Ground planes in circuit boards

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I teach hand soldering and ground planes are something we touch on because of how the copper mass affects heat transfer and solder flow. Until recent googling, I was always under the assumption that this was the main purpose.

I want to be sure I’m getting the big picture concept. They’re essentially for a quick path to ground for returning electricity, correct? That’s the main purpose? Additionally, they eliminate (or greatly reduce) crosstalk in electronics? Is there an increase in their use in newer boards because the circuitry is becoming more complex? Lastly, and most impactful to my teaching, is the heat spreader aspect just an (in)convenient by- product of the ground plane or is it more intentional than that?

In: Engineering

Heat spreader is definitely a byproduct. Their original primary purpose is just to make an easy ground path for any circuit on the board. Without it, you’d have to route all grounding to a pin on the board which is then grounded or some other method. With it, you just have to make a path to the ground plane. However, since the conductivity of heat, like the conductivity of electricity, is aided by free, mobile, electrons, adding a ground plane also adds thermal conductivity that distributes heat away from the soldering iron.

As far as reducing crosstalk, electromagnetic signals reflect off a solid grounded metal plane. If you’ve ever heard of a Faraday cage, it’s simply a wall of grounded metal or thin mesh that reflects signals of a certain frequency (the higher the frequency the smaller the hole needed in the metal or mesh to propagate rather than be reflected). So a properly designed Ground plane will help control electromagnetic interference by restricting electromagnetic propagation.

you also want large low-ohmic equipotential surfaces between different signal lines and sections as shielding against induction. especially high frequency components.
plus heat spread.
plus less etching area (less consumption on chemicals).
plus easy wiring.