So, the other day I was soldering up a circuit board, and when I soldered down the LED, it flashed.
This is an 0603 LED, viewed through an assembly microscope. I think that I had the chip that powers it soldered on already, so there may have been a current path. The pads were gold plated, the solder is tin-lead.
Anyone know whazzup? Does solder vs. gold make enough of a thermocouple to light an LED at 600 degrees F? Or must it have been something else?