PCB

PCB is stand for Printed Circuit Board, is a copper etched board that keeps printed the laid copper tracks. These tracks connect the components to each other in most electronics items. The board is stiff enough so that it can mechanically support components mounted over it. In common practice the boards are designed on computer aided design softwares and then the design is transferred over the PCB material for etching. The etching is a chemical process where the necessary copper is saved and extra copper is removed by chemical process. The printed paths after etching are known as tracks. Over etching removes the tracks completely or breaks the connections resulting into an open circuit. On the other hand, poor etching results into small hair-like copper shortages from one track to another. The unnecessary open circuit or short circuit of two conductive paths results into partial or complete failure of the board.  This is why the board etching is performed by the precision processing machines under controlled pressure, time, and chemical composition. Most PCBs are manufactured by fiberglass or glass-reinforced plastic materials with copper sheet on one side or both sides. The conductive paths, i.e., tracks, are made on the copper sheet side. The components are also soldered on the copper sheet side.

 

The PCBs in the current market of electronic products range from single layer, double layer and multilayer formats. In a multilayer PCB multiple copper conductive layers are stacked and glued over each other to enhance the signal density and reduce the PCB size. The other layers are etched and separated by the prepreg material and then joined together. In the raw form the PCB sheet is an insulating sheet of 1 to 2mm thickness coated with copper on one or both sides. The copper is coated over the entire insulator sheet in a small quantity, like 1 to 2 ounces per square feet. In common the copper thickness varies from 17 to 70µm. The high current sink or source circuits like power supply circuits need thicker and wider copper tracks whereas low power but high frequency signals need thinner copper tracks. The magnitude of current flow is determined from the thickness and width of the copper track.

 

In the electronics market a variety of PCBs are produced categorized by performance, availability, manufacturing facility and cost etc. The insulator material of the PCB, although not conducting, but also affects the signal health. It is why, for higher frequencies, special PCB materials are used. For higher frequencies specially developed low absorption materials are used. In common, FR-4 is used for single, double and multilayer PCBs manufacturing. Other easily available materials are CEM-3, CEM-4, CEM-5, FR-1, FR-5, Teflon and the Roger material. After manufacturing, an essential phase of qualification, the PCBs are inspected for surface level finishing, solder mask coating, top overlay printing etc...

 

Figure 1 and 2 show different types of PCBs.

 

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Figure 1:- PCB manufactured for high pin density components

 

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Figure 2:- PCB tracks and vias after etching and finishing of a manufactured PCB