In electronics, printed circuit boards, or PCBs, are utilized 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 element leads in thru-hole applications. A board design may have all thru-hole elements on the top or component side, a mix of thru-hole and surface install on the top just, a mix of thru-hole and surface area install elements on the top side and surface area mount components on the bottom or circuit side, or surface area mount parts on the top and bottom sides of the board.
The boards are likewise used to electrically connect the required leads for each element 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 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 consist of 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 production procedure. A multilayer board consists of a variety of layers of dielectric material that has actually been fertilized with adhesives, and these layers are used 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 innovations.
In a typical four layer board design, the internal layers are often used 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 part connections made on the leading and bottom layers of the board. Extremely complicated board styles might have a a great deal of layers to make the various connections for different voltage levels, ground connections, or for connecting the lots of leads on ball grid array gadgets and other large incorporated circuit package formats.
There are generally 2 kinds of material utilized to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet kind, typically about.002 inches thick. Core material is similar to an extremely thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, usually.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are 2 approaches used to develop the desired number 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 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 movie stack-up approach, a more recent innovation, would have core product as the center layer followed by layers of pre-preg and copper product built up above and below to form the final variety of layers needed by the board design, sort of like Dagwood constructing a sandwich. This method permits the producer flexibility in how the board layer densities are combined to satisfy the ended up product thickness requirements by varying the variety of sheets of pre-preg in each layer. When the product layers are completed, the entire 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 listed below for most applications.
The process of figuring out products, processes, and requirements to meet the customer's requirements for the board style based on the Gerber file details offered with the purchase order.
The procedure of moving the Gerber file information for a layer onto an etch resist film that is placed on the conductive copper layer.
The standard procedure of exposing the copper and other locations unprotected by the etch resist film to a chemical that gets rid of the vulnerable copper, leaving the secured copper pads and traces in place; more recent processes utilize plasma/laser etching rather of chemicals to eliminate the copper product, allowing finer line meanings.
The process 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 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 area and size is included 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 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. Prevent this process if possible since it includes expense to the completed board.
The procedure of using 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, protects versus solder shorts, and protects traces that run between pads.
The process of finishing 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 components have actually been placed.
The procedure of applying the markings for element designations and part outlines to the board. Might be used to just the top or to both sides if parts are installed on both top and bottom sides.
The process of separating numerous boards from a panel of identical boards; this process also permits cutting notches or slots into the board if needed.
A visual assessment of the boards; also can be the process of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The process of looking for connection or shorted connections on the boards by means applying a voltage in between various points on the board and figuring out if a current flow occurs. Depending upon the board complexity, this procedure may need a specially designed test component and test program to integrate with the electrical test system utilized by the board maker.