In electronics, printed circuit boards, or PCBs, are used to mechanically support electronic elements which have their connection leads soldered onto copper pads in surface install 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 leading or component side, a mix of thru-hole and surface mount on the top only, a mix of thru-hole and surface install components on the top and surface area mount parts on the bottom or circuit side, or surface area install parts on the leading and bottom sides of the board.
The boards are also utilized to electrically link the needed leads for each part using conductive copper traces. The component pads and connection traces are engraved 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 only, double agreed 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 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 engraved away to form the actual copper pads and connection traces on the board surface areas as part of the board manufacturing procedure. A multilayer board includes a variety of layers of dielectric material that has been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All of these layers are lined up 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 4 layer board design, the internal layers are typically 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 element 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 different connections for different voltage levels, ground connections, or for linking the many leads on ball grid range gadgets and other large incorporated circuit plan formats.
There are usually 2 types 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 form, typically about.002 inches thick. Core product resembles a very 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 product with 1 ounce copper layer on each side. In a multilayer board style, there are two methods utilized to build up the desired number of layers. The core stack-up approach, which is an older innovation, utilizes a center layer of pre-preg material 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 technique, a newer innovation, would have core material as the center layer followed by layers of pre-preg and copper material built up above and below to form the last number of layers needed by the board design, sort of like Dagwood developing a sandwich. This approach enables the maker flexibility in how the board layer densities are integrated to meet the completed product density requirements by varying the variety of sheets of pre-preg in each layer. As soon as the product layers are finished, the whole stack undergoes 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 making printed circuit boards follows the actions below for a lot of applications.
The procedure of determining products, processes, and requirements to meet the customer's specifications for the board style based on the Gerber file info offered with the order.
The process of transferring the Gerber file information for a layer onto an etch resist movie that is put on the conductive copper layer.
The standard procedure of exposing the copper and other areas unprotected by the etch resist movie to a chemical that gets rid of the unguarded copper, leaving the secured copper pads and traces in place; newer procedures utilize plasma/laser etching instead of chemicals to get rid of the copper product, allowing finer line meanings.
The procedure of aligning the conductive copper and insulating dielectric layers and pushing them under heat to trigger the adhesive in the dielectric layers to form a solid board material.
The procedure of drilling all of the holes for plated through applications; a second drilling procedure is utilized for holes that are not to be plated through. Info on hole location and size is included in the drill drawing file.
The procedure 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 area however the hole is not to be plated through. Avoid this process if possible because it includes expense to the finished board.
The process 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, safeguards against solder shorts, and secures traces that run between pads.
The process of finishing the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will take place at a later date after the parts have actually been placed.
The procedure of using the markings for part classifications and component describes to the board. May be used to simply the top side or to both sides if elements are mounted on both leading and bottom sides.
The process of separating multiple boards from a panel of similar boards; this process likewise permits cutting notches or slots into the board if needed.
A visual assessment of the boards; likewise 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 connection or shorted connections on the boards by means using a voltage in between different points on the board and figuring out if a present circulation occurs. Depending upon the board intricacy, this process may require a specially created test fixture and test program to incorporate with the electrical test system used by the board producer.