In electronics, printed circuit boards, or PCBs, are used 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 part side, a mix of thru-hole and surface install on the top side only, a mix of thru-hole and surface area mount elements on the top side and surface install parts on the bottom or circuit side, or surface install parts on the leading and bottom sides of the board.
The boards are likewise utilized to electrically link the required leads for each part 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 developed as single sided with 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 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 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 actual copper pads and connection traces on the board surfaces as part of the board manufacturing process. A multilayer board consists of a number of layers ISO 9001 consultants of dielectric material that has actually been fertilized with adhesives, and these layers are utilized to separate the layers of copper plating. All of 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 innovations.
In a common 4 layer board design, the internal layers are typically used 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 top and bottom layers of the board. Really complicated board designs might have a large number of layers to make the different connections for various voltage levels, ground connections, or for linking the many leads on ball grid variety gadgets and other large incorporated circuit package formats.
There are generally two kinds of product utilized to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet kind, typically about.002 inches thick. Core material is similar to an extremely thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, typically.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are 2 methods utilized to build up the preferred variety of layers. The core stack-up technique, which is an older technology, uses a center layer of pre-preg material with a layer of core product above and another layer of core material below. This mix of one pre-preg layer and two core layers would make a 4 layer board.
The movie stack-up technique, a more recent innovation, would have core product as the center layer followed by layers of pre-preg and copper product developed above and listed below to form the last variety of layers needed by the board design, sort of like Dagwood building a sandwich. This technique allows the maker versatility in how the board layer thicknesses are integrated to meet the completed item density requirements by varying the variety of sheets of pre-preg in each layer. As soon as the material layers are finished, the whole 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 procedure of determining materials, processes, and requirements to fulfill the client's specs for the board design based on the Gerber file details offered with the order.
The procedure of transferring the Gerber file information for a layer onto an etch withstand movie that is placed on the conductive copper layer.
The conventional process of exposing the copper and other areas unprotected by the etch resist film to a chemical that eliminates the vulnerable copper, leaving the protected copper pads and traces in place; more recent processes use plasma/laser etching rather of chemicals to get rid of the copper material, permitting finer line meanings.
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 the holes for plated through applications; a second drilling procedure is used for holes that are not to be plated through. Info on hole location and size is consisted of in the drill drawing file.
The process 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 but the hole is not to be plated through. Prevent this process if possible since it includes expense to the completed board.
The process of applying a protective masking material, a solder mask, over the bare copper traces or over the copper that has had a thin layer of solder used; the solder mask protects against environmental damage, supplies insulation, safeguards against solder shorts, and protects traces that run in between pads.
The procedure of covering the pad areas with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering procedure that will take place at a later date after the components have actually been positioned.
The procedure of using the markings for part designations and part lays out to the board. Might be applied to just the top or to both sides if elements are installed on both top and bottom sides.
The procedure of separating multiple boards from a panel of identical boards; this process also permits cutting notches or slots into the board if needed.
A visual assessment of the boards; also can be the process of inspecting 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 applying a voltage between different points on the board and identifying if a current circulation takes place. Relying on the board complexity, this process might require a specifically developed test fixture and test program to incorporate with the electrical test system used by the board manufacturer.