In electronic devices, printed circuit boards, or PCBs, are used to mechanically support electronic elements which have their connection leads soldered onto copper pads in surface area mount 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 leading or element side, a mix of thru-hole and surface area mount on the top side only, a mix of thru-hole and surface area install components on the top side and surface install parts on the bottom or circuit side, or surface install elements on the top and bottom sides of the board.
The boards are likewise utilized to electrically connect the needed leads for each part using conductive copper traces. The part pads and connection traces are etched 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 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 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 etched away to form the real copper pads and connection traces on the board surface areas as part of the board manufacturing process. A multilayer board includes a number of layers of dielectric product 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 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 normal four layer board style, the internal layers are often utilized to offer power and ground connections, such as a +5 V plane layer and a Ground airplane layer as the 2 internal layers, with all other circuit and component connections made on the leading and bottom layers of the board. Very intricate board styles may have a large number of layers to make the various connections for different voltage levels, ground connections, or for connecting the numerous leads on ball grid array gadgets and other large integrated circuit bundle formats.
There are typically two types of material utilized to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet form, typically about.002 inches thick. Core product is similar to a really thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, typically.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two techniques utilized to develop the desired number of layers. The core stack-up approach, which is an older technology, utilizes a center layer of pre-preg product 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 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 number of layers needed by the board style, sort of like Dagwood constructing a sandwich. This approach allows the producer flexibility in how the board layer densities are integrated to satisfy the ended up product thickness requirements by differing the variety of sheets of pre-preg in each layer. When the product layers are finished, the whole 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 of producing printed circuit boards follows the actions listed below for the majority of applications.
The procedure of identifying products, procedures, and requirements to satisfy the customer's specs for the board design based ISO 9001 Accreditation Consultants upon the Gerber file info offered with the purchase order.
The process of transferring the Gerber file information for a layer onto an etch resist movie that is placed on the conductive copper layer.
The standard procedure of exposing the copper and other areas unprotected by the etch withstand movie to a chemical that eliminates the unprotected copper, leaving the protected copper pads and traces in location; newer procedures utilize plasma/laser etching instead of chemicals to eliminate the copper product, permitting finer line meanings.
The procedure of aligning the conductive copper and insulating dielectric layers and pushing them under heat to activate the adhesive in the dielectric layers to form a strong board product.
The process of drilling all the holes for plated through applications; a 2nd drilling procedure is utilized for holes that are not to be plated through. Info on hole location and size is contained 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 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 due to the fact that 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 actually had a thin layer of solder applied; the solder mask protects versus environmental damage, supplies insulation, secures against solder shorts, and secures 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 procedure that will occur at a later date after the elements have actually been put.
The process of applying the markings for part designations and part details to the board. May be applied to just the top side or to both sides if elements are installed on both top and bottom sides.
The procedure of separating numerous boards from a panel of identical boards; this procedure likewise allows cutting notches or slots into the board if needed.
A visual evaluation of the boards; likewise can be the procedure of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The process of checking for continuity or shorted connections on the boards by methods using a voltage in between different points on the board and determining if a current flow takes place. Depending upon the board complexity, this process might need a specially designed test component and test program to integrate with the electrical test system used by the board producer.