I have a vehicle battery maintainer (20A) that was overloaded and stopped working. On inspection I found a group of traces blown, however all the traces are connected at both ends. It looks like a plane that was divided into 4 traces with the coating removed and solder spread across the traces. There are other traces like these in the surrounding area.
I could easily bridge these point with wires, but my Question is why would they design the board like this? Is it done for RF cancelling or as a safety precaution in case of overload (such as what happened)?
EDIT: It looks like the traces are from the transformer to a diode bridge and a coil.
Best Answer
A solder proof mask is usually used to cover unconnected areas of copper in a circuit to prevent solder from tinning the copper during the manufacturing process. This type of circuit is soldered by running the preheated pcb over a wave of solder so that the whole board back is exposed to solder.
In circuits where the copper has to carry large amounts of current the copper connections are left exposed so that they get tinned. This increases the metal thickness and hence the current carrying capability.
Tinning a large single area of copper is difficult and will lead to an uneven thickness of solder over the copper area. By breaking down the area into individual unmasked "tracks" the tinning process works much better.