Basics of Manufacturing Printed Circuit Boards

In electronics, 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 component leads in through-hole applications. A board design may have all through-hole components on the top or component side, a mix of through-hole and surface mount on the top side only, a mix of through-hole and surface mount components on the top side and surface mount components on the bottom or circuit side, or surface mount components on the top and bottom sides of the board.

The boards are also used to electrically connect the required leads for each https://www.hemeixinpcb.com/company/news/313-types-of-hdi-pcb-stackup.html component using conductive copper traces. The component 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 sided with 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 number of internal copper layers with traces and connections.

Single or double sided boards consist of 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 actual copper pads and connection traces on the board surfaces as part of the board manufacturing process. A multilayer board consists of a number 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 aligned and 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 typical four layer board design, the internal layers are often used to provide power and ground connections, such as a +5V plane layer and a Ground plane layer as the two internal layers, with all other circuit and component connections made on the top and bottom layers of the board. Very complex board designs may have a large number of layers to make the various connections for different voltage levels, ground connections, or for connecting the many leads on ball grid array devices and other large integrated circuit package formats.

There are usually two types of material used to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet form, usually about .002 inches thick. Core material is similar to a very thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, usually .030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are two methods used to build up the desired number 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 material 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 method, a newer 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 final number of layers required by the board design, sort of like Dagwood building a sandwich. This method allows the manufacturer flexibility in how the board layer thicknesses are combined to meet the finished product thickness requirements by varying the number of sheets of pre-preg in each layer. Once the material layers are completed, 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.