Printed Circuit Boards: The Layers’ Functions for Electronic and Biomedical Engineering

Abstract

This paper describes the fabrication opportunities that Printed Circuit Boards (PCBs) offer for electronic and biomedical engineering. Historically, PCB substrates have been used to support the components of the electronic devices, linking them using copper lines, and providing input and output pads to connect the rest of the system. In addition, this kind of substrate is an emerging material for biomedical engineering thanks to its many interesting characteristics, such as its commercial availability at a low cost with very good tolerance and versatility, due to its multilayer characteristics; that is, the possibility of using several metals and substrate layers. The alternative uses of copper, gold, Flame Retardant 4 (FR4) and silver layers, together with the use of vias, solder masks and a rigid and flexible substrate, are noted. Among other uses, these characteristics have been using to develop many sensors, biosensors and actuators, and PCB-based lab-on chips; for example, deoxyribonucleic acid (DNA) amplification devices for Polymerase Chain Reaction (PCR). In addition, several applications of these devices are going to be noted in this paper, and two tables summarizing the layers’ functions are included in the discussion: the first one for metallic layers, and the second one for the vias, solder mask, flexible and rigid substrate functions.

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“…Electronic components are projected to be soldered to a printed circuit board (PCB) to form an electronic circuit with a particular function. 255 , 256 There are two categories of electronic components: passive and active. Passive electronic components include resistors, capacitors, diodes and inductors, all of which lack gain or directionality.…”

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“…Manufacturers usually produce cheaper electronic devices of single copper layered PCBs. The standard level of copper thickness on plane layers is about 35 µm [19]. The PCB's solder mask provides the visually observable green color.…”

“…The solder mask is also known as "LPI" or "LPISM," which means a liquid photo imageable solder mask [23]. The solder mask's purpose is to prevent molten leakage [19]. The metal that facilitates the transfer of current between the board and any attached components is solder, which also serves a dual purpose due to its adhesive properties [24].…”

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“…Several etching processes are then repeated to obtain the designed copper traces. 68 An epoxy solder mask is then used to passivate the circuit lines to protect the copper layer from oxidation, which is finally followed by the baking of the PCBs to cure the solder mask (Fig. 3b).…”