Desoldering: Was (Re: Advice on Lisa 2 restoration)

You do not know it, but you are. ICs, and to a lesser extent transistors, are made to be soldered *once*, and in a well controlled heated environment. Heating up an IC pin often will stress the die and introduce cracking in the silicon, as the chip expands in a non-uniform manner. Most of the time these microscopic cracks do not immediately kill the device, but they will reduce the expected lifetime of the chip. Basically, the reliability plummets due to these "latent failures" caused by thermal stress. If you need to desolder an IC for reuse, the best thing to do is to mimic the action of the machines that stuffed the boards in the first place. Heat up the entire device gently with a heat gun set on low, so the entire die expands more or less uniformly. Even just raising the chip temperature 30 degrees C over ten or twenty seconds will help immensely. And when the device is removed, let it cool naturally, -- Will