In electronic devices, printed circuit boards, or PCBs, are utilized to mechanically support electronic elements which have their connection leads soldered onto copper pads in surface mount applications or through rilled holes in the board and copper pads for soldering the component leads in thru-hole applications. A board style might have all thru-hole parts 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 install parts on the top and surface mount components 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 connect the required leads for each component 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 just, double agreed copper pads and traces on the leading and bottom sides of the board, or multilayer styles with copper pads and traces on the 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 production procedure. A multilayer board includes a number of layers of dielectric material 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 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 typical 4 layer board design, the internal layers are often utilized to offer 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 top and bottom layers of the board. Really intricate board styles may have a large number of layers to make the various connections for different voltage levels, ground connections, or for linking the numerous leads on ball grid array gadgets and other large incorporated circuit bundle formats.
There are usually two types of material utilized to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, generally about.002 inches thick. Core material is similar to a very 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 product with 1 ounce copper layer on each side. In a multilayer board style, there are 2 techniques used to develop the wanted variety of layers. The core stack-up method, which is an older innovation, utilizes a center layer of pre-preg material with a layer of core material 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 innovation, 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 number of layers required by the board design, sort of like Dagwood constructing a sandwich. This method allows the maker versatility in how the board layer densities are integrated to meet the completed product density requirements by differing the number of sheets of pre-preg in each layer. When the product layers are finished, the entire 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 procedure More interesting details here of making printed circuit boards follows the actions below for many applications.
The procedure of identifying products, procedures, and requirements to fulfill the consumer's specifications for the board design based on the Gerber file info supplied with the purchase order.
The process of transferring the Gerber file data 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 withstand film to a chemical that eliminates the unprotected copper, leaving the protected copper pads and traces in place; newer processes utilize plasma/laser etching instead of chemicals to eliminate the copper product, permitting finer line meanings.
The procedure of lining up the conductive copper and insulating dielectric layers and pushing them under heat to activate the adhesive in the dielectric layers to form a solid board material.
The procedure of drilling all the holes for plated through applications; a 2nd drilling procedure is used for holes that are not to be plated through. Information 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 placed 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. Avoid this procedure if possible because it adds expense to the completed board.
The procedure 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 used; the solder mask safeguards versus ecological damage, supplies insulation, safeguards versus solder shorts, and safeguards traces that run in between pads.
The procedure of coating the pad areas 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 elements have been placed.
The process of applying the markings for component classifications and part describes to the board. May be applied to just the top or to both sides if components are installed on both leading and bottom sides.
The process of separating multiple boards from a panel of identical boards; this process likewise permits cutting notches or slots into the board if needed.
A visual examination of the boards; likewise can be the procedure of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The procedure of checking for continuity or shorted connections on the boards by methods using a voltage between various points on the board and determining if an existing flow occurs. Relying on the board complexity, this process may require a specifically created test fixture and test program to incorporate with the electrical test system utilized by the board manufacturer.
