Just Quality Systems

Apr 15, 2019

In electronic devices, printed circuit boards, or PCBs, are utilized to mechanically support electronic elements which have their connection leads soldered onto copper pads in surface area install 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 components 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 mount parts on the top and surface install parts on the bottom or circuit side, or surface area mount components on the leading and bottom sides of the board.

The boards are also utilized to electrically link the required 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 designed as single agreed 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 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 engraved away to form the actual copper pads and connection traces on the board surface areas ISO 9001 Certification Consultants as part of the board manufacturing procedure. A multilayer board includes a variety of layers of dielectric material that has been fertilized with adhesives, and these layers are utilized to separate the layers of copper plating. All 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 design, the internal layers are typically used to supply power and ground connections, such as a +5 V aircraft 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. Very complicated board styles may have a large number of layers to make the numerous connections for different voltage levels, ground connections, or for linking the many leads on ball grid range gadgets and other big integrated circuit bundle formats.

There are usually two 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 because it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, generally.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are 2 techniques used to build up the preferred number of layers. The core stack-up technique, which is an older technology, utilizes a center layer of pre-preg material with a layer of core product above and another layer of core material listed below. This combination of one pre-preg layer and 2 core layers would make a 4 layer board.

The movie stack-up technique, a more recent technology, would have core material as the center layer followed by layers of pre-preg and copper product built up above and below to form the last number of layers needed by the board style, sort of like Dagwood constructing a sandwich. This technique allows the producer flexibility in how the board layer densities are integrated to fulfill the finished product density requirements by differing the number of sheets of pre-preg in each layer. Once the product layers are completed, the whole 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 making printed circuit boards follows the actions listed below for the majority of applications.

The procedure 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 order.

The process 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 areas unprotected by the etch withstand film to a chemical that eliminates the unprotected copper, leaving the secured copper pads and traces in location; more recent procedures use plasma/laser etching rather of chemicals to remove the copper material, allowing finer line meanings.

The process 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 material.

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 place and size is contained 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 positioned in an electrically charged bath of copper.

This is required when holes are to be drilled through a copper location however the hole is not to be plated through. Avoid this procedure if possible due to the fact that it adds expense 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 applied; the solder mask secures versus environmental damage, offers insulation, safeguards against solder shorts, and protects traces that run between pads.

The process of covering the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering procedure that will happen at a later date after the components have been positioned.

The process of applying the markings for element classifications and part outlines to the board. Might be used to simply the top side or to both sides if elements are installed on both leading and bottom sides.

The procedure of separating several boards from a panel of identical boards; this process also enables cutting notches or slots into the board if required.

A visual examination 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 techniques.

The procedure of checking for continuity or shorted connections on the boards by ways applying a voltage between different points on the board and figuring out if a present flow takes place. Depending upon the board intricacy, this process might need a specifically created test component and test program to incorporate with the electrical test system used by the board maker.