In electronic devices, 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 element leads in thru-hole applications. A board style may have all thru-hole components on the top or element side, a mix of thru-hole and surface area install on the top only, a mix of thru-hole and surface install elements on the top and surface area install parts on the bottom or circuit side, or surface area mount elements on the leading and bottom sides of the board.
The boards are likewise used to electrically link the needed leads for each element utilizing 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 just, double agreed 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 real copper pads and connection traces on the board surface areas as part of the board production procedure. A multilayer board consists of a number 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 of 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 typical 4 layer board design, the internal layers are typically utilized to provide 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 element connections made on the top and bottom layers of the board. Really intricate board designs might have a large number of layers to make the various connections for various voltage levels, ground connections, or for linking the many leads on ball grid range gadgets and other large incorporated circuit plan formats.
There are normally 2 kinds of product used to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet form, typically about.002 inches thick. Core product resembles 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, normally.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are two approaches used to build up the wanted variety of layers. The core stack-up method, which is an older technology, uses a center layer of pre-preg product with a layer of core material 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 approach, a more recent innovation, would have core material as the center layer followed by layers of pre-preg and copper product developed above and listed below to form the last number of layers required by the board design, sort of like Dagwood building a sandwich. This method permits the manufacturer versatility in how the board layer thicknesses are integrated to fulfill the finished item thickness requirements by varying the number of sheets of pre-preg in each layer. Once the material layers are finished, 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 making printed circuit boards follows the actions listed below for the majority of applications.
The procedure of figuring out products, procedures, and requirements to fulfill the customer's specs for the board design based upon the Gerber file information offered with the order.
The process of moving the Gerber file information for a layer onto an etch resist movie that is placed on the conductive copper layer.
The conventional procedure of exposing the copper and other locations unprotected by the etch resist film to a chemical that removes the unguarded copper, leaving the protected copper pads and traces in place; more recent processes use plasma/laser etching rather of chemicals to remove the copper product, permitting finer line definitions.
The process of lining up the conductive copper and insulating dielectric layers and pressing them under heat to activate the adhesive in the dielectric layers to form a solid board product.
The procedure of drilling all the holes for plated through applications; a second drilling procedure is used for holes that are not to be plated through. Info on hole location 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 placed in an electrically charged bath of copper.
This is needed when holes are to be drilled through a copper location but the hole is not to be plated through. Avoid this Reference site process if possible due to the fact that it adds cost to the finished board.
The process 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 used; the solder mask protects against environmental damage, offers insulation, protects against solder shorts, and protects traces that run in between pads.
The procedure of finishing the pad areas 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 components have been put.
The process of using the markings for part designations and part describes to the board. May be applied to simply the top or to both sides if components are mounted on both top and bottom sides.
The procedure of separating several boards from a panel of identical boards; this procedure likewise allows cutting notches or slots into the board if required.
A visual evaluation of the boards; also can be the process of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The procedure of checking for continuity or shorted connections on the boards by ways using a voltage between various points on the board and identifying if an existing flow occurs. Relying on the board intricacy, this procedure might require a specially designed test fixture and test program to integrate with the electrical test system used by the board maker.