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 mount applications or through rilled holes in the board and copper pads for soldering the component leads in thru-hole applications. A board design may have all thru-hole parts on the leading or element side, a mix of thru-hole and surface mount on the top only, a mix of thru-hole and surface area install elements on the top and surface area install components on the bottom or circuit side, or surface install components on the top and bottom sides of the board.
The boards are likewise used to electrically link the required leads for each element utilizing conductive copper traces. The part pads and connection traces are etched 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 just, 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 material, such as FR-4 epoxy fiberglass, with copper plating on one or both sides. This copper plating is etched away to form the actual copper pads and connection traces on the board surface areas as part of the board production process. A multilayer board includes a variety 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 these layers are aligned 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 innovations.
In a common four layer board design, the internal layers are frequently utilized to offer power and ground connections, such as a +5 V airplane layer and a Ground aircraft layer as the two internal layers, with all other circuit and part connections made on the top and bottom layers of the board. Very complex board designs may have a large number of layers to make the various connections for various voltage levels, ground connections, or for linking the numerous leads on ball grid variety gadgets and other large integrated circuit plan formats.
There are typically 2 types of product used 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 material resembles a really thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, generally.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are 2 methods used to develop the preferred variety of layers. The core stack-up approach, which is an older innovation, uses a center layer of pre-preg product with a layer of core product above and another layer of core material listed below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The movie stack-up technique, a newer 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 required by the board design, sort of like Dagwood building a sandwich. This approach allows the manufacturer versatility in how the board layer thicknesses are integrated to satisfy the finished product thickness requirements by differing the variety of sheets of pre-preg in each layer. As soon as the material layers are completed, the entire stack is subjected to 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 process of producing printed circuit boards follows the actions listed below for the majority of applications.
The procedure of determining materials, procedures, and requirements to satisfy the consumer's specifications for the board style based on the Gerber file information provided with the purchase order.
The procedure of moving the Gerber file data for a layer onto an etch withstand movie that is put 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 vulnerable copper, leaving the protected copper pads and traces in place; more recent processes utilize plasma/laser etching instead of chemicals to remove the copper product, allowing finer line definitions.
The procedure of lining up 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 of the holes for plated through applications; a second drilling process is utilized for holes that are not to be plated through. Information on hole area and size is contained in the drill drawing file.
The procedure of applying 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. Avoid this procedure if possible due to the fact that it adds cost to the ended up 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 ecological damage, supplies insulation, protects against solder shorts, and secures 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 process that will take place at a later date after the elements have been put.
The process of using the markings for element classifications and element lays out to the board. Might be used to just the top or to both sides if parts are mounted on both leading and bottom sides.
The process of separating multiple boards from a panel of identical boards; this procedure also permits cutting notches or slots into the board if required.
A visual inspection 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 procedure of checking for connection or shorted connections on the boards by means applying a voltage in between numerous points on the board and figuring out if an existing flow happens. Relying on the board complexity, this procedure might need a specially designed test fixture and test program to incorporate with the electrical test system used by the board maker.