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Conductors and Components on a Printed Circuit Board
Posted on 28/08/2015

Printed Circuits Boards are cleverly designed items that are used to not only connect electronic components but also mechanically support the functions of many electronic devices. The market for bare PCB’s worldwide was valued at $60.2 Billion in 2014 (US). Components are connected and operated by the conductive pathways, tracks or what is known as signal traces which are etched from copper sheets. This connection is made possible by the distinction between the copper sheets and the non-conductive substrate laminated on to the board. The resistance of the board is determined by the width and the thickness of the traces that expose the copper. The use of the board is also considered when inserting the tracks and traces for example some power and ground traces are usually wider then signal traces. The size and capability of these tracks and traces are described as impedance control. PCB Global not only delivers Printed Circuit Boards to your specifications, we can also assist with your impedance control requirements with predetermined layer stack up including track width and spacing recommendations to ensure impedance matching.

FR4 (Flame Resistant 4) is the most commonly used epoxy which is a woven fiberglass cloth impregnated with the epoxy resin. It has good insulation properties with good arc resistance making it very useful to both single and multilayer boards. The copper is laminated onto the FR4, providing a greater distinction of the conductive pathways as previously described that the FR4 has a high insulation effect. Multilayer PCB’s will have multiple layers of materials which will be laminated together. In some cases, multilayer boards may be required to contain a solid copper layer to act as a shield or ‘ground plane’ for power return.

Copper thickness in any single or multilayer PCB will determine the current-carrying capacity of the board. It is preferable to use heavier copper to increase the carrying capacity as well as increase the resistance of thermal strains. 1oz and 2oz copper are the preferred and more common choices for many single and multilayer PCB’s. Chemical etching is a process using lead and tin to electroplate the copper to increase the thickness. This is achieved by a mixture involving either ammonium persulfate or ferric chloride. The purpose of the chemical etching is to etch away the excess copper on the areas that should not contain copper. The solder, tin, gold or nickel used to plate the PCB acts as a corrosion resistant coating/barrier. The most common method is hot air solder levelling or HASL.

Components such as resistors, capacitors and active devices are usually soldered onto the bare PCB. In some cases, more advanced PCB’s will have their components embedded in the substrate. This offers greater connection and conduction, advancing the function of the loaded PCB. Components embedded throughout different layers of the PCB are made possible by the connection of vias. Multilayer PCB’s in this case will always allow for a higher conduction through component density. In the case that the board does not have any embedded components as described above, the more correct terminology for this item is know as a Printed Wiring Board (PWB) or Etched Wiring Board. It is common for the PWB to be known as a Printed Circuit Board or PCB.

Through-hole technology is the method commonly used to mount electronic components by leads on the boards. The components are soldered onto the copper traces usually on both sides of the board. The soldering can either be done manually or by a wave soldering machine which increases the efficiency. Surface mount technology (SMT) is another method by which the components were redesigned to enable more efficient soldering on the PCB rather then passing wires through the board. This also allows for smaller PCB assemblies and enables a higher density of circuits. PCB Assembly is also known as ‘PCBA’. Assembled PCB’s can be very sensitive to static therefore is placed in anti-static bags during transport to their destinations. When handled, the person must be earthed as the accumulation of static can damage or destroy the components.

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