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 install applications or through rilled holes in the board and copper pads for soldering the part leads in thru-hole applications. A board design might have all thru-hole elements on the top or ISO 9001 Certification Consultants part side, a mix of thru-hole and surface area install on the top just, a mix of thru-hole and surface mount components on the top and surface install components on the bottom or circuit side, or surface mount parts on the leading and bottom sides of the board.
The boards are also used to electrically connect the required leads for each part using conductive copper traces. The element pads and connection traces are etched 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 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 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 surface areas as part of the board manufacturing process. A multilayer board includes a variety of layers of dielectric material that has actually been impregnated 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 common 4 layer board design, the internal layers are typically used to supply 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 part connections made on the top and bottom layers of the board. Extremely complex board designs may have a a great deal of layers to make the different connections for different voltage levels, ground connections, or for linking the numerous leads on ball grid selection gadgets and other big integrated circuit package formats.
There are normally 2 types of product utilized to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, typically about.002 inches thick. Core material resembles an extremely thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, typically.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are 2 techniques used to build up the desired number of layers. The core stack-up approach, which is an older technology, uses 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 two core layers would make a 4 layer board.
The film stack-up technique, a newer technology, would have core material as the center layer followed by layers of pre-preg and copper material built up above and listed below to form the last number of layers required by the board style, sort of like Dagwood constructing a sandwich. This method permits the producer flexibility in how the board layer thicknesses are combined to meet the ended up product 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 process of producing printed circuit boards follows the steps below for many applications.
The process of determining products, procedures, and requirements to meet the client's specifications for the board design based on the Gerber file details provided with the order.
The process of moving the Gerber file information for a layer onto an etch withstand movie that is put on the conductive copper layer.
The conventional procedure of exposing the copper and other areas unprotected by the etch resist film to a chemical that removes the unprotected copper, leaving the secured copper pads and traces in place; more recent processes use plasma/laser etching instead of chemicals to eliminate the copper product, enabling finer line definitions.
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 strong board material.
The process of drilling all of the holes for plated through applications; a second drilling process is used for holes that are not to be plated through. Information on hole place and size is consisted of 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 location but the hole is not to be plated through. Avoid this process if possible because it adds cost to the finished board.
The process of applying 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 applied; the solder mask safeguards against environmental damage, provides insulation, secures against solder shorts, and safeguards traces that run in between pads.
The procedure of coating the pad locations with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering process that will occur at a later date after the elements have actually been positioned.
The process of using the markings for component designations and component details to the board. May be used to just the top side or to both sides if parts are mounted on both leading and bottom sides.
The procedure of separating numerous boards from a panel of identical boards; this procedure also enables cutting notches or slots into the board if needed.
A visual examination of the boards; likewise can be the procedure of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The process of checking for continuity or shorted connections on the boards by means applying a voltage in between various points on the board and identifying if an existing flow happens. Relying on the board complexity, this process might need a specifically created test fixture and test program to incorporate with the electrical test system used by the board manufacturer.