magic smoke

magic smoke n.  A substance trapped inside IC packages that
   enables them to function (also called `blue smoke'; this is
   similar to the archaic `phlogiston' hypothesis about
   combustion).  Its existence is demonstrated by what happens when a
   chip burns up -- the magic smoke gets let out, so it doesn't work
   any more.  See {smoke test}, {let the smoke out}.

   Usenetter Jay Maynard tells the following story: "Once, while
   hacking on a dedicated Z80 system, I was testing code by blowing
   EPROMs and plugging them in the system, then seeing what happened.
   One time, I plugged one in backwards.  I only discovered that
   *after* I realized that Intel didn't put power-on lights under
   the quartz windows on the tops of their EPROMs -- the die was
   glowing white-hot.  Amazingly, the EPROM worked fine after I erased
   it, filled it full of zeros, then erased it again.  For all I know,
   it's still in service.  Of course, this is because the magic smoke
   didn't get let out."  Compare the original phrasing of {Murphy's
   Law}.