thick. Core material resembles an extremely thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, typically.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are two approaches used to build up the preferred variety 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 material above and another layer of core material below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The movie stack-up method, a newer innovation, would have core material as the center layer followed by layers of pre-preg and copper material developed 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 enables the manufacturer flexibility in how the board layer densities are combined to satisfy the finished item thickness requirements by varying the variety of sheets of pre-preg in each layer. Once the material layers are finished, the entire 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 the majority of applications.
The procedure of identifying materials, procedures, and requirements to satisfy the consumer's specifications for the board design based upon the Gerber file details supplied with the order.
The process of moving the Gerber file information for a layer onto an etch resist movie that is placed on the conductive copper layer.
The standard procedure of exposing the copper and other locations 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; more recent procedures use plasma/laser etching rather of chemicals to get rid of the copper material, allowing finer line definitions.
The procedure of lining up the conductive copper and insulating dielectric layers and pressing them under heat to activate the adhesive in the dielectric layers to form a solid board product.
The process of drilling all of the holes for plated through applications; a second drilling process is used for holes that are not to be plated through. Info on hole place and size is consisted of in the drill drawing file.
The process 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 needed when holes are to be drilled through a copper location but the hole is not to be plated through. Prevent this process if possible since it includes expense 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 secures versus ecological damage, offers insulation, safeguards versus solder shorts, and secures traces that run between pads.
The process of finishing the pad locations 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 ISO 9001 date after the parts have been positioned.
The process of using the markings for part classifications and part describes to the board. Might be applied to just the top or to both sides if elements are mounted on both leading and bottom sides.
The process of separating numerous boards from a panel of identical boards; this process also permits cutting notches or slots into the board if required.
A visual examination 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 process of looking for connection or shorted connections on the boards by methods applying a voltage in between numerous points on the board and figuring out if an existing flow occurs. Relying on the board complexity, this procedure may need a specifically developed test fixture and test program to integrate with the electrical test system used by the board maker.