I've been working with PDIPs and SIOCs but a new project required a chip with 16 analogue inputs so I had to move to the TQFP footprint. I thought, no big deal, just more leads, but when it came, it was in a vacuum sealed pouch with a level 3 caution on it saying it's moisture sensitive. That it has to be mounted in a certain time after being opened and other whatnots. What's this about? Is it just moisture sensitive for the soldering process, because of heat expansion or something? Is it always moisture sensitive?