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PCB Board BlownI 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.

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    \$\begingroup\$ Probably it was a single large "trace" but the mask only exposed thinner traces. I believe this is to help control the uniformity/thickness of the tin layer during reflow. This is common in PSUs that supply large currents. \$\endgroup\$
    – Wesley Lee
    Jan 30, 2017 at 19:56
  • \$\begingroup\$ So would I be correct to assume there should be no issues in a jumper wires repair as it was just a manufacturing control? \$\endgroup\$
    – Troy Mac1ure
    Jan 30, 2017 at 19:58
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    \$\begingroup\$ I think it might be time for a photo of what you are describing to prevent misunderstandings. :P \$\endgroup\$
    – Wesley Lee
    Jan 30, 2017 at 20:02
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    \$\begingroup\$ I some situation you divide large copper areas because of the soldering. Copper is very well in heat conducting. So if you try to solder a part on the PCB it's almost impossible to do this, if the pad is connected to a large solid copper area.The solution is diving the area by spaces. to disrupt the heat conduction. \$\endgroup\$
    – auoa
    Jan 30, 2017 at 20:06
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    \$\begingroup\$ You often see this done where wave soldering is used to prevent pooling on large surface areas. \$\endgroup\$
    – Jack Creasey
    Jan 30, 2017 at 20:09

2 Answers 2

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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.

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    \$\begingroup\$ Also, under high current conditions the copper/solder will get hot and try to expand. A single large area will undergo major stress and may even delaminate. By providing relief areas this problem is avoided. \$\endgroup\$
    – WhatRoughBeast
    Jan 30, 2017 at 22:27
  • \$\begingroup\$ It also serves thermal properties to hatch a polygon pour, as you'll get most of the electrical conductivity, but less thermal conductivity. \$\endgroup\$
    – Voltage Spike ♦
    Jul 10, 2020 at 15:08
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Many years ago I read that the impedance of parallel tracks was lower than the plain copper fill. (Impedance not resistance.) It is related to the skin effect, and the reason for litz wire. To find the source now is close to mission impossible!

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