In electronics, printed circuit boards, or PCBs, are used to mechanically support electronic elements which have their connection leads soldered onto copper pads in surface area mount 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 elements 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 mount elements on the top and surface mount parts on the bottom or circuit side, or surface install components on the leading and bottom sides of the board.
The boards are also used to electrically link the required leads for each element utilizing conductive copper traces. The element 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 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 variety 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 etched away to form the real copper pads and connection traces on the board surface areas More interesting details here as part of the board production process. A multilayer board consists of a variety of layers of dielectric product that has actually been fertilized with adhesives, and these layers are utilized to separate the layers of copper plating. All these layers are lined up 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 typical four layer board style, the internal layers are often utilized to offer power and ground connections, such as a +5 V aircraft layer and a Ground plane layer as the 2 internal layers, with all other circuit and element connections made on the leading and bottom layers of the board. Really complicated board designs may have a large number of layers to make the various connections for different voltage levels, ground connections, or for connecting the lots of leads on ball grid selection gadgets and other large integrated circuit plan formats.
There are usually two types of material utilized to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet kind, normally about.002 inches thick. Core product resembles a really thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, generally.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two methods used to develop the desired variety of layers. The core stack-up technique, which is an older innovation, utilizes a center layer of pre-preg product with a layer of core material above and another layer of core material listed below. This combination of one pre-preg layer and 2 core layers would make a 4 layer board.
The movie 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 needed by the board style, sort of like Dagwood developing a sandwich. This method allows the producer flexibility in how the board layer thicknesses are integrated to meet 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 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 manufacturing printed circuit boards follows the steps listed below for many applications.
The procedure of figuring out materials, processes, and requirements to fulfill the consumer's specs for the board style based upon the Gerber file details supplied with the order.
The procedure of moving the Gerber file data for a layer onto an etch resist movie that is put on the conductive copper layer.
The standard process of exposing the copper and other locations unprotected by the etch resist movie to a chemical that eliminates the unprotected copper, leaving the safeguarded copper pads and traces in place; newer procedures use plasma/laser etching instead of chemicals to remove the copper product, enabling finer line meanings.
The procedure of lining up 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 procedure 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. Info on hole location and size is included 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. Avoid this process if possible due to the fact that it adds expense to the completed board.
The process of using 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 used; the solder mask safeguards against environmental damage, offers insulation, protects against solder shorts, and protects traces that run between pads.
The procedure of finishing the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering procedure that will occur at a later date after the components have been put.
The process of using the markings for part designations and element lays out to the board. Might be used to just the top or to both sides if elements are installed on both leading and bottom sides.
The procedure of separating multiple boards from a panel of identical boards; this procedure also permits cutting notches or slots into the board if required.
A visual assessment of the boards; also can be the process of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The process of checking for continuity or shorted connections on the boards by means applying a voltage in between different points on the board and determining if a current circulation happens. Depending upon the board complexity, this procedure may need a specially developed test component and test program to incorporate with the electrical test system used by the board maker.