The Basics Of Quality Systems

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 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 elements 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 area mount components on the top side and surface mount parts on the bottom or circuit side, or surface install parts on the top and bottom sides of the board.

The boards are likewise used to electrically link the required leads for each component 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 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 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 surfaces as part of the board production process. A multilayer board Click here consists of a number of layers of dielectric material that has been impregnated with adhesives, and these layers are utilized 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 technologies.

In a common four layer board design, the internal layers are frequently utilized to supply power and ground connections, such as a +5 V plane layer and a Ground airplane layer as the two internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Very complex board designs may have a large number of layers to make the different connections for various voltage levels, ground connections, or for connecting the many leads on ball grid array devices and other big incorporated circuit package formats.

There are typically 2 types of product utilized to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, generally about.002 inches thick. Core product resembles an extremely thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, typically.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are 2 techniques utilized to develop the wanted variety of layers. The core stack-up method, which is an older technology, uses a center layer of pre-preg material with a layer of core product above and another layer of core material below. This combination of one pre-preg layer and two core layers would make a 4 layer board.

The film stack-up technique, a more recent technology, 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 style, sort of like Dagwood developing a sandwich. This technique allows the manufacturer versatility in how the board layer densities are integrated to satisfy the ended up item thickness requirements by differing the number of sheets of pre-preg in each layer. When the material layers are completed, the whole stack is subjected to 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 procedure of producing printed circuit boards follows the steps listed below for a lot of applications.

The procedure of figuring out products, procedures, and requirements to satisfy the customer's requirements for the board style based on the Gerber file information provided 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 conventional procedure of exposing the copper and other locations unprotected by the etch withstand movie to a chemical that gets rid of the vulnerable copper, leaving the safeguarded copper pads and traces in place; more recent processes utilize plasma/laser etching instead of chemicals to get rid of the copper material, enabling finer line definitions.

The procedure of aligning 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 material.

The procedure of drilling all the holes for plated through applications; a second drilling process is utilized for holes that are not to be plated through. Details on hole location and size is consisted of in the drill drawing file.

The process of using 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 needed when holes are to be drilled through a copper area however the hole is not to be plated through. Prevent this procedure if possible because it includes cost to the ended up 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 secures against ecological damage, provides insulation, secures versus solder shorts, and secures traces that run in between pads.

The process of finish the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will happen at a later date after the parts have actually been placed.

The process of applying the markings for part classifications and component describes to the board. Might be applied to simply the top side or to both sides if components are mounted on both leading and bottom sides.

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

A visual inspection of the boards; also can be the procedure of checking 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 takes place. Relying on the board complexity, this process might require a specifically developed test component and test program to integrate with the electrical test system used by the board producer.