[LittleProton]

No, I did not attach a heat sink to the sensors, but instead of soldering on wires to the pins we did our own circuit board to reverse the positive voltage and ground voltage supply. (If i'm not mistaken that would require less heat)
I am fairly certain that the problem is not with the soldering. We had a fully functional prototype, but now, after lots of test, it's not functional. So my question is about hooking these sensors directly to 5V.