Harmful Printed Circuit Board Effects 101

circuit-boardDesigning a printed circuit board is not as easy as what you think of. There are several considerations to take into account. Since printed circuit boards are composed of one or more conductor patterns and insulating layers, some errors can happen in a circuit. These errors can be harmful to the performance of circuit.

Often, printed circuit board designers do not take into account the electrical characteristics of PCBs. This leads to degraded overall performance. Some of the dangerous PCB effects are spurious voltage drops, leakage resistances, dielectric absorption and stray capacitance.

Leakage Resistances

The most common mistake that engineers do is considering all PCB traces and wires as resistors. These wire interconnections and trace resistances can cause harmful effects. Most engineers think that think that copper is a very strong conductor, but in reality it is not. The copper used in most PCBs has only resistance of 0.48 Ω/square which is not good enough.

PCB trace resistances become erroneous under unfavorable conditions. To avoid any problems with precision circuits you should utilize a heavier copper and create wider traces. The main key here is designing with intensive care and not overlooking items that look safe on the surface.

Only with high resolutions or precision the resistive voltage drop can be significant. Since large signal currents flow in this case, the error gained can be compensated.

To avoid any voltage drops, the use of separate sense (S) and force (F) connections is usually done. However, this solution is only applicable to systems with negative feedback. You cannot utilize this arrangement to systems with equal accuracy because feedback takes only from one point. Additional methods should be done.

Ground Issue

PCBOne of the major concerns during the process of grounding is the return current. The most common approach here is the assumption that there will be no ground voltage using the concept of infinite ground conductivity. However, it cannot be applied circuits with high precision. It can only cause major disasters. The next approach to this grounding issue is the impedance analysis and noise voltages minimalization.

This one is more realistic than the first approach. On this concept, it is assumed that voltage drop can be caused by the current of signal return which flows in complicated impedances.

PCBs with two sides and multiple layers

There should be a minimum of one completed layer intended for a ground plane. Usually, if you have a printed circuit board with double sides, the one side is for the interconnections while the other side is for ground planes. However, it does not happen in reality because some portions of ground planes should be eliminated for crossovers of power and signal. The rule here is at least 75% of the area must be retained.

There should be no any secluded ground islands. Moreover, there should be no any skinny connections because these can degrade the ground plane’s performance. It is recommended to utilize manual intervention techniques on printed circuit board with mix signals to avoid any disaster.