In electronics, printed circuit boards, or PCBs, are used to mechanically support electronic parts which have their connection leads soldered onto copper pads in surface mount applications or through rilled holes More interesting details here in the board and copper pads for soldering the component leads in thru-hole applications. A board design might have all thru-hole components on the leading or part side, a mix of thru-hole and surface install on the top side only, a mix of thru-hole and surface install elements on the top and surface area mount parts on the bottom or circuit side, or surface mount components on the leading and bottom sides of the board.
The boards are also used to electrically link the needed leads for each part using 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 agreed copper pads and traces on one side of the board only, double sided with copper pads and traces on the top 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 include 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 real copper pads and connection traces on the board surface areas as part of the board manufacturing procedure. A multilayer board includes a variety 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 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 technologies.
In a normal four layer board style, the internal layers are typically used to supply power and ground connections, such as a +5 V plane layer and a Ground aircraft layer as the 2 internal layers, with all other circuit and element connections made on the leading and bottom layers of the board. Extremely complex board designs might have a large number of layers to make the various connections for different voltage levels, ground connections, or for connecting the many leads on ball grid selection devices and other large integrated circuit package formats.
There are usually 2 kinds of material utilized to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet form, normally about.002 inches thick. Core product is similar to a really thin double sided board because it has a dielectric material, 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 style, there are two approaches utilized to build up the preferred 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 material above and another layer of core product listed below. This combination of one pre-preg layer and 2 core layers would make a 4 layer board.
The movie stack-up approach, a more recent technology, would have core material as the center layer followed by layers of pre-preg and copper product built up above and listed below to form the last variety of layers required by the board style, sort of like Dagwood developing a sandwich. This approach allows the producer flexibility in how the board layer thicknesses are integrated to satisfy the finished item thickness requirements by differing the number of sheets of pre-preg in each layer. Once the material layers are completed, the whole stack is subjected to 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 manufacturing printed circuit boards follows the steps listed below for many applications.
The procedure of determining materials, processes, and requirements to meet the customer's specs for the board style based on the Gerber file details provided with the order.
The procedure of transferring the Gerber file information for a layer onto an etch resist film that is put on the conductive copper layer.
The conventional procedure of exposing the copper and other locations unprotected by the etch resist film to a chemical that removes the unprotected copper, leaving the protected copper pads and traces in location; newer procedures utilize plasma/laser etching instead of chemicals to remove the copper product, enabling finer line definitions.
The procedure 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 strong board product.
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 place and size is consisted of 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 placed in an electrically charged bath of copper.
This is needed when holes are to be drilled through a copper area but the hole is not to be plated through. Prevent this process if possible due to the fact that it includes expense to the completed board.
The process 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 applied; the solder mask safeguards versus ecological damage, offers insulation, secures versus solder shorts, and safeguards traces that run in between pads.
The procedure of finish the pad areas with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering process that will occur at a later date after the components have been positioned.
The process of applying the markings for part designations and part details to the board. Might be used to simply 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 needed.
A visual examination 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 process of checking for continuity or shorted connections on the boards by methods applying a voltage between different points on the board and identifying if a present flow occurs. Depending upon the board intricacy, this process may require a specifically designed test component and test program to integrate with the electrical test system utilized by the board maker.