Moisture Absorption
Encapsulated polymer packages absorb ambient vapor during shop floor exposure before surface mount reflow. Polymeric body materials permit ingress through permeable boundaries, reaching internal interfaces where trapped water expands rapidly under thermal stress. Stored components absorb atmospheric moisture continuously until assembly lines process the bobbins or trays.
Elevated temperatures inside infrared reflow ovens vaporize this absorbed liquid instantly, generating internal vapor pressure that exceeds the tensile strength of the molding compound. Plastic dual in-line packages and surface mount components crack when internal pressure exceeds material limits, destroying bond wires and creating micro-defects known as popcorn cracking. Baking procedures reverse this absorption prior to soldering, driving trapped moisture outward through standard desorption paths until dry weight criteria are met.
Thermal Threshold
Standardized packaging classifications dictate specific floor life durations that limit ambient exposure before thermal processing begins. Component manufacturers assign numerical ratings from one to six to define allowable exposure windows inside controlled factory environments. Factory operators track this exposure using humidity indicator cards placed inside sealed barrier bags alongside the components.
Exceeding the assigned floor life forces baking cycles at specified temperatures to restore dry conditions before placement on the pick and place machine. Dried parts reenter the production queue once bake timers expire, preventing delamination events during subsequent infrared heating.
Desiccation Control
Sealed metallized bags protect vulnerable components against atmospheric humidity during transport and warehouse storage. Desiccant packets absorb residual vapor trapped inside the barrier bag during vacuum sealing operations, maintaining internal relative humidity below ten percent. Factory personnel monitor these barrier enclosures for punctures or seal breaches that compromise dry storage integrity.
Components transferred from controlled storage to active production lines begin countdown timers immediately upon bag opening. Exposure limits dictate whether parts undergo immediate assembly or return to dry cabinets for storage before thermal reflow occurs.
