I have also come across PCBs that had aluminum traces instead of copper. They had mechanical clamped connections because they were not easy to solder to. THAT might be the problem.

 

but why copper clad boxes.

The box on the left was to mount a circuit board on and mount that to a board for a science display (for my daughter in middle school). The other was a quick-and-dirty 18650/18500 battery holder. I wanted to do capacity testing and didn't have any 18650 holders at the time.