My answer to a FB Arduino group question on Sept 17
Dan Rogers has the right idea. The protoboard, with all the holes in it, was never meant to be permanent. The contacts in each hole lose their springiness as they are used to hold wires. The contacts can become intermittent after awhile. As time goes on, the contacts corrode, and the corrosion makes the contacts intermittent or high resistance, and the circuit may have strange problems. Things that draw higher current, such as relays, can work unreliably or not at all. The corrosion causes noise in sensitive circuits.
The worst thing that can happen to a protoboard circuit is vibration. If you have one in a robot or vehicle, it’s almost certain that there will soon be a problem.
The telephone companies have billions of connections and had this corrosion problem. The solution is they create a connection that is “gas tight” to keep out gas and liquids. This is called IDC, insulation displacement connectors. The connection still has wire insulation around it which keeps out air, humidity, water and thus prevents corrosion.
The push in wires and contacts in a protoboard do not have IDC. Depending on the environment, humidity, contamination, water, the connections could last from weeks to years, but it’s just a matter of time before they fail. Solder is the only permanent solution.