Electronic – Inductive vs. capacitive PCB layout


I've noticed that some high-speed switching PCB's (i.e. microwave) use a layout, where each net is maximized and the 'traces' are the non-copper. Is this to decrease capacitive reactance in the circuit?

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Best Answer

There is no simple answer to this as you'd have to consider the needs of each circuit individually.

e.g. For RF, this is to create a trace with a certain electromagnetic radiation pattern. This gives it particular characteristics, e.g. impedance or to act as an antenna or filter. Often Electromagnetic field solving tools are used to design such features.

If this is a high speed digital circuit, it is to create a certain return current path, providing a low inductance and/or low resistance path for the return currents used to drive signal traces.

Sometimes it is for copper balance. If different areas or layers of the PCB have different copper densities, forces build up in the PCB material during formation, these forces are released during solder reflow, causing the board to bend and warp.

More than often it's just to save money. If the circuit PCB is 'negative' then less copper is etched, saving pollution and requiring less cleaning and refreshing of etchant chemicals used in the PCB manufacturing process.