In electronics, 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 ISO 9001 the board and copper pads for soldering the component leads in thru-hole applications. A board design may have all thru-hole parts on the top or element side, a mix of thru-hole and surface area install on the top only, a mix of thru-hole and surface area install elements on the top and surface install parts on the bottom or circuit side, or surface mount parts on the top and bottom sides of the board.
The boards are also used to electrically connect the needed leads for each element 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 developed as single sided with copper pads and traces on one side of the board only, double agreed copper pads and traces on the leading 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 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 actual 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 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 innovations.
In a typical 4 layer board style, the internal layers are typically used to offer 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. Extremely intricate board designs might 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 big incorporated circuit package formats.
There are typically 2 kinds of product used to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet form, generally about.002 inches thick. Core product is similar to a very thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, generally.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two approaches used to build up the desired number of layers. The core stack-up approach, which is an older technology, utilizes a center layer of pre-preg product with a layer of core material 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 product built up above and listed below to form the final number of layers required by the board design, sort of like Dagwood developing a sandwich. This method permits the producer flexibility in how the board layer thicknesses are combined to fulfill the finished product thickness requirements by varying the variety of sheets of pre-preg in each layer. As soon as the material layers are finished, the whole stack undergoes 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 process of making printed circuit boards follows the actions listed below for most applications.
The process of identifying products, procedures, and requirements to satisfy the customer's specifications for the board style based on the Gerber file details supplied with the purchase order.
The process of transferring the Gerber file data for a layer onto an etch resist movie that is placed on the conductive copper layer.
The traditional process of exposing the copper and other areas unprotected by the etch resist film to a chemical that removes the unprotected copper, leaving the secured copper pads and traces in place; more recent processes utilize plasma/laser etching instead of chemicals to remove the copper product, enabling finer line definitions.
The process of aligning the conductive copper and insulating dielectric layers and pushing them under heat to activate the adhesive in the dielectric layers to form a solid board material.
The procedure 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. Details on hole location and size is included in the drill drawing file.
The process of applying 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. Avoid this process if possible since it adds cost to the completed 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 applied; the solder mask safeguards versus ecological damage, provides insulation, secures versus solder shorts, and secures traces that run between pads.
The procedure 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 put.
The process of applying the markings for part designations and component describes to the board. May be applied to just the top side or to both sides if components are mounted on both leading and bottom sides.
The procedure of separating multiple boards from a panel of similar boards; this procedure likewise allows 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 methods.
The procedure of looking for continuity or shorted connections on the boards by means using a voltage between different points on the board and figuring out if a current circulation happens. Relying on the board complexity, this procedure might require a specifically developed test component and test program to incorporate with the electrical test system used by the board maker.