Humidity sensitive components
Many electronic components absorb moisture from the air, if they are exposed to it unprotected. The maximum permissible storage time without proper packaging is given in the MSL standards (moisture Sensitivity Level). If this storage time has been exceeded by the time the components are to be processed, then the component need to be dried (baked). If components with excessive storage length which have not been dried properly are soldered in a reflow process, there is the danger that, because of the fast rise in temperature the internal moisture will vaporize. The vapor pressure that comes to exist inside the component body may cause cracks or even make the component burst. This latter is referred to as the popcorn-effect. Humidity sensitive components need to be stored in special packaging that protects them from the intruding humidity.