In electronics, printed circuit boards, or PCBs, are used to mechanically support Reference site electronic elements which have their connection leads soldered onto copper pads in surface area install applications or through rilled holes in the board and copper pads for soldering the part leads in thru-hole applications. A board design may have all thru-hole elements on the leading or component side, a mix of thru-hole and surface mount on the top only, a mix of thru-hole and surface area install elements on the top and surface mount components on the bottom or circuit side, or surface area mount components on the leading and bottom sides of the board.
The boards are also used to electrically link the required leads for each element using conductive copper traces. The element pads and connection traces are etched 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 just, 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 product, 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 manufacturing process. A multilayer board includes a variety of layers of dielectric product that has been fertilized with adhesives, and these layers are utilized 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 technologies.
In a common 4 layer board design, the internal layers are typically utilized to offer power and ground connections, such as a +5 V airplane layer and a Ground plane layer as the two internal layers, with all other circuit and element connections made on the leading and bottom layers of the board. Very complicated board designs might have a large number of layers to make the different connections for different voltage levels, ground connections, or for connecting the lots of leads on ball grid variety devices and other big incorporated circuit plan formats.
There are generally 2 kinds of material utilized to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet form, normally about.002 inches thick. Core material resembles a very 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 material with 1 ounce copper layer on each side. In a multilayer board design, there are 2 techniques used to build up the preferred variety of layers. The core stack-up technique, which is an older innovation, uses a center layer of pre-preg product with a layer of core product above and another layer of core product listed below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The movie stack-up method, a more recent innovation, would have core material as the center layer followed by layers of pre-preg and copper product developed above and below to form the final variety of layers required by the board style, sort of like Dagwood building a sandwich. This approach enables the producer flexibility in how the board layer thicknesses are combined to fulfill the finished product thickness requirements by differing the number of sheets of pre-preg in each layer. Once the product layers are completed, 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 process of making printed circuit boards follows the actions listed below for a lot of applications.
The procedure of figuring out products, processes, and requirements to fulfill the consumer's specs for the board style based upon the Gerber file information supplied with the purchase order.
The process of moving the Gerber file information for a layer onto an etch resist film 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 gets rid of the vulnerable copper, leaving the safeguarded copper pads and traces in place; more recent procedures use plasma/laser etching instead of chemicals to remove the copper material, allowing finer line definitions.
The process of aligning 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 material.
The process of drilling all of the holes for plated through applications; a 2nd drilling process is utilized for holes that are not to be plated through. Details on hole area and size is contained 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 however the hole is not to be plated through. Prevent this process if possible because it adds 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 safeguards against environmental damage, supplies insulation, safeguards against 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 happen at a later date after the elements have been placed.
The procedure of applying the markings for part designations and part details to the board. Might be used to simply the top side or to both sides if parts are installed on both leading and bottom sides.
The procedure of separating numerous boards from a panel of similar boards; this procedure also permits cutting notches or slots into the board if required.
A visual evaluation 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 procedure of looking for continuity or shorted connections on the boards by ways using a voltage in between various points on the board and identifying if an existing circulation occurs. Depending upon the board intricacy, this process might require a specially developed test component and test program to integrate with the electrical test system utilized by the board producer.