ISO 9001 Certification Consultants
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 mount applications or through rilled holes in the board and copper pads for soldering the element leads in thru-hole applications. A board design might have all thru-hole elements on the top or part side, a mix of thru-hole and surface mount on the top side just, a mix of thru-hole and surface install parts on the top and surface area mount components on the bottom or circuit side, or surface mount elements on the leading and bottom sides of the board.
The boards are also utilized to electrically link the required leads for each part utilizing conductive copper traces. The element pads and connection traces are engraved from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are designed as single sided with copper pads and traces on one side of the board only, double agreed copper pads and traces on the top and bottom sides of the board, or multilayer designs with copper pads and traces on the 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 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 consists of a number 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 aligned 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 typical 4 layer board design, the internal layers are frequently utilized to supply power and ground connections, such as a +5 V aircraft 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. Very complex board styles might have a a great deal of layers to make the various connections for various voltage levels, ground connections, or for connecting the numerous leads on ball grid variety gadgets and other large integrated circuit package formats.
There are normally 2 kinds of material used to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, normally about.002 inches thick. Core product is similar to an extremely thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, normally.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are 2 approaches utilized to build up the desired variety of layers. The core stack-up method, which is an older innovation, utilizes a center layer of pre-preg product with a layer of core material above and another layer of core product below. This mix of one pre-preg layer and 2 core layers would make a 4 layer board.
The film stack-up approach, a more recent technology, 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 final variety of layers required by the board style, sort of like Dagwood building a sandwich. This method allows the maker versatility in how the board layer densities are combined to fulfill the finished product density requirements by differing the variety of sheets of pre-preg in each layer. Once the product layers are finished, the entire stack undergoes heat and pressure that causes 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 the majority of applications.
The process of identifying materials, processes, and requirements to satisfy the client's specifications for the board design based on the Gerber file info offered with the purchase order.
The process of moving the Gerber file information for a layer onto an etch withstand movie that is placed on the conductive copper layer.
The standard process of exposing the copper and other locations unprotected by the etch resist movie to a chemical that eliminates the vulnerable copper, leaving the secured copper pads and traces in place; more recent processes utilize plasma/laser etching instead of chemicals to remove the copper material, enabling finer line meanings.
The procedure of aligning 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 the holes for plated through applications; a second drilling procedure is utilized for holes that are not to be plated through. Details on hole location and size is consisted of in the drill drawing file.
The process 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 required 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 adds cost 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 safeguards against ecological damage, supplies insulation, protects versus solder shorts, and safeguards traces that run between pads.
The procedure of coating the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering process that will take place at a later date after the elements have been positioned.
The process of using the markings for element classifications and component outlines to the board. Might be used to simply the top side or to both sides if components are mounted on both top and bottom sides.
The process of separating numerous boards from a panel of similar boards; this procedure likewise allows cutting notches or slots into the board if required.
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 approaches.
The process of checking for connection or shorted connections on the boards by means using a voltage in between various points on the board and figuring out if an existing flow takes place. Relying on the board complexity, this process might need a specifically designed test fixture and test program to integrate with the electrical test system used by the board manufacturer.
ISO 9001 Certification Consultants