In electronics, printed circuit boards, or PCBs, are utilized to mechanically support electronic components 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 part leads in thru-hole applications. A board design may have all thru-hole elements on the top or component side, a mix of thru-hole and surface area mount on the top side just, a mix of thru-hole and surface area install components on the top and surface install elements on the bottom or circuit side, or surface install components on the top and bottom sides of the board.
The boards are likewise used to electrically connect the required leads for each element using conductive copper traces. The component pads and connection traces are engraved from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are created as single sided with copper pads and traces on one side of the board just, double agreed 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 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 actual copper pads and connection traces on the board surfaces as part of the board production procedure. A multilayer board consists of a number of layers of dielectric product that has been fertilized with adhesives, and these layers are used 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 technologies.
In a normal 4 layer board design, the internal layers are often used to provide power and ground connections, such as a +5 V aircraft layer and a Ground aircraft layer as the two internal layers, with all other circuit and component connections made on the leading and bottom layers of the board. Very complicated board designs may have a a great deal of layers to make the various connections for various voltage levels, ground connections, or for connecting the many leads on ball grid array devices and other large incorporated circuit plan formats.
There are usually 2 types of material utilized to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet form, typically about.002 inches thick. Core material resembles a really thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, usually.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are two approaches utilized to develop the wanted variety of layers. The core stack-up approach, which is an older innovation, uses a center layer of pre-preg material with a layer of core product 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 approach, a newer technology, would have core material as the center layer followed by layers of pre-preg and copper product developed above and below to form the last variety of layers needed by the board design, sort of like Dagwood building a sandwich. This approach permits the manufacturer versatility in how the board layer thicknesses are combined to fulfill the finished item thickness requirements by differing the number of sheets of pre-preg in each layer. As soon as the material layers are finished, the entire stack goes through 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 procedure of making printed circuit boards follows the steps listed below for most applications.
The process of determining materials, procedures, and requirements to meet the client's specifications for the board style based upon the Gerber file info offered with the purchase order.
The procedure of moving the Gerber file data for a layer onto an etch withstand film that is put on the conductive copper layer.
The traditional procedure of exposing the copper and other areas unprotected by the etch withstand movie to a chemical that gets rid of the unprotected copper, leaving the safeguarded copper pads and traces in location; more recent procedures utilize plasma/laser etching instead of chemicals to remove the copper product, allowing finer line definitions.
The process of lining up the conductive copper and insulating dielectric layers and pressing them under heat to trigger 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 second drilling procedure is used for holes that are not to be plated through. Details on hole place 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 location however the hole is not to be plated through. Prevent this process if possible since it includes cost to the finished board.
The procedure of using a protective masking material, a solder mask, over the ISO 9001 Accreditation bare copper traces or over the copper that has had a thin layer of solder used; the solder mask safeguards against environmental damage, supplies insulation, safeguards against solder shorts, and protects traces that run in between pads.
The procedure of finish the pad locations with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will occur at a later date after the elements have actually been placed.
The process of using the markings for element designations and part outlines to the board. May be used to simply the top side or to both sides if parts are installed on both leading and bottom sides.
The process of separating multiple boards from a panel of identical boards; this process also allows cutting notches or slots into the board if required.
A visual inspection of the boards; likewise can be the process of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The procedure of looking for connection or shorted connections on the boards by methods using a voltage in between various points on the board and identifying if a current circulation occurs. Depending upon the board complexity, this procedure may need a specially designed test component and test program to incorporate with the electrical test system utilized by the board manufacturer.